| The Ediacaran-Cambrian transition was an important time span from both geologic and biologic perspectives. It was a time of dramatic evolutionary changes such as the diversification of early metazoans, the development of resistant skeletons in many taxa, and the escalation of prey-predator systems. In North America, the transition is well recorded in terminal Neoproterozoic to Cambrian strata of Esmeralda County, Nevada, and adjacent Inyo County, California. Strata recording this transition are the Deep Spring Formation (Ediacaran-Cambrian), and the Campito, Poleta, and Harkless formations (Cambrian).;For many years the Deep Spring, Poleta, and Harkless formations were informally divided into mappable members. New, formal names are proposed for the members of these formations. In ascending order the new members are the Dunfee, Montezuma, and Gold Point members of the Deep Spring Formation; the Lida, Indian Springs, and Clayton members of the Poleta Formation; and the Weepah and Alkali members of the Harkless Formation. Two formal members of the Campito Formation, the Andrews Mountain Quartzite and the Montenegro Member, have long been recognized.;The Deep Spring Formation and succeeding formations have the transition from a microorganism-dominated record to the more diverse and complex record of the Phanerozoic. Stromatolites are common in the Dunfee Member of the Deep Spring Formation, and fossilized microbial mats ("wrinkle structures") are present in siltstone layers of the Montezuma Member. Microbial mats or microbially stabilized substrates are inferred to be responsible for the fine preservation of Ediacaran trace fossils as well as sedimentary structures. In Cambrian strata, microbial related structures are mostly wrinkle structures and gas escape structures.;Trace fossils have a trend toward increasing diversity, complexity, and abundance across the Ediacaran-Cambrian transition, although behavioral patterns are conserved. These changes parallel faunal changes across the same interval of strata. Trace fossils in the Ediacaran part of the Deep Spring Formation include Bergaueria, Palaeophycus, Planolites, and other simple resting, dwelling, and perhaps foraging traces. A new genus and species of trace fossil, Nevadichnos planum, is described from the Montezuma Member of the Deep Spring Formation. Cambrian trace fossils of the Nevada-California succession include Bergaueria, Monomorphichnus, Palaeophycus, Planolites, Rusophycus, and Treptichnus pedum. Although the morphologies of Cambrian tracemakers may have been different in the Cambrian than in the Ediacaran, the basic behavioral patterns of feeding and dwelling were already developed in the Ediacaran.;Chalcopyrite and limonite commonly occur within burrows, especially in Planolites. Precipitation of these minerals is probably related to decay processes associated with biofilm development in burrows. |
