Abstract

Regional, eastward trending piercing lines defined by stratigraphic truncations and depositional pinchouts in Jurassic and Cretaceous strata in north-central New Mexico allow 5 to 20 km of right slip between the eastern margin of the Colorado Plateau and the craton to the east in Laramide (Late Cretaceous–Paleogene) and younger time. Estimates of 60–170 km of Laramide right slip by previous workers were based largely on (1) the amount of presumed crustal shortening across thrust and reverse faults in the Wyoming province north of the plateau or (2) offset of piercing lines defined by a Proterozoic, regionally subhorizontal, isobaric metamorphic surface that intersects preexisting structures and steep stratigraphic contacts. Major right slip inferred on the basis of these metamorphically defined piercing lines in Proterozoic rocks must therefore predate the Laramide orogeny and cannot be used to support a model postulating large-scale Laramide right slip. Restoration of 60–170 km of right slip creates lateral offset of the north-south extent of the Jurassic Todilto Formation, producing an untenable paleodepositional basin geometry.

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