Evidence of the earliest humans in the Southern Deseado Massif (Patagonia, Argentina), Mylodontidae, and changes in water availability

Quaternary International xxx (2014) 1e19

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Evidence of the earliest humans in the Southern Deseado Massif (Patagonia, Argentina), Mylodontidae, and changes in water availability G.A. Brook a, *, N.V. Franco b, P. Ambrústolo c, M.V. Mancini d, L. Wang a, P.M. Fernandez e a

University of Georgia, Department of Geography, Athens, GA 30602, USA CONICET, University of Buenos Aires, Argentina CONICET, University of La Plata, Argentina d National University of Mar del Plata, Argentina e CONICET-INAPL, University of Buenos Aires, Argentina b c

a r t i c l e i n f o

a b s t r a c t

Article history: Available online xxx

Mylodontidae bones from La Gruta 3 rockshelter, which date to 11,077e10,571 cal BP (9560
30 e9470
30 14C BP) and 9539e9466 cal BP (8540
30 14C BP), indicate that the extinct giant ground sloth was in the area after it was first occupied by humans during the late Pleistocene at 12,799 e12,049 cal BP (10,845
61e10,477
56 14C BP). Sediment characteristics at La Gruta 1 and 3 rockshelters (LG1 and LG3) suggest that conditions were wetter during major periods of human occupation and this is supported by pollen data. Lacustrine silts and clays in La Barda, and La Gruta Lagoons 1 and 3, provide evidence of an arid interval prior to about 6500 cal BP (5690
35 14C BP) followed by wetter conditions. This may explain why there is no evidence of humans between ca. 7760 and 5583 cal BP (7500
250 and 4770
25 14C BP) either at La Gruta or at La Martita and Viuda Quenzana, which are ca. 25 km away. There is considerable evidence for occupation at Viuda Quenzana after 5581 cal BP and scanty evidence for occupation at La Gruta around 3800 cal BP with more abundant evidence after 1880 cal BP. In the last 1500 years, six radiocarbon ages show that humans occupied LG1 and LG3 before (1372e1271 cal BP) and after (539e156 cal BP), but not during, the Medieval Climate Anomaly, which may have been a time of increased aridity in the area. The findings at La Gruta show that Mylodontidae was probably present in the southern Deseado Massif after the first humans arrived but data from southern Patagonia show that it became extinct soon afterwards. Ó 2014 Elsevier Ltd and INQUA. All rights reserved.

Keywords: Early humans Mylodontidae Patagonia Caves Paleoclimate

1. Introduction Water is an important resource in arid and semiarid environments for hunter-gatherer populations (e.g. Smith et al., 2005; Veth, 2005). Early human occupation of Patagonia has been linked to periods with more available water (e.g. Heusser and Streeter, 1980; Heusser and Rabassa, 1987; Heusser, 1995; Coronato et al., 1999; Paez et al., 1999; Miotti and Salemme, 2003; Brook et al., 2013).

* Corresponding author. E-mail addresses: [email protected] (G.A. Brook), [email protected] (N. V. Franco), [email protected] (P. Ambrústolo), [email protected] (M.V. Mancini), [email protected] (L. Wang), pablomarcelofernand@gmail. com (P.M. Fernandez).

The late glacial interval was characterized by substantial changes in effective moisture, related to stepwise changes primarily in temperature. Vegetation throughout southernmost Patagonia, during the PleistoceneeHolocene transition, in Andean and extra-Andean regions, was steppe and heath with substantial open ground with precipitation lower than today (e.g. VillaMartínez and Moreno, 2007; Tonello et al., 2009; Bamonte and Mancini, 2011). After 11,000 cal BP, the slight but continuous development of the forest, shown by the increase in Nothofagus values together with the presence of the grass steppe, reflect the establishment of the forest-steppe ecotone (Mancini, 2009; Sottile et al., 2012). Significant changes in the vegetation occurred throughout Patagonia during the early Holocene (11,500e 8000 cal BP) (Bamonte and Mancini, 2011; Sottile et al., 2012; De Porras et al., 2012). In the Central Deseado Massif in South Patagonia, and in nearby areas, there are fewer ages indicating human

http://dx.doi.org/10.1016/j.quaint.2014.04.022 1040-6182/Ó 2014 Elsevier Ltd and INQUA. All rights reserved.

Please cite this article in press as: Brook, G.A., et al., Evidence of the earliest humans in the Southern Deseado Massif (Patagonia, Argentina), Mylodontidae, and changes in water availability, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.04.022

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G.A. Brook et al. / Quaternary International xxx (2014) 1e19

occupation during arid periods (Brook et al., 2013), although there is still no agreement as to how aridity affected human populations (e.g. Miotti and Salemme, 2003; Borrero, 2012). In fact, a significant number of ages documenting the initial human exploration of Patagonia have come from sites in the Deseado Massif, with more recent ages being obtained from adjacent areas and areas closer to the Andean ranges (e.g. Miotti and Salemme, 2003, 2004; Paunero et al., 2007; Paunero, 2009), while others have been obtained from the Magellan Strait region (e.g. Massone, 1987, 1996; Mengoni, 1987; Nami, 1985-86; Nami and Nakamura, 1995). This paper presents evidence showing that the first huntergatherers in the southern Deseado Massif shared the environment with Lama guanicoe (guanaco) and probably Mylodontidae at a time when water may have been more abundant than today. Although we will focus on the latest information from La Gruta area, information from areas within 25 km of La Gruta with very variable environmental conditions today, including La Martita Cave 4 (Aguerre, 2003), Viuda Quenzana 8 (Franco et al., 2013) and El Verano Cave 1 (Durán et al., 2003), will be discussed also, as each of these areas would have presented different problems and different opportunities for hunter-gatherers (Figs. 1 and 2). 2. The southern Deseado Massif The area around La Gruta is an ancient volcanic landscape, with abundant natural depressions frequently occupied by shallow lagoons, water levels depending on rainfall. Some lagoons are semipermanent, while others are markedly seasonal, the difference depending largely on the size of the lagoon catchment. A few lagoons with large catchments even have small streams flowing into them. Almost all of the lagoons in the area show evidence of water levels having been higher in the past, with ancient beach ridges well above present water levels and thick deposits of silt/clay in the

floors attesting to slow sedimentation in water. Caves and rockshelters in ignimbrites (Bahía Laura Formation) or fossiliferous sandstones of the Monte León Formation (Panza and Marin, 1998) are relatively rare but where they occur they frequently preserve important archaeological and paleontological deposits. In contrast, the Viuda Quenzana and La Martita areas have abundant caves, seasonal streams, occasional perennial streams, and springs are more common than at La Gruta (Fig. 1). Highquality siliceous rocks are more abundant at La Martita and Viuda Quenzana than La Gruta (Franco et al., 2012), due to differences in bedrock geology (Panza and Marin, 1998) and the localized occurrence of siliceous rocks deposited by ancient hot springs containing Fe and Mn (Claudio Iglesias, pers. comm. 2014). 3. Rockshelters at La Gruta Three rockshelters have been excavated at La Gruta since 2007. These are in cliffs around the margins of two lagoons (Fig. 2a). La Gruta 1 is a shallow cave in silicified ignimbrite (Claudio Iglesias, pers. comm. 2014) overlooking a small lagoon about 6 m below (Fig. 3a). In contrast, La Gruta 2 and La Gruta 3, which are about 50 m apart, have formed in a fossiliferous sandstone cliff along the southern margin of a large basin (Fig. 3b). After modest rains, two shallow lagoons occupy the topographically lowest sections of this basin but after heavy rains these water bodies combine into a single lake that fills the entire depression. The floor of La Gruta 2 is about 3 m above the adjacent lagoon floor, while the floor near the back wall of La Gruta 3 is only about 1.5 m above it. As recently as 1983 the lagoon at La Gruta 2 and La Gruta 3 filled with water to the extent that La Gruta 3 was flooded. Flotsam along the eastern, downwind margin of the basin delimits the elevation reached by the floodwaters and shows that the entire basin was filled by a lake up to ca. 4 m deep (Figs. 11b and 12a and b). Excavations at the three

Fig. 1. Locations of Southern Deseado sites mentioned in the text. LG: La Gruta; VQ: Viuda Quenzana; EV: El Verano; LMrt: La Martita.

Please cite this article in press as: Brook, G.A., et al., Evidence of the earliest humans in the Southern Deseado Massif (Patagonia, Argentina), Mylodontidae, and changes in water availability, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.04.022

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Fig. 2. Google Earth satellite images showing La Gruta 1, 2, and 3 rockshelters (triangles), La Gruta Lagoon 1 and 2 sediment sampling locations (circles) LAG1 and LAG2 (A), and La Barda Lagoon sampling location EB1 (B).

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La Gruta rockshelters have provided important information, including bones of extinct animals and evidence of when the first humans entered this region of Patagonia, and what conditions were like at that time. Munsell colors of samples from sediment units exposed by the excavations were determined on dry samples using the U.S. Department of Agriculture soil manual. Samples were then sieved through a 2 mm sieve. Particles with diameters larger than 2 mm were weighed and bagged separately, while those smaller than 2 mm were analyzed for grain-size distribution. In this analysis about 5e10 g of sediment was pretreated using 30% hydrogen peroxide to remove any organic material and then 50 g/L sodium metaphosphate solution was added to disaggregate clay agglomerations. The proportions of clay, silt, and sand in each sample were measured and calculated using the pipette method of Indorante et al. (1990). The sand portion was dried and sieved at one-phi intervals. Folk and Ward (1957) descriptive statistics of grain-size distribution were calculated using GRADISTAT 4.0 (Blott and Pye, 2001) and granulometric histograms showing the particle-size distribution were constructed to emphasize the different size modes in each unit (Figs. 5 and 8). In addition, subsamples of the <2 mm fraction of each sample were subjected to dilute double acid extraction of easily-soluble elements using the Mehlich 1 method (Mehlich, 1953). The M1 extracting reagent is a mixture of 0.05 N HCl and 0.025 N H2SO4. Extracted elements were measured using EPA Method 6010C (U.S. EPA, 2014) on the Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES) at the Center for Applied Isotope Studies, University of Georgia (Figs. 6 and 9). Palynological information on past vegetation was obtained from archaeological excavations at La Gruta and from other archaeological sites in the Deseado Massif (La Martita Cave 4, Los Toldos and La María archaeological localities) as well as from “mallines” to the west such as La Tercera (Bamonte and Mancini, 2011; Brook et al., 2013). Vegetation characteristics and paleoclimatic interpretations of the pollen data are based on present-day pollene vegetation relationships which indicate that shrubs (Asteraceae subf. Asteroideae) and dwarf shrubs (Ephedra, Nassauvia) record drier conditions, while higher frequencies of grasses and herbs are related to wetter conditions (Mancini, 1998; Mancini et al., 2012).

