Acta Micropalaeontologica Sinica

PALEOGENE CALCAREOUS NANNOFOSSIL BIOSTRATIGRAPHY, RESPONSES TO MAJOR GEOLOGICAL EVENTS, AND APPLICATIONS IN THE WESTERN TARIM BASIN

The Paleogene signifies a pivotal transitional phase in Earth's history from a "greenhouse" to an "icehouse" state. Due to the exceptional preservation of calcareous nannofossil in marine settings, they serve as ideal proxies for high-resolution biostratigraphic studies and the investigation of major geological events. Nonetheless, a systematic synthesis of detailed Paleogene calcareous nannofossil biostratigraphy and their applications in studying major geological events has still not been made to date. The present work offers a comprehensive review of Paleogene calcareous nannofossil biostratigraphy and their application in "Golden Spike"(Global Boundary Stratotype Section and Point, GSSP) studies and major geological event investigations. The study on t he western Tarim Basin highlights the significant importance of calcareous nannofossils in determining stratigraphic ages and investigating major geological events. Calcareous nannofossils experienced a rapid evolutionary radiation throughout the Paleogene and are categorized into 25 biozones(NP1–NP25). These microfossils play a pivotal role in defining Paleogene GSSPs: the second radiation event of the genus Fasciculithus and the First Appearance Datum(FAD) of Blackites inflatus, respectively, serve as the principal markers for the GSSPs of the Selandian and Lutetian stage bases. Furthermore, calcareous nannofossils serve as significant auxiliary fossils for the six recognized Paleogene GSSPs globally. Significant geological events occurred during the Paleogene, such as the Paleocene-Eocene Thermal Maximum(PETM), the Eocene-Oligocene Glaciation(Oi-1 event), and the Oligocene-Miocene Cooling Event(Mi-1 event). Calcareous nannofossils underwent considerable evolutionary turnover in response to these event s, exhibiting unique biotic signatures associated with each particular event. The western Tarim Basin features the well-developed Paleogene marine sediments with abundant and well-preserved calcareous nannofossils. Use of these microfossils facilitated acc urate dating of key stratigraphic intervals, allowing the first identification of exact PETM records in this region, and precisely constrains the timing of the Tethys regression event. This study demonstrates that calcareous nannofossils provide significant potential for correlating global stratigraphic standards and resolving regional geological problems. Future research should enhance the use of calcareous nannofossil in studies of relevant marine strata and geological events in China. This would improve the accuracy of stratigraphic correlation and refine the interpretation of paleoenvironments and paleoclimate events.

International Symposium on the Tethys Evolution and Biotic and Environmental Responses was held successfully in Beijing

THE MAXIMUM DIAGENETIC TEMPERATURE OF FOSSILS FROM THE ORDOVICIAN XILIANGSI FORMATION IN THE SOUTHERN SHAANXI: A RAMAN SPECTROSCOPY APPROACH

Diagenesis plays a critical role in determining fossil occurrence patterns, mineralogical composition, and preservation fidelity. Abundant three-dimensionally preserved fossils(e.g., antipatharians, graptolites and conodonts) have recently been recovered from the Darriwilian(Middle Ordovician) calcareous nodules of the Xiliangsi Formation at the Fanjiagou Section, Ningqiang, southern Shaanxi, yet the mineralization pathways and subsequent diagenetic overprints remain virtually unexplored. Here we present a diagenetic investigation of organic-carbon-rich antipatharians, graptolites, and conodonts from this locality. Combined analyses of SEM-EDS and Raman spectroscopy reveal that, apart from minor Si, Al, and Fe, the originally protein-and chitin-dominated antipatharians are preserved primarily as organic carbon, with incipient secondary phosphatization; graptolites exhibit an exclusively organic-carbon preservation devoid of any phosphatization signal; whereas conodonts display a dominant organic-carbon phase accompanied by pervasive secondary phosphate precipitation. The fossil assemblage of the Xiliangsi nodules thus resembles Cambrian Orsten-type preservation in the taphonomic style, but its mineralogical composition is taxon-dependent. Application of Raman geothermometry indicates a maximum diagenetic temperature of 200±20℃ for the Xiliangsi fossils —substantially lower than other known Cambrian Konservat-Lagerstätten(236–308℃). We propose that the variety of mineral composition among different taxa from the Xiliangsi Formation derives not only from the original skeletal composition, depositional facies, and early diagenetic fluid-sediment interactions, but also from the low-thermalmaturity evolution of organic matter during subsequent diagenesis.

