New paleomagnetic results from Blind River: Revised magnetostratigraphy and tectonic rotation of the Marlborough region, South Island, New Zealand

Abstract

Part of the Upper Miocene-Lower Pliocene mudstone section at Blind River, northern Marlborough, which was the subject of a paleomagnetic study by Kennett and Watkins in 1974, has been resampled and the data reinterpreted. The new results do not concur entirely with those of Kennett and Watkins. In particular, we do not find the uppermost normal event of their record. This implies a more uniform deposition rate and a later date of 5.6 m.y. for the first occurrence of Globorotalia conomiozea in the section.The new data also show a declination anomaly of 36 ± 4° to the east. This is thought to be due to clockwise rotation within the active tectonic belt of New Zealand, between the Pacific and Australian plates. This declination anomaly is slightly larger than those reported from sites in the northern part of the tectonic belt, suggesting thatthedeformation is more complex than a simple block rotation.

Relocation of the tectonic boundary between the Raukumara and Wairoa Domains (East Coast, North Island, New Zealand): Implications for the rotation history of the Hikurangi margin

“…Data published in their appendix show that 50% of samples were AF demagnetised at only 10-20 mT, the level at which stable behaviour had been observed in pilot samples demagnetised to 30 mT. This blanket demagnetisation approach is no longer considered adequate (Opdyke & Channell 1996), especially in the presence of the strong magnetic overprints common in New Zealand Cenozoic mudstones; several studies have demonstrated that detailed stepwise thermal demagnetisation of all samples is required to properly isolate primary components in such rocks (Turner et al 1989;Turner & Kamp 1990;Roberts 1992;Pillans et al 1994;Roberts et al 1994;Roberts 1995;Turner 2001).…”

Application of a palaeomagnetic reversal stratigraphy to constrain well correlation and sequence stratigraphic interpretation of the Eocene C1 Sands, Maui Field, New Zealand

“…Initially, thermal demagnetization was used, as this has usually been more successful than alternating field methods in younger New Zealand marine shales (Turner et al 1989;Roberts et al 1994). An example of the results obtained for a shale specimen from Maui-6 is shown in…”

The age of the Tortonian/Messinian boundary

“…They derived an age of 6.44 Ma or 5.40 Ma, pending two different interpretations of the nannofossil record [9]. Magnetostratigraphic studies from outside the Mediterranean yielded similar ambiguous results with ages ranging between 5.6 and 6.44 Ma for the FOD of G. conomiozea [10][11][12][13][14]. For the actual dating of the T/M boundary these studies are considered less critical because it is questionable whether the FOD of G. conomiozea, which represents a migratory event in the Mediterranean [15,16], is globally synchronous [17].…”