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ASSESSING THE PRESERVATION POTENTIAL OF BIOGENIC FEATURES IN PRE-NEOGENE TUFAS AND TRAVERTINES- APPLICATIONS TO EXOBIOLOGY

Justin Richardson

A Thesis

Submitted to the Graduate College of Bowling Green State University in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE

May 2005

Committee:

James Evans, Co-Advisor

Margaret Yacobucci, Co-Advisor

Justin Richardson

ABSTRACT

James Evans and Margaret Yacobucci, Advisors

If evidence for life on Mars is found, it may come from Martian paleo- groundwater deposits (tufas and travertines). Tufas and travertines uniquely preserve evidence of life from both surface and subsurface environments. What is known about tufa and travertine is biased towards Holocene examples. Most geologically older examples remain poorly studied, possibly due to poor preservation potential, or from being overlooked or misclassified. This study examines preservation potential of lithologic and biogenic features in pre-Neogene paleo-groundwater deposits, focusing on biogenic microstructures detected using SEM, EDS, and petrography. This study compares pre-Neogene deposits from the Eocene Chadron Formation (Badlands of South

Dakota), the Jurassic Shuttle Meadow Formation (Hartford Basin of Connecticut), and

Triassic Mercia Mudstone Group (south Wales, United Kingdom) to Neogene tufa and travertine (San Ysidro Quadrangle, central New Mexico). The goal is to discern trends in biogenic microstructure preservation potential through geologic time. Dominant microstructures observed of probable biogenic origin include clotted micrite, pseudo- stromatolitic features (e.g., shrub-and-ray dendrites), microcolonial fungal sacs, coccoliths, and extracellular polymeric substances (EPS). Neogene samples include pisolites, coated grains, lithoclasts, encapsulated algae, shrub-and-ray dendrites, EPS, and calcite ice. Eocene samples include pisolites, coated grains, lithoclasts, shrub-and-ray dendrites, macrofossils (molluscs, ostracodes, and vertebrate bones), charophyte stems iv

and gyrogonites, microcolonial fungal sacs, coccoliths. Jurassic samples include pisolites, shrub-and-ray dendrites, EPS, calcite ice, calcite microspherules associated with algal and/or bacterial growth, and Fe-Mn oxide star structures. Triassic samples are dolomitized, but show "ghosts" of pisoids and Fe oxide star structures. In summary, paleo-groundwater deposits on Earth contain distinctive features observable through the

Late Triassic. Some features are inorganic or biologically mediated, such as pisolites, lithoclasts, and dendrites. Others are clearly biogenic. Eocene paleogroundwater deposits contain oncoids, coated grains, EPS, macrofossils (molluscs, ostracods, and vertebrates), and microfossils (coccoliths and microcolonial fungal sacs). Deposits as old as the Jurassic contain Fe- oxide star structures and spherules. Triassic deposits contain

Fe- oxide star structures. The quality of preservation of these features does not substantially decline in samples as old as the Late Triassic, suggesting that tufas and travertines uniquely preserve evidence of life from surface, subsurface, and potentially ancient environments. v

To my family and friends. vi

ACKNOWLEDGMENTS

I would like to thank Dr. Evans for suggesting paleo-groundwater deposits as a possible avenue of research. I would like to thank both Dr. Evans and Dr. Yacobucci for guidance and review of the thesis, in addition to providing additional contacts to researchers. I am grateful for the valuable suggestions from Dr. Jeremy Young of the

Natural History Museum of London, Dr. David Watkins of the University of Nebraska,

Dr. Don Steinker of Bowling Green State University, Dr. Charles Kahle (emeritus) of

Bowling Green State University, Dr. Penelope Boston of New Mexico Tech, and Dr. Jack

Farmer of Arizona State University regarding data collection and interpretation of samples.

I wish to thank Dr. R. P. Steinen for providing Jurassic samples from Coe’s

Quarry, Connecticut. The samples were collected by Dr. R. P. Steinen, John Jansky, Jon

Byrnes, and John Mooney at the University of Connecticut. I wish to thank Dr. Evans for providing both the Eocene samples from the Badlands, South Dakota, and the Triassic samples from Wales, U.K. Karen Waggoner and Lori Manship assisted in the collection of field data at San Ysidro Quadrangle, New Mexico. Scanning Electron Microscope work was conducted through the Biology Department at Bowling Green State University with the assistance of Marilyn Cayer. The assistance of these people is gratefully acknowledged. This project received funding support from the Geological Society of

America, the Paleontological Society, and Bowling Green State University. vii

TABLE OF CONTENTS

Page

ABSTRACT...... iii

ACKNOWLEDGEMENTS...... vi

TABLE OF CONTENTS...... vii

LIST OF FIGURES ...... x

LIST OF TABLES...... xiv

CHAPTER I. INTRODUCTION...... 1

Carbonate Geology ...... 1

Tufa and Travertine...... 2

Economic Significance...... 4

Depositional Environments and Basin Analysis...... 5

Life in Extreme Environments and Exobiology ...... 10

Purpose of Study...... 14

CHAPTER II. TUFAS AND TRAVERTINES...... 15

Mode of Formation ...... 15

Classification and Description of Features ...... 17

Macroscopic Features...... 21

Microscopic Features...... 25

Neogene Tufas and Travertines ...... 30

Ancient Tufas and Travertines...... 30

CHAPTER III. GEOLOGIC BACKGROUND OF FIELD SITES...... 31

Regional Geology of New Mexico Research Site ...... 31 viii

Regional Geology of South Dakota Research Site ...... 32

Regional Geology of Connecticut Research Site...... 37

Regional Geology of South Wales (UK) Research Site ...... 39

CHAPTER IV. METHODOLOGY...... 42

Sample Collection...... 42

Sample Treatment ...... 42

Contamination ...... 43

Scanning Electron Microscope Analysis ...... 44

CHAPTER V. RESULTS ...... 46

Neogene travertine from San Ysidro, New Mexico...... 46

General Description ...... 46

Macroscopic Features ...... 47

Microscopic Features...... 48

Paleogene tufa and travertine from the Badlands of South Dakota...... 61

General Description ...... 61

Macroscopic Features ...... 62

Microscopic Features...... 62

Early Jurassic tufa and travertine of the Hartford Basin,

Connecticut ...... 74

General Description ...... 74

Macroscopic Features ...... 75

Microscopic Features...... 75

Late Triassic travertine from south Wales (UK)...... 87 ix

General Description ...... 87

Macroscopic Features ...... 88

Microscopic Features...... 88

CHAPTER VI. DISCUSSION...... 92

CHAPTER VII. SUMMARY AND CONCLUSIONS ...... 102

REFERENCES ...... 104

APPENDIX A. Instrument Operations and Guides...... 109 x

LIST OF FIGURES

Figure Page

1 Progradational and Backstepping Models of Carbonate Deposition at

Angel Terrace, Mammoth Hot Springs, Yellowstone National Park ...... 7

2 Illustration of Lobate Carbonate Deposition...... 8

3 Illustration of Carbonate Cascade with Barrages and Pools...... 8

4 Sketch of Subaerial Spring with Paludal Cache ...... 9

5 Crossbedding seen by Mars Exploration Rovers at “Burns Cliff” ...... 13

6 Millimeter-scale Concretion in Rock Matrix and Loose on Martian Soil ..... 13

7 Photomicrographs of Allochems Present in Carbonate Rocks ...... 23

8 Illustrations of Crystallographic and Noncrystallographic

Dendrite Formation...... 27

9 Photograph of CaCO3 Preserved Air Bubbles...... 29

10 Geographic location and topographic profile of Milpas anticline ...... 33

11 Photograph of Milpas Anticline and perched springline

travertine formation ...... 33

12 Map location of Badlands, South Dakota sampling site...... 34

13 Outcrop photographs of South Dakota paleogroundwater deposits ...... 35

14 Internal features of tufas and travertines, Badlands, South Dakota...... 36

15 Geographic position of sampling site in Connecticut and Geologic map

of CT sampling site...... 38

16 Geographic and stratigraphic position of south Wales (UK) sampling site... 40

17 Internal features of Late Triassic travertines, south Wales (UK) ...... 41 xi

18 SEM images of controlled contaminated samples...... 45

19 EDS analysis of Au-Pd sputtercoated NM samples...... 51

20 Photomicrograph of pisolites in samples from NM...... 53

21 SEM image of ooids in tufa and travertine from NM...... 53

22 Photograph of chlorophyll bearing biogenic lamination in NM travertine.... 54

23 Photomicrograph of laminations and shrub banding in NM samples...... 55

24 Photomicrograph of crystallographic shrub banding in NM samples ...... 56

25 SEM image of bedding plane view of aragonite shrubs in NM samples...... 57

26 Photomicrograph of clotted micrite in NM samples...... 57

27 Photomicrograph of clotted micrite, dendrites, and calcite ice in NM ...... 58

28 SEM images of calcified bacterial trichomes and sheathing in NM samples 59

29 SEM images of trichomes, sheathing, and microspheres in NM samples..... 59

30 SEM image of calcified EPS filaments in NM samples ...... 60

31 SEM image of long calcified EPS filament in NM samples...... 60

32 EDS analysis of carbon coated samples from the Badlands of SD...... 66

33 Photomicrograph of a pisolite from the Badlands of SD...... 67

34 Photomicrograph of ooids from the Badlands of SD...... 67

35 Photomicrograph of noncrystallographic dendrites in samples from SD ...... 68

36 Photomicrograph of clotted micrite in samples from the Badlands of SD .... 68

37 Photomicrograph of isopachous chalcedony rim and pore filling

chalcedony in samples from the Badlands of SD ...... 69

38 SEM images of chalcedony rim with opal-CT bladed lepispheres in

samples from the badlands of SD ...... 69 xii

39 SEM images of calcified air bubbles in samples from the Badlands of SD .. 70

40 SEM images of microspheres on calcified air bubbles in samples from

the Badlands of SD ...... 71

41 SEM images of microcolonial fungal sacs in samples from the

Badlands of SD ...... 72

42 SEM images of coccoliths in samples from the Badlands of SD ...... 73

43 EDS analysis of Au-Pd and carbon coated tufa and travertine samples

from the Hartford Basin of CT...... 78

44 Photomicrograph of a pisolite, Hartford Basin of Connecticut ...... 80

45 Photomicrograph of ooids, Hartford Basin of Connecticut ...... 80

46 SEM image of ooids in travertines, Hartford Basin of Connecticut...... 81

47 Photomicrograph of detrital quartz grains and micrite intraclasts in travertines, Hartford Basin of Connecticut ...... 81

48 Photograph of a large tufa lithoclasts with surrounding micrite intraclasts

in travertine, Hartford Basin of Connecticut...... 82

49 Photomicrograph of noncrystallographic dendrites in travertines,

Hartford Basin of Connnecticut...... 82

50 Photomicrograph of clotted micrite in travertine, Hartford Basin of CT ...... 83

51 Photomicrograph of ghost features present in clotted micrite samples

of travertines, Hartford Basin of Connecticut...... 83

52 SEM images of calcified air bubbles in travertines, Hartford Basin of CT... 84

53 Photomicrograph of clotted micrite and calcite ice, Hartford Basin of CT... 84

54 SEM images of calcified microspheres representing an algal or xiii

bacterial microcolony in travertines, Hartford Basin of Connecticut...... 85

55 SEM images of calcified EPS filaments, Hartford Basin of CT...... 85

56 SEM images of Fe-Mn microfossils, Hartford Basin of CT...... 86

57 Internal features of tufas and travertines, Badlands, South Dakota...... 89

58 Internal features of tufas and travertines, Badlands, South Dakota...... 90

59 Internal features of tufas and travertines, Badlands, South Dakota...... 91

xiv

LIST OF TABLES

Table Page

1 Dunham (1962) Classification of Limestones ...... 18

2 Folk Classification of Limestone Fabric (1959,1962) ...... 18

3 Classification of Tufa and Travertine Based on Fabric ...... 20

4 Depositional Facies of Angel Terrace Spring, Mammoth Hot Spring,

Yellowstone National Park, U.S.A...... 20

5 XRD Analysis of New Mexico Sample...... 52

6 XRD Analysis of South Dakota Sample...... 66

7 XRD Analysis of Connecticut Sample ...... 79

8 XRD Analysis of south Wales (UK) Sample...... 90

9 Assessment of Macroscopic and Microscopic Features Present Within

New Mexico, South Dakota, and Connecticut Sampling Areas ...... 93

10 Interpretation of Depositional Facies Preserved Within New Mexico,

South Dakota, and Connecticut Sampling Areas based on Assessed

Macroscopic and Microscopic Features...... 100

11 Comparison of Preserved Macroscopic and Microscopic Features Within

Tufas and Travertines of Neogene, Paleogene, and

Late Triassic/Early Jurassic Age...... 101

CHAPTER I. INTRODUCTION

Carbonate Geology

Carbonates compose 10-15% of rock strata deposited during the last 500 m.y. of the Earth’s history and approximately 20-25% of the total of all sedimentary rocks in the rock record (Boggs 1992). The vast majority of carbonate deposits are marine in origin, but a small percentage are associated with terrestrial sources of water. The literature on freshwater carbonates divides them into speleothems (subterranean groundwater deposits), travertine and tufa (surficial groundwater deposits), and carbonate lake deposits

(saline, alkaline, or hard-water lakes).

The terms “tufa” and “travertine” are somewhat controversial, with overlapping definitions. Tufa was first used as the Roman word tophus by Pliny to describe a range

of substances which included tuff as well as calcareous tufa (Hancock et al. 1999).

