Cretaceous Sequence Stratigraphy of Westrenzagros Outcrops from Kurdistan Region, N.Iraq

Abstract

The exposed Cretaceous sequence in Kurdistan region were studied from four outcrops sections (Qamchuqa, Dokan, Smaqwly and Safin),and correlated also with oil wells (Taq-Taq and Chamchaml).They were deposited in pre-foreland and foreland basin within a time framework extends from the Barremian to the late Maastrchtian including Qamchuqa, Dokan, Gulneri, Kometan, Shiranish and Tanjero Formations. In this work Cretaceous sequence subdivided into four 3rd order sequences, bounded by five sequence boundaries of type 1 or 2,and occasioanly type three ,they are; 1-Intra- Barremian (S.B.T.1),2- Upper Early to middle Cenomanian (S.B.T.2),3- Upper most late Cenomanian (S.B.T.2),4- Middle Campanian (S.B.T.2),and 5-late Maastrchtian(S.B.T.1).The nature and duartion of each sequnecs and their bounadries emphasized by large and/or planktonic foraminifera zonations. The first third order ( Intra-Barremian to lower early Cenomanian) represents by Qamchuqa Formation, which consists of aggradational to progradational rudist bearing carbonate ramp facies associations (600m thicK). This sequence was terminated either by drowning or by sub aerial erosion indicated by Cenomanian unconformity and coincides with the international Cenomanian-Turonian euxinic event (OAE2).The Late Cenomanian 2nd third order sequence consists of Oligosteginal carbonates are related to Dokan formation, terminated with submarine erosion .The next third order resembled by Gulneri Formation (Turonian to E. Campanian) present as condensed section of black shale. The fourth 3rd sequences ,represnt by Kometan formation of remarkable shallowing upwards succession from deep outer to middle and inner shelf and capped by hard ground surface within middle Companian unconformity surface. late Campanian to late Maastrchtian third order sequences of outer shelf , turbidities facies and reef build up(Aqra Fn.), occasionally intercalated with oceanic red bed (ORB), within the Zagros foreland basin acts as the best productive reservoir in the upper Cretaceous of Kurdistan region.