LATEST DEVONIAN-EARLY CARBONIFEROUS OSTRACODS IN DUSHAN, GUIZHOU PROVINCE

Ostracods of the Latest Devonian-Early Carboniferous(Mississippian) are reported for the first time from the Qilinzhai section in Dushan, Guizhou, South China. A total of 29 species belonging to 16 genera in 6 superfamilies, including one new species(i.e., Bairdia qilinzhaiensis sp. nov.) are identified and figured from the Tangbagou Formation in the Qilinzhai Section. The ostracod assemblage is dominated by the Order Podocopida(22 species belonging to 10 genera), with fewer Orders Palaeocopida(4 species belonging to 3 genera) and Platycopida(3 species belonging to 3 genera). Based on the characteristics of the ostracod assemblage, combined with previous studies on conodonts and carbon isotopes, the age of the Tangbagou Formation is assigned to the Late st Devonian to the Early Carboniferous(Mississippian), and the Devonian–Carboniferous boundary located approximately at 13 meters in the lower limestone–mudstone Member of the Tangbagou Formation. The ecological assemblage of ostracods belongs to the Smooth–podocopid association(i.e., Eifelian Mega–Assemblage), which implies an offshore environment for the Tangbagou Formation. The ostracod assemblage of the Tangbagou Formation shows similarities with contemporaneous assemblages from Russia and Western Europe, suggesting that the transgression beginning in the Early Carboniferous(Tournaisian) facilitated the close biogeographic connections between the ostracod faunas of South China and those of the Euramerican regions. The ostracod fauna near the Devonian–Carboniferous boundary in the Qilinzhai section may have been influenced by the Hangenberg Event, exhibiting a low abundance and a rapid recovery pattern.

EVOLUTION OF THE PALEOGENE HYDROCARBON SOURCE ROCKS IN THE QINNAN SAG AND ITS RESPONSE TO PALEOCLIMATIC CHANGES

In order to determine the hydrocarbon potential and the main controlling factors of source rocks of the Qinnan Sag, the geochemical and paleontological characteristics of the drilled wells are analyzed. It is clear that three sets of effective source rocks are developed in the study area. They are the 3rd Member of Dongying Formation, the 1st Member and the 3rd Member of Shahejie Formation. The quality of source rock from the 3rd member of Shahejie Formation is the highest, followed by the 1st Member, while the 3rd Member of Dongying Formation source rocks are of the lowest quality. The origin of the source rock is analyzed through the recovery of paleoclimate analysis. T he organic matter of hydrocarbon generation in the 3rd member of Shahejie Formation source rocks is primarily composed of amorphous materials, with dinoflagellates playing a significant role. The 1st Member source rocks consist of a combination of aquatic amorphous materials and sporinite, while 3rd Member of Dongying Formation source rocks are dominated by terrestrial plant components, with sporopollen facies comprising terrestrial amorphous materials, structured organic matter, and some sporinite. The paleoclimate from the bottom to the top shows a gradual decrease in temperature and frequent fluctuations in humidity. The study confirms that paleoclimate has an important influence on the enrichment of organic matter. The warm and humid climate is conducive to the development of higher plants, and the content of terrestrial organic matter has risen sharply in the source rock. The subtropical humid climate is conducive to the prosperity of plankton algae, while the arid climate has a significant inhibitory effect on the distribution of plankton algae.

