Paleomires of Eocene lignites of Bhavnagar,Saurashtra basin (Gujarat), western India: Petrographic implications

The Tertiary basins of Gujarat have always been a potential target for their hydrocarbon resources. The lignite resources of the region have also been an important field of research. The present paper presents the results of the petrological study carried out on the lignites of the Saurashtra basin. For this purpose samples were collected from lower and upper lignite seams from the Surkha lignite mine of Bhavnagar, Saurashtra. These samples were subjected to detailed petrographic analysis (both maceral and microlithotype). The study reveals that these lignites are dominantly composed of huminite group macerals while liptinite and inertinite group macerals occur in subordinate amounts. These lignites have attained a thermal maturity up to 0.28-0.30 percent vitrinite reflectance (VRr) which classifies them as ‘low rank C’ coals. Moreover, Bhavnagar lower lignite seam shows relatively less gelification as compared to the upper seam which suffered relatively more biochemical degradation. These lignites are characterized by high gelification index (GI) and low tissue preservation index (TPI).With the help of petrography based facies models an attempt has been made to reconstruct the environment of the paleomire of these lignites.     

K-Ar age of Ukra glauconites from the Kutch Basin, India

The present paper reports the K-Ar ages determined on glauconitic samples collected from the Ukra Member of the Mesozoic Bhuj Formation in two different sections, one located on the Ghuneri-Ghaduli road near Katesar Mahadeo temple and the other at the base of the Ukra hill in the northwestern part of the Kutch Mainland area. Three glauconite samples viz., Ukra_KT-1, Ukra_KT-4 and Ukra_UH-3 have yielded K-Ar ages of 107.9 ± 3.4 Ma, 105.5 ± 3.3 Ma and 103.5 ± 3.4 Ma, respectively. The sample Ukra_KT-l treated with 0.5N HC1 and analysed in duplicate has yielded a mean age of 104 ± 2.3 Ma while the sample Ukra_KT-4 treated with 0.1N HCl has given an age of 106.5 ± 3.3 Ma. The ages of the treated and untreated glauconites are indistinguishable within 2σ uncertainty with a mean of 105.2 ± 1.3 Ma, which has been interpreted as the depositional age of the Ukra Member of the Mesozoic Bhuj Formation. The study has further indicated that mild acid treatment (up to 0.5N HCl) does not lead to any loss of radiogenic argon in the glauconites and can be helpful in purification of the samples.     

Palynology and depositional facet of lower Permian (Artinskian) sediments from New Majri opencast mine,Wardha basin,India

Coal samples and the associated sediments from New Majri open cast mine have been analysed palynologically with the following objectives: to date the sediments on the basis of the palyno-assemblage recognised; to carry out an inter-basinal, intra-basinal and Gondwana wide correlation; to interpret the palaeoenvironment and depositional facet of the coal field on the basis of dispersed organic matter analysis and sedimentary facies analysis. Based on the qualitative and quantitative analysis of the spore and pollen content one palyno-assemblage-Scheuringipollenites and Faunipollenites has been recognised which is typical of lower Barakar Formation. This has been correlated with known palyno-assemblages from Wardha basin and other basins in India, while with the Gondwana continents the assemblage has been broadly correlated with early Permian Australian, African, South America palynofloras as well as early Permian palynoflora of Antarctica. Consequently, a tentative late Early Permian, Artinskian age is proposed for the sediments from New Majri open cast mine. Palynological studies also revealed that the peat forming vegetation was mainly composed of gymnosperms represented by glossopterids (Scheuringipollenites, Ibisporites, Platysaccus, Cuneatisporites, Primuspollenites and Sahnites), conifers (Faunipollenites, Striatites, Striatopodocarpites, Verticipollenites, Distriatites) and cordaites (Parasaccites, Plicatipollenites, Crucisaccites, Divarisaccus, Densipollenites). Spores were represented mainly by filicopsids (Horriditriletes, Brevitriletes, Callumispora) and sphenopsids (Latosporites). The relative abundance of structured organic matter implies the existence of a fairly dense cover of vegetation in the hinterland. Anaerobic, reducing, water logged peat-forming conditions have been inferred by the presence of biodegraded organic matter and amorphous organic matter. The charcoal fragments recovered from the present study area reflects a possible wildfire in the accumulated swamps or a wildfire in the hinterland after which the sediments were flushed by fluvial systems into the swamps. The coalfield exhibits horizontal bedding pattern which may be due to deposition by suspension settling or horizontal accretion. Further the alternating high and low energy regime is noticed in the sandstone-shale intercalated beds overlying the coarse grained yellow sandstone which forms the roof of the coal seam. Comprehensively the sediments are deposited as overbank / levee deposits.     

