A summary of the Geology of the Waipara Valley prepared by Diane Holding.
Triassic & Jurassic
The whole of Canterbury is underlaid by Triassic and Jurassic “Torlesse” basement rocks. These comprise compacted grey sandstones, black mudstones (greywacke and argillite), and, more rarely, limestones, volcanic flows and conglomerates (consolidated gravels). In the present day, the Torlesse basement rocks crop out only at the centres of structural high points, namely in the Mt Grey district, the Doctors Range, the Onepunga Anticline and the Cass Anticline.
Between 190 and 100 million years ago uplift of these Torlesse rocks formed a massive mountain range that ran the length of the South Island (this range preceded the present day Southern Alps).
Late Cretaceous
Over the next few million or so years, erosion of this early mountain range allowed the sea to reclaim the young land. The sea blanketed the remnants of the worn-down mountains with a series of younger sediments. The land surface was also deeply leached by terrestrial weathering (Clarence & Raukumara period).
Weathered estuarine and shallow-water mudstone and sandstones accumulated inshore in the ancient coastal waters. In what became today’s WVW region, the deposits were mainly siltstone. Outcrops of this sequence of rock shows a characteristic yellow efflorescence due the oxidation of sulphides of iron (Mata period). There is no evidence in the soil maps of the general area that any vineyards within the WVW Region are sited on soils of this age.
Tertiary
As the sea continued to advance over the weathering mountains, a thin sequence of fine marine sediments was deposited, mainly glauconitic (calcareous or bentonitic) siltstones and mudstones, and marls (Dannevirke & Arnold period). These depositions have since been weathered from the structural highs, and buried in the structural lows so they crop out only along major folds in the district. There is no soil map evidence that these soils directly underlie any vineyards in the WVW region.
Tertiary seas deposited thick layers of fine-grained white limestone and marls over the preceding sequences (Landon period). Warping of the deposition area caused considerable variation in the thickness of this layer. Amberley Limestone and the overlying Weka Pass Stone form distinctive escarpments throughout the district. Weka Pass Stone is more resistant to weathering than the underlying Amberley limestone which is softer due to its glauconite content. The Landon soil series appears in only one part of the WVW region, namely along the tops of the hills immediately seaward of Omihi Rd segment of SH1. The limestone in this part is not very chalky. At the site of the now abandoned Omihi Lime Co works in Omihi Rd, the limestone was of particularly high purity and was worked for agricultural lime. The soil maps indicate that in the upper slopes of Omihi Crossing Vineyard, Artemis Estate Vineyard and Limestone Creek Vineyards, this soil type is the major underlying soil type.
Later still in time deepwater-marls were deposited in the eastern area (Pareora period). The lowest layer consists of blue calcareous siltstone and minor creamy fine sandstone, cemented in places. The next most recent layer consists of blue-grey calcareous siltstone. The Pareora soil series are now exposed only on the limbs of major folds.
During the Wanganui period marine conglomerates and silts were deposited followed by freshwater conglomerates and silts. The Waipara River developed its present course during this period.
As the sea began to retreat again about 65 million years ago (Southland period), hastened by the uplifting earth movements that created today’s Southern Alps, rocks, sand and mud were eroded from the land and covered the sea floor. The general eastward tilting of the Waipara region resulted in deposition of coarser sediments in the west and finer sand and siltstone sediments in the east, including the entire WVW region.
Early Pleistocene
Deposits of freshwater gravels and sands were laid down during this period. The source of the gravels was probably alpine and resulted in an enormous flood of reddish and yellowish greywacke gravels that extended eastward and covered the whole of the Waipara area apart from a few islands formed by the highest folds projecting above the alluvial plain. Sands and silts occur as lenses. The lower marine part around Weka Creek dips at about 15-30? and contains scattered shell beds. The upper part dipping more gently consists of freshwater gravels and pebbles being deeply weathered so that they crack readily under the hammer. These gravels are about 200 feet deep in Weka Creek.
