中、下扬子地区下寒武统黑色页岩微量元素富集特征

中国南方扬子地区下寒武统黑色页岩分布广泛,主要由黑色页岩、黑色白云质页岩,黑色粉砂质页岩和黑色硅质页岩等组成;并伴生有较厚的磷块岩矿床、钒矿床和镍、钼多元素硫化物矿床。对黑色页岩岩石学特征、元素地球化学特征进行系统研究,并详细分析微量元素的富集成因,结果表明：黑色页岩主要形成于静水还原的浅海-半深海缓坡环境,层状元素富集带为沉积成因,海底热流体提供了丰富物质来源。总体上,Co、Be、Mn、Ga等元素含量较低;Cu、V、Ni、Mo等元素的含量较高,多数超过北美页岩平均值;以Ni、Mo为主的多元素富集层通常位于磷块岩之上,以黑色页岩、黑色白云质页岩中的硫化物和硫酸盐矿物为主要载体,其中有机碳（TOC）含量可达12.2%以上,远高于其他元素富集层,随着页岩内硅质成分增加,Ni、Mo、Fe、Co等元素含量明显降低;以V为主的多元素主要赋存于黑色硅质页岩中的水云母,与页岩内硅质成分具有较好的正相关关系;黑色页岩中稀土元素含量为(76.22~290.67)×10-6,轻重稀土比值LREE/HREE介于1.21~4.22,说明轻稀土更为富集,Sr/Ba值为0.04~0.34,δEu正异常,且北美页岩标准化配分曲线呈现平缓左倾,为沉积过程中存在海底热水流体提供了进一步证据。     

Paleoceanographic Indicators for Early Cambrian Black Shales from the Yangtze Platform,South China: Evidence from Biomarkers and Carbon Isotopes

The lower Cambrian Niutitang Formation, a widespread black shale deposition, is of geological interest because of its polymetallic beds, Cambrian explosion, depositional ages, dramatic environmental changes and so on. Previous study focused mainly on inorganic geochemistry and few studies have investigated the organic fractions of upper Neoproterozoic-lower Cambrian strata in South China. Here we report a study of biomarkers plus organic carbon isotopes for black shales from Ganziping, Hunan Province (China). All the saturated hydrocarbon fractions have a unimodal distribution of n-alkanes, a high content of short-chain alkanes and maximize at C 19 or C 20 (C 23 for sample Gzh00-1). The C 27 /C 29 sterane ratio ranges from 0.77 to 1.20 and 4-methylsteranes are in low abundance. These parameters indicate that algae and bacteria are the important primary producers. Furthermore, biomarker maturity proxies show the samples to be higher maturity. The low Pr/Ph values (<0.7) suggest that the samples were deposited under anoxic conditions and, likely, under stratified water columns. In addition, 25-norhopanes and gammacerane are present as diagnostic indicators of normal marine salinity and dysoxic to anoxic conditions. During the Early Tommotian, known to coincide with a transgression event, small shelly fossils increased in abundance and diversity. Moreover, positive δ 13 C org excursions close to 1.4‰ occur at the base of the Tommotian stage. In summary, the Early Cambrian black shales were deposited under dramatic paleoenvironmental changes, including oceanic anoxia, higher primary productivity and sea-level rise.     

Trace- and rare-earth element geochemistry and Pb–Pb dating of black shales and intercalated Ni–Mo–PGE–Au sulfide ores in Lower Cambrian strata, Yangtze Platform, South China

