Pennsylvanian and Early Permian depositional framework, southeastern Arizona
Charles A. Ross
This summary of the Pennsylvanian and Early Permian depositional framework in southeastern Arizona and adjacent regions is based in large part on the data and conclusions presented earlier in more detail by Ross (1973, 1978). The general stratigraphy of the Pedregosa, Orogrande and Permian basins and much of the literature has recently been summarized by Greenwood and others (1977).
In southeastern Arizona, Pennsylvanian and Permian strata are well exposed in many of the Basin and Range uplifts, where they may be studied in considerable detail. Mesozoic and Cenozoic structures, including local thrust faulting, and the attendant possibility of considerable lateral displacement of some Paleozoic stratigraphic sections, tend to obscure the late Paleozoic tectonic and depositional framework in part of this region. Also much of the Pennsylvanian and Early Permian (Wolfcampian) strata are lithologically similar, being generally well-bedded, medium to light gray limestone and shale with minor amounts of sandstone and conglomerate that locally may reach a combined thickness of 1200 m (4000 ft). This combination of similar lithologic units that extend through considerable thickness of section and the overprint of major Mesozoic and Cenozoic structural disturbances have caused difficulty in recognizing stratigraphic position within this part of the section.
Studies of the biostratigraphy of this succession started with aid and encouragement from Floyd F. Sabins, Willis W. Tyrrell and others because of the abundance of fusulinaceans in several sections in the area (Sabins and Ross, 1963, 1965; Ross and Sabins, 1965; Ross and Tyrrell, 1965; Ross, 1969a). The results of these studies indicated that the different series and stages of the Pennsylvanian and Early Permian, as identified by fusulinacean zones, were represented by markedly different thicknesses in relatively nearby sections. Clearly additional field work and data was needed. In the succeeding three years the author measured and collected from many stratigraphic sections in southeastern Arizona (fig. 1) to form as complete a coverage as seemed possible. Many sections were restudied several times. A total of more than 800 fusulinacean-bearing rocks were collected and assigned ages in these stratigraphic sections.
- Ross, Charles A., 1978, Pennsylvanian and Early Permian depositional framework, southeastern Arizona, in: Land of Cochise, Callender, J. F.; Wilt, Jan C.; Clemons, R. E.; James, H. L., New Mexico Geological Society, Guidebook, 29th Field Conference, pp. 193-200.