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Inclination is the angle of a magnetization vector from horizontal. Clastic sedimentary rocks often experience inclination shallowing whereby syn- to post-depositional processes result in flattened detrital remanent magnetizations relative to local geomagnetic field inclinations. The deviation of recorded inclinations from true values presents challenges for reconstructing paleolatitudes. A widespread approach for estimating flattening factors (f) compares the shape of an assemblage of magnetization vectors to that derived from a paleosecular variation model (the elongation/inclination [E/I] method). Few studies exist that compare the results of this statistical approach with empirically determined flattening factors and none in the Proterozoic Eon. In this study, we evaluate inclination shallowing within 1.1 billion-year-old, hematite-bearing red beds of the Cut Face Creek Sandstone that is bounded by lava flows of known inclination. Taking this inclination from the volcanics as the expected direction, we found that detrital hematite remanence is flattened with (Formula presented.) whereas the pigmentary hematite magnetization shares a common mean with the volcanics. Using the pigmentary hematite direction as the expected inclination results in (Formula presented.). These flattening factors are consistent with those estimated through the E/I method (Formula presented.) supporting its application in deep time. However, all methods have significant uncertainty associated with determining the flattening factor. This uncertainty can be incorporated into paleomagnetic poles with the resulting ellipse approximated with a Kent distribution. Rather than seeking to find “the flattening factor,” or assuming a single value, the inherent uncertainty in flattening factors should be recognized and incorporated into paleomagnetic syntheses.

The natural remanent magnetization (NRM) of high sedimentation rate sediments provides significant information about paleomagnetic secular variation of the Earth's magnetic field and can also potentially be used for stratigraphy. However, NRM acquisition depends on conditions inherent to the depositional environment. In addition to recording a precise annual chronology, varved sediments reflect marked annual sedimentary changes. The Earth's magnetic field does not vary significantly over such a short period, so magnetic changes recorded by varves are expected to reflect the influence of depositional parameters on the recording process. We focus here on a sequence of 27 ± 1 varves from the former proglacial Lake Ojibway (∼8.5 ka cal BP) from which individual cm‐thick summer and winter beds were sampled. Paleomagnetic, granulometric and geochemical analyses were conducted on each bed. A mean inclination shallowing of 24.3° is observed in winter beds, along with an 11.3° shallowing in summer beds. Magnetic declinations follow, on average, the expected field direction, but differences of up to 20° occur between successive beds. Summer beds are thicker than winter beds and have stronger magnetic susceptibility, higher Ca/Fe ratios and coarser sedimentary and magnetic grains. This grain size pattern reflects the input of coarser detrital particles during summer, while the finer fraction remained in suspension until it was deposited in winter. A combination of differential compaction between the winter and summer beds, seasonally varying physical and magnetic properties of sediments, and delayed NRM acquisition explains the variable and coercivity‐dependent inclination shallowing. Key Points: The seasonal variations have an impact on the remanent magnetization in varved sediments [ABSTRACT FROM AUTHOR]

Abstract The natural remanent magnetization (NRM) of high sedimentation rate sediments provides significant information about paleomagnetic secular variation of the Earth's magnetic field and can also potentially be used for stratigraphy. However, NRM acquisition depends on conditions inherent to the depositional environment. In addition to recording a precise annual chronology, varved sediments reflect marked annual sedimentary changes. The Earth's magnetic field does not vary significantly over such a short period, so magnetic changes recorded by varves are expected to reflect the influence of depositional parameters on the recording process. We focus here on a sequence of 27 ± 1 varves from the former proglacial Lake Ojibway (∼8.5 ka cal BP) from which individual cm‐thick summer and winter beds were sampled. Paleomagnetic, granulometric and geochemical analyses were conducted on each bed. A mean inclination shallowing of 24.3° is observed in winter beds, along with an 11.3° shallowing in summer beds. Magnetic declinations follow, on average, the expected field direction, but differences of up to 20° occur between successive beds. Summer beds are thicker than winter beds and have stronger magnetic susceptibility, higher Ca/Fe ratios and coarser sedimentary and magnetic grains. This grain size pattern reflects the input of coarser detrital particles during summer, while the finer fraction remained in suspension until it was deposited in winter. A combination of differential compaction between the winter and summer beds, seasonally varying physical and magnetic properties of sediments, and delayed NRM acquisition explains the variable and coercivity‐dependent inclination shallowing.

Rapidly deposited layers (RDL) such as turbidites or hyperpycnites are mostly studied for their sedimentological properties, but are carefully avoided in paleomagnetic studies due to the disturbances caused by such sudden and rapid sediment accumulation. Therefore, these layers can also be seen as potential indicators of sediment parameters susceptible of affecting the alignment of magnetic grains and ultimately the acquisition of the natural remanent magnetization (NRM). We have compiled 13 Holocene rapidly deposited layers from core MD99-2222 in the Saguenay Fjord, eastern Canada (St-Onge and al., 2004) with varying thicknesses (from 7.1 cm to 1,510 cm) and 4 Quaternary turbidites of different origins, to document the influence of sedimentary and magnetic parameters on natural remanent magnetization acquisition. We found a logarithmic relationship between rapidly deposited layers thickness on the one hand, and the amplitude of inclination changes and magnetic grain sizes on the other. Inclination and magnetic grain sizes are themselves correlated to each other by a logarithmic law. As there is no relationship between inclination deviation and stratigraphic depth, compaction alone cannot account for such large effects on inclination. Flocculation is grain size sensitive, but it is expected to affect mainly the natural remanent magnetization intensity, rather than its direction. Turbulence that prevails during the rapid deposition of sediments during such events is most likely the dominant factor.

Abstract Inclination is the angle of a magnetization vector from horizontal. Clastic sedimentary rocks often experience inclination shallowing whereby syn‐ to post‐depositional processes result in flattened detrital remanent magnetizations relative to local geomagnetic field inclinations. The deviation of recorded inclinations from true values presents challenges for reconstructing paleolatitudes. A widespread approach for estimating flattening factors (f) compares the shape of an assemblage of magnetization vectors to that derived from a paleosecular variation model (the elongation/inclination [E/I] method). Few studies exist that compare the results of this statistical approach with empirically determined flattening factors and none in the Proterozoic Eon. In this study, we evaluate inclination shallowing within 1.1 billion‐year‐old, hematite‐bearing red beds of the Cut Face Creek Sandstone that is bounded by lava flows of known inclination. Taking this inclination from the volcanics as the expected direction, we found that detrital hematite remanence is flattened with f=0.650.560.75 whereas the pigmentary hematite magnetization shares a common mean with the volcanics. Using the pigmentary hematite direction as the expected inclination results in f=0.610.550.67. These flattening factors are consistent with those estimated through the E/I method f=0.640.510.85 supporting its application in deep time. However, all methods have significant uncertainty associated with determining the flattening factor. This uncertainty can be incorporated into paleomagnetic poles with the resulting ellipse approximated with a Kent distribution. Rather than seeking to find “the flattening factor,” or assuming a single value, the inherent uncertainty in flattening factors should be recognized and incorporated into paleomagnetic syntheses.

Hematite-bearing red beds are renowned for their chemical remanent magnetization (CRM). If the CRM was acquired substantially later than the sediment was formed, this severely compromises paleomagnetic records. To improve our interpretation of the natural remanent magnetization, the intricacies of the CRM acquisition process must be understood. Here, we contribute to this issue by synthesizing hematite under controlled 'Earth-like' field conditions (≲100 μT). CRM was imparted in 90 oriented samples with varying inclinations. The final synthesis product appeared to be dominated by hematite with traces of ferrimagnetic iron oxides. When the magnetic field intensity is ≳40 μT, the CRM records the field direction faithfully. However, for field intensities ≲40 μT, the CRM direction may deviate considerably from that of the applied field during synthesis. The CRM intensity normalized by the isothermal remanent magnetization (CRM/IRM@2.5 T) increases linearly with the intensity of growth field, implying that CRM could potentially be useful for relative paleointensity studies if hematite particles of chemical origins have consistent properties. CRM in hematite has a distributed unblocking temperature spectrum from ~200 to ~650 °C, while hematite with a depositional remanent magnetization (DRM) has a more confined spectrum from ~600to680°C because it is usually coarser-grained and more stoichiometric. Therefore, the thermal decay curves of CRM with their concave shape are notably different from their DRM counterparts which are convex. These differences together are suggested to be a potential discriminator of CRM from DRM carried by hematite in natural red beds, and of significance for the interpretation of paleomagnetic studies on red beds.

Hematite-bearing red beds are renowned for their chemical remanent magnetization (CRM). If the CRM was acquired substantially later than the sediment was formed, this severely compromises paleomagnetic records. To improve our interpretation of the natural remanent magnetization, the intricacies of the CRM acquisition process must be understood. Here, we contribute to this issue by synthesizing hematite under controlled 'Earth-like' field conditions (≲100 μT). CRM was imparted in 90 oriented samples with varying inclinations. The final synthesis product appeared to be dominated by hematite with traces of ferrimagnetic iron oxides. When the magnetic field intensity is ≳40 μT, the CRM records the field direction faithfully. However, for field intensities ≲40 μT, the CRM direction may deviate considerably from that of the applied field during synthesis. The CRM intensity normalized by the isothermal remanent magnetization (CRM/IRM@2.5 T) increases linearly with the intensity of growth field, implying that CRM could potentially be useful for relative paleointensity studies if hematite particles of chemical origins have consistent properties. CRM in hematite has a distributed unblocking temperature spectrum from ~200 to ~650 °C, while hematite with a depositional remanent magnetization (DRM) has a more confined spectrum from ~600to680°C because it is usually coarser-grained and more stoichiometric. Therefore, the thermal decay curves of CRM with their concave shape are notably different from their DRM counterparts which are convex. These differences together are suggested to be a potential discriminator of CRM from DRM carried by hematite in natural red beds, and of significance for the interpretation of paleomagnetic studies on red beds.

