Pondering the Precambrian #42

Proterozoic:

NeoProterozoic:

Changes to the carbon cycle and environment  were detected from the Ediacaran/Cambrian boundary in China.

Using boron to detect the salinity of the paleooceans gives some interesting twists.

Evolution of multiple basins from the Neoproterozoic are described.

Is there a biochemical signal dividing metazoan clades into two?

Did animal-like embryos predate actual metazoans (animals).

How NOT to become a metazoan.

A Cryogenian interglacial deposit has been found in China.

When did the Sturtian glaciation begin during the Cryogenian in South China?

Mesoproterozoic:

Where was South China in the Nuna/Columbia and Rodinia supercontinents during the Mesoproterozoic?

The Stenian Copper Harbor and Nonesuch Formations have a marine origin.

PaleoProterozoic:

Evidence of explosive basalt volcanism found from the paleoproterozoic.

In French Guiana, a gold rich Rhyacian Period formation has been found.  It contains sedimentary layers within the volcanic ones.  Are they fossiliferous?

After the Lomagundi-Jatuli Event, the carbon-sulfur cycle seemed to return to strong activity in the aftermath in the Rhyacian/Orosirian Periods.

Archean:

It appears during the GOE, the ocean basins remained anoxic.

Earth's magnetic field may have been in place during the Archean.

Evidence of subduction from the Late Archean comes from Australia.

The Kaapvaal Craton may be a remnant of the Pilbara Craton that split off in the MesoArchean.

Extraterrestrial impacts might have triggered bursts in plate tectonics.

Ancient microbes played an important role in warming the early Earth.

Hadean:

The impact history of Earth should NOT be correlated to other planets in the solar system.

Origin of Life:

There is a hyperacidic, hypersaline geothermal system in Dallol, Ethiopia that is lifeless and that has implications for the origin of life.

DNA is only one of several possible genetic information molecules.

Lifelike chemistry has been created in the lab.

Ribose and other sugars have been found in meteorites.

Some of the earliest animal fossils are possibly chemical 'gardens' that produce pseudofossils.

Pondering the Precambrian #41

Proterozoic:

Glauconite is rare is precambrian deposits of the Bhima Basin.  Why?

NeoProterozoic:

There is evidence of the oxygen and other environmental conditions across the Ediacaran/Cambrian boundary from southern China.

Could the marine waters have been highly alkali at the terminal Ediacaran?

Cloudina acted as an anchor for Ediacaran reefs.

Sulfur and carbon cycles from the Ediacaran formations of the Lower Yangtze block.

Oxygen levels during the NeoProterozoic were transient.

There were two episodes of phosogenesis in the ocean water of the Doushantou formation.

The Doushantou and Datangpo formations from the Ediacaran and Cryogenian have been argued to represent evidence of photosynthetic productivity during the Snowball Earth episodes.  This is probably wrong.

There is evidence from India of biofilms from the Neoproterozoic.

The microfossils of the Katanga Supergroup are probably pseudofossils, alas.

Boxonia bearing stromatolites from Mongolia suggest variation in their formation compared to others.

Ediacaran Biota-like disc fossils have been found in the Cryogenian, 80 million years earlier than ever before.

The Cryogenian basin deposits of south China suggest massive hydrothermal activity during the Sturtian Glaciation (Snowball Earth).

What was the stratosphere of the Snowball Earth like?

The Tonian Callana Group has a carbon anomaly that does not match the one observed at Bitter Springs.

MesoProterozoic:

There is evidence of the breakup of the Columbia Supercontinent from Brazil.

PaleoProterozoic:

Kimberlites from the Siderian suggest there is an isolated mantle reservoir.  And may be fingerprints of the ancient makeup of the world's geology.

There was a very long lived tectono-magmatic event 1.8 billion years ago.

The geochronology of the Hart Dolerite of Australia is documented.

Archean:

There is evidence of oceanic crust subduction from the NeoArchean.

There is also evidence of mountain building from the NeoArchean.

