Paper No. 300-8
Presentation Time: 10:45 AM
MODERN AND ANCIENT MICROBIALITE DEPOSITS FROM A SHALLOW ALKALINE LAKE: LOWER PAHRANAGAT LAKE, CENTRAL NEVADA
Ancient lacustrine microbialites have become progressively more important in the geoscience community due to their potential for exobiological interpretation and as potential petroleum source rocks and reservoirs. Detailed understanding of these microbialites is somewhat hampered by a lack of clear modern analogues. The Lower Pahranagat Lake (LPL) near Alamo, NV is a spring fed, shallow lake, no deeper than approximately 1 m. It is alkaline, with very high evaporation rates (evaporation:precipitation > 10). Conductivity in January 2014 ranged from 2.52-3.9 ms with salinity ranging from 0.887-1.84 ppt. The shoreline is covered with an evaporitic crust that is in turn surrounded by marshy brush. A paleo-shoreline ~5m above the current lake level shows domal and stratiform stromatolites, as well other textures suggestive of microbial and spring activity, concentrated in an area immediately south of a possible extinct spring source. Additionally, modern microbialite samples were found on the northern edge of an ephemeral island and show a similar morphology to that of LPL paleo-shoreline microbialites. Paleo-shoreline microbialite samples were polished and slabbed in order to characterize internal textures and overall microbialite morphology. Morphologies of the Pahranagat lake region include: 1) Finely laminated; 2) Eggshell stromatolites; 3) Columnar; 4) Tufaceous forms with high porosity and surface clots. Finally, we examined variability in Lower Pahranagat Lake microbial communities using 16s rRNA Amplicon Pyrosequencing to begin to develop a more clear picture of the microbial communities that participate in microbialite formation at LPL. The Horse Spring Formation in the nearby Lake Mead region shows a diverse range of microbialite morphologies and internal textures, similar to microbialites identified from the previously mentioned paleo-shoreline at the Lower Pahranagat Lake. These Miocene microbialites also appear to be closely associated with a nearby spring source (see Bernardi et al., this meeting). The Lower Pahranagat Lake system offers an environment to better understand the formation and lithifaction of modern microbialites in addition to being a potential modern analog for the Horse Spring Formation microbialites.