Keywords

Introduction

Movement for gathering information, goods, or social reasons is very important in hunter-gatherer societies. Besides utilitarian reasons, obtaining knowledge and social information is essential for small-scale bands (Whallon, 2011). Networks may link persons over wide geographic regions, and the movement of goods, persons, and information may exceed the traditionally considered kinship (Binford, 2006). This topic has been studied through different lines of evidence such as obsidian transfer distances (Pearce & Moutsiou, 2014), lithic point types (Buchanan et al., 2017), shell beads (Miller et al., 2018), ostrich eggs (Mitchell, 1996) and ceramic distributions (Quinn & Burton, 2016), among many others.

In the Pampas of Argentina, some studies were conducted to evaluate interaction through the analyses of the traveling of particular artifacts. Interaction networks have been explored through the analyses of marine shell distribution (Bonomo, 2007), ceramic motifs and manufacture (Catella, 2017; Di Prado, 2018), and lithic studies (Flegenheimer et al., 2003; Politis et al., 2003; Berón, 2006; Martínez, 2017; Martínez et al., 2017; Berón et al. 2015; Messineo et al., 2019; Messineo & Barros, 2021; among others). In particular, lithic artifacts have traditionally been used in interaction studies, as their source of origin can sometimes be easily traced (Belardi et al., 2006; Pallo & Borrero, 2015). Moreover, in addition to the excellent preservation of this type of materials, good quality raw materials are usually transported over long distances (Meltzer, 1989; Kuhn, 1995).

The recent excavation of the Hangar site in the Pampas region provides valuable information on social interactions. This site is dated about 1000 years BP and has a high relative frequency of silicified limestone, a raw material not available in the nearest outcrops usually exploited (e.g., Tandilia). In addition to the presence of this rock, other characteristics differentiate Hangar from other sites of earlier periods, such as the high number of projectile points, abundant ceramic sherds, and the presence of unusual tools in the regional context such as crutch-shaped drills. In this chapter, we evaluate all these aspects, focusing on the silicified limestone frequency, the chaîne opératoire, and the probable sources of the rocks. The main objective is to evaluate and discuss the frequency and use of this rock at Hangar. These data are compared and integrated with information from other sites where silicified limestone is represented to analyze its distribution in the region. We explore aspects related to territoriality and social interaction during the end of the late Holocene. For this period, it is proposed that, in a context of high human demography, the circulation of goods, people, and ideas among different sectors of the Pampas and neighboring regions would have increased (Berón, 2004, 2007; Curtoni, 2006; Mazzanti, 2006; Curtoni & Berón, 2011; Martínez et al., 2017; Messineo & Barros, 2021).

Regional Setting and Lithic Resources of the Pampas

The Pampas of Argentina is a large ecosystem of grasslands that have been inhabited by hunter-gatherers, at least since ca. 12,200 14C years BP (Politis, 2008). This extensive plain is located in the eastern part of Argentina between 30° and 39° south latitude and 57° and 65° west longitude. The Pampas are mainly humid temperate prairies covered by grass (Soriano et al., 1992). To the south and west of this region, there is also a large number of arboreal as Prosopis caldenia belonging to the southern sector of the Espinal phytogeographic province (Oyarzábal et al., 2018). The Pampas are characterized by an east–west moisture gradient and increasing continentality toward the northwest. Average temperatures are between 20 and 24 °C in summer and 7 and 10 °C in winter. The annual total rainfall increases toward the east; from 400 mm in the southwest to 1000 mm or more in the northeast (Burgos, 1968). Typical animals of the Pampas inhabit open grasslands (Ringuelet, 1961). Today, some mammals, such as guanaco (Lama guanicoe) and pampas deer (Ozotoceros bezoarticus), are almost absent from the region, although they were abundant in the past (Merino, 2003; Politis et al., 2011).

The Hangar site is located in the basin of the Salado Creek, in the humid Pampas subregion, province of Buenos Aires, in the depressed Pampa; from a phytogeographical point of view, it corresponds to the hygrophyte and halophyte grassland unit (Oyarzábal et al., 2018). Along this basin and the nearby shallow lakes, several archaeological sites have been recorded; most of them dated to the Middle and Late Holocene (Crivelli Montero et al. 1987, 1997; Eugenio, 1994; Kaufmann & González, 2013; Barros et al., 2018). These contexts are located in the plains between two hilly systems, named Ventania and Tandilia. This inter-hill grassland presents abundant shallow lakes and streams (Zárate & Rabassa, 2005) and has no rocks available for knapping.

