Middle Eocene calcareous algae from Southwestern Kachchh,Gujarat

The Fulra limestone (middle Eocene) exposed in the areas around Jhadwa and Harudi villages, southwestern, Kachchh reveals presence of a rich assemblage of calcareous algae belonging to the Chlorophyceae and Rhodophyceae along with abundant foraminifera. In the present paper, eight species belonging to eight genera of calcareous algae are described. These include Dissocladella longijangensis, Sporolithon keenani, Corallina crossmanni, Arthrocardia sp. Misra et al. 2001, Lithothamnion ishigakiensis, Melobesioideae gen. et spec. indet. 1, Melobesioideae gen. et spec. indet. 2 and Lithoporella melobesioides. Out of these, one taxon belongs to the family Dasycladaceae. Among the remaining taxa, one taxon to the family Sporolithaceae, three taxa to the family Corallinaceae and three to the family Hapalidiaceae. Two coralline species, Corallina crossmanni and Lithothamnion ishigakiensis, are recorded for the first time from India. Another species (Dissocladella longijangensis), though known from other areas of India, is new to the study area.     

Characterization of organic carbon in black shales of the Kachchh basin,Gujarat, India

Thirty-three black shale samples from four locations on the onland Kachchh basin, western India were analyzed to characterize organic carbon (OC), thermal maturity and to determine the hydrocarbon potential of the basin. Upper Jurassic black shales from the Jhuran Formation (Dhonsa and Kodki areas) are characterized by the presence of chlorite, halloysite, high \(T_{\mathrm{max}}\), low OC, low hydrogen index and high oxygen index. These parameters indicate the OC as type IV kerogen, formed in a marine environment. The rocks attained thermal maturity possibly during Deccan volcanism. Early Eocene samples of the Naredi Formation (Naliya-Narayan Sarovar Road (NNSR) and the Matanomadh areas) are rich in TOC, smectite, chlorite and framboidal pyrite, but have low \(T_{\mathrm{max}}\). These indicate deposition of sediments in a reducing condition, probably in a lagoonal/marsh/swamp environment. Organic carbon of the Naredi Formation of NNSR may be considered as immature type III to IV kerogen, prone to generate coal. Core samples from the Naredi Formation of the Matanomadh area show two fold distribution in terms of kerogen. Organic carbon of the upper section is immature type III to IV kerogen, but the lower section has type II to III kerogen having potential to generate oil and gas after attaining appropriate thermal maturity.     

Fossil neocheilostomine bryozoans from the tertiary rocks of western Kachchh, Gujarat

Paper describes six species of neocheilostomine bryozoans occurring in the Middle Eocene-Early Miocene rocks of Western Kachchh, Gujarat, India. Taxa belong to the families Quadricellariidae Gordon, 1984, Vinculariidae Busk, 1852 and Poricellariidae, Harmer, 1926. Of these three species are new. These are Vincularia feddeni nov sp. Poricellaria waioriensis nov sp. and Poricellaria sakurkari nov sp. Two species, Nellia tenella (Lamarck, 1816) and Vincularia kutchensis (Tewari & Srivastava, 1967) already known from this region, are further reported here. Poricellaria complicata (Reuss, 1869)? is reported for the first time and indicates oldest record from India so far. Phylogenetic analysis using PAST programme indicates that Poricellariids and Vinculariids have not evolved from the same ancestor Nellia tenella (Lamarck, 1816)     

Molluscan assemblage from the marine Palaeocene sequence in southwestern Kachchh,Gujarat

Presence of oldest marine Tertiary rocks in Kachchh for a long time has remained debatable and controversial. To resolve the issue in better way authors have worked out a section along tributary of Kakdi Nadi about 0.5 km west of village Nareda in southwestern Kachchh and collected molluscan fauna. Systematic study of these fauna reveals presence of 15 taxa of which 12 are of bivalves and 3 of gastropods. This molluscan assemblage leads to the presence of marine Palaeocene sequence around Nareda. Recorded assemblage hitherto not known earlier from Kachchh.     

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.     

