Environmental and sea-level changes on Banks Peninsula (Canterbury, New Zealand) through three glaciation-interglaciation cycles

A greater than 200 ka record of marine transgressions and regressions is re corded from a 75 m core from Banks Peninsula, Canterbury, New Zealand. This record comprises thick suites of muddy sediments attributed to back barrie r, lake and lagoonal environments alternating with thin soil and loess comp lexes. These deposits have been dated using radiocarbon and thermoluminesce nce (TL) techniques supported by proxy data (diatoms, phytoliths, pollen an d sedimentology), The aqueous deposits are attributed to three interglacial s and an interstadial (Marine Isotope Stages 1, 5a, 5c, 6, and 7), The loes ses and paleosols date to the intervening stadials (Isotope Stages 2, 5d (o r 6?) and probably 8), On the basis of transgressive beach facies. back bar rier swamps and barrier-blocked lake deposits, a partial sea-level curve in cluding data from Isotope Stage 5 is presented. Our data indicate that Bank s Peninsula has been tectonically stable over that period and we provide se a-level points that support the existing isotope curve during Stages 5 and 6. Detailed diatom records are limited to Isotope Stage 1 and the latter pa rt of Stage 5. Diatom histories recorded from these stages are remarkably c onsistent. Both indicate a progressive floral change from marine types thro ugh freshwater colonising species to freshwater planktonic assemblages. The se reflect parallel histories of coastal evolution during the two interglac ials. In both cases, marine transgression in the early part of the isotope phase was followed by lagoon development implying that a gravel spit extend ed across the embayment from the west. This was succeeded by lake developme nt when the lagoon was cut off by the juncture of the spit with Banks Penin sula. This lake deepened as the coast rotated into swash alignment and the spit was converted into a gravel barrier. The vegetation history of the sit e indicates that mixed podocarp broadleaf forests, similar to the pre-Europ ean flora of Banks Peninsula, occupied the region during Isotope Stages 1 a nd 7. This contrasts with the palynological interpretation of a marine reco rd (DSDP Site 594) from off the Canterbury coast which suggested that Isoto pe Stage 7 was markedly cooler than the Holocene. During glacial periods, f orest was eliminated and replaced by a tall shrubland of mixed montane and coastal affinities. (C) 1999 Elsevier Science B.V. All rights reserved.