Abstract
Abstract. New data from a continuously cored succession, the Mossy Grove core, near Jackson, central Mississippi, recovered ∼137 m of marine clays (Yazoo Formation), spanning ∼5 Ma and including the critical Eocene–Oligocene transition (EOT) event. These clay-rich sediments yield well-preserved calcareous microfossil and palynomorph assemblages. Here, we present a new organic-walled dinoflagellate cyst (dinocyst) biostratigraphic framework, including the recognition of 23 dinocyst bioevents. These are integrated with new age constraints based on calcareous nannofossil biostratigraphy and a reassessment of the existing radiometric dates and planktonic foraminiferal biostratigraphy, permitting the establishment of a robust and significantly refined age model for the core. According to this new age model, a major increase in sedimentation rate – from ∼2.1 to ∼4.7 cm kyr−1 – is observed at a core depth of ∼89.1 m (∼34.4 Ma). In the new age model the section is significantly older than previously thought, by up to 1 Ma, with the Eocene-Oligocene boundary (∼33.89 Ma) placed ∼34 m below the level previously identified. With these more accurate age estimates, future isotopic and palaeoecological work on this core can be more precisely integrated with other, globally distributed records of the EOT.
Highlights
The Eocene–Oligocene transition (EOT: ∼ 34.0 Ma; Westerhold et al, 2014) represents a phase of accelerated climatic and biotic change that began before and ended after the Eocene-Oligocene boundary (EOB: 33.89 Ma)
Spiniferites species dominate in most samples and account for ∼ 50 % of the overall count, followed by Hystrichokolpoma and Operculodinium (∼ 6 % each); Charlesdowniea (C. coleothrypta) (∼ 4 %); Heteraulacacysta; Lingulodinium
Machaerophorum) and Cleistosphaeridium (3 % each); and Cordosphaeridium, Dinopterygium (D. cladoides), Glaphyrocysta, Homotryblium, Saturnodinium (S. pansum), and Thalassiphora (∼ 2 % each). These genera account for nearly 90 % of all dinocysts counted in the section, there are other significant occurrences of Achomosphaera alcicornu, Dapsilidinium pastielsii, Enneadocysta arcuata, and Hystrichosphaeridium tubiferum
Summary
The Eocene–Oligocene transition (EOT: ∼ 34.0 Ma; Westerhold et al, 2014) represents a phase of accelerated climatic and biotic change that began before and ended after the Eocene-Oligocene boundary (EOB: 33.89 Ma). The presence of distinct rapid positive steps in high-resolution benthic foraminiferal oxygen isotope (δ18O) records are interpreted as representing at least two pulses of accelerated ice-sheet growth (Coxall et al, 2005; Scher et al, 2011). These steps appear to be orbitally paced, with a duration of 40 kyr, separated by a 300–400 kyr interval of relative stability, or plateau (Coxall et al, 2005; Scher et al, 2011; Westerhold et al, 2014). The second step in δ18O is thought to be dominated by ice-volume expansion (Katz et al, 2008; Lear et al, 2008), a sharp deepening of the ocean carbonate saturation depth (Coxall et al, 2005), and Published by Copernicus Publications on behalf of The Micropalaeontological Society
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