Travertine was either derived from the Roman Tibur River Stone (Wyatt 1996) or from

Tivertino, which is an old Roman name for Tivoli, Italy, where travertine deposits are

found (Julia 1983).

The terms travertine and tufa have also been used interchangeably or as

subdivisions of each other. Julia (1983) describes the term travertine as an accumulation

of calcium carbonate in karstic springs, hydrothermal springs, small rivers, and swamps

formed mainly by cement precipitation and/or biochemical precipitation. Ford and

Pedley (1996) limit travertine to a dominantly hard, crystalline precipitate with frequent

thin lamination and shrub-like bacterial growths. Julia (1983) designates tufa as non-

marine carbonate deposits specific to highly porous, spongy formations that are typically

formed around living plant material, while Ford and Pedley (1996) describe tufa as a 2 carbonate precipitated in cool water that can contain micro- and macrophytes, invertebrates and bacteria. Ford and Pedley (1996) also suggest that tufas can be precipitated at the same locations as travertines as waters cool laterally away from their thermal source. Sanders and Friedman (1967) use travertine in the broadest sense as all non-marine carbonates formed in or near lakes, springs, rivers, and caves. Pentecost

(1995) uses environment to assign travertine to hot springs, tufa to cool-temperature springs, waterfalls, and dams, and speleothems to precipitates in subterranean caves or fracture systems. Finally, calcareous sinter is another all-inclusive term commonly used to refer to both travertine and tufa (Boggs 1992). This study will adapt definitions by

Ford and Pedley (1996), in which the term travertine is used to describe a dense carbonate deposit with typical stromatolitic banding while the term tufa is used to describe a less dense, often highly porous carbonate deposit, typically associated with aquatic vegetation.

Tufa and Travertine

Travertines can form by two different processes, either by predominantly physico- chemical processes or by predominantly biochemical processes (Julia 1983, Chafetz and

Folk 1984). The precipitation of calcium carbonate is dependent on high concentrations

++ of Ca and low concentrations of CO2, which is in turn controlled by the concentration of CO2 gas, biochemical activity from photosynthesis (Julia 1983), and temperature

(Boggs 1992). The amount of dissolved carbon dioxide in waters precipitating calcium carbonate plays a major role in the solubility of calcium carbonate by decreasing pH. For

+ - each mole of water and CO2 that react, there is a possible yield of H2CO3, H + HCO3 , 3

2- and/or CO3 (Garrels and Christ 1965). The predominance of CO2 species present is

- related to the pH of the CO2/water system, in that H2CO3 and HCO3 are key in a pH of

- 2- less than 7.5 and HCO3 and CO3 are key in a pH of greater than 7.5 (Milliman 1974).

Any process that brings CO2 out of the water causes a drop in the partial pressure of CO2

and an increase in the pH of the system, which will result in a change of equilibrium and

++ precipitation of CaCO3 as long as Ca is present (Boggs 1992).

The equilibrium equations for the formation of calcium carbonate as aragonite or

as calcite (Garrels and Christ 1965) are displayed as equations 1 through 4.

CO2 + H2O Ù H2CO3 (1)

+ - H2CO3 Ù H + HCO3 (2)

- + 2- HCO3 Ù H + CO3 (3)

++ - CaCO3 +H2CO3 Ù Ca + 2HCO3 (4)

For example, travertine precipitation is favored by degassing of CO2. Loss of

CO2 drives equation (1) to the left, which reduces the concentration of carbonic acid

(H2CO3) in solution. This loss of H2CO3 would drive equation (4) to the left, producing

more calcite (CaCO3). Degassing of CO2 can occur when surface water saturated in

CaCO3 passes over rapids and waterfalls. Degassing can also occur when water drips

into subterranean caves. The degassing in a cave causes precipitation of speleothems.

Carbonate precipitation can also occur when photosynthesis occurs. The biochemical

uptake of CO2 also drives equations (1) and (4) to the left, favoring calcite precipitation.

Such carbonate often forms a chalk-like deposit on plants or the substrate. It has been shown that bacterially precipitated calcite as a product of photosynthesis typically 4 constitutes a large percentage of the carbonate in many terrestrial spring deposits

(Chafetz and Folk 1984).

Economic Significance

Historically as well as today, travertine has been an important dimension stone, used as a decorative construction and finishing material on the exterior and interior of buildings, monuments, and homes. Approximately 1.30 million tons of dimension stone, valued at $257 million, were sold or used in the U.S. in 2004, of which 28%, by tonnage, was carbonate (limestone, travertine, and tufa) (USGS 2005). Slightly more than half of all travertine used in the U.S. is imported, the majority of which comes from Turkey

(33.1%), Italy (32.6%), and Mexico (22.3%) (Marble and More 2003). Aesthetically pleasing specimens of travertine have also been used for carvings, pottery, and jewelry as far back as the time of the Egyptians and Aztecs (Merril 1895). A small percentage (5%) of carbonate dimension stone is also used for rubble and other nonbuilding purposes, such as lime production (USGS 2005). Broken and crushed travertine is a small percentage along with the quarrying and mining of other calcareous rocks and minerals, used for the production of lime, following the equation:

CaCO3 + heat => CaO + CO2 (5)

The production of lime for the U.S. alone was estimated at 20.4 million metric tons

(worth $1.4 billion dollars in 2004). Lime is used in steelmaking, flue gas desulfurization, cement, coating paper, and for water treatment (USGS 2005). Tufa and travertine deposits also have research value, are associated with potential hydrocarbon deposits, and can be used in a method known as travitonics to detect neotectonic 5

attributes of structures using geophysical relationships between fissure type and travertine

morphology, as well as using U-series dating methods to interpret fissure movements

over geologic time (Hancock et al. 1999).

Depositional Environments and Basin Analysis

Facies models have been constructed for Late Cenozoic tufas and travertines by

Pedley (1990) and Ford and Pedley (1996). They identify subaerial springs, paludal

(wetlands), fluvial, and lacustrine tufas as the four main members in a tufa continuum.

An example of subaerial spring deposits is given by hot spring travertines at

Angel Terrace, Mammoth Hot Springs, Yellowstone National Park. Fouke et al. (2000)

and Pedley et al. (2003) show rapid precipitation of spring deposits in progradational and

backstepping models as follows: the initial deposits of lithoclast and intraclast breccias build up and cover the paleotopography (Fig. 1), followed by prograding lobes of carbonates that form a gently convex to flat upper surface with primary cavities being formed as ends of older lobes are covered by new lobes (Fig. 2).

Subaerial spring environments can be divided into sub-environments. For

example, where changes in topography are sufficiently steep, a sub-environment called

“carbonate cascades” are frequently formed at waterfall sites due to physico-chemical precipitation through CO2 degassing (Pedley et al. 2003). Carbonate cascades are often

subdivided in turn into overhanging bryophyte curtains, foot splash zones, holding pools

with stromatolitic banding, and barrages (dams), such as shown in Figure 3 (Pedley et al.

2003). It is thought that, in mature subaerial springs that have developed a nearly flat

surface, pooling of water to form shallow marshes can develop with precipitation of 6

paludal travertine and tufa at depths of decimeters to wetted surfaces and allow for substantial vegetative growth (Fig. 4), but such sub-environments are not recognized today (Pedley et al. 2003).

The other end-member environments include fluvial, lacustrine, and paludal tufas

(Pedley et al. 2003). Fluvial tufas are subdivided into tufa dams (barrages) that form

across rivers and braided-stream tufas (where tufa growth cements gravel clasts together).

Lacustrine tufas are subdivided into shore-margin deposits (often tabular stromatolites, ooids, and oncoids) and basin deposits (laminated marl and chalk). Paludal tufas are predominantly found in waterlogged areas, and precipitation of micrite as subhorizontal laminae predominates in these sites. While spring mounds may form, lithification of individual beds is very rapid and occurs before the decay of vegetation. Highly porous phytoherms of grasses and rushes are the most diagnostic feature of this model, along with intercalated sapropels and peats (Pedley et al. 2003).

7 A.

Figure 1. Progradational (A) and backstepping (B) models of carbonate deposition at

Angel Terrace, Mammoth Hot Springs, Yellowstone National Park (from Fouke et al.

2000). 8

Figure 2. Illustration of a perched spring, with diverted intermittent drainage (1). The

growth of the perched-springline mound is on the eroded margin of an earlier fluvial

terrace (2), and displays primary cavities (3) as well as early lithoclast and intraclast

breccias filling an earlier valley (4). (Pedley et al. 2003).

Figure 3. Illustration of carbonate cascade, showing A: cross-sectional view of the bryophyte curtain, with barrages (2,4) and pools (1,3,5) below, and B: map view of the cascade (Pedley et al. 2003). 9

Figure 4. Facies model diagram of subaerial springs, showing: (a) resurgence point or vent with apron and channel, (b) paludal development or pool, with (c) thick lobate framework built by terracettes, (d) proximal slope, and (e) distal slope, overlying (f) paleosols, topographic infilling, or lithoclast breccias. (Ford and Pedley 1996, Pedley et al. 2003). 10

Life in Extreme Environments and Exobiology

The study of planetary geology has become increasingly more practical ever since

the Viking lander missions to Mars in the 1970s. Recent technological advances in

remote sensing and robotics have enabled scientists to perform a virtual hands-on study

of Mars. In the last decade, NASA has taken the initiative to determine if life once

existed or still does exist on Mars. Currently NASA has two field geology robotic units

on Mars as part of the Mars Exploration Program. The Spirit and Opportunity Missions

to Mars consist of two identical rovers designed to cover roughly 100 meters each

martian day, that carry a panoramic camera, three types of spectrometers, a rock abrasion

tool, and a microscopic imager.

Recently, scientists interested in exobiology have been looking in extreme

environments on Earth, both at the surface and subsurface. The emphasis has been on

microscopic structures and minerals in carbonates that can indicate fossil life. Examples include studies on Mono Lake tufa deposits in California to determine the ability of this depositional environment to ideally preserve biogenic material (Farmer and DesMarais,

1999). In addition, studies on speleothems at Carlsbad Caverns in New Mexico may show how extreme environmental conditions in the subsurface still harbor life that can be preserved well enough to be identified in the fossil record (Boston, 2000).

Much of the reason for this interest has been the recognition that Mars once had a

more hospitable environment that may have supported life. Although atmospheric

pressure on Mars is now in the range of 6 to 9 mb, the total volume of previous volatile

outgassing has been estimated to be at least 1.6x104 times the current atmospheric volume, suggesting that a greater atmosphere may have once existed on Mars (Durand- 11

Manterola 2003). If the Martian atmosphere was once more dense in comparison to

today from volcanic outgassing (mantle convection), surficial liquid phase water may

have been present for great periods of time (Acuna et al. 1999, Kirschvink and Weiss

2002). Dendritic drainage patterns plus streamlined features found on Mars could be interpreted as flood channels and imply a formerly wet climate on Mars, and other

surface structures present the possibility of paleolakes and ponds that existed in excess of

104 years (Cabrol and Grin 2003). With the exception of atmospheric pressure and

ultraviolet radiation levels, present conditions on Mars are very much comparable to

present conditions in the Antarctic Dry Valley on Earth (McKay 2003, Cabrol and Grin

2003).

Criticism for the Blue Mars theory is based on alternative explanations for

surficial features, such as liquid CO2 degassing to explain outburst flood channel

structures. In addition, lack of massive carbonate deposits suggests a long, dry history

for Mars (Hoffman 2001). However, recent scientific explorations by the Mars

Exploration Rovers (MER) have provided microscale evidence in support of the Blue

Mars theory, such as the presence of hydrated minerals like hematite, jarosite, and

goethite (Kerr 2004). Micro- and macroscale lithological observations by the MER show

crossbedding of exposed rock units (Fig. 5) which could indicate either subaerial or

subaqueous sediment transport. In addition, photographs have been taken by the MER of

what may be millimeter-sized concretions or coated grains that exist within rocks at the

surface (Fig. 6). On Earth, concretions tend to form at geochemical interfaces such as

water table positions in soils or redox changes in wet sediments. 12

Martian meteorites recovered on Earth, such as the famous ALH84001 meteorite, have been studied for possible microfossils, with the initial interpretation of nanometer- scale morphological features of possible nanobacterial origin (McKay et al. 1996).

Bradley et al. (1998) discussed a potential misinterpretation of the structures found by

McKay et al. (1996) in that the same morphological features could be produced artificially through SEM preparation with metallic coating of samples. At the nanometer scale, problems arise when trying to differentiate inorganic and organic features based on morphology alone, especially when nanometer-scale biological processes, fossilization processes, and taphonomic frameworks are poorly understood (Cady et al. 2003). Thus, questions still remain about whether the observed structures are of biotic or inorganic origin and whether Mars once hosted or still hosts life (Thomas-Keprta et al. 2000,

Friedmann et al. 2001, Golden et al. 2001).

