Discovery of seep carbonate nodules as new evidence for gas venting on the northern continental slope of South China Sea

The geotectonic evolution of the northern South China Sea (SCS) is controlled by the Eurasian, the Pa-cific and the Indian-Australian Plates. With regard to its tectonic evolution, the northern margin composed of faulted terraces and basins and deposited …     

First discovery and characterizations of late Cretaceous seep carbonates from Xigaze in Tibet, China

Hydrocarbon seeps,widely occurring in continental margins,have become increasingly focused owing to their close relationships with gas hydrates,strong greenhouse gas methane,and biological resources in extreme environments.Ancient hydrocarbon seeps have already been recognized from Devonian to Quaternary strata worldwide based on seep carbonates or seep-related fossil chemosynthetic assemblages.However,seep-related deposits are rarely found from ancient strata in the mainland China.Here,we report the first discovery of an ancient seep deposit,specifically late Cretaceous seep carbonates from Xigaze in Tibet,China.Xigaze seep carbonates,occurring as nodules,are enclosed in upper Cretaceous turbidite strata in Xigaze forearc basin.These carbonates are composed of authigenic carbonate(56.2% on average),clastic quartz and feldspar(27.3% on average),and clay minerals(chlorite,illite and smectite,16.5% on average).Clotted micrites,peloids and framboid pyrites are frequently observed,all of which are common in modern seep carbonates.The carbonates have negative δ13 C values varying from 27.7‰ to 4.0‰(V-PDB),suggesting that thermogenic methane is the primary carbon source.Ce/Ce* values revised by eliminating La effects show no real Ce anomaly,indicating the carbonates were primarily precipitated in a weak reducing environment.Overall,these features provide unequivocal evidences that the seafloor of Xigaze forearc basin developed hydrocarbon seeps in late Cretaceous.     

Glycerol ether biomarkers and their carbon isotopic compositions in a cold seep carbonate chimney from the Shenhu area,northern South China Sea

At modern cold seeps,the anaerobic oxidation of methane(AOM)is the dominant pathway for methane consumption in marine sediments.AOM,which is mediated by a consortium of methane oxidizing archaea and sulfate reducing bacteria,is proposed to be responsible for authigenic carbonate formation.A methane-derived carbonate chimney was collected from the Shenhu area, northern South China Sea.The membrane lipids and their very low carbon isotopic compositions(?115‰to?104‰)in the Shenhu chimney suggest the presence of an AOM process.Three specific archaeal and bacterial biomarkers were detected,including Ar,DAGE 1f,and monocyclic MDGD.Their strongly depleted??13C values(?115‰to?104‰),which are lower than those of the normal marine lipids in sediments,reveal biogenic methane as their origin.The carbonate deposits exhibiting a chimney structure indicate that a vigorous methane-rich fluid expulsion may have occurred at the seafloor.We propose that the decomposition of gas hydrates at depth is the likely cause of seepage and cold seep carbonate formation in the Shenhu area.     

塔里木盆地奥陶系碳酸盐岩碳氧稳定同位素地球化学特征

中-下奥陶统碳酸盐岩储层是塔里木盆地塔中地区的主要油气产层.利用碳氧稳定同位素的分布特征和变化规律,可分析影响碳酸盐岩沉积环境和成岩作用的因素.中-下奥陶统的碳酸盐岩可在垂向上把δ13C和δ18O值的变化趋势划分为三段,二者的变化趋势是一致的.中-上奥陶统岩层碳氧稳定同位素比值明显下降,证明中-下奥陶统经历过一次短暂的抬升暴露和随后的大面积海水加深淹没事件.海水淹没时期,大量C转到海水之中,海水中沉淀出的碳酸盐岩的δ13C值相对较低.     

姬塬地区长8油层组碳酸盐胶结物特征与成因

碳酸盐胶结物是姬塬地区长8油层组储层砂岩中的主要自生矿物.薄片分析、碳氧同位素测试、电子探针成分分析表明该区碳酸盐胶结物主要类型为微晶无铁方解石、亮晶或连晶铁方解石与含铁方解石.微晶无铁方解石形成于成岩作用早期,含量高,但分布局限,与局部过饱和的碱性湖水沉淀有关.亮晶与连晶铁方解石或含铁方解石1δ3CPDB值为-4.1‰~-13.1‰,1δ8OPDB值为-19.7‰~-32.3‰,胶结类型多样,分布普遍,为该区主要方解石类型,其形成主要与烃源岩中泥岩矿物有机质演化有关,为中成岩A期—B期阶段产物,形成时代相对较晚.碳酸岩胶结作用对储层具有较为明显的负作用.     

