Sequence Stratigraphy, Third-Order Accommodation Events and Related Diagenetic History of the Middle Cambrian Bonanza King Formation, Southern Great Basin

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The proposed research involves a combined sequence stratigraphic and diagenetic analysis of cyclic passive margin carbonates of the Middle to Late Cambrian Bonanza King Formation of the southern Great Basin (California and Nevada). The formation ranges from 300 to 1350 meters and forms a westward-thickening wedge from craton margin to shelf-edge and base-of-slope facies. The Bonanza King is composed of 200 meter-scale carbonate cycles that provide a remarkable strip record of Middle to Late Cambrian third-order relative sea-level oscillations. Preliminary results suggest that four and a half third-order sequences can be recognized and mapped out across the Bonanza King platform. Intervals of thick subtidal cycles appear to characterize the transgressive systems tracts, intervals of thin peritidal cycles characterize the highstand systems tracts and thin zone of peritidal cycles exhibiting evidence of sporadic exposure probably manifest sequence boundary zones. Intracyclic abundance of early dolomite decreases systematically from craton margin to outer platform. Cycles in sequence boundary zones and upper highstand systems tracts are dominantly dolomite whereas cycles in transgressive systems tracts and lower highstand systems tracts retain abundant limestone. The objectives of the research are fourfold: 1) Dissect the internal anatomy of carbonate stratigraphic sequences using the excellent exposures, broad outcrop area and extraordinary cyclicity of the Bonanza King Formation as the data base. Predictable variations in cycle stacking patterns and cross-platform trends will be used to identify the component systems tracts and bounding unconformities. 2) Develop a reliable Middle to Late Cambrian accommodation curve of comparison to other published curves to determine the degree of eustatic control on sequence development. 3) Document the effects of sea-level fluctuations of all frequencies on early diagenesis of Bonanza King carbonates. 4) Evaluate the textural, petrophysical and geochemical changes that occur in early diagenetic facies during fluid-rock interaction throughout burial. This study integrates the sequence stratigraphy with the sea- level and diagenetic history recorded in the Bonanza King Formation and is the first major attempt to decipher the diagenetic history of early Paleozoic carbonates of the Cordilleran passive margin.