Enigmatic deep-water depositional mechanisms, upper part of the Oquirrh Group, Utah

Abstract Textures, body fossil assemblages, trace fossil assemblages, and lack of sedimentary structures formed by tractive currents indicate that Upper Pennsylvanian and Wolfcampian sandstones and limestones of the Oquirrh Group in northwestern Utah were deposited in deep water. However, the abundant thick bedded to massive sandstones are not classical turbidites. The depositional mechanisms of five deep-water lithofacies have been inferred: 1) massive and thickly bedded sands were transported by turbidity currents and deposited by grain flows; 2) rippled sands were deposited from turbidity currents; 3) bioclast packstones, similar to Walker's (1978) pebbly sandstones, formed from sediments emplaced by turbidity currents and grain flows; 4) non-channelized conglomerates were deposited by dense turbid flows, gram flows, and debris flows; and 5) thinly bedded siltstones are of hemipelagic origin. The lateral continuity of individual beds is generally not known, but it is well documented that 100-m-thick sets of beds are continuous over several kilometers of distance and that units dominated by a single lithofacies can be mapped from 10 to over 100 kilometers. Nevertheless, the lateral depositional geometry of the upper part of the Oquirrh Group remains enigmatic. Indications of an integrated submarine fan distribution system are vague at best.