INTERPRETATION AND SIGNIFICANCE OF UPPER MISSISSIPPIAN (CHESTERIAN) TERRESTRIAL LYCOPODS (STIGMARIA) IN THE MARINE CARBONATE/REDBED SUCCESSION AT THE BASE OF THE GLOBAL STRATOTYPE SECTION AND POINT FOR THE BASAL BASHKIRIAN/PENNSYLVANIAN, ARROW CANYON, SOUTHERN NEVADA, USA

A two-meter thick stratigraphic section across the contact of the upper Battleship Wash and lower Indian Springs formations at the base of the GSSP for the basal Pennsylvanian in Arrow Canyon contains numerous large fragments of Stigmaria stellata, which is probably a root system for the Carboniferous lycopod tree, Lepidodendron. The Stigmaria are primarily located on two well exposed dip slopes, which collectively cover about 1200 square meters. The two dip slope surfaces may represent two distinctive exposure surfaces, separated by a small marine transgression. Over 210 fragments were observed, measured, and the orientation of each was plotted on our map. Our observations, measurements, and mapping support the assignment of the woody remains to Stigmaria, and suggest that the fragments represent in situ forest growth, and were not derived from some unidentified terrestrial source and rafted into a shallow carbonate environment. Most of the fragments are Stigmaria rhizophores. No true stumps, trunks, branches, leaves, or any other plant remains were observed. Many of the rhizophores have articulated “rootlets”, which would be reasonably stripped-off during transport. The rootlets are delicate, and have the appearance of small leaves. They are confined to an approximately six inch horizon that is selectively silicified and dissolved (as evidenced by external molds of crinoid ossicles). Excluding those rhizophores that appear to represent single trees in a larger forest, there is no indication of preferential orientation that one might expect if the fragments were rafted into a shallow lagoon. Although the two lycopod-bearing horizons probably indicate low order marine cyclicity inherently recognized by strata within the GSSP, the magnitude of sea-level drop represented by these horizons appears to be lithologically more significant than the regressive phases of the seven observable cycles within the overlying GSSP.