HOLOCENE EVOLUTION OF THE CHANGUINOLA PEAT DEPOSIT, PANAMA: SEDIMENTOLOGY OF A MARINE-INFLUENCED TROPICAL PEAT DEPOSIT ON A TECTONICALLY ACTIVE COAST

by

Stephen Phillips

B .A., University of Waterloo, 1971 B.Sc., University of Victoria, 1990

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

in

THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF GEOLOGICAL SCIENCES

We accept this thesis as conforming to the required standard

THE UNIVERSITY OF BRITISH COLUMBIA

March, 1995

© Stephen Phillips, 1995 ______

In presenting this thesis in partial fulfillment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.

(Signature)

Department of (E&-çfc4-L The University of British Columbia Vancouver, Canada Date /3///9s_: ABSTRACT

The evolution and structure of a large peat deposit on the Caribbean coast of western Panama,

Central America is evaluated as a possible analogue for the deposition of low-ash, low sulphur coals.

Effects of earthquake-driven subsidence events on the peat and the peat-forming vegetation are investigated, and implications of tectomc subsidence on the evolution of this deposit and on the currently developingmodel of coastal tropical coal depositionare described.

The deposit is approximately 80 2km in extent, averages 6.5 m in thickness, and occupies the width of the narrow coastal plain betweenthe Talamanca Cordillera and barrier beach on a seismically active part of the Caribbean coast. Basedon vegetation zonation , topography and hydrology, the modern Changuinola mire complex can be dividedinto a raised, concentrically zoned, ombrotrophic western section, and a dissected and partially rheotrophiceastern section. Differing hydrological regimes of these two sections are reflected in the physical and chemical stratigraphy of the peat. In the western section, a vertical succession of peat types, highly humified at the base and margins, and more fibric in the upper central part, is the result of internal hydrologicalboundaries, created by density and permeability variations in the peat. The mire is insulated from marine and fluvial influences by topography and hydrology, and displays no evidenceof fluctuating sea level. Coal formed in such an environment would be low in sulphur and ash, dull and massive at the base and margins, and finely banded in the upper central part. The eastern section of the mire is in part rheotrophic, with a complex mosaic of vegetation types, and is segmentedinto distinct drainage areas by tidal blackwater creek channels. Effects of this marine influenceare localizedto the bay and channel margins. Coals formed

11 in this environmentwould have large variations in sulphur over distances of a few metres laterally, and a few centimetres vertically.

Earthquake-driven coastal subsidence is greatest in the southeast, and has lead to drowning of the deposit. Subsidence events raise the level in the blackwater creeks, movingthe front of marine influenceto the northwest (inland), and leadingto the replacement of freshwater vegetation with mangroves. The degree of penetration of marine waters remains restricted, however, to marginal peats.

An increase in the scale of subsidence events may overcomethe response capability of the mangroves and lead to disruption of internal hydrological boundaries and ultimate deflation and drowning of the mire.

111 TABLE OF CONTENTS

ABSTRACT ii

TABLE OF CONTENTS iv

LIST OF FIGURES

LIST OF PLATES xi

LIST OF TABLES xii

DEDICATION xiii

ACKNOWLEDGEMENTS xiv

FOREWORD xv

CHAPTER 1: iNTRODUCTION 1

1.1 OBJECTiVES 2 1.2 PRESENTATION 6 1.3 REFERENCES CITED 8

CHAPTER 2: SEDIMENTOLOGY OF THE CHANGUINOLA PEAT DEPOSIT: 9 ORGANIC AND CLASTIC SEDIMENTARY RESPONSE TO PUNCTUATED COASTAL SUBSIDENCE

2.1 ABSTRACT 10 2.2 INTRODUCTION 12 2.3 METHODS 14 a) Measures of Earthquake-induced Subsidence 14 b) Levelling Surveys 17 c) Remote Sensing 17 d) Hydrology 19 e) Clastic Sediments 19 J) Vegetation Survey 19 g) Peat Sampling 21 h) Peat Characterization 21 2.4 GEOLOGICAL SETTING 26 2.5 GEOMORPHOLOGY 28 2.6 VEGETATION 30 2.7 AGE AND GEOMETRY OF THE DEPOSIT 31

iv

3.6 3.5

3.4

3.3

3.2 2.12 2.11

3.1

CHAPTER

2.10

2.9

2.8

POLLEN

RESULTS

2.10.3

METHODS 2.10.2 2.10.1

GEOGRAPHY iNTRODUCTION

ABSTRACT

2.9.2

2.9.1

ORGANIC

SEA

REFERENCES

CONCLUSIONS DISCUSSION

fi

g)

a)

d)

a)

e) b)

c)

a) a)

COASTAL

a)

b) b)

a)

b) d)

c)

c) b) a)

a)

b)

LEVEL

Peat

Levelling

Pollen

Collection

Problems

Satellite

Peat

3:

Coring

Degree ORGANIC

Almirante CLASTIC

Peat

Vegetation Eastern Barrier

Transgressive

Changuinola Barrier

Long

Geochemical Subsidence

Western

Changuinola

IMPLICATIONS HYDROLOGICAL

CLASTIC

DISTRIBUTION

VEGETATION

ii)

1)

Active

AND ii)

i)

i)

ii)

Classfi

M”D)

Basal

Characterization

Term

Counts

CHANGE

Mappable

of

Sedimentary

Western of

PEAT

Description

Beach

System

Eastern

Section

Imagery

Grain

AND

Section

Surveys

CITED

Peat

INTERPRETATION

Hum/I

and

Bay

Clastic

SEDIMENTS

Distribution

CLASTIC

Sediments

SEDIMENTATION

Sea

in

SEDIMENTARY

cation,

Parameters

River

River

and and

CLIMATE

1991

SWAMP,

Identification

Size

and

Level

Section

Section

cation,

AND

Vegetation

Sedimentation

Pollen

Regressive

FOR

Pollen

Floodplain

and

Collection

Floodplain

ZONES

of

Structures

CONTROLS

SEDIMENTOLOGY

Change

the

PUNCTUATED

Mineralogy

COAL

Ash

BOCAS

Diagrams

Preparation

Phasic

AND

of

and

Zones

Signatures

RESPONSE

of

Plants

GEOLOGY

Surface

Moisture

Communities DEL

DIAGNOSTIC ON

V

PEAT

and

TORO,

SUBSIDENCE

Samples

and

Content

TO

Identification

the

ACCUMULATION

PANAMA

RECENT

Relation

POLLEN

TECTONISM

of

PROFILES

Peat

Deposition

OF

A

to

110

99 97

98

97

95

96 95 92 92

92

90

90 88

85 77 71

83 74

82 71

67 61

63 59

62 59

56 50 45

54 48 45

59 51 48 43

43

43 40

40

40

35

34 38

5.6 5.5

5.4 5.1

5.3 4.9

5.2 CHAPTER 4.8

4.7

4.6

4.5

4.4

4.3 4.2

4.1

CHAPTER 3.8

3.7

3.9

DISCUSSION

INTRODUCTION

CONCLUSIONS RESULTS ABSTRACT

REFERENCES

IMPLICATIONS

DISCUSSION

SAMPLING

CONCLUSIONS

RESULTS

REGIONAL

iNTRODUCTION

ABSTRACT

SAMPLiNG

REFERENCES DISCUSSION

SUMMARY

a)

b)

PEAT d)

b)

c) a)

c) b) a)

a)

c)

b)

INDICATOR a)

COAL

b)

Sulphur

5: Forms

Forms

Total Sulphur

Sulphur

Sulphur, Geological

4:

Total

Pollen

Geochemical

Geomorphology

Geography, Surface

SWAMP:

EARTHQUAKE-INDUCED

ii)

z)

SULPHUR

ii) 1)

ii) ii)

I) 1)

Sulphur,

Sulphur

AND

AND

SETTING

AND

of

of

From

Organic

B13:

Sulphur

Sulphur

Inorganic

BDD

Sulphur,

and

Sulphur

Pollen

and

and

pH

CITED

Sulphur

Sulphur

CITED

OF

FOR

Setting

EXPERIMENTAL

EXPERIMENTAL

CONCLUSIONS

Climate

Climatic

and

Tectonic

Vegetation

Cores

Parameters

A An

23:

THE

Distribution

Salinity

Diagrams

IN

MODERN

andpH and

Forms

ENVIRONMENTAL

and

Marine

Example

Salinity

An

Forms

THE

ENVIRONMENTS

Salinuy

p1-I

and

Influence

Influence

Example

and

in

CHANGUINOLA

Influence

Biology

and

ofa

the

p1-f

ANALOGUE

pH

Western

Group

of

PROCEDURES

FLOODING

in

Group

the

vi

III

STUDIES

Section

Eastern

OF

land

Peat

FOR

PEAT

DEPOSITION

OF

Group

HIGH

of

Section

OF

the

A

DEPOSIT

TROPICAL

COAL

Deposit

IlPeats

SULPHUR

of

the

OF

AS

Deposit

PEAT

AN

COASTAL

COALS

AND

188 185

183 180

183 180

183 180 178

177

172

176 170 168

167

166 162 154

163 159 154

162 148

152 145

148 142

142 142 140

140

137

139 137 134

135

133 121

129 116

126 110 5.7 REFERENCES CITED 190

CHAPTER 6: CONCLUSIONS 191

6.1 CONCLUSIONS 191 6.2 SUGGESTIONS FOR FURTHER RESEARCH 193

APPENDICES 195

APPENDIX A SAMPLE SITE LOCATIONS AND ANALYTICAL KEY 195

APPENDIX B SAMPLE DESCRIPTIONS 198

APPENDIX C RESULTS OF WET SIEViNG 216

APPENDIX D POLLEN COUNTS FROM CORES 222

APPENDIX E POLLEN DESCRIPTIONS AND PLATES 225

APPENDIX F RESULTS OF VEGETATION SURVEY 233

APPENDIX G ANALYTICAL PROCEDURES AND DEFiNITIONS 235

APPENDIX H REMOTE SENSING 243

APPENDIX I LEVELLING SURVEYS 244

vii

Figure Figure

Figure

Figure Figure

Figure

Figure

Figure Figure

Figure

Figure

Figure

Figure

Figure Figure

Figure

2.14.

2.12.

2.13.

2.11.

2.10.

2.9.

2.8. 2.7.

2.6.

2.5.

2.4. 2.3

2.2

2.1

1.2

1.1

palynological

plain.

panel:

part

shoreline.

2.1, beach

blackwater

the

of

Insert and

Upper

Colour

False False

The

Map

Cross

Areas

Large Landsat

Regional

Panama

NW-SE

Photograph

Comparison

Photograph

Photograph

shore

bathymetry

including

of

end

shows

western

the

Results

of

colour

colour

panel.

sections

of

map

infrared

of

the

of

deposit.

satellite

and

creeks.

observed

cross

map

Almirañte

the

the

analysis

the

study shows

of

half

SPOT

SPOT

of

of

of

Costa

SW-NE

of

of

surveyed

location

of

and

section particle

Changuinola

air

bedding

laminated drowned

the

the

of image

southern

area

general

photo and

high

satellite Rica

satellite

of

the

results

continental

Bay.

cross

core

showing

from

modelled

of

size barrier

of

transect.

structures and

tree

as

LIST

of

the

silts,

geology

western

Central

of

Ed

section

part a

analysis

image image

the

low

peat

on

study

result

wet

3.

beach,

OF

sands,

sample

shelf

Changuinola

the

of

uplift

discharge

deposit.

sieving

of of

in

America

of Panama

FIGURES

the

of

area.

of

shore

(wet

viii

the

a off

the

part

the

and

peats

the

and

subsided

trench

sites

the

narrow area

sieving)

peat

(particle

side

April of

cross

rates

subsidence

and

showing

and

referred

study

the

River

of

across

deposit

of

eastern

22,

margin

sections

in

cm-thick

the Limon

coastal

the

of

area

size

the

to

detail

1991

to

major

the

beach 8

Almirante

along

three along

cores

distribution)

in

in Costa

-

of

plain

beach

of

Bocas

Ms=7.5

the

leaf northwestern

map

the

tectonic

berm the

largest

the

survey

across

text.

Rica.

and

beds

peat

berm

barrier

marked

del

Caribbean

Bay.

at

barrier earthquake.

deposit

brackish

of

Toro

the

elements.

site

line.

with

at

the

at

Beach

western

in

Panama.

Beach

the

Basin,

alluvial

Figure

Lower

along

coast

2.

2.

55 44

42

41

36

33

24 24

23

22

20

18

16

15

4 3

Figure

Figure

Figure Figure Figure

Figure Figure

Figure Figure

Figure

Figure Figure

Figure Figure

Figure

Figure

Figure Figure

Figure

Figure

Figure

Figure

3.9

3.10 3.8 3.7-c

3.7-f 3.7-d 3.7-b

3.7-e

3.7-a 3

3.6-e 3.6-c

3.6-b 3.5

3.6-a 3.4

3.3

3.1

3.2 2.16.

2.17. 2.15.

.6-d

in

vegetation

vegetation.

vegetation periodic

analysis.

Bay.

Pollen

Pollen

NE-SW

Lateral

Interpretive

False-colour

Location

cores

Pollen

NW-SE

Pollen Pollen

Photograph

Pollen

Pollen

Pollen

Photograph

Photograph

Photograph

Photograph

A

Proposed A

generalized

comparison

and

diagram

diagram

punctuated

fingerprint,

sequence

fingerprint, fingerprint,

fingerprint,

fingerprint,

Cross-section

fingerprint,

zoned

and

map

Cross-section

surface

model

map

SPOT

of

pollen

of

of

of

of

of

of

of

into

view

vegetation

of

the

of

vegetation

of

vegetation

vegetation

vegetation

core

core

vegetation

of

subsidence.

the

from

the

from

from

phasic

from

multispectral

phasic

from

analyses.

from

Changuinola

peat

of

of

wet

BDD-23.

ED-3.

area

of

wet

surface

surface

surface

surface

the

surface

surface

development

the

communities communities

sieving

in

in

in

in in

shown

sieving

deposit

zones.

Phasic

Changuinola

Phasic

Phasic

Phasic

Phasic

peat,

peat, peat,

peat,

peat,

image

peat,

peat

results

in

results

along

Community

the

Community

Community

Community

Community

of

of of

ix

of

of

deposit

on

of

of

from (PC’s).

Phasic

Phasic

Phasic

Phasic

satellite

Phasic

for

Phasic

the

the

levelling

peat across

core

mangrove

barrier

mire

showing

deposit

Community

Community

Community

Community

Community

Community

7:

image

3:

the

2:

6:

BDD

5:

showing

transect,

Myrica-Cyrilla

Raphia

Campnosperma

coastline

Back-mangrove

sawgrass-stunted

marine

sample

as

fringe

23

(Fig.

interpreted

with

concentrically

7.

palm

5.

3.

4.

showing

2.

margin

3.3).

1.

to

as

sites

palynological

bog

a

swamp

result

used

bog

of

plain.

forest

forest.

surface

from

forest

Almirante

plain.

in

of

zoned

pollen

122

120

118 115. 113

115

113 111

111

109 104

106

101

101 100

94 93

91

58

69 57 89

Figure

Figure Figure Figure

Figure

Figure

Figure

Figure

Figure Figure

Figure

Figure Figure

Figure

Figure Figure

4.13

5.2 4.12 4.10

5.1 4.11

4.9

4.7-2

4.8 4.7-1

4.6

4.5 4.3

4.4 4.2

4.1

Table marine

columns

cm peat

swamp

and

with

244.

144.

Site Variation

Spatial Variation

Areal

Scatter

Site

Scatter Scatter

Scatter

Wt

Geochemical

Total

Geochemical

core

pH

pH

II

deposit.

the

of

5.2.

map:

are

%

transgression

vs

vs

core

and

from

depict

standard

study

sulphur

variation

salinity plot

plot plot

plot

sulphur

depth

depth

in in

depth

from

Site

the

of

of

of

particle particle

of

on

variation

characteristics characteristics

in

in

sulphur

sulphur

sulphur

and

name

vs total

central

the

deviation

Caribbean distribution

-

in

the

the

salinity

Depth

following

total

pH

margin

size

size

sulphur

eastern

western

is

part

in (logarithmic

(logarithmic

vs (logarithmic

followed

sulphur

for

(humification),

(humification),

sulphur

in

groups

Depth

coast

(LAKE

of

italics.

of

section

5

(logarithmic

section

1991

of of

the

mangrove

sulphur

core a

and

for

by

of

defined

fractions

deposit

coastal

earthquake-induced

2).

Panama.

the

scale)

scale)

scale)

of

a

of

salinity

BDD23.

Group the

x

the

Groups

mean

pH

pH

cores.

in

scale)

mangrove

(MILE

vs

vs

vs

deposit;

deposit;

for

the

and and

Block

of

depth,

depth, pH.

II

total

eight

text.

I,

peat channel-margin

vs

sulphur

sulphur

5).

II

sulphur

n=3

salinity;

diagram

n=32

western

eastern

and

peat

n

samples, across

=

87.

subsidence.

III

216.

concentration

concentration

1.

core

content

in

marine

section

illustrates

n

section

based

the (B13).

=

peat,

213.

Changuinola

in

margin,

of

on of

core

brackets,

deposit.n

Groups

deposit.n

extent

in in

data

an

a

CS

forest-

from

Insert

870

of

3. I, =

=

II

184

179 160

156

158 153

151 151

149

149

147

146

144 136 143

PLATE PLATE

PLATE

3

2

1

Fusiformisporites

equatorial

Tricolporate

Tricolporate Palmae:

33; Salpichlaena

7)

1780);

Angiosperm

Fern

(10

Monolete

10)

pm

spores:

3)

Periporate

scale

11)

Periporate

and

type

type

type

Raphia

Pollen: sp.;

polar bar):

1)

Tnchomanus

2

54;

1;

sp.

4)

type

8)

views;

type

1)

4)

taedigera;

Cyathea

A

1)

Monolete

7)

Tricolporate

Campnosperma

39;

5)

Campnosperma

Myrica

39,

Fusformisporites

LIST

2)

11)

low

multzflora(?);

crinitum;

Detail

type

Triporate

12)

mexicana;

and

OF

type

Raphia

PLATES

3

high of

xi

9)

panamensis

exine

panamensis;

2;

2)

type

focus;;

Monolete

8)

phytolith;

Cyclopeltis

5)

5)

sp.

decoration

Myrica

40;

Lindsaea

Tricolporate

C

20

12)

type

low

jim

type

2)

13)

Triporate

semicordata

and

of

8

sp.;

Campnosperma-type;

scale

Euterpe

A;

10)

Campnosperma

type

high

6)

bar:

9)

cf.

Monolete

type

26;

Triporate

focus

Metaxya

precatoria.

4)

Sw.;

6)

48.

in

both

type

3)

type

sp.

(x

1;

3)

232

230 227 LIST OF TABLES

Table 2.1 Radiocarbon ages of 4 peat samples. 32

Table 2.2 Results of thin section analysis of barrier and basal sands. 46

Table 2.3 Grain size distribution of sands. 47

Table 2.4 Summary of some physical and chemical characteristics of the Changuinola peats. 49

Table 2.5-A Core descriptions, western section. 52

Table 2.5-B Core descriptions, eastern section. 53

Table 4.1 Forms of sulphur at four levels in core BI 3. 155

Table 4.2 Forms of sulphur at four levels in core BDD 23. 155

Table 4.3 Total sulphur content of some parts from this and other studies. 165

Table 5.1 Total sulphur, salinity and pH of 46 peat samples. 181

Table 5.2 Sulphur fractions in 8 peat samples from BI 3. 182

xii DEDICATION

to

Marlene Rice without whom this would not have begun,

Sammy Sanchez without whom it would undoubtedly have ended abruptly,

and

Doris Phillips without whom it would never have been completed.

Gracias a todos.

xiii ACKNOWLEDGEMENTS

I must first thank Marc Bustin for the inspiration and the instigation of this project, which began as a Master’s thesis and became a way of life. He was a superb supervisor, unflinching in his support of a challenging project. Thanks also to the members of my committee, who never hesitated to help when asked, and whose expertise and good sense made the thesis possible. I admire and am grateful to you all.

The research was supported by graduate fellowships from The University of British Columbia, the Natural Sciences and Engineering Research Council of Canada and the International Development Research Council of Canada. Logistical support was provided by The Smithsonian Tropical Research Institute, Panama, el Instituto de Recursos Hidraulicos y Electrificacion of the Government of the Republic of Panama, the Chiriqui Land Company, Changuinola, Panama and Transworld Explorations, Panama.

A great many individuals contributed to the completion of this project. I am particularly indebted to the people of Boca del Drago, Panama, without whose help this project would have been impossible. Thanks to the entire Serracin family, particularly to Sr. Jose Wilfredo Serracin de Leon, and to the Sanchez family, in particular Sr. Gilberto Sanchez. Also in Panama, I express my deepest gratitude to Eduardo Reyes, Lulu and Bibi Ferranbach, Isabel Barra.za, Enrique Moreno, Paul Colinvaux, Tony Coates, Gonzalo Cordoba, Arturo Ramirez, Andres Hernandez, Mark and Connie Smith, Cameron Forsythe, Alberto Cheng, Julio Benedetti, Clyde Stevens, Ruben Chaw, Jo-Anne Ng, Paul and Anna Shaffer, Roman, Julio, Temistocle, Nicodemo, and to the memories of Captain Pete Burch, and Sra. Ligia Paget. Finally, to Sr. Samuel Sanchez, who knows as much about the Changuinola peat deposit as I do, and to whom I refer all further inquiries.

In Canada, I am indebted to all those in the Department of Geological Sciences at The University of British Columbia who eased this project along. In particular, thanks to Tim England, to Michelle Lamberson, who was always ready with advice and suggestions, to Glenn Rouse, John Ross, and Bill Barnes, each of whom contributed much to both the work and the necessary attitude adjustment. Thanks to Lawrence Lowe and Carol Dyck in the soils lab, and to Carter Kagume and Sophie Weldon, who did the bulk of the lab work. Finally, thanks to my dear friend Judith Knight, who encouraged and supported me when I needed it most, and my mother Doris Phillips, who had faith in me.

xiv

British Five

microscope,

am Rouse Departments

terminology.

samples,

vegetation

guidance by

the

the

papers

papers,

contributed

disciplinary

Dr.

grateful

individuals

agreement

is

provided

R.M.

co-authored

Columbia.

have

The

Science

each

and

throughout

and

to

papers

to approach

been

as

Bustin,

with

he

of

He

each

the

of

who

palynology

well

Botany

is

patiently

guidance

also

the

submitted

a

a

Dr.

end

on

of by

distinct

collaborative

have

as

thesis

the

Committee,

to

provided

my

which

Lowe’s

Dr.

his

result.

and

a

research.

contributed.

and

in

co-authors

editorial

large

L.E.

supervisor,

of

focus,

Geological

for

preparation

Chapters

the

critically

In

laboratory

full

Lowe

publication

subject.

addition,

deposit,

the

discipline,

and

expertise.

The

access

thesis

for

of

who

Two,

guided

each

Sciences,

paper

techniques,

the

FOREWORD

their

As

performed

is

to

in

has in

has

forming

co-authored

and

a

Department

Three,

accordance

his

xv

professional

The

which

the

result,

invaluable

provided

taken

this

laboratory

The

manuscript

paper

Four

photography

a

forms study

analysis

the

the

University

chapter

which

expertise

assistance. by with

advice,

of

and

form

journals,

has

the

and

Dr.

Soil

of

Five

through

University

of

attempted

basis

of

forms

darkroom,

sulphur G.E.

Science,

support

the

of

a

and

are of

series

British

each

of

thesis.

many

Rouse

the

palynological

based

its

Chapter

forms

guidelines,

and

many

naming

to

The

basis

of

and

Columbia.

individuals

take

four

of

All

are

editorial

University

on

the

revisions.

of

shared

Three,

four

co-authored

a

research

as

12

Chapter

multi

co-authors

and

peat

of

his

has

Dr.

on

these

with

of

best I All of the research, analysis and interpretation not specificallymentioned above was performed by Stephen Phillips, in accordance with the guidelines of the University. The papers which relate to the aforementioned Chapters are as follows:

Publications:

1.Phillips,S., Bustin,R. M. andLowe,L. E., 1994, Earthquake-inducedfloodingof a tropicalcoastal peat swamp: a modemanaloguefor high-sulphurcoals.Geology,v. 22, No. 10,p. 929-932.

2. Phillips, S. and Bustin,R. M., (acceptedwithminorrevisions) Sulphurdistributioninthe Changuinolapeat deposit,Panama as an indicatorof the environmentsof depositionof peat and coal. Journalof SedimentaryResearch.

Publicationssubmitted:

1. Phillips, S., Rouse, G.E, and Bustin,R.M, (in review).Vegetationzonesand diagnosticpollen profilesof a coastalpeat swamp.Bocas delToro, Panama. Palaeogeography.Palaeoclimatology.Palaeoecology.

2. Phillips, S. and Bustin,R. M., (submitted). Sedimentologyof the Changuinolapeat deposit:organic and elastic sedimentaryresponseto punctuatedcoastal subsidence. GeologicalSocietyof AmericaBulletin.

xvi

process

inorganic

predominantly

of

accumulating

of

organic

its

the

environmental

thousands

disciplinary

are

vegetation

palaeoenvironmental

past

environmental

of

decomposition.

an

components

ecosystems

processes

being

changes

imbalance,

of

matter

In

The

detrital

increasingly

accumulation.

the of

and

examinations

last

years.

in

organic

by

normal

organic

conditions,

preserved, and

change

climate

return

local

of

which

material,

half

In

the

the

In

peat

information,

as

debris.

of

to

measure

studied

material

has

implications

in

inability

turn,

thick

well

the the

palaeo-wetlands,

In the

deposition

and of

grown

and

twentieth

ecosystem

order

modern in

deposits

as

earths

This

as

by

other

of

recent

derived

global

of

analogues

what

a

things,

for

comprising

normal

can

realization

of

CHAPTER

surface

inorganics

peat-forming

the

this

of

years,

century

enviromnental

enviromnents.

as

be mechanisms

from

peat

latter

it

raw

due

process,

decompositional

over

is

for

would

extensive

the

expected

can

has

to

as

material

predominates.

of

ancient

generated

large

preserved

1:

rapid

they

the

accumulate,

seen

systems,

which

be

they

INTRODUCTION

importance

change.

areas

do

Coal

obscured

modem

accumulation, that

coal

an

for

might

a

may

biochemically

increasing

the

detailed

remains

when

processes

deposits

of

scientists

depositional

Peat

Along

the

in

continuation

be

wetlands,

be

by

of

what

an

termed

earth’s

preserved.

is

it.

and

of

the

organism

have

with

awareness

a

or

are

to

manner

Thus

sediment,

geological

sometimes

keep

to

and

systems.

particularly

‘peatification’,

coming

surface,

long

this

suppression

of

a

geochemically

along

up

peat

dies, interest

the

they

been

world-wide

with

an

to

system.

record

for

By

continuous

with

deposit

record

it

an

utilized

accumulation

in

will

the

tens

detailed,

in

understanding

of

to

tropical

associated

present

as

rate

decompose

the

proceed,

to

changing

Were

is

during

an

of

as

hundreds

an

mechanisms

of

record

the

sources

indicator

multi

latitudes,

indication

all

fragility

of

the

certain

dead

of

and

of

of

of of physical and chemical conditions must be present. Thus peat sedimentationis associated with particular

environmentswhich meet these conditions. In turn, variations Within these environments are associated

withvariations within the resulting peat deposits, andgiventhe right conditions, within coal measures that may eventually form from the peat. Most of the materialthat makes up a peat deposit is added at the top, within a few centimeters of the growing surface. Changesoccurring at the surface, such as in the type of vegetation or the proportions of organic to inorganic deposition,will be reflected in a horizontal stratification of the deposit which is evidentboth macroscopicallyin cores or hand specimens, and microscopically in the assemblage of preservedpalynomorphsand in microtomedthin sections. Thus peat deposits can appropriately be studied in stratigraphic columnsas are other sediments, variations in the stratigraphy and sedimentologyallowing for inferencesas to the environmentof deposition.

The peat deposit which is the focus of this study is locatednear the town of Changuinola on the

Caribbean coast of Panama, in the humid tropics of Central America (Fig. 1.1). The site is a wetland lying within a few centimetres of sea levelin a regionwhich is tectonicallyactive and subject to periodic earthquakes. It is one of many coastal mires to be found in this regionof Central America - several are marked in Figure 1.2, a Landsat satellite image of western Panama and eastern Costa Rica - and is of particular interest because its lateral extent (about 80 )2km andthickness are comparable to palaeo-mires which have given rise to economiccoal deposits. The deposit is thus felt to provide an appropriate analogue for the deposition of tropical, coastal coals in tectonicallyactive settings. It is hoped that the present work may contribute to the continuingdevelopmentand refinementof a process model for the accumulation of coal deposits, particularly in tropical coastal environments.

1.1 OBJECTIVES AND METhODS

This investigation into the evolutionand structure of the Changuinolapeat deposit has two main objectives. The first is to evaluate the deposit as a possible analogue for the deposition of low-ash, low

2 WE

- Limon - l3ocas CARIBBEAN :1Toro.Bain PLATE -

-

COCOS

PLATh

PLATh 00’ W

Figure 1.1. Southern Central America. Major tectonic features on both the Caribbean and Pacific sides ofthe Central America Arc are shown, including the aseismic Cocos Ridge, which has effectively choked-off subduction at the eastern end ofthe Middle America Trench, and the north Panama thrust belt, which converges with the coast near Puerto Limon. Dashed line outlines extent ofthe Limon - Bocas del Toro back-arc basin. Cone-shaped symbols are volcanos. The rectangle outlines the area of the Landsat image shown in Figure 1.2. J •f•...-..I;.I

‘‘ : :: ,,

. 1•_.

Figure 1.2. Landsat satellite imageof the area of western Panama and eastern Costa Rica outlined in Figure 1.1. The Changuinola River (CR), Chiriqui Lagoon (CL) and several coastal wetlands (CW) along both the Caribbean (top) and the Pacific (bottom) coast are visible. Note the contrast in coastal morphology between wave-dominated(wd), river-dominated(rd) and tide-dominated (td) shorelines. The

Caribbean coast is microtidal (.-0.3 in) and the Pacific coast is macrotidal (—.8 m). Prevailing winds are from the N (top) to NE.

4 sulphur coals. The second objective is to documentthe effects of earthquake-driven subsidence events on the peat and the peat-forming vegetation, and to assess the implicationsof such events on the evolution of this deposit and on the currently developingmodel of coastal tropical coal deposition.

In order to address the first of these objectives it is necessary to utilize techniques which lend themselves to interpretation in terms of coal geology. Environmentalstudies of coal use a variety of approaches, including palynologyand palaeobotany of the peat-formingvegetation, geochemistry and isotopic composition of the coal, distribution of coal macerals and mineral matter, and studies of associated clastic depositional environments(the rocks which surround the coal). At the onset of the study, it was evident that certainlarge-scale aspects of the Changuinola deposit needed to be addressed in order to establish a context in which detailedanalysis would have any meaning. The geometry, internal stratigraphy, and evolutionary history of the deposit had to be established, and the absence of any information on the nature of the peat-forming vegetationaddressed, in order to determine the applicability of the deposit to coal studies. An initial study by Dr. A.D. Cohenand others (Cohen et al., 1989, 1990) laid the groundwork, and a fundamental series of papers on the coastal peat deposits of tropical Malesia

(Anderson, 1964, 1983; Anderson and Mueller, 1975; Bruenig, 1976, 1990; Esterle, 1990; Cobb and

Cecil, 1993) provided a model of mire evolutionthrough increasing oligotrophy. These bodies of work formed the starting point for this study. It was decidedthat phyteral analysis and detailed petrography of the peat would be more appropriate tools for a secondphase of analysis. This study utilizes a survey of the modern vegetation, palynological profiles, the results of particle-size analysis (a quantitative measure of the degree of humification of the peat), sulphur chemistry, ash (mineral matter) content, and pH and salinity measurements to characterize the peat. In addition, it looks at the nature of the barrier sand body which underlies much of the deposit, and forms the seaward margin of the modern mire.

) The second objective is to assess the effects of coseismiccoastal subsidence and sudden sea level change on the mire, and the implicationsfor the evolutionof the deposit of a tectonic setting which included punctuated coastal subsidence. The study commenced10 weeks after a major (M =7.5) earthquake shook the region. Many lives were lost, roads, bridges and airstrips were destroyed, and the entire infrastructure of the region was damaged. Measurements of sea level change were made along the affected coastline, and levelingsurveys used to establish the amount of local subsidence. Over the course of three years, detailed salinity and pH measurementswere made in transects across the marine margin of the deposit, and an analysis of sulphur forms used to detect changes in geochemistry and microbial activity brought on by sudden subsidence and marine inundation. Evidenceof former subsidence events was sought in the stratigraphy of long submergedpeat beneath and on the shores of Almirante Bay. This line of inquiry suggests a subject for further, much more detailed research, as a datable record of earlier earthquakes would help to establish the cyclicityof such events, and possibly mitigate potential disasters in the future.

1,2 PRESENTATION

The four central chapters of this thesis each represent an individual manuscript, prepared for publication in refereedjournals, which together comprise a unified body of work, in accordance with university guidelines. It is for this reason that each main chapter has its own Abstract, Conclusions and

References, and thus forms a self-containedunit for readers interested in only certain aspects of this multi faceted study. A certain amount of repetition is unavoidable in such circumstances, particularly when discussing methods and providingbackground, but the goal of making the results of this research available to the interested public in as accessible and comprehensivea form as possible, I hope, outweighs the risk of boring readers of the entire thesis. Some internal referencesto appropriate chapters of the thesis have been inserted, in parentheses, along with external references. This is intendedto benefit the reader of the thesis, without compromisingthe integrity of individualmanuscripts.

6 The second chapter presents an overviewof the geological and geomorphological setting of the

Changuinolamire system,and discussesthegeometry,internalstructureand hydrologyof the peat deposit.

It presents an interpretationof the responseof organicand elasticsedimentaryprocessesto the regional tectonic setting, and proposes a model for the structural evolutionof the deposit within the context of punctuated coastal subsidence.

Chapter Three presents the results of a botanical survey of the modern mire system, and discusses the floral composition of the peat-formingvegetationthroughout the history of peat deposition, based on palynological analysis of the peat and of surface litter. By this means, a history of floral succession, which in turn reflects the fundamentalhydrologicalevolutionof the mire, is described. The chapter compares the results of this study with the Anderson (1964) modelof mire evolution developed from observations of peat deposits in the Old World tropics.

The fourth chapter discusses somegeochemicalcharacteristics of the peat. It deals specifically with the relationships between sulphur content,pH and salinity of the peat, and defines the manner in which the climate, biology and tectonic setting are expressed in the peat geochemistry. It then suggests some implications of the data for the environmentalinterpretation of coal deposits.

Chapter Five addresses the effects of the 1991earthquake on the geochemistry of peat along the newly submerged marine margin. It comparespH and salinity values onshore and offshore, and describes changes in the distribution of forms of sulphur which have taken place as a result of the sudden rise in sea level. In this way it lays a groundwork for analysis of forms of sulphur in coals which bear a transgressive signature as a result of rapid, tectonically-drivenrather than gradual, eustatically-driven subsidence.

7 The work concludes in Chapter Six by addressingthe broader goals of the investigation, and

suggests some directions for future research which have come out of this study. There is then a series of

Appendices which contain the raw data from whichthe conclusionsare drawn, and a brief explanation of

terminology and procedures used.

1.3 REFERENCES CITED

Anderson, J.A.R., 1964. The structure and developmentof the peat swamps of Sarawak and Brunei. Journal of Tropical Geography, v.18, -71p. 6. Anderson, J.A.R., 1983. The tropical peat swamps of Western Malesia. j : A.J.P. Gore (ed.), Ecosystems of the World 4B - Mires: Swamp, Bog, Fen and Moor; Chapter 6. Elsevier, Amsterdam

Anderson, J.A.R. and Muller, J., 1975. Palynologicalstudy of a Holocene peat and a coal deposit from NW Borneo. Review of Paleobotanyand Palynology, v.19, p.29 1-351.

Bruenig, E.F., 1990. Oligotrophic forested wetlands in Borneo. j: A.E. Lugo, M. Brinson and S. Brown, (eds.), Ecosystems of the World 15: ForestedWetlands, Elsevier 1990, Chapter 13.

Bruenig, E.F., 1976. Classifying for mapping of peat swamp forest examples of primary forest types in Sarawak, Borneo. : P.S. Ashton (ed.), The Classification and Mapping of Southeast Asian Ecosystems, Univ. of Hull Misc. Ser. 17:57-75.

Cobb, J.C. and Cecil, C.B., 1993. (eds.) Modem and Ancient Coal-forming environments. G.S.A. Special Paper 286, Boulder. pp.198.

Cohen, A.D., Raymond, R.Jr., Ramirez, A., Morales, Z. and Ponce,F., 1989. The Changuinola peat deposit of northwestern Panama: A tropical back-barrier peat (coal)-forming environment. In: P.C. Lyons and B.Alpern (eds.), Peat and Coal: Origin, Facies and Depositional Environments. mt.J. Coal Geol., v.12, p. 157-192

Cohen, A.D., Raymond, R.Jr., Ramirez, A., Morales, Z. and Ponce, F., 1990. Changuinola Peat Deposit of Northwestern Panama, 3 vols. Los AlamosNational Laboratory pub. LA-11211, July 1990.

Esterle, 3.S., 1990. Trends in petrographic and chemical characteristics of tropical domed peat deposits in Indonesia and Malaysia as analogues for coal formation. Unpublished PhD thesis, University of Kentucky, Lexington, O.27pp.

8 CHAPTER 2

SEDIMENTOLOGY OF THE CHANGUINOLA PEAT DEPOSIT: ORGAMC AND

CLASTIC SEDIMENTARY RESPONSE TO PUNCTUATED COASTAL SUBSIDENCE

9 CHAPTER 2: SEDIMENTOLOGY OF THE CHANGUNOLA PEAT DEPOSIT: ORGANIC

AND CLASTIC SEDIMENTARY RESPONSE TO PUNCTUATED COASTAL SUBSIDENCE

2.1 ABSTRACT

An extensive peat deposit on the Caribbean coast near Changuinola, Panama has developed

in an area subject to periodic earthquake-drivencoseismic subsidence. Thick, low-ash, low-sulphur peat is accumulating immediatelybehind an aggrading and prograding barrier system, and adjacent to a flood-prone, sediment laden river. Measurementsof changes in local sea level as a result of a recent

(April, 1991) earthquake reveal 30 to 50 cm of subsidence,greatest at the southeastern extent of the study area, where the peat surface is submergedto a depth of 3 metres beneath the shallow waters of

Almirante Bay. In the eastern part of the deposit, the effects of sea-level rise are evident in the degree of humification, ash and sulphur contentof mangroveand back-mangove peats offshore or immediatelyadjacent to the marine margin, and in peats associated with brackish tidal channels which drain the deposit. However, most of the deposit shows no indications of marine influence, even though approximately 40% of the deposit is belowpresent sea level. The western section of the deposit has evolved from low-lying,Raphia palm swamps originatingin swales on the barrier bar, into an oligotrophic bog-plain with a water table elevated6.75 m above sea level. As the mire evolved, transitions in vegetation resulted in transitions in peat types. Highly humified forest-swamp and palm- swamp peats underlie and surround well-preserved,fibric sedgepeats, and create a partial hydrological bounding surface which restricts subsurface drainage from the central bog. The high water table and elevated topography of the mire, and the low permeability and erosion-resistance of the dense, woody peat effectivelyinsulate the deposit from both elastic influx and the extensive

10 intrusion of marine waters. It is evidentthat thick peat, and hence coal, deposits can accumulate due to tectonically driven, punctuated subsidence, rather than gradual eustatic sea level rise, without leaving a record of high elastic input withinthe peat, even immediatelyadjacent to environments of active elastic deposition.

11 2.2 TNTRODUCTION

The usefulness of depositionalmodels in coal exploration is well established. Detailed descriptions of depositional environmentsand tectonic settings can be generalised into predictive models that are of economicvalue in both exploration and mine planning (Home et al., 1978).

However, correlation of compositionalvariations in coals with paleoenvironments of peat deposition requires detailed descriptions of like environments(McCabe, 1987). Thick coal beds require very thick accumulations of peat, and provide sciencewith one of the most certain, yet most puzzling, records of environmental conditions at particular locations over geological time spans. Certain because we know, or think we know, what kind of conditionsof climate and hydrology must prevail in order to allow peat to accumulate, and somewhat less certainly, for how long. Puzzling because, given the dictum of uniformitaranism, we see few if any modern day examples of analogous peat accumulation. Early analogues were sought in the boreal and temperate peatlands of Eurasia and

Canada, and the subtropical swamps of southeastern United States, but recent attention has focused on thick coastal peats accumulating in the Old World tropics. Tropical coastal depositional environments are believedto have been the settings for many known coal deposits (Wanless et al., 1969; Anderson and Muller, 1975; Cobb and Cecil, 1994). Tropical coastal peats, however, are still relatively poorly understood, and differ in a number of ways from the temperate and sub-tropical studies on which early depositional models are based. Tropical climate affects air and water temperatures, water table and hydroperiod, seasonality, growth and decompositionrates, andthe composition of the peat-forming floral community. The focus of this study is the relationshipbetween organic and elastic sedimentation in a large peat deposit near the townof Changuinola in northwest Panama. The object is to determine the effects of periodic coseismiccoastal subsidence on the character and geometry of peat accumulation and preservation, and by extension,on analogous coals.

12 environments

accumulating swamps from tectonically occupies complex (Pirazzoli diurnal) Almirante about Alamos Republic Anderson and deposit forest

net between

study sea epicentred

subsidence

level,

coal-fired

coastal

60

commenced

vegetation

may

National

of shoreline

organic mire

the

km2

Extensive of

unlike

(1964).

1991),

Bay.

90

Indonesia

active

Panama

be

strand outcrops

along

in

system

km onshore,

thermoelectric

in

domed

coastal

the Cohen

productivity

surrounding and

Laboratories

part

at

to

area

10

Accumulation

plain

part

coastal

alluvial

9°20’

the

(IRHE),

has possibly

weeks

and

but

of

in

that

and

et

Panama

west of

the

behind

a

developed

never al.

Malaysia

N

the

manner

peats

another

has

Malaysian after

mire latitude,

(1989,

facility.

in

and

with

a

for

seismically

and

plain

experienced the

studied

an

at

are

of

a

complex,

decomposition. much

the

the

least

similar

actively

valley M

20

within

(Anderson,

organic

1990)

currently

of

82°

They

objective

Instituto

km2

7.5

mires,

(Bohnenberger

sedges,

longer:

since

20’

of

active

to

first a

(surface

such

prograding offshore

found

local sediments

few the

the W

the

which

being

described

grasses de lignites

of 1963,

longitude

Rio

that

Caribbean

Malaysian hundred

stabilization

coseismic

the Plant

13 Recursos assessing

magnitude)

Estrella, beneath deposited

are

40%

peat

1984;

(peat)

and

barrier of

and

growth

almost

the

metres

probable

on

of

to

Dengo,

coast

stunted

subsidence.

peat

Hidraulicos

its

Cobb

the

the

the in deposit,

be

Costa

of

beach in

earthquake resource

this

and

all

up

shallow

volume

of

deposits Caribbean

sea

a

of

and

above

variety

to

1978). the Miocene

vegetation

peat

setting

Rica,

Panama.

level

on

studied

9

Cecil,

wave-dominated

metres

a

potential

y

The of accumulation

marine

mean

described

which

microtidal

some

Electrificacion

of

on The

reflects

the

coast

age

jointly

peat

sedimentary

1993)

April

Like

suggested

deposit

thick,

sea

Changuinola

4500

sediments

resulted

have

(Fig.

as

deposit

an

level.

the

in

peat

22,

by

fuel

(range

and

years

been

imbalance

detail

have

is

vast

2-1).

the

1991, coast,

has

that

in now for

the

of

The covers

of

U.S.

collected

variable

ago

peat

of

exceeded

the

by

a

been

deposit

the

dense This

below

present

peat-

30 in

Los

a

cm, coastal subsidence in the area, and the floodingof parts of the marine margin of the deposit along the shore of Almirante Bay (Fig. 2-2).

Peat deposition has occured in many geological settings, includingmontane and alluvial settings in which burial and preservation, and hencethe developmentof significant coal deposits, is unlikely. As with other sediments,peat accumulationand preservation requires accommodation space, subsiding sedimentary basins. There are both similaritiesand significant differences between the setting of the now well-knowncoastal Malaysian peats and this Neo-tropical deposit in Panama. As in Malaysia, the Panamanian climate is humid-tropical, and temperature averages 26°C, with a ± 3° range. However, there is no dry season on the Caribbean coast of Panama; the annual precipitation of

3000 mm is unifonnly distributed throughout the year (IRHE, 1988). Tidal effects are minimal, and strong tradewind-driven longshorecurrents transport sedimentsto the southeast. Tropical storms and hurricanes pass to the north, but associated flood events are frequent. This extensive peat deposit owes its existence to the ever-wetclimate, and its morphologyto the interaction between tectonically driven coastal subsidence, river sedimentation,and coastal processes related to waves, tide and current.

2.3 METhODS

a) Measures of Earthquake-induced Subsidence

The most recent coseismicsubsidence in the study area occurred during the April 22, 1991 event. The very small (30 cm) normal tide range, and the presence of a tidal station at Almirante permitted measurement of post-earthquake sea levelsalong about 30 km of shoreline bordering two sides of the peat deposit. Liquefactionof soils (fine-grainedsands) was widespread on the alluvial plain as a result of the 1991 earthquake. The problem of distinguishingbetween liquefaction effects and extensive preserved peat (coal) deposits are frequentlyassociated with coastal margins of actively

14 Figure 2-1. Insert showsthe locationof the study area on the Caribbeanside of the TalamancaCordillera,opposite the northeast moving Cocos Ridge. Large map shows general geology of part of the Limon-Bocas del ToroBasin, and bathymetry of the continental shelf off the study are in northwestern Panama. Legend: QR-Ala Quatemaly Alajuela Fm. -alluvium,peat (vegetationpattern), corals Tm Miocene Venado?Fm. -calcarenites,lutites, sst TM-GAus Miocene Gatun Group: Gatun-Uscari Fm. -mdst, 1st,cgl, pyroci TM-CAvi Miocene Canazas Group: ViriguaFm. -ands,basalts, breccias, dike swarms TO-SEus Oligocene Senosri-UscariGroupand Fm. -mdst, cgl, sst, tuffs K-CHA Changuinola Group and Fm. -1st,mdst, sst, lavas, tiffs, andesites.

15 published Figure (1992), Costa Ward metresE

r2 t-+1

L2 L_1

Generalized p

(1992),

Rica

2-2.

with

and

g

as

I

• I I I I I

I I I I I

Areas

additional

Phillips

a

unpublished

result

of

I I I I I I I I I I I I

profile

observed

8300’

(1992) of

subsidence

the :5SSS

data

April of

and

and

elevaflon

by

Soulas ——

22nd,

data

modelled

Astorga

-I-.

I I I I I I I I I I

I I I

I

from

1991

(unpub.

(1991), — change -S

uplift

this

Ms=7.5

data).

study.

and

Denyer

16

earthquake. *

subsidence

The

T-_

I I

I I I

I I I I I I

and r-..

profile

Arias

along 5-..

The

of _L_

(1992),

elevation

model

2 — 0 C

the -I---.

1-.

I

i I I I I I I I I I

I

Caribbean

CARIB44AN

OVSICORI •--.

is —----S

change

adapted — ——

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U

coast m&re c

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generalized

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Ward and true structural subsidence was addressed by measuring subsidence at sites where bedrock is exposed in the intertidal zone at the northeast and northwest corners of Pta. Serrabata, two locations on Isla Carenero, and at Hospital Point on Isla Bastimentos in the Bocas del Toro archipelago. The extent to which the (non-bedrock)margins of the peat deposit were affected by subsidence was established through conversation with knowledgeablelocal inhabitants, and by the degree to which shorelinevegetation showed the effects of drowningand saline intrusion into the groundwater (Phillips et al., 1994). Low-levelcolour infrared air photographs of the margin 2 years after the earthquake show a die-back zone varying from 5 to 50 m along the shores of Almirante Bay (Fig 2-3).

b) Levelling Surveys

Vertical control and topography across the deposit and the barrier beachwas established by the surveying of levellinglines (Fig. 2-4). Elevationson the landward side of the deposit are based on bench marks established by IRHE along the Almiranterailway line. These bench marks, and datum at the Almirante tide station were corrected by IRHE in 1992. Elevation at the barrier coast is tied to estimates of coastal subsidence based on changes in the swash zone, trenching across the beach, and on the drowning of shorelinevegetation. Elevationchange for the affected outer coastline is shown in

Figure 2-2.

c) RemoteSensing

Drainage patterns and hydrologyof the deposit, and present vegetation zonation were established on the basis of SPOT multispectral satellite imagery, high altitude black and white, and low altitude colour infrared photography. Non-surveyed sampling sites were located using a

Magellan®GPS (Global Positioning System) receiver.

17 *

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Figure 2.3. Low level, oblique, colour infrared air photograph of part of the subsided margin of the peat deposit along the shore of Almirante Bay. The mangrove fringe forest, salt-tolerant sawgrass, and hardwood swamp are all healthy shades of pink and red. In the centre foreground, marine water has permeated 100rn into the swamp, as shown by the dying vegetation (green tint). The peat deposit is 6 m thick at this site, and it extends 1 km offshore beneath the bay. The white spot in the centre foreground is a boat at drill site BDD 22D on Figure 2.4.

18 d) Hydrology

Cross-sections of the major drainage channels (blackwater creeks) were constructed, and

flow rates during high and low-precipitationperiods in 4 major creeks were used to estimate

fluctuations in discharge .(Fig.2-5). Discharge rates are difficultto measure confidently, however, due to the tidal nature of the drainage in the eastern section, and the dispersed western drainage pattern.

