ALPINE GEOWARPINGS IN THE ZAGROS-TAURUS RANGE - INFLUENCE ON HYDROCARBON GENERATION, MIGRATION AND ACCUMULATION

Megascale monoclinal flexures ("geowarpings") with maximum angles of dip ranging from 5-degrees to 13-degrees occur in the Zagros-Taurus range of Iraq and Iran. They face south and SW, with amplitudes of 1.4 to 14.44 kms and axial lengths of 43 to 230 kms. Their axes are parallel to the host mountain range and lie in an en echelon configuration, and many are located in the high mountain zone, at or close to the mountain front (i.e. the border with the foothills zone). Neotectonic and stratigraphic evidence suggests the contemporaneous development of these flexures with their host fold-belt during the collision of the Eurasian and Afro-Arabian Plates, which culminated during Upper Miocene-Pliocene time. Differential vertical movements caused greater shortening and thickening in the upwarded regions (10-33%), which lie closer to the plate suture zones, compared to the downwarped regions (3-17%). Development of the geowarpings resulted in circumstances favourable for hydrocarbon generation in downwarped regions, where source rocks were buried sufficiently deeply to produce oil and gas; this then migrated upwards to be trapped in the growing folds, and was sealed by Miocene evaporites. On the other hand, upwarped regions were elevated, and suffered extensive erosion, leading to a reduction in the depth of burial of potential source rocks, and consequently limited possibilities of hydrocarbon generation. Furthermore, the non-deposition and/or erosion of Miocene evaporites in upwarped regions led to the dissipation of considerable volumes of the hydrocarbons which might have been generated. The effect of geowarpings on oil and gas reserves is evident from the distribution of oil- and gasfields, which are almost exclusively located in the downwrapped foothills zone. Geowarpings may be located in the Taurus Range of E Turkey and NE Syria, but a lack of accurate data makes this difficult to investigate. Further studies are needed to develop an efficient exploration plan for oil and gas in that area.