Chronology of the Middle Pleistocene Kidnappers Group, New Zealand and correlation to global oxygen isotope stratigraphy

Abstract

Middle Pleistocene strata of the Kidnappers Group consist of a conformable sequence of alternating fluvio-lacustrine and shallow marine sediments exposed along coastal cliffs near Cape Kidnappers, southern Hawkes Bay, New Zealand. Three major paleomagnetic polarity intervals are recognised and interpreted as Jaramillo Normal Subchron, upper Matuyama Reversed Chron and Brunhes Normal Chron. This and biostratigraphy indicates an age range of 0.97 to 0.54 Ma for the group, compared to 0.85 to < 0.33 Ma previously suggested by fission track ages of tuffs.The new age control and facies interpretations suggest that the upper part of the group represents oxygen isotope stages 22 to 15. The duration and magnitude of isotope stages is reflected in the relative thicknesses of lithological units. Glacial periods are recorded as alluvial aggradation in the form of braidplain conglomerates, while estuarine and subaerial sands and muds with temperate climate pollens represent interglacial periods. This contrasts with many coastal and shelf sequences where glacial periods are represented by unconformities.Chemical and paleomagnetic characterisation of silicic tuffs in the Kidnappers Group establishes correlation to other sections and cores in New Zealand, the Tasman Sea and the western Pacific Ocean, thus providing temporal correlation for a range of sedimentary environments.