The Marwar Basin in western Rajasthan is one among the many Proterozoic sedimentary basins developed in Peninsular India that preserve rich records of the geological history and is traditionally considered as Trans-Vi...The Marwar Basin in western Rajasthan is one among the many Proterozoic sedimentary basins developed in Peninsular India that preserve rich records of the geological history and is traditionally considered as Trans-Vindhyan basin developed across Delhi and Aravalli orogens.It contains sedimentary package classified under Marwar Supergroup thought to be equivalent to the Vindhyan Supergroup.However,recently acquired radiometric dates suggest that the Marwar Supergroup is distinctively younger than the Vindhyan Supergroup,and the two basins were independently developed although they shared some of their provenance regions(Malone et al.,2008;McKenzie et al.,2011;Davis et al.,2014;Turner et al.,2014).展开更多
The Marwar Supergroup(NW Peninsular India)is thought to be of Ediacaran-Cambrian age,based on previous paleontological and geochronological studies.However,direct constraints on the onset of sedimentation within the M...The Marwar Supergroup(NW Peninsular India)is thought to be of Ediacaran-Cambrian age,based on previous paleontological and geochronological studies.However,direct constraints on the onset of sedimentation within the Marwar basin are still scarce.In this study,we report U–Pb zircon,LA-ICP-MS,and SIMS ages from the Chhoti Khatu felsic volcanic rocks,interlayered with the Jodhpur Group sandstones(Lower Marwar Supergroup).The cathodoluminescence images of the zircons indicate complex morphologies,and core-rim textures coupled with the wide range of ages indicate that they are likely inherited or in the case of thin poorly indurated ash-beds,detrital in origin.The age spectra of 68 zircon analyses from our sampling display a dominant 800–900 Ma age peak corresponding to the age of basement"Erinpura granite"rocks in the region.The youngest inherited zircon from a felsic ash layer yielded a U–Pb age of651 Ma±18 Ma that,together with previous studies and paleontological evidence,indicates a postCryogenian age for the initiation of Marwar sedimentation following a~125 Ma hiatus between the end of Malani magmatism and Marwar deposition.展开更多
The noncarbonaceous Ediacaran discs of variable morphologies from the Jodhpur Sandstone Formation of the Marwar Supergroup, western Rajasthan, suggest different biologic affinities of plant and animal kingdom. These d...The noncarbonaceous Ediacaran discs of variable morphologies from the Jodhpur Sandstone Formation of the Marwar Supergroup, western Rajasthan, suggest different biologic affinities of plant and animal kingdom. These discs are commonly preserved on the bedding surfaces of siliciclastic sandstone and shale in strong positive relief and appear to possess a flexible to rigid body. Discs assignable to Aspidella, Cyclomedusa, Nimbia and Heimalora;all possibly inclining towards cnidarian affinity are being reported from the sandstone beds in Sursagar area. Variable morphologies among discs preserved in siliciclastic shale beds from the Artiya Kalan area support scyphozoan affinity (earlier named Marsonia from the same locality) and cnidarian affinity for small discs comparable with Funisia (considered being the first animals having sexual reproduction). Disc’s morphologies also suggest ephyra stage of Aurilia (a cnidarian form) or budding stages of some fungi, like Germinosphaera (multicellular benthic fungal fossils) and noncarbonaceous discs with well preserved wrinkles and folds like in Chuaria. Discs from the Jodhpur Sandstone, may at times display taphonomic interplay, but consistency and repetition in morphology support variable biological affinities representing diverse assemblage and advance ecosystem prevailing during Ediacaran period. A degree of genetic variability can be expected within any taxa, and this may be compounded by preservation factors affecting the Jodhpur Ediacaran discs. Sudden increase in size or gigantism is a common feature of Ediacaran life, which is evident in case of Jodhpur discs also. On the basis of fossil assemblage, the Jodhpur Group (the Marwar Supergroup) is regionally correlated with the Bhander Group of the Vindhyan Supergroup and Krol Group of Lesser Himalaya. Globally, the assemblage is comparable with the Long Mynd Group, Shropshire, UK, Fermuse Formation Newfoundland, South Australia, Russia and Norway.展开更多
Ediacaran discs from the Jodhpur Sandstone of the Marwar Supergroup, Rajasthan, exhibit a wide size ranging from a few millimetres to 75 cm in diameter. Exceptionally large size of the discs in these rocks represent t...Ediacaran discs from the Jodhpur Sandstone of the Marwar Supergroup, Rajasthan, exhibit a wide size ranging from a few millimetres to 75 cm in diameter. Exceptionally large size of the discs in these rocks represent the largest reported so far from any Ediacaran assemblage. Although, larger medu-soid discs have been reported from USA, they are from the middle Cambrian and even younger rocks. Presence of microbial mats and weed-like structures with well preserved hold fasts and horizontal rhizome-like structures in association with some of these large-sized discs support their animal affinity, which probably feed on this weed-like vegetations. This association also supports their benthic habitat. Unlike the general trend of sudden increase in size of organisms in Ediacaran period and further decrease in size during Cambrian, these discs continued increasing in size in Cambrian also.展开更多
