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Is there a great Unconformity between Xiamaling and Longshan formations in the North China Craton?

Science China Earth Sciences 2023年第5期66卷 959-984页

作者： Hongwei KUANG Nan PENG Yongqing LIU Yuchong WANG Mingming CUI Xiaoshuai CHEN Dawei QIAO Keining QI Institute of Geology Chinese Academy of Geological SciencesBeijing100037China School of Earth Science and Mapping Engineering China University of Mining and Technology(Beijing)Beijing100083China School of Resource and Environmental Engineering Hefei University of TechnologyHefei230009China

The existence of a 0.3 Ga"great Unconformity"between the Mesoproterozoic"Undefined System"Xiamaling Formation and the"Neoproterozoic"Longshan Formation has long been controversial.In this study,stratigraphy,sedimentology,detrital zircon dating,lithium isotope,and major and trace elements were applied to systematically analyze their relationship.Results demonstrate that coarse to fine sandstone-mudstone normal cycles with different grades and thicknesses exist from the Xiamaling to the Longshan formations.Sedimentary succession formed from a restricted platform with lagoon-shallow marine shelf-tidal flat-beach and tidal shoal developing in ascending order.The pebbly sandstone at the bottom of the Long shan Formation does not have the properties of basal conglomerate with tectonic significance.The youngest detrital zircon is older than 1.6 Ga for the Long shan Formation and overlying Jing'eryu Formation sandstones.In addition,no(zircon)provenance has been found from the large igneous province of 1.32-1.2 Ga in Xiamaling Formation.Theδ^(7)Li isotope values exhibit a gradually increasing trend.The Li content and CIA(Chemical index of alteration)gradually decreases from the top of the Xiamaling Formation to the lower part of the Long shan Formation.Simultaneously,as K_(2)O/Al_(2)O_(3)and FeO/Fe_(2)O_(3)decreases,Na_(2)O/Al_(2)O_(3)increases,and Li/Al,V/Cr,and V/(V+Ni)fluctuates slightly.At the boundary,the Ce/Ce^(*)and Eu/Eu^(*)show positive and negative anomalies,respectively.Further,the Rb/Sr and Al/Si values decrease,and U/Th values increase.This indicates that the geochemistry of the weathering crust at the interface of the Xiamaling Formation-Long shan Formation is not characteristic.However,it indicates a weakening of continental weathering intensity from the bottom to the top of the interface.These results do not support the existence of a large Unconformity between the Xiamaling and the Longshan formations.Therefore,it is suggested that the Long shan Formation-Jing'eryu Formation should be moved to the lower l

关键词： North China Craton Mesoproterozoic Transition period Unconformity Continuous sedimentation

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The role of the Mid-Cimmerian Unconformity on the quality of the underlying Skagerrak sandstone reservoir in the Kittiwake Field,central North Sea

Energy Geoscience

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Energy Geoscience 2021年第4期2卷 254-273页

作者： Abdulati Araibi Dorrik Stow Helen Lever Zeinab Smillie Department of Earth Science Elmergib UniversityAlkhomsLibya Institute of Geo-Energy Engineering School of EnergyGeoscienceInfrastructure and SocietyEdinburghUK

The central aim of this paper is to address the role of unconformities in affecting reservoir quality.Do they facilitate diagenesis that leads to either enhanced or reduced porosity through dissolution or cementation?Or,do they have little effect?We have investigated the Late Triassic Skagerrak sandstone reservoir underlying the Mid-Cimmerian Unconformity in the Kittiwake Field,central North Sea.There is strong evidence for the development of secondary porosity through the dissolution of unstable silicate minerals,primarily feldspars.This includes the presence of oversized pores,partial dissolution of framework grains,and complete dissolution of grains leaving remnant grain margins and partially filled cores.This dissolution as a late-stage event is demonstrated by the complete lack of compaction effects on the secondary pores and diagenetic products despite present burial depths in excess of 3000 m.These observations,coupled with an absence of systematic trends linked to the Unconformity surface in respects of reservoir porosity,feldspar amount and dissolution,and kaolinization,lead to the conclusion that there has been no effect of the Mid-Cimmerian Unconformity on reservoir quality in the Kittiwake Field.There is no evidence for leaching or cementation linked to meteoric water influx either shortly after deposition or following the uplift and exposure,which led to development of the Mid-Cimmerian Unconformity.Instead,we propose that the late-stage dissolution of feldspar and generation of secondary porosity are most likely related to the influx of organic acids and carbon dioxide generated either from thermogenic maturation of the source rock or from biodegradation of oil within the reservoir near the oil-water contact(OWC)transition zone.

