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Highlights • Elemental Ce-Cr-V-Mo data indicate anoxic conditions, U shows minor mobility. • Fe geochemistry fits the criteria of a reduced paleosol with loss of isotopically light Fe(II). • Loss of metals (Zn, Ni, Co), Y > Ho to hydrosphere. • Isotopically light Cr signature in the paleosol originating from magmatic processes. Abstract Oceanic element inventories derived from marine sedimentary rocks place important constraints on oxidative continental weathering in deep time, but there remains a scarcity in complementary observations directly from continental sedimentary reservoirs. This study focuses on better defining continental weathering conditions near the Archean-Proterozoic boundary through the multi-proxy (major and ultra-trace element, Fe and Cr stable isotopes, µ-XRF elemental mapping, and detrital zircon U-Pb geochronology) investigation of the ca. 2.45 billion year old (giga annum, Ga) Cooper Lake paleosol (saprolith) developed on a sediment-hosted mafic dike within the Huronian Supergroup (Ontario, Canada). Throughout the variably altered Cooper Lake saprolith, ratios of immobile elements (Nb, Ta, Zr, Hf, Th, Al, Ti) are constant, indicating a uniform pre-alteration dike composition, lack of extreme pH weathering conditions, and no major influence from ligand-rich fluids during weathering or burial metasomatism/metamorphism. The loss of Mg, Fe, Na, Sr, and Li, a signature of albite and ferromagnesian silicate weathering, increases towards the top of the preserved profile (unconformity) and dike margins. Coupled bulk rock behaviour of Fe-Mg-Mn and co-localization of Fe-Mn in clay minerals (predominantly chlorite) indicates these elements were solubilized primarily in their divalent state without Fe/Mn-oxide formation. A lack of a Ce anomaly and immobility of Mo, V, and Cr further support pervasively anoxic weathering conditions. Subtle U enrichment, if primary, is the only geochemical evidence that could be consistent with oxidative element mobilization. The leaching of ferromagnesian silicates was accompanied by variable mobility and depletion of transition metals with a relative depletion order of Fe ≈ Mg ≈ Zn > Ni > Co > Cu (Cu being significantly influenced by secondary sulfide formation). Mild enrichment of heavy Fe isotopes (δ56/54Fe from 0.169 to 0.492‰) correlating with Fe depletion in the saprolith indicates open-system loss of isotopically light aqueous Fe(II). Minor REE + Y fractionation with increasing alteration intensity, including a decreasing Eu anomaly and Y/Ho ratio, is attributed to albite breakdown and preferential scavenging of HREE > Y by clay minerals, respectively. Younger metasomatism resulted in the addition of several elements (K, Rb, Cs, Be, Tl, Ba, Sn, In, W), partly or wholly obscuring their earlier paleo-weathering trends. The behavior of Cr at Cooper Lake can help test previous hypotheses of an enhanced, low pH-driven continental weathering flux of Cr(III) to marine reservoirs between ca. 2.48–2.32 Ga and the utility of the stable Cr isotope proxy of Mn-oxide induced Cr(III) oxidation. Synchrotron µ-XRF maps and invariant Cr/Nb ratios reveal complete immobility of Cr despite its distribution amongst both clay-rich groundmass and Fe-Ti oxides. Assuming a pH-dependent, continental source of Cr(III) to marine basins, the Cr immobility at Cooper Lake indicates either that signatures of acidic surface waters were localized to uppermost and typically unpreserved regolith horizons or were geographically restricted to acid-generating point sources. However, given detrital pyrite preservation in overlying fluvial sequences, it is probable that the oxidative sulfide corrosion required to drive surface pH < 4 lagged behind in this region relative to other early Proterozoic sequences. The entire saprolith exhibits a consistently light stable Cr isotope composition (δ53/52Cr: −0.321 ± 0.038‰, 2sd, n = 34) that cannot be linked to Cr(III) oxidation and is instead interpreted to have a magmatic origin. The combined paleosol chemical signatures and preservation of detrital pyrite/uraninite indicate low atmospheric O 2 during weathering at ca. 2.45 Ga in the rift-related environment of the Lower Huronian. The aqueous flux from the reduced weathering of mafic rocks was presumably characterized by a greater transition metal (Fe, Mn, Zn, Co, Ni) load with isotopically light Fe(II) compared to modern environments, as well as higher Eu/Eu* and Y/Ho than the source rock. In most models of Precambrian ocean element inventories, hydrothermal fluids are viewed as the main supplier of several metals (e.g. , Fe, Zn), although the results herein suggest that a riverine metal supply may have been substantial and that using Eu-excess as a strict proxy for hydrothermal flux may be misleading in near-shore marine sedimentary deposits. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Discovery of Huronian Glaciation Event (HGE) in the Wutai Shan, China. • The identified glacigenic diamictite sequence deposited at 2.2–2.1 Ga. • The diamictites show striated and faceted boulders and dropstone structures. Abstract Paleoproterozoic glacigenic diamictites have provided key evidence for the Great Oxidation Event (GOE) at ∼2.3 Ga associated with the widespread Huronian Glaciation Event (HGE). Here we report for the first time Paleoproterozoic glacigenic diamictite from the Sijizhuang Formation of the Hutuo Group in Wutai Shan, China formed during the late stage of HGE. The Sijizhuang Formation comprises diamictite, sandstone and siltstone-mudstone facies, conforming to a glaciomarine association. The diamictites show weak sorting and roundness, and carry a few striated and faceted boulders. Typical dropstones and associated structures are present in the sandstone and siltstone-mudstone facies. Diamictite facies, which characterizes the lower portion of the Sijizhuang Formation, displays an upward decrease, with a concomitant increase in the proportions of sandstone and siltstone-mudstone facies. The lithofacies associations of diamictite with sandstone and siltstone-mudstone indicate a frequently changing hydrodynamic environment. The petrochemical compositions of different lithofacies show that the clasts were multi-sourced and generated by limited weathering, in keeping with a cold climate. Available isotope age data constrain the glacigenic deposition of the Sijizhuang Formation to between 2.40 and 2.13 Ga, and most likely from 2.2 to 2.1 Ga. This estimate compares well with the 2.4–2.1 Ga age of the widespread HGE but the Sijizhuang diamictite appears to be younger than the last glacial unit (Gowganda Formation) in the type area of the HGE in Canada and suggests a locally protracted glacial event. [ABSTRACT FROM AUTHOR]

