The rarity of high-quality paleomagnetic data leads to significant uncertainties regarding the paleogeography of the West African Craton (WAC) during the Proterozoic. Several well-dated mafic intrusive suites in the Anti-Atlas Belt (AAB) of Morocco present an opportunity for paleomagnetic studies. Here, we report the paleomagnetic and rock magnetic results for mafic intrusions from seven inliers in the AAB. Thirty-seven sites show a characteristic remanent magnetization with SE-shallow directions, of which the corresponding paleomagnetic pole overlaps with the similar to 300 Ma segment of the apparent polar wander path of the WAC, coeval to the Hercynian orogeny that pervasively affected the AAB. No correlation is observed between the trend and the remanence declination of the dikes, and the anisotropy of magnetic susceptibility is decoupled from the trend of the dikes. Additional rock magnetic data indicate the remagnetization mechanism is chemical instead of purely thermal. Koenigsberger diagrams show that most of the samples have been remagnetized by hydrothermal/metamorphic fluids, with attendant mineralogical changes that are visible in regional hyperspectral imagery. Forty-six sites fail to yield consistent directions within a site, which could be due to lightning, significant leaching of iron minerals, or crystallization of coarse-grained magnetite during background greenschist metamorphism that lowers the relaxation time of the remanence. Following this approach, we also re-evaluate the published paleomagnetic results from the Proterozoic rocks in the AAB. We tentatively delineate a Hercynian overprint front in the AAB, the east of which seems to be less affected and has a better chance for isolating primary paleomagnetic results.

The Tagragra d’Akka inlier, located in the Western Anti-Atlas, is a significant area for gold exploitation. In this region, gold mineralization primarily occurs as quartz veins and shear zones in the sandstone-pelite units of the Paleoproterozoic age. This study used various types of satellite imagery, including SPOT 5 and ASTER data to map and analyze the geometry of dyke swarms through visual interpretation and identify minerals related to hydrothermal alteration, respectively. Image processing techniques, comprising band ratios (BR), principal component analysis (PCA), minimum noise fraction (MNF), and mixture tuned matched filtering (MTMF), were applied to the ASTER image to delineate hydrothermal alterations. The results from SPOT 5 imagery indicate that the Tagragra d’Akka inlier is intersected by mafic dykes which show four main orientations, with a dominance of NE-SW-trending dykes, followed by E-W, N-S, and NW-SE trending directions. Furthermore, the ASTER data highlight the spatial distribution of alteration zones characterized by Fe-Mg-OH, hydroxyl-bearing, and iron oxide minerals, which are closely associated with structurally complex zones, and distributed along the mafic dykes. This demonstrates a clear structural control on the circulation of mineralizing fluids. The spatial distribution of hydrothermal halos was constrained through detailed field investigations. Integrating advanced image processing techniques with supervised classification of ASTER imagery, supported by field observations and laboratory analyses, was effective in delineating new areas with mineral potential.

The mid-Proterozoic geomagnetic field has been hypothesized to contain significant non-dipolar components, but constraints on field dipolarity are limited by scarce paleomagnetic observations and a lack of quantitative approaches. To overcome these difficulties, we acquired new paleomagnetic data from -1.46 Ga magmatic units in Baltica. Utilizing a geologically constrained plate reconstruction, we compared newly updated apparent polar wander paths for Baltica and Laurentia between -1.78 and -1.26 Ga. We found that incorporating -20-25% axial octupole can significantly reduce the arc distance between the paired poles at -1.46 Ga and yield a tighter and more circular clustering of virtual geomagnetic poles. Additionally, an increase in the Model G a parameter from -1.4 to -1.1 Ga coincides with a decline in dipole dominance and field strength, implying that the axial quadrupole could be an important factor in controlling paleo-field intensity. These results provide quantitative support for a more complex mid-Proterozoic geomagnetic field structure than the dipolar model that is commonly assumed.

