Decades of commercial planting and other anthropogenic processes are posing a threat to the riparian landscapes of the Cauvery river basin, which supports a high floral diversity. Despite this, the habitats in the ups...Decades of commercial planting and other anthropogenic processes are posing a threat to the riparian landscapes of the Cauvery river basin, which supports a high floral diversity. Despite this, the habitats in the upstream sections of the River Cauvery are still intact, as they are located in sacred groves. To understand the dynamism of riparian forests exposed to anthropogenic pressures, the upstream stretch of Cauvery extending from Kushalanagara to Talacauvery （~102 km） was categorized into two landscapes： agro ecosystem and sacred （i.e. preserved）. The tree species were sampled using belt transects at 5 km intervals and the regeneration status of endemic species assessed using quadrats. A total of 128 species belonging to 47 families, and representing 1,590 individuals, was observed. Amongst them, 65% of unique species were exclusive to sacred landscapes. A rarefaction plot confirmed higher species richness for the sacred compared to the agro ecosystem landscapes, and diversity indices with more evenness in distribution were evident in sacred landscapes. A significant loss of endemic tree species in the agro ecosystem landscapes was found. Overall, this study demonstrates that an intense biotic pressure in terms of plantations and other anthropogenic activities have altered the species composition of the riparian zone in non-sacred areas. A permanent policy implication is required for the conservation of riparian buffers to avoid further ecosystem degradation and loss of biodiversity.展开更多
The repetitive influx of coarse clastics of mixed composition,siliciclastics and carbonates,locally common in the lower part of the Upper Cretaceous marine Kallankurichchi Limestone specifies a resurgence of tectonic ...The repetitive influx of coarse clastics of mixed composition,siliciclastics and carbonates,locally common in the lower part of the Upper Cretaceous marine Kallankurichchi Limestone specifies a resurgence of tectonic unrest in the Cauvery rift basin,India.The basin-margin scree and its derivatives elicit diverse modes of emplacement and differ in many ways from denoting it only as basal conglomerate.The study meticulously reveals the depositional history of these basin-margin coarse clastics.The scree conglomerate bodies are wedge-shaped in appearance and often have flat,eroded tops.At places,their surfaces,tops and flanks,are encrusted with Inoceramus although internally,they are mostly unfossiliferous.They are clast-supported and extremely poorly sorted,having interstitial spaces filled by sand-sized grains at the basal part.The clasts can be traced into the underlying Sillakuddi Sandstone and the granitic basement.The clasts derived from the sandstone are angular and measure up to 60 cm in length,while the basement-derived clasts dominate the smaller(maximum diameter measured 5 cm)and more rounded population.The elongated clasts are chaotically arranged,even oriented sub-vertically,reclining on other clasts.The lowermost scree conglomerate has a sharp base,and the pebbles sunk into the underlying sandstone,although no discernible impact laminae wrapping their bottom were ever observed.Evidently,the scree fans were initiated under the sea,which permitted the slow sinking of assorted rock fragments dropped from above.The sporadic occurrence of marine fossils further corroborates this contention.The scree conglomerates at different stratigraphic levels transitioned laterally into conglomerates of mass flow origin and then to massive calcarenite,together forming wedge-shaped bodies.The initial alignment of clasts parallel to bedding transforms to a chaotic alignment representing the transition from internally sheared flow to debris flow and associated shapes.Matrixsupported fabric grades into massive calcarenite,suggesting gravity-driven transformation.Further down the wedge,the massive calcarenite turns into cross-stratified facies,making it evident that laminar flow turned turbulent in the course of body transformation of the sediment-driving flows.It can be presumed that these flows were triggered by subsidence,which resulted from renewed gaps in formation and led to the collapse of scree cones.Facies variability suggests scree deposits giving way downslope to debris flow and related deposits.Eventually,all the scree products pass laterally into the carbonate formation basinwards.展开更多
