Geochronology/Stratigraphy

From Wikiversity
Jump to: navigation, search
The image shows rock strata in Cafayate, Argentina. Credit: travelwayoflife.

Stratigraphy is concerned with the order and relative position of strata and their relationship to the geological time scale.

The image at the right shows rock strata in Cafayate, Argentina, the subject of stratigraphy.

Theoretical stratigraphy[edit]

Def. the "study of rock layers and the layering process"[1] is called stratigraphy.

Stratigraphy[edit]

This is an International Chronostratigraphic Chart. Credit: K.M. Cohen, S. Finney, and P.L. Gibbard, International Commission on Stratigraphy.

Dates have been assigned to specific geologic stratigraphy frames, columns, or columnar units.

Stratigraphic columns[edit]

This is the stratigraphic column for Dinosaur National Monument. Credit: Emmett Evanoff, National Park Service.

As an example of a stratigraphic column, the image at the right shows one for the Dinosaur National Monument, Utah and Colorado, USA.

Each geographic location on the rocky surface of the Earth has a stratigraphic column. Correlating each stratum that has been shown to be in a geologic time period with others around the world is part of the fun of stratigraphy.

Geography[edit]

Main sources: Locations/Geography and Geography
A well-developed veined network, a fossilised soil structure, extends down from the top of a greyish red siltstone unit, and is underlain by a zone of calcareous nodules. Credit: P. J. Barrett, B. P. Kohn, R. A. Askin & J. G. McPherson.

At the right is a small portion of the stratigraphic column between the Hatherton and MacKay glaciers in Antarctica. The top rock layer is a greyish red siltstone. The next downward is a greenish grey siltstone penetrated by sinuous tubes that may be roots or root-like structures. Underlaying this is "a zone of calcareous nodules."[2]

"The Beacon Supergroup (Barrett, 1970) in the Transantarctic Mountains is largely a flat-lying, nonmarine sequence from Devonian or older to Jurassic in age. It consists of the Taylor Group (Devonian or older), a quartzose sandstone sequence, and the Victoria Group (Permian and Triassic), dominantly a coal-bearing sandstone-siltstone sequence (Harrington, 1965)."[2]

"The Taylor Group comprises up to 1,450 m of quartzose sandstone, with smaller conglomerate, arkosic and shaly units [...]. [The] youngest Taylor Group unit [is] the Aztec Siltstone [of which the image at the right exhibits]."[2]

Glacial sediment layers[edit]

Dead ice occurs below sandur deposits on the Brúarjökull forefield. Credit: L.R. Bjarnadóttir.
Layers of glacial sediments are resting on chalk base. Credit: Evelyn Simak.

The cross section of a sandur deposit on the right from Iceland shows strata of various sand-like material atop dead ice from a former surge of the glacier Brúarjökull.

In the second image down on the right: "The pebble beach at Weybourne marks the start of the cliff section of the Norfolk coast that extends in easterly direction. This change in the character of the coastline is due to the properties of the chalk, which is harder to the east. The cliffs resting on this chalk base are composed of layers of glacial sediments of flints and fossils."[3]

Varves[edit]

Pleistocene age varves at Scarborough Bluffs, Toronto, Ontario, Canada. The thickest varves are more than half an inch thick. Credit: Bruce F. Molnia, USGS.

Def. "a pair of sedimentary layers, a couplet, that form in an annual cycle as the result of seasonal weather changes"[4] is called a varve.

"Typically formed in glacial lakes a varve couplet consists of a coarser grained summer layer formed during open-water conditions, and a finer grained winter layer formed from deposition from suspension during a period of winter ice cover. Many varve deposits contain hundreds of couplets."[4]

Lias[edit]

Def. a "stratigraphic group from the lower Jurassic period, consisting of thin layers of blue limestone [present in parts of southern England]"[5] is called a lias.

Calabrian[edit]

Lithologic and magnetostratigraphic correlations are for the Calabrian GSSP. Credit: Maria Bianca Cita, Philip L. Gibbard, Martin J. Head, and the ICS Subcommission on Quaternary Stratigraphy.
The Vrica section and surrounding area includes specifically the GSSP of the Calabrian Stage fixed at the top of layer ‘e’. Credit: Maria Bianca Cita, et al.

