Quaternary (map symbol W, Q)

The Quaternary period is subdivided into earlier (lower Quaternary, W) and later (upper Quaternary, Q) parts.

Distribution
There are no areas in New Zealand entirely free of Quaternary sediments, even if it is only present-day river alluvium or slope debris. Quaternary deposits are an important part of the present-day landscape and wide tracts of country are entirely of Quaternary age, such as the sand dune deposits of Northland, the huge volcanic plateau of the central North Island, the alluvial plains of Hawkes Bay, Wairarapa, Canterbury and Southland, and the glacial deposits of the South Island high country.

Content In the North Island, sediments of both marine and non-marine origin occur, and volcanic deposits are widespread in the north. South Island sediments are mainly non-marine.

Quaternary marine sediments are all of early Quaternary age and are restricted to the Wanganui, Wairarapa, Hawkes Bay, and Bay of Plenty areas, and around Parnassus in north Canterbury. In general these are shallow water deposits of sand and mud with shell beds and some limestone, commonly with a high pumice and ash content particularly in the Bay of Plenty and northern areas of Hawkes Bay. Barnacle coquina limestone is present in the Wairarapa, whereas the limestone in Hawkes Bay is made up of other shelly material and contains more muddy lenses.

Non-marine deposits vary depending on their locality, with glacial and fluvial deposits being predominant in the South Island, and fluvial and aeolian sediments common in the North Island. In the north of the North Island, lake muds, fluvial gravel and sand with a high pumice and ash content, and commonly forming terraces, represent the early Quaternary. Dune sands started to build the Ninety Mile Beach and the prominent bars to the Kaipara, Manukau, Raglan, Kawhia, and Tauranga harbours. In the southern part of the North Island gravel derived from the rapidly rising mountain ranges was deposited at the margins of the marine basins, especially in inland Hawkes Bay, Wairarapa and Wanganui. Later in the Quaternary the marine basins had disappeared and the deposits were mainly fluvial gravels and sands. Spectacular flights of river and coastal terraces were formed at this time, as well as the bulk of dune deposits around the coasts, the dunes of the Manawatu plains being a fine example. A very fine grained wind-blown deposit called loess is widespread and quite thick in some parts of the south of the North Island.

Quaternary image

In the South Island, lower Quaternary deposits are mainly represented by alluvial gravels and coastal deposits in north Canterbury, Southland and coastal southern Fiordland. The oldest gravels in these areas are probably Pliocene in age but deposition continued well into the Quaternary. Later on in the Quaternary the deposits are mainly glacial in origin, with till and outwash gravels being particularly prominent on the West Coast and in the mountainous areas. The Canterbury Plains are built up from outwash gravel, and once extended beyond the present-day coastline. Thick loess deposits, especially in south Canterbury and south Otago, also date from this time. In many areas around the coast there are remnants of marine benches, as well as substantial dune accumulation, while inland, valleys were infilled with alluvium.

The products of intense Quaternary volcanism are readily visible in the northern part of the North Island. The main area of volcanic rock is concentrated in a "V" shaped area with the Tongariro National Park volcanoes forming the southern apex and widening to include the Rotorua area and most of the Bay of Plenty. This area is known as the Taupo Volcanic Zone. The most common rock type in the zone is ignimbrite, formed when extremely explosive eruptions forced vast glowing clouds of hot gaseous ash and debris to flow at great speed to considerable distances from their source - up to 60 kilometres. The heat in the flow caused the particles to weld together. The ignimbrite can be up to 150 metres thick and forms flat-topped plateau areas around and north of Lake Taupo. Other types of eruptions formed rhyolite domes such as those around Rotorua and Taupo, notably Mounts Tarawera, Ngongotaha, and Tauhara, and dacite is present south of Rotorua. Eruptions were not only of lava, but copious quantities of ash and pumice were also erupted to settle in great thicknesses over the landscape. Ash and pumice are major constituents of Quaternary sediments in areas quite a distance from the volcanic activity. Pumice, particularly, is found a long way from its origin (e.g., on Wellington beaches), as it is light enough to float and is easily transported by the sea and rivers. The more recent eruptions of the Taupo Volcanic Zone have been andesitic in character, as demonstrated by the Tongariro Park volcanoes, Mount Edgecumbe, and White Island, while the most recent eruption of Mount Tarawera in 1886 was basaltic.

TVZ image

Quaternary volcanism was not confined to the Taupo Volcanic Zone. In Northland and around Auckland city, basaltic volcanoes were active, erupting basalt and building scoria cones. Offshore, Little Barrier Island was formed from andesite, and islands east of Coromandel from andesitic and rhyolitic eruptions. On the west coast, Pirongia and Karioi built up cones of basaltic andesite in the early Quaternary, while at the same time in the Taranaki region the Sugar Loaf Islands were built of andesite. Taranaki volcanism then migrated south through the cones of Kaitake and Pouakai to Mount Egmont (Taranaki), all andesitic in character and successively younger in age.

