秦岭大巴山地区紫阳毒重石矿床成因: 矿石组构、氧化还原敏感元素和碳-氧同位素证据

秦岭大巴山地区钡矿资源极为丰富,以蕴含世界罕见的层状毒重石矿床为特色。本研究在紫阳毒重石矿床中发现了玫花瓣状结构,经显微镜观察和电子探针分析表明,玫花瓣体由板柱状重晶石呈放射状排列而成,与前人报道的矿物组成明显不同。紫阳灰黑色毒重石矿石有较高的V、Ni、Cr、U、Mo含量,较低的Th/U比值(<0.04),较高的V/(V+Cr)比值(>0.8)和V/(V+Ni)比值(>0.9),指示寒武纪紫阳毒重石矿床的沉积环境为较还原的环境。紫阳毒重石矿石的C同位素分布在-10.9‰~-16.0‰, O同位素分布在18.1‰~22.3‰之间,表明毒重石中CO₃^2-是有机质通过氧化作用或脱羧基(生物有机质降解)作用提供的低¹³C的碳与同期海水提供的高¹³C的水溶性HCO₃^-或CO₃^2-的混合来源。综合研究表明,该区毒重石矿床的形成可能与寒武纪早期的海底热液成矿作用有关。     

Characterization of trace elements in sulphur-rich Late Permian coals in the Heshan coal field,Guangxi, South China

The concentration of trace elements and their distribution in the late Permian coal in the Heshan coal field, Guangxi Autonomous Region, were analysed in this paper. The late Permian coal of the Heshan mining district was developed in a low energy and shallow, confined carbonate platform. Heshan coal is a low volatile bituminous coal characterized by a high sulphur content, ranging between 2.0% and 8.2%. Compared with the worldwide average content of the trace elements in coal, the content of some trace element in the study coal is markedly high (Bi, Ce, Cr, Cs, Cu, Ga, Hf, Sr, Ta, Th, U, V, W, Y, Zr, La, Mo, Nb and Sc).The trace element associations were investigated by means of intracorrelation analysis. Some elements, such as Cl, F and Sr are found in coal in association with the carbonate minerals. V, Cr, Zn, Mo, Ni and As contents in coal vary significantly amongst the coal samples. They are mainly concentrated in the lower part of the coal #4 upper of Suhe and Lilan mines and the coal #4 lower of Dong mine, and these possibly occurring in minerals such as arsenide and sulphide. The content of U in Heshan coal is high and is mainly concentrated at the upper and the lower parts of the coal seam and it is associated with mineral assemblages with Ba, Mo, V, Ni, Zn, Rb and Cr. Furthermore, La and Ce are highly correlated with those found in phosphate minerals and Pb, Sc, Ga, Th, Y and Sn to those in aluminosilicate minerals. The enrichment of some elements such as V, Cr, Zn, Mo, Ni, Rb as well as total sulphur and iron in the lower part of most coal seams might be associated with the formation of soil horizon before the accumulation of peat in the basin. Some other elements such as Cl, F, Sr and Ca are locally concentrated in the top of specific coal seams as a result of the leaching from overlying carbonates.     

Changes in palaeoenvironmental conditions during deposition of the Permian Kupferschiefer (Lower Rhine Basin, northwest Germany) inferred from molecular and isotopic compositions of biomarker components

Biomarker distributions based on GC and GC-MS data supplemented by stable carbon isotopic compositions based on irm (isotope ratio monitoring) GC-MS data have been used to investigate changes in depositional conditions in a number of samples from a 2 m core (Rheinberger Heide) covering the entire deposition of the Permian Kupferschiefer (Lower Rhine Basin, northwest Germany). Compound classes investigated are aliphatic and aromatic hydrocarbons and maleimides (1H-pyrrole-2,5-diones). The core has been previously divided into four sections: TI, TIIA, TIIB and TIII based on lithology. The biomarker distributions and the δ¹³C values of components indicate contributions from cyanobacteria, algae, green sulphur bacteria and higher plants (minor) throughout Kupferschiefer deposition. All of the phytoplanktonic components show ¹³C enrichment in the lowest section, suggesting a greater productivity. The occurrence of components derived from green sulphur bacteria (Chlorobiaceae) indicates that the entire deposition was characterised by periods of photic zone anoxia. Such conditions were rapidly established after the initial transgression of the Zechstein Sea and may have been productivity-driven, but were less prevalent during deposition of the upper core sections.     

