Chemostratigraphy of Flood Basalts in the Garze-Litang Region and Zongza Block: Implications for Western Extension of the Emeishan Large Igneous Province, SW China

The Late Permian Emeishan Large Igneous Province (ELIP) is commonly regarded as being located in the western part of the Yangtze craton, SW China, with an asymmetrical shape and a small area. This area, however, is just a maximum estimation because some parts of the ELIP were not recognized or dismembered and destroyed during the Triassic to Cenozoic tectonism. In this paper, the chemostratigraphical data of the Zongza block, the Garze-Litang belt and the Songpan-Garze block suggest that the Late Permian basalts in these areas have remarkable similarities to the ELIP basalts in petrography and geochemistry. Flood basalts in the Sanjiangkou area are composed of the lower part of the low-Ti (LT) tholeiite and the upper part of the high-Ti (HT) tholeiite, which is the same as the flood basalts on the western margin of the Yangtze craton. Flood basalts in the Zongza and Songpan-Garze areas, which are far from the Yangtze craton, consist of HT tholeiite only. This is the same as the flood basalts within the Yangtze craton. Therefore we argue that these contemporary basalts all originated from the Emeishan mantle plume, and the ELIP could have a significant westward extension with an outcropped area of over 500,000 km2. This new scenario shows that the LT tholeiite occurs on the western margin of the Yangtze craton, while the HT tholeiite overlying the LT basalts occupies the whole area of the ELIP.

Advances in sediment geochemistry and chemostratigraphy for reservoir characterization

Sedimentary sequences preserve the records of changes in major controls of sedimentation namely,tectonics,climate,relative sea level and sediment production and preservation.The potential to characterize these changes in spatial and temporal scales has led to the development of the branch of chemostratigraphy.Chemostratigraphic study of sedimentary sequences commenced from recognizing identical/contrasting geochemical features across major geochronological boundaries,and evolved into one of the essential tools in exploration,characterization,and well development strategies.Chemostratigraphy incorporates applications on continuous,real-time geochemical mapping and direction of lateral drilling,and machine learning,among others.As the sedimentary systems operate on a variety of temporal scales that range from few hours(tidal cycles)to few tens of millions of years,within which many perturbations such as catastrophic and diagenetic events take place,that lead to unique geochemical signature which can be correlated at appropriate spatial and temporal scales.The application of chemostratigraphic technique in hydrocarbon exploration and reservoir characterization has gained momentum in recent years,particularly with the advent of developments in analytical instrumentation.This has also led to the integration of a variety of data from field sedimentary structures,mineralogy,major,trace and isotopic chemical compositions of whole rock,selected components of rocks,organic and inorganic components of oil and gas,etc.,for reservoir characterization more accurately than ever.The geochemical fingerprinting of oil and gas reservoir components plays a major role in the identification of source rocks,discrimination of oil families,characterization of reservoir,source,and seal segments in petroleum systems.Future trends indicate the relevance and growing applications of machine learning techniques,artificial intelligence in real-time assessment,monitoring and planning of hydrocarbon exploration and production.

Testing carbonate chemostratigraphy across differentiated ancient shallow-platform environments(Early Kimmeridgian,S Iberia)

Shallow-platform settings with marked differences in paleoplatform bottom physiography influence the degree of connection with oceanic waters and overall circulation patterns,even when sharing the same palaeoclimatic conditions.Two Kimmeridgian shallow-marine settings have been explored to test the sensitivity and reliability of carbonate chemostratigraphy to detect such differences.An integrated overview of the obtained elemental trends depicted four major facies,shared along specific stratigraphic intervals of both depositional records.Diagenesis obliterated original geochemical signals only throughout the siliciclastics-rich interval,corresponding to the most landward setting.For the remaining facies,elemental features could be attributed to the differential action of forcing mechanisms operating along the south-Iberian paleomargin during Kimmeridgian times.The highest degree of continental influence can be recognized by a strong relationship between Fe and Mn for the most proximal setting,which fades out along the mixed carbonate-fine siliciclastic rhythmic deposition in more open settings.A characteristic geochemical signature of progressively more positiveδ^(13)C values and significantly higher Sr content is identified for the interval dominated by biogenic sponge buildups.Such a local response is related to local forcing by upwelling in the surroundings of a coral fringe.The geochemical signature of a hydrothermal origin can be clearly differentiated from the influence of mere terrigenous pulses.Accordingly,the decoupling of Fe and Mn along marginal settings is the clue to detecting major events of palaeogeographic restructuring.Observed temporal variations in Mg content along both studied sections are attributed to tectonic activity influencing nearshore/coastal water masses.By integrating chemostratigraphic information and complementary evidence,the palaeoenvironmental mechanisms promoting differentiated sedimentary records along ancient subtropical,shallow,coastal settings can be disentangled.

