High-resolution bio- and chemostratigraphy of an expanded record of Oceanic Anoxic Event 2 (Late Cenomanian–Early Turonian) at Clot Chevalier, near Barrême, SE France (Vocontian Basin)

Abstract

A newly located exposure of the Niveau Thomel, an organic-rich level at the Cenomanian-Turonian boundary, provides a highly expanded record of Oceanic Anoxic Event (OAE) 2, excepted for the lower relatively condensed glauconite-rich part of the section. The new locality, close to Barrême in the Vocontian Basin, SE France, is developed in deep-water hemi-pelagic facies (shales, marls, marly limestones, variably enriched in organic matter) and provides an improved understanding of palaeoceanographic events associated with OAE 2. Investigation of the biostratigraphy (nannofossils and planktonic foramininfera), organic and inorganic geochemistry (bulk carbonate δ 18 O, total organic carbon (TOC), bulk organic, biomarker-specific and carbonate δ 13 C, major and trace elements, and Rock-Eval data) has allowed characterization of the sediments in great detail. The combined study further constrains the detailed relationship between bio-and chemostratigraphy (particularly with respect to the details of the well-displayed positive carbon-isotope excursion) for this interval. The section also provides new evidence, in the form of a positive oxygen-isotope excursion and an offset between carbonate and organic-carbon carbon-isotope records, which confirms the importance of cooling accompanied by a drop in dissolved CO 2 in near-surface waters during the Plenus Cold Event that characterized the early part of OAE 2. Evidence for increased oxygenation of bottom waters, together with elevated concentrations of redox-sensitive and chalcophilic elements registered elsewhere through the level of the Plenus Cold Event, may be reflected in enhanced concentrations of iron (in glauconite) and nickel in coeval strata from the Clot Chevalier section.

Unraveling short- and long-term carbon cycle variations during the Oceanic Anoxic Event 2 from the Paris Basin Chalk

“…S1). Correlations between OAE2 sections have generally been established on the basis of integrated stratigraphy (e.g., Gale et al, 1993, Gale et al, 2018Jarvis et al, 2006;Sageman et al, 2006;Elrick et al, 2009;Meyers et al, 2012b). Most of OAE2 studied sections come from pelagic to hemipelagic settings, although nearshore marine setting can preserve the OAE2 with high fidelity.…”

A Re‐evaluation of the Plenus Cold Event, and the Links Between CO2, Temperature, and Seawater Chemistry During OAE 2

“…Accelerated burial rates of planktonic organic matter, whose biosynthesis led to preferred incorporation of the lighter 12 C isotope, resulted in a marked positive carbon‐isotope excursion recorded in different sedimentary archives around the world (e.g., Bowman & Bralower, ; Jarvis et al, ; Jenkyns et al, ; Schlanger et al, ; Scholle & Arthur, ; Tsikos et al, ; Voigt et al, ; Wendler, ). The canonical model suggests that, eventually, increased rates of organic‐carbon burial would have caused a drawdown of atmospheric CO 2 , ultimately triggering global cooling that led to a weakening of the factors promoting carbon burial (Arthur et al, ; Gale et al, ; Jenkyns et al, ; Kuypers et al, ; Sinninghe Damsté et al, ; van Bentum et al, ).…”

“…This period of cooling was termed the “Plenus Cold Event” (PCE) after the Plenus Marls, a relatively clay‐rich interval in the English Chalk where the fall in temperature is registered (Figure ; Jenkyns et al, ). Cooling during OAE 2 has been identified from a number of sea‐surface temperatures (SST) proxies from marine sections across the Northern Hemisphere (e.g., Desmares et al, ; Forster et al, ; Gale et al, ; Jarvis et al, ; Sinninghe Damsté et al, ; van Helmond et al, ), suggesting that the entire North Atlantic Ocean and its surrounding epicontinental seas were affected. Broadly synchronous with the PCE, a period of extensive bottom‐water re‐oxygenation occurred throughout the Western Interior Seaway of North America and the North Atlantic (Eicher & Diner, ; Eicher & Worstell, ; Eldrett et al, ; Forster et al, ; Friedrich et al, ; Keller et al, ; Keller & Pardo, ; Leckie, ; Zhou et al, ).…”

“…Many authors have attributed the PCE to a decline in atmospheric p CO 2 (e.g., Barclay et al, ; Gale et al, ; Jarvis et al, ; Sinninghe Damsté et al, ), suggesting that the transient negative δ 13 C excursion signifies reduced global burial of organic carbon under more oxygenated conditions, recorded at sites around the world (Erbacher et al, ; Hasegawa et al, ; Jarvis et al, ; Voigt et al, ). Estimates of the magnitude of the atmospheric p CO 2 decrease during OAE 2 range from 20–25% (Freeman & Hayes, ; Jarvis et al, ) to 40–80% (Kuypers et al, ).…”

Complex Interactions Between Large Igneous Province Emplacement and Global‐Temperature Changes During the Cenomanian‐Turonian Oceanic Anoxic Event (OAE 2)

“…The thick, gray dashed line marks the CTB horizon; the dark gray area indicates the stratigraphic extent of the OAE 2 level; the pale blue area shows the strata that record cooling interpreted as the PCE. The lowest natural terrestrial value of 187 Os/ 188 Os (0.13; Allègre et al, 1999) 10.1029/2020PA004016 Caron et al, 2006;Falzoni et al, 2016;Gale et al, 2018;Jarvis et al, 2011;Jones et al, 2019;Nederbragt & Fiorentino, 1999;Voigt et al, 2008; see also Figures 3 and S1), and which also correlates with trends of increasing 187 Os/ 188 Os (i) values in all of the Wunstorf, Pont d'Issole, and SH #1 records (Figure 3). However, if the negative δ 13 C org excursion in the Bass River core is indeed equivalent to such a subsidiary CIE, it is not clear why no stratigraphically lower negative excursion in δ 13 C org is preserved between 592 and 590 mbs, correlative with the evidence for SST cooling.…”