Water table fluctuations are estimated from field observations,but no quantitative data on hydropenod

are available.

e) Clastic Sediments

Sediment samples were taken at a point bar 2 km upstream from the mouth of the

Changuinola River, at the mouth, and at 4 sites along the lengthof the barrier beach (Fig. 2-4), Beach samples are from the upper 5 cm of the beach, at the top of the normal swash zone. Grains were examined in thin section for size, shape, sorting, and mineralogy,and sieved into the followinggrain sizes: -id), 0d, +1d1,+2c, +3d and +4(I). Similar procedures were followedfor 4 samples taken from the base of the peat deposit using a Macauley-typehand operated corer, and samples recovered from rotaly drill holes at 2 additional sites, from depths of 10and 20 m. Characteristics of the samples were compared in order to establish the nature of the basal sediments. Sediment from 78 cores was recovered and described in the field as to colour, grain size and estimated organic matter content. Sedimentary structures in the barrier beach were examinedin three shallow trenches dug at right angles to the coast, 2 across the beach berm and one in the back beach, 13 months after the 1991 subsidence event (Fig. 2-6).

f) VegetationSurvey

Vegetation distribution was determinedusing multispectral SPOT satellite imagery (Fig. 2-

7), high and low level air photographs, and by ground surveys. Major peat-forming plant species were collected with the assistance of Sr. A. Hemandez and staff of the herbaria of the Smithsonian

19 Figuie 2-4. Map of the Changuinola peat deposit, showing sample sites referred to in Chapter 2. The heavy SW-NE line is the surveyed transect cross-section (Fig. 2-9), and the lighter NW-SE line is that of the longitudinal cross-section (Fig. 2-12). Heavy dashed line separates Eastern and Western sections.The Eastern Section of the deposit is that part influenced by the 4 major blackwater creeks shown (see also the satellite image Fig. 7). Arrows show sites at which subsidence was measured or estimated. Large capitals are sites at which detailed physical or chemical analyses were performed. Other sample sites are shown for easy reference to cross-sections.

20 Tropical Research Institute in Balboa and the Universityof Panama, Panama City. Pollen slides were prepared from surface samples from sites representativeof the 7 vegetation zones (phasic communities) identifiedin the vegetation survey, and from 2 cores, one in the central part of the deposit and the second near the eastern margin. Pollen was concentrated, using standard palynological techniques, from the fme fraction of the peat (< 0.25 mm).

g) Peat Sampling

Peat cores from the surface to the base of the deposit were taken at 78 sites, using hand operated Hiller- and Macauley-type coring devices,and a 3.5 cm diameter vibracore. Samples were recovered in 25 or 30 cm incrementswheneverpossible, described in the field, double-bagged and stored at room temperature until they could be refrigerated or frozen. Salinity and pH for most samples were measured at the time of collection,and verified in the laboratory using a Cardy®Model

PHi digital pH meter, and a Cardy®Model C121digital salt meter. Surface litter samples were collected (to 5 cm depth) and 25 cm cubes cut witha machete.

h) Peat characterization

A variety of methodswas used to characterize the peat recovered in cores. In addition to pH and salinity, total sulphur content (dry weight percent) of 203 samples (dried at 50°C, crushed to 100 mesh) was determinedusing a Leco®SC-l32 Sulphur Analyzer (see Tabatabai, 1992, p.313 for a description of this instrument)and verifiedusing wet chemicalmethods (Appendix G). Mineral matter content (wt % ash) of 137 samples was determinedby weight loss on ignition in a muffle furnace at

550°C (ASTM-D 2974: Jarret, 1982). Peat is definedaccording to ash content using the Organic

Sediments Research Centre, Universityof South Carolina, standard (Andrejko et al., 1983). By this standard, peat is definedas Low (<5 wt%), Medium(5-15 wt%) and High Ash (15-25 wt%). Above

25 wt% is carbonaceous sediment. Moisture content of wetpeat, drained of superficial water, was

21 Discharge rates Caño Sucio oj m%ec SaL = U.2 pH = Low High il= 1.90 pH = 7.37 9.2 21.2

Rio Banano

sal = 0.92 pH = 7.21 3.9

11= 2.10 pH = 7.32

Canal Viejo

sal = 0.86 pH = 6.88 3.2 4.8 ° = I J Om 5 10 15m

Figure 2-5. Cross sections, and high- and low-dischargerates measuredin the three largest blackwater creeks. Salinity and pH of bottom and surfacewateris shown. The banks of the channels are peat, and the channel floors are clean medium grained sands. Measurementswere taken 1 km upstream from Almirante Bay (see Fig. 2-4).

22

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site The Figure 2.7. False colour spot satellite image of the area of the detail map (Fig. 2.4). Concentric zoning of vegetation is most obvious in thc western part of the deposit, but is also visible around 3 lesser domes in the eastern section. A larger scale SPOT image is reproduced on page 93. Black is sediment laden water, and white is clear water (see Fig. 2.8).

Figure 2.8. False colour SPOT satellite image of the narrow coastal plain and barrier shoreline. The sediment plume of the Changuinola River is clearly visible trailing off to the east. A plume of sediment is entering Almirante Bay on the flood tide (right centre), but most of the bay margin of the peat deposit is free of elastic input, and is an area of carbonate deposition (dark blue). Bananas are in pink on the floodplain. 24 measured by air drying at 50°C (wt % moisture lost), and is used in plots as an approximation of the density of the peat. Degree of humificationof the peat was established by particle-size distribution of each sample. Degree of humification of the peats is based on the relative proportions of coarse, mediumand fine constituents as determinedusing a wet-sievingprocedure modified from Staneck and

Silo (1977), according to the followingscheme(Esterle et al., 1987):

Coarse (C) >25% >20 mm <30% <0.25 mm ( von Post fibric to coarse hemic)

Medium (M) <25% >2.0 mm <30% <0.25 mm (=hemic)

Fine (F) <25% >2.0 mm >30% <0.25 mm (=hernic to fine hemic)

These three categories are used for the plotting of core data. In this study we chose to use wet sieving as a means of measuring tissue preservation because the technique lends itself well to the large incremental samples recoveredby Macauley and Hillyer corers, usually 25 or 30 cm of core at a time. We report the results of sievingas percentagesof total by dry weight, as the methods of measuring volume are less accurate, and do not lendthemselveswell to woody or fibric peats. The degree of stratigraphic correlation possible using the bulk technique is necessarily limited, but the spacing of sample sites (500 to 1500 m at best), and the absence of continuous marker beds such as a volcanic ash fall, make precise correlation impossibleby any of the means at our disposal. The method thoroughly homogenizesthe increment,and thus generalizes the interpretation to a 25 or 30 cm scale. However, there is little literature on the discriminatingability of wet sieving of peat, particularly woody tropical peat (Staneck and Silc, 1977), thus only by comparison to other methods could we judge the effectivenessof the technique. Particle size by wet sieving is compared with palynological analysis for a site in the central deposit (ED 3) and one from the eastern section (BDD

23).

Mineral matter was separated-out by gravity, and the results of sieving with 2 0 mm and

0.25 mm sieves were dried in a 50°C oven, weighed,and plotted as the proportion of C, M and F

25 components for 13 core sites (Fig. 2-4). Tissue preservation (degreeof humification) is described in field observations, and in the written descriptions in this report using a modified von Post

Humification Scale adapted to tropical peats by Esterle (1990). There are 5 field categories: sapric, fine hemic, hemic, coarse hemic and fibric. The traditional use of field-determinedpeat types has been used only sparingly in the study of these tropical peats, as recent work (Esterle, 1990) suggests low correspondence between field classifications and the actual particle-size distributions as determined by point counting or sieving methods. Referenceis made to the field categories, alongside particle-size distributions, because peat workers are familiar with this index of tissue preservation (von Post,

1922). No sapric peat was encountered in any core. Peat Classification is based on the identification of macroscopic plant parts and palynomorphs in the peat, compared to plant and pollen associations identified in the surface samples, and uses botanical (e.g. Rhizophora peat, sedge peat) nomenclature.

2.4 GEOLOGICAL SETFING

The Changuinola deposit is situated at the easternmost onshore extent of the Lirnón-Bocas del Toro sedimentary basin (Fig. 1-1). The Bocas del Toro Basin in Panama, and its westward extension in Costa Rica, the Limón Basin, together make up the Tertiary and Quaternary back-arc basin behind the volcanic ranges of the Guanacaste and Central Cordilleras in Costa Rica, and the uplifted Tertiary marine sedimentsand intercalatedUpper Miocenevolcanics and plutonic rocks of theTalamanca Cordillera of western Panama. The onshore part of the basin extends about 400 km from the Costa Rica-Nicaragua border southeastward into Panama, narrowing eastward and becoming an offshore feature east of Laguna Chiriqui (Escalante, 1990).

The Costa Rica - Panama island arc was created by subduction of the Cocos plate beneath the western edge of the Caribbean plate. Andesiticarc buildingproceeded from latest Cretaceous through Eocene, and uplift and expansion of the emergentisland arc continued through the Miocene.

26 The oldest sedimentary rocks are of the Cretaceous ChanguinolaFormation, interbedded foramimferal

limestones,tuffs and lava flows, knownfrom a singleexposure in the valley of the Rio Changuinola

(Fisher and Pessagno, 1965). OverlyingTertiary and Quaternary sequences, approximately 7000

metres of predominantly marine elastic deposits, are known from exploratory drilling carried out by

several oil companies since the 1920’s. The major island arc sedimentarysequences were deposited

from the Oligoceneto the middle Mioceneas basaltic talus deposits, pro-delta and shallow offshore

sandstones, limestonesand shales. During Middle Mioceneuplift of the Talamanca Cordillera,

subsidence in the Limón Basin resulted in depositionof the Gatun Formation. This is a succession of volcaniclastics and carbonates that also includesisolated lignitelenses. Lignites and lignitic siltstones are interbedded with argillaceous and sandy sedimentaryrocks (Bohnenbergerand Dengo, 1978).

From Miocene to late Pliocene, the basin was the site of gradually shoaling marine deposition. The top of the sequence is the La Gruta LimestoneMember, approximately 450 metres thick. From early

Pleistoceneto the present, the region has experienceda significant rate of emergence (72 rn/Ma.;

Coates and Obando, in press), likely in responseto shallow subduction of the Cocos Ridge (Collins et al., in press).

The aseismic Cocos Ridge has effectivelyblocked subduction at the eastern end of the

Middle America Trench, leadingto deformationin an overall SW-NE compressional regime across the

Isthmus of Panama. The structural geologyof the Caribbean coastal area adjacent to the Ridge is dominated by a series of southwest dippingthrust faults, strikingNW-SE sub-parallel to the coast

(Camacho and Viquez, 1992; Denyer et a!., 1992).The general emergenttrend, related by Collins and others (in press), and Coates and Obando (in press) to crustal domingis punctuated by occasional coseismic vertical movements;uplift and coseismicfolding near LimOn(Denyer et al., 1991), and subsidence and localised marine transgression in the area of AlmiranteBay. The M=7.5 earthquake in the Valle de la Estrella, Costa Rica, on April 22, 1991, and subsequent aftershocks affected 150 km

27 of the Caribbean coastline of Costa Rica and Panama (Fig. 2-2). Part of the affected coastline, from the mouth of the Rio Changuinola southeast 12 km to the Boca del Drago channel, consists of a barrier beach behind which the large Changuinolapeat swamp has developed (Fig. 2-4). Studies conducted since the earthquake of April 1991 suggest that the break in the trend of the coastline marked by Almirante Bay may be related to as-yet unmapped faults which segment the coast into a series of tilted blocks (E. Camacho, personal communication),

Offshore in the Panama Basin, the North Panama Deformed Belt (Fig. 2-1) is an extensive, thick (to 7000 m) accretionary wedge which displays recent compression-related thrust faulting and soft-sediment deformation. The Belt approaches the coast in the near-offshore between Puerto Limón and Laguna Chiriqui, where continuous seismic reflection profiles show faulting, upthrusting and deformation in the most recent sediments(Clowes, 1987). These profiles also reveal erosion, in the form of canyons and coast-parallel channels (near-shore profile CSP3-4; Clowes Fig. 5.2a).

2.5 GEOMORPHOLOGY

The northwest coast of Panama is a site of active elastic and organic sediment deposition.

Much of the coastal plain is under a variable cover of Quaternary and Recent alluvium, and the coast is characterised by a series of barrier beaches behind which lagoons and extensive paralic swamps are developed. The uplifted and folded sedimentaryrocks of the Talamanca Range are deeply incised by a number of large rivers, whichtransport sedimentnorthward off the Cordillera to the Caribbean coast.

The Changuinola peat deposit has developedbehind a barrier beach extending 12 km southeast from the mouth of the Changuinola River, which drains an area of approximately 3200 .2km Wind driven currents move sediment consistentlyalongshoreto the southeast, as shown in Figure 2-8, a satellite view of the sediment plume of the ChanguinolaRiver. Sedimentation rates are high along this

28 microtidal (± 30 cm) coast, creating the ridge-and-swalemorphologytypical of prograding barrier

systems (Reinson, 1984). Cores behindthe shorelineshow well-sortedbarrier sands (Table 2-2) underlying Raphia palm peat 4 km landward of the present coastline and 673 cm below sea level.

Thus the barrier coastline is both aggrading in responseto subsidenceand prograding seaward across the continental shelf. Nearshore bathymetryreveals a shelf widest to the northwest off the coast of

Nicaragua (Fig. 2-1), which becomesnarrower and more frequentlyincised by submarine canyons to the southeast near Limón. Canyons are present off the narrow shelf northwest of Limón, where subsidence was recorded as a result of the 1991earthquake (Plafker and Ward, 1992). Southeast of the point at Linión, the shelf widenssomewhat,and is free of canyons until past the Panama border at the Sixaola River, beyond which it again narrows rapidly, and a canyon is present at the 100 fathom contour 12km off the Changuinola River mouth. Another, larger canyon is present seaward of Boca del Toro (Fig. 2-1). The shelf seaward of the barrier is narrow (12.5 km) and has a gradient of 4.2 ni/lan out to the 20 fathom line about 9 km offshore. A surface current of 1 to 2 knots moves sediment consistently to the southeast of the river mouth (personal observations). The size and shape of the sediment plume, which sweeps to the east and away from the remnant canyon, is revealed in false-colour SPOT multispectral satelliteimagery (Fig. 2-8). The barrier coastline terminates at Punta

Serrabata, where a tombolo connects the barrier beach to a rocky outcrop which was formerly an island.

Shelf bathymetry reflects erosionof the exposedcoastal plain during the last glacial lowstand. In particular, the distribution of submarine canyons gives some indication of the underlying structural control on coastal morphology,and of the lateral migration of the major rivers during the

Holocene. Major drainage across the coastal plain is directedtowards those segments of the coast which are experiencing coseismic subsidence,such as the regionaround the mouth of the Rio Matina northwest of the point at Puerto Lirnón,and the sectionof coast to the southeast of the Rio Sixaola in

29 Panama, which is the focus of this study. Subsidingcoastal regions are distinguished by extensive paralic swamps, and in some cases embayments,whereasthose parts of the coast which recorded uplift in the most recent earthquake are typically emergentsandy or rocky shores with dismpted and irregular drainage of the coastal plain. To the southeast of the Changuinola mire, Almirante Bay is a recessive coastal feature which is likelyrelated to the tectonic regime described above.

2.6 VEGETATION

Floral diversity in the present peat deposit is low and distinctly zoned (Cohen et al, 1989;

Phillips et a!., in review) into a sequenceof ‘phasiccommunities’similar to those described for the oligotrophic peat swamps of Western Malesia (Anderson, 1964; 1984) and Borneo (Bruenig, 1990).

Factors which account for floral zonation on peat are not fully understood, but are related to microtopography, nutrient levels, water table and pH of the groundwater, and to variations in the porosity and permeability of the peat itself. Concentric zonation in surface vegetation is echoed in a vertical floral succession from the base to the top of the deposit resulting from peat accumulation, elevated water table, and increasing oligotrophyof the mire. The ‘Andersonmodel’of domed peat developmenthas been summarized by numerous authors (Bruenig, 1990; Phillips et al., 1994) and related to coal depositional environmentsby others (Esterle, 1990; Cobb and Cecil, 1993). The

Changuinola deposit includes 7 phasic communities,6 of which contribute a distinctive peat type to the accumulating deposit. These phasic communitiesare: i) Rhizophora mangrove fringe swamp; ii) mixed back-mangrove swamp; iii) Raphia taedigera palm swamp; iv) Carnpnosperniapanamensis forest swamp; v) mixed forest-swamp; vi) sawgrass ± stunted forest swamp; vii) Myrica-C’yrilla bog- plain. Distinctive communitiesof peat-formingplants, along with their associated groundwater environments, determine much about the character of the peat which develops, and result in a stratigraphic succession which reflects the trophic evolutionof the mire through time. Consequently,

30 schemes which identify and classify peat (and coal) according to the principal floral components inherently imply much about the environmentof deposition.

False-colour satellite imagery shows the deposit to have two regions with differing vegetation patterns and surface drainage (Fig. 2-7). The western part displays a radial drainage pattern and concentrically zoned vegetation which reflects a domed topography attributed in the

Anderson model to an evolutiontoward increasingoligotrophy with increasing peat accumulation. No large streams flow west or north out of the mire; surface drainage off the central dome is principally as a sluggish sheet-flow in the low-gradientareas from the central bog plain towards the Talamancas.

Channelizedflow, in blackwater creeks which extendto the base of the peat, drains the higher-gradient margins towards the barrier and Almirante Bay. Creeks draining into the bay are stratified and brackish up to 3 km upstream, despite the low tidal range (Fig. 2-5). These creeks dissect the eastern part of the deposit into hydrologicallydistinct units visible in the satellite imagery. In this study we relate peat characteristics in the western and eastern parts of the deposit to their respective states of ombrotrophy and rheotrophy, which in turn are related to the factors controlling height of the water table, and of sea level.

2.7 AGE AND GEOMETRY OF THE DEPOSIT

The main body of the peat deposit is roughly rectangular in shape with long axis parallel to the coast and occupies the entire 8 km width of the coastal plain between the Talarnanca hills and the outer barrier. Peat extends from the lower alluvial plain of the Changuinola river 12.5 km southeast to the marine margin of Almirante Bay, and at least another 1 km beneath the bay. Greatest thickness of peat sampled was 950 cm (Cohen at al., 1989)and 833 cm (this study), and overall average peat thickness is estimated at 650 cm. Maximum elevationof peat measured is +667 cm above datum, and

31 the greatest depth -673 cm. Approximately40% of the volumeof the deposit is below present sea level. Datum (mean sea level)is consideredaccurate to within 10 cm.

Table 2-1: Radiocarbon Ages of Peat Samples (Beta Analytic Inc.) No. ID Sample Depth C14 C131C12 C13 adj o/oo age 1 24/92 BDD 19A 475 2160+/-60 -28.2 2110+/-60 2 72024 MILE5 810 3040+/-80 -25.0 3040+/-80 3 72025 MILE5 475 850+/-80 -25.0 850+/-80 4 71989* BDD 34 475 1910+/-60 -27.1 1880+/-60 Note: * denotes AMSdating, CAMS-i3316, L. LivermoreNatl Laboratory

Estimates of the age of the peat deposit are based on the 4 radiocarbon dates listed in Table

2-1. These dates give the followingaccumulation rates for different peat types:

- mangrove/back mangrove peat (No.1) 2.25 mm/a (from -4.75 m below present SL to present SL),

- mangrove/back mangrove/forestpeat (No.4) 2.52 mm/a (from -4.75 m to present SL),

- palm/forest peat (No.2) 1.48 mm/a (from 8 m to 4.75 m below peat surface), and

- sedge peat (No.3) 5.58 mm/a (from 4.75 m belowpeat surface to peat surface).

The oldest peat tested, from 54 cm above the base of core MILE 5 in the central western section, gave a corrected age of 3040 ± 80 BP in woody, hemicRaphialmixed-forest peat over grey sand. The base of the deepest peat core sampled (LAKE 9 - not dated) is topographically some 2 rn below the dated sample, and thus may represent an additional 1000to 1500years of peat accumulation, giving an approximate age of 4000 to 4500 years for the deposit. This age is similar to that of many Malesian coastal peat deposits (Anderson, 1983). It is possible that older peat may exist at lower elevations, most likely close to the Talamanca foothills,but none were dated in this study.

The surface of the peat in the western section is an asymmetrical ‘dome’,only slightly raised on the shore side, and slopingmore steeply close to the barrier (Fig. 2-9). The maximum measured gradient, in palm forest along the northern margin, is 1 rn in 330 m, comparable to gradients in most

32 Legend 10km Upper panel Lower panel LJL coarsepeat sand El shadingrepresentsresults of wet-seiving,in weightpercent medium peat clayparting [[J Percentof MineralAsh riioca,on fine peat IC14:3O4O’J-8 Percentof Coarseparticles — Percentof Mediumparticles wood> 2cm [] L-. Percentof Fineparticles ash spike Figure 2-9. Top: SW-NE cross-section of the peat deposit, showing location of cores and distribution of Coarse, Medium and Fine peat in relation to the generalized peat stratigraphy. At ED 3, near the centre, a schematic core shows results of pollen analysis (see Fig. 2-14). Bottom: Results of the particle size analysis (wet sieving) of 8 cores along the transect, showing uniformly moderate- to highly hunilfied peat at the marginsand base. The greatest contrast in humification is between the upper and lower parts of LAKE 10, ED3 and to a lesser extent MILE 5. Black shading, and dotted spikes indicate mineral matter> 4%. No correlation between mineral layers was possible. 33 Malesian mires, which commonlygrade at 1 m in 300 to 500 m (Anderson, 1983), but in contrast to the river-margin gradients of 1 in 25 (McCabe, 1987)to 1in 65 (Esterle, 1990) in some Sarawak mires, probably influencedby erosion of the banks. The margin bordering the Talamanca hills grades at about 1 m in 1km. No topographic survey data are available for the flood-plain margin, but analysis of SPOT imagery using the width of concentricvegetationzones to approximate topographic contours suggests a gradient no steeper than 1 in 500.

Topographic control of the underlyingbasal sands is provided by two transects normal to the coast, and by isolated sample sites parallel to the barrier. The barrier has a ridge-and-swale architecture characteristic of prograding barrier coastlines (Reinson, 1984), that can be traced at the base of the peat (Figs. 2-6 and 2-9). Cores are spaced at around 500 m intervals, but probes were made at closer spacing, as the modem, subaerial barrier has a ridge ‘wavelength’of between 50 and

100 m. Traces of the barrier stmcture are also visibleup to 2.5 km shoreward of the barrier in false- colour satellite imagery (Fig. 2-7). Peat originates in the swale immediatelybehind the beach berm where, despite the high porosity of the barrier sand, a linear marsh or swamp is established, due to high growth rates, dense vegetative cover, and precipitationwhich nonnally exceeds evapotranspiration rates (Fig. 2-6). Along a surveyedtransect, the distance from the top of the swash zone to the nearest measured thickness of ‘swale’peat (40 cm of peat, under 50 cm standing water in

Raphia swamp) is 94 metres.

2.8 SEA LEVEL CHANGE AND PUNCTUATED SUBSIDENCE

“Noliveswerelost,here {PuntaMono}orat the otherIndiansettlements,in the neighbourhood,but the groundappearedrent in variousplaces,thesandonthebeachwaseitherraisedin ridges,or depressedin furrows; a placewhich,in theeveninghadbeena smalllagoon,or pond, in which severalcanoeswerefloating,wasnowbecomequitedry; mostof the huts wereviolentlycrackedand twisted;and the effects,ofthe earthquake,wereeverywherevisible.” from Voyagesand Excursionsin CentralAmerica, by Orlando Roberts, 1827.

34 There exists a popular and historical record of seismic actitvity on the coast of Panama and

Costa Rica dating back to at least 1798, and reports of such events back to the late 1500’s(Camacho and Viquez, 1993). Earthquakes are knownto have occurred in 1798, 1822, 1912 (2) and 1991, all estimated (by Guendel, 1991)or recordedas greater than magnitude 7 on the Richter scale (Roberts,

1827; Gonzalez-Viquez, 1910; Guendel, 1991). Roberts’observations at Punta Mono in 1822 could have been repeated almost verbatim in 1991 whenthe Point was again uplifted, a nearby river mouth closed, and parts of the back-barrier lagoon were left high and dry.

a) Subsidence in 1991

Coseismic subsidence occurred along 30 km of the coast between the mouth of the Rio

Changuinola and Hospital Point on the northwest tip of Isla Bastimentos during the April 22, 1991 earthquake. Liquefaction effects were widespreadand spectacular throughout the alluvial plain

(Astorga, 1991; Denyer et a!., 1991; Guendel, 1991). Describing the scene a few days after the event,

Guendel (1991) wrote that Changuinola “perhaps represents one of the most dramatic cases of local to regional soil liquefaction ever documentedin Central America”. Mobilized sedimentwas consistently very fme-grained grey sand, which erupted as sand volcanoes and sheet flows from crevasses up to

500 m in length throughout the lower flood plain. Liquefaction-relatedsubsidence was widespread, but uplift may also have occurred, leadingto shoalingof dredged channels. Areas of coarser-grained sediment, however, such as the beach and river-mouthbars, were free of any signs of liquefaction, and we estimate a maximum 35 cm subsidenceat the river mouth, based on measurements of the degree of burial or submergence of trees rooted in beach sand (Fig. 2-10), and on sedimentary structures described in a later section.

35 *

Figure 2.10. Photograph of drowned tree on the shore side of the beach berm at site Beach 2. The tree was growing at a spot that is now 33 cm below present mean sea level.

36 The problem of distinguishingbetweenliquefactioneffects and true structural subsidence

occupied several investigators after the 1991event (Astorga, 1991; Camacho et a!., 1991; Denyer et

al., 1991; Guendell, 1991; Sherstobitoff 1991). Greatest reported subsidence, and greatest

earthquake damage, was in the communitiesof Changuinola,Almirante and Bocas del Toro.

The former is on the Changuinola floodplain, and experiencedextensive liquefaction and surface

fissuring, as well as local subsidencewhich left irrigation pumps standing suspended on their pipes 50

cm above ground level. The latter two towns are built in part on dredged fill in former mangrove

swamps, and variable subsidence in the filledareas can be attributed to liquefaction and settling.

Bocas del Toro, however, experienceda uniform subsidencewhich unhappily left the entire sewer

system below sea level (personal observations, and personal communicationswith Ing. E. Reyes and others, IRHE). Extensive shorelineobservationswere neededto establish the degree and extent of subsidence directly affecting the peat deposit and barrier beach. Destruction of the tide gauge at

Almirante necessitated re-surveyingof bench marks used for topographic control in this study, and we consider the elevations published here to be internallyconsistent, but with the possibility of an absolute error of a few centimetres.

Plafker et al. (1992) studied elevationchange from the 1991 event along the affected coast from the Matina River in Costa Rica southeastto Punta Mona, and one site in Panama. They found the effects more or less consistent with movementon a 25° to 40° SW dipping thrust fault at a depth of 40 km beneath the valley of the Rio Estrella in Costa Rica (Fig. 2-2). Southeast of the Changuinola

River, the amount of subsidence increases. At the easternmost extent of the barrier beacha tombolo connects the beach to Punta Serrabata (Fig. 2-1). the exposed coast of which consists of limestones and shelly sandstones of the Late MioceneWater Cay Formation and the Pliocene La Gruta Member.

We estimate subsidence of 50 cm at Boca del Drago, and about 70 cm at Isla Carenero, the most profoundly affected location on the coast, based on measurementson dock pilings and rocky

V 37 shorelines. Across the Boca del Toro channel, 500 rn southeast of Carenero at Hospital Point and at

Bastimentos, no subsidence was detected along the rocky shore.

b) Long-term Sea Level Change

Regional Holocene estimates of sea levelchange are much more poorly constrained than local historical data. Three published studies of Holocenesea levelchange in the western Caribbean, based on radiocarbon dating of mangrove peats (Bartlett and Barghoorn, 1973; Woodroffe, 1988;

Berger, 1983), and a predicted sea level curve for eastern Panama (Peltier, 1988) give a poorly constrained estimate for regional sea level changein the study area (Pirazzoli, 1991). Since the

Pleistocene sea level low stand of about 18,000years ago, Caribbean Central America experienced a generally transgressive regimeuntil about 4500 years ago, when sea level more or less stabilized and the modern Changuinola peat deposit began to accumulate. The Bartlett and Barghoom curve, located closest to the area now under consideration,is based on a single radiocarbon date of 35,500 yr.BP which Bush et a!. (1992) considerto be of questionablevalue, since it implies considerable uplift of the Gatun Lowlands (Canal Zone of central Panama). Ampleevidenceexists for Holocene sea level change in the area of the Changuinolapeat deposit, but no data on local long-term sea level change has been published. Regional sea levelestimates for 4000 yr.BP are between -7.5 m and -1 m, and for

2000 yr.BP, less than 1 m below present sea level(Pirazzoli, 1991). In this study a maximum 1m eustatic rise in regional sea levelover the past 2000 years is assumed, due to the high degree of uncertainty associated with the higher estimates (Bush et al., 1992). This estimate is compared to 2 sub-sea level dates (a C14 standard date and an AMS date) of mangroveand forest peat from sites now lying offshore in Almirante Bay (Fig. 2-1; Table 2-1). This shallow body of salt-water forms the eastern termination of the barrier coastline, and terrigenous sedimentsextend a considerable distance beneath the bay. Submerged peat was sampledat water depths of more than three metres. The peat is underlain by medium grained grey sand, and in places overlain by a thin layer of silty sands, lime mud,

38 and from cm of 2000 than consisted peat Macauley which taken by where showing

and Above zone, in The estimates, subsidence

fine subsidence

2010

fine

between

below

coral.

back-mangrove

hemic

dated

from

at

around

years

on

with

peat accumulation

hemic

the

present. ±

that

a

of

Radiocarbon

present the

60

series

Raphia

due

base, sheltered

Beneath a

woody

is

(Table

until of

350

mangrove

Macauley

10 the

mangrove (BDD

preserved,

base

to

2.1

m

and

Taking the taken

fairly

site

the

mean

peats.

depth palm

to 2-1;

to

the

peat shore peat,

450 19A)

did

was

absence

2.6 the

in

recently. (Rhizophora)

dates

grey

corer

Figure

sea

peat

peat,

into not

and down

cm

alternates top

mm/a.

195 within

representing

and

essentially

level

keep

sands,

in account thus

over

show

of

in

of

cm now

1880 2-4; to

2000

the

60

at

any

the

Autocompaction

were

water at pace

that

rooted

at

that a

cm

uncemented

dating between core

least ±

mangrove

apparent site

yrs,

and

the -475

free

the

60

dated

water

with periods

local

depth

(-510

at

medium

30

50 back-mangrove

yr.

a

of

shoreline

by

cm

which maximum

subsidence.

cm Raphia

metres.

clastic

BP relative depth

by

Beta

at

density

(sample

cm

fringe when

tidal calcareous

a

radiocarbon

(BDD

grained

peat

of

to site

39

Analytic

at

during

sediment

and

the the

-195

range,

sea-level -

the

increases

rate

600

back salinity accumulation

34).

site peat

forest-swamp

BDD

outer

(Rhizophora

grey

cm;

of

that

m

mud

local

mc).

mangrove

was

BDD19A

and

has about input.

offshore

rise

sample

34

7%, sand

limit

period

with

with

alternately

not sea AMS

is

Two

has

2.2

containing

a

The

of

pH

depth

evidently

level been abundant

series

was

salinity

in

been

zone

peat, -

the

is

samples

mm/a.

methods

Laguncularia

5.76),

Almirante

base

a

factored-in in

pre-earthquake

in some

combination

proceeding throughout

at

of

and

Almirante

the

of

at

17

kept

and

suggests

large coral 50

of

with

600 the suiphurous

the

extremely

%,

cm

peat

above

Bay. pace

core

drowned

wood

fragments

m

a

to

long pH -

corrected

from for the

farther

Bay

average

Acrostichum)

vibracore

these

with

at

sea

7,07),

The

mangrove

fragments.

half-cores

more

period

compact

673

mangrove has

475-478

level.

site,

core

east

occurs

cm

risen

(net)

than

age

for

is punctuated greater net history higher series the volcanic peat two sedimentary

peat floodplain sands, medium-ash matter) closer

rate

Changuinola

cores

deposit.

occurs

of

to

than

cm-thick

of lateral

of content

coseismic

rock

the

Evidence

Sediments

the

(BDT

2.2

(Fig.

subsidence

that

over

rocks

mire. peat

mire.

Sediments

fragments.

extent to

varying

at

2-12). leaf

5 mire

2.6 about

(range

which

and of

events,

In from

beds, of

mm/a.

of

the

the to

has

4)

the

the The 1000 2.9

from

the

consist 0.9 the

northern

mangrove

same

located

To

and

and

been

floodplain

deposit

ORGANIC

for

cores

southeast

to

Changuinola

m,

the

30.3

thin

the

the study,

12.9

the

the

of

southeast

about

a) Talamanca are

to stratigraphy

2.9.1

boulder

past

peats in

peat norm

intervening

wt%

Changuinola

61.6

the

occupy

not

a

(Fig.

AND

500 core 2000

can

(Fig.

past

ash)

peat, during

peat

CLASTIC

wt%

of

and

2-1),

m

accumulate 2.4

the years. 60

CLASTIC range.

suggests

throughout

2-1

deposit

and

but

of

cobble-

at

sediments

km

that

km2,

and

floodplain,

the

the

40 1).

River

rather

1000

from

Historically,

period.

SEDIMENTS River

interfinger

marine-marginal

site

Cohen

between

suggests

a

to

rn in

Floodplain

SEDIMENTOLOGY slower

are

closest the the

being silt-size

the from

bar

the

et

carbonaceous

The

entire river

eastern

the

al.

clastics

4000

interfingered

rate

lateral with

the

to

this upper

sediments

(1990)

(BDT

SanSan

the

945

nearest

of

or

the

subsidence

part

peats

transition

river, subsidence are

more

cm

rate

northwestern

13)

reported

mire

dominated

of

sediment

depth.

active

suggests

originating

is

consisted and floodplain

years

the

evidently

on

from

has deposit, 27.2

channel

the

during

the

of

with

that

occurred

by

ash subsidence,

margin

to

alluvium

northwest

of

silts

in

slightly

feldspar 43.8

the low-

ash this

and

content

the

on

and

early

the

(mineral

the

of

style wt% folded

to

as

to

the

and

a

and

of

at

of

a *

Figure 2 11. Lanunated silts, sands, peat and cm-thick leaf beds of the alluvial plain. Deposits are moderately bio-turbated; entrances of two rodent burrows can be seen, centre and right of centre.

41 o —

CD -o t;.) CD

CD — — z — -t o°. o C)

CD

CD

.D) • !fl

-

CD

-•CD

16km Sediment Legend Core Legend t.pi pç CD bog-plain sedge Campnosperma carbonate sediments coarse peat []sand peat I : peat C) 0.. 0. sawgrass I stunted mixed forest shelly carbonates medium peat clay parting .000 I’,’,—’ forest peat cn peat fine peat 1C14:3040+/-8OI back-mangrove Raphia peat peat radiocarbon wood> 2cm age medium - fine sand \“, Rhizophora [] peat I-i (rooted) tidal

America, development

unbroken record

landward sand progradation. ‘wavelength’ progradation I) were and cm. beds with normal subsidence, dipping dipping overlain

Sedimentary

Beach

range

At

ridges, a

of

made

is

wave

the wave

site

beds, fine

by written

where

Most

by Morphology decrease

on

2,

at

back-berm

finer the

Beach the

of

tidal cut of

sands

are

close conditions.

two the

corresponding

40-5

structures studies

facies

barrier

highest

seasonal

notch

by

evident

grained

morphology

channels

sites:

in

of

2

to

hurricanes.

0

the

elevation

the

m the models

above

of

overlie

of

had

of

between

present Beach

in

storms

the pre-earthquake

landward-dipping

barrier river

Trenching -

which

and

the

resumed

The

to barrier

the

in

of

mouth

is

sedimentary

seldom

a

1,

the

The effects

are shoreface

top

barrier

beach is

seaward-dipping ridges

a

remnant

at

consequence

the

‘60’s

the

is

its a

across of

Changuinola

(Fig.

central

shown

most

overtopped

the

of and

original

norm reflects

beaches

back-beach. and

b)

beach

rapid

is

swash

2-6).

the

beds

strandplain structures

seaward

Barrier

medium

‘70’s

and

point

in

berm

the

height

subsidence

of

Figure

face,

of

(Glaeser,

At

zone.

much

barrier

came

beds

43

by

ongoing

the relation

on

Beach

System

revealed

(1.68 grained

storm overlying

The

revealed

the arid

post-earthquake

of

2-6. evolution

from of

A

beach

the

barrier

the medium few

was 1978).

m,

and

subsidence between

1,

waves.

The

the

sand,

former

steep

landward

event-driven

1.44

weeks

by

not

subsequent

and is

temperate

have

exposed

7.5

microtidal

trenching

However,

experiencing

sands steeply

m,

(20°)

truncating

rates

berm-face

km

after

recognized

0.6

of

(present)

dipping

from

medium

are the

of

barrier

m

the dipping

Holocene aggradation

eastern

on

subsidence

data

and

at

shoreline. in

earthquake-induced the

shallow

the

Beach turn

to

(6°)

washover

back-beach,

wave-dominated,

consists

for

the

grained

Changuinola

a

barrier.

(20°) seaboard

depth

truncated

planar

much

stratigraphic

importance

1).

landward

and

and

The

seaward,

of

seaward

of

The

during

of

washover

Trenches

3 of

about

to

the

and

parallel

North

River,

a

of

30 Figure 2.13-a. Planar laminated back beach sands at site Beach 2.

Figure 2.13-b. Photograph of bedding structures in a trench across the beach berm at Beach 2, shown schematically in Figure 2.6. In the photo, the sea is to the left, and flat-lying washover beds rest on steeply seaward-dipping beach face sands. The barrier aggraded about 30 cm, and prograded several metres in the 13 months that elapsed between the subsidence of the beach and the trenching 44 thickness of 30 to 50 cm (Figs. 2-13-a and 2.13-b). This sequence is interpreted as a record of the landward-stepping of the beach face, caused by coseismicsubsidence, followed by rapid aggradation and progadation of the beach face and back beach.

ii) Grain-size and Mineralogy - Table 2-2 shows the distribution of grain size of sediments from 12 sites shown in Figure 2-4, including a point bar in the Changuinola River, proximal and distal sands along the length of the barrier, and basal samples from belowthe peat deposit. Mineralogy, sorting, grain size and rounding from 12 sites are listed in Table 2-3. Grain size of the proximal barrier sands changes little along 9 km of barrier shoreline:well-sortedmediumto fine grained, angular to sub- angular sands, with an immature mineralogyincludingpyroxenes, feldspar and volcanic glass and less than 10% quartz grains. Heavy minerals are rapidly winnowedout down-coast (Tables 2-2 and 2-3).

Basal sand landward of Beach 1 (halfway along the modem bar, site Lake 3) plots in the same grain size range as the barrier sands. At the distal end of the barrier (Beach 4, 11 km), siliciclastics are predominantly very fine sand (> 4 1) dominatedby felspathic grains, to which a coarse to very fine carbonate component originating in the offshore barrier reef is added. The distal barrier experienced a greater degree of subsidence (an estimated 50 cm); the beach berm has not regained its former elevation, and the beach face is submerged and impassable due to fallen trees.

c}Peat Basal Sediments

Sedimentsunderlyingthe peat deposit can be dividedinto clean medium to fine grained barrier sands, fineto very finesands with palm and sedge roots associated with drainage channels and thin palm-swamp peat, and silts and clays associated with drainage from the Talamancan slopes along the southwest margin of the deposit. Those from greater depth (-10 m, well below the peat-sand contact) are similar in grain size to the barrier sands, and display the same trend of decreasing heavy mineral content and increasing feldspars and volcanic rock fragments with increasing distance from

45 TABLE 2-2: Results of Thin Section Analysis of Barrier and Basal Sands Distance from opaques quartz feldspar volcanic rf pyroxene amph olivine mica carbonates Sample River Mouth Sorting Ab Ro Sz Ab Ro Sz Ab Ro Sz Ab Ro Sz Ab Ro Sz Ab Ro Sz Ab Ro Sz Ab Ro Sz Ab Ro Sz

Point bar 2km poor 5 sr .07 tr r .13 55 a .13 35 r .13 tr r .07 upstream Beach 0 0 km mod 40 sr- .20 tr sa .26 25 a .20 tr a .26 30 a .20 tr sa .07 sa Beach 2 1 km well 75 r .13 tr sr .13 10 a .26 10 a .33

Beach 1 7.5 km mod 15 sa .13 5 sa .26 30 a .26 35 a .26 15 a .26

LakelO 8.5km well 10 a .20 10 a .26 5 a .26 70 a .46 tr a .46 tr a .46 tr a .13 D=8 m Outer beach 9 km mod 5 sa .07 5 sa .13 30 sa .20 50 sa .20 5 sa .13 tr a .07 tr sa .13

Beach 4 11 km vpoor tr sa .07 5 a .13 20 a .13 tr a .13 2 a .07 tr a .13 70 a 1.3

BDD 23 13.5 km poor tr r .07 5 r .07 50 a .26 45 a .33 tr a .07 C- D=6 m CS 3 13.5 km mod 5 sr .07 5 a .13 80 a-sr .78 5 sr .13 5 sa .13 tr sa .13 tr .13 D=3.5 m BDD 22D 14 km well tr sr .13 5 a .26 70 sr-a .26 5 r .26 15 a .26 tr a .13 D=10 m BDD 22D 14 km well tr a .26 100 a .39 D=20 m BDD33 18 km mod 5 a .07 45 a .33 50 sr .39 tr a .07 tr a .13 D=10 m

Notes: Sz = estimated mean grain size in mm, Ab = abundance, Ro = roundness = rounded, s = sub-, a = angular; volcrf = volcanic rock fragments. feldspar is both plagioclase and kspar; pyroxene is almost all clino-, possibly with a trace of olivine and amphibole. carbonates are shells, coral fragments, and lime mud. D = Depth of sample in metres

46 TABLE2-3 Grain Size Distributionof Sands Seive Sizes (Phi scale) Distance Sample >—14) >04) >14) >24) >34) >44) 4+4) from River

Point bar % 0.00 0.08 2.25 5.01 22.41 44.30 25.83 2 km upstream Beach 0 % 0.00 0.00 0.06 7.64 72.71 19.63 0.03 0 km

Beach 2 % 3.61 0.01 0.07 10.94 67.56 17.61 0.15 1 km shell&pebble Beach 1 % 0.00 0.00 0.02 5.61 76.37 17.94 0.05 7.5 km

Outer % 0.00 0.01 0.05 5.32 78.60 16.16 0.06 9 km beach Beach 4 % 1.97 9.77 11.60 15.77 26.26 33.44 1.40 11km shell and coral BDD 22D % 0.08 1.27 3.17 33.14 51.96 8.90 1.50 14km D=lOm BDD 22D % 5.05 15.29 10.48 10.11 9.46 10.28 39.33 14km D=20m BDD 33 % 0.11 0.47 5.30 31.09 53.77 8.08 0.96 18km D=lOm BDD23-b % 0.21 1.01 2.15 11.66 47.37 15.18 22.51 13.5 km D=5m BDD 23-b % 1.23 3.99 3.74 12.53 41.77 16.99 19.89 13.5 km D=6m Lake 3 % 0.05 0.69 0.77 15.97 65.48 9.67 7.40 7.5 km D=3.3m

47 the

basal less and

transported of distal Talamancas

carbonate clastic

size success,

least table

averaged represent salinity

section.

the

main

2-3). well-sorted

distribution

20

sands

shows

sediment

deposit

sediments,

and

m

to

river

Fine-grained

values

a The

mud,

beneath

determine

at toward

special

ash

high, also

and

channel.

20

physical

plume

than

and

for

(lime

from

enter

m

however,

in

low

the

case Pta.

the depth

numerous

the

the

the

of

mud, the

and

the

clastic

basal

and

eastern Basal

Pondsock.

beach

deeper

in

the

nature

domed,

is

bay

mean

the

and

chemical

and

Changuinola poorly

sands

sediments sands

east.

coralline via samples,

and 2.9.2

north-central

active

coral

of

values

ombrotrophic

the

underlying

of

western sorted

Most

from

Significant

characteristics

core

debris)

Rio

carbonate ORGANIC

a)Peat

and

forms.

although

enter

of

sites River

d)

carbonate Banano,

BDD31

standard sections,

the

Airnirante

part

were

the

sediments.

characterization associated

Two

bay

(Fig. differences west

sedimentation

lithologically

Boca of

48

SEDIMENTATION

found

(Table from

margin

offshore of the

with

deviation and and

2-8)

the

del

Bay

bay.

the

to

the for

with a

Carbonate

and

2-3).

peat

Drago

in

slightly

bordering at

southwest

dissected, selected

patch

Fine

all

are least

long-lived

for

similar.

is

are

parameters

occurring.

channel

deposited

pH,

clastics

sunnnarized reefs

bimodal

6

sediments

mangrove

in

the

total

corner

and

To

depth

were

channels

swamp

on

sourced

the

in

sulphur,

along distribution

are

the

Sediments

of

drilled, part at

southeast

with

peat in

evident the

both

flood

is

the

Table

(eg.

rheotrophic

on

essentially

bay

a

wt samples,

with

sites,

eastern

the

bimodal

tide

BDD

are

%

in

(Tables

and

2-4. beneath

flanks

moisture,

limited the

as

and

an

are

23)

the

which

The

margin

free

algal

eastern grain

to

of

2-2

are

the

at

the

of TABLE 2-4: Summary of Some Physical and Chemical Characteristics of Changuinola Peats Western Section Eastern section Rhizophora mangrove peats mean s n mean s n= mean s pH 4.38 0.59 321 5.74 1.09 389 6.5 0.58 70 high - low 6.29-2.82 7.89-2.67 7.6 - 5.4 wt% Sulphur 0.23 0.18 227 2.24 2.55 143 3.52 1.09 36 high-low 0.51-0.08 13.7-0.08 5.9-0.4 wt%Salinity <0.01 n.d. n.d. 0.69 0.87 413 1.42 0.96 104 high-low 2.7-0 2.7-0 wt%Moisture 92.74 5.1 76 84.28 7.66 134 84.49 5.45 45 high - low 99.2-67.1 95.7-60 94.1-67.5 %Ash 3.29 6.39 85 10.49 9.19 43 18.57 19.72 21 high - low 38% -0% 54%-1% 92%-4% Notes: s.d. = one standard deviation; n = number of samples in data set

49 b) Geochemical Parameters

In previous reports (Phillips et al., 1994; Phillips and Bustin, in press) the relationship between pH, salinityand total sulphur content of the peats has been explored in detail. High sulphur content is spatially related to marine or brackish influence. Coastal mangrove and back-mangrove peats with moderately high S content (1 to 5 wt% S) and high salinity (> 0.5 wt%) dominate the eastern margin and extend beneath the salt water and shallow marine sediments of the adjoining bay.

Marine influence extends only a short distance onshore, except in the vicinity of brackish blackwater creeks which drain the swamp into AlmiranteBay. Peats associated with these channels are low in salinity (< 0.5 wt%) but very high in S (5 to —14wt% S), around 90% of which is carbon-bonded sulphides, apparently the result of an ongoingbiogeochemicalchain of S reactions leading to the concentration of C-S fonns. The western part of the deposit is domed and oligotrophic, and the vegetation and the peat are concentrically zoned. Stunted, sawgrass-dominatedvegetation produces fibric, very low S (<0.25 wt% S) peat found in the upper few metres of the central bog plain. Around and below the bog plain peats, dense hemic and fine hemicpeat, the product of mixed-forest and palm-forest swamp vegetation, has consistentlyhigher S content, averaging between 0.25 and 0.5 wt%

S.

The highest sulphur content (>5 wt%) is found in peats near the brackish influence of blackwater drainage channels up to several km from the coast. Very high sulphur was also found in the basal peats in the deepest parts of the deposit (Cohen et al., 1989), which are interpreted to have

been associated with channels. Very high sulphur content is found even where salinity is undetectable

in peat, porewater or basal sediments,and despite the low pH of these peats that normally inhibits

bacterial sulphate reduction.

50 c) Degree of Hunufication, Ash, and Moisture Content

Tissue preservation is a standard parameter in environmentalstudies of both peat and coal

(Stach et al., 1982). Diessel (1986) deviseda Tissue Preservation Index (TPI), based on the relative volumes of structured (i.e. well-preservedcell walls) and unstructured (finelycomniinuted, or gelifled) tissue which he then used in interpretingthe degree of wetness of the mires in which some

Australian coals originated. Numerous authors (Lamberson et al., 1991; Obaje et al., 1994) have since applied this principle to other coals, with various qualifications, but with the common assumption that highly degradedhumic coals originate in a relatively oxygenated environment, and coals with a high proportion of structured tissue in a waterlogged,acidic and poorly oxygenated mire.

In coal studies, the TPI is determinedby the point counting of macerals, a volumetric measure. It is possible to apply volumetric estimates to peat samples, by measuring the volume of sieving results

(Stanec and Silc, 1971), or point counting of thin sections (Cohen, 1968) or polished epoxy- impregnated blocks (Esterle et al., 1990). However,direct volumetric comparisons of peat to coal cannot be made, due to the variable compactabilityof different peat types, and also the selective loss of matrix material during coalification(Shearer, 1994),thus proportions by weight are used in this study. The method, although not directlycomparable to coal methodology,is accurate and allows for the analysis of large samples.

