stratigraphy composition and form of the deccan basalts western ghats india in the western ghats between latitudes 18 20 n and 19 15 n 7000 km2 of deccan basalt have been mapped with the primary objective of establishing a flow stratigraphy as a guide to the volcanic history of the flood basalts using over 70 measured vertical sections major and trace element analyses of nearly 1200 samples and rare earth and87sr 86sr determinations for over 60 samples we divide the basalt into three subgroups and ten formations in this paper we describe the seven principal formations in the area and the most prominent individual flows

upheavals during the late maastrichtian volcanism climate and faunal events preceding the end cretaceous mass extinction abstract the late maastrichtian was a time of major climate evolution and extinction extremes rapid climate warming of 2 3 c in intermediate waters between 69 5 and 68 ma top c31r to base c30n accompanied maximum evolutionary diversification 43 increase zone cf5 to low cf4 in planktic foraminiferal history followed immediately by a cluster of extinctions during the last 250 ky of the maastrichtian c29r zones cf2 cf1 rapid warming of 4 c in intermediate waters and 8 c on land resulted in high stress environments ending in the mass extinction the end cretaceous mass extinction is recorded in sediments between massive deccan lava flows in india and attributed to so 2 and co 2 outgassing leading to ocean acidification the early late maastrichtian climate and faunal upheavals are not well known here we document the faunal similarities of both events from the indian ocean through the tethys and gulf of mexico results show that both extreme warm events are marked by high stress environments characterized by decreased abundance and diversity of large specialized species and dwarfing high abundance of low oxygen tolerant species and disaster opportunist surface dweller guembelitria blooms the similarity in faunal response with the deccan warming of c29r cf2 cf1 suggests that volcanism was also responsible for the warming and faunal upheaval of the early late maastrichtian major volcanic activity at this time included the onset of deccan eruptions and ninetyeast ridge volcanism the role of the chicxulub impact appears to have been a contributing rather than causal factor in the mass extinction

tectonic setting and timing of the final deccan flood basalt eruptions the role of extensional tectonics in the generation of basaltic melt and eruption of continental flood basalts is controversial and yet it remains crucial to understanding the origin and cause of these large volume eruptions establishing the timing of lithospheric extension continental rifting and the onset of continental flood basalt volcanism is therefore of importance to petrogenetic models detailed mapping along the mumbai coast india reveals three chemically distinct sets of dikes which together with high precision 40 ar 39 ar dating demonstrate the temporal relationship between lithospheric extension and deccan volcanism the east west extension evident along the west coast of india which led to the separation of the seychelles from the indian plate only began during the final phases of the basalt eruptions and cannot have initiated the large volume eruptions of the deccan flood basalt province

relating petroleum system and play development to basin evolution west african south atlantic basins abstract sedimentary basins can be classified according to their structural genesis and evolutionary history and the latter can be linked to petroleum system and play development we propose an approach in which we use the established concepts in a new way breaking basins down into their natural basin cycle division then defining the characteristics of each basin cycle including the type of petroleum systems and plays they may contain and comparing them with similar basin cycles in other basins thereby providing a means to learn through a greater population of perhaps not immediately obvious analogues furthermore we introduce the use of the trajectory plot as a new tool in such an analysis this methodology has been applied to the west african south atlantic marginal basins between cameroon and angola and we demonstrate that the similar tectonostratigraphic evolution of the individual basins along this margin has led to the development of similar types of petroleum systems and play level s consequently we can make analogue comparisons among these basins in order to evaluate and predict the presence of potential yet undiscovered hydrocarbon accumulations in less well explored parts of the margin

high frequency seismic noise characteristics at the four united kingdom type arrays the noise spectra are described from 0 3 to 8 hz for the united kingdom uk type medium aperture arrays eka yka gba and wra these arrays have been operating in the same configuration since the mid 1960 s and therefore provide a unique source of high quality data for frequencies in this range the array noise spectra are compared to spectra recorded at sites lajitas norsar and rstn specifically selected for high frequency signal recording at nearly all of these stations and arrays borehole or near surface the characteristic noise spectrum follows a linear trend above 2 hz with displacement amplitude slope varying from f 1 7 to f 2 5 the gba spectrum is an exception in that it flattens above 4 hz apparently due to locally generated high frequency noise trapped near the surface this shows that spectral flattening is not an infallible indicator of system noise contamination system noise imposes no significant limitation on the ability to recover seismic signal or noise spectra to at least 8 hz for eka gba and yka the wra seismic noise spectra are contaminated by system noise above 3 to 4 hz apparently due to transmission link problems it seems likely that borehole seismometers at yka gba and wra would achieve noise levels between those recorded at norsar and the very quiet lajitas site i e similar to those at the quieter rstn sites rsnt rson and rssd

