Enhanced storm-induced turbiditic events during early Paleogene hyperthermals (Arabian continental margin, SW Iran)

摘要

Early Paleogene hyperthermal episodes including the Paleocene-Eocene Thermal Maximum (PETM) have long been viewed as analogues of the Anthropocene global warming. Few studies, however, have analyzed the environmental consequences of such climatic anomalies in deep-water turbidite-rich successions. This integrated sedimentological, biostratigraphic, and stable-isotope study of the Paleogene Pabdeh Formation, deposited along the Arabian continental margin of southwestern Iran, allowed us to document the geological response of hyperthermal events in deep Neo-Tethyan Ocean. The late Thanetian event (Pre-Onset Excursion or long-term late Paleocene climatic perturbation), the Early Eocene Climate Optimum, and the Middle Eocene Thermal Maximum were successfully identified within the Pabdeh Formation. The PETM event could not be documented because the Paleocene/Eocene boundary corresponds to a prolonged non-depositional hiatus marked by a glauco-phosphorite interval. Based on high-resolution microfacies analysis, three different processes in a carbonate slope to basin-margin environment were distinguished including pelagic settling, upwellingcondensation-reworking, and storm-induced turbiditic deposition. Detailed sedimentological analysis revealed an anomalous abundance of storm-induced proximal to distal turbidites represented by packstones with deepwater and reworked shallow-water bioclasts occurring during the hyperthermal intervals. A close causal link between climate warming and tropical storms during the early Paleogene hyperthermal events is thus envisaged. As a principal mechanism, we propose that rapid warming in response to massive carbon release triggered pronounced sedimentological changes along low-latitude tropical margins, leading to generation of storminduced calciturbidite and re-deposition in the deep sea during hothouse stages.