New Data on Sequence Stratigraphy of Dashtak and Khaneh Kat Formation and Re-evaluation as Effective Cap Rock in Zagros Basin

Dashtak Formation composed of dolomite, anhydrite and limestone acts as an effective seal whereas Khaneh Kat Formation composed of dolomite, shale and limestone excluding evaporites has no cap rock characteristics. Both Formations deposited in a homocline carbonate ramp with depositional facies including supratidal, tidal flat, lagoon, shoal and mid ramp. However a relatively more deep setting wherein no more evaporites were deposited for Khaneh Kat Formation.These formations were evaluated in 8 subsurface and 3 outcrops. Data gathered from field observation, thin sections, geophysical data (GR, Sonic and Neutron logs) and strontium isotope. Dashtak Formation comprises 4 sequences and Khaneh Kat Formation has 5 sequences. Southeast ward part of uppermost sequence of Dashtak Formation has been removed due to post depositional erosion. Lowermost sequence extends in whole of basin with carbonate facies,is equivalent of Kangan Formation. Sequences 2 to 5 of Khaneh Kat Formation are equivalents of Dashtak Formation. These sequences show a distinct lateral facies changes from Sartal#1 borehole toward Kuh-E-Manghasht and OshtoranKuh from evaporite dominated facies to carbonates. An increase in thickness of Dashtak Formation has been revealed toward boreholes Dalan#1, Kuh Siah#1, Dashtak#1; however high anomalously thickness in Sartal#1.