Impure marble

Unit symbol: Onim
Age range Ordovician (485.4 to 443.4 Ma)
Lithology: Metamorphic
Group name: Layered sequence (Nome Complex)
“Buff- to orange-weathering, chlorite-, white mica-, and albite-bearing calcite marble that underlies rounded hills. The unit crops out poorly; rare outcrops show well foliated impure marble to calcareous schist. Impurities are most commonly chlorite and albite. Lenses (up to a meter across) and fine layers of chlorite and albite are diagnostic of the unit, and [they] trace [the] foliation and folds. Chlorite-albite lenses and layers are more abundant near the base of the unit; pods of fine-grained metabasite are also more common in the lower part of the unit. The pods can be recognized in the field as piles of massive medium-gray rubble several meters across; one is 0.5 km across. In rare instances the unit may include pure marble or orange-weathering dark-gray dolostone. The unit is a minimum of 1.2 km thick. Conodonts of Early through Middle Ordovician age have been obtained from a dolostone lens in the upper part of the unit in the Solomon D-6 quadrangle * * *” (Till and others, 2011)

Source map information

Source map Till, A.B., Dumoulin, J.A., Gamble, B.M., Kaufman, D.S., and Carroll, P.I., 1986, Preliminary geologic map and fossil data, Solomon, Bendeleben, and southern Kotzebue quadrangles, Seward Peninsula, Alaska: U.S. Geological Survey Open-File Report 86-276, scale 1:250,000.
Symbol Oim
Unit name Impure chlorite marble
Description Buff to orange weathering impure marble characterized by lenses and layers of chlorite-albite schist
Lithology Sedimentary

Correlated geologic units

Label Oim
Description Nome Complex, impure marble (Oim, BN002; BN004; KZ003; NM005; SO002; SO004; SO005; TE004; Pzim, BN002; SO002)
Geologic age Ordovician
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Marble < Metacarbonate < Metasedimentary < Metamorphic Major
Mica-schist < Schist < Metamorphic Minor