In this study,we report for thefirst time an Early Palaeozoic basement diorite from the drilled well Nirona-A in the Banni Half-Graben of the Kutch basin,western India.The 40Ar–39Ar dates provided a plateau age of 441...In this study,we report for thefirst time an Early Palaeozoic basement diorite from the drilled well Nirona-A in the Banni Half-Graben of the Kutch basin,western India.The 40Ar–39Ar dates provided a plateau age of 441.84±2.66 Ma and another pseudo plateau of 441.28±5.82 to 388.08±16.65 Ma for the basement diorite.These ages constrain the basement formation age to the Late Ordovician-Early Silurian period.The obtained basement ages are correlatable with the later part of Cambro-Ordovician alkaline magmatism that has been reported from the Huqf area in Central Oman,whereas their lithological and petrographic correlativity with base-ment diorites occurring in the Dinsi Body of Nagar Parkar igneous complex in Pakistan can also be envisaged.The geochemical studies characterized the diorite with enrich-ment of LILE(Rb,Ba,and K)and LREE(La,Ce,Nd),strong depletion of HFSE(Nb,Sr,P,and Ti),along with weakly negative Eu anomalies.The geochemical signatures indicate their petrogenetic affiliation with mantle-derived magmas,as well as their tectonic setting to be arc-related,having post-collisional continental-arc type affinity.The*440 Ma basement of Kutch,therefore,appears to rep-resent the later thermal event associated with the reworked Neoproterozoic subduction-related suite from Greater India’s northwest edge,which has implications for Gond-wana assembly in the northwest Indian subcontinent.展开更多
Present short communication reports about beach stranding of Porpita porpita(Linnaeus 1758)from the Coast of Mandvi,Kutch during August 2021.Also,this is the first record of the blue button jellyfishes for the norther...Present short communication reports about beach stranding of Porpita porpita(Linnaeus 1758)from the Coast of Mandvi,Kutch during August 2021.Also,this is the first record of the blue button jellyfishes for the northern Gulf of Kutch region.A study was carried out by primary observation and measurements of common environmental parameters such as Sea Surface Temperature(SST),Wind Direction&Wind Speed.Aboral and oral parts were observed and described.It is assumed that the large biomass of blue button jellyfish on the beach is due to strong shoreward Monsoon winds.展开更多
Mineralogical,geochemical and isotopic(Sr and Nd) studies on the recently reported ca. 124 Ma'anorogenic lamproite' dyke from the Palanpur area, Kutch seismogenic rift zone, northwestern India, are presented. ...Mineralogical,geochemical and isotopic(Sr and Nd) studies on the recently reported ca. 124 Ma'anorogenic lamproite' dyke from the Palanpur area, Kutch seismogenic rift zone, northwestern India, are presented. We propose a new classification for the dyke as a damtjernite(ultramafic lamprophyre; UML)based on its porphyritic-panidiomorphic texture, abundance of phlogopite, presence of nepheline in the groundmass, and the composition of liquidus phases such as olivine, phlogopite, magnetite, and clinopyroxene(diopside). The Palanpur UML is primitive(Mg# =74-77),silica-undersaturated(SiO_2<40 wt.%),potassic to slightly sodic in nature, and is strikingly similar to the ~69 Ma UML dykes and sills of the Tethyan Indus suture zone, which are considered as the earliest yet known manifestations of the Deccan Large Igneous Province(LIP). Bulk-rock(^(87)Sr/^(86)Sr)_i(0.70460-0.70461) and ε_(N)d(t)(+2.56 to-0.69) of the Palanpur UML signify derivation from a slightly depleted mantle source similar to that of asthenospheric magmas such as OIB. This is further attested to by the high incompatible trace element ratios(viz., La/Ba, Nb/U, Nb/La and Ta/Yb) that are typical of plume-type magmas. However, the Neoproterozoic T_(DM) depleted mantle Nd model ages( ~655-919 Ma) also necessitate some involvement of a lithospheric mantle component in its genesis. High bulk-rock Fe_2 O_3~t and TiO_2 contents require the involvement of a fertile peridotitic mantle source, whereas high La/Yb(60-80) implies a control by residual garnet. Higher Rb/Sr and lower Ba/Rb suggest phlogopite as a residual phase and high Nb and lower La/Sm favour carbonatite, rather than silicate melt as metasomatising agent. Low degrees of partial melting of a primitive garnet lherzolite mantle can account for the observed REE patterns in the Palanpur UML. The Palanpur UML shares a temporal similarity to the Kerguelen plume-derived Rajmahal basalts and associated alkaline rocks from the eastern India. The tectonomagmatic significance of its emplacement during the mid-Cretaceous vis-a-vis various models involving the timing of eruption of the Deccan and the Rahmahal Traps and the rifting in the Kutch basin induced by far-field plate reorganization is evaluated.展开更多