SPOROPOLLEN ASSEMBLAGE OF THE ZHILUO FORMATION IN THE NINGDONG AREA， ORDOS BASIN AND ITS PALAEOCLIMATIC IMPLICATIONS

The Middle Jurassic Zhiluo Formation in the Ningdong area on the western margin of the Ordos Basin is an important host horizon for sandstone-type uranium deposits. However， palynological evidences for paleoclimate in this region remains scarce. To clarify the paleovegetation and paleoclimate characteristics during the deposition of the Zhiluo Formation， this study conducted systematic palynological analysis based on drill core samples from the Shicao Village in Ningdong area. The results show that the sporopollen assemblage of the studied interval is characterized by the Cyathidites minor- Osmundacidites- Disacciatrileti- Cycadopites assemblage. Cyatheaceae spores dominate the assemblage， followed by bisaccate conifer pollen. Monosulcate and primitive sulcate pollen are relatively well developed， while Taxodiaceae， Araucariaceae and Osmundaceae spores are present in certain proportions， and Cheirolepidiaceae pollen occurs continuously. The assemblage indicates a late Middle Jurassic age. The reconstruction of paleoclimate and vegetation shows that the climate changed from warm and humid to semi-arid and arid during the deposition of Zhiluo Formation. The specific performance is as follows: in the early stage， the wet Cyatheaceae vegetation flourished， while in the late stage， the xerophytic components increased， which clearly recorded the process of gradual aridification of the climate. These results provide direct palynological evidence for a deeper understanding of the late Middle Jurassic paleoenvironmental evolution and the uranium metallogenic setting on the western margin of the Ordos Basin.

THE PALYNOLOGICAL ASSEMBLAGES OF THE LATE TRIASSIC IN WELL SY-A IN THE SANTANGHU BASIN， XINJIANG

The Santanghu Basin is rich in oil and gas resources. With the development of oil shale and new blocks， Preexploration Well SY - A， has been deployed in this basin. To determine whether this exploration well has drilled into the Triassic strata and whether high-quality source rocks have developed， palynological fossils analysis was carried out in the mud shale section， and abundant Triassic palynological fossils were discovered. According to the types and content changes of palynomorphs， two assemblages were divided. They are Assemblage I: Aratrisporites-Chasmatosporites-Apiculatisporis Assemblage and Assemblage II: Concavisporites-Aratrisporites-Osmundacidites Assemblage. The geological ages and distributions of the main taxa in the assemblages were discussed. By comparing with relevant palynological assemblages， Assemblage I was assigned to the Late Triassic Huangshanjie Formation， and Assemblage II was assigned to the Late Triassic Haojiagou Formation. This provides strong evidence for the determination of Triassic strata in this area. From the vegetation ecological characteristics reflected by palynological fossils， it is inferred that this period had a relatively warm and humid subtropical climate， and the period of the Haojiagou Formation was hotter and more humid than that of the Huangshanjie Formation.

EARLY LATE CRETACEOUS PALYNOLOGICAL ASSEMBLAGES FROM THE 3^TH MEMBER OF THE YETANG FORMATION IN XINGNING AREA， GUANGDONG AND THEIR PALAEOCLIMATIC SIGNIFICANCE

The Late Cretaceous represents a typical greenhouse period in geological history， and its climatic patterns provide crucial insights for understanding modern global climate change. The continental basin systems in southern China preserve a record of typical arid climate during this interval， whose formation may be closely related to the palaeo-atmospheric circulation pattern， and the presence of coastal mountain ranges along the western margin of the Palaeo-Pacific. However， robust palaeontological and climatic evidence from this region has long been insufficient. This study focuses on the Yetang Formation in the Xingning Basin， eastern Guangdong Province. Our palynological analysis of its Third Member obtains a palynological assemblage dominated by Exesipollenites (53.0%–80.8%) and Cranwellia (up to 27.0%) of an early Late Cretaceous (late Turonian to Santonian) age. The overwhelming dominance of xerophytic and thermophilic gymnosperm pollen in the assemblage suggests a seasonal arid， tropical-subtropical desert shrubland vegetation. This result supports the existence of a wide， persistent arid belt in eastern China during the early Late Cretaceous， which may result from a combined effect of the planetary atmospheric circulation and the rain shadow of the coastal mountain range. This climatic condition promoted the development of enclosed or semi-enclosed salt lakes， which are particularly favorable for the enrichment of lithium.

