Pondering the Precambrian #11

Proterozoic:

NeoProterozoic:

The problematic Orbisiana fossil from the Ediacaran of Russia is reevaluated.

Ediacaran life formed complex ecological communities.

Dickinsonia is confirmed to be an Ediacaran animals.  In fossils from the White Sea, molecular traces of steroids were found.

There is more evidence of sponges being present on the sea floor during the Cryogenian.

Precambrian Research is doing a special issue on the Cryogenian and especially the Tonian/Cryogenian transition.

There is evidence of the Rodinia supercontinent breakup during the Tonian.

MesoProtoerozoic:

From during the Stenian, there is evidence of an intracontinental rift forming in Australia.

There is evidence the shallow waters of the MesoProterozoic were anoxic.

Where and when did the PaleoAsian Ocean form?   Another view.

PaleoProterozoic:

There is evidence Africa and Brazil were part of the Congo-Sao Francisco continent during the PaleoProterozoic and of mountain building from that timeframe.

Carbonatite found in China gives a precise time for the beginning of the breakup of the Columbia supercontinent during the Orosirian.

Archean:

There is evidence of sulfur munching microbes from NeoArchean hydrothermal system ~2.7 billion years ago.

The oldest known paleosols - soil fossils - may have been found and date from the EoArchean.

The trace fossils from the PaleoArchean attributed to life might NOT be anything of the sort.

Hadean:

Hadean into the Archean, Earth seems to have lost an ocean's worth of water.  Or at least the hydrogen from it.

There is evidence suggesting there might have been banded iron formations and chert deposits laid down in the Hadean.

Do plate tectonics date from the Hadean?!

Origin of Life:

A new timeline has been proposed for the evolution of life.

What was the origin of life in the Hadean to PaleoArchean?

What was the time period for the origin of life?

Aging may have been a fundamental property of life and dates from life's actual origin..

Could formamide been the original prebiotic solvent?

Did liquid crystals help with the formation of life?

The ancestral eukaryote is slowly being understood.

Ws early photosynthetic life on Earth purple?

Evidence of Sunspots From the Early Permian Forest Fires

Fossil forest reveals sunspot activity in the early Permian

Authors:

Luthardt et al

Abstract:

Modern-day periodic climate pattern variations related to solar activity are well known. High-resolution records such as varves, ice cores, and tree-ring sequences are commonly used for reconstructing climatic variations in the younger geological history. For the first time we apply dendrochronological methods to Paleozoic trees in order to recognize annual variations. Large woody tree trunks from the early Permian Fossil Forest of Chemnitz, southeast Germany, show a regular cyclicity in tree-ring formation. The mean ring curve reveals a 10.62 yr cyclicity, the duration of which is almost identical to the modern 11 yr solar cycle. Therefore, we speculate and further discuss that, like today, sunspot activity caused fluctuations of cosmic radiation input to the atmosphere, affecting cloud formation and annual rates of precipitation, which are reflected in the tree-ring archive. This is the earliest record of sunspot cyclicity and simultaneously demonstrates its long-term stable periodicity for at least 300 m.y.

How Long did the Ediacaran NeoProterozoic Shuram Event Last?

Rock magnetic cyclostratigraphy of the Doushantuo Formation, South China and its implications for the duration of the Shuram carbon isotope excursion

Authors:

Gong et al

Abstract:

The Shuram excursion (SE), one of the largest-known negative carbon isotope anomalies, has been globally observed in Ediacaran rocks. Precisely determining the duration of the SE is pivotal to understanding its controversial origin. Here, we present a detailed paleomagnetic, rock magnetic, cyclostratigraphic and carbon isotopic study of the SE in the Doushantuo Formation at the Dongdahe section in eastern Yunnan Province, South China. Although paleomagnetic results likely show a late Mesozoic remagnetization, careful mineralogic analyses indicate that the rock magnetic cyclostratigraphy carried by detrital pseudo-single domain (SD) or small multidomain (MD) titanomagnetite grains faithfully records orbitally-forced climate cycles in the Ediacaran. Multi-taper method (MTM) spectral analysis of magnetic susceptibility (MS) and anhysteretic remanent magnetization (ARM) series reveals significant spectral peaks at similar frequencies. Based on the ratios of their frequencies, these spectral peaks are assigned to a suite of Milankovitch cycles (long eccentricity, short eccentricity, obliquity and precession), yielding a sediment accumulation rate of 1.0 cm/kyr for the Doushantuo Formation. A 9.1 ± 1.0 Myr duration is indicated for the entire SE in South China. This result is in good agreement with independent estimates from North America and South Australia, thus supporting a primary origin for the SE. In combination with published geochronologic data, we suggest that the onset of the SE occurred at ca. 560 Ma, which provides a chronostratigraphic framework for evaluating the relationship between the SE and the evolution of metazoans in Ediacaran time.

