Sedimentology encompasses the study of modern
sediments such as sand [ Raymond Siever, Sand, Scientific American Library, New York (1988), ISBN 0 7167 5021 X.] , mud (silt), [ P.E. Potter, J.B. Maynard, and P.J. Depetris, Mud and Mudstones: Introduction and Overview Springer, Berlin (2005) ISBN 3 5402 2157 3.] and clay, [ Georges Millot, translated [from the French] by W.R. Farrand, Helene Paquet, Geology Of Clays - Weathering, Sedimentology, Geochemistry Springer Verlag, Berlin (1970), ISBN 0 4121 0050 9.] and understanding the processes that deposit them. [Gary Nichols, Sedimentology & Stratigraphy, Wiley-Blackwell, Malden, MA (1999), ISBN 0 6320 3578 1.] It also compares these observations to studies of ancient sedimentary rocks[Donald R. Prothero and Fred Schwab, Sedimentary Geology: An Introduction to Sedimentary Rocks and Stratigraphy, W. H. Freeman (1996), ISBN 0 7167 2726 9.] and sedimentary structures. Sedimentologists apply their understanding of modern processes to historically formed sedimentary rocks, allowing them to understand how they formed.
Sedimentary rocks cover most of the
Earth's surface, record much of the Earth's history, and harbor the fossil record. Sedimentology is closely linked to stratigraphy, the study of the physical and temporal relationships between rock layers or strata.
Uniformitarian geology, the premise that the processes affecting the earth today are the same as in the past, is the basis for determining how sedimentary features in the rock record were formed. By comparing similar features today - for example,
sand dunes in the Saharaor the Great Sand Dunes National Parknear Alamosa, Colorado- to the ancient sandstones such as the Wingate Sandstoneof Utahand Arizona, of the southwest USA; since both have the same features, both can be shown to have formed from aeolian (wind) deposition Fact|date=March 2007.
edimentary rock types
There are four primary types of
sedimentary rocks: clastics, carbonates, evaporites, and chemical.
Clastic rocksare composed of particles derived from the weatheringand erosionof precursor rocks and consist primarily of fragmental material. Clastic rocks are classified according to their predominant grain size and their composition. In the past, the term "Clastic Sedimentary Rocks" were used to describe silica-rich clastic sedimentary rocks, however there have been cases of clastic carbonate rocks. The more appropriate term is siliciclasticsedimentary rocks.
** Organic sedimentary rocks are important deposits formed from the accumulation of biological detritus, and form
coaland oil shaledeposits, and are typically found within basins of clastic sedimentary rocks
* Carbonates are composed of various
carbonate minerals(most often calcium carbonate(CaCO3)) precipitated by a variety of organic and inorganic processes. Typically, the majority of carbonate rocks are composed of reefmaterial Fact|date=March 2007.
Evaporites are formed through the evaporation of water at the Earth's surface and are composed of one or more salt minerals, such as haliteor gypsumFact|date=March 2007.
* Chemical sedimentary rocks, including some carbonates, are deposited by precipitation of minerals from aqueous solution. These include
Importance of sedimentary rocks
Sedimentary rocks provide a multitude of products which modern and ancient society has come to utilise.
Art: marble, although a metamorphosed limestone, is an example of the use of sedimentary rocks in the pursuit of aesthetics and art
* Architectural uses: stone derived from sedimentary rocks is used for
dimension stoneand in architecture, notably slate, a meta- shale, for roofing, sandstonefor load-bearing buttresses
* Ceramics and industrial materials:
clayfor potteryand ceramics including bricks; cementand lime derived from limestone.
Economic geology: sedimentary rocks host large deposits of SEDEX ore deposits of lead- zinc- silver, large deposits of copper, deposits of gold, tungstenand many other precious minerals, gemstonesand industrial minerals including heavy mineral sands ore deposits
petroleum geologyrelies on the capacity of sedimentary rocks to generate deposits of petroleum oils. Coaland oil shaleare found in sedimentary rocks. A large proportion of the world's uraniumenergy resources are hosted within sedimentary successions.
Groundwater: sedimentary rocks contain a large proportion of the Earth's groundwater aquifers. Our understanding of the extent of these aquifers and how much water can be withdrawn from them depends critically on our knowledge of the rocks that hold them (the reservoir).
The aim of sedimentology, studying sediments, is to derive information on the depositional conditions which acted to deposit the rock unit, and the relation of the individual rock units in a basin into a coherent understanding of the evolution of the sedimentary sequences and basins, and thus, the Earth's geological history as a whole.
The scientific basis of this is the principle of uniformitarianism, which states that the sediments within ancient sedimentary rocks were deposited in the same way as sediments which are being deposited at the Earth's surface today.
Sedimentological conditions are recorded within the sediments as they are laid down; the form of the sediments at present reflects the events of the past and all events which affect the sediments, from the source of the sedimentary material to the stresses enacted upon them after
diagenesisare available for study.
