ABSTRACT
The upper Jurassic Todilto formation is a laminated sequence of limestone and gypsum of nonmarine or saline-paralic origin in northwestern New Mexico. The 10–13-year sunspot cycle and 60-, 85-, 170-, and 180-year cycles were recorded in the varved sequence. The presence of the sunspot cycle indicates that the laminations were deposited annually. The limestone member was deposited in about 14,000 years and the gypsum member in about 6,000 years.
Deposition began with a two-fold clastic-organic varve and progressed through a sequence of increasing and decreasing varve complexity accompanied by a decrease and increase in clastic content. The end result is a transitional lithologic change from sandstone to limestone to gypsum to shale brought about by changes in individual varve laminae. The progression of changes is related to a cyclic change from clastic to evaporite and back to clastic deposition described here as the varved clastic-organic-evaporite (c-o-e) cycle.
The varved cycle is nearly complete in the Todilto sequence and is present in the Green River basin of Colorado and Wyoming, the Delaware basin of Texas and New Mexico, the Paradox basin of Utah and the Four Corners region, and in most other evaporite deposits.
