Canterbury Land District

The Canterbury district comprises four regions: the high main divide of the Southern Alps forming the western margin, composed of greywackes and argillites; the range-and-basin terrain of the foothills of similar rocks interspersed with later sediments and some volcanics; the extensive piedmont Canterbury Plains veneered with Quaternary alluvium; and to the east the volcanic complex of Banks Peninsula.

The rugged mountain ranges of the Southern Alps were uplifted during the Kaikoura Orogeny over much of their length to over 8,000 ft, culminating in peaks such as those of Mount Tasman, (11,475 ft) and Mount Cook (12,349 ft). They are formed from complexly folded and faulted greywackes and argillites, thought to be mainly of Triassic age. Large advancing glaciers and the effects of a periglacial climate have subjected the rocks to typical ice and freeze-thaw sculpturing; this has already been seen in Southland.

The second region comprises the foothills of the Alps, the basement greywackes and argillites of which apparently become progressively younger in an easterly direction. The oldest rocks are thought to occur in some of the ranges marginal to the Alps in South Canterbury, for instance, in the Kirkliston Range and Hunters Hills, which are greywackes and argillites, locally schistose, probably of Permian and Lower Triassic age. The greywackes and argillites of the foothills north-east from the Hunters Hills (for example, Torlesse and Puketeraki Ranges) are of Triassic age. These rocks continue eastwards to floor the Canterbury Plains. Where outcrops occur, as in the Cheviot area, they contain Upper Jurassic fossils. This eastward younging is shown in section D of diagram 6.

The present range-and-basin topography of this region results from diastrophism accompanied and followed by sedimentation. During the mid-Mesozoic Rangitata Orogeny, the basement rocks were uplifted and deformed. There was also a brief outburst of volcanic activity in the Mount Somers and Rangitata River area when andesites and rhyolites were erupted, together with some ash, to form beds several thousands of feet in thickness. A period of peneplanation and deep weathering produced clays. In late Cretaceous times slow marine transgression led to deposition of freshwater coal measures and marine greensands (containing marine reptiles at Waipara) followed by early Tertiary limestones, the best known being the Amuri limestone exposed at Weka Pass and widespread elsewhere in North Canterbury and Marlborough.

With the onset of the Kaikoura Orogeny the sea retreated and, during the uplift of the Southern Alps, the region was fractured by numerous faults. Extensive fault-bounded blocks were raised to varying heights and tilted to angles commonly of 10–20°. The tilted fault blocks so formed comprise the foothills of the Alps, the intermontane “lows” corresponding to depressed or little raised blocks, for example, the Mackenzie Plains and Hanmer Basin. (Cross-section D shows this tectonic structure with the more recent glacially scooped Lakes Pukaki and Tekapo lying on the Mackenzie Plains.) As the uplifted blocks rose, the relatively weak cover of Cretaceous and Tertiary strata was rapidly stripped from the Mesozoic basement rocks so that the younger rocks are preserved only in some marginal areas, as at Waipara and Weka Pass. The tectonic basins filled with Quaternary debris.

The material derived from the stripping of the fault blocks during the late Tertiary was deposited in the sea immediately to the east over the submerged Mesozoic basement rocks. These constitute the deeper strata of the third region of the land district, the piedmont plains. During Pleistocene glacial periods this aggradation was accelerated. Ice erosion attacked both the soft cover and hard basement rocks of the uplifted blocks, and vast quantities of coarse debris were deposited by glaciers as terminal moraine and thence washed down to the plains by huge rivers, such as the Waimakariri, Rangitata, and Rakaia. Enormous depths of gravels accumulated in the intermontane basins and built up the present surface of the Canterbury Plains. Loess deposited under periglacial conditions mantles the gravels and is sometimes up to 60 ft thick.

The fourth region, comprising the two basaltic and andestic cones of Banks Peninsula, was built up in the early and middle Pleistocene, and volcanic activity also occurred at this time near Timaru and Geraldine in South Canterbury. Both the Banks Peninsula cones have been cliffed by the sea and radial drainage has eroded numerous valleys, now drowned in their lower parts by the post-glacial rise in sea level to form bays as at Port Levy and Pigeon Bay. The sea has breached both cones, gaining access to the craters and forming Lyttelton and Akaroa Harbours.

Earthquakes occur frequently in Canterbury, especially the northern part, indicating that the earth movements responsible for the rise of the Southern Alps and other ranges are still proceeding. The Hope Fault, which branches off the Alpine Fault and extends along the southern side of the Hanmer Basin and into the Seaward Kaikouras of Marlborough seediagram 8), is particularly active and movement on it in 1888 (Glynnwye earthquake) produced horizontal displacements. An earthquake in 1929, locally known as the Arthur's Pass earthquake, had its epicentre on this fault. The Cheviot earthquake of 1901 produced some superficial slumping but no known scarp, as any movement in the underlying Mesozoic rocks was probably cushioned by the cover of soft Tertiary strata.

Canterbury is not well endowed with economic mineral deposits, but it does have abundant supplies of limestone in the Tertiary rocks, small areas of marble in the greywackes and argillites, and plentiful good quality gravel deposits. The Canterbury Plains form an important ground water system, providing water for domestic and industrial use and for irrigation.