Ash content is also used as an environmentalindicator in coal studies, and has been related to particle size or degree of humificationin low ash peats (Davis et al., 1984). It is generally assumed that: a) oxygenated environmentswhich produce highly degraded peat will also selectively concentrate whatever mineral matter happens to be present; andb) that peat deposited in mires close to sites of active clastic sedimentationwill contain higher proportions of mineral matter than more distant sites.

51 TABLE 2-5A: COPE DESCRIPTIONS OF PEATS FROM THE WESTERN SECTION OF THE DEPOSIT 5 ED 3 CORE MILE 1 MILE 1.5 MILE 3 MILE Peat Elevation: Top ± 617cm + 637cm + 655cm + 655cm + 624cm and Base + 148 cm ÷ 7 cm - 165cm - 209 cm - 186 cm (+ above SL; - below SL

Modem Vegetation Raphia palm-swamp Mixed forest-swamp Sawgrass/ stunted Myrica rn..Cynlla r., Mynca ni.-Cyrilla r., forest sedges, grasses: bog- sedges, grasses: bog. plain plain

HumilIcation 49.9% to 21.4% n.d. 58.8% to 19.6% 66.2% to 4.0% 60.6% to 5.40% (percent coarse fibres) avg. 32.5% avg. 39.6% avg. 36.1% avg. 39.9%

SalinityRangc(wt%) <0.01 <0.01 <0.01 <0.01 <0.01

Total Sulphur Range (wt%) n.d. 0.1610 0.51 nd. 0.l4toO.3 nd. pH Range 3.6 (top) to 49 (base) 3.3 (top) 104.8 (base) 3.8 (top) to 5.1 (base) 3.6 (top) to 5.5 (base) 3.6 (top) to 5.6 (base)

MoistureRange n.d 91.3%to94,9% nd. 90.3%to97.l% n.d. avg. 93.1% avg. 94.4%

Ash Range n.d. 14% 10< 1%;spikes 1.0%or less except 10% to < 1%: spikes 6% to <1%; spikes at at 120cm (4%) and for a single spike at at 90(10%), 390 60cm (6%), 240 cm 510cm (14%) 300cm (14%) (4%), 480(6%) and (4%) and the basal 570 cm (4%) metre (8%)

Basal Sediments Rooted grey clay Peaty grey clay Peaty silt and VF Yellowish-grey peaty Rooted F grey sands grey sand sand, over F grey Channel sands

Peat Classification 0-124 F Hemic 0-270 C Hemjc-Fjbric 0-270 Fibric-C Hernic 0-330 Fibric-C Hemic 0-630 Fibric-C Hemic (depths in cm) 124-304 Hemic 270-510 Hernic, 300-810 Hemic; much 330-840 Hemic-F 630-750 C Hemic 304-394 C Hemic- woody at 270-330 wood 690-750 Hernic; much wood Hemic, woody Fibric; Woody Hemic 510-570 C Hemic from 600 to base 750-8 10 F Hemic to 454

Table 2-5A: Continued CORE LAKE 10 LAKE 8 LAKE 6.5 LAKE 2 NL I + cm + 150 cm Peat Elevation : Top + 500cm + 397 cm + 342 cm 254 and Base -320cm -295cm - 193cm -76cm - 130cm (+=aboveSL;-=belowSL)

Modem Vegetation Myrica m. - Cyi-illa Myrica in. - Cyrilla SawgrassI stunted Mixed forest-swamp Raphia palm-swamp r, sedges. grasses: r.., sedges, grasses: forest bog-plain tree hammock

Humification 73.7% to 5.60% 39.8% Tb 18.1% 40.2% to 15.0% 22.4% to 2.8% 26.4% 105.10% (percent coarse fibres) avg. 32.0% avg. 29.7% avg. 29.2% avg. 10.8% avg. I.69% Salinity Range (wt%) <0.01 throughout <0.01 throughout <0.01 throughout 0.02 (top) to <0.01 0.01 (top) to <0.01

TotalSulphurRange(wt%) nd. n.d. nd. 0.23to0.33 n.d. pH Range 3.6 (top) to 5.8 (base) 3.7 (top) to 5.4 (base) 3.2 (top) to 5.2 (base) 2.8 (top) to 4.9 (base) 3.9 (top) to 4.9 (base)

Moisture Range nd. n.d. n.d. 78.6% to 95.2% n.d. avg. 88.8%

AshRange <1%throughout

BasalSediments PeatyFandVF CleanFandVFgrey PeatyFandVF CleanFandVFgrey Peaty,rootedgrey yellowish grey sand sand yellowish grey sand sand (Barrier) sand (Barrier-swale) over clean F grey sand over clean F grey sand

Peat Classification 0-300 Fibric-C Hemic 0-225 C Bernie 0-475 Hemic F Hemic throughout F Bernie throughout (depths in cm) 300-550 Hemic 225-550 Hemic 475-500 C Hemic 550-62sWoodyHemic 550-675 F Hernic 500-550 F Hernic 625-750 F Hemic Notes: C = coarse, F fine, n.d. as not determined

52 TABLE 2-5B: CORE DESCRIPTIONS FOR THE EASTERN SECTION

CORE BDD 23 BDD 22 BDD 31 Peat Elevation Top + 10 cm + 5 cm sea level (high tide line) and Base -450cm -590cm - 400cm (+ above SL; - = below SL)

Modem Vegetation Campnosperma Rhizophora mangle fringe Rhizophora mangle fringe panamensis forest-swamp forest forest

Humiuication 30% to 16% 27% to 3.7% 22% to 2.5% (percent coarse fibres) avg. 19% avg. 12% avg.12%

Salinity Range (wt%) <0.01 throughout 0.59 to 2 20 0.11 to 0.41

Total SulphurRange (wt%) 0.27 to 13.7 n.d. l.O7to 8.43 pH Range 3.6 (top) to 5.9 (base) 6.7 (top) to 7.9 (base) 4.3 to 7.4

Moisture Range 76% to 95% n.d. 75.4% to 85.3% avg. 90% avg. 81.7%

Ash Range 16% to <1% 65% (shells, diatoms, 57% to <1%: spikes at spike at 100cm (16%; no ostracodes, forams, sponge 100cm (57%; no carbonate) carbonate) spicules) to 5% (mineral and 150cm (38%; shelly) grains,mixedlitholon’)

Basal Sediments RootedF to VF sand, over Carbonate:rounded coral Clean F to VF sand cleanF to VF sand, andshell fragments, plus (Banier) (Channel sands) dispersedmineral grains

Peat Classification 0 - 285 Coarse Hemic 0 - 150Hemic 0. 165 Hemic andFine (depths in cm) 285 -450 Bernie andFine 150- 590Fine Hernic Hernic, Woody Hemic 165- 400 Fine Hemic Notes: C coarse, F fine, n.d. as not determined

53 The proportions of coarse, mediumand fine organic particles in bulk peat samples

representing 25 or 30 cm core incrementsare used to generate plots depictingthe degree of

humification of the peat at 3 sites in the eastern section of the deposit and 8 sites along a surveyed transect in the west. All proportions are given as per cent of the total dry weight of the sample on a

mineral-matter free basis. Moisture content,also recorded for some samples, is related to the degree

of humification and the density of the peat. The deposit is divided into eastern and western sections on the basis of vegetation zonation, and hydrologicalcharacteristics, and the results are presented

separately in Table 2-5A and 2-5B.

1) Western Section: --- Giventhe permanentlyhigh water table associated with everwet climate, the preservation of structured plant parts is good in oligotrophicmires, where low pH of the groundwater and low nutrient availability discouragesboth bacterial activity and luxuriant subaerial biomass production. Plants thriving in such conditionstend to have stunted above-ground components, but extensive root systems, that contribute to the fibrous componentof the resultant peat. Figure 2-9

(upper panel) shows a cross sectionthrough the western part of the deposit illustrating the distribution of well-preserved fibric peat and more humifiedhemicand fine hernicpeat along the SW-NE cross- section shown in Figure 2-4. Stratigraphy is based on the degreeof tissue preservation (particle size distribution) in 8 cores (Fig. 2-9 lower panel) along a surveyedtransect from the foothill margin to the barrier. Characteristics of the peat are summarizedin Table 2-5A, and peat type is correlated with pollen stratigraphy in core ED 3, near the centre of the transect (Fig. 2-14). As can be seen in the

lower panel (Fig. 2-9) particle size andhumificationin the marginal peats (Mile 1 near the southwest margin, NL1 and Lake 6.5 toward the barrier bar) tend to be uniform for the full depth of the peat. In the central deposit ( Lake 10, Ed 3, Mile 5 and Mile 3 in the central bog plain, and Lake 8 in a

Myrica-Cyrilla tree ‘hammock’)there is a contrast between the upper fibric and coarse hemic peats,

54 1 ______

Myrica+ Cyrilla Palmae

F: ::::.I

BogPlain

II

11 ii Sawgrass- U StuntedForest U U , U I Campnosperma ForestSwamp

U Raphia PalmSwamp I I I I I 1O%5% I I I I I 0%20 40 60 percentoftotal percentoftotal cm 0 5% 10 0 2(Y340 Ashcontent Resultsofwetsieving Successioninterpretedfrompollenanalyses

Figure 2-14. Comparison of the results of wet sieving (particlesize distribution)with palynological analysis of core ED 3 from the central part of the bog-plain. Myrica+ Cyrilla, and Palmae (Raphiapollen + palm phytoliths) represent the trend clearly. The wet sieving results distinguishbasal hemic and fine hemic forest-swamppeats from upper fibric and coarse hemic sedgepeats, reflectingvegetationchanges and increasing oligotrophy in the mire. The sawgrass/stunted forest-swamppollen zone is transitional,and variableboth in palynomorph assemblages and in degree of humiflcatiomof the peat. Pollen data is discussedin detail in Chapter 3. Particle sizes are as follows: Coarse >2.0 mm Medium > 0.25 mm Fine <0.25 mm VonPostclasses are defined on page 21, and described in the Appendices.

55 and underlying hemic and fine hemicpeats. Degreeof humificationis greatest in areas of greatest

surface gradient.

ii) Eastern Section: --- The complexvegetationzonation of the eastern part of the deposit, visible in

Figure 2-7, reflects an equally complextopography,hydrology,and peat stratigraphy in that part of the deposit which is drained by the brackish blackwater creeks emptying into Almirante Bay.

Sedimentation within the mangrove fringe varies with location, from sandy peat to limey peat.

Rhizophora mangle (the red mangrove)is the only mangrovecolonizingthe marine margin - the white mangrove species Languncularia raceniosa is commonto dominant in the immediate back-mangrove

swamp and bordering brackish blackwater creeks. Rhizophora does not favour either silty or carbonate substrates, and isolated individualsare found rooted in coral as much as a kilometre offshore. A species of thin-shelledoyster (Crcissostrea sp.?), easily recognizable in core, is normally found attached to Rhizophora rootsfrom the upper limitto about 30 cm below the lower limit of the tidal zone, and when found stratified within otherwiseshell-freepeat suggest possible past subsidence events. In addition to the mangrovefringe and back-mangroveforest swamps along the bay and creek margins, there are three areas of domed,oligotrophicsawgrass marsh and stunted forest-swamp, each surroundedby a complex of Raphia and hardwoodforest-swamps. Figure 2-15 shows particle size variation in three cores in a cross section from Almirante Bay through one of these lesser domes to a the blackwater channel, Canal Viejo. Particle size in the forest-swamp and mangrove swamp peats is uniformlyfine; at the coastal sites the <2.0 mm componentaverages 87% to 93%, and in only 2 samples was there a fibric (>2.0 mm) componentgreater than 25%. All samples were classified as hemic or fine hemic;there was no sapric peat encountered,despite the high degree of humification.

Peat characteristics are summarizedin Table 2-5B.

56 ____

Peat Core Legend Sediment Legend

large wood fragments Campnosperma Rhizophora peat peat F,‘ ‘I [:. : mineral ash layer mixedforest medium- finesand shelly layer peat (rooted) Organic particle sizes: Raphia peat carbonatesediments coarse, fibrous I back-mangrove shellycarbonates medium; <2.0 mm peat bog-plainsedge sawgrass/ stunted flne;<0.25mm :::: peat forestpeat

Figure 2-15. A generalizedviewofwetsievingresultsofcoresfrom acrossthemarinemargin ofAlmirante Bay and up Canal Viejo, a brackishblackwatercreek. The section approximates the SE end of the cross section in Figure 2-12, although BDD 31 is displaced. BDD 31 is a typical mangrove peat core, highly humified throughout, and havingboth carbonate-richand elastic ash layera. BDD 22 representsa saline estuarine site, alsoin themangrovefringe-forest.Thesedimentsare not strictlyspeaking peat, as they contain>25% non-humic materials. The ash includesscattered grains of feldspar,mica and quartz, but is dominated by the remains of marine organisms. The peat is very highly humifled, fine hemic throughout. BDD 23 is also highly humifled throughout, and is associatedat the basewith brackish drainage. Near the base the sulphur content is almost 14 wt%. The basalpeat was depositedin a back-mangrovezone. Figure 2-16 relates the results of particle size analysis to the palynologyof core BDD 23.

57

in

mineral

Raphia Figure Ash

60 1899.

40

content

2-16. palm

20

ash

The

spike

peat

A

site

comparison

Results

is

at tends 20

I

about

100

to

cm

40

of I

50

be

of

is

wet

m

less

unknown,

the

60 north

I

sieving

humified

wet

80

of sieving

I

the

but

than

present

may

results

woody

Rhizophora

be

channel.

58

related

Acrostichum for

nrnnt

angiosperm I

#

core

Succession Laguncularia

nf

in BDD

In

some a.

I

23 forest-swamp

÷

way

interpreted

with

to

]

I

I

j

I Ii

rwnt

palynological

an

Campnosperma

pariamensis attempt

if

peats. from

I L ntI

-

at

pollen

The

dredging

analysis

source

Back-mangrove

Campnosperma

Palm

analyses

Forest

Forest

Swamp

(Chapter

Canal

Raphia

Mixed

of

Swamp

the

Swamp

Swamp

Viejo 3). BDD 31 is an example of an intertidal mangrove site (Fig. 2-15). Between 100 and 150 cm depth there is a shelly layer and a silty layer suggestinga possible subsidence event, followed by a resumption of mineral-free peat accumulation. The BDD 22 core (upper part) represents a modem estuarine site, taken at the outlet of a tidal blackwater creek. Due to the high content of bivalve shell fragments, diatom frustules, ostracode valves, foram tests, fish scales and teeth and sponge spicules

(24% to 72% by weight), the sediment is not true peat. Estuarine microfauna are not present in the basal 160 cm of the peat. Silt-sized quartz, mica and other grains were present throughout the core.

Below the silty base of the peat is carbonate sand consistingof well-roundedshell and coral fragments. These deposits are consideredto represent shallow offshore (back-reef) sediments over which the barrier and peat deposit have prograded. The base of site BDD 23 represents an earlier channel margin site influenced by the brackish waters of a blackwater creek. Transitions in peat te from top to base of the core echo lateral transitions in surface vegetation (Phillips et al., in review), from Campnospermaforest-swamp peat, to mixed-forest,Raphia palm, and back-mangrove peat. The history of floral succession, interpretedfrom the palynology of the core, is plotted alongside particle size distribution and ash content of the peat in Figure 2-16.

2.10 DISCUSSION

2.10.1 CLASTIC SEDIMENTARY RESPONSE TO RECENT TECTONISM

a) Changuinola River Floodplain

Rivers draining the Caribbean side of the Cordillera are prone to flooding, (2 such events occurred in the Changuinola flood plain during the 3 years of this study), and the sedimentological record is written by the interelationship between flood events and tectonic events. The lower

Changuinola flood plain has been affected by agricultural activity, but certain inferences can be made regarding the Holocene evolution of the floodplainbased on sedimentary response to recent subsidence. In the early Holocene it appears that the Changuinola river may have flowed southeast

59 from the defile at which it exits the foothills,along or parallel to the course of the present Rio Banano

(see Fig. 2-4), and crossed the continentalshelf via the deep canyon of Boca del Toro (Fig. 2-1), A

180 m deep incised channel extends from near the mouth of the Rio Banano across Almirante Bay

(much of which is less than 5 m deep) and through the Boca del Toro passage, indicating erosion to a very low base level. Local records and locallyproduced maps of the lower Changuinola floodplain

(unpublished data of the Chiriqui Land Company; C. Stephens, pers. comm.) since the turn of the century document numerous changes in the main channelof the Changuinola River. Before 1920the

Changumola drained to the northeast during floods,through the mouth of the neighbouring SanSan

River. A channel switch, which occurred at the defile,and dam building by the banana companies, brought an end to this, and the Changuinolanow absorbs all the floodwaters.

In July 1991, 10weeks after the earthquake, a major storm struck the stretch of coast affected by the earthquake, with very differenteffects in regions of uplift and of subsidence. On the coast 60 km to the northwest, 10,000 hectares of the coastal plain shoreward of the mouth of the Rio

Estrella, the major river in the area, were devastatedby flooding,the result of uplift at the coast which partially dammed the river mouth and caused floodwatersto back-up onto the alluvial plain. The areas of coastal uplift are not prone to the developmentof extensivemires, despite their susceptibility to flooding, as the rivers deposit much of their sedimentload on the coastal plain. The flooding

Changuinola River did not, however, inundatethe coastal plain nor the immediatelyadjacent peat swamp to the southeast, the surface of which is somewhatelevated above normal flood levels and heavily forested with Raphia palm and hardwoods. Earthquake-inducedsubsidence lowered the elevation of the alluvial plain; the floodingriver broached a levee, but remained channelized, entering an abandoned oxbow and breaching the loweredbarrier beachovernight. During the flood, the introduction of overbank sedimentsinto the peat swamp was minimal, and has been restricted to areas within 500 - 1000 m of the river during the entire period of peat accumulation, as evident from the low

60

coal.

detennine

Each

barrier

factors

of

fore-arc

tectonics

calculated

seaward

marine

rate

barrier

established

apparently

Punctuated

erodability

insulated

allowing

ash

barrier

of

content

has

Barrier

sedimentation.

in

subsidence

carbonates,

will

or

migration

geological

Four also

generating the

its

islands

from

The

that

back-arc

in

whether

of

step

subsidence

of

morphology

sands

accumulation

detennine

30

the

tectonic

factors

24%

peats

flood

seaward

to

or

peat.

also

of

display

such

50

significance,

barrier

the

of

settings),

barrier

2

influence

the

defme

the

cm

km

setting

determines

provides

thickness

the

as

barrier.

and

or

world’s

increments.

away.

structures

of

beaches.

are

effective

coastlines,

landward,

the

composition:

and

low

dictates

than

present

depositional

accommodation

and

of

Subsidence

Shelf

that

barrier

ash

whether

areas

the

width

would

A

and

strand

the

there

increases

at

and

The

supply gradient

barrier

the

coastlines

mineralogy

of

b)

scale

organic

of

tides

tectonic

amount

leave

is

alluvium,

Barrier

environment plain

south-eastern

events

the

no

of

sand

of

to

may

and

space

61

continental

a correlation

sand-size

evolution

peats.

the

sedimentation

signature

of

setting,

are

body

evidently

storms

not

which

Beach

by

subsidence,

southeast,

for

associated

be

virtue

The

of

is

the

extreme

sediment,

sediment

dictate a

reflect

greater of

the

between

shelf,

on

limiting

aggradation

resulted

areas

the

of

the

barrier

although

is

which

barrier,

their

with

tectonic

which

barrier

of

terrigenous

confining

in

of

source,

and

shelf

the

factor;

that

in

peat

seas

beach,

elevation

determines

channelized

tidal

eventually

barrier

it

of

in

morphology

direction.

gradient

influence.

deposition

has

marginal

climate

both

the

Glaeser

rocks

flux

working

peat,

not

sand

system.

and

time

are

of

and

yet

whether

may

and

or

stream

The

the

(1978)

to

body,

Bedding

a

are

the

and

and

in

shallow

the

been

strand-plain

arcs

tidal

low

limit

Regional

cumulative

consort

better

controlling

space.

back

presence

flow,

the

(i.e.

range.

the

to still structuresand beachmorphologyreflectthe styleof subsidence,whichoccursas discreteearthquake- drivenevents,and whichis greatestto the southeast. Threesedimentsourcescontributeto the barrier beach. Immaturesands of the ChanguinolaRiverare the principalsource,originatingat the northwest endof the barrier. The secondsourceis an offshorecoral reef,presentat the extremesoutheastendof the barrier, whichboth donatescarbonatesandsand debristo the barrier and creates a low-energy beachand a sedimenttrap in the shallowback-reefenvironmentseawardof the barrier. Thethird sedimentsourceis the lushtropicalvegetation,whichrespondsto subsidencethrough changesin phasic communityalongthe marinemargins,stabilizesbeachridgesand depositspeat in swales.

2.10.2 HYDROLOGICALCONTROLSON PEATACCUMULATION

Hydrologicalcontrolson peat accumulationand peat characterincludesourceof recharge, rate of recharge,hydroperiod,rate of dischargefromthe mire,natureand morphologyof the confining layer, and penneabilityand heterogeneityof the peat (Clymo,1983). In the case of ombrotrophic mires,rechargeis limitedto atmosphericsources,and waterentersthe mirefrom above and flowsout.

In rheotrophicmires,somewater flowsin, enteringfromthe bottomor edgesof the mire. Rate of rechargeis the amountof waterentering,and hydroperiod,whichis the periodof fluctuationof the watertable, is a measureof the regularityof recharge(Myers, 1990). The confininglayer is the seal whichpreventsthe mirefromdraining. Peat accumulateswhenthe watertable is abovethe mire surface,and deteriorateswhenit driesout.

Peat permeabilityis highlyvariableand verypoorlyconstrained,but generallyvaries directlywithpeat density,andthus withparticlesizeand compaction.We do not have a great dealof quantitativedata on peat permeabilityin the Changuinoladeposit, and substitutemoisturecontentand particle sizedistributionsas proxydata for degreeof humificationand thus peat density. Two studies of peat permeabilitybasedonthe rate of intrusionof salinewatersintofreshwaterpeat at sites in

62 Almirante Bay, althoughnot complete,indicateverylowpermeabilityfor mangrovepeat, whichtends to be denseand compact(85% moisture),and slightlyhigherpermeabilitiesfor Raphia and forest- swamp peats (85-90%moisture). The bog-plainsedgepeats and stuntedforest peats sampledin this study average 95% moisturecontent,andhavemuchhigherpermeability.

a) WesternSection: — Hydrologydictatesthe fundamentalphysicaland chemicalcharacteristicsof the organicsedimentsin the westernsectionof the deposit. At the presentstage of evolutionof the deposit,hydrologicalcontrolsin the ombrotrophicwesternregionare internallydriven,ratherthan being a reflectionof tectonicforces. As thereis no evidencethat rechargeoccurs frombelowthe modemmire is assumedto be effectivelyombrotrophic.At the Talamancanmargin andthe

ChanguinolaRiver margin,dischargewaterflowsout of the depositas surface sheetflow,and in shallow(<50 cm) streams. Alongthe back-barriermargin,whichhas the steepestgradient,drainage has beendisruptedby the dredgingof a canalintowhichfive smallstreamsdischarge. Oneof these cuts to the base of the peat, and connectsfour smallsandybottomedlakeswhichare remnantsof back-barrier lagoons.

There is somevariationinthe heightofthe watertable across the westernpart of the deposit,and a corresponding variation in the degreeof humificationof the peat. The surfaceis slightlydomed,and the vegetationandthe peatare concentricallyzoned. The Andersonmodelof floral successionand increasingoligotrophyinthe evolutionof raisedforestedmires in SE Asia has been shownto be applicableto the Changuinolamiresystemas well(seeChapter3; Phillipset al., in review). Tissuepreservationas estimatedby particlesizerevealsthe sameoverallstratigraphic pattern seenin sulphur and pH profilesandmoisturecontent,andgenerallycorrelateswithmore detailedpalyno-stratigraphicanalyses(Fig.2-14). The marginsof the depositare generallywell

63 the of concentration humification woody hemic woody between very which decomposed original or but assimilatory, plain incorporate 0.25 5 sulphur mcrease

m

the

another

biotic

with

of

low

wt%

peats,

water

and

data

fibric peat peats,

concentrations. plant

wt%

ash

higher

pH

processes

It

Stunted,

S)

fibric

are factor

sulphur.

is mixed-forest (Raphia,

table

content hemic

sites

to in peat

and

we

material, total

of

apparent

available.

low-sulphur

coarse

S

organic peat

find

the

than content,

if such found

sawgrass

sulphur

and

involved

they

as

high

It Campnosperma,

from

no

hemic

on

as

well. although

fine that

is

in Again,

significant sulphur

are

and

the the expected

Thus

level between

the

bog-plain

and

hemic

degree

peats

(sedge)-dominated

subject

in

peat

However palm-forest

measured

sulphur

upper

wt%

the of

however, either

not

compounds

humification overlie

peat

(Phillips

0.25

degradation that of

difference

thoroughly

to

ash

few

vegetation.

content

humification

the

mixed

fluctuating

m

from

pH the

and

(HTA)

metres

beyond more this ash swamps

of same

and

0.5

top

in

forest-swamp),

of content

study

the

in

decomposed

concentrates woody vegetation of

studied,

Bustin,

for

the wt%

of

to

the

process

the

peat

64

woody

produce

water

the is

base,

all

no

original

total

broadest

much

is

S.

in

peat

central

low

significant

not in

still

table,

whereas

cores.

of

debris

The

sulphur

press).

produces

hernic

ash

more than

directly

concentration

hemic

phyterals

resistant

are

and

distinction sulphur

bog

or

(<10%)

leads High

less those

dependent

the

and

if

in content

correlation

plain. and

We

the

related

fibric,

most

significant

variable

compounds,

fine

to

levels

must

processes

in

fine

conclude

plant

and

approximately

these

between

Around

of of

by

hemic

low

to

hemic

be

on low

of

the

the

community

digestion

(r

sulphur degree

peats

sought

humification hydroperiod

pH 2

than

different

central

S =

which that

peat,

and

peat herbaceous

including (<0.5%)

0.04)

and

is

the

of

some

in content

below

still

principally

would (Fig.

very produce

double humification, bog

is degree

explaining

has

types

found

low

aspect

peats

and

plain

occur those

low

2-9).

the

a

serve

and

of

large

the

in

of

of

height coarse

bog

S the

for

pH,

3

of

that

in

(<

to

to subaerialbiomass. Water table fluctuationsare greatestwheresurfacegradientsare steepest(between

NL 1and Lake 6.5 in Figure2-9), correspondingto the zoneof denseforest-swamp. Theseare the sites of mostuniformhemicpeat accumulation,andalso presumablysites of highevapo-transpiration fromthe luxuriantfoliage. Highestconsistentwatertable is in Raphia swampon shallowpeat around the marginsof the deposit,and in the centralbog-plainandthe lesserdomesto the east (Fig. 2-7), whichare vegetatedwith algal mats and a sparseand stuntedflora, and whereevapo-transpiration rates are accordinglylow. Raphia peats tendto be coarsehemicto hemic,and sedgepeats fibricto coarsehemic.

The most distinctivefeaturesof the bog-plainpeats are their fibricnature, reddishcolour and extremelyhighmoisturecontent. Drainedof superficialwater,westernpeat samplesaveraged

93%moisturecontent(averageincludesthe deeperforest-swamppeats: rangeis 67% to 99%), comparedto an averageof 84% for the easternpeats (Tables2-5Aand B). Equallydistinctiveis the calculatedrate of accumulationof 5.58 mm/a.,basedon a radiocarbonage of 850 ± 80 years for coarsehemicpeat (45% fibrous)475 cm belowthe surface. This highrate contrasts sharplywith rates publishedby Anderson(1983)for peats inthe upperpart of Malaysiandomeddeposits (2.22 mm/a for the upperS m of peat in his phasiccommunity6). Andersonfoundthat accumulationrates werelowerin the later-stage(hisphasiccommunity6 and 7), oligotrophicswamps,possiblydueto reducedbiomassproduction. However,the centraldomesof the Malaysiandepositsare stuntedbog- forests,not sawgrass swamps , andthe peat surfaceof the bog-forestsfrequentlydries out. The

Changuinoladepositis apparentlyquitedifferentinthis respect;the bog plain surface is not only normallysubmerged,but alongmuchof the surveyedtransect,the upper root-matis effectively floatingon a very watery ‘soup’of fineand medium-sizedgranulardebris,and up to 60% well preservedroots and other fibres. In the lightof the wetnessof the bog-plainpeats,the in situ

65 accumulation rate uncorrected for moisture content means little, if the water table were to drop in the

central plain, the peat surface would follow it down, possibly to the extent of creating a depression.

The effective elevationof the central bog plain along the surveyed transect is I m in 7 km,

withmargin gradients a maximum1 in 330. Winston (1994) has successfully fittedtheoretical curves

to existing peat dome profiles from Malaysian mires, assuming constant hydraulic conductivity

(permeability)of all peat in the profile. However, his models do not account for the significant

vertical variations in conductivitythat are inherentin deposits fitting the Anderson model (as described

in detail by Esterle, 1990), despite his recognitionthat vegetation type has an effect on hydraulic

conductivity. In citing the case of a Germanbog in which later peat accumulation rates increasedover

early rates, he ascribes it to the effects of ongoinganaerobic decay at depth which creates an apparent

increase in accumulation rate withtime, without accommodatingthe implied increase in density and thus decrease in permeability. In situ accumulation rates meanlittle without factoring-in density variations. It may be that stacked hydraulic modelscan accommodate density changes, whetherthey be due to autocompaction, ongoinganaerobic decay, or floral succession. In the case of the

Changuinola deposit, the profile is felt to be the result of ponding within a basin of low-permeability hemic and finehemic peat.

The densest peats sampled,mangroveand forest peats, accumulate at rates comparable to

Anderson’slate-stage peat (mangrovepeat at ca. 2.25 mm/aand back mangrove peat at ca. 2.52 mm/a

(this study), vs. 2.22 mm/aof Anderson,1983). The very high in situ rate of accumulation of sedge peats reflects lack of compaction. The domedcentral bog plain is essentially a mass of well- preserved root material floating in an acidic, nutrient-poor bath, contained within a basin of dense, woody peat of extremely low permeability. Dischargefrom the central mire is by surficial drainage, subsurface flow being effectivelydammedby the surrounding forest-swamp peat, and

66 evapotranspirationis limitedby the stuntedvegetation. Onlytowardthe steeperNE margindoesthe surfacedry out and watertable drop to 10-20cm belowthe peat surface. The dispositionof hemic and finehemicpeat at the base and marginsof the deposits,whichforma type of internalbounding surface, suggeststhat thesedense, lowpermeabilitypeats forma bowlwithinwhichthe floatingbog- plain has developed. The rate of accumulationof thesepeats is in inverseproportionto peat density, and suggestsa processin whichthe variablehydrologicalcharacteristicsof the peat dictatethe height of the watertable, and hencethe surfacetopography. The differentialin accumulationratesthat allowsfor the evolutionof a lip’of dense,low-permeabilitypeat is a functionof the differencein biomassproductionof forestpeat vs sedgepeat - i.e. it is createdby increasingoligotrophy,as

Andersonconcluded. Increaseddegradationdueto occasionaldrying-outof the surface servesto increasedensity,and decreasepermeability,but doesnot appearto be enoughto counterbalancethe highrate of biomassproduction. This is undoubtedlydueto the highrainfalland relativelysmall fluctuationsin watertable.

b) Eastern Section: — In the westernpart of the deposit,the majortransitionsin peat characteristics are the stratigraphicboundariescreatedby the upwardevolutionof the mire. Sea level,whichalmost bisectsthe westerncross sectionof the deposit,doesnot appearto forman hydraulicbounding surface,as there is no indicationof salineinfluenceat the base of the peat. In contrast,the complex hydrologyof the easternsectionhas createda complexstratigraphy,overwhichin placesa transgressivemarinesignatureis superimposed.The overridinghydrologicalcontrolthroughoutis the amount,andtrend, of punctuatedsubsidence. The complexityis evidentin palynologicalanalyses,but verymuchgeneralizedin analysisbasedon degreeof humificationat the resolutionattemptedin this study (Fig.2-16). Plotsof changesin humification,and of variationsin thegeochemical characteristics,allowthe constructionof a generalizedstratigraphyin whichcontrollingtrendsare evident(Figs.2-9 and 2-15).

67 There are 4 major tidal blackwater creeksdraining the eastern section of the mire into

Almirante Bay (two have been modifiedby dredging,and one of those now forms part of a canal).

The mire is discharging down-dip,the streams flowingparallel to the barrier in the direction of

maximumsubsidence. All are long-lived,extendrightto the base of the peat, have sandy or silty

sedimentsat the channel floors, and have a stratified salinity profile, with fresh water at the surface

and salinities of 19 to 23 ppt in the bottom waters. Discharge rates fluctuate considerably between

drier and wetter periods (Fig. 2-5). A few smallercreeks are eroded into the peat, but the major

channels effectively dividethe eastern sectionof the deposit into hydrologicallydistinct sectors

bounded by channel-marginpeats with a distinctivegeochemicalsignature which has low salinity and

very high (5 to 14 wt%) sulphur. Each of these sectors has its owndischarge pattern. SPOT satellite

imageryreveals small domes in 3 of the eastern sectors, based on vegetation zoning and surface water

drainagepatterns (Fig. 2-7). There are two possibleexplanations for these domes: firstly, they may be

incipient bog plains experiencingelevationand increasingoligotrophy; secondly, they may be

remnantsof a more widespread bog plain which is ‘deflating’due to incision by blackwater creeks

(Fig. 2-17). Present surface vegetationzoning,whichis roughly concentric about the domes, suggests

the former. However, coringhas revealedfibricpeat at sites in the east which are now heavily

forested, but may at one time have borne a stuntedvegetation. Spacing of coring sites is inadequateto

make a finaljudgement. The implicationsare profound; either the mire is evolvingtoward a more extensive bog plain, or it is drowning.

The high rate of basement subsidencealong the eastern margin of the mire has resulted in a

second form of hydrological boundary withinthe eastern section of the deposit, the sea level boundary.

This boundaryis diachronous, trending approximatelyat right angles to the above-mentioneddrainage

68 Freshwaterpalm-swampandforestswamppeaton alluvialplain,andInswaleonbarrier.

DrainageofthedepositIsrepresentedbythesymbols: r\ = Surfacedrainage , (thickarrow=highfloworchannelizedflow) j • = Flowoutofdeposit(towardviewer) + = FlowIntodeposit(awayfromviewer) subsidence — Mangroveandback-mangrovepeat 2 \ aroundtidalchannels; \. Mixedforest-swamppeatexpandsover .fl% alluvialandswalepeats; 4__.mj• _• Barrieragaradesandprogrades.

.-- periodic subsidence events 3 Riverchannelshiftsduetosubsidence; Peataccumulatesfasterthansubsidence 4— Forestswampexpandslaterallyand verticallywithrisingwatertable; . Barrieraggradesandprogrades.

•-- periodic subsidence events —- Sawgrass-stuntedforest-swamppeat accumulateswithincreasingoligotrophy Incentralarea; Barrieraggradesandprogrades,followed seawardbyforest-swamp.

Continued small 1k 1k 1k 1k 111 1k 1k 1k 1k III 1k * 1k 1k 1k 1k subsidence events - , 1111k 1k_1l— Bog-plaindevelopsonpartialhydrological 1kW boundingsurfacesofdensepeat Aggmdahonandprogradationofbarrierandpeat domecontinue. or Larger subsidence event SeawaterIntrudesIntodepositviablaclcwatercreeks- k1k1k1k1k backmangroveandmangrovepeataccumulates; Moredirectdrainageintothesealeadsto higher dlschaia viacreeks,andpartialcollapseofperched watertableIndome; I Partofdepositdrowns;

Figure 2-17. Proposed model of peat developmenton the barrier coast as a result of periodicpunctuated subsidence. Black shadingindicatesmangroveand back-mangrovepeats. Solid greys are forest-swampandpalni swamp peats. Patterned areas are fibric sawgrass/stuntedforest-swampand bog plain peats.

69 channelsand normalto the trend of the outercoastline,definedby the northwest-migratingmarginof

AlmiranteBay. This boundarystepseastwardwitheach subsidenceevent,drivingbiologicaland geochemicalresponseswithinthe miresystemintimewiththe tectonicclock,and thus can be expected to overprintthose areas susceptibleto floodingwithits transgressivesignature,and drive the stratified, brackishheadwatersof the blackwatercreeksdeeperintothe deposit.

The highestsulphurcontent(>5 wt%)is foundin peats proximalto the brackish influenceof blackwaterdrainagechannelsup to severalkmfromthe coast. Veryhigh(-‘14wt%) sulphurwas also foundin the basal peats in the deepestparts of the deposit(Cohenet al., 1990),whichare thus interpretedto have beenassociatedwithearlierchannels. Veryhighsulphurcontentis foundeven wheresalinityis undetectablein peat, porewateror basal sediments,and despitethe low pH of these peats whichinhibitsbacterial sulphatereduction(Fig.4-6). Peats associatedwiththese channelsare lowin salinity(< 0.5 wt%) and veryhighin S (5 to -‘14wt% S), around90% of whichis stable carbon-bondedsuiphides,apparentlythe resultof a biogeochemicalchainof S reactionsleadingto the concentrationof carbon-bondedsulphurforms(Chapter4). The peats are formedin a back-mangrove swamp,froma complexvegetativecommunitythat includessalt-tolerant(Raphia, Laguncularia,

Acrostichum) and non-salttoleranttree species(includingSymphoniaglobuhjèra, Campnosperma panamensis andflex gulanensis) and shrubs(Miconia curWpetulata, Cespedezia niacrophylla and

Ouratea sp.). Sedges,grasses and fernsare common.The resultantpeats are medium-to fine-granular hemic to finehemic),consistingalmostentirelyof degradedwood,withoccasionalwoodfragments and roots. They are lighterin colour,and slightlylessdenseand higherin moisturecontentthan

Rhizophora peat.

70 2.10.3: IMPLICATIONS FOR COAL GEOLOGY

a) Transgressiveand regressivesignatures, and the relation ofpeat deposition to active ciastic

sedimentation

Coal geologistsoftenassumethat low-lyingcoastal peat depositsmust be highlysusceptible

to stormgeneratedclastic‘contamination’,as is commontoday in North America. The inter-tropical

convergencezone,which is freeof cyclonicstorms,is relativelynarrow,but hurricane-freecoastlines

may wellhave beenmoreextensiveinthe past, witha differentdistributionof continentalmassesand

oceanic-atmosphericcirculation. Hencethe developmentof extensivewave-rather than storm-

dominatedcoasts shouldnot be discounted. Suchcoastlinesare idealfor the formationof lowash,

low sulphur strand-plaincoalsimmediatelyadjacentto environmentsof activeclastic deposition.

In the Changuinoladepositthick, low-ashpeat is accumulatingon a rapidly subsiding

coastlinewithinlessthan a kilometreof botha flood-prone,sediment-ladenriver, and an actively

progradingand aggradingbarrier beach. Bothclimateand tectonicsfind eloquentand subtle

expressionin this seeminglyunlikelycombination.Estimatesvary, but most agreethat compaction

ratios of 7:1 to 10:1are not unreasonablefor peat to bituminouscoal (Ryerand Langer, 1980);the

factor may be less for densewoodypeat (< 85% moisture),and considerablymore for verywet (>

90% moisture)peat. The Changuinoladeposit,preservedin its presentconfiguration,potentially representsa singlecoal bed some8 km in widthand 12km in length,orientedNW-SE withthe long axis parallelto the coastline. Onthe northwestand southwestmargins,the hypotheticalbed interfingerswith alluviumand clays,and thickensquicklyfrom carbonaceoussedimentsto 60 to 100 cm of low ash coal (700 cmof peat), overa distanceof 500 m (Figs. 2-9 and 2-12). To the northeast, behindthe shoreline,the bedtapers-outmoregradually,over2500 m, cut by occasionalchannels.To the southeast,withmorecomplexgeometry,the bedtapers out beneathshallowmarinecarbonates,

71 again over about 2500 m, and in places ends abruptly in vertically walled channels, 3 to 10 rn wide and up to 3 km in length, oriented roughly parallel to the barrier sand body.

The cessation of peat accumulation, andthe burial and preservation of the deposit, could result from both tectonic and climatic causes. The observedtrend of drowning and burial beneath shallow marine sediments in the southeast, as a result of an increase in the net rate of subsidence, may escalate until mangrove growth is impossible. This has occurred already in the southeast, as shown by the presence of drowned peat surfaces several kilometresaway in Almirante Bay, and the focus of peat deposition has migrated northwest with ongoing subsidence. Thus a transgressive termination of peat deposition is consideredthe most likelyend. A second possible cause is a change toward a drier and more seasonal climate, which could lead to increased degradationand partial ‘deflation’of the deposit, and also to an increase in siliciclastic sedimentinflux (Cecil et al., 1993). This may eventuallyresult in aggradation of the coastal plain and burial of the deposit beneath fluvial sediments.

At present, the Caribbean coastline southeast of Puerto Limén is in an overall regressive regime, despite the fact that it is subsiding rather than being uplifted, from about the Sixaola River to

Punta Serrabata (Collins et al., 1994; Miyamura, 1975). The northwest section of the peat deposit bears what, in terms of coal geology,would be considereda regressivesignature. Well-sorted barrier beachsands are aggrading in responseto subsidenceand prograding seaward over shallow marine carbonates and silts of the continental shelf. The peat behindthe barrier sands is prograding along with the barrier, is aggrading as the water table is elevated by internalhydrologicalprocesses, and is successionallyzoned both vertically and horizontally. Cores from near the centre of the deposit carry no indicationsof transgression throughout perhaps 4000 years of peat deposition. A few km to the southeast, and in places at the base of the deposit, back-mangrovepeat is overlain by a successionof freshwater forest-swamp peats. Coal resultingfrom this part of the deposit would be low in sulphur

72

sulphur

induced

overprint

would

teredolites

brackish

and

of

otherwise

expressions

to

greatest

whether

formed

its

40%

deposits,

in

sand

rising

and

a the

beach

history.

brackish

redistribution

ash,

of

body,

trend

be

sea-level

in

flooding

during

the

to

the

drainage

freshwater

There

in

deposits

the

and

has

carbonate-free

To

ichnofacies;

the

the

of

peat

of

If

and

peat

marginal

marine-

the

resulted

would

preserved

the

southeast.

the

tectonically-driven

form

remains

(Phillips

lies

in

deposit

accumulation

southeast,

channels,

coast

of

transgressive

behind

the

peats

in

be

of

sulphur

and

in

pests

presence

the

Savrda,

judged

an

and

some

is

as

the

and

et

the

with

brackish-influenced

Hence

irregular aggradation

below

coal,

the

al.,

marine

the

(Chapter

burial

forms

berm

relatively

question

a

regressive

rate

peat

1994), of

1991) long

signature

marine

the

the

present

local

large

crest,

of

that

transgression,

has

xylic

is

transgression

environment

axes

a

5).

beneath

coherent

and

as

and

low-ash

transgression.

kept large

occurs

numbers

signature.

rather

sea

(peat)

to

from

At

include

of

in

the

how

ahead

both

the

area

level,

Chapter

peats

fine

somewhat

in-seam

as

than

mangrove

and

hardground

flooding

73

profoundly

of

would

the

the

of marked

sea

is

grained

of

despite

In

resists

(Phillips

buried

within

proceeding

drowned

presence

peat

or

water

Chapter

4,

The

evidence.

be

fallen

the

surface,

ambiguous

and

by

deposit

having

erosion.

carbonates

logs

net

interpreted

the

with

periodically

distribution

transgressing

and

the

peat

back-mangrove

of

behind

5

rate

peat.

and

from

the

superposition

abundant

Bustin,

shelly

and

and been

Evidence

under

of

Were

stumps,

short-term

bedding

southeast

relative

subsidence

the

along

and

as

more

layers

of

inundates

in

carbonates

transgressive;

major

it

marine

corals.

teredo-bored

total

press)

of

preserved,

the

some

extensive

structures

sea

peats, within

the

of

effects

to

margins

sulphur

sand

has

seaward

level

waters

are northwest,

influence

in

previously

and

growth

and

cores

determined

bodies.

examined.

of

during

the

rise,

i.e.the

of

logs

and

of

silts.

earthquake-

can

indications

on

coal

the

of

the

of

which

position,

forms

(the

parallel

landward

fresh

Internal

much

deposit

barrier

rapidly

About

roof

The

is

of of difficultyof distinguishingprimarysulphurfromsecondary,‘transgressive’sulphur in mangroveand

back-mangrovepeats has beenapproachedbut not yet fully resolved. In most samplesdescribedin

those studiesmarinepenetrationwas limitedto 1to 2 rn,and sulphurcontentdid not increasewith

flooding. However,it is difficultto extendshort term observationsof transgressedpeats to

transgressivecoals. It is likelythat the rate of subsidenceand subsequentsedimentationmayaffect

the degreeto whichmarinewatersultimatelyaffectthe coal. The shortterm observations,however,

point to the importanceof the progenitorvegetation,whichdeterminespeat densityand permeability,

in admittingor limitingmarineinfluence.

Lithotypevariationsin a hypotheticalcoalbed wouldpreservea recordof syndepositional

variationsin degreeof huniification,andthus reflectvariationsin vegetation,peat densityand hence

the hydrologyand trophicstate of the progenitormire. Highlyhumifiedwoodypeats fromthe margins

and base of the centraldepositwouldyieldmassive,dull, fine-grainedcoal,high in huminite. Fibric

and coarsehemicsedgepeats fromthe centralbog plainand lesserdomesin the southeastwouldform

finelybandedbrightcoalwithabundantstructuredmacerals. Becauseof the variationsin peat density

betweenforestpeats and sedgepeats it is likelythat upon burial and dehydrationthe relative

proportionsof woodycoal overherbaceouscoal wouldshift in the directionof a relativelygreater

volumeof woodycoal. The largevolumeof herbaceousbog plainpeat wouldbecomea relatively

smallvolumeof brightbandedcoal,fulfillingobservationsof Phillipsand DiMichele(1981)that most

economiccoals have formedfromlargewoodyvegetation.

2.11 CONCLUSIONS

The Andersonmodelof floralsuccessionand increasingoligotrophywith increasingpeat accumulationappearsto accountfor the evolutionof the Changuinolapeat deposit,withtwo

importantdifferencesrelatedto the depositionalenvironmentwhichmanifestthemselvesin the

74 hydrological peat where may which area punctuated dry from drains conductivity climate subsidence southeast results effectively and Discharge 40% it swamp

is

season

forest-swamp

restricted

deposition. where be

of

the

the

displays

slowly

in

has

the

the applied

Malaysian

periodic

The Asian On

swamp

from

a

and

the

is bog

deposit

subsidence drowned

suspension

controls in

the

earthquake-driven,

in

to

western

peat

no the

hence

to

plain

the

bog a

that

The

Panama

is

radial the

peals rapid

internal

dense

is

central

deposit

and

influenced

forest

due

part

surface amount

on below

of

interpretation

part

has

rise which of the

Indonesian

pattern, peat

to

marginal

coast of

evidence

peats. well-preserved

been

bog

of

the

has

regular

sea

in

the

never

of accumulation.

the

act

relative

by

inability

is thick,

drowned

level,

very deposit subsidence

and

and

Thus

deposit

restricted

tidal

as

forest

dries

drying-out prototypes of

of

the

occurs

close low-permeability

low-ash

marine

the

environments

sea

climate blackwater

in

of

resulting out,

beneath

peals.

is

root influence

the

the

to

level

to a in

instantaneously

The

but

peat domed influence

the southeast

peats surface mangrove

material of

are:

and

rather Underlying

marine

is environmental

the

most 75 oligotrophic

accumulation

creeks.

tectonic

commonly

of

i)

have

of

ombrogenous

peat

flow,

punctuated

than

hydrological tectonically-driven

is

recent coal

in

where

waters.

vegetation

not accumulated

surface a

gradual

the

setting

dilute

probably

deposition.

and

apparent

event

submerged

bog

the

bog

factors

rates

incrementally.

However,

which

granular coastal

subsidence

bog

produces result

to

plain bounding eustatic was

as

during

keep-up

in

in

with

that

greatest

a

strongly

most

an in

are

subsidence.

beneath

punctuated

result

matrix.

although

a

an distinguish

rise; environment

a

the

stratified

variant

surfaces.

rate

body

of

with

elevated

The

of

last

to

and

the

influences

is

10-20

low

the

Only

the

of

greatest

net

approximately

2000

deposit.

of

subsidence,

ii)

In peat

palm-swamp

southeast,

hydraulic

subsidence,

this

water the Rainwater

rate

cm

the

in in

absence

years

which

model

the which

deposit

the

of

of

ever-wet

and

table Rather,

clastic

water.

of

the

an that

of

is

that

or

a to these unhesitating ACKNOWLEDGEMENTS to northwest discharge uniformly hydrological support, British low-permeability driven of Electrificacion) Research large of from vegetation subsidence sediments Sanchez leaving subsidence

tectonically Eduardo

the

active

all

areas

laterally

deposit

by

Columbia.

a

but

family, as

elastic

record

Grant

The The

internal

into

with of high,

and

of

by preserved.

well Reyes,

a

support

the control,

and the

narrow

development research restricted blackwater

extensive

driven

peat

each

of

and

92-1201-18 deposition.

as

Bibi, of

base

mangrove

bottom

hydrological

burial

the

Andres

The

expertise

increased

type

the

subsidence

of

that

punctuated

and

marine

Lulu,

Government

Thus

was

the

Smithsonian

marine

parts

peat

through beneath

of

of

the

creeks

Hernandez,

Chiriqui

of

supported and

Chiriqui and

rising

(Phillips)

it and

elastic swamps,

margin,

barrier,

of

partial

is

controls.

hydrological

event.

back-mangrove

Sammy

the

would encouragement,

time, evident shallow subsidence,

sea

of

Land

Changuinola input

Tropical

Lagoon

hydrological

and and

Panama.

by

and

starting level. Enrique

and

At

lead

Sanchez.

that

Rapid

marine

Company.

areas

in within

NSERC

higher

NSERC

an

to influence

the

and At thick

rather

Research

indication

with

a

Moreno,

The punctuated

in

peats eastern,

low

carbonates. the

lowering

net

as Almirante

deposit

76

close bounding

peat,

PGS3

grant

than mangrove

did

work

net peat,

subsidence

The

accumulate,

is

Institute

IRHE

proximity

Paul subsidence

and

in of

transgressed

gradual

the

5-87337

authors would

even

of

fellowship

the

changes

subsidence

Bay

surfaces

hence

the

degree

Colinvaux,

A

islands.

