New biostratigraphic data for the Chikkim Formation (Cretaceous, Tethyan Himalaya, India)

The Chikkim Formation as exposed in the Tethyan Himalaya (India) has been studied at its type locality, using planktonic foraminifera for a detailed biostratigraphic elaboration. Divided into two members, the Lower and Upper Chikkim members, this formation ranges in age from Albian to early Maastrichtian(?), and reaches a maximum thickness of 150 m. Examination of thin sections has yielded 34 species of foraminifera in five genus-level assemblages. The Lower Chikkim Member is about 55 m thick; its basal portion is of Albian age based on the presence of Biticinella breggiensis and Planomalina buxtorfi. At 26 m above the base, Whiteinella archaeocretacaea documents OAE 2 (Oceanic Anoxic Event 2), and thus the Cenomanian/Turonian boundary in this section. The carbonate sequence is capped by a Santonian-age hardground with iron oxide crusts and bioturbation. Macrofossils, including belemnites (at the base) and irregular echinoids (upper part), are present. The basal carbonaceous marls of the Upper Chikkim Member yield both large (benthic) rotaliid as well as planktonic foraminifera (Globotruncanita elevata, Gl. stuartiformis, Gl. stuarti, Gansserina gansseri and others), indicating a Campanian age. The co-occurrence of Gl. elevata and G. gansseri in a single thin section results either from condensation or reworking in the basal part of the Upper Chikkim Member. Late Cretaceous index foraminifera such as Gl. elevata document deposition within the Tethyan Realm. The original thickness of the Upper Chikkim Member is uncertain, but would have been around 100 m; the unit appears markedly reduced through weathering at a height of about 5000 m above sea level. Equivalent sediments are exposed in the Zanskar area to the northwest, and in Nepal and Tibet. Cretaceous Oceanic Red Beds (CORBs) are probably missing due to the proximality of these pelagic settings.     

Planktic Foraminiferal Biostratigraphy of the Cretaceous Oceanic Red Beds in Kangmar,Southern Tibet,China

The planktic foraminifera of the Chuangde Formation (Upper Cretaceous Oceanic Red Beds, CORBs) as exposed at Tianbadong section, Kangmar, southern Tibet has been firstly studied for a detailed for a detailed biostratigraphy elaboration. A rich and well-preserved planktic foraminifera were recovered from the Chuangde Formation of the Tianbadong section and the Globotruncanita elevata, Globotruncana ventricosa, Radotruncana calcarata, Globotruncanella havanensis, Globotruncana aegyptiaca, Gansserina gansseri and Abathomphalus mayaroensis zones have been recognized. The planktic foraminiferal assemblage points to an early Campanian to Maastrichitian age for the CORBs of the eastern North Tethyan Himalayan sub-belt, which also provides a better understanding of the shifting progress of the Indian Plate to the north and the evolution of the Neotethyan ocean. The lithostratigraphy of the Chuangde Formation of the Tianbadong section comprises two lithological sequences observed in ascending succession: a lower unit (the Shale Member) mainly composed of purple (cherry-red, violet-red) shales with interbedded siltstones and siliceous rocks; and an upper unit (the Limestone Member) of variegated limestones. The strata of the Chuangde Formation in the Tianbadong section are similar to CORBs in other parts of the northern Tethyan Himalaya area of Asia (Gyangze, Sa’gya, Sangdanlin, northern Zanskar, etc.). The fossil contents of the Chuangde Formation in the sections (CORBs) studied provide a means of correlation with the zonation schemes for those of the northern Tethyan Himalayan sub-belt and the Upper Cretaceous of the southern Tethyan Himalayan sub-belt. Paleogeographic reconstruction for the Late Cretaceous indicates that the Upper Cretaceous Chuangde Formation (CORBs) and correlatable strata in northern Zanskar were representative of slope to basinal deposits, which were situated in the northern Tethyan Belt. Correlatable Cretaceous strata in Spiti and Gamba situated in the southern Tethyan Belt in contrast were deposited in shelf environments along the Tethyan Himalayan passive margin. CORBs are most likely formed by the oxidation of Fe(II)-enriched, anoxic deep ocean water near the chemocline that separated the oxic oceanic surface from the anoxic.     

