mesozoic and cenozoic reconstructions of the south atlantic abstract the movement of antarctica with respect to south america has a number of implications for paleocirculation as well as for the reconstructions of gondwanaland recent papers on the southwest indian ridge have published new or revised poles of opening for africa and antarctica which can be combined with the poles of opening between south america and africa to give resultant motions between south america and antarctica the first indication of a complete closure between south america and the antarctic peninsula is at anomaly 28 time 64 ma as the two continents are now configured between anomaly 28 time 64 ma and anomaly m0 time 119 ma the amount of closure does not change greatly and the small computed overlap can be explained by minor uncertainties in the rotation poles used for the reconstructions or some slight extension between east and west antarctica by 135 ma some rotation or translation of the antarctic peninsula with respect to east antarctica must be postulated in addition to any presumed extension between east and west antarctica in order to avoid an overlap of south america with the antarctic peninsula having determined what we feel to be a viable reconstruction of western gondwanaland and holding south america fixed we rotated africa and antarctica with respect to south america for eight different times during the past africa moved away from south america in a more or less consistent manner throughout the time period closure to present while antarctica moved away from africa in a consistent manner only between 160 ma and 64 ma at 64 ma its motion changed abruptly it slowed its north south motion with respect to africa and began slow east west extension with respect to south america this change supports the hypothesis that a major reorganization of the triple junction between africa antarctica and south america occurred between 60 and 65 ma the triple junction changed from ridge ridge ridge to ridge fault fault at the time of the major westward jump of the mid atlantic ridge just south of the falkland agulhas fracture zone the mesozoic opening of the somali basin moved madagascar from its presumed original position with africa in gondwanaland the closure of sri lanka with india produces a unique fit for india and sri lanka with respect to africa madagascar and antarctica this fit juxtaposes geological localities in southeast india against similar localities in enderhy land east antarctica the late jurassic opening in the somali basin is tied to opening of the same age in the mozambique basin since this late jurassic movement represents the initial break up of gondwanaland it is assumed that similar movement must have occurred in what is now the western weddell sea and may also explain the opening evidenced by the rocas verdes region of southern south america

india madagascar paleo fit based on flexural isostasy of their rifted margins the present study contributes new constraints on and definitions of the reconstructed plate margins of india and madagascar based on flexural isostasy along the western continental margin of india wcmi and the eastern continental margin of madagascar ecmm we have estimated the nature of isostasy and crustal geometry along the two margins and have examined their possible conjugate structure here we utilize elastic thickness te and moho depth data as the primary basis for the correlation of these passive margins we employ the flexure inversion technique that operates in spatial domain in order to estimate the spatial variation of effective elastic thickness gravity inversion and flexure inversion techniques are used to estimate the configuration of the moho crust mantle interface that reveals regional correlations with the elastic thickness variations these results correlate well with the continental and oceanic segments of the indian and african plates the present study has found a linear zone of anomalously low te 1 5 km along the wcmi similar to 1680 km which correlates well with the low te patterns obtained all along the ecmm we suggest that the low te zones along the wcmi and ecmm represent paleo rift inception points of lithosphere thermally and mechanically weakened by the combined effects of the marion hotspot and lithospheric extension due to rifting we have produced an india madagascar paleo fit representing the initial phase of separation based on the te estimates of the rifted conjugate margins which is confirmed by a close fit correlation of moho geometry and bathymetry of the shelf margins the matching of tectonic lineaments lithologies and geochronological belts between india and madagascar provide an additional support for the present plate reconstruction c 2014 international association for gondwana research published by elsevier b v all rights reserved

crust beneath the northwestern deccan volcanic province india evidence for uplift and magmatic underplating the northwestern deccan volcanic province of india and its pericratonic rift basins were reactivated during different stages after the breakup of india from the gondwanaland and collision with the asian plate in this study we present results of crustal thickness and average crustal vp vs ratios beneath this plume affected region using common conversion point imaging and h k stacking analysis of 6893 receiver functions using data from a network comprising 58 broadband seismic stations sited on diverse tectonic terrains we find large variations in crustal thickness with the moho depths varying from 28 to 43 km in the kachchh rift 28 to 38 km in the cambay rift 39 5 41 5 km in the north and eastern parts of the cambay rift and 29 to 39 km in the saurashtra region and south gujarat a moho upwarp of 6 to 7 km in the saurashtra region can be attributed to positive buoyancy and uplift due to thermal influx affected by the reunion plume high crustal vp vs ratios beneath the kachchh rift 1 8 to 2 05 coastal areas of saurashtra 1 75 to 2 06 and north gujarat 1 81 to 1 85 indicate dominance of a mafic ultramafic crust high regional heat flow high electrical conductivity large intracrustal s wave velocity reduction and high average crustal poisson s ratios are consistent with partial melt related to the process of magmatic underplating in the lower crust at other stations the crust appears to be felsic with vp vs ratios in the range of 1 57 to 1 76

the seismic structure of the saurashtra crust in northwest india and its relationship with the reunion plume summary the saurashtra peninsula in northwest india lying at the northern boundary of the deccan volcanic province is almost entirely covered by these volcanics analogue seismic refraction wide angle reflection data along a 160 km long profile from navibandar to amreli were collected during 1977 to determine the crustal configuration reprocessing of these data after digitization has yielded a crustal model that is significantly different from the earlier model of kaila et al the model shows the upper crust down to a depth of 16 km in the west and 13 km in the east and underplating velocity of 7 20 km s 1 o fthe lower crust the moho is at a depth of 36 km in the western part and at 32 33 km in the eastern part the change of depth is quite sharp almost in the middle of the profile similar depth changes are seen in other crustal horizons indicating a deep fault that is in line with the extension of the proterozoic aravalli trend in to the saurashtra peninsula the crustal structure in the eastern part is similar to that in the cambay basin and indicates that the crust to the east of the proposed fault is uplifted the uplifted region extends as far as another arm of the aravalli trend that turns eastwards crustal underplating in large parts of western india is confined to the corridors affected

bentonites in the chalk of central eastern england and their relation to the opening of the northeast atlantic abstract within the post cenomanian chalk sequence of central eastern england about 20 thin persistent marl horizons occur these marls contain from 30 to 65 non carbonate material the bulk of which is composed of a well crystallised mg rich smectite with a notable paucity of illite and quartz the chalk matrix above and below the marls contains up to 2 0 of non carbonate matter which again is dominated by the presence of an mg rich smectite but which contains a larger proportion of illite and quartz than occurs in the marls for both sets of non carbonate materials the excellent crystallinity and mg rich nature of the smectite strongly suggest that it was formed by the in situ alteration of an aeolian transported volcanic ash i e it is a true bentonite quartz and illite in the chalk matrix are probably detrital components relative to a standard shale non carbonate materials from the chalk marl horizons exhibit a highly anomalous trace element pattern with accentuated levels of zr nb and th but depleted levels of ba rb and k this trace element chemistry corroborates a volcanogenic origin for the smectite insofar as it is not explicable in terms of any realistic sedimentary process the chemistry is best interpreted in terms of the magnetic processes responsible for the formation of the original ash precursor of the marls it appears that this precursor had a pantelleritic composition and therefore originated from a source overlying an area where incipient continental rifting was taking place micromorphological examinations prove that residues from the chalk marls contain small amounts of pyroclastic debris including pumice and fragments of sideromelane glass the morphology of the fragments suggests that the volcanic eruptions responsible for the ejection of the original ash into the air were of the shallow water phreatomagmatic surtseyan type the distribution of marls in the chalk of eastern england suggests that the ashfalls responsible for their origin were of the tropospheric type and were drawn by westerly winds from a centre to the west or northwest of mainland britain of the numerous volcanic centres that lie in offshore areas to the west the anton dohrn seamount in the rockall trough appears to a likely centre of origin for the ashfalls however ashfalls responsible for the formation of the traces of smectite in the chalk matrix were probably of the general background stratospheric type and may have been drawn from more distant centres volcanism at the anton dohrn seamount was related to tensional effects in the continental crust that immediately preceded the formation of the rockall trough and the separation of greenland from northwestern europe during tertiary times activity at the centre and cretaceous bentonites derived therefrom therefore represent the earliest stages in the development of the thulean igneous province

the barremian aptian arid phase in western europe abstract evidence is presented from nine areas in western europe speeton yorkshire southern north sea channel and weald basins southern england jeanne d arc lusitanian and aquitanian basins of the north atlantic continental margins lower saxony basin north germany the paris basin and southern france for a phase of aridity which began during the hauterivian middle barremian and continued to dominate the climate of the region until the mid aptian although conditions during this period were not uniformly dry throughout criteria for recognising arid environments include the occurrence of evaporites abundances of carbonate rich sediments red beds firmgrounds carbonate nodules and pyrite concretions depletion of kaolinite spore assemblages of limited morphological diversity and the presence of numerous coniferalean and cheirolepidiacean pollen grains the change from generally humid to dry climates during the barremian is thought to have been linked to a lowering of sea level the arid phase clearly falls within the time span of the first cretaceous oceanic anoxic event

seismic imaging of the aftershock zone of the 2001 mw 7 7 bhuj earthquake india 1 detailed seismic tomography reveals that the 2001 mw 7 7 bhuj earthquake was associated with a 10 14 increase in vp and vs and a 10 decrease in vp vs in the 10 to 35 km depth range covering a 2750 km2 area beneath the aftershock zone this anomaly could be attributed to the existence of a lithological heterogeneity or a pluton of mafic composition that might have intruded during the rifting in early jurassic 160 ma the banni basin and the wagad uplift are found to be associated with high velocity intrusive bodies extending from 5 to 35 km depth a few patches of low vp and vs and high vp vs between 10 to 30 km depth have also been detected on the causative 45 south dipping north wagad fault nwf for the 2001 mainshock which may be attributed to a fluid filled fractured rock matrix

morphotectonic segmentation and spatial variability of neotectonic activity along the narmada son fault western india remote sensing and gis analysis abstract morphotectonic analysis of landscape using remote sensing and gis is an effective way of deducing the pattern and spatial variation of neotectonic activity along poorly investigated active faults in this paper we evaluate the neotectonic activity along a part of the seismically active but poorly understood narmada son fault nsf a more than 1000 km long ene wsw trending fault transecting through the central part of the indian plate the nsf in the study area is geomorphologically expressed as an ene wsw trending line of north facing scarps that delimit the rugged mountainous topography of the uplands to the south and the alluvial basin to the north which prominently slope away from the scarps the scarps are developed in the south dipping basaltic flows belonging to the deccan trap formation of the late cretaceous eocene and continue westward into tertiary rocks and further as a paleobank of the narmada river field studies have revealed that the nsf in the study area is divisible into four morphotectonic segments i to iv which is attributed to the tilakwada karjan madhumati and rajpardi faults cutting across the nsf we characterize the neotectonic activity of the segments through dem analysis using geomorphic indices which include the mountain front sinuosity hypsometric curves hypsometric integral asymmetry factor stream length gradient index and channel sinuosity interpretations of morphometric data are well supported by field data both the entire length of the nsf and the cross faults are found to be neotectonically active we demonstrate that segment ii has undergone the highest intensity of neotectonic activity followed by segments iii i and iv this is corroborated by the highest elevation of scarps and the alluvial deposits the deepest incision 40 m depth and steep northward slope of the alluvial plain in segment ii we infer that the nsf is characterized by differential uplift in recent past which agrees with the high angle reverse faulting with oblique slip movements along the cross faults