Paleogeography of the Ediacaran Period has remained poorly understood because of paleomagnetic studies commonly yielding perplexing or conflicting data. Here, we report new magnetostratigraphic data from the Ediacaran Ouarzazate Group in the Anti-Atlas Mountains of Morocco, which have primary magnetizations supported by a positive conglomerate test and stratigraphically consistent directions within volcanic units across multiple localities. Comprehensive magnetostratigraphic sampling shows highly variable directions, consistent with a rapidly changing geomagnetic field along a longitudinally preferred band. High-precision geochronology constrains the geomagnetic variability to ~568 to 562 million years and suggests rates that are likely too rapid for true polar wander or plate tectonic interpretations. Comparison of igneous- and sedimentary-derived data, using a new statistical approach combining Bingham and Fisher distributions, indicates a high-inclination paleomagnetic direction that is compatible with independent evidence for regional glaciation. Our analysis produces a late Ediacaran paleogeographic reconstruction that is consistent with paleomagnetic and geologic constraints.

The timing and mechanisms by which the supercontinent Nuna broke up are still enigmatic, although the details have implications for global tectonic activity through Mesoproterozoic periods of alleged quiescence. The proposed breakup time of Nuna has ranged from ca. 1.6 to 1.2 Ga based on the episodic eruptions of large igneous provinces (LIPs) and associated large-scale continental rift systems. Paleomagnetic data from Proterozoic cratons can quantify their motions and directly test these competing inferences. In this study, new paleomagnetic results, which passed baked-contact tests and a reversal test, are reported from 32 dikes from the North China craton (NCC). An isotope dilution-thermal ionization mass spectrometry (ID-TIMS) baddeleyite date from one of these dikes constrains dike emplacement at 1235.6 +/- 2.0 Ma, which provides a new, well-dated paleomagnetic pole (27.7 degrees N, 168.5 degrees E, A95 = 5.0 degrees) for the NCC. Combined with the previously published 1.45-1.04 Ga paleomagnetic and geologic data from Laurentia, the NCC, Baltica, and Australia, the divergence of their apparent polar wander paths suggests that the core of Nuna (Laurentia, Baltica, and Siberia) broke up with East Nuna (Australia and the NCC) at ca. 1.38 Ga. Thereafter, the breakup of East Nuna, denoted by the separation of the NCC and Australia, occurred after ca. 1.32 Ga, and the breakup of the core of Nuna, denoted by the breakaway of Baltica from Laurentia and Siberia, occurred at ca. 1.26-1.22 Ga. The stepwise breakup process of Nuna was similar to that of Pangea, providing evidence for a robust tectonic regime in Earth's middle age.

The chemical history of seawater provides key information on Earth’s geologic processes and is fundamental for robust CO2 reconstructions. The knowledge of the secular evolution of the oceanic boron isotope budget is particularly important for CO2 reconstruction from boron isotopes. The boron isotope composition of seawater (δ11Bsw) is homogeneous, but varies on multi-million year time scales, given its residence time of approximately 10 million years. To date, the secular evolution of the oceanic boron isotope budget has been difficult to constrain, posing a major uncertainty for boron-based pH and CO2 reconstructions from Earth’s geologic past and critically limiting our understanding of the global biogeochemical cycling of this important element through time. Evaporitic minerals bearing fluid inclusions – and halites in particular – have provided important insights on past variations in major and minor ion composition, and present a highly appealing archive for reconstructing δ11Bsw (as well as other isotopic systems) given their direct origin from seawater. However, the interpretation of their signatures is not straightforward due to the possibility of fractionation during evaporation, crystallisation, and local biogeochemical interactions. Here we present data illuminating the evolution of boron isotopes and various other elements during evaporite formation from laboratory experiments and natural modern evaporitic settings across the globe, accompanied by new analytical developments for high-precision single fluid inclusion measurement using laser ablation. These data enable us to critically evaluate the evaporite archive, paving an avenue to robust seawater and CO2 reconstructions from Earth’s geological past.

The structure of the Proterozoic geomagnetic field is debated, hampering our understanding of ancient plate paleogeography and core evolution. We reassess the geocentric-axial-dipole (GAD) model for Proterozoic time using improved statistical methodologies and an expanded dataset of paleomagnetic directions from mafic dike swarms covering larger areas than previously considered. In addition to commonly used Fisher statistics, we employ Bingham and Kent statistics to evaluate both the tightness and elongation of virtual geomagnetic pole (VGP) distributions. Our results indicate that the Proterozoic field was predominantly a GAD, with a potential axial octupole (G(3)) component of similar to 10-15% in certain time intervals. Our findings do not support the previous assertions of significantly larger (25-29%) non-dipolar contributions in the Proterozoic. The identified Proterozoic non-dipolar component could result in apparent paleolatitude shifts of similar to 10 degrees shallowing, insufficient to explain low-latitude glaciations but potentially accounting for some offset paleomagnetic latitudes of Proterozoic paleoclimate records. Our study also shows that expanding the spatial distribution of VGPs using paleomagnetically independent paleogeographic reconstructions can improve the test's sensitivity and provide tighter constraints on the structure of the geomagnetic field.

