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22-764: The Pennine Coal Measures Group is a lithostratigraphical term referring to the coal -bearing succession of rock strata which occur in the United Kingdom within the Westphalian Stage of the Carboniferous Period . In formal use, the term replaces the Coal Measures Group as applied to the succession of coal-bearing strata within the Pennine Basin which includes all of the coalfields of northern England and

44-423: A barrier. The results are presented as a correlation scheme (A). Practical correlation has a lot of difficulties: fuzzy borders of the layers, variations in composition and structure of the rocks in the layer, unconformities in the sequence of layers, etc. This is why errors in correlation schemes are not seldom. When the distances between available cross-sections are decreasing (for example, by drilling new wells)

66-471: A formation of sedimentary rock, then we can say that the igneous intrusion is younger than the sedimentary rock. The principle of superposition states that a sedimentary rock layer in a tectonically undisturbed stratum is younger than the one beneath and older than the one above it. The principle of original horizontality states that the deposition of sediments occurs as essentially horizontal beds. The principles of lithostratigraphy were first established by

88-399: A largely non-productive sequence of red beds . Descriptions of the coal seams are found within (or linked from) articles on the individual coalfields . Many of the sandstones give rise to distinct features in the landscape as they are more resistant to weathering and erosion than the intervening shales. Some have been quarried for building material, including flagstones for paving. East of

110-479: A lithostratigraphic unit includes a stratotype which is usually a type section . A type section is ideally a good exposure of the unit that shows its entire thickness. If the unit is nowhere entirely exposed, or if it shows considerably lateral variation, additional reference sections may be defined. Long-established lithostratigraphic units dating to before the modern codification of stratigraphy, or which lack tabular form (such as volcanic domes), may substitute

132-450: A type locality for a type section as their stratotype. The geologist defining the unit is expected to describe the stratotype in sufficient detail that other geologists can unequivocally recognize the unit. Lithosome : Masses of rock of essentially uniform character and having interchanging relationships with adjacent masses of different lithology . e.g.: shale lithosome, limestone lithosome. The fundamental Lithostratigraphic unit

154-449: Is called an unconformity . Four types of unconformity: To correlate lithostratigraphic units, geologists define facies, and look for key beds or key sequences that can be used as a datum. Geological correlation is the main tool for reconstructing the geometry of layering in sedimentary basins . The lithological correlation is a procedure, decisive what layers (strata) in geological cross-sections located in different places belong to

176-761: Is given a geographical name combined with either a rock name or some term describing its form. The term suite is deprecated. Also formalized is the term complex , which applies to a body of rock of two or more genetic classes (sedimentary, metamorphic, or igneous). This establishes two hierarchies of lithodemic units: Similar rules have been adopted in Sweden. However, the 1994 International Stratigraphic Guide regards plutons and non-layered metamorphic rocks of undetermined origin as special cases within lithostratigraphy. Principle of original horizontality The principle of original horizontality states that layers of sediment are originally deposited horizontally under

198-413: Is the formation . A formation is a lithologically distinctive stratigraphic unit that is large enough to be mappable and traceable. Formations may be subdivided into members and beds and aggregated with other formations into groups and supergroups. Two types of contact: conformable and unconformable . Conformable : unbroken deposition, no break or hiatus (break or interruption in the continuity of

220-864: The English Midlands . It includes the largely concealed Canonbie Coalfield of southern Scotland and the coalfields of northeast Wales and the minor Anglesey coalfield. The sequence mainly consists of mudstones and siltstones together with numerous sandstones , the more significant ones of which are individually named. Some are laterally extensive, others are more restricted in their range. There are numerous coal seams , again with some being more laterally continuous than others. Those which were economically valuable were named though any individual seam may have attracted different names in different pits and different districts. Marine bands preserving distinctive and dateable marine fossils such as goniatite cephalopods and brachiopods are widespread within

242-735: The Pennines , the following main sandstone beds are recorded (note that not all will be present in any one district; multiple entries on one line are of broadly the same age): To the west of the Pennines, the following are recorded: Lithostratigraphy In general, strata are primarily igneous or sedimentary relating to how the rock was formed. Sedimentary layers are laid down by deposition of sediment associated with weathering processes, decaying organic matter (biogenic) or through chemical precipitation. These layers are often distinguishable as having many fossils and are important for

