Nubian Sandstone: Difference between revisions
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SEDIMENTARY ROCKS ARE SO GAY |
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'''Nubian Sandstone''' refers to a variety of [[sedimentary rocks]] deposited on the [[Precambrian]] [[basement]] in the eastern [[Sahara Desert|Sahara]], north-east Africa and [[Arabia]]. It consist of continental [[sandstones]] with thin beds of [[Marine (ocean)|marine]] limestones, and [[marl]]s. Nubian sandstone was deposited between the Lower [[Paleozoic]] and Upper [[Cretaceous]], with marine beds dating from the [[Carboniferous]] to Lower Cretaceous.<ref>Issawi 1973, p.1433</ref> |
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==Formation== |
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Nubian sandstone ranges in age from the Cambrian to Upper Cretaceous eras. Positioning of the [[paleoequator]] and [[paleolatitude]] at 20° S was derived from [[paleomagnetic]] data showing Nubian sandstone was originally deposited in the paleoequatorial to subequatorial zone. These paleomagnetic results corroborated previous studies suggesting there was no polar wandering and [[continental drift]] in Africa during 210 to 110 million years and extended this period to 85 million years. Nubian sandstone is deposited under a [[tropical]] to subtropical climate and is formed under a variety of continental conditions, excluding [[eolian]] merging intermittently into shallow marine.<ref>El-Shazly 1982</ref> |
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==Characteristics== |
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[[Image:AmramColumns.jpg|thumb|Nubian Sandstone formation of Amram Columns, Eilat Massif, Israel]] |
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The Nubian sandstone complex has a thickness varying from under 500 m to over 3000 m, resting on the Precambrian basement. This is complicated by various structural [[fault]]s and fold axes traversing the region in a north-eastern direction. Maximum development occurs in the Ain Dalla basin, a downthrown structural block south-west of the [[Bahariya]] oasis. [[Basement]] features present a dominant control on the complex's structural and sedimentological form. Despite many structural complications, Nubian sandstone likely constitutes a single hydrogeological system west of the [[Gulf of Suez|Suez Gulf]]. To the east, on the [[Sinai peninsula]], a second system might exist with some connection to the primary western system in the north. The main western system, extending into [[Libya]] and Sudan, consists of a multi-layered [[artesian]] basin where massive groundwater reserves accumulated, principally during pluvials of the [[Quaternary]]. Locally, [[carbonate]] rocks overlying the complex display [[karst]] features and are recharged by upwards leaks from the underlying major [[aquifer]].<ref>A. Shata</ref> [[Fluvial]] and structural interpretations from 2007 show the desert in western Egypt was induced by fluvial action, including recently mapped [[alluvial fans]]. In central areas, braided channels are spatially aligned to a north-east structural trend, suggesting preferential water flow paths. Alluvial fans and structurally enclosed channels coincided to gentle slopes and optimal recharge conditions between 1 and 5%, indicating high groundwater potential. [[Synthetic Aperture Radar]] (SAR) interpretations correlated with anomalies from groundwater in 383 wells, suggesting a connection between the spatial organization of fluvial and structural features with low-[[salinity]] groundwater, which exists adjacent to alluvial fans and the south-west reaches of structurally enclosed channels. Wells in the vicinity of structures contained low-salinity water.<ref>El-Baz & El-Shazly, 2007</ref> |
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==Derived soils== |
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Nubian sandstone exposures in sub-humid, semi-arid, and [[arid]] conditions produce [[soil]] that is red-sandy but very different in other aspects. Only in sub-humid zones do these soils contain a moderately developed profile, including a textural [[B horizon]] lacking soluble salts and [[carbonates]]. In semi-arid and arid zones, profile differentiation is either weak or does not exist. In arid zones soils are shallow and contain carbonates, and soluble salts, including [[gypsum]]. The sole [[clay]] common to all Nubian sandstone parent materials is [[Kaolinite]], which is the major clay mineral in sub-humid zone soil. In semi-arid soils [[smectite]] is a second major clay component. In arid zones small amounts of smectite and [[palygorskite]] accompany kaolinite. It is likely that smectite and palygorskite are products of [[pedogenic]] neoformation. [[Aeolian]] material was probably introduced into the [[silt]] and fine sand fractions from semi-arid and arid soils. It is also possible that some contamination of clay fractions occurred.<ref>A. Singer 1974, p. 310</ref> |
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===Nubian Sandstone in Arabia=== |
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When in contact with Upper Cretaceous [[limestone]], Nubian sandstone underlies the latter conformably. In [[Lebanon]], [[Anti-Lebanon]] and [[Hermon]] it is underlaid by Jurassic limestone. Its upper strata is likely from the Lower or Middle Cretaceous age. However, Jurassic limestone is absent in southern areas. In Western Sinai, Nubian sandstone rests on Carboniferous limestone, and by the [[Dead Sea]] on Cambrian limestone: at [[Petra]] and other locations it rests unconformably on [[Crystalline]] rocks. While age calculation for Nubian sandstone is relatively simple in Lebanon, Anti-Lebanon and Hermon, it is much more complicated in Western Sinai and the Dead Sea. Since sandstone is assumed to form more rapidly than other rocks it is difficult to conceive that the 2,000 feet of sandstone in the southeastern Dead Sea was in the formative process from the Cambrian to the Cretaceous. |
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==Appearance== |
