Possible ctenophoran affinities of the Precambrian "sea-pen" Rangea

The Namibian Kuibis Quartzite fossils of Rangea are preserved three-dimensionally owing to incomplete collapse of the soft tissues under the load of instantaneously deposited sand. The process of fossilization did not reproduce the original external morphology of the organism but rather the inner surface of collapsed organs, presumably a system of sacs connected by a medial canal. The body of Rangea had tetraradial symmetry, a body plan shared also by the White Sea Russian fossil Bomakellia and possibly some other Precambrian frond-like fossils. They all had a complex internal anatomy, smooth surface of the body, and radial membranes, making their alleged colonial nature unlikely. Despite a different style of preservation, the Middle Cambrian Burgess Shale frond-like Thaumaptilon shows several anatomical similarities to Rangea. The body plan of the Burgess Shale ctenophore Fasciculus, with its numerous, pinnately arranged comb organs, is in many respects transitional between Thaumaptilon and the Early Cambrian ctenophore Maotianoascus from the Chengjiang fauna of South China. It is proposed that the irregularly distributed dark spots on the fusiform units of the petaloid of Thaumaptilon represent a kind of macrocilia and that the units are homologous with the ctenophoran comb organs. These superficial structures were underlain by the complex serial organs, well represented in the fossils of Rangea. The Precambrian "sea-pens" were thus probably sedentary ancestors of the ctenophores.     

Nautiloid debris oriented by long-shore currents along a late Ordovician-early Silurian rocky shore

Siphuncular fragments from arminocerid cephalopods are abundant along 350 m of a well defined rocky shore of late Ordovician or early Silurian age exposed near Churchill in northeastern Manitoba, Canada. The paleoshore is composed of the Precambrian Churchill Quartzite, which is dramatically abutted by carbonate strata gently dipping north beneath Hudson Bay. At one end of the exposure, a former sea stack or sea arch extends prominently outward for 15 m perpendicular to the otherwise linear paleoshore. Probably it acted as a natural groin with some influence on local currents and waves. The orientations of 189 siphuncular fragments were recorded and found to be dominantly perpendicular to the trend of the ancient shore. They are far more cylindrical in shape than conical, and are interpreted to have been rolled to their final resting place pushed by long-shore currents. Concentration of nearly 80% of the fragments towards one end of the shore is consistent with transport by long-shore currents. Ripple marks preserved at a different stratigraphic level form a 45-degree angle to the trend of the paleoshore, providing additional evidence that wave trains must have set up long-shore currents from time to time.     

Quartzite Qua Lithic Material in Archaeology:

Abstract

Quartzite is considered as a lithic material with particular reference to use-wear analysis. Since information concerning the use of quartzite is very scarce, experiments producing and observing wear on quartzite were performed. Differences in wear were observed for different tasks, but the differences are subtle enough and the wear general enough that the need for much further work is apparent. As quartzite is commonly found in some areas such as the Central Rocky Mountain States, understanding of manifestations of use on quartzite is seen as important, especially since there is some reason to believe it was used frequently in unmodified flake form. Quartzite is thought to be different enough from other lithic materials that generalizations on wear from such materails to quartzite may be invalid. Cursory experimentation with heat treatment of quartzite was also performed.     

Integrated sedimentological,ichnological and sequence stratigraphical studies of the Koti Dhaman Formation (Tal Group), Nigali Dhar Syncline,Lesser Himalaya,India: paleoenvironmental,paleoecological, paleogeographic significance