A significant question regarding exobiological research on the surface of Mars is

where to look for evidence− which materials on the planet’s surface should be regarded

as the most likely candidates to preserve fossil evidence of life, and on what scale would

the best evidence be found? Using Planet Earth as our only available guide for known

life, the most abundant forms of life are bacteria, algae, and fungi. These organisms

typically exist in solitary and colonial form, occupy nearly every habitat on Earth, are

known to leave microfossils in the rock record, and are common constituents in tufas and travertines. Given the importance of water for life, and given the apparent evidence of

groundwater on Mars, tufas and travertines may be the key geologic materials to examine

because they have the ability to preserve evidence of life from both surface and

subsurface environments. 13

Figure 5. Crossbedding seen by Mars Exploration Rover at “Burns Cliff” (NASA 2004)

Figure 6. Possible evidence of concretions on Mars from the Mars Exploration Rover

Opportunity (NASA 2004). A: Photograph (field of view approximately 3cm wide) from Opportunity of concretions present within the rock matrix at an outcrop at Stone

Mountain, Meridiani Planum, Mars. B: Mosaic image of concretions that have been found loose on the Martian soil near Stone Mountain, Meridiani Planum, Mars. 14

Purpose of This Study

The purpose of this study is to evaluate the preservation potential of lithologic and

biogenic structures within tufa and travertine deposits that range in age from Late

Cenozoic to Triassic. The implications of this study will increase knowledge of ancient

terrestrial carbonate petrography, micropaleontology and taphonomy. This study uses

Scanning Electron Microscopy (SEM), Electron Dispersive Spectroscopy (EDS), and

petrography to identify and compare preservation of lithologic and biogenic structures

within tufa and travertine deposits of Holocene, Eocene, Jurassic, and Triassic age, from

New Mexico, South Dakota, and Connecticut and Wales, UK, respectively. Tufas and

travertines can preserve microbial fossils and evidence of microbial activity within

biogenic structures, but it is unclear how well these features are preserved over geologic

time. By comparing the type, nature, abundance, and preservation of primary biogenic

features in tufa and travertine deposits through geologic time, the objective of this study

is to assess the potential of finding biogenic structures in increasingly older paleo-

groundwater deposits on Earth, with the possible application to ancient paleo-

groundwater deposits on Mars. If the result of this research is to promote the search for travertines in exobiologic studies, new avenues of research may be formed in planetary geology, the micropaleontology of travertines, and many new areas of study in exopaleontology and evolutionary biology.

CHAPTER II. TUFAS AND TRAVERTINES

Mode of Formation

Tufa and travertine outcrop in two main modes of formation as a function to the

local relief and source of precipitating water; either vertically in hanging or draping

components as part of speleothem, perched springline, or lacustrine shoreline deposits, or horizontally as laminae in any type of groundwater deposit (Julia 1983). Hancock et al.

(1999) suggest that outcrops of perched springline travertine can be precipitated in alignment with active or once active fault zones.

In hand sample, the most obvious feature of Late Cenozoic tufa and travertine is the primary pore space that may later become filled in as a product of cementation

(lithification) or diagenesis. There is a terminological difficulty distinguishing

lithification and diagenesis in tufas and travertines due to the unusual properties of their formation. Tufas and travertines precipitate at the surface or near surface, and are continuously modified by early cementation, erosion, transport and re-deposition of reworked lithoclasts, and further cementation and infill of primary pore space (Pedley

1990, Fouke et al. 2000, Julia 1983, Pedley et al. 2003). Pore space is repeatedly created,

infilled by cement or non-carbonate material, and modified by calcite-aragonite inversion

and early dissolution-replacement reactions (Fouke et al. 2000). While non-carbonate

sediments as well as biological materials are deposited or trapped and compacted within tufas and travertines, compaction associated with their deposition is limited in comparison with compaction associated with burial (Julia 1983, Pedley et al. 2003). All of these processes, often associated with diagenesis and deep burial, are in fact happening in a surficial environment. 16

Traditionally, diagenesis is viewed as rock-water interactions that occur at

significant depth. However, Ford and Pedley (1996) show that diagenesis of tufa and

travertine occurs early in the lithification process, with modification of original fabrics

due to microbiological activity and infill (replacement) by carbonate cements. The

differentiation of primary versus diagenetic fabrics is tenuous, because fabrics gradually

become less distinct and even cryptic in older deposits as a result of loss of primary

shrub-and-ray dendrites, primary porosity, and early micritic cement to later crystalline

calcite, and loss of early stromatolite fabrics to later thrombolitic fabrics (Pedley et al.

2003). One characteristic of diagenesis is non-selective dissolution of primary fabric

(Pedley et al. 2003), and therefore total loss of primary fabric to diagenetic fabric must be

considered as the possible end member feature of the tufa and travertine diagenetic

system. If a tufa or travertine has not been totally modified by diagenesis, it may be possible to recognize primary features as “ghosts” (primary textures and structures still faintly recognizable through petrographic or SEM analysis).

The paleo-groundwater deposits used in this study have all been affected by

lithification and early diagenesis. Major effects of burial diagenesis, such as non-

selective dissolution of all primary fabric can be shown to be absent, however.

Supporting studies (see later section) suggest these paleo-groundwater deposits were not

subjected to deep burial (> 1 km).

Classification and Description of Features

Terminology used in the classification and description of carbonate lithology is

based on two classification schemes: Dunham (1962), later modified by Embry and

Klovan (1971), and by Folk (1959, 1962). These classification schemes are shown in

Tables 1 and 2, respectively. Tufas and travertines nominally fall within Dunham’s

defined categories of mudstone, wackestone, packstone, or grainstone. Mudstones and

wackestones are matrix-dominated carbonates where mudstones are characterized as

being composed of at least 90% micrite or cryptocrystalline carbonate and wackestones

contain more than 10% sand sized grains. Packstones and grainstones are grain

supported carbonates; packstones contain some micrite and grainstones consist of spar

with little to no micrite present. Boundstones, like phytoherm tufa, are rocks made of

organically bound sediments consisting of organisms that act as baffles (bafflestones),

that encrust and bind (bindstones), or that build a framework (framestones). A

classification scheme limited specifically to tufa and travertine on the basis of hand

sample observation of these same characteristics has been developed by Ford and Pedley

(1996) and is given as Table 3.

On the other hand, the Folk (1959, 1962) system emphasizes that the major

components of carbonate rocks are allochems, micrite, and spar. Classifications are

termed based on the major macroscopic allochem present, typically intraclasts, ooids,

peloids, or bioclasts (described in later section). Folk's classification scheme consists of five classes of carbonates. Divisions between Class I and Class II are based on composition of matrix, micrite (aragonite needles) and spar (blocky calcite), with respective suffixes of sparite and micrite attached. Micrite and dismicrite (some spar 18

Table 1. Dunham (1962) classification of carbonates.

Source: from Dunham (1962) and Embry and Klovan (1971)

Table 2. Folk (1959) classification of limestones.

Source: based on Folk (1959, 1962). 19

content) are Class III rocks that have less than 10% carbonate allochems. Biolithites are

Class IV rocks made of laminated organics, and are almost synonymous with

boundstones. Class V rocks are not shown but consist entirely of replacement dolomite.

For subaerial hot spring travertine at Angel Terrace, Yellowstone National Park,

Wyoming, a specific facies model has been developed that identifies vent, apron and

channel, pond, proximal-slope, and distal-slope facies as the main depositional

components of a carbonate spring system (Table 4) (Fouke et al. 2000). Depositional

facies are assessed by their temperature, basic morphology, mineralogical components,

centimeter to millimeter-scale fabrics, and micron-scale fabrics. While temperature,

basic morphology, mineralogical components, centimeter to millimeter-scale fabrics, and

micron-scale fabrics can be identified and assessed in modern tufa and travertine systems,

ancient tufa and travertine deposits are typically buried and only partly exposed. In addition, the onset of time has caused any groundwater or piping system to be radically altered in comparison to when ancient waters were precipitating the deposit, which

renders the geochemical or temperature analysis of modern water useless. Ancient tufa and travertine deposits are limited to the assessment of mineralogical components,

macroscopic features, and microscopic features for their recognition and for determining

depositional facies.

Table 3. Classification of tufa and travertine based on hand sample.

Source: Ford and Pedley (1996)

Table 4. Depositional facies of Angel Terrace Springs, Mammoth Hot Springs,

Yellowstone National Park, U.S.A., according to morphology, mineralogical components, micron-scale fabrics, and centimeter to millimeter-scale fabrics.

Source: based on Fouke et al. (2000) 21

Macroscopic Features

The most commonly observed macroscopic features are allochems, and include ooids, peloids, intraclasts, aggregate grains, lithoclasts, pisoids, oncoids, and bioclasts

(Fig. 7). Ooids (Fig. 7A) are spherical grains less than 2 mm in diameter that have concentric laminae around a central nucleus of either clastic or biochemical origin. Ooids often show either a radial structure or concentric laminae in structure. Peloids (Fig. 7B) are grains composed of micrite that lack any internal structure and can be spherical to elliptical and regular to irregular in shape. Intraclasts, grain aggregates, and lithoclasts are bits of reworked material that have been re-cemented in place. Intraclasts (Fig. 7C) are typically bits of locally-derived material that may be coated by micrite. Grain aggregates (Fig. 7D) have a number of recognizable particles that are cemented together and can be botryoidal in appearance. Lithoclasts (Fig. 7E) are fragments of previously lithified sediment that may display sedimentary characteristics of their origin (bedding or laminations) and have been eroded, transported, and redeposited. Pisoids (Fig. 7F) are spherical grains larger than 2 mm in diameter that have concentric laminae around a grain or group of grains. Oncoids (Fig. 7G) are grains larger than 2 mm in diameter that have irregular or asymmetrical growth of laminae.

Macroscopic biomarkers in tufas and travertines include bioclasts and biolithites.

Bioclasts (Fig 7H) are mineralized hard parts of organisms such as shells and bones or molds and casts of original structures that are still observable. Types of bioclasts that could be present within tufas and travertines vary widely depending on the age of the deposit, the depositional setting, the path of the groundwater and surface water, and the rock age and composition through which the groundwater is flowing. Within a paludal or 22 lacustrine setting, bioclasts can potentially be composed of aquatic mollusks (gastropods and bivalves), aquatic vertebrates (reptiles, fish, amphibians, and mammals), aquatic arthropods (ostracodes and water spiders), and plants (charophytes, stems, leaves, roots).

Material brought into a paludal or lacustrine setting through surface water transport includes terrestrial mollusks (gastropods), terrestrial vertebrates (reptiles, amphibians, and mammals), terrestrial arthropods, and terrestrial plants (leaves, stems, roots).

Microscopic biomarkers in tufas and travertines are not restricted by lithological unit, but may include both biogenic features and true body fossils of microbes, which can be loosely defined to consist of single celled eukaryotes (plants, animals, fungi, and protists) and prokaryotes (archaea and true bacteria). Because body fossils may include organisms living in the spring as well as reworked fossil material from older units, the geologic age of a biomarker and the precipitating carbonate deposit may not be coincident. If reworked microfossils can be preserved in tufa and travertine, evidence for biologic activity could be preserved in more than one deposit, thereby increasing the possibility of recovering evidence of life. The age of the fossils may not need to be coincident with the age of the tufa or travertine, except only as a precursor to the precipitation of the tufa or travertine. While the probability of preserving reworked fossils is much less than primary fossils, the major restrictions for their preservation is the presence of a microfossil-bearing geologic unit for transport to the precipitating carbonate or presence of such a unit within the groundwater flow path of the spring, and appropriate physico-chemical conditions required for transport and re-deposition. 23

A. B.

C. D.

E. F.

G. H.

Figure 7. Photomicrographs of allochems present in carbonate rocks (Adams et al.

1984). A: Stained thin section showing ancient ooids with concentric laminae and radial

structure, Upper Jurassic, Cap Rhir, Morocco. B: Stained thin section showing peloidal

fabric, Upper Jurassic, from Cap Rhir, Morocco. C: Stained thin section showing

intraclasts of coated bivalve fragments from the Urswick Limestone, Lower

Carboniferous, of Towbarrow, Cumbria, England, U.K. D: Stained thin section of

aggregate grains of quartz and shell fragments from the Ouanamane Formation, Middle

Jurassic, Ait Chehrid, Western High Atlas of Morocco. E: Stained thin section of

lithoclasts from the Sutton Stone, Lower Jurassic, Ogmore-by-Sea of South Wales, U.K.

F: Pisoliths in an unstained thin section from the Wenlock Limestone, Silurian, of

Malvern Hills, England, U.K. G: Oncoids seen in a polished surface of the Llanelly

Formation, Lower Carboniferous, from Blaen Onneu, South Wales, U.K. H: Bioclasts

seen in a stained thin section of the Eyam Limestone, Lower Carboniferous, from

Ricklow Quarry, Derbyshire, England, U.K. 25

Microscopic Features

Numerous terms have recently been introduced to describe carbonate microtextures and fabrics. Some examples include calcite bubbles, calcite ice, banding, dendrites, crystal shrubs, bacterial shrubs, and ray-crystals. Because the literature is not yet standardized, there is some overlap of terminology. For example, the terms

“dendrite” and “shrub” seem synonymous, but ranges of shrubs such as bacterial shrubs and ray-crystal crusts indicate biotic factors in their production, whereas dendrites are described as abiotic features (Chafetz and Guidry 1999).

Dendrites are described as abiotically-produced single tree or woody shrub- shaped crystals composed of calcite (Jones and Renaut 1995). Dendrites commonly have multiple levels of branching and either crystallographic or non-crystallographic orientations (Fig. 8). Non-crystallographic dendrites are divided into feather dendrites and scandulitic dendrites. Within spring environments, feather dendrites have been identified from spring vents, pools, and pool-rim dams, and are made up of non- crystallographic branches up to 4 cm long and 2 cm wide and lack gravitational orientation (Jones and Renaut 1995). Scandulitic dendrites have been identified from terracettes, pool-rim dams, and orifices, and are made of en echelon stacked calcite plates that form crystals up to 2 cm long and 0.2 cm wide that are perpendicular to bedding

(Jones and Renaut 1995). While crystal shrubs are very similar in morphology and morphological range to dendrites, biotic factors are described as having a role in their production while dendrites have been reported as having no biologic associations and are a product of high disequilibrium conditions (Chafetz and Guidry 1999). 26

Bacterial shrubs are named for their morphological similarity to woody plants

(Chafetz and Folk 1984) and have been described as irregular in morphology and crystallographic to non-crystallographic in orientation (Chafetz and Guidry 1999). While

geographically widespread, no previous studies have restricted their existence to thermal-

temperature travertine systems (Chafetz and Guidry 1999). Ray-crystal crusts are

composed of coarse calcite spar and are observed as fan-shaped arrays typically an order

of magnitude larger than bacterial and crystal shrubs. Ray-crystal crusts are described as

having bands or lenses of micrite between spar layers (Chafetz and Guidry 1999). Shrubs

range from widely spaced individual formations to structures so densely packed that

individual forms cannot be distinguished, while branch orientation is dominantly oriented

perpendicular to the substrate (Chafetz and Guidry 1999). Iron, manganese, and

aragonite mineral shrubs have also been identified in travertine systems and are described

as being similar in their range of morphologies as well as their mode of formation

(Chafetz and Guidry 1999).

