Hominid Alluvial Corridor (HAC) of the Guadalquivir and Guadaíra River Valleys (Southern Spain): Geoarchaeological Functionality of the Middle Paleolithic Assemblages during the Upper Pleistocene

Citation: Díaz del Olmo, F.; Caro Gómez, J.A.; Borja Barrera, C.; Recio Espejo, J.M.; Cámara Artigas, R.; Martínez Aguirre, A. Hominid Alluvial Corridor (HAC) of the Guadalquivir and Guadaíra River Valleys (Southern Spain): Geoarchaeological Functionality of the Middle Paleolithic Assemblages during the Upper Pleistocene. Geosciences 2023,13, 206. https://doi.org/10.3390/ geosciences13070206 Academic Editors: Jesús F. Jordá Pardo and Jesus Martinez-Frias Received: 5 May 2023 Revised: 30 June 2023 Accepted: 3 July 2023 Published: 8 July 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). geosciences Article Hominid Alluvial Corridor (HAC) of the Guadalquivir and Guadaíra River Valleys (Southern Spain): Geoarchaeological Functionality of the Middle Paleolithic Assemblages during the Upper Pleistocene Fernando Díaz del Olmo 1, JoséA. Caro Gómez 2,* , César Borja Barrera 1, JoséM. Recio Espejo 3, Rafael Cámara Artigas 1and Aránzazu Martínez Aguirre 4 1Department of Geography and A.G.R., University of Sevilla, C/María de Padilla s/n, 41004 Sevilla, Spain; [email protected] (F.D.d.O.); [email protected] (C.B.B.); r[email protected] (R.C.A.) 2Department of History, University of Córdoba, Plaza del Cardenal Salazar, 3, 14071 Cordoba, Spain 3Department of Ecology, Botany and Plant Physiology, University of Córdoba, Campus de Rabanales s/n, 14071 Cordoba, Spain; bv1r[email protected] 4 Department of Applied Physics I, University of Sevilla, Ctra. Utrera, km 1, 41013 Sevilla, Spain; [email protected] *Correspondence: jacar[email protected] Abstract: This research addresses the geomorphological connectivity existing amid the piedmont’s karstic fillings (Sierra de Esparteros) and the Guadaíra and Guadalquivir Rivers’ alluvial terraces (SW of Spain), spotted with vestiges of human activities (Middle Palaeolithic). This study includes the analysis of 20 geoarchaeological sites and 28 lithic assemblages, with a total of 13,233 lithic pieces. Techno-typological and use–wear (SEM) analyses were conducted on these artifacts. Depending on the raw materials and the provenance of these lithic industries, two groups of assemblages were identified: one made of quartzite from the north, and another made of flint from the south. Two main geochronological periods were established (OSL and U/Th): (1) a short duration (MIS6/MIS5) and (2) a long duration (MIS5/MIS3). Techno-typological analysis showed three sorts of activities: (a) the provision and distribution of raw materials, (b) knapping, and (c) other activities that imply the use of a lithic workshop (LW), along with the settlement characteristics of habitual or recurrent (HS), temporary (TS), and indeterminate (IN). This geoarchaeological connectivity is called the “hominid alluvial corridor” (HAC). The underlined features are the geomorphological units, the continuum alluvial series, the raw material of the lithic industries as an indicator of provenance and transportation throughout the alluvial system, and the use–wear analysis of the tool-kit to interpret the functionality of the pieces. Keywords: Middle Paleolithic; hominid corridor; Upper Pleistocene; use–wear; Guadaíra and Guadalquivir Rivers; Spain 1. Introduction: Alluvial Geoarchaeological Hominid Corridor Watersheds provide excellent geomorphological connectivity [ 1 ]. This connectivity can be categorized into two types: structural and functional. Structural connectivity refers to the connection between adjacent geomorphological units, such as slopes, alluvial terraces, piedmonts, thalwegs, etc. Functional connectivity occurs when there is a linkage between units through hydro-geomorphological processes within and beyond the alluvial floodplain, including features like watershed floods, rill wash, and channel bars [ 2 – 4 ]. These two forms of connectivity facilitated the dispersal of human groups during the Middle Paleolithic, serving as pathways for accessing and stockpiling natural resources. According to Sánchez Hernández et al. [ 5 ], Neanderthals in the Mediterranean Iberian Peninsula possessed a comprehensive understanding of the territory. Therefore, the structural connectivity played a significant role and was utilized for Species Distribution Models (SDMs), which Geosciences 2023,13, 206. https://doi.org/10.3390/geosciences13070206 https://www.mdpi.com/journal/geosciences Geosciences 2023,13, 206 2 of 32 involved statistical modeling of the structural connectivity between Neanderthals and anatomically modern humans (AMHs) to identify optimal habitat patches during the period of 48–40 ka BP. A detailed analysis revealed that the deterioration and reduction of their habitats was primarily attributed to the loss of structural connectivity among these habitat patches rather than solely being a result of climate change. This loss of connectivity was identified as the most crucial factor leading to the extinction of Neanderthals in Europe [ 6 ]. The significance of the habitats in the Mediterranean Iberian Peninsula for Neanderthal survival strategies further strengthens this conclusion [5]. Alluvial sediments in watersheds have accumulated with the highest concentration in Middle Paleolithic open-air archaeological sites, some with paleontological remains and some without. We use the term “hominid alluvial geoarchaeological corridor” to describe a watershed that serves as a geomorphological unit with human settlements, which can be occasional, recurrent, or temporary. These settlements may or may not contain fauna remains and have defined functionalities, sometimes complementing each other, such as hunting grounds, butchery practices, and lithic workshops. Additionally, these corridors may contain primary outcrops (geological outcrops) or secondary outcrops (superficial geomorphological formations) that provide high-quality raw materials [ 7 – 13 ]. Therefore, the significance lies in the entire geoarchaeological assemblage within the watershed, rather than specific individual sites. One such landscape with these characteristics can be identified in the Guadalquivir Valley in southern Spain. Here, a Pleistocene sequence of the Guadalquivir River Valley was established, including relative and absolute chronologies (U/Th, OSL), for the Acheulian techno-complexes found in the high and middle terraces (Middle and Upper Pleistocene), as well as for the Middle Paleolithic in the lowest terraces (Upper Pleistocene). This was due to the dispersal of hunter–gatherer groups throughout the watershed [14–23]. This paper specifically focuses on the territorial dispersion at the regional watershed scale, with a particular emphasis on the Guadaíra River watershed [ 3 ]. The Guadaíra River is a left bank tributary of the Guadalquivir River, located in the province of Seville, Spain. From a geomorphological perspective, the Guadaíra River provides alluvial connectivity between the limestone and flint outcrops of the Subbetic or Mesozoic–Betic Chain and the middle-lower fluvial terraces of the Guadalquivir River, which contain quartzite pebbles from the Sierra Morena Paleozoic (Figure 1). The interest in this connectivity stems from the fact that both the Guadalquivir and Guadaíra Rivers have Middle/Upper Pleistocene terraces that harbor Middle Paleolithic lithic assemblages, predominantly consisting of quartzite industries from the Guadalquivir River terraces and flint industries from the Guadaíra River terraces. We have termed the geomorphological continuum between the karstic piedmont of Sierra de Esparteros (Subbetic Mountains) and the alluvial terraces and colluvial deposits of the Guadaíra and Guadalquivir Rivers as the hominid alluvial corridor (HAC). Within this corridor, the lithic industries made of quartzite and flint are intermixed and dispersed. The HAC is characterized by four key features: (1) the presence of geomorphological units, (2) the continuum of alluvial series, (3) the raw material used in lithic industries as an indicator of provenance and transportation within the alluvial system, and (4) the use–wear analysis of the tool-kit to interpret the functionality of the artifacts. The main objective of this paper is to define and characterize the HAC from a geoarchaeological and chronocultural perspective. The locations within the HAC exhibit a wide range of geoarchaeological variability, illustrating the geomorphological continuum between the alluvial terraces and the piedmont of the Sierra de Esparteros in Morón de la Frontera, Seville. Within this context, the deposits were interpreted based on the local and regional geomorphological evolution. To enhance the investigation, a physical–chemical characterization and a macro–microscopic analysis of the edges of quartzite flakes were conducted to identify traces of use. Geosciences 2023,13, 206 3 of 32 Geosciences 2023, 13, x FOR PEER REVIEW 3 of 33 Figure 1. Location of studied area. The main objective of this paper is to define and characterize the HAC from a geoarchaeological and chronocultural perspective. The locations within the HAC exhibit a wide range of geoarchaeological variability, illustrating the geomorphological continuum between the alluvial terraces and the piedmont of the Sierra de Esparteros in Morón de la Frontera, Seville. Within this context, the deposits were interpreted based on the local and regional geomorphological evolution. To enhance the