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 plant 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 Miocene 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 Cretaceous 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 — ——
_—I —
_1
U
coast m&re c
0
5*4
-
is
II /
_J
I II I( from I,
(1991),
—:“‘,‘
generalized
I I, [I,
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of
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-2-
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and
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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
in surveyed
Inserts The
BEACH
Figure
500x.
1908,
Cross-section
sediment
2-6.
show
palm
Rap
is
1.
elevation
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hia
Sediment
Cartoon
sedimentary
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as
of
across
is
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a
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visible
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the
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the
in
line
Changuinola
is
Figure
barrier
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in
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the
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at
as
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BEACH
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is
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imagery
23
is
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(Figs.
177
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Site
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2
the
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of
at
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of
by
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the
The
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barrier
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is
at
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dredged
about
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
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
9°
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 Berger, R., 1983. Sea levelsand tree-ring calibrated radio-carbon dates. In: P.M. Masters and M.C. Flemming(eds.), Quaternary Coastlinesand Marine Archaeology.Academic Press, London. p.51-61. Anderson, J.A.R., 1964. 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Earthquake-inducedflooding of a tropical coastal peat swamp: a modem analogue for high-sulphur coals? Geology,v. 22, No.10. p.929-932. 79 Phillips, S. and Bustin, R. M., (in review)Tectonic,climatic and biologicalcontrols on sulphur distribution in a coastal tropical peat deposit:implicationsfor environmental interpretation of coal deposits. Journal of SedimentaryResearch. Phillips, S., Rouse, G.E. and Bustin, R.M., (in review).Vegetationand diagnostic palynology of a tropical Caribbean peatland, Changuinola,Panama. Palaeo-3. Phillips, T.L. and DeMichele,W.A., 1981. Paleoecologyof a Middle Pennsylvanian age coal swamp in southern Illinois: Herrin Coal Memberat Sahara Mine No.6. In: K.J. Niklas, ed., Paleobotany, Paleoecology,and Evolution.v.1, Praeger, New York. p.233-297. Pirazzoli, P.A., 1991. World Atlas of HoloceneSea Level Changes. Elsevier Oceanography Series, v. 58. Amsterdam. pp.300. Plaficer,G. and Ward, S.N., 1992. 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BC Professional Engineer, Nov. 1991, -5p.10 Staneck,W. and Sue,.T., 1977. Comparisonsof four methods for determinationof degree of humification (decomposition)with emphasison the von Post method. Canadian Journal of Soil Science, v. 57, p.109117 Tabatabai, M.A., 1992. Methods- of measurementof sulphur in soils. In: Howarth, R.W., Stewart, J.W.B. and Ivanov, .M.V., eds. 1992. Sulphur Cyclingon the Continents;Wetlands, Terrestrial Ecosystems and AssociatedWater Bodies. SCOPE 48. Wiley and Sons, Chichester, p307-344. von Post, L., 1922. Sverigesgeologiska undersokningstorvinventeringoch nâgre av des hittillsvunna resultat. Sv. MosskulturfOr.Tidskr. 