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34-501: The Coimbra Formation (Also known as Camadas de Coimbra or Calcários de S. Miguel ) is a geological formation of Sinemurian ( Lower Jurassic ) age in the Lusitanian Basin of Portugal . The unit represents a series of peritidal to intertidal facies of a Carbonate platform mostly of Obtusum–Oxynotum age, that gradually evolve to open marine/hemipelagic units Vale das Fontes Formation and Lemede formation . This unit

68-558: A 1:75,000 geology map of the island, 6 maps (1:25,000) containing topography, street directory and geology, a sheet of cross section and a locality map. The difference found between the 1976 Geology of Singapore report include numerous formations found in literature between 1976 and 2009. These include the Fort Canning Boulder Beds and stretches of limestone. In the United Kingdom , the term geological map

102-649: A feature that is angled at 34 degrees below the horizontal at an angle that is just east of true south). The oldest preserved geologic map is the Turin papyrus (1150 BCE), which shows the location of building stone and gold deposits in Egypt. The earliest geologic map of the modern era is the 1771 "Map of Part of Auvergne, or figures of, The Current of Lava in which Prisms, Balls, Etc. are Made from Basalt. To be used with Mr. Demarest's theories of this hard basalt. Engraved by Messr. Pasumot and Daily, Geological Engineers of

136-403: A long "strike" line, which is perpendicular to the direction of greatest slope along the surface of the bed, and a shorter "dip" line on side of the strike line where the bed is going downwards. The angle that the bed makes with the horizontal, along the dip direction, is written next to the dip line. In the azimuthal system, strike and dip are often given as "strike/dip" (for example: 270/15, for

170-542: A newly designated formation could not be named the Kaibab Formation, since the Kaibab Limestone is already established as a formation name. The first use of a name has precedence over all others, as does the first name applied to a particular formation. As with other stratigraphic units, the formal designation of a formation includes a stratotype which is usually a type section . A type section

204-617: A permanent natural or artificial feature of the geographic area in which they were first described. The name consists of the geographic name plus either "Formation" or a descriptive name. Examples include the Morrison Formation , named for the town of Morrison, Colorado , and the Kaibab Limestone , named after the Kaibab Plateau of Arizona. The names must not duplicate previous formation names, so, for example,

238-522: A region or predict likely locations for buried mineral resources. The boundaries of a formation are chosen to give it the greatest practical lithological consistency. Formations should not be defined by any criteria other than lithology. The lithology of a formation 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

272-516: A significant rise in sea level. Individual Stromatolite mounds are clearly defined, either as separate structures lined up next to each other or as irregular, flat to wavy layers that merge at the base. Palynology includes Classopollis ( Cheirolepidiaceae Conifer) and Botryococcus as the dominant continental components, while marine palynomorphs include the genera Tasmanites and Cymathiosphaera ( Prasinophyte algae) as well Zygnemataceae . The recent discovery of Dinosaur tracks revelated

306-458: A single lithology (rock type), or of alternating beds of two or more lithologies, or even a heterogeneous mixture of lithologies, so long as this distinguishes them from adjacent bodies of rock. The concept of a geologic formation goes back to the beginnings of modern scientific geology. The term was used by Abraham Gottlob Werner in his theory of the origin of the Earth, which was developed over

340-449: A strike of west and a dip of 15 degrees below the horizontal). Trend and plunge are used for linear features, and their symbol is a single arrow on the map. The arrow is oriented in the downgoing direction of the linear feature (the "trend") and at the end of the arrow, the number of degrees that the feature lies below the horizontal (the "plunge") is noted. Trend and plunge are often notated as PLUNGE → TREND (for example: 34 → 86 indicates

374-528: A stronger influence from land and more oxygen in the environment, leading to lower TOC levels. As we move up, group B shows a reduced land influence. At the top, group A takes over, with more marine particles and fewer plant materials, suggesting a transition to a more open marine environment. Overall, the Coimbra Formation is made up of shallow marine deposits formed in a low-energy setting, with occasional stronger events like storms or floods. The area

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408-449: Is not a valid lithological basis for defining a formation. The contrast in lithology between formations required to justify their establishment varies with the complexity of the geology of a region. Formations must be able to be delineated at the scale of geologic mapping normally practiced in the region; the thickness of formations may range from less than a meter to several thousand meters. Geologic formations are typically named after

