ABSTRACT

A pronounced lithic change coincides with the contact between the "Antelope" Shale (Cenomanian) and the Venado Formation (Turonian). Most previous investigators have either interpreted an unconformity at this position or have implied that this contact is the lateral manifestation of an unconformity. At this contact occur two excellent examples of pebbly to bouldery mudstone deposits of the type generally attributed to submarine mass movements. One has been previously described by Brown and Rich (1960); the other is described herein. Both deposits consist, in large part, of debris derived from the "Antelope" and lower stratal units, thus tending to corroborate earlier investigators' interpretation of an unconformity at this position in the section, regardless of the manner in which the debris was transported and deposited. It is suggested that, if these deposits are directly associated with an unconformity, their stratigraphic and historical importance is far greater than has been previously indicated. Similar deposits elsewhere, particularly those which contain debris reworked from lower stratigraphic levels, should be evaluated for their stratigraphic significance as well as for mechanics of deposition.