A high-resolution chemostratigraphy of post-Marinoan Cap Carbonate using drill core samples in the Three Gorges area, South China

Cap Carbonates overlie the Marinoan Snowball Earth-related glacial diamictite, and possibly record the drastic surface environmental change and biological evolution after the Snowball Earth. We conducted on-land drilling from the Liantuo Formation, through the Nantuo, to the lower Doushantuo Formation in the Three Gorges area of South China to collect fresh, continuous samples in the Three Gorges area. We obtained high-resolution chemostratigraphies of ~13C and 6180 values of carbonates from the topmost part of the Nantuo Formation to the Cap Carbonate, in order to decode the detailed surface environmental change in the shallow marine setting. The δ3C chemostratigraphy possesses some unique characteristics： （1） stable δ13C values as a whole, but ubiquitous low δ13C anomalies through the Cap Carbonate, （2） increase of the δ13C values from -3 to ＋5‰ across the C2/C3 boundary, （3） no δ13C anomaly between the CI and C2 boundary, and （4） presence of an anomalous high δ13C value （＋2.3%0） and a faint positive correlation between δ13C and δ18O values in the C1 unit. Evidence of quite low δ13C anomalies （with a nadir of -41‰）, ubiquitous negative δ13C anomalies through the Cap Carbonate, and a high 613C anomaly accompanied with a faint positive correlation between δ13C and δ18O values in the C1 unit supports decomposition and formation of methane hydrate during Cap Carbonate formation. The drastic increase of δ13C values from the upper C2 to C3 units in- dicates enhancement of primary productivity and organic carbon burial, possibly due to high continental fluxes after the Snowball Earth event, evidenced by high Sr isotope values. The increase is restricted to the proximal side of the inner shelf in South China, and the timing of the increase of δ13C values of carbonates is earlier at Three Gorges area than any other area, suggesting that the enhancement of primary productivity started in the proximal environment because of higher continental influxes. The increase in oxygen contents of seawater due to the enhanced primary productivity possibly resulted in the emergence of multicellular animals soon after Cap Carbonate deposition.

bPermian, Lopingian, strontium isotopic ratio, conodont zone, marine carbonate, stable isotope chemostratigraphy

The Lopingian is one of the fastest rising periods of seawater strontium isotopic ratios （^87Sr/^86Sr） in earth history, and its mechanisms and increasing rates of the ^87Sr/^86Sr evolution were still disputed widely. These disputations among researchers were caused mainly by timeframe selection （sections＇ thickness or data of radiometric ages）, and different stratigraphic boundaries and un-upmost dated ages. This paper examined published ^87Sr/^86Sr data of the Lopingian, and projected them on timescales based on evolutionary and age constrained conodonts fossils. ^87Sr/^86Sr evolution vs fossil constraining timescales was re-established in this period. This research suggests： （1） ^87Sr/^86Sr excursion projects on fossil zones can truly support ^87Sr/^86Sr evolutionary pattern in the period; （2） ^87Sr/^86Sr evolution provides a new approach for stratigraphic research of marine carbonate sections in lieu of biostratigraphic data; （3） ^87Sr/^86Sr stratigraphy works on marine carbonate sections of different sedimentation rates even between different basins; （4） the ^875r/^86Sr data and its shift was dependent on samples materials and chemical treatment methods; （5） the increasing rate of marine water ^875r/^86Sr in the Late Permian is suggested as 5.4× 10^-5/Ma or slightly lower; （6） sedimentation age and its ^875r/^86Sr of the Lopingian marine carbonate suggested as： Dpro=259-（Rs- 0.70695）/5.4×10^-5 （Ma）.

