Record-low 2016 Antarctic sea ice due to ‘perfect storm’ of tropical, polar conditions

While winter sea ice in the Arctic is declining so dramatically that ships can now navigate those waters without any icebreaker escort, the scene in the Southern Hemisphere is very different. Sea ice area around Antarctica has actually increased slightly in winter — that is, until last year. A new study shows the lack of Antarctic sea ice in 2016 was in part due to a unique one-two punch from atmospheric conditions both in the tropical Pacific Ocean and around the South Pole.

Ecological water requirement of plant–soil systems along the Silk Road Economic Belt: A case study of the Guanzhong–Tianshui region, China

“The Belt and Road” refers to the Silk Road Economic Belt and the 21st‐Century Maritime Silk Road. In this paper, the Guanzhong–Tianshui region is selected as a case study, which is located at the starting point of the Silk Road Economic Belt. First, the spatial distribution maps of plant and soil types are obtained based on the TM remote sensing images and the soil texture data. The boundaries of the third‐level watershed are extracted based on the digital elevation model data. Then the corresponding mathematical models are used to evaluate the ecological water requirements of the plant–soil systems. Also, the spatial distribution characteristics are analysed at the landscape scale and the third‐level watershed scale. The results show that the spatial differences of ecological water requirement in the Guanzhong–Tianshui are obvious. At the plant–soil landscape scale, the ecological water requirement per unit area of the woodland‐clay loam is the highest, about 0.4777 m3/m2, while that of the grassland‐gravel loam is the lowest, about 0.2813 m3/m2. At the third‐level watershed scale, the ecological water requirement per unit area in the Weihe watershed (Jinghezhangjiashan above) is the highest, about 0.4123 m3/m2, while that in the Weihe watershed (Longmen to Sanmenxia) is the lowest, about 0.3002 m3/m2. The study offers scientific references for the regional ecological environment protection and ecosystem management.

Characterization of the Lower Silurian Longmaxi marine shale in Changning area in the south Sichuan Basin, China

On the basis of the core description, thin sections, and geochemistry data, we characterized the Lower Silurian Longmaxi marine shale in the Changning area in the south Sichuan Basin. Ten lithofacies were identified in the Lower Silurian Longmaxi marine shale: (a) massive silty shale (Lithofacies A); (b) laminated siliceous calcareous shale (Lithofacies B); (c) calcareous shale (Lithofacies C); (d) silty dolomitic shale (Lithofacies D); (e) argillaceous siltstone (Lithofacies E); (f) siltstone (Lithofacies F); (g) laminated silty shale (Lithofacies G); (h) silty calcareous shale (Lithofacies H); (i) argillaceous lime shale (marl) (Lithofacies I); and (j) bentonite (Lithofacies J). Obvious heterogeneity occurred in different lithofacies in terms of mineralogy, total organic carbon (TOC) content, porosity, permeability, pore surface area, total pore volume, and total gas content. Among these lithofacies, Lithofacies B has the highest porosity (5.4%), pore surface area (12.79 m2/g), total pore volume (0.015 cc/g), TOC content (4.37%), total gas content (3.4 m3/ton), and relatively high brittle minerals, suggesting great shale gas potential. Lithofacies A, C, and D have a relatively high brittle minerals, porosity, pore surface area, total pore volume, TOC content, and total gas content, which means that these 3 lithofacies show relatively good potential for shale gas. The rest of the lithofacies have low brittle minerals content, porosity, pore surface area, total pore volume, TOC content, and total gas content, representing poor shale gas potential.