The Early Eocene Climatic Optimum (EECO; ~53–49 million years ago, Ma), that represents the Cenozoic peak of temperature and atmospheric CO2 concentrations, significantly affected planktic foraminiferal (PF) assemblages. The main change documented is the permanent decline in abundance and diversity of the symbiont-bearing mixed-layer dweller genus Morozovella, coupled with an increase in abundance and diversity of the genus Acarinina at the beginning of the EECO in the tropical Pacific Ocean (Sites 1209-1210), similar to the previously documented record from the Atlantic Ocean. A second significant variation is the change in coiling direction of morozovellids that moved from dominantly dextral to sinistral close to the K/X event (52.85 Ma), in contrast to Acarinina which does not show any preferential coiling direction throughout. In addition, the deep-dweller genus Chiloguembelina virtually disappeared at the K/X event. Even though a link between these PF changes and EECO climatic change appears evident, the driving causes are still unknown. With the aim of evaluating whether a possible temperature increase may have impacted the observed PF changes, we performed Mg/Ca analysis to derive paleotemperatures from diverse species of Morozovella and Acarinina, and on the thermocline-dweller Subbotina from tropical Pacific sites 1209-1210 using laser ablation (LA)-ICP-MS. Our B/Ca and Sr/Ca results in all the examined samples/species, along with the observed low PF test-fragmentation allow us to exclude a significant influence of contamination or diagenesis on the reconstructed temperatures. As uncertainties in the interpretation of Mg/Ca data remain when working with extinct species, the temperatures were evaluated with both a ‘Trilobatus sacculifer-like’ calibration (no pH correction) and with a ‘Globigerinoides ruber-like’ calibration (pH-correction).In both cases a mixed-layer mean temperature increase of at least 1°C is recorded, with much warmer absolute temperature resulting from the former calibration approach.We hypothesize that the temperature rise may have impacted the morozovellid symbiotic relationship that, in turn, can represent a reason for their decline in abundance, given the many examples of the evolutionary benefits of symbiosis in modern oligotrophic mixed-layer habitats. Although there may have been several contributing factors resulting in photosymbiont bleaching at this time, increased temperature is considered a primary factor of bleaching in modern tropical larger benthic foraminifera. Our assumption appears supported by the lower δ13C values exhibited by the surviving sinistral morozovellids (Luciani et al. 2021 GloPlaCha) while the new dominant genus, Acarinina that does not record lower δ13C values displays greater ecological adaptability. Our evidence appears in line with the hypothesis of Davis et al. (2022 PlosOne) that acarininids changed their symbiotic associations in response to the extreme warming of the PETM (~56 Ma) (but not the subsequent smaller hyperthermals), resulting in long term evolutionary success.

The late Ediacaran to early Cambrian witnessed significant Earth system changes, including animal life diversification and an enigmatic paleomagnetic record. This study focuses on the Nama Group, a key geological unit for understanding the Ediacaran‐Cambrian transition. Previous paleomagnetic studies in the Nama Group identified complex remagnetization patterns but lacked a detailed examination of remanence carriers. To address this, we conducted a series of rock magnetic experiments on unweathered borehole core samples to better constrain the remagnetization mechanisms. Thermal demagnetization identified two magnetic components. C 1 , a recent viscous remanent magnetization, used for borehole core orientation, and C 2 , a stable remagnetization component carried by single‐domain (SD) pyrrhotite and magnetite. Magnetic mineralogy and paleomagnetic data suggest that the remanence acquisition mechanism of C 2 is best explained by thermoviscous remanent magnetization (TVRM) and thermal remanent magnetization (TRM), rather than chemical remanent magnetization (CRM). The presence of low unblocking temperatures, coupled with thermochronological evidence of prolonged heating during tectonic collisions and subsequent cooling, supports this interpretation. The remagnetization event is linked to the final consolidation of West Gondwanaland during the late stages of megacontinent assembly (∼490–480 Ma), coinciding with regional uplift and a stable geomagnetic field during the Moyero reverse superchron. These findings challenge the CRM hypothesis, as the quasi‐synchronous remagnetization across cratonic blocks and the predominance of single reverse polarity are better explained by thermal processes. This study highlights the critical role of thermoviscous relaxation in large‐scale remagnetization and provides new insights into the tectonic evolution of West Gondwanaland.

