Role of tephra in dating Polynesian settlement and impact, New Zealand

Tephrochronology in its original sense is the use of tephra layers as time-stratigraphic marker beds to establish numerical or relative ages (Lowe and Hunt, 2001). Tephra layers have been described and studied in New Zealand for more than 160 years (the German naturalist and surgeon Ernst Dieffenbach described ‘recognizable’ tephra sections in his 1843 book Travels in New Zealand), and the first isopach map, showing fallout from the deadly plinian basaltic eruption of Mt Tarawera on 10 June 1886, was published in 1888 (Lowe, 1990; Lowe et al., 2002). More recently, a wide range of tephra-related paleoenvironmental research has been undertaken (e.g., Lowe and Newnham, 1999; Newnham and Lowe, 1999; Newnham et al., 1999, 2004; Shane, 2000), including new advances in the role of tephra in linking and dating sites containing evidence for abrupt climatic change (e.g., Newnham and Lowe, 2000; Newnham et al., 2003). Here we focus on the use of tephrochronology in dating the arrival and impacts of the first humans in New Zealand, a difficult problem for which this technique has proven to be of critical importance

Stratigraphy and chronology of a 15ka sequence of multi-sourced silicic tephras in a montane peat bog, eastern North Island, New Zealand.

We document the stratigraphy, composition, and chronology of a succession of 16 distal, silicic tephra layers interbedded with lateglacial and Holocene peats and muds up to c. 15 000 radiocarbon years (c. 18 000 calendar years) old at a montane site (Kaipo Bog) in eastern North Island, New Zealand. Aged from 665 +/- 15 to 14 700 +/- 95 14C yr BP, the tephras are derived from six volcanic centres in North Island, three of which are rhyolitic (Okataina, Taupo, Maroa), one peralkaline (Tuhua), and two andesitic (Tongariro, Egmont). Correlations are based on multiple criteria: field properties and stratigraphic interrelationships, ferromagnesian silicate mineral assemblages, glass-shard major element composition (from electron microprobe analysis), and radiocarbon dating. We extend the known distribution of tephras in eastern North Island and provide compositional data that add to their potential usefulness as isochronous markers. The chronostratigraphic framework established for the Kaipo sequence, based on both site-specific and independently derived tephra-based radiocarbon ages, provides the basis for fine-resolution paleoenvironmental studies at a climatically sensitive terrestrial site from the mid latitudes of the Southern Hemisphere. Tephras identified as especially useful paleoenvironmental markers include Rerewhakaaitu and Waiohau (lateglacial), Konini (lateglacial-early Holocene), Tuhua (middle Holocene), and Taupo and Kaharoa (late Holocene)

Late Holocene palynology and palaeovegetation of tephra-bearing mires at Papamoa and Waihi Beach, western Bay of Plenty, North Island, New Zealand.

