湘西北和鄂西云台观组孢子组合及其地层意义

通过对孢子组合的研究,确定云台观组属中泥盆统(季维特阶)。该地层不仅产出有丰富并保存完好的孢子,而且还有一些疑原类、虫颚和几丁虫碎片。文中描述的孢子包括19个属、30个种和变种,其中新种2个、新联合种1个,即小刺凸刺弓形脊三缝孢、多刺冠环三缝孢以及大刺剑刺三缝孢(新联合)。与北半球同类组合对比表明:湘西北和鄂西云台观组孢子组合主要为季维特阶的属种,从整个组合特征看,可能属晚季维特阶。文中还讨论了云台观组的沉积环境和地层意义。     

Detrital composition of Ordovician sandstones from the Rügen boreholes: implications for the evolution of the Tornquist Ocean

The Lower Palaeozoic sequences of the Rügen boreholes are composed of pelitic-clastic sediments which range in age from the Cambro-Ordovician boundary to the Late Ordovician. Provenance studies have been carried out on Cambro-Ordovician sandstones from the Loissin borehole and on Middle-Upper Ordovician greywackes of the Rugen 5 borehole.The Loissin sandstones were deposited as turbidites and debris flows in an unstable sedimentary basin. They form immature arkoses and subarkoses with high matrix contents. Their debris derived from a polycyclic, sedimentary cratonic provenance and from a monocyclic magmatic provenance. This is reflected in the heavy mineral spectrum, which is dominated by an anhedral, coloured zircon fraction and a euhedral, transparent zircon fraction.The Middle-Upper Ordovician Rügen greywackes derived from proximal, high energy turbidites which were transported into a deep marine basin. They form homogeneous lithic arkoses and arkosic litharenites. Their debris derived from a composite provenance with an ultramafic-mafic, ophiolitic source, an acidic magmatic source and a heterogeneous sedimentary cratonic source.Although the Loissin sandstones probably originated in an intracratonic, rift-related sedimentary basin, the debris of the Rugen greywackes is regarded as derived from a heterogeneous active continental margin. Results and interpretations of the provenance study are discussed in the light of proposed Lower Palaeozoic palaeogeographic reconstructions.     

论华南碳硅泥岩型层控铀矿床的形成地质背景和成因的多样性

华南广泛分布的碳硅泥岩型铀矿床是比较典型的层控矿床,按控矿层位可分为震旦寒武系和上古生界两大类。该类矿床的铀源层形成与华南地区地壳演化有密切关系。铀源层的改造成矿具有较大的复杂性和多样性,据此,过去一般划分为沉积成岩型,淋积型和热造(热液改造)型三亚类,其中前两类并不多见,而且沉积成岩型也不够确切。热造型是这类矿床的最主要代表,但它们在成因上也表现出不同特征,特别是它们与附近花岗岩体的关系比较复杂,以致过去对其成因有不同认识。本文讨论了某些有代表性的矿床的地质学、地球化学特征并提出了对这类矿床的进一步分类意见。     

单断裂多源应力场初探

本文提出一个单断裂多段闭锁的孕震力学模型,对其产生的附加应力场进行了推导和计算;讨论了震前多源应力场的时空分布特征。证明多源前兆场演变过程的复杂性和震前地应力变化形态的多样性。     

弓长岭太古代条带状硅铁建造中长英质变质岩的原岩恢复及地层学意义

弓长岭太古代条带状硅铁建造中的长英质变质岩为该地层的标志层(K和K_S层)。原岩恢复表明二矿区黑云母石英钠长变粒岩(K层)为含火山灰的中酸性火山熔岩;而岭东区的石榴云母石英片岩(K_S层)为含火山灰的泥砂质沉积岩,二者不能对比。据此,本文补充和完善了该区地层剖面。它表明弓长岭硅铁建造生成于大陆边缘的陆棚浅海环境,其铁矿层赋存于一海进层序的中上部。该建造的沉积岩组合特征与绿岩带不同,而与典型的高级区表壳岩组合类似。     

滇池地区沉积磷块岩中胶磷矿矿物学特征及其研究意义

本文从物理性质、化学成分及其成因结构等方面,对云南滇池地区胶磷矿进行了矿物学特征研究。提出该区胶磷矿主要以三种形式赋存在磷块岩中。对不同矿石类型中胶磷矿做扫描电镜研究,得知胶磷矿主要由超微晶低碳氟磷灰石集合体、磷酸盐显微莓群以及纤维放射状磷灰石等构成。经化学分析、红外、晶胞参数测定,不同胶磷矿有一定差异,特别是碳和磷,经矿物学对比发现,反映随变质作用的加深,胶磷矿有向晶质氟磷灰石演化的趋势,脱碳作用表现明显。本区胶磷矿稀土元素含量不高,钇族较富,铈族较贫。球粒陨石标准化后为铈亏损型模式。     

