Late Pleistocene human occupation of inland rainforest, Bird s Head, Papua

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1 Archaeol. Oceania 37 (2002) Late Pleistocene human occupation of inland rainforest, Bird s Head, Papua JULIETTE M. PASVEER, SIMON J. CLARKE and GIFFORD H. MILLER Abstract This paper reports new AMS dates for Late Pleistocene occupation of the Ayamaru Plateau in the central Bird s Head of Papua. Two cave sites, Kria Cave and Toé Cave, together provide occupation sequences that span the Holocene and extend back to the Last Glacial Maximum. The associated faunal remains suggest that this lowland area has supported continuous rainforest cover throughout the entire period of occupation. During the Last Glacial Maximum a suite of montane mammal species extended their altitudinal range down onto the plateau, some persisting locally until around 6000 BP. While the Late Pleistocene age of the basal deposit in Toé Cave was previously suggested, new AMS radiocarbon dates on Casuarius eggshell confirm occupation from 24,000 cal BP. Amino acid racemisation data paired with the AMS dates, provide additional support for the improved chronology. The new dates indicate consistent human exploitation of lowland rainforest environments in a relatively rugged and remote region of the central Bird s Head. JMP: Groningen Institute for Archaeology, University of Groningen, the Netherlands, and Dept. of Archaeology and Natural History, Research School of Pacific and Asian Studies, Australian National University; SJC: School of Geosciences, University of Wollongong; GHM: Center for Geochronological Research, Institute of Arctic and Alpine Research, and Department of Geological Sciences, University of Colorado, Boulder Papua (formerly Irian Jaya) is one of the least archaeologically explored areas in the Pacific region. Until 1995, archaeological research was limited to some site surveys and test excavations (Hope and Hope 1976; Solheim 1998). In 1995, excavations were carried out in two cave sites (Kria Cave and Toé Cave) in the interior of the Bird s Head. The caves are located c km inland of the southwestern Bird s Head coast, and lie close to the Ayamaru Lakes (Fig. 1) at the centre of an extended karst plateau situated c. 350 m above sea level. Earlier reports on Kria and Toé Caves (Jelsma 1998; Pasveer 1998; Pasveer and Aplin 1998) gave a broad overview of the stratigraphy and archaeological sequences in each cave. In brief, Kria Cave contains an archaeologically rich, 235 cm thick sequence that appears to be relatively undisturbed (Pasveer 1998; Pasveer and Aplin 1998). Although some anomalously young charcoal dates were obtained, the remaining charcoal and bone dates suggest a phase of relatively rapid build-up of the deposit between an extrapolated basal date of 8000 BP and approximately 4000 BP, followed by a probable hiatus and a resumption of deposition over the last years. The upper stratigraphic unit contains sparse ceramics. Toé Cave contains a relatively shallow ( cm) but archaeologically rich deposit. Jelsma (1998) characterised the deposit as a composite of two archaeological sequences and as heavily impacted by sink action, animal activity or a possible collapse disconformity. He speculated that the basal unit was Late Pleistocene ( glacial ) in age, based primarily on the presence of mammal species that are today confined to montane rainforest habitat and that would presumably require locally cooler conditions. Today the nearest montane habitat is located more than 50 km away and can only be reached through intervening, rugged limestone karst terrain. The overlying unit was judged to be of late Holocene age based on a radiocarbon date on bone from cm depth and the presence of typical lowland fauna. Pasveer and Aplin (1998) revisited the faunal stratigraphy of Kria and Toé Caves, based on more precise identifications (Aplin et al. 1999) and a detailed quantification of the montane vs lowland components. Although they supported Jelsma s view that the lower unit of Toé Cave had accumulated under glacial conditions, they failed to find any evidence of a major disconformity or excessive disturbance of the deposit. Instead, they identified a transitional zone between the lower and upper units, and posited a progressive loss of montane elements over several thousand years. Important support for this model came from the basal sediments of Kria Cave, where a limited suite of montane species were found in association with a typical lowland fauna and dating to the period c BP. The palaeoecological evidence from Kria and Toé Caves is of considerable interest for several reasons. First, it raises the possibility that glacial conditions had a significant impact on the lowland environment of the Ayamaru Plateau, presumably with cool but moist conditions to support a local rainforest habitat with at least structural similarities to present day lower montane rainforest. And second, it suggests that these cool but moist conditions persisted on the Plateau for at least 6000 radiocarbon years after the onset of deglaciation and widespread vegetational response at higher elevations. Pasveer and Aplin (1998) suggested that flooding of the Arafura Shelf from around 12,000 BP may have led to locally persistent cloud cover over lowland areas in southern Papua, and that this may have been sufficient to account for the lag in local environmental response (see also Hope and Tulip 1994; Van der Kaars 1995). We report here new AMS radiocarbon dates and amino acid racemisation data on cassowary (Casuarius sp.) eggshell from Kria and Toé Caves, obtained as part of a broader study of eggshell biogeochemistry currently underway by SJC and GHM. Ratite eggshell represents 92

