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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 48 (1964)

Issue: 4. (April)

First Page: 521

Last Page: 522

Title: Sedimentary Structures: Mississippi River Previous HitDeltaicNext Hit Plain: ABSTRACT

Author(s): James M. Coleman, Sherwood M. Gagliano

Article Type: Meeting abstract

Abstract:

Minor sedimentary structures were studied in cores and exposures from the Previous HitdeltaicNext Hit and marginal Previous HitdeltaicNext Hit plains of the Mississippi River. Selected active Previous HitenvironmentsNext Hit were sampled, and the occurrence of sedimentary structures from each was recorded. Individual structures were found to occur in more than one environment; however, suites of structures were characteristic. Within the study area the following twelve depositional Previous HitenvironmentsNext Hit have been investigated: shelf, prodelta, delta front (distal bar, distributary mouth bar, channel, and subaqueous levee), subaerial levee, marsh and swamp, interdistributary bay, mudflat, and fresh-water lake.

Shelf deposits consisted of: (1) fine-grained clastics, burrowed and showing parallel laminations and (2) marine organic debris. Prodelta deposits are similar to clayey shelf deposits, but contain lenticular and parallel lamination with finely divided plant inclusions. The delta front is a complex of sub-Previous HitenvironmentsNext Hit constituting the advancing locus of active deposition of the prograding delta. The sloping seaward margin on this zone--the distal bar--exhibits current structures such as trough cross-laminations and current ripples as well as parallel and lenticular laminations, wave ripples, and burrows. The silty and sandy distributary mouth bar is characterized by a variety of small-scale, multi-directional cross-laminations and gas-heave structures. Channel deposits exhibit trough c oss-laminations, scour and fill, and distorted laminations, whereas subaqueous levees contain abundant ripple and unidirectional cross-laminations, parallel, wavy, and distorted laminations. In addition, subaerial levees are burrowed and oxidized. Marsh and swamp deposits are distinguished by abundant plant remains, burrows, and parallel laminations. Lenticular laminations, wave ripples, burrows, shell, and plant remains are characteristic of both interdistributary bay and fresh-water lakes. The mudflat assemblage of structures includes lenticular laminations, current and wave ripples, burrows, and shell remains.

Not only are associations of sedimentary structures

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important in recognizing individual Previous HitenvironmentsNext Hit of deposition; equally important is the association of the Previous HitenvironmentsNext Hit to one another. This relationship must be understood for correct paleogeographic reconstruction of ancient Previous HitdeltaicNext Hit deposits. The manner in which a sequence of marine and Previous HitdeltaicTop deposits might accumulate in a segment of a basin with resulting stratigraphic relationships of associated environmentally determined facies, is illustrated.

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