"The [Calabrian] GSSP occurs at the base of the marine claystone conformably overlying sapropelic bed ‘e’ within Segment B in the Vrica section. This lithological level represents the primary marker for the recognition of the boundary, and is assigned an astronomical age of 1.80 Ma on the basis of sapropel calibration."[6]

"The boundary falls between the highest occurrence of Discoaster brouweri (below) and the lowest common occurrence of left-coiling Neogloboquadrina pachyderma (above), and below the lowest occurrences of medium-sized Gephyrocapsa (including G. oceanica) and Globigerinoides tenellus."[6]

In the image on the right, the Vrica section includes specifically the GSSP of the Calabrian Stage fixed at the top of layer ‘e’.

Gelasian[edit]

The base of the marly layer overlying sapropel MPRS 250, located at 62 m in the Monte San Nicola section, is the defined base of the Gelasian Stage. Credit: D. Rio, R. Sprovieri, D. Castradori, and E. Di Stefano.

"The base of the Quaternary System [shown in the image on the right] is defined by the Global Stratotype Section and Point (GSSP) of the Gelasian Stage at Monte San Nicola in Sicily, Italy, currently dated at 2.58 Ma."[7]

"The astrochronological age of sapropel MPRS 250 (mid-point), corresponding to precessional cycle 250 from the present, is 2.588 Ma (Lourens et al., 1996), which can be assumed as the age of the boundary."[8]

Zanclean[edit]

Main sources: History/Zanclean and Zanclean
A view of the Eraclea Minoa section has the GSSP of the Zanclean Stage and of the Pliocene Series. Credit: John A. Van Couvering, Davide Castradori, Maria Bianca Cita, Frederik J. Hilgen, and Domenico Rio.

"The boundary-stratotype of the stage is located in the Eraclea Minoa section on the southern coast of Sicily (Italy), at the base of the Trubi Formation. The age of the Zanclean and Pliocene GSSP at the base of the stage is 5.33 Ma in the orbitally calibrated time scale, and lies within the lowermost reversed episode of the Gilbert Chron (C3n.4r), below the Thvera normal subchron."[9]

In the chronostratigraphic correlation in the Piacenzian section, the base of the Zanclean is marked as the '0' point.

Cenozoic[edit]

This image is a detail of the K/Pg boundary with a Tunisian coin as scale on the rusty layer. Credit: Eustoquio Molina, Laia Alegret, Ignacio Arenillas, José A. Arz, Njoud Gallala, Jan Hardenbol, Katharina von Salis, Etienne Steurbaut, Noël Vandenberghe, and Dalila Zaghbib-Turki.

"The GSSP section near El Kef contains one main feature that allows for a direct correlation of this marine section with continental sections: the Ir anomaly at the base of the Boundary Clay."[10]

The Global Boundary Stratotype Section and Point for the base of the Danian Stage is also the base GSSP for the Paleocene, Paleogene, "Tertiary", and Cenozoic at El Kef, Tunisia.

Mesozoic[edit]

The diagram shows the Permian-Triassic boundary at the base of the Induan. Credit: Yin Hongfu, Zhang Kexin, Tong Jinnan, Yang Zunyi and Wu Shunbao.
Hindeodus parvus is now recognized as the index fossil, occurring in the Zone above the P-T boundary. Credit: Yin Hongfu, Zhang Kexin, Tong Jinnan, Yang Zunyi and Wu Shunbao.

In the diagram on the right, the Permian-Triassic boundary is at the base of the Induan limestone that occurs within the Yinkeng Formation.

"The Global Stratotype Section and Point (GSSP) of the Permian-Triassic boundary [...] is defined at the base of Hindeodus parvus horizon, i.e. the base of Bed 27c of Meishan section D, Changxing County, Zhejiang Province, South China."[11]

"Hindeodus parvus is now recognized as the index fossil" occurring in the Zone above the P-T boundary.[11]

Famennian[edit]

The diagram shows the detailed succession of beds around the GSSP level between beds 31g and 32a. Credit: G Klapper, R Feist, R T Becker and M R House.
Photograph of the succession shows that the GSSP lies between Bed 31g and 32a. Credit: G Klapper, R Feist, R T Becker and M R House.
Fossil is of Platyclymenia intracrostata Credit: Wikipek.
This is another example of Clymenia laevigata. Credit: Hectonichus.

