Partial high-pressure aragonitization of micritic limestones in an accretionary complex, Tavşanlı Zone, NW Turkey

Pelagic micritic limestones within an upper Cretaceous accretionary complex in the Tavşanlı Zone, NW Turkey, preserve textures indicating incomplete prograde transformation of micritic calcite to aragonite, representing the only known example of this type. Aragonitization starts at the central parts of the micritic limestone beds and advances towards the lower and upper parts of the layers at the expense of micrite. Micrite is very fine grained (<0.003 mm) and contains radiolaria, foraminifera and thin shell fragments. Aragonite forms large crystals, up to 3 cm across, with straight grain boundaries and c-axis mostly subparallel to the carbonate beds. Relict micritic portions are devoid of any aragonite grain. Stylolites characterized by the accumulation of clay minerals, Fe-Mn-hydroxides and quartz are concentrated in the upper and lower parts of the beds. Stylolite formation precedes aragonitization. Conditions of aragonitization are estimated as 200 ± 50 °C and 0.45–0.65 GPa, based on metamorphic mineral assemblages observed in associated basalts. Several features such as (i) constant composition of micritic calcite (98–99 mol.% CaCO₃) throughout individual beds, (ii) enormous grain size difference between micritic calcite and aragonite (up to 1200 times), and (iii) absence of any aragonite grains within the relict micritic portions suggest that kinetic rather than thermodynamic factors controlled selective aragonite formation in the central portions of carbonate layers.     

Pleistocene subglacial tunnel valleys in the central North Sea basin: 3‐D morphology and evolution

Four phases of cross‐cutting tunnel valleys imaged on 3‐D seismic datasets are mapped within the Middle–Late Pleistocene succession of the central North Sea basin (Witch Ground area). In plan the tunnel valleys form complex anastomosing networks, with tributary valleys joining main valleys at high angles. The valleys have widths ranging from 250 to 2300 m, and base to shoulder relief varying between 30 and 155 m, with irregular long‐axis profiles characteristic of erosion by water driven by glaciostatic pressures. The youngest phase of tunnel valleys are smaller and have a thinner infill than the older generations. The fill of the larger valleys comprises three seismic facies, the lowermost of which has high amplitudes and is discontinuous. The middle facies consists of wedge‐shaped packages of low‐angle dipping reflectors and is overlain by a facies characterised by sub‐horizontal reflectors, which onlap the valley margins. The seismic character, and comparison with lithologies identified in other northwest European Pleistocene tunnel valleys both onshore and offshore, suggests that the lower two seismic facies are most likely sand and gravel‐dominated, while the uppermost facies consists of glaciolacustrine and marine muds. The 3‐D morphology of the valley margins combined with the geometry of the infill packages suggest that episodic discharge of subglacial meltwater was responsible for incising the valleys and depositing at least some of the infill. Proglacial glaciofluvial deposits are inferred to account for some of the fill overlying the subglacial deposits. Glaciolacustrine and marine muds filled remaining valley topography as the ice sheet retreated. The preserved valley margins are shown to be time‐transgressive erosion surfaces that record changes in geometry of the tunnel valley system as it evolved through time, implying that valleys associated with each ice‐sheet advance/retreat cycle were dynamic and probably long‐lived. Within the constraints of the existing stratigraphy the oldest tunnel valleys in the Witch Ground area of the central North Sea are most likely to be Marine Isotope Stage (MIS) 12 (Elsterian, ca. 470 ka) in age and the youngest pre‐MIS 5e (last interglacial, ca. 120 ka). If each tunnel valley phase was formed during the retreat of a major ice sheet then four glaciations with ice coverage of the central North Sea are recorded in the pre‐Weichselian, Middle–Late Pleistocene stratigraphy. Copyright © 2006 John Wiley & Sons, Ltd.     

