STRATIGRAPHY AND STRUCTURE OF THE LATE LARAMIDE CARTHAGE–LA JOYA BASIN, CENTRAL NEW MEXICO

Abstract

The elongate, north-northwest trending Carthage–La Joya basin of central New Mexico developed in the middle Eocene, late in the Laramide orogeny. Sedimentary strata in the basin consist of a fluviatile red-bed succession of sandstone, conglomerate, and minor mudstone as much as ~300 m thick. Sediments were derived mostly from the nearby Sierra uplift to the west, and were deposited on an east-facing, braided-alluvial piedmont system. Local inverted unroofing successions in these deposits show that the structural development and erosional history of the Sierra uplift was complex. In the 5 northern part of the Carthage–La Joya basin, scattered remnants of southwest-facing piedmont deposits are preserved. These deposits may provide a depositional record of the Montosa uplift to the northeast. An axial-river facies stratigraphically intervenes between deposits of the opposing piedmont facies in parts of the northern basin, and is also present on the east flank of the basin where it shows evidence for southeasterly paleoflow. These axial-river deposits are dominated by well-rounded, varicolored quartzite clasts that appear to have been derived from the Mogollon Highland far to the west in central Arizona, and record an extrabasinal river that at times spilled over the Sierra uplift from the Baca basin. The Carthage–La Joya basin region is extraordinarily complex structurally, but relatively few structures can be definitively shown to be Laramide. These include the thrust faults and folds of the Amado–Cañas structural zone in the west-central part of the basin and the Singleton thrust fault in the northern part. Two northeast-striking systems of high-angle Laramide faults in the northern part of the basin (the Parida and Milagro fault zones) may be related to the dextral-oblique Montosa fault system to the east. These northeast-striking zones may have provided a kinematic link between the Laramide Sierra and Montosa uplifts.