DEOKPORI THRUST FAULT
A spectacular thrust fault
is exposed along a relatively new highway roadcut (still an unopened road as of
September 2004) on the eastern side of the city of Yeongwol (southern Gangwon
South Province) in northeastern South Korea.
This new cut is just off Rt.
31/Rt. 38 in Yeongwol, along the southeastern side of the Dong River (Tong
River). GPS of cut: 37° 11.157’ North, 128° 29.409’ East.
The Deokpori Thrust Fault
(also known as the Gakdong Thrust Fault) is beautifully exposed here.
Much of Korea is significantly structurally deformed, making geologic
interpretations somewhat difficult to make at times. The geology at this
cut, however, is unambiguously black & white. North-south striking
thrust faults are common in the Yeongwol area of South Korea. The fault
planes are westward-dipping, so the thrust sheets were moving eastward.
Facing ~S. East is to the left & west is to the right.
Facing ~S.
The prominent diagonal feature in the pics (from upper
left to lower right) is the fault. Below the fault is blackish shales of
nonmarine (alluvial-fluvial-lacustrine) origin - the Daedong Supergroup
(Upper Triassic-Jurassic). Immediately above the fault is whitish
Cambrian limestones (with grayish & brownish Cambro-Ordovician limestones
above that). The limestones are part of the Yeongwol Group.
So, we’ve got
Cambro-Ordovician limestones above Triassic-Jurassic black shales -
older rocks above younger rocks, an apparent violation of the Principle
of Superposition. But superposition as a principle is valid only in
undisturbed successions (faulted rocks do not an undisturbed succession make).
Facing ~S.
Faulting in the Yeongwol
area took place during the Late Jurassic’s Daebo Orogeny (the same orogeny that
produced the widespread Daebo Granite intrusive complex). This
part of Korea has been subjected to two additional tectonic events - the
Songnim Orogeny (mid-Triassic), and the Bulguksa Orogeny (Cretaceous to early
Paleogene).
Info. mostly provided by
William Fitches.