Fig. 3. La Gruta rockshelters. La Gruta 1 in silicified ignimbrite overlooking relict beach ridges in the adjacent lagoon that record high water levels (a). La Gruta 2 and La Gruta 3 rockshelters in a sandstone cliff along the southern margin of a large complex lagoon 2.5 km from La Gruta 1 (b). La Gruta 2 is to the right of the introduced trees in (b) and La Gruta 3 is just to the left of the trees. The photographs were taken in March 2013 after heavy rains that ponded water in the lagoonal depressions.

Please cite this article in press as: Brook, G.A., et al., Evidence of the earliest humans in the Southern Deseado Massif (Patagonia, Argentina), Mylodontidae, and changes in water availability, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.04.022

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Fig. 4. Simplified stratigraphic sections of the four walls of the La Gruta 1 excavation showing pollen, sediment and radiocarbon sample locations as well as Units A-C (modified after Mancini et al., 2013). Charcoal samples were collected during excavation so equivalent locations in the profile were determined by extrapolation.

New uncalibrated AMS radiocarbon ages reported here are in radiocarbon years BP or years before 1950 AD, and were calculated using a 14C half-life of 5568 years (Tables 1 and 2). Errors are one standard deviation and reflect both statistical and experimental

errors. Ages were corrected for isotopic fractionation to a d13C value of 25&. These and previously published radiocarbon ages in 14C BP were calibrated at the 2s probability level in calendar years BP (cal BP) using CALIB 7.0 (Stuiver and Reimer, 1993) and the Southern Hemisphere (SHcal13) atmospheric calibration curve of Hogg et al. (2013). 3.1. La Gruta 1 A 1  1 m test pit excavated in the floor of La Gruta 1 rockshelter was started in 2007 and reached bedrock in 2008. The excavation exposed three stratigraphic units AeC, two of them (A and B) showing lithologic variations within the unit (Figs. 4e6; Table 3). Three sediment samples from basal Unit A, resting on bedrock, show it to be yellowish brown muddy sandy gravel, with

Fig. 5. Variations in sediment texture between units at La Gruta 1 rockshelter. For clarity, histograms for adjacent units are shaded differently. VC ¼ very coarse; C ¼ coarse; M ¼ medium; F ¼ fine, and VF ¼ very fine. See Fig. 4 for locations in the profile.

Fig. 6. Variations in elemental concentrations in La Gruta 1 sediment units. Values are in parts per million (ppm) for particles < 2 mm diameter. Note the different scales in the upper and lower diagrams.

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a Folk and Ward (1957) graphic mean grain size of medium sand (two samples) and fine sand (one sample). All samples are poorly sorted, very fine skewed and platykurtic (see Table 3 for definitions). The three samples consisted of 32e40% gravel, 33e40% sand, 15e20% silt, and 8e10% clay (27e29% silt þ clay). The overlying Unit B varied laterally with sample LG1-8 being similar to sediments in Unit A (brownish yellow, muddy sandy gravel, mean in medium sand range), suggesting it may have been reworked from the underlying layer. It consists of 40% gravel, 38% sand, 15% silt, and 8% clay (22% silt þ clay) and is very poorly sorted, very fine skewed, and mesokurtic. In contrast, samples LG1-3 and LG1-4 are somewhat finer being dark yellowish brown gravelly muddy sand with a mean grain size in the fine sand range.

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Both samples are very poorly sorted and very fine skewed; LG1-3 has a platykurtic grain size distribution and LG1-4 a very platykurtic distribution. Gravel ranges from 20 to 26%, sand from 41 to 53%, silt 18 to 20%, and clay 9 to 13% (silt þ clay is 27e33%). Therefore, Unit B is finer with a higher content of silt and clay and less gravel than Unit A. The upper Unit C is somewhat similar to Unit A; samples from the charcoal-rich layer and from a layer of ash are dark grey (because of the charcoal and dung mixed with the sediments) muddy sandy gravel with a mean grain size of coarse sand, very poorly sorted, and very fine skewed, with kurtosis being mesokurtic (LG1-5) or leptokurtic (LG1-6). Gravel ranges from 48 to 50%, sand from 32 to 33%, silt 13 to 14%, and clay 4e5% (silt þ clay is 18e19%).

Table 1 Radiocarbon ages from La Gruta and nearby areas. La Gruta 1, 2 and 3 data are shaded differently for greater clarity.

Site***

Lab ID

Material

Radiocarbon Age (14C BP) 32,650 ± 140 24,410 ± 35

2 Radiocarbon Age (cal BP) 36,934-36,136 28,654-28,211

this paper this paper

10,845 ± 61 10,840 ± 62 10,790 ± 30 10,720 ± 30

12,799-12,653 12,801-12,650 12,730-12,663 12,711-12,562

Franco et al. 2010 Franco et al. 2010 Franco et al. 2010 this paper

10,656 ± 54 10,477 ± 56 9560 ± 30

12,692-12,434 12,549-12,049 11,077-10,678

Franco et al. 2010 Franco et al. 2010 this paper

9470 ± 30 8540 ± 30

10,748-10,571 9539-9466

this paper this paper

8090 ± 30 7560 ± 30 8050 ± 90 7940 ± 260

9029-8774 8403-8208 9121-8599 9429-8207

Mancini et al. 2013 Franco et al. 2013 Aguerre 2003 Aguerre 2003

charcoal

8960 ± 140

10,294-9551

Durán et al. 2003

charcoal guanaco bone*h guanaco bone*h charcoal charcoal charcoal charcoal

7500 ± 250 4770 ± 25 4740 ± 25 4520 ± 50 4475 ± 95 3487 ± 38 1888 ± 39

8972-7760 5583-5325 5578-5320 5307-4891 5311-4846 3832-3594 1881-1704 (AD 69-246) 1826-1589 (AD 124-361) 1372-1271 (AD 578-679) 539-503 (AD 1411-1447) 493-327 (AD 1457-1623) 491-324 (AD 1459-1626) 438-156 (AD 1512-1794) 438-156 (AD 1512-1794)

Durán et al. 2003 Franco et al. 2013 Franco et al. 2013 Aguerre 1982 Aguerre 1982 Franco et al. 2010 Franco et al. 2010

La Gruta 3(1) La Gruta 3 Entrance Pit (a) La Gruta 1(a) La Gruta 1(b) La Gruta 1(c) La Gruta 3(2)

UGAMS-12427 UGAMS-15124

La Gruta 1(d) La Gruta 1(e) La Gruta 3-523/1(3)

AA-76792 AA-84225 UGAMS-13611

La Gruta 3-523/2(4) La Gruta 3-516(5)

UGAMS-15766 UGAMS 15765

La Gruta 1(f) La Gruta 2 La Martita Cave 4 La Martita Cave 4

El Verano Cave 1 Viuda Quenzana 8 Viuda Quenzana 8 La Martita Cave 4 La Martita Cave 4 La Gruta 1(g) La Gruta 1(h)

UGAMS-7540 UGAMS-9113 CsIC-506+ Teledyne Isotopes I.11, 903 Teledyne Isotopes I.13, 797-No 1 INGEIS 2854 UGAMS-9111 UGAMS-9112 CsIC-505+ I-11904 AA-84226 AA-83474

La Gruta 1(j)

AA-83476

charcoal

1829 ± 47

La Gruta 1(i)

AA-83475

charcoal

1452 ± 38

La Gruta 3(6)

UGAMS-13609

charcoal

530 ± 20

La Gruta 1(k)

UGAMS-7541

charcoal

400 ± 20

La Gruta 3(7)

UGAMS-13610

charcoal

390 ± 20

La Gruta 3(8)

UGAMS-12430

guanaco bone*h

290 ± 20

La Gruta 3(9)

UGAMS-12429

guanaco bone*h

290 ± 20

El Verano Cave 1

AA-84224 AA-84223 UGAMS-7538 UGAMS- 12428

puma rib* unidentified bone** charcoal charcoal charcoal guanaco phalanx bone* charcoal charcoal Mylodontidae vertebra** Mylodontidae** Mylodontidae vertebra** charcoal guanaco bone*h charcoal charcoal

Reference

Franco et al. 2010 Franco et al. 2010 this paper this paper this paper this paper this paper

* bone collagen age; ** bone bioapatite age; h bone shows evidence of human action. *** LG1 = La Gruta 1, LG2 = La Gruta 2, LG3 = La Gruta 3. Radiocarbon sample locations (in parentheses) are shown in Figs. 4 (LG1) and 7 (LG3). + Laboratorio de Geocronología, Instituto de Química Física, Rocasolano.

Please cite this article in press as: Brook, G.A., et al., Evidence of the earliest humans in the Southern Deseado Massif (Patagonia, Argentina), Mylodontidae, and changes in water availability, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.04.022

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Fig. 7. Stratigraphic profile of the LG3 Main Excavation showing Units 1 through 6 and sediment, pollen, and radiocarbon dating sample locations, and a diagrammatic profile of Entrance Pit near the drip line of the shelter showing Units EA to EC. Bone and charcoal samples were collected during excavation so equivalent locations in the profile were determined by extrapolation.