Microbes may be recognizable in tufas and travertines and are broadly defined to

include all microscopic eukaryotes and prokaryotes (bacteria). As with macroscopic biogenic indicators, types of microbes that could be present within tufas and travertines vary widely depending on the age of the deposit, the depositional setting, the path of the groundwater and surface water, and the rock age and composition through which the groundwater is flowing. 27

Figure 8. Diagram representing crystallographic versus non-crystallographic orientations of dendrite formation with scandulitic and feather dendrites (Jones and

Renaut 1995). Scandulitic dendrites are non-crystallographic dendrites composed of calcite plates, while feather dendrites are composed of a central stem with feather-like branches. 28

Carbonate ice sheets and bubbles have also been reported from high and low

temperature travertine systems (Fouke et al. 2000, Chafetz et al. 1991). On the wet

surfaces of various depositional facies, air bubbles can precipitate microcrystalline calcite

on their walls at the air-water interface, can be transported on the water surface by wind,

and can sink and be preserved (Fig. 9) (Fouke et al. 2000). These encrusted bubbles are

50 to 200 μm in diameter, have a smooth inner wall at the time of formation and act as nucleation sites on which blocky calcite and aragonite needles form (Chafetz et al. 1991,

Fouke et al. 2000). The process is similar with calcite ice but no air bubble is needed; a

thin sheet of calcite can be precipitated at the air-water interface can then break up and sink due to wind (Fouke et al. 2000).

Extracellular polymeric substances (EPS) are substances widely produced by

microbes (Decho 1990). Features that can be produced by EPS include protective

envelopes (bacterial sheathing) and anchors for microbe communities (biofilms and mats)

(Riding 2000). Calcification or impregnation of external sheaths of microbes by calcite is

common; fossils are readily identifiable based on their morphological similarities to the

microbes they once enveloped (Riding 2000). Biofilms are typically tens to hundreds of

micrometers in size, and may be arranged to allow for a three-dimensional array of

microbe communities that allow water to filter through for nutrients, oxygen, and waste

to be transported (Lawrence et al 1991). A mat community is on the order of millimeters

in size and allow for larger communities of microbes on the flat surface. Successions of

mineral precipitation, microbe communities, and grain trapping characteristic of mat communities can form more complex structures such as stromatolites (Riding 2000).

A. B.

Figure 9. SEM images of CaCO3 preserved air bubbles from Late Cenozoic travertine springs north of Durango, Colorado, U.S.A. (Chafetz et al. 1991). A: SEM image of the exterior of a calcite-encrusted gas bubble shows blocky calcite and aragonite needle growth. B: SEM image of the interior view of a broken calcite-encrusted gas bubble shows the bubble exterior is rough with blocky calcite and aragonite needles, but the interior wall is relatively smooth. 30

Neogene Tufas and Travertines

Examples of Neogene tufas and travertines are numerous and are typically

associated with semi-arid, subtropical, and temperate regions from Europe, Asia, Africa,

North and South America, Australia, and New Zealand (Ford and Pedley 1996). It is accepted by many that identification of older Late Cenozoic paludal and perched springline deposits has been difficult due to partial erosion of tufas, partial burial of tufa deposits, and disagreements about recognition of characteristic outcrop features (Pedley et al. 2003). Morphological studies of perched springline tufas in Italy indicate that lobe- top tufas may produce gently convex or even flat surfaces that can pond water to create extensive shallow marshes where paludal tufas may be created (Violante et al. 1994).

Other surfaces on perched springline tufas may not pond water, but instead develop

organic-rich deposits that can support terrestrial vegetation (Pedley et al. 2003).

Ancient Tufas and Travertines

The majority of tufa and travertine examples are from the Late Cenozoic. It has

been argued that geologically older carbonate spring deposits may have been missed in

the field because of oversight, or physical erosion, or because partial burial may conceal

outcrops from recognition (Ford and Pedley 1996, Evans 1999, Pedley et al. 2003).

Bioturbation may also occur where large vegetation may overgrow outcrops and destroy

them with root growth and soil formation (Pedley et al. 2003). While still thought of as

rare artifacts by many, literature describing ancient tufa and travertine deposits exists. A

few examples have been recognized and described from the Paleogene of Spain(Ordonez

and Garcia del Cura 1983) and the Badlands of South Dakota (Evans 1999). Early 31

Jurassic travertine from Connecticut has been identified and described by Mooney (1984) and Steinen et al. (1987). Triassic tufa and travertine has been identified and described from south Wales, U.K. (Leslie et al. (1992) and Scotland (Donovan 1975). Tufa and travertine possibly as old as the Precambrian have been located, although misrecognized as an alluvial fan carbonate, in the Upper Peninsula of Michigan (Elmore 1983).

CHAPTER III. GEOLOGIC BACKGROUND OF FIELD SITES

Regional Geology of New Mexico Research Site

Late Cenozoic hydrothermal travertine deposits are numerous in New Mexico.

The deposits of interest are located within the Milpas Anticline of the San Ysidro

Quadrangle, located approximately 15 km northwest of the Albuquerque metropolitan area (Fig. 10). The travertine appears as a large mound in the axis of the anticline (Fig.

11). Very little study has been done on tufas and travertines of the San Ysidro

Quadrangle; the only previously published description of these spring carbonates lists them as being deposits, deriving from modern hot springs, up to 15 m thick, on top of the

Petrified Forest Member of the Chinle Formation (Woodward and Ruetschilling 1976).

The travertines are light tan in color and thin or thick in bedding (Woodward and

Ruetschilling 1976). Observations of this outcrop during sampling show it to be a perched springline deposit over 10 m thick in places, with active springs discharging water. Travertine preservation ranges from currently precipitating to actively eroding.

While the vast majority of the travertine is light tan in color, some small seeps have produced dark iron-manganese stains and streaks beneath the active springs. The 32

travertines consist of mostly sparry banding associated with shrub-and-ray dendrites and

rod-shaped structures indicative of calcite ice formation.

Regional Geology of South Dakota Research Site

Tufa and travertine of Late Eocene age have been identified from the uppermost portions of the Chadron Formation, in the Badlands region (Fig. 12) of South Dakota

(Evans 1999). These deposits consist of tufas, travertines, and non-pedogenic

calcrete/silcrete deposits interbedded with fluvial deposits. The paleo-groundwater

deposits are the result of a regional groundwater system that originated during the

Laramide uplift of the Black Hills (Evans 1999). The Eocene tufas consist of poorly

organized, alternating layers of pisoid-intraclast wackestone, oncoids, and porous and dense micrite (Evans 1999). Charophyte bits, mudstone intraclasts, tufa lithoclasts and peloids with occasional micrite coating on clasts as well as meniscus cement are found in the tufa (Evans 1999). Travertines display typical banding associated with shrub-and-ray dendrites (Evans 1999). Photos of outcrop morphologies and internal features were taken by Evans (1999), presented as Figures 13 and 14, and indicate that these deposits are fluvial, lacustrine, and perched-springline tufas and travertines and possibly share a mix of thermal and cool source waters for their deposition.

Figure 10. Location and geologic profile of Milpas anticline.

Figure 11. Photograph of Milpas Anticline and travertine mound (arrow) in center. 34

Figure 12. Map location of Badlands, South Dakota sampling site.

Figure 13. Eocene paleo-groundwater deposits from the Chadron Formation, Badlands of

South Dakota (Evans 1999). A: Tufa barrage (t.b.) and phytoherm reef interbedded with fluvial deposits. B: A pinnacle shows tufa drapes that display differential weathering within tufa layers and vertical pipe structures (arrows) that indicate the direction of paleo-

groundwater flow (scale = 15 cm). C: An outcrop of staggered lobes of perched-

springline tufas, with rock hammer for scale (70 cm). 36

Figure 14. Internal features of Eocene tufas and travertines from the Chadron Formation,

Badlands of South Dakota (Evans 1999). A: Alternating dense and porous layers in tufa

(pencil 15cm). B: Asymmetric growth in a pisolite (scale bar = 1mm). C: Mudstone intraclast (scale bar = 1mm). D: Tufa lithoclast conglomerate with meniscus cement

(scale bar = 1mm). E: Asymmetric oncoid (scale bar = 1mm). F: Coated charophyte stems (scale bar = 50mm). G: Polished section of travertine banding associated with shrub-and-ray dendrites (scale in cm). H: Shrub structure in a travertine (scale bar =

100μm). I: Ray crystal morphologies in a travertine (scale bar = 100μm).

Connecticut Research Site Regional Geology

Early Jurassic travertine deposits from the Shuttle Meadow Formation at Coe’s

Quarry in North Branford, Connecticut (Figure 15) were studied by Steinen et al. (1987).

The Coe’s Quarry carbonate consists of cellular tufa, algal/bacterial tufa, micrite, and banded travertine. The outcrop has subsequently been destroyed by human development; originally it was laterally discontinuous, approximately 5.5m thick, and had a lateral extent of from 250 to 400m (Krynine 1950, Mikami and Digman 1957). The tufas and travertines are primarily calcite, but contain impurities such as quartz, feldspar, and mica in minor amounts. Lithification of the tufas and travertines resulted in formation of chalcedony cements, and feldspar and quartz overgrowths. Partial diagenesis has occurred to a lesser extent in the formation, resulting in alteration of some of the calcite to ferroan dolomite. The carbonate ranges from pale yellow-tan to dark orange-brown or even black on a fresh surface, but weathers to a uniform pale yellowish brown. Access to the quarry is now impossible due to development for residential use.

Figure 15. Geographic position of sampling site in Connecticut (A) and Geologic map of CT sampling site (B).

Regional Geology of South Wales (UK) Research Site

Travertines of Late Triassic age have been identified from interbedded carbonates

between the Triassic Mercia Mudstone Group and the Carboniferous limestone at Sully

Island and Dinas Powys in South Wales, UK (Fig. 16) (Leslie et al. 1992). These marginal carbonates measure over 100m in thickness and consist of dolomites and evaporites overlain by calcretes, travertines, and dolomite interbedded between the

Mercia Mudstone Group (Fig. 16). The Late Triassic travertine deposits are up to 1 m in thickness and 5-6 m in diameter in size, are interbedded with laminated and stromatolitic limestones (?), and are locally patchy within a steep sided paleovalley (Leslie et al.

1992). Travertines consist of alternating layers of pisoid-intraclast wackestone, ooids,

oncoids, and porous and dense micrite flowstone with occasional calcite ice (Leslie et al.

1992). Ostracods, Carboniferous limestone intraclasts, and peloids with occasional micrite coating on clasts as well as meniscus cement are found in the travertine (Leslie et al. 1992). Travertines also display typical banding associated with shrub-and-ray dendrites (Leslie et al. 1992). Photos of internal features were taken by Leslie et al.

(1992) and are presented as Figure 17. These deposits were interpreted by Leslie et al.

(1992) as perched-springline and lacustrine travertines, and possibly share a mix of thermal and cool source waters for their deposition.

Figure 16. Geographic position of (A) Sampling sites and at Sully Island and Dinas

Powys in South Wales, UK, and (B) Stratigraphic position of marginal carbonate deposits

(Leslie et al. 1992). 41

A. B.

C. D.

Figure 17. Internal features of Upper Triassic travertines in marginal carbonates underlying the Mercia Mudstone Group from Sully Island and Dinas Powys in South

Wales, UK (Leslie et al. 1992). A: Photomicrograph of travertine banding associated with shrub-and-ray dendrites (scale bar = 0.1mm). B: Interlaminated calcite and silty dolomitic sediment (scale bar = 0.5mm). C: Isopachous micrite rims on peloids and as laminae, now irregular rims and convoluted laminae (scale bar = 0.5mm). D: Calcite ice in clotted micrite, now microspar (scale bar = 0.1mm).

CHAPTER IV. METHODOLOGY

Sample Collection

Tufa and travertine samples have been gathered from their identified locations or acquired from previous collectors. Approximately 45 kg of Holocene tufas and travertines from New Mexico were randomly collected over the surface of the actively precipitating spring, over 10 m along the surface downslope from the spring, and 5 m vertically through a fissure at a non-precipitating fissure 15 m from the active spring.

Chips of Late Eocene tufas and travertines from South Dakota were donated by Dr.

Evans, most of which were dense travertine samples. Chips of Early Jurassic tufas and travertines from Connecticut have been provided by Dr. Randolph Steinen, emeritus professor of geology at the University of Connecticut. Chips of Late Triassic travertine were randomly collected from outcrop in south Wales by Dr. Evans for this study.

