Terrace formation in the Illawarra region of New South Wales

Summary

The formation of river terraces is generally attributed to fluctuations in climate, sea level or tectonic activity. In this study we argue that they can form when critical thresholds intrinsic to an alluvial system are exceeded. This conclusion is drawn from a comparative study of ancient terrace deposits and modern floodplains, rather than from an attempt to fit terrace sequences into a climatic chronology. While climatic change cannot be ignored, it is the character of the terrace deposits, especially their stratigraphy, which provides the key for deciphering stream history. Variations in types of floodplains, which can be explained in terms of the character of contemporary depositional environments, are virtually identical to those which can be seen in Holocene and Pleistocene terraces throughout this region.