Contribution to the stratigraphy of the Walash Group, Sulaimani area, Kurdistan, Iraq

Abstract

The Walash Group represents sequences of siliciclastic sediments with alkaline volcanics at the upper part. It forms the lowermost thrust sheet of the Zagros Suture Zone. Three localities around Sulaimani area of Kurdistan region of north Iraq were chosen for sedimentological and stratigraphic review of this group. Examination includes field measurements, description, and correlation, and petrographic and biostratigraphical analyses. The Walash Group sequence in the study area has variable thickness, with the highest reaching 150 m, and generally consists of greenish gray silty calcareous shale which alternates with thin- to thick-bedded, coarse-grained sandstone and limestone. Sandstone beds show sedimentological evidences of turbidite origin. Based on occurrences of volcanic admixtures, the group is subdivided into two basic lithostratigraphic units: lower sedimentary unit and upper sedimentary–volcanic unit. Petrographic analysis shows that the sandstones include two basic types: lithicarenites which is dominated by carbonate, quartz, chert, and volcanic rock fragments, and calcarenite with bioclasts and benthic forams as the main type of grains. Biostratigraphic analysis of the shale interlayer samples near Kinjurine Village reveals the occurrence of both benthonic and planktonic foraminifera. Stratigraphic ranges of the identified planktonic foraminifera show occurrence within the Paleogene biozones P5–P9 which indicate Ypresian age (Lower Early Eocene). Similar age inferences were reached from benthic foraminiferal assemblages. Based on correlation with other areas, the study calls attention to a review of the stratigraphic status of the group by renaming the upper part and introducing new name for the lower part.