Variation on Foraminiferal Composition in Cretaceous Black-Gray-Red Bed Sequence of Southern Tibet, China

An Upper Cretaceous black-gray-red bed sequence was deposited in the Tethys-Himalayan Sea where abundant foraminifera, especially planktons, were yielded. In the shallow shelf to the upper slope on the north margin of Indian plate was recorded an extinction-recovery-radiation cycle of foraminiferal fauna highly sensitive to paleoceanographical changes. The black unit, consisting of the Late Cenomanian-earliest Turonian beds, displays a major extinction, with keeled planktonic and many benthic species as the principal victims at the end of the Cenomanian when existed only low diversity, sin-face water-dwelling foraminifera. The gray unit spans a long-term recovery interval from the Turonian to the early Santonian with keeled planktonic foraminifera returning stepwise to the water colunm. The planktonic biota in the red unit, extremely abundant, indicate a biotic radiation during the Late Santonian and the Early Campanian, implying that the high oxygen levels had returned to all the oceanic depth levels,and that the water stratification disappeared, followed by the radiation of all depth-dwellers. The variation on foraminiferal faunas from the whole sequence refers to the extreme warm climate that appeared in the Middle Cretaceous and to the declined temperature toward the late epoch. Substantial deposits for this warming and cooling zones represent the black shales in the Middle Cretaceous and the red beds in the later period of the southern Tibet. The change in the foraminiferal composition corresponded to the formation of dysaerobic facies and to the development of high-oxidized circumstances.     

西藏仲巴县特提斯喜马拉雅早白垩世日朗组玄武岩地球化学特征及其构造意义

特提斯喜马拉雅地层中广泛分布早白垩世火山碎屑岩,但对这套火山碎屑岩的源区缺乏有力的约束。在特提斯喜马拉雅中西段仲巴地区白垩系日朗组地层中发现一套玄武岩夹层,该玄武岩为碱性玄武岩,表现为LREE富集的分布型式,与典型的OIB和区域上的板内玄武岩类似。玄武岩Nb含量介于下地壳与上地壳之间,Th含量略低于下地壳,具有较高的Th/Nb比值和较低的Ce/Pb,指示岩浆在演化过程中遭受了一定程度的地壳混染,与雅鲁藏布蛇绿岩混杂岩带中的海山明显不同。构造环境判别图解显示玄武岩形成于大陆板内裂谷环境,结合日朗组地层沉积环境的分析,该玄武岩可能为日朗组火山碎屑岩提供物源。     

西藏南部晚白垩世-古新世大洋红层的分布与时代

特提斯—喜马拉雅北沉积亚带沉积有一套大洋红色岩层,由东往西在羊卓雍错、江孜、萨迦、萨嘎、札达一带断续出露,并与宗卓组上部地层相关。这套海相红层,根据岩性特征和浮游有孔虫可以直接进行区域对比。其时代在江孜地区为Santonian晚期—Campanian中期,包括Dicarinella asymetrica, Globotruncanitaelevata,Globotruncana ventricosa 和Globotruncanita calcarata 浮游有孔虫带;在萨迦地区限于Campanian期,鉴定有Globotruncanita elevata, Globotruncana ventricosa 和G. linneiana等具时代意义的浮游有孔虫;在萨嘎—吉隆地区为Maastrichtian期,识别出Gansserina gansseri 和Abthomphalus mayaroensis 浮游有孔虫带;在札达地区为古新世早期,以Glibigerina eugubina G. fringa化石带为代表。海相红层在西藏南部由东往西其时代逐渐变新,主要沉积时代分布在Santonian晚期—古新世早期。其总体时间跨度较大,大约长达20Ma。而事件在各个地点的延续时间有限,基本在3~8 Ma之内。根据对海相红层和沉积基质中浮游有孔虫的研究,该沉积带宗卓组的顶界时代已超出白垩纪,进入了古新世。     

