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Article Excerpt
Abstract
The SE-SZ-8 site of Nanggu is a large Lapita site in the Reef/Santa Cruz group of the Southeast Solomon Islands. This paper provides a detailed discussion of its geomorphological and environmental context on Santa Cruz and the within site position of four marine shell dates from it, followed by a Bayesian analysis of the radiocarbon dating of the site. The analysis includes two new marine shell dates on additional species to overcome possible problems due to species selected for dating. Together these data indicate that despite recent critique of the sequence of the three excavated decorated Lapita sites (SE-SZ-8, SE-RF-2, SE-RF-6) proposed by Green (1991a) for the Reef/Santa Cruz Group there is little basis to suggest the Nanggu site is not both the oldest dated Lapita site in the sequence, but also earlier than any other so far identified within the period of early Lapita colonization of Remote Oceania.
Keywords: Lapita, Bayesian chronology, geomorphology, environment
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The Lapita settlement of the Reef/Santa Cruz Islands in the southeast Solomon Islands represents the first major open ocean crossing into previously uninhabited Remote Oceania (Green 1991b) and crossing from Near Oceania required nothing more than sailing due east with the seasonally prevailing winds along a zenith star path (Irwin 2006:73). As such the nature and timing of this settlement is of considerable importance to our consideration of the colonization of Oceania (Sheppard and Walter 2006). Recent critique of the dating and interpretation of the chronology of the Reef/Santa Cruz Lapita sequence with implications for our understanding of regional change in ceramic sequences (Best 2002, Felgate 2003) makes it imperative that we review and enhance, where possible, the basic data available on the sites in question. The SE-SZ-8 has long been considered the best candidate for the oldest investigated site in the Reef/Santa Cruz site sequence (Green 1991a). However, it has been recently suggested, based on possible overlap in the age of SZ-8 with RF-2 and theories of ceramic change, that this site is possibly the youngest (Best 2002:93) in the series of three Lapita sites (SZ-8, RF-2, RF-6) reported by Green. Best (2002:90) has also called for the publication of more detailed information on the excavation context of all published dates in order to evaluate their "integrity". This report collects together data, including new and revised data, on the geological and environmental context of the site, its relationship to local tephrachronology, site layout, stratigraphy, site sampling and a basic calibration of new and previously available SZ-8 radiocarbon data. It also reports a Bayesian analysis designed to estimate the timing and duration of the occupation associated with the SZ-8 archaeological record.
From 1976 onwards (Green 1976, 1979, 1991a: Table 3) two Tridacna marine shell radiocarbon determinations have been available as an indication of the approximate age of the SE-SZ-8 dentate-decorated Lapita site of Nanggu, on the island of Nendo or Santa Cruz, in the Outer Eastern Islands of the Solomons. However, a more precise calibrated date has never been possible, although general estimations have been published using a default [DELTA]R value of zero or a composite one of 100 (Kirch and Hunt 1988: Table 2.3, Spriggs 1990:11, Table 1). Thus the most cautious assessment of the site's age, using those [DELTA]R marine values, had been set out by Green (1991a:201) along the following lines.
1. The four charcoal dates for the SE-RF-2 Nenumbo Lapita site make it the most securely dated site in the Reef/Santa Cruz region. The spatial distribution of excavated artifacts and features suggested the occupation was of short duration.
2. The two then available SZ-8 marine shell dates overlapped statistically at 1 standard deviation with the RF-2 site when the SZ-8 DR was estimated at or 100.
3. Based on its ceramic and lithic content the SZ-8 site appeared to be older than RF-2, although probably on the order of less than a century or two.
Useful advances on these 15 year-old assessments are now possible. First, at SE-RF-2, two additional Tridacna marine shell dates have been added to the four published charcoal date determinations. With these six dates from the one site, analysis has been performed (Jones, et al. 2007) (a) to obtain marine DR values by the method of charcoal/shell pairs, and (b) to achieve, using Bayesian methods, a statistically valid pooled outcome for its probable age that in fact is more mathematically sound than the previously published pooled mean age (Green 1991a). This is primarily because the pooling protocol used here entials only an assumption of a penecontemporary age relationship in respect of each of the six samples ages rather than one in which all individual [sup.14]C outcomes are assumed to stem from a single dated wholly synchronous event.
