Earth Events Research Articles

Manganese Deposits of Africa

Africa hosts just over 80 percent (%) of the world's known land-based ore resources of manganese metal and produced some 41.1% of the 18 million tonnes (Mt) of manganese metal in ores, that was mined during 2014. The deposits are mainly of sedimentary and supergene origin comprising four major types, namely banded iron formation (BIF)-hosted, black shale-hosted, oolitic and supergene/karst-hosted deposits. The BIF-hosted Kalahari Manganese Field (KMF) is by far the largest of these deposits holding some 4,200 Mt of manganese metal that represents about 77% of the world's known land-based resource. Other major deposits are present in the Francevillian of Gabon, represented by high-grade supergene manganese oxide ores derived from weathering of rhodochrosite-bearing black shale source rock, and manganese carbonates interbedded with black shale and greywackes associated with volcanicdominated orogenic belts in the Birimian of West Africa and Lukoshi Complex at Kisenge in the Democratic Republic of the Congo (DRC). High-grade supergene manganese oxide ores cap the manganese carbonate beds. All these major ore deposits formed in the interval 2.0-2.2 Ga. Additional deposits that contain only relatively small resources but that hold important scientific information about the Earth's history include the ~ 2.4 Ga BIF-hosted Rooinekke deposit of the Transvaal Supergroup, which formed prior to the ~ 2.32 Ga Great Oxidation Event (GOE), karst-hosted deposits of the Postmasburg area that formed along a 2.0 Ga palaeoweathering profile below red beds of the Gamagara/Mapedi succession in South Africa, the ~1.9 Ga Tolwe deposit that represents the oldest known example of oolitic manganese ore in the world and the BIF-hosted Otjosondu deposit in Namibia, related to the Neoproterozoic Sturtian Snowball Earth Event (an extremely cold period of time in geologic history when Earth was covered by a virtual global ice cap). The manganese carbonates present in most of these deposits are all highly enriched in light organic carbon isotopes indicating that they were derived from reduction of original manganese oxide precipitates by organic carbon during diagenesis. This implies that the water columns from which the sedimentary manganese beds originally precipitated, as well as the floors of the depositories, were oxygenated. Post Archaean Australian Shale (PAAS)-normalized cerium (Ce) anomalies in Rare Earth Element (REE) data, support the presence of oxic conditions in the basins. It is thus not surprising that all the major 2.0-2.2 Ga deposits formed after the GOE. In this regard the relatively small BIF-hosted Rooinekke manganese deposit is very significant in that it formed prior to the GOE suggesting that at least some free oxygen was present in ocean basins before that time. There also appears to have been a major tectonosedimentary control on the distribution of the major 2.0- 2.2 Ga deposits. All of them, including the KMF, apparently formed in back-arc basinal settings immediately prior to amalgamation of cratonic blocks along Eburnian orogenic belts and formation of the supercontinent Columbia.

Phosphogenesis associated with the Shuram Excursion: Petrographic and geochemical observations from the Ediacaran Doushantuo Formation of South China

The Ediacaran Period witnessed one of the largest phosphogenic events in Earth's history. Coincidently, some phosphorite deposits in South China are associated with the largest-known carbon isotope negative excursion (i.e., Shuram Excursion), suggesting an intimate coupling of the biogeochemical carbon and phosphorous cycles. However, the geomicrobiological linkage between these anomalies remain poorly understood. In this study, we investigated the phosphorite samples from the uppermost Doushantuo Formation in South China. Carbon isotope compositions of authigenic calcite cements and nodules in the phosphorites are as low as –34‰ (VPDB). Petrographic and geochemical investigations indicate that the 13C-depleted carbonates likely formed as the result of microbial sulfate and iron reduction that released phosphorous from iron oxyhydroxide, concentrating phosphorous in pore waters, and thereby promoting phosphate mineralization. The timing of this event appears to coincide with enhanced sulfate delivery to seawater through continental weathering. The basin-scale distribution of Doushantuo phosphorites suggests a redox control on the availability of iron oxyhydroxide and the recycling of pore water phosphorous. Both inner and outer shelf regions were likely characterized by an oxic water column, and were the main loci for phosphogenesis; on the contrary, intra-shelf and slope regions, which are lean in phosphorite, were subjected to euxinic or ferruginous water column conditions. The intimate coupling between Ediacaran phosphogenesis and the Shuram Excursion suggests strong links among seawater redox conditions, C-S-P-Fe cycling, and fossil phosphatization. Increased microbial sulfate reduction driven by enhanced sulfate reservoir in the Ediacaran ocean may have played an essential role on these biogeochemical events.

