50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...

indicates pressures of ca. 10-12kbar during aureole
development in Wet Jacket Arm. Amphibolite
facies assemblages remain outside the aureole
indicating that equilibration to granulite facies
assemblages only occurred within the immediate
vicinity of the Malaspina Gneiss suggesting
reaction kinetics were an important control on the
extent to which granulite facies assemblages
developed in country rocks intruded by the WFO.
ORAL
LATE NEOGENE BARNACLE-RICH
LIMESTONES, MATAPIRO-OMAHU,
HAWKE’S BAY: THEIR LIFE FROM
DEPOSITION TO UPLIFT
R.A. Baggs 1,2 ,C.S.Nelson 2 , P.J.J. Kamp 2 ,K.J.
Bland 2 & S.D. Hood 2
1 CRL Energy Ltd. P.O. Box 290, Greymouth
2 Dept of Earth Sciences, University of Waikato,
Private Bag 3105, Hamilton
(rachelbaggs_nz*hotmail.com)
A new GIS-based 1:40,000 scale geological map
has been produced for the Matapiro-Omahu region,
between the Tutaekuri and Ngaruroro Rivers, west
of Napier city in eastern North Island. The rocks
occupy the southern part of the regional Matapiro
Syncline, are of late Pliocene-early Pleistocene age
(Nukumaruan), are contained within the Petane
Group, and comprise a cyclothemic succession of
formations of terrigenous mudstone and limestone,
with some conglomerate.
The three limestone units, in ascending order the
Tangoio Limestone, Matapiro Limestone and
Puketautahi Limestone, tend to stand proud in the
landscape and provide good mappable horizons,
while the intervening mudstones are poorly
exposed. The Tangoio Limestone is restricted to the
eastern limb of the Matapiro Syncline and grades to
fossiliferous greywacke gravels (Sherenden
Conglomerate Member) towards the west. The
pebbly Matapiro Limestone is distributed
throughout the southern part of the syncline, while
the Puketautahi Limestone caps the hills on the
western limb.
Sedimentological and petrographic analyses of the
three limestones indicate that they are all barnacledominated
with an increasing proportion of bivalve
material up through the units, and with small
amounts of bryozoans, echinoderms, benthic
foraminifera, and occasional serpulids and red
algae. Skeletal grains are commonly microbored.
The rocks are mainly skeletal grainstones, less
commonly skeletal packstones, and carbonate
contents average 70-80%. Cements involve a
variety of calcite spar fabrics, including syntaxial
rim, isopachous fringe, meniscus and equant types,
usually non-ferroan and with non- to dull
cathodoluminescence. The spar cements were
precipitated during shallowest burial (likely no
more than about 200 m), involving mild pressuredissolution
of skeletons, and during subsequent
uplift when dissolution of aragonitic shells
provided a later stage of equant and micro-equant
cement. Most of the limestones retain moderate
porosity in outcrop.
The skeletal composition is consistent with
deposition of all three limestones in a similar high
energy, current swept seaway environment
(Ruataniwha Strait) at inner shelf depths.
Deposition was associated with rapidly
transgressing seas coupled with low terrigenous
sediment supply, forming relatively thin
transgressive systems tract (TST) carbonate
deposits. Highstand systems tract (HST) deposits
are represented by the intervening, thicker, midshelf
mudstones, which accumulated over longer
durations than the limestones. Four major
cyclothems (TST + HST) are identified for the
mapped succession, the depositional settings being
primarily controlled by glacio-eustatic sea level
fluctuations near the opening of the Ruataniwha
Strait into Hawke Bay in the Nukumaruan, during a
period of slow basin subsidence followed
eventually by uplift and exhumation of the whole
succession.
ORAL
FISH, FRUSTULES, FRUITS, A FLOWER -
AND LOTS OF LEAVES: AN
INVESTIGATION INTO THE BIOTA OF AN
EARLY MIOCENE MAAR LAKE
J.M. Bannister 1 &D.E.Lee 2
1 Departments of Botany & Geology, University of
Otago, PO Box 56, Dunedin
2 Department of Geology, University of Otago, PO
Box 56, Dunedin
(jmb*clear.net.nz)
Preliminary findings from a finely varved diatomite
deposit formed during the Early Miocene in a maar
lake near Middlemarch, Otago are presented. The
varves are alternately dark and light and the light
coloured layers are made up almost entirely of
diatom frustules with some freshwater sponge
spicules. The diatom flora is overwhelmingly
dominated by a single species, Encyonema jordanii
(Grunow) Mills. The sponge(s) probably encrusted
plant material such as stems of water plants and
dead leaves. Limited excavations in the upper few
metres of the deposit have yielded several entire
fish skeletons up to 15 cm long that belong to a new
species of galaxiid. The diatomite contains
numerous fruits and seeds in different states of
preservation; these are mainly small and difficult to
identify, but some of the larger fruits may be
50 th Kaikoura05 -2- Kaikoura 2005