Regressive Coastal Deposits on Quaternary Continental Shelves: Preservation and Legacy
Published:January 01, 1991
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Michael E. Field, Fabio Trincardi, 1991. "Regressive Coastal Deposits on Quaternary Continental Shelves: Preservation and Legacy", From Shoreline to Abyss: Contributions in Marine Geology in Honor of Francis Parker Shepard, Robert H. Osborne
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Regressive coastal deposits containing internal downlapping surfaces are common on continental shelves of the world. Through theoretical considerations and evaluation of examples from the literature and our own studies in California and Italy, we have examined the conditions that lead both to the formation and preservation of these deposits.
Coastal downlapping deposits form by progradation of coastal and deltaic lithosomes during stable and falling sea level. in addition to the rate and direction of sea-level change, the major controls governing the development of downlapping deposits are sediment availability and shelf morphology (gradient, surface irregularity, and depth of shelf break). Continental margins receiving a large, continuous supply of sediment commonly have vertical stacks of thick, laterally extensive deposits; those fed by relatively small coastal streams may have well-developed shelf-margin deposits if accommodation space was available. in the absence of feeder streams, shelf-margin downlapping deposits can form from locally derived sediment.
Regressive coastal deposits are preserved in a variety of settings, but they are least likely to be preserved on broad, low-gradient (coastal plain) shelves, where small drops in relative sea level were accompanied by large seaward shifts of the shoreline. Even on high-gradient tectonic margins, downlapping deposits commonly are not preserved on the midshelf. The process of shoreface erosion during a transgression is efficient at planing off deposits from previous depositional cycles. Where the deposits are thin, the deposit is partially or wholly reworked; where they are thick, the basal part may be preserved.
Regressive deposits are most likely to be preserved along the shelf margin, where relatively thick sequences form at or below the position of the lowstand sea level. On many continental shelves, the coarse sandy texture of outer-shelf sediment largely reflects original deposition in a regressive coastal environment during a fall and lowstand of relative sea level.
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From Shoreline to Abyss: Contributions in Marine Geology in Honor of Francis Parker Shepard
From Shoreline to Abyss: Contributions in Marine Geology in Honor of Francis Parker Shepard - Francis P. Shepard left a rich scientific legacy including more than 230 published papers and books primarily addressed to the study of submarine canyons and turbidity currents, continental shelves and associated sediments, coastal processes and sediments and marine physiography and tectonics. He is best remembered for his work on submarine canyons; however, his broad range of scientific interests and his remarkable ability to break new ground in each of these disciplines have served as a model for at least four generations of ?Shepard? students. This new work from these Shepard students addresses problems in marine geology from the global scale to the local outcrop scale. Relationships among tectonics, eustacy and both siliciclastic and carbonate sedimentation create a unifying theme. Special topics include coastal processes, shelf and slope evolution, and submarine canyon and fan systems.