New Data of Phosphatized Acritarchs from the Ediacaran Doushantuo Formation at Weng'an,Guizhou Province,Southwest China

Abundant phosphatized acritarchs are preserved in the late Precambrian （Ediacaran） Doushantuo Formation at Weng＇an, Guizhou Province, southwest China. Most of them are large with various spinous ornaments and multilayered outer walls. The general characters of these fossils are quite similar to those found from the homochronous deposits of the Yangtze Gorges, southern China. Therefore the Doushantuo Formation in the Weng＇an area can be correlated directly with the Doushantuo Formation of the Yangtze Gorges. Four species in four genera, including two new genera, two new species and one uncertain species are systematically described for the first time from the studied locality. The taxa are Bacatisphaera baokangensis Zhou, Brasier et Xue, 2001, Taeniosphaera doushantuoensis gen. et sp. nov., Rugospinasphaera speciosa gen. et sp. nov. and Meghystichosphaeridium sp. The new data enriches the famous Weng＇an biota, especially the marine microplankton flora in the Ediacaran Doushantuo Formation.

The Early Evolution of the Acanthomorphic Acritarchs in China and Their Biostratigraphical Implication

On the basis of a study of the acanthomorphic acritarchs discovered in the Late Proterozoicto Early Cambrian Meishucunian Stage in different regions of China, especially in southernShaanxi and the Yangtze Platform, coupled with a study of the assemblages, morphological cor-relation, microstructure, and evolutional relations of the acanthorphic acritarchs, as well as awide correlation with those found in different regions of the world, the authors discuss the earlyevolutionary stages of the acanthomorphs, features of their assemblages in various stages, theirbiostratigraphical significance, and their evolutionary trend in China.

Fluorescence intensity studies of Triassic acritarchs from the Yanchang Formation in Ordos basin,northwestern China

Fluorescence properties of Early Cambrian acri-tarchs were investigated using Leica das Mikroskop(DM)microscopy with a mercury lamp.Well-preserved autoflures-cence properties show a correlation between acritarchs morphology and the intensity of emitted fluorescence.In accordance with the fluorescence intensity of organic cell walls,two groups of microfossils were distinguished.Results of observation in this study,which are consistent with those of the previous foreign studies,are in good agreement with regular difference in autofluorescence intensity among paly-nomorphs reported by McPhilemy(1998).Spores and algae,including Botryococcus,have very bright fluorescence while acritarchs often show less intense fluorescence.Dark brown microfossils have been reworked,and have little or no fluorescence.

Depth zonation of Arenigian acritarchs in South China

STAPLIN revealed that palaeoenvironment changes seem to control acritarch distribution patterns. However, scientists have been puzzled by the fact that characteristic offshore acritarchs occur with nearshore ones. This note demonstrates depth zonation of Arenigian acritarchs in South China and reveals the variation of water depth in South China during the Arenig Age.

POST-BURIAL CONTRACTION CRACKS IN PRECAMBRIAN ACRITARCHS

Recently, we delved into Precambrian shale-facies microfossils of China by observation from petrographic thin sections. After having examined a large number of thin sections cut parallel to lamination under the light microscope, we discovered an interesting phenomenon, acritarchs with post-burial contraction cracks.

Organic-walled Microfossils from the Early Middle Cambrian sediments of the Holy Cross Mountains,Poland：Possible Implications for Sedimentary Environment in the SE Margin of the Baltica

An association of organic-walled microfossils consisting of filamentous cyanobacteria, algal coenobia and acanthomorphic acritarch have been documented from non-calcareous claystones and mudstones of the Pepper Mountains Shale Formation（PMSF）, located in its stratotype area in the Pepper Mountains, which are part of the Holy Cross Mountains in Poland. These sediments represent the oldest strata of the ？ysogóry Unit, deposited on the edge of the East European Craton（Baltica）. Non-branched, ribbon-like and thread-like cyanobacteria trichomes exhibit morphological similarities to families Nostocaceae and Oscillatoriaceae. Cells assembled in rounded to irregular clusters of monospecific agglomerations represent multicellular algal coenobia, attributed to the family Scenedesmaceae. The co-occurrence of acritarchs belonging to species as Eliasum llaniscum, Cristallinium ovillense and Estiastra minima indicates that the studied material corresponds to the lower Middle Cambrian. Deposition of the PMSF took place in shallow marine environment, influenced by periodical freshwater inputs. The varying degree of coloration of organic-walled microfossils is interpreted in this study as factor indication of possible different source of their derivation. Dark brown walls of cells assembled in algal coenobia might have sustained previous humification in humid, terrestrial environments, which preceded their river transport into the sea together with nutrients, causing occasional blooms of cyanobacteria in the coastal environment and the final deposition of both groups of organisms in marine deposits.