黔南坳陷油苗来源:碳、硫同位素及生物标志物证据

为明确黔南坳陷不同层位油苗来源,在广泛采集不同层位烃源岩、油苗样品的基础上,采用GC、GC-MS及GC-IRMS等方法对其碳、硫同位素及生物标志物特征进行系统分析,进而开展了油源对比.结果表明:油苗的δ13C值为-33.04‰～-31.63‰,平均-32.26‰(n=18);δ34S值为+16.06‰～+23.06‰,平均+18.99‰(n=4);油苗遭受不同程度生物降解,常规甾、萜烷面貌特征差异较大,但普遍含有较丰富的三环萜烷、伽玛蜡烷、三芳甾烷、芳基类异戊二烯烃、惹烯和硫芴;C25三环萜烷/C24四环萜烷值、二苯并噻吩/菲与Pr/Ph相关图表明油苗为典型海相原油;Ts/(Ts +Tm)、C29甾烷20S/(20S+ 20R)及甲基菲指数等均表明油苗为成熟-高熟原油.研究区下寒武统牛蹄塘组黑色泥岩干酪根δ13C值为-35.79‰～-29.88‰,平均-32.85‰(n=35),与油苗相关性良好,而泥盆系、石炭系和二叠系烃源岩δ13C值显著偏重,均大于-29‰;下寒武统牛蹄塘组黑色泥岩干酪根δ34S值为+ 14.78‰～+ 17.60‰,平均+16.32‰(n=4),与油苗具有很好的可比性,而下、中泥盆统黑色泥岩干酪根δ34S值分别为-9.10‰～-6.78‰和+0.63‰～ +7.93‰,二叠系煤系地层有机质δ34S值为-7.40‰～+4.00‰,均显著偏轻.此外,下寒武统黑色泥岩普遍含有较丰富的伽玛蜡烷、三芳甾烷、芳基类异戊二烯烃和惹烯,三芴系列中硫芴含量极高,其它几套黑色泥岩则不合或贫含三芳甾烷和惹烯,伽玛蜡烷和硫芴含量亦较低.综合认为油苗具相同来源,且均与研究区下寒武统黑色泥岩具有较好亲缘关系.     

The San Gregorio Magno lacustrine basin (Campania,southern Italy): improved characterization of the tephrostratigraphic markers based on trace elements and isotopic data

Central–southern Italy is one of the most suitable areas in the world for tephrostratigraphic studies, owing to the numerous volcanic sources with explosive activity during the Pleistocene. This work presents a systematic investigation of the chemical (trace elements) and isotopic (Sr and Nd) compositions of the main tephra markers within lacustrine sediments of the San Gregorio Magno Basin (Campania, southern Italy). This study: (i) provides full geochemical (trace elements and isotopes) characterization of eight significant Upper Pleistocene marker layers (X‐6, X‐5, C‐22, MEGT/Y‐7, CI/Y‐5, C‐10, Y‐3, NYT/C2) widely dispersed over the Mediterranean area; (ii) proposes a new tephra marker for Marine Isotope Stage 7, dated to 240 ka; and (iii) refines the correlations of tephra levels belonging to the investigated sequence. This study highlights that in most cases the Nd isotope composition of the glass and Sr isotope composition of the coexisting minerals are more reliable than ⁸⁷Sr/⁸⁶Sr of the glass, and hence is more helpful as a further tool for tephrostratigraphic correlations, as recently proposed in the literature. Moreover, this study is a first step towards the construction of a complete geochemical database for future tephra investigations in the Mediterranean area. Copyright © 2019 John Wiley & Sons, Ltd.     