442-734: Is also used informally to describe the odd shapes (forms) that rocks acquire through erosional or depositional processes. Such a formation is abandoned when it is no longer affected by the geologic agent that produced it. Some well-known cave formations include stalactites and stalagmites . Geologic map A geologic map or geological map is a special-purpose map made to show various geological features. Rock units or geologic strata are shown by color or symbols. Bedding planes and structural features such as faults , folds , are shown with strike and dip or trend and plunge symbols which give three-dimensional orientations features. Stratigraphic contour lines may be used to illustrate

476-560: Is central to the geologic discipline of stratigraphy , and the formation is the fundamental unit of stratigraphy. Formations may be combined into groups of strata or divided into members . Members differ from formations in that they need not be mappable at the same scale as formations, though they must be lithologically distinctive where present. The definition and recognition of formations allow geologists to correlate geologic strata across wide distances between outcrops and exposures of rock strata . Formations were at first described as

510-425: Is gathered new geologic units may be defined). However, in areas where the bedrock is overlain by a significantly thick unconsolidated burden of till , terrace sediments , loess deposits, or other important feature, these are shown instead. Stratigraphic contour lines, fault lines, strike and dip symbols, are represented with various symbols as indicated by the map key. Whereas topographic maps are produced by

544-455: Is ideally a good exposure of the formation that shows its entire thickness. If the formation is nowhere entirely exposed, or if it shows considerably lateral variation, additional reference sections may be defined. Long-established formations dating to before the modern codification of stratigraphy, or which lack tabular form (such as volcanic formations), may substitute a type locality for a type section as their stratotype. The geologist defining

578-552: Is known for its fossil content, including Invertertebrate and vertebrate ichnofossils and fossils. The sediments in the Coimbra Formation represent the shallow sections of an inner carbonate platform, adjacent to the Paleozoic basement in the E. They are rich in organic matter and are found alongside marl layers in a shallow marine setting. The organic material is divided into three groups (A, B, and C), showing how it

612-468: Is spread across different layers. The middle section mainly consists of group B, with a lot of microbial mat particles and very few plant particles. This layer has the highest level of Total organic carbon (TOC), indicating it was deposited in a restricted and stagnant area with little water movement. In the upper section, all three groups (A, B, and C) are present. The lower part of this section contains more plant debris and fewer marine particles, suggesting

646-586: Is used. The UK and Isle of Man have been extensively mapped by the British Geological Survey (BGS) since 1835; a separate Geological Survey of Northern Ireland (drawing on BGS staff) has operated since 1947. Two 1:625,000 scale maps cover the basic geology for the UK. More detailed sheets are available at scales of 1:250,000, 1:50,000 and 1:10,000. The 1:625,000 and 1:250,000 scales show both onshore and offshore geology (the 1:250,000 series covers

680-480: The United States , geologic maps are usually superimposed over a topographic map (and at times over other base maps) with the addition of a color mask with letter symbols to represent the kind of geologic unit . The color mask denotes the exposure of the immediate bedrock , even if obscured by soil or other cover. Each area of color denotes a geologic unit or particular rock formation (as more information

714-470: The 1:50,000 scale. Small scale thematic maps (1:1,000,000 to 1:100,000) are also produced covering geochemistry , gravity anomaly , magnetic anomaly , groundwater , etc. Although BGS maps show the British national grid reference system and employ an OS base map, sheet boundaries are not based on the grid. The 1:50,000 sheets originate from earlier 'one inch to the mile' (1:63,360) coverage utilising

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748-562: The King." This map is based on Nicolas Desmarest 's 1768 detailed study of the geology and eruptive history of the Auvergne volcanoes and a comparison with the columns of the Giant's Causeway of Ireland. He identified both landmarks as features of extinct volcanoes. The 1768 report was incorporated in the 1771 (French) Royal Academy of Science compendium. The first geological map of the U.S.

