Fission-track ages of late Pleistocene tephra on the Bay of Plenty coast, North Island, New Zealand

Abstract

In the area surrounding Opotiki on the Bay of Plenty coast, tephra deposits are classified into 3 units: post-Hamilton tephras, Hamilton Ash, and Tablelands Tephra Formation. Each is separated by well-developed paleosols or unconformities. The Rotoehu Ash and the Ohinewai Tephra are located at the bases of the post-Hamilton tephras and the Hamilton Ash, respectively.Tablelands Tephra Formation (new) is defined and tentatively subdivided into upper and lower members by paleosols or unconformities that commonly occur at different exposures. This formation contains several characteristic pumice layers which are very useful for tephrochronological correlation. Obsidian fragments from 3 of the pumice layers in the lower member were collected for fission-track dating, which yielded ages between 0.21 and 0.18 m.y. The fission-track ages of these tephras are consistent with their stratigraphy."Present address:

The last interglacial sea-level record of New Zealand (Aotearoa)

“…On the North Island, two tephras have been used consistently as stratigraphic markers to constrain and identify MIS 5 terraces and associated sediments: the Rotoehu Ash and the Hamilton Ash (Pullar and Grant-Mackie, 1972;Chappell, 1975;Pain, 1976;Iso et al, 1982;Ota et al, 1989;Berryman, 1993;Wilson et al, 2007;Claessens et al, 2009 Fleming, 1972-120-80 -Mildenhall, 1995-125-70 Pillans, 1991 MIS 5e Chappell, 1970;5 ± 3 120 Chappell, 1974Bloom et al, 1974Pillans, 19831990b5 120 Chappell & Veeh, 1978Palmer, 1988-c. 120 Pillans, 1985Berryman, 19936 ± 5 124 ± 5 Chappell & Shackleton, 1986Kim and Sutherland, 2004 3 ± 2 120 Lambeck & Chappell, 2001Litchfield and Lian, 2004-128-113 Chappell et al, 1996Cooper and Kostro, 20065 ± 2 c. 125 Veeh & Chappell, 1970Harmon et al, 1983;Chappell et al, 1996;Stirling et al, 1996Wilson et al 20070 ± 5 125 ± 5 Pillans et al, 1998Oakley et al, 20175 ± 2 124.5 ± 5.5 Lambeck & Chappell, 2001Siddall et al, 2007 MIS 5c Chappell, 1970;-14 104 Chappell, 1974Bloom et al, 1974Berryman, 1993...…”

“…Alternatively, Briggs et al (2006) found the designation as a Formation 1000 inappropriate given that some of the tephra beds could be found preserved as individual layers in the Maketu areanear to the locus of Mid-Pleistocene TVZ activity, the likely source of the tephras. Where both are present, the Hamilton Ash sequence is overlain by the Rotoehu Ash (Ward, 1967;Vucetich and Pullar, 1982;Iso et al, 1982;Lowe et al, 2001). The Hamilton Ash has been used to constrain marine terrace development or associated dune sand deposition with the understanding that the youngest tephra bed dated to ~MIS 6/5 (Pullar and Grant-Mackie, 1972;Chappell, 1975;Pain, 1976;Iso et al, 1982;Ota et 1005Ota et al, 1989.…”

“…On the North Island, tephrochronology is commonly used both as a regional stratigraphic marker and to assist in constraining marine terrace age (e.g. Pullar and Grant-Mackie, 1972;Chappell, 1975;Pain, 1976;Iso et al, 1982;Ota et al, 1989;Berryman, 1993;Wilson et 110 al., 2007;Claessens et al, 2009). For the purposes of determining last interglacial age the tephras most commonly referred to are the Rotoehu Tephra at ~47 ka (Danišík et al, 2012;Flude and Storey, 2016), providing a minimum age, and the Hamilton Ash at ~340 ka (Pillans et al, 1996;Lowe et al, 2001) providing a maximum age (Section 5.3.2).…”

Pleistocene marine terraces in New Zealand: A review

“…With the first applications of fission-track dating in New Zealand by Barry Kohn and Diane Seward at about the same time, a versatile technique became available for dating widespread rhyolitic tephra. Although initially applied to dating central North Island ignimbrites (Kohn 1973) and reworked tephra of Wanganui Basin (Seward 1974(Seward , 1976, fission-track dating of tephra in nonmarine cover beds has been used by Barter (1976), Iso et al (1982), and Pillans (1983) to constrain the ages of terraces in three areas of the North Island.…”

230Th-238U age of Rotoehu Ash and its implications for marine terrace chronology of eastern Bay of Plenty, New Zealand

“…Matakaoa Terrace is considered to be formed during the penultimate interglacial stage, because it is overlain by Tablelands Tephra Formation, which has fission-track ages of c. 200 ka (Iso et al 1982), and by youngertephra. Otamaroa Terrace is the most widely preserved terrace, and it is underlain by thick marine deposits at major river mouths suggesting that it was formed at the time of a majorstage of transgression.…”