2 Laboratory Depth Unit Radiocarbon 13C Calibrated A/I ratios Dated material ref. no. below (level)* years BP (, PDB) age (2 ) in surface (cm) years BP# OZE ** I(6) 1840 ± pig bone GrA II(3) 4370 ± animal OZF II(6) 5120 ± ± Casuarius eggshell GrA II(8) 4970 ± charcoal GrA III(5) 5690 ± animal GrA IV(2) 420 ± charcoal GrA V(1) 5940 ± animal OZF V(2) 6080 ± ± 0.01 Casuarius eggshell GrA V(9) 260 ± charcoal GrA V(10) 6760 ± animal OxA V(11) 6900 ± charcoal Table 1. Radiocarbon dates from the excavation in Kria Cave. New dates are indicated in bold. Notes: * All samples except OxA 6043 and OZE 542 come from Square 0N0E. ** The top levels in Unit I run virtually horizontal, hence OZE 542 from Square 1N1E is equivalent to cm depth in Square 0N0E. ++ OxA 6043 comes from a depth of cm in Square 1N1E; due to a slope in the deposit, this sample is equivalent to cm in Square 0N0E. # Calibrated with CALIB 4.3 (Stuiver & Reimer 1993) using the dataset of Stuiver et al. (1998). As the sites are located only just below the Equator, the dates have not been corrected for Southern Hemisphere These dates are based on the alkaline fraction of a bulk bone sample, predominantly remains of a wallaby (Dorcopsis muelleri). Figure 1. Ayamaru Lakes area and the excavated sites. an ideal archaeological material for radiocarbon dating for three reasons. Firstly, the dense calcite structure preserves indigenous inorganic carbon because it is resistant to diagenetic alteration. Secondly, the extent of amino acid racemisation serves as an independent check on sample age. And thirdly, the presence of eggshell is often directly linked to human activity, especially in cave sites. The radiocarbon dates were determined by accelerator mass spectrometry on the carbon dioxide evolved by the acid digestion of eggshell calcite. Prior to submission of the samples to the accelerator, at least 50% of the eggshell carbonate was removed by stoichiometric addition of 2N HCl to minimize contamination by exchange with younger CO 2. The amino acid data comprises the extent of isoleucine epimerisation determined by the ratio 93

3 Laboratory Depth Square Radiocarbon 13 C Calibrated A/I ratios Dated material Ref. No. below years BP (, PDB) age (2 ) in surface (cm) * years BP # OxA S0E 2930 ± ,320 2,870 animal OxA S0E 220 ± charcoal OxA S0E 111 ± charcoal OxA S0E 240 ± charcoal AA S0E 10,150 ± ,320 11, ± Casuarius eggshell AA N1E 5290 ± ,280 5, ± Casuarius eggshell AA N1E 8860 ± ,210 9, ± Casuarius eggshell AA N1E 12,870 ± ,990 14, ± Casuarius eggshell AA N1E 12,885 ± ,990 14, ± ** Casuarius eggshell OZF N1E 13,130 ± ,270 14, ± Casuarius eggshell OZF N1E 20,320 ± $ 24,730 23, ± Casuarius eggshell Table 2. Radiocarbon dates from the excavation in Toé Cave. New dates are indicated in bold. Notes: * The deposit in Toé Cave is subject to a slope of some cm, dropping from Square 2N1E to Square 1S0E over a horizontal distance of 3 m. # See note at Table Species not identified. ** This eggshell sample is burnt, resulting in a relatively high A/I ratio. $ Value estimated. ++ The uncalibrated date falls beyond the limit of the dataset for atmospheric samples by 55 years; the calibrated age range is based on the maximum date for this dataset: 20,265 BP. of D-alloisoleucine to L-isoleucine (A/I ratio) in the total acid hydrolysate. The present results confirm the Late Pleistocene age of the glacial unit of Toé Cave, and provide further insights into the dating and stratigraphy of both caves. We also report a new AMS radiocarbon date on pig bone (OZE 542) from the uppermost unit of Kria Cave. For sake of completeness, the tables include all dates currently available from each of the two sites. Table 1 shows all available dating results from Kria Cave, including A/I ratios. The AMS dates and A/I ratios for Casuarius eggshell from cm and cm represent paired determinations on single eggshell fragments. With the exception of the two charcoal dates from cm and cm, the results are stratigraphically consistent and the two new Casuarius eggshell dates support the earlier interpretation of the timing and mode of accumulation of this deposit. The one minor date inversion between cm (OZF 245) and cm (GrA 6310) could be the product of minor local disturbance, or slight contamination of one or other samples. The two sub-modern charcoal dates are not sufficient grounds in themselves to challenge the general conclusion that the Kria Cave deposit is well stratified and virtually undisturbed. Table 2 shows all available dating results from Toé Cave, including A/I ratios. As before, paired AMS dates and A/I ratios for single Casuarius eggshell fragments are indicated. The new Casuarius eggshell dates, together with the paired and associated A/I ratios, provide a greatly improved chronology for the Toé Cave deposit. The series of six dates from Square 2N1E are in correct stratigraphic order and extend back into the Late Pleistocene, as anticipated from the palaeoecological evidence. Eggshell fragments with AMS dates falling in the time range 20,000 to 10,000 BP have associated A/I ratios that are consistently 2-3 