An exposure of the Paleoproterozoic Gordon Lake Formation in the Bruce Mines area, Ontario, Canada, contains abundant soft-sediment deformation structures (SSDS), including load casts, convolute bedding, pseudonodules, ball-and-pillow structures, flame structures and one dewatering pipe. These features are developed in siltstone to fine-grained sandstone beds and are between 1 and 120 cm in width and 3–78 cm high. The primary trigger mechanism is interpreted to be storm or tsunami activity, however seismic shock, overloading brought about by density inversions, or a combination of these processes, may have influenced the formation of SSDS to a lesser degree. Several beds also contain flat to wavy carbonaceous laminae, locally with a botryoidal texture and concentrations of heavy minerals, which are interpreted as relicts of microbial mats. Microbial mats may have played a minor role in the formation of SSDS, but do not appear to have been a prominent driving mechanism. Soft-sediment deformation structures observed in the Baie Fine, Flack Lake, and Cobalt plains regions of Ontario, are smaller and not as abundant as in the study area, suggesting that the deposits in the study area were either affected by local events or different magnitudes of sedimentary processes. In contrast to the tidal flat paleoenvironment interpreted for the Gordon Lake Formation in the Flack Lake area, the stratigraphically lower beds at the studied outcrop more closely resemble shallow shelf deposits. [ABSTRACT FROM AUTHOR]