Late Silurian to Early Devonian Palynomorphs from Qujing,Yunnan,Southwest China

Well-preserved and diversified spores,cryptospores,and acritarchs have been recorded from a relatively continuous sequence that encompasses the Silurian-Devonian boundary in Qujing, Yunnan,southwest China.Four spore assemblage zones from Late Silurian to Early Devonian in age are proposed based on the first appearance datum（FAD）of characteristic spore species.In ascending stratigraphic order,they are Ambitisporites dilutus-Apiculiretusispora synorea（DS;Late Ludfordian to Early Pridoli）,Synorisporites verrucatus-Apiculiretusispora plicata（VP;Pridoli）,Apiculiretusispora minuta-Leiotriletes ornatus（MO;Lochkovian）,and Verrucosisporites polygonalis-Dibolisporites wetteldorfensis（PW;Pragian）.The acritarch assemblage from the upper part of the Yulongsi Formation,the Xiaxishancun Formation,and the lower-middle parts of the Xitun Formation indicates an age of Late Silurian.Based on palynological evidence,the upper part of the Yulongsi Formation is considered Late Ludfordian to Early Pridoli in age;the Xiaxishancun Formation is believed to be Pridoli in age;the Xitun Formation is considered Late Pridoli to Early Lochkovian in age;the Guijiatun Formation is considered Lochkovian in age;and the Xujiachong Formation is Late Lochkovian to Pragian in age.The Silurian-Devonian boundary is recognized between the VP and the MO spore biozones,and occurs within the middle part of the Xitun Formation.

An Early Paleozoic Tectonic Mélange at the Western Margin of West Cathaysia: Constraints from Organic-walled Microfossils

The Jiangshan-Shaoxing-Pingxiang Fault(JSP Fault) is traditionally considered as the boundary between the Yangtze and Cathaysia blocks in South China. Whether the previously defined Shenshan and Kuli formations located along the JSP fault and near the Xinyu City, Jiangxi Province, are continuous strata or parts of a tectonic mélange is important for understanding the geological history of South China. A carbonaceous phyllite from the area, previously considered as part of the Neoproterozoic Shenshan and Kuli formations, is analyzed palynologically in this study. The AsteridiumComasphaeridium acritarch assemblage found in the slate can be correlated with the basal Cambrian AsteridiumHeliosphaeridium-Comasphaeridium(AHC) acritarch assemblage in Tarim and the Yangtze Block. The early Cambrian biostratigraphical age assignment for the carbonaceous phyllite indicates the presence of both Neoproterozoic and Cambrian rocks in the sedimentary package, and supports that the package is a part of tectonic mélange rather than a continuous Neoproterozoic strata. The Cambrian slate is the youngest known lithology in the mélange at present.

The fungal and acritarch events as time markers for the latest Permian mass extinction:An update

The latest Permian extinction(252 Myr ago)was the most severe in the geologic record.On land,widespread Late Permian gymnosperm/seed-fern dominated forests appear to have suffered rapid and almost complete destruction,as evidenced by increased soil erosion and changes in fluvial style in deforested areas,signs of wildfires,replacement of trees by lower plants,and almost complete loss of peat-forming and fire-susceptible vegetation.Permian-Triassic boundary strata at many sites show two widespread palynological events in the wake of the forest destruction:The fungal event,evidenced by a thin zone with>95%fungal cells(Reduviasporonites)and woody debris,found in terrestrial and marine sediments,and the acritarch event,marked by the sudden flood of unusual phytoplankton in the marine realm.These two events represent the global temporary explosive spread of stress-tolerant and opportunistic organisms on land and in the sea just after the latest Permian disaster.They represent unique events,and thus they can provide a time marker in correlating latest Permian marine and terrestrial sequences.

Paleoproductivity and Paleoredox Condition of the Huai Hin Lat Formation in Northeastern Thailand

The petroleum exploration has been conducted in the Khorat Plateau since 1962 and two gas fields have been discovered and commercially produced. The lacustrine facies of the Huai Hin Lat Formation is believed to be one of the main source rocks of the gas. Therefore, investigation and analysis of the Huai Hin Lat shale for understanding the paleoenvironment and petroleum source rock are carried out in this study. Petrographical study and geochemical analysis of shale samples were performed to explain the paleoproductivity and past redox condition. The palynofacies assemblage comprises abundant AOM, acritarchs, phytoclasts, and very small amount of spores and pollen. Geochemical analysis was used to determine the total organic carbon（TOC） and the concentration of major, trace, and rare earth elements. The paleoproductivity proxies are composed of palynofacies, TOC, excess SiO2, Ba/Al, and P/Al. They reflect a high paleoproductivity except the middle of the lower part（bed 3） and the lower bed 13 of the upper part. Bed 3 shows the highest peak of TOC and the lower bed 13 exhibits a relatively lower TOC, which can be explained by the excellent and the poorer preservation condition, respectively. The paleoredox proxies consist of U/Th, V/Cr, Ni Co,（Cu＋Mo）/Zn, Ni/V, and Ce anomaly. They are used to establish the depositional environments, to characterize the organic matter content, and to assess the source rock potential. They reflect many high peaks and predominantly high values of paleoredox proxies except the middle part and the lower bed（lower bed 13） of the upper part. They indicate that the section was mainly under anoxic or reducing condition, which is supported by the high Ce/Ce＊（〉0.8） and V/Cr（〉2.0） values. The middle of the lower part（bed 3） shows lower productivity but it contains the highest peak of TOC, which is conformed to be the excellent preservation of organic matters in the strong reducing condition. The middle part, which shows high productivity, contains relatively lower TOC as it possesses a less reducing condition compared to the more reducing intervals. The lower bed 13 of the upper part shows a less reducing condition and a lower TOC, which conforms to a lower productivity. The organic matters of the Huai Hin Lat Formation consist mainly of AOM and acritarchs and possess good to excellent TOC（2%–7%）. They belong mainly to type I and type II kerogens with some mixture of type III as indicated by the presence of phytoclasts, spores, and pollen. The organic matters of the Huai Hin Lat Formation, based on the kerogen type and the thermal history, have already generated significant amount of oil and some gas to the Sap Phlu Basin.

