Global Eocene-Oligocene unconformity in clastic sedimentary basins

Abstract

Global sedimentary hiatuses are well-documented in ancient pelagic sediment, and include Paleocene, Eocene-Oligocene boundary, and Miocene hiatuses. Less clear is the extent of these hiatuses in continental margin settings. Here, we test the hypothesis that global hiatuses evident in pelagic sections are also manifested in siliciclastic basins of continental margins globally. We choose to focus on the Eocene greenhouse to Oligocene icehouse transition, a period that is remarkable as the most profound climatic transition of the Cenozoic, and a period characterized by extreme cooling and expansion of polar ice, sea-level fall, and global changes to ocean circulation. We perform a comprehensive review of marine siliciclastic basin literature to produce a global inventory of Eocene-Oligocene unconformities. We find evidence for a prominent Eocene-Oligocene unconformity in sedimentary basins along the margins of every continent. The globally-widespread distribution of unconformities suggests global controls on their development. Furthermore, Eocene-Oligocene erosion surfaces are common in shelf settings, as well as in deep-water settings from slope to basin floor, indicating unconformity-generating processes across a wide range of water depths. Global sea-level fall may have driven subaerial shelf exposure and erosive down-slope processes including submarine canyon cutting and mass wasting. Meanwhile, the intensification of deep-ocean thermohaline currents potentially induced erosion of not only pelagic successions, but also of clastic successions. Overall, our documentation of globally-widespread Eocene-Oligocene unconformities suggests global controls, of which the extreme climatic and oceanographic changes of the greenhouse to icehouse transition seem particularly compelling.