Gravity Survey of North Canterbury (Culverden Basin).

N Canterbury has a basin range topography, the ranges consisting of Permian - Jurassic Greywackes with the basins filled with younger sediments and gravels. The residual anomoly contour map of the basin considered with the geological data, shows that the SE side is a reverse fault. The sediments rise to an anticline along the centre of the basin and descent again to a syncline except near Mt Culverdon, where a transverse anticline enters from the NW side. An accompanying transverse syncline enters at Pahau River. These two features appear to curve SW to join the central fold. Towards the NW end of the basin the central fold is faulted. The basement contact along the NW side is gently dipping and depositional N of Mt Culverdon, but is very steep and possibly locally faulted to the S. The largest residual anomoly observed is 20 mgal at Rotheram, indicating approximately 6,500 ft of sediments.