Variations of Eu/Eu* ratio in Vendian shales of the Volga-Ural region and the boundary traced between the Redkino and Kotlin Horizons

Variations of Eu/Eu* ratio in shales from the upper Vendian Kairovo and Shkapovo groups of the Shkapovo-Shikhan depression, the Volga-Ural region, are considered. Shales in the lower part of the Karlin Formation are established to be similar in geochemistry to the shale member with abnormally low Eu/Eu* ratios at the base of the Upper Vendian Kotlin Horizon of the East European Platform. According to these data, the studied formation appears to be a lithostratigraphic unit of the Kotlin Horizon, while the Baikibashevo, Staropetrovo and Salikhovo formations belong to the Redkino Horizon of the upper Vendian.     

Provenance composition and features of geological evolution of the Late Vendian foreland basin of the Timan orogen

The provenance composition and geological evolution of different segments in the distal zone of the Late Vendian foreland basin of the Timan orogen were deciphered on the basis of sequence stratigraphic reconstructions and precision geochemical data on the Upper Vendian fine-grained terrigenous rocks from the Southeast White Sea region, Vychegda, Verkhnekama, and Shkapovo-Shikhan basins, and the Kvarkush-Kamennogorsk and Bashkirian meganticlinoriums. The Upper Vendian of the Southeast White Sea region is subdivided into four sequences: Agma, Solza, Zimnie Gory, and Erga. The tracing of sequence boundaries and lateral facies associations from the Southeast White Sea Region to the South Urals made it possible to identify the main stages of the evolution of sedimentary filling of the foreland basin: (I) shallow water epiplatformal basin, (II) isolated basin, (III) lowstand system tract, and (IV) progradation of delta platforms. Position of data points of the Upper Vendian shales, silty mudstones, and mudstones plotted in the diagrams Th-La, Ni-Cr, Gd_N/Yb_N-Eu/Eu*, Sc-Th/Sc, La/Sm-Sc/Th, and Co/Hf-Ce/Cr, together with their REE systematics and data on Nd model ages indicates that the Proterozoic, including Neoproterozoic rocks of the Timan thrust-folded belt served as the main source for fine aluminosiliciclastic material in the distal zones of the Timan foreland basin. Obtained results are consistent with the concept that the Vendian stage of the evolution of the Eastern European platform is related to the intense input of allochthonous material in its peripheral area owing to the activation of orogenic processes in the adjacent mobile belts and allow us to significantly specify the paleogeographical reconstructions.     

Lithogeochemistry of the Vendian fine-grained clastic rocks in the southern Vychegda trough

Lithogeochemical features of the Vendian mudstones and silty mudstones taken from Borehole Keltma 1 in the southern part of the Vychegda trough of the Mezen syneclise are discussed. It is shown that fine-grained clastic rocks of the Ust-Pinega, Krasavino, and Mezen formations have similar chemical compositions, suggesting their accumulation in sufficiently similar settings. The main part of the studied samples has K₂O/Al₂O₃ < 0.4. This fact, in combination with the absence of TM-FM and NPM-HM correlations, indicates a significant contribution of recycled aluminosiliciclastics in their composition. At the same time, the absence of correlation between CIA and indicator ratios of rock composition in the paleodrainage basins, such as Th/Cr and Th/Sc, indicates that CIA and some other lithochemical indicators appropriately reflect the paleoclimatic conditions in source areas surrounding a basin. The CIA value in most of the analyzed samples is no more than 70. Thus, the Keltma section is similar to Upper Vendian sequences of the Kvarkush-Kamennogorsk anticlinorium and the Shkapovo-Shikhany depression. It has been established that felsic and intermediate magmatic rocks coupled with a significant contribution of quartz-rich sediments served as the source of fine aluminosiliciclastics for the southern Vychegda trough during the Vendian. High Ce/Cr values in the mudstones and silty mudstones suggest that the geochemically primitive Archean protoliths were not involved in the washout. In the SiO₂-K₂O/Na₂O diagram, the Vendian mudstones and silty mudstones are plotted in the field of sediments of active continental margins. Typical low values of Mo/Mn and some other redox indices in these rocks indicate that oxidizing environment predominated in bottom waters of the sedimentation basin during the entire Vendian. Analysis of variations of the lithochemical indicators upward the Vendian sedimentary successions in borehole Keltma 1 made it possible to divide the section into three sequences of different lithofacies and paleontological compositions.     

