煤田资料的铀矿二次开发技术及其找矿意义——以二连盆地ZS煤田铀矿点的发现为例

在中国北方主要盆地铀矿地质调查工作中,煤田自然伽马异常作为主要矿化信息和找矿线索,为一系列铀矿床(点)的快速发现奠定了坚实基础。为进一步提高煤田资料铀矿二次开发的高效性和准确性,运用水成铀矿理论,以中国二连盆地ZS煤矿区典型铀矿点的发现为例,初步探讨了煤田资料的铀矿二次开发技术,提出了"异常筛选与选区分析、原位验证与环境判别、等时地层格架建立与沉积体系分析、综合分析与靶区定位"四位一体的煤矿区铀矿地质调查模式。这对中国北方含煤盆地铀矿地质调查工作提供了新的找矿思路和技术路线,具有较重要的指导意义。     

景洪市嘎栋地热井特征及成井工艺总结分析

景洪盆地内蕴藏有丰富的地热资源。通过对景洪市嘎栋地热资源勘查地热井地质、施工情况及成果进行介绍,结合勘查施工实践,针对地热资源勘查开发、地热钻井施工、成井工艺及钻井过程中地质问题等有关内容进行经验总结并分析,对地热地质条件与地热井施工之间结合进行一些经验探讨,并对现行地热井规范中关于井身结构设计、取水层位确定、单井资源量计算等问题提出一定疑问。旨在通过实践及疑问探讨,力图找出为地热资源勘查开发提供值得借鉴的经验和教训。     

内蒙古达来诺尔湖湖泊沉积物中敏感粒度组分沉积环境及地层分析

对达来诺尔湖北岸岸边(DL-0)、湖中心(DL-1)和湖南岸(DL-2)3个点的岩心沉积物进行了详细的岩性分析、粒度分析和粒度参数垂向分布序列分析。对沉积环境变化较为敏感的粒度组分的分析发现DL-0与DL-1和DL-2井岩心沉积物敏感粒度组分的峰值有较大差别,其粒度分布范围相差较大,表明湖北岸岸边、湖中心和湖南岸的沉积物来源和沉积环境的时空差异。敏感粒度组分含量随深度变化的初步分析表明,湖北岸岸边(DL-0)和湖中心(DL-1)两个点的沉积环境较为稳定;而位于湖南岸(DL-2)点的沉积环境变化比较大,包含了5个明显的沉积波动旋回,并对达来诺尔湖由北至南进行了沉积地层分析。在达来诺尔湖水下1.5m内主要是粒径0~200μm的颗粒,岩性为粘土、粉砂和砂,以粘土和粉砂为主,随着深度的增加,黏土含量增大,粉砂和砂含量减小。     

贵州威宁麻窝山岩溶盆地沉积物中粘土矿物特征及其古气候指示意义

利用X射线衍射等分析方法,对贵州威宁麻窝山岩溶盆地沉积物中粘土矿物进行研究,获得了粘土矿物的组成、相对含量、结晶度指数、化学指数以及相对含量比值等方面的信息,探讨该盆地的沉积环境演化特征。研究表明,粘土矿物以伊/蒙混层矿物(30%~75%)和绿泥石(10%~45%)为主,高岭石(5%~20%)和伊利石(10%)次之,基本不含蒙脱石。伊/蒙混层矿物和绿泥石含量呈负相关性。高岭石含量在剖面底部较稳定,在484cm上部出现较大的波动。伊利石结晶度和化学指数与伊/蒙混层矿物含量具有较好的正相关性,且在第Ⅰ阶段相对于其它指标较敏感,出现波动。通过综合对比分析,将研究区剖面划分为4个阶段,其是3个冷暖干湿的大循环和若干个小循环气候环境的物质记录。     

Anthropogenic impacts on nitrogen fixation rates between restored and natural Mediterranean salt marshes