Geotourism in Kutch has an exemplary potential of being designated as a site for perfect establishment of a National Geopark. The paper is aimed to describe the geological significance of the sites with basic concept ...Geotourism in Kutch has an exemplary potential of being designated as a site for perfect establishment of a National Geopark. The paper is aimed to describe the geological significance of the sites with basic concept of creation of geoparks and promote geotourism. The financial, infrastructural aspects, deliverables to the society are presented primarily focusing on the local economic and sustainable development of Kutch. The need for development of infrastructure for geotourism is urgently required as the rare geological heritage of Kutch region is eroding and being destroyed due to manmade activities.展开更多
Unconsolidated siliciclastic sediments can undergo post-burial deformation, which leads to the formation of distinctive sedimentary structures, known as soft-sediment deformation structures(SSDS). The presence of a se...Unconsolidated siliciclastic sediments can undergo post-burial deformation, which leads to the formation of distinctive sedimentary structures, known as soft-sediment deformation structures(SSDS). The presence of a series of sand volcanoes confined to a particular lithostratigraphic horizon can represent a paleoseismic activity and, thereby, exemplifies the concept of “seismite”. The Kutch Basin has been a tectonically active region since the initiation of eastern Gondwana rifting followed by a tectonic inversion during the Cenozoic due to the collision of the Indian and Eurasian plates. A stratum-bound series of sand volcanoes belonging to the Khari Nadi Formation(KNF) is exposed along the banks of Khari River. They separate the shallow marine deposits below and non-marine deposits above with their characteristic marine and paleosol trace fossil suites, respectively. Although a seismogenic origin has been much debated for the SSDS,the ichnofabric analysis of the sand-volcano-bearing stratum unequivocally points toward such an origin under a shallow seafloor condition. In addition to the sedimentary regime change from an open shallow-marine setting to a continental depositional environment concomitant with basinal uplift, the behavior of the burrowing crustaceans testifies to a syn-depositional development of a fault network associated with the fluidization, sand volcanism, and the resilience of the trace-producers in surviving those processes until the sedimentary regime change in the overlying strata. Although the ichno-sedimentological evidence apparently differs from the previous works that proposed a continuous base-level rise from the beginning of deposition of the Khari Nadi Formation up to the middle part of the overlying Chhasra Formation, the paleoseismic activity,its ichnologic signature, and the depositional regime change refer to a higher-resolution(i.e., lower-order)sequence-stratigraphic change causing a short-duration regression within a longer-duration cycle of base-level rise.展开更多
This paper investigates the provenance of Middle Jurassic to Early Cretaceous sediments in the Kutch Basin, western India, on the basis of mineralogical investigations of sandstones composition (Quartz-Feldspar-Lith...This paper investigates the provenance of Middle Jurassic to Early Cretaceous sediments in the Kutch Basin, western India, on the basis of mineralogical investigations of sandstones composition (Quartz-Feldspar-Lithic (QFL) fragment), Zircon-Tourmaline-Rutile (ZTR) index, and mineral chemistry of heavy detrital minerals of the framework. The study also examines the compositional variation of the sandstone in relation to the evolution of the Kutch Basin, which originated as a rift basin during the Late Triassic and evolved into a passive margin basin by the end Cretaceous. This study analyzes sandstone samples of Jhumara, Jhuran and Bhuj Formations of Middle Jurassic, Upper Jurassic and Lower Cretaceous, respectively, in the Kutch Mainland. Sandstones record a compositional evolution from arkosic to subarkosic as the feldspar content decreases from 68% in the Jhumara Formation to 27% in the Bhuj Formation with intermediate values in the Jhuran Formation. The QFL modal composition indicates basement uplifted and transitional continental settings at source. Heavy