Journal of Asian Earth Sciences最新文献

Rivers adjust their equilibrium profiles to base-level changes induced both by climatic fluctuations and tectonic movements. It is crucial, yet challenging, to differentiate their distinct roles in shaping the evolution of fluvial systems when both forces are involved. In contrast to the broader, regional-scale impact of climatic changes, the various tectonic deformation at local-scale can be recorded as various terrace deformation patterns. The Dongda River, located on the northeastern edge of the Tibetan Plateau, crosses active folds and thrusts, providing a unique opportunity to isolate the effects of climatic and tectonic forces. In this study, we identified five river terraces along Dongda River, designated as T1, T2, T3, T4a, and T4b, from lowest to highest. Radiocarbon and OSL dating results reveal abandonment ages of 4.2 ± 0.3 ka, 6.1 ± 0.5 ka, 12.4 ± 2.5 ka, 16.4 ± 0.2 ka, and 27.4 ± 2.5 ka, showing rhythmic alignment with climatic fluctuations since the late Pleistocene. Elevation profiles of the terraces demonstrate base-level aggradation at the footwall of the Fengle fault between T4a/b and T2, highlighting a tectonically dominated process of river incision at its hanging wall. Differential uplift rates were estimated to be 2.2 ± 0.3 mm/a at the North Qilian Shan hinterland, 1.1 ± 0.2 mm/a in the Huangcheng Basin, 0.2–0.4 mm/a in the Yangxiang Basin, and 1.1 ± 0.2 mm/a within the foreland fold-and-thrust belt of Dahuang Shan, respectively. In contrast, an accelerated incision rate (>1.8 mm/a) has been observed throughout the entire basin since the abandonment of T2, coinciding with the adjustments in the Asian monsoon and westerlies systems since the Mid-Holocene. This study provides insights into the complex interplay between climatic variability and tectonic activity in fluvial systems, enhancing our understanding of how these competing forces have shaped the evolution of the fluvial landscape over time.

There have been many studies conducted on the Eocene source rocks (Shahejie Formation Mbrs 1 and 3) (E₂s₁ and E₂s₃) of the Bozhong Sag, Bohai Bay Basin in East China. However, Oligocene source rocks (Dongying Formation Mbrs 2 and 3) (E₃d₂ and E₃d₃) have also made significant contributions to petroleum accumulations in this region. Their organic matter (OM) enrichment mechanisms, environmental and ecological variations, and laterally variable facies remain subjects of debate, particularly in the lower Dongying Formation Mbrs 2 (E₃d₂^L). Thus, we investigated the geochemical properties, depositional environments, and OM origins of E₃d₂^L and E₃d₃ source rocks from seven prospecting wells in southwestern Bozhong Sag. Our findings indicate that E₃d₂^L source rocks are of poor-to-medium quality, whereas E₃d₃ source rocks are classified as good-to-excellent quality. Notable differences in the geochemical characteristics between E₃d₂^L and E₃d₃ source rocks were observed. Hierarchical cluster analysis identified five genetic organic facies. The E₃d₂^L source rocks comprises facies D2-Ⅰ, D2-Ⅱ, D2-Ⅲ, and D2–D3, whereas E₃d₃ contains facies D3 and D2–D3, with D2–D3 being common to both source rocks. Additionally, an integrated OM enrichment model was established to evaluate Oligocene source rocks. The five genetic organic facies exhibit distinctive differences and some similarities regarding redox conditions, water salinity, and OM origins. Their geochemical characteristics within the same intervals display pronounced lateral heterogeneity from deep source rocks deposits to more marginal water depths. The established model provides guidance for the prediction and exploration of effective Oligocene source rocks in the Bohai Sea and research on the Paleogene and Neogene petroleum systems. Moreover, the integration of biomarkers and hierarchical cluster analysis methods for organic facies analysis has significant implications for predicting of source-rock heterogeneity in other lacustrine rift basins.

The Kachchh paleo-rift basin located in the western India stands out as one of the highly seismic intra-plate regions in the world, which falls under zone-IV (high risk) as per seismic zonation map of India. This study examines morphotectonic landforms within a broad deformation zone of the Kachchh Mainland Fault (KMF) to elucidate its neotectonic evolutionary history and associated seismic hazard. Morphometric analysis along the KMF indicates that approximately 47% of the 2800 km² study area exhibits neotectonic activity. By analyzing changes in strike-parallel and perpendicular river channel steepness through swath profiles, we identified seven distinct segments along the KMF. Our findings suggest diverse ground responses to steepness changes in each segment, which align well with geomorphic and geodetic data. Tectono-geomorphic investigations reveal the KMF as an oblique-slip fault, exhibiting both transtensional and transpressional movements. Optical chronology of tectonic landforms indicates ∼15 deformation episodes spanning the Late Pleistocene at 25 ka, 23 ka, 19.8 ka, 18 ka, 17 ka, and the Early Holocene at 10 ka, 8 ka, and 7 ka. Additionally, three Middle Holocene earthquake events at ∼ 5 ka, 4 ka, and 3 ka, and four Late Holocene earthquake events at ∼ 2 ka, 1.3 ka, and 870 years have been identified. Finally, we present an active fault map of the KMF zone by integrating all available data (geomorphologic, geodetic, and geologic) which will be useful for seismic hazard assessment across the region.