(the

form

immediately

small

rates, provided

peat

not could

eustatic

would

(Bustin) to

and

Instituto

coal,

rates, in

of

of

have

brackish

and

is

surface

peats,

reduction

the

a

humification result

marine imposes

it

an

deposits

front

like

the

is

sea

IDRC

laboratory

been vegetation

trophic

effect

and

likely

de

adjacent is

Serracin

to

in

level

and

which

drainage

a

influence

Recursos

possible

The

express the

an

in

Young

record

of

can

that

eventual

state

the

rise,

external

infilling

changes

University

of

and migrates

responds;

to

accumulate

family,

increased

net

peat

of

of

without

channels. Canadian

environments their without

is

Hidraulicos

logistical

the

rate

coseismic

excluded

drowning

of

is

in

gratitude

mire the

to

of

these

dense,

of

the

the

due

In

y 2.12 REFERENCES CITED

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Woodroffe,

Winston,

Weyl,

R.,

p. 5 35- 5 39.

R.B.,

level

bodies.

1980.

C.D.,

changes,

1994.

Geology

G.S.A.

1988.

Models

and

Mangroves Bulletin,

of

present

Central

of

the

v.106,

sea

and

geomorphology,

America,

level

sedimentation

p.1594-1604.

trends?

2nd

81

edition.

Proc.

hydrology

in

reef

6th

Berlin,

environments:

mt.

and

Coral

Gebnider

development

Reef

indicators

Borntraeger.

Symp.,

of

domed

Australia.

of

past

pp.371.

peat

sea v.3,

VEGETATION

ZONES

AND

SWAMP,

DIAGNOSTIC

BOCAS

CHAPTER

82

DEL

POLLEN

TORO,

3

PROFILES

PANAMA

OF

A

COASTAL PEAT

impeded

forming

Almirante

limited

blackwater

both

low

margin,

peat

pollen

forest-swamp;

surface

vegetation

swamp;

Holocene

the

CHAPTER

energy,

Province

the

cores,

profile

number

monospecific

The

peat

drainage

in

Changuinola

A

3)

Bay.

history

order

creeks are

survey

one

mangrove-dominated

Raphia

Changuinola

samples

of

3:

of

defmed

of

6)

from

The

Bocas

to

each

of

VEGETATION

specialised

of

much

of

Sawgrass

construct

the

taedigera

Raphia

peat

the

the

and

stands.

River

phasic

and

del

mire,

as

deep

dominant

accumulation

collected

mire

Toro,

mapped:

it

mouth,

PEAT swamp

±

community.

a

is

species,

leading

central

Increasing

palm

stunted

history,

originated

today,

Panama,

bay.

ZONES

vegetative

SWAMP,

from

probably

swamp;

was

1)

to part

only

and

forest-swamp;

The

by

Rhizophora

on

doming,

dominant

accumulation succeeded

as

of

These

has

floral

formerly

this

one

AND

early

freshwater

the

behind 3.1

4)

cover

BOCAS

been

of

coast.

mixed

deposit

succession,

profiles

increased

ABSTRACT

swamp

DIAGNOSTIC

which vegetation

83

undertaken

by

of

extended

mangle

a

7)

barrier

Seven

a

hardwood

forest-swamp;

DEL

of

palm

(Campnosperma

and

large

Myrica-Cyrilla

are

was

woody

oligotrophy,

of mangrove

the

TORO,

then

phasic

considerably

swamps

at

likely

bar

domed

the

as

second representative

peat

forest-swamp

compared

POLLEN

and

an

4000

drained

communities

PANAMA

initial

coastal

promoted

freshwater

that

5)

swamp;

and

from

year

bog-plain.

Campnosperma

panamensis),

developed

farther

step

to

establishment

to

PROFILES

swamp

a

evolution

the

pollen

sites

site

dominated

2)

by

in

lagoon of

in

southeast

mixed reconstructing

near

the

is

peat-forming

Pollen

the

near

in

distribution

used

everwet

of

close

is the

direction

OF

system,

back-mangrove

Changuinola

panamensis

of

the

prone

by

extracted

to

marine

by

A

bog-plain

proximity

deposit.

a

prepare

COASTAL

climate brackish

very

to

and

in

of

the

2

from

a

a

in to

colonize

phase

conditions

which

and

in

is

institute

the

common

oldest,

peat

central

to

accumulation

the

peat

regions

swamps

of

in

the

a

of

variety

mire.

southeast

84

Mire

of

freshwater

Asia,

development

as

the

and

palm

did

brackish

not

Rciphia

require

environments.

tciedigera

the

initial

is

able

mangrove to

Bruenig

development

Anderson

1961,1964,

and

vegetation,

as

increasing

times

Carboniferous,

in

high

persist

evapotranspiration

scale

1989; Barber

been

with

a

fact,

Cecil,

result

latitudes

of

changing

used

of

others).

(1990)

year-round.

be

Recently,

vast,

1981),

hundreds

Peat-forming

has

1994).

of

awareness

moribund

in

1983; to

in

the

tropical

lead construct

long-lived

of

the

and

and

as

conditions

Thick

emergence

the

Anderson

Pioneering

attention

Old

well

to

of

Esterle

throughout

the

Today

northern

and

the

of

thousands

or

extensive

World

mires

as

stratigraphy

histories

the

sub-tropical

forested

development

in

some

and

of

has

the

and importance

of

retreat.

work

growth

are

tropics,

hemisphere.

a

Ferm

turned most

most

Muller

Cretaceous

to

peat

process

of

dynamic

peatlands

millions

on

environmental

In of

extensive,

of

and

conditions

deposits

(1994).

described

the

of

to

the

coal

of,

the

1975),

model

what

the

preservation.

evolution

organo-chemical

geological

and

3.2

These

year,

in

of

and

measures

study

tropical

may

years

is

and

INTRODUCTION

growing

for

and

in

Tertiary

(Anderson

now

allowing

formed

85

change

detail

of

deposition

summarized

develop

of most

(volumes

Holocene

termed

past,

is

forest-swamps

and

Stratification

threat

used

in

coals,

studied,

as

vegetated over

subtropical

however,

and

Anderson’s

wherever

systems

an

the

to

of

edited

to,

effect periods

bear

tropical

Muller,

and

reconstruct

coals

Anderson

peatlands

tropical

to

which

wetlands

witness

by

the

precipitation

of

within

in

derived

climes.

some

own

of

Scott,

peat

1975;

southeast

continental

large

several

forest

evolve

model

are

publications

environmental

extent

Holocene

to

swamps,

with

Esterle

coal

from

1987;

the

found

ecosystems,

thousand

of

through

Asia

exceeds

high

existence

deposits

formalized

primarily

glaciation,

domed

Lyons

et

in

in

peat

by

water

al.,

the

(Anderson part

time

J.A.R.

changes

years

deposits

peat and

of

middle

1989;

in

and

due

arborescent

tables

by

the

and

earlier

in

Alpem

partly

(e.g.

to

concert

Cobb

may,

on

and

has

to a

forested

photographs

River

communities’,

and forest-swamps

‘phasic

mires.

increasingly

which

river

surface

rainfall

over

to

becomes

and

a

rather

Anderson

last

domed,

in

colonizing

prograde,

delta

flood

creating which

mangrove

zones

3000-4000 becomes

Anderson conmiunities’,

The

than

of

throughout

in

alluvial

available

Anderson’s

of which

waters,

vegetation

also

the

Sarawak.

more

radiating

from

domed.

fully and halophyte

a

of

increasingly

final

protected

clays.

describes

(1964)

peninsular becomes

years a

the

specialized

forest-swamps

developed

the

perched,

the to

stage

succeed

perimeter

Anderson

out

develops

work

a

peat

The

Critical

year

along

defines

succession

(mangrove)

from

environment

the

increasingly

in

surface

swamp

Malaysia

concentrates

oligotrophic.

maintains

non-saline,

the

domes

plant

each

the

coastal

a

to

in to

a

constructs

succession

central

of

lower

lateral

this

a

the

other

takes

associations

expression

of

series

vast

(reproduced

community

are

centre swamps

process increasingly

the

amongst

elevated.

reaches

acidic

bog-plain according sequence

size,

the

on

less-developed

of

Shortage water

a

has

the

of depositional

form

stages,

and

is of

of

water

the the

of vegetation, occupying

not

stabilizes

table

an

86 in

this

peninsular

As of

of peat

occupied

the to

less fully

Anderson, mass

ever-wet

of

been in

a it

six

table

the

succession

and

Baram

nutrients

flattened

which

builds

thicknesses

salt-tolerant

developed

identifiable

examples,

degree of

model reached.

a allows

develops

the

soil

mangrove

by

silty

Malaysia,

climate, recognizable

above

and

raised

1983)

a

chemistry,

and dome

based

of

can

stunted,

prograding

the

Rejang

oligotrophy Marudi

up which

plant

within

greater the

forest

as be

central

accumulation

in

or to

on

roots.

and

a

clearly

reach

which

inverted

17

vegetational series

low species

Rivers

are types,

topography associations

organic

domed

Sumatra,

acidity

m,

portions

shoreline,

The

elevated

diversity

of

abundant and

which seen

of

nutrient-rich

of

or

pie-plate,

as

new

deposit

roughly

detritus

result

doming.

of

northern

‘phasic

the

in

which

of

have

thick

succession,

to

environment

aerial

and

trapping

community

of

shoreline

these

(-.3000

a

in

on

plants,

concentric

lesser stratigraphy

accumulating

developed

the

peat,

are

a

Borneo.

The

the tidal

domed sequence

centre

planar

sediments

mm/a)

Baram

the

degree, planar

termed

continues

in

and

which

of

in

of

of the

Christen,

peatlands

vegetation

phasic

winds

mainly

pollen

forest-types

many

being

point

vegetational

generally

Correlation

(1975)

1974), concentrations

rapid

increasing

phasic

representing

prevalent

communities,

Until

of

of

out lack

insect

1973;

in

the

transitions

which

show

more

and

that the

Palyno-stratigraphic

communites

echo

of

very

could

plants.

pollinated,

of

Cohen succession,

Neo-tropics,

information where

size,

palynological

that

certain.

in

are

the pollen

the

recently,

that

are

not

towards

indistinguishable.

a

and

lateral

occurring

final

et In

in

vertical

higher

be

area

in al.,

some addition,

PC5

makes

and

distinguished

the

reflecting

phase

overviews

about

sequence

and

1985,

result

the

through this

(Bruenig

analysis

peat cases

sequence

on

correlation

their

analysis

margins

in

the

pollen

in

the

1989,

in

cores

the

the

conjunction

increasing

restricted

local

existence

of

of

PCI

relatively

of

On model

1990,

peat

due

of

phasic

world cannot

to 1990;

of

the

of

floral

the

represent

between

pollen

pollen

peat

the

to

is

Marudi

referencing

of

other

the

peat

thinner.

pollen

bibliography was

communities.

oligotrophy

generally

deposit.

steep

with

dome cores

biology,

87

facies

of

presence

distribution rarely

stratification

hand,

distinctive

surface peats

the

transport.

edges

by development,

is

The

density

unpublished

be pollen

Muller

mentioned

the

has

present

through

of

of

in differentiated

vegetation

zones

principal

several

From the

some

Lottes

associations

have

production

This

of

(1963,

in

dome,

from

the approximate

time,

the

these his

limitations,

in made

and

factor

species work

tree

the

peat

reveals

foliage,

phasic

the

1964)

where

was

Ziegler,

observations

at

little

literature

and

by

base

species

of

reduces and

the

of

constructed.

and

Salfeld,

arboreal communit

that

drainage

dispersal

and

mention

the

principal

species

topographic

zonation

to

1994).

Anderson

the

are

vertical

genus

the

overlap

(exceptions

surface

believed

a

1974

generally

species,

level,

of

is

model

mechanisms

in

among

Shorea,

Cohen (PC)

better

extensive

The

transitions

the

between

and

contours,

and

and

of

of

surface

authors

to

generally 6.

include

Waughman,

them

and

weak

Muller

the

et

specific

be the

Anderson’s

al.

peat.

nutrient

of

with of (1989) describe the large coastal peat deposit near Changuinolain western Panama, studiedjointly by the

U.S. Los Alamos National Laboratories and the Instituto de Recursos Hidraulicos y Electrificacion of the

Republic of Panama withthe objectiveof assessing its resource potential as fuel for a peat-fired thermoelectric facility. They found the peat to be up to 9 metres thick, and the dense forest vegetation surrounding a plain of sedges,grasses and stunted vegetationsuggestedthat the deposit might be domed.

The present study presents an overviewof the dominantpeat-formingvegetation of the Changuinola mire, defining 7 phasic communitiesaccording to their principal species. Pollen ‘fingerprints’ (sensu Cohen,

1975) for each phase are then constructed using counts of the dominant identifiable pollen types concentratedfrom surfacelitter,and surface(upper 25 cm) peat samples. Finally, the pollen stratigraphy of two peat cores is recorded, one from the thick central regionand a second from near the eastern margin of the deposit. By correlating transitions in the cores withthe modernvegetation, the Anderson modelis tested and a history of the evolutionof the mire proposed.

3.3 GEOGRAPHY ANDCLIMATE

The Changuinola peat deposit has developedin a back-barrier setting on the Caribbean coast of

90 Panama, at 20’N latitude, 82° 20’W longitude,on a microtidal (- 30 cm), wave dominated shoreline

(Fig. 3.1). Although tidal effects in the western Caribbean are minimal, strong wind-driven longshore currents transport sedimentsto the southeast. Tropical stormsand hurricanes pass well to the north, but associated floods are frequent. The climate is humid-tropicaland temperature averages 26°C, witha ± 30 range. There is no dry season; the annualprecipitationof 3000 mm is uniformly distributed throughout the year (IRHE, 1988). SurfIce winds are predominantlyfrom the north to north-east throughout the year, but strong south- westerliesblow downthe slopes of the Talamancan Ranges one or two days in each month. Normal windblowntransport of pollenis fromNE to SW, from the Caribbean barrier bar toward the centre of the mire. The NE margin is occupiedby dense Raphia-swarnpand mixed forest- swamp. There is no mangrovefringe forest present along the windwardmargin of the mire.

88 ••...

EAN.c.i COSTA CU’ A .•• . )ocl- lain

L41Rz*ç ‘V ) \44KR1o D8 BDT14’-._... / I. ) ‘ / r U D

ILE 1.5 BDD BDD 25 4 8D029 -

Republicof Panama - SOD31 CHANC POLLENCORESTFS ALMIRANTE N O9 1 * SURFACEPOLLEN SiTES x * OThER SAMPL.Esrrs BAY

EXTENTOF PEAT

- - - iailway PONDSOCK

Figure 3.1: Location map of the Changuinola peat deposit on the Caribbean coast of Panama. Sample sites which are mentioned in the text are shown, as are lines representing the NW-SE cross-section, and the NE-SW levelling traverse and cross-section. The shaded area includes that part of the deposit that has been sampled offshore of the mangrove fringe zone in Almirante Bay

89 The NW coast of Panamais a regionof activeclasticand organicsedimentdeposition. Muchof

the coastal plain is coveredby Quaternaryand Recentalluvium,and the coast is characterizedby a series

of progradingbarrier bars behindwhichoccasionallagoonsand extensiveparalic swampsare developed.

Sedimentationrates are high,andthe peatdeposithas developedadjacentto the ChanguinolaRiver,on

the back of a progradingbarrier bar, the characteristicridge-and-swalearchitectureof whichcan be

traced at the base of the peat. (Fig.3.2) The present-daymire occupiesthe narrowcoastal plainbetween

the foldedMiocenesedimentsof the TalamancaRangefoothillsand the exposedCaribbeancoast. At the

easternterminusof this coastline,wherethe terrigenoussedimentsextendbeneathAlmiranteBay,peat

occurs submergedto depthsof threemetresor more,underlainby mediumgrainedgrey sand,and in

places overlainby a thin layerof siltysands,limemud,and coral. Approximately40% of the depositis

belowpresent sea levelandthe base of the peat is 670 cm belowsea levelat the lowestmeasuredpoint.

Most basal sedimentsare well-sortedmediumgrainedgrey sands similarto those currentlybeing

depositedon the coast by the ChanguinolaRiver.

3.4 METhODS

a) Problems:

The coastalmiresof CaribbeanCentralAmericaare not wellknown. Accessto mostof the 1000

km of coast betweenCabode HondurasinnortheastHonduras,and Colonin easternPanamais almost

exclusivelyby boat and lightaircraft. Botanicalstudiesin the regionare mostlylimitedto those

concerningthe welfareof plantationcrops suchas bananasand cacao, and thus havefocusedon the vegetationof the alluvialplainsratherthan that of the extensiveand virtuallyimpenetrableforest-swamps that occupymuchof the coastalplain. The Changuinolamire is used, but little knownby the local

inhabitants,who clearwet pasturesand hunt for foodaroundthe margins,cut timberalongthe banksof the blackwatercreekswhichdrain intoAlmiranteBay,and attemptthe occasionalricecrop betweenthe

stumps left by smallscale logging. A systematicdescriptionof the vegetationof the area, indeedof the

90 PC6 PC4 PC7 PC3 —

:W

10km

Figure3-2. NE-SWcross sectionof the depositalong levellingtransect,showingsurfacevegetationzonedinto concntric phasic communities (PCs). Vegetationzonescorrespondto those visible in satelliteimages(Fig. 3-3), verifiedby sampling. Verticalexaggerationis x 500.

91 establish 25 in Ms determine Magellan® community colour photography, zonation drainage films), using

only province (notably

approximately

or

(surface

local

30

a

satellite

and

combination

Cores Three

The

cm by of channels datum

of

if

names

GPS

SPOT

the descriptions

Hoidridge Bocas

the

magnitude)

increments,

mapping

particularly

were

levelling

images

phasic

surface before

(Global

were

50

multispectral

and

del

taken

cm

of

of

Toro, communities

identification and

available were

levelling

normal

surveys

is

to of

7.5

wherever Positioning vegetation

d)

from in

domed.

the

Budowski, coseismic

generated. earthquake,

the has

Coring

categories

and

the

were

satellite lines

complex

for

yet

possible,

A

surface

oblique

zones

in

the

to

of

of

System)

complication subsidence conducted could

the

1956,

be

Peat many

majority

Using

imagery

epicentred

in eastern

attempted,

in raised

c)

b)

to

air be

the

using

and most

summarised

Levelling

of

receiver

the Satellite

‘groundtruth’

run.

photos

digital

the

from

western

of

across

Collection

(Fig.

section

base

of Hiller-

arose

plants 90

vegetation

92

the

although

the

for

(using

of

images Imagery

km 3.3;

Surveys

the

80

in of

section

the

or margins

in

positioning,

in

to

also

that

study the km2

developed

Porter,

Macauley-type

of

the

peat

the black

and

some

types

Surface

deposit

at

Figs.

mire.

did Changuinola

west

area.

at

to

the

photo-based

and

1973).

reference

not 78

the required

2.7

in

we

start

during

Samples white,

sites.

(see

Thus

emerge,

centre

the

and

have

of

At

hand

Rio

Fig.

low-level the

it 2.8).

the

mire material Samples

normal

the

assigned

of

maps.

was

Estrella

however,

2.3).

operated

cutting

the

study,

onset

was

Detailed

necessary

swamp

colour

is The

were

aerial

accomplished

of

7

in

valley,

of

available

phasic

coring

until

the

April

trails,

concentric

recovered

mapping

and

in

project,

to

order

false-

resulted

1991, infrared

re devices.

and

to

of

a

in

a Figure 3.3. False colour SPOT satellite image of the Changuinola peat deposit. The black area (top and right) is silt-laden surface water in the Caribbean and Almirante Bay. The large white patch is clear shallow water in the Bay. Areas of peat doming are in shades of blue and green (central western bog plain, and 4 smaller areas in the eastern section; PC 7). These bog-plains are surrounded by gold (sedge and stunted forest-swamp; PC 6). The yellow areas are Raphia palm swamp (PC 3). Red and flecked white are mixed forest-swamp and Campno.srierma p. forest swamp (PC 4 and 5). 93 Phasic Figure —.‘

Communities 3.4.

,s

/

F

L—..

I_I

Vegetation-zone

,.-

_...c-i ‘—

are

N

c) ‘—

N shaded ht,:

map

$r i

according

of

the

A

area li

to

shown

the

legend. -

in

the

94

v:.%w4i!.L”

SPOT

Oli

image.

•: ‘

II

Interpretation

OOOOOOO8’

‘‘1

?\

of

the

%

distinguishable till Salinityand pH for each sampleweremeasuredat the timeof collection,and verifiedin the laboratory

(distilledwater), usinga Cardy®ModelPH1digitalpH metre,and a Cardy®ModelCl 21 digitalsalt

metre. In addition, surfacelittersampleswerecollected(to 5 cm depth)and 25 cm cubescut witha

machete,at onesite in each of the 7 phasiccommunities.All samplesweredouble-baggedand storedin

as coola locationas possibleuntiltheycouldbe refrigeratedor frozen.

e) Collectionand Identf1cationofPlants

Leavesand, wherepossible,flowers,of majorspeciesfromeachof the 7 phasiccommunities

werecollectedwiththe assistanceof Sr. AndresHernandez, botanistwiththe ForestDynamicsProject

of the SmithsonianTropicalResearchInstitute(STRI),Barro ColoradoIsland,Panama. Arborealpollen

was collectedby Sr. SammySanchezwitha .22 calibrerifle. Identificationwas madeby Sr. Hemandez

and staff of the herbariaof the SmithsonianTropicalResearchInstitutein Balboaandthe Universityof

Panama, PanamaCity. A list of the majorspeciesidentifiedis includedas AppendixF.

J Peat Class/Ication, Pollen Preparation and Ident/1cation

Pollenslideswerepreparedfromsurfacesamplesfromsites representativeof 6 of the 7 phasic communities,and from2 cores,onein the centralpart of the depositandthe secondnearthe eastern margin. Pollenwas preparedand concentratedusingstandardpalynologicaltechniquesfromthe fine fractionof the peat (< 0.25 mm). Sampleswerefirst separatedinto coarse,mediumand finefractions usinga wet-sievingproceduremodifiedfromStaneckand Silc(1977). Bythis method,the sampleis thoroughlymixedbeforethe pollenis extracted. This systemwas usedin orderto makea quantitative assessmentof the degreeof humificationof the peat. Degreeof humificationis traditionallydescribed usinga modifiedvonPost HumificationScale,adaptedto tropicalpeats by Esterle(1990). The categoriesare sapric, finehemic,hemic,coarsehemicand fibric.The use of field-determinedpeat types has beenused onlysparinglyinthe studyof thesetropicalpeats, as recentwork (Esterle,1990)suggests

95 low correspondence betweenfield categories and the actual particle-size distributions as determinedby

point counting or sievingmethods. Peat classificationis based on the identificationof macroscopic plant

parts and palynomorphs in the peat, comparedto plant and pollen associations identified in the surface

samples, and uses botanical (eg. Rhizophora peat, sedgepeat) nomenclature (Cohen, 1968).

Following identificationof the dominantspeciespresent in the modem vegetation, descriptions

and photomicrographs of the pollen were prepared. Publisheddescriptions for some Panamanian pollen

species are available, notably in Bartlett and Barghoom (1973), Graham (1979, 1988a and b) and in the

superb publication of Roubik and Moreno (1991). Referenceslides from the collections in the

paleoecology department of STRI, Balboa,were made avalable. Finally, as many gaps as possible were

filled using the herbarium collectionsat The Universityof Panama, and the SmithsonianTropical

Research Institute,and by collectionof fresh sampleson-site in the mire. Descriptions of some speciesof

interest, or for which no prior publication was found,are includedhere as Appendix E.

g) Pollen Countsand Pollen Diagrams

As indicatedby the title of this paper, the palynologicalanalysis presented here is intendedto

establish a stratigraphy of the deposit sufficientto reveal its broad evolutionary history. To accomplish this it is necessary to relate the pollen preserved in the peat with modem plants, plant associations and communities. A complicationencounteredin attemptingecologicalinterpretation from pollen stratigraphy is selectivepreservation. For example,the pollenof cerillo (Symphoniaglobulfera), a dominant tree, was absent from surface samplesand most of the cores. One can only count what is preserved, and it is quite possible that what is preservedsignificantlymisrepresents what actually was.

To minimize this selectivebias, pollen profiles were prepared that would be representative of the preserved pollen record for each community. To establishthe pollen ‘fingerprint’for each phasic community, a count of 1000grains, where possible, was made from surface litter and surface peat

96 samples(3 sites producedlessthan 750 grainseachfrommultipleslides). The resultswerecombined,

and the percentageof the total countplottedforthe mostnumerouspalynomorphs.Althoughit wouldbe

preferableto comparecountsfromnumeroussimilarsitesto betterrepresenteach phasic community,it

was feltthat includingthe upper 25 cm of the peatgaveconsiderablerangeto the sample,and giventhe

samplingintervalin the cores (25 or 30 cm) finerdiscriminationwas not necessary. No attemptis made

to relatethe pollenfoundin the peat to the specieswhichnumericallydominateeach community- the

problemsassociatedwithproportionalrepresentationof dominantplants in pollenprofilesare well

known. Rather it was hopedthat recognizable‘fingerprints’wouldemergewhichcouldthen be relatedto

pollenrecoveredfromcores.

Countsof 200 grains for each 25-30 cm incrementof two coreswereusedto constructthe pollen

stratigraphyof the centraland easternsectionsof the deposit(AppendixD). Pollendiagramsof the two

coreswereconstructedusingselectedpalynomorphsor combinationsof palynomorphsthat are considered

to be valid markers,as determinedfromthe surfacesamples(fingerprints),and whichbest define

transitionsin vegetation. In both surfaceand core samples,the followinggrains wereomittedfromthe

counts:all single-celledfungalspores,all fungalhyphae,all fragmentslessthan 2/3 complete,and any

ambiguouspalynomorph. In identifyingpalynomorphs,botanicalnamesare used whereverpossible.

3.5 RESULTSANDINTERPRETATION

a) VegetationDistribution

All of the vegetationdescribedin this studyis rootedin peat varyingin depthfrom lessthan 1m,

in a narrow strip behindthe barrierbar, to about 9 m in the centralmire. Vegetationon mineralsoil

adjacentto the Changuinolamirecomplexis diverseand luxuriant. In a trial 20 m x 20 m quadrant(the basic unit of a forestmonitoringsystemdevelopedby the ForestDynamicsProgramat STRI), 164 speciesof trees and shrubs > 2 cm dbh (diameter,breastheight) wereidentified. This diversityis typical

97 of humidforested lowlands(A. Hernandez, pers. comm.). Floral diversity on peat soils is low (Myers

1990): 54 major specieswere identified,along multipletransects through all phasic communitiesin the mire complex (AppendixF). No detailedaccountingof species present in forest sample plots (400 )2m along the transects was possible for this preliminarysurvey. Vegetation communitieswere identifiedby

comparing field notes taken during the cuttingof trails for levellingsurveys with low-level(300 m) aerial

photographs. Identificationof the major phasic communitieswas then verified by the rather laborious

process of cutting trails into areas of interest visible on high altitude air photos in order to identifi the

trees.

The domed western sectionof the mire is mapped as a set of phasic communitiesin a somewhat

similar manner to that describedfor the oligotrophicpeat swamps of Western Malesia and Borneo

(Anderson 1964, 1984),and that tenninology has been adopted in this study. The easternsection is a

complex mosaic of forest types, and includesthree areas in which incipient doming is evident. Large

areas of the mire are occupiedby denseRaphia palm-swamp (locally called ‘Matomba’(the plant) and

‘matombal’(the swamp) in Panama, ‘Yolillo’and yolilal in Costa Rica) and a variety of sawgrasses

(‘cortadera’and cortaderal), on both shallow and deeppeat.

i} Mappable VegetationZones: --- Multispectral SPOTsatellite imagery with a resolution of about 15m

was used to distinguishthe distribution of phasic communitiesby isolating and enhancingthe spectral

characteristics of the various vegetationtypes present in the Changuinola mire. Factors like opennessof

canopy, reflectivity of foliage,and the extentto whichstanding water is present serve to distinguish

vegetation zones, which can be mapped in false colour. A false colour vegetation map is reproducedas

Figure 3.3 and interpreted in Figure 3.4. The concentriczonation of vegetation around the large central bog plain can be clearly seen. In addition, incipientdomingis evident in three areas to the east, two of

98 whichmay be coalescing. The narrowmangrovefringeforestand back-mangrove(PCi and PC2), and

variationsin the mixedforest-swamp(PC4)types,cannotbe reliablydistinguishedat this scale. Phasic

communities3, 6 and 7 are distinctand 4 is mappedas hardwood-dominatedforest. Elevationof the sites

varies from 0 m (intertidal)at BDD25, to 6.24 m in the bog-plain(ED 3).

ii) Description of the Phasic Communities:— Thevegetationof the Changuinolamirehas beendivided

into 7 phasic communitiesrepresentingthe sequenceof zonesfromthe marginto the centreof the deposit:

1)Rhizophora manglemangroveswamp; 2) mixedback-mangroveswamp; 3) Raphia taedigera palm

swamp; 4) mixedforest-swamp; 5) Campnospermapanamensisforest-swamp;6) Sawgrass± stunted

forest-swamp;7) Myrica-Cyrillabog-plain. The pH and salinityof peat cores fromeach communityare

shownin the lowerpart of Figure3.5.

Phasic Community1:Rhizophoramanglemangroveswamp

Site Description:BDD 25

The mangrovefringeforestis a narrowzonerestrictedto the shelteredshorelineof AlmiranteBay and extendingeastwardinto shallowareas of LagunaChiriqui. This communityis nowherepresenton the outer coast, but dominateslargeareas of the shallowoffshorein the leeof the Bocasdel Toro

Archipelago. In the shallowoffshore,Rhizophoramangleand an epiphyticClusia sp., are dominant,but in the fringeforest,the communityis slightlymorevaried. Evenin shelteredwaters,wherethe communitythrives, its extentis limitedto about 30 metresbreadthby the smalltidal range (normally30 cm).

The dominantspeciesare: Rhizophoramangle,Acrostichumaureum, Raphia taedigera, and a few salt-tolerantgrasses and sedges,of whichonly Rhynchosporamacrostachya (Cyperaceae)has been identified. Rhizophora mangle is the red mangrove,the dominantarborescentspeciesand commonlythe

99 Zonation in the

0

_—_---- pH sallrflty—-pH

Myrica - Cyrilla mixed forest-swamp Campnosperma Raphia palm-swamp back-mangrove Rhizophora bog-plain forest-swamp forest swamp fringe-forest

Figure 3-5. Cartoon showing typical lateral sequence of‘hasic Communities, from mangrove fringe to bog plain. Representative core data shows pH and salinity (wt%) profiles from the surface to the base ofthe peat. (Pitheceilobiuni Centre Figure showing Figure 3.6-b. foregound, 3.6-a. root mass Photograph Photograph sp.). a and small pneumatophores Euterpe of of Campnosperma PC2 precatoria (Back-mangrove ; left and forest palm; background 101 swamp, swamp): left and !4 showing right centre - Rhizophora of -a centre, the fallen distinctive, the prop Laguncularia fine roots. foliage uniform . . of racemosa, canopy. gavilan’ only mangrove present in the fringe forest. Acrostichum aureum, known locally as helecho de manglar or mangrove fern, is a large (to 3 metres) and vigorouslyopportunistic colonizerof sheltered shorelines. It is particularly in evidencealong the recentlysubsided shoreline,where it is thriving amongst the debris of salt-killed mixed forest, and is even present as new growth in the intertidal zone. Raphia taedigera, the

Raphia palm, is commonimmediatelyshoreward of the mangrove fringe, and occasionally present at the high tide line. Raphia standing offshore as a result of earthquake-inducedsubsidence appeared to be slowly succumbing to the high salinity (30 to 34 %o) 30 months after the seismic event.

Phasic Community2: Back-mangroveforest-swamp

Site Description: BDD 26A (Fig. 3.6-a)

The back-mangrove swamp is one of the more complex communitiesevaluated in the

Changuinola swamp complex. The observations here incorporate a number of sites, both coastal back- mangrove forest, and mixedforest marginal to the blackwater creeks which drain the eastern section of the peat swamp into Almirante Bay. Thus the sites have close associations with both true marine and brackish environments. The forest community is dominatedby Laguncularia racemosa and Raphia taedigera, but open sawgrass swamps (‘cortaderal)are also commonbehindthe mangrove fringe. Along the banks of blackwater creeks, secondaryspeciesvary withdistance upstream from the coast; the community grades from an essentially Rhizophora fringe-forestnear the coast, to a mixed freshwater forest-swamp and floating sedge-grass swamp at about 2 km upstream. Figure 2.5 shows salinity profiles of three major creeks measured 1 km upstream, after one weekof dry weather.

In the lower stream reaches, Laguncularia racemosa , Rhizophora, and Acrostichum aureum dominate. Secondary species include a Clusia sp. epiphyteon the roots of the red mangrove. More than

1 km inland, the followingadditional species may occur: Raphia. Euterpe precawria, a stilt palm;

Pithecellobiurn sp. tree; Cassipourea eliptica, a small to medium sized tree; Chrvsobalanus icaco, a

102 shrub or small tree; C’yclopeltissemicordata, a fern commonaround the roots and bases of white and red

mangroves, sedges, grasses and sawgrass. The fleshy-rooted,spiney arrowhead plant Dieffenbachia

longispata is common.The above all show salt toleranceto some degree.

Non-salt tolerant species includeSymphoniaglobuhfera, an important prop-rooted upper story

tree (Ca.30 m); Campnospermapanamensis, an importantbuttressedtree; an Aichornea sp., a rare,

buttressedtree; the shrubs Miconia curvipetulata, Cespedezia macrophylla, Ouratea sp. andNeea sp.1.

Bromeliadepiphytesare common. Rexguianensis, a mediumto largetree (locallycalled‘plomo’),is

present, althoughmorecommonin the mixed-forestzones. The occurrenceof Rex guianensis has

previouslybeenassociatedwithhigherelevations,andwithmarkedlyseasonalrainfall (Johnston,1949)

althoughits presencein Bocasdel Toro is notedby Bartlettand Barghoorn(1973).

Phasie Community3: Raphia faedigera PalmSwamp

Site Description:BDD 8 (Fig.3.6-c)

Raphia taedigera Martius(Calamaea)is a largepalm havingmultipletrunks 50-80 cm in

diameter,and enormousleaves 15m or morein length,spreadingwidelyfromjust abovegroundlevel.

The plant is a significantcontribttor to peat deposition,as it has an extensiveroot systemwith

pneumatophores(“pneumatozones”- Kahnand de Granville,1992). In-situtrunk baseshavebeen

encounteredat depthsof threemetresin peat cores,incidentallysettlingthe questionof whetherRaphia

may be an introducedspeciesin CentralAmerica(Otedoh,1977). Raphia is oneof onlythreespecies

whichforms monospecificstandsin the Changuinolaswampcomplex(the othersare Campnosperma panamensis, and Rhizophora mangle). It formslargestands in all the marginalareas of the deposit,as wellas beinga significantcomponentin the back-mangroveand mixedforest-swanipcommunities.The monospecific Raphia forestis dark and almostfreeof understoryvegetation. Water table can be up to a

103 ..

Figure 3.6-c. Photograph of PC3 Raphia palm swamp, with sedge marsh in foreground: centre - dense Raphia taedigera forest; Symphoniaglobuflferaemergents.

104 metreabovethe peat surface. Thetwo herbsSagittaria andDieffenbachia are common. In thin freshwaterpeat, Saggittaria can reacha heightof 3 metres,althoughbothare normallya metreor less.

The large prop-rootedSymphoniaglobu1fera (‘cerillo’)is the commonestemergent hardwood,foundas isolatedindividualsor smallgroups. IsolatedbuttressedCampnospermap. ernergentsare also present,as are hex. Other shrubs,herbsand fernsare presentbut not identifiedin this community.

Phasic Communtv 4: Mixedforest-swamp

Site Description:LAKE 2

The mixedforest-swampis not a singlecommunity,but a generaldescriptionof the tree- dominatedswamplandswhichare not monospecificstands. The variousphases are defmedby thetwo or three dominanttree species. Mixedforestsmappablefromlowlevelair photos are: i) Raphia

Campnosperma;ii) Raphia-Symphonia-Euterpe;iii)Symphonia-Raphia± other hardwoodsiv)

Symphonia-Campnosperma-sawgrassv) Raphia + hardwoodsonthin peat. Symphoniais the most commonand distinctivedominant,observedin all the hardwood-dominatedforests,but it doesnot form monospecificstands. Allen(1956)reportsthat it doesformsuchstands in Costa Ricanfresh water swampson the Pacificcoast. The loop-rootsof this speciesare pervasiveover largeareas of the mixed forest-swampsurface. Scattered Rex (‘plomo’)is also commonto all the forest-swamptypes encountered. The site LAKE2 is typical of Typeiii)Symphonia-Raphia-hardwoodforest.

PhasicCommunity5: Campnospermapanamensis forest-swamp

Site Description:BDD 23 (Fig. 3.6-b)

Campnospermapanamensis formslargemonospecificstandson moderatelydeeppeat. These standsare easilyrecognizableby the irregular,unbrokencanopy,and by the slendermottledwhitetrunks, branchlessfor 10to 15metres. Air photosfrom 1954, 1981and 1992revealstrikingdifferencesin the distributionof the distinctiveCampnospermacanopywithinthe complexregionof mixedforest-swamp in the eastern part of the mire. It thus appearsthat thesedensestandsdeveloprapidlyand are quiteshort- lived. Secondarytrees in the middlestoreyare: Euterpe precatoria, a stilt palm; Cassipourea eliptica

105 Figure 3.6-d. Photographof PC6 Sawgrass/ stuntedforest-swamp: The medium-sized,lobate leafedtree in the foregroundis Can2pnosperrnapanamensis, Cyrilla race,nflora are visible beyondthe workers,and a Symphoniaglobuflferain the upper left corner.

106 andPithecellobium sp., bothof whichattaingreatersizeoutsidethis community,and Ternstroemia tepazapote, whichis rare inthe swamp. The understoryvegetationis quite sparseand open. Principal shrubs are Miconia curvipetulata, Tococagulanensis and an Ardisia species,Sagittaria is the common arrowheadplant, and Smilaxis a commonvine.The fern Trichomanes crinitum is foundaroundthe bases of Campnosperma.

Phasic Community6: Sawgrass/ stuntedforest-swamp(Fig. 3.6-cl)

No singlesite representsthis phasiccommunity.Extensiveopen-canopiedforest,gradinginto sparsely-treedsawgrassswamps(‘cortaderal’in Spanish)can be seenfromthe air, and in satellite imagery,as a transitionzonebetweenthe closedmixedforest-swampsand the bogplain. However,on the groundthe floral compositionis highlyvariable. Thus the PC 6 sawgrass/ stuntedforest-swampis distinctas a mappingunit, but is a transitionalvegetationzone. Identificationof the variousgrassesand sawgrasses(Gramineae,Cyperaceae)was not possible,withthe exceptionof Rhynchospora macrostachya, for whichflowerswereavailable. Somesawgrasses(Cyperus ligularis, Cyperus odoratus) were identifiedfromopenareas aroundthe marginsof the swamp,on shallowpeat in runnels on the barrier bar, and in pastures,and mayalso be representedin the stuntedforestand bog plain.PC 6 is foundboth marginalto the bogplaincommunity,whereit formsa transitionzonefromforest-swamps, and as islandswithinthe easternforest-swamps.Inthe east, this communitymay be associatedwithboth old drainagechannels,and ‘topographic’highs(representingincipientpeat doming,not basementhighs).

In all situations,highwater table is common,as are ‘floating’surfaces. Peat recoveredfromthis environmentis very wet (difficultto sample)orange-red,fibrousto coarsehemic,and of lowbulkdensity.

StuntedCampnospermaand shrubbySyniphoniaoccur,but the dominanttrees areMyrica mexicana and

Cyrilla racemflora. Bartlettand Barghoorn(1973)reportthatMyrica is foundonlyalongthe margins of residualpatches of forestin high,dry windsweptgrasslandsabove600-800rnelevation. C’yrillahas beenreportedfromonlyone isolatedsite in Panama,at relativelyhighelevationat CerroJefe,nearthe

107 CanalZone (A. Hernandez,pers. corn.). In the OkefenokeeSwampof Georgia,however,C’yrilla racemflora is the dominantspeciesformingtree “hammocks”,isolatedclumpsof low-growingtrees withinopenswampareas (Cohen,1975). Bothof thesetreesare knownlocallyas ‘manglecimarron’or

‘bushmangrove’becauseof the wet conditionsin whichtheygrow. A rare arborescentClusia sp., a large tree with enormousprop rootsoriginating4 metresor moreabovethe peat surface,has not beenreported elsewherein Panama(A. Hernandez,pers. comm). ilex gulanensisoccursas a commonshrub inthis phasic community. Chrysobalanusicaco is a dominantshrub,andMiconia curvipetulata andMyrsene pelucido-puntata are present. Ferns,including Salpichlaena sp. are foundintergrownin the sawgrass.

Mossesare also present.

Phasic Community7: Myrica-Cyrilla bog-plain

SiteDescription:LAKE 10 (Fig. 3.6-e)

The term bog-plainhereuses bog in the senseof an ombrotrophicmire, a systemdepending entirelyon rainfallfor its water and nutrients(Moore, 1989)ratherthan as a communitydominatedby mosses. Mossesand stuntedsedgesand grasses are present,as are algalmats in the openwaterbetween the bases of the sawgrassand shrubs. Woodyvegetationis stuntedand shrubby. Myrica mexicanaand

Cyrilla racemflora are dominant,both as shrubs in the openareas, and as low-growingtrees (diameterto

20 cm or more,b.h.) formingthe ‘hammocks’whichare scatteredacrossthe plain. Chrysobalanusicaco and very stuntedCampnospermaand Clusia sp., smallSagittaria, and fernsare present. Cohenet al.

(1989) identifiedSphagnum,and the insect-eatingDrosera (sundew)and Utricularia (bladderworts).

Walkingacross this terrainonemust step on the basesof the sedgeplants, as the moss-or algae-covered surface will not support weight. Water depthis a metreor more. Themore ‘solid’groundin the shrub hammocksis also at least partiallyfloating,and if allowedto, the corerwilldrop severalmetresunderit’s ownweight.

108 Figure 3.6-e. Photograph of PC7 Myrica-Cyrilla bog plain: Algal mats are visible in the right foreground, along with stunted sedgesand grasses anda small Carnpnosperrna p.; Myrica mexicana along the horizon,(smallleaves).

[09 3.6 POLLEN DISTRIBUTION

The aim of the palynological investigationwas, in combinationwith particle size and geochemical data, to identify major trends in changingecologicalconditionswithinthe coastal swamp during its approximately 4000 year history. Pollen ‘fingerprint&representing6 of the phasic communitieswere constructed, (Fig. 3.7-a to 3.7-f), from counts of surface samples in the hope that those communities could be recognizedin the peat stratigraphy. Thus any sequentialsuccession in the vegetation would be revealed, which could then be related to conditionsof trophic state, pH, and pore water salinity associated with present vegetation. Selectedpalynomorphsreferred-toin the followingsection are described and illustrated in Appendix E and in the Plates. PC 6, the sawgrass / stunted forest-swamp, is a variable communitythat represents a transition; no single site was thoughtto be representative of this community, hence no pollen fingerprint was constructed.

a) Surface Pollen Diagrams

PC 1:Rhizophora fringe forest (Fig. 3.7-a)

The most common palynomorphsfrom this site are an unidentifiedtricolporate pollen Type 1,

Rhizophora mangle, monoletefern spores, Rex guianensis, and fungal spores. Rhizophora pollen has been shown to be a good sea-level indicator (Muller, 1959;Van der Hammen, 1963), although in this study it represents only about 9% of the total count in both PC 1and PC 2. Thus the pollen record significantly underrepresents the species. This is undoubtedlydue to the narrowness of the mangrove fringe, as observed by Van der Hammen (1963), and the fact that the prevailing wind blows offshore across the mangrove fringe. Type 1, along with a secondunidentifiedtricolporate, Type 2, were encountered only in mangrove fringe and back-mangrovesamples. Rex pollen, which is clearly allochthonous, is present in almost all samples from the Changuinolamire. In addition, this is the only site at whichMyrica mexicana pollen is absent. Acrostichuniaureun is also absent from this sample, although that fern is common in this phasic communityand was observed in other niangove peat from

110 ______

Figure 3.7-a

Phasic community 1 Sample:BDD25 Tot count % of total PC 1: Rhizophora Rhizophora fringeforest 498 fringe forest Species

1 Rhizophora mangle 43 8.6 0 5 10 15 20 25 2 Tricolpate type 1 115 23.1

I I 3 Tricolpate type 2 10 2.0 1 2 4 Campnosperma panamensis 1 0.2 5 Myncamexicana 0 0.0 4 6 Ilexguianensis 19 3.8 5 7 Cyperaceae 0 0.0 6 8 Gramineae 1 0.2 7 9 Trilete ferns 2 0.4 8 10 Monolete ferns 47 9.4 9 11 opaque fungal spore 29 5.8 10 12 Other fusiform spores 25 5.0 11 124 24.9 12 Other 374 75.1

Figure 3.7-b

Phasic community2 Sample:BDD26A Tot count % of total Back-mangrove swamp 279 Species PC 2: Back-mangrove 1 Rhizophora mangle 22 7.9 swamp 2 Lagunculaña racemosa 15 5.4 3 Campnosperma panamensIs 4 1.4 0 5 10 4 Myncamexicana 8 2.9 5 Ilexguianensis 0 0.0 6 Raphia taedigera 5 1.8 7 Cyperaceae 23 8.2 8 Gramineae 26 9.3 5 9 Acrostichum aureum 3 1.1 10 Monolete ferns 27 9.7 11 Other Fusiform spores 0 0.0 12 Other fungal spores 22 7.9 155 55.6 Other 114 40.9 ii 12

Figure 3-7. Pollen‘fingerprints’from surface peat samples, PC I and PC 2.

111 cores. The pollen diagram reflectsthe low diversityof this community. The medium size fraction (<2.0

mm and >0.25 mm) of this surface sample containedabundant calcareous foraminifera and ostracodes.

PC 2: Back-mangrove forest-swamp (Fig. 3.7-b)

Sampling at this site was by 3.5 cm diametervibracore, the top 30 cm of which was processed for pollen analysis, thus surface litter was not well represented. Palynomorphs were few and poorly preserved, and fewer than 300 grains were countedfrom multiple slides. Rhizophora, Laguncularia and

Acrostichum are present, as they are in the present vegetation,and both Cyperaceae and Gramineae are well- and perhaps over-represented. Monoletefern spores represent about 10% of the total count.

Tricolporates Type 1 and Type 2 are present but much reducedfrom PC 1. Microforaminiferatests are present, and dinoflagellate cysts are abundant, but were not counted. Many fragments, damagedand pitted grains were found. The absence of Rex pollenmay be a function of the small number of total grains encountered.

PC 3: Raphia palm swamp (Fig. 3.7-c)

The pollen of Raphia taedigera, flingalspores, monoletefern spores and a diverse arboreal pollen component characterize this site. An unidentifiedChenopodipollis (7) -type of periporate pollen,

Type 39, is the second most abundant grain (9%), andRex is plentiful (6.5%). Also common is a spikey spherical phytolith, superficially identicalto those found in the epidermis of certain Old World palm leaves (Rosen, 1992) and here assumedto be associatedwith Raphia, rather than the much rarer palm

Euterpe precatoria. An importantpalynomorphis the large fungal spore Fusiformisporites sp., which is present in Raphia swamp peats, but is much more commonin the mixed forest and Campnosperma forest-swamp peats.

112 15 14 13 12 ii 10 9 8 7 6 5 13 12 4 3 10 2 11 1 9 8 7 6 5 4 2 3 1

other Figure Other Fusiformispo,ites other Monolete Monolete Tnlete Cyclopeltiss. Cyperaceae tricolporate Gramineae tncolporate Raphia flex Mynca Species Mixed Carnpnospenna Sample:

Phasic Figure Other Other Fusiformispolites Triletefems Monolete Fungal Gramineae Cyperaceae Raphia pericolporate ilex Myrica Mynca Campnosperrna Species Sample: Raphiaswamp

Phasic Figure guianensis guianensis f-form monolete forest-swamp fern f-form mexicana community taedigera spore type mexicana taedigera

community 3-7 fern

fern 3.7-d LAKE

ferns 3.7-c BDD8 of E 0 spores A spores

(48) cont’d. Met 2 (40)(Tiliaceae?) 1 type C ferns 2 (39) panamensis axya panamensis 14 4 3

sp.

