Review of structure and basement control of the lapstone structural complex, Sydney basin, eastern New South Wales

In the western Sydney Basin, the Lapstone Structural Complex is a major north-trending association of monoclines and faults that forms the frontal ridge of the Blue Mountains Plateau. At Kurrajong Heights, the Lapstone Structural Complex is dominated by an east-facing monocline with a gently dipping central limb containing several different homoclinal segments. At the Hawkesbury Lookout section, strata are steeply dipping to near vertical along the main east-facing monocline. The Lapstone Structural Complex has been related to either steep east-dipping extensional faulting or to moderate to steep west-dipping contraction faults. Strike-slip displacement may also have played a role in its development. The Hawkesbury Lookout section is interpreted in the subsurface as a moderately west-dipping thrust fault. The historical development of the Lapstone Structural Complex has been difficult to resolve although palaeomagnetic data from the southern part are indicative of Late Cretaceous to Cenozoic deformation. Neotectonic activity may also have occurred along the structure. Basement to the Sydney Basin is the eastern Lachlan Fold Belt, which includes moderately west-dipping faults that may have been reactivated as thrust faults in the present-day stress regime. These structures provide a potential analogue for a basement-controlled fault that has generated the Lapstone Structural Complex.