# Living on sand. A functional and PDSM analysis of obsidian and other volcanic rock tools from two coastal settlements: Playa Chica and Dunas de Maspalomas (Gran Canaria, Spain)

Idaira Brito-Abrante, Laurence Astruc, Jonathan Santana, Jacob Morales, Amelia Rodríguez-Rodríguez

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Idaira Brito-Abrante, Laurence Astruc, Jonathan Santana, Jacob Morales, Amelia Rodríguez-Rodríguez. Living on sand. A functional and PDSM analysis of obsidian and other volcanic rock tools from two coastal settlements: Playa Chica and Dunas de Maspalomas (Gran Canaria, Spain). Archaeological and Anthropological Sciences, 2025, 17 (6), pp.129. 10.1007/s12520-025-02245-z. hal-05489764

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# Living on sand. A functional and PDSM analysis of obsidian and other volcanic rock tools from two coastal settlements: Playa Chica and Dunas de Maspalomas (Gran Canaria, Spain)

Idaira Brito-Abrante<fnref n="1" /> ID · Laurence Astruc<fnref n="2" /> ID · Jonathan Santana<fnref n="1" /> ID · Jacob Morales<fnref n="1" /> ID · Amelia Rodríguez-Rodríguez<fnref n="1" /> ID

Received: 5 February 2025 / Accepted: 6 May 2025 / Published online: 21 May 2025
© The Author(s) 2025

## Abstract

The state of the surfaces of prehistoric stone tools must be assessed before initiating traceological research as they may have suffered from post-depositional surface modifications (PDSM) stemming from sediment and aeolian abrasion and trampling that could have eliminated their original use-wear traces. PDSM research not only serves to avoid misinterpreting the use-wear but can shed light on formation processes of archaeological sites. Recognising these modifications helps determine the choice of which stones to study, especially in the case of industrial volcanic rock assemblages where use-wear analyses require a deep understanding of their physical characteristics. Observations of tools from two coastal indigenous settlements on the Island of Gran Canaria, notably Playa Chica (sixth-thirteenth centuries AD) and Dunas de Maspalomas (eighth-eleventh centuries AD), reveal the problems of identifying the use-wear in the framework of activities carried out in open, sandy environments. Moreover, the composition and granulometry of the sands of each site differ. The objective of this study is thus to identify the effects of the mechanical alterations provoked by these sands on the macro and micro use-wear of the different archaeological tools hewn from obsidian and other volcanic rocks. This was carried out by means of a programme of experimentation involving knapping a series of tools of both obsidian and other volcanic rocks, working them with different types of contact materials (animal and plant) to observe their use-wear, and ultimately simulate the PDSM they suffered in a vibration device using sand samples collected at each of the two sites. The findings shed new light on the post-depositional taphonomic alterations affecting the surfaces and use-wear of archaeological volcanic rocks tools.

**Keywords** Use-wear analyses · PDSM (post-depositional surface modification) · Sand · Experimentation · Volcanic rocks · Canary Islands

## Introduction

Archaeology attempts to offer responses to questions concerning the evolution of human behaviour through the study of material evidence. Stone tools were one of the most important artefacts for the survival of ancient societies (Odell 2000; Key et al. 2020). Understanding the purpose of

their design and use serves to explore issues related to technological evolution, adaptive processes, and the adoption of different cultural strategies or dynamics (Tomasello 1999; Whiten and Van Schaik 2007; Brown et al. 2012; Marreiros et al. 2020). Stone tool functional analyses also yield significant information regarding these questions. They allow identifying and interpreting the traces left on tools resulting from working different types of contact materials, as well as cast light on voluntary and involuntary actions affecting them. It is nonetheless often difficult to come to good diagnoses as many of these pieces have suffered from PDSM processes (Keeley 1980; Levi-Sala 1986) that have eliminated their original use-wear. Whether anthropic (mechanical, such as trampling or digging, and human-generated chemical effects) or natural (aeolian and water abrasion, alterations stemming from animals or plants), these post-depositional

<figure><img src="image_2.png" /></figure>

<footnote>Idaira Brito-Abrante
idaira.brito@ulpgc.es</footnote>

<footnote n="1">¹ Tarha Research Group, Departamento de Ciencias Históricas, Universidad de Las Palmas de Gran Canaria, C/Pérez del Toro, 1, 35001 Las Palmas de Gran Canaria, Canary Islands, Spain</footnote>

<footnote n="2">² ArScAn (UMR7041), VEPMO, CNRS, Université Paris I-Université Paris Ouest Nanterre, Paris, France</footnote>
processes not only can have an effect on lithic assemblages but other artefacts as well. Observations of the impact of post-depositional processes on stone tools, first on siliceous and metamorphic materials, have yielded significant information serving to understand archaeological sites (e.g., Márquez et al. 2001; Lemorini et al. 2014; Bustos-Pérez and Ollé 2024). However, this type of research on volcanic lithic industries remains rare (Asryan et al. 2014).

The indigenous settlements of Gran Canaria (Canary Islands) established along the coast offer the possibility of exploring the post-depositional processes that altered their raw materials as they were subjected to a combination of anthropic and wind/sand actions. The Canary Islands is a volcanic archipelago off the northwestern coast of Africa. Although there is evidence of early sojourns by Romanised seafarers, the first permanent settlements were established around the turn of the era by Amazigh groups originating in the Maghreb (Serrano et al. 2023). Although this colonisation was homogeneous and took place relatively rapidly, inter-island contacts subsequently broke down after only a few centuries leading each isle, despite sharing common features, to develop its own culture (Santana et al. 2024). The settlers adopted agropastoral economies combining the cultivation of cereals and legumes of Mediterranean origin with collecting native wild species (Morales et al. 2023). Their livestock consisted of goats, sheep, and pigs, and there is evidence they consumed marine resources such as ichthyofauna and malacofauna (Rodríguez-Santana 1994; Castellano-Alonso et al. 2016). The ensuing Castilian conquest of the archipelago in the fifteenth century ultimately led to drastic changes and a relatively rapid demise of the indigenous cultures (Brito-Mayor et al. 2023).

The adaptation of the indigenous populations to the different isles of the archipelago was conditioned, among other aspects, by the absence of metal ores. This led them to knap tools from stones, notably obsidian and other volcanic rocks such as basalt, trachyte, and phonolite (Rodríguez-Rodríguez and Francisco 2012; Rodríguez-Rodríguez et al. 2017). Traditionally, the study of these tools has focused on technological processes applied to their production and typology. The knapping techniques consisted mainly of direct percussion with hard tools (hammerstones) and, to a lesser extent, soft percussion tools (wood). Indirect percussion has only been identified in the manufacture of rotary querns (Naranjo-Mayor and Rodríguez-Rodríguez 2015; Lacave Hernández et al. 2024). Obsidian, especially small fragments, was knapped by means of the bipolar anvil technique (Galván Santos and Hernández Gómez 1996; Rodríguez-Rodríguez 1993). The different methods mainly intended to yield flakes, although other specific artefacts were also designed, notably picks, bifacial tools, and large-edged scrapers. Little traceological research has to date been carried out on the stone tools of the Canary Islands. The few studies, centred

mainly on the islands of La Palma, Tenerife, and Gran Canaria, highlight the use of stones to work plant, animal, and mineral materials (Rodríguez-Rodríguez 1993, 1998; Naranjo-Mayor and Rodríguez-Rodríguez 2015). As there is currently a trend towards more exhaustive research on the function of stone tools, it is necessary to likewise focus on the post-depositional alterations affecting their surfaces.

The initial observations of the traceological analyses of the archaeological tools from the two ancient coastal settlements of this study revealed that they suffered from severe PDSM alterations. This led to the current experimental programme intended to specifically identify and classify the taphonomic processes affecting the macro and micro-wear of the obsidian and other volcanic rock tools provoked by the different sands characteristic of the environments of each of the two archaeological sites.

# Material and method

## Archaeological framework

The archaeological materials examined in this study are from two sites (Fig. 1) located on opposite sides of the island of Gran Canaria: Playa Chica (PC) and Dunas de Maspalomas (DUMAS).

Playa Chica (Municipality of Gáldar) (Fig. 1c) is a beach line rock shelter that was occupied between the sixth and thirteenth centuries AD. Its stratigraphy, combining layers of dark volcanic sand and pebbles is almost two metres thick, has been completely uncovered by intense marine erosion. The sequence comprises five phases of occupation each associated with features, notably numerous well-preserved combustion structures. The layers consist of fine beach sand capped by a layer of gravel stemming from the weathering of the shelter's natural wall. Each of the phases yielded organic elements, notably remains of the fuel and waste generated by human activities. The investigations carried out to date have identified two areas separated by a wall. Excavations in Zone 1 were limited to recording the site's most recent phase of occupation. This consisted of an open space covered by a roof of perishable materials that saw use between the eleventh and thirteenth centuries (Table 1). Activities during this phase took place on a loose, sandy layer marked by numerous hearths, at times quite large, each revealing multiple uses. Although this sector shows signs that the suits were mainly oriented towards the processing of fish and shellfish, there is evidence of a domestic consumption of terrestrial fauna and cereals. The fauna is dominated by the osteological remains of various species of fish, as well as by a vast quantity of fish scales. This zone has also revealed a compelling bone industry linked to fishing (fishhooks and modified goat horns for scaling).