Chemostratigraphic Characterization Tests on Sedimentary Formations in the Côte D’Ivoire Offshore Basin: Case of A-X and B-X Wells

The tests performed with two hundred and thirty-nine (239) samples from the A-X and B-X drillings help to know their sedimentological and chemostratigraphic characters. In sedimentological term formations are composed of sand, sandstone, limestone, siltstone and argillite that alternate along the drill. In chemostratigraphic term two megasequences (MS1 and MS2) have been identified. A correlation of chemostratigraphic data completed by the lithology results allowed a subdivision of oil wells that shows two main types of deposits environments. First, a proximal marine environment to continental and to Albian marked by a detrital flow deducted from the concentrations evolution of indicator elements of terrigenous material that are K, Mg, and Rb. On the other hand, a deep to shallow marine environment of Cenomanian to Paleocene marked by the presence of predominantly clay sediments and abundant glauconite in the lower Senonian. Nevertheless, there is a transition or intermediate environment that is characterized by the presence of glauconite and detrital flows.

Organic Carbon Isotopic Evolution during the Ediacaran-Cambrian Transition Interval in Eastern Guizhou,South China: Paleoenvironmental and Stratigraphic Implications

Secular variations of carbon isotopic composition of organic carbon can be used in the study of global environmental variation, the carbon cycle, stratigraphic delimitation, and biological evolution, etc. Organic carbon isotopic analysis of the Nangao and Zhalagou sections in eastern Gnizhou reveals a negative excursion near the Precambrian-Cambrian boundary that correlates with a distinct carbonate carbon isotopic negative excursion at this boundary globally. Our results also demonstrate that several alternating positive and negative shifts occur in the Meishucunian, and an obvious negative anomaly appears at the boundary between the Meishucunian and Qiongzhusian. The isotope values are stable in the middle and lower parts but became more positive in the upper part of the Qiongzhusian. Evolution of organic carbon isotopes from the two sections in the deepwater facies can be well correlated with that of the carbonate carbon isotopes from the section in the shallow water facies. Integrated with other stratigraphic tools, we can precisely establish a lower Cambrian stratigraphic framework from shallow sheff to deep basin of the Yangtze Platform.

Biostratigraphic and Chemostratigraphic Correlation for the Base of the Middle Ordovician between Yichang and Western Zhejiang Areas,South China

The base of the Middle Ordovician （i.e. Dapingian Stage） has been defined at the first appearance datum （FAD） of conodont Baltoniodus？ triangularis at Huanghuachang, Yichang, China,but the precise correlation of the boundary to regions of other facies remain to be resolved. Herein we review the biostratigraphy and chemostratigraphy of the Huanghuachang Global Standard Stratotype-Section and Point （GSSP） section, and present our latest stratigraphic work on the nearby Chenjiahe s ection in Yichang, and the Hengtang Quarry section, Jiangshan, Zhejiang, which is regarded as representative of slope facies. The conodont and graptolite biostratigraphy as well as chemostratigraphy of the Chenjiahe section indicate that the base of the Middle Ordovician also falls within the graptolite Azygograptus suecicus Zone, and coincides with a high or maximum δ13C value within a minor positive carbon isotope excursion, suggesting that the base boundary can be readily recognized across the entire Yangtze Gorges area. The integrated graptolite and conodont biostratigraphy and chemostratigraphy of the Hengtang section, Jiangshan, indicates that the basal boundary probably falls within the graptolite lsograptus caduceus imitatus Zone that overlies the Azygograptus suecicus Zone, and coincides with a remarkable drop of δ13C. This difference indicates that a multi-disciplinary approach is critical to identify the base boundary in those regions where the Baltoniodus ？ triangularis is absent.

Geochemical Record of the Cenomanian-Turonian Anoxic Event in Tunisia:Is it Correlative and Isochronous to the Biotic Signal?

