Keywords

Introduction

Over the last decade, the long-held paradigm of the initial peopling of the New World from Beringia through an ice-free corridor by terrestrially adapted big-game hunting groups who rapidly spread south has been critically revised. In general, innovative theoretical views based in new multidisciplinary evidence suggest that pre-Clovis populations existed and that the colonization of the Americas was the consequence of diverse cultural processes with high diversity of habitats occupied by early hunter-gatherer groups with different subsistence strategies and technologies (Borrero 1999; Dillehay 2000, 2009; Faught 2008; Goebel et al. 2008; Waters and Stafford 2007) . In northwestern North America, in particular, the growing interest in submerged prehistoric archaeology as a nascent subdiscipline critical to understanding early coastal occupations and migration routes (Gusick and Faught 2011) is closely related to the “coastal migration theory” initially proposed by K. Fladmark (1979). This alternative hypothesis suggests that prior to 13,000 cal BP, large coastal plains with terrestrial resources and productive marine environments were available for maritime adapted people due to Pleistocene lower sea levels enabling human and animal migrations (Dixon 2001; Erlandson 2008; Faught 2008; Mandryk et al. 2001; Waters and Stafford 2007) .

Recent research projects in northwestern North America are focused on locating evidence to support the hypotheses of a coastal migration into the New World following the Pacific Rim route (Faught and Gusick 2011). By applying paleolandscape modeling and archaeological sampling these investigations have been successful in locating submerged cultural material (Easton and Moore 1991; Fedje and Christensen 1999; Fedje and Josenhans 2000; Josenhans et al. 1997) . A geoarchaeological-based approach and predictive modeling have been applied off the Oregon coast (Davis et al. 2009) . Finally, the southern Gulf of California’s archaeological potential has been recently initially explored through a paleolandscape model and diving operations (Faught and Gusick 2011). In Southern California several hundred mortars and ground-stone artifacts (Masters 1983, 1985), and shell middens (Bickel 1978) have been reported from the early 1900s .

However, evidence for Late Pleistocene and Early Holocene sites on the Atlantic continental shelf , including areas like the Gulf of Mexico and Florida, continues to be far more substantial and recurrent than that for the Pacific (Stright 1990, 1995) . This contrasting situation is evident in Florida alone, where these sites are reported to be presumably older, more abundant, and larger in size to those known along the West Coast (Faught 2004) .

The relatively reduced evidence of submerged prehistoric sites along the Pacific Coast of North America has been explained due to narrow continental shelves, active volcanism and tectonism, and high-energy marine conditions which are less favorable for preservation, except in bays, inlets, and island clusters (Faught and Gusick 2011). Stright (1995) , analyzing the archaeological potential of the continental shelves of North America, stresses that if the rate of relative sea-level change is held constant, the Pacific shelf would have the lowest potential for preservation of in situ archaeological deposits and the Gulf of Mexico would have the highest . Additionally, while geomorphology of the eastern Pacific coastal environments, with rocky shores and deep basins, offers natural shelters for the preservation of archaeological remains, the exceedingly high wave action of the eastern Pacific can erode away sea cliffs and cut terraces (Inman 1983), and represents a powerful disturbing agent for the submerged archaeological record (Gusick and Faught 2011) .

When referring to the Americas or the New World, research reviews on marine submerged prehistoric archaeology have addressed basically projects conducted in North America (Faught and Gusick 2011; Gusick and Faught 2011; Johnson and Stright 1992; Masters and Flemming 1983) . This is not surprising, since in South America with very rare exceptions, (Bayon and Politis, this volume) early submerged prehistoric sites are virtually unknown, and thus the investigation of the archaeological potential of the Pacific continental shelf is practically nonexistent.

In this chapter, the authors provide a general overview of the research conducted on GNL Quintero 1 (GNLQ1), a Late Pleistocene paleontological submerged site located in the Pacific coast of Central Chile, and examine this evidence in light of the known association between extinct megafauna and early human adaptations in the area. Finally, the authors propose and discuss an initial digital simulation model developed to better understand this first postglacial-drowned terrestrial landscape discovered along the Andean Pacific coast.