Reconstructing Sea Level Rise and Fall Since the NeoProterozoic

Reconstructing first-order changes in sea level during the Phanerozoic and Neoproterozoic using strontium isotopes

Authors:

van der Meer et al

Abstract:

The eustatic sea-level curves published in the seventies and eighties have supported scientific advances in the Earth Sciences and the emergence of sequence-stratigraphy as an important hydrocarbon exploration tool. However, validity of reconstructions of eustatic sea level based on sequence stratigraphic correlations has remained controversial. Proposed sea level curves differ because of site-to-site changes in local tectonics, depositional rates, and long-wavelength dynamic topography resulting from mantle convection. In particular, the overall amplitude of global Phanerozoic long-term sea level is poorly constrained and has been estimated to vary between ~ 400 m above present-day sea level to ~ 50 m below present-day sea level. To improve estimates of past sea level, we explore an alternative methodology to estimate global sea level change. We utilise the Phanerozoic-Neoproterozoic 87Sr/86Sr record, which at first order represents the mix of inputs from continental weathering and from mantle input by volcanism. By compensating for weathering with estimates of runoff from a 3D climate model (GEOCLIMtec), a corrected 87Sr/86Sr record can be obtained that solely reflects the contribution of strontium from mantle sources. At first order, the flux of strontium from the mantle through time is due to increases and decreases in the production of oceanic crust through time. Therefore, the changing levels of mantle-derived strontium can be used as a proxy for the production of oceanic lithosphere. By applying linear oceanic plate age distributions, we compute sea level and continental flooded area curves. We find that our curves are generally within the range of previous curves built on classical approaches. A Phanerozoic first order cyclicity of ~ 250 Myr is observed that may extend into the Neoproterozoic. The low frequency (i.e., on the order of 10 to 100 My) sea level curve that we propose, while open for improvement, may be used as baseline for refined sequence-stratigraphic studies at a global and basin scale.

Evidence of a Radical PaleoOcean Chemistry Change Circa 545 Million Years Ago From Russia

Demise of Ediacaran dolomitic seas marks widespread biomineralization on the Siberian Platform

Authors:

Wood et al

Abstract:

The trigger for biomineralization of metazoans in the terminal Ediacaran, ca. 550 Ma, has been suggested to be the rise of oxygenation or an increase in seawater Ca concentration, but geochemical and fossil data have not been fully integrated to demonstrate cause and effect. Here we combine the record of macrofossils with early marine carbonate cement distribution within a relative depth framework for terminal Ediacaran to Cambrian successions on the eastern Siberian Platform, Russia, to interrogate the evolution of seawater chemistry and biotic response. Prior to ca. 545 Ma, the presence of early marine ferroan dolomite cement suggests dominantly ferruginous anoxic "aragonite-dolomite seas," with a very shallow oxic chemocline that supported mainly soft-bodied macrobiota. After ca. 545 Ma, marine cements changed to aragonite and/or high-Mg calcite, and this coincides with the appearance of widespread aragonite and high-Mg calcite skeletal metazoans, suggesting a profound change in seawater chemistry to "aragonite seas" with a deeper chemocline. By early Cambrian Stage 3, the first marine low-Mg calcite cements appear, coincident with the first low-Mg calcite metazoan skeletons, suggesting a further shift to "calcite seas". We suggest that this evolution of seawater chemistry was caused by enhanced continental denudation that increased the input of Ca into oceans so progressively lowering Mg/Ca, which, combined with more widespread oxic conditions, facilitated the rise of skeletal animals and in turn influenced the evolution of skeletal mineralogy.

Is the Shuram Event Still Younger Than the 580 Million Years agoEdiacaran NeoProteorozoic Gaskiers Glaciation Though?

