The geology and landforms of Northeast Tasmania

The Northeast is a geologically distinctive region of Tasmania. The Northeast is founded on marine turbidite rocks (the Mathinna Group) intruded by granitic rocks. This assemblage is distinctly different from the contemporaneous shallow marine shelf carbonates and clastics found west of the Tamar. It was formed at some distance from the 'Western Tasmania Terrane' and was transported to its present location by movements along the Tamar Mobile Belt. Much of northeast Tasmania has been relatively uplifted during long periods of its subsequent history, with only thin sequences of younger Permian sedimentary rocks being deposited in the present highland areas. The Permian rocks were intruded by extensive sheets of dolerite magma in mid-Jurassic times at the start of the breakup of Gondwana. Landform evolution during the Tertiary Period followed the development of increased landscape relief due to block faulting in Cretaceous to Early Tertiary times. Fluvial processes have shaped the landscape during most of its subsequent development, although basaltic lavas tilled some valleys and altered drainage patterns during the Tertiary. An extensive area of the pre-Permian erosional surface has been exhumed and forms a prominent component of the present-day n01theast Tasmanian highlands. The higher peaks, capped by resistant remnants of the dolerite sheets, underwent accelerated erosion during glacial climatic stages. The arid climatic conditions of the last glacial stage allowed the formation of extensive dune fields on the Bass Strait plains, a portion of which are preserved on the north coastal platform. The heights of relict shorelines of last interglacial age suggest that northeast Tasmania has undergone greater Quaternary uplift than most of mainland Australia. Land use patterns in northeast Tasmania have been strongly influenced by distinctive topographies and soils on particular bedrock and landform systems. Since geology and landforms also influence the distributions of biological communities. the conservation of biodiversity in the Northeast faces the problem that, whilst those communities which are least disturbed and least endangered have the best statutory protection, those most endangered are likely to be those characteristic of the more heavily disturbed bedrock and Iandform assemblages which have been favoured for settlement and agriculture.