Angledool 1:250 000 geological map (second edition) and explanatory notes
The newly released Angledool 1:250 000 second edition geological map sheet covers Lightning Ridge and surrounding areas, including Cumborah, Goodooga and Narran Lake, in northern New South Wales. The area is situated in the southern part of the Mesozoic Surat Basin (part of the Great Australian Basin), and overlies buried rocks of the Palaeozoic Lachlan Orogen. The Angledool map is particularly important as the area contains the world's premier black opal fields of the Lightning Ridge district.
The Early Cretaceous Griman Creek Formation crops out along ridges and is the host to the opal deposits of the region. All of the known opal fields are plotted on the map face, along with interpreted faults and other features. The Griman Creek Formation is overlain by Miocene gravels, which are commonly silcreted, and form a resistant capping to the ridges. Cross-sections on the map provide information on the sedimentary rocks of the Surat Basin at depth, including the positions of aquifers.
The Quaternary fluvial sediments, which constitute the area locally referred to as the black soil plains, have been subdivided, based upon geomorphological characteristics, into two major units. The Bugwah Formation represents a high energy riverine system formed during the waning stages of the last glacial maximum and was deposited up to about 6 000 years before present. It includes the Nullawa Member which was deposited in a fluvial distributary system. The Marra Creek Formation constitutes the modern riverine system and is characterised by tightly constrained meandering channels with broad flood plains.
A special feature of the Angledool map is that on the back there is a full colour poster with a rich source of general information about the geology of the area, opal, fossils, the opal fields, opal prospecting and mining as well as mining history.
The Angledool map is accompanied by a set of explanatory notes. This soft cover, 88 page full colour book provides more detailed information about the geology of the Angledool map sheet area. It contains descriptions of local geological units, structure, weathering and economic geology with supporting figures, photos and data tables and includes information on the rich diversity of Early Cretaceous freshwater fossils, from invertebrates to dinosaurs.