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10 Incredible Geological Formations
10 Incredible Geological Formations
Published: 2014/03/15
Channel: Alltime10s
25 Strangest Geological Formations On Earth
25 Strangest Geological Formations On Earth
Published: 2013/07/26
Channel: list25
18 Photos Of The STRANGEST Geological Formations
18 Photos Of The STRANGEST Geological Formations
Published: 2017/02/26
Channel: American Eye
17 Most Unreal Rock Formations
17 Most Unreal Rock Formations
Published: 2016/09/15
Channel: Talltanic
20 Strangest Geological Formations in the US
20 Strangest Geological Formations in the US
Published: 2017/09/19
Channel: American Eye
Makhtesh Ramon Pt.1 Geological Formation
Makhtesh Ramon Pt.1 Geological Formation
Published: 2017/03/16
Channel: Michael Welch
How Was the Grand Canyon Formed?
How Was the Grand Canyon Formed?
Published: 2016/04/29
Channel: Smithsonian Channel
Appalachian Geology 4
Appalachian Geology 4
Published: 2011/02/06
Channel: WildwoodClaire1
The Formation of the Mediterranean Sea
The Formation of the Mediterranean Sea
Published: 2016/06/04
Channel: ZorakGoesOn
Where Terranes Collide: The Geology of Western Canada
Where Terranes Collide: The Geology of Western Canada
Published: 2015/04/28
Channel: Geology
Top 10 Most Amazing Geological Wonders In The World
Top 10 Most Amazing Geological Wonders In The World
Published: 2015/05/24
Channel: facts@WEB
Appalachian Geology, Pt 1
Appalachian Geology, Pt 1
Published: 2011/02/06
Channel: WildwoodClaire1
Geological Isostatic Adjustment and The Great Lakes Region
Geological Isostatic Adjustment and The Great Lakes Region
Published: 2012/04/05
Channel: David Yole
Preview_The Geological Formation of Bainbridge Island_1
Preview_The Geological Formation of Bainbridge Island_1
Published: 2016/08/02
Channel: snowproductionsBI
Weird geological formation
Weird geological formation
Published: 2016/07/28
Channel: smalltownmoto 1
The Geological History of Earth
The Geological History of Earth
Published: 2015/03/18
Channel: GeoScience Videos
Formation of an ore deposit
Formation of an ore deposit
Published: 2015/08/24
Channel: W. W. Norton-Marshak Geology
Seven Teacups- Unique Geological Formation (4K Aerial Footage)
Seven Teacups- Unique Geological Formation (4K Aerial Footage)
Published: 2016/04/22
Channel: Matt Skuta
Geological Requirements for the Formation of Springs
Geological Requirements for the Formation of Springs
Published: 2015/01/23
Channel: james pake
Scientist says: Mysterious Geological Formation of Planet Mars Caused by a Massive Asteroid Impact
Scientist says: Mysterious Geological Formation of Planet Mars Caused by a Massive Asteroid Impact
Published: 2017/07/18
Channel: Close Encounters UFO
70 Million Years In 2 Minutes - The Himalayas Forming
70 Million Years In 2 Minutes - The Himalayas Forming
Published: 2012/12/17
Channel: злодейский Ломбардо
Basics of Geology  All About Rocks and Minerals
Basics of Geology All About Rocks and Minerals
Published: 2014/03/09
Channel: ambachke
Geology
Geology
Published: 2015/08/31
Channel: Bozeman Science
Geological Time Scale with reference to India - 4 Eras & 10 Periods Explained
Geological Time Scale with reference to India - 4 Eras & 10 Periods Explained
Published: 2016/04/13
Channel: Examrace
HOW THE EVEREST WAS FORMED ! Amazing Geology Documentary
HOW THE EVEREST WAS FORMED ! Amazing Geology Documentary
Published: 2016/03/24
Channel: OBZURV
Amazing Crater - Saudi Arabia Geological Rock Formation
Amazing Crater - Saudi Arabia Geological Rock Formation
Published: 2013/08/05
Channel: Bruce Fenton
