SHE Analysis: A New Technique in Biostratigraphic Correlation and Hydrocarbon Exploration

SHE Analysis: A New Technique in Biostratigraphic Correlation and Hydrocarbon Exploration

Brent Wilson
Petroleum Geoscience Programme, Faculty of Engineering, University of the West indies, St. Augustine, Trinidad and Tobago
In any multispecies population of organisms-no matter whether birds, trees or fossil foraminifera-some species will be abundant and others rare. The extent to which species abundances differ within an area is termed the population structure. Since the mid 1990s, research on benthonic foraminiferal population structures in (palaeo)-ecology has made increasing use of SHE Analysis, a novel tool in biostratigraphic correlation that delineates (i) regions called abundance biozones (ABs) with differing population structures and (ii) the population structures within the separate ABs. SHE Analysis has decided advantage over traditional cluster analysis, which delineates biofacies; by accumulating samples one at a time along a transect, SHE Analysis produces simpler patterns that can be more readily interpreted and used in correlation and the ecological interpretation of fossil communities. This talk highlights four studies that document the application of SHE Analysis in the eastern Caribbean:
1. Epiphytal foraminifera were monitored on seagrasses and calcareous algal substrates for a year in two bays off Nevis, eastern Caribbean Sea. SHECSI (SHE Analysis for Community Structure Identification) indicated logarithmic series population structures on five of six substrates. Despite differences in diversities as measured using the mean information function, the rate of increase in the number of species during the accumulation of the samples differed little between substrates.
2. The 3 m-long Core EN20-2 was collected near Nevis from middle bathyal depths and entrained the Pleistocene\Holocene boundary. Samples contained up to 58% allochthonous, epiphytal foraminifera. SHEBI (SHE Analysis for Biozone Identification) did not find an AB boundary coincident with the Pleistocene\Holocene boundary. Similar environmental trends, however, were indicated by both the allochthonous and autochthonous assemblages.
3. Examination of a Lower Miocene succession on Trinidad using SHEBI on raw abundance data indicated different AB boundaries depending on whether samples were accumulated from the base or top of the succession. It is suggested that bottom upward accumulation of samples is to be preferred.
4. In a study of intertidal foraminifera in the Caroni Swamp, Trinidad, the number of foraminifera per sample (N) fluctuated widely. To accommodate this, SHEBI was modified to commence with a matrix of proportional abundance data rather than absolute abundances. Comparison with the raw abundance data suggested that the Modified SHEBI more reliably indicated AB boundaries under such circumstances than did the original, classical form of SHEBI. Where N fluctuates little, Modified SHEBI and its original, classical version indicate the same AB boundaries.

Download Presentation

Dr. Brent Wilson FGS

Brent Wilson currently lectures micropalaeontology and sedimentology for the B. Sc. Petroleum Geoscience Programme in the Department of Chemical Engineering at The University of the West Indies, St. Augustine. His main research focus is on benthonic foraminifera of the eastern Caribbean region, concentrating especially on epiphytal foraminifera of the Lesser Antilles and Neogene foraminiferal palaeoecology of Trinidad and Tobago. Both research lines have drawn him increasingly into using SHE Analysis to determine population structures and the boundaries between abundance biozones characterized by differing structures. Prior to joining the UWI, Brent worked for many years as a high school teacher on the island of Nevis, being posted there by the British charity Voluntary Service Overseas, which sends skilled workers to aid in the Developing World. The story of his time there, during which he obtained a doctorate in micropalaeontology, is told in his autobiographical worst-seller, Living on an Arc: A Caribbean Memoir. He is the Trinidad correspondent for the magazine Geology Today.

Comments or Questions?