Sedimentological observations from the Paleoproterozoic Huronian Supergroup are suggested to mark the rise in atmospheric oxygen at that time, which is commonly known as the Great Oxidation Event (GOE) and typically coupled with a transition from mass-independent fractionation (MIF) to mass-dependent fractionation (MDF) of sulfur isotopes. An early in situ study of S three-isotopes across the Huronian Supergroup by Papineau et al. (2007) identified a weak MIF–MDF transition. However, the interpretation and stratigraphic placement of this transition is ambiguous. In this study, all four S isotopes were analyzed for the first time in two Huronian drill cores by secondary ion mass spectrometer (SIMS), and both Δ33S and Δ36S were calculated. Based on improved precision and detailed petrography, we reinterpret the dominance of pyrrhotite in the studied sections, which was previously proposed as “early authigenic” in origin, as resulting from regional metamorphism. Small but analytically resolvable nonzero values of Δ33S (from −0.07‰ to +0.38‰) and Δ36S (from −4.1‰ to +1.0‰) persist throughout the lower Huronian Supergroup. Neither pronounced MIF-S signals nor a MIF–MDF transition are seen in this study. Four scenarios are proposed for the genesis of small nonzero Δ33S and Δ36S values in the Huronian: homogenization by regional metamorphism, recycling from older pyrite, dilution by magmatic fluids, and the occurrence of MDF. We argue that the precise location of the MIF–MDF transition in the Huronian remains unsolved. This putative transition may have been erased by postdepositional processes in the lower Huronian Supergroup, or may be located in the upper Huronian Supergroup. Our study highlights the importance of integrated scanning electron microscopy and secondary ion mass spectrometry techniques in deep-time studies and suggests that different analytical methods (bulk vs. SIMS) and diagenetic history (primary vs. metamorphic) among different basins may have caused inconsistent interpretations of S isotope profiles of the GOE successions at a global scale. Key Words: Great Oxidation Event (GOE)—Secondary ion mass spectrometer (SIMS)—Paleoproterozoic—Sulfur isotopes—Mass independent fractionation (MIF). Astrobiology 18, 519–538. [ABSTRACT FROM AUTHOR]

New measurements of the surface heat flux and radiogenic heat production in deep boreholes at 8 different sites are added to 10 older data to determine the heat flow field around the Sudbury basin, Ontario, Canada. This structure straddles the boundary between the Archean Superior Province to the North and the PaleoProterozoic Southern Province to the South, which terminates against the Grenville Front. The structure, that includes the Sudbury Igneous Complex (SIC), was created by a meteorite impact ca. 1.85 Ga. The mean value of the heat flux (50 mW m −2 ) is higher than that for the Superior Province (40 mW m - 2 ). Heat flow values are hardly perturbed by the presence of the SIC and require a regional enhancement of heat production in the upper crust with respect to the average Superior, due mostly to the enriched Huronian metasediments of the Southern Province. The average radiogenic heat production of SIC lithologies (1.2 μ W m - 3 ) is higher than that of the local Archean basement, indicating that the impact melt sheet was partly derived from Huronian sediments. Local variations in heat flux can be related to heat production differences between the Abitibi upper crust and the Huronian metasediments as well as thrusting and tectonic thickening in the Southern Province. The higher than average values of heat flux and crustal heat production in the Southern Province imply elevated crustal temperatures and a weak rheology in the lower crust at the time of the meteorite impact and of the contemporaneous Penokean orogeny. Large variations of crustal thermal structure at the edge of the Superior Province may have led to along-strike differences in the style and extent of thrusting during the Grenville Orogeny. [ABSTRACT FROM AUTHOR]

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 to 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. [ABSTRACT FROM AUTHOR]

New U-Pb zircon geochronology data suggest that the Yintun Formation is younger than ~1895 Ma and is late Paleoproterozoic. The Yintun Formation may represent the first sedimentary cover of the North China Craton (NCC) based on its stratigraphic sequence and the ages of its sediments. Gravels in the conglomerates from the lower member of the Yintun Formation are characterized by obvious glacial origins. It is possible that these glacial gravels are the re-deposited sedimentary products of the Huronian Glaciation from the Indian continent. This can also provide sedimentary evidence for the relative location of the Indian continent and the NCC in the reconstruction of the Columbia supercontinent. [ABSTRACT FROM AUTHOR]

The Paleoproterozoic Gordon Lake and Bar River formations, Huronian Supergroup, contain a variety of sedimentary structures in the Flack Lake area of Ontario, Canada, that have been considered of debatable origin. We identify these structures as microbially induced sedimentary structures (MISS). The preserved MISS are related to microbial mat destruction and decay, and include sand cracks, mat chips, remnant gas domes, pyrite patches, and iron laminae. A biological origin for the fossil structures is supported by their similarities to modern and ancient documented examples of MISS, the sand-dominated nature of the substrate in which they are preserved, and key microtextures identified in thin section. Microtextures include curled, frayed and layered mat chips, carbonaceous laminae, oriented grains, and concentrated heavy minerals. On outcrop scale, the presence of desiccation cracks, flaser and lenticular bedding, and ripples in association with the types of MISS identified in the Gordon Lake Formation support the interpretation of a tidal flat depositional environment. The Gordon Lake Formation contains a greater number and diversity of MISS than the overlying Bar River Formation, as a result of lower energy deposition in the former. The quartz arenite of the Bar River Formation contains fine-grained to pebbly granulestone characterized mainly by tangential and planar cross beds, which is consistent with a tidal channel or sand shoal setting. Although fossil evidence of life is rare in the rocks of the Huronian Supergroup, identification of MISS in the Flack Lake area provides a significant and convincing indication of microbial colonization at the time of deposition. [ABSTRACT FROM AUTHOR]

