Continental Bridge Research Articles

Central Asia as a Continental Bridge or Thucydides Trap?

When the Western press and media report on Xinjiang, they tend to focus on the situation of the Uyghurs in this autonomous region of China. The fact that Xinjiang is of the highest strategic importance for China as a raw materials base, gateway to Central Asia and starting point of the New Silk Road, which is orientated towards Europe, and that real geopolitics is all about precisely these things, is often neglected. Of course, the starting point of the New Silk Road is in the strategists' crosshairs and it goes without saying that Central Asia and the South Caucasus are also targeted. After all, the shortest transport corridors to Europe run through these areas, now that the transport routes via Russia have been cancelled by Russia's war in Ukraine. This is where the Chinese New Silk Road and the European Global Gateway meet. What is the situation in Central Asia? What role does the International Trans-Caspian Transport Route play? How are China, the USA and Europe acting where the future of the New Silk Road is ultimately at stake? This article aims to provide a few answers to these questions, which should therefore only be understood as an approach to the topic of "Central Asia as a continental bridge or Thucydides' trap?".

Revisiting the species list of freshwater fish in Israel based on DNA barcoding.

Israel's region forms a continental bridge; hence, the freshwater fish fauna in Israel consists of unique populations of species that originated from Africa, Asia, or Europe and are often endemic or at the edge of their distribution range. Worldwide, fish biodiversity suffers significantly from pressures and disturbances of freshwater habitats, especially in arid regions, such as in parts of Israel. Biodiversity conservation requires efficient tools for monitoring changes in populations. DNA barcoding, by complementing and enhancing species identification, provides such monitoring tools. In this study, over 200 specimens representing over 28 species were DNA barcoded and together with previously available records, a DNA barcoding database for freshwater fish of Israel was established. Of the 71 distinct barcodes generated, 37% were new, attesting to the uniqueness of fish populations in Israel. For most species, morphological and molecular species identifications agreed. However, discrepancies were found for five genera. Based on DNA barcoding, we propose Acanthobrama telavivensis as a junior synonym for Acanthobrama lissneri. In Garra spp., we propose splitting Garra nana into two species and assigning Garra rufa in the region to Garra jordanica, or possibly to two species. Israeli Pseudophoxinus kervillei is not the same species as in Syria and Lebanon. However, Pseudophoxinus syriacus might not be endangered since it is genetically very similar to Pseudophoxinus drusensis. In Israel, instead of five reported Oxynoemacheilus species, combining DNA barcoding with morphology suggests only three. Genetic and geographic separation suggested that Aphanius mento is likely a species complex. The study provides a thorough barcoding database, suggests significant species reconsiderations in the region, and highlights the Sea of Galilee and the Beit She'an valley streams as biodiversity "hotspots." This study will therefore promote further studying of the fish species in the region and their ecology, as well as the monitoring and conservation of freshwater fish biodiversity in Israel and the region.

Phylogeny, biogeography, and integrative taxonomic revision of the Afro-Arabian rodent genus Ochromyscus (Muridae: Murinae: Praomyini)

Abstract The analyses of Plio-Pleistocene speciation processes in the Horn of Africa are relevant for understanding the evolution of biodiversity patterns of this understudied part of the world. Here we analyse comprehensive genomic and morphological data of the recently delimited murid genus Ochromyscus, one of the few with Afro-Arabian distribution. Using an integrative taxonomic approach, we delimit three species in the genus: two in eastern Africa (O. brockmani and O. niveiventris) and one in southern Arabia (O. yemeni), and detail their distribution, genetic structure, and evolutionary history. Despite their morphological similarity, the three species split before the Pleistocene, and their interspecific genetic divergence level is comparable to that between sister genera of murine rodents. The split between two taxa living on opposite sides of the Red Sea (O. brockmani vs. O. yemeni) is younger than the separation of their ancestor and O. niveiventris living in eastern Africa. The colonization of Arabia can be explained either by the presence of a relatively recent continental bridge or by the past occurrence of the genus along the eastern coast of the Red Sea and subsequent spreading through the Sinai Peninsula.

