Generations of spreading basins and stages of breakdown of Wegener’s Pangea in the geodynamic evolution of the Arctic Ocean

Chronological succession in the formation of spreading basins is considered in the context of reconstruction of breakdown of Wegener’s Pangea and the development of the geodynamic system of the Arctic Ocean. This study made it possible to indentify three temporally and spatially isolated generations of spreading basins: Late Jurassic-Early Cretaceous, Late Cretaceous-Early Cenozoic, and Cenozoic. The first generation is determined by the formation, evolution, and extinction of the spreading center in the Canada Basin as a tectonic element of the Amerasia Basin. The second generation is connected to the development of the Labrador-Baffin-Makarov spreading branch that ceased to function in the Eocene. The third generation pertains to the formation of the spreading system of interrelated ultraslow Mohna, Knipovich, and Gakkel mid-ocean ridges that has functioned until now in the Norwegian-Greenland and Eurasia basins. The interpretation of the available geological and geophysical data shows that after the formation of the Canada Basin, the Arctic region escaped the geodynamic influence of the Paleopacific, characterized by spreading, subduction, formation of backarc basins, collision-related processes, etc. The origination of the Makarov Basin marks the onset of the oceanic regime characteristic of the North Atlantic (intercontinental rifting, slow and ultraslow spreading, separation of continental blocks (microcontinents), extinction of spreading centers of primary basins, spreading jumps, formation of young spreading ridges and centers, etc., are typical) along with retention of northward propagation of spreading systems both from the Pacific and Atlantic sides. The aforesaid indicates that the Arctic Ocean is in fact a hybrid basin or, in other words, a composite heterogeneous ocean in respect to its architectonics. The Arctic Ocean was formed as a result of spatial juxtaposition of two geodynamic systems different in age and geodynamic style: the Paleopacific system of the Canada Basin that finished its evolution in the Late Cretaceous and the North Atlantic system of the Makarov and Eurasia basins that came to take the place of the Paleopacific system. In contrast to traditional views, it has been suggested that asymmetry of the northern Norwegian-Greenland Basin is explained by two-stage development of this Atlantic segment with formation of primary and secondary spreading centers. The secondary spreading center of the Knipovich Ridge started to evolve approximately at the Oligocene-Miocene transition. This process resulted in the breaking off of the Hovgard continental block from the Barents Sea margin. Thus, the breakdown of Wegener’s Pangea and its Laurasian fragments with the formation of young spreading basins was a staged process that developed nearly from opposite sides. Before the Late Cretaceous (the first stage), the Pangea broke down from the side of Paleopacific to form the Canada Basin, an element of the Amerasia Basin (first phase of ocean formation). Since the Late Cretaceous, destructive pulses came from the side of the North Atlantic and resulted in the separation of Greenland from North America and the development of the Labrador-Baffin-Makarov spreading system (second phase of ocean formation). The Cenozoic was marked by the development of the second spreading branch and the formation of the Norwegian-Greenland and Eurasia oceanic basins (third phase of ocean formation). Spreading centers of this branch are functioning currently but at an extremely low rate.     

New results of OSL dating of Quaternary sediments in the Upper Katun’ valley (Gorny Altai) and adjacent area

Several sections have been studied to understand the distribution and interrelation of basic genetic types of Quaternary deposits in the Uimon basin and adjacent area. The OSL date of 101 ± 10 ka from the glaciolacustrine terrace on the northeastern rim of the basin corresponds to the cool substage of MIS 5. The glaciolacustrine sediments of the northern rim are covered with widespread diamictic flows of the outburst draining of the ice-dammed lake. The diamicts are overlain by a subaerial complex of loesses and three fossil soils. From the OSL loess dates in the range of 43 to 49 ka we infer that the complex formed from the early MIS 3 through the Holocene. This is also supported by radiocarbon dates from alluvial deposits incised into the glaciolacustrine terrace and into megaflood sediments of the final draining of the last paleolake. The OSL dates in the range of 77 to 89 ka from alluvial sediments indicate that postglacial downcutting of the present-day Katun’ valley probably started just after MIS 5. The discrepancy between the beryllium dates from dropstones and Holocene TL-dates of the Katun’ valley floods ranging from 23 to 6 ka can be explained if the younger floods are related to the draining of moraine- and rock slide dammed rather than ice-dammed lakes. The younger floods, though being less voluminous than the glacial megafloods, were capable of producing giant ripple marks.     

