The Himalayan peripheral foreland basin developed when India and Asia collided.Previous studies in the Himalayan foreland were mostly concentrated on Neogene continental clastic sedimentation in sub-Himalaya or Paleog...The Himalayan peripheral foreland basin developed when India and Asia collided.Previous studies in the Himalayan foreland were mostly concentrated on Neogene continental clastic sedimentation in sub-Himalaya or Paleogene shallow marine sedimentation along Pakistan,India,and Nepal in Lesser Himalaya. The lack of early stage of underfilled。展开更多
Sequence stratigraphic concepts and methods provide novel tools for performing stratigraphic analysis,allowing us to improve our understanding of depositional models and basin evolution.Main controls and depositional ...Sequence stratigraphic concepts and methods provide novel tools for performing stratigraphic analysis,allowing us to improve our understanding of depositional models and basin evolution.Main controls and depositional elements(e.g.,surfaces,systems tracts,parasequences,etc.)recognized in conventional sequence stratigraphy are designed for marine-related systems.In contrast,the sequence stratigraphy of lacustrine successions is much more complex and poorly understood,because it is not driven by sea-level changes,but by a complex interaction between tectonics and high-frequency climatic cycles.The comprehensive analysis of the water balance of lacustrine systems allows the recognition of three types of lake conditions:Underfilled,balanced-fill and overfilled lakes.Understanding the lake conditions in ancient successions is fundamental for unraveling lacustrine sequence stratigraphy,since these conditions effectively control water salinity,internal stacking pattern and the characteristics of systems tracts.Underfilled lakes are hydrologically closed lakes,and consequently,the lake-level can highly fluctuate,driven by high-frequency wet-dry climatic cycles.During wet periods,rivers supply water and sediments,resulting in fining-and thinning-upward elementary depositional sequences(EDS's)accumulated during the transgressive systems tract(TST).In contrast,dry periods are characterized by a relative lake-level fall with the subaerial exposure of lake margin areas during the regressive systems tract(RST).Lake water salinity can fluctuate from brackish to hypersaline.Balanced-fill lakes are partially closed lakes,and consequently,they have characteristics of both underfilled and overfilled lakes.During the TST,the lake is in underfilled condition,and consequently,the introduction of water and sediment will accumulate a fining-upward interval until reaching the spill point during the maximum flooding.The RST is accumulated under an overfilled lake condition,with coarseningupward progradational littoral deltas and related subaqueous delta deposits.Lake water salinity fluctuates from brackish to freshwater.Overfilled lakes are hydrologically open lakes.Most deposits accumulate during the RST,forming coarsening-upward progradational littoral deposits,with associated subaqueous deltas.All overfilled lakes are freshwater lakes.Subsidence is crucial for allowing the long-term preservation of lacustrine deposits.Lakes can temporarily store water and sediments in areas that lack subsidence,but these deposits will not be preserved in the stratigraphic record.Consequently,two types of lakes are recognized:1)subsiding lakes,which have permanent accommodation space and 2)hanging lakes,having temporary accommodation space.Although they cannot permanently store sediments,hanging lakes are fundamental for lacustrine sequence stratigraphy,since they can flood subsiding lakes with the near-instantaneous release of a substantial volume of water,creating favorable conditions for the accumulation of organic-rich shales.This rapid flooding from hanging lakes induced a forced transgression(FT),which is a large-scale rapid transgression(xenoconformity)not related to the normal sediment and water supply from local source areas.展开更多
The Jiachala Formatiom is a new lithostratigraphic unit set up in this paper. This is the first report on the Paleogene marine sequences and microfaunas in Gyangze to the southern side of the Yarlung-Zangbo suture zon...The Jiachala Formatiom is a new lithostratigraphic unit set up in this paper. This is the first report on the Paleogene marine sequences and microfaunas in Gyangze to the southern side of the Yarlung-Zangbo suture zone. On the basis of fossil abundance, species diversity, dominant species and first and last occurrences of key species, three dinoflagellate assemblages and three polynological assemblages were recognized in the Jiachala Formatiom. They are in ascending order as follows: Apectodinium quinquelatum-Apectodinium hyperacanthum, Cannin- gia chinensis-Palaeoperidinium pyrophorum and Cymatiosphaera reticulosa-Samlandia chla- mydophora dinoflagellate assemblages, and Arliaceoipollenites baculatus-Anacolosidites sub- trudens, Aglaoreidia cyclops-Pinuspollenites microinsigis, and Elaeangnacites asper-Ilexpol- lenites iliacus polynological Assemblages. According to the assemblages, the age of the Jiachala Formation is referred to Paleocene-early Eocene. The preliminary study on the Jiachala Forma- tion shows that this group of Paleogene deposits accumulated in an underfilled peripheral fore- land basin which was in response to the load of the crust thickening resulted from the Asia-India collision. The stratigraphic evidences provided by the evolution of foreland basin indicate that the India-Asia initional collision should occure near the Cretaceous/Paleogene boundary. The de- velopment and evolution of the southern Tibet foreland basin was under the control of the stress field from the subduct-collision between India and Asia and the structure pattern of the basement. The withering of Tethys Sea might occur after early Eocene in the Gyangze basin and should be after Priabonian of late Eocene in southern Tibet.展开更多
