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Abstract: Stratigraphic Analysis of Neoproterozoic-Cambrian Boundary Interval, Eastern California: Which Stratigraphy Works Best?



The Neoproterozoic-Cambrian boundary in the Providence and Kelso Mountains of the craton margin, eastern Mojave Desert, California, is a subtle disconformity between the middle member Stirling Quartzite and a locally unique facies succession below "classic" middle member Wood Canyon Formation. This unique interval contains facies that previously were correlated lithostratigraphically with upper middle and upper members Stirling Quartzite and lower member Wood Canyon Formation in miogeoclinal sections of the Death Valley region. These correlations are understandable, but they are indefensible from a genetic facies perspective where natural linkages are considered. Facies replications above the disconformity produce the illusion of laterally continuous sheets across the disconformity.

A sequence stratigraphic approach, unclouded by formal stratigraphic terminology, reveals the real stratigraphic relationships and on a regional scale. The disconformity correlates to the base middle member Wood Canyon disconformity in miogeoclinal sections of the Death Valley region where it clearly lies above the biostratigraphically defined Neoproterozoic-Cambrian boundary. What was interpreted previously as cratonward thinning of stratigraphic units by onlap, now can be demonstrated as significant thinning by erosional truncation beneath this disconformity. Shingled facies on both sides of this sequence boundary produce a facies architecture that has important implications for stratigraphic unit recognition and relative sea-level change. Hence sequence stratigraphy is critical for understanding early continental margin evolution, especially as it relates to cratonal-miogeoclinal hinge location and development, and rift-to-drift transition.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California