Old Red Sandstone

Old Red Sandstone series of red and brown sandstones, conglomerates, and shales deposited in Wales and Scotland and in England near the Welsh and Scottish borders in the Devonian period of geologic time. The Old Red Sandstone, in contrast to the typical formations of the Devonian, is largely a continental formation, laid down in freshwater and on land as a result of the erosion of the highlands of the Silurian period . It is very thick in Scotland and contains a large assemblage of well-preserved fossils, particularly of the Devonian fishes. The Old Red Sandstone was correlated with the marine Devonian by the British geologists Rodney Murchison and Adam Sedgwick. The New Red Sandstone is a thick red sandstone of Permian and Triassic age found in the British Isles.

old red sandstone Geological term for freshwater deposits of the Devonian period found in Britain. These strata are noted for their fish fossils among which are jawless fishes (ostracoderms), the first jawed fishes (placoderms), and the first true bony fishes (osteichthyes).

Old Red Sandstone Early in the geological exploration of the British Isles the red-bed non-marine part of the Devonian system, known as the Old Red Sandstone, was recognized as a distinctive unit in the Welsh Borderlands and South Wales, and in parts of Scotland. Some geologists regarded it as essentially part of the sequence that also incudes the Carboniferous, but the classical studies of Sir Roderick Murchison and Professor Adam Sedgwick in England and Wales and the essays of Hugh Miller in Scotland soon established the separate identity of these rocks. Notable within these red beds was the presence of some remarkable fossil fishes.

Sedgwick and Murchison were in 1834 to establish the correlation of the Old Red Sandstone with the marine rocks in south-west England which they named ‘Devonian’. The Old Red Sandstone facies has been identified elsewhere in parts of mainland Europe, Spitsbergen, Greenland, and eastern North America as post-orogenic continental basin-fills ranging in age from Late Silurian to early Carboniferous. Local volcanic centres in Scotland contributed lavas and pyroclastic rocks, but for the most part the sediments are clastics. Sedimentary environments range from piedmont fans through alluvial and flood-plain to lacustrine and deltaic-marine.

Fossils are relatively scarce; however, the agnath, placoderm, and osteichtyan fishes are locally common. Less so are fossil invertebrates, including various arthropods, ostracods, and bivalves. Plant fossils are small, primitive, and scarce in the Lower Old Red Sandstone, but rich floras include giant tree ferns in the Middle and Upper Old Red Standstone.

Similar facies with plant and vertebrate fossils are also extensive in parts of Siberia, North and South China, Australia, and Antarctica. Although the global distribution of the vertebrates shows strong provincality in early Devonian times, it was cosmopolitan by the later part of the period. All these regions appear to have been adjacent to, or within, active orogenic areas or uplifts in equatorial to temperate latitudes; and whatever barriers to migration had existed at the beginning of Devonian time, they had been overcome by the end of the period.

D. L. Dineley

Bibliography

Dineley, D. L. (1984) Aspects of a stratigraphic system: the Devonian. Macmillan, Basingstoke.
McMillan, N. J., Embry, A. F., and Glass, D. J. (eds) (1988) Devonian of the world. Proceedings of the Second International Symposium on the Devonian System, Calgary, Canada.
Ziegler, P. A. (1989) The evolution of Laurussia: a study in Late Palaeozoic plate tectonics. Kluwer Academic Publishers, Dordrecht.