Quartz types of the Eocene Broken River Formation, Mount Somers, South Island, New Zealand

Quartz arenites are a very common geological feature on the South Island of New Zealand. The provenance of the quartz grains that form these arenites is not well constrained because standard point-counting techniques do not provide enough detailed information. In this study we distinguish different quartz types using scanning electron microscopy-cathodoluminescence combined with standard optical microscopy on the same individual quartz grains. This is done on a suite of samples collected from shallow marine quartz arenites of the Paleocene-Eocene Blondin Sand Member of the Broken River Formation (Eyre Group) at Mt Somers in the Canterbury basin on the South Island of New Zealand. Our results show that the volcanic quartz grains were derived from local volcanic source rocks, whereas metamorphic quartz grains may have been derived from either local source rocks of the Torlesse Supergroup or from distant metamorphic sources rocks via longshore transport. Plutonic quartz grains were exclusively derived by long-distance transport. Warm and humid climatic conditions and the presence of humic acids in the associated coal-forming depositional environment probably increased the proportion of quartz in the sampled rocks.