Vindhyan Supergroup Research Articles

Plume and Plate Tectonics Model for Formation of some Proterozoic Basins of India along Contemporary Mobile Belts: Mahakoshal – Bijawar, Vindhyan and Cuddapah Basins

Abstract Proterozoic basins in India mostly belong to two periods, viz. Paleo-Mesoproterozoic (~1.9-1.6 Ga) and Meso-Neoproterozoic (1.1-0.7 Ga) periods that show a long hiatus of ~0.5 Ga between the upper and the lower groups. We have considered Mahakoshal – Bijawar, lower Vindhyan and lower Cuddapah (Cuddapah Supergroup) basins in the former group while the latter consists of upper Vindhyan, and upper Cuddapah (Kurnool) basins. They mostly occur along the contemporary Proterozoic collision zones and are sub parallel to them. The Mahakoshal and Bijawar Supergroups occur along the Satpura Mobile Belt (SMB) and Bundelkhand craton, respectively with Bundelkhand craton as basement and are overlain by the Vindhyan Supergroup of rocks along the SMB. They are almost sub-parallel to the mobile bet, SMB. The Cuddapah Supergroup of Paleoproterozoic period and the Kurnool Group of Neoproterozoic period of Cuddapah basin occur along the Eastern Ghat Mobile Belt (EGMB). Based on the exposed contemporary dyke swarms and sills of mafic and ultramafic rocks that are exposed far apart and their extent sub-surface based on geophysical data, it is suggested that a large plume/superplume existed during Paleoproterozoic period (~1.9 Ga) under the Indian continent. It was responsible for the breakup (rifting) of the then cratons and provided margins for deposition of the former older group of rocks with shelf type of sediments and large scale mafic/ultramafic intrusives. The latter younger groups formed during subsequent convergence in Meso-Neoproterozoic period (~1.1-0.7 Ga) as foreland basins on the stable platform of the rifted cratons. That largely explains their undisturbed nature and absence of magmatic rocks. This convergence also caused large scale deformation as folds and faults in the former group of rocks as they collided with adjoining cratons and formed orogenic belts of that time. In the above examples, the Mahakoshal, Bijawar, lower Vindhyan and lower Cuddapah basins of Paleoproterozoic period formed during the rifting phase due to the plume/superplume while the upper Vindhyan and upper Cuddapah (Kurnool) basins of Neoproterozoic period formed during subsequent convergence as foreland basins. As they formed during different stages of plate tectonics viz. rifting and convergence, they show long hiatus of 0.5-0.6 Ga between the older and the younger groups. The same plume/superplume at 1.9 Ga might also be responsible for the breakup of the contemporary Columbia supercontinent as rocks of similar ages have been reported from other parts of this supercontinent.

Chapter 6 Proterozoic Vindhyan Basin: configuration and evolution

Abstract This chapter attempts an understanding of the Proterozoic Vindhyan Basin history in the broad framework of central India. Although the entire Vindhyan Supergroup is within the scope of this work, particular attention is paid to the little-known northwestern fringe exposures. Distinctive facies assemblages and diverse palaeocurrents in these exposures of the Lower Vindhyan play a pivotal role in the interpretation. Analysis of outcrop and subsurface data that extend under the Gangetic alluvium to the north of the Vindhyan outcrops further supports the hypothesis that an east–west-elongated basement ridge initially separated the master Vindhyan Basin from smaller contemporary basins to the north. Deposition took place in isolated lacustrine and fluvial basins north of the divide and largely in a marine realm south. Dextral shear accompanying rifting generated ridges that criss-crossed the Lower Vindhyan seafloor to the south. The uniform character of the Upper Vindhyan throughout, nevertheless, testifies to later drowning of the divide and unification of all of the basins as a consequence of regional tilt northward. However, the extended Vindhyan Sea was restricted by a second east–west-elongated ridge from merger with the contemporary Proterozoic sea further north, disparate sediments of which have been encountered in a few drill cores only.

