16 research outputs found
Infrared spectroscopic biosignatures from hidden cave, New Mexico: possible applications for remote life detection
Subsurface environments are known to support and preserve diverse microbial communities. Giant pool fingers from Hidden Cave,
New Mexico consist of mm-scale dark micritic calcite layers alternating with clear dogtooth spar crystals and contain morphological
and geochemical evidence of past microbial communities. We used Fourier Transform infrared spectroscopy to identify fatty acids,
proteins, PO2-carrying compounds, and polysaccharides spatially related to morphological fossil filaments throughout the surface
micritic laminations and central pool finger regions. These biomolecular signatures are important components that contribute to the
biosignature suite under development that identify microbial involvement in carbonate precipitation on Earth and remotely
LowerâMiddle Ordovician carbon and oxygen isotope chemostratigraphy at HĂ€llekis, Sweden : implications for regional to global correlation and palaeoenvironmental development
A high-resolution chemostratigraphical (coupled ÎŽ13Ccarb and ÎŽ18Ocarb) study of the topmost Floian through the middle Darriwilian (Ordovician) succession at the HĂ€llekis quarry, Kinnekulle, southern Sweden, shows relatively steady isotopic values with overall minor changes, although some notable short- and long-term shifts are discernible. A pronounced positive shift in ÎŽ13C in the uppermost part of the study succession is identified as the Middle Darriwilian Isotopic Carbon Excursion (MDICE), representing the only named global isotopic excursion in the data set. Regional and global comparisons suggest that few details in the different carbon and oxygen isotope curves can be confidently correlated, but longer-term patterns appear quite consistent. Trends in the isotope data are in agreement with palaeogeographical reconstructions. Differences in stratigraphical patterns of both carbon and oxygen isotopes between localities suggest strong secular development at several spatiotemporal scales; any global signal involving relatively minor isotopic shifts is often masked/subdued by local and regional overprinting and care should be taken not to overinterpret data sets. Collectively, the data suggest rising sea levels and cooling climates through the studied time interval, but detailed interpretations remain problematic
LowerâMiddle Ordovician carbon and oxygen isotope chemostratigraphy at HĂ€llekis, Sweden: implications for regional to global correlation and palaeoenvironmental development
Lava Cave Microbial Communities Within Mats and Secondary Mineral Deposits: Implications for Life Detection on Other Planets
The role and impact of freshwater?seawater mixing zones in the maturation of regional dolomite bodies within the proto Floridan Aquifer, USA
Lateâstage calcites in the Permian Capitan Formation and its equivalents, Delaware Basin margin, west Texas and New Mexico: evidence for replacement of precursor evaporites
Comparison of Upper Guadalupian foreâreef, reef and backâreef strata from outcrops in the Guadalupe Mountains with equivalent subsurface cores from the northern and eastern margins of the Delaware Basin indicates that extensive evaporite diagenesis has occurred in both areas. In both surface and subsurface sections, the original sediments were extensively dolomitized and most primary and secondary porosity was filled with anhydrite. These evaporites were emplaced by reflux of evaporitic fluids from shelf settings through solutionâenlarged fractures and karstic sink holes into the underlying strata. Outcrop areas today, however, contain no preserved evaporites in reef and foreâreef sections and only partial remnants of evaporites are retained in backâreef settings. In their place, these rocks contain minor silica, very large volumes of coarse sparry calcite and some secondary porosity. The replacement minerals locally form pseudomorphs of their evaporite precursors and, less commonly, contain solid anhydrite inclusions. Some silicification, dissolution of anhydrite and conversion of anhydrite to gypsum have occurred in these strata where they are still buried at depths in excess of 1 km; however, no calcite replacements were noted from any subsurface core samples. Subsurface alteration has also led to the widespread, lateâstage development of largeâ and smallâscale dissolution breccias. The restriction of calcite cements to very nearâsurface sections, petrographic evidence that the calcites postâdate hydrocarbon emplacement, and the highly variable but generally âlightâcarbon and oxygen isotopic signatures of the spars all indicate that calcite precipitation is a very late diagenetic (telogenetic) phenomenon. Evaporite dissolution and calcitization reactions have only taken place where Permian strata were flushed with meteoric fluids as a consequence of Tertiary uplift, tilting and breaching of regional hydrological seals. A typical sequence of alteration involves initial corrosion of anhydrite, one or more stage