FOSSIL BEETLE EVIDENCE FOR A SHORT WARM INTERVAL NEAR 40,000 YR BP ATTITUSVILLE, PENNSYLVANIA

A brief cold-warm-cold climate change during the middle Wisconsinan is described for the first time in North America, based on fossil beetle assemblages at Titusville, Pennsylvania. AMS dating of insect chitin and wood suggests the change occurred between 39,000 and 43,500 yr B.P . Basal peats in river terrace deposits contain arctic-subarctic beetl e species representing a climate similar to that found at treeline in Canada, where mean July temperatures range from 10 degrees to 13 degre es C. These cold-adapted beetles were replaced by species representing a climate similar to the mixed coniferous-deciduous forests of southe rn Canada, where mean July temperatures range from 18 degrees to 20 de grees C. In turn, these warmer-adapted beetles were replaced by arctic -subarctic species in the upper part of the section, representing a cl imate with mean July temperatures in the range 10 degrees-13 degrees C . The brief warm interval is informally designated the Titusville inte rstade. The difference in temperature between the colder and wanner in tervals is about 5 degrees-7 degrees C. The Titusville interstade is c orrelated with the Upton Warren Interstade of the British Isles which is of similar age and intensity. It is also correlated with the high s ea-surface temperature interval between Heinrich events 4 and 5 repres ented in North Atlantic Sediment cores. (C) 1996 University of Washing ton.