The present review is aimed at correlating major geologic events of the Cauvery Basin with analogous global episodes. The Cauvery Basin came into existence due to Gondwana break up during Late Jurassic-Early Cretaceou...The present review is aimed at correlating major geologic events of the Cauvery Basin with analogous global episodes. The Cauvery Basin came into existence due to Gondwana break up during Late Jurassic-Early Cretaceous by taphrogenic rift process. The first marine transgression close to Aptian/Albian boundary at the western margin of the basin terminates the syn-rift tectonic phase, which is also precise in adjoining Krishna-Godavari （KG） Basin. Two regional tectonic episodes are well documented in the basin which have global significance viz. （1） A major basinal uplift during late Turonian caused by Marion hot mantle plume resulted in widespread subaqueous volcanism in the southern part of the Cauvery Basin. This uplift also ted to relative sea level （RSL） fall of about 100 m in Cauvery and KG Basins and an unconformity of a magnitude of 2.3 Ma. The RSL fatt closely correlates with global sea level faU. This volcanic episode also resulted in Madagascar detachment from India. （2） The reunion hot mantle plume that ted to Deccan volcanism in central India resulted in E-SE tilt of the Cauvery Basin during upper Maastrichtian （CFI-CF3 zones）. This tilt caused a sea level fall of about 80 m and lateral withdrawal of sea by about 50 km developing a major erosional unconformity ranging in magnitude of -1.8-30 My. The magnitude of RSL correlates wetl with global sea level fall. This sea level fall caused widespread development of canyon features in the Cauvery Basin resulting in differential subaqueous erosion. The globally significant ocean anoxic events viz. OAE-Ib, OAE-1d, OAE-2 and OAE-3 are fairly discernible in the Cauvery Basin. The new isotopic palaeotemperature data suggests that southern India and Madagascar were located apparently in middle latitudes within the tropical-subtropical climatic zone during Atbian and early Maastrichtian. The magnitude of hiatus across K-Pg boundary varying from 0 to 30 Ma is estimated based on ptanktic foraminifera for subsurface sections. The magnetostratigraphy of outcrop sediments with rich fossil evidences reveals that magnetic polarity reversals consist of 13 mag- netozones in the Late Cretaceous sedimentary strata.展开更多
The Cretaceous(Albian-Cenomanian) Dalmiapuram Formation is one of the economically significant constituents in the hydrocarbon-producing Cauvery rift basin, SE India that opened up during the Late Jurassic e Early Cre...The Cretaceous(Albian-Cenomanian) Dalmiapuram Formation is one of the economically significant constituents in the hydrocarbon-producing Cauvery rift basin, SE India that opened up during the Late Jurassic e Early Cretaceous Gondwanaland fragmentation. The fossil-rich Dalmiapuram Formation,exposed at Ariyalur within the Pondicherry sub-basin of Cauvery Basin, rests in most places directly on the Archean basement and locally on the Lower Cretaceous(Barremian-Aptian) Basal Siliciclastic Formation. In the Dalmiapuram Formation, a facies association of tectonically-disturbed phase is sandwiched between two drastically quieter phases. The early syn-rift facies association(FA 1), records the first carbonate marine transgression within the basin, comprising a bar-lagoon system with occasionally storms affecting along the shore and a sheet-like non-recurrent biomicritic limestone bed on the shallow shelf that laterally grades into pyrite e glauconite-bearing dark-colored shale in the deeper shelf. Spectacular breccias together with varied kinds of mass-flow products comprise the syn-rift facies association(FA 2). While the breccias occur at the basin margin area, the latter extend in the deeper inland sea. Clast composition of the coarse clastics includes large, even block-sized limestone fragments and small fragments of granite and sandstone from the basement.Marl beds of quieter intervals between tectonic pulses occur in alternation with them. Faulted basal contact of the formation, and small grabens filled by multiple mass-flow packages bear the clear signature of the syntectonic activity localized contortions, slump folds, and pillow beds associated with mega slump/slide planes and joints, which corroborates this contention further. This phase of tectonic intervention is followed by another relatively quieter phase and accommodates the late syn-rift facies association(FA 3). A tidal bar-interbar shelf depositional system allowed a transgressive systems tract motif to grow eventually passing upwards into the Karai Shale Formation, whose contact with the Dalmiapuram Formation is gradational.展开更多
