GEOLOGICAL SETTING AND STRATIGRAPHY

The climate and environment of the late Pleistocene period in south-central Chile are characterized by the shift from a cold, periglacial, sandur setting in the site area to an intermittent cold to cool temperate rain forest from ~11,000 to 19,000 cal yr BP (Heusser et al., Reference Heusser, Heusser and Lowell1999; Denton et al., Reference Denton, Lowell, Heusser, Schlüchter, Andersen, Heusser, Moreno and Marchant1999; Dillehay et al., Reference Dillehay, Ocampo, Saavedra, Sawakuchi, Vega, Pino and Collins2015). This shift was accompanied by vegetational changes that facilitated a human presence during warm months and probably limited human activity during cold months, particularly in the Andean mountains 40 km east of Monte Verde, where glaciers existed until about ~17,500 cal yr BP. Deglaciation and climatic amelioration after ~17,500 cal yr BP resulted in the development of the cool temperate, open rain forest and precordillera lakes present in the area today (Denton et al., Reference Denton, Lowell, Heusser, Schlüchter, Andersen, Heusser, Moreno and Marchant1999; Moreno et al., Reference Moreno and León2003, Reference Moreno, Denton, Moreno, Lowell, Putnam and Kaplan2015). Drier conditions and increased forest fires occurred in the area after ~6500–7000 cal yr BP (Abarzua and Moreno, Reference Abarzua and Moreno2008). During this entire period the coastal climate and environment, located ~60 km west of Monte Verde, were generally milder and more hospitable to human occupation.

Four previously defined natural stratigraphic layers (MV-1 to MV-3 and MV-7; Pino, Reference Pino and Dillehay1989; Dillehay and Pino, Reference Dillehay, Pino and Dillehay1989), excluding the cultural horizons reported previously (Dillehay et al., Reference Dillehay, Ocampo, Saavedra, Sawakuchi, Vega, Pino and Collins2015) and the use-surfaces described here, have been identified in most areas of CH-I, with a total exposed thickness varying between ~1.3 and 1.5 m (Figs. 3 and 4). CH-I is higher in elevation and farther away from the paleochannel of the Chinchihuapi Creek than site MV-II, thus strata MV-4 to MV-6, which are associated exclusively with the creek and lower terrace basins, are not present (see Pino, Reference Pino and Dillehay1989, Dillehay and Pino, Reference Dillehay1997). At the time of human use of CH-I, the paleochannel was about 30 m farther north, 6–7 m lower than the cultural horizons in site CH-I, and about 2 m wide.

Stratum MV-1 is a developed sod zone of friable soil of weak to moderate granular structure and has a relatively uniform thickness of ~15–40 cm in the Monte Verde area. The color is 10YR 3/4 to 10YR 3/2 (dark yellowish brown to dark brown). This stratum contains intermittent yet extensive evidence of forest fires that occurred primarily in the 1930s and 1960s and is absent or thin (2–3 cm) in some areas due to erosion from yearly heavy rainfall after vegetation burn-off. For instance, at site MV-II, there is no evidence of burning in stratum MV-1 (see Supplementary Fig. 18 in Dillehay et al., Reference Dillehay, Ocampo, Saavedra, Sawakuchi, Vega, Pino and Collins2015). Where it does exist in other areas, its thickness varies significantly depending upon differential vegetation loss and erosion. The extant base of stratum MV-1 at the CH-I site is radiocarbon dated to 928–1056 cal yr BP (D-AMS-021819; Table 1).

MV-2 is an oxidized medium to orange-gray to dull yellow-orange (10YR 3/6 and 10YR 6/4) sandy sediment that varies from 15 to 55 cm in thickness when it is present at CH-I. MV-2 was initially deposited sometime around or after ~5600 cal yr BP (Dillehay, Reference Dillehay1997). Due to increased forest fires and erosion from rainfall beginning ~6000–7000 cal yr BP (Abarzua and Moreno, Reference Abarzua and Moreno2008), as well as fire and erosion in the last century, this stratum varies in presence and thickness at CH-I. MV-2 is present in Units 1–3 and 5–6 but absent in Units 7–10 at CH-I (see Supplementary Figs. 1 and 2). The absence of stratum MV-2 produces a nonconformity between strata MV-1 and MV-3 at site CH-I. Where stratum MV-2 is present in the site (Units 1–3 and 5–6), the three use-surfaces are ~30–45 cm deeper from the reference datum at ground surface (Supplementary Fig. 2). Where it is absent due to erosion (e.g., Units 7 and 8), the use-surfaces are ~30–45 cm more shallow from the reference datum than they are in Units 1–3 and 5–6 (cf. Figs. 3 and 4, Supplementary Figs. 1 and 2). Nonetheless, the presence or absence of stratum MV-2 has no bearing on the integrity and chronostratigraphic correlation of the use-surfaces, which are in complete agreement in the deeper, older strata MV-3 and MV-7.

