Sedimentary Expressions of the Early Jurassic Jenkyns Event in an Inland Lacustrine System in the Yin'gen-Ejinaqi Basin,North China

The Jenkyns Event,more widely known as the Toarcian Oceanic Anoxic Event(T-OAE),is marked by globally distributed negative carbon-isotope excursions,widespread oxygen depletion,and large-scale organic carbon burial,which indicate major climate/environmental perturbations in Earth's surface systems during the Early Jurassic.Although extensive research has been conducted in European continental settings,particularly in the western peri-Tethys regions,the impacts of this event beyond Europe remains largely unexplored.Here,a multiapproach study including investigations into the sporepollen assemblages,pyrite framboids,clay minerals,total organic carbon(TOC)levels,and organic carbon isotope(δ13Corg)levels in a lacustrine borehole section(MED1)from the Yin'gen-Ejinaqi Basin,North China,provides evidence of the occurrence of the Jenkyns Event and its extensive sedimentary responses in the eastern Tethys terrestrial systems.Two distinct spore-pollen assemblages have been identified in MED1(drilling depth:982.4 m to 1267.5 m),with the Cycadopites-Protopinus-Osmundacidites assemblage in the lower part(1267.5 m to 1132.9 m)indicating a middle Early Jurassic age and the Classopollis assemblage in the upper part(1132.9 m to 985.7 m)suggesting a Toarcian age.Framboidal pyrite data suggest more anoxic conditions during the deposition of black mudstone and shale intercalations in the lower part of the Classopollis assemblage(1132.9 m to 1066.9 m),which combined with organic carbon enrichment and negativeδ13Corg excursions,are considered the paleoenvironmental response to the Jenkyns Event in the study area.Furthermore,the evolution of vegetation groups changed from plant groups characterized by bisaccate and cycad pollen,as well as fern spores,to vegetation groups represented by Cheirolepidiaceae pollen across the Jenkyns Event,as evidenced by sporepollen data,together with the clay mineral assemblage change characterized by a notable increase in illite at the expense of kaolinite,suggests that while a subtropical-temperate climate persisted,a change toward warmer and drier conditions most likely occurred in the early Toarcian in the study area.In contrast to the humidification evidenced in many coastal settings,this aridification trend in the Yin'gen-Ejinaqi Basin aligns with the conditions in many inland areas.It is hypothesized that the underlying cause of these divergent changes may be linked to certain patterns of spatially variable water availability on land,potentially driven by extremified hydrological conditions.

Megafossils of Betulaceae from the Oligocene of Qaidam Basin and their paleoenvironmental and phytogeographic implications

Understanding the paleoenvironment and phytogeographical history of the Tibetan Plateau,China relies on discovering new plant fossils.The Qaidam Basin has long been regarded as an ideal‘field laboratory’to investigate the paleoclimate and paleobiological evolution of the northern Tibetan Plateau.However,fossil angiosperms from the Qaidam Basin are rare,and our knowledge of its paleovegetation is poor.Here,we report fossil leaves and fruits of Betulaceae found from the Oligocene Shangganchaigou Formation of northwestern Qaidam Basin(Huatugou area).Comparative morphological analysis led us to assign the fruits to the Betula subgenus Betula and the leaves to Carpinus grandis.These findings,together with other reported fossil plants from the same locality,reveal a close floristic linkage between the Qaidam Basin and Europe during the Oligocene.The northern pathway of this floristic exchange may have crossed through the Qaidam Basin during the late Paleogene.This floristic linkage may have been facilitated by the continuous narrowing of the Turgai Strait and stronger westerlies,which transported moisture and provided favorable climatic conditions.Indeed,fossil plants collected from the Qaidam Basin suggest that during the Oligocene this region had warm and humid deciduous broad-leaf forest,which differs from the region’s modern vegetation and indicates that the Qaidam Basin may have been a suitable region for these plants to flourish and spread during the Oligocene.

