Microfossils, carbonate lysocline and compensation depth in surface sediments of the northeastern South China Sea

Based on the quantitative analyses of abundance of planktonic foraminifera, benthic foraminifera, calcareous nannofossils, the ratios of calcareous to siliceous microfossils, and the determination of carbonate contents in the surface sediments of the northeastern South China Sea, it has been found that the carbonate contents, the abundance of planktonic foraminifera and calcareous nannoplankton, and the ratio of calcareous microfossils decrease rapidly while the ratio of the benthic foraminifera to the total foraminiferal fauna, specific value of siliceous microfossils, and the percentage of the agglutinated tests in the benthic foraminiferal fauna increase with the water depth. The results indicate that the microfossils abundance and ratio, and the carbonate content are closely related to the carbonate lysocline and carbonate compensation depth (CCD) in the study area. In addition, the carbonate lysocline and the CCD are different between the southern and northern parts of the South China Sea. Both the lysocline and the CCD are deeper in the south with 2 600 and 3 600 m than in the north with 2 200 and 3 400 m, respectively.

Microfossils from the Chert in the Lower Cambrian Shuijingtuo Formation at Miaohe, Zigui, Hubei Province

This paper reports for the first time on the microfossils discovered in the black cherts of the basal part of the Lower Cambrian Shuijingtuo Formation at Miaohe village, Zigui County, Hubei Province, all of which were observed in thin sections. Nine genera, 9 species and 3 indeterminate species (including a new species) are described. According to these microfossils, the conclusion is made that the microfossil zone may be equivalent to the small shelly fossil assemblage zones 2—3 of the Meishucun stage. They have provided another important line of evidence for the correlation of the Sinian-Cambrian boundary strata with those of the adjacent areas.

滨海海底边界层对底栖微体化石仿真模拟的影响

计算流体力学CFD(computational fluid dynamics)近年来在古生物学研究中已有大量应用。该方法在研究生物化石的个体形态、器官功能,以及其与生存环境之间的关系方面具有重要意义。目前古生物领域的CFD仿真对象多为厘米级别体型的生物,而对于毫米级别大小的微体生物的仿真则相对较少。区别于厘米级别的宏体生物,底栖型微体生物的生活环境局限于海床上方垂直高度较小的区域,受海底黏性边界层低流速区域的影响更为明显,因而在设置这类化石仿真的水流环境时应当考虑对于边界层流域水体流速以及海床表面地理环境的还原。本文基于随机表面生成的方法,构建了不平坦的滨海海床表面模型,并模拟了水流在海底边界层附近受海床表面地形影响的流动状态;基于获得的仿真流速数据,我们仿真了寒武纪微型底栖刺细胞动物化石Quadrapyrgite在起伏的海床表面环境中四个不同位置的受水流阻力情况。仿真结果显示,近海床表面处的水体流动可形成明显的低流速区域,且低流速区域的厚度随着入口速度增大而变薄。在起伏表面的凹凸区域中,凸起地带的迎水面形成的低流速区域较薄,流速变化较快;而在凸起地带背水面以及凹陷地带形成的低流速区域较厚,流速较缓且易形成涡旋。流速的差异体现在不同位置的Quadrapyrgite的受阻力大小不同上,其差值可达数倍到数十倍。这种量级的受阻力差值可以在毫米级到厘米级尺度上塑造、影响底栖型生物的分布甚至其自身的摄食行为。本文的研究为CFD方法模拟底栖微型化石的生存环境提供了更加深入的思路和方法。

长江中游2个湖泊沉积物枝角类微化石密度的垂直变化

为了重现湖泊枝角类的群落演替历史,反映人类活动对湖泊生态的干扰强度,选择长江中游的龙感湖和武昌湖分别设置2个和1个采样点,每个样点采集2根沉积柱,鉴定沉积物中的枝角类卵鞍和象鼻溞属壳刺并计数,测定沉积物样品的总氮和总磷含量并鉴定沉积物年代,探究枝角类微化石组成、密度垂直变化及其人类活动的影响。结果显示,在龙感湖和武昌湖沉积物中,分别鉴定出9种和12种枝角类卵鞍。龙感湖沉积物中的枝角类总卵鞍密度(均以干重计)为2.27个/g,高于武昌湖1.63个/g;象鼻溞壳刺的平均密度459.40个/g,显著高于武昌湖1.52个/g。自20世纪60年代以来,武昌湖沉积物中枝角类的优势类群由裸腹溞属、尖额溞属种类向裸腹溞属、盘肠溞属种类转变;50年代以前,龙感湖枝角类卵鞍的优势种群为盘肠溞属种类,之后其优势类群由盘肠溞属、裸腹溞属种类向象鼻溞属种类转变。2个湖泊沉积物中枝角类卵鞍和象鼻溞壳刺密度的垂直变化与湖泊富养化过程及渔业养殖历史一致。研究表明,人类活动的干扰强度影响了长江中下游湖泊沉积物中枝角类微化石的组成和密度变化。