MV-3 is a hard, compact, heavily oxidized, yellowish-red to reddish-yellow (5YR 3/2 to 5YR 6/8) soil layer that directly overlies stratum MV-7 in site CH-I. The thickness ranges from ~20 to 50 cm. The layer is characterized by interbedded facies of small clasts of iron oxides and hematite–limonite and thin lenses of brown peat and white clays, especially in its lower part. The lower layer at site CH-I is radiocarbon dated between ~9000 and 10,800 cal yr BP (Beta-6753; Dillehay, Reference Dillehay1997).

The underlying upper MV-7 stratum is composed of medium and fine gray sands (7.5YR/N6) with occasional thin, small gravel lenses (0.5–2.5 cm thick). MV-7 roughly dates between 12,000–15,060 and 36,262–38,828 cal yr BP (Dillehay, Reference Dillehay1997), from top to bottom, and varies from ~1.5 to 3 m in thickness. Strata MV-3 and MV-7 reveal no burning and erosion due to extensive fires and heavy rains, although the upper layer of MV-3 likely has been slightly eroded in areas where stratum MV-2 eroded.

Where stratum MV-2 is absent, the slightly undulating use-surfaces US-1 to US-3 reported here are located at approximate depths of 22–23, 28–32, and 88–95 cm, respectively (Figs. 3 and 4), from the reference datum at ground level in Units 7–10. Where stratum MV-2 is present in other areas of site CH-I (Units 1–3 and 5–6), the three use-surfaces are 30 to 45 cm deeper from the reference datum, that is, approximately 60, 70, and 130–135 cm in depth, respectively (see Dillehay et al., Reference Dillehay, Ocampo, Saavedra, Sawakuchi, Vega, Pino and Collins2015). That is, due to the presence, absence, or thinness of stratum MV-2 across site CH-I, depth discrepancy below reference datum among use-surfaces varies from unit to unit (cf. Figs. 3 and 4, Table 1, Supplementary Figs.1 and 2). Despite this discrepancy, the stratigraphic chronology and numerical dating of the natural strata and cultural use-surfaces are in agreement across the site. Table 1 presents the 2013 and 2017 radiocarbon dates for the use-surfaces.

US-1 is located in the uppermost layer of stratum MV-3, almost at its interfacing nonconformity with the base of stratum MV-1 in Units 7 and 8; US-2 is located a few centimeters below, also in the upper level of MV-3; and US-3 lies in the middle layer of MV-7. US-1 and US-2 are separated by ~5–8 cm of culturally sterile sediments. Approximately 55–65 cm of sterile sediment exists between US-2 and US-3. The three use-surfaces vary in thickness from ~1.0 to 1.5, 1.3 to 3.2, and 0.5 to 1.1 cm, respectively.

The analysis of horizontal orientations on the planar use-surfaces was a primary interest of the field analysis, focusing on the thin lenses of associated artifacts and intact burned features deposited upon and embedded within the fine-grained sediments of the use-surfaces (Fig. 5). The use-surfaces are thought to be minimally impacted by the complications of any taphonomically charged site-formation processes. That is, we observed no obvious postdepositional processes that may have obscured latent structure in the configurations of features and artifacts.

Figure 5. (color online) Projectile point fragment recovered from US-2. Note darker areas of a burned feature to the left.

More specifically, we observed the strike (horizontal orientation) and dip (vertical orientation) of artifacts for any disturbance by overbank stream flow, pedoturbation by biological activity, and other forces. The configuration and spatial distribution of the in situ artifactual materials exhibited heterogeneity of orientations among elongated objects of lithics, which is consistent with a deposition that is not a function of, or substantially displaced by, water flow. That is, the horizontal orientations of elongated lithics were not aligned with the direction of the river flow at the time of the deposition. Only two excavated flakes were estimated to have dips greater than 45°, and these were in US-2. Furthermore, we recovered no artifactual material, cultural features, or charcoal from sterile sediments between the use-surfaces, suggesting no downward filtration of lithics, bone, or charcoal occurred. In these cases, the stratigraphic and taphonomic analyses confirm the integrity of the cultural deposits. As noted, there is no observable evidence of burning and fluvial erosion in strata MV-3 and MV-7, in contrast to strata MV-1 and MV-2.