Flat-footed Females and Missing Males:A New Genus and Species of Pleciofungivoridae(Diptera:Bibionomorpha)Represents the First Record of the Family from Mid-Cretaceous Kachin Amber

A new genus and species,Cretopleciofungivora simpsoni gen.et sp.nov.,from the extinct family Pleciofungivoridae(Diptera:Bibionomorpha),is discovered in mid-Cretaceous Kachin amber.Previously,this family was known only from imprints in sedimentary rocks of the Jurassic and the Lower Cretaceous.Discovery of a representative of Pleciofungivoridae in Kachin amber confirms the presence of the family in the Upper Cretaceous.The new species has a unique structure of fore tarsus,with lobed and extended tarsal segments Ⅱ to Ⅳ,a feature hitherto known only in a few species of extant Sciaroidea.Although not particularly rare,the new species is currently known only from female specimens.Possible reasons for this phenomenon,very unusual in Sciaroidea,are briefly discussed,including parthenogenesis as a potentially plausible hypothesis.

Reconstruction of the Yangtze Ramp during Floian to Darriwilian(Ordovician)in South China:Its Morphology,Controlling Factors and Significances

A robust stratigraphic framework and a coherent depositional ramp model for the Zitai,Dawan,Meitan and Ningkuo formations of Floian–Darriwilian age(Early–Middle Ordovician)in the Yangtze(Daoba,Xiangshuidong,Daling,Gudongkou and Honghuayuan sections)and Jiangnan regions(Nanba section)was created based on lithofacies and major element analysis.Three siliciclastic(LF1–3)and six carbonate(LF4–9)lithofacies are recognized representing sediments that were deposited in mixed siliciclastic and carbonate ramp environment.The intensity of mixed sedimentation and terrigenous input were evaluated using the elemental proxies Intensity of Mixed sedimentation(IM)and Aluminum Accumulation Rate(Al AR),as well as their mean values during certain time intervals.Mixed sediments are most well-developed along the marginal Yangtze region,strongly impacted by recurrent influx of westerly derived terrigenous materials in response to global eustatic changes and regional tectonic movements,shaping the gently southeast-dipping morphology.Regular terrigenous influx resulted in periods of enhanced primary productivity on the Yangtze Ramp as evidenced by matching biodiversity peaks in planktonic organisms,i.e.,chitinozoans and acritarchs.Brachiopods and other shelly fauna were also able to proliferate as new niches developed along the gently dipping ramp floor with substrate changes.The biodiversification patterns suggest that terrigenous influx controlled in part by regional tectonics played a more important role than previously thought in the development of Great Ordovician Biodiversification Event in South China.

Phylogenomics and integrative taxonomy reveal two new species of Amana(Liliaceae)

Until now the genus Amana(Liliaceae),known as ’East Asian tulips’,has contained just seven species.In this study,a phylogenomic and integrative taxonomic approach was used to reveal two new species,Amana nanyueensis from Central China and A.tianmuensis from East China.A.nanyueensis resembles Amana edulis in possessing a densely villous-woolly bulb tunic and two opposite bracts,but differs in its leaves and anthers.Amana tianmuensis resembles Amana erythronioides in possessing three verticillate bracts and yellow anthers,but differs in aspects of its leaves and bulbs.These four species are clearly separated from each other in principal components analysis based on morphology.Phylogenomic analyses based on plastid CDS further support the species delimitation of A.nanyueensis and A.tianmuensis and suggests they are closely related to A.edulis.Cytological analysis shows that A.nanyueensis and A tianmuensis are both diploid(2n=2x=24),different from A edulis,which is either diploid(northern populations) or tetraploid(southern populations,2n=4x=48).The pollen morphology of A.nanyueensis is similar to other Amana species(single-groove germination aperture),but A.tianmuensis is quite different because of the presence of a sulcus membrane,which creates the illusion of double grooves.Ecological niche modelling also revealed a niche differentiation between A.edulis,A.nanyueensis and A.tianmuensis.

