Quaternary tephra marker beds and their potential for palaeoenvironmental reconstruction on Chatham Island, east of New Zealand, southwest Pacific Ocean

Abstract

Tephras provide one of the most reliable methods of time control and synchronisation within Quaternary sequences. We report on the identification of two widespread rhyolitic tephras -the Kawakawa and Rangitawa tephras -preserved in extensive peat deposits on Chatham Island $900 km east of New Zealand. The tephras, both products of supereruptions from the Taupo Volcanic Zone, occur as pale, fine-ash dominated layers typically 10-150 mm thick. Mineralogically they are dominated by rhyolitic glass, together with subordinate amounts of quartz, feldspar, hypersthene, hornblende, Fe-Ti oxides and zircon. Phlogopite/biotite was identified additionally in Rangitawa Tephra. Ages for each tephra were obtained via mineralogical and major element glass compositionbased correlation with well-dated equivalent deposits on mainland New Zealand, and we also obtained a new zircon fission-track age for Rangitawa Tephra (350 AE 50 ka) on Chatham Island. Both tephras were erupted at critical times for palaeoenvironmental reconstructions in the New Zealand region: the Kawakawa at ca. 27 cal. ka, near the beginning of the 'extended' LGM early in marine isotope stage (MIS) 2; and the Rangitawa at ca. 350 ka near the end of MIS 10. The time constraints provided by the tephras demonstrate that Chatham Island peats contain long-distance pollen derived from mainland New Zealand, which provides a reliable proxy for identifying glacial-interglacial climate conditions, in this case during the MIS 11-10 and MIS 2-1 cycles. The two tephras thus provide important chronostratigraphic tie-points that facilitate correlation and synchronisation not only across the Quaternary deposits of the Chatham Islands group but also with climatically significant terrestrial and marine records in the wider New Zealand region.

Tephrochronology and its application: A review

“…340 ka being obtained for the tephra and hence correct reassignment to late MOI stage 10 Holt et al, 2010).…”

“…Similarly the Kawakawa/Oruanui tephra, erupted from northern New Zealand ca. 27.1 ka cal BP, forms a key isochron linking numerous terrestrial and marine sequences extending more than 1500 km across the New Zealand and southwest Pacific region near the start of marine oxygen isotope (MOI) stage 2 (Newnham et al, 2007a;Lowe et al, 2008aLowe et al, , 2010Holt et al, 2010). At each location, the Kawakawa/Oruanui tephra deposit represents a time span probably of just a few months over which the entire eruption episode took place (Wilson, 2001;Manville and Wilson, 2006), together with the short times needed for atmospheric dispersion and marine settling.…”

“…340 ka Rangitawa tephra (Fig. 4A) in the New ZealandSouth Pacific region, noted earlier as being the subject of controversy regarding its age, was dated using zircon-and glass-based fission-track analysis, glass-ITPFT analysis, infra-red stimulated luminescence, thermoluminescence, K/Ar and single-crystal laser fusion 40 Ar/ 39 Ar analysis, and orbital tuning estimated via oxygen isotope stratigraphy in deep-sea cores Alloway et al, 2007a;Holt et al, 2010).…”

TephraNZ: a major and trace element reference dataset for prominent Quaternary rhyolitic tephras in New Zealand and implications for correlation

“…The new reference material built by this project will allow more definitive identification and correlation of tephras within these cores, specifically post-2 Ma. However, the reports currently published on these deposits suggest that there are many more tephra deposits to be found in these 740 marine and offshore sites than we have in the TephraNZ dataset (Carter et al, 2003;Alloway et al, 2005;Holt et al, 2010Holt et al, , 2011. The TephraNZ dataset can provide a formalised correlation framework from which other unknown deposits can be determined, characterised, and integrated into a holistic tephrostratigraphic reconstruction.…”

Using Soil Stratigraphy and Tephrochronology to Understand the Origin, Age, and Classification of a Unique Late Quaternary Tephra-Derived Ultisol in Aotearoa New Zealand

“…The white, c. 0.5-m-thick Rangitawa Tephra is c. 340 ka in age. Erupted from Whakamaru Volcanic Centre ( Figure 1B) as the product of a super-eruption [170], it fell late in MOI Stage 10, thereby providing a key paleoclimatic marker throughout New Zealand and beyond for this period [65,[171][172][173][174][175]. Rangitawa Tephra is overlain in turn by a c. 3-m thick sequence of weathered, yellowish brown to brown to reddish brown weathered, clayey tephra beds and buried soils-the Hamilton Ash beds-that must represent MOIS 9 to 5 (Figure 3) [55].…”