Stratigraphy and Paleogeographic Significance of the Pennsylvanian-Permian Bird Spring Formation in the Ship Mountains, Southeastern California.

摘要

A thick sequence of limestone, dolomite, and minor sandstone assigned to the Pennsylvanian and lower Permian Bird Spring Formation is exposed in the Ship Mountains about 85 kilometers (km) southwest of Needles, California, in the eastern Mojave Desert. These strata provide a valuable reference section of the Bird Spring Formation in a region where rocks of this age are not extensively exposed. This section, which is about 900 meters (m) thick, is divided into five informal members: 1. A lower member of thick-bedded to massive limestone and dolomite (180 m thick); 2. A limestone and dolomite member (200 m thick) lithologically similar to member 1, but separated from member 1 by a fault of undetermined offset; 3. A member of sandy limestone, calcareous sandstone, quartzite, and minor limestone (80 m thick); 4. A thick.bedded to massive, fossiliferous limestone member (55 m thick); and 5. An upper member of thin- to thick-bedded dolomite, limestone, silty to sandy limestone, and quartzose sandstone (385 m thick). Member 1 contains conodonts and other fossils of Early Pennsylvanian age; member 4 and the lower part of member 5 contain fusulinids of early Permian age. Member 4 also contains early Permian corals. Member 1 overlies Mississippian limestone assigned to the Monte Cristo Limestone, and member 5 is overlain by sandstone questionably assigned to the Lower Triassic Moenkopi Formation. The contact between the bird Spring and Moenkopi Formations is obscured by Quaternary alluvium and a Jurassic dike.