--> Rapid Rhythmic Paleoclimatic Change during the Upper Cretaceous Recorded by Limestone/Marlstone Couplets in Sergipe Basin, Northeastern Brazil, by A. M. Carmo and L. M. Pratt; #90986 (1994).

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Abstract: Rapid Rhythmic Paleoclimatic Change during the Upper Cretaceous Recorded by Limestone/Marlstone Couplets in Sergipe Basin, Northeastern Brazil

Ana Maria Carmo, Lisa M. Pratt

About 90 bedding couplets are present within a single bivalve biozone from the early Turonian, Cotinguiba Formation, Sergipe Basin. High rates of sediment accumulation in deep basins adjacent to carbonate swells allow recognition of bedding couplets with estimated frequencies in the range of 10 Ka. The studied section is well exposed in the walls of the Votorantim cement Quarry. Limestone beds are bioturbated micrites with organic carbon contents of 0.1 to 0.3 weight percent. Marlstone beds are laminated to partially bioturbated, micrites with organic carbon contents of about 0.5 to 2 wt percent. Foraminifera and coccoliths are present but difficult to remove from the micritic matrix. Biostratigraphic zonation is best determined using inoceramid bivalves and ammonites. Several discont nuities in sediment accumulation are expressed by reworked hardgrounds and by surfaces of subtle onlap.

Carbon isotopic compositions of organic matter in both limestone and marlstone shows two positive and one negative shift (each about 1.5 per mil in magnitude) away from background (-25.5 per mil). Visual identification and elemental composition of kerogen indicate that the source of organic matter is uniformly amorphous marine. Thus, these isotopic excursions are driven by global changes in partitioning of carbon and can provide a high-resolution stratigraphic framework for correlation of northeastern Brazil with early Turonian strata in the North American Western Interior and the European chalks.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994