There is evidence of a subduction/accretion/collision event at the end of the NeoArchean, confirming full blown plate tectonics were in progress at that time frame.

Mesoarchean deposits from islands suggest the pelagic environment was rich in boron.

Paleoarchean microfossils show a continuous cell wall amongst other characteristics.

Can Xenon help determine if the carbon traces in ancient rocks is biogenic or not?

The fingerprints of Ur, the earliest supercontinent, are in the Bastar Craton in India.

Hadean:

The energy budget and structure of the earth get modeled during and after the Thea impact.

Origin of Life:

Bacterial gene duplicates are more common in eukaryotes than expected.

Is there a relation between hydrothermal chemistry and the origin of cellular life?

META:

Archaea's biochemistry may give hints as to ancient ocean temperature.

A large virus may have helped make the first eukaryote allow endosymbiosis allowing for the evolution of photosynthesis in eukaryotes.

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 #28

Proterozoic:

NeoProterozoic:

Ediacaran:

A cyanobacteria normally associated with the Phanerozoic has been found in Ediacaran deposits in China.

There was a significant shift in what the limiting nutrients were across the Ediacaran/Cambrian boundary.

How did the black shales form across the Ediacaran/Cambrian boundary?

Was the Sao Francisco Basin a restricted basin during the Ediacaran?

A section in China appears to be a record of the late Ediacaran glaciations, showing a cold, dry climate.

The Cathayasian block was attached to Gondwana since 630 million years ago.

The fate of an inland sea from during the Neoproterozoic gets discussed.

Evidence of the Milkanovich cycles is preserved in Ediacaran deposits.

Tubular fossils from the Weng'an Biota are algae, not metazoans.

Weng'an Biota also provides examples of preserved encysting of eukaryotes.

Cryogenian:

Could the banded iron formations of the Cryogenian be related to ocean acidification?

There is evidence of a less than complete snowball earth from China during the Marinoan Glaciation.

Cryogenian Period deposits of Datangpo Formation of China from the interglacial period between the Sturtian and Marinoan glaciations show a very stratified ocean.

The majority of the time, the NeoProterozoic oceans were anoxic and were supersaturated with dolomite.

Tonian:

Fungus fossils appear to have been found in Tonian (neoproterozoic) or Stenian (mesoproterozoic) deposits in Canada.

There appears to have been a paleorifting event during the Tonian of the Sao Francisco-Congo continent.

The Sognefjel complex appears to have formed in the Asgardian Sea during the early Tonian.

Did the Paleo-South China Ocean close during the Tonian?

MesoProterozoic:

The Eastern European Craton has a Mesoproterozoic signal.

The southern Grenville formation dates from Mesoproterozoic and is from purely Laurentian sources.

Reported stromatolites from a Stenian lake cannot be proven to be biogenic.

Paleoproterozoic:

600 million years of sedimentation is examined from the Paleoproterozoic of Lapland.

Statherian Period evolution of the Oolongbuluke terraine is explained.

In Brazil, the Sobreiro Formation appears to be from the Orosirian/Statherian boundary.

Archean:

There is evidence of retreating oceanic slab subduction from the NeoArchean of China.

Evidence from India suggests there was significant local variation in Archean ocean conditions.

The Caozhuang basin appears to be a case of sagduction.

Fossils from paleoarchean South Africa show bacteria dividing and they appear to be very similar to cyanobacteria Pleurocapsales.

Eoarchean stromatolites get examined.

Hadean:

Was the Earth covered in a lava ocean before Theia impacted and created the moon?

META:

What are the implications of a hotter mantle, but colder subduction during the Precambrian?

Pondering the Precambrian #26

Proterozoic:

NeoProterozoic:

The Earth's magnetic field was 10% of what it is today during the Ediacaran and the Earth's solid core may date from that period.

Evidence from Murmansk supports the weak magnetic field hypothesis during the Proterozoic.

Trace fossils from the Ediacaran have been found in Brittany, France.

Ediacaran environmental changes are recorded in Brazil.

The iodine content of the the Doushanto deposits of the Ediacaran.

