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Kenneth Miller, Rutgers University (United States)
James Browning, Rutgers University (United States)
Miriam Katz, Rensselaer Polytechnic Institute (United States)
James Wright, Rutgers University (United States)
Marie-Pierre Aubry, Rutgers University (United States)
Bridget Wade, Rutgers University (United States)
Benjamin Cramer, University of Oregeon (United States)
Andrew Kulpecz, Rutgers University (United States)
Yair Rosenthal, Rutgers University (United States)
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The St. Stephens Quarry, Alabama (SSQ) outcrop and corehole offer a unique opportunity to evaluate the largest global climate cooling event of the Cenozoic (∼33.8-33.5 Ma; latest Eocene-earliest Oligocene) in which warm, high CO2 greenhouse conditions gave way to the icehouse climates that still prevail today. We integrate upper Eocene-lower Oligocene lithostratigraphic, magnetostratigraphic, biostratigraphic, stable isotopic, Mg/Ca, benthic foraminiferal faunal, downhole log, and sequence stratigraphic studies from the SSQ corehole, that provides a superior record to the adjacent outcrop because of limited weathering. The SSQ succession is dissected by hiatuses associated with sequence boundaries: North Twistwood Creek-Cocoa (35.4-35.9 Ma), mid-Pachuta (33.9-35.0 Ma), Shubuta-Bumpnose (lowermost Oligocene; ∼33.6 Ma), Mint Spring-Red Bluff (33.0 Ma), Byram-Glendon (30.5-31.7 Ma), and Bucatunna-Chickasawhay (the famed mid-Oligocene fall; ∼30.2 Ma). Here, we integrate three proxies (ä18O, Mg/Ca, sequence stratigraphy) from SSQ with deep-sea Sites 522 (South Atlantic) and 1218, (Pacific) ä18O and Mg/Ca records to delineate for the first time the three components of the greenhouse-to-icehouse transition (cooling, ice-volume increase, and sea-level fall). A ∼1 ‰ ä18O increase in the SSQ corehole is correlated to the global earliest Oligocene (Oi1) event using magnetobiostratigraphy; this increase is associated with the Shubuta-Bumpnose contact, an erosional surface, and a biofacies shift in the corehole, providing a first-order correlation between ice growth and a sequence boundary that indicates a sea-level fall. A precursor ä18O increase of 0.5‰ (33.8 Ma, mid-Chron C13r) at SSQ correlates with a 0.5‰ increase in the deep Pacific and Atlantic Ocean. Our comparisons reveal that the Eocene-Oligocene transition occurred in two to three steps, with increasing influence by ice volume relative to cooling. In total, ice sheets grew to ∼125% larger than they are today, with an associated ∼105 m relative sea-level (∼67m eustatic) fall. Our study establishes the relationships among ice volume, ä18O, and sequences: a latest Eocene cooling and minor ice-volume event was followed by an earliest Oligocene ice-volume and cooling event that lowered sea-level and formed a sequence boundary during the early stages of eustatic fall.
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