Research Article
Structural Characteristics and Exploration Significance of the Lower Paleozoic Detachment Thrust Belt in the Eastern Ordos Basin
Issue:
Volume 15, Issue 1, February 2026
Pages:
1-9
Received:
1 September 2025
Accepted:
16 September 2025
Published:
23 January 2026
Abstract: Utilizing 2D and 3D seismic data, a large-scale detachment thrust structure within the Lower Paleozoic Ordovician Majiagou Formation (O1m) has been identified west of Lishi in the eastern Ordos Basin. This study investigates the structural characteristics, spatial distribution, evolutionary stages, and exploration potential of this structure. The results indicate: (1) The Lower Paleozoic Lishi West Detachment Thrust Belt (DTB) in the eastern Ordos Basin margin is 5–10km wide, extends nearly north-south parallel to the Lishi Fault Zone, and has considerable strike length. (2) The main faults of the Lishi West DTB initiated in the Precambrian and subsequently underwent four major evolutionary stages: stable sedimentation in the Ordovician epicontinental sea; formation of the detachment thrust belt from the Late Ordovician to Late Carboniferous; stable sedimentation from the Late Carboniferous to Middle Jurassic; and compressional uplift from the Middle Jurassic to Cretaceous. (3) The Lishi West DTB originated during the Caledonian period as a deep-seated structural weak zone. During the Yanshanian period, the eastern basin margin experienced westward compression, leading to regional tilting and uplift. Stress release along this pre-existing weak zone caused significant variations in formation dip angles and fault characteristics across the belt. This DTB is interpreted as the boundary separating the Jinxi Warp-Fold Belt and the Yishan Slope. (4) The detachment thrust belt in the eastern margin plays a critical role in hydrocarbon accumulation and subsequent migration/readjustment. The area west of the belt is favorable for exploring various coal-measure hydrocarbon resources, including deep coalbed methane (CBM) and in-source to near-source tight gas. A series of positive structural traps with large aerial extent have developed within the O1m Formation along the Lishi West DTB, demonstrating high exploration potential.
Abstract: Utilizing 2D and 3D seismic data, a large-scale detachment thrust structure within the Lower Paleozoic Ordovician Majiagou Formation (O1m) has been identified west of Lishi in the eastern Ordos Basin. This study investigates the structural characteristics, spatial distribution, evolutionary stages, and exploration potential of this structure. The r...
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Research Article
Geochemical Characterization of Rasulpur - Subarnarekha River Mouths Estuarine Complex, EC of India: Provenance, Palaeo Weathering and Depositional Environment
Issue:
Volume 15, Issue 1, February 2026
Pages:
10-29
Received:
30 August 2025
Accepted:
9 October 2025
Published:
2 February 2026
DOI:
10.11648/j.earth.20261501.12
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Abstract: Major and trace element geochemistry of sediments is a very useful tool for understanding the provenance, intensity of weathering, tectonic settings, and depositional environment of the sediments. Sediments collected from different geomorphic domains (onshore and nearshore) of Rasulpur to Subarnarekha River mouths estuarine complex, East coast of India, were analyzed for their geochemical (major, trace contents) and mineralogical characteristics to determine their provenance, compositional maturity, paleo-weathering condition, and depositional environment. From geochemical studies, it is evident that the samples from the nearshore area suffered more weathering than the onshore samples. Geochemistry of the sediments suggests the protolith of the area to be of intermediate to felsic source rocks. A relative increase in the Al2O3/TiO2 ratio in sediments also suggests that they are derived mainly from intermediate to felsic source rocks. A strong positive correlation between Fe2O3, MnO, K2O, MgO, CaO, P2O5, and major oxides with respect to Al2O3 indicates that they are associated with micaceous/clay minerals. The Index of Compositional Variability (ICV) indicating low compositional and mineralogical maturity of the sediments. The Chemical Index of Alteration (CIA) value clearly pointing towards intense to intermediate weathering in the source area sediments. Similarly, Chemical Index of Weathering (CIW) results also supporting the same trend of weathering. The results of Plagioclase Index of Alteration (PIA) suggesting moderate destruction of feldspars during source weathering, transport, sedimentation, and diagenesis. The Ternary plot of A-CN-K and the binary plot of CIA/ICV also suggest that both geomorphological domains are immature in nature and suffered intense to moderate weathering. Trace-element concentrations in sediments result from the competing influence of provenance, weathering, diagenesis, and sediment sorting. The felsic province is also corroborated by elevated values of Ba, K, and Sr. EPMA analysis reveals the presence of heavy minerals comprising Ilmenite, garnet as major constituents followed by sphene and rutile. Other minerals include sphene, epidote, amphibole, pyroxene, biotite, apatite, chlorite, tourmaline, muscovite, and alumino-silicate. The concentration of TiO2 in Ilmenitedepicting a metamorphic signature with an igneous source. Micro-textural studies reveal different types of surface features of the grains, the various micro features have been produced by different transportational processes under different environmental conditions. Based on all geochemical and mineralogical data and different plots, it is evident that the sediments from both geomorphological domains are immature in nature and suffered intense to moderate weathering derived from mixed igneous and metamorphic sources.
Abstract: Major and trace element geochemistry of sediments is a very useful tool for understanding the provenance, intensity of weathering, tectonic settings, and depositional environment of the sediments. Sediments collected from different geomorphic domains (onshore and nearshore) of Rasulpur to Subarnarekha River mouths estuarine complex, East coast of I...
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Research Article
Rainfall Variability and Prolonged Drying of the Menarandra Riverbed (2000–2017) in the District of Bekily (Southern Madagascar)
Tinahindraza Mampionona Albertin*
Issue:
Volume 15, Issue 1, February 2026
Pages:
30-43
Received:
4 January 2026
Accepted:
15 January 2026
Published:
2 February 2026
DOI:
10.11648/j.earth.20261501.13
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Views:
Abstract: The Menarandra River, located in the Androy region of southern Madagascar, flows through a semi-arid environment characterized by severe water stress, a long dry season lasting seven to nine months, and a short, highly variable rainy season concentrated between December and March. Rainfall records from the Bekily meteorological station over 2000–2017 highlight pronounced interannual variability, with alternating wet years (e.g., 2001, 2005, 2011, annual totals >1,000 mm) and deficit years with totals below 700 mm (e.g., 2002, 2004, 2016, 2017). To better link raw rainfall data to effective rainfall in terms of hydrological response, the analysis incorporates the Turc formula, widely used in water balance studies to estimate potential evapotranspiration and effective rainfall. This approach allows a more precise characterization of hydrological conditions associated with rainfall variability and their potential role in riverbed drying. Rainfall analysis is complemented by qualitative interpretation of Google Earth satellite images processed in QGIS, together with field observations. Comparison of images from December 2014 and October 2018 reveals marked reduction and fragmentation of water-covered areas, indicating increasing spatial discontinuity of surface flow. While the temporal correspondence between rainfall variability and riverbed drying suggests a strong association, river intermittency likely reflects the combined influence of seasonal and interannual rainfall patterns and local hydrological controls. Overall, results indicate a progressive shift of the Menarandra toward a more intermittent flow regime, improving understanding of river drying dynamics in semi-arid southern Madagascar and informing sustainable water resource management under increasing drought conditions.
Abstract: The Menarandra River, located in the Androy region of southern Madagascar, flows through a semi-arid environment characterized by severe water stress, a long dry season lasting seven to nine months, and a short, highly variable rainy season concentrated between December and March. Rainfall records from the Bekily meteorological station over 2000–20...
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