Astrophysically Useful Parameters for Some Vibronic Transitions of AlH and BH

For molecular identification in astrophysical sources, an astrophysicist needs some spectroscopic parameters such as dissociation energy, vibrational or rotational temperature of the source, band or line wavelengths, transition probability parameters, etc. The Franck-Condon(FC) factors are proportional to the transition probabilities. In this study, the FC factors and r-centroids for the vibronic (vibration-electronic) transitions C ¹ Σ ⁺ → X ¹ Σ ⁺ of aluminium hydride (AlH), b ³ Σ ^{( −)} → a ³ Π, C ¹ Σ ⁺ → A ¹ Π & C ^′1 Δ → Δ ¹ Π of boron hydride (BH) have been evaluated and the results are presented in tables which include band origin/head wavelengths. The physical & astrophysical significances of our evaluated FC factors & r-centroids have been discussed and the possible presence of AlH in sunspot umbral spectra is also predicted. PACS: 33 · 70 · Ca     

Pleistocene fluvial sediments,palaeontology and archaeology of the upper River Thames at Latton,Wiltshire, England

Pleistocene fluvial sediments of the Northmoor Member of the Upper Thames Formation exposed at Latton, Wiltshire, record episodic deposition close to the Churn–Thames confluence possibly spanning the interval from Marine Isotope Stages (MIS) 7 to 2. The sequence is dominated by gravel facies, indicating deposition by a high‐energy, gravel‐bed river. A number of fine‐grained organic sediment bodies within the sequence have yielded palaeoenvironmental and biostratigraphical data from Mollusca, Coleoptera, vertebrates, pollen and plant macrofossils. The basal deposit (Facies Association A) contains faunal material indicating temperate conditions. Most of the palaeontological evidence including a distinctive small form of mammoth (Mammuthus cf. trogontherii), together with the U‐series age estimate of >147.4 ± 20 kyr suggest correlation with MIS 7. The overlying deposits (Facies Associations B and C) represent deposition under a range of climatic conditions. Two fine‐grained organic deposits occurred within Association B; one (Association Ba) in the northern part of the pit as a channel fill and the other (Association Bb) in its southern part as a scour‐fill deposit. The coleopteran assemblages from Ba, indicate that it accumulated under temperate oceanic conditions, while Bb, which also yielded a radiocarbon age estimate of 39 560 ± 780 ¹⁴C yr BP, was formed under much colder and more continental climatic conditions. The sequence is considered to represent deposition within an alluvial fan formed at the Churn–Thames confluence; a depositional scenario which may account for the juxtaposition of sediments and fossils of widely differing age within the same altitudinal range. Copyright © 2006 John Wiley & Sons, Ltd.     

China’s rising influence on climate governance: Forging a path for the global South

China’s influence on climate governance has been steadily increasing since the adoption of the Paris Agreement on climate change in 2015. Much of this influence, this article argues, has come from China forging a path for climate adaptation and mitigation for the global South. This is having far-reaching consequences, the article further argues, for the politics of global climate governance. China’s discursive and diplomatic power in climate politics is growing as China builds alliances across the global South. China is leveraging this enhanced soft power to elevate the importance of adaptation in multilateral climate negotiations, advance a technocentric approach to climate mitigation, export its development model, and promote industrial-scale afforestation as a nature-based climate solution. China’s strategy is enhancing climate financing, technology transfers, renewable power, and adaptation infrastructure across the global South. To some extent, this is helping with a transition to a low-carbon world economy. Yet China’s leadership is also reinforcing incremental, technocratic, and growth-oriented solutions in global climate governance. These findings advance the understanding of China’s role in global environmental politics, especially its growing influence on climate governance in the global South.     