Microorganisms are the source of organic carbon found in Sichuan from the Ediacaran into the Cambrian. 

It appears Cloudina and other tubular organisms from the terminal Ediacaran appear to have reproduced asexually.

There is evidence of hydrothermal activity altering various deposits during the Ediacaran.

Evidence of the breakup of Rodinia to the accretion of Gondwana in the Ediacaran from Paraguay.

A new biomarker has been found from the Cryogenian that hints at how complex life evolved after the Snowball Earth.

There was a deep marine organic reservoir in the Cryogenian.

Starting in the Cryogenian until the start of the Carboniferous, there was significant lack of impacts.  There might be evidence of the Snowball Earth via a global wiping of the impact craters from before that point, too.

Could the Great Noncomformity be due to the Snowball Earth?

The Great Noncomformity represents a 200to 300 million year gap in the depositional history of the world according to evidence from the North China Craton.

There are graphite particles in Cryogenian deposits of Nantuo.

Manganese ore deposits in South China were formed in the interglacial between the Sturtian and Marinoan glacials by microbial activity.

Is hydrothermal activity from the Tonian of the Western Australian Craton evidence of the breakup of Rodinia?

Mesoproterozoic:

Eukaryotes diversified earlier than previously thought, starting in the Ectasian.

Paleoproterozoic:

There was a 30 degree shift in the mafic dyke swarms during the Paleoproterozoic.

The surface conditions of at the start of the Great Oxygenation Event were anoxic.

There is evidence from the Yangtze Block that contradicts the hypothesis that there was a shutdown of plate tectonics during the PaleoProterozoic.

Archean:

A coupled crust/mantle formed before 2.5 billion years ago.

Evidence from the MesoArchean to the Paleoproterozoic of Norway show how the continents were built up.

More evidence of episodic crust growth starting in the MesoArchean.

There may be EoArchean deposits in the North China craton.

Sarmatia, Pilbara, and Kaapvaal Cratons were all part of the single supercontinent Vaalbara.

There's no evidence of pre 3.95 billion year old fossils.

Hadean:

Did the impact with Theia provide the volatiles the Earth needed for life?

Did asteroid impacts have a central role in the formation of the original continents?

META:

There is a 600 million year superocean cycle modulating a longer supercontinent.

Could sulfur dioxide have helped with the start of prebiotic carbohydrates?

There are biochemical hints that the last common universal ancestor - the last life form from which everything alive is descended - was not a hyperthermophile.

Reconstruction the Last Eukaryote Common Ancestor's genome to understand the evolution from the First Eukaryote Common Ancestor to the LECA.

Chunks of RNA can be formed prebioticly.

Studying algae suggest eukaryotes have received numerous DNA additions from bacteria.

Pondering the Precambrian #7

Proterozoic:

NeoProterzoic:

The Tarim Craton may have been connected to the North India Block rather than Australia within the supercontinent of Rodinia during the Tonian.

Has evidence of mountain building during the Tonian been found in Scotland?

The Tonian/Cryogenian transition seems to have been located in Svalbard.

How complete is the evidence of glaciations during the Cryogenian in Scotland?

How oxygenated was the ocean between the Snowball Earth episodes?

Caution with carbon-13 shifts are urged in Cryogenian deposits as they are deposit dependent.

Evidence of hydrothermal modification of a dolostone during the Marinoan Glaciations.

Was there a delayed oxygenation of the oceans from the Cryogenian to the Ediacaran?

Evidence from Mongolia's 540 million year old Khesen formation documents the rise of animals.

Evidence that Ediacaran Parvancorina was motile and could sense benthic currents.

Were there constant anoxic bottom waters during the Ediacaran?

Cyanobacterial-algal crusts have been found from Ediacaran paleosols.

MesoProterozoic:

Cyanobacterial microfossils are examined from Calymmian China.

Were tellurium and selenium weathered from sandstones into the Mesoproterozoic oceans?

PaleoProterozoic:

Biosignatures have been found for eukaryotes from Statherian China.

