Geology of the Hailes Knob area, northwest Nelson, New Zealand

Page, Diana Jane, 1972-

This thesis describes the geology of a ninety square kilometre area centred around Hailes Knob, northwest Nelson, South Island, New Zealand. The area lies within the Eastern Sedimentary Belt of the Takaka Terrane, in the Western Province. It incorporates part oftwo north-south trending fault bound units recognised in the Eastern Sedimentary Belt- the Takaka Gorge Slice and the Pikikiruna Slice. The Wangapeka Formation (pelagic mudstone) and Arthur Marble 2 (basinallimestone) ofthe Mount . Arthur Group and the Hailes Quartzite (basinal to shallow-marine sandstone) of the Ellis Group form the Paleozoic marine sedimentary sequence in both the Takaka Gorge and Pikikiruna Slices but have different stratigraphic relationships in each slice. The differing internal stratigraphy of the two slices reflects a period of varied depositional environments and suggests that a facies change occurred within the Eastern Sedimentary Belt in late Ordovician time. The sediments accumulated off the coast of Gondwana during the Ordovician-Silurian as an upward-shallowing sedimentary pile, largely in a basin-slope environment, within a passive margin setting. Three periods of deformation in the Silurian-Devonian (i.e. between 420 and 367 Ma), folded and refolded the Paleozoic rocks, more or less coaxially, about axes lying in the N-NW/S-SE sector (in the Takaka Gorge Slice) and the NNE-SSW sector (in the Pikikiruna Slice) into a series of recumbent folds, some thrust-bound. Associated metamorphism which peaked during Dz strongly recrystallised parts of the Arthur Marble 2, and created the Pikikiruna and Onekaka Schists. Two formations of the mafic-ultramafic Riwaka Complex, which intruded the Riwaka Syncline in the Late Devonian, are recognised in the field area, - the Campbell Gabbro and Brooklyn Diorite. A boudinaged east-west trending, ?Late Triassic, peralkaline dyke - the Sams Creek Granite, intrudes the metasedimentary sequence in the Takaka Gorge Slice. The bryozoan-molluscan-rich Takaka Limestone began accumulating in the field area in the Waitakian as a result of marine transgression associated with the peak development of the Late Eocene-Miocene Challenger Rift System when the northern and southern segments linked over northwest Nelson. Eight facies are recognised in the Takaka Limestone, ranging from mixed siliciclastic and carbonate sediments to 'purer' limestone. Takaka Limestone was gradationally overlain by Tarakohe Mudstone in the middle to late Altonian, when marine regression commenced. The upper levels of the Tarakohe Mudstone contain a sparse but diverse molluscan assemblage with several new species. The overlying shallowmarine Waitui Sandstone indicates that marine regression continued through the Southland Series, with the source area for sediment becoming increasingly proximal. By the Waiauan Stage the field area, and much of northwest Nelson, was emergent. In the late Miocene east-w~st compressional tectonics associated with the Kaikoura Orogeny commenced. Late Miocene--Pliocene reverse motion on the Karamea-Pisgah-Pikikiruna Fault System uplifted the Pikikiruna and Arthur Ranges. Compression folded the sediments in the upper Takaka Valley into a synclinal fold -the Upper Takaka Syncline, and the Waipounamu erosion surface on Barron Flat was tilted to dip at approximately 10° east. Field evidence shows the range-front fault in the study area -the Pisgah Fault, is a fault zone creating stratigraphic inversions in the Paleozoic and Cenozoic sequence. Late Miocene, initial rapid uplift on the Pisgah Fault emplaced a partly gravity-driven thin skinned thrust sheet of Arthur Marble 2 westward unconformably over the Waitui Sandstone. The remnants of this deposit occur as a sheet of Arthur Marble 2 'mosaic-rubble breccia'. Pliocene dextral displacement on the Karamea Fault juxtaposed the "zone B" Arthur Marble 2 of Hoary Head, and the Onekaka Schist and Riwaka Complex to the east, against "zone A" Arthur Marble 2, having dextrally offset the northern continuation of these formations by 5 km to the northeast. Late Cenozoic deposits are restricted to almost unweathered proglacial river gravels underlying the two terraces in Upper Takaka depression, assigned to the Otiran glaciation, and localised active and calcitecemented, inactive, marble 'mixed breccia' scree deposits mantling the base of the Pisgah Fault Scarp south of Upper Takaka.

xix, 247 leaves : ill. (some col.), maps (some col.) ; 30 cm.

1998Page

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