The distinctive sedimentation patterns of the late Neoproterozoic Girbhakar Sandstone were investigated within the context of a Precambrian sedimentation system devoid of vegetation.This comprehensive study utilized a...The distinctive sedimentation patterns of the late Neoproterozoic Girbhakar Sandstone were investigated within the context of a Precambrian sedimentation system devoid of vegetation.This comprehensive study utilized an integrated approach,incorporating facies analysis,fluvial architectural elements analysis,and palaeocurrent analysis,to offer detailed insights into the controlling factors of sedimentology and depositional settings within the studied interval.Process-based facies analysis revealed thirteen distinct facies types organized into five associations,uncovering a diverse range of depositional palaeoenvironments—from alluvial fan and braided fluvial to transitional marine settings.An alluvial fan,dominated by debris flow and multiple ephemeral channels at the basin margin,emerged initially.The stratigraphic architecture of this alluvial fan and the associated ephemeral fluvial system was primarily influenced by water table fluctuations in arid to semiarid climatic conditions.A transition to a semi-perennial to perennial braided fluvial system occurred as the depositional slope decreased.However,the stratigraphic architecture of these fluvial systems exhibited distinctive variations in response to fluctuating base level rise.Notably,the basal segment,characterized by an unconformity below and a granular lag succeeded by wave-agitated sandstone above,represented the lowstand systems tract(LST).During the early LST,channel belts prograded at the northern distal end of upstream aggradational semi-perennial braided systems in response to the transgression of Girbhakar Sea from the north,aligning with the late Neoproterozoic Indian plate configuration.The coarsening upward deposits suggest a potential classification as a braid-delta,formed by a gradual rise in base level,low epeiric gradient,and episodic flashy discharges,which facilitate the downstream development of this deposit.During the late LST,the evolution of perennial fluvial systems resulted in braid-plain deposits throughout the study area,with a transitional marine unit at the downstream site.An accelerated rate of base level rise facilitated marine reworking,leading to the deposition of transitional marine sediments.The final phase of base level rise marked the cessation of terrestrial deposition,culminating in the submergence of the site underneath the sea.The study highlights the unique responses of alluvial sediments to diverse controlling factors along the deposition downslope.This enhances insights into Neoproterozoic alluvial sedimentation dynamics and the resulting stratigraphic architecture in time and space from a broad perspective.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
文摘The Marwar Basin in western Rajasthan is one among the many Proterozoic sedimentary basins developed in Peninsular India that preserve rich records of the geological history and is traditionally considered as Trans-Vindhyan basin developed across Delhi and Aravalli orogens.It contains sedimentary package classified under Marwar Supergroup thought to be equivalent to the Vindhyan Supergroup.However,recently acquired radiometric dates suggest that the Marwar Supergroup is distinctively younger than the Vindhyan Supergroup,and the two basins were independently developed although they shared some of their provenance regions(Malone et al.,2008;McKenzie et al.,2011;Davis et al.,2014;Turner et al.,2014).
基金JGM by the US National Science Foundation Grant EAR09-10888HRX by the National Natural Science Foundation of China Grant 41974078。
文摘The Marwar Supergroup(NW Peninsular India)is thought to be of Ediacaran-Cambrian age,based on previous paleontological and geochronological studies.However,direct constraints on the onset of sedimentation within the Marwar basin are still scarce.In this study,we report U–Pb zircon,LA-ICP-MS,and SIMS ages from the Chhoti Khatu felsic volcanic rocks,interlayered with the Jodhpur Group sandstones(Lower Marwar Supergroup).The cathodoluminescence images of the zircons indicate complex morphologies,and core-rim textures coupled with the wide range of ages indicate that they are likely inherited or in the case of thin poorly indurated ash-beds,detrital in origin.The age spectra of 68 zircon analyses from our sampling display a dominant 800–900 Ma age peak corresponding to the age of basement"Erinpura granite"rocks in the region.The youngest inherited zircon from a felsic ash layer yielded a U–Pb age of651 Ma±18 Ma that,together with previous studies and paleontological evidence,indicates a postCryogenian age for the initiation of Marwar sedimentation following a~125 Ma hiatus between the end of Malani magmatism and Marwar deposition.
