Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Vicissitudes of the Eocene, Radical Overturning of Middle Eocene Planktonic Biostratigraphy
(1) Geology & Geophysics, Texas A&M University, Bryan, TX.
(2) School of Earth and Environment, University of Leeds, Leeds, United Kingdom.
The middle to late Eocene is a critical transition period from the Eocene hothouse to Oligocene icehouse conditions, the how and why of this shift is still widely debated. What role did CO2 play, when did high latitude glaciations commence, was this transition from hothouse to icehouse abrupt, or as recent studies suggest, occurred in a stepwise manner?
This study examines and interprets marine sediment samples obtained during Ocean Drilling Project (ODP) Leg 171B Blake Nose in the western North Atlantic Ocean. The ecological behavior of middle Eocene planktonic foraminifera at Blake Nose depends on biological, chemical and physical factors. A change in any of these elements drives changes in behavior that can be interpreted. Changes in marine sediment color and magnetic susceptibility data are proxies for changes in lithology. This cyclic variation in the record is a result of Milankovitch orbital cycles, the primary effect of which are changes in seasonality affecting sedimentation rates, and biota recorded in the sediment record. Recognizing that cyclic signature in marine sediments depict changes climate and ocean circulation in response to changes in Earth’s orbital configuration, these changes can be used for calibration of other proxies.
The diversity and preservation of planktonic foraminifera present in this study interval in addition to the number of species with first and/or last occurrence within this time period allows for refinement and recalibration of foraminiferal Zones E7-11. The foraminifera are also utilized for delta 13C, and delta 18O isotope and trace element analysis.
This study provides an important tool for unraveling dynamic changes resulting in a biostratigraphic and climatic record for the middle Eocene period from 42-44 Ma. The relationship between the foraminiferal assemblage and their environment are inherently applicable and relevant to the present day Gulf Coast region as during the time period of this project there was no barrier between Blake Nose and the Gulf Coast.