Subglacial bed conditions during Late Pleistocene glaciations and their impact on ice dynamics in the southern North Sea

Passchier, S., Laban, C., Mesdag, C.S. & Rijsdijk, K.F. 2010: Subglacial bed conditions during Late Pleistocene glaciations and their impact on ice dynamics in the southern North Sea. Boreas, Vol. 39, pp. 633–647. 10.1111/j.1502‐3885.2009.00138.x. ISSN 0300‐9483. Changes in subglacial bed conditions through multiple glaciations and their effect on ice dynamics are addressed through an analysis of glacigenic sequences in the Upper Pleistocene stratigraphy of the southern North Sea basin. During Elsterian (MIS 12) ice growth, till deposition was subdued when ice became stagnant over a permeable substrate of fluvial sediments, and meltwater infiltrated into the bed. Headward erosion during glacial retreat produced a dense network of glacial valleys up to several hundreds of metres deep. A Saalian (MIS 6) glacial advance phase resulted in the deposition of a sheet of stiff sandy tills and terminal moraines. Meltwater was at least partially evacuated through the till layer, resulting in the development of a rigid bed. During the later part of the Saalian glaciation, ice‐stream inception can be related to the development of a glacial lake to the north and west of the study area. The presence of meltwater channels incised into the floors of glacial troughs is indicative of high subglacial water pressures, which may have played a role in the onset of ice streaming. We speculate that streaming ice flow in the later part of the Saalian glaciation caused the relatively early deglaciation, as recorded in the Amsterdam Terminal borehole. These results suggest that changing subglacial bed conditions through glacial cycles could have a strong impact on ice dynamics and require consideration in ice‐sheet reconstructions.     

Distribution of arsenic and other minor trace elements in the groundwater of Ischia Island (southern Italy)

The island of Ischia belongs to the active volcanic area of Naples. It is formed from Quaternary volcanic rocks and exhibits intense hydrothermal activity, which is manifested through numerous springs, fumaroles and sporadic geysers. The content of minor and trace elements in groundwater has been analyzed, including some elements that are considered toxic for humans. Mean concentrations of As, B, Fe, Mn, Sb, and Se in samples from 43 aquifer points exceed the WHO recommended values and the limits set by European and Italian legislation (98/83/CE and DM 471, respectively). In general, the spatial distribution of the elements follows a common pattern: it is governed by a marked structural control, which favors hydrochemical processes that liberate the elements into the water.     

福建政和县东际金（银）矿床黄铁矿微量元素和硫-铅同位素及锆石年龄研究

东际金(银)矿床赋存于燕山晚期南园组火山岩中,是东南沿海地区一个隐爆角砾岩型贵金属矿床,已探明金资源量达12.5 t,银资源量135.9 t。通过开展主要金属硫化物黄铁矿电子探针和硫-铅同位素分析,讨论了成矿作用和成矿物质来源等问题。研究表明,东际金(银)矿床黄铁矿Co/Ni值3～94(平均值23)且Co含量为500×10-6～1070×10-6(均值799×10-6),Fe/(S+As)值0.827～0.871(均值0.860),Au/Ag值0.9～5.5(均值2.6),反映该矿床是与陆相火山作用有关的浅成中低温热液型矿床。黄铁矿δ34S在-6.6‰～-0.7‰,206Pb/204Pb为17.9801～18.4303,207Pb/204Pb为15.2689～15.9397,208Pb/204Pb为37.9052～38.7871,指示成矿物质主要来源于具有壳幔混源性质的花岗质岩浆,此外含矿热液也活化萃取了部分基底变质岩和火山岩围岩的金属元素。通过锆石U-Pb年代学研究和区域成矿资料对比,东际金(银)矿床成矿时代可被限定于早白垩世晚期。     

Influences of ore formation on biomarkers in the Kupferschiefer from the Lubin mine, Poland

Molecular biomarkers are the important maturity parameters for sedimentary organic matter.They have also been widely used for determining the maturity of organic matter in ore deposits. However,during the study of organic matter in the Kupferschiefer from the Lubin mine, it had been found that the biomarkers were influenced by sulfide formation. In order to probe into the degree of influence on biomarkers, seven samples collected from a Kupferschiefer section from the Lubin mine were analyzed by various geochemical methods. The results indicated that in the samples with higher copper contents, the values of biomarkers are lower than in the samples with lower copper contents. In highly mineralized samples, hydrogen donation for thermochemical sulfate reduction (TSR) occurred in alkylated phenanthrenes and naphthalenes, leading to the decrease of 12 biomarker parameters during the Kupferschiefer mineralization.     

