Geology of part of Swinburn survey district, North Otago.

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Sang Lyen, Albert.

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INRODUCTION A geological investigation of part of Swinburn Survey District , North-east Otago_was undertaken in partial fulfillment for requirements of the degree of 1'-l.Sc. at the University of Otago, Dunedin. The area covers about 42 square miles at the western foot-hills o~ Kakanui Ranges and forms the most-easterly extension of Maniototo Plain. Much of the area is under 2 1500 feet elevation above sea-level. Swinburn Peak (Trig. I., 2 1395 feet), Flat Hill (Trig. K. , 2,760 feet ), and Trig. L (2,536 feet) ,are the most elevated areas. However, the lowest recorded elavations are greater than 11 300 feet. Field work was based on use of aerial photographsj' sujljllemented by the New Zealand Cadastral 1\-fap Survey District Series, Otago (OT ) 77, and Williamson (1939, Map. No.5). A base map of the area ~as compiled from the aerial photographs and then the geographic features were incorporated from data given in the Cadastral Map, Otago (OT) 77. The final map (Pl.1) was not drawn on the conventional scheme, but its orientation has been selected to suit the requirements . of the student. Contouring of the surface was not attempted due to the limited number of available spot ht.ghts. The whole area is covered by NZMS. 1 : 63,360, Sheet Number S 135 .I The aerial photographs that were used are , Runs 2R!56 1 2857, 2858 , and 2868.0nly parts of the Flight Runs were n@~ded. 2. which has not been published yet o The basement rocks are divided into Chl.2 semischists and CH1.3 schists on textural grounds. Above Chl . 3 schists in the present area are a succession of marine and non-marine sediments. The sediments may be overlain by Late Tertiary vol~anic flows. The sediments belong to Hogburn , Swinburn , Wedderburn, and ~'laori Bottom Formations. Recent and Terrace gravels are widespraed. Microfossil dating indicates Duntroonian age for the Swinburn Formation. Much of Wedderburn Formation of previous workers is now included i n Swinburn Formation on fossil evidenceo Volcanic material s are divided into ten petrographically distinct flows. An intrusive alkaline o l ivine-dolerite is described. Movements of great displacement are indicated for the Waihemo Fault Complex. The last major post- volcanic movement i ndicates a displ acement of at least 2 , 300 feet vertically with Kakanui Ranges as the upthrown block . GENEHAL ACCOUNT OF THE AREA . The present area has easy access to Dunedin via Provincial Highways 85 and 87. Highway 85 is ' Pigroot Road ' passing through Palmerston (South) while Highway 87 passes through Middlemarch. The ~~~iunal centre is Ranfurly a t a distance of 12.6 miles to the west o A general aridity of the area is reflected in the small volume or euen l ack of water in the numerous int ermitent creeks 3. and streams that drain the area. This is especially true during the long dry, hot sunmters. Among the vegetable growth the soil can support only tussock and feed-grass for the scanty eattle and shepp. In winter extremely cold conditions prevail. The mountain tops on the Kakanui Ranges to the East are snow-covered. The snow-cover may extend to the low - lands during the severest parts of winter (July- August). Geological investigation of the Central Otago division has attracted the earlier geologists. A historical sketch has been given by Cotton ( 1917). Following Cotton who agrees well with McKay (1884,) much of the Central Otago land surface, is an old prolonged erosion surface named the 'Cretaceous Peneplain '. This fossil plane has been tilted, f a ulted, folded and later covered by Tertiary sediments. The sediments may be capped by Late Tertiary volcanic flows. The present Central Otago topography of alternating basinal and fold mountains have been attributed to ' Block movements' in which the movements are accomplished through faulting or by faulting replaced to a minor extent by monoclinal flexures (Cotton, 1917). As such, the S.W. flange of the Kakanui Ranges to the East forms a tilted, fold mountain with a ma turely dissected fault scarp facing ~ianiototo Plains to the West, across the Taieri River. Southward, the area extends into Barewood Plateau which is an undulating maturely dissected schist surfa ce 4. with a l arge number of schist-tors. The area forms the head water region of the s .E.- ward flowing Shag Hiver, ( also named the Waihemo River) with t he Pi groot Creek as its main contributary branch, and forming a deeply entrenched course into the basement schist. The deep incision into schist however dimi nishes to form a gradually widening valley as the coast is approached to the south-east. The Shag is a permanent, moderately fast flowing river in contrast to some of the intermittent streams that drain the area to the general -.-'est and South-west. Such rivers and streams include certain fe eding channels of the Swinburn and Houndburn Hivers, both of which however are permanent streams entering into t he Tai eri River at Kokonga, a small railway-station on the Central Otago ~l ailway line. Much of t he stream courses t hat have been incised into the underly ing rocks have little or no water and serve only as irregularities into the topographic picture. Except for the development of small minor pools, the only other bodies of non-flowing water are the sca ttered man-made dams for sheep and cattle. Large-scale faulting and folding movements have taken place affecting both the undermass of schist and greywacke, and the overmass of sediments and volcanics. The largest of such faulting movements is along the Waihemo (Shag Valley) Fault Complex along which great vertical eomponental movements have taken place. Also 5. important are faults in the sedimentary and schist rocks in which the trends of such faults subparallel the Waihemo Fault trace. PREV'IOUS WORKS. The earliest geologic mapping and investi~ation of the present area must be credited to Williamson (1939) who produced a geological map on the scale of 1 : 63,360, and then made brief references to the area. McKay (1884) , Hector (1865), Henderson (1929), and Morgan (1920) all have been in some proportions responsible for earlier works on which Williamson (1939) has made references. Harrington (1955) redescribed the Tertiary Formations of Naseby District , and proposed a recognition of a post-volcanic non-marine Formation.t. This non-marine Formation containing freshwater Diplorlon sp. was not found in thepresent area. Raeside ( 1953) suggested criteria for recognition of Wedderburn Formation beds f rom a later Maori Bottom Formatd.on. The suggested criteria cannot be successful.ly applied ih the present area wherP. Maori Bottom beds never overly Wedderburn beds A detailed petrographic study of the volcan~c rocks on Siberia Hill - Mount Dasher area, lying to the east of the present area was complieted by Brown ( 1955 ) who compiled a series of successi~e flows. Some of the flows in this area are closely paralled in the present area. The two locallities are separated through a vertical distance of at least 2,300 feet across the Waihemo }i'aul t Complex. I The post-volcanic non-marine beds belong to the Surface Hill Formation (Harrington , 1955). 6 . The latest description of metamorphic rocks of the present area is by Turner (in Williamson , 1939) , who classified the rocks as ranging in metamorphic textural grade from Chl.1 to Chl.4 Subzones of the Chlorite Zone.However , no true Chl . l or Chl.4 Subzone rocks were found during the present field work .

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145 leaves : illus. (part col.), map in pocket ; 27 cm.

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1962Sang_Lyen

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POLYGON ((170.277021565143826 -45.141364077055364,170.366763239514626 -45.118223753006156,170.418038602108425 -45.174651007440978,170.440624097871961 -45.166585569337698,170.475141805506098 -45.19971572215271,170.371266383587852 -45.238811946066626,170.277021565143826 -45.141364077055364))

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http://download.otagogeology.org.nz/temp/Abstracts/1962Sang_Lyen.pdf

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Sang Lyen, Albert., “Geology of part of Swinburn survey district, North Otago.,” Otago Geology Theses, accessed May 22, 2024, https://theses.otagogeology.org.nz/items/show/12.

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