Thus, in Jones et al. (2007) the Bayesian marine DR value for the Reef/Santa Cruz region is determined to be 8164 during the Lapita period. Secondly, the data support a short occupation span of 50 years or less and an age estimate for RF-2 between 2825-2983 and 2949-3145 cal BP at a 68% CI and at 95% between 2724-3062 and 2878-3271 cal BP. Here we abandonan earlier 300 year duration estimated for SZ-8 (Green 1991b: 203; see also Specht 2002:45) and on a much sounder appraisal of its span of occupation reduce that to a more plausible 100 years.
These two advances then make possible the proper calibration of marine shell [sup.14]C determinations for SZ-8, (a) as a check on the previous outcomes, and (b) to see if other shell species might return different values or comparable ones, and (c) to ensure that all age determinations from each of the Reef/Santa Cruz sequence (RF-6, RF-2 and SZ-8) are represented by 3 or 4 radiocarbon dates, thereby enhancing statistical evaluation of the sequence order.
A second advance, offering an improved interpretation of the SZ-8 Nanggu Lapita site, is related to a much fuller reconstruction of its environmental context at circa 3000-3100 years ago. This has come about because of additional archaeological information about decorated and plainware Lapita pottery sites in the Reef/Santa Cruz region during the 1980s (McCoy and Cleghorn 1988) and currently (Doherty 2007), and geological and land resource studies which have appeared since 1976 (Hughes et al. 1981, Wall and Hansell 1976). In particular, it attempts to contextualize SZ-8 as part of a set of five other nearby Lapita sites (SZ-50,10,40,41,42) within the early highly decorated portion of that regional pottery tradition of this particular area of southeast Nendo. These are all new decorated and plainware Lapita sites recorded in AD 1977-1979, during the second stage of the Outer Eastern Islands archaeological investigations (Yen 1982:58-63). They too need to be integrated into any discussion of dating SZ-8. We begin our discussion with the general context and then move to a discussion of the site and the context of dated samples and finish with a new Bayesian analysis of the radiocarbon dates.
An environmental context for Nanggu and nearby Lapita sites
When they were initially reported, the physical setting of the two Nanggu area Lapita sites (SZ-8, SZ-10) on Nendo were described as occurring in soils overlying coralline Quarternary limestone and were said to be "in very similar environments to the Lapita sites on the Main Reef Islands, despite the fact that Nendo is largely a volcanic high island" (Green 1976:250). At this time other sites with Lapita pottery, whether plain or decorated, had proven very hard to find on Nendo. However, by 1979, the number of Lapita sites in the vicinity of SZ-8 had risen to three; two (SZ-40, 41) were on the southeast raised coralline coast of the mainland and the other (SZ-10) on the adjacent raised coral island of Tomotu Noi (Green 1979:51). The SE-SZ-8 site was now described as situated a carefully measured 468 metres inland from the present coastline, with perhaps two raised beaches in between. Elevations taken during the measurement process showed the site now lay at 5 or 6 metres above an estimated present day high tide level. Similar sites have since been reported from the raised limestone regions to the west of Graciosa Bay, from which three more decorated phase, and two plainware phase sites in the Lapita tradition were located (McCoy and Cleghorn 1988). Now these sites can be seen as examples of the expanding group of originally coastal Lapita sites where tectonic uplift of segments of the island arc has placed them in current locations well above the reach of hydro-isostatic fluctuations in sea level. The site of SZ-8 has been cited as a prime example of this (Dickinson and Green 1998). Given this additional data, evidence is now sufficient to attempt a reconstruction of the paleo-environment of the Lapita sites on the southeast corner of Nendo, one which makes far more comprehensible the location of the Nanggu and other sites found in that particular locality.
In geologically recent times, the raised terraces, entrenched drainage systems, and stranded reefs of the coastlines of Nendo testify to the prolonged emergence of most of the numerous fault block units of this high island (Craig 1981:41, Fig. 3; a version of this appears here as Figure 1). Thus only two minor faults appear to be submergent. One of the submergent zones lies in the vicinity of the West Channel between Note Luowe point at the northwestern tip of Nendo and the raised coral island Tomotu Neo (Craig 1981:61). This small submergent landscape has an interesting connection with two very low-lying decorated Lapita sites, SE-SZ-23 and SE-SZ-45, found and investigated by McCoy and Cleghorn (1988:106-7). They now lie on either side of a recently navigable but currently infilling channel, with one near Malo on the southeast coast of Tomotu Neo and the other on the small islet...
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