Electron-scale measurements of magnetic reconnection in space

Magnetic reconnection is a fundamental physical process in plasmas whereby stored magnetic energy is converted into heat and kinetic energy of charged particles. Reconnection occurs in many astrophysical plasma environments and in laboratory plasmas. Using measurements with very high time resolution, NASA's Magnetospheric Multiscale (MMS) mission has found direct evidence for electron demagnetization and acceleration at sites along the sunward boundary of Earth's magnetosphere where the interplanetary magnetic field reconnects with the terrestrial magnetic field. We have (i) observed the conversion of magnetic energy to particle energy; (ii) measured the electric field and current, which together cause the dissipation of magnetic energy; and (iii) identified the electron population that carries the current as a result of demagnetization and acceleration within the reconnection diffusion/dissipation region.

Silicon stable isotope fractionation between metal and silicate at high-pressure, high-temperature conditions as a tracer of planetary core formation

AbstractThe largest differentiation event in Earth and other terrestrial planets was the high-pressure, high-temperature process of metal core segregation from a silicate mantle. The abundant element silicon (Si) can be partially sequestered into the metallic core during metal–silicate differentiation, depending on pressure, temperature and planetary oxidation state. Knowledge of the Si content of a planet's core can constrain the conditions of core formation, but in the absence of direct samples from planetary cores, quantifying core Si content is challenging. One relatively new tool to study core formation in terrestrial planets is based on combining measurements of the Si stable isotopic composition of planetary crust and mantle samples with measurements of the Si stable isotope fractionation between metal and silicate at high-temperature and high-pressure conditions. In this study we present the results of a small set of high-pressure, high-temperature (HPT) experiments and combine these with a review of literature data to investigate how the Si isotope fractionation behaviour between metal and silicate varies as a function specifically of experimental run time and temperature. We show that although there is no debate about the sign of fractionation, absolute values for Si isotope fractionation between metal and silicate are difficult to constrain because the experimental database remains incomplete, and because Si isotopic measurements of metals in particular suffer from the absence of a true inter-laboratory comparison. We conclude that in order to derive accurate quantitative estimates of the Si content of the core of the Earth or other planets a wide range of additional experiments will be required.

LATE TRIASSIC DUROPHAGY AND THE ORIGIN OF THE MESOZOIC MARINE REVOLUTION

The evolutionary history of marine predator-prey interactions is a topic with important implications for a broad array of paleoecological questions. Has predation of marine organisms intensified through time? How have mass extinction events affected these interactions over longer time scales? What is the role of predator-prey interactions in species diversity and paleoecological structure of marine communities? The conditions that lead to complex marine ecosystems and the response of these systems to disruptive events in Earth's history are of direct importance to understanding and predicting the response of modern ocean ecosystems to changing conditions in the Common Era. Characterizing even the most general trends of marine predation through the Phanerozoic has proven to be a complex problem due to the difficulties in quantifying predation among and between the wide range of taxa, morphological adaptations, behaviors, and modes of life involved. In Vermeij's (1987) classic book on escalation, he outlined an impressive array of anti-predation adaptations distributed among many different phyla that can be quantified and tracked through time including shell thickness and size, degree of ornamentation, and the ability to cement or swim. In addition to these morphologic features, adaptive radiations of various specialized predators and changing frequencies of predation traces could be correlated to the appearance of many shelly invertebrate taxa with anti-predator adaptations. Most of the unique adaptations in predators and shelly prey were present by the Jurassic Period, while frequencies of predatory drill holes rapidly increased during the Cretaceous, leading Vermeij (1977) to term this phenomenon the Mesozoic Marine Revolution (MMR). Identifying an escalatory influence between durophagous predators and their shelly prey requires more than correlation of appearances and taxonomic radiations of predators and prey (Harper and Skelton 1993; Deitl and Kelley 2002). Unlike the Cretaceous coupling of taxonomic radiations of predatory gastropods with increased frequencies of …

