--> ABSTRACT: Sequence Stratigraphy and Biostratigraphy of the Cenomanian and Turonian Source Rock Interval in NW South America, by Tomas Villamil, Claudia Arango; #91020 (1995).

Datapages, Inc.Print this page

Sequence Stratigraphy and Biostratigraphy of the Cenomanian and Turonian Source Rock Interval in NW South America

Tomas Villamil, Claudia Arango

The Cenomanian-Turonian source rock interval in northwest South America (the La Luna Formation and part of the Villeta Group) shows dynamic and rapid changes in the distribution of micro- and macrofossils, particularly planktic foraminifers, ammonites, and bivalves. Micro- and macrofossils show marked variations in morphotypes and population structure from the Late Cenomanian braid systems tract (sandstones and siltstones of an unnamed unit of the Villeta Group), across a latest Cenomanian transgressive surface (shales and hemipelagic limestones of the base of the La Luna Formation in NW Venezuela and base of the La Frontera Formation in Colombia), to an earliest Turonian maximum flooding/condensed section. Some important variations in fossil assemblage (^approxpopulation structure are changes in diversity (H) and abundance (A). H and A decrease from the Late Cenomanian braid to the Cenomanian-Turonian boundary; then H and A increase to the Early Turonian maximum flooding surface. The Early Turonian condensed section is characterized by a concretion interval that is extremely rich in micro- and macrofossils and can be traced from southern Colombia to Eastern Venezuela. This concretion interval differs from others in that it contains abundant xylic remains, miniature specimens of the bivalve Anomia cf. papyracea, and a highly diverse mollusk assemblage. Fossil species and population changes are consistent in all studied sections therefore, they can be used for regional correlation. Vertical biostratigraphic differences respond to regiona areal shifts of facies that correspond to relative changes in sea level which control the development of depositional sequences.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995