Penecontemporaneous Deformational Structures in the Glauconitic Sandstone, Semri Group (Vindhyan Supergroup), Sonbhadra District, Uttar Pradesh, India and their Structural Analysis

The Glauconitic sandstone is well exposed in the Newari area of Sonbhadra district of Uttar Pradesh, India. Conjugate pairs of kink bands are confined within the laminated sandstone and are present half km west of Newari near the confluence of a tributary with the Son river. The conjugate kink bands are plunging at 130 and 360 in SE (S580E) and NE (N560E). This shows that ephemeral compressional stress regime was responsible for the development of conjugate set of kink bands. The stress axis would have been oriented from NE-SW direction. A major fault F1 passes through the glauconitic sandstone in the west of the Newari village. This fault is a reverse fault and strikes at N25ºW - S25ºE. Another fault F2 oblique to F1 passes in the direction N70ºE-S70ºW. In view of the fact that the kink bands are confined within the laminated sandstone, it is inferred that they have been formed as a result of penecontemporaneous deformation and suggest seismic activities that might have occurred around 1080±40 Ma ago as a result of activation of the faults present in the Newari area of the Sonbhadra district, Uttar Pradesh, India those may be companion faults of the Son-Narmada Fault system.

Petrological study of the Kaimur Group sediments, Vindhyan Supergroup, Central India: implications for provenance and tectonics

The Mesoproterozoic Kaimur Group (1.1 Ga) belongs to the upper part of the Vindhyan Supergroup, which overlies the carbonate-rich sequence of the Semri Group (Lower Vindhyan), conformably in the Son Valley, Central India. The Kaimur Group consists predominantly of sandstones. On the basis of the present study they are classified as subarkose, sublitharenite, and quartz arenite in the Quartz (Q)-Feldspar (F)-Rock fragment (R) triangular diagram. The XRD patterns indicate that illite is the most prominent clay mineral. The Kaimur sequence can be divided into the Lower and Upper Kaimur Groups. The modal analyses data and the mineralogical ratios [Quartz/Feldspar (Q/F), Quartz/Lithic fragments (Q/L), Monocrystalline Quartz/Polycrystalline Quartz (Qm/Qp), Quartz/(Feldspar + Rock fragment) (Q/(F + R))] suggest that the Lower Kaimur Group has a fining upward sequence characterized by a decrease in textural and compositional maturity. In contrast, the Upper Kaimur terrigenous rocks have a coarsening upwards sequence with an increase in compositional and textural maturity. Monocrystalline Quartz-Feldspars and granite fragments-Lithics plus quartzose varieties (Qm-F-Lt) and total Quartz-Feldspar-Lithics (Qt-F-L) ternary plots, Polycrystalline Quartz-Non-undulose Quartz-Polycrystalline Quartz-Undulose Quartz ((Qp)-Q(nu)-(Qp)-Q(u)) diamond diagram and the types of lithic fragments suggest that the Lower Kaimur was derived mainly from a craton interior plutonic provenance (uplifted Bundelkhand craton that lies to the north of the basin). The Upper Kaimur terrigenous rocks are dominantly product of a recycled orogen composed of medium-to high-grade metamorphic rocks from the south (Mahakoshal metasediments and Chhotanagpur Gneissic Complex (CGC) of the Central Indian Tectonic Zone (CITZ)). The Polycrystalline Quartz/(Feldspar + Lithics) (Qp/(F + L)) vs. Quartz total/(Feldspar + Lithics) (Qt/(F + L)) ratios represent the deposition of Kaimur sandstones in the warm humid climate.

Microbial mat records in siliciclastic rocks: Examples from Four Indian Proterozoic basins and their modern equivalents in Gulf of Cambay

Microbial mat-related structures (MRS) in siliciclastics have been investigated from four Proterozic formations in India, namely the Marwar Supergroup, the Vindhyan Supergroup, the Chhatisgarh Supergroup and the Khariar Group for their spectral variations, genetic aspects, palaeo–environmental significance and influence on sequence stratigraphic architecture. The maximum diversification of MRS has been experienced in shallow marine coastal Precambrian successions. Observations made from modern environment as well as Precambrian rock records clearly indicates that the features like petee ridges, sand-cracks, gas domes, multi-directed ripples, reticulate surfaces, sieve-like surfaces and setulf are most likely to form in the shallowest part of the marine basins, in upper intertidal to supratidal conditions while wrinkle structures, roll-up structures and patchy ripples had a broader range of palaeogeographic settings from the supratidal to subtidal conditions. Discoidal microbial colony (DMC) represents a special variety of the mat-layer feature in modern environment that may have diverse internal architecture, sometimes falsely resembles Ediacaran medusoids. The uniqueness in sequence stratigraphic architecture of the microbial mat-covered sediment is reflected by the presence of more amalgamated HSTs compare to that of TSTs. The preservation of forced and normal regressive deposits on low-gradient epeiric shelf under low continental freeboard indicates microbial mat-infested sea-floor impedes erosion and concomitant sediment supply may facilitate formation and preservation of regressive packages.

