Pondering the Precambrian #40

Proterozoic:

NeoProterozoic:

Palaeopascichnus jiumenensis can be used to determine the Ediacaran/Cambrian boundary.

There's a new way to determine oxygen levels during paleo time periods.  It seems to check out in the Neoproterozoic-Cambrian transition based on comparison to other methods.

A bilateralan metazoan (animal) fossil and trackway was found in China dating from the Ediacaran.

The rise of siliceous sponges helped shift the Ediacaran ecosystems to the modern Cambrian. 

The differences between the Weng'an and Kuanchuanpu biotas is largely due to how they were preserved.

Acritarchs from the Ediacaran Doushantuo Formation allow for biostratigraphic correlation with the Tanarium conoideum–Cavaspina basiconica Assemblage Zone.

There appears to have been long term denudation of the continents from the middle Ediarcaran based on Nd isotope traces in carbonates.

A new formation has been found dating from the Cryogenian with evidence of bacterial and algae life in South China.

How much hydrothermal activity was there during the Marinoan Glaciation (snowball earth episode) during the Cryogenian?

There is evidence of a large igneous province in the Tonian.

MesoProterozoic:

Horodyski moniliformis, regarded by some as a eukaryote fossil from the Calymmian, has been declared a pseudofossil.

PaleoProterozoic:

Plate tectonics have evolved over the last 2.5 billion years.

Is there evidence for the oxygen overshoot hypothesis from the Orosirian?

There was a paleocontinent named 'Atlantica' proposed.  Recent research suggests it was configured rather differently than proposed.

Evidence has arisen supporting a snowball earth scenario during the Huronian glaciation.

An asteroid impact has been IDed from the Rhyacian in Australia.

Did the supercontinental cycle begin in the PaleoProterozoic?

Archean:

There is evidence of a PaleoArchean continent.

Origin of Life:

Prebiotic amino acids can bind to lipid membranes and stabilize them.

When did eukaryotes originate?  Do we have a way to understand that?

Did the lack of nitrogenase limit early life?

Pondering the Precambrian #4

NeoProterozoic:

Ediacaran:

From Brazil, Ediacaran vase shaped fossils have been found.  is this the earliest known protist fossils yet?

How are the various frond critters of the Ediacaran related to each other?

How did the Ediacaran critter Dickinsonia grow?

A mixed Cloudinia-Corumbella-Namacalathus assemblage shows increasing ecological complexity over the course of the Ediacaran.

Cryogenian:

Did a freshwater layer exist on the world's oceans and persist after the Snowball Earth episodes like the one in the Cryogenian?

As the Snowball Earth ended, how much oxygen weathering took place and what were the biotic impacts?

Tonian:

There was a huge Andes-like mountain range on the northwest of Rodinia that may have lasted for 100 million years during the Tonian 800 million years ago.

MesoProterozoic:

Wind patterns have been inferred from dunes from Calymmian Brazil.

The diversity of Eukaryote microfossils of Calymmian China is impressive.

PaleoProterozoic:

In Statherian China, there is evidence of a sillicified microbiota from the Dahongyu Formation.

The Sudbury Impact appears to have caused long lived volcanic eruptions during the Orosirian PaleoProterozoic.  Since it was one of 150 impacts within a relatively short period, combined with this above volcanism, it should be no surprise life didn't recover to take a second stab at complexity for a billion years.

The Sudbury Basin continued to have geothermal heat during the Huronian snowball earth.

Can the Rhyacian/Siderian Glaciations (huronian snowball earth) be dated based on subglacial hydrothermal activity?

Beginning in the Siderian, ancient carbon was subsumed into the Earth's mantle.

Did anaerobic oxygenic photosynthesis (read the paper) come about in cyanobacteria prior to modern aerobic photosynthesis?

During the Siderian, Earth had a hazy, methane filled atmosphere.

Did eukaryotes arise during the Siderian?

Archean:

Lenticular organisms from South Africa are related to the Pilbara forms.

Did life arise during the EoArchean WITHOUT using phosphate?

Fossils were found from the Eoarchean 3.77 billion years ago in Quebec, Canada.

How did the crust form?

Hadean:

The Earth probably began with a solid shell for a crust, like Mars.

META:

New branches have been found in Archaea.

Iron eating, methanogen organisms probably kept the Earth warm for its first 2 billion years.

Mineral self assembly was common in the early years of the Earth.

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.

Rhyacian PaleoProterozoic Magnesite Deposits are NOT Deposited Under Hydrothermal Conditions

Genesis of a giant Paleoproterozoic strata-bound magnesite deposit: Constraints from Mg isotopes

Authors:

Dong et al

Abstract:

Giant strata-bound magnesite deposits are absent in modern and most Phanerozoic sedimentary environments but occur predominantly in Precambrian strata. These deposits may have formed directly through precipitation of evolved Mg-rich seawater in an evaporative shallow-marine setting or, alternatively, by epigenetic–hydrothermal replacement of the Mg-rich carbonate precursor. To test these hypotheses, we obtained the first Mg isotope data from the world’s largest strata-bound magnesite deposit belt, hosted by the ca. 2.1 Ga Dashiqiao Formation in Northeast China. The Mg isotope compositions (δ26Mg) of most magnesite ores in the Huaziyu deposit are heavier (–0.75 ± 0.26‰) than most Proterozoic sedimentary dolostones. The Mg isotope compositions and major and trace element data indicate that the magnesites are probably not of hydrothermal origin. Instead, a Mg-rich carbonate precursor precipitated from evaporating seawater in a semi-closed system. Diagenetic brines altered the Mg-rich carbonate precursor to magnesite. Subsequently, recrystallization during regional metamorphism produced coarsely crystalline and saddle magnesite. These interpretations are consistent with the geological features and other geochemical data (element concentrations and C and O isotopes) for the magnesite ores. Hence, we interpret the formation of the Huaziyu magnesite deposit to be dominated by evaporative sedimentation and brine diagenesis.