New ESR/U-series dates of the lowest Acheuleo-Yabrudian levels of Qesem cave

Qesem cave is a Middle Pleistocene site located close to Tel Aviv, Israel, assigned to the Acheuleo-Yabrudian Cultural Complex (AYCC) of the Lower Palaeolithic. The site provides rich assemblages of knapped flint, animal remains and some human teeth making it of particular interest. Its location in the Levantine corridor confers a major interest to the understanding of human dynamics during the Middle Pleistocene.A series of 6 herbivorous teeth from the base of the 11 m archaeological sequence of AYCC Qesem Cave was analysed by combined ESR/U-series method; this complements previous dating series carried out on teeth and on heated flints on higher parts of the sequence (Mercier et al., 2013; Falguères et al., 2016) The teeth were measured according a regular protocol for which each tissue was analysed by inductively coupled plasma-quadrupole mass spectrometry (ICP-Q-MS) for U-series using a combination of a Thermo iCAP-RQ mass spectrometer coupled to a Cetac Aridus III desolvator system, and ESR analyses were implemented on enamel tissue. All these data were combined in order to yield modelled ages.The goal was to find out whether there was a time gap between the carbonates layers dated to 420 ka (Gopher et al., 2010) and archaeological layers of the AYCC found throughout the cave's sequence. The new results yield ages ranging between 220 and 430 ka confirming a great antiquity and a long duration of AYCC in the Levant.     

ESR chronology of the fluvial sequence of Cueva del Silo (Sierra de Atapuerca,Spain)

The Cueva del Silo is part of the lower karst level of the Cueva Mayor-Cueva del Silo karst system (Sierra de Atapuerca, Burgos, Spain), whose evolution has preserved an impressive archeo-paleoanthropological sequence since the Early Pleistocene. Cueva del Silo is remarkable for the presence of fluvial deposits that record the entry of the Arlanzón River water in the cave system, providing a key sequence to investigate the fluvio-karstic relationships that give rise to this endokarst system. In order to provide a chronological framework to these fluvial deposits, six sediment samples were dated by Electron Spin Resonance and 16 samples by paleomagnetism, collected from two outcrops: Galería de las Arenas and Sala del Caos. Our results provide maximum mean age of around 1600 ka and a minimum age of 916 ± 136 ka for the deposits in Sala del Caos. The younger date from Sala del Caos might represent the last fluvial input from Arlanzón River in the lower karst level. In contrast, ESR ages estimates of 1268 ± 133 ka and 1262 ± 108 ka were obtained for Galería de las Arenas sequence, which could indicate re-sedimentation processes from the intermediate karst level where similar ages were published. The annual dose might be wrongly assessed due to the re-sedimentation processes inside the karst, hence, ESR ages for these facies should be treated with extreme caution.     

柴达木盆地大浪滩梁ZK02孔早—中更新世石盐纯液相流体包裹体均一温度及其对钾盐成矿的约束

运用低温冷冻成核方法,对柴达木盆地大浪滩地区梁ZK02孔早—中更新世石盐样品的纯液相流体包裹体进行均一温度测试,获得158个均一温度数据。所测石盐样品的镜下形貌显示有石盐“人”字晶特征,其内部流体包裹体呈负立方体晶形,且测试均一温度数据与包裹体粒度相关性不明显,指示了测试石盐及包裹体原生性良好,其最大均一温度可代表古代夏季气温。最大均一温度测试结果表明:(1)早更新世最大均一温度主要分布于25~30 ℃温度区间,高泥质、粉砂岩性特征指示早期气候较为温和,淡水补充相对丰富;晚期盐类矿物含量升高,反映干旱程度升高;个别时间段夏季温度高于40 ℃,呈高温干旱特征。(2)中更新世温度位于30~35 ℃温度区间,出现了更新世以来最高温度50.6 ℃,包裹体最大均一温度与高含量盐类矿物共同指示了高温干旱环境特征。与早更新世相比,中更新世环境温度总体呈升高趋势,蒸发盐含量升高,干旱程度增加,温度波动加剧,显示出中更新世更加不稳定的气候特点,与世界范围内中更新世总体气候特征一致,且盐类分布显示这种气候不稳定性在大浪滩地区自早更新世晚期就开始显现了。结合石盐包裹体古温度研究成果,对阿尔金山前砂砾岩孔隙含钾卤水矿成矿模式进行补充:早更新世较为温和湿润的环境下,风化盐分和N22古盐发生溶滤,汇聚形成含盐卤水,赋存于阿尔金山前冲洪积扇砂砾岩孔隙中,历经中更新世的高温蒸发,最终形成KCl砂砾岩孔隙储层卤水矿床。     