investigation, a physical–chemical characterization and a macro–microscopic analysis of the edges of quartzite flakes were conducted to identify traces of use. 2. Methods 2.1. Geoarchaeological Field Work Geomorphological transects were conducted in the sediments of the Middle–Upper Pleistocene Guadaíra watershed, spanning from the Subbetic Mountains to the alluvial connection with the Guadalquivir River. Four cross-sections were implemented for this geomorphological analysis, namely the karstic piedmont–Sierra de Esparteros, Upper Guadaíra–Balbuan, Middle Guadaíra–Rozalejo, and Low Guadaíra–Barranca– Marchenilla–Membrilla–La Liebre. In the Guadalquivir River, the T11 (+44 m) and T12 (+28 m) terraces connected to the Guadaíra River and the geomorphological surface deposits from the T6 to T10 terraces were studied. Throughout these areas, a total of 20 geoarchaeological sites (with 28 lithic assemblages) were identified. These sites are associated with industries found in the alluvial sediments of the Guadalquivir, Guadaíra, and Rozalejo rivers, the karstic fillings of the Sierra de Esparteros piedmont (Cerro Santisteban), the colluvial deposits in Rozalejo and La Liebre, and the geomorphological surface deposits (Figure 2; Table 1). Figure 1. Location of studied area. 2. Methods 2.1. Geoarchaeological Field Work Geomorphological transects were conducted in the sediments of the Middle–Upper Pleistocene Guadaíra watershed, spanning from the Subbetic Mountains to the alluvial connection with the Guadalquivir River. Four cross-sections were implemented for this geomorphological analysis, namely the karstic piedmont–Sierra de Esparteros, Upper Guadaíra–Balbuan, Middle Guadaíra–Rozalejo, and Low Guadaíra–Barranca–Marchenilla– Membrilla–La Liebre. In the Guadalquivir River, the T11 (+44 m) and T12 (+28 m) terraces connected to the Guadaíra River and the geomorphological surface deposits from the T6 to T10 terraces were studied. Throughout these areas, a total of 20 geoarchaeological sites (with 28 lithic assemblages) were identified. These sites are associated with industries found in the alluvial sediments of the Guadalquivir, Guadaíra, and Rozalejo rivers, the karstic fillings of the Sierra de Esparteros piedmont (Cerro Santisteban), the colluvial deposits in Rozalejo and La Liebre, and the geomorphological surface deposits (Figure 2; Table 1). The alluvial and colluvial deposits are correlated with the entire Middle–Upper Pleistocene alluvial terraces in the Guadalquivir River [ 14 , 22 – 24 ]. Based on the provenance of the raw materials used in the pebble industries, two distinct groups have been identified: quartzites from the north and flint from the south. As for the nomenclature of the fluvial terraces, we have maintained our customary classification, which is based on the morphogenesis and morphotopographic position, ranging from T1 (the oldest terrace) to T14 (the most recent) [ 25 ]. Laboratory methods were employed for particle size distribution using the Soils Survey England and Wales guidelines [ 26 ], total carbonates analysis [ 27 ], and color assessment using the Munsell Color system [28]. Geosciences 2023,13, 206 4 of 32 Geosciences 2023, 13, x FOR PEER REVIEW 4 of 33 Figure 2. Geomorphological profile of the Middle–Upper Pleistocene sediments in the Guadaíra River basin, between Sierra Subbética and the alluvial connection with the Guadalquivir River (a) and its cartographic correspondence (b). Table 1. Location and main characteristics of the archaeological sites analyzed: location; archaeological site; terrace level; deposit; number of pieces; raw material (Qt, quartzite; F, flint; Qz, quartz; O, others); rounded (R0, unrounded; R1, slightly rounded; R2, moderately rounded; R3, very rounded). Location Archaeological site Terrace level Deposit Pieces nº Raw material (%) Rounded Qt F Qz O R0 R1 R2 R3 GUADALQUIVIR RIVER TAR-II T11 Loam-clay 2885 72 25 2 1 95 5 0 0 TARIII-1 T11 Gravel bars 264 92 5 2 1 99 1 0 0 TARIII-2 T11 Loam-clay 118 94 2 3 1 95 5 0 0 TARIII-3 T11 Gravel and sand bars 727 95 3 1 1 95 5 0 0 TARIII-4 T11 Gravel bars 1275 85 2 5 8 60 30 9 1 TARIII-5 T11 Floating gravels 25 84 4 8 4 95 5 0 0 MUH-4 T7 Loam-clay 273 92 7 1 0 96 4 0 0 SAL-2 T10 Loam-clay 312 78 20 0 2 81 17 2 0 CAS-1 T10 Geomorph. surface 330 89 10 0 1 85 14 1 0 PIO-1 T12 Gravel bars 62 70 25 0 5 11 27 51 11 PIO-2 T12 Gravel and sand bars 222 74 22 2 2 7 37 38 18 PIO-3 T12 Gravel and sand bars 108 48 50 0 2 17 43 31 9 PIO-4 T12 Loam-clay 54 92 8 0 0 90 4 6 0 AER-2 T12 Loam-clay 45 78 22 0 0 16 84 0 0 REY-1 T12 Gravel bars 27 99 1 0 0 0 7 27 64 REY-3 T12 Loam-clay 128 90 9 0 1 58 40 2 0 Figure 2. Geomorphological profile of the Middle–Upper Pleistocene sediments in the Guadaíra River basin, between Sierra Subbética and the alluvial connection with the Guadalquivir River (a) and its cartographic correspondence (b). 2.2. Lithic Industries: Techno-Typological Analysis, Traceology Protocol, and Use-Wear The lithic industries recovered from TAR-II, TAR-III, MUH-4, SAL-2, CAS-1, PIO (1, 2, 3, and 4), AER-2, REY (1 and 3), PIL-1, MOL-1, MAJ-1, CORT-1, CAL-1, TOR-3, PAD- 1, BAR-1, MEM-1, LIE-1, ROZ-1, and SAN-1 (Table 1) were typologically characterized, following the frameworks of Bordes [ 29 ], Tixier [ 30 ], Clark [ 31 ], Boëda et al. [ 32 , 33 ], and Caro [ 21 , 34 ]. The analysis included a technological examination of the assemblages to identify operative schemes and retouched pieces. The cores were analyzed based on three criteria: (1) the number, distribution, and hierarchy of extractions; (2) the number of flaking planes; and (3) the quantity and typology of percussion planes. Four parameters were utilized to assign the industry to a mode, including the ratio between flake tools and flakes, the variability of types of flakes, the variability and complexity of operative chains, and the proportion of large tools (presence/absence and variability factors, primarily of biface tools) [16,31,35–44]. In terms of morphometric analysis, two elements were considered: first, a comparison between the size and lithology of the raw material to assess the selection processes, and second, the categorization of the rounded lithic industries (R) into four categories: R0 (unrounded), R1 (slightly rounded), R2 (moderately rounded), and R3 (very rounded) [21,34]. Furthermore, a techno-typological analysis was conducted, following a traceology protocol applied to quartzite notches, consisting of three steps [ 45 ]: (1) use–wear analysis of the lithic pieces; (2) analysis on a binocular microscopic scale using equipment such as the Wild Heerbrugg and the Leica DMLM at the Department of Physical Geography, University of Seville; and (3) gold metallization (Sputtering, EDWARDS, Scancoat-Six) and scanning electron microscope (SEM) analysis (Jeol 6460LV) at CITIUS, Microscopy Service, University of Seville, Spain, with the magnification ranging from 100 to 1000 times. The use–wear analysis involved studying micro-traces related to the main features, such as polish, rounding, striation, or ridge concavities. Additionally, an experimental analysis was conducted. Geosciences 2023,13, 206 5 of 32 Table 1. Location and main characteristics of the archaeological sites analyzed: location; archaeological site; terrace level; deposit; number of pieces; raw material (Qt, quartzite; F, flint; Qz, quartz; O, others); rounded (R0, unrounded; R1, slightly rounded; R2, moderately rounded; R3, very rounded). Location Archaeological Site Terrace Level Deposit Pieces nº Raw Material (%) Rounded Qt F Qz O R0 R1 R2 R3 GUADALQUIVIR RIVER TAR-II T11 Loam-clay 2885 72 25 2 1 95 5 0 0 TARIII-1 T11 Gravel bars 264 92 5 2 1 99 1 0 0 TARIII-2 T11 Loam-clay 118 94 2 3 1 95 5 0 0 TARIII-3 T11 Gravel and sand bars 727 95 3 1 1 95 5 0 0 TARIII-4 T11 Gravel bars 1275 85 2 5 8 60 30 9 1 TARIII-5 T11 Floating gravels 25 84 4 8 4 95 5 0 0 MUH-4 T7 Loam-clay 273 92 7 1 0 96 4 0 0 SAL-2 T10 Loam-clay 312 78 20 0 2 81 17 2 0 CAS-1 T10 Geomorph. surface 330 89 10 0 1 85 14 1 0 PIO-1 T12 Gravel bars 62 70 25 0 5 11 27 51 11 PIO-2 T12 Gravel and sand bars 222 74 22 2 2 7 37 38 18 PIO-3 T12 Gravel and sand bars 108 48 50 0 2 17 43 31 9 PIO-4 T12 Loam-clay 54 92 8 0 0 90 4 6 0 AER-2 T12 Loam-clay 45 78 22 0 0 16 84 0 0 REY-1 T12 Gravel bars 27 99 1 0 0 0 7 27 64 REY-3 T12 Loam-clay 128 90 9 0 1 58 40 2 0 PIL-1 T9 Geomorph. surface 590 91 7 1 1 91 8 1 0 MOL-1 T9 Geomorph. surface 2159 94 5 0 1 4 92 4 0 MAJ-1 T6 Geomorph. surface 195 99 1 0 0 0 58 37 5 COR-1 T6 Geomorph. surface 222 98 1,5 0 0,5 0 54 44 2 CAL-1 T8 Geomorph. surface 91 90 9 0 1 20 79 1 0 TOR-3 T7 Geomorph. surface 190 85 12 1 2 94 6 0 0 PAD-1 T7 Geomorph. surface 950 93 6 0 1 14 51 28 7 GUADAIRA RIVER BAR-1 Geomorph. surface 44 75 23 2 0 75 25 0 0 MEM-1 T (+10) Gravels and fine grav. 3 0 100 0 0 100 0 0 0 LIE-1 Geomorph. surface 45 96 2 0 0 100 0 0 0 ROZ-1 Coll/alluv Geomorph. surface 208 18 80 0 2 100 0 0 0 KARSTIC PIEDMONT SAN-1 Karst detrial fill 1656 2 92 0 6 100 0 0 0 2.3. Functionality Criteria of the Archaeological Sites To interpret the functionality of the archaeological sites as part of the HAC, two sets of criteria were employed. The first set focused on the operative chain, considering the technological aspects, such as the breadth and balance of the series, the dimensions and composition of the artifacts, the presence or absence of knapping remains, and the abundance of retouched tools. The second set of criteria pertained to taphonomic features, including the type of deposit, the lithic rounded index, etc. Geosciences 2023,13, 206 6 of 32 Based on these criteria, four categories of functionality were established: (HS) habitual or recurrent site, (TS) temporary site, (LW) lithic workshop, and (IN) indeterminate. However, this paper does not address subsistence strategies [ 46 – 48 ], as fauna remains were only found in the detrital fill site of the Cerro Santisteban karst, and they have not yet undergone stratigraphic analysis. Similarly, the Pioneer (PIO) site exhibits displaced fauna remains (Equus sp., Bos sp., etc.) that have not been thoroughly studied. 