Sector XXIV
This Sector is in the middle rear of the cave, 2 m to the south of Sector XII (Fig. 3.2). The present cave floor slopes ~30° upwards from just south of Sector XII to the conglomerate wall at the rear of the cave. In 2011, the western half of Sector XXIV (1 x 2 m in area) was excavated to a depth of ~4 m. The primary goal of this excavation was to document the possible southernmost extent of tephra T3 (~50–47 ka), a key stratigraphic layer that overlies all known H. floresiensis remains (Sutikna et al., 2016). This tephra was observed across the entire area of Sector XII (excavated in 2007) at around 2.2–2.8 m depth, with its base angled slightly upwards toward the south. Thus, the aim was to observe whether T3 was present in Sector XXIV and, if so, whether it abutted the stratigraphically underlying deposits. If T3 was not present in Sector XXIV, then it must have terminated at some point in the area between Sectors XII and XXIV (Fig. 3.2).
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During the excavation of Sector XXIV, T3 was encountered in the northern part as a thin lens that sloped upward toward the south and terminated ~60 cm from the north baulk (Fig. 3.3). Although the main goal of the excavation had been achieved with the identification of T3, further questions arose because more than 3,000 faunal specimens per cubic metre were recovered – almost double that from any other Sector. This large accumulation of faunal remains suggested either a major difference in the taphonomy of the deposits or perhaps their age.
A charcoal sample from 152 cm depth in Sector XXIV (D-AMS-005947) was selected for 14C dating and returned an unexpectedly early age of ~34 ka (Table 3.2). This result was 15 millennia older than any of the 14C ages obtained previously at Liang Bua (Roberts et al., 2009) (Table 3.1), which raised the possibility that much of the unexplored rear of the cave may preserve deposits within the critical time interval (46– 20 ka ago) missing from the other excavated areas. Accordingly, four additional charcoal samples were selected for dating: three from the same stratigraphic layer and similar depths (143, 152 and 153 cm) as sample D-AMS-005947, and one from the underlying stratigraphic layer at 201 cm depth (Fig. 3.3). These four samples yielded ages of ~34–31 ka (Table 3.2 and Fig. 3.3), thereby corroborating the original age determination.
Depth δ13C 14C Median Calibrated
Sample Code (cm) Methods1 (‰) (yr BP) (yr cal. BP) 68% CI2 95% CI2 D-AMS-007550 143 ABA / AMS –26.3 27,954 ± 125 31,605 31.75–31.42 32.03–31.29 D-AMS-005947 152 ABA / AMS –28.1 30,168 ± 158 34,161 34.32–33.98 34.52–33.85 D-AMS-007546 153 ABA / AMS –28.0 27,466 ± 120 31,263 31.36–31.16 31.46–31.07 D-AMS-007547 154 ABA / AMS –23.7 27,587 ± 107 31,328 31.43–31.27 31.53–31.13 D-AMS-007549 201 ABA / AMS –33.2 29,074 ± 153 33,258 33.49–33.04 33.66–32.82 D-AMS-007555 137 ABA / AMS –22.1 20,516 ± 58 24,616 24.77–24.45 24.95–24.36 D-AMS-007551 237 ABA / AMS –21.7 36,323 ± 259 40,930 41.25–40.64 41.48–40.31 D-AMS-007552 239 ABA / AMS –27.1 33,817 ± 173 38,284 38.54–38.07 38.70–37.67 D-AMS-007553 250 ABA / AMS –20.4 22,288 ± 94 26,463 26.61–26.28 26.85–26.14
2
CI, confidence intervals.
1 ABA, acid–base–acid pretreatment; AMS, accelerator mass spectrometry measurement technique.
Table 3.2 New 14C ages for charcoal samples from Sectors XXIV and XXVII.
X
X
V
II
Age
Calibrated Range (ka)
X
X
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Furthermore, evidence of fire use – a hearth – was found in the west baulk of Sector XXIV in sediments dated to between ~41 and 24 ka cal. BP (Fig. 3.3). Micromorphology analyses have recently confirmed anthropogenic burning activity in these sediments, which contain ash and charcoal (Morley et al., 2016).
