PRIMARY AND SOFT-SEDIMENT STRUCTURES IN THE MIDDLE RED MEMBER OF THE MOENKOPI FORMATION

The middle red member of the Moenkopi Formation (Lower Triassic) is well exposed along the road to the top of Hurricane Mesa, a few miles west of Zion National Park. The middle red member contains a variety of both primary sedimentary structures and soft-sediment deformation structures. Primary structures include: oscillation and current ripple marks, mud cracks (seen in both edge and plan view), cross beds, and a few fossils. Soft sediment deformation structures include: ball and pillow structures and numerous, well defined tepee structures. Tepee structures have tops that are both pointed and rounded and range in size from a few centimeters to a decimeter. The ridge–like character is well represented. These structures are particularly well developed in the more gypiferous layers. All of these structures, plus the general sedimentation sequence, are indicative of a sabkhas-peritidal environment.