Sedimentology of the Greenland Group in the Paparoa Range, West Coast, South Island

Abstract

The Greenland Group of the Paparoa Range consists of alternating beds of indurated sandstone and mudstone interpreted to be a turbidite succession. Sandstones show sedimentary features such as graded bedding, sharp basal contacts, directional sole marks, load casts, flame structures, and a vertical sequence of internal laminations indicative of a progressively declining flow regime during deposition. Limited evidence from sole marks suggests that the turbidite sandstones were derived from the east or south-east. They were probably deposited on a submarine fan complex. Mudstones, and the upper portion of sandstone beds, commonly contain cross-laminated horizons considered to have been formed by traction currents. A bimodal traction current pattern at right angles to the dominant turbidity current trend is attributed to tidal currents acting parallel to a paleoslope striking north-east, south-west. The sandstones are quartz-rich (up to 90 percent of sand-sized particles consist of quartz) and have minor quantities of sodic plagioclase and rock fragments. These latter consist of sandstone and mudstone, quartzite, and representatives of a spilitic volcanic suite. The sediments are inferred to derive mainly from a deeply weathered granitic terrain, with a locally uplifted part of the Greenland Group succession acting as a subsidiary source. Adjacent sedimentary successions in the Paparoa Range previously assigned to Greenland and Waiuta Groups have closely similar petrography, sedimentary facies, and paleocurrent patterns and so are best placed in one sedimentary unit. Comparison of the sediments with other Greenland and Waiuta sequences further afield also show no significant differences, and the name “Waiuta” is considered redundant.