Random Formation
Random Formation | |
---|---|
Stratigraphic range: | |
Bonavista Fm and others[4] | |
Overlies |
|
Thickness | From a few metres to 250 m[6] |
Lithology | |
Primary | Herringbone-crossstratified white arenites |
Other | Grey-green silts and shales |
Location | |
Region | Newfoundland |
Country | Canada |
Type section | |
Named for | Random Island |
Bedrock distribution of the Random Formation |
The Random Formation is a rock unit in
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
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
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
The Cambrian stage 2 - stage 3 boundary (
Palaeontology
The trilobite-like trace fossils
References
- ^ a b "BEDROCK GEOLOGY OF THE CAPE ST. MARY'S PENINSULA, SOUTHWEST AVALON PENINSULA, NEWFOUNDLAND" (PDF). Retrieved 8 June 2017.
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(help) - ^ a b "LATE NEOPROTEROZOIC (EDIACARAN) STRATIGRAPHY OF AVALON ZONE SEDIMENTARY ROCKS, BONAVISTA PENINSULA, NEWFOUNDLAND" (PDF). Retrieved 8 June 2017.
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(help) - ^ Normore (2012). "Current Research". Report 12-1.
{{cite journal}}
: Cite journal requires|journal=
(help) - ^ doi:10.1139/e84-143.
- ^ a b c d 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: 121โ145.
- doi:10.1139/e82-180.
- doi:10.1139/e82-180.
- ISBN 978-1-4899-2429-2.
- .
- ^ doi:10.1139/e74-027.
- doi:10.1139/e84-143.
- S2CID 131211543.
- ^ S2CID 129916056.
- doi:10.1139/e83-050.