2.4. Chronological Framework The chronological framework was established using optically stimulated luminescence (OSL) and uranium–thorium (U/Th) dating techniques conducted by two different laboratories: the Laboratorio de Datación Radioquímica (LDR) at the Autonomous University of Madrid, and the Laboratorio de Física Aplicada I at the University of Seville, both located in Spain. The Tarazona III chronologies are based on chronological analysis using OSL dates, which were previously published [ 22 ]. On the contrary, the samplings from La Barranca and Marchenilla were studied for the first time in this study. OSL dating and the additive dose method were carried out in order to determine the time elapsed since the last exposure to sunlight of the sediments. The samples were subjected to a previous anomalous decay test; this study was carried out from the OSL response (TL-DA-10 system) obtained from the samples in a second scan, after being stored in the dark for a period of time of 600 h. Thus, when the detected signal losses were less than 3%, the test was considered negative, and the possible anomalous decay phenomenon was insignificant. The signal losses detected in the samples studied were always less than 1%. Based on these results, the selected dating method was the fine-grained one [ 49 ], consisting of a selection of the mineral fraction with a grain size between 2 and 10 microns. The total dose stored by each sample since it underwent its last solar bleaching process (equivalent dose) was evaluated by the additive dose method. Increasing doses were supplied by a Sr-Y90 source with a dose rate of 0.0404 Gy/sec. In order to determine a possible supralinear behavior, a second scan was carried out, with small beta doses [ 50 ]. The effectiveness of the alpha particles in producing OSL (K factor) was determined by delivering increasing alpha doses using an Am 241 source, with a dose rate of 0.0297 Gy/sg. The annual doses received by the samples were calculated by combining two types of measurements, including the determination of the beta radioactivity from the K-40 present in the samples using a Geiger–Müller counting system and the measurement of alpha activity from uranium and thorium, also present in the samples, in this case, using a solid scintillation (ZnS) counting system. In the latter method, no activity losses were observed as a consequence of possible radon leaks. The gamma activity from cosmic radiation was measured in situ during the sampling by means of an INa(TL) solid scintillation counting system. Conversions of the alpha, beta, and cosmic count rates to the dose rate were made based on studies by Nambi and Aitken [51]. The errors associated with the estimated ages took into account both the systematic and statistical errors corresponding to the OSL measurements, established dose rates, and calibration processes of the radioactive sources and equipment used [52,53]. U/Th analyses were conducted on the sediments filling the Cerro Santisteban site. Specifically, ten samples of bones and teeth, as well as two samples of carbonated sediments from palustrine facies, were studied. The sample treatment involved dissolving 1 to 5 g of a bone or tooth sample in concentrated nitric acid. Known amounts of 232U and 229Th were added to the solutions prior to the precipitation of Fe hydroxides, along with U and Th isotopes. The precipitate was then dissolved in HCl, and controlled precipitation to pH 2.5–3.0 was carried out to separate P and U from Th. A solvent extraction method using TBP and xylene was employed to further separate P from U and Fe from Th. Finally, both elements underwent additional purification using anion exchange resin (Dowex AG1- X8). The purified samples were electro-deposited on stainless steel discs and measured Geosciences 2023,13, 206 7 of 32 using alpha spectrometry. The results of the analyses indicate isotopic equilibrium in all the samples, suggesting consistency with the obtained isotopic data and providing a chronology ranging from the Late–Middle Pleistocene to the Upper Pleistocene. 3. Results 3.1. Guadaíra Watershed: Distribution of Archaeological Sites with Lithic Industries per Geomorphological Units The alluvial terrace system of the Guadaíra River is located between the Subbetic karstic piedmont and the T12 terrace level of the Guadalquivir River, which is situated at an elevation of +26 to +29 m. 3.1.1. Karstic Piedmont of the Sierra de Esparteros and Cerro Santisteban Among the limestone formations on the northern slope of the Sierra de Esparteros and within the Guadaíra watershed, remnants of a karstic piedmont can be observed at an approximate elevation of 320 m. This piedmont has undergone erosion and dissection due to the fluvial activity of the Guadaíra River and its tributaries, such as the Rozalejo River. The limestone outcrops are situated at a higher morphotopographic position, forming a prominent hill known as Cerro Santisteban (250 m). This hill is composed of oolitic limestones and displays a karstified piedmont surface. The ridges of Cerro Santisteban exhibit an epikarst layer, with an underlying sequence of detrital fill referred to as SAN-1 (Figure 3). The detrital deposit in SAN-1 reveals a lower section (level 2.1, Table 2) comprising silt, sand, limestone fragments, and flint clasts. In the upper part (level 2.2, Table 2), a brecciated conglomerate is present, consisting of clasts, lithic industries, herbivorous bones, and teeth. The isotopic dating of carbonate samples from bones and teeth yielded a chronology ranging from 135.5 ±9.9 ka to 74.8 ±13.2 ka BP (U/Th) (Table 3). Geosciences 2023, 13, x FOR PEER REVIEW 8 of 33 3. Results 3.1. Guadaíra Watershed: Distribution of Archaeological Sites with Lithic Industries per Geomorphological Units The alluvial terrace system of the Guadaíra River is located between the Subbetic karstic piedmont and the T12 terrace level of the Guadalquivir River, which is situated at an elevation of +26 to +29 m. 3.1.1. Karstic Piedmont of the Sierra de Esparteros and Cerro Santisteban Among the limestone formations on the northern slope of the Sierra de Esparteros and within the Guadaíra watershed, remnants of a karstic piedmont can be observed at an approximate elevation of 320 m. This piedmont has undergone erosion and dissection due to the fluvial activity of the Guadaíra River and its tributaries, such as the Rozalejo River. The limestone outcrops are situated at a higher morphotopographic position, forming a prominent hill known as Cerro Santisteban (250 m). This hill is composed of oolitic limestones and displays a karstified piedmont surface. The ridges of Cerro Santisteban exhibit an epikarst layer, with an underlying sequence of detrital fill referred to as SAN-1 (Figure 3). The detrital deposit in SAN-1 reveals a lower section (level 2.1, Table 2) comprising silt, sand, limestone fragments, and flint clasts. In the upper part (level 2.2, Table 2), a brecciated conglomerate is present, consisting of clasts, lithic industries, herbivorous bones, and teeth. The isotopic dating of carbonate samples from bones and teeth yielded a chronology ranging from 135.5 ± 9.9 ka to 74.8 ± 13.2 ka BP (U/Th) (Table 3). Figure 3. Cerro Santisteban’s stratigraphic levels description: (1) substratum outcrop; (2.1) detrital fill (silt, sand–limestone, and flint clasts); (2.2) detrital fill (brecciated conglomerate, clast; herbivorous teeth and bones; lithic industry); (3) breccia (clasts and stone blocks). Figure 3. Cerro Santisteban’s stratigraphic levels description: (1) substratum outcrop; (2.1) detrital fill (silt, sand–limestone, and flint clasts); (2.2) detrital fill (brecciated conglomerate, clast; herbivorous teeth and bones; lithic industry); (3) breccia (clasts and stone blocks). Geosciences 2023,13, 206 8 of 32 Table 2. Cerro Santisteban’s stratigraphic levels description (elements and chronologies). Site Stratigraphical Levels and Processes Particle Size Distribution Blue: Sands Red: Silt-Clay Munsell Colour C0=3 %Lithology Chronology U/Th Industry Cerro Santisteban: karstic piedmond 5.- Pedogenesis Geosciences 2023, 13, x FOR PEER REVIEW 9 of 33 Table 2. Cerro Santisteban’s stratigraphic levels description (elements and chronologies). Table 3. Santisteban’s U/Th results and chronologies. All bones and the tooth were dated using the early uptake model. No diacritical corrections were made in any of the samples. The 234U/238U activity ratio in the last column is the activity ratio between both uranium isotopes at the initial time. Sample 238U 234U 234U/238U 230Th 230Th/234U 230Th/232Th T (ky) 234U/238U G2.1-1 15.36±0.32 17.23±0.34 1.122±0.025 9.64±0.21 0.559±0.017 80±12 87.3±3.9 1.155±0.033 G2.1-2 13.03±0.35 14.55±0.38 1.117±0.036 8.23±0.29 0.566±0.025 56.7±11.3 88.9±5.9 1.149±0.046 G2.2-1 14.49±0.31 17.25±0.34 1.191±0.028 12.02±0.30 0.697±0.022 89±17 123.6±7.1 1.270±0.040 G2.2-2 13.22±0.29 15.75±0.33 1.192±0.028 11.53±0.37 0.733±0.028 26.1±3.6 135.5±9.9 1.280±0.041 G2.3-1 2.567±0.071 3.147±0.081 1.226±0.042 1.939±0.252 0.616±0.082 20.7±9.6 99.9±21.2 1.299±0.056 G2.3-2 2.560±0.072 3.108±0.081 1.214±0.041 2.290±0.147 0.737±0.051 12.7±2.5 136.4±18.1 1.313±0.060 G2.4-1 2.005±0.047 2.478±0.053 1.236±0.034 1.658±0.082 0.669±0.036 13.1±2.2 114.2±10.5 1.324±0.047 G2.4-thooth 1.147±0.040 1.402±0.044 1.223±0.054 0.869±0.078 0.620±0.059 96.1±56.1 100.9±15.3 1.296±0.072 G2.5-1 3.478±0.083 3.942±0.089 1.133±0.033 1.986±0.241 0.504±0.062 23.7±10.9 74.8±13.2 1.164±0.040 Site Stratigraphical levels and processes Particle size distribution Blue: sands Red: silt-clay Munsell colour C0=3 % Lithology Chronology U/Th Industry Cerro Santisteban: karstic piedmond 5.