Distribution Prediction of Middle-deep Lacustrine Source Rocks in Eocene Wenchang Formation in the Kaiping Sag,Pearl Mouth Basin

Oil and gas shows are rich in drilling wells in Kaiping sag,however,large oilfield was still not found in this area.For a long time,it is thought that source rocks were developed in the middle-deep lacustrine facies in the Eocene Wenchang Formation,while there is no source rocks that in middle-deep lacustrine facies have been found in well.Thickness of Wenchang Formation is big and reservoirs with good properties could be found in this formation.Distribution and scale of source rock are significant for further direction of petroleum exploration.Distribution characterization of middle-deep lacustrine facies is the base for source rock research.Based on the sedimentary background,fault activity rate,seismic response features,and seismic attributes were analyzed.No limited classification method and multi-attributes neural network deep learning method were used for predicting of source rock distribution in Wenchang Formation.It is found that during the deposition of lower Wenchang Formation,activity rate of main fault controlling the sub sag sedimentation was bigger than 100 m/Ma,which formed development background for middle-deep lacustrine facies.Compared with the seismic response of middle-deep lacustrine source rocks developed in Zhu I depression,those in Kaiping sag are characterized in low frequency and good continuity.Through RGB frequency decomposition,areas with low frequency are main distribution parts for middle-deep lacustrine facies.Dominant frequency,instantaneous frequency,and coherency attributes of seismic could be used in no limited classification method for further identification of middle-deep lacustrine facies.Based on the limitation of geology knowledge,multi-attributes of seismic were analyzed through neural network deep learning method.Distribution of middle-deep lacustrine facies in the fourth member of Wenchang Formation is oriented from west to east and is the largest.Square of the middle-deep lacustrine facies in that member is 154 km²and the volume is 50 km³.Achievements could be bases for hydrocarbon accumulation study and for exploration target optimization in Kaiping sag.     

滇西漕涧地区崇山杂岩带始新世花岗岩的发现及其地质意义

崇山杂岩带为滇西三江造山系西侧边缘的一条重要边界构造,属青藏高原造山带的南东缘.带内岩浆活动强烈,前人认为其主要由晚元古代、中生代的花岗岩组成;而据地质调查发现,带内新生代的岩浆作用十分发育.本文对带内新发现的灰白色黑云二花岗岩进行研究,获得了锆石U-Pb LA-ICP-MS年龄为34.88 Ma和35.25 Ma,表明其侵位于古近纪始新世.岩石地球化学表明,黑云二花岗岩为钾玄质-高钾钙碱性系列的过铝质花岗岩类,稀土元素配分曲线为右倾,其中LREE明显富集,HREE为不同程度亏损,具明显的负Eu异常;富集Rb、Th、Ce、Sm和亏损K、Ba、Ta、Hf、Y等元素,且为淡色花岗岩特征;据锆石Hf同位素测试分析,εHf(t)值为–2.35～+2.33和TDM2为962～1259 Ma,表明了花岗岩岩浆源区为壳幔混合的产物,以及源岩主要源自中元古代—新元古代陆壳基底物质的部分熔融.综合研究认为,始新世黑云二长花岗岩形成于喜马拉雅期碰撞造山向造山晚期转换阶段,是一套典型的"超厚地壳"部分熔融和壳幔相互作用的淡色花岗岩;以及其侵位时间代表了漕涧地区喜马拉雅碰撞造山阶段的完成和造山晚期阶段的开始,且转换时间约为35 Ma.     

Integration of zircon and apatite U–Pb geochronology and geochemical mapping of the Wude basalts(Emeishan large igneous province):A tool for a better understanding of the tectonothermal and geodynamic evolution of the Emeishan LIP

Radiogenic isotopic dating and Lu–Hf isotopic composition using laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS)of the Wude basalt in Yunnan province from the Emeishan large igneous province(ELIP)yielded timing of formation and post-eruption tectonothermal event.Holistic lithogeochemistry and elements mapping of basaltic rocks were further reevaluated to provide insights into crustal contamination and formation of the ELIP.A zircon U–Pb age of 251.3±2.0 Ma of the Wude basalt recorded the youngest volcanic eruption event and was consistent with the age span of 251-263 Ma for the emplacement of the ELIP.Such zircons hadε_Hf(t)values ranging from7.3 to+2.2,identical to those of magmatic zircons from the intrusive rocks of the ELIP,suggesting that crust-mantle interaction occurred during magmatic emplacement,or crust-mantle mixing existed in the deep source region prior to deep melting.The apatite U–Pb age at 53.6±3.4 Ma recorded an early Eocene magmatic superimposition of a regional tectonothermal event,corresponding to the Indian–Eurasian plate collision.Negative Nb,Ta,Ti and P anomalies of the Emeishan basalt may reflect crustal contamination.The uneven Nb/La and Th/Ta values distribution throughout the ELIP supported a mantle plume model origin.Therefore,the ELIP was formed as a result of a mantle plume which was later superimposed by a regional tectonothermal event attributed to the Indian–Eurasian plate collision during early Eocene.     

