--> Abstract: An Outcrop Record of Complex Sediment Gravity Flow Mechanisms; #90063 (2007)

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An Outcrop Record of Complex Sediment Gravity Flow Mechanisms

 

Plink-Bjorklund, Piret1, Mary Carr2, Robert Amerman1, Jim Borer1, Grace Ford1, Estelle Mortimer3, Douglas Paton1, David Pyles1, Bruce Trudgill1, Richard Wilde4 (1) Colorado School of Mines, Golden, CO (2) Colorado School of Mines, (3) University of Potsdam, Potsdam, Germany (4) Chevron Energy Technology Company, Houston, TX

 

The Gosau basin is a small basin bounded by growing structures. The basin infill consists of a large variety of sediment gravity flow deposits and mass transport complexes (MTC-s, here defined as slump and slide deposits). The changing character of the sediment gravity flows, and MTC-s across the basin and through the stratigraphy records the growth of structures on the basin margins.

 

The sediment gravity flow deposits consist of conglomerates and breccias, laminated sandstones, and normally-graded, thin “Bouma turbidites”. The breccias and conglomerates form a large proportion of the basin fill volume, and range from clast-supported to matrix-supported. The matrix consists of sand or granules, mixture of the latter and mud, or mainly mud. Some beds are well structured, others display grading, are structureless or soft-sediment-deformed. This implies that a variety of sediment gravity flows was operating in the basin; ranging from turbidity currents, supported mainly by fluid turbulence; to cohesive debris flows, supported dominantly by matrix strength; to cohesionless debris flows or perhaps grain flows, where dispersive pressure was the main grain-support mechanism.

 

Moreover, complex nature of many beds suggests that the grain support mechanisms of some of the operating flows changed through the vertical profile, through the duration of the flow; or along the downslope profile of the flows. Some flows may have been driven by an overriding flow. Such complex beds include slump or cohesive debris flow deposits overlain by turbidites, turbidites overlain by structureless siltstones, grain-supported and graded conglomerates overlain by matrix supported conglomerates.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California