Alternative chronologies for Late Quaternary (Last Interglacial–Holocene) deep sea sediments via optical dating of silt-sized quartz

We summarize the results of a test on the potential of optical dating for the age assessment of Late Quaternary deep-sea sediments. Our approach combines a single aliquot regeneration (SAR) protocol for equivalent dose (D_e) estimation on fine silt-sized quartz with a time-dependent evaluation of supported and unsupported long-lived radioisotopes within the deposited sediment matrix. For this purpose nine samples from two independently dated deep-sea cores from the Indian Ocean were obtained. The SAR analysis resulted in mean D_e estimates with precisions ranging from 0.9% to 3.7%. Combination of these data with measured radioisotope concentrations resulted in stratigraphically sensible ages ranging from ca 7 to 120 ka. These ages exhibit good agreement with existing chronologies for the cores based on radiocarbon age determinations and correlation of key volcanic, palaeoecological and isotopic events. Optical dating may provide an important additional dating method for Late Quaternary deep-sea sediments.     

Evaluating igneous sources of the Taveyannaz formation in the Central Alps by detrital zircon U–Pb age dating and geochemistry

Late Palaeogene syn-tectonic volcanic products have been found in the Northern Alpine foreland basin and in the South Alpine hemipelagic basin. The source of abundant volcanic fragments is still in debate. We analyzed the geochronology and geochemistry of detrital zircons, and evaluated their temporal and genetic relationships with potential volcanic sources. The study shows that the detrital zircon U–Pb age patterns have two major age groups: a dominance (ca. 90%) of pre-Alpine zircons was found, as commonly observed in other Alpine flysch formations. These zircons apparently derived from erosion of the early Alpine nappe stack in South Alpine and Austroalpine units. Furthermore, a few Neo-Alpine zircons (ca. 10%) have ages ranging from Late Eocene to Early Oligocene (~ 41–29 Ma). Both source materials were mixed during long riverine transport to the basin margins before being re-deposited by gravity flows. These Palaeogene ages match with the activity of Peri-Adriatic magmatism, including the Biella volcanic suite as well as the Northern Adamello and Bergell intrusions. The values of REE and ¹⁷⁶Hf/¹⁷⁷Hf_(t) ratios of the Alpine detrital zircons are in line with the magmatic signatures. We observe an in time and space variable supply of syn-sedimentary zircons. From late Middle Eocene to Late Eocene, basin influx into the South Alpine and Glarus (A) basins from the Northern Adamello source is documented. At about 34 Ma, a complete reorganisation is recorded by (1) input of Bergell sources into the later Glarus (B) basin, and (2) the coeval volcaniclastic supply of the Haute-Savoie basin from the Biella magmatic system. The Adamello source vanished in the foreland basin. The marked modification of the basin sources at ~ 34 Ma is interpreted to be initiated by a northwestern shift of the early Alpine drainage divide into the position of the modern Insubric Line.     

Zircon geochronology constraints on the age and nature of ‘Precambrian metamorphic rocks’ in the Xing’an block of Northeast China

