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The Cretaceous Oceanic Events (Anoxia and Hiatus) within a Sequence Stratigraphic Framework

JACQUIN, THIERRY, Universite de Bourgogne, Dijon, France, P. DE GRACIANSKY, Ecole Nationale des Mines de Paris, Paris, France, F. MAGNIEZ-JANNIN and C. PONSOT, Universite de Bourgogne, Dijon, France, and P. R. VAIL, Rice University, Houston, TX

Our revision of the stratigraphy and organic geochemistry of the North and South Atlantic DSDP boreholes has demonstrated the large range of occurrences and settings of the Cretaceous black shales during the so-called Oceanic Anoxic Events (OAE1--Late Aptian/Early Albian, OAE2--Cenomanian/Turonian, and OAE3--Coniacian/Santonian). No simple model has yet been found to explain the exact timing (synchronism and diachronism) of the anoxic layers and stratigraphic gaps associated with these three particular events. Sequence stratigraphic analyses of outcrop sections in the Western Interior basin (Black Hills area), in the Paris basin, and in the Southeast basin of France provide data to precisely date the timing of the anoxia and oceanic gaps and to show their relationship to long and shor term changes of relative sea level.

The Oceanic Anoxic Events (OAE1 and OAE2) correspond to periods of severe starvation events (E1 and E2) where several depositional sequences, and more particularly their maximum flooding surfaces, are merged. Three strongly condensed stratigraphic periods are recognized in the deep Atlantic ocean: event E1a during the early Aptian, event E1b during the late Aptian-early Albian, and event E2 from the late Cenomanian to the middle Turonian. They coincide on the adjacent landmass with the overall backstepping of the depositional environments due to the overall rapid rising of relative sea level.

Layers, or sets of layers, with the highest TOC values associated with OAE1 and OAE2 in the Atlantic Ocean coincide with the maximum flooding surfaces of sequences that are defined on U.S. and European outcrop sections. In the DSDP boreholes where the starvation was not so high, we can document the same sequences and systems tracts. The occurrences of anoxic layers during Coniacian and Santonian time (OAE3) do not correspond to periods of severe starvation with several condensed depositional sequences, but to the maximum flooding surface of single sequences.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)