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Fine‐grained, siliciclastic units of the >1642 ± 3.9 Ma late Palaeoproterozoic Limbunya Group, Birrindudu Basin host rich, well‐preserved organic‐walled microfossil assemblages that include members of total‐group eukaryotes. These assemblages include taxa characteristic of this interval such as Tappania plana and Satka favosa, as well as less common taxa such as Gigantosphaeridium fibratum, Gigantosphaeridium floccosum, Kamolineata elongata (= Valeria elongata; new combination), and four new species. The new taxa include Limbunyasphaera operculata gen et sp. nov., the oldest known operculate taxon; the large septate filaments of Siphonoseptum bombycinum gen. et sp. nov.; the platy tubular form Birrindudutuba brigandinia gen. et sp. nov.; and Filinexum torsivum gen. et sp. nov., which bears a spirally twisted wall constructed of bound fibres. Our data show that eukaryotic fossils are particularly abundant in marginal marine environments such as tidal flats and back‐barrier lagoonal settings. This is exemplified by the Blue Hole Formation, which features an especially diverse and complex assemblage. We also present a new within‐formation eukaryotic species richness estimate for the Palaeoproterozoic to Tonian. This estimate indicates that the oldest eukaryote‐bearing units already show species richness levels similar to those of the much younger and more heavily sampled Tonian period. Additionally, these oldest eukaryotic assemblages show significant morphological disparity, particularly in vesicle construction. These high levels of eukaryotic species richness and morphological disparity suggest that although late Palaeoproterozoic units preserve our oldest record of eukaryotes, the eukaryotic clade has a much deeper history. [ABSTRACT FROM AUTHOR]

New detrital zircon ages from biostratigraphically well-controlled Ordovician sandstones in southeast Australia are compared with published counterparts in southern Zealandia. During Rodinia supercontinent assembly (RA), Australia and Zealandia age patterns are similar, everywhere with ubiquitous late Mesoproterozoic magmatic zircon sources. However, during earliest Gondwana supercontinent assembly (GA), the age patterns have different sediment sources: (1) those of late Neoproterozoic age are more strongly represented in Zealandia but of uncertain location, but (2) those of late Cambrian-Ordovician age are more prominent in eastern Australia, having probable origins in the Ross-Delamerian Orogen. In particular, a distinctive zircon component, ca. 600–650 Ma, is ubiquitous in Zealandia but rare in Australia. Early Paleoproterozoic and Archean (Nuna, NU) zircon sources (2000–3200 Ma) become important (and locally up to 25% total) in Zealandia but not in Australia. It is difficult to reconcile all these sediment source requirements within disparate and distant Australian-Antarctic Precambrian complexes. Instead, it is proposed that, through the early Palaeozoic, Zealandia had only local sediment sources in a discrete Rodinia basement continental block outcropping in South Zealandia that was formerly adjacent to South China. [ABSTRACT FROM AUTHOR]

The present-day mantle is divided into the African and Pacific domains by the circum-Pacific subduction girdle. Very little is known about the mantle composition of the Pacific Domain before 120 Ma due to the scarcity of the oceanic record, having mostly been destroyed by subduction processes. Accreted oceanic lithosphere (ophiolites) in orogens along the Paleo-Pacific margins provide rare opportunities to partially fill this knowledge gap. The early Cambrian (530–505 Ma) Weraerai ophiolite mélange in the New England Orogen in Eastern Australia represents fragments of the now-consumed Paleo-Pacific oceanic plate, predecessor of the Panthalassa and Pacific oceanic plates, accreted to east Gondwana during c. 410–277 Ma. Early work revealed the presence of an accreted volcanic island(s) of possible mantle plume origin. However, due to their heavy alteration and weathering, the geochemical signature of the mafic rocks in the Weraerai ophiolite cannot be used to certify their plume origin with confidence. Therefore, mantle rocks found in the ophiolitic belt offer an alternative way to decipher the origin of the oceanic lithospheric fragments in the Weraerai ophiolite mélange. Here, we report the petrographic, major and trace elements composition, including highly siderophile elements (HSE), and Re–Os isotope composition for 16 serpentinized spinel harzburgite samples from Woodsreef and Port Macquarie. The observed spinel–orthopyroxene symplectite intergrowth textures are interpreted as garnet-breakdown textures due to cooling from an initial high temperature of >1200°C. Silicon and Al contents and Mg# of serpentinized spinel harzburgite, as well as heavy rare earth element modeling results, suggest a high-degree of melt extraction of 20–30% in the garnet stability field and in an anhydrous environment, probably in ocean island or oceanic plateau environments. The samples in this study have HSE concentrations interpreted to have resulted from post-melting processes rather than a melt extraction feature, indicating that their Re–Os model ages need to be interpreted with caution. Nevertheless, the melt depletion ages obtained from the Woodsreef and Port Macquaries samples range between 1.4 and 1.1 Ga, consistent with previous studies on other Pacific-rim ophiolitic rocks. We argue that these ages might be related to a major depletion event during the transition between supercontinents Nuna and Rodinia. Such depletion events affected a large proportion of this section of the mantle before the incorporation of the peridotites into the oceanic lithosphere in the Paleo-Pacific associated with rapid ascent of mantle plumes. This interpretation is consistent with the occurrence of accreted volcanic islands in the Weraerai ophiolite mélange, as shown by the OIB chemical signatures of some of the mafic rocks, and their association with shallow water limestones that formed in near-equatorial latitudes. The proposed c. 530–510 Ma Paleo-Pacific Ocean mantle plume event coincides with a global peak of oceanic mantle plume events that may record the legacy of a circum-Rodinia subduction girdle driving antipodal mantle superplume episodes. [ABSTRACT FROM AUTHOR]

