Estimating aboveground biomass of the mangrove forests on northeast Hainan Island in China using an upscaling method from field plots,UAV-LiDAR data and Sentinel-2 imagery     

《International Journal of Applied Earth Observation and Geoinformation》2020

The mangrove forests of northeast Hainan Island are the most species diverse forests in China and consist of the Dongzhai National Nature Reserve and the Qinglan Provincial Nature Reserve. The former reserve is the first Chinese national nature reserve for mangroves and the latter has the most abundant mangrove species in China. However, to date the aboveground ground biomass (AGB) of this mangrove region has not been quantified due to the high species diversity and the difficulty of extensive field sampling in mangrove habitat. Although three-dimensional point clouds can capture the forest vertical structure, their application to large areas is hindered by the logistics, costs and data volumes involved. To fill the gap and address this issue, this study proposed a novel upscaling method for mangrove AGB estimation using field plots, UAV-LiDAR strip data and Sentinel-2 imagery (named G∼LiDAR∼S2 model) based on a point-line-polygon framework. In this model, the partial-coverage UAV-LiDAR data were used as a linear bridge to link ground measurements to the wall-to-wall coverage Sentinel-2 data. The results showed that northeast Hainan Island has a total mangrove AGB of 312,806.29 Mg with a mean AGB of 119.26 Mg ha⁻¹. The results also indicated that at the regional scale, the proposed UAV-LiDAR linear bridge method (i.e., G∼LiDAR∼S2 model) performed better than the traditional approach, which directly relates field plots to Sentinel-2 data (named the G∼S2 model) (R² = 0.62 > 0.52, RMSE = 50.36 Mg ha⁻¹<56.63 Mg ha⁻¹). Through a trend extrapolation method, this study inferred that the G∼LiDAR∼S2 model could decrease the number of field samples required by approximately 37% in comparison with those required by the G∼S2 model in the study area. Regarding the UAV-LiDAR sampling intensity, compared with the original number of LiDAR plots, 20% of original linear bridges could produce an acceptable accuracy (R² = 0.62, RMSE = 51.03 Mg ha⁻¹). Consequently, this study presents the first investigation of AGB for the mangrove forests on northeast Hainan Island in China and verifies the feasibility of using this mangrove AGB upscaling method for diverse mangrove forests.  相似文献   

Zircon provenances provide paleogeographic constraints on models reconstructing the Paleoproterozoic Columbia Supercontinent     

《Gondwana Research》2020

Paleoproterozoic orogens of the North Australian Craton are related to the assembly of the Columbia Supercontinent. The roles of the distinct orogens in the Paleoproterozoic craton amalgamation are poorly understood due to the lack of surface exposure. The age and isotopic systematics of detrital zircon grains hosted in Paleoproterozoic sedimentary sequences are used to unravel the geological history of the craton, in terms of paleogeography and tectonic setting. The oldest (Early Paleoproterozoic) metasedimentary units are characterised by detrital zircon ages peaking at ca. 2500 Ma. The zircon ε_Hf values show large variations in the different orogens and range from −18 to +6. The overlaying youngest turbiditic units show minor accumulation of Archean detritus. Units from apparently different metasedimentary sequences have a major detrital zircon age population at ca. 1865 Ma, and a relatively restricted range of zircon ε_Hf values between −7.3 and +2.6. The isotopic distinctiveness of the oldest units is attributed to local variations in the depositional environment, probably due to horst-graben architecture of the early Paleoproterozoic basin. The youngest turbiditic units blanketed this early horst-graben architecture and in part have a local provenance. Potential detritus sources include South Australian Craton, Dharwar Craton and Aravalli-Lesser Himalayan terrains in India, South China, and Madagascar (Africa). This finding indicates that these regions might have been connected before the Columbia Supercontinent was formed. The ubiquitous ca. 2500 Ma magmatic event records the assembly of these cratonic fragments in a previous supercontinent called Kernorland. In addition, the data do not support a proximity of the North Australian Craton with the North China Block, Western Laurentia (North America), and Kaapvaal Craton (Africa) during Columbia amalgamation.  相似文献   

Weakening laws of slip zone soils during wetting–drying cycles based on fractal theory: a case study in the Three Gorges Reservoir (China)     

