Late-Glacial and Early Holocene Vegetational History at the Kolarik Mastodon Site, Northwestern Indiana

Abstract

Analyses of pollen and plant macrofossils from the Kolarik Mastodon Site provide important refinements of the late-glacial and early Holocene vegetational record for northwestern Indiana. The record spans the period from> 12,000 to 9500 years B.P. Regional vegetation from> 12,000 to at least 11,000 years B.P. consisted of open, spruce-dominated forest or woodland. Both black and white spruce were present locally, along with aspen, fir and tamarack. The mastodon recovered from the site was associated with this vegetation. Vegetation of the region between 11,000 and 9500 years B.P. consisted of pine, spruce and hardwoods (oak, ash, hickory, hornbeam). Macrofossils indicate local presence of jack pine, white pine, tamarack, spruce, fir, alder and birch (probably paper birch). A radiocarbon date from a wood sample indicates that the upper boundary of the spruce-herb pollen zone in the region may be as young as 10,800 years B.P., 1000 years younger than suggested by previous studies in northern Indiana. The age discrepancy may result from carbonate contamination of bulk lake sediments. INTRODUCTION We present results of pollen and macrofossil studies of sediments collected during excavation of mastodon and other vertebrate remains from the Kolarik Site (Ellis, 1981) in Starke Co., Indiana (Fig. 1). These studies provide the basis for reconstructions of vegetation and environment associated with the vertebrate assemblage. In addition, our studies contribute new information on the late-glacial and early Holocene vegetational history of northwestern Indiana and provide chronological and taxonomic refinements of the regional pollen stratigraphy. Bailey (1972) has provided a general outline of postglacial vegetational development in northwestern Indiana. Bailey's studies are based on pollen and radiocarbon stratigraphy of two lakes in LaPorte County, 55 km N of the Kolarik Site (Fig. 1). Because these lakes are in areas of calcareous till, the sediments are susceptible to contamination by dead Paleozoic carbonate, making the radiocarbon dates of bulk lake sediments subject to significant error (Bailey, 1972; Ogden, 1967). The availability of radiocarbon dates based on plant macrofossil samples in clear stratigraphic association with the pollen sequence at the Kolarik Site provides an opportunity to test and refine the regional chronology. In addition, identification of macrofossils from bulk sediments at the Kolarik Site permits identification of palynologically indistinguishable taxa (e.g, species of spruce, pine and birch) and documents the presence of palynologically silent taxa (e.g, aspen, tamarack, herbs, aquatic macrophytes). These identifications form the basis for a more detailed understanding of regional and local vegetational change.2 SITE DESCRIPTION The study site is situated on the property of Andrew Kolarik immediately N of the Starke Co.-Pulaski Co. line in Starke Co. (Bass Lake 7.5' Quadrangle, T32N, R2W, Sec. 36, SE 1/4, SW 1/4, SE 1/4, SW 1/4) (Fig. 1). Elevation of the site is 218 m above mean sea level. 1Present address: Department of Biological Sciences, Idaho State University, Pocatello 83209. 2Vascular plant nomenclature after Fernald (1950).