Distinctive Unifacial Technology during the Early Holocene in Southern South America

The early Holocene archaeological record in Northwest Santa Cruz province in southern Argentina is remarkable in its richness. Among the lithic remains, most notable is a stemless triangular projectile point dating to ~8.5 10 uncalibrated kya. As part of a long term program directed to explore and understand diverse aspects of lithic technologies from Patagonia, this paper reports new observations on a set of notable unifacial tools existing in the assemblage accompanying them. Based on archaeological and experimental data we hypothesize they were produced from thick flake-blanks with one face totally or partially covered by flake scars sometimes reaching the longitudinal symmetry axis. This fact suggests that before being finished, it was reduced by detaching flakes from the edge to its center. This recent technological discovery allowed deepened on a new regional issue related with early Holocene unifacial tools that emerge as a peculiar style of covering unifacial flaking with subtle production differences to other similar implements. Together with the triangular points, this particular way of preforming the tool before and/or during the final shaping might be another distinctive manufacturing technique used by early Holocene hunter-gatherers in the area.


Introduction
Located in the Patagonian region in southern Argentine Republic, the Northwest of Santa Cruz province is a significant place in the history of the archaeology of the southern part of South America.There, an important record of hunter-gatherer occupations has been identified in several stratified and surface sites (e.g.Gradín et al., 1976Gradín et al., , 1987)).Since the early 1980s a long-term archaeological project has been underway in the studied area in particular (Aschero, 1981-82).
As part of a long term research program directed to explore and understand diverse aspects on lithic technologies from the Americas in general and Patagonia in particular, a set of unifacial tools were the subject of observational and experimental replicative studies (e.g.Nami, 2010, among many others).Hence, this paper reports the preliminary results on a specific technique of stone tool manufacture identified in the lithic assemblage used by early Holocene hunter-gatherers from southern Patagonia.

Provenance of the Artifacts.
The examined specimens come from three sites (Figure 1).Cerro Casa de Piedra (47˚57'S, 72˚05'W) is a volcanic rhyolitic hill with several rock shelters facing northwards.It is situated in the transition ecotone of a deciduous wood and bushy steppe in the Lake Burmeister and Roble River valleys in Perito Moreno National Park (Figure 1).One of the main sites, the Cerro Casa de Piedra 7 (CCP7) cave, has a sedimentary deposit ~2 m deep spanning the Pleistocene-Holocene transition to the Late Holocene.The stratigraphic section shows 19 natural layers deposited on the cave´s bedrock.Following the retreat of the local glaciers at the end of the Pleistocene, dung and bone recovered from layer 19 shows that at ~10.6 kya, it was a refuge for extinct and extant fauna (the milodontidae family and Lama guanicoe).Furthermore, the archaeological remains show a long sequence of human occupation spanning 10.6 and 3.4 kya (Aschero et al., 2007), as well as a very short occupation at 1.9 kya (Civalero et al., 2006-07).The lower layers (14 to 18) at CCP7 yielded evidence of diverse topics related to hunter-gatherers living there during the initial Holocene at ~7.8 -9.6 uncalibrated kya (Civalero, 2009;Civalero & Aschero, 2003;Civalero & Franco, 2003;Civalero & De Nigris, 2005), or ~8.5 -11.4 calibrated kya (Table 1).
The Milodón Norte 1 cave (CMN1, S 47˚18'22.4"71˚53'55.9"W) is currently situated ~2 km east of Lake Pueyrredón.However, at the time of human occupation, it was located close to the shore of an ancient paleolake (Horta & Aschero, 2010;Horta et al., 2011Horta et al., , 2013;;Sacchi et al., 2016).The deposit yielded vestiges of hunter-gatherers who inhabited the area up to 7.9 uncalibrated kya.Below a tephra layer deposited by one of the Hudson volcano eruptions at ~6.8 uncalibrated kya (Stern pers. comm. 2008), the lower stratigraphic layers (7 and 8) Figure 1.Map of South America and the location of Santa Cruz province and XII region in Argentina and Chile, respectively, in southern Patagonia.The Cerro Casa de Piedra 7 (CCP7), Mylodon cave north 1 (MN1) and Laguna de los Cisnes (LC) sites in Northwest Santa Cruz province, shown as a rectangle (after Google Maps, 2016).contain the remains of the initial regional occupation.Among them, there are two remarkably large unifacial tools (Figure 2(l)) that were recovered very close to one another at the bottom of and below a large inclined rock without any contextual relationship.Due to its location, material rarity, and lack of and/or scarce use, this find was considered to be a cache (Sacchi et al., 2016).Radiocarbon assays obtained from the layers containing the remains of the initial occupations of CCP7 and CMN1 are shown in Table 1.They were corrected with the , a significant number of finds were attributed to the initial Early Holocene occupation (Civalero, 2016).
Different from points, and produced from diverse materials (obsidian, chert, basalt, among others) the assemblage accompanying them include unifacial implements characterized by their morphological and dimensional variability (Gradín et al., 1976;Aguerre, 1979), and display a wide degree of resharpening (Dibble, 1995, Baena Preysler & Carrión Santafé, 2010).From a production viewpoint, many were simply made by short retouches on thin flake-blanks less than 12 mm thick.However, at the above sites others were produced from blanks thicker than those previously mentioned (e.g.Civalero & Franco, 2003, Civalero, 2016).Besides the flake-blanks clearly detached by direct percussion, a significant number display attributes that indicate bipolar flaking (Nami, 2000).
This was used to reduce exhausted percussion cores, discarded tools used as bipolar cores, and obsidian nodules probably coming from Pampa del Asador, located ~50 km from CCP7.A notable fact about this group of unifacial tools is that one blank's surface is totally or partially covered by flake scars that some-times reach the longitudinal symmetry axis.This phenomenon suggests that before finishing them with short retouches, the face was reduced by detaching flakes from the edge to its center (Figures 2(j)-(p)).Different to large flake-scars resulting from shaping the working edge of a thick unifacial tool, such as scraper planes (Gradín et al., 1987:   ), or blades and thin laminar flakes with one or two arrises (Gradín et al., 1987: Figure 22, Figure 25-27;Gradín & Aguerre, 1994: Figure 3;Onetto, 1994).These variations might be considered stylistic (Sackett, 1982;Reedy & Reedy, 1994;Nami, 1997-98).In fact, scraper production and manufacturing style (Weedman Arthur, 2008: p. 83) are issues that may be considered in our case (Civalero, 2016).We think that the particular way of making the tools reported here represents a particular type of technological knowledge (Schiffer & Skibo, 1987) mainly related to its fabrication method during the early Holocene.
In light of the aforementioned facts, it was possible to identify unifacial tools with a similar manufacturing method from other sites in southern Patagonia.In the Pali Aike volcanic region in the Chico River basin, a tool with remarkable unifacial covering flaking was exhumed from the lower levels of the Alero del Valle rockshelter (Figure 2(m), Nami, 2009).Moreover, in Fell's cave there is a specimen with these features in the layer 8, associated with triangular points and dated at 6485 ± 115 and 6560 ± 115 uncalibrated radiocarbon years (Bird, 1988: Figure 76, middle row right).Cueva del Medio in southern Chile yielded similar points both on the surface and in the stratigraphy (Nami, 1987).Interestingly, some unifacial implements from the surface show technological similarities to those found at the sites reported above (Figure 2(n)-(p)).