Miao  Fasheng  Wu  Yiping  Li  Linwei  Tang  Huiming  Xiong  Feng 《Acta Geotechnica》2020,15(7):1909-1923

Acta Geotechnica - Slip zone soils play a crucial role in the evolution of landslides. In this paper, slip zone soils of the Huangtupo Landslide in the Three Gorges Reservoir area, which is an...  相似文献   

基于分布式控制力矩陀螺的水下航行器轨迹跟踪控制   总被引：2，自引：0，他引：2  

黄道敏  徐瑞昆  唐国元  冯雷  刘智  徐国华 《海洋工程》2018,36(6):69-76

基于控制力矩陀螺群(CMGs)的水下航行器具有低速或零速机动的能力。采用基于分布式CMGs的水下航行器方案,并研究其水平面的轨迹跟踪控制问题。通过全局微分同胚变换将非完全对称的动力学模型解耦成标准欠驱动控制模型,并根据简化的模型构建其轨迹跟踪的误差动力学模型,将轨迹跟踪控制问题转化为误差模型镇定问题。基于一种分流神经元模型和反步法设计了系统的轨迹跟踪控制律,该控制器不需要对任何虚拟控制输入进行求导计算,且能确保跟踪误差的最终一致有界性。仿真结果表明该控制器能够实现在不依赖动力学参数先验知识的情况下对光滑轨迹的有效跟踪。  相似文献   

Zircon U–Pb ages and Hf isotope compositions of migmatites from the North Qinling terrane and their geological implications     

Q. Liu  Y.‐B. Wu  H. Wang  S. Gao  Z.‐W. Qin  X.‐C. Liu  S.‐H. Yang  H.‐J. Gong 《Journal of Metamorphic Geology》2014,32(2):177-193

Migmatites are predominant in the North Qinling (NQ) orogen, but their formation ages are poorly constrained. This paper presents a combined study of cathodoluminescence imaging, U–Pb age, trace element and Hf isotopes of zircon in migmatites from the NQ unit. In the migmatites, most zircon grains occur as new, homogeneous crystals, while some are present as overgrowth rims around inherited cores. Morphological and trace element features suggest that the zircon crystals are metamorphic and formed during partial melting. The inherited cores have oscillatory zoning and yield U–Pb ages of c. 900 Ma, representing their protolith ages. The early Neoproterozoic protoliths probably formed in an active continental margin, being a response to the assembly of the supercontinent Rodinia. The migmatite zircon yields Hf model ages of 1911 ± 20 to 990 ± 22 Ma, indicating that the protoliths were derived from reworking of Palaeoproterozoic to Neoproterozoic crustal materials. The anatexis zircon yields formation ages ranging from 455 ± 5 to 420 ± 4 Ma, with a peak at c. 435 Ma. Combined with previous results, we suggest that the migmatization of the NQ terrane occurred at c. 455–400 Ma. The migmatization was c. 50 Ma later than the c. 490 Ma ultra‐high‐P (UHP) metamorphism, indicating that they occurred in two independent tectonic events. By contrast, the migmatization was coeval with the granulite facies metamorphism and the granitic magmatism in the NQ unit, which collectively argue for their formation due to the northward subduction of the Shangdan Ocean. UHP rocks were distributed mainly along the northern margin and occasionally in the inner part of the NQ unit, indicating that they were exhumed along the northern edge and detached from the basement by the subsequent migmatization process.  相似文献   

Deciphering the impact of land-uses on terrestrial organic matter and mercury inputs to large boreal lakes of central Québec using lignin biomarkers     

《Applied Geochemistry》2014

To evaluate watershed impacts of anthropogenic activities on terrestrial organic matter (TOM) and total mercury (THg) dynamics in large boreal lake ecosystems, we studied sediment cores retrieved in eight large lakes of Québec (Canada). Two lakes with pristine watersheds were considered as reference lakes and six lakes with watersheds affected by different types of anthropogenic activities (e.g. logging and/or mining activities) were used to illustrate the influence of land-use on TOM and Hg cycling in lakes. A Geographical Information System (GIS) approach was used to correlate the evolution of anthropogenic land-uses from 1979 to 2010 (e.g. logging and mining activities) to TOM and THg contents measured in sediment cores. In each core, THg concentrations gradually increased over the recent years. Using lignin biomarkers, we noticed that the presence of both intense logging and mining activities in the watershed does not necessarily correspond to noticeable changes in the relative amount of terrestrial organic matter (TOM) exported from the watershed to the sediments and by extension to the level of THg measured in sediments. Apparently large-scale watersheds show some “buffering” capacity to land-use disturbance.  相似文献   