The Lower Cambrian black shale sequence of the Niutitang Formation in the Yangtze Platform, South China, hosts an extreme metal-enriched sulfide ore bed that shows >10,000 times enrichment in Mo, Ni, Se, Re, Os, As, Hg, and Sb and >1,000 times enrichment in Ag, Au, Pt, and Pd, when compared to average upper continental crust. We report in this paper trace- and rare-earth-element concentrations and Pb–Pb isotope dating for the Ni–Mo–PGE–Au sulfide ores and their host black shales. Both the sulfide ores and their host black shales show similar trace-element distribution patterns with pronounced depletion in Th, Nb, Hf, Zr, and Ti, and extreme enrichment in U, Ni, Mo, and V compared to average upper crust. The high-field-strength elements, such as Zr, Hf, Nb, Ta, Sc, Th, rare-earth elements, Rb, and Ga, show significant inter-element correlations and may have been derived mainly from terrigenous sources. The redox sensitive elements, such as V, Ni, Mo, U, and Mn; base metals, such as Cu, Zn, and Pb; and Sr and Ba may have been derived from mixing of seawater and venting hydrothermal sources. The chondrite-normalized REE patterns, positive Eu and Y anomalies, and high Y/Ho ratios for the Ni–Mo–PGE–Au sulfide ores are also suggestive for their submarine hydrothermal-exhalative origin. A stepwise acid-leaching Pb–Pb isotope analytical technique has been employed for the Niutitang black shales and the Ni–Mo–PGE–Au sulfide ores, and two Pb–Pb isochron ages have been obtained for the black shales (531±24 Ma) and for the Ni–Mo–PGE–Au sulfide ores (521±54 Ma), respectively, which are identical and overlap within uncertainty, and are in good agreement with previously obtained ages for presumed age-equivalent strata.Editorial handling: R. Coveney Jr.     

贵州金鼎山下寒武统黑色岩系的有机地球化学特征

对贵州遵义金鼎山下寒武统牛蹄塘组黑色岩系的氯仿沥青“A”及族组分做了成分检测,并进行了岩石氯仿抽提物中饱和烃气相色谱分析。结果表明,黑色岩系属生油岩,且为腐泥型和混合型生油岩,以腐泥型为主;黑色岩系有机质丰度高,有机质主要来源于海生低等菌、藻类生物;黑色岩系姥姣烷与植烷比值、岩性和生物特征指示其形成于一种缺氧还原沉积环境。     

Silicalites of Hydrothermal Origin in the Lower Cambrian Black Rock Series of South China

A silicalite bed was found in the hanging wall and foot wall of the sulfide-rich bed of the Lower Cambrian black rock series in South China.Its origin was not described before,On the oxide(SiO2-Al2O3,SiO2-MgO,SiO2-k2o Na2O)diagrams for discriminating silicalites of chemical,biological and volcanic origins(Liu Xiufeng,1991),most of the data points of silicalites fall within the areas representing silicalites of chemical and volcanic origins.On the Al-Fe-Mn diagram for discriminating silicalites of hydrothermal and biological origins(Yamamoto,1987),the data points fall within the areas representing silicalites of hydrotermal and hydrothermal-biological origins.On the SiO2-Al2O3 diagram for discriminating silicalites of hydrothermal and hydrogenous origins(Bonatti,1975),the data points mostly fall within the hydrothermal area.The ratios of SiO2/Al2O3,SiO2/(K2O Na2O),SiO2/MgO,and K2O/Na2O in the silicalites stand between those of volcanic sediments and of seafloor hydrothermal sediments.The total amount of rare-earth elements in the silicalites is low;the North american Shale-normalized REE patterns decline leftward with obvious negative Ce anomaly.The trace elements Mo,Zn,As,Sb,Se,U,and Ba are higher than those in non-hydrothermal sediments and U/Th≥1.The present authors think that the silicalites are derived from seafloor hot brines which had attracted elements from igneous rocks.     

华南双桥山群和河上镇群凝灰岩中的锆石SHRIMP U-Pb年龄—对江南新元古代造山带演化的制约

通过西澳科庭大学离子探针中心的远程测试,在双桥山群横涌组和安乐林组斑脱岩中获得大量锆石,其SHRIMP U-Pb加权平均年龄为831Ma±5Ma(横涌组)、829Ma±5Ma(安乐林组),在河上镇群上墅组中获得加权平均年龄767Ma±5Ma.锆石SHRIMP U-Pb年龄表明华南地区广为发育的双桥山群应归入新元古界,该年龄为标定双桥山群在地层柱中的位置提供了准确的年代学依据.     