In the Pampas region, there are several sources of good knapping quality rocks, which were used for making tools. In the northwestern sector of the Tandilia hilly system, there is a white orthoquartzite outcrop, recently discovered at the Don Guillermo locality (Fig. 1a) (Barros et al., 2021). Approximately 40 km east, different rocks have been found such as granite, orthoquartzite SBG (Sierras Bayas Group), silicified dolomite, chert, and quartz (Fig. 1b; Politis, 1984; Messineo et al., 2004; Messineo & Barros, 2015). In the central portion of the Tandilia hilly system, there are outcrops of orthoquartzite SBG, chert, silicified dolomite, diabase, and granitoid rocks (Fig. 1c; Flegenheimer, 1991; Flegenheimer et al., 1996; Flegenheimer & Bayón, 2002; Paulides, 2007; Colombo, 2011). In the southeastern portion, there are outcrops of quartzites and quartz of the Balcarce Formation (Fig. 1d; Mazzanti, 1997; Donadei Corada, 2019; Bonnat 2021). Outcrops of silicified tuff, quartzite sandstones, and coarse-grained quartzites have been detected in the plains located between the two hilly systems (Fig. 1e; Politis, 1984; Madrid & Salemme, 1991). A wide variety of siliceous rocks, basalt, and quartzite are available on the coast of Buenos Aires province in the form of coastal cobbles and pebbles (Fig. 1f; Bonomo, 2005).

Fig. 1
A spatial map of the Pampas plots the places with silicified limestones and main lithic resources. An inset map of South America on the bottom right highlights a part of Argentina within a rectangular box.

Sites of the Pampas region with presence of silicified limestone and main lithic resources used in the region

References = (1) Meseta del fresco (source); (2) El Carancho 1 (source); (3) El Encuentro; (4) Médanos Lote 18; (5) Médanos Lote 24; (6) El Castillo; (7) Médanos de Villa; (8) Chenque 1; (9) La Casona; (10) El Molino; (11) Manantial Curacó; (12) Tapera Moreira 1; (13) Confluencia 2; (14) La Chola; (15) La Colorada Grande; (16) Médanos de Costilla; (17) Médanos de Phagouapé; (18) Médanos de Alduncín; (19) La Cascada; (20) Bajo de Atreucó; (21) Laguna La Tigra; (22) Laguna Guatraché; (23) Bajo de Marcelino; (24) Médano San Sixto; (25) Luis Otero; (26) Bajada la Minnesota; (27) El Carmel; (28) ChLillhué 1 y 3; (29) Médanos de Peñín; (30) Laguna Chapalcó; (31) Laguna de Montoya; (32) Manantial Naicó; (33) Laguna de Paisani; (34) Laguna de la Ruta; (35) Bajo del Medio; (36) Laguna del Fondo; (37) Laguna Traru Lauquen; (38) Don Isidoro 2; (39) Laguna de Rojo; (40) Laguna del Lote 4; (41) Laguna del Lote 15; (42) El Puma 3; (43) La Modesta; (44) Zoko Andi; (45) Laguna de los Pampas; (46) Laguna Giaccone; (47) Cabeza de Buey 2; (48) La Susana 1; (49) Laguna Chica; (50) Huencú Nazar; (51) Médano Santa Clara; (52) Médano La Enriqueta; (53) La Montaña sitio 1; (54) Los Chilenos sitio 2; (55) San Martín 1; (56) Laguna Chasicó; (57) Salinas Chicas; (58) Las Brusquillas 1; (59) Las Brusquillas 2; (60) La Barrancosa 2; (61) Arroyo Tapalqué 1; (62) Paso Mayor; (63) Las Toscas; (64) Laguna La Vizcacha; (65) Hangar; (a) orthoquartzite; (b) granite, orthoquartzite SBG, silicified dolomite, chert and quartz; (c) orthoquartzite SBG, chert, silicified dolomite, diabase and granitoid rocks; (d) quartzites and quartz; (e) silicified tuff, quartzite sandstones and coarse-grained quartzites; (f) siliceous rocks, basalt and quartzite; (g) rhyolite, metaquartzite and orthoquartzite; (h) metaquartzite, sandstone and quartz; (i) chalcedony, quartzite, xylopal, silicified limestones, schist and quartz; (j) basalt, chalcedony, siliceous rocks, andesite, quartzite, quartz, xylopal, rhyolite and obsidian; (k) silicified limestone (Meseta del Fresco); (l) silicified limestone (El Carancho); (m) silicified limestone (Valle Daza); EA) Escuela Agropecuaria; LS) Laguna Seca; LM2) Laguna Muscar 2; FN) Fortín Necochea. The dotted line indicates the micro-region of study

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In the western sector of the Ventania hilly system, there are outcrops of rhyolite, metaquartzite, and orthoquartzite from La Mascota, La Lola, Trocadero, and Napostá Formations (Fig. 1g; Bayón & Zavala, 1997; Oliva & Moirano, 1997; Catella, 2014). Secondary pebble and cobble deposits of metaquartzite, sandstone, and quartz are also available in the fluvial courses that drain the southwestern flank of the Ventania system, like the Sauce Grande River that reaches the Atlantic Ocean coast (Fig. 1h; Bayón & Zavala, 1997; Bayón et al., 2006). In the Chasicó-Salinas Chicas basin, there are remnants of the Tehuelche gravel mantle, which include a great lithological variety with a predominance of volcanic and plutonic rocks and a smaller proportion of chalcedony, quartzite, xylopal, silicified limestones, schist, and quartz (Fig. 1i; Oliva & Moirano, 1997; Oliva et al., 2006; Martínez et al., 2009; Catella et al., 2010, 2013; Catella, 2014).

