Sedimentology and Sequence Stratigraphy of the Early Campanian Masuk Formation, Henry Mountains Syncline, Utah
Despite a long history of research, the stratigraphic relationships among Upper Cretaceous successions of the Henry Mountains in southern Utah and the classical exposures of the Book Cliffs to the northeast have never been fully resolved. In this paper, we document a sedimentological and stratigraphic analysis of the early Campanian Masuk Formation in the Henry Mountains syncline, and from a sequence stratigraphic framework show likely correlations of this interval with the Book Cliffs succession. The Masuk Formation, in its type section near Blind Trail, is a ~220m thick succession of interbedded sandstone, mudrock and coal, with minor conglomerate. Six facies are recognized within the unit: Facies 1, coal and carbonaceous shale interpreted as coastal swamp environments, Facies 2, grey to grey-green mudrock believed to be floodplain and lacustrine deposits, Facies 3, interlaminated siltstone and sandstone with a low diversity trace fossil assemblage and bimodal paleocurrent distribution from current ripples, suggesting tidal lagoon or estuarine deposition, Facies 4, thicker interbedded sandstone and siltstone with low angle bedding and bivalve resting traces that indicate a distal fluvial or estuarine origin, Facies 5, widespread sheet-like and lens shaped bodies of trough cross-bedded sandstone interpreted as single to multi-storey fluvial and tidal channels, and Facies 6, intraformational conglomerate, thought to be basal channel lags and bank collapse units. Facies analysis and tracing of key surfaces suggest that the Masuk Formation is a series of distal, coastal plain deposits spanning one long term (third order) stratigraphic sequence. The basal sequence boundary is in the underlying Muley Canyon Sandstone and the upper sequence boundary lies at the contact with the overlying Tarantula Mesa Sandstone. Within the Masuk Formation, multi-lateral channel sandstone bodies are traceable over considerable distances, suggesting an allogenic control on stacking patterns. We suggest that a series of high-frequency sequences are nested within the overall, longer-term sequence of the Masuk. Similarities in facies successions and in apparent age suggest that the Masuk Formation correlates to the Blackhawk Formation of the Book Cliffs, and that the base-Tarantula Mesa Sandstone sequence boundary correlates to the sequence boundary at the base of the Castlegate Sandstone.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009