藏南仲巴地区早白垩世日朗组物源分析及其构造意义

藏南仲巴地区早白垩世日朗组出露于特提斯喜马拉雅北亚带,整体为黄绿色火山岩屑砂岩,局部层位可见页岩与泥岩,分析为一套深海海底扇沉积组合。本文仔细分析了日朗组砂岩岩石学特征及鲍马序列和槽模沉积构造等沉积学特征,结果表明:日朗组砂岩成分成熟度和结构成熟度均不高,具有近源物源的特点;槽模构造古水流数据统计表明古流向由南向北,指示物质组分来源于南侧特提斯喜马拉雅和/或印度克拉通。砂岩碎屑组分统计结果表明日朗组的物源区构造背景属于克拉通内部及石英再旋回区。碎屑锆石U-Pb年龄频谱图对比进一步表明其物源区为印度稳定大陆边缘,外加一套早白垩世火山碎屑物质的输入。仲巴地区日朗组物源特征反映了印度大陆北缘早白垩世由深部断裂引起的一次强烈的火山事件,可能与印度大陆从澳大利亚-南极大陆裂解有关。     

Response of Reactive Phosphorus Burial to the Sedimentary Transition from Cretaceous Black Shales to Oceanic Red Beds in Southern Tibet

The mechanism of sedimentary transition from the Cretaceous black shales to the oceanic red beds is a new and important direction of Cretaceous research. Chemical sequential extraction is applied to study the burial records of reactive phosphorus in the black shale of the Gyabula Formation and oceanic red beds of the Chuangde Formation, Southern Tibet. Results indicate that the principal reactive phosphorus species is the authigenic and carbonate-associated phosphorus (CaP) in the Gyabula Formation and iron oxides-associated phosphorus (FeP) in the Chuangde Formation which accounts for more than half of their own total phosphorus content. While the authigenic and carbonate-associated phosphorus (CaP) is almost equal in the two Formations; the iron oxides-associated phosphorus is about 1.6 times higher in the Chuangde Formation than that in the Gyabula Formation resulting in a higher content of the total phosphorus in the Chuangde Formation. According to the observations on the marine phosphorus cycle in Modern Ocean, it is found that preferential burial and regeneration of reactive phosphorus corresponds to highly oxic and reducing conditions, respectively, leading to the different distribution of phosphorus in these two distinct type of marine sediments. It is the redox-sensitive behavior of phosphorus cycle to the different redox conditions in the ocean and the controlling effects of phosphorus to the marine production that stimulate the local sedimentary transition from the Cretaceous black shale to the oceanic red beds.     

藏南晚白垩世旋回地层学研究:以定日贡扎剖面为例

旋回地层学是提高地质年代标尺精度的一种重要方法。特提斯海相沉积是旋回地层学研究的良好对象,与西特提斯比较,东特提斯的旋回地层学研究程度较低,第四纪之前的研究精确度有待进一步的提高。西藏南部广泛出露海相白垩系,其中定日贡扎剖面出露的上白垩统尤为连续和完整。在对贡扎剖面野外观察及其层束厚度测量的基础上,通过快速傅立叶变换(FFT),分析该地层蕴含的地球轨道周期,得到了与理论值较为接近的结果:偏心率周期,4092 ka/周期(E1),1279 ka/周期(E2),93 ka/周期(E5);斜率周期,512 ka/周期(O1),409 ka/周期(O2),389 ka/周期(O2)。在功率谱分析过程中,利用层束和超层束组的关系进行了调谐的处理,并比较调谐前后结果,来确定调谐的重要性,证明该地层沉积速率的变化:地层由老至新,其沉积速率的变化趋势整体为由小变大,变化范围为086～253 cm/ka。进一步对比东西特提斯和其他地区研究结果,证明东西特提斯海相沉积在外形、成因和所蕴含的轨道周期的一致性,地球轨道周期变长与理论值变化的一致性。最后给出了下一步工作的建议。 关键词：藏南; 定日; 晚白垩世; Coniacian阶; 旋回地层学     

