Rajmahal Hills Research Articles

Bentonite deposits intercalated with the Rajmahal volcanic rocks of eastern India

Bentonite is distributed widely in the Rajmahal Hills of eastern India, usually in association with volcaniclastic deposits. Although bentonite occurs between the successive flow units, it always forms pockets, rather than a continuous bed. The occurrence of bentonite in the lower part of the Rajmahal lava pile (characterised by fossiliferous sedimentary interbeds) is consistent with its formation in a subaerial or lacustrine environment. The bentonite appears to have formed as a result of alteration of basaltic pyroclastic rocks. The Rajmahal bentonite is of non-swelling type. The exchangeable base is Ca, which is substituted by Na. Petrographic studies reveal that montmorillonite is the predominant mineral in the bentonite, together with minor kaolinite and illite. Cristobalite constitutes the main non-clay mineral. Nontronite, saponite, dickite, nacrite, anauxite and beidellite have also been identified. The bentonite is completely devoid of attapulgite, dolomite and organic material. Rajmahal bentonite with high Fe 2 O 3 CaO ratio is gritty in texture and low plasticity, whereas bentonite with high Al 2 O 3 Fe 2 O 3 and CaO Al 2 O 3 and low Fe 2 O 3 CaO ratios is grit-free and of high plasticity. The latter material is superior in quality when compared to the former. Based on surface and drill core data, a total economic reserve of ∼177,000 t of bentonite is estimated in the Rajmahal Hills. Of this total, 82,300 t is Grade I quality and 94,400 t is Grade II quality.

A palaeomagnetic and rock magnetic study of the northern Rajmahal Volcanics, Bihar, India

A new palaeomagnetic study of mid Cretaceous lavas from 23 localities in the northern part of the Rajmahal Hills gives a mean virtual geomagnetic pole at 10.4°N, 296.6°E, confirming the results of earlier workers. Stepwise thermal and alternating field demagnetisation indicates that 21 out of 23 sites are normally magnetised, whereas two sites in the northwest of the area have recorded two different transitional directions. We have measured the strong-field thermomagnetic behaviour, DC and AC hysteresis parameters, and the variation at low temperature of low-field susceptibility of these and other samples from the Rajmahal Volcanics. These rock magnetic studies reveal that the basaltic lavas contain titanomagnetites which have hardly been oxidised at high temperature, but have undergone low temperature oxidation. The reddened lavas of Gandeswari Hill, on the other hand, show evidence of extensive high temperature deuteric oxidation of titanomagnetite.

Petrographic characterization and evolution of the Permian coal deposits of the Rajmahal basin, Bihar, India

Lower Gondwana rocks are exposed as narrow bands and discontinuous patches along the western edges of the Rajmahal Hills covering a large area of the Bengal Basin, North Bengal and Pumea. Two coalfields — Hura and Chuperbhita — have productive coal mines. Pillar coal samples from the working coal seams of Hura and Chuperbhita coalfields were collected and subjected to a detailed petrographic and geochemical study using refined procedures on a large number of samples. The results of the micropetrographic study reveal that the Rajmahal coals are rich in liptinite and inertinite contents. The fluorescence microscopy indicates that a major part, identified as argillaceous mineral matter under white incident light, is composed of liptinite macerals such as bituminite fluorinite and exsudatinite. The volatile matter and reflectance suggest these coals are subbituminous to high volatile bituminous B/C in rank. The quantitative relationships among maceral and microlithotype suggest that these coals were deposited in limnic to limno-telmatic conditions under very wet conditions that resulted from undisturbed peat that developed in situ along with subaquatic (limnic) sedimentation in swampy lakes. Further, the GI and TPI values indicate that the Hura coals were formed under oxic moor conditions with sudden episodes of flooding, while the Chuperbhita coals have originated in wet moors with intermittent moderate to high flooding. In addition, G.I. values suggest the formation of these coals in an upper delta/alluvial valley with braided plains.

Early Permian plant fossils from the Barakar formation of Auranga coalfield, Bihar

Plant fossil assemblage of Auranga Coalfield recovered from the Fireclay of Barakar Formation being mined in Murup and Datum areas of Palamau district, Bihar is represented by various species of the genera Neomariopteris, Gangamopteris, Glossopteris, Saportaeae, Rhipidopsis and Ginkgoites. Glossopterid-ginkgopsid association is the characteristic feature of this flora. Which is closely comparable with the Glossopterid-ginkgopsid association of the Hura Coalfield, Rajmahal Hills, Bihar.

Osmundaceous fronds in Lower Cretaceous beds at Chunakhal, Rajmahal Hills, Bihar, India

Osmundaceous remains from the intertrappean beds of the Rajmahal Formation at Chunakhal, Rajmahal Hills, Bihar, are referred to Todites Seward, Osmundopsis Harris, Phyllopteroides Medwell and Cacumen Cantrill & Webb. Osmundopsis, Cacumen and Phyllopteroides are recorded for the first time from India. Thinnfeldia chunakhalensis Sah & Sukh-Dev is transferred to Phyllopteroides laevis Cantrill & Webb. This is a significant Neocomian index species in eastern Australia and suggests a Neocomian age for this intertrappean bed at Chunakhal.

