Folding in the Middle Jurassic Todilto Formation, New Mexico-Colorado, USA

Spencer G. LUCAS, Karl KRAINER, William R. BERGLOF

Abstract


The Middle Jurassic (Callovian) Todilto Formation of northwestern New Mexico–southwestern Colorado, USA, is a carbonate/evaporite lithostratigraphic unit that was deposited in a large paralic salina culminated by a gypsiferous evaporitic lake. Intraformational folds of the limestone-dominated lower part of the Todilto Formation (Luciano Mesa Member) range in scale from millimeters to meters, and many of the large folds are the loci of uranium mineralization. A diverse literature has attributed the formation of intraformational folds of the Todilto Formation to several causes, including syndepositional or postdepositional tectonics, soft-sediment deformation due to sediment loading or gravity sliding, diagenetic alteration (primarily the hydration/crystallization of gypsum/anhydrite), the growth of stromatolitic bioherms or the formation of tepee-like structures. We examine in detail two characteristic outcrops of intraformational folds in the Todilto Formation, in west-central New Mexico, to conclude that folds and domal structures present in the Todilto limestone facies at different stratigraphic levels and at different scales have resulted from varied processes that produced dome-like stromatolitic mounds, tepee-like structures, small-scale enterolithic folds and large-scale folds of likely diagenetic origin.

Keywords


Jurassic; Todilto Formation; salina; microfolding; stromatolites; tepee-structures

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