A geochemical appraisal of oil seeps from the East Coast Basin, New Zealand

Oil seeps and stains from the East Coast Basin, New Zealand have been investigated using biomarker and stable carbon isotope analyses to determine oil-oil correlations. Oils sampled from the Raukumara Peninsula (northern East Coast Basin, North Island) and Marlborough (southern East Coast Basin, South Island) are derived from Late Cretaceous-Paleocene marine source rocks with a minor terrestrial content and are isotopically light. In contrast, oils sampled from Hawke’s Bay and Wairarapa (central and southern East Coast Basin, North Island) are derived from Paleocene marine source rocks, which contain high abundances of C30 regular steranes and 28,30-bisnorhopane, and are isotopically heavier than the other group. Biomarkers and bulk carbon isotopes show that there are at least two distinct sources of hydrocarbons in the basin.