Calcareous nannofossil, nummulite and ostracod assemblages from Paleocene to Miocene successions in the Bekaa Valley (Lebanon) and its paleogeographic implications

Abstract

Paleogeographic interpretations have been carried out in Lebanon by means of paleontological analysis. This study is complementary to previous records which have explained the paleogeographic setting of the western side of Lebanon during the Cenozoic. Extensive fieldwork and sampling were performed in the area of Zahle (west part of the Bekaa Valley). Samples collected from this locality provided diverse microfossil assemblages. The results show that there is a major change in the paleogeographic setting during the transitional period extending from early Eocene to Miocene. These changes in paleogeographic setting resulted from repeated episodes of emergence and submergence due to oscillating tectonic movements, leading to variations in the sedimentation patterns across the Bekaa Basin. The new findings of calcareous nannofossils in the chalky facies of Zahle area frame the paleogeographic settings during the Paleocene and early Eocene. Regression was clearly recognized during the early middle Eocene, which was revealed by the change in marine setting from the deep in the early Eocene (represented by the chalky facies), to the shallow settings in the middle Eocene where the nummulite banks were formed. This sedimentation pattern appears to coincide with major break in the sea level curve already reported by many researchers. During the Oligocene, the collision between the African-Arabian and Eurasian plates started causing further uplift of the Lebanese structures and consequent partial erosion (non-sedimentation) of the above-mentioned lithologies. The sedimentation pattern during the Miocene in Lebanon reveals a major change shifting from a primarily marine regime to fully lacustrine.