Silicified glendonites in the Ediacaran Doushantuo Formation (South China) and their potential paleoclimatic implications

Authors:

Wang et al

Abstract:

The Ediacaran Period is punctuated by the ca. 580 Ma Gaskiers glaciation in Newfoundland. However, paleoclimatic data are scarce in Ediacaran successions in South China, where abundant geochemical and paleobiological data are shaping current understanding of Ediacaran evolutionary and environmental history. Here, we report the occurrence of silicified glendonites in the Ediacaran Doushantuo Formation deposited in an inner-shelf environment on the South China block. Petrographic evidence suggests that these silicified glendonites are pseudomorphs after syndepositional or early authigenic ikaites formed at near-freezing temperatures. The glendonite-bearing stratigraphic interval is characterized by positive δ13C values. It predates both the negative δ13C excursion EN3 (widely believed to be an equivalent of the Shuram negative excursion) and excursion EN2. Although alternative interpretations may be possible, these glendonites may be related to and correlated with the Gaskiers glaciation. If confirmed, this correlation suggests that the Shuram event postdates the Gaskiers glaciation, thus having important implications for Ediacaran climate changes, carbon cycles, and biological evolution.

Could the mid Ediacaran Shuram Event be Significantly Older Than 551 Million Years Ago?

The stratigraphic complexity of the middle Ediacaran carbon isotopic record in the Yangtze Gorges area, South China, and its implications for the age and chemostratigraphic significance of the Shuram excursion

Authors:

Zhou et al

Abstract:

The middle Ediacaran Shuram excursion represents the most pronounced negative carbon isotopic shift in Earth history, and has been considered as evidence for a profound disturbance to the global carbon cycle and proposed as a key chemostratigraphic marker for Ediacaran stratigraphic subdivision and global correlation. Previous study has revealed a pronounced negative δ13C shift (EN3) in the upper Doushantuo Formation of South China, which has been interpreted as an equivalent of the Shuram excursion. Detailed δ13C investigation of multiple sections of the Ediacaran Doushantuo Formation around the Huangling Anticline, western Hubei Province, South China, indicates that the δ13C variation in the upper Doushantuo Formation is more complex than previously reported. In the western region of the Huangling anticline, a moderately positive δ13C excursion (here termed the Diaoyapo positive excursion) bisects two strongly negative δ13C excursions (here termed the Jiuqunao negative excursion and the younger Miaohe negative excursion), with a ∼551 Ma ash bed capping the Miaohe negative excursion. In the central region, there is only one negative δ13C excursion, whereas in the eastern region, the negative δ13C excursion is absent. The variable stratigraphic expression of these δ13C excursions is most parsimoniously interpreted as reflecting local facies variation, diagenesis, and/or a cryptic unconformity. The more complete but more complex δ13C chemostratigraphic record in the western region of Huangling Anticline implies that, depending on how this record is correlated with the Shuram excursion, the latter may be significantly older than 551 Ma if it does represent a global chemostratigraphic marker.

Using Zinc and Cadmium Isotopes to Determine Post Snowball Earth Environmental Conditions

Zinc and cadmium stable isotopes in the geological record: A case study from the post-snowball Earth Nuccaleena cap dolostone

Authors:

John et al

Abstract:

Zinc and cadmium are important biologically cycled nutrients in the modern ocean. Recent analytical advances and sampling efforts such as GEOTRACES have led to measurements of the global distribution of Zn and Cd and their stable isotope ratios (δ66Zn and δ114Cd), providing an understanding of how biological processes cycle these elements and their isotopes in the modern ocean. This opens the door to better application of δ66Zn and δ114Cd as tracers of biogeochemical processes archived in the geological record. Here we present new measurements of [Cd] and δ114Cd on samples from the Nuccaleena cap dolostone in South Australia, which was deposited during deglaciation of the ca. 635 Ma old Marinoan snowball Earth. Our new data are combined with previously measured δ66Zn data from the same samples. The combined record of δ114Cd and δ66Zn is used to explore various hypotheses about the sources and sinks of Cd and Zn in the post-Marinoan ocean. Key features of this record are that [Zn] and [Cd] remain relatively similar throughout, that δ66Zn and δ114Cd change at the same stratigraphic level and in the same direction, and that δ66Zn changes are about four times larger than δ114Cd changes even though both quantities reflect a similar fractional mass difference. We suggest that both Zn and Cd concentration and isotopic data are consistent with a change in the sink by which Zn and Cd are removed from the oceans. We propose that no isotope fractionation is expressed during removal of Zn and Cd as sulfides, while Zn and Cd removed with biological material are about 0.6‰ and 0.2‰ lighter than deep ocean δ66Zn and δ114Cd, respectively. Many previous studies attribute the burial of isotopically light biological Zn to preferential assimilation of isotopically lighter Zn by phytoplankton. In contrast, we propose that lighter biological δ66Zn occurs mostly because isotopically heavy Zn was scavenged by organic matter, which causes dissolved δ66Zn in the surface ocean to be lighter than deep ocean δ66Zn. The organic matter originated from primary producers that thrived in the surface ocean during deglaciation. For Cd, whose isotope cycling in the modern ocean is dominated by preferential assimilation of isotopically lighter Cd by phytoplankton, much less biological fractionation is expressed. The combined analyses of δ66Zn and δ114Cd provide insight into the biogeochemical processes which occurred after the Marinoan snowball Earth glaciation, and may be a useful new tool to explore the history of life on Earth in other geological records as well.

Current molded, storm damaged, sinuous columnar stromatolites From Ectasian Mesoproterozoic China

Current molded, storm damaged, sinuous columnar stromatolites: Mesoproterozoic of northern China

Authors:

Tosti et al

Abstract:

A thin (~ 50 cm) horizon of sinuous stromatolites occurs within a succession of elongate upright columns in the ~ 1.4 Ga Tieling Formation, near Jixian, China. The upright columns form aligned closely spaced ridges, separated by narrow runnels with signs of current scour. The sinuous and upright stromatolites, and their intervening matrix, were originally mainly composed of carbonate mud. In end-on view, the sinuous columns incline back and forth. Each column consists of well-defined laminae that successively rotate relative to column curvature, maintaining their orientation approximately at right-angles to the column axis. In inclined parts of the columns, laminae are typically asymmetric and the steeper side faces the direction of column inclination. We interpret this column sinuosity to be a response to changes in current-direction, with accreting laminae facing into currents that supplied sediment. We find no evidence for heliotropism (mat growth towards the sun) in these examples. Adjacent columns typically show similar shapes, bending back and forth together, but their angles of curvature and inclination can change laterally from column to column, from near vertical to 45°, over distances of 30 cm. Columns can show breakage and separation of adjacent laminae. Some of this is enhanced by compaction and stress, but the occurrence of sinuous columns on their sides or upturned, in spaces between undisturbed columns, indicates that column curvature developed during growth and that toppling of columns was syndepositional. We infer that sinuosity developed in response to changes in current direction, that column inclination reflects current strength, and that breakage and toppling was produced by strong currents. Curved and sinuous columns could reflect shoaling. This would also have exposed them to storm damage and to the effects of currents that scoured sufficient matrix to locally break and topple columns. Markedly sinuous Mesoproterozoic columns also occur in Siberia and North America, suggesting that similar conditions and processes of stromatolite formation may have been widespread at this time. Formation and preservation of the sinuous stromatolites described here required a combination of conditions that included abundant fine-grained carbonate sediment, microbial mats capable of trapping it, reduced early lithification, and absence of bioturbation.

Was Delayed Intercontinental Seas' Euxinia A Vital for Eukaryotes to Survive During the Statherian PaleoProterozoic?

Delayed euxinia in Paleoproterozoic intracontinental seas: Vital havens for the evolution of eukaryotes?

Authors:

Spinks et al

Abstract:

Increased flux of sulfate to the oceans in the aftermath of the Great Oxidation Event (GOE) ∼2.4 billion years ago (Ga) caused major changes in seawater chemistry, which eventually contributed to the cessation of iron formation deposition ∼1.8 Ga. It is generally accepted that this engendered heterogeneous stratified redox conditions, with anoxic and sulfidic (euxinic) conditions in shallow open-marine environments and anoxic ferruginous conditions in deeper environments. However, the redox evolution of intracontinental marine basins following the cessation of iron formation deposition remains poorly understood.