There is evidence of an impact in India during the Siderian.

Was there a subduction cessation during the Siderian in China?

More evidence of warm subduction during the Orosirian from Cameroon.

Was the Great Oxygenation Event really an abiotic process?!

There appears to have been gradual oxygenation in the oceans (in some cases) just prior to the GOE.

A large igneous province is detected from India from the Rhyacian.

Was the early biosphere nutrient limited?

Archean:

Evidence from China, specifically the North China Craton, about the composition of NeoArchean sea water.

Inland lakes appear to have fostered the diversification of microbial life during the MesoArchean.

The oldest known paleosols (fossil soil) date from the PaleoArchean (3.46 billion years ago) and originate in Australia and may have formed from sulfuric acid weathering.

Could there be a problem with the cherts being used from the PaleoArchean to claim microbial life?

Or is there a definitive example of fossil life from the PaleoArchean?  Does that mean life is common in the universe?

Is some of Earth's magma ocean preserved in PaleoArchean rock?

META:

Exploring the Precambrian lithosphere of Zambia and Malawi.

The effect of paleoseawater chemistry on hydrothermal ridges.

Origin of Life:

The origin and diversification of the endosymbiont known as the mitochondria.

A new lineage of eukaryotes has given information on mitochondrial genome reduction.

Pondering the Precambrian #6

Proterozoic:

NeoProterozoic:

There is evidence of a potential blacksmoker vent from the NeoProterozoic.

Ocean subduction evidence has been found in China.

Comb Jellies appear to have be the oldest divergent, yet still living, branch of animals.

Ediacaran:

An Ediacaran protist fossil seems to show how those organisms' reproduction in action.

Evidence of the opening of the Iapetus Sea in Russia during the Ediacaran has been uncovered.

The submerged Batavian Knoll is a microcontinent with evidence of the assembly of Gondwana.

Biostratigraphical evidence is coming together for the Ediacaran from China.

The nuclei and nucleoli in the embryos found in Ediacaran China's Weng'an Biota.

Understanding the Ediacaran paleoecologies.

Should the extinction of Cloudina lucianoi mark the Ediacaran/Cambrian boundary?

Could Ediacaran rangeomorphs actually burrow?

Cryogenian:

It appears the Sturtian Snowball Earth episode began circa 717 million years ago.

Tonian:

The Tonian/Cryogenian boundary has been proposed for specific spots in Scotland.

A vase shaped microfossil has been found in the Tonian deposits around the world.

There appears to have been a mass extinction during the Tonian prior to the Snowball Earth episodes.

Mesoproterozoic:

There is evidence Archean granites were reworked and uranium deposited during the Calymmian in the Olympic Dam Breccia in Australia.

Eukaryote fossils were found in Calymmian deposits in China.

Are some fossils that are normally thought to be NeoProterozoic (Tonian/Cryogenian) found in the MesoProterozoic deposits of Russia?

At the dawn of the Mesoproterozoic, at the Statherian/Calymmian boundary, Australia made contact with northwestern Laurentia and began a long slide along its margin.

Paleoproterozoic:

Evidence of an island arc from the Paleoproterozoic came from West Africa.

There may have been two island arcs in Finland during the PaleoProterozoic.

How the Francevillian formation formed in the Rhyacian.

The microfossils of the Francevillian Biota get examined.

Evidence from India for proto continents in the Rhyacian.

Archean:

Findings from the NeoArchean from the North American Craton support local evidence of plate tectonics.

Did the development of carbonate platforms in the NeoArchean pave the way for the Great Oxygenation Event?

Is there evidence of biogenic atmospheric oxygen during the MesoArchean?

The emergence of the continents may have happened over multiple differentiation events.

Evidence of life was found in EoArchean sediments from Labrador, Canada.

Hadean:

Caution should be taken when examining Hadean zircons.

Did life form in warm little pools?

Pondering the Precambrian #5

Proterozoic:

Evidence of anoxic and alkaline oceanic conditions in the Vempalle and Tadpatri formations in India from stromatolites.

