GEOLOGICAL EVOLUTION IN VIET NAM

Archeozoic Era In the history of the Earth, Archeozoic is the oldest with the age of 4500-2600 Ma, i.e. existing in a duration of 1900 mill. years. In Việt Nam Archean formations have been found only in the centre of the Kon Tum Geoblock, consisting of highly metamorphosed rocks exposed in the Kan Nack area with a thickness of about 3000 m, attributed by geologists to the Kan Nack Group.

Proterozoic Era Following the Archeozoic Era, the Proterozoic one began in 2600 mill. years ago and had a duration of 2030 mill. years (2600-570 mill. years before present). In Viet Nam Proterozoic formations occur usually in some places in the Red River, Phan Si Pan, Song Lo, Song Ma, Phu Hoat and Kon Tum zones, including: - Paleoproterozoic crystalline rocks attributed to the Song Hong Group (in East Bac Bo), Xuan Dai Group (in West Bac Bo) and Ngoc Linh Group (in the Kon Tum Geoblock). - Paleo-Mesoproterozoic metamorphic rocks attributed to the Kham Duc Group, exposed in the South of North Trung Bo. - Neoproterozoic metamorphic rocks usually exist in sections transiting into Lower Cambrian, containing microphytons, belonging to the Song Chay Formation (in North Bac Bo), Sa Pa and Nam Co Formations (in West Bac Bo), Bu Khang Formation (in North Trung Bo) and Chu Se Formation (in the Kon Tum Geoblock).

Cambrian fossils Paleozoic Era The Paleozoic Era began since 570 mill. years before present, extending in a duration of 325 mill. years (570-208 mill. years before present). It is divided into 6 periods : Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian. - Lower Cambrian formations usually have close relation to Neoproterozoic formations as presented above.   - Middle Cambrian - Lower Ordovician formations are largely distributed and differ from one another in different regions. In North Bac Bo, West Bac Bo and North Trung Bo they consist mainly of carbonate sediments interbedded with terrigenous ones of shallow-sea, littoral facies, containing fossils of trilobites and brachiopods. In North and East Bac Bo they are composed mainly of terrigenous sediments with, sometimes, lenses of limestone, containing trilobites. - Ordovician-Silurian formations in Viet Nam occur mainly in the north of the country. They have usually close relation in continuous sections.   Silurian sea   - Devonian formations are largely distributed in the North and West Bac Bo, more restricted in East Bac Bo, North Trung Bo and scarcely in Nam Bo. - Carboniferous and Permian formations are rather largely in Viet Nam and mainly distributed in Bac Bo, North Trung Bo, a part in the western and southwestern margins of the Kon Tum Geoblock and Southwest Nam Bo. They correspond to 3 sedimentary cycles: Devonian - Early Carboniferous, Early Carboniferous - Middle Permian and Late Permian.

Pteranodon with Archaeopteryx at the end of Jurassic

Mesozoic Era

The Mesozoic Era began since 245 mill. years before present and has a duration of 179 mill. years (245-60 mill. years before present), composed of 3 periods:

- Triassic with a duration of 37 mill. years (245-208 mill. years before present);

- Jurassic with a duration of 64 mill. years (208-144 mill. years before present); and

- Cretaceous with a duration of 78 mill. years (144-60 mill. years before present).

The history of development of the Earth’s crust during Mesozoic in Viet Nam passed through two great stages: pre-Norian Triassic and Norian-Jurassic-Cretaceous.

Before Norian, Triassic is characterized mainly by marine sediments interbedded with volcanogenic beds. At the end of the stage the transgressive regime in some regions was replaced by the continental regime.

The Norian-Jurassic-Cretaceous stage was characterized mainly by coal-bearing continental and red continental formations (in the North) and continental interbedded with marine formations during Jurassic (in the South).

Prehistoric men in South Africa

Cenozoic Era

The Cenozoic Era began since 66 mill. years before and extends to present days. It is composed of 3 periods:

- Paleogene with a duration of 42 mill. years (66-24 mill. years before present);

- Neogene with a duration of 22 mill. years (24-2 mill. years before present)

Pleistocene mammals

- Quaternary with a duration of 2 mill. years (2 mill. years ago to present).

In Viet Nam Cenozoic formations are very diversified.

Paleogene formations are a little exposed on the surface. Up to now, exposures of Paleogene sediments have been known in West Bac Bo (Pu Tra volcanogenic formation) and Extreme West Bắc Bộ (Nậm Bay red continental formation).

Neogene-Quaternary formations exist in coastal regions and on the continental shelf, including sediments of different origins, containing leaf impressions, spores and pollens, foraminiferas and interbeds of basalts.

Quaternary formations in Viet Nam occur in coastal plains, mountainous plains and on islands. In mountainous areas, Quaternary formations usually include sediments of fluvial, fluvio-proluvial facies and basalts of Pleistocene and Holocene ages. Besides, there are sediments of old outwash fans, cave sediments containing fossils of vertebrates and archeologic objects.