Sample Treatment

Samples have been cleaned with distilled water and acid etched with dilute (10%) hydrochloric acid to remove surficial organic contamination. Thin sections, polished slabs, and x-ray diffraction samples have been made (by me or others). Thin section samples have been tested for dolomitization and magnesium content following widely accepted testing methods established by Warne (1962). Because of the low concentration of minerals other than calcite, dolomite, silica, and helvite, X-ray diffraction (XRD) was unable to obtain the trace mineral content of travertine samples (Appendix B). Polished slabs have been created to generate a non-weathered surface for sample description. 43

Samples were prepared for Scanning Electron Microscope (SEM) analysis by

chiseling approximately 1 cm3 from a clean sample, and sputtercoating with a gold-

palladium alloy or carbon coat. Initially, tests were made of the effects of acid etching in

dilute (10%) HCl acid to remove matrix and more clearly show fossils or structures. The samples that underwent etching were dried at 50ºC for 24 hours before coating. It was

found that acid etching resulted in significant destruction of SEM features at the 50 μm

scale, and an inability to identify features that were smaller than 25 μm. Because this

procedure proved to destroy microstructures, acid etching of SEM samples was

discontinued after initial trials. Otherwise, SEM analyses were conducted according to

BGSU procedures for SEM operation (Appendix A).

Contamination

A control group of carbonate chips were created to address the possibility of

contamination of clean samples (Fig. 18). The contaminated test samples were soiled by

a combination of airborne dust, by rubbing or rolling on various dirty surfaces, then

sputtercoated for analysis. The results showed that these contaminated samples contained

fibers or hairs at the 25 to 50 μm scale, as well as individual dust particles at a scale of 2

to 10 μm. Features found were distinctively disaggregated and displayed no similarities

to microstructures of interest to this study. This contamination is specific to

contamination during laboratory preparation of samples, and does not include geologic

contamination of samples. One example of geologic contamination would be a

secondary incorporation of biomineralization or fossils from biologic activity that has

taken place after all lithification or diagenesis has taken place. Microbes that are 44

autolithotrophs (living on and within lithified rock) would be the most likely candidate

for geologic contamination. The presence of autolithotrophs in samples is problematic

for ancient deposits; their differentiation from primary biogenic features is discussed

within “SEM Analysis” (below).

SEM Analysis

SEM images of samples have been interpreted by comparison with

paleontological and microscopy databases, atlases, previous publications on

micropaleontology and SEM work, as well as personal communications with Dr. Jeremy

Young of the National History Museum of London, Dr. David Watkins of the University

of Nebraska, Dr. Penelope Boston of New Mexico Tech, Dr. James Evans of Bowling

Green State University, Dr. Margaret Yacobucci of Bowling Green State University, and

Dr. Don Steinker of Bowling Green State University for possible fossil and structure identification. Identifiable fossils have been cross-checked with the interpreted age of the

spring deposit to see if any major discrepancy exists that would suggest secondary

incorporation. Structures for each sampling site have been described in detail within the

corresponding results section below, and a compilation table of all structures seen for

each sampling site has been created to evaluate preservation potential between sampling

sites.

Figure 18. SEM images of controlled contaminated samples. A: SEM image of disaggregated dust and debris that composes most of the control samples ranges within a

2 to 10 μm scale (Scale bar = 20 μm). B: SEM image of a hair or fiber is readily

identifiable at the 50 μm scale (Scale bar = 20 μm).

CHAPTER V. RESULTS

Neogene tufa and travertine from San Ysidro, New Mexico

General Description

Outcrops of travertine within the Milpas Anticline of the San Ysidro Quadrangle

in New Mexico are massive, perched-springline mounds and lobes (Fig. 11). Travertine

preservation ranges from currently precipitating to actively eroding. While the vast

majority of the tufas and travertines are light tan in color, active seeps commonly are

discolored orange or black due to iron-manganese stains and streaks. In hand specimens,

the deposits consist of buff to light tan layers of pisoid-lithoclast-grain aggregate

wackestones and packstones, arenaceous packstones, and bindstones and framestones

(biolithite), alternating with layers of porous and dense mudstone (micrite).

EDS analyses of Au/Pd sputtercoated samples indicate varying amounts of

calcium (Ca), iron (Fe), and manganese (Mn) (Fig. 19). Au/Pd sputtercoat masks the

presence of silica (Si) in EDS analysis, but the presence of Si is inferred due to detrital

quartz grains found within grain aggregates during thin section analysis. The calcium is

CaCO3 as both calcite and aragonite, based on thin section and SEM observations of

micrite, rhombohedral calcite crystals, and aragonite shrubs. XRD analysis confirms the presence, in at least 10% concentration, of aragonite and calcite (Table 5).

In thin section, features present include layers of feather dendrites (shrub

structures), pisoids, ooids, grain aggregates, intraclasts, lithoclasts, calcite ice, and clotted micrite. Deposits primarily display alternating layers of: (1) grains, (2) feather dendrites

(shrub-and-ray crystals), and (3) clotted micrite. In SEM analysis, features present include bacterial rods, EPS in the form of calcified bacterial sheathings and biofilms that 47 coat crystals, dendrites (aragonite shrub structures), and ooids.

Macroscopic Features

Pisoids and Ooids. Seen in Figures 17 and 18, pisoids and ooids are found as spherical to elongate grains. The ooids are between 100 μm – 900 μm in diameter and the pisoids are greater than 1 mm in diameter. Both pisoids and ooids commonly display a cortex (isopachous aragonite cement) approximately 50 μm thick around a nucleus.

The nuclei can consist of grain aggregates, tufa lithoclasts, detrital quartz grains, or micrite intraclasts (Fig. 20). In SEM analysis, ooids are spherical, approximately 100 to

400 μm in diameter, and display radial crystal growth around a replaced nucleus of blocky calcite (Fig. 21). While the ooids are similar in exterior appearance and dimensions to calcified air bubbles, the presence of internal structure has never been documented in calcified air bubbles.

Coated Grains and Grain Aggregates. In Figure 20, some pisoid nuclei are coated grains or grain aggregates. Coated grains consist mostly of angular to sub-rounded detrital quartz grains that range from approximately from 50 μm to > 100 μm across the long axis of the grain. Grain aggregates consist mostly of several detrital quartz grains that have been coated in micrite. Some larger grain aggregates are composed of combinations of detrital quartz grains and tufa lithoclasts in micrite.

Lithoclasts and Intraclasts. Tufa lithoclasts consist of well rounded clasts 100 μm to > 0.6 mm in diameter that have later been incorporated as the nucleus of pisolites and ooids (Fig. 20). Tufa lithoclasts can be recognized by internal features of the clasts, such as banding or clotted micrite. Intraclasts consist of homogenous micrite clasts 100 to 300 48

μm in diameter that occasionally include a few detrital quartz grains.

Biogenic Lamination. Figure 22 shows that tufas and travertines are buff to light green in appearance where precipitation is taking place because photosynthetic algae and bacteria are engulfed by aragonite or calcite cement in the deposits. Evidence of photosynthetic algae and bacteria is also visible in thin section by their chlorophyll content. These photosynthetic microbes are trapped within irregular (non- crystallographic) dendrites as framestone and in between laminations as boundstone (Fig.

23). Irregularities in these laminations represent the following sequence of events: (1) a time of non-precipitation and/or corrosion (dissolution of calcite), (2) algal and bacterial recolonization of the surface and creation of a new micro-topography, (3) calcite precipitation on the micro-topographical surface when conditions favored it, (4) the growth of calcite cement engulfing the algal and bacterial colonies into the travertine, and

(5) a repeated episode of non-precipitation or dissolution. Lamination immediately above algal and bacterial colonies appear to show greater iron staining than other layers, possibly from incorporated desert varnish (high Fe and Mn concentrations), which is airborne dust trapped in algae and bacteria. This may suggest periodic episodes of dryness.

Microscopic Features

Dendrites and Dendrite Lamination (Shrubs). Dendrites are found in

crystallographic and non-crystallographic forms; however, most banding is produced by

crystallographic dendrites (Figs. 24 and 25). Individual shrub structures can be easily

viewed when within a micrite matrix, but typically the shrubs are so densely packed 49

together that individual forms cannot be distinguished (Fig. 24). Shrubs vary in morphology from irregular shapes to well-developed branching forms (i.e., feather

dendrites) where the orientation is dominantly perpendicular to bedding. Aragonite

shrubs are found as clusters of dendrites forming a sheet overlying micrite laminae. The

shrubs vary in length from 1 to 10 μm and in thickness from approximately 700 nm to 1

μm thick (Fig. 25).

Clotted Micrite. Seen in Figure 26, clotted micrite is only a small component of

thin sections and is typically found with non-banded dendrite accumulations. Individual

clots are iron stained and range in size from approximately 80 μm to > 150 μm.

Calcite Ice and Calcified Air Bubbles. Calcite ice is rare but typically found

within micritic portions of thin sections (Fig. 27). Calcite ice are sheets that appear as

rods in thin section. The rods are 50 to 100 μm thick and 100 to > 600 μm long, and are

commonly coated by micrite. The darkness of the calcite ice (in comparison to the

surrounding micrite) may indicate that the rods and surrounding micrite coating are

composed of denser calcite than the surrounding matrix. Alternatively, the darker

coloration of the calcite ice may be due to airborne dust that was trapped on the ice surfaces during subaerial exposure that took place during its formation.

Biogenic Structures. Biogenic features include bacterial rods, EPS sheathing, and

EPS biofilm strands (Figs. 28-31). Bacterial trichomes are approximately 1 μm in

diameter by 10 μm in length, which is more than an order of magnitude smaller than calcite ice rods. These trichomes can be found encased by calcified EPS sheathing which is seen to be occasionally encrusted by 1 to 2 μm diameter microspheres (Fig. 28). Some

calcified EPS sheathing is found as hollow tubes that presumably housed bacterial rods 50 that are no longer present (Fig. 28B). Although composed of calcite, trichomes, sheaths, and encrusting microspheres seen here are nearly identical in morphology to siliceous features identified in some silica-precipitating modern hot springs (Jones et al. 1997).

Calcified EPS biofilm is found in the form of strands connecting blocky calcite grains.

EPS biofilm varies in width from 1 to 2 μm and in length from 1 to over 100 μm (Figs. 30 and 31). These features are identical in morphology to features described as mucus meniscus bridges by Folk and Lynch (2001). 51

Figure 19. EDS analysis of Au/Pd sputtercoated New Mexico samples. A: EDS shows a high concentration of Ca with minor amounts of Mn. B: EDS shows a high concentration of Fe with significant amounts of Ca.

Table 5. XRD analysis New Mexico sample.

Compound Name Displacement [°2Th.] Chemical Formula

Calcite, syn -0.080 Ca ( C O3 ) Aragonite -0.150 Ca C O3 Calcite -0.046 Ca C O3 53

Figure 20. Photomicrograph of pisolites (P) with grain aggregates (A), tufa lithoclasts

(T), detrital quartz grains (Q), and micrite intraclasts (M) as pisoid nuclei in tufa and

travertine from San Ysidro Quadrangle, New Mexico (Scale bar = 0.5 mm).

Figure 21. SEM image of ooids in a travertine from San Ysidro Quadrangle, New

Mexico. Ooids are approximately 100 to 400 μm in diameter. The left ooid (outlined)

displays a cortex (C) of isopachous aragonite approximately 150 μm thick around nucleus

(N). The nucleus was subsequently dissolved and replaced by calcite spar (Scale bar =

100 μm). 54

Figure 22. Photograph of a hand specimen showing biogenic lamination due to layers

(L) and clumps (C) of bright green photosynthetic algae and bacteria alternating with

laminae of gray micrite (M). The green color is due to chlorophyll still present within the travertine. The photosynthetic algae and bacteria also trapped and bound detrital grains such as quartz, tufa lithoclasts, and intraclasts. Specimen from San Ysidro Quadrangle,

New Mexico (Scale bar in cm).

Figure 23. Photomicrograph of repetitive series of laminations and non-crystallographic shrub banding in travertine from San Ysidro Quadrangle, New Mexico. A repetition of cement, a bounding surface, algal growth, and biogenic lamination is seen to repeat at least three times in this travertine sample. Micrite cement is followed by a bounding surface. Bounding surfaces (B) are found above cement layers repetitively after a sequence of algal growth, biogenic lamination and cement. These surfaces may represent periods of non-precipitation or corrosion leading up to microbe colonization, and the darkness of these layers may be dust or organics trapped. Above bounding surfaces, clumps of trapped and bound photosynthetic algae and bacteria are easily recognizable by the still-present chlorophyll (C). Recolonization by algal and bacterial colonies creates a new topography for biogenic laminations and cement (Scale bar = 0.5 mm).

Figure 24. Photomicrographs showing cross sectional views of crystallographic shrub banding in travertine from San Ysidro Quadrangle, New Mexico. A: Outlined crystallographic shrubs (C) are oriented perpendicular to laminae (L), and are accentuated by iron staining. (Scale bar = 0.5 mm).

A. B.

Figure 25. SEM image showing a bedding plane view of aragonite shrub structures in travertines from San Ysidro Quadrangle, New Mexico. A: Shrubs display growth perpendicular to the bedding surface (B) and are found so densely packed (arrow) that individual forms cannot be distinguished (Scale bar = 50 μm). B: Close-up of individual shrubs (arrow) that are approximately 1 to 10 μm in length and are ≤1 μm in width (Scale bar = 10 μm).

Figure 26. Photomicrograph of clotted micritic in tufa and travertine from San Ysidro

Quadrangle, New Mexico (Scale bar = 0.5 mm). 58

Figure 27. Photomicrographs of clotted micrite (CM), dendrites (D), and calcite ice (CI).

A: Calcite ice (sheet like) appears in cross sectional view as rods coated by meniscus cement (M). B: Calcite ice appears within areas of clotted micrite with occasional dendrites. Sample from San Ysidro Quadrangle, New Mexico (Scale bar = 0.5 mm).