Elemental concentrations at LG1 show trends within and between units (Fig. 6). The basal sediments of Unit A (A-7 and A-2) have higher values of Al and Fe (1903 and 2625 ppm) and relatively low values of the more soluble elements Ca, Mg, Na and K (231, 21, 39, and 190 ppm). Al and Fe decrease near the top of Unit A (A-1) (1038 and 1415 ppm) while values of Ca, Mg, Na, and K increase (312, 39, 66, and 226 ppm). The basal sediments of Unit B, as with Unit A, have lower concentrations of Ca, Mg, Na, and K (198, 18, 54, and 244 ppm) than sediments near the top of the unit (319, 28, 111, and 383 ppm). Fe in Unit B decreases from 1842 ppm near the base to 1117 ppm near the top although this is not mirrored by a decrease in Al, which increases slightly from 1160 in the lower sediments to 1553 ppm in the upper. P is noticeably higher (2433 ppm) in the basal sediments of Unit A where the oldest ages for use of the shelter were obtained and may be an indication of human activity. The concentration of P drops to 1225 ppm in the upper part of Unit A where no evidence of occupation was found. Levels of all elements are much higher in Unit C, which has animal dung, abundant charcoal and a layer of ash as well as mineral grains. The organic remnants certainly explain the high

values and suggest that high values lower in the sediment sequence could also record human use of the rockshelter. Charcoal concentrations from La Gruta 1 in Unit A have provided the oldest evidence of human presence in the area and indicate an earliest occupation between ca. 12,799e12,653 cal BP (10,845
61 14C BP) with the first period of occupation lasting from about 12,799 to 12,049 cal BP (10,845
61e10,477
56 14C BP) (Table 1; Franco et al., 2010). Charcoal concentrations revealed by the excavation were limited in extent, being typically up to 10  20 cm in extent, although the deepest is partially covered by the large boulder visible in the north wall of the excavation, which has not yet been removed (Fig. 4). The charcoal scatters are also separated vertically (i.e. in time) and spatially (i.e. in location) despite the floor area of the shelter being small, although it may have been more extensive in the past. These observations suggest that the first humans only used the rockshelter occasionally so that occupation of the shelter was discontinuous over the 250e750 year period indicated by the charcoal ages (12799e12549 cal BP ¼ 250 years; 12799e12049 cal BP ¼ 750 years).

Table 2 Radiocarbon ages for organic matter in lagoon sediments of La Gruta area.

Lagoon

Laboratory ID

La Barda

UGAMS 14755 UGAMS 14754 UGAMS 14759 UGAMS 14758 UGAMS 14700 UGAMS 14700

La Gruta 1 La Gruta 2

Depth (cm) 10-15 35-40 14 55 25 65

Sample ID

13

EB-8 EB-3 GRUT2-2 GRUT2-1 LGLAG2-4 LGLAG2-1

-24.4 -24.9 -24.9 -24.9 -24.5 -25.0

C‰

Age (14C BP) 2250 ± 30 5690 ± 35 2660 ± 30 4900 ± 30 2820 ± 30 4710 ± 35

Calibrated Age (2 cal BP) 2329-2150 6525-6311 2842-2548 5657-5482 2958-2783 5576-5310

Please cite this article in press as: Brook, G.A., et al., Evidence of the earliest humans in the Southern Deseado Massif (Patagonia, Argentina), Mylodontidae, and changes in water availability, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.04.022

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Radiocarbon ages for charcoal in sediment Unit A, at the base of the excavation, date it to the PleistoceneeHolocene transition. Small flakes and charcoal concentrations were identified in the deeper sediments of Unit A and at different locations within Unit B. Artifacts of local and non-local material were recovered, the latter including grey obsidian most likely transported from Pampa del Asador (Franco et al., 2011). Early Holocene use of the rockshelter is indicated by an age of 9029e8774 cal BP (8090
30 14C BP) on charcoal from the base of a hearth near the top of Unit A (Site (f) in Fig. 4). However, charcoal from the top of this hearth dated to 3487
38 14C BP (3832e3594 cal BP) showing that huntergatherers re-used the specific location of the old hearth later on in time. The substantial difference in age between the lower and upper sections of this hearth suggest either a hiatus in sedimentation or a period of erosion between the deposition of Units A and B. It is possible that the upper section of the hearth is even younger than the age we obtained because older charcoal may have been incorporated into the new hearth when it was created at the same location as the old hearth. Therefore, we consider the age of 3487
38 14C BP (Site (g) in Fig. 4) to be a maximum age for the upper hearth, and also for the basal sediments of Unit B in which it is located. A hearth near the top of Unit B (Site (k) in Fig. 4) has provided an age of 400
20 14C BP (493e327 cal BP or AD 1457e 1626) for the youngest sediments in Unit B, indicating deposition during the Little Ice Age (LIA) (Table 1).

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probably a well-documented flood in 1983, deposited flotsam into the entrance area of the rockshelter and on nearby slopes (Fig. 11b). The fact that the lagoon may be able to flood this rockshelter means that flood deposits could be present in the sediments and also that there could have been erosion of some deposits that may have contained evidence of humans, during past floods. However, a line of collapse ceiling blocks between the drip line of the shelter and the back wall provide a protected area in front of the back wall where sediments would be protected from erosion. A test pit in La Gruta 3, begun in 2012, reached bedrock at approximately 60 cm depth. It is close to the rear of the rockshelter and behind large sandstone blocks that collapsed from the ceiling (Fig. 11a). The sheltered location may partly explain preservation of the sediment sequence in this part of the rockshelter. Six sediment units (1e6) could be differentiated (Figs. 7e9). Units 1 and 2 have similar texture containing 3.3% and 3.1% gravel and 33.2% and 32.7% silt þ clay, respectively. They are both light yellowish brown slightly gravelly muddy sand with a Folk and Ward (1957) mean grain size in the very coarse silt range. Both deposits are very poorly sorted, fine skewed and Unit 2 is mesokurtic and basal Unit 1 platykurtic. The overlying Unit 3 is the finest of the six units with 4.7% gravel and 39.5% silt þ clay. It is light yellowish brown slightly gravelly muddy sand with a mean grain size in the very coarse silt range. It is very poorly sorted, fine skewed, and platykurtic. Elemental concentrations at LG3 differ from those at LG1, largely

Table 3 Color and texture of La Gruta 1 sediments.

Color Unit

C C B B B A A

Sample ID LG1-6 LG1-5 LG1-4 LG1-3 LG1-8 LG1-1 LG1-2

A

LG1-7 Mean: Sorting: Skewness:

Kurtosis:

Verbal Description

Munsell Value

Gravel %

Sand %

Silt %

Clay %

Verbal Description

Folk and Ward Statistics and Verbal Descriptions Mean (um)

Sorting

Skewness

Kurtosis

Verbal based on Mean

muddy sandy gravel 559.6 9.9 (vps) -0.79 (vfs) 1.20 (l) coarse sand muddy dark gray 10YR4/1 50.2 32.1 13.5 4.1 sandy gravel 645.1 9.0 (vps) -0.81 (vfs) 1.1 (m) coarse sand dk yellowish gravelly brown 10YR4/4 26.0 41.3 19.6 13.1 muddy sand 145.8 15.4 (vps) -0.38 (vfs) 0.6 (vp) fine sand dk yellowish gravelly brown 10YR4/6 19.7 53.5 17.9 8.8 muddy sand 200.7 12.1 (vps) -0.43 (vfs) 0.8 (p) fine sand brownish muddy yellow 10YR6/6 39.7 37.9 14.8 7.6 sandy gravel 373.7 11.5 (vps) -0.68 (vfs) 0.9 (m) medium sand yellowish muddy brown 10YR5/6 40.0 32.8 17.5 9.7 sandy gravel 278.1 13.6 (vps) -0.64 (vfs) 0.7 (p) medium sand yellowish muddy brown 10YR5/8 35.4 39.8 15.4 9.5 sandy gravel 278.1 13.6 (vps) -0.64 (vfs) 0.7 (p) medium sand yellowish muddy brown 10YR5/6 32.3 39.1 20.0 8.5 sandy gravel 279.5 12.7 (vps) -0.59 (vfs) 0.8 (p) medium sand Graphic mean grain size is calculated as the size of the 16th, 50th, and 84th percentile divided by 3. Very poorly sorted sediments are those in which grain sizes are mixed (large variance) whereas well sorted indicates that the sediment sizes are similar (low variance). In Table 3 and 4 vps = very poorly sorted; ps = poorly sorted. A grain size distribution may be symmetrical (s) or skewed. If the bulk of the data is at the left and the right tail is longer, the distribution is positively or fine skewed indicating a tail of fine grains; if the peak is to the right and the left tail is longer, the distribution is negatively or coarse skewed indicating a tail of coarse grains. In Tables 3 and 4 vfs = very fine skewed; fs = fine skewed; s = symmetrical. In a distribution of grain size kurtosis is the height and sharpness of the peak relative to the rest of the data. Higher values indicate a higher, sharper peak and lower values a lower, less distinct peak. A low, broad peak is platykurtic (p), a high, sharp peak is leptokurtic (l), and a “normal” peak is mesokurtic (m). In Tables 3 and 4 vp = very platykurtic; p = platykurtic; m = mesokurtic; l = leptokurtic; vl = very leptokurtic. dark gray

10YR4/1

48.2

32.7

14.4

4.6

3.2. La Gruta 2 and 3 La Gruta 2 and 3 rockshelters have formed in Monte León Formation sandstone along the margin of a complex lagoon (Figs. 2a and 3b). The test pit at La Gruta 2 reached bedrock and provided an oldest age for a guanaco bone showing human action of 8403e 8208 cal BP (7560
30 14C BP). Some 50 m away, the floor of La Gruta 3 lies close to the level of the lagoon floor and a major flood,

because of the different substrates: fossilifierous, carbonate-rich sandstone and silicified ignimbrite, respectively (Figs. 6 and 9). Levels of Al, Fe, and Mn are much lower at LG3 while Ca, Mg, Na, K, Sr and Si are higher. Basal Units 1e3 in the Main Excavation at LG3 have generally higher Al, Fe, Mn and Si concentrations than overlying Units 4e6, while the opposite is the case for Ca, Mg, Na, K, and Sr, with these elements increasing in the upper units. Elemental levels in the Entrance Pit, near the drip line of the rockshelter, do

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G.A. Brook et al. / Quaternary International xxx (2014) 1e19

not differ significantly from those in the lower units of the Main site. The basal Unit 1 sediments contained puma bones, including a rib fragment, two thoracic vertebrae, and a second and a third phalanx (ungual). Collagen in the rib bone provided an age of 36,934e36,136 cal BP (32,650
140 14C BP). Sediment samples were collected at intervals through the profile for pollen analysis but insufficient pollen was extracted from Unit 1 to allow useful counts for paleoenvironmental reconstruction. Units 2 and 3 also contained animal bones, namely of guanaco and Mylodontidae (Figs. 7 and 10). In addition, a rib fragment of an unknown animal was recovered as well as a bone that could not be identified. Collagen from a guanaco phalanx from Unit 2 dated to 12,711e 12,562 cal BP (10,720
30 14C BP) and was stained by manganese, suggesting exposure to water (Site (2) in Fig. 7). The Mylodontidae bones included a rib, fragments of a thoracic vertebra, and remains that could be from a pelvis or sacrum. A fragment of a Mylodontidae thoracic vertebra (523/1) and two other Mylodontidae bone fragments (523/2) from Unit 2 (Table 1; Site (3) in Fig. 7) provided bioapatite ages of 9560
30 and

