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Late Pleistocene human occupation of inland rainforest, Bird's Head, Papua. (Research Reports).

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 Toe 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 Toe 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.

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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 Toe Cave) in the interior of the Bird's Head. The caves are located c. 25-35 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.

[FIGURE 1 OMITTED]

Earlier reports on Kria and Toe 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 2-3000 years. The upper stratigraphic unit contains sparse ceramics.

Toe Cave contains a relatively shallow (110-140 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 35-40 cm depth and the presence of typical lowland fauna.

Pasveer and Aplin (1998) revisited the faunal stratigraphy of Kria and Toe 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 Toe 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. 8000-6000 BP.

The palaeoecological evidence from Kria and Toe 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 Toe Caves, obtained as part of a broader study of eggshell biogeochemistry currently underway by SJC and GHM. Ratite eggshell represents 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.sub.2]. The amino acid data comprises the extent of isoleucine epimerisation determined by the ratio 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 Toe 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 65-70 cm and 130-135 cm represent paired determinations on single eggshell fragments.

With the exception of the two charcoal dates from 110-115 cm and 165-170 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 65-70 cm (OZF 245) and 75-80 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 Toe Cave, including A/I ratios. As before, paired AMS dates and A/I ratios for single Casuarius eggshell fragments are indicated.

The new Casua'rius eggshell dates, together with the paired and associated A/I ratios, provide a greatly improved chronology for the Toe 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 95-100 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.

The improved dating of the Kria and Toe 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 [+ or -] 150 BP (OZF 847) from Toe 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 813C value of -13.0%,. The sample originates from 95-100 cm depth in Square 2NIE, 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 [+ or -] 110 BP). The new date further supports the claim that the Ayamaru area was inhabited prior to the Last Glacial Maximum.
Table 1. Radiocarbon dates from the excavation in Kria Cave.
New dates are indicated in bold.

Laboratory    Depth           Unit         Radiocarbon
ref. no.      below           (level) *    years BP
              surface (cm)

OZE 542       10-15 **        I(6)         1840 [+ or -] 40
GrA 9100      50-55           II(3)        4370 [+ or -] 50
OZF 245       65-70           II(6)        5120 [+ or -] 60
GrA 6310      75-80           II(8)        4970 [+ or -] 60
GrA 9101      100-105         III(5)       5690 [+ or -] 50
GrA 6312      110-115         IV(2)         420 [+ or -] 60
GrA 9102      125-130         V(1)         5940 [+ or -] 50
OZF 246       130-135         V(2)         6080 [+ or -] 60
GrA 6313      165-170         V(9)          260 [+ or -] 60
GrA 9103      170-175         V(10)        6760 [+ or -] 50
OxA 6043      155-160 (++)    V(11)        6900 [+ or -] 80

Laboratory        [delta] 13C          Calibrated
ref. no.      ([per thousand], PDB)    age (2[sigma]) in
                                       years BP#

OZE 542            -23.3               1870-1630
GrA 9100           -25.8               5210-4840
OZF 245            -12.2               5990-5730
GrA 6310           -25.7               5890-5590
GrA 9101           -26.5               6640-6320
GrA 6312           -25.7               540-315
GrA 9102           -25.8               6890-6660
OZF 246            -13.5               7180-6750
GrA 6313           -26.2               470-2
GrA 9103           -25.0               7680-7510
OxA 6043           -26.4               7930-7590

Laboratory    A/I ratios              Dated material
ref. no.

OZE 542                               pig bone
GrA 9100                              animal bone (@)
OZF 245       0.167 [+ or -] 0.004    Casuarius eggshell
GrA 6310                              charcoal
GrA 9101                              animal bone (@)
GrA 6312                              charcoal
GrA 9102                              animal bone (@)
OZF 246       0.225 [+ or -] 0.01     Casuarius eggshell
GrA 6313                              charcoal
GrA 9103                              animal bone (@)
OxA 6043                              charcoal

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 10-15 cm depth in Square 0N0E.
(++) OxA 6043 comes from a depth of 155-160 cm in Square 1N1E; due to
a slope in the deposit, this sample is equivalent to 175-180 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 offset. (@) These dates are based on the alkaline
fraction of a bulk bone sample, predominantly remains of a wallaby
(Dorcopsis muelleri).
Table 2. Radiocarbon dates from the excavation in Toe Cave. New dates
are indicated in bold.