We test whether X-ray micro-computed tomography (microCT) imaging can be used as a tool for screening magnetite grains to improve the accuracy and precision of cosmogenic ³He exposure dating. We extracted detrital magnetite from a soil developed on a fanglomerate at Whitewater, California, which was offset by the Banning strand of the San Andreas Fault. This study shows that microCT screening can distinguish between inclusion-free magnetite and magnetite with fluid or common solid inclusions. Such inclusions can produce bulk 3He concentrations that are significantly in excess of the expected spallation production. We present Li concentrations, major and trace element analyses, and estimated magnetite (U_Th) = He cooling ages of samples in order to model the contribution from fissiogenic, nucleogenic, and cosmogenic thermal neutron production of ³He. We show that mineral inclusions in magnetite can produce 3He concentrations of up to 4 times that of the spallation component, leading to erroneous exposure ages. Therefore, grains with inclusions must be avoided in order to facilitate accurate and precise magnetite 3He exposure dating. Around 30% of all grains were found to be without inclusions, as detectable by microCT, with the largest proportion of suitable grains in the grain size range of 400-800 µm. While grains with inclusions have 3He concentrations far in excess of the values expected from existing 10Be and 26Al data in quartz at the Whitewater site, magnetite grains without inclusions have concentrations close to the predicted depth profile. We measured ³He concentrations in aliquots without inclusions and corrected them for Li-produced components. By comparing these data to the known exposure age of 53.5±2.2 ka, we calibrate a production rate for magnetite 3He at sea level and high latitude (SLHL) of 116±13 at g-1 a-1.We suggest that this microCT screening approach can be used to improve the quality of cosmogenic 3He measurements of magnetite and other opaque mineral phases for exposure age and detrital studies. [ABSTRACT FROM AUTHOR]

Subduction plate margins have an intrinsically poor preservation potential for pre-subduction settings because most rocks sink and disappear into Earth's mantle. However, a preserved pre-subduction setting has been reported in the Lower Penninic Units (Valaisan Basin) of the Italian Western Alps (Beltrando et al., 2012). Here, we review two main aspects of the Valaisan Basin cropping out in Italy: the nature of the syn-rift detrital sediments and the characteristics of the metabasalts in proximity to the continental crust metagranitoid. New fossil findings are reported, which confirm a Mesozoic age for the Valaisan rifting. Field and petrographic data from metabreccias and pillowed metabasalts near the fossil-rich high-pressure metasediments support the interpretation of the Valaisan Domain in the Breuil valley (Aosta) as a fossil ocean-continent transition zone. [ABSTRACT FROM AUTHOR]

Detrital zircon U‐Pb data are routinely used to assess provenance in sedimentary systems. However, recent studies have suggested that zircon provenance interpretation may be biased by grain‐size‐dependent selective transport and deposition. In this study, we present zircon grain‐size and U‐Pb data from 11 sandstone and 11 mudstone samples from the late Paleozoic Eagle and Paradox basins to test whether apparent provenance changes between sandstone and mudstone samples can be explained by changes in zircon grain‐size alone. The Eagle and Paradox basins formed in association with the Ancestral Rocky Mountains (ARM). These basins provide an excellent system to test grain‐size/provenance relationships because they are filled with cyclic stratigraphy that records, via grain size and facies changes, flooding/exposure driven by interglacial/glacial cycles. These cycles are interpreted to have substantially altered sediment transport pathways and provenance of ARM‐related sedimentary rocks. Data presented here suggest that although zircon grain size does correlate to sample grain size in most samples, age spectra appear to be independent of grain size. As such, differences in age spectra between sandstone and mudstone samples appear to be the result of changes in relative inputs of two endmember sources: (1) grains eroded from adjacent basement‐cored ARM uplifts and (2) far‐traveled sediment sourced from outside the ARM system. The data presented in this study also provide a successful proof‐of‐concept test for a manual method of determining zircon grain size. This method is simple and straightforward and can be applied to any sample analyzed using the Chromium off‐line targeting software. Key Points: Detrital zircon age spectra, grain size, and sample grain size are correlated, but this does not affect provenance interpretationsWe present a simple method for quantifying grain size in detrital zircon samples [ABSTRACT FROM AUTHOR]

This paper presents the results of U–Th–Pb geochronological study of detrital zircons from cement of the Jurassic conglomerates of the Strelka Depression extending in the sublatitudinal direction along the border between the southern margin of the Selenga-Stanovoy superterrane and the Mongol–Okhotsk fold belt. It has been shown that Paleoproterozoic and Neoarchean zircons overwhelmingly dominate in the conglomerate cement. This indicates that the main input of the material to the sedimentation basin was carried from the Southeast border of the North Asian craton (from the north in modern coordinates). In our opinion, the Strelka Depression formed after the completion of orogenic processes associated with the formation of the Mongol–Okhotsk structure. [ABSTRACT FROM AUTHOR]

Laser-ablation ICPMS U-Pb and Lu-Hf isotope data on detrital zircon in sandstone from the Palaeoproterozoic Waterberg Group in the Waterberg and Nylstroom basins of northeastern South Africa contain a dominant Palaeoproterozoic (2 000 to 2 150 Ma) age fraction and minor, late Archaean zircon (2 650 to 2 780 Ma). Zircon in the 2 200 to 2 350 Ma age range is very scarce. There are no statistically significant differences in detrital zircon age distributions of sandstones in the two basins. In contrast, conglomerate from the northern margin of the Waterberg basin (Mogalakwena Formation) is dominated by a late Archaean age fraction (2 600 to 2 700 Ma, with minor 3 200 to 3 300 Ma), which resides in quartzite clasts. Zircon ages alone cannot distinguish between potential sources of detritus in the Kaapvaal Craton and Limpopo Belt. Hf isotope data, however, suggest that the main input to the basins was from recycled Archaean to Palaeoproterozoic sedimentary cover successions on the Kaapvaal Craton, supplemented by material from late Archaean granitic intrusions and the felsic igneous rocks of the Rooiberg Group and / or felsic members of the Bushveld Complex. The only known source of a prominent group of ca. 2.0 Ga detrital zircon with epsilon-Hf = 0 to -3 would be the youngest generation of granites in the Limpopo Belt (e.g. Mahalapye Granite). The Waterberg Group or its equivalents have provided only minor amounts of detritus to the Neoproterozoic to Cambrian basins at the western margin of the Kalahari Craton, directly or through recycling of intermediate deposits. However, erosion of the rocks in the Waterberg and Nylstroom basins provided material to the lower stratigraphic levels of the adjacent, Karoo-age Ellisras and Springbok Flats basins. [ABSTRACT FROM AUTHOR]

Abstract We conduct sandstone-composition analysis, U-Pb detrital-zircon dating, and apatite fission-track thermochronology to determine how basin development was associated with the Cenozoic deformation across central Tibet. Our results are consistent with a two-stage basin development model: first a single fluvial-lacustrine system formed (i.e., Paleo-Qaidam basin) in between two thrust belts (i.e., the Fenghuoshan and Qilian Shan thrust belts) in the Paleogene, which was later partitioned into two sub-basins in the Neogene by the Kunlun transpressional system and its associated uplift. The southern sub-basin (i.e., Hoh Xil basin) strata have detrital-zircon age populations at 210–300 Ma and 390–480 Ma for the Eocene strata and at 220–310 Ma and 400–500 Ma for the early Miocene strata; petrologic analysis indicates that the late Cretaceous-Eocene strata were recycled from the underlying Jurassic rocks. The northern sub-basin (i.e., Qaidam basin) strata yield detrital-zircon age clusters at 210–290 Ma and 370–480 Ma in the Eocene, 220–280 Ma and 350–500 Ma in the Oligocene, 250–290 Ma and 395–510 Ma in the Miocene, and 225–290 Ma and 375–480 Ma in the Pliocene. Proterozoic ages of the detrital zircon are most useful for determining provenance: the pre-Neogene Hoh Xil and Qaidam strata all contain the distinctive age peaks of ~1800 Ma and ~2500 Ma from the Songpan-Ganzi terrane south of the Kunlun fault, whereas detrital zircon of this age is absent in the Neogene Qaidam strata suggesting the emergence of a topographic barrier between the two basins. This inference is consistent with our fission-track thermochronological data from the Eastern Kunlun Range that suggest rapid cooling within the range did not start until after 30–20 Ma. Our new data support the Paleo-Qaidam hypothesis that requires the Hoh Xil and Qaidam basins were parts of a single Paleogene basin bounded by the Qilian Shan and Fenghuoshan thrust belts. Highlights • Conducted sandstone-composition analysis, U-Pb detrital-zircon dating, and apatite fission-track thermochronology in central Tibet. • Results support a two-stage basin-development model during Cenozoic uplift of the Tibetan plateau • A single Paleogene basin was partitioned into two Neogene basins starting at 25–20 Ma. [ABSTRACT FROM AUTHOR]

