鄂尔多斯盆地宜川地区二叠纪孢粉化石组合特征

通过对延长油矿延223井晚古生代孢粉组合研究以及古植被的恢复,探讨了该区晚古生代孢粉植物化石组合的地层学和古气候意义。根据孢粉化石主要属种的时代分布及其在各样品中百分含量的规律性变化,自下而上建立了3个孢粉组合:Gulisporites cochlearius-Laevigatosporites minimus组合、Sinulatisporites-Florinites组合和Lueckeisporites permianus-Platysaccus radialis组合。根据对划分孢粉组合的特征分析,通过与邻区及华北地区晚古生代孢粉组合的对比,探讨了孢粉组合的时代意义。通过孢粉组合,推测了相应时期的古植被类型,并与前人在相同地质时期所建立的大植物化石带进行了对比,分析了各地质时期植被的兴起、发展、繁盛以及衰退绝灭的历史过程,研究区二叠纪植物群属于典型的华夏植物群,反映了一种温暖潮湿的热带雨林气候,二叠纪晚期随着松柏类植物所占比例的增加,气候有变干旱的趋势。     

Zircon U–Pb age, trace element and Hf isotope composition of Kongling terrane in the Yangtze Craton: refining the timing of Palaeoproterozoic high-grade metamorphism

U–Pb age, trace element and Hf isotope compositions of zircon were analysed for a metasedimentary rock and two amphibolites from the Kongling terrane in the northern part of the Yangtze Craton. The zircon shows distinct morphological and chemical characteristics. Most zircon in an amphibolite shows oscillatory zoning, high Th/U and ¹⁷⁶Lu/¹⁷⁷Hf ratios, high formation temperature, high trace element contents, clear negative Eu anomaly, as well as HREE-enriched patterns, suggesting that it is igneous. The zircon yields a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of 2857 ± 8 Ma, representing the age of the magmatic protolith. The zircon in the other two samples is metamorphic. It has low Th/U ratios, low trace element concentrations, variable HREE contents (33.8 ≥ Lu_N≥2213; 14.7 ≤ Lu_N/Sm_N ≤ 354) and ¹⁷⁶Lu/¹⁷⁷Hf ratios (0.000030–0.001168). The data indicate that the zircon formed in the presence of garnet and under upper amphibolite facies conditions. The metamorphic zircon yields a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of 2010 ± 13 Ma. These results combined with previously obtained Palaeoproterozoic metamorphic ages suggest a c. 2.0 Ga Palaeoproterozoic collisional event in the Yangtze Craton, which may result from the assembly of the supercontinent Columbia. The zircon in two samples yields weighted mean two-stage Hf model ( T _DM2) ages of 3217 ± 110 and 2943 ± 50 Ma, respectively, indicating that their protoliths were mainly derived from Archean crust.     

浅析宁波盆地膏盐地层的时代──兼对“宁波盆地北部的长河群”之时代质疑

宁波盆地地下揭示的一套包含暗色膏硝质泥岩、泥质白云岩在内的紫红、灰紫色泥岩、棕褐色砂砾岩、细砂岩和玻屑凝灰岩的地层，均称方岩组，内含膏盐并具油色显示。对其时代有早、晚白垩世和早第三纪之认识，笔者从70～90年代地质工作中所获化石分析认为，虽然宁波盆地这一层位含化石不丰，但从分布及数量上比较，相对占优势的应该是孢粉和植物化石，其时代意见也较为一致，指示为早白垩世。     

The Lower Permian Wasp Head Formation,Sydney Basin: high‐latitude,shallow marine sedimentation following the late Asselian to early Sakmarian glacial event in eastern Australia

