Quantifying vertical movements in fold and thrust belts: Subsidence, uplift and erosion in Kurdistan, northern Iraq

Traditional structural analysis in fold and thrust belts has focused on quantifying horizontal movements. In this paper, the importance of quantifying vertical movements is illustrated using a case study from Kurdistan, northern Iraq. The subsidence history of this area can be determined by analysis of the stratigraphic record from deep exploration wells. A phase of thermal subsidence from Middle Permian to Late Cretaceous (tectonic subsidence 1.8–1.9 km) was followed by flexural subsidence in the Late Cretaceous and Cenozoic (tectonic subsidence >0.6 km) in response to the closure of the Neo-Tethys Ocean. The main phase of continental collision during the Neogene resulted in the development of the Zagros fold and thrust belt; the amount of uplift at individual anticlines can be estimated from their amplitude (up to 3 km), but regional cross-sections indicate that approximately 1 km of additional basement-involved uplift is present NE of the Mountain Front. The timing of basement-involved uplift is interpreted to be coeval with the deposition of a Pliocene– Quaternary growth sequence adjacent to the Mountain Front. The amount of erosion resulting from the uplift can be estimated from vitrinite reflectance and cross-sections; these estimates show a similar pattern, with maximum erosion in the mountains NE of the Mountain Front (>1.5 km) and lesser erosion in the adjacent foreland basin (generally <0.8 km). The results provide a quantitative understanding of subsidence, uplift and erosion, and have been used to define prospective and high-risk areas for petroleum exploration.