Late Pleistocene to Holocene record of changing uplift rates in southern Calabria and northeastern Sicily (southern Italy, Central Mediterranean Sea)

A combination of published and new radiometric dates on uplifted Holocene fossil beaches from northeastern Sicily and southern Calabria (southern Italy) is compared with the altitude of the inner margin of the Last Interglacial (LIg) (Late Pleistocene, 124 ka) and older marine terraces in order to gain a regional-scale outline of uplift rates and their temporal changes in a region which is one of the fastest uplifting sectors of the Central Mediterranean Sea. Late Holocene radiocarbon dates from Ioppolo (southern Calabria) and Ganzirri (northeast Sicily), two newly discovered sites are here presented for the first time. The Holocene uplift rates are highest at St. Alessio and Taormina in eastern Sicily (2.4 mm/y) and at Scilla in southwestern Calabria (2.1 mm/y), two sites located across the Messina Straits and which separate the island of Sicily from mainland Italy. Uplift rates decrease towards the south and north from this centre of uplift. Late Holocene uplift rates show an apparent increase of between 64 and 124% when compared with the longer-term uplift rates calculated from the LIg highstand terraces. Furthermore, we discovered that the locations of fastest Late Pleistocene and Late Holocene uplift rates spatially coincide. To what extent the Holocene increase in uplift rates results from incomplete elastic strain release along the major extensional faults which frame the seismotectonic of the area, or indicate a true change in regional tectonic processes, is not resolved. Nonetheless, the heterogeneity of uplift, with a well-defined centre that crosses the Messina Straits, and its persistence at different time-scales indicates a tight connection between wider regional processes and fault-related displacement in controlling crustal instability in this area.     

全球不同构造环境蛇纹岩全岩和矿物微量元素组成及非传统稳定同位素(Fe-Zn-Cu同位素)特征

蛇纹岩对地球深部和浅部的元素循环以及氧化还原状态调节具有非常重要的作用。蛇纹岩中的流体活动性元素(fluid-mobile element, FME)是揭示地幔岩石水化、脱水以及元素循环的关键。本文系统收集和分析了前人报道的不同构造环境的蛇纹岩矿物化学、全岩微量元素和非传统稳定同位素(Fe、Zn、Cu)的组成特征,试图从多个角度总结蛇纹岩脱水过程的元素迁移规律及流体性质。蛇纹岩主要矿物蛇纹石微量元素含量具有以下主要特征：(1)不同变质程度的蛇纹岩中的蛇纹石既包含轻稀土元素(light rare earth element, LREE)富集,又包含LREE亏损的特征;(2)纤蛇纹石的REE和微量元素分布在利蛇纹石和叶蛇纹石的范围内,利蛇纹石重稀土元素(heavy rare earth element, HREE)整体上略高于叶蛇纹石且更加富集FME;(3)通过中度不相容元素与REE含量相结合,能够较好地区分橄榄石和辉石蛇纹石化所形成的蛇纹石,即辉石形成的蛇纹石富集相容元素(如Sc、Zn、Cr、Y和Ti等)并具有较高的HREE,而橄榄石形成的蛇纹石则表现为平坦且整体较低的REE分布型式。在...     

