Black chert

Unit symbol: Pzcu
Age range lower Paleozoic, Devonian or older (541 to 358.9 Ma)
Lithology: Sedimentary
Group name: Black chert
Predominantly black and gray chert, but also includes rare white, buff, red, or green bedded to massive chert. Occasionally vitreous, banded, or fractured. Interbedded or structurally interleaved with minor amounts of limestone, amygdaloidal basalt, and thin intervals of pitted calcareous graywacke. Occurs in the southwest corner of the Taylor Mountains quadrangle and northwest corner of Dillingham quadrangle (Wilson and others, 2006a, in press [SIM 2942]). This map unit is distinguished from the rainbow chert of this map (unit Crc) by the dominance of black and gray chert and, based on field notes of J.M. Hoare and W.H. Condon, the uncommon red and green chert, which is much more common in the rainbow chert unit. Hoare and Jones (1981) reported lower Paleozoic (Devonian? and pre-Devonian) and Paleozoic(?) radiolarians in the area shown for this unit as well as Permian megafossils. The limited geologic information provided in Hoare and Jones (1981) does not indicate the nature of the occurrence of the Permian fossils, and we suggest that these locations may be due to inclusion of fault-bounded blocks or slivers of the mélange (unit KMmu) or units KMt and Pcs that can't be resolved with the available map data. Based on lithology and crude age, the black chert may correlate with the Ordovician chert and phyllite of the Medfra quadrangle (unit Oc; Patton and others, 2009)

Source map information

Source map Hoare, J.M., and Condon, W.H., 1969-1970, Unpublished data.
Symbol ePzc
Unit name Black chert
Description Predominantly of black and gray chert but also includes rare white, buff, red, or green bedded to massive chert. It is occasionally vitreous, banded or fractured, and is interbedded with minor amounts of limestone, amygdaloidal basalt, and thin pitted calcareous greywacke. We believe that, in part, the mixture of ages is due to inclusion of some of this unit in the melange
Lithology Metamorphic

Correlated geologic units

Label Pzec
Description Lower Paleozoic black chert. Derived from 1969-1970 Condon and Hoare field notes
Geologic age Paleozoic to Devonian
Geologic setting Sedimentary, slope-and-deep-water
Lithology Form Importance
Chert < Chemical < Sedimentary Bed Major