Site GNL Quintero 1 (GNLQ1)

Site GNLQ1 is located in Quintero Bay (32°46′ S), located ~ 50 km north of Valparaíso, on the Pacific coast of Central Chile (Fig. 8.1a). This is a shallow embayment, ~ 3 miles long and ~ 1.5 miles wide, roughly oriented N–W with a maximum recorded depth of 55–60 m. River Campiche, located at the N–E side of La Herradura beach and some other minor streams drain into the bay, with permanent to perennial flow. Coastal lagoons and wetlands are trapped by mound dunes at the N–E and S–W ends of the bay (Villa-Martínez and Villagrán 1997) . The resulting structural context is a shallow bay with gently sloping nearshore bathymetry with little sediment yield from rivers.

Fig. 8.1
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a Location map for the study area in Quintero Bay, central coast of Chile. b Bathymetric profile of the area with site GNLQ1.

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Quintero Bay is an active harbor and contains important energy, mining and industrial infrastructure. Site GNLQ1 located 650 m offshore and 13 m underwater (Fig. 8.1b) was discovered in 2005 during an archaeological investigation of the seabed as part of a Cultural Resource Management (CRM) project . Through extensive diver survey operations a cluster of discretely exposed and shallowly buried bone deposits were identified by archaeologists close to a rigid oil submarine pipeline installed by the National Oil Company (ENAP) during the 1970s. Intensive visual examination and hand fanning techniques revealed that these loci were formed by faunal remains deposited within a consolidated bed of sediment and partially buried under 5–10 cm of modern sands.

Methodology

As part of the CRM project, a series of subsurface test excavations and mechanical coring samples were conducted at the site in 2007 at several targeted points distributed across transects within an area of 40 × 25 m (ARKA Consultores 2008). In particular, one locus, a well-delimited bone concentration barely visible on the seabed, was selected and sampled through a test excavation 1 × 1 m unit (unit K8_2). The excavation was carried out using a 3″ induction water dredge and the material excavated was deposited first in a 6.5 mm holding basket underwater and then transferred to the surface for further examination. Skeletal remains were exposed by careful excavation using in situ decapage techniques and recovered with their sedimentary matrix in order to be microexcavated in the laboratory, thereby minimizing loss of contextual information and physical deterioration potentially caused during underwater extraction (Fig. 8.2).

Fig. 8.2
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a Controlled recovery of the faunal remains using underwater archaeology excavation techniques. b Megafauna fossil bones deposited within a consolidated bed of sediment

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A total of 224 bone specimens were recovered (Cartajena and López 2008; Cartajena et al. 2011) (Table 8.1). The remains belong mainly to excavation unit K8_2. Only two isolated bone specimens were registered deposited on the surface of unit K7, while another two surficial bones were recovered at unit K4.

Table 8.1 Distribution of recovered bones in survey and excavation units
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Conservation

Once microexcavated at the laboratory, the structurally sound recovered bones underwent a conservation treatment to remove the soluble salts in order to make the material stable (Hamilton 1998) . The salts were diffused out by rinsing in successive baths of water, starting with 100 % sea water and increasingly incorporating fresh water (local tap water) until straight fresh water was completed. Distilled water was then substituted for the fresh water until the soluble salts were removed. Mechanical removal of stains was achieved using hand tools (Morales 2008) .

Stratigraphy

In particular, one core sample (T1) 74.3 cm long was selected for morphological and sedimentological analyses and represents a complete stratigraphic sequence for the site, with three stratigraphic units exhibiting clearly different sedimentological features (Vargas and Ortega 2008) (Fig. 8.3). Unit 1 contains surficial well-sorted fine sand that is brown in color, 5 cm thick. Underneath, Unit 2 is a clayey-gravel clast-supported formed by high hardness agglomerates of fine sand and clay and eventually microcrystalline quartz (chalcedony), orange and gray in color, some exhibiting a patina of charcoal in a fine sand-silt matrix. Millimetric charcoal lenses are intercalated In the higher and lower parts of this unit. The faunal remains were recorded in the upper portions of this deposit, horizontally distributed over an extensive area and in both clear and direct association to charcoal lenses present within the first 5 cm of Unit 2. Finally, Unit 3 consists of fine clayey sand that is brown and orange in color. Core T1 did not yield pollen remains (A. Maldonado, personal communication).

