Random Formation

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Random Formation
Stratigraphic range: Early Cambrian
Random Formation photo.jpg
Some facies of the Random Formation: Synaresis cracks in mudstones, with overlying white cross-bedded tidal sandstones
Type Formation
Unit of Young's Cove Group, [1] Musgravetown Group, [2] or none, [3] depending on authority (and location)
Underlies(Unconformably) Bonavista Fm and others [4]
Overlies
ThicknessFrom a few metres to 250 m [6]
Lithology
PrimaryHerringbone-crossstratified white arenites
OtherGrey-green silts and shales
Location
RegionDominion of Newfoundland Red Ensign.svg  Newfoundland
CountryFlag of Canada (Pantone).svg  Canada
Type section
Named for Random Island
Random Formation map.svg
Bedrock distribution of the Random Formation

The Random Formation is a rock unit in Newfoundland dating to the early Cambrian period, dominated by tidal quartz arenites deposited in a near-shore environment, but also incorporating intertidal and open-shelf deposits, including glauconitic and mud-cracked mudstones (now shales), and red channel sandstones. [4] [7] It was deposited quickly and is approximately 175 m (574 ft) thick. [8] The Blue Pinion Formation was originally recognized as a separate formation, but is now interpreted as an expression of the Random Formation. [9] [10]

Contents

Sedimentology

Its white arenitic sandstones are very distinctive, recognizable from their herringbone cross-stratification that denotes the influence of storm systems. Interbedded green-grey sands and silts represent an intertidal setting. [5]

Spatial distribution

It is widespread throughout Newfoundland unlike its underlying units. It was deposited in intertidal mud flats to subtidal setting, then (later) near the bottom of an open marine shelf. [11]

The top of the unit intergrades with the overlying strata. [10]

Stratigraphy

Synaresis cracks in the Random Formation, Trinity Bay, Newfoundland Random Formation synaresis cracks.jpg
Synaresis cracks in the Random Formation, Trinity Bay, Newfoundland

Some studies [1] assign the Random Formation as the lowest unit of the Adeyton Group, but strictly it is below that group. [5]

It overlies the Chapel Island formation, which contains the Precambrian/Cambrian boundary. [12]

The unit is often strongly folded. [5]

Age

Megaripples in the quartz arenites of the Random Formation Random Formation megaripples.jpg
Megaripples in the quartz arenites of the Random Formation

The formation is difficult to date, but is considered Precambrian, as it lies unconformably under the Bonavista Formation and conformably above Ediacaran strata. [2] It does sit above the Chapel Island Formation on the Burin peninsula meaning that, at that location, the lower boundary is in the Lower Cambrian. Inarticulate brachiopods have been found in its upper strata, dating these to the late early or even early mid Cambrian. [10]

However, it is likely that the unit is diachronous and may date into the Ediacaran further to the east. [10]

The Cambrian stage 2 - stage 3 boundary (Tommotian/Atdabanian) has been reported as being within the Random Formation, or possibly in the overlying Bonavista Formation. The overlying Smith Point Formation hosts the first trilobites. [13]

Palaeontology

The trilobite-like trace fossils Rusophycus and Cruziana occur in the Random Formation, alongside a range of other ichnofossils including Diplocraterion, Paleodictyon, Scolicia, and Squamodictyon . [13] Body fossils include the small shelly fauna Aldanella attleborensis assemblage. [14]

See also

Related Research Articles

<span class="mw-page-title-main">Ediacaran</span> Third and last period of the Neoproterozoic Era

The Ediacaran is a geological period of the Neoproterozoic Era that spans 96 million years from the end of the Cryogenian Period at 635 Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last period of the Proterozoic Eon as well as the last of the so-called "Precambrian supereon", before the beginning of the subsequent Cambrian Period marks the start of the Phanerozoic Eon, where recognizable fossil evidence of life becomes common.

The Precambrian is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the Phanerozoic Eon, which is named after Cambria, the Latinized name for Wales, where rocks from this age were first studied. The Precambrian accounts for 88% of the Earth's geologic time.

<i>Charnia</i> Genus of frond-like lifeforms

Charnia is an extinct genus of frond-like lifeforms belonging to the Ediacaran biota with segmented, leaf-like ridges branching alternately to the right and left from a zig-zag medial suture. The genus Charnia was named for Charnwood Forest in Leicestershire, England, where the first fossilised specimen was found. Charnia is significant because it was the first Precambrian fossil to be recognized as such.

<span class="mw-page-title-main">Glauconite</span> Iron potassium phyllosilicate mineral of blue-green to green color

Glauconite is an iron potassium phyllosilicate mineral of characteristic green color which is very friable and has very low weathering resistance.

