Spencer G. Lucas, Orin J. Anderson
One of the most distinctive Jurassic lithostratigraphic units in the American Southwest is the Todilto Formation of northern New Mexico and southwestern Colorado (Figure 1). This relatively thin (>75 m) unit is mostly carbonates and evaporates in a thick section otherwise dominated by siliciclastic eolianites (Figures 2, 3). The To dilto Formation is extremely significant economically as a source rock for petroleum (Vincelette and Chittum, 1981)and uranium (Chenoweth, 1985); it also provides all the gypsum mined in New Mexico (Weber and Kottlowski,1959).Some earlier workers regarded the Todilto as having been deposited in a marine embayment of the Middle Jurassic Curtis seaway (e.g., Harshbarger etal., 1957; Ridgley and Goldhaber, 1983), but morerecent studies of stratigraphy, paleontology, and geochemistry indicate that any marine connection tothe Todilto Basin was short-lived or intermittent(Lucas et al., 1985; Kirkland et al., 1995). Todilto deposition took place in a paralic salina culminated by a gypsiferous evaporitic lake.
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