The Upper Valanginian–Hauterivian Meloussi Formation outcropping in Central Tunisia includes alternating sandstones, dolostones, and marls that developed within a paleodeltaic system. The present work aims to characterize the dolomites and interpret the dolomitization in three geological sections (Jebel Meloussi, Jebel Kebar, and Jebel Siouf), which covered the whole paleodeltaic system. The dolomites are studied using a multidisciplinary approach based on sedimentological, mineralogical, geochemical, and stable isotope analyses. According to the different analytical results, it seems that the dolomitic facies distribution and dolomitization were remarkably controlled by the paleogeography of Central Tunisia at that time. Indeed, the dolomites that developed at Jebel Meloussi include features indicating the transition between the delta plain and delta front, whereas, those developed at Jebel Kebar indicate largely the delta front. The dolomites at Jebel Siouf developed in the transitional zone between the delta front and the prodelta. In such a paleogeographic setting, the dolomitization would have been achieved according to the seawater–freshwater mixing zone model, with a decreasing impact of meteoric waters from Jebel Meloussi (proximal zone) to Jebel Siouf (distal zone). Nevertheless, according to the oxygen and carbon stable isotopic data, the dolomitization may have occurred during sedimentary and early burial diagenetic stages.