POLLEN MORPHOLOGY AND ECOLOGICAL INDICATIONS OF 16 RARE PINACEAE SPECIES(EIGHT GENERA) IN CHINA

This study aims to systematically investigate the pollen morphological characteristics of 16 rare plant species from eight genera of Pinaceae in China， and to explore the adaptive relationship between these characteristics and the ecological environment. The findings are intended to provide a scientific basis for the taxonomic identification， conservation， and paleoenvironmental reconstruction of Pinaceae plants. Pollen samples were observed and measured at multiple scales using optical microscopy and scanning electron microscopy. Data were then analyzed in depth through correlation analysis and principal component analysis.The results are summarized as follows: (1) Based on the air sac structure， Pinaceae pollen can be classified into three distinct types: bisaccate (Abies， Picea， Pinus， Keteleeria， Cathaya， Pseudolarix)， perisaccate (Tsuga)， and non-saccate (Larix). Significant morphological differences were observed among genera， while morphology within genera was relatively consistent， though variations in size， surface ornamentation， and air sac development were noted. (2) Measurement data revealed significant differences in pollen size among genera. Keteleeria pollen was the largest (total length of Keteleeria cyclolepis: 145.44 μm)， whereas Cathaya pollen was the smallest (65.07 μm). The air sacs of Picea were the most developed (air sac length of Picea jezoensis: 94.96 μm)， and the exine of Keteleeria was the thickest (>2.0 μm). (3) Statistical analysis indicated that the overall dimensions of bisaccate pollen (PL2， PW2) were strongly positively correlated with air sac development (AL， AW) (p<0.01)， which together represented the main axes of morphological differentiation. Furrow width (FW) showed a significant negative correlation with air sac length (AL) (r=-0.560， p<0.05)， suggesting a functional trade-off in morphology. (4)Pollen morphological characteristics exhibited a clear synergistic relationship of "morphology–function–environment" with the ecological habits and distribution of the plants.This study provides detailed morphological data on Pinaceae pollen， offering not only key reference information for species identification and conservation， but also a reliable modern analog for the identification of fossil pollen in Quaternary strata.

NEW CHANCELLORIID FOSSIL MATERIALS FROM THE CAMBRIAN XINJI FORMATION ON THE SOUTHWESTERN MARGIN OF THE NORTH CHINA BLOCK

Chancelloriid fossils， which proliferated in the aftermath of the Cambrian Explosion， are currently regarded as a problematic group of basal epitheliozoans with a debated phylogenetic position within the stem group of Eumetazoa. The basal Cambrian Xinji Formation on the North China Platform yields abundant small shelly fossils (SSFs). Here， we present a systematic study of chancellorids based on new materials recovered through acid-processing of rocks collected from the Dazhuang section in Shaanxi Province and the Guanyintang in Henan Provinces. Three genera and four species are identified， belonging to the characteristic chancellorid genera: Chancelloria Walcott， 1920， Allomnia Doré and Reid， 1965， and Archiasterella Sdzuy， 1969. For the first time， at least five distinct types of basal ornamentation on Chancelloria sclerites are systematically recognized， revealing previously overlooked micro-morphological disparity. Microfacies and elemental analyses suggest a high-energy shallow marine depositional setting， in which the robust Chancelloria-dominated assemblage indicates a coupling between sclerite morphology and environmental conditions. This study not only expands the paleogeographic distribution of chancelloroids on the North China Clock， but also provides key evidence for understanding their adaptive radiation and the complexity of early metazoan ecosystems during the early Cambrian.