轮古西地区奥陶系碳酸盐岩古岩溶储层碳、氧同位素地球化学特征

中—下奥陶统鹰山组碳酸盐岩古岩溶储层是塔里木盆地轮古西地区的主要油气产层 .为了弄清储层的成因类型、储层古岩溶过程中的流体性质和古水文条件 ,为预测和评价此类储层提供有关的地球化学信息 ,讨论了储层形成过程中记录的碳、氧稳定同位素特征 .结果表明 :轮古西地区奥陶系鹰山组碳酸盐岩古岩溶储层中的δ13C和δ18O值的变化范围较大 ,δ13C值为 -0 .70‰～ -6.5 0‰ ,平均值 -1 .76‰ ;δ18O值为 -3 .75‰～ -1 7.1 0‰ ,平均值 -9.42‰ .碳酸盐岩基质、冲积岩和方解石胶结物的δ13C和δ18O分布具有一定的差异 .三类样品的δ18O值均具有明显偏负特征 ,表明在碳酸盐岩成岩过程中受到大气成因的淡水影响 ,反映了当时的风化壳岩溶成岩环境 .冲积岩样品的δ13C值的偏负程度较高 ,其物源可能来自石炭—二叠系地层     

The biomarkers of 2,6,10,15, 19-pentamethylicosenes and their carbon isotopic composition in the sediments from the Gulf of Mexico

The methanogenic archaea and sulfate reduction bacteria are flourishing in the sediments associated with gas venting and gas hydrate settings on the sea floor, where the anaerobic oxidation of methane (AOM) me-diated by these bacteria is the dominant path…     

准噶尔盆地西北缘乌尔禾??风城地区二叠系风城组白云岩地球化学特征及成因分析

以白云岩的地球化学方法为主,对准噶尔盆地西北缘乌尔禾?风城地区二叠系风城组广泛发育的白云岩化岩类进行详细的研究.通过对乌尔禾?风城地区二叠系风城组白云岩化岩类的元素分析、碳氧同位素和古盐度、古温度的研究,得出研究区白云岩类以白云质泥岩、泥质白云岩和凝灰质白云岩三种形态存在.白云质岩类富含陆源碎屑(泥质)或凝灰岩组分;白云质岩类中c(Mg)/c(Ca)分布范围较宽,主要分布于0.636～4.785,平均值为1.532,大部分分布于1～2,说明研究区有丰富的Mg2+供应;白云质岩类中w(Sr)较高,主要为95.9×10?6～783.6×10?6,平均值为464.95×10?6, w(V)/w(Ni)为0.8～4.8,主要为2～3;研究区二叠系白云质岩类的δ18O和δ13C值分布范围较大,δ13C为?1‰～5.2‰,平均值为3.1‰,δ18O为?14.8‰～3.2‰,平均值为?2.8‰.由地球化学元素分析结合古温度和古盐度分析认为研究区风城组白云岩形成于一盐度较高、温度偏低的环境中,火山喷发的热液活动对白云岩的形成也有一定的影响.白云质岩类形成大部分发生为成岩早期,少部分白云岩化发生为成岩中晚期的埋藏时期,总的来说白云质岩类形成于早成岩阶段的陆相咸水湖泊中.     

川东L2井三叠系飞仙关组碳酸盐样品的锶同位素年龄标定

测试了四川盆地东部L2井三叠系飞仙关组碳酸盐样品87Sr/86Sr比值,以及相应的Mg,Sr和Mn的含量.在对样品进行成岩蚀变性评价的基础上,根据锶同位素地层学的原理,尝试对这些样品进行了年龄标定.4个样品分别位于L2井深度为3 297.6 m,3 290.0 m,3 268.8 m和3 201.6 m处;其87Sr/86Sr比值分别为0.707 330,0.707 340,0.707 348和0.707 383;年龄的标定结果分别为245.3 Ma,245.2 Ma,245.1 Ma和245.0 Ma.除深度3 201.6 m的样品因成岩蚀变,其年龄值的可靠程度较低以外,其余3个样品的年龄值都具有较高的可靠程度.     

墨西哥湾盆地陆棚区油气田数量与储量规模的分形分析

在对墨西哥湾盆地陆棚区已探明油气田储量规模划分的基础上, 应用分形理论对油气田数量与储量规模之间的分形关系进行了研究, 讨论了油气田储量规模分布的分数维值D的含义。油气田储量规模分布的分数维值D反映了油气田的勘探开发程度, 勘探开发程度越高, 分数维值D越大; 勘探开发程度越低, 分数维值D越小。利用分形方法可以较好地分析油气田储量规模与数量之间的关系, 评判油气田勘探开发的程度, 预测未来发现油气田的数量及其储量规模。     

广西大厂铜坑矿床中闪锌矿微量、稀土元素及氢氧同位素特征

位于江南古陆西南缘、右江盆地北东侧的大厂矿田是中国重要的有色金属矿产地,铜坑矿床是大厂矿田内规模最大、成矿元素最复杂、成矿特征最典型的一个超大型锡多金属矿床,由上部锡多金属矿体和深部锌铜矿体组成。以铜坑矿床不同类型矿体(锡多金属矿体、锌铜矿体)中的闪锌矿为研究对象,开展了微量、稀土元素及H—O同位素分析,进一步探讨区内成矿物质、成矿流体来源,并深化矿床成因认识。结果显示,铜坑矿床不同类型矿体中的闪锌矿均以富集Cu、Pb、Fe、Sb、In等元素,贫Ge为特征;闪锌矿的稀土配分模式多为轻稀土富集的“V”形右倾曲线,以轻、重稀土比值LREE/HREE较高、Eu和Ce负异常为特征;闪锌矿H—O同位素组成指示成矿流体以岩浆为主,伴随有大气降水的混入。上述特征表明,铜坑矿床成矿物质和成矿流体主要来源于岩浆,矿床成因属岩浆热液充填-交代形成。     

Re-Os Dating of Galena and Sphalerite from Lead-Zinc Sulfide Deposits in Yunnan Province,SW China

Dating of lead-zinc deposits is of critical importance for better understanding of ore ge-nesis, but has long been a big challenge due to the lack of suitable minerals that can be unequivocally linked ...