Landscape evolution of the Blue Mountains revealed by longitudinal river profiles and Cenozoic basalts and gravels

Abstract

For the past 200 years, there have been numerous investigations and much speculation concerning the formation of the dramatic valleys of the Blue Mountains of NSW. In this paper, further evidence for the uplift and erosional history of the Blue Mountains is obtained from longitudinal river profiles, detailed mapping of the Rickabys Creek Gravel on the Lapstone Structural Complex and consideration of the topographical position of Miocene basalts. Knickpoints on the main rivers flowing east from the Great Dividing Range are identified and interpreted to be due to uplift events linked to the northward movement of the Australian continent over mantle inhomogeneities. At the Lapstone Structural Complex on the eastern range front, the occurrence of the Rickabys Creek Gravel and the nature of the over-steepened reaches on the rivers and streams crossing the Complex, suggest a more recent ongoing phase of uplift and antecedent river erosion. The Miocene basalts provide evidence of this landscape 20–15 Ma. Their locations with respect to the current rivers and ridges are interpreted to show additional evidence for recent uplift that has resulted in the formation of the Lapstone Structural Complex. It is suggested that this uplift commenced 10–5 Ma when the contemporary compressive stress field was established.KEY POINTSLongitudinal profiles for major rivers in the Blue Mountains are consistent with a model of initial Cretaceous uplift followed by further Cenozoic uplift associated with dynamic topography.Mapping of Rickabys Creek Gravel within the Lapstone Structural Complex suggests the presence of antecedent rivers.Within the Lapstone Structural Complex, stream profiles, gravels and nearby outcrops of Miocene basalts are interpreted to indicate a third phase of uplift, possibly since 10 Ma.