Abstract

Study of Pennsylvanian (Virgilian)–Permian (Wolfcampian) strata of the western United States (parts of Idaho, Utah, New Mexico, and Kansas) reveals complex relations between relative changes in sea level and shifts in climate. Relative falls in sea level are indicated by subaerial exposure of subtidal sediments and fluvial incision through subtidal sediments. Changes in the character of pedogenesis and sediment transport, deposition, and supply, and the variable distribution of climatically sensitive lithofacies within cyclothems are interpreted to reflect shifts in climate during deposition of each cyclothem. The majority of stratal relationships documented herein from a number of long-term climatic, sedimentologic, and shelf settings are consistent with a hypothesis that relative highs in sea level are accompanied by more seasonal conditions, whereas relative lows are characteristically more arid. Uncommon deviations are present, however, and may be due to (1) shoaling caused by sedimentation or tectonic uplift, independent of a eustatic-climatic signal; (2) complex sedimentologic or geomorphic responses to climate change; (3) leads, lags, or thresholds in either glacial advance and retreat or the climatic response to such changes.

This study shows that coupled climatic shifts and changes in sea level exert a pronounced, but varied, influence on stratigraphic architecture in depositional settings across late Paleozoic ramps. The proposed climatically enhanced cyclic and reciprocal sedimentation model predicts that during a single eustatic fall, updip areas have features indicating a more seasonal or humid climate that are overlain or overprinted by characteristics suggesting more arid climate. In downdip areas that were not subaerially exposed until the late stages of a eustatic fall, only more arid climatic features are represented in the terrestrial or subaerial exposure features.

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