Permian biostratigraphy of the northern Okhotsk region (Northeast Asia)     

A. S. Biakov 《Stratigraphy and Geological Correlation》2007,15(2):161-184

Fossil biota and detailed biostratigraphy of the Permian northeastern Okhotsk and Ayan-Yuryakh sedimentary basins located in the northern Okhotsk region are characterized. The biota core is represented by bivalves associated with gastropods, brachiopods, and other faunal groups. It is shown that a new regional stratigraphic scale of northeastern Russia based on brachiopods and bivalves may be used for subdivision of Permian sections in these basins. Fossil assemblages have many features in common with their counterparts from the Verkhoyansk region; at the same time, there are endemic species and the big group of species characteristic of the Omolon basin. The upper part of the Khivach regional horizon is subdivided into subzones based on the evolutionary lineages of the Maitaia and Intomodesma genera. Changes in the taxonomic composition of coeval communities in different basins are shown to be largely controlled by the basin depths and facies environments. Impoverished fauna of the Ayan-Yuryakh basin was less diverse in taxonomic aspect, represented almost entirely by bivalves (mostly Inoceramus-like) accompanied by rare gastropods. The discovered taxa are figured in majority, and table of their stratigraphic distribution is presented.  相似文献   

Structural styles of Albian rafts in the Espírito Santo Basin (SE Brazil): Evidence for late raft compartmentalisation on a ‘passive’ continental margin     

《Marine and Petroleum Geology》2017

In recent years, hydrocarbon exploration offshore SE Brazil has been focusing on Lower Cretaceous strata deformed by gravity gliding above Aptian salt. A three-dimensional (3D) seismic volume from the Espírito Santo Basin, SE Brazil is here used to: a) test the parameters considered to control raft tectonics on a margin tectonically reactivated in the Cenozoic, and b) investigate the impact of prolonged halokinesis on raft deformation. Offshore Espírito Santo, the combined effects of halokinesis and multiple (Andean) tectonic phases are expressed by local collapse, fault reactivation and late segmentation of Albian rafts. As a result of this deformation we observe four main raft geometries: a) rolled-over rafts, b) tabular rafts, c) collapsed rafts, and d) folded and tilted rafts on the flanks of salt rollers. This work shows that salt rollers formed buttresses to moving Albian-Cenomanian rafts, with withdrawal of salt from underneath some of the rafts leading to their collapse and welding onto pre-salt strata. This process occurred in the studied part of the Espírito Santo Basin with minimum control of post-raft overburden thickness on raft compartmentalisation. Salt withdrawal from underneath the rafts is an important phenomenon as it enhanced connectivity between pre-salt and post-salt units, potentially promoting the migration of hydrocarbons from syn-rift source units into post-salt reservoirs.  相似文献   

基于地学知识的大尺度土地利用/土地覆盖精细化分类方法研究   总被引：4，自引：0，他引：4  

杜国明  刘美  孟凡浩  匡文慧  春香  冯悦 《地球信息科学学报》2017,19(1):91-100

人类活动对生态环境具有显著影响,大尺度土地利用/覆盖变化（Land Use/Cover Change,LUCC）作为人类活动最直接的表征,能够很好地反映这一过程,因此进行精确而迅速的大尺度土地利用/覆盖分类与提取方法研究尤为关键。全球覆盖产品GlobCover（2005/2006）数据已经具有良好的空间精度和数据准确度,但仍然存在一些分类误差。为提高地表覆被分类精度,本文以GlobCover（2005/2006）的巴西数据为例,以2005年Landsat TM/ETM影像为主要信息源,结合相应地学知识与辅助数据,利用人机交互逐栅格修改方法得到2005年土地利用数据产品。结果表明：通过对GlobCover数据和本次成果数据进行精度评价与对比分析,GlobCover数据巴西地区的总体精度为67.17%,Kappa系数为0.58,改进后产品总体精度为93.39%,Kappa系数为0.91。此外,改进后数据显示巴西常绿阔叶林面积最大,面积比例达45.67%;农地/自然植被镶嵌面积次之,比例为19.19%;封闭灌丛面积最小,比例为12.34%。农地/自然植被镶嵌和灌丛与草地2种地类的修改比例最大,其中混合像元地类比例减少3.54%,灌丛与草地比例增加3.81%。综上,改进方法可以有效地提高土地利用/覆盖分类的效率和精度,为后续大尺度LUCC产品的制作和以LUCC产品为基础的相关研究提供参考。  相似文献   

赣东北-皖南元古代造山带构造格架及演化   总被引：20，自引：0，他引：20  

邓国辉  刘春根  冯晔 《地球学报》2005,26(1):9-16

赣东北-皖南元古代造山带位于扬子板块南缘江南造山带东段,经历了晋宁早期俯冲和晚期碰撞两个造山阶段,自北而南可划分为九岭褶皱变形区、鄣公山构造混杂岩带、江山-绍兴对接带,其间均以区域性构造带相隔,变形强度依次增强,中元古代变质地层分属于史密斯、有限史密斯、非史密斯地层范畴,难以建立总体地层层序而区别于传统的“史密斯”地层;同时,该套地层又形成于元古代扬子、华夏两板块的张开-闭合过程中的统一大地构造背景下,存在着一定的必然联系而有别于“地体构造”、“构造混杂岩”;依据地层组成结合岩石化学研究,在“构造混杂岩”基础上建立了“双列岛弧”的“沟弧盆体系”模式。  相似文献   

