Jones Ridge Limestone and related units

Unit symbol: OCjr
Age range Ordovician to Cambrian (541 to 443.4 Ma)
Lithology: Sedimentary
Group name: Jones Ridge Limestone and related units
Map unit includes three formally defined formations in the Charley River and Black River quadrangles of eastern Alaska: the Jones Ridge Limestone, the Hillard Limestone, and the Funnel Creek Limestone. The Jones Ridge Limestone is about 915 m thick and is divided into two members; lower 610 m of the lower member is mainly very light-gray, massive, extensively silicified and commonly oolitic, pisolitic, or laminated limestone and dolostone. Upper 285 m of lower member is pale-yellowish-brown, very fine-grained, thin- to thick-bedded limestone. Upper member, about 18 m thick, is pale-yellowish-brown, thick-bedded, bioclastic limestone (Dover, 1992; Van Kooten and others, 1996). Hillard Limestone is very fine- to medium-grained, thick-bedded, pale-yellowish-brown, laminated limestone interbedded with limestone conglomerate and oolitic and sandy limestone (Dover, 1992). Funnel Creek Limestone consists of light-gray, fine- to medium-grained, extensively silicified and commonly oolitic, cliff-forming, laminated limestone and dolostone approximately 1,300 ft (400 m) thick (Brabb and Churkin, 1969). Unit is not fossiliferous, but age is considered Early Cambrian on the basis of stratigraphic position. Also included in map unit is dark-gray, fine-grained, medium- to thick-bedded, partly silicified limestone in the Demarcation Point quadrangle (Reiser and others, 1980). It contains minor dolostone, conglomeratic sandstone, and fossiliferous orange-weathering shaly limestone that has interlaminated calcareous sandstone as well as minor tuffaceous limestone and black bedded, locally conglomeratic chert (Reiser and others, 1980). Late Cambrian brachiopods and trilobites are reported from the unit (Reiser and others, 1980). This unit is associated with an argillite unit in eastern Alaska that is herein correlated with the Adams Argillite (Ca). In northeast Alaska, the limestone is also associated with much more extensive volcanic rock unit (unit Cv). No similar volcanic rock unit is known from east-central Alaska

Source map information


Correlated geologic units

Label OCjr
Description Jones Ridge Limestone, massive oolitic, typically silicified limestone
Geologic age Cambrian to Ordovician
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Dolostone < Carbonate < Sedimentary Bed Major
Limestone < Carbonate < Sedimentary Bed Major