Oceanic events and biotic effects of the Cenomanian-Turonian anoxic event, Tarfaya Basin, Morocco

Abstract

a b s t r a c tProfound biotic changes accompanied the late Cenomanian d 13 C excursion and OAE2 in planktic foraminifera in the Tarfaya Basin of Morocco. Planktic foraminifera experienced a severe turnover , though no mass extinction, beginning with the rapid d 13 C excursion and accelerating with the influx of oxic bottom waters during the first peak and trough of the excursion. Species extinctions equaled the number of evolving species, though only the disaster opportunists Guembelitria and Hedbergella thrived along with a low oxygen tolerant benthic assemblage. The succeeding d 13 C plateau and organic-rich black shale deposition marks the anoxic event and maximum biotic stress accompanied by a prolonged drop in diversity to just two species, the dominant (80-90%) low oxygen tolerant Heterohelix moremani and surface dweller Hedbergella planispira. After the anoxic event other species returned, but remained rare and sporadically present well into the lower Turonian, whereas Heterohelix moremani remained the single dominant species. The OAE2 biotic turnover suggests that the stress to calcareous plankton was related to changes in the watermass stratification, intensity of upwelling, nutrient flux and oxic levels in the water column driven by changes in climate and oceanic circulation. Results presented here demonstrate a 4-stage pattern of biotic response to the onset, duration, and recovery of OAE2 that is observed widely across the Tethys and its bordering epicontinental seas.

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

“…Contrary to other places where a general warming is observed (Jenkyns et al, 1994;Norris et al, 2002;Wilson et al, 2002;Voigt et al, 2004;Forster et al, 2007;Sinninghe Damsté et al, 2010), at Chrummflueschlucht, the evolution of the d 18 O record suggests a change in the regional hydrological cycle related to a possible cooling and more contrasted climate or more arid period (Keller et al, 2008).…”

“…At Chrummflueschlucht, the small plateau of higher oxygen-isotope values at the onset of OAE 2 (peak "a") may relate to this cooling episode. An alternative explanation consists in an input of fresh water at the onset of the shift (Sageman et al, 1998;Keller et al, 2008). At Chrummflueschlucht, the good…”

Planktonic foraminiferal turnover across the Cenomanian – Turonian boundary (OAE2) in the northeast of the Tethys realm, Kopet-Dagh Basin

“…The C-T boundary has been studied worldwide (Luderer & Kuhnt 1997;Leckie et al 1998;Luciani & Cobianchi 1999;Keller et al 2001Keller et al , 2008Coccioni & Luciani 2005;Mort et al 2008 among others) but this boundary was little known in Iran. Only a few studies have been conducted in the Kopet-Dagh basin.…”

“…Production of a lot of organic matter during the time of decreasing oceanic circulations leads to an anoxic condition and superimposition of three crises during the event: wide scale occurrence of black shales (Arthur & Premoli Silva 1982;Luciani & Cobianchi 1999;Coccioni & Luciani 2005), faunal turnovers (Leckie et al 1998;Keller et al 2001Keller et al , 2008Keller & Pardo 2004;Caron et al 2006;Soua et al 2009Soua et al , 2011) and a positive δ 13 C excursion (Paul et al 1999;). …”

Cenomanocarcinus vanstraeleni Stenzel, 1945 (Crustacea, Decapoda, Brachyura, Cenomanocarcinidae) from the Late Cretaceous (Turonian) of Morocco

“…The Tarfaya Basin is a tectonically stable Mesozoic basin stretching 1000 km along the western margins of the Sahara Desert including a well-documented Upper Cretaceous succession (El Albani et al, 1999) in presence of high sedimentary rates of anoxic cyclic marine deposits (Keller et al, 2008) and fluctuating climatic conditions during the Cenomanian-Turonian (C-T) boundary (Tantawy, 2008). The C-T succession crops out along the basin, preserving a rich invertebrate fauna, mostly composed of Late Cretaceous 300 300 (Turonian) cephalopods, which have been recently offered by local diggers onto the open international fossil market.…”