A eukaryote assemblage intercalated with Marinoan glacial deposits in South Australia

Composite hematite–silica structures recovered from a siltstone bed in the Elatina Formation of South Australia include (1) sub-circular to whorl-shaped forms, (2) elongate to half-moon-shaped forms and (3) and lozenge-shaped forms locally linked into chains. They range from 200 to 500 µm in diameter and are interpreted as eukaryote tests. Evidence for internal etching of a calcite core of some tests indicates that at least some of the hematite–silica fabrics were acquired through replacement. Carbon isotope values of −20‰ δ 13 C are suggestive of precipitation by microbial activity, and imply a change in ambient fluid chemistry associated with a pH reduction. The tests occur within sandstone beds that were deposited on a tidally modulated braidplain during the Marinoan glaciation at the end of the Cryogenian. The quartz grains in the sandstone sample lack the typical textures (surface striae, internal fractures or irregular grain boundaries) expected for glacially transported material. Thus, on textural grounds we argue that the eukaryote tests represent a proglacial ecosystem during a late Cryogenian snowball Earth event. Supplementary material: Video files of digital X-ray tomographs (μCT) in the longitudinal and transverse planes are available at: https://doi.org/10.6084/m9.figshare.c.2209723 .

Variability, Instabilities, and Eddies in a Snowball Ocean

Abstract Oceanic variability and eddy dynamics during snowball Earth events, under a kilometer of ice and driven by a very weak geothermal heat flux, are studied using a high-resolution sector model centered at the equator, where previous studies have shown the ocean circulation to be most prominent. The solution is characterized by an energetic eddy field, equatorward-propagating zonal jets, and a strongly variable equatorial meridional overturning circulation (EMOC), on the order of tens of Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1), restricted to be very close to the equator. The ocean is well mixed vertically by convective mixing, and horizontal mixing rates by currents and eddies are similar to present-day values. There are two main opposite-sign zonal jets near the equator that are not eddy driven, together with multiple secondary eddy-driven jets off the equator. Barotropic stability analyses, the Lorenz energy cycle (LEC), and barotropic-to-baroclinic energy conversion rates together indicate that both baroclinic and barotropic instabilities serve as eddy-generating mechanisms. The LEC shows a dominant input into the mean available potential energy (APE) by geothermal heat flux and by surface ice melting and then transformation to eddy APE, to eddy kinetic energy, and finally to mean kinetic energy via eddy–jet interaction, similarly to the present-day atmosphere and unlike the present-day ocean. The EMOC variability is due to the interaction of warm plumes driven by geothermal heating that reach the ocean surface, leading to ice-melt events that change the stratification and, therefore, the EMOC. The results presented here may be relevant to the ocean dynamics of planetary ice-covered moons such as Europa and Enceladus.

Calcium and calcium isotope changes during carbon cycle perturbations at the end-Permian

Negative carbon and calcium isotope excursions, as well as climate shifts, took place during the most severe mass extinction event in Earth's history, the end-Permian (∼252 Ma). Investigating the connection between carbon and calcium cycles during transient carbon cycle perturbation events, such as the end-Permian, may help resolve the intricacies between the coupled calcium-carbon cycles, as well as provide a tool for constraining the causes of mass extinction. Here we identify the deficiencies of a simplified calcium model employed in several previous studies, and we demonstrate the importance of a fully coupled carbon cycle model when investigating the dynamics of carbon and calcium cycling. Simulations with a modified version of the Long-term Ocean-atmosphere-Sediment CArbon cycle Reservoir model, which includes a fully coupled carbon-calcium cycle, indicate that increased weathering rates and ocean acidification (potentially caused by Siberian Trap volcanism) are not capable of producing trends observed in the record, as previously claimed. Our model results suggest that combined effects of carbon input via Siberian Trap volcanism (12,000 Pg C), the cessation of biological carbon export, and variable calcium isotope fractionation (due to a change in the seawater carbonate ion concentration) represents a more plausible scenario. This scenario successfully reconciles δ13C and δ44Ca trends observed in the sediment record, as well as the proposed warming of >6°C.