Genesis and diagenetic evolution of Habo formation,Kachchh, Gujarat

The Kachchh Basin is a pericratonic rift basin situated at the western margin of the Indian plate. The Habo Dome embodies an important exposure of Bathonian to Kimmergian sediments among the Kachchh Mainland exposures. Based on vertical facies transitions, facies associations were documented: mixed shallow marine (Facies association 1), shoreface and lagoon deposits (Facies association II) and subtidal innershelf below fair weather wave base (Facies association III). The documented facies associations reflect that Habo Dome sediments deposited in a variety of environments from shallow marine to fluvio-deltaic and were strongly influenced by fluctuation of relative sea level. The dominance of floating grains and point contacts in the sandstone indicate that detrital grains do not show much pressure effects as a result of either shallow burial or early cementation. The sandstones were cemented by iron oxide, carbonate and silica in order of abundance. Three types of cements, blocky, rim and fibrous cement occur in the studied limestone representing phreatic, fresh water phreatic and deep burial diagenetic stages. Neomorphism and micritization are common. Both primary and secondary porosity exists in these sediments. Different graphs of porosity versus depth suggest a depth of burial in the range of 615–769 m.     

Morphometric evidence of seismicity around Wagad and Gedi Faults, eastern Kachchh, Gujarat

Recent studies suggest that the eastern Kachchh is a potential zone for major earthquakes in the near future. Particularly, the E-W trending faults are considered capable of generating large magnitude earthquakes is further indicated by the recent concentration of the earthquake shocks, which, show two prominent clustering around west and north of the Wagad upland. In view of this, the conventional morphometric analyses of a terrain bounded by the E-W trending North Wagad Fault (NWF) and the Gedi Fault (GF) has been undertaken to ascertain the influence of seismicity in the evolution of the drainage basin. The study suggests that the fifth order drainage basins responded to the seismicity associated with both the NWF and GF. However, compared to the GF, the NWF seems to be more active. In addition to this, based on the stream morphology, we could identify two lineaments trending N-S and E-W. The former appears to be associated with the activity along the Manfara Fault (MF), whereas, the later seems to be the splays of the NWF. Further, a preferential westward shift of the streams suggests left lateral displacement of the E-W trending faults. Overall it can be suggested that the terrain is in juvenile stage implying tectonic instability.     

Some Calloporid (Bryozoa: Cheilostomata) species from the Cenozoic sediments of western Kachchh,Gujarat

Seven species of Calloporid (family Calloporidae Norman, 1903) Bryozoa are described from the Cenozoic sediments of the western Kachchh, Gujarat, India. Among these Planicellaria walsariensis, Dionella sp., Pyriporella charopadiensis, P. vadsariensis and Wilbertopora sp. are new and the other species viz; Crassimarginatella blandfordi and Reptoporina chhasraensis are reported for the second time from these sediments. The phylogenetic analysis suggests all the species of Calloporid bryozoans are monophyletic i.e. all of these species have common ancestor.     

Some fossil Margaretta (Ascophora:Bryozoa) from the Cenozoic sediments of Western Kachchh,Gujarat

Four species of Schizoporellid (family Margarettidae Harmer,1957) Bryozoa are described from the Cenozoic sediments of the Western Kachchh, Gujarat, India. Among these Margaretta amplipora, and M. hariparensis are new to science and the other species viz; M. guhai nom. nov. and M. rajui Guha & Gopikrishna, 2007 are reported for the second time from these sediments. The erect delicate articulated zoarial growth forms of these species indicate shallow water, moderate to high energy settings. The phylogenetic analysis suggests all the species of Margaretta are monophyletic i.e. all of these species have common ancestor.     

Strong ground motions from two moderate size (Mw5.5) Kachchh intraplate earthquakes,Gujarat, India

Natural Hazards - During 2006–2016, a strong motion seismic network of twenty 3-component accelerogarphs was deployed by the National Geophysical Research Institute, Hyderabad, India, in the...     

High energy transgressive deposits from the Late Jurassic of Wagad,Eastern Kachchh,India

