Suchergebnisse

Focused fluid flow shapes the evolution of marine sedimentary basins by transferring fluids and pressure across geological formations. Vertical fluid conduits may form where localized overpressure breaches a cap rock (permeability barrier) and thereby transports overpressured fluids towards shallower reservoirs or the surface. Field outcrops of an Eocene fluid flow system at Pobiti Kamani and Beloslav Quarry (ca 15 km west of Varna, Bulgaria) reveal large carbonate‐cemented conduits, which formed in highly permeable, unconsolidated, marine sands of the northern Tethys Margin. An uncrewed aerial vehicle with an RGB sensor camera produces ortho‐rectified image mosaics, digital elevation models and point clouds of the two kilometre‐scale outcrop areas. Based on these data, geological field observations and petrological analysis of rock/core samples, fractures and vertical fluid conduits were mapped and analyzed with centimetre accuracy. The results show that both outcrops comprise several hundred carbonate‐cemented fluid conduits (pipes), oriented perpendicular to bedding, and at least seven bedding‐parallel calcite cemented interbeds which differ from the hosting sand formation only by their increased amount of cementation. The observations show that carbonate precipitation likely initiated around areas of focused fluid flow, where methane entered the formation from the underlying fractured subsurface. These first carbonates formed the outer walls of the pipes and continued to grow inward, leading to self‐sustaining and self‐reinforcing focused fluid flow. The results, supported by literature‐based carbon and oxygen isotope analyses of the carbonates, indicate that ambient seawater and advected fresh/brackish water were involved in the carbonate precipitation by microbial methane oxidation. Similar structures may also form in modern settings where focused fluid flow advects fluids into overlying sand‐dominated formations, which has wide implications for the understanding of how focusing of fluids works in sedimentary basins with broad consequences for the migration of water, oil and gas. ; Integrated School of Ocean Sciences (ISOS) Kiel ; European Union's Horizon 2020 http://dx.doi.org/10.13039/100010661 ; Bulgarian Science Fund

Coastal regions are the most densely populated areas in the world with an average population density nearly 3 times higher than the global average. Freshwater resources in coastal states and island nations are therefore under enormous stress, and their quantities and qualities are rapidly deteriorating. This problem is exacerbated by population growth, pollution, climate change and political conflicts. Problems are especially felt in arid areas, such as Malta, where groundwater is the only source of freshwater and the periods of highest demand (e.g., agricultural and tourist seasons) coincide with the periods of lowest recharge from precipitation. By comparison, Cape Town, South Africa is the first major city in the modern era to face the threat of running out of drinking water, and other large cities like Jakarta, and Beijing are likely to follow suit. Offshore aquifers (OAs) have been proposed as an alternative source of freshwater to cover demand by domestic, agricultural and tourist industries in coastal regions. During the Last Glacial Maximum (19-22,000 years ago), modern shelf areas were sub-aerially exposed, leading to the development of extensive water tables recharged by atmospheric precipitation (meteoric water), rivers, lakes and, in some areas, glacial melt water. In view of the fact that sea level has been much lower than today for 80% of the Quaternary period (last 2.6 million years), and that meteoric groundwater systems migrate landwards more slowly than rising sea levels, remnants of meteoric groundwater occur extensively offshore. ; N/A

10 pages, 3 figures, 1 table, supporting information https://doi.org/10.1029/2020GL091909.-- Data Availability Statement: Data for this research are available at http://doi.org/10.5281/zenodo.4304549 ; Carbonate lithologies host considerable quantities of the Earth¿s freshwater resources and partially supply a quarter of the global population with drinkable water. Carbonates constitute substantial amounts of the global coastlines, yet it is not known if and how they can sustain freshened groundwater offshore. Here, we use controlled source electromagnetic, seismic reflection, and core sample data to derive a lithological model for the eastern margin of the Maltese Islands and identify four distinct resistivity anomalies within the Upper Coralline Limestone, Globigerina Limestone, and Blue Clay formations. The anomalies hosted in the former are likely associated to low porosities, whereas the anomaly within the latter is indicative of pore fluid freshening. Hydrogeological modeling suggests that freshened pore fluids, emplaced during sea-level lowstands and preserved in low permeability units, are potentially still found within carbonate shelves. However, resource potential is low due to its relict nature and low permeability host environment ; This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Program (grant agreement no 677898; MARCAN). [.] Open access funding enabled and organized by Projekt DEAL. [.] With funding from the Spanish government through the 'Severo Ochoa Centre of Excellence' accreditation (CEX2019-000928-S)

10 pages, 3 figures, 1 table, supporting information https://doi.org/10.1029/2020GL091909.-- Data Availability Statement: Data for this research are available at http://doi.org/10.5281/zenodo.4304549 ; Carbonate lithologies host considerable quantities of the Earth¿s freshwater resources and partially supply a quarter of the global population with drinkable water. Carbonates constitute substantial amounts of the global coastlines, yet it is not known if and how they can sustain freshened groundwater offshore. Here, we use controlled source electromagnetic, seismic reflection, and core sample data to derive a lithological model for the eastern margin of the Maltese Islands and identify four distinct resistivity anomalies within the Upper Coralline Limestone, Globigerina Limestone, and Blue Clay formations. The anomalies hosted in the former are likely associated to low porosities, whereas the anomaly within the latter is indicative of pore fluid freshening. Hydrogeological modeling suggests that freshened pore fluids, emplaced during sea-level lowstands and preserved in low permeability units, are potentially still found within carbonate shelves. However, resource potential is low due to its relict nature and low permeability host environment ; This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Program (grant agreement no 677898; MARCAN). [.] Open access funding enabled and organized by Projekt DEAL. [.] With funding from the Spanish government through the 'Severo Ochoa Centre of Excellence' accreditation (CEX2019-000928-S)