Fig. 8.3
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Stratigraphic sequence of site GNLQ1

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The analysis of the stratigraphic unit containing the fossil remains (Unit 2) suggests an estuarine-lagoon or wetland environment in the process of desiccation (Vargas and Ortega 2008) . Although very preliminary, this evidence is consistent with other studies which suggest essentially a cold and wet environment, with a general tendency toward desiccation around ~ 13,000 cal BP for the study area (Kim et al. 2002; Valero Garcés et al. 2005; Villagrán and Varela 1990) .

Radiocarbon Dating

Two taxon samples were selected for radiocarbon analyses, but the lack of collagen, including that of the dentine, precluded age estimation. For this reason the sedimentary matrix containing the bones was 14C dated and reported 13,640 ± 40 years BP (UGAMS#9194, δ13C, ‰−25.4) (16,605-16,196 cal. BP, OxCal 4.2, SH Cal 13 [Bronk Ramsey and Lee 2013]).

The Faunal Assemblage: Taxonomic and Taphonomic Analyses

Much of the research effort regarding site GNLQ1 has been focused on the taxonomy and taphonomy of the faunal assemblage recovered (Cartajena and López 2008; Cartajena et al. 2011; Cartajena et al. 2013; López et al. 2012) . Most of the materials show a homogenous and slight degree of abrasion on the bone surface as expected in an aqueous environment with abrasive sediment. Early weathering stages also affected most of the sample (Behrensmeyer 1980) , supporting the idea that the remains were exposed to subaerial conditions before they were buried and subsequently submerged by sea-level rise. This is coincident with the evidence of root marks on the surface of all the bones, which indicates the growth of a vegetation cover over the fossil deposits previous to the marine transgression.

Although some specimens show signs of initial states of weathering such as longitudinal cracks in diaphysis fragments, which could have affected the fragmentation of the assemblage, the conservation of the bones is optimal. A significant percentage of the assemblage could be reassembled and taxonomically determined, even up to the family level. In most of the cases the bones presented complete epiphyses or diagnostic traits such as tooth. However, some remains have been assigned to more general taxonomic categories (order level), such as a selenodont-type deciduous molar that has been assigned to Artiodactyla, due to the lack of other diagnostic traits.

A total minimal number of eight individuals corresponding to at least seven different taxa were recovered. The identified bones show a high diversity of terrestrial extinct megafauna, including Camelidae, Cervidae, Equidae, and Xenarthra but also smaller size animals such as a fox-size carnivore, a rodent, and a bird (Table 8.2).

Table 8.2 Taxonomical and anatomical unit representation, expressed in NISP and MNI
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Xenarthra bones correspond to an ungueal phalanx (Fig. 8.4a), an osteoderm, and the complete sequence of molariforms of the right mandible. A Camelidae (cf. Palaeolama sp.) anterior superior extremity (distal humerus and radius-ulna) was recovered, which corresponds to a large size camelid in the range of Palaeolama (López et al. 2004; Fig. 8.4e, f). The Cervidae remains belong to the left and right mandible from a large-size cervid (Fig. 8.4g) and from Equidae two juvenile premolars were identified (Fig. 8.4b). A calcaneus and a canine tooth of Canidae were recovered, whose morphology and size are similar to the present day Lycalopex culpaeus (Fig. 8.4c, d). An incisor from a Cricetidae rodent of insufficient taxonomic diagnosis was also recovered. Finally, two bird remains from another unit (K7) were registered at the surface. Their morphology and size is compatible with specimens from the Phasanidae family.

Fig. 8.4
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Faunal assemblage recovered from site GNLQ1. a Ungueal phalanx of Xenarthra. b Premolars of Equidae. c and d Canine tooth and calcaneus of Canidae. e and f Distal humerus and fourth carpal of cf. Palaeolama sp. g Molars of Cervidae

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The Quintero faunal assemblage exhibits high taxonomic diversity, mostly similar to that of sites yielding extinct Pleistocene fauna located around the coast of Los Vilos District, in the northern semiarid zone (31°29′ S) (Jackson 2003; Jackson et al. 2007; Méndez et al. 2004; Núñez et al. 1994b) . These coincident evidences suggest similar paleoenvironmental conditions, which during the Terminal Pleistocene favored the congregation of diverse mammalian resources hunted by Paleoindian human groups around productive lowland areas such as streams, lagoons, estuaries, fertile plains, and wetlands, as has been suggested for north-central Chile by Núñez et al. (1987).

