Marble of the Gambier Bay Formation

Unit symbol: Dgbm
Age range Devonian (419.2 to 358.9 Ma)
Lithology: Metamorphic
Group name: Gambier Bay Formation, undivided
Dark-gray to white, thin- to thick-bedded, fine- to medium-grained marble that is locally dolomitic, intercalated with greenstone and greenschist of the Gambier Bay Formation (S.M. Karl, unpub. data). On Admiralty Island, Lathram and others (1965) reported Middle Devonian(?) corals from the Gambier Bay Formation, but suggested that rocks older than Devonian may be included in the unit. On Kupreanof Island a possibly equivalent unit of schist and marble contains Silurian or Devonian crinoid, conodont, stromatoporoid, and rugose coral fossils, but age-diagnostic fossils suggested an age of Emsian (late Early Devonian) to Famennian (Late Devonian) (Karl and others, 1999). A Triassic age was inferred for this unit by Kelley (1990b), but the fossil of that age was most likely from the Triassic Hyd Group (unit ^hg). A probable correlation is with the limestone of map unit Dlse, which consists of the Wadleigh, Black Cap, and similar limestone units

Source map information

Source map Karl, S.M., Haeussler, P.J., Himmelberg, G.R., and Brew, D.A., 1998, Unpublished data.
Symbol Dgm
Unit name Gambier Bay Formation Marble
Description Dark gray to white, medium to thick bedded marble. Calcite grains in marble contain deformed lamellae with sutured grain boundaries reflecting high pressure deformation. Minor interstitial quartz, albite, and tremolite grains. Contains poorly preserved amphipora and corals. Marble forms lenses up to a few hundred meters thick.
Lithology Metamorphic

Correlated geologic units

Label Dmg
Description Gambier Bay Formation Marble
Geologic age Devonian
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Marble < Metacarbonate < Metasedimentary < Metamorphic Major