Journal of Archaeological Science xxx (2011) 1e8 Contents lists available at SciVerse ScienceDirect Journal of Archaeological Science journal homepage: http://www.elsevier.com/locate/jas Experimental production of bending and radial flake fractures and implications for lithic technologies Thomas A. Jennings* Center for the Study of the First Americans, Texas A&M University, 4352 TAMU, College Station, TX 77843, United States article info abstract Article history: Bend and radially broken flake tools have been identified in Paleolithic and Paleoindian assemblages, and Received 21 July 2011 their presence raises important questions. Were these breaks intentionally produced to serve as tool Received in revised form edges or were broken flakes simply scavenged? More importantly, can we distinguish between inten- 26 August 2011 tionally produced breaks and those produced incidentally? Experimental archaeology can help answer Accepted 27 August 2011 these questions. In this paper, three sets of experimentally produced bend and radial flake breaks were compared. Flakes were intentionally broken by percussion, and these breaks were compared to those Keywords: produced during bifacial core reduction and by flake trampling. The presence of point of impact markers, Bend break Radial break near ninety degree break angles, and an assemblage with high percentages of bend and radial breaks Experimental archaeology distinguish intentional fracture from incidental fractures produced during bifacial reduction. High Paleoindian percentages of radial breaks distinguish intentional fracture from trampling. Finally, it may not be Paleolithic possible to identify intentional breaks in a bifacial reduction assemblage severely affected by flake-on- Pseudoburin flake trampling. Lithic technology Ó 2011 Elsevier Ltd. All rights reserved. Flake fracture 1. Introduction identify shared or individual knapping signatures. Recognizing an intentionally produced bend and radial break technology can Flaked stone technologies are dominated by tools made by provide an additional line of evidence to help understand the striking cores to remove flake blanks which are then either used as- knapping strategies, technological organization, and site-level is or retouched into formal tools. Because of their relative scarcity activities of a single group of people or help distinguish the tech- compared to other tool classes, intentionally broken bend or radial nological signatures of one culture from another. As a first step flake fracture tools have received less attention from lithic analysts. towards defining criteria diagnostic of bend/radial break produc- Bend and radial fractures used as tools, intentionally produced by tion technologies, this paper presents the results of an experi- striking the center of bifaces or flakes, have been identified in mental program comparing bend and radial breaks produced by Paleolithic and Paleoindian technologies (Bergman et al., 1987; intentionally striking flakes to breaks produced incidentally during Ferring, 2001; Frison and Bradley, 1980; McAvoy and McAvoy, bifacial core reduction and breaks produced by flake trampling. 2003; Surovell, 2009; Waters et al., 2011). The thick, damage- resistant edges created by these breaks are ideal for but not restricted to scraping and engraving tasks (Barton et al., 1996; 1.1. The mechanics of bend and radial breaks Crabtree, 1977; Deller and Ellis, 2003; Frison and Bradley, 1980; Root et al., 1999). While the production process of bend or radi- Lithic experts distinguish between three types of fracture initi- ally broken bifaces and flakes has been described (c.f. Bergman ation and two types of fracture propagation (Andrefsky, 2005; et al., 1987; Deller and Ellis, 2003; Miller, 2006; Root et al., 1999), Bonnichsen, 1977; Cotterell and Kamminga, 1987; Crabtree, 1972; few studies have directly compared intentionally produced breaks Odell, 2003). Hertzian and bending initiations result in stiffness- to incidental breaks. controlled propagations, while wedging initiation produces Lithic analysts rely on core reduction and tool production and compression-controlled propagation. The final phase is termina- use strategies to define cultures, reconstruct adaptations, and tion. With Hertzian and bending initiations, flakes can terminate in feather, hinge, or step terminations, while wedging typically results * Tel.: þ1 214 236 4484. in axial termination (Odell, 2003). For this paper, the most impor- E-mail address: [email protected]. tant termination is stepping. Step terminations occur when 0305-4403/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jas.2011.08.035 Please cite this article in press as: Jennings, T.A., Experimental production of bending and radial flake fractures and