Search Results (3)

The Middle Tonian tectonic setting of the Jiangnan Orogen, South China, remains intensely debated, and is centered on two competing models: subduction–collision versus mantle plume. This study addresses this critical knowledge gap through an integrated, multi-proxy investigation of the Middle Tonian Fanjingshan Group. This region preserves a continuous volcano-sedimentary and magmatic record, offering key insights into the orogen’s full lifecycle. To test these hypotheses, we employed a synthesis of geological survey, sediment provenance analysis, detrital zircon U-Pb geochronology of clastic rocks to determine sediment provenance and basin evolution, and petrogenetic study of coeval magmatic suites (pillow lava, mafic–ultramafic sills, and granitoids) to evaluate their magmatic processes and tectonic setting. Analysis of 1736 detrital zircon U-Pb ages from Middle Tonian strata reveals a four-stage provenance evolution: (1) SW Yangtze sources in a passive margin basin before 870 Ma; (2) bidirectional sources in an 870–835 Ma arc-derived basin; (3) syn-collisional detritus during 835–820 Ma amalgamation; and (4) post-collisional and northern Yangtze inputs in an 800 Ma rifting basin. Geochemical data from ~845–840 Ma basalts and coeval sills reveal calc-alkaline affinities and marked subduction-fluid signatures. Their calculated mantle potential temperature (1404 °C) is significantly lower than that expected for plume-derived melts (1570 °C), which is consistent with melting in a subduction-modified mantle wedge, supporting a continental rear-arc basin setting. The ~845–832 Ma mafic–ultramafic sills exhibit symmetrical geochemical zoning and two-stage emplacement, recording sustained magma recharge in the rear-arc basin. Furthermore, the ~830 Ma Fanjingshan granite is identified as a crust-derived, syn-collisional S-type granite. Synthesizing these findings, we demonstrate that the sedimentary and magmatic records collectively point to plate margin setting. A four-stage tectonic model is suggested: (1) pre-870 Ma passive margin without significant magmatic activity; (2) 870–835 Ma continental arc development at an active continental margin; (3) 835–820 Ma Yangtze–Cathaysia collision; and (4) post-820 Ma post-orogenic rifting. This work provides a robust regional case study, demonstrating that integrating records of deep magmatic processes with coeval shifts in sedimentary provenance and basin architecture is essential to reconstruct the complete evolution of ancient orogens. Full article

The lithological dichotomy in the Hammam Faraun Member (Gulf of Suez, Egypt) reveals a stable western flank with Nullipore carbonate deposits, contrasting with the clastic-prone eastern margin influenced by tectonic activity. This study aims to decipher multifactorial controls on spatial lithological variability and reservoir implications through (1) foraminiferal-based paleoenvironmental reconstruction; (2) integrated sequence stratigraphic–petrophysical analysis for sweet spot identification; and (3) synthesis of lateral facies controls. This study uniquely integrates foraminiferal paleoenvironmental proxies, sequence stratigraphy, and petrophysical analyses to understand the multifactorial controls on spatial variability and its implications for reservoir characterization. Middle Miocene sea surface temperatures, reconstructed between 19.2 and 21.2 °C, align with warm conditions favorable for carbonate production across the basin. Foraminiferal data indicate consistent bathyal depths (611–1238 m) in the eastern region, further inhibited in photic depths by clastic influx from the nearby Nubian Shield, increasing turbidity and limiting carbonate factory growth. Conversely, the western shelf, at depths of less than 100 m, supports thriving carbonate platforms. In the sequence stratigraphy analysis, we identify two primary sequences: LA.SQ1 (15.12–14.99 Ma), characterized by evaporitic Feiran Member deposits, and LA.SQ2 (14.99–14.78 Ma), dominated by clastic deposits. The primary reservoir comprises highstand systems tract (HST) sandstones with effective porosity ranging from 17% to 22% (calculated via shale-corrected neutron density cross-plots) and hydrocarbon saturation of 33%–55% (computed using Archie’s equation). These values, validated in Wells 112-58 (ϕe = 19%, S_hc = 55%) and 113M-81 (ϕe = 17%, S_hc = 33%), demonstrate the primary reservoir potential. Authigenic dolomite cement and clay content reduce permeability in argillaceous intervals, while quartz dissolution in clean sands enhances porosity. This research emphasizes that bathymetry, sediment availability, and syn-sedimentary tectonics, rather than climate, govern carbonate depletion in the eastern region, providing predictive parameters for identifying reservoir sweet spots in clastic-dominated rift basins. Full article

Deep saline aquifers in the eastern part of Drava Basin were screened for potential storage sites. The input dataset included three seismic volumes, a rather extensive set of old seismic sections and 71 wells. Out of all identified potential storage objects, only two sites were found to be situated in the favorable geological settings, meaning that the inspected wells drilled through structural traps had a seal at least 20 m thick which was intersected by only a few faults with rather limited displacement. Many more closed structures in the area were tested by exploration wells, but in all other wells, various problems were encountered, including inadequate reservoir properties, inadequate seal or inadequate depth of the identified trap. Analysis was highly affected by the insufficient quality and spatial distribution of the seismic input data, as well as in places with insufficient quality of input well datasets. An initial characterization of identified storage sites was performed, and their attributes were compared, with potential storage object B recognized as the one that should be further developed. However, given the depth and increased geothermal gradient of the potential storage object B, it is possible that it will be developed as a geothermal reservoir, and this brings forward the problem of concurrent subsurface use. Full article