Modern pollen-vegetation relationships along altitudinal vegetation belts in the Leigong Mountain of southwestern China

Understanding the distribution,dispersal,and correlation of modern pollen with vegetation in mountainous regions is essential for establishing accurate modern analogs for fossil pollen records.This study,conducted in Leigong Mountain on the YunnanGuizhou Plateau of southwestern China,involved the collection of 35 surface soil samples from diverse vegetation communities along an elevational gradient ranging from 1210 to 1875 meters.The results reveal a close correspondence between modern pollen assemblages and vegetation zones.Principal Component Analysis(PCA)results indicate that pollen assemblages can effectively distinguish between subtropical montane evergreen broad-leaved forest(SEBF)and subtropical montane deciduous broadleaved forest(SDBF).However,both SEBF and SDBF show significant overlap with subtropical montane evergreen-deciduous broad-leaved mixed forest(SEMF).Detrended Correspondence Analysis(DCA)results clearly distinguish the three vegetation zones,and the first axis of DCA shows a significant positive correlation with elevation(p<0.01,R=0.48).Discriminant Analysis(DA)successfully assigns 94.4%of the modern pollen samples to their respective vegetation zones.Pollen taxa such as Impatiens,Astertype,and Rosaceae exhibit significant indicative capabilities for the SEBF zone,effectively distinguishing this vegetation zone from others.Pinus and Alnus display overrepresentation in the Leigong Mountain region,while Quercus(D,deciduous-type)and Poaceae exhibit high representation in the SEBF zone.In the SEBF zone,both pollen diversity and richness are the lowest.Our study reveals the complex relationship between the richness and diversity of pollen and vegetation.The diversity and richness of tree and shrub pollen are found to be lower than those of the corresponding plants.The pollen-vegetation relationship elucidated in this study serves as a critical reference for reconstructing ancient environments from fossil pollen retrieved in this region.

SHRIMP zircon U-Pb age, fitho- and biostratigraphic analyses of the Huaiyu Domain in South China,— Evidence for a Neoproterozoic orogen, not Late Paleozoic-Early Mesozoic collision

In the last few decades, the Late Paleozoic-Early Mesozoic tectonic evolution of South China has been quite controversial. The focus of debate is on both the age of ophiolites and the Late Paleozoic-Early Mesozoic geological and geodynamic environment. The Huaiyu Domain is located in the NE part of South China and exposes numerous significant geological features that are keys to understand the tectonics of South China. In this paper, we present some new evidence on stratigraphy, petrology and SHRIMP zircon U-Pb geochronology, and together with other geological and geochemical data available in the literature, and the following conclusions are suggested： 1） The eastern Jiangnan ophiolites belt, dated at 858±11 Ma by SHRIMP zircon U-Pb method, was generated during the Neoproterozoic, but not the Late Paleozoic; 2） The sedimentary rocks associated with these oceanic rocks do not contain radiolarians but Neoproterozoic acritarchs; 3） During Permian-Early Triassic times, the Huaiyu Domain was dominantly characterized by a shallow sea depositional environment since deep sea sediments are absent; and 4） The pre-Devonian tectonics of South China has been reworked by late polyphase tectonism through the Triassic and the Cretaceous periods. A Late Paleozoic-Early Mesozoic deep marine domain floored by oceanic crust never existed in the study area. The geochronological and structural data do not comply with a Late Paleozoic-Early Mesozoic South China Ocean.