Remanent voids of former open-pits can be re-used in different directions with major benefits, irrespective of their future use, due to the fact that they involve the rehabilitation and the reentry into the economic or ecological circuit of large areas of degraded mining land. An increasingly common method, applied worldwide, is the flooding of remanent voids and the formation of artificial lakes that can take up many functions. Artificial lakes formed in former open-pits are also known as "open-pit lakes." These occur after the cessation of exploitation as a result of naturally or artificially flooding of the remanent voids. In Romania, this method is less known, but it must be taken into account that the functions that an open-pit lake can take and their major benefits, will play an important role in the sustainable development of a former mining regions. In the case of deep open-pits, as in the case of lignite open-pits, with a high probability of intercepting deep aquifers with high water inflows, the formation of artificial lakes is the optimal choice as natural floods are favored, and the costs are minimal. The present paper presents the case of the North Pesteana lignite open-pit, for which, at the moment of the cessation of the exploitation activity, the flooding of the remanent void is pursued. The remanent void of the North Pesteana open-pit will be of impressive dimensions. It presents a high flooding opportunity, primarily due to the very favorable hydrogeological conditions in the region. The lake formed in the remanent void of the North Pesteana open-pit will bring a number of benefits to local communities and beyond, these being detailed in this paper. The general aim of the paper is to increase, at national and regional level (at the level of Rovinari Mining Basin), the degree of knowledge regarding the possibilities of flooding of the remanent voids and the use of artificial lakes formed in former lignite open-pits, but also the benefits that they can have, on a medium and long term, on human communities, from a socio-economic and environmental point of view. [ABSTRACT FROM AUTHOR]

Abstract Detrital ages constrain the timing of deposition, along-strike paleo-geographic variations and the nature of erosional sources in sedimentary basins and can be used to constrain the transition between orogenic cycles. The Connecticut Valley-Gaspé (CVG) trough is a major Upper Ordovician-to-Devonian sedimentary basin that extends for >1000 km in the Northern Appalachians and was deposited during the Salinic and Acadian orogeneses. In Quebec and northern New England, the CVG trough is host to the Gaspé Belt and correlative units of the Connecticut Valley sequence (CVS). In southern Quebec, the Gaspé belt sedimentation occurred during late Silurian-to-Early Devonian crustal extension related to the Salinic orogeny. This study reports detrital U/Pb zircon and 40Ar/39Ar muscovite ages from the Ayers Cliff and Compton formations, Quebec and the correlatives Waits River and Gile Mountain formations, Vermont. Detrital zircon ages suggest that proximal early Silurian-to-Devonian erosional sources were submerged during sedimentation, which is consistent with an extension-related marine transgression marked by the Ayers Cliff and Waits River formations. The lack of Ediacaran zircons in the Ayers Cliff Formation contrasts with the Waits River Formation, suggesting that the nature of erosional sources varied during deposition of the lowermost part of the basin. Stratigraphically higher Compton and Gile Mountain formations have similar detrital zircon provenance suggesting homogenization of detrital contributions. This is attributed to the encroachment of Avalonian terranes and ongoing erosion, probably during uplift of Laurentia and Avalonian terranes leading to foreland basin development and deposition of the uppermost part of the Compton and Gile Mountain formations which yielded youngest mean ages of ca. 413 Ma and ca. 401 Ma, respectively. Low-grade metamorphic conditions allow the preservation of detrital 40Ar/39Ar muscovite ages which highlight the contribution of erosional sources that experienced Grenvillian, Taconian and Salinic metamorphism. Highlights • Transition of orogenic cycles reflected by timing of deposition, along-strike paleo-geographic variations and nature of erosional sources of syn-orogenic basin. • Implication of approaching Avalonian terranes in the transition from Salinic to Acadian orogenic cycles • Maximum age of deposition of the Gaspé Belt and Connecticut Valley sequence is c. 413 Ma and c. 401 Ma, respectively. • Sources having experienced Grenvillian, Taconian and Salinic metamorphism contributed to the Gaspé Belt sedimentation. • U Pb cristallisation age of the Averill Pluton is 367.8 ± 0.3 Ma [ABSTRACT FROM AUTHOR]

New detrital zircon U–Pb dates for seven late Viséan to Bashkirian (Middle Mississippian to Lower Pennsylvanian) Mattson and Kindle formation sandstone samples from the Mattson delta complex in the Liard Basin of northeastern British Columbia, combined with two previously published detrital zircon samples from these units, indicate a dominant Greenland Caledonian clastic wedge and orogen source with a small contribution of Ellesmerian-aged material. This provenance remained consistent over time. The Labrador–Greenland high was the only paleogeographically viable source area during the time of deposition of the Mattson delta complex. Detritus deposited on the western margin of Laurentia in the Mattson delta complex was likely transported southwestward by a late Viséan to Bashkirian pancontinental river system. This conclusion contrasts with previous interpretations which proposed that these sediments were recycled from the Ellesmerian clastic wedge. Tectonic uplift and denudation of eastern Greenland provided detritus from the Silurian to Devonian Caledonian clastic wedge and orogen to the western margin of Laurentia and detritus from the Caledonian orogen to the Serpukhovian to middle Bashkirian (Namurian) conglomeratic successions of the Millstone Grits in England. Detrital zircon U–Pb dates for two samples from the unconformably overlying Cisuralian (lower Permian) Tika formation are similar to those of the Mattson delta complex samples, as are those from the Pennsylvanian Spray Lakes Group of the southern Prophet Trough, indicating they all probably shared the same dominant source areas. The Tika formation was mainly derived from recycling of the Mattson and other Caledonide-sourced sediments of northern Laurentia. [ABSTRACT FROM AUTHOR]

To investigate the timing of deposition and provenance of early Mesozoic strata in the northeastern North China Craton (NCC) and to understand the early Mesozoic paleotectonic evolution of the region, we combine stratigraphy, U-Pb zircon geochronology, and Hf isotopic analyses. Early Mesozoic strata include the Early Triassic Heisonggou, Late Triassic Changbai and Xiaoyingzi, and Early Jurassic Yihe formations. Detrital zircons in the Heisonggou Formation yield ~58% Neoarchean to Paleoproterozoic ages and ~42% Phanerozoic ages and were sourced from areas to the south and north of the basins within the NCC, respectively. This indicates that Early Triassic deposition was controlled primarily by the southward subduction of the Paleo-Asian oceanic plate beneath the NCC and collision between the NCC and the Yangtze Craton (YC). Approximately 88% of the sediments within the Late Triassic Xiaoyingzi Formation were sourced from the NCC to the south, with the remaining ~12% from the Xing'an-Mongolia Orogenic Belt (XMOB) to the north. This implies that Late Triassic deposition was related to the final closure of the Paleo-Asian Ocean during the Middle Triassic and the rapid exhumation of the Su-Lu Orogenic Belt between the NCC and YC. In contrast, ~88% of sediments within the Early Jurassic Yihe Formation were sourced from the XMOB to the north, with the remaining ~12% from the NCC to the south. We therefore infer that rapid uplift of the XMOB and the onset of the subduction of the Paleo-Pacific Plate beneath Eurasia occurred in the Early Jurassic. [ABSTRACT FROM AUTHOR]

Poles from continental redbeds are a large fraction of the world's palaeomagnetic database. Nonetheless, the time of acquisition and origin of the remanent magnetization of redbeds has been long debated. We report palaeomagnetic data, rock magnetic data and microscope observations for Lower Cretaceous redbeds in southern Mexico. These data allow us to discriminate between the hysteresis properties of remanent magnetizations of detrital and chemical origin, and to establish the early origin of a chemical remanence. Red sandstones of the Zicapa Formation contain a multicomponent remanence revealed by thermal demagnetization, and consisting of three stable components with partially overlapping laboratory unblocking temperatures of <250 °C, ~300 to ~500 °C and >600 °C, (low, intermediate and high temperature, respectively). They are interpreted as a viscous remanence residing in detrital magnetite, a chemical remanence residing in authigenic hematite and a depositional remanence residing in detrital hematite, respectively. The low-temperature component is nearly parallel to the recent dipole field. The tilt-corrected overall site means of the intermediate (chemical) and high temperature (depositional) components are indistinguishable (Dec = 282.0°, Inc = 12.4°, k = 13.33, a95 = 10.1°, N = 17, for the intermediate temperature; and Dec = 272.5°, Inc = 16.5°, k = 14.04, a95 = 11, N = 14, for the high temperature). Elongation/inclination analysis suggests that depositional and chemical components require applying an f = factor of approximately 0.4. Both of these components define a magnetic polarity zonation, but the polarity of the chemical and detrital components may or may not be the same. The chemical remanence coincides, more often than not, with the polarity of the depositional remanence of the overlying (younger) strata, suggesting a delay in remanence acquisition of tens to a few hundred ka for the chemical component. Pigmentary and detrital haematite were recognized with microscopic observations. The particle size of haematite ranges from approximately 10 to 300 µm for detrital haematite (martite, specularite and laterite), and from ca. 0.2 to 1 µm for pigmentary haematite flakes. The IRM of these rocks can be modelled with components of low coercivity (H1/2 between 5 and 10 mT interpreted as detrital magnetite), and components of a wide coercivity range (prevailing H1/2 from ~400 to 600 mT interpreted as haematite). Hysteresis ratios show a systematic correlation with demagnetization behaviour, with lower Hcr/Hc values and higher Mrs/Ms values for samples with a dominant chemical component, than form samples with a significant (>40 per cent) depositional component. [ABSTRACT FROM AUTHOR]

