Cambrian Paleogeography of the Great Basin

Abstract

The Cambrian Period encompasses an interval from about 570 Ma to about 505 Ma. Rock sequences, aggregating more than 4 km thick, were originally deposited as clastic and carbonate sediments in fluvial, nearshore, and marine settings along the western Cordilleran passive margin, which was located 10-15{degree} north of the equator. One of the more easily studies areas within the Cordillera is the Great Basin province in the western United States, where Cambrian strata are well exposed within at least 75 block faulted mountain ranges. The Lower Cambrian of the Great Basin was dominated by fluvial and nearshore marine siliciclastics deposited across a broad passive margin. Although shallow marine carbonates were generally restricted to the southeastern Great Basin, a regionally extensive carbonate platform development near the end of the Early Cambrian. The last major influx of cratonally derived clastics completely covered the carbonate platform at the onset of the Middle Cambrian. The carbonate platform reestablished itself in a more cratonward position throughout the rest of the Cambrian, although complex facies patterns resulted from environmental shifts, periodic siliciclastic input, and several drowning events. This resulted in highly variable lithologic mosaics, which may partially account for the over one hundred formational designations currentlymore » in use for the Cambrian of the Great Basin.« less