Determination of regional soil geochemical baselines for trace metals with principal component regression: A case study in the Jianghan plain,China     

《Applied Geochemistry》2014

The soil geochemical baseline is an important index in environmental assessment. Detailed baseline studies are necessary in large areas with complex geological settings, landforms and soil types. The Jianghan plain, a major industrial and agricultural region located in central China, has a soil geochemical baseline that has yet to be fully defined. The objective of this paper is to study the baseline of Cd, Pb and Zn in the topsoil of the Jianghan plain in a subarea using principal component regression (PCR). A total of 9030 samples were collected from the surface layer, and 2 soil profiles and 2 sedimentary columns were sampled near the Yangtze and Han rivers. Fifty-two elements and two parameters were analyzed. Data processing and the creation of spatial distribution maps of the elements were performed using MapGIS, R and SPSS software. The results show that the distributions of Cd, Pb and Zn are mainly controlled by parent material, drainage system and soil type. The study area is divided into 3 subareas, with factors reflecting the physico-chemical characteristics of the soil using factor analysis (FA). The geochemical baseline model is established in every subarea to predict the Cd, Pb and Zn values using principal component regression analysis (PCR); the exceptional values (as a result of anthropogenic input or mineralization) are distinguished by residuals (γ); and the natural background values and anthropogenic contributions are clearly distinguished. Therefore, the PCR method in these subareas is objective and reasonable, and the conclusion provides effective evidence of exceptional high values for further environmental assessment.  相似文献   

The fault-controlled skarn W–Mo polymetallic mineralization during the main India–Eurasia collision: Example from Hahaigang deposit of Gangdese metallogenic belt of Tibet     

《Ore Geology Reviews》2014

The Hahaigang W–Mo polymetallic skarn deposit is located in the central-eastern part of Gangdese tectono-magmatic belt in Lhasa terrane, Tibet. The deposit was discovered in 2007 with currently proven 46 million tons of WO₃ ores, 12 million tons of Mo ores, and 1.31 million tons of combined Cu–Pb–Zn ores, at an average grade of 0.20% WO₃, 0.07% Mo, 0.026% Cu, 0.49% Pb, and 3.1% Zn. Ore bodies occur in veins or disseminations, and are confined within the NE-striking Dalong fault zone which is hosted by the Lower-Permian Pangna Group of dominantly quartz sandstone and slate. Several granitic plutons are exposed in the area or known from drill-holes. Ages of these granitic plutons are determined by using zircon U–Pb LA–ICP–MS method. For example, the biotite monzogranite yields a ²⁰⁶Pb/²³⁸U–²⁰⁷Pb/²³⁸U concordia age of 58.66 ± 0.90 Ma and a weighted mean ²⁰⁶Pb/²³⁸U age of 57.02 ± 0.42 Ma. The granite porphyry yields a ²⁰⁶Pb/²³⁸U–²⁰⁷Pb/²³⁸U concordia age of 109.1 ± 8.9 Ma and a weighted mean ²⁰⁶Pb/²³⁸U age of 114.0 ± 2.6 Ma. The biotite monzogranite yields a weighted mean ²⁰⁶Pb/²³⁸U age of 56.1 ± 1.1 Ma. Re–Os isochron age of 63.2 ± 3.2 Ma from 5 molybdenite samples collected from the W–Mo skarn ores is also obtained in this study. The zircon U–Pb and molybdenite Re–Os geochronological data suggest that the W–Mo mineralization was not temporally associated with any of the dated igneous plutons. However, the molybdenite Re–Os age of 63.2 ± 3.2 Ma indicates that the W–Mo mineralization might have occurred during the main India–Eurasia collision that was initiated around 65 Ma. Microprobe analysis of ilvaite that occurs in two generations in the W–Mo skarn ores reveals a close relationship to Ca–Fe–F-rich hydrothermal fluids, which were probably derived from deeply-seated magmas. We suggest that ascent of the fluids was strictly controlled by the ore-controlling Dalong fault zone, and that chemical interaction and metasomatism between the fluids and the Lower-Permian Pangna quartz-feldspathic host rocks produced the ilvaite and the W–Mo polymetallic skarn deposit during the main India–Eurasia collision. Although the majority of the polymetallic deposits in the Gangdese belt are reported to be either pre- or post-main collision, it is evident from this study that the main collision also produced W–Mo polymetallic mineralization within the belt.  相似文献   