Organic geochemistry and petrology of barren and Mo–Ni–PGE mineralized marine black shales of the Lower Cambrian Niutitang Formation (South China)

Marine black shales of the Lower Cambrian Niutitang Formation in southern China host Mo–Ni–platinum group elements (PGE) mineralization confined to a phosphate- and pyrite-rich stratiform body (max. 20-cm thick). The H/C atomic ratio, carbon isotopic composition, FTIR spectra of bulk organic matter, and spectra of extractable part of organic matter indicate similar sources and thermal evolution of organic matter in barren and mineralized black shales.The morphology and relative abundance of organic particles in barren and mineralized shales are different. In barren black shales, organic particles comprise only elongated bodies and laminae 2–10 μm across or elongated larger bodies (> 10 μm) with R_max = 2.96–5.21% (Type I particles). Mineralized black shales contain Type I particles in rock matrix (90–95 vol%), small veinlets or irregular organic accumulations (Type II particles, 1–5 vol%) that display weak to well developed mosaic texture and a variable reflectance (R_max = 3.55–8.65%), and small (< 1 to 5 μm) rounded or irregular Type III organic particles (1–4 vol%) distributed within phosphate nodules and sulphide rip-up clasts. Type III particles show similar reflectance as particles of Type I in rock matrix. Type I particles are interpreted as remnants of in situ bacterially reworked organic matter of cyanobacteria/algal type, Type II as solidified products or oil-derived material (migrabitumen), and Type III particles as remnants of original organic matter in phosphatized or sulphidized algal/microbial oncolite-like bodies. Equivalent vitrinite reflectances of Type I and III particles in barren and mineralized rocks are similar and correspond to semi-anthracite and anthracite. Micro-Raman spectra of organic particles in rocks display a wide belt in the area of 1600 cm^− 1 (G belt) and approximately the same belt in the area of 1350 cm^− 1 (D belt). The ratio of integrated areas of the two belts correlate with R_max values.The Mo–Ni–PGE mineralized body is interpreted as to represent a remnant of phosphate- and sulphide-rich subaquatic hardground supplied with organic material derived from plankton and benthic communities as well as with algal/microbial oncolite-like bodies that originated in wave-agitated, shallow-water, nearshore environment.     

华南双桥山群和河上镇群凝灰岩中的锆石SHRIMP U—Pb年龄——对江南新元古代造山带演化的制约

通过西澳科庭大学离子探针中心的远程测试,在双桥山群横涌组和安乐林组斑脱岩中获得大量锆石,其SHRIMP U—Pb加权平均年龄为831Ma±5Ma（横涌组）、829Ma＋5Ma（安乐林组）,在河上镇群上墅组中获得加权平均年龄767Ma±5Ma。锆石SHRIMP U—Pb年龄表明华南地区广为发育的双桥山群应归入新元古界,该年龄为标定双桥山群在地层柱中的位置提供了准确的年代学依据。     

Carbon isotope chemostratigraphy of a Precambrian/Cambrian boundary section in the Three Gorge area, South China: Prominent global-scale isotope excursions just before the Cambrian Explosion

Carbon isotope chemostratigraphy has been used for worldwide correlation of Precambrian/Cambrian (Pc/C) boundary sections, and has elucidated significant change of the carbon cycle during the rapid diversification of skeletal metazoa (i.e. the Cambrian Explosion). Nevertheless, the standard δ¹³C curve of the Early Cambrian has been poorly established mainly due to the lack of a continuous stratigraphic record. Here we report high-resolution δ¹³C chemostratigraphy of a drill core sample across the Pc/C boundary in the Three Gorge area, South China. This section extends from an uppermost Ediacaran dolostone (Dengying Fm.), through a lowermost Early Cambrian muddy limestone (Yanjiahe Fm.) to a middle Early Cambrian calcareous black shale (Shuijingtuo Fm.). As a result, we have identified two positive and two negative isotope excursions within this interval. Near the Pc/C boundary, the δ¹³C_carb increases moderately from 0 to + 2‰ (positive excursion 1: P1), and then drops dramatically down to − 7‰ (negative excursion 1: N1). Subsequently, the δ¹³C_carb increases continuously up to about + 5‰ at the upper part of the Nemakit–Daldynian stage. After this positive excursion, δ¹³C_carb sharply decreases down to about − 9‰ (N2) just below the basal Tommotian unconformity. These continuous patterns of the δ¹³C shift are irrespective of lithotype, suggesting a primary origin of the record. Moreover, the obtained δ¹³C profile, except for the sharp excursion N2, is comparable to records of other sections within and outside of the Yangtze Platform. Hence, we conclude that the general feature of our δ¹³C profile best represents the global change in seawater chemistry. The minimum δ¹³C of the N1 (− 7‰) is slightly lower than carbon input from the mantle, thus implying an enhanced flux of ¹³C-depleted carbon just across the Pc/C boundary. Hence, the ocean at that time probably became anoxic, which may have affected the survival of sessile or benthic Ediacaran biota. The subsequent δ¹³C rise up to + 5‰ (P2) indicates an increase of primary productivity or an enhanced rate of organic carbon burial, which should have resulted in lowering pCO₂ and following global cooling. This scenario accounts for the cause of the global-scale sea-level fall at the base of the Tommotian stage. The subsequent, very short-term, and exceptionally low δ¹³C (− 9‰) in N2 could have been associated with the release of methane from gas hydrates due to the sea-level fall. The inferred dramatic environmental changes (i.e., ocean anoxia, increasing productivity, global cooling and subsequent sea-level fall with methane release) appear to coincide with or occur just before the Cambrian Explosion. This may indicate synchronism between the environmental changes and rapid diversification of skeletal metazoa.     