The long-term history of the Earth–Moon system as reconstructed from the geological record remains unclear when based on fossil growth bands and tidal laminations. A possibly more robust method is provided by the sedimentary record of Milankovitch cycles (climatic precession, obliquity, and orbital eccentricity), whose relative ratios in periodicity change over time as a function of a decreasing Earth spin rate and increasing lunar distance. However, for the critical older portion of Earth’s history where information on Earth–Moon dynamics is sparse, suitable sedimentary successions in which these cycles are recorded remain largely unknown, leaving this method unexplored. Here we present results of cyclostratigraphic analysis and high-precision U–Pb zircon dating of the lower Paleoproterozoic Joffre Member of the Brockman Iron Formation, NW Australia, providing evidence for Milankovitch forcing of regular lithological alternations related to Earth’s climatic precession and orbital eccentricity cycles. Combining visual and statistical tools to determine their hierarchical relation, we estimate an astronomical precession frequency of 108.6 ± 8.5 arcsec/y, corresponding to an Earth–Moon distance of 321,800 ± 6,500 km and a daylength of 16.9 ± 0.2 h at 2.46 Ga. With this robust cyclostratigraphic approach, we extend the oldest reliable datum for the lunar recession history by more than 1 billion years and provide a critical reference point for future modeling and geological investigation of Precambrian Earth–Moon system evolution. [ABSTRACT FROM AUTHOR]

In an effort to improve our understanding of the seismic character of the crust beneath southeast Australia and how it relates to the tectonic evolution of the region, we analyse teleseismic earthquakes recorded by 24 temporary and 8 permanent broadband stations using the receiver function method. Due to the proximity of the temporary stations to Bass Strait, only 13 of these stations yielded usable receiver functions, whereas seven permanent stations produced receiver functions for subsequent analysis. Crustal thickness, bulk seismic velocity properties, and internal crustal structure of the southern Tasmanides – an assemblage of Palaeozoic accretionary orogens that occupy eastern Australia – are constrained by H – κ stacking and receiver function inversion, which point to the following: a ∼ 39.0 km thick crust; an intermediate–high Vp/Vs ratio (∼ 1.70–1.76), relative to ak135; and a broad (> 10 km) crust–mantle transition beneath the Lachlan Fold Belt. These results are interpreted to represent magmatic underplating of mafic materials at the base of the crust. a complex crustal structure beneath VanDieland, a putative Precambrian continental fragment embedded in the southernmost Tasmanides, that features strong variability in the crustal thickness (23–37 km) and Vp/Vs ratio (1.65–193), the latter of which likely represents compositional variability and the presence of melt. The complex origins of VanDieland, which comprises multiple continental ribbons, coupled with recent failed rifting and intraplate volcanism, likely contributes to these observations. stations located in the East Tasmania Terrane and eastern Bass Strait (ETT + EB) collectively indicate a crust of uniform thickness (31–32 km), which clearly distinguishes it from VanDieland to the west. Moho depths are also compared with the continent-wide AusMoho model in southeast Australia and are shown to be largely consistent, except in regions where AusMoho has few constraints (e.g. Flinders Island). A joint interpretation of the new results with ambient noise, teleseismic tomography, and teleseismic shear wave splitting anisotropy helps provide new insight into the way that the crust has been shaped by recent events, including failed rifting during the break-up of Australia and Antarctica and recent intraplate volcanism. [ABSTRACT FROM AUTHOR]

