LATE PENNSYLVANIAN CLIMATE IN WESTERN EQUATORIAL PANGEA

Plant fossils from Late Pennsylvanian strata deposited in the easternmost part of the Paradox basin geologic province (Colorado, USA) include Neuropteris, Pecopteris, and Calamites. The fossils are preserved in Cutler Formation strata that were deposited in an upland setting along the flank of the Uncompahgre uplift portion of the Ancestral Rocky Mountains. The fossil locality was situated between the Uncompahgre uplift and the Late Paleozoic paleoshoreline at equatorial paleolatitudes.

These fossils indicate that warm and wet climate conditions were present at the time of deposition. The fossils and the characteristics of the encasing sedimentary rock succession together indicate an overall semi-arid to sub-humid and seasonally wet climate. This climate regime is consistent with most previous interpretations based on analysis of continental and nearshore marine rocks of similar age in equatorial western Pangea. Our interpretation differs substantially from that proposed by some other studies which have ascribed deposition of the same rocks in the same region to glacial or pro-glacial processes. The paleoclimate information provided by the fossils coupled with analysis of the Cutler Formation in the same area indicates that the fossils were preserved near the apex of an alluvial fan complex deposited adjacent to the flank of the Uncompahgre uplift.

The results of this study suggest that upland settings at equatorial latitudes in western Pangea did not experience glacial or pro-glacial conditions during the Late Pennsylvania. Further, seasonality trends in the upland setting appear to be related to regional climate trends in western Pangea.