<figure><img src="image_3.png" /></figure>
<figure><img src="image_4.png" /><figcaption>**Fig. 1** a) Map of the Canary Islands archipelago indicating its location off the northwestern coast of Africa; b) detail indicating the position of the island of Gran Canaria; c) detail of Gran Canaria with the position of the sites of Playa Chica (PC) and Dunas de Maspalomas</figcaption></figure>

(DUMAS); d) view of lithic artefacts in the sandy matrix of Phase I of PC; e) view of lithic artefacts and other archaeological materials in the sandy layer of DUMAS

The excavation of Zone 2, smaller than Zone 1, also revealed an earlier stratigraphic sequence corresponding to the shelter's oldest phases. Following a sequence from most recent to oldest, the second phase of Playa Chica, only excavated in Zone 2, is centred around a dry-stone building that is very damaged by sea erosion. It contained a beaten earth floor that extended beyond the walls unifying both areas of the site. This floor capped a third phase dating between the seventh and ninth centuries AD. The

fourth phase, only identified in the profile of Zone 1, has not yet been excavated. It comprises a succession of beaten earth floors yielding a great number of archaeological materials ranging between the seventh and eighth centuries. This phase in Zone 2 is represented by a fill comprising stones and archaeological finds in secondary position, that attained, in the northern profile of the trial trench, an alignment of stones in Zone 1. This stone alignment, in turn, limited the extension of the beaten earth floor. It
<table><caption>**Table 1** Radiocarbon datings of the sites of Playa Chica (PC) and Dunas de Maspalomas (DUMAS)</caption><thead><tr><th>Site</th><th>Zone</th><th>Phase</th><th>Strat. unit</th><th>Material</th><th>Species</th><th>Quantity</th><th>LabID</th><th>CRA</th><th>Error</th><th>Calib-<br>trated<br>(68%)</th><th>Calib-<br>trated<br>(95%)</th><th>Method</th><th>Reference</th></tr></thead><tbody><tr><td>Playa Chica</td><td>1</td><td>V</td><td>24</td><td>Bone</td><td>Capra hircus</td><td>Singular</td><td>Beta-457376</td><td>1460</td><td>30</td><td>590</td><td>645</td><td>560</td><td>650</td><td>AMS</td><td>Santana et al. 2024</td></tr><tr><td>Playa Chica</td><td>1</td><td>IV</td><td>27</td><td>Bone</td><td>Sus domestica</td><td>Singular</td><td>Beta-457377</td><td>1370</td><td>30</td><td>640</td><td>675</td><td>600</td><td>775</td><td>AMS</td><td>Santana et al. 2024</td></tr><tr><td>Playa Chica</td><td>2</td><td>III</td><td>1009</td><td>Charred seed</td><td>Hordeum vulgare</td><td>Singular</td><td>Beta-593529</td><td>1240</td><td>30</td><td>690</td><td>870</td><td>675</td><td>880</td><td>AMS</td><td>Morales et al. 2023</td></tr><tr><td>Playa Chica</td><td>1</td><td>I</td><td>2</td><td>Charred seed</td><td>Laurus novocanar-<br>iensis</td><td>Singular</td><td>Beta-593527</td><td>880</td><td>30</td><td>1155</td><td>1220</td><td>1045</td><td>1230</td><td>AMS</td><td>Morales et al. 2023</td></tr><tr><td>Playa Chica</td><td>1</td><td>I</td><td>2</td><td>Charred seed</td><td>Pinus canariensis</td><td>Singular</td><td>Beta-593528</td><td>870</td><td>30</td><td>1160</td><td>1220</td><td>1045</td><td>1265</td><td>AMS</td><td>Santana et al. 2024</td></tr><tr><td>Dunas de Maspalo-<br>mas</td><td>1</td><td>I</td><td>2</td><td>Charred seed</td><td>Hordeum vulgare</td><td>Singular</td><td>Beta-359513</td><td>1200</td><td>30</td><td>780</td><td>885</td><td>705</td><td>945</td><td>AMS</td><td>Rodríguez-Rodríguez<br>et al. 2021</td></tr><tr><td>Dunas de Maspalo-<br>mas</td><td>1</td><td>I</td><td>2</td><td>Charred seed</td><td>Vicia faba</td><td>Singular</td><td>Beta-359511</td><td>1120</td><td>30</td><td>890</td><td>980</td><td>770</td><td>995</td><td>AMS</td><td>Rodríguez-Rodríguez<br>et al. 2021</td></tr><tr><td>Dunas de Maspalo-<br>mas</td><td>1</td><td>I</td><td>2</td><td>Charred seed</td><td>Hordeum vulgare</td><td>Singular</td><td>Beta-359512</td><td>1050</td><td>30</td><td>985</td><td>1030</td><td>895</td><td>1035</td><td>AMS</td><td>Rodríguez-Rodríguez<br>et al. 2021</td></tr></tbody></table>

is probable that this alignment, perpendicular to the wall of the shelter, formed part of some type of building. This phase capped a level of collapse of blocks from the cliff that simultaneously covered a fifth phase associated with another stone structure observed in the profile of Zone 1 (dated to between the sixth and seventh centuries) which extends throughout the shelter. Archaeological finds from Zone 2 are more characteristic of domestic contexts: pot-sherds, bone and stone tools, and medium-sized domestic fauna such as goat (*Capra aegagrus hircus*) and pig (*Sus scrofa domestica*). This area also yielded carbonised carpological materials: barley (*Hordeum vulgare*), wheat (*Triticum sp.*), lentil (*Lens culinaris*), broad bean (*Vicia faba*), and fig (*Ficus carica*).

The knapped stones from PC consist mainly of coarse-grained volcanic rocks (basalt, trachyte and phonolite) and obsidian. The first were beach cobbles collected near the settlement. Obsidian can be broken down into trachytes and phonolities. Neither is not found locally meaning they had to be procured elsewhere on the island. The first comes from mines in the island's western area. The source of the second, less common, is currently unknown (although small blocks can be collected in secondary contexts especially in the south and southwest of the island). Most of the coarse-grained flakes are not the result of *plein débitage*. They are cortical or semi-cortical fragments stemming from the first phases of knapping pebbles and blocks, a common strategy of coastal sites of Gran Canaria (Rodríguez-Rodríguez et al. 2022). The flakes have well-developed bulbs indicative of direct percussion with stone hammers. The small size of the obsidian suggests it was knapped by means of the bipolar technique, which consisted of placing a core or fragment on a stone anvil and applying direct percussion with a hard hammer. This technique does not generate standardised products and its flakes bear scars oriented in opposite directions. Only several obsidians and very few coarse-grained volcanic rock flakes bear signs of retouches in the form of notches and denticulations (0.8%).

The second site, Dunas de Maspalomas (Municipality of San Bartolomé de Tirajana) (Fig. 1c), is an open-air settlement on a dune field stabilised by vegetation. Occupied intermittently between the eighth and eleventh centuries, it rested directly on a dark yellowish sand containing a mixture of volcanic clasts and bioclasts mainly of plant origin (e.g., coralline algae). The site has been interpreted as a seasonal camp devoid of any significant construction. It was presumably linked to the use of pastures and to an opportunistic exploitation of coastal resources. Its materials are spread around a large combustion structure that saw multiple uses. Finds include domestic fauna such as goat (*C. aegagrus hircus*) and marine resources (ichthyofauna, and malacofauna). Here the carpological remains are rare, limited to a modest

<figure><img src="image_5.png" /></figure>
range of cultivated plants: barley (*H. vulgare*), beans (*Vicia/
Pisum* sp.), and fig (*F. carica*). Although finds of knapped
stones are relatively abundant, pottery and bone are scarce.

The stone tools at DUMAS consist mainly of coarse-
grained volcanic rocks, once again dominated by phonolite,
and a lesser quantity of basalt knapped from cobbles and
blocks collected near the settlement. As at PC, the knapped
flakes are mostly cortical, although there are also some
examples of mainly multidirectional and unidirectional *plein
debitage*. They reveal well-developed bulbs, indicative of
direct percussion with stone hammers. Once again, the per-
centage of retouched pieces is very low, even lower than at
PC (0.4%). Obsidian is less common. Here again there are
types: trachytites and phonolites. The more common trachyt-
ites were extracted from the mines cited above, meaning that
DUMAS is so far the site on Gran Canaria the most distant
from the source of this rock. The phonolitic obsidian, on the
other hand, possibly is from a nearer, unknown, outcrop to
south of the island. These volcanic glasses were knapped
also with the bipolar technique (Rodríguez-Rodríguez et al.
2021).

