On the Cainozoic uplift of the southeastern Australian highland

Abstract

The uplift history of the southeastern highlands is determined using middle to late Cainozoic river beds; these are preserved as river gravels overlain by basaltic lavas. Along major rivers in the highlands old river beds have a reasonably constant slope; this slope is similar to that of the present river bed, and similar to a line joining the summits along the valley margin. The approximately parallel relation suggests that the beds of most major rivers remained at a constant height and slope while the highland was uplifted. The relative heights of the river beds of different ages are consistent with uplift at a constant rate during the last 45 m.y. The present level of the pre‐uplift river beds is thought to be just above the present valley margins, so if there was only one uplift and if that was at a constant rate then uplift started about 90 m.y. ago. The total amount of uplift is given by the inferred amount of total river downcutting. Within the highland this is generally about 0.6 km north of Goulburn, and 0.8 to 1.3 km south of Goulburn. The area with over 0.5 km total uplift is almost coincident with the area of late Cainozoic uplift defined as the region with no thick alluvial deposits in river valleys; this suggests that the uplift pattern has not changed much with time.