The Cuddalore Formation of the Cauvery Basin received siliciclastic detritus from inland areas of the Southern Granulite Terrain(SGT).It represented continental-fluvial sedimentation in the eastern continental margin ...The Cuddalore Formation of the Cauvery Basin received siliciclastic detritus from inland areas of the Southern Granulite Terrain(SGT).It represented continental-fluvial sedimentation in the eastern continental margin of South India during the Miocene.Indian Summer Monsoon was thought to be initiated in the early Miocene and intensified during the middle Miocene causing major climatic shifts in the Indian subcontinent.In the present work,detailed mineralogical and geochemical studies on the siliciclastic Cuddalore Formation have been carried out to understand the provenance and paleoclimatic conditions during the Miocene.The paleocurrent direction,textural immaturity and framework detrital modes of sandstones suggest rapid uplift of basement and sediment source from nearby Madras Block of SGT.Various diagnostic immobile trace element ratios such as Th/Sc,Co/Th,La/Sc,La/Co suggest a tonalite-trondhjemite-granodiorite-charnockite provenance,and somewhat more felsic composition of source area compared to the present upper continental crust(UCC).Rare earth element mixed model suggests that sediments were dominantly(80%)sourced from felsic charnockite,with a minor contribution(20%)from mafic granulites.Higher abundance of advanced-weathering products like kaolinite,very high(>98)chemical index of alteration(CIA)values,severe depletion of mobile elements(Ca,Na,K,Mg,Ba,Rb)in comparison to UCC,significantly higher a Mg,a Ca,a Na,a K,a Sr and a Ba values(higher than the unity),all suggest the extreme chemical weathering in source terrain and/or in the sedimentary basin.Calculations based on CIA show high average surface temperature between 29.3℃and 29.5℃and high mean annual precipitation ranging from 2339 mm/yr to 2467 mm/yr.The geochemical data are consistent with the paleogeographic position of the depositional basin(Cauvery Basin)and suggest the deposition of Cuddalore sediments(the Cuddalore Formation)in a nearequatorial location under a warm climate condition with abundant monsoonal precipitation.展开更多
This study was conducted during March to May of 2010 dry season, giving prime thrust to determine the metal concentrations in commercial fish species of Catla catla and Labeo rohita, collected from various points alon...This study was conducted during March to May of 2010 dry season, giving prime thrust to determine the metal concentrations in commercial fish species of Catla catla and Labeo rohita, collected from various points along the river Cauvery. The liver, gill and muscle tissues of fish were analyzed for Fe, Pb, Zn, Ni, Mn, Cu, Cr and Cd using Atomic Absorption Spectrophotometry (AAS-model: 6300). The Catla catla has shown more accumulation potency for all the metals than Labeo rohita. The liver in both fish species has better accretion capacity compared to gill and muscle and the same was noticed by bioaccumulation factor. The results of bioaccumulation factor were in the order of Ni > Zn > Cu > Mn > Fe > Cr > Pb > Cd. Elevated trend was noticed among the essential metals and decreased trend among the nonessential metals were observed in both fish species.展开更多
文摘Decades of commercial planting and other anthropogenic processes are posing a threat to the riparian landscapes of the Cauvery river basin, which supports a high floral diversity. Despite this, the habitats in the upstream sections of the River Cauvery are still intact, as they are located in sacred groves. To understand the dynamism of riparian forests exposed to anthropogenic pressures, the upstream stretch of Cauvery extending from Kushalanagara to Talacauvery （~102 km） was categorized into two landscapes： agro ecosystem and sacred （i.e. preserved）. The tree species were sampled using belt transects at 5 km intervals and the regeneration status of endemic species assessed using quadrats. A total of 128 species belonging to 47 families, and representing 1,590 individuals, was observed. Amongst them, 65% of unique species were exclusive to sacred landscapes. A rarefaction plot confirmed higher species richness for the sacred compared to the agro ecosystem landscapes, and diversity indices with more evenness in distribution were evident in sacred landscapes. A significant loss of endemic tree species in the agro ecosystem landscapes was found. Overall, this study demonstrates that an intense biotic pressure in terms of plantations and other anthropogenic activities have altered the species composition of the riparian zone in non-sacred areas. A permanent policy implication is required for the conservation of riparian buffers to avoid further ecosystem degradation and loss of biodiversity.
基金Department of Geological Sciences,Jadavpur University for the infrastructural facility and DST INSPIRE(Code-DST/INSPIRE Fellowship/2017/IF170730)for providing fellowship.
