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

Abstract

A 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.

Stratigraphy, Sedimentology and Geochemistry of the Oligocene – Lower Miocene Maikop Group in Dagestan, Ne Caucasus

“…11). The negative δ 13 C values in the terminal Eocene (between 11.5 and 18 m) correspond to a similar negative excursion which has been recorded in many other areas worldwide (Barrera et al, 1993;Salamy and Zachos, 1999;Zachos et al, 2001;Pälike et al, 2006;Coxall and Pearson, 2007;Armstrong et al, 2016;Messaoud et al, 2020) and therefore likely represents a global-scale signal. The Eocene-Oligocene transition, covering the uppermost Belaya Glina Formation and the basal part of the Maikop Group, is characterized by a short-term positive shift in δ 13 C by about 0.8 ‰.…”

“…Above this interval, the δ 13 C record for the Pacific, Atlantic and Southern oceans (Salamy and Zachos, 1999;Zachos et al, 2001;Pälike et al, 2006;Coxall and Pearson, 2007;Armstrong et al, 2016) and the southern NeoTethys (Tunisia: Messaoud et al, 2020) tend towards positive values during the early Oligocene. In the Chirkey section, this interval is marked by abrupt fluctuations in δ 13 C of about 1.2 ‰, indicating environmental instability.…”

Geochemistry and cyclostratigraphy of homogeneous deposits using high-resolution hand-held X-ray Fluorescence: Outcrop to subsurface correlation, sequence stratigraphy, and constraints on hiatuses (middle-Upper Eocene, Tunisia)

“…Grain size stratigraphic trend ( ning or coarsening) is a strong sequence stratigraphic tool to identify progradation and retrogradation trends in homogenous sedimentary Formations (Frugone-Álvarez et al, 2017; Macquaker et al, 2007;Thöle et al, 2019;Ver Straeten et al, 2011). Determining regular stratigraphic variations in monotonous mudstone's inorganic/organic geochemistry has lately been utilized to create sequence stratigraphic frameworks (Messaoud et al, 2020;Thöle et al, 2019). HH-XRF is an analytical method to determine the chemical composition of metal, cement, and oil, along with mining (mineralogy and geology), and for environmental analysis of water and waste materials (Chatellier et al, 2015;Hosseininejad et al, 2013;Löwemark et al, 2011;Rush, 2010;Thöle et al, 2019;Zhang et al, 2017).…”