Quantitative environmental impact assessment of the Open cast mining in Sonbhadra district, Uttar Pradesh, India

The district Sonbhadra, previously a part of Mirzapur district in Uttar Pradesh, India, was created as a separate district in 1991.Geologically the area consists of Vindhyan supergroup, Mahakoshal group and Dudhi granitoid complex.The district Sonbhadra has rich mineral resources and their potential. The area is known for production of cement grade Limestone and Dolomite; the other minerals are Clay, Calcite, Silimanite and base metals for more than last three decades. These mining areas show impacts on the environmental status of the district. In the present study, the different mining and environmental parameters have been considered for analysing the environmental impact assessment (EIA). A matrix method has been used to delineate the quantitative EIA in the area. Finally, the resulted assessment impact value index (-2861.76), shows significant impact on environment such as degradation of forest land, air contamination due to mining dust, water quality and related health aspect of the area. Thus, major environmental control measures should be taken for sustainable development of the study area such as improvement of mining equipments, proper dumping of the mining waste and large scale plantation.

Paleomagnetism of Bhander Sediments From Bhopal Inlier, Vindhyan Supergroup

Paleomagnetism of Bhander Sediments From Bhopal Inlier, Vindhyan Supergroup

Study of major and trace elements in groundwater of Birsinghpur Area, Satna District Madhya Pradesh, India

The present paper deals with major and trace elements geochemistry from the groundwater of Birsinghpur area, Satna district, Madhya Pradesh, India. Geologically, the area comprises sandstone and shale formations of the Proterozoic Upper Vindhyan Supergroup. The study reveals that the water is hard to very hard (The classification as hard to very hard is possibly based on incorrect analytical data); the elevated hardness is attributed to the calcareous nature of the aquifer. The concentrations of cations are characterized by Ca >Mg> Na> K. Elevated concentrations of calcium (possibly incorrect analytical data) in some localities are related to the aquifer lithology. Concentrations of magnesium, sodium and potassium are generally within the permissible limits. The concentration of anions are characterized by HCO3 > SO4 > Cl > NO3 >F. Bicarbonate and sulphate concentrations exceed the permissible limits in a few samples; elevated concentrations appear to be related to the aquifer lithology. The fluoride concentration exceeds the desirable limit in some areas; the elevated fluoride values are attributed to the application of chemical fertilizers in agriculture and to the occurrence of fluoride bearing minerals in shale formation. Six trace elements (Fe, Cu, Ni, Pb, Mn, Cd) were also analysed. The iron concentrations ranged from 0.27 to 2.98 mg/L, exceeding the permissible limit in drinking water in 4% of the samples mainly in lateritic aquifers Nickel, and cadmium concentrations are well within the permissible limits. The manganese concentrations ranged from 0.20 to 0.282 mg/L, 30% of the samples exceeding the desirable limit: the elevated manganese concentrations are associated with iron ores (?) as well as lateritic mining. The elevated concentrations of trace elements are combined effects of geogenic sources as well as of mining activities and excessive use of chemical fertilizers. It is recommended to control anthropogenic activities adequately in order to minimise the pollution problems. Key words: Major and trace elements, groundwater, Birsinghpur, Satna, Madhya Pradesh, India.

