Submarine fans within small basins: examples from the Tertiary of New Zealand
This study uses the example of two small sedimentary basins to draw lessons for the stacking patterns of submarine fan facies in restricted basins. The Te Anau and Waiau basins are located in southwest New Zealand. They developed from the Middle Eocene onwards close to and under the direct influence of the evolving Australia-Pacific plate boundary. Although never more than a few tens of kilometres wide, both basins accumulated sedimentary successions more than 6 km thick. We discuss the scale, nature and composition of submarine fans within the basins. Sediment stacking patterns are characterized by rapid lateral and vertical changes within the full range of facies predicted by most submarine fan models. Despite the small basin size, some submarine fans contain sandstone bodies of impressive thickness (50 m) and many kilometres lateral extent. Such bodies of well-sorted, highly permeable sandstone are excellent potential hydrocarbon reservoirs. The occurrence of complete Bouma sequences and well-developed couplets of clastic- and hemipelagic mudstones indicates that such features are not restricted to large-scale fans (covering thousands of square kilometres). Even in small sedimentary basins, submarine fans can develop that show an impressive range of sedimentary facies and architectural elements, commonly described only from their large-scale counterparts.