Petrology of nepheline syenite gneiss from Amazonian Brazil     

G. R. Lowell  R. Netuno Villas 《Geological Journal》1983,18(1):53-75

Nepheline syenite gneiss is exposed in three localities near the village of Boca Nova (47·04′W, 1°51′S) in northeastern Pará, Brazil. Isotopic and chemical evidence for an igneous premetamorphic history include: (1) bulk compositions which plot in the Q–Ne–Ks system on a peralkaline fractionation curve; (2) bulk compositions which fall on the Hviddal igneous trend in the SiO₂–Al₂O₃–Na₂O + K₂O molecular diagram; (3) an average K/Rb ratio identical to the average for nepheline syenites of the Khibina massif; (4) K/Rb ratios which lie on the ideal igneous fractionation curve; (5) Nb(Ta) contents far in excess of average crustal abundance; and (6) a low Sr₈₇/Sr⁸⁶ value (0·7034) characteristic of mantle derivation. Post-kinematic lit-par-lit injections, discordant veins, and concordant pods of leucocratic nepheline–alkali feldspar pegmatite partially replaced the metamorphic assemblage and destroyed any microscopic equilibrium texture that may have been present. The final disequilibrium assemblage consists of Fe-rich biotite and two generations each of sodic plagioclase, microcline, and nepheline. Some minor metasomatic chemical effects may be present in the rocks but a case for nephelinization of crustal rocks cannot be documented. Field, petrographic, and chemical constraints indicate that the Boca Nova gneiss is an early-stage migmatite formed by anatexis of metamorphosed igneous nepheline syenite or its volcanic equivalent. Regional metamorphism and partial melting opened the Rb-Sr system so that the whole-rock Rb/Sr isochron age of 724 m.y. has no unambiguous interpretation. A K/Ar age of 580 ± 10 m.y. from biotite denning the metamorphic foliation is regarded as a minimum date for the regional metamorphism and anatexis. No other alkaline rocks of comparable age are known in the Sao Luis Craton.  相似文献   

Comparing water use patterns of sand-binding species in an alpine semi-arid desert     

Lihui Tian  Huawu Wu  Haijiao Wang  Dengshan Zhang  Xiaofan He  Qiaoyu Wang 《水文研究》2023,37(1):e14798

The processes of species obtaining water resources are crucial to evaluate the adaptability of plantations, which can affect the establishment and survival of restored ecosystems and functions of water-limited ecosystems. However, there are still limitations in understanding water use patterns of different four plantations (Populus sylvestris, Salix cheliophe, Hippophae rhamnoides and Artemisia ordosica) in the Qinghai Lake basin. Stable isotopes of xylem water of four individual species were analysed at different dunes located at the eastern shore of Qinghai Lake in 2018 and 2019. The purpose of this study was to explore potential water sources used by different life form plants, to identify whether the soil moisture content and root distribution determined the plants water use patterns. Results from the Bayesian mixing model MixSIAR showed that all species mainly uses three levels of soil water, but they extracted soil water from different layers in different growing seasons among species. All species primarily depended on water from upper soil layers at the early growing stage, but P. sylvestris and S. cheliophe also absorbed much proportion middle and deep soil layers' water in dry year of 2019. All four species shift to use middle or deep soil layer water rather than shallow water in July with the most rainfall and soil water content (SWC). However, it was only used by P. sylvestris and H. rhamnoides in 2018. In all, seasonal water use pattern of different species was affected by SWC, soil texture and root distribution. Compared with moratorium plantations such as S. cheliophe, mixed afforestation of P. sylvestris and H. rhamnoides maximized of soil water sources absorbed by the plants. The study can shed light on plant–water relationships to facilitate the woody species for afforestation and desertification restoration management in the semi-arid desert ecosystem.  相似文献   

Deforestation in the Brazilian Amazon could be halved by scaling up the implementation of zero-deforestation cattle commitments     

《Global Environmental Change》2023

Deforestation for agriculture is a key threat to global carbon stocks, biodiversity, and indigenous ways of life. In the absence of strong territorial governance, zero-deforestation commitments (ZDCs), corporate policies to decouple food production from deforestation, remain a central tool to combat this issue. Yet evidence on their effectiveness remains mixed and the mechanisms limiting effectiveness are poorly understood. To advance understanding of ZDCs’ potential at reducing deforestation, we developed the first spatially explicit estimates of farmers’ exposure to ZDC companies in the Brazilian Amazon cattle sector. Exposure was measured by determining the market share of ZDC firms from the first full year of ZDC adoption in 2010 until 2018. Our analysis evaluated how variation in this exposure influenced deforestation. We found the G4 Agreement, the most widespread and strongly implemented cattle ZDC, reduced cattle-driven deforestation by 7,000 ± 4,000 km² (15 ± 8%) between 2010 and 2018. Additionally, had all firms adopted and implemented an effective ZDC, cattle-driven deforestation could have dropped by 24,000 ± 13,000 km² (51 ± 28%). These results for the world’s principal deforestation hotspot suggests supply chain policies can substantially reduce deforestation. However, their effectiveness is contingent on widespread adoption and rigorous implementation, both of which are currently insufficient to prevent large scale deforestation. Increased adoption and implementation could be incentivized through greater pressure from the Brazilian government and import countries.  相似文献