Secondary deposits of cobbles and pebbles of the Tehuelche mantle are concentrated in fluvial valleys, such as the Salado-Curacó, Colorado, and Negro rivers (Fig. 1j; Berón, 2006; Martínez et al., 2009; Santos Valero, 2015; Carrera Aizpitarte & Berón, 2021). These deposits are composed of rocks of different lithology, among which basalt, chalcedony, siliceous rocks, andesite, quartzite, quartz, xylopal, rhyolite, and obsidian are the most important (Berón et al. 1995; Berón, 2006; Carrera Aizpitarte, 2014).

Silicified Limestone Sources

The sources of silicified limestone are located in the Espinal and Monte phytogeographic provinces (Dry Pampas subregion) and are Meseta del Fresco, El Carancho, and Valle Daza localities (Fig. 1k, l, m; Charlin, 2002; Berón, 2006; Carrera Aizpitarte et al., 2015).

The limestones of the El Fresco Formation (facies V) were described by Melchor and Casadío (1999) as oolitic grainstones, bioclastic grainstones, calcareous arenite, and peloidal grainstone with dispersed gastropods with different degrees of silicification. According to the authors, the sediments of this Formation were deposited in a depressed area, episodically occupied by a freshwater or slightly saline lake. Rubin (1990) interprets outcrops close to those of the Meseta del Fresco as deposited in a tidal plain. Recently Carrera Aizpitarte et al. (2015) described the Meseta del Fresco peloidal and skeletal limestones as partially silicified, while in others, the silicification was total and prevented to recognize the compositional characteristics of the original limestone. At Meseta del Fresco (Fig. 1k), the silicified limestone is a high-visibility source of supply, with good quality for knapping (Berón & Curtoni, 2002; Curtoni et al., 2004; Berón, 2006). The rocks show high variability of colors and differences in the degree of silicification. The range of shades goes from white and beige to pink, red, and burgundy (Berón & Curtoni, 2002; Curtoni et al., 2004). Oolites and drusites are present in the rock sectors where the original limestone has not been completely silicified (Carrera Aizpitarte & Berón, 2021).

For the El Carancho locality, there are no geological antecedents; however, according to Berón and Carrera Aizpitarte (2019), the silicified limestone outcropping there would have been deposited in a continental shallow lake environment. The materials studied from El Carancho by one of the authors (AB) showed stromatolitic texture or biolamination, so they were associated with biogenic carbonates, as a result of biological processes in environments with the presence of microbial mats. The silicified limestone recognized in the southern margin of the El Carancho shallow lake (Fig. 1l) was identified as partially opalized clay (Berón, 1996–1998, 2004, 2006; Berón & Curtoni, 2002). This one has low visibility and good quality for knapping. The shades vary from light beige to dark gray and their macroscopic characteristics are similar to the rocks found in Meseta del Fresco. However, at the microscopic level, there are differences, since the rocks of El Carancho do not show skeletal carbonate grains (Carrera Aizpitarte & Berón, 2021).

Finally, a silicified limestone source was identified in Valle Daza (Fig. 1m). This is a low abundant and low visibility outcrop. The nodules are small and the quality of knapping is poor (Charlin, 2002). This source has not been characterized so far (Berón & Carrera Aizpitarte, 2019). Until now, there is evidence that the silicified limestone that outcrops in Meseta del Fresco and El Carancho were transported to various sites in the Pampas region (Berón, 2004, 2006; Messineo, 2008; Massigoge, 2011, 2012; Carrera Aizpitarte, 2014; Santos Valero, 2015, 2017; Santos Valero & Armentano, 2017; Barros et al., 2020; Berón & Carrera Aizpitarte, 2019). However, it is also important to note that there may be sources of this raw material that have not yet been identified.

The Hangar Site

The Hangar site is located at 37°14′37.40″S and 61°14′5.04″W, on a gentle slope in the Salado Creek. In 2017, we made a collection on a surface of 11,750 m2 and we excavated 11 m2. Two radiocarbon dates were obtained on guanaco bones at the Laboratoire des sciences du climat et de l’environnement (France): 835±30 years BP (GifA18041; median of 706 years cal BP) and 1335±30 years BP (GifA18042; median of 1226 years cal BP). These dates together with geomorphological characteristics, the faunal association, and the presence of abundant pottery inform that the occupations correspond to the end of the Late Holocene. The site has been impacted by the digging action of armadillos and agricultural livestock production, which have generated displacement and fragmentation of archaeological materials (Álvarez et al., 2020).

Lithic artifacts from the site include end scrapers, projectile points, side scrapers, drills, and knives. The presence of cores, flakes, and micro-flakes indicates the manufacturing and maintenance activities of the tools. The most used rocks were chert, orthoquartzite, and silicified limestone. Artifacts manufactured by abrasion and polishing were also recovered, such as bola stones and grinding tools mainly made on granitoid rocks. The detailed analysis of the projectile points (n = 46) shows that they were made, reactivated, recycled, and discarded at the site. These would have been part of weapon systems such as bows and arrows and darts (Barros et al., 2018).

