New Zealand Journal of Geology & Geophysics abstracts
The northern Grey Valley Trough and the Montgomerie Fault, north
Westland, New Zealand
R. P. Suggate
GNS Science
PO Box 30368
Lower Hutt 5040, New Zealand
p.suggate@gns.cri.nz
Abstract Seismic lines in the northern Grey
Valley Trough
show Upper Cretaceous-Paleocene Paparoa Coal Measures, locally over
0.75 km thick, overlain unconformably by thin Oligocene Cobden
Limestone. The following Neogene succession, up to c. 4 km thick, thins
to c. 3 km northeastwards along the trough. Initial southwest
thickening of the sedimentary fill was followed, after a minor
mid-Miocene hiatus, by thickening to the northeast. The Grey Valley
Syncline, whose axis lies close to the axis of the depositional trough,
resulted from Quaternary deformation overriding the effects of the
differing patterns of Neogene sedimentation. The few seismic lines that
extend across the steep northwest flank of the asymmetrical syncline
lose their sedimentary character northwestwards, and a major fault,
considered to be the Montgomerie Fault, is inferred. Field data show
this fault to extend from within basement rocks in the middle of the
Paparoa Range south to the margin of the Grey Valley Syncline, and
thence southwest along that margin for 20 km before continuing into
Paleogene rocks of the Brunner Anticline. The fault, known to be active
in one area, forms part of the regionally active west side of the
Grey-Inangahua Depression. The extent and thickness of the Paparoa Coal
Measures, the early Cenozoic erosion, and the extent of the Montgomerie
Fault are important in the context of inversion tectonics previously
postulated for the region.
Keywords New Zealand; Grey-Inangahua Depression;
Grey Valley
Trough; Grey Valley Syncline; Paparoa Coal Measures; Neogene
sedimentation; Quaternary deformation; Montgomerie Fault; active
tectonics
G05054; Online publication date 27 November 2006; Received 9
November 2005; accepted 21 November 2006
New Zealand Journal of Geology & Geophysics, 2006, Vol. 49:
491–502
0028–8306/06/4904–0491 © The Royal Society of New Zealand
2006
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