The late Carboniferous to Triassic tectonic history of eastern Australia includes important periods of regional-scale crustal extension and contraction. Evidence for these periods of tectonism is recorded by the extensive Pennsylvanian (late Carboniferous) to Triassic basin system of eastern Australia. In this study, we investigate the use of U-Pb dating of detrital zircons in reconstructing the tectonic development of one of these basins, the eastern Galilee Basin of Queensland. U-Pb detrital zircon ages were obtained from samples of stratigraphically well-constrained Cisuralian and Lopingian (early and late Permian, respectively) sandstone in the Galilee Basin. Detrital zircons in these sandstones are dominated by a population with ages in the range of 300-250 Ma, and ages from the youngest detrital zircons closely approximate depositional ages. We attribute these two fundamental findings to (1) appreciable derivation of detrital zircons in the Galilee Basin from the New England Orogen of easternmost Australia and (2) syndepositional magmatism. Furthermore, Cisuralian sandstone of the Galilee Basin contains significantly more >300 Ma detrital zircons than Lopingian sandstone. The transition in detrital zircon population, which is bracketed between 296 and 252 Ma based on previous high-precision U-Pb zircon ages from Permian ash beds in the Galilee Basin, corresponds with the Hunter-Bowen Orogeny and reflects a change in the Galilee Basin from an earlier extensional setting to a later foreland basin environment. During the Lopingian foreland basin phase, the individual depocentres of the Galilee and Bowen basins were linked to form a single and enormous foreland basin that covered >300 000 km2 in central and eastern Queensland. [ABSTRACT FROM AUTHOR]

The time of origin of Earth's dynamo is unknown. Detrital zircon crystals containing ferromagnetic inclusions from the Jack Hills of Western Australia have the potential to contain the oldest records of the geodynamo. It has recently been argued that magnetization in these zircons indicates that an active dynamo existed as far back as 4.2 Ga. However, the ages of ferromagnetic inclusions in the zircons are unknown. Here we present the first detailed characterization of the mineralogy and spatial distribution of ferromagnetic minerals in Jack Hills detrital zircons. We demonstrate that ferromagnetic minerals in most Jack Hills zircons are commonly located in cracks and on the zircons' exteriors. Hematite is observed to dominate the magnetization of many zircons, while other zircons also contain significant quantities of magnetite and goethite. This indicates that the magnetization of most zircons is likely to be dominantly carried by secondary minerals that could be hundreds of millions to billions of years younger than the zircons' crystallization ages. We conclude that the existence of the geodynamo prior to 3.5 Ga has yet to be established. [ABSTRACT FROM AUTHOR]

The Abrigo del Molino archaeological site is located in the valley of the Eresma river, near Segovia in central Spain. It consists of a shallow cave of fluvio-karstic origin, which has been completely filled with detrital deposits. Geo-archaeological interpretation of the genesis of these deposits differentiates three groups: a lower group with sandy loams and fine sands interbedded with pebble and gravel layers, deposited respectively by palaeofloods and slope contributions; a middle group with massive silt and grain-supported boulders, formed by alternating contributions from the overlying slope, karst mudflows and rockfalls from the shelter roof; and an upper group of silt cemented by carbonates, final backfill alteration and degradation of the host rock. The techno-typological characteristics of the lithic assemblage confirm the existence of Mousterian levels at the site, and optically stimulated luminescence (OSL) dating of these levels obtains an age range of 31–60 ka for the detrital deposits, presenting the occupation by Neanderthal groups for the first time in karstic environments in the northern Iberian plateau, the southern part of the Duero basin. [ABSTRACT FROM AUTHOR]

Detrital soil contamination during wood harvesting cannot be avoided without a further cleaning step. The objective of the current study was to determine the effect of Piedmont soil on pinewood pyrolysis products. Ash content was varied at 0.56%, 1.16%, 2.77%, 4.40%, 6.87%, 8.35%, and 15.52% by adding soil to woodchips to mimic the highly soilcontaminated biomass that can be found in biorefineries. This study found that bio-oil yield decreased from 47.1% to 26.3% with an increase in ash content from 0.56% to 15.52%. However, the oxygen content of the bio-oil decreased and the carbon content increased, which led to an increase in heating value from 22.5 to 24.9 MJ kg-1. Inorganics in the soil aided in the catalytic cracking and dehydration reactions for bio-oil formation. A slight increase in the total acid number (106 to 117 mg KOH g-1) and water content (20.72% to 24.99%) was observed with more soil inclusion in the pyrolysis. The effect of soil on biochar O/C and H/C ratios was minimal even though the heating value decreased with an increase in soil content. This study showed that soil (4%wt to 7%wt) in the biomass assisted in deoxygenating the bio-oil and lowered the total mass yield while keeping the total energy yield almost constant. [ABSTRACT FROM AUTHOR]

Detrital zircon age spectra from the siliciclastic rocks of the Lalla Mouchaa Calcschists and El Jadida Dolomitic formations (the Coastal Block of the Moroccan Meseta) are dominated by Paleoproterozoic and Ediacaran ages. The provenance of these two formations is a composite Proterozoic crystalline basement. El Jadida rhyolite (584.2 ± 4.8 Ma) represents the Ediacaran crystalline basement of the El Jadida dome. El Jadida rhyolite is unconformably overlain by the microbreccia, arkosic sandstone and dolostone of the El Jadida Dolomitic Formation with a maximum depositional age of ca. 539 Ma (Lower Cambrian). Detrital zircon-age spectra from El Jadida Dolomitic Formation (ca. 583–582 Ma) suggest direct recycling of El Jadida rhyolite as an exclusive original primary source. However, in the Western Rehamna massif, detrital zircon-age spectra from pre-Middle Cambrian microbreccia and arkosic sandstone of the Lalla Mouchaa Calcschists Formation (ca. 2.05–2.03 Ga) indicate exclusive recycling of the ca. 2.05 Ga-aged crystalline basement rocks (original primary source). Detrital zircon contents of the siliciciclastic rocks from these two formations of the Coastal Block are consistent with derivation from either Eburnian (Paleoproterozoic) or Cadomian/Pan-African (Ediacaran) igneous rocks. The discovery of this composite Proterozoic crystalline basement in the Moroccan Meseta stresses that Cadomian/Pan-African magmatic arcs were built on an Eburnian basement in a paleoposition close to the West African craton, as part of the northern peri-Gondwanan realm. [ABSTRACT FROM AUTHOR]

The Dom Feliciano Belt represents the major geotectonic unit in southeastern South America, being part of the Neoproterozoic western Gondwana. The Porongos Complex comprises the southernmost Brazilian supracrustal sequence of this belt, overlying the Paleoproterozoic Encantadas gneiss (c. 2.2–2.0 Ga). Until recently, these rocks were traditionally interpreted as a single early Neoproterozoic (Tonian, c. 790 Ma) basin. Here we present new U-Pb detrital zircon ages for the Capané Antiform, located in the northern part of the Porongos Complex. The central sector, interpreted as a basement domain, shows both pronounced Paleoproterozoic (2.2–2.0 Ga) and Neoproterozoic (Tonian, 830–780 Ma) age peaks. The latter accounted for the rift-related Porongos succession that is tectonically imbricated with basement rocks. In contrast, metavolcano-sedimentary units from the eastern and western sectors reflect predominant Cryogenian-Ediacaran provenance (peaks at 615–580 Ma). This new detrital zircon signature challenges the traditional view of a single Neoproterozoic depositional episode for the Porongos Complex by implying two different sequences termed Porongos I and II of Tonian and Ediacaran ages, respectively. The Porongos I sequence is made up of mica schist from the central sector, showing Tonian maximum depositional ages. On the contrary, the younger volcano-sedimentary units of the two peripheral sectors display the Porongos II sequence deposited in a Cryogenian-Ediacaran basin. The Porongos I sequence may have evolved in an extensional setting as a marginal basin with rift-related units, whereas Porongos II formed during compression related to active thrusting, which resulted from the collision with the Pelotas Batholith. Therefore, the present age data combined with previously published geochronological, stratigraphic, and tectonic data sets identify the Capané Antiform as a key area to understand the tectonic evolution of the Porongos Complex. Its protracted evolution has recorded a tectonic history of more than 200 million years, lasting from the break-up of Rodinia to the Gondwana amalgamation. [ABSTRACT FROM AUTHOR]

Here we present detrital apatite fission track (AFT), zircon fission track (ZFT) and a few apatite (U–Th)/He (AHe) data of Middle Pleistocene to modern Rhine, Meuse and Elbe river sediments in order to resolve processes that control detrital age distributions (provenance, erosion and mineral fertility). We used a modelling approach to compare observed with theoretically predicted age distributions from an interpolated in situ AFT and ZFT age map. In situ cooling ages do show large differences in the Rhine drainage basin, facilitating the differentiation between different source regions. Inconsistencies between observed and theoretical age distributions of the Meuse and Elbe samples can be explained by mixing and reworking of sediments with different provenances (Meuse Middle Pleistocene terrace sediment) and a yet unexplored source region with old AFT ages (Elbe samples). Overall, the results show that detrital thermochronology is capable of identifying the provenance of Middle Pleistocene to modern sediments. The AFT age distributions of Rhine sediments are dominated (~70%) by AFT ages representing the Alps. A possible explanation is higher erosion rates in the Alps as compared to areas outside the Alps. A Late Pleistocene sample from the Upper Rhine Graben contains apatite grains from the Molasse and Hegau volcanics, which we explain with a shift of the headwaters of the Rhine to the north as a result of intense Middle Pleistocene Riss glaciation. Contrary to the observed dominance of Alpine-derived AFT ages in Rhine sediments, the relative contribution of zircon ages with sources in the Alps is lower and significantly decreases downstream, suggesting a major source of zircons outside the Alps. This can be explained by increased zircon fertility of sediments derived from the Rhenish massif. Therefore, we conclude that erosion and mineral fertility are the main processes controlling detrital AFT and ZFT age distributions of the sampled river sediment. In case of the Rhine samples, AFT age distributions are mainly controlled by differences in erosion rates, whereas this impact is completely balanced by differences in mineral fertility for the ZFT data. [ABSTRACT FROM AUTHOR]

