Geochemical characteristics of gases from the largest tight sand gas field (Sulige) and shale gas field (Fuling) in China

This study performed a detailed geochemical analyses of the components, stable carbon isotopes of alkane gas and CO₂, stable hydrogen isotopes of alkane gas and helium isotopes of reproducing gas from the largest tight gas field (Sulige) and shale gas (Fuling) field in China. The comparative study shows that tight gas from the Sulige gas field in the Ordos Basin is of coal-derived origin, which is characterized by a positive carbon and hydrogen isotopic distribution pattern (δ¹³C₁ > δ¹³C₂ > δ¹³C₃ > δ¹³C₄; δ²H₁ > δ²H₂ > δ²H₃), i.e., the carbon and hydrogen isotopes increase with increasing carbon numbers. Carbon dioxide from this field are of biogenic origin and the helium is crust-derived. Shale gas from the Fuling shale gas field belongs to oil-derived gas which has complete carbon and hydrogen isotopic reversal of secondary alteration origin (δ¹³C₁ < δ¹³C₂ < δ¹³C₃; δ²H₁ < δ²H₂ < δ²H₃), i.e., the carbon and hydrogen isotopes decrease with increasing carbon numbers. Such complete isotopic reversal distribution pattern is due to the secondary alteration like oil or gas cracking, diffusion and so on under high temperature. In that case, positive carbon or hydrogen isotopic distribution pattern will change into complete isotopic reversal as the temperature increases. Carbon dioxide is of abiogenic origin resulting from the thermal metamorphism of carbonates and helium is crust-derived.     

Geochemical investigation of oils from Cretaceous to Eocene sedimentary sequences of the Abadan Plain,Southwest Iran

Oil samples from Lower Cretaceous to Eocene reservoirs in southwest Iran were analyzed using gas chromatography–mass spectrometry and gas chromatography–isotope ratio mass spectrometry for genetic classification of oil families and determining their maturity. The Studied oil samples are non-biodegraded and their gravity range from 18.3 to 37° API. The slight even/odd n-alkane predominance, coupled with low Pr/Ph values, suggests their likely source rocks with a predominance of algal organic matter, type IIS kerogen deposited under strongly reducing marine environments. The biomarker distribution of investigated oils is characterized by high concentration of both C₂₉ and C₃₀ hopanes and ratios of C₂₉/C₃₀H are generally greater than unity. There is a marked predominance of C₂₉ regular sterane over C₂₇ and C₂₈ homologs in our studied oils. High sterane/hopane values and cross plot of the δ¹³C sat versus δ¹³C aro show contribution of marine organic matter. Medium value of gammacerane index and other salinity indices show water density stratification and high salinity conditions of the environment of deposition. It can be concluded that the studied reservoirs, due to their variable maturity have different API gravity and contain two oil families (types A and B) with latter being deeper and comprising more mature oils.     

Geochemical characteristics of the Paleogene shales in the Dongying depression,eastern China

Fluctuations in lacustrine sedimentary environments significantly affect distributions of organic matter (OM), uranium, and other elements in shales. In this study a high-resolution geochemical record of fluctuations in the paleo-depositional environment of a terrestrial lake basin is provided on the basis of extensive samples collected from the Member 3 of the Paleogene Shahejie Formation (Es₃) of the Niu-38 well in the Dongying Depression, Eastern China. These samples were tested for total organic carbon (TOC), element concentrations, and biomarkers to study the evolution and fluctuation in the depositional environments of an ancient lake basin and associated geochemical response. The evolution and fluctuation of the sedimentary environment from a deep lake to a semi-deep lake and then to a shallow lake delta were indicated by geochemical response. During this evolution, the values of TOC, S₁, S₂, Sr, and Ts/(Ts + Tm) remarkably decreased, whereas those of Co, Ni, Rb, Na, Fe/Mn, Fe/(Ca + Mg), and C₂₉ mortane/C₂₉ hopane significantly increased. The deep lake basin shows depositional fluctuations, as indicated by rock lithofacies and their geochemical parameters. A close interrelationship was observed among U concentration, TOC content, and inorganic element content. Uranium concentrations are positively correlated with TOC contents, Ca and Sr concentrations, and Sr/Ba and Ca/Mg ratios but negatively with K, Na, Ba, and Rb contents and Fe/(Ca + Mg) and Fe/Mn ratios. The observed increase in U concentration in the lower Es₃ section is closely related to surface adsorption by clay minerals and OM, together with some replacements of Ca and Sr by U in the shales.     