Palynology of the Mesozoic sediments exposed near Ellichpur, Maharashtra

The paper records palynofossils from the dark grey shales/clays (inliers) exposed at Belkher Village, north of Ellichpur town in Maharashtra. The assemblage contains 41 species assigned to 22 genera and is characterised by pteridophytic and bryophytic components, viz., Callispora potoniei, Contignisporites glebulentus, Murospora, Triporoletes reticulatus, Coptospora kutchensis, Cooksonites cf. C. rajmahalensis, etc. The prominence of Callialasporites followed by Podocarpidites, Alisporites and Araucariacites is noteworthy. The assemblage is comparable to the palynozones-D of Rajmahal Hills, the assemblage recovered from Sivaganga area of Cauvery Basin, and Dharesi nala section of Bhuj Formation, Kutch Basin, which are assigned a Neocomian-Aptian age. The presence of spore-pollen, algal or fungal entities suggests freshwater conditions during deposition.

Palynostratigraphic correlation of lower Gondwana sediments in the Chuparbhita and Hura Basins, Rajmahal Hills, Eastern India

Correlation of palynostratigraphic zones of the adjacent Chuparbhita and Hura Basins reveals similar depositional environments. Distinct changes in climatic and ecological phases are key features of the depositional environment in the two adjacent basins. Three climatic phases recognised in the Chuparbhita Basin are (I) monosaccate Plicatipollenites-Parasaccites, (II) nonstriate disaccate Scheuringipollenites and (III) striate disaccate Striatopodocarpites-Striatites, while a single climatic phase of nonstriate disaccate Scheuringipollenites is recognized in the Hura Basin. Climatic phases are suggested from the relative abudance of the different saccate types viz., monosaccates, nonstriate disaccates and striate disaccates as cool, temperate and warm humid conditions respectively. Ten ecological phases have been identified in the Chuparbhita Basin within the three climatic phases and seven in the single climatic phase of the Hura Basin. Scheuringipollenites is the most extensive climatic phase of deposition in both the basins in which identical ecological phases are recognised at some corresponding horizons. Two marker horizons are recognised within the Scheuringipollenites climatic phase in the Chuparbhita and one in the Hura Basin. The marker horizons contain a distinctive assemblage of trilete and monolete taxa in addition to diverse acritarchs and prasinophytes viz., Peltacystia, Circulisporites, Tetraporina, Kagulubeites, Haplocystia and Maculatasporites. The Marker horizon I of PN H-5 of Hura is distinguished by the occurrence of diverse acritarch suites along with the key trilete genus Lalmatiasporites. PN C-9, with the key trilete genus Ghoshiatriletes and diverse acritarch suites identified as Marker horizon II, has not been encountered in the Hura Basin. The marker horizons may be considered as representing phases of brackish water transgression in the essentially continental sequence of deposition. Palynological evidence indicates an Early Permian age for both basins.

Pachwarophyllum santhalensis gen. et sp. nov. from the lower Gondwana of Bihar, India

Pachwarophyllum santhalensis gen. et sp. nov. is described from coal bearing beds of the Barakar Formation in the Pachwara Coalfield, Rajmahal Hills, India. The new genus is characterised by flabellate non-petiolate leaves with an obcordate apex and repeatedly forked non-anastomosing veins.

A new interpretation on the structure of Sahnia nipaniensis Mittre from the Rajmahal Hills

Description of five, serial, longitudinal sections cut through a male flower Sahnia nipaniensis of the Pentoxyleae, collected from the Rajmahal Hills, Bihar has been given. The flower was borne terminally on a dwarf shoot. Sporophylls are spirally arranged around a cylindrical receptacle. Sporangia are produced in opposite rows. Restoration of the flower is also given.

Palynostratigraphy and Environment of deposition in the Lower Gondwana sediments of Chuparbhita Coalfields, Rajmahal hills

Palynostratigraphy and Environment of deposition in the Lower Gondwana sediments of Chuparbhita Coalfields, Rajmahal hills

Study of amino acids in petrified plants from the Rajmahal Hills

Chemistry of fossil plants collected from the Rajmahal Hills, Bihar (India) is studied. Amino acids extracted from the petrified woods, rachides and fructifications are identified with the help of paper chromatography. Implications of the chemical study of fossil plants in relation to taxonomy and evolution are discussed.

Sphenopsids from the Barakar Formation of Hura Tract, Rajmahal Hills, Bihar

Sphenopsids from Lalmatia Incline (Lalmatia Top Seam, Barakar Formation), Rajmahal Hills, Bihar, belong to Sphenophyllum gondwanensis sp. nov., Lelstotheca sp. and equisetalean axes. Previous records of northern species of Sphenophyllum in Lower Gondwana sediments are reviewed and reassessed.