赣南地区石雷石英闪长岩的成因:岩石化学、副矿物微量元素、锆石U-Pb年代学与Sr-Nd-Hf同位素制约

石雷石英闪长岩是赣南崇-余-犹地区比较特殊的闪长质侵入体。锆石的原位U-Pb定年表明,该岩体侵位于433.5±3.4Ma。全岩主量元素特征上显示出中偏酸性(SiO2=56.92%～64.70%),富Al(Al2O3=14.10%～14.83%),富碱(Alk=6.41%～7.40%)特别是富钾(K2O=3.86%～4.85%),镁、铁含量较高,MgO:3.47%～5.95%,FeOT:5.23%～8.14%以及低磷(P2O5=0.27%～0.4%)的特点;微量元素上主要富集K、Rb、Cs等大离子亲石元素和轻稀土元素,亏损Nb、Ta、Ti、P等高场强元素。磷灰石微量元素特征上显示高度富集稀土元素特别是轻稀土元素的特征;具有Eu的负异常(δEu=0.37～0.45)。ISr位于0.7073～0.7132之间,εNd(t)变化于-8.41～-4.97之间,两阶段钕模式年龄介于1.58～1.86Ga之间,Hf同位素组成相对均一,εHf(t)主要集中变化于-8～-2之间,两阶段Hf模式年龄加权平均为1.77±0.09Ga,这些特征都暗示了该石英闪长质岩体的形成是强烈壳幔相互作用的产物,区内加里东晚期可能发生了局部的岩石圈的减薄。     

Geochemistry of environmentally sensitive trace elements in Permian coals from the Huainan coalfield, Anhui, China

To study the geochemical characteristics of 11 environmentally sensitive trace elements in the coals of the Permian Period from the Huainan coalfield, Anhui province, China, borehole samples of 336 coals, two partings, and four roof and floor mudstones were collected from mineable coal seams. Major elements and selected trace elements were determined by inductively coupled plasma optical emission spectrometry (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS), and hydride generation atomic absorption spectrometry (HAAS). The depositional environment, abundances, distribution, and modes of occurrence of trace elements were investigated. Results show that clay and carbonate minerals are the principal inorganic constituents in the coals. A lower deltaic plain, where fluvial channel systems developed successively, was the likely depositional environment of the Permian coals in the Huainan coalfield. All major elements have wider variation ranges than those of Chinese coals except for Mg and Fe. The contents of Cr, Co, Ni, and Se are higher than their averages for Chinese coals and world coals. Vertical variations of trace elements in different formations are not significant except for B and Ba. Certain roof and partings are distinctly higher in trace elements than underlying coal bench samples. The modes of occurrence of trace elements vary in different coal seams as a result of different coal-forming environments. Vanadium, Cr, and Th are associated with aluminosilicate minerals, Ba with carbonate minerals, and Cu, Zn, As, Se, and Pb mainly with sulfide minerals.     

Concentration and distribution of elements in Late Permian coals from western Guizhou Province,China

With the aim of better understanding geochemistry of coal, 71 Late Permian whole-seam coal channel samples from western Guizhou Province, Southwest China were studied and 57 elements in them were determined. The contents of Al, Ca, Co, Cr, Cu, Fe, Ga, Hf, K, Li, Mn, Mo, Nb, Ni, Sn, Ta, Ti, Th, U, V, Zr, and REEs in the Late Permian coals from western Guizhou Province are higher than the arithmetic means for the corresponding elements in the US coals, whereas As, Ba, Br, F, Hg, P, Se, and Tl are lower. Compared to common Chinese coals, the contents of Co, Cr, Cu, Ga, Hf, Li, Mn, Mo, Ni, Sc, Sn, Ti, U, V, Zn, and Zr in western Guizhou coals are higher, and As, F, Hg, Rb, Sb, Tl, and W are lower. Five groups of elements may be classified according to their mode of occurrence in coal: The first two, Group A, Tm–Yb–Lu–Y–Er–Ho–Dy–Tb–Ce–La–Nd–Pr–Gd–Sm, and Group B, As–Sr–K–Rb–Ba–F–Ash–Si–Sn–Ga–Hf–Al–Ta–Zr–Be–Th–Na, have high positive correlation coefficients with ash yield and they show mainly inorganic affinity. Some elements from Group B, such as Ba, Be, Ga, Hf, and Th, are also characterized by significant aluminosilicate affinity. In addition, arsenic also exhibits high sulfide affinity (r_S–Fe>0.5). The elements, which have negative or lower positive correlation coefficients with ash yield (with exceptions of Bi, Cs, Nb, Mn, Se, and Ti), are grouped in other four associations: Group C, Cr–V–Mo–U–Cd–Tl; Group D, Hg–Li–Sc–Ti–Eu–Nb–Cs–W; Group E, Bi–Sb; and Group F, Co–Ni–Cu–Pb–Zn–Mg–Se–Ca–Mn–S–Fe. The correlation coefficients of some elements, including Co, Cr, Cu, Fe, Hg, Li, Mo, Ni, P, S, Sc, U, V, and Zn, with ash yield are below the statistically significant value. Only Cr and Cu are negatively correlated to ash yield (−0.07 and −0.01, respectively), showing intermediate (organic and inorganic) affinity. Manganese and Fe are characterized by carbonate affinity probably due to high content of epigenetic veined ankerite in some coals. Phosphorus has low correlation coefficients with any other elements and is not included in these six associations. There are five possible genetic types of enrichment of elements in coal from western Guizhou Province: source rock, volcanic ash, low-temperature hydrothermal fluid, groundwater, and magmatic hydrothermal inputs.     