The Ouarzazate Group in the Anti-Atlas Belt of southern Morocco, part of the West African Craton (WAC), is a significant Proterozoic lithostratigraphic unit formed during the late Ediacaran period. It includes extensive volcanic rocks associated with the early stages of Iapetus Ocean opening. Zircon U-Pb dating and geochemical analyses of the Oued Dar’a Caldera (ODC) volcanic succession in the Saghro Massif reveal two major eruptive cycles corresponding to the lower and upper Ouarzazate Group. The 1st cycle (588–563 Ma) includes pre- and syn-caldera volcanic succession characterized by basaltic andesite to rhyolitic rocks, formed in a volcanic arc setting through lithospheric mantle-derived mafic magmatism and crustal melting. A major caldera-forming eruption occurred approximately 571–562 Ma, with associated rhyolitic dyke swarms indicating a larger caldera extent than previously known. The 2nd cycle (561–543 Ma) features post-caldera bimodal volcanism, with tholeiitic basalts and intraplate felsic magmas, signaling a shift to continental flood basalts and silicic volcanic systems. The entire volcanic activity spans approximately 23–40 million years. This succession is linked to late Ediacaran intracontinental super-eruptions tied to orogenic collapse and continental extension, likely in association with the Central Iapetus Magmatic Province (CIMP), marking a significant transition in the geodynamic evolution of the WAC.

Plate tectonics is a unique feature of Earth, but its proposed time of initiation is still controversial, with published estimates ranging from ca. 4.2 to 0.7 Ga. Paleomagnetic data can provide a robust argument for one essential aspect of plate tectonics: large-scale relative lateral motions of distinct, rigid crustal blocks. Previously, the oldest relative horizontal motion between two or more blocks was constrained to a broad age interval of ca. 2.7-2.17 Ga using paleomagnetic data. In this study, we obtain a robust ca. 2.48 Ga paleomagnetic pole from Wyoming craton. Combining this result with the ca. 2.7-2.17 Ga apparent polar wander paths from Wyoming and Superior cratons, we suggest that they assembled during ca. 2.7-2.5 Ga and remained directly juxtaposed until ca. 2.17 Ga. Tectonostratigraphic data and geological proxies also suggest Wyoming and Superior collided at ca. 2.6 Ga. The results provide strong evidence for relative horizontal motion between crustal blocks during the Neoarchean. Together with other tectonic proxies, the data suggest plate mobilism in operation prior to 2.5 Ga.

Precambrian paleomagnetic studies are critical for testing paleogeographic reconstructions in deep time but rely on the fidelity of the assumption of the geocentric axial dipole (GAD) hypothesis. With high-reliability data from mafic dykes and volcanic rocks, the scatter of individual virtual geomagnetic poles (VGPs) can be used to test simple GAD models. In order to conduct such a test, the VGPs must be adequate in number and in spatial coverage of the sampling sites. In this study, we targeted the 2.1 Ga Indin dyke swarm of the Slave craton. Building on previous sampling of the Indin dyke swarm in the western and central parts of southern Slave craton, we report results from 9 additional sites in the central and eastern parts of the craton, sites that significantly expand the width of the dyke swarm across the entire craton. The VGPs obtained from 7 of 9 newly identified Indin dykes are broadly similar to previously reported directions, expanding the total of VGPs for individual Indin dykes to n = 28, which is sufficient for a test of the GAD-based statistical models using VGP scatter. The high VGP scatter of the Indin swarm can be attributed to the relatively high paleolatitude of 56 degrees +/- 6 degrees for the Slave craton at the time of dyke emplacement. The Indin data have VGP scatter that is consistent with field models associated with the GAD hypothesis for the indicated paleolatitude, thus confirming the fidelity of the GAD field at ca. 2.1 Ga.