THEMIS statistical study on the plasma properties of high-speed flows in Earth’s magnetotail

Using Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations from 2007 to 2011 tail seasons, we study the plasma properties of high speed flows (HSFs) and background plasma sheet events (BPSs) in Earth’s magnetotail (|Y GSM|<13RE, |ZGSM|<5RE,–30RE<XGSM<–6RE), and their correlations with solar wind parameters. Statistical results show that the closer the HSFs and BPSs are to the Earth, the hotter they become, and the temperature increase of HSFs is larger than that of BPSs. The density and temperature ratios between HSFs and BPSs are also larger when events are closer to Earth. We also find that the best correlations between the HSFs (BPSs) density and the solar wind density occur when the solar wind density is averaged 2 (3.5) hours prior to the onset of HSFs (BPSs). The normalized densities of both HSFs and BPSs are correlated with the interplanetary magnetic field (IMF) θ angles \(\left( {\theta = \arctan \left( {{B_z}/\sqrt {B_x^2 + B_y^2} } \right)} \right.\) which are averaged 3 hours before the observation time. Further analysis indicates that both HSFs and BPSs become denser during the northward IMF period.

Predicting loss of evolutionary history: Where are we?

The Earth's evolutionary history is threatened by species loss in the current sixth mass extinction event in Earth's history. Such extinction events not only eliminate species but also their unique evolutionary histories. Here we review the expected loss of Earth's evolutionary history quantified by phylogenetic diversity (PD) and evolutionary distinctiveness (ED) at risk. Due to the general paucity of data, global evolutionary history losses have been predicted for only a few groups, such as mammals, birds, amphibians, plants, corals and fishes. Among these groups, there is now empirical support that extinction threats are clustered on the phylogeny; however this is not always a sufficient condition to cause higher loss of phylogenetic diversity in comparison to a scenario of random extinctions. Extinctions of the most evolutionarily distinct species and the shape of phylogenetic trees are additional factors that can elevate losses of evolutionary history. Consequently, impacts of species extinctions differ among groups and regions, and even if global losses are low within large groups, losses can be high among subgroups or within some regions. Further, we show that PD and ED are poorly protected by current conservation practices. While evolutionary history can be indirectly protected by current conservation schemes, optimizing its preservation requires integrating phylogenetic indices with those that capture rarity and extinction risk. Measures based on PD and ED could bring solutions to conservation issues, however they are still rarely used in practice, probably because the reasons to protect evolutionary history are not clear for practitioners or due to a lack of data. However, important advances have been made in the availability of phylogenetic trees and methods for their construction, as well as assessments of extinction risk. Some challenges remain, and looking forward, research should prioritize the assessment of expected PD and ED loss for more taxonomic groups and test the assumption that preserving ED and PD also protects rare species and ecosystem services. Such research will be useful to inform and guide the conservation of Earth's biodiversity and the services it provides.

A high-resolution chemostratigraphy of post-Marinoan Cap Carbonate using drill core samples in the Three Gorges area, South China

Cap Carbonates overlie the Marinoan Snowball Earth-related glacial diamictite, and possibly record the drastic surface environmental change and biological evolution after the Snowball Earth. We conducted on-land drilling from the Liantuo Formation, through the Nantuo, to the lower Doushantuo Formation in the Three Gorges area of South China to collect fresh, continuous samples in the Three Gorges area. We obtained high-resolution chemostratigraphies of δ13C and δ18O values of carbonates from the topmost part of the Nantuo Formation to the Cap Carbonate, in order to decode the detailed surface environmental change in the shallow marine setting. The δ13C chemostratigraphy possesses some unique characteristics: (1) stable δ13C values as a whole, but ubiquitous low δ13C anomalies through the Cap Carbonate, (2) increase of the δ13C values from −3 to +5‰ across the C2/C3 boundary, (3) no δ13C anomaly between the C1 and C2 boundary, and (4) presence of an anomalous high δ13C value (+2.3‰) and a faint positive correlation between δ13C and δ18O values in the C1 unit.Evidence of quite low δ13C anomalies (with a nadir of −41‰), ubiquitous negative δ13C anomalies through the Cap Carbonate, and a high δ13C anomaly accompanied with a faint positive correlation between δ13C and δ18O values in the C1 unit supports decomposition and formation of methane hydrate during Cap Carbonate formation. The drastic increase of δ13C values from the upper C2 to C3 units indicates enhancement of primary productivity and organic carbon burial, possibly due to high continental fluxes after the Snowball Earth event, evidenced by high Sr isotope values. The increase is restricted to the proximal side of the inner shelf in South China, and the timing of the increase of δ13C values of carbonates is earlier at Three Gorges area than any other area, suggesting that the enhancement of primary productivity started in the proximal environment because of higher continental influxes. The increase in oxygen contents of seawater due to the enhanced primary productivity possibly resulted in the emergence of multicellular animals soon after Cap Carbonate deposition.