The whole sedimentary succession (ca 600 m thick) of Wagad area ranging in age from Callovian to Early Kimmeridgian has been divided in to three Formations namely Washtawa, Kanthkot and Gamdau in ascending order. Prograding Kanthkot Formation was frequently interrupted by transgressions. Field and petrographic investigations revealed that the Kanthkot Formation represents three fossiliferous marker beds corresponding to Transgressive sequence I; Transgressive sequence II and Transgressive sequence III. These transgressive sequences are composed of two lithounits: medium to coarse grained/gritty, graded to massive, sheetlike, fossiliferous calcareous sandstone (storm lag unit I) and fossiliferous mudrocks (swell lag unit II). The thickness of the unit I varies from 5 to 75 cm and contains mostly convexly oriented shell fragments and whole shell of Pelecypods, Cephalopods and Brachiopods. Unit II (5–15 cm) is distinguished by sheetlike, massive or laminated, yellowish colour, soft fossiliferous mudrocks. This unit is intercalated with moderately bioturbated sandy siltstone. Unit I is dominant over Unit II in the sequences.Study suggests that the transgressive units were deposited close to wave base by high energy storm flows followed by low energy marine swells during transgression. The intense storms played a major role in the distribution of siliciclastics and nonclastic materials. Storms are evidenced by the occurrence of two distinctly different types of units (storm lags and swell lags). High energy levels are characterized by sand dominated sequence, abundance of reworked sediment particles, high proportion broken shells with convex up orientation and erosional and sharp nature of basal contacts of units together with well preserved bioclasts. Sudden short term changes from high to low energy during transgression are explained by the occurrence of medium to coarse grained siliciclastics interbedded with moderately bioturbated mudrocks. Moderately bedded individual strata, high content of coarse clastics along with polished granule size quartz and abundance of comminuted shells indicate a significant change in depositional setting, possibly closure approach of the source of terrigenous fraction or source uplift. Synrift sedimentation in the present study is documented by an abundance of coarse clastics and an over all aggradational nature of transgressive sequences.     

Stratigraphy and Sedimentology of Middle Jurassic Sequence of Chorar Island,Patan District,Kachchh Basin,Gujarat

Chorar Island exposes ～109 m thick middle Jurassic (Bathonian-Callovian) succession in the eastern most part of the Kachchh Basin, Patan District, Gujarat and is divided into two, Khadir and Gadhada formations. It mainly comprises of mixed siliciclastic-carbonate sediments and limestones; the shales dominate the lower part of the succession while the top of the succession is marked by ferruginous sandstone which also forms the vast, prominent peripheral zone of the Chorar dome. The field and laboratory analysis of the succession reveals nine lithofacies which includes ferruginous sandstone, cross bedded white sandstone, micritic sandstone, allochemic sandstone, sandy micrite, mudstone, sandy allochemic limestone, coralline limestone and shale. The mix siliciclastic-carbonate sediments and ferruginous facies are fossiliferous in nature and display sedimentary structures, like ripple marks, cross- and planar- lamination with biogenic sedimentary structures. Coralline limestone facies comprise of large size (>1m diameter) corals, which are diagenetically modified severely and have lost its original internal structures. The sediment characteristics and associated bioclasts indicates low to moderate wave and current energy in shoreface-offshore subsequently changing to wave dominated shoreface during the deposition of the middle Jurassic sediments of the Chorar Island.     

3-D seismic structure of the Kachchh,Gujarat, and its implications for the earthquake hazard mitigation

Several pieces of studies on the January 26, 2001, Bhuj earthquake (Mw 7.6) revealed that the mainshock was triggered on the hidden unmapped fault in the western part of Indian stable continental region that caused a huge loss in the entire Kachchh rift basin of Gujarat, India. Occurrences of infrequent earthquakes of Mw 7.6 due to existence of hidden and unmapped faults on the surface have become one of the key issues for geoscientific research, which need to be addressed for evolving plausible earthquake hazard mitigation model. In this study, we have carried out a detailed autopsy of the 2001 Bhuj earthquake source zone by applying three-dimensional (3-D) local earthquake tomography (LET) method to a completely new data set consisting of 576 local earthquakes recorded between November 2006 and April 2009 by a seismic network consisting of 22 numbers of three-component broadband digital seismograph stations. In the present study, a total of 7560 arrival times of P-wave (3820) and S-wave (3740) recorded at least 4 seismograph stations were inverted to assimilate 3-D P-wave velocity (Vp), S-wave velocity (Vs), and Poisson’s ratio (σ) structures beneath the 2001 Bhuj earthquake source zone for reliable interpretation of the imaged anomalies and its bearing on earthquake hazard of the region. The source zone is located near the triple junction formed by juxtapositions of three Indian, Arabian, and Iranian tectonic plates that might have facilitated the process of brittle failure at a depth of 25 km beneath the KRB, Gujarat, which caused a gigantic loss to both property and persons of the region. There may be several hidden seismogenic faults around the epicentral zone of the 2001 Bhuj earthquake in the area, which are detectable using 3-D tomography to minimize earthquake hazard for a region. We infer that the use of detailed 3-D seismic tomography may offer potential information on hidden and unmapped faults beneath the plate interior to unravel the genesis of such big damaging earthquakes. This study may help in evolving a comprehensive earthquake risk mitigation model for regions of analogous geotectonic settings, elsewhere in the world.     

