Palaeoenvironmental changes of lower and middle Cenomanian sediments (Slenfeh formation) in the southern part of AL Sahyleh chain (Syria)

Abstract

A quantitative study of Slenfeh formation sediments (Lower- Middle Cenomanian) by using the palaeoecological indicators calcareous nannofossils was done in AlNasera and Safita sections in the southern part of costal chain. The results of this study showed that the abundance changes of some species have the same trends in the studied sections. The lower part of Cenomanian were characterized with high values of relative abundance for the species W. barnasae, and R.asper, wherever these values were decreased in the upper part of middle Cenomanian. On the other hand, the relativity abundance of B.constans,and Z.erectus were gradually increased from lower to middle Cenomanian. Principal Component Analyzes (PCA) were identified two factors that affecting on the abundance of calcareous nannofossils. The first factor is the increase of seawater temperature during the middle Cenomanian, associated with the increase of warm water species abundance such as, W. barnasae, R. asper. The second factor can be related to the change in the fluctuation of organic matter during the lower Cenomanian as result of increase the abundance of high-productivity species such as (B .constans, Z.erectus).

The results showed that Autotrophic conditions were dominated in the lower Cenomanian and associated with increase in the organic matter fluctuation. In addition, low biological productivity conditions during the middle Cenomanian were associated with an increase the depth of the sedimentation environment in the two studied sections.