Pollen fingerprints Total otat 1039 439 600 163 104 32 436 574 1010 13 34 45 42 63 29 12 38 20 101 52 0 58 75 1 42 4 91 66 28 44 5 0 4 8 count

coun 113 % % 42.3 57.7

15.7 10.0 from 3.1 43.2 56.8 of 1.3 3.3 4.3 4.0 0.0 0.1 6.1 2.8 1.2 3.7 0.4 10.0 1.9 of 5.1 0.5 5.7 7.4 0.0 0.4 4.2 9.0 6.5 0.8 2.8 4.4 total

total PC ______14 13 15

12 3 10 12 1 9 8 6 1

9 and 0 0 ______PC

PC PC

4: 4. 3: 5 Mixed Raphia 10

5

forest swamp 15 20 10 flex andMyrica pollenare commonin both Raphia and mixed forest-swamp. These species were previously only reported togetherat higher elevations,associated with a marked dry season. This combination is noted by Bartlett and Barghoorn (1973, p.245) and used as a basis for interpretinga periodof cooler,drier climate in the Isthmus of Panama during the period 7300-4200 B.P. Clearly the combination is also present within a few metres of sea levelin an equable, everwet regime. Pollen of flex sp is found in association with Rhizophora at 35,500 BP (Bartlett and Barghoom, 1973).

PC 4: Mixed forest-swamp (Fig. 3.7-d)

High dicotpollen diversity, and a large proportion of both trilete and monoletefern spores (37% of the total count)characterizethis community. Noteworthy is the absence of pollen of Symphonia globulfera, which is the dominanttree presentlygrowing at this site, and throughout much of the mixed forest-swamp. Only6 grainsof Symphonia pollen were counted in the entire study, the paucity possibly indicating entomophily. Despitethe prolific floweringof this species, it is clearly not a viable palynostratigraphic indicator. Sedgeand grass pollenare virtually absent. Fusformisporites is common.

PC 5: Campnospermq forest-swamp (Fig 3.7-c)

Pollen of both Campnosperma panamensis and another Anacardiaceae-type pollen are abundant in this environment. The secondspecies differs from Carnpnosperma in being more prolate (P/E of 1.6 vs 1.2to 1.4), but bears very similar exine structure. Raphia and Euterpe are both present in the pollen profile, as they are in the modem vegetation. Fusformisporites sp.A and sp.C are about equally represented, and fungalspores as a group are more commonin this than any other phasic community.

Fusformisporites is of particular interest, as it has been described in the Eocene(Fusformisporites crabbii, Rouse, 1962; F pseudocrabbii, Elsik, 1968, Texas; F rugosus Sheffey and Dilcher, 1971,

Tennesseeand Kentucky); and Paleoceneand Plio-Pleistocene(Elsik, 1980) of North America as well as from the Lower Eocene, and Holocene(possibly as re-workedgrains)of Jamaica, (Germeraad, 1979)but

114 ______

Figure 3.7-e

Phasic community 5 Sample:BDD23 Total count % of total Campnosperma forest-swamp 1016 PC 5: Campnosperma Species forest—swamp 1 Campnosperma panamensis 188 18.5 2 Campnosperma type 198 19.5 3 Mynca mexicana 6 0.6 4 Myricatype 20 2.0 0 5 10 15 20 L 5 flex guianensis 17 1.7 1 6 tricolporate F (33) 10 1.0 7 Raphia faedigera 62 6.1 8 Euterpe precatoria 10 1.0 9 Palm phytolith 9 0.9 10 Cyperaceae 53 5.2 11 Gramineae 14 1.4 12 Trilete ferns 33 3.2 9 13 Monolete ferns 30 3.0 14 FusiformispodtesA 10 1.0 11 15 Fusiformispofites C 9 0.9 13 16 Other f-form spores 37 3.6

706 69.5 15 Other 310 30.5

Figure 3.7-f

Phasic community 7 Tot count % of total Sample:LAKEIO PC 7: Bog plain Bog plain 741 Species 0 5 10 15 20 1 Campnosperme panamensis 11 1.5

2 Mynca mexicana 23 3.1 1

3 CytilIaracemiflora 14 1.9 2 4 flex guianensis 14 1.9 3 5 tricolporate A (26) 128 17.3 4 6 tricolporate B (54) 17 2.3 5 7 Cyperaceae 14 1.9 6 8 Gramineae 19 2.6 9 Tnlete ferns 36 4.9 8 10 Monolete ferns 13 1.8 g 11 SporangiumA 54 7.3 10 12 other fungal spores 40 5.4 ii 383 51.7 12 Other 358 48.3

Figure 3-7 contd. Pollen fingerprints from PC 5 and PC 7.

115 not, to our knowledge,from modern peat. Trilete and monoletefern spores each represent about 3% of the total count.

PC 6: Sawgrass / stunted forest-swamp

No pollen fingerprintwas constructed for this phasic community,despite its utility as a mapping unit, as it is transitional betweenforest-swamp and bog plain communities,and is highly variable in floral composition.

PC 7: Bog plain (Fig. 3.7f)

The presence of Cyrilla racemflora, both in the modern vegetation and in the observed pollen record, is restricted to phasic community7. Two unidentifiedtricolporate species (Types 26 and 54) are also commonand exclusiveto the bog-plain sites. Tnletes dominatethe spore count only in this environment. Several speciesof trilete spores together account for 5% of the total. Monoletefern spores are scarce.

b) Pollen From Cores

Pollen analysis was performedon two cores, one from the domed centre (ED-3, Fig. 3.8) anda second (BDD-23, Fig. 3.9) from the planar eastern part of the Changuinola mire. ED-3 is an 802 cm peat core collected from a bog plain site of stunted shrubs, sawgrass and algal mats. The peat was sampled in 30 cm incrementsfrom the surface, at an elevationof 6.24 m, to the base in rooted,fine grained grey sand 178cm below present sea level. BDD-23 is a 450 cm peat core over 40 cm of peaty, rootedsand, on a base of clean,grey, carbonate-free sand at 490 cm. The site is 1.5 km from the present marine margin, and all but the upper 15 cm of this core is below sea level. The BDD-23 site is presently at the edge of a monospecificstand of Campnosperma, adjoiningan area of Raphia / mixed hardwood

116 swamp. Sampling was attempted in 25 cm increments,but recoverywas erratic due to the large amounts

of wood encountered.

ED-3 (PC 7) Pollen Diagram (Fig. 3.8)

The pollen diagram for ED-3 was constructedusing those palynomorphs or combinationsthat

best illustratestratigraphicvariationsin the core. The palynomorphassemblagefromthe earlieststageof

mire development(810-720 cm) at this site is consistentwith a PC 3 Raphia palm-swamp, including

dominant monolete ferns and Pa[maepollen. Raphia and Euterpe palms and the distinctive periporate

Type 39 are present. Palm phytoliths, includedin Palmae, are abundant in the deepest sample (23% of

the total grains counted). hex and many monoleteferns are also well represented in this earliest stage.

Fusformisporites A and C are also present. Halophytesare absent, andthere is no evidenceof marine

influence. Basal sedimentsare angular medium-grainedgrey sands containing abundant roots, and

closely resemblethe sedimentsof the present barrier bar.

The second stage, from 720 to 630 cm, is dominatedby Campnosperrna, and fungal spores. l’his

assemblage is interpreted as PC 5 (Carnpnosperma forest-swamp) succeedingthe palm swamp.

Fusformisporites spp. disappear at 660 cm, but other dicellular spores persist. Both palms are present,

and ferns become reducedin bothnumbers and diversityin the upper half of this stage. Sedges and grasses occur at their lowest levels.

In stage three, between 630 and 390 cm, there is first a decrease in hardwoods(except hex) and an increase in palms, followedby a decrease in palm pollen as well. Grasses and sedges increase

substantially, and ferns are plentiful. Cyrilla makes its first appearance at 510 cm. and Raphia disappears. The gradational change that is apparent throughout this section represents the PC 6 transitional, open, somewhat stunted forest / sawgrass zone which occupies a large proportion of the

117 (c

00 :1 I Laguncularia

and conditions diversity vegetation. present brackish sample observed Campnosperma sample basal From BDD-23 of this oligotrophy Campnosperma western

Cyrilla,

the

zone,

peats

490

had is

between halophytes

From From

Stage mire

waters,

of

(PC

in

very

and -

(Phillips

Myrica,

from

minor by

the 450

Raphia

of

and

4)

285

600 and

become

four

the

high

far

PC

cm,

pollen 450

gradually Pollen

probably

450

indicates

arboreal

the Acrostichum, maturing

to

to

disappear.

consists 2 Ct

and in

pollen

rooted,

and

pollen 490

up

150

least al.,

sulphur

increasingly

supports

Diagram

Types

to

350

cm cm

1994;

due

and disappear.

incipient

species. grains,

285

of

fingerprint, domed

suiphurous

the

depth

cm,

Fusiformisporues

the

to (13.7

26

phytoliths,

cm

Phillips this

here

(Fig. pollen

proximity

but

and

upper

and

common. bog-plain.

is at

doming.

From

wt%).

interpretation.

plotted

dominated

is this

54. The

the

3.9)

assemblage

peaty

it

absent

and 390

may

and

site,

most

Grasses, 150

assemblage

to

This

Bustin, together,

cm

Types

sand

brackish

Type

to

still

clean

from

poorly

by of

is

has

100

abundant,

with be

119 the

a indicates

sedges

39

26

the

in

grey

been

PC

cm,

a

and

represents core,

preserved, review).

pollen blackwater

and

function

abundant

300-350

2

sand

a

interpreted

the

and

back-mangrove

54

mixed

dominated

the

as

are

Types

make with

fungal

are

The

succession of

cm

PC

abundant.

of wood

forest-swamp

creeks,

sample

occasional fern

all

their

sample.

presence

1

7,

as

spores

and

by

those

and

fragments

an

spores,

appearance

a rather

2 size,

assemblage indication

of

records

steady

hex

tricolporates.

are

studied.

As

of

Raphia

roots

as and

assemblage

common.

than

this and

Laguncularia

occurs.

the

increase

the

there

was

Myrica

absence

of

true at

palm-swamp

The 300-350

of

increasing

the the

recovered.

is

marine

Rhizophora,

Pollen

450

hex

flex

in bottom influence

a

dominates.

increase

was

high

the

cm

cm and

is

and

in

also pollen

also

peat

of

the

of Rhzophora Laguncularia + Campnosperma + Mynca + Cyperaceae + Acrostichum Types I + 2 Camp.- type Type 39 °almae Mynca A lax Gramineae Fuslformispoiites PHASIC COIvTvIUNITY

o I] I CAMPNOSPERMA 5° I FOREST-SWAMP ioo U I U fi MIXED 125 FOREST-SWAMP

RAPHIA 175 . 200 I I PALM SWAMP 0 225 ::I 250 flJ 285 I ?5 BACK-MANGROVE 400J I] HI I I SWAMP 450[i1 I ! I I 0 10 20 0 0 20 40 60 0 10 20 0 5 10 0 10 20 30 0 5 10 0 20 40 0 10 20

120 Figure 3.9. Pollen diagram of core BDD 23. Data is in Appendix D. Palmsdecreaseas dicotsincrease,and thereis a peakin Fuszformisporites abundance. Symphonia

globuhfera pollenoccursat the top of this section(2 grains).

The upper 100cm is dominatedby Campnosperma and Campnospern?a-tvpepollen,and by a

diverseassemblageof minordicots. Palmpollenand phytolithsare also plentiful. Type 39 tapers-out,

and Fusformisporites is presentbut muchreduced. The assemblageis consistentwiththe presentPC 5

Campnospermaforest-swampvegetationat this site.

3.7 DISCUSSION

Descriptionof the floralsuccessionfromsingleor widelyseparatedcores is necessarilyrestricted to broadlygeneralinterpretations,and no seriousattemptcan be madeto correlatebetweenthe two cores analysedhere, whichare separatedby 6.5 kmof tracklessswamp. Nonetheless,the two pollenrecords fromthe Changuinoladepositrevealsuccessionalchangesin vegetationboth in the domedcentralpart of the depositand in the eastern,planar sectionapproachingthe marinemarginof BahiaAlmirante (Fig.

3.10). The centralmirehad its originsas a freshwaterRaphia palmswampupon sandysedimentsvery similarto those of the modernbarrierbar. The comparableRaphia communitypresentlyexistsonthe thin peats in the runnelsanddirectlybehindthe modernbarrier. Furthereast at BDD23, back-mangrove forest-swamp,likelycloseto brackishblackwatercreeksdrainingintoAlmiranteBay,weresucceededby

Raphia palm swamp. A similarcircumstanceis seenin the denseRaphia forestwhichcrowdsthe back- mangrovezonealongpresentblackwatercreeks,and evenbehindmangrovefringe-forest,whereRaphia provesto be remarkablysalt-tolerant. Swamp-forestsuccessionbasedon early colonizationby Raphia taedigera has beenpostulatedin Costa Ricancoastalswamps (Anderson and Mori, 1967; Myers, 1990) and in Africanpalm swamps(Richards,1952). Andersonand Mori (1967)describea successionin which the early, closedRaphia forestcanopyeventuallymaturesandopens-up,allowingthe successionof

121 RIO TNI CHA IA 14* BAHIA

ALMIRANTE - BDD 20 A ‘° SEA LEVEL

I:: —t

,,, ‘

‘.-

GENERALIZED PEAT PACIES based on pollen analysis and suiface vegetafio PC 3: Raphia palm swamp

--j PC?: Bog-plain PC 2: Back mangrove

PC 6: Sawgrass / stunted forest-swamp PCi: Mangrove fxinge

PC 4 & 5: Forest-swamp Undifferentiated sands, silt, clay

Figure 3-10. NW-SE cross section ofthe Changuinola peat deposit, as interpreted from pollen in cores and surface vegetation zones. Location ofthe cross section is shown on Fig. 3-1. Sites marked with an asterisk (*) core data from Cohen et al., 1990. Vertical exaggeration is x 500. hardwood forest-swamp. A similar sequence is seen in both cores, one to a mixed forest (Fig. 3.10) and

the other to monospecificCampnospermaforest-swamp(Fig 3.9).

The succession from forest-swamp, through a progressivelyless diverse, less arboreal and more

ecologically specializedplant community,to oligotrophicbog-plain, is admittedly a broadly generalized one. The limitednumber of samples and the resolutionof the sampling program does not permit a detailed stratigraphy, and it is certain that many variations can occur within and between cores, but the general vertical trend is clear. The phasic communities,at least in some sites in the Changuinola deposit, succeed each other in the order in which they are numbered. This is not to say that they must always occur sequentially, nor that they have equal roles in the developmentof the deposit. In the modernmire,

Raphia-swampoccupies a far greater area, and is ecologicallyfar more variable than is monospecific

Campnospermaforest-swamp. It may not be reasonableto suggestthat Canpnosperma forest represents a true phase in a succession,given its present limiteddistribution, and it is with somesurprisethat we foundthe PC 5 pollenfingerprintoccurringin bothcores. The AsianspeciesCarnpnospermacoriacea, and Campnospermasquamaa are reportedlyprolificpollenproducers(Andersonand Muller, 1975),and it is possiblethat the counterpartCampnosperinapanarnensis is significantlyoverrepresentedin some areas of the Changuinolamire. Nonetheless,the pollenof that speciesis decidedlynot ubiquitous,nor do its numbersovershadowotherspecies,so its presenceis consideredsignificant.

Lateral relationsbetweenthe phasiccommunities,movingfromthe marginstowardthe centreof the mire,are somewhatvariable,but generallyfollowa similarsequenceto that describedin the vertical sequence. The mirecomplexis roughlyrectangularin plan view. Each sideis physiographicallydistinct: the SE is a low energy,mangrove-fringedmarineshore,the NE a highenergy,wavedominatedbarrier coastline,the NW a large,flood-pronealluvialplain,andthe SW an abrupt transitionto deeplyeroded hill country. On all sidesbut onethe samegeneralsequenceis seen: Frommineralsoil supportinga

123 Walther’s the the geological between observations and imply peat mangrove complex, Almirante eventually dating that exceed brackish mixed vegetation. space diverse

phasic

distribution

effect

term,

depth

will

an

forest-swamp,

of

the

vegetation,

We

Anderson

lateral

conditions,

inevitable

peat

and

Law)

and

in fringe

be

communities Bay.

concept

the

is

rate

Anderson

have

these

of not

vertically

doming

bog in

we

of

and

of

zoning

states

Here

forest cores.

significantly

adopted

are

coseismic

vegetation

(1964)

relations.

plain

of

peat

successional

vertical

coastal

to

not facies

and

vegetation

that

relates

toward in

contiguous

may

depth

Describing ampnosperma

is

able

the

also

the

increasing

reached. in

relations

relations subsidence

subsidence,

be

The

zones

an Changuinola

both

term

less.

increases

to

uses

the

absent,

evolving

sequence,

state forms

concept

centre

gradient

in

the

directly ‘phasic

a Incipient

The

oligotrophy

within

is

time.

12

that

concept

a

including

and intended through

the

m

swamp, exception

of complex

depositional

of

mire the

but

community’

core,

and

to

one This

periodically

the

small

doming

‘facies

the

gradient

rather

of

doming

are Malaysian

of

a

to

Anderson

clearly

have

in

the

domed

belt

a

domes mosaic

these

to

describe

not 124

some

“catenary

association’

Raphia

is

is

this

system,

of not

of

from occurring, sufficiently

to

intended

applies small rising

Raphia topography

may

cases

the

which

sequence

proceeded

peat

peat

(1983)

observable

Anderson,

palm

peat

eventually

sequence”

units domes,

sea

accumulation

to

swamps,

to

(defined

reflects

to

palm

sawgrass

however.

surface

reports

level.

swamp. the

well-controlled

describe

is

which

to

of

in

the

Changuinola

swamp.

the

believing

relations,

the

the

the

of

coalesce.

in in In

sequence

the

controls

are

same

phasic just

Malaysian

the

this

swamp

SE the

influence

If

rates

following

laterally

peat

geological

along

The

observed

the

area

degree,

that

rather

communities

based to

the

is Moving

same

(Fig. deposit

accumulation

Raphia

drainage

justif’

variable,

the it

of

distribution

peat

contiguous

is radiocarbon

than

marine

even

on

3.10),

sense continuity

shore

not

sense

deposits. (Fig.

from

radiocarbon

gives

the

imply

though

meant

is

and

that

of

to and

use and

by

more

the

3.10).

rates

way

relate

in

of

any

cause

the

of

to

the the

Our

to

of dates: 5 m = 2255 ± 60; 10m = 3850 ± 55; 12m = 4270 ± 70. These give accumulation rates of 4.76

mm per annum for the early (12-10 m) basal (mangrove)peat, 3.14 mm/afor the intermediate(forest-

swamp) stage, and 2.22 mm/afor the upper (PC 6?) 5 m of peat. This slowing of accumulation accounts for a deposit which, while generally domed, is quite steep on the edges and flat in the raised centre.

Accumulation rates for the Changuinoladeposit portray a somewhat different history, summarized for different peat types as follows. Dates are the radiocarbon age in years before present

(BP) from three cores:

4.75 m =2110 ± 60 BP in fine hemicmangrovepeat throughout,

4.75 m = 1880 ± 60 BP in woody, fme hemicmangrove/backmangrove peat,

4.75 m = 850 ± 80 BP in fibric, bog-plain sedgepeat, and 8.0 m = 3040 ± 80 BP in woody, hemicpalm / mixedforest peat.

These dates give the followingaccumulation rates for differentpeat types:

mangrove/back mangrove peat 2.25 mm/a(from 4.75 m below present SL to present SL),

back mangrove/ forest peat 2.52 mm/a(from 4.75 m to the present surface),

palm/forest peat 1.48mm/a (from 8 m to 4.75 m), and sedge peat 5.58 mm/a(from 4.75 m to surface)

It can be seen from these results, particularly in the sedge peats, that there is a great deal of variationin rates of accumulation olin situ peat. The above valuesare as much an indication of variationsin bulk density and compaction as they are of accumulation rate. The rate of accumulation is in inverse proportion to peat density (Chapter 2.), and a true comparison of preservation and accumulation in different environments would require factoring-incompactionand density variations. The above in situ values, however, suggest that the hydrologicalcharacteristics of the peat dictate the height of the water table, and hence the surface topography. The densestpeats sampled, mangrove and forest peats, accumulate at rates comparable to Anderson’slate-stagepeat. The very high rate of accumulation of

125 sedge peats reflects lack of compaction. (The flbric nature of these peats makes it difficult to remove

youngerroot material,and great care mustbe takento avoidcontamination.)The domedcentralbog

plain is essentially a mass of well-preservedroot material floating in an acidic, nutrient-poor humic soup,

containedwithin a basin of dense, woody peat of extremelylow-permeability. Drainage of the central

mire is superficial, subsurface flow being effectivelydammedby the surrounding forest-swamppeat.

3.8 SUMMARY AND CONCLUSIONS

The general trend of vegetational developmentand peat accumulation in the Changuinoladeposit

can be seen in Figure 3.10. The deposit originatedas freshwater palm swamps that developedin close

proximity to both the Changuinola River mouth, probably behind a barrier bar and freshwater lagoon

system, and a low energy, mangrove dominatedbay. The early swamp was likelydrained to the southeast

by brackish blackwater creeks much as it is today, and formerly extendedconsiderablyfarther in the

direction of AlmiranteBay. The Raphia swamp was succeededby hardwood forest-swamp dominatedby

a limitednumber of specialised species, only one of which, Campnosperma panarnensis, is prone to

formingmonospecific stands. Increasing accumulationof woodypeat promoted by the everwet climate

impededdrainageof the mire, leadingto increased oligotrophy,and establishmentof bog-plain conditions

in the oldest, central regionsof the mire. It is significantthat peat developmentdid not require the mangrove phase commonto the Sarawak peat swamps, as Raphia taedigera is able to colonizeand institutepeat accumulation in a variety of environments. Raphia is found thriving on both mineralsoil and deep peat, with pH varying from 8 to 3, and salinityup to about 30 ppt.

The Changuinola mire complexhas several features in commonwith the extensivecoastal mires of southeast Asia, as well as some fundamentaldifferences. In surface morphology,and in the zoned distribution of vegetation,this neo-tropical mire closely resemblesthe swamps of Malesia described by

J.A.R. Anderson (1961,1964), although the degreeof doming is so slight that the term is more useful as a

126 categoryof mirethan as a descriptionof the topography: the maximumgradientrecordedis im in 330m,

in mixedforest swampnearthe NE marginof the mire. Pollenanalysisshowsa successionof vegetation

fromthe base to the surfaceof the peat depositwhichechoesthe lateralsequenceof phasic communities

from the marginsto the centreof the mire. Thus the modelof peat accumulationin an environmentof

increasingoligotrophydescribedby Andersonappliesto the Changuinolamire complex,despite

significantdifferencesin geography,vegetation,anddepositionalenvironmentcomparedto the southeast

Asian deposits.

Thick, extensivepeat depositscan developon a highenergyshorelinein closeassociationwith

active elastic sedimentationif the sedimentsupplyis sufficientto causeaggradation-progradation,andan

everwetclimatemaintainshighwatertables.

In this region,mangrovesare not essentialto the developmentof extensivecoastalpeats. Raphia is a primary colonizerin the Changuinolamire,and representsthe first stage in the successionin non- mangroveenvironments.

Doming,sufficientto excludefloodwaters,can be relatedto factors otherthan differentialpeat accumulationrates, and is dependenton peat densityand permeability. Peat densityis associatedwiththe peat-formingvegetationand thus withecologicalconditions. The late-stagebog-plainaccumulationrate is very rapid, becausethe densityis very low - the sedgepeats are not denseand compactedlikethe forest peats, and they are mostlyfloating.

The conceptof ‘faciesassociation’(in thegeologicalsense,whichstates that in an evolving depositionalsystem,unitswhichare laterallycontiguousin space willbe verticallycontiguousintime -

Waither’sLaw) appliesto the organicsedimentsof the Changuinolamire,and in the broadestsensecould

127 be expected to apply to petrographic variations in coals originatingin domed peat swamps. This would

apply whether dealing with palynofacies, or with lithofaciesif it can be shown that there is a relation

between coal-forming vegetation and microlithotypes.

In the course of this study, certain practical considerationsbecame apparent. The first is that,

with sufficientwork ‘onthe ground’,satelliteimagerycan be usednot onlyto determinethe existenceand

extent of tropical peatlands,but also the vegetationtypes, some aspects of the drainage patterns, ‘degree

of wetness’,etc., all valuable elements in the monitoringand managingof wetland resources. This is

particularly important in remote areas, and in developingcountries.

Ecological and climatic interpretationbased on pollen profiles is fraught withdanger, as

exemplifiedby the association of cooling, and increasedseasonalitywiththe Myrica-Rex pollen

connection in the Bartlett and Barghoom (1973) core from 7200-4300 B.P. Much more work is needed

in the tropics before we can apply palynologicalprincipals with the same degree of confidenceas in high

latitudes. In the present case, a more in-depthpalynologicalstudy, with better representation of pollen

fingerprints to their vegetation, would includemultiplecore and surface samples from each phasic

communityin order to reduce the under- and over-representationinevitablefrom single-site sampling.

ACKNOWLEDGEMENTS

Supported by the International DevelopmentResearch Centre, Ottawa, Y.C.R. Grant 92-1201-18 (SP), the Natural Sciences and EngineeringResearch Council of Canada Grant 5-87337 (RMB), and The University of British Columbia. The authors are grateful to The SmithsonianTropical Research Institute, Balboa, Panama, the Instituto de Recursos Hidraulicosy Electrificacionof the Republic of Panama, and the Chiriqui Land Company, Changuinola, for their unhesitatingsupport throughout the duration of this project. In particular, thanksto Dr. Paul Colinvauxand Sr. Enrique Moreno of STRI for their aid and the use of their labs, Sr. Andres Hernandez of the Forest Dynamics Unit, Barro Colorado, for his willingnessto cheerfullyjoin us in the swamp, and Ing. Eduardo Reyesof IRHE for his surveying skills and his continuing efforts on our behalf. Special thanks to the Serracin family and the Sanchez family of Boca del Drago, and to the eagle-eyedSr.Sammy Sanchez.

128 Cohen, Cohen, Cohen, Cohen, Bruenig, Barber, Anderson, Anderson, Christen, Bartlett, Allen, Anderson, Anderson,

P.H.,

A.D., A.D., A.D., A.D.,

Apr. deposit characterization Tropical of particular mt. P.C. Forestry, Brown, past K.E., Amsterdam. (ed.), Costa Ecosystems Journal in

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Vegetation Rica.

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132 CHAPTER 4

SULPHUR IN THE CHANGUINOLA PEAT DEPOSIT, PANAMA, AS AN INDICATOR

OF THE ENVIRONMENTS OF DEPOSITION OF PEAT AND COAL

133

reflects western

vegetation

found

of

content

produce

peat,

zoned.

suiphides. apparently

with

onshore,

shallow

and

peat

greatest

biological

content

state,

the

high

CHAPTER

these

occupies

is

to

groundwater.

and

the

is

part

now

Stunted,

dense

be

INDICATOR

of

marine

to

The

except

salinity

in

and

tidal

regional

and

the

The

peat

comparable

the

proximity

of

proportion

below

sulphur

climate. hemic thç

result

the

southeast, tectonic

western

channels

sediments in

in

sawgrass-dominated

4:

(>

central

deposit,

a

the

sea

structural

The

0.5

large

and

of

SULPHUR

(S)

to

vicinity

level.

OF

to

The to

factors

a

part

wt%)

marine

distribution

are

fine

bog biogeochemical content

leading

the

back-barrier

published

of

THE

and

distribution

of

low

Coastal

the

hemic

degree

trend

plain.

dominate

of

the

of

the

influence,

ENVIRONMENTS

adjoining

in IN

brackish

of

to

the

SE

deposit

of

salinity

peat

drowning

values

of

coal

Around

of

THE

mangrove

vegetation

depositional coseismic

-

mire

humification

organic

NW

the

of

with

is

chain

of

blackwater

bay.

CHANGUINOLA

is

high

for

(< eastern

4.1

frequently

on

transgression

the

the

domed,

higher

of

0.5

temperate

the

peats

ABSTRACT

of

and

sulphur

which

Marine

subsidence

bog mire

134

the

environment.

wt%)

S

Caribbean

margin

inorganic

reactions

deposit

of

and

S plain,

OF

with

in

creeks

used

produces

content,

the

peats

influence

and

which

DEPOSITION

the

and

moderately

parallel

peat,

and

mixed-forest

to

greatest

beneath

very

vegetation

which

subtropical

PEAT

coast

in

sulphur

leading

infer

it

extend

between

the

and Earthquake-generated

fibric,

was

high

extends

to

drain

aspects

of

eastern

to

Almirante

DEPOSIT,

both

the

deposited.

to

high

forms

beneath

Panama

in

the

very

and

0.25

the

and

OF

trend

S

the

peats,

are

only

southeast.

S

(5

of

and

the

concentration

low

PEAT

in

palm-forest

swamp.

content

and

independent

to

the

of

a

paleo-climate,

is

the

Bay,

peat

despite

low

PANAMA,

-.44

S

short

In

related

the

0.5

salt

(<0.25

tropical

AND

this

sulphur

are

and

coastline (1

wt%

wt%

Peats

distance

water

subsidence

differences

to

study,

concentrically

to

40%

swamps

COAL

of

of

5

S),

wt%

S.

peats

climatic,

associated

wt%

in

AS

the

and

C-S

trophic

of

The

the

the

5)

pH

AN

the

are

S)

S

S

is in shallow-marine deposits, plants back-barrier coastal ppm In ombrotrophic source of subsidence (Fig. minerotrophic Reduced 0S03) Plants tration sulphur, 80 very seawater

addition, oxidation

km2,

high in

4.1).

and

use

of

(Luther

peat

seawater;

in

Primary Sulphur

about

in

sulphur,

and are

(>10%

polysaccharides,

sulphur

the

bacteria.

The a is

the

swamp

states,

coal

variety important

are

leading

bogs

oxygen,

mires,

20

and

deposit

association sediments

content

sulphur

frequently

dry

deposition. Gross

km2

as

found

and

in Church

near

of

Aqueous

suiphide,

and to

weight),

the

of

as

is amino

sources.

swamps,

deposition

1982).

and

in Changuinola

content

which

those

in form CO2.

makes

choline

peat of

1992;

used

a

distribution

The

tectonically

acids much sulphate a

may

of

with

for

is

thick,

Sulphate

(concentration

the of In

it in

polysulphides,

Giblin

offshore

peat

of

an sulphate, respiration,

be

brackish the

peat

and

higher

brackish

atmosphere

carbonate

excellent

laterally taken in

deposit,

(SO42-)

reconstruction

4.2

related

is

western

are

and

is

active

dependent

beneath

than

INTRODUCTION

reduced

up

phenols, important

and

Wieder

and

extensive

and

of

which compounds,

by analogue

in sediments

can

setting,

is

elemental,

marine-influenced

Panama

135

marine

sulphur

rain,

rootlets,

the

the

fix

by

be

on 1992).

and

averages of

sole

some

shallow

factors

accounted

respiring

groundwater

the

in

paleoenvironments peat

for

influence

has

other

is

over

which

source

and

or

availability

and

from

of

marine

In

deposit

been

pyritic

in

marine

the peat.

6

compounds

subsequently

as

plants

the

to

earthquake-generated

for

of

sulphur, (ie.

studied

so-called

peat,

8

influenced

evaluation

and

primary

with sulphur. by

m

sediments

rheotrophic),

and

8 of

in

pore-water

sulphur the

ppm

alluvial,

aqueous

as

thickness,

(Casagrande

sulphur-reducing as

of

ester oceans

re-oxidized

a

sulphur,

carbon-bonded

coal

in

In

tropical

model

of

of

concentration

fresh

strictly

sulphates

peat

barrier-bar,

sulphate measures.

Almirante

sulphate

is

groundwater

has

for

the

whereas

water,

and

coal

coastal

et

to

an

low-sulphur

principal

al.,

coal

a

(C

deposits.

to

area

concen

bacteria.

variety

885

(C-S)

Bay

A

living

can in 1976).

and

large

of

and

be America testing Figure one standard 7, (MEAN CHANGUINOLA Republic 4.1. are x.* CONTENT) shows marked. ( C Site of 14) SAMPLE deviation, SULPHUR EXTENT Panama T5(Ol2*TU the map location Site STANDARD PEAT showing (O2*).o BDT2Q* DEVIATiON OF SITE in (034).4 name italics. DEPOSIT PEAT of the is the *BDT23 followed (O1 known site xLE9 tGZ),o7 * ______on T1(039)05 extent the by (O.52 .) \JI the northwest of mean the 136 31(3 1)46 Changuinola total coast 8)18 r4 sulphur of ______dqo.20(3 Panama. ALMIRANTE BDDI(37)26 XS)D19A(38)9 STUDY peat UNTA content

c ___ AREA 2)5 deposit. 25 PONDSOCK Sample - I of the •: BAY Inset sites core (236)1 I BI for map in ______.a.sv PANAM4- •:-.- brackets, ISLA sulphur COLON of NOga - Central 20’_ 15’. and freshwater,particularlyombrotrophic,settings,sulphurcontenttendsto be low(< 1%dry weight).

Thus the sulphur contentof a coalis frequentlyusedto inferthe trophicnatureof the progenitormire,

and its proximityto marineinfluences(Williamsand Keith 1963;Raymondand Davies 1979;

Chandraet al. 1983;Shimoyama1984;Hunt andHobday 1984;Querolet al. 1991;others).

In coals in whichno marineinfluenceis evident,sulphurcontenthas beenrelatedto other aspects of the geochemistryof the precursorpeat (Cecilet al. 1979;Rentonet al. 1979;Rentonand

Bird 1991). Theseauthorsobservethat acidpeats (pH <4) are characterizedby well-preservedplant materials, lowdegreesof humification,and lowsulphurcontent. In moreneutralpeats (pH 4 to 8), the environmentis morefavourablefor bacterialactivity,hencehumificationrates are likelyto be high,preservationpoor, and sulphurtendsto becomeconcentrated. Acidityin turn may reflectthe trophic state of the mire,the presenceof buffersinthe groundwaterand associatedsediments,the degreeof marineinfluence,andthe compositionof the peat-formingflora.

Sincethe early 1960’s,workin modernpeat-formingenvironmentshas contributedmuchto the understandingof sourcesof sulphurin peat and coal. Numerousproblemsremainhowever, particularlywith regardto rapidlateralandverticalchangesin sulphurformand concentration,the relationbetweenpeat sulphurand overlyingmarineelasticsand carbonates,and the signaturesleftby rapid subsidenceand marineinundation.The uniquesettingof the Changuinoladepositprovidesan opportunityto addresssomeof theselongstandingproblems,as wellas take a first detailedlookat

Neo-tropicalforest-swamppeats fromthe perspectiveof coal science.

4.3 REGIONALSETrING

a) Geography, Climate and Biology

Tropical coastaldepositionalenvironmentsare believedto havebeenthe settingsfor many knowncoal deposits.(Wanlesset al. 1969;Andersonand Muller 1975) Tropicalcoastalpeats, however,are still relativelypoorlyunderstood,and differin a numberof ways fromthe temperateand

137 sub-tropicaldepositson whichmanycurrentdepositionalmodelshave beenbased. Tropicalclimate

affects air and water temperatures,seasonality,growthand decompositionrates, andthe composition

of the peat-formingfloral community.

The Changuinolapeat deposithas developedin a back-barriersettingon the Caribbeancoast

of Panama, at 9020’ N latitude,82° 20’W longitude(Fig.4.1), on a microtidal(30 cm), wave

dominatedshoreline. Althoughtidal effectsinthe westernCaribbeanare minimal,strongwind-driven

longshorecurrentstransport sedimentsto the southeast. Tropicalstormsand hurricanespass to the

north, but associatedfloodeventsare frequent.The climateis humid-tropicalandtemperature

averages26°C, with a ±3° range. Thereis no dry season;annualprecipitationis about 3000 mm,

uniformly distributedthroughoutthe year.

Vegetationon mineralsoil is diverseand luxuriant. In a 20mx 20m quadrant, 164speciesof trees and shrubs wereidentified(See Chapter3, Appendices).This diversityis typical of humid forestedlowlands(A. Hemandez,personalcomm.).Floraldiversityin the peat deposit,however,is low (54 major speciesrepresentingthe entirepeat swamp)and distinctlyzonedinto a sequenceof

‘phasiccommunities’(terminologyof Anderson1964,and Bruenig 1976)similarto those describedfor the oligotrophicpeat swampsof WesternMalesia(Anderson1964; 1983)and Borneo(Bruenig1990).

The factors whichaccountfor floral zonationon peatare not fully understood,but are generally consideredto be relatedto nutrientlevels,watertableand pH of the groundwater. Thus distinctive phasic communitiesof peat-formingflora,alongwiththeirassociatedgroundwaterenvironments determinethe characterof the peat whichwilldevelop. Consequently,schemeswhichidentifyand classifypeat accordingto its principalfloralcomponentsinherentlyimplymuchabout the environment of deposition. The Changuinoladepositincludes7 phasiecommunities,someof whichcan be further subdividedaccordingto the presenceof secondaryspecies. Theseare: i) Rhizophora mangle mangrove-swamp;ii) mixedback-mangroveswamp;iii) Raphia taedigera palm-swamp;iv)

138 Campnospermapanamensis forest-swamp:v) mixedforest-swamp;vi) Cyperaceae(sawgrass)*

stuntedforest-swamp;vii) Cyperaceaebog-plain.

b) Geomorphology

The NW coast of Panama is a site of activeclasticand organicsedimentdeposition. Muchof

the coastal plain is undera variablecoverof Quaternaryand Recentalluvium,andthe coast is

characterisedby a seriesof progradingbarrier bars behindwhicha chainof lagoonsand paralic

swampsis developed. Severallargeriverstransport sedimentsnorthwardoff the Talamanca

Cordillera,and winddrivencurrentsmovesedimentsconsistentlyalongshoreto the southeast.

Sedimentationrates are high,andthe peat deposithas developedonthe back of a progradingbarrier bar, the characteristicridge-and-swalearchitectureof whichis describedin Chapter2. Basal sedimentsare well-sortedmediumgrainedgrey sands similarto thosecurrentlybeingdepositedonthe coast by the ChanguinolaRiver. At the easternterminationof this coastline,wherethe terrigenous sedimentsextendbeneathAlmiranteBay,peat occurssubmergedto depthsof 3 m or more,underlain by mediumgrainedgreysand,and in placesoverlainby a thin layerof siltysand, limemud, and coral.

Levellinglinessurveyedacrossthe peat depositshowa slightlydomedsurfacethat has a maximumelevationof 6.75 m inthe centreof the swamp,a maximumgradientof 1:330(the NE margin) and a base that is from4 to7 m belowsea level. An estimated40% of the volumeof the peat is belowpresent sea level. An offshoresamplefrom475 cmbelowsea levelwas radiocarbondatedat

2110 ± 60 a. This mangrovepeat is overlainby 265 cm of brackish-waterpeat, 15cm of carbonate sediment,and 195cm of salt water. Assumingdepositioncloseto meansea level,and onlyminor changesin regionalsea leveloverthis period(Pira.zzoli1991;Chapter2), about 4.5 m of net subsidenceis estimatedto haveoccuredin the past 2000 years, includingthat generatedby a M

(surface magnitude)7.5 earthquakein April 1991, 10weeksbeforethe start of this study.

139 c) Geological Setting

The studyarea is at the eastemmostonshoreextentof the Limon-Bocasdel Toro sedimentary

basin. The Bocasdel Toro Basinin Panama,and its westwardextensionin Costa Rica, the Limon

Basin, togethermake up the Tertiary and Quaternaryback-arcbasin behindthe volcanicrangesof the

Talamanca Cordilleraof southeasternCentralAmerica. Chapter2 givesan overviewof the regional

geology,and the tectonicsettingof the area.

Regionalverticalmovementalongthe coasthas beenestablishedon the basis of sea level

changesas observedin the degreeof exposureof near-shorecoral reefs,limitsof intertidalorganisms

on dockpilings,and changesin the swashzoneon beachesat eighteenpoints betweenthe mouthof the

Rio Matina in the northwestand Punta Mona(Gandoca)to the southeast(Astorga 1991;Plaflcerand

Ward 1992). Theseobservationshavebeenaugmented(Camacho,unpublisheddata; See Chapter2) to includethe coastlineof Panamafromthe Rio Sixaolaat the Costa Rica borderto the Boca delToro channeland Cayo Solarteto the southeast. In additionto regionalverticalmovementsare local liquefactioneffects,on a scaleof tens to hundredsof metres,both of subsidenceand uplift (Camacho et al. 1992). It is concludedthat 50 cmto 70 cmof regionalstructuralsubsidenceoccurred. These conclusionsare basedon aerialphotographs,observationsof the swashzoneof beachesand of plant mortalityalong vegetatedshorelinesin the area, andon interviewswith individualsfamiliarwiththe area and with a workingknowledgeof sea andriverlevelsbeforethe event.

4.4 SAMPLINGANDEXPERIMENTAL

Figure4.1 showsin plan viewthe extentof the peat depositsbetweenthe ChanguinolaRiver and Isla Colon. Markedsamplesitesrepresentcorestakento the base of the peat, by Cohenand others (1989) and by Phillipsand Bustin(1991to 1993). Most sampleswerecollectedusingHiller or Macauley-typehand-operatedcoringdevices. Samplesweredescribedin the field,and baggedin

25 cm or 30 cm increments. Continuouscoreswerecollectedin 3.5 cm.diameterplastic sleevesusing a smallvibracore,refrigeratedand subsequentlyfrozenfor longterm storage. Salinityand pH

140 weremeasuredin the fieldand verifiedin the laboratory. A digitalpH-meter(Cardy®ModelPHi)

was usedboth in the fieldand the laboratoryto measurethe pH of the wet peat and porewater. At the

sametime, salinitywas measuredusinga digitalsalt-meter(Cardy®ModelC121),whichmeasures

sodiumion concentration,and then appliesa correctionfactorto calculatetotal salinityfor values>

0.01 wt%. Total sulphurcontent(dryweightpercent)of 203 samples(driedat 50°C, crushedto 100 mesh)was determinedusinga Leco®SC-132SulphurAnalyzer(seeTabatabai 1992,3p. 13for a descriptionof this instrument)and verifiedusingwet chemicalmethods. For a coastalsamplesite,

and for site BDD23adjacentto a majordrainagechannel,total sulphurwas sub-dividedintoorganic

sulphur, in both carbon-bondedsulphide(C-S) and ester sulphate(oxidizedcompoundsreducibleby

HI) form,and inorganicformsexpressedas mineralsulphate,elementalsulphurand pyritic (+

marcasite)sulphur. The proceduresfor determiningthe proportionsof the variousformsof sulphur are describedin detailby Lowe(1986)and Tabatabai(1992)(AppendixG), whoalso discusssomeof the shortcomingsof the methods. In addition,previouslypublishedtotal sulphurvaluesof another206 samples(CohenCt al. 1990)are incorporatedin this study.

Degreeof humificationof the peats is basedonthe relativeproportionsof coarse,mediumand fine constituentsas determinedusinga wet-sievingproceduremodifiedfrom Staneckand Silc (1977), accordingto the followingscheme(Esterleet al 1987):

Coarse >25% >2.0 mm <30% <0.25 mm

Medium <25%>2.Omm <30% <0.25mm

Fine <25% >2.0 mm >30% <0.25mm

The procedureis describedin detail in Chapter2. Degreeof humificationis describedusinga modifiedvon Post HumificationScaleadaptedto tropicalpeats by Esterle(1990) (AppendixG). The categoriesare sapric, finehemic,hemic,coarsehemicand fibric. Peat classificationis basedon the identificationof macroscopicplant parts and palynomorphsin the peat, comparedto plant and pollen associationspresentin the modemswamp. For somesamples,the percentmoisturecontentof

141 drained wet peat was measuredby re-weighingafter drying at 50°C until no further weight loss

occurred.

4.5 RESULTS

a) GeochemicalParameters

i) Sulphur and Salinity.---Sulphur contentof the Changuinolapeat varies from less than .01

wt% to in excessof 13wt%. Althougha full spectrum of sulphur values is present, the samples fall

into low-sulphur (.01 to 1.0wt%) and high-sulphur(> 1.0 wt%) populations when plotted against

other parameters such as pH (Fig. 4.2). Average sulphur content of each core, shownon Figure 4.1,

shows a geographicaldistribution, in whichthe western part of the deposit is madeup of low sulphur

peats (mean of 0.23 wt%, standard deviation .18; Fig. 4.3), The easternpart, comprising peat

within 3 km of AlmiranteBay, has much higher sulphur content and much greater variability (meanof

2.24 wt%, s = 2.55; Fig. 4.4). Figure 4.4 furtherreveals two populations of sulphur values in the

eastern section, a lower- and a higher-sulphurgroup. Both plots suggest that there is little correspon

dence between sulphur content and depth of burial (and hence age) of the sample, but that lateral

distance from the south-east marinemarginis significant.

To claril’ the apparent relationshipbetweenaverage sulphur content and proximity to the

marine influence of AlmiranteBay, the salinity of all samples was plotted againstsulphur. Salinityis

readily measurable in the field, and in the present study proved a useful indicator of the presence of marine influence in porewaters. Salinitycannot be related directly to aqueous sulphate content without qualification: aqueous sulphate maynot diffusethrough peat pore water in the samemanner

as other mineralsalts. Sulphate diffusion is biologicallymediated (Brown 1985) andthus drivenby a differential that is heavilymodifiedby an ongoing“sulphatereduction front”, whereas diffusionof mineral salts is determinedprimarily by the ability of groundwater to circulate. This may create complication in using salinity to approximate the movementof sulphate-rich waters in rheotrophic mires, but is unlikelyto be a problem in ombrotrophicsituations, in which the supply of atmospheric

142 Figure

4.2: Sulphur

(wt%)

wt% Total

Sulphur

0.01 100

0.1

10

1 2.50

(logarithmic

IW n

n U U U 3.50

scale) UU U

vs

143

p!-I. U U 4.50

n216. U

, U U , U

. .UU U

5.50 U pH 3 U U U: U

6.50 U

u U U U U

7.50

8.50

143 Note Figure Figure (logarithmic (logarithmic

the sulphur sulphur scale) scale)

4.4.

4.3. wt% wt% distinct Scatter Scatter

bimodal 0.01 0.01 100 100 0.1 0.1 10

10 plot plot 1 10

10 of of ______distribution wt% wt% sulphur sulphur

a A a m in sulphur vs vs a

i A 144

depth depth, content. A a for western A a A samples Depth Depth LA n

*

m

part 100 100 = ______in in in

144. of cm cm

the

the eastern

a deposit. part aa n a of =

244. a

the La a deposit. a Ia A M a 1000 1000 * sulphur to the mire can be assumed to be relativelyconstant, and uniformly distributed. With the

exception of three basal samples, the highestsalinityfound in the ombrotrophic western peats is 0.02

wt%, the vast majorityof the samples beingbelowthe sensitivityof the meter (0.01 wt%). This is

also true of the porewater in the basal sedimentsat all sites measured. In the easternpeats, some of

which are rheotrophic, salinity is highlyvariable (<0.01 to 2.7 wt%). For interpretive purposes three

sample populations are differentiatedbasedon a plot of S vs salinity(Fig. 4.5). These are:

Group I: sulphur < 1.0 wt%; salinity < 1.0wt%

Group II: sulphur> 1.0wt%; salinity < 1.0wt%

Group III: sulphur> 1.0 wt%; salinity> 1.0wt%

The three groups can be used to map porewater environments. Figure 4.6 (plan view and cross-

section) approximates the three-dimensionaldistributionof the three groups. In the western section,

all peat is Group I, except at the bases of the three deepestcores, which are placed in Group II (based

on low basal porewater salinity of nearbysites). In the easternsection, the distribution is more complex (reflecting the complexhistory of the marinemargin). Some inland sites are entirely Group I, whereas all the marine-marginand offshore sites are Group ifi. Group II samples (mediumto high

sulphur, low salinity) are found only near major drainagefeatures (blackwater creeks). Salinity of surface waters (upper 3 m) along the marinemarginsis between2.9 and 3.2 wt%. Salinity profiles of the three major blackwater creek channels whichdrainthe easternhalf of the deposit are shown in

Figure 2-5. Salinityand pH were measuredat points 1km into the swamp. Streambanks are lined with dense stands of mixedRhizophora mangle (redmangrove)and Laguncularia racemosa (white mangrove), and tidal effects andmixingare prominentdespitethere being only a 30 cm tidal range.

Salinity of creek bottom water is 70% of the salinityof the bay, and at 1 m below the surface creek water is 25%, of bay water salinity.

ii) Sulphur and pH. —The pH of all samples collectedwas measured in the field, and pH of localwaters was also tested at regular intervals: pH of rainwater is 6.9 to 7.0, and the sea water in the

Caribbean and AlmiranteBay between6.9 and 7.4 in

145 Total Sulphur wt% QI GROUELJIL 2.5

2.0 I------I . I 1.5 — — - - - - — I- - - - - I I Salinity I (wt%) I II 1.0 —-i”.. 0.5 ————-- II I I I

0 zLHIIfl IIIflI LI 111 I!!UII iz GROUP I GROUP II

Figure4.5. Scatterplot of total sulphur(logarithmicscale)vs salinity. The fields GroupI, GroupII and Groupifi represent sulphur-salinitygroupsas definedin the text. n = 213.

146 Wt % total sulphur 0.1 02 03 0.4 0.3

LAKE 9

8

:CHANGUINOLA: :::::: :2: ::::: : : : : : :2::::: : :

W 18km

LI Group I - low sulphur, low salinity Group II- high sulphur, low salinity Group ifi - medium sulphur, high salinity Figure 4.6. Areal and depth distribution of sulphur Groups 1,11 and ill in the Changuinola peat deposit Across the top of the diagram, variations in total sulphur and pH with depth along a W-E cross section. Below, plan view and cross section from Changuinola River to Almirante Bay. Asterisk () signifies data from Cohen et aL, 1989. the upper 3 m. The pH of water in the blackwater creeks, measured after about one week of dry weather, is near-neutral (Fig. 2.5). The near-neutralityof the drainage water in the blackwater creekscontrasts withthe commonlylow pH of water drainingfrom temperate peat bogs. For example, very acidic bog water results in fish kills in Norwegianstreams at the end of dry periods, when low water tables resulted in the oxidation of suiphidesin the acrotelm. The resulting sulphate is then flushed out of the peat, withthe onset of wet weather (Brown 1985). The ever-wet conditionsin the Changuinola swamp, combinedwith the buffering effect of admixedseawater, presumeably maintain a high pH, and thus very favourable conditionsfor bacterial sulphate reduction, at least in the immediatevicinityof the creeks.