Abstract

Integrated ichnology, sedimentology and sequence stratigraphy of the Lower Quartzite Member to the Arkosic Sandstone Member of the Koti Dhaman Formation (Cambrian Series 2, Stage 4), Tal Group, Nigali Dhar Syncline, Lesser Himalayan lithotectonic zone are presented. Trilobite traces of Gondwanan affinity i.e., Cruziana salomonis, Cruziana fasciculata, Rusophycus dispar and Rusophycus burjensis are recorded along with Arenicolites isp. and Skolithos isp. from the Lower Quartzite Member. A rich and diverse ichnoassemblage attributed to the Cruziana ichnofacies is described for the first time from the Arkosic Sandstone Member of the same formation. Seven ichnofossil assemblages, i.e., Cruziana-Rusophycus, Planolites-Palaeophycus, Cruziana problematica, Diplichnites, Cochlichnus anguineus, Bergaueria perata and Psammichnites gigas have been recognized in the Lower Quartzite to Arkosic Sandstone members of the Koti Dhaman Formation. Seven sedimentary facies i.e., sandstone–shale facies (FT1), cross-bedded (trough and planar) sandstone (FT2), bedded sandstone facies (FT3), shale facies (FT4), shale–sandstone facies (FT5), shale-rippled sandstone facies (FT6) and planar and trough cross-laminated sandstone (FT7) and four facies associations FA1-FA4 are identified in the Koti Dhaman Formation. The formation contains shallowing upward parasequences of a tidal flat complex. Overall, two major events are recognized: i) the break in sedimentation between the Lower Quartzite Member and the overlying Shale Member probably related to forced-regressive event and ii) the facies shift from FT6 to FT7 of the Arkosic Sandstone Member represents an erosive transgressive event; the surface is interpreted as wave ravinement surface, which also serves as a sequence boundary. Integrated ichnology, sedimentology and sequence stratigraphic studies indicate that the Lower Quartzite Member was deposited in a shallow subtidal sand sheet complex and tidal flat complex; the Shale Member was deposited in a mud flat setting of a tidal flat complex, and the Arkosic Sandstone Member in a mixed-flat (tidal flat complex) to sand sheet complex front and margin (subtidal sand sheet complex). Overall, the lower to middle part of the Koti Dhaman Formation represents a tide-dominated shallow subtidal–intertidal to mud-flat subenvironments of the tidal flat complex. A palaeogeographic reconstruction of lower Cambrian (516–514?Ma) is presented based on the distribution of trilobite traces from the Lesser Himalaya and the Bikaner–Nagaur area of Peninsular India (eastern Gondwana), Egypt, Jordan, Turkey (western Gondwana) and Canada (Avalonia).     

New information concerning the age of the beds immediately overlying the Armorican Quartzite in Central Portugal

Graptolitic and shelly faunas have been collected from the base of the Cacemes Formation, central Portugal. The assemblages occur to within about 10 cm of the top of the underlying Armorican Quartzite Formation and indicate a Lower Llanvirn age. Prior to this record the basal beds of the Cacemes Formation were recently considered to be of Arenig age. The faunas are listed and the trilobites (Ogyginus cf. armoricanus, Neseuretus (Neseuretus) tristani tristani, Colpocoryphe cf. thorali conjugens, Eodalmanitina sp.) and graptolites (Didymograptus (Didymograptus?) cf. spinulosus, D. (D.?) aff. spinulosus, D. (D.?) cf. pseudogeminus) are figured. The significance of the faunas in terms of the age of the top of the Armorican Quartzite Formation is discussed.     

The early evolution of life: solution to Darwin's dilemma

Recent studies of Precambrian fossils indicate that life on Earth originated earlier than assumed, microscopic life was prevalent in the Precambrian Eon, the tempo and mode of evolution during the Precambrian period were different from other periods, and that only the Precambrian fossil record can be used as evidence of early life. Implications for future research include directing the search for the origin of life away from the geological record, modification of hypotheses about molecular change, use of Precambrian microfossils in dating younger geological units, and progress in defining the nature of major events in early evolution.     

广西百色六合遗址发掘简报

六合遗址位于百色盆地右江南岸第4级阶地上, 于2005年6月至11月进行了抢救性发掘, 揭露面积1000㎡。遗址地层分为5层, 其中第①、②和③层为次生堆积, 第④层为原生的网纹红土, 第⑤层为砾石层。本次发掘出土71件文化遗物, 包括磨制石器2件、打制石器69件; 此外还发现1件玻璃陨石。打制石器以大型和中型为主, 包括石核、石片、工具、断块等, 以断块居多; 工具类型有砍砸器和手镐。石制品原料采自遗址附近第4级阶地砾石层, 有石英岩、角砾岩、细砂岩、硅质岩、中砂岩和石英, 以石英岩为主。根据出土的玻璃陨石, 并结合地层、石制品特征比较, 六合遗址打制石器的年代可能为中更新世早期。     

A model for diurnal patterns of carbon fixation in a Precambrian microbial mat based on a modern analog

Microbial mat communities are one of the first and most prevalent biological communities known from the Precambrian fossil record. These fossil mat communities are found as laminated sedimentary rock structures called stromatolites. Using a modern microbial mat as an analog for Precambrian stromatolites, a study of carbon fixation during a diurnal cycle under ambient conditions was undertaken. The rate of carbon fixation depends primarily on the availability of light (consistent with photosynthetic carbon fixation) and inorganic carbon, and not nitrogen or phosphorus. Atmospheric PCO2 is thought to have decreased from 10 bars at 4 Ga (10(9) years before present) to approximately 10(-4) bars today, implying a change in the availability of inorganic carbon for carbon fixation. Experimental manipulation of levels of inorganic carbon to levels that may have been available to Precambrian mat communities resulted in increased levels of carbon fixation during daylight hours. Combining these data with models of daylength during the Precambrian, models are derived for diurnal patterns of photosynthetic carbon fixation in a Precambrian microbial mat community. The models suggest that, even in the face of shorter daylengths during the Precambrian, total daily carbon fixation has been declining over geological time, with most of the decrease having occurred during the Precambrian.     