mineral content of these sandstones reveals the occurrence of zircon, tourmaline, rutile, garnet, apatite, monazite and opaque minerals. Sub-rounded to well-rounded zircon grains indicate a polycyclic origin. ZTR indices for samples in Jhumara, Jhuran and Bhuj Formations are 25%, 30% and 50% respectively. Chemistry of opaque minerals reveals the occurrence of detrital varieties such as ilmenite, rutile, hematite/magnetite and pyrite, in a decreasing order of abundances. Chemistry of ilmenites in the Jhumara Formation reveals its derivation from dual felsic igneous and metabasic source, while those in Jhuran and Bhuj Formations indicate a metabasic derivation. Chemistry of garnet reveals predominantly Fe-rich (almandine) variety of metabasic origin. X-ray microscopic study provides the percentage of heavy minerals ranging from 3% to 5.260. QFL detrital modes reflect the evolution of the basin from an active rift to a passive margin basin during the Mesozoic. Integration of results from QFL modal composition of the sandstones, heavy mineral analysis and mineral chemistry, suggests sediment supply from both northern and eastern highlands during the Middle Jurassic. The uplift along the Kutch Mainland Fault in the Early Cretaceous results in curtailment of sediment input from north.展开更多
The lignite deposits of Kutch, India are stratigraphically referred to the Naredi Formation and considered to be Early Eocene in age. The biostratigraphy of the older mine at Panandhro and a newly opened mine at Matan...The lignite deposits of Kutch, India are stratigraphically referred to the Naredi Formation and considered to be Early Eocene in age. The biostratigraphy of the older mine at Panandhro and a newly opened mine at Matanomadh has constrained the upper age limit of lignite to the early Bartonian. Its lower age may extend to the late Lutetian. Temporally the formation of lignite corresponds to the warming event of the Middle Eocene and suggests a humid climate at the onset of the warming. The previous palynological studies have already suggested dominance of tropical angiospermic pollen. A diverse assemblage of fossil whales and other vertebrates, many of them supposedly the oldest representatives, were reported from Panandhro mine. These were initially assigned to the Early Eocene and later to the Lute? tian age. The present biostratigraphic study revises their age to the Early Bartonian.展开更多
The Eocene Epoch passed through multiple hyperthermal events and recorded highest temperatures in the Cenozoic. Very few studies from Eocene palaeotropical sites have recorded changes in shallow marine foraminiferal a...The Eocene Epoch passed through multiple hyperthermal events and recorded highest temperatures in the Cenozoic. Very few studies from Eocene palaeotropical sites have recorded changes in shallow marine foraminiferal assemblages. The present study investigates the foraminiferal biofacies of shallow marine successions from a palaeotropical site in western India (Kutch Basin) to understand the palaeoclimate and its impact on the ecology of foraminifera. The sections were biostratigraphically con strained using planktic and larger benthic foraminifera. Four biofacies are recognized by detrended correspondence analysis of the sample-wise distribution of foraminifera. Low diversity and dwarfed foraminifera characterize Bulimina-Chiloguembelino biofacies (SBZ5/6-SBZ10), corresponding to the interval of Paleocene-Eocene Thermal Maxima (PETM) and Eocene Thermal Maxima 2 (ETM 2). Rectilinear benthic foraminifera and biserial and triserial planktic foraminifera, typical of high runoff, upwelling or eutrophic conditions, are dominant taxa in this biofacies. The specialist taxa increased significantly in Asterigerina-Cibicides biofacies, corresponding to SBZ11 (Early Eocene Climatic Optimum, EECO), and the environment became oligotrophic. The Jenkinsina-Brizalina biofacies (E12) is distinguished by foraminiferal assemblage ecologically like that of Bulimina-Chiloguembelina biofacies. It is characterized by high abundance of rectilinear benthic foraminifera and bloom of triserial planktic foraminifera, suggesting eutrophy and high runoff at the initiation of Middle Eocene Climatic Optimum (MECO). The foraminifera were more diverse and abundant in Cibicides-Nonion biofacies. The highly diverse larger benthic foraminiferal assemblage in this biofacies, signify warm and clear-water oligotrophic sea that promoted the development of platform carbonate in Kutch Basin and other basins in western India. The EECO and MECO did not have an adverse impact on shallow marine foraminifera, and particularly the larger benthic foraminifera attained high diversity, high abundance, larger size and wider latitudinal distribution in the middle Eocene.展开更多
