Glacial diamictite may provide important information on paleoenvironment and average composition of the upper continental crust(UCC).In this study,we report sedimentary facies,petrological and geochemical characterist...Glacial diamictite may provide important information on paleoenvironment and average composition of the upper continental crust(UCC).In this study,we report sedimentary facies,petrological and geochemical characteristics of Neoproterozoic diamictite from a profile of the Luoquan Formation on the southern margin of the North China Block(NCB).Upwards the sampling profile,lithostratigraphic strata vary from massive diamictite with poorly sorted carbonate gravels to laminated diamictite with small gravels of terrestrial detrital materials.Along the profile,CaO-MgO-LOI-Sr values decrease with the increase of SiO_(2)-Al2O_(3)-K2O contents.All these petrological and geochemical variations indicate a change from lodgement till deposition in the proximal of ice sheet to ice-rafting deposition in glacial-marine environment with less dolomite to supply their source.Together with previous studies on diamictite from other outcrops on the NCB,the deposition of Luoquan diamictite reflects that the glaciation on the NCB vanished and the ice-rafting effect weakened with glacial transgression process.In addition,significant co-variations of various elements with La and Al2O_(3)confirm the significant conservation of most analyzed elements during the sedimentary processes to produce diamictite.展开更多
The Late Precambrian Luoquan Formation occurring on the southern margin of the North China platform is of important significance for the study of the tectonics, palaeogeography, palaeoclimatology and regional stratigr...The Late Precambrian Luoquan Formation occurring on the southern margin of the North China platform is of important significance for the study of the tectonics, palaeogeography, palaeoclimatology and regional stratigraphy of the North China and Yangtze platforms. The origin of diamictites of the formation has long been a subject of controversy. Recently a certain type of cross bedding structure has been recognized in the massive diamictite. Analysis of the process of deposition indicates that the structure was formed by the basal melt-out process of the glacier and, to some extent, its form is the manifestation of the primary structure of basal debris-rich glacial ice. The discovery of this sedimentary structure is inducive to the understanding and reconstruction of the features and environmental conditions for the development of the glaciers in the Luoquan Glacial Epoch.展开更多
The Guandacol Formation corresponds to glacial episode 4 of the“Late Paleozoic Ice Age”in western Gondwana.It represents the final glaciation of westernmost Gondwana and the beginning of deglaciation that swept acro...The Guandacol Formation corresponds to glacial episode 4 of the“Late Paleozoic Ice Age”in western Gondwana.It represents the final glaciation of westernmost Gondwana and the beginning of deglaciation that swept across the supercontinent throughout the rest of the Paleozoic.A succession of transitional sedimentary facies associations characterizes the eastern outcrops of the Guandacol Formation.These facies associations are interlayered with several deposits of mass-transport complexes(MTC)and present the occasional opportunity to conduct a deep-time analysis of the effect of tectonism in what is interpreted to be glacially-influenced deposits.Six sedimentary facies associations were recognized in the lower part of the Guandacol Formation.Facies association 1(interbedded diamictites,sandstones,and mudstones)overlies MTC 1 and is interpreted as sedimentation into a marine glacially-influenced outwash fan.Facies association 2(ponded interbedded sandstones,mudstones,and diamictites)was deposited as subaqueous underflows/turbidites and debris flows covering the irregular paleotopography of MTC 2.Facies association 3(white medium-to coarse-grained sandstones and conglomerates)represents a small deltaic system.Facies association 4(rhythmites with dropstones and sandstones)was deposited in a partially ponded water body resulting from the collapse and paleotopography of MTC 3.Facies association 5(coarsening-upward cycles of mudstones and sandstones)was deposited in prodelta to delta front environments.Finally,facies association 6(conglomerates,sandstones,and mudstones)corresponds to the subaerial deltaic platform.The evolution of depositional environments suggests three glacially-linked stages:Stage 1—Initial retreat of the nearby ice masses(facies association 1);Stage 2—Further retreat of glaciers and the progressive decoupling between ice masses and sea(facies associations 2 and 3);and Stage 3—Postglacial sedimentation dominated by deltaic progradation during highstand conditions(facies associations 4 to 6).The importance of the paleogeographic context is emphasized in which the tectonism triggered recurrent events of MTC that continually modified the topography and sedimentary patterns,interrupting and complicating the stratigraphy of the interpreted glacial and postglacial sedimentation.展开更多
