Petrology of the Topfer Formation: First Triassic Gondwana sequence from New Zealand

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Abstract
The 2 km2 outcrop of Topfer Formation is the only known sedimentary formation of Triassic age in New Zealand's Western Province. It consists mainly of uniform medium‐grained massive, well sorted felsic volcaniclastic sandstone with minor mudstone, conglomerate and coal. Two distinct petrofacies (litharenite and feldspathic litharenite) are distinguishable on both detrital and diagenetic composition. On the basis of common framework modes, heavy‐mineral assemblages, depositional environment, intrusion by Jurassic dolerite and association with Palaeozoic quartzose sandstone, we relate the Topfer Formation to the Middle to Late Triassic Gondwana sequences of the Sydney Basin, Tasmania and Antarctica. Some similarities in composition of sandstones and igneous conglomerate clasts of the Topfer Formation and those of the coeval Murihiku Terrane of New Zealand's Eastern Province suggest a common continental magmatic‐arc source area (possibly the intervening Median Tectonic Zone). The tiny area of Topfer Formation thus provides a key stratigraphic and palaeogeographic link between Gondwana and the Eastern Province terranes of New Zealand.