Chapter IIT

GENERAL GEOLOGY

The rocks in the Nechako River map-area range in age from late Palzozoic
to Recent. The most widespread sedimentary and volcanic formations are of Upper
Triassic and Lower Jurassic, Middle Jurassic, and Tertiary age; the principal
intrusive rocks are those of the Lower Jurassic Topley Intrusions and intrusions
of post-Middle Jurassic age.

Table of Formations

Era Period or epoch Formation Lithology
Recent Stream and lake deposits, talus, soil
Pleistocene Glacial and glacio-fluvial deposits
Cenozoic Erosion interval
Miocene and (?) later Endako Group Basalt, andesite; related tuff and breccia;
ibe minor shale and greywacke
ES = NY)
Angular unconformity
Mesozoic Upper Cretaceous to Ootsa Lake Group Rhyolitic and dacitic tuff and breccia;
and Lower Miocene shale, sandstone, conglomerate
Cenozoic ¥
o- ty 5 :
@ Rhyolite, dacite, trachyte, andesite;
minor basalt; related tuff and breccia
Basalt, andesite; minor rhyolite, sand-
stone, and conglomerate
Erosion interval
Post-Middle Jurassic- Biotite granite, granodiorite, quartz
pre-Upper Cretaceous diorite, diorite; minor gabbro
loo -tgo
Mesozoic Not in contact

16

Upper Jurassic (Callovian)

+o

Argillite, argillaceous limestone