南海北部湾东部海域表层沉积物地球化学特征

通过对南海北部湾东部海域61 个站位表层沉积物粒度和地球化学组成的相关分析和因子分析,探讨了其空间分布特征、元素相关性以及元素组合特征, 揭示了元素在区域上的分布规律和主控因素。结果表明: 绝大多数常微量元素具有相似的平面分布特征, 而MnO、Zr、CaO 和Sr 空间变异系数较大,在部分区域出现了异常高值, 表明其沉积环境受到正常陆源沉积以外其他因素的影响。元素和Al₂O₃的比值分布特征表明, 广西和海南岛近岸沉积物主要由陆源碎屑沉积组成, 在潮汐和近岸径流作用下,由近岸向远海输送; 而研究区西部海域沉积物主要为来自红河的物质。元素相关分析和因子分析结果表明, 研究区表层沉积物中绝大多数常微量元素主要受沉积物粒度的控制; CaO 和Sr 含量主要受生物活动活跃程度控制; Zr 含量分布主要受控于源区母岩矿物组成以及自源区的搬运距离; 而MnO 含量则受陆源、海底热液以及自生作用等多种来源共同影响。     

北部湾SO-50柱状沉积物地球化学特征及其物源分析

通过对北部湾SO-50柱状沉积物进行粒度、Sr-Nd同位素、主微量元素及AMS14C分析,结果表明该柱状沉积物可以划分为两段,即上段（0~540 cm,0~3.0 ka BP）和下段（540~571 cm,3.0~3.3 ka BP）,它们反映了不同的物质源区贡献。下段较上段砂含量相对较高,主量元素（除SiO₂外）及稀土元素含量相对减少,87Sr/86Sr与ε_Nd除异常点外,总体变化幅度不大。研究结果显示SO-50柱状沉积物的物质来源比较稳定,具有强烈的陆源特征,下段沉积物的源区主要是琼州海峡东侧原有沉积物的再搬运和台湾岛河流携带沉积物的混合,上段沉积物除了琼州海峡东侧和台湾岛的贡献外,周边陆区海岸侵蚀物的贡献相对加强。根据SO-50柱状沉积物的研究结果表明,北部湾东部泥质区的物质来源除了琼州海峡东侧沉积物和沿岸侵蚀物的贡献外,台湾岛河流携带的沉积物对其影响也应引起重视。     

冲绳海槽沉积物孔隙水地球化学特征及其指示意义

通过对东海外陆坡–冲绳海槽GSW1孔沉积物孔隙水δ13C、δ18O、δ11B、δ37Cl同位素和Cl−、${\rm{SO}}_4^{2-} $、K+、Na+等离子指标的分析,探讨了沉积物早期成岩作用、流体来源、迁移和氧化环境的变化。研究发现,GSW1孔孔隙水溶解无机碳主要来自海水和有机质,${\rm{SO}}_4^{2-} $浓度随深度下降比较平缓,Cl−浓度远低于海水,该孔表层沉积物中硫酸盐消耗主要由有机质硫酸盐还原作用（OSR）所控制,甲烷厌氧氧化作用（AOM）发生在4 m以下更深的层位。OSR产生的H2S向上扩散富集并被氧化,是导致GSW1孔110～360 cm处 ${\rm{SO}}_4^{2-} $浓度未明显下降的主要因素。孔隙水${\rm{SO}}_4^{2-} $浓度整体随着深度增加呈减小的趋势,表明GSW1孔沉积环境由氧化、次氧化环境逐渐转变为还原环境。δ11B、δ37Cl值垂向变化波动较大,一方面受到早期成岩阶段有机质降解的影响,也可能与孔隙流体扩散以及沉积物/孔隙水相互作用有关。     

