Organic-walled dinoflagellate cyst biostratigraphy of the upper Eocene to lower Oligocene Yazoo Formation, US Gulf Coast

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.

Multi-proxy evidence for sea level fall at the onset of the Eocene-Oligocene transition

“…This sequence stratigraphic framework is, however, difficult to translate onto sections such as the MGC in central Mississippi, which are lithologically more uniform – with the entire Yazoo Formation in central Mississippi occurring as an undifferentiated marine clay unit 25 – and show continuous deposition through the latest Eocene and earliest Oligocene (~37.5–33.1 Ma; Figs. 1 – 5 , Source data) 28 – 30 . Notable for this study is the placement of an uppermost Eocene, intra-Pachuta Marl major hiatus in the SSQ core section at ~50.38 m, representing ~1 million years (Ma) of missing time, and interpreted as a sequence boundary.…”

“… a Lithostratigraphy 25 and biostratigraphy 28 . b Geologic timescale 31 , regionally-inferred sequences 23 , and sedimentation rates.…”

“…1 – 5 , S2 , Source data). The MGC age-depth model is based on an integration of biostratigraphic and chemostratigraphic constraints and absolute age dates 28 , 31 (Fig. 1 , Source data).…”

“…1 , Source data). Based on age constraints from calcareous nannofossil assemblages 28 , existing radiometric dates 32 , and δ 13 C-tuned dates we present a significantly refined age-depth model for the MGC (Fig. 1 , Source data).…”

Eocene/Oligocene global disruption and the revolution of Caribbean mangroves

“…9). Of these records, the Saint Stephens Quarry (SSQ) outcrop is the best constrained chronologically and has the highest resolution and has been one of the keystone sites used to characterize global EOT paleoenvironmental shifts (Keigwin & Croliss, 1986;Katz et al, 2008;Miller et al, 2008;Wade et al, 2012;De Lira Mota et al, 2020). In this record, three main events were recognized around the , which demonstrated the stepwise, rather than continuous, nature of this transition (Katz et al, 2008).…”