A particular type of deposit associated with the volcanic centres of Tongariro and Taranaki is that formed by lahars. This deposit is made up of a chaotic assortment of volcanic material which has flowed down the mountain and then spread out over the surrounding countryside. A lahar may be generated by collapse of a volcanic cone, by earthquake activity, or by particularly heavy rainfall. If water from a crater lake is involved, the amount and size of debris that is transported and the distance travelled can be very large. During glacial periods the mountain tops were capped with ice and snow which melted when an eruption took place and was a source of water for transport. The conical hills on the western slopes of Mount Egmont are a good example of a landscape formed by lahars.

The only Quaternary volcano near the South Island is the andesitic Solander Island west of Foveaux Strait.

It is relevant to consider present-day deposits, as we still exist in Quaternary time and geological processes are continuing. The material in present-day river valleys and beaches has been mainly deposited since the last glacial stage ended, about 14 000 years ago. From then until about 6000 years ago there was a substantial warming of climate which caused a rise in sea level; some cliffs, terraces, and dune deposits are recognised as having formed at the time that sea level rise ended. Sea level has dropped again slightly since that time. Lakes, including artificial ones, are presently collecting mud and sand and will eventually fill, while many river flood plains are building up with each flood. Sand dunes naturally advance, blown by the wind until stabilised by vegetation; evidence of Maori middens being covered by advancing dunes is common. Volcanoes may erupt to build higher cones or explode destructively; ash showers continue to fall on the land while geysers and boiling mud pools are evidence of activity beneath the ground. Earthquakes create deposits by shaking which causes landslides and further erosion.

Floods

Humans are having a small effect on geological processes, mainly by controlling rivers, and developing the countryside. Floods are prevented by building stop banks, channelling material out to sea instead of over the flood plain; this affects the buildup of deltas and beaches, and erosion. River valleys can become choked with debris because clearance of natural vegetation and overstocking can cause landslides and gully erosion, providing more material than the river can carry away. Coastal buildup and erosion is also affected by human activities; building groynes and sea walls may protect one area but expose an adjacent area, while dredging sand and gravel can also affect the natural processes. Hydro-electric power schemes and irrigation schemes divert rivers and form lakes, markedly changing the natural fluvial regime.

Paleogeographic conditions
In the early Quaternary the southern part of the North Island was under a shallow sea, as were parts of the east and west coasts of the South Island. By the mid Quaternary, tectonic movements, uplift and deposition had brought New Zealand to roughly the shape it is today. The rapidly rising areas of the Southern Alps contributed masses of debris to the rivers, and filled depressions and river valleys.

Periods of cold climate occurred throughout the Quaternary, not only in New Zealand but globally. During the coldest periods the high parts of the Southern Alps were under a permanent ice field, and valley glaciers carved their way both west and east, and coalesced into ice sheets where the topography became more gentle. Vast amounts of debris were carried within and on top of the glaciers as well as pushed in front of them. This debris (till) was dumped when the ice melted and forms a distinctive hummocky ground surface, well illustrated by the topography of the Mackenzie basin. Meltwater from the glaciers carried debris away and formed large outwash fans. Each major phase of glaciation built up moraines and outwash plains, and successive terraces were subsequently cut by rivers draining through them. The spectacular terraces on the Canterbury Plains were built up in this way. The worldwide glaciations caused sea level to drop, as much water was bound up in ice and snow. During warmer interglacial periods, the ice melted and sea level rose. The effect of these oscillating sea levels is clearly seen in uplifted coastal terraces, each flat surface marking the position of an earlier high sea level. Periods of low sea level and cold climate created expanses of bare earth and sand with little vegetation. Winds blew the coastal sand into dunes while dust particles were blown and deposited on rocky and planar surfaces to become loess.

In the North Island there was little active glaciation except in the very highest mountain areas. The effects of cold and oscillating sea levels were the same as for the South Island, so that marine benches and flights of river terraces were formed. The buildup of sand dunes and loess accumulation, were a result of low sea levels and cold climate.

Deformation
The Kaikoura Orogeny continued from the Pliocene throughout the Quaternary, as it does to the present-day, with earthquakes and fault movements. The New Zealand landscape, as we know it, is the result of this orogeny, as is the recent past and present volcanic activity. Some of the marine sediments of early Quaternary age are folded and tilted quite substantially especially if associated with faulting, but most sediments of Quaternary age are essentially flat-lying. Volcanism is certainly not extinct, as illustrated by continued activity in the Taupo Volcanic Zone.