华南造山带下寒武统和中奥陶统发现放射虫

在华南造山带江西萍乡下寒武统牛角河组泥质板岩和湖南永州中奥陶统烟溪组硅质岩中首次发现放射虫。放射虫的发现表明萍乡—永州一带寒武纪—中奥陶世存在相当规模的处于低纬度的海盆。     

Submarine hydrothermal contribution for the extreme element accumulation during the early Cambrian,South China

Throughout the geological history of the Earth, submarine hydrothermal activity has played an important role in seawater chemistry, biological evolution and enrichment of metals in the Earth crust. However, the prospect of hydrothermal activity for extreme element accumulation during the early Cambrian, a key geological period, in South China has not been well-constrained. This study reports geochemical (e.g. REE and Sr isotope) investigations of a coarse-grained limestone layer and associated calcite veins in Zunyi and Nayong areas, Guizhou Province, to constrain the hydrothermal activity and evaluate the significance of hydrothermal contribution to extreme element accumulation during the early Cambrian, South China. Our results reveal positive Eu anomalies and higher initial ⁸⁷Sr/⁸⁶Sr ratios (0.7083–0.7150) for carbonate samples than those of early Cambrian seawater, indicating the presence of hydrothermal processes. Combined with constraints from the spatial relationships and coincidence with adjacent mineralization, these hydrothermal processes provide the most probable contribution for polymetallic Ni–Mo–PGE mineralization. Furthermore, there are abundant hydrothermal dolomite and barite-calcite veins in the dolostone of the Dengying Formation, indicating the occurrence of a variety of hydrothermal fluids. Overall, multi-stage hydrothermal pulses with different fluid compositions spanned the Ediacaran–Cambrian transition in South China. In particular, these hydrothermal fluids with positive Eu anomalies and enriched radiogenic Sr, originating from Proterozoic mafic/ultramafic rocks, may have flowed through the underlying Precambrian silicate clastic rocks (e.g., Xiajiang, Banxi and Lengjiaxi Groups) and may have been crucial for the marine environment, biological diversity and extreme element accumulation during the early Cambrian, South China.     

华南地区新元古代年代地层标定及地层对比

华南地区新元古代地层区域上涉及中国上、下扬子地区,包括中国地层表中的青白口系、南华系和震旦系,时代上分别对应国际地层年代表中拉伸系、成冰系和埃迪卡拉系。传统划分是以晋宁运动(四堡运动)为标志划分为中元古界和新元古界,近年来,通过地层中凝灰岩锆石SHRIMP U-Pb的测定,华南地区新元古代年代表已进行了有效年代学标定,突出了地层对比的可靠性和新的构造观点解译。华南古陆构造演化研究需要以构造为纲,明确了古陆周缘地层发育了中元古代晚期相关沉积记录,而华南古陆内部,特别是江南造山带为武陵运动的构造运动产物。本文将报道桂西地区青白口系拱洞组底部SHRIMP锆石U-Pb年代学测定数据(799.8±5.5)Ma,江西与湖南交界长安组底部获得凝灰岩锆石年龄(770±10)Ma,湘西北长安组底部获得凝灰岩锆石年龄(758.6±5.4)Ma和湾溪口村长安组冰碛岩距底部十多米处获得凝灰岩锆石年龄(743.8±4.1)Ma。上述年龄进一步提供华南地区冰碛岩地层的年代学依据。     