NeoProterozoic:

The evolution of sponges is reviewed.

Ediacaran:

There was a very negative and unexplained carbon-13 shift during the aftermath of the Snowball Earth episode.

At the dawn of the Ediacaran, during the retreat of the Ghaub Glaciation, the Ediacaran oceans' oxygen levels fluctuated.

Relatives of Cloudina from China are helping our understanding of the Ediacaran biomineralized metazoan.

Using x-ray tomography, attempts are made to interpret trace fossils made by metazoans during the Ediacaran.

Why did metazoans start growing in size during the Ediacaran?

Could the discovery of certain acanthomorphic acritarchs allow for better correlation of different Ediacaran fossils localities?

A unique fossil of Rangea has been found in ironstone and demonstrates a semi rigid skeleton for the Ediacaran critter.

There was an anoxic ocean volume in Brazil during the Ediacaran.

A transitional fauna from the end Ediacaran was found in Nevada.

Cryogenian:

A very thick layer of sediment from the Cryogenian has been found in Death Valley.  Evidence of glacial activity and rifting is present.

Tonian:

Did animals diverge into different lineages in the Tonian prior to the Snowball Earth episode?

The chemical weathering and Rodinia's continental drift in the Tonian contributed to the lead up to the Cryogenian Snowball Earth episode.  It also had a lot of parallels with the lead up to the Huronian Snowball Earth episode.

The evidence of evolutionary radiation of eukaryotes in Africa at the time of the MesoProterozoic/NeoProterozoic boundary.

Vase shaped microfossils have been found in Arizona, USA from the Tonian.

MesoProterozoic:

Was there an oceanic oxygenation spike during the Ectasian 1.36 billion years ago?

Evidence from Mauritania suggests what the paleoecology of the MesoProterozoic might have been like.

PaleoProterozoic:

Examining a paleoproterozoic gold deposit suggests there were two different sources for its carbon content and some caution about inferring the deposition temperatures from Raman spectroscopy.

Examining a paleosol from the Statherian shows atmospheric carbon dioxide was 4.8x preindustrial levels.

Evidence of continental assembly prior to the supercontinent Columbia from Brazil during the Orosirian.

There is evidence of significant geological turmoil during the Orosirian and is interpreted as a true polar wander.

The iron deposits of the Dongshan in China from the Orosirian show evidence of two different sources for the iron.

Siderian fossils from Western Australia seem to show benthic microbial mats seem to have continued to thrive during the Great Oxidation Event.

The evidence from the first known Snowball Earth episode during the Siderian appears to support the Jormungund scenario (slushball earth).

Archean:

Microbial dissimilatory iron reduction was common across the Archean/Proterozoic Boundary.

Plankton-like micro fossils from Australia have been found in South Africa.

Evidence of anaerobic photosynthetic microbes has been found from the PaleoArchean of Australia.

Did life really start on land?

META:

How did the Earth stay warm enough for life despite the Faint Young Star Paradox?

The importance of methane to prebiotic chemistry.

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.

Ediacaran NeoProterozoic Skeletal Metazoan Cloudina was Separate From Other Ediacaran Lifeforms

Flexible and responsive growth strategy of the Ediacaran skeletal Cloudina from the Nama Group, Namibia

Authors:

Wood et al

Abstract:

The Ediacaran skeletal tubular putative metazoan Cloudina occurs globally in carbonate settings, which both provided lithified substrates and minimized the cost of skeletonization. Habitat and substrate preferences and the relationship of Cloudina to other metazoans have not been fully documented, so we know little as to its ecological demands or community dynamics. In situ Cloudina from the Nama Group, Namibia (ca. 550–541 Ma), formed mutually attached reefs composed of successive assemblages in shallow, high-energy environments, and also communities attached to either stromatolites in storm-influenced deep inner-ramp settings or thin microbial mats in lower-energy habitats. Each assemblage shows statistically distinct tube diameter cohorts, but in sum, Cloudina shows an exponential frequency distribution of diameter size. In reefs, we document a periodicity of size variation, where mean, minimum, and maximum tube diameters vary together and show a systematic increase toward the top of each assemblage. We conclude that most Nama Group Cloudina represent one ecologically generalist taxon with highly variable size, that size was environmentally mediated, and that Cloudina could respond rapidly to periodic environmental changes. While Nama Group skeletal metazoans coexisted with soft-bodied biota, there was no apparent ecological interaction, as they were segregated into lithified carbonate and non-lithified clastic microbial mat communities, respectively. We infer that ecological flexibility allowed Cloudina to form varied communities that colonized diverse carbonate substrates under low levels of interspecific substrate competition. This is in notable contrast to the earliest Cambrian skeletal epibenthos that formed biodiverse reef communities with specialist niche occupancy.