The uplift of the Qinghai-Tibetan Plateau (QTP) is one of the most significant geological events in the Cenozoic era. While most studies have focused on the latitudinal differences in the uplift process of the QTP, there has been scant attention to its longitudinal differentiation. The Miocene epoch is pivotal for understanding both the uplift of the QTP and associated climatic changes. Wildfire events not only record changes in vegetation composition but also reflect climatic fluctuations and their driving forces. However, investigations into the interactions among these factors remain limited. This study aims to explore the coupling between the uplift of the QTP, climatic changes and wildfire frequency (or intensity) from northeastern QTP by analyzing microcharcoal concentrations and length-to-width ratios from the Miocene Youshashan Formation in Wulan County, Qinghai Province. The results indicate that the development of wildfires could be divided into three stages. Compared with the intervals 18–15 Ma and 11–8.7 Ma, the middle stage (15–11 Ma) experienced the highest wildfire frequency. This finding underscores the synchronous and close relationship between wildfire occurrences, the uplift of the QTP, and consequent climatic fluctuations. The ratio of length-to-width of microcharcoal indicates that Miocene wildfires in the Wulan Basin primarily occurred at the transitional zones between forests and grasslands. Moreover, the highest peak of wildfire events at six sites gradually shifted from the northeastern to the northwestern QTP from 18–8.7 Ma. This fact demonstrates spatiotemporal disparities in wildfire events from northern QTP, likely stemming from asynchronous uplifts there.

The South China Sea (SCS) is widely accepted as an active margin that is associated with the subduction of the Paleo-Pacific plate during the Mesozoic. However, the exact location of the subduction or suture zone remains unclear. Understanding the location of the subduction zone is crucial for comprehending the Mesozoic tectonic evolution of the South China Block and the Cenozoic rifting process of the SCS. To clarify the position of the subduction zone and the influences of preexisting structures, we used a multichannel seismic reflection profile to investigate the crustal architecture. The seismic profile reveals a crustal “crocodile” structure that is interpreted as relict subduction in the Chaoshan Depression and a set of south-dipping crust-mantle reflectors related to the initial rifting in the continent–ocean transition (COT) zone. The results indicate that a Mesozoic subduction zone is located at the northeastern margin of the SCS and that preexisting structures (subduction-related structures) facilitated the rifting process. Combined with previous studies on the oceanic plateau collision-accretionary zone of the northern SCS and the Mesozoic accretionary zone in Palawan of the southern SCS, we infer that a section of the suture zone of the Paleo-Pacific plate subduction is preserved at the northeastern SCS margin and that the rifting of the SCS may have initiated at the suture zone.

The correlation between the seismicity and strain rate (SR, in 10^-9/yr) is investigated through a combined Bayesian statistical approach to identify the possible locales of seismic hazard in the Himalaya and adjacent areas. The primary result shows that the maximum number of earthquakes in all magnitude (M_w) classes occur in the moderate 30 – 60 SR class. The Bayesian modelled parameter (µ) value for earthquakes in all four SR classes is 0.1315 (0 – 30), 0.1286 (30 – 60), 0.1386 (60 – 90), and 0.1504 (90 – 180). As the µ value is highest in the SR class (90 – 180), the probability of occurrence of larger magnitude event is more. The probability analysis indicates that the future seismic hazard (M_w > 6.0) will be collocated in the highest SR class (90 – 180) with a probability of 35.10 %. This SR class occupies 15 % of the studied area. However, the other SR classes are equally significant for M_w > 6.0 earthquake where the probability varies between 20.55 % (0 – 30), 21.29 % (30 – 60), and 23.06 % (60 – 90) covering 40 %, 30 %, and 15 % of the studied area respectively.

The Central Asian Orogenic Belt was formed by the subduction to closure of the Paleo-Asian Ocean (PAO). However, it is highly controversial about the closing time of the PAO, especially its middle segment in the northern Alxa orogenic belt (NAOB). In this study, the new and published zircon U–Pb and Hf data for the Carboniferous to Permian sediments across the NAOB have been integrated to reply the above problem. The depositional ages have been constrained as the Carboniferous to Permian by the detrital zircon ages, fossil assemblages and stratigraphic correlation. The Carboniferous sandstones are dominated by the Paleozoic zircons (mainly around 380–510 Ma) with a few Precambrian zircons. The late Cambrian to early Carboniferous zircons with positive to slightly negative ε_Hf(t) values were probably sourced from the orogen itself. The early Paleozoic zircons with slightly to extremely negative ε_Hf(t) values and the late Archean to Paleoproterozoic zircons were likely derived from the surrounding cratonic blocks in the south. For the Permian samples, the Carboniferous to Permian age signal is enhanced. The Permian zircons yield similar age peaks around 278–279 Ma and similar ε_Hf(t) values, and thus shared a similar source. Thus, the Carboniferous to Permian sediments received detritus across the PAO, indicating the closure of the PAO. Subsequently, the NAOB entered into an extensional setting based on the detrital zircon age patterns, rift-related volcanic rocks and basin analysis. Finally, a tectono-paleogeographic reconstruction from the Carboniferous relic sea and marine transgression to Permian marine regression-transgression-regression with crustal extension was proposed.