Upper Riphean and Vendian sandstones of the Bashkirian anticlinorium

The analysis of lithogeochemical data on the Upper Riphean and Vendian sandstones from the Bashkirian anticlinorium showed that sandstone associations formed in a passive sluggish tectonic regime in the middle Late Vendian were replaced by associations accumulated in the more active tectonic settings. This is well seen in the SiO₂-K₂O/Na₂O and (Fe₂O₃^* + MgO)-TiO₂ diagrams reflecting the particular and median compositions of psammites. The lithochemical characteristics of sandstones were examined to determine the compositional variation of rock complexes eroded on paleodrainage areas. Quartz-rich sedimentary, metasedimentary, and metamorphic rocks, as well as felsic igneous rocks prevailed in the paleodrainage areas throughout the entire Late Riphean and Early Vendian, while the main sources of clastic material in the Late Vendian were igneous intermediate and basic rocks. With allowance made for the previous comparative-lithological data and some other materials, significant similarity in the position and orientation of compositional fields of psammites from the middle and upper levels of the Asha Group (Bashkirian anticlinorium) with fields of psammites from different syncollisional (flysch and molasse) basins in the SiO₂-K₂O/Na₂O, K₂O/Na₂O-SiO₂/Al₂O₃, F1–F2 and other diagrams suggests that the middle Late Vendian (beginning from the Basa level) was marked by a variation in tectonic/geodynamic settings of sandstone accumulation and in composition of the eroded paleodrainage systems. The revealed trend agrees well with concept of the existence of the Late Riphean-Vendian Pechora paleocean.     

Composition of sediment provenances and patterns in geological history of the Late Vendian Mezen Basin

Formation conditions of sedimentary successions in the Mezen Basin are considered on the basis of Cr, Th, Sc, Ni, Hf, and REE distribution and model Nd age of the Upper Vendian fine-grained terrigenous rocks. Geochemistry of mudstones and shales of the Lyamitsa, Verkhovka, Zimnie Gory, and Erga formations in the Belomorian-Kuloi Plateau, as well as the Ust-Pinega and Mezen formations in the Vychegda Trough, does not allow us to consider these stratigraphic units as erosion products of the primitive Archean basement of the Baltic Shield or the central segment of the East European Craton (EEC) basement. Taking into account sedimentological data on the direction of paleoflows in the basin and the model Nd age of the fine-grained terrigenous rocks, we suggest that the Mezen Basin was filled in the Late Vendian mainly with erosion products of the Riphean igneous and metasedimentary complexes of the Timan-Pechora region. These conclusions are consistent with the sequence-stratigraphic architecture of sediments in the basin. According to the new model proposed, the Late Vendian Mezen Basin was a foredeep formed as a result of subsidence of the northeastern margin of the EEC under the load of overthrusted rock masses of the Timan-Pechora Foldbelt. The clastic material was derived from the emerging orogen.     

Upper Precambrian sandstones in the Volga-Ural region: Mineralogy, petrography, lithogeochemistry, and formation conditions