"The boundary for the Frasnian/Famennian Stage Global Stratotype Section and Point (GSSP) [...] is drawn [above] in a section exposed [in the second image above] near the Upper Coumiac Quarry in the southeastern Montagne Noire, France."[12]

A specimen of Clymenia laevigata from the Upper Devonian Famennian of Poland is on the right.

On the left is a fossil of Platyclymenia intracrostata also from the Famennian of Poland.

Telychian[edit]

Current Telychian GSSP is arrowed parallel to the bedding. Credit: Jeremy R. Davies, Richard A. Waters, Stewart G. Molyneux, Mark Williams, Jan A. Zalasiewicz, Thijs R. A. Vandenbroucke & Jacques Verniers.

On the right is an image of the type locality for the Telychian base GSSP indicated by an arrow which points parallel to the bedding. Older bedding of the Aeronian is to the right. The Telychian GSSP is in the Wormwood Formation, Cefn Cerig quarry.

In the section below for the Aeronian, the lower Telychian is marked with a Ⓣ.

Aeronian[edit]

Diagram has the Rhuddanian to early Telychian sea level curves where Ⓐ marks the horizon of the Aeronian GSSP. Credit: Jeremy R. Davies, Richard A. Waters, Stewart G. Molyneux, Mark Williams, Jan A. Zalasiewicz, Thijs R. A. Vandenbroucke & Jacques Verniers.
The arrow indicates the Aeronian lower GSSP perpendicular to the bedding. Credit: Jeremy R. Davies, et al.

The diagram above has the GSSP for the base of the Aeronian symbolized by a Ⓐ. The upper GSSP for the end of the Aeronian is symbolized by a Ⓣ.

On the right is the type locality for the base of the Aeronian indicated by the arrow. Actual beds are perpendicular to the arrow. The base of the Aeronian is in the Cefngarreg Sandstone Formation (formerly Trefawr Formation), Trefawr track section, Crychan Forest, Central Wales.

Sandbian[edit]

Nemagraptus gracilis, Sandbian graptolites, are from the Caparo Formation, Venezuelan Andes. Credit: J.C. Gutiérrez-Marco, D. Goldman, J. Reyes-Abril, and J. Gómez.

"The Lower Sandbian Nemagraptus gracilis Zone comprises one of the most widespread, and easily recognizable graptolite faunas in the Ordovician System. The base of the N. gracilis Zone also marks the base of the Upper Ordovician Series, and is internationally defined by the FAD of the eponymous species, with the Global Stratotype Section and Point (GSSP) located at Fågelsång in Scania, southern Sweden (Bergström et al., 2000, 2009)."[13]

Guzhangian[edit]

The image shows exposure of the GSSP for the base of the Guzhangian Stage (coinciding with the FAD of Lejopyge laevigata) in the Huaqiao Formation, Luoyixi section, Guzhang County, Hunan Province, China. Credit: Shanchi Peng, Loren E. Babcock, Jingxun Zuo, Huanling Lin, Xuejian Zhu, Xianfeng Yang, Richard A. Robison, Yuping Qi, Gabriella Bagnoli, and Yong’an Chen.
The image shows an exoskeleton of the cosmopolitan agnostoid trilobite Lejopyge laevigata. Credit: Shanchi Peng et al.

"The Global boundary Stratotype Section and Point (GSSP) for the base of the Guzhangian Stage (Cambrian Series 3) is defined at the base of a limestone (calcisiltite) layer 121.3 m above the base of the Huaqiao Formation in the Louyixi section along the Youshui River (Fengtan Reservoir), about 4 km northwest of Luoyixi (4 km southeast of Wangcun), in northwestern Hunan, China."[14]

"The GSSP level contains the lowest occurrence of the cosmopolitan agnostoid trilobite Lejopyge laevigata [in the image on the left] (base of the L. laevigata Zone)."[14]

Ediacaran[edit]

Amongst the depositional sequences of the Ediacaran and Cambrian is the Ediacaran base GSSP. Credit: James G. Gehling and Mary L. Droser.