The vegetation history of two mires associated with Holocene dunes near the western Bay of Plenty coast, North Island, New Zealand, is deduced from pollen analysis of two cores. Correlation of airfall tephra layers in the peats, and radiocarbon dates, indicate that the mires at Papamoa and Waihi Beach are c. 4600 and c. 2900 conventional radiocarbon years old, respectively. Tephras used to constrain the chronology of the pollen record include Rotomahana (1886 AD), Kaharoa (700 yr B.P.), Taupo (Unit Y; 1850 yr B.P.), Whakaipo (Unit V; 2700 yr B.P.), Stent (Unit Q; 4000 yr B.P.), Hinemaiaia (Unit K; 4600 yr B.P.), and reworked Whakatane (c. 4800 yr B.P.) at Papamoa, and Kaharoa and Taupo at Waihi Beach. Peat accumulation rates at Papamoa from 4600 - 1850 yr B.P. range from 0.94 to 2.64 mm/yr (mean 1.37 mm/yr). At Waihi Beach, from 2900 yr B.P. - present day, they range from 0.11 to 0.21 mm/yr (mean 0.20 mm/yr). Peat accumulation at both sites was slowest from 1850 to 700 yr B.P., suggesting a drier overall climate during this interval. At both sites, the earliest organic sediments, which are underlain by marine or estuarine sands, yield pollen spectra indicating salt marsh or estuarine environments. Coastal vegetation communities declined at both sites, as sea level gradually fell or the coast prograded, and were eventually superseded by a low moor bog at Papamoa, and a mesotrophic swamp forest at Waihi Beach. These differences, and the marked variation in peat accumulation rates, probably reflect local hydrology and are unlikely to have been climatically controlled. The main regional vegetation during this period was mixed northern conifer-angiosperm forest. Kauri (Agathis australis) formed a minor component of these forests, but populations of this tree have apparently not expanded during the late Holocene at these sites, which are near its present southern limit. Occasional shortlived forest disturbances are detectable in these records, in particular immediately following the deposition of Taupo Tephra. However, evidence for forest clearance during the human era is blurred by the downward dislocation of modern adventi ve pollen at these sites, preventing the clear differentiation of the Polynesian and European eras

Palynology, vegetation and climate of the Waikato lowlands, North Island, New Zealand, since c. 18,000 years ago

The vegetational and climatic history of the Waikato lowlands during the last c. 18,000 years is inferred from the palynology of sediment cores from Lakes Rotomanuka, Rotokauri, and Okoroire. Intra- and inter-lake correlations were aided by multiple tephra layers interbedded with the lake sediments. The detailed chronological resolution given by these tephra sequences shows that late glacial-post glacial vegetational and climatic changes were nearly simultaneous throughout the Waikato lowlands

Advances in Quaternary tephrostratigraphy and tephrochronology in New Zealand

This paper summarises recent studies on Quaternary tephra deposits in New Zealand, and refers to a range of tephrochronological applications including sequence stratigraphy, palaeoclimatic reconstruction, and archaeology. Topics touched upon include tephrostratigraphy, geochronology, geochemical correlation techniques, volcanology, and volcanic hazards and impacts. Some key tephra marker beds, ranging in age from 0.65 ha to 1.63 Ma, are identified. Recently-acquired tephra-bearing cores from both terrestrial and deep-sea environments, extending through or beyond the Quaternary, provide great potential for detailed, fine-resolution volcanological and palaeoenvironmental studies. The tephra-based research in New Zealand demonstrates the importance of tephra deposits as stratigraphic markers, dating tools, and recorders of volcanic eruption history. An extensive reference list is provided

Ages of 24 widespread tephras erupted since 30,000 years ago in New Zealand, with re-evaluation of the timing and palaeoclimatic implications of the Lateglacial cool episode recorded at Kaipo bog

