--> ABSTRACT: Influence of Depositional Processes on the Composition of Sandstone in a Wave-Dominated Fan Delta, by Lee J. Suttner, Lindsay A. Hood, and Prodip K. Dutta; #91030 (2010)

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Influence of Depositional Processes on the Composition of Sandstone in a Wave-Dominated Fan Delta

Lee J. Suttner, Lindsay A. Hood, Prodip K. Dutta

Sandstone in the Lower Pennsylvanian (Morrowan-Atokan) portion of the Fountain Formation in the Manitou Springs, Colorado, area was derived from Precambrian granite gneiss and deposited in associated medial alluvial-fan, foreshore, shoreface, and offshore environments constituting a wave-dominated fan delta. The sandstone facies are arranged in six vertically stacked progradational sequences. The regressive marine portions of the sequences rest on a transgressive lag conglomerate and range from 5 to 9 m thick. The alluvial deposits capping each sequence are up to 20 m thick.

The different sandstone facies of the fan delta system show variations in mineralogical composition. Because all of the sandstone facies share a common first-cycle provenance and burial history, differences in composition largely reflect differences in depositional-process control on composition. Foreshore sandstones possess maximum compositional maturity (QFR-70:25:5); offshore sandstone is most immature (QFR-45:50:5). Apparently feldspar is winnowed out of the foreshore sand, bypasses the shoreface, and is concentrated in offshore, storm-deposited sand. Alluvial and shoreface sandstone are intermediate in composition with QFR content of 55:35:10 and 60:35:5, respectively.

Dominant authigenic minerals in the alluvial facies are chlorite, kaolinite, and illite; in the foreshore, quartz and kaolinite; in the shoreface, kaolinite; and in the offshore, microcrystalline quartz.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.