Pediculate Brachiopod Diandongia pista from the Lower Cambrian of South China

The Chengjiang Lagerstatte has been celebrated for prolific soft-bodied fossils. Based on specimens recently excavated in the Chengjiang Lagerstatte by the Early Life Institute, Northwest University, Diandongia pista Rong, 1974, is directly revealed to be a pediculate brachiopod, assigned to the Family Botsfordiidae, as is further confirmed by the exceptionally preserved vascular system including dorsal and ventral mantle canals. These specimens described herein exhibit some peculiarities, notably the extremely thin and long pedicles, which suggest that Diandongia is epifaunal rather than burrowing brachiopod. A study of this group of animals indicates that they may be vital to understand the relationship between the lingulids and the remaining brachiopods, and the character evolution of the early Cambrian brachiopods.     

Enrichment and Origin of Some Trace Elements in Black Shales from the Early Cambrian in Eastern Guizhou Province

The analysis is based on the elemental geochemistry, ¹³C, ¹⁸O isotope and lithology combination of the black shale, a set assemblage mud and carbon of lithology , in East Guizhou. The coordinated change in spider diagrams of race elements suggests those elements have the same source. The ¹³C, ¹⁸O isotopes, mode of REE partition and characteristic enrichment of elements assemblage in carbonaceous shale show that the deep thermal fluid is added, and the shelf sea basin edge with distribution of hydrothermal activity is propitious to precipitation of ore elements. Evidence from the ³⁴S isotope and redox-sensitive elements show that the hydrostatic hypoxia environment is also conducive to precipitation of elements. The lithologic features (phosphorus, coal-bearing layers) and high content of organic carbon indicate that the deposits are influenced by the upwelling ocean current.     

Petrogenesis and tectonic implications of Neoproterozoic, highly fractionated A-type granites from Mianning, South China

The origin of Neoproterozoic intrusions (ca. 860–750 Ma) along the western part of the Yangtze Craton has been the subject of debate in recent years, with two competing models proposed. The plume model argues for an extensional setting and emphasizes the role of a superplume in the Rodinia breakup, whereas the arc model argues for the presence of a subduction zone in the Yangtze Craton. As a contribution to this animated dispute, geochronologic and geochemical analyses have been carried out on the Mianning granite, which is the largest pluton (700 km²) in the northern Kangdian rift of the western Yangtze Craton. It is shown that the Mianning granites were emplaced at ca. 780 Ma and display highly fractionated feature (i.e., SiO₂ > 75 wt%; Eu/Eu* = 0.03–0.50; enrichment of K, Rb, Th, U, Zr, Hf, Y and REEs; depletion of Nb, Ta, Ba, Sr, P, Eu and Ti). They are metaluminous to strongly peraluminous (A/CNK = 0.93–1.55) and contain abundant perthite and minor alkali riebeckite and sphene, sharing the petrological and geochemical characters of A₂-type granites. Positive _Nd (t) (2.97–5.24) and zircon _Hf (t) (9.2–12.1) values are consistent with a derivation by partial melting of a relatively young crust formed about 1000–900 Ma. Given the general absence of A-type granites in arc settings, the Mianning A-type granites are suggestive of an anorogenic, crustal extensional environment for the western Yangtze Craton during the Neoproterozoic. The data presented in this study are therefore consistent with an intracontinental rift model, but are not sufficient to identify plume involvement in the Neoproterozoic magmatism.     

