NewChlamys delicatulalocalities in the central North Island and uplift of the Ruahine Range

Abstract

The scallop Chlamys (Zygochlamys) delicatula (Hutton) now lives mainly in the subantarctic area south of New Zealand, and is common only as far north as Otago Peninsula. The limits of its northward migration during early Nukumaruan (late Pliocene or early Pleistocene) glacial periods are defined by scattered localities in the lowlands of Hawke's Bay and Wanganui, and in the northern Ruahine Range. Five new localities near the northern limits of its northward migration are reported: Ashcott Hill, Ruataniwha Plains; crest of the northeastern Ruahine Range west of Big Hill; western side of Mt Kohinga, near Kuripapango, Napier-Taihape Road; eastern side of Gentle Annie Hill, near Kuripapango; and summit of Te Rakaunuiakura, Mangaohane limestone plateau, western Ruahine Range east of Taihape. That most of the elevation of the Ruahine Range occurred during the last 1 million years (i.e., since early Castlecliffian time) is demonstrated by 3 lines of evidence: the widespread outliers of Nukumaruan marine rocks on the northern Ruahine Range; the simultaneous appearance of large quantities of Mesozoic clasts, derived form the Ruahine Range, in Castlecliffian conglomerate on both sides of the range; and the faulting of Castlecliffian rocks against Mesozoic basement along the eastern Ruahine Range. The mean rate of uplift of the range was at least 1.3 mm per year.