SEEING THE FOREST FROM THE LEAVES: APPLICATION OF DIGITAL LEAF PHYSIOGNOMY TO THE PALEOCENE/EOCENE CHICKALOON AND ARKOSE RIDGE FORMATIONS, SOUTH-CENTRAL ALASKA

Late Paleocene-Early Eocene time (57-54 Ma) was characterized by remarkably high global temperatures. Alaska’s Matanuska Valley and Talkeetna Mountains preserve fossil plant assemblages of this age in the Chickaloon and Arkose Ridge formations. These records provide a glimpse of sub-polar environmental and ecological conditions during a greenhouse climate phase. Previous studies on dicot leaf collections from these units have employed leaf margin analysis (LMA), leaf area analysis (LAA) and the climate leaf analysis multivariate program (CLAMP) and have indicated warm, wet, temperate biome conditions with mean annual temperature (MAT) estimates of ~11-15 ^oC and mean annual precipitation (MAP) estimates ~110-160 cm/yr.

 In this study, we use Digital Leaf Physiognomy (DiLP) on the previously analyzed study collections from these same units. DiLP involves digitally imaging leaf compressions and quantifying a series of leaf shape/size characters of each dicot morphotype including teeth area, blade area, and total leaf perimeter. These morphometric data are compared to a calibration dataset of known correlations of these leaf characters to climatic variables in the present day. DiLP-derived MAT from the Arkose Ridge collection was 15.7 ^oC while the Chickaloon was 15.5 ^oC (SE = ~4 ^oC). DiLP-derived MAP estimates were 187 cm/yr and 217 cm/yr for the Arkose Ridge and Chickaloon respectively. This method therefore provides paleoclimate estimates that are slightly warmer and wetter than published studies. Continued analysis of leaf collections from sub-polar paleolatitudes at this period of time could provide insight into what biome structure might exist in this region in a future warmer world.