Marlborough Land District

A dominant feature of Marlborough geology is the presence of major active transcurrent faults which slice the region into blocks. The Wairau Fault, one of the branches of the Alpine Fault, divides Marlborough into two regions of contrasting geological structure. Northward lie the Upper Paleozoic greywackes and schists of the Richmond and Bryant Ranges and the Marlborough Sounds; southward lie basement greywackes and argillites of Triassic to Cretaceous age with younger sediments in tectonic depressions see section C of diagram 6). The fault pattern imposes an overall north-east-trending series of tilted mountain blocks, fault scarps, and faultangle valleys; drainage is parallel and to the northeast, the whole land district dipping toward Cook Strait, this being more pronounced north of the Wairau Fault.

The region north of the Wairau Fault is composed of greywackes and argillites of Permian and Carboniferous age, merging into a wide central belt of schists which are terminated abruptly to the south by the fault itself. The Alpine Fault, extending through the south-eastern part of Nelson district, in the Tophouse area, splits to give the Wairau Fault and (in Nelson district) the Eighty-Eight Fault and its continuation, the Whangamoa Fault, which bound the Richmond and Bryant Ranges to the north. The Marlborough Sounds, a complex system of embayments formed where these ranges dip into Cook Strait, have probably been formed by the drowning of entire valley systems during the worldwide rise of sea level which followed the melting of the Pleistocene ice. Tilting movements of the entire block between the Whangamoa and Wairau Faults may also be partly responsible see inset, diagram 8).

The region south of the Wairau Fault is split by further branches of the Alpine Fault, the major ones being the Awatere, Clarence, Kekerengu, and Hope-Kaikoura Faults. (These may be correlated with North Island faults; see inset, diagram 8.) The Mesozoic basement greywackes and argillites are thus faulted into a series of blocks, the most impressive of which are the Seaward and Inland Kaikoura Ranges, culminating in the peak Tapuaenuku (9,465 ft), of Jurassic and Cretaceous greywackes and argillites intruded by dyke swarms. See section C of diagram 6.) These geosynclinal deposits continued to accumulate throughout the Cretaceous period, so that a remarkably complete sequence of Cretaceous rocks is exposed, as, for instance, in the tectonic depression of the Clarence Valley, where may be seen the transition in later Cretaceous times to more massive, less indurated sandstones and mudstones of the Mata Series, which include flint beds, sulphurous mudstones, shales, and greensand. These are succeeded in many places by Tertiary marine sediments, the oldest being Paleocene flint beds, overlain by the Amuri limestone and bentonitic mudstones. This limestone forms dramatic white ridges which may be followed almost the length of the Clarence Valley, continuing around the “nose” of the seaward Kaikoura Range to form Ben More and other peaks. Amuri limestone also forms the resistant cliffs of the Kaikoura Peninsula and the small peninsula of Piripaua (Amuri Bluff), famous as the site of richly fossiliferous Upper Cretaceous strata, the source of some of New Zealand's large Cretaceous reptile fossils.

Volcanism is much in evidence in Marlborough. Intense volcanic activity took place late in the Rangitata Orogeny during mid-Cretaceous times when many dyke swarms and a few sills were intruded through the greywacke, particularly in the Inland Kaikoura Range (for example, Tapuaenuku). Terrestrial and marine basalt flows and tuffs were extruded on the surface, and the largest mass of these rocks forms Mount Lookout (5,933 ft) in the Upper Awatere Valley, towering over an area some 10 miles square of olivine-basalt lavas and interbedded tuffs up to 3,000 ft thick. The feeder dykes for these flows are well exposed.

The Kaikoura Orogeny (named from this region) began in Marlborough in the mid-Miocene. The Kaikoura Ranges and other Marlborough mountains were upthrust, and the Alpine Fault and its ramifications block-faulted the basement greywackes and their Cretaceo-Tertiary cover rocks, reaching a climax in the late Pliocene and Pleistocene. As the land rose, marine sedimentation became restricted to the depressions between rising mountain blocks and erosion stripped much of the cover of early Tertiary rocks, so that these are preserved only in fault-angle valleys. Blenheim stands on Quaternary alluvium which floors the Wairau Valley, a broad fault-angle depression bounded to the north by the Wairau Fault.

As may be seen in diagram 8, many active fault traces transect Marlborough and prominent scarplets are known along all of the major faults. Movements on these faults are continuing at the present day, giving many tremors and earthquakes. Precise annual surveys across some of them have disclosed horizontal displacements of over an inch per annum. The Wairau earthquake of 1848 caused subsidence of 5 ft in the lower Wairau Valley and was widely felt throughout the southern part of the North Island.

Marlborough's economic resources mainly consist of gravel, sand, and limestone, though alluvial gold, derived from the schists, has been won in the Wairau Valley.

by Geoffrey Conrad Shaw, B.SC., New Zealand Geological Survey, Lower Hutt and Graeme Roy Stevens, M.SC.(N.Z.), PH.D.(CANTAB.), Paleontologist, New Zealand Geological Survey, Lower Hutt.

• New Zealand Geological Survey Bulletin, n.s. 66, “The Geological Map of New Zealand 1:2,000,000”, Grindley, G. W., Harrington, H. J., Wood, B. L. (1959)
• Geomorphology, seventh edition, Cotton, C. A. (1958)
• geological maps, geological and palaeontological bulletins issued by New Zealand Geological Survey, Department of Scientific and Industrial Research; geological and palaeontological articles in theNew Zealand Journal of Geology and Geophysics, New Zealand Journal of Science and Technology and Transactions of the Royal Society of New Zealand
• Tuatara 10 (2), “New Zealand Biogeography”, Fleming, C. A. (1962)
• Descriptive Atlas of New Zealand, McLintock, A. H. (ed.), 1959.