ABSTRACT: Influence of Antler Tectonism on Upper Devonian-Mississippian Stratigraphic Sequences of Western Utah

NICHOLS, K. M., and N. J. SILBERLING,* U.S. Geological Survey, Denver, CO

Upper Devonian to Mississippian (Famennian through Meramecian) strata in western Utah can be interpreted as four stratigraphic sequences representing depositional cycles of third-order scale. Traced westward, to westernmost Utah and eastern Nevada, all four of these sequences have been affected by uplift related to episodic tectonism along the continental margin. Either their sedimentation was influenced by such tectonism, or they were eroded toward the west beneath the consequent disconformities. Sequences 1 and 2, generally of Famennian age, include the lower and upper Pilot Shale and their continentward carbonate facies. Fine-grained siliciclastics of these sequences were deposited inboard of the foreland bulge resulting from initial flexural loading of the margin by the Antler all chthon. Craton-derived terrigenous clastics of the Pilot were retained on the shelf by back-bulge subsidence. Sequence 3 in Utah consists of carbonate rocks of Kinderhookian age preserved as a highstand tract that prograded toward the northwest. Sequence 4 has at its base an aggradational systems tract recording prolonged, widespread intertidal to shallow-subtidal carbonate deposition, giving way upward to agitated, open-shelf deposition. The subsidence that accommodated accumulation of these strata in Utah was linked with uplift of more outboard parts of the shelf. The sea level maximum in Utah during deposition of sequence 4 coincided with initiation of the Delle phosphatic event. The transgressive systems tract of sequence 4 in Utah was formed mainly of craton-derived, fine-grained, d trital sediment whose retention on the shelf was controlled again by forebulge development farther toward the margin. Maximum progradation at the top of the ensuing highstand tract of sequence 4 is recorded within the Humbug Formation in strata of Late Mississippian age.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)