Faunal remains recovered include guanaco, greater rhea (Rhea americana), vizcacha, pampas deer, Canidae, cow (Bos taurus), different species of armadillos, and micromammals. Some of these taxa such as guanaco, greater rhea, and vizcacha show evidence of human butchery (Barros et al., 2018).

The ceramic sherds found at the site correspond to vessels with simple contours and globular or sub-globular shapes. The firing of the pieces would have involved a long, stable process under non-oxidizing conditions (Borges Vaz et al., 2022). Smoothing, brushing, and painting were recognized as finishing techniques, while decorative techniques common to the Pampas region, such as incisions and impressions, are still absent (Politis et al., 2001; González & Frère, 2010; Di Prado, 2013). Some of the sherds showed traces of soot on the external surface, suggesting that some of the containers were used for food preparation and cooking (Borges Vaz et al., 2022).

The human remains found at the site were scattered on the surface and could have been exhumed by armadillo activity in conjunction with agricultural activities. These remains were not yet dated and belonged to infants and adults. The presence of red paint on the cortical surface of a few specimens indicates that at least some of the burials are secondary (Álvarez et al., 2020).

In sum, different analyses carried out so far indicate that the Hangar would have functioned as a base camp where various activities were carried out, such as the manufacture, replacement, and conditioning of lithic artifacts, along with the butchering and cooking of different prey (Barros et al., 2018).

Materials and methods

Part of the lithic materials analyzed are those collected in the surface context. The analyses followed a technological and techno-morphological perspective in order to assess the main characteristics of the assemblages as well as to build the chaîne opératoire (Aschero, 1975, 1983; Bellelli et al. 1985–1987; Pelegrin, 1991, 1995; Geneste, 1991; Perlès, 1991; Inizan et al., 1995). First, the artifacts were separated by raw material based on macroscopic criteria. Each group was classified by artifactual categories (cores, tools, knapping products). Quantitative (e.g., length, width, thickness, weight) and qualitative variables (e.g., blank, platform, typological group of the tools) were considered. In the case of modules, the criteria proposed by Bagolini (1968) and modified by Aschero (1975) were used. The chaîne opératoire was reconstructed for the most abundant rocks, although in this chapter we present the results only for the silicified limestone.

In the case of materials from excavation, the frequency of silicified limestone was calculated for excavation and screening materials.

Five silicified limestone artifacts were selected for thin sections. The pieces chosen were those that showed the greatest macroscopic differences among them. The petrographic study enabled a comparative and tentative analysis with previously studied silicified limestones from Meseta del Fresco and El Carancho. In the samples where the depositional texture of the limestone was recognized, before siliceous replacement, the classification of Dunham (1962) was used. It is important to note that there could be other limestone facies that have not been sampled. For this reason, it is not possible to have a correlation or similarity with the whole range of silicified limestone outcroppings in the two mentioned places.

We conducted a bibliographic survey of the sites with silicified limestone in the Pampas region. For this purpose, a database was built where the following variables were recorded: site, location, chronology, presence of silicified limestone, and percentage of this rock about the total raw materials. These data were used to construct fall-off curves by plotting the proportion of silicified limestone against the distance to the sources (Renfrew et al., 1968; Renfrew, 1975). We calculate the average of the values by grouping contexts into 50 km intervals from each source (Meseta del Fresco and El Carancho) to construct a summary distance-decay model. The shape of the curve allows us to examine the relative importance of the silicified limestone as a function of distance from sources and to infer possible foraging ranges. Moreover, we used the QGIS software version 3.22.2 to produce a map using the Hot Spot Analysis tool. This tool calculates the clustering of spatial phenomena. These maps allow easy visualization to display event density or occurrence.

Results

Lithic Assemblage and Silicified Limestone Artifacts in Hangar Site

In the surface lithic assemblage, the most represented raw material is chert (n = 752; 52.26%), followed by orthoquartzite SBG (n = 399; 27.73%), and silicified limestone (n = 155; 10.77%). Among the materials recovered in silicified limestone are tools (n = 23; 1.59%) and flakes (n = 132; 9.17%) (Table 1). In the excavation of the site, 3 artifacts and 166 micro-flakes on this raw material were also recovered.