Formation of Industrial and Logistics Hub in the Border Areas of Kazakhstan and Uzbekistan

Central Asia is a strategic region of the China-Europe continental bridge. The conflict between Russia and Ukraine has seriously affected international supply chains, which has led to the intensification of the development of alternative corridors and the construction of new regional logistics hubs along them. The purpose of the research is to determine, on the basis of these sources, the factors of the formation of industrial and logistics hubs, as well as the directions of their development on the example of the border regions of Kazakhstan and Uzbekistan. In preparing this article, a mixed research strategy was used, which implies quantitative and qualitative methods. It consists not only of the systematic study of the literature on the research topic and statistical information but also involves the implementation of theoretical studies, comparison, generalization and analysis of the results, argumentation and formulation of conclusions. The study identified the main constraining factors for the development of such centres delays in customs inspection, inconsistency in the legal framework of the transportation process, underdevelopment of infrastructure, low level of digitalization and the use of information systems, the use of non-tariff barriers, low level of digitalization and the use of information systems. The creation and development of integrated transport services based on a digital platform will speed up this process. In addition, taking into account these factors, the components of an industrial and logistics hub are proposed: an industrial zone, a logistics zone, a trading zone, a certification zone with appropriate services, as well as a digital platform as a link between all components.

Comparative analysis of driving forces of land use/cover change in the upper, middle and lower reaches of the Selenga River Basin

The Selenga River Basin is an important section of the Sino-Mongolian Economic Corridor. It is an important connecting part of the Eurasian Continental Bridge and an important part of Northeast Asia. Comparative analysis of land use changes and their driving forces in the middle and lower reaches of the watershed is an important tool to reveal regional ecosystem changes, which is of great scientific guidance to ensure regional ecological security. This paper takes Selenge County in the upper reaches of Selenga River Basin, Sukhbaatar City in the middle reaches and Ulan-Ude City in the lower reaches as the case areas to compare and analyse the land use change changes based on Landsat remote sensing image data. The partial least squares regression model is used to discuss the driving forces by combining natural and socio-economic factors. The results show the following: (1) Selenge County is overloaded with overgrazing; Sukhbaatar city, as a region with very suitable soil and water conditions in Mongolia, the area of cultivated land is expanding. Since the disintegration of the Soviet Union in Ulan-Ude, the abandonment of farming has been severe due to the reduction of the agricultural population, resulting in a reduction in the area of cultivated land. (2) The upper reaches of the region should focus on preventing overgrazing, which leads to desertification. In the middle reaches, it is necessary to prevent the over-cultivation of cultivated land. In the lower reaches, the damage to the Lake Baikal ecosystem, a natural heritage of mankind, should be prevented by the rapid expansion of urban space.

Analysis of Land Use/Cover Change and Driving Forces in the Selenga River Basin.

The Selenga River basin is an important section of the Sino-Mongolian Economic Corridor. It is an important connecting piece of the Eurasian Continental Bridge and an important part of Northeast Asia. Against the background of the evolution of the geopolitical pattern since the disintegration of the Soviet Union and global warming, based on the land cover data in the Selenga River basin from 1992, 2000, 2009, and 2015, this paper describes the dynamic changes in land use in the basin. Through a logistic model, the driving factors of land cover change were revealed, and the CA-Markov model was used to predict the land cover pattern of 2027. The results showed that (1) from 1992 to 2015, the agricultural population in the Selenga River basin continued to decrease, which led to a reduction in agricultural sown area. The intensification of climate warming and drying had a significant impact on the spatial distribution of crops. Grassland expansion mostly occurred in areas with relatively abundant rainfall, low temperature, and low human activity. (2) The simulation results showed that, according to the current development trend, the construction land area of the Selenga River basin will be slightly expanded in 2027, the area of arable land and grassland will be slightly reduced, and the areas of forest, water/wetland, and bare land will remain stable. In the future, human activities in the basin will increase in the process of the construction of the China-Mongolia-Russia economic corridor. Coupled with global warming, the land/cover of the basin will be affected by both man-made and natural disturbances, and attention should be paid to the possible risk of vegetation degradation.