In Tunisia, five Bahloul spaced sections, Bargou, Jerisa, Guern Halfaya, Kherij and Gafsa were analyzed for biostratigraphy （foraminifera and radiolarians） and major and trace elements. This high-resolution biostratigraphic and chemostratigraphic integrated analyses for the Late Cenomanian-Early Turonian Bahloul Formation provide new insight into the palaeoceanographic evolution of the southern Tethyan margin. Relative low abundance of related terrigenous Ti/Ai and K/ Al ratios and enrichment of some productivity proxies such as Ba, Cu, and Ni （organic matter related trace elements） suggests that the Bahloul, deposited during a relatively short period （0.5 Ma）, was of relatively elevated primary productivity and minimal detrital input. While higher D＊ values concurrent with lower Ti/AI ratios are interpreted as caused by enhanced fluvial material contribution, due to more humid climate during the OAE-2. Enhanced humidity triggered probably fluvial influxes, resulted in a sluggish water circulation and consequent anoxic/euxinic conditions favoring the preservation of organic matter at the bottom. Enrichments in redox-sensitive trace metals U, V, and Mo in the Bahloul Formation deposits and redox indices, such as V/（V＋Ni）, U/Th, V/Cr, and Ni/Co, indicate that oxygen-restricted conditions prevailed during the Late Cenomanian to earliest Turonian times and correlate well with relative abundances of some foraminiferal and radiolarian paleo- environmental relevant indicators. High Ba~ values and Uauth may indicate anoxic conditions at least at the water-sediment interface during the Bahloul Formation deposition and provide information about low to moderate sulfate-reduction reactions.

Hierarchical delineation and multivariate statistical discrimination of chemozones of the Cauvery Basin,south India:Implications on spatio-temporal scales of stratigraphic correlation

Success in locating oil pools in the Cauvery Basin,south India had been found to be based on the ability to delineate precisely the stratigraphic traps resulting from frequent sea level changes.However,recognition and delineation of them in terms of depositional units through conventional stratigraphic methods have been elusive owing to the limitations of such methods and lack of unified stratigraphic markers that could be traced at regional and basinal scale.This paper attempts to recognize depositional units in terms of chemozones,chronologic and lithostratigraphic units by assigning distinct geochemical signatures.Geochemical signatures were assigned through hierarchical delineation and discriminant function analysis.It is observed that individual depositional units could be recognized statistically with whole-rock geochemical composition.The strata under study show two second order chemozones comprising six major chemozones that in turn correspond to third order sea level cycles and minor chemozones at the scale of fourth order and/or further shorter sea level cycles.The geochemical signatures showed 100% distinctness between sample populations categorized according to chronostratigraphy and lithostratigraphy.The durations of these stratigraphic units range from 18 million years to less than a million years and indicate distinct geochemical compositional change at different time slices.By implication and also due to the close correspondence between sea level variations reported from this basin and global sea level cycles,it is suggested that recognition and correlation of individual depositional units with distal counterparts could be made accurately.Implication of these results is that stratigraphic units,at varying scales either temporally or spatially,could be assigned with unique geochemical signature,with which accurate prediction and correlation of similar units elsewhere is possible with measurable accuracy.

Sr-Isotopic Characteristic of the Typical Carbonate Neoproterozoic Siberia Sections

First Sr isotopic data for the type of Neoproterozoic carbonate sediments of the South Siberia are reported. Upper Riphean complex is represented by terrigenous -carbonate rocks of Tungysic Formation,Yenisey Mountain Ridge.Isotopic age of this Formation shows a wide range,from 924±40 Ma(K-Ar method)to 753±6 Ma(U-Pb method).Sediments of Zabit Formation,Bokson Series(East Sayan)and

Sedimentary Precambrian deposits in southwestern Transbaikalia (Siberia): phytoliths content, lateral correlations and geodynamics

The Baikal Group is one of the most important stratigraphic units in the geology of East Siberia (Upper Riphean). This paper focuses on litological-facies features based on the analysis of organic remains (stromatolites, microphitolites and microfossils), in order to better precise the age and environmental deposit conditions of the Baikal Group. The results are used to draw a correlation between all the Precambrian of deposits of the South of East Siberia. The stratigraphy of the Baikal Group is then compared to the geodynamic evolution of this region, characterized by the break-up of the supercontinent Rodinia and subsequent opening of the Paleo-Asian Ocean. Stratigraphic analogs to the Baikal Group display in most areas deposits of various minerals (complex ores, phosphoresces, bauxites etc. have been dated of the same age), so the present study would also provides an economic interest.