stratospheric circulation features deduced from sams constituent data abstract stratospheric circulation is investigated by further analyses of three years of stratospheric and mesospheric sounder sams data eddy effects on constituent transport are investigated with two transport formulations the transformed eulerian mean formulation and the effective transport formulation the transformed eulerian mean formulation together with calculated residual mean winds v w is used to delineate regions or times of significant eddy contributions to constituent transport significant regions are found in the stratosphere in all seasons not only in the northern hemisphere nh winter high latitudes where contributions from nonlinear and nonsteady perturbations in sudden and final warming events are expected but also in the midlatitude middle stratosphere in autumn and at winter summer low latitudes near the stratopause questionably large calculated 0 1 m magnitudes near the stratopause during solstice suggest that the use of residual winds calculated here may be i

elemental and nd sr pb isotope geochemistry of flows and dikes from the tapi rift deccan flood basalt province india abstract the deccan traps are a large rift associated continental flood basalt province in india parts of which have been studied extensively in terms of geochemistry palaeomagnetism and stratigraphy however the basalts of the tapi rift in the central part of the province have been little studied thus far two ene wsw trending tectonic inliers of the deccan basalts in this region forming ridges rising from younger alluvium are made up of basalt flows profusely intruded by basaltic dikes both of these ridges lie along a single lineament although they are not physically continuous the flows are aphyric plagioclase phyric and giant plagioclase basalts and the dikes are aphyric or plagioclase phyric we consider the two inliers to have been originally continuous from the presence of bouldery remnants of a major dioritic gabbro dike along both samples of this dike from both ridges have previously yielded typical deccan ages of 65 6 0 5 ma and 65 6 0 6 ma by the 40 ar 39 ar incremental heating technique initial 87 sr 86 sr ratios and end t values and present day pb isotopic ratios of most dikes indicate that they are isotopically similar to lavas of the mahabaleshwar and panhala formations of the western ghats about 450 km to the south their mantle normalized trace element patterns have small pb and ba peaks one dike has a strong bushe formation affinity and a nd sr isotopic composition more extreme than that of any other deccan rock yet sampled with end t 20 2 and 87 sr 86 sr t 0 72315 its mantle normalized element pattern shows large pb th and u peaks and large nb ta troughs its elemental and isotopic chemistry reflects substantial continental contamination the flows cut by the mahabaleshwar type dikes are isotopically similar to the poladpur formation lavas of the western ghats their mantle normalized element patterns show modest peaks at rb ba and pb and rather low nb and ta relative to la indicating that they have been contaminated to intermediate degrees the mantle normalized element patterns of all the flows and dikes show enrichment in the light rare earth elements with small or no eu anomalies the entire flow dike sequence is similar to the wai subgroup of the western ghats in terms of its elemental and isotopic chemistry and stratigraphic relationships wai subgroup like lavas i e some of the younger magma types originally identified from the southern part of the western ghats are previously known from the central northern and northeastern deccan and many have been thought to be far travelled flows erupted in the southwestern deccan although at least the dikes and probably the giant plagioclase basalt flows of our study area are locally generated and emplaced our new data extend the known outcrop area of these widespread magma types substantially and these magma types indeed appear to have a nearly province wide distribution

the roza member columbia river basalt group a gigantic pahoehoe lava flow field formed by endogenous processes we present studies on the physical volcanology of the 15 ma roza member of the wanapum formation in the columbia river basalt group the roza member represents a compound pahoehoe flood basalt lava flow field with an area of 40 300 km 2 and a volume of 1300 km 3 it consists of 4 major lava flows each composed of numerous decimeter to kilometer long pahoehoe lobes roza lavas feature a wide range of pahoehoe surface structures such as lava rise plateaus tumuli and surface breakouts and we illustrate that the lava morphology is inconsistent with previous proposals of rapid emplacement for these lavas an integral component of the roza flow field is the sheet lobe with internal structures identical to those of inflated pahoehoe sheet lobes from hawaii and iceland both at the same scale and at much larger scales we identify a three part division of the sheet lobes into basal crust lava core and lava crust which are interpreted as the equivalent to the bottom crust the liquid lava core and the surface crust of an active inflating pahoehoe lobe the upper lava crust grows continuously during lava emplacement and its growth rate can be approximated by conductive cooling this relationship is used to calculate the emplacement time for individual roza sheet lobes and to derive a first order estimate on the duration of the roza eruption the results indicate that the emplacement of individual roza lobes lasted for months to years and that the lava flow field was constructed over a period of at least 14 years we propose that the roza flows achieved great areal dimensions and thicknesses by inflation and endogenous growth as the lava flowed from vent to flow front it traveled under an insulating crust which maintained cooling rates of 0 1 c km and allowed for efficient transport of lava over distances up to 300 km