Explicating the mechanisms of land cover change in the New Eurasian Continental Bridge Economic Corridor region in the 21st century

Explicating the mechanisms of land cover change in the New Eurasian Continental Bridge Economic Corridor region in the 21st century

Magnetostratigraphy and Paleoenvironments of the Kuntila Lake Sediments, Southern Israel: Implications for Late Cenozoic Climate Variability at the Northern Fringe of the Saharo-Arabian Desert Belt

The Negev Desert in southern Israel hosts a number of late Cenozoic lacustrine and palustrine sedimentary sequences that attest for past wetter conditions in what today constitutes one of the driest deserts on Earth. These sequences are of special importance because the Negev Desert forms part of the Levantine Corridor, which was probably the only continental bridge that enabled initial out-of-Africa expansion of our genus Homo.Yet, the paleoclimatic significance of these sequences still remains unknown, mainly due to their uncertain (late Pliocene to early Pleistocene) age. Here we present a combined sedimentologic, paleontologic and magnetostratigraphic study of one of these sedimentary sequences, the so-called Kuntila Lake sediments, which was carried out at the 30 m-thick Kuntila Gate section in the Nahal Paran basin, southern Israel.Sedimentological evidence and ostracod faunas indicate that these sediments accumulated in a long-lasting lacustrine basin that underwent periodic lake-level variations. Magnetostratigraphic measurements enable the recognition of a normal (N1) and a reverse (R1) polarity zones in the lower and upper halves, respectively, of the Kuntila Gate section. Correlation of N1 to the Olduvai Subchron (1.778 and 1.945 Ma) appears as the most likely option in view of previously published 10 Be ages derived for the uppermost part of the Kuntila Member in nearby sections. The large errors associated with these ages, however, suggest that correlation of N1 to Subchron C2An.1n (2.582-3.032 Ma) is also possible. Although our results do not resolve the age of the Arava Formation, they unequivocally relate the Kuntila Lake sediments with a long period of enhanced climatic variability because the tops of both subchrons are associated with 400 kyr eccentricity maxima. The inferred wetter conditions in the Negev Desert concurred, regardless of the age correlation, with periods of lake expansion in East Africa and clusters of short-lived expansions of the savannah throughout much of the Sahara. This would have led to the biogeographic connection between Africa and Eurasia, greening the path for the initial out-of-Africa dispersal of Homo. Further research on the Kuntila Lake sediments will be necessary to better determine the timing, extent and significance of such biogeographic connection.

Delimiting the Neoproterozoic São Francisco Paleocontinental Block with P-wave traveltime tomography

SummaryThe São Francisco Paleocontinental Block (SFPB) represents part of the Congo-São Francisco Paleocontinent (CSFP), amalgamated around 2 Ga. In the Neoproterozoic, a branched continental rift system evolved to ocean basins around most edges of the SFPB that remained only partially linked to the Congo Paleocontinent by means of the Bahia-Gabon Continental Bridge. After the Brasiliano—Pan-African orogeny, two relatively preserved CSFP sectors formed the São Francisco and Congo cratons, surrounded by Neoproterozoic orogenic belts. Recent results of upper mantle P-wave seismic tomography allowed us to suggest a delimitation in lithospheric depths of the Neoproterozoic SFPB, which comprise the São Francisco Craton, and that this would have been connected with the Congo Paleocontinent along the Araçuaí Belt. It is characterized by high-velocity anomalies and its boundaries with other blocks are marked by low-velocity anomalies at lithospheric depths. We tested the resolution of the tomographic results through synthetic models obtained by a ray tracing scheme using the observed ray configuration. We observe that the lateral resolution is adequate, but the method used was not able to set the depth reached by the SFPB. Our results indicate that the SFPB area in lithospheric depths is larger than the surface area ascribed to the São Francisco craton, and thus, the SFPB basement deeply extends beneath neighboring orogenic regions, suggesting that these Neoproterozoic mobile belts, such as Araçuaí Orogen and the Brasilia Fold Belt, reworked the continental crust. We observe a low-velocity anomaly in the SFPB central region, corresponding to the Pirapora aulacogen. Our results have a good spatial correspondence with the low Bouguer anomalies used to define the SFPB in previous studies. The limits of the SFPB are consistent with deviation of the mantle flow, as suggested by SKS fast polarization.

