Precambrian Research Articles

Cellular self-organization: An overdrive in Cambrian diversity?

During the early Cambrian period metazoan life forms diverged at an accelerated rate to occupy multiple ecological niches on earth. A variety of explanations have been proposed to address this major evolutionary phenomenon termed the "Cambrian explosion." While most hypotheses address environmental, developmental, and ecological factors that facilitated evolutionary innovations, the biological basis for accelerated emergence of species diversity in the Cambrian period remains largely conjectural. Herein, we posit that morphogenesis by self-organization enables the uncoupling of genomic mutational landscape from phenotypic diversification. Evidence is provided for a two-tiered interpretation of genomic changes in metazoan animals wherein mutations not only impact upon function of individual cells, but also alter the self-organization outcome during developmental morphogenesis. We provide evidence that the morphological impacts of mutations on self-organization could remain repressed if associated with an unmet negative energetic cost. We posit that accelerated morphological diversification in transition to the Cambrian period has occurred by emergence of dormant (i.e., reserved) morphological novelties whose molecular underpinnings were seeded in the Precambrian period.

A crown-group cnidarian from the Ediacaran of Charnwood Forest, UK

Cnidarians are a disparate and ancient phylum, encompassing corals and jellyfish, and occupy both the pelagic and benthic realms. They have a rich fossil record from the Phanerozoic eon lending insight into the early history of the group but, although cnidarians diverged from other animals in the Precambrian period, their record from the Ediacaran period (635–542 million years ago) is controversial. Here, we describe a new fossil cnidarian—Auroralumina attenboroughii gen. et sp. nov.—from the Ediacaran of Charnwood Forest (557–562 million years ago) that shows two bifurcating polyps enclosed in a rigid, polyhedral, organic skeleton with evidence of simple, densely packed tentacles. Auroralumina displays a suite of characters allying it to early medusozoans but shows others more typical of Anthozoa. Phylogenetic analyses recover Auroralumina as a stem-group medusozoan and, therefore, the oldest crown-group cnidarian. Auroralumina demonstrates both the establishment of the crown group of an animal phylum and the fixation of its body plan tens of millions of years before the Cambrian diversification of animal life.

Silica-Carbonate of Ba(II) and Fe2+/Fe3+ Complex as Study Models to Understand Prebiotic Chemistry.

The Precambrian era is called the first stage of the Earth history and is considered the longest stage in the geological time scale. Despite its duration, several of its environmental and chemical characteristics are still being studied. It is an era of special relevance not only for its duration but also because it is when a set of conditions gave rise to the first organism. This pioneer organism has been proposed to have been formed by a mineral and an organic part. A chemical element suggested to have been part of the structure of this cell is iron. However, what special characteristic does iron have with respect to other chemical elements to be proposed as part of this first cell? To answer this and other questions, it is indispensable to have a model that will allow extrapolating the first chemical structures of the pioneer organism formed in the Precambrian. In this context, for several decades, in vitro structures chemically formed by silica-carbonates have been synthetized, called biomorphs, because they could emulate living organisms and might resemble primitive organisms. It has been inferred that because biomorphs form structures with characteristic morphologies, they could resemble the microfossils found in the cherts of the Precambrian. Aiming at providing some insight on how iron contributed to the formation of the chemical structures of the primitive organism, we evaluated how iron contributes to the morphology and chemical–crystalline structure during the synthesis of these compounds under different conditions found in the primitive atmosphere. Experimentally, synthesis of biomorphs was performed at four different atmospheric conditions including UV light, nonionizing microwave radiation (NIR-mw), water steam (WS), and CO2 in the presence of Fe2+, Fe3+, and Fe2+/Fe3+, obtaining 48 different conditions. The produced biomorphs were observed under scanning electron microscopy (SEM). Afterward, their chemical composition and crystalline structure were analyzed through Raman and IR spectroscopy.

Intracellular ATP Concentration and Implication for Cellular Evolution.