文摘The noncarbonaceous Ediacaran discs of variable morphologies from the Jodhpur Sandstone Formation of the Marwar Supergroup, western Rajasthan, suggest different biologic affinities of plant and animal kingdom. These discs are commonly preserved on the bedding surfaces of siliciclastic sandstone and shale in strong positive relief and appear to possess a flexible to rigid body. Discs assignable to Aspidella, Cyclomedusa, Nimbia and Heimalora;all possibly inclining towards cnidarian affinity are being reported from the sandstone beds in Sursagar area. Variable morphologies among discs preserved in siliciclastic shale beds from the Artiya Kalan area support scyphozoan affinity (earlier named Marsonia from the same locality) and cnidarian affinity for small discs comparable with Funisia (considered being the first animals having sexual reproduction). Disc’s morphologies also suggest ephyra stage of Aurilia (a cnidarian form) or budding stages of some fungi, like Germinosphaera (multicellular benthic fungal fossils) and noncarbonaceous discs with well preserved wrinkles and folds like in Chuaria. Discs from the Jodhpur Sandstone, may at times display taphonomic interplay, but consistency and repetition in morphology support variable biological affinities representing diverse assemblage and advance ecosystem prevailing during Ediacaran period. A degree of genetic variability can be expected within any taxa, and this may be compounded by preservation factors affecting the Jodhpur Ediacaran discs. Sudden increase in size or gigantism is a common feature of Ediacaran life, which is evident in case of Jodhpur discs also. On the basis of fossil assemblage, the Jodhpur Group (the Marwar Supergroup) is regionally correlated with the Bhander Group of the Vindhyan Supergroup and Krol Group of Lesser Himalaya. Globally, the assemblage is comparable with the Long Mynd Group, Shropshire, UK, Fermuse Formation Newfoundland, South Australia, Russia and Norway.
基金Financial assistance from DST, New Delhi in form of a WOS-A project No. SR/OY/WOS-A/ES-20/ 2008
文摘Ediacaran discs from the Jodhpur Sandstone of the Marwar Supergroup, Rajasthan, exhibit a wide size ranging from a few millimetres to 75 cm in diameter. Exceptionally large size of the discs in these rocks represent the largest reported so far from any Ediacaran assemblage. Although, larger medu-soid discs have been reported from USA, they are from the middle Cambrian and even younger rocks. Presence of microbial mats and weed-like structures with well preserved hold fasts and horizontal rhizome-like structures in association with some of these large-sized discs support their animal affinity, which probably feed on this weed-like vegetations. This association also supports their benthic habitat. Unlike the general trend of sudden increase in size of organisms in Ediacaran period and further decrease in size during Cambrian, these discs continued increasing in size in Cambrian also.
文摘The distinctive sedimentation patterns of the late Neoproterozoic Girbhakar Sandstone were investigated within the context of a Precambrian sedimentation system devoid of vegetation.This comprehensive study utilized an integrated approach,incorporating facies analysis,fluvial architectural elements analysis,and palaeocurrent analysis,to offer detailed insights into the controlling factors of sedimentology and depositional settings within the studied interval.Process-based facies analysis revealed thirteen distinct facies types organized into five associations,uncovering a diverse range of depositional palaeoenvironments—from alluvial fan and braided fluvial to transitional marine settings.An alluvial fan,dominated by debris flow and multiple ephemeral channels at the basin margin,emerged initially.The stratigraphic architecture of this alluvial fan and the associated ephemeral fluvial system was primarily influenced by water table fluctuations in arid to semiarid climatic conditions.A transition to a semi-perennial to perennial braided fluvial system occurred as the depositional slope decreased.However,the stratigraphic architecture of these fluvial systems exhibited distinctive variations in response to fluctuating base level rise.Notably,the basal segment,characterized by an unconformity below and a granular lag succeeded by wave-agitated sandstone above,represented the lowstand systems tract(LST).During the early LST,channel belts prograded at the northern distal end of upstream aggradational semi-perennial braided systems in response to the transgression of Girbhakar Sea from the north,aligning with the late Neoproterozoic Indian plate configuration.The coarsening upward deposits suggest a potential classification as a braid-delta,formed by a gradual rise in base level,low epeiric gradient,and episodic flashy discharges,which facilitate the downstream development of this deposit.During the late LST,the evolution of perennial fluvial systems resulted in braid-plain deposits throughout the study area,with a transitional marine unit at the downstream site.An accelerated rate of base level rise facilitated marine reworking,leading to the deposition of transitional marine sediments.The final phase of base level rise marked the cessation of terrestrial deposition,culminating in the submergence of the site underneath the sea.The study highlights the unique responses of alluvial sediments to diverse controlling factors along the deposition downslope.This enhances insights into Neoproterozoic alluvial sedimentation dynamics and the resulting stratigraphic architecture in time and space from a broad perspective.
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.