Figures 4.7-1 and 4.7-2 plot pH againstdepth for samples in the western section (n = 321) and the eastern section (n = 387) of the deposit respectively. In the west, pH is low (mean of 4.4) and fairly uniform (standarddeviationof 0.6), and displays a moderatepositive correlation with increasing depth (r = 0.4). Eastern samples are on average less acidic (mean of 5.7) and more variable (s = 1.1).

Correlation with increasing depth is very weak(r = 0.16). The higherdegree of variability reflectsthe complexhistory of the easternsection and the presence of marine and brackish influences at varying levels in cores.

The contrast in geochemicalvalues betweeneastern and western data sets, as well as differences in vegetation, and the physical character of the peat, reflects differing hydrological conditions in the ombrotrophic western part of the deposit and the locally rheotrophic, marine influencedeastern section (See Chapter 2). In order to clarifythe distinctions, the results will be described under separate headingsfor east and west.

b) Total Sulphur Distribution

i) Sulphur andpH in the WesternSection of the Deposit.---The western section of the deposit is a slightly domed, roughly concentrically-zonedmire, the centre of which is an extensive bog-plain.

148 _____

pH pH 3 4 5 6 7 2 4 Depth — — Depth in cm — in cm -I — >0 100 —C) .C) 100 U — —— — flU

— 200 I. - U ‘0 — — 200- — —____ — • __ 300 “+: IIt_

C) .‘

300 - — • — 400 - - . ,• • — _II_ _ — — •

500 -

400 - -

600 - -

__— 500-- • — — U 700 - - • —: : H 600 1. 800 - -

700 900 - - Figure 4.7-2. pH vs Depth in the eastern section ofthe Figure 4.7-1. pH vs Depth in the western section ofthe deposit; deposit; n = 387, mean pH = 5.7 (s.d.=1.1), range 2.67 to 7.89. n = 321, mean pH = 4.4 (s.d.’O.6), range 2.82 to 6.29. r (correlation) = +.16 r (correlation) The surface of this region is permanently submerged, and drainage is by surface run-off in a radial pattern. The bog plain vegetation is an impoverished community dominatedby sawgrass(sedges), togetherwithSagittaria Iancfo1ia, Dieffenbachia longispata, ferns,grasses, mossesand algae.

StuntedMyrica mexicana-Cyrilla racemflora treehammocksare scatteredsparselyacrossthe plain.

Sawgrass-stuntedforest-swamp,Campnosperma panamensis and mixedforest-swamp,andRaphia palm-swampsurroundthe centralbogplain.

Despitethe variationsin vegetation,the absolutesulphurcontentof all peat types is low.

Sulphuris lowestin the bogplainpeats, and slightly higherinthe marginalzones. Towardsthe barrier bar, windbornesuphatemayadd to nutrientavailability,and in shallowpeat towardsthe southwestmargingroundwater-bornenutrientsmay be moreavailable. In all cores,pH (dashedlines in Fig. 4.6) showsan erratic but overall increasewithdepth,coincidingwith increasesinthe degreeof humificationof the peat. This increaseovershadowsthe effectof concentratedhumicand fulvicacids in the moredegradedpeats, whichwouldtendto lowerthe pH at depth,but the sametrendof increasingpH withdepth is foundin almosteverycore. Thetrend in pH does, however,echo transitionsin peat type, and in floralassociationas detenninedby pollenanalysis,fromprincipally

Campnospermapanamensisandmixedforest-andpalm-swamppeat in the lowerparts to bog-plain sawgrasspeats in the upper parts of the cores. Utilizingparticlesizedistributionby wet-seivingto quantifythe degreeof humificationof the peat, a veryclosecorrespondencebetweenincreasesin humificationand increasedsulphurconcentrationis found(Figure4.8).

In the bog-plaincores,the pH of the underlyingforest-swamppeats is higherthan that of the overlyingsawgrasspeats. Thus higherpH is associatedwithforest-swamppeat, increasingdepth

(age),and slightlyhighertotal sulphurcontent. To furtherexplorethesethree relationships, data fromthe bog plain (MILE5 - Fig.4.8) is comparedto that fromsite LAKE2, locatedin mixedforest- swamp 1200m fromthe barrierbeach. This core,Figure4.9, is composedof fmehemicwoodypeat throughoutits entiredepth,andthe particlesizedistributionis consistentthroughout. The sulphur

150 pH % Size Distribution Wt% Sulphur 3.5 45 5.5 20 0 0.2 0.4

Figure 4.8. Variationin particle size (humification) pH and sulphur in an 870 cm core from the central part of the deposit (MILE 5) showing the close correspondencebetween increasesin humification and increases in sulphur content. The particle size categories are coarse (c >2.0 mm), medium (m> 0.25 mm), and fine (f< 0.25 mm). —z

1NCRE4S1NG INCRFASING HUMIFIQ4TION SULPHUR

pH % Size Distribution Wt% Sulphur 4 5 o o 6o 0.2 0.3 0.4

Figure 4-9. Variationin particle size (humiflcation) pH and sulphur concentration in a forest-swampcore from near the marginof the western section (LAKE2), showing an inverse relationship betweenpH and sulphur content Particle sizes are as for Fig. 4.8.

iNCREASING INCREASING HUMIFICATION SULPHUR-

151 concentration is higher than in sawgrass peat, and decreases slightly with depth independentof

humification. The pH of the LAKE 2 forest-swamppeat is lower (avg. 3.7) than that of the MILE S

core (avg. 4.2), and pH increaseswith depth. This low pH peat is both highly humifled,and relatively

high in sulphur content. Low sulphur peats originatingfrom forest-swamp vegetationhave higher

sulphur content than do sawgrass peats from the bog plain, regardless of pH. The range in sulphur

variation is considerable (0.16 wt%); thus fine hemicpeats have about twice the sulphur content of

coarse hemic peat. All samples had salinity below 0.02 wt% (Group I).

ii) Sulphur, Salinity and pH in the Eastern Section of the Deposit.---The upper panel in

Figure 4.6 shows sulphur and pH values for a series of cores along the NW-SE cross-sectionfrom the

Changuinola River floodplainto the submergedpeat beneath Almirante Bay. The eastern part of the

deposit is that part withinthe influenceof tidal creeks which drain into Alnürante Bay, representedby

cores BDD 8, 23, 20 and 19Ain Figure 4.6.. Present vegetationis a complex mosaic of mixedforest

swamp, monospecific stands of Campnospermapanamensis, Raphia palm and sawgrass

(Cyperaceae), with mixed mangroveand back-mangrovecommunitiesbordering the creeks up to 2 km from the coast. The bay margin is borderedby Rhizophora mangrove fringe forest. The complexity of the vegetation reflectsthe complexhydrologyof this section, which is divided by the three major channels (Figs. 4.1 and 2.5) into areas of low salinity and sulphur (Groupl) forest and sedgepeats, bordered by Group II back-mangrovepeats, and Group III Rhizophora peats.

Site BDD 8 is in mixed forest-swampnear the head of a blackwater creek 3 km inland, and

BDD 23 is 1.5 km closer to the bay, in similar vegetation. The sites are about 50 m from the present channel of Canal Viejo, and salinity is <0.1%. In the upper 2.5 m at both sites the peat is forest- swamp and Raphia peat, pH is below 4.5, and sulphur content is less than 0.5 wt% (i.e. Group I).

Lower in the cores, pH increases rapidly to near-neutrality. Sulphur remains low at the inland site, but increases to 13.7 wt% at BDD 23 in back-mangrove(Laguncularia-Acrostichum-Rhizophora) peat (Group II). At the coast (BDD 20) pH varies between5.4 and 6.3. Sulphur averages 3.2 wt%,

152 pH

2 4 6 8

— I I 25

50

75

100

125

150 S pH

175

200

D 225 (cm) 250

275

300

325

350

375

I I I I I

0 2 4 6 8 10 Wt% Sulphur

Figure4.10. Total sulphurand pH vs Depth for core CS 3.

153 and increases with depth (Fig. 4.6). About 600 m offshore at BDD 19A, sulphur is slightly higher

(mean 3.8) and pH is neutral to alkaline (7 to 7.6). Both are Group III, predominantlyRhizophora,

peat.

In the coastalmangrovefringe (Group III) peats, pH averages around 5.8 (s = 1.35; n =

237). The peat is consistentlylow in moisture contentand highlyhumified(Fine Hemicto Hemic).

Group II forest-swamp peats associated with drainage channels also are highly humifiedwoody peats,

but are lower in pH. Figure 4.10 shows pH and total sulphur for core CS 3, a site located 25 m from

the banks of Caflo Sucio (Black Creek) and 2 km upstream from the mouth. pH for peat in the core

averages 3.4. Sulphur contentvaries from 0.52 to 8.09 wt% with no relation to pH. The basal sand

25 cm below the contacthas a pH of 7.46 and a sulphur content of 3.19 wt%. From such cores it is

evident that highlyhumified,high sulphur peat can form in a low pH environment.

c) Forms of Sulphur

In order to comparethe sulphur distributionof Groups I, II, and III peats in the complex

coastal zone, the total sulphur content of a coastal mangrovepeat (site BI 3) and forest-swamp - back mangrove peat (the upper and lower parts of core BDD 23 respectively)is sub-dividedinto organic

(C-S or carbon-bonded 5, and ester sulphate), and inorganic forms (mineral sulphate, pyritic S and elemental S). The results of the analysis are summarizedin Tables 4.1 and 4.2.

I) BI 3: An Example of a Group III Peat.---The pH, total S, salinity and the distribution of forms of sulphur in a 2.5 m mangrove peat core taken at site BI 3, across Almirante Bay on the shore of Isla Colon are shown in Figure 4.11. The top of the core is above sea level, but the peat pore water becomes strongly saline with depth. There is a very close correspondencebetween increase in salinity of the peat and the sulphur content, most particularly in aqueous sulphate content, and also in ester sulphate. It is not clear why the pH decreases at the levelwhere salinity increases; dissitnilatory

154 TABLE4.1: SULPHUR FRACTIONSIN BI3 RHIZOPHORAPEAT No SPMPLESITE DEPTH TOTALSULPH %INORGANIC HI-S S04 PYRITIC ELEMENTAI %ORGANIC C-S ORGSO4

1 813-0-25 25 1.16 0.27 0.015 0.006 ad pH=6.42 0.22 0.013 0.004 0.014 mean 0.24 0.014 0.005 0.916 0225 means as % of Total 100% 2% 1.19% 0.04% nd 98% 79% 19.40% 2 813-50-75 75 2.28 1.53 0.555 0.02 0.106 pH=5.7 1.42 0.576 0.022 0.112 mean 1.48 0.563 0.021 0.109 0.802 0.785 means as % of Total 100% 30% 24.70% 0.93% 4.80% 70% 35% 34.40% 3 813-100-125 125 4.33 1.81 0.86 0.07 0.106 pH=5.63 1.66 0.778 0.013 0.261 mean 1.74 0.819 0.042 0.184 2.59 0.692 meansas% ofTotal 100% 24% 18.90% 0.10% 4.20% 76% 60% 16% 4 813-150-175 175 3.78 1.31 0.713 0.016 ad pH6.22 0.93 0.81 0.015 mean 1.12 0.762 0.015 2.66 0.371 means as % of Total 100% 20% 20.10% 0.40% nd 80% 70% 9.80%

Table 4.1. Forms of sulphur at four levelsin core BI 3.

TABLE42: SULPHUR FRACTiONS INODD23 FOREST PEATand BACK-MANGROVEPEAT No SAMPLESITE DEPTh TOTALSULPH %INORGANIC HI-S S04 PYRITIC ELEMENTAI %ORGANIC C-S ORGSO4

1 BDD23-5 175 0.38 0.0718 0.001 ad ad pH4.07 0.0572 0.0006 Campnospema mean 0.0645 0.0008 0.316 0.064 meansas%oftoIalS 100% 020% 0.20% ad ad 99.80% 83% 16.80% 2 BD023-8 250 0.78 0.1301 0.008 ad ad pH=4.38 0.1415 0.007 forest-swamp mean 0.1358 0.008 0.644 0.128 means as % of total S 100% 0.60% 0.60% nd ad 99.40% 83% 16.40% 3 8DD23-11 400 13.70 2.9685 0.93 0255 0.11 pH=4.96 3.1548 0.744 0.254 0.069 back-mangrove mean 3.0617 0.837 0.255 0.09 10.64 1.88 means as % of total S 100% 8.30% 6.10% 1.86% 0.70% 91.70% 78% 13.70% 4 BDD23-13 450 1.43 0.8647 0.367 0.026 0.015 pH5.94 0.9173 0.317 0.033 0.01 back-mangrove 0.018 mean 0.891 0.342 0.029 0.014 0.539 0.505 means as % of total S 100% 27% 23.90% 2.08% 1.00% 73% 38% 35% Note: HI-S is sulphur reducible by HI; C-S is carbon-bonded sulphur. n.d. = not determined

Table 4.2. Forms of sulphur at 4 levelsin core BDD 23

155 pH % of Total Sulphur 5.0 6.0 7.0 20 40 60 80 0 1:0 2:0 3:0 4:0 5.0Sulphur cm S Sal

+ 50 I.

+ H 100

+ 150 -h

+ 200 c_s sulphate + 1 elemental pyrite 250 + Formsof Sulphur datafrom Table4.1 ,)* Ô 0:4 1:2 1:6 Wt%Salinity

Figure 4.11. Summary of the geochemicalcharacteristicsof a coastal mangrove - back mangrovepeat core, taken just above the high tide line at site BI 3. Variationsin salinity,total sulphur,forms of sulphur and pH with depth are shown. The increase in the proportion of inorganicsulphatecorrespondswith an increase in salinity. Sulphurdata from Table 4.1.

156 the particularly exactly =05) than salinity intrusion. comparing prior Thus 24% fresh driven tide the (1985) content (1994) salinity result from buffers

sulphate

general

intrusion

level,

in

of

to 6.4 groundwater

there

of

of

subsidence

(ester (ester other

typical,

pore profiles in and the

subsidence, Casagrande There

total

recent

reduction,

to

but

particular

Offshore

the

has

trend

sulphur

5.4

aqueous

from

water

of mangrove

sulphate sulphate

sulphur

13

is

B13

been

seismic

marine in resembling

of

an

is

months

the

the

(See

five system,

pH

peats

to

the

in

added

cores

salinity

substantial and

is

sulphate

uppermost

upper

content: a

high

averaged averaged

(Giblin

higher

mangrove-peat

process waters Chapter

activity. peats

decrease

others

with

earlier,

are

complication

combined

sulphur neither

in

1

tested.

more than

is

intertidal

m.

is and

this 2.19

carried

modification 5;

(1977; reasonable,

19.9% 18.9%

sample,

not this

When

in

Phillips

Wieder the

normal

core

peats.

saline, salinity

at

apparent

site with

An

BI

onshore

cores,

on

of of

sampled,

mangrove

would 1986)

in

are

was

analysis 3,

total total

by

low

particularly analysing for

This

et

1992),

with

vs

however,

considered

of

al., 3 sulphate-reducing

50

here.

mangrove

permeability

have

found

nor

3.45

onshore S S

agrees the

depth

the cm

in in 1994).

157

but

peats

of

the

porewater

Fraser Panamanian

been

for

The

higher peat

shoreline

means

that

any

and

offshore

in

fairly near

and 34 to

shows

peat. opposite

Samples

the

lower.

surface

ester

buffering

other

be

other

delta

in

of

test the

2

onshore well

applicable

from>

elevation

geochemistry

the cores

Additionally,

a

sulphate

curves.

top.

bacteria,

aspects

(paired

peats).

mangrove

significant

peat),

Consequently,

at

occurs,

with

dense from

effect

core

from

cores,

Again,

500

the

and

farther

and

2-sample

of The

normally

woody

Those

to

B13

increases

the as

m

from

findings

the

mangrove-fringe peats.

with

difference

as

somewhat as

the

offshore,

relationship the

the

was

Changuinola

distribution,

hydraulic

a

onshore

studies

peat, the this

pore

total

Lowe BI

result

t-test;

comprises

10

alkalinity,

Figure

of

aqueous

3

activity

resists cm water

sulphur

core

Phillips

and

in

and farther

documented

of

show

n

head above between

means

earthquake- =

4.12

shows

is

deposit

Bustin

pH

marine 34)

or

sulphate

peats.

around

not

that

which

is

et

onshore.

in

from

plots drops

high

(cc

lower

al.

the

that

as

a Wt% Salinity 0 1 2 3 25

75 (offshore — core) BDD27 125

I BDD32 (offshore 175 :c::. core)

225

275 Depth (cm) 325

375

425 r)BDD 31 475

525 .I 565

Figure4.12: Wt%salinityvs Depth inS mangrovecores. 2 of the coresarenow offshoreandpermanentlysubmergedand 3 are in the intertidalmangrovefringeforest.

158 marine-margin peats which have not been overprintedwith a transgressive signature (see Chapter 5), and suggests that in this core both 34.4% (at 75 cm) and 9.8% (at 175 cm) are unusual values. This spatial variability in ester sulphate content likelyreflectsvariable responses to the recent transgression due to the heterogeneityof redox environmentsand bacterial populations within the peat. The specific causes and direction of, changes in this fraction are unclear and difficult to interpret. High ester sulphate, along withhigh(>4%) elementalsulphur content in the middleof core BI 3, suggest that sulphate-reducingbacteria may be activelyproducing 2SH stimulated by the influx of marine water. Lowester sulphate content can also be an effect of bacterial reduction of organic sulphates, but withthe very high aqueous sulphate concentrationin this sample (20.1%), bacteria are not expected to favour ester sulphates for reduction. Pyrite content is very low.

ii) BDD 23: An Example of Group land Group II Feats .---The sulphur profile of core BDD

23 recordsa change in the environmentof depositionat this site, from a back-mangrove forest nearthe base, to Raphia - sedge,andthen to Campnosperma - mixedforest in the upper 250 cm. The transition is reflected in the change from Group II at the base to Group I above. Group I is definedas low salinity, low sulphur, and Group II as low salinity,high sulphur peat. Table 4.2 and Figure 4.13 summarizethe results of the analysis of forms of sulphur at four levelsof core BDD 23. The samples are from depths of 175, 250, 400 and 450 cm. In all samples organic sulphur is dominant, comprising from 99.8% to 91.7% in the peat samples, and 73% of total sulphur in the sandy peat at 450 cm. The total sulphur curve shows the remarkable contrast betweenthe upper 250 cm and the lower 240 cm of peat in this core. The transition is evidentin the % moisture curve; the forest-swamp and sedge peals are wetter, less dense, and more acid (pH around 4.15 vs 5) than the back-mangrovepeat.

In the low-sulphur (Group I) samples from the upper part of the core the distribution of sulphur forms is consistent with peat from an onibrotrophicmire: there is a small amount of aqueous sulphate present, but the bulk is split betweencarbon bonded(C-S) sulphur (83% of total S) and organic (ester) sulphate (>16%). These values are similar to those recorded by Casagrande et al.

159 ______

pH Wt% Sulphur 60 510 710 % of Total Sulphur cm ‘ ‘ 20 40 60 80 (S %M

100

I 200k J I * + [ j I ...,.... 300 ...

+ IE . 400 Ii.lU. /.:

ll%sulphate C-S i.•fester sulphate elemental 600 ‘pyrite Forms of Sulphur • • , , data fromTable 4.2 70 75 80 85 90 95 % Moisture

Figure 4.13. Summaryof the geochemicalcharacteristicsof coreBDD 23, locatedabout 50 m fromCanalViejo,a tidal blackwatercreek whichdrainsthe easternpart of the depositinto AlmiranteBay. Shownarevariations in forms of sulphur,total sulphur,moisturecontentandpH withdepth. Moisturecontent is used as proxydata for peat density,as describedin Chapter2. Sulphurdata fromTable4.2.

160 (1977) for low sulphur peatsfrom the OkefenokeeSwamp. The source of this assimilatory sulphur is

predominantly the peat-formingvegetationitself, as discussed later. Variations in concentrationmay

reflect specific vegetation,or the degreeto which atmospheric sulphate is available for assimilation.

Periodic high water table and high surface runoff may lead to little sulphate enteringthe soil, whereas

drier conditions and‘morepermeablepeatmay increase available sulphur in the system. Atmospheric

sourcedsulphate is rapidlyassimilatedinto the organic sulphur pool, in a matter of hours or days

(Brown 1985) under anaerobic conditionsthroughthe mediumof dissimilatory sulphate-reducing

bacteria. However, the absence of detectableelementalsulphur andthe uniform proportions of ester

sulphate and C-S suggest very low levelsof bacterial sulphate reduction. The pH of these peats (mean of 4.15) is below normal tolerance for sulphate-reducingbacteria (Postgate 1984). Sources of 2+Fe in this elastic-sediment starved ombrotrophicenvironmentare limitedto plant materials and pyrite

fonnation is likely Fe as well as pH-limited. Thus the sulphur content of peat at the upper levelshas

not been influenced by sulphate-richwater present in the nearby tidal creek or groundwater.

The lower levelsin core BDD 23 have high total sulphur content, particularly at the 400 cm

level (13.7 wt% S), which is 90 cm above the base of the peat. Aqueous sulphate has been in ample

supply, although it is presently in much lower concentration(6.1% of total) than it is in the basal

sandy peat (23.9%), or in the newly-floodedpeats of BI 3 (24.7%). Aqueous sulphate is present in the

same proportion as in BI 3 mangrovepeat that is not affected by secondary enrichment(i.e. normalfor a marine-margin peat). Proportionally,the sulphur distribution most resembles that of the uppermost sample at B! 3, and others whichhave not been overprinted, although here the ester sulphate fraction is somewhat lower than in those samples. This may reflect a difference between mangrove fringe vegetation (BI 3) and this mixed-mangrovevegetation. The higher aqueous sulphate content of the basal sandy peat may be due to lower levelsof sulphate reduction, or to its greater permeabilityand proximity to the underlyingrootedsand, and brackish waters of the creek, but salinity is below .01 wt%. Pyrite represents 2% of total S in the basal sediments, 1.9% at 400 cm., andwas not detected in the top 2.5 m. This low pyrite content differs from the BDT 3 site analysed by Cohen et al. (1990)

161 in which pyrite was interpretedto be the dominantsulphur form, basedon SEM and petrographic

analysis. That sample is mangrovepeat with 14.9wt% total sulphur. Rhizophora root peat frequently

has high pyrite content (Cohen et al. 1984;Altschuleret al. 1983). However, at pH 4.9, the mixed-

mangrove peat in this sample is somewhatmore acidic than previously studied mangrove peats.

4.6 DISCUSSION

a) Sulphur, pH and Marine Influence

There is a clear relationshipbetweenmarine influenceand sulphur content in the Changuinola

peats. In the western section of the deposit the peat is consistentlylow in sulphur. Cohen et al (1990)

observed that sulphur content increasedto the northeast, in the direction of the barrier bar, and

suggested a possible marine influencefrom the CaribbeanSea. This study found no evidenceof

marineinfluence (beyond windblownsalineaerosols) in the peals developedbehindthe barrier.

Cohen et al. (1990) also found the lowest sulphur values associated with sedge-grass-fern peats

(0.1%-0.3%), and somewhat higher values for the forest-swamppeats, as is confirmed by this study.

Increase in sulphur coincideswith higher degreeof humificationtowards the margins of the deposit,

just as it does towards the base, where pahn-forest and swamp-forestpeats dominate. Sulphur in

these peats is principally assimilatory and highdegreesof humificationconcentrate resistant

compounds, including those that incorporate sulphur.

The variability evident in the easternpart of the cross-section (Figs. 4.1, 4.4) reflects the

profound effects, but limitedextent, of marineinfluence. In the upper half of core BDD 23 (Fig.

4.13), 50 m from a tidal channel and almost completelybelowsea level, sulphur, pH and salinity

trends resemble those of the ombrotrophic western samples (i.e. MILE 5, Fig. 4.8). Sites associated

with channels are lower in pH, and higher in sulphur content,although more variable than the strictly

marinesamples, and resemblethe lower part of BDD 23. Total sulphur and pH of coastal mangrove-

fringe sites at the shoreline resemblethose of BDD 20 (Fig. 4.6), andto some extent BI 3 (Fig. 4.11), particularly the uppermost part of that core. In the inter-tidalenvironmenttotal sulphur content tends

162 to increase in the upper metre or so, to 3% to 4% sulphur, and remain at those levels until near the

basal sediments,where it decreases. The relationshipbetween assimilatory sulphur concentrationand

degree of humificationthat is found in the low sulphur peats of the central part of the deposit is not

evident in the marine- and channel-marginpeats: the scale of variation in total sulphur is so great in

samples associated with drainagechannelsthat any relationshipto degree of humiflcationis

overshadowed.

The expected relationshipbetweenhigh sulphur content and near-neutral pH, based on the pH preferances of the sulphur-reducing bacteria, is not evident in the brackish peats. Channel margin peats have pH around5 and yet high sulphur content (5 - 14 wt%, 92% of which is organically bound). This highreducedorganic sulphur content is a most interestingaspect of these channel- marginpeats. Carbon-bondedsulphur compoundsin peat and soil are not well understood, but includethiols, organic sulphidesand disulphides,and sulphur-containinghurnic and fulvicacids which could be diageneticproducts of reactions under reducing conditions between lignin-typematerials and inorganic reducedsulphur (SH-, )2Sf (Luther and Church 1992). Given anoxic conditions, microenvironmentsof tolerable pH, an ongoingsupply of mineral sulphate, and sufficientorganic matter, these very high concentrationsimply an enduring biogeochernicalchain of sulphur reactions, with carbon-bondedforms as the end result.

b) Sulphurand Vegetation

High degreesof humificationare associated withwoodyforest-swamp peats and lesser degrees with bog-plain peats. This is in part a reflectionof environmentalconditions,and secondarily a consequenceof the floral responseto these conditions. Preservation is best and humification lowest in the topographically high central region. Here, the floral communityof sparse sawgrasses, stunted arborescent species, shrubs, mosses and algae reflects the oligotrophic state of the mire. Competition for available nutrients contributes to the highdegreeof preservation: for example. Sphagnumspp. adapted to highly stressed environments,have the capacity to lower the pH of the growing

163 environment,reducingits viabilityfor lessadaptabletaxa, andthus reducingspeciesdiversity. Low

pH, combinedwith a largeproportionof the biomassof the stuntedvegetationbeingin the formof

roots and rootlets,meansthat biomassproductionis lowbut preservationis high. The fibricand coarse hemicpeats whichare formedin this environmentare of relativelylow bulk density,highmois ture content,and do not concentratesulphurto highlevels. ObservedS levelsfor coarsehemic sawgrasspeats are around0.10to 0.25 wt% sulphur.

Woodyforestpeats formin environmentsdominatedby a luxuriantarborescentvegetation, muchof the biomassof whichis abovethe peat surface. Intensedegradationabove andjust belowthe surface results in a highproportionof fine-to clay-sizeparticlesinthe upper levelof the peat. To thesemay be addedmoreresistantlignin-richelementsof wood,bark and cuticle,resins,sporesand pollen,ingrownroots, and a significantchitinouscomponentfrominsects. Table 4.3 liststhe total sulpur contentof a numberof freshplantparts fromthis and otherstudies. The finehemicand hemic peat thus formedis denseand compact,with relativelylowmoisturecontentand high bulkdensityand sulphur content. The mosthighlydegradedforest-swamppeats (LAKE2, Figure4.9, for example) contain0.25 to 0.5 wt%.sulphur

Halophytesof the marinemangrovefringeforestand back-mangroveassociationcolonizethe marginof AlmiranteBayand forma distinctivefine,densehemicpeat composedprimarilyof rootlets and root tissues. (FloridaRhizophora peat has beencharacterisedby Cohen(1968) as root peat and sedimentarypeat, the latter distinguishedby containingmorethan 5% non-rootmaterial.) Dominant plants in this narrow fringeforestare Rhizophora mangle, Acrosticum aureum, Raphia taedigera, and salt-tolerantsedgesandgrasses. Sulphurcontentof 36 Rhizophora peat samplesfrom shoreline and now-submergedoffshoresitesaveraged3.52 wt% (s = 1.1,rangefrom 1.07to 5.98).

Behindthe mangrovefringe,any of severalsub-classesof mixedforest-swamp,monospecific

Campnosperma panamensis (hardwood)or Raphia taedigera (palm)forest occur. The woody peats

164 TABLE 4.3 A: Total sulphur content of some plant parts from this study:

Forest-swamp wt% sulphur Campnosperma panamensis wood/bark 0.093 Heliconia latispatha leaf 0.48 Symphonia globulfera resin 0.39 Bog plain Myrica mexicana wood/bark 0.045 Mangrove association Rhizophora mangle root 2.1 Acrosti chum aureum base 0.15 Raphia taedigera base 1.33

TABLE 4.3 B: Some published total S content of plants: wt% sulphur source Rhizophoram. leaf 0.18 a Rhizophora m. root 0.23 a Laguncularia r. leaf 0.25 a Laguncularia r. root 0.06 a plants (Little Shark River) 1.83 b plants (Minnie’s Lake) 0.078 b surface litter (“) 0.028 b plants (Chesser Prairie) 0.24 b surface litter (“) 0.093 b Mariscusjamaicense leaves 0.058 c basal calm 0.049 c rootstock 0.166 c fine rootlets 0.072 c

Source: a = Price and Casagrande, 1991 b= Casagrandeetal., 1976 c = Altschuler et al., 1983

165 Acrostichum,

temperate prominent peats or this the clastic comparable and Mean in climate was two associated compared was wt%) at 3.6%; 8

temperate

the the

on

subsidence

breadth

different

18.9% measurable found

the

respectively.

onshore range,

range total

elemental

sediment

determines

A

distribution

to

climes

comparison

in

to with

in sulphur

to brackish

of of

even

94.2%

the

coastal

be

the

etc)

Changuinola

those

possibilities event, shoreline.

these

starved only

80

sulphur

tropical

at

temperate.

though

is

vegetation,

Thus for

m

the

for

found

currently

fringe

about

sedge of forest-swamps

saline

onshore,

of

12 present

the

sulphur environment.

peat.

1.6%

pyrite

peats in

A

tropical

in

Fraser of

sites peats.

peats

175 intrusion many

new

The

temperate

marine

establishing

and

vs

time, and

in

is

cm

fractions

which

community

unaffected

this inorganic c)

1.1%;

Mean cases lower

peats,

samples

extensive

is

(Chapter

Sulphur

are

climate

into

influence

reflected

study

Mineral

experienced

brackish they

in and organic

consistently

and

the in

the itself

is

fractions

with

coastal

pyritic

by woody of is

extend

organic and

5),

peat

3.02

tropical

sulphate not in

in

recent

halophytic

across

sulphur

while

peats temperate

the

Climatic 166 very

shoreward

&

a

coseismic

sulphur

forest-swamp peats. to

strong

0.9 in

vary dying-off sulphate

marine

at within

peat,

similar

of

the the

and

wt%, content

a

the

slightly

Influence second subsided upper

The peat-forming

high

influence

0.6%

probably elemental

Fraser of

15

subsidence

inundation

represents

environments.

compared

of

proportions

the

for sulphur

rn

end

all

vs

peats

more:

site

of

high

the

marine

Delta

non

1.2%,

on

of

the

limited

sulphur

(BDD

tropical

do

the

total

tide mineral

peats

species

to

19.9% salt-tolerant (i.e.

and

shoreline.

(Lowe

not

for

a

margin.

of low-sulphur

line

35)

mean by

marine

sulphur Thirteen

primary

sulphur are suggests

seem tropical

peats

in

Fe (Rhizophora,

sulphate

at

heightened

and

slightly

the

of

availability

one

to Detailed

inundation

Bustin, concentrations

species

tested

3.03

tropical

sulphur)

months

fractions

be

and

that

site

(0.25

4.7%

forming

more

±

temperate

(B!

although

is

salinity

1.58

study

across

1985).

to after

peats,

94%,

are

in

vs

3)

found hint

1.0

this

for

in

of uplift. of peats part decimetre peats very or sulphur effectively the sediments vegetation April development along high erosion

regional in Caribbean in

the the the

topographic

northwest

of

high

sedimentation

are

reflects

this

high 1991

sulphur Changuinola

the

of

content

Tectonically-driven

structural

found

sulphur

or

are

emergent

carbonates

by

parallel Changuinola

tide coast

event,

more

of

this

thus halophytic

of

distribution

lows

level.

extensive

in has

this

of

geometry:

peats have

forest

above

recording

to movements

rates

area, southern

accumulated

coastline.

(old

study

the

and

Farther

a

are

peat

have swamp

mangrove-fringe

and drainage) sea

long overall

low-lying

redeposition

in

area,

exclusively

regional

Central

the level, regional medium-sulphur

deposit.

the

west, moved

recorded

However,

have

zones,

in peat.

trend

due

tectonic

d)

and

now

Costa

freshwater

very

created

Sulphur

America

sea-level

the

to

vertical

In

of

Since of

in

including associated history

below

rising

this

shoreline low

90

the

Rica,

the offshore

forest, setting

both

km

coastline. the

regime,

S entire and

trends.

has

peats

sea

fluctuations

sea

swamps, of

peats

coastal

to

late

localized

and within

of

167 causing

been Tectonic

level

with

level; bar the seaward

centre

now the

Holocene

are

transgression

eventual

Peat

east

sediments.

uplift

in

present

in

The

Changuinola

metres

localised

high-end

underlie

found

an

a

subsidence.

of

regressive

are with in

Influence

(Collins

region

distribution

overall

the

has

Panama,

drowning,

the

stabilization

tidally

of

in

both

western

exposed

Almirante

low replacement

developing

the

ultimate

There

which

is

et

regressive

very

deposit

and

from

mangrove

sulphur

influenced

a!.,

seismic

This

of

are

part

as

transgressive is

1994).

high nearshore

SE

medium control

experiencing

of

observed has

Bay

no

is

bog-plains

of

global (0.5 of

to

events,

and mode,

in

major

resulted

fringe

the

at

drainage NW forest

At

some

on

to

very all

and

deposit.

reefs

the

sea

in

and

peat

1.0

in

coastal

including

Sites

and

coastlines.

ways

swamp

high

the

same low

elevated in the

overall

level,

wt%

and

uplift

channels,

deposition

the

centimetres

sampled;

eastern

deposit,

primary

sulphur

Organic

reflected

swamps

time

caused

S)

the

and

the

a

To 4.7 IMPLICATIONS FOR ENVIRONMENTAL STUDIES OF COAL

As has long been knownto coal geologists,mediumto high total sulphur content in peat is spatially related to marine or brackish influence(Williamsand Keith 1963). This studyconfirmsthe relation. In addition,despitethe short-termnatureof theseobservationscomparedto coal studies,the distribution of sulphur in the Changuinolapeat deposit provides some new insights into sulphur in coal and its usefulness as an environmentalindicator.

As withthe peat in this study, it may be possibleto distinguish betweenprimary syndepositional sulphur, secondaryor overprintedsulphur due to transgression, and sulphur associatedwith channelsand brackish environmentsin coal, based on proportions of forms of sulphur present. Diagenetic changesto organic and inorganiccomponentsduringcoalification inevitably smear depositional chemical signatures. However,clarification of the origins and proportions of labile and conservative S forms associated withparticular conditionsprovides the startingpoint for environmental interpretation. For example, high stable C-S sulphur content in high sulphur coals is likely an indication of estuarine environments,or brackish drainage associated withchannels, in which primary C-S tends to be high. Channels in peat tend to be long-livedand highly resistant to erosion, and restriction of brackish influencecan be due to low permeability of the peat, domingof the peat surface, or hydraulic pressure from the high water table. Thus high C-S sulphur coals may be laterally restricted, and adjacent coals a few metres away may be low in prry sulphur, even though diagenetically enriched in pyrite.

Coals which originated as distinctly marine peats (i.e. from halophytes) are likelyto have significant pyrite, both primary and diagenetic, but organic forms still dominate the primary component. The above characteristics can developin both transgrcssivc and regressivedepositional regimes. The marine mangrovepeat in this study has moderatetotal sulphur content (2 to 5 wt%),

168 the directly pockets proportion biomass pH woody peats, sulphur material of flooding experienced little increases forms sulphate. low. sulphate includes diagenetic principally %

raised

of

highly

of

direct

total

In

the

there

(Phillips

peat

with may of

In coals

Coals

highly (forest-swamp is of

fraction,

bog-plain

in

precursor

However,

variable

pyrite sulphur.

secondary

oligotrophic

less of

relation

in coastal

is

(Raphia, total

marine

be the

mobile

organic

in

no

with

et significant

variable

concentrated

which

degree

resulting

significant sulphur

a!.,

over

penneability peats

environments.

to

a

transgression

peat.

such

sulphur

distinct pyrite

ampnosperrna,

1994; forms

pH.

cm-scale

no

settings

peats) of

ester

by

content.

coals

marine

from In

than humification

Peat-forming

formation

Chapter sulphate-rich

difference but

Changuinola

at transgressive

forms

sulphate

produce

the

are

with the

levels

of

with

distances,

and influence

Beyond

Tectonically

peat.

degree

not

influx

relative

no

5).

a

are

double

in

content

mixed).

between necessarily a

significant

of

groundwater

The

coal. woody, plant

In

now

sea

of

of

the peats

is the

signature

is

the

to

secondary

humification

due

influx that

water.

evident,

peat,

stable and

broad submerged

communities

longer

the driven The

with

highly

to

169

of

inorganic

an high

total

which

of the

variable

more

are distinction

C-S

sulphate

Over no

increase

sulphur

term,

marine

coseismic

inorganic

heterogeneity

hurnifled in

marine

sulphur

likely

sulphur,

display

total

in in fibrous,

the

which

this

component.

turn

low-sulphur

sulphur

waters

sources,

content

short in

to

sulphur.

influence,

between

overprinting

content

the

subsidence

hemic

have

sulphur,

broadly

a

have but

root-dominated

transgressive

term

proportion

content

has

of

has

has

a

total

and

a

pore

large

of herbaceous

Coastal

Pyrite

the

peats. resulted

high

reflects

total and

been not

the

fine

sulphur

can

variability

of

would water

proportion

resulted

possibly

proportion

different

sulphur

related

varies

the of

hernic

lead In

peats

signature

peat

in

peat

inorganic

turn,

original environments

likely

content

a

peats

to

larger

from

type,

in

to peat that

(sedge

from

content

in long

types

degree

of

large

the

of

result

and the

which

have

plant

0.1 in

sulphur

of

but

subaerial

sulphur

term ester

inferred

of

ester

which

peats)

woody

peat

varies

to

of

bears

in

and

3.6

is

as humification is much more dependenton the heightof the water table than on the pH of the peat or porewater. Thus it is risky to infer high paleo-pH of a coal swamp on the basis of highly humified peat precursors alone. High levels of humificationoccur in very low pH sites if the water leveldrops, or if the plant communityhas a large subaerial biomass. The sulphur found in these low-sulphur peats is overwhelminglyorganic in form. Anypyrite in coal associated with peats from ombrotrophic bog environmentis likely post-depositional.

4.8 CONCLUSIONS

The followingobservations can be made regardingthe distribution of sulphur in the

Changuinola peat deposit:

High sulphur content is spatially related to marine or brackish influence.

The highestsulphur content (>5 wt%) is found in pêats proximal to the brackish influenceof blackwater drainage channels up to several km from the coast. Very high sulphur was also found in the basal peats in the deepest parts of the deposit, which are interpretedto have been associated with channels. Very high sulphur content is found even where salinity is undetectable in peat, porewater or basal sediments, and despite the low pH of the peat, which inhibits bacterial sulphate reduction.

High sulphur peat is not necessarilyhigh in pyrite, axidlarge quantities of sulphur may be bound in unreactiveorganic compounds from which it is unlikelyto be released biogenically.

Peat-forming plant communitieswhichhave a high proportion of subaerial biomass (ie. ombrotrophie forest-swamp peats) produce a woody,highly humifiedhemicand fine hemic peat in which sulphur may be concentrated at levelsdoublethat of more fibrous, root-dominatedpeat of raisedbog-plain environments.

In the absence of marine influence,total sulphur content varies directly with the degree of humification of the peat, which in turn broadly reflects peat t3pe. However, beyondthe broadest distinction, between herbaceous and woody peats. there is no significant differencebetween the total sulphur content of the different types of woody peat (Raphia. C’ainpnosperma. mixed forest-swamp).

170 the the water on humification ACKNOWLEDGEMENTS Thus 92-1201-18 oligotrophic for science

87337 Sanchez

the

their

manuscript.

Smithsonian

the

level

pH

(Bustin),

laboratory

Degree Supported

support:

and

variable

of

drops,

(Phillips),

mire

the

in Serracin

low-sulphur

of

the

Tropical

We peat

the

with

sulphur

or

humification

for

by

International

also

if

Instituto

or

of the

analyzing

no

and

the

porewater.

Boca

thank

groundwater

Research

Natural

content

plant

The

peats.

de

del

the

University

in

community

forms

Recursos

Development

of

Drago, Sciences peat

following

Institute,

High

the

of

sulphate

is

original

much

Panama. levels

S,

of

Hidraulicos

and

has

and

individuals British

and

Research

more

Engineering

sources, of

a

plant

Dr.

in 171

large

humification

particular

Columbia.

dependent

Lowe

material

y

subaerial

total

and

Centre

Electrificacion,

and

Research

organizations

sulphur

Ing.

is

on

Dr.

can

Young

We

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the

Eduardo

Bill occur

thank

significant

Council content

height

Canadian

Barnes

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in

L.E

in

However,

Reyes,

Chiriqui

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Lowe

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Canada Republic

Researcher

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Company,

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and Barofflo,

1984,

SiLc,

Coal-bearing

1992,

In:

Ecosystems

Keith,

p307-344.

Ivanov,

beds:

of

Geological

(decomposition)

v.57,

Dapples, T.,

Sulphur

Sedimentologists

Methods

J.R.

1977.

Economic

M.L.,

p.109-117.

M.V.,

and

Sequences.

and E.C.

concentration

Society

Comparisons

1963,

of

Trescott,

eds.

Associated

Geology,

and

measurement

with

1992.

Relationship

of

Hopkins.\l.E.,

Special

Am’ emphasis eds.R.A.

P.C.,

Sulphur

in

v.5X.

of

\1ater

the

four Publication

175

I

of

969,

p.720-729. special

Japanese

Rhamani

on

between

sulphur

Bodies. methods

Cycling

the

Conditions

1969.

von

Paper

(1984)

in

sulphur and

SCOPE

Paleogene

on

for

Post

soils: eds.,

the

R.M.

determination

114,

of

7,

method.

Continents;

Environments

in

48. in

deposition

p.36

Boulder,

Flores,

Howarth,

coals coal:

Wiley

1-372.

Canadian

In;

and

International

of

Colorado,

and

Wetlands,

of

Sedimentology

the R.W.,

degree

of

Pennsylvanian

Sons,

Coal

occurrence

Journal

Stewart,

of

1969.

of

of

of

1 EARTHQUAKE-INDUCED

MODERN

ANALOGUE

FLOODING

CHAPTER

OF

FOR

176

A

HIGH

TROPICAL

5

SULPHUR

COASTAL

COALS

PEAT

SWAMP:

A during following opportunity waters sulphur Salinity the increased

inundation: remains redistribution infiltration cannot

CHAPTER

organic

High

a

into

form

in and

seemingly

1991

peat

by

the

sulphur

the of

sulphate inorganic to

pH

by flooding,

5:

SWAMP:

marine of newly

earthquake,

evaluate formation.

peat

measurements short-term

sulphur

EARThQUAKE-INDUCED

content unaffected.

is

fraction flooded

or

forms,

restricted

but

the

A

brackish

forms.

When

that

sulphate-rich

MODERN

of

periodic role

peat

particularly

becomes

coal

the across

Heightened of

to

a

Our

waters vs

short-term

distribution is large

<

flooding

adjacent,

generally

2

results

the

highly ANALOGUE

m

seawater peat

measured

mineral

both 5.1

new

bacterial

events

indicate

deposit

variable; ABSTRACT marine

subaerial marine

vertically

attributed

of

FLOODING

sulphate, sulphur

inundated

177

on

such

activity on flooding FOR

that

margin

time

and

the peat

and

to as

high forms

HIGH

the

make

scales

marine

Caribbean

storms

the

OF

horizontally.

reveals

is

indicate

on

carbon-bonded

sulphur

seen

margin

differs

A

sulphur

up

SULPHUR

of

TROPICAL but inundation

as a

that

hundreds

that

higher

coast

must content

a

markedly

of

likely total

abundance

the

penetration

A

of reflect

proportion

comparison

COALS deposit,

sulphur sulphur during

to of

mediator

Panama

COASTAL

after

thousands

coals

long

and

or

providing of

content content

marine

and

subsided

shortly of

term

in

chemistry.

saline

of

the

this

peats

forms of

PEAT

is

total;

years.

the

not

of the depositional has, importance the phenols, related 885 brackish content states,

sulphate

earthquake-induced near clastic

peat, penetrating

concentration

principal

oxygen

ppm

however,

Changuinola,

It

newly

Part

leading

sediments

compounds,

is of

and

concentration.

and

in

a

peat

of

for

of

paradigm

seawater.

into

drowned

inundation

source

other

the marine-influenced

never

short-term

and

to

respiration,

is

the

Caribbean

the

(Fig. dependent

distribution

compounds.

Panama,

and

of large been subsidence,

formation

peat,

in

Sulphate

5.1).

S of

as

coal

inundation

tested.

found

back-barrier

peat

and

so-called and

coast

on

led

On geology

of

fix by

the of immediately

peat, to in

is

Reduced

and

April

Aqueous

a

of

polysuiphides

brackish

reduced peat.

some

50

availability

variety

by

thick ester

Panama

S that —

5.2

22,

swamp.

marine concentration

70

S,

Concentration

S

sulphates

high

peat

INTRODUCTION

sulphate

by of 1991

cm

as

or may

adjacent

is

carbon-bonded respiring

marine

S

of

of

beds waters

sulphur

undergoing

The

forms a

and

be

coseismic

178

aqueous

magnitude

subsequently

(SO42-)

(C-0S03)

are

effects

of

subaerial

waters can

on

are

elemental (S)

plants of

overlain

S

be

S

sulphate assessed

coals

marine

content

of

subsidence

is

in

high,

(e.g.

7.4

(C-S),

and

that

from

peat.

in rain,

by

result reoxidized

earthquake

or

polysaccharides,

Home

and S-reducing

rapid

transgression

of to

by

shallow-water

pyritic groundwater

in

By

peat living

is

comparing

a

and from

taking

flooding

variety

et

not

8

and,

al.,

resulted S.

ppm to

plants

syn-

(Camacho

limited

bacteria.

a

The

1978). advantage

by

of

variety

as

in

or on

and

long-submerged

carbonate

choline

amino and analogy,

primary

fresh a

in

post

by

the

result

the

marine

The

bacteria.

pore-water

et

of

Plants

water

oceans

acids

al.,

of

oxidation

sulphate,

of

S

coals

a

and

waters

1993)

use

and

and

is

In ______

Figure the transgression /

mangrove lime

/ /

sand

1991

sample

coral’

epicentre earthquake April1991

5.1.

mud

peat

sites

I , I

earthquake

&

Site

at

=0 N

site

of

the

BI

in

of

study

3 the :.:

as

Rio

a

on -

result

Estrella

the ______

Caribbean of

Earthquake-induced

earthquake-induced

valley, - - /,

pre-earthquake /

coast

Costa

sample

of

Rica.

Location ______

Pnma

179

subsidence.

The

5

of

km

sea

is

block

4%

shown,

transgression

sites

level

diagram ______

W08227

lower

deposit

peat

illustrates

BDD

left,

Pta.

in

29

relation 0

BDD

t_Bay

Pondsok

the %44%

extent

tAlm;rante 19A

to

the

W08220 ______

\

of

epicentre

marine

site

--i

N15

12m

of measurable mineral dominate formation ester following (Fig. except are On wt%). depth, blown of high substantial not

the

eight

described

elevated

near

sulphate 5.1).

Samples

Shallow

peat.

to

salt

adjacent

Salinity

sulphate,

samples,

the

the

the

analyses

of

and

At

spatial

subsidence

compared Significantly,

very

range

peat

peat-water

by

(oxidized

the

onshore

were

wave

onshore

to

Lowe

elemental

high

transect fonning

forms

the

variation

were

of

collected

5.3

washover.

3.0—4.5

high

sulphur

to samples

(1986)

event,

compounds SAMPLING

is

performed:

of

interface

onshore

total consistently site, vegetation,

tide

S

5,

(Fig.

across

were

this

wt%.

and and

coals

red

line, have

S

Below

a)

5.2).

in

values. study

(maximum

Tabatabai pyritic

determined: mangrove

reducible Total

the

where

a

pH,

Although

(>5% low

AND

both

sea

low

sea-level,

Sulphur

now attempts

total salinity

(+ Sulphur,

level

5.4 higher

at

(<0.08

EXPERIMENTAL

S),

marcasite)

inundated

(1992). (Rhizophora

2.1 the

by

S

total

RESULTS

transect particularly

organic

content (0.29—0.65

HI) and

180 to

surface

wt%),

S

salinity

wt%)

Salinity

values

provide

S

forms, total

increases

and

and

S S

and of

and

and

(0.94

(Table in

S

both

mangle) the

much

the

and

insight wt%),

from

and

on

decreases

both

spatially

throughout

basal

role

all

onshore

steadily

PROCEDURES

wt%)

pH

inorganic

5.2).

three more

carbon-bonded

samples

and

into

of and

carbonate

reflects

variable.

short-term

irregularly

low

The submerged

saline

the

with

and

sawgrass

the

forms

salinity processes (Fig.

analytical

offshore

peat

depth,

part

the

sands

Offthore,

5.1,

expressed

suiphide

extent marine

cores.

down

(Rhyncospora

of

offshore

(0.02—0.05

there

the

is increase

Table

that

methods

low

to

of

transect

The

flooding.

is

lead

(C—S)

salinity

the

wind

as

sites also

5.1).

