PESSAGNO, EMILE A., JR., DONNA MEYERHOFF HULL, MICHAEL KELLDORF, Programs in Geosciences, University of Texas at Dallas, Richardson, TX and JOSE F. LONGORLA, Department of Geology, Florida International University, Miami, FL

ABSTRACT: Tectonostratigraphic Significance of the San Pedro del Gallo Area, Durango, Western Mexico

The San Pedro del Gallo area, Durango (western Mexico), lies astride the boundaries between the "Parral" terrane and the "Sierra Madre Oriental" terrane, but bears little resemblance to either terrane. Our preliminary data indicate that the San Pedro del Gallo area includes eugeoclinal, Boreal, bathyal to upper abyssal Jurassic and Cretaceous strata which are juxtaposed against strata to the east (Sierra Madre Oriental terrane), which are miogeoclinal and Tethyan in character. The San Pedro del Gallo succession is clearly part of a new terrane, which we refer to herein as the "San Pedro del Gallo" terrane The proximity of the San Pedro del Gallo terrane to the boundaries of the Parral terrane and the Sierra Madre Oriental terrane as well as the Walper megashear make it a cornerstone i deciphering the mosaic of suspect terranes which form western Mexico. It is probable that the Mazapil area (Zacatecas) to the south is also part of the San Pedro del Gallo terrane. Burckhardt also recorded Boreal megafossils (Buchia) in Upper Jurassic strata near Mazapil. Moreover, the lithostratigraphic successions of the Mazapil area and the San Pedro del Gallo area, though not identical, appear to be closely related.

The paleolatitudinal signature of the San Pedro del Gallo terrane supplied by faunal analysis indicates that this terrane was transported tectonically from higher paleolatitudes (Southern Boreal province) during the Late Jurassic to lower paleolatitudes (Tethyan realm) by the Early Cretaceous. We suggest that this movement was from northwest to southeast along the Walper megashear. Our previous studies indicate that this same sense of movement along the Walper megashear can be detected in the Huayacocotla segment of the Sierra Madre Oriental in the states of Veracruz, Puebla, Hidalgo, and San Luis Potosi.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.