P51A-1385
In-situ Detection of Squalane in Sedimentary Organic Matter Using Monoclonal Antibodies
Sedimentary geolipids can serve as powerful tools for reconstructing ancient ecosystems, but only if investigators can demonstrate that the hydrocarbons are indigenous to their host rocks. The association of molecules with primary sedimentary fabrics could indicate a syngenetic relationship. However, traditional biomarker analyses require extraction from large quantities of powdered rock, confounding detailed spatial correlations. Biological studies commonly use antibodies as extremely sensitive molecular probes. When coupled with fluorescent labels, antibodies allow for the visual localization of molecules. Here we show that monoclonal antibodies that bind specifically to geolipid compounds can be used for in situ detection and labeling of such compounds in mineral-bound organic macerals. Monoclonal antibodies to squalene, produced for human health studies, also react with the geolipid, squalane. We show that squalene antibodies do not react with other common sedimentary hydrocarbons. We also show that squalane antibodies bind specifically to isolated organic-rich lamina in Eocene-age, squalane-containing rocks. These results suggest that squalane is confined to discrete organo-sedimentary fabrics within those rocks, providing evidence for its syngeneity. The chemical similarity of squalane to other sedimentary hydrocarbons hints at the potential for developing monoclonal antibodies to a variety of biomarkers that could then be localized in rocks, sediments, and extant cells.
P51A-1386
Environmental Controls on Hopanoid Distributions: Field and Culture Studies
Hopanoid biomarkers play an important role in reconstructions of the earth's past biogeochemistry and evolution. Despite their excellent preservation potential and utility for microbial paleontology, relatively little of the earth's modern microbial biosphere has been explored with respect to hopanoid production. Due to the fact that hopanoids are used by bacteria to tune the physical properties of their cell membranes, geochemical gradients in nature may be associated with systematic changes in hopanoid diversity and abundances. Bacteriohopanpolyols (BHPs) are produced by both sulfur-oxidizing and sulfur-reducing bacteria. We hypothesize that BHPs are important for microbial adaptation to pH and sulfide concentrations in sulfur-oxidizing microbial communities. We investigated this hypothesis using both pure laboratory cultures and with samples of natural biofilms collected across oxygen and sulfide concentration gradients in the field. Samples were collected from the sulfidic Frasassi cave system, Italy, where the geomicrobiology of abundant sulfur cycling biofilms has previously been studied in detail (Macalady et al. 2007, Macalady et al. 2008). Culturing experiments were performed with two sulfur-oxidizing bacteria, an Acidithiobacillus sp. isolated from extremely acidic (pH 0-1) snotittes, and Beggiatoa alba, a neutrophilic sulfur oxidizer with close relatives in the Frasassi biofilms. Cultures were grown at range of pH and sulfide concentrations, harvested, freeze-dried and analyzed by atmospheric pressure chemical ionization liquid chromatography/mass spectrometry (APCI- LC/MS). We observed six different BHPs for the Acidithiobacillus sp. including one novel structure. Acidithiobacillus BHPs change in response to changes in the pH of the growth medium, becoming more polar and more abundant at lower pH. These observations are consistent with the production of less fluid, more polar membranes to counteract proton leakage into cells as pH decreases. Macalady, J. L., S. Dattagupta, I. Schaperdoth, G. K. Druschel, D. Eastman. 2008. Niche differentiation among sulfur-oxidizing bacterial populations in cave waters. ISME Journal 2: 590-601.
P51A-1387
Microbial biosynthesis of wax esters during desiccation: an adaptation for colonization of the earliest terrestrial environments?
Biosynthesis of wax esters (WE) by prokaryotes in natural systems, notably bacteria from hot springs and marine phytoplankton, is poorly documented, primarily because saponification is a routine step in the analysis of microbial mat lipids. Use of this preparative procedure, critical for characterization of the diagnostic distributions of carboxylic acids in phospholipids, precludes recovery of intact WE. Examination of non-saponified lipids in emergent and desiccated mats with comparable microbial communities from the Warner Lake region, Oregon, reveals increases in the relative abundance (18.6 to 59.9μg/g Corg) and average chain length (C38 to C46) of WE in the latter, combined with assimilation of phytol and tocopherol moieties. Prokaryotes can accumulate WE as storage lipids in vitro, notably at elevated temperature or under nitrogen limiting conditions, but we propose that biosynthesis of long-chain WE that have a low solubility and are resistant to degradation/oxidation may represent an evolutionary strategy to survive desiccation in evaporative environments. Moreover, aeolian transport of desiccated mat-rip-ups between lake flats allows for migration of microbial communities within and between lake flats and basins during arid conditions. Subsequent rehydration within an alkaline environment would naturally saponify WE, and thereby regenerate alcohol and acid moieties that could serve as membrane lipids for the next viable microbial generation. The evolutionary cradle of WE was likely abiotic generation under hydrothermal conditions, which is consistent with the antiquity of the ester linkage necessitated by its integral role in the membranes of Eubacteria (though not Archaea) and in bacteriochlorophyll. The subsequent capability of microbes to biosynthesize WE may have facilitated their survival when nutrients were limiting, and production of long-chain WE (>C40) may represent a further critical evolutionary threshold that enabled their persistence through and during dehydration or desiccation cycles. Thus, production of WE may have facilitated microbial migration to the lake environments that represented the earliest terrestrial ecosystems, and survival through the Great Oxygenation Event.
