Stratigraphy and facies analysis of the Cenomanian-Turonian boundary succession in the Japaratuba area, Sergipe Basin, Brazil

A facies analysis of the Cenomanian-Turonian (Cretaceous) boundary beds was carried out in the Japaratuba area, Sergipe Basin, north-eastern Brazil, on the basis of seven outcrop sections. The lower part of the succession is represented by dolomitic limestones and marly limestones, whereas the upper part is dominated by chalky, nodular limestones and bedded and coquinoid limestones. Three microfacies types are recognized in the upper part of the succession, where biostratigraphic work has indicated the position of the Cenomanian-Turonian boundary. Two of these microfacies types (foraminiferal mudstone, wackestone) occur only in the nodular limestone unit and are referred to an outer carbonate ramp setting. The uppermost part of the succession is dominated by echinoderm-inoceramid packstones, which probably were deposited in a mid-ramp setting. In the late Cenomanian, deposition took place in the outer-ramp distal area of an open-marine basin, which gradually became shallower during the Cenomanian-Turonian transition, as evidenced by the increase in macrofaunal debris to the northeast. In addition to macrofossil fragments, some thin sections contain abundant planktic and benthic foraminifers, calcispheres, and roveacrinids; the latter are potentially useful for stratigraphic purposes. Biostratigraphic data suggest that the lowermost Turonian is missing in the southern part of the Japaratuba area.