Tephras are important for the NZ-INTIMATE project because they link all three records comprising the composite inter-regional stratotype developed for the New Zealand climate event stratigraphy (NZ-CES). Here we firstly report new calendar ages for 24 widespread marker tephras erupted since 30,000 calendar (cal.) years ago in New Zealand to help facilitate their use as chronostratigraphic dating tools for the NZ-CES and for other palaeoenvironmental and geological applications. The selected tephras comprise 12 rhyolitic tephras from Taupo, nine rhyolitic tephras from Okataina, one peralkaline rhyolitic tephra from Tuhua, and one andesitic tephra each from Tongariro and Egmont/Taranaki volcanic centres. Age models for the tephras were obtained using three methods: (i) 14C-based wiggle-match dating of wood from trees killed by volcanic eruptions (these dates published previously); (ii) flexible depositional modelling of a high-resolution 14C-dated age-depth sequence at Kaipo bog using two Bayesian-based modelling programs, Bacon and OxCal's P_Sequence function, and the IntCal09 data set (with SH offset correction -44 ± 17 yr); and (iii) calibration of 14C ages using OxCal's Tau_Boundary function and the SHCal04 and IntCal09 data sets. Our preferred dates or calibrated ages for the 24 tephras are as follows (youngest to oldest, all mid-point or mean ages of 95% probability ranges): Kaharoa AD 1314 ± 12; Taupo (Unit Y) AD 232 ± 10; Mapara (Unit X) 2059 ± 118 cal. yr BP; Whakaipo (Unit V) 2800 ± 60 cal. yr BP; Waimihia (Unit S) 3401 ± 108 cal. yr BP; Stent (Unit Q) 4322 ± 112 cal. yr BP; Unit K 5111 ± 210 cal. yr BP; Whakatane 5526 ± 145 cal. yr BP; Tuhua 6577 ± 547 cal. yr BP; Mamaku 7940 ± 257 cal. yr BP; Rotoma 9423 ± 120 cal. yr BP; Opepe (Unit E) 9991 ± 160 cal. yr BP; Poronui (Unit C) 11,170 ± 115 cal. yr BP; Karapiti (Unit B) 11,460 ± 172 cal. yr BP; Okupata 11,767 ± 192 cal. yr BP; Konini (bed b) 11,880 ± 183 cal. yr BP; Waiohau 14,009 ± 155 cal. yr BP; Rotorua 15,635 ± 412 cal. yr BP; Rerewhakaaitu 17,496 ± 462 cal. yr BP; Okareka 21,858 ± 290 cal. yr BP; Te Rere 25,171 ± 964 cal. yr BP; Kawakawa/Oruanui 25,358 ± 162 cal. yr BP; Poihipi 28,446 ± 670 cal. yr BP; and Okaia 28,621 ± 1428 cal. yr BP. Secondly, we have re-dated the start and end of the Lateglacial cool episode (climate event NZce-3 in the NZ-CES), previously referred to as the Lateglacial climate reversal, as defined at Kaipo bog in eastern North Island, New Zealand, using both Bacon and OxCal P_Sequence modelling with the IntCal09 data set. The ca 1200-yr-long cool episode, indicated by a lithostratigraphic change in the Kaipo peat sequence to grey mud with lowered carbon content, and a high-resolution pollen-derived cooling signal, began 13,739 ± 125 cal. yr BP and ended 12,550 ± 140 cal. yr BP (mid-point ages of the 95% highest posterior density regions, Bacon modelling). The OxCal modelling, generating almost identical ages, confirmed these ages. The Lateglacial cool episode (ca 13.8-12.6 cal. ka BP) thus overlaps a large part of the entire Antarctic Cold Reversal chronozone (ca 14.1-12.4 cal. ka BP or ca 14.6-12.8 cal. ka BP), and an early part of the Greenland Stadial-1 (Younger Dryas) chronozone (ca 12.9-11.7 cal. ka BP). The timing of the Lateglacial cool episode at Kaipo is broadly consistent with the latitudinal patterns in the Antarctic Cold Reversal signal suggested for the New Zealand archipelago from marine and terrestrial records, and with records from southern South America

High-resolution radiocarbon chronologies and synchronization of records

It is now accepted that the precise dating of certain periods is complicated by extreme variability of atmospheric ¹⁴C content shown at times in the ¹⁴C calibration curve. This complication arises from variations in atmospheric ¹⁴C content and is known as wiggles in the calibration curve. Radiocarbon age ‘plateaus’, are caused by a decrease in the atmospheric ¹⁴C concentration and appear as a slowing down of the ¹⁴C clock such as occurred during the Younger Dryas (YD) chronozone. In effect, similar ¹⁴C ages apply across a range of up to 500 calendar years. The opposite is observed when atmospheric ¹⁴C levels increase so that the ¹⁴C clock appears to speed up. In such cases, which include the beginning of the YD and Pre-Boreal intervals, the true age of a sample, taking dating errors into account, may spread across a comparatively wide ¹⁴C age rang

