Fossil Beetle Evidence for a Short Warm Interval near 40,000 yr B.P. at Titusville, Pennsylvania

Abstract

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 beetle species representing a climate similar to that found at treeline in Canada, where mean July temperatures range from 10° to 13°C. These cold-adapted beetles were replaced by species representing a climate similar to the mixed coniferous–deciduous forests of southern Canada, where mean July temperatures range from 18° to 20°C. In turn, these warmer-adapted beetles were replaced by arctic–subarctic species in the upper part of the section, representing a climate with mean July temperatures in the range 10°–13°C. The brief warm interval is informally designated the Titusville interstade. The difference in temperature between the colder and warmer intervals is about 5°–7°C. The Titusville interstade is correlated with the Upton Warren Interstade of the British Isles which is of similar age and intensity. It is also correlated with the high sea-surface temperature interval between Heinrich events 4 and 5 represented in North Atlantic sediment cores.