A new pipoid frog (Anura, Pipimorpha) from the Paleogene of Patagonia. Paleobiogeographical implications

The aim of the present contribution is to describe a new genus and species of Pipoidea from the Huitrera Formation (Eocene) from Patagonia, Argentina. The new genus shows a unique combination of characters indicating that it is a valid taxon different from other pipimorphs, including the coeval Llankibatrachus truebae. The phylogenetic analysis resulted in the nesting of the new taxon within a previously unrecognized endemic clade of South American aglossans. This new clade turns out to be the sister-group of crown-group Pipidae. This phylogenetic proposal reinforces the hypothesis sustaining the dispersal of pipids between Africa and South America through an island chain or a continental bridge across the Atlantic Ocean by Early Tertiary times.

A new genus of pipimorph frog (Anura) from the Early Cretaceous Crato Formation (Aptian) and the evolution of South American tongueless frogs

Pipimorpha is a clade of tongueless anurans with a wide fossil record. Furthermore, the oldest South American fossils come from the Late Cretaceous (Cenomanian) of Patagonia, Argentina. The aim of the present contribution is to describe a new genus and species of Pipimorpha from the Crato Formation (Aptian, Early Cretaceous), Araripe Basin, Brazil. The new specimen consists of a nearly complete skeleton that shows several anatomical similarities with other fossils from South America. Phylogenetic analysis resulted in the nesting of the new taxon within a previously unrecognized endemic South American clade. Further, some traditional groupings within Pipimorpha were not recognized. The new phylogenetic analysis reinforces previous biogeographical hypotheses sustaining dispersal of pipimorph between Africa and South America through an island chain or continental bridge across the Atlantic Ocean.

新亚欧大陆桥经济走廊土地覆被变化及驱动力分析

新亚欧大陆桥经济走廊土地覆被变化及驱动力分析

Rhyacian-Orosirian isotopic records from the basement of the Araçuaí-Ribeira orogenic system (SE Brazil): Links in the Congo-São Francisco palaeocontinent

Assembled during the Rhyacian-Orosirian boundary, the Congo-São Francisco palaeocontinent remained linked by a continental bridge from ca. 2 Ga to the Atlantic Ocean opening in the Cretaceous. To the south of that bridge, precursor basins and orogenic outcomes encompassed by the Neoproterozoic-Cambrian Araçuaí-Ribeira orogenic system (AROS) and its African counterparts, developed. The AROS discloses reworked basement units, like the Juiz de Fora, Pocrane and Quirino complexes, which are key units to retrieve the Palaeoproterozoic history of the Congo-São Francisco palaeocontinent. This paper presents new U-Pb ages, and the first Lu-Hf in zircon signatures from those complexes. All magmatic zircon grains show Rhyacian and Orosirian ages, ranging from c. 2250 Ma to c. 1850 Ma. The best Concordia ages range from 2184 ± 9 Ma to 2080 ± 19 Ma. Hf in zircon and whole-rock Sm-Nd data disclose mantle-related signatures for both, the Pocrane and Juiz de Fora complexes, suggesting igneous protoliths with no or very few involvement of continental crust, similarly to juvenile magmatic arcs. Conversely, Hf in zircon data for the Quirino complex show an evolved signature compatible with a magmatic arc developed on a continental older crust with Archaean components. Together with a thorough compilation on Rhyacian-Orosirian orogenic systems (ROOS), our data allow us to envisage links within the Congo-São Francisco palaeocontinent, comprising orogens characterised by mostly evolved isotopic signatures and zircon inheritance. They are grouped into the: (i) W-ROOS, including the Mantiqueira complex, the west segment of the Eastern Bahia belt, intrusions in the south Gavião and Porteirinha blocks, and parts of the Mineiro belt; and (ii) E-ROOS, comprising the Quirino complex, basement rocks of the Cabo Frio tectonic domain, the coastal Eastern Bahia belt, and, in Africa, Eburnean and Kimezian complexes, as well as the western Angola shield. Assembled between the W-ROOS and E-ROOS, an orogenic system with prominent juvenile to moderately juvenile isotopic signature (JU-ROOS) includes the Juiz de Fora and Pocrane complexes, and the Buerarema complex at the central segment of the Eastern Bahia belt.

