Varieties of glauconite in late Cretaceous and early Tertiary rocks of the South Island of New Zealand, and new proposals for classification

Abstract

Abstract Glauconites from 142 samples of Upper Cretaceous and lowermost Tertiary rocks in the South Island of New Zealand, and Chatham and Campbell Islands, were analysed comprehensively to provide data for paleoenvironmental, paleogeographic, and stratigraphic studies. All morphological varieties and all internal textures of glauconite that have been previously distinguished by Triplehorn and Konta were found in the suite of samples. Two new morphological classes are defined: (1) fragmentary glauconite, comprising angular (Subclass A) or rounded (Subclass B) fragments of once larger grains; (2) spongy glauconite, comprising grains with a porous surface morphology which is subdividable with scanning electron microscopy into “cauliflower” and “serrulate” varieties. Fragmentary grains reflect transportation and abrasion; spongy grains probably reflect diagenetic alteration. Neither glauconite type is suitable for radiometric determination of the time of sediment accumulation. One new class of internal textu...