Taphonomic analysis allowed macroscopic identification of natural marks (punctures) associated with big and small size carnivores. By applying Scanning Electron Microscope (SEM) micrographs to fossil bones, marks and color alterations were identified. Marks could be related to rodent gnawing and trampling while color alterations were attributed to diagenesis processes.

The distal humerus of the cf. Palaeolama sp. presents a spiral fracture on the fresh bone. Although this type of fracture can be considered to be typical of that of human activity, diverse analyses determined the degree of ambiguity of this trait, as it can also be the result of natural agents (Borrero and Martin 1996; Haynes 1983a, 1983b; Myers et al. 1980) . Although the humerus does not show any signs of notches or negative characteristics of human modifications, fresh bone flakes (derivates) were found.

By means of the use of Energy Dispersive Spectroscopy (EDS) analysis, spheroidal bodies of pyrite in the osseous matrix of the cf. Palaeolama sp. humerus were found, suggesting an anoxic depositional environment and the action of sulphur-reducing bacteria (Borrego et al. 2003; Brown et al. 2010; Saheb et al. 2008) . This is coincident with the oxidation staining found in all the assemblage resulting from the interaction of the bones with an interface of gravel clay sediment and water, which is characteristic of the depositional environment of the GNLQ1 site (Dunbar et al. 1989; Noakes et al. 2009) .

Paleolandscape

One of the critical aspects for finding submerged prehistoric sites is determining local sea-level history . Pleistocene shorelines were inundated around the world largely as a direct consequence of global, eustatic sea-level rise. Global sea levels were ~ 120 m lower than present at the Late Wisconsinan maximum glaciation, 20,000 to 18,000 BP (Fairbanks 1989) . However, in areas directly or indirectly affected by glaciation, calculating sea-level history is far more complex due to the intricate interplay between tectonic, eustatic, and isostatic change, which may result in drastic differences from a generalized sea-level curve (Bailey and Flemming 2008; Fedje and Christensen 1999; Stright 1995) . This is the case for Chile, where coastal areas register diverse uplift rates and important tectonic activity. However, uplift rates for Holocene marine deposits on the central coast of Chile where Quintero Bay is located have been calculated in a moderate range, with a minimum mean estimate of 0.4 m/ka (Encinas et al. 2006) . This range is consistent with the slight Holocene tectonic uplift and low uplift rates since the last Interglacial reported for north-central Chile (Leonard and Wehmiller 1991; Ota and Paskoff 1993) .

There are no Holocene sea-level curves available for north-central Chile, therefore to determine the Relative Sea Level (RSL) for Quintero Bay SELEN 3.2 (Spada and Stocchi 2007) , the authors used a Fortran computer program for solving the “sea-level equation” (SLE). In this process, a linear integral equation allowed the users to determine the sea-level variations driven by the melting of the Pleistocene ice-sheets, and was corrected with an assumed constant uplift range of 0.5 m/ka.

For reconstructing the paleolandscape underwater, a navigation chart with available high-resolution local bathymetric and terrestrial elevation data was combined and merged using HYPACK Max 10 hydrographic software. Although the navigation chart worked only for general survey area purposes, local bathymetric data processing was combined with sedimentological samples. By combining this information with the SELEN Quintero RSL curve contour maps, 3D wireframe maps representing the simulation of the paleolandscape were created using SURFER 10 .

According to this initial simulation, the inlet of land oriented SE which forms modern Quintero Bay did not exist prior to ~ 16,000 BP (Fig. 8.5). Between about 16,000 BP and 14,000 BP the sustained postglacial sea-level rise caused the progressive and substantial inundation of ~ 3.2 km of the coast in a general SE direction. Due to local geomorphology, the shoreline prograded ~ 0.9 km between 14,000 BP and 12,000 BP. Between 12,000 BP and 10,000 BP the shoreline moved forward another ~ 1.5 km, with most of this progress occurring during the first thousand years, when Quintero Bay acquired most of its modern shape. Site GNLQ1 was last under subaerial conditions by ~ 11,000 BP (Fig. 8.6).

