New Zealand Journal of Geology and Geophysics abstracts
Stratigraphy, paleontology, and tectonics of lower Miocene rocks in the
Waipatiki/Mangatuna area, southern Hawke's Bay, New Zealand
C. M. REID
Geology Department
The University of Auckland
Private Bag 92019
Auckland, New Zealand*
*Present address: School of Earth Sciences, University of Tasmania, G.P.O. Box
252-79, Hobart, Tasmania 7001.
Abstract Three lower Miocene units occur in the
Waipatiki/Mangatuna area: Mangapuku Mudstone (Otaian), Westcott Sandstone
(Otaian-Altonian), and Tunakore Mudstone (Altonian). They are regarded as
members of the Ihungia Formation and crop out mostly in the axis of the
Waipatiki Syncline. Major faults near Toi Flat trend west-east and, with an
associated zone of minor faults, appear to thicken Westcott Sandstone in this
area.
Rocks showing gradual deepening from initially shallow water (Westcott
Sandstone and Tunakore Mudstone) overlie those of deep-water origin (Mangapuku
Mudstone).
Mangapuku Mudstone is a dark-grey, calcareous, sandy mudstone with rare
macrofaunas and diverse and abundant foraminiferal faunas of abyssal to shelf
break origin. It is separated from older units by a deep-water unconformity and
was uplifted at rates of up to 1.1 km/m.y. to shallow-water depths, with
submarine erosion preceding deposition of Westcott Sandstone.
Westcott Sandstone is dominated by grey, calcareous, fossiliferous muddy
sandstones to sandy siltstones with intercalated unfossiliferous turbidite
sandstones, deposited in a forearc basin subsiding from inner shelf to shelf
break depths. Westcott Sandstone has diverse and abundant shallow molluscan
faunas along with rich non-molluscan macrofaunas and foraminiferal faunas.
Tunakore Mudstone is a dark grey, calcareous, sandy mudstone with minor thin
sandy turbidites, deposited at shelf break to mid-bathyal depths, and grades up
from Westcott Sandstone from continued subsidence. It contains rare macrofaunas
and highly diverse foraminiferal faunas.
Sedimentation in Westcott Sandstone and Tunakore Mudstone was
>225 m/m.y. in combination with an average basement subsidence rate of
880 m/m.y.
Keywords Waipatiki; Mangatuna; southern Hawke's Bay; Otaian;
Altonian; Ihungia Formation; Mangapuku Mudstone; Westcott Sandstone; Tunakore
Mudstone; tectonics; paleontology; stratigraphy
New Zealand Journal of Geology and Geophysics, 1998, Vol. 41: 115-131
0028-8306/98/4102-0115 $7.00/0 (c) The Royal Society of New Zealand
1998
PDF file of entire paper: medium quality (1594K); (scanned from paper original: notes about this process)
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