P51A-1388
Probing the Proteome on Earth and Beyond
Less than a decade ago, protein sequencing was the bane of paleobiology. Since that time researchers have completely sequenced proteins in >50 Ka fossils, been dazzled by reports of collagen peptides in dinosaur bones, and witnessed the development of phylogenetic trees from ancient protein sequences. Enlisting proteomics as biosignature is now in our grasp. In this talk the pitfalls and challenges of mass spectrometric approaches to protein sequencing will be illustrated and phylogenetic applications will be discussed. Work on extinct organisms at Michigan State University, University of Michigan and York University will provide a vantage point to assess methodologies, explore diagenetic alterations, evaluate mass spectra and illustrate issues associated with data base searching. Challenges encountered in the study of paleoproteomics, such as the absence of sequences for extinct organisms in commercially available databases, protein diagenesis and low concentrations of target are parallel to those that will be encountered when protein sequencing is extended to extreme and extraterrestrial environments. Thus, lessons learned from interrogating the ancient proteome are important and necessary step in developing proteomics as a biosignature tools.
P51A-1389
Tracing the origin of carbonaceous matter and apatite in Neoarchean banded iron formations from Abitibi
The low metamorphic grade of Neoarchean banded iron formations (BIFs) from Abitibi, Québec, allows for the study of BIFs with minimal post-depositional alteration. Biological oxidation of ferrous iron has been suggested as a possible process by which BIFs form and if correct, organic remains of these microbial communities may be preserved within such sedimentary rocks. An investigation of the organic carbon in the BIFs from this region was performed to determine the mode of its occurrence and its association with apatite, which can form from the diagenetic maturation of organic remains. In a thin section of jasper-magnetite-chert BIF, two grains of apatite were found to exist in association with organic carbon, whereas the other grains are associated with carbonate, magnetite and hematite. These observations were confirmed via Raman spectroscopy and SEM. Carbonaceous material associated with apatite is characterized by D- and G-band peak intensities consistent with the metamorphic history of these rocks. Carbon isotopic compositions and concentrations were determined on several micro-drilled areas on various BIF thick sections, representing the mineral diversity of the samples. The δ13C values range between -15 to -45 ‰ (δ13Caverage = -29.2 ‰; n = 67), and the average organic content was 0.25% (range between 0.04 and 1.00 %;). Significant carbon isotope fractionations with large negative δ13C values could be biological in origin, but abiological processes could also be responsible for these ranges. Our observations in the studied BIFs collectively suggest that this organic matter was part of the original depositional environment and that apatite and carbonate likely formed during diagenesis.
P51A-1390
Detection of Biosignatures using Geomatrix-Assisted Laser Desorption/Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry: Implications for the Search for Life in the Solar System
Detection of bio/organic signatures, defined as an organic structure produced by living organisms or derived from other biogenic organic compounds, is essential to investigating the origin and distribution of extant or extinct life in the solar system. In conjunction with mineralogical, inorganic, and isotopic data, the detection and identification of bio/organic signatures can assist in linking biochemical and geochemical processes. Geomatrix-assisted laser desorption/ionization (GALDI) in conjunction with a Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) is a proven method of obtaining bio/organic signatures from a range of geological materials. Sulfate salts were studied because they are found on Mars and Jovian satellites. The goal here was to determine (1) which combinations of bio/organic compounds and sulfate salts produced distinctive spectral signatures, and (2) the detection limit of the method. In these experiments, thenardite (Na2SO4) was mixed with stearic acid to determine the detection limit of GALDI-FTICR-MS, previously estimated to be 3 ppt, which corresponds to approximately 7 zeptomoles (10-21) per laser shot. All spectra were collected with little to no sample preparation and were acquired using a single laser shot. Unlike conventional analytical practices, the signal-to-noise ratio increased as the concentration of bio/organic compounds decreased relative to the mineral host. In combination with thenardite, aromatic amino acids were observed to undergo simple cation attachment ([M+Na]+) due to the π-bonded aromatic ring. Subsequent cation substitution of the carboxyl group led to formation of peaks representing double cation attachment ([M-H+Na]Na+). Spectra from naturally occurring thenardite and jarosite (XFe3(OH)6(SO4)2) revealed the presence of high mass cluster ions; analysis of their isotopic distribution suggested the presence of bio/organic compounds. High mass cluster ions, both organic and inorganic, readily form in the gas phase during analysis; identification of such cluster ions requires systematic procedures based on isotopic distribution. Coupled with specialized software, GALDI-FTICR-MS can systematically identify the presence of biological matter from a wide range of synthetic and naturally occurring geological materials, while operating with high spatial resolution and high mass accuracy.