Permian integrative stratigraphy and timescale of China

A series of global major geological and biological events occurred during the Permian Period. Establishing a highresolution stratigraphic and temporal framework is essential to understand their cause-effect relationship. The official International timescale of the Permian System consists of three series(i.e., Cisuralian, Guadalupian and Lopingian in ascending order) and nine stages. In China, the Permian System is composed of three series(Chuanshanian, Yansingian and Lopingian) and eight stages, of which the subdivisions and definitions of the Chuanshanian and Yangsingian series are very different from the Cisuralian and Guadalupian series. The Permian Period spanned ～47 Myr. Its base is defined by the First Appearance Datum(FAD) of the conodont Streptognathodus isolatus at Aidaralash, Kazakhstan with an interpolated absolute age 298.9±0.15 Ma at Usolka, southern Urals, Russia. Its top equals the base of the Triassic System and is defined by the FAD of the conodont Hindeodus parvus at Meishan D section, southeast China with an interpolated absolute age 251.902±0.024 Ma. Thirty-five conodont, 23 fusulinid, 17 radiolarian and 20 ammonoid zones are established for the Permian in China, of which the Guadalupian and Lopingian conodont zones have been served as the standard for international correlation. The Permian δ13 Ccarbtrend indicates that it is characterized by a rapid negative shift of 3–5‰ at the end of the Changhsingian, which can be used for global correlation of the end-Permian mass extinction interval, but δ13 Ccarbrecords from all other intervals may have more or less suffered subsequent diagenetic alteration or represented regional or local signatures only. Permian δ18 Oapatitestudies suggest that an icehouse stage dominated the time interval from the late Carboniferous to Kungurian(late Cisuralian). However, paleoclimate began to ameriolate during the late Kungurian and gradually shifted into a greenhouse-dominated stage during the Guadalupian.The Changhsingian was a relatively cool stage, followed by a globally-recognizable rapid temperature rise of 8–10°C at the very end of the Changhsingian. The87 Sr/86 Sr ratio trend shows that their values at the beginning of the Permian were between 0.70800,then gradually decreased to the late Capitanian minimum 0.70680–0.70690, followed by a persistent increase until the end of the Permian with the value 0.70708. Magenetostratigraphy suggests two distinct stages separated by the Illawarra Reversal in the middle Wordian, of which the lower is the reverse polarity Kiaman Superchron and the upper is the mixed-polarity Illawarra Superchron. The end-Guadalupian(or pre-Lopingian) biological crisis occurred during the late Capitanian, when faunal changeovers of different fossil groups had different paces, but generally experienced a relatively long time from the Jinogondolella altudensis Zone until the earliest Wuchiapingian. The end-Permian mass extinction was a catastrophic event that is best constrained at the Meishan section, which occurred at 251.941±0.037 Ma and persisted no more than 61±48 kyr. After the major pulse at Bed 25, the extinction patterns are displayed differently in different sections. The global end-Guadalupian regression is manifested between the conodont Jinogondolella xuanhanensis and Clarkina dukouensis zones and the endChanghsingian transgression began in the Hindeodus changxingensis-Clarkina zhejiangensis Zone. The Permian Period is also characterized by strong faunal provincialism in general, which resulted in difficulties in inter-continental and inter-regional correlation of both marine and terrestrial systems.

