Rhynie chert

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Coordinates: 57°20′12″N 002°50′29″W / 57.33667°N 2.84139°W / 57.33667; -2.84139

Hand sample of the Rhynie chert.
Surface view of a polished piece of Rhynie chert showing many cross-sections of Rhynia stems (axes). Scale bar is 1 cm.
Thin section of a piece of Rhynie chert viewed by transmitted light showing the cross-section of a stem of Rhynia

The Rhynie chert is an Lower Devonian sedimentary deposit, part of the Old Red Sandstone. It has extraordinary fossil details, and is a Lagerstätte.

The chert is exposed near the village of Rhynie, Aberdeenshire, Scotland. A second unit, the Windyfield chert, is located some 700 m away.

The Rhynie chert contains exceptionally preserved plant, fungus, lichen and animal material preserved in place by an overlying volcanic deposit. The bulk of the fossil bed consists of primitive plants (which had water-conducting cells and sporangia, but no true leaves), along with arthropods, lichens, algae and fungi.

Significance[change | change source]

Date[change | change source]

This fossil bed is remarkable for two reasons. First, the age of the site, formed about 410 million years ago.[1][2] This places it at an early stage in the colonisation of land.

Quality[change | change source]

Second, these cherts are famous for their exceptional state of preservation, with individual cell walls easily visible in polished specimens. Stomata have been counted and lignin remnants detected in the plant material. The book lungs of some early spiders can be seen in cross-sections. Fungal hyphae can be seen entering plant material, acting as decomposers and mycorrhizal symbionts.

The oldest known insect (Rhyniognatha hirsti), which resembles the modern springtails, was found in the Rhynie chert,[3] pushing dates for the origination of insects back to the Silurian period.[4]

History of research[change | change source]

The chert was discovered by William Mackie while mapping the western margin of the Rhynie basin in 1910–1913.[5]

Since 1980, the chert has been examined by the Münster group, and from 1987 by Aberdeen University. They showed the chert was indeed produced by a hot spring setting.[5] Cores were drilled in 1988 and 1997.[5]

Conditions of formation[change | change source]

The chert was formed when silica-rich water from volcanic springs rose and rapidly petrified the early terrestrial ecosystem in situ. Organisms are petrified that way by hot springs today,[6] although that quality of preservation has not been found in recent deposits.[7] Hot springs, with temperatures between 90 to 120 °C (194 to 248 °F),[6] were active; the water had probably cooled to under 30 °C (86 °F) before it reached the fossilised organisms.[8][9] The deposits are interbedded with sands, shales and tuffs, which speaks of local volcanic activity.[10] Deposition was very rapid.[11][10]

The texture of the silica formed is like that found today in freshwater streams at Yellowstone National Park. They are typically alkaline (pH 8.7) and tepid 20 to 28 °C (68 to 82 °F).[7]

Living vegetation covered around 55% of the land area, with litter covering 30% and the remaining 15% of the ground being bare.[8][12][8]

Other websites[change | change source]

References[change | change source]

  1. Rice C.M. et al. (1995). "A Devonian auriferous hot spring system, Rhynie, Scotland". Journal of the Geological Society, London 152: 229–250. doi:10.1144/gsjgs.152.2.0229.
  2. Natural Environment Research Council
  3. Whalley, Paul; Jarzembowski, Ed (1981). "A new assessment of Rhyniella, the earliest known insect, from the Devonian of Rhynie, Scotland". Nature 291: 317. doi:10.1038/291317a0.
  4. Engel, Michael S.; Grimaldi, DA (2004). "New light shed on the oldest insect". Nature 427 (6975): 627–30. doi:10.1038/nature02291. PMID 14961119.
  5. 5.0 5.1 5.2 Trewin N.H. (2003). "History of research on the geology and palaeontology of the Rhynie area, Aberdeenshire, Scotland". Transactions of the Royal Society of Edinburgh Earth Sciences 94. doi:10.1017/S0263593300000699.
  6. 6.0 6.1 Trewin N.H. (1996). "The Rhynie cherts: an early Devonian ecosystem preserved by hydrothermal activity". Ciba Found Symp. 202: 131–45. PMID 9243014.
  7. 7.0 7.1 Trewin N.H.; Fayers S.R; Kelman R. (2003). "Subaqueous silicification of the contents of small ponds in an early Devonian hot-spring complex, Rhynie, Scotland". Canadian Journal of Earth Sciences 40 (11): 1697–1712. doi:10.1139/e03-065. http://article.pubs.nrc-cnrc.gc.ca/ppv/RPViewDoc?_handler_=HandleInitialGet&articleFile=e03-065.pdf&journal=cjes&volume=40. Retrieved 2008-05-15.
  8. 8.0 8.1 8.2 Trewin N.H.; Wilson E. (2004). "Correlation of the early Devonian Rhynie chert beds between three boreholes at Rhynie, Aberdeenshire". Scottish Journal of Geology 40 (1): 73–81. doi:10.1144/sjg40010073.
  9. Powell C.L.; Trewin, N. H.; Edwards, D. (2000). "Palaeoecology and plant succession in a borehole through the Rhynie cherts, Lower Old Red Sandstone, Scotland". Geological Society London Special Publications 180: 439. doi:10.1144/GSL.SP.2000.180.01.23.
  10. 10.0 10.1 Rice C.M.; Trewin N.H.; Anderson L.I. (2002). "Geological setting of the early Devonian Rhynie cherts, Aberdeenshire, Scotland: an early terrestrial hot spring system" (abstract). Journal of Geological Society 159 (2): 203. doi:10.1144/0016-764900-181. http://jgs.lyellcollection.org/cgi/content/abstract/159/2/203. Retrieved 2008-05-15.
  11. Wellman, Charles H. (2006). "Spore assemblages from the Lower Devonian ‘Lower Old Red Sandstone’ deposits of the Rhynie outlier, Scotland". Transactions of the Royal Society of Edinburgh Earth Sciences 97. doi:10.1017/S0263593300001449.
  12. Fayers S.R.; Trewin, Nigel H. (2003). "A review of the palaeoenvironments and biota of the Windyfield chert". Transactions of the Royal Society of Edinburgh Earth Sciences 94. doi:10.1017/S0263593300000729.
    Contains useful reconstructions of both the plant associations, and the regional setting.