A combined micropalaeontological and sedimentological investigation of the Early Eocene Naredi Formation (thickness varying between 20 m and 60 m) reveals a complete third-order cycle and six fourth-order sea level cy...A combined micropalaeontological and sedimentological investigation of the Early Eocene Naredi Formation (thickness varying between 20 m and 60 m) reveals a complete third-order cycle and six fourth-order sea level cycles. Within the third-order cycle the foraminiferal abundance and diversity gradually increase upwards and reach their maximum values at about 41 m thickness above the base of the formation and subsequently decrease upward and finally give way upward to an unfossiliferous zone at the topmost part. Within a fourth-order cycle foraminiferal abundance and diversity exhibit a similar increasing and decreasing pattern. Bounded between two unconformities the Naredi Formation represents a sequence. A highly fossiliferous Assilinabearing limestone interval represents the maximum flooding zone which separates the transgressive systems tract at the base from the highstand systems tract at the top.展开更多
Based on integration of field,petrographic and heavy mineral chemical data,this study highlights the source and tectonic setting of the Mesozoic sandstones of Kutch,Saurashtra,Narmada and Cambay basins at the western ...Based on integration of field,petrographic and heavy mineral chemical data,this study highlights the source and tectonic setting of the Mesozoic sandstones of Kutch,Saurashtra,Narmada and Cambay basins at the western margin of India,formed by the progressive splitting of the eastern Gondwanaland.The Kutch Basin is dominated by arkosic sandstone,whereas Saurashtra,Narmada and Cambay basins show the predominance of sub-arkose and sub-litharenite.The modal analyses of framework grains in Kutch sandstones indicate basement uplift and transitional continent settings.In contrast,the sandstones of Saurashtra,Narmada and Cambay basins bear imprints of recycled orogenic and craton interior belts.The presence of abraded and detrital quartz overgrowth and rounded zircons in most sandstones reveal the recycling of sediments in these basins.Tourmaline and rutile mineral compositions constrain the possible lithology of source rocks.The tourmaline mineral chemistry(Ca-Fe_(tot)-Mg plot)suggests the derivation of sediments from various sources,including Li-poor granitoids associated with pegmatites,aplites,Ca-poor metapelites,metapsammites and quartz-tourmaline-rich granitic rocks.The compositions of rutile grains(Cr vs.Nb plot)in sandstones indicate metapelitic sources.The gamut of all mineral chemical data supports the predominance of sediment sources from quartzo-feldspathic rocks with minor inputs from mafic rocks.Based on available paleocurrent data and correlation of source compositions,we infer that the Mesozoic sediments of Kutch,Saurashtra,Narmada and Cambay basins were primarily sourced by various lithologies of the Aravalli Craton.The Narmada Basin possibly received additional sediment input from the Bundelkhand Craton.展开更多
The Kutch Basin of western India is famous for its rich assemblages of the Callovian-Oxfordian ammonites.The family Oppelidae Douvillé is the second most diverse ammonite group after perisphinctids during the Mid...The Kutch Basin of western India is famous for its rich assemblages of the Callovian-Oxfordian ammonites.The family Oppelidae Douvillé is the second most diverse ammonite group after perisphinctids during the Middle-Upper Jurassic.Hecticoceratinae is the most diverse subfamily within Oppelidae and has wide palaeobiogeographic(near cosmopolitan) and temporal distributions(Bathonian-Oxfordian).Some species were well timediagnostic and thus help in interprovincial correlation.The taxonomy of the subfamily Hecticoceratinae of Kutch was in a state of flux until recently.It was not revised since Spath’s(1927-1933) great contribution.Many genera and species were morphogenera or morphospecies and they again suffer from excessive subjective splitting.It was therefore badly needed for a comprehensive taxonomic revision of the subfamily with modern aspects of systematics i.e.,sexual dimorphism and population dynamics.A lithostratigraphic framework has already been well documented in the Kutch Basin of western India.A high resolution biostratigraphy incorporating stage-intrastage fossil assemblages have been used in interbasinal correlation based on the Callovian-Oxfordian hecticoceratins.Near cosmopolitan distribution of many hecticoceratin genera were widely used for biostratigraphic zonation as well as an understanding of the palaeobiogeographic pattern.The phylogeny of the subfamily Hecticoceratinae has been used to construct the cladograms depicting area relationships among different provinces during the Callovian-Oxfordian.展开更多
