Journal of Earth Science最新文献

Articulated natural assemblages contain direct evidence of the element numbers, morphologies, positions and structures for reconstructing the feeding apparatuses of conodont animals, but these kind of materials are very rare in fossil records. Here we report ten new conodont natural assemblages from Member II of the Guanling Formation in Luoping County, eastern Yunnan Province, southwestern China. These assemblages were obtained from the fossil-bearing layers of the Luoping Biota, dated to the early Middle Triassic Anisian stage (Pelsonian substage). These fossiliferous laminated limestones mainly consist of calcites and dolomites, with platy clay minerals and pyrites as subordinate components, indicating that the conodont assemblages were preserved in a lower energy and anoxic sedimentary environment. The new natural assemblages preserve the primary collapse orientations of the Nicoraella feeding apparatus from the Luoping Biota, showing the relative original positions of the S, M and P elements, that could be further used to refine the architecture of this apparatus in space variable M elements and the position unclear P₁ elements. Integrating previously reported three-dimensional and bilaterally symmetrical fused clusters, we statistically analyze the size of the positional homogenous elements within different sized materials, in particular S₄, S₃, or S₂ elements, indicates that elements ontogenic changes do not affect the apparatus architecture. Architecture of Nicoraella apparatus remains stable in the process of ontogeny, so our reconstructed model is credible. It is the first time that ample types of materials have been used to restore a conodont apparatus within one genus, namely natural assemblages (articulated and disarticulated), fused clusters (articulated, disarticulated, compressed, and relatively three-dimensional), and abundant discrete elements, respectively. These materials together record the most complete information on architecture in the gondolelloid apparatuses, thus enabling us to reconstruct a reliable fifteen-element apparatus and propose it as a standard template for gondolelloid apparatus reconstruction.

The granites of ambiguous geodynamic mechanism in the Qin-Fang tectonic belt (SW China) were studied in detail based on petrological, element geochemical, zircon U-Pb geochronological, and Hf isotopic data. LA-ICPMS U-Pb analyses on zircon yield ages of 248–245 Ma for the granites from the Qin-Fang tectonic belt. The geochemical data show that they are high-K, calc-alkaline, and peraluminous series. Their ε_Hf(t) values are from −14.01 to −7.75 with two-stage model ages of 1.74–1.43 Ga. These data, integrated with low Al₂O₃/TiO₂, Rb/Sr, Rb/Ba, and (Na₂O + K₂O)/(FeO^T + MgO + TiO₂) ratios, and high CaO/Na₂O ratios for the granite, suggest an origin from psammite source which was contaminated by mantle-derived components. These observations, in combination with the age data and stratigraphic records in the Jinshajiang, Ailaoshan, and Hainan Island areas suggest that the granites were formed in a post-collision tectonic setting. The Qin-Fang tectonic belt was likely a branched ocean basin of the eastern Paleo-Tethys.