seismic noise in northcentral north carolina ambient seismic noise in the frequency range 0 5 to 7 hz is investigated for a portion of northcentral north carolina three component digital data were collected as part of the state s bid for the superconducting super collider stations were established along the proposed collider ring position and were intentionally located near sources of transient vibration the absence of transient vibrations over all or a significant portion of the recording interval at six stations allowed seismic noise to be investigated noise spectra display similarities in shape all spectra decay with approximately constant slope roughly f 3 below 1 hz and all flatten in the frequency range 2 to 3 hz vertical component spectra decay with roughly constant slope f 2 1 for f 4 hz at most stations spectral levels for horizontal components are greater than vertical component levels for f 4 hz vertical component spectra are similar in shape and magnitude to vertical spectra computed for rstn station rscp the most likely source for the ambient seismic noise is higher mode surface waves produced by cultural activity ambient noise cannot be attributed to system noise or to the direct effects of traffic higher mode surface waves are suggested by low coherence values computed for orthogonal components and extremely complex particle motion diagrams large horizontal particle motions and high spectral levels for horizontal components suggest that a significant portion of the noise particularly for f 4 hz is being produced by love waves rayleigh waves contribute to the noise in the band 2 to 3 hz

cosmic markers 40ar 39ar dating and paleomagnetism of the kt sections in the anjar area of the deccan large igneous province abstract bhandari et al bhandari et al geophys res lett 22 1995 433 436 bhandari et al geol soc am spec paper 307 1996 417 424 reported the discovery of iridium bearing sediments sandwiched between basalt flows in the anjar area kutch province india they concluded that the signature of the k t impact had been recorded and that onset of volcanism in the deccan traps preceded the k t boundary excluding the possibility of a causal connection this paper reports complementary analyses of anjar outcrops by a joint indo french team where we focused on cosmic markers iridium and spinels in the intertrappean sediments and 40ar 39ar dating and paleomagnetism of the lava flows anomalous ir concentrations up to 0 4 ng g are confirmed with up to three thin and patchy enriched layers which cannot be traced throughout the exposed sections despite careful search no ni rich spinels were found eight basalt samples provided 40ar 39ar results four on plagioclase bulk samples four on whole rocks spectra for whole rocks all indicate some amount of disturbance and ages based on plagioclase bulk samples seem to be consistently more reliable hofmann et al earth planet sci lett 180 2000 13 28 the three flows underlying the ir bearing sediments are dated at 66 5 ma and two overlying flows at 65 ma magnetic analyses both thermal and by alternating fields uncovered clear reversed primary components in the upper flows and more disturbed normal components in the lower flows with evidence for an additional reversed component there are reports bajpai geol soc india mem 37 1996 313 319 bajpai j geol soc london 157 2000 257 260 that the intertrappean sediments contain uppermost maastrichtian dinosaur and ostracod remains above the uppermost ir bearing level and may not be mechanically disturbed we propose the following scenario to interpret these multiple field and analytical observations deccan trap volcanism started within uppermost maastrichtian normal chron c30n at 66 5 67 ma in the anjar area volcanism then stopped at least locally and lacustrine sediments were deposited over a period that could be in the order of 1 2 ma the k t bolide impact was recorded as a deposit of ir and possibly though not necessarily spinels volcanism resumed shortly after the k t boundary within reversed chron c29r as witnessed by the three reversely magnetised overlying basalt flows dated 65 ma this was responsible for erosion and destruction of part of the uppermost sediments including spinels if there were any and heterogeneous and non uniform redeposition of ir at a number of underlying sedimentary levels this was also responsible for the partial remagnetisation of the underlying flows these findings generally confirm and complement those of bhandari et al bhandari et al geophys res lett 22 1995 433 436 bhandari et al geol soc am spec paper 307 1996 417 424 and are compatible with the occurrence of the k t impact at the paleontological k t boundary and of deccan trap volcanism straddling the boundary and starting before the impact anjar provides evidence for minor volcanism somewhat earlier than suggested by some authors though still within normal chron c30n there is no indication contradicting the view that the bulk of deccan trap volcanism occurred over only three chrons c30n c29r c29n courtillot evolutionary catastrophes the science of mass extinctions cambridge university press 1999 courtillot et al earth planet sci lett 80 1986 361 374 vandamme et al rev geophys 29 1991 159 190

