Chapter 7 Chert-Bearing Formations of New Zealand

Abstract

Abstract Chert occurs in a variety of sedimentary formations, of Early Paleozoic to Early Cenozoic age. Cambrian and Ordovician clastic sequences include beds and lenses of grey chert and cherty limestone. Bedded cherts in sequences of the Permian-Jurassic Rangitata Orogen, and minor siliceous rocks in Early Cretaceous formations, are closely associated with submarine (spilitic) volcanic rocks and red-green mudstone. Silica may have been partly derived from volcanic sources. Late Cretaceous mudstone and shale contain rare chert nodules. Lenticular-bedded, dolomitic chert of the Mead Hill Formation (Maastrichtian-Danian), a basal member (up to 300 m thick) of the Amuri Limestone, shows evidence of replacement of both quartzose sandstone and mi critic limestone. the silica is most likely biogenic. Chert lenses and nodules are common in parts of the Amuri, and lithologically equivalent Early Tertiary limestones. Permian-Jurassic clastic sequences are interpreted, in part, as submarine fan deposits, while Late Cretaceous-Early Tertiary sediments probably accumulated in an extensive, moderately shallow basin.