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?

Evidence of "El Nino" Like Cycles From the Siderian PaleoProterozoic Huronian Glaciations

Climatic cycles recorded in glacially influenced rhythmites of the Gowganda Formation, Huronian Supergroup

Authors:

Howe et al

Abstract:

The Gowganda Formation of the 2.45-2.2 Ga Huronian Supergroup contains glacially-induced, varve-like rhythmites that potentially preserve a detailed record of climatic conditions during the Paleoproterozoic Era. Four rhythmic couplet thickness records were measured at two outcrops near Wharncliffe, Ontario for the purpose of time-series analysis. The couplets, which range from 1 – 32 mm thick, are composed of alternating layers of siltstone and claystone. Time-series analysis of the couplet thickness records using the MTM Toolkit of Mann and Lees (1996) consistently revealed periodicities in the range of 2.2-2.9 couplets per cycle, which is consistent with climatic cycles such as the quasi-biennial oscillation (QBO) and the El Niño Southern Oscillation (ENSO) observed in modern times. This periodicity suggests that the rhythmic couplets represent annual deposits (i.e. varves). Evidence for the presence of cycles at 3.0-4.9 couplets, 6.6-6.9 couplets, 8.8-9.2 couplets, 22.8 couplets, and 30.1-31.0 couplets were also observed in some couplet thickness records; however, the presence of these longer term cycles was inconsistent from site to site.

Did the Oceans get Arsenic Poisoning at the end of the Huronian Glaciations/Siderian PaleoProterozoic Snowball Earth?

By examining rocks at the bottom of ancient oceans, an international group of researchers have revealed that arsenic concentrations in the oceans have varied greatly over time. But also that in the very early oceans, arsenic co-varied with the rise of atmospheric oxygen and coincided with the coming and going of global glaciations. The study was recently published in the Nature Group Journal, Scientific Reports.

"In the article we argue that when we first see the appearance of complex life on Earth, is when life have developed mechanisms to resist catastrophic chemical changes forced by global glaciations. And that this enabled the expansion of complex life in oceans, and paved the way for our own evolution", says Dr Ernest Chi Fru of Stockholm University, who has led the research group.

The first appearance of oxygen in the atmosphere occurred at a time when marine arsenic concentrations were dramatically low, at about after 2.45 billion years ago. This is also a period when Earth experienced its first known global glaciation. At the end of these glaciations, considerable rise in marine arsenic concentrations concurred with rapid demise of atmospheric oxygen.

The authors infer -- from the way modern photosynthetic organisms react to changing marine arsenic concentrations -- that this event was due to widespread ocean toxicity resulting from the release of toxic elements into the oceans when the ice melted.

link.

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.

Oxygen-17 Evidence of the PaleoClimate of Snowball Earths Past

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

Authors:

Herawartz et al

Abstract:

The oxygen isotopic composition of hydrothermally altered rocks partly originates from the interacting fluid. We use the triple oxygen isotope composition (17O/16O, 18O/16O) of Proterozoic rocks to reconstruct the 18O/16O ratio of ancient meteoric waters. Some of these waters have originated from snowball Earth glaciers and thus give insight into the climate and hydrology of these critical intervals in Earth history. For a Paleoproterozoic [∼2.3–2.4 gigayears ago (Ga)] snowball Earth, δ18O = −43 ± 3‰ is estimated for pristine meteoric waters that precipitated at low paleo-latitudes (≤35°N). Today, such low 18O/16O values are only observed in central Antarctica, where long distillation trajectories in combination with low condensation temperatures promote extreme 18O depletion. For a Neoproterozoic (∼0.6–0.7 Ga) snowball Earth, higher meltwater δ18O estimates of −21 ± 3‰ imply less extreme climate conditions at similar paleo-latitudes (≤35°N). Both estimates are single snapshots of ancient water samples and may not represent peak snowball Earth conditions. We demonstrate how 17O/16O measurements provide information beyond traditional 18O/16O measurements, even though all fractionation processes are purely mass dependent.

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.

Was the Siderian/Rhyacian PaleoProterozoic Huronian Glaciation Really a Snowball Earth, or Even Global?

Contradictory correlations of Paleoproterozoic glacial deposits: local, regional or global controls?

Author:

Young

Abstract:

There is little agreement among recently proposed correlation schemes for Paleoproterozoic glaciogenic rocks scattered thinly around the globe. Correlations are hindered by the dearth of tight geochronological control on the ages of glacial deposits, which are notoriously difficult to date. Most attempts at global correlation are based on comparison to the Huronian Supergroup in Canada, which contains three glaciogenic formations. Although the two lower glacial units were deposited in a rift setting and have a restricted distribution even in North America, they have been used in attempts to effect international correlations. The Gowganda Formation, together with correlatives, comprises the thickest and by far the most widespread Paleoproterozoic glacial deposits in North America. Glacial deposits are also reported from South Africa, Western Australia and elsewhere, where they appear to fall within the time period as the Huronian Supergroup (2.45-2.2 Ga) but attempts to correlate individual diamictite-bearing units to the three Huronian glaciogenic formations have proved difficult. None of the Huronian glacial formations has been precisely dated. Until such geochronological data are available it is practical and prudent to recognize that, during the early Paleoproterozoic, as in the Cryogenian, the Earth was susceptible to glaciations that could be triggered by a variety of local events including uplift, related to rifting and compressional orogeny. Within the 250 million years of the ‘Huronian Glacial Event’ (2.45 - 2.2 Ga) it is commonly assumed that ice sheet fluctuations were globally synchronous but this has not been demonstrated.

Dating Siderian Palaeoproterozoic Glacial Deposits of the Kola Peninsula, Russia

Dating Palaeoproterozoic glacial deposits of the Fennoscandian Shield using detrital zircons from the Kola Peninsula, Russia

Authors:

Gärtner et al

Abstract:

New age constraints from detrital zircon U-Pb geochronology from clastic sediments and diamict deposits obtained maximum depositional ages for the Seidorechka and Polisarka Sedimentary formations of the Imandra-Varzuga Greenstone Belt of theKola Province, NW-Russia. These delimit the deposition of Palaeoproterozoic Huronian-age glacial deposits of the Fennoscandian Shield from c. 2430 Ma to less than 2411 Ma. The time constraint allows comparison to the first two of three possible glacial intervals recognized in the Huronian Supergroup, Canada, and South African diamict deposits. Intercontinental comparisons support these constraints, the assumption of a glacial origin of the diamictites and, further, the eventually global extent of the event.Similar age distributions and depositional ages of c. 2400 Ma within the Neverskrukk Formation of the Pechenga Greenstone Belt support a correlation with the Imandra-Varzuga Greenstone Belt succession, which was traditionally based on lithostratigraphic observations.

The detrital zircon age spectra of eight analysed samples show an Archaean dominance and reoccurring peaks around 2800-2750 Ma,which indicate similar origins for the zircons. Such peaks are corroborating with a major global crustal generation event being recorded in detrital zircon spectra worldwide. Additionally, certain age populations around 2440 Ma and 2500 Ma are present andindicate a correlation with intrusive magmatism that affected the region at that time and support a correlation based on overlapping age distributions