Snapshot of an early Paleoproterozoic ecosystem: Two diverse microfossil communities from the Turee Creek Group,Western Australia

Eighteen microfossil morphotypes from two distinct facies of black chert from a deep‐water setting of the c. 2.4 Ga Turee Creek Group, Western Australia, are reported here. A primarily in situ, deep‐water benthic community preserved in nodular black chert occurs as a tangled network of a variety of long filamentous microfossils, unicells of one size distribution and fine filamentous rosettes, together with relatively large spherical aggregates of cells interpreted as in‐fallen, likely planktonic, forms. Bedded black cherts, in contrast, preserve microfossils primarily within, but also between, rounded clasts of organic material that are coated by thin, convoluted carbonaceous films interpreted as preserved extracellular polymeric substance (EPS). Microfossils preserved within the clasts include a wide range of unicells, both much smaller and larger than those in the nodular black chert, along with relatively short, often degraded filaments, four types of star‐shaped rosettes and umbrella‐like rosettes. Large, complexly branching filamentous microfossils are found between the clasts. The grainstone clasts in the bedded black chert are interpreted as transported from shallower water, and the contained microfossils thus likely represent a phototrophic community. Combined, the two black chert facies provide a snapshot of a microbial ecosystem spanning shallow to deeper‐water environments, and an insight into the diversity of life present during the rise in atmospheric oxygen. The preserved microfossils include two new, distinct morphologies previously unknown from the geological record, as well as a number of microfossils from the bedded black chert that are morphologically similar to—but 400–500 Ma older than—type specimens from the c. 1.88 Ga Gunflint Iron Formation. Thus, the Turee Creek Group microfossil assemblage creates a substantial reference point in the sparse fossil record of the earliest Paleoproterozoic and demonstrates that microbial life diversified quite rapidly after the end of the Archean.     

Late Mesoproterozoic – early Neoproterozoic organic‐walled microfossils from the Madhubani Group of the Ganga Valley,northern India

The age of the sedimentary basement of the Ganga Valley in northern India, which is represented by the entirely subsurface Ganga Supergroup, is key for addressing issues related to the tectonic history of the Himalaya. However, the stratigraphic correlations between the Ganga Supergroup in the Ganga Valley, the Vindhyan Supergroup in cratonic India to the south, and Proterozoic successions in the Lesser Himalaya to the north have long been a matter of controversy. This is largely because of the poor age constraint of the Madhubani Group of the upper Ganga Supergroup, which has been variously interpreted as Proterozoic, lower Palaeozoic, or even Mesozoic. To address this issue, we used a low manipulation maceration technique to extract organic‐walled microfossils from the Ujhani and Tilhar formations of the lower Madhubani Group. Our study recovered a total of 24 taxa, including Devisphaera corallis gen. et sp. nov. The co‐occurrence of Trachyhystrichosphaera aimika, Caudosphaera expansa and Annulusia annulata in the lower Madhubani Group indicates a late Mesoproterozoic to early Neoproterozoic age. Thus, the biostratigraphical data suggest a >300 myr depositional gap between the Madhubani Group and the immediately underlying Bahraich Group, which has been independently constrained to be upper Palaeoproterozoic to lower Mesoproterozoic in age. Therefore, the first‐order stratigraphic architecture, with a Palaeoproterozoic–Mesoproterozoic succession unconformably overlain by a Mesoproterozoic–Neoproterozoic succession, is closely similar throughout the Vindhyan Basin, Ganga Valley and Lesser Himalaya, suggesting a shared sedimentary and tectonic history among them.     

