Togiak-Tikchik Complex, undivided

Unit symbol: KDt
Age range Mesozoic to Devonian (419.2 to 66 Ma)
Lithology: Metamorphic
Group name: Togiak-Tikchik Complex, undivided
Thick marine unit that consists of volcanic, sedimentary, and possibly plutonic rocks including pillow basalts, intermediate to mafic flows, breccia, crystal-lithic tuff, thin-bedded to massive tuffaceous chert and siltstone, argillite, graywacke, pebble-cobble conglomerate, and limestone. Formerly called the Gemuk Group (Hoare and Coonrad, 1959a, 1961a, b), this unit consists of a wide variety of rock types in a structural collage of blocks. As originally defined, the Gemuk Group consisted chiefly of dense, dark, massive siltstone that contained interbeds of chert, volcanic rocks, limestone, graywacke, and breccia (Cady and others, 1955). The assemblage was subsequently redefined as the Togiak-Tikchik Complex on the basis of its structural character (Wilson and Coonrad, 2005). Unit crops out in a wide belt through the Taylor Mountains, Bethel, and Goodnews Bay quadrangles from the Eek Mountains in the north, southwest to Goodnews Bay, making up most of the northwestern Ahklun Mountains. It is unconformably overlain by rocks of the Late Cretaceous Kuskokwim Group (Kk) and Early Cretaceous (Valanginian) calcareous graywacke and siltstone (Kcgc). Early Cretaceous rocks have been reported in the northern part of the Togiak-Tikchik Complex (Miller and others, 2007; unit K^vs here). Permian limestone (unit Ptls) that contains Atomodesma sp. is interbedded throughout the unit. Hoare and Coonrad (1978, see also samples 74B61, 70ACo6, or 70Ahr28 among others for example at, accessed July 30, 2015) collected samples that contain corals of Permian age and crinoids, bryozoans and Halobia of Triassic age. They also collected brachiopods (including several productoid forms, Cleiothyridinoid genus, and a spiriferoid), a pleurotomarian gastropod, and pelecypods of late Paleozoic (probably Permian) age. Hoare and Coonrad (1978) reported that the unit contains volcanic rocks of Triassic, Permian, and Devonian ages. D.C. Bradley (oral commun., 2011) reported a U/Pb zircon age that suggested the presence of a Pennsylvanian pluton in the Bethel quadrangle. Included here are mildly altered pillow and columnar-jointed amygdaloidal basalt flows, breccia, diabasic intrusive rocks, and a few sandy tuffs; these were previously mapped and described as unit Pb of Box (1985) and unit Pv of Hoare and Coonrad (1978). Unit crops out near Goodnews Bay and north of Nuyakuk Lake. In the Goodnews Bay area, unit is interbedded with volcaniclastic sedimentary rocks. Hoare and Coonrad (1978) did not separate these rocks from their undivided unit MzPz in the vicinity of Goodnews Bay. In the Nuyakuk Lake area, unit lies stratigraphically above and grades downward into Permian limestone (Mertie, 1938, p. 45–46). Near lowest part of section north of Nuyakuk Lake fossils identified in an interbed or fault sliver of limestone include brachiopods Calliprotonia sp., Neochonetes(?), Neophricadothyris sp., Neospirifer(?) sp., Thamnosia sp., Waagenoconcha(?) sp., and Yakovlevia sp. of Permian age; foraminifera Schwagerina jenkinsi Thorsteinnson of Permian age; stenoporoid bryozoans of Permian age; and echinoderm debris of Permian age (see sample 79AHr 2, Outcrops in the vicinity of Goodnews Bay were included in the Goodnews terrane by Box (1985), outcrops near Nuyakuk Lake lie within his Togiak terrane. Subdivided into the following 11 units: MzPzm, JPs, Pcs, Ptls, Crc, MDv, MzPzgs, MzPzp, MzPzsk, and MDm

Source map information

Source map Hoare, J.M., and Coonrad, W.L., 1978, Geologic map of the Goodnews and Hagemeister Island quadrangles region, southwestern Alaska: U.S. Geological Survey Open-File Report 78-9-B, 2 sheets, scale 1:250,000.
Symbol MzPz
Unit name Mesozoic and Paleozoic rocks, undivided
Description Thick, widespread, marine unit consisting of volcanic and sedimentary rocks ranging in age from Early (?) Ordovician to Early Cretaceous. Unit consists of thin-bedded to massive tuffaceous cherts and siltstones, argillite, graywacke, pebble-cobble conglomerate, and limestone. Pillow basalts and other volcanic rocks are commonly interbedded with tuffaceous cherts or other fine-grained volcanogenic rocks.
Lithology Sedimentary

Correlated geologic units

Label MzPzt
Description Togiak-Tikchik Complex, formerly Gemuk Group, chiefly siltstone and lesser chert and volcanic rocks
Geologic age Devonian to Cretaceous
Geologic setting Undivided
Lithology Form Importance
Mafic-volcanic < Volcanic < Igneous Flow Major
Siltstone < Clastic < Sedimentary Bed Major
Metavolcanic < Metaigneous < Metamorphic Zeolitic (prehnite-pumpellyite) Indeterminate, major
Metasiltstone < Metaclastic < Metasedimentary < Metamorphic Zeolitic (prehnite-pumpellyite) Indeterminate, major
Chert < Chemical < Sedimentary Bed Indeterminate, major
Conglomerate-sandstone < Mixed-clastic < Clastic < Sedimentary Bed Indeterminate, major
Limestone < Carbonate < Sedimentary Bed Minor
Graywacke < Sandstone < Clastic < Sedimentary Bed Minor