- Pedogenesis 10YR 5/3 7.5YR 4/4 7.5YR 4/6 - 4.- Palustrine carbonates. 7.5YR 7/6 76 69.8 ± 2.7 ka 71.7 ± 3.7 ka Karstification espisode 3.- Breccia (clast and stone block) 2.2.- Detrital fill (brecciated conglomerate, clast; herbivorous teeth and bones) 10YR 4/3 10YR 4/4 50 0 Limestone Flint 74.8 ± 13.2 ka 78.2 ± 5.5 ka 87.3 ± 3.9 ka 88.9 ± 5.9 ka 99.9 ± 21.2 ka 100.9 ± 15.3 ka 114.2 ± 10.5 ka 123.6 ± 7.1 ka 135.5 ± 9.9 ka 136.4 ± 18.1 ka Middle Palaeolithic 2.1.- Detrital fill (silt, sand and limestone and flint clasts). 10YR 6/2 7.5YR 8/4 56 90 Limestone Flint 1.- Substrate outcrop 10YR 5/3 7.5YR 4/4 7.5YR 4/6 - 4.- Palustrine carbonates. Geosciences 2023, 13, x FOR PEER REVIEW 9 of 33 Table 2. Cerro Santisteban’s stratigraphic levels description (elements and chronologies). Table 3. Santisteban’s U/Th results and chronologies. All bones and the tooth were dated using the early uptake model. No diacritical corrections were made in any of the samples. The 234U/238U activity ratio in the last column is the activity ratio between both uranium isotopes at the initial time. Sample 238U 234U 234U/238U 230Th 230Th/234U 230Th/232Th T (ky) 234U/238U G2.1-1 15.36±0.32 17.23±0.34 1.122±0.025 9.64±0.21 0.559±0.017 80±12 87.3±3.9 1.155±0.033 G2.1-2 13.03±0.35 14.55±0.38 1.117±0.036 8.23±0.29 0.566±0.025 56.7±11.3 88.9±5.9 1.149±0.046 G2.2-1 14.49±0.31 17.25±0.34 1.191±0.028 12.02±0.30 0.697±0.022 89±17 123.6±7.1 1.270±0.040 G2.2-2 13.22±0.29 15.75±0.33 1.192±0.028 11.53±0.37 0.733±0.028 26.1±3.6 135.5±9.9 1.280±0.041 G2.3-1 2.567±0.071 3.147±0.081 1.226±0.042 1.939±0.252 0.616±0.082 20.7±9.6 99.9±21.2 1.299±0.056 G2.3-2 2.560±0.072 3.108±0.081 1.214±0.041 2.290±0.147 0.737±0.051 12.7±2.5 136.4±18.1 1.313±0.060 G2.4-1 2.005±0.047 2.478±0.053 1.236±0.034 1.658±0.082 0.669±0.036 13.1±2.2 114.2±10.5 1.324±0.047 G2.4-thooth 1.147±0.040 1.402±0.044 1.223±0.054 0.869±0.078 0.620±0.059 96.1±56.1 100.9±15.3 1.296±0.072 G2.5-1 3.478±0.083 3.942±0.089 1.133±0.033 1.986±0.241 0.504±0.062 23.7±10.9 74.8±13.2 1.164±0.040 Site Stratigraphical levels and processes Particle size distribution Blue: sands Red: silt-clay Munsell colour C0=3 % Lithology Chronology U/Th Industry Cerro Santisteban: karstic piedmond 5.- Pedogenesis 10YR 5/3 7.5YR 4/4 7.5YR 4/6 - 4.- Palustrine carbonates. 7.5YR 7/6 76 69.8 ± 2.7 ka 71.7 ± 3.7 ka Karstification espisode 3.- Breccia (clast and stone block) 2.2.- Detrital fill (brecciated conglomerate, clast; herbivorous teeth and bones) 10YR 4/3 10YR 4/4 50 0 Limestone Flint 74.8 ± 13.2 ka 78.2 ± 5.5 ka 87.3 ± 3.9 ka 88.9 ± 5.9 ka 99.9 ± 21.2 ka 100.9 ± 15.3 ka 114.2 ± 10.5 ka 123.6 ± 7.1 ka 135.5 ± 9.9 ka 136.4 ± 18.1 ka Middle Palaeolithic 2.1.- Detrital fill (silt, sand and limestone and flint clasts). 10YR 6/2 7.5YR 8/4 56 90 Limestone Flint 1.- Substrate outcrop 7.5YR 7/6 76 69.8 ±2.7 ka 71.7 ±3.7 ka Karstification espisode 3.- Breccia (clast and stone block) 2.2.- Detrital fill (brecciated conglomerate, clast; herbivorous teeth and bones) Geosciences 2023, 13, x FOR PEER REVIEW 9 of 33 Table 2. Cerro Santisteban’s stratigraphic levels description (elements and chronologies). Table 3. Santisteban’s U/Th results and chronologies. All bones and the tooth were dated using the early uptake model. No diacritical corrections were made in any of the samples. The 234U/238U activity ratio in the last column is the activity ratio between both uranium isotopes at the initial time. Sample 238U 234U 234U/238U 230Th 230Th/234U 230Th/232Th T (ky) 234U/238U G2.1-1 15.36±0.32 17.23±0.34 1.122±0.025 9.64±0.21 0.559±0.017 80±12 87.3±3.9 1.155±0.033 G2.1-2 13.03±0.35 14.55±0.38 1.117±0.036 8.23±0.29 0.566±0.025 56.7±11.3 88.9±5.9 1.149±0.046 G2.2-1 14.49±0.31 17.25±0.34 1.191±0.028 12.02±0.30 0.697±0.022 89±17 123.6±7.1 1.270±0.040 G2.2-2 13.22±0.29 15.75±0.33 1.192±0.028 11.53±0.37 0.733±0.028 26.1±3.6 135.5±9.9 1.280±0.041 G2.3-1 2.567±0.071 3.147±0.081 1.226±0.042 1.939±0.252 0.616±0.082 20.7±9.6 99.9±21.2 1.299±0.056 G2.3-2 2.560±0.072 3.108±0.081 1.214±0.041 2.290±0.147 0.737±0.051 12.7±2.5 136.4±18.1 1.313±0.060 G2.4-1 2.005±0.047 2.478±0.053 1.236±0.034 1.658±0.082 0.669±0.036 13.1±2.2 114.2±10.5 1.324±0.047 G2.4-thooth 1.147±0.040 1.402±0.044 1.223±0.054 0.869±0.078 0.620±0.059 96.1±56.1 100.9±15.3 1.296±0.072 G2.5-1 3.478±0.083 3.942±0.089 1.133±0.033 1.986±0.241 0.504±0.062 23.7±10.9 74.8±13.2 1.164±0.040 Site Stratigraphical levels and processes Particle size distribution Blue: sands Red: silt-clay Munsell colour C0=3 % Lithology Chronology U/Th Industry Cerro Santisteban: karstic piedmond 5.- Pedogenesis 10YR 5/3 7.5YR 4/4 7.5YR 4/6 - 4.- Palustrine carbonates. 7.5YR 7/6 76 69.8 ± 2.7 ka 71.7 ± 3.7 ka Karstification espisode 3.- Breccia (clast and stone block) 2.2.- Detrital fill (brecciated conglomerate, clast; herbivorous teeth and bones) 10YR 4/3 10YR 4/4 50 0 Limestone Flint 74.8 ± 13.2 ka 78.2 ± 5.5 ka 87.3 ± 3.9 ka 88.9 ± 5.9 ka 99.9 ± 21.2 ka 100.9 ± 15.3 ka 114.2 ± 10.5 ka 123.6 ± 7.1 ka 135.5 ± 9.9 ka 136.4 ± 18.1 ka Middle Palaeolithic 2.1.- Detrital fill (silt, sand and limestone and flint clasts). 10YR 6/2 7.5YR 8/4 56 90 Limestone Flint 1.- Substrate outcrop 10YR 4/3 10YR 4/4 50 0 Limestone Flint 74.8 ±13.2 ka 78.2 ±5.5 ka 87.3 ±3.9 ka 88.9 ±5.9 ka 99.9 ±21.2 ka 100.9 ±15.3 ka 114.2 ±10.5 ka 123.6 ±7.1 ka 135.5 ±9.9 ka 136.4 ±18.1 ka Middle Palaeolithic 2.1.- Detrital fill (silt, sand and limestone and flint clasts). Geosciences 2023, 13, x FOR PEER REVIEW 9 of 33 Table 2. Cerro Santisteban’s stratigraphic levels description (elements and chronologies). Table 3. Santisteban’s U/Th results and chronologies. All bones and the tooth were dated using the early uptake model. No diacritical corrections were made in any of the samples. The 234U/238U activity ratio in the last column is the activity ratio between both uranium isotopes at the initial time. Sample 238U 234U 234U/238U 230Th 230Th/234U 230Th/232Th T (ky) 234U/238U G2.1-1 15.36±0.32 17.23±0.34 1.122±0.025 9.64±0.21 0.559±0.017 80±12 87.3±3.9 1.155±0.033 G2.1-2 13.03±0.35 14.55±0.38 1.117±0.036 8.23±0.29 0.566±0.025 56.7±11.3 88.9±5.9 1.149±0.046 G2.2-1 14.49±0.31 17.25±0.34 1.191±0.028 12.02±0.30 0.697±0.022 89±17 123.6±7.1 1.270±0.040 G2.2-2 13.22±0.29 15.75±0.33 1.192±0.028 11.53±0.37 0.733±0.028 26.1±3.6 135.5±9.9 1.280±0.041 G2.3-1 2.567±0.071 3.147±0.081 1.226±0.042 1.939±0.252 0.616±0.082 20.7±9.6 99.9±21.2 1.299±0.056 G2.3-2 2.560±0.072 3.108±0.081 1.214±0.041 2.290±0.147 0.737±0.051 12.7±2.5 136.4±18.1 1.313±0.060 G2.4-1 2.005±0.047 2.478±0.053 1.236±0.034 1.658±0.082 0.669±0.036 13.1±2.2 114.2±10.5 1.324±0.047 G2.4-thooth 1.147±0.040 1.402±0.044 1.223±0.054 0.869±0.078 0.620±0.059 96.1±56.1 100.9±15.3 1.296±0.072 G2.5-1 3.478±0.083 3.942±0.089 1.133±0.033 1.986±0.241 0.504±0.062 23.7±10.9 74.8±13.2 1.164±0.040 Site Stratigraphical levels and processes Particle size distribution Blue: sands Red: silt-clay Munsell colour C0=3 % Lithology Chronology U/Th Industry Cerro Santisteban: karstic piedmond 5.- Pedogenesis 10YR 5/3 7.5YR 4/4 7.5YR 4/6 - 4.- Palustrine carbonates. 7.5YR 7/6 76 69.8 ± 2.7 ka 71.7 ± 3.7 ka Karstification espisode 3.- Breccia (clast and stone block) 2.2.- Detrital fill (brecciated conglomerate, clast; herbivorous teeth and bones) 10YR 4/3 10YR 4/4 50 0 Limestone Flint 74.8 ± 13.2 ka 78.2 ± 5.5 ka 87.3 ± 3.9 ka 88.9 ± 5.9 ka 99.9 ± 21.2 ka 100.9 ± 15.3 ka 114.2 ± 10.5 ka 123.6 ± 7.1 ka 135.5 ± 9.9 ka 136.4 ± 18.1 ka Middle Palaeolithic 2.1.- Detrital fill (silt, sand and limestone and flint clasts). 10YR 6/2 7.5YR 8/4 56 90 Limestone Flint 1.- Substrate outcrop 10YR 6/2 7.5YR 8/4 56 90 Limestone Flint 1.- Substrate outcrop Geosciences 2023,13, 206 9 of 32 Table 3. Santisteban’s U/Th results and chronologies. All bones and the tooth were dated using the early uptake model. No diacritical corrections were made in any of the samples. The 234U/238U activity ratio in the last column is the activity ratio between both uranium isotopes at the initial time. Sample 238U234U234U/238U230Th 230Th/234U230Th/232Th T (ky) 234U/238U G2.1-1 15.36 ±0.32 17.23 ±0.34 1.122 ±0.025 9.64 ±0.21 0.559 ±0.017 80 ±12 87.3 ±3.9 1.155 ±0.033 G2.1-2 13.03 ±0.35 14.55 ±0.38 1.117 ±0.036 8.23 ±0.29 0.566 ±0.025 56.7 ±11.3 88.9 ±5.9 1.149 ±0.046 G2.2-1 14.49 ±0.31 17.25 ±0.34 1.191 ±0.028 12.02 ±0.30 0.697 ±0.022 89 ±17 123.6 ±7.1 1.270 ±0.040 G2.2-2 13.22 ±0.29 15.75 ±0.33 1.192 ±0.028 11.53 ±0.37 0.733 ±0.028 26.1 ±3.6 135.5 ±9.9 1.280 ±0.041 G2.3-1 2.567 ±0.071 3.147 ±0.081 1.226 ±0.042 1.939 ±0.252 0.616 ±0.082 20.7 ±9.6 99.9 ±21.2 1.299 ±0.056 G2.3-2 2.560 ±0.072 3.108 ±0.081 1.214 ±0.041 2.290 ±0.147 0.737 ±0.051 12.7 ±2.5 136.4 ±18.1 1.313 ±0.060 G2.4-1 2.005 ±0.047 2.478 ±0.053 1.236 ±0.034 1.658 ±0.082 0.669 ±0.036 13.1 ±2.2 114.2 ±10.5 1.324 ±0.047 G2.4-thooth 1.147 ±0.040 1.402 ±0.044 1.223 ±0.054 0.869 ±0.078 0.620 ±0.059 96.1 ±56.1 100.9 ±15.3 1.296 ±0.072 G2.5-1 3.478 ±0.083 3.942 ±0.089 1.133 ±0.033 1.986 ±0.241 0.504 ±0.062 23.7 ±10.9 74.8 ±13.2 1.164 ±0.040 G2.5-2 2.875 ±0.061 3.434 ±0.069 1.194 ±0.029 1.793 ±0.081 0.522 ±0.026 15.2 ±2.5 78.2 ±5.5 1.242 ±0.036 W1.CR2-1 2.387 ±0.045 2.825 ±0.052 1.184 ±0.014 1.360 ±0.029 0.481 ±0.014 25.8 ±1.7 69.8 ±2.7 1.223 ±0.017 W1.CR2-2 2.464 ±0.047 2.879 ±0.054 1.168 ±0.014 1.411 ±0.044 0.490 ±0.018 24.2 ±2.2 71.7 ±3.7 1.206 ±0.017 Geosciences 2023,13, 206 16 of 32 Geosciences 2023, 13, x FOR PEER REVIEW 16 of 33 Figure 5. Pioneer lithic industry. PIO-1: scrapers (4, 6, and 8), handaxe (14); PIO-2: chopping tool (1), natural backed knives (2), backed knives (3), scraper (5), notch (10); PIO-3: scrapers (7 and 9), notch (11), borers (12 and 13). Raw materials: quartzites (1, 2, 3, 4, 5, 6, 7, 8, 10, 11, and 14); flint (9, 12 and 13). 