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The Lower Eocene siliciclastics in the northern steep slope of the Dongying Depression, Bohai Bay Basin, are described and interpreted as subaqueous fans associated with a thick succession of lacustrine deposits. As a whole, the complicated interplay between the depositional process of these lacustrine fans and slope topography is underrepresented. An integrated study of cores, well-logs, seismic sections and seismic attribute maps have enabled the identification of three types of subaqueous fans at the root of slope, including channelized near-shore subaqueous fans, non-channelized near-shore subaqueous fans and slump turbidity fans. Channelized near-shore subaqueous fans, characterized by straight or slightly curved multi-distributary channels in N-S direction, are mainly filled with conglomerates or pebbly sandstones interbedded with mudstones. In contrast, non-channelized near-shore subaqueous fans are lobate in plane-view, lacking major channels. Slump turbidity fan typically shows an elongate shape with a single, straight-to-weakly meandering channel fronted by terminal splay. Spatial distribution and the types of these subaqueous fans varied through time along the strike of steep slope during the Eocene Es4s depositional time. Slope geomorphology from which the sediments were derived has been reconstructed. The steep slope, evolved from the joining points of extensional fault scarps, preserves numerous gullies incised downdip the whole slope. These gullies, acting as conduits for transporting sediments through the steep slope into the lacustrine basin, are downslope - oriented, ca 4 km long, ca 1 km wide and

Investigation of major unconformities and large-scale palaeo-uplifts that developed during basin deformation is key in determining the geodynamic setting and hydrocarbon accumulation. Based on the integral analysis of seismic, logging, and outcrop data, the distribution and erosion amounts of Mesozoic major unconformities, the uplifts of the Tabei Uplift and the geodynamic setting in the Kuqa–Tabei region of the Tarim Basin are documented in this study. The Tabei Uplift underwent four stages of uplifts, resulting in four regional angular unconformities and significant changes in palaeo-geomorphology. The deformation occurring at the end of the Permian is characterised by the uplift in the Midwest and the development of an angular unconformity (TT) with maximum erosion thickness of 1200 m. Another deformation occurred at the end of the Triassic, leading to significant uplift of the palaeo-uplift and producing an extensive angular unconformity (TJ) with maximum denudation thickness of 400 m. The end-Jurassic deformation resulted in another uplifting along the palaeo-uplift and generated a regional unconformity (TK) with maximum erosion thickness of 500 m. The Late Cretaceous deformation is characterised mainly by the development of the Wensu Palaeo-uplift in the western margin of the study area. The associated angular unconformity (TE) has a limited distribution mainly along the palaeo-uplift with maximum erosion thickness of 300 m. Four stages of uplifts are attributed to the Palaeo–Tethys oceanic closure; the Qiangtang collision; the Lhasa collision; and the Kohistan collision, respectively. Triangular unconformity belts in the paleo-uplift slope area are favourable for petroleum accumulation.

The distribution and erosional features of the Paleozoic major tectonic unconformities in the Tarim Basin, and their genetic relation to the development of paleo-uplifts as well as the evolution of geodynamic settings, are documented in this paper based on the integral analysis of seismic, drilling, and outcrop data. During the Paleozoic, the Tarim Basin underwent three major tectonic deformation stages, which resulted in three angular unconformities and in significant changes in basin geomorphology and paleogeography. The tectonic deformation at the end of the Middle Ordovician was characterized by development of the southern central paleo-uplift, the northern depression, and the southeastern Tangguzibasi depression in the basin. The thickest denudation belts of the unconformity ( T g5-2 ) are distributed mainly along the thrust structural highs. A stronger deformation event took place at the end of the Late Ordovician and formed a huge uplift along the southwestern and southeastern basin margins and the western part of the Tabei uplift along the northern basin margin, producing an extensive angular unconformity ( T g5 ) with maximum erosion thickness of 1500–2000 m. This tectonic event resulted in an abrupt change in overall geography of the basin, from a deepwater marine environment at the late stages of the Late Ordovician to a littoral and neritic basin in the Early Silurian. The deformation that occurred at the end of the Middle Devonian was the strongest in the Paleozoic. It generated the most widespread angular unconformity ( T g3 ) within the basin and led to extensive erosion, with maximum denudation thickness of 3000–5000 m in the northern and northeastern parts of the basin. The topography of the basin during the late Devonian was characterized by a high in the northeast and a low in the southwest, forming an embayment basin opening to the southwest during the Early Devonian to Carboniferous. The transgression in general from southwest to northeast deposited extensive coastal sandstones onlapping the erosion-leveled unconformity ( T g3 ). Comparative analysis of uplifting in the basin with the regional tectonic setting shows that deformation that took place during the three periods was related to the evolution of the paleo-oceanic plates and the orogenesis around the basin. The closure of the North Kunlun Ocean and subsequent collision is suggested to be the main cause for the development of the central paleo-uplift at the end of the Middle Ordovician and the strong uplift and erosion of the southwestern and southeastern basin margin at the end of the Late Ordovician. The large-scale uplift and denudation of the northern part of the basin, including the Tabei–Kongquehe uplift belt, as well as the folding and hinging of the Manjiaer depression, was coeval with, and more related to, the subduction and collision of the South Tianshan orogenic belt and the Altyn trench-arc-basin system at the end of the Middle Devonian.

Black shales and thin-bedded cherts in the basal Cambrian are widespread worldwide and they carry important information on the formation of sedimentary basins and on the tectonic history. We studied the geochemical signatures of the early Cambrian black shales and bedded cherts from the Northern Tarim Basin, China, with the objectives of understanding the depositional setting of these rocks and inferring the tectonic history in the region. Twenty two black shales, ten cherts, and two nodular phosphorites were collected from two outcrops at Xiaoerbulake and Sugaitebulake in the Northern Tarim Basin, spanning vertical sections of 8.8 and 7.5 m, respectively. A suite of techniques, including field investigations, X-ray diffraction, electron microscopy, trace element, rare earth element (REE), and isotope geochemistry, were employed to characterize the geochemical signatures of these rocks. Field evidence indicates that the black shales and bedded cherts are over- and underlain by dolomites, suggesting a shallow marine depositional environment. Mineralogical and trace element data suggest that the Tarim black shales and cherts were deposited in a suboxic continental shelf environment, and hydrothermal activity may have extracted certain trace elements from mafic continental crust and concentrated them in the sedimentary basin. REE characteristics for the cherts are very similar to those that are known to be deposited in pelagic ocean floor settings, suggesting that the hydrothermal fluids may be derived from the infant southern Tianshan Ocean in the north of the Tarim Basin. Os isotope signatures at the time of deposition (187Os/188Osi = 1.1–2.7) are typical of crustal signatures, and the radiogenic Os isotope signatures rule out the mantle as a possible source of Os and other metals. A positive correlation between 187Os/188Os and eNd is consistent with upper crust-derived basin sediments that contain a variable contribution of hydrothermal fluids possibly derived from ancient mafic continental crust. These trace element, REE, and isotope systematics collectively suggest that incorporation of hydrothermal fluids derived from ancient, mafic continental crust combined with deposition in relatively reducing conditions may have controlled the chemical and isotopic compositions of these rocks. We infer that the hydrothermal fluid was carried to the continental shelf by upwelling during the initial stages of formation of the southern Tianshan Ocean, where the fluid interacted with thinned, mafic crustal basement lithologies and was subsequently incorporated into the black shales and bedded cherts in the Northern Tarim Basin. This study provides important geochemical evidence for the creation of the Tianshan Ocean, which is a result of break-up of the Rodinia Supercontinent during the early Cambrian.