Stepwise paleoceanographic changes during the lastdeglaciation in the southern South China Sea: Records of stable isotope and microfossils

Quantitative analyses of microfossils and stable isotopic analysis were carried out for Core SCS-12 in the southwestern slope of the South China Sea (SCS). A high-resolution paleoceanographic record for the last 13 ka was revealed with the AMS 14 C dates. The southern SCS has experienced stepwise paleoceanographic changes since the last deglaciation. The oxygen isotopic stage 1/2 boundary around 12.05 ka B.P. and the end of the last deglaciation around 7.70 ka B.P. are two rapid change periods (corresponding to the termination I\-A and termination I\-B, respectively), in between is a slow change period. The authors infer that the sea level stood at -110 m before the termination I\-A, roughly the same as today after the termination I\-B, and about -50 m in between. Subsequently, the average winter sea surface temperature and salinity obviously increased while paleo-productivity decreased since 12.05 ka B.P. The early Holocene CaCO\-3 preservation spike, coupled with a high abundance of pteropoda and CaCO\-3 content, occurred around 7.70 ka B.P.

Microfossils from the siltstones and muddy slates:Constraint on the age of the Taowan Group in the Northern Qinling Orogenic Belt,Central China

The age of the Taowan Group is still a hot topic in the Northern Qinling Orogenic Belt, because of limited fossil evidence from these strata and different ideals on the Cambrian fossils of the conglomerate beds and limestone blocks. Early Ordovician acritarchs, chitinozoa and scolecodonts occur in the siltstone and muddy slate beds of the Guoling, Sanchakou, Fengmaimiao and Goushenmiao Formations of the Taowan Group, indicating the age of the Taowan Group should be the Ordovician. These fossil assemblages consist of 7 genera and 13 species of acritarchs, 7 genera and 9 species of chitinozoa, and 2 genera and 2 species of scolecodonts.

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 and significance of microfossils from Qinbaikouian Dazhuang Formation in Luonan, Shaanxi Province

THE microfossils were obtained by using 5%—7% HF acid from Qingbaikouian Dazhuang Formation in Luonan County, Shaanxi Province, with an age of 800—1000 Ma. The fossils may be one type of the oldest skeletal mierofossils.

Paleoproterozoic Underwater Volcanism and Microfossil-Like Structures in the Metasedimentary Siliceous Rocks,Hogland Island,Russia

Geological surveys showed that rhyolite and basalt strata with pillow structures typical for underwater volcanism form sheets over the Svecofennian basement. Original geochemical and isotope-geochemical data confirmed that the rhyolites were formed contemporaneously with the rapakivi granites of the Wiborg Massif（1 640 Ma）, and the basalts are similar to gabbro-anorthosites. Abnormally high content of K2O and relatively low content of Na2O in rhyolites and basalts are interpreted as a result of hydrothermal interaction of eruptive magmas with K-enriched hot seawater. The strata of siliceous metasedimentary rocks（microquartzites） within basaltic and rhyolitic lavas were formed in processes of chemogenic sedimentation and subsequent contact metamorphism during underwater volcanism. Microquartzites showed carbon vastly depleted of heavy isotope 13С. This is typical for rocks formed with participation of living substance. The Raman spectra of the remaining carbon-containing substance have graphite bands. In the microquartzites among basalts and rhyolites we found a community of structures with external and internal morphology similar to modern or fossilized marine microorganisms： spiral cyanobacterias, amoebas, diatoms, foraminifers, virus capsids, flagellates and multicellular organisms. It is assumed that these silificated and ferruginizated microfossils represent the Paleoproterozoic community of marine microorganisms.