Criteria serving to select the lithic industry
for the use-wear analysis

The morpho-technical analysis of the prehistoric stone
tool assemblages of the two sites resorted to the methods
advanced by previous research on Canarian volcanic rocks
(Galván Santos et al. 1987; Rodríguez-Rodríguez 1993).
This consisted of combining the Analytical Logic System
with proposals from the French school (Tixier et al. 1980;
Carbonell et al. 1983; Rodríguez-Rodríguez and Francisco
2012). Furthermore, the types of raw materials, identified
de visu, were verified by geochemical analysis. Size was the
first criterion of selection for the use-wear analysis. This
consisted of selecting both cortical and *plein debitage* flakes
of coarse-grained rocks surpassing 3 cm in length. Debris
and chunks were discarded. The criterion for selecting the
obsidian flakes was that they surpass 1 cm in length. A sec-
ond criterion was the presence of a usable edge. This meant
excluding all fragments and flakes with irregular edges. The
preliminary analysis focused on 96 artefacts. It is noteworthy
that this test revealed that many of their surfaces had been
altered, an observation that led to developing the current
experimental programme.

The experimentation (working contact materials
to generate use-wear)

The first step of the experimental programme consisted of
knapping 44 flakes (22 obsidian; 22 coarse-grained volcanic
rocks) by direct percussion with a hard basalt hammerstone.

Forty were then used in the second step to work a series of animal and plant contact materials (Table 2). The resulting experimental use-wear on their surfaces was then precisely described and recorded graphically to be able to later compare it with that produced in the subsequent phase. The description applied the common specialised vocabulary (scars, rounding, abrasion, striations, and polish) gleaned from traceological research (Mansur-Franchomme 1986; Hurcombe 1992; Rodríguez-Rodríguez 1998; Kononenko 2011; Huidobro 2018; Brito-Abrante and Rodríguez-Rodríguez 2024). The traces of use along the edges of each piece were precisely identified and recorded for re-analysis after their alteration during the experiment. The criteria serving to describe the experimental alterations derives from research focusing on scar presence, position, and morphology, striation type and disposition, friction polish, the presence of holes and micropits, and patina (Anderson 1980; Keeley 1980; Levi-Sala 1986; McBrearty et al. 1998; Burroni et al. 2002; Thiébaut 2007; Mazzucco et al. 2013; Asryan et al. 2014).

Simulating post-depositional surface alterations
with a mechanical vibrating device

The second phase of the experimental programme consisted
of subjecting the surfaces of the tools marked by traces use-
wear from contact materials to simulated PDSM processes.
For this, the experimental tools were placed in circular metal
canisters containing 2 cm of volcanic sand from each of the
two archaeological sites. The results of the measurement of
the diameters of 50 grains of sand from each site indicate
the sand from PC to be coarse while that from DUMAS to
be fine, with a granulometry affected by aeolian actions.
The tools were then subjected to artificial vibration with an
electromagnetic sieve (Fig. 2) during intervals of 20 min
(20'and 40') at a speed of 3000/3600 vibrations per minute
which led to a displacement of the tools in the sand, an effect
intended to simulate dragging and friction. The simulations
in the mechanical device were initially carried out on groups
of four experimental tools at a time. They were later repeated
with only one tool at a time of each type of rock which had
served exclusively to process a hard animal contact material
(pig or boar tooth enamel). The reasoning behind the one
tool at a time simulations was to avoid the potential effects
of collisions between tools.

Cleaning and optical equipment

The experimental pieces were first cleaned individually
with neutral soap and water. They were then placed in an
EMAG Emmi-H30 ultrasonic tank containing water, neu-
tral soap, and pure acetone (C₃H₆O) during various 20 min
<table><caption>**Table 2** General information regarding the raw material, dimensions of the flakes and their edges; nature and characteristics of the contact materials, and type and time of action</caption><thead><tr><th>Registration number</th><th>Rock type</th><th>Length (mm)</th><th>Width (mm)</th><th>Thickness (mm)</th><th>Edge length (mm)</th><th>Grain</th><th>Edge delineation</th><th>Contact material</th><th>State</th><th>Action</th><th>Direction</th><th>Time (min)</th></tr></thead><tbody><tr><td>1</td><td>Obsidian</td><td>30</td><td>22</td><td>8</td><td>27</td><td>Medium</td><td>Straight</td><td>Unused</td><td></td><td></td><td></td><td></td></tr><tr><td>2</td><td>Obsidian</td><td>17</td><td>14</td><td>6</td><td>15</td><td>Medium</td><td>Straight</td><td>Unused</td><td></td><td></td><td></td><td></td></tr><tr><td>4</td><td>Obsidian</td><td>21</td><td>32</td><td>7</td><td>30</td><td>Medium</td><td>Convex</td><td>Leather</td><td>Dry</td><td>Cutting</td><td>Unidirectional</td><td>80</td></tr><tr><td>32</td><td>Obsidian</td><td>18</td><td>16</td><td>5</td><td>16</td><td>Medium</td><td>Convex</td><td>Leather</td><td>Dry</td><td>Scraping</td><td>Unidirectional</td><td>60</td></tr><tr><td>97</td><td>Obsidian</td><td>54</td><td>22</td><td>5</td><td>34</td><td>Medium</td><td>Straight</td><td>Leather</td><td>Dry</td><td>Cutting</td><td>Unidirectional</td><td>60</td></tr><tr><td>34</td><td>Obsidian</td><td>26</td><td>27</td><td>7</td><td>23</td><td>Medium</td><td>Straight</td><td>Leather</td><td>Dry</td><td>Scraping</td><td>Unidirectional</td><td>10</td></tr><tr><td>239</td><td>Obsidian</td><td>34</td><td>19</td><td>5</td><td>28</td><td>Fine</td><td>Straight</td><td>Fish</td><td>Fresh</td><td>Scraping</td><td>Unidirectional</td><td>11</td></tr><tr><td>241</td><td>Obsidian</td><td>41</td><td>15</td><td>5</td><td>24</td><td>Medium</td><td>Straight</td><td>Fish</td><td>Fresh</td><td>Scraping</td><td>Unidirectional</td><td>15</td></tr><tr><td>244</td><td>Obsidian</td><td>42</td><td>26</td><td>3</td><td>36</td><td>Medium</td><td>Concave</td><td>Fish</td><td>Fresh</td><td>Cutting</td><td>Unidirectional</td><td>15</td></tr><tr><td>245</td><td>Obsidian</td><td>29</td><td>24</td><td>3</td><td>27</td><td>Fine</td><td>Straight</td><td>Fish</td><td>Fresh</td><td>Cutting</td><td>Unidirectional</td><td>15</td></tr><tr><td>111</td><td>Obsidian</td><td>24</td><td>27</td><td>5</td><td>28</td><td>Medium</td><td>Straight</td><td>Cereals</td><td>Ripe</td><td>Harvesting</td><td>Unidirectional</td><td>150</td></tr><tr><td>206</td><td>Obsidian</td><td>25</td><td>22</td><td>4</td><td>22</td><td>Medium</td><td>Straight</td><td>Cereals</td><td>Ripe</td><td>Harvesting</td><td>Unidirectional</td><td>80</td></tr><tr><td>286</td><td>Obsidian</td><td>32</td><td>17</td><td>3</td><td>27</td><td>Medium</td><td>Concave</td><td>Rush</td><td>Fresh</td><td>Harvesting</td><td>Unidirectional</td><td>60</td></tr><tr><td>288</td><td>Obsidian</td><td>27</td><td>19</td><td>6</td><td>21</td><td>Medium</td><td>Convex</td><td>Rush</td><td>Fresh</td><td>Harvesting</td><td>Unidirectional</td><td>60</td></tr><tr><td>52</td><td>Obsidian</td><td>57</td><td>29</td><td>11</td><td>44</td><td>Medium</td><td>Straight</td><td>Bone</td><td>Fresh</td><td>Scraping</td><td>Unidirectional</td><td>90</td></tr><tr><td>69</td><td>Obsidian</td><td>48</td><td>20</td><td>7</td><td>43</td><td>Medium</td><td>Straight</td><td>Bone</td><td>Fresh</td><td>Sawing</td><td>Bidirectional</td><td>5</td></tr><tr><td>13</td><td>Obsidian</td><td>51</td><td>32</td><td>10</td><td>48</td><td>Medium</td><td>Straight</td><td>Wood</td><td>Fresh</td><td>Scraping</td><td>Bidirectional</td><td>60</td></tr><tr><td>106</td><td>Obsidian</td><td>55</td><td>15</td><td>6</td><td>47</td><td>Coarse</td><td>Straight</td><td>Wood</td><td>Dry</td><td>Sawing</td><td>Bidirectional</td><td>15</td></tr><tr><td>122</td><td>Obsidian</td><td>48</td><td>32</td><td>7</td><td>43</td><td>Medium</td><td>Straight</td><td>Wood</td><td>Dry</td><td>Scraping</td><td>Unidirectional</td><td>65</td></tr><tr><td>104</td><td>Obsidian</td><td>54</td><td>31</td><td>11</td><td>50</td><td>Medium</td><td>Straight</td><td>Wood</td><td>Dry</td><td>Sawing</td><td>Bidirectional</td><td>60</td></tr><tr><td>249</td><td>Obsidian</td><td>14</td><td>18</td><td>3</td><td>13</td><td>Medium</td><td>Straight</td><td>Enamel</td><td>Dry</td><td>Sawing</td><td>Bidirectional</td><td>5</td></tr><tr><td>252</td><td>Obsidian</td><td>33</td><td>18</td><td>4</td><td>30</td><td>Medium</td><td>Straight</td><td>Enamel</td><td>Dry</td><td>Scraping</td><td>Bidirectional</td><td>5</td></tr><tr><td>3</td><td>Basalt</td><td>44</td><td>32</td><td>12</td><td>40</td><td>Coarse</td><td>Straight</td><td>Unused</td><td></td><td></td><td></td><td></td></tr><tr><td>5</td><td>Basalt</td><td>34</td><td>20</td><td>6</td><td>27</td><td>Coarse</td><td>Straight</td><td>Unused</td><td></td><td></td><td></td><td></td></tr><tr><td>224</td><td>Basalt</td><td>49</td><td>26</td><td>6</td><td>43</td><td>Coarse</td><td>Straight</td><td>Leather</td><td>Fresh</td><td>Scraping</td><td>Unidirectional</td><td>10</td></tr><tr><td>338</td><td>Basalt</td><td>27</td><td>23</td><td>5</td><td>24</td><td>Fine</td><td>Straight</td><td>Leather</td><td>Fresh</td><td>Scraping</td><td>Unidirectional</td><td>20</td></tr><tr><td>340</td><td>Basalt</td><td>43</td><td>20</td><td>7</td><td>40</td><td>Coarse</td><td>Straight</td><td>Leather</td><td>Fresh</td><td>Cutting</td><td>Bidirectional</td><td>3</td></tr><tr><td>341</td><td>Basalt</td><td>41</td><td>20</td><td>9</td><td>38</td><td>Coarse</td><td>Convex</td><td>Leather</td><td>Fresh</td><td>Scraping</td><td>Unidirectional</td><td>15</td></tr><tr><td>240</td><td>Phonolite</td><td>44</td><td>36</td><td>10</td><td>42</td><td>Coarse</td><td>Straight</td><td>Fish</td><td>Fresh</td><td>Scraping</td><td>Unidirectional</td><td>15</td></tr><tr><td>243</td><td>Basalt</td><td>33</td><td>21</td><td>11</td><td>27</td><td>Fine</td><td>Straight</td><td>Fish</td><td>Fresh</td><td>Cutting</td><td>Unidirectional</td><td>2</td></tr><tr><td>246</td><td>Trachyte</td><td>37</td><td>40</td><td>11</td><td>32</td><td>Fine</td><td>Straight</td><td>Fish</td><td>Fresh</td><td>Cutting</td><td>Unidirectional</td><td>15</td></tr><tr><td>247</td><td>Basalt</td><td>57</td><td>41</td><td>8</td><td>50</td><td>Fine</td><td>Straight</td><td>Fish</td><td>Fresh</td><td>Cutting</td><td>Unidirectional</td><td>15</td></tr><tr><td>352</td><td>Phonolite</td><td>40</td><td>27</td><td>5</td><td>40</td><td>Fine</td><td>Straight</td><td>Cereals</td><td>Ripe</td><td>Harvesting</td><td>Unidirectional</td><td>180</td></tr><tr><td>361</td><td>Phonolite</td><td>23</td><td>48</td><td>7</td><td>23</td><td>Fine</td><td>Straight</td><td>Cereals</td><td>Ripe</td><td>Harvesting</td><td>Unidirectional</td><td>180</td></tr><tr><td>168</td><td>Basalt</td><td>27</td><td>33</td><td>11</td><td>27</td><td>Fine</td><td>Convex</td><td>Rush</td><td>Fresh</td><td>Harvesting</td><td>Unidirectional</td><td>60</td></tr></tbody></table>