times higher than those obtained from any Kria Cave samples, again consistent with a Late Pleistocene age. The fact that two pieces of eggshell from one spit at cm differ in age by 7200 radiocarbon years is perhaps not entirely unexpected given the relative shallowness of the deposit and the fact that it has a natural dip into the rear of the cave, with clear scope for local erosion and conflation within the sequence (Jelsma 1998; Pasveer and Aplin 1998). As argued above, one of the advantages of ratite eggshell as an archaeological dating material, especially for cave sites, is that it is extremely unlikely to have entered the deposit other than through direct human activity. Each of the determinations can thus be taken as evidence of human occupation during that time period. Accordingly, we suggest that the results document the presence of people in the Ayamaru Plateau region at c. 20,000 BP (or 24,000 cal BP), just prior to the Last Glacial Maximum (at which time the area was at least 160 km inland of the southwestern coast line, and 90 km from the northwestern coast, but with intervening mountain ranges), again during the period of rapid deglaciation around 13,000 BP (15,000 cal BP), and at several periods during the early to mid-holocene. Combined with the evidence from Kria Cave, the overall impression is thus one of a relatively continuous human presence on the Ayamaru Plateau through the last 24,000 years. An important point in this context is that the Ayamaru Lakes are themselves only of mid-holocene antiquity (Dam pers. comm.), hence the immediate area of the sites may have had little special attraction through most of this period. 94

4 The improved dating of the Kria and Toé Cave deposits has important implications for Melanesian palaeoecology and archaeology. Firstly, it provides chronological support for previous claims that montane faunal elements extended onto the plateau during the Last Glacial Maximum, and that these animals persisted through to the early Holocene. Secondly, the improved record documents the presence of human populations in the interior of the Bird s Head back to at least 24,000 cal BP. Although this is well short of the earliest evidence of human occupation of New Guinea or even remote island Melanesia, it is nonetheless significant on account of the great distance of the Ayamaru Plateau from the LGM coastline, the sheer remoteness and inaccessibility of the location, and the fact that the associated faunal evidence points to a densely rainforested environment. The Bird s Head evidence thus complements evidence from New Britain (Pavlides and Gosden 1994) that inland rainforest habitat in Melanesia was exploited prior to and during the LGM, contrary to the predictions of Bailey et al. (1989) who posited a far shorter history of human adaptation to rainforest habitats on a global scale. Note added in proof An additional AMS date on Casuarius eggshell of 23,140 ± 150 BP (OZF 847) from Toé Cave has been received during the proof stage of this paper. In the absence of a measured value, the conventional age is based on an assumed 13C value of The sample originates from cm depth in Square 2N1E, and thus comes from the same level as OZF 251 and 516. Preliminary stable isotope values suggest that the new date comes from a different egg than the one that produced OZF 516 (dated to 20,320 ± 110 BP). The new date further supports the claim that the Ayamaru area was inhabited prior to the Last Glacial Maximum. Acknowledgments The archaeological research was carried out as part of the Dutch-Indonesian ISIR project (Irian Jaya Studies, a programme for Interdisciplinary Research), funded by the Netherlands Foundation for the Advancement of Tropical Research (WOTRO). The radiocarbon dates mentioned in this paper were provided by the National Science Foundation Radiocarbon Facility, University of Arizona (code AA); Australian Nuclear Science and Technology Organisation (ANSTO code OZE and OZF); Centre for Isotope Research, Radiocarbon Laboratory, Groningen University (code GrA); and The Radiocarbon Accelerator Unit, Research Laboratory for Archaeology and the History of Art, Oxford University (code OxA). OZE 542 was funded by AINSE grant 99/020 to Wallace Ambrose and Matthew Spriggs (ANU). The OZF dates on eggshell were funded by AINSE grant 01/107 to Colin V. Murray-Wallace, Gifford H. Miller, Allan R. Chivas and Simon J. Clarke. Amino acid racemisation analyses were made at the University of Colorado, with support provided by the U.S. NSF grant (ATM ). We thank Prof. Matthew Spriggs for his comments on the paper. References Aplin, K.P., J.M. Pasveer and W.E. Boles Late Quaternary vertebrates from the Bird s Head Peninsula, Irian Jaya, Indonesia, including descriptions of two previously unknown marsupial species. Records of the Western Australian Museum, Supplement No. 57: Bailey, R.C., Head, G., Jenike, M., Owen, B. and R. Rechtman Hunting and Gathering in Tropical Rainforests: Is It Possible? American Anthropologist 91: Hope, G.S. and J.H. Hope Man on Mt. Jaya. In G.S. Hope, J.A. Peterson, U. Radok and I. Allison (eds), The equatorial glaciers of New Guinea. Results of the Australian Universities Expeditions to Irian Jaya: survey, glaciology, meteorology, biology and palaeoenvironments. Pp Hope, G.S. and J. Tulip A long vegetational history from lowland Irian Jaya, Indonesia. 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