The Niutitang Formation in the South China Block might be a source of hydrocarbon as it contains an enormous quantity of organic matter. Black rock of the Early Cambrian Niutitang Formation is widely distributed in the Yangtze region, but detailed geochemical understanding of it is still emerging. This research discusses the detailed geochemical characteristics of the Niutitang Formation to reconstruct the paleoenvironmental conditions, employing total organic carbon (TOC) content, major, trace, and rare earth element data. For this purpose, black rock specimens of the Niutitang Formation from two outcrop sections were utilized for geochemical characterization, and the results compared with another eight sections from the South China Block. The average total organic carbon in these sediments is significantly higher (5.80 wt.%). In the platform region, lower quantities of TOC indicate a poor potential to produce hydrocarbons. At the same time, significantly higher TOC is observed in the deep shelf and slope sediments, indicating a significant potential to produce hydrocarbons. The average Ce, Eu and Y anomalies from both Longbizui and Sancha sections studied are 0.74, 0.86, 1.77, 1.07, and 1.19, 1.30, respectively. The chemical index of alteration (CAI) throughout the Yangtze block is higher (averaging 71.32) than that of Post Archean Australian Shale (PAAS 69), indicating a moderately weathered source of the Niutitang Formation relative to PAAS. As the sediments are moderately weathered, this suggests these rocks might have been derived from felsic rocks, mainly granite-granodiorite. The normalization of REEs in the black rocks reveals a reduction of light REEs with increase in heavy REEs enrichment. Similarly, a positive Eu anomaly, negative Ce anomaly, and a moderate Y/Ho (34.61) are clues to a hybrid depositional mechanism associated with hydrothermal action and terrigenous input. These anomalies are also evidence of upwelling in the paleo-ocean and mixing of organic matter, which created anoxic bottom water during the deposition of the Niutitang Formation in the basin and upper oxic water conditions before deposition. The main controlling factors for the distribution of rare earth elements in these black rocks of the Niutitang Formation are pH, terrigenous input, source rock composition, tectonism, an upwelling mechanism, and hydrothermal activity.

Mountain Excavation and City Construction (MECC) represents a prominent anthropogenic endeavor aimed at facilitating urban expansion in the Loess Plateau of China. It is important to comprehend the long-term settlement behavior at MECC engineering sites to effectively assess the project’s success in reshaping landscapes and expanding urban areas. In this study, a typical MECC project, specifically the upstream area of the Liujiagou Valley within the new district of Yan’an City, is selected as a case study to investigate long-term settlement characteristics. The research involved conducting creep tests on soil samples with varying dry densities and moisture content and continuous in-situ monitoring of ground surface settlement at 17 specific points. Furthermore, a numerical model was developed and calibrated using the in-situ monitoring data to predict the long-term settlement. The findings reveal that an increase in soil dry density and a decrease in soil water content contribute to reduced deformation. Notably, settlement primarily manifests within the filled areas, with greater soil thickness exacerbating settlement effects. Over time, cumulative settlement exhibits a progressively diminishing rate of deformation until it attains a stable state. These results provide insights for assessing the long-term stability of MECC projects, facilitating decision-making in future endeavors within this region.

The residual oil in the fluvial reservoir of Gudong Oilfield is still widely developed even after decades of development. In order to explore the remaining oil in the subsurface fluvial reservoir, we need to have a better understanding on fluvial sandbody characteristics. This paper aims to demonstrate how to quantify anatomy on meandering fluvial architecture. Sedimentologic data from core descriptions of Guantao Formation in Gudong Oilfield were used to identify architectural elements. The upper Guantao Formation consists of ten lithofacies composing five different types of architectural elements. By integrating the available core, well logs, and seismic data, the fluvial sandbody distribution was analyzed. To characterize the fluvial channel geomorphology, we used seismic inversion to explore the stratigraphic correlation and stacking patterns of different channels, and the sandbody isopach map was obtained by the sandbody thickness in each layer. The architectural elements distribution in the plane was mapped by the sandbody isopach map and its profile characteristics. According to the investigation of meandering fluvial outcrops, subsurface meandering fluvial seismic geomorphology, and modern river morphology, the upstream-bar portions are always eroded because of the downstream channel migration. Statistics on the morphometric parameters (bar width/looplength, upstream deflection angle, downstream deflection angle, etc.) of modern meandering river (Ob River) were obtained from the Google Earth. It is found that the bar width/looplength and upstream deflection angle, upstream deflection angle and downstream deflection angle in modern meandering river have a good relationship, and we can have a quantitative architectural characterization on the point bar. This study quantified lithofacies thickness and proportion in different architectural elements of Guantao Formation, which ensures a high resolution anatomy on the small scale architecture. By using this method, the lithofacies proportion in each architectural element was computed, and through the statistics of architectural elements proportion in the Gudong Oilfield, the different lithofacies proportions in the block 6 can be computed.