Random Formation

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]

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]

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]

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]

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]