Geochemical Sourcing of New Zealand Obsidians by Portable X-Ray Fluorescence from 2011 to 2018

Abstract

Temporal coverage Collections include artefacts that may date from the initial settlement by the ancestors of Māori around AD 1280 through the period of regular contact with Europeans after AD 1850. (2) Methods Each artefact was assessed mid-z elements (Nb, Rb, Y, Zr, Sr) and other elements (Fe, Mg) using a pXRF and then matched to a geochemically distinct natural source of obsidian. Geographically ambiguous source assignments, such as assignment to a general volcanic zone, were not included. We note that out of the 15 known geochemically distinct natural sources of New Zealand obsidian [12], only 13 have been identified in archaeological collections. Steps The two university laboratories that produced this data each specified procedures in a series of publications. The specific lab protocols and machines used evolved over this period and so readers are directed to original studies for a fuller description. Examples of methods for Bruker pXRF, a type used in both laboratories, is summarised below.

Social network analysis of obsidian artefacts and Māori interaction in northern Aotearoa New Zealand

“…The spatio-temporal patterning of obsidian use was evaluated by splitting the dataset into two smaller temporal subsets based on the associated radiocarbon dates of the archaeological sites. While the reported calibrated date ranges of the sites (see [ 21 ] [ 25 ] [ 29 ] [ 30 ] [ 43 ]) are not completely discrete, it is possible to categorize sites into those that probably predate AD1500 (Early) and those that probably postdate AD 1500 (Late). To investigate temporal patterning we created community bipartite graphs for sites in those two temporal categories ( Fig 10 and Fig 11 ).…”

“…In nearly all cases these locations correspond to a single site number in the New Zealand Archaeological Association’s geodatabase of archaeological sites ( www.archsite.org.nz ), and we use the term site to refer to these locations. The temporal associations of the sites vary, and for 13 of these, we determined whether the assemblages from the sites likely pre or post-date AD 1500 based on the reported radiocarbon dates (see Table 1 , and [ 21 ] [ 25 ] [ 29 ] [ 30 ] [ 43 ]). The largest assemblage from a site, in terms of the number of artefacts, is Ponui Island with 565 artefacts, while the sites with the smallest assemblages are Taputiketike and the Sundae site, with 20 and 22 artefacts, respectively.…”

“…Our analysis incorporates data on obsidian artefacts collated from four previous pXRF obsidian sourcing studies in the Auckland area and Northland [ 21 ] [ 29 ] [ 30 ] [ 31 ]. We also incorporate data summarized in a regional database [ 43 ][ 44 ] that includes data from Kneebone [ 26 ] and Cruickshank [ 25 ] and new data from Great Mercury Island, Coromandel Peninsula. We use cosine metrics to define similarities between archaeological sites based on the proportions of obsidian artefact source material found at the sites.…”

On provenance studies of New Zealand obsidians: A pXRF‐based geochemical reference dataset and a review of analytical methods

“…; McCoy et al . ; Mills et al . ), data quality assurance has become especially important (see Golitko ).…”