Stable organic carbon isotope stratigraphy across Oceanic Anoxic Event 2 of Demerara Rise, western tropical Atlantic

Abstract

[1] Ocean Drilling Program (ODP) Leg 207 recovered expanded sections of organic-carbon-rich laminated shales on Demerara Rise (western tropical Atlantic). High-resolution organic carbon isotope and total organic carbon (TOC) records are presented, which span the Cenomanian-Turonian boundary interval (CTBI), including the Oceanic Anoxic Event (OAE) 2, from four sites oriented along a NW striking depth transect. These records represent the first high-resolution carbon isotope records across OAE 2 from the South American margin of the tropical Atlantic. Due to the scarcity of age significant fossils, the main purpose of this study was to develop a detailed carbon isotope stratigraphy in order to correlate the CTBI across the depth transect and to tie this to biostratigraphically well-defined sections in the Western Interior Basin (Pueblo, USA), boreal shelf seas (Eastbourne, England), and western Tethys (Oued Mellegue, Tunisia). All four sections studied document a 6% increase of d 13C org values at the base of the CTBI, which is followed by an interval of elevated d 13 C org values and a subsequent decrease. Our results supply an important stratigraphic base for subsequent paleoceanographic studies on Late Cenomanian to Early Turonian sediments from Demerara Rise and elsewhere.

Nd isotopic excursion across Cretaceous ocean anoxic event 2 (Cenomanian-Turonian) in the tropical North Atlantic

“…The Demerara sequence is unusual in that deposition of laminated black shales began millions of years before and continued millions of years after OAE2. The OAE2 interval is clearly recognizable based on a well-documented 6%o positive 6'^C"" excursion (Erbacher et al, 2005), but it is not lithologically distinct from sediment above and below. Fish debris is common to abundant in both the black shale and the overlying Campanian-Maastrichtian chalks.…”

Secular variation in Late Cretaceous carbon isotopes: a new δ13C carbonate reference curve for the Cenomanian–Campanian (99.6–70.6 Ma)

“…The Gun Gardens section has become established as a reference for the Cenomanian/Turonian boundary succession in the chalk facies of NW Europe (Tsikos et al 2004;Amédro, Accarie & Robaszynski, 2005;Erbacher et al 2005;Kolonic et al 2005;Kuhnt et al 2005). Published data will be used here to illustrate the consistency of major carbon-isotope trends across the boundary interval.…”

“…The person (circled) is 1.8 m high. Robaszynski, 2005;Erbacher et al 2005;Kolonic et al 2005;Li et al 2006). Jenkyns, Gale & Corfield (1994) defined eight correlative events between east Kent and Italy for the Cenomanian-Lower Campanian.…”

“…The Eastbourne Gun Gardens section in West Sussex (Figs 1, 5) is the most expanded boundary section in chalk facies in NW Europe (Paul et al 1999), and is increasingly being used as an international reference for biostratigraphic and chemostratigraphic studies (Amédro, Accarie & Robaszynski, 2005;Erbacher et al 2005;Kolonic et al 2005;Kuhnt et al 2005). Carbon-isotope curves for the Cenomanian/Turonian Boundary Event at Culver, Dover, Trunch and Speeton are illustrated in Figure 3, and a detailed δ 13 C correlation between Eastbourne and Dover is shown in Figure 6, which compares these sections with the Turonian Global boundary Stratotype Section and Point at Pueblo, Colorado, USA.…”

Dominant eukaryotic export production during ocean anoxic events reflects the importance of recycled NH 4 +

“…A well-defined positive carbon isotope excursion in this section is contained within the high total organic carbon (TOC) interval commonly associated with the OAE (39) (Fig. 1A).…”