The paper presents data on the mineralogy, petrography, and lithogeochemistry of Riphean and Vendian sandstones in the Volga-Ural region. The studied rocks generally differ in several parameters. The Zr/Sc and Th/Sc values typical of psammites suggest that the rocks are dominated by the petrogenic clastic material. This conclusion is supported by median K₂O/Al₂O₃ values (from 0.39 to 0.45). The fine-grained clastic rocks associated with sandstones are also characterized by sufficiently high K₂O/Al₂O₃ values, indicating the prevalence of the first cycle material therein. It is shown that the Prikamsk and Tukaevo sandstones include, in addition to the petrogenic quartz, a significant amount of lithogenic (multifold redeposited) quartz, whereas ratio of these rock types is approximately equal in the Leonidovo and Baikibashevo sandstones. Sandstones of the Kairovo and Shkapovo groups are dominated by the petrogenic quartz. Analysis of the ln(Q/L + CE)-ln(Q/F) diagram shows that the Vendian psammites are dominated by disintegration products of plutonic rocks, whereas the Riphean psammites contain a significant portion of clastic material (related to the erosion of metamorphic rocks) along with felsic and intermediate-felsic igneous rocks. Relationships of feldspars, rock clasts, polycrystalline quartz, and quartz, in general, reflected in the Q_t/(F + R)-Q_p/(F + R) diagram indicate that the Riphean psammites were deposited in a humid setting; the Vendian psammites, in a semihumid/semiarid setting.     

西准噶尔晚石炭世哈拉阿拉特山组烃源岩发育沉积环境与有机质富集因素分析

准噶尔盆地西北缘哈拉阿拉特山地区发育一套晚石炭世哈拉阿拉特山组灰黑色泥岩层系,是该地区石炭系油气藏的主要烃源岩之一,但到目前为止,对该套烃源岩发育的沉积环境和有机质富集因素的认识尚不清楚。本文基于西准噶尔哈拉阿拉特山地区晚石炭世哈拉阿拉特山组乌和公路剖面,进行了详细的沉积学和岩石学研究,系统采集了17件新鲜泥岩样品,并开展了有机碳含量、主量元素和微量元素实验分析。通过综合分析野外调查结果和室内实验数据,得到如下几点认识：1）哈拉阿拉特山组泥岩发育在深海-半深海的沉积环境中,受浊流沉积频发的影响,底层水体一直处于富氧-缺氧的动荡变化过程之中;2）低V/Cr和U/Th比值,以及低V和U元素含量,指示了泥岩总体上形成于偏氧化的沉积环境;3）高的P和Ni元素含量,反映了当时水体具有较高的古生产力;4）在较高古生产力背景下,哈拉阿拉特山组泥岩有机质丰度（TOC平均为0.49%）偏低,原因是偏氧化的保存条件。因此,可以认为哈拉阿拉特山组泥岩有机质质富集主要受控于沉积水体的保存（氧化还原）条件。     

Late Vendian unfolded Molasse in the northeastern, eastern, and southwestern peripheries of the east European platform: Distinctive lithogeochemical features

The paper reports data on the lithogeochemistry of sandstones and silty mudstones from Upper Vendian sedimentary sequences in the northeastern, eastern, and southwestern peripheries of the East European Platform belonging to the so-called unfolded molasse. The sequences are dominated by wackes, arkoses, subarkoses, litharenites, and sublitharenites, i.e., chemically immature and moderately mature psammites, and can be classed with rocks produced by clastic material brought from orogens surrounding the platform. The higher TiO₂, Al₂O₃, FeO_tot, MgO, Na₂O, and K₂O concentrations of the psammites than those in the average cratonic Phanerozoic sandstone (APhSa) testify that the chemical maturing of the rocks was not completed. The silty mudstones accompanying the sandstones have a composition closer to those of the average cratonic Phanerozoic shale (APhSh), but this is likely explained by the fact that the rocks were produced of material brought from erosion territories of much greater area. The lithogeochemical data generally indicate that these territories were dominated by acid and intermediate magmatic rocks with variable fraction of sedimentary rocks when the Late Vendian sedimentary associations in question were produced. The distribution of certain indicator trace elements in the sandstones and silty mudstones show that the average composition of the eroded complexes was close to the composition of the post-Archean upper continental crust, but the erosion areas occasionally (in the Vychegorskii trough and the Shkapovsko-Shikhanskaya depression) contained relatively primitive source rocks. The data points of the great majority of the sandstones and silty mudstones plot in the SiO₂-K₂O/Na₂O and F1–F2 diagrams in the fields of sediments typical of the environments of active continental margins, which is consistent with the arrangement of the data points of these rocks in the La-Th-Sc, Th-Sc-Zr/10, and Th-Co-Zr/10 diagrams. All of these features confirm that the sedimentary rocks in question affiliate with rock associations produced at an active tectonic regime.     