A. B.

Figure 28. SEM images of calcified bacterial trichomes and sheathing in travertines from San Ysidro Quadrangle, New Mexico. A: Trichomes (T) are 1 μm in diameter and

10 μm in length and can be encased by EPS sheathing (scale bar = 5 μm). B: Hollow sheaths (arrow) have been permineralized or replaced by calcite (scale bar = 2 μm).

A. B.

Figure 29. SEM image of bacterial trichomes (T), microspheres (M), and sheathing (S)

in tufas and travertines from San Ysidro Quadrangle, New Mexico. A: Microspheres encrust the sheaths around bacterial rods that are no longer present (Scale bar = 3 μm).

B: Magnified image of microspheres approximately 1 to 2 μm in diameter and composed

of blocky calcite or aragonite shrubs (Scale bar = 1 μm). 60

Figure 30. SEM image of calcified EPS filaments (arrows) coating blocky calcite grains

in tufas and travertines from San Ysidro Quadrangle, New Mexico (Scale bar = 5 μm).

Figure 31. SEM image of calcified EPS filament (arrows) in tufas and travertines from

San Ysidro Quadrangle, New Mexico (Scale bar = 20 μm).

Paleogene tufa and travertine from the Badlands of South Dakota

General Description

Most of the tufa deposits within the Badlands of South Dakota consist of

lacustrine tufas (pond deposits), fluvial tufas, and distal perched springline tufas (lobes).

Travertines compose small resurgences, fluvial stromatolites, and fluvial barrages. Tufa

deposits are poorly organized layers of pisoid-intraclast wackestone and packstone alternating with layers of porous and dense micrite. The porous layers are created by differential weathering of the intraclasts, pisolites, oncoids, and micrite (Evans 1999).

Travertine deposits are shrub-and-ray crystal laminae alternating with layers of porous

and dense micrite. In hand specimens, tufas and travertines are buff to light tan in color

and consist of mudstones (micrite), pisoid-lithoclast-intraclast wackestones, arenaceous

packstones, and bindstones (biolithites).

EDS analysis of carbon coated samples indicates varying amounts of Ca and Si

(Fig. 32). Calcium is in the form of CaCO3 as calcite, as seen in thin section and SEM as

micrite and rhombohedral calcite crystals. Silica present is in the form of chalcedony

rims found around grains or pore-filling silica within the micrite matrix (Evans 1999).

XRD analysis confirms the presence of SiO2 and CaCO3 in concentrations of at least 10%

(Table 6).

Features present in thin section include clotted micrite, pisolites, intraclasts,

lithoclasts, ooids, dendrite-produced banding, and silica overgrowths. Features found in

SEM analysis include coccolithophores, micro-colonial fungal sacs, EPS biofilm,

calcified air bubbles, and siliceous rosettes.

Macroscopic Features

Pisoids and Ooids. Pisoids and ooids are found as spherical to elongate grains.

Ooids range in size from approximately 200 μm to 250 μm in diameter (Fig. 33). Pisoids

range in size from 2 mm to 1 cm in diameter (Fig. 34) (Evans 1999). The nuclei of

pisoids and ooids are typically composed of coated lithoclasts or detrital quartz grains

that display a cortex of isopachous cement approximately 150 μm thick (Fig. 33). Ooids are more uniform in size, and display both radial crystal orientation and a cortex of isopachous cement approximately 80 μm thick (Fig. 34).

Lithoclasts and Intraclasts. Intraclasts are locally common. They are grains

approximately 1 to 2 mm in diameter that appear irregular to slightly flattened in shape,

and are composed of mudstone (micrite) with occasional detrital quartz grains (Evans

1999). Lithoclasts within the fluvial tufa are composed of angular to subangular clasts of

reworked tufa, and range from approximately 250 μm to 1 mm in diameter (Evans 1999).

Microscopic Features

Dendrites and Dendritic Lamination (Shrubs). Non-crystallographic dendrites

(shrub structures) have been found to vary in morphology from irregular to branching

(feather dendrites), with growth perpendicular to bedding. In some samples, dendrites

have been partially converted to clotted micrite, but retain most of their structure (Fig.

35). Like New Mexico samples, individual shrubs have been identified within micrite

matrix, but shrubs are typically found so densely packed within banding that individual forms cannot be distinguished.

Clotted Micrite. Clotted micrite is common in all thin sections. Individual clots 63 are not iron-stained like samples from New Mexico, but appear as dark tan due to the denseness in comparison to the surrounding porous micrite. Individual clots range in size from approximately 80 μm to > 150 μm (Fig. 36).

Chalcedony Rims and Rosettes. Chalcedony rosettes, isopachous fibrous rims, and blocky silica pore-filling cement occur in some samples. The isopachous rims average 50 μm thick. The pore-filling cements are found within 250 μm to > 1 mm pores or fracture fills within micrite (Fig. 37). In SEM analysis, the siliceous rosettes appear as matted to hemispherical clusters on siliceous rim coatings or as isolated spherical clusters (Fig. 38). Individual blades on the rosettes measure approximately 0.5

μm at maximum thickness and 1.5 μm in length. EDS analysis of these rosettes confirms they are composed of chalcedony (Fig. 32B). The morphology and Si composition of the rosettes are consistent with paracrystalline opal-CT in bladed lepisphere form, as described by Lynne and Campbell (2004).

Calcite Ice and Calcified Air Bubbles. Micritic to blocky calcite hemispherical structures between 15 and 80 μm in diameter are found in some samples (Fig. 39). Some of these structures display a partial transition from a smooth surface to blocky calcite.

Some calcite structures have been cleaved to display a hollow cross section with a shell of blocky calcite spar, while several appear to be composed totally of micrite with no internal structure. Chafetz et al. (1991) describe the inner walls of calcite bubbles as smooth and the outer wall of the bubble as a nucleation site for aragonite needles and blocky calcite, which implies that the outer walls of calcite bubbles are much rougher in texture than the inner walls. In this case, the spheres’ smoothness suggests the structures seen here are internal molds of calcified bubbles, rather than the bubbles themselves. 64

Biogenic Features. Some smooth calcite bubbles display evenly spaced “bumps”

or depressions on their surface (Fig. 40). These “bumps” are approximately 1 μm in diameter and appear as microspheres and dented microspheres, which is over an order of magnitude smaller than the calcite bubbles themselves. The occasional appearance of these features on the surface of calcite bubbles and their difference in size in comparison to calcite bubbles suggests that they are not additional calcite bubbles. Figure 40 shows a microsphere that appears to have ruptured, which suggests that the microspheres are calcified remains of some colonial organism occupying the surface of the bubble.

Micro-colonial fungal sacs are ellipsoid in shape, approximately 10 μm in wide by

15 μm in long (Fig. 41). The fungal sacs have been preserved within a pocket of EPS

biofilm and are distributed within the pocket. Sacs appear as flattened, broken open to

reveal a hollow center, or as wholly undisturbed. Near the broken sac is a segmented

structure approximately 5 μm in length by 3 μm in width (Fig. 42B). The proximity of

the segmented structure to the broken sac is suggestive that the segmented structure

origin came from within the broken sac. This structure is nearly one third the total size of

the structure to the top of the EPS pocket but is nearly identical in morphology. The

strong resemblance between the two structures and proximity to the broken sac suggests

that it may represent an early colony of microfungi (Boston, personal comm.).

Coccoliths are also found within these tufas (Fig. 42). They are 3 μm diameter

muroliths, meaning that they are formed of crystal-units of complex shape and display

elevated rims without well-developed shields (Young 1992). The strong clockwise

imbrication, or tilting of the calcite grains, seen in SEM are features characteristic of

Zeugrhabdotus sp., which are significantly different in size and morphology from the few 65 previously known non-marine coccoliths (Young, personal comm.). 66

Figure 32. EDS analysis of carbon-coated samples of tufas and travertines from the

Badlands of South Dakota. A: EDS bulk measurement shows high concentrations of Si

and Ca. B: EDS measurement of bladed spheres shows a high concentration of Si with minor amounts of Ca.

Table 6. XRD analysis of South Dakota sample.

Compound Name Displacement [°2Th.] Chemical Formula

Calcite -0.058 Ca ( C O3 ) Quartz low, syn -0.067 Si O2 Calcite -0.035 Ca C O3 67

Figure 33. Photomicrograph of a pisolite showing nucleus (N) (ferruginous micrite with

detrital quartz grains) and cortex (C) (micrite). Sample from the Badlands of South

Dakota (Scale bar = 0.5 mm).

Figure 34. Photomicrograph of ooids (O) with isopachous micrite rims. Dissolution created secondary porosity that was subsequently lined by isopachous chalcedony (IC).

Thin section is from a tufa in the Badlands of South Dakota (Scale bar = 0.5 mm).

Figure 35. Photomicrograph of non-crystallographic feather dendrites (D and outlined) in a travertine sample from the Badlands of South Dakota. Shrubs are oriented perpendicular to laminae and have been replaced in part by micrite (M) and calcite spar

(CS) (Scale bar = 0.5 mm).

Figure 36. Photomicrograph of clotted micrite in a travertine from the Badlands of

South Dakota (Scale bar = 0.5 mm). 69

Figure 37. Photomicrograph of isopachous chalcedony rim (CR) with pore-filling chalcedony (PFC) surrounded by micritic matrix with ooids (O) and coated grains (CG).

Sample from the Badlands of South Dakota (Scale bar = 0.5 mm).

A. B.

Figure 38. SEM images of chalcedony rim with opal-CT bladed lepispheres in tufas and travertines located in the Badlands of South Dakota. A: Chalcedony rim (CR) is approximately 4 μm thick within the micrite pore and is internally coated with opal-CT blades (CT) (Scale bar = 10 μm). B: Individual bladed lepispheres (outlined) are approximately 3 to 8 μm in diameter (Scale bar = 10 μm). 70

A. B.

C. D.

Figure 39. SEM images of calcified air bubbles in travertine samples from the Badlands of South Dakota. A: Calcified bubbles (arrow) are composed mostly of blocky calcite and range from 10 to 20 μm in diameter (Scale bar = 5 μm). B: Calcified bubbles shown here are of a 225 μm in diameter bubble (arrow) that is composed partially of micrite and partially of blocky calcite. The cross section of a calcified bubble (outlined) can be seen

by its curvature (Scale bar = 50 μm). C: Magnified image of the cross section of a

calcified bubble (arrows) show the thickness of the bubble wall to be approximately 10

μm (Scale bar = 20 μm). D: Two bubbles have been preserved that share a bubble wall

(arrow) (Scale bar = 10 μm).

A. B.

Figure 40. SEM images of calcified air bubbles in travertine samples from the Badlands of South Dakota. A: Evenly spaced “bumps” or depressions on the surface of these calcified air bubbles may represent calcified remains of some colony of organisms that occupied the surface of the bubble (Scale bar = 10 μm). B: These “bumps” are approximately 1 to 2 μm in diameter, appear as microspheres and dented microspheres, and have left depressions on the surface of the bubble that can be seen in their absence

(Scale bar = 10 μm).

A. B.

Figure 41. SEM images of microcolonial fungal sacs in tufa samples from the Badlands of South Dakota. A: Fungal sacs appear within a 30 μm EPS biofilm pocket (BP) and are distributed to the top and bottom (Scale bar = 23.1 μm). B: Magnified image of individual fungal sacs show flattening (top), and rupturing (bottom) of sacs along with a small microcolony (arrow). Individual large fungal sacs are elliptical, approximately 10

μm in width and 15 μm in length (Scale bar = 7.5 μm).

A. B.

Figure 42. SEM images (A and B) and diagram (C) of coccoliths in tufas and travertines located in the Badlands of South Dakota. A: Individual coccoliths are approximately

3μm in diameter, are formed of crystal-units of complex shape, display elevated rims

without well-developed shields, and have strong clockwise imbrication characteristic of

Zeugrhabdotus sp. B: Coccoliths have been deposited in abundance and are broken and

poorly preserved. C: Diagram showing 3-D view and cross-section of coccoliths with

murolith shape (modified from Young, 2005).

Early Jurassic tufa and travertine of the Hartford Basin, Connecticut

General Description

Steinen et al. (1987) reported that tufa and travertine deposits in the Hartford

Basin of Connecticut appear as laminated deposits that range from pale yellow-tan to

dark brown or gray on a fresh surface, but typically weather to a mostly gray or pale

yellowish brown. The tufas and travertines are primarily calcite, with impurities such as

quartz and, to a lesser extent, mica. In hand specimen, the tufas and travertines are light

tan/gray to dark gray in color and consist of mudstone (micrite), arenaceous packstone,

and bindstone (biolithite).

EDS analysis of Au/Pd sputtercoated and carbon-coated samples indicates

varying amounts of Ca, Fe, and Mn (Fig. 40). Au/Pd sputtercoat hides the presence of

silica in EDS analysis, but silica was found in carbon-coated samples as detrital quartz

grains. However, EDS analysis of carbon-coated samples without quartz grains did not

detect Si, meaning that Si is not found as cement within the samples. Steinen et al.

(1987) stated that partial dolomitization had occurred within these deposits, however, Mg

was not detected during EDS analysis of any Au/Pd sputtercoated or carbon-coated

samples. Calcium identified in the travertine is in the form of CaCO3 as calcite, seen in

thin section and SEM as micrite and rhombohedral calcite crystals, however no aragonite shrubs have been found. XRD analysis confirms the presence of calcite, quartz, and helvite (Mn8Be6Si6O24S2) in concentrations of at least 10% (Table 7). Helvite is a

mineral associated with hydrothermal settings and contact metamorphism, and its

presence confirms the presence of thermal waters.