implications for lithic technologies, Journal of Archaeological Science (2011), doi:10.1016/j.jas.2011.08.035 2 T.A. Jennings / Journal of Archaeological Science xxx (2011) 1e8 bending forces act perpendicular to the initial fracture and repre- and these include occasional Hertzian cones, ring cracks, and sent a second fracture event independent of the first Hertzian or lipping of the fracture edge. Miller (2006) experimentally broke bending initiation. Hertzian and bending initiations are the most bifaces, some of which broke by radial fracture, but the focus of this common during many controlled lithic reduction and flake experiment was replicating perverse fractures rather than bend or production techniques (i.e. bifacial reduction, blade production), radial fractures. while wedging is typically associated with bipolar reduction. The above bend and radial fracture experiments have identified In addition to core reduction, these same mechanics of fracture potential markers of intentional breakage, but they fall short of can be used to break individual flakes. For Cotterell and Kamminga providing systematic comparisons between intentionally produced (1987:Figure 15), percussion applied to the center point of a flake breaks to those produced incidentally. Under the umbrella of can result in fracture either by bending or compression forces. If use-wear analysis, innumerable other experiments have been there is no opposing force directly under the point of impact, designed to identify tools and distinguish between intentional and bending fracture will cause the flake to snap transversely. In some natural damage, but these experiments focus primarily on micro- cases, bending induced transverse fractures, also referred to as snap scopic edge damage and use-wear rather than larger-scale bend or fractures, have virtually no propagation phase, and the force travels radial flake breakage (Andrefsky, 2005; Odell, 2003). Likewise, straight down from the impact point creating a ninety degree numerous core reduction and flake production experiments have fracture angle. Deller and Ellis (2003) also suggest that snap frac- been designed to replicate various aspects of prehistoric technol- tures can result from classic Hertzian cone initiation in which ogies, but because these studies often focus on other questions, few a cone began to form prior to median/lateral fracture propagation. report the incidence of bend and radial flake breakage produced However, they note that even on percussion produced snap breaks, during the reduction process. Important exceptions include the cones of force are often absent making it impossible to determine work of Root et al. (1999) and Tallavaara et al. (2010). In their core whether the force was produced by bending or Hertzian fracture. reduction experiment, Root et al. (1999), found that only 3of 622 Alternatively, if an opposing force is placed directly opposite the flakes larger than 5.6 mm exhibited radial fractures. Tallavaara et al. impact force, compression fracture will propagate from the striking (2010) experimentally produced 413 flakes and recorded the inci- surface (Cotterell and Kamminga, 1987). Compression fracture dence of accidental bending and radial fractures. The 201 frag- results in what have been termed radial breaks which are produced mented flakes were produced by combinations of 152 bending and when the percussive force causes the flake to split into three or 125 radial fractures. They show that knapping skill, indenter type, more pieces (Deller and Ellis, 2003). These also can exhibit lips and and relative flake thickness significantly impact fracture rate. cones of force (Deller and Ellis, 2003) as well as ring cracks, Previous experiments have provided important data on the crushing, and eraillure scars at the point of force (Moore et al., frequency and attributes of bend and radial breaks produced 2009). Radial fractures can also accompany perverse fractures intentionally and incidentally. This paper builds on these studies by when propagation follows radial fissures (Miller, 2006). providing new data on how often radial breaks are produced by processes other than intentional breakage, specifically by bifacial 1.2. Distinguishing intentional from incidental fracture core reduction and trampling, and refining criteria for dis- tinguishing intentional breaks from incidental fractures. Flintknapping experiments have revealed how bend and radial fractures occur, and archaeological analyses demonstrate that 2. Methods prehistoric knappers used bend and radial fractured bifaces and flakes for tools. Yet the question remains, were these breaks To compare bend and radial fractures produced intentionally intentionally created by prehistoric knappers for tool use, or did and incidentally,