Rare earth elements geochemistry characteristics and their geological implications of lacustrine oil shale from Chang 7 oil layer in southern Ordos Basin, China

Located in the middle‐western area of China, Ordos Basin is a large continental basin with vast petroleum resources. Oil shale of Chang 7 oil layer from Triassic Yanchang Formation represents the typical lacustrine oil shale in China. Oil shale samples were collected from Chang 7 oil layer to study the characteristics of elements geochemistry. The rare earth elements (REEs) concentration of oil shale samples varies from 138.51 to 206.36 μg/g with an average of 162.64 μg/g, close to the average REEs content of the North American shale Composite and slightly higher than the upper continental crust. The chondrite‐normalized and North American shale composite‐normalized REEs distribution patterns explain that oil shale samples, together with silty mudstone samples, may have been derived from a similar terrigenous source. The oil shale deposited mainly in early diagenetic stage B period and the paleoclimate condition was warm and humid with moderate chemical weathering. The whole sedimentary rate of oil shale was low. The source rocks of oil shale were mainly from the felsic rocks and deposited in the continental island arc tectonic setting. The total REE of oil shale samples show positive correlations with Al, Si, K, and ash yield concentration and negative correlations with oil yield, Fe, P, and total sulfur concentration, illustrating that REEs concentration in clay minerals is more than that in organic matter. In addition, the light REEs and heavy REEs are both present in clay minerals and controlled by land‐derived detritus.

Sequence stratigraphy and depositional system analysis in Paleogene Nanpu Sag: Sequence model and sediment partition

In this study, we use 3D seismic, well‐log, and core data to investigate the sequence stratigraphy and facies associations of the Paleogene in the Nanpu Sag, Bohai Bay Basin, East China. Three second‐order sequences—SQEs3‐SQEs2, SQEs1, and SQEd—and 12 third‐order sequences are identified. Fan‐delta, braid‐delta, sublacustrine fan, and lacustrine systems are identified. Four types of tectonic‐induced sequence models are distinguished, which consist of fault‐cliff type, fault‐slope type, axial ramp type, and multiple fault‐terrace type. Sequence architecture of third‐order sequences is dominated by thin lowstand systems tracts with thick transgressive systems tracts (TST) and highstand systems tracts (HST). High‐resolution sediment‐partition pattern analysis shows that a large volume of sediments can be delivered into prodelta/deep‐lacustrine environments during transgressive periods and lake‐level highstand. This study also shows that sand/strata ratios in fan‐delta/braid‐delta front of systems tracts scale have a negative correlation with the subsidence rate, which is demonstrated by the finding that higher subsidence rates correspond to lower sand/strata ratios. This result suggests that subsidence rate has a significant influence on high‐frequency sequences. The occurrence of the high volume of sand‐rich deposits developed in TST and HST and relatively high sand/strata ratios within these sequence units reveal that TST and HST could also have a high hydrocarbon potential. The strongly asymmetrical accommodation generated by an early rapid tectonic subsidence and late tectonic quiescence results in sequence architecture variations between passive‐margin basins and rift basins. Different subsidence rates among different structural belts result in sequence architecture variations within different sequence models.

The genesis of the Xujiagou copper deposit, Mian-Lue-Ning area of Shaanxi Province, NW China: Constraints from mineral chemistry and in situ Pb isotope composition