P51A-1391
Tunable Laser Spectrometer (TLS) for Sample Analysis at Mars (SAM) Suite on the 2009 Mars Science Laboratory (MSL) Mission
The Tunable Laser Spectrometer (TLS) in one of three instruments (QMS, GC, TLS) that make up the Sample Analysis at Mars (SAM) analytical chemistry lab on NASA's 2009 Mars Science Laboratory (MSL) mission. TLS has unprecedented capability for measuring methane, water, and carbon dioxide abundances in the Martian atmosphere and evolved from heated soil samples. In addition, TLS will measure the 13C/12C isotope ratios in both CH4 and CO2, and the 16O/17O/18O isotope ratios in CO2. Using an interband-cascade and a tunable diode laser, TLS has capability to determine atmospheric methane abundance to 2 percent accuracy and to a lower limit of 1 part-per-trillion with SAM pre- concentration. The instrument and recent test data results will be described in context with the needs for understanding Martian atmospheric and geophysical processes. © 2008 California Institute of Technology. Government sponsorship acknowledged.
P51A-1392
Carbon Isotope Equilibrium Between Methane and Carbon Dioxide in two Continental Hydrothermal Systems: Implications for Methane Production on Mars
We use an isotope mass-balance model to interpret the carbon isotope composition of co-existing methane and carbon dioxide from two continental hydrothermal spring systems: Great Boiling Springs, NV, and Surprise Valley Hot Springs, CA. The agreement between the data and the model demonstrate that an equilibrium relationship likely exists between carbon dioxide and methane gases collected from several hot spring pools associated with these two hydrothermal spring systems at temperatures as low as 155°C. The carbon isotope values of carbon dioxide for Great Boiling Springs and Surprise Valley Hot Springs range from -24.8‰ to -8.5‰, and those for methane range from -51.2‰ to -24.9‰. These data indicate that despite having relatively depleted carbon isotope values, the minimum formation temperature precludes the possibility that the methane in these systems formed directly from the action of microorganisms. Implications from this study contribute to the growing set of data suggesting that abiogenic methane production may be more common than previously thought. These results also provide a terrestrial analog of continental hydrothermal spring systems that can be used to better understand the origin of methane and carbon dioxide on Mars and elsewhere in the solar system.
P51A-1393
The Oxygen Isotope Composition of PO4 Extracted From Lost City Hydrothermal Vents -- a Potential Biosignature for Vent Hosted Microbial Ecosystems
The oxygen isotope composition of phosphate is a useful indicator of biological P cycling in low to moderate temperature environments, such as those that characterize most of the habitable zone of Earth. In microbially active systems, phosphate oxygen isotope compositions are driven towards a temperature- dependent, thermodynamic equilibrium offset from water. Enzymatic reactions involving organophosphorus compounds, pyrophosphate, and polyphosphates promote the exchange of oxygen atoms between water and phosphate. These enzyme driven reactions are key to the attainment of isotopic equilibrium under conditions in which the rate of inorganic oxygen exchange is slow. We have examined the phosphate oxygen isotope systematics of the Lost City hydrothermal vent system, which is located on a gabbroic and peridotitic massif, 15km off-axis of the Mid Atlantic Ridge. The Lost City hydrothermal system's fluid chemistry and heat budget are controlled by serpentinization reactions. Fluids vent at temperatures up to around 80°C and with a pH around 9-10. Vent mineralogy is dominated by calcite, aragonite, and brucite, with mineral layers intercalated by biofilms. Phosphorus content ranges from 400 - 1000 ppm (by mass as P2O5) in the vent samples we have analyzed. The oxygen isotope composition of phosphate extracted from the vent solids is a few per mil lighter than that of phosphate dissolved in ambient sea water. This oxygen isotope composition reflects exchange of phosphate oxygen with water oxygen at elevated temperature. We show that under a wide range of conditions, abiological reaction rates are too slow to produce these isotopic compositions. This suggests that cycling of the phosphate by the vent system's microbial community has imprinted the phosphate with a stable isotope signature of biological activity. The oxygen isotope composition of lattice-bound phosphate preserves well in the geologic record, commending phosphate oxygen isotope measurements as a tool for the detection of life in ancient terrestrial and in extraterrestrial rocks.