Microfossils from loess of the Miaodao Islands, Bohai Sea

Microfossils from the Malan Loess profiles, Miaodao Islands, have been quantitatively studied. The microfauna is composed mainly of benthic foraminifers together with a few planktonic foraminifers, ostracods, gastropods, bivalves and echinoid spines. With the exception of indigenous gastropods, benthic foraminifers, ostracods, bivalves and echinoid spines were transported from the north or northwest of the Bohai Sea in the glacial period by the prevailing winter monsoon, while planktonic foraminifers were probably driven from the Yellow Sea or even the northern East China Sea by southerly winds. The upward decrease of marine microfossil abundance and diversity in the Malan Loess profiles shows that the microfossil transportation occurred mainly at the beginning of the regression.

Sedimentological and microfossil records of modern typhoons in a coastal sandy lagoon off southern China coast

To determine the characteristics and potential indicators of modern typhoon deposition in a sandy lagoon off the coast of Guangdong Province(southern China),we analysed the ^(210)Pb,sedimentology,and microfossils of samples from ten cores obtained before and after the passage of Typhoon Rammasun in 2014.Typhoon deposition showed a thinning trend from internal areas of the lagoon to its mouth,with the maximum thickness inside the lagoon of~35 cm.These typhoon deposits are dominated by overwash and differ from sediments deposited under normal weather conditions.Under normal weather conditions,lagoon sediment has a210 Pb curve that follows a model of exponential decay,has a unimodal granularity frequency curve,and lacks organic matter and microfossils(diatoms and foraminifera).However,210 Pb is low in the typhoon deposits,the grain size is coarse,and the granularity frequency curve is obviously bimodal.There are also abundant foraminifera in the typhoon deposits.We found a clear double-layered structure in the typhoon deposits,which was caused by strong hydrodynamic disturbance that mixed sediments originally from the offshore area with those of the lagoon.The lower layer has coarse-grained particles with medium sorting,low organic matter content,and low diatom content.The upper layer has fine-grained particles with poor sorting,high organic matter content,and abundant diatoms.The rate of fragmentation of diatoms in the upper layer was very high(40%-60%).The diatom assemblage contained offshore and freshwater species carried by storm runoff.Therefore,we believe that the sediments of this typical sand bar-lagoon environment retain evidence of typhoon events along the southern China coast that is displayed in the marked sedimentological and microfossil characteristics.

New material of microfossils from the Ediacaran Doushantuo Formation in the Zhangcunping area, Yichang, Hubei Province and its zircon SHRIMP U-Pb age

The Zhangcunping area is located at the north limb of the Huangling anticline in Yichang, Hubei Prov-ince. Here, the sedimentary succession of the Ediacaran Doushantuo Formation is similar with that in the Weng'an area, Guizhou Province. A large number of new microfossils (mainly acanthoacritarchs) from the Doushantuo Formation in this area are reported in this paper. The fossil assemblage shows similarity as the phosphatized biota of the Doushantuo Formation at Weng'an, Guizhou Province and the silicified biota of the Doushantuo Formation at the Yangtze Gorges, which suggests that the Zhangcunping area is a key for correlation of the Doushantuo Formation between the Weng'an area, Guizhou Province and the Yangtze Gorges. Besides, a new zircon SHRIMP U-Pb age (614.0±7.6 Ma) is first obtained from a horizon underneath the exposed surface in the middle of the Doushantuo Forma-tion in the Zhangcunping area. This age not only provides a new datum for subdivision of the Ediacaran Doushantuo Formation, but also indicates that the age of the exposed surface in the middle of the Doushantuo Formation in the Yangtze Platform should be posterior to 614.0±7.6 Ma. Due to the horizon of the Weng'an biota situated above the exposed surface, the age of the Weng'an biota should be pos-terior to 614.0±7.6 Ma as well.

A simulation experiment on phosphatized spherical microfossils

The identification and characterization of the phosphate preservation of the spherical microfossils in the Ediacaran Doushantuo time and the Early Cambrian has long been controversial.Modern artificial simulation experiments of phosphate animal eggs can provide scientific evidence to settle the aforementioned disputes.This experiment simulated environmental changes to observe the early morphological changes of the Bluntnose black bream eggs(Megalobrama amblycephala).It was found that the eggs can show a different morphology in the phosphate environment and that these eggs exhibited considerable morphological variations under different conditions.Thus,those eggs cannot be ascribed to the same species based only on the features.The experimental results are expected to provide a useful reference for the identification of phosphatized microfossils and provide a more empirical basis for their genesis.