Abstract: The magnetization of a sediment is acquired when ferromagnetic detrital particles align with the Earth's magnetic field as they settle through the water column. The relative continuity and ubiquity of the global sedimentary record makes sediments and sedimentary rocks an ideal target for studies of relative paleointensity (RPI) and the evolution of the Earth's magnetic field. However, processes including flocculation, contact with the substrate, bioturbation, and compaction disrupt this alignment, leading to shallowed remanent inclinations and biased intensities. The inclination of the depositional field also exerts an influence on the remanent intensity, thus affecting RPI estimates and leading to complications in interpretations of the global record. We present a series of 12 deposition experiments conducted in varying field strengths and inclinations, from which we determine RPI estimates. We then correct these estimates using a modified anisotropy‐based inclination correction technique. We find experimentally that our correction reduces the inclination dependence of relative paleointensity while preserving the RPI's dependence on the depositional intensity. Our results suggest that the anisotropy‐based correction should improve RPI estimates obtained from natural sediments and sedimentary rocks. [ABSTRACT FROM AUTHOR]

Long-term variations of the geomagnetic dipole moment (GDM) during periods of stable polarity and in transitional states (reversals and excursions) provide key information for understanding the geodynamo regime. Following several studies dealing with the Brunhes chron and the Matuyama–Brunhes transition, this study presents a new authigenic 10 Be/ 9 Be ratio (Be-ratio) record obtained from the MD97-2143 core (western Pacific Ocean). This new Be-ratio series yields a record of GDM variations covering the early Brunhes and mid to late Matuyama time period (i.e. 700–2140 ka), independently from the relative paleointensity (RPI) record obtained from the same core, that can be compared with available RPI records and stacks. Stratigraphic offsets measured between the Be-ratio peaks and the corresponding RPI minima reach 2 to 14 cm. They can be assigned to (post-) detrital remanent magnetization (pDRM) effects leading to magnetization locking-in delays varying from 2 to 12 ka in the studied core. 10 Be overproduction episodes triggered by geomagnetic dipole moment lows (GDL) linked to polarity reversals and excursions confirm the global control exerted by the GDM on cosmogenic radionuclides production. A dipole moment reconstruction derived from the Beryllium-10 (BeDiMo) was compiled and calibrated using absolute paleointensity data. This independent record complements the available paleomagnetic RPI records, permitting 1) to overcome the pDRM lock-in offsets induced below the mixing layer, 2) to confront and increase the robustness and precision of GDM reconstructions and, 3) to better constrain the chronology of geomagnetic field instabilities during the mid to late Matuyama chron. Our new 10 Be derived inventory is fully compatible with the GDL series linked to geomagnetic polarity reversals and events (Matuyama–Brunhes transition, Jaramillo and Olduvai subchron boundaries, Cobb Mountain, Réunion) and it strengthens the occurrence of several excursions (Kamikatsura, Santa Rosa, Punaruu, Bjorn, Gilsa, Gardar) that were until now reported from only sparse locations. [ABSTRACT FROM AUTHOR]

Paleogeographic reconstructions based on paleomagnetic data rely on the reliability of the natural remanent magnetization (NRM) as a primary geomagnetic signal. Remagnetizations, however, can be common in many rock types, including late Paleozoic and Mesozoic red beds, and they complicate paleogeographic interpretations. Extracting the primary NRM from partially remagnetized rocks, and understanding the remagnetization mechanism are important in these contexts. We carried out a systematic paleomagnetic study of red bed samples from the Triassic Huangmaqing Formation, Nanjing (32.0°N, 118.9°E), South China. Two NRM components carried by secondary and primary hematite are isolated in 47 of the 94 samples studied, where the latter component has a direction in stratigraphic coordinates of D = 29.2 ° , I = 34.6 ° ( α 95 = 10.9 ° , 47 samples from 6 sites) that yields a paleopole of λ = 60.8 °N, ϕ = 228.1 °E, d p / d m = 12.5 / 7.2 , which is consistent with Triassic pole positions for the South China Block. A secondary chemical remanent magnetization (CRM) ( D = 227.1 ° , I = 80.8 ° , α 95 = 7.3 ° ) is documented in all 94 samples from 10 sites and is carried by pigmentary hematite that is inferred to have been generated by magnetite oxidation during orogenic activity. This secondary component has steep inclinations and is interpreted to have been influenced by a combination of the remanence carried by original parent magnetite, the orogenic stress field, and the prevailing geomagnetic field direction during deformation. This CRM direction is recorded commonly by red beds from the South China Block, and is significant for regional tectonic studies in the area. [ABSTRACT FROM AUTHOR]

This study presents new zircon Hf isotopic data, which, combined with previous zircon U-Pb geochronological, in-situ Hf and whole-rock Nd isotopic data from the Western Block of the North China Craton (NCC), provide a new insight into global-scale continental crustal growth and evolution of early Earth. In particular, igneous zircons and detrital zircons from the Yinshan Block yield 207 Pb/ 206 Pb ages of 2446–2733 Ma, with an age peak at 2524 Ma. Of those, 86% have positive ε Hf (t) values and Archean Hf model ages ( T DM C ) (2.6–2.9 Ga) peaking at 2840 Ma. This indicates that those basement rocks of the Western Block are most likely derived from a depleted mantle source, implying a crust-mantle differentiation event at 2.8–2.7 Ga followed by extensive reworking at ∼2.5 Ga. More than 95% detrital zircons from the Khondalite Belt have ages converging on 2.2–2.0 Ga and their ε Hf (t) values vary from −5.43 to +9.54, of which 80% are positive and yield Hf model ages ( T DM C ) peaking at 2250 Ma. These characteristics of ε Hf (t) values in the Khondalite Belt are also documented in the basement rocks of the Ordos Block under same age frame of 2.2–2.0 Ga. This suggests that the Ordos Block may be a juvenile crust with addition of older materials. The initiation of subduction under the southern margin of the Ordos Block leads to the formation of a 2.2–2.0 Ga magmatic arc, which is likely related to the assembly of the supercontinent Columbia. [ABSTRACT FROM AUTHOR]

Detrital thermochronology is often employed to assess the evolutionary stage of an entire orogenic belt using the lag-time approach, i.e., the difference between the cooling and depositional ages of detrital mineral grains preserved in a stratigraphic succession. The impact of different eroding sources to the final sediment sink is controlled by several factors, including the short-term erosion rate and the mineral fertility of eroded bedrock. Here, we use apatite fertility data and cosmogenic-derived erosion rates in the Po river catchment (Alps–Apennines) to calculate the expected percentage of apatite grains supplied to the modern Po delta from the major Alpine and Apenninic eroding sources. We test these predictions by using a cutting-edge dataset of trace-element and Nd-isotope signatures on 871 apatite grains from 14 modern sand samples, and we use apatite fission-track data to validate our geochemical approach to provenance discrimination. We found that apatite grains shed from different sources are geochemically distinct. Apatites from the Lepontine dome in the Central Alps show relative HREE enrichment, lower concentrations in Ce and U, and higher 147 Sm/ 144 Nd ratios compared to apatites derived from the External Massifs. Derived provenance budgets point to a dominant apatite contribution to the Po delta from the high-fertility Lepontine dome, consistent with the range independently predicted from cosmonuclide and mineral-fertility data. Our results demonstrate that the single-mineral record in the final sediment sink can be largely determined by high-fertility source rocks exposed in rapidly eroding areas within the drainage. This implies that the detrital thermochronology record may reflect processes affecting relatively small parts of the orogenic system under consideration. A reliable approach to lag-time analysis would thus benefit from an independent provenance discrimination of dated mineral grains, which may allow to proficiently reconsider many previous interpretations of detrital thermochronology datasets in terms of orogenic-wide steady state. [ABSTRACT FROM AUTHOR]

The article focuses on the study using Detrital Zircon Geochronology conducted on sandstones from Kaishantun (KST) Formation and Kedao (KD) Group in Yanbian Area, to ascertain the final closure of the Paleo-Asian Ocean (PAO) in the eastern segment of Central Asian Orogenic Belt (CAOB) in North East China. Tables and Diagrams are presented to support the study.

