New Zealand Journal of Geology and Geophysics abstracts
Folding and the formation of bedding-parallel faults on the western limb of
Grey Valley Syncline near Blackball, New Zealand
ANDREW NICOL
SIMON NATHAN
Institute of Geological & Nuclear Sciences Ltd
P.O. Box 30 368
Lower Hutt, New Zealand
Abstract Fresh roadside exposures of faults on the western
limb of Grey Valley Syncline near Blackball (West Coast, South Island) provide
new information on the kinematics of folding since c. 2.5 m.y. ago. These
faults are parallel to, or dip within 10deg. of, steep bedding (60->90deg.)
in Pliocene Old Man Group, and offset two gently dipping Quaternary gravel
formations. Deformed gravel sequences record reverse-fault displacements of
0.5-c. 80 m and bed dips of 5-50deg., which accumulated over the last c.
450 000 yr. The dip of Quaternary gravel beds and fault displacements
decrease up-sequence, suggesting that gravel deposition and deformation were
synchronous. Bedding-parallel faults in Old Man Group are typically located at
the boundaries between mudstone beds and coarser grained sandstone or
conglomerate beds. The bedding-parallel orientations of the faults, fault
slickenside striations approximately normal to the hinge of Grey Valley
Syncline, and total fault displacement across the fold limb are consistent with
these structures being flexural-slip faults formed during folding. Small
amounts of bedding-parallel shortening and extension within Pliocene strata
between faults indicate non-rigid deformation of the limb and departure of
folding from an ideal flexural-slip model.
Keywords bedding-parallel faults; Old Man Group; Grey Valley
Syncline; flexural-slip folding
New Zealand Journal of Geology & Geophysics, 2001, Vol. 44:
127-135
0028-8306/01/4401-0127 $7.00/0 (c) The Royal Society of New Zealand
2001
PDF file of entire paper: medium quality (2496K); (scanned from paper original: notes about this process)
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