HETEROGENEITY AND DIMENSIONAL VARIABILITY OF FLUVIAL SANDBODIES IN OUTCROPS: BLACKHAWK FORMATION, WASATCH PLATEAU, UTAH

Fluvial systems are abundant in rock record and their overwhelming presence in outcrops offers excellent opportunity to explore their detailed sedimentologic and stratigraphic entities paramount to 1) evaluate sediment supply drive from source to sink, 2) identify them as potential suite for subsurface aquifer build-up, and 3) establish their proposition as significant avenues for hydrocarbon reservoir development. Integrating photomosaics, measured sections, GPR and LIDAR data of superbly cropped out sections of the Cretaceous Blackhawk Formation along the eastern Wasatch Plateau, Utah, this study documents various scales of lithological heterogeneity and dimensional compilation of channel sandbodies and coastal-plain mudstones at a range of distribution and scales that, as a conditioning dataset, provides constraining parameters for improved and effective fluvial reservoir analysis.

Individual channel sandbodies are 2-15 m thick, medium-grained, and contain predominantly dune cross-stratification, with paleocurrents directed towards the north and northeast. Architectural element analysis demonstrates large-scale heterogeneity associated with alternating fluvial channel sandbodies and coastal-plain mudstones, intermediate-scale heterogeneity developed due to various architectural elements like bar-accretion and crevasse splays within individual sandbodies, and small scale heterogeneity related to facies variations within individual architectural elements. Along lateral-accretion beds, finer-grained sandstones become distinctly coarser-grained and amalgamated downdip. In convex-up crevasse-splay elements (c. 7m thick), individual beds show lateral facies change from proximal, ripple-laminated sandstones to distal, silty mudstones over a length of c. 20 m. Helicopter-borne LIDAR data from six contiguous, steep and inaccessible cliff-faces (~ 18km²) were used to generate a virtual outcrop model illustrating distribution (isolated vs. amalgamated) and connectivity (lateral vs. vertical) of fluvial elements. Behind-outcrop core provides additional control in mapping channelized sandbodies in 3D across the six cliff-faces.