Chemical, biological and hydrological controls on the C content of cold seep carbonate crusts: numerical modeling and implications for convection at cold seeps     

G. Aloisi  K. Wallmann  J.-F. Saliège 《Chemical Geology》2004,213(4):359-383

Understanding the hydrology of cold seep environments is crucial to perform accurate estimates of fluid and chemical fluxes at sedimentary wedges. Shallow convection processes may affect fluid flux estimates and could favor the destabilization of gas hydrate accumulations, increasing the sediment-ocean methane flux. Evidence for the occurrence of convection at cold seeps, however, is still limited. We use the concentration of ¹⁴C (D¹⁴C) in carbonate crusts formed at cold seeps of the eastern Mediterranean Sea as a tracer for convective recirculation of seawater-derived fluids. A numerical model is applied to investigate the controls on ¹⁴C incorporation in cold seep carbonates. Our simulations show that increased amounts of CH₄ in the expelled fluids result in elevated crust D¹⁴C, while high Ca²⁺ and HCO₃⁻ concentrations produce the opposite effect. Convection is the only transport process that can significantly increase crust D¹⁴C. Advection, bioirrigation, eddy diffusion and bioturbation instead, have little effect on, or produce a decrease of, crust D¹⁴C. In addition, the presence of old or modern carbon (MC) in host sediments prior to cementation and the ¹⁴C-decay associated to the time needed to form the crust contribute in defining the D¹⁴C of carbonate crusts. We then use the model to reproduce the ¹⁴C content of the eastern Mediterranean Sea crusts to constrain the chemical and hydrological conditions that led to their formation. Some crusts contain relatively low amounts of ¹⁴C (−945.0<D¹⁴C ‰<−930.2) which, assuming no ageing after crust formation, can be reproduced without considering convection. Other crusts from two sites (the Amsterdam and Napoli mud volcanoes), instead, have a very high ¹⁴C-content (−899.0<D¹⁴C ‰<−838.4) which can only be reproduced by the model if convection mixes deep fluids with seawater. Order-of-magnitude calculations using the Rayleigh criterion for convection suggest that the slow seepage (about 10 cm year⁻¹) of low salinity (20‰) fluids at the Amsterdam sites could trigger haline convection there. On the Napoli mud volcano, where high-density brines are expelled, density-driven convection cannot take place and other processes, possibly involving the rapid movement of free gas in the sediment, could be important.  相似文献   

卫星导航定位系统中伪随机码的研究   总被引：6，自引：0，他引：6  

卢晓春  陈清刚  胡永辉 《时间频率学报》2004,27(1):23-32

伪随机码在扩频通信中得到广泛应用。目前的卫星导航定位系统大多采用扩频通信技术来传输导航信息 ,常用的伪随机码是平衡Gold码。对平衡Gold码的特性和产生方法作了研究 ,对全球定位系统 (GPS)粗码的平衡性作了分析 ,最后给出了在SystemView平台上相应的仿真结果。此研究对开展相关领域的研究工作具有借鉴意义  相似文献   

小井径双源距碳氧比C/O测井的影响因素及处理   总被引：6，自引：1，他引：6       下载免费PDF全文

吴文圣  付赓  张智  庄人遴 《地球物理学报》2005,48(2):459-464

研究各种地层和井眼环境因素对碳氧比C/O测井长、短源距探测器的影响规律，可以为C/O测井仪器的刻度方法提供指导，为解释模型的建立和数据处理提供依据.本文用Monte Carlo方法，计算了C/O值随井眼直径、水泥环厚度、套管直径、孔隙度、含油饱和度、地层岩性和油密度的变化规律.从中看出，当井内流体为油时，井径或套管直径增大，C/O值增大，井眼影响增大；当井内流体为水时，井径或套管直径的增大，C/O值减小；水泥环厚度增加时C/O值减小；当井眼条件不变时，地层孔隙度越大，含油饱和度越大，C/O值越大，对测井越有利；反之，地层孔隙度越小，含油饱和度越小，C/O值越小，对测井不利；地层岩性对C/O值的影响显著，相同条件下，碳酸盐岩比砂岩的C/O值高；油密度越大，C/O值越大.文中还提出了一种消除这些因素影响的数据处理方法  相似文献   

Simulation of ~(14)C in IAP/LASG L30T63 Ocean Model   总被引：2，自引：0，他引：2       下载免费PDF全文

