Aloe dichotoma (Quiver tree) occurs in the arid regions of Namaqualand and Bushman land in South Africa, and in arid regions of southern Namibia. The Quiver trees are not only threatened by agricultural expansion, ove...Aloe dichotoma (Quiver tree) occurs in the arid regions of Namaqualand and Bushman land in South Africa, and in arid regions of southern Namibia. The Quiver trees are not only threatened by agricultural expansion, overgrazing, and mining;but also by climate changes and droughts. Previous studies show that Quiver trees are very sensitive to environmental changes, and do not respond well to extreme hot and dry conditions. This study investigates the current status of the Quiver tree within its existing environment, and also assesses the projected future changes of the Quiver tree habitat under different climatic scenarios. It provided evidence regarding the importance of the study to understanding the climate change impacts on the Quiver tree and its geographical response to climate changes.展开更多
The Gabon Coastal Basin is a typical saliferous basin located in the middle portion of the West African passive continental margin. Complex salt tectonics make sedimentary sequences and structural frameworks difficult...The Gabon Coastal Basin is a typical saliferous basin located in the middle portion of the West African passive continental margin. Complex salt tectonics make sedimentary sequences and structural frameworks difficult to interpret and can lead to difficulties in construction of balanced cross-sections and reconstruction of basin evolutionary processes. Sedimentary facies and salt structur- al patterns displaying zonation are based on seismic reflection profiles and drilling data. Two near-vertical fault systems, NW-SE and NE-SW, caused basin to be subdivided E-W zoning and N-S partitioning. Scarp slopes and extension faults formed in the Hinge belt III zone where salt diapir piercement occurred and numbers of salt pillars, salt stocks and salt rollers developed under transten- sion of coupled near-orthogonal fault systems. The zone east of Hinge belt III is characterized by small-scale salt domes and salt pillows. To the west are large-scale salt walls and salt bulge anticlines caused by diapirism promoted by tension and torsion that also resulted in formation of numerous salt pillars, salt stocks and salt rollers. Our modeling of salt tectonic structures indicates that they were produced by plastic rheological deformation of salt under regional stress fields that varied during three distinct phases of extension, compression and re-activation. Hinge belt III was active from Coniacian to Early Eocene, which was a critical period of formation of salt structures when many extension-related salt structures formed and salt diapirism controlled the distribution of turbidite fans. Rootless extrusion-related salt stocks developed throughout the Late Eocene to Early Oligocene as a result of lo- cal ephemeral low-intensity tectonic inversion. Post Oligocene salt diapirism was weak and salt tecton- ics had a weak influence on sedimentation. Balanced cross-sections of two saliferous horizons crossing different tectonic units from east to west reveal that the basin tectonic evolution and sediment filling processes can be divided into three stages containing seven episodes of rifting, transition and drifting.展开更多
Previous studies demonstrated that melting,initiated by supercritical fluids in the 375-400℃range,occurred as part of anthracite metamorphism in the Appalachian Basin.Based on the known behavior of vitrinite at high ...Previous studies demonstrated that melting,initiated by supercritical fluids in the 375-400℃range,occurred as part of anthracite metamorphism in the Appalachian Basin.Based on the known behavior of vitrinite at high temperatures and,to a lesser extent,at high pressures,it was determined that the duration of the heating,melting,and resolidification event was about 1 h.In the current study,featureless vitrinite within banded maceral assemblages demonstratesthe intimate association of melted and resolidified vitrinite with anthracite-rank macerals.By analogy with metamorphosed inorganic rocks,such associations represent diadysites and embrechites,i.e.,cross-cutting and layered migmatites,respectively.Even though the temperature of formation of the anthracite structures is several hundred℃lower than that seen in metamorphosed inorganic rocks,anthracites are metamorphic rocks and the nomenclature for metamorphic rocks may be appropriate for coal.展开更多
文摘Aloe dichotoma (Quiver tree) occurs in the arid regions of Namaqualand and Bushman land in South Africa, and in arid regions of southern Namibia. The Quiver trees are not only threatened by agricultural expansion, overgrazing, and mining;but also by climate changes and droughts. Previous studies show that Quiver trees are very sensitive to environmental changes, and do not respond well to extreme hot and dry conditions. This study investigates the current status of the Quiver tree within its existing environment, and also assesses the projected future changes of the Quiver tree habitat under different climatic scenarios. It provided evidence regarding the importance of the study to understanding the climate change impacts on the Quiver tree and its geographical response to climate changes.
基金supported by the National Natural Science Fundation of China(Nos.40839902 and 40739901)
文摘The Gabon Coastal Basin is a typical saliferous basin located in the middle portion of the West African passive continental margin. Complex salt tectonics make sedimentary sequences and structural frameworks difficult to interpret and can lead to difficulties in construction of balanced cross-sections and reconstruction of basin evolutionary processes. Sedimentary facies and salt structur- al patterns displaying zonation are based on seismic reflection profiles and drilling data. Two near-vertical fault systems, NW-SE and NE-SW, caused basin to be subdivided E-W zoning and N-S partitioning. Scarp slopes and extension faults formed in the Hinge belt III zone where salt diapir piercement occurred and numbers of salt pillars, salt stocks and salt rollers developed under transten- sion of coupled near-orthogonal fault systems. The zone east of Hinge belt III is characterized by small-scale salt domes and salt pillows. To the west are large-scale salt walls and salt bulge anticlines caused by diapirism promoted by tension and torsion that also resulted in formation of numerous salt pillars, salt stocks and salt rollers. Our modeling of salt tectonic structures indicates that they were produced by plastic rheological deformation of salt under regional stress fields that varied during three distinct phases of extension, compression and re-activation. Hinge belt III was active from Coniacian to Early Eocene, which was a critical period of formation of salt structures when many extension-related salt structures formed and salt diapirism controlled the distribution of turbidite fans. Rootless extrusion-related salt stocks developed throughout the Late Eocene to Early Oligocene as a result of lo- cal ephemeral low-intensity tectonic inversion. Post Oligocene salt diapirism was weak and salt tecton- ics had a weak influence on sedimentation. Balanced cross-sections of two saliferous horizons crossing different tectonic units from east to west reveal that the basin tectonic evolution and sediment filling processes can be divided into three stages containing seven episodes of rifting, transition and drifting.
文摘Previous studies demonstrated that melting,initiated by supercritical fluids in the 375-400℃range,occurred as part of anthracite metamorphism in the Appalachian Basin.Based on the known behavior of vitrinite at high temperatures and,to a lesser extent,at high pressures,it was determined that the duration of the heating,melting,and resolidification event was about 1 h.In the current study,featureless vitrinite within banded maceral assemblages demonstratesthe intimate association of melted and resolidified vitrinite with anthracite-rank macerals.By analogy with metamorphosed inorganic rocks,such associations represent diadysites and embrechites,i.e.,cross-cutting and layered migmatites,respectively.Even though the temperature of formation of the anthracite structures is several hundred℃lower than that seen in metamorphosed inorganic rocks,anthracites are metamorphic rocks and the nomenclature for metamorphic rocks may be appropriate for coal.