P51A-1394
Challenges in Establishing Criteria for the Recognition of Biominerals (Biosignature)
Morphology and uniform size of extracellular or intracellular biominerals are often taken as evidence of biological activity in natural environments and ancient rocks. However, morphology alone is insufficient and a deeper understanding of the crystal growth mechanisms in abiotic and biogenic systems is necessary if we are to establish criteria for recognizing biominerals in natural systems in both terrestrial and extraterrestrial environments. To distinguish between exclusively inorganic and biologically controlled crystallization, we conducted comparative abiotic and biogenic laboratory experiments and investigated the nucleation and growth characteristics of carbonate and phosphate (hydroxyapatite) minerals. Advanced imaging and analytical techniques, including cryo-electron tomography (cryo-ET), immunogold labeling, freeze-fracture and nano secondary ion mass spectrometry (NanoSIMS), revealed that both protein and inorganic ions influence the crystal growth and morphology. Nevertheless, the mode of crystal growth was distinct in the two modes of crystallization. Deviation from the ideal crystal habit was more pronounced in protein-based nucleation and growth compared to the abiotic system. For hydroxyapatite, size, shape and composition of the crystals were identical for the three different biogenic systems (i.e., serum, bacteria, and mammalian cells). In contrast, crystal morphology in the abiotic system was variable and dependent upon the initial composition of the solution and experimental conditions. These results suggest that in biogenic systems there is a common mechanism for the precipitation of biominerals. As we observed an association of specific proteins with crystal growth, it is likely that the nucleation and growth of biominerals is mainly controlled by the proteins; however, the nature of the interaction of the protein with the crystal faces remains unresolved. Although the differences in growth patterns between abiotic and biogenic crystals may provide potential indicators of biological activity within geological systems, it is difficult to apply this approach to ancient samples.
P51A-1395
In situ dating of the oldest morphological traces of life on Earth
Sea floor pillow basalts contain tubular and granular bioalteration micro textures in their glassy margins1,2 created by microbes etching the rock3,4, hypothetically to get access to nutrients and electrons donors5. The etched pits in the rock can be regarded as trace fossils6 that later become mineralized by titanite (CaTiSiO5). Such trace fossils are known from recent oceanic crust to some of the oldest preserved Archean ocean floor, in the Barberton greenstone belt (BGB), in S-Africa7. However, the antiquity of BGB trace fossils has been questioned by some since only the host rock was dated until now8. Here, we report for the first time in situ U-Pb radiometric dating of titanite mineralizing the BGB trace fossils using LA-MC-ICPMS. An U-Pb date of of approx. 3.15 ± 0.05 Ga (95.4 % confidence) for the titanite demonstrates the antiquity of the BGB trace fossils. This result confirms the BGB trace fossils as the oldest directly dated morphological trace of life on Earth. We will present addition data to reveal the mineralization of trace fossils by titanite, comparing the BGB trace fossils to other similar tubular titanite mineralized textures from different locations and younger ages. Our data confirms that a sub-oceanic biosphere was already established in the early Archean by at least 3.2 Ga. Further the results highlight the importance of the sub-ocean habitats for the development and possibly refuge for life on (early) Earth. 1. Furnes, H. et al. Bioalteration of basaltic glass in the oceanic crust. Geochemistry Geophysics Geosystems 2, (2001). 2. Staudigel, H. et al. 3.5 billion years of glass bioalteration: vulcanic rocks as a basis for microbial life. Earth-Science Reviews 89, 156-176 (2008). 3. Furnes, H. et al. Links Between Geological Processes, Microbial Activeties and Evolution of Life. Dilek, Y., Furnes, H. and Muehlenbachs, K. (eds.), pp. 1-68 (Springer,2008). 4. McLoughlin, N. et al. Current Developments in Bioerosion (Erlangen Earth Conference). Wisshak, M. and Tapinla, L. (eds.), pp. 372-396 (Springer, Berlin,2008). 5. Santelli, C. M. et al. Abundance and diversity of microbial life in ocean crust. Nature 453, 653-6U7 (2008). 6. Bertling, M. et al. Names for trace fossils: a uniform approach. Lethaia 39, 265-286 (2006). 7. Furnes, H., Banerjee, N. R., Muehlenbachs, K., Staudigel, H. and De Wit, M. Early life recorded in archean pillow lavas. Science 304, 578-581 (2004). 8. Rincon, P. Early life thrived in lava flows. BBC News Channel . 4-22-2004.
P51A-1396
Entrapment and protection of biosignatures by the jarosite group minerals
Since the discovery of jarosite on Mars, extensive research focuses on linking this mineral group with possible detection of biosignatures in the geologic record on Earth and Mars. The mineral jarosite can be generated abiotically or biotically. Because microbes can produce jarosite, it is possible that biomolecules could be trapped with the mineral. Multiple analytical methods, including extraction and mass spectrometry techniques, identify biomolecules in jarosite samples. Specifically, the amino acid glycine has been found associated with natural jarosite samples from various locations around the world. The simple amino acid may be merely physically mixed with the mineral. Alternatively, the biomolecule may be incorporated into the structure because jarosite is known as a "garbage" mineral because it easily incorporates substitutions. The jarosite end-members jarosite (sensu stricto-potassium jarosite), natrojarosite (sodium jarosite), and ammoniojarosite (ammonium jarosite) have potentially different susceptibilities to substitution as well as different thermodynamic stabilities and decomposition rates. Therefore, we have investigated whether a simple biomolecule, glycine, can be substituted into the structure of jarosite. If a biomolecule is entrapped within a mineral matrix, then it may be persist longer in the geologic record, even with exposure to the extreme conditions such as those on Mars. Glycine was introduced into the synthesis procedure of each jarosite end-member to elucidate the effects that glycine has on the stability of the mineral group and also determine if it produces a structural effect. Laser desorption/ionization Fourier transform mass spectrometry was used to determine that glycine was present with the jarosite after each synthesis. An understanding of the thermal and structural effects provides clues about whether the biomolecule is entrapped in the mineral, which may affect how persistent this bioorganic signature would be in the geologic record. Thermal gravimetric analysis was used to determine the effect that glycine has on the relationship between the thermodynamic stability of the end members and on the thermal decomposition behavior of each end member. X-ray and neutron diffraction have been used to investigate the structural relationship of glycine with each jarosite end member type. The results reveal distinct differences between jarosite that is merely physically mixed with glycine and jarosite that is synthesized in the presence of glycine for some end member groups. These differences suggest that glycine can be incorporated into the structure of jarosite. Therefore, it is possible that some biomolecules can be entrapped within a mineral matrix, which may be able to protect the biomolecules, allowing them to survive in the geologic record.
