Late Campanian–Maastrichtian sequence stratigraphy from Kurdistan foreland basin, NE/Iraq

Abstract

The Kurdistan foreland basin (NE Iraq) was formed as a result of the ophiolite-radiolarites obduction of the Iranian plate on the Arabian Plate. Extensive fieldwork for the determination of nine facies associations has been integrated with the planktonic and large foraminifera and other macrofossils biostratigraphic data in order to identify the sequence stratigraphic framework of the studied (late Campanian-Maastrichtian) successions comprising the Shiranish, Tanjero and Aqra formations. The studied successions are identified sensu Vial et al. (Payton CE (ed) Seismic stratigraphy application to hydrocarbon exploration memoir of the American association of the petroleum geologists, Tulsa, vol 26, pp 49-62, 1977) concepts, as three third-order depositional systems, within one major second-order depositional system, which is bounded by a sequence boundary of type one at its base and top. The Late Campanian-Early Maastrichtian third order is bounded by a middle Campanian gap as a sequence of boundary type one. The rapid drowning starts with planktonic foraminiferal-rich mudstone which indicates pre-flysch facies associations within starved foreland basin conditions and maximum flooding surface (MFS175). The sea level fell by the Early Maastrichtian, as characterized by a sequence boundary of type SBT2. The distal, medial and proximal turbidites flysch facies of the Tanjero formations manifest the second third-order depositional system. This may indicate a progressive shallowing upwards and characterized by MFS 180, which is placed at the top of the last planktonic-rich shale parasequences. The last third order is represented by rudist (Hippurites)-dominated carbonate parasequences (Late Maastrichtian-Aqra formation). The aggradational stacking pattern of the rudist lithosomes indicates the last MFS 190 during the Maastrichtian greenhouse. The sequence boundary is of type one which separates the Palaeocene molasses of Swais Group from the Maastrichtian sequence in the imbricated zone, while in the high folded zone it is replaced by Kolosh siliciclastic (Palaeocene) due to migrations of the Kurdistan foreland basin depocentre towards south-west. The reactivation of the deep-seated transversal faults is in addition to the sea level changes with south-westwards migration of the Zagros deformations front controlling the late Campanian-Maastrichtian supersequences framework.

Late Miocene Deformation Kinematics Along the NW Zagros Fold‐Thrust Belt, Kurdistan Region of Iraq: Constraints From Apatite (U‐Th)/He Thermochronometry and Balanced Cross Sections

“…In the study area, within the NW Zagros inner belt, the MFF appears to be composed of different segments with variable degrees of foreland propagation, as observed NW of the Erbil cross section, where deformation was less advanced, resembling fault segment linkage patterns via tip propagation (Figure 2b). This structural limit of the MFF also corresponds to the geographic distribution of the Tanjero Formation, which shows a rapid reduction in thickness from ~2,000 to 500 m across the hinterland, with the greater thicknesses SE of the study area (Ahmed et al, 2016; Bellen et al, 1959; Lawa, 2018). The similarity of spatial distribution of the proto‐Zagros foreland basin and the location of the curvilinear MFF feature might be controlled by structures associated with the early Mesozoic Arabian rift margin.…”

“…Tectonics rapid reduction in thickness from~2,000 to 500 m across the hinterland, with the greater thicknesses SE of the study area (Ahmed et al, 2016;Bellen et al, 1959;Lawa, 2018). The similarity of spatial distribution of the proto-Zagros foreland basin and the location of the curvilinear MFF feature might be controlled by structures associated with the early Mesozoic Arabian rift margin.…”

“…The length of the restored top Cretaceous is ~280 km for the Erbil cross section and ~232 km for the Sulaimani cross section. Thicknesses of Phanerozoic rock units in the NW Zagros were compiled from Bellen et al (1959), Janvier et al (1984), Cater and Tunbridge (1992), Najar (1999) in Al‐Hadidy (2007), Frehner et al (2012), Ghienne et al (2010), Ahmed et al (2016), Liu et al (2017), Lawa (2018), and Koshnaw et al (2019). Cross sections construction and kinematic forward models were performed using Move software (2D).…”

“…During the Maastrichtian, the intraoceanic convergent margin within the Neotethyan ocean reached the NE margin of the Arabian plate, leading to ophiolite obduction onto the Arabian continental margin, and initiation of the proto-Zagros foreland basin (Barber et al, 2018(Barber et al, , 2019Farahpour & Hessami, 2012;Homke et al, 2009;Lovelock, 1984;Saura et al, 2011). In response, a thick (locally >2 km) package of deep-marine clastic sediments (Tanjero Formation; equivalent to Amiran Formation in Iran) was deposited in a flexural basin, sourced from obducted ophiolites and older carbonate rocks to the NE (Ali & Mohmmad, 2018;Bellen et al, 1959;Çelik & Salih, 2018;Karim & Surdashy, 2005a;Koshnaw et al, 2017;Lawa, 2018). Flexural subsidence in proto-Zagros foreland basin continued into the Paleogene with deposition of the Kolosh and Gercus Formations and their equivalents in the Amiran basin of the Lurestan segment in Iran (Barber et al, 2018;Saura et al, 2011).…”

“…Within the Mesozoic passive‐margin succession, other relatively mechanically weak formations include the Lower Triassic Mirga Mir (marly limestone and shale, 200 m) and Beduh (shale and marl, 65 m) Formations, the Upper Triassic Kurra Chine (limestone and shale, 834 m) and Baluti (shale and marl, 65 m) Formations, and the Jurassic Sargelu (limestone and shale, 115 m) and Chia Gara (limestone and shale, 200 m) Formations (Bellen et al, 1959). The Upper Cretaceous Tanjero Formation of the proto‐Zagros basin varies from NE to SW, from a ~2,000 m thick succession of conglomerate, sandstone, and siltstone to a ~500 m section of shale, marl, and limestone (Abdel‐Kireem, 1986; Ahmed et al, 2016; Bellen et al, 1959; Karim & Surdashy, 2005b; Lawa, 2018), followed by the Paleogene Kolosh (shale, fine sandstone, 780 m) and Gercus (shale, marl, mudstone, 840 m) Formations (Bellen et al, 1959). Up section, the Neogene Zagros foreland basin contains the incompetent Fatha (Lower Fras) Formation (mixed clastic‐carbonate–evaporite, ~600 m) that is widely distributed in the NW Zagros (Aqrawi et al, 2010; Koshnaw et al, 2020; Shawkat & Tucker, 1978).…”