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