Study on elastic P-wave propagation law in unfavorable geologic structures with discontinuous deformation analysis method

The propagation of elastic P-wave in unfavorable geologic structures is a complex process which contains reflex, transmission, and refraction. In this paper, the discontinuous deformation analysis (DDA) method is introduced, and the viscous boundary condition and stress wave input way are applied to enable the DDA method to simulate the seismic dynamic response of underground rock mass. The improved DDA program is used to analyze the propagation laws of elastic P-wave in joints and weak interlayer. The results show that (1) for a range of joint stiffness, the difference of transmission coefficient of joint surface between DDA calculation and theoretical solution is small; (2) the lower the joint stiffness, the more obvious the attenuation of the elastic P-wave is; (3) varied joint spacing and joint number play different roles on the attenuation of elastic P-wave; (4) the DDA calculation result is consistent with the theoretical solution for the transmission coefficient of interface; (5) the thickness and elastic modulus of weak interlayer will affect the interference effect of multiple transmission waves; (6) with the increasing weak interlayer thickness H (or a), the attenuation of the elastic P-wave is more obvious; and (7) the lower the wave impedance ratio of weak interlayer, the more obvious the attenuation of the elastic P-wave is.     

Spatial distribution and the scale effect of influencing factors of specialized and sophisticated enterprises that produce new and unique products in the Yangtze River Delta region: Based on the buffer and MGWR analyses北大核心CSCD

High-quality cultivation of specialized and sophisticated enterprises that produce new and unique products is an important starting point for consolidating the security foundation of China's industrial chain and supply chain. Using buffer zone analysis and the multi-scale geographically weighted regression (MGWR) model, this study explored the spatial distribution of specialized and sophisticated enterprises that produce new and unique products in the Yangtze River Delta region and influencing factors in 2021. The study found that: 1) Spatially, Shanghai is the main area where specialized and sophisticated enterprises that produce new and unique products are concentrated, followed by provincial capitals and cities on the coast and along rivers; The overall composition of the industry is unbalanced, and the real economic industries such as machinery and equipment manufacturing and high-tech manufacturing account for a relatively high proportion, but there are differences in different regions. 2) In terms of spatial agglomeration, differences between circles and the scale effect are obvious. Within each province, the spatial distribution of specialized and sophisticated enterprises that produce new and unique products in different cities is uneven. Region-wide, the overall spatial distribution pattern of "one pole and multiple cores" is evident. Shanghai is the main agglomeration area for these enterprises, and the provincial capital cities and cities that are the regional economic centers are the secondary agglomeration areas of these enterprises. 3) The four dimensions of influencing factors—physical geography, government, market, and society—have a scale effect on the spatial distribution of specialized and sophisticated enterprises that produce new and unique products. The degree of land development acts at a small scale, which is a local variable, and shows a large difference in the impact on the spatial distribution of these enterprises across the region. Factors such as elevation, government-business relationship, degree of marketization, number and scale of enterprises, degree of openness, logistics development level, and innovation environment are global variables, and except that the degree of marketization and the number of enterprises have a significant negative impact on the spatial distribution of these enterprises, the impact of all other factors is significantly positive. The research results can provide support for the optimization of the layout of new special expertise enterprise space in the Yangtze River Delta region, in order to provide reference for the formulation of new special expertise policies and industrial planning. © 2023, Editorial office of PROGRESS IN GEOGRAPHY. All rights reserved.     

Diatom assemblage dynamics during abrupt climate change: the response of lacustrine diatoms to Dansgaard–Oeschger cycles during the last glacial period

The sedimentary record from the paleolake at Les Echets in eastern France allowed a reconstruction of the lacustrine response to several abrupt climate shifts during the last glacial period referred to as Dansgaard–Oeschger (DO) cycles. The high-resolution diatom stratigraphy has revealed distinct species turnover events and large fluctuations in stable oxygen isotope values in diatom frustules, as a response to DO climate variability. More or less identical species compositions became re-established during each DO stadial and interstadial phases, respectively. However, the relative abundance of the most dominant species within these assemblages varies and might indicate differences in climatic conditions. Interstadial phases are characterized by identical species successions. Transitions from stadial to interstadial conditions show a distinct Fragilaria–Cyclotella succession, which resembles the diatom regime shifts that have been recognized in some lakes in the Northern Hemisphere since the mid-nineteenth century.     

黔东北地区下寒武统牛蹄塘组页岩气特征及主控因素分析*

黔东北地区页岩气资源丰富,其下寒武统牛蹄塘组具有巨大的勘探潜力。在对几口探井分析的基础上,结合露头资料及地球化学特征,认为研究区牛蹄塘组页岩具有厚度大、分布广、有机碳含量高、热演化程度相对较高、储集条件较好等特征。但由于大部分针对牛蹄塘组页岩气的钻井遇到的都是含气量低、甲烷含量低、氮气含量高的页岩,因此对黔东北地区页岩气富集的主控因素进行了系统分析,认为该地区牛蹄塘组页岩气具有沉积控带、断裂控藏的明显特征。     