Source parameters and scaling relations for small earthquakes in the Kachchh region of Gujarat,India

The scaling relationships for stress drop and corner frequency with respect to magnitude have been worked out using 159 accelerograms from 34 small earthquakes (M _w 3.3–4.9) in the Kachchh region of Gujarat. The 318 spectra of P and S waves have been analyzed for this purpose. The average ratio of P- to S-wave corner frequency is found to be 1.19 suggestive of higher corner frequency for P wave as compared to that for S wave. The seismic moments estimated from P waves, M ₀(P), range from 1.98 × 10¹⁴ N m to 1.60 × 10¹⁶ N m and those from S waves, M ₀(S), range from 1.02 × 10¹⁴ N m to 3.4 × 10¹⁶ N m with an average ratio, M ₀(P)/M ₀(S), of 1.11. The total seismic energy varies from 1.83 × 10¹⁰ J to 2.84 × 10¹³ J. The estimated stress drop values do not depend on earthquake size significantly and lie in the range 30–120 bars for most of the events. A linear regression analysis between the estimated seismic moment (M ₀) and corner frequency (f _c) gives the scaling relation M ₀ f _c ³  = 7.6 × 10¹⁶ N m/s³. The proposed scaling laws are found to be consistent with similar scaling relations obtained in other seismically active regions of the world. Such an investigation should prove useful in seismic hazard and risk-related studies of the region. The relations developed in this study may be useful for the seismic hazard studies in the region.     

Satellite image based quantification of invasion and patch dynamics of mesquite (Prosopis juliflora) in Great Rann of Kachchh,Kachchh Biosphere Reserve,Gujarat, India

The invasion of alien species is a significant threat to global biodiversity and the top driver of climate change. The present study was conducted in the Great Rann of Kachchh, part of Kachchh Biosphere Reserve, Gujarat, India, which has been severely affected by invasion of Prosopis juliflora. The invasive weed infestation has been identified using multi-temporal remote sensing datasets of 1977, 1990, 1999, 2005 and 2011. Spatial analyses of the transition matrix, extent of invasive colonies, patchiness, coalescence and rate of spread were carried out. During the study period of three and half decades, almost 295 km² of the natural land cover was converted into Prosopis cover. This study has shown an increment of 42.9% of area under Prosopis cover in the Great Rann of Kachchh, part of the Kachchh Biosphere Reserve during 1977 to 2011. Spatial analysis indicates high occupancy of Prosopis cover with most of the invasion (95.9%) occurring in the grasslands and only 4.1% in other land cover types. The process of Prosopis invasion shows high patch initiation, followed by coalescence, indicating aggressive colonization of species. The number of patches within an area of < 1 km² increased from 1977 to 2011, indicating the formation of new Prosopis habitats by replacing the grasslands. The largest patch of Prosopis cover increased from 144 km² in 1977 to 430 km² in 2011. The estimated mean patch size was 7.8 km² in 1977. The mean patch size was largest during 2011, i.e., 9 km². The annual spread rate for Prosopis has been estimated as 2.1% during 2005–2011. The present work has investigated the long term changes in Prosopis cover in the Great Rann of Kachchh, part of Kachchh Biosphere Reserve. The spatial database generated will be useful in preparing strategies for the management of Prosopis juliflora.     

Karst bauxite deposits in the Zagros Mountain Belt,Iran

More than 190 occurrences of bauxitic–lateritic deposits were investigated in seven areas within the Zagros Simply Folded Mountain Belt in southwestern of Iran. The bauxitic horizons are situated in eroded major NW–SE trending anticlines and occur in karst cavities near or at the boundary between the Sarvak and Ilam Formations. Uplift in the Cenomanian–Turanian period had exposed the Sarvak limestone to karst weathering and, during a period of unconformity, layers of ferruginous–argillaceous limestone debris developed and accumulated on its surface. The ferruginous–argillaceous debris was partly converted to bauxite. Folding and faulting in Oligocene–Miocene time, with ensuing erosion, exposed the bauxitic horizons on the limbs and cores of anticlines. The karst bauxite deposits are probably of authigenic origin, as evidenced by their lithologic associations, textural and mineralogy.