Early Pleistocene vegetation of eastern Kansas and Nebraska.

Abstract

The vegetational environment of the Early Pleistocene is poorly understood. The main reason for this is a lack of physical evidence. During the summer and fall of 1985, several pieces of wood were discovered buried in the lower gray till at two separate locations in northeastern Kansas, and in the lower gray till along the south bank of the Platte River near Fremont, Nebraska. Observation of the macerated wood with an optical microscope and photographing the wood samples under a scanning electron microscope are the two processes used to identify the wood. Characteristics of the features observed in the wood, such as tracheids, resin canals, wood rays and bordered pits all demonstrate that the wood is spruce. I propose that the first Kansan gla~ial advance overrode a forest which was dominated by spruce. The vegetational history of the Late Pleistocene should serve as a model for the vegetational makeup of the Early Pleistocene. Evidence from pollen sequences show that during the maximum extent of the Wisconsin glaciation spruce forest covered most of the eastern and central United States. In southern Minnesota there is evidence that tundra vegetation existed adjacent to the ice sheet. As the ice lobes retreated the spruce forest was succeeded by deciduous forest and this in tum was succeeded by grasslands. The gray till in northeastern Kansas has long been recognized as being deposited by the Kansan glaciers, and the gray till in Nebraska as being deposited by the Nebraskan glaciers. There has been debate over whether these tills have two separate origins, or if they were both deposited during the Kansan glaciation. The fact that wood was found both in Kansas and Nebraska argues in favor of the proposal that they are the same tills.