There Were two DIFFERENT Sources for the Rhyacian PaleoProterozoic Banded Iron Formations

Decoupled sources of the 2.3-2.2 Ga Yuanjiacun banded iron formation: Implications for the Nd cycle in Earth’s early oceans

Authors:

Wang et al

Abstract:

The recognized worldwide gap in BIF deposition between 2.4-2.0 billion years ago has long been considered as an obstacle to fully determining the geochemical composition of seawater at that time. However, the recently dated 2.3-2.2 Ga Yuanjiacun banded iron formation (BIF) in the North China Craton (NCC) offers a possibility to redress these uncertainties. Shale-normalized rare earth element-yttrium (REE+Y) patterns of the BIF and interlayered meta-chert samples show features characteristic of other Archean and Paleoproterozoic BIFs, with HREE enrichment relative to LREE, positive La and Eu anomalies, and superchondritic Y/Ho ratios comparable to modern seawater. Very low Al2O3 (less than 0.5 wt%) and high field strength elements (HFSE) concentrations (less than 10 ppm) indicate an essentially detritus-free depositional setting, while positive Eu anomalies are attributed to an imprint of high-temperature hydrothermal fluids. Sm-Nd isotopic features further point to two periodically interacting water masses controlling the deposition of the BIF. The first is seafloor-vented hydrothermal fluids (εNd(t)∼+3.5) derived from interaction with a depleted mantle source and associated with high Fe fluxes. The second is ambient surface seawater (εNd(t)∼-2.4), which obtained its signature through weathering of the nearby landmasses and associated with high Si fluxes. Our findings suggest that the REE budget of the oceans prior to 2.3 Ga was generally dominated by hydrothermal circulation of seawater through depleted mantle-derived source rocks. However, where evolved local continental crust and/or an enriched mantle source were present, this positive mantle Nd signal became discernible in the BIFs. By comparing the Nd isotopic features of similar aged BIFs and marine carbonates, it is concluded that similar to modern oceans, the early Precambrian ocean was not well-mixed with respect to its Nd isotopic composition.

Tracking Copper Through the Great Oxidation Event

Cu isotopes in marine black shales record the Great Oxidation Event

Authors:

Fru et al

Abstract:

The oxygenation of the atmosphere ∼2.45–2.32 billion years ago (Ga) is one of the most significant geological events to have affected Earth’s redox history. Our understanding of the timing and processes surrounding this key transition is largely dependent on the development of redox-sensitive proxies, many of which remain unexplored. Here we report a shift from negative to positive copper isotopic compositions (δ65CuERM-AE633) in organic carbon-rich shales spanning the period 2.66–2.08 Ga. We suggest that, before 2.3 Ga, a muted oxidative supply of weathering-derived copper enriched in 65Cu, along with the preferential removal of 65Cu by iron oxides, left seawater and marine biomass depleted in 65Cu but enriched in 63Cu. As banded iron formation deposition waned and continentally sourced Cu became more important, biomass sampled a dissolved Cu reservoir that was progressively less fractionated relative to the continental pool. This evolution toward heavy δ65Cu values coincides with a shift to negative sedimentary δ56Fe values and increased marine sulfate after the Great Oxidation Event (GOE), and is traceable through Phanerozoic shales to modern marine settings, where marine dissolved and sedimentary δ65Cu values are universally positive. Our finding of an important shift in sedimentary Cu isotope compositions across the GOE provides new insights into the Precambrian marine cycling of this critical micronutrient, and demonstrates the proxy potential for sedimentary Cu isotope compositions in the study of biogeochemical cycles and oceanic redox balance in the past.

Pondering the Precambrian #3

Proterozoic:

NeoProterozoic:

The Royal Tyrrell Museum has a lecture on the Ediacaran.

There is stronger evidence for the biomarkers for sponges being present starting in the Cryogenian.

MesoProterozoic:

The shallow seawaters of the Calymmian MesoProterozoic were very hypoxic, showing evidence of having .1% of the current oxygen in seawater.

PaleoProterozoic:

There is evidence of intracontinental rifting from China during the Rhyacian Paleoproterozoic.

Was there a 'Mawson continent' during the Paleoproterozoic?

Archean:

The SETI Institute has a lecture on volcanism during the Archean.

PaleoArchean:

At least part of the trace fossils from Australia are pseudofossils (not real fossils).

EoArchean:

There is evidence of atmospheric oxygen from the EoArchean, 800 million years earlier than ever detected (or suspected) before.

Hadean:

In an almost extraordinary claim, the Siberian Craton may have bits of the crust from the Hadean!