Rare earth element characteristics of the carboniferous Huanglong Formation dolomites in eastern Sichuan Basin,southwest China: Implications for origins of dolomitizing and diagenetic fluids

Marine dolostones of Carboniferous Huanglong Formation constitute major gas reservoir rocks in eastern Sichuan Basin. However, the investigation with respect to sources of dolomitizing and diagenetic fluids is relatively underexplored. The current study attempts to investigate the REE characteristics of dolomites using seawater normalization standard, and therefore discusses the origins of dolomitizing and diagenetic fluids, on the basis of continuous 47.33-m-long core samples from the second member of Huanglong Formation (C₂h₂) in eastern Sichuan Basin. Low Th, Sc, and Hf concentrations (0.791 × 10⁻⁶, 4.751 × 10⁻⁶, and 0.214 × 10⁻⁶, respectively), random correlation between total REE concentration (ΣREE) and Fe or Mn abundance, and seawater-like Y/Ho ratios (mean value of 45.612) indicate that the carbonate samples are valid for REE analysis. Based on petrographic characteristics, four dolomite types are identified, including micritic-sized dolomite (type Dol-1), fine-to medium-sized dolomite (type Dol-2), medium-to coarse-sized dolomite (type Dol-3), and coarse-to giant-sized saddle dolomite (type Dol-4). Dol-1 dolomites, characterized by positive Ce anomaly (mean value of 6.398), light REE (LREE) enrichment, and heavy REE (HREE) depletion with mean LREE/HREE ratio of 12.657, show micritic calcite-like REE patterns, indicating seawater origin of their dolomitizing fluids. Dol-1 dolomites were formed in sabkha environment whereas the dolomitizing fluids originated from evaporative brine water due to their micritic crystal sizes and tight lithology. Dol-2 dolomites, particularly subtype Dol-2a barely developing vuggy porosity, also show micritic calcite-like REE patterns, suggesting their dolomitizing fluids were seawater or seawater-derived fluids. This inference is confirmed by low Fe and Mn concentrations, which range from 651 μg/g to 1018 μg/g (mean value of 863 μg/g) and 65 μg/g to 167 μg/g (mean value of 105 μg/g), respectively, whereas homogenization temperatures (T_h, mean value of 103 °C) indicate that Dol-2 dolomites were formed under burial environment. Dol-3 dolomites, in form of cements of Dol-2 dolomites, show similar REE patterns to their host minerals (i.e., Dol-2 dolomites), indicating their parent source was possibly derived from Dol-2 dolomites. Dol-3 dolomites have high Fe and Mn concentrations with mean values of 3346 μg/g (ranging from 2897 μg/g to 3856 μg/g) and 236 μg/g (ranging from 178 μg/g to 287 μg/g), respectively, indicating the involvement of meteoric water. Meanwhile, it confirms that the dissolution in Dol-2 dolomites was caused by meteoric water leaching. Positive Eu anomalies (mean value of 1.406) in Dol-4 dolomites, coupled with high homogenization temperatures (mean value of 314 °C), suggest that Dol-4 dolomites precipitated from hydrothermal fluids. High Fe and Mn concentrations (mean values of 2521 μg/g and 193 μg/g, respectively) in Dol-4 dolomites likely results from interactions of hydrothermal fluids with deep burial clastic rocks.     

