Abstract: The carbonate source rocks of Middle-Upper Ordovician in Tarim basin are widely distributed in different sedimentary environments at the same period such as platform margin slope, platform inner sag, continental shelf, abyssal basin, etc. According to the differences of sedimentary facies and environment, the source rock are divided into four types such as lime-mud reef in platform margin, platform inner sag, deep-water flat slope or continental shelf, abyssal basin. The lime-mud reef type is distributed in platform margin of Upper Ordovician, the remained three types are widely distributed in Cambrian-Ordovician system. The carbonate platform margin and platform inner sag margin could be recognized from analysis of sedimentary environment of the Middle-Upper Ordovician source rocks for the purpose of determination of the sedimentary environments of source rocks of platform slope, platform inner sag and continental shelf. In addition, by means of seismic profiles, the platform margin and the platform inner sag margin can be finally identified, integrated with distribution of organic reefs. It is shown that the distribution of organic reefs is of great significance in indicating the distribution of source rocks.

Key words: Tarim basin, Middle Ordovician, Upper Ordovician, source rock, sedimentary environment, organic reef