Table 1 Lithic artifacts recovered in the Hangar site
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The silicified limestone knapping objective was linked to the production of a wide variety of tools such as end scrapers (n = 9), projectile points (n = 5), crutch-shaped drills (n = 2), composite tools (n = 2), knives (n = 2), biface (n = 1), side scraper (n = 1) and retouched flake (n = 1) (Fig. 2; Table 1). For the manufacture of the end scrapers, interior flakes obtained in reduction stages after decortexing were selected. Except for one item, all end scrapers are complete and are small in size (in a range of 14.2 × 13.2 × 3.9 mm and 23.8 × 19.5 × 7.7 mm). Considering the moduli width/thickness, blanks are very thick and thick, and the length/width moduli indicate the presence of various categories such as very short, short, medium-normal, and medium-elongated. The delineation of the edges was carried out in a direct (n = 7) and inverse unifacial (n = 2) manner using marginal and summary retouching. About the projectile points, five fragments correspond to stemless artifacts. In three of them, only the base (straight and attenuated convex) is present, in one the mesial sector and the base (attenuated convex,) and in another the apex and the mesial sector. Due to their condition and degree of modification, it was not possible to characterize the selected blanks. The most common perimeter shape is the short triangular, followed by the elongated triangular, while the cross-section is asymmetrical biconvex and only in one case symmetrical biconvex. Bifacial work is important in manufacturing, which consists of extended knapping and marginal retouching (Barros et al., 2018). The analyses of the weapon system showed that two items correspond to arrows and one to a dart (Kaufmann et al., 2021).

Fig. 2
4 photos of silicified limestone artifacts in different shapes.

Silicified limestone artifacts from the Hangar site: (a) crutch-shaped drill, (b) end scraper, (c) biface, (d) projectile point. Scale = 1 cm

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Two crutch-shaped drills were also manufactured on silicified limestone. The larger item is a recycled projectile point in which the active part of the drill was shaped on the apical blade and the original attenuated convex base of the point was maintained. This is a medium-small size and medium-elongated module, which presents an oblique fracture in the active part (Fig. 2a). The second artifact has a longitudinal fracture on the active part and a longitudinal fracture on both sides of the body. Both drills were made by bifacial thinning. On the other hand, the composite tools have an end scraper edge and a notch, are complete, and were made on thick and very thick flakes, the length/width modules are represented by the category short-very wide and medium-elongated and are of small size. The delineation of the edges was made by micro-retouching and unifacial marginal retouching. Knives, with one complete artifact and one fractured artifact, were made on thin flakes and the module of length/width is medium-normal, while the size is medium-small. Edge delineation was performed by micro-retouching and bifacial retouching. The biface is complete, of medium-small size, and normal laminar module; it may correspond to the roughout of a tool. Lastly, the side scraper is fractured and made on a thick flake. Micro-retouching and unifacial retouching were used to delineate the edge. The retouched flake has a small size and short length/width module and presents summary retouching. The knapping products that are part of the assemblage (n = 121) are reduction flakes and micro-flakes, thinning flakes, formatization, and reactivation of the cutting edge, obtained by direct percussion and bipolar in a smaller proportion. These types of flakes are related to stages of finalization and maintenance of the tools.

Petrographic Thin Sections

The petrographic study made it possible to know the types of silicification present in the replaced limestone. It also allowed us to determine the presence of allochemical components and of siliciclastic clasts. The main results are described below.

Thin section # 1. Silicified wackestone. Scattered in the micrite are sparse carbonate grains (cg) and agglutinated grains (ag). Cryptocrystalline to microcrystalline quartz (mqz) and opal replace the micrite. There are also sectors of voids or fractures with bands of opal (op) and chalcedony (cl) to the center of the pore. There are also laminae of organic matter (Fig. 3).

Fig. 3
Left. 4 macroscopic views of 4 samples. Center and right. 8 microphotographs of the 4 samples, with 2 each on a row. The carbonated grains are the highest in samples 1, 2, and 3.

Macroscopic view of the analyzed samples (left); microphotographs under petrographic microscope (center and right). References: carbonate grains = cg, agglutinated grains = ag, feldspars = F, quartz grains = Qz, microcrystalline quartz = mqz, opal = op, chalcedony = cl, palisade quartz = cle, plumose chalcedony = clp, megaquartz = mgqz, s/n = parallel nicol, c/n = crossed nicols

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Thin section #2. Silicified mudstone (fine limestone) brecciated with isolated siliciclastic grains, of medium sand-sized feldspars and quartz. Limestone has been replaced by cripto- to micro-crystalline (mqz) to crypto-crystalline quartz. Chalcedony (cl) or palisade quartz (cle), and feathery chalcedony (clp) have precipitated in the fractures and pores (Fig. 3).

Thin section #3. Silicified packstone. In the silicified micrite, some agglutinated carbonatic grains, non-skeletal carbonate grains with micritic coating, pellets and grains of quartz and feldspars are observed. The micrite was replaced by micro-crystalline to crypto-crystalline quartz. Presents voids coated by bands of opal, chalcedony, or palisade quartz and sometimes mega-quartz have precipitated into the fractures (Fig. 3).

Thin section #4. Silicified packstone. Several sectors are observed, some with banding, others with some allochemical components such as subspherical non-skeletal carbonate grains with a micritic coating (possibly oolites with surface coating), agglutinated grains, and others with carbonate lithic clasts. The limestone is replaced by micro-quartz and the allochemical components by opal and chalcedony. In the banded sector, the replacement is by opal and micro-quartz. Opal, chalcedony, and meso-quartz have precipitated in the void or fractures (Fig. 3).