3.2.2. Sand Bars of Alluvial Deposits with Pebble and Fine Gravels in Matrix (T11 Pioneer and Tarazona III Sites) The lithological composition is dominated by quartzite (60–65%) and quartz (20– 25%), accompanied by sandstone, shale, limestone, and other materials. Within the lithic assemblages, simple flakes comprise the majority (M = 55%), followed by cores (M = 32%) and tools (M = 17%). The presence of large tools, specifically trihedrons, is merely sporadic and even less common in PIO-2, where there is only one bifacial index value of 17. Quartzite is the predominant raw material, accounting for over 80% of the assemblages, particularly in the T11 series (TARIII-1, 3, 4, and 5) (Figure 6). However, in the assemblages of T12, the proportion of flint increases (22% in PIO-2 and 50% in PIO-3) (Figure 5). Figure 6. Lithic industry. Tarazona III (TARIII-4): choppers (1, 2, and 3); scrapers (4, 5, and 6); notches (7, 8, and 9) and denticulate (10) (in quartzites). Tarazona II (TARII): handaxes (11 and 12); cleaver (13); scrapers (14, 15, and 16); Levallois flake (17); Levallois point (18, 19, and 20); Mousterian point (21) and borer (22). Raw materials: quartzite (11, 12, 13, 14, and 17); flint (15, 16, 18, 19, 20, 21, and 22). The rounding of the tools exhibits a dual modality: in the T11 series, they appear with little to no rounding (R1 and R0), while in the T12 series, although some elements lack rounding, the majority exhibit a high level of rounding (R2 and R3). From a technological perspective, there is a general absence of the Levallois group, except in PIO-3, where it has a small representation (9%), and there is an acceptable presence of Groups II and III (M= 22% and 20% respectively), except in PIO-2 (3%). Conversely, Group IV is well represented in T11 (15%), while in T12, it appears only minimally, in contrast to the high representation of notches found in every site (M= 27%). The faceting index is minimal or absent throughout the entire series. Geosciences 2023,13, 206 17 of 32 3.2.3. Massive Loam–Clay or Sandy–Clay Alluvial Deposits (T7 to T12: Muharra, Saltillo, Caleras, Toril, Tarazona II, Tarazona IIII, Pioneer, Aeropuerto, and Fuente del Rey sites) The Upper Pleistocene alluvial terraces of the Guadalquivir River frequently exhibit deposits containing pebbles and fine gravels, either suspended within the matrix or found in small channels. The lithology of these pebbles and fine gravels is predominantly composed of quartzite (45%), quartz (25%), quartzite sandstone (15%), and other materials (15%). Quartzite is the primary raw material utilized for knapping in two types of assemblages: those with a minimal presence of flint (MH4, TARIII-2, PIO-4, and REY-3), and those where the flint exceeds 20% (SAL-2, TAR-II, and AER-2). Technologically, simple flakes (M= 55%) and tools (>20%) are prominent. Macro-tools are particularly notable in TAR-II (Figure 6). The artifacts generally appear unrounded (90% R0) or lightly rounded (8% R1), occasionally with some showing moderate rounding (2% R2). The series exhibits significant Levallois indices (Li 16%). In the TARIII-2 series, no Levallois elements are present, perhaps due to the scarcity of recovered artifacts. Group II is the most represented across practically all series, with its peak in AER-2 (78%), consisting primarily of various types of scrapers. Group III is similarly represented (M= 15%) in AER-2 and TARIII-2. Denticulates also appear in similar percentages in the majority of the series (M= 5%), with a notable presence of 14% in TARIII-2. Notches are observed in varying proportions: low (M= 8%), elevated (>20%), and one remarkable case reaching 57% (TARIII-2). The lithic assemblage faceting index in this deposit is one of the highest (Fi 15), although it should be noted that certain assemblages of retouched flakes exhibit considerably higher indices of Fi 25 (SAL-2) or Fi 22 (TARIII-2). 3.2.4. Surface Geomorphological Deposits (T6 to T10: Pilar, Molinillos, Majapán, Cortés, Caleras, Toril, Padrecito, and Castilleja sites) The archaeological sites situated on the surface of geomorphological deposits reveal extensive assemblages characterized by a significant presence of simple flakes (M= 47%), accompanied by a noteworthy abundance of utensils (M= 28%), most of which are in flake form. The Levallois group is well represented in the assemblages (M= 14%), with CAS-1 displaying the highest values (Li 28) (Figure 7), and Group II being the most prominent (M= 42–60%) . Group II consists primarily of various types of scrapers, with simple scrapers being the most common. Group III also exhibits good representation (M = 19%), reaching up to 33% in certain assemblages, making it the most prevalent in CAL-1. Group IV is present in all the assemblages (5–15%), except for TOR-3. Notches are consistently present across all series, typically averaging around 9%. These surface assemblages generally exhibit low faceting indexes, although some pieces show a significant increase in the index value when retouched flakes are included (CAL-1, Fi 29). From a lithological perspective, quartzite dominates the assemblages (92%), while flint comprises a smaller proportion (5–10%). The majority of the series displays unrounded artifacts (90% R0), with elements exhibiting mild rounding (R2) reaching up to 30%. In the higher terraces (T6 and T7), artifacts displaying high levels of rounding (R3) become more prominent. 3.3. Raw Material, Lithic Industry Assemblages, and Use–Wear SEM Analyses This section of the study examines the Middle Paleolithic lithic assemblages found in the open-air archaeological sites situated on the Middle–Low Terraces of the Guadalquivir and Cerro Santisteban, along with five additional archaeological sites that have not yet been published, located in the lower section of the Guadaíra slope. In total, the study analyzed and interpreted 28 archaeological sites. Geosciences 2023,13, 206 18 of 32 Geosciences 2023, 13, x FOR PEER REVIEW 18 of 33 10%). The majority of the series displays unrounded artifacts (90% R0), with elements exhibiting mild rounding (R2) reaching up to 30%. In the higher terraces (T6 and T7), artifacts displaying high levels of rounding (R3) become more prominent. Figure 7. Castilleja (CAS-1) lithic industry: Handaxe (1), Levallois flakes (2, 3, and 4), scrapers (5, 6, and 7), truncated piece (8), borers (9 and 10), end scrapers (11, 12, 13, and 14). Raw materials: quartzite (1, 2, 3, 4, 5, 6, 7, 10, 12, and 13); flint (8, 9, and 11). 3.3. Raw Material, Lithic Industry Assemblages, and Use–Wear SEM Analyses This section of the study examines the Middle Paleolithic lithic assemblages found in the open-air archaeological sites situated on the Middle–Low Terraces of the Guadalquivir and Cerro Santisteban, along with five additional archaeological sites that have not yet been published, located in the lower section of the Guadaíra slope. In total, the study analyzed and interpreted 28 archaeological sites. 3.3.1. Raw Material: Significant Geographical Distribution of Archaeological Sites The search for higher-quality raw materials for knapping was a consistent pursuit during the Middle Paleolithic [55–59]. In line with this interpretation, recent studies have emphasized the role of medium-sized tributary rivers’ watersheds as a geoarchaeological Figure 7. Castilleja (CAS-1) lithic industry: Handaxe (1), Levallois flakes (2, 3, and 4), scrapers (5, 6, and 7), truncated piece (8), borers (9 and 10), end scrapers (11, 12, 13, and 14). Raw materials: quartzite (1, 2, 3, 4, 5, 6, 7, 10, 12, and 13); flint (8, 9, and 11). 