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

We have compiled the distribution of gas hydrates
on the Fiordland margin based on the occurrence of
BSRs in an extensive database of seismic reflection
data, acquired by academic, government and
petroleum research cruises over the last 30 years.
Bottom simulating reflections (BSRs) are thereby
found in an area of approximately 2200 sq km on
the continental slope south-west. Main
characteristics of the BSRs include:
1. predominately negative polarity compared to
the seafloor reflection, which infers to a
2.
decrease in acoustic impedance,
the reflections follow the morphology of the
seafloor, thereby crosscutting strata, and
3. strong variations of amplitudes with offset
(AVO), indicating the presence of free gas
below the reflection. In addition, the existence
of free gas is supported by a reduced interval
velocity distribution below the BSR, with
velocity decreases of up to 30% compared to
the overlaying layers.
Because seismic reflection data is the only available
data source in the Fiordland region (other a priori
information like well information is not available) a
simultaneous AVO inversion algorithm is used to
obtain rock property attributes of P-impedance,
vp/vs, and density, respectively. This information is
used to verify the quantities of gas hydrate and their
potential as a gas reserve in this region.
POSTER
MID-PLEISTOCENE EXTINCTION OF
DEEP-SEA OSTRACODA?
F.J. Gaiger &K.Swanson
Geological Sciences, University of Canterbury,
Private Bag 4800, Christchurch
(fjg17*student.canterbury.ac.nz)
The last identified global marine extinction event
(‘the Stilostomella extinction’) occurred about 600-
900ka during the mid Pleistocene climate transition.
It is not only the most recent deep-sea extinction,
but also least studied because recovery of sediments
of that age and environment of deposition are still
most effectively achieved by examination of
relatively few, widely distributed cores. This
extinction affected benthic foraminifera, in
particular 82 species and 17 genera, including one
complete family (Stilostomellidae – 21 species). A
second family (Pleurostomellidae – 24 species) also
suffered significant extinction, however two species
of that group have been recovered in sediments
which post-date the mid-Pleistocene event.
In an attempt to determine whether benthic
ostracods (Podocopida) have also been affected by
the ‘Stilostomella event’ as an ongoing MSc thesis
project, a single ODP core from the northern flank
of the Chatham Rise, New Zealand, is being
examined. Ostracods are crustaceans in which the
soft anatomy is encapsulated in a bivalved,
calcareous carapace. Valves of this microscopic
organism are commonly preserved in deep-sea
sediments and as result, ostracods present the most
complete biogeographic and stratigraphic record of
any metazoan in the deep sea. This fact provides an
opportunity to examine whether more complex,
benthic deep-sea marine organisms were also
affected by the extinction event and if so, to then
provide an additional insight into what
environmental factors led to the significant loss of
biodiversity. The results of this project will also
make a contribution to our understanding of
ostracod diversification through time with
particular reference to significant Late Pliocene-
Pleistocene events described for bradleyinid and
trachyleberid species especially from the Southern
Ocean. Significant problems relating to taxonomy
and taphonomy have and continue to hinder
progress.
Samples studied are from the ODP core 1125
located about 600km east of the South Island at
1359 m depth on the northern side of the Chatham
Rise. The samples are from the top of the core
down to approximately 42 mbsf, covering the last
2.5 Ma, i.e. late Pliocene to Recent. There is a
significant variation between samples in terms of
grain size, ostracod population (total number of
specimens and diversity) and the disproportionate
number of juvenile valves. Some groups are well
represented, including Bradleya, Taracythere,
Krithe and Apatihowella, which form the main
cluster of target species for this project. The
occurrence of Bradleya pygmaea in core 1125
(1359 m) is significant because it has been recorded
in Pliocene abyssal/bathyal sediments elsewhere in
the Southwest Pacific, and was also recovered in
uppermost Quaternary sediment from that Plateau.
It is, however, no longer living on the Campbell
Plateau, which implies steepening thermal gradients
and an associated shoaling as significant influences
on both the latitudinal and depth distribution of
Podocopid ostracods.
ORAL
50 th Kaikoura05 -28- Kaikoura 2005