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