Eocene spheroidal dolomite from the western Sirte Basin, Libya

Scanning electron micrographs of crypto-crystalline (< 4 μm) dolomites found in cores taken from the lower Eocene Facha Member reservoir of the Zella and Aswad fields in Libya show that they consist of tiny globular bodies mixed with anhedral crystals, producing a chalky texture. The sedimentary sequence indicates deposition in upper intertidal/supratidal arid environments and in saline lagoons. The crypto-crystalline dolomite is facies-controlled and probably formed as a primary precipitate, similar to those reported from present-day subaqueous environments in the Coorong of South Australia and Holocene supratidal crusts off Florida. Such chalky-textured dolomites could form local fluid-migration barriers within hydrocarbon reservoirs.     

Palynology,sedimentology and palaeoecology of the late Holocene Dead Sea

Palynological and sedimentological studies were performed at two Holocene profiles in erosion gullies (Ze’elim and Ein Feshkha) which dissect the retreating western shore of the Dead Sea. The aim of the project was to analyse possible links between climate, lithology, and vegetation development. The section in Ze’elim shows both lacustrine and fluvial sediments, whereas sedimentation at Ein Feshkha is predominantly lacustrine. The Ze’elim profile, previously used for paleo-lake reconstruction provides an opportunity to compare climate triggered lake levels as paleo-hydrological indicators and vegetation history by use of palynology. The vegetation development in Ze’elim and Ein Feshkha is influenced by both climate and human impact. The pollen record of Ze’elim begins in the Pottery Neolithic, the section of Ein Feshkha in the Late Bronze Age, both records end in the Middle Ages. The Ze’elim section is characterized by sedimentary hiati between the beginning of the Chalcolithic Period until the Middle Bronze Age and within the Late Bronze Age. Settlement periods during the Middle Bronze Age, Iron Age and Hellenistic–Roman–Byzantine Period are indicated by high values of anthropogenic indicators and/or Mediterranean trees. Collapses of agriculture, which can be related to climate effects, are evident during the Late Bronze Age, during the Iron Age and at the end of the Byzantine Period when the lake level curve indicates arid conditions. A comparison of the two pollen records, from different environments, illustrates a more prominent influence of Mediterranean vegetation and cultivated plants in the pollen diagram of Ein Feshkha. The southern Dead Sea region (at the desert fringe) is more vulnerable to regional climate change.     

Middle Eocene ostracoda from the Tadkeshwar lignite mine, Cambay Basin, Gujarat

Previous work on the fauna and flora of the Cambay shale underlying as well as inter-bedded within the lignite seams of Vastan lignite mine, Gujarat allows the shale to be assigned a Lower Eocene age. However, there is no record of occurrence of any fossil from the sedimentary beds succeeding the shale-lignite sequence that might fix upper age limit of the Cambay shale. We record a characteristic Middle Eocene ostracod assemblage from the Nummulitic marl/limestone, immediately overlying the shale-lignite sequence from the Tadkeshwar lignite mine close to the Vastan lignite mine. The assemblage comprises 22 species, many of which widely occur in the Middle Eocene beds of Kachchh, Rajasthan and adjacent areas of Pakistan.     

A reconnaissance of the Recent sediments of the Ranns of Kutch, India

The Ranns of Kutch are flat salt-covered desert areas (sabkhas) which are just above the normal tidal range and may be regarded as supratidal flats. They are flooded annually by the storm tides of the Southwest Monsoon. As the waters recede and evaporate they leave behind a crust of halite, and gypsum crystals grow within the clays and sands. The increase in salinity of the interstitial waters as they are traced inland is reflected in the higher boron content of the clays. The Mg²⁺/Ca²⁺ ratio of these waters increases from 3 on the coast, to 240 in the evaporite environment of the shoreline of Pachham Island. Much of the sediment of the Ranns was probably once derived from the Indus and Nara rivers which used to flow into the western end of the Great Rann. Clay is now probably carried in by the monsoon storm tides after being transported along shore from the Indus, and also from the rivers of Kutch and Kathiawar. Coarser siliciclastic sediment is carried into the eastern inland portion of the area by the Luni and other intermittently flowing rivers and streams. Some sand and silt is blown into the Ranns from the surrounding hilly areas. Foraminifera are found concentrated in the sandier fractions of the sediments, having been transported there primarily by tidal currents and also by the wind. One species of Ammonia is almost the only fauna found in the sediments of the very saline environment around Pachham Island.     