Australian terranes concealed beneath Mesozoic cover record complex Precambrian tectonic histories involving a successive development of several Proterozoic to Paleozoic orogenic systems. This study presents an integrated approach combining K-Ar, 40Ar-39Ar, and Rb-Sr geochronology of Precambrian authigenic illites from the recently discovered Millungera Basin in north-central Australia. Brittle deformation and repeated fault activity are evident from the sampled cores and their microstructures, probably associated with the large-scale faults inferred from interpretations of seismic survey. Rb-Sr isochron, 40Ar-39Ar total gas, and K-Ar ages are largely consistent indicating late Mesoproterozoic and early Proterozoic episodes (~ 1115 ± 26 Ma, ~ 1070 ± 25 Ma, ~ 1040 ± 24 Ma, ~ 1000 ± 23 Ma, and ~ 905 ± 21 Ma) of active tectonics in north-central Australia. K-Ar results show that illites from fault gouges and authigenic matrix illites in undeformed adjacent sandstones precipitated contemporaneously, indicating that advection of tectonically mobilised fluids extended into the undeformed wall rocks above or below the fracture and shear (fault gouge) zones. This study provides insight into the enigmatic time-space distribution of Precambrian tectonic zones in central Australia, which are responsible for the formation of a number of sedimentary basins with significant energy and mineral resources. [ABSTRACT FROM AUTHOR]

• We present a new paleomagnetic pole for Australia in the Paleoproterozoic (1792 Ma). • Our data suggests minor plate motion of proto-Australia between 1800 and 1600 Ma. • Comparison of Australian and Laurentian paleopoles suggests two stage assembly of Nuna. We present new paleo- and rock magnetic results from the ca. 1792 Ma Hart Dolerite sills that intrude the strata of the Kimberley craton, Western Australia. From 24 sites sampled, 23 are directionally clustered and the site mean directions were used to calculate a grand mean direction. Ten of the 23 sites have 95% confidence intervals ( α 95 ) less than 16°. A positive reversal test, dissimilarity of the corresponding paleopole from known younger Australian poles, and a previously reported positive baked contact test, indicate that our paleomagnetic results are of primary origin, and the results are consistent with the geologic interpretation that the Hart Dolerite sills represent a multiphase magmatic emplacement over the duration of several million years. The new ca. 1792 Ma paleopole for the Kimberley craton is applicable to the entire North Australian Craton. A comparison of Paleoproterozoic poles from the North and West Australian cratons supports the occurrence of a previously proposed 40° intracontinental rotation between the two cratons during latest Neoproterozoic time. Furthermore, comparing these Australian poles with similar aged Laurentian poles shows that the apparent polar wander paths of the two continents have a similar history between ca. 1800 and 1730 Ma and between ca. 1650 and 1400 Ma. To achieve a fit within uncertainty limits, an additional relative latitudinal motion is necessary during the transition interval (1730–1650 Ma). We suggest that a two-stage evolution occurred between Laurentia and Australia during the assembly of the supercontinent Nuna. Australia and Laurentia traveled together between ca. 1800 Ma until ca. 1730 Ma in a semi-stable configuration. During 1730–1650 Ma, they underwent a net relative latitudinal motion, leading to the final assembly of Nuna after ca. 1650 Ma. [ABSTRACT FROM AUTHOR]

Abstract: The ages of deposition and metamorphism of low-grade Precambrian metasedimentary sequences can be difficult to define in the absence of interlayered volcanogenic rocks. Monazite and xenotime can grow at temperatures below 400°C and can give vital evidence for the timing of diagenesis, hydrothermal fluid flow, and low-grade deformation and metamorphism in Precambrian basins. The histories of sedimentary basins in the eastern Capricorn Orogen of the West Australian Craton are generally poorly constrained. However, sandstones and siltstones of the basal Yelma Formation in the Earaheedy Basin contain authigenic monazite and xenotime associated with sulphide minerals related to Mississippi Valley Type base-metal mineralization hosted within carbonate of the overlying Sweetwaters Well Member. In the Teague area, within the Earaheedy Basin, siliciclastic rocks overlying granites of the Yilgarn Craton contain authigenic monazite that gives an in situ SHRIMP 207Pb/206Pb age of 1811±13Ma. Monazite in weathered sandstones and siltstones of the Cano secondary Pb deposit on Magellan Hill, overlying the Yerrida Basin, gives an indistinguishable age of 1815±13Ma. The Cano monazite is interpreted to have been intergrown with primary sulphide minerals and therefore to record the age of mineralization. Xenotime outgrowths on detrital zircons from Cano have high common Pb but define an isochron with an age of 1832±36Ma. The isochron is co-linear with Pb isotope ratios from Pb ore at Magellan, suggesting that xenotime growth is also related to mineralization. The timing of fluid flow is synchronous with the 1820–1770Ma Capricorn Orogeny, and is the first evidence for activity of this age in the eastern part of the Capricorn Orogen. The age of mineralization provides a firm minimum age for the Yelma Formation, and constrains its deposition to between ∼2.0Ga, the youngest age of detrital zircons, and the mineralization age. [Copyright &y& Elsevier]