The Great Xing’an Range in Northeast China is located in the eastern part of the Central Asian Orogenic Belt. From north to south, the Great Xing’an Range is divided into the Erguna, Xing’an, and Songliao blocks. Previous U–Pb zircon geochronology results have revealed that some ‘Precambrian metamorphic rocks’ in the Xing’an block have Phanerozoic protolith ages, questioning whether Precambrian basement exists in the Xing’an block. We present laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb dating results for zircons from suspected Precambrian metamorphic rocks in the Xing’an block. Meta-rhyolites of the Xinkailing Group in Nenjiang yield magmatic ages of 355.8 Ma. Detrital zircons from phyllites of the Xinkailing Group in Duobaoshan yield populations of ca. 1505, ca. 810, and ca. 485 Ma, with the youngest peak constraining its depositional age to be <485 Ma. Zircons from amphibolitic gneisses of the Xinkailing Group in Nenjiang have magmatic ages of 308.6 Ma. Mylonitic granites of the Xinkailing Group in Nenjiang have zircon magmatic ages of 164 Ma. Detrital zircons from two-mica quartz schists of the Luomahu Group in the Galashan Forest yield ca. 2419, ca. 1789, ca. 801, ca. 536, ca. 480, and ca. 420 Ma, with the youngest peak indicating its depositional age as <420 Ma. Detrital zircons from mylonitized sericite–chlorite schist of the Ergunhe Formation in Taerqi yield populations of 982–948, ca. 519, and ca. 410 Ma, with the youngest peak demonstrating that its depositional age is <410 Ma. These zircon ages for a range of lithologies show that the Great Xing’an Range metamorphic rocks formed during the Phanerozoic (164–485 Ma) and that this crust is mostly Palaeozoic. Based on these results and published data, we conclude that there is no evidence of Precambrian metamorphic basement in the Xing’an block. In summary, the age data indicate that Precambrian metamorphic basement may not exist in the Xing’an region.     

Assessment of cadmium contamination in the sediments of Changjiang （Yangtze） River by reflectance spectroscopy

The Takab area in NW of Iran is an important gold mineralized region with a long history of gold mining. In this study ASTER data is used to evaluate environmental effects of gold mining. The results show that mining activities have resulted in release of potentially toxic metals （PTMs） in the area. Principal component analysis （PCA） of ASTER data is used to map sources of PTMs and their secondary hosts （iron oxides） through alteration mapping. The results show that selective PCA is a robust yet time consuming technique for alteration mapping. A color composite is created for finding common hydrothermally altered rocks. The created color composite successfully mapped the known deposits and anomalous areas identified by geological survey of Iran. Because of the low spatial resolution of ASTER sensor, the iron oxide mapping is restricted to the wider portions of the streams. Spectral analyses confirm the presence of hematite and goethite in stream sediments. This is in accordance with measured pH values.     

The ‘urban–rural divide’ at question: exploring the long-term shift of marital age in Greece

GeoJournal - While marital age is the highest worldwide, spatial disparities still exist among European regions. Although Mediterranean societies were traditionally characterized by high propensity...     

Thermodynamic simulation of the effect of eutrophication on the behavior of heavy metals in bottom sediments by the example of the Inan’kovsky water reservoir

A thermodynamic model of the behavior of heavy metals in bottom sediments during their eutrophication is developed. The results show that liberation of heavy metals from the reduced ferrous sorbent is accompanied by sorption on clay and organic sorbents. The process is complicated by competitive correlations between heavy metals and calcium ions, while the formation of carbonate cement in the sediments yields additional sorption. As a result, the predicted concentrations of the majority of microelements, namely heavy metals, in the interstitial water of the reduced bottom sediments do not exceed the maximum permissible concentration (MPC).     

The age of high-pressure metasomatism in shear zones during collision-related metamorphism in the Lapland granulite belt: The Sm-Nd method of dating the paragenesises from sillimanite-orthopyroxene rocks of Por’ya Guba nappe

The Sm-Nd isotope-chronological method is used for the first time to investigate the whole rock and rock-forming minerals from metasomatic sillimanite orthopyroxene rocks in the Por’ya Guba nappe of the Lapland granulite belt. As a result isochrone values of the age are obtained, which allows estimate the minimum time intervals that have passed from the moment of formation of the investigated rocks. They indicate that peak conditions of collision metamorphism in fluid-permeable shear zones of the LGB occurred in the Paleoproterozoic Svekofennian age when high-temperature high-pressure sillimanite-orthopyroxene metasomatic rocks were formed. The obtained data make it possible to assume that, with regard to the measurement errors, high-pressure metasomatism did not last over 10 Ma, and this process did not coincide in time with older medium pressure metamorphism.     

