New Zealand Journal of Geology and Geophysics abstracts
Identification of a Waipawa Formation equivalent in the upper Te Uri Member of
the Whangai Formation - implications for depositional history and age
KARYNE M. ROGERS
HUGH E. G. MORGANS
GARY S. WILSON1
Institute of Geological & Nuclear Sciences
P. O. Box 30 312
Lower Hutt, New Zealand
1Present Address: Department of Earth Sciences, University of
Oxford, Parks Road, Oxford, OX1 3PR, United Kingdom.
Abstract Stable isotopes and biomarkers have identified a
unit with similar organic geochemistry to the Waipawa Formation, in the upper
Te Uri Member of the Whangai Formation, exposed in the Akitio River, at
Tawanui, southern Hawke's Bay, New Zealand. At Tawanui, the uppermost greensand
of the Te Uri Member contains a large positive δC isotopic excursion from
-27.0‰ to -20‰ and an increase in total organic
carbon from 0.1% to 1.0%. Biomarker analyses demonstrate a similar C30 sterane
fingerprint to other deposits of the Waipawa Formation.
We propose that the uppermost greensand of the Te Uri Member at Tawanui is a
condensed stratigraphic equivalent of the Waipawa Formation at nearby Angora
Stream and other East Coast Basin localities. This correlation demonstrates
that Waipawa Formation is middle Teurian (middle Paleocene) and precedes the
late Paleocene thermal maximum event by c. 5 m.y. The likely upwelling event
that resulted in deposition of the Waipawa Formation was geographically
widespread but probably restricted to the outer shelf/upper slope. In places,
biogenic activity prevented the preservation of organic carbon in equivalent
condensed stratigraphic intervals. Localised restriction of upwelling and black
shale deposition may be demonstrated by the occurrence of a thick black shale
at Angora Stream only c. 10 km from the coeval greensands at Tawanui.
Alternatively, Oligocene-Miocene east-west shortening and structural
reorganisation in the East Coast Basin may have juxtaposed facies that were
originally many tens of kilometres apart.
Our correlation also implies that the Te Uri Member is diachronous. It may
have been on the outermost shelf to upper slope during lowstand conditions,
where it is oldest, to higher on the shelf during transgression and highstand
conditions.
Keywords Waipawa Formation; black shale; Te Uri Member;
Whangai Formation; δ13C isotopes; biomarkers; glaucony; East
Coast Basin; Tawanui; Angora Stream
New Zealand Journal of Geology & Geophysics, 2001, Vol. 44:
347-354
0028-8306/01/4402-0347 $7.00/0 (c) The Royal Society of New Zealand
2001
PDF file of entire paper: medium quality (2527K); (scanned from paper original: notes about this process)
This year's abstracts |
Journal home page |
All abstracts |
Publishing home page
