Green glauconitic marl bed as a sequence stratigraphical key for interpretation of contact between Qamchuqa and Bekhme formations in Bekhal area, Kurdistan region, NE Iraq

This study incorporates a study of stratigraphy and sedimentology of the green glauconitic marl bed between Qamchuqa and Bekhme Formations in selected section of the Iraqi Kurdistan region. The studied area is located in Gali Garukaju near Rwanduz in Erbil Governorate, northeastern Iraq. Instead of Basal Conglomerate bed, the thin beds of green glauconitic marl occurs along the contact between Qamchuqa and Bekhme Formations in the studied section. Six samples were collected from this section, two samples for XRD and four samples for petrography analysis. Samples for XRD and petrographic analysis were taken from green glauconitic marl beds at the contact between two formations and from upper contact of Qamchuqa Formation and lower contact of Bekhme Formation. XRD analysis data proved the presence of glauconite in green marl bed. General petrographic observations of other remaining four samples in thin sections reveal that the upper contact of Qamchuqa Formation and lower contact of Bekhme Formation are dolomite and dolomitic limestone. The dolomite bed represents type 1 or type 2 depending on the thickness and extension of dolomite bed. Color, morphology, maturity and abundance of glauconite grain were the dominant factors used in the determination of the surface between the two formations. The result emphasizes that the surface was not a gradational surface consisting of low stand and condensed system tract (LST/CS). Two factors, color and morphology, of glauconite grains were analyzed by binocular microscope under reflected light. The morphology of most glauconite grains in this section is ovoidal and tabular with green to dark green in color. Based on these two factors the glauconite grains were within stages 3 and 4 of McCracken et al. (1996) classification and can be interpreted as evolved and high evolved in view of maturity. The presence, increase in concentration and mature grains of glauconite (evolved and high evolved) in marl beds at lower part of Bekhme Formation indicate transgressive or maximum flooding surfaces