Laboratory    Depth             Square     Radiocarbon
Ref. No.      below                        years BP
              surface (cm) *

OxA 6201      35-40             1S0E         2930 [+ or -] 65
OxA 6223      45-50             1S0E          220 [+ or -] 70
OxA 6224      60-65             1S0E          111 [+ or -] 55
OxA 6046      65-70             1S0E          240 [+ or -] 40
AA 32920      115-120           1S0E       10,150 [+ or -] 65
AA 32921      25-30             2N1E         5290 [+ or -] 75
AA 33404      60-65             2N1E         8860 [+ or -] 70
AA 33405      80-85             2N1E       12,870 [+ or -] 110
AA 33406      80-85             2N1E       12,885 [+ or -] 90
OZF 251       95-100            2N1E       13,130 [+ or -] 110
OZF 516       95-100            2N1E       20,320 [+ or -] 110

Laboratory    [delta][sup.13]C         Calibrated
Ref. No.      ([per thousand], PDB)    age (2[sigma]) in
                                       years BP (#)

OxA 6201      -20.1                    3,320-2,870
OxA 6223      -25.3                    460-0
OxA 6224      -28.7                    290-0
OxA 6046      -25.7                    425-3
AA 32920      -12.4                    12,320-11,340
AA 32921      -14.6                    6,280-5,910
AA 33404      -15.1                    10,210-9,630
AA 33405      -12.4                    15,990-14,410
AA 33406      -12.8                    15,990-14,440
OZF 251       -15.9                    16,270-14,660
OZF 516       -13.0 ($)                24,730-23,210 (++)

Laboratory    A/I ratios                 Dated material
Ref. No.

OxA 6201                                 animal bone (@)
OxA 6223                                 charcoal
OxA 6224                                 charcoal
OxA 6046                                 charcoal
AA 32920      0.254 [+ or -] 0.007       Casuarius eggshell
AA 32921      0.149 [+ or -] 0.004       Casuarius eggshell
AA 33404      0.252 [+ or -] 0.004       Casuarius eggshell
AA 33405      0.354 [+ or -] 0.004       Casuarius eggshell
AA 33406      0.432 [+ or -] 0.006 **    Casuarius eggshell
OZF 251       0.420 [+ or -] 0.011       Casuarius eggshell
OZF 516       0.449 [+ or -] 0.013       Casuarius eggshell

Notes: * The deposit in Toe Cave is subject to a slope of some
20-30 cm, dropping from Square 2N1E to Square 1S0E over a horizontal
distance of 3 m. (#) See note at Table 1. (@) 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.


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-9709806). We thank Prof. Matthew Spriggs for his comments on the paper.

References

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Hope, G.S. and J.H. Hope 1976. 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 1971-1973 Australian Universities' Expeditions to Irian Jaya: survey, glaciology, meteorology, biology and palaeoenvironments. Pp.225-239. Rotterdam: A.A. Balkema.

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Stuiver, M., P.J. Reimer, E. Bard, J.W. Beck, G.S. Burr, K.A. Hughen, B. Kromer, F.G. McCormac, J. Van der Plicht and M. Spurk 1998. INTCAL98 Radiocarbon age calibration 24,000-0 cal BP. Radiocarbon 40:1041-1083.

Van der Kaars, S. 1995. Preliminary palynological results on the Pleistocene-Holocene transition, Seram Trench, offshore Irian Jaya, Indonesia (extended abstract). Geologie en Mijnbouw 74:285-286.

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
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Author:Pasveer, Juliette M.; Clarke, Simon J.; Miller, Gifford H.
Publication:Archaeology in Oceania
Article Type:Statistical Data Included
Geographic Code:8PAPU
Date:Jul 1, 2002
Words:3238
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