140 SEDIMENTARY ROCKS/Rudaceous Rocks Deep Water Rudaceous Deposits Rudaceous deposits, both terrigenous and carbonate, occur in deep-water environments, ranging from turbidites to mega-boulder complexes Gravels in turbidites are restricted to the basal part of the graded bed, and increase in size and abundance towards the source Isolated clasts occur in debris and grain flows At the other extreme is the ‘Wild-Flysch’ of Alpine geologists, termed ‘olostostroma’ by Italians These are irregularly shaped formations that contain clasts the size of skyscrapers and jumbo-jets Such deposits usually occur at the foot of submarine fault scarps, and are associated with tectonic disturbances of violent intensity Conclusions The clasts of rudaceous sediments hold important information about not only the rock types of the hinterland from which they were derived, but also about its geological history As a terrain is unroofed it will shed progressively older and more lithified clasts into the depositional system With continuous or discontinuous uplift erosion unmantles progressively older or more changed, often more highly metamorphosed materials, which are transported and deposited in the resultant conglomerates and breccias Structurally or compositionally weak rocks not preserve as well as stronger materials and allowance must be made in attempting to reconstruct unroofing histories Furthermore, it is generally the more chemically stable silica-rich rocks that contribute to rudaceous deposits Thus, of all of the sediments it is sandstones and cherts that are preserved at the expense of shales and limestones, of metamorphic rocks quartzites are preserved at the expense of slate and schist Of all of the igneous rocks, pebbles of rhyolite are more usually preserved than those of basalt or gabbro Now that our understanding of the processes leading to the formation of rudaceous deposits is fairly advanced, much present research is moving into the field of exploring the geological characteristics of ancient catchments, even to the level of distinguishing separate phases of advance of thrust sheets into an area during orogeny The rudaceous rocks have much to offer the sedimentologist and the geological historian The ability to recognize particular depositional environments in the ancient record and to recreate the conditions at the land surface during mountain-building enables the geologist to postulate the locations of potential metalliferous and hydrocarbon economic resources Gold and uranium occur in Precambrian rudaceous rocks in Canada, the USA, Brazil and South Africa, wherein those of the Witwatersrand basin are probably the best known Rudaceous rocks host placer ores in many parts of the world Because they are composed of clasts, which of their very nature are tough, and therefore of low porosity, Rudaceous rocks are seldom good petroleum reservoirs But it is as aggregates for road building and construction that unconsolidated rudaceous sediments are economically most important See Also Sedimentary Environments: Alluvial Fans, Alluvial Sediments and Settings; Lake Processes and Deposits; Shoreline and Shoreface Deposits Sedimentary Processes: Depositional Sedimentary Structures; Fluvial Geomorphology; Glaciers; Landslides Weathering Further Reading Bluck BJ (1967) Sedimentation of beach gravels; examples from South Wales Journal of Sedimentary Petrology 37: 128 156 Bluck BJ (1980) Structure, generation and preservation of upward fining braided stream cycles in the Old Red Sandstones of Scotland Transactions of the Royal Soci ety of Edinburgh, Earth Sciences 71: 29 46 Bluck BJ (1999) Clast assemblages, bed forms and structure in beach gravels Transactions of the Royal Society of Edinburgh, Earth Sciences 89: 291 323 Bluck BJ (2000) Old Red Sandstone basins and alluvial systems of Midland Scotland In: Friend PF and Williams BPJ (eds.) New Perspectives on the Old Red Sand stone, 180, pp 417 437 London: Geological Society of London Bray M, Workman M, Smith J, and Pope DJ (1996) Field measurements of shingle transport using electronic tracers In: Proceedings of 31st Ministry of Agriculture, Fisheries and Food Conference on River and Coastal Engineering Keele: University of Keele Bull WB (1977) The alluvial fan environment Progress in Physical Geography 1: 222 270 Cailleux A (1945) Distinction des galets marins et fluviatiles Bulletin of the Geological Society of France 5: 125 138 Dobkins JE and Folk RL (1970) Shape development on Tahiti Nui Journal of Sedimentary Petrology 40: 116 203 Glennie KW (2002) Permian and Triassic In: Trewin NH (ed.) Geology of Scotland, 4th ed, pp 301 322 London: The Geological Society of London Griffiths JC (1967) Scientific Method in the Analysis of Sediments, p 508 New York: McGraw Hill Krumbein WC (1941) Measurement and geological signifi cance of shape and roundness of sedimentary particles Journal of Sedimentary Petrology 11: 64 72 Lane EW (1955) Design of stable channels Transactions of the American Society of Civil Engineers 120: 1234 1279 Laming DJC (1966) Imbrication, paleocurrents and other sedimentary features in the lower New Red Sandstone,