Gullying has been widespread in the Ethiopian Highlands during the 20th century. It threatens the soil resource, lowers crop yields in intergully areas through enhanced drainage and desiccation, and aggravates flooding and reservoir siltation. Knowing the age and rates of gully development during the last few decades will help explain the reasons for current land degradation.In the absence of historical written or photographic documentation, the AGERTIM method (Assessment of Gully Erosion Rates Through Interviews and Measurements) has been developed. It comprises measurements of contemporary gully volumes, monitoring of gully evolution over several years and semi-structured interview techniques. Gully erosion rates in the Dogu'a Tembien District, Tigray, Ethiopia, were estimated in three representative case-study areas.In . The successful application of the AGERTIM method requires an understanding of the geomorphology of the study area and an integration of the researchers with the rural society. It reveals that rapid gully development in the study area is some 50 years old and is mainly caused by human-induced environmental degradation. Under the present-day conditions of 'normal' rain and catchment-wide soil and water conservation, gully erosion rates are decreasing.

Ground-based hyperspectral imaging combined with terrestrial lidar scanning is a novel technique for outcrop analysis, which has been applied to Early and Late Albian carbonates of the Pozalagua Quarry (Cantabrian Mountains, Spain). An image processing workflow has been developed for differentiating limestone from dolomite, providing additional sedimentary and diagenetic information, and the possibility to quantitatively delineate diagenetic phases in an accurate way. Spectral absorption signatures can be linked to specific sedimentary or diagenetic products, such as recent and palaeokarst, hydrothermal karst, (solution enlarged) fractures and different dolomite types. Some of the spectral signatures are related to iron, manganese, organic matter, clay and/or water content. Ground-truthing accessible parts of the quarry showed that the classification based on hyperspectral image interpretation was very accurate. This technique opens the possibility for quantitative data evaluation on sedimentary and diagenetic features in inaccessible outcrops. This study demonstrates the potential of ground-based imaging spectroscopy to provide information about the chemical-mineralogical distribution in outcrops, which could otherwise not be established using conventional field methods.

The Pozalagua Quarry in the Basque-Cantabrian Basin of northern Spain exposes a unique set of fault-associated dolomites that can be studied on a decametre scale. The dolomites developed along the Pozalagua Fault system in slope-deposited limestones of Albian age. Following marine phreatic diagenesis, the limestones were subject to meteoric karst formation. The resulting cavities were filled either by angular limestone fragments in a black clay-rich matrix, or by cave floor/pond (now dolomitized) sediments. The subsequent diagenetic history reflects repeated periods of fracturing, fluid expulsion, dissolution and cementation. Contrasting fluid pulses resulted in the formation of a network of hydrothermal karst and the subsequent development of coarse-crystalline calcite cement, zebra dolomite, recrystallized coarse-crystalline dolomite, elongated blue-grey coarsecrystalline dolomite cement in the open fault and, finally, coarse-crystalline saddle dolomite. Decimetre-size reworked host-rock fragments present in the latter two dolomite phases probably reflect roof collapse fragments of a cave system that developed along the Pozalagua Fault system. However, there are also metre-scale host-rock fragments that apparently 'float' in the coarsecrystalline saddle dolomites, implying that either fragment assimilation was a widespread process or violent expulsion of fluids occurred along the Pozalagua Fault system. The presence of pre-dolomite and post-dolomite stylolites, parallel to bedding, supports a linkage between the diagenetic events and the Late Albian tectonism that affected the region.

Hydrothermal dolomite (HTD) bodies are known as high-quality hydrocarbon reservoirs; however few studies focus on the geometry and distribution of reservoir characteristics. Across the platform-to-basin transition of the Ramales Platform, fault-controlled HTD bodies are present. Three kinds of bodies can be distinguished based on their morphology, that is, elongated HTD corridors, a massive HTD body (Pozalagua body) and an HTD-cemented breccia body. The differences in size and shape of the HTD bodies can be attributed to differences in local structural setting. For the Pozalagua body, an additional sedimentological control is invoked to explain the difference in HTD geometry.A (geo)-statistical investigation of the reservoir characteristics in the Pozalagua body revealed that the HTD types (defined based on their texture) show spatial clustering controlled by the orientation of faults, joints and the platform edge. Porosity and permeability values are distributed in clusters of high and low values; however, they are not significantly different for the three HTD types. Two dolomitization phases (i.e. ferroan and non-ferroan) can be observed in all HTD bodies. In general, the HTDs resulting from the second non-ferroan dolomitization phase have lower porosity values. No difference in permeability is found for the ferroan and non-ferroan dolomites.

International audienceOverbank sediments contaminated with metalliferous minerals are a source of toxic metals that pose risks to living organisms. The overbank sediments from the Geul river in Belgium contain 4000–69,000 mg/kg Zn as a result of mining and smelting activities, principally during the 19th century. Three main Zn species were identified by powder Zn K-edge EXAFS spectroscopy: smithsonite (ZnCO3), tetrahedrally coordinated sorbed Zn (sorbed IVZn) and Zn-containing trioctahedral phyllosilicate. Smithsonite is a primary mineral, which accounts for approximately 20–60% of the Zn in sediments affected by mining and smelting of oxidized Zn ores (mostly carbonates and silicates). This species is almost absent in sediments affected by mining and smelting of both sulphidic (ZnS, PbS) and oxidized ores, presumably because of acidic dissolution associated with the oxidation of sulphides, as suggested by the lower pH of this second type of sediment (pH(CaCl2) <7.0 vs. pH(CaCl2) >7.0 for the first type). Thus, sulphide minerals in sediment deposits can act as a secondary source of dissolved metals by a chemical process analogous to acid mine drainage. The sorbed IVZn component ranges up to approximately 30%, with the highest proportion occurring at pH(CaCl2) <7.0 as a result of the readsorption of dissolved Zn2+ on sediments constituents. Kerolite-like Zn-rich phyllosilicate is the major secondary species in all samples, and in some the only detected species, thus providing the first evidence for pervasive sequestration of Zn into this newly formed precipitate at the field scale