LI Qingquan  SHI Guangyu 《Acta Meteorologica Sinica》2005,19(4):436-446

1. Introduction14C is a radioactive isotope of carbon, whose halftime is about 5730 yr. Under natural circumstance,14C comes into being in the stratosphere because of thenitrogen explosion of cosmic radial. 14C is mixed inthe atmosphere, absorbed by oceans, and then trans-ported into deep ocean. 14C radioactively reduces asits age increases. The reduction process of 14C canuncover the evolvement process of sea water's age andrenewal time.14 C content is usually described with one in athousan…  相似文献   

桂林甑皮岩洞穴遗址钙华板14C年代学研究   总被引：2，自引：3，他引：2       下载免费PDF全文

王华  张会领  涂林玲  覃嘉铭  冯玉梅 《地球学报》2005,26(4):333-336

甑皮岩遗址是新石器时代保存较完整的一个人类洞穴遗址，距今有8．0～12．0ka的历史。本文通过对洞穴遗址钙华板^14C年代的测定，并对比了遗址内贝壳和木炭的^14C年代。初步论证了钙华板^14C年代的可靠性，并探讨甑皮岩古人类活动及穴居的最后年代为6．6ka BP。通过对钙华板^14C年代研究为遗址洞穴地层的划分提供了新的年代依据。  相似文献   

东太平洋海隆热液活动区沉积岩心的地球化学研究     

薛发玉  翟世奎 《地球学报》2005,26(Z1):200-201

东太平洋隆是现代海底热液活动及热液沉积分布最为广泛的构造环境之一。本文对采自 EPR13°N 现代海底热液活动区附近的两个沉积物岩心分别进行了元素地球化学分析，并结合沉积物中有孔虫壳体对岩心进行关键层位 14C 年代学研究。目的在于通过对比距现代海底热液喷口不同距离的两岩心的地球化学特征，研究热液活动在岩心沉积物中所何存的地球化学记录，探讨海底热液活动对洋中脊附近沉积作用的贡献，以及热液活动在一定地质历史时期内的变化规律。显示，距热液喷口区相对较近的 B13－26 岩心沉积物含有丰富的热液特征组分，绝大多数微量元素和 REE 都与 Fe和Mn 成较强的正相关关系，而与 Al、Na、Ca、Mg、Ti 等元素相关性较弱或呈负相关，说明这些元素的富集机制主要是热液成因非晶质 Fe－Mn 化合物对热液及海水中元素的吸附作用。距热液喷口区相对较远的 B13－62岩心上部沉积物中元素的富集特征与 B13－26 岩心相似，但中下部沉积物中 Fe 与 Mn 无明显的相关关系，说明这些元素的富集主要受深海粘土沉积的影响，而受热液活动的影响减弱或消失。由于与海隆扩张轴距离的不同，两岩心受热液活动影响的强度不同。由海隆扩张轴向外，沉积作用受热活动的影响逐渐减弱，正常深海沉积作用逐渐加强。两个岩心沉积物地球化学上的共性是 Ca 和 Sr 都与其他元素呈现负相关关系或极微弱的正相关关系，表明生物碳酸盐沉积作用的独特性。有孔虫 14C 年龄测定结果表明，B13－26 岩心 35～250cm 段年龄十分接近，前后相差仅在几百年内。根据年龄测量中的误差范围，可以断定这段沉积物岩心是短时间内快速沉积的产物。结合热液活动特征性元素在岩心中的分布特征，判断该岩心段记录一次强烈的热液活动事件，从而形成了典型的事件沉积。在 B13－62 岩心的45～50cm 处测得有孔虫的 14C 年龄为距今 32900±530 yr。由于 14C 测年方法上的局限性，在岩心 135～140cm 处 14C 测年只能给出大于40000 yr 的结果。显然，B13－62 岩心处早期并没有受到热液活动明显的影响，沉积速率非常缓慢，只是在近期受到了热液活动的影响，形成了上部富含 Fe、Mn、Zn、Cr、Co、Ni、V 等热液活动特征元素的沉积。  相似文献   

Bed thickness characteristics of inner-shelf storm deposits associated with a transgressive to regressive Holocene wave-dominated shelf, Sendai coastal plain, Japan     