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[[Image:Wall Patterns.jpg|thumb|Liesegang rings made of [[iron oxide]] in sandstone from a chamber in [[Petra, Jordan]]]] |
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Nubian Sandstone is most commonly brown or reddish, but in places it shows a much wider variety of color. The ancient temples and tombs in Petra were carved from this rock. In certain places it is extremely [[friable]], and in others compact and hard. Sand in the Arabian deserts was primarily derived from it, carried by prevailing western winds. Where it is covered by a sheet of eruptive rock (''charrah''), it is protected from [[erosion]]. Nubian sandstone frequently includes strata of clay and shale and thin seams of [[coal]] or [[lignite]]. This indicates that it was deposited in seas that were relatively shallow at the time. |
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==Etymology== |
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The term ״Nubia sandstone״ was first introduced to the Egyptian [[stratigraphy]] by Joseph Russegger in 1937, who used the term "Sandstein von Nubien" to designate nonfossiliferous sandstone |
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sections of Paleozoic or Mesozoic age. Russegger followed and studied this series of sandstone formations from the [[Sudan]], [[Egypt]], [[Nubia]], and Arabia Petrsea.<ref>R. Tate pp. 404-406</ref> |
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==See also== |
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*[[Nubian Aquifer System]] |
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*[[Arabian-Nubian Shield]] |
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*[[Sedimentary rock]] |
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*[[Shield (geology)|Shield]] |
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*[[Craton]] |
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*[[platform (geology)|Platform]] |
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*[[basement (geology)|Basement]] |
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*[[continental platform|Platform basement]] |
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==Notes== |
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{{reflist|2}} |
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==References== |
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<div class="references-small"> |
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*B. Issawi, ''Review of Upper Cretaceous-Lower Tertiary Stratigraphy in central and southern Egypt''. - American Association of Petrol. Geol. Bull., Vol. 56 No.8, 1973 |
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*El Shazly, Atomic Energy Establishment, Egypt 1982 |
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*A.A. Shata, [http://qjegh.geoscienceworld.org/cgi/content/abstract/15/2/127 ''Hydrogeology of the Great Nubian Sandstone Basin''] Desert Research Institute, Egypt 1982 |
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*Tate, Ralph, ''On the Age of the Nubian Sandstone'': ''Quarterly Journal of the Geological Society'' (1871); Vol. 27 No. 1-2 |
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*[http://geosys.bg.tu-berlin.de/archiv/downloads/NAS_syn.pdf Essay and Maps: Groundwater Resources of the Nubian Aquifer System] |
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*El Sayed. [http://adsabs.harvard.edu/abs/2001AGUSM...H22D01D ''A Study of Hydrogeological Conditions of the Nubian Sandstone Aguifer in the Area between Abu Simbel & Toschka, Western Desert, Egypt''] American Geophysical Union 2001 |
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*A.C. Seward: ''Leaves of Dicotyledons from Nubian sandstone of Egypt'', Geological Survey, 1935. |
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*El-Baz and El-Shazly, [http://www.ingentaconnect.com/content/klu/10040/2007/00000015/00000001/00000091?crawler=true ''The Nubian Aquifer in Southwest Egypt'']: ''Hydrogeology Journal'', Vol. 15 No. 1, 2007 |
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*''Paleogeography & Paleomagnetism of the Nubian Sandstone Eastern Desert of Egypt'': in the ''International Journal of Earth Sciences''. Vol. 62, No. 1. 1973 [[ISSN]]:1437-3254 |
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*[http://www-naweb.iaea.org/napc/ih/Nubian/IHS_nubian.html International Atomic Energy Agency: NSAS Project] |
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*A. Singer, [http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-2389.1974.tb01127.x?journalCode=ejs ''Characteristics of Nubian Sandstone - Derived Soils''] ''European Journal of Soil Science'' 1974 |
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==External links== |
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*[http://jgslegacy.lyellcollection.org/cgi/content/abstract/27/1-2/404 Quarterly Journal of the Geological Society] |
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*[http://geosys.bg.tu-berlin.de/archiv/downloads/NAS_syn.pdf Essay and Maps: Groundwater Resources of the Nubian Aquifer System] |
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*[http://weekly.ahram.org.eg/1999/417/special.htm The Eastern Desert of Egypt in Ancient Times] |
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*[http://nabataea.net/ppark.html The Petra Archeological Park; Petra was carved into lower Paleozoic sandstone.] |
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*[http://www.dmmr.gov.sa/geology-ksa.php Geology of Saudi Arabia] |
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[[Category:Geology of Libya]] |
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[[Category:Sedimentary rocks]] |
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[[Category:Building stone]] |
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[[Category:Geologic formations]] |
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[[Category:Geology of Egypt]] |
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[[he:אבן חול נובית]] |
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Revision as of 08:48, 4 January 2009
SEDIMENTARY ROCKS ARE SO GAY