Sedimentology simply encompasses the study of sediments such as sand, silt, and clay, and the processes that result into their formation (erosion and weathering), transport, & deposition.
Sedimentologists apply their understanding of modern processes to interpret geologic history via observations of sedimentary structures and sedimentary rocks.
Sedimentary rocks, as proven, cover up to 75% of the Earth's surface, record much of the Earth's history, and harbor the fossil record. Sedimentology is closely related to stratigraphy, which is the study of both the physical and temporal relationships between rock layers/stratas.
This is the guide for today's post:
- Sedimentary rock types
- Importance of sedimentary rocks
- Basic principles
- Methodology of sedimentology
- Recent developments in sedimentology
- Other posts on geology
- References
Sedimentary rock types
There are four basic types of sedimentary rocks, they are:
- clastics,
- carbonates,
- evaporites, and
- chemical.
siltstones and sandstones, southwestern Utah
Clastic rocks are made up of particles gotten from the weathering and erosion of precursor rocks and consist basically of fragmental material. Clastic rocks are grouped according to their predominant grain size and their composition. In time past, the term "Clastic Sedimentary Rocks" were used to describe silica-rich clastic sedimentary rocks.
Organic sedimentary rocks are important deposits formed from the mixture of biological detritus and coal & oil shale deposits, and are mostly found within basins of clastic sedimentary rocks.
Carbonates are made up of various carbonate minerals (mostly calcium carbonate CaCO3) followed by various kinds of organic and inorganic processes.
Basically, most carbonate rocks are made up of reef material; reef meaning a chain of rocks or a ridge of sand at/near the surface of water.
Evaporites are formed via the evaporation of water at the Earth's surface and it does commonly include halite or gypsum.
Chemical sedimentary rocks including some carbonates, are deposited by the precipitation of mineral substances from aqueous solution. These also include jaspilite and chert.
Importance of sedimentary rocks
Sedimentary rocks provide a variety of products which both modern and ancient society have come to utilise.
Mi Vida uranium mine in redox mudstones near Moab, Utah
I will be listing just 5 major importance among the varities of importance available. they are:
- Art: marble, although a coined limestone, is an example of the use of sedimentary rocks in the timely pursuit of aesthetics and art;
- Architectural uses: stones gotten from sedimentary rocks are used for dimension stone and in architecture, notably slate, for roofing, and sandstone used for load-bearing buttresses;
- Ceramics and industrial materials: clay for pottery and ceramics including bricks; cement and lime gotten from limestone.
- Economic geology: large deposits of sedex ore of lead-zinc-silver are hosted by sedimentary rocks, large deposits of copper, deposits of gold, tungsten, Uranium, and many other precious minerals, gemstones and industrial minerals including heavy mineral sands ore deposits
- Energy: petroleum geology relies mostly on the ability of sedimentary rocks to generate deposits of petroleum oils. Coal and oil shale are found in sedimentary rocks. A large portion of the world's uranium energy resources are hosted within sedimentary successions.
Basic Principles
In Sedimentology, conditions are recorded within the sediments as they are laid down; the form of the sediments at present stands as a reflection of the activities of the past and all activities or events which affect the sediments, starting from the source of the sedimentary material to the stresses implemented upon them after diagenesis are available for study.
The principle of superposition is crucial to the interpretation of sedimentary sequences, and in older metamorphic terrains or fold and thrust belts where sediments are often severely folded or deformed, taking cognizance of younging indicators or graded bedding is crucial to interpretation of the sedimentary section and most often the deformation and metamorphic structure of the region.
Folding in sediments is therefore analysed with the principle of original horizontality, which spelt out 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 therefore can be "unfolded" and interpreted according to the information contained in the sediment.
The principle of lateral continuity states that layers of sediment at first extend in all directions unless if its obstructed by a physical object, substance or topography.
The principle of cross-cutting relationships states that whatever cuts across or intrudes into the layers of strata is younger than the layers of strata.
Methodology of Sedimentology
The methods used by sedimentologists to harness data and evidence on the nature and depositional conditions of sedimentary rocks include;
- Measuring and describing the outcrop and distribution of the rock unit;
- process of giving description of the rock formation, a formal way of documenting thickness, lithology, outcrop, distribution, contact relationships to other formations
- Mapping the distribution of the rock unit, or units
- Describing the rock core (drilled and derived from wells during hydrocarbon exploration)
- Sequence stratigraphy
Explains the progression of rock units within a basin - Describing the lithology of the rock;
Petrology and petrography; especially the measurement of texture, grain size, grain shape (sphericity, rounding, etc.), sorting and composition of the sediment - Analysing the geochemistry of the rock
Isotope geochemistry, inclusive of the use of radiometric dating, to determine the age of the rock, and its affinity to source regions.
Recent developments in sedimentology
The understanding of how some mudstones form has been disapproved ane challenged by some geologists at the Indiana University (Bloomington) and the Massachusetts Institute of Technology. The research, which came up on the 14th of December 2007, Science edition, 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 depicts that some mudstones may have formed in fast-moving waters: "Mudstones can be deposited under more energetic conditions than wide assumptions, requiring a reappraisal of many geologic records."
Macquaker and Bohacs, while reviewing the research of Schieber et al., opined that "these results call for critical reappraisal of all mudstones previously interpreted as having been constantly deposited under still waters. Such rocks are widely used to infer past climates, ocean conditions, and orbital variations."
Recent research into mudstones has been triggered by the recent effort to commercially manufacture hydrocarbons from them, in both the Shale gas and Tight Oil (or Light Tight Oil) plays.
This is all i have been able to gather from my findings in the last two days.
Science is life!
Geography is nature!!
Geology is my daily bread!!!
References
Geology Dictionary.
Raymond Siever, Sand, Scientific American Library, New York (1988), ISBN 0-7167-5021-X.
Georges Millot, translated [from the French] by W.R. Farrand, Helene Paquet, Geology Of Clays - Weathering, Sedimentology, Geochemistry Springer Verlag, Berlin (1970), ISBN 0-412-10050-9.
Gary Nichols, Sedimentology & Stratigraphy, Wiley-Blackwell, Malden, MA (1999), ISBN 0-632-03578-1.
Donald R. Prothero and Fred Schwab, Sedimentary Geology: An Introduction to Sedimentary Rocks and Stratigraphy, W. H. Freeman (1996), ISBN 0-7167-2726-9.
Edward J. Tarbuck, Frederick K. Lutgens, Cameron J. Tsujita, Earth, An Introduction to Physical Geology, National Library of Canada Cataloguing in Publication, 2005, ISBN 0-13-121724-0
You can also check on my recent posts on geology:
Questions as regards any of these posts will be entertained. We learn new things everyday.
My appreciation goes to 
And to my esteemed followers. Thanks for your support, you guys kept on encouraging me to do more research..
Expect posts on openmic by me soon. Still making some arrangement as to getting my keyboard/piano.
says thanks once again.
see you around