Early Eocene leucocratic sill/dike swarms in the Gangdese belt,southern Tibet: Tectonic implications for Indo-Asian collision

The timing of the initial Indo-Asian collision is a subject of debate for a long time. Besides, the magmatic trace of the collisional process is also unclear. In the present study, the authors report Early Eocene leucocratic sill/dike swarms in the northern edge of the Nymo intrusive complex of the Gangdese belt, southern Tibet. The Nymo intrusive complex was emplaced at ca. 50 –47 Ma and surrounded by the metamorphosed Jurassic-aged Bima Formation volcano-sedimentary sequence along its northern side. At outcrops, the leucocratic sills/dikes intruded along or truncated the deformed foliations of the host Bima Formation, which has been subject to high-temperature amphibolite-facies metamorphism at ca. 50 –47 Ma. Detailed cathodoluminescence image analyses reveal that the zircon grains of the leucocratic sills/dikes have core-mantle textures. The cores yield the Jurassic ages comparable to the protolith ages of the Bima Formation. In contrast, the mantles of zircon grains yield weighted mean ages of ca. 49–47 Ma, representing the crystallization timing of these leucocratic sills/dikes. The coeval ages for the Nymo intrusive complex, the high-temperature metamorphism, and the leucocratic sills/dikes indicate that a close relationship exists among them. The authors tentatively suggest that these leucocratic sills/dikes were generated from partial melting of the Jurassic-aged Bima Formation volcanic rocks, triggered by the high heat from the magma chamber of the Nymo intrusive complex. This Early Eocene tectono-thermal event of coeval magmatism, metamorphism and partial melting was most likely formed during the Indo-Asian collisional setting.©2021 China Geology Editorial Office.     

东营凹陷牛38井沙三段高分辨率旋回地层研究

自然伽玛测井资料取自山东省东营市胜利油田的牛38井。该井的沙河街组划分为四个段,其中沙三段依据含艾氏鱼群组合的鲱科化石和沉积物旋回堆积速率(AR)等研究,可与北美始新统绿河组进行对比。根据上世纪90年代沙三段古地磁研究结果,井深3263m处C18n.1n/C18n.1r界线调整为38.975MaBP。通过频谱分析和数字滤波计算,得出了沙三段几个界线的年龄值,其中,在沙三下、中亚段界线算出的36.9MaBP,岁差旋回幅度有明显变化,这一变化与Palike(Palikeetal.,2001)在ODP71线1052孔中发现的类似图像(36.7Ma)可比较。     

Controlling factors on the morphology and spatial distribution of methane-related tubular concretions – Case study of an Early Eocene seep system

Up to 10 m in length and >1 m in diameter tubular, calcite-cemented sandstone concretions are hosted by the faulted Dikilitash unconsolidated sands and sandstones. These structures document shallow subsurface pathways of Early Eocene methane seepage in the Balkan Mountains foreland (NE Bulgaria). Their exceptional exposure allowed a unique study of the factors governing the morphology and spatial distribution of such fossilized fluid conduits. The large dimensions and subvertical, cylindrical shape of the most common tube type primarily reflects the buoyancy-driven, vertical path of an ascending gas-bearing fluid through permeable, mainly unconsolidated sandy host sediments. Tube morphology was also influenced by local stratigraphic anisotropies and might as well document differences in former seepage conditions. Mapping of >800 tubular concretions showed the NNW–NNE elongation and alignment of tube clusters and massive cemented sandstone structures. This suggests that Paleogene fault systems played a major role in directing the movement of fluids. However, within a single tube cluster, tubes are preferentially aligned, over distances up to 50 m along directions at an angle between 10° and 36° with respect to the inferred NNW–NNE, cluster parallel fault traces. In addition, cylindrical tubes of analogue dimensions are aligned over distances >100 m along N15° to N25°-oriented directions. It is hypothesized that this spatial geometry of tubular concretions reflects the complex geometry of deformations structures in fault damage zones along which fluids were preferentially channelled.     

