AMBER INCLUSIONS IN THE PALEOCENE/EOCENE CHICKALOON FORMATION, MATANUSKA VALLEY, ALASKA

Amber deposits that include arthropod and botanical inclusions are globally scarce in the Late Paleocene/Early Eocene terrestrial rock record. Here we report on preliminary investigations of new amber collections from coal and organic-rich shale beds that represent floodplain and mire depositional environments in Paleocene/Eocene strata of the upper Chickaloon Formation in south-central Alaska. The fossiliferous strata were laid down during an anomalously warm global climate phase and thus provide a glimpse into an atypical paleoenvironment at subpolar high latitudes with warm yearly-averaged climate conditions. Our >3000 dispersed amber samples from this unit have yielded several arthropod inclusions, including aphid nymphs and an ant (Formicidae). These fossils represent the first insect remains found near the Paleocene/Eocene boundary in Alaska. Dozens of botanical inclusions have also been discovered in the amber pieces including palynomorphs, leaf fragments, and wood/bark debris from multiple plant species. The amber samples exhibit very high clarity as most have avoided oxidation; the color is primarily a pale yellow but varies to dark orange-red. Many teardrop-shaped samples appear to have fallen into ponded or flowing water, supporting previous interpretations of a floodplain/ mire depositional environment. The amber and its organismal inclusions are part of a greater paleobiological assemblage from the upper Chickaloon Formation that includes leaf and seed megafloral remains, permineralized cupressaceous wood, abundant palynomorphs, and a freshwater gastropod fauna. Ongoing work is investigating significant evidence of leaf herbivory in the fossil megafloral assemblage and whether it could even represent feeding traces from insects found within the amber samples.