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Abstract:
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A lot of unconformities and stratigraphic gaps have been discovered in the Paleozoic and
Mesozoic stratigraphy of Bac Bo region (North Viet Nam), but their role in the regional geology
was not accessed yet in detail. This paper is the first attempt to describe the most significant
unconformities and stratigraphic gaps and discussing their role in regional geology. The most
important is the angular unconformity of Norian‐Rhaetian formations upon various formations of
different formations; it marked the change tectonic regime of the region resulting from the indosian
orogeny in Viet Nam and in Southeast Asia in common. The gap of Lower Devonian red beds
formations (Si Ka Formation, Song Cau Group) upon Lower Paleozoic formations (Upper Cambrian ‐
Than Sa Formation, Lower Ordovician ‐ Lutxia and Na Mo formations) is a regional unconformity,
which had been taken place in the epicaledonian terranne of South China and North East of Viet
Nam. The gap between the Da Mai Formation and the Dong Dang Formation was a result of a crust
rising, but was not through the orogeny activity, although after this gap the structural plan was
more differentiated. Other unconformities and stratigraphic gaps seems to be local unconformities,
for instance, the one of the Tan Lap Formation (D2g‐D3 fr tl) upon the Ban Pap Formation (D1p‐D3 fr bp)
and the unconformity between the Sinh Vinh (O3‐S sv) and the Ben Khe (ε‐O1 bk) formations. |