Inversion of Late Jurassic-Early Cretaceous extensional faults of the Bisbee Basin, southeastern Arizona and southwestern New Mexico
Timothy F. Lawton
Laramide shortening in the southwestern United States inverted Late Jurassic-Early Cretaceous extensional faults. Evidence for inversion includes: (1) up-dip and along-strike changes from normal to reverse stratigraphic offset on individual faults; (2) abrupt changes in thickness of Lower Cretaceous strata at Laramide reverse and oblique-slip faults; (3) abrupt changes in the Mesozoic subcrop across reverse faults, with Paleozoic strata more deeply eroded on hanging walls than footwalls; (4) fault-zone horses of basement or strata older than adjacent rocks in either hanging wall or footwall; (5) intermontane Laramide basins positioned at abrupt transitions in thickness of the Jurassic-Cretaceous section, usually flanking thick uplifted successions and overlying thin footwall successions. Pre-Laramide extensional faulting formed the Late Jurassic Early Cretaceous Bisbee basin, part of a rift-basin assemblage extending from southern California to the Gulf of Mexico. Jurassic-Lower Cretaceous sections are as much as 4700 m thick in the proposed axis of the Bisbee basin, but thin away from the axis in a stepwise fashion across northwest-trending, basement-involved faults. In the Late Jurassic and Early Cretaceous, these structures were steep normal faults that bounded half-graben basins. In the latest Cretaceous, the same structures were reverse and oblique-slip faults that accommodated shortening oblique to the structural trend established during the Jurassic. Documented examples of inversion structures are restricted to faults within the former Bisbee rift basin; Laramide structures north of the Burro uplift, although basement-involved, do not demonstrably reactivate older faults.
- Lawton, Timothy F., 2000, Inversion of Late Jurassic-Early Cretaceous extensional faults of the Bisbee Basin, southeastern Arizona and southwestern New Mexico, in: Southwest passage. A trip through the Phanerozoic, Lawton, Timothy F.; McMillan, Nancy J.; McLemore, Virginia T., New Mexico Geological Society, Guidebook, 51st Field Conference, pp. 95-102.