Detailed sedimentological analysis of the Pokaran Boulder Bed,representing the most basal unit of the Neoproterozoic-Lower Cambrian Marwar Supergroup,clearly indicates its glacial origin.The glacial sediments are inte...Detailed sedimentological analysis of the Pokaran Boulder Bed,representing the most basal unit of the Neoproterozoic-Lower Cambrian Marwar Supergroup,clearly indicates its glacial origin.The glacial sediments are interpreted as an ice-contact submarine fan deposit.Based on the detrital and inherited zircon population of the Marwar Supergroup sediments and interlayered pyroclastic deposits,a Marinoan cryochron of the Cryogenian Period is envisaged for the Pokaran Boulder Bed.The well-preserved Ediacaran elements in the post-glacial sedimentary succession also support a Cryogenian to Early Cambrian age of the Marwar Supergroup.The glacial deposition at the base of the Marwar Supergroup strengthens the regional correlation between the studied sediments with the Lesser Himalayan Blaini-Krol-Tal sediments and the Haqf Supergroup of Oman.The available zircon ages and paleomagnetic data of the Malani Igneous suite,along with the Marinoan glacial deposits,detrital zircon ages,and Ediacaran fossil elements of the Marwar Supergroup add significant information to the Neoproterozoic Earth history.展开更多
For more than 150 years, geologic characteristics claimed to be evidence for pre-Pleistocene glaciations have been debated. Advancements in recent decades, in understanding features generated by mainly glacial and mas...For more than 150 years, geologic characteristics claimed to be evidence for pre-Pleistocene glaciations have been debated. Advancements in recent decades, in understanding features generated by mainly glacial and mass flow processes, are here reviewed. Detailed studies of data offered in support of prePleistocene glaciations have led to revisions that involve environments of mass movements. Similarities and differences between Quaternary glaciogenic and mass movement features are examined, to provide a more systematic methodology for analysing the origins of more ancient deposits. Analyses and evaluation of data are from a) Quaternary glaciogenic sediments, b) formations which have been assigned to pre-Pleistocene glaciations, and c) formations with comparable features associated with mass movements(and occasionally tectonics). Multiple proxies are assembled to develop correct interpretations of ancient strata. The aim is not per se to reinterpret specific formations and past climate changes, but to enable data to be evaluated using a broader and more inclusive conceptual framework.Regularly occurring pre-Pleistocene features interpreted to be glaciogenic, have often been shown to have few or no Quaternary glaciogenic equivalents. These same features commonly form by sediment gravity flows or other non-glacial processes, which may have led to misinterpretations of ancient deposits. These features include, for example, environmental affinity of fossils, grading, bedding, fabrics, size and appearance of erratics, polished and striated clasts and surfaces(“pavements”), dropstones, and surface microtextures.Recent decades of progress in research relating to glacial and sediment gravity flow processes have resulted in proposals by geologists, based on more detailed field data, more often of an origin by mass movements and tectonism than glaciation.The most coherent data of this review, i.e., appearances of features produced by glaciation, sediment gravity flows and a few other geological processes, are summarized in a Diamict Origin Table.展开更多
基金supported by the National Natural Science Foundation of China (Mos.41776069 and 41572047 to Yuanyuan Xiao)Strategic Priority Research Program of the Chinese Academy of Sciences (No.XDB42020302)+1 种基金the Taishan Scholar Program of Shandong (No.ts201712075)Aoshan Scholar Program of the Pilot National Laboratory for Marine Science and Technology (Qingdao) to Weidong Sun。
文摘Glacial diamictite may provide important information on paleoenvironment and average composition of the upper continental crust(UCC).In this study,we report sedimentary facies,petrological and geochemical characteristics of Neoproterozoic diamictite from a profile of the Luoquan Formation on the southern margin of the North China Block(NCB).Upwards the sampling profile,lithostratigraphic strata vary from massive diamictite with poorly sorted carbonate gravels to laminated diamictite with small gravels of terrestrial detrital materials.Along the profile,CaO-MgO-LOI-Sr values decrease with the increase of SiO_(2)-Al2O_(3)-K2O contents.All these petrological and geochemical variations indicate a change from lodgement till deposition in the proximal of ice sheet to ice-rafting deposition in glacial-marine environment with less dolomite to supply their source.Together with previous studies on diamictite from other outcrops on the NCB,the deposition of Luoquan diamictite reflects that the glaciation on the NCB vanished and the ice-rafting effect weakened with glacial transgression process.In addition,significant co-variations of various elements with La and Al2O_(3)confirm the significant conservation of most analyzed elements during the sedimentary processes to produce diamictite.
基金This research(Project No.4917013)was supported by the National Natural Science Foundation of China
文摘The Late Precambrian Luoquan Formation occurring on the southern margin of the North China platform is of important significance for the study of the tectonics, palaeogeography, palaeoclimatology and regional stratigraphy of the North China and Yangtze platforms. The origin of diamictites of the formation has long been a subject of controversy. Recently a certain type of cross bedding structure has been recognized in the massive diamictite. Analysis of the process of deposition indicates that the structure was formed by the basal melt-out process of the glacier and, to some extent, its form is the manifestation of the primary structure of basal debris-rich glacial ice. The discovery of this sedimentary structure is inducive to the understanding and reconstruction of the features and environmental conditions for the development of the glaciers in the Luoquan Glacial Epoch.
