DEAKIN ANTICLINE

Description of Place

The site contains a well-developed anticline (convex fold), at the eastern margin of the outcrop in volcanoclastic fine sandstone and siltstone of the Yarralumla Formation (late Middle Silurian). The Yarralumla Formation was created during the last major episode of marine sedimentation in the Canberra area. This period represents a hiatus in the otherwise volcanically dominant Silurian Period, at the end of which all the earlier sedimentary and volcanic formations were uplifted and folded. The anticline structure was developed during these folding episodes in middle to late Palaeozoic times

Several features of the geometry of the anticline such as axial plane, axial trace, and plunge are readily visible in three dimensions. In addition, there is a well-developed axial-plane cleavage and the relationship of this to the fold geometry is well demonstrated. Later joint structures are also well displayed.

Statement of Significance

The outcrop is an important example of the sedimentary rocks that comprise the Yarralumla Formation within the ACT and is a clear illustration of a simple anticlinal structure. It is a highly visible feature of the last marine incursion into the Canberra region. It is an important teaching site in that the structure of an anticline is clearly shown and readily accessible.