Sedimentology and stratigraphy of oyster concentrations in the Pliocene of Wanganui Basin (New Zealand)

MACMILLAN, L.; ROMERO, M.V.; CASADÍO, S.; NELSON, C.S.; BREZINA S.S.

GENERAL ROCA

Congreso; 11° CONGRESO DE LA ASOCIACIÓN PALEONTOLÓGIVA ARGENTINA; 2016

Oyster shells can equally act as archives of paleoenvironmental information (e.g. salinity, temperature) and shellbeds are useful indicator in sequence stratigraphy. The Pliocene Wilkies Shellbed in the Wanganui Basin (North Island, New Zealand) comprises oyster accumulations up to 15 m thick involving the extinct oyster Crassostrea ingens (Zittel, 1864). Individuals are up to 30 cm long, 7 cm thick and weigh as much as 2 kg. The shellbed consists of a lower onlap shellbed (transgressive lag) and an overlying backlap shellbed (biostrome). The widespread shell δ18O (-3.0 to 3.0?) and δ13C (-2.6 to 1.8?) isotopic values support a range of marginal marine to marine environmental conditions. The lower onlap shellbed had estuarine influence, while the upper part had affinities with a nearshore (