Structure and Petroleum Potential of Eastern Chatham Rise, New Zealand

Abstract

ABSTRACT Paleozoic-Mesozoic metamorphic rocks and Mesozoic to Tertiary sedimentary sequences exposed on the Chatham Islands have been correlated with sequences shown by marine seismic profiling to underlie the eastern Chatham Rise. The offshore sedimentary sequence appears to be more complete than that exposed onshore. Provinces of igneous intrusion have been delineated by magnetic profiling. Characteristic horst and graben basement topography of the eastern Chatham Rise is consistent with regional arching and flexural fracturing. The grabens contain thickened Mesozoic-Tertiary accumulations, whereas only thin Tertiary deposits may drape the horsts. Reinterpretation of the geologic history of the eastern Chatham Rise leads to a new paleogeographic reconstruction of the New Zealand region. In this new interpretation, the New Zealand geosyncline is considered to have existed between foreland blocks partly comprising the Campbell Plateau and Lord Howe Rise. Late in Mesozoic time, the framework of crustal blocks became fragmented, and during northward drift a dismembered eastern block commenced relative clockwise rotation. The triangular oceanic basin so developed assumed the character of a sphenochasm. The petroleum source, reservoir, and trap potentials of the presumed prospective offshore sections are assessed by comparison with sequences of similar age in the Chatham Islands and New Zealand. The petroleum potential of the area relates to the development of source-bed and reservoir rocks principally in sedimentary-drape and/or combination traps around basement-horst structures.