To test the effects of site and successional stage on nitrogen fixation rates in salt marshes of the Venice Lagoon, Italy, acetylene reduction assays were performed with Salicornia veneta‐ and Spartina townsendii‐vegetated sediments from three restored (6–14 years) and two natural marshes. Average nitrogen fixation (acetylene reduction) rates ranged from 31 to 343 μmol C₂H₄·m^?2·h^?1 among all marshes, with the greatest average rates being from one natural marsh (Tezze Fonde). These high rates are up to six times greater than those reported from Southern California Spartina marshes of similar Mediterranean climate, but substantially lower than those found in moister climates of the Atlantic US coast. Nitrogen fixation rates did not consistently vary between natural and restored marshes within a site (Fossei Est, Tezze Fonde, Cenesa) but were negatively related to assayed plant biomass within the acetylene reduction samples collected among all marshes. Highest nitrogen fixation rates were found at Tezze Fonde, the location closest to the city of Venice, in both natural and restored marshes, suggesting possible site‐specific impacts of anthropogenic stress on marsh succession.     

Bicyclic alkanes in source rocks of the Triassic Yanchang Formation in the Ordos Basin and their inconsistency in oil-source correlation

The Triassic Yanchang Formation is the main source rocks for Mesozoic oil in Ordos Basin. The formation includes 10 oil-bearing beds (Ch 1–Ch 10), that each can be further divided into two to three intervals. Abundant C₁₂–C₁₄ and C₁₅–C₁₆ bicyclic alkanes have been detected in the formation in the Xifeng oilfield, Ordos Basin. The C₁₂–C₁₄ group is dominated by C₁₂ and C₁₃, and the C₁₅–C₁₆ group contains abundant C₁₅. The groups show three distribution patterns: A) the C₁₂–C₁₄ group is the major component in the non-source rocks of the Ch 7-1 and Ch 8-1 intervals; B) both groups are abundant and are common in source rocks of the Ch 7-3 interval; and C) the C₁₅–C₁₆ group is the major component in source rocks of the Ch 7-3 interval and also in sediments that contain type Ⅰ or partial sapropel type Ⅱ₁ organic matter (OM) in the Ch 7-2 and Ch 8-1 intervals. Although thermal maturities of the source rocks in the Ch 7 section are similar, they show significant differences with respect to the drimane isomerisation index, which indicates that the drimane rearrangement is controlled by thermal evolution of the sediments, but may also be closely related to the depositional environment. This study determined that reducing environments are more conducive to preservation of drimane than oxic environments. The drimane isomerisation index and the value of the hopane parameter Tm/Ts are positively correlated. The parameter Tm/Ts varies over a wide range within the sequence, and the large variations may be a result of terrigenous OM input by turbidity currents and/or gravity flows, mixed with the autochthonous sediments. Abundant homodrimane in both source rocks may reflect reducing environments in deep lakes and major input of higher plant OM. Organic-rich shale and oil shale in the Ch 7-3 interval of the Yanchang Formation are the primary sources of oil in reservoirs in the Xifeng area. The crude oil is rich in bicyclic alkanes that are dominated by C₁₅–C₁₆ as source rocks with pattern C for bicyclic alkanes, which indicates an origin mainly from the Ch 7-3 interval. The main peaks in all of the crude oils are associated with 8β(H)-drimane and lower abundance of rearranged drimane. However, most of the source rocks have a main peak associated with 8β(H)-homodrimane or rearranged drimane. Weak microbial action, selective degradation and water washing may be the cause of the significant difference in bicyclic sesquiterpane composition between the crude oil and the source rocks. The result suggests that oil-source correlations based on the bicyclic sesquiterpanes are questionable.     