paleogene monsoons across india and south china drivers of biotic change monsoonal climates at low latitudes 32 n are an inevitable consequence of seasonal migrations of the inter tropical convergence zone itcz but the character of these monsoons depends on continental configuration orographic expression and the strength of hadley circulation to explore the evolution of monsoon systems across southern asia we compare climate signatures archived in ten paleogene floras from northern india tibet and southern china occupying low palaeolatitudes at a time of extreme global warmth and elevated co2 fossil leaf form reveals that under such hothouse conditions megathermal early eocene to earliest miocene forests were exposed to strong monsoonal climates typical of those experienced today arising from annual migrations of the itcz possibly enhanced by a lower equator to pole temperature gradient throughout the paleogene an elevated tibetan highland produced no discernable modification of this itcz monsoon although rainfall seasonality similar to that of the modern south asia monsoon sam is observed in northern india as early as the beginning of the eocene despite its near equatorial palaeoposition in south china rainfall seasonality increased progressively achieving modern monsoon like wet season dry season precipitation ratios by the early oligocene despite evidencing weak rainfall seasonality overall fossil leaves from south china have exhibited monsoon adapted morphologies comparable to those seen in today s indonesia australia monsoon for at least 45 million years together the indian and south china fossil leaf assemblages show that the evolution of megathermal ecosystems across southern asia has been influenced profoundly by monsoonal climates for at least the last 56 million years the paleogene itcz driven monsoon system strongly impacted india as it transited the equator likely eliminating gondwanan taxa not able to adapt to seasonal precipitation extremes furthermore powerful seasonally reversing winds and associated surface ocean currents are likely to have facilitated two way biotic transfer between india and eurasia long before closure of the tethys ocean

subsidence history of the tethys himalaya abstract this article reconstructs the evolution of the passive northern margin of peninsular india facing the neotethys from the earliest rifting stages in the carboniferous to final collision with the active southern margin of asia in the early eocene classical techniques of basin analysis were applied to an extensive and coherent stratigraphic data base facies analysis biostratigraphic dating and palaeoenvironmental interpretation of an over 10 km thick sedimentary succession from eight main composite sections allowed us to draw accurate sedimentation and backstripped subsidence curves and to place quantitative constraints on the palaeotectonic scenario inferred from the sedimentary record in each of the investigated composite sections three major stratigraphic gaps are consistently recognised in the rift sequence the rift unconformity mississippian the carboniferous permian hiatus largely kasimovian to asselian and the break up unconformity mid sakmarian two or even all three gaps may merge into a single hiatus spanning up to 70 ma overall gaps are associated with rift shoulder uplift which after calculation of backstripped subsidence sums up to 600 m at least in three of the investigated sections thermal subsidence and low sedimentation rates are documented by the mid permian to middle triassic drift sequence deposited while the neotethys was expanding between northern gondwana and the detached peri gondwanan blocks a marked increase in accumulation rates is recorded in the carnian norian but calculations of uniform lithospheric stretching suggest that extension was minor and associated with tectonic processes affecting distant parts of gondwana the tethys himalayan margin was uplifted around the jurassic cretaceous boundary at the onset of a major volcanic episode finally uplift exceeding in magnitude all previous events is documented by the uppermost units of the stratigraphic column deposited during the earliest stages of collision between india and asia in the latest paleocene to early eocene

intensity estimation for the 2001 bhuj earthquake india on esi 07 scale and comparison with historical 16th june 1819 allah bund earthquake a test of esi 07 application for intraplate earthquakes abstract on 26th january 2001 an earthquake of magnitude mw 7 7 occurred near bhuj in northwestern india resulting in severe environmental effects no unequivocal primary surface rupture was observed for the earthquake but it caused widespread liquefaction and lateral spreading in the rann of kachchh and little rann after the earthquake several researchers collected field evidence of secondary surface rupture rockfall dry craters and surface manifestations of liquefaction including the formation of mud volcanoes and lateral spreads in the meizoseismal area analysis of pre and post earthquake satellite images suggests that several dry streams in the rann of kachchh began to flow due to extensive liquefaction induced by the earthquake in this present study the macroseismic intensity of the bhuj earthquake is evaluated by considering these environmental effects and applying the esi 07 intensity scale to the affected area as an outcome the epicentral intensity of the 2001 bhuj earthquake was determined to be xi according to historical records and seismic catalogs 16th june 1819 allah bund earthquake caused prominent surface rupture which was not so clear in the case of 2001 bhuj earthquake but the secondary effects were similar for both earthquakes considering the environmental effects caused by the 1819 allah bund earthquake an intensity of xi was estimated for the epicentral area for both earthquakes the esi scale yields a significant difference of one to two degrees with the traditional intensity scales the 2001 bhuj earthquake and 1819 allah bund earthquake shows similar esi 07 intensity of xi despite of different epicentral locations this implies the reliability of esi 07 scale application for different earthquakes of similar dimensions in the same geological setting this study contributes to the application of esi 07 scale for indian earthquakes especially reverse faulting events and to the future improvement of the esi scale with emphasis on its applicability to historical earthquakes on the indian subcontinent also this study may help in future land use planning in the meizoseismal area of 1919 allah bund and 2001 bhuj earthquakes

magnetovariational study over a seismically active area in the deccan trap province of western india this paper presents the results of a magnetovariational study undertaken over a basalt covered region of western india which has been experiencing a swarm of seismic activity since early 1986 the most striking feature of the transient variations is the anomalous enhancement of the east west y component at stations bounding the seismically active belt from the nature of the horizontal transfer functions and the anomalous induction arrows it is inferred that this behaviour is related to the presence of a resistive body embedded in a north south oriented conductive belt consistent with an evolutionary model of deccan volcanism and other geophysical data it is suggested that the central resistive block coincident with the concentrated belt of earthquake epicentres represents either a dormant volcanic plug or a plutonic body rooted in upwarped conducting mantle to account for the phase relationship between the anomalous y variations and the normal north south x variations it is proposed that the upwarped asthenosphere with its associated high geothermal anomaly acts as a conducting path to channel induced current from the region of the cambay triple junction located towards the northwest of the array the existence of the strong induced currents in the region of the triple junction conforms with the induction arrow pattern observed at the array stations

palaeoseismic investigations along the kachchh mainland fault a comprehensive review and new insights of the past earthquakes in the kachchh basin western india abstract the intraplate kachchh rift basin has been hit by several devastating earthquakes in the historic past including the 1819 allah bund earthquake and the 2001 bhuj earthquake the source region of these earthquakes within the basin have been studied by several workers in the last two decades to understand their potential for earthquake recurrence however very little information is available on the palaeoseismic and geomorphic characterization of kachchh mainland fault kmf therefore in the present study six trenches were excavated across the kmf between lakhpat and nirona to understand ground deformation pattern and timing of the historic earthquakes based on geomorphic and palaeoseismic investigations five palaeoearthquakes of early to late holocene have been identified between 10 000 890 yrs apart from the holocene an earthquake of late quaternary period was also identified which possibly occurred around 19 800 yrs bp fault related parameters were analyzed to understand the geometry of the active fault scarp along kmf the results of the analyzed fault geometric parameters show that the vertical displacement along the kmf is higher than the horizontal displacement the slip rate of the kmf from the western portion to the middle portion decreases from 0 08 to 0 04 mm yr and increases towards east from 0 22 mm yr to 0 36 mm yr as the kachchh district of the gujarat state is rapidly developing in terms of infrastructural development the outcome of this research might provide significant inputs for micro zonation studies and also in the evaluation of the seismic hazard in the kachchh region

sedimentological evidence concerning the paleoceanography of the cretaceous western north atlantic ocean abstract black clays developed as a result of progressively intensifying intermittent anoxic conditions from the early through mid cretaceous the preservation of primary sedimentary structures of authigenic minerals such as pyrite and siderite and of significant amounts of organic carbon testify to the stagnant conditions intermittent anoxic conditions prevailed in the deepest portion of the basin resulting from vertical migration of an intrasediment anoxic interface middle aptian variegated clays within the black clay sequence at several low latitude sites suggest a widespread oxygenation event of short duration occurred there greater thicknesses of black clays accumulated in low latitudes implying that surface or intermediate depth currents redistributed the sediments south ward millimeter scale laminae characterizing the early and mid cretaceous sediments represent seasonal sediment input where seasons during the cretaceous had durations measured in years cenomanian variegated clays succeeded the black clay interval and represent deposition under totally oxygenated conditions thus the sluggish and stagnant conditions present in the early and mid cretaceous were followed by increased current activity these currents were derived from more northern latitudes as iberia was rifted from north america cooler temperatures presumably increased the oxygen capacity of the water and its ability to sink into the deep basin to relieve the stagnant conditions present the late cenomanian through late campanian was a time of widespread marine transgression resulting in the deep ocean becoming a sediment starved basin clastics and carbonates accumulated on the shelves as the calcite compensation depth ccd shallowed appreciably the late campanian through maastrichtian interval is characterized by calcium carbonate accumulation throughout much of the deep basin a significant lowering of sea level paralleled by a deepening ccd caused this sedimentation pattern

palynostratigraphy and palynofacies of the early eocene gurha lignite mine rajasthan india abstract a 105 m early eocene section exposed in the gurha mine in the nagaur ganganagar basin rajasthan india archiving remains of equatorial vegetation at a time of extreme global warmth and close to the onset of the india eurasia collision is investigated using palynostratigraphic and palynofacies analyses four palynozones e g palmidites plicatus singh botryococcus braunii kutzing triangulorites bellus kar and ovoidites ligneolus are identified stratigraphically on the basis of abundance of these pollen taxa over others the occurrence of taxonomically highly diverse angiosperm pollen in all the four palynozones attests to an extremely rich near coastal tropical flora subject to frequent wildfires under a strongly seasonal precipitation regime palynotaxa characteristic of these palynozones are widely distributed in other early paleogene sediments of india sedimentary organic matter structured terrestrial biodegraded amorphous grey amorphous resins charcoal black brown debris and algal remains recovered from mire and lacustrine sediments are of terrestrial origin recording fluctuations in burial anoxia and salinity episodes of elevated salinity are due either to seepage of marine waters and or a periodic excess of evaporation over precipitation at times when the depositional system was closed

