New Zealand Journal of Geology and Geophysics abstracts

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Definition, age, and correlation of the Clarence Series stages in New Zealand (late Early to early Late Cretaceous)

James S. Crampton¹
Andy J. Tulloch²
Graeme J. Wilson¹
Jahan Ramezani³
Ian G. Speden¹

¹Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
email: j.crampton@gns.cri.nz

²Institute of Geological & Nuclear Sciences
Private Bag 1930
Dunedin, New Zealand

³Department of Earth, Atmospheric, and Planetary Sciences
Massachussetts Institute of Technology
Cambridge, MA 02139, USA

Abstract  The New Zealand local Clarence Series spans the Lower/Upper Cretaceous boundary and includes three stages, in ascending order, the Urutawan, Motuan, and Ngaterian. All three were defined originally from a type section at Motu Falls, Raukumara Peninsula. To address problems with their original definitions and to improve correlations between the New Zealand time-scale and Global Chronostratigraphic Scale, four key sections have been re-studied: the Motu Falls and adjacent Te Waka sections, and the Coverham and Seymour sections in the Clarence valley, Marlborough. The sections contain locally abundant macrofossils and have been sampled at a reconnaissance level for dinoflagellates. In addition, a middle Motuan tuff bed in the Motu Falls section has yielded a zircon U-Pb age of 101.6 ± 0.2 Ma, and an upper Ngaterian basalt flow in the Seymour section has yielded a plagioclase Ar/Ar age of 96.1 ± 0.6 Ma. The older of these dates allows, for the first time, direct age correlation of Clarence Series stages that are based on marine strata in eastern New Zealand, with non-marine rocks in the west. Thus, the Stitts Tuff, at the base of the Pororari Group in the western South Island, is shown to be middle Motuan.Based on the new data, we emend the definitions of the Clarence Series stages. The base of the Urutawan is defined using the lowest occurrence of the inoceramid bivalve Mytiloides ipuanus in the Motu Falls section. The base of the Motuan is defined using the lowest occurrence of the bivalve Aucellina euglypha in the same section. The base of the Ngaterian is defined using the lowest occurrence of the inoceramid “I.” tawhanus in the Te Waka section. In all three cases, the placements of the lowest occurrence datums are subject to uncertainties that can only be resolved by further biostratigraphic and/or taxonomic study. Based on biostratigraphic data and the new radiometric dates, the following international correlations are proposed: Urutawan Stage = lower-middle Albian (108-103 Ma); Motuan Stage = middle-upper Albian (103-100 Ma); Ngaterian Stage = upper Albian to middle Cenomanian (100-95 Ma).

Keywords  Albian; biostratigraphy; Cenomanian; chronostratigraphy; Clarence Series; Early Cretaceous; Late Cretaceous; Marlborough; Motuan Stage; Ngaterian Stage; radiometric dates; Raukumara Peninsula; time-scale; Urutawan Stage

G02050; Online publication date 25 February 2004
Received 23 September 2002; accepted 4 September 2003
New Zealand Journal of Geology & Geophysics, 2004, Vol. 47: 1-19
0028-8306/04/4701-0001 © The Royal Society of New Zealand 2004

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