Thin section #5. Silicified grainstone to packstone with subspherical nonskeletal carbonate grains with a micritic coating (possibly surface oolites) and agglutinated grains. Limestones are replaced by micro-quartz and allochemical components by opal and chalcedony. No banded sectors were seen (Fig. 3).

The results of the thin-section analysis indicate that the silicified limestones of Hangar present biogenic carbonates, as a result of biological processes in environments with the presence of microbial mats. The observations made in the present work have not allowed us to find allochemical components such as ooids, skeletal fragments, peloids, etc., typical of the not totally silicified limestones of the Meseta del Fresco. On the other hand, simple dispersed carbonate clasts (with a superficial micritic envelope), carbonate aggregates gathered by biofilms, banding of organic matter, and carbonate layers (biolamination), which were later silicified, were recognized. These petrographic characteristics lead to postulate a biogenic origin of the materials associated with the development of microbial mattes. Based on the results obtained in this study, lithological and genetic similarity is found between the materials of El Hangar site and those of El Carancho locality.

Distribution and Fall-off Curves of Silicified Limestone

Sixty-five sites with 80 contexts with the presence of silicified limestone were recorded. The chronological range goes from 7400 years BP to the end of the nineteenth century. Most of the contexts (n = 30) could be assigned to the Late Holocene, while others were dated to the initial (n = 10) and final (n = 7) Late Holocene and historical period (n = 3). Six of the contexts correspond to the middle Holocene, one to the early Holocene, and in 23 cases, the chronology is unknown.

In the first place, two graphs were made with the percentages of silicified limestone in archaeological contexts in the Pampas region and their distance to the sources of Meseta del Fresco and El Carancho, respectively. When Meseta del Fresco is considered as the zero point (Fig. 4a), a low frequency of silicified limestone is observed in the contexts located less than 200 km from the source (Fig. 4a). Between 200 and 300 km, there are more sites and higher percentages of this rock. Then, the percentages and the number of sites with this raw material start to decrease. On the other hand, if El Carancho is considered as the zero point (Fig. 4b), the largest number of sites and highest percentages of silicified limestone are located in the first 250 km. Then, low frequencies are recorded, up to 500 km, which is the last context with this rock. The Hangar site, in both cases, is located in the low-frequency zone of silicified limestone, but it stands out from the rest of the contexts due to its higher percentage of this rock.

Fig. 4
A and B. 2 scatterplots plot negative correlations between silicified limestone versus Meseta Del Fresco and El Carancho respectively. C. A hotspot analysis map plots the archaeological sites, silicified limestone sources, and the silicified limestone percentage. The highest silicified limestone percentage is around Valle Daza and El Carancho.

Silicified limestone sites distribution and distance to the main sources. (a) Scatter graph and trend line showing the distance to Meseta del Fresco (x-axis) and the proportion of silicified limestone (y-axis); (b) Scatter graph and trend line showing the distance to El Carancho (x-axis) and the proportion of silicified limestone (y-axis), (c) Hot Spot Analysis Map

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Among the sites with high frequencies of silicified limestone (around 50% and higher) are Don Isidoro 2, Laguna Traru Lauquen, Laguna del Fondo, Laguna de Paisani, Laguna de Montoya, Médanos de Peñín, and Laguna Chapalcó (Charlin, 2002; Berón, 2004; Carrera Aizpitarte, 2007, 2014). Distances from these sites to El Carancho vary between 8 and 136 km (Supplementary Table 1). With percentages of around 20–30% are El Molino, Médanos de Phagouapé, Laguna La Tigra, El Carmel, Laguna de la Ruta, Médano Santa Clara, and the Laguna Chasicó sites (Berón, 2004; Carrera Aizpitarte, 2007; Catella, 2014; Berón et al., 2015; Páez, 2021; Santos Valero & Messineo, 2021). Distances from these sites to El Carancho vary between 72 and 213 km. The remaining sites, with lower percentages of silicified limestone, are found between 78 and 501 km from El Carancho (see Fig. 4c; Supplementary Table 1).

Second, the fall-off curves were constructed, again considering the distance to the two sources mentioned above. In the case of Meseta del Fresco (Fig. 5a), an atypical curve is observed, since in the first 200 km the percentages of silicified limestone are low and gradually rise to their maximum peak, in the range of 200–250 km. Then, the curve descends, although there is a slight increase that corresponds to the range of distances in which the Hangar contexts are found (500–550 km from Meseta del Fresco). Concerning El Carancho (Fig. 5b), a more expected curve is observed, given that the frequencies of silicified limestone are high in the first 100 km and begin to decrease until 250 km, where it stabilizes at low percentages, except for Hangar (300–350 km from El Carancho).

Fig. 5
2 line graphs plot the initial inclining and declining trend for silicified limestone versus Meseta Del Fresco and the initial declining and plateauing trend for silicified limestone versus El Carancho.

