Beschreibung: The application of acoustic techniques, such as multibeam echosounders, has permitted the identification of Maltese submarine landscapes and landforms that were progressively inundated during the postglacial sea-level rise. Remarkably, geomorphological features due to fluvial, gravity-induced and karst processes that took place under former subaerial conditions can be clearly recognised on the present seafloor around the Maltese archipelago, and they were only slightly modified by sea action during the postglacial transgression phases. The analysis of the submerged landforms described in this chapter is crucial for understanding the evolution of the Maltese Islands during the last ca. 20,000 years.

Beschreibung: Carbonates are widespread at methane and petroleum seeps and are often precipitated as consequence of an alkalinity increase due to the anaerobic oxidation of methane (AOM) or, less often reported, of higher hydrocarbons. These carbonates are taphonomic windows into Earth's history, because they excellently protect the in situ formed microbial signatures (e.g. lipid biomarkers) from diagenetic destruction. A complication for paleoreconstructions, however, is that seep carbonates also encapsulate variable amounts of allochthonous organic matter, sometimes even completely obscuring authigenic microbial signatures. Seep carbonates from the Holocene Black Sea, the Pleistocene Enza River and the Pliocene San Lorenzo (both Northern Apennines, Italy) provide hints to better understand (i) the importance of processes other than AOM for the formation of seep carbonates and (ii) the controls of allochthonous and autochthonous contribution of biomarkers to organic matter in seep carbonates. Biomarker distributions in different parts of a Black Sea carbonate clearly demonstrate that high allochthonous organic matter is entrapped if AOM carbonates are formed intrasedimentary, particularly if methane supply is relatively low and external organic matter input high. High allochthonous contributions were also found in the biomarker inventory of ancient seep carbonates from the Italian Northern Apennines (Enza River and San Lorenzo) pointing at their precipitation within the sediment. Specific and complex conditions were indicated from our data for the Enza River location. Carbonate facies and particularly biomarker compositions, with abundant signatures of sulfate reducing bacteria, suggest that sulfate reduction using alkaline, and eventually sulfate- and higher hydrocarbon-enriched fluids triggered the growth of these seep carbonates. Our and other data suggest that this process has to be more considered if interpreting seep settings, particularly where microbial processes rely on rising fluids from deep petroleum reservoirs.

Beschreibung: The Maltese Islands, located in the central Mediterranean Sea, are intersected by two normal fault systems associated with continental rifting to the south. Due to a lack of evidence for offshore displacement and insignificant historical seismicity, the systems are thought to be inactive and the rift-related deformation is believed to have ceased. In this study we integrate aerial, marine and onshore geological, geophysical and geochemical data from the Maltese Islands to demonstrate that the majority of faults offshore the archipelago underwent extensional to transtensional deformation during the last 20 ka. We also document an active fluid flow system responsible for degassing of CH4 and CO2. The gases migrate through carbonate bedrock and overlying sedimentary layers via focused pathways, such as faults and pipe structures, and possibly via diffuse pathways, such as fractures. Where the gases seep offshore, they form pockmarks and rise through the water column into the atmosphere. Gas migration and seepage implies that the onshore and offshore faults systems are permeable and that they were active recently and simultaneously. The latter can be explained by a transtensional system involving two right-stepping, right-lateral NW-SE trending faults, either binding a pull-apart basin between the islands of Malta and Gozo or associated with minor connecting antitethic structures. Such a configuration may be responsible for the generation or reactivation of faults onshore and offshore the Maltese Islands, and fits into the modern divergent strain-stress regime inferred from geodetic data.

Beschreibung: We present the neodymium isotopic composition (epsilon-Nd) of mixed planktonic foraminifera species from a sediment core collected at 622 m water depth in the Balearic Sea, as well as epsilon-Nd of scleractinian cold-water corals (CWC; Madrepora oculata, Lophelia pertusa) retrieved between 280 and 442 m water depth in the Alboran Sea and at 414 m depth in the southern Sardinian continental margin. The aim is to constrain hydrological variations at intermediate depths in the western Mediterranean Sea during the last 20 kyr. Planktonic (Globigerina bulloides) and benthic (Cibicidoides pachyderma) foraminifera from the Balearic Sea were also analyzed for stable oxygen (d18O) and carbon (d13C) isotopes. The foraminiferal and coral epsilon-Nd values from the Balearic and Alboran seas are comparable over the last ~13 kyr, with mean values of -8.94 ± 0.26 (1 Sigma; n = 24) and -8.91 ± 0.18 (1 Sigma; n = 25), respectively. Before 13 ka BP, the foraminiferal epsilon-Nd values are slightly lower (-9.28 ± 0.15) and tend to reflect higher mixing between intermediate and deep waters, which are characterized by more unradiogenic epsilon-Nd values. The slight epsilon-Nd increase after 13 ka BP is associated with a decoupling in the benthic foraminiferal d13C composition between intermediate and deeper depths, which started at ~16 ka BP. This suggests an earlier stratification of the water masses and a subsequent reduced contribution of unradiogenic epsilon-Nd from deep waters. The CWC from the Sardinia Channel show a much larger scatter of epsilon-Nd values, from -8.66 ± 0.30 to 5.99 ± 0.50, and a lower average (-7.31 ± 0.73; n = 19) compared to the CWC and foraminifera from the Alboran and Balearic seas, indicative of intermediate waters sourced from the Levantine basin. At the time of sapropel S1 deposition (10.2 to 6.4 ka), the epsilon-Nd values of the Sardinian CWC become more unradiogenic (-8.38 ± 0.47; n = 3 at ~8.7 ka BP), suggesting a significant contribution of intermediate waters originated from the western basin. We propose that western Mediterranean intermediate waters replaced the Levantine Intermediate Water (LIW), and thus there was a strong reduction of the LIW during the mid-sapropel (~8.7 ka BP). This observation supports a notable change of Mediterranean circulation pattern centered on sapropel S1 that needs further investigation to be confirmed.

Beschreibung: The largest coherent cold-water coral (CWC) mound province in the Atlantic Ocean exists along the Mauritanian margin, where up to 100 m high mounds extend over a distance of ~400 km, arranged in two slope-parallel chains in 400-550 m water depth. Additionally, CWCs are present in the numerous submarine canyons with isolated coral mounds being developed on some canyon flanks. Seventy-seven Uranium-series coral ages were assessed to elucidate the timing of CWC colonisation and coral mound development along the Mauritanian margin for the last ~120,000 years. Our results show that CWCs were present on the mounds during the Last Interglacial, though in low numbers corresponding to coral mound aggradation rates of 16 cm kyr**-1. Most prolific periods for CWC growth are identified for the last glacial and deglaciation, resulting in enhanced mound aggradation (〉1000 cm kyr**-1), before mound formation stagnated along the entire margin with the onset of the Holocene. Until today, the Mauritanian mounds are in a dormant state with only scarce CWC growth. In the canyons, live CWCs are abundant since the Late Holocene at least. Thus, the canyons may serve as a refuge to CWCs potentially enabling the observed modest re-colonisation pulse on the mounds along the open slope. The timing and rate of the pre-Holocene coral mound aggradation, and the cessation of mound formation varied between the individual mounds, which was likely the consequence of vertical/lateral changes in water mass structure that placed the mounds near or out of oxygen-depleted waters, respectively.