The Lower Permian Wasp Head Formation (early to middle Sakmarian) is a ～95 m thick unit that was deposited during the transition to a non‐glacial period following the late Asselian to early Sakmarian glacial event in eastern Australia. This shallow marine, sandstone‐dominated unit can be subdivided into six facies associations. (i) The marine sediment gravity flow facies association consists of breccias and conglomerates deposited in upper shoreface water depths. (ii) Upper shoreface deposits consist of cross‐stratified, conglomeratic sandstones with an impoverished expression of the Skolithos Ichnofacies. (iii) Middle shoreface deposits consist of hummocky cross‐stratified sandstones with a trace fossil assemblage that represents the Skolithos Ichnofacies. (iv) Lower shoreface deposits are similar to middle shoreface deposits, but contain more pervasive bioturbation and a distal expression of the Skolithos Ichnofacies to a proximal expression of the Cruziana Ichnofacies. (v) Delta‐influenced, lower shoreface‐offshore transition deposits are distinguished by sparsely bioturbated carbonaceous mudstone drapes within a variety of shoreface and offshore deposits. Trace fossil assemblages represent distal expressions of the Skolithos Ichnofacies to stressed, proximal expressions of the Cruziana Ichnofacies. Impoverished trace fossil assemblages record variable and episodic environmental stresses possibly caused by fluctuations in sedimentation rates, substrate consistencies, salinity, oxygen levels, turbidity and other physio‐chemical stresses characteristic of deltaic conditions. (vi) The offshore transition‐offshore facies association consists of mudstone and admixed sandstone and mudstone with pervasive bioturbation and an archetypal to distal expression of the Cruziana Ichnofacies. The lowermost ～50 m of the formation consists of a single deepening upward cycle formed as the basin transitioned from glacioisostatic rebound following the Asselian to early Sakmarian glacial to a regime dominated by regional extensional subsidence without significant glacial influence. The upper ～45 m of the formation can be subdivided into three shallowing upward cycles (parasequences) that formed in the aftermath of rapid, possibly glacioeustatic, rises in relative sea‐level or due to autocyclic progradation patterns. The shift to a parasequence‐dominated architecture and progressive decrease in ice‐rafted debris upwards through the succession records the release from glacioisostatic rebound and amelioration of climate that accompanied the transition to broadly non‐glacial conditions.     

遗迹化石在层序地层学研究中的应用

以济阳坳陷古近系沙河街组和塔里木盆地志留系为例,探讨了遗迹化石与层序地层学的关系,表现在3个方面:1)层序界面的识别层序界面位置发育有特征性的受基底控制的遗迹相,且界面上下遗迹组合类型发生变化;2)准层序界面的识别较深水环境中,界面上下生物扰动强度明显差异,界面之下扰动强度较大,扰动指数可达到3,而界面之上几乎没有生物扰动,且在同一准层序内部,由下至上,扰动强度逐渐增大;3)旋回层序的识别:在潮控滨线环境中,单个准层序内部,由下至上,高能环境的Skolithos遗迹组合逐渐变为中低能环境的Planolites-Palaeophycus遗迹组合和低能环境的Cochlichnus-Planolites遗迹组合,由下至上呈现旋回性变化特征。     

内蒙古正蓝旗羊蹄子山-磨石山钛矿区硅质岩地球化学特征及沉积环境意义

文章通过详细的野外地质调查和系统的岩石化学、稀土元素、微量元素及硅、氧同位素等研究,探讨了羊蹄子山-磨石山钛矿区无矿白色硅质岩和富钛硅质岩的成因及形成地质构造环境。研究结果表明,呈厚层状产出的无矿白色硅质岩具较高的SiO2、Al2O3含量及Al/(Al Fe Mn)、Al2O3/(Al2O3 Fe2O3)比值,稀土元素总量很低,其北美页岩标准化配分模式为向右倾的曲线,无明显铈异常和铕异常,表明其形成于受陆源影响的大陆边缘构造环境;赋矿岩系中薄层状富钛硅质岩的TiO2、Fe2O3、Cu、V含量较高,但Al/(Al Fe Mn)、Al2O3/(Al2O3 Fe2O3)比值较低,稀土元素总量较高,北美页岩标准化曲线为明显左倾型-平坦型,具弱的负铈异常,表明其形成于洋脊及附近环境。两种硅质岩的δ30Si值为变化较小的负值,与热水沉积和某些生物成因硅质岩的硅同位素组成相似,两者的δ18O值范围和平均值均相似。两类硅质岩的成因及形成构造环境不同,富钛硅质岩的地球化学特征表明,该矿床的形成与本区元古宙海底火山热液喷流作用有关。     

冲绳海槽有孔虫壳体的微量元素Sr,Nd同位素地球化学

钙质生物壳的微量元素组合和Sr,Nd同位素组成是识别海底混合源沉积物中生物源物质相对贡献的重要参数.冲绳海槽有孔虫壳体强烈富集Sr,P,Mn和Ba,富集Li,U,Th,Sc,Co,Pb,Zn,Cr,Rb,Y,Sb和轻稀土元素,弱富集V,Ga,Zr,Nb,Cd和中稀土元素,相对贫Ge,Mo,In,Sn,Cs,Hf,Ta,W,Tl,Bi和重稀土元素,海水中微量元素的背景含量和生物活动对微量元素的选择性吸收是有孔虫壳体中微量元素发生富集和贫化的主要机制,冲绳海槽有孔虫壳体的稀土元素配分模式与海水和太平洋有孔虫的有明显差异,表现出中稀土元素相对富集,并具有微弱的负Ce异常.有孔虫壳体的Sr,Nd同位素比值也与大洋海水不同,分别为0.709769和0.512162,前者略高于大洋海水,后者略低于大洋海水,表明冲绳海槽海水明显受大陆河水影响.     