The Archean eon is a chronometrically defined subdivision of the Precambrian that extends from 3800 to 2500 Ma. In the Australian continent, Archean rocks (i.e. those with sedimentary deposition or igneous crystallisation ages confidently interpreted to be older than 2500 Ma) occur in the Pilbara and Yilgarn Cratons of Western Australia, the Mulgathing and Sleaford Complexes in the Gawler Craton of South Australia and as minor inliers in the Pine Creek Orogen of the Northern Territory. Metamorphosed lithological components with igneous or sedimentary precursors inferred to be of Archean age also occur in the Browns Range Dome and Billabong Complexes of the Tanami Inlier, Northern Territory, and possibly also in the Broken Hill Inlier. This contribution outlines aspects of the historical development of geochronological methods applied to the Archean of Australia, the respective strengths and weaknesses of these methods and how our understanding of the continent's Archean geology and tectonics was related to this development. The geological formation of the Yilgarn and Pilbara Cratons is investigated using a new statistical approach based on the distribution of SHRIMP U-Pb zircon and monazite dates obtained from rock samples that may have complex mineral age populations. Spatial and temporal characteristics of the magmatic episodes identified in the Yilgarn and Pilbara granite-greenstone terranes are atypical of rift/collision processes attributable to tectonic-plate interactions, but are consistent with their interpretation as a response to major mantle convection events. The strengths of this geochronology-based approach are demonstrated by its application to the Narryer Gneiss Complex of the northwestern part of the Yilgarn Craton. It is shown that this approach offers unique insights into geological events that may be under-represented at the outcrop scale due to later crustal re-working. [ABSTRACT FROM AUTHOR]

The pole position for the late Mesoproterozoic Alcurra (formerly Kulgera) Dyke Swarm (ADS), Musgrave Block, central Australia, has been revised by adding new data from two more dykes. A palaeomagnetic fold test is positive at the 99 percent confidence level and the pole position is latitude = 2.8° S, longitude = 80.4°E . New 40Ar/39Ar determinations on single biotite grains from country-rock gneiss 20 cm from the contact with an Alcurra dyke yield ages from 1068 ± 2 Ma to 1085 ± 2 Ma (2σ). In addition, 40Ar/39Ar determinations on two samples of aggregates of very fine-grained biotite from the mesostasis of a Stuart Dyke (SD), Arunta Inlier, Northern Territory, yield ages of 1059 ± 2 and 1066 ± 3 Ma (2σ). These new ages are in agreement with those of the ∼1070 Ma Warakurna large igneous province, west-central Australia, indicating that both the ADS and SD belong to that suite. Palaeomagnetic poles determined by others for the ADS and SD are indistinguishable from each other but cannot be presently combined as a single pole because the published information on the SD is incomplete. An analysis of the palaeogeography implied by the dispersed palaeomagnetic poles from members of the extended Warakurna suite shows that the present relationships between the major Precambrian cratons (West, North and South Australian), which constitute Australia west of the Tasman Line, are inconsistent with the inferred relationship at ∼1070 Ma. Nor is it apparent that internal deformations within the separate cratons are the cause of the dispersion. Our findings imply that these major Australian Cratons must have finally assembled sometime after ∼1070 Ma. [ABSTRACT FROM AUTHOR]