藏南措美残余大火成岩省的西延及意义

在西藏南东部和澳大利亚南西部新识别出的早白垩世Comei-Bunbury大火成岩省的范围还未能得到很好约束。为探讨这一问题,本文报道了西藏南东部浪卡子-洛扎以西、江孜、康马地区广泛分布的近东西向基性岩墙和少量玄武岩的岩石学和地球化学数据。这些以辉绿岩、辉长岩为主的镁铁质岩石属于碱性-亚碱性玄武岩系列,在地球化学上主要包括高Ti的洋岛玄武岩型和低Ti的大洋中脊玄武岩型,两者的εNd(t)值分别为(+0.9～+2.0)和(+4.6～+5.8)。这两种类型岩石的地球化学特征均与措美残余大火成岩省内的对应类型可比,暗示它们与措美残余大火成岩省一样,均形成于由地幔柱作用于大陆岩石圈引起的伸展背景,代表该残余大火成岩省的西延。本文研究结果使得现今保留在特提斯喜马拉雅带上的Comei-Bunbury大火成岩省的残余面积接近50000km2。该大火成岩省的大规模岩浆活动可能是引发研究区甚至全球早白垩世大洋缺氧事件的一个重要因素。     

羌塘盆地侏罗纪末—早白垩世沉积特征与地层问题

羌塘盆地侏罗纪末至早白垩世地层包括扎窝茸组、雪山组、白龙冰河组和索瓦组上段，目前对它们的划分、对比和相互间关系的认识不一。笔者根据各组的含义和时代依据，指出各地层组为岩石地层单元，目前资料尚不足以作进一步年代学划分。通过全面统计各组的分布情况，分析各组的沉积特征，发现白龙冰河组为陆棚相，仅见于盆地北西部；索瓦组上段为海湾泻湖相，见于盆地中部；雪山组和扎窝茸组为河流一三角洲相，见于北东部。为此，认为各地层组是盆地内同期异相沉积，作为上下关系处理是不妥的，据此又提出了新的地层对比方案，认为盆内最高海相层位应该跨入了下白垩统，海水最终是向北西方向逐步退出盆地的。     

西藏当惹雍错晚侏罗世—早白垩世扎列拿组、郎穷组和荣纳组的建立

通过1∶25万邦多区幅地质调查,发现晚侏罗世—早白垩世则弄群中存在2个喷发-沉积不整合界面,将则弄群自然分成3个部分,对应3个火山喷发-沉积旋回。新创建扎列拿组、郎穷组和荣纳组。描述了3个组的定义及层型、次层型的岩性、岩相、古生物、同位素年代特征及其分布情况。     

Burial Records of Reactive Iron in Cretaceous Black Shales and Oceanic Red Beds from Southern Tibet

One of the new directions in the field of Cretaceous research is to elucidate the mechanism of the sedimentary transition from the Cretaceous black shales to oceanic red beds. A chemical sequential extraction method was applied to these two types of rocks from southern Tibet to investigate the burial records of reactive iron. Results indicate that carbonate-associated iron and pyrite are relatively enriched in the black shales, but depleted or absent in red beds. The main feature of the reactive iron in the red beds is relative enrichment of iron oxides （largely hematite）, which occurred during syn-depostion or early diagenesis. The ratio between iron oxides and the total iron indicates an oxygen-enriched environment for red bed deposition. A comparison between the reactive iron burial records and proxies of paleo-productivity suggests that paleo-productivity decreases when the ratio between iron oxides and the total iron increases in the red beds. This phenomenon could imply that the relationship between marine redox and productivity might be one of the reasons for the sedimentary transition from Cretaceous black shale to oceanic red bed deposition.     

Discovery of Pseudofrenelopsis gansuensis from the Lower Cretaceous of Wangqing, Jilin Province, and Its Significance in Correlation of Cretaceous Red Beds in China

New data from abundant vegetative shoots and cuticular analysis are provided for the Cretaceous cheirolepidiaceous conifer Pseudofrenelopsis gansuensis Deng, Yang et Lu. The material was found from a new locality of the Lower Cretaceous strata in the Luozigou Basin, Wangqing, Jilin Province, northeastern China. Pseudofrenelopsis is a common plant in the Dalazi Formation of the Yanji Basin about 150 km from Wangqing, but there exists different species, Pseudofrenelopsis dalatzensis only. Both P. dalatzensis and P. gansuensis have been recorded from the Lower Cretaceous of Jiuquan, Gansu Province, but they are in different stratigraphic horizons. The Lower Cretaceous plant-bearing strata in Luozigou have used to correlate with the Dalazi Formation of the Yanji Basin. The discovery of P. gansuensis, which is lower in horizon than P. dalatzensis in Jiuquan, may indicate that they are also different in horizon in Jilin. Cheirolepidiaceous conifers are among the few fossils of red beds of the Early Cretaceous in China. The present discovery of Pseudofrenelopsis gansuensis provides important evidence for classification, correlation and determination of geological ages of the Early Cretaceous non-marine red deposits of the two separate basins in remote areas of North China.     

