Sequence stratigraphic analyses of Naokelekan Formation (Late Jurassic), Barsarin area, Kurdistan region—Northeast Iraq

Abstract

A sequence stratigraphic analysis of Naokelekan Formation (Late Jurassic succession) in Barsarin area, Kurdistan region, NE Iraq was constructed based on surface lithologic and thin section analyses. The formation consists of thin- to medium-bedded, black, bituminous limestones, and dolomitic limestone, intercalated with thin, black, calcareous shale in lower and upper parts. The petrographic study shows that the limestones are dominated by mudstones. The skeletal grains include ammonites, thin planktonic gastropods, forams (planktonics and benthonics), pelecypods, and ostracods. Non-skeletal grains include peloids. Facies analysis demonstrated an array of facies associations, which suggest deposition in subtidal (lagoon) environment in the lower and upper parts of the formation, and shallow open marine in its middle part. One second-order sequence can be identified, which comprises Middle and Upper Jurassic rock units. This sequence consists of two third order sequences. Third-order sequence 1 is represented by whole succession of underlying Sargelu Formation and lower part of Naokelekan Formation. While third order sequence two corresponds to middle and upper part of Naokelekan Formation. Each of the third-order sequences is comprised of transgressive and highstand system tracts. These system tracts in turn, consist of vertically stacked parasequences of shallowing upward packages.