Evidence of a Rhyacian Paleoproterozoic Supercontinent From Brazil

Crustal evolution of the northern Brasília Belt basement, central Brazil: a Rhyacian orogeny coeval with a pre-Rodinia supercontinent assembly

Authors:

de Sousa et al

Abstract:

The Brasília thrust and fold belt developed in the course of Neoproterozoic Brasiliano orogeny, during the convergence of São Francisco, Amazonian and Paranapanema cratons, in an early phase of Gondwana agglutination. A Paleoproterozoic terrane cropping out in its northern segment -represents the basement of the belt and corresponds to a magmatic arc. The arc developed during Rhyacian, possibly on the margin of an Archean-Paleoproterozoic block that is today represented by the São Francisco craton. The Paleoproterozoic arc evolution starts following a calc-alkaline trend between 2.30 and 2.16 Ga, changing from a typical juvenile to crustal contaminated terrane with slightly negative ɛNd(t) values, as revealed by tonalites and granodiorites of Conceição do Tocantins Suite. By c. 2.17-2.15 Ga, a collisional event took place, triggering crustal melting and generating peraluminous granites. These syn-collisional granites present strongly negative ɛNd values and belong to Aurumina Suite. Natividade, Almas-Conceição do Tocantins and Cavalcante-Arraias domains within the basement do not represent distinct tectonic blocks. The first two are areas where mainly plutonic arc rocks crop out and in the last one, syn-collisional granites are the most common lithology. Syn-collisional granites characterize granitogenesis produced by collision of another landmass against São Francisco landmass. The arc development is contemporary with collisional orogens that culminated in a conjectural Paleoproterozoic pre-Rodinia supercontinent. Since Rhyacian, these rocks are part of the landmass that would become the São Francisco craton and compose Brasília Belt basement.

Siderian/Rhyacian PaleoProterozoic Environment of Western Australia Across the Great Oxygenation Event Through Huronian Glaciations

Sedimentology, chemostratigraphy, and stromatolites of lower Paleoproterozoic carbonates, Turee Creek Group, Western Australia

Authors:

Martindale et al

Abstract:

The ca. 2.45–2.22 Ga Turee Creek Group, Western Australia, contains carbonate-rich horizons that postdate earliest Proterozoic iron formations, bracket both Paleoproterozoic glaciogenic beds and the onset of the Great Oxidation Event (GOE), and predate ca. 2.2–2.05 Ga Lomagundi-Jatuli C-isotopic excursion(s). As such, Turee Creek carbonate strata provide an opportunity to characterize early Paleoproterozoic carbonate sedimentation and carbon cycle dynamics in the context of significant global change. Here, we report on the stratigraphy, sedimentology, petrology, carbon isotope chemostratigraphy, and stromatolite development for carbonate-rich successions within the pre-glacial part of the Kungarra Formation and the postglacial Kazput Formation.

Kungarra carbonate units largely occur as laterally discontinuous beds within a thick, predominantly siliciclastic shelf deposit. While this succession contains thin microbialite horizons, most carbonates consist of patchy calcite overgrowths within a siliciclastic matrix. C-isotopic values show marked variation along a single horizon and even within hand samples, reflecting spatially and temporally variable mixing between dissolved inorganic carbon in seawater and isotopically light inorganic carbon generated via syn- and post-depositional remineralization of organic matter.

In contrast, the Kazput carbonates consist of subtidal stromatolites, grainstones, and micrites deposited on a mixed carbonate–siliciclastic shelf. These carbonates exhibit moderate δ13C values of −2‰ to +1.5‰ and likely preserve a C-isotopic signature of seawater. Kazput carbonates, thus, provide some of the best available evidence that an interval of unexceptional C-isotopic values separates the Lomagundi-Jatuli C-isotopic excursion(s) from the initiation of the GOE as inferred from multiple sulfur isotopes (loss of mass independent fractionation). The Kazput Formation also contains unusual, m-scale stromatolitic buildups, which are composed of sub-mm laminae and discontinuous, convex upward lenticular precipitates up to a few mm in maximum thickness. Laminae, interpreted as microbial mat layers, contain quartz and clay minerals as well as calcite, whereas precipitate lenses consist of interlocking calcite anhedra, sometimes showing faint mm-scale banding. These cements formed either as infillings of primary voids formed by gas emission within penecontemporaneously lithified mats, or as local seafloor precipitates that formed on, or within, surface mats. It is possible that both mechanisms interacted to form the unique Kazput stromatolites. These microbialites speak to a distinctive interaction between life and environment early in the Paleoproterozoic Era.

Explaining the Rhyacian PaleoProterozoic Lomagundi Event

The rise of oxygen and siderite oxidation during the Lomagundi Event

Authors:

Bachan et al

Abstract:

The Paleoproterozoic Lomagundi Event is an interval of 130–250 million years, ca. 2.3–2.1 billion years ago, in which extraordinarily 13C enriched (greater than 10‰) limestones and dolostones occur globally. The high levels of organic carbon burial implied by the positive δ13C values suggest the production of vast quantities of O2 as well as an alkalinity imbalance demanding extremely low levels of weathering. The oxidation of sulfides has been proposed as a mechanism capable of ameliorating these imbalances: It is a potent sink for O2 as well as a source of acidity. However, sulfide oxidation consumes more O2 than it can supply CO2, leading to insurmountable imbalances in both carbon and oxygen. In contrast, the oxidation of siderite (FeCO3 proper, as well as other Fe2+-bearing carbonate minerals), produces 4 times more CO2 than it consumes O2 and is a common—although often overlooked—constituent of Archean and Early Proterozoic sedimentary successions. Here we propose that following the initial rise of O2 in the atmosphere, oxidation of siderite provided the necessary carbon for the continued oxidation of sulfides, burial of organic carbon, and, most importantly, accumulation of free O2. The duration and magnitude of the Lomagundi Event were determined by the size of the preexisting Archean siderite reservoir, which was consumed through oxidative weathering. Our proposal helps resolve a long-standing conundrum and advances our understanding of the geologic history of atmospheric O2.

