Sequence stratigraphy and paleogeography reconstruction of the reference Lower-Middle Turonian successions of Jebel Bireno (Central Tunisia): a semi-quantitative approach

The Early-Middle Turonian carbonates of central Tunisia (Kef Formation, Bireno Member) are considered as ramp deposits. The correspondence analysis statistical method used here is based on the relative abundance of carbonate components and the occurrences of specific structures within beds. It was applied to the bed-by-bed sampled succession in the Jebel Bireno area in central Tunisia concerning 399 samples from 11 studied stratigraphic sections. We propose the reconstruction of the facies based on the allochem distribution (Axis 1) along the proximal to distal ramp environments. The proposed pattern brings out successive facies shifts interpreted in terms of sequence stratigraphy: along Axis 1, abrupt shifts to negative values correspond to sequence boundaries and/or regressions; positive excursions express transgressive events or maximum flooding surfaces. Trends in this Axis 1 and key surfaces allow the identification of main system tracts of third-order sequences as well as variations of paleogeography. Four dated sequences were identified within the Jebel Bireno Early-Middle Turonian series. Correlation of system tracts highlights facies and thickness variations mainly controlled by N130–N90 trending synsedimentary normal faults. Paleogeographic maps for the Bireno Mb plead in favor of a distal ramp, subtidal high-energy deposits (barrier), and proximal ramp environment.