New Zealand Journal of Geology and Geophysics abstracts
Paleoenvironmental and tectonic changes across the Cretaceous/Tertiary
boundary at Tora, SE Wairarapa, New Zealand: a link between Marlborough and
Hawke's Bay
M. G. Laird1
K. N. Bassett1
P. SchiØler2
H. E. G. Morgans3
J. D. Bradshaw1
S. D. Weaver1
1Department of Geological Sciences
University of Canterbury
Private Bag 4800
Christchurch, New Zealand
2Geological Survey of Denmark and Greenland
Thoravej 8
2400 Copenhagen, Denmark
3Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
Abstract The Late Cretaceous–Paleocene succession exposed
on the Tora coast, near the southeastern tip of the North Island, is distinguished
by an unusual lithofacies of the Whangai Formation, and by an apparently unique
formation, Manurewa Formation, which spans the Cretaceous/Tertiary (K/T)
boundary. The Late Cretaceous siliceous Whangai Formation at Tora includes
zones of slumps and olistostromes, containing megaclasts of limestone up
to 3 m long. The olistostromal deposits suggest steep submarine topography
with a high rate of erosion, and imply tectonic activity. The common occurrence
of hummocky cross-stratification suggests deposition in shelf depths above
storm wave base. The sharply overlying Manurewa Formation is interpreted
as the infill of a major shallow channel complex, perhaps >9 km wide and
spanning the K/T boundary in time. The older of two channelled units is of
latest Cretaceous (latest Haumurian/late Maastrichtian) age, and consists
of bioturbated alternating thin sandstone and mudstone with thin conglomerate
lenses and limestone beds. It is likely to have been deposited in a low-energy
environment, probably deeper than that of the Whangai. The younger channel
system, of early Paleocene (early Teurian) age, erodes into the older in
the northeast, and into the underlying Whangai Formation in the southwest.
Basal deposits consist predominantly of medium to coarse, thick-bedded, glauconitic
sandstone, with local low-angle cross-stratification and microflora typical
of low salinity conditions, suggesting deposition in shallow shelf depths.
These deposits contain olistrostromes with megaclasts up to 1 m long of limestone
and rarer dark grey siltstone or very fine sandstone clasts typical of Whangai
Formation. The inclusion of megaclasts of Whangai Formation indicates that
local emergence and erosion of older strata was occurring. Deposits grade
upward into well-sorted bioturbated sandstones of the Awhea Formation, with
prominent low-angle cross-stratification, interpreted as very shallow marine,
probably nearshore deposits. The channel system represented by the Manurewa
Formation records an initial relative sea-level rise, followed by an abrupt
sea-level fall at, or close to, the K/T boundary. New Zealand was in a passive
margin tectonic setting at the time, but the widespread presence of olistostromes,
some including clasts derived from older strata, suggest that local tectonic
activity and uplift was occurring. The effects may have been enhanced by
a climatic shift in storm tracks and intensity in the latest Cretaceous,
which is supported by the evidence of strong wave activity. By contrast,
to the south in Marlborough, the K/T boundary succession is commonly characterised
by an apparently conformable lithologic change from limestone to chert, although
with local hiatus. To the north, in southern HawkeÕs Bay, the coeval
succession is characterised by a disconformity separating greensand from
underlying light grey, slightly calcareous mudstone of the Whangai Formation.
The Tora sequence may provide the link between two distinctly different lithologic
successions.
Keywords Cretaceous; Paleocene; Cretaceous/Tertiary
boundary; Haumurian; Teurian; Maastrichtian; Glenburn Formation; Whangai
Formation; Manurewa Formation; Awhea Formation; sedimentology; tectonics;
sea levels; submarine channels; olistostromes; Wairarapa; East Coast Basin
G02013 Received 28 February 2002; accepted 10 March 2003; published 30
June 2003
New Zealand Journal of Geology & Geophysics, 2003, Vol. 46: 275–293
0028-8306/03/4602-0275 $7.00/0 © The Royal Society of New Zealand
2003
PDF file of entire paper: Print-quality (7086K)
|screen-quality (350K)
This year's abstracts |
Journal home page |
All abstracts |
Publishing home page
