Upper Cenozoic structural history, coastal Southern Hawke's Bay, New Zealand

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Abstract
The structural high (Coastal High) trending northeast along coastal Southern Hawke's Bay comprises Upper Cretaceous to Miocene successions that have been complexly folded and thrust-faulted. Major tectonic melange and crushed zones are associated with thrusts. The high developed in Late Oligocene time in conjunction with a slope basin to the west. Continued deformation led to westward growth of the high by incorporating. older basin-fill sequences. A thick wedge of flysch subsequently accumulated within the landward-migrating slope basin. The progressively tilted margins shed cohesive debris flows which interdigitate with the flysch. On the high, sedimentation is typified by a greatly condensed mudstone succession with local unconformities and onlaps which disappear basinwards. An earlier Oligocene deformation resulted from northward movement of an allochthonous gravity slide sheet, recognised by local east-west-trending structures, inverted sequences, and northward transposition. Overprinting by the subsequent phase of imbricate thrusting led to the present NNE-SSW to northeast-southwest structural fabric of the region. West of the Coastal High, the Elsthorpe Anticline propagated as an offshoot during Quaternary time. Deformation of the basin-fill tectonically thickened the western limb by a series of en echelon bedding thrusts. Quaternary tensional faulting affecting the Coastal High reflects major gravitational collapse. There is no evidence for major transcurrent faulting. Petroleum source and reservoir beds are known throughout the East Coast region. However, substantial traps may prove difficult to locate because of the intensity and type of deformation. The numerous seeps in the area reflect voiding of trap structures.

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