Geochemical overview and undiscovered gas resources generated from Hamitabat petroleum system in the Thrace Basin,Turkey

Since the first drill in 1957, three oil, 19 gas and condensate fields have been discovered in the Thrace Basin. However, any petroleum system with its essential elements and processes has not been assigned yet. This study consists of two parts, (1) geochemical overview of the previous work in order to get a necessary help to construct a petroleum system and (2) calculation of quantitative undiscovered hydrocarbon resources generated from this system. An extensive overview study showed that the primary reservoir and source rocks in the Thrace Basin are the Middle Eocene Hamitabat sandstones and shales, respectively, hence it appears that the most effective petroleum system of the Thrace Basin becomes the Hamitabat (!) petroleum system. Currently, 18.5 billion m³ of in-place gas, 2.0 million m³ (12.7 million bbl) in-place waxy oil as well as minor amount of associated condensate were discovered from this system. This study showed that the regional distribution of the oil and gas fields almost overlapped with the previously constructed pod of active Hamitabat shales implying that short and up-dip vertical migration pathway of hydrocarbons from the source to trapping side was available. Thermal model demonstrated that hydrocarbon generation from the Hamitabat shales commenced in the Early Miocene. The amount of quantitative gas generation based on the mean-original TOC = 0.94 wt%, mean-original HI = 217 HC/g TOC and the volume of the pod of active source rock = 49 km³ is approximately 110 billion m³ of gaseous hydrocarbons that results in a high generation–accumulation efficiency of 17% when 18.5 billion m³ of already discovered hydrocarbons are considered.     

Geological age of the Yokawa Formation of the Kobe Group (Japan) on the basis of terrestrial mammalian fossils

Abstract   The age of the Yokawa Formation of the Cenozoic Kobe Group distributed in Hyogo Prefecture of western Japan based on mammalian fossils is discussed. Two fossil dental specimens of terrestrial mammals discovered from the lowest part of the Yokawa Formation in the Sanda area are described. These two fossils described here are: (i) a right mandibular fragment with p2–m3 of Bothriodon sandaensis sp. nov. (selenodont anthracotheriid artiodactyl), which appears to be the most primitive among the species of the genus; and (ii) right m1–m3 of cf. Hyrachyus sp. (primitive rhinocerotoid perissodactyl). In the lower part of the Yokawa Formation, Zaisanamynodon (amynodontid perissodactyl) was previously reported. The morphology ('evolutionary stage') of B. sandaensis is indicative of the latest Middle to Late Eocene, that of cf. Hyrachyus sp. is indicative of the Early to Middle Eocene, and Zaisanamynodon is indicative of the Late Middle to Late Eocene. Therefore, the fossil mammals of the Yokawa Formation indicate an latest Middle Eocene ( ca . 38 Ma) correlation for the lower part of the formation, as a working hypothesis. Although the resolution of the geological age based on these mammalian fossils is relatively low compared to that based on marine index fossils, this result is concordant with the recent radiometric correlation of the lower part of the Yokawa Formation in the Sanda area.     

Fossil nothofagaceous leaves from the Eocene of western Antarctica and their bearing on the origin, dispersal and systematics of Nothofagus

Fossil leaves resembling Nothofagaceae have been investigated from the Eocene of western Antarctica and a new form genus Nothofagofolia is proposed for these kinds of fossils. Some new specimens belonging to this form genus are described. They were collected from the Fossil Hill locality of Fildes Peninsula, King George Island, South Shetland Islands, western Antarctica. Two new species, two new combinations and an unnamed species are reported. A number of published Nothofagus leaf fossils from the same locality are discussed and revised. As a result of these studies of Nothofagus leaf morphology, we conclude that (1) Nothofagus probably originated in high latitudes of the Southern Hemisphere during the middle-late Late Cretaceous and diversified, dispersed gradually to the lower latitudes of the same hemisphere; (2) leaf morphological characters are significant for the systematics of the family Nothofagaceae, especially at the intrageneric level; and (3) extant species of Nothofagus known from southern temperate areas have more primitive leaf morphological characters and lower leaf ranks than those from tropical mountains as well as those of the Fagaceae and Betulaceae. Supported by the Foundation of State Key Laboratory of Palaeobiology & Stratigraphy, Nanjing Institute of Geology and Palaoentology, Chinese Academy of Sciences (Grant No. 013106), the National Natural Science Foundation of China (Grant No. 30670159) and the Fund of Innovation Program by Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences     

藏南岗巴—定日地区始新世化石碳酸盐岩微相与沉积环境

藏南岗巴-定日地区发育着西藏最晚期的海相沉积，对这套海相沉积的研究，可提供关于西藏特提斯演化晚期的良好信息，本文对岗巴-定日地区始新世遮普惹组的化石碳酸盐岩微相进行了较为详细的分析和研究。参考Wilson(1975)的标准微相，初步识别出10种微相和5种生物相类型。同时对遮普惹组中的砾状灰岩的成因机制作了有益的探讨，它完全是由沉积作用而成；胶结物不是源于物质的重新分配，而是台地边缘斜坡的等深流沉积。以此为基础，对西藏特提斯晚期沉积环境的演变进行了较为详细的分析。笔者认为：岗巴-定日盆地在始新世Ypresian-Lutetian早期接受海侵；自Lutetian晚期开始，区内总体处于一种海退环境，但由于受板块碰撞作用的影响，岗巴地区在Lutetian晚期-Bartonian晚期成为-深水坳陷盆地；至Priabonian早期，海水完全退出本区。