LINKING NEOPROTEROZOIC TO CAMBRIAN STRATA FROM SONORA TO UTAH

A substantial portion of Ediacaran to Cambrian strata in southwestern North America are difficult to fit into our understanding of the major biotic, climatic, and tectonic events that characterized this interval. This is because (1) such strata are dominated by coarse fluvial facies that lack abundant chemostratigraphic, geochronologic, and biostratigraphic cues, (2) they are poorly correlated regionally/stratigraphically due to disparate historical naming conventions, and (3) because they are geographically separated by Basin and Range extension or large-scale transform structures. Yet these strata contain erosional remnants of marine influenced fossiliferous facies, young populations of detrital zircons, as well as remnants of volcanic facies.

Scaffolding on our work with many colleagues, we present updated reference sections for several of these stratigraphic packages, with emphasis on the Prospect Mountain Quartzite, Tintic Quartzite, and Browns Hole Formation. We compare these strata to updated regional reference sections for the La Ciénega and Puerto Blanco formations in Mexico and for eastern exposures of the Stirling Quartzite and Wood Canyon Formation of Nevada, which have been augmented with new δ¹³C and ⁸⁷Sr/⁸⁶Sr chemostratigraphy, sequence stratigraphy, and detrital zircon geochronology. This stratigraphic work fosters direct comparison of the latest Ediacaran and Terreneuvian volcanics from each of these five successions, for which we present petrographic and geochemical characteristics. Considered together, these data suggest at least one coeval, genetically related rifting event in the region, which was locally punctuated by basaltic magmatism. Deposition of these volcanics, together with the bulk of these siliciclastic packages, appears to pre-date or in some cases overlap onset of the Sauk transgression.