KIDDER, David L. and WORSLEY, Thomas R., Geological Sciences, Ohio Univ, Athens, OH 45701-2979, kidder@ohiou.edu

Rapid end-Permian extinctions probably intensified conditions that were already developing on Earth including: 1) extreme warmth, 2) deep-sea stratification and anoxia facilitated by warm, saline bottom water, 3) limitation of nutrient availability, and 4) reduction in atmospheric oxygen levels. All of these factors could have delayed Early Triassic biotic recovery. Decay of unburied biomass would release considerable carbon dioxide to the atmosphere. Destruction of most photosynthetic organisms (land plants and phytoplankton) would sustain warmth by sharply reducing Earth’s capability for CO2 drawdown. Water lost during forest destruction would facilitate desertification that would foster erosion resulting in depletion of soil nutrients and release of CO2. Additional greenhouse gas probably entered Earth’s atmosphere from the Siberian Traps eruptions, gas hydrate release, and ocean overturn. Absence of active, low-latitude Late Permian orogenic belts had already reduced long-term silicate weathering and CO2 drawdown.

Early Triassic gaps in chert, phosphate, and coal accumulation suggest limited nutrient availability in both terrestrial and marine settings. Minimal marine nutrient supplies should have resulted from reduced terrestrial chemical weathering and limited ocean circulation. This is consistent with low diversity biotas characterized by disaster taxa such as stromatolites, which successfully filled the reef niche, lingulid brachiopods, and perhaps opportunistic phytoplankton.

Atmospheric oxygen levels had probably been declining earlier in the Permian. Rapid oxidation of unburned biomass probably lowered oxygen levels even further, hindering recovery of higher life forms. If the extinctions were triggered by extraterrestrial impact, the presence of the fungal spore horizon rather than a soot layer is consistent with low atmospheric oxygen levels that would prevent ignition of impact-generated forest fires.

Depleted tropical soils, mid-latitude dryness, and extreme warmth would slow the recovery of plant life. Thriving Early Triassic floras in moist, high paleolatitude settings would contribute minimally to CO2 drawdown because of the very small occupied area and because of restricted photosynthesis during long winter darkness.

Earth System Processes - Global Meeting (June 24-28, 2001)
Session No. T6
Controls on Phanerozoic Diversifications and Extinctions: Long-Term Interactions Between the Physical and Biotic Realms
Edinburgh International Conference Centre: Tinto
10:00 AM-2:30 PM, Tuesday, June 26, 2001