9470
30 14C BP (11,077e10,678 and 10,748e10,571 cal BP). These ages are statistically identical at the 2s uncertainty level and overlap when calibrated even at the 1s level. They also have similar d13C values of 12.2& and 11.6& suggesting that the ages are reliable. A bioapatite age was also obtained for a third Mylodontidae bone, a fragment of vertebra that was found in horizontal position (suggesting that it may not have been affected by bioturbation) in sediment Unit 3 (516 in Table 1; Site 5 in Fig. 7). This age of 8540
30 14C BP (9539e9466 cal BP) is younger than those from Unit 2 and the bioapatite has a higher d13C value of 9.5&. Based on bone size, fusion state, and external morphology, the Mylodontidae bones from Units 2 and 3 at LG3 appear to be from a single individual. If correct, this suggests contamination of one or more of the dated bone samples by older or younger carbon that was not eliminated by laboratory pre-treatments for AMS radiocarbon dating. The two oldest ages are for different bone fragments from the same part of Unit 2; the ages are identical (11,077e10,678 and 10,748e10,571 cal BP), so we consider them to be reliable. We cannot entirely rule out that the Mylodontidae bone from Unit 3 is from a different individual, and if so this might explain the younger age from a bone in a younger sediment unit. If all the bones are from only one individual, then this bone is the most likely to have been contaminated. In any event, the three ages suggest that Mylodontidae was in the area during the late Pleistocene to early Holocene, a conclusion that is supported by the previously mentioned late Pleistocene collagen age of 10,720
30 14C BP (12,711e12,562 cal BP) for a guanaco phalanx bone that came from sediment Unit 2 (Site (2) in Fig. 7). Pollen data for Unit 2 indicate grass steppe with dwarf shrubs (Ephedra, Nassauvia) so that conditions were probably slightly wetter than today. To date, we have found no clear evidence of human presence during deposition of Units 1 and 2. It is possible that the Mylodontidae bones in Unit 3 were eroded from Unit 2 as a result of post depositional processes, as they were found very close to a pit. Supporting this is the evidence that the bones appear to be from one individual. The unidentified rib fragment has lost part of the cortical surface due to abrasion. This could have occurred as a result of water action in the past possibly when the lagoon extended into the shelter or when seepage waters entered the back of the cave along fissures and bedding planes. There is a small spring a few meters west of the shelter that was used by the

Fig. 8. Variations in sediment texture at La Gruta 3 rockshelter (top: Main Excavation; bottom: Entrance Pit). For clarity, histograms for adjacent units are shaded differently. See Fig. 7 for abbreviations and sample locations in the profile.

Fig. 9. Variations in elemental concentrations between units at La Gruta 3 rockshelter. Values are in parts per million (ppm). Note the different scales in the upper and lower diagrams.

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previous owner of Estancia La Gruta for fresh water. After heavy rain, similar seepages may develop in the rockshelter itself and could have contributed to the uneven upper surfaces of some units by eroding channels in them. A few isolated, small, worked flakes were recovered from Unit 3, but their origin has not yet been determined. Close to the drip line of La Gruta 3 rockshelter, at a lower elevation than the Main Excavation site, there is a distinct lightcolored layer of sediment rich in gravel and sand that is cemented by secondary carbonate (Fig. 11a). Conditions at the time the sediments accumulated may have been very like the lake conditions shown in Fig. 12a and b. A 50  50 cm pit (Entrance Pit; Fig. 7 and Table 4) was excavated in this deposit to establish stratigraphy and to obtain material for dating.

9

Bones were recovered from 8.5, 16.5, 18, and 19 cm depth in the sequence and bone fragments from 18 cm were dated. These provided a bioapatite age of 24,410
35 14C BP (28,654e28,211 cal BP). The d13C value for the bioapatite is 8.9&, which appears high, suggesting the possible incorporation of inorganic carbon from the calcareous sandstone of the rockshelter. If this did occur, then the estimated age of the bone should be considered a maximum value as incorporated carbon would have virtually no 14C, making the bone appear older than its true age. Using a tape and inclinometer, we determined that the old surface of the cave floor at the back of the rockshelter, where the Main Excavation was undertaken, is 0.735 m above the Entrance Pit deposit. As the Main Excavation reached bedrock at w0.55 m this means that the upper surface of the Entrance Pit deposit is only 18.5 cm below the base of the

Table 4 Color and texture of La Gruta 3 sediments (see Table 3 for list of abbreviations).

Color Unit

Sample ID

6b (surf gravel) 6a

LG3-f2

5

LG3-e

4b (sand) 4a

LG3-d2

3

LG3-c

2b (silt)

LG3-b2

2a

LG3-b1

1

LG3-a

EC

LG3E-3

EB

LG3E-2

Verbal Description

Folk and Ward Statistics and Verbal Descriptions Munsell Value

Gravel %

Sand %

Silt %

Clay %

Verbal Description

Mean (um)

Sorting

Skewness

Kurtosis

multiple sand colors light yellowish brown very dark gray** light gray

N/A

12.0

87.0

0.9

0.0

gravelly sand

911.5

2.2 (ps)

-0.14 (fs)

1.20 (l)

2.5Y/6/4

9.9

75.5

7.2

7.3

289.7

5.7 (vps)

-0.11 (fs)

1.31 (l)

2.5Y/3/1

8.7

64.0

16.0

11.2

143.1

9.4 (vps)

-0.27 (fs)

0.88 (p)

2.5Y/7/2

0.2

91.0

5.0

3.7

116.5

2.2 (ps)

-0.21 (fs)

1.82 (vl)

light yellowish brown* light yellowish brown, light yellowish brown light yellowish brown light yellowish brown grayish brown

2.5Y/6/4

8.4

58.6

18.3

14.7

90.4

10.1 (vps)

-0.22 (fs)

0.79 (p)

2.5Y/6/4

4.7

55.7

20.1

19.4

62.3

8.8 (vps)

-0.20 (fs)

0.70 (p)

2.5Y/6/4

5.9

61.1

15.7

17.3

44.7

7.3 (vps)

-0.25 (fs)

1.06 (m)

2.5Y/6/4

3.1

64.1

14.5

18.4

54.00

7.6 (vps)

-0.28 (fs)

0.88 (p)

2.5Y/6/4

3.3

63.5

17.5

15.7

46.4

6.8 (vps)

-0.28 (fs)

1.02 (m)

2.5Y5/2

5.7

56.6

19.2

18.4

61.2

11.8 (vps)

-0.25 (fs)

0.64 (vp)

light brownish gray EA LG3E-1 light yellowish brown *different colored gravels ** visible organic matter

2.5Y6/2

3.3

73.1

12.3

11.2

57.1

6.2 (vps)

-0.29 (fs)

2.53 (vl)

2.5Y6/4

9.7

63.7

15.5

11.2

gravelly muddy sand gravelly muddy sand slightly gravelly sand gravelly muddy sand slightly gravelly muddy sand gravelly muddy sand slightly gravelly muddy sand slightly gravelly muddy sand gravelly muddy sand slightly gravelly muddy sand gravelly muddy sand

93.6

10.8 (vps)

-0.08 (s)

1.05 (m)

LG3-f1

LG3-d1

Excavation was difficult because the material was heavily cemented in some layers and was only possible using a geologic hammer. Weathered and fractured bedrock was reached at about 21 cm depth and 3 units EA, EB, and EC were exposed. At the base is yellowish brown gravelly muddy sand of Unit EA, 6 cm thick, containing 28.5% gravel and very coarse and coarse sand and 26.6% silt and clay. Mean grain size is very fine sand, the unit is very poorly sorted, and the particle size distribution is symmetrical and mesokurtic. The overlying Units EB and EC (10 and 6 cm thick respectively) are light brownish grey slightly gravelly muddy sand and grayish brown gravelly muddy sand both with a mean grain size of very coarse silt. These units contain 12.0% and 22.8% gravel and very coarse and coarse sand, respectively. Units EB, and EC contain 23.5% and 37.6% silt and clay, are very poorly sorted, fine skewed, and very leptokurtic and very platykurtic, respectively. Significantly, Unit EB with 41.6% fine sand was the finest of the three units and also the most cemented.

Verbal based on Mean coarse sand medium sand fine sand very fine sand very fine sand very coarse silt very coarse silt very coarse silt very coarse silt very coarse silt very coarse silt very fine sand

excavation where puma and Mylodontidae bones were found. Therefore, it is possible that Entrance Pit Unit EA and Unit 1 at the Main Excavation are of the same age. The possibility of this is perhaps increased by sediment characteristics. If we assume that the medium sand to clay fractions of each deposit total 100%, then Unit 1 has 62.6% medium, fine and very fine sand, and 37.4% silt and clay. In comparison, Unit EA has 62.7% medium, fine and very fine sand, and 37.3% silt and clay, virtually identical to Unit 1. In terms of the finer grain components therefore, the deposits are identical and so could represent one unit, which extended from the front to the back of the rockshelter. The basal Unit 1 sediments containing the puma bones (36,934e 36,136 cal BP) are separated considerably in age from the overlying Unit 2 sediments with Mylodontidae and guanaco bones dating in the range 12,711e10,571 cal BP (10,720
30e9470
30 14C BP) (Table 1). The upper surface of Unit 1 in the southern wall of the excavation, near the back wall of the rockshelter, shows very little