文摘In this study,we report for thefirst time an Early Palaeozoic basement diorite from the drilled well Nirona-A in the Banni Half-Graben of the Kutch basin,western India.The 40Ar–39Ar dates provided a plateau age of 441.84±2.66 Ma and another pseudo plateau of 441.28±5.82 to 388.08±16.65 Ma for the basement diorite.These ages constrain the basement formation age to the Late Ordovician-Early Silurian period.The obtained basement ages are correlatable with the later part of Cambro-Ordovician alkaline magmatism that has been reported from the Huqf area in Central Oman,whereas their lithological and petrographic correlativity with base-ment diorites occurring in the Dinsi Body of Nagar Parkar igneous complex in Pakistan can also be envisaged.The geochemical studies characterized the diorite with enrich-ment of LILE(Rb,Ba,and K)and LREE(La,Ce,Nd),strong depletion of HFSE(Nb,Sr,P,and Ti),along with weakly negative Eu anomalies.The geochemical signatures indicate their petrogenetic affiliation with mantle-derived magmas,as well as their tectonic setting to be arc-related,having post-collisional continental-arc type affinity.The*440 Ma basement of Kutch,therefore,appears to rep-resent the later thermal event associated with the reworked Neoproterozoic subduction-related suite from Greater India’s northwest edge,which has implications for Gond-wana assembly in the northwest Indian subcontinent.
文摘Present short communication reports about beach stranding of Porpita porpita(Linnaeus 1758)from the Coast of Mandvi,Kutch during August 2021.Also,this is the first record of the blue button jellyfishes for the northern Gulf of Kutch region.A study was carried out by primary observation and measurements of common environmental parameters such as Sea Surface Temperature(SST),Wind Direction&Wind Speed.Aboral and oral parts were observed and described.It is assumed that the large biomass of blue button jellyfish on the beach is due to strong shoreward Monsoon winds.
文摘Mineralogical,geochemical and isotopic(Sr and Nd) studies on the recently reported ca. 124 Ma'anorogenic lamproite' dyke from the Palanpur area, Kutch seismogenic rift zone, northwestern India, are presented. We propose a new classification for the dyke as a damtjernite(ultramafic lamprophyre; UML)based on its porphyritic-panidiomorphic texture, abundance of phlogopite, presence of nepheline in the groundmass, and the composition of liquidus phases such as olivine, phlogopite, magnetite, and clinopyroxene(diopside). The Palanpur UML is primitive(Mg# =74-77),silica-undersaturated(SiO_2<40 wt.%),potassic to slightly sodic in nature, and is strikingly similar to the ~69 Ma UML dykes and sills of the Tethyan Indus suture zone, which are considered as the earliest yet known manifestations of the Deccan Large Igneous Province(LIP). Bulk-rock(^(87)Sr/^(86)Sr)_i(0.70460-0.70461) and ε_(N)d(t)(+2.56 to-0.69) of the Palanpur UML signify derivation from a slightly depleted mantle source similar to that of asthenospheric magmas such as OIB. This is further attested to by the high incompatible trace element ratios(viz., La/Ba, Nb/U, Nb/La and Ta/Yb) that are typical of plume-type magmas. However, the Neoproterozoic T_(DM) depleted mantle Nd model ages( ~655-919 Ma) also necessitate some involvement of a lithospheric mantle component in its genesis. High bulk-rock Fe_2 O_3~t and TiO_2 contents require the involvement of a fertile peridotitic mantle source, whereas high La/Yb(60-80) implies a control by residual garnet. Higher Rb/Sr and lower Ba/Rb suggest phlogopite as a residual phase and high Nb and lower La/Sm favour carbonatite, rather than silicate melt as metasomatising agent. Low degrees of partial melting of a primitive garnet lherzolite mantle can account for the observed REE patterns in the Palanpur UML. The Palanpur UML shares a temporal similarity to the Kerguelen plume-derived Rajmahal basalts and associated alkaline rocks from the eastern India. The tectonomagmatic significance of its emplacement during the mid-Cretaceous vis-a-vis various models involving the timing of eruption of the Deccan and the Rahmahal Traps and the rifting in the Kutch basin induced by far-field plate reorganization is evaluated.
