Geology of western Koranga Valley, Raukumara Peninsula

In western Koranga Valley gently folded Lower Cretaceous (Urutawan Stage: Albian) shelf sediments overlie steeply dipping, indurated alternating sandstone and siltstone (Urewera Group: Upper Jurassic‐Lower Cretaceous) with marked angular unconformity. Two distinct facies of Cretaceous sediments are represented: in the east, a 1 · 5 km thick Lower to Upper Cretaceous (Clarence to Mata Series) transgressive sequence of richly fossiliferous conglomerate, sandstone, and siltstone; in the west, a thicker (minimum 1 · 5‐2 km) sequence of Lower Cretaceous (Clarence Series) sandstone and siltstone with intraformational breccia units, here mapped as part of the Urewera Group. The two facies are separated by a NNE‐striking fault zone containing infaulted Teratan (Coniacian‐Santonian) and Haumurian (Maastrichtian) sediments. The eastern shelf facies consists of Urutawan to Arowhanan (Albian to Turonian) sediments unconformably overlain by transgressive Haumurian glauconitic sandstone and siliceous siltstone, grading up into Lower Tertiary (Dannevirke Series) calcareous siltstone. Landon Series (Oligocene) glauconitic sandstone unconformably overlies Mata to Dannevirke Series sediments. East‐west and NNE‐NNW folds in Clarence Series sediments are largely pre‐Haumurian; folding was probably associated with faulting in late Raukumara (Mangaotanean‐Teratan) times. Major NNE‐striking faults, some rotational, have undergone several periods of movement, the latest in the Late Tertiary to Recent.