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Abstract

The uppermost 27 m of the Shattuck Member of the Queen Formation (Middle Guadalupian) and the lower 156 m of the overlying Seven Rivers Formation (Late Guadalupian) represent portions of two depositional sequences (Fig. 1). A subaerial sabkha surface near the top of the Shattuck Member is interpreted to be a sequence boundary and separates the two sequences. This disconformity is widespread over the Permian Basin, correlates with a toplap surface at the Goat Seep platform margin, and suggests a major sea-level drop at the end of Goat Seep deposition. Deposition of the basin-restricted Manzanita Member of the Cherry Canyon Formation is interpreted to have occurred during this lowstand in sea level. The immediately overlying 7 to 11 m of the topmost Shattuck contains fossilized and dolomitized Permian soil caliche (dolocalcrete). The dolocalcrete occurs in a repeated series of soil profiles overlain by evaporite solution residues. These dolocalcrete cycles are interpreted to have been deposited during a time of slowly rising sea level toward the end of the Manzanita lowstand and just prior to deposition of the Capitan Reef Complex (Sarg, 1985).

The dolocalcretes consist of nodular, massive, and mottled textures containing clotted and fractured micrite, microspar, equant spar-filled solution channels, coated fractures, and pisolites similar to modern caliche fabrics. Profiles are thin (approximately 0.5 m) and incomplete, and record short-lived soil-forming conditions with little external addition of CaCO3. The upper surfaces of the dolocalcretes are hard and undulatory, and erosional in part. The overlying evaporite solution residues are composed of interbedded green/red clayey siltstone and thin, discontinuous zones of red calcitic dolomite. The dolomite consists of small angular clasts of microcrystalline dolomite in a coarsely crystalline calcite matrix. Overlying dolomite beds are commonly brecciated (Sarg, 1977, 1985).

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