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Random Formation

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Random Formation
Stratigraphic range: Early Cambrian
TypeFormation
Unit ofYoung'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
Region Newfoundland
Country Canada
Type section
Named forRandom Island

Bedrock distribution of the Random Formation

The Random Formation is a near-shore rock unit dating to the early Cambrian period, dominated by tidal quartz arenites, but also incorporating intertidal and open-shelf deposits, including glauconitic and mud-cracked mudstones (now shales), and red channel sandstones.[7][8] It was deposited quickly and isn't super thick - 175m perhaps at a max.[9] The Blue Pinion Formation was originally recognized as a separate formation, but is now interpreted as an expression of the Random Formation.[10]Attention: This template ({{ref doi}}) is deprecated. To cite the publication identified by doi:10.1139/e74-027, please use {{cite journal}} with |doi=10.1139/e74-027 wrapped in <ref> instead.

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 speak to an intertidal setting.[11]

Spatial distribution

It is widespread throughout Avalonia - Canada, and Boston, unlike its underlying units. It was deposited in intertidal mud flats / subtidal setting, then (later) near the bottom of an open marine shelf.[12] The top of the unit intergrades with the overlying strataAttention: This template ({{ref doi}}) is deprecated. To cite the publication identified by doi:10.1139/e74-027, please use {{cite journal}} with |doi=10.1139/e74-027 wrapped in <ref> instead.

Stratigraphy

Some maps[1] refer it to the Adeyton group, but strictly it's below this.[13]

It overlies the Chapel Island formation, which contains the Precambrian/Cambrian boundary.[14]

The unit is often strongly folded.[15]


Age

Difficult to date; Some authors slip it in before the Cambrian, by virtue of its lying unconformably underbneath tbe Bonavista formation and conformably above Edaiacarn strata. [2] It does sit (conformably?) above the Chapel Island formation on the Burin peninsula, meaning that at least there its lower boundary is in the Lower Cambrian; and places inarticulate brachiopods have been found in its upper strata, dating these to the late early or even early mid Cambrian.Attention: This template ({{ref doi}}) is deprecated. To cite the publication identified by doi:10.1139/e74-027, please use {{cite journal}} with |doi=10.1139/e74-027 wrapped in <ref> instead.

That said, it is likely that the unit is diachronous, so it may go back into the Ediacaran further east.Attention: This template ({{ref doi}}) is deprecated. To cite the publication identified by doi:10.1139/e74-027, please use {{cite journal}} with |doi=10.1139/e74-027 wrapped in <ref> instead.


On the other hand, the Stage 2 - Stage 3 boundary (Tommotian/Atdabanian) has been supposed to lie within the Random Formation, or possibly in the overlying Bonavista Formation; the Smith Point Formation above that hosts the first trilobites.[16]

Palaeontology

The triolobite-like trace fossils Rusophycus and Cruzianaoccur in the Random Formation, alongside a range of other ichnofossils including Diplocraterion, Paleodictyon, Scolicia, and Squamodictyon.[16] Body fossils include the small shelly fauna Aldanella attleborensis assemblage.[17]

References

  1. ^ a b "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); Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  2. ^ a b "LATE NEOPROTEROZOIC (EDIACARAN) STRATIGRAPHY OF AVALON ZONE SEDIMENTARY ROCKS, BONAVISTA PENINSULA, NEWFOUNDLAND" (PDF). Retrieved 8 June 2017. {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  3. ^ Normore (2012). "Current Research". Report 12-1. {{cite journal}}: Cite journal requires |journal= (help)
  4. ^ S. A. Smith, R. N. Hiscott, Can. J. Earth Sci. 21, 1379–1392 (1987).
  5. ^ Normore, L. S. 2012: GEOLOGY OF THE RANDOM ISLAND MAP AREA (Nts 2C/04), Newfoundland. Current Research (2012) 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 19:2028–2042.
  7. ^ S. A. Smith, R. N. Hiscott, Can. J. Earth Sci. 21, 1379–1392 (1987).
  8. ^ 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. doi:10.1139/e82-180.
  9. ^ 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. p. 177. doi:10.1007/978-1-4899-2427-8_6. ISBN 978-1-4899-2429-2.
  10. ^ 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. doi:10.2475/ajs.281.6.807.
  11. ^ Normore, L. S. 2012: GEOLOGY OF THE RANDOM ISLAND MAP AREA (Nts 2C/04), Newfoundland. Current Research (2012) Newfoundland and Labrador Department of Natural Resources Geological Survey Report 12-:121–145.
  12. ^ Smith, S. A., and R. N. Hiscott. 1987: Latest precambrian to Early Cambrian basin evolution, Fortune Bay, Newfoundland fault–bounded basin to platform. Canadian Journal of Earth Sciences 21:1379–1392.
  13. ^ Normore, L. S. 2012: GEOLOGY OF THE RANDOM ISLAND MAP AREA (Nts 2C/04), Newfoundland. Current Research (2012) Newfoundland and Labrador Department of Natural Resources Geological Survey Report 12-:121–145.
  14. ^ 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). doi:10.1017/S001675680100509X.
  15. ^ Normore, L. S. 2012: GEOLOGY OF THE RANDOM ISLAND MAP AREA (Nts 2C/04), Newfoundland. Current Research (2012) Newfoundland and Labrador Department of Natural Resources Geological Survey Report 12-:121–145.
  16. ^ a b Peter Crimes, T. (1987). "Trace fossils and correlation of late Precambrian and early Cambrian strata". Geological Magazine. 124 (2): 97–119. doi:10.1017/S0016756800015922.
  17. ^ 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. doi:10.1139/e83-050.
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