New Zealand Journal of Geology and Geophysics abstracts

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The mid-Castlecliffian Mangatuna Formation of the Gisborne district, North Island, New Zealand

G. NEEF

Department of Applied Geology
University of New South Wales
Sydney 2052, Australia

With appendices

Petrology of pebbles in the
Matokitoki Member

W. A. WATTERS

Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand

Calcareous nannofossils from Mangatuna Formation

A. R. EDWARDS

Stratigraphic Solutions Ltd.
P.O. Box 295
Waikane, New Zealand

Abstract  The type area of the mid-Castlecliffian Mangatuna Formation is described and three members are proposed. The formation unconformably overlies marine Pliocene strata in an area of Quaternary uplift at Gisborne, eastern North Island, New Zealand. The strata dip <5deg. towards the northwest and were at least 120 m thick (top eroded) near Calhome Station, where the Calhome (oldest), Matokitoki, and Town Hill Members are mapped. The Calhome Member is composed of nonmarine siltstone, tephras, and minor sandstone and gravel, whereas the lower part of the Matokitoki Member, formed of gravel, represents the deposits of a mid-Castlecliffian? braided Waipaoa River. The Town Hill Member contains nonmarine and estuarine molluscs and at one locality fossil tree trunks.

At the commencement of deposition of the formation there was, locally, substantial mid-Castlecliffian (mid-Pleistocene) relief of at least 70 m, including the north-trending Valley Road Hill, Mangatuna Ridge, and Calhome valley. This relief was buried by the time the Town Hill Member was deposited. The presence of Matokitoki Member within the Calhome valley implies that the ancient Waipaoa River flowed along the northern margin of the Poverty Bay flats. A mid-Castlecliffian age for the formation is deducted largely from nanofossils.

Keywords  Mangatuna Formation; Castlecliffian; topography; stratigraphy; structure; geological history; calcareous nanofossils

New Zealand Journal of Geology and Geophysics, 1996, Vol. 39: 551-558

0028-8306/96/3904-0551 $2.50/0 (c) The Royal Society of New Zealand 1996

PDF file of entire paper: medium quality (1618K); (scanned from paper original: notes about this process)

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