One of the global characteristic features of the Eocene is the extensive development of carbonate platforms in various regions of Tethys.Paleogene sequences of the Shillong Plateau from west to east are exposed in the...One of the global characteristic features of the Eocene is the extensive development of carbonate platforms in various regions of Tethys.Paleogene sequences of the Shillong Plateau from west to east are exposed in the steep Garo,Khasi and Jaintia hills.In the Khasi and Jaintia hills,Paleogene successions are represented by alternating carbonates and siliciclastics and provide datable micropaleontological fossils,whereas in the Garo Hills,which is in the south-western part of the Shillong Plateau,the Paleogene succession is mainly represented by siliciclastics and fewer carbonates.As the carbonates in this area are mostly marly,the recovery of carbonate microfossils is difficult.Accurate age assignment is important to correlate the sedimentary successions of the Khasi,Jaintia and Garo hills,which are mostly time transgressive and different lithologies were deposited at the same time.A detailed palynological investigation of 65 samples from the 25-m-thick sedimentary succession of the Siju Formation,Western Garo Hills,has yielded well-preserved and diverse organic-walled dinoflagellate cysts and calcareous nannofossils.Dinoflagellate cysts(Heteraulacacysta porosa,H.leptalea)and nannofossils(Discoaster barbadiensis,D.saipanensis,Reticulofenestra bisecta,R.erbae,and R.reticulata)indicate a middle Eocene age(Bartonian)for the studied section.The synthesis of nannofossils and dinocysts with records from India and Australia reveals a major late Bartonian transgression in the Indo-Pacific known as the‘Kirthar transgression'.展开更多
This study determines the geochemical and depositional environment analysis of the sediments of the Sohnari Member of the Laki Formation, Northern Kirthar Fold Belt of Pakistan. The Energy-Dispersive-X-Ray Spectroscop...This study determines the geochemical and depositional environment analysis of the sediments of the Sohnari Member of the Laki Formation, Northern Kirthar Fold Belt of Pakistan. The Energy-Dispersive-X-Ray Spectroscopy (EDS) technique is used for the detection of major elements and the effects of shifting depositional climatic conditions of six representative samples which were acquired from the Sohnari Member of the Laki Formation at Lakhra area, Sindh, Pakistan. The sedimentological studies clarify that the sediments the Sonahri Member are relatively immature and most migrated in clastic mode. The availability of Silica shows that the Member was formed due to biochemical precipitation and detrital mode and was deposited at a fast rate of sediment deposition under the fluvio-deltaic depositional system. This is also deduced that the rapid rate of sediment deposition might be created a reducing atmosphere and allowing for the mineralization of sulphur.展开更多
基金National Institute of Oceanography,Goa for the support and infrastructural facilities(Contribution no.7362)funding from DST INSPIRE project(GAP3560)。
文摘One of the global characteristic features of the Eocene is the extensive development of carbonate platforms in various regions of Tethys.Paleogene sequences of the Shillong Plateau from west to east are exposed in the steep Garo,Khasi and Jaintia hills.In the Khasi and Jaintia hills,Paleogene successions are represented by alternating carbonates and siliciclastics and provide datable micropaleontological fossils,whereas in the Garo Hills,which is in the south-western part of the Shillong Plateau,the Paleogene succession is mainly represented by siliciclastics and fewer carbonates.As the carbonates in this area are mostly marly,the recovery of carbonate microfossils is difficult.Accurate age assignment is important to correlate the sedimentary successions of the Khasi,Jaintia and Garo hills,which are mostly time transgressive and different lithologies were deposited at the same time.A detailed palynological investigation of 65 samples from the 25-m-thick sedimentary succession of the Siju Formation,Western Garo Hills,has yielded well-preserved and diverse organic-walled dinoflagellate cysts and calcareous nannofossils.Dinoflagellate cysts(Heteraulacacysta porosa,H.leptalea)and nannofossils(Discoaster barbadiensis,D.saipanensis,Reticulofenestra bisecta,R.erbae,and R.reticulata)indicate a middle Eocene age(Bartonian)for the studied section.The synthesis of nannofossils and dinocysts with records from India and Australia reveals a major late Bartonian transgression in the Indo-Pacific known as the‘Kirthar transgression'.
文摘This study determines the geochemical and depositional environment analysis of the sediments of the Sohnari Member of the Laki Formation, Northern Kirthar Fold Belt of Pakistan. The Energy-Dispersive-X-Ray Spectroscopy (EDS) technique is used for the detection of major elements and the effects of shifting depositional climatic conditions of six representative samples which were acquired from the Sohnari Member of the Laki Formation at Lakhra area, Sindh, Pakistan. The sedimentological studies clarify that the sediments the Sonahri Member are relatively immature and most migrated in clastic mode. The availability of Silica shows that the Member was formed due to biochemical precipitation and detrital mode and was deposited at a fast rate of sediment deposition under the fluvio-deltaic depositional system. This is also deduced that the rapid rate of sediment deposition might be created a reducing atmosphere and allowing for the mineralization of sulphur.