(0.4

with

base

to

wt%) used

sp.)

and

is

the

is TABLE 51. TOTAL SULPHUR, SALINITY AND pH OF 46 PEAT SAMPLES Site Depth pH Salinity Total S (cm) (wt%) (wt%) Samples from transect BIT3-1 10 6.14 0.02 0.52 BIT3-2 42 5.90 0.06 3.59 BIT3-3 10 6.36 0.04 0.47 BIT3-4 45 5.80 0.04 2.68 BIT3-5 10 6.30 0.03 0.29 BIT3-6 36 5.71 0.08 3.79 BIT3-7 10 6.39 0.02 0.52 BIT3-8 53 6.44 0.04 1.75 BIT3-9 10 6.54 0.02 0.63 BIT3-10 39 6.25 0.03 1.34 BIT3-11 45 5.99 0.03 1.70 BIT3-12 90 5.65 0.04 3.75 BIT3-13 10 6.35 0.02 0.61 BIT3-14 53 6.30 0.03 3.35 BIT3-15 10 6.20 0.03 0.54 BIT3-16 33 5.50 0.06 3.50 BIT3-17 10 6.45 0.05 0.52 BIT3-18 32 6.35 0.06 3.75 BIT3-19 10 6.41 0.03 0.65 BIT3-20 39 6.57 0.06 4.00 BIT3-21 10 6.09 0.94 0.53 BIT3-22 53 5.79 0.17 3.69 BIT3-23 10 6.42 0.04 1.16 BIT3-24 25 6.25 0.08 1.56 BIT3-25 50 5.70 1.70 2.28 BIT3-26 75 5.40 1.70 4.22 BIT3-27 100 5.63 1.50 4.33 BIT3-28 125 5.66 0.98 3.26 BIT3-29 150 6.22 1.10 3.78 BIT3-30 195 6.87 1.20 1.24 BIT3-31 200 6.92 1.30 1.98 BIT3-32 70 6.90 2.10 1.98 BIT3-33 80 6.79 2.00 3.08 BIT3-34 113 6.59 1.80 3.78 Submerged samples from offshore cores BDD 19A 350 7.48 2.20 4.01 BDD 19A 425 7.57 2.50 3.02 BDD 19A 475 7.06 2.10 3.21 BDD 19A 510 7.07 1.70 5.08 BDD29 25 5.58 2.10 1.94 BDD 29 50 5.60 1.70 2.22 BDD 29 75 5.19 1.40 2.08 BDD29 100 5.21 1.30 4.17 BDD29 425 6.60 1.30 3.19 BDD 29 450 6.49 1.50 3.93 PTA POND 575 3.57 1.40 3.53 PTA POND 600 2.89 1.30 3.03

Table 5.1. Total sulphur data, BI 3 and offshore sites.

181 TABLE5.2. SULPHUR FRACTIONS IN EIGHT PEAT SAMPLES No. Sample Site Depth Total Inorganic HI-S ESS Pyritic Elemental Organic C-S Organic (cm) Sulphur Sulphur (wt%) (wt%) Sulphur Sulphur Sulphur Suiphu Sulphate (wt%) (%) (wt%) (wt%) (%) (wt%) (wt%)

1 BIT3-23 10 1.16 2 0.24 0.014 0.005 n.d. 98 0.916 0.225 % of total 100% 1.19% 0.04% 79% 19.4% 2 BIT3-25 50 2.28 30 1.48 0.563 0.021 0.109 70 0.802 0.785 % of total 100% 24.7% 0.93% 4.8% 35% 34.4% 3 BIT3-27 100 4.33 24 1.74 0.819 0.042 0.184 76 2.59 0.692 % of total 100% 18.9% 0.1% 4.2% 60% 16% 4 BIT3-29 150 3.78 20 1.12 0.762 0.015 nd. 80 2.66 0.371 % of total 100% 20.1% 0.4% 70% 9.8% 5 BIT3-9 10 0.63 7 0.17 0.041 0.004 n.d. 93 0.461 0.123 % of total 100% 6.6% 0.9% 73% 19.5% 6 BIT3-12 90 3.75 9 1.12 0.237 0.037 0.061 91 2.63 0.788 % of total 100% 6.3% 1% 1.6% 70% 21% 7 BIT3-32a 55 1.98 32 1.44 0.319 0.072 0.233 68 0.543 0.812 % of total 100% 16.1% 3.6% 11.8% 27% 41% 8 BIT3-33a 85 3.78 37 1.65 1.109 0.072 0.208 63 2.126 0.264 % of total 100% 29.4% 1.9% 5.5% 56% 7% Note: HI-S is sulphur reducible by HI; ESS is easily soluble mineral sulphate; C-S is carbon bonded sulphur. n.d. = not determined

182 Total S was also determinedfor 12peat samples collectedfrom three sites that have been submerged for much longerperiods. One sample (BDD19A)from 475 cm below present sea-level, radiocarbon dated at 2110 ± 60 yr., has a total S of 3.21 wt% (salinity of 2.0 wt%). It is overlam by

265 cm of peat, 15 cm of carbonate sediments,and 195cm of salt water. Total S for all the long- submerged peats averages 3.2 ± 1.04wt% (Table 5.1).

b) Forms of Sulphur

1)Organic Forms --- Organic forms predominatein all samples (Table 5.2) ranging from 63 — 98% of total S. All onshore samples have> 90% organicS, whereas offshore samples have < 80% organic S. The two samples withthe lowest proportion of organicS (samples 7 and 8) are submerged, and thus not surprisingly have the highestpore-water salinity and pH of all samples tested. Onshore, ester sulphate is uniformat 19 — 21% of total S. C-S ranges from 73 — 79%. In contrast, offshore ester sulphate varies widely, from 7% to 41% of total 5, and generally decreases with depth. C-S varies from 27 — 70% of total S offshore,and increases with depth.

ii) Inorganic Forms - In all samples, mineral sulphate is the dominant inorganic form. Onshore, mineral sulphate comprises 1.2 — 6.6% of total S. ElementalS was only detectable in one sample, at

1.6%. Pyritic S represents 0.04 — 1%of total S. Offshore,mineral sulphate is found in much higher proportions, varying from 16.1 — 29.4% of total S. ElementalS constitutes 4.2— 11.8% of total S, and pyritic S 0.1 — 3.6%. The presence of 2SH could be detectedby a faint smell in all samples but was not measured.

183 ______

OFFSHORE SUITE ONSHORESUITE

PRESENT SEALEVEL

- 20% 0.03 0.08 3.0% ...... •.. PREEARTHQUAKE*/L SA LEVEL 10T[17

U20’ SULPHUR 1m : 8 : smwr .:• . . :728 Sample no.341fromTable2 56 influenced .::jhflHHTiflfl estersuIphate byinundafion 4:: entoIS Forms of Sulphur for 8 Samples

2m 5m

Figure 5.2. Spatial variation in total sulphur and salinity of peat acrossthenewly-submergedmarine margin. Sample sites in boxes are also shownin Figure 5.1. Inset columns I - 8 depictvariationin sulphur fractionsfor the eight numberedsamples, based on data in Table5.2. The columnsare arranged from left to right in increasing distancefromthe peatfsaltwater interface,illustratingthe effectsof inundationon the relativeproportionsof C-S and ester sulphate,and the increase in aqueous sulphate. Iso-sulphurcuves (dotted lines) of 1,2 and 3%S reveal the spatial variability of these geochemicalsignatures:the depressedregion is aroundthe remainsof a 1cm diametermangrove root, whichprovidesa conduitforrainwater. Verticalexaggerationis xlO.

184 matter attributable down-seam. that decrease month formed constant as Much Bustin (Given results necessary result Florida is show found laboratory

still

the

metabolic

The the

Sulphur

of

water in higher

not

exposure

with

et

in

and

in

Everglades

secondaiy samples with

in

trend

a!.,

S

a primary

reducing

clear,

study

Miller, S

enrichment

marine-influenced

burial, to

passes

Such

S

1987) content

increasing

concentration

ongoing

S042

observed

content,

to

however,

this

collected

a

S

marine

leading

1985;

(Casagrande environment enrichment

downward

tends

distribution

content

took

with

uptake

assimilatory

near

on

depth, in

Cohen to

what

only

depth waters

near the to

coals.

increase the

in

of

from

concentration

environment

order

(Brown

marine-roofed

following

a

the

as

environmental

the

peat

(Eh

et

et is

has

few

of

it Rather,

water

considered

a!., al., peat

site

bacterial

does

peats

of -

been

surface

with

days.

and

100 1989). 1977),

10

of

in

5.5

inundating

marine

in

used depth

total

this of

wt%, this

Macqueen,

my.)

by

of

this

Once

due

DISCUSSION

this

reduction,

coal

and to

resistant

conditions study the

Higher

study

to

S

in study.

was

has

inundation, reflect to

185

study.

in

suggest

reducing

progradation

levels is

the

stimulation

marine-influenced

a

been

(Cohen

commonly is

recorded

peat

upper S

moderately 1984).

compounds

the

and

concentration

as

Brown

lead

established that

surface

conditions

progressive high

increased

et

it few

to

in

marine

clearly

Most

al.,

of

of

highest

and

as

high-ash,

such

cm,

anaerobic

a

high

may

1989;

13.7 in

mangrove

Macqueen

high-S

then

near

or

were high the

requires

decomposition

toward

peats

bacterial

at

but

be

wt%

brackish

Phillips

older,

the

remains

the

brackish

delayed

S

established,

typical

peats,

sulphate

(Altschuler

content.

top (92%

the peat

more

fringed

(1985)

more

depletion

et

and

base

water

however,

relatively

surface.

until

of

peats organic

al.,

time

of

reduction.

degraded decreases

peats

If

shoreline

determined

of

molecular

in

inundation organic

the

et

it

than

the

from

press).

of

is

al.,

having

)

do

In

the

peat

was

S042

the

their

1983;

the

not

peat.

The

is

It

13 the not maintains greater together cores mineral allowed of substantial content diffusion diffusion process limited dependent present roots S

content

submergence

sudden decrease

of

The

Pore

(Table

to

depths

to

of

sulphate or

the

mangroves.

with

rate driven

of

presence a

a

the

on

from

water

flooding

sulphate-reducing

introduction high

2

greater

the

consistently

5.1)

variations

sulphate

of

m.

offshore

in

the and inundated

by

water

in the

salinity H2S04

suggest

Such

biologically of the

extent

of subsequent

Pyrite, no

newly

a

the concentration

samples, table onshore

restricted

indications

significant

in

of

and

with

in

minimal

peat

in vs.

permeability

aqueous

inundated

linked

dilute

and

samples

pH

bacterial

onshore

depth,

with

oxidation samples

mediated

(average

positive

distribution

marine

aqueous to

percolation

of

amount

sulphate seawater.

of

bacterial either

total peat.

7

samples

activity.

the

and

of

is

infiltration

concentration hydraulic

21% of

the

low

enrichment

inundating solutions.

of proportionately

8, Salinity

dissimilatory

into

indicate

elemental

peat.

activity

of

where

of

In (1.19%

that

Elemental

186 seawater

total

the

fact,

head

any

may

and

The

elemental

peat.

that

In

waters,

in beyond

5),

iso-S

to

gradients

measurable

S

the

in

higher

mangrove

be

S

6.6%

hydrogen

the

in

suggests

down

values S the or

However,

due

present

contours

offshore

may

lateral

in

was

that

groundwater

S

of

salinity,

to

through

absolute

proceeded

concentrations

result total

from

generally

the

expected

that

peats

sulphide,

increase

study

extent

samples

mineral

(Fig.

ever-wet

S).

the

inundation

and

directly

the

(Cohen

terms.

it

5.2)

of long-submerged

at

system for

is

comparable

peat

high

occurred

for

sulphate

marine

may

a

not

climate,

mangrove

are

rate

and

from

example

The

et

during

mineral

evident

has

indicate

al.,

year-round,

depressed

pH

that,

proportion infiltration

the

as

content

indeed

1984)

which

the (6.9

to

a

reduction

sulphate

although

around

peat. from

result

the

offshore

period

and

is

to

does

total

also

of

is

of the elemental that organic peatification, ester fraction fraction. ester al., coals, magnitude In 20% bacterial in reasonable sulphate Stewart, 6.59) sulphate reduction

the

sample

ester

1977;

samples

of

sulphate

sulphate

Onshore,

are

ester

and

total

matter

represents

sulphate reducing by

1992); reduction,

The highest.

is

S,

Bustin

7,

as

of

proportion

sulphate

bacteria

expected.

recombining

ester

a 5,

appears

that as

two are

fraction

few

has

the

comparable

thus

it

et

fraction much

flux. bacteria sulphate

samples is

All

organic only been

centimetres

al.,

but

fraction,

(Altschuler

in

changes

to

of of

may

Like

low

1987). in

more

7%

Depletion

found

be

these

ester

with

this may

now

closest is S

the

occur

S

to

of

anaerobic

fraction

the

and

in peats. variable

sulphate

values case to the

humic factors

norm

apart

be

Both

exists

the

et

dominant

be

the

as

caused

total,

of

to

al,

aqueous

environment

more

the

the

Thus, for

can

the the

results

compounds reported is

in

indicate

1983). in

bacterial

in

dominated

and

result

marine the

organic

marine

ester the

undergo

by

high-S conservative

form

it

offshore

SO42 75

offshore

reported

bacterial

Thus, is

sulphate

of

for

that

possible cm

activity, peats.

influence

(41%).

S

are

187

peats bacterially

in

variable

other

content,

by

a

below

is no

the

more

more peat.

than

here

in

digestion C-S

decrease

than unaffected

Onshore fraction

peat marine

to

ample

increases

However,

that,

display

likely

may onshore

secondary

favorable forms

speculate

and

the

reduced

(Casagrande

9.8%.

supply give

and the

may

ester

of

as

ester

to

similar

very

by

in organic

a

be samples.

a relative

brackish

some

also

result

environment

elemental inorganic few

on sulphate

effects.

secondary

sulphate

reflected

Assuming

and

high

a

to

be

cm

et bacterially

indication

matter

is of

proportions

those

ester

affected

al.,

peats

lower The

preferred

direct

Enrichment

fraction

is

S,

S

in

enrichment,

1977).

consistently

20%

and found sulphate

C-S

the and in

for

(Casagrande

in

bacterial

the

of

directly

mediated

pyrite ester heterotrophic

the

increased

pool

to

(Howarth

over

the

of

in

form

Depletion

be

core,

of

high-S

C-S content.

sulphate

potential

in

are

a

organic

it

the

by

around of

seems

to

flux that

pH

et

and

of and Eh dependent,and thus not inconsistentwithvariableestersulphatecontent. In this study, the highestpyritic and elementalS contentsare foundin the samplewiththe highestester sulphate,the lowestC-S fraction,and the highestpH. Microenvironmentsof varyingoxidation-reduction potentialassociatedwith rootpenetration,or otherpermeabilityfactors,may result in variable bacterialactivityand may be a factor in the largevariationsin estersulphate.

5.6 CONCLUSIONS

In the studyarea on the Caribbeancoast of westernPanama,tectonicallydrivensubsidenceis leadingto inundationof a thickpeat depositand burialbeneathmarinesediments. No evidenceof enhancementof total S concentrationin peats inundatedby normalmarinewater is evident. Spatial distributionof S fractionsand of elevatedpore-watersalinitysuggests—175cm of penetrationof marinewaters both horizontallyand verticallyin the 13monthsthat elapsedsince inundation.

Sulphurconcentrationincreaseswithdepthin the upper 175cm, up to a leveltypical of, but no higherthan, other mangrovepeats sampledinthis area.

The distributionof S formsdiffersmarkedlybetweenonshoresamplesunaffectedby inundationand thosenowunderwater. Inorganic S formsrepresenta much largerproportionof total

S in offshorepeat. A higherproportionof mineralsulphateis foundin the offshoresamples.

Significantquantitiesof elementalS are presentin all but the deepestof the offshoresamples, whereasit is undetectablein the onshoresamples. PyriticS is presentin all samplesbut is only>1% of total S in oneof the offshoresamples. Pyriteis not a dominantS form,and is not seento be formingat the expenseof ester sulphate.

188 The short-term effects of marine inundationare to increase the relative proportion of inorganic

over organic S in peat andto introduceconsiderablevariability in the ester sulphate content. Thus the proportion of ester sulphate may be the best indicator of the geochemical histoty of a peat deposit. The geologicalimplicationsremainto be determinedby detailed analyses of forms of S in marine-roofed coals.

By analogy withpeats of this study, the high sulphur content of coals cannot reflect short-term or periodic stormfloodingevents but must reflectprolonged infiltration, probably measured on time scales of hundreds to thousands of years.

ACKNOWLEDGEMENTS Supported by the Natural Sciencesand EngineeringResearch Council of Canada grant 5- 87337, the InternationalDevelopmentResearch CentreYoung Canadian Researcher award 92-1201- 18, and The Universityof British Columbia.

189 5.7 REFERENCES CITED

Altschuler, Z. S., Schnepfe,M. M., Silber, C. C. and Simon, F. 0., 1983, Sulphur diagenesis in Everglades peat and originof pyrite on coal: Science,v. 221, P. 221-227.

Brown, K. A. and Macqueen, J.F., 1985, Sulphate uptake from surface water by peat: Soil Biology and Biochemistry, v. 17, p. 411-420.

Bustin, R. M., Styan, W. S. and Lowe, L. E., 1987, Variability of sulphur and ash in humid- temperate peats of the Fraser River delta, British Columbia: Compte Rendu, 10th International Congress of Carboniferous Stratigraphy and Geology, Madrid, Spain; v. 3, p. 79- 94.

Camacho, E., Viquez, V. and Espinosa, A., 1993,Ground deformation and liquefaction distribution in the Panama Caribbean coastal region: Universityof Panama,Panama City in press).

Casagrande, D. J., Seiffert, K., Berschinski,C. and Sutton, N., 1977, Sulphur in peat forming systems of the OkefenokeeSwamp and Florida Everglades:Originsof sulphur in coal: Geochinñca et CosmochimicaActa: v. 41, p. 161-167.

Cohen, A. D., Raymond, R. Jr., Raniirez, A., Morales, Z. and Ponce, F., 1989, The Changuinola peat deposit of northwestern Panama: Los AlamosNational Laboratory Report LA-i 1211, v. 2,83 p.

Cohen, A. D., Spackman, W. and Dolsen, P., 1984, Occurrenceand distribution of sulphur in peat forming environmentsof southern Florida: Coal Geology,v.4, p. 73-96.

Given, P. H. and Miller, R. N., 1985, Distributionof forms of sulphur in peats from saline environments in the Florida Everglades:InternationalJournal of Coal Geology, v.5, p. 397-405.

Home, 3., Ferm, J. C., Carnccio, F. T. and Baganz, B. P., 1978, Depositional models in coal exploration and mine planning: Bulletinof the AmericanSociety of Petroleum Geologists, v. 62,p. 2379-2411.

Howarth, R. W. and Stewart, 3.W. B., 1992, The interaction of sulphur with other elements in ecosystems. inHowarth, R. W. et al., eds.: Sulphur cyclingon the continents; wetlands, terrestrial ecosystems and associated water bodies. (SCOPE 48): Chichester, United Kingdom, Wiley& Sons. 350 p.

Lowe, L. E., 1986, Application of a sequentialextraction procedure to the determination of the distribution of sulphur forms in selectedpeat materials: Canadian Journal of Soil Science, v. 66, p. 337-345.

Tabatabai, M. A., 1992, Methods of measurementof sulphur in soils, in Howarth, R.W. et al., eds. Sulphur cycling on the continents; wetlands,terrestrial ecosystems and associated water bodies, (SCOPE 48): Chichester, United Kingdom,Wiley& Sons, p. 307-344.

190 CHAPTER 6

6.1 CONCLUSIONS

“Let us supposean earthquake,possessingthe characteristic undulatorymovement of the ernst, in whichI believeall earthquakesessentiallyto consist,suddenlyto have disturbedthe levelof the widepeat-morasses,and adjoiningflat tracts of foreston the one side, andthe shallowsea on the other. The ocean,as usual in earthquakes,woulddrain off its waters for a moment,fromthe great Stigmaria marsh,and fromall the swampyforests whichskirtedit, and, by its recession,stir up the muddysoil,and drift awaythe fronds,twigs and smallerplants, and spreadthese,andthe mud,broadlyoverthe surfaceof the bog Presently,however,the sea wouldroll in with impetuousforce,and, reachingthe fast land,prostrateeverythingbeforeit.” HenryDarwinRogers, 1842 Transactions of the Association ofAmerican Geologistsand Naturalists, Vol.1,p.433-474.

When HenryRogers,inthe 1840’s,was seekingto understandthe processesby whichthe

Appalachiancoal strata cameabout, he imaginedthe swampy,tropicalcoast of ancientPennsylvania wrackedby periodicviolentearthquakes,the suddensubsidenceand subsequenttsunamisand flooding bringinga violentendto peat depositionand producingthe widespreadcarbonaceousshalepartingsthat he was findingin his explorations. It is a facultyof the humanmindto imaginethe processeswhichaccount for the worldaroundus, and is a particularlyvaluableficulty for the geologist,whois oftentryingto reconstrnctevents,muchof the evidenceof whichis longobliterated.

Detaileddocumentationof an eventsimilarto that imaginedby HenryRogersmaynot supporthis conjectures,as in the presentstudyof the Changuinolapeat deposit,but boththe speculationandthe documentationhavetheir rolesinthe evolutionof a modelwhichfits processesto products. Rogers imaginedhis PennsylvanianSf1gmaria marshas a vast, perfectlyplanarmarinesavannah. The closest knownmodemanaloguesto coal-formingmires,the Changuinolamiresystemand the knownthick peat depositsof southeastAsia,do not conformto this pattern,but developan elevatedtopographyand an

191 internalstructurethat encouragescontinuingpeat accumulation,and insulatesthem fromthe surrounding clastic sedimentaiyenvironments..Severalgenerationsof geologistshave sincecontributedto our understandingof the palaeogeographyandtopographyof coal-formingmires. In any event,it would requirea far more destructiveearthquakethan the Ms 7.5 shockwhichstruckthe Panamacoast in 1991to leavethe kind of geologicalevidenceenvisagedby Rogers.

The goals of this investigationwereto evaluatethe Changuinolapeat depositas a possible analoguefor the depositionof lowash, low sulphurcoals,andto documentthe effectsof earthquake- drivensubsidenceeventson the peat and the peat-formingvegetation. The depositdiffersin significant ways from previouslystudiedtropicalpeats, andthus providessomenew insightintothe processof thick peat accumulation,and hencethe nature of coal-fonningdepositionalenvironments.In addition,and perhaps surprisingly,it is evidentthat the impactof rapid coseismicsubsidenceon the peat depositis considerablymore subtlethan HenryRogerswouldhaveexpected.

This study showsthat the developmentof elevated,oligotrophicbogs, as describedin the

Andersonmodel,and the accumulationof thickpeat and hencecoal depositscan occur in responseto tectonically-drivenpunctuatedsubsidence,as wellas gradualeustatic sea levelrise. The processcan proceedwithout leavinga recordof increasedclasticinputwithinthe peat, evenimmediatelyadjacentto environmentsof activeclasticdeposition. The approximately10m of reliefon the basal sands,a product of the modeof subsidenceand sedimentaryresponsewithwhichthe barrier sands aggradeand prograde,is a significantdifferencebetweenthe Changuinoladepositand the modernsoutheastAsianpeats, which have planar bases and are almostentirelyabovesea level.

Climaticinfluenceshavea profoundeffecton the nature of peat deposition. On this wave-rather than storm-dominatedcoastline,the back barrierenvironmentis freeof all but minoraeolianclasticinput.

192 In the tropical climatepeat accumulateson barrier sandsin swalesdirectlybehindthe beach, and

progradesseawardwiththe barrier shoreline,withoutthe colonizingmangrovefringecommonto the

Malesiandeposits. In fact, the greaterpart of the depositdisplaysno internalevidenceof marine

influence,despitebeingapproximately40 % belowsea level. Althoughinstantaneoussubsidenceof 30 -

50 cm left its mark in structuresin the barriersandbody,it is not detectablein the peat behindthe barrier.

The part of the depositwhichdoesdisplaymarineinfluenceis at the southeasternextentof the barrier

coast, adjacentto and beneaththe shallowwatersof AlmiranteBay. There,the presenceof marine

influence,evidentin the dominanceof halophyte(mangrove)peats, and in the distributionof sulphur,

reflectsthe regionalstructuraltrend of greatestsubsidenceto the southeast. Evidenceof the punctuated

nature of that subsidenceis foundin the presenceof shellylayerswithinotherwisecarbonate-free

mangroveand back-mangrovepeats. In addition,at least in the short-term,the distributionof forms of

sulphur in newly-inundatedpeat is significantlydifferentfromthe distributionin peat that has not been

flooded. This suggestsa future lineof inquiiyintolonger-termgeochemicalsignaturesof rapid coseismic

subsidenceand marineinundationof coastalpeatlands.

6.2 SUGGESTIONSFOR FURTHERRESEARCH

The Changuinolapeat depositis an excellentanaloguefor coaldeposition,for the reasonsstated

above. One of the most valuableaspectsof the depositfor coal studiesis its almostuntouchedstate. Like the Europeanpeats, manyof the southeastAsiandepositsare sitesof intensehumanactivity,havebeen drainedor mined,and the forestshavebeenlogged. Differencesin structureand hydrologybetweenthis depositand those of southeastAsia leadsto the questionof whetherthereare peat depositsin tropical

Americawhichare developedon a base of lessrelief,and whichmorecloselyfit the Asianmodel.

There are numerouspossibilitiesfor moreextensiveand intensivestudyof the evolutionandthe

detailedhydrologyof the Changuinoladeposit. Of interestare the longterm effectsof suddeninundation

193 on coastal peats, and burial of peat beneath lime-mud and coral. Also, there is the possibility of addressing one of the chiefproblems inherentin the use of modernpeats as analogues for coal; the changes in the nature of coal-formingvegetationthrough time. Althoughthe problem is greatest for Paleozoic coals, modem palm peat may well provide a very close analogue to Tertiary palm coals. The use of palm peat in artificial coalificationstudies thus has potentialto reduce the problems inherent in assessing the effects of vegetation change. Finally, in additionto its potential for refiningthe evolvingmodel of tropical coal development,the Changuinoladeposit has interest because of the possibility of determininga history of coseismic subsidencefor this part of the Caribbean coast basedon radiocarbon datingof earthquake related stratification in submergedpeat.

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; AAAAAAAAAAAAA AAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAA 0000000000000 00000000000000 0000000000000 000000 00000 0•0•0•0 0000 000000 000 000 000 00000 — - I I 1 ‘ — — — III I — 1 1 ) 1 1 — — 1 — 1 1 1 — 1 1 1 1 1 — ‘ .< I I I I I I I I I I I I I I I IIII I II I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I II MiLE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE NUMBER

SAMPLE

2-14 2-10 2-1 2-18 2-15 2-12 2-11 2-8 2-5 2-2 2-19 2-16 2-13 2-9 2-7 2-6 2-3 2-17 2-4 2-20

1.5-15 1.5-20 1.5-17 1.5-14 1.5-13 1.5-10 1.5-21 1.5-18 1.5-12 1.5-11 1.5-8 1.5-5 1.5-19 1.5-16 1.5-9 1.5-7 1.5-6 1-15 1.5-4 1.5-1 1.5-3 1.5-2 1-17 1-14 1-16 1-13

480-510 420450 480-510 390420 450480 270-300 424-454 420450 300-330 2 600-630 390420 300-330 210-240 454-469 570-600 450480 270-300 240-270 330-360 240-270 469-484 510-540 570-600 360-390 540-570 360-390 330-360 510-540 394-424 364-394 540-570

150-180 120-150 120-150 180-210 180-210 150-180 RANGE

DEPTH 90-120 90-120

60-90 60-90 30-60 30-60

10-240

0-30 0-30

(cm)

DEPTH

PLOT

450 420 480 454 450 420 240 630 300 240 469 480 360 270 360 270 484 424 600 330 210 600 510 390 210 570 540 540 330 510 390 300 570 394

120 180 150 150 120 180

60 60 30 90 90

0 —

4.79 4.37 4.09 449 4.56 4.33 4.46 4.08 4.34 4.37 4.63 4.85 4.52 432 485 447 4.27 4.33 4.36 414 3.43 4.76 4.79 3.99 3.71 3.25 4.48 4.45 4.21 3.90 3.87 4.72 3.84 3.52 3.40 3.33 438 3.96 3.54 3.69 3.58 3.44 3.79 3.79 3.45

pH

APPENDIX

SULPHUR

212

TOTAL

(wt%)

0.25 0.25 0.26 0.22 0.18 0.22 0.51 0.24 0.23 0.22 0.18 0.17 0.19 0.18 0.27 0.25 0.26 0.22 0.16 0.16 0.21

B

SALINiTY

<0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 (%) <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01

0.01

MOISTURE

DRAINED

(wt%)

93.9 93.9 93.5 84.8 92.4 94.6 94.0 92.6 91.4 92.2 92.6 93.6 93.3 93.1 93.7 91.4 92.2 91.3 93.3 94.6 94.9

14C adjusted)

(a.

B.P.

AGE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MiLE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE MILE NUMBER

SAMPLE

4-7 4-4 4-3 3-18 4-12 4-11 4-8 4-5 4-2 4-1 3-27 3-23 3-20 3-17 3-14 3-10 3-7 3-4 3-1 2-23 4-13 4-10 4-9 4-6 3-25 3-24 3-21 3-15 3-12 3-11 3-9 3-8 3-5 3-2 2-24 2-22 2-21 4-14 3-26 3-22 3-19 3-16 3-13 3-6 3-3 3-0

600-630 690-720 630-660 630-660 660-690 480-510 270-300 660-690 690-720 420-450 240-270 210-240 600-630 570-600 540-570 450480 240-270 780-8 510-540 390-420 300-330 750-780 720-750 360-390 330-360 330-360 210-240 360-390 270-300 390-420 300-330

120-150 150-180 180-210 180-210 120-150 RANGE 150-180

Surface

DEPTH

90-120

90-120

60-90 30-60 60-90 30-60

0-30 0-30

(cm)

10

DEPTH

PLOT

690 690 720 630 450 420 240 720 630 660 480 300 270 660 810 600 510 330 210 750 570 540 360 240 780 390 300 270 420 330 210 360 390 120 180 150 150 180 120

60 30 90 60 30 90

0 —

4.79 4.34 406 4.27 4.06 4.15 407 4.79 4.36 4.35 4.03 429 4.79 4.63 4.01 3.91 3.91 4.86 4.55 3.93 3.97 3.83 3.84 3.83 4.21 3.78 4.64 3.80 4.06 4.20 3.84 416 4.18 4.44 4.12 3.67 3.98 3.93 3.99 3.95 5.15

p11

APPENDIX

SULPHUR

213

TOTAL

(wt%)

B

SALIMTY

<0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0,01 <0.01 <0.01 <0.01 (wt%) <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01

MOISTURE

DRAINED

(wt%)

14C adjusted)

(a.

B.P.

AGE APPENDIX B

SAMPLE DEPTH PLOT pH TOTAL SALINiTY DRAINED 14CAGE NUMBER RANGE DEPTH SULPHUR (wt%) MOISTURE (a. B.P. (cm) — (wt%) (wt%) adjusted) MILE 4-15 420-450 450 4.22 <0.01 MILE 4-16 450-480 480 4.36 <0.01 MILE 4-17 480-510 510 4.39 <0.01 MILE 4-18 510-540 540 4.48 <0.01 MILE 4-19 540-570 570 4.39 <0.01 MILE 4-20 570-600 600 4.18 <0.01 MILE 4-21 600-630 630 4.63 <0.01 MILE 4-22 630-660 660 467 <0.01 MILE 4-23 660-669 669 4.67 <0.01 MILE 4-24 669-690 690 4.43 <0.01 MILE 4-25 690-720 720 4.89 <0.01 MILE 4-26 720-750 750 5.06 <0.01 MILE 4-27 750-756 756 5.06 <0.01 MILE 4-28 756-780 780 5.39 <0.01

MILE 5-1 0-30 30 3.89 0.14 <0.01 92.4 MILE 5-2 30-60 60 3.79 0.20 <0.01 93.1 MILE 5-3 60-90 90 3.69 0.21 <0.01 93.1 MILE 5-4 90-120 120 3.60 0.20 <0.01 94.8 MILE 5-5 120-150 150 3.89 0.19 <0.01 93.0 MILE 5-6 150-180 180 3.79 0.21 <0.01 95.5 MILE 5-7 180-210 210 3.82 0.20 <0.01 94.5 MILE 5-8 210-240 240 4.05 0.18 <0.01 95.0 MILE 5-9 240-270 270 4.02 0.20 <0.01 95.6 MILE 5-10 270-300 300 3.77 0.20 <0.01 95.6 MILE 5-11 300-330 330 4.10 0.17 <0.01 95.3 MILE 5-12 330-360 360 4.30 0.18 <0.01 96.0 MILE 5-13 360-390 390 4.12 0.20 <0.01 94.0 MILE 5-14 390-420 420 4.29 0.26 <0.01 93.1 MILE 5-15 420-450 450 3.92 0.17 <0.01 94.5 850+/-80 MILE 5-16 450-480 480 4.28 0.15 <0.01 97.1 MILE 5-17 480-5 10 510 4.50 0.20 <0.01 95.3 MILE 5-18 510-540 540 4.43 0.23 <0.01 94.8 MILE 5-19 540-570 570 4.45 0.26 <0.01 96.2 MILE 5-20 570-600 600 4.25 0.23 <0.01 94.9 MILE 5-21 600-630 630 428 0.17 <0.01 93.8 MILE 5-22 630-660 660 .4.54 0.24 <0.01 96.0 MILE 5-23 660-690 690 4.53 0.23 <0.01 90.3 MILE 5-24 690-720 720 4.44 0.19 <0.01 92.7 MILE 5-25 720-750 750 4.63 0.21 <0.01 93.7 MILE 5-26 750-780 780 4.83 0.24 <0.01 95.7 3040+/-80 MILE 5-27 780-810 810 5.29 0.29 <0.01 93.6 MILE 5-28 810-840 840 5.40 0.30 <0.01 93.3 MILE 5-29 840-870 870 5.52 0.22 <0.01 93.3

NL1 0 0 3.87 0.01 NL 1-1 0-25 25 3.87 0.01 NL 1-2 25-50 50 3.96 <0.01

214 > - I- I- — — • l- ) I I I I I I t I I I ! ———.J

VIVI Vivi 3CVI)C LIi o . VI .

CVI CCCVI >VICVI

V. I- 1 C —. 00 -.. Vi C V. C C V. C C C Vi C Vi C Vi C

4...... -a00VI -c’.—oo—00VI c, —‘- LI. tO CV. 3

!! CCC•C — — — — — — — — — — ‘— I-< e a VIC JI APPENDIX C :: IAPPENDIXC: RESULTSIIOF WET SIEViNG %f = Moisture content of drained peat, in wt%. Z = Plotted depth of sample, in cm. %Ash = wt% of mineral grains, separatedby flotation. % C = dry wt% of particles> 2.0 mm, by sieving. %M=diywt%ofparticles<2.Ommand>025mm. % F = dry wt% of particles < 0.25 mm.

SAMPLE Depth %M Z %Ash % C % M % F Comments

BDD 22 l3ase=Mineralsof mixed lithology and no coral frags: note ostracodesand forains disappear at base. diatoms,bugs,fragmental 1 BDD 22-1 0 Hemic 0 24.4 10.7 30.7 34.2 2 BDD 22-2 100 — C Hemic 100 32.8 20.6 20.4 26.2 ‘picles,tooth,diatoms,etc fishscales,forams,frags 3 BDD 22-3 150-200 Hemic 175 52.1 6.4 18.7 22.8 4 BDD 22-4 200-250 F Hemic 225 50.8 1.8 7.1 40.3 stracods,forains,diatoms,spicu1es OStX4spp,forX2spp,wOOd,shells 5 BDD 22-5 300-350 Hemic 325 59.0 4.6 18.1 18.3 6 BDD 22-6 400-450 — Hemic 425 65.4 2.7 19.2 12.7 C:shells : diat,spic,ost,for,shell 7 BDD 22D-1 560-590 F Hemic 560 5.0 9.6 32.4 53.0 flOOO 8 BDD 22D-2 600+BASE not peat 600 72.0 2.5 10.5 15.0 filmS, pollen,no coral 9 BDD 22-7 600-650 not peat 625 rounded corai&shefls,ost,for,mins NL1 10 NL 1-1 0-25 F: Hemic 25 0.0 26.4 17.6 56.0 clear water water 11 NL 1-2 25-50 F: Hemic 50 0.0 25.9 29.7 44.0 clear 12 NL 1-3 50-75 F: Hemic 75 0.0 24.0 33.9 42.1 13 NL 1-4 75-100 F: Hemic 100 0.0 17.0 35.5 47.5 14 NL 1-5 100-125 F: Hemic 125 0.0 19.0 40.8 40.2 15 NL 1-6 125-150 F: Hemic 150 0.0 19.6 36.4 44.0 16 NL 1-7 150-175 F: Hemic 175 0.0 13.9 35.6 50.5 Campnospermaseed”a 17 NL 1-8 175-200 — F: Hemic 200 0.0 12.5 44.7 42.8 18 NL 1-9 200-225 F: Hemic 225 0.0 11.4 32.9 55.7 19 NL 1-10 225-250 F: Heinic 250 0.0 10.9 41.1 48.0 20 NL 1-11 250-270 F: Hemic 270 0.1 5.1 43.3 51.5 fewangularsandgrains 21 NL 1-12 270-300 280 LAKE 6.5 Disseminated mins throughout in Evaporate fraction; occ more concentrated. 22 LAKE 6.5-1 0-50 F Hemic 25 0.0 27.8 29.2 43.0 s5y,WOOdfrS.S: xtals 23 LAKE 6.5-2 75-100 CHemic 100 0.0 37.1 26.3 36.6 Camp seeda,roots: xtals 24 LAKE 6.5-3 100-125 Hemic 125 0.0 28.9 33.2 33.9 grassy: XtalS 25 LAKE 6.54 125-150 Hemic 150 0.0 31.5 34.7 33.8 grassy: xtals 26 LAKE 6.5-5 150-175 Hemic 175 0.0 30.0 40.0 30.0 (Estimateduetoloss).grassy:xtals cork Palm wood, woodfrags:xtals 27 LAKE 6.5-6 175-200 ‘ Fibric 200 0.0 40.2 36.4 23.4 28 LAKE 6.5-7 200.225 — Hemic 225 0.0 28.8 38.9 32.3 grassy.woodfrags 29 LAKE 6.5-8 225-250 — C Hemic 250 0.0 35.0 37.1 27.9 smwoodfrag,grass 30 LAKE 6.5-9 250-275 Hemic 275 9.9 22.9 32.4 34.8 numerous seed d,grassy: LTA LTA 31 LAKE 6.5-10 275-300 Hemic 300 2.3 25.9 45.0 26.8 twig, minerals,grassy: 32 LAKE 6.5-111300-325 FHemic 325 0.0 20.2 50.9 28.9 whitemould 33 LAKE 6.5-1j25.350 Hemic 350 0.0 34.0 43.8 22.2 gt’’i’ags 34 LAKE 6.5-13 350-375 — Hemic 375 0.0 27.0 46.5 26.5 grassfrags 35 LAKE 6,5-14 375-400 — Hemic 400 0.0 32.3 48.4 19.3)’

216 APPENDIX C SAMPLE Depth %M Z %Ash % C % M % F Comments

36 LAKE 6.5-15 400-425 Hemic 425 4.1 29.3 36.6 30.0 detritalmins 37 LAKE 6.5-16 425-450 CHemic 450 0.1 35.5 40.0 24.4 ‘Y 38 LAKE 6.5-17 450475 Hemic 475 0.1 25.9 47.0 26.0 gIy 39 LAKE 6.5-18 475-500 C Hemic 500 5.7 36.3 38.0 20.0 40 LAKE 6.5-19 500-525 F Hemic 525 10.0 15.0 35.0 40.0 wood,barkfrags LTAonfmes 41 LAKE 6.5-20 525-550 notpeat 550 76.8 2.5 8.4 12.3 fotpeat HTALTAonfmes LAKE 8 Base= frosted white, grey, and pale greensilt, no carbonate, much wood with embeddedmineral grains. 42 LAKE 8-1 0-50 — FHemic 50 0.0 18.1 46.6 35.3 gry,r0otu00stt 43 LAKE 8-2 50-75 C Hemic 75 0.0 38.9 38.2 22.9 gry,roots 44 LAKE 8-3 75-100 — Hemic 100 0.0 21.5 41.1 37.4 H2Oalmost clear 45 LAKE 84 100-150 Fibric 150 0.0 55.3 29.4 15.3 Cyrillaleaf,wood,bark 46 LAKE 8-5 150-175 — Fibric 175 0.0 39.8 32.2 28.0 peanut-shapedroot tubes 47 LAKE 8-6 175-200 Hemic 200 0.0 30.6 43.5 25.9 peanuts, grassy,H2Oclear 48 LAKE 8-7 200-225 Fibric 225 0.0 38.4 38.4 23.2 fewerpeanuts, moreflatfibres 49 LAKE 8-8 225-250 — Hemic 250 0.0 24.0 43.4 32.6 H20 still clear 50 LAKE 8-9 250-300 Hemic 300 0.0 30.9 51.5 17.6 M:sniall seed 51 LAKE 8-10 400425 Hemic 425 0.0 33.2 36.6 30.2 C:mass ofs. fibres-mossy? 52 LAKE 8-11 500-525 — Hemic 525 0.0 29.0 47.3 23.7 C:rootlet-penetiatedroot ortwig 53 LAKE 8-12 525-550 Hemic 550 0.0 32.7 40.7 26.6 H2Ostillck5r 54 LAKE 8-13 550-575 Hemic 575 0.0 23.9 44.2 31.9 clear 55 LAKE 8-14 575-600 — Hemic 600 0.0 23.4 49.3 27.3 F:axmuli,M:sheath-likesheetsmoss? 56 LAKE 8-15 600-625 — Hemic 625 0.0 23.2 47.7 29.1 F:annuli M:seedhead(moss?) 57 LAKE 8-16 625-650 Hemic 650 0.0 20.6 47.9 31.4 seed”g’: less annuli 58 LAKE 8-17 650-675 FHemic 675 0.0 18.6 52.9 28.5 g”x2nowoodoinerals 59 LAKE 8-18 675-692 not peat 692 91.0 3.0 3.0 3.0 lunitedlithxta]sembedinwood LAKE 10 Colourless elongate xtals below 600;volc glass? + detrital xtals at base. 6OLAKE1O 0 0 61 LAKE 10-1 0-25 C: Fibric 25 0.0 46.9 28.0 25.1 gr,toots 62 LAKE 10-2 75-100 F: Hemic 100 0.0 22.2 36.5 41.3 g’ 63 LAKE 10-3 100-125 C: Fibric 125 0.0 73.7 21.1 5.2 Campnospemed,fruita 64 LAKE 10-4 125-150 C: Fibric 150 0.0 50.0 35.0 15.0 small! 65 LAKE 10-5 150-190 C: CHemic 190 0.0 47.1 22.3 30.6 Campnospermaseed 66 LAKE 10-6 190-200 C: CHemi 200 0.0 48.8 31.4 19.8 wood, seedc 67 LAKE 10-7 200-250 M: Hemic 250 0.0 27.5 53.3 20.2 68 LAKE 10-8 290-300 C: Fibric 300 0.0 62.5 23.2 14.3 woody roots 69 LAKE 10-9 425450 M: Hemic 450 0.0 9.7 57.7 32.6 70 LAKE 10-10 450475 M: Hemic 475 0.0 13.1 55.5 31.4 ‘Y 71 LAKE 10-11 475-500 — M: Hemic 500 0.0 18.1 52.9 29.0 72 LAKE 10-12 500-525 — M:Hemic 525 0.0 5.6 52.5 41.9 gy 73 LAKE 10-13 525-550 M:Hemic 550 0.0 10.6 55.9 33.5 74 LAKE 10-14 560-575 — C Hemic 575 0.0 41.5 34.9 23.6 barlcblackfrags 75 LAKE 10-15 575-600 — CHemic 600 0.0 42.6 32.2 25.2 wood,bark,grass 76 LAKE 10-16 600-625 — C: Hemic 625 0.0 36.3 37.6 26.1 Wood,bS ss: many long xtals 77 LAKE 10-17 625-650 — FHemic 650 0.0 19.8 38.5 41.7 Y” 78 LAKE 10-18 675-700 — FHemic 700 0.1 26.8 35.6 375 many xtals 79 LAKE 10-19 715-725 — M: Hemic 725 0.1 20.2 42.3 37.4 blaekvolcglass,otherxtals 80 LAKE 10-20 725-750 M: Hemic 750 0.1 17.3 45.7 37.0 glyfranents

217 APPENDIX C

SAMPLE Depth O/,4 Z %Ash % C % M % F Comments

81 LAKE 10-21 800-820 820 MILE 1 82 MILE 1-1 4-34 — F Hemic 34 0.0 23.2 27.7 49.1 palm phytoliths, diatoms 83 MILE 1-2 34-64 C Hemic 64 0.0 33.3 36.6 30.1 murky water, phytoliths,diatoms 84 MILE 1-3 64-94 — Hemic 94 0.0 25.2 29.7 45.1 twigs,murky 85 MILE 1-4 94-124 Hemic 124 0.0 21.4 39.9 38.7 rooty,twiggy 86 MILE 1-5 124-154 CHemic 154 0.0 33.2 37.6 29.2 Iog(reinoved), wood 87 MILE 1-6 154-184 C Hemic 184 0.0 31.8 41.2 27.0 wood, twigs, sedge?grass 88 MILE 1-7 184-214 C Hemic 214 0.0 37.7 37.7 24.6 WoOdy,rootS,graSS 89 MILE 1-8 214-244 Hemic 244 0.0 27.0 43.1 29.9 g’ 90 MILE 1-9 244-274 Hemic 274 0.0 29.5 46.7 23.8 barlç twigs, grass 91 MILE 1-10 274.304 — CHemic 304 0.0 34.9 38.0 27.1 bark, grass,twigs 92 MILE 1-11 304-334 Fibric 334 0.0 43.3 33.7 23.0 bulbous root, twigs 93 MILE 1-12 334-364 Fibric 364 0.0 49.9 30.1 20.0 Campnospermaseedx6,bark 94 MILE 1-13 364-394 Fibric 394 0.0 38.8 34.6 26.6 seed, bark, grass,wood 95 MILE 1-14 394424 424 0.1 25.2 43.7 31.0 palm?wood, wood 96 MILE 1-15 424454 454 0.1 33.0 41.3 25.6 wood, granulartexture 97 MILE 1-16 454469 469 98 MILE 1-17 469484 484

MILE 3 330-630, White frosted mm grains disseminatedthroughout, earthy yellow magnetic mm at 300, 330 99 MILE 3-0 Surface — C:Fibnc 0 0.0 47.7 24.2 28.1 nioss?,roots,wood 100 MILE 3-1 0-30 C:CHemic 30 0.0 44.3 31.0 24.7 moSS?,roots 101 MILE 3-2 30-60 C:Fibric 60 0.0 47.9 25.1 27.0 Charcoal in M! moss? 102 MILE 3-3 60-90 — C:Fibric 90 0.0 58.1 18.3 23.6 “conns”,moss?, wood 103 MILE 34 90-120 C:Fibric 120 0.0 52.2 26.9 20.9 “coflfls”,WOod 104 MILE 3-5 120-150 C:Hemic 150 0.0 43.1 34.9 22.0 twif 105 MILE 3-6 150-180 C:Hemic 180 0.0 43.4 34.7 21.9 large red wood(excluded) 106 MILE 3-7 180-210 C:Fibric 210 0.0 48.5 24.6 26.9 107 MILE 3-8 2 10-240 C:Fibric 240 0.0 47.7 29.2 22.9 wood 108 MILE 3-9 240-270 — C:Hemic 270 0.0 41.7 25.7 32.6 WOOd, black H20, large spore? 109 MILE 3-10 270-300 — F:FHemic 300 14.4 28.5 22.5 34.6 white, earthy yellowmagmins 110 MILE 3-11 300-330 F:Hemic 330 1.0 33.5 31.0 345 mixgr,white,magmms,Campseed 111 MILE 3-12 330-360 — C:Fibric 360 00 41.9 29.2 28.9 ‘‘‘ 112 MILE 3-13 360-390 — C:Fibric 390 0.0 58.8 25.3 15.9 longfibres,clearwater 113 MILE 3-14 390-420 C:Hemic 420 0.0 36.0 36.0 28.0 l.fibres 114 MILE 3-15 420-450 C:Hemic 450 0.0 42.0 26.8 31.2 115 MILE 3-16 450480 C:Hemic 480 0.0 35.7 35.1 29.2 Camp seed, woodfrags 116 MILE 3-17 480-510 — C:Hemic 510 0.0 44.5 32.2 23.3 lg.wood.bark(included),noss? 117 MILE 3-18 510-540 — C:Hemic 540 0.0 39.6 35.0 25.4 grassy, long fibres, less wood 118 MILE 3-19 540-570 — F:Hemic 570 0.0 28.9 40.0 31.1 Seed e,fibres 119 MILE 3-20 570-600 C:Hemic 600 0.0 35.3 35.6 29.1 twigs,’tubes’,Fruitb 120 MILE 3-21 600-630 M:Hemic 630 0.0 30.6 40.2 29.2 121 MILE 3-22 630-660 660 0.0 0.0 0.0 0.0 122 MILE 3-23 660-690 — C:Hemic 690 0.0 39.0 31.0 30.0 lgwooth2 123 MILE 3-24 690-720 — M:Hemic 720 0.0 21.6 48.0 30.4 V00’ 124 MILE 3-25 720-750 C:Hemic 750 0.0 37.8 37.8 24.4 Woody 125 MILE 3-26 750-780 M:Hemic 780 0.0 22.9 50.0 27.1 woodfrags

