Neoproterozoic peritidal phosphorite from the Sete Lagoas Formation (Brazil) and the Precambrian phosphorus cycle   总被引：1，自引：0，他引：1       下载免费PDF全文

Justin B. R. Drummond  Peir K. Pufahl  Claudio G. Porto  Mariana Carvalho 《Sedimentology》2015,62(7):1978-2008

The Neoproterozoic Sete Lagoas Formation (ca 610 Ma) of the São Francisco Basin, Brazil, is a succession of siltstone, limestone and phosphorite. Phosphorite forms part of a previously unrecognized 150 to 200 m thick, unconformity bounded depositional sequence. Lithofacies stacking patterns indicate that deposition was punctuated by higher order fluctuations in base level that produced aggradational parasequences. These shallowing‐upward cycles record the progradation of phosphate‐rich intertidal flats over shallow subtidal deposits as accommodation filled. The presence of mudcracks, authigenic chert nodules, lack of coarse terrigenous clastics and the abundance of silt with fine, abraded quartz grains suggests accumulation along an arid coastline with significant aeolian input. Delivery of phosphorus adsorbed on aeolian Fe‐(oxyhydr)oxide and clay is interpreted as having stimulated phosphogenesis in peritidal environments. Lithofacies associations indicate that windblown phosphorus promoted the establishment of cyanobacterial communities along the coast, which produced photosynthetic oxygen and the suboxic conditions necessary for the precipitation of authigenic carbonate fluorapatite. As in other Precambrian phosphatic systems, nearshore oxygen oases were a prerequisite for phosphorite accumulation because redox sensitive phosphogenic processes were pushed into the sediment to concentrate phosphorus. In more distal, anoxic environments phosphorite could not form because these biotic and abiotic processes were suspended in the water column, which cycled phosphorus in sea water rather than at the sediment–water interface. Such shallow‐water phosphorite is unlike larger, younger Neoproterozoic–Phanerozoic phosphatic deposits inferred to have formed in deeper‐upwelling related environments. The increasing size of phosphatic deposits through the latest Precambrian is interpreted as reflecting the progressive ventilation of the oceans during the Neoproterozoic Oxygenation Event, and resultant expansion of phosphogenic environments into distal settings. The widespread cycling of bioavailable phosphorus at the sea floor not only produced the first true phosphorite giants, but may have also been an important precondition for the evolution of multicellular animals.  相似文献   

Abundance,distribution, and fluxes of dissolved organic carbon (DOC) in four small sub-tropical rivers of the Tampa Bay Estuary (Florida,USA)     

《Applied Geochemistry》2015

The delivery of organic carbon (C) from rivers to the coastal ocean via estuaries is recognized as an important component of the global C budget however, smaller river systems are often overlooked and modern flux estimates are not very different from historical estimates. Here, the seasonal (wet vs. dry) concentration and fluxes of dissolved organic C (DOC) were measured in five small sub-tropical rivers that drain into the Tampa Bay (FL, USA) estuary. DOC distributions were highly variable among riverine, mesohaline, and marine end-member samples in all river catchments and no significant differences were observed among or between DOC concentrations with respect to river catchment, season, or year of sampling. In general, DOC mixed non-conservatively during the wet seasons, and conservatively during the dry seasons, with the estuarine reaches of each river serving as a sink of DOC. Fluxes were strongly tied to discharge irrespective of season, and the estuaries removed 15–65% of DOC prior to export to coastal Bay and Gulf of Mexico waters. DOC concentrations were similar to others reported for low-elevation sub-tropical rivers, and a combination of elevation, residence time, and climate appear to control the abundance and variability of DOC in sub-tropical vs. tropical river systems. The characterization of DOC in small, sub-tropical rivers, which share characteristics with both their temperate and tropical counterparts, is critical for quantitatively constraining the importance of these systems in local-to-regional scale ocean C budgets. In addition to geomorphic properties, the role of past, present, and future land cover and other environmental change in small coastal rivers also exerts control on the quantity and flux of DOC in these systems.  相似文献   

