Michel Cousin

Occurrence of marine mid-Cretaceous sediments along the Guinean slope (Equamarge II cruise): their significance for the evolution of the central Atlantic African margin

Abstract During the Equamarge II cruise (1988), several coring attempts made along the slope edge of the southern Guinean Plateau led to the recovery of middle Cretaceous sediments in two cores. One contained a carbonate block, dated as middle Albian (H. rischi Zone); the micropaleontological and sedimentological data suggest an open marine environment and paleodepths of approximately 150–200 m. Another core included a dark shale level corresponding to the global anoxic event “CTBE” (Cenomanian/Turonian Boundary Event, W. archaeocretacea Zone). As shown by seismic reflection profiles, these mid-Cretaceous beds lie very close to a major unconformity, which distinctly divides the sedimentary cover into two units (the lower one folded and faulted, the upper one undisturbed). Geodynamic and paleoenvironmental implications of these new data better constrain models of evolution for this crucial area of the Atlantic realm. The compressive and extensional events which affected the Equatorial Atlantic during the progressive separation of Africa from South America are thus more accurately dated. These results also strengthen the hypothesis of an open seaway between the Central and South proto-Atlantic as early as the middle Albian.

Enregistrement sedimentaire d'un episode d'approfondissement brutal de la marge sud-guineenne au Quaternaire Recent

Abstract During the equamarge II cruise (1988) along the Guinean continental margin (central Equatorial Atlantic) a 2.17 m long core has been sampled at 840 m water depth on the top of one of the volcanic seamounts cropping out in this area. Planktonic foraminiferal assemblages observed within the 2.13 m unconsolidated sediments indicate an age of 0.20 to 0.15 Ma, corresponding to the transition from interglacial to glacial events. Depth of deposition of the calcareous sand ranges between 150–200 m and progressively decreased during the glacial stage onset. Detailed sedimentological and micropaleontological studies, carried out on the 4 cm thick indurated core cap, indicate a deposition depth of 50–100 m, or even less. Taking into account the Pleistocene sea level fluctuations, these data suggest a rapid subsidence of the magmatic seamount since the upper most Pleistocene.

Contribution a l'etude geologique des Prealpes carniques orientales (Alpes meridionales, province d'Udine, Italie)

A lower Liassic to upper Miocene sedimentary sequence, west of Tagliamento, marks a transition from the reef facies of the Friuli zone to the deep water sediments of the Julian Alps. Three distinct tectonic regions can be separated by their stratigraphy: the Pradis-Forgaria autochthon of upper Cretaceous rudistid limestone and lower Eocene flysch underlying Oligocene marls and Miocene molasse; an inclined fold in the Pala-Prat-Pedroc area consisting of Norian to Paleocene fossiliferous limestones; and the Corno-Covria unit. The major tectonics are considered to be post-Pontian.