The geology of the Round Hill area, upper Hakataramea Valley

Falconer, Mark Lloyd.

Permian sediments outcropping in the Round Hill area in the upper Hakataramea Valley comprise interbedded sandstones and mudstones of the Rakaia Terrane (Torlesse), which have been regionally metamorphosed to prehnite-pumpellyite facies. The interbedded sandstones and mudstones are inferred to have formed as part of a submarine fan complex. The Torlesse also locally includes small volumes of highly altered porphyritic dykes. The Torlesse strata have been deformed by pre-Cenozoic folding and faulting followed by postfold emplacement of quartz veins. A late Cretaceous to early Tertiary erosion surface on the Torlesse is overlain by a transgressive-regressive sequence of Tertiary sediments. Estuarine deposits of the Broken River Formation, with a low diversity fossil assemblage similar to the "Pomahaka Fauna", unconformably overlie the Torlesse and are the basal sediments of the marine transgression. The age of the estuarine deposits constrain the base of the Tertiary units as being no older than Arnold Series. A landward transgression of marine facies during the late Eocene to early Oligocene has resulted in a sequence of clastic sediments ranging from shoreface-littoral sands rapidly grading upward to mid to outer shelf glauconitic silts and muds, with probable periods of reduced deposition represented by greensand horizons. A period of slow, quiet deposition is represented by calcareous and glauconitic sediments in the mid to late Oligocene followed by a Miocene-Piiocene regressive sequence of progressively coarser-grained marine and non-marine terrigenous sediment. Block faulting during the Pliocene and Quaternary, due to increased tectonism associated with the Kaikoura Orogeny, has resulted in the up thrusting of structural blocks. Tertiary sediments are preserved on the back-tilted flanks between these structural blocks. Pleistocene glacial outwash gravels form conspicuous terraces which once formed a broad outwash plain around the elevated Round Hill area. The western part of the Round Hill area is covered in wedges of alluvial fan material derived from the Kirkliston Range.

iv, 89 leaves : col. ill., maps (some folded) ; 30 cm.

2000Falconer

Abstract Only

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