Calcareous graywacke and mudstone, volcanic graywacke and conglomerate

Unit symbol: Kcvg
Age range lower Upper or upper Lower Cretaceous (113 to 93.9 Ma)
Lithology: Sedimentary
Group name: Calcareous graywacke and mudstone, volcanic graywacke and conglomerate
Cyclically interbedded fine- to coarse-grained, highly calcareous graywacke; hard, fine- to medium-grained, carbonaceous, volcanic graywacke; and dark carbonaceous mudstone in west-central Alaska (Patton and others, 2009). Also includes turbidite deposits of fine-grained to gritty graywacke and laminated micaceous mudstone, which are composed largely of carbonate detritus and lesser quartz, chert, volcanic rock, and mica clasts. Graywacke is typically graded and sole-marked. Contains abundant carbonized plant debris. Mudstone intervals typically display fine, convolute, cross laminations and current ripple marks. Unit grades from a high graywacke-to-mudstone ratio in the southwest of its exposure area to a low graywacke-to-mudstone ratio in the northeast part of its exposure area (Patton and others, 2009). Patton and others (2009) interpreted unit to represent middle and outer submarine fan lobe deposits; some locally thick sections of mudstone probably represent basin plain deposits. Paleocurrents generally indicate transport to northeast. Poorly preserved marine mollusks of late Early Cretaceous(?) age present in unit in Selawik quadrangle. A single collection of palynomorphs from Norton Bay quadrangle is Cretaceous in age, possibly late Early or early Late Cretaceous (Albian or Cenomanian). Abundance of detrital carbonate, quartz, and mica fragments suggest that the unit was derived largely from carbonate and schist units of the Seward terrane of Patton and others (2009) (units Pzcn and PzPxnc here)

Source map information

Source map Patton, W.W., Jr., Wilson, F.H., Labay, K.A., and Shew, Nora, 2009, Geologic map of the Yukon-Koyukuk basin, Alaska: U.S. Geological Survey Scientific Investigations Map SIM-2909, 26 p., 2 sheets, scale 1:500,000.
Symbol Kcvg
Unit name Carbonate and volcanic clast graywacke and mudstone
Description Cyclically interbedded fine- to coarse-grained highly calcareous graywacke; hard, fine- to medium-grained, carbonaceous, volcanic graywacke; and dark carbonaceous mudstone. Graywacke is typically graded and sole-marked. Carbonized plant debris is abundant. Graywacke/mudstone ratios are generally high. The unit is interpreted to represent middle and outer submarine fan lobe deposits; some locally thick sections of mudstone probably represent basin plain deposits. Paleocurrents are generally to the northeast. Unit appears to be transitional between the carbonate-rich deposits of map unit Kcg and the volcanic-rich deposits of map unit Kvg.
Lithology Sedimentary

Correlated geologic units

Label Kcvg
Description Calcareous graywacke and mudstone, volcanic graywacke, and volcanic conglomerate
Geologic age Albian to Cenomanian
Geologic setting Sedimentary, shallow-marine-siliciclastic
Lithology Form Importance
Mudstone < Clastic < Sedimentary Carbonaceous Indeterminate, major
Graywacke < Sandstone < Clastic < Sedimentary Calcareous Indeterminate, major
Graywacke < Sandstone < Clastic < Sedimentary Carbonaceous Indeterminate, major