Late Cenozoic and early Quaternary stratigraphy of the Eketahuna District (N153) (print copy)

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Neef, G. 1984 Late Cenozoic and early Quaternary stratigraphy of the Eketahuna District (N153). Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey bulletin 96. 101 p.

Abstract: This bulletin describes the strata present in the NZMS1, N153 Eketahuna sheet district. The strata are composed of very thick, indurated, lithified sandstone and mudstone of Mesozoic age which form the basement on which a thick cover sequence of rapidly deposited, slightly indurated, late Cenozoic marine rocks was deposited.The Mesozoic rocks crop out over most of the western part of the sheet district. They have not been studied as exhaustively as the late Cenzoic rocks which crop out in most of the central and eastern parts of the district. These late Cenozoic strata are subdivided into 25 formations and 42 members. Apart from a stratigraphic description of the late Cenzoic strata, this work is concerned with a reconstruction of the environment of deposition, which is deduced from aspects of the lithology of the rocks and from the presence of certain species of Foraminifera, invertebrate macrofossils, and pollen.The sheet district is cut by some 11 major, largely active NNE-trending faults which are chiefly dextral but are characteristically downthrown on their eastern sides to form fault-angle depressions. Between the major faults there are minor faults which merge with or trend normal to the major faults, and macroscopic folds.The oldest Cenozoic strata, present in the south eastern part of the sheet district, are Tongaporutuan (late Miocene) littoral neritic, macrofossil-rich sandstones. These strata are overlain successively by a siltstone, mudstone, turbidite sequence which was deposited in deepening seas.  During the Opoitian (early Pliocene) much of the central and eastern parts of the sheet district lay along the trend of a deep, NNE-trending, deep water basin, but neritic sandstone is present in the southwestern part of the basin; by the late Opoitian the deep water basin had been infilled by a thick sequence of mudstone, turbidite, bedded sandstone, and massive sandstone (axial part of the basin) and by a thick sequence of massive siltstone (flanks of the basin).During the Waipipian to Nukumaruan stages (late Pliocene to early Pleistocene) a NNE-trending marine strait resembling the present day English Channel lay along the eastern and central parts of the sheet district, in which a thick sequence of neritic sandstone, siltstone, and limestone was deposited as the basement was continuosly downwarped.Since the Nukumaruan the sheet district has not been inundated by the sea. Progressive uplift has caused the development of a number of alluvial terraces, the oldest of which are now at some considerable height above sea level.

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