Late Tertiary ‘grey billy’ and the age and origin of surficial silicifications (silcrete) in South Australia

A late‐Tertiary age, as well as the commonly accepted mid‐Tertiary age, is proved for widespread silcretes in S.A. This is demonstrated by stratigraphic relationships with palynologically dated sequences, and evidence of erosion of silcretes. The age limits are Early Eocene to Early Miocene and Medial Miocene to Early Pleistocene, probably Late Pliocene. The late‐Tertiary silcrete dominates the duricrusted landscape flanking the north of the Willouran and Flinders Ranges, and forms patches throughout the Tarkarooloo Lobe (Lake Frome area). Silica type varies according to the material cemented; chalcedony and opal are more common in finer grained, less permeable, clayey clastics, and micro‐ to crypto‐crystalline quartz ('grey billy’ or ‘terrazzo') in porous permeable arenites and regoliths.

‘Grey billy’ silcretes with pedogenic features resembling massive nodular calcretes were probably formed close to phreatic surfaces or in the soil zone, and result from deposition of silica and titania from surface waters near ground level. They can be used to mark unconformities. Those without such features were formed at depths of several to tens of metres in the phreatic zone, beyond the effects of a fluctuating groundwater table.

The varying composition of groundwaters and fluctuations of the phreatic surface probably occurred as the result of climatic changes from wet to arid to wet, causing alternate solution and redeposition of silica. Silcrete was essentially a late Mesozoic‐Cainozoic phenomenon, this being a time of general uplift of the Australian continent during intervals of climatic fluctuation. However, the time spans of Australian silcretes are not sufficiently known to make correlations with major climatic events, which are on a finer time‐scale.     

Dinosaur material from the Lower Greensand Group of Upware,Cambridgeshire, and the age of ‘Wealden’ vertebrates from the ‘Bedfordshire Straits’

Post-Wealden dinosaur remains are rare in the UK, so any material from late Early or Late Cretaceous deposits is potentially of palaeoecological and palaeobiogeographical significance. Four dinosaur specimens collected from the Woburn Sands Formation (Aptian) of Upware, Cambridgeshire were described briefly by Walter Keeping in 1883, but have not been reappraised since. These specimens are identified herein as a ?turiasaurian sauropod tooth and indeterminate iguanodontian ornithopod remains (a tooth, middle caudal vertebra, pollex ungual). Although collected from the Woburn Sands Formation, it is likely that all of these fossils were reworked from older (now absent) sediments and they have usually been regarded as either ‘Wealden’ or Neocomian in age, presumably due to previous identifications of some of these specimens as Iguanodon. However, consideration of UK dinosaur faunas and regional geology indicates that these fossils could potentially be older. Further work is needed on the derived terrestrial fossils of the Lower Greensand Group in order to constrain their ages more precisely so that they can be incorporated into broader studies of regional diversity and palaeoecology.     

Socio-economic determinants of women’s livelihood time use in rural Bangladesh

Achieving gender well-being and equality is one of the 17 Sustainable Development Goals of the United Nations. A close examination of female livelihood time allocation can reveal gender inequality in livelihood choices between males and females. Using the feminist political ecology framework, this paper examines how gendered knowledge, roles, and responsibilities influence female livelihood time use in a patriarchal society like Bangladesh. We use a nationally representative household survey data to create Multiple Linear Regression Model to understand the association between economic, cultural, and environmental shocks with the total time allocation toward livelihood activities by women. Our results suggest that use of ‘Purdah’ by Muslim women acts as a negative detrimental factor towards their livelihood time allocation, thus affirming the complex role of culture and gendered economic activities. Women also allocate less time toward livelihood activities during pregnancy and/or breastfeeding. We find that female livelihood time use also depends on their ability to speak in public, their autonomy in livelihood decision processes, and their ownership in business enterprises. This research suggests creating more robust and gender sensitive policies in Bangladesh that can help achieve the United Nation’s goals of Sustainable Development.

     

Analytical Conditions for the Formation of Arctic Amplification in the Earth’s Climate System

Doklady Earth Sciences - Analytical conditions for estimating the contribution of various internal and external factors to the formation of Arctic (polar) amplification under warming of the...