Relative Role of Eustacy, Climate, and Tectonism in Continental Rocks
Relative Role of Eustasy, Climate, and Tectonism in Continental Rocks - The renaissance in stratigraphy over the last two decades has been largely driven by the belief that stratigraphic packaging is determined by allocyclic controls. An understanding of the controls on stratigraphy allows us to make better predictions
Evolution of a Braided River System: The Salt Wash Member of the Morrison Formation (Jurassic) in Southern Utah
Published:January 01, 1998
John W. Robinson, Peter J. McCabe, 1998. "Evolution of a Braided River System: The Salt Wash Member of the Morrison Formation (Jurassic) in Southern Utah", Relative Role of Eustacy, Climate, and Tectonism in Continental Rocks, Gary Kocurek
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The Salt Wash Member of the Upper Jurassic Morrison Formation in the Henry Mountain region of southern Utah is up to 160 m thick and consists of sandstones, interpreted as fluvial-channel deposits, and mudrocks, interpreted as overbank or abandoned channel-fill deposits. The strata are interpreted to have been deposited by a braided river system based on the high sandstone:mudrock ratio, the paucity of ripple lamination in the upper part of fining-upward units, the coarse grain size of many of the sandstones, a lack of lateral accretion bedding, the sheetlike nature of the sandstone bodies and the low dispersion of paleocurrent vectors. The rivers appear to have had a highly flashy discharge with relatively little preservation of falling-stage and low-stage sedimentary features. There is an up-section change in stratal geometry from thin, highly amalgamated, sheet sandstone bodies, to thicker, more isolated, sheet sandstone bodies. This change suggests an increase in the rate of creation of accommodation over time— this may be related to expansion of lacustrine systems downstream. There may also have been a climatic change from arid to semi-arid conditions that resulted in larger streams and more stabilized banks. Perpendicular to the paleoflow direction there is a marked change in thickness of the strata with an increasing percentage of overbank/flood-plain mudstone in thinner sections— this change is interpreted to be the product of differential subsidence within the basin of deposition. An understanding of fluvial strata like the Salt Wash Member requires a holistic view of allocyclic controls on sedimentation including temporal and spatial variations in climate, tectonism and base level.