ON CRETACEOUS PALEOCLIMATE IN THE SONGLIAO BASIN

ON THE MEANING OF PHYTOLITH AND ITS CLASSIFICATION IN GRAMINEAE

A new term is formerly put forward to unify the ever increasing difference in translations of “Opal phytolith” and “Silica bodies”, etc. in China. Much confusion exists in the classification and descriptive terminology of grass phytoliths. This paper introduces and summarizes the current phytolith classifications in Gramineae. A detailed comparison is made to show their difference and some possible correlations. It is anticipated that the unified glossary of terms, and standardisation of nomenclature in phytolith classification will greatly promote the development of phytolith research in various scopes.

THE LATE CRETACEOUS BIO EVOLUTION AND ANOXIC EVENTS IN THE ANCIENT LAKE IN THE SONGLIAO BASIN

CHARACTERISTICS AND AGE OF THE DINGQING OPHIOLITE IN XIZANG (TIBET) AND THEIR GEOLOGICAL SIGNIFICANCE

The sequences of the Dingqing Ophiolite in East Tibet are complete. Late Triassic radiolarians were discovered from the siliceous rocks of abyssal sediments, consisting mainly of Capnuchosphaera theloides, C. triassica, Palaeosaturnalis triassicus, Pseudoheliodiscus latus, Xenorum flexum, Pseudostylosphaera gracilis, Veghicyclia austriaca, Perispongidium tethyus, Spongostylus tortilis, S. carnicus, Annulotriassocampe sulovensis, Canoptum triassicum, Poulpus piabyx, Xiphotheca karpenissionensis, Laxtorum(?) carnicum which are of Carnian age. Discovery of these radiolarians indicates that a comparatively mature ocean basin was developed during Triassic in the Dingqing belt and that the evidence was provided for the evolution of the Neo Tethys.

HIGH RESOLUTION SPOROPOLLEN RECORD AND ENVIRONMENTAL CHANGE SINCE HOLOCENE IN THE WULUNGU LAKE, XINJIANG

According to high resolution sporopollen analysis from a core of the Wulungu Lake, Xinjiang, we have discovered that the climate since Holocene in the research region can be divided into four stages. During about 9.99—7.72 cal. kaBP, climate was mild and dry. Stage of 7.72—3.62 cal. kaBP, climate gradually turned to warm and moderately dry condition from mild and moderately humid condition. In 3.62—1.24 cal. kaBP climate shifted from cool and dry condition into cool and moderately humid, and then to mild and humid condition. From 1.24 cal. kaBP to today, climate was generally mild and dry condition. During the four stages, some abrupt cooling events can be identified at time slices of 8.90, 8.35, 3.62? ?.80, 0.82—0.45 and 0.23 cal. kaBP. During about 9.99—7.72 cal. kaBP, sporopollen assemblage can only reflect aquatic vegetations around the Wulungu Lake which evolved from domination of Phragmites into aquatic flora dominated by Sparganium. Since 7.72 cal. kaBP, the assemblage can represent regional vegetation. Corresponding to climate, regional vegetation experienced several changes as following successionally: desert-steppe vegetation → desert vegetation → desert-steppe vegetation → steppe or desert vegetation → steppe vegetation → desert vegetation → desert-steppe vegetation.

REVIEWS AND PROSPECTIVES ON THE STUDIES OF BIOLOGICAL EVOLUTION

Evolution is the most charming and ever lasting phenomenon of life and nature. In this paper, we summarized the various evolutionary theories emerged in the history of science: Lamarkism, Darwinism, neo Darwinism, the synthetic theory of evolution, the neutral theory of molecular evolution, neo Catastrophism and the theory of punctuated equilibrium etc. We also briefly discussed the several important branches of biology and life science involved in the current studies of evolutionary biology, focusing on several issues alive and continually debated in the fields of evolutionary studies. Meanwhile, we present our perspectives of evolutionary biology and evolutionary theory in the 21st century: under the direction of philosophy and concrete theories of methods, the big comprehensiveness of evolutionary studies and a new synthesis of evolutionary theories will emerge in the near future as the development of life science and other natural sciences and the union of the ideas of genetics, developmental and evolutionary biology.