Here, we report contrasting paleoredox conditions in two shale units of the lower McArthur Basin, northern Australia, soon after the cessation of iron formation deposition ∼1.84 Ga. Our data shows that the ∼1.78 Ga McDermott Formation was deposited in a sulfur-limited, anoxic shallow-marine environment, whereas the younger ∼1.73 Ga Wollogorang Formation was deposited in a euxinic shallow-marine environment. This implies a delay in the development of euxinia in a shallow intracontinental basin following the onset of euxinia in the open marine realm. Since bioessential metals are sequestered by pyrite deposition under euxinic conditions, protracted low-sulfidic conditions in 1.78 Ga intracontinental shallow environments could have provided vital niches for nitrogen-fixing prokaryotes and eukaryotes. Thus the ability for localized Paleoproterozoic intracontinental basins to remain non-euxinic after the onset of euxinia in shallow open-marine shelves highlights the importance of intracontinental environments to the evolution and diversification of microbial life, perhaps throughout the wider Proterozoic.

Determining the Aerosols of Earth's Archean PaleoAtmosphere

Follow the Carbon: Isotopic Labeling Studies of Early Earth Aerosol

Authors:

Hicks et al

Abstract:

Despite the faint young Sun, early Earth might have been kept warm by an atmosphere containing the greenhouse gases CH4 and CO2 in mixing ratios higher than those found on Earth today. Laboratory and modeling studies suggest that an atmosphere containing these trace gases could lead to the formation of organic aerosol haze due to UV photochemistry. Chemical mechanisms proposed to explain haze formation rely on CH4 as the source of carbon and treat CO2 as a source of oxygen only, but this has not previously been verified experimentally. In the present work, we use isotopically labeled precursor gases and unit-mass resolution (UMR) and high-resolution (HR) aerosol mass spectrometry to examine the sources of carbon and oxygen to photochemical aerosol formed in a CH4/CO2/N2 atmosphere. UMR results suggest that CH4 contributes 70–100% of carbon in the aerosol, while HR results constrain the value from 94% to 100%. We also confirm that CO2 contributes approximately 10% of the total mass to the aerosol as oxygen. These results have implications for the geochemical interpretations of inclusions found in Archean rocks on Earth and for the astrobiological potential of other planetary atmospheres.

Evidence of Extensive Mercury Pollution During Permian Triassic Mass Extinction

Isotopic signatures of mercury contamination in latest Permian oceans

Authors:

Grasby et al

Abstract:

Sedimentary records from the northwest margin of Pangea and the Tethys show anomalously high Hg levels at the latest Permian extinction boundary. Background δ202Hg values are consistent with normal marine conditions but exhibit negative shifts coincident with increased Hg concentrations. Hg isotope mass-independent fractionation (Δ199Hg) trends are consistent with volcanic input in deep-water marine environments. In contrast, nearshore environments have Δ199Hg signatures consistent with enhanced soil and/or biomass input. We hypothesize that the deep-water signature represents an overall global increase in volcanic Hg input and that this isotope signature is overwhelmed in nearshore locations due to Hg from terrestrial sources. High-productivity nearshore regions may have experienced stressed marine ecosystems due to enhanced Hg loading.

Oxygen Levels may Have Never Crashed During the Mesozoic

A modeling case for high atmospheric oxygen concentrations during the Mesozoic and Cenozoic

Authors:

Mills et al

Abstract:

Changes in atmospheric oxygen concentration over Earth history are commonly related to the evolution of animals and plants. But there is no direct geochemical proxy for O2 levels, meaning that estimations rely heavily on modeling approaches. The results of such studies differ greatly, to the extent that today's atmospheric mixing ratio of 21% might be either the highest or lowest level during the past 200 m.y. Long-term oxygen sources, such as the burial in sediments of reduced carbon and sulfur species, are calculated in models by representation of nutrient cycling and estimation of productivity, or by isotope mass balance (IMB)—a technique in which burial rates are inferred in order to match known isotope records. Studies utilizing these different techniques produce conflicting estimates for paleoatmospheric O2, with nutrient-weathering models estimating concentrations close to, or above, that of the present day, and IMB models estimating low O2, especially during the Mesozoic. Here we re-assess the IMB technique using the COPSE biogeochemical model. IMB modelling is confirmed to be highly sensitive to assumed carbonate δ13C, and when this input is defined following recent compilations, predicted O2 is significantly higher and in reasonable agreement with that of non-IMB techniques. We conclude that there is no model-based support for low atmospheric oxygen concentrations during the past 200 m.y. High Mesozoic O2 is consistent with wildfire records and the development of plant fire adaptions, but links between O2 and mammal evolution appear more tenuous.

