Sediments, Geomorphology, Magnetostratigraphy, and Vertebrate Paleontology in the San Pedro Valley, Arizona

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Abstract
The San Pedro Valley in southern Arizona was probably formed by block faulting during the Miocene. Sediments that filled the valley, primarily the St David Formation, have yielded a robust vertebrate fossil record, calibrated during the last 25 years by magnetostratigraphy and isotopic dating of volcanic eject. This chronologic framework is combined with new sedimentologic, paleomagnetic, and geomorphic data to evaluate the influence of subsequent tectonism within the basin. We conclude that tectonism in the San Pedro Vally has been relatively quiescent following the initial block faulting and suggest that ensuing rates of sedimentation and incision were most likely controlled by climatic factors rather than tectonic-geologic ones. Vertebrate datum planes established in 1975 are revised on the basis of new paleontologic and geologic-isotopic data. We now recogonized only three faunal datum planes in the St. David Formation, and have abandoned the youngest (Lepus) datum plane.