Abstract: Nannofossil and Sequence Chronostratigraphy of a Marine Flooding Surface in the Turonian of Trinidad

Ting-Chang Huang

A multi-well regional study in the Southern basin, Trinidad, reveals a very pronounced marine flooding surface in Turonian-age sediments. This surface is correlatable with global Turonian marine transgressions and genetically ties with the best hydrocarbon source rocks known in Trinidad.

The Turonian marine flooding surface yields abundant nannoplankton. Most notable is Lithastrinus moratus Stover, a short-ranging marker of the Lithastrinus evolutionary series. Two morphotypes of Lithastrinus moratus have been found. The more delicate eight-rayed form evolves from Lithastrinus floralls in early Turonian time. Based on observations in Ste. Croix-1, Rocky Palace-1, Rochard-1, Marac-1, Momga East-15, Iguana River-1, Lizard Spring-1 and Antilles Brighton-102, it occurs more frequently in the lower Turonian, but is rare in Trinidad. It has a more robust seven-rayed descendant that appears to be restricted to a narrow interval associated with peak Turonian marine transgression and usually dominates the nannofossil assemblage in the conden ed section. The highest stratigraphic occurrence of this form coincides with the lowest occurrence of Marthastentes furcatus based on core sample studies. The age of the marine flooding surface is therefore well constrained to be in zone CC12 and is considered to be correlative with the 89 million year marine flooding surface.

The marine flooding surface appears intercontinentally correlatable as it has also been identified in the Arcadia Shale of the Eagle Ford Group in Texas. Because of its wide areal distribution and ease of paleontological recognition, this surface is ideal for regional hydrocarbon source rock mapping, stratal correlation and structural control.

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