Tectonostratigraphic and structural imprints from balanced sections across the north-western Zagros fold-thrust belt, Kurdistan region, NE Iraq

Abstract

Listen

Translate article

The giant oil and gas fields discovered in the north-western segment of the Zagros fold-thrust belt in the Kurdistan region (NE Iraq) became targets for oil companies and academics around the world. This work deals with tectonostratigraphic and cross-sectional balancing across several structural domains and a stratigraphic framework that measures and analyzes supersequences from the Early Jurassic to the Late Pliocene in age. The structural complexity passes through different tectonic zones, starting from an imbricated zone, then a high folded thrust zone and terminating at the boundary with a low folded thrust zone. Accordingly, three major cross sections have been constructed based on a new ratified geological map and a stratigraphic column of exposed sequences, oil wells data which are integrated with the few available valuable seismic profiles. The total shortening measured in the tertiary rocks ranges between 4.55 and 6 % and 15.3 and 20.7 % in the Cretaceous sequence, while in the Jurassic interval, it is between around 12.9 and 20.8 %. The measured partial shortening percentages of the Bazian–Sagrma–Qaradagh, Pira Magroon, Surdash and Azmar anticlines range from 9.8 to 12.5 %, 47.3 to 73.2 %, 29 to 41.3 % and 20.9 to 60.5 %, respectively. The Kometan Formation (M. Turonian to Santonian) in the B–B cross section can be adopted as the best measure for shortening in this area, and this is equal to 20.7 %. The partial shortening percentages obtained from the Bazian–Sagrma–Qaradagh anticlines range from 9.8 to 12.5 %; these increase in the Pira Magroon anticline, from 47.3.8 to 73.2 %, and for the Surdash anticline, they are from 29 to 41.3 % and the Azmar anticlinorium from 20.9 to 60.5 %. The total shortening values are, in general, low and attributed to the influence of thick-skinned tectonics during extensional tectonic phases that changed to thin-skinned tectonics during Oligocene and Miocene times, as well as being due to variations in their decollement nature, while the partial shortening values of the cross sections studied mostly coincide with those in the Iranian Zagros segment.