• Effect of thermal maturity on average δ13C of n -alkanes can reach 6.8‰ • Strong linear correlations between thermal maturity and compound-specific isotopes. • δ13C 'isotope slope' inversion from positive to negative with increasing maturity. • First study combining maturity and CSIA in the Proterozoic. Carbon (δ13C) and hydrogen (δ2H) compound-specific isotope analyses on sedimentary hydrocarbons are widely used for ecological reconstructions and oil-source rock or oil-oil correlations. However, the effects of thermal alteration on isotopic composition are not fully understood, potentially imparting a bias on interpretation of older and more mature sedimentary sequences. We measured δ13C and δ2H of n -alkanes in 23 extracted bitumens from the 1.64 Ga Paleoproterozoic Barney Creek Formation in the southern McArthur Basin, Australia. The samples cover a wide range of thermal maturities with calculated vitrinite reflectance (Rc) values from 0.4% to 1.3%. Our results illustrate that while δ13C of kerogen remains relatively constant, the δ13C and δ2H of n -alkanes have a strong positive correlation with thermal maturity. Average δ13C alk increase by 6.8‰ and δ2H alk by 69‰ among the samples in the analysed maturity range. At the same time, the carbon isotopic offset between n -alkanes and kerogen (Δδ13C alk–ker) climbs from 1.3‰ to 8.5‰ with increasing maturity. Therefore, the substantial maturity influence on stable carbon and hydrogen isotopes of n -alkanes must be considered in palaeoecological and petroleum correlation studies. In the initial stages of maturation, n -alkanes from the Barney Creek Formation display increasingly positive "isotope slopes" in plots of δ13C alk against carbon number. However, with further maturation, the slopes became increasingly negative. The isotope slope inversion indicates that the dominant mechanisms for n -alkane generation and degradation changed during the progression from early diagenesis to metagenesis. Numerical models suggest that the formation of positive and negative isotope slopes may be driven by the balance of the formation of n -alkanes from kerogen and their subsequent degradation, and by dependence of the degradation rate constant k on n -alkane chain length. [ABSTRACT FROM AUTHOR]

Abstract: The abundant and diverse assemblage of filamentous microbial fossils permineralized in the ~3465Ma Apex chert of northwestern Australia — among the oldest records of life — are arguably the “best studied,” by the most workers using the most advanced techniques, in the history of science. Despite the extensive body of data establishing the biogenicity of the demonstrably cellular carbonaceous Apex fossils, Pinti et al. (2013) and Marshall and Marshall (2013) have raised issues regarding the interpretation of their studies of the Apex chert presented in our recent review article (Schopf and Kudryavtsev, 2012). We agree with the assessment of both of the relevant papers by Pinti et al. (2009, 2013): the observations they report do not apply to the bona fide microscopic fossils of the Apex chert. Similarly, like the minute objects reported by Pinti et al. (2009, 2013), the “quartz and haematite-filled fractures” discussed by Marshall and Marshall (2013) are mineralic pseudofossils that are not relevant to interpretation of the Apex fossil microbes and their suggestion that “multiple populations of carbonaceous material may be a wide-spread issue through out the Precambrian” is without merit. [Copyright &y& Elsevier]

The ca. 1730 Ma Wollogorang Formation is a mixed carbonate-siliciclastic unit in the southern McArthur Basin of northern Australia. It is an exploration target for base metals and may be a petroleum source unit and unconventional reservoir. Facies analysis indicates that the Wollogorang Formation records deposition in supratidal to offshore environments. Lateral consistency in facies, thickness, and stratigraphic architecture suggests deposition on an east-west trending (present coordinates) epeiric platform. According to recent tectonic models for northern Australia, this epeiric platform likely deepened to the present-day east. The Wollogorang Formation comprises one second-order and five nested third-order sequences. Despite the unavailability of biostratigraphy and biofacies, and the general poor time control in Precambrian basins, we are able correlate third-order (i.e., our lowest rank) sequences over tens to hundreds of kilometers using high-resolution facies and petrophysical logs. As the distinction between stratigraphic sequences (related to shoreline shifts) and sedimentological bedsets (not related to shoreline shifts) becomes more difficult with decreasing hierarchical level, sedimentological, stratigraphic, paleontological, and mineralogical (including diagenetic) criteria were recently proposed to distinguish these cycles. Our study suggests that sedimentological and stratigraphic criteria are the most useful in Precambrian sequence stratigraphy. In contrast, paleontological criteria are irrelevant in Precambrian successions. Mineralogical (including diagenetic) criteria have not been tested in this study. In addition to further study these criteria, we suggest testing geochemical criteria, such as the enrichment of redox-sensitive trace elements and minor carbonate carbon isotope variation, to distinguish stratigraphic sequences from sedimentological bedsets. • 1730 Ma Wollogorang Formation reflects supratidal to offshore environments of an east-west directed epeiric sea that deepened to present-day east. • Wollogorang Formation comprises one second-order and five nested third-order sequences. • Poor time control and lack of biofacies can be compensated by detailed understanding of depositional environments in Precambrian sequence stratigraphy. [ABSTRACT FROM AUTHOR]