New Zealand Journal of Geology and Geophysics abstracts
Orbitally controlled cyclicity around the Cretaceous/Tertiary boundary,
northern South Island, New Zealand
Brad D. Field
Chris J. Hollis
Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
email: b.field@gns.cri.nz
Abstract Outcrop gamma ray measurements are used as
a proxy for terrigenous clastic component in Cretaceous-Paleocene carbonate-chert
successions in northern South Island, New Zealand, and show Milankovitch-scale
periodicity above the Cretaceous/Tertiary (K/T) boundary. Higher baseline
values of the gamma ray records from sections in the south compared to those
in the north reflect increased terrigenous clay content associated with shallowing
in paleobathymetry towards the south. In each northern section, the gamma
ray baseline level increases across the K/T boundary, consistent with an
increase in terrigenous clay in the early Paleocene; this might record increased
erosion due to destruction or change of vegetation or a fall in relative
sea level. Peak amplitudes in the gamma ray record are higher for the early
Paleocene, perhaps recording more pronounced climatic variability after the
K/T boundary event, and consistent with a South Atlantic record. Cycle frequencies
in the Late Cretaceous are not well constrained due to the sparseness of
biostratigraphic events but could be consistent with eccentricity. Biostratigraphic
age control in the Paleocene constrains cycle frequency to c. 120 000 yr
and suggests the early Paleocene climate in the high latitude, southwest
Pacific, was modulated by orbital eccentricity.
Keywords Paleocene; orbital cycles; Milankovitch; Marlborough;
Mead Stream; Branch Stream; Woodside Creek; Waipara River; gamma ray; paleoclimate
G02030 Received 14 June 2002; accepted 14 Febuary 2003; published 30 June
2003
New Zealand Journal of Geology & Geophysics, 2003, Vol. 46: 235-241
0028-8306/03/4602-0235 $7.00/0 © The Royal Society of New Zealand
2003
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