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264-523: The Danish naturalist, Nicolas Steno , in his 1669 Dissertationis prodromus . A lithostratigraphic unit conforms to the law of superposition , which in its modern form states that in any succession of strata , not disturbed or overturned since deposition , younger rocks lies above older rocks. The principle of lateral continuity states that a set of bed extends and can be traceable over a large area. Lithostratigraphic units are recognized and defined on

286-467: The action of gravity . It is a relative dating technique. The principle is important to the analysis of folded and tilted strata . It was first proposed by the Danish geological pioneer Nicholas Steno (1638–1686). From these observations is derived the conclusion that the Earth has not been static and that great forces have been at work over long periods of time, further leading to the conclusions of

308-510: The basis of observable physical rock characteristics. The lithology of a unit includes characteristics such as chemical and mineralogical composition, texture, color, primary depositional structures , fossils regarded as rock-forming particles, or other organic materials such as coal or kerogen . The taxonomy of fossils is not a valid lithological basis for defining a lithostratigraphic unit. The descriptions of strata based on physical appearance define facies . The formal description of

330-410: The formal terms lithodeme , which is comparable to a formation; a suite , which is analogous to a group, and a supersuite , similar to a supergroup. A lithodeme is the fundamental unit and should possess distinctive and consistent lithological features, comprising a single rock type or a mixture of two or more types that distinguishes the unit from those around it. As with formations, a lithodemic unit

352-407: The geological record). The surface strata resulting is called a conformity . Two types of contact between conformable strata: abrupt contacts (directly separate beds of distinctly different lithology, minor depositional break, called diastems ) and gradational contact (gradual change in deposition, mixing zone). Unconformable : period of erosion/non-deposition. The surface stratum resulting

374-484: The internal friction between grains which prevents them slumping to a lower angle without additional reworking or effort. This is known as the angle of repose , and a prime example is the surface of sand dunes . Similarly, sediments may drape over a pre-existing inclined surface: these sediments are usually deposited conformably to the pre-existing surface. Also, sedimentary beds may pinch out along strike , implying that slight angles existed during their deposition. Thus

396-457: The quality of correlation is improving, but meanwhile the wrong geological decisions could be made that increases the expenses of geological projects. The law of superposition is inapplicable to intrusive, highly deformed, or metamorphic bodies of rock lacking discernible stratification. Such bodies of rock are described as lithodemic and are determined and delimited based on rock characteristics. The 1983 North American Stratigraphic Code adopted

418-474: The same geological body now (or belonged in the past). The identification is based on comparison of physical and mineralogical characteristics of the rocks, and on general assumptions known as the Steno's principles: 1. The sedimentary strata occurred sequentially in time: the youngest at the top. 2. The strata are originally horizontal. 3. The stratum extends in all directions until it thins out or encounters

440-469: The science of plate tectonics ; that movement and collisions of large plates of the Earth's crust is the cause of folded strata . As one of Steno's Laws, the principle of original horizontality served well in the nascent days of geological science . However, it is now known that not all sedimentary layers are deposited purely horizontally. For instance, coarser grained sediments such as sand may be deposited at angles of up to 15 degrees, held up by

462-552: The sequence and enable correlation to be made between sequences in one part of the basin and another and with other basins. The term Productive Coal Measures was formerly used for this succession. The Group comprises the: The Pennine Coal Measures Group is preceded (underlain) by the Millstone Grit Group which is of Namurian age. It is succeeded (overlain) by the Warwickshire Group which comprises

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484-497: The study of biostratigraphy . Igneous layers occur as stacks of lava flows, layers of lava fragments (called tephra ) both erupted onto the Earth's surface by volcanoes, and in layered intrusions formed deep underground. Igneous layers are generally devoid of fossils and represent magmatic or volcanic activity that occurred during the geologic history of an area. There are a number of principles that are used to explain relationships between strata. When an igneous rock cuts across

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