New Maikhanellid Shells and Siphogonuchitid Spicule Bundles from the Cambrian Fortunian Stage of South China

Maikhanellids are a distinct group of Cambrian Fortunian small shelly fossils by the cap-shaped profiles and scaly shell ornamentation. According to the individual shell shape and ornamentation feature types of 50 maikhanellids fossils which were collected from Xixiang botia, we confirmed the family Maikhanellidae content of six genera, which are Maikhanella, Ramenta, Purella, Ramentoides, Yunnannopleura and Mediata. Unlike the halkieriid animals whose shells and spicules are articulated on different body parts, maikhanellids were presumably yielded by siphogonuchitid spicules penetrating the intermediate matrix (the "spicule shell" hypothesis), and this is the reason that some researchers treated maikhanellids and co-occurring siphogonuchitids as synonyms. The affinities of Maikhanellids and siphogonuchitids remain debatable. Here, we report three dimensionally phosphatized maikhanellid shells and siphogonuchitid spicule bundles from the Cambrian Fortunian small shell faunas of South China. They differ from all the previously reported maikhanellids and siphogonuchitids, and may represent new types. The intact and smooth surface underneath the partially preserved scales of the shells challenges the "spicule-shell" hypothesis. The present siphogonuchitid spicules differ from the maikhanellid scales in size, morphology, and .arrangement pattern, thus the spicules might not be derived from the shells. Whether the shells and spicule bundles were articulated on different body parts of the same animals remains unknown.     

Multiple Sources of Metals of Mineralization in Lower Cambrian Black Shales of South China: Evidence from Geochemical and Petrographic Study

Black shales of the Lower Cambrian Niutitang Formation in southern China (Huangjiawan mine, Zunyi region, northern part of the Guizhou Province) host regionally distributed stratiform polymetallic Ni‐Mo‐platinum group elements (PGE)‐Au phosphate‐ and sulfide‐rich ores. These are confined to a ≥0.2‐m thick ore horizon composed of mineralized bodies of algal onkolites, phosphate nodules, and sulfide and shale clasts in a mineralized phosphate‐ and organic matter‐rich matrix. Compared to footwall and hanging wall shales, the ore bed is strongly enriched in Ni (up to 100‐fold), As (up to 97‐fold), Mo (up to 95‐fold), Sb (up to 67‐fold), Rh (up to 49‐fold), Cu (up to 37‐fold), Pd (up to 33‐fold), Ru (up to 24‐fold), Zn (up to 23‐fold), Pt (up to 21‐fold), Ir (up to 15‐fold), Co (up to 14‐fold), and Pb (up to 13‐fold). Even footwall and hanging wall black shales are significantly enriched by Mo (21‐fold) and Ni (12‐fold) but depleted in Cr in comparison to average Cambrian black shale. Organic matter is represented by separate accumulations dispersed in the rock matrix or as biotic bitumen droplets and veinlets in ore clasts. Similar organic carbon (C_org) values in an ore bed and enclosing footwall and hanging wall shales of little mineralization indicate that metal accumulation was not controlled only by biogenic productivity and organic matter accumulation rate. Evaporitic conditions during sedimentation of the basal part of the Niutitang Formation were documented by an occurrence of preserved Ni‐, V‐, Cr‐, and Cu‐enriched phosphate‐rich hardground with halite and anhydrite pseudomorphs on the paleosurface of the underlying Neoproterozoic carbonates. Neoproterozoic black shales of the Doushantuo Formation are characterized by increased metal concentrations. Comparison of metal abundances in both hardground and Doushantuo black shales indicate that black shales could have become a source of metal‐rich hardground during weathering. The polymetallic Ni‐Mo‐PGE sulfide‐rich ore bed is interpreted to represent a remnant of shallow‐water hardground horizon rich in metals, which originated in a sediment‐starved, semi‐restricted, seawater environment. During the Early Cambrian transgression an influx of fresh seawater and intensive evaporation, together with the hydrothermal enrichment of seawater in a semi‐restricted basin, resulted in the formation of dense metalliferous brines; co‐precipitation of metals together with phosphates and sulfides occurred at or above the oxic–anoxic sediment interface. Metal‐enriched hardground was disintegrated by the action of waves or bottom currents and deposited in a deeper part of the anoxic basin. Contemporaneously with the formation of a polymetallic Ni‐Mo‐PGE‐Au sulfide ore bed, economic sedimentary exhalative (SEDEX)‐type barite deposits were forming in a stratigraphically and geotectonically similar setting. The results of geochemical study at the Shang Gongtang SEDEX‐type Ba deposit indicate that concentrations of Ag, As, Cr, Cu, Fe, Mn, Ni, Pb, Sb, V, Zn and other metals decrease from top of the barite body toward the hanging wall black shale. Lower Cambrian black shales of the Niutitang Formation above the barite body also display similar element abundances as Neoproterozoic black shales of the Doushantuo Formation, developed in the footwall of the barite body. But the geochemical composition of the sulfide layer is different from the Ni‐Mo ore bed, showing only elevated Pb, Cu, Ni and Mo values. It is suggested that hydrothermal brines at Shang Gongtang might have leached metals from footwall Neoproterozoic sequences and became, after mixing with normal seawater, an additional source of Ag, Cr, Cu, Pb, Sb, Zn, Ni, PGE, V and other metals.     