文摘The repetitive influx of coarse clastics of mixed composition,siliciclastics and carbonates,locally common in the lower part of the Upper Cretaceous marine Kallankurichchi Limestone specifies a resurgence of tectonic unrest in the Cauvery rift basin,India.The basin-margin scree and its derivatives elicit diverse modes of emplacement and differ in many ways from denoting it only as basal conglomerate.The study meticulously reveals the depositional history of these basin-margin coarse clastics.The scree conglomerate bodies are wedge-shaped in appearance and often have flat,eroded tops.At places,their surfaces,tops and flanks,are encrusted with Inoceramus although internally,they are mostly unfossiliferous.They are clast-supported and extremely poorly sorted,having interstitial spaces filled by sand-sized grains at the basal part.The clasts can be traced into the underlying Sillakuddi Sandstone and the granitic basement.The clasts derived from the sandstone are angular and measure up to 60 cm in length,while the basement-derived clasts dominate the smaller(maximum diameter measured 5 cm)and more rounded population.The elongated clasts are chaotically arranged,even oriented sub-vertically,reclining on other clasts.The lowermost scree conglomerate has a sharp base,and the pebbles sunk into the underlying sandstone,although no discernible impact laminae wrapping their bottom were ever observed.Evidently,the scree fans were initiated under the sea,which permitted the slow sinking of assorted rock fragments dropped from above.The sporadic occurrence of marine fossils further corroborates this contention.The scree conglomerates at different stratigraphic levels transitioned laterally into conglomerates of mass flow origin and then to massive calcarenite,together forming wedge-shaped bodies.The initial alignment of clasts parallel to bedding transforms to a chaotic alignment representing the transition from internally sheared flow to debris flow and associated shapes.Matrixsupported fabric grades into massive calcarenite,suggesting gravity-driven transformation.Further down the wedge,the massive calcarenite turns into cross-stratified facies,making it evident that laminar flow turned turbulent in the course of body transformation of the sediment-driving flows.It can be presumed that these flows were triggered by subsidence,which resulted from renewed gaps in formation and led to the collapse of scree cones.Facies variability suggests scree deposits giving way downslope to debris flow and related deposits.Eventually,all the scree products pass laterally into the carbonate formation basinwards.
文摘The present review is aimed at correlating major geologic events of the Cauvery Basin with analogous global episodes. The Cauvery Basin came into existence due to Gondwana break up during Late Jurassic-Early Cretaceous by taphrogenic rift process. The first marine transgression close to Aptian/Albian boundary at the western margin of the basin terminates the syn-rift tectonic phase, which is also precise in adjoining Krishna-Godavari （KG） Basin. Two regional tectonic episodes are well documented in the basin which have global significance viz. （1） A major basinal uplift during late Turonian caused by Marion hot mantle plume resulted in widespread subaqueous volcanism in the southern part of the Cauvery Basin. This uplift also ted to relative sea level （RSL） fall of about 100 m in Cauvery and KG Basins and an unconformity of a magnitude of 2.3 Ma. The RSL fatt closely correlates with global sea level faU. This volcanic episode also resulted in Madagascar detachment from India. （2） The reunion hot mantle plume that ted to Deccan volcanism in central India resulted in E-SE tilt of the Cauvery Basin during upper Maastrichtian （CFI-CF3 zones）. This tilt caused a sea level fall of about 80 m and lateral withdrawal of sea by about 50 km developing a major erosional unconformity ranging in magnitude of -1.8-30 My. The magnitude of RSL correlates wetl with global sea level fall. This sea level fall caused widespread development of canyon features in the Cauvery Basin resulting in differential subaqueous erosion. The globally significant ocean anoxic events viz. OAE-Ib, OAE-1d, OAE-2 and OAE-3 are fairly discernible in the Cauvery Basin. The new isotopic palaeotemperature data suggests that southern India and Madagascar were located apparently in middle latitudes within the tropical-subtropical climatic zone during Atbian and early Maastrichtian. The magnitude of hiatus across K-Pg boundary varying from 0 to 30 Ma is estimated based on ptanktic foraminifera for subsurface sections. The magnetostratigraphy of outcrop sediments with rich fossil evidences reveals that magnetic polarity reversals consist of 13 mag- netozones in the Late Cretaceous sedimentary strata.