关键词： North sea Kittiwake field Unconformity Skagerrak sandstone

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The Unconformity in Miocene sequence of western Qaidam Basin and its tectonic significance

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Science China Earth Sciences 2010年第8期53卷 1126-1133页

作者： WANG Liang XIAO AnCheng GONG QingLin LIU Dong WU Lei ZHOU SuPing SHEN ZhongYan LOU QianQian SUN XiaoWen Department of Earth Sciences Zhejiang UniversityHangzhou 310027China Beijing Geological Survey Beijing 102206China Institute of China National Petroleum Corporation Zhuozhou 072750China Qinghai Oilfield Company of China National Petroleum Corporation Dunhuang 736202China Lakes Oil Level 14500 Collins StreetMelbourne 3000Australia

An angular Unconformity has been identified between the upper and the lower Youshashan Formation based on the study of the regional geology, drillhole, and geophysical data of the Altyn Tagh Mountain foreland, western Qaidam Basin. The distribution of the Unconformity, the contacts between the upper and the lower Youshashan Formation, and its relation to the characteristics of the paleo-structure belts suggest a close relationship between the unconformities in the southern flank of the Altyn Tagh Mountain in the west of the Qaidam Basin and the activity of the Altyn Tagh Fault. It was the same time when the Atlyn Tagh Fault Zone was transformed from regional uplifting to rapid-strike-slipping movement during the Miocene, resulting in the cessation of the regional uplift and subsequent massive regional transgression during the deposition of the upper Youshashan Formation, which unconformably overlies (onlaps) the underlying strata of different ages.

关键词： Qaidam Basin Altyn Tagh Fault Miocene angular Unconformity strike slip movement

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Revisiting the mechanisms of mid-Tertiary uplift of the NE Tibetan Plateau

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National Science Review 2023年第4期10卷 169-190页

作者： Hong-Hong Wei Guo-Li Wu Lin Ding Long-Gang Fan Lin Li Qing-Ren Meng State Key Laboratory of Tibetan Plateau Earth System Environment and Resources (TPESER) Institute of Tibetan Plateau Research Chinese Academy of Sciences Institute of Geomechanics Chinese Academy of Geological Sciences State Key Laboratory of Lithospheric Evolution Institute of Geology and Geophysics Chinese Academy of Sciences Department of Geosciences University of Arizona University of Chinese Academy of Sciences

Contrasting views exist on timing and mechanisms of Tertiary crustal uplift in the NE Tibetan Plateau based on different approaches, with many models atributing surface uplift to crustal shortening. We carry out a comprehensive investigation of mid-Tertiary stratigraphy, sedimentology, and volcanism in the West Qinling, Hoh Xil and Qaidam basin, and the results challenge previous views. It was held that the discordance between Oligocene and Miocene strata is an angular Unconformity in the West Qinling, but our field observations show that it is actually a disconformity, indicative of vertical crustal uplifting rather than crustal shortening at the Oligocene to Miocene transition. Widespread occurrence of synsedimentary normal faults in mid-Tertiary successions implicates supracrustal stretching. Miocene potassic–ultrapassic and mafic–ultramafic volcanics in the Hoh Xil and West Qinling suggest a crucial role of deep thermomechanical processes in generating crust-and mantle-sourced magmatism. Also noticeable are the continuity of mid-Tertiary successions and absence of volcanics in the Qaidam basin. Based on a holistic assessment of stratigraphic–sedimentary processes, volcanic petrogenesis, and spatial variations of lithospheric thicknesses, we speculate that small-sale mantle convection might have been operating beneath northeast Tibet in the mid-Tertiary. It is assumed that northward asthenospheric flow was impeded by thicker cratonic lithosphere of the Qaidam and Alxa blocks, thereby leading to edge convection. The edge-driven convection could bring about surface uplift, induce supracrustal stretching, and trigger vigorous volcanism in the Hoh Xil and West Qinling in the mid-Tertiary period. This mechanism satisfactorily explains many key geologic phenomena that are hardly reconciled by previous models.

关键词： NE Tibetan Plateau mid-Tertiary Unconformity volcanism edge convection

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Exploration Significance of Unconformity Structure on Subtle Pools

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地学前缘 2009年第S1期16卷 136-136页

作者： Kongyou Wu,Ming Zha,Jiangxiu Qu Faculty of Geo-Resource and Information,China University of Petroleum,Qingdao 266555,China.