This paper reports LA–ICP–MS U–Pb zircon ages and geochemical data from the Zhaobeishan Formation on the northern margin of the North China Craton (NCC). These data are used to better constrain the depositional age, provenance characteristics and tectonic evolution regarding particularly the final closure of the Paleo-Asian Ocean in the eastern segment of the Central Asian Orogenic Belt (CAOB). Major, trace, and rare earth element (REE) characteristics show that the Zhaobeishan Formation formed in an active continental margin environment. Clastic particles in the formation display varied provenance sources from basic to intermediate–acid arc igneous rocks. Twenty-two zircon rim analyses from a diopside granulite yield a weighted mean 206 Pb/ 238 U age of 245 ± 2 Ma (MSWD = 3.2), which represents the timing of metamorphism, whilst 45 concordant zircon core analyses yield apparent ages of 257–2592 Ma that fall into eight age populations. The depositional age of the Zhaobeishan Formation is constrained to be between 257 and 245 Ma, based on the youngest concordant 206 Pb/ 238 U age of the zircon cores and the metamorphic age of zircon rims. The provenance of the formation is dominated by Paleozoic magmatic arcs of the northern margin of the NCC, with material also derived from the interior of the NCC and the Songliao Block (SLB). Mixed detrital zircons from the NCC and SLB, which were separated by the Paleo-Asian Ocean, indicate a short distance between the NCC and SLB, and a narrow ocean at the time of sedimentation. The Paleo-Asian Ocean still existed in the eastern segment of the CAOB during the late Permian to Early Triassic, and the metamorphic age (ca. 245 Ma) of zircon rims in the diopside granulite sample may represent the timing of final closure of the Paleo-Asian Ocean. [ABSTRACT FROM AUTHOR]

The Archean stage of sedimentation has been first substantiated for the granulite-gneiss terranes of the Sharyzhalgai uplift (southwest of the Siberian craton). High-alumina paragneisses contain detrital zircons varying in age from 3.7 to 2.74 Ga and corresponding in REE patterns to magmatic zircons. The Paleoproterozoic (~ 1.86 Ga) metamorphic zircons are strongly depleted in HREE and Y as a result of their formation in equilibrium with garnet. Zircons with an age of ~ 2.5 Ga also show geochemical signs of alteration during metamorphism. The formation of terrigenous sedimentary rocks preceded the Neoarchean stage of magmatism (~ 2.7-2.6 Ga), and their metamorphism occurred at the Neoarchean-Paleoproterozoic boundary and in the Late Paleoproterozoic. The sources of detrital zircons were mainly Mesoarchean rocks, such as magmatic protoliths of granulites and intermediate-felsic magmatic rocks. The single Eoarchean and Paleoarchean detrital zircon grains in the paragneisses are the first direct evidence for the oldest crust (up to 3.7 Ga) in the granulite terranes of the Sharyzhalgai uplift. The set of geochronological data for granulites and paragneisses suggests the following sequence of geologic events for the granulite-gneiss terranes: ~ 3.7—the beginning of crustal formation, 3.4-3.2 Ga—intermediate-felsic magmatism, including the recycling of the more ancient crust, and ~ 3.0 Ga—coeval magmatic and metamorphic processes and differentiation of the continental crust. Thus, the whole cycle from the beginning of crustal growth to the crustal differentiation and turn into continental crust proceeded from 3.7 to 3.0 Ga. [ABSTRACT FROM AUTHOR]

Combined with the previous detrital zircons U-Pb ages of the two Precambrian successions, i.e. the Shilu Group and the Shihuiding Formation in Hainan Island of South China, the in situ Lu-Hf isotopes of detrital zircons were performed to evaluate the growth and reworking of Hainan Island continental crust during Precambrian. The results of 171 Hf-isotopic analyses on zircon grains from the Shihuiding Formation yield 176 Hf/ 177 Hf ratios between 0.280786 and 0.281188, 176 Lu/ 177 Hf ratios between 0.000228 and 0.003388, Hf model ages (T DM C ) between 3.8 Ga and 1.2 Ga, and ε Hf (t) values ranging from −12.5 to +10.6. The analyzed results of 272 Hf-isotopic data on zircon grains from the Shilu Group exhibit a wide range of 176 Hf/ 177 Hf ratios (0.280810–0.282512), 176 Lu/ 177 Hf ratios (0.000062–0.004060), T DM C ages (3.7 Ga–1.1 Ga), and ε Hf (t) values (−20.5 to +12.3). The continental crust of Hainan Island maybe appeared firstly at ca. 4.0–3.8 Ga and then was reworked. The 91.8% of detrital zircon grains from the Shihuiding Formation and 93.8% of the ones from the Shilu Group have crustal incubation time larger than 300 Ma, indicating an involvement of reworked materials into the sedimentation of both the successions. Unambiguously, the crustal basement rocks in Hainan Island were formed mainly through reworking the previous continental components with minor input of juvenile materials. The generation of juvenile curst in Hainan Island predominantly occurred at ca. 2.7 Ga and ca. 1.5–1.0 Ga, which are consistent with that for the assembly of the Kenorland, and the Columbia breakup and subsequent amalgamation of the Rodinia, respectively. The present study further reveals that the crustal growths in Hainan Island are present at 2.7 Ga, 2.3 Ga and 2.1–1.8 Ga, which is more favorable to the episodic growth mode. Moreover, a rough trend of decreasing maximum crustal incubation time of Hainan Island demonstrates that the incubation time of the juvenile crust is shorter when compared with that of the Cathaysia Block in the late Mesoproterozoic. Link to the previously reported geological works, we consider that Hainan Island did not share the same evolution history with the Cathaysia Block of South China during Precambrian. [ABSTRACT FROM AUTHOR]

We conducted several redeposition experiments in laboratory using natural and artificial sediments in order to investigate the role of grain size and lithology on sedimentary remanence acquisition. The role of grain size was investigated by using sorted sediment from natural turbidites. Taking advantage of the magnetic grain size distribution within turbidites, we compared redeposition experiments performed with coarse magnetic grains taken from the bottom layers of a turbidite with fine grains from the upper layers of the same turbidite. In order to document the magnetization acquired for increasing sediment concentrations that is analogous to increasing depth in the sediment column, the samples were frozen at temperatures between -5 and -10 °C. Magnetization acquisition behaved similarly in both situations, so that little smearing of the palaeomagnetic signal should be linked to grain size variability within this context. Other series of experiments were aimed at investigating the influence of lithology. We used clay or carbonated sediments that were combined with magnetic separates from basaltic rocks or with single-domain biogenic magnetite. The experiments revealed that the magnetization responded differently with clay and carbonates. Clay rapidly inhibited alignment of magnetic grains at low concentrations and, therefore, significant magnetization lock-in occurred despite large water contents, perhaps even within the bioturbated layer. Extension of the process over a deeper interval contributes to smear the geomagnetic signal and therefore to alter the palaeomagnetic record. In carbonates, the magnetization was acquired within a narrow window of 45-50 per cent sediment concentration, therefore, little smearing of the geomagnetic signal can be expected. Finally, experiments on carbonate sediments and biogenic magnetite with increasing field intensities indicate that magnetization acquisition is linear with respect to field intensity. Altogether, the results suggest that sediments with dominant carbonate content should be favoured for records of geomagnetic field changes provided that the minor clay fraction does not vary excessively. They confirmthe advantage of using cultures of magnetotactic bacteria for redeposition experiments. [ABSTRACT FROM AUTHOR]

The ∼800 km long Heihe River in northwestern China originates from the North Qilian Mountain, and passes through the Beishan Mountain before it reaches the Juyanhai Lake. Geologically, the river crosscuts the North Qilian Orogenic Belt, the Alax Terrane, and the Beishan Orogenic Belt. LA-ICP-MS U-Pb dating of detrital zircon from Heihe River sediments shows four age groups: 2700–1700 Ma, 1700–650 Ma, 650–358 Ma, and 358–230 Ma, and age peaks at ∼2450 Ma, ∼1850 Ma, ∼950 Ma, ∼520 Ma, 505 Ma, ∼480 Ma, ∼450 Ma, ∼430 Ma, ∼380 Ma, ∼320 Ma, and ∼295 Ma. The age distribution patterns indicate that Heihe River sediments were mainly sourced from the North Qilian Orogenic Belt. The detrital zircon ages demonstrate that the North Qilian Orogenic Belt may have Archean to late Paleoproterozoic rocks. Several tectonothermal events are also identified: opening of the North Qilian Ocean (part of the Paleo-Tethys Ocean) at early Neoproterozoic, subduction of oceanic lithosphere and formation of a trench-arc-basin system at late Neoproterozoic to late Ordovician, closure of the oceanic basin at late Ordovician, and collision of the Qaidam and Alax terranes at early Devonian. Our study indicates that the formation of the North Qilian Orogenic Belt was mainly related to the formation and closure of the Paleo-Tethys Ocean. [ABSTRACT FROM AUTHOR]

In this paper we report on Longgudong, an Early Pleistocene cave site in south China which was systematically excavated in 1999 and 2000, and where human teeth and associated stone artifacts were discovered within the same stratigraphic layer. The age of this site was estimated from faunal comparisons and palaeomagnetism and has been attributed to the Early Pleistocene, most probably the earlier Early Pleistocene. The human teeth from this site have been well studied. However, the stone artifacts are still unknown to most scholars. This paper thus presents an analysis of the lithics as the first firmly demonstrated stone tools associated with Early Pleistocene human fossils in south China. [ABSTRACT FROM AUTHOR]

This study uses detrital zircon U-Pb geochronology from shallow-water carbonates of the Bighorn Dolomite in Wyoming, USA, to provide robust evidence for long-distance eolian sediment transport during the Ordovician. The Bighorn Dolomite was deposited in a shallow-water carbonate platform that developed approximately 10° south of the Ordovician paleoequator on the western edge of Laurentia. The ages and textures of detrital zircons from the Bighorn indicate that the grains were transported by winds through saltation and suspension from the paleo east where rocks of the Paleoproterozoic Trans- Hudson orogenic belt were exposed in present-day Manitoba and Saskatchewan. Our interpretation of long-distance eolian transport is consistent with the paleogeography of Laurentia and expected prevailing wind directions and draws on modern analogs where Saharan sediment is transported by trade winds for distances of more than 3000 km. [ABSTRACT FROM AUTHOR]