"In the central Flinders Ranges the 4.5 km thick Umberatana Group encompasses the two main phases of glacial deposition (see Thomas et al., 2012). The carbonaceous, calcareous and pyritic Tindelpina Shale Member, of the interglacial Tapley Hill Formation, caps the Fe-rich diamictite and tillite formations of the Sturt glaciation. The upper Cryogenian glacials of the Elatina Formation are truncated by the Nuccaleena Formation at the base of the Wilpena Group and the Ediacaran System."[15]

"In 2004, the Global Stratotype Section and Point (GSSP) for the terminal Proterozoic was placed near the base of the Nuccaleena Formation in Enorama Creek in the central Flinders Ranges [in the image on the right], thus establishing the Ediacaran System and Period (Knoll et al., 2006). As the Nuccaleena Formation has not been accurately dated, a date of c. 635 Ma from near-correlative levels in Namibia and China is presumed for the base of the Ediacaran (Hoffmann et al., 2004; Condon et al., 2005; Zhang et al., 2005)."[15]

Sediment cores[edit]

This is a sediment core taken from the coast of New England. Credit: Joe Fudge, Christopher Hein, VIMS.

Sediment cores may be obtained "by drilling or jack-hammering a steel rod or shoving a hand auger or hollow "push core" into a beach or marsh or water bottom, and pulling up sediment samples for analysis."[16]

"You can think of a sediment core as being more or less a tape recorder of time. Within that sediment core, we work with proxies, or environmental proxies, and these can be very simple measures of grain size or composition or some organic geochemical property or maybe pollen."[17]

"There are environments that preserve storm records that are buried in the sea bed, so that you can go down through time and actually develop a record of the intensity and frequency of cyclonic storms. That's something that's pretty high up on the radar for coastal inhabitants. Kind of understanding the pattern of these storms through time helps us to understand what might be coming down the pike."[17]

"You take a sediment core through a barrier island and under that is marsh, bay, marsh, mainland. You have maybe an old forest, roots. Looking back in time at that location, hundreds of thousands of years ago, you get this vertical succession of these different layers."[18]

Technology[edit]

Main source: Technology
A VIMS field crew collects sediment cores on the landward side of the Plum Island barrier island. Credit: VIMS.

"A VIMS field crew [assembled in the image on the right] collects sediment cores on the landward side of the Plum Island barrier island in May 2014. These cores were collected with a Geoprobe drill rig [shown] and went as much as 60 feet below the surface of the island. Cores were collected in 4 feet sections and brought back to VIMS for processing."[19]

Hypotheses[edit]

Main source: Hypotheses
  1. To obtain stratigraphic columns in locations where exposures do not occur, corings may provide alternatives.

See also[edit]

References[edit]