Current Progress on the Geological Record of Microbialites and Microbial Carbonates

This paper reviews the current progress and problems in the study of microbialites and microbial carbonates. Microbialites and microbial carbonates, formed during growth of microbes by their calcification and binding of detrital sediment, have recently become one of the most popular geological topics. They occur throughout the entire geological history, and bear important theoretical and economic significances due to their complex structures and formative processes. Microbialites are in place benthic microbial buildups, whereas microbial carbonates can be classified into two categories： stabilized microbial carbonates（i.e., carbonate microbialites, such as stromatolites and thrombolites） and mobilized microbial carbonates（i.e., microbial carbonate grains, such as oncoids and microbial lumps）. Various texture, structures, and morphologies of microbialites and microbial carbonates hamper the systematic description and classification. Moreover, complex calcification pathways and diagenetic modifications further obscure the origin of some microbialites and microbial carbonates. Recent findings of abundant sponge spicules in previously identified ＂microbialites＂ challenge the traditional views about the origins of these ＂microbialites＂ and their implications to reef evolution. Microbialites and microbial carbonates did not always flourish in the aftermath of extinction events, which, together with other evidences, suggests that they are affected not only by metazoans but also by other geological factors. Their growth, development, and demise are also closely related to sea-level changes, due to their dependence on water depth, clarity, nutrient, and sunlight. Detailed studies on microbialites and microbial carbonates throughout geological history would certainly help understand causes and effects of major geological events as well as the coevolution of life and environment.

The Global Boundary Stratotype Section and Point （GSSP） for the base of Changhsingian Stage （Upper Permian）

The Global Stratotype Section and Point （GSSP） for the base-Changhsingian Stage is defined at the First Appearance Datum （FAD） of the conodont Clarkina wangi within the lineage from C. longicuspidata to C. wangi at a point 88 cm above the base of the Changxing Limestone in the lower part of Bed 4 （base of 4α-2） at Meishan D section, Changxing County, Zhejiang Province, South China. This level is consistent with the first appearance of Changhsingian index fusulinid Palaeofusulina sinensis and tapashanitid ammonoids. The speciation event from Clarkina longicuspidata to C. wangi occurs just above the flooding surface of the second parasequence in the Changxing Limestone. In addition, the boundary interval is clearly recognizable by the depletion of isotopic carbon ratios and the normal polarity zone appearing above the Late Wuchiapingian reversed polarity zone. Section C, about 300 m to the west of Section D, exposes more of the upper Longtan Formation. It clearly shows the transitional nature of deposition across the Longtan/Changxing formational boundary, and thus is described as a supplementary reference section.

Xingxueanthus: An Enigmatic Jurassic Seed Plant and Its Implications for the Origin of Angiospermy

The origin of angiosperms has been tantalizing botanists for centuries. Despite the efforts of palaeobotanists, most of the pre-Cretaceous angiosperms are regarded either non-convincing or misdated. The applications of SEM and LM （light microscope） enable us to recognize a coalified fossil plant, Xingxueanthus sinensis gen. et sp. nov., from the Haifanggou Formation （Middle Jurassic, 〉160 Ma） in western Liaoning, China. Xingxueanthus is an ＂inflorescence＂ with more than 20 female units spirally arranged. Each female unit is situated in the axii of a bract. The female unit is composed of an ovule-container and a style-like projection at the top. There is a vertical column bearing several ovules in the ovule-container. The general morphology and the internal structure of Xingxueanthus distinguish itself from any known fossil and extant gymnosperms, and its structures are more comparable to those of angiosperms. Xingxueanthus, if taken as a gymnosperm, would represent a new class, demonstrate an evolutionarily advanced status of ovule-protection in gymnosperms never seen before, and provide new insights into the origin of angiospermy. Alternatively, if taken as an angiosperm, together with Schmeissneria, it would increase the diversity of Jurassic angiosperms, which has been underestimated for a long time, and suggest a much earlier origin of angiospermy than currently accepted.