the effects of thermal maturity on distributions of dimethylnaphthalenes and trimethylnaphthalenes in some ancient sediments and petroleums abstract the distributions of di and trimethylnaphthalenes in two sedimentary sequences from western australia have been examined by capillary gas chromatography and combined gas chromatography mass spectrometry a general decrease was observed in the relative proportions of dimethylnaphthalenes and trimethylnaphthalenes with increasing thermal maturity similar trends were also observed for six crude oils which have very different ratios of ethylcholestane epimers indicating very different thermal histories these results suggest that changes in the relative abundances of certain methyl substituted naphthalenes may be useful indicators of thermal maturity of sedimentary organic matter and the use of a number of isomer ratios is illustrated

luminescence chronology of river adjustment and incision of quaternary sediments in the alluvial plain of the sabarmati river north gujarat india river adjustment and incision in the sabarmati basin gujarat india have been examined at a site near mahudi towards this the morphostratigraphy and depositional chronometry of the middle alluvial plains were investigated the upper fluvial sequence along with the overlying aeolian sand and riverbed scroll plains provide clues to the evolution of the present sabarmati river sedimentological analyses of the upper fluvial sequence indicate its deposition by a meandering river system during what is believed to be a persistent wetter phase luminescence chronology bracketed this sequence to between 54 and 30 ka which corresponds to oxygen isotope stage 3 during which the sw monsoon was enhanced the overlying aeolian sand has been dated to 12 ka indicating that dune accretion occurred simultaneously with the strengthening of the sw monsoon during the early holocene adjustment of the sabarmati along a n s transect is placed around 12 ka and the incision is bracketed between 12 and 4 5 ka river adjustment could have been tectonic however the incision was facilitated by the availability of continuous flow in the river caused by the sw monsoon the basin experienced two tectonic events at about 3 and 0 3 ka as demonstrated by the morphology of the scroll plains

tethyan carbonate carbon isotope stratigraphy across the jurassic cretaceous boundary an indicator of decelerated global carbon cycling the carbon isotope record in four pelagic carbonate sections from the southern alps northern italy across the jurassic cretaceous boundary has been correlated to biostratigraphy and magnetostratigraphy the carbon isotope curve from bulk carbonates shows a decrease from kimmeridgian to early tithonian cm24 cm22 values of 13c 2 07 0 14 to late tithonian and berriasian cm18 cm14 values of 13c 1 26 0 16 the change in the carbon isotope record coincides with changes in tethyan calcite and silica accumulation rates with a drop in the calcite compensation depth in the atlantic and tethys oceans and with changes in organic carbon burial along the eurasian margin of the tethys reduced surface water productivity due to diminished transfer rates of biolimiting elements into the atlantic and tethys oceans can explain these observations the decreased transfer rates of elements such as silica or phosphorus from continents into the oceans resulted from drier climatic conditions and decreased water runoff on continents bordering the tethys and atlantic oceans the proposed changes in tithonian berriasian ocean chemistry and paleoclimate suggest that variations in the global carbon cycle were coupled with changes in the global hydrological cycle and in associated material cycles

crustal structure along mehmadabad billimora profile in the cambay basin india from deep seismic soundings abstract deep seismic sounding dss investigations were carried out along a 220 km long n s profile from mehmadabad 22 50 n 72 46 e to billimora 20 46 n 72 58 e in the cambay basin india for studying the detailed crustal structure in the region seismic refraction as well as narrow and wide angle reflection travel time data were obtained for various crustal boundaries starting from the sedimentary section down to the moho by continuous profiling analysis of reversed reflection and refraction travel time data has yielded crustal velocity depth functions for the mehmadabad broach and broach navsari sections along the profile which are significantly different from each other the average velocities at depths in the magmadabad broach section have been found to be considerably lower than those in the broach navsari section by about 25 at 5 km 17 at 10 km 7 at 20 km and 2 at the moho depth and even deeper down in the upper mantle the presence of a relatively thicker sedimentary section especially in the jambusar broach area as revealed by the reversed refraction data analysis is responsible for this gross difference in the average velocity functions for the two parts of the profile and the same have therefore been used for obtaining the detailed crustal depth along the profile the cambay basin which is well known to be bounded by step faults on the eastern and western margins is also dissected into seven major crustal blocks in the n s direction from mehmadabad to billimora the various crustal blocks identified are from the north 1 i mehmadabad block 2 ii tarapur block 3 iii petlad katana block 4 iv jambusar broach block 5 v kosamba block 6 vi surat block and 7 vii navsari billimora block these blocks are displaced up or down relative to the adjacent blocks due to movements along the faults bounding them most of the faults have been found to extend quite deep and to affect the moho boundary considerably as is quite evident from the relief of the moho found along the profile further the seismic activity observed in the region during historical as well as modern times suggests that these deep faults may even be currently active the jambusar broach block which is well known as a broad regional syncline with the maximum thickness of cenozoic sediments has been found to be a major graben revealing a maximum crustal thickness of 38 40 km the granitic basement in this graben is also the deepest at 6 0 6 5 km depth towards the north and south of this major graben the moho as well as the granitic basement are found to be at relatively shallower depths in various crustal blocks the boundary velocity at the moho has been found to be 8 1 8 2 km sec whereas at the granitic basement level there seems to be a lateral velocity variation from 5 7 to 6 3 km sec the crustal depth section obtained in the present study reveals a close relationship between the deep and shallow structural features in this region the deccan traps which form the basement of the overlying tertiary sediments over most part of the profile vary in thickness from 1 0 to 1 8 km however the trap surface rises to very shallow depths on the southern part of the profile the boundary velocity in the deccan traps has been found to vary between 4 8 and 5 2 km sec in the anklesvar kosamba area there is also evidence for the presence of a 1 2 km thick layer of mesozoic sediments with a velocity of about 4 0 km sec underlying the 1 1 km thick deccan traps layer

structural imaging of mesozoic sediments of kachchh india and their hydrocarbon prospects travel time modelling of first and second arrivals has been used to produce p wave velocity models of the shallow sub surface structure of kachchh india using new wide angle reflection refraction profiles results obtained from the 2 d tomographic modelling have also been corroborated with magnetotelluric and borehole data within the proximity of these profiles based on multiple geophysical data a composite sub surface model is presented in this article the prominent features of the model include the presence of more than 3 km thick mesozoic sediments residing above the precambrian basement its correlation with available lithological knowledge shows that the mesozoic rocks have been deposited from early triassic to late cretaceous until the eruption of the deccan flood basalts at the cretaceous tertiary boundary the new results suggest that the mesozoic rocks of kachchh can be sub divided in two major parts which correspond to late and early mesozoic deposits respectively the sub surface models successfully demarcate the regional variations in the basaltic layer across the region and show maximum thickness of 1 2 km the modelling results also exhibit that the precambrian basement in this region varies between 4 and 6 km depth the new data provide a much clearer picture than was hitherto available of the entire sedimentary succession in the basins that underlie the kachchh region they show a significant variability in thickness of the various sedimentary layers and in particular illustrate a marked topographic irregularity at the base of the sedimentary succession

transient electromagnetic investigations in a tectonic domain of the kachchh intraplate region western india a morphotectonic study of the kachchh mainland fault

temporal profiling of uplift rate along an active fault using river long profile in the kuchchh region western india abstract river long profiles are widely used as tectonic event markers incision uplift rate estimations based on the dating of river terrace or exposed scarp sediment give long term averaged uplift rate values with the limitation of not giving the intermediate phases of highs and lows on the other hand gps based estimates provide only decadal scale uplift rate estimates in our study we adopted the long profile inversion methodology to obtain a temporal profile of uplift rate history over the late pleistocene holocene time period along an active fault the kuchchh mainland fault in kuchchh region western india which has experienced several large magnitude earthquakes in recent past we also used long profiles analysis to quantify the transient response of kuchchh landscape to uplift activity along the kuchchh mainland fault steepness index and chi profiles were estimated to display the spatial variability in landscape disequilibrium integral method based chi profiles were used to obtain the optimum value of basin area exponent of the stream power incision model spim our estimates provide a mean uplift rate value of 1 1 1 4 mm yr along the kuchchh mainland fault during the late pleistocene holocene period which matches with the average uplift rate derived from other independent observations in this region further a chronology of major tectonic phases from the estimated uplift rate time series also corroborates with field based estimates of major incision events in kuchchh region we also tested the robustness and sensitivity of our uplift rate estimates to model parameters such data can be complementary to the existing sparsely both spatially and temporally distributed uplift rate database which is imperative to seismic hazard assessment

regional uplift associated with continental large igneous provinces the roles of mantle plumes and the lithosphere the timing and duration of surface uplift associated with large igneous provinces provide important constraints on mantle convection processes here we review geological indicators of surface uplift associated with five continent based magmatic provinces emeishan traps 260 million years ago ma siberian traps 251 ma deccan traps 65 ma north atlantic phase 1 61 ma and phase 2 55 ma and yellowstone 16 ma to recent all five magmatic provinces were associated with surface uplift surface uplift can be measured directly from sedimentary indicators of sea level in the north atlantic and from geomorpholocial indicators of relative uplift and tilting in yellowstone in the other provinces surface uplift is inferred from the record of erosion in the deccan north atlantic and emeishan provinces transient uplift that results from variations in thermal structure of the lithosphere and underlying mantle can be distinguished from permanent uplift that results from the extraction and emplacement of magma transient surface uplift is more useful in constraining mantle convection since models of melt generation and emplacement are not required for its interpretation observations of the spatial and temporal relationships between surface uplift rifting and magmatism are also important in constraining models of lip formation onset of surface uplift preceded magmatism in all five of the provinces biostratigraphic constraints on timing of uplift and erosion are best for the north atlantic and emeishan provinces where the time interval between significant uplift and first magmatism is less than 1 million years and 2 5 million years respectively rifting post dates the earliest magmatism in the case of the north atlantic phase 1 and possibly in the case of siberia the relative age of onset of offshore rifting is not well constrained for the deccan and the importance of rifting in controlling magmatism is disputed in the emeishan and yellowstone provinces in these examples rifting is not a requirement for onset of lip magmatism but melting rates are significantly increased when rifting occurs models that attempt to explain emplacement of these five lips without hot mantle supplied by mantle plumes often have difficulties in explaining the observations of surface uplift rifting and magmatism for example small scale convection related to craton or rift boundaries edge driven convection cannot easily explain widespread 1000 km scale transient surface uplift emeishan deccan north atlantic and upper mantle convection initiated by differential incubation beneath cratons the hotcell