Photosynthesis 3.5 thousand million years ago

The recent discovery of stromatolites and microfossils in 3.5-Ga-old sedimentary rock formations is evidence for the existence of phototrophic prokaryotes at that time. Values of ¹³C for sedimentary organic carbon strongly suggest autotrophic CO₂ fixation, and the existence of large deposits of sedimentary sulfate is consistent with a photosynthesis dependent on reduced sulfur compounds for reducing power. The ancient photoautotrophs are though to have contained only one kind of reaction center with either chlorophyll a or bacteriochlorophyll a as primary electron donor and with one or more iron-sulfur centers as secondary electron acceptors. Light-harvesting pigments might have been chlorophyll a, bacteriochlorophyll a, or possibly bacteriochlorophyll c.A new proposal is made to explain how these organisms could have survived an intense UV flux at the earth's surface in the absence of an ozone layer. Photochemically produced ferric iron was abundant in sediments, and the UV-absorption of this ferric iron would have been sufficient to shield those organisms living below the watersediment interface.In honor of Prof. L.N.M. Duysens on the occasion of his retirement.     

A DISCUSSION AND PROPOSAL CONCERNING THE USE OF THE TERM CALCISPHERES

Abstract:  The terminology and grouping of spherical, calcareous microfossils of unknown biological affinity, usually referred to as calcispheres, are diffuse. The term calcispheres is inconsistently used, the morphological and taxonomical concepts are mostly ill-defined and a formal definition is lacking. To resolve this issue, we propose, in analogy with the erection of the Acritarcha for organic microfossils of unknown origin, a new group called Calcitarcha, including all calcareous microfossils with a central cavity for which the biological affinities remain unknown.     

宁夏六盘山盆地海参1井上侏罗统—上白垩统微体化石组合

六盘山盆地海原凹陷肖家湾构造的海参1井钻遇中生代地层。其中安定组见孢粉化石Pinuspollenites-Ali-sporites-Araucariacites组合,时代定为晚侏罗世。和尚铺组含介形类和孢粉化石Cypridea(Cypridea)unicosta-ta-Cypridea(Ulwellia)koskulensis组合、Pinuspollenites-Classopollis-Schizaeoisporites组合和大量Peckisphaera paragranulifera,李洼峡组含轮藻和孢粉化石Aclistochara huihuibaoensis-Mesochara cf. voluta-Sphaerochara组合、Classopollis-Cicatricosisporites-Granudiscus组合和介形类Damonella cf. mediocris,Cypridea(Yumenia) sp.等,和尚铺组和李洼峡组的时代可归于早白垩世早中期(Hauterivian—Barremian)。乃家河组产轮藻化石Raskyae-chara sp.,Obtusochara cf. subcylindrica等,时代可能是晚白垩世。     

河北兴隆中元古代古海底黑烟囱中微生物化石的发现及其意义

采用显微镜以及扫描电镜对冀东中元古代块状硫化物黑烟囱样品进行研究,首次发现了矿化微生物化石。它们为丝状体,均已黄铁矿化,经过激光拉曼光谱测试发现还保留少量有机质,可以与现代海底黑烟囱周围矿化微生物对比。这些化石微生物的鉴别基于大小、形状和群落聚集等物理标志。     

SYSTEMATIC DESCRIPTION AND PHYLOGENETIC AFFINITY OF TUBULAR MICROFOSSILS FROM THE EDIACARAN DOUSHANTUO FORMATION AT WENG'AN, SOUTH CHINA