Simple SummaryThe lens organ of the eye and muscle tissue exist at opposite ends of the metabolic spectrum. Lens is metabolically quiescent using little energy, while muscle has high energy requirements. However, both tissues contain excessively high millimolar concentrations of adenosine triphosphate (ATP) molecules, the biochemical energy source for all of life’s activities. Nature does not manufacture excess ATP molecules, and thus the question becomes: Why this dichotomy? To answer this question, we prepared a compilation of measured ATP concentrations from cells/tissues/organs across three phylogenetic domains of life: eukaryotes, archaea, and prokaryotes. Among a total of 136 organ/tissue/cell sources, we found that all specimens examined contained excessively high concentrations of ATP (average~4.4 millimolar), regardless of how they lived or their function. Since these specimens only require a small micromolar amount of ATP for energy metabolism, this observation reinforced the notion that ATP has another major function in life. The recent demonstration that ATP acts as a protein solvating agent keeping proteins in their active forms prevents aggregation and in high concentrations may avert a multitude of diseases. The presence of high concentrations of ATP across phylogenetic domains suggests another role for ATP fundamental to cellular/tissue/organ function and biological, biochemical, and biophysical evolution.Crystalline lens and striated muscle exist at opposite ends of the metabolic spectrum. Lens is a metabolically quiescent tissue, whereas striated muscle is a mechanically dynamic tissue with high-energy requirements, yet both tissues contain millimolar levels of ATP (>2.3 mM), far exceeding their underlying metabolic needs. We explored intracellular concentrations of ATP across multiple cells, tissues, species, and domains to provide context for interpreting lens/striated muscle data. Our database revealed that high intracellular ATP concentrations are ubiquitous across diverse life forms including species existing from the Precambrian Era, suggesting an ancient highly conserved role for ATP, independent of its widely accepted view as primarily “metabolic currency”. Our findings reinforce suggestions that the primordial function of ATP was non-metabolic in nature, serving instead to prevent protein aggregation.

New Paleointensity Data Suggest Possible Phanerozoic‐Type Paleomagnetic Variations in the Precambrian

AbstractThe state of the geomagnetic field throughout the Precambrian era is largely unknown. Approximately 8% of global paleointensity records account for ∼4 billion years of Earth history. Despite this severe sparsity, the data are used to constrain models that predict the timing of significant deep earth events such as inner core nucleation. This carries with it the assumption that the Precambrian paleomagnetic field was less variable when compared to the Phanerozoic, or at least that the sparse data can be averaged to accurately represent a particular time period. This study reports new paleointensities from the West Australian Craton at 755 Ma (the Mundine Wells dyke swarm) and 1,070 Ma (the Bangemall Sills); both of which occurred within ∼30 Ma from times at which extremely weak and anomalously strong fields, respectively, have been reported. Virtual dipole moments of 6.3 ± 0.1 Am2 × 1022 and 1.8 ± 1.2 Am2 × 1022 have been obtained from the two suites of mafic rock units which are substantially different to the previous measurements for the two respective ages. The findings suggest that field variability over tens of Myrs in the Precambrian was greater than has previously been assumed. This is supported by comparisons of paleosecular variation and distributions of virtual dipole moments. If variability in the Precambrian field is similar to that observed in the Phanerozoic, spatial or temporal anomalies may introduce significant bias to statistical analyses and model constraints, implying that caution should be employed in the interpretation of the Precambrian dipole moment records.

Радиоэкологическая оценка отложений урановых хвостов (Сумсар, Шекафтар, Терек-Сай)

The article presents the results of radio ecological studies of the territories of uranium tailings in Kyrgyzstan (Sumsar, Shekaftar and Terek-Sai), as well as their current state and assessment of the radioactive contamination’s potential risks. The ore field of this region is characterized as an extremely complex structure and covers about 30 ore occurrences of lead and rare metals. Starting from the Precambrian period both applicative and disjunctive disturbances within its boundaries have been widely developing and being manifested many times throughout the history of geological development. Oxidized and sulfide ores have been developed within the deposit. Unfortunately, serious miscalculations were made. As result of natural disasters; such as earthquakes, landslides, mudflows, etc., several uranium tailing dumbs have been damaged. Day by day, the risk of destruction and the threat of radioactive contamination of the Kyrgyz Republic territory are increasing. There are eight tailing dumps on the territory of Shekaftar uranium natural-technogenic province, the total volume of which is 1194 thousand m3 of radioactive waste. There are 15 mountain dumps of substandard ore with an ore volume of 4585.6 thousand m3 hour, in local areas it exceeds 500 μR/h.