 I think I am going to drop a note to the authors and ask if they have compared the carbon 13 isotopes in the limestones and dolostones to modern ones... or at least to Phanerozoic ones.  Just to potentially rule out this.  ;)

The Paleo Recipe for Complex Life on Earth

Let's step back through deep time to consider an intriguing event. One which has been written about, but far from sufficiently and its existence could have some pretty profound implications about Earth and life's history.

 

Looking back to the Precambrian.  

The Earth is racked by global glaciations.  Ones which have been called the Snowball Earth.  They stretch over the entire planet from the poles through the equator.  There is some dispute whether or not the oceans were completely frozen over (a slushball earth vs snowball), but the glaciations are acknowledged as real.

The monstrous glaciation is understood to have been triggered by a sudden drop in the atmospheric carbon dioxide levels.  This, in turn, is believed to have been caused by photosynthetic organisms drawing down the CO2 levels while spiking the oxygen levels (relatively speaking).  Yes, the snowball earth events are, like in the Eocene's Azolla Event, examples of biogenic climate change.

Within 100 million years of the end of the Snowball Earth complex life arose.  Except it would vanish from the fossil record, probably having gone extinct and changing the biological fate of the Earth.

Wait.  You thought I was talking about the Cryogenian and Ediacaran?

After all, the Cryogenian's Marinoan Glaciation (or maybe Sturtian or Kaigas), NeoProterozoic Oxygenation Event, Ediacaran with its biota and then Cambrian do parallel all of the above.  Except that complex life is obviously still around and the Phanerozoic is quite biologically diverse, to say the least.

But, no, despite the parallels, I am not talking about the rise of modern complex life.  Rather I am talking about events which took place more than a billion years earlier, during the PaleoProterozoic.

Oxygen, Glaciers and Complex Life, oh my!

There has been up talk of the Great Oxygenation Event.  This is when life puped out oxygen in sufficiently large quantities oxygen were poured into the atmosphere by photosynthetic life, namely something like the cyanobacteria.  This may have been one of the first mass extinctions because obligate anaerobes cannot survive in the presence of oxygen, for one, and for the second, it radically changed the climate.

By pulling down the carbon dioxide and releasing free oxygen, the cyanobacteria tipped the earth from a greenhouse climate to an icehouse climate.  This in turn, without the 'modern' feedback loops, turned into what is suspected to be the earliest Snowball Earth, during the Siderian and Rhyacian.  This glaciation, called the Huronian, lasted (as far as we can tell) for 300 million years, from the mid Siderian to about 50 million years before the end of the Rhyacian. 

In 2010, a remarkable find was brought to light from Gabon, Africa.  There appeared to be colonial, or even possibly true complex life in the Rhyacian.  Further study of the fossils strongly suggested they were some form of complex life.  However, strangely, not like our complex life which seems to have arisen piecemeal during the Cryogenian into the Ediacaran and exploded during the Cambrian.  The timing of the appearance of the Francevillian Biota

Reflections in the Mirror: Parallel Events, Evolution? | ?noitulovE, stnevE lellaraP

The Francevillian Biota has several biotic members.  Its easy to see some physical parallels between the Ediacaran Biota members and those above.  There are forms which are reminicent but not the same as the Edaicaran discoid, Dickinsonia and rangeomorph fossils.  They are not the same, by any means, but the suggested parallels are interesting.  No, I am not saying the Ediacaran forms evolved form the Rhyacian!  Quite the contrary!  Rather, I am suggesting there is an event of parallel evolution taking place.  Independently.  Form follows function.  However, this is more suggestively so than closely (unlike the classic of sharks, ichthyosaurs and dolphins), but what's even better of a parallel is the events which led up to the both the evolution of the Francevillian and Ediacaran Biotas.

The events of the two different time frames, Siderian/Rhyacian & Cryogenian/Ediacaran (global glaciations, O2 spike and the seeming rise of complex life) is pretty exciting.  Is this what it would take to have Earth-evolved life to produce complex life forms?  Perhaps.  Its worth looking into.  However, the huge question becomes, if complex life evolved 2.05 billion years why is there a hiatus for over a billion years.  Those years sometimes being called the Boring Billion (more properly, the MesoProterozoic).  During that time frame, we have evidence of microbial life, but nothing like an animal or plant.  So?  What happened?  It must have gone extinct.  There are two possible explanations, assuming this is in fact complex life in the Francevillian Biota.

One is the Francevillian Biota didn't produce a proper Gaia-like feedback system and they tipped over into a feedback loop which caused them to ruin their own environment.  Or rather they ran out of their nutrients.  Or failed to develop a self sustaining ecosystem.  Its a biological failure then.  Producing Gaia is hard.  At best its 50-50 proposition of true.

