The Application of Quantitative Biostratigraphy in Complex Tectonic Settings, Offshore Trinidad

Gregg H. Blake, Anthony Gary

Planktonic and benthic foraminifera have been used to define the onshore stratigraphy of Trinidad for the last 40 years. Foraminiferal biostratigraphy has been an important tool for correlation because 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 Tertiary formations was established from well-exposed outcrop sections. In contrast, isolated outcrop samples and subsurface well penetrations were used to correlate Cretaceous planktonic zones and the Mesozoic formational units. Based on well cutting samples from exploratory wells drilled in offshore Trinidad, it is apparent that there is a difference between the age of the onshore formational units and the equivalent stratigraphic units encountered in the offshore wells.

Due to the large number of variables (species) and the geologic complexity we applied 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 distributions were determined for both onshore and offshore stratigraphic intervals using multivariant statistical techniques, including principle components and factor analysis. Lastly, the improved offshore zonation was correlated to the onshore sections. The resultant stratigr phic framework establishes an improved correlation across structurally complex areas between the offshore formational units and those defined for the onshore sections.

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