Paleoenvironmental reconstruction of the Barremian-lower Aptian deposits of Lebanon : sedimentology and micropaleontology

Abstract

Lower Cretaceous rocks of the Abeih Formation in the sense of Walley (1983)-upper part of the “Grès de Base” of Maksoud et al. (2014) are here studied from the sedimentological and micropaleontological viewpoints. Nine stratigraphic sections were raised and systematically sampled for microfossils in the central area of Mount Lebanon (Qehmez, Ain Dara, Azzouniye, Barouk and Jezzine). Five depositional sedimentary environments have been identified based on facies and microfacies analyses: 1) fluvial, 2) coastal freshwater lakes, 3) estuarine (intertidal and subtidal), 4) shallow marine and 5) carbonate sand shoal. These deposits provided a diverse microfossil association composed of 7 species of charophytes, 7 species of ostracods as well as foraminifera, dasycladal thalli, echinoid remains, mollusk shells and vertebrate fragments. The ostracod fauna is reported here for the first time including a new species. All recovered microfossils are here described and illustrated providing new insights about their paleoecology, paleobiogeography and biostratigraphy. Three microfossil assemblages can be distinguished in agreement with the facies succession and taphonomical aspects: 1) Coastal lake; 2) Estuary; 3) Shallow marine. The paleobiogeographical analysis of the charophyte and ostracod assemblages indicates an opposite distributional pattern within the Peri-Tethyan realm. On the one hand, ostracods display a cosmopolitan distribution occurring in both northwest and southeast margins of the Tethys. On the other hand, charophytes show a regional distributional pattern within the Middle East and northeastern Africa representing a separate bioprovince. Based on the biostratigraphic range of some of the microfossils recovered, the proposed age of the upper boundary of the studied lithologic units (in the proximity of the Banc de Mrejatt) is late Barremian to early Aptian.