BUNDEOKCHI PASS Section
A narrow mountain path
traditionally connected the small village of Machari with the city of Yeongwol
in southern Gangwon South Province, South Korea. The path was recently
expanded into a two-lane paved road. Road construction resulted in
several new outcrops, including one at Bundeokchi Pass. The Bundeokchi
Pass roadcut exposes highly deformed rocks of the Machari Formation. The
beds on the western side of the cut show strongly contorted folding. A
major thrust fault plane is exposed on the eastern side of the cut.
GPS of cut: 37° 13.660' North, 128°
27.839' East.
Above: looking NW at the western
side of Bundeokchi Pass roadcut, showing strongly folded rocks of the Machari
Formation.
Above: Looking SW at the western
side of Bundeokchi Pass roadcut, showing tilted beds of the Machari Formation.
Above: Fault plane surface of the
Machari Thrust Fault (here, a relatively high-angle thrust fault)
developed in rocks of the Machari Formation.
The Machari Formation of
South Korea is an upper Middle Cambrian to Upper Cambrian unit of dark
mudshales. The Bundeokchi Pass section exposes the middle Machari
Formation, which is fossiliferous. It produces trilobites from the Glyptagnostus
reticulatus Interval-zone (the basal Upper Cambrian biozone). Several
people found good Glyptagnostus reticulatus trilobites during this
visit.
Glyptagnostus reticulatus is a highly distinctive
agnostoid trilobite. Agnostoids were a group of blind, relatively small,
planktonic trilobites that had equal-sized heads & tails and only two body
segments. Their biostratigraphic range is from the Lower Cambrian to the
Upper Ordovician. The are critically important guide fossils in Middle to
Upper Cambrian rocks throughout the world.