A detrital zircon U–Pb and Hf isotopic transect across the Son Valley sector of the Vindhyan Basin, India: Implications for basin evolution and paleogeography

The Vindhyan Supergroup, located in central peninsular India, is one of the largest and thickest Precambrian sedimentary successions of the world, outcropping over an area of over 104,000km2. The Vindhyan is the largest of the so-called “Purana” (Hindi for “ancient”) basins in India. The Vindhyan Supergroup is subdivided into the upper Vindhyan and the lower Vindhyan. The age of the Lower Vindhyan is reliably constrained to the Paleo-Mesoproterozoic interval whereas the age of the Upper Vindhyan sedimentary sequence is the subject of considerable controversy. This study provides a very large and integrated detrital zircon database that provides constraints on the age of the Upper Vindhyan sequence and its relationship to the nearby Marwar Supergroup. In some scenarios, these two basins are considered as coeval and Neoproterozoic in age whereas in other models the basins are thought to have evolved during different time intervals. Multiple hypotheses have been proposed concerning basin closure: some argue for an early Neoproterozoic to late Mesoproterozoic closure (~1050Ma) of Upper Vindhyan sedimentation whereas others argue for an Ediacaran–Cambrian age. Our study indicates that although both the Marwar and Vindhyan basins share some similar source regions, their evolutionary histories cannot be reliably linked. We argue that deposition of the Upper Vindhyan sequence closed near the end of the Mesoproterozoic (~1000Ma) whereas deposition in the Marwar basin was confined to the Ediacaran–Cambrian interval (~570–521Ma). This argument is indirectly supported by previously published paleomagnetic data from both the Upper Vindhyan and the Marwar sequences. Although the basins have distinct depositional histories, Hf isotopic data show that the Vindhyan and Marwar shared similar sources, most likely from the Aravalli region. We conclude that the so-called “Purana Basins” of India formed during distinct intervals of Precambrian time (Paleo-Mesoproterozoic, Mesoproterozoic and Ediacaran-Cambrian). The formation of these sedimentary basins may be related to the supercontinents of Columbia (Lower Vindhyan), Rodinia (Upper Vindhyan) and Gondwana (Marwar). The sedimentary sequences in the Marwar Basin may be part of a large trans-Gondwana series of basins that include the ‘nearby’ Salt Range (Pakistan), Huqf Supergroup (Oman) and Molo Group (Madagascar).

Facies-Dependent Occurrence of Shrinkage Cracks in the Glauconitic Sandstone, Semri Group, Vindhyan Supergroup

This paper displays a relationship between shrinkage cracks and lithofacies occurring in the glauconitic sandstone of the Semri Group, Vindhyan Supergroup, and interprets origin of the shrinkage cracks. The glauconitic sandstone member contains cross- and thin- bedded, and laminated sandstone facies. The spindle-shaped cracks are associated with the thin-bedded sandstone and the polygonal cracks are associated with the laminated sandstone. The cross- and thin-bedded sandstones contain well rounded particles that suggest reworking of the sediments by waves and tides in the shoreface zone. The presence of wave-formed ripples and wavy bedding in the laminated sandstones is an indication of the wave-dominated foreshore environment. The occurrence of glauconite suggests that the glauconitic sandstone deposited during transgression as a condense sequence. In view of the fact that the sandstones are devoid of clay content, it is interpreted that both the spindle-shaped cracks and polygonal cracks developed as a result of compaction during the process of synaeresis and the microbial mat added cohesion to the sediments.

Recent advances in the study of the Mesoproterozoic geochronology in the North China Craton