<figure><img src="image_6.png" /></figure>
<table><caption>**Table 2 (continued)**</caption><thead><tr><th>Registration number</th><th>Rock type</th><th>Length (mm)</th><th>Width (mm)</th><th>Thickness (mm)</th><th>Edge length (mm)</th><th>Grain</th><th>Edge delineation</th><th>Contact material</th><th>State</th><th>Action</th><th>Direction</th><th>Time (min)</th></tr></thead><tbody><tr><td>175</td><td>Basalt</td><td>27</td><td>35</td><td>12</td><td>27</td><td>Fine</td><td>Convex</td><td>Rush</td><td>Fresh</td><td>Harvesting</td><td>Unidirectional</td><td>60</td></tr><tr><td>195</td><td>Basalt</td><td>53</td><td>30</td><td>10</td><td>48</td><td>Fine</td><td>Straight</td><td>Bone</td><td>Dry</td><td>Sawing</td><td>Bidirectional</td><td>15</td></tr><tr><td>347</td><td>Basalt</td><td>33</td><td>28</td><td>10</td><td>30</td><td>Fine</td><td>Straight</td><td>Bone</td><td>Dry</td><td>Scraping</td><td>Unidirectional</td><td>52</td></tr><tr><td>143</td><td>Basalt</td><td>42</td><td>30</td><td>11</td><td>40</td><td>Fine</td><td>Straight</td><td>Wood</td><td>Fresh</td><td>Scraping</td><td>Unidirectional</td><td>20</td></tr><tr><td>155</td><td>Basalt</td><td>40</td><td>53</td><td>9</td><td>36</td><td>Fine</td><td>Convex</td><td>Wood</td><td>Fresh</td><td>Sawing</td><td>Bidirectional</td><td>15</td></tr><tr><td>158</td><td>Basalt</td><td>50</td><td>26</td><td>12</td><td>48</td><td>Fine</td><td>Straight</td><td>Wood</td><td>Fresh</td><td>Sawing</td><td>Bidirectional</td><td>20</td></tr><tr><td>161</td><td>Trachyte</td><td>45</td><td>48</td><td>12</td><td>40</td><td>Fine</td><td>Straight</td><td>Wood</td><td>Fresh</td><td>Sawing</td><td>Bidirectional</td><td>10</td></tr><tr><td>250</td><td>Basalt</td><td>19</td><td>35</td><td>3</td><td>15</td><td>Fine</td><td>Concave</td><td>Enamel</td><td>Dry</td><td>Scraping</td><td>Bidirectional</td><td>21</td></tr><tr><td>251</td><td>Basalt</td><td>30</td><td>31</td><td>6</td><td>28</td><td>Fine</td><td>Concave</td><td>Enamel</td><td>Dry</td><td>Sawing</td><td>Bidirectional</td><td>5</td></tr></tbody></table>

<figure><img src="image_7.png" /><figcaption>**Fig. 2** View of the mechanical vibration device (sieve) adapted to simulate the taphonomic conditions provoked by sandy sediments. **a)** Base of the device; **b)** metal canister containing the sand; **c)** original distribution prior to the experiment of the obsidian tools in sand from the site of DUMAS, **d)** and their distribution after 40 min of vibration; **e)** original distribution prior to the experiment of other volcanic rock tools in sand from PC, **f)** and their distribution after vibration for 40 min</figcaption></figure>

intervals. Cleaning was carried out systematically after each interval. Photographs of the pieces were also taken at each stage of the process (Nikon D750 camera) prior to observations with a Nikon SMZ1000 binocular magnifying glass (8X – 80X) (BMG) and a more powerful Nikon Labophot-2 metallographic microscope (100X – 400X) (MM) to analyse and record both the experimental wear and the alterations. Photographs of the pieces were taken through each of the two microscopes with a DS-Fi2 camera from various heights controlled by NIS Elements 4.30 software. The images were compiled with the Helicon Focus 6 application and processed with Photoshop CS4. Granulometric measurements of the sands were carried out with ImageJ 1.8.0 software.
# Results

## Description of the experimental use-wear traces prior to the mechanical alteration

All the fragments of this first phase of the experiment revealed modifications to their surfaces after working the contact materials. It is essential to keep in mind that these traces differed depending on whether the tools were hyaline obsidian or other volcanic rocks characterised by a heterogeneous internal structure. The use-wear attributes were then described based on the findings of prior research (Keeley 1980; Richards 1988; Hurcombe 1992; Rodríguez-Rodríguez 1998; Álvarez 2003; Walton 2019; Bello-Alonso et al. 2020; Brito-Abrante and Rodríguez-Rodríguez 2024). Tables 3 and 4 summarise the most characteristic attributes.