The Global Boundary Stratotype Section and Point （GSSP） for the base of the Hirnantian Stage （the uppermost of the Ordovician System）

The Global boundary Stratotype Section and Point （GSSP） for the base of the Hirnantian Stage （the uppermost of the Ordovician System） is defined at a point 0.39m below the base of the Kuanyinchiao Bed in the Wangjiawan North section. The section is located near Wangjiawan village, 42 km north of Yichang city （western Hubei, China）, at 30° 58′56″N and 111° 25′10″E. The GSSP level coincides with the first appearance of the graptolite species Normalograptus extraordinarius （Sobolevskaya）. Secondary markers include the onset of a positive carbon-isotope excursion, and a slightly earlier first appearance of Normalograptus ojsuensis （ Koren and Mikhailova ）. The Wangjiawan North section possesses continuity of sedimentation and biozonation with completeness of exposures, abundant and well-preserved graptolites and shelly fossils, i. e. the Hirnantia- Dalmanitina shelly fauna which is a key element for recognition of the Hirnantian Stage. The Wangjiawan North, South and Riverside sections possess favorable facies and widespread correlation potential, are free from structure complication, metamorphism and other alteration, and have good accessibility. The Riverside section in particular possesses amenability to isotopic age determination. The beginning of the Hirnantian was followed by a global episode of a major extinction event, which happened in the Diceratograptus mirus Subzone. The proposal was voted by the International Subcommission on Ordovician Stratigraphy in October, 2004, approved by the International Commission on Stratigraphy in February, 2006, and ratified by the International Union of Geological Sciences in May, 2006.

Sedimentary Evolution and Transgressions of the Western Subei Basin in Eastern China since the Late Pliocene

Sedimentary sequences in the Subei Basin are complex and have been affected by interactions between the ocean and rivers since the Late Pliocene, including the Yellow River, Huaihe River, and the Yangtze River. This sedimentary evolution, in particular the timing of Pleistocene transgressions, has long been a matter of controversy owing to the lack of precise chronological evidence. The aim of this study is to explore the evolution of the sedimentary environment throughout the past 3.00 Ma in this region on the basis of a comprehensive analysis of particle size and foraminifera and ostracods collected in the TZK9 core from the Subei Basin combined with geochronological studies of magnetostratigraphy, AMS^(14)C and optically stimulated luminescence(OSL). The results show that fluvial facies in the sedimentary environment from 3.00 to 1.01 Ma. There were fluvial facies and reflects six sea-level high stands from 1.01 to 0.25 Ma. The study area was affected by four large-scale transgressions since 0.25 Ma. The four marine sedimentary layers known as DU7(buried at 48–52 m), DU5(buried at 35–41 m), DU3(buried at 16–23 m), and DU1(buried at 2–4 m) are recorded in the MIS7(210–250 ka), MIS5, MIS3, and Holocene, respectively. The magnitude of the DU5 transgression was identical to that of the DU3 transgression, both were larger than the DU7 transgression, and the DU1 transgression was the weakest. The variation of transgression strength reflects the influence of global changes in sea level, tectonic subsidence, shell ridges, and sand dams. In the TZK9 core, we found evidence of seven sea-level high stands from the Early–Middle Pleistocene, and the first one caused by regional rapid subsidence and could be traced back to 0.83-0.84 Ma. The sea-level high stands and the age of the first one recorded above was different from other cores in eastern China, this was caused by the lack of absolute age control and the differences in paleotopography during this period. This study reconstructs sedimentary evolution, determines the transgression and its age, establishes the chronology since the Late Pliocene, and provides a scientific framework for further paleoenvironmental and tectonic studies. The results of this study highlight the important role that local tectonics and global sea level play in the sedimentary evolution and transgressions that have occurred in the western Subei Basin.

Temporal Distribution of Diagnostic Biofabrics in the Lower and Middle Ordovician in North China:Clues to the Geobiology of the Great Ordovician Biodiversification Event

The temporal distribution of the diagnostic biofabrics in the Lower and Middle Ordovician in North China distinctly illustrates that the sedimentary systems on the paleoplate have been changed markedly as consequences of the Great Ordovician Biodiversification Event （GOBE）. The pre-GOBE sedimentary systems deposited in Tremadoc display widespread microbialite and flat-pebble conglomerates, and a less extent of bioturbation. Through the transitional period of early Floian, the sedimentary systems in the rest of the Early and Mid- Ordovician change to GOBE type and are characterized by intensive bioturbation and vanishing flat-pebble conglomerates and subtidal microbial sediments. The irreversible changes in sedimentary systems in North China are linked to the GOBE, which conduced the increase in infaunal tiering, the expansion of infaunal ecospace, and the appearance of new burrowers related to the development of the Paleozoic Evolutionary Fauna during the Ordovician biodiversification. Thus, changes in sedimentary systems during the pivotal period of the GOBE were consequences of a steep diversification of benthic faunas rather than the GOBE＇s environmental background.

