Abstract The Zagros Mountains lie within the Middle East as a part of the world girdle of Alpine mountain ranges. It is now well documented, although perhaps not yet fully assimilated by all those working in the oil industry elsewhere, that, even though incompletely explored, the Middle East contains two-thirds of the world’s proven reserves of oil and one-third of the world’s reserves of gas (Beydoun, 1991). Some 98% of these vast volumes are lodged in the fields lying in a broad belt (approximately 2500 by 500 to 700 km, or 1555 by 310 to 435 mi) running from northern Iraq to Oman, including southwestern Iran, eastern Saudi Arabia, and the Gulf States, in an area constituting the pre-Neogene northeastern continental shelf of the Arabian plate (Figure 1). This belt of prolific oil and gas fields (Figure 2; see Table 1 for field/discovery names) is bounded on the northeast by the high Zagros mountain range (the fields lie in the foothills of this range and across the Arabian plains areas), and on the south and west by the outcropping crystalline basement of the Arabian shield. The southeastern end lies at the Arabian Sea margin of Oman, now bounded by Indian Ocean crust, and the northwestern end is formed by the convergence of the High Zagros with the prominent north-south structural feature of the Ha’il-Ga’ara arch (Figure 1), west of which a more restless geologic history with important stratigraphic gaps has been much less favorable to hydrocarbon generation/retention. The Zagros mountain range

ABSTRACT We investigated the sequence stratigraphic architecture of Neogene deposits in the Zagros region using 12 measured stratigraphic sections and performing strontium isotope measurements on 10 samples. We combined our data with 44 previous published Sr isotope measurements and five paleomagnetostratigraphic sections in order to place the foreland deposits in a chronostratigraphic framework. Two chronostratigraphic charts were created, and transgressive-regressive system tracts were identified in the western and eastern sectors of the Zagros. These results show that the southward migration of the Zagros fold-and-thrust belt led to broadly upward-coarsening, progradational sequences due to progressive uplift and seaward (south-westward) migration of the Zagros fold-and-thrust belt. In addition, we show distinct differences in the sequences between the eastern and western sectors. It can be inferred that, in the strike-parallel direction, the Zagros foreland basin did not respond in a simple manner to tectonics and global sea-level changes during the Neogene. The different architecture of the sequences and mismatch of Neogene sedimentary architecture with global sea-level curves imply different orogen-parallel evolutionary histories and strong impact of tectonics on the basin evolution as compared to eustasy. Finally, we present evidence for a retrogradational sequence related to a period of enhanced deformation and related crustal thickening during the middle Miocene in the eastern Zagros.