Correlation of the upper part of the Middle Jurassic San Rafael Group in northeast Arizona, northwest New Mexico, and southeast Utah

In east-central Utah, the Middle Jurassic San Rafael Group consists, in ascending order, of the Page Sandstone, Carmel Formation, Entrada Sandstone, Curtis Formation, and Summerville Formation, with a combined thickness of about 365 m. In northwestern New Mexico, the sequence, only about 80 m thick, consists of the Entrada Sandstone overlain by the Wanakah Formation the basal part of which is the distinctive Todilto Limestone Member. The San Rafael Group includes a mixture of terrestrial, marine, and marginal marine deposits. An unconformity, termed “J-3”, underlies the Curtis Formation and can be traced into northwestern New Mexico where it lies near the middle of the Wanakah Formation. Previously, the Curtis Formation had been correlated with the Todilto Limestone Member. However, the Todilto lies beneath the J-3 unconformity and is separated from it by about 20 m of strata. All of the Summerville Formation is truncated by another unconformity, termed “J-5”, in east-central Utah, and the formation does not extend into New Mexico and adjacent areas.