Permian Fusuline Fauna from the Lower Part of the Lugu Formation in the Central Qiangtang Block and its Geological Implications

A Kubergandian （Kungurian） fusuline fauna from the lower part of the Lugu Formation in the Cuozheqiangma area,central Qiangtang Block is described.This fusuline fauna belongs to the Southern Transitional Zone in palaeobiogeography,and is characterised by the presence of the distinctive bi-temperate genus Monodiexodina and many genera common in lower latitude Tethyan areas such as Parafusulina and Pseudodoliolina.The occurrence of Monodiexodina in the fauna confirms that the seamount-type carbonates of the Lugu Formation did not originate from the Palaeotethys Ocean,but rather from a branch of the Neotethys Ocean after the rifting of the Qiangtang Block from the Tethys Himalaya area in the Artinskian.

Fossil charcoal from the Middle Jurassic of the Ordos Basin,China and its paleoatmospheric implications

The Yah＇an Formation of the Ordos Basin is a sequence of four members, consisting of si- liciclastic sediments deposited in alluvial, lacustrine and mire settings during the Middle Jurassic. Samples collected from Members Two and Four contain abundant blackened plant material identified through standard analytical techniques as fusain （fossil charcoal）. The occurrence of fusain in fluvial sandstones at multiple horizons in the outcrops, combined with the previously reported high concentra- tion of inertinite in the coals of Member One, indicates that paleowildfire was a common occurrence in the Ordos Basin during Yan＇an deposition. Sedimentary evidence from Yan＇an outcrops suggests that the paleoclimate was seasonal during deposition of Members Two through Four, which may have contributed to the wildfire frequency. The presence of fusain in the Yah＇an Formation indicates that atmospheric oxygen levels were clearly above the minimum required for sustained combustion during the Middle Jurassic. This conclusion contradicts previous geochemical models for paleoatmospheric composition, but supports more recent studies.

The Global boundary Stratotype Section and Point （GSSP） of the Drumian Stage （Cambrian） in the Drum Mountains, Utah, USA

The Global boundary Stratotype Section and Point （GSSP） for the base of the Drumian Stage （Cambrian Series 3） is defined at the base of a limestone （calcisiltite） layer 62 m above the base of the Wheeler Formation in the Stratotype Ridge section, Drum Mountains, Utah, USA. The GSSP level contains the lowest occurrence of the cosmopolitan agnostoid trilobite Ptychagnostus atavus （base of the P. atavus Zone）. Secondary global markers near the base of the stage include the DICE negative δ^13C excursion, the onset of a long monotonic ^87Sr/^86Sr isotopic shift, and the transgressive phase of a eustatic event. Faunal turnovers close to the base of the Drumian Stage are recognized as the base of the Bolaspidella Zone （polymerid trilobites） in Laurentia, the historic base of the Floran Stage in Australia, the base of the Dorypyge richthofeni Zone （polymerid trilobites） in South China, and the base of the Gapparodus bisulcatus-Westergaardodina brevidens Assemblage-zone （conodonts） in Baltica and South China. The last occurrence of the cosmopolitan trilobite Ptychagnostus gibbus occurs in the lower part of the Drumian Stage, and the base of the Hydrocephalus hicksii Zone （polymerid trilobites） as used in Siberia and Baltica occurs near the base of the stage.