锶、碳同位素演化在新元古代地层定年中的应用——以胶辽徐淮地层分区为例

根据Sr、C同位素地层学原理，利用胶辽徐淮地区晚前寒武纪地层Sr、C同位素数据，与国际上已有的Sr、C同位素演化曲线对比，结果表明，胶辽徐淮地区晚前寒武纪地层是同一时期的沉积物，沉积主体之间Sr、C同位素比值的对比性很好，沉积时限约在750-860Ma之间，并延续到震旦纪，为北方青白口纪及其后的沉积。同时也表明，Sr、C同位素演化相结合是解决缺乏大化石的晚前寒武纪地层对比的有效方法。     

New Bivalved Arthropods from the Cambrian (Series 3, Drumian Stage) of Western Hunan,South China

We report two new three-dimensionally phosphatized microfossils, Cambrolongispina reticulata gen. et sp. nov. and Cambrolongispina glabra gen. et sp. nov., from the middle Cambrian （Series 3, Drumian Stage） at Wangcun, Yongshun County, western Hunan, South China. They are bivalved arthropods, with thin, pliable, originally chitinous or chitin-calcareous shields （c. 350-517 I1 m long）. The shields are equipped with a pair of antero-dorsal spines. The spines are internally hollow, varying in length from 1/2 of to as long as the shield length in C. reticulata, and uniformly longer than the shield length in C. glabra. The spines of C. reticulata are ornamented with a longitudinal row of conical or blade-shaped denticles along the posterior edge. Cambrolongispina lacks marginal rims, valve lobation and sulci which are diagnostic of the Bradoriida sensu stricto. It also lacks a donblure/duplicature characteristic of phosphatocopids and some bradoriids. It could be related to the Monasteriidae （which may belong to Bradoriida sensu lato）, both characterized by a pair of antero-dorsal spines. Cambrolongispina may have been meiofaunai detritus feeders that lived on or within sediments. The antero-dorsal spines may have been sensory organs to detect nearby predators. The posterior denticles on these spines might have facilitated the sensory function of the spines.     

Geochemistry of the Upper Neoproterozoic and Lower Cambrian siliciclastic rocks and U-Pb dating on detrital zircons in the Central Iberian Zone,Spain

Sandstones and shales from the Upper Neoproterozoic (UN) succession in the Central Iberian Zone (CIZ) show parallel REE patterns and relatively restricted and similar ranges and average values of some element ratios such as Al₂O₃/TiO₂, Ti/Nb, Eu/Eu*, (La/Yb)n, (Gd/Yb)n and Th/U. This remarkable geochemical homogeneity for related medium- and fine-grained rocks is unusual, and strongly suggests a recycled source area. However, the Lower Cambrian (LC) equivalent rocks are, in general terms, geochemically less mature, more heterogeneous and more fractionated. Their average REE patterns are practically coincident, probably as a consequence of REE redistribution related to the reworking of sediments during a stage of sea level fall in Lower Cambrian times. Ti and Zr abundances, chemical index of alteration (CIA) values and element ratios such as Al₂O₃/TiO₂, K/Rb, Ti/Nb and Rb/Zr can be used for discriminating purposes between the UN and LC siliciclastic rocks. Detrital zircons from a UN and a LC sandstone display morphological differences. However, U-Pb data are discordant and cannot be interpreted in a straightforward manner. Nevertheless, age data are compatible with a model in which the continent of Gondwana would have supplied zircons, showing a bimodal age distribution, in variable proportions to the respective sandstone units.