Fig. 8.5
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General contour map of Quintero Bay’s early postglacial sea-level change

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Fig. 8.6
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Orthographic 3D wireframe of Quintero Bay with site GNLQ1’s location enhanced by 400 % vertical. Estimated early postglacial paleoshorelines at 16  ka, 14 ka, 12 ka, and 10 ka are represented

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A side-scan sonar remote sensing survey was conducted on the GNLQ1 site area in 2011. The seafloor sediments in the area are characterized by uniform low-backscatter acoustic data, typical of fine-grained sediments, with no recognizable topographic features. This surficial layer of unconsolidated modern sands exhibits ripple-marks indicating a high-energy marine environment. High-resolution acoustic images of site GNLQ1 depicts the partially exposed Pleistocene consolidated clayey gravel deposits containing the fossil bones as a discrete reflector with a general NE-SW distribution (Fig. 8.7). ENAP’s Ø 42” pipeline, orientated NW-SE is clearly visible as a strong reflector toward the center of the sonograph. Remote sensing data is consistent with sediment analysis and bathymetry data processing which indicated that the area is located in the upper shoreface under the influence of tidal and wave activity dominated by SW winds (Vargas and Ortega 2008) .

Fig. 8.7
figure 7

780 kHz sonograph of site GNLQ1. Note the exposed Pleistocene-consolidated deposits with a general NE–SW distribution covered by modern sands. The National Oil Company (ENAP) Ø 42” pipeline runs across it in a NW–SE direction

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Discussion

The paleontological record of site GNLQ1 reveals the presence of exposed Late Pleistocene deposits on the seabed containing a primary stratigraphic context of continental faunal remains with scarce postdepositional alterations. Although located in a relatively low-depth coastal high-energy marine environment, and partially affected by development projects, the site indicates a high integrity and resolution .

As indicated, the recurrent association between extinct fauna and early human occupation of north-central Chile has been interpreted as a circum-lacustrine adaptation at the Pleistocene/Holocene transition, during which megafauna restricted to shrinking lacustrine environments subject to aridity stress, were exploited by Paleoindian groups (Núñez et al. 1987) . During this period human occupations were characterized by open campsites, near to aquatic environments, and with high residential mobility (Jackson et al. 2004; Méndez 2011) . Examples of classic Paleoindian occupations that exhibit definitive evidence of human-megafauna interaction dating to ~ 13,000 calibrated years are Quebrada Santa Julia (Jackson et al. 2007) and sites Tagua-Tagua 1 and 2 (Núñez et al. 1994a).

In the semiarid zone of Chile, despite the presence of early prehistoric sites located close to the Pacific coastline, sites do not exhibit relevant exploitation of marine resources until the Early Holocene (Jackson et al. 2007). It is noteworthy that consistently a substantial part of the paleontological records of Terminal Pleistocene fauna found near the coast corresponds eminently to terrestrial fauna as well (Méndez et al. 2004). In particular, the record of site GNLQ1 and those of other sites with similar faunal assemblages like Quereo (López et al. 2004; Núñez et al. 1994b) indicate a wide distribution of grazers and browsers taxa, suggesting environments that combine pasture lands and woods (Cartajena et al. 2011; Cartajena et al. 2013) . This evidence is consistent with the assumption that a significant coastal area, now covered by the sea, was available during late glacial and early postglacial periods to both fauna and early terrestrial hunter-gatherers in the New World, who occupied valleys and estuaries (Bonnichsen et al. 2005; Richardson III 1981; Sandweiss 2003) .

No evidence of human activity has been inferred at GNLQ1 so far. Neither artifacts nor evident human modifications of bones were found. However, the excavated sample is still small and identifying conclusive cultural indicators on early terrestrial sites is not an unproblematic research issue. Of at least 24 known sites in the semiarid coast of Chile with Pleistocene extinct fauna there are only two, Quebrada Santa Julia and Quereo, which exhibit primary stratigraphic records of anthropogenic origin (Jackson et al. 2007) . In this latter site, artifactual evidence is undiagnostic and ephemeral, and most human intervention is represented by bone artifacts and cut marks, and fractures of the bones (Jackson et al. 2004). It is known that several factors will affect the visibility of potential cultural features within the archaeological record of a prehistoric submerged site, including site functionality, taphonomic agents, and differential conservation, among others (Stewart 1999; Stright 1995; Waters 1992) . Thus, human agency on underwater sites similar to GNLQ1 should be carefully evaluated and tested considering that substantial recovered prehistoric evidence on land suggests a rather discrete but recurrent human occupation of a well-delimited area during the Late Pleistocene (Méndez 2011) . Applying proxy indicators might prove an efficient research strategy in light of the presence of charcoal lenses and charcoal patina in the stratigraphic unit containing the fossil remains.