贺兰山汝箕沟地区及中卫探区上三叠统烃源岩初步评价?

贺兰山中卫探区是中国石化胜利油田分公司2002年8月登记的勘探新区,迄今为止,探区内还没有钻井资料,总体的勘探程度非常低。为研究中卫探区上三叠统烃源岩的生烃能力,对探区以北汝箕沟地区上三叠统露头区暗色泥岩进行了取样分析,结果表明：该泥质岩的有机碳含量为3.03%,总烃含量0.0025%;干酪根显微组分以镜质组为主,类型指数-72.5,属Ⅲ型干酪根;Ro值为0.93％,有机质热演化已达到成熟阶段。与探区以东鄂尔多斯盆地延长组、石炭系-二叠系煤系地层相比较,汝箕沟地区上三叠统泥质岩样品的有机质丰度较高,成熟度好,可作为较好的气源岩。晚三叠世时期,中卫探区和汝箕沟地区同属滨浅湖相沉积环境,中卫探区更靠近湖盆中心,为更有利的生烃沉积相带。中卫探区上三叠统烃源岩应具有较好的生气能力,应以该套烃源岩为基础,加强中卫探区内天然气的勘探。     

Systematics of rare earth elements, Th, Hf, Sc, Co, Cr, and Ni in the vendian pelitic rocks of the Serebryanka and Sylvitsa groups from the western slope of the Central Urals: A tool for monitoring provenance composition

This paper presents the first data on the systematics of rare earth elements (REE), Th, Hf, Sc, Co, Cr, and Ni and the Nd model ages of fine-grained aluminosilicate clastic rocks of the Serebryanka and Sylvitsa groups of the Vendian from the Kvarkushsko-Kamennogorskii meganticlinorium (western slope of the Central Urals). It was found that the REE distribution patterns of shales and mudstones of the two groups are similar to those of the majority of post-Archean fine-grained terrigenous complexes. The presence of pelitic rocks with Gd_N/Yb_N > 2.0 in a number of Vendian levels suggests a contribution from an Archean component in the composition of the fine aluminosilicate clastic material. This is probably also indicated by the high degree of heavy REE depletion in some mudstone samples. The REE systematics allow us to suppose a heterogeneity of Vendian paleocatchments and variations in their composition with time. The eroded areas had the most mature composition in the beginning of Serebryanka. Starting from the second half of Serebryanka, mafic and/or ultramafic rocks started playing a significant role in the provenances. The rocks of the lower portion of the Serebryanka Group show T_Nd(DM) values of about 2.0 Ga, whereas the upper part of the section is dominated by rocks with T_Nd(DM) ? 1.77–1.73 Ga. This indicates that during the Taninskaya and Koiva time periods, fine aluminosilicate clastic material was supplied into the sedimentation region mainly from the west, from the eastern areas of the east European platform, where Archean and Early Proterozoic crystalline complexes dominated. A decrease in model ages was related to the addition of juvenile mantle material to the mature continental crust. Such processes can be illustrated by the mafic-ultramafic complexes (Dvoretskii, Shpalorezovskii, Vil’vinskii, etc.) located in the field of Vendian sedimentary sequences, which show T_Nd(DM) values from 824 to 707 Ma. It was concluded that the history of the formation of an Early Vendian rift in the western slope of the central Urals included only one rifting event (rather than three, as was previously supposed), which was supported by a variety of recent geological and isotope geochemical data.     