Microfossil assemblage characteristics in Core B10 and implication for paleoenvironmental evolution in the southern Yellow Sea

Microfossil assemblage and pollen zone characteristics in Core B10 recorded the history of environmental changes in the southern Yellow Sea since Wiirm Subinterglaciation. Environmental variations reflected by these glacial and interglacial sediments coincide with general characteristics of paleoenvironmental and sedimentary changes in the Yellow Sea. In the section of 550-520 cm, microfossil foraminifera have low abundance and diversity, and pollens are composed mainly of those of herbaceous vegetation, indicating climate change during Wiirm Subinterglaciation. In the section of 520-140 cm, the changes from a few microfossils to no microfossils reflect the sedimentary environment variation from coastal to terrestrial facies. Paleoclimate reflected by pollen also underwent the changes from conifer-broadleaf mixed forest to grassland, indicating the climate changes from temperate and cool type to warm and dry one. In the section of 140-0 cm, the general microfossil characteristics are the gradual increase in abundance with most species being neritic species, the major pollen being ligneous pollen and the rapid increase in small Hystrichosphaera content, which indicates that the air temperature increased and the sea level gradually rose.

上海基底地层格架的锆石LA-ICP-MS U-Pb年龄及微体化石特征制约

基底地层特征对构造单元和地震地质背景认识具有重要意义。上海位于扬子克拉通和华夏造山系的交界区,同时位于江南造山带北东侧,构造位置比较特殊,但长期以来对其基底地层特征的认识比较薄弱。本文对典型钻孔揭露的变质岩、凝灰岩开展了锆石LA-ICP-MS U-Pb定年和疑源类化石分析,斜长角闪岩和花岗质糜棱岩分别获得1091.1±8.8 Ma、1753±24 Ma的原岩年龄,片麻岩获得上交点年龄2445±27 Ma、下交点年龄581±110 Ma,安山质糜棱岩206Pb/238U谐和年龄有2708~2447 Ma、1371~1097 Ma和956~903 Ma三个区间,凝灰岩获得801±13 Ma、774±12 Ma的原岩年龄,板岩中含较多炭化剧烈的Leiosphaeridia化石。认为区内基底自下而上可划分出金山群、惠南板岩和河上镇群,分别形成于古元古代初期—中元古代、青白口纪早—中期和青白口纪晚期,总体年龄特征表现出与华夏造山系的亲缘性特征。2447~2507 Ma、1753 Ma、1091.1 Ma、801~774 Ma和581±110 Ma等建造和改造事件是对凯若兰超大陆、哥伦比亚超大陆、罗迪尼亚超大陆和冈瓦纳超大陆汇聚裂解过程的响应。

华南黄陵背斜西翼兴山地区乡儿湾剖面埃迪卡拉系陡山沱组微体化石

本文首次报道并描述了华南黄陵背斜西翼湖北宜昌兴山县乡儿湾剖面埃迪卡拉系陡山沱组二段中上部的燧石结核和条带中的疑源类微体化石,经系统鉴定共识别出8属8种,包括Appendisphaera grandis,Crassimembrana multitunica,Leiosphaeridia minutissima,Megasphaera inornata,Schizofusa zangwenlongii,Symphysosphaera basimembrana,Urasphaera nupta,Variomargosphaeridium gracile。该化石组合包含Liu Pengju and Moczyd?owska(2019)所建立的第二生物组合带(Tanarium tuberosum-Schizofusa zangwenlongii组合带)的特征分子Schizofusa zangwenlongii,因此,可尝试性地与第二生物组合带相对比,但未见黄陵背斜东南翼陡山沱组二段的常见属Tianzhushania,据此推测黄陵背斜两翼在古环境上可能有所差异。

