T297 Lakes of the World through Time and Space II

Wednesday, 25 September 2019
1:30 PM - 5:30 PM
Room 222BC, North Building

THE NECESSITY OF SCIENTIFIC DRILLING FOR RECOGNITION OF PERMO-TRIASSIC CONTINENTAL ECOSYSTEMS OF EQUATORIAL PANGEA

Paper number: T297-15
Program: Technical Sessions
Time: 5:00 PM – 5:15 PM

Authors

Abstract

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.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-334675

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