The Mian-Lue-Ning area, bounded by the Hanjiang fault zone in the south and the Mian-Lue suture in the north, is one of the most important polymetallic mineralization concentration regions in the Qinling orogenic belt. The Xujiagou copper deposit is representative in this area with chalcopyrite and pyrrhotite as the main ore minerals, subordinate sphalerite, and pyrite. However, the source of the ore-forming materials and the genesis of the Xujiagou copper deposit are still in a controversy due to the lack of detailed study on the mineral composition. In this study, the electron probe micro-analyzer (EPMA) analysis shows that the pyrrhotite in the Xujiagou copper deposit is mostly monoclinic pyrrhotite of low-temperature phase, indicating that the metallogenic temperature should be below 304 °C. The percent of FeS molecules in sphalerite is 8.16–12.1%, indicating that the metallogenic temperature is 230–258 °C, which is mesothermal mineralization. The in situ Pb isotope composition of chalcopyrite (206Pb/204Pb = 19.087–20.861; 207Pb/204Pb = 15.533–16.062; 208Pb/204Pb = 38.121–39.391) and pyrrhotite (206Pb/204Pb = 20.241–20.664; 207Pb/204Pb = 15.7–15.996; 208Pb/204Pb = 38.659–39.372) in the Xujiagou copper deposit was analysed by fLA-MC-ICPMS, and it indicates that the ore-forming materials were mainly sourced from the upper crust. Moreover, the contents and ratios of Co and Ni in pyrrhotite (Ni: 500–1600 ppm, Co < 630 ppm, Co/Ni = 0.03–1.71) suggest that the ore-forming material of the Xujiagou copper deposit could be extracted from the spilite of the Guojiagou Formation, and the ore minerals inherited the geochemical characteristics of the spilite. Combined with previous studies of the Tongchang copper deposit in the Mian-Lue-Ning area, it is proposed that the Xujiagou and Tongchang copper deposits have similar ore-forming materials source and evolution processes, and their formations may be related to the breakup event of the Rodinia supercontinent. However, the relatively lower 207Pb/204Pb and 206Pb/204Pb ratios of the Tongchang chalcopyrite and pyrite than those of the Xujiagou chalcopyrite and pyrrhotite indicate that the Tongchang copper deposit suffered more intense influence of the lower crust materials due to the emplacement of the Tongchang diorite.

The genesis of the Xujiagou copper deposit, Mian‐Lue‐Ning area of Shaanxi Province, NW China: Constraints from mineral chemistry and in situ Pb isotope composition

The Mian‐Lue‐Ning area, bounded by the Hanjiang fault zone in the south and the Mian‐Lue suture in the north, is one of the most important polymetallic mineralization concentration regions in the Qinling orogenic belt. The Xujiagou copper deposit is representative in this area with chalcopyrite and pyrrhotite as the main ore minerals, subordinate sphalerite, and pyrite. However, the source of the ore‐forming materials and the genesis of the Xujiagou copper deposit are still in a controversy due to the lack of detailed study on the mineral composition. In this study, the electron probe micro‐analyzer (EPMA) analysis shows that the pyrrhotite in the Xujiagou copper deposit is mostly monoclinic pyrrhotite of low‐temperature phase, indicating that the metallogenic temperature should be below 304 °C. The percent of FeS molecules in sphalerite is 8.16–12.1%, indicating that the metallogenic temperature is 230–258 °C, which is mesothermal mineralization. The in situ Pb isotope composition of chalcopyrite (206Pb/204Pb = 19.087–20.861; 207Pb/204Pb = 15.533–16.062; 208Pb/204Pb = 38.121–39.391) and pyrrhotite (206Pb/204Pb = 20.241–20.664; 207Pb/204Pb = 15.7–15.996; 208Pb/204Pb = 38.659–39.372) in the Xujiagou copper deposit was analysed by fLA‐MC‐ICPMS, and it indicates that the ore‐forming materials were mainly sourced from the upper crust. Moreover, the contents and ratios of Co and Ni in pyrrhotite (Ni: 500–1600 ppm, Co < 630 ppm, Co/Ni = 0.03–1.71) suggest that the ore‐forming material of the Xujiagou copper deposit could be extracted from the spilite of the Guojiagou Formation, and the ore minerals inherited the geochemical characteristics of the spilite. Combined with previous studies of the Tongchang copper deposit in the Mian‐Lue‐Ning area, it is proposed that the Xujiagou and Tongchang copper deposits have similar ore‐forming materials source and evolution processes, and their formations may be related to the breakup event of the Rodinia supercontinent. However, the relatively lower 207Pb/204Pb and 206Pb/204Pb ratios of the Tongchang chalcopyrite and pyrite than those of the Xujiagou chalcopyrite and pyrrhotite indicate that the Tongchang copper deposit suffered more intense influence of the lower crust materials due to the emplacement of the Tongchang diorite.