Paleoecological Analysis of Cheilostome Bryozoa from Venezuela - British Guiana Shelf Sediments, 1963-09-14 to 1963-09-19 (NCEI Accession 7100130)

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The abundance of cheilostome Bryozoa in many Cenozoic sublittoral marine facies, their sedentary existence, minute size and sensitivity to environmental conditions qualify them as a potentially important tool for paleoecological interpretation. Bryozoa have seldom been used in paleoecological studies, however, because only meager information is available on the relationship between modern Bryozoa and their environmental requirements and tolerance. Nevertheless, the usefulness of employing Bryozoa as a basis for paleoecological interpretation recently has been demonstrated in studies by Cheetham (1963) and Lagaaij and Gautier (1965).

Distribution patterns of benthonic organisms along continental shelves are due in part to ecological factors and in part of subsequent, postmortem transportation and mixing of the skeletal remains and sediments. The aim of the present study is to examine the environmental and sedimentary conditions that may govern the composition and distribution of thanatocoenose bryozoan associations in Venezuela-British Guiana Shelf sediments.

Faunule composition varies quantitatively and qualitatively from station to station; thus the definition of both associations and biofacies has posed a problem common to many paleoecological investigations. An attempt was made in this study to define numerically associations and biofacies on the basis of Bryozoa content by clustering techniques involving R-mode and Q-mode analysis.

Paleoecologic interpretation based on thanatocoenose assemblages depends not only on principles of ecology, but also on local sedimentation and geologic history. The study of Bryozoa from sediments along the modern Venezuela-British Guiana shelf has been complemented by data on sediments and the marine environment, and by information on the recent geological history of the Venezuela-British Guiana shelf based on sediment studies by Nota (1953) and Koldewign (1958), and foraminiferal studies by Drooger and Kaaschieter (1958).