Vertical structure of an Unconformity can be divided into three layers:basal conglomerate or transgressive sand,weathered clay layer and leached rock.When the weathered clay layer has a little thickness or limited distribution,the overlying and underlying strata will contact directly,and the lithology is often different.This lithologic difference causes different fluid transporting capacity,and it also

关键词： Unconformity structure subtle pools accumulation simulation

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Structural Characteristics and their Significance for Hydrocarbon Accumulation in the Northern Slope of the Central Sichuan Paleo-uplift

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Acta Geologica Sinica(English Edition) 2022年第4期96卷 1451-1470页

作者： TIAN Xingwang LIU Guangdi LUO Bing YANG Yu WEN Long ZHANG Benjian CHEN Xiao SU Guiping SONG Zezhang PENG Hanlin ZHOU Gang YAN Wei YANG Dailin WANG Yunlong SUN Yiting DOU Shuang State Key Laboratory of Petroleum Resources and Prospecting China University of PetroleumBeijing 102249China College of Geosciences China University of PetroleumBeijing 102249China Research Institute of Exploration and Development Southwest Oil and Gas Field CompanyPetroChinaChengdu 610041China

Based on 2D and 3D seismic data,the latest drilling data and field outcrop data of the northern slope of the Central Sichuan paleo-uplift,the structural analysis method is used to analyze Unconformity development characteristics and fault characteristics during the key structural transformation period,discussing the influence of the structural characteristics on the hydrocarbon accumulation of deep carbonate rocks.The results show that:(1)The two key unconformities of the Tongwan and Caledonian periods were primarily developed in deep carbonate rocks.Firstly,Tongwan’s unconformities are characterized by regional disconformities between the second and third members of the Dengying Formation,the top formation of the Sinian and the lower Cambrian,strips of which zigzag through the north and south sides of the study area.Secondly,the Caledonian Unconformity is characterized by a regional unconformable contact between the lower Permian and the ower Paleozoic strata.From NE to SW,the age of the strata,which were subject to erosion,changes from new to old,the denudation distribution showing as a nose-shaped structure which inclines towards the ENE.(2)Boundary fault and transtensional strike-slip faults developed in the Sinian to Paleozoic strata.In profile,there are three types of structural styles:steep and erect,flower structures,’Y’and reversed’Y’type faults.In plane view,the Sinian developed extensional boundary faults extending in an almost NS direction,strike-slip faults developing and extending linearly in approximately EW,WNW and NE strikes in the Cambrian,with characteristically more in the south and less in the north.(3)The faults in the northern slope show obvious zonal deformations in transverse view as well as significant stages and stratified activity in a longitudinal direction.Among them,the activity of faults in the Sinian was the strongest,followed by the activity in the Cambrian period,the activity intensity of faults in the Permian period being the weakest.This fault activity can be divided into four

关键词： northern slope of paleo-uplift Unconformity structural characteristics hydrocarbon accumulation Central Sichuan paleo-uplift Sichuan Basin

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Regional unconformities and their controls on hydrocarbon accumulation in Sichuan Basin, sW China

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Petroleum Exploration and Development 2023年第3期50卷 573-587页

作者： YANG Weij WEI Guoqi WU Saijun XIE Wuren JIN Hui ZENG Fuying HAO Cuiguo BAI Zhuangzhuang SU Yiqing LI Rong PetroChina Research Institute of Petroleum Exploration and Development Beijing 100083China Key Laboratory of Gas Reservoir Formation and Development CNPCLangfang 065007China

Based on outcrop,seismic and drilling data,the main regional unconformities in the Sichuan Basin and their controls on hydrocarbon accumulation were systematically studied.Three findings are obtained.First,six regional stratigraphic unconformities are mainly developed in the Sichuan Basin,from the bottom up which are between pre-Sinian and Sinian,between Sinian and Cambrian,between pre-Permian and Permian,between middle and upper Permian,between middle and upper Triassic,and between Triassic and Jurassic.Especially,16 of 21l conventional(and tight)gas fields discovered are believed to have formed in relation to regional unconformities.Second,regional Unconformity mainly controls hydrocarbon accumulation from five aspects:(1)The porosity and permeability of reservoirs under the Unconformity are improved through weathering crust karstification to form large-scale karst reservoirs;(2)Good source-reservoir-caprock assemblage can form near the Unconformity,which provides a basis for forming large gas field;(3)Regional Unconformity may lead to stratigraphic pinch-out and rugged ancient landform,giving rise to a large area of stratigraphic and lithologic trap groups;(4)Regional Unconformity provides a dominant channel for lateral migration of oil and gas;and(5)Regional Unconformity is conducive to large-scale accumulation of oil and gas.Third,the areas related to regional unconformities are the exploration focus of large gas fields in the Sichuan Basin.The pre-Sinian is found with source rocks,reservoir rocks and other favorable conditions for the formation of large gas fields,and presents a large exploration potential.Thus,it is expected to be an important strategic replacement.

