The geology of Coverham and the Upper Waima Valley, Marlborough

Abstract

Coverham and the Upper Waima Valley are situated on the complex north limb of the Seaward Kaikoura Anticline, East Marlborough. The strata are at least 13,000 feet thick and are divided into 12 formations ranging from Jurassic to Miocene in age. Greywacke (Puaroan-? Motuan), Pikes Formation (Motuan), Ouse Siltstone (Motuan), Wharfe Sandstone (Motuan), and Sawpit Mudstone (Ngaterian) are geosynclinal turbidities and massive mudstones with rare conglomerate bands. Nidd Sandstone (Arowhanan-Lower Teratan) is a glauconitic sandstone underlying and passing laterally into Burnt Creek Formation (Mangaotanean-Upper Teratan) conglomerates, turbidites, and massive siltstones, which rest with major unconformity on Greywacke. This is overlain by glauconitic Paton Sandstone (Upper Teratan-Piripauan), and sulphurous Whangai Shale (Haumurian). Amuri Limestone (Haumurian-Waitakian) is divided into seven members, including bedded flints, limestone, bentonite, and greensand, and is overlain by calcareous Waima Siltstone (Waitakian-Altonian) and massive Great Marlborough Conglomerate (Altonian-Lillburnian). Scour cast directions show that the majority of the Cretaceous turbidity currents flowed into the geosyncline from the south-west. The rocks have been folded along north-east striking axes, and cut into slivers by north-east trending faults which are dominantly reverse and have a strong dextral component. The Clarence and Chalk Range Faults divide the area into three blocks; Greywacke to the north, Tertiary rocks along the centre, and dominantly Cretaceous rocks to the south. The geological history is outlined, and a list of fossils used for dating the rocks has been compiled.