Comparative Genomics Provides Insight into the Function of Broad-Host Range Sponge Symbionts.

ABSTRACTThe fossil record indicates that the earliest evidence of extant marine sponges (phylum Porifera) existed during the Cambrian explosion and that their symbiosis with microbes may have begun in their extinct ancestors during the Precambrian period. Many symbionts have adapted to their sponge host, where they perform specific, specialized functions. There are also widely distributed bacterial taxa such as Poribacteria, SAUL, and Tethybacterales that are found in a broad range of invertebrate hosts. Here, we added 11 new genomes to the Tethybacterales order, identified a novel family, and show that functional potential differs between the three Tethybacterales families. We compare the Tethybacterales with the well-characterized Entoporibacteria and show that these symbionts appear to preferentially associate with low-microbial abundance (LMA) and high-microbial abundance (HMA) sponges, respectively. Within these sponges, we show that these symbionts likely perform distinct functions and may have undergone multiple association events, rather than a single association event followed by coevolution.

Cyclostratigraphy of the Cryogenian Fiq Formation, Oman and its implications for the age of the Marinoan glaciation

Cyclostratigraphy is a powerful tool in chronostratigraphic studies, and has shown its potential in Precambrian time. The Cryogenian Period is one of the most dynamic and intriguing intervals in Earth history and it is a witness to the most extreme climate changes on the planet, known as two Snowball Earth events. However, a robust chronostratigraphic framework is still lacking especially for the younger Marinoan Snowball Earth event, hampering the stratigraphic correlation and comparison among geographically separated records, as well as the understanding of the initiation and termination of this global-scale glaciation. The Cryogenian Fiq Formation in Oman is thought to be Marinoan-equivalent. The duration of the nonglacial units in the Fiq Formation could provide a conservative age constraint on the previously not well-determined onset age of the Marinoan glaciation. In this work, a cyclostratigraphic study has been conducted on three drill cores of the Fiq Formation. The multi-taper method (MTM) spectral analysis, the correlation coefficient (COCO), and the evolutionary correlation coefficient (eCOCO) analyses were performed on the high-resolution gamma-ray (GR) data from the three cores. A hierarchy of Milankovitch cycles (eccentricities, obliquities, and precessions) has been identified, which was used to estimate the optimal sedimentary accumulate rates and the duration of the Fiq Formation in each core. Based on the cyclostratigraphic results, the time scale of the Fiq Formation is at least ~6 Myr. Integrating the radiometric ages and the cyclostratigraphic data from other continents, the onset age of the Marinoan glaciation is suggested to be 650–641 Ma. This new result helps improve the chronostratigraphic framework for the Cryogenian Period and also provides critical temporal constraints for the geological and numerical models that explore the possible mechanisms for the Snowball Earth events.

The Colombian geochronological database (CGD)