吉南地区万隆组燧石相微生物化石及其古环境意义

拉伸纪作为承接中元古代蓝菌时代以及成冰纪生物锐减的关键地质历史时期,是探索早期生命与环境演化最重要的时期之一。吉林南部地区地处华北板块东北缘,拉伸系发育完整、出露全,在燧石条带、燧石结核和泥页岩中富含微生物化石,是开展拉伸纪古生物学、生物地层学和古环境研究的理想地区。本次工作利用岩石切片法在吉林南部二道江地区万隆组顶部燧石中发现微生物化石6属9种,其中丝状蓝菌1属4种Siphonophycus robustum,S.typicum,S.kestron,S.solidum;球状蓝菌3属3种Eoentophysalis belcherensis,Gloeodiniopsis lamellosa,Scissilisphaera bistratosa;分类位置未定2属2种Glenobotrydion majorinum,Globophycus rugosum。这些微体化石的发现为开展万隆组古环境分析及生物地层对比研究提供了新的素材。研究显示,万隆组燧石相微生物组合以发育管鞘藻席(Siphonophycus mat)为主要特征,丝状蓝菌呈横向展布,长可达400μm以上,显示原地或近原地埋藏的特点。生物群落古环境综合分析表明,吉林南部二道江地区万隆组顶部形成于潮下带或潮间带下部低能静水的沉积环境。

长江三角洲北翼ZKA01钻孔第四纪晚期以来的沉积环境演化

第四纪晚期以来的年代地层框架及海侵问题一直以来都是长江三角洲地区的研究热点。由于长江三角洲地区河道往复摆动、河流下切侵蚀导致地层频繁缺失,目前尚未在该地区同一个钻孔内发现完整的海侵记录。基于长江三角洲北翼东台地区ZKA01钻孔岩石地层、生物地层、古地磁年代学和光释光(OSL)测年研究,对比区域钻孔资料确定了该孔第四纪以来的地层年代框架,发现ZKA01钻孔完整地记录了晚更新世以来长江三角洲地区的5次海侵事件。结果表明,ZKA01孔B/M界线位置在108.00m处,M/G界线位置为300.25 m处。中、上更新统界线位于第Ⅲ海相层底部,即92.95m处。上更新统与全新统界线置于该钻孔发现的第Ⅰ海相层底部,即16.65m处。晚更新世以来,前3次海侵发生在MIS5(128~74 ka)阶段,其中MIS5.1海侵规模较大,仅次于全新世时期的海侵规模。第4次海侵发生在MIS3阶段(60~24 ka),在深度上和年代上相当于MIS3时期的“第Ⅱ海相层”。第5次海侵发生在MIS1(12 ka至今)阶段,沉积环境为滨岸浅水的浅海环境,该次海侵规模最大。同时发现MIS5阶段初次海侵记录在该地区各钻孔埋深大致相当,该界面可作为长江三角地区的地层划分与对比研究的标志性地层。以上研究成果对于长江三角洲地区第四纪晚期地层划分对比、沉积环境研究分析具有极其重要意义。

银额盆地额济纳旗伊很乌苏地区下白垩统巴音戈壁组的微体化石及沉积环境

银额盆地额济纳地区中生代地层分布广泛,近些年的研究表明,盆地内发现的油气多来源于中生代地层的烃源岩,因此研究银额盆地中生代地层具有十分重要的意义。通过对银额盆地额济纳地区微体化石进行分析研究,发现鉴定了孢粉3属3种,介形类3属6种,其共存时限为早白垩世。据此将前人原划上侏罗统重新厘定为下白垩统巴音戈壁组,并根据岩石组合特征将其划分为3个岩性段。结合化石古生态、沉积构造和区域地质背景,认为巴音戈壁组3个岩性段分别代表了近岸水下扇、滨—浅湖、扇三角洲平原的淡水—微咸水内陆河湖相沉积环境,揭示其沉积经历了湖盆从产生、发展到萎缩的演化过程。巴音戈壁组岩石组合、沉积环境和化石组合特征的研究结果,有助于区域地层研究对比,为研究油气基础地质和区域演化提供基础资料。

深海锰结核——核形石的新类型

对东太平洋深海锰结核用偏光显微镜、扫描电镜和透射电镜进行了研究。结果表明其由核心和叠层石包壳组成,具有核形石特有的结构和构造。因此,深海锰结核是一种锰质核形石。根据包壳中叠层石的种类,东太平洋锰质核形石可分为两种类型:一种表面光滑,内部致密,包壳主要由微小叠层石组成;另一种表面呈瘤状,内部疏松,包壳主要由奇异叠层石组成。透射电镜研究表明,锰质核形石的建造者是纳米级超微生物。其中微小叠层石(Minima)是由中华微放线菌(Miniactinomyces chinensis sp.nov.)建造的;奇异叠层石(Admirabilis)是由太平洋螺球孢菌(Spirisosphaerospora pacifica sp.nov.)建造的。