CHRONOLOGY

Numerical dating was conducted by AMS on single pieces of wood charcoal and a burned chestnut (Luma apiculata) seed in small hearths in the three use-surfaces and on a burned bone associated with lithics in the underlying deeper levels (Table 1). The AMS data for the recent excavations indicate ages of 8773–9257 cal yr BP (D-AMS-021817) on charcoal for US-1. This is the level associated with an end scraper made of an exotic gray chalcedony, with a heavily ground and polished bifacial fragment, and with unretouched lithic debitage (see Supplementary Figs. 3 and 4). An age of 9780–10,240 cal yr BP (D-AMS 021818) was obtained for US-2 in Unit 7, which was associated with two fragmented Paijan-like projectile points (Fig. 6). This age chronologically overlaps with the assay of 10,290–10,579 cal yr BP (Beta-343109) derived from charcoal in a hearth associated with a Paijan-like point excavated at approximately the same level at CH-I in 2013 (Dillehay et al., Reference Dillehay, Ocampo, Saavedra, Sawakuchi, Vega, Pino and Collins2015). The age range of the new and previous dates for US-2 indicates that it was deposited during the Early Holocene, around four millennia after the ~14,500 cal yr BP occupation at the MV-2 site (Dillehay and Pino, Reference Dillehay, Pino and Dillehay1997; Dillehay et al., Reference Dillehay, Ramírez, Pino, Collins, Rossen and Pino-Navarro2008). An AMS date on wood charcoal of 14,134–14,731 cal yr BP (D-AMS-022486) was recovered from US-3 in Unit 7, roughly the middle level of stratum MV-7, and associated with the medial section of a rhomboidal-formed biface, a probable projectile point, made of an exotic white quartz (Fig. 6). A date of 14,170–14,835 cal yr BP (D-AMS-028838) was obtained from a burned chestnut seed from a small hearth at the same level of the biface and the assay of 14,134–14,731 cal yr BP in Unit 7. The 2013 date for a comparable stratigraphic cultural level, 14,034–15,058 cal yr BP, is present in stratum MV-7 of Unit 5 at CH-I (Beta-65842) and overlaps with these two new assays. An unretouched, percussion-struck flake of local rhyolite, a spherical stone (see Supplementary Figs. 5 and 6), and a burned bone fragment of an unidentified small animal, possibly deer or paleo-camelid, were recovered from a deeper level of stratum MV-7 and dated at 20,042–20,564 cal yr BP (D-AMS-022485: see BETA-372889 assay in Dillehay et al., Reference Dillehay, Ocampo, Saavedra, Sawakuchi, Vega, Pino and Collins2015). In the nearby MV-I and MV-II sites, 55 previous ¹⁴C and optically stimulated luminescence dates for strata MV-3 to MV-7 generally agree with the dates and stratigraphic order presented for US-3 in CH-I (Dillehay 1998; Dillehay et al. Reference Dillehay, Ocampo, Saavedra, Sawakuchi, Vega, Pino and Collins2015). There is no evidence of Holocene-dated cultural materials, and thus no presence of US-1 and US-2, in the sediments overlying the MV-I, MV-II, and CH-II sites as there is for the CH-I site.

Figure 6. (color online) Fragmented Paijan-like projectile point from US-2 dated around ~9780–10,240 cal yr BP.

ARTIFACTS AND FEATURES

All artifacts at site CH-I were recovered from stratified layers, almost exclusively from the use-surfaces. The assemblages from use-surfaces include projectile point and biface fragments, an end scraper, grinding-stone fragments, a perforator, subspherical and spherical stones, nonstandardized flake tools, discarded flakes, shatters, other lithic debris (see Table 2, Supplementary Figs. 7 and 8a), plant remains, and a small burned bone fragment. Technologically, with the exception of the bifaces, all lithic tools show evidence of simple reduction sequences, whether reduced from a pebble or prepared core, and typological variation, all of which do not differ from previous assemblages recovered at MV-I, MV-II, CH-I, and CH-II.

Table 2. Temporal placement of lithic groups by specimen type frequencies.

At CH-I, the artifacts recovered in 2017–2018 are divided into two scales of variation according to typological and technological change: simple tools made of local basalt, andesite, rhyolite, granite, and exotic obsidian and chalcedony, and bifacial tools made of exotic quartz and local basalt. Formed artifacts from the use surfaces are limited in number (n = 10) and characterized by a reductive technique. Others are predominantly an expedient knapping strategy. Flakes are the most abundant artifacts in the use-surfaces, accounting for a large majority of the total assemblage, most of them ranging from small to medium size (<60 mm). The frequencies of each lithic type for each use-surface are described in Table 2 (see Supplementary Material). There were some small-sized tools made from basalt and andesite flakes, 15 of which are struck from pebbles, which are similar to those found at the MV-II site dated around 14,500 cal yr BP (Collins, Reference Collins and Dillehay1997; Dillehay et al., Reference Dillehay, Ocampo, Saavedra, Sawakuchi, Vega, Pino and Collins2015). An end scraper from US-1 was made from a large, exotic gray chalcedony flake (Supplementary Fig. 3). The rhomboidal biface fragment of white quartz, directly associated with charcoal and a chestnut seed, both dated ~14,500 cal yr BP in US-3, reveals a reductive sequence very similar to the three rhomboidal point fragments previously recovered from site MV-II (Fig. 7), also dated ~14,500 cal yr BP. To date, this type of quartz has been found only along the Pacific coast to the west. A flake of an exotic dark greenish-brown chalcedony also was recovered in US-3 (Supplementary Fig. 8b). Its source is unknown but like from the Andean mountains to the east. Except for the obsidian and chalcedony flakes and the quartz biface fragment, no further exotic artifacts were found in the deposits. The nearest obsidian sources are ~50–60 km to the northeast in the mountains. One large secondary flake of rhyolite and two spherical stones, one formally pecked and ground and showing an impact scar (see Supplementary Figs. 5 and 6), were recovered from deeper levels in stratum MV-7.