The second possible reason is even more compelling.  Why?  Because of the time and energy involved.  27 million years after the Francevillian fossils were deposited, one of the biggest asteroid impacts the Earth has seen since the Late Heavy Bombardment took place.  And 150 million years after that, a comparable asteroid smashed into the world.  Both of these impacts dwarf the Chicxulub Crater.

Say Hello to my Little Friend.  Ahem, BFG.  Twice.

It has already been established giant impacts can cause mass extinctions.  The impact in Chicxulub, Mexico 66 million years ago, wiped out 50% of life on the planet.  The KT or K-Pg Extinction made way for our modern ecology and our own evolution.  The Chicxulub impact was the equivalent of over 100 teratons of explosives, roughly over 1000 times the combined nuclear arsenals on Earth.  There are two impacts which followed the Francevillian Biota which were significantly more powerful.

The Vredefort Impact took place 'first.'   The astrobleme for Vredefort is in southern Africa and dates to 2.023 billion years ago.  The crater it left was 300 km in diameter: Chicxulub is 'only' 180 km in diameter.  The impact would have been significantly more energetic than Chicxulub.  This is guaranteed mass extinction.  In fact, its a significantly more devastating mass extinction because the Francevillian Biota is almost assuredly younger and less robust than when our lineage dating from the Cryogenian took it in the shorts from Chicxulub.  Had Chicxulub happened before the Cambrian Exoplosion, its probable there wouldn't be anything remotely complex on the planet.  Vredefort was worse.

As if Vredefort was not enough, 150 million years later, circa 1.849 billion years ago, came the Sudbury Impact.  It was of a comparable energy and bollide size. If any thing complex survived the Vredefort, which would be doubtful, the Sudbury almost assuredly finished them off.  The two impacts, btw, bracket the Orosirian Period.

Interestingly, a paper which just came out supports the scenario.  Although the authors are studying about two different impacts at an earlier time, they found geological evidence of the upper sea boiling from the devastation wrought.  The Sudbury and the Vredefort Impacts both have the potential to done the exact same thing.  Given the Francevillian Biota was a shallow water assemblage, its entirely likely they were wiped out in one or both of the events.

The surviving largely microbial life would trundle on in a relatively stable environment for another billion years thence.

Every Earth Deserves a Second Chance

Assuming the Francevillian Biota was, in fact, complex life, Earth would need another billion years until the Ediacaran to take another stab at complex life.  This time it would be successful and continue into the present, despite mass extinctions.  Fortunately, there have been no bollides of comparable mass or energy as the Vredefort or Sudbury since.  Their descendents are us.

The hypothesis we had extremely distant cousins makes for some interesting conjectures.

• Under the right stimulus, it seems complex life arises when working with earth evolved organisms.  However, it does seem to require those proper chain of events.  

• Additionally, as soon as life had a chance, it also appears to (inadvertently) triggered the events which led up to complex life.  This, in turn, suggests complex life may be common where it is possible to evolve.  

• However, it is also possible to wipe out complex life without requiring too crazy of events (or intelligent intervention).

• It seems likely Mars will definitely not have any traces of complex life.  If the Earth was still getting battered at 1.85 billion years ago, that is well past the point when Mars' atmosphere thinned.  Additionally, the Hellas Basin is an impact crater which is 2,300 km in diameter.  If Vredefort was tough, then Hellas was hell and the likelihood of anything surviving through that impact is almost nil.  The Hellas Impact took place ~3.8 billion years ago.  For that matter, the Argyre Planitia is also another impact basin and it is 1,800 km in diameter, if not as deep as the Hellas.  Its highly unlikely any life survived past these events.  There's a slim chance Earth could have reintroduced life, but by the time the Francevillian Biota arose, Mars had something akin to its present atmosphere.

The story outlined above, the hypothesis which I've hung out there in my first paleo post in some time, hangs together quite well in view of the science.  However, it needs to be tested.  We can only test the hypothesis by finding other locales similar to Franceville.  Likewise, a lot of detailed examination of the Francevillian Biota as known is needed. Likewise, deposits from after Vredefort and in similar paleoenvironmental conditions are needed from the Orosirian.  

Then what's needed is to understand why the MesoProterozoic didn't have any glaciations and, thus, did not produce the complex life as we (squintingly) know it earlier.

Evidence of Tectonic Uplift From Siderian/Rhyacian PaleoProterozoic China

Palaeopedogenesis of red palaeosols in Yunnan Plateau, southwestern China: Pedogenical, geochemical and mineralogical evidences and palaeoenvironmental implication

Authors:

Lu et al

Abstract:

Red palaeosol, as an important archive of ancient pedoenvironments, effectively reflects the palaeoenvironmental change and tectonic uplift history of the plateau. Four red palaeosol profiles were collected at 2200 to 2400 m elevations from the Yunnan Plateau (YP) to investigate the pedogenic features, chemical weathering process and mineral assemblages of soils. Pedological, geochemical and mineralogical techniques were used to understand the palaeopedogenic, palaeoenvironmental change and landscape evolution of the Plateau. Pedologically, the red palaeosols were characterized by the dark red color (a hue of 5YR or redder), strong acidity (pH < 5.4), and high free iron oxide (> 50 g kg− 1) and clay (> 50%) contents. The red palaeosols were enriched with Fe2O3, Al2O3, and TiO2 with very low contents of CaO, MgO, Na2O, and K2O and slightly low contents of Si2O and MnO. Chemical weathering indices, such as CIA (CIA = [Al2O3 / (Al2O3 + CaO + Na2O + K2O)] × 100), Sa (Sa = SiO2 / Al2O3), Saf (Saf = SiO2 / Al2O3 + Fe2O3), and A–CN–K diagram (Al2O3–CaO + Na2O–K2O), indicated that the red palaeosols had experienced strong chemical weathering processes. Scanning electron microscopy analyses revealed that quartz grains of the red palaeosols were characterized by a number of deep dissolution pits and cracks on their surfaces. The clay minerals of the red palaeosols were composed of kaolinite, gibbsite, hematite, and vermiculite in the order of abundance. Pedogenical, geochemical and clay mineralogical evidences revealed that the red palaeosols were developed by palaeopedogenic processes under tropical climatic environments. The presence of highly weathered soils at an altitude of 2200–2400 m indicated the influence of tectonic uplift on the soil vertical distribution. It is estimated that the red palaeosols had uplifted about 1600–2000 m since their initial formation. Palaeopedogenesis of red palaeosols provides new insight into the palaeoclimatic and palaeoenvironmental reconstruct and tectonic movement of YP.

A Continguous (!?!!!) Section Across the Great Oxidation Event From Siderian/Rhyacian PaleoProterozoic Australia

Sedimentology of the Paleoproterozoic Kungarra Formation, Turee Creek Group, Western Australia: A conformable record of the transition from early to modern Earth

Authors:

Van Kranendonk et al

Abstract:

This paper presents the first, detailed sedimentological analysis of the Paleoproterozoic Kungarra Formation, the lowermost of three formations comprising the Turee Creek Group in Western Australia, which was deposited across the rise in atmospheric oxygen (the Great Oxidation Event, or GOE) and the transition from early to modern Earth.

The data show that the Kungarra Formation has a gradational, conformable lower contact with underlying banded iron-formation of the Hamersley Group and predominantly comprises an upward-shallowing succession from deepwater shales and siltstones, through rippled fine-grained sandstones and stromatolitic carbonates, to tidal flat deposits that immediately underlie coastal–fluvial deposits of the overlying Koolbye Formation.

At the base of the Kungarra Formation is a gradual transition from alternating units of magnetic green shale and thin units of banded iron-formation that pass upsection to units of non-magnetic shale and ferruginous chert and grey chert, reflecting a gradual loss of iron from the world's oceans accompanying the rise of atmospheric oxygen. A falling stage systems tract is recognised above this transition in the Hardey Syncline area, capped by stromatolitic carbonates and a period of exposure marked by an erosional unconformity and carbonate beachrock. Two glacio-eustatic cycles are recognised within the middle to upper parts of the Kungarra Formation, each of which is marked by the rapid onset of falling systems tracts and characterised by falling systems tracts during and following diamictite deposition.

Stratigraphic data are used to infer a depobasin filled by a sediment wedge prograding from southeast to northwest, in contrast to previous models of a north-northeastward deepening foreland basin. The lack of seismites or internal unconformities within the formation precludes a foredeep setting. Rather, deposition is interpreted as having occurred within an intracratonic basin, with detritus sourced from erosion of uplifted bedrock to the southeast.

Rhyacian PaleoProterozoic Carbon Dioxide Levels Were 3.7x Modern

Metasaprolite in the McGrath Gneiss, Minnesota, USA: viewing Paleoproterozoic weathering through a veil of metamorphism and metasomatism

Authors:

Medaris et al

Abstract:

A 2100 Ma, 420 cm–thick metasaprolite, which is devoid of plagioclase but contains abundant microcline, occurs in the Archean McGrath Gneiss beneath the overlying Paleoproterozoic Denham Formation. Despite being recrystallized under amphibolite–facies conditions and chemically modified by potassium metasomatism, mass fluxes related to weathering and metasomatism of the McGrath metasaprolite can be estimated by judicious application of several geochemical parameters and the A–C*N–K plot (Fedo et al., 1995). The metasaprolite yields values of 67–94 for the Plagioclase Index of Alteration, 62–72 for the Chemical Index of Alteration, and 47 for the Feldspar Index of Weathering, and the total mass flux removed by weathering is a minimum of 2.4 moles/cm2. Such values correspond to an intermediate degree, or intensity, of weathering compared to other, more intensely weathered paleosols in the region, such as those beneath the Baraboo and Sioux quartzites. Potassium metasomatism occurred at 1742 Ma during the geon 17 Yavapai tectonothermal event, when a minimum of 0.33 moles/cm2 K2O was added to the metasaprolite. Although the absence of pedogenic textures precludes interpretation of climatic conditions during weathering of the McGrath Gneiss, the level of atmospheric pCO2 can be estimated by application of Sheldon's (2006) method, which yields a minimum of 3.7 × PAL for a weathering duration of 100,000 years.

