New Zealand Journal of Geology and Geophysics abstracts
History of oceanic front development in the New Zealand sector of the Southern
Ocean during the Cenozoic--a synthesis
CAMPBELL S. NELSON
PENELOPE J. COOKE
Department of Earth Sciences
University of Waikato
Private Bag 3105
Hamilton, New Zealand
email: c.nelson@waikato.ac.nz
Abstract The New Zealand sector of the Southern Ocean (NZSSO)
has opened about the Indian-Pacific spreading ridge throughout the Cenozoic.
Today the NZSSO is characterised by broad zonal belts of antarctic (cold),
subantarctic (cool), and subtropical (warm) surface-water masses separated by
prominent oceanic fronts: the Subtropical Front (STF) c. 43deg.S, Subantarctic
Front (SAF) c. 50deg.S, and Antarctic Polar Front (AAPF) c. 60deg.S. Despite a
meagre database, the broad pattern of Cenozoic evolution of these fronts is
reviewed from the results of Deep Sea Drilling Project-based studies of
sediment facies, microfossil assemblages and diversity, and stable isotope
records, as well as from evidence in onland New Zealand Cenozoic sequences.
Results are depicted schematically on seven paleogeographic maps covering the
NZSSO at 10 m.y. intervals through the Cenozoic.
During the Paleocene and most of the Eocene (65-35 Ma), the entire NZSSO was
under the influence of warm to cool subtropical waters, with no detectable
oceanic fronts. In the latest Eocene (c. 35 Ma), a proto-STF is shown
separating subantarctic and subtropical waters offshore from Antarctica, near
65deg.S paleolatitude. During the earliest Oligocene, this front was displaced
northwards by development of an AAPF following major global cooling and biotic
turnover associated with ice sheet expansion to sea level on East Antarctica.
Early Oligocene full opening (c. 31 Ma) of the Tasmanian gateway initiated
vigorous proto-circum-Antarctic flow of cold/cool waters, possibly through a
West Antarctic seaway linking the southern Pacific and Atlantic Oceans,
including detached northwards "jetting" onto the New Zealand plateau where
condensation and unconformity development was widespread in cool-water
carbonate facies. Since this time, a broad tripartite division of antarctic,
subantarctic, and subtropical waters has existed in the NZSSO, including
possible development of a proto-SAF within the subantarctic belt. In the
Early-early Middle Miocene (25-15 Ma), warm subtropical waters expanded
southwards into the northern NZSSO, possibly associated with reduced ice volume
on East Antarctica but particularly with restriction of the Indonesian gateway
and redirection of intensified warm surface flows southwards into the Tasman
Sea, as well as complete opening of the Drake gateway by 23 Ma allowing more
complete decoupling of cool circum-Antarctic flow from the subtropical waters.
During the late Middle-Late Miocene (15-5 Ma), both the STF and SAF proper were
established in their present relative positions across and about the Campbell
Plateau, respectively, accompanying renewed ice buildup on East Antarctica and
formation of a permanent ice sheet on West Antarctica, as well as generally
more expansive and intensified circum-Antarctic flow.
The ultimate control on the history of oceanic front development in the NZSSO
has been plate tectonics through its influence on the paleogeographic changes
of the Australian-New Zealand-Antarctic continents and their intervening
oceanic basins, the timing of opening and closing of critical seaways, the
potential for submarine ridges and plateaus to exert some bathymetric control
on the location of fronts, and the evolving ice budget on the Antarctic
continent. The broad trends of the Cenozoic climate curve for New Zealand
deduced from fossil evidence in the uplifted marine sedimentary record
correspond well to the principal paleoceanographic events controlling the
evolution and migration of the oceanic fronts in the NZSSO.
Keywords New Zealand; Southwest Pacific; Antarctica; Southern
Ocean; Cenozoic; paleoclimate; paleoceanography; oceanic fronts; DSDP cores;
ice sheets
New Zealand Journal of Geology & Geophysics, 2001, Vol. 44:
535-553
0024-8306/01/4404-0535 $7.00/0 (c) The Royal Society of New Zealand
2001
PDF file of entire paper: medium quality (7761K); (scanned from paper original: notes about this process)
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