Vertical Structure of Near-Surface Sediments in the Central Parts of the Yaghan and Scan Basins (Scotia Sea)

The structure of the sediment sequence of the Scotia Sea is the basis for reconstructing the geological history of the development of its floor in the late Quaternary. One of the most important elements of the floor of the southern Scotia Sea is the Scan Basin, the formation of which played a substantial role in the breakup of the American–Antarctic continental bridge that connected the Bruce and Discovery banks. By now, the main parameters of the sediment sequence in the Scan Basin have been reconstructed, but the literature reflects the lack of data on the upper part of the section. On an observation profile, the Spanish R/V Hesperides, using a TOPAS PS 18/40 high-resolution seismic profiler, distinguished three beds in the central part of the basin. The total mean thickness of the first reflector is 3.7 ms; the second, 2.3 ms; and the third, 1.8 ms. The beds have a relatively consistent thickness and are distinctly traced along the profile. The literature data on the sedimentation parameters make it possible to estimate the total mean deposition time for the first bed of 133 ka; the second, 84 ka; and the third, 64 ka; the total mean sediment accumulation time for all three beds is 281 ka.

Age of the Floors of the Protector and Dove Basins (Scotia Sea)

The tectonic evolution of the transition zone from the Pacific Ocean to the Atlantic Ocean is closely linked with the destruction of the American–Antarctic continental bridge in the Scotia Sea. The western segment of the bridge combines the Terror, Pirie, and Bruce banks, as well as the Protector and Dove basins between them. Modeling—primarily based on original geological and geophysical materials—of linear magnetic anomalies and calculation of the floor kinematics in these basins have made it possible for the first time to reveal that the collapse of the western segment of the American–Antarctic continental bridge occurred 18–25 Ma ago via a two-stage separation of the Pirie Rise from the Bruce Rise with the formation of the Dove Basin and a two stage separation of the Terror Rise from the Pirie Rise with the formation of the Protector Basin.

Risks along the Silk Road Economic Belt owing to natural hazards and construction of major projects

The Belt and Road Initiative was first proposed by Chinese President Xi Jinping during his visit to Kazakhstan in 2013 in order to strengthen economic ties, deepen mutual cooperation, and widen the field of development. The Silk Road Economic Belt has cultural connotations of the ancient Silk Road, a regional cooperation strategy between the Asian and African continents. This belt is important for the promotion of the Chinese economy and the development of economic and trade cooperation between China and countries located along the route. However, the Silk Road Economic Belt passes through the harshest geographical and climatic conditions in the world. The region contains complex geological structures, and is characterized by frequent earthquake activity, large differences in terrain elevation, poor engineering geological conditions, as well as intensive rainfall caused by a monsoon climate. As a result, different kinds of natural disasters, such as earthquakes, geo-hazards, floods, droughts, and dammed lakes, seriously hinder in-depth cooperation and communication between countries located along the Silk Road Economic Belt. This paper presents research on the Silk Road Economic Belt. Primary and secondary natural hazards related to geological events and climate change, such as earthquakes, climatic hazards, and geo-hazards triggered by earthquakes and extreme climatic changes, are analyzed. According to the inventory map of earthquakes, droughts, and geo-hazards, the earthquake-prone areas in this region include Central and Western Asia, the Sino-Pakistan Economic Corridor, the Sino-Mongol-Russia Junction Belt, and the New Euro-Asian Continental Bridge. The flood-prone region is located mainly in Southeastern Asia, in countries such as India, Bangladesh, and Myanmar, while the drought-prone region is located primarily in Inner Asia. The region most susceptible to geo-hazards is the mountainous area around the Tibet Plateau. The tendency of frequent natural hazards to develop and their effects on major projects along the Silk Road Economic Belt are discussed in detail. The results show that seismic activity is likely to be high until approximately 2050 and will become relatively quiescent in the second half of the 21st century. Precipitation will increase by 2%–3% until 2020, and by 5%–7% until 2050. Three high-frequency snow hazard regions are formed, including the central area of Inner Mongolia, the northern region of the Xinjiang Tianshan Range, and the Northeastern Tibet Plateau. Although the inter-annual variability of snow hazards changes significantly, the general trend shows an increase. Drought hazards have become more severe in the Qinghai-Tibet Plateau and have expanded in recent years due to global climate change and other factors. Secondary natural hazards have increased due to the rise in earthquake activity and extreme climatic changes. Strategies for disaster mitigation and natural hazards risk analysis are proposed for major projects such as high-speed railways, oil and gas pipelines, and water and electricity infrastructure. In order to reduce the risk of natural hazards and major construction, six countermeasures are proposed: (1) to perform detailed field investigations and build a database of hazards and related data, including climatic, hydrological, topographical, and geological settings; (2) to integrate engineering protection techniques against natural hazards and develop new mitigation techniques; (3) to develop a space-, sky-, and earth-based real-time monitoring and early warning system; and (4) to comprehensively assess the risk of natural hazards and major project construction. In addition, we face five key scientific and administration challenges regarding the safety of major project construction along the Silk Road Economic Belt: (1) formation mechanisms of large-scale natural hazards; (2) trend and forecast of natural hazards along the Silk Road Economic Belt in the context of climatic change; (3) dynamic and quantitative risk assessment of mega-hazards triggered by the coupling of endogenic and exogenic forces; (4) key techniques and an integrated system for risk reduction for major projects; and (5) coordination mechanism for information sharing and mitigation against mega-hazards among multiple countries.