藏南昂仁县贡久布地区晚二叠世孢粉组合的特征及其意义

贡久布一带的敌布错组分布于隆格尔-南木林地层分区,含较丰富的孢子花粉化石,以华夏植物群孢子花粉为特征,同时采获大量的植物化石,其时代为晚二叠世早期.根据地层中孢子花粉的演化规律,可建立Vetreisporites signatus-Limitisporitesrectus孢子花粉组合带.丰富了古生物学的研究内容,为研究该区晚二叠世的沉积环境、古生态、生物古地理分区和地质演化历史提供了基础资料.结合区域资料分析,认为植物组合由冈瓦纳植物群与华夏植物群混生到典型华夏植物群是逐渐演化的.     

Paleoenvironmental reconstruction of a Late Quaternary lagoon system in southern Brazil (Jaguaruna region,Santa Catarina state) based on multi‐proxy analysis

This paper provides a paleoenvironmental reconstruction of a Late Quaternary lagoon system in the Jaguaruna region of Santa Catarina state, southern Brazil. Integrated results of bulk sedimentary organic matter characterization (δ¹³C, δ¹⁵N and C/N), microfossil (pollen and diatom) and grain‐size analysis from three shallow cores (～2.5 m depth) allowed us to propose an evolving paleogeographic scenario in this coastal region for the last ca. 5500 cal a BP. The lagoonal system in this area was more extensive during the mid‐Holocene than today, with a gradual and continuous lagoon–sea disconnection until the present. We add to the debate regarding relative sea‐level (RSL) variations for the Brazilian coast during the Holocene and discuss the importance of sedimentary dynamics for interpreting changes in coastal ecosystems. The multi‐proxy analysis suggests that changes in coastal ecosystems could be directly related to local sedimentary processes, which are not necessarily linked to RSL fluctuations and/or to climatic variations. Copyright © 2011 John Wiley & Sons, Ltd.     

The origin of rhythmic sulphide bands from the Permian sandstones (Weissliegendes) in the footwall of the Fore-Sudetic “Kupferschiefer” (Poland)

Rhythmic copper sulphide bands occur in the Weissliegendes sandstones, in the footwall of the Kupferschiefer in the mining district of SW Poland. The δ ³⁴S values of sulphides vary from −39 to — 44‰ (6–7‰ lighter than Kupferschiefer sulphides). The copper sulphides are represented mainly by digenite and chalcocite. According to microprobe results their Pb, Ni, Zn and Ag contents are similar to those in the Kupferschiefer. The bands are assumed to be formed by diffusion of bacterially produced hydrogen sulphide from the Kupferschiefer into the porous volume of the white sandstones containing dissolved copper. The sulphides were precipitated in almost equidistant bands, from top to bottom, probably according to the Ostwald-Prager supersaturation theory. The increase of isotopically heavier sulphur towards the lower levels in the sandstone might be explained by closing of the bacterial sulphate reduction system. Contribution to the IGCP Project No. 254     

