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

摘要

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.