New Zealand Journal of Geology and Geophysics abstracts
Base of the Devonian Baton Formation and the question of a pre-Baton
tectonic event in the Takaka Terrane, New Zealand
MARGARET A. BRADSHAW
Department of Geological Sciences
University of Canterbury
Private Bag 4800
Christchurch, New Zealand
Abstract Previous interpretations of the Baton River area
proposed a significant pre-Baton (Late Silurian-Early Devonian) tectonic event,
during which Ordovician and Silurian sediments were folded, cleaved, and eroded
before deposition of the Lower Devonian Baton Formation. This interpretation
was based on an apparent lack of a penetrative cleavage in Baton sediments, and
on the presence of a rudite at the base of Baton Formation in the Moran
Creek/Skeet River area that was identified as a "basal conglomerate".
Current studies show a pre-Baton event to be untenable and indicate that the
Devonian was laid down in the same Takaka Terrane sedimentary basin as the
underlying Ellis Formation and experienced the same deformation. Features of
the Baton Formation rudite are consistent with a mass-flow rather than with a
"basal conglomerate" origin and the rudite is reinterpreted as a multistoried
lobe of debris flows that laterally interfinger with mudstone. Baton Formation
appears to conformably follow limestones or sandstones of Ellis Formation. The
transition shows four sedimentary patterns. Pebbles in Ellis limestone and
sandstone close to the base of the Baton Formation in Fowler Creek may
represent a distal expression of the Moran Creek/Skeet River debris flows.
Rocks preceding the Baton Formation are referred to as Ellis Formation rather
than Hailes Quartzite as the lateral equivalency of these two formations is
uncertain and under review. Fowler Formation, previously the highest part of
the Ellis Group, is shown to be stratigraphically continuous with, and
lithologically identical to, the Baton Formation, and is discarded. The base of
Baton Formation appears to mark an abrupt increase in water depth with a change
from mainly arenaceous shelf sedimentation to deeper water, finer grained
lithologies.
Structural studies show that Baton Formation is as deformed as the older
rocks, and no structures can be attributed to a pre-Baton event.
Keywords Devonian; Baton Formation; Ellis Formation; Hailes
Quartzite; Tuhua Orogeny; Takaka Terrane
New Zealand Journal of Geology & Geophysics, 2000, Vol. 43:
601-610
0028-8306/00/4304-0601 $7.00/0 (c) The Royal Society of New Zealand
2000
PDF file of entire paper: medium quality (3606K); (scanned from paper original: notes about this process)
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