Woodchopper Volcanics, and Schwatka unit of Weber and others (1992)

Unit symbol: Dvec
Age range Devonian (419.2 to 358.9 Ma)
Lithology: Igneous - Volcanic
Group name: Woodchopper Volcanics and Schwatka unit of Weber and others (1992)
Woodchopper Volcanics are described as amygdaloidal basalt, pillow basalt, and aquagene tuff, subordinate interbedded chert, argillite, quartzite, and limestone of Late(?) to Early Devonian age in the Charley River quadrangle (Brabb and Churkin, 1969). Brabb and Churkin (1969) also mapped several hundred feet of dark-gray laminated shale that contains minor interbeds of limestone associated with the Woodchopper Volcanics, which we have included here; Dover and Miyaoka (1988) included these sedimentary rocks in their redefined Nation River Formation, which we do not believe is an appropriate assignment, as the Nation River Formation is a plant- and coal-bearing clastic unit. Schwatka unit of Weber and others (1992) is included here; it is mapped in Livengood and Circle quadrangles, offset from the Woodchopper Volcanics by the Tintina Fault System. The Schwatka consists of massive basalt flows, agglomerate, tuff, fine-grained volcaniclastic rocks, minor thin lenses of laminated platy impure limestone, and local lenticular bodies of calcite-cemented conglomerate interbedded with Devonian limestone (Weber and others, 1992). The Schwatka unit is metamorphosed to greenschist facies

Source map information

Correlated geologic units

Label Dwv
Description Woodchopper Volcanics, amygdaloidal basalt, pillow basalt, ..., equivalent to Schwatka unit?
Geologic age Early-Devonian to Late-Devonian
Geologic setting Extrusive
Lithology Form Importance
Basalt < Mafic-volcanic < Volcanic < Igneous Flow, pillows Major
Basalt < Mafic-volcanic < Volcanic < Igneous Pyroclastic, tuff Minor
Argillite < Metaclastic < Metasedimentary < Metamorphic Incidental
Limestone < Carbonate < Sedimentary Bed Incidental
Chert < Chemical < Sedimentary Bed Incidental
Shale < Mudstone < Clastic < Sedimentary Bed Incidental
Sandstone < Clastic < Sedimentary Bed Incidental