Geology of the Murihiku Area
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20 Geology of the Murihiku Area 1 : 2 5 0 0 0 0 g e o l o g i c a l m a p I. M. Turnbull A. H. Allibone (compilers) BIBLIOGRAPHIC REFERENCE Turnbull, I.M.; Allibone, A.H. (compilers) 2003: Geology of the Murihiku area. Institute of Geological & Nuclear Sciences 1:250 000 geological map 20. 1 sheet and 74 p. Lower Hutt, New Zealand. Institute of Geological & Nuclear Sciences Limited. Edited, designed and prepared for publication by P.J. Forsyth, P. L. Murray, P. A. Carthew and D.W. Heron. Printed by Graphic Press & Packaging Ltd, Levin ISBN 0-478-09800-6 © Copyright Institute of Geological & Nuclear Sciences Limited 2003 FRONT COVER The most prominent geological feature in the Murihiku area is the Southland Syncline. The north limb, seen here looking southeast from south of Lumsden, is outlined by prominent strike ridges trending away through the Hokonui Hills. The axis of the syncline lies to the south (right) and passes under the area of cloud in the far distance. The syncline is formed in Permian to Jurassic Murihiku Supergroup sedimentary rocks, with these strike ridges in Early to Middle Triassic North Range Group. The active Hillfoot Fault separates the Hokonui Hills from the extensive Quaternary gravels of the Waimea Plains (left), underlain by Permian Maitai Group sedimentary rocks. Photo CN43841/16: D.L. Homer ii CONTENTS ABSTRACT .................................................................. v QUATERNARY ............................................................ 41 Early Quaternary deposits ........................................... 41 Keywords ...................................................................... v Middle Quaternary deposits ........................................ 41 INTRODUCTION .......................................................... 1 Late Quaternary deposits ............................................ 42 OFFSHORE GEOLOGY ................................................ 46 THE QMAP SERIES ....................................................... 1 The Geographic Information System ............................. 1 TECTONIC HISTORY ................................................ 48 Data sources .................................................................. 1 Eastern and Western provinces ................................... 48 Reliability ....................................................................... 1 Mesozoic deformation within the Median Batholith .... 49 REGIONAL SETTING .................................................... 2 Late Cretaceous tectonics............................................ 49 Cenozoic tectonics and basin development................. 49 GEOMORPHOLOGY ...................................................... 6 Quaternary tectonics ................................................... 50 Northern ranges and basins........................................... 6 Southland Syncline ........................................................ 7 ENGINEERING GEOLOGY ......................................... 51 Te Anau and Waiau basins ............................................ 7 Paleozoic to Mesozoic rocks ........................................ 51 Southland and Waimea Plains...................................... 12 Late Cretaceous and Tertiary sedimentary rocks ......... 51 Takitimu Mountains and Longwood Range................. 12 Quaternary sediments .................................................. 51 Stewart Island .............................................................. 12 Offshore physiography ............................................... 12 GEOLOGICAL RESOURCES ..................................... 52 STRATIGRAPHY ........................................................ 14 METALLIC RESOURCES ............................................. 52 Hard-rock gold mineralisation ...................................... 52 SILURIAN TO DEVONIAN ......................................... 14 Alluvial gold ................................................................ 52 Takaka terrane ............................................................ 14 Silicon and ferrosilicon ................................................ 52 CARBONIFEROUS TO CRETACEOUS ....................... 14 Other metallic minerals ................................................. 53 The Median Batholith ................................................. 14 NON-METALLIC RESOURCES ................................... 54 Median Batholith from Longwood Range Coal .............................................................................. 54 to Ruapuke ............................................................ 14 Peat .............................................................................. 55 Permian Brook Street terrane intrusives within the Hydrocarbons .............................................................. 55 Median Batholith ................................................. 16 Aggregate .................................................................... 55 Triassic- Jurassic intrusives ........................................ 16 Limestone .................................................................... 56 Median Batholith on Stewart Island ............................ 19 Silica sand .................................................................... 56 Carboniferous ............................................................. 19 Serpentinite .................................................................. 56 Middle Jurassic ........................................................... 19 Clay .............................................................................. 56 Late Jurassic to earliest Cretaceous ........................... 19 Building stone and riprap ............................................ 56 Early Cretaceous ......................................................... 22 Groundwater ................................................................ 56 Plutonic rocks of Fiordland and offshore islands ........ 22 GEOLOGICAL HAZARDS ......................................... 57 PERMIAN TO JURASSIC ............................................ 23 Brook Street terrane ................................................... 23 Earthquakes (by G. L. Downes) .................................... 57 Unassigned mélange units ........................................... 26 Tsunami (by G. L. Downes) .......................................... 60 Murihiku terrane......................................................... 26 Landslides.................................................................... 60 Willsher Group ............................................................. 28 Volcanic hazard ............................................................ 62 Dun Mountain-Maitai terrane .................................... 29 Subsidence due to mining............................................ 62 Caples terrane ............................................................. 31 Groundwater contamination......................................... 62 Paterson Group ............................................................ 33 AVAILABILITY OF QMAP DATA ............................... 63 CRETACEOUS SEDIMENTARY ROCKS ................... 34 ACKNOWLEDGMENTS ............................................. 63 EOCENE TO PLIOCENE ............................................... 35 Eocene non-marine sedimentary rocks ........................ 35 REFERENCES ............................................................. 64 Oligocene to Pliocene sedimentary rocks .................... 36 Te Anau and Waiau basins (Waiau Group) ................. 36 APPENDIX 1 Winton Basin and Southland shelf .............................. 36 Late Miocene to Pliocene non-marine sediments ........ 39 Nomenclature of units mapped on Stewart Island ....... 72 iii Te Puka o Taakitimu - Monkey Island This rocky knob near Orepuki, which becomes an island at high tide, has significance to Maaori as Te Puka o Taakitimu – the anchor stone of the legendary Taakitimu waka/canoe which was wrecked in Te Waewae Bay. It is said that the waka was turned to stone as the Taakitimu Mountains, and the bailer of Taakitimu became the Hokonui Hills. iv ABSTRACT The Murihiku 1:250 000 geological map covers 18 000 km2 Except on Stewart Island, these basement terranes are of south Otago and Southland, in the South Island of New overlain by discontinuously preserved Cretaceous and Zealand, and includes Stewart Island (Rakiura). more extensive Eocene and younger sedimentary rocks of Topography varies from flat-topped ranges and intervening the Ohai, Nightcaps, Waiau and East Southland groups. basins in northern Southland, to prominent strike ridge The contact is the widespread Late Cretaceous to Cenozoic topography of the Kaihiku, Hokonui, and North ranges, Waipounamu Erosion Surface in northern Southland. The the jagged Takitimu Mountains, the lower bushclad fault-controlled Cenozoic Waiau Basin contains up to 5 Longwood and Twinlaw massifs, and the extensive km of marine and non-marine clastic sedimentary rocks; Southland Plains. Stewart Island has generally subdued coeval but much thinner shelf sedimentary rocks, typically bush and scrub-covered topography, with rolling hills and limestones, extend beneath the Winton and Eastern the swampy Freshwater Depression in the centre. Southland basins and the Waimea Plains. Numerous other offshore islands dot the shallow waters of Foveaux Strait and the fringes of Stewart Island. The Quaternary glaciation in Fiordland and northern Southland Waiau Basin lies in the far southwest, on the eastern edge produced