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G.A. Brook et al. / Quaternary International xxx (2014) 1e19

relief (<5 cm). In contrast, the upper surface of Unit 2 has a relief of around 10 cm suggesting some erosion of the sediments after deposition. This would support the idea proposed earlier, that the Mylodontidae bones in Unit 3 were eroded from Unit 2. 4. Evidence of past water levels in La Gruta area lagoons Flood debris near La Gruta 3 rockshelter provides evidence of past flooding events in the adjacent lagoon. However, to obtain additional information on past conditions in lagoons in La Gruta area, whether they contained water at particular times and how high lake levels were, we examined sediments in La Gruta Lagoons 1 and 2 and in a nearby lagoon La Barda (Fig. 2). La Gruta 1 rockshelter formed in a steep cliff along the southern margin of La Gruta Lagoon 2 while La Gruta 2 and 3 rockshelters formed in steep cliffs bordering the southern margin of La Gruta Lagoon 1. La Gruta Lagoon 2 is about 900 m long from west-to-east and consists of three separate basins separated by rock-cored ridges mantled by beach gravels that preserve relict shorelines of former higher lagoon levels. The largest basin is to the west and it is 470 m long and up to 200 m wide. To the east is a second basin 125 m WeE and 170 m wide, and east of this a third that is 150 m WeE and up to 90 m wide. Small streams up to 1 km long enter from the west and south but these have very small catchments. When full, the large basin to the west may have been 3e4 m deep. La Gruta Lagoon 1 is 1.4 km NNWeSSE and a maximum of 1.05 km WeE. The lagoon depression has two separate basins that fill independently but as water levels increase they coalesce to form a single lake. The northern depression is the deepest and is 775 m NeS and 750 m WeE. The second basin in the southwest is 536 m NeS and 362 m WeE. Relict beach ridges and shorelines around the depression but mainly on the east and southeast margins (the downwind side) show that when full the lake would be up to 10 m deep in the northern depression and 6e7 m deep in the southern depression. In the broad flat north of La Gruta 3 rockshelter the water would be 6 m or more deep. La Gruta Lagoon 1 differs from Lagoon 2 in that it is fed by a stream that extends to the north and west for about 18 km. The channel of this stream enters the eastern side of the lagoon depression and winds across the floor to the deeper northern depression. Recent extensive flooding of La Gruta Lagoon 1 is presumably a result of this large stream input and this must also have occurred in the past and been more frequent during periods of increased moisture. La Barda is a 375 m long, triangle-shaped depression elongated WeE; it is broad in the west and narrows to a point in the east. There are two distinct basins separated by an arcuate 1.5 m high gravel beach bar produced by wave action generated by the prevailing westerly winds when the large basin was flooded. The basin to the west is 225 m WeE and 225 m across at its widest point; the smaller basin to the east is 150 m long and at its widest only 50 m across. When flooded, the westerly basin is probably occupied by a lake 2e3 m deep. In most years, all three lagoons dry out during the dry season, allowing examination of sediments in the basins. However, based on satellite evidence water persists in La Gruta Lagoon 1 longer than Lagoon 2, which in turn contains water longer than La Barda. During 2012 and 2013, excavations in the sediments covering the floors of these three lagoons provided information on their age and therefore on when the lagoons contained water. At La Barda (48 49.7960 S; 69 31.9900 W; 319
5.5 m elevation) an excavation in the middle of the larger basin to the west exposed sediments to 50 cm depth with the basal material being a coarse gravel. Samples were taken continuously from 5 cm increments making 10 samples. The samples from 35 to 40 cm and 10e15 cm below the surface provided AMS radiocarbon ages of 5690
35 and 2250
30 14C BP

(6525e6311 and 2329e2150 cal BP). A pit was also excavated at the approximate center of La Gruta Lagoon 2 (48 49.4730 S; 69 23.9390 W; 275
4.9 m elevation) to a depth of 65 cm. Samples from the base of this excavation and from 25 cm depth provided AMS radiocarbon ages of 4710
35 and 2820
30 14C BP (5576e5310 and 2958e2783 cal BP). A third pit 60 cm deep was excavated in a relict beach/river bar to the north of La Gruta 3 rockshelter (48 50.2340 S; 69 22.3770 W; 259
4.9 m elevation). Organic material from 55 cm and 14 cm depth provided AMS radiocarbon ages of 4900
30 and 2660
30 14C BP (5657e55482 and 2842e 2548 cal BP). Excavations in all three lagoons reached gravel suggesting that prior to sediment deposition, which began around 6500 cal BP, there was a period of dry, windy conditions with deflation of fine sediments from the lagoon basins. Ages of 2329e2150, 2958e 2783 and 2842e2548 cal BP (2250
30, 2820
30, and 2660
30 14C BP) from 10 to 15, 25, and 14 cm depth suggest deposition of fine sediments in water up to at least 2100 cal BP. The implication of these results is that conditions were much drier than today prior to 6500 cal BP and at least as wet as today after this date. This suggests that after humans first entered La Gruta area around the time of the PleistoceneeHolocene transition, there was a major dry interval of climate. The timing of this dry interval corresponds closely with the lack of evidence for human occupation of the three La Gruta rockshelters around this time. Therefore, humans may have entered this area when water was reasonably abundant in the lagoons. They may then have used the area less frequently in the Holocene between ca. 8000e 6500 cal BP due to much drier conditions when the lagoons were largely bare windblown surfaces with no water, as indicated by the basal gravels in all three excavations. Human groups may have moved to nearby areas with more reliable water supplies during this period. In 1983, there was significant flooding of La Gruta Lagoon 1 to the extent that the lagoon inundated a farmhouse on Estancia La Gruta just west of La Gruta 3 rockshelter (Fig. 12a and b). The house is at about the same elevation as the floor near the entrance to La Gruta 3 rockshelter. Driftwood associated with the flood is widely distributed around the east and southeast margins of the lagoon basin, striking evidence of how high the waters reached (Fig. 11b). Historical photographs show the extent of the flooding which caused the farmer to re-locate the house and associated structures; these photographs are an indication of what the area may have been like in the past when the climate was somewhat wetter than today or when there were heavy rainfall or snowmelt events. There appears to have been above-average snowfall prior to the 1983 flood (Florence Kemp, Estancia 17 de Marzo, pers. comm. 2014), and melting snow may have been a large component of the floodwaters. The images of the flood in Fig. 12a and b clearly show water carrying a great deal of sediment in suspension. As floodwaters subside, any suspended silt and clay accumulates on the floor of the lagoon and in sediments around the shore (including in the rockshelter if waters are high enough) when there is limited wave action. If the prevailing southwesterly winds strengthened when the lagoon was flooded, beach bars would form due to wave action on the shore in the downwind direction. We would therefore expect that an increase in fines in the rockshelter sediments might record a period of increased moisture when flooding was more frequent and the extent and duration of floods greater than today. The 1983 flood also shows what conditions may have been like in the past, and that occupation of the shelter would have been difficult when flooding was more frequent and more prolonged. The level of water in 1983 also shows that sediments in the back of the rockshelter could have been eroded by waves, particularly during fall as the

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11

Fig. 10. Mylodontidae bones from the Main Excavation at La Gruta 3 rockshelter.

southwesterly wind belt migrated northwards and strengthened as winter approached. 5. Interpretation of La Gruta rockshelter sediment sequences The sediments in a rockshelter commonly result from simultaneous inputs from geogenic and biogenic sediments due to a variety of processes such as rockfall, wind action, and human activity (Farrand, 2001). Geogenic sediments may originate either inside the cave (endogenic) or outside (exogenic) and can include: roof fall (either spalling or collapse); disintegration of the cave bedrock by chemical and freeze-thaw weathering; inwashing of colluvium and

soil through the cave mouth or through fissures leading to the cave; fallout of aeolian sand- or silt-sized dust; stream deposition, from waters entering the cave via fissures or bedding planes or from external streams flowing into the cave mouth; beach sand or gravel, if the cave is now or was close to a lake. Granulometric histograms showing the particle-size distribution of the sediment can reveal modes in particle size that can help to establish the dominant processes responsible for sediment being transported to the rockshelter. A very coarse mode is likely to reflect breakdown of the cave ceiling possibly by freeze-thaw weathering, a silt mode probably aeolian material blown into the cave, and a clay mode input of soil through cracks and fissures in the rockshelter walls and

Fig. 11. Evidence of flooding near La Gruta 3 rockshelter. Cemented muddy sandy gravel at the entrance to the shelter being excavated (Entrance Pit). The Main Excavation is below the seated figure at the back of the shelter (a). Branches deposited along the shore of La Gruta Lagoon 1 to the east of La Gruta 3 rockshelter most likely during the 1983 flood (see also Fig. 12). La Gruta 3 rockshelter is just beyond the point of the sandstone cliff in the upper left of the photograph (b).

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G.A. Brook et al. / Quaternary International xxx (2014) 1e19

Fig. 12. Flooding of La Gruta Lagoon 1 in 1983 and how this affected La Gruta 3 rockshelter. It is clear that the rockshelter could have been flooded at this time. Photographs (a) and (b) were provided by Carlos Baetti who obtained them from the previous owners of Estancia La Gruta. We use them here with Baetti’s permission.

ceiling or a period of surface stability and soil development in the cave (Farrand, 2001). A diffuse sand mode can indicate introduction of beach deposits into the shelter. However, a coarse mode of angular rock fragments may also be produced by hydration weathering or the frequent wetting and drying of a rock surface. Periods of relative stability and weathering of rockshelter sediments can often be interpreted from color and clay content. Dark brown or reddish brown (oxidized) colors in a sediment sequence that is generally light-colored can indicate a weathered horizon, while enrichment in clay content relative to overlying and underlying strata is also evidence of pedogenic alteration of primary minerals into clay minerals. Finally, bioturbation by plant roots and burrowing animals, as well as pits dug by humans for the emplacement of hearths or burials, obscure the original stratification. Farrand (2001) notes that the occupants of the Abri Pataud rockshelter (Dordogne, France) removed sediment from under the overhanging rockshelter where they were living, creating a depression along the back wall at least 75 cm deep that truncated older strata (see also Farrand, 1975a,b). The granulometric histograms for La Gruta 1 and 3 rockshelters reveal multiple modes in size frequency (Figs. 5 and 8) as do the data in Table 5 of summary statistics for each of the three sediment sequences examined (LG3 Main, LG3 Entrance Pit, and LG1). Table 5

reveals that LG1 sediments (gravel to clay size) have modes in the gravel (36.5%) and silt (16.6%) size ranges. This differs from the LG3 sequences where the peaks are in the coarse sand (12.1% Main and 7.65% Entrance) and very fine sand (17.75% and 27.2%) ranges. If we consider only particle sizes finer than very coarse sand, and convert these to 100%, then the modes at LG1 are coarse sand (17.8%) and silt (32.5%) and at LG3 coarse sand (14.6% Main and 8.8% Entrance) and very fine sand (21.3% and 31.4%). La Gruta 1 rockshelter is a few meters above the floor of the adjacent lagoon and is never flooded as it is higher than the overflow for the lagoon. As a result, it is dominated by gravel produced by breakdown of the walls and ceiling of the shelter and by silt that is blown into the shelter by wind. In contrast, La Gruta 3 is close to the level of the adjacent lagoon basin floor and is known to flood after heavy rains, as it did in 1983 (Fig. 12a and b) so that sediments there have modes in the coarse and very fine sand ranges although they still contain high proportions of silt and clay. The elevations of relict beach ridges around the lagoon suggest that it may have flooded beyond the 1983 level in the past, in which case it is possible that the floodwaters would have inundated parts of La Gruta 3 rockshelter. If the shelter was flooded occasionally, then sediments in its floor may preserve evidence. The dominance of sand at La Gruta 3 is also related to the sandstone bedrock, which breaks down to produce

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G.A. Brook et al. / Quaternary International xxx (2014) 1e19

sand-sized particles more readily than the silicified ignimbrites at La Gruta 1.

