Sedimentology
Sedimentology encompasses the study of modern
Sedimentary rocks cover up to 75% of the
The
Sedimentary rock types
There are four primary types of
- Clastic rocks are composed of particles derived from the weathering and erosion of 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.
- 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 reef material [citation needed].
- Evaporites are formed through the evaporation of water at the Earth's surface and most commonly include halite or gypsum.[5]
- Chemical sedimentary rocks, including some carbonates, are deposited by precipitation of minerals from aqueous solution. These include jaspilite and chert.
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 roofing, sandstone for load-bearing buttresses
- lime derived from limestone.
- gemstones and industrial minerals including heavy mineral sands ore deposits
- Energy: petroleum geology relies on the capacity of sedimentary rocks to generate deposits of petroleum oils. Coal and oil shale are found in sedimentary rocks. A large proportion of the world's uranium energy 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 Our understanding of the extent of these aquifers and how much water can be withdrawn from them depends critically on our knowledge of the rocks that hold them (the reservoir).
Basic principles
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.[citation needed]
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.[citation needed]
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 diagenesis are available for study.[citation needed]
The
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.
The principle of lateral continuity states that layers of sediment initially extend laterally in all directions unless obstructed by a physical object or topography.
The
Methodology
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 documenting thickness, lithology, outcrop, distribution, contact relationships to other formations
- Mapping the distribution of the rock unit, or units
- Describing the
- Descriptions of rock core (drilled and extracted from wells during hydrocarbon exploration)
- Sequence stratigraphy
- Describes the progression of rock units within a basin
- Describing the lithology of the rock;
- texture, grain size, grain shape (sphericity, rounding, etc.), sorting and composition of the sediment
- Analysing the geochemistry of the rock
- Isotope geochemistry, including use of radiometric dating, to determine the age of the rock, and its affinity to source regions
Recent developments
The longstanding understanding of how some
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."[7]
Considerable recent research into
Recent research by an Australian sedimentologist, Dutkiewicz, has described how geocirculation is related to global temperatures and climate change. The research described carbon and water circulation, and impacts of heat on current and future capacity of carbon capture by the ocean. [9]
See also
- Clastic rocks
- Coal
- Geology
- Important publications in sedimentology
- Oil shale
- Ore genesis
- Rock formation
- Sequence stratigraphy
- Vegetation-induced sedimentary structures
References
- ISBN 0-7167-5021-X.
- ISBN 0-412-10050-9.
- ISBN 0-632-03578-1.
- ISBN 0-7167-2726-9.
- ISBN 0-13-121724-0
- PhysOrg.com(accessed 27 December 2007).
- ^ Joe H. S. Macquaker and Kevin M. Bohacs, "Geology: On the Accumulation of Mud," Science, 14 December 2007: 1734-1735.
- ^ Robert G. Loucks, Robert M. Reed, Stephen C. Ruppel, and Daniel M. Jarvie "Morphology, Genesis, and Distribution of Nanometer-Scale Pores in Siliceous Mudstones of the Mississippian Barnett Shale", Journal of Sedimentary Research, 2009, v. 79, 848-861.
- ^ "Global warming speeds up currents in the ocean's abyss". Samachar Central. 2022-03-25. Retrieved 2022-04-16.
External links
- Media related to Sedimentology at Wikimedia Commons