Abstract

The uppermost 11 m of the Shattuck Member of the Queen Formation (Permian Shelf, Middle Guadalupian) contains fossilized and dolomitized Permian soil caliche (dolocalcrete), which overlies an interpreted exposure surface in the Shattuck. It occurs approximately 16 km behind the Goat Seep shelf margin, and represents one of the few caliches present in Permian Shelf strata. The dolocalcrete occurs in a repeated series of soil profiles overlain by evaporite solution residues. 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 (≃ 0.5m) 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.

Recognition of the Shattuck dolocalcrete and the underlying exposure surface suggest that the upper Queen contact is disconformable, at least in part, and that the Permian shelf probably was exposed to vadose conditions. This disconformity is widespread and correlates with a toplap surface at the Goat Seep shelf-margin, suggesting a major sea level drop at the end of Goat Seep deposition. Deposition of the basin center Manzanita Member of the Cherry Canyon Formation probably occurred during this lowstand in sea level. The dolocalcrete cycles are interpreted to have been deposited during a time of slowly rising sea level toward the end of a major lowstand in sea level just prior to deposition of the Lower Capitan reef complex.