micromorphology clay mineralogy and geochemistry of calcic soils from western thar desert implications for origin of palygorskite and southwestern monsoonal fluctuations over the last 30 ka abstract the thar desert with intense aeolian activity and calcrete formation is one of the hottest arid regions of the world little is known about the formation of calcic soils with a large amount of palygorskite in the western thar in this study we have used microscopy sub microscopy clay mineralogy and geochemistry of three calcic soils from western thar to understand the pedogenesis in response to fluctuating southwestern monsoon over the last 30 ka thin sections of the soils show a dominance of weakly developed pedofeatures with powdery to well indurated pedogenic calcium carbonate that influenced weathering of primary mineral grains sub microscopy of the calcretes shows a large amount of fibrous palygorskite in pore spaces of micritic and sparitic nodules xrd of the total clay

palaeogeography of radiolarite and organic rich deposits in mesozoic tethys siliceous and marine organic rich deposits are sometimes associated sometimes separate in space and time however both are generally accepted to be the result of high planktonic productivity among the siliceous marine deposits the phtanite family facies is distinguished from the radiolarite family facies by several characteristics they contain organic material and as a result are blackish vs red green for radiolarite facies their time of deposition corresponds with strong faunal modifications and they are deposited generally in shallower environments a palaeogeographic analysis of locations of tethyan biosiliceous and marine organic rich rocks both resulting from a high planktonic palaeoproductivity for three mesozoic high sea level intervals toarcian kimmeridgian and cenomanian show a during jurassic times these tethyan deposits were dissociated the siliceous deposits being closer to open ocean waters than the organic rich ones this is a common disposition in modern upwelling systems and suggests a common process b during cretaceous times these tethyan deposits were often associated i e both occur at the same site and are probably the result of a different process from that in the jurassic

gis based approach for the measurement of variability in tectonomorphic signatures using dem s data a case study from the habo dome in the kachchh area india the kachchh region of western india is located in a plate interior region but falls under one of the highest seismic zones of india having very active crustal deformation and erosion the drainage system as well as the geomorphic evolution of the region under a semi arid climate zone with high to very high strength of rocks in areas with high relief is dominantly controlled by the seismic instability associated with continual tectonics in the present paper we have analysed a block close to the epicentre of the 2001 bhuj earthquake to understand the role of relative active tectonics in the evolution of domal landscape morphology shuttle radar topographic mission digital elevation model data were used to extract drainage network in the gis platform and evaluate active tectonics using different geomorphic indices of the habo hill the second largest domal structure situated in northern hill range of the kachchh region the average cumulative weightage of different geomorphic indices provides a quantitative tool index of relative active tectonics irat which shows significant variations in and around the habo dome activation of earlier lineaments and generation of new lineaments controlled the morphometric evolution of the fault bound block of the region to form the habo dome the undulating topography in addition to the domal shape of the study area resulted from the differential movements along several active transverse faults striking ne sw n s and nw se and the regional faults striking e w the kachchh mainland fault the kas fault and the jikadi fault stress propagations from the himalayan range in the northeast and suleiman range in the northwest are identified to be the causative factors for active tectonics and drainage anomalies in the area

luminescence chronometry and geomorphic evidence of active fold growth along the kachchh mainland fault kmf kachchh india seismotectonic implications abstract the kachchh region of western india is a pericratonic basin experiencing periodic high magnitude earthquakes events in 2001 a catastrophic seismic event occurred at bhuj measuring mw 7 7 the epicenters of both the 1956 and 2001 earthquakes were along the kachchh mainland fault kmf proximal to the eastern end of the northern hill range nhr the latter is a topographic expression of an active fault related fold on the hanging wall and is controlled by a south dipping blind thrust the present study deals with the eastern sector of nhr and uses optical dating to reconstruct the chronology of tectonically caused incisions along the backlimb of the nhr incision ages on channel fills and valley fill terraces progressively decrease from 12 ka to 4 3 ka this age progression along with geomorphic evidences decrease in topographic relief drainage capture and drainage migration across the fold nose suggests an active vertical and lateral fold growth along the kmf optical ages suggest that during the late holocene the average uplift rate along the eastern nhr was 10 1 mm a recent gps based estimates on crustal shortening are 12 mm a the kmf and the south wagad fault swf represent the bounding faults of a transtensional basin that formed during the initial rifting this basin is termed as the samakhiali basin the compressive stresses on account of structural inversion from normal to reverse phase resulted in lobate shaped anticlines along kmf and swf zone these anticlines subsequently coalesced and formed linked and overlap segments the present study suggests that eastward lateral deformation across the eastern portion of kmf has continued and has now resulted in its interaction with a left step over transfer fault called the south wagad master fault swmf this implies an increasing transpersional deformation of the samakhiali basin we therefore suggest that the eastward nhr ridge propagation along kmf resulted in the thrust faulting on the south dipping swmf resulting in the bhuj 2001 event the increasing strain on this basin may cause enhanced seismicity in the future along the eastern kmf and wagad region

sedimentologic and stratigraphic constraints on the orientation of the late triassic northern indian passive continental margin abstract the orientation and distribution of the northern indian passive continental margin basin during different epochs constrained the geometric characteristics of the hyperextended northern indian edge greater india traditional paleogeographic reconstructions envisage the late triassic northern indian passive continental margin as e w trending whereas paleomagnetic data support an 55 counterclockwise rotation during northward drifting this case study of upper triassic units from the northern indian margin based on facies analysis sandstone petrography heavy mineral assemblages u pb detrital zircon geochronology and stratigraphic correlation from the zanskar range to southern tibet provides new constraints and suggests that the northern indian passive continental margin might have been n s trending in the late triassic given the dominance of quartz sandstones with zircon tourmaline and rutile indicating a provenance from continental blocks and the recycling of older quartz rich sandstones and detrital zircon age spectra characterized by a neoproterozoic detrital zircon u pb age peak 921 13 ma the upper triassic sandstones widespread along the tethyan himalayas may have been partly derived from the eastern ghats mobile belt in eastern india and the rayner orogen in eastern antarctica the upper triassic quartzite series comprises feldspatho quartzose to pure quartzose sandstones with intercalated bioclastic oosparites deposited in backshore foreshore and shoreface coastal environments without considering the subsequent counterclockwise rotation of india the consistent pattern of the upper triassic bidirectional e w paleocurrent observed throughout the himalaya suggests that the paleoshoreline was striking near n s approximately perpendicular to the regional orientation of the northern indian margin progressive eastward thickening of the sandstone layers and eastward younging of the quartzite series suggest diachronous sedimentation such stratal patterns and the strike of the late triassic paleoshoreline were attributed to the neo tethys transgression from the zanskar range to southern tibet

active tectonics of eastern segment of the south wagad fault zone kachchh western india abstract the present study describes the active tectonic features of the eastern segment of the south wagad fault zone swfz of the kachchh rift basin krb the swfz defines the southern margin of the wagad uplift with a series of small domes and anticlines forming a low hill range geomorphologically the swfz is expressed by the presence of the south wagad hill range to the north and the south sloping samkhiyali and lakadia plains to the south the easternmost part of the swfz consists of domes and anticlines having a rugged topography which comprises of mesozoic to neogene rocks and is practically unexplored as far as their active tectonic characterizations are concerned the geomorphic expression of the swfz in the eastern segment consists of the gagodar kanmer guan and mardak domes and anticlines they are exposed as a series of linear mounts projected amidst the little rann of kachchh and surrounded by the alluvial sediments of easterly flowing rivers as well as the rann sediments the active nature of the eastern swfz is portrayed by warping flexuring alluvial fans tilted quaternary deposits scarps gullied surfaces slickensides and knickpoints presence of wave cut cliff and notches at mardak bet suggests that the eastern segment of swfz is marginally uplifted during middle to late holocene period we provided a detailed morphotectonic map of the eastern segment of swfz which can be used for future infrastructural development town planning and seismic hazard assessment in the region further the study suggests that the seismically silent eastern segment of the active swfz is capable of generating a large magnitude earthquake similar to the 2001 bhuj earthquake or the 1819 allah bund earthquake in the future owing to long term stress accumulation

life at the top of the greenhouse eocene world a review of the eocene flora and vertebrate fauna from canada s high arctic early middle eocene ca 53 38 ma sediments of the eureka sound group in canada s arctic archipelago preserve evidence of lush mixed conifer broadleaf rain forests inhabited at times by alligators turtles and diverse mammals including primates tapirs brontotheres and hippo like coryphodon this biota reflects a greenhouse world offering a climatic and ecologic deep time analog of a mild ice free arctic that may be our best means to predict what is in store for the future arctic if current climate change goes unchecked in our review of the early middle eocene arctic flora and vertebrate fauna we place the arctic fossil localities in historic geographic and stratigraphic context and we provide an integrated synthesis and discussion of the paleobiology and paleoecology of these eocene arctic forests and their vertebrate inhabitants the abundance and diversity of tapirs and plagiomenids both rare elements in midlatitude faunas and the absence of artiodactyls early horses and the hyopsodontid condylarth hyopsodus well represented at midlatitude localities are peculiar to the eocene arctic the eocene arctic macrofloras reveal a forested landscape analogous to the swamp cypress and broadleaf floodplain forests of the modern southeastern united states multiple climate proxies indicate a mild temperate early middle eocene arctic with winter temperatures at or just above freezing and summer temperatures of 20 c or higher and high precipitation at times this high precipitation resulted in freshwater discharge into a nearly enclosed arctic ocean basin sufficient to cause surface freshening of the arctic ocean supporting mats of the floating fern azolla fluctuating arctic ocean sea level due to freshwater inputs as well as tectonics produced temporary land bridges allowing land plants and animals to disperse between north america and both europe and asia

petro chemical characterisation and depositional paleoenvironment of lignite deposits of nagaur western rajasthan india the objective of this study was to know about the depositional environment and petrographic characteristics of lignite deposits of the nagaur district rajasthan india and to decipher source rock potential lignite samples have been collected from all the working and exposed lignite seams from matasukh lignite mines of nagaur following the pillar sampling method the petrographic study has been done following the international committee for coal and organic petrology and iso norms the study has shown that nagaur lignites are mostly dominated by the huminite group of macerals followed by liptinite group the huminite group is mainly represented by attrinite textinite and ulminite whereas liptinite is represented mainly by primary liptinites such as resinite sporinite suberinite and cutinite an inertinite group of macerals occurs in the least concentration as compared to the huminite and liptinite group macerals and mainly represented by the semifusinite funginite and inertodetrinite in these lignites carbonate mineral matters are dominating over the pyrite and argillaceous mineral matter the maceral constituents present in the studied samples indicate a high proportion of type iii kerogen and are capable of generating gases only based on the reflectance of eu ulminite b maceral nagaur lignites may be classified as low rank b lignite b the study reveals that lignites originated in the bog forest under ombrotrophic to mesotrophic hydrological conditions gelification index and the tissue preservation index suggest an accumulation of peat in the marshy environment

