Late to post-Variscan molassic basins of Late Pennsylvanian-Permian age are exposed in Sardinia(Italy). Here, the compositional and stratigraphic evolution of the Mulargia-Escalaplano sedimentary basin(central Sardini...Late to post-Variscan molassic basins of Late Pennsylvanian-Permian age are exposed in Sardinia(Italy). Here, the compositional and stratigraphic evolution of the Mulargia-Escalaplano sedimentary basin(central Sardinia) has been investigated to highlight how the tectono-magmatic processes have influenced the sedimentation. Ruditic and arenitic samples were collected along well-characterized stratigraphic sections to provide a new insight into the impact of the tectono-magmatic processes on siliciclastic sedimentation. As a result, the conglomerates are mainly clast-supported, petromictic, and thus immature, with no defined maturity trend upwards. Nevertheless, pebble composition changes in times from Variscan basement pebble-rich to volcanic rock-rich, as a consequence of the basin widening and the dismantling and reworking of the coeval volcanic activity. The sandstone composition clearly changes from quartzolithic to feldspatholithic upwards, as a response to the same change of feeding and reworking of the volcanic rocks. Occasionally, interbedded quartzolithic arenites suggest exceptional floods carrying debris from the far borders of the basin. Also, the immature sandstone composition has been interpreted as being controlled by a continuous supply of fresh debris and to a rapid burial rate. In addition, the disappearance of metaradiolarite(lydite AA) Paleozoic grains in the sandstone mineral suite could represent a distinctive marker of a progressive unroofing of the Variscan chain and a clastic supply from deeper tectonic units.展开更多
The important event in Jurassic tectonics in Mongolia was the subduction and closure of the Mongolia-Okhotsk ocean;correspondingly,basin evolution can be divided into two main stages,related to the orogeny and collaps...The important event in Jurassic tectonics in Mongolia was the subduction and closure of the Mongolia-Okhotsk ocean;correspondingly,basin evolution can be divided into two main stages,related to the orogeny and collapse of the orogenic belt,respectively.The developing of Early-Middle Jurassic basins to the north of the ocean resulted from back-arc extension.The fossil sutures,from the China-SE Asia sub-continent to the south of the ocean,were rejuvenated by subduction-related orogeny;in addition,the Yanshanian intra-continental movement occurred.Three Early-Middle Jurassic molasse basins were developed by movement in Inner Mongolia,all of which stretched westwards (or northwards) into Mongolia;therefore,the molasse basins in eastern and southern Mongolia had the same geometric and kinematic features as the basins in the Inner Mongolia.Owing to the collapse of the MongoliaOkhotsk orogenic belt,a group of rift basins developed during the Late Jurassic.In eastern Mongolia,the NE orientated extensional basins were controlled by the neogenic NE-structure.The contemporary basins in southern Mongolia and the neighboring areas in China were constrained by remobilization (inherited activation) of the latitudinal or ENE-directional basement structures.Three stages can be recognized in the evolution of the Early-Middle Jurassic basins after reversal;the basins also experienced four episodes of reformation.展开更多
基金supported by Cagliari University (2018-2020 FIR grant to L. G. Costamagna)Calabria University (S. Criniti)。
文摘Late to post-Variscan molassic basins of Late Pennsylvanian-Permian age are exposed in Sardinia(Italy). Here, the compositional and stratigraphic evolution of the Mulargia-Escalaplano sedimentary basin(central Sardinia) has been investigated to highlight how the tectono-magmatic processes have influenced the sedimentation. Ruditic and arenitic samples were collected along well-characterized stratigraphic sections to provide a new insight into the impact of the tectono-magmatic processes on siliciclastic sedimentation. As a result, the conglomerates are mainly clast-supported, petromictic, and thus immature, with no defined maturity trend upwards. Nevertheless, pebble composition changes in times from Variscan basement pebble-rich to volcanic rock-rich, as a consequence of the basin widening and the dismantling and reworking of the coeval volcanic activity. The sandstone composition clearly changes from quartzolithic to feldspatholithic upwards, as a response to the same change of feeding and reworking of the volcanic rocks. Occasionally, interbedded quartzolithic arenites suggest exceptional floods carrying debris from the far borders of the basin. Also, the immature sandstone composition has been interpreted as being controlled by a continuous supply of fresh debris and to a rapid burial rate. In addition, the disappearance of metaradiolarite(lydite AA) Paleozoic grains in the sandstone mineral suite could represent a distinctive marker of a progressive unroofing of the Variscan chain and a clastic supply from deeper tectonic units.
文摘The important event in Jurassic tectonics in Mongolia was the subduction and closure of the Mongolia-Okhotsk ocean;correspondingly,basin evolution can be divided into two main stages,related to the orogeny and collapse of the orogenic belt,respectively.The developing of Early-Middle Jurassic basins to the north of the ocean resulted from back-arc extension.The fossil sutures,from the China-SE Asia sub-continent to the south of the ocean,were rejuvenated by subduction-related orogeny;in addition,the Yanshanian intra-continental movement occurred.Three Early-Middle Jurassic molasse basins were developed by movement in Inner Mongolia,all of which stretched westwards (or northwards) into Mongolia;therefore,the molasse basins in eastern and southern Mongolia had the same geometric and kinematic features as the basins in the Inner Mongolia.Owing to the collapse of the MongoliaOkhotsk orogenic belt,a group of rift basins developed during the Late Jurassic.In eastern Mongolia,the NE orientated extensional basins were controlled by the neogenic NE-structure.The contemporary basins in southern Mongolia and the neighboring areas in China were constrained by remobilization (inherited activation) of the latitudinal or ENE-directional basement structures.Three stages can be recognized in the evolution of the Early-Middle Jurassic basins after reversal;the basins also experienced four episodes of reformation.