Impacts of Infrastructure on One Country’s Trade— An Analysis based on the “new Eurasian Continental Bridge Economic Corridor” along the “One Belt One Road”

In nowadays context of global economic integration, China has proposed the “One Belt One Road” Strategy in 2014, which fits into the new changes in global economy and finds us a new growth in economy development. This article has selected the panel data of 23 countries along the “new Eurasian Continental Bridge Economic Corridor” in 2002-2016 and analyzed the influences of one country’s economic infrastructure and social infrastructure upon its national trades using the fixed effect model. The research result shows that the construction of energy infrastructure may produce less obvious negative effects on one country’s national trade while the influences of the railway and aviation infrastructure will be varied because of the different natural endowments of the country. And one country’s trade will increase as construction of communication infrastructure develops. For social infrastructure, the effects upon one country’s trade are not obvious from education infrastructure construction, scientific research infrastructure construction, medical infrastructure construction and environmental infrastructure construction.

Oblique rifting and the Late Eocene–Oligocene demise of Laurasia with inception of Molloy Ridge: Deformation of Forlandsundet Basin, Svalbard

Final breakup of the Laurasian supercontinent occurred within a residual continental bridge that spanned Svalbard, Greenland and Arctic Canada from Late Cretaceous to Oligocene time, but the timing and precise kinematics of that breakup have remained obscure. Dextral oblique motion between Svalbard and northeastern Greenland initially generated the West Spitsbergen Fold-Thrust Belt (a transpressional orogen) but evolved into oblique rifting until the ultimate demise of the continental bridge with the Early Miocene formation of the Molloy Ridge. The Forlandsundet basin stands as a critical entity within the Svalbard continental margin whose fill captured the progressive transition between oblique convergence and divergence. The basin originated as a Late Eocene piggyback basin within the fold-thrust belt during deposition of the oldest unit, the marine fluvio-deltaic Sarsbukta conglomerate. Structural mapping highlights early deformation of the Sarsbukta strata expressed as (1) fractured cobbles in which fractures formed by consistent NNW–SSE stretching were injected with sandy matrix (when poorly lithified), (2) stylolites recording WSW–ENE shortening, and (3) conjugate dextral- and sinistral-normal mesoscale faults that indicate WSW–ENE shortening (P axes) and NNW–SSE extension (T axes). Between 38 and 31Ma, this episode of orogen–normal shortening with orogen–parallel extension evolved progressively into oblique divergence (NW–SE extension) recorded in the Sarsbukta strata as basin-wide strike-slip/normal faults, transtensional folds, and sub-horizontal stylolite surfaces (subvertical P axes). Thus NW–SE extension, consistent with present spreading on the Molloy Ridge, was established at least 9m.y. before the first emergence of recognized oceanic lithosphere. Deformation occurred at upper-crustal temperatures of ≤104°C based on new vitrinite reflectance data. Transtension resulted in intrabasinal exposures of the Caledonide metamorphic basement during deposition of the second unit, the ≥31Ma marine fan-deltaic Sarstangen conglomerate, in the Forlandsundet graben sensu stricto. Such oblique stretching severed the continental bridge heralding ultimate oceanic spreading at the Molloy Ridge.

