The geology of the Nelson City area

Abstract

The geology of 25 square miles near Nelson City is described. Three major rock groups are recognised; 1. Upper Paleozoic, Brook Street volcanics and strongly folded Maitai sediments; 2. Tertiary beds that range from Eocene to Pliocene in age; 3. Pleistocene and Holocene beds. Brook Street Volcanic Group is defined and divided into four formations. Atomodesma and Peruvispira show the age to be upper Paleozoic. The three upper, of the four Maitai Series formations are represented. They are tightly folded, four fold axes crossing the area mapped. A substantially complete Eocene to Pliocene sequence was probably deposited, but the Tertiary rocks are strongly deformed, not well exposed, and few clear sections were seen. A northeast plunging syncline is the major structural feature. Divisions in terms of New Zealand stages, are based on paleontology. An active normal-dextral-transcurrent fault displaces periglacial topography.