Foraminiferal biostratigraphy and correlations in the Gulf of Alaska Tertiary Province

Abstract

INTRODUCTION As part of ongoing research by the U.S. Geological Survey on the geology and resource potential of the Gulf of Alaska Tertiary Province, a vast amount of data has been accumulated over the past 25 years on the lithology and paleontology of bedded rocks in the province. This report brings together available information on the occurrence, age, and paleoecological significance of benthonic foraminifers and presents correlations based on these data from 16 measured stratigraphic sections and 12 exploratory wells. Relatively few reports employing modern taxonomic methods developed during the past 40 years have been published on foraminiferal biostratigraphy of the Gulf of Alaska. Reports by Cushman (1941), Cushman and Todd (1947), Tappan (1951), Todd (1953), Loeblich and Tappan (1953), Todd (1957), Rau (1963), Cooper (1964), and Todd and Low (1967) are primarily concerned with taxonomy, ecology and paleoecology, or the geologic age of assemblages from isolated outcrops. Almost no data have been published on foraminiferal correlations of measured sections and wells. Thus, the paucity of such information has prompted the synthesis and interpretation of foraminiferal data that provide the framework of correlation presented in this report. Some of the benthonic provincial stages that have been assigned to lower and middle parts of the Tertiary of other west coast areas are recognized for the Gulf of Alaska. Divisions for the upper part of the Tertiary are broad, but specific faunal occurrences are recognized as possible aids to correlations. Regional correlations presented in this report are necessarily broad and may be modified and refined when new data become available from the current round of exploratory drilling for petroleum in the offshore part of the Gulf of Alaska Tertiary Province. It is anticipated that this report will be of particular interest to readers associated with petroleum exploration. As a convenience to them and because most foraminiferal data from wells, including those of this report, are from cuttings, all checklists are arranged to show plainly the highest occurrence of each species within each measured section and well. Furthermore, in conformity with these data, all sections and wells are described from the top to bottom. The text describes the stratigraphic and paleoecologic significance of foraminifers by biostratigraphic units and by individual sections and wells. A comparable synthesis of marine molluscan data from the measured sections (Addicott, Winkler, and Plafker, 1978) may be used to compare and evaluate the suggested correlations as based independently on the microfauna or the macrofauna.