文摘Geotourism in Kutch has an exemplary potential of being designated as a site for perfect establishment of a National Geopark. The paper is aimed to describe the geological significance of the sites with basic concept of creation of geoparks and promote geotourism. The financial, infrastructural aspects, deliverables to the society are presented primarily focusing on the local economic and sustainable development of Kutch. The need for development of infrastructure for geotourism is urgently required as the rare geological heritage of Kutch region is eroding and being destroyed due to manmade activities.
基金Science and Engineering Research Board (SERB), Government of India (Grant # CRG/2018/000259 to SDG)Industrial Research and Consultancy Centre (IRCC), IIT Bombay (Seed Grant # RD/0517-IRCCSH0-035 to SDG)Council of Scientific and Industrial Research (CSIR) (doctoral scholarship for AS),University Grants Commission (doctoral scholarship for KC),IIT Bombay and Ministry of Education of India (doctoral scholarship for MD)。
文摘Unconsolidated siliciclastic sediments can undergo post-burial deformation, which leads to the formation of distinctive sedimentary structures, known as soft-sediment deformation structures(SSDS). The presence of a series of sand volcanoes confined to a particular lithostratigraphic horizon can represent a paleoseismic activity and, thereby, exemplifies the concept of “seismite”. The Kutch Basin has been a tectonically active region since the initiation of eastern Gondwana rifting followed by a tectonic inversion during the Cenozoic due to the collision of the Indian and Eurasian plates. A stratum-bound series of sand volcanoes belonging to the Khari Nadi Formation(KNF) is exposed along the banks of Khari River. They separate the shallow marine deposits below and non-marine deposits above with their characteristic marine and paleosol trace fossil suites, respectively. Although a seismogenic origin has been much debated for the SSDS,the ichnofabric analysis of the sand-volcano-bearing stratum unequivocally points toward such an origin under a shallow seafloor condition. In addition to the sedimentary regime change from an open shallow-marine setting to a continental depositional environment concomitant with basinal uplift, the behavior of the burrowing crustaceans testifies to a syn-depositional development of a fault network associated with the fluidization, sand volcanism, and the resilience of the trace-producers in surviving those processes until the sedimentary regime change in the overlying strata. Although the ichno-sedimentological evidence apparently differs from the previous works that proposed a continuous base-level rise from the beginning of deposition of the Khari Nadi Formation up to the middle part of the overlying Chhasra Formation, the paleoseismic activity,its ichnologic signature, and the depositional regime change refer to a higher-resolution(i.e., lower-order)sequence-stratigraphic change causing a short-duration regression within a longer-duration cycle of base-level rise.
