Mid-Eocene deep water, the Late Palaeocene Thermal Maximum and continental slope mass wasting during the Cretaceous–Palaeogene impact
R. D. Norris, A. Klaus, D. Kroon, 2001. "Mid-Eocene deep water, the Late Palaeocene Thermal Maximum and continental slope mass wasting during the Cretaceous–Palaeogene impact", Western North Atlantic Palaeogene and Cretaceous Palaeoceanography, Dick Kroon, R. D. Norris, A. Klaus
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A series of widespread Maastrichtian and Palaeogene reflectors in the western North Atlantic have been interpreted to record episodes of vigorous bottom-water circulation produced by periodic flooding of the deep North Atlantic basins with southern source waters. In general, the ages of these reflectors have been poorly known with estimated ages spanning several million years. New seismic and core data from Ocean Drilling Program Leg 171B tightly constrain the ages of several of the most prominent reflectors and demonstrate that several of them are associated with geologically short-lived events associated with major palaeoclimatic, palaeoceanographic and evolutionary transitions. On Blake Nose in the western North Atlantic, Reflector Ac formed shortly after the close of the early Eocene warm period between 48 and 49 Ma. The reflector corresponds to an abrupt inception of vigorous deep-water circulation that winnowed foraminiferal sands at 2000–2500 m water depth and caused mass wasting into the deep basins of the Bermuda Rise. Reflector Ac is correlative with a sequence of unconformities present in nearly every part of the global ocean from the shallow shelf to the deep sea, suggesting that this time interval is associated with global change in ocean circulation, including a major sea-level lowstand. The reflector and unconformities are roughly equivalent in age to glacial tillites on the Antarctic Peninsula, suggesting a link to an early phase of southern hemisphere glaciation. Another widespread reflector, Ab, has a late Palaeocene to earliest Eocene age on the Bermuda Rise. On Blake Nose, the equivalents of Reflector Ab consist of a stack of three closely spaced hiatuses ranging from early late Palaeocene (58.5–60.5 Ma) to latest Palaeocene (c. 55.5 Ma) age. The youngest of these hiatuses is associated with the carbon isotope excursion at the Late Palaeocene Thermal Maximum (LPTM), when there was a major reorganization of deepwater circulation and dramatic, transient warming of high latitudes. Bottom currents appear to have prevented the widespread deposition of sediments at water depths shallower than c. 2200 m from the LPTM until early mid-Eocene time. Erosion on Blake Nose was produced by a strengthened, southward-flowing deep western boundary current at the same time that a southern source watermass produced extensive erosion on the Bermuda Rise. We suggest that the increased flow of the deep western boundary current reflects a stronger outflow of warm intermediate waters shallower than 2000 m from Tethys. The combination of warmer intermediate waters and erosion along the margin may have helped to trigger slope failure of gas hydrate reservoirs around the North Atlantic margin and set the LPTM—greenhouse feedback system in motion. Reflector A* is correlative with highly deformed Maastrichtian sediments on Blake Nose and Maastrichtian chalk interbedded with red claystone on Bermuda Rise. Seismic and coring evidence from Blake Nose shows that the K–P boundary slumping was associated with the magnitude c. 11–13 Richter Scale earthquake generated by the Chicxulub impact event. The chalk sequence on the Bermuda Rise appears to represent the distal turbidites produced by slumping of the margin. Correlation of the chalk beds with Reflector A* shows that the mass wasting deposits are found over nearly the entire western North Atlantic basin. Apparently, much of the eastern seaboard of North America must have catastrophically failed during the K–P impact event, creating one of the largest submarine landslides on the face of the Earth.
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Palaeogene and Cretaceous palaeoceanography has been the focus of intense international interest in the last few years, spurred by deep ocean drilling at Blake Nose in the North Atlantic as well as the need to use past climate change as input for modelling future climate change. This book brings together a number of review papers that describe ancient oceans and unique events in the Earth’s climatic history and evolution of biota. The papers show evidence of periods characterized by exceptional global warmth such as the Late Palaeocene Thermal Maximum and Cretaceous anoxic events. Geochemical records and modelling will make the reader aware that these periods were forced by greenhouse gases. This information is essential for understanding the response of the ocean—climate system to the current input of fossil fuels. In this sense, the book contributes to the understanding of fundamental aspects of Earth’s climate, the carbon cycle, and marine ecosystems. A number of papers describe massive mass wasting deposits resulting from the energy released by the bolide impact at the Cretaceous—Tertiary boundary as well as the geochemistry of the boundary itself. Additional papers cover aspects of cyclostratigraphy and biostratigraphy of Palaeogene and Cretaceous records.
This book will be of interest to a broad audience of Earth Scientists interested in Palaeogene—Cretaceous palaeoceanography, extreme climate modelling, Cretaceous—Tertiary boundary, Late Palaeocene Thermal Maximum, Cretaceous anoxic events, as well as those specifically interested in radiolarian, dinoflagellate and coccolithophorid stratigraphy.