The Strontium Cycle of the NeoProterozoic was Driven by Seemingly Unique Paleogeography

Paleogeographic forcing of the strontium isotopic cycle in the Neoproterozoic

Authors:

Goddéris et al

Abstract:

The period spanning from 825 to 540 Ma is characterized by major changes in the surficial Earth system. This extraordinary interval starts with the breakup of the Rodinia supercontinent and eruption of a series of large igneous provinces and ends with the assembly of Gondwana, giving rise to the Pan-African orogenies. This paleogeographic reorganization is accompanied by a global climatic cooling, including the paroxysmal Cryogenian “snowball” glacial events. The 87Sr/86Sr of seawater displays a major long-term rise over this interval that is punctuated by episodic, smaller declines and inflections. We use a coupled deep time climate-carbon numerical model to explore the complex role of tectonics and climate on this distinct evolution in seawater 87Sr/86Sr. We show that the modulation of the weathering of the erupted large igneous provinces by continental drift explains the changes in seawater 87Sr/86Sr from 800 to 635 Ma. The subsequent sharp rise in seawater 87Sr/86Sr from 635 to 580 Ma is the result of erosion of radiogenic crust exposed in the Pan-African orogens. Coeval evolution of atmospheric CO2 displays a decrease from about 80 times the pre-industrial level around 800 Ma to 5 times just before the beginning of the Phanerozoic.

How Salty Were the Seas of the Rhyacian PaleoProterozoic?

PIXE and microthermometric analyses of fluid inclusions in hydrothermal quartz from the 2.2 Ga Ongeluk Formation, South Africa: implications for ancient seawater salinity

Authors:

Saito et al

Abstract:

The Ongeluk Formation mainly consists of submarine volcanics (pillow lavas and sheet flows) composed of basaltic andesites that is between underlying and overlying glaciogenic deposits (i.e., the Makganyene diamictite and a dropstone layer at the base of the Hotazel Formation, respectively). The stratigraphic position of the Ongeluk Formation indicates that the Ongeluk volcanism occurred during a period of global glaciation. The Ongeluk volcanic rocks are host to subseafloor hydrothermal quartz deposits as drainage cavities and interpillow voids. The hydrothermal quartz contains many primary (Type 1) and secondary (Type 2) liquid-vapor fluid inclusions, as well as inclusions that are randomly distributed without a trace of secondary healed cracks (Type 3). All these fluid inclusions types were individually analyzed with microthermometry and particle-induced X-ray emission (PIXE) methods. The results show that Type 1 fluid inclusions are highly saline, whereas Type 2 fluid inclusions are relatively less saline. Type 3 fluid inclusions have bimodal peaks of salinity corresponding to those of Type 1 and Type 2 fluid inclusions and thus appear to represent mixtures between latter two inclusion types. Among the various fluid inclusion salinities of fluid inclusions, a wide range in Na/Ca values was identified in the high-salinity fluid inclusions (i.e., Type 1 and a subset of Type 3) which are thought to represent subseafloor fluids circulated by the Ongeluk submarine volcanism. The wide range in Na/Ca values can be explained by a mixing process between Na-rich and Ca-rich fluids associated with albitization of the host basaltic andesites. In the albitization process, Na is removed from the fluids and fixed by the host rocks; by contrast Ca is released from the host rocks into the fluids. PIXE analysis also showed two distinct trends (i.e., vertical and horizontal) on variation diagram of Ca/Cl versus Cu/Cl and positive correlations between Mn/Cl, Cu/Cl, Zn/Cl and Pb/Cl. These data are best explained by the presence of other mixing processes between; 1) a Na-rich, Ca- and Cu-poor fluid, 2) a Ca-rich, Na- and Cu-poor fluid, and 3) a Na- and Cu-rich, Ca-poor fluid. The Cu-, Mn-, Zn- and Pb-rich fluid likely represents a high-temperature hydrothermal fluid from a deep reaction zone in the Ongeluk subseafloor hydrothermal system. By contrast, the (1) Na- (and K-) rich, Ca- and Cu-poor endmember for the high-salinity primary inclusions is considered to represent the composition of 2.2 Ga Ongeluk seawater. We propose the estimation of 2.2 Ga Ongeluk seawater composition is > ∼2,237 mmol/kg of Na, 200–1,000 mmol/kg of K, < 135 mmol/kg of Ca, ∼3,230 mmol/kg of Cl (average values), and ∼400–500 of Cl/Br.