P51A-1397
Preservation of modern and ancient microbial ichnofossils in basaltic glass by titanite mineralization
Subaqueous volcanic rocks are a relatively new setting in the search for early life on Earth but recent studies have demonstrated that submarine basaltic glass in pillow rims and hyaloclastites are suitable microbial habitats. Microbes rapidly colonize the glassy surfaces along fractures and cracks that have been exposed to water producing characteristic granular and/or tubular bioalteration structures. The minerals within these structures have been investigated using micro X-ray diffraction that confirms early formation of titanite and other mineral phases associated with microbial alteration structures in modern basaltic glass. Incipient titanite formation in modern samples implies that mineralization of these trace fossils is penecontemporaneous with bioalteration. The early precipitation of sub-micron titanite grains within the biologically etched alteration structures serves as an agent for preservation that may persist for geologically extended periods of time in the absence of later penetrative deformation. Titanite-mineralized microbial alteration structures have been observed in several Archean greenstone belts including the Abitibi greenstone belt (2.7 Ga), Pilbara craton (3.35 Ga), and the Barberton greenstone belt (3.5 Ga). The ubiquity of these bioalteration structures and their relative durability compared with many other purported trace fossils makes them attractive as a biomarker for Archean Earth and, potentially, Mars. Basaltic rocks are commonplace on Mars and could have easily come into contact with water in the past. Archean subaqueous volcanic rocks thus provide an excellent analogue for studies addressing the presence of early life on Mars and the potential for the preservation of traces of microbial life in the Martian crust.
P51A-1398
Biosignatures Preservation Potential and Habitability in Phyllosilicates vs. Iron-rich Environments
Phyllosilicates have been identified on the surface of Mars by the OMEGA-Mars/Express [e.g., 1], the Mars Reconnaissance Orbiter (MRO) instruments, i.e., HiRISE and CRISM, as well as inferred from rover observations in Gusev Crater [2]). A better understanding of the preservation potential and habitability in phyllosilicates and hematite-rich materials, achieved by studying analog sites, will therefore provide critical information in support of next decade missions landing site selection e.g., 2009 Mars Science Laboratory (MSL), the ESA Pasteur ExoMars. We present geochemical (d13C-org, d13N-tot, CN ratios) and microbiological proxies i.e., Adenosin-Triphosphate (ATP-based) and Limulus-Amebocite-Lysate (LAL-based biomass) from a suite of phyllosilicate and iron-rich environmental samples e.g., Rio Tinto (Spain), Death Valley (CA, USA), Atacama Desert (Chile), and the California coast. Phyllosilicates-rich zones (47-74wt.%) from the Rio Tinto (RT) region can preserve up to 10-time higher amount of organics (C-org = 0.23 wt.%) than the embedding hematite/goethite-rich (34-89 wt.%) rocks i.e., C-org: ~0.05 wt.% [4]. It is possible that under low pH and highly oxidizing conditions [e.g., 3] surface-derived organics are rapidly oxidized within the shallow hematite/goethite-rich materials, but preserved in phyllosilicates (smectites/illite) where conditions are more conducive [4]. ATP-based biomass was detected in some oxidized-rock samples where roots materials were present (750-1245 RLUs). Geochemical and microbiological analyses are underway to confirm the preservation/ habitability trends observed in the Rio Tinto near surface. Preliminary results suggest that oxidized, goethite-rich, sandstone (Purisima formation, CA) have higher ATP- and LAL-based (Gram negative) biomass contents i.e., 2.0 107 cell/g (35.05 EU/mL) and 3891 RLUs, than the overlying clays units i.e., 1.34 107 cell/g (22.0EU/mL) and 1143 RLUs. REFERENCES: [1] Bibring et al., 2006, Science 312:400-404; [2] Wang et al., 2006 JGR E02S16 Vol. 111; [3] Sumner, 2004, JGR, 109; [4] Bonaccorsi and Stoker, Astrobiology 2008; in press.
