硅质岩沉积地球化学研究现状   总被引：5，自引：0，他引：5  

盛吉虎  陈中新 《地域研究与开发》1998,(Z1)

硅质岩是造山带中分布最为广泛的岩石类型之一,硅质岩沉积环境的确定对深海沉积作用、大陆边缘地质学及大地构造格架的厘定具有重要意义。目前,在硅质岩沉积地球化学研究方面有以下主要进展：①硅质岩沉积地球化学研究;②与蛇绿岩有关的硅质岩沉积地球化学研究;③物质来源研究;④古氧化还原条件研究;⑤硅质岩构造环境判别  相似文献   

Distribution patterns of interstitial polychaetes in sandy beaches of southern Brazil   总被引：1，自引：0，他引：1  

Maikon Di Domenico  Paulo da Cunha Lana  & André R. S. Garraffoni 《Marine Ecology》2009,30(1):47-62

This study describes the distribution patterns of interstitial polychaetes along morphodynamic gradients on six exposed sandy beaches in Santa Catarina and Paraná (South Brazil). Three random transects were sampled at two points on each beach, one at the swash and another at the surf zone, in winter and summer conditions. Six sediment replicates were collected at each sampling point using a corer of 4.6 cm internal diameter that removed 10 cm into the sediment. Abundance and composition of interstitial polychaete were correlated to wave height, slope, grain size, CaCO₃, chlorophyll a , omega indexes, temperature and relative tide range using a canonical correspondence analysis (CCA). A factorial ANOVA showed that taxa richness, mean density and Shannon's diversity were significantly higher at the reflective beaches, but average values differ significantly between transects and these differences change according to the beach zones on both sampling dates. PERMANOVA showed that polychaete associations differ among transects according to the beach zones. The composition of interstitial polychaete associations was significantly correlated to beach morphodynamics and features (P < 0.01). Polychaete associations of reflective beaches were more diverse than in other morphodynamic states. Intermediate beaches may also sustain diverse associations due to temporal variability of the morphodynamic patterns. Beaches presenting extreme dissipative morphodynamics and compacted sediments appear to be unfavourable for the occurrence of interstitial polychaetes.  相似文献   

基于耗散结构系统熵模型的乡村生产空间系统有序性研究   总被引：2，自引：0，他引：2  

王成  周明茗  李颢颖  何焱洲  马小苏 《地理研究》2019,38(3):619-631

通过分析乡村生产空间系统的耗散结构特征,建立系统熵模型,运用关联熵和运行熵,从系统的主体（多元主体）、客体（地）和环境三要素入手构建指标体系,讨论系统内部结构和运行状态的有序性,并以重庆市合川区龙市镇为研究区予以实证,研究表明：研究区乡村生产空间系统关联熵先增后减,系统内部结构有序性呈现阶段性特征,2008—2011年主要受城市化无序扩张和土地利用方式低效粗放等因素影响,系统内部结构趋于混乱无序,2011—2015年主要因财政支农力度增强、农业投入产出水平提高、生态修复力度加大等因素刺激,系统内部结构逐渐趋于有序化;2008—2015年,乡村生产空间系统运行熵逐年减小,在农业综合开发投入大幅增加引起的生产条件改善、产业结构调整与提档升级等驱动下,呈现出持续有序化的发展态势;围绕乡村生产空间系统的内部结构及运行状态的演化规律,从优化土地利用结构、构建现代农业产业体系、编制和完善相关规划、培育新产业新业态入手,提出相关策略,以促进乡村生产空间系统有序健康发展。  相似文献   

Abodes for life in carbonaceous asteroids?     