Ordovician integrative stratigraphy and timescale of China

In this chapter, starting with a brief review of the research history and current status in the studies of the Ordovician chronostratigraphy in China, the subdivision of the Ordovician System, definition and recognition of its series and stage boundaries, and possible stratigraphic gaps are discussed in details in order to establish a multidisciplinary stratigraphic correlation through an integrated approach including lithostratigraphy, biostratigraphy, radiometric dating, chemostratigraphy and magnetostratigraphy. Being internationally accepted, the Ordovician System is now subdivided into three series and seven stages, in ascending order, Lower(Tremadocian, Floian), Middle(Dapingian, Darriwilian) and Upper series(Sandbian, Katian,Hirnantian). Three of the seven "Golden Spikes" defining the bases of the Ordovician stages, which were established in 1997–2007, are located in China. As a regionally applied chronostratigraphy, the Ordovician System was subdivided in China into Lower(Xinchangian, Yiyangian), Middle(Dapingian, Darriwilian) and Upper series(Neichiashanian, Chientangkiangian,Hirnantian). This scheme agrees largely with the standard international classification, which can actually be directly applied to China, except for some special circumstances where the Neichiashanian and Chientangkiangian stages of the Upper Ordovician are used. Based on the new studies in recent years and distinctions and differences recognized in the development of the Ordovician System in the constituent terranes of China, a new framework for correlation among the major Chinese palaeoplates or terranes, e.g. South China, North China(including Tarim and Qaidam) and Xizang(Tibet)-western Yunnan, has been established. However, it has been recognized herein that uncertainties still remain on defining the base of the Tremadocian,Dapingian and Katian, and on the correlation between different mega-facies. More specifically, for the Tremadocian, the precise correlation of its base will depend on the better-defined conodont taxonomy, while for the Dapingian and Katian, on the correlation between different mega-facies. It is worthwhile to note that the chemostratigraphic studies of the Ordovician System in China produced the carbonate δ13 C curves for the Darriwilian(Middle Ordovician) and Katian(Upper Ordovician), which show significant differences from the composite global curve. Record of the Ordovician isotopic dating is relatively rare in China, with only three reliable ages from zircons that are all from the upper Katian to Hirnantian of the Upper Ordovician.Abundant bentonite beds in the Upper Ordovician of South China will also provide unique opportunities to advance the isotopic dating and related researches. Studies on the Ordovician magnetostratigraphy need to be significantly enhanced in China, as currently all the available results are restricted to the Lower Ordovician of North China, although they can be correlated with those known from other parts of the world. The analysis of the durational unevenness of the seven stages in the Ordovician supports the possibility to further subdivide the long-durational Tremadocian, Darriwilian and Katian stages, each into two substages.

Carbon isotopic variations of Proterozoic carbonates in Jixian, Tianjin, China

Along the Proterozoic stratigraphic sections of Jixian, Tianjin, the ??13C values of carbonates are mostly negative in the Changchengian (Changcheng System), varying approximately within a range of (0±1)‰ in the Jixianian (Jixian System), and have commonly positive values of (2±2)‰ in the Qingbaikouan (Qingbaikou System). From Chuanlinggou Formation to Dahongyu Formation, i.e. from ca. 1700 Ma to 1600 Ma, the δ13C values of carbonates increase from about -3‰ to 0‰, but oscillate with large excursion in Dahongyu Formation. Two large excursions occur in the Jixianian, one in Yangzhuang Formation and the other in the third submember of Wumishan Formation overlaying. These integrated and continuous records of carbon isotope reflect secular variations of δ13C value in ancient seawater from ca. 1700 Ma to ca. 800 Ma. The increase and subsequent oscillation of seawater δ13C value occurring from the ages of ca. 1700 to ca. 1600 Ma and ＜1300 Ma may signify two correlative global tectonic events.

Ediacaran integrative stratigraphy and timescale of China

Ediacaran successions occur widely in various depositional facies in South China and yield a series of fossil Lagerst?tten, providing a complete fossil record for the evolution of marine ecosystems after the terminal Cryogenian global glaciation. Carbonate-dominated Ediacaran successions in shallow water facies in South China record a nearly complete δ^(13)C profile that may reflect variations of marine carbon isotopic composition during the Ediacaran Period. The Ediacaran fossils andδ^(13)C profiles from South China permit stratigraphic correlation and subdivision of the Ediacaran strata. Based on biostratigraphic, chemostratigraphic, and geochronometric data from the Ediacaran successions in South China, we propose that the Ediacaran System in China can be subdivided into two series, with three stages in each series. The lower series is characterized by acanthomorphic acritarchs and the upper series by Ediacara-type macrofossils, and the two series are separated by the declining limb of a pronounced δ^(13)C negative excursion(EN3) in the upper Doushantuo Formation. The basal boundary of Stage1 is the same as the basal boundary of Ediacaran System, which has been defined at the base of the cap carbonate unit. Stage 2 represents the first radiation of Ediacaran microscopic organisms, with δ^(13)C feature representing by positive values(EP1). The base of the Stage 2 is placed at the first appearance level of a spiny acritarch species. Stage 3 is characterized by the occurrence of more diverse acritarchs and δ^(13)C feature EP2, with its basal boundary defined by a δ^(13)C negative excursion(EN2) occurring in the middle Doushantuo Formation. The basal boundary of Stage 4 is the same as the upper series. Stage 5 is marked by the occurrence of macrfossils of Miaohe biota, and its lower boundary can be placed at the level where δ^(13)C values transition from positive to negative in MNE, or the first appearance level of macrofossils of the Miaohe biota. Stage 6 is characterized by the occurrences of Ediacara-type Shibantan biota and Gaojiashan biota, with its lower boundary defined by the first appearance level of Conotubus hemiannulatus. The formal establishment of the aforementioned series and stages requires further and more detailed integrative stratigraphic study on the Ediacaran successions in China. Some of the Ediacaran successions in South China have great potential to become global standards in Ediacaran subdivision.