volcanological and tectonic control of stratigraphy and structure in the western deccan traps many of the world s flood basalt provinces form elevated plateaux at the margins of continents although in most cases their present large elevation is not the result of mountain building processes several explanations have recently been put forward to explain such occurrences of epeirogeny the deccan trap basalt province forms one such elevated plateau and results are presented here showing how the epeirogenic uplift in this region combined with crustal subsidence probably associated with the rifting of the indian continental margin has affected the structure of the basalt sequence trace element analytical data are used for samples from numerous vertical sections through the deccan traps lava series along and around the western ghats ridge in india the results reinforce the previously defined stratigraphy of the mahabaleshwar area and extend it over a region covering some 36 000 km2 reaching as far south as belgaum and the trap basement contact these results show that the lava pile is not flat lying but forms a very low amplitude anticlinal fold structure plunging southwards by up to 0 3 over most of the area although in the south there is evidence of a reversal of this plunge the fold is interpreted as being the result of two tilting processes 1 westward tilting near the coast due to the foundering of the passive continental margin and 2 epeirogenic uplift along the whole west coast of india producing the observed topography and the peninsula wide drainage patterns and also the easterly component of dip variations in the magnitude of the latter effect along the western continental margin may also be important in generating the plunge of the fold although the possibility of some component of depositional dip may also be important this latter possibility can be modelled using a simple computer program the results of this modelling show that a migrating linear volcanic edifice fits the observations best

magnetostratigraphy and 40ar 39ar geochronology of the malwa plateau region northern deccan traps central western india significance and correlation with the main deccan large igneous province sequences abstract basaltic lava flows of malwa plateau together with the mandla area and the toranmal section constitute the northern deccan province in central western india with the present outcrop area of 80 000 km2 the malwa flows form an extensive but relatively thin sequence we sampled deccan basalts along two 100 km each n s and e w transects along the western and southern rims of the malwa plateau the 67 12 0 44 ma 40ar 39ar age obtained in the present study clearly shows that the eruption of the malwa flows started during the magnetochron c30n by mapping the magnetic c30n c29r transition on the western and southern edge of the plateau the total volume and eruption rate can be calculated 42 000 km3 0 03 km3 a furthermore the results point towards the narmada tapi rift zone as the possible source area for the malwa lava flows the malwa sequence is older and partly synchronous with the thick sequences of the western ghats since their eruption centers are spatially independent they should not be correlated with younger although geochemically similar formations of the western ghats other northern deccan flows show clear similarities with the malwa flows and can be magnetostratigraphically and geochemically correlated we therefore suggest a new subgroup for the northern deccan province the narmada subgroup defined on the geochemical and magnetic characteristics of the malwa mandla and toranmal flows the introduction of this new subgroup clarifies the position of the northern deccan province in the deccan stratigraphy and is a step towards a better understanding of the deccan eruption history

high frequency seismic noise as a function of depth abstract evidence is presented supporting the view that high frequency seismic noise decreases with increased depth noise amplitudes are higher near the free surface where surface wave noise cultural noise and natural wind induced noise predominate data were gathered at a hard rock site in the northwestern adirondack lowlands of northern new york between 15 and 40 hz noise levels at this site are more than 10 db less at 945 m depth than they are at the surface and from 40 to 100 hz the difference is more than 20 db in addition time variability of the spectra is shown to be greater at the surface than at either 335 or 945 m depths part of the difference between the surface and subsurface noise variability may be related to wind induced noise coherency measurements between orthogonal components of motion show high frequency seismic noise is more highly organized at the surface than it is at depth coherency measurements between the same component of motion at different vertical offsets show a strong low frequency coherence at least up to 945 m vertical offsets as the vertical offset decreases the frequency band of high coherence increases