218 APPENDIX C SAMPLE Depth %M Z %Ash % C % M % F Comments

126 MILE 3-27 780-810 M:Hemic 810 1.0 19.6 49.1 30.3 ED 3 POLLEN DONE______127 ED 3-1 0-30 Fibric 30 0.0 45.8 22.9 31.3 mogrOOtmass 128 ED 3-2 30-60 — Fibric 60 0.0 43.5 23.9 32.6 COflhlSSY 129 ED 3-3 60-90 Fibric 90 0.0 50.9 20.8 28.3 Y,10O 130 ED 3-4 90-120 C Hemic 120 0.0 35.9 17.9 46.2 ‘Y 131 ED 3-5 120-150 Fibnc 150 0.0 46.9 23.2 29.9 132 ED 3-6 150-180 — Fibric 180 0.0 43.4 24.6 32.0 133 ED 3-7 180-210 — Fibric 210 0.0 53.1 23.3 23.6 WOOd 134 ED 3-8 210-240 Fibric 240 0.0 57.1 29.4 13.5 135 ED 3-9 240-270 Fibric 270 0.0 57.1 23.7 19.2 136 ED 3-10 270-300 Fibric 300 0.0 60.3 27.1 12.6 C POOSP ma seed 137 ED 3-11 300-330 Fibric 330 0.0 60.6 24.8 14.6 138 ED 3-12 330-360 Fibric 360 0.0 60.5 29.3 10.2 139 ED 3-13 360-390 Fibric 390 0.0 56.4 27.5 l6.l°° 140 ED 3-14 390-420 F Hemic 420 0.0 20.7 33.7 45.6 BIackI-120, woody granularpeat woodygranularpeat 141 ED 3-15 420-450 F Hemic 450 0.0 23.4 28.0 48.6 BlackH2O, 142 ED 3-16 450-480 — Fibric 480 0.0 44.9 29.3 25.8 Fibrous, grassy,clearH2O clearH2O 143 ED 3-17 480-510 Fibric 510 0.0 48.6 28.4 23.0 Fibrous, grassy, 144 ED 3-18 510-540 — F Hemic 540 0.0 22.8 34.6 42.6 BlaekH2O,woodygranularpeat 145 ED 3-19 540-570 Hemic 570 0.0 34.8 37.6 27.6 Fibrous,grassy,clearH2O clearH2O 146 ED 3-20 570-600 Hemic 600 0.0 31.9 40.3 27.8 Fibrous,grassy, 147 ED 3-21 600-630 Hemic 630 0.0 34.5 38.1 27.4 H20 grey 148 ED 3-22 630-660 F Hemic 660 0.0 18.7 32.3 49.0 Black(burnt?)pithyfrags,blackH2O 149 ED 3-21 660-690 Heniic 690 0.0 34.0 40.0 26.0 Black(burnt?)pithyfrags,blackH2O 150 ED 3-22 690-720 Fibric 720 0.0 52.8 26.2 21.0 WoOd frags woodfrags 151 ED 3-23 720-750 Fllemic 750 0.0 21.7 49.2 29.1 152 ED 3-24 750-780 FHemic 780 0.0 5.4 58.0 36.6 H2Oslighilymurky 153 ED 3-25 780-810 F Hemic 810 0.0 10.8 36.5 52.7 tf5.C of mineral BDD 23 POLLEN DONE Base=frostedsand, mixed lithol., mica, mins embedded in woodfrags: Charcoal at top and base 154 BDD 23-1 0-50 92.2 F Hemic 50 0.0 18.7 26.5 54.8 root5,o51,bk.Ck 155 BDD 23-2 100 91.7 Hemic 100 18.2 24.6 24.9 32.3 flUfls,iHTAM&F 156 BDD 23-3 125 91.9 FHemic 125 0.0 15.8 39.6 44.6 H2Oslmurky 157 BDD 23-4 150 949 FHemic 150 0.0 16.0 42.4 41.6 Fusiformisporites,seed”i” 158 BDD 23-5 175 93.8 FHemic 175 0.0 17.8 39.3 42.9 159 BDD 23-6 200 94.2 FHemic 200 0.0 21.7 46.2 32.1 Fsporites 160 BDD 23-7 225 94.2 FHemic 225 0.0 26.1 42.3 31.6 lVOOfra5,” 161 BDD 23-8 250 95.0 F Heniic 250 0.0 21.2 46.5 32.3 same 162 BDD 23-9 250-285 92.7 F Hemic 285 0.0 15.9 34.1 50.0 palmfrags?,seed,H2Oblack wood/barkfrags,seeds,rootlets 163 BDD 23-10 300-350 81.0 F Hemic 350 0.0 21.7 32.7 45.6 164 BDD 23-11 350-400 84.6 FHemic 400 0.0 16.0 46.0 38.0 Campseed,annuli;H2Oblack:LTA mixedmins,frosted,charcoalH,LTA 165 BDD 23-13 415-450 760 notpeat 450 76.6 2.5 8.3 12.6 166 BDD 23-14 450-500 72.2 notpeat 500 woodfrags,fibres 167 BDD23-15 550-600 699 notpeat 600 BDD 31 Sedimentarypeat like BDD23 base; mins frosted_grey&white,_mica,silty. Resin balls and fuic granules. 168 BDD 3 1-1 0-25 82.4 F Hemic 25 0.0 20.9 29.9 49.2 IWOOd,leaflitter,blackH2O 169 BDD3L-2 25-50 84.1 Fllemic 50 0.0 16.9 27.7 434I”f’,20bl5

219 APPENDIX C

SAMPLE Depth O/ Z %Ash % C % M % F Comments

170 BDD 31-3 50-75 781 FHemic 75 5.0 14.8 27.9 573 SpiCules, silty 171 BDD 31-4 75-100 75.4 FHemic 100 56.9 11.7 13.5 18.0 spicules,silty,mica,nocarb 172 BDD 31-5 100-125 81.8 F Hemic 125 5.0 3.4 23.7 68.6 silty, resins?, finefibres 173 BDD 31-6 125-150 83.5 FHemic 150 37.8 10.3 23.3 28.6 j,sheh1s”P’ 174 BDD 31-7 150-175 80.7 F Hemic 175 2.0 12.9 30.0 55.1 asabove,H2Oblack seed,fmef,bres,mica 175 BDD 31-8 175-200 821 F Hemic 200 1.0 12.0 37.2 50.0 176 BDD31-9 200-225 84.4 FHemic 225 0.0 9.2 31.8 59.0 177 BDD 31-10 225-250 83.0 F Hemic 250 0.0 8.4 35.5 55.8 Resin balls,H20 black,bark 178 BDD 31-11 250-275 84.4 FHemic 275 2.0 10.3 38.5 49.2 worootlfrostedinins 179 BDD 31-12 275-300 85.3 FHemic 300 0.0 6.7 45.0 48.3 180 BDD 31-13 325-350 784 FHemic 350 0.0 7.8 35.7 56.5 181 BDD 31-14 375-400 79.8 F Hemic 400 0.0 2.5 45.4 52.1 nul&t 182 BDD 31-15 400-440 69.2 notpeat 440 940 2.0 2.0 2.0 not peatnot carbonate LAKE 2 183 LAKE 2-1 0-20 84.2 Hemic 20 0.0 17.4 41.1 41.5 Fusiforanisporites 184 LAKE 2-2 25-50 92.1 FHemic 50 0.0 2.8 27.4 69.8 185 LAKE 2-3 50-75 786 F Hemic 75 0.0 12.0 33.8 54.1 186 LAKE 2-4 100-125 90.6 F Hemic 125 0.0 5.1 43.4 51.4 Seed 187 LAKE 2-5 125-150 93.4 Hemic 150 0.0 22.4 39.3 38.3 188 LAKE 2-6 175-200 95.2 F Hemic 200 0.0 7.4 47.4 45.2 189 LAKE 2-7 225-250 83.7 FHemic 250 0.0 11.8 45.4 42.8 190 LAKE 2-8 275-300 94.1 F Hemic 300 0.0 9.4 43.9 46.7 SCCdS 191 LAKE 2-9 300-325 87.7 FHemic 325 0.0 9.3 34.6 56.1 traceofsandgrains 192 LAKE 2-10 325-350 754 notpeat 350 98.0 LTA MILES 193 MILE 5-1 0-30 924 C: Fibric 30 0.0 56.5 23.4 20.1 Y 194 MILE 5-2 30-60 93.1 C: CHenaic 60 0.0 51.9 30.3 17.8 SSY 195 MILE 5-3 60-90 93.1 F: Hemic 90 0.0 21.2 21.2 57.6 bark?, fern annuli 196 MILE 5-4 90-120 94.8 C: C Hemic 120 0.0 47.4 21.1 31.5 gy 197 MILE 5-5 120-150 93.0 C: Fibric 150 0.0 56.5 17.3 26.2 ‘Y 198 MILE 5-6 150-180 95.5 C: CHemic 180 0.0 42.5 23.6 33.9 7cmwood,twisedgeleaf 199 MILE 5-7 180-210 94.5 C: C Hemic 210 0.0 40.4 23.2 36.4 yelloWWood lxO.5 cm 200 MILE 5-8 210-240 950 F: Hemic 240 0.0 25.5 28.9 45.6 201 MILE 5-9 240-270 95.6 C: C Hemic 270 0.0 44.2 24.3 31.5 202 MILE 5-10 270-300 95.6 * 300 0.0 203 MILE 5-11 300-330 95.3 C: Fibnc 330 0.0 58.2 23.7 18.1 2typesofwood 204 MILE 5-12 330-360 96.0 F: Hemic 360 0.0 34.4 27.4 38.2 blakfrags, wood, fiujitb 205 MiLE 5-13 360-390 94.0 F:FHemic 390 0.0 24.8 28.1 47.1 fruitb 206 MiLE 5-14 390420 93.1 F: FHemic 420 0.0 18.6 29.9 51.5 lgwoodandpalinfrags 207 MILE 5-15 C 420450 945 F: Hemic 450 0.0 33.7 29.5 36.8 seed, large wood 208 MILE 5-16 450480 97.1 C: C Hemic 480 0.0 45.0 27.7 27.3 209 MILE 5-17 480-5 10 95.3 F: Hemic 510 0.0 26.2 30.0 43.8 large wood, bark 210 MILE 5-18 510-540 94.8 F: Hemic 540 0.0 22.8 27.4 49.8 211 MILE 5-19 540-570 96.2 F Hemic 570 0.0 11.4 30.3 58.3 Seed 212 MILE 5-20 C 570-600 949 C: Wood 600 0.0 66.2 16.2 17.6 gugpo 213 MILE 5-21 600-630 93.8 C: Fibric 630 0.0 48.3 24.4 27.3 wood, long roots 214 MILE 5-22 630-660 96.0 C Hemic 660 0.0 30.6 28.9 40.5 mostly wood, black (palm) frags

220 APPENDIX C SAMPLE Depth %M Z %Ash % C % M % F Comments

mostly Wood,Cainp seed, 215 MILE 5-23 660-690 90.3 F: Hemic 690 0.0 18.5 31.0 50.5 blaekH2O ALL WOOD! 216 MILE 5-24 690-720 92.7 C: Wood 720 0.0 76.1 14.2 97 mostly wood 217 MILE 5-25 720-750 93.7 C:Wood 750 0.0 45.5 25.7 28.8 WOOd,tWig 218 MILE 5-26 C 750-780 95.7 F Hemic 780 0.0 11.4 21.9 66.7 219 MILE 5-27 780-810 93.6 F Hemic 810 0.0 11.9 31.2 56.9 red wood, Ig root, black H2O 220 MILE 5-28 810-840 93.3 FHemic 840 0.0 4.0 26.2 69.8 Black H20 LTAonwlioleandfines 221 MILE 5-29 840-870 93.3 not peat 870 50.0 3.4 31.1 65.5 1Y BI 3 222 BI 3-1 0-25 84.0 F Hemic 25 0.0 7.9 22.6 69.5 black H20, fine 223 BI 3-2 25-50 85.9 F Hemic 50 7.9 4.9 26.0 61.1 J4TA 224 BI 3-3 50-75 81.8 F Hemic 75 0.0 5.4 36.9 57.7 blackwater,blackfrags 225 BI 3-4 75-100 83.6 F Hemic 100 7.6 3.9 34.5 54.0 seed: HTA 226 BI 3-5 100-125 81.8 F Hemic 125 0.0 14.7 34.5 50.8 227 B13-6 125-150 83.1 FHemic 150 0.0 10.3 23.6 66.1 228 BI 3-7 150-175 79.2 FHemic 175 2.8 2.2 15.3 79.7 muchshell,sandandsilt 229 BI 3-8 170-195 86.6 F Hemic 195 0.0 6.3 27.4 66.3 black water 230 BI 3-10 175-200 77.9 notpeat 200 7.9 0.7 22.9 68.5

221 Jugbndaceae oooooeooooooeoee00000000e

Compostae 00OOOOOO00OC0O0OOO0O000 000000000000

ci. Mlconlasp. 0 00000000 0 00 00 0 00 00 000000000000

IlexgulanensIs ‘00U

Cyrilla iacemifl.ora U) N 0 — N — 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

MyricatypeB 000000000000000000000 00000 000000000000

MyricatypeA 00000000r)000000000000000 0000CO00

U) .. U) U) C U) U) I- C lb l. ID U) U) U) U) lb U) N — — C) 0 lb 0 0 0 N 0 0 0 0 — ,..: Mydca mexicana — e 0 - c —

tncolporate F (33) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 — 0 0 0 0 0 0 0 0

tncolporate E (48) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 N .— 0 0 0 0 0 0 0 0 0 0 0 0 0

tricolporate D (40) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 — 0 0 0

tricolporate C (39) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 — 0 0 0 0 0 0 0 0 — — N N (0 c. ci — CO

tricolporate 8 (54) ( — 0 — 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 000000000000 tricolporateA(26) 0 00000000 ! Campnosperma type 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 lb U) 0 0 0 — 0 — 0 0 0 0

, Campnospermap. 0000000N0 N’ U)000!

. tricolpateType2 00000000000000000000000000 0000000000 co. tricolpateTypel 00000000000000000000000000 000000000

Lagunculadar. 00000000000000000000000000 00000000N0O

. Rhizophoiram. 00000000000000000000000000 00000000)0N 8<

.! e__ I. ipNCO’U)(0-U)O) cf Verrucatospotites oe——

Salplchlaenasp. 000000’

Cyclopeitiss.Sw. 00OtN000!

Monoletefem8 000OOO0O0000ON)0000D.N 0000O0N000’

Monolete fern 3 0 0 0 0 0 0 0 0 0 0 0 0 0 — 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C

Monoleteferri2 0000000000000e00000e’t 00000000000C

MonoIetefem1 0000000000000 O0O0O0Lfl0

cf.Laevlgatospontes (D’tlO

Acrostichum a. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 —

(.4 cf.Mefaxyasp. O0000000000000r..ee!OO000 000000000000

Unknowntnletespores* U0N_U

PaimphytohthA 0 000000000000000000000000 ON0t000O

Euterpeprecatorta 0 0 0 0 0 0 0 0 0 0 0 0 N — 0 0 0 0 0 — N 0 0 0 0 0

Raphia taedigera 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 N D 0 N N —

— 0 0 0 0 0 0 0 0 PA pe 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Graminiae

Cyperacea . , C z0

223 TOTALCOUNT C’4C4C4 C4C1 8888888 .C1’ (‘4

%OtherDicots

U) (DO) (‘4 U) U) U) U) at) U) U) (0 U) U) C) Co (0 % None-arboreal an d Z a’ ‘i ‘ (‘I C’) C) — Co O (‘i

it) (0 0) an o U) CO U) U) U) an an C’ C’) 4) an an an an an U) Co an an r- 2 AuOthers an o o an an a.. r- a — o ci ! r d .

an — an an (‘1 an ag an an an a-..a-.-.an an an in C) an in -‘ %identified

00000000000000000000000000 oeooooo’rZeO Dm0-cysts C..’ c1

FuslfomiisporifesC 00O00000000000000000000

Fusifonni spodtes B 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

FusifonnisporitesA 0000000000000000000000 0CoCo0

SporangiumA 0000000000000000000000000 000000000000

a’) a’) U) a’) U) a’) a’) (‘4 C) 0 (‘4 C’) 0 0 tetrahedron 0 0 0 0 0 0 0 0 0 0 — 0 0 0 0 0 0 0 opaque Fungalspores APPENDIXE: POLLENDESCRIPTIONS

(Plates 1 to 3)

PLATE 1-1 Trichomanes crinhtum(Hymenophyllaceae); Monolete fern spore, irregular ovoid, 41- 51jim x 30-40 jim; scierine plicate, echinate. Ref. PC5, fresh material.

PLATE 1-2 Cyclopeltis semicordata (Polypodiaceae - Tectariaceae): Monolete fern spore, kidney- shaped, 41gm X 25gm; laesura 22gm long, thickened margo, 1.5gm thick. Scierine irregularly verrucate. Ref. PC4, fresh material, LAKE 2 type 4. GL 30.6,121.1; 31.3,126.4. Photos 19,20.

PLATE 1-3 Salpichlaena sp. (Blechnaceae): Monolete fern spore, kidney-shaped, 33-43gm x 29gm, laesura Ca. 22gm long, exinethin, finelyrugulate; sclerine frequently has one to several plicae paralleling or crossing the laesura. Ref. fresh material. GL 29.2,121.4. Photos 23,30.

PLATE 1-4 Cyathea(?) rnultflora(?) (Cyatheaceae): Trilete fern spore, amb triangular, 40-45gm x 32gm, laesurae Ca. 10gm long. Exine stratified, scierinethin, psilate. Ref. fresh material (immature sample?), GL - Photos 21,22.

PLATE 1-5 Lindsaea sp. (Dennstaetiaceae): Monolete fern spore, 36gm x 29gm. oblate, often pointed at ends, with laesura extending into points. Laesura irregular, extends length of spore; ends of laesura sometimes branching; margo entire, >1gm thick. Exine scabrate. Ref pc 7, fresh material. GL 30.1,121.2. Photos 31,32.

PLATE 1-6 Monolete fern type 1: Kidney-shaped spore, 57gm x 27gm, laesura 2/3 length of spore, distinct margo 2gm wide, 3 jim thick; scierine psilate, perine psilate with 1 to several prominent folds (plicae), often merging or intersecting. Ref pc 4, LAKE 2 type 1. GL 34.3,110.7 Photo 24.

PLATE 1-7 Monolete fern type 2: Kidney-shaped spore, 63gm x 4 1gm, laesura 35gm long, scierine psilate. Ref pc4, LAKE2type2.GL31.9,113.3. Photo 27

PLATE 1-8

225 cf. Verrucatosporites sp., monolete fern type 3: Kidney-shaped spore, 41.im x 25iim, laesura 25iim long, sclerine weakly verrucate, perine psilate. Ref. pc4, LAKE2type3. GL32.8,113.5. Photo 26.

PLATE 1-9 Monolete fern type 8: Kidney-shaped spore, 35i.tmx 25iim, laesura 19im long Ref. pc 1, BDD 25 type A. GL 28.9,127.3. Photo 2.

PLATE 1-10 cf. Metaxya sp. (Cyatheaceae) (Roubik & Moreno), trilete fern spore: amb rounded- triangular, eq. dia. 44-50jim, laesurae 18-22j.imlong, 2-3j.tmwide, scierine thin, unstratified, scabrate to clavate. Ref. PC4, LAKE 2 type 29. GL 29.6,112.8. Photo 25.

PLATE 1-11 Raphia taedigera (Palmae): Monocolpate, shape irregular-reniformto sub-spherical, 23- 27i.tmx 17-19i.tm,colpus straight, 15-l9iim long x Ca. 1.8j.tmwide. Exine reticulate Ref. Pc 3, fresh sample. Photos 33,34.

PLATE 1-12 Palm phytolith, probably Raphia taedigera. spikey sphere, 10-30 imin diameter.

PLATE 1-13 Euterpe precatoria (Palmae): (Euterpe precatoria is the only palm, other than Raphia t., present in the swamp, but attempts to secure fresh pollen of this species failed): prolate, 25.tm x15.tm, monolete; laesura straight, 22j.tmlong x 1.5-2.3i.tmwide, with distinct margo; exinethin, scabrate. Ref. PC5, BDD 23 type 32.GL 24.8,119.1; 24.2,119.2. Photos 9,12.

226 [ 2 3

•1

5

6 4

8

7 9 10

12 20jL 11 13

PLATE 1: Fern spores: 1) Trichomanes criniturn; 2) C’yclopeltisseniicordata Sw.; 3) Salpichiaena sp.; 4) Cyathea n;ultf1ora(?); 5) Lindsaea sp.; 6) Monolete type 1; 7) Monolete type 2; 8) Monolete type 3; 9) Monolete type 8; 10) cf. Meiaxya sp.; Palmae: 11) Raphia taedigera; 12)Raphia phytolith; 13) Euteipe precatoria.

227 PLATES 2-1; 3-1 and 3-2 (details) Campnospermapanamensis (Anacardiaceae): tricolporate, prolate, 27-30 gm x 17-21gm. Exine ca 1.8gm thick, nexine thicker than sexine; sexine striate, 0.7gm thick, striae 0.5gm wide, absent near pores. Colpi ca. 22gm long, evenly spaced, costae colpi small. Ref. pc 5, fresh material; BDD 23-23, 23-36. GL 43.5,1 19.6;43.5,120.3 Photos 35-38

PLATE 2-3 Tricolporate type 1: Prolate, 28gm x 15gm, prominent transverse colpi Ref pc 1, BDD 25-1. GL27.5,112.8;24.3,117.8 Photos 1,3.

PLATE 2-4 Tricolporate type 2: Prolate, 24.tm x 16gm, well-developed transverse colpi. Ref. pc 1, BDD 25-36. GL 30.2,111.2; 36.4,118.3 Photo 4.

PLATE 2-5 Tricolporate type 26: Oblate-spheroidal, 20gm x 22gm, exine 2gm thick, stratified, sexine psilate, pores (ora?) open, with well developed vestibulum 4gm wide x 4-6gm deep. Ref. pc 7, LAKE 10-type 26.GL 37.7,124.5 Photo 13.

PLATE 2-6 Tricolporate type 54: Oblate, 23gm x 16gm, exine 1.5gm thick, stratified, sexine rugulate, separated from nexine at pores, pores (ora?) open, 6gm wide, with vestibulum, and membrane across oral floor; colpi about 3 gm deep, with margos about 1.5 gm wide. Ref. pc 7, LAKE 10-type 54. GL 38.7,119.5 Photo 39.

PLATE 2-7 Myrica mexicana: triporate, sub-oblate, amb rounded-triangular, 26gm, exine scabrate, ca 1.2gm thick; annulus arched, with fine teeth on lower surface. Ref pc 3, BDD 8-28 GL 39.4,111.3. Photo 16.

PLATE 2-8 Myrica-type A: triporate, amb rounded-triangular with a distinct 3-armed fold around the pole; dia. 27gm, exine finely scabrate, ca 1.2gm thick; pores open, 2.2gm wide, vestibulum rounded, 6gm x 3gm deep; annulus arched, with prominent inward notch (lower left) and teeth-like projections on inner surface (arrow). Ref pc 3, BDD 8-41 GL 31.4,118. Photo 19.

PLATE 2-9 Tricolporate type 33: 3-brevicolporate, amb circular, 23-27gm dia, exine 1.75gm thick, baculate, semi- tectate; endexinous thickenings beneath colporoids show as dark areas (arrows). (cf. Mortoniodendron?) (Graham, 1979). Ref pc 5, BDD 23 type 33 GL23.8,118.9, Photo 10.

228 bacculate-echinate. Ref. PLATE Ref. PLATE Ref. PLATES Unknown 2.5j.tm Tricolporate equatorial; present, 25.tm Tricolporate pores

LAKE

pc

PC

irregular

long.

thick,

4,

2-12 2-11

5,

weak

2-10,

LAKE type

BDD

sexine

2-48

type type

reticulum

margo,

ovoids

39:

3-3

8-39,

GL

2-40

48 40

clavate,

(details)

cf.

(Tiliaceae?): (Tiliaceae?):

35.8,116.2;

without

atrium

GL

8-40. Chenopodipollis

ca

semi-tectate;

1.5j.tm

35.6,115.8.

GL

present

margo,

26.5,112.4

thick. 27.

amb

amb

1,121.4.

but

Ca.

Photo

circular,

exine

rounded, sp.,

reduced,

4x2gm;

229

Photos

amb

Photo

28. has

3-brevicolpate,

circular-hexagonal,

1

3-brevicolpate,

exine

with

to

29. 17,18.

several

vestibulum;

stratified,

plicae

dia.

dia

>2im

32-36iim,

exine

Ca.

21-24j.tm,

27-31

4im

thick,

reticulate,

jim;

wide

colpi

sexine

periporate;

costa

and

Ca.

colpi

22- 1 2 3 4

8 5 6 7

2OI 11

9

10 12

PLATE 2: 1) Carnpnosperrnapanarnensis; 2) Carnpnosperrna-type; 3) Tricoiporate type 1; 4) Tricolporate type 2; 5) Tricolporate type 26; 6) Tricolporate type 54; 7) Myrica mexicana; 8)Myrica type A; 9) Triporate type 33; 10) Periporate type 39; 11) Triporate type 40; 12) Tnporate type 48.

230 PLATE 3-1 Campnospermapanamensis low and high focus equatorial (left, top and bottom), and polar (right, top and bottom) views.

PLATE 3-2 Campnospermapanamensis exine detail.

PLATE 3-3 Unknown type 39: cf. Chenopodipollis sp. details of pore (top) and exine (bottom).

PLATE 3-4 Fusformisporites sp. A: Fusiform dicellate fungal spore,73- 80j.tmx40- 50j.tm,ovoid, striate; striations >3.tm wide running length of hemisphere, branching in a few cases; central divider a thickened ring rather than a solid wall. Ref. pc 4, LAKE 2-41 GL42.5,117.0 Photo 14.

PLATE Fusfonnisporites sp. B: Fusiform dicellate fungal spore, 15tm x lOj.tm,blunt-ovoid, striate; striations Ca. him wide, Ca. 10-12 per hemisphere, unbranched, running length of hemisphere. Ref. pc 4, LAKE 2-57 GL 30.1,125.6 Photo 15.

PLATE 3-5 Fusfonnisporites sp.C: Fusiform dicellate fungal spore, 3611mx 9jim, striate; striations Ca. 1urn wide, 14-16 per hemisphere, running length of hemisphere, occ. branched. Poles with internal thickenings. Central divider is apparently a solid wall. Ref. pc 5, BDD 23 GL 20.4,118.5. Photos 7,8.

231 — I :-

A

4

1L

PLATE 3 (10 im scale bar): 1) Carnpnosperniapananiensis low and high focus in both equatorial and polar views; 2) Detail of exine decoration of Carnpnosperma (x 1780); 3) Periporate type 39, low and high focus. (20 im scale bar): 4) Fusforrnisporites sp. A; 5) Fusiformisporites sp. C.

232 APPENDIX

Anacardiaceae Blechnaceae Aquifoliaciae Annonaceae Alismataceae Hymenophyllaceae Guttiferae Euphorbiaceae Araceae Apocynacae Guttiferae Euphorbiaceae Dennstaetiaceae Cyperaceae Burseraceae Guttiferae Cynillaceae Cyperaceae Bignoniaceae Cyperaceae Combretaceae Lauraceae Cyperaceae Cyatheaceae Chrysobalanaceae FAMILY

APPENDIX

F:

List

of

species.

F:

PLANTS

Aichornea Alchornea Lindsaea Protium Rex Laguncularia Rhynchospora Salpichlaena Dieffenbachia Symphonia Sagittaria Guatteria Clusia Cyperus Cyperus Campnosperma Cyperus Cyathea? Ocotea Calophyllurn Cyrilla Chrysobalanus Tabebuiea Thevetia SPECIES

Trichomanes

Dom

guianensis

sp.

pyraniidata

racemzflora

panamense

sp.

odoratus ligularis

ahouai IDENTIFIED =

sp.

multzjlora?

inuncta

1ancfolia

sp.

larifolia

rosea

dominant:

globu4fera

belizense sp.

crinitum

racemosa

longispata

macrostachya.

icaco

panamensis

233

C

iN =

common:

THE

CHANGUINOLA

R

Dom NAME/NOTES tree! TYPE/COMMON fern! Dom C fern! fern! C C C filamentous) fern! R sawgrass/ sawgrass/ C R (spiney) C Dom C sawgrass! sawgrass! R C (red C R =

tree! tree! tree! tree/ tree! tree! herb! herb! tree! tree! shrub! shrub! shrub!

rare.

bark)

mangle

tree

ostrich

base

tree!Orey, tree!

tree!

White

Higo Plomo Maria Roble

“Round-leaf’

Otoye

Otoye

Huevo

hammock

of

Cerillo,

cimarron

1

On

MIRE

de

mangrove

de de

On

de

sabana

(m

lagarto

lagarto

barillo

gato

“a” Leguminosae Cae Cassia reticulata R shrub! Leguminosae Mim Inga spectabilis R tree! Guaba machete

Leguminosae Mim Pithecollobium gp. C tree! Gavilan; Rain tree Leguminosae Pap ErythrinaJisca R tree! Gallito

Liliaceae Smilaxsp. C vine

Malvaceae Hibiscus pernambucensis R shrub!

Melastomataceae Miconia curvipetiolata C shrub!

Melastomataceae Tococa guianensis C shrub! Moraceae Cecropia insignins R tree! Guarunio Moraceae Cecropia peltata R tree! Guarumo; trumpet tree Musaceae Heliconia latispatha C herb!Oja de Bijao

Myrsinaceae Ardisia sp. C shrub!

Myrsinaceae Myrsine pellucido-puntata C tree!

Nyctaginaceae Neea sp. 1 R shrub!

Nyctaginaceae Neea sp. 2 R shrub!

Ochnaceae Cespedezia macrophylla Dom tree!

Ochnaceae Ouratea sp. C shrub

Palmae Euterpe precatoria C palm! Palmae Raphia taedigera Dom palm! Matomba

Polypodiaceae Acrostichum aureum Dom fern! helechode manglar

Rhizophoraceae Cassipourea eliplica C tree!

Rhizophoraceae Rhizophora mangle Dom tree! red mangrove

Rubiaceae Cephaelis tomentosa C herb! labios ardientes

Rubiaceae Palicourea triphylla C shrub! Sterculiaceae Herrania purpurea R shrub! cacao cimarron

Sterculiaceae Sterculia sp. R shrub!

Tectariaceae Cyclopeltis semicordata (s.w.) C fern! ostrich 2

Theaceae Ternstroemia tepazapote Dom shrub; R tree! Miguelario; Manglillo

234 composition APPENDIX sand) inorganic et defined Centre, patterns, the part waterlogged, carbonaceous sufficiently thus heterogeneity mangrove has used Peat mire. groundwater. both the receive 10% and peat

varying (oligotrophic),

a!.,

acroteim, peat

now

significant

of

encourages

deposits

low to

in rainwater

has

1989).

It

the

Europe

water 25% as

University

The

Peat

Rheotrophic

The degrees

surface.

is,

been

and

in

material greater

swamp,

Low

peat

however,

long

mineral

of American

terms G:

mineral

may

and the

can

and

only Peat

expanded

while sediment.

They

and organic-rich

inorganic to

which (<5

the

TERMS

of

the time

underlying

than

yet

Rheotrophic be

evolutionary form

refer

(ash);

of a

is as

‘bog’,

consistency.

groundwater.

flora

wt%),

matter

the

expansion

may

saline

classified

matter

the

defined

a

South

at

rainfall.

(Moore,

is 50%

Society

fundamental

to

in

denser,

a into

commonly

growing

relatively

‘moor’, clayey

AND

have

sedimentation.

level virtually any

Medium

wetland,

(ash).

ash,

Carolina,

sediments:

is

topography

the

according

non-saline

‘high

complex

mires

according

In for of

potential 1989) ANALYTICAL

such

less

peat

concept

dry ‘marsh’

To

both the

surface

Ombrotrophic

Testing

poorer

any

(5-15

above permeable,

ash’.

most element would

weight.

that

tend

(or

definition.

or

standard

types

humid

to

internal by

and

minerotrophic

on

of of sandy

the

to peat-forming

Ombrotrophic

is authors, to wt%) Fresh

ash in

the

and

definition,

strictly

wetland

a

which

their

not

be ‘swamp’

in

organic of species

Less

mire

groundwater

content

climate,

Materials

the

peat)

(Andrejko

nutrient-rich mires,

waterlogged

drowned, and

peat

drainage

PROCEDURES

235

source

they

(or than

raised speaking

evolution

complex

systems.

High

and

has material

is

are

ombrogenous peat

the

using

wetland

if

accumulate.

frequently

10%

mires

(Cameron

of

stunted all

25%

the

systems, (ASTM,

bogs or Ash

water

et

water, contains

table,

applied

the in be

part

a!., buried

(eutrophic) mineral of groundwater

near In

tend

to

(15-25

acknowledgment

excluded or

many system

Organic

table

the

1983).

in

50%

is

aerated

the

‘high 90%

a

the

1969) et

to

its

the

by

to

-Stach

present less

diverse

The

matter

al.,

tropical

nature

be can

wt%).

growth, ash,

surface

peat-forming

inorganic

(Moore,

catoteim

water

moors’

By

than

nutrient-poor

from

Sediments

term

due

sets

1989)

and

be

table

and

et

this

study, is and

of

either

to

Above

25%

al., standards by

permeable,

mire

the

mire

‘low-ash’

remains

and

are

peaty

the

remains

the mires

1989).

standard,

of

luxuriant

weight sediments.

(Moore,

1982)

definition

ombrotrophic

the dry

the the

drainage

complexes,

above

influx

Research

is

wetlands,

25

clay

a

are

marginal

resulting

weight

This peat,

wt% for

general

mires

(Cameron

for

is

or

1989). peat

fed

of flora, (or

the

termed

a

of

below

That

usage

is

and

peaty

by

with

is

and

one marshes table, margins, mires, peats with assumption vegetation written peats, for marsh become a in Fibric: surfaces Coarse Sapric: Fine Hemic:

size In

variety

higher

this

some

distributions

profound

Hemic:

by

and

they

with

(Cameron

study,

descriptions

Hemic: progressively Types ‘Swamp’ ‘Marsh’ Stach ‘Bog’

Coarse

and

Dominant

Primarily (hence Esterle

where of of latitudes,

Tissue root fewer common

and

drainage -

may

perched

that the geomorphological

sedges,

swamps

reference

is

Dominant

few

et

or

effects

of

above

the

and ‘raised’),

be large

the land

(1990).

is

al.

Abundant

preservation

et

wood

is mires determined

coarse

fine relatively large to

freshwater

fine

peat

away

al.,

shallow-water

context (1982) rushes, water

fine in

that

(Cameron dense

root

on

tenns, more

this

particulate fragments.

is

particulate (from 1989).

is

fine

fibrous root

the and

There

from

fibrous is

made

tables

and

thinner,

report

tend

coarse

grasses.

luxuriant.

forests

wet, will

biology

open,

particulate and

the

by

and

Moore,

(degree

(telmatic processes.

wood

the

are to

to et

wet particles clarify

soft relative fed

many

particles.

wood

using

the

fibrous

wetland centre,

al., matrix

use the

matrix

saturated

in

5

sieving, by

and

fragments

It

and

field

the

of field

Vegetation

1989):

substrate

the 1989).

is

authors

the

fragments. a

rainfall,

or

matrix

humification)

impermeability

chemistry

tropics.

spongy, modified normally with

which

material They

with particles

terms categories,

limnic), dominated categories

hydrologic

or

because

rare

minor than

use

with

shallow-water are

236

may which

tends

‘reed-swamp’,

ranges

and

Raised

with

von

rheotrophic.

occurrence

of with commonly

generic or

hemic

minor

provide

peat

and described

amounts

by the

underlain

experience to

nature

is

form

Post

occasional

particulate

of

from

be

described trees.

bogs

deposit.

the

workers

peat.

amounts

the

identifiers particularly

Humification

in

plant

of

vonPost

moss

wetland

lens-shaped,

of catotelm closed

may of

‘forest-swamp’

by It

the

by

large brackish

coarse

too

nutrients, large are

Esterle

in

peat.

matrix site.

contain

(Sphagnum)

of

field depressions

is

system,

familiar

dominated

coarse

(Mangrove

root

results

normally nutrient-poor.

roots

fibrous

In

Bogs

Scale

(1990)

observations,

and

or with

areas the or

and

fibrous

and

marine

or

alongside wood

may occasional. with in

case

adapted

domed

particles

and

wood

the

of rheotrophic. by a

that

as

‘moss-swamp’

swamp)

domed

occur

this

swamp of

particles.

follows:

herbaceous vegetation

stunted

particles

influences,

result

fragments

rheotrophic

Near

or

particle-

index to

and

and

within

large convex

water

tropical

on

or

from

the

in trees

the

of

and

the tissuepreservation(vonPost, 1922). A scaleoften is usedto gradethe peat by degreeof decompositionin the von Post system: Hi: Completelyunhumifiedand muck-freepeat;uponpressinginthe hand,givesoff only colourless,clearwater. H2: Almostcompletelyunhumifledand muck-freepeat; uponpressing,givesoff almostclearbut yellow-brownwater. H3: Littlehumifledand littlemuck-containingpeat;uponpressing,givesoff distinctlyturbid water, no peat substancespass betweenthe fingersandthe residueis not mushy. H4: Poorlyhumifledor somemuck-containingpeat; uponpressing,givesoff stronglyturbid water. The residueis somewhatmushy. H5: Peat partially huniifledor with considerablemuckcontent. Theplant remainsare recognizablebut not distinct. Uponpressing,someof the substancepasses betweenthe fingerstogetherwithmuckywater. The residueinthe handis stronglymushy. H6: Peat partiallyhumifledor with considerablemuckcontent. The plant remainsare not distinct. Uponpressing,at the most, onethird ofthe peat passesbetweenthe fingerstogetherwith muckywater. The residuein the handis stronglymushy,but the plant residuestandsout more distinctlythan in the unpressedpeat. H7: Peat quite wellhumifledor with considerablemuckcontent,in whichmuchof the plant remainscan stillbe seen. Uponpressingabout half of the peat passes betweenthe fingers. if water separatesit is soupyandverydark in colour. H8: Peat well humifledor withconsiderablemuckcontent. The plant remainsare not recognizable.. Uponpressingabouttwothirdsofthe peat passesbetweenthe fingers. If it gives off waterat all, it is soupyand verydark in colour. The remainsconsistmainly of more resistantroot fibres,etc. H9: Peat very wellhumifiedor muck-like,in whichhardlyany plant remainsare apparent. Upon pressing,nearlyall of the peat passes betweenthe fingerslikea homogenousmush. HiO: Peat completelyhumifiedor muck-like,in whichno plant remainsare apparent. Upon pressingall of the peat passes betweenthe fingers. The traditionaluse of field-determinedpeat typeshas beenused onlysparinglyinthe studyof these tropical peats, as recentwork (Esterle, 1990)suggestslow correspondencebetweenthe traditional fieldclassificationsand the actual particle-sizedistributionas determinedby point countingor sievingmethods.

237 The palynomorphs measuring Mineral mesh) Fine and description ignition samples, Medium (1977), sample. determination, determination discussed Coarse was sulphur sieves reduction 50°C difference sulphur.

1972).

fine

results

determined

were was (wt

Pyritic according

was in

matter

constituents

Degree

and

Peat Total Moisture Mineral Degree

and

by

% between

a

volume

determined

of of

dried

muffle

determined

moisture

Lowe

uses

by this colorimetric

sieving

in

Classification

using

sulphur

was

sulphur

by

of

the

HI

of

in

to

botanical matter

instrument).

are

humification total soxhlet

(1986,

content

furnace

<25% >25% <25%

separated-out

a

humification

reduction

the the peat,

as

are

50°C

lost), less

using

was

determined

content

by

sulphur following methods

content

recorded

compared >2.0 >2.0 >2.0

accurate, determination

1992) extraction

extraction of

oven at

determined

and (e.g.

a

is

wet

550°C

Leco® and

based

mm mm mm

Procedures (dry

of is

and

to

Rhizophora and

(wt of outlined

by

peat,

scheme

used

Bi-colorimetric as

the

using

constant

the

and

weight to

the

flotation, %

Lowe (ASTM-D

with

percentages on

with SC-132

peats

plant

>30% <30% by <30%

peat

drained

in

ash)

sum

the do

of

a

by

plots

(Esterle

chloroform Zn-HC1

a

wet-sieving

for

and

H2S.

not

percent)

was identification

is

weight.

of

0.1

and

Williams

of

peat,

<0.25 <0.25 <0.25

Sulphur

based

and

the

lend

of 137

Bustin as

238 elemental

2974:

M

established

pollen

The

of

superficial

determination

an determination eta!,

reduction the

sedge

CaCI2

samples

themselves

total

mm mm mm

of

on

approximation

total

for

results

and

Analyzer Jarret,

procedure (1985)

203

associations

the

1987):

(= (= (=

peat)

by

three

sulphur,

of

solution

Steinberg

organic

samples

relative

hemic) hemic fibric

was

by

macroscopic

dry

of

water,

of

1983).

and

nomenclature.

hours

the

particle-size

well

sieving (see

of

weight,

of

determined

modified

to

to

are

followed

sulphate

whole

H2S

sulphur

sulphur

proportions

was

to (dried coarse

identified

of

fine

Tabatabai, (1959).

followed

summarized

woody

the

(Kowalenko with

as

measured

hemic)

peat

plant

at

from

density

the

hemic)

was

sulphur

forms

by

distribution

by

2.0

5

Elemental

or

followed

0°C,

by

methods in sulphate

parts

weight

of

determined

Staneck

1992,

mm

fibric

the

Zn-HC1

have

coarse,

of

here.

by

and crushed

and

and

surface

the and

air

p.3

loss

peats.

been

by

of

pyritic

sulphur

of

and

Lowe, peat.

Sulphate

drying

0.25

medium

13

H2S

each

on

by

to

Sue

for

mm

100

at

a For determinationof carbon-bondedsulphur and organic sulphate sulphur (C-O-S form of sulphur) the entire peat was reducedby HI and 2SH was determinedby colorimetry. HI reduction reduces elemental sulphur, sulphate sulphur, organic sulphate sulphur and pyritic sulphur to 2SH (Freney, 1961). Organic sulphate sulphur was estimated by subtracting elemental sulphur, sulphate sulphur and pyritic sulphur fromthe HI reducible sulphur. Carbon-bonded sulphur was estimated by the differencebetweentotal sulphur and HI reducedsulphur. If any acid soluble suiphides are present, they are removedby Zn-HCI reduction and thus lumped with pyritic sulphur. Pollen slides were prepared from surfacelitter and shallow peat samples, and from 2 cores, one in the central part of the deposit and the secondnear the eastern margin. Pollen was prepared and concentrated using standard acetolysistechniquesfrom the finefraction of the peat (< 0.25 mm). The use of HF was avoidedto enable phytolithsto be counted. Samples were first separated into coarse, medium and finefractions using a wet-sievingprocedure modifiedfrom Staneck and Silc (1977). Pollen profiles were prepared for each phasic community. To establish the pollen ‘fingerprint’for each phasic community,a countof 1000grains, where possible, was made from surface litter and surface peat samples (3 sites producedless than 750 grains each from multiple slides). The results were combined,and the percentageof the total countplotted for the most numerous palynomorphs. Although it would be preferableto compare counts from numerous similar sites to better represent each phasic community,it was felt that includingthe upper 25 cm of the peat gave considerable range to the sample, andgiventhe sampling interval in the cores (25 or 30 cm) finer discriminationwas not necessary. No attempt is made to relate the pollen found in the peat to the actual species which dominateeach community - the problems associated with proportional representativenessof dominantplantsin pollenprofiles are well known. Rather it was hoped that an easily recognizable‘fingerprint’would emergewhich could then be related to pollen recovered from cores. Counts of 200 grains for each 25-30 cm incrementof two cores were used to construct the pollen stratigraphy of the central and eastern sectionsof the deposit (Appendix D). The pollen diagrams of the two cores were constructed using selectedpalynomorphs or combinations of palynomorphs which are consideredto be valid markers, as determinedfrom the surface samples, and which best define transitions in vegetation. In both surface and core samples, the following grains were omitted from the counts: all single-celledfungalspores, all fungal hyphae, all

239 fragments less than 2/3 complete, and any ambiguous grain. In identifying palynomorphs, botanical names are used wherever possible, and pollen and spore genera where necessary.

240 Andrejko, American American REFERENCES Esterle, Freney, Jarret, Cameron, Kowalenko, Esterle, Lowe, Lowe,

Lowe,

L.E., L.E., P.M.,

L.E.

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Fraser 1987.

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M.J.,

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C.W.

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1961.

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mosses,

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ASTM

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Lowe,

F. humus American

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R.M., by

J.S.

the Durig, Testing

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STP

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L.E.,

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Agriculture Cohen,

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Pa.,

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Physical Environment,

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humic

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424-432.

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ashing

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botany

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Standards,

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chemistry

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Tropical

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peat

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Wetlands,

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nâgre

Wiley

P.C.

D.

Howarth,

Enviromnents.

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chemical

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SCOPE

review.

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Depositional

G.H.,

the

torvinventering

Journal

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Bodies.

methods

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of

processes:

four

Taylor,

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Water

pp.,

of

sulphur

Sulphur

M.,

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peat-forming

soils..

Associated

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Mackowsky,

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340-3

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Terrestrial

hwniflcation

B.Alpern

Geol.,

P.D.,

E.,

Post,

von

Williams,

Stach, Staneck, Tabatabai, Moore, APPENDIX H REMOTE SENSING

Access to the central areas of the Changuinolamire is extremelydifficult, and necessitated the use of multiple remotesensingtechniques. Digital satellite imagery from both Landsat and

SPOT® satellites was utilizedin this study. Landsat imageryof western Panamais available from the image archives of the US GeologicalSurvey.Eros Data Centre. The imageused in this study

was acquiredin January 1979 by the Landsat 3 satellite.

SPOT satellite imagerywas acquiredand interpretedby the author specificallyfor this

study. The image, whichhas a ground resolutionof 20 m, was obtainedby the SPOT 3 satellite on January 7, 1994. The images publishedherein were generated from 3-band multispectral (Green, Red and Near-infrared)digital data using E. R. Mapper®imageanalysis software. Digital manipulationswereperformedto enhancecontrastsin reflectivityof vegetationtypes,and to highlightthe presence of standingwater. The digital data, and a large number of interpreted images are on file at the Universityof British Columbia.and images are available to interested parties on diskette as .TIF files.

Low level, obliquenormal colour and colour infraredphotographs were taken by the author and used in the mapping of vegetationzones and drainagechannels. Colour infraredis particularly useful in assessingthe health of vegetationand thus is useful in monitoringthe extent of saline intrusion into freshwater wetlands. High altitude air photograph stereopairs are available for part of the deposit from the Instituto Geografico ‘TommyGuardia’, PanamaCity, and were used to map detailed vegetationzones.

243 Almirante theodolite geometry extensive elevation Attempts Instituto on water of cm APPENDIX irregular, Instituto accuracy, University section impractical interference

single-receiver

all

wooden

cross encountered

between

A

Site

Geografico de

in

to

and of as

and became

- total

of

pads Recursos in the

sections. Changuinola

use

of

the

locations is

I

British

thus

treed

in

the

overhead

marginal

of

LEVELLING

satellites

GPS Lake

some which

GPS

problematic

9

case

by

have

areas.

km

‘Tommy

Columbia

for

Hidraulicos

this The

10

not

cases

data.

in

supported

not of

foliage.

and areas elevation

railway.

at

method much surveyed

SE

survey

the

been

may

All Ed

Guardia’, ends

SURVEYS

in

of

and time

of

3.

positions

included

At areas

the be

y was lines

it

control The

the

of

were

will Electrificacion.

Thus

at

the

of

as

peat

the

central

40

what

were acquisition, NW where

much

time be

Panama

determined

levelling

this

cm,

deposit,

in

were

recorded

made

end

was

the run

of

as

the

part

region.

near

abandoned

writing,

244

text. was

50

by

City. deemed

available

peat

lines and of

Lake

but

m

the

in

Accuracy

by

tied

the

out. They

In

surface Appendix

20

is author

were

Magellan® The

the

transect such the 10.

to

more

cm

to

due

This

are, sea

use

survey

peat

tied

It

interested

in

areas,

was

is and

to was

frequently

level

of

however, the

inaccuracy

A

considered

to

is

‘surface’.

the

GPS

Ing.

submerged,

are

data

Model

represented central

not

benchmarks

the

using

accuracy

thus

Eduardo

parties

possible

in

tripod

and

archived

the

surveying

5000

tidal

regions.

The

limited

can

to

field

result

be

was

on extremely

limits,

by

data

be

deepest

to

Pro

Reyes

along

within

notes

request.

a

traverse due at

to

placed

of

The

OPS

straight is from

The

at

about

the

the

considered to of

are

standing

best

10

use

soft,

the

the

receiver.

the

on

the

cm

15

line of

I

10

Sm

and

m,

the