The Cenomanian-Turonian Oceanic Anoxic Event, I. Stratigraphy and distribution of organic carbon-rich beds and the marine δ ¹³ C excursion

Abstract

S U M M A R Y :Marine strata deposited during late Cenomanian and early Turonian time display lithological, faunal, and geochemical characteristics which indicate that significant parts of the world ocean were periodically oxygen deficient. At, or very close to, the Cenomanian-Turonian boundary, between 90.5 and 91.5 million years ago, oxygen deficiencies were particularly marked over a period of less than 1 my. This short-lived episode of oceanic oxygen deficiency has been termed the Cenomanian-Turonian 'Oceanic Anoxic Event' (OAE). Marine sediments deposited during this event are, when compared with most of the Phanerozoic record, uncommonly rich in dark-grey to black, pyritic, laminated shales with total organic carbon contents that range from between 1 and 2% to greater than 20% which is largely of marine planktonic origin. The general lack of bioturbation in these beds is taken to indicate an absence of a burrowing fauna due to anoxic conditions. In coeval pelagic and shelf limestone sections the dark shales may be lacking; in such sections the Cenomanian-Turonian boundary is marked by 313C values of up to + 4.0%o or + 5.0%o in contrast to 613 C values of + 2.0%0 to + 3.0%o in limestones directly above and below the boundary. The high 613C values are taken to indicate an enrichment of the global ocean in 13 C values as a result of the preferential extraction of 12 C by marine plankton, the organic components of which were not recycled back to the oceanic reservoir during this period of enhanced organic-carbon burial. In many basins benthonic foraminiferal faunas are lacking in strata at or near the Cenomanian-Turonian boundary or consist of depauperate agglutinate faunas whereas diverse planktonic foraminiferal faunas and radiolarian remains are locally abundant. These zones free of benthonic foraminifera have been previously interpreted as the result of bottom-water oxygen deficiencies.A correlation between high positive 613C values and manganese enrichment in shelf chalks has been pointed out by other workers; data presented here substantiates this correlation.Sediments that display one or more of the above characteristics have been studied and identified from diverse basinal settings such as Pacific Basin mid-ocean plateaus, North American cratonic interior seaways, European shelf and interior seaways, circum-African embayments and seaways, Tethyan margins and the Caribbean region. The oxygen-deficient water masses are proposed to have taken the form of an expanded and intensified oxygenminimum zone. Palaeobathymetric interpretation of strata from European and African shelf sequences and sections in the US Western Interior Basin show that shallow embayments, flooded by the rapid Cenomanian-Turonian transgression, were particularly favourable to deposition of anoxic sediments as were the neighbouring shelves and cratonic shallow seaways. The distribution of carbonaceous black shales and coeval light-coloured to red shallow-water limestones marked by a ~13 C 'spike' indicates that the upper surface of the w...

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

“…The global nature of these events, particularly the large positive excursion spanning the Cenomanian/Turonian boundary, has been confirmed subsequently by many workers (e.g. Schlanger et al 1987;Arthur et al 1990;Gale et al 1993Gale et al , 2005Pratt et al 1993;Jenkyns, Gale & Corfield, 1994;Jenkyns, Mutterlose & Sliter, 1995;Hasegawa, 1997Hasegawa, , 2003Voigt & Hilbrecht, 1997;DeCabrera, Sliter & Jarvis, 1999;Hasegawa & Hatsugai, 2000;Voigt, 2000;Keller et al 2001;Wang et al 2001;Jarvis et al 2002;Tsikos et al 2004; Table 1). The isotope profile is shown in Figure 3.…”

“…3) is one of the largest and best documented carbon-isotope events in the geological record (Jenkyns, 1980(Jenkyns, , 1985Scholle & Arthur, 1980;Schlanger et al 1987). This event is conventionally interpreted as being related to accelerated burial of marine organic matter, particularly in the Atlantic, but also in other ocean basins (Herbin et al 1986;Arthur et al 1990;Kuypers et al 2002Kuypers et al , 2004.…”

Changes in paleo-circulation and the distribution of ammonite faunas at the Coniacian–Santonian transition in central Poland and western Ukraine

“…Its usefulness for global correlation has been proved by different authors for different intervals (e.g. Schlanger et al 1987;Arthur et al 1990;Jenkyns et al 1994;Voigt and Hilbrecht 1997;Voigt 2000;Voigt and Wiese 2000;Gale et al 2005Gale et al , 2007Lamolda and Paul 2007; for a complete review see Jarvis et al 2006). Jarvis et al (2006) provided detailed carbon stable isotope data for the Cenomanian -Campanian plotted against the lithoand biostratigraphic logs of the Chalk succession in England.…”

Evidence for oxic conditions during oceanic anoxic event 2 in the northern Tethyan pelagic realm

“…The Late Cenomanian sedimentary record encompasses one of the best-studied OAEs, labelled OAE 2 (Schlanger and Jenkyns, 1976;Jenkyns, 1980;Schlanger et al, 1987;Jenkyns et al, 1994;Strasser et al, 2001;Leckie et al, 2002;Sageman et al, 2006;Caron et al, 2006;Mort et al, 2007;Voigt et al, 2007;Adams et al, 2010;Montoya-Pino et al, 2010). Major climatic and paleoceanographic changes have been associated with this event (Jenkyns et al, 1994;Huber et al, 2002;Norris et al, 2002;Forster et al, 2007).…”

“…Major climatic and paleoceanographic changes have been associated with this event (Jenkyns et al, 1994;Huber et al, 2002;Norris et al, 2002;Forster et al, 2007). The onset of OAE 2 is characterized by an important positive excursion in the d 13 C carbonate bulk-rock record of approximately 2.5& (Schlanger and Jenkyns, 1976;Jenkyns, 1980;Schlanger et al, 1987;Gale et al, 1993;Erbacher et al, 1996;Jarvis et al, 2006;Voigt et al, 2006). OAE 2 is also marked by an extinction event and turnover in planktonic foraminifera, radiolaria and nannofossil assemblages (Eicher and Worstell, 1970;Hart and Bigg, 1981;Caron and Homewood, 1992;Leckie, 1985;Hart and Ball, 1986;Lamolda et al, 1997;Grosheny and Malartre, 1997;Keller et al, 2001;Leckie et al, 2002;Erba, 2004;Caron et al, 2006;Grosheny et al, 2006), a sealevel rise (Haq et al, 1987) Sr ratio (Jones and Jenkyns, 2001).…”