multicyclic history of the northern india continental margin northwestern himalaya 1 the geologic evolution of northern india is best recorded in the stratigraphic succession of the zanskar range northwestern himalaya which represents the most complete transect through this ancient continental margin sedimentary history began in the late proterozoic and recorded a late pan african orogenic event around the cambrian ordovician boundary when the gondwana supercontinent was eventually assembled the following long period of epicontinental deposition in shallow seas linked to palaeo tethys lasted until the early permian when a neo tethyan rift began to open between paleo india and the cimmerian microcontinents neo tethyan history can be subdivided into two sedimentary megasequences both recording a major tectonic and magmatic event in the lower part the first one began with breakup in the late permian and lasted until the end of the jurassic the second one started in the early cretaceous with the final detachment of india from gondwana and the opening of the indian ocean and ended with the india eurasia collision in the early eocene the two megasequences can be in turn subdivided into six transgressive regressive supersequences bounded by tectonically enhanced unconformities basal sandstone units of early permian late permian norian callovian early cretaceous and paleocene age are invariably associated with oolitic ironstones or reworked glauco phosphorites and mark the transgre sive part of each supersequence next condensed nodular carbonates or shales with pelagic fauna are typically overlain by thick shallowing upward marly units capped by regressive platformal carbonates the six tectono eustatic supercycles reflect successive rifting episodes which punctuated the progressive separation of india from the rest of gondwana and document the combination of plate microplate reorganizations and eustatic climatic and oceanographic changes in the tethyan domain after the onset of collision between india and asia close to the paleocene eocene boundary obduction of the remnants of the neo tethys ocean floor onto the indian margin began and the latter underwent multiphase deformation with fold thrust shortening followed by heating and extension after the main metamorphic event ophiolitic nappes were re thrusted and finally emplaced with their sedimentary sole on top of the passive margin succession

palaeoclimatic significance of changes in clay mineralogy across the jurassic cretaceous boundary in england and france abstract clay mineralogical changes across the jurassic cretaceous boundary from the northern to the southern part of western europe show similar patterns in the mudrocks exposed on the yorkshire coast the paralic sediments of the dorset wessex basin and the jura and vocontian trough of s e france this comprises a change from smectite poor sediments in the jurassic with correspondingly abundant illite and kaolinite to sediments with abundant smectite in the jurassic cretaceous boundary beds depleted in kaolinite this change occurs in the oxfordian in the south to latest volgian in the north of the study area kaolinite reappears in abundance in the late ryazanian or stratigraphic equivalent in all the locations studied comparison with other climatic indicators and other areas suggest that these variations can be ascribed to a phase of latest jurassic earliest cretaceous aridity the onset of which appears to be diachronous across w europe possible causes for the climatic change towards aridity are examined the orographic effect of mountains or plateaus to the east of the study area is considered most likely

three dimensional gravity modelling of kutch region india abstract understanding the crustal architecture of kutch rift region india is important due to the presence of thick mesozoic sediments and also due to occurrence of earthquakes we present here three dimensional gravity models the major features of our shallow crustal model are 1 thickness of deccan traps is almost negligible towards northern side of vigodi fault and katrol hill fault 2 mesozoic sediment thickness is about 3 km on the southern side and 3 several undulations in the basement on the wagad uplift the model is consistent with the geological observation that the basin slopes towards southwest the observed bouguer gravity anomalies are explained by 10 km thick granitic upper crust of 2 7 g cm 3 10 km thick intermediate mid crust of 2 82 g cm 3 15 km thick mafic lower crust of 2 91 g cm 3 density crustal thickness is about 40 45 km on wagad uplift and near katrol hill fault the modelled gravity data do not require presence of anomalous amount of fluids melts and or magma chambers in the deep crust of kutch region

structure and tectonics of the southwestern continental margin of india abstract a nnw sse trending graben in the inner shelf 40 60 m isobaths a mid shelf basement ridge 60 150 m isobaths a shelf margin basin 150 1000 m isobaths and the prathap ridge complex in the slope 1000 2000 m isobaths extend as linear features along the southwestern continental margin of india between 12 20 n and 15 00 n the basic structural framework of the margin seems to be influenced by the pre existing precambrian structural fabric of the continent the mid shelf basement ridge and the prathap ridge complex are interpreted as manifestation of the rift phase volcanism when india separated from madagascar around 84 ma

petroleum generation and migration from talang akar coals and shales offshore n w java indonesia abstract the oligocene talang akar formation is the major source for petroleum oil and gas in the ardjuna sub basin source rock quality varies within the deltaic to marginal marine complex with coals deposited on the lower delta plain being distinctly oil prone whereas the surrounding delta plain shales are largely gas prone shales and drifted coals laid down in marine influenced interdistributary bay environments show increasingly oil prone characteristics possibly due to preferential transport of hydrogen rich plant components to more distal setting molecular characteristics of the coals and shales are similar with higher plant angiosperm biomarkers and their aromatic derivatives occuring widely kinetic studies of hydrocarbon generation and stimulated maturation experiments using hydrous pyrolysis indicate that the delta plain coals are the major source for crude oils in the basin with a secondary but minor contribution from marine influenced interdistributary bay shales delta plain shales are interpreted to expel gaseous products only the stratigraphic and spatial location of oil and gas fields were examined with respect to their position relative to oil and gas generating source rocks the field distribution could not be explained in terms of source rock geochemistry alone and phase behavior of petroleum during secondary migration was shown to exert an important influence on the distribution of oil and gas deposits in the basin

rise and demise of the bahama grand banks gigaplatform northern margin of the jurassic proto atlantic seaway abstract an extinct 5000 km long jurassic carbonate platform and barrier reef system lies buried beneath the atlantic continental shelf and slope of the united states a revised stratigraphic framework a series of regional isopach maps and paleogeographic reconstructions are used to illustrate the 42 m y history of this bahama grand banks gigaplatform from its inception in aalenian early middle jurassic time to its demise and burial in berriasian valanginian time early early cretaceous aggradation progradation rates for the gigaplatform are comparable to those of the familiar capitan shelf margin permian and are closely correlated with volumetric rates of siliciclastic sediment accumulation and depocenter migration siliciclastic encroachment behind the carbonate tracts appears to have been an important impetus for shelf edge progradation during the early cretaceous sea level changes combined with eutrophication due to landward soil development and seaward upwelling and the presence of cooler upwelled waters along the outer shelf appear to have decimated the carbonate producers from the carolina trough to the grand banks this allowed advancing siliciclastic deltas to overrun the shelf edge despite a notable reduction in siliciclastic accumulation rates however upwelling did not extend southward to the blake bahama megabank so platform carbonate production proceeded there well into the cretaceous subsequent stepwise carbonate abatement characterized the blake plateau basin whereas the bahamas have maintained production to the present the demise of carbonate production on the northern segments of the gigaplatform helped to escalate deep water carbonate deposition in the early cretaceous but the sudden augmentation of deep water carbonate reservoirs in the late jurassic was triggered by other agents such as global expansion of nannoplankton communities

cool equatorial terrestrial temperatures and the south asian monsoon in the early eocene evidence from the gurha mine rajasthan india abstract early eocene 55 52 ma laminated lacustrine sediments overlying lignites in the gurha mine 27 87398 n 72 86709 e rajasthan india yield a diversity of fossil leaves flowers fruits seeds and insects clamp multivariate foliar physiognomic analysis of two horizons separated by an estimated several tens of thousands of years of deposition indicates cool equatorial 10 n temperatures and a pronounced monsoon signature a lower assemblage consisting of 54 leaf morphotypes and an upper assemblage of 57 leaf forms yielded mean annual temperatures mat of 24 7 and 23 9 c respectively the uncertainty 2 82 c means these temperature regimes are identical despite few similarities in the morphotypes between the two assemblages the mean annual range of temperature mart was approximately 9 7 c for both assemblages when corrected for evapotranspirational cooling these temperature regimes are similar to those experienced today at 10 n on the west coast of india and surprisingly cool for the tropics at a time of extreme global warmth growth was year round the tropical to paratropical fossil floras also suggest a moist regime 80 annual relative humidity and high mean annual precipitation of 1800 mm for both assemblages but with a pronounced wet dry seasonality indicative of a pronounced monsoonal regime the lower assemblage has a stronger monsoon index 11 8 than the upper assemblage 8 8 the two assemblages seem to have been deposited less than 100 ka apart this suggests that not only a pronounced south asian monsoon existed when india and asia first made contact but also a variation in monsoon strength existed that cannot be ascribed to tectonic drivers

oil source correlations as a tool in identifying the petroleum systems of the southern taroom trough australia abstract a geochemical study of crude oils and samples of various permian triassic and jurassic organic rich rock units from the southern taroom trough was undertaken to test the prevailing permian source hypothesis for the petroleum reserves of the bowen surat basin seventy three core and cuttings samples were screened using organic petrography total organic carbon analysis rock eval pyrolysis and solvent extraction saturated and aromatic hydrocarbon fractions of selected source rocks kerogen hydrous pyrolysates and thirteen oils were then analysed by gas chromatography gas chromatography mass spectrometry and isotope ratio mass spectrometry for the purpose of oil to source correlation on the basis of their bulk carbon isotopic compositions and terpane sterane and aromatic biomarker signatures two oil families were identified those oils sourced by the snake creek mudstone and reservoired in the showgrounds sandstone both the middle triassic age at roswin north and rednook are assigned to the snake creek showgrounds petroleum system the remaining oils belong to the blackwater precipice system these originated in the late permian coal measures of the blackwater group but are produced from the precipice sandstone and other reservoir rocks of permian to jurassic age along the southeastern and southwestern margins of the trough

attenuation characteristics of coda waves in mainland gujarat india abstract the attenuation characteristics based on coda waves of mainland gujarat india have been investigated in the present study the broadband waveforms of 53 local earthquakes mw 1 1 3 3 having focal depths in the 6 0 33 6 km range recorded at five stations of mainland gujarat region has been used for the analysis the frequency dependent relationships q q0fn for coda q qc and dependency of coda q on lapse time windows have been determined for the said region the average lapse time dependent coda q relations estimated for the region are qc 87 13 f 1 01 0 06 lapse time 30 s qc 112 20 f 0 94 0 08 lapse time 40 s and qc 120 22 f 0 76 0 07 lapse time 50 s the increase in qc values with lapse time shows the depth dependence of qc as longer lapse time windows will sample larger area the observed quality factor is strongly dependent on frequency and lapse time which indicates that the upper lithosphere is more heterogeneous and seismotectonically active while the lower lithosphere is homogeneous and relatively less active a comparison of the coda q estimated for mainland gujarat region with those of nearby kachchh and saurashtra regions shows that mainland gujarat region is more heterogeneous the rate of decay of attenuation q 1 with frequency for the relations obtained here is found to be comparable with those of other regions of the world though the absolute values differ the obtained relations are expected to be useful for the estimation of source parameters of the earthquakes in the mainland gujarat region where no such relations were available earlier these relations are also important for the simulation of earthquake strong ground motions in the region