3.3.1. Raw Material: Significant Geographical Distribution of Archaeological Sites The search for higher-quality raw materials for knapping was a consistent pursuit during the Middle Paleolithic [ 55 – 59 ]. In line with this interpretation, recent studies have emphasized the role of medium-sized tributary rivers’ watersheds as a geoarchaeological framework for developing mobility strategies, including the search for raw materials and the implementation of subsistence activities [ 8 , 60 , 61 ]. Thus, in this regard, we offer an interpretation of the connectivity between the Guadalquivir and Guadaíra watersheds. The presence of Middle Paleolithic lithic industries, consisting of well-crafted flint and quartzite knapped in situ, serves as the geoarchaeological evidence for hominid mobility strategies during the late Middle Pleistocene (TAR-II) and the entire Upper Pleistocene period (Figure 8). Geosciences 2023,13, 206 19 of 32 Geosciences 2023, 13, x FOR PEER REVIEW 19 of 33 framework for developing mobility strategies, including the search for raw materials and the implementation of subsistence activities [8,60,61]. Thus, in this regard, we offer an interpretation of the connectivity between the Guadalquivir and Guadaíra watersheds. The presence of Middle Paleolithic lithic industries, consisting of well-crafted flint and quartzite knapped in situ, serves as the geoarchaeological evidence for hominid mobility strategies during the late Middle Pleistocene (TAR-II) and the entire Upper Pleistocene period (Figure 8). Figure 8. Comparative graph of the use of raw materials in percentages in the different geomorphological areas of the HAC. The lithic assemblages obtained exhibit minimal or no displacement (R0). This mobility strategy is evident in two significant geographical references: first, the distribution of quartzite pebbles from the Guadalquivir’s alluvial deposits, which were transported by hominids to the Guadaíra watershed for in situ knapping; second, the presence of flint lithic assemblages that were transported from the Subbetic limestone outcrops in the Guadaíra region to the archaeological sites in the Guadalquivir alluvial terraces, where they were also knapped in situ. In the deposits of the Guadalquivir’s T10, T11, and T12 Middle Terraces, which consist of channel bars and lake–palustrine sediments, the Middle Paleolithic assemblages are predominantly made of quartzite raw material (M = 70–80%). The presence of flint ranges from 25% to 50% in the T12 deposits, which can be attributed to the Subbetic outcrops located approximately 44 km away in a straight line or slightly more (50 km) following the Guadaíra–Rozalejo thalweg. The lithic industries found at the top of these alluvial terraces are associated with hydromorphic formations (10YR) or Vertisol soils (TARIII-2, 10 Figure 8. Comparative graph of the use of raw materials in percentages in the different geomorphological areas of the HAC. The lithic assemblages obtained exhibit minimal or no displacement (R0). This mobility strategy is evident in two significant geographical references: first, the distribution of quartzite pebbles from the Guadalquivir’s alluvial deposits, which were transported by hominids to the Guadaíra watershed for in situ knapping; second, the presence of flint lithic assemblages that were transported from the Subbetic limestone outcrops in the Guadaíra region to the archaeological sites in the Guadalquivir alluvial terraces, where they were also knapped in situ. In the deposits of the Guadalquivir’s T10, T11, and T12 Middle Terraces, which consist of channel bars and lake–palustrine sediments, the Middle Paleolithic assemblages are predominantly made of quartzite raw material (M= 70–80%). The presence of flint ranges from 25% to 50% in the T12 deposits, which can be attributed to the Subbetic outcrops located approximately 44 km away in a straight line or slightly more (50 km) following the Guadaíra–Rozalejo thalweg. The lithic industries found at the top of these alluvial terraces are associated with hydromorphic formations (10YR) or Vertisol soils (TARIII-2, 10 YR 6/4), all of which are younger than 104 ka BP [ 22 , 23 ]. The lithic artifacts found in these deposits are mostly unrounded (R0) and made of quartzite (85%). Geosciences 2023,13, 206 20 of 32 In the Guadaíra region, where it intersects with the limestones and flint of the Subbetic units, the Middle Paleolithic industries are consistently characterized by unrounded artifacts (R0) (SAN-1). The two highest-quality raw materials used for lithic knapping in this area are flint and quartzite. Since there are no Paleozoic quartzite outcrops within the Guadaíra watershed, the quartzite pebbles used in knapping are believed to have come from the alluvial deposits of the Guadalquivir terraces. The Rozalejo River archaeological site served as a gathering spot for hominids to obtain quartzite raw material. Therefore, the absence of rounded artifacts (R0) suggests that the quartzite was knapped in situ. The Santisteban archaeological site (SAN) presents a different scenario. It is located in the piedmont of the Sierra de Esparteros, and its lithic industry consists entirely of flint. The assemblages at this site date from the Middle Pleistocene to the beginning of the Upper Pleistocene. 3.3.2. Lithic Industry Assemblages and Techno-Typological Analysis The lithic assemblages in these sites are characterized by the dominance of cores and flakes, occasionally accompanied by macro-tools. Discoidal cores of various sizes, ranging from middle-sized (5–7 cm) to small cores (2–4 cm), derived from knapping waste, are common in these assemblages. The presence of flint in a site is often associated with a more diverse range of flake tools, including scrapers, notches, and end scrapers. There seems to be a relationship between the increased use of flint and the development of more complex technical processes. A faceting index (Fi) value of ≥ 10 is typically observed in lithic assemblages with a significant percentage of flint ( ≥ 20). These assemblages are found in loam–clay or sandy–clay deposits at the top of alluvial terraces, either on the geomorphological surface of the terrace or in detritic fills in the karstic piedmont. However, it should be noted that a high percentage of flint does not always correlate with a high faceting index (Fi), as it may be the case when smaller lithic assemblages or incomplete operational chains are found. The lithic industries in the mentioned loam–clay or sandy– clay deposits exhibit a higher Levallois index (Li). Similarly, lithic assemblages on the geomorphological surface, composed of flint and quartzite, show a high faceting index (Fi) on the butts of the tools. In terms of the progressive increase in the use of flint in different archaeological sites, it does not correspond to a regression curve, which indicates a minimal increase in the application of the Levallois technique (Figure 9). Furthermore, the Levallois transformation index (Lti) is generally very high in almost all lithic assemblages where this technique is present, regardless of the quantity of raw material used. The techno-typological analysis revealed that Group II (Middle Paleolithic) predominates throughout the archaeological sequence, although other technical groups coexist. Group I (Levallois) stands out in three geoarchaeological formations: karstic fill, loam–clay or sandy–clay alluvial deposits, and superficial deposits. Denticulates (Group IV) and notches are most commonly found in assemblages associated with gravel and sandy deposits, as well as some on the geomorphological surface. Group III (Upper Paleolithic), although less numerous, is well represented in some archaeological series on the surface and in loam–clay or sandy–clay deposits. From a chronostratigraphic perspective, there is an observed increase in Group II and, especially, Group I from the oldest to the most recent series. Conversely, denticulates and notches, which have prominent percentages in the oldest series, decrease in importance in more recent assemblages. Geosciences 2023,13, 206 21 of 32 Geosciences 2023, 13, x FOR PEER REVIEW 20 of 33 YR 6/4), all of which are younger than 104 ka BP [22,23]. The lithic artifacts found in these deposits are mostly unrounded (R0) and made of quartzite (85%). In the Guadaíra region, where it intersects with the limestones and flint of the Subbetic units, the Middle Paleolithic industries are consistently characterized by unrounded artifacts (R0) (SAN-1). The two highest-quality raw materials used for lithic knapping in this area are flint and quartzite. Since there are no Paleozoic quartzite outcrops within the Guadaíra watershed, the quartzite pebbles used in knapping are believed to have come from the alluvial deposits of the Guadalquivir terraces. The Rozalejo River archaeological site served as a gathering spot for hominids to obtain quartzite raw material. Therefore, the absence of rounded artifacts (R0) suggests that the quartzite was knapped in situ. The Santisteban archaeological site (SAN) presents a different scenario. It is located in the piedmont of the Sierra de Esparteros, and its lithic industry consists entirely of flint. The assemblages at this site date from the Middle Pleistocene to the beginning of the Upper Pleistocene. 