الملخص

Oligocene deposits in Butmah and Rafan areas northwestern Iraq were penetrated by three core holes (BW-CH1, BE-CH1 and RF-CH1). The depositional basin evolved through two stages, generating two sedimentary cycles, which were separated by exposure surface as represented by conglomerate beds in core holes BW-CH1 and RF-CH1. Six microfacies were recognized in the Oligocene formations (Shurau Fn., Sheikh Alas Fn. and Bajwan Fn.), comprising three microfacies association allocated to: reef (Sa1) and back reef (Sh1, Sh2) in the first cycle (Early Oligocene), and back reef (B1, B2, B3) in the second cycle (Late Oligocene). Oligocene rocks have been affected by many diagenetic processes of cementation, dissolution, dolomitization (by mixing process) and dedolomitization. The paleogeographic distribution of the microfacies in conjunction to the previous work elucidates that the studied area is representing the eastern margin of the Sinjar Oligocene basin.