PERENNIAL POND DEPOSITS IN TOPOGRAPHIC INVERTED CHANNELS IN THE EARLY CRETACEOUS CEDAR MOUNTAIN FORMATION, EASTERN UTAH: A POTENTIAL NEW TARGET FOR LIFE ON MARS

Elevated topographic inverted channels are present in the Early Cretaceous Ruby Ranch Member of the Cedar Mountain Formation south of Green River, Utah. These channels serve as analogs for geomorphically similar channels on Mars. Previous studies have concentrated on the interpretation of channel morphology and hydrology. To further understand the processes that influenced channel geomorphology, this study characterized the internal lithofacies architecture of the deposits utilizing 3-D reconstructions attained from drone photography, combined with detailed lithofacies analysis. Distinct pond accumulations are preserved between coarse-grained fluvial deposits in elevated channel B near the junction of segments 4 and 5 according to Harris’s 1980 nomenclature. Trough cross-bedded conglomerate and coarse-grained sandstone lie sharp contact below and in erosional contact above the pond deposits. At this locality, the pond deposits are up to 1.2 m thick and consist of four distinct, fine-grained, fining-upward sandstones separated by laminated grey mudstones. The sandstone beds vary in thickness from 3 to 12 cm. The four beds record a change from rapid sedimentation, soft-sediment deformation in the lowermost bed to tractional ripple deposits in the upper-most bed. All beds exhibit sparse horizontal bioturbation on basal bedding planes, mud-sand vertical tubes, and escape structures. To the east of this locality in channel B preserved pond deposits contain stromatolites. Pond formation was caused by impeded channel drainage resulting from bar migration. Sandstone beds represent flood events that inundated the otherwise placid pond. Organisms dwelt in the ponds within the channels and the deposits preserve this past life on Earth; if cognate geologic markers are found in the elevated channel on Mars, they may provide direction in the search for evidence of past microbial life.