Ice and High-Magnitude Climate Change in Equatorial Pangaea

Soreghan, G.S.¹ (1) University of Oklahoma, Norman, OK

The late Paleozoic is Earth's best-documented pre-Quaternary icehouse, long thought analogous to the recent. Emerging data from the Ancestral Rocky Mountains (western equatorial Pangaea), however, suggest glaciation extended to low latitudes and elevations. For example, enigmatic Unaweep Canyon (Uncompahgre uplift) dates from the late Paleozoic, and exhibits geomorphic attributes and sedimentary fill best reconciled with glaciation. The Permo-Pennsylvanian Cutler Formation (proximal Paradox basin) onlaps the canyon and contains facies of inferred glaciolacustrine and glaciofluvial origin. The Cutler deposystem ultimately extended to sea level in the distal Paradox basin. Maximum depositional gradients on this system yield maximum elevations of 500-1000 m for the ice terminus, implying substantially cooler temperatures than the Quaternary and more widespread glaciation than previously considered. Yet, lowland deposits from equatorial regions clearly record cyclic (interglacial) warm-water carbonate deposition. Reconciling these observations requires appeal to abrupt, high-magnitude climate change operating on a sub-cyclothemic scale. The sea-level effects of such change are well appreciated, but the phenomenon of abrupt, high-magnitude climate change (known from the recent) remains underappreciated for the deeper time record, where climate inferences are commonly time-averaged over millions of years. Such change is critically important to understanding the full spectrum of Earth's climate behavior and climate impacts on various Earth systems.