基金Department of Science and Technology, Government of India for financial support through grant SR/ S4/ES-709/2014
文摘This paper investigates the provenance of Middle Jurassic to Early Cretaceous sediments in the Kutch Basin, western India, on the basis of mineralogical investigations of sandstones composition (Quartz-Feldspar-Lithic (QFL) fragment), Zircon-Tourmaline-Rutile (ZTR) index, and mineral chemistry of heavy detrital minerals of the framework. The study also examines the compositional variation of the sandstone in relation to the evolution of the Kutch Basin, which originated as a rift basin during the Late Triassic and evolved into a passive margin basin by the end Cretaceous. This study analyzes sandstone samples of Jhumara, Jhuran and Bhuj Formations of Middle Jurassic, Upper Jurassic and Lower Cretaceous, respectively, in the Kutch Mainland. Sandstones record a compositional evolution from arkosic to subarkosic as the feldspar content decreases from 68% in the Jhumara Formation to 27% in the Bhuj Formation with intermediate values in the Jhuran Formation. The QFL modal composition indicates basement uplifted and transitional continental settings at source. Heavy mineral content of these sandstones reveals the occurrence of zircon, tourmaline, rutile, garnet, apatite, monazite and opaque minerals. Sub-rounded to well-rounded zircon grains indicate a polycyclic origin. ZTR indices for samples in Jhumara, Jhuran and Bhuj Formations are 25%, 30% and 50% respectively. Chemistry of opaque minerals reveals the occurrence of detrital varieties such as ilmenite, rutile, hematite/magnetite and pyrite, in a decreasing order of abundances. Chemistry of ilmenites in the Jhumara Formation reveals its derivation from dual felsic igneous and metabasic source, while those in Jhuran and Bhuj Formations indicate a metabasic derivation. Chemistry of garnet reveals predominantly Fe-rich (almandine) variety of metabasic origin. X-ray microscopic study provides the percentage of heavy minerals ranging from 3% to 5.260. QFL detrital modes reflect the evolution of the basin from an active rift to a passive margin basin during the Mesozoic. Integration of results from QFL modal composition of the sandstones, heavy mineral analysis and mineral chemistry, suggests sediment supply from both northern and eastern highlands during the Middle Jurassic. The uplift along the Kutch Mainland Fault in the Early Cretaceous results in curtailment of sediment input from north.
文摘The lignite deposits of Kutch, India are stratigraphically referred to the Naredi Formation and considered to be Early Eocene in age. The biostratigraphy of the older mine at Panandhro and a newly opened mine at Matanomadh has constrained the upper age limit of lignite to the early Bartonian. Its lower age may extend to the late Lutetian. Temporally the formation of lignite corresponds to the warming event of the Middle Eocene and suggests a humid climate at the onset of the warming. The previous palynological studies have already suggested dominance of tropical angiospermic pollen. A diverse assemblage of fossil whales and other vertebrates, many of them supposedly the oldest representatives, were reported from Panandhro mine. These were initially assigned to the Early Eocene and later to the Lute? tian age. The present biostratigraphic study revises their age to the Early Bartonian.
基金University Grants Commission(UGC)India for providing the funds to carry out the research work
文摘The Eocene Epoch passed through multiple hyperthermal events and recorded highest temperatures in the Cenozoic. Very few studies from Eocene palaeotropical sites have recorded changes in shallow marine foraminiferal assemblages. The present study investigates the foraminiferal biofacies of shallow marine successions from a palaeotropical site in western India (Kutch Basin) to understand the palaeoclimate and its impact on the ecology of foraminifera. The sections were biostratigraphically con strained using planktic and larger benthic foraminifera. Four biofacies are recognized by detrended correspondence analysis of the sample-wise distribution of foraminifera. Low diversity and dwarfed foraminifera characterize Bulimina-Chiloguembelino biofacies (SBZ5/6-SBZ10), corresponding to the interval of Paleocene-Eocene Thermal Maxima (PETM) and Eocene Thermal Maxima 2 (ETM 2). Rectilinear benthic foraminifera and biserial and triserial planktic foraminifera, typical of high runoff, upwelling or eutrophic conditions, are dominant taxa in this biofacies. The specialist taxa increased significantly in Asterigerina-Cibicides biofacies, corresponding to SBZ11 (Early Eocene Climatic Optimum, EECO), and the environment became oligotrophic. The Jenkinsina-Brizalina biofacies (E12) is distinguished by foraminiferal assemblage ecologically like that of Bulimina-Chiloguembelina biofacies. It is characterized by high abundance of rectilinear benthic foraminifera and bloom of triserial planktic foraminifera, suggesting eutrophy and high runoff at the initiation of Middle Eocene Climatic Optimum (MECO). The foraminifera were more diverse and abundant in Cibicides-Nonion biofacies. The highly diverse larger benthic foraminiferal assemblage in this biofacies, signify warm and clear-water oligotrophic sea that promoted the development of platform carbonate in Kutch Basin and other basins in western India. The EECO and MECO did not have an adverse impact on shallow marine foraminifera, and particularly the larger benthic foraminifera attained high diversity, high abundance, larger size and wider latitudinal distribution in the middle Eocene.