In thin section, features present include clotted micrite, pisolites, intraclasts, 75

ooids, calcite ice, and shrub (dendrite) produced banding. In SEM analysis, features

present include calcified microcolonial algae and bacteria, EPS in the form of biofilm that

coats crystals and strands between crystals, calcified air bubbles, ooids, and 1 to 2 μm Fe

or Mn oxide star structures.

Macroscopic Features

Pisoids and Ooids. Pisoids and ooids are found as spherical to elongate grains.

Pisoids are approximately 1 to >2 mm in diameter, and display a 150 μm isopachous rim

around a micrite nucleus (Fig. 41). Ooids found are approximately 0.06 mm (60 μm) in

diameter, uniform in size, and display both radial and concentric laminae (Fig. 42). In

SEM analysis, cross-sections of ooids are 60 μm spheres that display a 30 μm isopachous

rim around a 30 μm diameter nucleus of blocky calcite (Fig. 43).

Lithoclasts and Intraclasts. Intraclasts consist of micrite and are sub-angular 100

μm to > 3 mm clasts that are found accompanied by detrital quartz grains (Fig. 44). Tufa

lithoclasts are a few cm in size; angular clasts 3-10 cm in length have been found (Fig.

45).

Microscopic Features

Dendrites and Dendrite Lamination (Shrubs). Non-crystallographic (feather)

dendrites form laminae that have been partially converted to clotted micrite but still retain

most of their structure (Fig. 46). Individual shrubs can be identified within micrite

matrix, but shrubs are typically found so densely packed within banding that individual forms cannot be distinguished. Dendrites vary in morphology from irregular to 76

branching, which are oriented perpendicularly to bedding.

Clotted Micrite. Clotted micrite is abundant in all thin sections (Fig. 47).

Individual clots are diffuse and range from 200 to > 500 μm. In Figure 48, it is possible to

identify dendrite lamination features that have been partially to mostly converted to

clotted micrite. Identification of these ghost features is restricted to what appear to be

irregular dendrite laminations, but still retain structure seen by the faint images of the

laminations.

Calcite Ice and Calcified Air Bubbles. Calcified air bubbles appear as blocky

calcite hemispherical structures between 25 and 80 μm in diameter (Fig. 49). These

calcified air bubbles do not display a smooth micritic surface (or even a partial transition

from smooth micrite to blocky calcite) as seen in younger samples. Calcite ice appears as

micrite coated rods that are 50 μm thick and 100 to > 600 μm long. Calcite ice is

typically isolated to within the micritic portions of thin sections.

Biogenic Structures. Microcolonial spherical organisms have been found on

pitted micritic surfaces and are found within micrite, suggesting that the micrite has lithified around the microcolonies (Fig. 51). Individual spheres are approximately 1 to 2

μm in diameter and drape over existing grains and matrix, creating a botryoidal surface.

Sub-micron scale morphological detail is seen in hemispherical cracking on the surface of

these microspheres, which suggests that these microspheres are not the hollow Opal-A

spheres described by Lynne and Campbell (2004).

Calcified EPS biofilm (Fig. 52) is found in the form of strands between calcite

grains and as strands connecting blocky calcite grains. Individual strands vary in width

and length from 1 to 2 μm and from 1 to over 100 μm, respectively. EDS analysis of EPS 77 biofilm strands indicate the presence of Fe and Mn (Fig. 40B).

Seen as Figure 53, star structures are approximately 1 μm in diameter and are found in clusters. EDS analysis strongly indicates the presence of Fe and Mn in comparison to the surrounding matrix, suggesting that their composition is Fe, Mn, or a partial combination of the two (Fig. 40B). Nearly identical star structures with Fe-Mn contents have been reported as either putative bacteria or minerals derived from bacterial precipitation within Lechuguilla Cave in Carlsbad Caverns, New Mexico (Boston, 2004).

Figure 43. EDS analysis of Au/Pd sputtercoated (A and B) and carbon-coated (C)

Connecticut samples. A: EDS shows a high concentration of Ca and Fe. B: EDS shows a high concentration of Ca with Mn and Fe. C: EDS shows a high concentration of Ca with minor amounts of Si due to detrital quartz grains. 79

Table 7. XRD analysis of Connecticut sample.

Compound Name Displacement [°2Th.] Chemical Formula

Calcite -0.001 Ca ( C O3 ) Helvite 0.236 Mn8 Be6 Si6 O24 S2 Calcite 0.015 Ca C O3 Quartz 0.038 Si O2 80

Figure 44. Photomicrograph of a pisolite outlined to show the nucleus (N) and cortex

(C). Travertine sample from the Hartford Basin of Connecticut (Scale bar = 0.5 mm).

Figure 45. Photomicrograph of ooids (arrow) with isopachous micrite rims.

Surrounding area has been filled by calcite spar. Travertine sample from the Hartford

Basin of Connecticut (Scale bar = 0.1 mm).

Figure 46. SEM image of ooids in travertine samples from the Hartford Basin of

Connecticut. Spheres are approximately 60 μm in diameter. The bottom ooid (outlined) displays an isopachous cortex (C) approximately 25 μm thick around a 25 μm diameter

nucleus (N) of blocky calcite (Scale bar = 20 μm).

Figure 47. Photomicrograph of a detrital quartz grains (Q) and micrite intraclasts (M) surrounded by micrite in a travertine sample from the Hartford Basin of Connecticut

(Scale bar = 0.5 mm). 82

Figure 48. Photograph of a large tufa lithoclast (T) >5 cm long, with surrounding micrite intraclasts (M) within a travertine sample from the Hartford Basin of Connecticut (Scale bar in cm).

Figure 49. Photomicrograph OF non-crystallographic (feather) dendrites (outlined) in a travertine sample from the Hartford Basin of Connecticut. Shrubs are oriented perpendicular to laminae (Scale bar = 0.5 mm). 83

Figure 50. Photomicrograph of clotted micrite in a travertine sample from the Hartford

Basin of Connecticut (Scale bar = 0.5 mm).

Figure 51. Photomicrograph of clotted micrite displaying ghost features of irregular

(non-crystallographic) dendrite lamination in a travertine sample from the Hartford Basin of Connecticut (Scale bar = 0.5 mm).

Figure 52. SEM image of calcified air bubbles (outlined) in travertine samples from the

Hartford Basin of Connecticut. Calcified bubbles are composed mostly of blocky calcite and range from 25 to 80 μm in diameter (Scale bar = 20 μm).

Figure 53. Photomicrograph of clotted micrite and calcite ice (CI) in a travertine sample

from the Hartford Basin of Connecticut (Scale bar = 0.5 mm).

A. B.

Figure 54. SEM image of spheres representing a calcified algal or bacterial microcolony in travertine samples from the Hartford Basin of Connecticut. A: Spheres are 1 to 2 μm in diameter (Scale bar = 2 μm). B: Magnified image shows the cluster of spheres with hemispherical cracks on the surface are draped over calcite grains and micrite, creating a botryoidal surface (Scale bar = 2 μm).

A. B.

Figure 55. SEM images of calcified EPS filaments between grains (A) and coating

grains (B) in travertine samples from the Hartford Basin of Connecticut. A: Individual

strands (arrow) stretch for nearly 100 μm in length, and also appear as detached strands

(arrow) (Scale bar = 20 μm). B: Thicker strands (arrow) coat the surfaces of grains

(Scale bar = 5 μm). 86

A. B.

Figure 56. SEM photographs of Fe-Mn stars in travertine samples from the Hartford

Basin of Connecticut. A: Stars appear in clusters within pore spaces of samples (Scale bar = 5 μm). B: Stars are approximately 1 to 2 μm in diameter (Scale bar = 2 μm).

Upper Triassic travertine of South Wales, UK

General Description

Leslie et al. (1992) previously described these marginal carbonates as perched-

springline and lacustrine travertines that measure approximately 1 m in thickness and 5-6

m in diameter, and that they are interbedded with laminated and stromatolitic limestones

and possibly share a mix of thermal and cool source waters for their deposition. Samples

previously described consist of alternating layers of pisoid-intraclast wackestone, ooids,

oncoids, and porous and dense micrite flowstone with occasional calcite ice (Leslie et al.

1992). Ostracods, Carboniferous Limestone intraclasts, and peloids with occasional

micrite coating on clasts as well as meniscus cement are found in the travertine (Leslie et

al. 1992). Travertines also display typical banding associated with shrub-and-ray

dendrites (Leslie et al. 1992).

EDS analysis of Au/Pd sputtercoated samples indicates varying amounts of Ca,

Si, Mg, and Fe (Fig. 57). Au/Pd sputtercoat typically hides the presence of silica in EDS

analysis, but silica was found in such abundance as that it overshadowed the Au/Pd

sputtercoat. Leslie et al. (1992) stated that partial to complete dolomitization had

occurred within these deposits, which is confirmed by the presence of Mg in EDS

analysis of all sputtercoated samples. Calcium identified in the travertine is in the form

of CaCO3 as calcite and CaMg(CO3)2 as dolomite, as seen in thin section and SEM as

spar and rhombohedral crystals. No aragonite shrubs have been found. XRD analysis

confirms the presence of calcite, quartz, and dolomite in concentrations of at least 10%

(Table 8).

In thin section, dolomitization of samples has resulted in the near complete failure 88

to identify features that may have been present from the time of deposition until

alteration. Features found consist mostly of calcite or dolomite spar and probable ghost

features of pisoids or ooids. In SEM analysis, star structures are present within the samples and account for the only presence of Fe in EDS analysis.

Macroscopic Features

Pisoids and Ooids. Pisoids and ooids have been potentially recognized by internal

structures within dolomite crystals. Pisoids or ooids occur as approximately 0.5 to 1 mm

in diameter, and are most recognizeable by an approximately 75 μm irregular rim around

a calcite or dolomite spar nucleus (Fig. 58). While the features found do not display an

original nucleus or radial and concentric laminae, the faintly recognizeable spherical rim

suggests that these are ghost structures of oods or pisoids.

Microscopic Features

Biogenic Structures. Seen as Figure 59, star structures are approximately 1 μm in

diameter and are found in clusters. EDS analysis indicates the only presence of Fe in

samples near these features, suggesting that their composition is Fe (Fig. 57B). Nearly

identical star structures with Fe-Mn oxide contents have been reported as either putative

bacteria or minerals derived from bacterial precipitation within Lechuguilla Cave in

Carlsbad Caverns, New Mexico (Boston, 2004). A. 89

Figure 57. EDS analysis of Au/Pd sputtercoated south Wales samples. A: EDS shows a

high concentration of Mg, Ca, and Si, which indicates mostly calcite (Ca), dolomite (Mg and Ca), and quartz (Si). B: EDS shows a high concentration of Ca with Mg, Al, Si, K, and Fe, which indicates the presence of dolomite (Mg and Ca), calcite (Ca), clays (Al, Si, and K), and iron oxides (Fe). 90

Table 8. XRD analysis of south Wales sample.

Compound Name Displacement Chemical Formula [°2Th.] Dolomite -0.084 Ca Mg ( C O3 )2 Calcite 0.015 Ca ( C O3 ) Quartz low -0.022 Si O2 Calcite 0.028 Ca C O3

Figure 58. Photomicrograph of dolomitized ooids/pisoids (outlined) to show the faintly recognizable spherical rim. Travertine sample from south Wales (UK) (scale bar = 0.5

mm).

Figure 59. SEM photograph of Fe oxide stars in travertine samples from south Wales

(UK). Stars are approximately 1 to 2 μm in diameter and appear as a cluster within a pore space of a sample (scale bar = 2 μm).

CHAPTER VI. DISCUSSION

Macroscopic and Microscopic Features

An assessment of macroscopic and microscopic features in sampling areas is

shown in Table 9. While not associated directly with biologic activity, lithoclasts and

intraclasts are also common features that remain preserved through geologic time. Grain

aggregates are well-preserved within the Neogene samples but are not found within any

other samples.

Calcite ice is found within Neogene and Triassic/Jurassic samples. Calcite ice

represents precipitation of larger calcite rafts at the air-water interface, and compilations of small rods in cross-section view may indicate the fracturing of one of these rafts and preservation of a pile of fragments that became submerged after fracturing (Chafetz et al.

1991). Examples of Neogene and Triassic/Jurassic samples of calcite ice are nearly identical in morphology. While not associated directly with biologic activity, preservation of these features does not necessarily degrade through time.

Calcified air bubbles are seen preserved within Paleogene and Early Jurassic

samples. Within Paleogene samples, calcified air bubbles are preserved as smooth-

surfaced internal molds of bubbles, while Triassic/Jurassic examples are preserved as

blocky calcite exteriors of bubble walls. It is believed that calcified air bubbles are

derived from oxygen bubbles that have been produced by photosynthetic activity of

microbes on or within the surface layer of carbonate of a tufa or travertine, after which the bubbles are trapped and encrusted with carbonate (Chafetz et al. 1991). While

calcified air bubbles were not identified in SEM analysis of Neogene samples, the 93

Table 9. Assessment of Macroscopic and Microscopic Features in Sampling Areas. 94

presence of photosynthetic microbes preserved within biogenic lamination would suggest that calcified air bubbles could be present, at least in some part of the deposit. Hence, further sampling may be productive in identifying Neogene calcified air bubbles.