Late Ordovician (Hirnantian) glacio-marine deposits in the Central and Eastern Taurides and Southeast Anatolian Autochthon Belt (SAAB) in Turkey are mainly composed of diamictites, subrounded granitic pebbles, and rounded/ subrounded lonestone pebbles.The granitic pebbles are dated as 576.5±3.3, 576.7±5.7, 598.4±7.5, 717.5±8.0, 789.5± 3.7, and 964.6±4.6 Ma. The geochemical signatures and dated granitic pebbles in the Central and Eastern Taurides are interpreted to have been derived from the Late Neoproterozoic granitoids/metagranitic rocks of the Arabian-Nubian Shield (ANS; the Sinai Peninsula and the Eastern Desert of Egypt). The youngest 206Pb/238U ages in the diamictites (499.1±4.2Ma in the SAAB, 530.5±5.3Ma in the Eastern Taurides, and 562.5±5.4Ma in the Central Taurides) and in the lonestones (528.2±4.5Ma in the Central Taurides, 530.8±5.2Ma in the Eastern Taurides) indicate that detrital zircons were directly transported mainly from the northern margin of Gondwana and/or Arabia during the Late Ordovician, not from peri-Gondwanan parts of the European margin. Kernel/probability density diagrams of zircon ages from the lonestone pebbles in the Eastern and Central Taurides are interpreted as evidence for their derivation from Late/Middle Cambrian siliciclastic rocks in the Israeli part of the Sinai Peninsula. The provenance of detrital zircon populations in the diamictites in the Central and Eastern Taurides is directly correlated with magmatic activity of the Elat (Taba)-Feiran island arc, the Sa'al island arc, and the postcollisionalmagmatic suites in the Sinai Peninsula (Egypt). However, the corresponding successions in the SAAB have more abundant Late Cryogenian age components, suggesting the Ha'il/Afif/Ad Dawadimi/Ar-Rayn terranes of the eastern Arabian Shield as their provenance. These distinctive age patterns indicate that glacio-marine successions in the SAAB had different paleogeographic positions than their equivalent units in theCentral and Eastern Taurides during deposition of the LateOrdovician glacio-marine units. [ABSTRACT FROM AUTHOR]

In the central Klamath Mountains, the Eastern Hayfork terrane (EHF) accreted directly seaward of the North Fork ophiolitic arc. The EHF trench mélange consists of very fine-grained, quartzose meta-argillite 1 boudinaged metachert layers as well as scattered blocks derived from both oceanic and inboard arc-margin sources. Among the exotic blocks are coarse-grained feldspathic metasandstones. Detrital zircon SHRIMP U-Pb ages ranging from the latest Archean to the early Proterozoic were reported by Scherer and colleagues in 2010 for five metasandstone blocks from the central and southern Klamaths; Phanerozoic zircons were totally lacking. It was concluded that the blocks were olistostromal and that erosion of a nearby thrust sheet outlier of the Proterozoic Antelope Mountain Quartzite of the Eastern Klamath belt, Yreka subterrane, was a likely source. To determine the provenance and time of deposition of the EHF muddy matrix host of the metasandstone blocks, we separated zircons from three very fine-grained, intimately interstratified, feldspar-poor meta-argillites from the Sawyers Bar map area. New laser ablation multicollector inductively coupled plasma mass spectrometry zircon U-Pb data indicate maximum sedimentary ages for the metaargillites as ~272, ~211, and ~201Ma. Thus, the muddy strata were deposited near the end of Triassic time. The metaargillites contain scattered Proterozoic and Paleozoic-early Mesozoic detrital zircons, indicating local inboard Klamath sources, including the Antelope Mountain Quartzite thrust sheet. St. Clair Creek distal turbidites in the landward North Fork terrane contain Paleozoic and Triassic-Early Jurassic (~188 Ma) zircons as well as scattered Precambrian grains similar to those in the EHF. The EHF surficially docked against the North Fork terrane by ~174- 173 Ma because the amalgamated but unmetamorphosed terrane contact was invaded by the English Peak plutonic complex beginning at ~172 Ma. Regional metamorphism and deformation took place throughout the central Klamath Mountains during the Siskiyou transpressive accretionary event at ~170-168 Ma. [ABSTRACT FROM AUTHOR]

New data on the U-Pb geochronology and Hf-isotopic composition of detrital zircons, along with the geochemistry of garnets, chromian spinel and feldspars from Permian and Triassic volcano-sedimentary sequences in the Southern and Eastern Alps reveal similarities in the nature and tectonomagmatic setting of the Early Permian and the Middle Triassic magmatic events. Detrital zircon U-Pb geochronology displays magmatic activity at 290-280 Ma (Early Permian) and at 245-235 Ma (Middle Triassic). The two-stage Hf-depleted mantle model ages obtained from Permian and Triassic zircons cluster around 1.7-1.6 and 1.3-0.8 Ga. Epsilon Hafnium analysis on dated detrital zircons suggests mixing of mantle and crustal components into the parental magmas of Permian and Triassic magmatism, the latter showing less crustal contribution. The composition of detrital feldspars from the Permian and Triassic volcaniclastic sandstones reveals provenance from intermediate to acidic igneous rocks. Garnet in Middle and Late Triassic beds suggests the incorporation of material comparable to the mafic rocks of the Ivrea-Verbano Zone into the parental melts of the Triassic magmatism. Chromian spinel in syn-magmatic Carnian sandstones indicates an origin associated with MORB-type peridotites and therefore, corroborates a mantle contribution to the Middle Triassic magmatism. The integration of detrital zircon U-Pb ages, Hf isotopes and composition of detrital minerals suggests that continuous lithospheric stretching at the transition from the post-Variscan to the Alpine orogenic cycle, with periods of strike-slip movements, presumably led to an asymmetrical continental rifting process, in which the Middle Triassic magmatic episode represents the earliest stage of the Alpine Tethys oceanic domain. [ABSTRACT FROM AUTHOR]

Zircon/bulk rock REE partition coefficients from natural samples correlate with REE concentration in zircon. The correlation is the strongest for the LREE and diminishes with decreasing ionic radius. The relationship between partition coefficient and REE concentration in zircon can be modeled as a power law and the coefficient (α) and exponent (β) terms for each of the REE are empirically determined using new and previously published data. A series of independent tests show that using variable partition coefficients based on the reported α and β terms commonly results in more accurate estimates of bulk rock REE concentrations than average partition coefficients, particularly for the LREE that have previously been difficult to constrain. These results provide a way to account for highly variable REE concentrations in zircon, which may be controlled by numerous processes such as surface enrichment, complex substitution mechanisms, or accidental sampling of sub-microscopic inclusions. The proposed method for estimating bulk rock REE concentrations is especially well-suited to detrital zircon investigations where there is no information available on the parent rock composition. [ABSTRACT FROM AUTHOR]

U–Pb ages of detrital zircons from the Wedington Sandstone member in northwest Arkansas provide evidence for Late Mississippian westward transcontinental sediment transport from the Appalachian foreland. The Late Mississippian Wedington Sandstone member of the Fayetteville Shale is a fine- to medium-grained quartzarenite. It separates the Fayetteville Shale into informal lower and upper intervals, and was deposited as a small constructive delta complex that prograded towards the south and southeast during the Late Mississippian. As a major influx of clastic sediments, the Wedington Sandstone member records the sediment source and dispersal in the mid-continent during the Late Mississippian. A total of 559 detrital zircon grains from six Wedington samples were recovered for U–Pb detrital zircon geochronological analysis. Results show that age distributions can be subdivided into six groups: ~350–500, ~900–1350, ~1360–1500, ~1600–1800, ~1800–2300, and > ~2500 Ma, and are characterized by a prominent peak for the age group of ~900–1350 Ma, a major peak at ~1600–1800 Ma, and a few other minor age clusters. Regional correlation and geological evidence from surrounding areas suggest that the transcontinental sediment dispersal started as early as the Late Mississippian. U–Pb detrital zircon age distribution suggests that the Wedington Sandstone member was likely derived from the Appalachian foreland with contributions from the Nemaha Ridge to the west where the Yavapai–Mazatzal sources were exposed during the Late Mississippian. Sediment was likely transported westward through or around the Illinois Basin, merged with mid-continent sediment, and then entered into its current location in northwest Arkansas. Transportation of this sediment from mixed sources continued along its course to the south, forming a delta on the Northern Arkansas Structural Platform. [ABSTRACT FROM PUBLISHER]

