GEOLOGY OF THE - GNS Science

volcanic tuff (MJv) deri ved from rhyolitic eruptions inthe Coromandel Peni nsula area (S haneer al. 1998). Thereare excellent exposures of sandstones rich in volcanicdelritus at Mah ia and at Gable End Foreland (Fig. 27;also back cover). Decimetre- to metre-bedded, finegrained,fossiliferous sandstones which form a prominenttableland in Mangatu Forest (Areoma Sandstone, Mlr)unconformably overli e Middle Miocene rocks(Mazengarb et al. 1991 a). A ridge·formi ng unit of LateMiocene fossiliferous sandy mudstone is present alongthe north coast ofTolaga Bay. Near Patutahi discon tin uousoutcrops of shelly limestone 10-20 m thick (patutahiLimestone, Mlp; Beu 1995; Fig. 28) are present with inmudstone and the basal contact may be partly or whollyunconformable. Shelly li mestone (Mil) present over asmall area aLTirihaua Station (Y 18/586275) is similar tothe slightly older Bexhaven Limestone and a simil arorigin is inferred.Latest Miocene and PlioceneThe latest Miocene to Pliocene Mangahcia G roup(Mazengarb er al. 1991 a) consists of up Lo 2000 10 ofshelly sandstone, sandstone and mudstone. It covers largeareas south of Whangaparaoa and in the vicini ty of EastCape, and is present between Tauwhareparae and TeKaraka (mai nl y in broad synclines). withi n the WairoaSyncl ine and in the western part of Mahia Pen insul a.Figure 26 Late Miocene Makaretu Sandstone forms prominent bluffs and spectacular dip slopes; it has potential as a hydrocarbon reservoirlithology in the Wairoa area. Pliocene limestone forms a scarp on the horizon at the extreme right (Whakapunake). The hummocky surface on thedip slope results from slumping.The view is towards the south. Photo CN42107/19: 0.L. Homer31