Triassic integrative stratigraphy and timescale of China

The Triassic rocks are widespread in China, and both marine and terrestrial strata are well developed. The Triassic stratigraphic architecture of China is very complex in both spatial variation of the so-called "South Marine and North Continental", i.e. the southern areas of China occupied mostly by marine facies while the northern China by terrestrial facies during the Triassic Period, and temporal transition of the "Lower Marine and Upper Continental", i.e. the lower part of the Triassic System composed mainly of marine facies and the upper part of terrestrial strata especially in South China. Although the Global Stratotype Section and Point(GSSP) of the Permian-Triassic boundary is located in South China, the Triassic of China except for some marine Lower-Middle Triassic depositions shows significantly local characteristics and is hardly correlated with the global chronostratigraphic chart. Consequently, the Triassic of China contains not only the international research hotspots but also difficult points in stratigraphic study. This paper aims to present a brief review of the Triassic in China, including chronostratigraphy, biostratigraphy, magnetostratigraphy and chemostratigraphy, and summarize an integrated Triassic stratigraphic framework of China. Accordingly, a stratigraphic correlation is proposed for the lithostratigraphic sequences among the three tectono-paleogeographic stratigraphic regions. The comprehensive study indicates that ammonoids are the classic index fossils in Triassic biostratigraphy but conodonts are more advantageous in the study and definition of the Triassic chronostratigraphic boundaries. China still has the potential to optimize the GSSPs of the Induan-Olenekian boundary and Olenekian-Anisian boundary. The correlation of the Permian-Triassic boundary between marine and terrestrial facies might be achieved with the help of the Permian-Triassic "transitional bed" and its related biotic and environmental events in association with the biostratigraphic study of conchostracan, vertebrate and plant fossils. In addition, the carbon isotopes have been proved to be one of the powerful methods in marine Triassic stratigraphic study, whereas the oxygen and strontium isotopes may be additional important bridges to establish the correlation between the marine and terrestrial strata, but as yet lacking of relevant studies in terrestrial strata. Considering the most stratigraphic intervals of the Triassic and the terrestrial Triassic in China are difficult to be correlated to the global chart, the proposed Chinese(regional) Triassic chronostratigraphic chart of marine and terrestrial stages would be of importance to the study of Chinese Triassic stratigraphy and related aspects, but the stages must be conceptually in line with international standards and studied as soon as possible in order to finalize the definition.