The Mesoproterozoic successions in the North China Craton (NCC) and the Qinling–Qilian–Kunlun Orogens have been revised using the new and highly reliable age data. Many Proterozoic strata in the Qinling–Qilian–Kunlun Orogens, such as the Qinling, Jinshuikou and Beidahe groups that have been ascribed to be Paleoproterozoic are actually of Mesoproterozoic Era. The most significant advances are recent geochronological studies on the Mesoproterozoic stratigraphy and magmatic events in the NCC. The boundary age between the Dahongyu Formation and the overlying Gaoyuzhuang Formation is well constrained to be ∼1600Ma, corresponding to the boundary age between Statherian and Calymmian. The boundary between the Tieling Formation and the overlying Xiamaling Formation is best positioned at ∼1400Ma, which is coeval with the boundary between Calymmian and Ectasian, and is about 400Myrs older than the conventional value of 1000Ma originally defined by the All China Commission of Stratigraphy. Hence the Jixianian System, including the Gaoyuzhuang, Yangzhuang, Wumishan, Hongshuizhuang and Tieling formations in ascending order, is comparable with the Calymmian System in the International Stratigraphic Chart. The lower boundary of the Changchengian System, the first system of the Mesoproterozoic in China Regional Stratigraphic Chart, also needs revision from the conventional 1800Ma to ∼1650Ma well constrained by the zircon U–Pb ages 1673±10Ma (LA-MC-ICP-MS) and 1669±20Ma (SHRIMP) of a granite-porphyry dike that was overlain unconformably by the basal conglomerate of the Changzhougou Formation, the first formation of the Changchengian System. Therefore, the earliest Mesoproterozoic sequence in the NCC represented by the Changchengian and Jixianian Systems in the Yanliao Aulacogen is identical to that of the Vindhyan Supergroup in Central Indian and the Riphean Series in Russia. On the other hand, a series of 1.8–1.6Ga anorogenic magmatic records were well-preserved around the NCC, which marked the initial rifting of the Columbia Supercontinent in the NCC. The magmatic events can thus be subdivided into three phases with peaks at ca 1.77Ga, ca 1.70Ga and ca 1.63Ga, respectively. In addition to 1.8–1.6Ga magmatic events, some minor volcanic eruptions at ca 1.56Ga and 1.44Ga, and wide-spread bi-modal magmatic intrusions at 1.35–1.32Ga have been recognized in the northern NCC, marking the continued rifting of the Columbia Supercontinent since ∼1.8Ga.

Paleomagnetism of Bhander Sediments from Bhopal Inlier, Vindhyan Supergroup

Abstract: Paleomagnetic investigations have been carried out on poorly determined radiometric age controls of Bhander sandstones within the vicinity of Bhopal Inlier of the Upper Vindhyan Supergroup. Available ages assigned to the Upper Vindhyan sequence range from Cambrian to the Mesoproterozoic and are derived from a variety of sources and methods. Paleomagnetic data generated from the Bhander Group of Bhopal Inlier yielded a mean declination of 357° and mean inclination of 58° (k=17.69, α95 = 16.38) with a Virtual Geomagnetic Pole (VGP) at 74° N, 69.0° E. This pole position is falling close to the Malani Igneous Suite (MIS) mean palaeomagnetic pole of 67.8° N and 72.5° E (A95=8.8°) by Gregory et al. (2009). The results obtained from this study and previous work on the 1073 Ma Majhgawan kimberlite, as well as detrital zircon geochronology of the Upper Bhander sandstone suggest that the Upper Vindhyan sequence may be older than is commonly thought earlier.

Groundwater quality and pollution potential studies around Baikunthpur Area, Rewa District, Madhya Pradesh, India

Hydrogeochemical investigations were carried out in Baikunthpur Area Rewa District Madhya Pradesh. In the study area, Rewa shale and Rewa sandstone of Vindhyan Supergroup are exposed. The groundwater samples were collected from 30 locations during post monsoon season of 2010 and analysed for major cations and anions. The study reveals that groundwater of the area is generally moderately hard to very hard, normal chloride, normal to higher sulphate and normal bicarbonate type. As per Chadha's scheme, the main hydrochemical facies are Ca-Mg-HCO3 and Ca-Mg-SO4-Cl types. The concentration of sulphate was higher due to gypsum bonds associated with Shale formation. Nearly on third of the samples have nitrate concentration beyond the permissible limit of 45 mg/L. In few samples concentration of fluoride exceeds the permissible limit of 1.5 mg/L due to the presence of fluoride bearing minerals associated with aquifers. Most of the physico-chemical parameters were within permissible limits of WHO and ISI for drinking purpose. For computation of Pollution potential, DRASTIC modeling has been adopted. The DRASTIC Index ranges from 124 to 203 suggest intermediate to high pollution susceptibility. In the high pollution susceptibility zone, water quality monitoring programme is suggested. Key words: Groundwater quality, DRASTIC INDEX, Baikunthpur, Rewa Madhya Pradesh.