ABSTRACT Geochronological databases are powerful tools for characterizing the crustal evolution and the age spectra of a region and allow comparison with other areas at a regional scale. In this contribution, we present the Colombian Geochronological Database (CGD), which contains a curated compilation of ca. 67,406 individual published U-Th-Pb, K-Ar, Ar-Ar, Rb-Sr, Sm-Nd, Lu-Hf, Fission-track, U-Th-He, and Re-Os mineral and whole rock ages that are reported in the published literature. Each date includes geographic coordinates, geological setting, petrologic and chemical information extracted from the respective publications. The structure of the database provides a powerful interface for constructing queries and allows searching and extracting information on geographic domains, provinces, stratigraphic units, isotopic systems, date interpretations, references, etc. This information establishes a framework for regional and global geological interpretations with geochronological, stratigraphic, structural and palaeogeographic implications. With the present effort we present to the geoscience community a clear insight, from a regional perspective, to the geology and tectonics of Colombia since Precambrian times. The comparison of all (detrital and magmatic) single zircon U-Pb dates from the Colombian (Gondwana sourced) geochronological database with the Global and North American (Laurentia sourced) databases provides a temporal constraint on the evolution of the South American continent. U-Pb zircon ages in Colombia define 13 peak clusters centred at 1767, 1530, 1325, 1178, 1007, 605,540, 468, 271, 237, 182, 76 and 10 Ma but of those, only few have a good correlation in all three databases: 1007 (Grenvillian/Orinoquian/Putumayo Orogeny), 605 (Braziliano/Pan-African Orogeny), 468 (Famatinian/Taconic Orogeny), and 182 Ma (Break-up of Pangea) zircon peaks. This correlation suggests that some tectonic events in Colombia are global and might represent crustal production and preservation while the other peaks might just represent local arc magmatic events.

Adakites and associated granitoids from the Serra da Prata Arc: Evidence for a Tonian subduction setting within the Araçuaí-Ribeira orogenic system (AROS), SE Brazil

Within deeply eroded orogenic belts, the geochemical signatures of metamorphosed igneous rocks can be used to constrain modern-like tectonic models operating in Precambrian times. One important aspect of this discussion is the presence or not of pre-collisional arc-related rocks that would represent the magmatic product of subduction processes imprinted on the upper plate of the convergent setting. New detailed geological and geochemical data of the northern segment of the Tonian to Cryogenian juvenile Outer Arc of the Araçuaí-Ribeira Orogenic System (AROS) are presented. Results were combined with recently published U–Pb and Hf data to contribute to a comprehensive tectonic model. The arc-related rocks (Serra da Prata Complex), transformed in foliated orthogneisses, are interlayered with dolomitic marbles, amphibolites, and psammo-pelitic paragneisses (Italva Group). This association is similar to the one described in the southern part of the orogenic system, pointing to the extension of the Outer Arc system until the Rio Doce River, in the transition zone between the Araçuaí and Ribeira segments of the AROS. New geochemical analyses together with reinterpreted published data indicate the presence of typical adakites that, together with normal calc-alkaline expanded series, island arc tholeiitic series, and A-type granitoids, corroborate with a modern style plate tectonic model. The envisaged model started in the Tonian, with E-verging subduction that resulted in the production of very juvenile arc-related rocks and associated fore-to back-arc basins filled with carbonatic rocks, meta-volcanic rocks, and MORB-like basaltic rocks. The typical adakites are considered the result of partial melting of young and hot oceanic lithosphere under moderate to high pressures in which garnet was an important stable residue. Potassic C-type adakitic rocks formed by the partial melting of thickened lower crust occur associated with the typical adakites. The occurrence of both adakites, together with A-type granitoids, characteristic of the investigated terminal sector of the Serra da Prata arc, is interpreted to result from a slab window gap, either associated with slab tearing/ridge subduction or slab roll-back, hampering an intracontinental model for the Ribeira orogen.

Influence of Abiotic Factors in the Chemical Origin of Life: Biomorphs as a Study Model.

Since the formation of the Earth, minerals have been the key to understanding how life originated. It is suggested that life arose from minerals; they are considered to favor the formation and replication of biomolecules. In conjunction with minerals, the abiotic factors of the Precambrian era enabled the origin, development, and maintenance of life. To explain and understand the chemical origin of life, theories have been postulated for decades, and some of them have gone from mere postulates to evidence that have contributed to science in this direction. Several research groups have developed study models elucidating which could have been the first forms of life; in this sense, calcium, barium, or strontium silica carbonates have been synthesized in vitro to emulate morphologies of organisms. Aimed at understanding better the influence of abiotic factors in the formation of different chemical structures, the importance of the different types of physical and chemical abiotic factors in the origin of life are reviewed, as well as their influence on the morphology of biomorphs.

