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

offshore west coast to offshore east coast. It
overlaps in part with the original 1:250 000 Mt
Cook, Hokitika, Hurunui & Christchurch geology
maps compiled in the 1960s (Gair 1967, Warren
1967, Gregg 1964, Suggate 1972). Aoraki’s
improvements over the earlier maps include the
detail of greywacke and schist mapping, more
extensive mapping of Quaternary deposits in hill
and mountain country, and the recognition and
detail of numerous new faults and folds, many
demonstrably active. As with other QMAPs, the
primary emphasis is compilation of existing data,
from published (e.g. maps, papers) and unpublished
(e.g. reports, theses) sources. Additional mapping
as part of QMAP aimed to fill data gaps, ensure
uniform levels of data detail, or resolve major
conflicts of interpretation. The map has been
compiled at 1:50 000 scale into a Geographic
Information System (GIS), but with sufficient
generalisation for legible presentation at 1:250 000
scale.
New mapping has added much improved
understanding of the Rakaia (Torlesse) terrane.
Greywacke/schist mapping emphasises textural
zonation (t.z.) rather than the mineral zonation
(chlorite, biotite, garnet) of the earlier maps,
although the new map also depicts mineral
isograds. Alpine schist fabrics and isograds vary
considerably along the plate boundary, and schist
units are not parallel to the Alpine Fault. Bedding
trends in t.z.1 greywacke are emphasised with
formlines. A regional swing in bedding strike (from
320° to 030°) commences around 60 km SE of the
Alpine Fault, mimicking the oroclinal bend of
Mesozoic terranes in the southern South Island.
Bedding faces mainly west or southwest, with
locally eastward-facing, overturned, sections up to
10 km thick. Steeply plunging folds become
progressively tighter and with shorter wavelength
approaching the Alpine Fault. En echelon
northeast-striking, reverse-dextral oblique-slip
faults dipping 40-60° NW are common in the
central Southern Alps. Steeply plunging folds are
transected, overthrust and rotated by late Cenozoic
displacement on these faults.
Relatively few changes have been made to the
mapping of Cretaceous to Pliocene sediments, a
tribute to the quality of Cenozoic stratigraphy and
paleontology in the 1960s. However, the QMAP
Aoraki units and legend contain more
lithostratigraphic information, reflecting the
Cretaceous-Cenozoic transgression and regression
in more detail than on the earlier maps. Quaternary
map units on QMAP Aoraki include scree,
colluvium & landslide debris, in addition to the
glacial and fluvial deposits emphasised by earlier
maps. Faults and folds are depicted as active only
where there is good geomorphic evidence of late
Quaternary deformation. Other structures,
particularly those outcropping in the mountainous
Southern Alps lack of evidence of activity, rather
than showing evidence of inactivity.
POSTER
LATE CRETACEOUS EUSTASY AND THE
EAST COAST BASIN - THE GOOD NEWS!
James S. Crampton 1 ,PoulSchiøler 2 &
Lucia Roncaglia 3
1 Institute of Geological & Nuclear Sciences, PO
Box 30368, Lower Hutt.
2 Geol. Surv. Denmark & Greenland, Ø. Voldgade
10, DK-1350 Copenhagen, Denmark.
3 Danish Oil & Natural Gas A/S, Agern Alle 24-26,
DK-2970 Hørsholm, Denmark.
(j.crampton*gns.cri.nz)
Distinguishing tectonic from supposedly eustatic
Upper Cretaceous sequences is highly problematic
for New Zealand successions that are structurally
and/or stratigraphically complex and remote from
well-studied Northern Hemisphere localities. The
problem is largely one of resolution in
chronostratigraphic correlation, and conclusions
may vary depending on philosophies and
approaches to correlation. A complementary study
(Schiøler et al., this volume), based on palynofacies
analysis and zonal correlations, found little
evidence for Late Cretaceous eustatic signatures in
the East Coast Basin. Here we take a different
approach that employs multidimensional graphic
correlation using constrained optimization
(CONOP) to derive a high-resolution correlation
for 15 Coniacian-Maastrichtian sections in the East
Coast Basin. The resulting composite section, based
on 398 well-constrained lowest- or highestoccurrence
bioevents, yields 183 event levels and
an average chronostratigraphic resolution of
approximately 142 Kyr. The age of the composite is
calibrated using seven dated bioevents; two of these
events are tied to geochemical or paleomagnetic
datums.
CONOP cannot resolve unconformities that occur
across all sampled sections. We suggest, however,
that such unconformities are represented by large
event-clusters at single composite levels, and 13
such event-clusters are identified. Of these, 10 lie
within hiatus intervals recorded from the New
Jersey coastal plain and interpreted as eustatic
sequence boundaries; the probability of this
coincidence arising by chance alone is c. 8%.
Although provisional, these results suggest that
high resolution quantitative stratigraphy can
provide a potent tool for the resolution and global
correlation of stratigraphic sequences. Furthermore,
our findings add support for recent studies that have
argued for the presence of Late Cretaceous eustatic
sea-level changes.
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