Akatarawa Conglomerate (Permian), Lake Aviemore South Canterbury

Abstract The Akatarawa Conglomerate occurs with sandstone, siltstone, volcanics, and fusilinid limestone in a fault‐bounded block 2 km northwest of Lake Aviemore. The conglomerate is underlain by massive sandstones, is about 100 m thick, steeply dipping, massive, and very indurated. It is fine grained (the clast size averaging 4 mm), polymodal, has little matrix, and contains large (up to 1‐m‐long) mudstone rafts. A grid count of 300 clasts indicated that most are cherty quartzite and coarse quartz, with fewer sandstone, microgranite, volcanic, mudstone, and black phosphate clasts. Some cherty quartzites contain possible radiolarian remains, but diagenesis has obscured them. Cherry clasts are more abundant in the conglomerate (and sandstone lenses within it) than in its enclosing sandstones, and indicate the influence of a different source for the time of its deposition. The siliceous clasts may partly be products of more than one erosion cycle. Their dominance does not necessarily indicate dominance in the provenance area, even as detrital clasts. Some clasts, in particular the phosphate and some sandstones, may have been locally derived. Polymodality and lack of sorting suggest either a nearby source or derivation from more than one source. Deposition may have been by mass flow in shallow water or deeper adjacent water.