Phanerozoic radiation of ammonia oxidizing bacteria

The modern nitrogen cycle consists of a web of microbially mediated redox transformations. Among the most crucial reactions in this cycle is the oxidation of ammonia to nitrite, an obligately aerobic process performed by a limited number of lineages of bacteria (AOB) and archaea (AOA). As this process has an absolute requirement for O2, the timing of its evolution—especially as it relates to the Great Oxygenation Event ~ 2.3 billion years ago—remains contested and is pivotal to our understanding of nutrient cycles. To estimate the antiquity of bacterial ammonia oxidation, we performed phylogenetic and molecular clock analyses of AOB. Surprisingly, bacterial ammonia oxidation appears quite young, with crown group clades having originated during Neoproterozoic time (or later) with major radiations occurring during Paleozoic time. These results place the evolution of AOB broadly coincident with the pervasive oxygenation of the deep ocean. The late evolution AOB challenges earlier interpretations of the ancient nitrogen isotope record, predicts a more substantial role for AOA during Precambrian time, and may have implications for understanding of the size and structure of the biogeochemical nitrogen cycle through geologic time.

Metallogenesis and depositional environment of the Archean-Proterozoic carbonaceous phyllites from the Dharwar Craton, India

Organic carbon rich meta-sedimentary rocks are important repositories of gold, PGE and vestiges of the biogeochemical cycles that prevailed during the Precambrian time. In this study, we report gold, PGE and δ34S concentrations of carbonaceous phyllites from Neoarchean Chitradurga, Gadag greenstone belts of western Dharwar Craton and Mangampeta of Proterozoic Cuddapah basin, eastern Dharwar Craton to understand their metallogenesis and depositional environments. Chitradurga phyllites (avg. Au = 180 ppb) show elevated concentrations of refractory gold compared to Gadag (avg. Au = 38 ppb) and Mangampeta shales (avg. Au = 23 ppb). The Archean carbonaceous phyllites display three generations of pyrites and their mineral chemistry suggests hydrothermal imprints while Proterozoic shales have two generations of diagenetic pyrites. Gadag has high PGE concentration (ΣPGE = 55 ppb) compared to Chitradurga (ΣPGE = 37 ppb) and Mangampeta (ΣPGE = 27 ppb). The PGE geochemistry is characterized by enrichment of PPGE over IPGE with Au > Pt > Pd and the Au/Pd, Pd/Pt, Ru/Ir, Ir/Pd ratios coupled with negative Pt (Pt/Pt*) anomalies indicate hydrothermal source. The Chitradurga and Gadag samples yielded low sulphur isotopic signatures (δ34S = 1.8–2 and 1.3–2‰ respectively) whereas the Proterozoic Mangampeta samples have comparatively higher values (δ34S = 8.4–34.3‰) suggesting hydrothermal and sea water sulphate sources respectively. Sulphate present in Archean and Proterozoic sea water was converted to sulphur by bacterial sulphate reduction which led to the formation of pyrites. In the Archean phyllites, the metal bearing bisulphide complexes were adsorbed into the pyrites while the Proterozoic shales are characterized by the partitioning of organo-metallic complexes into the pyrite during the diagenesis. Strong positive correlations of transition metals, redox sensitive elements with PGE indicate hydrothermal source and V/(V + Ni), U/Th, Th/U, authigenic U attest euxinic paleo-redox conditions. Thus, biogenically mediated redox depositional environments which prevailed during Archean and Proterozoic times have enhanced the metal sequestration processes that subsequently resulted in the ore formation in these carbonaceous phyllites.

