A reassessment of the early archaeological record at Leang Burung 2, a Late Pleistocene rock-shelter site on the Indonesian island of Sulawesi

Abstract

This paper presents a reassessment of the archaeological record at Leang Burung 2, a key early human occupation site in the Late Pleistocene of Southeast Asia. Excavated originally by Ian Glover in 1975, this limestone rock-shelter in the Maros karsts of Sulawesi, Indonesia, has long held significance in our understanding of early human dispersals into 'Wallacea', the vast zone of oceanic islands between continental Asia and Australia. We present new stratigraphic information and dating evidence from Leang Burung 2 collected during the course of our excavations at this site in 2007 and 2011-13. Our findings suggest that the classic Late Pleistocene modern human occupation sequence identified previously at Leang Burung 2, and proposed to span around 31,000 to 19,000 conventional 14C years BP (~35-24 ka cal BP), may actually represent an amalgam of reworked archaeological materials. Sources for cultural materials of mixed ages comprise breccias from the rear wall of the rock-shelter-remnants of older, eroded deposits dated to 35-23 ka cal BP-and cultural remains of early Holocene antiquity. Below the upper levels affected by the mass loss of Late Pleistocene deposits, our deep-trench excavations uncovered evidence for an earlier hominin presence at the site. These findings include fossils of now-extinct proboscideans and other 'megafauna' in stratified context, as well as a cobble-based stone artifact technology comparable to that produced by late Middle Pleistocene hominins elsewhere on Sulawesi.

Fig 1. Study locality and context.

Map of the Indonesian island of Sulawesi (a) showing the location of the Late Pleistocene rock-shelter site, Leang Burung 2 (b); the Holocene cave site, Ulu Leang 1, is located around 1.5 km to the north (c), plan view of Ian Glover’s 1975 excavations at Leang Burung 2; (d) stratigraphic profile of the south wall of the 1975 trench (redrawn from Fig 3 in [1]). Calibrated ¹⁴C ages are reported at the 95% confidence interval.

Fig 2. Faunal distributions recorded by Glover’s 1975 excavations at Leang Burung 2.

Data source: Glover’s 1975 excavations [1], as reported by Clason [17]. Fauna codes: 1, Strigocuscus celebensis (ground cuscus); 2, Ailurops ursinus (bear cuscus); 3, flying fox; 4, Macaca sp. (macaque); 5, Homo sapiens; 6, Carnivora (unident.); 7, rodent; 8, Sus celebensis (Celebes warty pig); 9, Sus. sp; 10, Sus/Anoa; 11, Sus/babirusa; 12, Babirusa; 13, Anoa; 14, Sus/Babirusa/Anoa size (unidentified); 15, bear cuscus/macaque size (unidentified); 16, rodent size (unidentified); 17, bird (unidentified); 18, terrapin/tortoise; 19, reticulated python; 20, snake (unidentified); 21, fish (unidentified); 22, crayfish (unidentified). Clason’s [17] Table 1 lists Layer I and Layers IV-V as containing one and two Sus scrofa specimens, respectively. We follow Simons and Bulbeck [18] in regarding these identifications as implausible, and thus have included them in Clason’s [17] Sus celebensis tally for those layers. We also excluded Clason’s [17] "?" category, which dominates percentages for each layer. According to Table 1 in Clason’s [17] report, a single element attributed to Homo sapiens was identified in the Layer I faunal assemblage; however, this specimen is not described elsewhere in Clason’s [17] paper and there is no further reference in the literature to human skeletal material from Leang Burung 2.

Fig 3. The cliff-foot rock-shelter at Leang Burung 2.

Photographs taken during the 2011 excavation season.

Fig 4. Cemented archaeological breccias on the rear wall of Leang Burung 2 shelter.

(a) Viewed from towards the front of the shelter, looking from west to east along the 2013 trench–the red arrow points to the main brecciated mass; the blue arrow points to the capping flowstone; (b) close-up view of the highlighted area shown in panel b.

Fig 5. Stratigraphy revealed by Glover’s 1975 trench at Leang Burung 2.

As viewed after emptying backfill in 2012; (a) north wall of square H9 and east wall of square G8; (b) south wall of Glover’s 1975 trench, squares E10 to G10.

Fig 6. South wall stratigraphic profile at Leang Burung 2 (2011–13 excavations).

The South Wall section illustrated here comprises a composite of two separate stratigraphic exposures, the southern trench faces of excavation squares E10-I10 and A11-E11, respectively, which are situated a distance of 1 m apart. With regards to ¹⁴C ages, all of the dated samples comprise freshwater gastropod (Tylomelania perfecta) shells; only dated shells collected in situ from the deposit are shown projected onto the stratigraphic profiles. The sampling locations for pIRIR samples LB2-OSL12 (Layer A) and LB2-OSL13 (Layer B) are not illustrated on the south wall profiles because they were collected from different trench faces.

