Geosciences

19 pages, 6521 KiB

Open AccessArticle

Hydrological Characteristics of Columnar Basalt Aquifers: Measuring and Modeling Skaftafellsheiði, Iceland

by Roel Dijksma, Victor Bense, Eline Zweers, Lisette Avis and Martine van der Ploeg

Geosciences 2025, 15(5), 160; https://doi.org/10.3390/geosciences15050160 - 25 Apr 2025

Basalt with columnar jointing can act as a good groundwater conductor. In areas with limited water resources in sedimentary rock, such as the Deccan Traps in India and the Columbia River basalt formations in Washington State (USA), large quantities of groundwater are abstracted from such basalt formations for drinking water supply and irrigation. The hydraulic properties of basaltic formations are difficult to quantify. To obtain a better understanding of their hydraulic properties, intensive field campaigns in Iceland were combined with a conceptual groundwater model in MODFLOW. The field experiments enabled us to derive the upper boundary conditions, like precipitation surplus, and obtain reliable ranges for the k_h (0.01–0.3 m d⁻¹) and k_v (0.01–10 m d⁻¹) of the basalt formations. The main objective was to test the concept of representative elementary volumes (REVs) for such basaltic regions. Precipitation excess for the Vestragil and Eystragil catchments was calculated by taking into account the orographic effect of precipitation. It was found that at higher elevations (600 m + msl) the precipitation was twice the amount compared to the base camp rain gauge at 100 m + msl. Calculated evapotranspiration (1–2 mm d⁻¹) is in line with the literature. In the MODFLOW model, best results were obtained when the top layer (organic soil, peat, and regolith) was considered to be most conductive (up to 10 m d⁻¹), with a gradual reduction in hydraulic conductivity with depth in the basaltic aquifers. This study shows that, when larger elementary volumes are used, a good model representation of basaltic regions can be created. Full article

(This article belongs to the Section Hydrogeology)

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21 pages, 128246 KiB

Open AccessArticle

Established and Proposed Geosites of Visean (Carboniferous) Plants from the Moscow Basin

by Yulia V. Mosseichik, Igor A. Ignatiev, Natalia N. Yashalova and Dmitry A. Ruban

Geosciences 2025, 15(5), 159; https://doi.org/10.3390/geosciences15050159 - 23 Apr 2025

Abstract

Fossil plant localities are potential geosites, but related information is limited for some paleofloristic domains. Four geosites representing Visean (Mississippian, Carboniferous) plant-bearing deposits are reported from two areas of the Moscow Basin (central eastern Laurussia). These are the Mountainous Msta area in the northwestern segment of this basin and the Tula Region in its southern segment. The localities were examined in the field and characterized with criteria related to geoheritage properties (e.g., geoheritage types, physical view, accessibility, vulnerability, and research importance). One of these localities has already been established as a geosite (official status of protected area) and three other localities are proposed as geosites in this work (two of them are situated in the planned protected area). It is established that all considered geosites represent notable assemblages of Visean plants, with some exhibiting unique preservation and interesting sedimentary features, such as the “Tula pipes”. Essentially, the localities are small natural outcrops and abandoned quarries with perfect accessibility. They have potential for future research projects, as well as for geological education and tourism. Presently, their vulnerability is only potential, but it can increase due to touristic exploitation in the nearest future; thus, this property requires special attention. More generally, these geosites are important sources of the knowledge of the Early Carboniferous equatorial vegetation in eastern Laurussia. Full article

(This article belongs to the Section Geoheritage, Geoparks and Geotourism)

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25 pages, 9019 KiB

Open AccessArticle

Petrography and Fluid Inclusions for Petroleum System Analysis of Pre-Salt Reservoirs in the Santos Basin, Eastern Brazilian Margin

by Jaques Schmidt, Elias Cembrani, Thisiane Dos Santos, Mariane Trombetta, Rafaela Lenz, Argos Schrank, Sabrina Altenhofen, Amanda Rodrigues, Luiz De Ros, Felipe Dalla Vecchia and Rosalia Barili

Geosciences 2025, 15(5), 158; https://doi.org/10.3390/geosciences15050158 - 23 Apr 2025

Abstract

The complex interaction of hydrothermal fluids and carbonate rocks is recognized to promote significant impacts on petroleum systems, reservoir porosity, and potential. The objective of this study is to investigate the fluid phases entrapped in the mineral phases of the Barra Velha Formation (Santos Basin), including their petrographic paragenetic relationships, relative timing, temperatures of migration events, and maximum temperature reached by the sedimentary section. The petrographic descriptions (387), Rock-Eval pyrolysis (107), fluid inclusion petrography (14), and microthermometry (428) were performed on core and sidewall samples from two wells from one field of the Santos Basin. Hydrocarbon source intervals were primarily identified in lithologies with high argillaceous content. Chert samples still retain some organic remnants indicative of their original composition prior to extensive silicification. Redeposited intraclastic rocks exhibit the lowest organic content and oil potential. A hydrothermal petroleum system is identified by fluids consisting in gas condensate, light to heavy undersaturated oil, occasionally accompanied by aqueous fluids influenced by juvenile and evaporitic sources, and localized flash vaporization events. These hydrothermal fluids promoted silicification and dolomitization, intense brecciation, and lead to enhanced porosity in different compartments of the reservoir. The relative ordering of paleo-hydrothermal oils and the main oil migration and accumulation events has improved our understanding of the petroleum systems in the basin. This contribution is significant for future regional research on the evolution of fluid systems and their implications for carbonate reservoirs. Full article

(This article belongs to the Special Issue Petroleum Geochemistry of South Atlantic Sedimentary Basins)

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Geosciences, Volume 15, Issue 5 (May 2025) – 3 articles

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