P51A-1399
Dolomite Formation within Microbial Mats in the Sabkha of Abu Dhabi (UAE) and Associated Microsedimentary Structures
The link between microbial activity and dolomite formation has been evaluated in the coastal sabkha of Abu Dhabi (UAE). This modern dolomite-forming environment is frequently cited as the type analogue for the interpretation of many ancient evaporitic sequences. The investigation of sabkha sediments along a transect from intertidal to supratidal zones revealed a close association between microbial mats and dolomite. Authigenic dolomite occurs within surface and buried microbial mats, which are comprised of exopolymeric substances (EPS). Dolomite forms as a direct consequence of mineral nucleation and growth within microbially produced EPS. The cation-binding effect of the EPS molecules influences the composition of the precipitate. The early stage of this process is characterized by the complexation of an amorphous Mg-Si precipitate, which promotes dolomite development. Mineral formation within EPS appears to be enhanced by evaporation with consequent supersaturation of the pore waters with respect to dolomite. Partial EPS degradation during diagenesis may also provide an additional source of cations. However, the specific mineral-template property of EPS, rather than an increase in cation concentrations, is the key factor for dolomite formation in the studied area of the sabkha. Indeed, within the modern microbial mat located at the surface, dolomite precipitates from pore waters whose composition is very close to seawater. In the supratidal zone, pore water analysis and stable isotope values did not reveal any linkage between dolomite formation and microbial excretion and/or consumption of metabolites along the sediment profiles. This is in contrast with current models, in which dolomite formation is mainly linked to microbial increase of pH and alkalinity or consumption of dissolved SO4 in pore-waters. The EPS of the microbial mats is characterized by an alveolar microfabric, which can be mineralized during early diagenesis, preserving fossil imprints of the original biofilm. Recognition of this biostructure, combined with the atypical Mg-Si phase, may be used to interpret ancient microbial dolomite throughout the geological record.
P51A-1400
Mineralogcial Biosignature of High-Magnesian Calcite
Some dolomite formations are associated with sediments where sulfate reduction is active. In general, sulfate has been considered to inhibit dolomite formation. However, it was also suggested that the reaction products of sulfate reduction, such as increased alkalinity, may play a more important role in increasing the formation rate of dolomite than sulfate does in inhibiting it. We have investigated the effect of sulfide on Mg-Ca carbonate precipitation. Our results show that high-magnesian calcite which contains as much as 34 mol% magnesite can precipitate from solutions with the presence of certain amount of dissolved sulfide and pyrite crystals. These high-magnesian calcites form unusual micro-scale spheres with cracks on them. High- resolution SEM and TEM results show that these spheres are actually composed of a great number of nano- crystals (~50 nm) stacking together with low-angle grain boundaries. Both synthesized and natural high-magnesian calcites indicate that dissolved and solid sulfides can catalyze the Mg incorporation into calcite lattice. We hypothesize that S2- (or HS-) ions and >S2 on pyrite surface will decrease the hydration / slovation energy of magnesium ions and thus promote nucleation and crystallization of the high-magnesian calcite. In nature environment, the sulfide could be related to microbe-induced sulfate reduction at low temperature using organic carbon and methane as electron donors. Such kind of high-magnesium calcite that is rich in light carbon also indicates involvement of sulfate reducing bacteria. This work is supported by NASA Astrobiology Institute (N07-5489).
P51A-1401
Carbonate Associated Sulfate in a Stromatolite from the Eocene Green River Formation
We measured the carbonate associated sulfate (CAS: sulfate trapped in the carbonate crystal lattice at the time of precipitation) in a ~51 myo stromatolite from the Tipton-Wilkins Peak contact in the Greater Green River Basin in southern Wyoming. The 8-cm-thick microdigitate stromatolite contained two alternating microstructures: a precipitated carbonate fan fabric and a micritic fabric (including trapped detrital grains). CAS values for the precipitated layers clustered narrowly between 392-431ppm; given the precipitated fabric, we suggest that CAS reflects lake chemistry at the time of formation. Adjacent micritic layers, on the other hand, had much greater variation (321-3479ppm) and substantially higher average values per layer (519- 1170ppm); we hypothesize that these values probably may not represent actual lake evaporative environments, the likely source of the micrite. We used average CAS values in the precipitated layers to estimate sulfate concentrations in the Greater Green River Basin at the time of carbonate formation using a CAS vs. sulfate concentration relationship established in a modern analog system at Walker Lake, Nevada. Our analysis suggests that lake sulfate was ~1.5mM, implying a moderate level of sulfate. Better constraints on the rate of carbonate formation and the depth-to-volume relationships of the lake basin are required before quantitative lake depth fluctuation calculations can be done. In lakes where this information is well-constrained, CAS could be used to determine lake volume fluctuations on relatively fine timescales. However, care is required to ensure that grains tested are representative of the in situ environment (e.g. not detrital or shell material).