Fig 7. Faunal remains and artifacts excavated from the upper levels of square D11 at Leang Burung 2 in 2011.

Fig 8. South wall stratigraphic profile at Leang Burung 2 (2007 excavations).

Calibrated ¹⁴C ages are reported at the 95% confidence interval (see Table 1).The ¹⁴C dating results are presented in Table 1. All of the dated shells are Late Pleistocene in age, with two exceptions: a shell from Layer II (spit 48) yielded an unexpectedly young age of 9–8.6 ka cal BP (OZO824), while the suspected intrusive shell from Layer B (spit 58) was similar in age (9.6–9.5 ka cal BP, Wk33233). We regard both shells as having been displaced from stratigraphically higher contexts, most likely during the excavations.

Fig 9. Elephantinae (genus and species indeterminate) molar plate fragment excavated from Layer I at Leang Burung 2.

Scale bar is 10 mm.

Fig 10

The deep deposits at Leang Burung 2 (Layers A to C). The photograph, taken during the 2011 excavations, is of the north wall of square D10 and the section covers a depth of approximately 5 m to 6.2 m below the surface.

Fig 11. Stone artifacts from the deep deposits at Leang Burung 2.

(a) limestone core, square D10, spit 54 (Layer A); (b) limestone core, square D11, spit 55 (Layer A/B); (c) retouched limestone flake, square D11, spit 47 (Layer I); (d) multiplatform limestone core, square D11, spit 55 (Layer A); (e) limestone flake, square D11, spit 50 (Layer A). Scale bars are 10 mm.

Fig 12. Stone artifacts from the deep deposits at Leang Burung 2.

(a) limestone radial core, square D10, spit 52 (Layer A); (b) large single platform limestone core, square D10, spit 52 (Layer A). Scale bars: a, 10 mm, b, 50 mm.

Fig 13. Stone artifacts from the deep deposits at Leang Burung 2.

(a) limestone flake, square D10, spit 51 (Layer A); (b) limestone flake, square D11, spit 48 (Layer A); (c) unifacially retouched limestone cobble ‘pick’, square D10, spit 55 (Layer A). Scale bars: a-b, 10 mm, c, 50 mm.

Fig 14. Fossil fauna from the deep deposits at Leang Burung 2.

(a) Anoa (Bubalus sp.) molar, square D11, spit 45 (Layer I/A); (b) anoa molar, square D11, spit 50 (Layer A); (c) Suidae M3, square D11, spit 51 (Layer A); (d) babirusa (Babyrousa sp.) lower canine (Layer A); (e) anoa molar, square D11, spit 51 (Layer A); (f) Suidae molar, square D10, spit 51 (Layer A)–NB: this tooth is U-series sample #3011A/B, which yielded a minimum age of 113 ± 10 ka (see Table 3); (g) anoa molar fragment, square D11, spit 60 (Layer B). Scale bars: a-c, e-g, 10 mm, d, 50 mm.

Fig 15. Results of Leang Burung 2 pollen analysis.

Fig 16. Example of the red TL data from Leang Burung 2.

(a, b) a comparison of the red TL signal characteristics using glow curves derived from a Liang Bua cave (Flores) sample WR1 (a) and from a Leang Burung 2 sample (SLBRG2-1, Layer I). The glow curves demonstrate that after 500 Gy dosing the low temperature peaks disappear with the introduction of the 260°C preheat, and the presence of a light sensitive shoulder (260–305°C) that is removed by one hour of bleaching. The Leang Burung 2 sample shows similarities with the Liang Bua sample, but has a more defined bleachable shoulder and a more intense signal; (c) Isothermal decay of the red TL signal from sample SLBRG2-1; (d) dose response curve for the unbleachable signal derived from aliquot 1; and (e) the dose response of the bleachable signal isolated from data derived from aliquot 1 and 2 (see [70] for methodological details).

Fig 17. pIRIR decay curve and the corresponding dose-response curve for one aliquot from LB12-OSL3.

Fig 18. pIRIR data from Leang Burung 2.

(a) Summary of the g-values obtained for individual aliquots from samples LB2-OSL3, LB2-OSL6, LB2-OSL10, LB2-OSL11, LB2-OSL12 and LB2-OSL13, respectively; (b-h) The fading-uncorrected (filled circles) and–corrected (triangles) D_e values for all the 2012 OSL samples shown in the radial plots.