GEOLOGY OF THE - GNS Science

In northern Raukumara Peninsula th e East CoastAllochthon and Tolaga Group units are unconformablyoverl ain by a shallow mari ne sequence of tu ffaceous,fossiliferous sandstone, calcareous mudsLOne and mi norlimestone (Te Kahi ka Formation of Chapman-Smi th &Grant-Mackie 197 1). Near East Cape the rocks comprisean up wards-coarseni ng and shal low ing seq uencedeposited at depths between upper bathyal to shelf(Ballance el a /. 1984). Between Te Puia and Tolaga Baythe Tolaga Group beds are unconformably overlain bybluff-forming shelly sandstone and muddy sandstone ofthe Tokomaru Sandstone (Mmk) which is locally up to500 m thick (B10m 1982, 1984; Mazengarb el al. 199 1a).The overl ying R amanui Formation (Pmz) consistsmainly ofaltern ating sandstone and mudstone, with lessersandstone, mudstone, tuff and limestone (M azengarb etal. 199 1a; Field, Uruski el a/. 1997). The basal contact isconformable in the Tau w hareparae area butunconform able in land fro m G isborne. In places massivesandstone units are di fferenti ated (Pms). The OrmondL imestone (Pmm) is known from near Gisborne, atWaihirere. Waerengaokuri and in the low hills betweenthere and Poverty Bay (Beu 1995; Field, Uruski el al.1997).South ofGisbome Early Pliocene Mangaheia Group rocksare mainly sandstones, some of which are tuffaceous(Pms), and mudstone ( Pmz). Several unconformi ty-Figure 27 Near-vertical, Late Miocene Tolaga Group alternating sandstones (white beds) and mudstones are well exposed in the sea cliffs atGable End Foreland (Z 17n13836) , so named by Captain James Cook because of the prominent white gable-shaped bed.The sandstones containabundant volcanic ash probably derived from contemporaneous volcanic eruptions in th e Coromandel Peninsula area. The view is towards thesoutheast. Photo CN12914A: D.L. Homer32