Cretaceous A-type volcanic–intrusive rocks and simultaneous mafic rocks along the Gan-Hang Tectonic Belt,Southeast China: petrogenesis and implications for the transition of crust–mantle interaction

ABSTRACT

Abundant evidence points to the Cretaceous crust–mantle interaction and plate subduction in the Gan-Hang Tectonic Belt (GHTB), southeastern China, but the evolutionary process remains poorly constrained. Here we conduct a comprehensive study on Daqiaowu granitic porphyry and diabase dikes in the eastern GHTB, in conjunction with previous studies on simultaneous felsic and mafic rocks along the GHTB, to demonstrate their petrogenesis and geodynamic evolutionary process. The Daqiaowu granitic porphyry (125 Ma), as well as the coeval granitic rocks, exhibits high zircon saturation temperatures, alkalis, 10⁴*Ga/Al ratios, and Zr + Nb + Ce + Y contents, concluding a distinctive belt of the Early Cretaceous (~137–125 Ma) A-type volcanic–intrusive rocks in the GHTB. Their ε_Nd(t) and zircon ε_Hf(t) values gradually increased through time from approximately ?9.0 to ?1.0 and ?10.0 to +4.0, respectively, implying increasing contribution of mantle-derived components to their formation, and hence progressively intensified crust–mantle interaction in an intra-arc rift environment (a geodynamic transition stage from continental arc to back-arc) during the Early Cretaceous. This plausibility is further supported by the Early Cretaceous Daqiaowu diabase dikes and coeval mafic rocks which exhibit arc-like magmatic signatures and were derived from mantle wedge. In contrast, the Late Cretaceous mafic rocks show ocean island basalt-like geochemical characteristics, reflecting a depleted asthenosphere mantle source. This discrepancy of mantle sources concludes that the geodynamic setting in the GHTB may have basically transferred to back-arc regime in the Late Cretaceous. Thus, the Cretaceous geodynamic evolutionary process in the GHTB can be defined as the Early Cretaceous gradually intensified crust–mantle interaction in a geodynamic transition stage (from continental arc to back-arc extension) and the Late Cretaceous back-arc extensional setting.     

Late Pleistostene-Holocene sedimentation in lakes of central Transbaikalia: Implications for climate and environment changes

We present integrated mineralogical, geochemical, and palynological data for Late Pleistocene-Holocene bottom sediments of Lake Arakhlei located in the Beklemishev tectonic basin in the southern Vitim Plateau (central Transbaikalia). The sediment samples were studied by X-ray diffractometry (XRD), Fourier-transform infrared (FTIR) spectroscopy, laser particle sizing, spore-pollen analysis, radiocarbon (¹⁴C AMS) dating, and XRF spectrometry. The cored 128 cm long section of lake sediments consists of two units: One is composed mainly of layered silicates (illite-smectite, illite, chlorite, chlorite-smectite, muscovite, and kaolinite) and organic matter (OM) but no carbonates from 0 to 80 cm and the other contains authigenic Ca-Mg carbonates (up to 30%) of Mg-calcite and excess-Ca dolomite from 80 to 128 cm. The sediments also contain a rare mineral weddellite CaC₂O₄2H₂O discovered for the first time in Transbaikalian lakes. The evolution of Lake Arakhlei and its drainage basin comprised four stages, with pollen zones that mark the Late Pleistocene and Holocene climate history of the Beklemishev basin. The reconstructed history of Lake Arakhlei for the past ~ 15,500 years followed general climatic changes in the Northern Hemisphere. Thus, integrated research, including detailed analysis of mineral components and spore-pollen assemblages in lake sediments, is a workable tool for studying climatic controls of continental sedimentation.