Evidence of Glaciations, Possibly Huronian, From PaleoProtoerozoic India

Carbon and oxygen isotope systematics of a Paleoproterozoic cap-carbonate sequence from the Sausar Group, Central India

Authors:

Mohanty et al

Abstract:

Well-preserved sedimentological features of the Paleoproterozoic age Sausar Group of central India indicate glaciogenic origin for the diamictite in the lower part of the unit. Deglaciation was responsible for a marine transgression and the deposition of proximal glaciomarine facies and a cap-carbonate, followed by fine clastics with manganese ore. Analyses of δ13C and δ18O contents in the carbonate unit overlying the diamictite, together with Sr and Ba contents and REE data, indicate the preservation of primary geochemical signatures. The average δ13Ccarb content ranges between − 3.1‰ and + 0.1‰ V-PDB, having peak negative δ13C excursions of up to − 7.4‰ V-PDB, similar to Paleoproterozoic and Neoproterozoic cap-carbonates elsewhere. High Sr and Ba contents indicate the presence of aragonite and barite precursors, similar to well-studied Neoproterozoic cap-carbonates. A single continuous carbonate unit shows δ13C excursions from − 4.4 to + 2.6‰ V-PDB. The lithological association and chemostratigraphy are comparable with the carbonate–tillite association of the Huronian Supergroup of Canada, the Snowy Pass Supergroup of the USA, the Transvaal Supergroup of South Africa, and the Turee Creek Group of Australia.

Can the PaleoEnvironment be Determined From the Clay Minerals of the Rhyacian PaleoProterozoic Francevilian Basin?

From detrital heritage to diagenetic transformations, the message of clay minerals contained within shales of the Palaeoproterozoic Francevillian basin (Gabon)

Authors:

Ngombi-Pemba et al

Abstract:

Unmetamorphosed and undeformed marine siliciclastics rocks of the FB, FC and FD of the Francevillian series (Gabon) were deposited in an epicontinental basin. Clay minerals found in black shale, siltstone and sandstone are dominantly illite and chlorite except in two levels of the FB formation, which contain smectite-rich randomly ordered mixed layers. Their survival in a 2.1 Ga old sedimentary series is not related to the abundance of organic matter (total organic carbon or TOC), nor redox conditions at the time of deposition as indicated by the Fe speciation (FeHR/FeT and FePy/FeHR ratios). Rather it results from an incomplete illitization reaction that reflects potassium deficiency. The K2O/Al2O3 ratio of shale, siltstone and sandstone vary along the series, and appear to conserve the signature of the original chemical composition of the rocks. K-feldspars which are present in the FC and FD formations are missing in the FB formation. Consequently, the smectite layers do not appear to be inherited from a detrital input in the basin but must be considered as representative of an intermediate stage of the illitization reaction reached during diagenesis.

Fossil Evidence of Iron Oxidizing Bacteria From the Great Oxidation Event

Fossil evidence of iron-oxidizing chemolithotrophy linked to phosphogenesis in the wake of the Great Oxidation Event

Authors:

Crosby et al

Abstract:

The oxygenation of Earth's atmosphere allowed for the diversification of metabolisms to include those that rely on oxygen and its derivatives. For example, chemolithotrophic oxidation of sulfide and iron both require oxygen or nitrate as terminal electron acceptors. A growing number of oxygen-utilizing chemolithotrophs are known to accumulate intracellular polyphosphate as an energy reserve that allows them to adapt to the fluctuating redox conditions in their distinctive-gradient habitats. Polyphosphate is also thought to play an important role in the formation of phosphatic mineral deposits. Here we present fossil evidence of iron-oxidizing bacteria preserved as filamentous iron oxides within phosphatic Paleoproterozoic stromatolites. The filaments include twisted stalks similar to those produced by modern iron-oxidizing bacteria that are known to metabolize polyphosphate and inhabit steep redox gradients. Fossil iron-oxidizing bacteria preserved within some of the oldest known phosphorites serve as indicators of O2-Fe(II) gradients that may have supported microbially mediated phosphogenesis via polyphosphate metabolism and/or an active iron redox pump.

Evidence of a Rhyacian PaleoProterozoic Volcanic Island Arc In Ghana

Geochemistry and Geochronology of Paleoproterozoic Granites from the Lawra Volcanic Belt; Northwestern Ghana: Constraints on Petrogenesis and Geologic Implications

Authors:

Asamoah Sakyia et al

Abstract:

Paleoproterozoic Birimian granitoid rocks from the Lawra volcanic belt of northwestern Ghana have been analyzed for their major, trace, REE concentrations and their zircon U-Pb age. Based on the mineral assemblages, the calc-alkaline, metaluminous to weakly peraluminous I-type granitoids were classified as: (1) gneissic biotite granite, (2) hornblende granodiorite, (3) biotite granite, (4) two-mica granite and (5) pyroxene hornblende gneiss. The high LaN/YbN (∼4-146) values of the granitoids, characterized by enriched LREE pattern and flat to depleted HREE pattern ((Dy/Yb)N = 0.95-3.47), is typical of rocks derived from an evolved magma or partial melting of the depleted mantle. Similarly, the slightly negative Sr- and Eu-anomalies indicate varying degrees of plagioclase fractionation. Their high but varying SiO2 contents (58.1-76.1 wt. %), K2O/Na2O ratios (0.17-1.2) and (FeO + Fe2O3)/MgO ratios (0.98-4.02), and low Ce and Ti suggest that they are volcanic arc granites (VAG). The granitoids have zircon U-Pb ages between 2130.8 ± 9.5 Ma and 2213 ± 76 Ma, and preclude the contamination of the juvenile Birimian crust by notable amounts of reworked Archean crustal material. However, these ages spanning ∼81 Ma were recorded by all the rock types in the study area, with no distinct age difference among them. Accordingly, the area could be described as an undifferentiated terrain that experienced erratic emplacement of pulses of granitic magma during the period. Furthermore, the oldest ages of 2211 Ma and 2213 Ma obtained for the first time in this study suggest that the emplacement of Birimian granitoids in Ghana may have commenced much earlier than previously reported in the literature. The results demonstrate the juvenile character of the granitoid rocks. We therefore infer that the Birimian granitoids of the Lawra volcanic belt formed from large-scale crustal growth process with large amounts of juvenile crust formed from the depleted mantle in an island arc environment

