Allen Lowrie¹, Susan Moffett²
(1) Consultant, Picayune, MS
(2) Independent, Picayune, MS

Abstract: High-frequency (4th order) Quaternary/Neogene sequence stratigraphy and tectonic implications in the northern Gulf of Mexico

The classical hierarchy of 1^st, 2^nd, and 3^rd order stratigraphic sequences in Exxon/Vail terminology are based on what is decipherable from industry (10 to 100Hz) seismic and well-log data. Third order cycles are documented worldwide. Over the past decades, analysis of outcrops, oceanic cores and high-frequency (from 100 to 1000 Hz) echograms and industry seismic data in high-deposition areas spanning Quaternary/Neogene and other geologic ages reveal 4^th order sequences of deci-millennial years duration. These sequences can be correlated with Milankovich cycles and long-term climate changes.

Recent interpretations indicate that during ice ages, there may be major river-flow reduction (as much as 10 - 20% highstand rates) along mid-latitude and tropical rivers. Exceptions occur when there have been post-glacial floods and debris flow-induced lake outbursts. These outbursts may be as much a ten- to hundred-fold increases in short-term (<100 years duration) floods. These variations in depositional rates, ranging from one to three orders of magnitude, may mean that there can be the equivalent of short-term, compressive tectonic "forces" impacting underlying sedimentary wedges.

Much lowstand deposition occurs along the continental slope and rise. These short-term "forces" can serve as "drivers" of salt and supra- and sub-salt tectonics. The loci of deposition are the loci of compression. Zones of weakness within the slope can e augmented or diminished by the sedimentary outburst. Rapid deposition increases geo-pressuring, and associated stresses increase sedimentary fracturing, thus enhancing fluid-flow and dewatering of sediments.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana