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The Devonian position of the South China Block (SCB) remains debated because apparently contradictory Devonian paleopoles have been documented. Here we report two characteristic remanent magnetization components from the mildly deformed Guanyang Devonian successions (Lochkovian-Famennian) within the cratonic interior of the SCB. Both components pass reversal tests and occur in different samples across the successions. Component A and associated paleopole DA (228.9°E, 37.7°N, A95 = 3.7°) are comparable with published Devonian data and were likely acquired before Permian-Triassic folding and likely reflect syn-depositional magnetization. Component B and its associated paleopole DB (204.6°E, 4.5°N, A95 = 5.5°) are distinct from published results and were probably acquired during minor tilting associated with the Late Devonian Liujiang orogeny. If paleopole DA was acquired prior to the Late Devonian Liujiang orogeny, the paleolatitude of the Guanyang successions varied little throughout the Devonian, but the azimuthal orientation of recorded declinations exhibits a 40° difference. The distinct positions of the two paleopoles are broadly consistent with existing enigmatic Devonian field records. Alternatively, given the uncertainty in the acquisition ages of both components in the Guanyang successions, a case can be made for component A being a secondary magnetization acquired during the Permian-Triassic Indosinian orogeny. Nonetheless, the similar distribution of Devonian paleopoles from Gondwana to those of cratonic interior of the SCB suggests a Devonian connection between the two continents, and adds further support for a non-uniformitarian geomagnetic field during this enigmatic time interval.

The NE China region involves a complex accretionary belt formed by multiple stages of assembly of micro-blocks from the Paleozoic to Mesozoic, the tectonics of which provides important clues on the evolution of the East Asian continental margin. With a view to evaluating the micro-block evolution in NE China, we used gravity and magnetic methods to analyze the geophysical characteristics of the micro-blocks and their boundaries. Combining with regional geology, paleomagnetism and paleontology, we reconstructed the micro-block assembly history in the eastern Central Asian Orogenic Belt. Five Paleozoic to Mesozoic micro-blocks are recognized in NE China: the Erguna, Xing'an, Songnen, Jiamusi and Nadanhada, and their boundaries show significant differences in gravity and magnetic fields. The boundary between the Erguna Block (EB) and the Xing'an Block (XB) shows as a continuous tectonic line in the gravity field, whereas the one between the XB and the Songnen Block (SB) exhibits a rather discrete but strong magnetic anomaly belt. The boundary between the SB and the Jiamusi Block (JB) is characterized by both distinct gravity and magnetic anomalies. The Nadanhada Micro-block (NMB) appears as an independent micro-block in the fourth-order detail field of the Bouguer gravity anomaly, where it shows as a short axis or circinate structure in this anomaly field. The Paleozoic to Mesozoic tectonic evolution of these micro-blocks in NE China is closely related to five sutures in the eastern Central Asian Orogenic Belt. The Xinlin-Xiguitu Suture was first formed at ~500 Ma, leading to the assembly of the EB and the XB, the Heihe-Hegenshan Suture was formed at 320–290 Ma, marking the amalgamation of the XB and the SB, the Mudanjiang-Yilan Suture was formed at ~200 Ma, marking the collision of the JB and the SB. The Paleo-Asian Ocean closed during 250–230 Ma in a scissor style. The subduction of the Paleo-Pacific Ocean was initiated at ~200 Ma. Based on the deep structural architecture imaged from gravity and magnetic anomalies, we propose an evolutionary model of the micro-blocks in the NE China, which provides important insights into the tectonic evolution of the NE China region during the Paleozoic to Mesozoic.

The process and mechanism of deformation in the northeastern Tibetan Plateau (NETP) are significant for understanding the remote effects of the India-Eurasia collision. Although increasingly more research has extensively addressed the post-Oligocene NETP growth history over the past two decades, geological dating of early Cenozoic sediments remains sparse, hampering our understanding of early-stage tectonic growth in this region. Here, we present magnetostratigraphic results from the oldest sedimentary record between ~54 and 40 Ma in the western part of the Linxia Basin based on correlation with the geomagnetic polarity time scale. This age exceeds that of the oldest strata previously known (29 Ma) and has great potential for recording paleoclimatic and paleontological evolution in the fossil-rich Linxia Basin. Integrating our paleomagnetic chronology, sedimentary facies, accumulation rate, and provenance results reveals that early-stage Linxia Basin development was associated with Eocene growth of the West Qinling. The U-Pb age distributions of detrital grains from pre-51 Ma strata are characterized by many 200–300 Ma ages; alluvial fans and north-directed paleocurrent data indicate a single and relatively proximal source. The northern segment of the West Qinling was the predominant source supplying sediments to the Linxia Basin before ~51 Ma. Subsequently, a pronounced increase in the sedimentation rate at ~51 Ma and southward migration of the sedimentary system during 51–47.8 Ma demonstrate that extension and fast exhumation of the sediment source occurred. Detrital zircon U-Pb age spectra since ~51 Ma reveal significant increases in Precambrian peaks (1500–2000 Ma and 2300–2600 Ma). These observations suggest accelerated growth of the southern segment of the West Qinling and/or eastern segment of the East Kunlun Shan between 51 and 47.8 Ma. The Eocene basin evolution and accelerated uplift of ranges in the NETP imply near-synchronicity of crustal shortening and deformation across the entire India-Eurasia collision zone.

In this study, we offer significant improvement over previous results that identified the Matuyama-Brunhes magnetic reversal in cave sediments from the Czech Republic in Central Europe. We collected discrete samples from the sedimentary profile in Za Hajovnou cave located in the eastern part of the Czech Republic. The rock magnetism measurements indicated that the magnetic carrier of most of the samples is maghemite. Characteristic remanent magnetization (ChRM) directions and related virtual geomagnetic pole (VGP) paths indicated that the Matuyama-Brunhes transition boundary was within 5.7 cm of the sediment, located in the upper part of the sampled sedimentary section. This result showed a new, more detailed behavior of the polarity transition from that of the central European location. The migration of the paleopole between eastern Africa and western North America was established as a significant marker for the central European paleomagnetic record in terms of global magnetic data. The transition duration was 8.1 ± 0.2 kyr, and the precursor of the reversal occurred 4 ± 0.2 kyr before the transition. In addition, we estimated the sedimentation rate of the studied section (~35 cm) in the cave as 0.7 ± 0.2 cm/kyr.

The Central China Orogenic Belt (CCOB) comprises, from the east to the west, the Tongbai-Dabie, Qinling, Qilian and Kunlun Orogens, and preserves abundant and important amalgamation records of the North China, South China, Qaidam, Tarim and Qiangtang Blocks. The CCOB offers an excellent window to the tectonic evolution from Proto-Tethys to Paleo-Tethys domains and the formation of East Asian continent. In this Centennial Review of Gondwana Research, we assemble comprehensive and multidisciplinary information of geological, geochemical, geophysical and high-precision geochronological dataset from individual orogens of the CCOB, together with a synthesis of Paleomagnetic data, to gain insights on the tectonic framework and evolutionary history of CCOB. The detailed and highly-integrated analysis leads to the following major conclusions. (1) Prior to ca. 550 Ma, break-up of the Rodinia supercontinent led to the formation of Proto-Tethys Ocean, wherein the above crustal blocks were isolated discrete units. (2) During ca. 541–485 Ma, spreading of all the embranchments of the Proto-Tethys Ocean at the early stage and the onset of subduction at the late stage. (3) Up to ca. 485–444 Ma, continued subduction of the Proto-Tethys Oceans resulted in opening and closing of the back-arc basin in the Qinling area. (4) During ca. 444–420 Ma, the Proto-Tethys Oceans along the Qilian and Shangdan were closing. (5) During ca. 420–300 Ma, the Paleo-Tethys Ocean in the Kunlun area inherited the Proto-Tethys Ocean, while the Paleo-Tethyan Mianlue Ocean experienced spreading. (6) At ca. 300–250 Ma, subduction retreat of the Kunlun Ocean occurred from the Aqikekulehu-Kunzhong suture to the Muztagh-Buqingshan-Anemaqen suture. (7) The Paleo-Tethys Ocean underwent eastward diachronous closing processes throughout the Kunlun to Qinling and Dabie areas during ca. 250–200 Ma; (8) The entire CCOB range has evolved into intracontinental deformation since 200 Ma.

Although alluvial fans are widely distributed along the western margin of the Junggar basin, NW China, uncertainties in their formation age and associated environment need to be resolved. In a well-developed alluvial fan in the upper reaches of the Baiyang River, a 137 m-deep hydrogeological drilling core (ZK1) has been extracted. Paleomagnetic analysis shows that this section has been deposited since 8 Ma, during three distinct phases: (1) a lower segment of muddy facies formed during 8–5.6 Ma; (2) a middle segment of alternating muddy and sandy and gravel layers formed during 5.6–3.6 Ma, and (3) the upper layer of gray conglomerate formed from 3.6 Ma to present. The fan began to develop at ~5.6 Ma, perhaps driven by the Mediterranean Messinian salinity crisis originally. At 3.6 Ma, the deposition rate increased significantly and the climate further dried and cooled, likely due to the uplift of the Qinghai-Tibet Plateau and its far-field structural and environmental impacts. However, the direct causes of the two events recorded in this section are related to the rapid uplift of Wuerkashier Mt., and to regional and global climate cooling.

The nearly 2000 m-thick Ikakern Formation is the basal sedimentary unit in the Argana basin of Morocco, consisting of fluvial red and purple conglomerates in the lower part and interbedded red conglomerates, sandstones, siltstones and mudstones in the upper part. It unconformably overlies deformed and metamorphosed Variscan basement rocks and is unconformably overlain by the finer grained lacustrine to fluvial sediments of the?Early to Late Triassic Timesgadiouine Formation. Vertebrate fossil and chronostratigraphic constraints indicate a post-Kiaman, Late Permian age for at least the sampled upper member (t2) of the Ikakern Formation. A stable, high unblocking temperature dual polarity characteristic magnetization that passes a local fold test gives a paleomagnetic pole for 14 sites at 48.8°N 246.3°E A95 = 7.2° after correction for inclination flattening and indicates a paleolatitude of 14°N for the nominal sampling location at 30.75°N 9.10°W. The Ikakern pole agrees well with poles of similar age deemed reliable in a recent assessment of published data from South America, Africa, Adria, and Australia, which together (N = 7) provide a mean Gondwana pole for an age bin centered on 260 Ma at 52.2°N 239.8°E A95 = 5.0° (NW Africa coordinates). In conjunction with a robust mean 260 Ma pole form Laurasia, these results confirm a Pangea A configuration for the Late Permian. This is in contrast to some recently published interpretations of paleomagnetic data from the Gondwanides of South America that would prolong the existence of a Pangea B configuration from the Late Carboniferous-Early Permian through the Late Permian but which instead probably reflect effects of remagnetization or local rotation.

We present results of rock and paleomagnetic magnetic analyses of a ~671 m-thick continuous vertical drill core (KZF-1) that intersect the lower Ecca Group (early-mid Permian) of the southwestern Karoo Basin, South Africa. Rock magnetic and optic microscopy experiments indicate monoclinic pyrrhotite and single-domain magnetite in the mudstones, shales, and siltstones as carriers of characteristic remanent magnetization (ChRM), which is likely a post-detrital remanent magnetization. Stepwise demagnetization and removal of low-coercivity and thermally less stable magnetizations reveal the preservation of a dual polarity ChRM in 90 samples. These are used to construct a magnetostratigraphic profile for the core that is dominantly reversed polarity with four short normal polarity subchrons. Correlation with published U Pb SHRIMP and CA TIMS ages and the proposed composite reference section for the Early Permian allows us to propose an Artinskian (281 Ma) to Kungurian (276 Ma) age for the lower Ecca Group rocks. Our magnetostratigraphic profile can be tied in with published profiles from the mid to Upper Ecca Group to produce the first composite profile that spans all of the Ecca Group in the southwestern region of the Karoo Basin.

Although central to an understanding of Earth's paleogeography and the myriad processes that it affects, the geometry of Pangea during the early phase of its lifetime has remained a topic of contention since the plate tectonic revolution. Despite decades of analysis and discussion, the crux of this debate still largely hinges on sparse, legacy paleomagnetic data derived from early Permian rocks of the Moroccan Meseta. In this work, we present the results of a study designed to revisit, update and expand on those key data, with the provision of new geochronologic and paleomagnetic results from six Permo-Carboniferous basins in central Morocco. New U-Pb zircon ages from volcanic rocks substantiate and refine existing geochronological data and reveal that volcanism among the studied basins spanned approximately 30 Ma, from at least 305 to 277 Ma, but was possibly punctuated by a more intense pulse in the mid-early Permian (~285 Ma). These new U-Pb data furthermore suggest that the age estimates previously assigned to the key poles from the Moroccan Meseta are probably too young, by some ~10 Ma. New paleomagnetic results from six basins yielded a common, well-defined remanent magnetization from 20 sites that is demonstrated to be pre-middle Permian in age. However, it remains unclear whether this magnetization (which is directionally similar to the previous paleomagnetic data from the same basins) is a primary magnetization acquired at ~285 Ma, or a syn-folding remagnetization that was acquired shortly thereafter, at ~275 Ma. In adopting both interpretations as alternative hypotheses, we examine the corresponding paleogeographic implications of both. Through exhaustive comparisons with reference apparent polar wander paths and the direct reconstruction of Gondwana using these new paleomagnetic results, we demonstrate that in either case (i.e. whether the remanent magnetization is primary or was acquired soon after during folding) the data is compatible with a Pangea A geometry during the early Permian. We close with a topical discussion of some persisting arguments used to defend Pangea B and why we consider them to be flawed.

A latest Permian timeline (251.9 Ma) can be constructed from the perspectives of: a global nickel spike attributed to emissions from the coeval Siberian flood-basalt eruptions, the correlative end-Permian marine mass extinction (EPME), a transition from reversed to normal paleomagnetism, and a negative anomaly in δ13Ccarb and δ13Corg. In a number of marine and non-marine localities, this timeline is also correlated (to within ≤30 ky) with palynological evidence for the latest Permian destruction of terrestrial vegetation and the accompanying short-lived global fungal (Reduviasporonites) event. This correlation suggests that devastation in marine and non-marine environments was essentially coeval at a time marked by hyperthermal conditions and anoxic oceans. We utilized this proposed timeline to estimate the relative timing of the extinction of latest Permian vertebrates in the Karoo Basin of South Africa. In several sections in the Karoo, the LAD of the therapsid Dicynodon, is correlated with the proposed timeline. In the Carlton Heights section in the Karoo we estimate that the palynological changes and the fungal event occurred within ≤30 ky of the LAD of Dicynodon. Further sampling in the Karoo and other Permian–Triassic non-marine basins would help to clarify the relative timing of the global marine extinctions, plant devastation and the disappearance of non-marine vertebrates.

A high-resolution, multiproxy analysis of a core from Tokotan Lake, Urup Island, illustrates the complex paleoenvironmental signals that can be preserved in sedimentary deposits from geologically active areas, such as the Kuril Archipelago. Diatom and geochemical analyses of the Tokotan core suggest a shallowing and lessening of the lake area over the last ∼3450 cal BP. Without other proxies, the record could be interpreted as showing a general decrease in precipitation over the Late Holocene. However, palynological data indicate no change in vegetation, thereby implying no significant climatic variation. Neither of these paleoclimatic interpretations agrees with Late Holocene reconstructions from the Kuril Archipelago or the Russian mainland. Paleomagnetic data imply variable sediment sources during the lake's history, indicating alterations within the Tokotan catchment (e.g., shifts in gradients or sediment loads in the inflowing streams). Such changes would be particularly important in the Shabalina River, which today has formed a partial dam across the lake's outlet. The results of the Tokotan study indicate that other factors (e.g., volcanism, seismic activity, sea-level changes) rather than climate were more probable determinants of the Late Holocene lake record. Given the geologic dynamism of the region, it is perhaps not surprising that paleo-records from the Kuril Islands display an inconsistency in the numbers and/or duration of proposed Holocene climatic oscillations, underscoring the importance of multiproxy investigations in areas that are or have been geologically dynamic.

The basins and orogens of the Mediterranean region ultimately result from the opening of oceans during the early break-up of Pangea since the Triassic, and their subsequent destruction by subduction accommodating convergence between the African and Eurasian Plates since the Jurassic. The region has been the cradle for the development of geodynamic concepts that link crustal evolution to continental break-up, oceanic and continental subduction, and mantle dynamics in general. The development of such concepts requires a first-order understanding of the kinematic evolution of the region for which a multitude of reconstructions have previously been proposed. In this paper, we use advances made in kinematic restoration software in the last decade with a systematic reconstruction protocol for developing a more quantitative restoration of the Mediterranean region for the last 240 million years. This restoration is constructed for the first time with the GPlates plate reconstruction software and uses a systematic reconstruction protocol that limits input data to marine magnetic anomaly reconstructions of ocean basins, structural geological constraints quantifying timing, direction, and magnitude of tectonic motion, and tests and iterations against paleomagnetic data. This approach leads to a reconstruction that is reproducible, and updatable with future constraints. We first review constraints on the opening history of the Atlantic (and Red Sea) oceans and the Bay of Biscay. We then provide a comprehensive overview of the architecture of the Mediterranean orogens, from the Pyrenees and Betic-Rif orogen in the west to the Caucasus in the east and identify structural geological constraints on tectonic motions. We subsequently analyze a newly constructed database of some 2300 published paleomagnetic sites from the Mediterranean region and test the reconstruction against these constraints. We provide the reconstruction in the form of 12 maps being snapshots from 240 to 0 Ma, outline the main features in each time-slice, and identify differences from previous reconstructions, which are discussed in the final section., Gondwana Research, 81, ISSN:1342-937X, ISSN:1878-0571

The late Cenozoic sediments in the rift basins in the northern Himalaya Mountains document important information about the uplift and deformation of the most active tectonic region in the Tibetan Plateau. However, these sediments have not been precisely dated, hindering our ability to address the basin development and termination associated with a series of uplifts in the southern Tibetan Plateau. Here, we report a detailed magnetostratigraphic study on the fluvio - lacustrine sedimentary sequence of the Dati Formation bearing abundant Hipparion forstenae fossils in the Dati Basin in the northern frontal region of the Himalaya Mountains. The 195 m – thick section yielded six normal and seven reversed polarity zones that correlate well with Chrons C3An.1r to C4r.2r of the geomagnetic polarity time scale, constraining the section age to ~8.6 – ~6.2 Ma. Together with the magnetostratigraphic results from other rift basins in the region, these results indicate that the horizons bearing the Hipparion fossils were deposited during the age interval of 7.1–6.5 Ma in the northern Himalaya Mountains. The regional tectonic activity and comprehensive magnetostratigraphic and sedimentologic comparisons suggest that the evolution of the rift basins in the northern Himalaya Mountains has involved three major stages since the late Cenozoic, i.e., (1) ~10.0–8.0 Ma, onset of the basins with fan delta facies; (2) ~8.0–3.0 Ma, expansion of the basins with mainly lacustrine facies; (3) ~3.0–1.7 Ma, shrinking and termination of the basins with alluvial fans. The basin evolutionary history indicates an accelerated tectonic uplift of the Himalaya Mountains at ~10.0 Ma, and two deformational events at ~3.0 Ma and at ~1.7 Ma.

Ophiolites, fragments of oceanic lithosphere exposed on land, are typically found as isolated klippen in intensely deformed fold-thrust belts spanning hundreds to thousands of kilometers along-strike. Ophiolites whose geochemistry indicates that they formed above subduction zones, may have been relics of larger, once-coherent, oceanic lithosphere tracts that formed the leading edge of an upper plate below which subduction occurred; such tracts were subsequently dismembered by deformation and erosion during orogenesis and uplift. However, to what extent the first-order original coherence is maintained between ophiolitic klippen is difficult to assess. Here, we aim to evaluate whether the Jurassic forearc ophiolites overlying subduction complex rocks in California, now scattered over 1000 km and dismembered by the wider San Andreas Fault Zone, still maintain their original lithospheric coherence. To this end we (i) compile available crustal ages from all ophiolite klippen exposed in the Jurassic ophiolite belt of the western United States; (ii) review and kinematically reconstruct post-middle Jurassic deformation that occurred between the modern western coast and the stable North American craton to restore the original positions of the ophiolite fragments relative to each other and to North America, and (iii) perform a paleomagnetic analysis of a sheeted dyke sections of the Mt. Diablo and Josephine ophiolites to estimate the orientation of the spreading axis at which the Jurassic Californian forearc ophiolites formed. The latter analysis reveals that the original ridge orientation likely trended ∼080–260°, near-perpendicular to the orientation of the trench along the western margin of the ophiolite belt. We show that with these constraints, a straightforward ridge-transform system can explain the age distributions of the ophiolites with spreading rates of 6–7 cm/a. Our analysis shows that the Jurassic ophiolites of California may be considered klippen of a single sheet of oceanic lithosphere that accreted at a supra-subduction zone spreading ridge. In addition, we show that kinematic and paleomagnetic analysis of ophiolite belts may provide novel constraints on the kinematic evolution of accretionary orogens and the plates now lost to subduction.

Meso– to Neoproterozoic geological and paleomagnetic data support a direct connection between Baltica and Laurentia in both Nuna and Rodinia supercontinents, however in different relative configurations. Previous paleomagnetic data limit the time of break-up of Nuna core configuration and ca. 90° rotation of Baltica relative to Laurentia between 1.27 Ga and 0.99 Ga. Despite the well documented relative motion of continents, the tectonic mode during the Meso– to Neoproterozoic has been questioned and the operation of single lid tectonics at 1.6–1.0 Ga during the Nuna-Rodinia supercontinent cycles has been proposed. In this study, new paleomagnetic and whole rock 40Ar-39Ar geochronological data from a basic dyke in Stugun central Sweden are combined with coeval data to produce a 1.22 Ga (1.244–1.200 Ga) moderate-quality paleomagnetic pole. This is done to better estimate the break-up time of the core of Nuna and explore the plate tectonics at the Mesoproterozoic. The new pole fills part of the 1.247–1.140 Ga gap in the paleomagnetic record of Baltica. By comparing apparent polar wander paths (APWPs) and calculated drift velocities, a break-up of Baltica and Laurentia at 1.12–1.04 Ga is suggested. Plate velocities calculated for Laurentia, Baltica and Siberia for the time of the Nuna supercycle are similar and low to moderately high corresponding with the present-day tectonic speeds. Furthermore, the obtained velocity peaks may be related with onset of the break-up of the Nuna supercontinent, the break-up of the direct Baltica–Laurentia connection in Nuna and nascent Rodinia. We suggest that the velocity peaks and large oscillating shifts in late Mesoproterozoic pole positions for Laurentia and Baltica result from a combination of relative plate motion and inertial interchange true polar wander (IITPW) events. Both IITPW events and relative plate motions argue for an operation of plate tectonics in the Meso– to Neoproterozoic. Validerad;2023;Nivå 2;2023-01-03 (joosat);Funder: Academy of Finland;Licens full-text: CC BY License

Majority of researchers consider the Arabian-Caucasus region as a corridor for migration of earliest hominins from their African motherland to Eurasia. The paper is devoted to geological position of main stratified localities of the earliest Paleolithic industries in the Arabian-Caucasus region and estimation of environment of creators of these industries. The following early Paleolithic localities are analyzed: ‘Ubeidiya in Israel, middle Orontes River, Halabiyeh-Zalabiyeh area in the Euphrates River valley, and Ain al Fil in Syria, Dursunlu in Central Turkey, Sambayat, Bostancik, Eskimalatya, and Kovancilar in Eastern Turkey, Karakhach, Muradovo, Agvoric, and Jradzor in NW Armenia, Dmanisi in Southern Georgia, the Azykh cave in Nagornyi Karabakh, Muhkai II in Dagestan, and Kermek in the Taman Peninsula. The evolution of large and small mammals and palynological data on changes of vegetation from the Late Pliocene to the early Middle Pleistocene are studied to determine the age of the earliest Paleolithic industries and climatic conditions of that epoch. Combined analysis of paleontological, paleomagnetic and radio-isotopic data and geological correlation of the sections available for the Halabiyeh-Zalabiyeh, Sambayat, Kovancilar, Karakhach, Dmanisi, Muhkai II, and Kermek localities shows that their age is ranged in time interval ca. 2.0–1.7 Ma. The 1.7–1.6 Ma age of the lowest layers of ‘Ubeidiya with Oldowan-type artefacts probably marks the end of this epoch. Removal of topographic effects of the late Calabrian and younger tectonic uplifts and offsets on major strike-slip faults shows that the topography of the late Gelasian – early Calabrian was much lower and less differentiated and main river systems were more passable than in the present time. The climate of the end of Gelasian was wet and relatively warm, with meadow-steppe and forest-steppe savanna-type vegetation in basins and valleys and coniferous and coniferous–broad-leaved forests in the mountains. Abundance of vegetation was supported by water resources of numerous rivers, lakes, and springs in the intermountain basins and valleys that were controlled partly by fault activity. This stimulated abundance of herbivorous mammals. In spite of relative aridisation at the beginning of Calabrian, vegetation continued to be freely available for herbivores. Hominin dispersal into the region was supported by rich resources of herbivores during the late Gelasian – early Calabrian time.

The Quaternary red clay (QRC) is one of the typical terrestrial sediments in southern China which contains abundant palaeoclimatic information. A natural QRC outcrop, named the Jingxian red clay section (JRCS), was developed in Jingxian City on the northern piedmont of Mt. Huangshan, offering a valuable archive for long-term palaeoclimatic study from a southern China perspective. The objective of this study is to reveal palaeoclimatic information of regional precipitation from the JRCS and its correlation with the East Asian summer monsoon (EASM) intensity, using grain-size measurements combined with dating via Electron Spin Resonance (ESR) and palaeomagnetism. The results indicate that: (1) Ten palaeoclimatic wetter periods (PWPs) designated as PWPI to PWPX from top to bottom were detected from the grain-size analysis results of the upper 9.4 m JRCS. These PWPs span a period from approximately 840 ka ago to present; (2) three PWPs (PWPVIII to PWPX) were basically determined to approximately 612–690, 720–762 and 792–822 ka ago, basically corresponding to China loess layers of L6, L7 and L8 and deep-sea isotope stages of MIS16, MIS18 and MIS20, respectively. Data suggests that the PWPs in the study area were observed mainly during glaciations; (3) regional precipitation in the study area should be negatively related to the EASM intensity since approximately 840 ka ago as a result of variations in North Hemisphere solar insolation and uplifts of the Tibetan Plateau; (4) the modern anti-phase of monsoonal rainfall at glacial-interglacial timescales seemed to have existed between northern China and southern China since the late Early Pleistocene (approximately 840 ka ago).

How the ultrahigh-pressure (UHP) terranes are exhumed to shallow levels but preserving intact relics of the UHP phase assemblages is among the most interesting but challenging topics in geosciences. We investigate all the paleolatitudes where the UHP terranes were exhumed. Our results show that all the UHP terranes in continental collision zones or oceanic accretionary wedges were exhumed within low latitudes (0°–30°), and the average paleolatitude for exhumations of the investigated 43 UHP terranes is ˜5.1° N. In contrast, those UHP xenoliths in mantle-derived igneous rocks could be brought to surface at higher paleolatitudes. Furthermore, the pattern of frequency for the UHP terranes exhumed at convergent boundaries is consistent with that of interglacial stages throughout the Earth history, indicating that the UHP exhumation is controlled by the climate and thus suggesting that the exhumed UHP terranes may be useful paleoclimate indicators.

Cosmogenic radionuclides have been widely used to decipher Earth surface processes. At the University of Tokyo Accelerator Mass Spectrometry facility (5 MV Tandem accelerator), we have been measuring both in-situ and meteoric cosmogenic 10Be and 26Al. In this paper, we report some development of methodology, including how to prepare target samples chemically to reduce their background. We then introduce some examples using the method to provide further insights into earth surface processes. These studies include: i) exposure dating to identify the growths and decays of the Antarctic ice sheet, ii) understanding ice shelf collapse history, iii) paleomagnetic excursion history reconstructions using ice cores, iv) understanding the erosion rates using depth profiles of mid latitude outcrops, v) identifying the timing of impact crater formation.

The thermal structures of eruption-fed, subglacial volcaniclastic deposits are poorly understood because their emplacement is hazardous to observe or obscured by the glacier. Determining deposit emplacement temperature, however, supports improved understanding of the flow dynamics and emplacement processes of volcaniclastic material beneath a glacier. Understanding the emplacement temperatures of ancient volcanic deposits is also important because they can be used, in combination with field studies, to infer the eruptive environment. Here, we use paleomagnetic techniques to quantify the emplacement temperatures of two ancient, proximal, eruption-fed density current deposits at Tongariro volcano, New Zealand. Stepwise thermal demagnetisation of lithic and recycled juvenile block-sized clasts reveal randomly orientated directions of magnetisation, suggesting that the clasts were rotated within the flow but not heated. Additional data from thermomagnetic, hysteresis, and isothermal remanent magnetisation tests indicate that the principal carrier of magnetic remanence is magnetite, and that the magnetisation directions are a primary remanence rather than post-depositional chemical remanent magnetisations. Following systematic removal of any viscous remanent magnetisation, the post-emplacement equilibrium temperatures for the deposits can be estimated at

Made available in DSpace on 2019-10-06T15:48:36Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-09-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Wenner-Gren Foundation Recent discoveries constrain the presence of hominins in North Africa since ca. 2.4 Ma and in China since ca. 2.1 Ma, providing a new temporal framework for the earliest migration out of Africa. No Paleolithic sites of such age exist in the Levant, the natural corridor between Africa and Asia. The Dawqara Formation in the Zarqa Valley, Jordan, has been known since the early 1980s because of the presence of artifacts at different stratigraphic levels within its fluvial sediments, consisting of choppers, cores, and flakes. Although most of the artifacts display signs of transport, they bear unambiguous evidence of manufacture, and document hominin presence in the Zarqa Valley during the deposition of Dawqara Formation. Based on integrated chronology provided by paleomagnetic, 40Ar/39Ar, and U-Pb dating methods, our study shows that the Dawqara Formation was deposited between 2.52 ± 0.01 Ma and the Matuyama–Olduvai geomagnetic reversal (1.95 Ma). By linear interpolation, the artifact-bearing stratigraphic levels within the Dawqara Formation have ages of ca. 2.48 Ma, 2.24 Ma, 2.16 Ma, 2.06 Ma, and 1.95 Ma, respectively, possibly documenting continuous hominin presence in the Zarqa Valley. These new ages for the Dawqara assemblage constrain the earliest hominin dispersal out of Africa to the beginning of the Pleistocene, and pre-date by ca. 300 kyr the hominin occupation of Chinese Loess Plateau. Universidade Estadual Paulista (UNESP) Instituto de Geociências e Ciências Exatas Universidade Federal do Paraná (UFPR) Departamento de Antropologia Istituto Italiano di Paleontologia Umana Oregon State University Argon Geochronology Laboratory Goethe-University Frankfurt Isotope & Element Research Center (FIERCE) Universidade de São Paulo (USP) Museu de Arqueologia e Etnologia Universidade de São Paulo (USP) Instituto de Estudos Avançados Universidade Estadual Paulista (UNESP) Instituto de Geociências e Ciências Exatas FAPESP: 2013/22631-2 FAPESP: 2016/04809-7 CNPq: 302127/2015-1 Wenner-Gren Foundation: 8991

A paleomagnetic and chronogical study has been performed on the Turinge gabbro-diabase formation and on a cross cutting basic dyke in central Sweden and on the Joulovaara gabbro intrusion in northe ...

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

A palaeomagnetic study was carried out on the newly identified 1888 ± 9 Ma Boonadgin dyke swarm of the Yilgarn Craton in Western Australia. The Bonnadgin dykes yield a mean direction of magnetisation of D = 143°, I = 13°, k = 37 and α95 = 8°, based on samples from 10 diabase dykes, with a corresponding palaeopole at 47° S, 235° E, A95 = 6°. A positive baked contact test establishes the primary nature of the magnetisation. The ca. 1.89 Ga palaeopole suggests that the Yilgarn Craton was near the equator at this time, and the Boonadgin dyke swarm can be interpreted to represent an arm of a radiating dyke swarm that shared the same plume centre with coeval mafic dykes in the Dharwar and Bastar cratons of southern India. We therefore propose that the West Australian Craton (WAC, consisting of the Yilgarn and Pilbara cratons) and the South Indian Block (SIB, consisting of the Dharwar, Bastar, and Singhbhum cratons) were connected ca. 1.89 Ga. Globally, available high-quality palaeopoles of similar age allow the West Australian Craton to be placed northwest of proto-Laurentia during the assembly of the supercontinent Nuna.

