Sea-level and paleoenvironmental changes revealed by benthic foraminifera across Oceanic Anoxic Event 2 (OAE 2) at Eastbourne (SE England)

Abstract

The Cenomanian–Turonian Oceanic Anoxic Event 2 (OAE 2) severely disrupted the global carbon cycle with widespread deposition of organic-rich marine sediments, resulting in a positive carbon isotope excursion. The Eastbourne section in southeastern England offers extensive benthic and planktonic foraminiferal data, revealing four distinct paleoenvironmental intervals across OAE 2.

The Grey Chalk interval below OAE 2, which is characterized by the highest species diversity of benthic foraminifera, represents outer neritic-upper bathyal paleodepths, oxygenated environments and low organic fluxes at the seafloor. Deep- and thermocline-dwelling planktonic foraminifera suggest meso-oligotrophic regimes with a well-stratified water column.

The onset of OAE 2 in Bed 1a of the Plenus Marl is marked by a sea-level fall supported by the maximum peak in abundance of shallow water agglutinated foraminifera (Ataxophragmium depressum, Arenobulimina, Plectina cenomana) and by the disappearance of bathyal taxa (e.g., Tristix excavata, Kalamopsis grzybowsky).

In Bed 1b of the Plenus Marl, corresponding to the onset of the Plenus Cold Event, Eggerellina, Gaudryina, and Textularia replace shallow agglutinated taxa indicating a transgressive phase. This assemblage also coincides with the occurrence of Boreal planktonic foraminifera that suggests the incursion of Boreal waters into the Anglo-Paris Basin.

The White Chalk, in the upper part and the interval above OAE 2, is interpreted as a Transgressive and Highstand Systems Tract with a change in the benthic foraminiferal assemblage towards the dominance of Marssonella, Gavelinella, Lingulogavelinella and Tritaxia with warmer and more mesotrophic waters recorded by the dominance of Tethyan planktonic foraminifera.