SEDIMENTOLOGY, STRATIGRAPHY, CHEMOSTRATIGRAPHY, AND GEOCHRONOLOGY OF THE PALEOCENE-EOCENE CHICKALOON FORMATION, ALASKA

The Paleocene-Eocene Chickaloon Formation of south-central Alaska records high- to mid-latitude terrestrial conditions and may contain the Paleocene Eocene Thermal Maximum (PETM). Facies analysis, U-Pb geochronology, and stable carbon isotope chemostratigraphy were conducted on exposures of the Chickaloon Formation at the abandoned Evan Jones Coal Mine in order to provide a contextual framework for understanding the high- to mid-latitude floral response to a greenhouse climate.

The studied strata represent a fluvio-lacustrine sequence dominated by floodplain, channel sandstone, crevasse lobe, and swamp/mire deposition. Floodplain environments are represented by medium gray shaly siltstone and cm-scale sheet-sandstone interbeds, which commonly contain ankeritic concretions. The majority of the channel sandstones are crevasse channels. They are generally small in scale, 2-5m in thickness, and grain size very rarely increases beyond medium-grained sandstone. Carbonaceous shale and coal are localized and indicate a high-rate of organic carbon accumulation in the area. Fossil floral material is common and often includes broad-leaf angiosperms, conifers, wood, and in-situ tree trunks; these suggest a highly vegetated or forested environment. Considered together, lithologic and paleontologic data suggest that locally the Chickaloon Formation represents a distal floodbasin environment with occasional crevasse channels reaching the area that originate from a main channel several kilometers away.

Because coalified fossil debris occurs throughout this sequence, a carbon isotope stratigraphy is being developed in order to identify the PETM in these strata, and to correlate the section to coeval sections elsewhere. One interbedded airfall tuff occurs in this section, and it should provide an independent age constraint on this exposure.