Wellman, H.W. 1971 Geology of the Kotuku oilfield, Westland. Lower Hutt: New Zealand Geological Survey. Report NZGS 48 46 p.
Abstract: Being the largest known natural occurrence of petroleum in New Zealand, the oil seepage at Kotuku in North Westland has attracted considerable attention over the years from prospectors and oil companies. Over forty holes have been drilled, and many geological reports written. This report summarises the surface and sub-surface geological data, and presents an interpretation of the stratigraphy and structure. Most of the data is from published and unpublished reports. Several days were spent in the Kotuku district examining the outcrops near the seepage. The detailed map of the Kotuku area, Fig 1, is based on an enlargement of NZMS 1 Sheet 851. Topography is taken from aerial photographs and has been adjusted to fit the enlarged map. The relief near the seepage is only a few hundred feet, and the adjustment needed was not large. The map differs considerably from that produced by Morgan (1911, opposite P. 146) which was copied by several later geologists, and in part this may be due to Deep Creek having changed its position slightly since the early survey was made in 1910.