Devonian stratigraphy and correlations in southeastern Arizona
Devonian strata in southeastern Arizona comprise a complex mosaic of interbedded dolomite, limestone, sandstone and shale which is widely exposed in the many mountain ranges of the area. Over the years, numerous names have been proposed for the Devonian rocks in central and southeastern Arizona based on lithologic and paleontologic characteristics and geographic distribution. Most of these names seem to apply to local faunal or facies zones and have not been recognized by subsequent workers, but five formation names have been widely adopted and remain in current usage. These are the Martin, Swisshelm, Portal, Morenci and Percha formations. The nomenclatural history of these formations has been reviewed by Pye (1959), Wright (1964), Teichert (1965) and Pine (1968). All these formations are of Late Devonian age, but their exact placement within the Upper Devonian has been uncertain because diagnostic macrofossils frequently are rare or absent. The age and correlation of the Martin and Percha formations in southern Arizona was discussed by Schumacher and others (1976); however the most complete regional synthesis is that of Poole and others (1967). The most current and comprehensive stratigraphic synthesis of Upper Devonian depositional complexes in the western United States by Sand-berg and Poole (1977) unfortunately does not include central and southern Arizona within its study area; however, their detailed maps and discussions are critical for anyone interested in the Devonian or Mississippian of Arizona.
The purpose of this paper is to summarize the nomenclature, dating and correlation of the Devonian formations of southern Arizona. Most of the data and new interpretations presented here are based on the results of recent stratigraphic and biostratigraphic investigations of the Devonian System in southern Arizona by Witter (1976), S. Meader (1976), Schumacher and others (1976), N. Meader (1977), Boyd (1978) and Schumacher and Witter (in preparation). The data summarized here are based on 54 principal stratigraphic sections (fig. 1 and Table 1) distributed across an area of more than 82,000 km2 (36,000 mil) that extends from the Mexican border north to the Salt River, and from the New Mexico border west to the Vekol Mountains.
Conodonts have played a vital role in interpreting Devonian stratigraphy. This has been made possible by significant advances in refining the Upper Devonian conodont zonation pro-posed and emended by Zeigler (1962, 1971) (see Sandberg and Poole, 1977, p. 148) and recent developments concerning our understanding of conodant biofacies and paleoecology (Seddon and Sweet, 1971; Sandberg, 1976; Schumacher, 1976; Klapper and Barrick, 1978). The standard Upper Devonian conodant zonation now consists of 28 zones, some of which can be subdivided laterally into 3-5 biofacies. The application of this highly refined zonation in southern Arizona has greatly clarified age relations and correlations within the Upper Devonian.
- Schumacher, Dietmar, 1978, Devonian stratigraphy and correlations in 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. 175-181.