Paleoclimatic and Environmental Reconstruction of Lacustrine Carbonates from the late Cretaceous to middle Eocene Sheep Pass Formation, Nevada
Abstract
Ancient lacustrine carbonate successions preserve valuable records of terrestrial paleoclimate, with particular utility for examining the sensitivity of terrestrial environments during global greenhouse intervals. The Sheep Pass Formation (SPF), located in the southern Egan Range of east-central Nevada, is a > 1km thick package of non-marine, majority-carbonate strata spanning late Cretaceous through middle Eocene time, and includes alluvial, fluvial and microbial carbonate facies. The SPF is believed to be one of a number of high altitude, fault-bounded lacustrine basins formed on top of the Sevier hinterland, and its age suggests that it may record significant climatic shifts related to the K-Pg boundary or the PETM. The SPF is characterized by five members that include alluvial conglomerates, bioclastic and microbial lacustrine carbonates, fluvial sandstones, and poorly lithified palustrine carbonates. Though past research has helped elucidate aspects of the sedimentology, chronology, biostratigraphy, and paleoaltimetry of the SPF, it has remained underutilized as a paleoclimate archive. This study melds field observations, thin section and cathodoluminescence (CL) microscopy, carbonate δ13C and δ18O analyses, and temperature estimates from clumped isotope analyses of the carbonates to refine the current environmental and paleoclimatic framework of these ancient high-altitude carbonate lakes. Preliminary results suggest SPF facies and micro-facies (reflective of formation micro-environments) are more varied than previously defined, especially with respect to the packstone facies. Clumped isotope temperature estimates record a large range between ~10-90°, including the highest temperature yet determined for any previous SPF samples. Preliminary CL petrography also highlights the complexity of facies in the formation. δ13C and δ18O values reflect several facies-specific trends, with large isotopic variability throughout the section. Lastly, the large range in isotopic values and temperatures for microbialite lacustrine carbonate samples in the ~100-meter-thick Member B demands greater attention in evaluating the extent to which facies (and therefore depositional or diagenetic processes) affect stable isotope signals and temperatures recorded throughout the formation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMPP0080012O
- Keywords:
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- 0448 Geomicrobiology;
- BIOGEOSCIENCES;
- 1039 Alteration and weathering processes;
- GEOCHEMISTRY;
- 3022 Marine sediments: processes and transport;
- MARINE GEOLOGY AND GEOPHYSICS;
- 4863 Sedimentation;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL