oa Biostratigraphy of Dashtak and Khaneh Kat Formations in Zagros Basin

Dashtak Formation composed of dolomite, anhydrite and limestone whereas Khaneh Kat Formation<br>composed of dolomite, shale and limestone excluding evaporites, both Formations deposited in a<br>homocline carbonate ramp with a widespread depositional facies including supratidal, tidal flat, lagoon,<br>shoal and lower mid ramp. These formations were evaluated in a basin wide cross section including 8<br>subsurface (Aghar#1, West Aghar#1, Naura#1, Dashtak#1, Dalan#1, Kuh Siah#1, Sartal#1,<br>Huleylan#1) and 3 outcrop sections (Kuh-E- Surmeh, Kuh-E-Manghasht, Oshteran Kuh). Data gathered<br>from field observations, thin sections of borehole cutting, geophysical data (GR, Sonic and Neutron<br>logs) and geochemical analysis were performed (strontium isotope only sartal#1). This study revealed<br>that Dashtak Formation comprises 4 sequences (middle to late Triassic) and Khaneh Kat Formation<br>composed of 5 sequences (middle to late Triassic). So, almost lack of considerable biota content<br>caused changes arise here is a comprehensive biostratigraphy for these formations can not be carry<br>out. Unfortunately subsequence pervasive dolomitization obliterated those few rare biotas scattered<br>throughout limestone beds. In some cases the preserved biota represents a wide range (from base to<br>the top of the formation) and hence can not be used for biostratigraphic per poses. Although relative<br>high accommodation as they assist the recognition of MFS’s, as it is evident. Tr 40 restricted only to<br>Khaneh Kat Formation contains Agathammina sp., Valvanids, and Endothyramidae. Tr 50 has been<br>terminated in an ooid grainstone (shoal environment) rich in bioclasts including Pelecypod,<br>Agathammina sp., Trocholina Cross, Involutina sp., and Hemigordius sp. Tr 60 was determinate in<br>limestone beds contain Agathammina, Involutina, Ophthalmidium, Pragsoconulus, Frondiculina sp.,<br>ostracoda, echinoids, Faverina sp. Iriondic and Glomospira. This surface in Khaneh Kat Formation<br>located in a limestone bed containing sponge spicules, Pelecypod, echinoids, gastropoda, and algae. Tr<br>70 was introduced in Sefidar dolomite member but in this research, we consider this surface shifted<br>downward in a fossiliferous limestone bed and containing Agathammina, Trocholina, Lituosepta,<br>echinoids, Gastropoda, ostracoda, Aulotorus, Glomospira, and Irandia. In Khaneh Kat Formation this<br>MFS contains algae, gastropoda, Involutina, Aulotorus and echinoids.