黄河中游河流阶地的形成与水系演化

本文据黄河中游各流域大量地质地貌实测资料，以连通各河流全线的各级阶地中,沉积物与古土壤的层位关系为主线，用年代学和古土壤断代法确定了阶地年代，阐述了四期九亚期水系演化史，并指出黄河中游及其主要支流诞生于更新世早中期167－145万年之间，之后发育了六级阶地和两级河漫滩。     

东海西湖凹陷始新统沉积环境及含油气性

东海西湖凹陷始新统平湖组为半封闭海湾沉积环境,海水由南往北侵入,平湖组下段为海湾浅水—滨岸—滨岸冲积平原相沉积;平湖组中段为潮坪—三角洲相沉积;平湖组上段为三角洲相沉积。业已证明,始新统平湖组不但具有极好的生油气条件,而且发育良好的储集层。油气分布除了受构造因素控制外,与沉积相有极为密切的关系。     

Naturally occurring arsenic in groundwater and identification of the geochemical sources in the Duero Cenozoic Basin, Spain

Arsenic concentrations surpassing potability limit of 10 μg/L in the groundwater supplies of an extensive area in the Duero Cenozoic Basin (central Spain) have been detected and the main sources of arsenic identified. Arsenic in 514 samples of groundwater, having mean values of 40.8 μg/L, is natural in origin. Geochemical analysis of 553 rock samples, assaying arsenic mean values of 23 mg/kg, was performed. Spatial coincidence between the arsenic anomaly in groundwater and the arsenic lithogeochemical distribution recorded in the Middle Miocene clayey organic-rich Zaratan facies illustrates that the rocks of this unit are the main source of arsenic in groundwater. The ferricretes associated to the Late Cretaceous–Middle Miocene siliciclastics also constitute a potential arsenic source. Mineralogical study has identified the presence of arsenic in iron oxides, authigenic pyrite, manganese oxides, inherited titanium–iron oxides, phyllosilicates and organomineral compounds. Arsenic mobilization to groundwater corresponds to arsenic desorption from iron and manganese oxides and from organic matter.     

Evolution of Cretaceous–Cenozoic quartz pebble conglomerate gold placers during basin formation and inversion, southern New Zealand

Numerous auriferous fluvial quartz pebble conglomerates (QPCs) are present within the Late Cretaceous–Recent sedimentary sequence in southern New Zealand. The QPCs formed in low-relief settings before, during, and after regional marine transgression, in alluvial fan and a variety of fluvial and near-shore depositional settings: In particular, during slow thermal subsidence associated with Late Cretaceous–early Cenozoic rifting, and during the early stages of orogenic uplift following mid Cenozoic marine regression. QPC maturity characteristics are complex and vary with sediment transport and recycling history, stratigraphic proximity to the transgressive Waipounamu Erosion Surface, and the amount of first-cycle detritus incorporated during recycling. For pre-marine QPCs, the amount of first cycle detritus varies with tectonic intensity and proximity of the depositional setting to remnant Cretaceous topography. For post-marine QPCs, it varies with tectonic intensity and proximity to Late Cenozoic uplift of basement ranges.QPCs do not form during a single bedrock erosion–sediment deposition cycle: Non-oxidised and/or oxidized groundwater alteration (kaolinisation) of labile minerals in immature sediment and the upper part of underlying basement, and repeated sedimentary recycling, are fundamental processes of QPC formation regardless of the tectonic or sedimentary settings. Altered immature rock disaggregates easily upon erosion, and alteration clays are winnowed to leave quartz-rich residues containing resistant heavy minerals such as zircon and gold. Detrital sulfide survives recycling if deposition and burial in saturated sediments are rapid. QPCs result only if sediment recycling is not accompanied by excessive erosion of fresh basement rock. Uplift of many parts of the Otago Schist belt since late Miocene has raised rocks above the water table, increased erosion rates, and inhibited groundwater alteration and QPC formation. QPC formation is still occurring in Southland, where the water table is high, sediments are saturated and undergoing alteration, and uplift and erosion rates, topography, and fluvial gradients are all low. The QPCs accumulate as residual gravel on the valley floors of low-competence streams that are slowly incising pervasively altered dominantly late Miocene–Pliocene immature conglomerates.QPCs formation essentially represents physical and chemical lagging of precursor strata. Accumulation of detrital gold and other heavy minerals is an inevitable consequence, and most QPCs contain some gold. Three types of significant gold placer have developed in the QPCs. Type 1 placers are essentially eluvial and/or colluvial in origin and form without significant fluvial transport, by residual accumulation in low-competence valleys during low-rate uplift, fluvial incision and QPC formation. Type 2 placers have formed during significant fluvial transport and subsequent fluvial incision, mainly in higher energy proximal and medial reaches of larger pre-marine (Eocene) and post-marine fluvial systems. Type 3 placers formed by wave-base and marine current winnowing in the shallow shelf setting during low-rate regional marine transgression, especially in the Eocene.