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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)

Abstract


Journal of Sedimentary Research, Section A: Sedimentary Petrology and Processes
Vol. 65A (1995)No. 1. (January), Pages 29-39

The Geometry and Dynamics of Low-Relief Previous HitBedNext Hit Forms in Heterogeneous Sediment in a Laboratory Channel, and their Previous HitRelationshipNext Hit to Water Flow and Sediment Transport

Sean J. Bennett (*), John S. Bridge

ABSTRACT

The geometry and dynamics of low-relief Previous HitbedNext Hit forms (pebble clusters, Previous HitbedNext Hit-load sheets, and bars) developed in a mixed-size and mixed-density sediment (sandy gravel) were studied in a laboratory channel. In most runs, equilibrium uniform flow was established with discharge 0.05 m3/s, mean flow depth 0.1 m, mean flow velocity 0.82-0.87 m/s, mean Previous HitbedNext Hit shear stress 1.6-2.2 Pa, dimensionless Previous HitbedNext Hit shear stress 0.04-0.07, and mean Previous HitbedNext Hit-load transport rate 0.009-0.013 kg/m-s. Low-relief Previous HitbedNext Hit forms were observed directly and in Previous HitbedNext Hit-height records and Previous HitbedNext Hit profiles measured with a high-resolution, ultrasonic Previous HitbedNext Hit profiler. Pebble clusters are groups of relatively large, temporarily immobile clasts with lee side and stoss side accumulations of finer sediment, and with adjacent scoured zones w th heavy-mineral concentrations. Pebble clusters are concentrated in relatively coarse areas of the Previous HitbedNext Hit such as in the troughs of Previous HitbedNext Hit-load sheets and bars. Asymmetric, sinuous-crested Previous HitbedNext Hit-load sheets ranged from one to two grain diameters up to 12 mm in height and 0.6-1.2 m in length. Migration rates determined from Previous HitbedNext Hit-form spacings and periods were typically 1-1.5 mm/s. These Previous HitbedNext Hit forms had relatively fine-grained crests and coarse-grained troughs and a well-mixed grain texture along the stoss side. Previous HitBedNext Hit-load sheets had little associated form drag. Low-relief bars were 10-17 mm high and 1.7-2.4 m long, and typical migration rates were 0.4 mm/s. The migration of these bars was associated with fluctuations in the water-surface slope and Previous HitbedNext Hit-load transport rate with periods of about two hou s. Low-relief Previous HitbedNext Hit forms in heterogeneous sediments appear to be ubiquitous features of lower-stage "plane" beds and those transitional to dune-covered beds where the Previous HitbedTop is not completely mobile.


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