<i>Aspidella</i> Genus of Ediacaran animals

Aspidella is an Ediacaran disk-shaped fossil of uncertain affinity. It is known from the single species A. terranovica.

<span class="mw-page-title-main">Ediacaran biota</span> Life of the Ediacaran period

The Ediacaranbiota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period. These were enigmatic tubular and frond-shaped, mostly sessile, organisms. Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms. The term "Ediacara biota" has received criticism from some scientists due to its alleged inconsistency, arbitrary exclusion of certain fossils, and inability to be precisely defined.

<span class="mw-page-title-main">Stratigraphy of the Cambrian</span>

The Stratigraphy of the Cambrian period currently has several schemes used for ordering geologic formations from the period. The International Commission on Stratigraphy−ICS scheme has set a stratotype section for the base of the Cambrian, dated quite accurately to 538.8 ± 0.2 million years ago. Russian and Chinese scientists have developed a different scheme.

<span class="mw-page-title-main">Syneresis crack</span>

Syneresis cracks are a sedimentary structure developed by the shrinkage of sediment without desiccation – not to be confused with desiccation cracks. Syneresis is the expulsion of a liquid from a gel-like substance. Syneresis cracks are formed by the contraction of clay in response to changes in the salinity of a liquid surrounding a deposit. The cracks can occur, for example, in mudstones deposited between two beds of sandstone. The markings would have been formed subaqueously on the bedding surface and could resemble desiccation mudcracks, but are not continuous and vary in shape. They commonly occur in thin mudstones interbedded with sandstones, as positive relief on the bottom of the sandstone, or as negative relief on the top of the mudstone. Subaqueous shrinkage cracks can develop on and through a surface that has been continuously covered in water. Syneresis cracks in some shales and lime mudstones may initially be preserved as small cavities, which then usually fill with silt and sand from either the overlying or underlying beds and laminae. Usually there is no pattern to the cracks, and they do not connect to form geometric shapes. Rather they are discontinuous and shaped in one of the following categories:

<span class="mw-page-title-main">Chapel Island Formation</span> Sedimentary formation in the Burin Peninsula, Newfoundland, Canada

The Chapel Island Formation is a sedimentary formation from the Burin Peninsula, Newfoundland, Canada. It is a succession of siliciclastic deposits, over 1,000 metres (3,300 ft) thick, that were deposited during the latest Ediacaran and earliest Cambrian.

The Attawapiskat Formation is a geologic formation in Ontario. It preserves fossils dating back to the Silurian period.

The Brigus Formation is a fossiliferous upper lower Cambrian geologic formation in Newfoundland and Labrador.

<span class="mw-page-title-main">Mistaken Point Formation</span>

The Mistaken Point Formation is a geologic formation in Newfoundland and Labrador. It is recognized as a Lagerstätte preserving fossils dating back to the Ediacaran period. It contains a stratum dated to 565 ± 3 million years ago.

The Ingta Formation is a geological unit containing green sandstones and shales; it crops out in the Canadian Mackenzie Mountains. Its age is poorly constrained, though it straddles the Precambrian/Cambrian boundary. Below the boundary its ichnofauna comprises subhorizontal Planolites burrows; above it, Phycodes burrows immediately appear, with Nemakit-Daldyn SSFs appearing soon after.

One of the major depositional strata in the Himalaya is the Lesser Himalayan Strata from the Paleozoic to Mesozoic eras. It had a quite different marine succession during the Paleozoic, as most parts of it are sparsely fossiliferous or even devoid of any well-defined fossils. Moreover, it consists of many varied lithofacies, making correlation work more difficult. This article describes the major formations of the Paleozoic – Mesozoic Lesser Himalayan Strata, including the Tal Formation, Gondwana Strata, Singtali Formation and Subathu Formation.

<span class="mw-page-title-main">Rencontre Formation</span>

The Rencontre Formation is a geological formation just below the Cambrian-Ediacaran boundary in Newfoundland, deposited in a fault-bounded enclosed basin. U-Pb dates obtained just below its base give a maximum age of 552 ± 3 million years ago.

The Smith Point Formation is an Early Cambrian, fossil-rich, pink to brick red limestone formation cropping out in Newfoundland.

<span class="mw-page-title-main">Mooring Cove Formation</span>

The Mooring Cove Formation is a formation of volcanic rock exposed in outcrops in Newfoundland.

The Vampire Formation is a formation of delta-front siliciclastics deposited in the early Cambrian. The upper unit is trilobitic Cambrian. Some authors place the underlying Ingta formation at least partially in the Cambrian; in places it overlies the sub-Cambrian unconformity.