Evidence of Hydrothermal Fluid, Escaping CO2 & Black Shale Interaction From Rhyacian PaleoProterozoic China

Fluid evolution of the Paleoproterozoic Hujiayu copper deposit in the Zhongtiaoshan region: Evidence from fluid inclusions and carbon-oxygen isotopes

Authors:

Jiang et al

Abstract:

The Zhongtiaoshan region, located in the southern margin of the North China Craton, is the host to a number of metamorphosed sediment-hosted stratiform copper deposits. These deposits are hosted by dolomitic marble and silicic albitite of the mid-Paleoproterozoic Zhongtiao Group and contain economically significant copper and cobalt. The formation of these deposits is considered to be closely associated with the evolution of the Paleoproterozoic “Zhongtiao” rift. The Hujiayu deposit, the second largest Cu deposit of this type, is mainly hosted in silicic albitite and dolomitic marble in the upper part of the Bizigou Formation but locally extends into carbonaceous shales at the bottom of the Yujiashan Formation. Mineralization of the Hujiayu Cu deposit can be divided into an early stage (diagenetic stage) with disseminated to veinlet sulfides and a late stage (metamorphism stage) with coarse-vein sulfides. Mineral assemblages are similar for the two stages, with major minerals as chalcopyrite, pyrite, and pyrrhotite and main gangue minerals as dolomite and quartz. Sulfide veinlets formed in the early stage are thin and discrete, and have irregular boundaries with the host rocks; whereas the ore-bearing veins of the late stage are controlled by fractures.

Five types of fluid inclusions are recognized in the Hujiayu Cu deposit and they are: (1) pure vapor and vapor-rich inclusion (V-type), (2) pure CO2 inclusion (PC-type), (3) CO2-H2O inclusion (C-type), (4) liquid-rich inclusion (L-type), and (5) daughter mineral-bearing inclusion (S-type). Microthermometric analysis shows that the ore-forming fluids of the early mineralization stage are characterized by high salinity (22-40 wt.% NaCl equiv.) and moderate temperature (120-280 °C). The ore-forming fluids of the late mineralization stage are characterized by CO2 enrichment, high salinity, high temperature and underwent significant unmixing at a temperature interval of 240 °C to 480 °C. Compositions of the ore-forming fluids in the early and late stages are interpreted to be mainly basinal brine and metamorphic hydrothermal solution, respectively. Carbon and oxygen isotope compositions suggest possible carbon isotope exchange between the ore-forming fluids and organic-rich carbonaceous shales during the early stage. In the late mineralization stage, both degassing of CO2 and isotopic exchange with organic carbon may have contributed to the formation of the more negative δ13CV-PDB values of mineralized carbonates.

The early stage mineralization of the Hujiayu Cu deposit may have occurred via interaction of oxidized Cu-bearing brines from the red-bed in the lower segment of the Bizigou Formation with the overlying reductive carbonaceous shales. Late stage mineralization at Hujiayu was mainly triggered by CO2 escaping from metamorphic hydrothermal solutions.

Evidence From China PaleoProterozoic Plate Tectonics did NOT Shutdown

Early Paleoproterozoic (2.45–2.20 Ga) magmatic activity during the period of global magmatic shutdown: Implications for the crustal evolution of the southern North China Craton

Authors:

Diwu et al

Abstract:

A global database of zircon ages from both granitoids and detrital sediments shows an exceptionally and robust ages gap between 2.45 and 2.20 Ga. The early Paleoproterozoic magmatism dramatically decreased on the Earth, which was proposed to relate to the global plate tectonic shutdown. However, the available data indicate that 2.45–2.20 Ga magmatic rocks are widespread in the Taihua Complex during the quiet interval. The Taihua Complex is located in both the Lushan and Xiaoqinling areas along the southern segment North China Craton (NCC). The Complex is composed mainly of a gneiss series and the Khondalite-dominated supracrustal rock. The latter, occurs as a linear structural belt and was named the Khondalite Belt. The gneiss series in the Lushan area has an age of 2.85–2.72 Ga, whereas the Xiaoqinling region contains widespread tonalitic–trondhjemitic–granodioritic gneisses with ages of 2.45–2.20 Ga. Significant variation of Hf isotopes in zircons and whole-rock ɛNd(t) values suggest that these rocks were produced by variable mixing of a juvenile materials with older crust in an Andean-type continental margin arc or island arc setting. The depositional age of the sedimentary protoliths of the khondalite series can roughly constrained to between 2300 and 1970 Ma. It has been considered that they were deposited on a stable continental margin environment. The U–Pb dating of metamorphic zircons from the Taihua Complex suggest that the southern NCC underwent a polyphase tectonic evolution during the period 1.97–1.82 Ga, the peak metamorphism coeval with crustal thickening has occurred at ∼1.94 Ga.