GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 297-14
Presentation Time: 5:00 PM


BENISON, Kathleen C.1, ANDESKIE, Anna Sofia1 and ZAMBITO IV, James J.2, (1)Department of Geology and Geography, West Virginia University, Morgantown, WV 26506-6300, (2)Department of Geology, Beloit College, 700 College St., Beloit, WI 53511

Modern saline continental environments are well known and easily studied by fieldwork in saline lakes, saline mudflats and sandflats, evaporite dunes, and desert soils. In contrast, well-preserved ancient saline deposits are known only from the subsurface, including salt mines and cores. Evaporite rocks require careful coring from depths of ~300 – 1000 meters for detailed sedimentological, geochemical, and biological studies.

In Kansas, the mid-late Permian Sumner and Nippewalla Groups are dominated by evaporites and red siliciclastics that formed in lakes and associated environments at ~ 5°N latitude. The late Permian Belfast Harbour Evaporite Formation and Triassic Mercia Mudstone Group of Northern Ireland are lithologically equivalent to their counterparts in Kansas, but formed later and at a higher latitude of ~30°N. The Nippewalla and Mercia Mudstone Groups contain bedded halite and displacive halite that precipitated from extreme acid saline lake and groundwater, respectively. These descriptions rely on rare, high-quality cores.

Detailed environmental conditions determined from Permo-Triassic red bed and evaporite cores from Kansas and Northern Ireland include lake water depths, lake water and groundwater compositions, flooding-evapoconcentration-desiccation cycles, and climate and weather characteristics. Evidence of organisms in the red siliciclastics consists of rare small root features and rare back-filled insect burrows. Bedded halite preserves microorganisms as solid inclusions and within primary fluid inclusions. Prokaryotes and algae are seen by microscopy in the 480 – 2000x magnification range. UV-vis florescent response is present, but duller than for microorganisms in modern halite, suggesting decay of organic material.

Existing core samples from the Permo–Triassic of Kansas and Northern Ireland record a biotic crisis in low-latitude equatorial Pangea that predates the end Permian mass extinction. Subaerial environments, represented by red siliciclastics, were hot and windy deserts with a restricted biome. Bedded halites show that saline lakes hosted extremophile microbial communities. More high-resolution, well-preserved cores are necessary to refine trends in extreme continental ecosystems which may be related to the end-Permian mass extinction.