Sedimentology and sequence stratigraphy of Neoproterozoic and Cambrian units across a craton-margin hinge zone, southeastern California, and implications for the early evolution of the Cordilleran margin

Neoproterozoic-basal Cambrian strata exposed in eastern California represen t the deposits of a craton-margin hinge zone that formed in response to the fragmentation of the Neoproterozoic supercontinent, Rodinia. One unresolve d question regarding the late Neoproterozoic stratigraphy in the southweste rn United States has been the interpretation of paleotectonic affinity for rocks deposited above the glaciogenic Kingston Peak Formation. Of central c oncern has been attempts to identify the position in this stratigraphy, whe re rift-related sediments give way to passive-margin deposits. Subsidence a nalyses suggest that rifting occurred near the start of the Cambrian, perha ps coincident with the feldspathic middle member Wood Canyon Formation. It rests on a disconformity that represents the base of the Sauk Supersequence and would Likely represent the break-up unconformity in subsidence analysi s models. Middle member Wood Canyon and overlying Lower-Middle Cambrian str ata extend far into the craton. Detailed sedimentary facies and sequence stratigraphic analysis of post-Kin gston Peak, pre-middle Wood Canyon rocks indicate that depositional facies in this succession (distal alluvial through shallow subtidal) are similar t o units deposited on the stable craton. Further, these pre-Sauk units, whic h can be divided into multiple, principally eustatically driven depositiona l sequences are correlated across long distances and even lap onto the edge of the stable craton. We suggest the Kingston Peak Formation is the princi pal rift-generated deposit and the overlying thick, predominantly silicicla stic, section represents the basal deposits of the Cordilleran passive marg in. Kingston Peak strata consist of thick, coarse diamictites interbedded w ith turbidites; such facies are unique in the overall stratigraphy but are similar to other known rift deposits. Although the age of the Kingston Peak Formation is not well constrained and may be as young as similar to 590 Ma , it may correlate with the Rapitan-Sturtian glaciation (similar to 720 Ma) , which would place middle Wood Canyon strata some 150 Ma younger than the start of rifting. (C) 2001 Elsevier Science B.V. All rights reserved.