Landscape maturity, fold growth sequence and structural style in the Kirkuk Embayment of the Zagros, northern Iraq

• Published in: Tectonophysics 2017-10, Vol.717, p.27-40
• Main Authors: Obaid, Ahmed K., Allen, Mark B.
• Format: Article
• Language: English
• Subjects: Anticlines; Banks (topography); Cenozoic; Digital Elevation Models; Drainage patterns; Folds; Geomorphic indices; Geomorphology; Growth; Kirkuk Embayment; Landscape; Maturity; Miocene; Pliocene; Sedimentation; Sequencing; Slope; Stratigraphy; Studies; Surface Index; Surface roughness; Thrust; Topography; Topography (geology); Zagros deformation
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/j.tecto.2017.07.006

The Kirkuk Embayment is located in the southwest of the Zagros fold-and-thrust belt of Iraq. Like fold-and-thrust belts worldwide, the Zagros is conventionally understood to have grown sequentially towards the foreland. Here we use landscape maturity analysis to understand anticline growth in the embayment. Digital Elevation Model (DEM)-based geomorphic indices Hypsometric Integral (HI), Surface Roughness (SR) and their combination Surface Index (SI) have been applied to quantify landscape maturity. The results inform new ideas for the sequence of anticline growth. Maturity indices are highest for the QaraChauq Anticline in the center of the Embayment, then Makhool/Himreen to the south and lastly, the Kirkuk Anticline to the north. The pattern suggests the growth sequence is not classical ‘piggy back’ thrusting. This result fits the exhumation record, which is loosely constrained by the stratigraphic exposure level. Favored hypotheses for fold growth order are either i) the folds have grown at different times and out of sequence (QaraChauq first, then Makhool/Himreen, and Kirkuk last), or, ii) the growth occurred with different rates of exhumation but at broadly the same time. There are few constraints from available data on syn-tectonic sedimentation patterns. Fold growth across much of the Embayment might have begun within a limited timeframe in the late Miocene–Pliocene, during the deposition of the Mukdadiyah Formation. Another hypothesis is that folds grew in sequence towards the foreland with different rates of exhumation, but we consider this less likely. We also construct a new cross-section for the Embayment, which indicates limited Cenozoic strain: ~5% shortening. Analysis of topography and drainage patterns shows two previously-undescribed anticlines with hydrocarbon trap potential, between the Makhool and QaraChauq anticlines. •Landscape maturity of the Kirkuk Embayment obtained using Shuttle Radar Topography Mission datasets (SRTM).•Results show that the sequence of anticline growth in the Kirkuk Embayment is not classical ‘piggy back’ thrusting.•Surface index (SI) reveals newly-identified anticlines between the QaraChauq and Makhool anticlines.•Late Cenozoic strain in the Kirkuk Embayment is in the order of 5% (~5km), which is relatively small-scale shortening.