New structural and geochronological data are presented for two orogenic events, the Blezardian and Yavapai orogenies, which affected the Paleoproterozoic Southern Province near Sudbury, Ontario, Canada. The Southern Province comprises ca. 2452 Ma metavolcanic rocks and metasedimentary rocks of the Huronian Supergroup, which were deposited along the southern margin of the Archean Superior craton during its evolution from a rifted to passive continental margin. Emplacement of the ca. 2415 Ma Creighton pluton during rifting was followed by its deformation and the development of a penetrative gneissic fabric during the ca. 2415 − ca. 2219 Ma Blezardian Orogeny. New laser ablation - inductively coupled plasma - mass spectrometry (LA-ICP-MS) U-Pb zircon ages of 2343 ± 17 and 2344 ± 47 Ma on two granitic dikes that cut this fabric provide a new minimum age of ca. 2.34 Ga for the Blezardian Orogeny. The Sudbury area was then impacted by a large extraterrestrial bolide at ca. 1.85 Ga and deformed during the Penokean Orogeny. The southern part of the Southern Province was later reworked by regional folding and north-directed thrusting during the younger 1.7 Ga Yavapai Orogeny. The 1744 ± 29 Ma Eden Lake Complex was emplaced and deformed during this event, which produced a strong foliation overprinting the complex. The foliation formed at pressures of 2.8-4 kbar (1 kbar = 100 MPa) and temperatures of 540-565 °C and was intruded by a weakly deformed 1704 ± 13 Ma old granitic dike, bracketing the Yavapai event between 1744 ± 29 and 1704 ± 13 Ma in the Sudbury segment of the Southern Province. Crustal thickening associated with the Yavapai event resulted, locally, in minor pressure increases before or during regional metamorphism as revealed by phase equilibria modeling in the Raft Lake area; this evolution may be recorded elsewhere in the Ontario segment of the Southern Province. [ABSTRACT FROM AUTHOR]

Abstract: The Paleoproterozoic (2.5–2.0 Ga) is one of the most important periods in Earthʼs history, and was characterized by a rise in atmospheric oxygen levels and repeated (at least three) severe glaciations (the Huronian glaciations). In this study, we investigate redox conditions in the atmosphere and in shallow-marine environments immediately after the first Huronian glaciation based on the isotopic composition of Os, and the abundance of redox-sensitive elements (Os, Re, and Mo) in sedimentary rocks from the Huronian Supergroup, Canada. We found no significant authigenic enrichment of Os in the sedimentary rocks deposited during the first Huronian deglaciation. The initial isotopic composition of Os in the sediments was close to that of chondrite at the time of deposition ( ). These results suggest that atmospheric O2 levels were insufficient to mobilize radiogenic Os through continental weathering ( present atmospheric level (PAL)). In contrast, we found enrichment of Re in the sedimentary rocks, which suggests the occurrence of oxidative weathering of Re under mildly oxidizing conditions ( PAL). Despite the Re enrichment, low abundances of Mo imply possible non-sulfidic conditions in shallow-marine environments at the time of deposition. Together with the results of organic carbon and sulfur analyses, we suggest that atmospheric O2 remained at relatively low levels of around PAL after the first Huronian deglaciation, which contrasts with proposed dramatic increases in O2 after the second and third Huronian deglaciations. These results imply that the second and third Huronian glaciations may have been global events, associated with climatic jumps from severe glaciations to super-greenhouse conditions and the subsequent blooming of photosynthetic cyanobacteria in the glacial aftermath. [Copyright &y& Elsevier]

Highlights: [•] A revised U–Pb zircon age for the Copper Cliff rhyolite is 2452.5±6.2Ma. [•] Six geochemically distinct lava series at Thessalon have been identified. [•] An origin involving mantle source heterogeneity is proposed. [•] An unusual high Th/Nb mantle reservoir is required. [ABSTRACT FROM AUTHOR]

