View source for Earth:Random Formation

{{Infobox rockunit
| image          = Random Formation photo.jpg
| caption        = Some facies of the Random Formation: Synaresis cracks in mudstones, with overlying white cross-bedded tidal sandstones
| type           = Formation
| age            = {{Geological range|Early Cambrian}} | period = Cambrian
| prilithology   = Herringbone-crossstratified white arenites
| otherlithology = Grey-green silts and shales
| namedfor       = Random Island
| namedby        =
| region         = {{Flag|Newfoundland}}
| country        = {{flag|Canada}}
| coordinates    = 
| unitof         = Young's Cove Group,<ref name="BEDROCK GEOLOGY">{{Cite journal |url=http://www.nr.gov.nl.ca/nr/mines/geoscience/publications/report06_02.pdf |title=BEDROCK GEOLOGY OF THE CAPE ST. MARY'S PENINSULA, SOUTHWEST AVALON PENINSULA, NEWFOUNDLAND |access-date=8 June 2017}}</ref> [[Earth:Musgravetown Group|Musgravetown Group]],<ref name="LATE NEOPROTEROZOIC">{{Cite journal |url=http://www.nr.gov.nl.ca/nr/mines/geoscience/publications/currentresearch/2005/obrien.pdf |title=LATE NEOPROTEROZOIC (EDIACARAN) STRATIGRAPHY OF AVALON ZONE SEDIMENTARY ROCKS, BONAVISTA PENINSULA, NEWFOUNDLAND |access-date=8 June 2017}}</ref> or none,<ref>{{Cite journal |author=Normore |year=2012 |title=Current Research |volume=Report 12-1}}</ref> depending on authority (and location)
| subunits       =
| underlies      = (Unconformably) Bonavista Fm and others<ref name="A. Smith, R. N 1987">{{cite journal | last1 = Smith | first1 = S. A. | last2 = Hiscott | first2 = R. N. | title = Latest Precambrian to Early Cambrian basin evolution, Fortune Bay, Newfoundland: Fault-bounded basin to platform | year = 1987 | journal = Can. J. Earth Sci. | volume = 21 | issue = 12 | pages = 1379–1392 | doi = 10.1139/e84-143 }}</ref>
| overlies       = * Chapel Island Fm (conformably, Burin Peninsula)
* Crown Hill Formation (conformably, Random Island)<ref name="Normore, L. S 2012">{{cite journal | last1 = Normore | first1 = L. S. | year = 2012 | title = GEOLOGY OF THE RANDOM ISLAND MAP AREA (Nts 2C/04), Newfoundland | journal = Newfoundland and Labrador Department of Natural Resources Geological Survey Report | volume = 12 | pages = 121–145 }}</ref>
| thickness      = From a few metres to 250&nbsp;m<ref>{{cite journal | last1 = Hiscott | first1 = R. N. | year = 1982 | title = Tidal deposits of the Lower Cambrian Random Formation, eastern Newfoundland; facies and paleoenvironments | journal = Canadian Journal of Earth Sciences | volume = 19 | issue = 10 | pages = 2028–2042 | doi = 10.1139/e82-180 | bibcode = 1982CaJES..19.2028H }}</ref>
| extent         =
| area           =
| map = Random Formation map.svg
| map_caption    = Bedrock distribution of the Random Formation
}}

The '''Random Formation''' is a rock unit in Newfoundland dating to the [[Earth:Early Cambrian|early Cambrian]] period, dominated by tidal quartz [[Earth:Arenite|arenite]]s deposited in a near-shore environment, but also incorporating [[Earth:Intertidal zone|intertidal]] and open-shelf deposits, including glauconitic and mud-cracked mudstones (now [[Chemistry:Shale|shale]]s), and red channel [[Earth:Sandstone|sandstone]]s.<ref name="A. Smith, R. N 1987"/><ref>{{Cite journal|doi=10.1139/e82-180|title=Tidal deposits of the Lower Cambrian Random Formation, eastern Newfoundland: Facies and Paleoenvironments |journal=Canadian Journal of Earth Sciences|volume=19|issue=10|pages=2028–2042|year=1982|last1=Hiscott|first1=Richard N.|bibcode=1982CaJES..19.2028H}}</ref>  It was deposited quickly and is approximately 175 m thick.<ref>{{cite book|doi=10.1007/978-1-4899-2427-8_6|chapter=The Record of Trace Fossils across the Proterozoic—Cambrian Boundary|title=Origin and Early Evolution of the Metazoa|volume=10|pages=177–202|series=Topics in Geobiology|year=1992|last1=Crimes|first1=Thomas Peter|isbn=978-1-4899-2429-2}}</ref> The '''Blue Pinion Formation''' was originally recognized as a separate formation, but is now interpreted as an expression of the Random Formation.<ref>{{cite journal|doi=10.2475/ajs.281.6.807|title=The Random Formation of southeastern Newfoundland; a discussion aimed at establishing its age and relationship to bounding formations|journal=American Journal of Science|volume=281|issue=6|pages=807–830|year=1981|last1=Anderson|first1=M. M.|bibcode=1981AmJS..281..807A |doi-access=free}}</ref><ref name="auto1">{{Cite journal|doi=10.1139/e74-027|title=New Fossil Localities and the Base of the Cambrian in Southeastern Newfoundland|journal=Canadian Journal of Earth Sciences|volume=11|issue=2|pages=319|year=1974|last1=Greene|first1=Bryan|last2=Williams|first2=Harold|bibcode=1974CaJES..11..319G }}</ref>