Paleogeography of the Ediacaran Period has remained poorly understood due to paleomagnetic studies commonly yielding perplexing or conflicting data. Here we report new magnetostratigraphic data from the Ediacaran Ouarzazate Group in the Anti-Atlas Mountains of Morocco, which have primary magnetizations supported by a positive conglomerate test and stratigraphically consistent directions within volcanic units across multiple localities. Comprehensive magnetostratigraphic sampling shows highly variable directions, consistent with a rapidly changing geomagnetic field along a longitudinally preferred axis. High-precision geochronology constrains the geomagnetic variability to ~568-562 Ma and suggests rates that are likely too rapid for true polar wander or plate tectonic interpretations. Comparison of igneous- and sedimentary-derived data, using a novel statistical approach combining Bingham and Fisher distributions, indicates a high-inclination paleomagnetic direction that is compatible with independent evidence for regional glaciation. Our analysis produces a late Ediacaran paleogeographic reconstruction that is consistent with paleomagnetic and geologic constraints.

The chemical history of seawater provides key information on Earth’s geologic processes and is fundamental for robust CO2 reconstructions. The knowledge of the secular evolution of the oceanic boron isotope budget is particularly important for CO2 reconstruction from boron isotopes. The boron isotope composition of seawater (δ11Bsw) is homogeneous, but varies on multi-million year time scales, given its residence time of approximately 10 million years. To date, the secular evolution of the oceanic boron isotope budget has been difficult to constrain, posing a major uncertainty for boron-based pH and CO2 reconstructions from Earth’s geologic past and critically limiting our understanding of the global biogeochemical cycling of this important element through time. Evaporitic minerals bearing fluid inclusions – and halites in particular – have provided important insights on past variations in major and minor ion composition, and present a highly appealing archive for reconstructing δ11Bsw (as well as other isotopic systems) given their direct origin from seawater. However, the interpretation of their signatures is not straightforward due to the possibility of fractionation during evaporation, crystallisation, and local biogeochemical interactions. Here we present data illuminating the evolution of boron isotopes and various other elements during evaporite formation from laboratory experiments and natural modern evaporitic settings across the globe, accompanied by new analytical developments for high-precision single fluid inclusion measurement using laser ablation. These data enable us to critically evaluate the evaporite archive, paving an avenue to robust seawater and CO2 reconstructions from Earth’s geological past.

There is a mid-Proterozoic stretch of Earth’s history (roughly 1.9–0.9 Ga) called, non-affectionately, the “boring billion”. The moniker was first inspired several decades ago by the apparent absence of any significant carbon isotope anomalies and was linked to the relatively “boring” interval in between Earth’s broadly two-step pattern in atmospheric oxygenation. However, in light of (i) the original evidence coming from a relatively stable carbon cycles, (ii) the souring over time of the non-flattering term “boring billion” and (iii) the more recent additional clues coming from solid and deep Earth too, we suggest a rebranding to the term the “Balanced Billion”. The first benefit of this change is that it circumvents the subjectivity of what is “boring” as well as the strawman argument used repeatedly in the literature and news media that a new discovery overturns what had previously been thought to be a boring interval. The second, more important benefit of this renaming is that it is not only better marketing but also potentially a more accurate reflection of Earth system processes during the peculiar time—not only the balanced carbon cycle, but also balanced mantle convection and a constant daylength.

The location of the Congo-S & atilde;o Francisco (CSF) craton, one of the largest cratons in Proterozoic paleogeography, has been poorly constrained for the supercontinent Nuna interval (ca. 1800-1300 Ma). Initial models of Nuna suggested that the CSF craton was part of the Atlantica continent, together with Amazonia, West Africa, and perhaps R & iacute;o de la Plata, as a separate continental block from other Nuna constituents. In other Nuna models the CSF craton has been placed adjacent to Baltica and Siberia, the core of Nuna, based mainly on ages of mafic magmatism and sparse paleomagnetic data. Through a geochemical, geochronological and paleomagnetic study of the WNW-trending Virei mafic dykes, which extend outward from the Mesoproterozoic Kunene Igneous Complex in southwest Angola, we provide a U-Pb baddeleyite age of 1385 +/- 5 Ma, geochemical signatures, and a robust Mesoproterozoic paleomagnetic pole to test the CSF craton's placement within Nuna. Including our new pole with quality-filtered poles from the other cratons during the Nuna interval, we propose a refined Nuna model with (1) southwest Congo / west Siberia cratonic connection at 1700-1500 Ma, (2) proximity of Amazonia and West Africa cratons, and (3) connection of southwest Congo craton with northwest West Africa at 1380 Ma. Our proposed 1500-1380 Ma reconstructions are further supported by matching large igneous province (LIP) records from these crustal blocks. The new 1385 Ma Virei pole, when considered relative to an earlier CSF pole at ca. 1500 Ma, requires substantial azimuthal rotation (similar to 85 degrees) of CSF in the intervening time interval. To accommodate both the matching LIP records and paleomagnetic data from CSF and neighboring cratons in Nuna, we propose an interval of transform motion near the supercontinent's periphery prior to more widespread mid-Mesoproterozoic supercontinental breakup.