Time in Maps: From the Age of Discovery to Our Digital Era eds. by Kären Wigen and Caroline Winterer

Reviewed by: Time in Maps: From the Age of Discovery to Our Digital Era eds. by Kären Wigen and Caroline Winterer Dudley B. Bonsal Time in Maps: From the Age of Discovery to Our Digital Era. Kären Wigen and Caroline Winterer, eds. Chicago: University of Chicago Press, 2020. Pp. 272, 80 maps, 25 color plates, index. $45.00, hardcover, ISBN 978-0-2267-1859-0. $44.99, eBook, ISBN 978-0-2267-1862-0. The cover of Time in Maps: From the Age of Discovery to Our Digital Era shows a spiral map that illustrates the geological stretch of time from the Precambrian era to the present. Titled "The Geologic Time Spiral—A Path to the Past" and created and published in 2008 by Joseph Graham, William Newman, and John Stacy for the US Geological Survey, it is an evocative representation of geological time's advance, showing representative landforms, flora, fauna, and a river flowing through the middle, and all spiraling upward as if moving closer and emerging out and into the viewer's here-and-now world. The genesis of the book was a conference titled Time in Space: Representing Time in Maps, held at the David Rumsey Map Center in November 2017. Covering a period roughly from 1450 to the twentieth century, with chapters written by conference participants and offering an abundance of beautifully rendered color images, the book addresses various approaches to mapping and imagery for orienting the reader in time as well as in space. Although the cover illustration is emblematic of a linear conception of time, the book explores a highly varied and inclusive range of maps and images that often move beyond such linearity. Of five propositions put forth in the introduction by editors Caroline Winterer and Kären Wigen, two of them—"Diversity persists" and "All maps tell time"—best indicate the variety to be found in the subsequent chapters. Their introduction and the first chapter, William Rankin's "Mapping Time in the Twentieth (and Twenty-First Century)," provide the most wide-ranging discussions about the cartographic representation of time. Winterer and Wigen declare their aim to "interpret the advent of digital mapping as an invitation to explore older maps with fresh eyes" (5)—that [End Page 141] there are many ways for static maps to symbolize a map subject's or map reader's situatedness in time or in its passing. Rankin's discussion addresses directly the representation of time in maps—that time is never instantaneous. Instead, as with a camera's shutter speed, a span of time, or what he refers to as the "cartographic moment" (19), is always a feature. The passing of time is also inherent in how readers gradually move their focus from one part of a map to another. The eight subsequent chapters are more place-specific, as they address a variety of historical mapping practices from three different regions of the world: (1) East Asia, (2) the Atlantic world, with the focus being pre-Hispanic Mesoamerica and Europe, and (3) the United States, having the third section to itself. Winterer and Wigen describe these eight chapters as comprising an "archival sampler." The description is apt, in terms of both content and interpretive approaches. Maps from Japan surreptitiously skirt governmental dictates against portraying conflict-laden current events by disguising them as three-hundred-year-old history. Mapmakers in China and Korea look to Jesuit mapping practices during the Ming period to find relationships between their own historical and present moments. Aztec illustrations show footprints marking the territorial borders until they branch off to trace the temporal destinies of five different altepetl rulers. Francis Walker leads the US Census office to document the country's westward territorial expansion in the Statistical Atlas of 1874. The graphic representation of time in these and other chapters ranges from innovative representations, such as the spiral rendering of geological time shown on the cover, to more basic representations, such as the inclusion of an inset map from another time period, to much more subtle representations that require historical understanding provided by the authors. Two chapters stand out for providing understandings of visual symbology being closely tied to rapidly changing...

The progressive onset and evolution of Precambrian subduction and plate tectonics

The regime of plate tectonics on early Earth is one of the fundamental problems in Earth sciences. Precambrian era takes the majority (ca. 88%) of Earth’s history and thus plays a key role in understanding the onset of plate tectonics and the mechanism, distribution and process of Precambrian subduction zones. This paper presents a review on the progresses of subduction and subduction zones in different stages of Precambrian era, and sorts out some key issues and fields that merits further attention. We suggest that there was progressive onset and evolution of subduction and plate tectonics from Archean to Proterozoic eras. We emphasize the importance of comprehensive studies on subduction mechanism, metamorphic type, plate tectonics regime, the compositional evolution of continental crust, and petrogenesis of diverse granitoids formed in the Archean. It is proposed that innovative analytical techniques, big data, experimental petrology and numerical geodynamic modeling will facilitate future studies of Precambrian subduction zones.

