New Zealand Journal of Geology and Geophysics abstracts
Fan deltaic-to-fluvial sedimentation of the Middle Jurassic Murihiku Terrane,
Southland, New Zealand
Atsushi Noda
Institute for Marine Resources and Environment, AIST
Tsukuba, Ibaraki 305-8567, Japan
email: a.noda@aist.go.jp
Makoto Takeuchi
Department of Earth and Planetary Sciences
Graduate School of Science
Nagoya University
Chikusa-ku, Nagoya 464-8602, Japan
Mamoru Adachi
The Nagoya University Museum
Chikusa-ku, Nagoya 464-8601, Japan
Abstract New results on the stratigraphy and sedimentary
environment of the Middle Jurassic strata of the Murihiku Terrane in the Waikawa
district, Southland, New Zealand, are presented. This area has not been subjected
to study for a long time, although the Murihiku Terrane is important to understand
the Mesozoic geology of New Zealand. Stratigraphically, from bottom to top,
the sequence consists of lithofacies associations A, B, C, and D, distinguished
by their lithology. Lithofacies association A (250 m thick) is composed of
boulder-grade conglomerate, coarse-grained massive sandstone, trough cross-stratified
sandstone, and minor fine-grained sediments. Lithofacies association B (90
m thick) contains alternating beds of sandstone and siltstone and fossil-bearing
massive siltstone. Lithofacies association C (280 m) consists of poorly to
moderately sorted pebble-cobble conglomerates and trough or planar cross-stratified
sandstones. The characteristic lithofacies of lithofacies association D (>140
m) are planar cross-stratified sandstone, planar horizontally stratified
sandstone, grey siltstone, and carbonaceous beds. The depositional age was
deduced from bivalve fossils in lithofacies association B, which indicate
a Middle Jurassic (Temaikan: Bajocian-Callovian) age. Paleocurrent flow directions
were from the southwest in lithofacies association A and from the southeast
in lithofacies associations C and D. Clast compositions also differed between
lithofacies associations A and C; andesite volcanic clasts were dominant
in A, and rhyolite volcanic clasts were dominant in C. The major sedimentary
environments were terrestrial and shallow marine and were affected by sea-level
changes. The sediments of lithofacies association B were deposited during
periods of transgression and high sea level, and the boundary between lithofacies
associations B and C is a depositional-sequence-bounding unconformity. Fluvial
sedimentation became dominant in lithofacies associations C and D. Due to
progressive aggradation of the sedimentary basin, the gradient became gentle,
and the fluvial pattern changed from a braided to a meandering river. The
sediment source, as determined from paleocurrent analyses and clast compositions,
was also different from that of lithofacies association A. Thus, the Waikawa
district sediments apparently were derived from multiple sources. The provenance
of the Murihiku Terrane sediments was probably a primitive volcanic or continental
margin arc. Volcanic activity in the hinterland fed large amounts of volcanic
detritus to the region by flood, debris flow, and fluvial transport.
Keywords Murihiku Terrane; stratigraphy; facies analysis;
delta; fluvial; conglomerate; Jurassic; New Zealand
G01007; published 27 September 2002 Received 12 November 2001; accepted
17 June 2002
New Zealand Journal of Geology & Geophysics, 2002, Vol. 45: 297-312
0028-8306/02/4503-0297 $7.00/0 © The Royal Society of New Zealand
2002
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