The stratigraphy and structure of the middle Awatere Valley (S.35) and Contributions to Antarctic geology

Abstract

In the middle Awatere Valley, steeply dipping, sparsely fossiliferous, Cretaceous and Lower Tertiary rocks are preserved as outliers in a complex fault-angle depression formed by the Awatere Fault. An unconformity inferred to mark the post-Hokonui Orogeny separates "basement greywackes" (Lower Clarence Series - ?Triassic) from Motuan rocks. The Lower Motuan rocks are redeposited conglomerates interbedded with carbonaceous sandstones and silty grits. They are termed the "redeposited conglomerate facies" and are inferred to mark the beginning of sedimentation after an appreciable and probably widespread erosion interval. Overlying these beds are 1000 feet of alternating redeposited sandstones and siltstones. They pass gradationally upward into about 1000 feet of Ngaterian mudstones which are interbedded near their top with 100 feet of possibly redeposited conglomerate. Basement greywackes, Motuan rocks and Ngaterian mudstones are unconformably overlain by over 2000 feet of Ngaterian volcanics. The Raukumara Series is not represented. The Mata and Dannevirke Series rocks (Amuri Limestone etc.) are preserved in an extremely complicated fault bounded strip and their order of succession is uncertain. The structure is complex. The area is divided into narrow strips by sub-parallel, probably transcurrent faults. The outlier of Motuan and Ngaterian rocks forms the eastern limb of a steep syncline which is faulted against a complicated outlier of Mata and Dannevirke series rocks, in the west. A description of important stream sections is given. The geology is illustrated by a detailed map with cross sections. A list of fossil localities is given in an appendix.