Iviagik group of Martin (1970)

Unit symbol: SOig
Age range Silurian, Llandovery, to Ordovician (470 to 427.4 Ma)
Lithology: Sedimentary
Group name: Iviagik group of Martin (1970)
Consists of two informal units: a lower, finer grained unit of slaty black argillite and siliceous shale that contains minor siltstone and chert; and an upper, coarser grained unit of lithic, sand-rich turbidite deposits (Moore and others, 2002). According to Moore and others (2002), the fine-grained unit is a thin- to medium-bedded basinal succession, more than 50 m thick, that contains sparse yellow-orange beds that may be bentonite. A diverse Early and Middle Ordovician graptolite fauna is present in the unit. The coarser unit consists of “channelized, thick-bedded, medium-grained sandstone, local pebbly sandstone, and minor siltstone” (Moore and others, 2002). It is at least 300 m thick and contains intercalated calcareous mudstone that yield early Silurian conodonts and graptolites

Source map information

Correlated geologic units

Label SOig
Description Iviagik Group, undivided
Geologic age Middle-Ordovician to Wenlock
Geologic setting Sedimentary, slope-and-deep-water
Lithology Form Importance
Shale < Mudstone < Clastic < Sedimentary Bed Major
Graywacke < Sandstone < Clastic < Sedimentary Bed Major
Chert < Chemical < Sedimentary Bed Minor
Siltstone < Clastic < Sedimentary Bed Minor
Felsic-volcanic < Volcanic < Igneous Pyroclastic, air fall Incidental