Search Results (4)

The Carboniferous Yanghugou Formation in the western margin of the Ordos Basin exhibits significant potential for oil and gas exploration. However, due to the influence of complex tectonic activities, there are substantial variations in stratigraphic thickness and depositional environments across the formation. The lack of a systematic source–sink comparative study has resulted in an unclear understanding of sediment sources and paleogeographic patterns, impacting the exploration for hydrocarbon accumulations. We conducted a comprehensive study of the source–sink system characteristics and paleogeography in the research area through field outcrop observations and drilling core sampling. By utilizing detrital zircon U–Pb geochronology and geochemistry, paleocurrent directions, lithofacies types, and sedimentary features, we delve into the understanding of the source–sink systems. Four major source–sink regions in the research area were identified: the Alxa, Yinshan, Alxa–Yinshan mixed and Qilian source–sink regions. The Alxa source–sink region formed a transitional delta-barrier-island sedimentary system. The northern part of the Yinshan source–sink region developed a transitional tidal-controlled delta-tidal-flat sedimentary system, while the southern deep-water area developed a shallow marine to semi-deep marine shelf sedimentary systems. The sediments of Alxa–Yinshan mixed source–sink region were deposited in a transitional tidal-controlled delta-tidal-flat barrier-island system. The Qilian source–sink region is characterized by small tidal-controlled delta-barrier-island system. From the analysis of the source–sink systems, it is inferred that the Alxa Block and the North China Craton had already merged before deposition of the late Carboniferous Yanghugou Formation. The delta sand bodies in the Alxa–Yinshan mixed source–sink region have the highest compositional and structural maturity, the best reservoir performance, and the great exploration potential. Full article

Our research focuses on the reconstruction of turbidity paleocurrents of the Cilento Group in the Cilento area (southern Apennines, Italy). These deposits were formed in the wedge-top basin above the oceanic Ligurian Accretionary Complex, the early orogenic wedge of the southern Apennines. The Cilento Group succession, whose age ranges between the uppermost Burdigalian and lowermost Tortonian, consists of a thick pile of sandstones, conglomerates, marls and pelites grouped in two formations (Pollica and San Mauro Fms). We retrieved information on the turbidity current directions through sedimentary features such as flute and groove casts, flame structures and ripple marks. The aim of this study is to shed light on the early tectonic evolution of the southern Apennines by reconstructing the geometry of this basin, the source areas that fed it and the paleogeography of the central Mediterranean area in the Miocene. We analyzed 74 sites in both formations and collected 338 measurements of paleocurrent indicators. Because the succession was affected by severe thrusting and folding, every paleocurrent measurement was restored, reinstating the bedding in the horizontal attitude. Results indicate a complex pattern of turbidity current flow directions consistent with a basin model fed by a spectrum of sources, including recycled clasts from the Ligurian Accretionary Complex, Calabria–Peloritani Terrane and the Apennine Platform units and volcaniclastics from the synorogenic volcanoes located in the Sardinia block. Full article

The Ordos Basin’s southern part is a composite zone made up of numerous continental blocks and has long been influenced by surrounding tectonism. However, only a few studies have investigated the existence of southern provenance supply and the basin’s southern boundary in the Middle Jurassic Zhiluo Formation. Based on sandstone detrital zircon U-Pb dating and zircon rare earth element analyses, net-sand ratio maps, paleocurrent direction and the field outcrop survey, this study establishes the source area and boundary of the Zhiluo Formation in the southern basin, and discusses the tectonic events. The study shows that the four main age peaks in the detrital spectra occurs at 2283 Ma, 1788 Ma, 432.5 Ma and 218.7 Ma, with a few of the zircons dated at 794.5–1235.2 Ma. The North Qilian orogenic belt (N-QLOB), the western part of the North Qinling orogenic belt (NQOB), and the southern margin of the North China Block (SNCB) contributed to the provenance. According to an integrated analysis of the provenance and tectonic background of continental blocks in the basin’s southern margin, the boundary of the basin in the depositional period of the Zhiluo Formation should reach the N-QLOB in the southwest, the NQOB in the south, and the Sanmenxia–Lushan fault belt in the southeast. On the basis of the aforementioned findings, the tectonic evolution of the continental blocks at the southern periphery of the Ordos Basin was restored. Full article

Analysis of lithofacies, paleoflow directions, and sandstone petrography of upper Paleocene-lower Eocene paralic and continental sediments exposed along the transpressional suture zone of the western margin of the Indian plate indicate that the process of deformation and uplift of the carbonate shelf in this area had started by late Paleocene time. This tectonic uplift and deformation is documented by: (1) an overall shallowing upward synorogenic sequence of sediments, (2) proximal conglomerate facies (consisting of lower Paleocene and Mesozoic clasts) dominating in the western part of the study area and distal facies of sandstone and shale dominating in the eastern part of the study area, (3) the existence of an unconformity of late Paleocene-early Eocene age in the Quetta and Kalat regions, (4) paleocurrent directions in deltaic and fluvial deposits indicating southeastward flowing sediment dispersal paths during late Paleocene-early Eocene time, which is opposite to that found in the late Cretaceous, suggesting a reversal in the depositional slope of the Cretaceous shelf, and (5) petrographic study of sandstones indicating a collision suture/fold thrust belt provenance. This episode of uplift and deformation could be the result of India-Arabian transpression with associated ophiolite obduction or, more likely, to represent the local response to initial India-Asia contact. The unroofing pattern and uplift geometry of the western Indian shelf suggests that this tectonism first started in the southern part of the study area (Kalat-Khuzdar area) during the late Paleocene-early Eocene and proceeded northward in a time-transgressive fashion. Full article