ABSTRACT

Exposures of the Cool Creek Formation (Canadian, Arbuckle Group) in Southern Oklahoma reveal that these sediments were deposited in a hypersaline peritidal setting. The major rock types in this 400 m unit are: (1) flat-pebble conglomerates; (2) peloidal wackestones, packstones, and grainstones; (3) oolitic packstones and grainstones; (4) thin, small-scale trough stratified quartz sands; and, (5) stromatolitic boundstone. Digitate stromatolites predominate in the boundstone lithologies and are generally found as small, circular to elongate heads, large mounds up to 2.5 m in thickness, and tabular beds. Thrombolites, cryptalgalaminites, LLH, SH, and oncolites are also present but in smaller quantities. Most stromatolitic material contains abundant spar-filled tubules or borings which range in size from 40-200 microns and impart a spongy appearance which is visible with a hand lens.

Bedded and nodular evaporites are not present in outcrops but are known from the subsurface. However, evidence for their former presence is extensive. Chert nodules containing abundant molds and pseudomorphs after gypsum, anhydrite and possibly halite are present. Distortion of the bedding surrounding these nodules, as well as disruption of interior textures, suggests that the evaporites grew displacively within the lime mud. All former evaporite nodules are partially to completely silicified as are most isolated evaporite pseudomorphs. This implies a remarkable selectivity of the chert for evaporites. Many detrital quartz grains in the evaporitic zones also have syntaxial euhedral quartz overgrowths. At least three 1-2 m thick breccias, interpreted to be of solution collapse origin, are present in the Cool Creek. They consist of thin, broken beds of quartz-rich, reddish lime mud with abundant, thin micro-faulted chert beds containing gypsum pseudomorphs and molds. Individual blocks range in size from a cm to .5 m in length. Other evidence of hypersaline conditions such as restricted faunas, high-relief stromatolites, syndepositionally broken ooids, and lengthslow chalcedony is less conclusive, but when combined with the breccias and chertified nodules, provides additional confirmation. Since the Cool Creek is known to contain evaporites in subsurface, it provides an excellent opportunity for the study of many of the various criteria which signal the former presence of now vanished evaporites.