The Proto-South China Sea (PSCS) represents the lithosphere that formerly occupied the region southeast of South China where the present-day South China Sea is located. The subduction and demise of the PSCS have attracted wide attention, whereas the pre-subduction history (particular the Mesozoic) of the region remains relatively neglected. In this paper, the radiolarian paleobiogeography of the region is analyzed to identify the paleobiogeographic affinity and paleo-connectivity of the PSCS with the Pacific and Tethys oceans during the Mesozoic. Then the continent–ocean configuration and tectonic evolution of the PSCS and adjacent areas are discussed through the integration of paleobiogeographical results and associated paleomagnetic, stratigraphic, and petrologic data. The main conclusions are as follows: (1) During the Triassic, the PSCS was situated in the transition zone between the Pacific and Tethys oceans, and its paleobiogeography was influenced by both oceans. The PSCS was characterized by complex tectonic overprinting by the Pacific and Tethyan tectonic regimes. (2) In the Early–Middle Jurassic, the PSCS was well connected to the Pacific Ocean but poorly connected to the Tethys Ocean, consistent with the paleobiogeography of the PSCS being mainly constrained by the Pacific Ocean. The PSCS was part of the Paleo-Pacific slab. (3) During the Late Jurassic–Cretaceous, the PSCS was in a semi-closed environment. The Late Jurassic–early Late Cretaceous PSCS was part of a west-facing Andean-type subduction zone, and the late Late Cretaceous PSCS was situated in an extensional tectonic setting.

Based on trend, cross-cutting relationships and U-Pb dating, Precambrian mafic dykes in the Singhbhum craton, earlier collectively identified as ‘Newer Dolerite Swarm’, have been separated into seven distinct swarms, which are thought to be the plumbing systems for Large Igneous Provinces (LIPs). These Singhbhum swarms range in age from ∼2.80 Ga to ∼1.76 Ga, and include the ∼2.80 Ga NE-SW trending Keshargaria swarm, ∼2.75–2.76 Ga NNE-SSW to NE-SW trending Ghatgaon swarm, the ∼2.26 Ga NE-SW to ENE-WSW trending Kaptipada swarm (based on a new U-Pb ID-TIMS age 2256 ± 6 Ma), the ∼1.77 Ga WNW-ESE trending Pipilia swarm, the early-Paleoproterozoic E-W to ENE-WSW trending Keonjhar swarm, the middle-Paleoproterozoic NW-SE to NNW-SSE trending Bhagamunda swarm, and the late-Paleoproterozoic N-S to NNE-SSW trending Barigaon swarm. Two of the Singhbhum swarms, the ∼2.26 Ga Kaptipada and ∼1.77 Ga Pipilia, are closely matched with the ∼2.26–2.25 Ga Ippaguda-Dhiburahalli and ∼1.79 Ga Pebbair swarms, respectively, of the eastern Dharwar craton. The correlations suggest that the Singhbhum and Dharwar cratons were close enough at these times to share two reconstructed LIPs, a 2.26–2.25 Ga Kaptipada– Ippaguda-Dhiburahalli LIP and a 1.79–1.77 Ga Pipilia-Pebbair LIP, and if so, both swarms must be present in the intervening Bastar craton (candidates are proposed). Also, the 2.76–2.75 Ga Ghatgaon swarm of the Singhbhum craton can be provisionally correlated with ∼2.7 Ga Keshkal swarm of the Bastar craton. The 2.26–2.25 Ga Kaptipada–Ippaguda-Dhiburahalli LIP of the Singhbhum-Bastar-Dharwar reconstruction has age matches in the Vestfold Hills of Antarctica (∼2.24 Ga dykes), the Kaapvaal craton (the ∼2.25–2.23 Ga Hekpoort lavas) and perhaps the Zimbabwe craton (2.26 Ga Chimbadzi troctolite intrusions). The 1.76–1.79 Ga Pipilia-Pebbair LIP of the Singhbhum-Bastar-Dharwar reconstruction has age matches in the North China, Australian Shield, Amazonian, Rio de Plata and Sarmatia cratons. The relevance of these matches for reconstructions will require future testing using paleomagnetic studies. While there are ∼2.7–2.8 Ga LIP-type greenstone belts in many crustal blocks, there are no precise matches with the 2.76–2.75 Ga Ghatgaon swarm of the Singhbhum craton. However, the 2.80 Ga Keshargaria swarm can be potentially linked with units in the Pilbara and Yilgarn cratons.

South China provides exceptional and unique sedimentary archives of Earth's fundamental changes in Ediacaran time. However, the lack of robust geochronological constraints renders a poorly-defined chronostratigraphic framework for Ediacaran-aged strata in South China, thus making it difficult to understand Earth's critical changes during this time interval. Magnetostratigraphy and rock magnetic cyclostratigraphy turn out to be a few reliable methods in chronostratigraphic studies, especially in the Precambrian. Here, we present a detailed paleomagnetic and rock magnetic study of the Ediacaran Doushantuo Formation in the Huanglianba section, Guizhou Province, South China. The section consists of ~75 m thick carbonate succession and has a record of one of the largest carbon isotope excursions in the Earth history, known as the Shuram excursion. Stepwise thermal demagnetization of Doushantuo carbonates reveals single-component magnetizations that yield a paleomagnetic pole consistent with the Late Triassic segment of the apparent polar wander path of South China. The secondary origin of Doushantuo carbonates' magnetization is supported by their magnetic mineralogy based on various rock magnetic experiments and scanning electron microscopic analyses. We interpret that the secondary magnetization resides mainly in authigenic pyrrhotite that likely precipitated from the reducing fluids during the late stage of Indosinian orogeny in the Triassic. Interestingly, the companion high-resolution cyclostratigraphic study of a 4-m thick succession at the upper layers of the Doushantuo Formation in the Huanglianba section indicates that the Milankovitch cycles were encoded in the variation of magnetic susceptibility, immune from the influence of remagnetization. Variation of magnetic susceptibility is attributed to changes in the abundance of paramagnetic minerals which, by implication, means that the amount of terrestrial materials transported from the continent was regulated by Milankovitch cycles during the deposition of Doushantuo carbonates. Therefore, our results suggest that even though carbonates are prone to remagnetization, astronomical modulation of deposition could be encoded in rock magnetics of the remagnetized carbonates. As a result, rock magnetic cyclostratigraphy has potential in remagnetized carbonates for providing a floating astronomical timescale that can be applied to constrain sediment accumulation rates, estimate the duration of geological events, and construct high-resolution chronostratigraphies.

Three-dimensional (3D) subsurface seismic data acquisition and modeling are rarely undertaken; consequently, the complex effects of oblique thrusting on the 3D morphology and kinematics of folds are still poorly understood. We use 3D seismic data to produce five 3D geometric models and compare our results with structural models of the Yanjinggou anticline in the Longmen Shan fold-and-thrust belt, to investigate the effects of oblique thrusting on 3D fold evolution. 3D geometric modeling results reveal that oblique thrusting may cause fold asymmetry, vertical axis rotation, and a curved fold axis. 3D seismic interpretations and structural modeling suggest that the Yanjinggou anticline developed as a trishear fault-propagation fold and experienced a maximum shortening amount of 1.2 ± 0.1 km. The 3D structural and geometric models are consistent with paleomagnetic results, suggesting that the anticline was affected by oblique thrusting at an angle of 55° above a listric thrust fault with three fault ramps (19°, 30°, and 40°), causing the fold to rotate and develop a curved morphology. The integrated method used in this study to investigate the effects of oblique thrusting on 3D fold morphology and kinematics can be applied to regional oblique thrusting in the Longmen Shan and other fold-and-thrust belts worldwide.

The present study employs petrology, rock magnetics, and paleointensity on four lava flows (seven sites) of the El Jorullo volcano; a historical (1759–1766 AD) cinder cone in the Michoacan-Guanajuato Volcanic Field. El Jorullo lava flows cover an extensive area of ∼10.8 Km2, and a volume ∼0.35 Km3. Rock-magnetic experiments and microscopic observations reveal pseudo-single domain size Ti-poor titanomagnetite as the main carrier of magnetization in all sampled flows. Notably the calculated mean direction from all the sites show a slight westwards bias when compared against the secular variation global models. The mean paleo-direction for the El Jorullo historical eruption is: Dec = 2.5°, Inc = 37.5°, kappa = 214, α95 = 1.8, N = 31; the Virtual Geomagnetic Pole has Plat = 87° N, Plong = 307° E, Kappa = 260, A95 = 1.6; paleointensity data: 45.4 ± 3.6 μT; and Virtual Dipole Moment: 10.3 ± 1 × 1022 Am2. The paleodirections and the paleointensity values from these lava flows are well-constrained and reliable. These results allow to improve the accuracy and reliability of the global and regional secular variation models available for the last centuries.

Onega Ice Lake developed in front of the receding Late Weichselian ice margin in Russian Karelia. Glacial varves that formed in Onega Ice Lake have been earlier studied by means of varve counts, palaeomagnetism and 14C AMS dates from small lakes north of modern Lake Onega and from Lake Onega proper. Synchronous changes in magnetic parameters and similar stratigraphy of these varve records together with the existence of basin-wide marker interval of pink-coloured varves have been used for core-to-core correlation and palaeogeographic interpretations. Unfortunately, there are missing varve-to-varve correlations between these cores. We present a 1155 yr long local varve chronology based on 3 parallel overlapping cores from two small lakes in the Zaonezhsky Peninsula at the northern coast of Lake Onega. Varve counts and matching of varve series were made from digital images. Following the textural, structural, colour and thickness changes of varves within Onega Ice Lake varve series, six characteristic varve units are identified. These clay units reflect changing sedimentary conditions at the time of accumulation that in general can be interpreted as a progressively increasing distance to the retreating ice margin. Variations in varve thickness superimposed on that overall trend, namely two episodes of abrupt and consistent decrease in varve thickness, do not correspond to known lake-level changes or shifts in outflow directions. AMS chronology for deglaciation of Lake Onega basin gives some evidences for correlation of above intervals of decreased varve thickness with the GI-1c2 and GI-1B cold events in NGRIP δ 18O event stratigraphy but further age estimations are needed to confirm presented correlations. Interval of reddish-brown varves – earlier described also as the ‘pink horizon’ – was observed in all studied sequences, and according to varve correlation, at the same stratigraphical level, which proves its basin-wide synchronous appearance. Ca 100 km south of our study area, Saarnisto and Saarinen (2001) reported ca 200 more varves compared to our results. Visual correlation of varve thickness graphs places these extra varves to the proximal part of the series and indicate a rapid ice recession from the main lake basin to the northern Lake Onega area with the ice recession rate ca 500 m per year.

Detailed records of the Earth's magnetic field have shown that it has occasionally reversed its polarity. Several cases have also been found when the Earth Magnetic Field has significantly deviated for a relatively short time from its usual position defining a geomagnetic excursion, a kind of aborted reversal. Although many transitional paleodirections were revealed during the last decade in Central Mexico, their reliability was questioned. Recent paleomagnetic studies along the Trans-Mexican Volcanic Belt report contradictory results on the evidence of intermediary geomagnetic regimes. This work provides new paleomagnetic data which, combined with the information already reported, evaluate the fidelity of such events registered in the lava flows associated to the Tequila and Ceboruco Volcanic Fields. This critical reassessment allowed to discard the evidence of the Levantine geomagnetic excursion (362 ± 13 kA) but strongly confirms the occurrence of the Big Lost event (592 ± 20 ka). These findings represent an important contribution to the geomagnetic instability time scale for the last 1 Ma.

Magnetic signals in basalts from the Sylhet traps (ST), Shillong Plateau, India is investigated using rock magnetism as a proxy to explain the potentiality of the ST basalts as an indicator of magnetic mineralogy. A paleomagnetic study was carried out in order to unravel the Paleopole. In detail, rock magnetic and Anisotropy of Magnetic susceptibility (AMS) results have been reported for the first time on the ST basalts. A total of 38 oriented block samples were collected from 8 sites along Cherrapunji-Shella bazaar road section, Meghalaya, India. Samples were subjected to rock magnetic measurements such as magnetic susceptibility (K), Isothermal Remanent Magnetization (IRM), hysteresis loops, backfield (coercivity remanence) and k-T (Susceptibility vs. Temperature) analysis to identify the magnetic properties of basalts. Advanced Variable Field Translation Balance (AVFTB) was used for some rock magnetic studies. A few samples were also subjected to Anisotropy of Magnetic susceptibility (AMS) study to understand the petrofabric orientations and shape anisotropy in the ST basalts. The Remanence ratio (Mrs/Ms) and the Coercivity ratio (Bcr/Bc) ranging from 0.105 to 0.333 and from 1.25 to 1.87 respectively indicate sizes of magnetic grains are mainly in the range of Pseudo Single Domain (PSD) limits with minority of them in the ranges of Single Domain (SD) limits. The results of k-T study in combination with other rock magnetic results shows that magnetite (Fe3O4) [Curie Temperature = 565-590 °C] as the dominant magnetic carrier with a subordinate content of titanomagnetite Fe2+(Fe3+Ti)2O4 [Curie Temperature = 380–450 °C]. From the AMS study, parameters like lineation, foliation are calculated, and results define all the three shape anisotropies present in the ST basalts. The ST basalts display paleomagnetic directions with mean declination = 255°, mean inclination = -57° (α95 = 3.44°; k = 16.74). The pole position of the ST at 117 Ma is -26.79 °N, 330.75 °E (dp = 3.6; dm = 5) with a paleolatitude 37.6 °S. This infers that the ST is a later volcanic event than Rajmahal traps (RT) which is considered contemporary to the ST.

Key in understanding the geodynamics governing subduction and orogeny is reconstructing the paleogeography of ‘Greater India’, the Indian plate lithosphere that subducted since Tethyan Himalayan continental collision with Asia. Here, we discuss this reconstruction from paleogeographic, kinematic, and geodynamic perspectives and isolate the evolution scenario that is consistent with all three. We follow recent constraints advocating a ~58 Ma initial collision and update a previous kinematic restoration of intra-Asian shortening with a recently proposed model that reconciles long-debated large and small estimates of Indochina extrusion. Our new reconstruction is tested against paleomagnetic data, and against seismic tomographic constraints on paleo-subduction zone locations. The resulting restoration shows ~1000–1200 km of post-collisional intra-Asian shortening, leaving a 2600–3400 km wide Greater India. From a paleogeographic, sediment provenance perspective, Eocene sediments in the Lesser Himalaya and on undeformed India may be derived from Tibet, suggesting that all Greater Indian lithosphere was continental, but may alternatively be sourced from the contemporaneous western Indian orogen unrelated to India-Asia collision. A quantitative kinematic, paleomagnetic perspective prefers major Cretaceous extension and a ‘Greater India Basin’ opening within Greater India, but data uncertainty may speculatively allow for minimal extension. Finally, from a geodynamic perspective, assuming a fully continental Greater India would require that subduction rates close to 20 cm/yr was driven by a down-going lithosphere-crust assemblage more buoyant than the mantle, which seems physically improbable. We conclude that the Greater India Basin scenario is the only sustainable one from all three perspectives. We infer that old pre-collisional lithosphere rapidly entered the lower mantle sustaining high subduction rates, whilst post-collisional continental and young Greater India basin lithosphere did not, inciting the rapid India-Asia convergence deceleration ~8 Myr after collision. Subsequent absolute northward slab migration and overturning caused flat slab subduction, Tibetan shortening, arc migration and arc volume decrease.

The Southern Granulite Terrane (SGT) of India is a collage of Archean to Neoproterozoic crustal blocks hosting several generations of mafic dykes. We report new paleomagnetic and geochronologic results from mafic dykes in the Salem Block of the SGT. The 2370 Ma Bangalore dyke swarm is confirmed in this area with a U-Pb zircon age of 2363 ± 6.6 Ma on dykes with steep dual-polarity paleomagnetic directions yielding a pole at 2° N and 73° E (A95 = 14°). These results precisely place the Dharwar Craton and northern SGT at high latitudes in the early Paleoproterozoic. The episodic Paleoproterozoic magmatic record of India is also recovered from the SGT. Several groupings of SGT paleomagnetic directions compare favorably with the 2.21 Ga, 2.18 Ga, and 1.88 Ga Dharwar craton dykes. We also report a grand mean pole of 81° N and 259° E (A95 = 11°) that we attribute to a widespread Ediacaran-age remagnetization associated with the final stages of Gondwana assembly. These paleomagnetic and geochronologic data permit a better resolved reconstruction of Indian crustal elements from the Paleoproterozoic onward.

A rock magnetic, mineralogical and Mossbauer spectroscopy study was undertaken on the Lower Triassic sediments from the West Spitsbergen Fold and Thrust Belt (WSFTB) in Svalbard as well as the foreland of this orogen for a thorough recognition of magnetic mineralogy, necessary for a better-constrained interpretation of paleomagnetic results. SEM and Mossbauer spectroscopy indicate the presence of magnetite and pyrrhotite, both most probably of secondary origin but altered clasts of volcanic origin and grains of ilmenite and detrital magnetite are also observed. Thermomagnetic curves of whole-rock samples exhibit paramagnetic behavior whereas ferromagnetic separates indicate the presence of magnetite. IRM component analysis shows three major contributors – magnetite, hematite, and pyrrhotite to the remanence, with ferromagnetic iron oxides the most dominant. Identified ferromagnetic minerals display a wide range of grain-size and magnetic behavior, with the domination of PSD particles. Rock magnetic characteristics of both areas are similar, but sites in the fold belt were most likely remagnetized, whereas those in the foreland carry the primary magnetization. The age of remagnetization was estimated as pre-Eurekan related to rift-controlled Mesozoic extensional phases of the Barents Sea Shelf (Clark et al., 2014) and/or Cretaceous injections of dolerites in the Svalbard Archipelago (Nejbert et al., 2011) as well as early stages of the WSFTB formation. However, Triassic remanence might persist in volcanic lithoclasts and detrital magnetite indicated along the WSFTB. The multicomponent nature of the NRM, displaying a broad range of grain size, might impede the paleomagnetic interpretation of Triassic rocks in Spitsbergen.

To identify the causes of complex magnetic anomalies on the three guyots located in the northeastern part of the Ulleung Basin, East Sea, a linear least-squares inversion method was implemented. Modeling under the assumption that the guyots are uniformly magnetized did not yield reliable results. However, an inhomogeneously-magnetized model shows relatively high goodness-of-fit parameters and low residual magnetic anomalies, indicating that these guyots are considerably nonuniformly magnetized. Our modeling results show that all three guyots show similar magnetic patterns. Magnetic anomalies north of guyots have different magnetic polarities at similar depths in the south, indicating that these magnetic anomalies were formed at different times. These results suggest that relatively short wavelengths and complicated magnetic anomalies in the study area are the compound result of different magnetic polarities. Paleomagnetic analysis on trachyandesite lavas and pyroclastic breccia indicates a thermo-chemical remagnetization activity after Reunion Subchron (2.138–2.122 Ma). This result also suggests that remagnetization contributes to the creation of complex magnetic anomalies to some extent as well. In addition, the upward continuation results up to 1500 m using a FFT routine show high positive magnetic anomalies with a linearly segmented shape at the base of guyots. These linear and positive magnetic anomalies are interpreted as volcanic eruptions along fissures because mafic lava should have much higher magnetic anomalies compared to continental crust, where guyots are located. Therefore, we interpret that the complex magnetic anomalies distributed in the study area are due to polarity reversals occurring at least twice, and were formed during the formation of the current guyots as volcanic eruptions derived from fissures.

Small lakes in low relief areas are atypical candidates for studies on paleoseismicity, but their sediments can contain seismically induced event layers (seismites) generated through strong ground shaking, sediment transport, hydrological reorganization and/or changes in groundwater chemistry and flow. Lakes Lungo and Ripasottile are shallow lakes (

We question the timing of continental breakup and early oceanization in Baffin Bay, North-East Atlantic. North of the Ungava fault zone, the breakup was syn-magmatic and led to the development of conjugate volcanic passive margins (VPMs). We investigated the innermost part of the W-Greenland VPM where a remarkable inner-SDR is fully exposed in the Svartenhuk area. Our new radiometric ages and paleomagnetic data from syn-tectonic basaltic lavas indicate that continental stretching and thinning spanned the C26r to, at least, the C24r period, giving an Eocene lower boundary age for continental breakup in Baffin Bay. These results contradict the proposed flooring of Baffin Bay by a Paleocene oceanic crust older than C24n and also question the accretion of oceanic crust before C22. We confront our results to the dynamics of the northward oceanic-rift propagation across the Ungava transform fault system, and we suggest that plate breakup in Baffin Bay occurred ~8 m.y. later than in N-Labrador Sea as a result of the thermal and mechanical barrier effect induced by the Ungava transform zone.

We present a paleomagnetic study of two Holocene lake sediment sequences from Northwest Spitsbergen on Svalbard, Norway. Core HAP-212 from Lake Hajeren preserves a rare combination of a well-defined Characteristic Remanent Magnetization (ChRM) and robust age control defined by 21 terrestrial macrofossil-derived radiocarbon dates—providing a unique opportunity to assess the stratigraphic potential of High Arctic Holocene paleomagnetic secular variation (PSV) close to 80° N. Core AMP-112 from Hakluytvatnet, which is also well dated, is a poor magnetic recorder and cannot be used for geomagnetic reconstruction. Comparison of the HAP-212 PSV record with poorly dated regional records show similar directional features, suggesting that PSV can be used for chronological synchronization. Comparison of the HAP-212 PSV with well dated records ∼1800 km to the southwest and southeast show that these records are in-phase at millennial timescales, within dating and magnetic uncertainties, indicating that a consistent geomagnetic signal is recorded at these temporal and spatial scales. These findings support the notion that PSV, when optimally recorded, can be used to import chronologies from lower latitudes to the High Arctic, where low organic content, hard water effects, lack of datable material, and other difficulties often preclude more conventional radiocarbon dating.

An oceanic Greater Indian Basin was hypothesized to have formed between ∼120 Ma and ∼65 Ma by regional extension that separated the cratonic India from its northern margin of Tethyan Himalaya (TH). However, the lack of paleomagnetic data from this critical time interval in the TH marks an important gap in our knowledge about the tectonic evolution of the Greater India. We have conducted a paleomagnetic study of a Cretaceous marine succession in Zhongba, southern Tibet that consists of predominantly purple reddish cherts and siliceous limestone. Paleomagnetic samples from 12 sites were subjected to stepwise thermal demagnetization that revealed either two- or three-component magnetizations with the high-temperature component (HTC) typically unblocked at ∼650 °C. The HTCs exhibit dual polarities that yield a positive reversed test at 95% confidence level, suggesting a primary origin of the remanence. With chronologic constraints from the combined analysis of the magnetostratigraphic and radiolarian data, the HTCs yield a mean of Ds = 336.9°, Is = −50.7°, ks = 18.0, α95 = 5.3° for the ∼120.8–93.9 Ma interval of the TH, which corresponds to a paleopole at 25.0°N, 285.7°E (dp/dm = 4.8/7.1°). The apparent polar wander path (APWP) of the TH overall resembles that of cratonic India, suggesting no polarward separation that is sufficiently large to merit an oceanic basin between the TH and cratonic India. Therefore, our new reliable paleomagnetic data from the critical time interval do not support the Greater Indian Basin hypothesis and its implied dual collisional processes between India and Asia. On the other hand, the APWPs exhibit relative shifts for the post-120 Ma segment and the pre-130 Ma segment, indicating relative motions between the TH and cratonic India that most likely resulted from shearing along boundary-parallel faults during the India-Asia collision.

Paleomagnetic data provide information on the evolution of the Earth's magnetic field, and are used to reconstruct plate motions. One fundamental assumption underlying these interpretations is that the magnetization of a rock reliably records the direction and intensity of the magnetizing field, i.e. that the magnetization is parallel to the field direction, and the intensity of magnetization is proportional to the field strength. Preferred alignment or anisotropic distribution of magnetic grains can affect both the direction and the intensity of magnetization. Therefore, correction techniques, employing the anisotropy of magnetic susceptibility (AMS), thermal remanence (ATRM), or anhysteretic remanence (AARM) are used to account for these effects. We find that AARM within the same rock can vary dramatically with coercivity/grain size, so that anisotropy corrections can also depend on how AARM was measured. A consequence of the dependence of AARM on coercivity is that although a specimen may have been magnetized in a single direction, different grain size fractions may record magnetizations in different orientations. These directional variations, as revealed during progressive alternating field (AF) demagnetization, could erroneously be interpreted as changes in field or reorientation of the rock unit, when in reality they are related to grain-size-dependent remanence anisotropy. Similarly, intensity variations caused by grain-size-dependent anisotropy may bias paleointensity estimates. These observations have important consequences for studies on the evolution of the Earth's magnetic field, magnetic overprinting, and paleogeographic reconstructions.