Geological Milieu of the Bijawar Basin based on interpretation of geophysical data; Central India

SummaryIntegrated interpretation through physical properties of rocks provides better approach towards understanding of geological set-up. High resolution heliborne time domain electromagnetic, magnetic and radiometric dataset acquired over Palaeo Proterozoic Bijawar Basin has been interpreted to enhance the geological understanding. The process involved knowledge driven analysis through correlation with geological units that outcrop and data driven analysis for extrapolation of information. Radiometric data in conjunction with spectral remote sensing data was used for generation of surface geology map. Spatial distribution of rock magnetization properties defines the subsurface extension of litho-structural elements and magnetic basement configuration. Electromagnetic data aided demarcation of resistive basement topography and various conductive layers. Radio-elemental distribution refines the unconformable contact shared by Bijawar Group with overlying and underlying group of rocks and also outlined the formational boundaries of arenaceous-argillaceouscarbonate-volcano-sedimentary sequence. Subsurface extent of basic volcanics is much more than its surface manifestation and appears to extend well below the overlying Vindhyan Supergroup of rocks. The unconformable contact of Bijawar Group with underlying basement and overlying Vindhyan Supergroup is marked by distinct change in conductivity parameter and has been outlined in depth to resistive basement topography. Fault system and its manifestation over different litho-units indicate multiple tectonic episodes.

Morphodiversity, complexity and macroevolution: revealed by the megascopic life of the Palaeo-Neoproterozoic Vindhyan Supergroup, India

Abstract Evidence of past life found in the Vindhyan Supergroup exhibits extensive diversity and taxonomically unresolved morphological complexities indicating varied biological affinities, advanced life and macroevolutionary dynamics of evolving clades. The megascopic life of the supergroup documents possibly two macroevolutionary modes, demarcated as: (i) the Palaeo-Mesoproterozoic transitional period, which is represented by the fossil assemblages of the Semri and Rewa groups, and exhibits the domination of a diversified prokaryotic cyanobacterial community and moderately diversified megascopic life; (ii) the Neoproterozoic (Bhander groups, Uppermost Vindhyans), represented by the diversified and morphologically complex megascopic eukaryotes, and the emergence of multicellularity among plant and animal clades, viz. structures resembling bryophytes, sporophyte and Ediacara fauna. The overall Vindhyan fossils exhibit episodes of adaptive innovations and the emergence of complex morphologies in separate lineages of evolutionary history, resulting in extensive morphodiversity. The present assemblage can be represented by that of prokaryotes, eukaryotes, possibly a symbiotic association, a Jacutianema -like Neoproterozoic form, specimens possibly of vaucheriacean affinity, mesoscopic intermediate forms inferred as transitional forms of microscopic–megascopic evolution, discs with process-like structures, the emergence of animal life (Ediacaran fauna) and a number of other complex morphologies that have no parallels in time and space. Traditionally and conventionally, the age of the Vindhyan Supergroup is considered to be that of Palaeoproterozoic–Neoproterozoic.

Provenance, tectonic setting and source-area weathering of Mesoproterozoic Kaimur Group, Vindhyan Supergroup, Central India

The siliciclastic of the Upper Kaimur Group of the Vindhyan Supergroup in Central India have been geochemically studied in order to understand their provenance, paleoweathering conditions and tectonic conditions. A-CN-K (Al2O3-CaO-K2O) ternary diagram and chemical index of alteration (CIA) values suggest that the granitic source rocks underwent moderate to high degree of chemical weathering under moderate weathering conditions for an extended period of time, or under humid weathering for shorter periods of time. Similar CIA values in all textural types indicate that recycling processes homogenized the shale and sandstone compositions. Various geochemical discriminants and elemental ratios such as K2O/Na2O, Al2O3/TiO2, SiO2/MgO, La/Sc, Th/Sc, Zr/Sc, Th/Cr, [Gd/ Yb]N and pronounced negative Eu anomalies indicate the rocks to be the product of post-Archean, Proterozoic granitic source, with minor granodioritic input and substantial sediment recycling. The geochemical signatures corroborate their deposition in a subsiding foreland basin over Bundelkhand craton with provenance from south, south westerly Chotanagpur granite gneiss.

Ediacaran Discs from the Jodhpur Sandstone, Marwar Supergroup, India: A Biological Diversification or Taphonomic Interplay?

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.