3.3.2. Lithic Industry Assemblages and Techno-Typological Analysis The lithic assemblages in these sites are characterized by the dominance of cores and flakes, occasionally accompanied by macro-tools. Discoidal cores of various sizes, ranging from middle-sized (5–7 cm) to small cores (2–4 cm), derived from knapping waste, are common in these assemblages. The presence of flint in a site is often associated with a more diverse range of flake tools, including scrapers, notches, and end scrapers. There seems to be a relationship between the increased use of flint and the development of more complex technical processes. A faceting index (Fi) value of ≥10 is typically observed in lithic assemblages with a significant percentage of flint (≥20). These assemblages are found in loam–clay or sandy–clay deposits at the top of alluvial terraces, either on the geomorphological surface of the terrace or in detritic fills in the karstic piedmont. However, it should be noted that a high percentage of flint does not always correlate with a high faceting index (Fi), as it may be the case when smaller lithic assemblages or incomplete operational chains are found. The lithic industries in the mentioned loam–clay or sandy–clay deposits exhibit a higher Levallois index (Li). Similarly, lithic assemblages on the geomorphological surface, composed of flint and quartzite, show a high faceting index (Fi) on the butts of the tools. In terms of the progressive increase in the use of flint in different archaeological sites, it does not correspond to a regression curve, which indicates a minimal increase in the application of the Levallois technique (Figure 9). Furthermore, the Levallois transformation index (Lti) is generally very high in almost all lithic assemblages where this technique is present, regardless of the quantity of raw material used. Figure 9. Relationship between the indices of the characterizing traits of the two groups of Middle Paleolithic lithic assemblages present in the Guadaíra–Guadalquivir human corridor: archaic substratum index (ISA) and novel impact index (IIN). The combination of both indices defines the following groupings: ( a ) No substratum and high impact: SAN-1 (1); ( b ) low substratum and high impact: BAR-1 (2); ( c ) medium substratum and high impact: TARII-1 (3); ( d ) medium substratum and medium impact: CAL-1 (7), PIO-3 (5), SAL-2 (4), and TOR-3 (6); ( e ) medium substratum and low impact: TARIII-2 (23); ( f ) high substratum and high impact: CAS-1 (8); ( g ) high substratum and medium impact: REY-3 (11); MOL-1 (12); PIO-4 (9); PAD-1 (13); PIL-1 (10), and MAJ-1 (14); ( h ) high substratum and low impact: TARIII-1 (20), 3 (17), 4 (15); PIO-2 (19); MH4 (18); COR-1 (22); PIO-1 (16) and AER-2 (21). The trend line is displayed in red color. These assemblages exhibit sequential continuity and can be divided into two major periods. The first period corresponds to the Acheulian tradition (archaic substrate) [ 17 , 62 ], found in the gravel bars of alluvial deposits, loam–clay and sandy–clay deposits at the top, and the most recent alluvial terraces of the Guadalquivir [ 14 , 16 – 20 , 22 , 23 ]. Characteristics of this period include the knapping of rounded pebbles, a high percentage of quartzite, limited flake varieties, and repetition of Early Paleolithic types. The second period corresponds to the progressive introduction of the Levallois technique, identified in archaeological sites located in sandy–loam and hydromorphic soils at the top of the Guadaíra alluvial terraces. This period is characterized by a higher number of artifacts, the generalization of the Levallois knapping technique, an abundance of centripetal cores, improved retouching, an enrichment of Group II, an increase in Group III, and the use of flint as a raw material (Figures 9and 10). It should be noted that the lithic assemblages from the Santisteban karstic fill show no evidence of the Acheulian technological tradition and represent a classic Middle Paleolithic assemblage [62]. 3.3.3. Use–Wear on the Quartzite Pieces’ Edges: SEM Analysis Scanning electron microscopy (SEM) analysis was conducted on six unrounded quartzite pieces (R0) from the archaeological site of Tarazona III. Five of these pieces were recovered from level TARIII-4, consisting of one borer (B), two denticulates (D1 and D2), one multiple piece (MP), and one double notch (DN). One atypical borer (AB) was found in level TARIII-5, which is characterized by floating gravel facies (matrix-supported gravels). All these pieces were made from fine-grained microcrystalline quartzite without any microfractures in the petrologic microstructure. Geosciences 2023,13, 206 22 of 32 Geosciences 2023, 13, x FOR PEER REVIEW 22 of 33 Figure 10. Comparative graphs of the characterizing techno-typological features of the two middle Paleolithic lithic assemblages present in the Guadaíra–Guadalquivir hominid corridor: those that maintained the Acheulean tradition (archaic substratum) and those that incorporated the new cultural guidelines (novel impact). (A) Sorted in chronological order; (B) sorted by geomorphological areas. 3.3.3. Use–Wear on the Quartzite Pieces’ Edges: SEM Analysis Scanning electron microscopy (SEM) analysis was conducted on six unrounded quartzite pieces (R0) from the archaeological site of Tarazona III. Five of these pieces were recovered from level TARIII-4, consisting of one borer (B), two denticulates (D1 and D2), one multiple piece (MP), and one double notch (DN). One atypical borer (AB) was found in level TARIII-5, which is characterized by floating gravel facies (matrix-supported gravels). All these pieces were made from fine-grained microcrystalline quartzite without any microfractures in the petrologic microstructure. In addition, an experiment was conducted where several retouched pieces were carved, including notches and denticulates. Among the pieces obtained, a fine-grained internal quartzite flake with a smooth top and a Siret-type fracture, denticulated, was selected and is referred to as M2 Exp. 4. Use–Wear on TARIII-4-level pieces The microwear analysis of the borer (B) revealed a generalized micro-polishing distribution along the edges. Different sections can be distinguished: the external section shows polished ridges and valleys (Figure 11(1)), while the inner section of the blade exhibits micro-polishing on the ridges with minimal wear on the valleys. It is relevant to note that we use the terms ridges and valleys, while Gibaja et al. [45] refer to raised and recessed zones. Upon closer examination, the micro-polishing disappears, but a light compaction of the granular surface can be observed in both the elevated zones and recesses. Figure 10. Comparative graphs of the characterizing techno-typological features of the two middle Paleolithic lithic assemblages present in the Guadaíra–Guadalquivir hominid corridor: those that maintained the Acheulean tradition (archaic substratum) and those that incorporated the new cultural guidelines (novel impact). (A) Sorted in chronological order; (B) sorted by geomorphological areas. In addition, an experiment was conducted where several retouched pieces were carved, including notches and denticulates. Among the pieces obtained, a fine-grained internal quartzite flake with a smooth top and a Siret-type fracture, denticulated, was selected and is referred to as M2 Exp. 1. Use–Wear on TARIII-4-level pieces The microwear analysis of the borer (B) revealed a generalized micro-polishing distribution along the edges. Different sections can be distinguished: the external section shows polished ridges and valleys (Figure 11(1)), while the inner section of the blade exhibits micro-polishing on the ridges with minimal wear on the valleys. It is relevant to note that we use the terms ridges and valleys, while Gibaja et al. [ 45 ] refer to raised and recessed zones. Upon closer examination, the micro-polishing disappears, but a light compaction of the granular surface can be observed in both the elevated zones and recesses. The denticulates (D1, D2) show different features. Denticulate (D1), with a circular shape, has a well-developed notch with a thick edge and a microdenticulated outline of 6.78 mm with several rabbets around 1 mm (Figure 11(2)). Geosciences 2023,13, 206 23 of 32 Geosciences 2023, 13, x FOR PEER REVIEW 23 of 33 Figure 11. Traces of wear on quartzite flakes: (1) Borer (B) of TARIII-4. Surface close to the edge, with an intense micro-polishing, both on edges and valleys. (2) Denticulate (D1) of TARIII-4. Edge with microdenticulate delineation, with traces of use that diminish in intensity towards the interior of the piece. (3) Denticulate (D2) of TARIII-4. (3a) Small-scale view (×30) of one of the concavities in which the deepest area hardly shows any signs of use, while in the outermost area, the polishing is intense; (3b) detail (×550) of an external area where the intensity of the traces of use can be appreciated. (4) Atypical borer (AB) of TARIII-5. Intense micro-polishing in the areas closest to the edge, both in valleys and on edges. (5) Experimental piece carved (M2.Exp.). (5a) The edge used shows a general microdenticulation on a small scale (×23); (5b) on a large scale (×600), micro-polishes and grooves that reach 1 mm towards the interior of the piece can be observed. The denticulates (D1, D2) show different features. Denticulate (D1), with a circular shape, has a well-developed notch with a thick edge and a microdenticulated outline of 6.78 mm with several rabbets around 1 mm (Figure 11(2)). The analysis of the edges showed ridges with more use–wear than in the valleys. On the blade, we distinguished three possible affected sections by the use–wear, with different sizes from the external zone to the D1 centers: (1) The first section has a size of around 50 microns, presenting polishing on the ridges but not recessed zones (valleys). (2) The second section measures 170 microns approximately, and it has partially lost the polishing of the use–wear. In these ridges, intense wear of the valley zones is recognized, with Figure 11. Traces of wear on quartzite flakes: ( 1 ) Borer (B) of TARIII-4. Surface close to the edge, with an intense micro-polishing, both on edges and valleys. ( 2 ) Denticulate (D1) of TARIII-4. Edge with microdenticulate delineation, with traces of use that diminish in intensity towards the interior of the piece. ( 3 ) Denticulate (D2) of TARIII-4. ( 3a ) Small-scale view ( × 30) of one of the concavities in which the deepest area hardly shows any signs of use, while in the outermost area, the polishing is intense; ( 3b ) detail ( × 550) of an external area where the intensity of the traces of use can be appreciated. (4) Atypical borer (AB) of TARIII-5. Intense micro-polishing in the areas closest to the edge, both in valleys and on edges. ( 5 ) Experimental piece carved (M2.Exp.). ( 5a ) The edge used shows a general