restricted access Chapter 4. Stratum C Paleoecology at the Lange/Ferguson Mammoth Site
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61 The Lange/Ferguson mammoth site contains a rich record of human and environmental interaction in the Late Pleistocene. This investigation documents the environmental conditions prevailing during deposition of a spring-fed pond overlying mammoth bones that have been recovered with evidence of Clovis butchering activity . Diatoms, ostracodes, and mollusks show fluctuations from freshwater to alkaline/saline conditions between 11 and 12 Ka. Introduction Using diatoms, ostracodes, and mollusks, this study documents the paleoenvironmental history of the Lange/Ferguson site. The main purpose of this investigation is to reconstruct the paleohydroclimate patterns that characterized the Younger Dryas (ca. 11–13 Ka) in the region. The Clovis culture across North America has attracted the attention of archaeologists for more than 60 years (Sellards 1952). The Lange/Ferguson site, located in the White River Badlands of South Dakota, was first identified by a local collector, Les Ferguson, in 1960. In 1980, L. Adrien Hannus met Ferguson and initiated research to understand the magnitude and direction of the human/ environment relationship at the time of Clovis occupation (Hannus 1985, 1989, 1990a, 1990b). Over the years, researchers in several fields have addressed at least two major questions: (1) What is the role of human activity in modifying biological communities and altering the natural structure of ecosystems? (2) How do ecosystems respond to differing scales of environmental change? How can microfossils help us approach these questions? The study of calcareous and siliceous organisms has proven a powerful tool for reconstructing ancient environments. The occurrence of diatoms, ostracodes, and mollusks at Lange/Ferguson offers the unique opportunity to identify the patterns of environmental change in South Dakota during Clovis occupation. Diatoms are microscopic siliceous algae of the division Bacillariophyta. The silica cell wall, called a frustule, consists of two highly ornamented valves of diverse forms (centric and pennate) (Round et al. 1990). The group evolved to form elaborate silica walls that reflect the types of habitat to which the particular species is adapted. Nearly all diatoms are microscopic, ranging in size from 2 µm to 500 µm (0.5 mm). Marine and nonmarine species are abundant around the world, in both the plankton and the benthos. They first appeared in the Early Jurassic marine realm, and probably earlier as a result of the Permian mass extinction (Medlin et al. 1997). It is not clear when diatoms migrated from the marine to the continental world. Records show their occurrence in Eocene deposits of Lac de Gras, Northwest Territories, Canada (Wolfe et al. 2006). Sensitive to water chemistry, diatoms are valuable tools in identifying recent and fossil environments. Many species have distinct ranges of pH and salinity that they tolerate, as well as other parameters (e.g., nutrient concentration , suspended sediment, flow regime, elevation, and different types of anthropogenic disturbance) (Stoermer and Smol 1999). In the geologic record, the fossilized silica frustules are the only remains of diatoms that may be used to reconstruct past environments. Low-energy environments favor preservation (Mannon 1987). Ostracodes are microscopic crustaceans characterized by a hinged bivalve carapace made of calcite and ranging in size between 0.5 and 2.0 mm. The carapace is the only body part that is preserved in the geologic record (Horne et al. 2002; Pokorný 1978). In continental waters they are mostly benthic, although some species are nektic and may swim around the vegetation (Forester 1991). This group colonized continental aquatic systems as early as the Carboniferous but has thrived in the oceans since Stratum C Paleoecology at the Lange/Ferguson Mammoth Site chapter four Manuel R. Palacios-Fest 62 Chapter Four the Cambrian. Today, ostracodes are diverse and abundant in marine and nonmarine environments. Paleontologists have devoted more time to the study of ostracodes than have biologists—hence the poorly understood ecology of ostracodes. Recent progress on the application of ostracodes as indicators of hydrogeologic variation, however , calls for additional studies of the ecology of springs and seeps, as well as their associated wetlands or ciénagas (Hall et al. 2012). Mollusks include the bivalve clams and mussels (Bivalvia ) and the univalve snails (Gastropoda). Mollusks are soft bodied and unsegmented, with a body organized into a muscular foot, a head region, a visceral mass, and a fleshy mantle that secretes a shell of proteinaceous and crystalline calcium carbonate (aragonite) materials. Both marine and nonmarine species exist. The nonmarine species, which are the subject of this study, include several families of snails (the aquatic Planorbidae, Ancylidae , and Lymnaeidae and the terrestrial Pupillidae) and at least one family...