Stromatolites in the Todilto Formation?
— Dana S. Ulmer-Scholle

The Middle Jurassic Todilto Formation is found in northern New Mexico and southwestern Colorado. In the Ambrosia Lake uranium district, previous workers have identified the large fold-like features in the Todilto Formation as intraformational folds that were produced by loading of the overlying Middle-Upper Jurassic eolian Summerville Formation on the water-saturated sediments of the Todilto Formation or by later structural deformation. A re-interpretation of the outcrops of Green (1982) near Mesa Montañosa, based on preliminary field data, suggests that these features are large, domal stromatolites or bioherms. The composition and morphology of these structures indicate microbial growth rather than loading as the source of the mounds. While similar structures elsewhere in the Todilto Formation have been attributed to intraformational or tectonic deformation, this study suggests that there may be more than one mechanism capable of producing fold-like structures in the Todilto Formation, and a reassessment of previously identified structures may be needed.