Quaternary research in New Zealand since 2000: an overview

With the AQUA milestone of 30 years it seems an appropriate time to review the progress and achievements of Quaternary research in New Zealand. This article highlights some of the major achievements since the formal review of New Zealand’s Quaternary record by Newnham et al. (1999). The focus here is on paleoclimate and geochronology and is by no means a comprehensive review. We encourage members to write future articles for Quaternary Australasia (QA) about their exciting projects to keep the wider Australasian community informed. One of the main differences between Australian and New Zealand Quaternary science is the wide use of tephrochronology to correlate and date deposits and events across the landscape, helping to link terrestrial and marine records, especially in the North Island. There have been significant advances using glass-based fission-track dating, corrected for annealing, and the use of the electron microprobe and laser ablation inductively-coupled plasma mass spectrometry for obtaining major- and trace-element analyses, respectively, to chemically fingerprint individual glass shards in tephras to aid their correlation (Shane, 2000; Lowe, 2011). Also the identification and analysis of cryptotephras (concentrations of glass shards not visible as a layer) have greatly expanded the geographic range of many tephras, allowing the application of tephrochronology as a stratigraphic and dating tool across much wider areas than previously possible (Gehrels et al., 2008)

Dating the Kawakawa/Oruanui eruption: Comment on "Optical luminescence dating of a loess section containing a critical tephra marker horizon, SW North Island of New Zealand" by R. Grapes et al.

An IRSL age of 17.0 ± 2.2 ka (and a “mean age” of ca. 19 ka) reported by Grapes et al. [Grapes, R., Rieser, U., Wang, N. Optical luminescence dating of a loess section containing a critical tephra marker horizon, SW North Island of New Zealand. Quaternary Geochronology 5(2-3), 164–169.] for the Kawakawa/Oruanui tephra, and other ages associated with a loess section in New Zealand are untenable: age data presented are inconsistent, no formal statistical treatments or error determinations were undertaken in age analysis, and the ages proposed are seriously at odds with multiple radiocarbon age determinations on tephra sequences bracketing the Kawakawa/Oruanui tephra and with palaeoenvironmental evidence elsewhere for the time period concerned. We suggest that the bulk polymineral IRSL ages on the tephra and encapsulating loess deposits were underestimated in part because of contamination of the loess by the integration of younger materials during slow deposition and continuous modification by upbuilding pedogenesis. Single-grain luminescence assays may reveal such contamination. A 14C-based age of ca. 27 ± 1 ka cal BP (2σ), reported in 2008, currently remains the best estimate for the age of eruption of the Kawakawa/Oruanui tephra

What was the original forest composition of Great Island (Three Kings)?

Following the extermination of goats (Capra bircus) from Great Island in 1946 the recovery of that island's vegetation has been of tremendous scientific interest. Numerous papers have been written on the subject and recent visits to Great Island by the Northland Conservancy have continued to document changes in forest structure. Since 1989 it is becoming evident that in many places the monotonous and extremely dense kanuka (Kunzea ericoides s.l.) canopy is starting to collapse, presumably due to the combined affects of old age and exposure to the often stormy maritime climate. Of interest is what the new forest structure will be. While in places the canopy and understorey is now dotted with rapidly growing specimens of porokaiwhiri (Hedycarya arborea), mangeao (Litsea calicaris) (Cameron et al. 1987; P.]. de Lange pers. obs.) and albeit less frequently, titoki (Alectryon excelsus var. grandis), the spread of these trees is being hampered by a lack of natural seed dispersers. Therefore many patches of forest either lack an understorey or have a forest composition comprising short-lived smaller trees such as pukanui (Meryta sinclairii), cabbage tree (Cordyline kaspar), Three Kings rangiora (Brachyglottis arborescens) or shorter stature trees (really large shrubs) e.g. Fairchild's kohuhu (Pittosporum fairchildii) and Oliver's mapou (Myrsine oliverii)