Pangea on Acid: Extreme Environments, Climate, and Life during Permo-Triassic Time - Public Lecture

Continental rocks of middle Permian to middle Triassic age are dominated by red bed siliciclastics and evaporites. Multiple lines of sedimentological, mineralogical, and fluid inclusion evidence show that tropical Pangea hosted deserts with some of the most geochemically extreme waters known from the Phanerozoic Eon.

Bedded and displacive halite and gypsum, along with quartz‑ and Fe‑oxide‑rich fine-grained siliciclastic rocks cemented with halite, gypsum, and kaolinite, were deposited in ephemeral lakes, saline and dry mudflats, desert soils, and rare dunes and ephemeral channels.

Lake waters and groundwaters had pH as low as –1, salinities more than ten times that of modern seawater, and complex chemical compositions. Fluid inclusions in bedded halite are enriched in bisulfate and sulfate, as well as unusually high concentrations of dissolved aluminium, iron, and silica. Minerals that form only in acidic conditions, including jarosite and alunite, are preserved in these deposits.

Primary fluid inclusions in halite also point to high air temperatures and large diurnal temperature ranges, indicating a hot, dry climate. The rocks are notably poor in carbonates, macrofossils, and organic sedimentary structures, yet extremophilic microorganisms are present in primary fluid inclusions.

These extreme environments were widespread across tropical Pangea, with red bed–hosted evaporites interpreted as acid brine lake and groundwater systems throughout the midcontinental USA, the UK, Morocco, and Brazil. Stratigraphic trends show an evolution from freshwater lakes to perennial neutral saline lakes and finally to ephemeral acid brine lakes as climate became progressively warmer and drier.

Physical reworking of red muds, salts, and extremophilic microbes by wind may have transported them into shallow tropical seawater, where they could have influenced turbidity, chemistry, and biology of the Panthalassan Ocean around the time of the end-Permian mass extinction.