Late Pennsylvanian glaciation: Evidence of icehouse conditions from Canyon and cisco units, Midland Basin, Texas

Abstract

Abstract The late Paleozoic has long been recognized a time of significant continental glaciation associated with high-frequency, high-amplitude glacioeustasy. Although, precise assessment of glacioeustatic amplitudes are difficult to extract from the stratigraphic record, best approximations may be possible by analyzing spatial and temporal distributions of depositional facies utilizing several wells across the study area. We used detailed sedimentologic description and depositional facies analysis from 12 wells and applied rigorous cycle stacking pattern analysis, exposure surfaces recognition and wireline logs to correlate timelines across the wells. On the basis of the high-resolution sequence stratigraphic framework built for the Scurry Area Canyon Reef Operators (SACROC) field, a highly-resolved glacioeustatic curve was generated for latest Desmoinesian to the latest Virgilian. Our eustatic curve suggests that the Missourian and Virgilian stages of the late Pennsylvanian are characterized by high frequency, high-amplitude eustatic fluctuations. The Missourian stage was a period dominated grainstone-capped cycles that are isopachous and conformable. These cycles reflect a eustatic amplitude of at least 37 m with an average duration of 100 ka suggesting the dominance of short-term eccentricity signal. The Virgilian stage is far more complicated and is characterized by highly shingled cycles compared to the Missourian stage. Deeper water phylloid boundstone and calichified shoal complex grainstones are juxtaposed next to each other which suggests a stronger eustatic amplitude (>40 m) compared to the Missourian stage. Although the eustatic amplitude of the Virgilian cycles is similar to those of the Missourian cycles, they have a longer frequency (343 ka) representative of long-term eccentricity. We conclude that the late Pennsylvanian stratigraphy of the SACROC field in the Midland Basin records extensive continental glaciation during the Missourian stage and increased and reached an acme during the Virgilian stage.