P51A-1402
Clumping as the Dynamic Initial Step in the Formation of Modern Conical Stromatolites
Modern analogs of ancient conical stromatolites are thought to be distinctly biogenic structures. To understand how biological processes shape these modern structures, we examine the early stages of cone- formation in enrichment cultures of cone-forming cyanobacteria from Yellowstone National Park. The growth of these communities can be divided into three stages: 1) lateral growth stage, 2) clump forming stage, and 3) cone forming stage. After the initial increase in cell density, gliding cyanobacterial filaments form 100-200 micrometer-diameter, regularly spaced clumps. Our measurements of oxygen profiles and photosynthetic rates show that both the photosynthetic and the respiratory rate are higher in the clumps than in the adjacent flat mat. If the clumps are dispersed, their gross photosynthetic rate decreases, showing that cyanobacteria benefit from living in the aggregate. Changes in environmental conditions such as light intensity, oxygen concentration or inorganic carbon concentration can lead to the disappearance of clumps or changes in their spacing in a predictable manner. Microscopic observations suggest that this increased metabolic activity in the clumps leads to the formation of numerous bubbles. As small bubbles raise the clump away from the mat, microbial growth and colonization continues on the newly elevated substrate and vertical structure develops. The repetition of this process in the presence of fast lithification could also have been responsible for the crestal thickening observed in some ancient conical stromatolites
P51A-1403
Ca and Mg Incorporation in Siderite at Low Temperatures (< 50° C): Results from Laboratory Experiments
Siderite (FeCO3) is a common mineral found in modern environments and in ancient rocks produce usually by microbia mediation [1,2]. It usually forms concretions with strongly varying chemical compositions which are governed by both pore-water origin and by microbial influence. In addition, siderite has also been identified in extraterrestrial material such as meteorites and dust particles [3,4]. The geochemical information stored in siderite provides valuable insights into the environmental conditions of mineral formation and the processes by which it is modified over time [5]. To unerstand the inorganic constraints on precipitation relative to natural compositions we undertook free drift experiments under anaerobic conditions at 25, 35 and 45°C with variable concentrations of Fe, Ca and Mg in solution. Samples of solution and solid were withdrawn at different time intervals (15, 21 and 30 days) during time course experiments to determine the composition of the solution and mineral precipitates, and the morphology and mineralogy of the precipitates. After 15 days of incubation a metastable phase was formed, whereas after 21 and 30 days of incubation siderite, Ca-siderite, Mg-siderite Ca-Mg siderite and/or Fe-pokrovskite (a hydrated magnesium hydroxy carbonate) were formed depending on the aqueous Fe, Ca and Mg concentrations in the solution. The Mg and Ca contents in the siderite increased with increasing Mg and Ca concentrations in the medium and with increasing temperature. Siderite precipitates ranged from 1.5 to 50.81 mol percent CaCO3 and from 0.54 to 41.38 mol percent MgCO3. Pokrovskite precipitates ranged from 48.8 to 57.7 mol percent MgCO3 and from 42.34 to 51.17 mol percent FeCO3. The Fe content in the pokrovskite increased with increasing temperature. These inorganic experiments will help to understand the mechanism of Ca-Mg-Fe carbonate formation in natural systems and they are of fundamental importance not only for understanding modern and extraterrestrial environments but also as a window into the geologic past. References [1] Kelts K (1988) Geol. Soc. Spec. Publ. 40, 3-26. [2] Garrels RM, Perry EA, Mckenzie FT (1973) Economic Geology 68, 1173-1179. [3] Romanek CS, Grady MM, Wright IP et al. Nature 372, 655-430. [4] Keller LP, Thomas KL, McKay DS (1994) Meteoritics 29, 480-481. [5] Woods TL, Garrels RM (1992) Geochim. Cosmochim. Acta 56, 3031- 3143.
P51A-1404
Simulating Succinate-Promoted Dissolution at Calcite {104} Steps
Organic molecules of a wide range of molecular weights from small organic acids, amino-acids, acidic peptides and acidic proteins to humic and fulvic acids play a key role in modulating nucleation, crystal growth and dissolution of calcium carbonate polymorphs. In general, these acidic molecules inhibit calcite growth and, promote dissolution preferentially along specific crystallographic directions, in the process, regulating crystal shape and size, and even whether a metastable polymorph (e.g., vaterite or aragonite) is nucleated first. For example, chiral faces of calcite are selected by chiral amino-acids and the unusual {hk0} faces are expressed in the presence of amino-acids [Orme et al., 2001], and unusual heptagonal dissolution etch-pit are seen in the presence of succinate compared to the normal rhombohedral pits in water alone [Teng et al., 2006]. Thus, the presence of unusual crystal morphologies may indicate organic-mediated growth, thus serving as a biosignature. We have conducted the Molecular Dynamics (MD) simulations using the Consistent Valence Force Field (CVFF) as implemented in the FORCITE© module of the Materials Studio © software package (Accelrys, Inc. TM) to model the adsorption of succinate, a dicarboxylic acid, and charge- balancing Na+ ions on dry and hydrated steps in different directions on the {104} cleavage face of calcite [Mkhonto and Sahai, in prep.]. At the site of succinate adsorption, we find elongation of the interatomic distances (Ca-OCO3,i) between surface Ca2+ cation and the oxygen of the underlying inorganic CO32- anion the first surface layer of calcite, compared to the corresponding distances in the presence of water alone, suggesting greater ease of surface Ca2+ detachment. This result is consistent with the empirically observed increase in overall dissolution rate with succinate [Teng et al., 2006]. Furthermore, succinate adsorption lowers the step energies, which explains the appearance of steps in the unsusual [42-1] and [010] directions in the presence of succinate as observed by Atomic Force Microscopy [Teng et al., 2006]. Finally, the calculated succinate adsorption energies at hydrated steps decreases in the sequence [-441] > [42-1] > [010], which also corresponds to the sequence of steps opening at dissolution etch-pits in the presence of succinate [Teng et al., 2006]. Our study provides a strong example of the utility of MD simulations in exploring organic-mediated mineral crystal dissolution (and growth) mechanisms, resulting in unusual morphologies, that may serve as biosignatures on Earth, and potentially on Mars and other worlds.