13

Unit B, similar to the semiarid conditions of today (Mancini et al., 2013; note that in this paper LG1 units are numbered not defined

Table 5 Textural frequency modes in the sediment sequences at La Gruta 1 and La Gruta 3 rockshelters. Modes are indicated by shading.

Sediment Size Category Gravel Very coarse sand Coarse sand Médium sand Fine sand Very fine sand Silt Clay TOTAL

La Gruta 3 Main Excavation (%) Entrance Pit A* B* A* 7.0 6.3 10.0 7.2 12.1 14.6 7.6 10.1 12.2 7.2 16.2 19.5 15.3 17.7 21.3 27.2 13.8 16.6 15.7 13.1 15.8 13.6 100% 100% 100%

(%) B*

8.8 8.3 17.7 31.4 18.1 15.7 100%

La Gruta 1 (%) A* 36.5 12.4 9.1 6.7 5.2 5.2 16.6 8.2 100%

B*

17.8 13.1 10.2 10.2 32.5 16.1 100%

* A: 100% includes gravel and very coarse sand; B: 100% excludes gravel and very coarse sand.

Unit A, at the base of the LG1 sediment sequence, has a darker color (yellowish brown) than other units. It has high gravel and clay contents, the former suggesting that water was available for hydration breakdown of the shelter walls or for freeze-thaw weathering. The color and high clay content suggest stable conditions in the cave and pedogenesis due to increased moisture availability. Unit B contains less gravel than Unit A and as a result sand, silt and clay percentages are reasonably high, particularly silt. Overall, we believe that conditions were somewhat drier during much of the period when Unit B was deposited. The lower sediments of Units A and B have higher Al and Fe and lower Ca, Mg, Na and K than the sediments above them, suggesting wetter conditions when they accumulated leading to some leaching of highly soluble elements. Lower levels of Al and Fe and higher levels of Ca, Mg, Na, and K in the top sediments of these two units indicate drier conditions and possibly a stable surface in the rockshelter for some considerable time. Pollen assemblages in Unit A (samples 1e8 in Fig. 4) and in the basal sediments of Unit B (samples 9e10) have high percentages of grass pollen attesting to wetter conditions. However, pollen samples 3, 11 and 12 from the upper deposits of Units A and B have lower levels of grass pollen, which together with higher levels of soluble elements is a strong indication of drier conditions (Fig. 13). The pollen data for Unit B show a trend to reduced grass and higher shrub percentages towards the top of the unit. The uneven upper surface of Unit A (lower around the large boulder exposed by the excavation), its variable thickness, high levels of soluble elements towards the top, and the apparent large age difference between it and Unit B, all indicate a lengthy period of surface stability with some erosion of the rockshelter floor, possibly under wetter conditions than today. High grass pollen percentages, higher Al and Fe and lower levels of easily-dissolved salts in the lower parts of Unit B, suggest wetter conditions that may have been partly responsible for erosion of the upper sediments of Unit A. High levels of Ca, Mg, Na and K in the upper part of Unit B may record a period of stability and a hiatus in sedimentation before deposition of Unit C. Unit C has the highest percentage of gravel in the sequence but lower silt and clay levels than the other units, suggesting relatively wet conditions. However, low percentages of medium and fine sand point to a drier climate than during deposition of Units A and B because the larger clasts were not broken down. Only one pollen sample (13) was taken from Unit C and this was near the base of the unit (Fig. 4). This records a drier climate than in the upper part of

by letters). The higher percentage of Chenopodiaceae in sample 13, compared with samples 11 and 12 from the upper part of Unit B, indicate lagoon desiccation, because these plants grow around the margins of water bodies that undergo frequent drying. The increase in Poaceae and reduction in the Chenopodiaceae in the surface pollen sample suggest slightly wetter conditions towards the present with more frequent flooding of the lagoon (Fig. 13). The sediments at La Gruta 3 differ from those at La Gruta 1 in having modes in different size categories. This is due to differences in bedrock at the two sites (fossiliferous sandstone at LG3 and silicified ignimbrite at LG1) and also to the elevations of the rockshelters above the adjacent lagoons. LG1 is a few meters above its lagoon, so that wind-blown, saltating sand particles near the ground surface cannot reach the shelter and so aeolian deposits here are largely of silt size. In contrast, because the floor of LG3 is close to the level of the adjacent lagoon, saltating sand grains can enter the shelter so that aeolian sediments here are largely in the very fine sand range (Table 5). At LG1, there is a silt particle size peak throughout the sediment sequence. In contrast, at LG3, fine sand is only a particle size peak in Units 1 and 2 but not in the overlying units. This suggests that while silt has been available for aeolian transport throughout the late Pleistocene and Holocene (as evidenced by the LG1 record), fine sand has not. We believe that aeolian input of fine sand to LG3 only occurred when fine sand was available in the basin of the adjacent lagoon, and because this would have required increased chemical weathering of the sandstone bedrock and/or transport of sand by streams entering the depression, more water would have been needed. Any increase in stream flow to the LG3 lagoon could have been accompanied by flooding of the depression, and this may have deposited fine sediment on the floor of the LG3 rockshelter. Significantly, Unit EA of the LG3 Entrance Pit sediment sequence has similar characteristics to those of Unit 1 at the Main Excavation and is broadly similar in age. Unit EA does have a slightly higher percentage of coarser grains but this is to be expected given its location close to the drip line of the rockshelter. Puma bones in Unit 1 date to ca. 36,500 cal BP and unidentifiable bones in Unit EA to ca. 28,300 cal BP, placing deposition of these units to roughly the same time period, namely before or during the Last Glacial Maximum (LGM), which would have brought very cold conditions to the area. Unit EB is also broadly similar in grain-size characteristics to Unit 2 at the Main Excavation and Unit EC is similar to Unit 3 (and also to Unit 4). Units 2 and EB are both dominated by a marked mode of

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G.A. Brook et al. / Quaternary International xxx (2014) 1e19

Fig. 13. Stratigraphic units and pollen assemblages in LG1 and LG3 sediments. Pollen sample numbers are indicated and radiocarbon ages in

very fine sand and low frequencies of coarser grains. In contrast, Units 3 and 4, like Unit C, lack a distinct mode of very fine sand but have less distinct modes of silt and fine sand and contain larger numbers of coarser grains ranging in size from medium sand to gravel. However, despite their location below the drip line of LG3, Units EA and EB contain relatively few coarse grains indicating little

14

C BP are shown at left.

breakdown of the ceiling of the shelter and of the rocks on the surface above it during deposition of these units. This implies that conditions were no wetter than semiarid when Units 1 and 2, and Units EA and EB, were deposited. Pollen sample 1 did not provide enough pollen for realistic paleoenvironmental inferences to be made about Unit 1. Absence of pollen could mean drier conditions with a reduced vegetation cover but more work will be necessary to

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G.A. Brook et al. / Quaternary International xxx (2014) 1e19

test this assumption. The absence of coarser rock fragments could also indicate much colder temperatures throughout the year. Temperatures consistently below freezing would limit freeze-thaw cycles, and therefore rock breakdown, even if water was sufficient. The substantial age difference between Units 1 and 2, of about 24,000 years, suggests that the upper part of Unit 1 may have been eroded before deposition of Unit 2. LG3 Unit 2, with ages between 12,711 and 10,571 cal BP (10,720
30 and 9470
30 14C BP), is late Pleistocene in age and may be contemporaneous with Unit A at LG1, which has provided ages between 12,799 and 8774 cal BP (10,845
61e 8090
30 14C BP). An increase in moisture would increase mechanical breakdown of the walls of the rockshelters at La Gruta, producing coarse particles up to gravel size. Gravel is abundant in Unit A at LG1, but larger rock fragments are less common in Units 1 and 2 at LG3, although they are more abundant in what we have argued to be equivalent Units EA and EB, near the drip line of the rockshelter, where more water would have been available. In many rockshelters, the rear of the shelter is drier than areas nearer the entrance and this could help to explain the absence of coarser particles in Units 1 and 2. Pollen data for LG1 Unit A and LG3 Unit 2 indicate a predominance of grass with dwarf shrubs (Ephedra, Nassauvia) (Fig. 13), which supports our interpretation of the sediment data as indicating semiarid conditions but with more available water than today. The character of the sediments at LG3 changes with deposition of Unit 3 and later Unit 4. While maintaining a predominance of finer particles, although at reduced levels, these units have a more even distribution of particle sizes compared to Units 1 and 2. This trend towards increased percentages of coarser particles suggests a transition to slightly drier conditions in the rockshelter with less sand being produced by chemical weathering and/or transported to the lagoon by streams and then blown into the rockshelter by wind. However, the moisture level during deposition of Units 3 and 4 was high enough to break down the rockshelter walls and ceiling, contributing fragments of medium sand to gravel-size to the floor of LG3. The trend to higher percentages of coarser fragments continued through Units 5 and 6 with the particle size mode in Unit 6 being coarse to very coarse sand. The increase in the percentage of coarser particles upwards in the sediment sequence was accompanied by lower concentrations of Al, Fe and Si, and higher concentrations of soluble elements Ca, Mg, Na, and K, both changes suggesting drier conditions. Pollen data for Unit 3 at LG3 suggest semiarid conditions similar to those of today. Current age data for Unit 2 and for the upper part of Unit 3 place deposition of Unit 3 sediments between ca. 10,748 and 503 cal BP. If the age for the Mylodontidae vertebra from Unit 3 is reliable, deposition may have occurred between 9539 and 503 cal BP. At present, we do not know if sedimentation was continuous, or if the age of 503 cal BP is for charcoal resting on a much older surface. Therefore, a reliable reconstruction of vegetation and environmental conditions for the area during the Middle and Late Holocene will clearly require further research. The south wall of the excavation near the back wall of La Gruta 3 exposes a well-defined animal burrow or human pit filled with Unit 4 sediments that extended through Unit 3 into Unit 2 (Fig. 7). The burrow or pit is close to where Mylodontidae bones were found in the upper sediments of Unit 3 and human or animal disturbance of the sediments may explain why Mylodontidae bones have been found in both Units 2 and 3. The filling of the burrow or pit in Units 3 and 2 by Unit 4 sediments suggests that Unit 4, and probably also Units 5 and 6, were deposited under relatively dry conditions when humans and small animals could occupy the shelter. Units 5 and 6 differ from Unit 4 in having larger percentages of coarse grains and a more even distribution of grain sizes. In Unit 5,