文摘The Cretaceous(Albian-Cenomanian) Dalmiapuram Formation is one of the economically significant constituents in the hydrocarbon-producing Cauvery rift basin, SE India that opened up during the Late Jurassic e Early Cretaceous Gondwanaland fragmentation. The fossil-rich Dalmiapuram Formation,exposed at Ariyalur within the Pondicherry sub-basin of Cauvery Basin, rests in most places directly on the Archean basement and locally on the Lower Cretaceous(Barremian-Aptian) Basal Siliciclastic Formation. In the Dalmiapuram Formation, a facies association of tectonically-disturbed phase is sandwiched between two drastically quieter phases. The early syn-rift facies association(FA 1), records the first carbonate marine transgression within the basin, comprising a bar-lagoon system with occasionally storms affecting along the shore and a sheet-like non-recurrent biomicritic limestone bed on the shallow shelf that laterally grades into pyrite e glauconite-bearing dark-colored shale in the deeper shelf. Spectacular breccias together with varied kinds of mass-flow products comprise the syn-rift facies association(FA 2). While the breccias occur at the basin margin area, the latter extend in the deeper inland sea. Clast composition of the coarse clastics includes large, even block-sized limestone fragments and small fragments of granite and sandstone from the basement.Marl beds of quieter intervals between tectonic pulses occur in alternation with them. Faulted basal contact of the formation, and small grabens filled by multiple mass-flow packages bear the clear signature of the syntectonic activity localized contortions, slump folds, and pillow beds associated with mega slump/slide planes and joints, which corroborates this contention further. This phase of tectonic intervention is followed by another relatively quieter phase and accommodates the late syn-rift facies association(FA 3). A tidal bar-interbar shelf depositional system allowed a transgressive systems tract motif to grow eventually passing upwards into the Karai Shale Formation, whose contact with the Dalmiapuram Formation is gradational.
文摘The Cuddalore Formation of the Cauvery Basin received siliciclastic detritus from inland areas of the Southern Granulite Terrain(SGT).It represented continental-fluvial sedimentation in the eastern continental margin of South India during the Miocene.Indian Summer Monsoon was thought to be initiated in the early Miocene and intensified during the middle Miocene causing major climatic shifts in the Indian subcontinent.In the present work,detailed mineralogical and geochemical studies on the siliciclastic Cuddalore Formation have been carried out to understand the provenance and paleoclimatic conditions during the Miocene.The paleocurrent direction,textural immaturity and framework detrital modes of sandstones suggest rapid uplift of basement and sediment source from nearby Madras Block of SGT.Various diagnostic immobile trace element ratios such as Th/Sc,Co/Th,La/Sc,La/Co suggest a tonalite-trondhjemite-granodiorite-charnockite provenance,and somewhat more felsic composition of source area compared to the present upper continental crust(UCC).Rare earth element mixed model suggests that sediments were dominantly(80%)sourced from felsic charnockite,with a minor contribution(20%)from mafic granulites.Higher abundance of advanced-weathering products like kaolinite,very high(>98)chemical index of alteration(CIA)values,severe depletion of mobile elements(Ca,Na,K,Mg,Ba,Rb)in comparison to UCC,significantly higher a Mg,a Ca,a Na,a K,a Sr and a Ba values(higher than the unity),all suggest the extreme chemical weathering in source terrain and/or in the sedimentary basin.Calculations based on CIA show high average surface temperature between 29.3℃and 29.5℃and high mean annual precipitation ranging from 2339 mm/yr to 2467 mm/yr.The geochemical data are consistent with the paleogeographic position of the depositional basin(Cauvery Basin)and suggest the deposition of Cuddalore sediments(the Cuddalore Formation)in a nearequatorial location under a warm climate condition with abundant monsoonal precipitation.
文摘This study was conducted during March to May of 2010 dry season, giving prime thrust to determine the metal concentrations in commercial fish species of Catla catla and Labeo rohita, collected from various points along the river Cauvery. The liver, gill and muscle tissues of fish were analyzed for Fe, Pb, Zn, Ni, Mn, Cu, Cr and Cd using Atomic Absorption Spectrophotometry (AAS-model: 6300). The Catla catla has shown more accumulation potency for all the metals than Labeo rohita. The liver in both fish species has better accretion capacity compared to gill and muscle and the same was noticed by bioaccumulation factor. The results of bioaccumulation factor were in the order of Ni > Zn > Cu > Mn > Fe > Cr > Pb > Cd. Elevated trend was noticed among the essential metals and decreased trend among the nonessential metals were observed in both fish species.