The early Paleoproterozoic (ca. 2.5-2.2 Ga) represents a critical juncture in Earth history, marking the inception of an oxygenated atmosphere while bearing witness to potentially multiple widespread and severe glaciations. Deciphering the nature of this glacial epoch and its connection with atmospheric oxygenation has, however, proven difficult, hindered by a reliance on disputed stratigraphic correlations given the paucity of direct radiometric age constraints. Nowhere is this more acute than within the South African Transvaal Supergroup: Here, while the loss of oxygen-sensitive mass-independent sulfur isotope fractionation (S-MIF) has been reported from both the Duitschland and Rooihoogte formations, divided opinion surrounding the time-equivalence of these units has prompted authors to argue for vastly different oxygenation trajectories. Addressing this debate, we present a depositional Re-Os age (2443 +/- 33 Ma) from diamictite samples preserved in drillcore of the upper Duitschland Formation. The 100-million-year separation between the Duitschland Formation and its previously presumed equivalent reveals at least two isolated disappearances of S-MIF, requiring that the Great Oxidation Event was dynamic and proceeded via discrete oxygenation episodes whose structure remains incompletely understood. Importantly, our revised framework aligns the lower Duitschland diamictite with the low-latitude glacigenic Makganyene Formation, supporting hypotheses of widespread regional, and potentially global, early Paleoproterozoic glaciation.

The Pongola Supergroup is a largely undeformed ca. 2.99 to 2.87 Ga succession of volcanic and sedimentary rocks on the southeastern Kaapvaal Craton. Understanding the palaeogeographic context of the Pongola Supergroup could shed light on the tectonic setting of laterally correlative gold-bearing Witwatersrand Supergroup and have implications for Archaean geodynamics. Two previous studies were limited in spatial coverage and yielded purported primary magnetisations that were strikingly different from one another. Here we report new palaeomagnetic results from volcanic rocks of the Nsuze Group, i.e., the lower Pongola Supergroup, that are based on broad geographic sampling of a total of 57 sites making provision for several stability field tests. We report several directional components of remanent magnetisation, including widespread Karoo (ca. 180 Ma) and sporadic Namaqua-Natal (Mesoproterozoic) remagnetisation; but two additional ancient components are also commonly observed. The first of these is a south down characteristic remanence from 16 sites, of which 14 sites were included in the calculation of a mean, which we interpret as a magnetic overprint associated with intrusion of the 2.65 Ga White Mfolozi dyke swarm based on an inverse baked contact test and poorer clustering upon application of structural corrections to restore bedding to palaeohorizontal. The south down pole is located at 75.4°S and 334.5°E with an A95 of 6.4°. Recorded over a much more geographically widespread area from 15 sites is a west down characteristic remanence. The west down remanence is constrained to be older than 2.65 Ga by the same inverse baked contact test on a White Mfolozi dyke. Clustering of the west down remanence improves when bedding is restored. Fold tests are statistically indeterminate, but best grouping at ~60% unfolding was illustrated from the Amsterdam syncline. The precise age of folding is unknown. Emplacement relationships between the ~2.87 Ga Thole Complex and the folded Mozaan Group suggest that the syncline could be older than 2.87 Ga, but folding has also been ascribed to emplacement of the ca. 2.72 Ga Nhlangano gneiss dome. The age of the west down remanence and pole (15.6°S, 340.2°E and A95 = 9.3°, assuming 60% unfolding of sites at the Amsterdam syncline; or 16.6°S, 338.7°E and A95 = 10.3°, assuming 100% unfolding of sites at the Amsterdam syncline), which could be either syn-folding or pre-folding, is constrained at 2.98 to 2.72 Ga given presently known data.