Lithology and stratigraphy of the Cenomanian Turonian boundary in Zagros orogenic belt examples from Kurdistan Region, Northeastern Iraq

Abstract EN

Cenomanian-Turonian (C/T boundary) is globally foci of intense geological study in the most part of the world due its organic matter content.

In Iraq, the representative of the boundary is defined previously as bituminous black shale and named “Gulneri Formation” which is about 2.5 meters thick.

In the country, the boundary is controversial both stratigraphically and lithologically; since it is assumed that its top and base are bounded by unconformity and deposited in euxinic and small relic basin.

In the present study, the previous studies are critically evaluated and many new results and new fact are documented about the formation through studying of nine sections.

The new results include changing of the lithology and boundary condition (rejecting of underlying and overlying previously indicated unconformities).

The lithology has amended to marl and marly limestone and the depositional basin is changed to large open basin in which Balambo and Kometan formations are deposited.

Additionally, many fish remains are found in the formation.

The remains are three types; the first is fish scales, which have circular shape with concentric rings and about 1 to 4 mm in diameters.

The second is fish backbones (skeletons), four skeletons are found, which belong to small fish about 4 to10 cm long and 5mm to2 cm wide.

The third is fish fins (pectoral fin), which are well preserved in hand specimens and have grey or brown color and consist of groves and ribs.

The fish remains are evidence that a depositional environment of the Gulneri Formation was deep, large and open sea.

Only the bottom of the sea was anoxic, which had preserved the organism remains that had fallen down from the surface of water and rested on the sea bottom.