TORU TAMURA  FUJIO MASUDA† 《Sedimentology》2005,52(6):1375-1395

Holocene inner-shelf storm deposits preserved beneath the Sendai coastal plain facing the Pacific coast of north-eastern Japan were formed during a transgressive–regressive cycle. The evolution of the Holocene wave-dominated depositional system along the Sendai coast is reconstructed using 76 AMS (accelerator mass spectrometers) ¹⁴C ages and the origin of bed thickness variations in the inner-shelf storm deposits is explored. The Holocene succession is <30 m thick and overlies latest Pleistocene to early Holocene non-marine deposits above a transgressive ravinement surface. It comprises transgressive ravinement and inner-shelf deposits, and regressive inner shelf, shoreface, and coastal plain deposits. The inner-shelf deposits comprise alternating sand and mud layers interpreted as stacked storm beds. The average preservation interval of a single storm bed is shortest during the transgression (5·7–20·6 years), and then increases to a maximum during the early regression (83·3–250·0 years), decreasing to 7·7–31·3 years with shoreline progradation. Average accumulation rates decreased during the transgression and then increased during the regression, but the sand/mud ratio varies little, reflecting inefficient sediment segregation downdip on the inner shelf. The vertical pattern of sand-layer thicknesses also shows no relationship to position within the cycle, although small-scale intervals of upward thickening and thinning probably relate to lateral switching of river mouths and/or random storm processes. The average thickness of storm beds is the highest in the interval deposited during the period from maximum flooding to early regression. This is probably because of the low preservation potential of thin beds associated with frequent, low-magnitude storms during this period of low accumulation rates and extensive reworking. This preservation bias and the nature of the Sendai inner shelf resulted in an absence of characteristic bed thickness trends in the preserved storm deposits.  相似文献   

环境小卫星S波段SAR监测土壤水分变化应用分析   总被引：1，自引：0，他引：1  

陈权  李震  王磊 《国土资源遥感》2005,16(2):12-15

通过IEM正演模型的模拟数据，发展了一种用S波段(3.0GHz)、VV极化数据反演土壤含水量相对变化的算法；选择典型的土壤含水量、地表粗糙度及入射角变化范围，模拟出两幅SAR图像，并把该算法应用到模拟图像中，对算法进行验证和改进； 将结果与输入值对比，结果表明，该算法能较好地提取土壤含水量时间和空间变化信息。  相似文献   

县级国土资源管理信息系统建设     

林春泉 《现代测绘》2005,28(5):45-46,48

国土资源管理信息系统是建设国土资源管理现代化、服务社会化、政务公开化的基础.结合工作实际情况,本文叙述了永安市国土资源管理信息系统的建设、结构,模块功能.子系统模块可根据工作职能的调整任意添加、卸载等设计特点.  相似文献   

Basaltic pyroclastic flows of Fuji volcano, Japan: characteristics of the deposits and their origin     

T. Yamamoto  A. Takada  Y. Ishizuka  N. Miyaji  Y. Tajima 《Bulletin of Volcanology》2005,67(7):622-633

Fuji volcano is the largest active volcano in Japan, and consists of Ko-Fuji and Shin-Fuji volcanoes. Although basaltic in composition, small-volume pyroclastic flows have been repeatedly generated during the Younger stage of Shin-Fuji volcano. Deposits of those pyroclastic flows have been identified along multiple drainage valleys on the western flanks between 1,300 and 2,000 m a.s.l., and have been stratigraphically divided into the Shin-Fuji Younger pyroclastic flows (SYP) 1 to 4. Downstream debris flow deposits are found which contain abundant material derived from the pyroclastic flow deposits. The new¹⁴C ages for SYP1 to SYP4 are 3.2, 3.0, 2.9, and 2.5 ka, respectively, and correspond to a period where explosive summit eruptions generated many scoria fall deposits mostly toward the east. The SYP1 to SYP4 deposits consist of two facies: the massive facies is about 2 m thick and contains basaltic bombs of less than 50 cm in size, scoria lapilli, and fresh lithic basalt fragments supported in an ash matrix; the surge facies is represented by beds 1 to 15 cm thick, consisting mainly of ash with minor amount of fine lapilli. The bombs and scoria are 15 to 30% in volume within the massive facies. The ashes within the SYP deposits consist largely of comminuted basalt lithics and crystals that are derived from the Middle-stage lava flows exposed at the western flanks. SYP1 to SYP4 were only dispersed down the western flanks. The reason for this one-sided distribution is the asymmetric topography of the edifice; the western slopes of the volcano are the steepest (over 34 degrees). Most pyroclastic materials cannot rest stably on the slopes steeper than 33 degrees. Therefore, ejecta from the explosive summit eruptions that fell on the steep slopes tumbled down the slopes and were remobilized as high-temperature granular flows. These flows consisted of large pyroclastics and moved as granular avalanches along the valley bottom. Furthermore, the avalanching flows increased in volume by abrasion from the edifice and generated abundant ashes by the collision of clasts. The large amount of the fine material was presumably available within the transport system as the basal avalanches propagated below the angle of repose. Taking the typical kinetic friction coefficient of small pyroclastic flows, such flows could descend the western flanks where scattered houses are below 1,000 m a.s.l. A similar type of pyroclastic flow could result if explosive summit eruptions occur in the future.Editorial responsibility: R Cioni  相似文献