Throughout all ages of tufas and travertines studied, pisoids and ooids are

common and well-preserved features. While individual pisoids in Neogene samples

display a clearly defined cortex and nucleus (Fig. 17), their boundaries are not as clear in

Paleogene and Early Jurassic samples. Some of the Paleogene and Early Jurassic pisoids

have been flattened or stretched. In Late Triassic samples, the nucleus or cortex has been

replaced, although “ghost” features remain visible. Ooids have long been thought to be

associated with biologic activity; Folk and Lynch (2001) indicate the majority of an ooid

may be precipitated in a bacterially-mediated process.

Dendrite preservation over time is of particular interest, because of the biological

origin of dendrites and their persistence. The clarity of preserved dendrites (shrubs) seen

in thin sections appears to differ greatly through sample areas and thus through geologic

time. Neogene dendrites have markedly clear boundaries between individual crystals and

between dendrites and the overlying and/or underlying substrate. Paleogene and Early

Jurassic dendrites can be recognized, but the coundaries decidedly less clearly defined or are cloudy. This cloudiness may be attributed to partial dissolution and diagenetic replacement by micrite. Similar alteration can be observed in Neogene samples, as some areas of dendrite lamination within the travertine are also cloudy. However, the few areas of cloudy dendrite lamination in Neogene samples contrast with virtually all of the

Paleogene and Early Jurassic samples that are not better described as ghost features. 95

Clotted micrite is another common feature that remains preserved in samples.

Clotted micrite samples from the Neogene and Paleogene are composed of large size

clots, while the Triassic/Jurassic samples display very small size clots. It is currently

believed that clotted micrite represents EPS calcification, although the origins and

processes involved are unclear (Riding 2000). The implication is that clotted micrite is a

possible indication of biologic mediation, and could therefore be proof itself of life. The

differences between large clots in Neogene and Paleogene samples and small clots in

Triassic/Jurassic samples may suggest that the clotted micrite in Neogene and Paleogene

samples is a primary feature, while clotted micrite within Triassic/Jurassic samples is a

secondary feature due to replacement of primary material.

Biogenic lamination is a clear indication of biologic activity. Biogenic lamination

is only seen within Neogene samples, and then only within microterracettes that were taken from the proximal-slope of an active spring. Assuming that the process of calcite engulfing chlorophyll-bearing microbes is not unique, the apparent lack of chlorophyll-

rich biogenic lamination elsewhere in Neogene samples can be attributed to the quick

decay of soft biological tissues. While this represents a loss of preservation potential

through time, no other literature found documents the preservation of chlorophyll within

an ancient geologic deposit.

EPS filaments are found within both Early Jurassic and Neogene samples and are

identical in morphology. This suggests that preservation of these features does not

necessarily degrade through time. While EPS filaments were not identified in SEM

analysis of Paleogene samples, their absence does not mean that they are not present in

the unit. Similarities between clotted micrite in Neogene and Paleogene samples would 96

suggest that EPS filaments should be present, at least in some part of the deposit. Hence,

further sampling may be productive in identifying Paleogene EPS filaments.

Microspheres of 1 to 2 μm in diameter are found in Neogene, Paleogene, and

Triassic/Jurassic samples. Microspheres in Neogene samples are found encrusting EPS sheathing of trichomes, and display sub-micron scale morphological detail of aragonite crystal growth. In Paleogene samples, microspheres are found on the surfaces of calcified air bubbles and display no detail other than their spherical to ellipsoid shape.

Triassic/Jurassic microspheres are found as botryoidal clusters unassociated with other

features and display sub-micron scale morphology in the hemispherical cracks across

their surface. Micron-scale spheres that occur in botryoidal clusters are widely thought to

be calcified microbe communities, but the nature of these fossils and poor understanding

of nanometer-scale fossilization processes and taphonomic frameworks prevents a more

detailed identification (Cady et al. 2003).

Coccoliths found within Paleogene samples have been identified as

Zeugrhabdotus sp. by Watkins (personal comm.) and Young (personal comm.). The genus Zeugrhabdotus falls within the Family Chiastozygaceae of the Order Eiffellithales, which are distinctively marine coccoliths (Brown and Young 1997). This type of coccolith construction is consistently observed through the Mesozoic and Early Cenozoic

with numerous subtle morphological variations. These variations produced a virtually

unworkable taxonomic group because very few distinctive and well-constrained species

exist, making a species-level identification of the coccoliths within the Paleogene tufas

and travertines nearly impossible (Brown and Young 1997). The genus Zeugrhabdotus is

found in Cretaceous to Paleocene-aged marine sediments (Tappan 1980). 97

A possible interpretation of the presence of Zeugrhabdotus sp. fossils within

Eocene spring deposits is that some Zeugrhabdotus sp. were freshwater coccoliths that lived in the ponds and streams of the Chadron Formation in South Dakota, in which case,

this is the first demonstrated occurrence of this taxa, or indeed, this morphology, within a

freshwater system. Few freshwater coccoliths are known, and are of a different

morphology than marine coccoliths (Young personal comm.). Another interpretation of

the presence of these fossils is that the coccoliths found within Eocene tufas and

travertines of South Dakota originated from the underlying Late Cretaceous Niobrara

Formation (Watkins, personal comm.). The Niobrara Formation lies between the

younger Pierre Shale and older Carlile Shale and consists of light colored limestones,

microfossiliferous chalk (including Zeugrhabdotus sp.), calcareous shales, and siltstones

(Schoon 1993, Meier 2005, Watkins personal comm.). This reworking would have been

accomplished by coccolith erosion out of the Niobrara Formation and could have been:

(1) wind transport that blew coccolith-bearing sediment across the ground surface and

into the tufa and travertine where it was trapped, (2) transport by streams flowing down

from the Black Hills that carried coccolith-bearing sediment to the site where it was

trapped and bound by tufa and travertine deposits, or (3) transport by groundwater piping

through the underlying rock units (where the Niobrara Formation is located) that carried

coccolith-bearing material to the surface of the Eocene springs (Watkins, personal

comm.). If the presence of Zeugrhabdotus sp. fossils is due to reworking of the

Cretaceous material, it raises the possibility that tufa and travertine deposits may not only

preserve evidence of contemporaneous biological activity, but also sample the fossil

record of older units through which the spring system passes. 98

Depositional Facies Preservation

An interpretation of depositional facies present within Neogene, Paleogene, and

Early Jurassic, and Late Triassic samples based on assessed macroscopic and microscopic

features is shown in Table 10. Because spring vents are self-sealing systems that migrate

over time periods, travertine fabrics vary both vertically and laterally beneath the uppermost fresh surface and represent different depositional facies than the current surface conditions (Fouke et al. 2000). Depositional facies may not show a consistent vertical or lateral trend because of the variation in springs and the surrounding environments. Because of this, it may only be possible to make a complete assessment of all depositional facies preserved though time at a particular geographic point if a core sample is taken, or if a stratigraphic section can be measured through a fissure in cm- scale increments. Because the samples collected for this study do not have the resolution required for facies analysis through time, the interpretation of depositional facies given is only an interpretation of the samples studied, and should not be assumed to be an interpretation of the entire range of depositional facies preserved at each sample site.

Comparison of Preservation Potential

A comparison of preserved microscopic and macroscopic features identified from

tufas and travertines of Neogene, Paleogene, Early Jurassic, and Late Triassic age is

presented as Table 11. Through geologic time, paleogroundwater deposits preserve

biologically-mediated features such as pisoids, ooids, intraclasts, lithoclasts,

stromatolites, calcified air bubbles, EPS filaments, and microspheres. In addition, both 99 biogenic features and true body fossils, such as fungal sacs and coccoliths, gastropods, bivalves, ostracodes, vertebrates, and plants can be preserved in ancient tufa and travertine samples. Preservation of reworked fossils requires a suitable fossiliferous source unit that source waters must contact, as well as groundwater chemistry (pH) that allows transport of material without total dissolution. The absence of coccoliths in

Neogene and Triassic/Jurassic samples suggests that source waters for these deposits never contacted a coccolith-bearing fossiliferous unit, or that groundwater chemistry was not suitable for transport and re-deposition of such delicate fossils.

Overall, samples show that preservation potential within ancient tufas and travertines does not significantly differ from preservation seen within recent terrestrial carbonates. The quality of preservation of both microscopic and macroscopic features does not substantially decline in samples as old as approximately 200 Ma. While some degradation of detail is seen, biogenic structures are still identifiable as such. The preservation of reworked fossil material within Paleogene samples is a significant indication of preservation potential. Because the fossil material is older than the spring itself, preservation potential in terrestrial carbonates is not restricted solely to biologic activity during the precipitation of the carbonate itself but instead can be widened to any biogenic material that is introduced into the system. The ability of a geologic deposit to preserve biogenic material older than itself would be an important requisite for a deposit used to look for life on other planets, where apparent surface biologic activity has ceased and the ability to search through underlying stratigraphic units is limited. Such exopaleontologic studies are currently being conducted on Mars. 100

Table 10. Interpretation of Depositional Facies Present within Neogene, Paleogene, and

Triassic/Jurassic Samples Based on Assessed Macroscopic and Microscopic Features.

101

Table 11. Comparison of Preserved Microscopic and Macroscopic Features Within Tufas and Travertines of Neogene, Paleogene, Early Jurassic, and Late Triassic Age.

102

CHAPTER VII. SUMMARY AND CONCLUSIONS

In summary, this study examines the preservation potential of lithologic and biogenic features in pre-Cenozoic paleo-groundwater deposits, focusing on biogenic microstructures detected using SEM, EDS, petrography, and correlating with published data. This study compares pre-Neogene tufas and travertines from the Eocene Chadron

Formation (Badlands of South Dakota), the Early Jurassic Shuttle Meadow Formation

(Hartford Basin of Connecticut), and Late Triassic Mercia Mudstone Group (south

Wales, United Kingdom) to Neogene tufa and travertine (San Ysidro Quadrangle, central

New Mexico). The goal is to discern trends in the preservation potential of biogenic microstructures through geologic time.

Paleo-groundwater deposits on Earth contain distinctive features observed back through the geologic record from today until at least the Triassic, a range of over 200 million years. Neogene samples include pisolites, coated grains, lithoclasts, encapsulated

“fresh” algae, aragonite shrub-and-ray dendrites, EPS, and calcite ice. Eocene samples include pisolites, ooids, coated grains, lithoclasts, and shrub-and-ray dendrites, in addition to oncoids, macrofossils (molluscs, ostracodes, and vertebrate bones), charophyte stems and gyrogonites, microcolonial fungal sacs, and coccoliths. Jurassic samples include pisolites, shrub-and-ray dendrites, EPS, calcite ice, calcite microspherules that have been associated with algal and/or bacterial growth, and Fe-Mn oxide star structures. Triassic samples have unfortunately undergone dolomitization but retain ghost features of ooids and Fe oxide star structures.

Some of the features found could be either inorganic or biologically mediated, such as pisolites, lithoclasts, and dendrites. Others are clearly biogenic, such as oncoids, 103 coated grains, EPS, macrofossils (Eocene in age), microfossils such as coccoliths, microcolonial fungal sacs, and microspherules (Jurassic in age). Dominant microstructures observed of probable biogenic origin include clotted micrite, pseudo- stromatolitic features (e.g., shrub-and-ray dendrites), microcolonial fungal sacs, coccoliths, and extracellular polymeric substances (EPS). The quality of preservation of these features does not substantially decline in samples as old as approximately 200 Ma.

Both biogenic features and true body fossils, such as fungal sacs and coccoliths, can be preserved in ancient tufa and travertine samples. The preservation of reworked fossil material within Paleogene samples is a significant indication of preservation potential.

The ability of a geologic deposit to preserve biogenic material older than itself would be an important requisite for a deposit used to look for life on other planets, where apparent surface biologic activity has ceased and the ability to search through underlying stratigraphic units is limited. If evidence for life on Mars is ever found, it may come from Martian paleo-groundwater deposits such as tufas and travertines. Tufas and travertines uniquely preserve evidence of life from surface, subsurface, and potentially from ancient environments. 104

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APPENDIX A- OPERATING PROCEDURES

Au/Pd Sputtercoating Procedure for Hummer VI-A Sputtercoater

1. Check that: a. TIMER is on AUTO (knob at 0) b. GAS CONTROL VALVE is CLOSED c. VOLTAGE CONTROL is OFF

2. Open chamber.

3. Insert samples.

4. Close lid on chamber.

5. Switch MAIN POWER ON to start vacuum.

6. Set MODE to PLATE DC.

7. Wait for vacuum to reach 20 millitorr, then: a. Open GAS CONTROL VALVE to flush chamber with argon to 200 millitorr b. Repeat 3x

8. Regulate gas pressure between 55-70 millitorr.

9. Turn VOLTAGE CONTROL ON.

10. Turn TIMER to 2.5 minutes.

11. Adjust VOLTAGE CONTROL to set purple field of ionization (between 10- 20 milliamps).

12. Maintain gas pressure and ionization field.

13. Wait for TIMER to automatically TURN OFF VOLTAGE.

14. Adjust GAS CONTROL VALVE to atmospheric pressure.

15. Close GAS CONTROL VALVE.

16. Remove samples and close chamber.

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BGSU Operating Procedure for Scanning Electron Microscope Use

1. Make sure that the SEM has been running.

2. Check chamber pressure gauge for high vacuum

3. Make sure that Gun Valve is closed, then decompress chamber

4. Insert sample or samples

5. Close chamber

6. Press chamber closed, and evacuate air

7. Once high vacuum has been reached, wait an additional 2 minutes

8. Open Gun Valve, and wait for High Voltage Control to open

9. Activate High Voltage Control

10. Increase filament saturation 1 notch every 30-45 seconds

11. Adjust screen and SEM brightness and contrast

12. In controls, adjust aperture for increased resolution of images.

13. For EDS analysis, sample must be at WD12 and EDS brought to 2.6cm.