Sabah A. Ismail

Geochemistry of Paleogene Red Beds in the northern Iraq foreland basin: evidence for provenance

The Paleogene Red Bed deposits in northern Iraq crop out as a narrow northwest-southeast trending belt within the thrust zone in an active foreland basin developed adjacent to the Zagraos orogenic belt. The Red Beds are divided vertically into four units. The lower part (unit 1) is mainly composed of red mudstone and siltstone. The middle part (unit 2) is mainly composed of sandstone with thin interbeds of red siltstone. The upper part is composed of conglomerate (unit 3) covered by 100-120 m of red mudstone, siltstone and sandstone (unit 4). The geochemical stratigraphy shows an increase in transition elements and REEs while LILE and HFSE elements decrease in the lower part of the sequence. These features indicate that a mafic source supplied detritus during the deposition of the lower Red Beds and decreased in importance during the deposition of the middle and upper parts as a result of erosion or tectonic activity.

Tectono-stratigraphy and structure of the northwestern Zagros collision zone across the Iraq-Iran border

Tectono-stratigraphic units within the Zagros Oroge n in northeast Iraq (foreland) and northwest Iran ( hinterland) are correlated to provide an integrated map along t he collision zone. Access to this part of Iraq duri ng the past four decades has been limited due to geopolitical s ituation. Structural cross-sections across the Zagr os Suture Zone in this area reveal the relationships between the tectonic terranes of various ages and different origins. Terranes of oceanic affinity have accreted onto the Arabian plate during collision-accretion events th at started in the Late Cretaceous. The collision resulted in clos ure of the Neotethys Ocean and the construction of a structurally complex suture zone. Jurassic-Cretaceo us deep ocean radiolarites of the Qulqula-Kermansha h terrane and ophiolitic melange serpentinites were s tructurally accreted against the Arabian passive ma rgin during an ophiolite arc-continent collision event in the L ate Cretaceous. The overthrust radiolarites and oph iolitic melange terranes initiated the development of the f oreland basin overlapping flysch (turbidites) and m olasse assemblages on the now active Arabian margin. Eocene-Oligocene volcano-sedimentary rocks of the WalashNaopurdan-Kamyaran terrane developed as an intra-oceanic island-arc within the intervening Neotethys O cean. They now structurally overlie the older ophiolite m elange and radiolarite terranes as a result of cont inued convergence onto the margin of the Arabian Plate. T hese younger thrust sheets and nappes have been tra nsported over the Miocene molasse unit of the Tertiary Red B eds in the flexural foreland basin and covered the Late Cretaceous accretionary complex terranes and forela nd basin assemblages. The Qulqula-Kermanshah terrane is exposed in a tectonic window in the northeastern pa rt of the mapped area indicating that the Late Cret aceous accreted terranes occur below the Walash-Naopurdan-Kamyaran thrust sheet. A Late Cretaceous ophiolitebearing terrane named the “Upper Allochthon” (i.e. Gemo-Qandil nappe, 97-118 Ma) was emplaced by younger thrust sheets over the Eocene-Oligocene Walash-Naopurdan-Kamyaran terrane by out-of-sequence thrusting. Mesozoic metamorphic rocks from the hinterland, including volcanic and intrusive rocks of the active I ranian continental margin (Sanandaj-Sirjan zone), were emplaced during continent-continent collision and occu r in the youngest nappes and klippes along the Zagros Suture Zone.