The significance of ice-rafted debris in Sturtian glacial successions

Globally, Sturtian (early Cryogenian) glacial deposits are well expressed, and belong to the oldest Neoproterozoic icehouse Earth event. The evidence for glaciation typically includes the phenomena such as striated pavements, striated clasts in diamictites, and abundant dropstones. More problematic, and potentially more significant, are intercalated deposits that exhibit no apparent evidence of a glacial influence on deposition. These apparently non-glacially-influenced intervals may represent deposition during interglacial periods, or at times when ice sheets transitioned to cold-based ice masses where sediment advection into basins was suppressed. Here, using three case studies from South Australia, northern Namibia, and Death Valley (USA), we show that many IRD-free intervals occur at the top of backstepping successions, where they are best interpreted as glacial minima deposits. In other cases, the volume of IRD in a succession shows less distinct increases and decreases upsection. Rhythmic intercalation of IRD-bearing and IRD-free intervals with glaciomarine turbidites can also be observed. These latter examples may be interpreted to record variations in debris content of ice margins, switch on/switch off of ice streams, or simply dynamic oscillation of a hinterland ice margin.

Revealing the climate of snowball Earth from Δ17O systematics of hydrothermal rocks

The oxygen isotopic composition of hydrothermally altered rocks partly originates from the interacting fluid. We use the triple oxygen isotope composition ((17)O/(16)O, (18)O/(16)O) of Proterozoic rocks to reconstruct the (18)O/(16)O ratio of ancient meteoric waters. Some of these waters have originated from snowball Earth glaciers and thus give insight into the climate and hydrology of these critical intervals in Earth history. For a Paleoproterozoic [∼2.3-2.4 gigayears ago (Ga)] snowball Earth, δ(18)O = -43 ± 3‰ is estimated for pristine meteoric waters that precipitated at low paleo-latitudes (≤35°N). Today, such low (18)O/(16)O values are only observed in central Antarctica, where long distillation trajectories in combination with low condensation temperatures promote extreme (18)O depletion. For a Neoproterozoic (∼0.6-0.7 Ga) snowball Earth, higher meltwater δ(18)O estimates of -21 ± 3‰ imply less extreme climate conditions at similar paleo-latitudes (≤35°N). Both estimates are single snapshots of ancient water samples and may not represent peak snowball Earth conditions. We demonstrate how (17)O/(16)O measurements provide information beyond traditional (18)O/(16)O measurements, even though all fractionation processes are purely mass dependent.

The marine environments encompassing the Neoproterozoic glaciations: Evidence from C, Sr and Fe isotope ratios in the Hecla Hoek Supergroup in Svalbard

