New Zealand Journal of Geology and Geophysics abstracts
Redefinition and interpretation of late Miocene-Pleistocene terrestrial
stratigraphy, Central Otago, New Zealand
J. H. YOUNGSON
D. CRAW
C. A. LANDIS
K. R. SCHMITT*
Geology Department
University of Otago
P.O. Box 56
Dunedin, New Zealand
*Present address: 9700 Lakeshore Blvd. NE, Seattle, WA
98115, U.S.A.
Abstract The stratigraphic succession in eastern Central
Otago consists of Eocene quartzose fluvial sediments and middle Tertiary marine
strata (Onekakara Group), early-middle Miocene quartzose fluvial sediments and
lake deposits (Manuherikia Group), late Miocene-Pliocene immature sandstones
and conglomerates, and Quaternary terrace and fan gravels. Published literature
contains at least 20 different approaches for subdivision of this succession.
The late Miocene-Pliocene conglomerates were formed during the rise of
fault-bounded greywacke and semischist mountain ranges. Conspicuous
conglomerates in the upper part of this succession are widely referred to as
Maori Bottom Formation, but that name was originally applied by miners to a
locally auriferous erosion surface beneath Quaternary terrace and fan gravels
in Otago. In addition, the term is culturally offensive.
We propose the name Hawkdun Group for the late Miocene-Pliocene
succession of tectonically generated sediments in the Maniototo, Ida, and
Manuherikia Basins, and propose the name Maniototo Conglomerate to
replace Maori Bottom. The Hawkdun Group in Central Otago can be subdivided into
two mappable units. The basal Wedderburn Formation consists predominantly of
late Miocene quartzose fluvial strata recycled largely from cover strata of the
St Bathans, Kakanui, and Hawkdun Ranges. Wedderburn Formation contains an
upwardly increasing component of first-cycle lithic detritus derived from these
ranges, and grades up into late Miocene-Pliocene Maniototo Conglomerate,
consisting of thick beds of greywacke-dominated conglomerate and interbedded
loess horizons. In previous usage, Wedderburn Formation included some strata
which more appropriately belong with the underlying Manuherikia Group.
Quartzose fluvial strata and intervening marine and lacustrine strata have
been aggregated by previous workers for regional mapping purposes. Correlation
problems leading to aggregation have arisen largely from stacking of up to
three lithologically similar quartzose conglomerate and quartzose sandstone
units, but also from the difficulty in differentiating between these units
where distinctive, intervening marine or lacustrine strata are absent, and
where unconformities are not exposed. The redefined units as proposed above are
individually mappable and eliminate the necessity for mapping of grouped units.
Usage of Stranraer Group, Maori Bottom Group, Maori Bottom Formation, and Blue
Gravel Member (of the latter) is discontinued. Contemporaneous, lithologic and
stratigraphic correlatives of the Hawkdun Group were deposited in the Nevis,
lower Manuherikia, Cromwell, and upper Clutha Basins in Central Otago, and in
many other basins on both sides of the plate boundary throughout the South
Island.
Keywords terrestrial stratigraphy; tectonics; Central Otago;
quartz pebble conglomerate; Maniototo Conglomerate; Hawkdun Group; Miocene;
Pliocene; new stratigraphic names
New Zealand Journal of Geology and Geophysics, 1998, Vol. 41: 51-68
0028-8306/98/4101-0051 $7.00/0 (c) The Royal Society of New Zealand
1998
PDF file of entire paper: medium quality (2057K); (scanned from paper original: notes about this process)
This year's abstracts |
Journal home page |
All abstracts |
Publishing home page