<span class="mw-page-title-main">Palaeopascichnid</span>

A "Palaeopascichnid" describes a multitude of elongate fossils made up of multiple sausage-shaped chambers. They appear only in Ediacaran sediments. Fossils of Palaeopascichnids consist of an occasionally branching series of globular or elongate chambers. These fossils started appearing in the Vendian about 580 million years ago. Fossils of Palaeopascichnids are found in East European platform, Siberia, South China (Lantian), Australia, India (Tethys), Avalonia

References

  1. 1 2 "BEDROCK GEOLOGY OF THE CAPE ST. MARY'S PENINSULA, SOUTHWEST AVALON PENINSULA, NEWFOUNDLAND" (PDF). Retrieved 8 June 2017.{{cite journal}}: Cite journal requires |journal= (help)
  2. 1 2 "LATE NEOPROTEROZOIC (EDIACARAN) STRATIGRAPHY OF AVALON ZONE SEDIMENTARY ROCKS, BONAVISTA PENINSULA, NEWFOUNDLAND" (PDF). Retrieved 8 June 2017.{{cite journal}}: Cite journal requires |journal= (help)
  3. Normore (2012). "Current Research". Report 12-1.{{cite journal}}: Cite journal requires |journal= (help)
  4. 1 2 Smith, S. A.; Hiscott, R. N. (1987). "Latest Precambrian to Early Cambrian basin evolution, Fortune Bay, Newfoundland: Fault-bounded basin to platform". Can. J. Earth Sci. 21 (12): 1379–1392. doi:10.1139/e84-143.
  5. 1 2 3 4 Normore, L. S. (2012). "GEOLOGY OF THE RANDOM ISLAND MAP AREA (Nts 2C/04), Newfoundland". Newfoundland and Labrador Department of Natural Resources Geological Survey Report. 12: 121–145.
  6. Hiscott, R. N. (1982). "Tidal deposits of the Lower Cambrian Random Formation, eastern Newfoundland; facies and paleoenvironments". Canadian Journal of Earth Sciences. 19 (10): 2028–2042. Bibcode:1982CaJES..19.2028H. doi:10.1139/e82-180.
  7. Hiscott, Richard N. (1982). "Tidal deposits of the Lower Cambrian Random Formation, eastern Newfoundland: Facies and Paleoenvironments". Canadian Journal of Earth Sciences. 19 (10): 2028–2042. Bibcode:1982CaJES..19.2028H. doi:10.1139/e82-180.
  8. Crimes, Thomas Peter (1992). "The Record of Trace Fossils across the Proterozoic—Cambrian Boundary". Origin and Early Evolution of the Metazoa. Topics in Geobiology. Vol. 10. pp. 177–202. doi:10.1007/978-1-4899-2427-8_6. ISBN   978-1-4899-2429-2.
  9. Anderson, M. M. (1981). "The Random Formation of southeastern Newfoundland; a discussion aimed at establishing its age and relationship to bounding formations". American Journal of Science. 281 (6): 807–830. Bibcode:1981AmJS..281..807A. doi: 10.2475/ajs.281.6.807 .
  10. 1 2 3 4 Greene, Bryan; Williams, Harold (1974). "New Fossil Localities and the Base of the Cambrian in Southeastern Newfoundland". Canadian Journal of Earth Sciences. 11 (2): 319. Bibcode:1974CaJES..11..319G. doi:10.1139/e74-027.
  11. Smith, S. A.; Hiscott, R. N. (1987). "Latest precambrian to Early Cambrian basin evolution, Fortune Bay, Newfoundland fault–bounded basin to platform". Canadian Journal of Earth Sciences. 21 (12): 1379–1392. doi:10.1139/e84-143.
  12. Gehling, James G.; Jensen, Sören; Droser, Mary L.; Myrow, Paul M.; Narbonne, GUY M. (2001). "Burrowing below the basal Cambrian GSSP, Fortune Head, Newfoundland". Geological Magazine. 138 (2): 213–218. Bibcode:2001GeoM..138..213G. doi:10.1017/S001675680100509X. S2CID   131211543.
  13. 1 2 Peter Crimes, T. (1987). "Trace fossils and correlation of late Precambrian and early Cambrian strata". Geological Magazine. 124 (2): 97–119. Bibcode:1987GeoM..124...97P. doi:10.1017/S0016756800015922. S2CID   129916056.
  14. Bengtson, Stefan; Fletcher, Terence P. (1983). "The oldest sequence of skeletal fossils in the Lower Cambrian of southeastern Newfoundland". Canadian Journal of Earth Sciences. 20 (4): 525. Bibcode:1983CaJES..20..525B. doi:10.1139/e83-050.