Fall-off curves of silicified limestone in relation to the distance to the mains sources. (a) Distance to Meseta del Fresco, (b) Distance to El Carancho

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Discussion

The Hangar is a site with low integrity as it has been affected by formation processes such as the action of tillage and animals of fossorial habits (Álvarez et al., 2020). However, it is characterized by a high temporal resolution (sensu Binford, 1981) with occupations concentrated at the end of the Late Holocene, which allows us to discuss some chronological trends. About the lithic assemblage, silicified limestone is the third most represented rock. The artifact assemblage made from this raw material includes tools, flakes, and micro-flakes. This rock could have entered the site in the form of prepared cores and bifaces (Kelly, 1988) from which flakes were extracted to manufacture tools such as end scrapers or were bifacially reduced to make projectile points. In some cases, these artifacts could also have entered the site already finished (e.g., projectile points) or in an advanced state of manufacture. Moreover, through bipolar reduction, it was sought the production of blanks on which several typological groups were made. However, evidence indicates that the façonnage was the main process for the manufacturing of projectile points, and end scrapers. Likewise, the presence of micro-flakes is mainly evidence of the maintenance of the edges of the tools. A case of recycling (sensu Schiffer, 1987) was also recorded on this rock; a drill was shaped on a projectile point that kept its original attenuated convex base.

Regarding the source of origin of the silicified limestone, petrographic analyses indicate that raw material found in Hangar can be linked with the studied sections of the outcrops in the El Carancho locality. The presence of agglutinated grains and non-skeletal carbonate grains, among other characteristics, indicates that these are biogenic carbonates, as a result of biological processes in environments with the presence of microbial mats. Still, it is not discarded that beyond these general trends, rocks from Meseta del Fresco and perhaps from sources such as Valle Daza or others that have not yet been identified may have been used. However, when considering the fall-off curves it is clear that Meseta del Fresco would not have been the main source of the rock for the studied assemblages. This is based on the low frequencies recorded at the sites closest to this source and the high increase near El Carancho, which would be the main place of supply. However, sampling biases cannot be discarded, given that survey in the Meseta del Fresco area is still under development.

The shape of the El Carancho fall-off curve shows a wide range of action, reaching up to 500 km from the source. The most intense use of the rock occurs in the first 100 km, where it is likely to be acquired as part of the groups’ mobility circuits (Binford, 1979). At greater distances, where low frequencies are recorded, acquisition through interaction with other groups is more likely. These trends are observed diachronically, averaging occupations of different chronologies, most of which correspond to the Late Holocene. At this point, it is interesting to mention the case of Hangar, which stands out for its percentage of silicified limestone (10%) about the other sites in the Salado basin.

In the references on the study microregion, there is no data on the presence of silicified limestone in the sites, although two projectile points manufactured on this rock were found on the surface of the Escuela Agropecuaria site (see Supplementary Fig. 1). These points were found by local settlers and are not part of the analyzed collection from this site. It is different from what occurs in the Hangar site, where the frequency of silicified limestone is relatively high about the distance of its sources. This, together with the record of several crutch-shaped drills, is associated with a chronology of the final Late Holocene (from ca. 1000 years BP to the European conquest; Quintana & Mazzanti, 2001). As different researchers have stated, in the Pampas region and neighboring areas, during the last millennia, there was a sustained process of complex social interactions that triggered, among other aspects, the exchange of goods of various kinds. The dynamics of the complexification process generated mechanisms of social articulation such as exchange, parental or political alliances, and specific long-distance travel, which connected the different hunter-gatherer groups (e.g., Barrientos, 1997, 2001; Martínez, 1999; Madrid & Barrientos, 2000; Politis & Madrid, 2001; Pedrotta, 2005; Mazzanti, 2006; Oliva et al., 2006; Catella, 2014; Berón et al., 2015).

The use of lithic raw materials at the Hangar as well as other contextual evidence from the site allow us to propose some ideas about territories, social interactions, and access to outcrops in the Pampas region. It is important to emphasize that these are hypotheses that will have to be tested based on future analyses. The final Late Holocene occupations of Hangar, as seen in this chapter, present a frequency of silicified limestone that is above that observed for other sites in the area. On a micro-regional scale, this context differs from other sites in the Salado basin by registering very even frequencies of orthoquartzite and chert. In sites such as Escuela Agropecuaria (Crivelli Montero et al. 1987–88; 1997; Eugenio, 1994; Ríos Malan, 2022), Laguna Seca (Barros et al., 2018), Fortín Necochea (Silveira, 1992; Crivelli Montero et al., 1997), and Laguna Muscar 2 (Barros et al., 2018; Kaufmann et al., 2019) orthoquartzite is present with percentages of ca. 60%, followed by chert with ca. 30%. We propose that chronology would be a very important aspect to consider to understand these results. The Hangar occupations support the idea that in a context of high human demography, the circulation of goods, people, and ideas between different sectors of the Pampas and neighboring regions will have increased (Mazzanti, 2006; Berón, 2007; Curtoni, 2007a; Berón et al., 2015; Martínez et al., 2017; Messineo & Barros, 2021). Beyond the presence of western rocks in the east, it is important to note that the reverse trend has also been recorded. Several researchers have noted the presence of orthoquartzite tools, such as side scrapers, in the western sites (Carrera Aizpitarte, 2014; Berón et al., 2015; Heider, 2015, 2016).

