The urban geology of Darwin, Australia

Abstract

Darwin, on the north coast of the Australian mainland lies only 12° south of the equator, and experiences a pronounced wet–dry tropical monsoonal climate. This latitudinal position has strongly influenced the local geology for Darwin is dominated by deeply weathered lateritic regolith formed on labile Cretaceous marine sediments. Close to 2 billion years of geological history is lost from this immediate region because the largely horizontally bedded Cretaceous strata unconformably overly folded Proterozoic metasediments. Models of the landscape evolution of this region, and indeed across much of northern Australia, have been based upon the incorrect interpretation of a type section, displaying weathered Cretaceous strata, close to Darwin city. A recent reinterpretation of this type section has shown that the landscape here is a function of deep weathering and structural controls within the Cretaceous strata rather than repeated cycles of uplift and pediplanation during the Cainozoic. The low relief of this landscape, low rates of denudation and preservation of Cainozoic deep weathering profiles and predominantly rocky shore have meant that Quaternary sediments are restricted to shallow alluvial deposits in creek valleys and marine sediments forming beaches with limited dune and beach ridge development.