15

sediment sample e1 has modes of coarse sand and silt while sample e2 has a single broad mode of fine sand. Nearer to the back wall of the cave Unit 6 contains more gravel (mode of very coarse to coarse sand) presumably from breakdown of the low ceiling at this location. Based on four radiocarbon ages, Units 4e6 appear to have accumulated during the last ca. 550 years. Pollen sample 10 from Unit 5 has high shrub percentages (Asteraceae Asteroideae) and a low proportion of grass pollen that suggest dry conditions. Pollen sample 12 from Unit 6, with a higher percentage of grass pollen, suggests a slight increase in moisture in recent times. The LG3 data for the last 500 years complement that from LG1. Both records reveal a semiarid environment similar to the present but with evidence of an early dry period followed by somewhat wetter conditions towards the present. All of the sediment units in the Main Excavation of LG3 rest against large collapse blocks but to the north, towards the rockshelter entrance, these sediments are buried beneath other collapse blocks that produced the pile of boulders visible in Fig. 11a. The upper surfaces of Units 2 and 3 are also very irregular suggesting erosion by water and by animals prior to burial by the overlying units. Bioturbation is particularly apparent in Unit 3 and in the upper part of Unit 2, including channels and animal burrows or human pits filled with Unit 4 sediments. Clearly, the back of the shelter was not flooded when these activities occurred. 6. Discussion Evidence from La Gruta area and from caves 25 km to the north and northwest of the area, including La Martita Cave 4 (Aguerre, 2003), Viuda Quenzana 8 (Franco et al., 2013) and El Verano Cave 1 (Durán et al., 2003) (Fig. 3) indicates human presence at La Gruta 1, in the southern Deseado Massif, during the PleistoceneeHolocene transition at ca. 12,799e12,049 cal BP (10,845
61e 10,477
56 14C BP) and at other sites during the early Holocene at ca. 9029e7760 cal BP (8090
30e7500
250 14C BP). At the time of the initial human occupation of the area, vegetation near La Gruta 1 resembled patches of grass that are found in the presentday dwarf-shrub steppe of the Deseado Massif above 700 m, suggesting cold and semi-arid conditions (Mancini et al., 2013) and similar pollen evidence has been found in Unit 2 at La Gruta 3. Mylodontidae bones have been discovered previously at Piedra Museo approximately 55 km to the north of La Gruta, in sediment units dating between 11,000
65 14C BP (12,994e12,713 cal BP) and 9230
105 14C BP (10,655e10,180 cal BP) or 15,686e15,076 to 10,655e10,180 cal BP if the oldest date of 12,890
90 14C BP from the site is accepted (Miotti et al., 1999; Miotti and Salemme, 2003). The finding of Mylodontidae bones at La Gruta 3 extends the known distribution of this giant ground sloth to the southern Deseado Massif, and the ages we have obtained correspond with the age range postulated for the Piedra Museo deposits. At Piedra Museo, Mylodontidae coexisted with other extinct mammals and guanaco and its presence in the archaeological record is seen as the result of different hunting events (Miotti and Salemme, 2003). To the south of La Gruta the closest site with Mylodontidae bones is a natural, undated deposit in the Yaten Guajen canyon 140 km to the south (Franco et al. 2007). South of Patagonia, extinct fauna have been recovered from a number of sites, mainly in Última Esperanza Province in Chile but also closer to the Atlantic Ocean. Mylodontidae darwini was herbivorous and has been linked traditionally to open areas and a temperate to cold semiarid climate (Brandoni et al., 2010). It is one of the few extinct ground sloths for which preserved dung has provided direct evidence of the plants eaten (Moore, 1978). Recent studies based on biomechanics and functional morphology (Bargo et al., 2006a, 2006b; Bargo and Vizcaíno, 2008) indicate that M. darwini was a mixed or selective-

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G.A. Brook et al. / Quaternary International xxx (2014) 1e19

feeder capable of selecting specific plants or parts of plants. The dominant plants in Mylodontidae darwini dung in a cave at Ultima Esperanza, in southernmost Patagonia, were grasses and sedges (Moore, 1978), which supports the morphological information obtained. In her study of pollen and cuticles in nine dung samples from Mylodontidae Cave in southern Chilean Patagonia, Markgraf found that “The pollen data revealed much greater plant diversity than the cuticle data” (Markgraf, 1985: 112). Heusser et al. (1992) analyzed five samples with good stratigraphic provenience dated between 11,330 and 12,570 14C BP obtained by Borrero and recognized that the samples offered a mixture of ingested and windblown pollen and spores, but observed that the results were concordant with the existence of a tundra or dwarf shrub heath at the end of the Pleistocene. The paleoecological implication is that the region was basically treeless at the time of the sloths. That was also Nordenskjöld’s conclusion on the basis of the absence of leaves in dung (Nordenskjöld, 1996 [1900]: 111). The conclusion from these botanical analyses is that open environments existed at the end of the Pleistocene in Ultima Esperanza (see also Villa-Martínez and Moreno, 2007), in an area where Mylodontidae remains were recovered. Taking into account the plant assemblage from the El Palmar Formation in northeastern Argentina and the feeding specializations considered for M. darwini, this species would have had a broad range of suitable vegetation to select as food, from cold and arid to warm and humid environments (Brandoni et al., 2010). At several sites, possible evidence of human action on Mylodontidae bones (e.g. cut marks) has been difficult to confirm (see for example Borrero and Martin, 2008 for Las Buitreras Cave), being in some cases related to animals (Martin et al., 2013; Prevosti and Martin, 2013). The Mylodontidae bones at La Gruta 3 are younger than the oldest ages for the presence of humans at La Gruta 1 only about 2 km away. This suggests that humans and Mylodontidae were probably both in the southern Deseado Massif during the late Pleistocene but does not reveal whether they encountered one another. What is apparent is that Mylodontidae continued to use the area even after the first humans had explored it. How humans and Mylodontidae co-existed and why Mylodontidae eventually became extinct have been subjects of intense debate (e.g. Borrero et al., 1997; Borrero, 2001; Long et al., 1998; Barnosky and Lindsey, 2010 and references therein). To date, there is no evidence of human occupation of La Gruta area between ca. 12,049 and 9029 cal BP (10,477
56 and

8090
30 14C BP), while our ages for the Mylodontidae bones date in the range 11,077e9466 cal BP (9560
30e8540
30 14C BP). However, there is evidence of occupation at La Martita Cave 4 and at El Verano Cave 1, 25 km to the northeast (Aguerre, 2003; Durán et al., 2003). This suggests that Mylodontidae was still in the area after humans explored La Gruta and presumably moved elsewhere, possibly because of drier conditions and a lack of a permanent source of water. We have found no clear evidence of humans in the area when Mylodontidae was there, or of human actions on Mylodontidae animals or bones. The absence of such information could be related to discontinuous human presence in the area, and/or to the small size of the human population at this time, as suggested by other researchers (e.g. Borrero, 1994-95). To date, only small flakes associated with the final stages of stone tool manufacture have been found in the oldest deposits at La Gruta 1. There is evidence for transport of grey obsidian, probably from Pampa del Asador in southern Patagonia, about 175 km northwest of La Gruta (Stern, 2000), or from its secondary area, which extends 30 km to the east (Belardi et al., 2006). Translucent chalcedony was also transported to LG1, probably from the Viuda Quenzana area about 25 km to the north. However, surface artifacts have been found that can probably be related to early human inhabitants due to their morpho-technological characteristics (Fig. 14). The preform shown in Fig. 14a has characteristics that resemble artifacts from Tres Arroyos, Tierra del Fuego, with radiocarbon dates of 10,280
110 and 10,420
100 14C BP (12,555e 11,407 cal BP) (Jackson, 2002). In addition, the preform of the stem shown in Fig. 14b resembles Fell 1 projectile points which also have old dates (e.g. Bird, 1988, Massone and Prieto, 2004). The archaeological sites of La Gruta 1, La Gruta 2, La Martita Cave 4, and El Verano Cave 1 have produced evidence of human occupation in the period 10,294e7760 cal BP (8960
140 and 7500
250 14C BP) suggesting that conditions were wet enough to sustain hunteregatherer activities at this time. During the early Holocene, pollen evidence shows that grass was even more dominant in the steppe vegetation at La Gruta than during the late Pleistocene suggesting even wetter conditions (e.g. Mancini et al., 2013). However, after ca. 7760 cal BP (7500
250 14C BP) there is no evidence of human occupation until 4770
25 14C BP (5583e 5325 cal BP) at Viuda Quenzana, at 4475
95 14C BP (5311e 4846 cal BP) at La Martita Cave 4 (Aguerre, 1982), and at 3487
38 14C BP (3832e3594 cal BP) at La Gruta 1 (Table 1; Franco

Fig. 14. Projectile point preform found on the ground surface at La Gruta (a) and stem of a projectile point preform found on the ground surface close to La Gruta area (b).

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G.A. Brook et al. / Quaternary International xxx (2014) 1e19

et al., 2013). The possible absence of humans in the southern Deseado Massif from about 7760 to 5583 cal BP (7500
250e 4770
25 14C BP) agrees well with the sedimentological evidence from the LG1, LG3 and La Barda lagoons, which indicates dry conditions prior to about 6500 cal BP (5690
35 14C BP) but somewhat

17

13,000 cal BP and slightly wetter conditions with grass steppe and dwarf shrub vegetation from ca. 13,000 to 11,500 cal BP. The vegetation changed to grass steppe after ca. 11,500 cal BP until ca. 8800 cal BP indicating wetter conditions during this period (Brook et al., 2013; Mancini et al., 2013).