Concluding Remarks
Recent discoveries and observations on a set of early Holocene unifacial tools from southern Patagonia allowed deepened on a new regional technological issue.Characterized by a uniform unifacial flaked face made before and/or during the final shaping, the described artifacts emerge as a peculiar style of covering unifacial flaking with subtle production differences to other similar tools.Curiously, a resembling unifacial reduction was still in use for making certain hidescrapers in Ethiopia during the twentieth century (Gallagher, 1977;Clark, 1981;Clark & Kurashina, 1981;Weedman Arthur, 2008).Ethno-archaeological research has revealed that during the first steps of manufacture, which were carried out in a quarry, the initial unifacial shaping was done intentionally to achieve the desired thickness and to reduce weight during transportation to the place of habitation (Gallagher, 1977: 408).Interestingly, Clark (1981: Figure 3) reported a notable unused scraper resembling certain Patagonian pieces (Figure 2(q)).Worth mentioning that, in other areas of South America there are pieces that might be manufactured in a similar way.Actually, from the comparative lithic technology viewpoint (Nami, 1997) or "tortoise scrapers" (Temme, 1982: 153: 1, 157) might be cited.
Ongoing research on more archaeological and experimental specimens will provide new and complementary information to understand unknown technological topics on unifacial reduction strategies in South America.
Oxcal 4.2.4 calibration program (Bronk Ramsey & Lee, 2013) employing the ShCal13 curve for the southern hemisphere (Hogg et al., 2013).Playa Cisnes 2 (PC2, 47˚30'20.8''S, 70˚34'27.3''W) is located in a steppe environment; it is an open-air site situated on the northwest beach of the endorheic Los Cisnes lagoon.Surface and partially buried lithic finds exposed along 30 m showed a significant morphological variation, suggesting a palimpsest of arti-

Figure 4
Figure 3. (a) Flake-scars and flakes detached by soft antler percussion flaking; (b) finished circular scraper with partial unifacial reduction, (c) (d) close-up of flake-scars obtained by soft (c) and hard (d) percussion flaking; (e) example of debitage obtained with an antler billet.

Figure 4 .
Figure 4. Examples of experimental specimens made with the technical features discussed in this paper.a) large side-scraper made on a partial bifacially reduced blank by soft percussion; (b) (c) unifacial tools flaked by hard and soft percussion flaking.Materials: (a) industrial glass; (b) dacite from Paso Limay, Río Negro, Argentina; (c) Obsidian, Maule lagoon, Chile.

Table 1 .
List of uncalibrated and calibrated radiocarbon dates from the CMN1 and CCP7 sites.
facts of different ages.However, by the finding diagnostic tool (Figures2(h)-