Palynology of Yanchang Formation of Middle and Late Triassic in Eastern Gansu Province and Its Paleoclimatic Significance

Xifeng （西峰） oilfield was recently found in the southwest of the Ordos basin. The oil source rocks are the Chang 7 Section of Yanchang （延长） Formation. In order to study the paleoclimate that controlled the formation of source rocks, a systemically palynological research on related beds in Yanchang Formation has been carried out. The core samples were analyzed with classical palynological techniques and the organic-walled sporomorphs from these samples were observed, identified and photographed under a light microscopy and a fluorescence microscopy. Abundant sporopollen were found in drilling cores from Chang 8 and Chang 7 sections, and two assemblages were distinguished： the Aratisporites-Punctatisporites assemblage and the Asseretospora-Walchiites assemblage. Their characteristics are similar to those of the assemblage of Tongchuan （铜川 ） Formation and the assemblage of Yanchang Formation in southeast Ordos basin, respectively. Their geological times are Ladinian of late Middle Triassic and Carnian of early Late Triassic, respectively. The correlation of palynoflora with their parent plants suggests the paleoclimate of eastern Gansu （甘肃） Province in the Middle and Late Triassic was warm and rainy with prosperous vegetation. The palynoflora indicated the area was in a temperate to subtropical zone then. Both the ecological types and differentiation degree curves of sporopollen indicated the period during Chang 8 and Chang 7 sections was warm and wet, and the phase accorded with large-scale lake transgression in Chang 8 Section and the largest lake area in Chang 7 Section. North China in Middle and Late Triassic was located in a warm and rainy, temperate and subtropi- cal zone. The palynofloras in Chang 8 and Chang 7 sections have the characteristics of North China flora, however they also indicate wetter and warmer climate due to their proximity to the large lakes. The period of Chang 8 to Chang 7 sections is the climax of the expansion of the lake, and the bloom of fresh algae during the period, which helped form the high-quality source rocks in Chang 7 Section.

Sedimentary microtopography in sequence stratigraphic framework of Upper Ordovician and its control over penecontemporaneous karstification,No.I slope break,Tazhong,Tarim block

In order to reveal the relationship between the penecontemporaneous karstification and sedimentary microtopography in sequence stratigraphy,the sequence stratigraphic framework of Lianglitage formation in Upper Ordovician is studied according to the well drilling,logging,geophysical data,detailed observations of core and the paleontology.The Lianglitage formation belongs to the sequence Ⅳ of Ordovician.The second member of Lianglitage formation is prograde sedimentation in highstand systems tract,and is favorable for developing reef flat.The development scale and thickness of reef flat are controlled by the variation of secondary sea level.The types and characteristics of karst in the highstand systems tract show that the late highstand systems tract is dissolved and cemented by the meteoric fresh water and mixed water.Penecontemporaneous karstification is developed at the top of parasequence and high place of geomorphology.Atmospheric diagenetic lens is formed.The developing regulations and controlling factors of penecontemporaneous karstification can provide new clues to the prediction and exploration of favorable reservoir in this area.

α-and β-diversity Change of Late Ordovician Hirnantia Fauna of Changning,Sichuan,Southwest China

A continuous Ordovician-Silurian boundary section from the upper Wufeng Formation through the Kuanyinchiao Formation to the lower Lungmachi Formation has been carefully measured and collected at Shuanghe of Changning, southern Sichuan Province. For the first time, the temporal changes of α- and β-diversities of the Hirnantia fauna have been discussed in great detail. The general trend of brachiopod diversity change, increasing upward, is consistent with the regional trend of the Yangtze Platform, which had been controlled by both intrinsic and extrinsic factors. However, the sudden drop of diversity for a short period in the upper Kuanyinchiao Formation might have been controlled by environmental factors rather than normal faunal turnover. Synecological analysis using numerical methods recognizes two brachiopod-dominated associations of the Hirnantia fauna, the Dalmanella-Kinnella Association and the Mirorthis Association, both living in an offshore, deeper water environment corresponding to BA3-upper BA4, particularly lower BA3.

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.