Mesozoic basin formation, mass-gravity sedimentation, and inversion in northeastern Sonora and southeastern Arizona
James W. McKee, Mary Beth McKee, Thomas H. Anderson, 2005. "Mesozoic basin formation, mass-gravity sedimentation, and inversion in northeastern Sonora and southeastern Arizona", The Mojave-Sonora Megashear Hypothesis: Development, Assessment, and Alternatives, Thomas H. Anderson, Jonathan A. Nourse, James W. McKee, Maureen B. Steiner
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The El Tule fault extends southeastward from the Huachuca Mountains area of Arizona to run along the base of the Sierra San José in northern Sonora. This fault, with the Jurassic and Cretaceous strata that lie on either side of it, helps to link the geologic histories of the Sierra San José, the Huachuca Mountains, and the Mule Mountains. This fault was active during the Jurassic and formed part of the southern and southwestern limit of a small Jurassic basin that accumulated Glance Conglomerate and contains the type locality of that unit; it was also active during the time of deposition of the upper part of the Bisbee Group, i.e., the Morita, Mural, and Cintura formations. This fault is an important marker for the northern margin of the Cananea high.
Three evidences suggest that a genetic distinction should be made between the basin that collected the Glance Conglomerate and the younger, wider, superposing basin that collected upper Bisbee rocks: (1) There was a depositional pause after active deposition of the Glance (and therefore after active opening of the Glance basin). (2) The subsequent, finer-grained upper Bisbee deposits do not extend entirely over the Cananea high, but are otherwise regional in extent, forming a thick blanket over the inactive fault basin and other similar basins elsewhere in the region. (3) The axial trends of the Jurassic fault basin(s) and the upper Bisbee basin do not coincide.
We offer the hypothesis that the Jurassic fault basins were caused by the same crustal stresses that caused the Mojave-Sonora megashear (their ages of activity and orientations are similar), and that the upper Bisbee basin was the probable result of crustal thinning associated with formation of the extensional Jurassic basins, and of eustasy. We offer this in contrast to the current hypothesis that the Bisbee basin is a rift basin, that is, the product of a single, ongoing Mesozoic process.
Large-scale mass-gravity deposits are signal features both of the Jurassic fault basin (a result of crustal extension) and of the overlying local Laramide basin (which followed crustal contraction). Historically, these deposits have been confusing. A mountainous mass of megaclasts (La Negrita Hills) within the Glance Conglomerate has been mistaken for the hanging wall of a Laramide thrust (a contractional feature) instead of the product of Jurassic crustal extension that it is. The 91 Hills have been considered an in situ array of mid-Cretaceous patch reefs instead of the Late Cretaceous convulsive mass-gravity deposits (a product of Laramide contraction and inversion) that they are.