Mesozoic depositional history of southeastern Arizona
— Philip T. Hayes and Harold Drewes

The area considered herein is roughly between Tucson and the southeastern corner of Arizona (fig. 1). It lies between the Mexican Border and latitude 32°15' N., and between New Mexico and longitude 111°15' W.

 

Interpretations of stratigraphic relations and regional cor-relation of Mesozoic rocks in this region are complicated by the lack of datable fossil material in most of the units and by structural complexities; since late Early Permian time, various parts of the region apparently have been subjected to about six episodes of faulting and nearly as many episodes of plutonism. Recently, however, much has been learned about these Mesozoic rocks by professors and students from universities, geologists associated with the minerals industry, and U.S. Geological Survey geologists. This paper is basically an updated version of an earlier paper (Hayes and Drewes, 1968). Although most of the conclusions reached in that paper are unchanged, some of the unnamed units referred to in that paper have been named, units probably correlative to units described in that paper have been found in additional localities, some tentative conclusions of that paper have been made more certain while others have been abandoned, and the worldwide geologic time scale has been revised. The data presented herein are largely presented in much more detail in Cooper (1971), Drewes (1971), Hayes (1970a, 1970b), and Simons (1972). We have also drawn from many older or less detailed recent reports. We obviously are heavily indebted to all of these previous workers, but are ourselves responsible for the interpretations presented here.

 

Our correlations (fig. 2) are based on analysis of local geologic relations, on paleontologic data of variable usefulness, on radiometric age determinations of variable reliability, on some petrologic studies, and on the assumption that major geologic events must have some degree of regional continuity. In our earlier paper we followed Holmes' (1965) time scale for most of the Mesozoic but used the more refined scale of Gill and Cobban (1966) for the Late Cretaceous. That time scale is shown on the left edge of the correlation diagram, and the time scale of Van Eysinga (1975) is shown on the right edge.