Stratigraphy and sedimentation rates of Upper Cretaceous deep-water systems of the Rhenodanubian Group (Eastern Alps, Germany)

In the Bavarian Alps (Germany), west of the Isar River, the abyssal deposits of the Lower Barremian to Upper Campanian Rhenodanubian Group consist of siliciclastic and calcareous turbidites alternating with hemipelagic non-calcareous mudstones. The up to 1500-m-thick succession, deposited in the Penninic Basin to the south of the European Plate, is characterized by a low mean sedimentation rate (c. 25 mm kyr⁻¹) over 60 million years. Palaeocurrents and turbidite facies distribution patterns suggest that sedimentation occurred on a weakly inclined abyssal plain. The highest sedimentation rates (up to 240 mm kyr⁻¹) were associated with the calcareous mud turbidites of the newly defined Röthenbach Subgroup, which includes the Piesenkopf, Kalkgraben and Hällritz formations (Middle Coniacian to Middle Campanian). These calcareous turbidites prograded from the west, and interfinger towards the east with red hemipelagic claystone. A high sea level presumably favoured pelagic carbonate production and accumulation on the shelves and on internal platforms in the western part of the basin, whereas siliciclastic shelves with steep slope angles have bordered the eastern part of the basin, where a dearth of turbidite sedimentation and increased Cretaceous oceanic red beds deposition occurred. In contrast to the eustatically-induced Middle Coniacian to Lower Campanian Cretaceous oceanic red beds (calcareous nannoplankton zones CC14 to CC18), red hemipelagites of Early Cenomanian age (upper part of calcareous nannoplankton zone CC9) and early Late Campanian age (upper part of zone CC21 and zone CC22) are interpreted as the result of regional tectonic activity.     

西藏嘉黎巴嘎地区早白垩世多尼组地层特征与沉积环境

研究区多尼组为一套含煤的灰色至黑色岩屑石英砂岩、长石砂岩、碳质粉砂岩和页岩, 生物地层特征指示其时代为早白垩世早期贝里阿斯期-凡兰吟期(Berriasian-Valanginian) 。岩性特征和碎屑岩粒度分析表明, 区内多尼组沉积环境主要为三角洲沉积, 包括前三角洲、三角洲前缘和三角洲平原 3个亚相, 三级层序总体表现为逐渐海进的特点。     

西藏南部二叠纪和早白垩世构造岩浆作用与特提斯演化:新观点

西藏高原前新生代时期的特提斯演化和新生代时期的高原隆升历史是西藏高原基础地质研究中两个长期被关注的重要科学问题,但迄今对西藏高原自身的物质组成和前新生代演化历史的认知程度仍然较低,直接限制了对新生代时期西藏高原隆升历史的更深入研究。新的地质和地球化学资料显示早—中二叠世时俯冲背景和伸展背景共存于现今的冈底斯带和喜马拉雅带,中二叠世末期(大约263Ma)侵位的皮康过铝质S型花岗岩以及同期发生的松多榴辉岩的高压变质作用和区域性角度不整合指示现今的冈底斯弧背断隆带在那时经历了同碰撞造山事件。中生代岩浆岩锆石U-Pb年龄和Hf同位素成分表明,冈底斯弧背断隆带和中冈底斯带存在以古元古代甚至太古宙物质为特征的古老基底物质,而北冈底斯带和南冈底斯则分别以中—新元古代新生地壳和显生宙新生地壳为特征。已有高质量年龄数据和锆石Hf同位素指示冈底斯带中北部地区在大约110Ma发生了带状岩浆大爆发并伴随着幔源物质显著增加。新的可靠的锆石U-Pb年龄指示喜马拉雅带东部措美(Comei)地区大面积出露的白垩纪火成岩侵位于132Ma左右,代表了新近在藏南和澳大利亚南西部识别出的经历了强烈变形和深位侵蚀的Comei-Bunbury大火成岩省的残余。以这些新资料为基础,讨论了西藏南部的晚古生代—中生代构造岩浆演化历史和特提斯演化过程。     