HOW EARTH WAS FORMED ! Amazing Geology Documentary
HOW EARTH WAS FORMED ! Amazing Geology Documentary
Published: 2016/03/30
Channel: OBZURV
Documentary ● Alps earth formation
Documentary ● Alps earth formation
Published: 2016/08/17
Channel: Explore the world
Geological mapping of El Gordo diapir and adjacent formations (Nuevo León, Mexico)
Geological mapping of El Gordo diapir and adjacent formations (Nuevo León, Mexico)
Published: 2017/10/09
Channel: Ramón López
3 Types of Rocks and the Rock Cycle: Igneous, Sedimentary, Metamorphic - FreeSchool
3 Types of Rocks and the Rock Cycle: Igneous, Sedimentary, Metamorphic - FreeSchool
Published: 2016/03/15
Channel: Free School
Geologic History of Southern California.mov
Geologic History of Southern California.mov
Published: 2011/08/22
Channel: Wendy Van Norden
Columnar Basalt - Geologist explains spectacular stone columns
Columnar Basalt - Geologist explains spectacular stone columns
Published: 2013/05/30
Channel: hugefloods
Evidence of ancient
Evidence of ancient 'geological Brexit' revealed
Published: 2017/04/05
Channel: News, Science, Tech and Health
ID Cone-in-Cone Structure in situ geological formation North Texas
ID Cone-in-Cone Structure in situ geological formation North Texas
Published: 2017/01/03
Channel: Healthy Family Variety Channel
Subnautica 22 Geological Formation Base
Subnautica 22 Geological Formation Base
Published: 2016/01/27
Channel: SnakeNACake _
explaining geological formations
explaining geological formations
Published: 2009/10/21
Channel: sos5181
Formation of Himalayas HD
Formation of Himalayas HD
Published: 2014/06/22
Channel: Digital Reading
Igneous Rocks - ACSSU153
Igneous Rocks - ACSSU153
Published: 2014/05/23
Channel: ClickView
Santorini - The Thera Cataclysm
Santorini - The Thera Cataclysm
Published: 2016/01/28
Channel: sirtommoore
Faces of Earth - Assembling America
Faces of Earth - Assembling America
Published: 2013/02/19
Channel: American Geosciences Institute
Geological Formations -- Mrs. Feist
Geological Formations -- Mrs. Feist's Science Class
Published: 2016/05/27
Channel: Rita Vondracek
The Formation of Coal 3D
The Formation of Coal 3D
Published: 2013/02/27
Channel: Winner Pictures / BTS-MEDIA
"Kande geological formation - Malawi" Cookieluc
"Kande geological formation - Malawi" Cookieluc's photos around Chintheche, Malawi
Published: 2011/05/17
Channel: Uawaudqomneyeie
Geological formations, Seaton cliffs nature reserve, 29-04-2010
Geological formations, Seaton cliffs nature reserve, 29-04-2010
Published: 2016/12/27
Channel: Adder Man
How GEOLOGY gave DONALD TRUMP the US Presidency
How GEOLOGY gave DONALD TRUMP the US Presidency
Published: 2017/01/19
Channel: Geologize
pharettface inspecting the geological formations
pharettface inspecting the geological formations
Published: 2015/11/16
Channel: Meeker Extreme
1954: Family exploring Wisconsin Dells geological formation park. MADISON, WISCONSIN
1954: Family exploring Wisconsin Dells geological formation park. MADISON, WISCONSIN
Published: 2016/01/11
Channel: StockFilm.com
Rock Layers - Geological Time (4/6)
Rock Layers - Geological Time (4/6)
Published: 2011/07/26
Channel: OpenLearn from The Open University
Geology of the Purcell Sill and Helena Formation Stromatolites in Glacier National Park
Geology of the Purcell Sill and Helena Formation Stromatolites in Glacier National Park
Published: 2015/08/05
Channel: Acid1930
Geology of Seattle and the Puget Sound
Geology of Seattle and the Puget Sound
Published: 2015/03/03
Channel: hugefloods
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WIKIPEDIA ARTICLE