Further observations on Cycadinorachis omegoides Sharma from the Rajmahal Formation, India

A petrified Cycadinorachis omegoides is reported from Sonajori in the Rajmahal Hills, Bihar. The number of bundles in the omega gradually reduces while the distinction of centripetal and centrifugal xylems increases towards the apex of the rachis (leaf). The ground tissue possesses mucilage ducts. The lamina has parallel veins and a more or less homogeneous mesophyll. Tracheids possess scalariform and contiguous bordered pits. The relationship of Cycadinorachis with allied extinct and extant plants is discussed.

Lelstotheca Maheshwari, from the Barakar Formation of Raniganj Coalfield

The genus Lelstotheca, known so far only from the Barakar Formation of Rajmahal Hills, Bihar is reported from the Barakar Formation of Raniganj Coalfield, West Bengal. The genus is represented by two species, viz., L. robusta (Feistmantel) Maheshwari and L. striata sp. nov. The new species is characterized by the presence of interconnecting striations running parallel to the median vein of the leaves. The taxonomic position of the genus and its records elsewhere are also discussed.

Gravity field and structures of the Rajmahal Hills: Example of the Paleo-Mesozoic continental margin in eastern India

A narrow strip of Gondwana basins separates the Rajmahal traps from the peninsular shield in eastern India. This part of the shield margin is associated with a conspicuous gravity high of 100 km wavelength and 48 mGal amplitude over an area of 25,000 km 2. Second order residual anomalies due to Gondwana sediments and traps are superposed on this wider gravity high. Gravity interpretation, partly constrained by seismic data, suggests that the wider high is caused by a denser metamorphic layer (amphibolite and granulite) up to 3.5 km thick. The metamorphic layer also extends below the eastern Rajmahal hills where the Gondwanas, traps and younger sediments have covered it. The Gondwanas are downfaulted against the shield edge and are preserved over an irregular basin floor whose deepest part underlies the eastern flank of the Rajmahal hills adjacent to the Bengal basin. It is inferred that the Gondwanas were deposited over a rifted and highly faulted shield margin that was intruded by the Rajmahal traps nearly 100 m.y. ago. High-grade metamorphism along the shield edge presumably preceded the continental rifting, perhaps occurring in the Precambrian as a part of the Eastern Ghats orogeny, along the east coast of India.

A reassessment of Taeniopteris daintreei from the Victorian Early Cretaceous: a member of the Pentoxylales and a significant Gondwanaland plant

Plant remains from the Early Cretaceous of Victoria are described. These are leaves referred to Taeniopteris daintreei, female fructifications referred to Carnoconites cranwellii and microsporangiate structures herein described as Sahnia laxiphora sp. nov. These are considered to belong to the extinct group, the Pentoxylales, originally described from localities variously dated as Jurassic or Early Cretaceous in the Rajmahal Hills of India. It is suggested that the Pentoxylales, long regarded as an obscure group, are in fact a major and important part of the mid Mesozoic Gondwana flora in Victoria.

Rajmahalispora, A new Cingulate spore genus from the Triassic of Rajmahal Basin, India

A new trilete-bearing cingulate miospore genus with rugulate ornamentation from the Triassic sediments of Rajmahal Hills, India is described.

Morphotaxonomy of Heterophyllous Lycopsid shoot from the Rajmahal Hills, India

Morphology of the herbaceous lycopsid shoot occurring commonly in several localities of Rajmahal Hills, India has been studied. In earlier records, the fossil was figured as Araucarites(?) gracilis. Later, it was described as Cheirolepis gracilis and thereafter as Lycopodites gracilis. However, the present study reveals that the form of the shoot is precisely like that of a creeping Selaginella having two dorsal and two ventral ranks of microphyllous leaves. Therefore, it is being described here as Selaginellites gracilis.

Studies on the transfusion cells in Petrified leaves of Ptilophyllum and Nipaniophyllum from the Rajmahal Hills, India

Transfusion cells have been recorded in the leaves of Ptilophyllum and Nipaniophyllum. In the former, the transfusion cells are found in close association with the vascular elements, while in the latter they surround the bundle sheath. The relationship is discussed with the plants possessing the allied types of arrangement of transfusion cells.

Cycadophytic leaves from Jurassic - Lower Cretaceous rocks of India

Under Cycadophytic leaves, various Indian species of Taeniopteris Brongniart, Morrisia Bose, Cycadites Brongniart, Anomozamites Schimper, and Pterophyllum Brongniart have been described here. The study is based on specimens described or figured since 1850 and a large number of specimens collected during the last two decades from the Jurassic-Lower Cretaceous rocks of India.
 It has been observed that the genera mentioned above are most abundant in some of the localities of the Rajmahal Hills. They are completely missing in most of the undoubted Lower Cretaceous beds of India. So far only a single species, viz., Pterophyllum princeps Oldham & Morris is known from the Lower Cretaceous beds of Than, Gujarat.