DID PANGEAN SALT, WIND, AND ACID CONTRIBUTE TO THE PERMO-TRIASSIC MARINE BIOTIC CRISIS?

Mid Permian – mid Triassic redbeds and evaporites preserve evidence of Pangean environments with extremes in lake and groundwater chemistry, climate and weather, and life. Here, we present an overview of data from cores from the subsurface of Northern Ireland, Kansas, and North Dakota, supplemented by outcrop observations. Sedimentary features document ephemeral saline lakes surrounded by mudflats and sandflats, dunes, and desert soils. Redbeds and evaporite strata hundreds of meters thick have a paucity of carbonate minerals and body and trace fossils. Unaltered primary fluid inclusions in bedded lake halite contain trapped lake waters, tiny crystals, air, microorganisms, and organic compounds. Petrography and geochemical analyses of fluid inclusions document lake waters with low pH (<2) and high metal concentrations, abundant chloride, sulfate, and iron oxide precipitation, and extremophilic microorganisms. Fluid inclusion homogenization temperatures record high air temperatures and a large diurnal temperature range. Although there was some chemical heterogeneity of acid brines among Kansas, North Dakota, and Northern Ireland, all hosted extreme continental environments. Repeated precipitation, dissolution, and eolian reworking of chemical sediments, including halite, gypsum, metal sulfates, iron oxides, and clays, were common.

We propose that wind transported products of acid brine lakes, sandflats, and mudflats were deposited in the ocean during the mid Permian – mid Triassic. Shallow seawater may have become turbid, decreasing the abundance of photosynthetic organisms. Dissolution of soluble chemical sediments, such as halite, would have released acids, metals, and extremophilic microorganisms to seawater. How much was pH, salinity, major and trace elements, and life in oceans affected? Quantification of the acid brine products transported into oceans remains a challenge. Although Permo-Triassic redbeds and evaporites are common, well-preserved, high-recovery cores that best preserve detailed environmental, paleoclimatic, and microbiological data are rare. Detailed examination of additional cores from other Permo-Triassic redbeds and evaporites is needed to test the geographic extent and longevity of such extreme environments.