基金supported by the Agencia Nacional de Promoción de la Investigación,el Desarrollo Tecnológico y la Innovación (PICT, 2020-01294)the University of Wisconsin-Milwaukee Center for Latin American and Caribbean Studies,the Nelson Cherkauer Lasca Legacy Scholarshipthe National Science Foundation (Grant No. 1559231)
文摘The Guandacol Formation corresponds to glacial episode 4 of the“Late Paleozoic Ice Age”in western Gondwana.It represents the final glaciation of westernmost Gondwana and the beginning of deglaciation that swept across the supercontinent throughout the rest of the Paleozoic.A succession of transitional sedimentary facies associations characterizes the eastern outcrops of the Guandacol Formation.These facies associations are interlayered with several deposits of mass-transport complexes(MTC)and present the occasional opportunity to conduct a deep-time analysis of the effect of tectonism in what is interpreted to be glacially-influenced deposits.Six sedimentary facies associations were recognized in the lower part of the Guandacol Formation.Facies association 1(interbedded diamictites,sandstones,and mudstones)overlies MTC 1 and is interpreted as sedimentation into a marine glacially-influenced outwash fan.Facies association 2(ponded interbedded sandstones,mudstones,and diamictites)was deposited as subaqueous underflows/turbidites and debris flows covering the irregular paleotopography of MTC 2.Facies association 3(white medium-to coarse-grained sandstones and conglomerates)represents a small deltaic system.Facies association 4(rhythmites with dropstones and sandstones)was deposited in a partially ponded water body resulting from the collapse and paleotopography of MTC 3.Facies association 5(coarsening-upward cycles of mudstones and sandstones)was deposited in prodelta to delta front environments.Finally,facies association 6(conglomerates,sandstones,and mudstones)corresponds to the subaerial deltaic platform.The evolution of depositional environments suggests three glacially-linked stages:Stage 1—Initial retreat of the nearby ice masses(facies association 1);Stage 2—Further retreat of glaciers and the progressive decoupling between ice masses and sea(facies associations 2 and 3);and Stage 3—Postglacial sedimentation dominated by deltaic progradation during highstand conditions(facies associations 4 to 6).The importance of the paleogeographic context is emphasized in which the tectonism triggered recurrent events of MTC that continually modified the topography and sedimentary patterns,interrupting and complicating the stratigraphy of the interpreted glacial and postglacial sedimentation.
文摘Detailed sedimentological analysis of the Pokaran Boulder Bed,representing the most basal unit of the Neoproterozoic-Lower Cambrian Marwar Supergroup,clearly indicates its glacial origin.The glacial sediments are interpreted as an ice-contact submarine fan deposit.Based on the detrital and inherited zircon population of the Marwar Supergroup sediments and interlayered pyroclastic deposits,a Marinoan cryochron of the Cryogenian Period is envisaged for the Pokaran Boulder Bed.The well-preserved Ediacaran elements in the post-glacial sedimentary succession also support a Cryogenian to Early Cambrian age of the Marwar Supergroup.The glacial deposition at the base of the Marwar Supergroup strengthens the regional correlation between the studied sediments with the Lesser Himalayan Blaini-Krol-Tal sediments and the Haqf Supergroup of Oman.The available zircon ages and paleomagnetic data of the Malani Igneous suite,along with the Marinoan glacial deposits,detrital zircon ages,and Ediacaran fossil elements of the Marwar Supergroup add significant information to the Neoproterozoic Earth history.
文摘For more than 150 years, geologic characteristics claimed to be evidence for pre-Pleistocene glaciations have been debated. Advancements in recent decades, in understanding features generated by mainly glacial and mass flow processes, are here reviewed. Detailed studies of data offered in support of prePleistocene glaciations have led to revisions that involve environments of mass movements. Similarities and differences between Quaternary glaciogenic and mass movement features are examined, to provide a more systematic methodology for analysing the origins of more ancient deposits. Analyses and evaluation of data are from a) Quaternary glaciogenic sediments, b) formations which have been assigned to pre-Pleistocene glaciations, and c) formations with comparable features associated with mass movements(and occasionally tectonics). Multiple proxies are assembled to develop correct interpretations of ancient strata. The aim is not per se to reinterpret specific formations and past climate changes, but to enable data to be evaluated using a broader and more inclusive conceptual framework.Regularly occurring pre-Pleistocene features interpreted to be glaciogenic, have often been shown to have few or no Quaternary glaciogenic equivalents. These same features commonly form by sediment gravity flows or other non-glacial processes, which may have led to misinterpretations of ancient deposits. These features include, for example, environmental affinity of fossils, grading, bedding, fabrics, size and appearance of erratics, polished and striated clasts and surfaces(“pavements”), dropstones, and surface microtextures.Recent decades of progress in research relating to glacial and sediment gravity flow processes have resulted in proposals by geologists, based on more detailed field data, more often of an origin by mass movements and tectonism than glaciation.The most coherent data of this review, i.e., appearances of features produced by glaciation, sediment gravity flows and a few other geological processes, are summarized in a Diamict Origin Table.
