--> ABSTRACT: Holocene Analogs for Forced Regression Sand and Gravel Bodies, by P. R. Hill, M. Roberge, and F. Baechtold; #91021 (2010)

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Holocene Analogs for Forced Regression Sand and Gravel Bodies

HILL, PHILIP R., M. ROBERGE, and F. BAECHTOLD

Isostatic rebound of areas covered by the Laurentide glaciation causes relative sea level (RSL) lowering. The coastline of Hudson Bay is currently emerging at a rate of 1 cm a{-1} and comparable rates were experienced in the St. Lawrence estuary region during the early Holocene. These regions provide field laboratories for studying the stratigraphic evolution and sedimentologic characteristics of forced regression coastlines.

The Metis River in the St. Lawrence region occupies an incised valley cut during Holocene RSL lowering. A morphological analysis of raised shoreline deposits associated with the incised valley indicates that an early Holocene falling-stage delta, deposited during a period of high sediment supply, was cannibalized and provided the sediment for later shoreline accretion. Younger shorelines below the delta are characterized by sets of gravelly beach ridges and laterally adjacent erosion surfaces and low cliffs. Shoreline evolution at this time was controlled in large part by the emerging antecedent topography.

The Great Whale River on the eastern shore of Hudson Bay is an example of a sandy, wave dominated, falling-stage delta at the mouth of an incised valley. The modern delta consists of a gradually downstepping sand body of two parts: an offshore prograding and downlapping set of clinoforms and a shoreface-dune complex. These two parts are separated by a shallow water platform which represents a zone of sediment bypassing. The resultant stratal architecture would likely consist of two superimposed sets of clinoforms separated by an apparent unconformity surface. This conforms with sections of the delta exposed in the incised valley walls where prodelta and shallow water sands are overlain disconformably by coarser beach and bar facies, these in turn being capped by eolian sands.

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.