--> Abstract: Soft-Sediment Deformation Structures as Potential Indicators of Synsedimentary Tectonic Control in Alluvial-Lacustrine Sequences, Green River Formation, Nine Mile Canyon, Uinta Basin, East-Central Utah, by D. Keighley, D. Andersson, S. Flint, and J. Howell; #90928 (1999).

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KEIGHLEY, DAVID, DANIEL ANDERSSON, STEPHEN FLINT, and JOHN HOWELL
Department of Earth Sciences, University of Liverpool.

Abstract: Soft-Sediment Deformation Structures as Potential Indicators of Synsedimentary Tectonic Control in Alluvial-Lacustrine Sequences, Green River Formation, Nine Mile Canyon, Uinta Basin, East-Central Utah.

Soft-sediment deformation structures are encountered at numerous stratigraphic levels within a 200 meter thick succession of alluvial-lacustrine strata (Middle Member, Green River Formation, Eocene) examined over a 15 square kilometer area of the Uinta Basin in east-central Utah. Structures include sand volcanoes, overturned cross-laminae, convolute laminations, large load structures, mudstone diapirs, vertical pipes of oolite, flow rolls, and flute-like marks. Although some of these soft-sediment deformational structures can be readily attributable to sedimentologic forces (e.g. recumbent-folded cross-laminae caused by tangential shear at the water-sediment interface), most may alternatively be directly or indirectly associated with tectonic activity influencing the sedimentary sequence.

Fluvial and overbank sandstones, floodplain mudstones and paleosols, high-energy-lacustrine shelly and oolitic limestones and sandstones, low-energy-lacustrine micritic limestones, and low-energy-lacustrine mudstones form a multiply cyclic succession (on two or possibly more scales) in the study area. Most of the soft-sediment deformation structures are associated with fluvial and overbank sandstones. Preliminary allostratigraphic correlations indicate that the deformations are most pronounced within certain of the larger-scale cycles: those containing lower connectivity alluvial sandstones that overlie minimally incised lacustrine strata. Though debatable, our working hypothesis is that non-seismically induced deformations would be expected to have affected these otherwise lithologically and structurally identical sandstones to a similar degree throughout the study interval. It is therefore proposed that tectonically driven basin-margin uplift maintained ample accommodation space and an abundant supply of sediment that was able to accumulate with a metastable density profile. Alternatively, the deformations might have been directly initiated by earthquake shaking — or potentially in tandem with the uplift-maintained high sediment supply.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas