New Mexico Geological Society Annual Spring Meeting — Abstracts

The Summerville Formation, San Rafael SWell, Utah is unfossiliferous, but intertongues with and grades down into the Curtis Fonnation, which contains lithologies and fossils identical to those in the Pine Butte Member of the Sundance Formation of late Middle Jurassic age(callovian). The Pine Butte is unconfonnably overlain by the Redwater Shale of Late Jurassic age (Oxfordian) , which in turn is unconfonnably overlain by the Windy Hill Sandstone of Late Jurassic age(Kimmeridgian). The Summerville and the Redwater Shale are unconfonnably overlain by the Tidwell Member of the Morrison. The Tidwell is the southwestern extension of the Windy Hill Sandstone. These correlations are constrained by the presence of the J-2, J-3 and J-5 unconformities in the San Rafael Swell and by presence of the J-2, J-4 and J-5 unconformities in southeastern Wyoming and in the Black Hills. Some or all of these unconformities have long been overlooked, looked for but not found, not looked for at all, misunderstood, misplaced, or misidentified, rrost recently by Anderson and Lucas (1992, NM Geol., v.14 no.4,p. 79-92) in the San Rafael Swell and vicinity. The resulting disagreements with prior work are due to the lack of effective means of cormrunicating stratigraphic field data. Some caveats and suggestions are offered to alleviate some of the differences of opinion.