The Lower Cambrian Zabriskie Quartzite in the Death Valley region of California and Nevada records deposition in both nearshore marine and terrestrial environments and represents two genetically distinct depositional units. The lower unit, defined by the Resting Springs Member, is a highstand-systems tract in which sandy braidplain deposits prograded over storm-influenced inner-shelf mudstone and sandstone. The top flooding surface of that systems tract is a sequence boundary (type 2). The upper unit, defined by the Emigrant Pass Member, is the lowermost deposit of a transgressive systems tract in which nearshore marine sediments progressively overstep/onlap the sequence boundary cratonward. It is herein suggested that in the Death Valley area the top of Lower Cambrian Grand Cycle B is coincident with this sequence boundary.
This work shows that nonmarine deposition characterized much of the southwestern margin of cratonic North America during Early Cambrian time (Bonnier-Olenellus zone). The stable tectonic setting and consistently low-latitudinal position of Laurentia during this time preclude tectonism and climactic variation, and associated changes in sediment flux, as principal forcing mechanisms of relative sea-level change. Consequently, eustatic variation was the probable first-order causative mechanism for systems-tract and facies development. The relative sea-level changes indicated in this study can be used to further aid the construction of global sea-level curves.