关键词： Unconformity large gas filed Sichuan Basin karst reservoir hydrocarbon accumulation control exploration potential

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Karstification characteristics of the Cenomanian-Turonian Mishrif Formation in the Missan Oil Fields,southeastern Iraq,and their effects on reservoirs

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Frontiers of Earth Science 2022年第2期16卷 435-445页

作者： Peiyuan CHEN Lina GUO Chen LI Yi TONG CNOOC International Ltd. Beijing 100028China CNOOC Research Institute Co. Ltd.Beijing 100028China

The Middle Cretaceous Mishrif Formation of the Cenomanian-Turonian age is an important Middle Eastern reservoir.Previous studies have shown that carbonates in the Mishrif Formation are affected by karstification and are concentrated at the top of the formation.However,there is a lack of systematic research on the effects of karstification on the formation’s reservoir characteristics.Based on core samples,scanning electron microscopy of thin sections,and geochemical analysis of C,O,and Sr isotopes from wells in the Missan Oil Fields,Unconformity was identified at the top of the B21 subzone of the Mishrif Formation.Core and cast-thin-section observations indicate that there is a significant lithological difference above and below the Unconformity,and dissolution pores and voids are well-developed beneath it.Vadose silt fills the intragranular pores and geopetal fabric is developed inside some mouldic pores beneath the Unconformity surface.The isotopic values of ^(87)Sr/^(86)Sr(0.707270-0.707722)and δ^(18)O(−5.94‰—−2.32‰)suggest that the top of the B21 subzone of the Mishrif Formation has been severely affected by syngenetic karst.Karstification is the key to high-quality reservoir formation and the reservoir’s oil-bearing heterogeneity.This study will inform oil and gas exploration in the Missan Oil Fields and in other areas with similar reservoir characteristics.

关键词： Unconformity karstification carbonate reservoir Mishrif Formation Missan Oil Fields southeastern Iraq

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Discovery of Neoarchean Unconformity and its implication for continental cratonization of North China craton

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Science China Earth Sciences 1999年第4期42卷 399-407页

作者：钱祥麟李江海

An ancient Unconformity event is identified within the granulite-facies province of North China, which is marked by the boundary between the overlying khondalite series (KS) and the basement grey gneiss complex (BGGC). REE patterns of KS suggest that their protoliths aM mature sediments. As documented by isotopic ages and metamorphic P-T-t paths, KS is originally deposited after the basement complex formed. Furthermore, the BGGC was overprinted by the metamorphic event associated with the KS. The binary structure of KS-BGGC is well preserved in the western part of North China craton (NCC), and it is structurally truncated and overlain by the Palaeoproterozoic Wntai rift, which suggests that the Unconformity occurred in the Neoarchean, and represents the major tectono-thermal episodes of the Neoarchean continental cratonization of NCC.

关键词： Neoarchean cratonization Khondalite series grey gneiss Unconformity event.

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The Unconformity and diastems in the postglacial sequence in the Changjiang Delta and Qiantangjiang Estuary

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Progress in Natural Science:Materials International 1996年第2期 80-90页

作者：李从先张桂甲

The sedimentary breaks of different time-space scales, such as Unconformity, stratigraphic surfaces and diastems in the postglacial sequence, are studied The Unconformity can be recognized by abrupt change in lithology, physical and engineering properties of sediments, paleosol, breaks in microfossil records and mutation in magnetic fabric parameter curves. The Unconformity diachronism in the directions parallel and perpendicular to the present coastline is discussed. Furthermore, the positions of transgressive surface (TS) and maximum flooding surface (MFS) in the postglacial sequence are analysed. The diastems can be attributed to fluvial, wave and tidal-fluvial, and can be classified into three grades according to their time-space scales.

关键词： Changjiang Delta Qiantangjiang Estuary sequence boundary Unconformity diastent.

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