1:1-27. Wanless, H.R., Barofflo, J.R. and Trescott, P.C., 1969. Conditionsof depositionof Pennsylvanian coal beds. In: Dapples, E.C. and Hopkins,M.E., 1969. eds., Environmentsof Coal Deposition. G.S.A. Special Paper 114, Boulder, Colorado, 1969. -p.105142 80 . 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. 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Tidskr. 1:1-27. 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 less biomass. the Eduardo Bill occur thank significant Council content height Canadian Barnes the in L.E in However, Reyes, Chiriqui very of the remains of Lowe for the than Canada Republic Researcher low critical water and and Land the in pH low. the an degree grant his table sites of readings Company, families soil award Panama if than 5- of the of Astorga American Anderson, Casagrande, Brown, Camacho, Bruenig, Bruenig, Anderson, Anderson, Altschuler, Cecil, Casagrande, Camacho, C.B, K.A., Amsterdam. varios consecuencia Geochimica p.25-32. Panama: in Brown, peats, deposit Journal Ecosystems, Biochemistry, mineral systems in Ecosystems Everglades 0., E.F., E.F., Society the E., E. Sarawak, J.A.R., J.A.R. J.A.R., Z.S., Stanton, A., D.J., D.J., and Viquez, Panama 1985, mosses, fractions 1976. 1990, from (eds.), of 1991, matter of Schnepfe, University Viquez, and for Gronli, Seiffert, 1983, Tropical 1964, the peat of CosmochimicaActa, R.W., Borneo. Univ. Sulphur NW Classifying Testing Oligotrophic del Muller, Informe V. vol.17, Ecosystems Okefenokee Caribbean humus the in of and terremoto and The The coal: V., K. Borneo: World peat: K., of Dulong, M.M., Geography, of origin and in distribution Espinosa, Hull and tropical structure 1992, 3., No.1, and tecnico Berschinski, Panama. W. P.S. origins 1975, Sutton,N., for 4B coastal Materials related Review Silber, Misc. Virg. forested of Swamp of del F.T. p.39-45. Ashton Historical 4.9 mapping - the pyrite peat sobre Mires: 22 and of A., Palynological v.18, In Econ. 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Terrestrial Science, Rica extraction Society 18. a of peat in of Sedimentologists A., Level Chapter tropical 174 and of faulting Effects F., the Sedimentology composisition coals p.327-346. coal earthquake: of Sydney sulphur Hagemann, materials: of J.W.B. 1979, form Pi a of Changes: v.65, 2nd macerals, the chemical Etsburg of Ecosystems procedure America peat: 6, of and Englewood of the Coal and Ed. p.125-144. environmental earthquake-generated Compositional p.53 forms and sulphur tectonic Teruel a Canadian Tectonics, Gunnedah coal: :Cambridge H.W., Guidebook, Elsevier, modem and coal 1-541. h’anov, of Special sulphur Abstract in to Coal and sulphur International Mining six model: Cliffs, in the uplift Dehmer, analogue coal: Associated Journal and M.V., Publication facies Amsterdam, sulphur determination v.11, basins, chemistry with relationships University v. along content N.J. District, Coal-bearing In: a 3. of No.4, eds. J., reflection Programs, of A.C Eastern species marine 498pp. W.V. for peats the Journal Juan, Soil Water of 1992. of No.7, marine-roofed Donaldson, p.709-718. Caribbean Spain: Netherlands, Press, coals sulphur Geol. of of Science, of R. and Australia: of of the Sulphur the v.11(7), Bodies. plants p.43-60. and peat 208 Coal Econ. Fraser in p. and the Williams, Wanless, Tabatabai, Staneck, Shimoyama, p.105-142. marine Terrestrial Deposition. coal J.W.B. humification Association Chichester, Coal Soil W. H.R., E.G. M.A., and beds: Science, T., and and roof 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. 194 :::::::::;;r;:;:;;:;:::::::: c4c- eeee C12 J L.J J Vi 00 00 00 00 00 00 00 -J - -.J -J -.) -1 —J —.1 -J - -J —) 00 —1 i- — — — -.- — — -.