A widespread, early Pleistocene tephra (Potaka tephra, 1 Ma) in New Zealand: Character, distribution, and implications

Abstract

About 1 Ma ago, a large eruption in the Taupo Volcanic Zone of North Island, New Zealand, produced an extensive silicic ignimbrite now found up to 200 km from the source, and a fallout ash up to 600 km distant. The eruptive products, collectively referred to as Potaka tephra, constitute an important marker horizon and temporal control point in many early Pleistocene sequences, which otherwise lack numerical age control. The tephra is identified at many localities using multiple criteria including lithology, mineralogy, glass and mineral chemistry, magnetostratigraphy, and isotopic ages. It shows a variety of facies including a primary nonwelded ignimbrite, ash fall, and reworked volcaniclastic deposits. Potaka tephra occurs near the top of the laramillo Subchron and is immediately overlain by a normal to reversed transition. The tephra is found in both marine and terrestrial facies, and on both major islands of New Zealand. Its identification allows correlation of (1) mid-shelf, glacioeustatic cyclothems on the western side of North Island with fluvial and lacustrine facies on the eastern side of North Island, and (2) the only known middle Pleistocene marine sequence in South Island with extensive sequences in North Island. Stratigraphic position and chronology suggest Potaka tephra was erupted during oxygen isotope stage 27. The distribution of Potaka tephra indicates rapid uplift of the main axial ranges in central North Island and progradation of coastlines in the last 1 Ma.

Evolution of the southern termination of the Taupo Rift, New Zealand

“…Before the late Quaternary, the Wanganui Basin may have extended east of the present-day axial ranges (Anderton 1981;Shane 1994) and northward across much of the area now occupied by the TVZ. The SWB was confined to the present basin boundaries by early Pleistocene, and by mid-late Pleistocene the depocentre had moved to the southeast (Anderton 1981) (Fig.…”

Marine Mollusca of isotope stages of the last 2 million years in New Zealand. Part 3. Gastropoda (Vetigastropoda - Littorinimorpha)

“…Castlecliffian: Castlecliffian specimens are recorded only from eastern New Zealand: Leader River, 'Mendip Hills' Station, Parnassus, North Canterbury, where it underlies Potaka Tephra (Warren 1995, fig. 20, 21), and so is older than 1.0 Ma (Shane 1994;Shane et al 1996), that is, approximately OIS 29Á31 or older (O32/ f8875; Beu & Maxwell 1990:352, pl Dimensions. O32/f8875, Leader River, Parnassus, early Castlecliffian: H 12.8, D 9.4, H (normal to aperture) 7.4 mm; GS5216, Puketapu, Hawke's Bay: H 11.5, D 8.0, H (normal to aperture) 6.5 mm; GS12386, Roro-o-kuri, Napier: H (incomplete) 11.4, D 9.8, H (normal to aperture) 7.6 mm; holotype of T. flora: H 10.0, D 7.3, H (normal to aperture) 6.0 mm (Marwick 1928:482).…”

Marine Mollusca of oxygen isotope stages of the last 2 million years in New Zealand. Part 2. Biostratigraphically useful and new Pliocene to recent bivalves

“…comm.) and so Pecten here is more than 1.0 m yr old (Shane 1994;Shane et al 1996;Alloway et al 2005;Pillans et al 2005), that is, deposited in about OIS 29-31, or possibly significantly earlier. The locality with abundant P. novaezelandiae at Herepuru Stream, coast W of Matata, Bay of Plenty, also possibly is older than the Brunhes-Matuyama transition, as it underlies a tuff dated at 0.62 ± 0.03 Ma (Nairn & Beanland 1989, table 1) by an interval of unknown duration, but this locality is assigned here to "about OIS 15".…”

“…However, in eastern New Zealand, the marwicki phenotype is known considerably earlier at two widely separated sites: Maraetotara Formation, Cape Kidnappers; and Leader River on "Mendip Hills" Station, inland from Parnassus, N Canterbury. At both these sites, Pecten occurs below Potaka Tephra (Black 1992;Shane 1994;Warren 1995, fig. 21;Proust & Chanier 2004, fig.…”

“…Records from Castlecliffian rocks higher than Butlers Shell Conglomerate were enclosed in parentheses by , indicating that he thought all were reworked from older rocks, but (as with Austrovenus stutchburyi forma crassitesta) this probably results from an assumption by Fleming that this species and genus are restricted to rocks older than Castlecliffian. The occurrence of abundant, fresh specimens at many horizons in the Rangitikei River Castlecliffian succession leaves no doubt that they are in situ, although as they occur in estuarine units that are not easily dated, all that is known of their age is that they range from at least as low as the Mangapipi shellbeds (OIS 45; Pillans et al 2005) and Rewa Tephra (OIS 35; 1.19 Ma; Shane et al 1996;Carter & Naish 1999;Alloway et al 2005;Pillans et al 2005) up to at least as young as Potaka Tephra (OIS 27; Carter & Naish 1999; 1.00 Ma; Shane 1994, Shane et al 1996Alloway et al 2005;Pillans et al 2005). Haweran records, helping confirm that B. crassidens probably survived until at least OIS 9, are: Brunswick Formation (OIS 9), former County Council quarry off Brunswick Road, W of Aramoho, Wanganui (GS12425, R22/f10, 1 large, fresh v) (Fig.…”