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A group is a set of two or more formations that share certain lithological characteristics. A group may be made up of different formations in different geographical areas and individual formations may appear in more than one group. Groups are occasionally divided into subgroups, but subgroups are not
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Formations are the primary units used in the subdivision of a sequence and may vary in scale from tens of centimetres to kilometres. They should be distinct lithologically from other formations, although the boundaries do not need to be sharp. To be formally recognised, a formation must have
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A member is a named lithologically distinct part of a formation. Not all formations are subdivided in this way and even where they are recognized, they may only form part of the formation. A member need not be mappable at the same scale as a formation.
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A supergroup is a set of two or more associated groups and/or formations that share certain lithological characteristics. A supergroup may be made up of different groups in different geographical areas.
153:, higher rank units generally comprising two or more units of lower rank. Going from smaller to larger in rank, the main lithostratigraphic ranks are bed, member, formation, group and supergroup.
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is a lithologically distinct layer within a member or formation and is the smallest recognisable stratigraphic unit. These are not normally named, but may be in the case of a
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is a stratigraphic interval that contains fossils that represent parts of the evolutionary lineage of a particular fossil group. This is a special case of a range zone.
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is a stratigraphic interval in which the abundance of a particular taxon (or group of taxa) is significantly greater than seen in neighbouring parts of the succession.
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from one another, but the contact need not be particularly distinct. For instance, a unit may be defined by terms such as "when the sandstone component exceeds 75%".
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mentioned in the North
American Stratigraphic Code, and are permitted under International Commission on Stratigraphy guidelines only in exceptional circumstances.
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is a stratigraphic interval that represents the occurrence range of a specific fossil taxon, based on the localities where it has been recognised.
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is a stratigraphic interval characterised by an assemblage of three or more coexisting fossil taxa that distinguish it from surrounding strata.
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The wedge-out of a component formation or formations may justify the reduction of a group to formation rank, retaining the same name.
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is a stratigraphic interval whose top and base are defined by horizons that mark the first or last occurrence of two different taxa.
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of identifiable origin and relative age range that is defined by the distinctive and dominant, easily mapped and recognizable
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97:. These strata make up much of the famous prominent rock formations in widely spaced protected areas such as
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260:. The five commonly used types of biozone are assemblage, range, abundance, interval and lineage zones.
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2004 North
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520:"Biostratigraphy from taxon to biozones and biozonal schemes"
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are subdivided on the basis of their shared or associated
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Formal names of lithostratigraphic units are assigned by
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497:North American Stratigraphic Code, p. 1569
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113:, cliff-forming, vertically jointed, red
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477:International Commission on Stratigraphy
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524:Stratigraphy: Terminology and Practice
440:. John Wiley & Sons. p. 200.
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473:"Chapter 5. Lithostratigraphic Units"
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131:Glen Canyon National Recreation Area
559:"Chapter 7. Biostratigraphic Units"
526:. Editions OPHRYS. pp. 64–73.
358:"North American Stratigraphic Code"
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522:. In Rey J.; Galeotti S. (eds.).
518:Thierry J.; Galeotti S. (2008).
93:demonstrate the principles of
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437:Principles of Stratigraphy
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117:, slope-forming, purplish
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129:sandstone. Picture from
103:Canyonlands National Park
434:Brookfield M.E. (2008).
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69:Lithostratigraphic units
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151:lithostratigraphic rank
121:, layered, lighter-red
238:Biostratigraphic units
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327:Sequence stratigraphy
125:, and white, layered
89:area of southeastern
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413:. pp. 129–130.
407:Mathur S.M. (2008).
220:Group (stratigraphy)
205:Geological formation
618:Geology terminology
410:Elements of Geology
317:Magnetostratigraphy
18:Stratigraphic units
307:Chronostratigraphy
158:geological surveys
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123:Moenkopi Formation
32:stratigraphic unit
613:Geological groups
115:Wingate Sandstone
111:Kayenta Formation
16:(Redirected from
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565:. 2013–2014
479:. 2013–2014
139:sedimentary
597:Categories
338:References
312:Glaciology
273:range zone
229:Supergroup
50:features (
44:lithologic
199:Formation
147:lithology
375:June 13,
301:See also
83:Jurassic
81:through
63:distinct
59:mappable
258:biozone
133:, Utah.
79:Permian
569:4 June
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483:4 June
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250:fossil
190:Member
52:facies
361:(PDF)
214:Group
571:2014
528:ISBN
485:2014
442:ISBN
415:ISBN
394:link
377:2020
254:taxa
141:and
101:and
91:Utah
77:The
61:and
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285:An
278:An
264:An
180:bed
168:Bed
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