Geochemical Characteristics and Sedimentary Control of Pinghu Formation (Eocene) Coal‐bearing Source Rocks in Xihu Depression,East China Sea Basin

Coal-bearing source rocks of the Pinghu Formation in the Xihu Depression comprise an important material basis of oil and gas resources in the East China Sea Basin.Based on drilling core observation results combined with the analysis and test results of macerals,trace/rare earth elements,and rock pyrolysis,the geochemical characteristics and sedimentary control of coal-bearing source rocks formation are discussed in a high-frequency sequence framework.The results indicate that the macerals composition of the coal-bearing source rocks of the Eocene Pinghu Formation in the Xihu Depression is dominated by vitrinite,with low-medium abundance of exinite and almost no inertinite.The coals and carbonaceous mudstones display higher amounts of total organic carbon(TOC)(14.90%-65.10%),S1+S2(39.24-136.52 mg/g),and IH(191-310 HC/g TOC)respectively,as compared to the mudstones.Organic matter is plotted in typeⅢkerogens and partially in typeⅡ;it is mainly in the low maturity stage.The trace elements results imply that the samples were deposited in a weakly reducing to weakly oxidizing environment and were occasionally affected by seawater.The coal-bearing source rocks were deposited in a relatively oxygen-containing environment.The coal-bearing source rocks development is jointly controlled by the coal accumulation environment,the water conditions affected by ocean currents in offshore basins in China,oxidation-reduction cycles of aqueous media and paleoclimate evolution in a high-frequency sequence framework.     

红色泥岩层系地球化学特征及物源分析——以松辽盆地东南隆起区上白垩统姚家组为例

对松辽盆地东南隆起区姚家组地层进行系统的地球化学分析,结果表明:本区细碎屑岩中含有较多的稳定组分。通过对微量元素PAAS标准化及稀土元素标准化曲线配分模式研究,研究区内姚家组地层应来自同一物源区。CIA值及Th/U值表明源区经历了中等的风化作用;Th/Sc和Zr/Sc比值变化范围小,地球化学特征基本受源岩控制,物源区岩石未经过沉积再搬运。根据源岩构造背景判别图解,并结合前人的研究成果认为:姚家组地层的母岩主要为花岗岩(海西期和燕山期),并有少量燕山期中酸性喷出岩;源岩来自大陆边缘,为大陆岛弧火山岩系。通过Sr/Cu,Ni/Co,V/Cr,U/Th等比值综合分析,姚家组沉积时为干热气候,水体富氧,因此造成姚家组厚层的红色泥岩沉积。     

Organic geochemical evaluation of the oil/gas-generative potential of organic matter in Cretaceous strata from the Lower Benue Trough,Nigeria

An analytical procedure involving Rock-Eval pyrolysis of whole-rocks was adopted on fresh outcrop samples covering the three lithostratigraphic units in the Afikpo Basin of the Lower Benue Trough. Three petroleum systems are present in the Cretaceous delta frame: the Asu-River Group, the Eze-Aku Group and proto-Niger Delta sequences. The Afikpo Basin has been correlated to three petroleum systems in the Lower Congo Basin, Niger Delta and the Anambra Basin. The organic geochemistry of the shales, carbonaceous mudstones and coal beds show relatively moderate to high total organic carbon contents. The best potential hydrocarbon source rocks are the Eze-Aku Group and proto-Niger Delta shales, carbonaceous mudstones and coal beds where maturation was attained. The high total or-ganic contents, thermal maturity and terrigenous characters of the Asu-River Group, Eze-Aku Group and proto-Niger Delta sediments, suggest the presence of a large amount of natural gas with a small quantity of oil accumulation. Variations in source rock facies were observed from one lithostratigraphic unit to another, and initial HI values as a function of TOC were proposed for each lithostratigraphic unit. The results also show that TOC, HI, OI, S2 and Tmax vary from older to younger rocks. The Tmax values discriminate the rocks into immature and mature source rocks. Source rocks with high Tmax suggest high geothermal gradient/or recycled organic matter. Also high Tmax and S2 yield indicate late and post maturity. Recycled organic matter is characterized by low Tmax. The principal source rocks for gas in the Afikpo Basin are the Eze-Aku Group and proto-Niger Delta beds deltaic systems, consisting mainly of III to IV kerogens with a subordinate amount of type II organic matter. Based on the obtained results, it is concluded that the Cretaceous shales, carbonaceous mudstones and coals in the Afikpo Basin of the Lower Benue Trough are capable of generating and expelling hydrocarbons in the case of sufficient maturity.     