Carboniferous integrative stratigraphy and timescale of China

The Carboniferous period lasted about 60 Myr, from ～358.9 Ma to ～298.9 Ma. According to the International Commission on Stratigraphy, the Carboniferous System is subdivided into two subsystems, i.e., Mississippian and Pennsylvanian, including 6 series and 7 stages. The Global Stratotype Sections and Points(GSSPs) of three stages have been ratified, the Tournaisian, Visean, and Bashkirian stages. The GSSPs of the remaining four stages(i.e., the Serpukhovian, Moscovian,Kasimovian, and Gzhelian) have not been ratified so far. This paper outlines Carboniferous stratigraphic subdivision and correlation on the basis of detailed biostratigraphy mainly from South China, and summarizes the Carboniferous chronostratigraphic framework of China. High-resolution biostratigraphic study reveals 37 conodont zones, 24 foraminiferal(including fusulinid) zones, 13 ammonoid zones, 10 brachiopod zones, and 10 rugose coral zones in the Carboniferous of China. The biostratigraphic framework based on these biozones warrants the precise correlation of regional stratigraphy of China(including2 subsystems, 4 series, and 8 stages) to that of the other regions globally. Meanwhile, the Carboniferous chemo-, sequence-,cyclo-, and event-stratigraphy of China have been intensively studied and can also be correlated worldwide. Future studies on the Carboniferous in China should focus on(1) the correlation between shallow-and deep-water facies and between marine and continental facies,(2) high-resolution astronomical cyclostratigraphy, and(3) paleoenvironment and paleoclimate analysis based on geochemical proxies such as strontium and oxygen isotopes, as well as stomatal indices of fossil plants.

Silurian integrative stratigraphy and timescale of China

Silurian is a period with the shortest duration in Phanerozoic except for the Neogene and Quaternary. It represents an important and unique interval when the biotic diversity recovered quickly after the end-Ordovician mass extinction, different paleoplates or terranes conjoined, big oceans disappeared or narrowed, climate and sea level changed frequently, global biotic provincialism became weaker, some primitive plants started to occupy the land. Silurian is also the first system of which all the chronostratigraphic stratotypes(i.e. the GSSPs) including four series and seven stages were established by the International Subcommission on Silurian Stratigraphy(ISSS). Nonetheless, during the post-GSSP studies conducted by ISSS in the middle1980 s, some Silurian GSSPs were found to have some congenital defects such as no index fossils available that hinder the high resolution subdivision and correlation on a regional or global scale. In this paper, based on the latest development of Silurian study in China, the progress in biostratigraphy, chronostratigraphy, event stratigraphy(such as facies differentiation, heterochrony of black shales, marine red beds, carbonate rocks and reefs), chemostratigraphy, and tectonic stratigraphy(e.g., widespread of the late Silurian rocks in South China and its tectonic implication) are systematically summarized. Some existing problems and the areas to be focused in future work are also discussed. It is suitable for chronostratigraphic study to concentrate not only on the boundary but also doing multidisciplinary analysis on the biotic, chemical, magnetic, environmental, and chronologic aspects, in order to enhance the reliability and the potential for regional and global correlation of a certain GSSP.Some important achievements are expected in these areas in the Silurian study in China:(1) ecostratigraphy and basin analysis of the Llandovery, and the correlation of integrative stratigraphy with a high resolution;(2) establishment of the Wenlock to Pridoli chronostratigraphic framework;(3) the chemo-and magnetic stratigraphy and the age of some key intervals and horizons;(4)further investigation on paleogeography and plate tectonics; and(5) origin and early evolution of the terrestrial ecosystem. Some new breakthroughs might occur in the restudy on some of those problematic GSSPs of some particular series and stages.

SIMS U-Pb Zircon Geochronological and Carbon Isotope Chemostratigraphic Constraints on the Ediacaran-Cambrian Boundary Succession in the Three Gorges Area, South China

The Ediacaran–Cambrian succession in South China records dramatic biological,oceanic and geochemical changes,but it is not well constrained geochronologically.This study reports a new SIMS U-Pb date of 543.4±3.5 Ma(MSWD=1.2)from a tuffaceous layer in the Zhoujiaao Section,and carbonate C-O isotopes in both Zhoujiaao and Sixi sections,Three Gorges area.This tuffaceous layer is present in the Upper Dengying Formation(i.e.,the Baimatuo Member)which is characterized by a stableδ13Ccarb plateau and the beginning of a negativeδ13Ccarb shift near its upper boundary.In accordance with the existing biostratigraphic and chemostratigraphic data,this new date corroborates that the upper boundary of the Dengying Formation in South China is approximately equivalent to the Ediacaran-Cambrian boundary(ca.541 Ma).This age also provides the minimum age of the last appearance of the Shibantan biota in the Three Gorges area,indicating that the terminal Ediacaran index fossils(e.g.,Cloudina,Sinotubulites)are not reliable stratigraphic markers for further subdivision of the uppermost Ediacaran.