Geologic history

Evolution of earth’s crust and orogenic movements in Iran is not very clear. But in 1988 Termier has pointed out a great intercontinental rift occurred on the continent by name pangea. It was separated into two continents N Laurasia and S. Gondwana. 

The geologic data show Iran was on Gondwanaland until the late of Devonian (405,000,000). The Saudi Arabia and Iran platform were separated. Each one created independent basin sedimentation.

In the Paleozoic period, a series of vertical orogenic movements happened on Cambrian and caused sudden changes to be created in lithologic layers.

Eftekhar Nezhad an Iranian geologist and geomorphologist believes that on the paleozoic period, a series of erosions occurred in west Elborz mountain in Tabriz and zonouz region. Also, a lot of orogenic activities have been observed in the  mentioned areas since Precambrian. Hubert Rieben, a French geologist, his studies were done on Azerbaijan province of Iran. In 1935, he suggested that limestone sedimentation of Cambrian has lain unconfortably on Devonian depositions.

Rieben , a French geologist  also pointed out about Hersinian orogenic movements that have occurred in Iran. He believed that the collision of N. Gondwanaland with European continent resulted to this orogenic movements in Azerbaiyan and Zonouz region. The orogenic movements of late Cretaceous period caused the sediment basins gradually to rise from the sea. This condition was being continued for the Paleocene time. Finally zonouz region like other part of Iran emerged from the sea. The formation of Eocene indicates that area was covered by shallow sea. After passing a long period of time, the tectonic and orogenic movements began and created some faults.

Two main faults were recognized on the zonouz river bed. They have extended N.W to S.E and N.E to S.W direction. Also a minor fault extended east to west direction (see geologic map 1).

On the Quaternary, some alluvial terraces have lain on the upper- level surfaces in comparing to the base- level. These are the evidence of water erosion that occurred in the zonouz valley. Alluvial deposits in the upper part of river are coarse- grained size sediments whereas fine- grained deposits are accumulated in the lower part of river.

photo 3                                                                                    By Dr Asgharpour