The Lac Panache (Nipissing) gabbro intrudes Huronian metasediments ca. 40 km southwest of the Sudbury Igneous Complex. The gabbro contains disseminated sulfides and is in contact with a chalcopyrite-rich quartz vein that crystallized from highly saline fluids (46.8 ± 3 equivalent wt.% NaCl) at a minimum temperature of 420 ± 27 °C. Chloride and carbonate inclusions in opened fluid inclusion cavities in the vein suggest that the brine contained dissolved metals (in addition to NaCl), such as Fe, Cu, Mn, and Co. The weakly altered quartz vein postdated regional metamorphism and was probably contemporaneous with the 1.7 Ga felsic magmatism and attendant albite alteration in the area. Cl-rich scapolite in the gabbro and highly saline fluid inclusions in the quartz vein suggest the existence of circulating hot brine throughout the tectonic evolution of the region. The 2.2 Ga old gabbro contains an abundance of Cl-rich scapolite intergrown with pyrrhotite and chalcopyrite that formed during the early hydrothermal (deuteric) alteration of the gabbro. [ABSTRACT FROM AUTHOR]

Abstract: Oxidative precipitation and authigenic enrichment of the redox sensitive element Mn in sedimentary rocks can serve as a proxy for the release of high levels of O2 during the Great Oxidization Event (GOE). Here we investigate Mn abundance in sedimentary rocks of the 2.45–2.22Ga Huronian Supergroup, Canada. We found authigenic Mn enrichments with high Mn/Fe ratios following the appearance of Fe oxides in the Firstbrook Member of the Gowganda Formation of the Huronian Supergroup, which was deposited immediately after the last Huronian glaciation. The Mn-bearing minerals in the Firstbrook Member are spessartine-rich almandine and Mn-bearing chlorite, which are likely to have been formed through post-depositional diagenesis and/or metamorphism using Mn oxides precipitated in the ocean at the time of deposition. When assuming the solution equilibrium between the atmosphere and shallow oceans, oxidative Mn precipitation requires that atmospheric O2 be higher than ~10−2 times the present atmospheric level (PAL). The cumulative Mn amount per unit area in the Firstbrook Member is comparable in magnitude to that in the Mn deposits in the Hotazel Formation of the Transvaal Supergroup, South Africa. Our results suggest an appearance of highly active aerobic biosphere immediately after the last Huronian glaciation, supporting the hypothesis that climatic recovery from the Huronian glaciation accelerated the GOE. [Copyright &y& Elsevier]

The marine stromatolitic dolomites of Palaeoproterozoic Vempalle Formation, of Cuddapah Basin, South India show significantly depleted δO (−8.19 to −18.25‰) and δC (−0.03 to −5.74) values and are consistent with the global Proterozoic data. A comparison of the stable isotope values from major localities of Proterozoic Basins of India has also been attempted in this study. Significantly depleted δO values of Vempalle carbonate samples could not be considered to be post-depositional modifications as there exists an inverse correlation relationship between C and O isotopic values. The Vempalle stromatolitic dolomite is likely to be precipitated in equilibrium with marine waters significantly depleted in oxygen isotopes (−10 to −15‰ SMOW) with respect to modern sea water. The negative δC values of the Vempalle carbonates are likely to be interpreted at the backdrop of global 'icehouse' as there is an indication of dropstone-like features in the lower part of the Vempalle Formation just 2 km, southwest of the study area. [ABSTRACT FROM AUTHOR]

