Par. Shane et al., EARLY TO MIDDLE PLEISTOCENE TEPHROCHRONOLOGY OF NORTH-ISLAND, NEW-ZEALAND - IMPLICATIONS FOR VOLCANISM, TECTONISM, AND PALEOENVIRONMENTS, Geological Society of America bulletin, 108(8), 1996, pp. 915-925
Thick volcaniclastic sequences of early to middle Pleistocene age in s
outhern North Island, New Zealand, contain rhyolitic tephra beds that
record the early history of the Taupo volcanic zone (TVZ). At least 54
different tephra beds are recorded, and their chronology is defined b
y glass fission-track ages and paleomagnetism, The tephra beds span th
e interval ca, 2.0-0.6 Ma and provide an event frequency of 1/19 ky.,
significantly higher than the frequency of sheet-forming ignimbrites p
reserved in the TVZ at this time (approximate to 1/100 k.y.). The dist
al tephra beds thus provide a record of volcanism not revealed in the
proximal volcanic region and suggest a major period of explosive activ
ity at ca, 1.79-1.60 Ma. Several important marker horizons are identif
ied: Pakihikura tephra (1.63 Ma), Mangatewaiiti tephra (1.24 Ma), Pota
ka tephra (1.00 Ma), Kidnappers B tephra (1.00 Ma), and Kaukatea tephr
a (0.88 Ma). These tephra beds allow direct correlation between (1) ma
rine and nonmarine facies and (2) the fore-are and back-are regions of
New Zealand. The tephra beds provide a framework for a paleoenvironme
ntal reconstruction of the southern North Island, Volcaniclastic trans
port routes from the TVZ to basins in the south and southeast, and thr
ough the site of present mountain ranges, supplied material to a terre
strial lowland fore-are area in the interval 1.64-0.7 Ma. Uplift and d
eformation since 0.7 Ma have disrupted paleodrainage routes, diverting
them to the north and southwest.