文摘The Himalayan peripheral foreland basin developed when India and Asia collided.Previous studies in the Himalayan foreland were mostly concentrated on Neogene continental clastic sedimentation in sub-Himalaya or Paleogene shallow marine sedimentation along Pakistan,India,and Nepal in Lesser Himalaya. The lack of early stage of underfilled。
文摘Sequence stratigraphic concepts and methods provide novel tools for performing stratigraphic analysis,allowing us to improve our understanding of depositional models and basin evolution.Main controls and depositional elements(e.g.,surfaces,systems tracts,parasequences,etc.)recognized in conventional sequence stratigraphy are designed for marine-related systems.In contrast,the sequence stratigraphy of lacustrine successions is much more complex and poorly understood,because it is not driven by sea-level changes,but by a complex interaction between tectonics and high-frequency climatic cycles.The comprehensive analysis of the water balance of lacustrine systems allows the recognition of three types of lake conditions:Underfilled,balanced-fill and overfilled lakes.Understanding the lake conditions in ancient successions is fundamental for unraveling lacustrine sequence stratigraphy,since these conditions effectively control water salinity,internal stacking pattern and the characteristics of systems tracts.Underfilled lakes are hydrologically closed lakes,and consequently,the lake-level can highly fluctuate,driven by high-frequency wet-dry climatic cycles.During wet periods,rivers supply water and sediments,resulting in fining-and thinning-upward elementary depositional sequences(EDS's)accumulated during the transgressive systems tract(TST).In contrast,dry periods are characterized by a relative lake-level fall with the subaerial exposure of lake margin areas during the regressive systems tract(RST).Lake water salinity can fluctuate from brackish to hypersaline.Balanced-fill lakes are partially closed lakes,and consequently,they have characteristics of both underfilled and overfilled lakes.During the TST,the lake is in underfilled condition,and consequently,the introduction of water and sediment will accumulate a fining-upward interval until reaching the spill point during the maximum flooding.The RST is accumulated under an overfilled lake condition,with coarseningupward progradational littoral deltas and related subaqueous delta deposits.Lake water salinity fluctuates from brackish to freshwater.Overfilled lakes are hydrologically open lakes.Most deposits accumulate during the RST,forming coarsening-upward progradational littoral deposits,with associated subaqueous deltas.All overfilled lakes are freshwater lakes.Subsidence is crucial for allowing the long-term preservation of lacustrine deposits.Lakes can temporarily store water and sediments in areas that lack subsidence,but these deposits will not be preserved in the stratigraphic record.Consequently,two types of lakes are recognized:1)subsiding lakes,which have permanent accommodation space and 2)hanging lakes,having temporary accommodation space.Although they cannot permanently store sediments,hanging lakes are fundamental for lacustrine sequence stratigraphy,since they can flood subsiding lakes with the near-instantaneous release of a substantial volume of water,creating favorable conditions for the accumulation of organic-rich shales.This rapid flooding from hanging lakes induced a forced transgression(FT),which is a large-scale rapid transgression(xenoconformity)not related to the normal sediment and water supply from local source areas.
文摘The Jiachala Formatiom is a new lithostratigraphic unit set up in this paper. This is the first report on the Paleogene marine sequences and microfaunas in Gyangze to the southern side of the Yarlung-Zangbo suture zone. On the basis of fossil abundance, species diversity, dominant species and first and last occurrences of key species, three dinoflagellate assemblages and three polynological assemblages were recognized in the Jiachala Formatiom. They are in ascending order as follows: Apectodinium quinquelatum-Apectodinium hyperacanthum, Cannin- gia chinensis-Palaeoperidinium pyrophorum and Cymatiosphaera reticulosa-Samlandia chla- mydophora dinoflagellate assemblages, and Arliaceoipollenites baculatus-Anacolosidites sub- trudens, Aglaoreidia cyclops-Pinuspollenites microinsigis, and Elaeangnacites asper-Ilexpol- lenites iliacus polynological Assemblages. According to the assemblages, the age of the Jiachala Formation is referred to Paleocene-early Eocene. The preliminary study on the Jiachala Forma- tion shows that this group of Paleogene deposits accumulated in an underfilled peripheral fore- land basin which was in response to the load of the crust thickening resulted from the Asia-India collision. The stratigraphic evidences provided by the evolution of foreland basin indicate that the India-Asia initional collision should occure near the Cretaceous/Paleogene boundary. The de- velopment and evolution of the southern Tibet foreland basin was under the control of the stress field from the subduct-collision between India and Asia and the structure pattern of the basement. The withering of Tethys Sea might occur after early Eocene in the Gyangze basin and should be after Priabonian of late Eocene in southern Tibet.