The paleogeography of East Asia in the supercontinent (Pangea) during the late Paleozoic to Mesozoic remains incomplete because the temporal and spatial constraints on the rigid attachment of East Asia to Eurasia is still unresolved. One fundamental obstacle to constructing a high-precision apparent polar wander (APW) path for East Asia is the uneven temporal coverage of available paleomagnetic poles with a severe lithologic bias towards sedimentary rocks. In reality, paleomagnetic data from sedimentary rocks are often biased towards a shallower paleomagnetic inclination, resulting in underestimation of paleolatitudes. In the present study, we tested whether the sedimentary paleopoles in the South China Block (SCB) and the North China Block (NCB) can be corrected for their shallow paleomagnetic inclinations. The shallow bias of paleomagnetic inclination in sedimentary rocks from the SCB was corrected using the elongation-inclination (E/I) method. According to paleogeographic comparisons, sedimentary paleopoles for the NCB and volcanic paleopoles for the SCB provide the most realistic paleogeographic distributions from 150 to 120 Ma. Therefore, we propose that the optimum paleogeography between the NCB and the SCB is as follows: (1) apparent polar wander (APW) path was constructed from volcanic data only from 150 Ma to 120 Ma; (2) for time intervals younger than 110 Ma, a new composite APW path was constructed both from volcanic and sedimentary results, with systematic E/I corrections.

A possible Mesozoic-Cenozoic trajectory for the North American craton is outlined from latitude changes of the craton derived from a revised apparent polar wander path, and from westward movement of the craton based on the assumption that Africa has been the least mobile continent geographically since the latest Paleozoic. During each of five time intervals that span 220 million years, the craton trajectory had a different vector. Each vector appears to be reflected in the Canadian Cordillera by the dominant style and orientation of structures formed during that interval. For much of the past ~ 220 million years, the ~meridionally-oriented western margin of the Pangea-Laurasia-North America Plate has been the site of arc magmatism where weak arc/back arc lithosphere, sandwiched between strong ocean-floor and craton lithospheres at times coupled across convergent or transform plate boundaries, focused and recorded strain. When the craton apparently moved due westward, between ~180–160 Ma and ~120–60 Ma, the dominant structures formed then record orogen-normal compression and were accompanied by orogeny. Structures formed during the earlier episode are mainly in the eastern and interior Cordillera and their formation shortly followed or coincided with accretion of most terranes to the craton margin. In the later episode, compressional structures span the entire Cordillera, which emerged as a tectonic and physiographic entity. Before and between these intervals, when the craton apparently moved mostly northwestward, mainly geological and paleomagnetic considerations indicate some terranes moved southward (sinistrally) relative to the craton. After ~60 Ma, southwestward movement of the craton was concurrent with large northward (dextral) strike-slip faults that disrupted the newly-established ancestral Cordillera. The coincidence between the age of structures that record dominant orogen-normal compression at times when the craton apparently moved due westward, and orogen-parallel displacements when the craton had either northward or southward components of motion, suggests the craton, acting as a “Continental Bulldozer”, was the primary driver of Cordilleran deformation and orogenesis.

The Alcantara River marks the northern border of Etna volcano, and along its NE sector, it forms a narrow NW-SE elongated valley that is carved in the Mts. Peloritani sedimentary sequences. The valley has been invaded by several lava flows during the growth of the main bulk of the stratovolcano edifice in the past 60 ky (Ellittico and Mongibello volcanoes). In this paper, we have constrained the age of the main lava flows forming the valley floor and reconstructed the length and volume of the main lava flow that impacted this area through a multidisciplinary approach integrating stratigraphic and aeromagnetic data analysis together with new paleomagnetic and 14C dating. The new age determinations showed that the evolution of the present-day geological and hydrographic setting of the valley was mainly conditioned by a few flank eruptions that occurred in the lower N flank of Etna during the activity of the Mongibello volcano. In particular, between 13.9 and 9.7 ka BP the valley floor was filled by the so-called Alcantara lava flow for its entire length up to the river mouth, reaching a maximum length of about 24 km. Later, two other flank eruptions – producing the so-called Mt. Dolce and Solicchiata lava flows – occurred at 9.1–7.2 and 7.3–7.2 ka BP (respectively), covering the eruptive fissure and the proximal portion of the Alcantara lava field and generated the most recent northward shift of the riverbed. Finally, 3D magnetic modeling allowed us to calculate the total on- and off-shore volume of the Alcantara lava flow as 1 km3, a value comparable to those of the long-lasting historical eruptions of Etna. Conversely, the 24 km length reached by this lava flow is anomalously high when compared to lava flows of the past 15 ky, likely because its emplacement occurred within the valley floor, preventing any possibility of lateral expansion.

Swartvlei is one of the most thoroughly investigated lacustrine coastal systems in South Africa. However, studies regarding the most recent past (i.e., the last 30–40 years) examining anthropogenic impacts on sediment deposition are missing completely. This study, covering the past 400 years, provides evidence for distinct environmental changes during this time most likely related to anthropogenic activities such as farming or water abstraction. A decrease in marine influence is observed starting somewhat earlier but was potentially supported by human management activities. In this respect age-depth-modelling is an important issue and needs further investigations in many coastal geoarchives of South Africa. Therefore, a multi-dating approach using several methods is suggested since errors in the chronology distinctly impact paleoenvironmental reconstructions (timing, flux rates etc.). In this context this is the first time that paleomagnetic secular variation data obtained from South African sediment records are used for dating purposes which is the only approach to establish a reliable chronology for recent sediments in this system.

The tectonic evolution of SE Anatolia is associated with the collision between the Taurides and the Arabian Platform in the early Cenozoic, after the final closure of the southern branch of the Neotethys ocean during Late Cretaceous to Early Eocene times. The ongoing deformation was characterized by northward movement of Arabia, followed by westward extrusion of Anatolia, having been displaced along the northern and eastern Anatolian transform faults. The neotectonic deformation history between the Anatolian Plate and the Arabian platform since the closure of the southern Neotethyan oceanic basin from Late Cretaceous to present has not been studied in detail paleomagnetically. Therefore we carried out a paleomagnetic study of Mesozoic and Cenozoic rocks at 34 localities along the Bitlis-Zagros suture zone in SE Anatolia located in the boundary region between the Taurides and the Arabian platform and delimited by the Dead Sea Fault. Paleomagnetic results from the area show clockwise rotations of 35.6° ± 14.1° and 26.7° ± 8.0° with respect to the African plate from Upper Jurassic - Lower Cretaceous and Upper Cretaceous limestones, respectively. The paleomagnetic results indicate also an earlier deformation/opening due to the Dead Sea Fault Zone (DSFZ). Farther north on the Tauride Block, counterclockwise rotation of −34.5° ± 12.5° is recorded by Upper Cretaceous limestones. In the SE of the study area on the northern margin of Arabia, however, smaller counterclockwise rotations of -12.3° ± 8.3° and −2.5° ± 10.0° in Late Cretaceous and −12.7° ± 13.6° in middle Eocene rocks show relative tectonic stability. Middle Miocene rocks close to the suture zone show counterclockwise rotation by about −39.4° ± 10.9°, while farther away from the suture zone counterclockwise rotations of −21.9° ± 9.9° and −7.5° ± 5.8° are observed. Paleolatitudinal motion from south to north from the Late Jurassic to the Present is in concordance with the apparent polar wander path of Eurasia and Africa.

We report detailed rock-magnetic and paleomagnetic results from a 27-m-long sedimentary core collected at depocenter of Lake Chapala, western Trans-Mexican Volcanic Belt. Rock-magnetic parameters point to PSD grain-size titanomagnetites as the dominant magnetic mineralogy. Observed variations, in both concentration and grain-size dependent magnetic parameters, reflect changes in the sediment supply through the studied depth, but mainly during the last half century. Stable characteristic remanent magnetization, representative of secular variation of the geomagnetic field, was retrieved after alternating field demagnetization of the natural remanent magnetization (NRM). The comparison of the obtained magnetic inclination and declination logs against the corresponding curves predicted by the Global Geomagnetic Field Model SHA.DIF.14k enables to establish an alternative sedimentation-rate independent age-depth model for the whole core, in reasonably good agreement with the one calculated using conventional radiocarbon dating. This approach works not only for Lake Chapala, but also for Lake Chalco. The correlation established between rock-magnetic parameters and paleoenvironments, based on diatom identification of representative samples within specific zones, can be considered as a novel proxy methodology. This approach opens a new perspective for new, more detailed rock-magnetic, paleomagnetic and paleoenvironmental investigations for better paleoclimatic reconstructions.