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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 33 (1983), Pages 145-152

Marginal Marine Evaporites, Lower Cretaceous of Arkansas

Brian E. Lock (1), Bruce K. Darling (2), Ilene D. Rex (3)

ABSTRACT

The mixed evaporite/carbonate/terrigenous clastic sediments of the De Queen Formation, in southwestern Arkansas, were deposited at the landward margin of a broad shallow lagoon formed behind the Glen Rose reef. About sixty percent of the sedimentary volume consists of mudstone, silt and sand with brackish water to hypersaline ostracod faunas, believed to result from influx of flood waters from the Ouachita highlands located a few miles to the north. The lower part of the formation contains discontinuous beds of gypsum, ranging in thickness from a few centimeters to composite beds of over three meters, and displaying mosaic structure with vertically oriented, elongate nodules. These beds, which are lenticular, are interpreted to result from subaqueous precipitation of vertical selenite crystals (subsequently recrystallized) in discrete ponds and pools on microtidal-range mud flats. Intrastratal growth of gypsum nodules and displacive halite occurred at the margins of the pools.

The upper part of the formation contains no gypsum beds, but halite pseudomorphs at the base of and within some of the thin limestones suggest the presence of supratidal brine pools. Several minor unconformities exist, of which one has a regional extent and is underlain by red-brown mudstones. Algal-mat lamination, lenticular gypsum pseudomorphs (an intrastratal growth form), and syneresis cracks occur in the limestones. A supratidal environment is envisaged for a significant proportion of the time of deposition.

The limestones generally have a restricted fauna of ostracods, bivalves, cerithid gastropods, serpulid worms, and miliolid foraminifera, and range in texture from lime mudstones to grainstones. The most abundant grain types are pellets, superficial ooliths, and terrigenous quartz. A paucity of dolomite is a striking feature. Some of the thinner bedded units are rippled, and some ripples were truncated during periods of emergence. The limestones are believed to represent periods of shallow water, slightly hypersaline to slightly hyposaline conditions of variable energy.

The regressive trend displayed by these two divisions continued with deposition of the overlying formation. The uppermost three meters of the De Queen consist of mudstone with a thin marl at the top. A conformable contact exists with the overlying Antlers Formation, which has basal mudstones becoming more silt- and sandrich upwards and finally giving way to the typical Antlers (Paluxy) sands.


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