The evolution and distribution of life in the Precambrian eon-Global perspective and the Indian record

The discovery of Precambrian microfossils in 1954 opened a new vista of investigations in the field of evolution of life. Although the Precambrian encompasses 87% of the earth’s history, the pace of organismal evolution was quite slow. The life forms as categorised today in the three principal domains viz. the Bacteria, the Archaea and the Eucarya evolved during this period. In this paper, we review the advancements made in the Precambrian palaeontology and its contribution in understanding the evolution of life forms on earth. These studies have enriched the data base on the Precambrian life. Most of the direct evidence includes fossil prokaryotes, protists, advanced algal fossils, acritarchs, and the indirect evidence is represented by the stromatolites, trace fossils and geochemical fossils signatures. The Precambrian fossils are preserved in the form of compressions, impressions, and permineralized and biomineralized remains.     

沟鞭藻的起源:分子地球化学证据

沟鞭藻为单细胞的原始的海洋生物。古生物学家根据形态特征,超微结构和生物化学信息认为沟鞭藻可能在前寒武纪时已存在,并推测古生代疑源类可能是现代沟鞭藻的先祖,但确凿的沟鞭藻囊孢的化石记录始于晚三叠世。生物标志物以分子化石的形式记录了沟鞭藻的起源及演化历史。在古生代及前寒武纪地层中甲藻甾烷及三芳沟鞭藻的检出,建立了沟鞭藻与其古代先祖（疑源类）的联系,提供了沟鞭藻先祖前寒武纪存在的证据。     

通过C27/C29甾烷和有机碳同位素来判断早古生代和前寒武纪的烃源岩的生物来源

在早古生代与前寒武纪的石油与源岩中,经常出现令人困惑的C29甾烷优势,而在有机地球化学中C29甾烷优势被认为是陆相有机质输入的标志。作者通过对比文献中各种海相藻类的热模拟产物分析,提出了早古生代与前寒武纪的石油与源岩中C29甾烷优势主要来源于浮游绿藻的观点,并通过C27甾烷/C29甾烷的比值提出了区分早古生代及前寒武纪石油源岩沉积环境的方法,对中国南方前寒武纪和早寒武世黑色岩系的有机地球化学分析也支持上述推断。此外,本文还提出了用有机碳同位素来进一步区分C29甾烷优势生物来源的方法。     

STUDY ON STROMATOLITIC DECLINE EVENT IN TERMINAL PRECAMBRIAN

In Precambrian, stromatolites, especially columnar stromatolites, underwent a marked evolutionary process from beginning of development through extensive flourish to rapid decline. The present paper makes a discussion on the exact data and cause of the stromatolitic decline in an attempt to reveal the evolution of biosphere and change of ecological environments in the terminal Precambrian according to a study of the stromatolitic decline event.     

Devonian and modern relatives of the Precambrian Eosphaera: possible significance for the early eukaryotes

The Middle Precambrian problematical microorganism Eosphaera Barghoorn and Eosphaera- like structures known from Early and Middle Precambrian banded iron formations have been compared with the recently discovered Devonian volvocacean alga Eovolvox Kaźmierczak and some modern colonial Volvocales. The volvocacean interpretation of Eosphaera implies that algal eukaryotes (green phytoflagellates) werc already prewmt in the earth biosphere before at least 1.9 b. y. ago (Gunflint Iron Formaticn), and probably before 2.7 b. y. ago (Soudan Iron Formation). The type of metabolism and thc oxygen requirements of modern colonial Volvocales indicate that Eosphaera was most probably a photoorgano-trophic (mixotrophic) organism able to live in the extremely oxygen-deficicnt or anoxy-genous Early Precambrian environment. As an oxygen-releasing photosynthesizer, Eosphaera could have played a considerable role in the production of free oxygen during the Precambrian. The abundance of Eospkaera- like ferriferous structures in the iron microbands of many banded iron formations implies active participation of these organisns in the formation of Precambrian sedimentary iron ores. The exclusively fresh-water habitat of extant volvocacean algae suggests that the Procambrian environments inhabited by Eosphaera were non-marine.     

PRAECAMBRIDIUM - A PRIMITIVE ARTHROPOD

The genus Praecambridium , from the Late Precambrian of South Australia, represents a segmented organism which appears to be related to early trilobites or chelicerates or both. A Late Precambrian fossil from Northern Russia which was recently named Vendia sokolovi Keller resembles Praecambridium.     

