Latest Quaternary Stratigraphic Framework of the Mississippi River Delta

By

KULP, MARK A.

University of New Orleans, New Orleans, LA,

HOWELL, PAUL D.

Univ. of Kentucky, Lexington, KY,

PENLAND, SHEA

University of New Orleans, New Orleans, LA,

KINDINGER, JACK

U.S. Geological Survey, St. Petersburg, FL,

WILLIAMS, STANLEY J.

Woods Hole, MA

Upper Quaternary stratigraphy of the Mississippi River delta region has been a topic of investigation for more than fifty years. Aside from furthering knowledge of regional late Quaternary history, an objective of these studies has been the characterization of sedimentation patterns on fluvio-deltaic dominated, continental margins. Recent suggestions that Late Quaternary sediment type and thickness may control delta-plain subsidence trends emphasize the continuing necessity of regional geologic framework studies.

Early workers separated the uppermost Quaternary stratigraphy into two major lithofacies. The stratigraphically lower of these, “substratum”, primarily consists of coarse-grained sediment deposited within lowstand-incised stream valleys. Relatively finer-grained “topstratum” overlies substratum; above interfluves, topstratum directly overlies weathered late Pleistocene sediments. However, the onshore to offshore distribution and architecture of these lithofacies was not well constrained.

This study integrates more than 800 published and unpublished offshore and onshore boreholes, with several, widely-spaced, high-resolution, seismic profiles from the continental shelf to aid in mapping the regional distribution of major substratum deposits as well as thickness and distribution of topstratum sediments. Significantly, a transgressive sand sheet commonly marks the base of the topstratum deposits, providing a stratigraphic marker to aid in regional lithostratigraphic correlations. Radiocarbon dated deposits and boreholes tied to oxygen isotope chronologies provide chronostratigraphic control. Excellent correlation of the transgressive into highstand interval has been found to exist which, coupled with more than 300 radiocarbon-dated peats has enabled construction of regional isopachous and structural elevation maps and cross sections detailing elements of the Late Quaternary stratigraphic framework.