Stratigraphy and sedimentology of the Middle Cretaceous (Albian-Cenomanian) Dakota Formation, southwestern Utah

The Middle Cretaceous (Albian-Cenomanian) Dakota Formation in southwestern Utah records a complex interplay among foredeep basin subsidence, eustatic sea-level rise, and small-scale fluctuations in sedimentation rates. From east to west across southern Utah the Dakota rests unconformably upon progressively older Jurassic strata and is disconformably overlain by and interfingers with progressively younger offshore marine deposits of the lower Tropic Shale. The Dakota ranges in thickness from less than 10 m in the east to greater than 350 m in the west. The Dakota is divided into three informal members: (1) a lower member that consists of gravelly braided stream deposit; (2) a middle member that consists of mudstone-dominated, alluvial-plain deposits; and (3) an upper member that consists of seven landward-stepping/progradational, storm-dominated, mixed energy, strand-plain deposits.;The lower member is present only within southeast-trending paleovalleys scoured into underlying eastward-dipping Jurassic strata. ate that streams flowed to the southeast from the Sevier Orogenic Belt. The lower member is unconformably overlain by the middle member, separated by a widespread pebble lag and pedogenically altered zone that is interpreted as a pediment surface.;The middle member consists of a lower coal zone, a middle alluvial zone, and an upper coal zone that record episodic fluctuating rates of foredeep basin subsidence and consequent fluctuating episodes of fluvial and lacustrine/swamp deposition. The middle member ranges in thickness from less than 10 m in the east to greater than 300 m in the west, recording syndepositional foredeep basin subsidence. The middle alluvial zone is characterized by upward-fining, alluvial-plain cyclothems.;The middle member is disconformably overlain by the upper member, which consists of seven, upward-coarsening, landward-stepping/progradational, storm-dominated, mixed-energy (mesotidal), strand-plain cyclothems. Both alluvial-plain cyclothems of the middle member and strand-plain cyclothems of the upper member record episodic fluctuations in sedimentation rates caused by either Milankovitch-style climate cycles or smaller-scale fluctuation in the rate of foredeep basin subsidence. The upper member increases in thickness from a feather edge in the east to greater than 200 m in the west, recording continued syndepositional foredeep basin subsidence.;Utilizing High-resolution Event Stratigraphy (HIRES), transgressive-regressive, strand-plain cyclothems of the Dakota Formation can be precisely correlated more than 1300 km eastward to limestone/shale couplets of the upper Hartland Shale and lower Bridge Creek Limestone in central Colorado. This base margin to basin center correlation indicates that allocyclic fluctuations in sedimentation rates was the forcing mechanism for cyclicity in the middle Cretaceous Western Interior Basin.