Omana Regional Park

O-manutere pa site showing ring ditch.

On the perimeter track, visitors will find a grassed area, overlooking the sea, which was the original site of a Ngai Tai pa[4] (see Maori Pa). This grassed area has a deep ditch whose internal bank would have once been much higher and topped with a strong palisade of posts. O-Manawatere is a relatively small pa. Maori were building pa (earthwork forts) throughout New Zealand, starting from around the 16th century. In total they built about 7,000 mainly in the North Island. Most pa were not permanently lived in, but were built close to kainga (villages) and were designed as safe places in case of attack. The depressions inside the pa are pits, once roofed over and used for storing kumara tubers, but now largely infilled but still visible.[5]

The parks name ‘Omana’ is short for O-Manawatere ("the dwelling place of Manawatere"). According to legend, "This man Manawatere came from Hawaiki, he did not come in a canoe (waka), he glided over the ripples of the waves".[6] The ARC information board beside the pa says he rode on the back of a taniwha.

Ngai Tai along with members of other Hauraki tribes, lived in the Omana park area for many generations. The park was part of William Fairburn's Maraetai Mission Station which included a small school for Maori from 1837 - 42. Omana was part of the mission farm, developed from 1837. The forest covering the park and surrounding area was felled for timber by European settlers who cleared the land for farming during the mid-1840s. Kauri felled in the Maraetai hills behind Omana was hauled by bullock teams down to the sea and then floated to mills in Auckland.[7] The Omana park area was also dug for kauri gum and even prospected for gold and silver.[8] In 1852 following the discovery of gold in Coromandel many searched the hills digging shafts wherever quartz veins could be located.[9]

Southern black-backed gulls at Omana.

At least twenty-six different types of bird are found in the park. natives include: pied stilt, pukeko (Porphyrio melanotus), kereru, tui which appears almost black except for a white tuft under its chin, fantail, grey warbler, red-billed gull, southern black-backed gull (see kelp gull), South Island pied oystercatcher and the closely related variable oystercatcher (Haematopus unicolor), pied shag, kingfisher, and white-faced heron.[10] The white-fronted tern can be found resting on the greywacke outcrops which become visible at low tide (see pic in geology section).

Omana shore platform, sandstones about 19 million years old.

The beach and extensive rock platform, form the northern boundary of the park. The whole of Omana Regional Park is underlain at a depth of 30 – 100m by ancient greywacke (a harder basement sedimentary rock).[11] The greywacke belongs to the Waiheke group. The softer more recent sandstone is of the Waitamata group.

Ancient (200-million-year-old) Greywacke outcrop. Omana.

The layered sandstones and siltstones (mudstones) are seen in the cliff faces and also form the shore platform around the north and west sides of the park. These softer, generally yellow-brown rocks are approximately 19-20 million years old and are made up of the Waitamata formation (East Coast Bays facies) of early Miocene (Late Otaian) age.[12] Distortion and faulted dipping, of this once soft strata, can be seen both in the cliffs and in the small ridges of the rock platform extending out from the beach at low tide.

Ancient Greywacke, poking through the 19-million-year-old mudstone shore platform.

What makes an interesting discovery is that protruding through the softer yellow-brown sedimentary sandstone and mudstone layers, there are ancient (200-million-year-old) tips of greywacke sea stacks from the Jurassic age.[12] They are older and harder (cut or formed from the original 200-million-year-old greywacke about 25 million years ago). They are about 1–2 meters high and are found in the shore platform, about 200 metres east of the park at Omana Beach.[12]

Holocene sands (less than 7000 years old) form the flat area behind Omana Beach and at Te Puru Creek.[10]

Greywacke - an ancient sedimentary rock. Omana.

200 - 150 million years ago sand eroded from the super-continent Gondwana into a deep trough in the sea floor. These deposits were kilometers thick and compressed, folded and heated became hard greywacke.

150 - 120 million years ago The hard greywacke was uplifted and became the first mountainous backbone of New Zealand. 120 - 70 million years ago the mountain ranges were eroded to a great degree. 35 – 15 million years ago the sea completely covered much of New Zealand. During this long quiet period, sediments were deposited over the old basement rock and gradually metamorphosed into sandstones. 15 – 5 million years ago The greywackes were again uplifted (Late Miocene). This second set of earth movements, known as the Kaikoura Orogeny, elevated large fault-bounded blocks to form the horsts (upfaulted blocks of land) of the Hunua and Coromandel Ranges, and threw down the grabens (down-faulted blocks) of the Firth of Thames and Hauraki Gulf which Omana now overlooks.[13]

Salt marsh, Te Puru creek. mangroves and kanuka

Apart from the pohutukawa and grass areas, there is a southern patch of mature tanekaha and a northern patch of puriri (ripe red berries) and taraire. Other large trees include rewarewa, mapou, kowhai, totara, tree ferns, cabbage trees, and kahikatea. Kanuka can be found on the slopes of the Te Puru creek (the estuarine mangrove salt marsh).[14]

Cockle shells on Omana beach.

The intertidal ecology is mainly composed of three areas:

• Rocky shore platform with small pools at low tide on north and west of the park are occupied by small barnacles, rock oysters, Neptune's necklace (a sea weed) and tube worms.
• Sand and mudflats surrounding the shore platform contain cockles, pipi (Paphies australis), crabs and Polychaete worms. Because of the cockle bed out in the sea, the cockle shells wash up high on the beach during storms. The sand can be found underneath.
• Mangroves with mud snails (Amphibola crenata), small mussels and barnacles.[15]

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  Puriri (Vitex lucens) at Omana with red berries in summer.
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  Neptune's necklace, Omana.
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  Dry grass of February. One sheep on the horizon, Omana.
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  Young kauri on the perimeter walk.
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  Oyster shells on Omana beach.
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  Raupo at Omana.
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  Kumara pit on the pa site.
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  Goats and cabbage trees in the ditch beside the pa site.
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  Goat with the pa ring ditch in the background.
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  Two variable oystercatchers Haematopus unicolor. Omana.
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  Mud snail near mangroves. Amphibola crenata (titiko).
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  White-fronted terns on ancient Greywacke sea stack.