ON THE MEANING OF PHYTOLITH AND ITS CLASSIFICATION IN GRAMINEAE

A new term is formerly put forward to unify the ever increasing difference in translations of “Opal phytolith” and “Silica bodies”, etc. in China. Much confusion exists in the classification and descriptive terminology of grass phytoliths. This paper introduces and summarizes the current phytolith classifications in Gramineae. A detailed comparison is made to show their difference and some possible correlations. It is anticipated that the unified glossary of terms, and standardisation of nomenclature in phytolith classification will greatly promote the development of phytolith research in various scopes.

HOLOCENE BENTHIC FORAMINIFERA AND OSTRACODA FROM THE SHELF MUD AREA OF THE EAST CHINA SEA AND THEIR PALEOENVIRONMENTAL IMPLICATIONS

Core MD06-3040 was taken from the mud area off the Zhejiang-Fujian coast of the East China Sea(27°43.3663'N,121°46.8822'E,water depth 47 m,core length 19.36 m).A total of 257 samples were quantitatively analyzed for paleontological study of planktonic,benthic foramini-fera and ostracods as well as their paleoenvironmental implications.Holocene paleoenvironmental evolution since 10.6 cal.kaBP has been discussed by benthic foramini-feral and ostracod assemblages and some important ecological indicators(infaunal/epifaunal,inner-shelf/inner-middle shelf,warm-water species groups).Results show a rapid sea-level rise during the early Holocene from the inner inner-shelf(10.6—9.8 cal.kaBP),outer inner-shelf(9.8—7.8 cal.kaBP) to the middle shelf with the highest sea-level(7.8—3.4 cal.kaBP).The Taiwan Warm Current is suggested to be developed since 8.0 cal.kaBP and its derived upwelling appeared during the periods of 5.7—2.8 and 0.7—0 cal.kaBP respectively,resulting in the rapid mud depo-sition on the shelf of the East China Sea.The marked increase in abundance of planktonic foraminifera Globigerina bulloides is referred to the enhancement of the Zhejiang-Fujian Coast Current during 4.9—3.2 cal.kaBP.

ADVANCE IN PHYTOLITH MORPHOLOGY RESEARCH

Phytolith morphology provides the basis for palaeoenvironment reconstruction of phytoliths,which may affect the accuracy of its application.In the respect of maternal plants from which phytoliths derive,this paper summaries the distinctive phytolith types and phytolith assemblages and compares the subtle differences between same phytolith types in different plants representing 21 herbaceous plants and 20 woody plants.Summary of previous works and the latest research achievements on phytolith morphology study may be helpful for future study on the application of phytolith in classification of modern plant and reconstruction of ancient environment.

BIOLOGICAL ORIGIN OF EARLY PALAEOZOIC AND PRECAMBRIAN HYDROCARBON SOURCE ROCKS BASED ON C₂₇/C₂₉ STERANE RATIO AND ORGANIC CARBON ISOTOPE

The predominance of C_ 29 sterane in early Paleozoic and Precambrian rocks and crude oils is puzzling, because the predominance of C_ 29 sterane is often taken as the result of high terrestrial plant input. Based on mainly the previously published investigations on various algae pyrolytic products , we proposed that the predominance of C_ 29 sterane in early Paleozoic and Precambrian source rocks and crude oils may have come from planktonic green algae, and the different sedimentary environments can be distinguished through C_ 27/C_ 29 sterane ratios. The organic geochemistry results of Precambrian and early Cambrian black shales from South China support this conclusion. We also bring forward a new method to recognize the different biological source for C_ 29 sterane predominance using organic carbon isotope.