The influence of Late Cretaceous tectonic processes on sedimentation patterns along the northeastern Arabian plate margin (Fars Province, SW Iran)

Abstract

Abstract During the Late Cretaceous the northeastern margin of the Arabian plate (Zagros–Fars Area) was characterized by significant variations in sedimentary facies, sedimentation patterns and accommodation space, and by shifting depocentres. A succession of events recording the evolution of the region from a passive to an active margin is documented by the study of eight outcrop sections and one well. This new study uses new age dating (benthic and planktonic foraminifers, nannoplankton and radiolarian biozonations and strontium isotope stratigraphy). The new observations provide a detailed overview of the response of the sedimentary system to changes in the tectonic regime related to obduction processes. These changes are very well shown in regional cross-sections and palaeogeographical maps. Three tectono-sedimentary phases are recognized indicating the evolution from a passive to an active margin: Phase I (Late Albian to Cenomanian, before obduction) comprises three depositional third-order sequences comparable with those of the other parts of the Zagros and Arabian plate. This interval is composed of shallow-water platform carbonates and intra-shelf basins. The platform facies consists of rudist and benthic foraminifer-dominated assemblages, whereas the intra-shelf basins contain an ‘ Oligostegina ’ facies. Eustatic sea-level variations and local differential subsidence controlled sediment deposition during this phase. Phase II (Turonian to Late Campanian, obduction phase) is characterized by major changes in depositional environments and sedimentary facies, as a result of obduction and foreland basin creation. It consists of pelagic and platform carbonates in the south, and a foreland basin with obducted radiolarites, ophiolitic and olistoliths or thrust slices in the north. During this phase, large volumes of turbidites and gravity flows with olistoliths were shed from both the SW and NE into the foreland basin. The age of the tectonic slices increases upward through the section, from Early Cretaceous at the base to Permian at the top. Based on various dating methods used on the far-travelled sediments, the depositional age of the radiolarites can be attributed to the Albian–Cenomanian, whereas the planktonic foraminifers are of Santonian to Campanian age. Phase III (Late Campanian to Maastrichtian, after obduction) shows the development of rudist-dominated carbonates in the NE prograding onto the deep basinal facies in the centre of study area. In the extreme NE no sediments of this age have been recorded, suggesting uplift at that time.