Figure 7. Fragments of bipointed rhomboidal projectile points recovered at site MV-II (two specimens on left) and from US-3 at site CH-I (specimen on right), all dated around 14,500 cal yr BP.

Preliminary refitting analyses were carried out for US-1 and US-2, which contained the largest number of flakes and burned features. Lithic debris from US-3 was minimal and not conducive to this type of study. Five and eight conjoining sets were recovered from US-1 and US-2, respectively, suggesting limited campsite sites or specialized activity areas with minimal postdepositional process. The lithic refits likely represent small moments in time and were probably derived from one to two basalt and andesite cores on each use-surface. The preliminary strike and dip results mentioned previously, coupled with the refitting sets, suggest intact use-surfaces. Nonetheless, we cannot presume that, because there are refitting sets, it follows that the spatial patterning of the distribution of lithics in relation to the burned features has not been slightly disturbed.

Functional and micro-usewear studies suggest that the simple tools and unmodified flakes had limited microwear, indicating sparse use, while the end scraper, the prepared and modified bifaces, and the perforator were used more intensively and for a longer time. As shown in Supplementary Figure 9, the micro-usewear patterns on the distal tip of the perforator from US-3 (Supplementary Fig. 8a) exhibits hinge and step fractures and bright polish more suggestive of punching and gouging than twisting and drilling. Edge wear on the quartz biface fragment was difficult to establish due to the hardness of this material and the brightness reflected under high-power microscopic light. Nonetheless, minute grain loss and slight rounding of a few aspects along the two edges of this piece suggest some use (Benson et al., Reference Benson, Franco and Dillehay2017).

Four burned features were discovered: one from US-1, two from US-2, and one from US-3 (Fig. 5, Supplementary Fig. 10), ranging from roughly 15 to 40 cm in diameter. Three of the four were thin lenses (~0.5–1.0 cm) composed of small flecks of charcoal, lithic debris, and occasional burned bone carbonized plant material. One moderate-sized hearth excavated in US-2 contained the remains of grasses possibly used as fuel or food (Scott-Cummings and Kovacik, Reference Scott-Cummings and Kovacik2017; Silva, Reference Silva2017). The burned features are not the result of burning associated with the upper MV-1 stratum or with more ancient fires, which would be evidenced by widespread horizontal burning, such as that seen in stratum MV-1 in Figures 3 and 4 and Supplementary Figures 1 and 2. The burned features also are not products of pyroclastic flows, which are present only 40–50 km to the east in the Andes. Such flows have never reached the Monte Verde area. Moreover, pyroclastic flows are sinuous and not semicircular or amorphous in form. Finally, the burned features on use-surfaces are associated with cultural artifacts and debris, unlike natural fire deposits and pyroclastic flows.

CH-I is located on a slightly higher terrace than the MV-II site, with no thick, permanently humid, peat lenses overlying the use-surfaces, and it therefore has poor preservation of organic materials. The macrobotanical remains from the burned feature in US-3 yielded carbonized seeds of chestnuts (Supplementary Fig. 11), which are available only at the end of summer or fall months (Silva, Reference Silva2017). The burned bone fragment recovered in the deeper level and associated with flakes and spherical stones in a slightly charred area was not identified to species. Macrobotanical analysis also indicates the site occupants used wood from unspecified conifer and hardwood trees/shrubs as fuel. Recovered lignified parenchymous tissue fragments could reflect unknown fruit or seed processing. However, they also may indicate other large fleshy plant organs, such as roots, leaves, cones, or bark, burned in fire. Phytolith and starch analyses also were conducted on a hearth fill in US-2 (Scott-Cummings and Kovacik, Reference Scott-Cummings and Kovacik2017). The phytolith signature indicates a local grass population dominated by cool-season grasses and including short grasses that thrive in the heat of summer. At least one of the local grasses belonged to the Stipeae tribe. One dicotyledonous plant accumulated silica, although it could not be identified. No starches were observed that might inform concerning use of this hearth.