Formation of low permeability reservoirs and gas accumulation process in the Daniudi Gas Field,Northeast Ordos Basin,China

The Daniudi Gas Field is a typical large-scale coal-generated wet gas field located in the northeastern Ordos Basin that contains multiple Upper Paleozoic gas-bearing layers and considerable reserves of gas. Based on integrated analysis of reservoir petrology, carbonate cement C–O isotope, geochemistry of source rocks and HC gas and numerical basin modeling, a comprehensive study focusing on the formation of low permeability reservoirs and gas generation process uncovers a different gas accumulation scene in Daniudi Gas Field. The gas accumulation discovered was controlled by the reservoir permeability reduction and gas generation process, and can be divided into two distinct stages by the low permeability reservoir formation time: before the low permeability reservoir formation, the less matured gas was driven by buoyancy, migrated laterally towards NE and then accumulated in NE favorable traps during Late Triassic to early Early Cretaceous; after the low permeability reservoir formation, highly matured gas was driven by excessive pressure, migrated vertically and accumulated in-situ or near the gas-generating centers during early to late Early Cretaceous. The coupling relationship between reservoir diagenetic evolution and gas generation process controlled on gas accumulation of the Daniudi Gas Field. This study will aid in understanding the gas accumulation process and planning further E&D of the Upper Paleozoic super-imposed gas layers in the whole Ordos Basin and other similar super-imposed low permeability gas layer basins.     

Mesozoic rift to post-rift tectonostratigraphy of the Sverdrup Basin,Canadian Arctic

Jurassic-Cretaceous rift successions and basin geometries of the Sverdrup Basin are reconstructed from a review and integration of stratigraphy, igneous records, outcrop maps, and subsurface data. The rift onset unconformity is in the Lower Jurassic portion of the Heiberg Group (approximately 200–190 Ma). Facies transgress from early syn-rift sandstones of the King Christian Formation to marine mudstones of the Jameson Bay Formation. The syn-rift succession of marine mudstones in the basin centre, Jameson Bay to Deer Bay formations, ranges from Early Jurassic (Pleinsbachian) to Early Cretaceous (Valanginian). Early post-rift deposits of the lower Isachsen Formation are truncated by the sub-Hauterivian unconformity, which is interpreted as a break up unconformity at approximately 135–130 Ma. Cessation of rift subsidence allowed for late post-rift sandstone deposits of the Isachsen Formation to be distributed across the entire basin. Marine deposition to form mudstone of the Christopher Formation throughout the Canadian Arctic Islands and outside of the rift basin records establishment of a broad marine shelf during post-rift thermal subsidence at the start of a passive margin stage. The onset of the High Arctic Large Igneous Province at approximately 130 Ma appears to coincide with the breakup unconformity, and it is quite typical that magma-poor rifted margins have mainly post-rift igneous rocks. We extend the magma-poor characterization where rifting is driven by lithospheric extension, to speculatively consider that the records from Sverdrup Basin are consistent with tectonic models of retro-arc extension and intra-continental rifting that have previously been proposed for the Amerasia Basin under the Arctic Ocean.     

Late Miocene–early Pliocene planktonic foraminifer event-stratigraphy of the Bajo Segura basin: A complete record of the western Mediterranean

The Bajo Segura basin (eastern Betic Cordillera) has one of the most complete late Miocene–early Pliocene marine records of the western Mediterranean. An updated planktonic foraminifer zonal scheme based on recent astronomically tuned biozones is presented for this interval, documenting a complete succession of biostratigraphic markers, from biozone MMi9 (earliest Tortonian) to MPl3 (latest early Pliocene), of likely significance for regional-scale correlation throughout the Mediterranean. The findings reveal a series of intrazonal events (some unreported until now in the Mediterranean Neogene basin), including the particularly interesting two influxes of the Globorotalia miotumida group during the Tortonian. These biostratigraphic findings are the basis for a framework of the major allostratigraphic units in the basin based on planktonic foraminifer event-stratigraphy: synthems Tortonian I, Tortonian II, Tortonian-Messinian I, Messinian II, and Pliocene. In addition, the timing of the main tectono-sedimentary and palaeogeographic events throughout the basin's evolution has been further constrained. Our results suggest that, at least in the Bajo Segura basin, the late-Messinian barren interval (non-distinctive zone) can be considered an ecobiostratigraphic zone (cenozone) characterized by dwarf fauna of planktonic foraminifera. Consequently, the Bajo Segura composite section can be regarded as a biostratigraphic reference section for Neogene basins in the Betic Cordillera and hence also in the Western Mediterranean.