Foraminifera from jurassic sediments of Keera Dome, Kutch

A foraminiferal assemblage comprising 30 species dominated by the family Vaginulinidae is recovered from the Chari Formation exposed at Keera Dome, Kutch. The paper presents a systematic account of eight species, reported for the first time form the Indian region. Preliminary interpretations regarding age and palaeoenvironment are drawn on the basis of the recovered foraminiferal assemblage. The assemblage supports a Callovian to Oxfordian age for the studied sequence. A near shore, open marine environment ranging from mid to outer shelf is interpreted on the basis of the foraminiferal assemblage.     

Facies analysis and depositional environment of the Jurassic, Jumara Dome sediments, Kachchh, western India

The study deals with the depositional environment of Jumara Dome sediments. The Jumara Dome is an important outcrop of Bathonian to Oxfordian sediments amongst the Kachchh Mainland exposures. On the basis of facies analysis three associations have been documented, namely, G-1 consisting of low energy facies comprising of cross-bedded sandstone, massive sandstone, grey shale and thin bedded sandstone, bioclastic — lithoclastic grainstone, bioclastic — lithoclastic packstone, microbioclastic packstone/wackestone, bioturbated laminated wackestone to mudstone and pelagic lime mudstone; G-II consisting of moderate energy facies comprising of laminated sandstone and grapestone or agglutinated grainstone; G-III consisting of high energy facies comprising of interbedded gypsiferous shale and sandstone/siltstone, oolitic grainstone to conglomerate and bioclastic grainstone. The facies associations reflect an ideal shallowing upward sequence representing slope, bioclast bar, lagoon and inner shelf. Presence of wide range of facies indicates that the rocks of the studied area were deposited during the fluctuating sea level, interrupted by the storms, in the shallow marine environment.     

Petrography of Middle Jurassic to Early Cretaceous sandstones in the Kutch Basin,western India:Implications on provenance and basin evolution

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 5.26%. 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.     

Preserved lignin structures in early eocene Surat lignites,Cambay Basin,Western India

Lignite samples from Vastan and Tadkeshwar lignite mines, Cambay Basin have been analysed to elucidate lignin precursor using thermochemolysis-gas chromatography-mass spectrometry. The thermochemolysis products of lignites are characterized by monomethoxy-, dimethoxy-, and trimethoxybenzene derivatives originated from p-hydroxyphenyl, guaiacyl, and syringyl units of lignin polymer, respectively. The other compounds obtained in thermochemolysates of studied lignites are some resin derived C₁₅ sesquiterpenoids, with a series of fatty acid methyl esters and n-alkanes/alkenes. The methylated guaiacyl and syringyl derivatives originate from the cleavage of β-O-4 linkages and subsequent methylation of acidic hydroxyl groups of preserved lignin. Gymnosperm lignin is characterized mainly by guaiacyl derivatives whereas angiosperm lignin yields some syringyl-type compounds in addition to guaiacyl-type compounds. By analogy with the lignin structure of modern trees, the abundant occurrences of syringyl derivatives in the thermochemolysis products of Surat lignites clearly demonstrate that the palaeofloral community was dominated by angiosperms during the deposition of these lignites.     

Nummulitids,lepidocyclinids and Sr-isotope data from the Oligocene of Kutch (western India) with chronostratigraphic and paleobiogeographic evaluations

Due to its intermediate geographical position between the Mediterranean and W Pacific, the Oligocene shallow-marine sequence of Kutch (India) is of key importance in paleobiogeographical interpretations. Larger benthic foraminifera (LBF) are a fundamental link for the correlation between the Mediterranean shallow benthic zones (SBZ) and the W Pacific ‘letter stages’. LBF were re-evaluated by morphometric studies of the internal test from five stratigraphic sections of the Maniyara Fort Formation. Based on their significant affinity to coeval fauna in the Mediterranean, they were assigned to W Tethyan SBZ zones, supported by Sr-isotope stratigraphy. In the Basal Member, traditionally considered as early Rupelian, we identified Nummulites bormidiensis, N. kecskemetii and Heterostegina assilinoides assigning it to the early Chattian SBZ 22B Zone. The Coral Limestone Member, previously considered as late Rupelian, is also assigned to this zone, for the presence of N. bormidiensis, Eulepidina formosoides-dilatata and Nephrolepidina morgani-praemarginata. Its early Chattian age (26.5–29 Ma) is further supported by Sr-isotope data. Miogypsinoides complanatus and Spiroclypeus margaritatus in the Bermoti Member (the top of the formation) document the late Chattian SBZ 23 Zone and the Sr-isotope data (22.5–24 Ma) place it close to the Oligocene–Miocene boundary.     

