Alluvial fans in the latest phase of the Messinian Salinity Crisis: An example from the Chaabet Et Tabbela Formation, northern Tunisia, Central Mediterranean

Abstract

Alluvial fan deposits record important information about paleoclimate, tectonic setting, and paleogeography that can be deciphered with detailed sedimentological analysis. The late Messinian Chaabet Et Tabbela Formation, in the western part of the Kechabta Basin in northern Tunisia, shows excellent examples of alluvial fans deposited during the latest phase of the Messinian Salinity Crisis, the Lago Mare event. This exposure provides the opportunity to investigate terrestrial depositional conditions during this period. The Chaabet Et Tabbela Formation was investigated through sedimentological logging and detailed facies analysis at eight locations. Sixteen facies types were identified and interpreted along with variation in clast compositions. These facies were further grouped into four facies associations: (1) proximal alluvial fan, dominated by gravity-driven processes, (2) medial alluvial fan, which mainly comprises a mix of debris flow and high-sediment load streamflow deposits, (3) distal alluvial fan, which consists of laterally continuous sheetflood and subordinate channels deposits, and (4) playa and floodplain, which are made of red mudstones with calcareous paleosols. Clast composition of these fan deposits comprises Triassic, Jurassic, and Cretaceous bedrock suggesting that sediment was sourced from the surrounding Maghrebian mountain chain. Two laterally adjacent alluvial fans were identified along the N-S Messeftine Fault. These fans have prograded during the Late Messinian, with an estimated radius of ca 2 km.The evolution of these alluvial fans is related to a complex interplay of allogenic processes. The uplift related to intra-Messinian tectonic event and climate variation contributed to the formation of these fans during the late Messinian. Although, these deposits are relatively limited in extension, similar continental deposits form synchronously in different marginal Mediterranean basins during the Lago Mare stage, suggesting that the alluvial fans of the Chaabet Et Tabbela Formation should be placed in a context of regionally change climactic and paleogeographic conditions.