--> Abstract: Influences of Relative Sea-Level Variations on Coastal-Plain Architecture in the Campaman Series of the Mesa Verde Area, by R. Eschard, G. Desaubliaux, B. Carpentier, and B. Doligez; #90987 (1993).

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ESCHARD, REMI, GUY DESAUBLIAUX, BERNARD CARPENTIER, BRIGITTE DOLIGEZ, Institut Francais du Petrole, Rueil Malmaison, France

ABSTRACT: Influences of Relative Sea-Level Variations on Coastal-Plain Architecture in the Campaman Series of the Mesa Verde Area

Large outcrops and numerous subsurface data in the Mesa Verde area (Colorado) make possible the correlations of genetic units from fluvial to open marine environments. The stratal pattern and the facies partitioning were directly a function of the accommodation space, which varied a lot during the deposition of the major regressive-transgressive cycle of the Campanian. The regressive and the transgressive wedges were both made up of 10 to 30 m thick genetic units, corresponding to short-term relative sea- or base-level allocyclic variations.

The regressive wedge shows a seaward stepping pattern of genetic units. In the coastal plain environments, each short-term relative base-level fall induced the incision of the floodplain sediments by large meander belts. At the same time occured a widespread progradation of a storm ramps, followed by a downward shift of shoreface/foreshore sediments over offshore deposits. As the relative base-level rose, valleys were first filled by stacked meandering channels, then coastal-plain deposits aggraded with small channels meandering in a muddy floodplain. The rise was also marked seaward by the formation of a ravinement surface capped by transgressive nearshore sandstones.

The transgressive wedge shows a landward stepping pattern of genetic units. In the coastal-plain domain, each short-term relative base-level fall was only marked by the incision of large estuarine complexes while a shoreface/foreshore wedge prograded seaward. The rise caused the entrapment of clastic material in the estuarine complexes and in tidal channels, and a rapid aggradation of marsh deposits. Seaward, a ravinement surface truncated the coastal-plain sediments as they aggraded, and the eroded material was redeposited in form of deepening upward transgressive sands.

The coastal-plain architecture is finally very different in the two wedges. The thin but sand-rich deposits in the regressive wedge contrast with the thick mud and coal-rich deposits in the transgressive wedge.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.