Climatic variations in MIS 11 recorded by stable isotopes and trace elements in a French tufa (La Celle,Seine Valley)

Marine Isotope Stage (MIS) 11 palaeoclimate has so far been documented in marine and ice sheet isotopic records. However, excepting some lacustrine pollen records, very little is known about palaeoclimatic conditions in continental areas. This study uses geochemical records in calcareous tufa deposits from rivers as a basis for reconstructing temperate palaeoclimatic conditions. Tufa deposits are now proven to record high‐quality palaeoclimatic information in recent to Holocene deposits. Work on older interglacial tufas is just starting and in this paper we present the first comprehensive results from a MIS 11 tufa. The tufa comes from the Seine Valley (La Celle, northern France). Geochemical data in the tufa calcite are interpreted to record primarily air temperature (δ¹⁸O) and humidity (δ¹³C and Mg/Ca and Sr/Ca). The combined data identify a warm and wet climatic optimum followed by two temperature decreases associated with oscillations in humidity. These marked climatic variations recorded through the La Celle profile are strongly coherent with the palaeoenvironmental reconstructions from malacological data. The abrupt climatic and environmental events recorded could be related to short‐term degradation of vegetation cover in Europe, which is itself controlled by global palaeoclimatic events. Copyright © 2012 John Wiley & Sons, Ltd.     

Sedimentology of the Madumabisa Mudstone Formation (Late Permian), Lower Karoo Group,mid-Zambezi Valley Basin,southern Zambia

Sediments of the Upper Carboniferous to Lower Jurassic Karoo Supergroup (∼ 4.5 km thick) were deposited in the mid-Zambezi Valley Basin, southern Zambia. The Upper Palæozoic Lower Karoo Group in this area ends with a Late Permian sedimentary unit called the Madumabisa Mudstone Formation. The formation is 700 m thick and comprises four lithofacies grouped into two facies assemblages, collectively interpreted as lacustrine deposits. Sediments of a massive mudrock facies assemblage were deposited from suspension, probably from sediment-laden rivers entering a lake. Concretionary calcilutite beds probably mark the positions of palæosediment-water interfaces where calcite was precipitated. A laminated mudrock facies assemblage is attributed to lacustrine deposition from inflowing rivers at the lake margins and shallow parts of the lake. Repeated thickening-upward cycles are evidence of upward shallowing, interrupted by events of more abrupt deepening. Sandstone interbeds are interpreted as fluvial deposits laid down during low lake stands, with cross-lamination and asymmetrical ripples indicating current rather than wave deposition. A fossil assemblage of ostracods, bivalves, gastropods, fish scales, the alga Botryococcus sp. and fossil burrows is consistent with a lacustrine origin for the formation.     

琼南晚白垩世基性岩墙群的年代学、元素地球化学和Sr-Nd同位素研究

系统的年代学、元素地球化学和Sr—Nd同位素地球化学研究表明，琼南晚白垩世基性岩墙群形成于81Ma，富K(K20约为1．95％～3．63％，K20／Na20约为0．61～1．12)、大离子亲石元素、轻稀土元素和Pb，亏损高场强元素，具高的^87Sr／86Sr初始值(0．7078～0．7084)和负的εNd(t)值(—3．2～—2．3)，为典型的钾玄质系列岩石，类似于与俯冲环境相关的高K／Ti—低Ti钾质岩石。该岩墙群形成于“后碰撞弧”的板内拉张环境，源自与俯冲作用有关的富钾和大离子亲石元素的交代地慢，并经历了明显的以单斜辉石为主的结晶分异作用。此外，琼南基性岩墙群和粤北及福建沿海地区晚白垩世基性岩脉的对比表明，晚白垩世中国东南部岩石圈地慢组成存在区域性的差异，这种差异很可能与区域构造演化历史的不同有关。