New Zealand Journal of Geology and Geophysics abstracts
Paleoecology of an early Miocene, rapidly submerging rocky shore,
Motuketekete Island, Hauraki Gulf, New Zealand
K. A. Campbell1
J. A. Grant-Mackie1
J. S. Buckeridge2
N. Hudson1
A. C. Alfaro2
J. Hoverd1
S. Morgan1
N. Horne1
A. Banfield1
1
Geology Department
University of Auckland
Private Bag 92 019
Auckland, New Zealand
2 Earth and Oceanic Sciences
Research Institute
Auckland University of Technology
Private Bag 92 006
Auckland, New Zealand
Abstract More than 70 macrofossil taxa (including
14 bivalves, 6 gastropods, 8 corals, 4 echinoderms, and 10 barnacles)
are recorded from early Miocene (Otaian) Kawau Subgroup strata (Cape
Rodney Formation and Motuketekete Limestone, lower Waitemata Group) at
Motuketekete Island, Hauraki Gulf, north of Auckland City. Both in
situ and transported fossils occur in deposits of greywacke
boulder conglomerate, cobble to pebble conglomerate/sandstone,
bioclastic calcareous grainstone, and an allochthonous breccia debris
event unit, which correspond to lithofacies A, C, D, and E,
respectively, of Ricketts et al. Greywacke boulders accumulated at the
base of a greywacke paleocliff or sea stack that was planed off at its
top to form a shore platform during the Miocene. A >2 m long,
16 cm thick coral colony grew atop a mixed substrate of boulders,
pebbles, and sand, and exhibits two successional regrowth phases
following debris-influx events. Boulders and cobbles bored by pholadid
bivalves (Parapholas aucklandicum Powell) are common in
these basal bouldery talus deposits. A diverse suite of macrofossils,
including chaliciform corals, occurs in somewhat finer grained deposits
that buried the greywacke basement and boulder talus pile, and
indicates either slightly deeper or more turbid conditions in the
shallow photic zone. The cross-bedded, bioclastic Motuketekete
Limestone overlies these coarse-grained Cape Rodney Formation units.
Its fauna indicates deepening, with replacement of shallow by offshore
taxa (e.g., Crenostrea with Bathylasma), as the
Waitemata Basin underwent rapid tectonic subsidence and redeposition of
sediments with the onset of subduction along the Hikurangi convergent
margin. A newly identified lens of “upper breccia” (lithofacies E) in
the Motuketekete Limestone contains rounded blocks of colonial coral
and Tertiary siltstone. The Motuketekete occurrence of lithofacies E
extends the known geographic range of this geologically instantaneous
deposit; it records a regional tectonic event that is interpreted as an
avalanche/debris flow triggered by faulting. The breccia appears to be
a reliable marker for local lithostratigraphic correlation in lower
Waitemata strata exposed north of Auckland.
Keywords paleoecology; early Miocene; Auckland;
Waitemata Group; Kawau Subgroup; Cape Rodney Formation; Motuketekete
Limestone; Otaian Stage; rocky shore; paleoenvironment; shallow-marine;
bathyal; fossils; Turbinaria; Bolma new species; Panis;
Chama; Pseudochama; Bathylasma; acrothoracican
barnacles; Gastrochaenolites; new taxonomic names
G03051; Received 23 May 2003; accepted 26 January 2004; Online
publication date 1 December 2004
New Zealand Journal of Geology & Geophysics, 2004, Vol. 47:
731-748
0028-8306/04/4704-0731© The Royal Society of New Zealand 2004
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