TROPICAL CYCLONES AND AQUATIC WETLANDS OF THE LATE CHESTERIAN BATTLESHIP WASH FORMATION (GREAT BASIN, ARROW CANYON, NEVADA)

The combination of a thanatocoenosis of brachiopods and crinoids with a biocoenosis of Lepidodendron rooting structures in the paleosols intercalated with normal marine carbonates of the Late Chesterian (Mississippian) Battleship Wash Formation at Arrow Canyon, southern Nevada suggests involvement of tropical cyclones in their formation. Absence of abrasion on marine allochems implies minimal transport and, thus, sourcing from nearby offshore environments, whereas the root casts (Stigmaria stellata) of Lepidodendron, based on preservation of delicate features, are judged to be in situ. Tropical storms of sufficient energy levels mixed clastic detrital material shed from the Antler Highland with offshore carbonate allochems and deposited this mixture in back-barrier areas (aquatic wetlands) of the shelf margin of the southeastern Great Basin. In these environments, the hydrophyte Lepidodendron established itself and soil formation took place until sealevel rise and decay or a catastrophic weather event terminated growth by removing all evidence of plant matter and debris except for the rooting structures that were later filled with sediment as decay progressed. This ‘event' with its devastation of the coastal aquatic systems was followed by subsidence of the coast and burial of the paleosols with marine carbonates replete with allochems. Sealevel fall and a subsequent tropical storm re-initiated the sequence of events of mixed sediment deposition, establishment of the lycopsid flora, soil formation, truncation by another ‘event' and burial by marine carbonates. This sequence of events was repeated four times in the upper Battleship Wash Formation. Ultimately, this sequence was covered by marine carbonates, which were eventually superseded by the mixed sediments of the Indian Springs Formation. Isotope and trace chemistry suggest stable marine conditions during formation and deposition of the brachiopods, while the coeval whole rock was altered in the presence of meteoric water under bacterial sulphate reducing conditions. The paleosols are inceptisols by virtue of their immature soil material development and chemistry. The chemistry further infers formation/alteration of the paleosol allochems in a mixture of meteoric and seawater under bacterial oxidizing conditions.