palaeoclimate control on sequence stratigraphic patterns in the late jurassic to mid cretaceous with a case study from eastern england abstract sediment supply is a fundamental control on the architecture of sedimentary sequences in clastic depositional environments the volume of sediment being transported into the basin of deposition is strongly dependent on both the nature of the weathering regime in the hinterlands and on runoff during arid low sea level phases in the late jurassic and early mid cretacwous clastic supply was reduced and long hiatuses became common at sequence boundaries or during maximum flooding these hiatuses amalgamated where sediment starvation produced strongly condensed super condensed sections in intervening humid higher sea level phases clastic supply was more abundant hence thick sediment packages separate sequence boundaries downlnpping surfaces should be apparent on seismic sections and condensed sections become rare where carbonate deposition dominates over clastic sediment formation is largely intrabasinal and the effects of palaeoclimate on sequence stratigraphy are less obvious knowledge of palaeoclimates may lead us to search for certain sequence stratigraphic patterns connected to changes in sediment supply

numerical modeling of seismicity and geodynamics of the kachchh rift zone gujarat india abstract the numerical block and fault model of lithosphere dynamics and seismicity bafd is used to understand crustal motion and features of the observed seismicity in the kachchh rift zone gujarat western india the block model allows simulating seismicity and geodynamics simultaneously unlike other modeling approaches for studying seismicity or geodynamics the model structure of kachchh rift zone is composed of seven major crustal blocks separated by fault planes based on the orientation of boundary crustal block movements we develop a set of numerical experiments to analyze the spatial distribution of earthquakes frequency to magnitude relationships earthquake focal mechanisms velocity field and fault slip rates in the model the main results of our modeling suggest that an nnw sse trending compression is a principal driving force in the kachchh rift zone that explains basic features of the regional seismicity direction of block motions and the presence of an extensional stress regime associated with the cambay rift zone large synthetic events occur on the fault segments associated with the allah bund fault katrol hill fault and north wagad fault which have been causative faults for the 1819 mw7 7 allah bund 1956 mw6 0 anjar and 2001 mw7 7 bhuj earthquakes the frequency magnitude distribution for both synthetic seismicity and observed seismicity shows a similar slope the focal mechanisms of the synthetic events are found to be consistent with those of earthquakes in the region a special attention has been paid to study long term and post seismic deformations our results are in a qualitative agreement with the gps post seismic observations in the kachchh rift zone we infer that the observed seismicity and crustal block motions are a consequence of the dynamics of the entire regional fault and block system rather than that of a single causative fault only

the influence of a sudden climatic change on marine deposition in the kimmeridgian of northwest europe a sudden change from humid style to semi arid style deposition markedly affected the accumulation of the upper kimmeridge clay in southern england many of the changes appear to be related to a change in sedimentation rate at this time thus softground faunas are replaced by firmground faunas diagenetic dolostones formed in the methanogenic zone are replaced by sulphate reduction zone carbonate nodules and depositional gradients recorded by lateral biofacies changes becomes steeper the evidence available is in accord with a decline in offshore sedimentation rates during this interval other changes such as a decline in kaolinite abundance were more directly controlled by the drying out of the hinterland similar changes elsewhere in the marine geological record could be used as climatic indicators the climatic change is part of a wider northern hemisphere dry event which affect a broad area in the late jurassic the kimmeridge clay of southern england was one of the last depositional environments to be influenced by the climatic change at this latitude

the effective source rocks in the north cambay basin india abstract source rock screening reveals five laterally extending potential sources ps in the paleogene the pss are sr5 and sr6 in dominantly marine early eocene to late paleocene cambay shale formation and sr7 sr8 9 and sr11 12 in dominantly freshwater early paleocene olpad formation only 3 pss sr11 12 sr8 9 and sr7 have attained vitrinite reflectance of 0 75 at 45 7 and 2 mybp respectively chromatographic and isotope data of oils and ps samples suggest that mainly the olpad source rocks sr7 and sr8 9 contributed to the discovered oils the cambay shale source rocks sr5 and sr6 contrary to the prevalent view possibly have no significant contribution towards the accumulated oils

a transient rise in tropical sea surface temperature during the paleocene eocene thermal maximum the paleocene eocene thermal maximum petm has been attributed to a rapid rise in greenhouse gas levels if so warming should have occurred at all latitudes although amplified toward the poles existing records reveal an increase in high latitude sea surface temperatures ssts 8 to 10 c and in bottom water temperatures 4 to 5 c to date however the character of the tropical sst response during this event remains unconstrained here we address this deficiency by using paired oxygen isotope and minor element magnesium calcium ratios of planktonic foraminifera from a tropical pacific core to estimate changes in sst using mixed layer foraminifera we found that the combined proxies imply a 4 to 5 c rise in pacific sst during the petm these results would necessitate a rise in atmospheric pco 2 to levels three to four times as high as those estimated for the late paleocene

hydrocarbon prospects across narmada tapti rift in deccan trap central india inferences from integrated interpretation of magnetotelluric and geochemical prospecting studies abstract as the mesozoic sediments contribute most of the oil and gas reserves of the world we present an integrated interpretation approach using magnetotellurics mt and surface geochemical prospecting studies to demarcate hydrocarbon prospective gondwana mesozoic formations underneath the deccan flood basalts of late cretaceous age across narmada tapti rift between bhusawal and barwah in central india the mt interpretation shows deep 5 km basement structure between southern and central part of the mt profile however it gradually becomes shallower to either ends of the profile with a predominant basement depth reduction in the northern end compared to the southern end the geophysical results suggest thick 2 3 5 km mesozoic sediments in the area characterized by deep basement structure the geochemical analysis of the near surface soil samples indicate higher concentrations of light gaseous hydrocarbons constituents over the area marked with thick sub basalt mesozoic formations analyses of the geochemical data imply that these hydrocarbons are genetically related generated from a thermogenic source and these samples fall in the oil producing zone the temperature depth estimations in the region supports favorable temperature conditions 80 120 c for oil generation at basement depths

comparison of clay mineral stratigraphy to other proxy palaeoclimate indicators in the mesozoic of nw europe this paper reviews the opportunities and pitfalls associated with using clay mineralogical analysis in palaeoclimatic reconstructions following this conjunctive methods of improving the reliability of clay mineralogical analysis are reviewed the mesozoic succession of nw europe is employed as a case study this demonstrates the relationship between clay mineralogy and palaeoclimate proxy analyses may be integrated with clay mineralogical analysis to provide an assessment of aridity humidity contrasts in the hinterland climate as an example the abundance of kaolinite through the mesozoic shows that while interpretations may be difficult the mesozoic climate of nw europe was subject to great changes in rates of continental precipitation we may compare sedimentological facies mineralogy geochemistry indicators of palaeoprecipitation with palaeotemperature estimates the integration of clay mineralogical analyses with other sedimentological proxy indicators of palaeoclimate allows differentiation of palaeoclimatic effects from those of sea level and tectonic change we may also observe how widespread palaeoclimate changes were whether they were diachronous or synchronous how climate sea level and tectonics interact to control sedimentary facies and what palaeoclimate indicators are reliable

tectonics and thermal structure of western satpura india abstract increased seismicity and occurrences of hot springs having surface temperature of 36 58 c are observed in the central part of india 74 81 e 20 25 n where the ne trending middle proterozoic aravalli mobile belt meets the ene trending satpura mobile belt earlier deep seismic sounding dss studies along thuadara sendhwa sindad profile in the area has showed mesozoic sediments up to around 4 km depth covered by deccan trap and the moho depth with a boundary velocity p n of 8 2 km s in the present study surface heat flow of 48 4 mw m 2 has been estimated based on p n velocity which agrees with the value of heat flow of 52 4 mw m 2 based on curie point isotherms estimates the calculated temperature depth profile shows temperature of 80 120 c at the basement which is equivalent to oil window temperature in mesozoic sediments and around 570 635 c at moho depth of 38 43 km and the thermal lithosphere is about 110 km thick which is comparatively higher than those of adjoining regions the present study reveals the brittle ductile transition zone at 14 41 km depth temperature around 250 600 c where earthquake nucleation takes place

early eocene leaves of northwestern india and their response to climate change abstract today the existence of tropical rainforests in the indian subcontinent is restricted to the fringes of the western ghats greater assam region and some small places in odisha however the palaeovegetation reconstruction in this study illustrates the existence of equatorial tropical forest in northwestern india bikaner rajasthan during the early eocene fossil leaves described here were collected from the gurha lignite mine of bikaner and showed affinities with holigarna grahamii anacardiaceae pterygota alata malvaceae syzygium spp s fruticosum and s cumini myrtaceae and gardenia spp g lucida and g gummiefra rubiaceae contrary to the present day dry and desertic conditions the fossil records provide strong evidence of humid tropical and paratropical evergreen forest with monsoon seasonality existing in and around the study area during the depositional period any shift in climatic conditions has drastic effects on the vegetation cover of a region in time and space this drastic change in climate has led to the extinction of tropical rain forest from this region this might be due to the northward movement of the indian subcontinent away from the equator formation of the himalayas and monsoon or changes in monsoon pattern

fluvial geomorphology and neotectonic activity based on field and gpr data katrol hill range kachchh western india abstract the largely rocky and rugged landscape of the katrol hill range composed of mesozoic rocks and structurally controlled occurrences of quaternary sediments is delimited to the north by north facing range front scarps of the seismically active e w trending katrol hill fault khf the landscape and drainage characteristics of the katrol hill range are documented together with ground penetrating radar gpr investigations along the khf to delineate its nature for understanding neotectonic activity in the contemporary tectonic setting the overall geomorphology is controlled by the south oriented tilt block structure of the range indicated by its pronounced influence on the morphology and drainage network the drainage comprises north flowing and south flowing rivers with the drainage divide located close to the northern edge of the range which also marks the highest topographic elevations the narrow zone between the crest line and the drainage divide has been identified as the zone of gorges where gorges and deeply incised fluvial valleys have been formed within quaternary sediments by the various north flowing streams the quaternary sediments consist of bouldery colluvial deposits in front of the range front scarps valley fill miliolites and alluvial deposits of late pleistocene age within the back valleys and scarp derived colluvium forming the youngest deposit based on the geomorphic and stratigraphic evidence three major phases of quaternary tectonic uplift in the katrol hill range are inferred the oldest pre miliolite phase middle pleistocene was followed by a prominent phase of fluvial incision with formation of gorges during early holocene and then by the last one during late holocene continuing at present uplift of the range occurred in well marked phases during the quaternary in response to differential uplift along the khf under an overall compressive stress regime gpr investigations at selected sites show that the khf is a steep south dipping reverse fault near the surface which becomes vertical at depth this suggests neotectonic reactivation of the khf under a compressive stress regime responsible for active southward tilting of the katrol hill range

