TREE BOLES REVEALED IN PACIFIC NORTHWEST LANDSLIDE DEPOSITS PROVIDE TREE-RING RECORD FOR PERIOD PRIOR TO DEGLACIATION

The discovery of multiple large tree boles in landslide deposits dated prior to the full-glacial provides a new source for paleo-climatic reconstructions from the northwestern coast of North America. Realignment of US Highway 20 between Corvallis OR through the Oregon Coast Range and onto Newport OR has uncovered significant organic deposits at depth that include the boles of large trees. To date, five large trees have been recovered from a single road-cut with the largest individual about 48” in diameter. Radiocarbon dates on subsurface organic material from the overall project area range from 17,850 ± 100 to >46,400 (radiocarbon dates B.P.). The deposit containing the recovered trees dates to >40,000 radiocarbon years B.P on wood recovered during initial geotechnical drilling. The sedimentary deposits are interpreted as paleo- translational landslides involving the Tyee Formation. Preservation of the wood material and associated macrofossils is excellent because of clay sediments that encased the material and halted decomposition. Analysis of the first recovered bole (tentatively identified as Western Red Cedar; Thuja plicata) shows excellent preservation of late-wood rings but the early wood is composed primarily of ghost trachieds. Yet, ring counts from a portion of this bole, a four inch block of outer rings, contained between 120 to 130 rings of annual growth with good sensitivity for climate reconstruction. The additional recovered boles are tentatively identified as Douglas-fir (Pseudotsuga menziesii) and are larger in diameter than the recovered Western Red Cedar tree. One of the Douglas-fir boles was discovered with remnants of the primary root structure still attached. In addition to paleobotanical and paleoclimatic information, the large amount of wood available will be used for radioisotope and stable isotope studies. Excavation continues through the summer of 2009 and again during the summer of 2010 with the potential of additional buried deposits being uncovered.