中国叠层石研究的历史和现状

中国前寒武纪地层分布广泛。在20世纪70-80年代,中国学者对晚前寒武纪的叠层石进行了系统的研究,描述了类型众多的叠层石属种,并把叠层石组合应用于地层的划分和对比。近年来,为了揭示叠层石的形态发生,中国学者正在探讨硅质叠层石的生物组构模式和叠层石微层理的成因,以及叠层石中微生物生长、运动和造席过程。     

Amino acids from the Late Precambrian Thule Group,Greenland

Amino acids were recovered at a concentration level of 10^–9 M/g from the interior of chert and dolomite of the Late Precambrian Thule Group. Examination of the stability of amino acids in chert under dry-heating conditions suggests that these amino acids have been preserved with a predominance of L-enantiomers in the Precambrian chert. Enantiomer analysis of amino acids in dolomite showed a thermal effect resulting from a late Precambrian igneous intrusion. This evidence indicates that the amino acids isolated from the Thule samples were chemical fossils and not recent contaminants.     

宁夏青铜峡鸽子山第15地点发掘报告

宁夏鸽子山遗址位于贺兰山西南余脉东侧的山前洪冲积扇前缘。2015年对第15地点的发掘面积约16m²。在约3m深的地层中共揭露3个原生文化层位。光释光测年数据显示第2层至第4层的时代跨度为0.12-12.3 ka,出土石制品共155件。其中第3层石制品最为丰富,共142件,石制品原料以石英岩和灰岩为主,类型主要有石片、石核和断块。石制品的基本信息显示该地区人类活动频度可能与环境变化与沙漠进退有紧密联系。     

A new type of Precambrian megascopic fossils: the Jinxian biota from northeastern China

Precambrian fossils are crucial for our understanding of the evolution of early organisms. Megascopic body fossils are more important because they potentially represent macroorganisms. However, the Precambrian fossil record is sparse and dominated by microfossils and microbial structures. Here we show a new type of megascopic fossils recovered from the Xingmincun Formation (probably Neoproterozoic age), northeastern China. The specimens are flat, flexible (easily corrugated) and discoidal in outline. Concentric or spiral ridges are preserved on both sides. Petrographical thin section examination indicates that the specimen consist of a thin layer of microcrystalline quartz grains (about 20–30 μm thick) wrapped by an outer sheath, composed primarily of chlorites. Field Emission Scanning Electron Microscopy (FE-SEM) coupled with an x-ray energy dispersive spectrometer system (EDX) analysis shows microstructures and relative element abundance of the fossils, but contributes little in solving their biological affinities. The fossils have previously been linked to discoidal impressions of the Ediacara biota. Close examination on new materials indicates that they are radically different from either the Ediacara impressions or any other Precambrian megascopic remains. Concentric or spiral ridges may result from rhythmic growth and the presence of twin specimens may suggest that the organisms undergo asexual reproduction or inhibition of growth in one direction. Referring them to any known fossil or living group has proved to be difficult. We conclude that they represent a distinct group of Precambrian megascopic organisms regardless of their affinities remaining problematic.     

ON THE DISCOVERY OF EIFELIAN FAUNA FROM WESTERN TSINLING

In soumeastern Kansu,there is a vast area of metamorphosed sed(?)mentary rockscomposed of quartzites,crystallized limestones and slates with some intercalations ofhematites exposed in the valley of Lengputze to the north of Wen Xian,and in the valleyof Sunchiayuan to the west of Kang Xian.In 1944,Yeh and Kwan named the abovementioned strata at Lengputze Lupanchiao Quartzite and referred it to Lower Carbo-niferous.Lately(1959),by the discovery of Tabulata(Favosites sp.),C.H.Huang re-garded it as the upper part of the so-called Pikou Group of Lower Palaeozoic in age.While carrying on a field exploration in 1960,one of the writers,Kuo,collected a fewfossils from the same section and the corresponding strata in Kang Xian.They arelisted helow:     

Are late Proterozoic carbonaceous megafossils metaphytic algae or bacteria?

Pre-Phanerozoic carbonaceous megafossils are generally considered to be the remains of metaphytic algae. While these fossils are not particularly common, they are significant for the understanding on the global evolutionary level of the pre-Phanerozoic biota. Ribbon-shaped vendotaenids were interpreted as brown algae and represent the youngest, most common and geographically most widespread Precambrian carbonaceous megafossils. It now appears that they may be better understood as abandoned giant sheaths of sulfide oxidizing organotrophic bacteria related to the Modern Thioptoca among the Beggiatoaceae. □ Thallophyta, algae, methaphytes, Vendotaenidae, late Proterozoic, Precambrian, Vendian, bacteria.