The boundary is defined as the first appearance of graptolitesParakidograptus acuminatus and Akidograptus ascensu 1.6 m above the base of the Birkhill Shale Formation. The shale section also contains chitinozoa and conodonts, but neither are well preserved. Dob's Linn has been criticized for the difficulty in relating its graptolite biostratigraphic sequence with shallow water sequences elsewhere, although the stratotype also appears to correspond with a carbon-13 isotope excursion in the latest Ordovician which can be identified worldwide.[5]
The area was first studied by Charles Lapworth in the late 19th century. His work established fossil graptolites as a method of understanding stratigraphic sequences.[6] A more recent description of the area, enumerating the zones established by Lapworth, is given in the British Regional Geology Monograph.[7] Before Lapworth's work, it was thought that the Silurian rocks of the Southern Uplands formed a single sequence, that would have to be about 6000m in thickness. By his identification of particular graptolite species in different zones of the Dob's Linn exposure, Lapworth was able to demonstrate that the Uplands consist of a much thinner layer, consistent with Silurian deposits elsewhere, that had been repeatedly folded and faulted, with multiple repetitions of the same strata, often upside down.[8] The understanding that sequences of sedimentary rocks could be inverted played an important part in the later resolution of the Highlands Controversy in which Lapworth was also involved.
Referencesedit
^National Trust for Scotland: Grey Mare's Tail Nature Reserve
^Hogg, James (1869). Thomson, Thomas (ed.). The works of the Ettrick shepherd. London: Blackie and Son. p. 77.
^Ogg, James. . Archived from the original on 18 June 2006. Retrieved 1 July 2006.
^"Dob's Linn". Scottish Geology. Hunterian Museum. Archived from the original on 18 May 2011. Retrieved 1 July 2006.
^Underwood, C J; S F Crowley; J D Marshall; P J Brenchley (July 1997). "High-resolution carbon isotope stratigraphy of the basal Silurian Stratotype (Dob's Linn, Scotland) and its global correlation". Journal of the Geological Society. 154 (4): 709. CiteSeerX10.1.1.502.6989. doi:10.1144/gsjgs.154.4.0709.
^Lapworth, Charles (1878). "The Moffat Series". Quarterly Journal of the Geological Society. 34 (1–4): 240–346. doi:10.1144/GSL.JGS.1878.034.01-04.23.
^Pringle, J. (1948). British regional Geology: The South of Scotland (2 ed.). London: Her Majesty's Stationery Office (HMSO). pp. 34–46.
^Oldroyd, David R (1990). The Highlands Controversy. Chicago: The University of Chicago Press. pp. 217–265. ISBN978-0-226-62635-2.
External linksedit
Clarkson, E.N.K.; Taylor, C.M. (1992). "Dob's Linn, Moffat - an excursion". from: Scottish Borders geology: an excursion guide. Scottish Academic Press. Retrieved 28 January 2019.
Galleryedit
Folds in the Rock Strata high up in the Dob's Linn Gorge
Plan of the typical locality of Dobb's Linn (sic) (after Lapworth)
Climacograptus wilsoni graptolite fossils on black shale (26 x 25 millimetres) of middle Ordovician age (Soudleyan Stage, ~mid-Caradocian) from the main cliff at Dob's Linn (about 36.1-43.1 metres below the Ordovician-Silurian boundary GSSP
Lapworth's original map of the exposure at Dob's Linn
linn, small, steep, valley, dumfries, galloway, just, north, a708, road, between, moffat, selkirk, scotland, part, grey, mare, tail, nature, reserve, which, owned, national, trust, scotland, according, tradition, named, covenanter, halbert, dobson, took, refug. Dob s Linn is a small steep valley in Dumfries and Galloway just north of the A708 road between Moffat and Selkirk in Scotland It is part of the Grey Mare s Tail Nature Reserve which is owned by the National Trust for Scotland 1 According to tradition Dob s Linn is named for a covenanter Halbert Dobson who took refuge there from Government troops during The Killing Time in the late 17th century 2 Dob s LinnLooking down Dob s Linn Gorge from the topDob s LinnFloor elevation300 m 980 ft GeographyCountryScotlandDistrictDumfries and GallowayCoordinates55 