Uranium mineralisation associated with felsic volcanism at Mohar, Shivpuri district, Madhya Pradesh

Several small lensoidal bodies of felsic volcanics are exposed in a curvilinear pattern within the brecciated granitoids of Bundelkhand Gneissic Complex (BGC) at Mohar. Sub-surface data reveals extensive presence of these felsic volcanics below the sediment of Vindhyan Supergroup. It occurs like a sheet with thickness varying from 12 m to 134 m. Its lateral extent has been traced upto 4.8 km. Multiple flows of felsic magma are identified based on colour, granularity, cross cutting relations and cyclic distribution of multiple vesicular bands along the entire thickness of felsic magma. The felsic rock contains upto 13.21% K2O. Chemical composition of these felsic volcanics varies across the column. Petrographically and chemically all these felsic volcanics are identified as rhyolite or rhyolite tuff.

Discovery of soft bodied metazoans and microphytofossils from the Mesoproterozoic sediments of Vindhyan Supergroup, India

An assemblage of microbial remains consisting two types of preservations are being recorded for the first time from the phosphoritic chert intercalated in Tirohan Limestone (Rohtas Limestone Formation) of Semri Group, Vindhyan Supergroup, exposed in Chitrakoot, Madhya Pradesh. The uniquely preserved, cryptic forms are multicellular, bilaterally symmetrical, monoecious, cylindrical elongated coiled body with clitellum and ornamented structures (setae). This assemblage shows possible biomineralized novel post embryonic developmental stages of the juvenile and young forms of the annelids. The dark brown organic-walled microfossils (prokaryote and protists) are sparse, cellularly preserved, distorted, small sized, simple sphaeromorphs. The present explored preliminary results are based on the Mesoproterozoic stray fossils of two bioentities in limited material, and are the authentic key events to consider remarkable potential value in understanding the evolution and divergence of the metazoan in India along with status of Indian subcontinents (geographic position) in geological past of world history. It is a team effort of the earth scientists (geologists, botanist, and zoologist) based on the extinct and extant annelids in present brief communication. Key words: Soft bodied metazoan, annelid, clitellum, Mesoproterozoic, Tirohan limestone, Vindhyan.

Problematic fossils from the Palaeo-Neoproterozoic Vindhyan Supergroup, India

Fossils of the Vindhyan Supergroup exhibit extensive diversity and variable biologic affinities represented by: bacteria, cyanobacteria, algae, fungi, acritarchs, metaphytes and metazoans (including members of the Ediacaran Fauna) and ranging from less than a micron to almost a metre in size. Besides identified fossils, a number of bizarre morphologies (due to deviation of morphology from conventional structures), present in various stratigraphic horizons, have been observed. It is very difficult to identify and decide their biologic affinities. In thin sections of Lower Vindhyan cherts, microfossils resembling lichen-like or fungal forms in which a sac encompassing a coiled filament may possibly indicate a symbiotic relationship, a Volvox colony-like structure and a vase-shaped body without an opening are unique. Among the carbonaceous fossils, very unusual and interesting fossil is a transparent disc comprising numerous appendages of an unidentified mesoscopic insect-like organism. Megascopic branching and associated Grypania-like structure is another form preserved as impression on micritic limestone. Petrographic thin sections of chert belonging to the Sirbu Shale Formation, exhibit presence of microscopic bizarre forms. The assemblage includes acritarchs and acanthomorphs of variable morphology and a dividing cell-like structure interpreted to be of rhodophycean affinity or a cleaving embryo of an animal affinity. Other peculiar morphologies among the carbonaceous fossils are: branched filaments that have attached sporangia-like vesicles, Chuaria-like body comprising cluster of very small-sized spheroids resemble scale-like structure, a chrysophycean alga or a multicellular tissue of a metaphyte. Another carbonaceous fossil represents a possible metazoan exhibiting an elongate body and a mid-gut-like structure or a Vaucheriacean alga. Although the biologic affinities of these bizarre forms can be a matter of debate, their biogenic nature is almost undoubted. The presence of such forms in the Vindhyans indicates advancement in morphology and a gradual evolution of life during the Palaeoproterozoic–Neoproterozoic period. In addition, presence of Ediacaran fossils in Bhander Group and large-sized acritarchs especially Trachyhystrichosphaera sp. in petrographic thin section of chert from the Sirbu Shale Formation, Bhander Group, Upper Vindhyans, suggests Ediacaran age as an upper age limit of the Vindhyan Supergroup.