Hautotara, Te Muna and Ahiaruhe Formations, middle to late Pleistocene, Wairarapa, New Zealand.

Abstract

The Hautotara, Te Muna and Ahiaruhe Formations are formally described for the first time. The Hautotara Formation contains the littoral marine and estuarine deposits of the Huangarua Cyclothem together with underlying freshwater deposits which have been added for mapping convenience, and is considered to be late Marahauan (c. 1.2 to 1.05 Myr) in age. The Te Muna Formation is a conformable sequence, 366 m thick, containing fifteen members. Alluvial gravels alternate with freshwater blue-grey silt and sand with lignite layers, tree roots in growth position and occasional paleosols. The Te Muna Formation also contains loess at one horizon, and localised rhyolitic tephra beds. The tephras and preliminary paleomagnetism indicate a Castlecliffian age (c. 1.0 to 0.4 Myr). The Ahiaruhe Formation consists of alluvial gravel varying from a few metres to more than 80 m in thickness, interbedded with water-laid, partly loessic silts locally containing Mount Curl Tephra (c. 0.23 ± 0.04 Myr; equals Ahiaruhe Tephra). It has a tilted but still well-defined depositional surface at the top forming terraces, and passes laterally westward to thick blue-grey lacustrine silt with a moa footprint and also containing Mount Curl Tephra. The tephra indicates an age greater than 0.2 Myr for the the base of the Ahiaruhe Formation and less than 0.26 Myr for the top. Kawakawa Tephra in overlying loess indicates an age greater than 0.02 Myr. The three formations correspond to most of the time represented by the late Nukumaruan Stage, Castlecliffian Stage and early Hawera Series. We infer that their deposition was controlled by climatic fluctuations and associated glacioeustatic sea-level changes coincident with Milankovitch cycles, superimposed on secular vertical tectonic movements.

Glass chemistry, paleomagnetism, and correlation of middle Pleistocene tuffs in southern North Island, New Zealand, and Western Pacific

“…The Rewa Pumice (0.74 Ma), Potaka Pumice (0.64 Ma), and the Brunhes-Matuyama paleomagnetic boundary provide absolute age control and correlation between the radiometrically dated tuffs in the Rangitikei section, Mangatarata Formation in southern Hawke's Bay, and Te Muna Formation in Wairarapa. This confirms the age of unfossiliferous alluvial and lacustrine strata proposed for the latter two regions (Lillie 1953;Collen & Vella 1984). Correlation of Potaka Pumice and Lower Te Muna Tephra to tuffs in Western Pacific deep-sea cores on which magnetostratigraphy are available further support the identification of the Brunhes-Matuyama boundary in Hawke's Bay and Wairarapa.…”

“…The thickest known sequence of Castlecliffian strata in southern Wairarapa is exposed in the Huangarua River (366 m) and is thought to represent most of the Castlecliffian Stage (Collen & Vella 1984). Only two tuff horizons occur in the section.…”

“…Note scale change for the Te Whanga section, which also applies to all sections to the right of it. Collen & Vella (1984) have suggested the BrunhesMatuyama boundary occurs near the middle of Castlecliffian strata exposed in Huangarua River (type section for Te Muna Formation). However, the polarity of that part of the section which contains the Te Muna Tephras was then unknown.…”

“…1). Tuff correlations have been proposed on stratigraphic and lithological grounds (Fleming 1953;Lillie 1953;Collen & Vella 1984) but have not been substantiated by any unique characteristics of the tuffs, such as glass chemistry. Correlation between the regions is further hindered by the predominance of alluvial and lacustrine facies in southern Hawke's Bay and Wairarapa, which do not allow biostratigraphic correlation to mainly marine strata exposed in the Wanganui area.…”

“…Three principal onshore sections were selected for investigation, which consist of a thick and relatively continuous Castlecliffian sequence: Rangitikei River, Wanganui (400 m); Huangarua River, Wairarapa (366 m; Collen & Vella 1984); and Mangatewaiiti Stream, southern Hawke's Bay (c. 600 m, new data). Other, shorter sequences were also examined ( Fig.…”