microdenticulation on a small scale ( × 23); ( 5b ) on a large scale ( × 600), micro-polishes and grooves that reach 1 mm towards the interior of the piece can be observed. The analysis of the edges showed ridges with more use–wear than in the valleys. On the blade, we distinguished three possible affected sections by the use–wear, with different sizes from the external zone to the D1 centers: (1) The first section has a size of around 50 microns , presenting polishing on the ridges but not recessed zones (valleys). (2) The second section measures 170 microns approximately, and it has partially lost the polishing of the use–wear. In these ridges, intense wear of the valley zones is recognized, with perpendicular scratches micrometers in size. (3) The farthest section from the denticulate edge (>225 microns) does not show any use–wear sign on the thick ridge or on the Geosciences 2023,13, 206 24 of 32 microdenticulated edge design. Denticulate D2, near their edge, has expanding waves, which are the remains of knapping affected by light marks of use–wear on the ridges, and a superimposed posterior impact that sharpened some of the ridges (Figure 11(3a)). On this same edge, we can distinguish a wide notch (2.9 mm) in the deepest area where there are no traces of wear, only a clear line of fragility produced by the carving (Figure 11(3a)). However, on both sides of the notch, we can distinguish small microdentulated protrusions (around 400 microns), which present a high degree of wear and micro-polishing (Figure 11(3b)), evidencing some use of this area of the piece. The multiple piece (MP) consists of a transverse concave scraper, with two contiguous lateral notches forming a large denticulate. The second piece analyzed is one double notch (DN). Neither of them shows signs of use–wear or micro-polishing nor any other modification on their structure, with all their edges sharp without polishing. The microwear analysis indicated that the polishing observed on the ridges and valleys of the TARIII-4 pieces suggests effective use–wear, except for the unused MP piece. The concentrated use–wear is mainly found along the edge and extends inward up to 200 microns. The borer and denticulates exhibit moderate uni-directional use–wear, indicating their functional usage. The D1 denticulate shows signs of use but to a lesser extent, as the polishing does not extend beyond its edge microscopically. On the other hand, the notch of denticulate D2 demonstrates a greater degree of use. However, it is possible that the notch could be the result of the later reuse of the piece, either through intentional knapping or as a result of a fracture caused by the knapping process. It is not possible to determine the exact cause of the notch. 2. Use–Wear on TARIII-5 level pieces The SEM analysis of the atypical borer (AB) revealed interesting findings. At low magnification (x65), it is observed that the concavities resulting from knapping are directed towards the interior of the piece, with occasional small, superimposed concavities. The interior of the notched ridge shows nearby areas with polishing, which also affects the waves of the knapping. At higher magnification ( × 500), the ridges exhibit a higher degree of polish, and perpendicular scratches are observed dropping towards the recessed zones [ 45 ], which also present some polishing (Figure 11(4)). However, the ridges and valleys in areas such as the end of the notch and the left edge of the piece do not exhibit use–wear. The atypical borer (AB) shows signs of use primarily in the area around the notched edge. The presence of superimposed concavities in this area suggests that they could have been caused by previous mechanical impacts within the deposit or during use. It is worth noting that the use of the piece seems to be more related to the notch rather than the perforator tip or the adjacent edges. 3. Use–Wear on M2 Experimental carved piece The M2 Exp. denticulate exhibits significant similarities to the denticulates found in archaeological sites. In the experiment, the M2 Exp. piece was used to saw olive wood for a duration of 15 min. A comparison between the experimental edge and the archaeological pieces from the deposits revealed that the former appeared generally more irregular and serrated in nature. As a result of the wood-sawing activity, the edge of the M2 Exp. denticulate displayed evident signs of use–wear extending inward for approximately 700 microns . This use–wear affected the entire undulations of the knapping on the edge (Figure 11(5a)). Notably, a microdenticulated ridge measuring less than 0.5 mm was identified, exhibiting pronounced polishing and featuring distinctive use–wear characteristics. These characteristics included small worn-down areas, micro-polishing on the sharp ridges with a tendency towards rounding, and distinct stripes running in various directions, all of which are indicative of the piece’s use in wood-related tasks. Moreover, the concavities of the microdenticulated ridge, located towards the end of the edge, were found to contain remnants of olive wood adhered to them (Figure 11(5b)). Comparing the details of the M2 Exp. experimental piece with the archaeological TARIII-4 D1 and D2 denticulates, which are unrounded quartzite pieces (R0), we found Geosciences 2023,13, 206 25 of 32 some similarities in the distribution of the knapping and use-related ridges. However, the M2 Exp. piece exhibits less polishing and less disaggregation of quartz microcrystals. On the other hand, the archaeological pieces show a deeper and more pronounced wear, without any microcrystal disaggregation. This characteristic can be attributed to three possible causes: the reutilization of the pieces, their use on materials other than olive wood, or their multifunctional nature. 4. Use–Wear general functional interpretation The microwear traits observed on the edges of the analyzed pieces (borer and denticulates) do not provide definitive evidence of their specific functions. However, the presence of surface polishing, predominantly perpendicular and unidirectional, suggests that these pieces were likely used in a transverse manner along the edge. They could have been employed for activities such as cutting, cleaning, or sharpening the woody stems of trees or scrub branches. In the absence of palynological registers for this area, which may imply paleo-environmental changes in the vegetation coverage (passing from thermo-Mediterranean conditions (olive groves) to a meso-Mediterranean climate (oaks)), and since there are no pedo-sedimentological climate archives, we discarded changes in the vegetal species. To confirm these potential uses, we compared the wear patterns of these pieces with the use–wear observed on the M2 Exp. experimental piece. The reutilization of lithic pieces, which involves either reuse in such a way that the destined use of the pieces is changed (recycling) or recovery of the piece (retrieval) [ 63 ], was not identified in the lithic assemblages of the hominid alluvial corridor of the Guadaíra and Guadalquivir Rivers. Consequently, what remains consistent throughout the archaeological sites within the HAC are the frequent and recurring visits by the same hominid group, characterized by a consistent techno-typological tradition and functional strategies. These practices were passed down from one generation to the next, spanning from MIS6/MIS5 to MIS3. When comparing our results with the findings of the use–wear analyses, it became apparent how challenging it is to identify the specific functions of Middle Paleolithic pieces. However, certain sites have provided evidence of recycling and retrieval practices. For example, in the Arlanza Valley (Burgos), Middle Paleolithic lithic assemblages showed intensive exploitation of flint and quartzite, indicating a recycling approach [ 64 ]. Similarly, the lithic workshop in El Cañaveral (Madrid) utilized old industries in flint sourced from the Acheulian and Mousterian colluvial deposits, demonstrating a retrieval strategy [ 65 ]. The El Esquilleu rock shelter in Picos de Europa (Santander) also exhibited recycling processes associated with changes in the operational chain during MIS3 [66,67]. In the Therdonne and Biache-Saint-Vaast archaeological sites from MIS7-6, Levallois points were identified as potential butchery knives, characterized by triangular flakes without a clear form–function relationship [ 62 ]. Microwear analyses of chipped edges on some denticulates suggested their use in penetrating animal carcasses, a hypothesis supported by experimental knapping [ 62 ]. Moreover, microwear analyses of small flakes in flint from Qesem Cave (Israel), dating back to the Middle Pleistocene Acheulo–Yabrudian Cultural Complex, revealed their use in longitudinal cutting movements associated with butchery activities [ 68 ]. This functional interpretation was confirmed through residue detection using Fourier transform infrared spectroscopy and experimental analysis on organic remains [62]. Functional analyses of Middle Paleolithic bifaces from Terra Amata (MIS11-MIS10) and Lazaret Cave (MIS6) in Nice (France) indicated their use in linear longitudinal movements [ 69 ]. At the same site, the functional analysis of Quina and demi-Quina scrapers, made of flint, demonstrated their predominantly transverse use in scraping activities related to hide processing. The scraping actions left longitudinal signs, both unidirectional and bidirectional, associated with cutting [ 70 ]. 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