Multiple controls on the paleoenvironment of the Early Cambrian marine black shales in the Sichuan Basin,SW China: Geochemical and organic carbon isotopic evidence

In order to understand the paleoenvironment of the Early Cambrian black shale deposition in the western part of the Yangtze Block, geochemical and organic carbon isotopic studies have been performed on two wells that have drilled through the Qiongzhusi Formation in the central and southeastern parts of Sichuan Basin. It shows that the lowest part of the Qiongzhusi Formation has high TOC abundance, while the middle and upper parts display relative low TOC content. Redox-sensitive element (Mo) and trace elemental redox indices (e.g., Ni/Co, V/Cr, U/Th and V/(V + Ni)) suggest that the high-TOC layers were deposited under anoxic conditions, whereas the low-TOC layers under relatively dysoxic/oxic conditions. The relationship of the enrichment factors of Mo and U further shows a transition from suboxic low-TOC layers to euxinic high-TOC layers. On the basis of the Mo-TOC relationship, the Qiongzhusi Formation black shales were deposited in a basin under moderately restricted conditions. Organic carbon isotopes display temporal variations in the Qiongzhusi Formation, with a positive excursion of δ¹³C_org values in the lower part and a continuous positive shift in the middle and upper parts. All these geochemical and isotopic criteria indicate a paleoenvironmental change from bottom anoxic to middle and upper dysoxic/oxic conditions for the Qiongzhusi Formation black shales. The correlation of organic carbon isotopic data for the Lower Cambrian black shales in different regions of the Yangtze Block shows consistent positive excursion of δ¹³C_org values in the lower part for each section. This excursion can be ascribed to the widespread Early Cambrian transgression in the Yangtze Block, under which black shales were deposited.     

珠江口盆地陆丰15披覆构造带油藏地球化学特征及油源对比

珠江口盆地陆丰15披覆构造带南、北部分别与陆丰22洼、陆丰15洼毗邻,常规的油源对比指标无法确定构造带上S2-1和S5-1油藏的油源,2个洼陷都有可能向其供烃。为揭示原油的成因来源,对该地区原油及烃源岩开展了生物标志物、碳同位素及含氮化合物等特征的精细对比。在研究区原油及源岩中新检测出4个C24四环萜烷：脱-A-奥利烷、脱-A-羽扇烷、新C24四环萜烷及C24 17,21-开环藿烷。研究对比发现,S2-1和S5-1油藏原油中C24四环萜烷分布特征与陆丰22洼文昌组烃源岩更加吻合,具有更强的亲缘关系。此外,全油碳同位素和正构烷烃单体烃碳同位素指示S2-1和S5-1油藏明显区别于陆丰15洼生成的原油,预示着其原油具有陆丰22洼烃源岩的贡献。含氮化合物示踪参数指示S2-1油藏具有近源充注特征,进一步验证了陆丰22洼烃源岩对S2-1和S5-1油藏的重要贡献。     

80 Ma以来海水Os同位素组成曲线的精细特征:中、西太平洋多金属结壳的记录

80 Ma以来的海水Os同位素标准曲线具有K/T（白垩纪/第三纪）界线低值、E/O（始新世/渐新世）界线低值和中新世“挠曲”3个特征形态，这可以解释为陨击事件或超基性岩风化事件造成的陆、幔源物质供给关系的变化。将海水Os同位素标准曲线与多金属结壳Os同位素组成曲线进行对比，根据形态和取值的贴合程度可以为结壳进行年代厘定。由于取样精度的限制和生长间断的广泛存在，仅以此3个特征比对曲线存在不确定性。本研究综合对比中、西太平洋6块结壳的Os同位素组成曲线，总结出了4种记录在结壳中的海水Os同位素曲线的特征规律：K/T界线之前的“早期异常（波动）”；E/O界线之后曲线上升过程中的“小停顿”；E/O界线之后曲线上升过程末尾的“异常偏高点”；“中新世‘挠曲’错后”至10 Ma左右。这些新的特征形态可作为年代控制点，使得结壳年代框架的厘定可以更准确可靠。这4种特征形态可以初步解释为地质历史时期海洋中、幔源物质的供应关系变化或是看作随着数据的积累而对标准曲线的细化和校正。     

