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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 69 (1985)

Issue: 2. (February)

First Page: 295

Last Page: 295

Title: Paleopedogenesis in Lower Cretaceous Hensel Formation, Central Texas: ABSTRACT

Author(s): J. H. Payne

Article Type: Meeting abstract


The extensive matrix facies of the Hensel Formation consist of calcretized (calichified) red mudstone, and thin, sheet sandstone, interpreted as paleosols and overbank deposits. Framework facies include cross-stratified lenses of conglomerate and sandstone that represent low-sinuosity to meandering streams of small fluvial systems. These systems were active during the transgression that resulted in deposition of Glen Rose and Fredericksburg Group carbonates. The pervasive development of calcrete, desiccation cracks, and pseudo-anticlines within the Hensel paleosols, as well as the overall depositional style of the unit, suggest an arid to semiarid, seasonal climate.

Paleopedogenesis resulted in the formation of authigenic kaolin and illite, intense red-orange coloration, and various types of calcrete. Paleocalcrete within the mudstone facies commonly assumed a nodular habit. It is frequently observed to be coalesced into honeycomb structures. Locally calcretized, thin-bedded sandstone and mudstone were buckled into pseudo-anticlines. These structures were partly produced by fluctuating ground water and other inferred soil-forming processes. Paleocalcrete accumulated in the sandstone facies as undulating hardpans and vertically oriented rhizoliths. Microscopic textures characteristic of all these calcretes include low-magnesian calcite, crystallaria, and circumgranular cracks.

Carbon and oxygen isotopic values from each type of calcrete confirm a pedogenic origin for the authigenic calcite. A "heavier" oxygen isotopic value in the dolomite, peculiar to the pseudo-anticline calcrete, denotes enrichment of meteoric ground water by extreme evaporation. These conditions would have existed near a continental playa, an environment compatible with the seasonal, arid to semiarid climate.

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