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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 67 (1983)

Issue: 9. (September)

First Page: 1467

Last Page: 1468

Title: Marginal Marine Evaporites, Lower Cretaceous of Arkansas: ABSTRACT

Author(s): Brian E. Lock, Bruce K. Darling, Ilene D. Rex

Article Type: Meeting abstract


The mixed evaporite/carbonate/terrigenous clastic sediments of the DeQueen formation, in southwestern Arkansas, were deposited at the

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landward margin of a broad shallow lagoon formed behind the Glen Rose reef. About 60% 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 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 > 3 m (10 ft), 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 hali e 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, and 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 3 m (10 ft) of the DeQueen consists of mudstone with a thin marl at the top. A conformable contac exists with the overlying Antlers formation, which has basal mudstones becoming more silt- and sand-rich upwards and finally giving way to the typical Antlers (Paluxy) sands.

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