Basin architecture and growth folding of the NW Zagros early foreland basin during the Late Cretaceous and early Tertiary

We present and use the chronostratigraphy of 13 field logs and detailed mapping to constrain the evolution of the early Zagros foreland basin, in NW Iran. Large foraminifera, calcareous nannofossil, palynological and 87Sr/86Sr analysis supplied ages indicating a Campanian-early Eocene age of the basin infill, which is characterizd by a diachronous, southwestward migrating, shallowing upwards, mixed clastic- carbonate succession. Growth synclines and local palaeoslope variations indicate syndepositional folding from Maastrichtian to Eocene time and suggest forelandward migration of the deformation front. We also illustrate the basin architecture with a synthetic stratigraphic transect. From internal to external areas, time lines cross the formation boundaries from continental Kashkan red beds to Taleh Zang mixed clastic-carbonate platforms, Amiran slope deposits and basinal Gurpi-Pabdeh shales and marls. The foreland basin depocentres show a progressive migration from the Campanian to Eocene (c. 83-52.7 Ma), with rates of c. 2.4 mm a-1 during the early-middle Palaeocene (c. 65.5-58.7 Ma) increasing to c. 6 mm a-1 during the late Palaeocene- earliest Eocene (c. 58.7-52.8 Ma). Coeval subsidence remained at c. 0.27 mm a-1 during the first 12.7 Ma and decreased to c. 0.16 mm a-1 during the last 4.2 Ma of basin filling. Finally, we integrate our results with published large-scale maps and discuss their implications in the context of the Zagros orogeny. © 2011 Geological Society of London.