Magmatic expression of tectonic transition from oceanic subduction to continental collision: Insights from the Middle Triassic rhyolites of the North Qiangtang Block     

《Gondwana Research》2020

The tectonic transition from subduction to collision is a fundamental process during orogenesis, yet the magmatic expression of this transition and related deep geodynamic processes remain unclear. This study focuses on a newly identified volcanic belt within the Moyun–Zaduo–Sulu area of the North Qiangtang Block and presents new zircon U-Pb data that indicate that this belt formed during the Middle Triassic (247–241 Ma), a time characterized by a regional transition from subduction to collisional tectonism. The volcanic belt is located to the south of a Permian to Early Triassic arc and is dominated by high-K calc-alkaline and peraluminous rhyolites. These rhyolites have low Mg^#, Nb/Ta, and δEu values, contain low contents of Sr, have high Rb/Sr and whole-rock ε_Nd(t) values, and show positive zircon ε_Hf(t) values, all of which suggest that they formed from magmas generated by the dehydration melting of juvenile crustal material. The migration of Middle Triassic volcanism in this region was most likely caused by rollback of the subducting Longmucuo–Shuanghu Tethyan oceanic slab. Combining our new data with previously published results of numerical modeling of subduction–collisional processes and regional data from north-central Tibet yields insights into the magmatic expressions and related deep geodynamics of the transition from oceanic subduction to continental collision. This combination of data also suggests that variations in oxygen fugacity can be used as a proxy for the discrimination of magmatism related to subduction, the transition from subduction to collision, and collisional tectonism.  相似文献   

Early Jurassic palaeoenvironments in the Surat Basin,Australia – marine incursion into eastern Gondwana     

Andrew D. La Croix  Jianhua He  Valeria Bianchi  Jiahao Wang  Sebastian Gonzalez  Jim R. Undershultz 《Sedimentology》2020,67(1):457-485

Interpretations of palaeodepositional environments are important for reconstructing Earth history. Only a few maps showing the Jurassic depositional environments in eastern Australia currently exist. Consequently, a detailed understanding of the setting of Australia in Gondwana is lacking. Core, wireline logs, two-dimensional and three-dimensional seismic from the Precipice Sandstone and Evergreen Formation in the Surat Basin have been used to construct maps showing the evolution of depositional environments through the Early Jurassic. The results indicate the succession consists of three third-order sequences (Sequence 1 to Sequence 3) that were controlled by eustatic sea level. The lowstand systems tract in Sequence 1 comprises braidplain deposits, confined to a fairway that parallels the basin centre. The strata were initially deposited in two sub-basins, with rivers flowing in different orientations in each sub-basin. The transgressive systems tract of Sequence 1 to lowstand systems tract of Sequence 3 is dominated by fluvio–deltaic systems infilling a single merged basin centre. Finally, the transgressive and highstand systems tracts of Sequence 3 show nearshore environments depositing sediment into a shallow marine basin. In the youngest part of this interval, ironstone shoals are the most conspicuous facies, the thickness and number of which increase towards the north and east. This study interprets a corridor to the open ocean through the Clarence–Moreton Basin, or the Carpentaria and Papuan basins, evidence of which has been eroded. These results challenge a commonly held view that eastern Australia was not influenced by eustasy, and propose a more dynamic palaeogeographic setting comprising a mixture of fluvial, deltaic and shallow marine sedimentary environments. This work can be used to unravel the stratigraphic relationships between Mesozoic eastern Australian basins, or in other basins globally as an analogue for understanding the complex interplay of paralic depositional systems in data poor areas.  相似文献