Middle and late Cenomanian oceanic anoxic events in shallow and deeper shelf environments of western Morocco

Abstract

The response of shallow‐water sequences to oceanic anoxic event 2 and mid‐Cenomanian events 1a and 1b was investigated along the west African margin of Morocco north of Agadir (Azazoul) and correlated with the deep‐water sequence of the Tarfaya Basin (Mohammed Beach) based on biostratigraphy, mineralogy, phosphorus and stable isotopes. In the deeper Mohammed Beach section results show double peaks in δ13Corg for mid‐Cenomanian events 1a and 1b (Rotalipora reicheli biozone, lower CC10a biozone), the characteristic oceanic anoxic event 2 δ13C excursion (Rotalipora cushmani extinction, top of CC10a biozone) and laminated (anoxic) black shale. In the shallow environment north of Agadir, a fluctuating sea‐level associated with dysoxic, brackish and mesotrophic conditions prevailed during the middle to late Cenomanian, as indicated by oyster biostromes, nannofossils, planktonic and benthonic foraminiferal assemblages. Anoxic conditions characteristic of oceanic anoxic event 2 (for example, laminated black shales) did not reach into shallow‐water environments until the maximum transgression of the early Turonian. Climate conditions decoupled along the western margin of Morocco between mid‐Cenomanian event 1b and the Cenomanian–Turonian boundary, as also observed in eastern Tethys. North of Agadir alternating humid and dry seasonal conditions prevailed, whereas in the Tarfaya Basin the climate was dry and seasonal. This climatic decoupling can be attributed to variations in the Intertropical Convergence Zone and in the intensity of the north‐east trade winds in tropical areas.

Response and recovery of the Comanche carbonate platform surrounding multiple Cretaceous oceanic anoxic events, northern Gulf of Mexico

“…13). This trend may reflect a regional environmental perturbation that caused progressively more negative (Gertsch et al, 2010) and perhaps represents degrading environmental conditions on the Comanche Platform. All four profiles display a 1.0e1.5‰ positive excursion at the MidCenomanian Event.…”

“…13). High-resolution data from the Natih Formation of Oman (Vahrenkamp, 2013) and organic carbon data from the Atlantic coast of Morocco (Gertsch et al, 2010) serve as additional records. Correlation of lower Cenomanian events is complicated by low-amplitudes of the excursions (<0.5‰).…”

Small-scaled lateral variations of an organic-rich formation in a ramp-type depositional environment (the Late Jurassic of the Boulonnais, France): impact of the clastic supply

“…However, in another geological setting (New Jersey margin), Deconinck and Vanderaveroet (1996) also observed a steep gradient of smectite proportions over a distance of < 50 km, which cannot be ascribed to a change in particle sources or the climate. See also how smectite differential settling and climate influence may be discussed for Cenomanian deposits of France or Morocco (AgadirTarfaya area; Chamley et al, 1990;Deconinck and Chamley, 1995;El Albani et al, 1999;Gertsch et al, 2010). In the case of the Boulonnais, the smectite gradient cannot be accounted for by climatic variations and only sea-level variation coupled to differential settling is put forward (possibly in conjunction with local factors such as currents, seabed topography or mixing of water masses with contrasting salinity that can be evoked in an embayment).…”

Realistic Paleobathymetry of the Cenomanian–Turonian (94 Ma) Boundary Global Ocean

“…This exactly spells out the difference between the two bathymetry dataset and highlights the importance of reconstructing the shelf-slope-wedge. This has special significance especially for the C-T time, as for decades the paleoclimate community has argued for extensive shallow epicontinental seas [36,[62][63][64][65][66][67][68][69][70][71][72][73][74][75][76] for example, to explain oceanic anoxic events. The OES C-T Ocean compared to Modern Ocean, has 4.75% more area (ocean area) less than 1000 m deep (maximum extent of combined euphotic and disphotic zone depth).…”