Paleoclimatic Environments of the Formation of Upper Vendian Rocks on the Belomorian-Kuloi Plateau,Southeastern White Sea Region

Reconstruction of Vendian climatic conditions on the East European Craton is of principle importance for elucidation of the Ediacarian biota habitat. However, paleogeographic reconstructions for this time are largely based on fragmentary and controversial paleomagnetic data. The degree of rock maturity deduced from lithochemical indicators allowed us to identify two stages of Late Vendian sedimentation on the Belomorian-Kuloi Plateau. The first (Lyamitsa-Verkhov) stage was characterized by the delivery of immature clastic material to the basin from a provenance with arid climate. The second (Erga-Padun) stage was marked by the input of relatively mature aluminosilicate clastics from a provenance with mild humid climate. The sedimentation stages approximately coincide with replacement of the shallow-water marine environment by the fluvioalluvial environment marked by steady and intense perennial river drainage from a highland in the northeast. In the Late Vendian (since 555 Ma ago), the northeastern area of the East European Craton was influenced by humid climate.__________Translated from Litologiya i Poleznye Iskopaemye, No. 3, 2005, pp. 267–280.Original Russian Text Copyright © 2005 by Grazhdankin, Podkovyrov, Maslov.     

鸡西盆地早白垩世烃源岩可溶有机质地球化学特征

应用气相色谱、色谱-质谱等分析方法,对鸡西盆地早白垩世烃源岩生物标志化合物特征进行了讨论,揭示了生物标志化合物对该区有机质生物来源、成熟度及沉积环境的指示意义。有机质热演化已进入成熟阶段,且煤岩热演化程度略高于泥岩。泥岩有机质母质来源主要为水生生物,同时有高等生物的输入;煤岩以陆生高等植物输入为主,同时也有水生生物输入。煤岩沉积环境为弱氧化环境,经历过较强的降解作用过程;泥岩沉积环境为还原环境,沉积介质咸化程度较高,更有利于有机质的保存和转化。     

Lithostratigraphy and geochemistry of Upper Vendian‒Lower Cambrian deposits in the northeastern Baltic monocline

The results of investigations of Upper Vendian?Lower Cambrian deposits in the northeastern part of the Baltic monocline specify views on the evolution of depositional environments of sedimentary successions constituting the basal part of the sedimentary cover in inner areas of the northwestern East European Platform. It is shown that the Late Vendian and initial Cambrian were characterized by the consecutive influx of relatively mature terrigenous detrital material that originated from both the weathering crust of the Baltic Shield and new sources. Its deposition was interrupted by notable, although likely asynchronous, hiatuses, which are registered at the base of the Upper Vendian Vasileostrovskaya and Voronkovo formations and Lower Cambrian Lomonosov Formation. In the Late Vendian, sedimentary material was transported from the Baltic Shield, while beginning from the initial Early Cambrian the additional contribution to the formation of the sedimentary cover of the Baltic monocline was provided by coarse-grained sedimentary material from the Timan margin of the Baltica as follows from U?Pb isotopic ages obtained for detrital zircons. At the same time, lithogeochemical parameters of fine-grained rocks experienced no substantial changes.     