Geochemical and stratigraphic indicators of late Holocene coastal evolution in the Gythio area, southern Peloponnese, Greece

The study of past changes in sea level, and of historical and pre-historical coastal evolution, using coastal sediment stratigraphies is well-established over a range of geographic areas, in both seismic and aseismic settings. In the eastern Mediterranean, however, such studies are less common, and, notably, the use of sediment geochemistry, and its combination with lithostratigraphic studies to analyze palaeoenvironmental and palaeo-sea-level change, has not been explored to any significant extent, despite the fact that geochemical data have been successfully used elsewhere to aid in the identification of sea-level changes. Here, we use a combined geochemical, stratigraphic and microfossil approach to reconstruct late Holocene coastal evolution and sea-level change at two sites near Gythio in the southern Peloponnese, Greece. The sites show stratigraphic and geochemical evidence of the presence in Late Helladic times (ca. 1500 BC) of barrier-protected coastal lagoonal/wetland environments, which have gradually infilled over the last ca. 3500 yr. Archaeological remains and ceramic and charcoal-bearing horizons within the sediment sequences indicate Late Roman occupation of the area, although there is no sedimentary evidence of significant pre-Roman activity at the study sites. An apparent brackish wetland peat deposit at − 3.4 m (overlain by anoxic lagoonal clays) at Kamares (Kato Vathi) Bay shows a calibrated radiocarbon age of 1640–1440 BC, suggesting a relative sea-level rise of 0.8–1 mm/yr in this area over the past 3500 yr, in good agreement with previous archaeological and sea-level modelling studies. There is no evidence, based on the stratigraphic, microfossil or geochemical record, of sudden marine flooding events related to local or regional seismic activity, despite the presence of the area in a seismically active zone known to be subject to periodic earthquakes and tsunami. The data highlight the utility of combining geochemical and stratigraphic studies in the reconstruction of coastal evolution and the study of palaeo-sea-level changes, particularly in sequences (such as those described here) where microfossils are poorly preserved.     

Geometry styles and quantification of inversion structures in the Jiyang depression,Bohai Bay Basin,eastern China

Inversion structures of Jiyang depression evolved during Mesozoic and Cenozoic are classified into positive and negative inversion geometry styles. The geometry styles of the reactivated faults in the study area are attributed to their multi-phase history, which includes at least four phases of compressive deformation and subsequent subsidence caused by extensional reactivation of faults since Mesozoic.     

Geochemical and isotopic characteristics of volcanic rocks from the northern East China Sea shelf margin and the Okinawa Trough

Volcanic rocks both from the northern East China Sea (NECS) shelf margin and the northern Okinawa Trough are subalkaline less aluminous,and lower in High Field Strength Elements (HFSE).These rocks are higher in Large Ion Lithophile Elements (LILE),thorium and uranium contents,positive lead anomalies,negative Nb-Ta anomalies,and enrichment in Light Rare Earth Elements (LREE).Basalts from the NECS shelf margin are akin to Indian Ocean Mid-Ocean Ridge Basalt (MORB),and rhyolites from the northern Okinawa Trough have the highest 207 Pb/ 204 Pb and 208 Pb/ 204 Pb ratios.The NECS shelf margin basalts have lower 87 Sr/ 86 Sr ratios,ε N d and σ 18 O than the northern Okinawa Trough silicic rocks.According to 40 K– 40 Ar isotopic ages of basalts from the NECS shelf margin,rifting of the Okinawa Trough may have been active since at least 3.65–3.86 Ma.The origin of the NECS shelf margin basalt can be explained by the interaction of melt derived from Indian Ocean MORB-like mantle with enriched subcontinental lithosphere.The basalts from both sides of the Okinawa Trough may have a similar origin during the initial rifting of the Okinawa Trough,and the formation of basaltic magmas closely relates to the thinning of continental crust.The source of the formation of the northern Okinawa Trough silicic rocks was different from that of the middle Okinawa Trough,which could have been generated by the interaction of basaltic melt with an enriched crustal component.From the Ryukyu island arc to East China,the Cenozoic basalts have apparently increasing trends of MgO contents and ratios of LREE to Heavy Rare Earth Elements (HREE),suggesting that the trace element variabilities of basalts may have been influenced by the subduction of the Philippine Sea plate,and that the effects of subduction of the Philippine Sea plate on the chemical composition of basaltic melts have had a decreasing effect from the Ryukyu island arc to East China.     

