Abstract: The Application of Quantitative Biostratigraphy in Complex Tectonic Settings, Eastern Venezuela and Trinidad

Gregg H. Blake

Planktonic and benthic foraminifera have been used to define the onshore stratigraphy of Venezuela and Trinidad for the last 40 years. Foraminiferal biostratigraphy has been an important tool for correlation because the eastern portion of Venezuela and the central and southern regions of onshore Trinidad are made up of a series of complex thrust sheets and associated anticlinal folds.

The correlation between the foraminiferal zones and the Cretaceous formations of eastern Venezuela was established from well-exposed outcrop sections. In contrast, isolated outcrops samples and subsurface well penetrations were used to correlate Cretaceous planktonic zones and the Trinidad formational units. Due to the tectonic complexity and facies changes associated with the Cretaceous continental margin, various formational names have been applied to the lithologic units. In order to present a depositional model for the northeastern South American during the Cretaceous, a regional stratigraphic framework is required that relates the equivalent stratigraphic units to major biostratigraphic events.

Due to the large number of variables (species) and the geologic complexity, a strategy using multiple quantitative techniques to increase the correlation resolution between the stratigraphic units, ranking and scaling were applied to the planktonic and benthic foraminiferal assemblages from various lithologic packages of the offshore sections. Graphic correlation was then used to further refine the foraminiferal events and their correlation to distinct lithologic units. Species assemblages and their distribution were determined for both onshore and offshore stratigraphic interval using multivariant statistical techniques, including principal components and factor analysis. Lastly, the improved offshore zonation was correlated to the onshore sections. The resultant stratigraphic framew rk establishes an improved correlation across structurally complex areas and facies changes from eastern Venezuela to offshore Trinidad.

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