New Zealand Journal of Geology and Geophysics abstracts
Stratigraphy of Tithonian (Ohauan-Puaroan ) marine beds near Port Waikato, New
Zealand, and a redescription of Belemnopsis aucklandica
(Hochstetter)
A. B. CHALLINOR
Department of Earth Sciences
The University of Waikato
Private Bag 3105
Hamilton, New Zealand
Abstract Some 1500 m of marine Ohauan and Puaroan strata in
the Port Waikato region of New Zealand are restudied in an attempt to resolve
lithostratigraphic and biostratigraphic anomalies in published works. New
correlations are proposed for some units of the Apotu Group. A lower 650 m
siltstone, previously correlated entirely with Kinohaku Siltstone, is here
regarded as including the interval Kinohaku Siltstone to Lower Puti
Siltstone (new member). The Waiharakeke Conglomerate is not represented in
the area by coarse sediments. A thin sandstone unit overlying the Lower Puti
Siltstone and previously correlated with Waiharakeke Conglomerate is here
correlated with the Ruakiwi Sandstone. The overlying 400 m siltstone, regarded
previously as the entire Puti Siltstone, is here recognised as a new member,
the Upper Puti Siltstone. The Coleman Conglomerate is much thicker in
the region than mapped, and located higher in the sequence. Biostratigraphy is
a key element in correlating the sequence with named units to the south. The
sequence is mostly siltstone, but sandstone units provide some
lithostratigraphic control. Belemnites are almost the only fossils found in the
Late Ohauan and Early Puaroan part of the sequence and are important in the
Late Puaroan. Formal belemnite zones, based in part on their stratigraphic
distributions in other parts of southwest Auckland, are erected. Occasional
ammonites provide tie points that correlate the succession with the standard
stratigraphic column for the Tethyan realm. Belemnopsis aucklandica
(Hochstetter) is redescribed and considered to be of full specific status as is
its former subspecies, Belemnopsis trechmanni Stevens. Many pre-adult
Belemnopsis aucklandica differ in form from adults; some have been
previously identified in the field as Hibolithes. Some earlier
identifications of belemnites from the Late Puaroan of Port Waikato are
incorrect; most are now included in Belemnopsis aucklandica.
Keywords Port Waikato; Ohauan; Puaroan; Tithonian;
lithostratigraphy; biostratigraphy; belemnite zones; Belemnopsis
aucklandica; Lower Puti Siltstone; Upper Puti Siltstone; new stratigraphic
names
New Zealand Journal of Geology & Geophysics, 2001, Vol. 44:
219-242
0028-8306/01/4402-0219 $7.00/0 (c) The Royal Society of New Zealand
2001
PDF file of entire paper: medium quality (4176K); (scanned from paper original: notes about this process)
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