Oleg Abramov  Stephen J. Mojzsis 《Icarus》2011,213(1):273-279

Thermal evolution models for carbonaceous asteroids that use new data for permeability, pore volume, and water circulation as input parameters provide a window into what are arguably the earliest habitable environments in the Solar System. Plausible models of the Murchison meteorite (CM) parent body show that to first-order, conditions suitable for the stability of liquid water, and thus pre- or post-biotic chemistry, could have persisted within these asteroids for tens of Myr. In particular, our modeling results indicate that a 200-km carbonaceous asteroid with a 40% initial ice content takes almost 60 Myr to cool completely, with habitable temperatures being maintained for ∼24 Myr in the center. Yet, there are a number of indications that even with the requisite liquid water, thermal energy sources to drive chemical gradients, and abundant organic “building blocks” deemed necessary criteria for life, carbonaceous asteroids were intrinsically unfavorable sites for biopoesis. These controls include different degrees of exothermal mineral hydration reactions that boost internal warming but effectively remove liquid water from the system, rapid (1-10 mm yr⁻¹) inward migration of internal habitable volumes in most models, and limitations imposed by low permeabilities and small pore sizes in primitive undifferentiated carbonaceous asteroids. Our results do not preclude the existence of habitable conditions on larger, possibly differentiated objects such as Ceres and the Themis family asteroids due to presumed longer, more intense heating and possible long-lived water reservoirs.  相似文献   

Climate change transformation: A definition and typology to guide decision making in urban environments     

Anna C. Hurlimann  Sareh Moosavi  Geoffrey R. Browne 《Chemie der Erde / Geochemistry》2010

Climate change presents a threat to the sustainability of cities and their societies, and must be adequately addressed. Urban environments (cities) are responsible for the creation of a significant amount of greenhouse gas emissions which are the source of climate change. Cities have been increasingly the focus of action to address climate change, yet emissions are not significantly reducing. Additionally, there a lack of integration between adaptation and mitigation. This prevents responses adequate to limit global warming to 1.5^OC, and to be well adapted to anticipated changes. This paper critically analyses existing definitions and typologies of climate change actions. A definition of ‘climate change transformation’ is proposed which includes the integration of adaptation and mitigation goals to enable a new regime in which global warming is limited to 1.5^OC. A new three-part typology: ‘coping, malaction and transformation,’ is presented for categorising climate change actions by the extent to which they integrate adaptation and mitigation, and define a new regime. The typology is accompanied by illustrations to demonstrate the relationship between adaptation and mitigation. The definition, typology and illustration serve to guide effective climate change decision making, and provides principles to guide application in urban environments.  相似文献   

Middle and late Cenomanian oceanic anoxic events in shallow and deeper shelf environments of western Morocco     

BRIAN GERTSCH  THIERRY ADATTE  GERTA KELLER  ABDEL AZIZ A.M. TANTAWY  ZSOLT BERNER  HAYDON P. MORT  DOMINIK FLEITMANN 《Sedimentology》2010,57(6):1430-1462

The response of shallow‐water sequences to oceanic anoxic event 2 and mid‐Cenomanian events 1a and 1b was investigated along the west African margin of Morocco north of Agadir (Azazoul) and correlated with the deep‐water sequence of the Tarfaya Basin (Mohammed Beach) based on biostratigraphy, mineralogy, phosphorus and stable isotopes. In the deeper Mohammed Beach section results show double peaks in δ¹³C_org for mid‐Cenomanian events 1a and 1b (Rotalipora reicheli biozone, lower CC10a biozone), the characteristic oceanic anoxic event 2 δ¹³C excursion (Rotalipora cushmani extinction, top of CC10a biozone) and laminated (anoxic) black shale. In the shallow environment north of Agadir, a fluctuating sea‐level associated with dysoxic, brackish and mesotrophic conditions prevailed during the middle to late Cenomanian, as indicated by oyster biostromes, nannofossils, planktonic and benthonic foraminiferal assemblages. Anoxic conditions characteristic of oceanic anoxic event 2 (for example, laminated black shales) did not reach into shallow‐water environments until the maximum transgression of the early Turonian. Climate conditions decoupled along the western margin of Morocco between mid‐Cenomanian event 1b and the Cenomanian–Turonian boundary, as also observed in eastern Tethys. North of Agadir alternating humid and dry seasonal conditions prevailed, whereas in the Tarfaya Basin the climate was dry and seasonal. This climatic decoupling can be attributed to variations in the Intertropical Convergence Zone and in the intensity of the north‐east trade winds in tropical areas.  相似文献   

The ebb and flow of capital in Indonesian coastal production systems     

Yunie N. Rahmat  Jeff Neilson 《Singapore journal of tropical geography》2023,44(2):300-321