The resumption of Sino–Central Asian trade, c. 1983–94: confidence building and reform along a Cold War fault line

ABSTRACTThe resumption of trade across the Sino–Central Asian border in 1983 accompanied a gradual thaw in relations between China and the Soviet Union. This paper argues that: (1) Economic liberalization in China (alongside the Soviet Union) created a climate encouraging cross-border exchange. (2) Starting in 1983, improving relations between China and the Soviet Union permitted cross-border exchange in Central Asia; over the subsequent decade, trade volume served as a marker of bilateral relations. (3) Beginning in 1990, efforts by the Chinese leadership to accelerate reform in North-West China, coupled with the independence of Central Asian republics, led to a rapid increase in trade. Hence, the resumption of Sino–Central Asian trade was not grounded in meta-geographical projections – Silk Road, New Silk Road, Silk Road Economic Belt, Eurasian Continental Bridge – but determined by political and economic transitions in the two countries, accompanied by normalizing bilateral relations.

Geochemistry of the apulian allochthonous karst bauxite, Southern Italy: Distribution of critical elements and constraints on Late Cretaceous Peri-Tethyan palaeogeography

A comprehensive study of pebbles from the 'Salento-type' allochthnous bauxite deposit (Otranto, southern Italy), originally derived from a pristine Campanian bauxite, has been performed for evaluating: 1) the chemical fractionation and inter-elemental relationships, especially for critical elements, 2) the climatic conditions that promoted bauxite formation, and 3) the provenance of the protolith(s) using zircon age data and conservative elemental proxies. The study confirms the capability of bauxite to concentrate many elements defined as critical by the European Union report on critical raw materials. Sc, Co, Ga, and especially Cr, are enriched when compared with the UCC composition and assuming Nb is immobile. Other critical elements such as the REEs, with the exception of La, are moderately depleted. R-mode factor analysis suggests that most of the variance in our chemical dataset is explained by a factor with significant weightings for TiO2, Al2O3, Fe2O3, Sc, V, Nb, REEs, Pb and Th. This arises from climate effects affecting the distribution of the more abundant oxides and some trace elements, including the critical metals Nb and REEs. The texture of the pebbles is typical for Apulian karst bauxites and consists of sub-spheroidal ooids composed of boehmite and dispersed in a fine-grained matrix. The growth of the ooids, which formed under dry climate, was described in terms of fractal geometry. The average fractal dimension value of the ooids in the pebbles is close to that of the diffusion-limited aggregation models suggesting the ooid growth can be modelled using a molecular diffusion pattern, based on Fick's first law. The calculated time required for growth of the boehmite concretions is ~45÷310ka. This finding is consistent with an intra-Campanian emersion event (74–76Ma) that occurred during a dry and warm climatic stage. Since most of the karst bauxites worldwide have an ooidic texture, evaluation of the composition of concretions and the time required for their growth represents a powerful tool in reconstructing the palaeoenvironment. The zircon grains collected from the pebbles of the Salento-type karst bauxite define several concordant age populations. The youngest cluster, Early Cretaceous in age (99÷127.5Ma), suggests that windborne particles from Cretaceous volcanics, possibly originating in the Carpatho-Balkan orogenic belts, provided material for further bauxitisation. The largest cluster (623÷689Ma) is of Neoproterozoic age, predominately from the Late Ediacaran and Cryogenian p.p.. The 900–540Ma Pan-African orogenic cycle was followed by continental-scale uplift and erosion, leading to the deposition of thick Cambrian–Ordovician siliciclastic sequences that represent the most widespread detrital sequence ever deposited on continental crust and that now cover large parts of North Africa. These Cambrian–Ordovician sandstones contain a large population of Neoproterozoic zircons of Cryogenian age. Neoproterozoic zircons also occur in the youngest (Silurian–Mesozoic) sandstones of the Saharan Metacraton. These sandstones also contain 1.0Ga detrital zircons, suggesting as the oldest zircons found in the Salento-type bauxite pebbles (866Ma and 941Ma in age) are younger representatives of the zircon cluster present in this sandstone unit.These zircon age determinations suggest that the source material for the Salento-type bauxite pebbles was a combination of magmatic material from a distant source and clastic material derived from a continental margin (North Africa). This result concurs with the Eu/Eu* vs. Sm/Nd binary diagram, on which bauxite pebbles fall close to a mixing curve with andesite and cratonic sandstone end-members. As our results indicate that material was sourced from the North African continental margin, we suggest that a continental bridge separated oceanic domains in the Late Cretaceous of the Peri-Tethyan domain.