Sentinel Butte: neutron activation analysis of White River Group chert from a primary source and artifacts from a Clovis cache in North Dakota, USA

Instrumental neutron activation analysis (INAA) was used to characterize the chemical composition of chert from a primary source in western North Dakota. Known as Sentinel Butte, this source is part of the Eocene-age White River Group (WRG), a widespread geological formation on the central and northern Plains. INAA results demonstrate that it is chemically distinct from other known chert-bearing WRG. Further, analysis of three bifaces from the nearby Beach Clovis cache site demonstrates that they are made of chert from Sentinel Butte, and most likely the other 55 White River Group Silicate (WRGS) bifaces in the cache are as well. Although Clovis caches typically are dominated by materials transported hundreds of kilometers, it is argued that the advance manufacture and caching of bifaces even a short distance from a source may be a highly effective tactic to reduce gearing up time and hence search costs associated with the pursuit of mobile game at the close of the Pleistocene.

Research highlights
► Naturally-occurring chert nodules of sufficient quality for flaked stone tool manufacture occur on Sentinel Butte, ND, USA, in White River Group (WRG) deposits.
► Instrumental Neutron Activation Analysis (INAA) demonstrates that Sentinel Butte chert possesses a distinctive chemical composition, enabling its separation from other northern and central Plains sources of White River Group Silicates (WRGS).
► INAA analysis of three WRGS bifaces from the Beach Clovis Cache reveals that they are made of Sentinel Butte chert.
► Despite the presence of the cache only 19 km from Sentinel Butte, the energetic expenditure involved in the manufacture and transport of some 58 bifaces to the cache site represents considerable time savings in the context of Clovis subsistence and technological organization.