The global fisheries sector has undergone both rapid industrialization and considerable resource depletion. Unlike fisheries in the Northern Hemisphere, the Indonesian (and indeed Southeast Asian) sector is still largely dominated by small-scale producers, who are partially embedded within a subsistence economy. Changes in the nature of production and livelihoods in the fisheries sector appear similar to those in land-based agriculture but have received far less attention in the literature and demand further analysis given the distinct characteristics of the natural resource base. Using national datasets complemented by insights from a two-month period of fieldwork in South Sulawesi, this paper presents the process of capital intensification underpinning national fisheries growth and how it is transforming small-scale production systems. Despite increasing market integration, we found that smallholders have persisted across coastal production systems to an even stronger degree than land-based agriculture. We suggest some reasons why this is so. However, we also observed evidence of internal class differentiation within coastal communities. Such differentiation, combined with resource degradation and depletion, exposes the poorest in the community to enhanced livelihood vulnerability.  相似文献   

壳幔岩浆混合作用与陆内环境高Sr/Y斑岩的形成及成矿：实例与探讨   总被引：2，自引：1，他引：1  

马星华  王志强  王超  鄢雪龙 《岩石学报》2014,30(7):2020-2030

产于陆内环境的含矿斑岩往往具有高Sr/Y特征,多数学者认为与岩浆起源于加厚或拆沉的下地壳有关。然而,目前这一模式仍存在较大争议。本文以敖仑花斑岩矿床为例,新报道了矿区内不成矿岩体的岩石学和地球化学特征,与同期成矿岩体进行对比,探讨含矿斑岩高Sr/Y原因及控制是否成矿的可能因素。相对于含矿斑岩,敖仑花贫矿黑云母花岗岩具有高SiO2(74%~78%)、低MgO(0.2%)和CaO(0.2%~1.1%)、贫Sr(30×10-6~251×10-6)和Cr(1×10-6~6×10-6)的特征,显示准铝质到过铝质性质(A/CNK=0.9~1.2),Mg#值(2~30)与玄武岩实验熔体成份相似,说明岩浆可能主要来自基性下地壳源区的部分熔融。而已有的研究表明含矿斑岩为壳幔岩浆混合成因,富集地幔起源的偏基性岩浆的加入提升了寄主长英质岩浆的Mg#值、大离子亲石元素(Sr、La等)含量及其氧逸度(fO2)。我们认为幔源岩浆的混合可能是导致陆内环境含矿斑岩高Sr/Y及有利成矿的根本原因;相反,来自纯壳源的花岗质熔体因缺乏富水、高fO2幔源岩浆的参与而不利于形成斑岩Cu±Au±Mo矿床。  相似文献   

Microbial Mediated Mineralizationin Kamchatka Hot Springs     

LI Yiliang  TANG Min 《《地质学报》英文版》2014,88(Z1):185-185

正Materials deposited in low-temperature environments are characterized by their small particle size.The activity of microorganisms in aqueous sedimentary environments may have effective impacts on the geochemical  相似文献   

Dynamics of the Mackenzie River plume on the inner Beaufort shelf during an open water period in summer     

Ryan P. Mulligan  Will Perrie  Steve Solomon 《Estuarine, Coastal and Shelf Science》2010

The oceanographic conditions of the Mackenzie River plume in the Arctic Ocean were examined during a 12-day period in August 2007. Field observations in the river channel and the delta region (2–6 m depth), ship-based observations on the shelf and satellite observations of sea surface temperatures indicate that movements of plume density fronts cause changes in water temperatures of over 10  C over a few days. We used a 1D model to compare the strength of stratification versus surface wind stress, and a 3D numerical model to simulate the plume motions under forcing from the river flows, local wind and water level variations from tides and wind-driven surge. The results indicate that the coastal region is stratified with a ∼2 m thick surface plume even in water depths of 3–4 m, resulting in strong vertical variation of horizontal currents. Moderate easterly winds of 5–10 m/s are sufficient to induce offshore transport of the surface plume and onshore transport of the deeper shelf water, leading to large fluctuations in temperature and salinity in the coastal region. This study examined a period of offshore transport and mean water level set-down, and indicates the rapid response of the plume to wind over the shallow delta.  相似文献