Saccorhytus coronarius: a Basal Deuterostome From the Ediacaran/Cambrian Boundary

Researchers have identified traces of what they believe is the earliest known prehistoric ancestor of humans -- a microscopic, bag-like sea creature, which lived about 540 million years ago.

Named Saccorhytus, after the sack-like features created by its elliptical body and large mouth, the species is new to science and was identified from microfossils found in China. It is thought to be the most primitive example of a so-called "deuterostome" -- a broad biological category that encompasses a number of sub-groups, including the vertebrates.

If the conclusions of the study, published in the journal Nature, are correct, then Saccorhytus was the common ancestor of a huge range of species, and the earliest step yet discovered on the evolutionary path that eventually led to humans, hundreds of millions of years later.

link.

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.

Ecological and Biological Shifts During the Late Ediacaran NeoProterozoic

Ediacaran distributions in space and time: testing assemblage concepts of earliest macroscopic body fossils

Authors:

Boag et al

Abstract:

The mid-late Ediacaran Period (∼579–541 Ma) is characterized by globally distributed marine soft-bodied organisms of unclear phylogenetic affinities colloquially called the “Ediacara biota.” Despite an absence of systematic agreement, previous workers have tested for underlying factors that may control the occurrence of Ediacaran macrofossils in space and time. Three taxonomically distinct “assemblages,” termed the Avalon, White Sea, and Nama, were identified and informally incorporated into Ediacaran biostratigraphy. After ∼15 years of new fossil discoveries and taxonomic revision, we retest the validity of these assemblages using a comprehensive database of Ediacaran macrofossil occurrences. Using multivariate analysis, we also test the degree to which taphonomy, time, and paleoenvironment explain the taxonomic composition of these assemblages. We find that: (1) the three assemblages remain distinct taxonomic groupings; (2) there is little support for a large-scale litho-taphonomic bias present in the Ediacaran; and (3) there is significant chronostratigraphic overlap between the taxonomically and geographically distinct Avalonian and White Sea assemblages ca. 560–557 Ma. Furthermore, both assemblages show narrow bathymetric ranges, reinforcing that they were paleoenvironmental—ecological biotopes and spatially restricted in marine settings. Meanwhile, the Nama assemblage appears to be a unique faunal stage, defined by a global loss of diversity, coincident with a noted expansion of bathymetrically unrestricted, long-ranging Ediacara taxa. These data reinforce that Ediacaran biodiversity and stratigraphic ranges of its representative taxa must first statistically account for varying likelihood of preservation at a local scale to ultimately aggregate the Ediacaran macrofossil record into a global biostratigraphic context.

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.

Ernietta from the late Edicaran NeoProterozoic Namibia was Weirdly Assymetrical

Ernietta from the late Edicaran Nama Group, Namibia

Authors:

Elliott

Abstract:

Ernietta plateauensis Pflug, 1966 is the type species of the Erniettomorpha, an extinct clade of Ediacaran life. It was likely a gregarious, partially infaunal organism. Despite its ecological and taxonomic significance, there has not been an in-depth systematic description in the literature since the original description fell out of use. A newly discovered field site on Farm Aar in southern Namibia has yielded dozens of specimens buried in original life position. Mudstone and sandstone features associated with the fossils indicate that organisms were buried while still exposed to the water column rather than deposited in a flow event. Ernietta plateauensis was a sac-shaped erniettomorph with a body wall constructed from a double layer of tubes. It possessed an equatorial seam lying perpendicular to the tubes. The body is asymmetrical on either side of this seam. The tubes change direction along the body length and appear to be constricted together in the dorsal part of the organism.