In this context, it is proposed that during the final Late Holocene, there was a greater social interaction among the hunter-gatherer bands occupying the Pampas region; the west-central portion of the Pampas region may have been part of a shared territory. The material evidence and the typological groups represented in the sites are in accordance with this proposal. A characteristic item of all these is the projectile points. These are medium and small-sized, triangular, stemless, and with straight to convex bases. These points are predominantly manufactured with rocks from the Tandilia hilly system such as orthoquartzite and chert (Messineo & Barros, 2021). Some projectile points with similar characteristics are made with rocks from the Ventania hilly system and silicified limestone. These items are also found in Central Pampean Dune fields (Messineo et al., 2019) and the Dry Pampas (Berón, 2004; Heider, 2015). Crutch-shaped drills are another type of artifact that share designs and rocks in several sites in the Pampas region, generally associated with Late Holocene chronologies. These artifacts are present in different areas of the Pampas such as the inter-hill plains (Bórmida, n.d.; Eugenio, 1994; Pedrotta, 2005), southern Pampas (Torres, 1922; Bayón et al., 2006; Vecchi et al., 2013), western Pampas (Viani, 1930) and the Dry Pampas (Berón, 2004; Carrera Aizpitarte et al., 2013).

In general, it has been proposed that during the Holocene, in the inter-hill area, access to the most distant sources, such as silicified limestone, did not occur through direct access to the sources, but rather exchange strategies were developed between groups occupying different territories (Messineo, 2008). By the time of the final Late Holocene, evidence from the Hangar indicates a change in the management of lithic resources. The procurement of orthoquartzite, chert, and silicified limestone could have been carried out under the same mobility system. This is referred to by some authors as direct access, meaning the size of the territory or foraging range that a human group usually occupied, and which is associated with social interaction among hunter-gatherer societies (Bamforth, 1986, 1990; Kuhn, 1995; Mangado, 2006; Hughes, 2011; Pallo & Borrero, 2015; Seeman et al., 2020). This increase in the frequency of these rocks occurs even in sectors of the territory far from these sources. The presence of rocks from the Pampean Caldenal in the northern sector of the Inter-hill plains and the southwest of the dune field, as well as the presence of orthoquartzites from Tandilia in the Caldenal, show a strong social interaction between these human groups. The interaction between the xerophytic forest environments in the western Pampas and the northwest sector of the Inter-hill plains would have been generated through the natural corridors. One of the most important was formed by a series of interconnected shallow lakes called Las Encadenadas. This corridor functioned as a very important route in historical times. According to several historic sources, this was called Camino a Salinas Grandes or Rastrillada de los Chilenos (Road of the Chileans) (García [1810](1969)). This consisted of a group of routes used by indigenous people to head cattle from Argentina to Chile. This route was also used by Argentina to obtain salt from the shallow lake system known as Salinas Grandes. Some authors (Berón, 2006; Berón et al., 2017; Curtoni, 2007b) indicate that this route constituted one of the main nodes in the organization of indigenous movements connecting the Humid and occidental Pampas. We propose that this route would have functioned as a corridor for the circulation of information, people, and goods and that it would have had an important time depth, dating back at least a thousand years BP.

Final Remarks

In this chapter, we evaluated and discussed the existence of social interaction based on the distribution of silicified limestone in different sites of the Pampas region. The evidence studied allowed us to determine that this raw material entered the Hangar site in the form of prepared cores and bifaces as well as finished tools. Different activities were carried out with this rock and different types of artifacts were manufactured. Its acquisition could have been by interaction or direct access. Although the evidence does not allow us to differentiate between these two options, we can propose that there was access to the silicified limestone source. Moreover, the petrographic analysis showed this source would be linked to the outcrops in El Carancho locality, which are biogenic carbonates resulting from biological processes. The fall-off curve is in accordance with these data, showing an intense use of silicified limestone in the first 100 km from the source. At greater distances, lower frequencies are recorded, and the Hangar site stands out for its percentage of 10% at a distance of 340 km. According to this curve, the silicified limestone source of El Carancho would have been widely used by the groups that inhabited the Pampean Caldenal and its presence would have reached very distant areas of the Pampas, such as the plains located between the Tandilia and Ventania hilly systems.

Considering different lines of evidence such as lithic projectile point types and raw material percentages, it is proposed that during the final Late Holocene, the west-central portion of the pampas region could have been part of a shared territory. In these periods, there was a context of higher human demography, and consequently, the circulation of goods, people, and ideas increased. These data are in accordance with the results already discussed by other researchers, who proposed a scenario of social complexity for the Late Holocene periods. In this sense, some corridors that connected nodes would have functioned for the circulation of information much earlier than in already-known historical times.