Introductory Perspectives

A basic premise implicit on this field trip is that the better we understand the origin of rocks and the processes under which they formed the better able we will be to make well founded stratigraphic predictions.

The Great Basin (see Figure 1) provides an excellent opportunity to study facies, facies transitions and depositional sequences in one of the world?s most stratigraphically complete and best exposed examples of a Paleozoic passive carbonate platform (Cook, 1988). The purpose of this field trip is to recognize and gain an understanding of both shallow water and deep-water carbonate settings and their facies. To this end emphasis is placed on understanding depositional environments, facies, diagenetic patterns, and the stratigraphic analysis of vertical facies successions as embodied in sequence stratigraphic principles. Better geologic interpretations of these elements in carbonate sedimentology and facies analysis are usually critical in both petroleum and mineral exploration for sediment-hosted minerals. Facies analyses are receiving wider importance in mineral exploration as world-class mineral deposits in Nevada and elsewhere are probably controlled by primary depositional facies patterns (for example, Raines and others, 1991; Cook, 1993; Lydon, 1996; Armstrong and others, 1998; Emsbo, 1999, 2000; Hofstra and others, 1999; Hofstra and Cline, 2000). Based on these and other papers, many of the sediment-hosted gold deposits of Nevada appear to have developed at or near platform margin/basin margin sites (see Figures 2 and 3).

One of the steps in petroleum or mineral exploration lies in predicting the location of porous and permeable zones likely to be commercial host facies. Depositional facies and facies patterns often control depositional porosity trends and strongly influence post-depositional diagenetic porosity patterns in carbonates. Thus, it follows that the correct recognition of environments and knowledge of carbonate depositional sequences in these environments can provide important advantages in designing exploration and production strategies.