Open Fissure Folds record coseismic loading and postseismic stress relaxation     

《Journal of Structural Geology》2015

Open Fissure Folds hosted by high pressure/low temperature metamorphic rocks of south Evia (Greece) are introduced, their structural and microstructural record is analysed, and a mechanical model is proposed. Open Fissure Folds are preserved as at least two parallel folded quartz–feldspar veins separated by narrow buckled rock columns. The veins originated as tensile cracks that propagated in the middle crust driven by high differential stress. Features diagnostic for Open Fissure Folds indicate that the rock columns represented the layers of high viscosity, and not the veins as consistently reported in many previous studies on folded veins. This record is taken to indicate that buckling of the rock columns initiated after arrest of the fractures and terminated prior to complete vein sealing. Accordingly, mechanical decoupling by open fissures allowed for buckling of the rock columns in response to episodic creep of the host rocks according to stress relaxation, as expected for postseismic deformation in the earthquake cycle. I propose that the parental fractures propagated in response to quasi-instantaneous coseismic loading of the middle crust. Buckling was attributed to transient postseismic creep and stress relaxation. Complete sealing of the veins occurred when stresses were largely relaxed. Each Open Fissure Fold records the stress and strain history of a single earthquake.  相似文献   

Life cycle of 70 Ma-old non-marine pennate diatoms     

《Cretaceous Research》2015

Life cycle variations in the morphological and behavioral traits of modern pennate diatoms are known for a wide variety of genera and it is assumed that patterns of asexual and sexual reproduction (e.g. size reduction and auxosporulation) have remained essentially unchanged since their origin. We show here that many characteristics of modern pennate diatoms and the communities they inhabit can indeed be recognized in remarkably well-preserved, non-marine fossil material from the Cretaceous (∼70 Ma) Huepac Chert in NW Mexico. Besides the incremental size reduction of the siliceous frustules in species including Fragilaria tarahumara, we also demonstrate the spatial arrangement and distribution of these cells in in situ microalgal communities, and present evidence for local production of dense exopolymeric substances, cell division, and possibly auxospores. This is the first time that such life cycle stages are reported for non-marine fossil diatoms.  相似文献   

Environmental impacts of household appliances in Europe and scenarios for their impact reduction     

Roland Hischier  Francesca Reale  Valentina Castellani  Serenella Sala 《Chemie der Erde / Geochemistry》2013

Assessing the environmental impact due to consumption of goods and services is a pivotal step towards achieving the sustainable development goal related to responsible production and consumption (i.e. SDG 12). Household appliances plays a crucial role and should be assessed in a systemic manner, namely considering all life cycle stages, technological efficiency, and affluence aspects. The present study assess the impact of such household appliances used in Europe, and tests scenarios of potential impact reduction at various scales. Life cycle assessment is applied to 14 different household appliances (ranging from dishwashers to television devices) selected to build a set of representative products, based on their economic value and diffusion in households in Europe. Related impacts are calculated with the Environmental Footprint method for calculating a Consumer Footprint “appliances” for the baseline year 2010. A number of scenarios encompassing eco-solutions on a technical level, changes in consumption pattern, behavioral changes, as well as the combination of all these aspects are run to estimate the Consumer Footprint related to household appliances for the year 2030, compared against this baseline scenario. The baseline Consumer Footprint is confirming the importance of the use phase in leading the impacts in almost all impact categories. Testing different scenarios concludes that there is a reduction of the impact for most of the categories (with up to 67% for the ozone depletion potential, and still around 35% for the global warming potential), while two of the here examined impact categories (i.e. land-use and mineral resource depletion) show an overall potential that is even negative – i.e. the results of all scenarios are higher than the ones of the 2010 baseline scenario. The increase in purchase and use of such appliances may offset energy efficiency benefits in some of the examined categories. Hence, the assessment of sustainability of appliances consumption should always include several scales, from the efficiency of the products (micro scale), to the improvement of the energy mix (meso scale), up to accounting for socio-economic drivers and patterns of consumption affecting the overall appliances stock (macro scale).  相似文献   

The Southern Ocean silica cycle     

《Comptes Rendus Geoscience》2014,346(11-12):279-286

The Southern Ocean is a major opal sink and plays a key role in the silica cycle of the world ocean. So far however, a complete cycle of silicon in the Southern Ocean has not been published. On one hand, Southern Ocean surface waters receive considerable amounts of silicic acid (dissolved silica, DSi) from the rest of the world ocean through the upwelling of the Circumpolar Deep Water, fed by contributions of deep waters of the Atlantic, Indian, and Pacific Oceans. On the other hand, the Southern Ocean exports a considerable flux of the silicic acid that is not used by diatoms in surface waters through the northward pathways of the Sub-Antarctic Mode Water, of the Antarctic Intermediate Water, and of the Antarctic Bottom Water. Thus the Southern Ocean is a source of DSi for the rest of the world ocean. Here we show that the Southern Ocean is a net importer of DSi: because there is no significant external input of DSi, the flux of DSi imported through the Circumpolar Deep Water pathway compensates the sink flux of biogenic silica in sediments.  相似文献   

