STORMS IN THE LATE PERMIAN AND EARLY TRIASSIC

We predict that storms were frequent, and perhaps particularly intense in warm Late Permian and Early Triassic climates. Our paleoclimate modeling calls for deep sea stratification and warm, saline bottom water that developed in the Permian and led to a slowing and then a cessation of thermohaline circulation. Presence of deep warm water has implications for the generation of storms because as these ancient storms drew strength from warm surface water, their growth as they extended their downward reach into deeper water was no longer limited by cold water. Late Permian and Early Triassic hurricanes could have persisted longer and travelled to higher paleolatitudes which were also warm at the time. In an atmosphere thickened by increased water vapor, strong wind shear might produce high intensity storms.

The predictions can be tested by looking at the frequency and intensity of storms in the geologic record. Preliminary frequency results suggest that although absolute numbers of Permian and Triassic storm deposits are quite low compared to other intervals, a strong Triassic peak results when numbers of deposits are normalized to outcrop area. The Permian normalized value is low, perhaps because of less storm activity in the Early Permian glaciated world. Preliminary data show that Late Permian storms were slightly more frequent than in the Early Permian. The highest frequency of Triassic storm deposits was in the Middle, with the Early and Late being roughly equal. Tests for intensity are problematic. Storm bed thickness might serve as a crude proxy for intensity, but other variables such as sediment availability complicate this. Pebbly storm beds should be particularly conspicuous in the Early Triassic as flat pebbles should have been relatively easy to generate when diminished levels of bioturbation facilitated early cementation of shallow sediment layers that could be ripped up by storms.