藏南拿日雍错片麻岩穹窿中新世淡色花岗岩的形成过程:变泥质岩部分熔融与分离结晶作用

拿日雍错片麻岩穹窿位于特提斯喜马拉雅带的东部,穹窿边部淡色花岗岩脉形成于21.8±0.3Ma,穹窿核部主体淡色花岗岩的结晶年龄为20.1±0.1Ma,其中1件样品记录了~17.3Ma热液蚀变事件。大部分淡色花岗岩具有以下特征:(1)较高的Si O2(72.9%),Al2O3(14.7%)和A/CNK(1.1),较低的Fe O、Mg O、Mn O和Ti O2;(2)高度变化的大离子亲石元素(如Rb、Sr、Ba)和高场强元素(如Nb、Ta、Hf、Th)和Rb/Sr、Nb/Ta、Zr/Hf比值;(3)富集轻稀土元素,亏损重稀土元素,Eu和Nd都显示负异常(Eu/Eu*0.7,Nd/Nd*=0.5~0.8);(4)Sr同位素比值变化范围较大(87Sr/86Sr(t)=0.7132~0.7330),但Nd同位素比值一致(εNd(t)=-12.4~-10.9)。这些特征表明:拿日雍错淡色花岗岩形成于20Ma,是变泥质岩部分熔融作用的产物,经历了不同程度的斜长石、锆石、独居石、磷灰石、富Ti矿物等的分离结晶作用。     

New abelisaurid remains from the Anacleto Formation (Upper Cretaceous), Patagonia,Argentina

New theropod remains with abelisaurid affinities from the Upper Cretaceous (Anacleto Formation, lower Campanian), NW Patagonia, Argentina, are here described. The specimen (MPCN-PV 69) consists of a partial premaxilla, fragmentary vertebrae, proximal portion of both humeri, distal portion of the pubis, and an incomplete pedal ungual. Characters linking with Abelisauridae are a premaxilla with a subquadrangular body, externally ornamented, and paradental plates with a striated surface; and humerus with bulbous proximal head, conical internal tuberosity, and reduced greater tubercle. The humerus is similar to those of Carnotaurus and Aucasaurus, due to the presence of a bulbous head and a discontinuity between the head and the internal tuberosity, but also differs from both taxa in the more distal location of the greater tubercle with respect to the internal tuberosity. Aucasaurus also comes from Anacleto Formation, but differences in the humeri suggest that MPCN-PV 69 is a different taxon. The phylogenetic analysis performed supports the affiliation to Abelisauridae, but fails to determinate a more precise relationship with others abelisaurids. However, a majority rule consensus of the analysis shows a position within Brachyrostra. Despite being fragmentary, MPCN-PV 69 probably represents a new abelisaurid from the Anacleto Formation, thus increasing the knowledge and diversity of Late Cretaceous South American abelisaurids.     

西藏岗巴地区海相上白垩统碳、氧同位素对比实验结果偏差分析

对西藏南部岗巴地区上白垩统部分全岩样品进行了碳、氧同位素不同实验室、不同时间的对比实验，目的在于了解样品处理过程可能对试验结果的影响程度。结果发现，不同实验室的结果偏差比同一实验室不同时间的结果偏差大，碳同位素比值的偏差比氧同位素比值的偏差大。不同实验室结果偏差的关键原因是样品制备方法和岩性的不同：手工碎样、选样、磨样较难避免徽裂隙中充填的方解石脉和小型生物扰动组构对同位素值的影响，而毫米级直径钻头刮样取样则很大程度上可以避免；钙质页岩和泥灰岩受影响的程度相对较小，生物碎屑灰岩受影响较大。碳同位素比值偏差大干氧同位素。前者基数比后者大4～5倍可能是主要原因。