GEOLOGY OF THE GREYMOUTH AREA - GNS Science

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Taramakau, suggest 3- 10 Ian right lateral shifts, althoughthe evidence is equivocal. For example, it is inferred thatthe glaciers that once filled the Kokatahi-Toaroha-Styxcatchment may have previously flowed into Lake Kaniere.Western mountainsThe north-trending Victoria and Brunner ranges and theNNE-trending Paparoa Range are separated by the Greyand Inangahua valleys, with range-and-basin topographyresulting from late Cenozoic tectonic shortening.The higher parts of the ranges show abundant evidencefor g lac iation including cirques, hanging va lleys anddeposits of till.The Paparoa Range has a maximum height of 1525 m atMt Uriah, where rugged peaks and ridge tops surroundglacial cirques cut in hard crystalline gneiss and granitoidrocks. The western flank of the Paparoa Range dropssharply to a large low-lying dissected area underlain byCenozoic sedimentary rocks. The eastern flank is morecomplicated with subsidiary ranges and two major riversystems (Grey and lnangahua).The Victoria Range, rising to 1749 m at Mt [vess, also hasglacial cirques and hanging valleys cut into hard crystallinerocks. The eastern flank of the Victoria Range descendssteeply into the Maruia River, whereas the western flankhas an intricate pattern of deeply incised rivers withmultiple branches in their headwaters.The Bullerand Grey rivers have incised deep gorges acrossthe Paparoa and Victoria ranges. The gorges arespectacular evidence that the rivers have maintained theirwestward path from the Southern Alps as the mountainshave been uplifted during the Quaternary. Many smallerstreams have been deflected to flo w parallel to the ranges.Tn a detailed analysis of the defonnation of terraces withinthe Upper BullerGorge (Fig. 9), Suggate (L 988) has shownthat uplift takes pLace by a combination of faulting androlding, reflecting deformation of the underlying Tertiarysediments that continues to the present day. Approximately350000 years ago the Buller River flowed along a muchwider floodplain, now preserved as high terraces, and hassubsequently cut a narrow gorge.Lowland areasBetween the major ranges extensive low-lying areasi!1 clude the Grey-lnangahua Depression and theMaruia vall ey. These areas are tectonic graben orhalf-graben that have been partially filled by MiddleMiocene to late Quaternary coarse-grained sand and graveldeposits.The lowland areas also have preserved a longhi story ofglacial and interglacial events, with deposits thatrecord at least five glaciations and three interglacials.Moraines are preserved near the coast in the southwestaround the western fl anks of Mt Greenland,and in an arcuate lobe between Kumara and Lake Haupiri,10 kmTasman SeaFigure 4 Shadedtopographic relief model ofthe Greymouth map areaderived from 20 metrecontour data supplied byLand Information NewZealand (L1NZ), illuminatedfrom the northeast.5
Figure 5 Lake Browning lies just below Browning Pass (1400 m), a low-altitude pass on the Main Divide just west ofMt Davie. The headwaters of the Wilberforce River (foreground) give access, via a historic zig-zag miners' track, up thesteep escarpment to the pass. The Arahura River, which drains Lake Browning, flows through deep gorges to the lowlyingland west of the Alpine Fault (distance), and thence to the sea.Photo CN10403l18: D.L HomerFigure 6 The Southern Alps are formed of hard, greywacke-type rocks of the Rakaia terrane. Rock avalanches andalluvial fans, often triggered by earthquakes, are a feature of the landscape. The large rock avalanche in the foregroundcollapsed from the northwest side of Falling Mountain during an earthquake in 1929, transporting an estimated 60million tonnes of broken rock into the west branch of the Otehake River.Photo CN38312121: D.L. Homer
Page 3 and 4: GEOLOGY OF THEGREVMOUT;H AREAScale
Page 5 and 6: CONTENTSABSTRACT . v LATE CRETACEOU
Page 7 and 8: 170" E: 175" E'%~O ::>_~ : ~- -- --
Page 9 and 10: ..""..""..""1 Angus 19842 Becker &
Page 11: Cretaceous & Cenozoic sedimentary r
Page 15 and 16: Figure 9 About 350 000 to 250 000 y
Page 17 and 18: Northwest of the Alpine Fault, the
Page 19 and 20: Figure 14 Gneissic rocks of the Bul
Page 21 and 22: Figure 15 Quarry in SluiceBox Limes
Page 23 and 24: 16Figure 17 A selection of U-Pb dat
Page 25 and 26: Figure 18 Typical lithologies of th
Page 27 and 28: Figure 20 Typical sedimentary litho
Page 29 and 30: association. The boundary between t
Page 31 and 32: Figure 22 Gently dipping Paparoa Co
Page 33 and 34: Figure 24 Aerial view of an opencas
Page 35 and 36: Figure 27 Panoramic view looking ea
Page 37 and 38: Late Miocene to Pliocene sedimentar
Page 39 and 40: Interglacial Glacial Ag. a-isotopeS
Page 41 and 42: Alluvial depositsAlluvial and f1u v
Page 43 and 44: Postglacial lake deposits of peat a
Page 45 and 46: J:,..,.~~ "'~}ii;~ ': ~, ' tf[' ~-;
Page 47 and 48: Figure 43 Deep opencast pit (centre
Page 49 and 50: Figure 44 A large lens of earliest
Page 51 and 52: UndergroundOpencastMeasured Indicat
Page 53 and 54: GEOLOGICAL HAZARDSSeismotectonic (e
Page 55 and 56: Figure 49 The hillside beneath Mt R
Page 57 and 58: Figure 51 Active landslides and scr
Page 59 and 60: REFERENCESAdams, CJ.; Harper, C.T.;
Page 61 and 62: 54Gair, H.S. 1962: Notes on the geo
Page 63 and 64:
Nathan, S. 1978b: Sheets S31 & part
Page 65 and 66:
Waight, T.E.; Weaver, S.D.; Muir, R
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