ASTRONOMICAL CALIBRATION OF A SOUTHERN-HEMISPHERE PLIOPLEISTOCENE REFERENCE SECTION, WANGANUI BASIN, NEW-ZEALAND

Wanganui Basin, New Zealand, contains one of the most complete late Ne ogene stratigraphic records in the world. The ca. 3 km thick basin-fil l for the last 3.6 Ma comprises 58 superposed fifth and sixth-order sh allow marine sedimentary cycles which correspond to individual 100 and 41 ka sea-level cycles since oxygen isotope stage MG6. Stages MG6 to 5 are represented by marine cyclothems, whereas stages 17 to 4 are rep resented by a suite of coeval and younger uplifted marine terrace sequ ences. Additionally, a predominantly glacial loess stratigraphy exists for isotope stages 12-2. The Milankovitch-frequency, shallow marine, cyclostratigraphy of Wanganui Basin is here correlated with the astron omically-calibrated Plio-Pleistocene timescale of Lourens ct al. (1996 , Paleoceanography, 11, 391-413). An integrated chronology is presente d for Wanganui Basin based on radiometric ages on interbedded rhyoliti c tephra, on biostatigraphic data, on paleomagnetic polarity measureme nts, and on cycle correlations with the oxygen isotope timescale. Nume ric ages on the tephra are consistent with the interpreted magnetostra tigraphy and cyclostratigraphy, and fit well with the astronomically-c alibrated timescale. Our cyclostratigraphic correlations provide age e stimates for 116 stratigraphic horizons in Wanganui Basin that are not otherwise able to be dated, and thereby establish an astronomical chr onostratigraphy for the New Zealand Plio-Pleistocene. The historic sub division of the New Zealand marine Plio-Pleistocene is based on the bi ostratigraphy of shallow marine strata in both Wanganui and East Coast basins, North Island. Based on the new cyclostratigraphic correlation s we re-evaluate the age of all New Zealand Plio-Pleistocene stage and substage boundaries. After making these revisions, the current age es timates for the base of the Opoitian, Waipipian, Mangapanian, Nukumaru an, Castlecliffian, and Haweran Stages are 5.25, 3.60, 3.03, 2.46, 1.0 7, and 0.34 Ma, respectively, and the ages of the Hautawan-Marahauan ( intra-Nukumaruan) and Okehuan-Putikian (intra-Castlecliffian) Substage boundaries are 2.15 and 0.78 Ma, respectively. (C) 1998 Elsevier Scie nce Ltd. All rights reserved.