Morphological and sedimentary features of sandy-muddy transitional beaches in estuaries and bays along mesotidal to macrotidal coasts     

Shaohua Zhao  Hongshuai Qi  Feng Cai  Jun Zhu  Xiang Zhou  Gang Lei 《地球表面变化过程与地形》2020,45(7):1660-1676

Sandy-muddy transitional beaches (SMT-Beaches), representing the transition from sandy beaches to tidal mudflats, should theoretically develop very different morphological and sedimentological characteristics in river estuaries and in semi-enclosed bays due to their contrasting dynamic sedimentary environments. Evidence, however, is rare in the scientific literature. To reveal these morphological and sedimentary differences, the sand–mud transition (SMT) boundary distribution, beach profiles, and surface and downcore sediment grain-size compositions of 27 SMT-Beaches located along mesotidal to macrotidal coasts of the western Taiwan Strait, southeastern China, were investigated. The results show that typical estuarine SMT-Beaches are mainly characterized by an ambiguous SMT, a long distance between the SMT and the coastline (31–302 m), lower SMT and inflection point altitudes (average –0.76 m and –0.04 m), and lower upper beach gradients (~0.068) with fine sand. Estuarine SMT-Beach sediments display clear interbedded mud and sand layers, implying potential SMT migrations over various timescales. By contrast, typical bay SMT-Beaches are characterized by distinct SMT, a short distance between the SMT and the coastline (11–52 m), higher SMT and inflection point altitudes (~0.24 m and ~0.35 m), and narrower upper beaches with higher gradients (~0.095) and coarse sand. Bay SMT-Beaches present relatively stable sedimentary sequences and a narrow gravel belt surrounding the inflection point and/or SMT. These morphological and sedimentary differences between the two SMT-Beach types are initially constrained by sediment supply and transport and are further affected by tide conditions and wave climate. Sediment supply and transport predominately control the sediment structures, while the tidal range strongly influences spatial variations in SMT distances. Wave climate normally drives SMT altitude variations. This study highlights the morphological and sedimentary differences in SMT-Beaches in estuaries and bays, providing important knowledge for further revealing their morphodynamic processes and potential future nourishment. © 2020 John Wiley & Sons, Ltd.  相似文献   

Assessing the relative contributions of the flood tide and the ebb tide to tidal channel network dynamics     

Liang Geng  Zheng Gong  Zeng Zhou  Stefano Lanzoni  Andrea D'Alpaos 《地球表面变化过程与地形》2020,45(1):237-250

Flood and ebb currents provide different contributions to the initiation and evolution of tidal channel networks, generating diverse network structures and channel cross-sections. In order to separate the effects of these contributions, a physical model of a sloping tidal-flat basin was set up in the laboratory. Depending on the degree of tidal asymmetry imposed offshore, either flood or ebb currents can be enhanced. The experimental results show that the ebb current has a higher capability to initiate and shape tidal networks than the flood current. Headward erosion is mainly induced by the ebb flow. The slightly inclined flat surface tends to reduce the energy of the flood current and to enhance the ebb current, thus prolonging the duration of morphodynamic activity as well as sediment motion. Overall, flood-dominated tides favour the formation of small-scale channel branches in the upper basin zone, while long lasting ebb-dominated tides result in more complex, wider and deeper tidal networks. © 2019 John Wiley & Sons, Ltd.  相似文献   

Tile‐based polygon overlay of vector data in a virtual globe     

Mengyun Zhou  Lizhe Wang  Xiaoyu Chen  Si Wu  Huawei Li 《Transactions in GIS》2020,24(4):1033-1046

The demand for analysis of large‐scale data has increased with increased access to spatial vector data. Polygon overlay of vector data in a virtual globe requires proprietary data structures and proprietary analysis algorithms. A vector data structure is designed for rapid polygon overlay in a virtual globe by recording the metadata of the triangles (TriMeta) that constitute polygons. A polygon overlay algorithm is proposed based on this data structure. The overlay of two complex GIS polygons is transformed into the intersection computation of their 3D triangular presentations. The intersection computation of two sets of triangles is reduced considerably by utilizing TriMeta to filter out the disjoint triangle pairs and rapidly identify the contained triangle. The new method improves the overlay efficiency in a virtual globe because the amount of computation required to calculate the intersections of two large polygons and drape the intersections onto a terrain surface is reduced.  相似文献   