The microfossils in phosphate deposit in Doushantuo stage, Sinian System, Weng' an, Guizhou Province

The aim of this study is to discuss the microfossils in phosphate deposit in the Doushantuo stage, Sinian System, weng’an, Guizhou Province. Based on the detailed observation in morphology and microstructures, it is considered that those acritarchs with interior spicules probably belong to sponge animals. However, some explanations for a part of soft-tissue are stili contrioversial. The reliable conciusion stili needs more evidence to study. The scientific significance of this study and the key questions for further studies are suggested here.

Early–Middle Cambrian Palynomorph Microfossils and Related Geochemical Events in South China

The earliest Cambrian acritarch ＇Asteridium-Heliosphaeridium-Comasphaeridium＇ assemblage and the Early Cambrian（＇Chiungchussuan＇） acritarch ＇Skiagia ornate-Fimbriaglomerella membranacea＇ assemblage in South China can be correlated with assemblages from synchronous strata elsewhere in the world. Recent geochemical study and biomarker evidence further confirm a biostratigraphic change between Cambrian Series 2 and Series 3 and support the recognition of a major geological and biotic event during this time interval.

Development background of Mesozoic high-quality source rocks: Evidence from microfossils in North Carnarvon Basin, Australia

Based on numerous microfossils in Mesozoic of North Carnarvon Basin in Australia,the Mesozoic paleoclimate and paleoenvironment were analyzed,the paleogeographic background and development model of Mesozoic high-quality source rocks were investigated and discussed.Variation of microfossil species and their relative contents in Mesozoic different intervals indicates changes of paleoclimate and paleoenvironment.The paleoclimate shows a cycle variation of aridehumidearidehumid,the regression occurred in the Early TriassiceLate Triassic and the transgression occurred in the Late TriassiceLate Cretaceous.Four sedimentary facieses including delta facies,littoral facies,restricted sea facies and open sea facies were developed in the Mesozoic.The open sea was mainly developed in the Early Triassic,the delta was distributed in the MiddleeLate Triassic,the restricted sea was especially well developed in the Jurassic,and the restricted sea and open sea were mainly distributed in the Cretaceous.Characteristics of microfossil assemblage in these four sedimentary facies are dramatically different.From the delta facies,littoral facies,restricted sea facies to open sea facies,content of pollen gradually decreases,but content of the dinoflagellate+acritarch gradually increases.The delta facies and littoral facies are dominated by the pollen.In the restricted sea facies,content of the pollen is equivalent to that of the dinoflagellate+acritarch.The open sea facies is dominated by the dinoflagellate and acritarch.Supply of sediment and formation of organic matter are influenced by the paleoclimate and paleoenvironment,and type of organic matter is controlled by the microfossil assemblage.Based on the palaeogeographic background,paleoclimatic condition and microfossil assemblage,two developmental models of the Mesozoic source rocks such as the development model of terrestrial organic matter under the background of large delta and the development model of mixed organic matter under the background of the restricted sea,were proposed.

Discovery of Ordovician acri-tarchs in Buqingshan ophio-lite complex, East Kunlun Mountains and its significance

This note reports the first discovery of Middle-Late Ordovician acritarchs from the Buqingshan ophio-lite complex of the southern ophiolite zone of East Kunlun. The acritarch assemblage is dominated with acanthomor-phids (approx. 32%) and sphaeromorphds (approx. 63%) and contains more characteristic forms, such as Lophos-phaeridium edenense, L. varum, Nothooidium sp.,? Bued-ingiisphaaeridium sp., Visbysphaera sp., Strophomorpha sp., etc. In addition, some tube-like fragments and tetrads, which are recognized as affinity to terrestrial plants and usual occurrence in Late Ordovician-Early Silurian strata, are preserved together with acritarchs. All the known fossil evi-dence indicates that the strata should be Middle-Late Ordo-vician in age. It not only provides paleontological proof for the existence of Ordovician ophiolite, but also challenges the usual ideas on strata composition of the studied area and the southern ophiolite zone of East Kunlun, and the models on tectonic framework and evolution of