Geomodelling of certain bauxite profiles from Kutch, Gujarat state, India

Bauxite deposits of Kutch occur in two different environments, viz. continental and marine, and hence it is of considerable interest from the points of view of genetic aspects, exploration and exploitation. Based on detailed exploration data some new softwares are developed to synthesise the geological and geochemical data. After studying the geostatistics, trend surface analysis has been carried out. With the aid of computer analysis and graphics, a geomodelling study has been attempted for the bauxite deposits that are derived from basalt (continental environment) and another one is presented which is associated with the marine environment. The significance of geomodelling study is substantially brought out.     

Distribution and geochemistry of selected trace elements in the lignites of Cambay basin,Gujarat, western India

In the present investigation all the working lignite seams of Cambay basin of Gujarat have been studied to see the distribution and geochemistry of selected major/minor elements like Fe, Ca, Na, K, Mg, and Mn and trace elements like Cu, Co, Cr, Cd, Ni, Pb and Zn. The vertical variation of these elements along the seam profiles has been studied to see the pattern of distribution of these elements and also to know the horizons of their enrichment and the probable cause. Further, these elements have been correlated among themselves and also with organic and inorganic matter of lignite. The correlation study indicates that in Tadkeshwar upper seam Fe has its affinity with huminite while Mg and Na have their affinity with liptinite and in Tadkeshwar lower seam Na has an affinity with liptinite. In Vastan upper seam Mn and Cu are associated with inertinite and Na with huminite while in Vastan lower seam Cu relates to huminite and Cd to liptinite and huminite. In Rajpardi seam Ca and Co are associated with huminite. The study provides information on the mode of occurrence of elements of less studied lignites of western India.     

The origin and maturation of lagoonal glauconites: a case study from the Oligocene Maniyara Fort Formation,western Kutch,India

An integrated study of the sedimentology, micropalaeontology, mineralogy and geochemistry of glauconites in the Oligocene Maniyara Fort Formation (western Kutch, India), has been undertaken. Authigenic glauconites, mostly of evolved type, formed within a back‐barrier lagoonal environment. Foraminifera help constrain the biostratigraphy and along with sedimentological evidence, provide information on the depositional conditions. Glauconite in the Maniyara Fort Formation occurs either as infillings within intra‐particle pores of larger foraminifers, or as an altered form of faecal pellets. X‐ray diffraction studies reveal the less mature nature of glauconite infillings compared to the glauconite pellets. Electron microprobe investigation confirms a relative enrichment of K₂O and total Fe₂O₃ in the latter. Both varieties of glauconite formed by initial authigenic precipitation of K‐poor glauconite and subsequently matured by addition of potassium in the interlayer sites and fixation of total iron in the octahedral sites; calcium, magnesium and aluminum were released from the glauconite structure concomitantly. Alkaline conditions during the entire process of glauconite formation did not allow dissolution of foraminiferal tests. Mineralogical and chemical characteristics of the Maniyara Fort Formation glauconites are more similar to deep marine glauconites than those reported from other shallow or marginal marine settings. A low negative cerium anomaly, as well as abundant pyrite, suggests formation of glauconite in sub‐oxic micro‐environments, created by decay of organic matter associated with foraminiferal chambers and faecal pellets. Sub‐oxic condition apparently prevailed relatively longer within the Maniyara Fort Formation lagoons. Copyright © 2011 John Wiley & Sons, Ltd.     

New Bathonian (Middle Jurassic) ammonite assemblages from Kutch, India

The Bathonian ammonite assemblages have been previously poorly recorded in Kutch. The present study has unearthed a rich array of ammonite taxa ranging from the Middle to Upper Bathonian. While Oxycerites Rollier (1909) is a new record from Kutch, the oldest occurrence of Choffatia Siemiradzki (1898) has been found from the Middle Bathonian horizon. Oxycerites cf. orbis (Giebel) is a zonal index of the Late Bathonian in other areas and thus facilitates interprovincial correlation. Besides, palaeobiogeographic and stratigraphic distribution of many species have been modified based on new information. For example, macrocephalitin species, i.e., Kamptokephalites cf. etheridgei Spath (1928), Macrocephalites bifurcatus transient intermedius Spath (1928), M. cf. mantataranus Boehm (1912) were previously known from West Pacific, Indonesia have been now found in Kutch. Gracilisphinctes Buckman (1920) has been previously known to occur during the Middle Bathonian time, the present work extends its stratigraphic distribution up to the definite Upper Bathonian horizon. Procerites hians (Waagen) an endemic species in Kutch previously known from the Upper Bathonian beds, its stratigraphic range has been extended down to the Middle Bathonian.Detail taxonomy of the newly obtained taxa has been done and in many cases sexual dimorphism has been recognized.     

