The Eocene‐Oligocene Transition in the South‐Western Neo‐Tethys (Tunisia): Astronomical Calibration and Paleoenvironmental Changes

Abstract

AbstractA detailed biostratigraphic, chemostratigraphic, and chronostratigraphic study was carried out in the South‐Western margin of the Neo‐Tethys ocean (Tunisia) covering the Eocene‐Oligocene interval to report potential paleoenvironmental and paleoclimatic changes associated with the growth of the Antarctic ice sheet (AIS). The studied section consists of marls and limestones extending from the Helicosphaera compacta nannofossil Zone (CNE21) to the Reticulofenestra umbilicus Zone (CNO2). The Bc of Clausicoccus subdistichus coincides in northeastern Tunisia with the extinction of hantkeninids and is thus used here to define the Eocene/Oligocene boundary (EOB) at 34.03 Ma. Calcareous nannofossil assemblages suggest a significant change from oligotrophic/warm surface waters during the late Eocene to eutrophic/cool waters during the early Oligocene. The observed changes in trophic conditions are synchronous with a shallowing trend testified by an increase in nearshore species and enhanced terrigenous input. Major environmental changes occurred at the EOB and across glaciation event Oi‐1a whereas we record a poor imprint of glaciation event Oi‐1. Three orbital configurations have been distinguished: (1) The late Eocene is characterized by a prominent 405‐kyr cycle and a weak obliquity component; (2) the onset of cooling at 34.35 Ma coincides with the rosette‐shaped discoaster extinction and is reflected by a shift toward enhanced obliquity and short‐eccentricity cycles. The installation of a fully developed AIS (event Oi‐1a, 32.75 Ma) shows the most pronounced obliquity imprint reflecting an increased influence of high‐latitude climate processes; (3) after 31.75 Ma, the obliquity decreases in coincidence with the return to a dominant long‐eccentricity cycle.