The principle of superposition is critical to the interpretation of sedimentary sequences, and in older metamorphic terrains or fold and thrust belts where sediments are often intensely folded or deformed, recognising
youngingindicators or fining up sequencesis critical to interpretation of the sedimentary section and often the deformation and metamorphic structure of the region.
Folding in sediments is analysed with the
principle of original horizontality, which states that sediments are deposited at their angle of repose which, for most types of sediment, is essentially horizontal. Thus, when the younging direction is known, the rocks can be "unfolded" and interpreted according to the contained sedimentary information.
principle of lateral continuitystates that layers of sediment initially extend laterally in all directions unless obstructed by a physical object or topography.
principle of cross-cutting relationshipsstates that whatever cuts across or intrudes into the layers of strata is younger than the layers of strata.
Methodology of sedimentology
The methods employed by sedimentologists to gather data and evidence on the nature and depositional conditions of sedimentary rocks include;
* Measuring and describing the outcrop and distribution of the rock unit;
** Describing the
rock formation, a formal process of documeenting thickness, lithology, outcrop, distribution, contact relationships to other formations
** Mapping the distribution of the rock unit, or units
* Descriptions of rock core (drilled and extracted from wells during hydrocarbon exploration)
** Describes the progression of rock units within a basin
* Describing the
lithologyof the rock;
Petrologyand petrography; particularly measurement of texture, grain size, grain shape (sphericity, rounding, etc), sorting and composition of the sediment
* Analysing the
geochemistryof the rock
Isotope geochemistry, including use of radiometric dating, to determine the age of the rock, and its affinity to source regions
Recent developments in sedimentology
The longstanding understanding of how some
mudstones form has been challenged by geologists at Indiana University (Bloomington)and the Massachusetts Institute of Technology. The research, which appears in the December 14th, 2007, edition of "Science", counters the prevailing view of geologists that mud only settles when water is slow-moving or still, instead showing that "muds will accumulate even when currents move swiftly." The research shows that some mudstones may have formed in fast-moving waters: "Mudstones can be deposited under more energetic conditions than widely assumed, requiring a reappraisal of many geologic records." [Juergen Schieber, John Southard, and Kevin Thaisen, [http://www.sciencemag.org/cgi/content/full/318/5857/1760 "Accretion of Mudstone Beds from Migrating Floccule Ripples,"] "Science", 14 December 2007: 1760-1763.
See also [http://www.physorg.com/news116777974.html "As waters clear, scientists seek to end a muddy debate,"] at "
PhysOrg.com" (accessed 27 December 2007).]
Macquaker and Bohacs, in reviewing the research of Schieber et al., state that "these results call for critical reappraisal of all mudstones previously interpreted as having been continuously deposited under still waters. Such rocks are widely used to infer past climates, ocean conditions, and orbital variations." [Joe H. S. Macquaker and Kevin M. Bohacs, [http://www.sciencemag.org/cgi/content/full/318/5857/1734 "Geology: On the Accumulation of Mud,"] "Science", 14 December 2007: 1734-1735.]
* Important publications in sedimentology
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Look at other dictionaries:
sedimentology — [sed΄ə mən täl′ə jē] n. the branch of geology that deals with sediment and sedimentary rocks sedimentologist n … English World dictionary
sedimentology — noun Date: 1932 a branch of science that deals with sedimentary rocks and their inclusions • sedimentologic or sedimentological adjective • sedimentologically adverb • sedimentologist noun … New Collegiate Dictionary
sedimentology — sedimentologic /sed euh men tl oj ik/, sedimentological, adj. sedimentologist, n. /sed euh meuhn tol euh jee/, n. Geol. the study of sedimentary rocks. [1935 40; SEDIMENT + o + LOGY] * * * Scientific discipline concerned with the physical and… … Universalium
sedimentology — noun The study of natural sediments and of the processes by which they are formed … Wiktionary
sedimentology — study of sediment Sciences and Studies … Phrontistery dictionary
sedimentology — sed·i·men·tol·o·gy … English syllables
sedimentology — sed•i•men•tol•o•gy [[t]ˌsɛd ə mənˈtɒl ə dʒi[/t]] n. gel the study of sedimentary rocks • Etymology: 1935–40 sed i•men to•log′ic ˌmɛn tlˈɒdʒ ɪk sed i•men to•log′i•cal,adj. sed i•men•tol′o•gist, n … From formal English to slang
sedimentology — jē noun ( es) Etymology: sediment (I) + o + logy : the description, classification, and interpretation of sediments … Useful english dictionary
Maturity (sedimentology) — In sedimentology, maturity describes the composition of grains in sandstones occurring from various amounts of sediment transportation. It occurs when the grains in a sediment become well sorted and well rounded due to weathering of the grains.… … Wikipedia
Imbrication (sedimentology) — In sedimentology imbrication refers to a primary depositional fabric consisting of a preferred orientation of clasts such that they overlap one another in a consistent fashion, rather like a run of toppled dominoes. Imbrication is observed in… … Wikipedia