Depth δ13
C 14C Median Calibrated
Sample Code (cm) Methods1 (‰) (yr BP) (yr cal. BP) 68% CI2 95% CI2 D-AMS-005940 45 ABA / AMS –26.6 460 ± 24 493 0.51–0.49 0.52–0.45 D-AMS-005941 66 ABA / AMS –27.5 774 ± 27 673 0.68–0.66 0.72–0.65 D-AMS-005942 89 ABA / AMS –26.3 1,233 ± 31 1,107 1.11–1.06 1.18–1.05 D-AMS-005943 104 ABA / AMS –23.0 2,018 ± 25 1,937 1.93–1.90 2.00–1.88 D-AMS-005945 127 ABA / AMS –20.5 2,143 ± 25 2,075 2.10–2.04 2.15–2.01 D-AMS-005944 116 ABA / AMS –21.7 2,196 ± 29 2,153 2.16–2.09 2.21–2.06 D-AMS-005946 140 ABA / AMS –22.8 2,337 ± 29 2,326 2.35–2.31 2.36–2.30 D-AMS-005948 143 ABA / AMS –27.4 2,639 ± 29 2,741 2.76–2.72 2.78–2.70 D-AMS-005949 171 ABA / AMS –9.6 4,062 ± 52 4,498 4.54–4.41 4.65–4.38 D-AMS-005950 178 ABA / AMS –22.7 4,067 ± 28 4,487 4.49–4.44 4.58–4.42 D-AMS-005951 247 ABA / AMS –29.9 5,557 ± 26 6,310 6.32–6.28 6.40–6.28 D-AMS-005952 279 ABA / AMS –24.3 7,391 ± 32 8,157 8.20–8.15 8.22–8.03 D-AMS-013410 411 ABA / AMS –26.1 10,237 ± 37 11,881 11.97–11.81 12.03–11.75 D-AMS-013409 395 ABA / AMS –23.9 10,350 ± 41 12,089 12.11–11.97 12.30–11.94
2
CI, confidence intervals.
Age
Calibrated Range (ka)
1 ABA, acid–base–acid pretreatment; AMS, accelerator mass spectrometry measurement technique.
XXVI
Table 3.3 New 14C ages for charcoal samples from Sector XXVI.
Depth δ13C 14C Median Calibrated
Sample Code (cm) Methods1 (‰) (yr BP) (yr cal. BP) 68% CI2 95% CI2 D-AMS-013388 88 ABA / AMS –19.0 1,643 ± 28 1,489 1.53–1.47 1.55–1.42 D-AMS-013389 89 ABA / AMS –30.8 1,275 ± 27 1,141 1.18–1.09 1.19–1.07 D-AMS-013390 98 ABA / AMS –21.3 2,180 ± 27 2,127 2.16–2.08 2.18–2.04 D-AMS-013391 100 ABA / AMS –16.6 2,054 ± 29 1,964 1.98–1.93 2.02–1.89 D-AMS-013392 105 ABA / AMS –18.6 2,587 ± 29 2,627 2.75–2.70 2.75–2.68 D-AMS-013393 109 ABA / AMS –14.6 2,365 ± 28 2,343 2.36–2.32 2.44–2.31 D-AMS-013394 117 ABA / AMS –21.6 3,142 ± 29 3,302 3.30–3.25 3.39–3.21 D-AMS-013395 120 ABA / AMS –10.9 2,746 ± 29 2,806 2.80–2.76 2.86–2.75 D-AMS-013397 133 ABA / AMS –15.2 3,258 ± 28 3,431 3.46–3.39 3.50–3.37 D-AMS-013396 133 ABA / AMS –30.5 3,614 ± 29 3,872 3.92–3.83 3.98–3.82 D-AMS-013399 139 ABA / AMS –22.4 3,301 ± 28 3,487 3.51–3.45 3.57–3.44 D-AMS-013398 143 ABA / AMS –21.3 4,029 ± 32 4,470 4.52–4.47 4.54–4.39 D-AMS-013401 150 ABA / AMS –18.3 3,575 ± 26 3,804 3.87–3.82 3.90–3.70 D-AMS-013400 153 ABA / AMS –28.4 4,141 ± 28 4,614 4.63–4.53 4.71–4.52 D-AMS-013403 155 ABA / AMS –26.1 3,796 ± 30 4,115 4.16–4.08 4.24–4.06 D-AMS-013404 157 ABA / AMS –24.0 4,085 ± 29 4,513 4.49–4.44 4.62–4.42 D-AMS-013402 159 ABA / AMS –21.2 3,897 ± 29 4,279 4.30–4.23 4.41–4.22 D-AMS-013406 196 ABA / AMS –19.3 5,398 ± 30 6,139 6.15–6.11 6.22–6.09 D-AMS-013405 202 ABA / AMS –26.1 5,214 ± 31 5,931 5.95–5.91 6.00–5.89 D-AMS-013407 303 ABA / AMS –26.3 8,635 ± 33 9,547 9.56–9.52 9.63–9.49 D-AMS-013408 497 ABA / AMS –23.3 11,107 ± 42 12,928 13.00–12.85 13.06–12.79
2
CI, confidence intervals.