Evidence of Sulfur Oxidizing Bacteria Prior to the Great Oxidation Event

Sulfur-oxidizing bacteria prior to the Great Oxidation Event from the 2.52 Ga Gamohaan Formation of South Africa

Authors:

Czaja et al

Abstract:

The first 2 b.y. of Earth's history was an important time for life when microbes evolved and diversified into essentially all of the metabolic forms that now exist. Because of feedbacks between biology and the surface environment, understanding Earth's biological history can help us understand the evolution of Earth itself. The morphological and geochemical evidence for this ancient biological history is sparse but is increasing. Here we report evidence for 2.52 Ga exceptionally large, organic, smooth-walled, coccoidal microfossils preserved in a deep-water black chert in the Gamohaan Formation of the Kaapvaal craton of South Africa. These fossils occur mainly as compressed solitary coccoids that range in size from 20 to 265 μm but occasionally occur in short chains of cells. Morphologically these fossils are similar to Proterozoic and Phanerozoic acritarchs and to certain Archean fossils interpreted as possible cyanobacteria. However, their exceptionally large size, simple cell wall microstructure, and paleoecological setting, as well as multiple sulfur isotope systematics of pyrite within the unit, suggest that the Gamohaan Formation fossils were sulfur-oxidizing bacteria similar to those of the modern genus Thiomargarita, organisms that live in anoxic and sulfidic deepwater settings. These are the oldest reported fossil sulfur bacteria and reveal a diversity of life and ecosystems, previously only interpreted from geochemical proxies, just prior to the Great Oxidation Event, a time of major atmospheric evolution.

Evidence of Atmospheric Sulfur During the MesoArchean

An atmospheric source of S in Mesoarchaean structurally-controlled gold mineralisation of the Barberton Greenstone Belt

Authors:

Agangi et al

Abstract:

The Barberton Greenstone Belt of southern Africa hosts several Mesoarchaean gold deposits. The ores were mostly formed in greenschist facies conditions, and occur as hydrothermal alteration zones around extensional faults that truncate and post-date the main compressional structures of the greenstone belt. Ore deposition was accompanied by the intrusion of porphyries, which has led to the hypothesis that gold may have been sourced from magmas. Because the transport of Au in the hydrothermal fluids is widely believed to have involved S complexes, tracing the origin of S may place strong constraints on the origin of Au. We measured multiple S isotopes in sulfide ore from Sheba and Fairview mines of the Barberton Greenstone Belt to distinguish “deep” S sources (e.g. magmas) from “surface” S sources (i.e. rocks of the volcano-sedimentary succession that contain S processed in the atmosphere preserved as sulfide and sulfate minerals). Ion probe (SIMS) analyses of pyrite from ore zones indicate mass-independent fractionation of S isotopes (Δ33S = −0.6‰ to +1.0‰) and the distribution of the analyses in the Δ33S–δ34S space matches the distribution peak of previously published analyses of pyrite from the entire volcano-sedimentary succession. Notwithstanding that the H2O–CO2 components of the fluids may have been introduced from a deep source external to the greenstone belt rocks, the fact that S bears an atmospheric signature suggests the hypothesis that the source of Au should also be identified in the supracrustal succession of the greenstone belt. Our findings differ from conclusions of previous studies of other Archaean shear-hosted Au deposits based on mineralogical and isotopic evidence, which suggested a magmatic or mantle source for Au, and imply that there is no single model that can be applied to this type of mineralisation in the Archaean.

Methane Did NOT Warm the Early Earth

For at least a billion years of the distant past, planet Earth should have been frozen over but wasn't. Scientists thought they knew why, but a new modeling study from the Alternative Earths team of the NASA Astrobiology Institute has fired the lead actor in that long-accepted scenario.