== 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.<ref name="Normore, L. S 2012"/>

==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.<ref>{{cite journal | last1 = Smith | first1 = S. A. | last2 = Hiscott | first2 = R. N. | year = 1987 | title = Latest precambrian to Early Cambrian basin evolution, Fortune Bay, Newfoundland fault–bounded basin to platform | doi = 10.1139/e84-143 | journal = Canadian Journal of Earth Sciences | volume = 21 | issue = 12 | pages = 1379–1392 }}</ref>

The top of the unit intergrades with the overlying strata.<ref name="auto1"/>

== Stratigraphy==
[[File:Random Formation synaresis cracks.jpg|thumb|Synaresis cracks in the Random Formation, Trinity Bay, Newfoundland]]
Some studies<ref name="BEDROCK GEOLOGY"/> assign the Random Formation as the lowest unit of the Adeyton Group, but strictly it is below that group.<ref name="Normore, L. S 2012"/>

It overlies the Chapel Island formation, which contains the Precambrian/Cambrian boundary.<ref>{{cite journal |title=Burrowing below the basal Cambrian GSSP, Fortune Head, Newfoundland |journal=Geological Magazine|volume=138|issue=2|doi=10.1017/S001675680100509X|year=2001|last1=Gehling|first1=James G.|last2=Jensen|first2=Sören|last3=Droser|first3=Mary L.|last4=Myrow|first4=Paul M.|last5=Narbonne|first5=GUY M.|pages=213–218 |bibcode=2001GeoM..138..213G|s2cid=131211543 }}</ref>

The unit is often strongly folded.<ref name="Normore, L. S 2012"/>

== Age==
[[File:Random Formation megaripples.jpg|thumb|Megaripples in the quartz arenites of the Random Formation]]
The formation is difficult to date, but is considered [[Earth:Precambrian|Precambrian]], as it lies [[Earth:Unconformity|unconformably]] under the [[Earth:Bonavista Formation|Bonavista Formation]] and conformably above [[Earth:Ediacaran|Ediacaran]] strata.<ref name="LATE NEOPROTEROZOIC"/>
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 [[Biology:Brachiopod|brachiopod]]s have been found in its upper strata, dating these to the late early or even early mid Cambrian.<ref name="auto1"/>

However, it is likely that the unit is [[Earth:Diachronous|diachronous]] and may date into the Ediacaran further to the east.<ref name="auto1"/>

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 [[Biology:Trilobite|trilobite]]s.<ref name="auto">{{cite journal|doi=10.1017/S0016756800015922|title=Trace fossils and correlation of late Precambrian and early Cambrian strata|journal=Geological Magazine|volume=124|issue=2|pages=97–119|year=1987|last1=Peter Crimes|first1=T.|bibcode=1987GeoM..124...97P |s2cid=129916056 }}</ref>

== Palaeontology ==
The trilobite-like trace fossils ''Rusophycus'' and ''Cruziana'' occur in the Random Formation, alongside a range of other ichnofossils including  ''[[Biology:Diplocraterion|Diplocraterion]], [[Unsolved:Paleodictyon|Paleodictyon]],
Scolicia, and ''Squamodictyon''.<ref name="auto"/>
Body fossils include the [[Biology:Small shelly fauna|small shelly fauna]] ''Aldanella attleborensis'' assemblage.<ref>{{cite journal|doi=10.1139/e83-050|title=The oldest sequence of skeletal fossils in the Lower Cambrian of southeastern Newfoundland|journal=Canadian Journal of Earth Sciences|volume=20|issue=4|pages=525|year=1983|last1=Bengtson|first1=Stefan|last2=Fletcher|first2=Terence P.|bibcode=1983CaJES..20..525B}}</ref>

== References ==
{{reflist}}

{{coord missing|Newfoundland and Labrador}}

[[Category:Rock formations of Canada]]

{{Sourceattribution|Random Formation}}