A Pilot Study Into the Use of Quartz Grain Microtextures for Resolving Palaeoenvironmental Change in the Cave and Lagoon Deposits of NW Australia’s Offshore islands.

Quartz is ubiquitous across continental areas; it is present in almost every environmental setting and archaeological site, and as a resistant mineral can preserve microtextural traces of its depositional origin and history. In Australia’s northwest, associated with post-glacial sea-level change, sand deposits have been remobilisation across the ancient coastal plain and deposited in beach, lagoon, cave, fluvial and alluvial environments. This pilot study explores quartz grain-surface microtextures from caves and lagoons of the Barrow-Montebello Island complex and how such textures may reflect the source, environments and processes of transport of the grains. Grain surface textures imaged via Scanning Electron Microscopy (SEM) from cave and lagoon settings are compared against reference textures from modern depositional environments across the terrestrial-coastal-marine divide, albeit with some overlap between these. Quartz grains in both cave and lagoon settings maintain the sub-rounded shape and surface microtextures from their coastal limestone source. Superimposed on these are a range of surface microtextures that reflect localised mechanical reworking and variable chemical palaeo-pedological alteration. Aeolian-derived deposits consistent with a more open cave environment are evident within the early deposits of Boodie Cave on Barrow Island, and much later, high-energy beach deposits reflect a proximal marine source. Similarly in Haynes rockshelter, grains are consistent with high-energy storm deposits near the base around the early stages of sea-level stabilisation. The microtextural scarring on quartz grains are a palimpsest of their multiple sedimentary histories, which whilst not definitive of any one depositional setting, still has value in any geoarchaeological study aimed at understanding site formation and past environmental change.