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A geologic cross section of the Grand Canyon. Black numbers correspond to groups of formations and white numbers correspond to formations (click on picture for more information).

A formation or geological formation is the fundamental unit of lithostratigraphy. A formation consists of a certain number of rock strata that have a comparable lithology, facies or other similar properties. Formations are not defined by the thickness of the rock strata they consist of and the thickness of different formations can therefore vary widely.

The concept of formally defined layers or strata is central to the geologic discipline of stratigraphy. Formations can be divided into members and are themselves frequently parcelled together in groups.

Usefulness of formations[edit]

The definition and recognition of formations allow geologists to correlate geologic strata across wide distances between outcrops and exposures of rock strata.

Formations were initially described to be the essential geologic time markers based on relative ages and the law of superposition. The divisions of the geological time scale were the formations described and put in chronological order by the geologists and stratigraphers of the 18th and 19th centuries.

Modern revision of the geologic sciences has restricted formations to lithologies, because lithological units are formed by depositional environments, some of which may persist for hundreds of millions of years and will transgress chronostratigraphic intervals or fossil-based methods of correlating rocks. For example, the Hamersley Basin of Western Australia is a Proterozoic sedimentary basin where up to 1200 million years of sedimentation is preserved within the intact sedimentary stratigraphy, with up to 300 million years represented by a single lithological unit of banded iron formation and shale.

Geologic formations are usually sedimentary rock layers, but may also be metamorphic rocks and volcanic flows. Igneous intrusive rocks are generally not divided into formations.

Defining lithostratigraphic formations[edit]

The Permian through Jurassic strata of the Colorado Plateau area of southeastern Utah demonstrate the principles of stratigraphy. These strata make up much of the famous prominent rock formations in widely spaced protected areas such as Capitol Reef National Park and Canyonlands National Park. From top to bottom: Rounded tan domes of the Navajo Sandstone, layered red Kayenta Formation, cliff-forming, vertically jointed, red Wingate Sandstone, slope-forming, purplish Chinle Formation, layered, lighter-red Moenkopi Formation, and white, layered Cutler Formation sandstone. Picture from Glen Canyon National Recreation Area, Utah.

Formations are the only formal lithostratigraphic units into which the stratigraphic column everywhere should be divided completely on the basis of lithology.

The contrast in lithology between formations required to justify their establishment varies with the complexity of the geology of a region and the detail needed for geologic mapping and to work out its geologic history.

Formations must be able to be delineated at the scale of geologic mapping practiced in the region. The thickness of formations may range from less than a meter to several thousand meters.

Geologic formations are typically named for the geographic area in which they were first described.

Strictly, formations cannot be defined on any other criteria except primary lithology. However, it is often useful to define biostratigraphic units based on paleontological criteria, chronostratigraphic units based on the age of the rocks, and chemostratigraphic units based on geochemical criteria.

Sequence stratigraphy is a concept which challenges the idea of strict lithostratigraphic units by defining units based on events in sedimentary basins such as oceanic regressions and transgressions. These sequences are a combination of chronostratigraphic units, linked by time, and depositional environment linked by the geologic events which occurred at that time, regardless of the grain size of the sediments.

The term "formation" is often used informally to refer to a specific grouping of rocks, such as those encountered within a certain depth range in an oil well.

Other uses of the term[edit]

"Formation" is also used informally to describe the sometimes odd shapes (forms) that rocks acquire through erosional or depositional processes. Such a formation is said to be abandoned when it is no longer affected by the geologic agent that produced it. Some well known cave formations include stalactites and stalagmites.

See also[edit]

Further reading[edit]

  • Brookfield, Michael E. (2008). Principles of Stratigraphy. John Wiley & Sons. pp. 111–114, 200. ISBN 9780470693223. 
  • Rey, Jacques; Simone Galeotti, eds. (2008). Stratigraphy : terminology and practice. Paris, France: Editions OPHRYS. ISBN 9782710809104. 


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