restricted access Chapter 3. Geochronology of the Lange/Ferguson Clovis Site
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29 The Lange/Ferguson site was found in 1960 when Les Ferguson of Hot Springs, South Dakota, discovered mammoth bones eroding out of the base of a small butte on the Lange Ranch. Excavations by L. Adrien Hannus (1980–1984) revealed the in-place bones of two mammoths and associated Clovis artifacts (Hannus 1985, 1989, 1990a, 1990b). The site is in the White River Badlands of southwestern South Dakota (fig. 24) and is located in Lange Creek Valley (E. White and Hannus 1985), which drains northwest to the White River. The landscape at the site is a rugged badland with erosion remnants (fig. 25) in the form of small tables or mesas, smaller flat-topped buttes, and three hoodoos (fig. 26). Hoodoos are small-diameter, tower­ like erosion remnants protected by erosion-resistant caps, most commonly of rock. In the Lange/Ferguson site area, however, it is the root mats at the top of Stratum G2 that have protected remnants of G2 alluvium from erosion. The hoodoos have given the site area its bizarre appearance (fig. 26b), but they will also eventually succumb to erosion once their protective caps are gone. The site lies about 70 km southwest of the Tertiary paleosol study area of Retallack (1983), near the classic slope retreat study area of Schumm (1956), and within the geomorphic study area of E. White (1982). Steep-sided erosion remnants are commonly drained by rills and are separated, for the most part, by miniature pediments (fig. 28) as described by K. Smith (1958). The sediments at the Lange/Ferguson site were first studied by E. White and Hannus (1985). The first Clovis point (fig. 27a) was found by avocational archaeologist Les Ferguson; just the tip of the point was sticking out of the base of Stratum C in Butte B (fig. 27d).1 Bones of the adult mammoth were in Stratum B3 (fig. 27b) below Stratum C in Butte A, about 17 m north of the first Clovis point find. The identification of specific stratigraphic units in the site area is made difficult by their similar lithology (table 4) and by the lack of stratigraphic continuity between buttes. It was hoped that radiocarbon (14 C) dating would solve this problem. However, redeposition of datable materials and the mobility of soluble organic matter (humic acids or humates) have made this task difficult. This has led to the radiocarbon dating of more samples than would normally be necessary to establish a firm chronology of the geologic processes involved in the formation of the stratigraphic framework. The 14 C dating of some topsoils helped determine which geomorphic surface, T-2a or T-2b, they belong to. All of the 55 14 C ages, except for the nine surface soil values, are in isotope-corrected uncalibrated years before present (BP = 1950) and are presented in table 5. As discussed later, the nine surface soil values are presented in table 5 as a percentage of modern 14 C rather than age because all contain nuclear age (bomb) carbon. The stratigraphic framework is composed of 12 strata and 25 substrata consisting of 22 alluvial units, two pond deposits, and a spring-derived sand. To avoid any possibility of confusing archaeological units with stratigraphic units, I designate the latter by stratum or substratum. As is typical of arroyos, much of the alluvium in the Lange/ Ferguson site area consists of sediment derived from adjacent slopes via surface runoff, that is, it is slopewash (see Leopold et al. 1966) as opposed to vertical accretion sediments derived mostly from farther upstream. Bank erosion also contributes significant volumes of sediment to ephemeral streams (Layzell and Mandel 2014), as will be seen in the evidence for redeposition of alluvium in the valley. In this chapter, I describe the sediments (table 4) exposed in erosion remnants along three east-west cross 1 Buttes A, B, and C as described here correspond with Localities A, B, and C elsewhere in the book. Geochronology of the Lange/Ferguson Clovis Site chapter three C. Vance Haynes Jr. 30 Chapter Three Figure 24. Topographic map of the White River Badlands showing location of the Lange/Ferguson site and other radiocarbon-dated strata in the region. 31 Geochronology sections (figs. 25, 30a, 30b, and 30c), one north-south cross section (fig. 30d), and four local stratigraphic profiles (fig. 31). The stratigraphic sequence and selected radiocarbon ages are shown in figure 29. The 14 C ages (table 5) are derived from (1) bulk sediment organic matter (BSOM...


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