Hydrocarbon inclusions in the Ordovician in the Tazhong-Ⅰ slope-break zone can be divided into four episodes of development according to their fluorescence characteristics

intercalating relationship with calcite vein

and homogeneous temperature

and so on.Based on the tectonic evolution of the area

it is believed these episodes correspond to four episodes of hydrocarbon pooling:low maturity oil accumulation at the end of Silu-rian

oil generation in the late Hercynian

condensate oil and wet gas accumulation in the early Himalaya

and dry gas accumulation in the late Himalayan.The distribution of these four episodes of inclusions presents clear zonation in the Ordovician reservoirs in the Tazhong-Ⅰbelt.Four zones are recognized from the shallow oil reservoir in the southeast to the deep oil reservoirs in the northwest.It is suggested that the fossil oil from the episode Ⅲ and Ⅳ played a dominant role in the formation of present hydrocarbon accumulations.