三亚东部近岸海域表层沉积物重金属元素地球化学特征及环境质量评价

本文对三亚东部近岸海域表层沉积物中7种重金属元素的地球化学特征和空间分布特征进行了研究,并应用地积累指数法和尼梅罗综合指数法对各重金属的污染程度进行了评价。研究发现, 三亚东部近岸海域表层沉积物中重金属含量总体较低,符合《海洋沉积物质量》一类标准,大多数重金属元素含量的空间分布主要受元素的“粒度控制律”制约,其物质来源主要为陆源细粒沉积。地积累指数法和尼梅罗综合指数法的评价结果均表明,研究区表层沉积物的重金属未达到污染程度,属清洁状态,环境质量良好。     

锂同位素地球化学及其在热液活动研究中的应用

在前人研究资料及成果的基础上,探讨了海底热液活动区锂和锂同位素地球化学组成及应用前景。与海底热液活动相伴的锂元素是海洋锂库的重要来源。海底热液系统中各部分锂及其同位素组成具有显著差异,热液流体中锂含量为20~1 421μmol/kg,δ7Li值为 2.6‰~ 11.6‰;孔隙水中锂含量为9.0~5 720μmol/kg,δ7Li值为 4.5‰~ 43.7‰;热液活动区沉积物中锂含量为(4.8~76)×10-6,δ7Li值为-4.31‰~ 9.36‰;风化玄武岩中锂含量为(6.97~75.5)×10-6,δ7Li值为 7.5‰~ 13.7‰;高温变质玄武岩中锂含量为(0.60~4.61)×10-6,δ7Li值为-2.1‰~ 4.8‰。因此,锂及其同位素组成能提供热液系统中有关水-岩反应、水-沉积物反应、物质来源及流体循环的信息,是洋壳岩石蚀变及海底热液循环非常有效的指示剂。热液系统锂及其同位素组成能预测海底水岩比率,是海底热液矿床规模预测的有效参数。     

天然海藻场沿岸表层沉积物有机质的分布特征与来源

海藻场是生物多样性最高的生态系统之一, 其内部的沉积物有机质是支撑海藻场生物多样性的重要物质基础之一。本研究以浙江省嵊山岛北部无人村沿岸的天然海藻场为研究对象, 在大型海藻凋落期6~8月采集沉积物和端元生物样本, 分析了沉积物样本的粒径组成、总有机碳 (TOC)、总氮(TN)、碳氮比值(C/N)和碳氮稳定同位素(δ¹³C和δ¹⁵N), 通过贝叶斯稳定同位素混合模型评估了沉积物有机质的来源及变化规律。结果显示, 1)海藻场沿岸沉积物中粉砂占比最大, 砂的占比最低, 沉积物类型为黏土质粉砂; 2)沉积物TOC、TN、C/N、δ¹³C和δ¹⁵N范围分别为0.70%~2.41%、0.11%~0.41%、5.53~6.48、–21.79‰~–19.60‰和1.56‰~4.26‰, 在空间分布上, TOC与TN含量均随离岸距离增加而下降; 3)沉积物粒径组成、C/N比值、δ¹³C和δ¹⁵N之间的关系显示沉积物有机质主要来源于大型海藻和浮游植物的混合贡献; 4)根据贝叶斯同位素混合模型计算结果显示, 大型海藻对沉积物有机质贡献率在2.30%~45.60%, 在空间分布上, 大型海藻对沉积物有机质的贡献率随离岸距离增加而下降; 5)海藻碎屑产生量和沉积物有机碳沉积量评估结果显示, 大型海藻产生的碎屑有机质中有11.98%进入海藻场及沿岸海域的表层沉积物中。本研究为评估海藻场碎屑的产生规模和时空分布, 以及渔业资源养护功能提供了数据支撑。     

