Cretaceous (Aptian-Turonian) sedimentary rocks in southwestern New Mexico were deposited in two stages that were controlled primarily by tectonism. During the first stage, from Aptian through middle Albian time, a maximum of 1,900 m of siliciclastic and carbonate sediment accumulated in a west-northwest-trending rift basin. Lithic and arkosic sediment was derived initially from intrabasin uplifts and subsequently from a west-northwest-trending, basement-cored rift shoulder that marked the northern boundary of the basin. Decreases in subsidence and siliciclastic sedimentation rate in mid-Albian time were a response to wearing down of the rift shoulder and marked the end of the first stage of sedimentation.

Beginning in late Albian time, what is now southwestern New Mexico experienced increases in tectonic subsidence and siliciclastic sedimentation rate. As much as 1,500 m of quartzarenite and shale was deposited in the southwestern part of the study area, and ∼300 m of upper Albian, Cenomanian, and Turanian sediment onlapped the former rift shoulder. Paleocurrent and facies data indicate that sediment dispersal was eastward, southeastward, and northeastward. The second stage of sedimentation took place in a retroarc foreland basin that was complementary to a compressional orogenic belt in what is now southeastern Nevada, southeastern California, western Arizona, and/or Sonora, Mexico.

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