Abstract: The largest known terrestrial impact melt sheet occurs within the 1850Ma Sudbury Structure, Ontario. In order to evaluate the relative contributions of different target lithologies to the melt sheet, we have investigated the Pb isotope compositions of feldspar separates from early-formed quartz diorite magmas within Offset Dykes from around the impact structure. The samples define a linear array on plots of age-corrected 206Pb/204Pb versus 207Pb/204Pb. Samples from Offset Dykes hosted by the Huronian Supergroup (South Range) have a range of 206Pb/204Pb1850 from 15.424 to 17.255 and 207Pb/204Pb1850 from 15.390 to 15.801, whilst those hosted by Archean gneisses of the Superior Province (North Range) cluster around 206Pb/204Pb1850 ≈14.8 and 206Pb/204Pb1850 ≈15.1. These values can be approximated by binary mixing between the two major groups of target lithologies. A mix of 60–70% of Superior Province gneisses with 30–40% of Huronian metasedimentary material closely matches the Pb isotope compositions of North Range Offset Dyke samples, whereas in the South Range the required Huronian component is up to ca. 80%. These mixing proportions are consistent with Sr, Nd and Os isotope and trace element constraints. A third minor component, either locally-exposed Paleoproterozoic mafic rocks or the lower crust is also required. However, the isotopic, trace element and Ni–Cu–platinum group element characteristics of the melt sheet can be accommodated without the involvement of an average lower crustal or meteoritic component. A major contribution of Huronian supracrustal material, which had a pre-impact thickness of up to 12km, is required to explain the chemical characteristics of the impact melts, which also have a strong upper crustal affinity (e.g. Eu/Sm=0.22, Rb/Sr=0.2–0.35). As such, a shallower level of melting is apparent than that predicted by many previous impact models for the Sudbury event. This can be accommodated by considering approach trajectories for the impactor oblique to the Earth’s surface. In addition, the isotopic and trace element variability identified indicates that the melt sheet was heterogeneous at an early stage, and may not have been completely homogenised during crater formation. Our findings have significant implications for the nature of the Sudbury impact event, the evolution of the melt sheet and the crustal sources of metals contained in Sudbury’s world class Ni–Cu–PGE sulphide ores. [Copyright &y& Elsevier]

The Cobalt Embayment is a large (-60,000 km²), irregular domain of Paleoproterozoic (2.5-2.2 Ca) silicielastic sedimentary rocks (i.e., the Huronian Supergroup) that unconformably overlies Archean basement rocks of the Abitibi greenstone belt. The Nipissing Diabase, regionally distributed complex of mafic sills and dikes intruded the Huronian sedimentary rocks ca. 2.2 Ga. The sedimentary rocks were subsequently affected by subgreenschist facies metamorphism and by a regionally distributed K and Na metasomatic events, at ca. 1.7 Ca, related to the Penokean orogeny. Although best known for the economically important Ag-Co veins of the Cobalt mining camp, the Cobalt Embayment also hosts numerous other hydrothermal, base and precious metal-mineralized calcite-quartz vein systems. The lead isotope compositions of pyrite and chalcopyrite from nine widely separated polymetallic vein systems yield a Pb-Pb errorchron age of 2236 + 180 Ma (n = 24). In contrast, the Pb isotope compositions of late-stage galena (n = 11) from six regionally distributed vein systems yield a Pb-Pb secondary isochron age of ca. 1675 Ma. These Pb isotope data for the mineralized vein systems demonstrate the occurrence of at least two major episodes of hydrothermal fluid activity throughout the Cobalt Embayment, ca. 2220 Ma and ca. 1700 Ma, indicate that the emplacement of the Nipissing Diabase was the most likely driver of regional hydrothermal fluid circulation at ca. 2200 Ma, and provide supporting evidence for the basin-wide extent of the regional K and Na naetasomatic event at ca. 1700 Ma, most likely related to the waning stages of the Penokean orogeny. [ABSTRACT FROM AUTHOR]

Abstract: Mass-dependently fractionated (MDF) sulfur isotopes in sedimentary sulfides and sulfates can provide information on the past activity of microbial metabolisms and serve as a proxy for the concentration of seawater sulfate. In conjunction with these proxies, mass-independently fractionated (MIF) sulfur isotopes can be used to track the rise of atmospheric oxygen. The anoxic–oxic transition of the surface environment in the Paleoproterozoic has been constrained by MIF sulfur in 2.47 Ga sulfides from Western Australian banded iron-formations, and the absence of MIF in diagenetic sulfides from 2.32 Ga black shales in the Transvaal Supergroup (South Africa). We report new multicollector ion microprobe data for individual sulfides from water-lain sedimentary units in the 2.45–2.22 Ga Huronian Supergroup (Ontario, Canada). The authigenecity of sulfides in these units is interpreted on the basis of host lithology, mode of distribution, sulfide chemistry and MDF sulfur isotopes. Sulfides interpreted to have an authigenic-sedimentary origin from the McKim Fm. have a range of 0.7‰ in Δ33S values and those in the Pecors Fm. preserve small magnitude MIF Δ33S values up to +0.88‰, which we propose represents the last remnants of an anoxic atmosphere. High δ 34S values (up to +31.2‰) and near-zero Δ33S values in authigenic sulfides from the stratigraphically higher Espanola and Gordon Lake Fms. suggest local variations of seawater sulfate concentrations and/or δ 34Ssulfate, consistent with increased atmospheric O2 levels. MIF sulfur is absent from the marine record after the second Huronian glaciation, which is analogous to the record of the Transvaal Supergroup where MIF is absent from the upper part of the interglacial sequence. Our results suggest that the possible simultaneous demise of MIF sulfur isotopes at these two localities may serve as a useful global geochemical marker to correlate Paleoproterozoic supergroups. We propose a new biogeochemical model where enhanced weathering rates during Paleoproterozoic post-glacial thawing served as a critical stimulus for interglacial blooms of oxygenic photosynthesis, the demise of methane, and ultimately to the irreversible rise in atmospheric oxygen. [Copyright &y& Elsevier]