The lesser and greater Himalayan sequences ( LH and GH) in Sikkim have been studied in detail recently. The LH consists mainly of pelitic lithologies with detrital zircon ages >1800 Ma and εNd(0) of −27.7 to −23.4 (with intercalated calcsilicates, metabasites and a sheared granite gneiss - the Lingtse gneiss). The metamorphic sequence is characterized by (i) a remarkably continuous and systematic metamorphic field gradient (~60-70 °C kbar−1), (ii) peak pressures as well as temperatures of metamorphism increasing at higher metamorphic grades (~5 kbar, 500 °C at the garnet zone to ~8 kbar, 700 °C at the sillimanite-muscovite-zone), (iii) clockwise P- T paths of a tight 'hairpin' shape with a prograde slope of 20-30°C kbar−1, (iv) initiation of garnet growth (Lu-Hf chronometry) at systematically older ages at higher grades (11-10.5 Ma at garnet zone to 16.8 Ma at sillimanite-K-feldspar zone), (v) peak of metamorphism simultaneously at all grades (13-11 Ma), (vi) deformed and folded metapelitic rocks but with little evidence of pervasive shearing and (vii) duration of melt formation and segregation on the order of a few 100,000 years. The degree of melting was low, as indicated by the presence of muscovite all through the sequence. This evidence indicates that the LH behaved as a coherent block, and thermomechanical models quantitatively reproduce many of these features as well as explain the formation of inverted metamorphic sequence in such a coherent block. The greater Himalayan sequence ( GH), also largely metapelitic, has different protoliths (with components as young as 800 Ma) and a different metamorphic history (extensive migmatization at higher grades ~8-12 kbar, 750-850 °C at an older age of largely >20 Ma along a different clockwise P- T path characterized by sharp, isothermal decompression followed by near isobaric cooling). Geochronological data (monazite, zircon, garnet) as well as cooling rate calculations (geospeedometry) reveal that the GH is made up of at least two blocks with distinct, complex and multistage P- T- t histories. Different stages of the high- T cooling were rapid (100's °C Ma−1 to 10's °C Ma−1 at different stages) and at least some of it was unrelated to exhumation; synthesis of these results with low- T thermochronometry allows the detailed multistage cooling and exhumation history of this block to be reconstructed. The reconstructed cooling and exhumation histories show that a number of interlinked processes operating on a hierarchy of timescales leads to the overall evolution. The P- T history with rapid cooling can be reproduced by thermomechanical models that consider conductive as well as advective heat transport and there is no need to invoke additional processes (such as the role of fluids). Metabasic inclusions within both the LH and the GH appear to record a different (? older in part) history. The role of these in the overall evolution, as well as the difference in metamorphic ages of the LH and GH remain open questions that need to be addressed in future research. [ABSTRACT FROM AUTHOR]

The Ignacio Quartzite—exposed in the San Juan Mountains of southwestern Colorado—is composed of red and brown arkose and subarkose sandstones and minor interbedded shales. The formation is newly divided here into the Tamarron Member (0–24 m) and the overlying Spud Hill Member (0–21 m). The Spud Hill Member has a greater abundance of sandstones with shale clasts, weakly fissile shale beds, and trace fossils than the Tamarron Member. The McCracken Sandstone Member of the Elbert Formation, which overlies the Ignacio, is chiefly white and off-white quartz-cemented quartzarenites. The McCracken is divided for the first time into the Mill Creek facies (0–12 m) to the south of Coal Bank Pass and the Sultan Creek facies (0–36 m) to the north of the pass. The Sultan Creek facies contains dolostone-sandstone parasequence tidal-flat cycles up to 70 cm thick with a composite thickness of 14 m. Eastward transgression across the western edge of the Transcontinental Arch permitted the accumulation of fluvial deposits of the lower Tamarron Member in the deepest channels incised into the craton. As sea level continued to rise, fluvial channels evolved into estuaries dominated by sandy tidal flats (upper Tamarron Member, Mill Creek facies, and Sultan Creek facies) and mixed sand and mud tidal flats (Spud Hill Member). Sandstone composition and ages of detrital zircons indicate that sand grains were derived from a complex terrain that included granitoid plutonic rocks (~0.46 to >2.4 Ga), metamorphic rocks, and well-rounded quartz sand from eolian ergs. The area between the present Coal Bank and Molas passes was a boundary between a northern fluvial source with an abundance of superbly rounded quartz grains of eolian erg origin from a southern fluvial source with few such grains, but large amounts of K-feldspar. The Ignacio and McCracken units are, at least in part, coeval and of Late Devonian age as shown by the stratigraphic distribution of rocks resting on the basement, the presence of an Ordovician zircon in the Ignacio, and the presence in the same Ignacio sample of oboloid brachiopods of questionably late Cambrian age with well-dated Late Devonian placoderm fish plates. [ABSTRACT FROM AUTHOR]

Regionally traceable paleosols in the lower Moodies Group of the Barberton greenstone belt (ca. 3.22 Ga, northeastern South Africa and Swaziland) contain locally abundant silicified nodules, originally composed of pedogenic carbonates and sulfates, interbedded with heavy-mineral laminae dominated by pyrite. Pyrite grains show rounded detrital cores and secondary idiomorphic rims with trace element concentrations and d34S ratios clearly different from those of the cores. While cores have low Co and Ni concentrations and high Co/Ni ratios, rims show as much as 5.5 wt% of these elements and low Co/Ni ratios, reflecting the weathering of nearby ultramafic rocks. In-situ sulfur isotope analyses of pyrite cores show d34SVCDT (Vienna Canyon Diablo troilite) values between +5‰ and -5‰, while the rims show d34SVCDT values between -20‰ and -24.5‰, suggesting biogenic fractionation of sulfur. The close spatial association and microtextural evidence for nearly contemporaneous formation of the pedogenic sulfate nodules and the secondary pyrite rims suggests microbial processing of sulfur in the paleosols, which provided reduced and 34S-depleted sulfur for the growth of authigenic pyrite. This indicates that vadose-zone soil-forming processes in the Archean involved not only physical and chemical modification of moist, unconsolidated sediment in a terrestrial environment but also already included its microbiological modification. [ABSTRACT FROM AUTHOR]

Liverpool Land, at the southern tip of the Greenland Caledonides, exposes a composite metamorphic terrane: the midcrustal granulite-facies Jaettedal Complex tectonically juxtaposed against the eclogite-facies, peridotite-bearing Tvaerdal Complex. The Jaettedal Complex is a Laurentian terrane, whereas the Tvaerdal Complex was proposed by earlier investigators to be a Baltic terrane. PT estimates (880°–920°C at 35–40 kbar) and Sm-Nd mineral isochrons from Tvaerdal eclogites indicate that recrystallization occurred under ultrahigh-pressure (UHP) metamorphic conditions ≈400 m.yr. ago, the same time and under similar conditions as the Western Gneiss Complex of the Norwegian Caledonides. Detrital zircons from the Tvaerdal Complex, analyzed for U-Pb, Lu-Hf, and trace elements by laser ablation inductively coupled plasma mass spectrometry, give concordant Mesoproterozoic ages but not the Archean and ≈1.8 Ga Proterozoic ages characteristic of Laurentian terranes. Most remaining concordant U-Pb ages are 411–375 Ma (i.e., Scandian), which contrast with older (≈460–410 Ma) zircon ages from the Jaettedal Complex as well as other Laurentian terranes. Both the Precambrian and the Scandian age sets confirm the Tvaerdal Complex as an orphaned Baltic terrane. The Jaettedal Complex underwent a lengthy Caledonian history as part of a continental arc system during the closure of Iapetus, whereas the Tvaerdal Complex was a fragment of the approaching Baltic passive margin. UHP metamorphism occurred when this margin subducted into the mantle beneath Laurentia. We propose that the Tvaerdal Complex separated from Baltica and rose through the hot mantle wedge to the base of the overriding Laurentian crust by diapirism, a process that may explain its abundant anatectic granitoid intrusions. [ABSTRACT FROM AUTHOR]

We have conducted the first geochronological study of the ultramafic–mafic succession (the Waterberg Project) located in the Southern Marginal Zone of the Limpopo Belt north of the Northern Lobe of the Bushveld Complex using U/Pb dating on zircons extracted from both mineralized reefs as well as on detrital zircons of the Waterberg Group unconformably overlying the mafics. This contribution is the first in a series of publications describing the well-mineralized succession and will therefore give an overview of the local geology. U/Pb baddeleyite ages for the main mafic sill intruding the area supplement the data. The succession is extremely well mineralized and therefore of interest to the wider geological community. The intrusion ages for the Lobe are 2059 ± 3 and 2053 ± 5 Ma and within error coeval with the intrusion ages of the Bushveld Complex. Detrital zircon age probability density distributions indicate a maximum age of deposition of c. 2045 Ma for the Waterberg Group and show abundant peaks of Archean age. Paleoproterozoic zircons are interpreted to represent zircon from the detritus of the now eroded roof rocks of the lobe, while the Archean zircons are most likely sourced from the Limpopo Complex to the northeast. The major dolerite sill intruding the project area has been confirmed to belong the Umkondo Igneous Province with a baddeleyite age of 1125 ± 5 Ma. The combination of these new age dates, local geology and existing literature is used to argue that (i) the ultramafic–mafic succession is related to the Bushveld Complex; (ii) a significant unconformity is present between igneous rocks and the overlying sediments, and (iii) the area was exposed to a level of Paleoproterozoic tectonism not previously observed in the Bushveld Complex. [ABSTRACT FROM AUTHOR]

The catalytic performance of some Ni Ce/Al 2 O 3 catalytic systems (11 wt.% Ni and 3 wt.% Ce) were checked after being submitted to different calcination and reduction treatments. It was found that, the reduced Ni Ce/Al 2 O 3 catalysts were more active and stable in the dry reforming reaction of methane than the corresponding not-reduced catalysts. This high activity was initially connected with the smaller size of pre-reduced Ni species, which at the same time leads on to the formation of filamentous carbon. The best overall performance was obtained for the reduced catalyst after being calcined at 1000 °C. This catalyst presents a very high stability, a low level of carbon formation, maintaining the nickel particle size constant during reaction. Surprisingly, although its reduction degree is only 12% at 750 °C, its catalytic activity is similar to the full reduced catalysts. So, the small number of reduced metallic particles of this catalyst shows a very high activity, much higher than the other catalysts. [ABSTRACT FROM AUTHOR]