  1. SemperBlotto (27 August 2014). "stratigraphy, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. Retrieved 2014-09-21. 
  2. 2.0 2.1 2.2 P. J. Barrett, B. P. Kohn, R. A. Askin & J. G. McPherson (1971). "Preliminary report on Beacon Supergroup studies between the Hatherton and Mackay glaciers, Antarctica". New Zealand Journal of Geology and Geophysics 14 (3): 605-14. doi:10.1080/00288306.1971.10421951. http://www.tandfonline.com/doi/pdf/10.1080/00288306.1971.10421951. Retrieved 2014-09-27. 
  3. Evelyn Simak (16 November 2007). "Layers of glacial sediments resting on chalk base". Photograph. Retrieved 2016-01-24. 
  4. 4.0 4.1 Eleyne Phillips (16 December 2004). "Glossary of Glacier Terminology". Reston, Virginia USA: United States Geological Survey. Retrieved 2014-11-09. 
  5. "lias, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 29 December 2014. Retrieved 2015-02-19. 
  6. 6.0 6.1 Maria Bianca Cita, Philip L. Gibbard, Martin J. Head, and the ICS Subcommission on Quaternary Stratigraphy (September 2012). "Formal ratification of the GSSP for the base of the Calabrian Stage (second stage of the Pleistocene Series, Quaternary System)". Episodes 35 (3): 388-97. http://www.stratigraphy.org/GSSP/Calabrian2.pdf. Retrieved 2015-01-18. 
  7. Philip L. Gibbard and Martin J. Head (September 2010). "The newly-ratified definition of the Quaternary System/Period and redefinition of the Pleistocene Series/Epoch, and comparison of proposals advanced prior to formal ratification". Episodes 33 (3): 152-8. http://www.stratigraphy.org/GSSP/Quaternary&Pleistocene.pdf. Retrieved 2015-01-20. 
  8. D. Rio, R. Sprovieri, D. Castradori, and E. Di Stefano (June 1998). "The Gelasian Stage (Upper Pliocene): A new unit of the global standard chronostratigraphic scale". Episodes 21 (2): 82-7. http://www.stratigraphy.org/GSSP/Gelasian.pdf. Retrieved 2015-01-20. 
  9. John A. Van Couvering, Davide Castradori, Maria Bianca Cita, Frederik J. Hilgen, and Domenico Rio (September 2000). [http://www.stratigraphy.org/GSSP/Zanclean.pdf "The base of the Zanclean Stage and of the Pliocene Series"]. Episodes 23 (3): 179-87. http://www.stratigraphy.org/GSSP/Zanclean.pdf. Retrieved 2015-01-23. 
  10. Eustoquio Molina, Laia Alegret, Ignacio Arenillas, José A. Arz, Njoud Gallala, Jan Hardenbol, Katharina von Salis, Etienne Steurbaut, Noël Vandenberghe, and Dalila Zaghbib-Turki (December 2006). "The Global Boundary Stratotype Section and Point for the base of the Danian Stage (Paleocene, Paleogene, "Tertiary", Cenozoic) at El Kef, Tunisia - Original definition and revision". Episodes 29 (4): 263-73. http://www.stratigraphy.org/GSSP/Danian.pdf. Retrieved 2015-01-19. 
  11. 11.0 11.1 Yin Hongfu, Zhang Kexin, Tong Jinnan, Yang Zunyi and Wu Shunbao (June 2001). [http://www.stratigraphy.org/GSSP/Induan.pdf "The Global Stratotype Section and Point (GSSP) of the Permian-Triassic Boundary"]. Episodes 24 (2): 102-14. http://www.stratigraphy.org/GSSP/Induan.pdf. Retrieved 2015-01-20. 
  12. G Klapper, R Feist, R T Becker and M R House (December 1993). "Definition of the Frasnian/Famennian Stage Boundary". Episodes 16 (4): 433-41. http://www.stratigraphy.org/GSSP/Famennian.pdf. Retrieved 2015-01-27. 
  13. J.C. Gutiérrez-Marco, D. Goldman, J. Reyes-Abril, and J. Gómez (2011). J.C. Gutiérrez-Marco, I. Rábano and D. García-Bellido. ed. A Preliminary Study of Some Sandbian (Upper Ordovician) Graptolites from Venezuela, In: Ordovician of the World. Madrid: Instituto Geológico y Minero de España. pp. 199-206. ISBN 978-84-7840-857-3. http://digital.csic.es/bitstream/10261/60947/1/ORDOVICIAN%20OF%20THE%20WORLD_199_206.pdf. Retrieved 2015-01-15. 
  14. 14.0 14.1 Shanchi Peng, Loren E. Babcock, Jingxun Zuo, Huanling Lin, Xuejian Zhu, Xianfeng Yang, Richard A. Robison, Yuping Qi, Gabriella Bagnoli, and Yong’an Chen (March 2009). "The Global Boundary Stratotype Section and Point (GSSP) of the Guzhangian Stage (Cambrian) in the Wuling Mountains, Northwestern Hunan, China". Episodes 32 (1): 41-55. http://www.stratigraphy.org/GSSP/Guzhangian.pdf. Retrieved 2015-01-21. 
  15. 15.0 15.1 James G. Gehling and Mary L. Droser (March 2012). "Ediacaran stratigraphy and the biota of the Adelaide Geosyncline, South Australia". Episodes 35 (1): 236-46. http://www.episodes.co.in/contents/2012/march/p236-246.pdf. Retrieved 2015-01-19. 
  16. Tamara Dietrich (1 January 2015). "VIMS geologists use sediment cores as a window to the past". DailyPress. Retrieved 2015-01-12. 
  17. 17.0 17.1 Steve Kuehl (1 January 2015). "VIMS geologists use sediment cores as a window to the past". DailyPress. Retrieved 2015-01-12. 
  18. Christopher Hein (1 January 2015). "VIMS geologists use sediment cores as a window to the past". DailyPress. Retrieved 2015-01-12. 
  19. Joe Fudge (31 December 2014). "Pictures: VIMS studies sediment core samples". Virginia: DailyPress. Retrieved 2015-01-12. 

External links[edit]

{{Geology resources}}

38254-new folder-12.svg Type classification: this is an article resource.