The Indian-Eurasian convergence has formed the Himalayas, one of the most youthful and dynamic orogeny on Earth, which is characterized by a unique “perfect arc” observed by seismicity, crustal deformation, and topographic relief. However, the presence of a significant topographic descent at the eastern end of the Himalayas, near the Eastern Himalayan Syntaxis (EHS) challenges the existing paradigm. The reason behind such significant topographic difference compared to other regions along the Himalayan mountains is still unclear. Based on the GPS velocity field, we determined the clockwise rotation of the North Indian Block (NIB) relative to the stable India plate with a Euler pole estimation of (89.566 ± 0.06°E, 26.131 ± 0.05°N, 1.34 ± 0.11°/Myr), implying that the NIB has broken away from the stable India plate. By reconstructing the position of the Northeast Indian Block (NIB) based on the Euler pole, we found that the collisional boundary between India and Eurasia is moving southward. Subsequently, a coupled fault model that accounted for continuous motion of fault can effectively match the topographic descent. Our result underscored the significant impact of the NIB rotation on regional geological evolution, an aspect that has received less attention in previous studies.

The Neoproterozoic tectonic correlation between the Central-South Altyn, Qilian, Qaidam, and East Kunlun blocks in northwestern China remains controversial, with competing models favoring separate blocks or a unified single block, and debatable paleo-positions in the Rodinia supercontinent. In this study, we present a systematic provenance study on the late Mesoproterozoic to Neoproterozoic metasedimentary rocks from the South Altyn Tagh. A mica quartz schist sample from the Bashikuergan group yielded a maximum depositional age of 1050 ± 31 Ma. Four paragneiss samples from the Altyn Complex yielded maximum depositional ages of 1106 Ma, 1065 Ma, 1054 Ma, and 870 Ma. Given that the Altyn Complex was intruded by numerous early Neoproterozoic granitoids (ca. 976–900 Ma), we propose that the sedimentary protoliths of the Altyn Complex and the Bashikuergan Group were deposited at two stages, i.e., ca. 1105–975 Ma and after 870 Ma. Provenance tracing indicates that these 1105–975 Ma sediments probably received detritus from the late Mesoproterozoic rocks of Western Australia, East Antarctica, and Central Indian Tectonic Zone in India. In contrast, the detritus of the paragneiss (deposited after 870 Ma) was likely sourced from local regions in the Altyn Tagh orogen. Combined with the comparable magmatic, sedimentary, and tectonic records, we propose that a few microcontinental fragments in northwestern China, including Central-South Altyn Tagh, Qilian, Qaidam, and East Kunlun blocks, constituted a unified block in the early Neoproterozoic and occupied a periphery position of the Rodinia supercontinent with a close paleogeographic affinity to South China and Northwest India.

The Hutuo Group was deposited from 2.14 to 2.0 Ga in Wutai Mountain, North China Craton. This group is composed of the Doucun and Dongye subgroups, which are likely contemporaneous heterotopic facies. The Hutuo Group displays well-known positive to negative drifts of inorganic carbon isotopes, large-scale stromatolitic carbonates, and red beds in epigenetic environments. Twelve storm-deposited lithofacies were identified in the Dongye Subgroup, which changes from sandstones, siltstones, and mudstones of the Qingshicun and lower Wenshan formations to carbonates of the upper Wenshan, Hebiancun, Jian’ancun, Daguanshan, Huaiyincun, Beidaxing, and Tianpengnao formations from bottom to top. The above sedimentary sequence transformation indicates a gradual transformation from terrigenous storm deposits in the Qingshicun and Wenshan formations to endogenous or mixed-source storm deposits in the Hebiancun, Jian’ancun, Daguanshan, and Huaiyincun formations. Additionally, coastal and shallow-marine storm deposits are revealed from sedimentary structures, including hummocky cross-stratification, intraclasts or boulder clays exhibiting radial or chrysanthemum-shaped stacking, and sinuous or torn stromatolites. These storm deposits, occurring with oolitic and stromatolitic carbonates of mid-low latitudes or tropical-subtropical zones, are characterized as tropical storm deposits. Based on reported ages, we propose that such tropical storms started from ca. 2.1 Ga and lasted for over 40 Myr. The long-term storm deposits indicate high temperatures and intense water circulation during the greenhouse climate. A climate change from icehouse to greenhouse is also evident by the extensive distribution of carbonates, evaporates, and organic-rich shales above the glacial diamictites in multi-cratons, and was probably driven by the transformative evolution of the atmosphere.