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Abstract: Late Cretaceous in Western Venezuela--A New Biostratigraphical Approach

Maria A. Lorente, Isbelia Duran, Maibi Ruiz

Two major cycles are considered on the late Cretaceous of the Maracaibo Basin: the (upper) La Luna-Tres Esquinas overlain by the Colon-Mito Juan cycle.

The (upper) La Luna-Tres Esquinas is a major transgressive-regressive unit. The diachronous nature of La Luna-Tres Esquinas has been previously documented. But the westward younger age trend of its top is probably related with an erosive and/or non-depositional Campanian event, not previously reported from this Basin.

For dating purposes of the uppermost La Luna-Tres Esquinas levels a selection of paleontological evidence can be geographically summarized as follows: to the East (Trujillo-Lara) ammonites species Peroniceras aff. canaense and Hauerlceras aff. gardeni dates the top as not younger than Coniacian to early Santonian. In central Lake Maracaibo Dicarinella asymetrica Zone dates Santonian to earliest Campanian. Further to the West (Perija) NK15-NK16 Zones dates as late Santonian. In the Western and Central Andes the Globotruncana ventricosa Zone dates the uppermost levels as Campanian. In some areas La Luna grades to the late Campanian (NK22-NK23 Zones) glauconitic-phosphatic Tres Esquinas Member. The absence of Globotruncanita calcarata and Globotruncanella havanensis Zones points to the p ssibility of an important hiatus involving part of late Campanian and up to earliest Maastrichtian not detected before in the basin. The section looks continous to the west (Colombia) where late Campanian and earliest Maastrichtian has been dated with ammonites and dinoflagellates. In the Maracaibo Basin sedimentation started again during the Maastrichtian with progradation of Colon Formation. Subtle discontinuities within this unit were proven using the evolutionary trend of Ceratolithoides. These discontinuities may be related with the change from passive to active margin during the Maastrichtian. The cycle ends during the Danian with the clastics and carbonates from Mito Juan and Guasare formations.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela