Interdistributary bay sequences and their genesis



    1. Department of Geology and Mineralogy, Parks Road, Oxford, OX1 3PR
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      Sedimentology Laboratory, Department of Geology, The University, Whiteknights, Reading RE6 2AH.


Interdistributary bay sedimentation is dominated by flood-generated incursions from the distributaries. There are three processes by which sediment-laden flood waters can be transferred to the bay: overbank flooding, crevassing and avulsion. These processes combine to produce a family of sedimentary sequences, the majority of which are small-scale coarsening upwards sequences representing infilling of the bay. Subordinate related sequences include those of small-scale (crevasse) channels and larger scale (distributary) channels. Spits or beaches at the mouth of open interdistributary bays produce larger scale, wave-dominated coarsening upwards sequences.

A model of bay sedimentation concerning a recently initiated (hypothetical) distributary is presented. Four phases of sedimentation (overbank flooding, crevasse splay, minor mouth bar—crevasse channel couplets and avulsion) characterize the history of the distributary, and it is postulated that the phases are genetically related to alluvial ridge development.