High resolution correlation of the Upper Cretaceous stratigraphy between the Book Cliffs and the western Henry Mountains Syncline, Utah, U.S.A.

摘要

Exposures of Upper Cretaceous strata in the Book Cliffs have played a key role in the formulation of modern sequence stratigraphic concepts, and yet correlations with time-equivalent strata in nearby regions remain uncertain, resulting in an incomplete understanding of regional paleogeography. This study presents detailed high-resolution correlations of the Upper Cretaceous stratigraphy between the Book Cliffs, the Wasatch Plateau, and the western Henry Mountains Syncline in Utah with emphasis on the Campanian interval. Two newly acquired measured vertical sections at Coal Canyon near Green River, in the Book Cliffs, and Blind Trail, in the Henry Mountains, inform the correlations, which also incorporate the substantial body of previous research. Correlations are further constrained by vertical and lateral facies stacking patterns, and changes in sediment dispersal directions at discrete stratigraphic horizons derived from paleocurrent measurements. Much of the Campanian succession can be characterized as a single, low-frequency (third order) depositional sequence, within which are nested numerous high-frequency sequences. While it is not possible to correlate every high-frequency sequence recognized in individual outcrop areas, we define four intervals (numbered 1-4, in ascending stratigraphic order) that we correlate across the entire region. Interval 1 (basal Campanian) is represented by initially deltaic and later wave-dominated shoreface strata of the Star Point Sandstone and equivalent basal Muley Canyon Sandstone. Interval 2 (lower Campanian) comprises coastal-plain facies passing eastward into shallow marine strata of the lower Blackhawk Formation and equivalent Muley Canyon Sandstone. Interval 3 (lower to mid middle Campanian) comprises a thick aggradational stack of coastal-plain fluvial strata that pass eastward into coastal and shallow marine facies (Blackhawk Formation and equivalent Masuk Formation). Interval 4, overlying a major facies dislocation (third-order sequence boundary), comprises amalgamated sheet fluvial deposits of the lower Castlegate Sandstone and equivalent Tarantula Mesa Sandstone. During the early to middle Campanian, the northern Wasatch Plateau and western Henry Mountains regions were along depositional strike with respect to one another. The Book Cliffs near Green River were located obliquely down depositional dip from the western Henry Mountains region during the Campanian. These new correlations, and the improved understanding of paleogeography that derive from them, have the potential to inform basin-scale stratigraphic interpretations to a greater extent than has been hitherto possible.