HIDDEN DIVERSITY OF A WET DESERT ECOSYSTEM—PRELIMINARY REPORT ON THE ICHNOLOGY OF THE NAVAJO SANDSTONE, SOUTHEASTERN UTAH

Trace fossils in the Lower Jurassic Navajo Sandstone (Ss) represent hidden biodiversity—biota not represented by body fossils—in a desert ecosystem that can be used to evaluate the distribution of biota in different portions of the eolian depositional system and interpret the environmental and hydroclimatic settings of the Navajo Ss. Lithofacies deposited in dune, dry interdune, and wet interdune environments (including 1^st, 2^nd, and 3^rd order bounding surfaces, supersurfaces) and in fluvial and lacustrine environments were evaluated near Moab, Utah. Different patterns of trace fossil assemblages associated with particular lithofacies and bounding surfaces record short- to long-term hiatuses in deposition and record weak to strong pedogenesis. Biolaminates and stromatolites in limestone represent chemotactic and phototactic behavior by prokaryotes and protozoans living in aquatic environments. Rhizoliths, rhizocretions, and rhizohaloes represent herbaceous, shrub, and tree roots and stems in wet interdune and water-margin environments. Traces interpreted as invertebrate activity include: Ancorichnus (Arthropod, beetle?); Arenicolites (Mayflies nymph—Ephemeroptera); Beaconites (Beetle? —Coleoptera); Cylindrichum (Tiger beetle larvae—Coleoptera, Cincinelidae); Entradaichnus (Arthropod—beetle? cockroach?); Fuersichnus (Mayflies nymph—Ephemeroptera); Lockeia (Clams—Mollusca, Bivalvia); Macanopsis (Spider—Araeneidae); Naktodemasis (Scarab beetle larvae—Coleoptera, Scarabaeidae); Palaeophycus (Arthropod?); Planolites (Arthropod?); Scolicia (Snails—Mollusca, Gastropoda); Scoyenia (Cranefly larvae—Diptera, Tipulidea); Skolithos (Arthropod—spider? wasp?); Steinichnus (Mole cricket—Gryphillidae); and Treptichnus (Rove beetle—Coleoptera, Staphylinidae). Large- (4 to 30 cm) to mega-diameter (> 50 cm) burrows and ornithopod and theropod footprints represent vertebrate activity. Traces occur mostly on bounding surfaces and super-surfaces in low (< 2 ichnogenera) to high (> 10 ichnogenera) diversity, depending on the time in between depositional events. Ichnodiversity of the Navajo Ss indicates a wet desert ecosystem in this area with periods of greater rainfall to support the primary productivity and detritivore-dominated nutrient cycling system.