analysis of anthropogenic and natural noise from multilevel borehole seismometers in an urban environment auckland new zealand abstract two short period seismometers were permanently installed at depths of 26 and 383 m beneath the eden park stadium in central auckland in october 2008 and incorporated into the auckland volcano seismic network in 2011 these borehole seismometers were temporarily augmented by a surface sensor to characterize the site response at this location despite the borehole installations seismic monitoring is challenging in this urban environment due to high anthropogenic noise that superimposes the earth s signal we analyze the power spectral density of continuous noise records over long and short time periods to quantify the reduction in noise with depth and the effect of temporal noise variations on the detection capabilities for earthquakes and volcanic tremor we identify natural and anthropogenic noise sources that temporarily elevate noise levels by 10 15 db using records from the rugby world cup matches held at the eden park stadium and by comparing records of daytime versus nighttime periods and windy versus calm days characterization of these noise sources shows that the frequency ranges of traffic and train noise at this site overlap 1 35 hz and 8 35 hz respectively however they exhibit distinct maxima at peak frequencies of 7 and 26 hz modeling of the structure beneath the stadium shows that the noise spectrum generated by the nearby train excites frequencies within the topmost waitemata sequences that get efficiently trapped in the low velocity waveguide beneath the 20 m thick basalt layer at the surface although the shallow borehole sensor generally shows a noise improvement of 5 db in comparison to the surface sensor it exhibits higher noise levels in the 8 35 hz frequency range due to the trapped noise waves wind causes increased microseismic noise at 0 1 1 hz that is coherent at all depth levels and shows the most pronounced time variation online material figures of earthquake and quarry blast locations spectrogram and coherency

geochemical stratigraphy of deccan flood basalts of the bijasan ghat section satpura range india abstract the 240 m thick bijasan ghat section exposes deccan basalt flows and dykes that have major and trace element compositions suggestive of variable amounts of contamination by continental material most flows and a dyke are chemically similar to lavas of the poladpur formation in the southwestern deccan one flow and one dyke are similar to lavas of the bushe formation in the southwest and one dyke is similar to lavas of the mahabaleshwar formation in the southwest the type sections of these formations are located 350 km to the south of bijasan ghat but many poladpur type lavas a few mahabaleshwar like lavas and dykes and a few broadly bushe like lavas and dykes have recently been identified in the satpura region lavas resembling the thick ambenali fm of the southwest are absent from bijasan ghat and nearby areas our data further extend the known outcrop area of poladpur like flows estimated at 3 105 km2 one of the most widespread deccan magma types seven giant plagioclase basalt flows encountered in seven different sections in this region cannot unambiguously be correlated at present either physically or chemically and therefore are of little use in deciphering the complicated stratigraphic and structural make up of the regional lava pile

stratigraphy and volcanic facies architecture of the torres syncline southern brazil and its role in understanding the parana etendeka continental flood basalt province abstract the torres syncline is a large structure that constitutes the eastmost outcrop of the parana etendeka cfb in south american side and this work focuses the stratigraphy and facies architecture of the volcanic pile in the syncline the volcanic sequence along the study area permits the division of three regions main valley intermediate zone and south hinge each of them with distinct stratigraphy which probably reflects the structural evolution of the syncline the stratigraphy of the torres syncline is composed by 1 botucatu palaeoerg 2 basic volcanic episode i 3 basic volcanic episode ii 4 acidic volcanic i 5 basic volcanic episode iii and 6 acidic volcanic episode ii the five volcanic episodes recognized in study area can be related to five volcanic facies architecture compound braided tabular classic tabular lobate escoriaceous dome field acidic lavas and tabular flows acidic lavas the basic episode i is composed by pahoehoe flows with a compound braided facies architecture that covered the botucatu palaeoerg the basic episode ii is a tabular classic facies architecture predominantly composed by simple flows 10 20 m thick reaching the total thickness of 500 m in main valley the acidic episode i is exposed in main valley and south hinge and is composed by acidic lavas forming lava dome field facies architecture with a thickness of 150 m the basic episode iii is predominantly constituted by a flows with tabular lobate escoriaceous facies architecture the acidic episode ii is constituted by tabular flow volcanic facies acidic flows and outcrops all along the study area the torres syncline constitute the eastmost on shore exposures of the parana etendeka cfb in south american side and detailed stratigraphic volcanological and structural studies in these area coupled with correlation with huab basin nw namibia africa will aim the understanding of the gondwana breakup process and the early stages of the south atlantic margin opening