25 47 N 3 16 11 W 55 4297 N 3 2697 W 55 4297 3 2697 Dob s Linn is important in geology as the location of the Global Boundary Stratotype Section and Point GSSP 3 which marks the boundary between the Ordovician and Silurian periods and marks the base of the Llandovery epoch on the geologic time scale Dob s Linn was ratified as the GSSP by the International Union of Geological Sciences in 1984 4 The boundary is defined as the first appearance of graptolites Parakidograptus acuminatus and Akidograptus ascensu 1 6 m above the base of the Birkhill Shale Formation The shale section also contains chitinozoa and conodonts but neither are well preserved Dob s Linn has been criticized for the difficulty in relating its graptolite biostratigraphic sequence with shallow water sequences elsewhere although the stratotype also appears to correspond with a carbon 13 isotope excursion in the latest Ordovician which can be identified worldwide 5 The area was first studied by Charles Lapworth in the late 19th century His work established fossil graptolites as a method of understanding stratigraphic sequences 6 A more recent description of the area enumerating the zones established by Lapworth is given in the British Regional Geology Monograph 7 Before Lapworth s work it was thought that the Silurian rocks of the Southern Uplands formed a single sequence that would have to be about 6000m in thickness By his identification of particular graptolite species in different zones of the Dob s Linn exposure Lapworth was able to demonstrate that the Uplands consist of a much thinner layer consistent with Silurian deposits elsewhere that had been repeatedly folded and faulted with multiple repetitions of the same strata often upside down 8 The understanding that sequences of sedimentary rocks could be inverted played an important part in the later resolution of the Highlands Controversy in which Lapworth was also involved References edit National Trust for Scotland Grey Mare s Tail Nature Reserve Hogg James 1869 Thomson Thomas ed The works of the Ettrick shepherd London Blackie and Son p 77 Ogg James GSSP for the Ordovician Silurian Boundary Archived from the original on 18 June 2006 Retrieved 1 July 2006 Dob s Linn Scottish Geology Hunterian Museum Archived from the original on 18 May 2011 Retrieved 1 July 2006 Underwood C J S F Crowley J D Marshall P J Brenchley July 1997 High resolution carbon isotope stratigraphy of the basal Silurian Stratotype Dob s Linn Scotland and its global correlation Journal of the Geological Society 154 4 709 CiteSeerX 10 1 1 502 6989 doi 10 1144 gsjgs 154 4 0709 Lapworth Charles 1878 The Moffat Series Quarterly Journal of the Geological Society 34 1 4 240 346 doi 10 1144 GSL JGS 1878 034 01 04 23 Pringle J 1948 British regional Geology The South of Scotland 2 ed London Her Majesty s Stationery Office HMSO pp 34 46 Oldroyd David R 1990 The Highlands Controversy Chicago The University of Chicago Press pp 217 265 ISBN 978 0 226 62635 2 External links editClarkson E N K Taylor C M 1992 Dob s Linn Moffat an excursion from Scottish Borders geology an excursion guide Scottish Academic Press Retrieved 28 January 2019 Gallery edit nbsp Folds in the Rock Strata high up in the Dob s Linn Gorge nbsp Plan of the typical locality of Dobb s Linn sic after Lapworth nbsp Climacograptus wilsoni graptolite fossils on black shale 26 x 25 millimetres of middle Ordovician age Soudleyan Stage mid Caradocian from the main cliff at Dob s Linn about 36 1 43 1 metres below the Ordovician Silurian boundary GSSP nbsp Lapworth s original map of the exposure at Dob s Linn 55 25 47 N 3 16 11 W 55 42972 N 3 26972 W 55 42972 3 26972 nbsp nbsp This Scottish history related article is a stub You can help Wikipedia by expanding it vte nbsp This paleontological site article is a stub You can help Wikipedia by expanding it vte nbsp This Dumfries and Galloway location article is a stub You can help Wikipedia by expanding it vte Retrieved from https en wikipedia org w index php title Dob 27s Linn amp oldid 1081584688, wikipedia, wiki, book, books, library,