## Results of the simulation of the taphonomic process

### Mechanical alteration of the obsidian experimental tools

**20 min of alteration of unused obsidian tools** The unused obsidian tools after 20 min of sand alteration reveal a high degree of damage to their edges. At the macroscopic level, the tools subjected to sand from both PC and DUMAS display irregular scars that begin with Hertz cones and end in a step, with a significative loss of raw material along the edges. Observations with the metallographic microscope indicate that each of the two types of sand provoke continuous abrasion along the edges and surfaces, loss of raw material, as well as some chaotic striations (Fig. 3a, b, c, d). The experimentation in this case was not pursued by a 40-min

<table><caption>**Table 3** Summary of the types of traces of use-wear visible on the experimental obsidian and volcanic rock tools after working wood and non-woody plants</caption><tbody><tr><td></td><td>Obsidian</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td>Contact material</td><td>Wood</td><td></td><td>Cereals</td><td>Rushes</td><td></td></tr><tr><td></td><td>State of the contact material</td><td>Fresh</td><td>Dry</td><td>Ripe</td><td>Fresh</td><td>Remoistened</td></tr><tr><td rowspan="2">Abrasion</td><td>Location</td><td>Mainly edge</td><td>Mainly edge</td><td></td><td>Both</td><td>Both</td></tr><tr><td>Distribution</td><td>Discontinuous</td><td>Discontinuous</td><td></td><td>Continuous</td><td>Continuous</td></tr><tr><td rowspan="2">Rounding</td><td>Location</td><td></td><td></td><td>Edge</td><td></td><td></td></tr><tr><td>Distribution</td><td></td><td></td><td>Continuous</td><td></td><td></td></tr><tr><td rowspan="3">Striations</td><td>Location</td><td>Near the edge</td><td>Far from the edge</td><td>Near the edge</td><td>Far from the edge</td><td>Far from the edge</td></tr><tr><td>Distribution</td><td>Discontinuous</td><td>Discontinuous</td><td>Continuous</td><td>Discontinuous</td><td>Discontinuous</td></tr><tr><td>Type</td><td>Fern-like</td><td>Rough-bottomed</td><td>Comet-shaped</td><td>Rough-bottomed</td><td>Rough-bottomed</td></tr><tr><td rowspan="5">Polish</td><td>Location</td><td>Near the edge</td><td>Far from the edge</td><td>Near the edge</td><td>Far from the edge</td><td>Far from the edge</td></tr><tr><td>Distribution</td><td>Discontinuous</td><td>Discontinuous</td><td>Continuous</td><td>Discontinuous</td><td>Discontinuous</td></tr><tr><td>Texture</td><td>Smooth</td><td>Smooth</td><td>Smooth</td><td>Smooth</td><td>Smooth</td></tr><tr><td>Morphology</td><td>Bumpy</td><td>Bumpy</td><td>Flat</td><td>Undulated</td><td>Flat</td></tr><tr><td>Other volcanic rocks</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td>Contact material</td><td>Wood</td><td></td><td>Cereals</td><td>Rushes</td><td></td></tr><tr><td></td><td>State of the contact material</td><td>Fresh</td><td>Dry</td><td>Ripe</td><td>Fresh</td><td>Remoistened</td></tr><tr><td rowspan="2">Abrasion</td><td>Location</td><td>Both</td><td>Both</td><td></td><td>Both</td><td>Edge</td></tr><tr><td>Distribution</td><td>Discontinuous</td><td>Discontinuous</td><td></td><td>Continuous</td><td>Discontinuous</td></tr><tr><td rowspan="2">Rounding</td><td>Location</td><td></td><td></td><td>Edge</td><td></td><td></td></tr><tr><td>Distribution</td><td></td><td></td><td>Continuous</td><td></td><td></td></tr><tr><td rowspan="3">Striations</td><td>Location</td><td>Far from the edge</td><td>Far from the edge</td><td>Near the edge</td><td>Near the edge</td><td>Far from the edge</td></tr><tr><td>Distribution</td><td>Discontinuous</td><td>Discontinuous</td><td>Continuous</td><td>Continuous</td><td>Discontinuous</td></tr><tr><td>Type</td><td>Rough-bottomed</td><td>Rough-bottomed</td><td>Sleek</td><td>Intermittent</td><td>Rough-bottomed</td></tr><tr><td rowspan="4">Polish</td><td>Location</td><td>Far from the edge</td><td>Far from the edge</td><td>Near the edge</td><td>Near the edge</td><td></td></tr><tr><td>Distribution</td><td>Discontinuous</td><td>Discontinuous</td><td>Continuous</td><td>Continuous</td><td></td></tr><tr><td>Texture</td><td>Smooth</td><td>Smooth</td><td>Smooth</td><td>Smooth</td><td></td></tr><tr><td>Morphology</td><td>Flat</td><td>Flat</td><td>Flat</td><td>Bumpy</td><td></td></tr></tbody></table>

**abrasion:** location (edge, surface, or both); distribution (continuous or discontinuous); **rounding:** location, distribution (low, medium, or high); **striations:** location, distribution, type of striations (rough-bottomed; sleek; flaked; intermittent; comet-shaped; fern-like); **polish:** location, microtopographic distribution: poor development (only along the edge), medium development (when it almost totally modifies the surface); high development (when the surface is totally modified); texture (very smooth, smooth, or rough); morphology (smooth, bumpy, or undulated)

<figure><img src="image_8.png" /></figure>
<table><caption>**Table 4** Summary of the types of traces of use-wear on the experimental obsidian and volcanic rock tools after working hard and soft animal materials</caption><tbody><tr><td></td><td>Obsidian</td><td></td><td></td><td></td></tr><tr><td></td><td>Contact material</td><td>Leather</td><td>Meat</td><td>Tooth enamel</td></tr><tr><td></td><td>State of the contact material</td><td>Dry</td><td>Fresh</td><td>Remoistened</td></tr><tr><td>Abrasion</td><td>Location</td><td>Both</td><td>Edge</td><td>Both</td></tr><tr><td></td><td>Distribution</td><td>Continuous</td><td>Discontinuous</td><td>Discontinuous</td></tr><tr><td>Rounding</td><td>Location</td><td>Edge</td><td></td><td></td></tr><tr><td></td><td>Distribution</td><td>Continuous</td><td></td><td></td></tr><tr><td>Striations</td><td>Location</td><td>Near the edge</td><td>Far from the edge</td><td>Far from the edge</td></tr><tr><td></td><td>Distribution</td><td>Continuous</td><td>Discontinuous</td><td>Discontinuous</td></tr><tr><td></td><td>Type</td><td>Rough-bottomed</td><td>Sleek</td><td>Rough-bottomed</td></tr><tr><td>Polish</td><td>Location</td><td>Near the edge</td><td></td><td>Far from the edge</td></tr><tr><td></td><td>Distribution</td><td>Discontinuous</td><td></td><td>Discontinuous</td></tr><tr><td></td><td>Texture</td><td>Smooth</td><td></td><td>Rough</td></tr><tr><td></td><td>Morphology</td><td>Flat</td><td></td><td>Flat</td></tr><tr><td></td><td>Other volcanic rocks</td><td></td><td></td><td></td></tr><tr><td></td><td>Contact material</td><td>Leather</td><td>Meat</td><td>Tooth enamel</td></tr><tr><td></td><td>State of the contact material</td><td>Dry</td><td>Fresh</td><td>Remoistened</td></tr><tr><td>Abrasion</td><td>Location</td><td>Both</td><td></td><td>Both</td></tr><tr><td></td><td>Distribution</td><td>Discontinuous</td><td></td><td>Discontinuous</td></tr><tr><td>Rounding</td><td>Location</td><td>Edge</td><td></td><td></td></tr><tr><td></td><td>Distribution</td><td>Continuous</td><td></td><td></td></tr><tr><td>Striations</td><td>Location</td><td>Near the edge</td><td>Far from the edge</td><td>Far from the edge</td></tr><tr><td></td><td>Distribution</td><td>Discontinuous</td><td>Discontinuous</td><td>Continuous</td></tr><tr><td></td><td>Type</td><td>Rough-bottomed</td><td>Sleek</td><td>Rough-bottomed</td></tr><tr><td>Polish</td><td>Location</td><td>Near the edge</td><td></td><td>Far from the edge</td></tr><tr><td></td><td>Distribution</td><td>Discontinuous</td><td></td><td>Discontinuous</td></tr><tr><td></td><td>Texture</td><td>Rough</td><td></td><td>Rough</td></tr><tr><td></td><td>Morphology</td><td>Flat</td><td></td><td>Flat</td></tr></tbody></table>

interval as this would have possibly completely destroyed the edges bearing the use-wear of the contact materials.

**20 min of alteration of the obsidian tools used to work plant materials** It was possible after 20 min in the vibration device to still identify the original traces of experimental use-wear on the obsidian tools. At the macroscopic level, the pieces subjected to PC sand alteration show triangular and trapezoidal wedging scars terminating in a hinge/step. Those subjected to the DUMAS sand also display irregular scars initiated by Hertzian cones and ending in feather/step. Observations under the more powerful microscope in both cases expose fine, chaotic striations superimposed on the use-wear, notably polish, as well as abrasion with micropits (Fig. 4a, b, d, e).