782-400: The colors and symbols to be used for rocks of differing types and ages. Geologists take two major types of orientation measurements (using a hand compass like a Brunton compass ): orientations of planes and orientations of lines. Orientations of planes are measured as a "strike" and "dip", while orientations of lines are measured as a "trend" and "plunge". Strike and dip symbols consist of

816-435: The eastern states of the present-day US. The first geologic map of Great Britain was created by William Smith in 1815 using principles ( Smith's laws ) first formulated by Smith. The first geological map of Singapore was produced in 1974, produced by the then Public Work Department. The publication includes a locality map, 8 map sheets detailing the topography and geological units, and a sheet containing cross sections of

850-478: The entire UK continental shelf ), whilst other scales generally cover exposures on land only. Sheets of all scales (though not for all areas) fall into two categories: The maps are superimposed over a topographic map base produced by Ordnance Survey (OS), and use symbols to represent fault lines, strike and dip or geological units, boreholes etc. Colors are used to represent different geological units. Explanatory booklets (memoirs) are produced for many sheets at

884-550: The essential geologic time markers, based on their relative ages and the law of superposition . The divisions of the geological time scale were described and put in chronological order by the geologists and stratigraphers of the 18th and 19th centuries. Geologic formations can be usefully defined for sedimentary rock layers, low-grade metamorphic rocks , and volcanic rocks . Intrusive igneous rocks and highly metamorphosed rocks are generally not considered to be formations, but are described instead as lithodemes . "Formation"

918-522: The formation is expected to describe the stratotype in sufficient detail that other geologists can unequivocally recognize the formation. Although formations should not be defined by any criteria other than primary lithology, it is often useful to define biostratigraphic units on paleontological criteria, chronostratigraphic units on the age of the rocks, and chemostratigraphic units on geochemical criteria, and these are included in stratigraphic codes. The concept of formally defined layers or strata

952-457: The island. Since 1974, for 30 years, there were many findings reported in various technical conferences on newfound geology islandwide, but no new publication was produced. In 2006, Defence Science & Technology Agency, with their developments in underground space promptly started a re-publication of the Geology of Singapore, second edition. The new edition that was published in 2009, contains

986-488: The period from 1774 to his death in 1817. The concept became increasingly formalized over time and is now codified in such works as the North American Stratigraphic Code and its counterparts in other regions. Geologic maps showing where various formations are exposed at the surface are fundamental to such fields as structural geology , allowing geologists to infer the tectonic history of

1020-441: The pre-grid Ordnance Survey One Inch Third Edition as the base map. Current sheets are a mixture of modern field mapping at 1:10,000 redrawn at the 1:50,000 scale and older 1:63,360 maps reproduced on a modern base map at 1:50,000. In both cases the original OS Third Edition sheet margins and numbers are retained. The 1:250,000 sheets are defined using lines of latitude and longitude, each extending 1° north-south and 2° east-west. In

1054-415: The presence of supratidal environments located in a shallow, tropical coastal area, likely near the shore. Formation (geology) A formation must be large enough that it can be mapped at the surface or traced in the subsurface. Formations are otherwise not defined by the thickness of their rock strata, which can vary widely. They are usually, but not universally, tabular in form. They may consist of

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1088-532: The surface of a selected stratum illustrating the subsurface topographic trends of the strata. Isopach maps detail the variations in thickness of stratigraphic units. It is not always possible to properly show this when the strata are extremely fractured, mixed, in some discontinuities, or where they are otherwise disturbed. Rock units are typically represented by colors. Instead of (or in addition to) colors, certain symbols can be used. Different geologic mapping agencies and authorities have different standards for

1122-527: Was a calm, shallow marine environment with limited water flow. Most sediments were fine-grained, showing low-energy conditions and a semi-arid climate. Microbialites formed during periods of slow sediment buildup, indicating low water movement. Occasional storms brought better oxygenated water, supporting brief marine life bursts. Fossils suggest shifts between restricted and open marine environments due to minor sea-level changes. Over time, open-marine conditions increased, with more typical marine fossils reflecting

1156-587: Was produced in 1809 by William Maclure . In 1807, Maclure undertook the self-imposed task of making a geological survey of the United States. He traversed and mapped nearly every state in the Union. During the rigorous two-year period of his survey, he crossed and recrossed the Allegheny Mountains some 50 times. Maclure's map shows the distribution of five classes of rock in what are now only

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