occurrences of large magnitude earthquakes in the kachchh region gujarat western india tectonic implications abstract moderate to large damaging earthquakes in the peninsular part of the indian plate do not support the long standing belief of the seismic stability of this region the historical record shows that about 15 damaging earthquakes with magnitudes from 5 5 to 8 0 occurred in the indian peninsula most of these events were associated with the old rift systems our analysis of the 2001 bhuj earthquake and its 12 year aftershock sequence indicates a seismic zone bound by two linear trends nnw and nne that intersect an e w trending graben the bouguer gravity values near the epicentre of the bhuj earthquake are relatively low 2 mgal the gravity anomaly maps the distribution of earthquake epicentres and the crustal strain rate patterns indicate that the 2001 bhuj earthquake occurred along a fault within strain hardened mid crustal rocks the collision resistance between the indian plate and the eurasian plate along the himalayas and anticlockwise rotation of the indian plate provide the far field stresses that concentrate within a fault bounded block close to the western margin of the indian plate and is periodically released during earthquakes such as the 2001 m w 7 7 bhuj earthquake we propose that the moderate to large magnitude earthquakes in the deeper crust in this area occur along faults associated with old rift systems that are reactivated in a strain hardened environment

oil source rock correlation using biological markers norwegian continental shelf abstract oil source rock correlation is an integral part of exploration geochemistry and biomarkers have been used successfully for this purpose this paper reports three case studies which illustrate some of the inherent problems in oil source rock correlations on samples from the norwegian continental shelf in the first study an oil is compared directly with mature source rocks on the structure showing that the oil must have been expelled very early in the second oils are compared with immature source rock units on the structure showing the potential of multivariate analysis for correlation problems finally an unusual barents sea oil is compared with triassic source rocks from spitsbergen it is shown that correlations based on individual characteristics can only be supported in rare cases multivariate analysis is a safer method of correlation of oils to a typical potential source rock of mixed kerogen facies and low maturity

eocene early oligocene climate and vegetation change in southern china evidence from the maoming basin although the eocene oligocene climate transition marks a critical point in the development of the icehouse global climate of the present little is known about this important change in the terrestrial realm at low latitudes our palynological study of the shangcun formation shows it to be early oligocene in age palyno assemblages in the lower part of the formation indicate a cool interval dominated by conifer pollen in the earliest oligocene followed by a warmer regime in the second half of the early oligocene to quantify middle eocene to late early oligocene climate conditions at low 20 n palaeolatitudes in southern asia several thousand leaf fossil specimens from the maoming basin southern china were subjected to a multivariate clamp analysis of leaf form for terrestrial palaeoclimate comparisons to be valid the palaeoaltitude at which the proxy data are obtained must be known we find that leaves preserved in the youganwo middle eocene huangniuling late eocene and shangcun early oligocene formations were likely to have been deposited well above sea level at different palaeoelevations in the youganwo formation fine grained sediments were deposited at an altitude of 1 5 km after which the basin dropped to 0 5 km by the time the upper huangniuling sediments were deposited the basin floor then rose again by 0 5 km reaching an altitude of approximately 1 km in which the shangcun formation fine grained sediments were accumulated within the context of these elevation changes the prevailing climates experienced by the youganwo lower huangniuling upper huangniuling and shangcun fossil floras were humid subtropical with hot summers and warm winters but witnessed a progressive increase in rainfall seasonality by the early oligocene rainfall seasonality was similar to that of the modern monsoonal climate of guangdong province southern china all floras show leaf physiognomic spectra most similar to those growing under the influence of the modern indonesia australia monsoon but with no evidence of any adaptation to today s south or east asia monsoon regimes the upper huangniuling flora rich in dipterocarp plant megafossils grew in the warmest conditions with the highest cold month mean temperature and at the lowest altitude

continental humid and arid zones during the jurassic and cretaceous abstract the global distribution of climatically significant criteria is surveyed for six successive time intervals hettangian toarcian aalenian callovian oxfordian tithonian berriasian barremian aptian cenomanian and turonian maastrichtian the criteria are primarily mineralogical evaporites coals bauxites ironstones and kaolinite but include sedimentological and palaeontological aspects of facies e g aeolian sands fossil ferns and xerophytes fresh water invertebrates in early and mid jurassic times an arid zone can be distinguished in low to mid latitudes in western pangaea with humid zones elsewhere in the late jurassic this arid zone spread northwards to embrace much of southern eurasia there followed in the early cretaceous a sharp reversal to more humid conditions over a large area extending from the eastern margin of north america to the middle east a major consequence of which was the widespread replacement of carbonates by coarse siliciclastic facies by late cretaceous times humid conditions were well established also in north america and the south atlantic margins and the tropical arid zone had contracted to a minimum the 87 sr 86 sr ratio of marine carbonates provides an independent monitor of continental runoff which is related to a area and b extent of aridity changes in the ratio confirm that taking sea level stand into account the late cretaceous was appreciably more humid than the late jurassic these climatic changes are related primarily to the progressive breakup of pangaea in the late jurassic and cretaceous which together with sea level rise in the mid to late cretaceous caused a significant increase in maritime influence this implies that monsoonal winds probably had a major role in promoting higher precipitation rates a puzzle remains as to why there was a spread of aridity in the late jurassic finally some implications for terrestrial plant evolution are noted

application of 3d inversion to magnetotelluric profile data from the deccan volcanic province of western india abstract using synthetic data siripunvaraporn et al 2005b demonstrated possible advantages of interpreting single profile mt data with a three dimensional 3d inversion program here we explore this idea further using real mt data from two profiles on the indian subcontinent the first profile 330 km long cuts across the deccan volcanic province of peninsular india the second 130 km long is in the narmada son lineament zone approximately 100 km further north using the data space occam inversion code of siripunvaraporn et al 2005a 3d inversion is carried out on each of these profiles independently and results are compared with previously published two dimensional 2d interpretations in addition to inversion of the full impedance tensor we consider 3d inversion of only the off diagonal components we also experiment with variants on the model covariance in particular allowing for longer smoothing length scales along the geoelectric strike not surprisingly the 3d inversion finds models that fit the data better than had been possible with the 2d programs many of the features inferred from these previous 2d interpretations are also present in the 3d inverse solutions but the positions and amplitudes of individual conductive features are in some cases changed the 3d models suggest substantial non uniqueness in the single profile data even without explicit or special treatment we find that the relatively modest near surface distortion effects in these datasets were well fit by the 3d inversion by inserting small scale conductive and resistive features in surface layers mostly off profile

outward growth of the tibetan plateau during the cenozoic a review abstract the surface uplift history of the tibetan plateau tp offers a key testing ground for evaluating models of collisional tectonics and holds important implications for processes ranging from global cooling to the onset of the asian monsoon various models have been proposed to reveal the surface uplift history of the tp but controversies remain we evaluate these models using data from sedimentology and stratigraphy structural geology magmatism exhumation and paleoaltimetry studies structural analyses indicate that thrust belts which spread from the central tp outward toward its surrounding margins accommodated most of the india asia convergence and facilitated crustal shortening and thickening in the central tp eocene adakitic rocks located in the qiangtang and the lhasa blocks likely were generated by partial melting of an eclogitic source paleogene 50 30 ma potassic rocks only occur in the qiangtang block whereas late oligocene late miocene 26 8 ma potassic rocks occur both in the qiangtang and lhasa blocks low temperature thermochronologic ages in the central tp are older than 40 35 ma whereas those in the margins are younger than 20 ma mostly late miocene and pliocene pleistocene in age independent paleoaltimetry estimates suggest that the lhasa and qiangtang terranes attained their current elevations during the eocene most likely due to the initial collision between india and lhasa whereas the hoh xil basin area to the north and himalayas to the south were still low even below sea level in the latter case we argue for an inside out growth pattern for the tibetan plateau the tp grew southward and northward from a nucleus of high topography and is likely to continue expanding along the mazar tagh fault to the northwest the kuantai shan hei shan longshou shan to the northeast the longquan shan to the east and the shillong plateau to the south if the northward force of india would not diminished

3d crustal resistivity structure beneath the wagad aftershock zone of the 2001 bhuj earthquake kutch india heterogeneous resistivity structure controlled by widespread fluid infiltration and clues to aftershocks pattern abstract the epicentral region of the 26 january 2001 bhuj earthquake 7 7 m w in the kutch region of india has been experiencing a vigorous and unique intraplate aftershock activity which shows a v shaped pattern and n ne migration along the western margin of the wagad uplift located to the northeast of the mainshock this study presents 3d resistivity structure of the wagad aftershock zone imaged using magnetotelluric mt data to understand the crustal geoelectric structure and subsurface geometry of faults lineaments which could provide critical inputs to evaluate and strengthen the earthquake generation mechanism and aftershocks pattern the obtained 3d conductivity structure showed a thick 3 km and homogeneous conductive 1 30 m layer of tertiary mesozoic sedimentary cover in the area a highly heterogeneous upper and middle crust characterized by a mix of conductive 300 m structures is imaged below the sedimentary cover enhanced conductivity zones showed spatial correlation with the surface trace of various faults lineaments and are interpreted as fluid enriched zones in the crust which play a critical role in earthquake triggering significantly higher fluid enrichment noticed in the crust below two minor faults khadir transverse fault ktf and manfara fault mf which are hitherto considered to have an insignificant role in the seismogenesis of the area the aftershock events seem to occur mostly on the resistive parts of the crust and its pattern shows good alignment with the anomalous conductive zones associated to the above two faults the results provide a strong clue to infer that the ktf and mf have a vital role in the observed aftershock activity and control the v shaped aftershocks pattern

mid holocene extreme hydrological events in the eastern great rann of kachchh western india abstract the present study is an attempt to reconstruct the paleohydrological conditions during the mid holocene in the hyper arid terrain of the northern great rann of kachchh remote sensing detailed field geomorphology sedimentology geochemistry and optical chronology suggests that the fluvial sediments fringing the khadir island were transported locally and deposited during the extreme hydrological events corresponding to the mid to late holocene indian summer monsoon ism variability overall five extreme hydrological events are deciphered during the last 5 ka which broadly correlates with periods of strengthened ism our data indicate that the emergence and decline of the harappan civilization was unrelated to any major fluvial system in the region

evidence for right lateral strike slip environment in the kutch basin of northwestern india from moment tensor inversion studies abstract 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