Serra do Navio, Guiana Shield lowland area, Brazil: a region with high diversity of Squamata

The Guiana Region is the area bordered by the Orinoco and Negro rivers to the west, by the Amazonas River to the south and by the Atlantic Ocean to the north and east. This area is a biogeographic unit known as the Guiana Shield, with a variety of landscapes. Located in the extreme north of Brazil, in the Guiana Shield lowlands, the state of Amapa presents great diversity of habitats. In this study we provide composition and diversity data of the Squamata from Serra do Navio (SN) region, in the northeastern part of the state of Amapa, Brazil, a lowland area of the Guiana Shield. The species list was based on data obtained from herpetological collections and collection expeditions carried out at 10 sites in the municipalities of Pedra Branca do Amapari and Serra do Navio. We consider literature data from 14 sites and SN data to compare the composition of herpetofauna between the lowland and highland areas in the Brazilian Amazon. We recorded 95 species, including 57 snakes, 36 lizards, and two species of amphisbaenians. Atractus aboiporu, A. trefauti, and Erythrolamprus rochai were described from the data collected in this study. The Squamata community of SN consists mainly of diurnal lizards and nocturnal snakes, with terrestrial and cryptozoic habits, present in pristine and altered environments. The most abundant species of lizard and snake were Loxopholis guianense and Atractus latifrons, respectively. The SN region has 17 exclusive Squamata species, with a fauna similar to the Tumucumaque Mountains and northern Para sites, geographically closer regions with similar altitudes.

RETRACTED: Detrital zircon age distribution characteristics of Jurassic sandstone from the Southern Yili basin, China

The Central Asia orogenic belt contains a wide range of structural elements, including micro continent, back arc system, ocean island/plateau, ophiolite and subduction accretion complex. But its final closing time has been controversial. Based on the magmatic age of the surrounding orogenic belt, the source of this set of clastic sediments is determined, which provides new important evidence for the evolution of the South Tianshan orogenic belt. The results show that the Jurassic detrital zircons from the study area were mainly derived from magmatic zircons and are deposited in a proximal source. The detrital zircon age of the Lower Jurassic Badaowan and Sangonghe Formation are concentrated in 290–260 Ma, and in 350–290 Ma and 460–390 Ma, respectively. The detrital zircon age of the Middle Jurassic Xishanyao Formation concentrates in 370–320 Ma and 450–390 Ma. There are very few zircons from the Precambrian period. These ages are consistent with the timing, indicating these clastic sediments were mainly originated from the southern margin of the Yili - Middle Tianshan Block. The Late Permian - Middle Triassic detrital zircons almost do not exist, implying that there were no contemporary magmatism related to collision or post-collision in the South Tianshan district, its complex evolution and orogenic stage are still a challenging topic. In the ancient active plate margin, the sedimentary records in the pre-arc basin can provide more information about the magmatic arc and basin-orogen coupling than the present exposed arc itself. The rhyolite, trachyte, and trachyandesite of the Dahalajunshan Formation were widely developed in the Yili - Middle Tianshan Block during the Early Carboniferous. During the formation of Wulang Formation in the Early Permian, a large number of rhyolite were developed. The age data of 75 detrital zircons were obtained from the sandstone (J1s-5) of the Sangonghe Formation, of which 74 zircons have a concordance degree of over 90%, and their age data also fall on the harmonic curv. In addition, the age of the youngest zircons increased gradually from Early to Middle Jurassic, indicating that the sediments in this period had the feature of uncovering. Our study provides a good reference for the analysis of provenance and regional tectonic evolution.

