Dating Human Occupation on Diatom-Phytolith-Rich Sediment: Case Studies of Mustang Spring and Lubbock Lake, Texas, USA

Abstract

ABSTRACT. The Great Plains of North America have a rich archaeological record that spans the period from Late Glacial to Historic times, a period that also witnessed significant changes in climate and ecology. Chronometric dating of archaeological sites in many areas of the Great Plains, however, is often problematic, largely because charcoal and wood-the preferred materials for radiocarbon dating-are scarce in this grassland environment with few trees. Two reference archaeological sites are studied here: Mustang Spring and Lubbock Lake, Texas, USA. We carry out a geochronological approach based on a cross-study of carbon-derived data: combustion yield,  13 C, 14 C age differences between high temperature and low temperature released carbon, and the 14 C age itself. A study that incorporates multiple approaches is required to solve issues induced by the sedimentological context, which is rich in both freshwater diatoms and phytoliths from quite different origins. Analysis of carbon-derived data allows us to draw a succession model of dry and wet episodes and to associate it with a chronological framework. In this way, we can assert that, for the Mustang Spring site, several human occupations existed from ~11 kyr BP to ~8.7 kyr BP along the 110-cm-long series with an interruption of ~150 yr that is associated with a palustrine environment between the Plainview and Firstview occupations.

Influence of increasing combustion temperature on the AMS 14C dating of modern crop phytoliths

“…For rice crop phytoliths, it has been found that the original physical characteristics are significantly altered when the extraction temperature exceeds 900°C 41 . Previous studies indicated that the relationship between the 14 C age and combustion temperature can be used to quantify the relative contributions of different pools of organic carbon 29 30 31 . For phytoliths in AD 2012 rice straw, the F m of PhytOC was depleted by approximately 4% when the sample was combusted below 1100°C and was even more depleted (to approximately 12%) when combusted over 1400°C.…”

“…The exact influence of these two components of PhytOC on 14 C dating needs to be examined in detail because previous attempts to date 14 C PhytOC have focused on the total organic matter within the phytolith, and these attempts have clearly failed. In some cases, the combustion temperature can be used to separate heterogeneous mixtures of labile and refractory carbonaceous components, each of which may have a different apparent radiocarbon age 29 30 31 . Recently, a more robust phytolith extraction protocol suitable for carbon isotopic analysis was reported 32 , and we use this protocol to further investigate the potential source of PhytOC.…”

The micromorphology of Younger Dryas-aged black mats from Nevada, Arizona, Texas and New Mexico

“…1). Lubbock Lake is a well-stratified archaeological site, discovered in 1936, that contains evidence of occupation by Native American populations beginning as early as 11,100 14 C yr BP (Holliday, 1985a;Johnson, 1987;Hatte et al, 2010). The Paleoindian-aged archaeological deposits are associated with alluvial, spring, marsh, and lacustrine sediments, and include Rancholabrean faunal remains with evidence of butchering (Johnson and Holliday, 1981;Stafford, 1981;Holliday, 1985a).…”

Radiocarbon Concentrations of Wood Ash Calcite: Potential for Dating

“…In the case of silicates minerals (e.g. phytoliths and diatoms), recent studies indicate that these materials interact with the CO 2 in the environment and change the original 14 C content (Hatté et al 2010;Santos et al 2010). Furthermore, when dealing with archaeological ash samples, a serious difficulty is the problem encountered by Koumouzelis et al (2001) and when dating calcitic plaster/mortar (Lindroos et al 2007), namely that the crystals are relatively unstable and undergo diagenetic alteration that results in the original 14 C concentration changing over time.…”