基金financial support (project No. SR/S4/ESe281/2007)
文摘A combined micropalaeontological and sedimentological investigation of the Early Eocene Naredi Formation (thickness varying between 20 m and 60 m) reveals a complete third-order cycle and six fourth-order sea level cycles. Within the third-order cycle the foraminiferal abundance and diversity gradually increase upwards and reach their maximum values at about 41 m thickness above the base of the formation and subsequently decrease upward and finally give way upward to an unfossiliferous zone at the topmost part. Within a fourth-order cycle foraminiferal abundance and diversity exhibit a similar increasing and decreasing pattern. Bounded between two unconformities the Naredi Formation represents a sequence. A highly fossiliferous Assilinabearing limestone interval represents the maximum flooding zone which separates the transgressive systems tract at the base from the highstand systems tract at the top.
基金Indian Institute of Technology Bombay for the financial support(RI/0220-1000613-001)to SB。
文摘Based on integration of field,petrographic and heavy mineral chemical data,this study highlights the source and tectonic setting of the Mesozoic sandstones of Kutch,Saurashtra,Narmada and Cambay basins at the western margin of India,formed by the progressive splitting of the eastern Gondwanaland.The Kutch Basin is dominated by arkosic sandstone,whereas Saurashtra,Narmada and Cambay basins show the predominance of sub-arkose and sub-litharenite.The modal analyses of framework grains in Kutch sandstones indicate basement uplift and transitional continent settings.In contrast,the sandstones of Saurashtra,Narmada and Cambay basins bear imprints of recycled orogenic and craton interior belts.The presence of abraded and detrital quartz overgrowth and rounded zircons in most sandstones reveal the recycling of sediments in these basins.Tourmaline and rutile mineral compositions constrain the possible lithology of source rocks.The tourmaline mineral chemistry(Ca-Fe_(tot)-Mg plot)suggests the derivation of sediments from various sources,including Li-poor granitoids associated with pegmatites,aplites,Ca-poor metapelites,metapsammites and quartz-tourmaline-rich granitic rocks.The compositions of rutile grains(Cr vs.Nb plot)in sandstones indicate metapelitic sources.The gamut of all mineral chemical data supports the predominance of sediment sources from quartzo-feldspathic rocks with minor inputs from mafic rocks.Based on available paleocurrent data and correlation of source compositions,we infer that the Mesozoic sediments of Kutch,Saurashtra,Narmada and Cambay basins were primarily sourced by various lithologies of the Aravalli Craton.The Narmada Basin possibly received additional sediment input from the Bundelkhand Craton.
基金completed under UGC Minor Research Project Scheme [F.PSW008/11-12(ERO)]
文摘The Kutch Basin of western India is famous for its rich assemblages of the Callovian-Oxfordian ammonites.The family Oppelidae Douvillé is the second most diverse ammonite group after perisphinctids during the Middle-Upper Jurassic.Hecticoceratinae is the most diverse subfamily within Oppelidae and has wide palaeobiogeographic(near cosmopolitan) and temporal distributions(Bathonian-Oxfordian).Some species were well timediagnostic and thus help in interprovincial correlation.The taxonomy of the subfamily Hecticoceratinae of Kutch was in a state of flux until recently.It was not revised since Spath’s(1927-1933) great contribution.Many genera and species were morphogenera or morphospecies and they again suffer from excessive subjective splitting.It was therefore badly needed for a comprehensive taxonomic revision of the subfamily with modern aspects of systematics i.e.,sexual dimorphism and population dynamics.A lithostratigraphic framework has already been well documented in the Kutch Basin of western India.A high resolution biostratigraphy incorporating stage-intrastage fossil assemblages have been used in interbasinal correlation based on the Callovian-Oxfordian hecticoceratins.Near cosmopolitan distribution of many hecticoceratin genera were widely used for biostratigraphic zonation as well as an understanding of the palaeobiogeographic pattern.The phylogeny of the subfamily Hecticoceratinae has been used to construct the cladograms depicting area relationships among different provinces during the Callovian-Oxfordian.