regional tectonic framework structure and evolution of the western marginal basins of india abstract the kutch saurashtra cambay and narmada basins are pericontinental rift basins in the western margin of the indian craton these basins were formed by rifting along precambrian tectonic trends interplay of three major precambrian tectonic trends of western india dharwar nnw sse aravalli delhi ne sw and satpura ene wsw controlled the tectonic style of the basins the geological history of the basins indicates that these basins were formed by sequential reactivation of primordial faults the kutch basin opened up first in the early jurassic rifting was initiated in late triassic along the delhi trend followed by the cambay basin in the early cretaceous along the dharwar trend and the narmada basin in late cretaceous time along the satpura trend the evolution of the basins took place in four stages these stages are synchronous with the important events in the evolution of the indian sub continent its breakup from gondwanaland in the late triassic early jurassic its northward drifting during the jurassic cretaceous and collision with the asian continent in the early tertiary the most important tectonic events occurred in late cretaceous time the present style of the continental margins of india evolved during early tertiary time the saurashtra arch the extension of the aravalli range across the western continental shelf subsided along the eastern margin fault of the cambay basin during the early cretaceous it formed an extensive depositional platform continuous with the kutch shelf for the accumulation of thick deltaic sediments a part of the saurashtra arch was uplifted as a horst during the main tectonic phase in the late cretaceous the present high thermal regime of the cambay bombay high region is suggestive of a renewed rifting phase

early and mid jurassic molluscan biogeography and the establishment of the central atlantic seaway abstract a new analysis of lower and middle jurassic bivalve faunas of western north america and the southern andes in comparison to europe supported by evidence from other molluscs throws further light on the establishment of a central atlantic epicontinental seaway prior to the formation of a true oceanic strait between eastern north america and africa south america some restriction to free communication persisted until the early callovian but there was an episode of relatively free intermigration in the toarcian to early bajocian time interval which is associated with major rise of sea level one of the most significant consequences of this event was a spread into northwest europe of taxa which were previously confined to the pacific margins to occupy niches vacated as a result of an early toarcian extinction event

magnetotelluric study to characterize kachchh mainland fault kmf and katrol hill fault khf in the western part of kachchh region of gujarat india abstract the kachchh mainland fault kmf is a major e w trending fault in the kachchh region of gujarat extending 150 km from lakhpat village in the west to the bhachau town in the east the katrol hill fault khf is an e w trending intrabasinal fault located in the central region of kachchh basin and the south of kmf the western parts of both of the faults are characterized and the sediment thickness has been estimated in the region using a magnetotelluric mt survey at 17 sites along a 55 km long north south profile with a site spacing of 2 3 km the analysis reveals that the maximum sediment thickness is 2 3 km quaternary tertiary and mesozoic in the region out of which the mesozoic sediments feature a maximum thickness of 2 km the estimated sediment thickness is found consistent with the thickness suggested by a deep borehole depth approx 2 5 km drilled by oil and natural gas corporation ongc at nirona northern part of the study area from 2 d inversion of the mt data three conductive zones are identified from north to south the first conductive zone is dipping nearly vertical down to 7 8 km depth it becomes north dipping below 8 km depth and is inferred as kmf the second conductive zone is found steeply dipping into the southern limbs near manjal village 28 km south of nirona which is inferred as the khf a vertical dipping down to 20 km depth conductive zone has also been observed near ulat village located 16 km north of manjal village and 12 km south of nirona village this conductive zone becomes listric north dipping beyond 20 km depth it is reported first time by a geophysical survey in the region

the 2001 bhuj earthquake tomographic evidence for fluids at the hypocenter and its implications for rupture nucleation 1 the january 26 2001 bhuj earthquake mw 7 6 is one of the most catastrophic indian earthquakes we have investigated the 3 d seismic velocity and poisson s ratio structures of the bhuj source area to understand the probable cause of triggering the earthquake we used 1948 p and 1865 s wave high quality arrival times from 331 aftershocks recorded at a temporary seismic network significant variations up to 5 in velocity and 10 in poisson s ratio are revealed in the aftershock area the mainshock is located in a distinctive zone characterized by high vp low vs and high poisson s ratio in the depth range of 20 to 30 km and extending 15 to 30 km laterally this feature is very similar to that of the 1995 kobe earthquake zhao et al 1996 the anomaly may be due to a fluid filled fractured rock matrix which might have contributed to the initiation of the bhuj earthquake

crustal structure of the gujarat region india new constraints from the analysis of teleseismic receiver functions abstract in this study receiver function analysis is carried out at 32 broadband stations spread all over the gujarat region located in the western part of india to image the sedimentary structure and investigate the crustal composition for the entire region the powerful genetic algorithm technique is applied to the receiver functions to derive s velocity structure beneath each site a detail image in terms of basement depths and moho thickness for the entire gujarat region is obtained for the first time gujarat comprises of three distinct regions kachchh saurashtra and mainland in kachchh region depth of the basement varies from around 1 5 km in the eastern part to 6 km in the western part and around 2 3 km in the northern part to 4 5 km in the southern part in the saurashtra region there is not much variation in the depth of the basement and is between 3 km and 4 km in gujarat mainland part the basement depth is 5 8 km in the cambay basin and western edge of narmada basin in other parts of the mainland it is 3 4 km the depth of moho beneath each site is obtained using stacking algorithm approach the moho is at shallower depth 26 30 km in the western part of kachchh region in the eastern part and epicentral zone of the 2001 bhuj earthquake large variation in the moho depths is noticed 36 46 km in the saurashtra region the crust is more thick in the northern part it varies from 36 38 km in the southern part to 42 44 km in the northern part in the mainland region the crust is more thick 40 44 km in the northern and southern part and is shallow in cambay and narmada basins 32 36 km the large variations of poisson s ratio across gujarat region may be interpreted as heterogeneity in crustal composition high values of 0 30 at many sites in kachchh and few sites in saurashtra and mainland regions may be related to the existence of high velocity lower crust with a mafic ultramafic composition and locally to the presence of partial melt the existing tectono sedimentary models proposed by various researchers were also examined

the present day state of tectonic stress in the offshore kutch saurashtra basin india abstract exploration activity in the kutch saurashtra area has drawn major attention and because of the recent hydrocarbon discoveries offshore kutch saurashtra basin is now moved from category iii to ii accurate understanding of the full present day stress tensor and pore pressure is critical for field development in this study pore pressure stress magnitudes and horizontal stress direction have been estimated from high resolution geophysical logs and various direct downhole measurements recorded in the studied offshore exploratory wells extensive availability of subsurface pressure measurements confirms hydrostatic pore pressure in the tertiary sediments magnitudes of vertical minimum and maximum horizontal stresses indicate a strike slip tectonic stress regime wellbore breakouts of a c qualities have been identified in density image logs and four arm caliper logs indicating a nne trend n10 e to n20 e of shmax maximum horizontal stress the same has been confirmed from shear wave anisotropy analysis as well the interpreted stress direction is in good agreement with the world stress map data available from the adjacent area this study is significant in understanding the subsurface behavior during drilling reservoir modeling future well stimulation and production optimization

early alkaline magmatism in the deccan traps implications for plume incubation and lithospheric rifting abstract significant lithospheric extension which usually accompanies continental flood volcanism has been generally thought to always follow the main volcanic episode however plume derived uncontaminated early alkaline magmas from the deccan traps india indicate considerable lithospheric extension 3 million yrs my before the main tholeiitic phase indeed such early alkaline magmatism known from many flood basalt provinces of the world seems a necessary and natural consequence of plume head incubation with lithospheric doming and rifting

low latitude vegetation and climate dynamics at the paleocene eocene transition a study based on multiple proxies from the jathang section in northeastern india abstract we present a multi proxy study of an upper paleocene lower eocene succession from the paleo equatorial region the study is carried out on a coal bearing shallow marine succession exposed at jathang east khasi hills meghalaya northeastern india the succession was deposited in a low energy coastal marsh bay complex dinoflagellate cyst biostratigraphy yields a late paleocene to early eocene age for the section the deposits of the lower part of the succession represent a transgressive systems tract tst defined by seven parasequences each starting with bay sediments deposited during transgression followed by a shallowing upward bay fill marsh deposit in the vertical succession each parasequence acquires an increasingly marine character culminating in a maximum flooding surface at the paleocene eocene boundary it is followed by four shallowing upward parasequences deposited in a highstand systems tract hst enhanced chemical weathering and high terrestrial supply are testified by raised sio2 and al2o3 contents and high percentages of terrestrial palynomorphs the pollen flora recovered from the jathang section was used for quantitative paleoclimate and vegetation reconstructions the coexistence approach was applied based on nearest living relatives nlrs of sixty fossil species recorded at different stratigraphic levels seven climate variables were determined for the fossil assemblages and as a measure of the seasonality of climate the number of dry months was estimated our study shows that during the paleocene there existed warm seasonally dry tropical climate conditions with mean annual temperature at ca 24 26 c and mean annual precipitation at ca 700 1800 mm and with a dry season of 5 6 months particularly warm and wet perhumid climate conditions with 26 27 c and 2200 3200 mm mean annual precipitation with a dry period of 2 3 months were reconstructed for the latest paleocene earliest eocene interval the study shows a distinct vegetational turnover from palm dominated seasonally dry tropical forest during the paleocene to highly diversified dicotyledonous megathermal rainforest during the latest paleocene early eocene the present study demonstrates that the reduced duration of the dry period during the latest paleocene earliest eocene due to a more active hydrological cycle played a major role in determining the climate and shaping the vegetation cover in the paleo equatorial region there is evidence from our data that seasonality of rainfall is the determining factor for the tropical forest vegetation pattern of the equatorial region rather than mean annual rainfall condition as the main trigger for the observed step wise changes of the hydrology along the studied succession the fast northward movement of the indian plate is inferred

bicadinanes in oils from the surma basin bangladesh abstract bicadinanes c 30 pentacyclic triterpanes have only been reported in crude oils and sediment extracts from s e asia the present investigation indicates that they are also widely present in land plant derived tertiary oils from the surma basin of n e bangladesh oleanane is also abundant in these oils though its distribution does not correlate with those of the bicadinanes this is consistent with separate specific land plant sources for these two classes of triterpanes and with the formation of bicadinanes during maturation of polymerised angiosperm tree resin

the palaeodelta of the proto vatrak and proto mahi rivers of northeastern gujarat india a remote sensing interpretation abstract detailed remote sensing studies carried out in northeastern gujarat india suggest that there has been a major change in the drainage system as evidenced by the presence of a large palaeo delta system the area is drained by two major rivers the mahi and vatrak originating from the aravalli hills to the east which discharge into the gulf of cambay in the indian ocean major lineaments palaeodrainage patterns and palaeodeltas of the vatrak and mahi rivers were delineated these were large rivers in the past with a high discharge and floodplains which were 5 10 km wide most of the palaeodrainage follows the ne sw precambrian lineaments faults indicating their structural control reactivation of these lineaments and differential uplift of the aravalli hills resulted in increased transportation of the eroded sediments and deposition of more than 5 km thick sediments into the tarapur block of the cambay basin the gulf of cambay extended up to the limbasi sojitra petlad area during the quaternary there are implications for petroleum exploration in the sense that the results when integrated with subsurface geological and geophysical data help to delineate the reservoir facies suitable for petroleum exploration along the eastern margin of the tarapur block