**40 min of alteration of the obsidian tools used to work plant materials** The surfaces of the obsidian tools display a significant amount of alteration after 40 min in the vibration device. At the macroscopic level, the pieces subjected to PC sands reveal a greater number of alterations displaying the same characteristics at their initiation as at their termination.

These alterations eliminated certain earlier use-wear such as edge rounding or abrasion characteristic of working plants. The DUMAS pieces show the same type of alterations, as well as certain cases with slightly rounded edges. Under the metallographic microscope, the alterations produced by both sand types generate a great number of micropits, as well as wider and deeper chaotic striations, abrasion superposed on the original use-wear, as well as breaks along sections of the edges (Fig. 4c, f).

**20 min of alteration of the obsidian tools used to work animal materials** The surfaces of obsidian tools having served to work both soft and hard animal materials after 20 min of sand alteration reveal a reduction of the original use-wear traces. Under the binocular magnifying glass, those altered with PC sands display trapezoidal and irregular scars initiated with Hertzian cones and terminating in a step. They likewise show a loss of certain earlier use-wear traces (abrasion and rounding of the edge). To those subjected to DUMAS sands one must also add scars initiated with wedging scars and terminating in feather/hinges.
<figure><img src="image_9.png" /></figure>

TOTAL TIME OF EXPERIMENT

<caption>**Fig. 3** Binocular (0.8X) and metallographic microscope (200X) views of the surfaces of unused obsidian tools. **a)** Exp. 1: unused obsidian tool prior to sand alteration; **b)** Exp. 1: after 20' of alteration with sand from PC; **c)** Exp. 2: unused obsidian tool prior to sand alteration; **d)** Exp. 2: after 20' of alteration with sand from DUMAS</caption>

<figure><img src="image_10.png" /></figure>
<figure><img src="image_11.png" /></figure>

TOTAL TIME OF EXPERIMENT

<caption>**Fig. 4** Binocular (0.8X) and metallographic microscope (200X) views of the surfaces of obsidian tools subsequent to working non-woody plants (top: rush; bottom: cereals). **a**) Exp. 288: harvesting rushes for 60' prior to sand alteration; **b**) Exp. 288: after 20' of alteration</caption>

with sand from PC; **c**) Exp. 288: after 40' of alteration with sand from PC; **d**) Exp. 111: harvesting cereals for 150' prior to sand alteration; **e**) Exp. 111: after 20' of alteration with sand from DUMAS; **f**) Exp. 111: after 40' of alteration with sand from DUMAS

Observations with the metallographic microscope indicate that each of the two types of sand generated chaotic, wide, and dark striations, abrasion with micropits, as well as the loss of the earlier traces of use-wear (striations and abrasion) (Fig. 5a, b, d, e).

**40 min of alteration of the obsidian tools used to work animal materials** The edges of obsidian tools after 40 min of sand alteration reveal a great degree of alteration. Under the magnifying glass, the pieces subjected to both types of sands began to lose their original use-wear, notably abrasion.
<figure><img src="image_12.png" /><figcaption>**Fig. 5** Binocular (0.8X) and metallographic microscope (200X) views of the alteration of the surfaces of obsidian tools subsequent to working animal materials (top: tooth enamel; bottom: leather). **a)** Exp. 249: sawing enamel during 5'prior to sand alteration; **b)** Exp.</figcaption></figure>

249: after 20'of alteration with PC sand; **c)** Exp. 249: after 40'of alteration with PC sand; **d)** Exp. 4: cutting leather during 80'prior to sand alteration; **e)** Exp. 4: after 20'of alteration with DUMAS sand; **f)** Exp. 4: after 40'of alteration with DUMAS sand

Moreover, each of the two sand types provoke irregular and trapezoidal scars initiated with Hertzian cones and terminating in feather/step. Microscopic observations indicate that these scars eliminated a significant part of the edges previously bearing use-wear. However, in the cases where

the original edges were preserved after being subjected to both sand types, it was possible to detect a greater amount of abrasion and pits together with chaotic, wide, and dark striations overlapping parts of the earlier traces (polish and striations) produced by the contact materials (Fig. 5c, f).

<figure><img src="image_13.png" /></figure>
## Mechanical alteration of the tools of other volcanic rocks

**20 min of the alteration of unused volcanic rock tools** Although the surfaces of the unused volcanic rock tools after 20 min in the vibrating device display signs of post-depositional alteration, they are less pronounced than those on the obsidian. Under binocular magnification, the tools exposed to the two types of sand bear some scars that begin with wedging marks and end in step/hinges. This provoked the loss of part of the original edge, especially the more prominent areas. Observations with the metallographic microscope, in turn, reveal an alteration characterised mainly by an increase of abrasion and pitting of the amorphous matrix, as well as loss of raw material (i.e. phenocrystals) along the edges (Fig. 6a, b, c, d).

**20 min of alteration of the volcanic rock tools used to work plant materials** The traces of use-wear on the experimental volcanic rock tools resulting from working plants remain visible after 20 min of sand alteration. The pieces subjected to PC sand under binocular magnification reveal little alteration. The exception concerns the tools used to saw wood which display some irregular scars initiated by wedging marks and terminating in a step. Most of the artefacts subjected to wear by DUMAS sands present scars initiating with Hertzian cones and terminating in a feather. Metallographic microscope observations of the effects of each of the types of sand reveal a greater amount of surface abrasion and pits, notably more intense among those subjected to the DUMAS sands. In this last case one observes a noticeable loss of the original use-wear (polish and striations) along the edges. The sand alteration also superposed itself both on the amorphous matrix and on the crystals (Fig. 7a, b, d, e).

**40 min of alteration of the volcanic rock tools used to work plant materials** The alteration of the surfaces of the volcanic rock tools after 40 min in the vibrating device, although less common, resembles that of the obsidian tools. Those subjected to each of the two types of sands under binocular magnification reveal a greater number of scars initiated by wedging marks and terminating in step/hinges provoking the loss of some of the original use-wear, notably edge and surface abrasion and slight rounding. Observations with the more powerful metallographic microscope reveal alteration characterised mainly by an increase of abrasion and pits on the amorphous matrix, especially among the tools subjected to sand from DUMAS (Fig. 7c, f).

**20 min of alteration of the volcanic rock tools used to work animal materials** Irregular scars initiated with Hertzian cones and terminating in step, as well as abrasion along the surface and edge, can be observed after 20 min of PDSM simulation with both types of sand. The traces of rounding also

disappeared. Under the metallographic microscope there are clear signs of wear such as friction polish, abrasion, and pits that eliminated a large part of the previous use-wear on the amorphous matrix and the crystals (Fig. 8a, b, d, e).

**40 min of alteration of the volcanic rock tools used to work animal materials** After 40 min, it is possible to observe modifications of the surfaces of the tools made of volcanic rocks used to work animal materials similar to those of volcanic glasses serving for the same task. Observations of the volcanic rock tools with the binocular magnifying glass reveal a greater number of scars initiated with Hertzian cones and terminating in a step. However, the traces of rounding and abrasion remained unchanged. Metallographic microscope observations, in turn, reveal more elimination of the original use-wear. While the alterations detected after 20 min of the simulation (abrasion, pits, or friction polish) persisted, it is possible to perceive in both cases a significant loss of the original use-wear such as polish and striations on the amorphous matrix (Fig. 8c, f).

## Granulometric analysis of the sands from the two archaeological sites

One of the questions raised in this study concerned the potential of different post-depositional effects on the artefacts of the two sites according to the granulometric characteristics of their sands. At first glance, there are clear distinctions between the two. While the sands from PC consist mainly of larger grains, those from DUMAS are smaller and more rounded. These differences were quantified by counting 50 grains of each type of sand from 1 ml samples. The task was carried out with a binocular microscope using a 1 mm scale (Fig. 9). The results indicate that the grains from PC are both larger (mean = 0.71 mm) and more irregular. The sands from DUMAS, in turn, are smaller (mean = 0.36 mm), more rounded, and uniform. These differences directly affected how they altered the surfaces of both the experimental and archaeological tools. In fact, the experimental pieces subjected to PC sands bear chaotic and deep striations. Moreover, a predominance of abrasion attributable to the larger size of the particles is noteworthy as they bear substantial modifications to their surfaces. The pieces subjected to the finer DUMAS sands, on the contrary, reveal a greater incidence of friction polish and rounded edges stemming from a more uniform and prolonged wear.