a comparison of the high frequency 1 hz surface and subsurface noise environment at three sites in the united states abstract surface and subsurface high frequency 1 hz noise data were recorded using nearly identical instrumentation at three widely separated sites in the united states amarillo texas datil new mexico and pinedale wyoming for extended periods of time under varying wind conditions while the sites are geologically distinct the near surface noise environments have many common features that we believe may be due in large part to the presence of a surficial layer of highly attenuative unconsolidated material at each site noise levels seen at or near the surface 5 m or less are much higher up to 30 db and much more variable power range up to 44 db than those seen at depth the smallest range was 9 db for 1951 m at amarillo the greatest gains in noise level reduction are realized within the first 100 m and probably much shallower

correlation of the deccan and rajahmundry trap lavas are these the longest and largest lava flows on earth abstract we propose that the rajahmundry trap lavas found near the east coast of peninsular india are remnants of the longest lava flows yet recognized on earth 1000 km long these outlying deccan like lavas are shown to belong to the main deccan traps several previous studies have already suggested this correlation but have not demonstrated it categorically the exposed rajahmundry lavas are interpreted to be the distal parts of two very large volume p hoehoe flow fields one each from the ambenali and mahabaleshwar formations of the wai sub group in the deccan basalt group eruptive conditions required to emplace such long flows are met by plausible values for cooling and eruption rates and this is shown by applying a model for the formation of inflated p hoehoe sheet flow lobes the model predicts flow lobe thicknesses similar to those observed in the rajahmundry lavas for the last 400 km of flow the lava flows were confined to the pre existing krishna valley drainage system that existed in the basement beyond the edge of the gradually expanding deccan lava field allowing the flows to extend across the subcontinent to the eastern margin where they were emplaced into a littoral and or shallow marine environment these lavas and other individual flow fields in the wai sub group may exceed eruptive volumes of 5000 km3 which would place them amongst the largest magnitude effusive eruptive units yet known we suggest that the length of flood basalt lava flows on earth is restricted mainly by the size of land masses and topography in the case of the rajahmundry lavas the flows reached estuaries and the sea where their advance was perhaps effectively terminated by cooling and or disruption however it is only during large igneous province basaltic volcanism that such huge volumes of lava are erupted in single events and when the magma supply rate is sufficiently high and maintained to allow the formation of very long lava flows the rajahmundry lava fields were emplaced around 65 ma during the later times of deccan volcanism probably just after the k t environmental crisis however many lava forming eruptions of similar magnitude and style straddled the k t boundary

the deccan tholeiite lavas and dykes of ghatkopar powai area mumbai panvel flexure zone geochemistry stratigraphic status and tectonic significance abstract mumbai city situated on the western indian coast is well known for exposures of late stage deccan pillow basalts and spilites pyroclastic rocks rhyolite lavas and trachyte intrusions these rock units and a little studied sequence of tholeiitic flows and dykes in the eastern part of mumbai city constitute the west dipping limb of a regional tectonic structure called the panvel flexure here we present field petrographic major and trace element and sr nd isotopic data on these tholeiitic flows and dykes best exposed in the ghatkopar powai area the flows closely resemble the mahabaleshwar formation of the thick western ghats sequence to the east in sr nd isotopic ratios and multielement patterns but have other geochemical characteristics e g incompatible trace element ratios unlike the mahabaleshwar or any other formation the flows may have originated from a nearby eruptive center possibly offshore of mumbai two dykes resemble the ambenali formation of the western ghats in all geochemical characteristics though they may not represent feeders of the ambenali formation lavas most dykes are distinct from any of the western ghats stratigraphic units some show partial e g sr nd isotopic similarities to the mahabaleshwar formation and these include several dykes with unusual concave downward ree patterns suggesting residual amphibole and thus a lithospheric source the flows and dykes are inferred to have undergone little or no contamination by lower continental crust most dykes are almost vertical suggesting emplacement after the formation of the panvel flexure and indicate considerable east west lithospheric extension during this late but magmatically vigorous stage of deccan volcanism

high frequency seismic noise generated from breaking shallow water ocean waves and the link to time variable sea states breaking waves in the nearshore are known to generate a significant amount of high frequency f 5 hz energy we investigate the correlation between the spectrum of seismic energy and the local sea states we deployed a single three component broadband seismometer approximately 50 m from the seashore and recorded continuously for approximately 10 days our observations show that during elevated sea states and presumably larger breaking waves in the surf zone the power spectral density of the wave generated seismic energy shifts to lower frequencies and higher spectral amplitudes this is similar to the observation that large plunging breakers generate 1 20 hz acoustic infrasound suggesting that a significant portion of the infrasound couples into seismic energy at the water sea floor interface based on our observations and previous models it appears that the seismic spectrum is sensitive to the wave size but not sediment movement regardless the correlation of the seismic spectral power to the height and period of ocean waves suggests that seismic observations can be used as a proxy for local sea states which may have implications for seashore sediment transport

