WARM PALEOENVIRONMENTAL INDICATORS IN THE PALEOCENE/EOCENE CHICKALOON FORMATION, MATANUSKA VALLEY, ALASKA

Warm climate signatures typify many paleoenvironmental records of early Tertiary time, including the Paleocene/Eocene Thermal Maximum (PETM).  The ecological and evolutionary response of terrestrial vegetation to hothouse conditions during this time has received much attention at localities in the low to middle modern- and paleolatitudes.  At higher modern latitudes, the Chickaloon Formation in the Matanuska Valley of southern Alaska contains Paleocene/Eocene fossil plant assemblages in fluvial deposits.  This study explores paleoclimatic indicators from leaf physiognomic analytical approaches, wood anatomy, and floral community composition/structure in order to assess the paleoenvironmental conditions of growth and preservation at the Wishbone Hill locality in the Chickaloon Formation.  Results suggest that the diverse Wishbone Hill flora grew under significantly warmer climatic conditions than there at present. Episodic increases in sedimentation rate preserved the flora nearly in situ.   Northward tectonic transport since deposition is estimated to be nearly ~15 degrees latitude based on paleomagnetic evidence (~62 degrees north today vs. ~47 degrees north in the early Tertiary).  A more southerly paleolatitude combined with a warmer Paleocene/Eocene global climate likely explains why this flora exhibits similarities in community composition and climatic signatures to modern North American forests growing at ~30 degrees latitude.