Evidence Ediacaran Biota Members Survived Into the Cambrian

Transitional Ediacaran–Cambrian small skeletal fossil assemblages from South China and Kazakhstan: Implications for chronostratigraphy and metazoan evolution

Authors:

Yang et al

Abstract:

The Ediacaran–Cambrian transition records distinct evolutionary changes of metazoans. The Ediacaran fossils (i.e., Ediacara-type biota and tubular fossils) are contrasting with the diverse small skeletal fossils (SSFs) from the early Cambrian. The apparent dissimilarities hindered studies deciphering their evolutionary relationships. This also led to a popular assumption that there exists a mass extinction of the Ediacara biota and cloudinids at the Precambrian–Cambrian (Pc–C) boundary. Here we report for the first time a transitional fauna which consists of typical elements of Ediacaran, i.e. cloudinids and related tubicolous organisms, together with Cambrian SSFs including protoconodonts, anabaritids and siphogonuchitids from South China and Maly Karatau (Kazakhstan). The sediments yielding the transitional fauna are characterized by siliceous rocks in both regions and were previously considered to be unfossiliferous. Their chronostratigraphic assignment in South China has been debated for years. Based on the new fossil assemblage, the siliceous strata of the Daibu Member (Northeast Yunnan, South China) and the basal Kuanchuanpu Formation (South Shaanxi, South China) can be assigned to the earliest Cambrian SSF biozone (Anabarites trisulcatus–Protohertzina anabarica Assemblage Zone) and thus can be considered of early Cambrian in age. A new subzone of the earliest SSF zone in eastern Yunnan (South China) is proposed herein defined as Ganloudina symmetrica–Rugatotheca typica Interval Subzone. The new fauna demonstrates that the cloudinids, originally confined to the late Ediacaran, persisted into the Cambrian Fortunian, and no major extinction event occurred at the Pc–C transition.

Is India's Infrakrol Formation the Same age as China's Ediacaran Doushantuo Formation?

Tianzhushania spinosa and other large acanthomorphic acritarchs of Ediacaran Period from the Infrakrol Formation, Lesser Himalaya, India

Authors:

Joshi et al

Abstract:

Covering a time span from Ediacaran (base of Blaini pink carbonates) to Early Cambrian (base of Tal Group), the Krol belt in the Lesser Himalaya (India), occurs as a series of synclines from Solan, Himachal Pradesh in the north-west to Nainital, Uttarakhand in the south-east. Various lithostratigraphic divisions of this belt reveal many palaeobiological entities, namely cyanobacteria, algae, acritarchs, small shelly fossils and trace fossils. Globally, large acanthomorphic acritarchs of the Ediacaran Period are used as significant biostratigraphic tools for global correlation. In the Krol belt, reports of acanthomorphic acritarchs from the Infrakrol and Krol ‘A’ formations of the Krol Group have further supported this notion. This paper reports well-preserved microfossils including acanthomorphic acritarchs, sphaeromorphic acritarchs, coccoids namely Tianzhushania spinosa, T. polysiphonia, Papillomembrana compta, Schizofusa sp., Gloeodiniopsis lamellosa, Sphaerophycus medium, and the unnamed forms A, B and C from the chert nodules of the Infrakrol Formation exposed in the Nainital Syncline of the Kumaun Lesser Himalaya. A biostratigraphic correlation based on acanthomorphic acritarchs suggests that the Infrakrol Formation is coeval to the lower Tianzhushania assemblage zone of the Doushantuo Formation of south China. Tianzhushania and Papillomembrana are significant additions to the previous record of the Ediacaran acanthomorphic acritarchs from the Lesser Himalaya of India and provide an independent evidence for construction of both biozonation scheme and paleogeography.

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.