Sedimentary and Source-to-Sink Evolution of Intracontinental Basins: Implications for tectonic and Climate Evolution in the Late Mesozoic (Southern Junggar Basin, NW China)

Sedimentary investigations, petrography, heavy mineral and conglomerate component analyses, and detrital zircon U-Pb geochronology were conducted to reconstruct the sedimentary and source-to-sink evolution of the Southern Junggar Basin, an intracontinental basin in the late Mesozoic. A paludal deltaic environment evolved into a fluvial environment, and abruptly prograded into alluvial fan and aeolian environments in the Late Jurassic, which was replaced by fan deltaic and lacustrine environments in the Early Cretaceous. Three source-to-sink systems were identified, according to different source-to-sink system features. In the northern piedmont of the Tianshan Orogenic Belt, the North Tianshan Orogenic Belt mainly provided sediments in the Late Jurassic. The North Tianshan and Central Tianshan Orogenic Belt both supplied sediments in the Early Cretaceous. In the northern piedmont of the Bogda Orogenic Belt, the Bogda Orogenic Belt was constantly the primary provenance, and the Tianshan Orogenic Belt also provided sediments. Sediment recycling occurred in the basin margin in the Late Jurassic and more metamorphic rocks were denudated in the Early Cretaceous. The source-to-sink system shrank in the Late Jurassic and expanded in the Early Cretaceous. This source-to-sink evolution and the conglomerates in the Kalazha Formation with seismite structures responded to the aridification in the Late Jurassic, the uplift of the Bogda and Tianshan Orogenic Belts in the Late Jurassic, and the exhumation of the Bogda and Tianshan Orogenic Belts in the Early Cretaceous.

Mesozoic–Cenozoic Uplift/Exhumation History of the Qilian Shan, NE Tibetan Plateau: Constraints From Low-Temperature Thermochronology

The Qilian Shan, which is located along the northeastern margin of the Tibetan Plateau, plays a key role in understanding the dynamics of the outward and upward growth of the plateau. However, when and how tectonic deformation evolved into the geographic pattern which is currently observed in the Qilian Shan are still ambiguous. Here, apatite fission track (AFT) thermochronology and sedimentology were conducted to interpret the low-temperature tectonic deformation/exhumation events in well-dated Late Miocene synorogenic sediment sequences in the Xining Basin, which is adjacent to the southern flank of the Qilian Shan. These new low-temperature thermochronological results suggest that the Qilian Shan experienced four stages of tectonic exhumation during the late Mesozoic–Cenozoic. The Late Cretaceous exhumation events in the Qilian Shan were caused by the diachronous Mesozoic convergence of the Asian Plate and Lhasa Block. In the early Cenozoic (ca. 68–48 Ma), the Qilian Shan quasi-synchronously responded to the Indian–Asian plate collision. Subsequently, the mountain range experienced a two-phase deformation during the Eocene–Early Miocene due to the distal effects of ongoing India–Asia plate convergence. At ca. 8 ± 1 Ma, the Qilian Shan underwent dramatic geomorphological deformation, which marked a change in subsidence along the northeastern margin of the Tibetan Plateau at that time. Our findings suggest that the paleogeographic pattern in the northeastern Tibetan Plateau was affected by the pervasive suture zones in the entire Qilian Shan, in which the pre-Cenozoic and Indian–Asian plate motions reactivated the transpressional faults which strongly modulated the multiperiodic tectonic deformation in northern Tibet during the Cenozoic. These observations provide new evidence for understanding the dynamic mechanisms of the uplift and expansion of the Tibetan Plateau.

Exploration Process and Genesis Mechanism of Deep Geothermal Resources in the North Jiangsu Basin, East China: From Nothing to Something

Geothermal resources, as an important member of clean renewable energy, of which the exploration, development, and utilization of geothermal resources, especially deep geothermal resources, are of great significance for achieving carbon peaking and carbon neutrality. Taking the North Jiangsu Basin (NJB) as an example, this paper reviews the exploration process of deep geothermal resources in the basin and presents the latest results. The study shows that the NJB is a typical “hot basin” with an average heat flow value of 68 mW/m2. In this region, the deep geothermal resource favorable areas in the NJB are mainly distributed in the depressions, in particular those near the Jianhu uplift, i.e., the Yanfu depression and the Dongtai depression. In addition, the genesis mechanism of the deep geothermal resource favorable area in the NJB is best explained by the “two stages, two sources” thermal concentration, that is, “two stages” means that the transformation of the lithospheric thermal regime are caused by the late Mesozoic craton destruction in East China, and the Cenozoic lithospheric extension; these two tectono-thermal events together lead to the deep anomalous mantle-source heat (the first source), and the upper crustal-scale heat control is mainly caused by thermal refraction (the second source). Overall, this case study underlines new ideas of understanding the geothermal genesis mechanism in East China, which can guide for the exploration and development of deep geothermal resources at the basin scale.

CHANGE IN THE GLOBAL DENUDATION BASE IN THE LATE MESOZOIC AND CENOZOIC AND ITS INFLUENCE ON THE FORMATION OF GEOMORPHOLOGICAL STRUCTURE IN AREAS WITH VARIOUS NEOTECTONIC REGIMES

The data on regional geology, stratigraphy and geomorphology accumulated by now permit one to compile a reliable and fairly complete model of changes in the World Ocean level in the interval from the Cretaceous period to the present. Global changes in the level of the World Ocean are primarily associated with slow and prolonged (107–108 y.) manifestations of plate tectonics (spreading of the ocean floor and decrease in the area of continents against the background of the formation of mountain relief due to collision processes at their borders) and faster, but short-term (103–106 y.) processes associated with the withdrawal of large amounts of water during the formation of large continental ice sheets and its return to the World Ocean during interglacial periods. The impact of the tectonic factor throughout the entire period under review was unidirectional, but uneven and led to intermittent decrease in the World Ocean level from 250–300 m above the present level to the current level, taken as 0 m. Prolonged periods of stable position of the World Ocean level in the second half of the Cretaceous, Paleogene and Early Neogene at 300, 250, 200 and 150 m led to the formation of regional peneplanation planes near these levels. Moreover, younger surfaces have never completely cut off the previous, higher level, leaving its relics in the form of table elevations on the surface of the younger peneplain. In tectonically passive areas, the hypsometric position of these geomorphological elements and associated sediments has stratigraphic significance, allowing the researchers to estimate their age, and in the case of their displacement, to evaluate the age and amplitudes of neotectonic movements.