high frequency analysis of seismic background noise as a function of wind speed and shallow depth we used a deep 1500 m cased borehole near the town of datil in west central new mexico to study high frequency 1 hz seismic noise characteristics the remote site had very low levels of cultural noise but strong winds winter and spring made the site an excellent candidate to study the effects of wind noise on seismograms along with a three component set of surface sensors teledyne geotech gs 13 a vertical borehole seismometer gs 28 was deployed at a variety of depths 5 43 and 85 m to investigate signal and noise variations wind speed was measured with an anemometer event triggered and time triggered data streams were recorded on a reftek 72 02 data acquisition system located at the site our data show little cultural noise and a strong correlation between wind speed and seismic background noise the minimum wind speed at which the seismic background noise appears to be influenced varies with depth 3 m sec at the surface 3 5 m sec at 43 m in depth and 4 m sec at 85 m in depth for wind speed below 3 to 4 m sec we observe omni directional background noise that is coherent at frequencies below 15 hz this coherence is destroyed when wind speeds exceed 3 to 4 m sec we use a test event md 1 6 and superimposed noise to investigate signal to noise ratio snr improvement with sensor depth for the low q valley fill of the datil borehole dbh site we have found that snr can be improved by as much as 20 to 40 db between 23 and 55 hz and 10 to 20 db between 10 and 20 hz by deploying at a 43 m depth rather than at the surface at the surface there is little signal above noise in the 23 to 55 hz frequency band for wind speeds greater than 8 m sec thus high frequency signal information that is lost at the surface can be recorded by deploying at the relatively shallow depth of 40 m because we observe only minor further reductions in seismic background noise sbn at deeper depths 40 m is likely to be a reasonable deployment depth for other high frequency monitoring sites in similar environmental and geologic conditions

a comprehensive approach for evaluating network performance in surface and borehole seismic monitoring t a stabile 1 2 g iannaccone 3 a zollo 1 a lomax 4 m f ferulano 5 m l v vetri5 and l p barzaghi5 1dipartimento di scienze fisiche universita di napoli federico ii naples italy e mail tony stabile imaa cnr it 2istituto di metodologie per l analisi ambientale cnr imaa tito pz italy 3istituto nazionale di geofisica e vulcanologia osservatorio vesuviano naples italy 4alomax scientific mouans sartoux france 5eni s p a e p division san donato milanese mi italy

cretaceous age for ir rich deccan intertrappean deposits palaeontological evidence from anjar western india micropalaeontological investigations of an iridium bearing lacustrine intertrappean sedimentary sequence at the western margin of the deccan volcanic province near anjar have revealed a profuse occurrence of theropod eggshell fragments ornithoid type in beds overlying the iridium enriched levels associated late cretaceous ostracods lack of evidence of reworking and the absence of any exclusively palaeocene taxa above the iridium levels taken together indicate that the extinction of dinosaurs in the indian subcontinent occurred after the deposition of ir layers at anjar and that these ir anomalies may significantly predate the k t boundary

high frequency 1 100 hz noise and signal recorded at different depths in a mine northwest adirondacks ny seismograms of noise recorded simultaneously at the surface and at two subsurface stations 335m and 945m below surface level show that high frequency 1 100 hz background noise is reduced at the subsurface stations seismometers at all three stations are well coupled to hard crystalline bedrock most of the noise reduction occurs between the surface and 335m depth between 1 and 3 hz seismic noise correlates well with wind speed at all levels above 3 hz wind speed up to 8 m sec does not influence high frequency noise levels at 335m or 945m depths at the surface however high frequency noise is associated with wind speeds in excess of 2 m s a site resonance is characteristic of the surface spectra but is not characteristic of the subsurface sites spectral signal to noise s n ratios measured for s waves from a regional earthquake delta 530 km m sub b 4 1 are roughly equal from 1 10 hz at all depths above 10 hz however s n is greater at the subsurface stations with s n greater than 1 up to 30 hz for the surface station approx 50 hz for the 335m station and approx 70 hz for the 945m station results indicate the advantage of employingmore high frequency sensors sufficiently below the surface to reduce the level of noise and to improve the s n ratio in the high frequency range such an advantage could be critically important for nuclear test detection and discrimination less