- ‘3 —. — —. — —. 00 ------00 — — _.) t) 00 C i-. — . - C C C ‘3 ‘3 00 00 t.3 00 00 C O’ C .I 4. 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I- 00 Vi Vi Vi t’ 0 Vi 0 — Vi 0 — Vi 0 Vi 0 \D Vi . . 4 4 . . . . 00000000000 000 Vi 00 Vi 0 Vi 0 Vi 0 Vi 0 0 0 0 0 0 - ViViViViViViViViVi44 ViViViViViViViVi aVi•Vi•Vi•00•\o•Vi•ViVi 0000’ 00Vi00D00ViC’. )00O0a’.--a 000 %0C’.00-J)---\000 0000ViViVi-C’.4) Cl) ; 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. determination J.R., J.S., and of thesis, near peats, ASTM, deposits Organic Australian J.S., selected 20. procedure Materials Coal v.66, distribution science delta, Fraser 1987. 1992. Society Society C.C., M.J., peat and B.Alpern C.W. 1986. 1992. Jambi. Ferm, 1990. Geol., 1983. 1961. p.337-345. British mosses, University River samples and Bustin, Fiene, Esterle, peat-forming Philadelphia. Soils, in for for ASTM and for Journal Indonesia Application J.C., Studies v.12, Trends plant Ed., of Sumatra, Some delta. Testing Testing Columbia. (eds.), of sulphate Lowe, F. humus American sulphur R.M., by J.S. the Durig, Testing and P. analisis, of STP observations of laboratory on in Canadian inorganic Kentucky, 105-156. and Peat and L.E., and and Agriculture Cohen, environments Indonesia. and petrographic the 1985. 820, forms analysis of D.T. The of Palmer, Society Malaysia and Materials Materials nature related a v. 1972. Peats Philadelphia, sequential 3, and Science A.D., in Distribution testing, Coal: Journal content Lexington, p. on in selected of for C.A., International and products. Supardi, Research, 79-86. soil Observations the and as sulphur from 1983. (ASTM), (ASTM), Origin, Testing of Organic in of of nature analogues science extraction chemical 1989. 2$ the peat Annual peats. Soil temperate Pa., of I Comparison p.270. 1987. ASTM, Total Facies in v. and sulphur of materials. Science, The and 1969. 1987. peat 1983, Soils, Peat 12, organic j on Book for Materials procedure characteristics Physical Environment, geology, plant p. P.M. and the humic and Society Philadelphia, coal 241 American D2607-69. forms D4427-84. 424-432. of v.65, bismuth Depositional of Canadian tropical sulphur analysis. Jarret, ASTM p. formation. ashing acids and ASTM botany Symposium p.531-541. in to six chemical Society the sulphide Ed., 113, latitudes. compounds from Standard of Standards, techniques Standard p1. Journal facies Communications and determination STP tropical Testing Unpublished Environments, p.1 the chemistry for on 820, 33-145. colorimetric properties of Fraser : of classification Testing classification Tropical peats domed V.4.08. of in for Soil P.C. 1983, soil. Peats River Elsevier, of of of Science, PhD Lyons and peat of Tnt. p.5- in the the Peat, and peat soil J. of of p. R, Coal J. 10, of Stewart, hittills Journal v. mt. available Sons, and des of degree R.W., av Wetlands, and of Teichmuller, Lyons Canadian Research, and indexes Berlin-Stuttgart. nâgre Wiley P.C. D. Howarth, Enviromnents. och 48. in : Continents; method. chemical determination the Agriculture soils, as Post Chandra, for of on Borntraeger, SCOPE review. in a von Depositional G.H., the torvinventering Journal and fractions Cycling Bodies. methods sulphur on 1:1-27. Gerbruder of processes: four Taylor, 242 Facies Water pp., of sulphur Sulphur M., Tidskr. Australian emphasis 535 Soil undersoknings Origin, 1992. with measurement peat-forming soils.. Associated 1959. eds. edition, of Coal: of Comparisons and Teichmuller, A., 3rd and geologiska MosskultuifOr. M.V., p. 109 - 117 . 1977. ecology Methods Australian Peat Sv. 57, M-Th., 89-104. T., v. (decomposition) Sveriges The p. Steinberg, Ivanov, p307-344 Petrology, Ecosystems some 1992. (eds.), Silo, in and and resultat. v.12, Coal 52. 1989. 1922. Science, and M.A., C.H. Mackowsky, L., W. 1982, sulphur 340-3 Chichester, vunna Soil J.W.B. 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