Origin of hydrocarbon fluids and discussion of abnormal carbon isotopic compositions in the Lishui-Jiaojiang Sag,East China Sea Shelf Basin

The hydrocarbon gases in the L1 gas field of the Lishui-Jiaojiang Sag have been commonly interpreted to be an accumulation of pure sapropelic-type thermogenic gas. In this study, chemical components, stable isotopic compositions, and light hydrocarbons were utilized to shed light on the origins of the hydrocarbon fluids in the L1gas pool. The hydrocarbon fluids in the L1 gas pool are proposed to be a mixture of three unique components:mid-maturity oil from the middle Paleocene coastal marine Lin...     

Petroleum accumulation in the deeply buried reservoirs in the northern Dongying Depression,Bohai Bay Basin,China: New insights from fluid inclusions,natural gas geochemistry,and 1-D basin modeling

The deeply buried reservoirs (DBRs) from the Lijin, Shengtuo and Minfeng areas in the northern Dongying Depression of the Bohai Bay Basin, China exhibit various petroleum types (black oil-gas condensates) and pressure systems (normal pressure-overpressure) with high reservoir temperatures (154–185 °C). The pressure-volume-temperature-composition (PVTX) evolution of petroleum and the processes of petroleum accumulation were reconstructed using integrated data from fluid inclusions, stable carbon isotope data of natural gas and one-dimensional basin modeling to trace the petroleum accumulation histories.The results suggest that (1) the gas condensates in the Lijin area originated from the thermal cracking of highly mature kerogen in deeper formations. Two episodes of gas condensate charging, which were evidenced by the trapping of non-fluorescent gas condensate inclusions, occurred between 29-25.5 Ma and 8.6–5.0 Ma with strong overpressure (pressure coefficient, P_c = 1.68–1.70), resulting in the greatest contribution to the present-day gas condensate accumulation; (2) the early yellow fluorescent oil charge was responsible for the present-day black oil accumulation in well T764, while the late blue-white oil charge together with the latest kerogen cracked gas injection resulted in the present-day volatile oil accumulation in well T765; and (3) the various fluorescent colors (yellow, blue-white and blue) and the degree of bubble filling (F_v) (2.3–72.5%) of the oil inclusions in the Minfeng area show a wide range of thermal maturity (API gravity ranges from 30 to 50°), representing the charging of black oil to gas condensates. The presence of abundant blue-white fluorescent oil inclusions with high Grain-obtaining Oil Inclusion (GOI) values (35.8%, usually >5% in oil reservoirs) indicate that a paleo-oil accumulation with an approximate API gravity of 39–40° could have occurred before 25 Ma, and gas from oil cracking in deeper formations was injected into the paleo-oil reservoir from 2.8 Ma to 0 Ma, resulting in the present-day gas condensate oil accumulation. This oil and gas accumulation model results in three oil and gas distribution zones: 1) normal oil reservoirs at relatively shallow depth; 2) gas condensate reservoirs that originated from the mixture of oil cracking gas with a paleo-oil reservoir at intermediate depth; and 3) oil-cracked gas reservoirs at deeper depth.The retardation of organic matter maturation and oil cracking by high overpressure could have played an important role in the distribution of different origins of gas condensate accumulations in the Lijin and Minfeng areas. The application of oil and gas accumulation models in this study is not limited to the Dongying Depression and can be applied to other overpressured rift basins.     