The Neoproterozoic Era records several important events in Earth history. The associations between BIF deposition, Snowball Earth events and the redox state of seawater are the key to explain the re-appearance of banded iron formations (BIF) during the Neoproterozoic. Unraveling ancient iron cycles provides important information about the linkage between the precipitation of BIF and the redox condition in the ocean, but current iron isotopic data are limited to sediments deposited only during the Sturtian glaciations and Ediacaran.We conducted a detailed geological survey of the Tonian to Ediacaran sedimentary succession in Nordaustlandet island, Svalbard. Our chemostratigraphies of δ13Ccarb from pre-Sturtian to post-Marinoan sedimentary successions in the Polarisbreen Group are consistent with those in coeval sediments.We first analyzed iron isotope ratios (δ56/54Fe) of individual pyrite grains with diverse shapes in carbonates, black shales, quartz arenites and diamictites in order to constrain the redox condition in seawater. We found large variations in iron isotope ratios; from ca. −2 to ca. +4‰. Positive δ56/54Fe values, over +1.0‰, are only preserved in euhedral and aggregated pyrite grains in black shales of the Backlundtoppen Formation and the MacDonaldryggen Member of the Elbobreen Formation. A partial oxidation of ferrous iron in seawater is necessary to explain such high δ56/54Fe values, which means that deep seawater was ferruginous (ferrous, iron-rich) before and after the Sturtian glaciation. This stands in opposition to the traditional idea that a glacial cover on an ocean is necessary for the accumulation of ferrous iron in Neoproterozoic seawater. This study presents the first evidence from iron isotopes that supports a deep ferruginous ocean around the Sturtian glaciation. If the deep ocean was intrinsically iron-rich, it is likely that Neoproterozoic BIFs formed by thermohaline circulation during the glaciation and by massive oxidation due to the expansion of oxic oceans after the glaciation.

The Snowball Earth events during the Proterozoic and formation of ore deposits

The Snowball Earth events during the Proterozoic and formation of ore deposits

Stable “Waterbelt” climates controlled by tropical ocean heat transport: A nonlinear coupled climate mechanism of relevance to Snowball Earth

AbstractOngoing controversy about Neoproterozoic Snowball Earth events motivates a theoretical study of stability and hysteresis properties of very cold climates. A coupled atmosphere‐ocean‐sea ice general circulation model (GCM) has four stable equilibria ranging from 0% to 100% ice cover, including a “Waterbelt” state with tropical sea ice. All four states are found at present‐day insolation and greenhouse gas levels and with two idealized ocean basin configurations. The Waterbelt is stabilized against albedo feedback by intense but narrow wind‐driven ocean overturning cells that deliver roughly 100 W m−2 heating to the ice edges. This requires three‐way feedback between winds, ocean circulation, and ice extent in which circulation is shifted equatorward, following the baroclinicity at the ice margins. The thermocline is much shallower and outcrops in the tropics. Sea ice is snow‐covered everywhere and has a minuscule seasonal cycle. The Waterbelt state spans a 46 W m−2 range in solar constant, has a significant hysteresis, and permits near‐freezing equatorial surface temperatures. Additional context is provided by a slab ocean GCM and a diffusive energy balance model, both with prescribed ocean heat transport (OHT). Unlike the fully coupled model, these support no more than one stable ice margin, the position of which is slaved to regions of rapid poleward decrease in OHT convergence. Wide ranges of different climates (including the stable Waterbelt) are found by varying the magnitude and spatial structure of OHT in both models. Some thermodynamic arguments for the sensitivity of climate, and ice extent to OHT are presented.

A melting pot world of species: reply to Speziale et al.

Native plants and animals are a natural heritage threatened by one of the six greatest extinction events in Earth's history. Humans, through habitat transformation, exploitation, and species introductions, are driving this extinction event. To turn this tide, Speziale et al. (2014) suggest reducing human dependence on non-native species by increasing the use, harvest, planting, and raising of native species, thereby increasing their cultural and economic value. The search for new or under-appreciated uses of native species is laudable, especially if it helps protect them and contributes to local cultural diversity. Such efforts are arguably an inherent trait of human curiosity and entrepreneurship and are a central platform of popular movements such as slow foods and native gardening. However, Speziale et al.'s hypothesis - that using native species can protect them - is less simple than they suggest. We refute the idea of nativism that underpins Speziale et al.'s proposal and makes it poorly defensible and considered the unaddressed consequences of the proposal for people and for conservation.

