The Cretaceous foreland basin in southwestern New Mexico
— Greg H. Mack, Joe A. Galemore, and Edward L. Kaczmarek

Early Cretaceous sedimentation in southwestern New Mexico began in a west–northwest-trending rift basin that was bordered on the north by a basement-cored rift shoulder. By late Albian and early Cenomanian time, the crest of the rift shoulder was substantially reduced in relief and was onlapped by the Sarten and Beartooth Formations, which consist of about 120 m of sandstone and shale derived from sedimentary source rocks located north of the basin. The Sarten Formation consists of two regressive cycles, the upper of which displays a change from offshore to fluvial facies. As the rift shoulder was onlapped, up to 1500 m of sandstone and shale of the Mojado Formation was deposited along the former axis of the rift basin. The Mojado Formation consists of lower and upper shallow-marine and shoreline members and a middle member composed of fluvial sediment. The Mojado Formation contains primarily monocrystalline quartz, but some sandstones also contain volcanic rock fragments and plagioclase, indicating a mixed sedimentary and volcanic source terrane. Eastward-directed fluvial paleocurrents suggest that the source terrane was located west of the basin.

 

By middle to late Cenomanian time, the rift shoulder was no longer a barrier to sedimentation, and foreland basin deposition was continuous across New Mexico. From middle Cenomanian to Campanian time up to 1000 m of marine and nonmarine sandstone and shale were deposited in at least two major transgressive and regressive cycles. Fluvial paleocurrent data suggest a northeastward paleoslope, and the presence of volcanic rock fragments, plagioclase, chert, pelitic rock fragments, and a high percentage of monocrystalline quartz indicate a mixed sedimentary and volcanic source terrane. The foreland basin was disrupted by Laramide deformation in latest Cretaceous and early Tertiary time.