Dynamic climatic changes during the Late Pennsylvanian icehouse: New insight from high-resolution geochemical records in the Cline Shale, North America

Abstract

The profound glaciations of the Late Paleozoic represent an extreme climatic perturbation during a time when much of the Earth was initially thought to have been covered with an ice cap for a single prolonged period. Recent research has typically interpreted the Late Paleozoic Ice Age as a dynamic climatic regime characterized by multiple short-term glaciations alternating with globally warmer interglacial conditions within a long-term icehouse epoch. However, the onset and extent of each glaciation interval are not well constrained, especially for the Late Pennsylvanian period. This study presents high-resolution carbon isotopic signatures and other bulk geochemical datasets for deep marine sediments from the Virgilian and Missourian Stages of the Cline Shale (Midland Basin) for the first time. Significant variations in chemical index of alteration (CIA) and chemical index of weathering (CIW) are interpreted as having been caused by climatic oscillations that drove variations in the intensity of chemical weathering on contemporary province areas. The CIA and CIW variation trends suggest a cycle of six cold and dry glacial periods punctuated by six well-defined, relatively warm and humid interglacial periods during the Late Pennsylvanian. In agreement with climate proxies, the coupling variation of the carbon isotope of marine organic matter (δ13Corg) reveals shifts in marine bicarbonate rather than variations of organic matter type. A covariation trend between the carbon isotope signatures of equatorial Russian Platform brachiopods, polar Karoo Basin organic matter, and organic matter in this study indicates a global climate control mechanism was at play, rather than local forcing factors.