## The functional analysis of the archaeological artefacts

A total of 96 artefacts from the two archaeological sites were retained for a preliminary test of their suitability to be analysed from the functional standpoint. The total was
<figure><img src="image_14.png" /><figcaption>**Fig. 6** Binocular (0.8X) and metallographic microscope (200X) views of the surfaces of unused volcanic rock tools. **a)** Exp. 3: unused basalt tool prior to sand alteration; **b)** Exp. 3: after 20' of alteration</figcaption></figure>

with sand from PC; **c)** Exp. 5: unused basalt tool prior to sand alteration; **d)** Exp. 5: after 20' of alteration with sand from DUMAS

<figure><img src="image_15.png" /></figure>
<figure><img src="image_16.png" /><figcaption>**Fig. 7** Binocular (0.8X) and metallographic microscope (200X) views of the alteration of the surface of tools made of volcanic rock used to work plants (top: wood; bottom: cereals). **a)** Exp. 158: sawing wood for 20' prior to sand alteration; **b)** Exp. 158: after 20' of alteration</figcaption></figure>

with PC sand; **c)** Exp. 158: after 40' of alteration with PC sand; **d)** Exp. 352: harvesting cereals for 180' prior to sand alteration; **e)** Exp. 352: after 20' of alteration with DUMAS sand; **f)** Exp. 352 after 40' of alteration with DUMAS sand

broken down into 19 of obsidian and 18 of phonolite from DUMAS, and 31 of obsidian and 28 of other volcanic rocks from PC. The use-wear analyses of these pieces suggest that most suffered from post-depositional alterations (Table 5). Specifically, of those from PC, only one of the 31 obsidian

artefacts retained use-wear that can be linked to a longitudinal working of hard material (Fig. 10a). The same applies to the other 28 coarse-grained rocks, as only one revealed traces of the cutting of an undetermined material (Fig. 10b). The same phenomenon was observed among the artefacts
<figure><img src="image_17.png" /><figcaption>TOTAL TIME OF EXPERIMENT</figcaption></figure>

**Fig. 8** Binocular (0.8X) and metallographic microscope (200X) views of the alteration of the surface of tools made of volcanic rock (basalt) subsequent to working animal materials (top: leather; bottom: enamel). **a)** Exp. 338: scraping leather during 20'prior to sand

alteration; **b)** Exp. 338: after 20'of alteration with PC sand; **c)** Exp. 338: after 40'of alteration with PC sand; **d)** Exp. 250: sawing enamel for 21'prior to sand alteration; **e)** Exp. 250: after 20'of alteration with DUMAS sand; **f)** Exp. 250: after 40'of alteration with DUMAS sand

from DUMAS as only one of the 18 volcanic rock tools retained traces associated with cutting non-woody plants (Fig. 10c). It was also only possible to identify one piece among the 19 obsidian fragments from DUMAS retaining

traces of a complex movement linked to working a hard material (Fig. 10d).

The analyses of the two lithic assemblages reveal different levels of alteration. At PC, 63.33% of the obsidian tools

<figure><img src="image_18.png" /></figure>
<figure><img src="image_19.png" /><figcaption>**Fig. 9** Results of the granulometric and diameter analyses of samples of sands from the archaeological sites of Playa Chica (left) and Dunas de Maspalomas (right). Column Y shows the measurements of the</figcaption></figure>

sand particles in units of mm. Column X indicates the number of particles (n = 50) measured in each graph

<table><caption>**Table 5** Results of the interpretation of the use-wear observed on tools of obsidian and other volcanic rocks from the archaeological sites of Playa Chica and Dunas de Maspalomas</caption><thead><tr><th>Archaeological site</th><th>Raw material</th><th>Motion</th><th>Contact material</th></tr></thead><tbody><tr><td rowspan="2">PC</td><td>Obsidian</td><td>Longitudinal</td><td>Hard material</td></tr><tr><td>Basalt</td><td>Longitudinal</td><td>Undetermined</td></tr><tr><td rowspan="2">DUMAS</td><td>Obsidian</td><td>Complex</td><td>Hard material</td></tr><tr><td>Phonolite</td><td>Longitudinal</td><td>Plant</td></tr></tbody></table>

examined in Zones 1 and 2 display post-depositional scars, abrasion, and chaotic striations. In the case of its volcanic rocks, 52% display scars, 20% rounding, and 16% surface abrasion (Fig. 11). Neither shows signs of the formation of patina or friction polish. At DUMAS, 66.67% of the obsidian tools retain traces of abrasion on both their edges and surfaces, and chaotic striations. Among its volcanic rock tools, 21.43% reveal abrasion along their edges and surfaces, 28.57% friction polish, and 35.71% patina (Fig. 12).

## Discussion

Comparisons of the traces observed on the artefacts recovered at each of the archaeological settlements of DUMAS and PC and those subjected to the experiment share

numerous similarities which confirms that the mechanical processes carried out experimentally yielded alterations similar to those observed on the archaeological tools. It is also key to note that it was possible to monitor the mechanical alterations provoked by the sands during the experimentation on the use-wear of both the obsidian and other volcanic rocks.

The results also suggest that the rate of taphonomic alteration is proportional to the time of exposure and type of sand. A notable increase was observed among the samples exposed to longer intervals (surpassing 20 min), a notion that coincides with the observations of Fernández-Jalvo and Andrews (2003) regarding the highly abrasive power of sandy sediments. The current study did nonetheless reveal different effects of the experimental sands regarding their persistence and degree of alteration. The finer, rounder, and lighter particles from DUMAS tended to yield more compact sediments, while the coarser and more heterogeneous grains from PC were looser and more disaggregated. These granulometric qualities led the two types of experimental raw materials to be affected differently. Thus, the DUMAS sands generated a greater number of scars and chaotic striations overlapping the use-wear of the obsidian tools than that of the coarse-grained volcanic rock tools. Previous research has confirmed the predisposition of obsidian to undergo alterations more quickly, rendering it difficult in some cases to observe the earlier use-wear (Hurcombe 1992;
<figure><img src="image_20.png" /><figcaption>**Fig. 10** Use-wear traces on archaeological artefacts from the sites of Playa Chica and Dunas de Maspalomas (scale = 1 cm). **a)** Use-wear on a fragment of obsidian from PC linked to longitudinal movements while working a hard material; **b)** traces on a fragment of basalt from PC associated with longitudinal movements while working an</figcaption></figure>

undetermined material; **c)** use-wear on a fragment of phonolite from DUMAS from longitudinal movements while working a non-woody plant; **d)** use-wear on and obsidian fragment from DUMAS linked to variable movements while working a hard material

<figure><img src="image_21.png" /></figure>
<figure><img src="image_22.png" /><figcaption>**Fig. 11** Post-depositional alterations of the archaeological artefacts from Playa Chica (top: obsidian; bottom: volcanic rocks) (200x). **a)** Deep and chaotic striations; **b)** wide and chaotic striations and sur-</figcaption></figure>

face abrasion; **c)** edge scars and surface abrasion; **d)** physical iron oxide alteration; **e)** alteration of the crystals and abrasion of the edge and surface; **f)** abrasion, rounding, and pits on the surface

<figure><img src="image_23.png" /><figcaption>**Fig. 12** Post-depositional alterations of the archaeological artefacts from Dunas de Maspalomas (top: obsidian; bottom: volcanic rocks) (200x). **a)** Chaotic striations and scars along the edge; **b)** surface</figcaption></figure>

abrasion; **c)** scars along the edge and polished surface with slight abrasion; **d)** polished surface, abrasion along the edge, and surface macro holes; **e–f)** polished surface and macro holes
Rodríguez-Rodríguez 1998). By contrast, the sandy grains from PC had a more intense effect on the coarse-grained volcanic rock tools than on the obsidian. Here the alterations took on the form of abrasion and pits leading to the disappearance of the earlier striations and polish. Thus, the findings of this study regarding the heterogeneous raw materials resemble those of prior research (Asryan et al. 2014; Mazucco et al. 2013). Furthermore, it is of essence to comment on the differences that exist between the sediments of each site. While that from DUMAS consists of a much finer sand combined with a high amount of suspended dust (and other elements), which is typical of dune environments (Borrazzo 2006), that from PC fundamentally consists of coarser and more angular minerals of volcanic origin. These particularities are reflected both in the experimental mechanical alteration and in the PDSM of the archaeological materials.

The observations of the similarity in the alteration patterns reinforces the hypothesis that certain types of raw material are particularly susceptible to taphonomic processes, even in cases of limited temporal exposure (Fernandes et al. 2008). Similar to what occurs with other raw materials of sedimentary or metamorphic origin, the development of use-wear traces and alterations does not affect the surfaces of obsidian with a hyaline matrix in the same manner as that of the surfaces of heterogeneous volcanic rocks characterised by an amorphous matrix and phenocrystals (Hurcombe 1992; Huidobro 2018).

While the use-wear traces develop quickly along the edge and surface of obsidian, other volcanic rocks require more time, a fact that complicates identifying the original traces of contact material (Mansur-Franchomme 1986; Clemente-Conte 1997). This difficulty is reflected in the present experiment. Although the pieces were subjected to the same experimental conditions (sand type, time interval, revolutions per minute, and physical conditions), the alteration process affected obsidian much more rapidly than volcanic rocks, which tended to retain its original use-wear. On the other hand, the different experimental time intervals generated distinctive signs of alteration, which not only allow to identify the mechanical agents responsible for the PDSM, but to determine the relationship between the traces and the surface properties of the different raw materials. These properties, notably coarseness, reactivity, and porosity, had a significant influence on the response of the materials to external agents. In the case of the surfaces of obsidian, the experiment revealed that the alterations are mostly associated with an abrasive contact. Volcanic rocks, in turn, display a greater susceptibility to wettability and porosity, which facilitate the elimination over time of the earlier traces of use-wear and the formation of abrasion.