Abstract:  This paper provides a systematic treatment of tubular microfossils collected from dolomitic phosphorites of the Ediacaran Doushantuo Formation at Weng'an, South China. These microfossils were investigated using petrographic, acid extraction and re-embedding techniques. Four morphological genera and five morphospecies are described: Ramitubus increscens gen. et sp. nov., Ramitubus decrescens gen. et sp. nov., Sinocyclocyclicus guizhouensis , Quadratitubus orbigoniatus , and Crassitubus costatus gen. et sp. nov. They are characterized by cylindrical ( R. increscens , R. decrescens , S. guizhouensis and C. costatus ) or tetragonal ( Q. orbigoniatus ) tubes with closely spaced cross-walls. Ramitubus has mostly complete cross-walls, whereas all other taxa have regularly intercalated complete and incomplete cross-walls. Some of them branch dichotomously ( R. increscens and R. decrescens ), others have a longitudinal ridge running along a curved tube ( C. costatus ).
The palaeoecology, ontogeny, and phylogenetic affinity of these microfossils are still uncertain. They probably represent non-biomineralizing organisms in the Ediacaran ocean. Ramitubus (and possibly all other morphotaxa described in this paper) was probably benthic and grew unidirectionally and episodically. The incomplete cross-walls could have been formed through terminal addition or, alternatively, through intercalary insertion. It is possible that some or all morphotaxa described may represent ontogenetic or ecophenotypic variations of one or a few closely related biological species. If so, then the combination of morphological features (complete and incomplete cross-walls, tetraradial symmetry, and longitudinal ridge) can negate a cyanobacterial or algal interpretation, and point to a tentative cnidarian affinity.     

REMOVING GOLD COATING FROM SEM SAMPLES

Abstract:  An essential tool in micropalaeontological studies is analysis and imaging using a scanning electron microscope (SEM). It is commonly necessary to coat the sample with a thin layer of gold or gold-palladium alloy in order to prevent charging of the surface, to promote the emission of secondary electrons so that the specimen conducts evenly, and to provide a homogeneous surface for analysis and imaging. However, coating a specimen with gold is a semi-destructive process that masks the surface of specimens, and a common curatorial practice is to prohibit coating of important specimens. We describe a non-destructive, simple and inexpensive technique that uses KCN (or NaCN), a glass jar, paper towels, cardboard and a fume hood for the removal of gold coatings from SEM samples. This technique requires little additional handling of the specimen, and there is no need to place the specimen in a solution.     

Molecular and Cellular Fossils of a Mat-Like Microbial Community in Geothermal Boratic Sinters

Silica and travertine deposits, the two most common surface manifestations of terrestrial hot springs, have so far been the only markers universally helpful in locating and interpreting geothermal systems and past lifeforms potentially associated with them. In the current study, we for the first time report microbial fossils from a third type of geothermal sinter, viz. the boron mineral deposits, which are characteristic of the relatively uncommon silicate-poor hot springs. Organic biomarker analyses of the boratic sinters framing the hot springs of Puga valley, Ladakh, identified molecular fossils (viz. respiratory and photosynthetic isoprenoid quinones and photosynthetic pigments) of a mat-like microbial community putatively comprised of algae, fungi, cyanobacteria and other photosynthetic bacteria, some of which may be proteobacteria. So far as microfossil preservation is concerned, mineralized mat-like biofabrics with diverse cellular morphotypes could be identified in scanning electron microscopy of sub-recent sediments as well as hard and consolidated old sinters. Though this putative past community is quite unusual in volcanic niches, its ubiquitous and enduring presence in the Puga geothermal area is highlighted by the discovery of its biosignatures along all of the three dimensions of the explored boratic deposits. These findings usher a new paradigm of looking at past or present geothermal life in as well as outside the Earth.     

Environmental changes define ecological limits to species richness and reveal the mode of macroevolutionary competition

Co‐dependent geological and climatic changes obscure how species interact in deep time. The interplay between these environmental factors makes it hard to discern whether ecological competition exerts an upper limit on species richness. Here, using the exceptional fossil record of Cenozoic Era macroperforate planktonic foraminifera, we assess the evidence for alternative modes of macroevolutionary competition. Our models support an environmentally dependent macroevolutionary form of contest competition that yields finite upper bounds on species richness. Models of biotic competition assuming unchanging environmental conditions were overwhelmingly rejected. In the best‐supported model, temperature affects the per‐lineage diversification rate, while both temperature and an environmental driver of sediment accumulation defines the upper limit. The support for contest competition implies that incumbency constrains species richness by restricting niche availability, and that the number of macroevolutionary niches varies as a function of environmental changes.