THE PHYTOGEOGRAPHIC IMPORTANCE OF THE MT. DALL FLORA (FAREWELL TERRANE, AK) IN THE PENNSYLVANIAN/PERMIAN

The Angaran phytogeographic province of the Carboniferous and Permian has been characterized as a distinct realm of the terrestrial biosphere at the time. This region was composed of present-day Siberia, the Russian Platform, and associated landmasses in mid to high northern paleolatitudes. Kazakhstan and other more southerly tectonic blocks are considered to be Subangaran and to have greater paleobotanical similarity to Euramerican regions. There is, however, a lack of paleobotanical data from northern North America during the late Paleozoic, imposing a spatial gap in our knowledge of phytogeographic patterns in the northern temperate latitudes. The Mt. Dall Conglomerate, located in Denali National Park, AK, contains a Late Pennsylvanian/Early Permian flora that is the only known paleobotanically fossiliferous locality of that age within a 1500 km radius. Interbedded within massive conglomerate beds are siltstones that preserve many taxa of Angaran affinity (Rufloria, Zamiopteris, etc.). These sediments were deposited as part of a braided-stream system in a foreland basin associated with a collisional event involving the Farewell Terrane and either the North American margin or another offshore entity. Although the paleogeographic location of the Mt. Dall Conglomerate is still debatable, the strong affinities of the flora with Siberian and Russian Platform collections corroborate earlier Paleozoic marine macro- and microfaunal biogeographic studies that link the Farewell Terrane to the late Paleozoic landmasses that make up the Angaran realm. With the Mt. Dall flora, however, I argue that a close paleogeographic proximity between the Farewell Terrane and mainland Angara in the late Paleozoic may not be the reason for the observed affinities. The temperate latitudinal belt extends across Angara proper and also includes northern North America in the late Paleozoic. Terranes peripheral or attached to North America at these paleolatitudes and within the same basic climate regime should be expected to contain floras similar in ecology and form to the Angaran types. The plant fossil similarity between the Mt. Dall flora and Angaran collections may therefore be uninformative with regard to the Farewell Terrane’s paleogeographic longitudinal placement but may be very important in its latitudinal placement.