层序地层格架下烃源岩地球化学研究:以尼日尔Termit盆地为例

如何利用有限的烃源岩样品的实验分析数据和地质资料尽可能地提高烃源岩评价和预测的精度,是当今烃源岩地球化学研究亟需解决的问题.采用层序地层学与油气地球化学相结合的方法,研究了非洲尼日尔Termit盆地基于层序地层格架下,上白垩统Yogou组烃源岩空间分布特征及有机质地球化学性质,初步展示了层序地层格架下烃源岩地球化学研究的方法、应用效果及优势.Termit盆地上白垩统Yogou组海相泥页岩是该盆地主要的烃源层,自下而上可划分为YSQ1、YSQ2和YSQ3共3个三级层序.根据层序/体系域发育特征、岩性录井和测井曲线响应特征,识别出外陆棚、内陆棚、三角洲、滨岸相泥岩及煤/炭质泥岩共5种不同沉积类型的烃源岩,不同层序与体系域具有不同的烃源岩纵向叠置关系和横向分布特征.不同类型的烃源岩有机质具有明显不同的地球化学性质:外陆棚和内陆棚泥岩有机质丰度中等-好,有机质生物来源中,低等水生生物贡献高,沉积于偏还原的沉积环境.滨岸和三角洲相泥岩有机质丰度高,具有低等水生生物和高等植物来源的双重贡献,沉积于偏氧化的沉积环境.三级层序或其体系域控制下的沉积相分布和演化导致不同类型烃源岩的发育和横向分布特征,同一沉积相类型的烃源岩具有相似的地球化学性质.与传统的以组、段为单元的烃源岩地球化学研究相比,层序地层格架下的烃源岩评价可以刻画不同层序、不同体系域和沉积相带烃源岩有机质地球化学性质的差异,提高资源评价和油-源对比的精度.      

Paleochannel and paleohydrology of a Middle Siwalik (Pliocene) fluvial system,northern India

Late Cenozoic fresh water molasses sediments (+6000 m thick) deposited all along the length of the Himalayan fore deep, form the Siwalik Supergroup. This paper reports the results of the paleodrainage and paleohydrology of the Middle Siwalik sub-group of rocks, deposited in non-marine basins adjacent to a rising mountain chain during Pliocene. Well-exposed sections of these rocks have provided adequate paleodrainage data for the reconstruction of paleochannel morphology and paleohydrological attributes of the Pliocene fluvial system.     

Provenance analysis of Eocene–Oligocene turbidite deposits in Pindos Foreland Basin, fold and thrust belt of SW Greece: constraints from framework petrography and bulk-rock geochemistry

The provenance of Eocene–Oligocene turbidites from the Pindos Foreland Basin, SW Greece, has been constrained using petrographical and geochemical techniques. Modal petrographic analysis of the studied sandstones shows that the source area comprises sedimentary, metamorphic, and plutonic igneous rocks deposited in a recycled orogenic environment and in magmatic arc province. The relative proportions of the detrital components indicate that the Late Eocene–Early Oligocene sandstones of West Peloponnesus are quartz-rich and were primarily derived from granitic and metamorphic basement rocks typically of a tectonically active area. Major, trace, and rare earth element (REE) concentrations in both sandstones and mudstones complement the petrographical data indicating an active continental margin/continental island arc signature. All the samples are light REE, enriched relative to heavy REE (HREE), with flat HREE pattern and positive Eu anomalies, suggesting that the processes of intra-crustal differentiation (involving plagioclase fractionation) were not of great importance. The results derived from the multi-element diagrams also suggest an active margin character and a mafic/ultramafic source rock composition.     

楚雄盆地北部桂花铜矿区晚白垩世含矿岩系沉积环境

楚雄盆地是青藏高原东缘“三江”构造带与扬子地台西缘结合部重要的含矿沉积盆地之一,以白垩纪地层赋存多个层位的砂岩型铜矿床为特征而不同于其他沉积盆地,长期备受关注。前人曾从矿床学角度进行砂岩铜矿床成矿作用相关研究,相对缺乏沉积学方面工作,进而导致对含矿岩系沉积环境及盆地属性和矿床成因认识的分歧。对楚雄盆地北部包括大村铜矿区在内的桂花地区晚白垩世含矿岩系进行了系统的地表调查、坑道及钻孔观测和沉积环境研究,认为该区上白垩统马头山组和江底河组是一套连续沉积组合,由河道亚相和边滩亚相沉积共同组成,形成于相对干旱的气候环境;沉积物源区位于盆地的北侧,曾出露有基性火山岩、花岗质岩石、碎屑岩、碳酸盐岩以及少量的变质岩等;晚白垩世时期,楚雄盆地具有北高南低的古地理格局,且在江底河组沉积成岩过程中,盆地总体曾经历了区域挤压作用引起的隆升破坏,也是区内砂岩型铜矿床的主要成矿时期。