黔中开阳地区震旦纪陡山沱期富磷矿沉积特征与成矿模式*

黔中开阳地区在震旦纪陡山沱期全球成磷事件的大背景下,发育了厚度较大的富磷矿层。通过岩石薄片观察、地层对比与划分及沉积相分析等手段,探讨黔中开阳地区震旦纪陡山沱期磷矿床沉积特征与成矿模式。结果表明:(1)开阳地区陡山沱期处于黔中古陆北缘的磷质海岸环境,磷矿层中分布最广泛、品位最高的矿石类型为砂屑磷块岩,为富磷沉积物在沉积、成岩过程中遭受多期次冲刷破碎、暴露淋滤及堆积胶结的产物。(2)开阳地区古地理环境和动荡的海水条件控制了磷矿的沉积和高品位矿石的分布,洋水、永温等地在震旦纪陡山沱期所处的海水深度适中的临滨带为成矿优势地带,而水体过浅的前滨带和过深的远滨带均不利于磷质的聚集和成矿。(3)开阳地区动态磷矿床成矿模式表明,陡山沱期海平面的频繁进退使临滨带已沉积的磷块岩遭受多期次的冲蚀、暴露、淋滤、胶结及磷质再沉积作用;通过物理分选作用和风化淋滤作用最终使磷质聚集,是研究区富磷矿形成的主要原因。     

A 140-year record of recent changes in aquatic productivity in a remote,tropical alpine lake in the Rwenzori Mountain National Park,Uganda

Environmental change in many tropical, alpine habitats remains poorly resolved due to an absence of proximate and sustained observations. In the Rwenzori Mountains of East Africa, glaciers have receded rapidly over the last century, and here we assess the impact of this recession through palaeolimnological analyses of a 45 cm sediment core (Buju3) from Lake Bujuku which is closest to the ice-fields and partly supplied by melt water in-flows. ²¹⁰Pb and ¹³⁷Cs suggest that Buju3 has an average sedimentation rate of 2.9 mm year⁻¹ and the base of the core can be dated to 1864 ± 20 years. Contemporary diatom taxa found in the lake are dominated by Tabellaria flocculosa and Synedra spp., but also include Achnanthes minutissima and Fragilaria pinnata. However, the diatom flora for Buju3 is less diverse and dominated by small, tychoplanktonic species of Fragilaria. Over the period associated with glacial recession, organic carbon isotope analysis (δ¹³C) suggests a small but distinct increase in within-lake productivity, which increases in rate since the mid 1970s up to the present day, in line with a shift towards increased algal productivity (as highlighted by C/N ratios). However, the diatom and pollen records appear rather insensitive to changes in glacier recession since the late 19th century.     

The impact of disposal and treatment of coal mining wastes on environment and farmland

In China, coal mining wastes have traditionally been dumped in cone-shaped heaps that have the potential to pollute air, soil and water environments and landscapes through dust generation, leachate production, self-ignition and as a consequence of an absence of vegetation cover. Since 1980s, the disposal technique for coal mining wastes has been changing and in many instances the wastes are now transported directly to subsided land as a fill to enable the reuse of that land. Thus, today, both coal mining waste dumps from the past and filled subsided lands are in existence. However, the comparative impacts of these different disposal techniques on the environment and farmland productivity have not been studied in detail. Using Dongtan (DT), Nantun (NT) and Xinglongzhuang (XLZ) coal mines as examples, the components of coal mining wastes and their potential pollution contribution to soil, surface water and ground water are tested in-situ. The results show that contaminants are released after self-ignition and weathering of coal mining wastes, but they are not above the allowable environmental standards. However, despite these findings, more and closer attention needs to be paid to the mobility, transportation and accumulation of these contaminants in the environment over time.     

川西高原理县黄土磁学特征及其影响因素

川西高原河谷阶地和断陷盆地广泛分布厚层风成黄土-古土壤序列,目前对其磁学性质变化机制及古气候意义研究还很薄弱。文章对该区理县黄土-古土壤剖面进行了系统的岩石磁学研究,确定了其磁性矿物种类、含量和颗粒大小的特征及其变化规律。通过结合粒度、色度与地球化学参数,进一步探讨了理县黄土-古土壤磁性的主控因素。结果表明:1)理县剖面同时含有强磁性矿物(为磁铁矿和磁赤铁矿)以及弱磁性矿物(为赤铁矿和针铁矿);2)相对黄土层,古土壤层含有更高比例的亚铁磁性矿物;3)成土过程中生成的大量细小强磁性矿物颗粒,是古土壤层S1磁化率增加的主导因素,该模式与黄土高原相似;4)结合色度以及磁学性质,可以较为明确地区分成壤强度;(5)理县黄土剖面物源复杂,磁学特征受到沉积物来源、后期流水和气候的共同作用,利用单一磁学性质(比如磁化率)进行古气候研究会造成多解性。     

贵州深部四级断裂构造特征及与重要矿产的关系

贵州位于扬子陆块、江南造山带、右江造山带的复合部位,自新元古代以来,发生了多次重要的构造伸展运动和构造挤压变形。晚古生代之后的沉积活动,掩盖了早期地质构造形迹。多位学者曾对贵州的深部断裂进行过推断,但由于资料不足、认识差异等原因,研究存在局限和争议。在充分借鉴已有研究成果的基础上,通过综合应用重力、航磁、地质等资料,提取了贵州深部四级断裂构造体系。所推测的贵州深部Ⅰ级断裂3条,呈"H型"结构;Ⅱ级断裂15条、Ⅲ级断裂12条,基底断裂若干条,这些断裂均在上一级断裂的基础上发展演化。根据人工地震剖面资料,进一步验证了5条深部Ⅰ至Ⅲ级断裂的展布特征,发现这些断裂沿不同倾向延伸、切割深度达6~12km,为切穿沉积盖层和基底的深大断裂。结合四级断裂构造体系及贵州省内重要矿产的分布,提出贵州金、铅锌、锑、锰、磷、铝土矿分布与Ⅰ、Ⅱ、Ⅲ级深部断裂构造具有空间联系。