Palynology of the Kazanian stratotype section (Permian, Russia): palaeoenvironmental and palaeoclimatic implications

Palynomorph assemblages reflect changes in land plant communities and are thus significant proxies to interpret palaeoenvironmental and palaeoclimatic changes. The Middle Permian of the East European Platform is crucial to the understanding of marine and non-marine palaeoclimate archives and interregional correlations of marine and non-marine successions, utilising palaeoclimate signatures documented in the palynological record. New palynological data from the Kazanian stratotype section are presented and interpreted with respect to palaeoenvironment and palaeoclimate. This dataset will serve as a basis for ongoing studies on the type area of the Kazanian and the mid-Permian biodiversity patterns, preceding the end-Guadalupian crisis and the changes of the end-Permian biotic diversification followed by the most severe extinction event in Earth’s history at the Permian-Triassic boundary.

Geochemical characterization of the Marinoan “Cap Carbonate” of the Niari-Nyanga Basin (Central Africa)

Despite recent works on the Schisto-calcaire Group of the West-Congolian Supergroup in Central Africa, Neoproterozoic Cap Carbonate have not been well documented in the Niari-Nyanga basin that extends from Gabon to Angola. The couplet “Cap Carbonate (SCIa) and Upper Diamictite”, that is a marker of the “Snowball Earth event” was studied in 5 sections from the Niari-Nyanga basin and in one section from the external zone of the Mayombe folded belt (MFB). Our paper presents a high-resolution data set based on results from petrography, geochemistry, mineralogy and stable isotope studies performed on Cap Carbonate samples. The estimation of the illite crystallinity indexes indicates different degrees of post-sedimentary transformations evolving from deep diagenesis in the syncline basin to an epimetamorphism in the external zone of the MFB. Thin-sections of rocks sampled in this latter section display metamorphic features materialized by recrystallization of minerals in a S1 cleavage plane. Despite such an observation, all our samples clearly show preservation of primary petrographic structures such as biolaminations, fenestrae and peloids. Geochemical data leads us to highlight that the Cap Carbonate is composed by a variety of carbonate types. These results support the fact that the Cap Carbonate was derived from a combination of biological and chemical processes: organomineralization and chemical precipitation from supersaturated solutions, with a negligible impact of post-depositional transformations. For all the studied sections, stable isotope profiles display a drop in δ13C values, from about −2.6‰ to −4‰, associated with δ18O values ranging from −6‰ to −10‰. Moreover, the similarity of the isotopic profiles of the studied Cap Carbonate (from the Niari-Nyanga basin and the MFB) and the close fit to the expected Neoproterozoic δ13C and δ18O seawater values constitute a strong indication of a weak impact of a diagenetic to epimetamorphic evolution on the carbon isotopic signature of the SCIa Cap Carbonate. In the light of this data set, our isotopic records must be considered as a reliable tracer of the Marinoan Glaciation within the West-Congolian Supergroup.

Life Origination Hydrate Theory (LOH-Theory) and the explanation of the biological diversification.

The Life Origination Hydrate Theory (LOH-Theory) considers the life origination process as a sequence of thermodynamically caused regular and inevitable chemical transformations regulated by universal physical and chemical laws. The LOH-Theory bears on a number of experimental, thermodynamic, observation, and simulation researches. N-bases, riboses, nucleosides, and nucleotides and DNAs and RNAs are formed repeatedly within structural cavities of localizations of underground and underseabed honeycomb CH4-hydrate deposits from CH4 and nitrate and phosphate ions that diffused into the hydrate structures; proto-cells and their agglomerates originated from these DNAs and from the same minerals in the semi-liquid soup after liquation of the hydrate structures. Each localization gave rise to a multitude of different DNAs and living organisms. The species diversity is caused by the spatial and temporal repeatability of the processes of living matter origination under similar but not identical conditions, multiplicity of the DNA forms in each living matter origination event, variations in the parameters of the native medium, intraspecific variations, and interspecific variations. The contribution of the last to the species diversity is, likely, significant for prokaryotes and those eukaryotes that are only at low steps of their biological organization; however, in the light of the LOH-Theory, of available long-term paleontological investigations, and of studies of reproduction of proliferous organisms, we conclude that, in toto, the contribution of interspecific variations to the species diversity was earlier overestimated by some researchers. The reason of this overestimation is that origination of scores of «spores» of different organisms in any one event and multiple reproductions of such events in time and Earth's space were not taken into consideration.