Assessment of Relative Tectonics Activity Zones in Masila Oil Field, Yemen

Masila oil field, a part of rift graben basin (Sayun-Masila basin), Yemen, is affected by several tectonic events since Pre-Cambrian period. The present study makes an effort to assess the relative tectonic activity in this oil field. Several geomorphic indices, lineaments, and depth structural anomalies were generated as thematic maps using remotely sensed data, wells data, and existing geological and seismic data in a GIS platform. The thematic maps were converted into a grid format, classified into different categories based on their relative importance, and integrated using the GIS integration tool. The final map, generated by the integration of thematic maps, was categorized into five relative tectonic zones, namely very high relative tectonic zone (9.2%), high relative tectonic zone (10.6%), moderate relative tectonic zone (30%), low relative tectonic zone (36%), and very low relative tectonic zone (14.2%). The surface lineament anomalies and subsurface geological cross-section were subsequently used to validate the derived results. The results obtained through this approach may be helpful for exploring resources, such as hydrocarbons, and predicting hazards. The study highlights the advantage of using different datasets from various sources and their overlay in a GIS platform for assessing relative tectonic activity.

Neoproterozoic Nafun Group Sediments from Oman Affected by an Active Continental Margin

The Neoproterozoic era is a time of major environmental change in Earth history. The Ediacaran period (635–541 Ma), the uppermost division of Precambrian time, is characterized by the remarkable Shuram excursion (largest C isotope negative excursion), a deep ocean water oxidation event, and Ediacaran biota. The Nafun Group of Oman provides a well-preserved and mostly continuous section of an Ediacaran succession. Based on geochemical data from the Nafun Group, the Shuram excursion (SE) and deep ocean oxidation hypotheses were proposed. Now, we sampled this section at high stratigraphic resolution, and present here the petrographical and geochemical analysis of the Khufai, Shuram and Buah Formations. The major and trace element analysis of shales from the Shuram Formation indicates that northern Oman was an active continental margin environment in Neoproterozoic times. The provenance of the Shuram Formation was primarily mafic and intermediate igneous rocks. With the unsteady tectonic setting, the development of the Nafun Group was influenced by hydrothermal supply and volcaniclastic input. Based on the V/Cr and U/Th ratio of the samples from the Nafun Group, our study reveals the transition of the ocean water redox environment, which is connected to the rise and fall of the Ediacaran biota. Our study constrains the tectonic setting of northern Oman and the petrography and geochemical data from the Nafun Group for the hydrothermal and volcaniclastic supply. Thus, our study acknowledges more factors for the explanation of the Ediacaran conundrums.

Microbial mineralization of botryoidal laminations in the Upper Ediacaran dolostones, Western Yangtze Platform, SW China

Botryoidal dolostones are abundant in the Second Member of the Upper Ediacaran Dengying Formation in the Western Yangtze Platform. Although they have been extensively discussed as important host rocks for giant gas reservoirs, there is no consensus on the microbial impact on mineralization processes in the botryoidal laminations. Typical botryoidal laminations were studied under optical microscopes and scanning electron microscopes (SEMs) to investigate their origin. There are three macroscopic morphological types of botryoidal lamination: stromatoid lamination, cavity-lining lamination, and spherical-encrusting lamination. These three types of lamination are composed of fibrous and bladed crystals growing perpendicular to the botryoidal laminae, which have hitherto been implicitly considered to be from abiogenic chemical precipitation. There are many lines of new evidence that demonstrate microbial activities in the interbedded dark and bright laminae constituting the laminations. In the dark laminae, euhedral dolomite rhombs are observed sticking to linear and tubular filaments, or wrapped in sheets of extracellular polymeric substances (EPS) with dolomite crystal sizes of generally <5 μm. The bright laminae are dominated by coarser dolomites and connected by radial sheaths and trichomes with dolomite crystal sizes of primarily around 10 μm. Different species of bacteria, which are closely related to the macroscopic morphology of the laminations, are present in both the bright and dark laminae. The results are useful in understanding the origin and formation mechanisms of the Neoproterozoic botryoidal dolostones. The new findings may also shed new light on the occurrence and evolution of early life on Earth in the Precambrian Era.