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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 44 (1994), Pages 768-768

Abstract: Formation of High-Frequency Sequences and Their Bounding Surfaces in a Paleogene Supply-Dominated System, Texas Gulf Coast, USA

L. D. Meckel III, W. E. Galloway

ABSTRACT

Short-term variations in accommodation and supply on the continental shelf cause imbalances within longer term dynamic equilibrium conditions. These imbalances result in the deposition of high-frequency sequences. The Eocene Yegua Formation of the Texas Gulf Coast is made of six such sequences, which have average durations of 0.8 million yr or less. They formed in response to distinct variations in the rate and quantity of sediment supply, increases and decreases in the average grain size carried into the basin, relative sea-level position, and the capacity of basinal energy regimes to transport and rework sediments.

Each sequence may be characterized by the mix of particular regime conditions that were dominant during its deposition. If the rate of sediment supply and the average grain size were more significant than the rate of relative sea-level change and the capacity for basinal transport, then the sequence was supply dominated and was characterized by deltaic deposition, progradation of parasequences, and river mouth bypassing onto the shelf and slope. If, instead, relative sea-level rise and basinal transport were the dominant factors, the sequence was accommodation dominated and was characterized by estuarine deposition, retrogradation of parasequences, and shoreface bypassing onto the shelf. When the accommodation and supply factors were in equilibrium, sequences containing both fluvial and estuarine deposits characterized by aggradational parasequence stacking were deposited.

No two consecutive sequences in the Yegua were dominated by the same mix of regime conditions. Therefore, the sequence boundaries are important indicators of changes in regime conditions. Significantly, all of the boundaries are highly correlatable, well-constrained regional marine flooding surfaces. Flooding of the shelf thus apparently either causes, or occurs as a result of, a fundamental readjustment in the dynamic interplay between sediment supply and accommodation.

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ACKNOWLEDGMENTS AND ASSOCIATED FOOTNOTES

Department of Geological Sciences, The University of Texas at Austin, Austin, TX 78712

Copyright © 1999 by The Gulf Coast Association of Geological Societies