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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 56 (1972)

Issue: 9. (September)

First Page: 1901

Last Page: 1901

Title: Waves, Currents, Sediments, and Sand Bars Associated with Low-Energy Coastal Environments: ABSTRACT

Author(s): A. W. Niedoroda

Article Type: Meeting abstract


Low-energy beaches are commonly characterized by a particular series of offshore sand bars which differ markedly, both in shape and sediment characteristics, from the classic offshore bar of high- and moderate-energy environments. This study reports on the physical interactions of waves and currents with low-energy bathymetric features that result in producing a distinct areal distribution of sediment parameters in the shallow offshore area. The trends in the sediment parameters are well correlated with the subtle bathymetric features of the offshore area and thereby may provide a method of determining low-energy environments in ancient deposits.

Prominent features in low-energy environments are subtle digital sand bars which trend perpendicular with, or at a high angle to, the beach face. These transverse bars have maximum relief of approximately 0.5 m with lengths ranging between 100 and 3,350 m and a quasi-regular spacing ranging from 300 to 2,000 m.

Investigations by several authors indicate that these bars act as avenues for onshore or offshore sediment transport. Recent studies by the writer have determined that the sediment is transported as a result of a nearshore current component caused by the transfer of momentum from unstable nearshore waves to the currents. The current component is characterized by a narrow relatively high-velocity current directed along the axis of the bars, with sluggish return currents between the bars. This current produces relatively coarse, well-sorted sediment along the crest of the bar and finer, less sorted sediment between the bars.

The scale of these features, as well as the obvious differences in sediment parameters, should permit their recognition in ancient deposits. Their presence allows inferences to be made about ancient wave energy levels and average wave approach directions.

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