1 ABA, acid–base–acid pretreatment; AMS, accelerator mass spectrometry measurement technique.
XVI
Table 3.4 New 14C ages for charcoal samples from Sector XVI.
Age
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Linear regression analysis of these five ages as a function of depth results in a slope that is not significantly different from zero (p = 0.50; R2 = 0.166). The poor linear fit is because the oldest age (~34 ka) derives from a similar depth to the three youngest ages (~31 ka). However, as all five ages are from within ~60 cm of each other vertically, it is likely that these two stratigraphic layers include deposits that are 34.5– 31.1 ka in age (upper and lower 95% CIs for the oldest and youngest ages, respectively). Moreover, these 14C results are consistent with speleothem U-series ages of ~47 ka obtained in 2004 from a test excavation, 0.5 x 0.5 m in area and ~2 m in depth, mostly in the eastern half of Sector XXIV, but extending into the southern part of Sector XXVII (Fig. 3.2) (Westaway et al., 2007a; Roberts et al., 2009). Previous studies had interpreted these U-series results as dating the same eroded ‘conglomerate’ or gravel- rich sediments as occur stratigraphically beneath the H. floresiensis deposits in Sectors VII and XI (Westaway et al., 2007a, 2009b; Roberts et al., 2009) (see Fig. 3.1). By contrast, the 2011 excavations of Sector XXIV suggested that this gravel-rich layer and its dated speleothems stratigraphically overlay tephra T3 (Sutikna et al., 2016). To resolve this issue, we subsequently excavated Sector XXVII.
Sector XXVII
This Sector, excavated in 2014, occurs directly between Sectors XXIV (to the south) and XII (to the north) (Fig. 3.2). Given the initial 14C age of ~34 ka in 152 cm depth of Sector XXIV, the goal of this new excavation was to observe the stratigraphic connections between Sectors XXIV and XII and obtain additional samples for 14C dating. The stratigraphy followed that of Sector XXIV, showing that these deposits continued to slope downward to the north (Fig. 3.3). Other important stratigraphic details included the presence of tephra T4 above T3, as seen in other Sectors (e.g., XI, XXI, XXIII and XV) but not in Sector XXIV. Instead, T4 terminated against the
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inclining lens of T3 near the southern extent of Sector XXVII and was overlain by gravel-rich sediments – the same layer where the aforementioned small test excavation had terminated (Fig. 3.3).
Figure 3.3 Stratigraphic profile of the western baulks of Sectors XXIV (at left) and XXVII (at right). The locations of the dated charcoal samples are shown projected on to the west wall as green circles with their median calibrated 14C ages (in ka). Colours are used to illustrate the spatial extent of each stratigraphic layer, with clasts of limestone and gravel shown in dark grey. Black arrows indicate a combustion feature (a hearth). Red arrows indicate the termination of T3 in Sector XXIV and tephras T3, T4 and T5 are indicated in the right margin.
Four charcoal samples from between 137 and 250 cm depth in Sector XXVII yielded ages of between 41.5 and 24.4 ka (upper and lower 95% CIs for the oldest and
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youngest ages, respectively; Table 3.2; Fig. 3.3). Linear regression analysis of these four ages as a function of depth results in a slope that is not significantly different from zero (p = 0.44; R2 = 0.312). In this instance, the poor linear fit is because the second youngest age (~26.5 ka; D-AMS-007553) is from the deepest sample (250 cm); we interpret this charcoal sample as having been reworked from a younger layer by post- depositional processes. Otherwise, the 14C ages for sector XXVII show reasonable stratigraphic consistency with those from Sector XXIV and indicate that immediately above the gravel-rich sediments and the ~47 ka speleothems that cover them – and which both overlie T3 and T4 – is up to 1 m of deposit that accumulated between 41.5 and 24.4 ka ago. This new 14C chronology shows unequivocally that these gravel-rich sediments are not the same age as those underlying the H. floresiensis-bearing sediments along the east wall of the cave (see Figs 3.1 and 3.3). Instead, it provides further support for an age of more than ~41 ka for the H. floresiensis-bearing deposits at Liang Bua.