Hydrothermal indications of Early Cretaceous red beds in lacustrine successions,North Yellow Sea Basin,eastern China

Controversies over the origin of globally distributed Cretaceous red beds have mainly focused on climate vs. weathering with potential hydrothermal influence. In comparison to Cretaceous Oceanic Red Beds, Cretaceous lacustrine red beds exhibit chronological inconsistencies and their diverse tectonic settings suggest differing genetic mechanisms. In this paper, Early Cretaceous red beds in the North Yellow Sea Basin, one of Mesozoic rift basins in eastern China that are associated with multi-phase magmatic activities, was chosen to document potential hydrothermal impact. Geological and geochemical analyses show that these red beds were syndepositional products developed in shallow to moderately deep lacustrine environments and that they were influenced by hydrothermal activity. Major and trace elements, including enhanced Al₂O₃-normalized Fe₂O₃ and Fe₂O₃ (total) values, Al/(Al + Fe + Mn) and (Fe + Mn)/Ti ratios, Ni-Co-Zn and Fe-Mn-(Ni + Co + Cu)*10, ∑REE-La/Yb, the concentrations of hydrothermally-related ions, invalid redox indicators of trace elements, abnormally high Fe₂O₃ (total) content, positive Eu anomaly, correlation of Fe₂O₃ (total) and Eu anomaly, and vitrinite reflectance (Ro) vs. total organic carbon (TOC), all show strong hydrothermal fluid influence and heating effects. By integrating and comparing data from previous studies, we propose a hydrothermally affected sedimentation model for Cretaceous red beds and associated sediments in magma-activated lacustrine basins, and conclude that the enriched metallic ions introduced by the hydrothermal fluids may be the most significant reason for the deposition of the red beds, and the flushed ferric ions, accompanied by hydrothermal fluid, are the main ions that are hosted inside hematite causing the red sediment. This model can be applied to similar lacustrine basins that experience strong magmatic activity.     

Stable carbon and nitrogen isotopes of sinking particles in the eastern bransfield strait (Antarctica)

A time-series sediment trap was deployed at 1,034 m water depth in the eastern Bransfield Strait for a complete year from December 25, 1998 to December 24, 1999. About 99% of total mass flux was trapped during an austral summer, showing distinct seasonal variation. Biogenic particles (biogenic opal, particulate organic carbon, and calcium carbonate) account for about two thirds of annual total mass flux (49.2 g m^-2), among which biogenic opal flux is the most dominant (42% of the total flux). A positive relationship (except January) between biogenic opal and total organic carbon fluxes suggests that these two variables were coupled, due to the surface-water production (mainly diatoms). The relatively low δ¹³C values of settling particles result from effects on C-fixation processes at low temperature and the high CO² availability to phytoplankton. The correspondingly low δ¹⁵N values are due to intense and steady input of nitrates into surface waters, reflecting an unlikely nitrate isotope fractionation by degree of surface-water production. The δ¹⁵N and δ¹³C values of sinking particles increased from the beginning to the end of a presumed phytoplankton bloom, except for anomalous δ¹⁵N values. Krill and the zooplankton fecal pellets, the most important carriers of sinking particles, may have contributed gradually to the increasing δ¹³C values towards the unproductive period through the biomodification of the δ¹³C values in the food web, respiring preferentially and selectively¹²C atoms. Correspondingly, the increasing δ¹⁵N values in the intermediate-water trap are likely associated with a switch in source from diatom aggregates to some remains of zooplankton, because organic matter dominated by diatom may be more liable and prone to remineralization, leading to greater isotopic alteration. In particular, the tendency for abnormally high δ¹⁵N values in February seems to be enigmatic. A specific species dominancy during the production may be suggested as a possible and speculative reason.