Abstract: Previous paleomagnetic studies of the glaciogenic Gowganda and Lorrain formations have identified several low-inclination magnetic components of high thermal stability, which suggest low-latitude glaciation during deposition of the Huronian Supergroup, Canada. While extraordinary claims demand extraordinary proof, prior authors have been unable to support their interpretations of these components conclusively with any of the classic field stability tests (e.g., conglomerate, fold, and baked contact) capable of demonstrating that the magnetization was acquired at or soon enough after the time of deposition to be used to constrain the paleolatitude of the Gowganda or Lorrain formations. We report here the results of a fold test from the “purple siltstone” member of the Lorrain Formation near the town of Desbarats, Ontario, which indicate that none of the reported components dates to the time of deposition. Hence, the paleolatitude of the Gowganda glaciation is uncertain. Comparison of the lithostratigraphic, paleomagnetic, and radiometric constraints on the Huronian sequence and the Transvaal Supergroup of Southern Africa implies that the one verified low-latitude Paleoproterozoic glacial event (the Makganyene glaciation, Transvaal Supergroup, South Africa) is younger than the three glacial units of Canada. With this correlation, the physical rock record indicates that the ‘great oxygenation event’ began in the time interval between the Gowganda and Makganyene glaciations. These data are consistent with the sudden evolution of oxygenic photosynthesis destroying a methane greenhouse and thereby triggering the first Snowball Earth event in Earth history. [Copyright &y& Elsevier]

The spatial relations between outliers of Huronian metasediment and the current outline of the Sudbury Igneous Complex (SIC) have been used previously to constrain the original size of the meteorite impact crater, despite un-certainty regarding their structure and origin. The outliers are tight to isoclinal, gently plunging synclines with northeast-southwest-trending axes, slightly overturned to the northwest. Major deformation of the Huronian Super-group preceded the 1849-Ma Sudbury meteorite impact event by sufficient time to permit peneplanation of the region. Impact occurred in a foredeep related to the subduction of the Laurentia plate under the Wisconson Magmatic Terranes. Faults truncate the northwest margins of most of the outliers. Where examined, at several localities, the northwest margin--bounding faults are invariably occupied by pseudotachylite. Structural considerations provide evidence for thousands of meters of slip along these surfaces, each of which was apparently accomplished in a single event, providing strong support for the contention that motion along these faults coincided with the collapse of the transient cavity after bolide impact to form the Sudbury Structure. The outliers, thus, owe their overall forms to preimpact folding long before the Penokean Orogeny. They owe their continued existence to large-scale normal fault motions related to collapse of the transient cavity during the Sudbury impact event. The current map-scale structural relations between the outliers and the outcrop area of the Sudbury Igneous Complex are largely due to the deep exhumation of a series of regional open folds that were formed during postimpact deformation, possibly at the termination of the Penokean Orogeny ca. 1840 Ma or during a later event ca. 1450 Ma. [ABSTRACT FROM AUTHOR]

Identifies the fundamental depositional conditions present in braided, gravel-dominated, fluvial systems that maximize the concentration of heavy minerals in gravel bars and in economic paleoplacer deposits. Difference between the North Saskatchewan and Huronian systems; Distribution of magnetite; Relationship between the various subenvironments of the Huronian braided rivers and the uranium content of the sediment.

Wonders if the structures associated with the collapse of a meteorite crater or orogenesis formed structures, have preserved the outliers of the Paleoproterozoic Huronian Supergroup, which is located north west of the Sudbury Igneous Complex (SIC). Information on the Sudbury Structure; Details on contents of the SIC; In-depth look at Sudbury Breccia.