Humans worry about greenhouse gases, but between 1.8 billion and 800 million years ago, microscopic ocean dwellers really needed them. The sun was 10 to 15 percent dimmer than it is today--too weak to warm the planet on its own. Earth required a potent mix of heat-trapping gases to keep the oceans liquid and livable.

For decades, atmospheric scientists cast methane in the leading role. The thinking was that methane, with 34 times the heat-trapping capacity of carbon dioxide, could have reigned supreme for most of the first 3.5 billion years of Earth history, when oxygen was absent initially and little more than a whiff later on. (Nowadays oxygen is one-fifth of the air we breathe, and it destroys methane in a matter of years.)

"A proper accounting of biogeochemical cycles in the oceans reveals that methane has a much more powerful foe than oxygen," said Stephanie Olson, a graduate student at the University of California, Riverside, a member of the Alternative Earths team and lead author of the new study published September 26 in the Proceedings of the National Academy of Sciences. "You can't get significant methane out of the ocean once there is sulfate."

Sulfate wasn't a factor until oxygen appeared in the atmosphere and triggered oxidative weathering of rocks on land. The breakdown of minerals such as pyrite produces sulfate, which then flows down rivers to the oceans. Less oxygen means less sulfate, but even 1 percent of the modern abundance is sufficient to kill methane, Olson said.

link.

Carbonate deposits from the ancient aqueduct of Béziers, France as Evidence of Local Environment During Roman Empire

Carbonate deposits from the ancient aqueduct of Béziers, France — A high-resolution palaeoenvironmental archive for the Roman Empire

Authors:

Passchier et al

Abstract:

Carbonate deposits from a Roman aqueduct in Béziers, southern France, record environmental conditions during the late first century C.E. These deposits formed in a steep section of the aqueduct with a high flow velocity, which caused rapid deposition of up to 11 mm of calcite per year over a period of 22–24 years. The microstructure, trace element and stable isotope composition show that regular deposition was interrupted by high-discharge events, probably in response to heavy rainfall during autumn and winter, transporting colloidally- and particle-bound elements and depositing calcite with elevated δ18O values. Individual autumn high-discharge events coincide with abrupt decreases in δ13C from − 8 to − 12‰ giving rise to a saw-tooth profile. In some years, several high flow events persisted throughout the winter, suppressing this profile. Event horizons of micrite capping sparite growth surfaces, enriched in Mg, may represent anomalously low water levels or periods when the channel fell dry. In comparison to carbonate deposits from Roman aqueducts in the Eastern Mediterranean, visible layering is less regular and pronounced in Béziers, reflecting a more complex precipitation pattern.

Evidence of Euxinia in Terminal Ediacaran Oceans

Redox-dependent distribution of early macro-organisms: Evidence from the terminal Ediacaran Khatyspyt Formation in Arctic Siberia

Authors:

Cui et al

Abstract:

The Ediacaran Period witnessed the first appearance of macroscopic animal life in Earth's history. However, the biogeochemical context for the stratigraphic occurrence of early metazoans is largely uncertain, in part due to the dearth of integrated paleobiological and chemostratigraphic datasets. In this study, a comprehensive geochemical analysis was conducted on the fossiliferous Khatyspyt Formation in Arctic Siberia, in order to gain insights into the Ediacaran paleoenvironments. This study was designed to specifically address the relationship between paleoredox conditions and Ediacaran fossil occurrences in the Khatyspyt Formation. Our data reveal a dramatic shift in pyrite sulfur isotope compositions (δ34Spyrite) from ca. − 20‰ to ca. 55‰, and this shift is intriguingly associated with the first occurrence of Ediacara-type macrofossils at the studied section, suggesting a possible link between seawater redox conditions and distribution of early macroscopic organisms. Based on multiple lines of sedimentological and geochemical evidence, we propose that the development of oceanic euxinia — which may be widespread in the continental margins due to enhanced oxidative weathering in the terminal Ediacaran Period — may have locally prohibited the colonization of Ediacara-type organisms and resulted in low δ34Spyrite values in the lower Khatyspyt Formation. In the middle and upper Khatyspyt Formation, progressive secular transition from euxinic to non-euxinic and more habitable conditions may have allowed for the colonization of Ediacara-type and other macro-organisms.