Stratosphere amplifies the global climate effect of wildfires     

Wei  Ke  Chen  Wen  Xu  Luyang  Zhou  Chunjiang 《中国科学:地球科学(英文版)》2020,63(2):309-311

The summer of 2019 witnessed a great number of wildfires around the globe.For example,wildfires scorched huge swaths of Alaska,British Columbia in Canada,and parts of Greenland.And forest fires in Siberia and the Far East of Russia were also very serious,affecting nearly 3 million hectares of land,and putting some parts of Russia into a state of emergency.In particular,forest fires in the Amazon region had attracted global attention.According to Science,as of August 24,BraziPs National Institute for Space Research had counted more than 41000 fires this year,86%more than last year,compared with 22000 in the same period last year.Scientists in Brazil and elsewhere believe that the recent increase of wildfires is closely related to the increasing ac・tivities of deforestation(Arruda et al.,2019;Escobar,2019).  相似文献   

虚拟仿真技术在地质学中的应用     

强伟帆  郭艳军  周哲  周勇义 《高校地质学报》2020,26(4):464-471

得益于计算机技术、人工智能技术、多媒体技术、传感器技术等的迅速发展，虚拟仿真在科学领域已经得到了广泛的应用并具有巨大的市场需求。在地质学中，国内外高校已经将虚拟仿真技术应用到教学中，使其打破了传统教学的时空限制。但目前虚拟仿真在该领域的应用还存在场景内容欠缺，交互感不足，细节展示不够等问题。为能够进一步拓展虚拟仿真技术在地质学中的应用思路，文章对虚拟仿真技术在多个科学学科中的应用情况进行研究，介绍了面向地学的综合型、国际化的沉浸式虚拟仿真实验室实例。综合型的地学虚拟仿真实验室的建立，将深度融合地学与虚拟仿真技术，为多学科交叉融合、国际化教学等未来的教学发展方向提供更有效的平台。  相似文献   

Risk assessment through multivariate analysis on the magnitude and occurrence date of daily storm events in the Shenzhen bay area     

Jing-Cheng Han  Yang Zhou  Yuefei Huang  Xiaofeng Wu  Zhe Liu  Yongqiang Wang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2020,34(5):669-689

Multivariate storm frequency modeling would help to gain improved understanding of complex storm process, and provide useful information for regulating flooding risk. In this paper, the dependency...  相似文献   

Ediacaran integrative stratigraphy and timescale of China     

Zhou  Chuanming  Yuan  Xunlai  Xiao  Shuhai  Chen  Zhe  Hua  Hong 《中国科学:地球科学(英文版)》2019,62(1):7-24