To more precisely evaluate how abrasion affects different raw materials, the experiment also included several unworked or unused tools of obsidian and volcanic rock.

This approach allowed focusing exclusively on the impact of the mechanical alteration of their surfaces and compare their resistance to the abrasion of moving sand. The results reveal notable differences between the two raw materials. Obsidian after only 20 min in the electromagnetic vibrotor displayed significant wear characterised by considerable edge fractures, widespread surface abrasion, and chaotic striations. These alterations suggest that obsidian, due to its fragility and vitreous structure, is particularly susceptible to sand abrasion, leading to rapid material loss and the formation of wear patterns that can be difficult to distinguish from other taphonomic processes. The volcanic rock tools, in turn, responded different to the experiment. Although they also developed edge fractures, these were less pronounced than those of obsidian, and their surface abrasion was comparatively more subtle (although marked by a loss of phenocrystals). This lower intensity of alteration suggests that these rocks possess greater structural resistance to mechanical abrasion, which may contribute to better preservation of their original use-wear in archaeological contexts.

Another relevant aspect is the differential persistence of the traces of use-wear depending on the contact materials. During the experimental process we observed that the wear generated by working non-woody plants, such as harvesting cereals and rushes, tends to be preserved on the edge of the tools even after being subjected to mechanical alteration. On the contrary, the use-wear stemming from processing animal materials is less resistant and deteriorates more quickly. These findings bolster the results of previous research in the sense that the durability of wear from working plants is greater than that generated by other less resistant contact materials. This phenomenon can be explained by the fact that these traces tend to penetrate more deeply into the edge, which facilitates conservation in adverse taphonomic conditions (Werner 2018). This can also be linked to the characteristics of the plants as they contain phytoliths bearing a high silica content (Brito-Abrante and Rodríguez-Rodríguez 2024).

The experimentation appears to have reproduced some of the types of PDSM alterations observed among the archaeological materials. However, it is necessary to highlight those alterations due to chemical processes, such as oxidation or the formation of patinas, could not be replicated in a controlled manner. Despite this, one must take into account that these chemical processes are key factors influencing the alteration of the surfaces of archaeological artefacts. Exposure to atmospheric agents, such as air salinity in the case of lithic artefacts found near the sea, probably contributes to the formation of layers of corrosion or alteration that can have an affect on the earlier traces of use-wear. Therefore, it is difficult to accurately replicate certain processes as there are always limits to detecting chemical agents due to the impossibility of simulating extended long-term time intervals or scenarios that can yield results similar to those

<figure><img src="image_24.png" /></figure>
affecting archaeological artefacts (Mazzucco et al. 2013; Berruti and Arzarello 2020). Even so, the findings of the current experiment contribute to the understanding of the phenomena of alteration affecting archaeological artefacts. The most obvious are of mechanical nature (scars, abrasion, chaotic striations, and friction polish). More difficult to pinpoint are those of chemical nature (patina and oxidation) as they may have been induced by water or sea spray provoking a dissolution and precipitation of silica or other minerals typical of volcanic rocks. Although there is a great amount of research concerning the formation of patina in siliceous rocks (Rottlander 1975; Semenov 1970; Michel et al. 2019), less attention has been paid to that of volcanic rocks, except for the experimentation intended to monitor the rate of patina formation from obsidian hydration in order to verify its suitability for dating programmes (Mazer et al. 1991; Rogers 2006; Stevenson et al. 2019).

In any case, the available archaeological data suggest that the two sites are characterised by different sequences of occupation, meaning the PDSM affecting their lithic artefacts presumably derived from different causes. The predominance at PC of the traces on both obsidian and coarse volcanic rocks associated with mechanical processes suggests an intense anthropic intervention. Here the visible features consist of fractures and scars along the edges, wide, chaotic striations, and surface abrasion, features suggesting a high degree of trampling or displacement. The relative protection of the site from sea winds may have limited their exposure to chemical processes (such as the dissolution/precipitation of salts), reducing the formation of patinas and other chemical weathering. Even so, certain pieces show evidence of having been affected by these processes. The mechanical agents at DUMAS mainly yielded friction polish. The chemical alterations observed at this site also provoked the formation of patinas, suggesting that the artefacts suffered greater exposure to external environmental conditions linked to water flow and wind. Although the two sites are near the sea, the dunar environment of DUMAS was marked by a great presence of salts that, combined that with the action of the wind, would have accelerated the physical weathering of the archaeological pieces (yielding greater rounding of their edges). Furthermore, previous research reinforces the notion that these characteristics are more common in dune littorals than in other sedimentary environments frameworks as the finer particles are more corrosive. Thus the combination of this type of sand with wind yields an aerodynamic environment resulting in an intense abrasion of the artefacts (Borrazzo 2006). Hence, the percolation of carbonate-laden solutions and the formation of crusts visible on the materials at DUMAS serve as evidence of active chemical processes that modified their surfaces (Rottlander 1975). The interaction between the taphonomic factors and the specific environment of each site thus seems to have influenced the

patterns of alteration of their lithic tools. It is true that the current experiment has focused exclusively on the mechanical alteration of the materials as this approach was much simpler to replicate. However, chemical phenomena also affected the artefacts and future experimentation must include this aspect. The site of PC with its buildings under a natural rock shelter offered relatively protected conditions facilitating the preservation of the artefacts from environmental factors, while simultaneously favouring mechanical alterations provoked by a prolonged transit by humans in the restricted space. On the contrary, the open dune environment and absence of buildings at DUMAS meant the site was subjected to a greater number of natural agents such as wind and environmental salinity. The absence of barriers here would have also favoured more random shifts of people and animals which would have accelerated artefact degradation.

## Conclusion

The initial functional and traceological study of the archaeological lithic tools from the sites of PC and DUMAS revealed frequent traces of sand abrasion, trampling, and pedogenetic agents which complicated the analyses and could lead to erroneous interpretations. This gave rise to an interest in analysing the PDSM processes affecting the original use-wear of these artefacts which, in turn, set in motion the experimental programme presented here. The results indicate that the simulations of PDSM of the experiment successfully reproduced the mechanical taphonomic effects (abrasion of sand, trampling, and material loss due to the collision of pieces) observed on the surfaces of the archaeological tools of the two sites. On the other hand, the experiment could not reproduce the chemical alterations suffered by these artefacts as no patterns were observed that could be compared with those on the archaeological tools. In any case, the experiment highlights the variability of resistance to alteration of the tool use-wear depending on the type of contact material that generated them. There are other compelling conclusions, such as that the use-wear along their edges linked specifically to working plant materials on both obsidian and other volcanic rocks displays a greater resistance to PDSM. This is the opposite to that stemming from working soft animal materials, which are more susceptible to elimination by external agents. This experimental study thus offers valuable insight into the mechanical post-depositional processes affecting volcanic lithic tools and their impact on the preservation of use-wear. Future experimentation in this field should attempt to refine and deepen these observations and cast light on other taphonomic processes such as aeolian alteration, patina formation, and the development of iron oxides affecting the surfaces of archaeological artefacts.
**Acknowledgements** This study was financed in the framework of the research project PID2023-151226NB-I00 financed by MICIU/ AEI/10.13039/501100011033 and FEDER, UE. The interventions at Playa Chica, as well as certain of the analyses, were carried out within the framework of the ERC Starting Grant IsoCAN project (no. 851733) and grants from the Servicio de Patrimonio Histórico of the Cabildo de Gran Canaria. The authors would like to thank all who participated in the research at the two sites. Idaira Brito-Abrante is beneficiary of a PhD grant from the Agencia Canaria de Investigación, Innovación y Sociedad de la Información de la Consejería de Universidades, Ciencia e Innovación y Cultura and Fondo Social Europeo Plus (FSE +) Programa Operativo Integrado de Canarias 2021–2027, Eje 3 Tema Prioritario 74 (85%).

**Author contributions** Conceptualization: [Idaira Brito-Abrante; Amelia Rodríguez-Rodríguez]; Methodology: [Idaira Brito-Abrante; Laurence Astruc; Amelia Rodríguez-Rodríguez]; Formal analysis and investigation: [Idaira Brito-Abrante; Amelia Rodríguez-Rodríguez]; Writing - original draft preparation: [Idaira Brito-Abrante; Amelia Rodríguez-Rodríguez]; Writing - review and editing: [Idaira Brito-Abrante; Laurence Astruc; Amelia Rodríguez-Rodríguez; Jonathan Santana; Jacob Morales]; Resources: [Amelia Rodríguez-Rodríguez; Jacob Morales; Jonathan Santana].

**Funding** Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature.

**Data availability** No datasets were generated or analysed during the current study.

## Declarations

**Competing interests** The authors declare no competing interests.

**Open Access** This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

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