P51A-1405
Non-chemically Pure Magnetites Produced from Thermal Decomposition of Ankerites
It has been claimed that chemically pure magnetites (Fe3O4) can be obtained from thermal decomposition of (Fe, Mg, Ca)CO3 (Golden et al., 2004). Such an observation is critical, since it opens the possibility of an inorganic way of formation of the magnetites found on Martian meteorite ALH84001. Such a chemical purity is one of the parameters used, so far, to recognize bacterial origin of natural magnetites (Thomas-Keptra et al., 2001), since it has been demonstrated that biologically-controlled magnetites are chemically pure (Bazylinski and Frankel, 2004) . However, while Golden et al. (2004) obtained pure magnetite from an almost pure precursor, the ankerite cores in ALH84001 in which magnetites are embedded are far from being chemically pure, since they contain considerable amounts of Ca and Mg (Kopp and Humayun, 2003). In this study we have performed several experiments to analyze the chemical purity of magnetites produced by thermal decomposition of four ankerite samples sinthetized in the laboratory, and containing different amounts of Ca, Fe and Mg. Such a thermal decomposition was achieved by two procedures: (1) by heating the samples at 470°C under CO2 pressure and (2) by decomposing the ankerite "in situ" under the TEM (Transmission electron Microscopy) electron beam. Magnetite produced by the first procedure was analyzed by XRD to determine whether or not the resulting solid was a mixture of oxides or rather a solid solution of (Ca, Fe and Mg)oxide. Magnetites formed by the two methods were studied by High Resolution TEM. The chemical composition of about 20 crystals of each experiment was analyzed by EDAX. Under our experimental conditions, ankerites decomposed in magnetite crystals of about 5 nanometers in size. Magentite crystals arranged to keep the morphology of the precursor. Our results confirm that any of these magnetites is chemically pure, but rather, each one of them is a solid solution of Ca and Mg. Therefore, chemically pure magnetites found in the meteorite ALH84001 cannot be obtained, as Golden et al. (2004) proposed, just by the thermal decomposition of the (Fe, Ca, Mg)CO3 precursor in which they were embedded.
P51A-1406
Distinctive Accessory Minerals, Textures and Crystal Habits in Biofilm Associated Gypsum Deposits
Gypsum-depositing environments near Guerrero Negro, Baja California Sur, Mexico were investigated in order to differentiate the influence of microbial activity versus nonbiological processes upon sedimentary fabrics and minerals. Field sites were located in sabkhas (mudflats and anchialine pools) and in seawater concentration ponds in the salt production facility operated by Exportadora de Sal, S. A. Gypsum (CaSO4.2H2O) was classified according to sedimentary environment (e.g., mudflats, anchialine pools, saltern ponds, surface and subsurface sediments), sedimentary texture, mineral composition, crystal habit, brine composition and other geochemical and biological factors. Gypsum types that develop in the absence of biofilms include water column precipitates (pelagic grains) and subsedimentary crystalline discs that form from phreatic brine ripening. Subsedimentary gypsum forming in sabkha environments had a sinuous axial microtexture and poikilitically enclosed detrital particles whereas water column precipitates exhibited euhedral prismatic habits and extensive penetrative twinning. Gypsum that was influenced by biofilms included cumulate crusts and gypsooids / gypsolite developing in anchialine pools and in saltern concentration ponds. Gypsum precipitating within subaqueous benthic microbial mats, or biofilm/sediment surfaces offered compelling evidence of biofilm influence on crystal textures and habits. Biofilm effects include irregular high relief surface textures, accessory minerals (elemental sulfur, Ca-carbonate, Sr/Ca-sulfate, Mg-oxide and Mg- sulfate) and distinctive crystal habits. Elemental sulfur, Ca-carbonate, and Sr/Ca-sulfate are known byproducts of bacterially mediated sulfate reduction (BSR). Populations of gypsum crystals within biofilms exhibited euhedral to lensoidal morphologies with unique equant and distorted prismatic forms. These forms had been shown to arise from form- and face-specific inhibition by bioorganic functional groups (Cody, 1991; Cody and Cody 1991). Biofilms therefore may play an active role in influencing brine chemistry, inducing crystallization and modifying crystal habits, evidence of which is preserved in grain morphologies.