Integrated stratigraphy of the lower Altonian (Early Miocene) sequence at Tangakaka Stream, East Cape, New Zealand

Abstract

The biostratigraphy of a rapidly deposited, deep bathyal, lower Altonian (Early Miocene) sequence through Whakai Formation, East Cape, is presented. We interpret the depositional milieu, identify and describe foraminiferal and nannofossil bioevents potentially useful in biostratigraphy, and relate these to the magnetostratigraphy, 40 Ar/ 39 Ar ages, and ages using the Sr isotope sea-water curve. Although lower and upper contacts of the 623 m section through Whakai Formation are obscured, a high (c. 0.9 m/ka) flux of muddy sediment has produced an amplified record of most of the lower Altonian Globorotalia incognita Zone and the base of the overlying Globorotalia zealandica Zone. No significant breaks were identified. Benthic foraminiferal paleodepth proxies suggest that the site was on the lower slope (>1000 m) throughout, but the moderate abundance of planktonic taxa shows that it was not in fully oceanic water. Planktonic assemblages identify warm-temperate water masses. Abundance data for both nannofossils and planktonic G00062;

Early Miocene magnetostratigraphy and a new palaeomagnetic pole position from New Zealand

“…3(i)) is the early Miocene part of the geomagnetic polarity timescale (GPTS) of Kent (1992, 1995). The biostratigraphic age control discussed above suggests correlation of the lowermost normal polarity interval with Chron C5En, by comparison with results from Tangakaka Stream, NE North Island, which are supported by an Ar-Ar age estimate on a key tephra layer (Morgans et al, 2002). This is in accord with the recommendations of Berggren et al, (1995) in their Cenozoic chronostratig- raphy and of Cooper (2004) in the New Zealand Geological Timescale.…”

“…4(A)), which disappears from the New Zealand region in the lower Globorotalia zealandica zone (Scott, 1992) also supports a mid Altonian age. Morgans et al (2002) place the base of the Globorotalia zealandica zone in Chron C5En (18.781-18.281 Ma). Rare Globorotalia praescitula ( Fig.…”

Late Paleocene to middle Eocene foraminiferal biostratigraphy of the Hampden Beach section, eastern South Island, New Zealand

“…In previous foraminiferal studies of this nature (Morgans et al 1999(Morgans et al , 2002, census populations contained little broken material; most were only slightly damaged, good enough to be recorded as whole specimens. Comparison with these early Miocene faunas reveals they contain much lower proportions of agglutinated taxa and elongate nodosariids, which dominate the broken specimens in the Hampden sequence.…”

Olistostromes marking tectonic events, East Coast, New Zealand

“…Several samples collected within underformed layers of the upper part of the sequence, as close as possible to the lowest exotic lenses, raised problems as the foraminiferal fauna commonly appeared to be winnowed, lacking reliable age-diagnostic taxa, and with assemblages commonly contaminated by older microfossils. An Oligocene age was proposed by Moore (1988b) but additional sampling of the Owahanga olistostrome showed it to be Otaian (late Aquitanianto lower Burdigalian; Morgans et al 1999Morgans et al ,2002; Table 1, samples U25/f205 and f325).…”

“…It underlies alternating well-bedded Miocene sediments and variably large lenses of exotic siltstone and marl, respectively, of latest Cretaceous and Oligocene ages. The youngest assemblages from samples collected within the blocky facies matrix between exotic lenses provide an Altonian (late Burdigalian; Morgans et al 2002) age for emplacement of the Mara olistostrome (Table 1, samples U25/f192andf316).…”