陆相火山地层研究方法——“火山构造-岩性岩相-火山地层”三位一体     

卢清地 《福建地质》2014,33(4):251-261

“火山构造-岩性岩相-火山地层”三位一体研究方法强调剖面研究必须与路线调查相结合,火山地层研究必须与火山岩相及岩性、火山构造研究相结合,按火山构造单元为范围建立火山地层层序和格架.通过1∶25万周宁县等4幅区域地质调查项目的实践,建立的火山地层格架客观、合理,火山构造面貌清楚、层次分明、具较强立体感,全面反映不同时期、不同阶段火山作用特点和演化规律,显著提高了火山地质研究程度.  相似文献   

辽东太子河地区中寒武世古气候特征     

吴子杰  潘玉啟  包洪伟 《江苏地质》2014,38(4):561-566

根据蒸发岩及伴生沉积构造、沉积红层、碳酸盐岩及鲕粒沉积、古生物、古风化壳类型、海绿石等沉积标志,恢复中寒武世古气候。以本溪地区为重点,结合太子河沉积区的特征,将该区中寒武世古气候划分为6个潮湿—干燥炎热气候变化周期,进而确定研究区当时属于温带—亚热带半干旱气候地区。  相似文献   

晋东北侏罗纪盆地早中侏罗世沉积充填记录及其构造意义   总被引：1，自引：0，他引：1  

李振宏  董树文  渠洪杰 《地球学报》2014,35(3):285-294

侏罗纪/白垩纪之交是中国中东部乃至东亚地区构造活动的重要时期,发生了构造变形、岩浆-成矿、气候环境突变等一系列重大的构造事件,被称为"燕山运动",但对于其启动时限的认识却一直存在着争议。本文以晋东北侏罗纪盆地为研究对象,在早中侏罗世沉积序列划分和重矿物组合特征变化研究的基础上,结合重点层位火山岩夹层锆石U-Pb同位素测年,详细刻画了这期构造事件启动的具体时限。研究认为,中侏罗统云岗组(J2yg)底部砾岩沉积时期,沉积序列由早期的湖进序列向湖退序列转换,碎屑岩的成分由早期的以石英、长石为主过渡为以长石、岩屑为主,重矿物组合由早期的以锆石为主过渡为以石榴子石为主,预示着侏罗纪构造活动进入了启动阶段。通过下侏罗统永定庄组(J1y)火山碎屑岩的年龄(179.2±0.79)Ma和中侏罗统云岗组(J2yg)顶部凝灰质碳酸盐岩年龄(160.6±0.55)Ma的制约,推测中侏罗统云岗组(J2yg)底部砾岩沉积时间大约为168 Ma,这个时间代表了侏罗纪构造活动(燕山运动)的起始时限。该成果在沉积学方面为燕山运动的起始时限提供了新的制约。  相似文献   

A new aquatic crustacean (Isopoda: Cymothoida) from the early Cretaceous of southern England and comparison with the Chinese and Iberian biotas     

Edmund A. Jarzembowski  B. Wang  Y. Fang  H. Zhang 《Proceedings of the Geologists' Association. Geologists' Association》2014

The first malacostracan crustacean is described and named from the English Wealden, Cymothoidana websteri gen. et sp. nov., a Cirolana-like, cymothoidan isopod. The problem of homoplastic convergence in somatic characters is discussed, and Cymothoidana is treated as a collective group (morphotaxon) under the International Code of Zoological Nomenclature for cirolanoid and cymothooid fossils which cannot be assigned to natural taxa on preservational grounds. The palaeoecology of early Cretaceous peracaridan malacostracans is considered, including the spelaeogriphaceans Liaoningogriphus from China (Jehol biota), and Spinogriphus from Spain (Las Hoyas Konservat-lagerstätte). There were probably no true stygobites, Spinogriphus perhaps a crenobite, but the colonisation of reduced salinity environments (Cymothoidana) and freshwater lakes (Liaoningogriphus) had commenced.  相似文献