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geology and geomorphology

The Tarkine Wilderness has been described as representing a microcosm of Tasmanian geology and geomorphology and its dominant features include:

• The Rocky Cape Region of the north-west which is largely Precambrian unmetamorphosed rocks.
• The Arthur Lineament which is a linear belt of Precambrian metamorphics cutting through the Tarkine along a north-east/south-west axis.
• The Dundas Trough in the south-west which is an area of late Precambrian to Devonian sequences.
• A linear belt of Devonian-Carboniferous granites along the coast south of Sandy Cape, as well as east of the lower end of the Arthur Lineament.
• Some tertiary basalts in the north-east.

The Tarkine Wilderness hosts outstanding examples of magnesite karst geomorphology. This is expressed within the Arthur Lineament as small undecorated caves, sub-surface cavities, sinkholes, springs, and surface features including gorges and pinnacle type formations.

Another exceptional example of the local geomorphology is the Huskisson Syncline - a fold structure "composed of Siluro-Devonian clastic sedimentary rocks underlain by Ordovician limestones and Cambrian ultramifics" (Sharples 1992a). It features two concentric ridges formed on resistant Siluro-Devonian quartz sandstones. A section of the syncline has been offset by a fault which also controls the course of the Alfred River.

The Rapid River is a particularly well-expressed example of a fluvial system influenced by geological lineament. According to Sharples (1992a) "[T]he river channel diverts along fold trends for short distances" but follows a generally linear course, "cutting directly across regional fold trends for some twenty kilometres" (32 miles). It is recognised as the largest example of a fault-controlled river channel in north-west Tasmania.

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