Late Pleistocene & Recent
Around this time, the general outline of the district was much as it appears today. The freshwater gravels laid down during the previous stage were however about 1000 ft above the present sea level. They filled the basin and covered the lower parts of folds and appeared as a broad plain with hills rising above it in substantially the same position as the high hills of the present day. As the shoreline retreated, thin marine deposits covered the shore platforms. The sea began to erode the shoreline. The Waipara River forged narrow gorges through structural highs and cut wide flood plains across structural depressions. Remnants of coastal benches at about 600ft above sea level show that the rivers were originally much higher. Benches cut by the early stages of degradation can be seen at a height of about 500 ft on the downs N-E of Amberley.
At around this time, the rocks in the Waipara area were folded. The folding imparted a dominant N-E trend throughout the region and in Waipara the main structural units to this day are N-E striking anticlines and synclines with axes generally plunging S-E with moderate dips in the S-E limbs of anticlines, and steep dips, in many places accompanied by overturning and faulting, in the N-W limbs.
Essentially the present Waipara area has 3 topographic units.
1. The Western Highlands including Mt Grey and the Doctors Range. Weka Pass and Waipara River cut through this highland area.
2. The Central Lowland, the downs and plains which are underlain by silt, sand and gravels of various ages, between a hundred and one thousand feet thick, being the Northern extension of the Canterbury Plain.
3. The Coastal Range including Mt Cass.
A broad depression parallel to the coast interrupts the westward increase in height and may represent the course of drainage immediately after the emergence of the coastal platform. The platform is highest near Motunau and lowest at its southern tip near the Waipara River.
The Teviotdale and Canterbury gravels are very young, geologically speaking, and were distributed along the rivers during the last glaciation. The Mound is a very fine isolated remnant of a Teviotdale gravel surface. These gravels comprise creamy-brown, leached gravels with thin bands of yellow-brown silts. The pebbles are mainly of greywacke or argillite and may be several hundred feet thick. The Canterbury Gravels, of similar rock material, are grey and brown-grey with a lower proportion of silty and sandy matrix than the Teviotdale Gravels.
During the last ice age (Hawera period) enormous glaciers carried even more gravels and sand from the mountains towards the sea, forming as they did the Canterbury plains.
The Nor’west wind blew fine yellow glacial dust (loess) from the river flats blanketing the entire area and especially depositing it up against the eastern hills. Loess was formed throughout this geological period but for obvious reasons accumulated more rapidly during periods of glaciation. In recent times there has been substantial degradation by rivers and erosion from the uplands. Remnants are confined mainly to the lower parts of the foothills.
Recent river-gravels form thin veneers of blue-grey, fresh, medium, rounded, greywacke, poorly sorted gravels with only a small proportion of sands and silts that form the matrix. They are seldom more than a few feet thick. Most of the vineyards adjacent to the rivers and streams including Mt Cass Vineyard, have this as their predominant soil type.
Structure
The tertiary rock that covered the Torlesse rock was eroded in many places but in Waipara tertiary limestones and sandstones still exist in pockets.
The Waipara River has exposed some of the late Cretaceous and Tertiary sediments.
Waipara soils are predominantly younger sediments and ice age sands and gravels.
Black Anticline
The Black anticline extends in a N-E direction from near the junction between the Omihi Stream and Waipara River to the N-E of the Waipara Valley.
Omihi Fault
Is inferred from the geology at the foot of the hills running roughly parallel with Omihi Rd. It runs alongside SH1 at Artemis Estate and roughly follows the path of SH1 in a N-E direction. It is this fault that separates the ridges of steeply dipping Pliocene and Miocene conglomerates on the S-E side of the fault from the gravel valley floor.
Cass Anticline
This is one of the major structural features of the area and although part of the Mt Cass range has little influence on viticultural land apart from protecting the valley from cold easterly winds.
Coordinates: E long 172? 35’ S lat 43? 05’
Magnetic Declination: 1957 20? 21’ East (Annual Variation +07’).
References:
Margaret A. Bradshaw, 1985, “Beneath our Feet – The Geology of Canterbury” Published by the Canterbury Museum.
D.D. Wilson, 1963, New Zealand Geological Survey: Bulletin n.s. 64 “Geology of Waipara Subdivision (Amberley and Motunau Sheets S68 and S69”, NZ Department of Scientific and Industrial Research.
