Integrating geoarchaeology and magnetic susceptibility at three shell mounds: a pilot study from Mornington Island, Gulf of Carpentaria, Australia

Abstract

a b s t r a c tIn coastal areas of the globe, open shell matrix sites are commonly used to establish regional chronologies of human occupation and identify patterns of cultural change, particularly for the Holocene, postsea-level stabilisation period. Despite this, many basic sedimentary analyses that are routinely applied to rockshelter deposits (e.g. geophysical characterisation, particle size etc) are rarely applied to these sites. Magnetic susceptibility, occasionally used in rockshelters, has never been used to investigate shell matrix sites in Australia, despite several international studies identifying its efficacy for other types of open sites. This paper reports a pilot project applying a range of conventional sedimentary and archaeological analyses, as well as magnetic susceptibility at three anthropogenic shell mounds on Mornington Island, Gulf of Carpentaria, Australia. Results are compared to, firstly, assess site integrity and, secondly, to ascertain whether magnetic signatures are related to cultural or natural site formation processes. The results establish that the mounds were repeatedly visited, despite the archaeological evidence, including radiocarbon ages, suggesting effectively 'instantaneous' deposition. This has important implications for studies of other shell mounds where the limitations of radiocarbon dating precision may also mask multiple deposition events.

Mid-Holocene Aboriginal occupation of offshore islands in northern Australia? A reassessment of Wurdukanhan, Mornington Island, southern Gulf of Carpentaria, Australia

“…This density is well within the parameters described for a naturally deposited assemblage, viz. >1000 foraminifera per 100 g of sediment (see Rosendahl et al, 2007Rosendahl et al, , 2014b. Five foraminifera taxa were identified, dominated by Elphidium sp.…”

“…Foraminiferal analysis was carried out on sediments from each excavation unit to assess the depositional context of deposits, with the exception of XU10 where no sediments were recovered (see Rosendahl et al, 2007Rosendahl et al, , 2014b. A sub-sample of the <2.3mm sediment sample was wet-sieved with freshwater through nested Endecotts sieves.…”

“…The Yiinkan Embayment was an ideal region to address these issues and to test models for human-environment interaction given the potential it provided to construct a secure local chronology of land formation processes and environmental conditions in which to contextualise the archaeological record (Rosendahl et al, 2014a(Rosendahl et al, , 2014b. Numerous fixed biological indicators in the form of black-lipped oyster (S.…”

A multi-proxy study of anthropogenic sedimentation and human occupation of Gledswood Shelter 1: exploring an interior sandstone rockshelter in Northern Australia

“…Sediment magnetic susceptibility has also been widely adopted as a means to explore issues about depositional mechanisms and human occupation of rockshelter and cave sites (Ellwood et al 1997;Ellwood et al 2004;Herries 2006;Herries and Fisher 2010), yet few such studies have been completed on Australian sites (exceptions include Davidson et al 1993;Keys 2009;Marwick 2005;Rosendahl et al 2014). Magnetic susceptibility is a measure of the ease with which a material can be magnetized in the presence of a magnetic field (Thompson and Oldfield 1986, p. 25), and can be used to detect magnetic minerals present in sediments (Evans and Heller 2003).…”

Short-term late Holocene dry season occupation and sandy-mud flat focused foraging at Murdumurdu, Bentinck Island, Gulf of Carpentaria

“…This means there are differences in the concentration of magnetic minerals within the deposits. On average, the upper deposits contain lower χfd%, and this could reflect younger soils (see Rosendahl et al 2014b). Cshell values suggest little interaction with terrestrial carbon sources, with carbonates being built primarily from marine reservoirs (see Petchey et al 2013).…”