2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 9
Presentation Time: 3:30 PM


WILKENS, Nathan D.1, FARMER, Jack D.1 and PIGG, Kathleen2, (1)Department of Geological Sciences, Arizona State University, Box 871404, Tempe, AZ 85287-1404, (2)School of Life Sciences, Arizona State Univ, Tempe, AZ 85287, nathan.wilkens@asu.edu

Several sites near Moab, Utah have preserved a unique picture of Jurassic Navajo Sandstone interdune deposits. It is surprising that these interdune deposits contain plant fossil remains, as only poorly preserved wood and rare putative Equisetum axes have been reported. Paleobotanical remains at these sites include fossilized coniferous wood of Araucarioxylon and at least one other as yet unidentified species with distinct growth rings. The fossilized wood varies in size from highly flattened logs (by 80% of their original thickness) up to 0.2 m in diameter to slightly flattened logs (by 20% of their original thickness) up to 1.0 m diameter. Although the cellular preservation of the wood appears poor, a fluorescence technique was developed that allowed for identification of the wood. Other plant remains include silicified leaf hash and intact silicified needles still attached to branches. The intact needles are triangular in cross section, 3.0x15.0mm in size and attached to branches >30 cm in length. Future research will include SEM identification of silicified needle stomata. Araucarites-like cone scale casts are also ubiquitous, with some limestone layers containing up to 50% in volume. Although no intact seed cones have been found, at least one complete silicified pollen cone has been discovered. Many leaf impressions and branch casts were also found. The leaf impressions are referable to the form genus Pagiophyllum, and possibly represent either the family Araucariaceae or Cheirolepidaceae. The discovery of these new sites will necessitate modifying existing facies models for the early Jurassic Navajo Sandstone interdune deposits. The massive size of some of the fossil wood implies long term stable interdune environments. The association of different plant species may help constrain the salinity environment of these interdune deposits. Further detailed paleobotanical work is in progress to shed more light on these environments. This work will be incorporated into a larger sedimentological and geochemical study of the Navajo Sandstone in southern Utah.