At first, the AMS 14C date for GNLQ1 (16,605-16,196 cal. BP) seems substantially earlier than the ~ 13,000 cal. BP date of the earliest human occupations in the area. However, this indicates the age of the sediments containing the fossil bones. It is worth noting that Jackson (2003) obtained a similar date for a Mylodon sp. sacrum associated with lithic remains from the site El Membrillo, near Los Vilos, 16,677 cal year BP, but this evidence should be interpreted with caution since it is a surface site (Jackson et al. 2007). New chronostratigraphic evidence of site GNLQ1 is needed, including AMS 14C dates on single bones of stratigraphically associated taxa.

At this stage of the investigation, a precise model of the Quintero paleolandscape cannot be reconstructed without a better understanding of both local uplift rates and sea-level variations. However, the initial simulation created by combining the SELEN Quintero RSL curve with a mean estimated uplift rate of 0.5 m/ka is considered to provide a reasonably accurate model of the submerged landscape and is consistent with more global sea-level curves (Lambeck et al. 2002) . The latter suggests that by early postglacial times (~ 16,000 BP), a significant part of modern Quintero Bay was exposed due to lower sea-levels and available for terrestrial fauna. Site GNLQ1 would have been located several kilometers inland as the paleoshoreline was farther out on the continental shelf, close to the 90 m isobath (≤ 5 km). This hypothesis is consistent with the taxonomical homogenous composition of the assemblage of vertebrate fossils and the absence of marine resources at the record, at least in the evidence documented so far.

In the future, a refined model of the Quintero paleolandscape should enable researchers to identify geomorphological, topographical, and sedimentary conditions most conducive to the underwater preservation and discovery of submerged landscapes. A better understanding of the formation processes involved in GNLQ1 might help explain where to search in Quintero Bay for exposed or shallowly buried terrestrial surfaces and Pleistocene landforms and the amount of marine sediment accumulation expected. According to the present model, the local paleoshoreline contemporaneous to the earliest human occupation of north-central Chile should be located close to the 50 m isobath implying necessarily a fragmentary and biased coastal archaeological record. As it has been suggested elsewhere (Bailey and Flemming 2008) , this potential underwater archaeological record does not simply add to what we already know about prehistoric sites on land, but might provide critical evidence about coastal environments that are now submerged and that provided productive conditions for plant and animal life during lowered sea level, late glacial, and early postglacial times .

Conclusions and Perspectives

Site GNLQ1 provides the first conclusive evidence for the existence and preservation of a drowned landscape viable for both extinct megafauna and early human occupation and movement along the Pacific Coast of South America during the Late Pleistocene. Although still necessarily limited, the data presented fills a gap in the record of sites in submerged contexts in the New World while offering significant possibilities for future research.

Effectively, the high inferential status of this remarkable and unique site is extremely promising. Although identified as part of a CRM project, the paleontological record has been studied by research methods and strategies common to submerged prehistoric archaeology projects in North America (Gusick and Faught 2011) . The development of an initial paleolandscape model for Quintero Bay to be tested is considered to be an important first step for further archaeological investigation of the Chilean continental shelf and may help improve our understanding of the environmental resources available for the earliest colonizing human groups in the region.

A new phase of focused research is already being conducted at GNLQ1. This geoarchaeological approach includes the comprehensive application of remote sensing tools (including high-resolution side-scan sonar and sub-bottom profiler surveys), paleoecological reconstructions, and systematic underwater excavations. The latter have enabled the recovery of a larger sample of fossil bones which confirms a high taxonomic diversity of Terminal Pleistocene terrestrial extinct fauna and substantiates site integrity and high-resolution contexts. Analysis is currently ongoing and any potential evidence of human modification is being carefully assessed.

Site GNLQ1 represents a primary and so far unknown source of data on now-submerged paleolandscapes, and although human association remains to be seen by future research, it provides a new and challenging insight into the early postglacial environment and habitats common to both extinct fauna and the initial human populations of the Andean Pacific coast.