Ediacaran successions occur widely in various depositional facies in South China and yield a series of fossil Lagerst?tten, providing a complete fossil record for the evolution of marine ecosystems after the terminal Cryogenian global glaciation. Carbonate-dominated Ediacaran successions in shallow water facies in South China record a nearly complete δ~(13)C profile that may reflect variations of marine carbon isotopic composition during the Ediacaran Period. The Ediacaran fossils andδ~(13)C profiles from South China permit stratigraphic correlation and subdivision of the Ediacaran strata. Based on biostratigraphic, chemostratigraphic, and geochronometric data from the Ediacaran successions in South China, we propose that the Ediacaran System in China can be subdivided into two series, with three stages in each series. The lower series is characterized by acanthomorphic acritarchs and the upper series by Ediacara-type macrofossils, and the two series are separated by the declining limb of a pronounced δ~(13)C negative excursion(EN3) in the upper Doushantuo Formation. The basal boundary of Stage1 is the same as the basal boundary of Ediacaran System, which has been defined at the base of the cap carbonate unit. Stage 2 represents the first radiation of Ediacaran microscopic organisms, with δ~(13)C feature representing by positive values(EP1). The base of the Stage 2 is placed at the first appearance level of a spiny acritarch species. Stage 3 is characterized by the occurrence of more diverse acritarchs and δ~(13)C feature EP2, with its basal boundary defined by a δ~(13)C negative excursion(EN2) occurring in the middle Doushantuo Formation. The basal boundary of Stage 4 is the same as the upper series. Stage 5 is marked by the occurrence of macrfossils of Miaohe biota, and its lower boundary can be placed at the level where δ~(13)C values transition from positive to negative in MNE, or the first appearance level of macrofossils of the Miaohe biota. Stage 6 is characterized by the occurrences of Ediacara-type Shibantan biota and Gaojiashan biota, with its lower boundary defined by the first appearance level of Conotubus hemiannulatus. The formal establishment of the aforementioned series and stages requires further and more detailed integrative stratigraphic study on the Ediacaran successions in China. Some of the Ediacaran successions in South China have great potential to become global standards in Ediacaran subdivision.  相似文献   

Primary investigation of statistical correlation between changes in ice volume and area of glaciers     

PuYu Wang  ZhongQin Li  ChunHai Xu  Ping Zhou  WenBin Wang  Shuang Jin  HongLiang Li 《寒旱区科学》2019,11(1):41-49

This study makes an attempt to investigate through statistical analysis the correlation between changes in ice volume and area of glaciers. Using data from nine sample glaciers in the Tian Shan, the results show that a linear relation exists between changes in ice volume and area, with a correlation coefficient of 0.700. However, the accuracy estimation is difficult due to the limited number of samples. The correlation was not improved after adding eleven glacier samples in other mountains. Two reference glaciers are then analyzed in more detail. The linear correlation coefficient is higher than 0.800 when using the observed changes in ice volume and area during different periods on Urumqi Glacier No. 1, which suggests that the linear relation is valid for one glacier for different periods if its shape does not change noticeably and also for other glaciers of the same shape during the same period. The relation between changes in ice volume and area of Qingbingtan Glacier No. 72 is different during different periods due to change in the shape of the glacier tongue and the influence of the debris cover. Moreover, errors in glacier-change monitoring and-volume estimation have an important influence on the correlation results. Therefore, further study needs to focus not only on the distinction between glacier types and between different periods but also on the accuracy of volume estimation.  相似文献   

Hyperspectral estimation model of soil Pb content and its applicability in different soil types     

Tian  Shiqi  Wang  Shijie  Bai  Xiaoyong  Zhou  Dequan  Lu  Qian  Wang  Mingming  Wang  Jinfeng 《中国地球化学学报》2020,39(3):423-433

Acta Geochimica - In order to obtain Pb content in soil quickly and efficiently, a multivariate linear regression (MLR) and a principal component regression (PCR) Pb content estimation model were...  相似文献   

琼东南盆地深水区松南-宝岛凹陷反转构造带发育特征及油气地质意义   总被引：1，自引：1，他引：0  

杨金海  杨希冰  周杰  甘军  宋爱学  江凡  杨璐 《海洋学报》2019,41(5):97-106

利用新三维地震资料对松南-宝岛凹陷反转构造带发育特征、形成期次进行研究，并从构造背景及力学机制两个方面探讨反转构造的成因机制。研究结果表明，松南-宝岛凹陷反转构造带主要发育一系列"上凸下凹"的大型褶皱背斜，伴生NWW向弱走滑断裂构造和NNW向张剪构造。反转构造及其伴生构造符合NEE右旋剪切应力场特征，形成时间与东沙运动一致，表明该反转构造带可能受晚中新世南海东北部东沙运动产生的右旋走滑应力场作用控制。反转构造有利于研究区圈闭的重建和改造，对琼东南盆地东部新区油气运移和重新优选分配的认识，具有重要的油气地质意义。  相似文献