Architecture and formation of transgressive-regressive cycles in marginal marine strata of the John Henry Member, Straight Cliffs Formation, Upper Cretaceous of Southern Utah, USA

Marginal marine deposits of the John Henry Member, Upper Cretaceous Straight Cliffs Formation, were deposited within a moderately high accommodation and high sediment supply setting that facilitated preservation of both transgressive and regressive marginal marine deposits. Complete transgressive-regressive cycles, comprising barrier island lagoonal transgressive deposits interfingered with regressive shoreface facies, are distinguished based on their internal facies architecture and bounding surfaces. Two main types of boundaries occur between the transgressive and regressive portions of each cycle: (i) surfaces that record the maximum regression and onset of transgression (bounding surface A); and (ii) surfaces that place deeper facies on top of shallower facies (bounding surface B). The base of a transgressive facies (bounding surface A) is defined by a process change from wave-dominated to tide-dominated facies, or a coaly/shelly interval indicating a shift from a regressive to a transgressive regime. The surface recording such a process change can be erosional or non-erosive and conformable. A shift to deeper facies occurs at the base of regressive shoreface deposits along both flooding surfaces and wave ravinement surfaces (bounding surface B). These two main bounding surfaces and their subtypes generate three distinct transgressive-regressive cycle architectures: (i) tabular, shoaling-upward marine parasequences that are bounded by flooding surfaces; (ii) transgressive and regressive unit wedges that thin basinward and landward, respectively; and (iii) tabular, transgressive lagoonal shales with intervening regressive coaly intervals. The preservation of transgressive facies under moderately high accommodation and sediment supply conditions greatly affects stratigraphic architecture of transgressive-regressive cycles. Acknowledging variation in transgressive-regressive cycles, and recognizing transgressive successions that correlate to flooding surfaces basinward, are both critical to achieving an accurate sequence stratigraphic interpretation of high-frequency cycles.