Trichodesmium erythraeum (Ehrenberg) bloom along the southwest coast of India (Arabian Sea) and its impact on trace metal concentrations in seawater

The incidence of a large scale Trichodesmium erythraeum bloom along the southwest coast of India (Arabian Sea) observed in May 2005 is reported. Around 4802 filaments of T. erythraeum ml⁻¹ seawater was observed and a colony consisted of 3.6 × 10⁵ cells. The bloom was predominant off Suratkal (12° 59′N and 74° 31′E) with a depth of about 47 m, covering an area of 7 km in length and 2 km width. The concentrations of Zinc, Cadmium, Lead, Copper, Nickel and Cobalt were determined in samples collected from the bloom and non-bloom sites using stripping voltammetry. The observed hydrographical and meteorological parameters were found to be favorable for the bloom. The concentrations of Zinc, Cadmium and Nickel were found to be higher at bloom stations, while the concentrations of Lead, Copper and Cobalt were found to be very low at bloom stations. Elevated concentrations of Cadmium and Cobalt were observed at Valappad mainly due to the decomposition of detrital material produced in the bloom. Statistically significant differences (P > 0.01) in metal concentrations between the bloom and non-bloom stations were not observed except for Copper. Metals such as Lead, Copper and Cobalt were removed from the seawater at all places where bloom was observed. Cadmium was found to be slowly released during the decaying process of the bloom.     

中国多金属结核开辟区间隙水中铜、锰、镍的分布规律

通过对东北太平洋海域中国多金属结核开辟区沉积物间隙水中铜、锰、镍等微量元素的详细研究表明,锰主要受沉积环境的影响,其含量的变化范围在0.16～8.61μg/dm3之间;铜和镍则主要与表层海水的初级生产力有关,研究区内间隙水中铜和镍含量的变化范围分别为0.16～20.8和0.80～3.12μg/dm3,且这些元素在沉积物—水界面处均存在最大浓度梯度.利用“Fick扩散定律”计算表明,锰在研究区主要是从上覆海水向沉积物扩散,是沉积物中锰的主要来源之一;而铜和镍则是从沉积物向上覆海水扩散,是底层海水中铜和镍的主要来源。与表层海水中铜和镍向底层海水的输送通量计算结果相比,底层海水中铜和镍的含量主要受沉积物的控制.     

Spatial and seasonal variations in depth profile of trace metals in saltmarsh sediments from Sapelo Island, Georgia, USA

This study was undertaken to elucidate the impact of early diagenetic processes on the accumulation of trace metals in Sapelo Island saltmarsh sediments as a function of time, space and sediment properties. Samples were collected from three sites in summer (May 1997) and winter (January 1998) along a transect from an unvegetated Creek Bank through a vegetated Tidal Levee to the vegetated midmarsh with evident lateral heterogeneity caused by hydrologic regime, macrophytes and microbial and macrofaunal activities. A suite of trace metals (As, Ba, Cr, Co, Cu, Cd, Mo, Ni, Pb, Th, Ti, U, V, Zn and Zr) was analyzed to obtain their depth-distribution at the three sites. Spatially marked differences were observed, that were primarily related to hydraulic flushing of trace metals away from the sites in high-energy regimes, rapid downward mixing and reworking of sediment via bioturbation, and below-ground degradation and production of Spartina biomass. Although sulfate reduction and the formation of acid volatile sulfide and pyrite were dominant processes throughout the marsh, the trace metal scavenging role of sulfides was not apparent. However, possible sulfurization of organic matter, leading to enhanced trapping of trace metals with organic carbon, may have played an important role in sequestration of trace metals.No similarity was observed visually between the depth trends of trace metals and sediment properties (grain size, iron-oxyhydroxide content, acid volatile sulfides and pyrite content) that are known to play a major role in trace metal partitioning. Only organic carbon content closely followed the trace metal profiles at all the three sites. Minor variation in depth-integrated sediment trace metal content was observed seasonally at each of the three sites. Furthermore, the depth trend of profiles of individual trace metals also did not vary significantly over the seasons either.