بحث عن Ordovician - بحث علمى عن Ordovician كامل بالتنسيق

بحث عن Ordovician - بحث علمى عن Ordovician كامل بالتنسيق




Ordovician was named so after the British tribe ordovice in whose territory the rocks of this period are most developed .
Ordovician rocks.
Ordovician rocks are all marine during the Ordovician period thick accumulation of shallow water sands and deep water black muds were deposited in a gradually sinking floor of some seas ,while carbonates were chemically or organically deposited in warm seas. Ordovician sediments constitute four geological facies.
,,,,ly facies 1-
Sandy and calcareous indicating shallow water deposits ,very fossiliferous containing trilopites ,brachiopods,corals,cystoids and gastropods.
Dolomitic facies. 2-
Being formed chemically or organically in warm and closer seas ,giving rise to thick lime stones and dolomites.


3- graptolitic (shaly) facies :thinner and finer sediments laid down far from the shore , containing common graptolites and abundant trilobites .
4- volcanic facies : chiefly lava flows, may be intrastratified with deposits of other facies ,often deposited upon the ocean floor.