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After the end of the Last Glacial Maximum, 450 km2 of former terrestrial and coastal landscape of the Maltese Islands was drowned by the ensuing sea level rise. In this study we use high resolution seafloor data (multibeam echosounder data, seismic reflection profiles, and Remotely Operated Vehicle imagery) and bottom samples to reconstruct ~ 300 km2 of this submerged Maltese paleolandscape. The observed paleolandscape is exceptionally well preserved and comprises former coastal landforms – (i) fault-related escarpments, (ii) paleoshore platforms and associated shorelines, (iii) paleoshoreline deposits, and (iv) mass movement deposits – and former terrestrial landforms – (v) river valleys, (vi) alluvial plains, (vii) karstified limestone plateaus, and (viii) sinkholes. These elements indicate that the paleolandscape has been primarily shaped by tectonic activity combined with fluvial, coastal, slope instability and karstic processes; these are the same processes the shaped the current terrestrial and coastal landscape. By correlating the identified landforms with the timing of known changes in sea level during the last glacial cycle, we infer that the alluvial plains and the shallowest limestone plateaus had up to 100 kyr to develop, whereas the paleoshoreline deposits are likely to have formed between 28 kyr and 14 kyr. The most prominent paleoshore platforms, shorelines and river valleys were generated between 60 kyr and 20 kyr. Fluvial erosion is likely to have been prevalent during periods of low sea level (Last Glacial Maximum and stadial conditions during MIS 3), whereas karst processes should have been more effective during warm and humid interstadial periods. Our results have implications for improving the characterization of past environments and climates, as well as providing a much needed background for prehistoric and geoarcheological research in the central Mediterranean region.

In this study, we investigate the tectonic and stratigraphic evolution of the northern Tanzania margin (western Indian Ocean) to provide new insights on the structural drivers governing the formation of Zanzibar and Pemba islands. Using 2D seismic reflection profiles and exploration wells, we have reconstructed the evolution of the submarine drainage network throughout the last 30 Myr, from the Oligocene to recent times, providing a tape-recorder with which we determine the different tectonic events that led to the eventual subaerial exposure of the islands. In detail, we observe a decrease in the number of slope canyon-channel systems during the lower-middle Miocene offshore Pemba Island that we interpret to represent the initial uplift of the island: tectonic deformation of the seafloor impeded up-dip to down-dip sediment transfer, forcing the abandonment of canyon-channel systems. At the same time, submarine canyons were still active offshore Zanzibar Island, located ~35 km south of Pemba, indicating that its uplift occurred later, likely during the upper Miocene to lower Pliocene. The uplift of the islands increased the slope gradient and promoted the formation of two newly discovered giant canyons that represent the main feeder systems to this sector of the western Indian Ocean since the Miocene. We propose a new conceptual model for the post-Oligocene evolution of the area, highlighting the main tectonic structures and their timing of formation. In this model, the onset of the anticlines of Pemba and Zanzibar islands resulted from tectonic inversion probably originated during the Oligocene-lower Miocene due to reactivation of Mesozoic-aged rift faults. This compressional phase is followed by the establishment of an extensional tectonic regime which promoted the subaerial exposure of the islands since the middle Miocene. Extensional faults, which dissect the post-Oligocene stratigraphy, create horsts and grabens on a variety of scales, such as Zanzibar and Pemba troughs. These grabens show comparative size and orientation to onshore rift basins, which may indicate a relation with the tectonics of the East African Rift System. Our results provide new insights on the evolution of one the least explored, though fascinating, continental margin settings worldwide that can support future source-to-sink investigations in the region.