Geochemical and Mineralogical Characteristics of Pleistocene Lignites and Associated Sediments of Marathousa Coal Field,Central Peloponnese,Greece

The mineralogy and geochemistry data are presented for thirty-seven shales,four concretions,two carbonate sediments and seven lignites from the Marathousa coal field of the Megalopolis Basin in Greece.The argillaceous rocks consist of chlorite,illite,kaolinte,albite,quartz.opal-A,calcite and dolomite;the concretions of aragonite,gypsum and pyrite;and the carbonate rocks of calcite,quartz and illite.The mineral matter in the lignites consists of gypsum,quartz,albite,chlorite,illite,opal-A,dolomite,pyrite,and rarely calcite and kaolinite Athree-factor model explains the total variaition of major and trace elements in the argillaceous sediments.The first factor is an aluminosilicate factor and involves the following elements:Al,Si,Mg,Na,K,Ti,Mn,Nb,Y,Rb,Zn,Cu,Ni,Cr,Nband V,associated with chlorite,albite and illite.The second factor involves the elements Ca,Sr,Ba,Znand Sc and is related to carbonate lithology and mainly the carbonate concretions with gypsum.The third factor involves Fe and Ce with a weak association with Mn.The diagenesis of the Marathousa sediments and lignites was not very advanced as indicated by (a) the total thickness of the sequence (500m),(b) the presence of biogenic silica(opal-A) and (c) the age of the deposit(Pleistocene).FOr these reasons the rpresence of chlorite,illite and kaolinite in the sediments and lignite is due not to diagenetic reactions but to weathering of the flysch and metamorphic rocks at the edges of the Megalopolis Basin and transport of the weathering products(illite,chlorite,kaolinite)into the basin of deposition.The diagenetic minerals of the Marathousa sequence include pyrite,gypsum,dolomite and aragonite.     

Evidence for right-lateral strike-slip environment in the Kutch basin of northwestern India from moment tensor inversion studies

The Kutch region located in northwestern part of India is an ancient rift basin that was active until Cretaceous period. The region falls close to the India–Arabia and the India–Eurasia plate boundaries and has experienced devastating earthquakes in the past, namely the 1819 Allah Bund earthquake, the 1956 Anjar earthquake and the 2001 Bhuj earthquake. To understand the tectonics of this region with respect to the adjacent plate boundaries, we invert seismic waveform data of 11 earthquakes in this region recorded by a network of the Institute of Seismological Research (ISR) during 2007–2009. The study yields focal mechanism solutions of reverse fault and strike-slip type mechanism. The inferred fault planes correlate well with the local trends of the known tectonic faults while the principal stress directions derived from stress inversion based on a linearized least squares approach, trend agreeably with the ambient stress field directions. A consistently right-lateral sense of shear is found on all the local faults as derived from each of the matching planes of the focal mechanism solutions computed in the present study. It is inferred that in the Kutch region a right-lateral strike-slip environment prevails along predominantly EW to NW-SE oriented deep-seated pre-existing faults in an otherwise compressive stress regime. This, in conjunction with the left-lateral movements along the Girnar mountain in southern Saurashtra, inferred from previous studies, indicates a westward escape of the Kutch–Saurashtra block as a consequence of the northward collision of the Indian plate with respect to the Eurasian landmass.     

New Bathonian (Middle Jurassic) ammonite assemblages from Kutch,India

The Bathonian ammonite assemblages have been previously poorly recorded in Kutch. The present study has unearthed a rich array of ammonite taxa ranging from the Middle to Upper Bathonian. While Oxycerites Rollier (1909) is a new record from Kutch, the oldest occurrence of Choffatia Siemiradzki (1898) has been found from the Middle Bathonian horizon. Oxycerites cf. orbis (Giebel) is a zonal index of the Late Bathonian in other areas and thus facilitates interprovincial correlation. Besides, palaeobiogeographic and stratigraphic distribution of many species have been modified based on new information. For example, macrocephalitin species, i.e., Kamptokephalites cf. etheridgei Spath (1928), Macrocephalites bifurcatus transient intermedius Spath (1928), M. cf. mantataranus Boehm (1912) were previously known from West Pacific, Indonesia have been now found in Kutch. Gracilisphinctes Buckman (1920) has been previously known to occur during the Middle Bathonian time, the present work extends its stratigraphic distribution up to the definite Upper Bathonian horizon. Procerites hians (Waagen) an endemic species in Kutch previously known from the Upper Bathonian beds, its stratigraphic range has been extended down to the Middle Bathonian.Detail taxonomy of the newly obtained taxa has been done and in many cases sexual dimorphism has been recognized.