Table 6 Summary data on human occupation of La Gruta area. Ages in cal BP or cal AD (where indicated) Kilian and Lamy (2012).

SEDIMENTS1 Age (cal BP) or Stratigraphic Unit Units 4&5, LG 3

Charcoal/guanaco bones (h)

Unit C, LG 1

Charcoal

HUMANS3 Age (cal BP)

Correlations4

Period (cal BP)

539-156 (AD 1411-1794) 493-327 (AD 1457-1623)

Little Ice Age

539-156 (AD 1411-1794)

Medieval Climate Anomaly

1266-539 (AD 571-1411)

Higher temperatures Antarctic EDC ice core; weaker Westerly winds.

6500-1270

Comments2

Dry interval no human occupation? 6525-2150 Unit B, LG 1 Unit B, LG 1

La Gruta Lagoons 1 & 2, La Barda Charcoal Charcoal Charcoal at La Martita guanaco bones (h) Viuda Quenzana

1881-1271 3832-3594 5311-4846 5580-5320

Hiatus in sediment deposition: LG1 Unit A to Unit B and LG3 Unit2 to Unit 3. Pollen indicate drier conditions guanaco bone (h) LG2 8403-8208 Unit A, LG 1 9029-8774 Charcoal 9429-8207 Charcoal La Martita 8972-7760 Charcoal El Verano Charcoal El Verano 10,294-9551 Unit 2, LG 3; Mylodontidae/guanaco 12,700-10,600 bones Charcoal Unit A, LG 1 12,799-12,049

36,500

Entrance Pit Unit EA unidentified bones Unit 1, LG 3; puma bones

YD warming followed by early Holocene temperature maximum in Antarctic EDC ice core; weaker Westerly winds. Pollen data indicate wetter conditions.

LGM including H1, H2, H3, ACR (1500013,000 cal BP); strong Westerlies. EPICA Dome C major dust period.

Hiatus in sediment deposition: LG3 Unit1 to Unit 2. Pollen indicate dry conditions prior to 13,000 cal BP. 28,500

Significant cooling Antarctic EDC ice core; stronger Westerly winds drier at Lago Cardiel.

None

Relatively warmer temperatures in Antarctic and Pacific slope at 37,000 and 29,000 cal BP; strong Westerly winds.

8000-6500

13,000-8000

29,000-13,000

ca. 37,000

1

Age of sediment unit determined by dating organic matter or animal bone (collagen or bioapatite). Presence of guanaco bones may or may not indicate human presence. If present, human action is indicated by (h) otherwise the bone is used to date sediment. Pollen information is from La Gruta, La Maria, Los Toldos and La Martita (see Mancini et al.; 2013 for summary and reference s). 3 Time of human presence determined by dating charcoal concentrations or distinct hearths. 4 Information on Antarctic EDC ice core, EPICA Dome C, and Antarctic and Pacific slopes from Kilian and Lamy (2012).

2

wetter conditions after this date. Pollen data from La Martita Cave 4 also document that this was a period of reduced moisture (Mancini, 1998) as do high levels of Ca, Mg, Na, and K in the upper sediments of Unit A at LG1 and in Unit 3 at LG3. These dry conditions may explain the lack of occupation of the Viuda Quenzana and La Gruta areas until ca. 5583 cal BP (4770
25 14C BP), although more excavations are needed to confirm this absence. Periods of sediment deposition and non-deposition in the rockshelters and lagoons at or near La Gruta are compared in Table 6 with times when there is evidence of human usage of the rockshelters or when humans were using the nearby area. Of course, when we deal with archaeological, geological, and palynological information, we are faced with differences in temporal and spatial resolution. However, we believe important trends can be discerned from the data we have used. For example, there is a significant break in sedimentation at La Gruta 3 between ca. 37,000 and 29,000 cal BP (Unit 1) and ca. 13,000 cal BP (Unit 2), the latter date agreeing closely with the oldest evidence for human occupation of La Gruta area from 12,799 to 12,049 cal BP based on ages from Unit A at La Gruta 1 rockshelter. Unit A at La Gruta 1 and Unit 2 at La Gruta 3 appear to have been deposited in the period ca. 13,000e8000 cal BP. Pollen data from La Gruta area, and from other areas of the Deseado Massif, indicate drier conditions prior to ca.

In contrast, the absence of any evidence for humans in the Viuda Quenzana and La Gruta areas from about 8800 to 5600 cal BP (Table 6) suggests a period of drought, a conclusion that is supported by sedimentological evidence from La Gruta Lagoons 1 and 2 and La Barda of dry conditions prior to ca. 6500 cal BP. Low lake levels at Lago Cardiel, to the west of the area, after ca. 8600 cal BP (Stine and Stine, 1990), and a change from grass steppe to shrub and dwarf shrub steppe at La Martita Cave 4 around 8900 cal BP, are further evidence of dry conditions (Mancini, 1998; Brook et al., 2013; Mancini et al., 2013). Evidence of humans at Viuda Quenzana after 5600 cal BP (guanaco bones showing human action), after 5308 cal BP at La Martita Cave 4, and at La Gruta after 3600 cal BP (charcoal scatters), and even more so after 1900 cal BP, corresponds with evidence of sedimentation in La Gruta lagoons between 6525 and 2150 cal BP indicating wetter conditions. We believe that this period may have led to some erosion of Unit A at La Gruta 1, and Unit 2 at La Gruta 3, leading to deposition of Units B and 3 near the end of the period. Pollen assemblages from Unit 3 at La Gruta 3 and from the basal sediments of Unit B at La Gruta 1 have relatively high grass pollen percentages suggesting slightly wetter conditions and possibly more frequent flooding of area lagoons.

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G.A. Brook et al. / Quaternary International xxx (2014) 1e19

In the last ca. 1500 years, six radiocarbon ages for human occupation of LG1 (2 ages) and LG3 (4 ages) fall into two distinct periods: 1372e1271 cal BP and 539e156 cal BP. These periods predate and postdate the Medieval Climate Anomaly (MCA) that lasted from ca. 1266 to 539 cal BP, which is considered to have been a drier interval in southernmost South America (e.g. Stine and Stine, 1990) (Table 6). 7. Conclusions Sediments in La Gruta area rockshelters and lagoons have provided discontinuous records of climate conditions and periods of animal and human occupation during the last ca. 37,000 cal BP (32,650
140 14C BP). Charcoal scatters at La Gruta 1 rockshelter date the first human occupation of the area to the late Pleistocene between 12,799 and 12,049 cal BP (10,845
61e 10,477
56 14C BP) and later to the early Holocene between 9029 and 7760 cal BP (8090
30e7500
250 14C BP). Mylodontidae bones at La Gruta 3 rockshelter, with dates of 9560
30e 8540
30 14C BP (11,077e9466 cal BP), indicate that the extinct giant ground sloth continued to use the area even after it had been occupied by humans. However, as the Mylodontidae dates do not overlap dated evidence of human occupation during the late Pleistocene or early Holocene, there is no proof of contact. The comparison between the pollen assemblages from LG1 and LG3 and other pollen data for the region, together with information from the rockshelter sediments, demonstrates that past physicalhuman environments can be reconstructed by analyzing taphonomic processes in areas of human occupation. An important consideration is the degree of stratigraphic resolution in the rockshelter data but, despite the discontinuities present in these profiles palynological richness is similar in both sequences. In addition, periods with similar pollen assemblages indicate vegetation mosaics in the pollen source area similar to the present mosaic. The characteristics of sediment units exposed by excavations at La Gruta 1 and 3 suggest wetter conditions beginning ca. 13,000 cal BP and lasting until ca. 8000 cal BP (10,845
61e 7500
250 14C BP) and then again from ca. 6500 to 1300 cal BP (5690
35e1452
38 14C BP for La Barda and LG1, respectively). The first of these intervals includes the late Pleistocene and early Holocene periods of human occupation suggesting humans utilized the area during times of increased moisture. Pollen data are available for the first of these periods and confirm the sediment data indicating more moisture at these times. Lacustrine silts and clays in La Barda, and La Gruta Lagoons 1 and 3 also indicate wetter conditions in the period 6500e1300 cal BP and in addition provide evidence of an arid interval prior to about 6500 cal BP (5690
35 14C BP). This may explain why there is no evidence of humans between ca. 7760 and 3830 cal BP (7500
250 and 3487
38 14C BP) who could have moved their activities to nearby areas with a more reliable water supply, such as the Chico River basin. However, there is clear evidence of human occupation of the Viuda Quenzana area after 5580 cal BP and at La Gruta around 3800 and even more so after 1900 cal B.P. The findings in La Gruta area show that Mylodontidae was probably present in the southern Deseado Massif after the first humans arrived as is also suggested by data from the Piedra Museo archaeological locality to the north. Based on evidence from southern Patagonia, Mylodontidae became extinct soon afterwards. Acknowledgements Funding was provided by PIP (CONICET) 0356, Cooperation project CONICET-NSF (Res.1838/13; 2013–2015), and the Franklin College of the University of Georgia. The University of Arizona and

University of Georgia radiocarbon dating laboratories assisted with radiocarbon dating. We thank paleontologists Eduardo Tonni, Scillato Yane, Federico Agnolin and also Sergio Bogan for their considerable help in identifying the Mylodontidae remains. We acknowledge the assistance of the managements of the Triton Mining Company S.A. and Piedra Grande mines, and appreciate the support and help of the Gobernador Gregores authorities (sr. Pablo Ramírez and Marcelo Cebeira). We thank, in particular, Carlos Baetti for his considerable assistance and for providing photographs of the historic 1983 flood at La Gruta Lagoon 1, taken by the Duncan family, from San Julián, the previous owners of Estancia La Gruta. We also wish to thank Lucas Vetrisano for digging the Entrance Pit at La Gruta 3. We also wish to thank geologist Claudio Iglesias, from Piedra Grande S.A. who helped us with the geology and specific rock types of La Gruta area. 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Please cite this article in press as: Brook, G.A., et al., Evidence of the earliest humans in the Southern Deseado Massif (Patagonia, Argentina), Mylodontidae, and changes in water availability, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.04.022