seismic emission activity of earth s crust in northern kanto japan abstract by using the semblance analysis of seismic noise prehistory of local earthquakes recorded by a dense seismic array we reconstruct the image of distributed sources of weak seismic radiation beneath the earth s surface array observations were carried out in the nikko area northern kanto japan in 1993 by joint seismic observation team the array consists of 195 three component seismometers distributed along perpendicular profiles whose array diameters are 7 km from the analysis of data several active volumes in the upper crust were identified and new features of seismic emission discovered a joint analysis of the coda and seismic noise shows that a mid crustal magma body that was identified before by reflection analysis is both a scattering region and a source of seismic emission another large active volume is visible to the east of the array at depths of 2 15 km it coincides with a known low velocity and high attenuation anomaly this emission region corresponds to an area of large earthquakes

morphology of rubbly pahoehoe simple flows from the deccan volcanic province implications for style of emplacement abstract lava flows with preserved bases and brecciated upper crusts constitute a morphological type that differs in character from typical pahoehoe and a a such flows have been reported from many provinces around the world previous studies had referred to these flows informally as pahoehoe flows with rubbly tops broken top pahoehoe and rubbly pahoehoe recent studies have formally applied the latter term to describe parts of the well studied laki flow in iceland as well as flows from the columbia river basalt province rubbly pahoehoe flows are abundant in the upper stratigraphic formations of the deccan volcanic province dvp and are more commonly known as simple flows this study presents detailed observations of such flows from various parts of the dvp and discusses their implications for understanding flow emplacement these flows which appear to be single units at the outcrop scale are generally much thicker and significantly more extensive than individual pahoehoe lobes that dominate the lower formations of the deccan stratigraphy they are characterised by preserved gently undulating tachylitic bases but variably disrupted crustal zones that grade into flow top breccias the breccias are constituted of highly vesicular and oxidised fragments of varying sizes that appear to have been derived from previously formed pahoehoe crusts previous work has indicated that the morphology of these flows might be related to initial inflation accompanied by rapid volatile exsolution and an increase in effusion rate and or viscosity with time this agrees reasonably well with the qualitative and quantitative models of emplacement developed for the laki flow the abundance of such flows in the upper formations of the deccan stratigraphy clearly hints at a significant shift in the nature of the deccan eruptions this could be indicative of higher eruption rates during this period this in turn raises the possibility of hazardous impact on the climate during the eruption of these flows which is also discussed in the paper

the deccan traps an interpretation in terms of progressive lithospheric flexure in response to a migrating load abstract structural and geochemical data from the western ghats india have been used to construct an accurate north south section of the volcanic stratigraphy of the southwest part of the deccan province the characteristic style of the section is one of southerly dip reversing in the extreme south southward overstep of higher units onto pre deccan rocks and down dip thinning of individual formations in contrast an east west section shows continuity of essentially horizontal stratigraphic units without overstepping relationships previous authors have interpreted these data in terms of the progressive southward migration of the volcanic source as india drifted northwards over a hot spot now centered beneath reunion we have compared the observed stratigraphy to the predictions of a geophysical model based on the flexural response of the continental lithosphere to a migrating volcanic load the best fit to the observed section is for the structurally lowest part of the modelled sections with an elastic thickness of the lithosphere of 100 km this value explains the present day width of the traps in peninsula india but requires that up to 5 5 km of the upper part of the flank section has been removed by erosion the origin of the erosion is not clear but it may be related to flexural rebound following removal of the cone loads that formed along the trace of the plume the model cannot explain the subsidence of the traps beneath the shelf off bombay or the rim uplift of the traps in the western ghats we attribute these modifications of the stratigraphy to vertical movements uplift and subsidence that followed rifting of india from the mascarene plateau during the eocene

analysis of high frequency seismic noise in the western united states and eastern kazakhstan seismographic stations were operated for several months during 1987 at three sites within 250 km of the kazakh test site in the u s s r and through most of 1988 and early 1989 at three sites within 250 km of the nevada test site in the united states we have analyzed surface and borehole noise levels at these sites as a function of wind speed using nearly 2000 recordings of ambient ground noise collected at the u s stations and several hundred noise measurements from the u s s r sites at the surface wind did not become a noticeable source of noise until a minimum speed of 4 to 5 m sec in the boreholes noise levels were affected by wind conditions to a much smaller degree than at the surface between 3 and 10 hz surface and borehole noise levels were typically comparable and western u s sites were generally quieter than kazakh sites in the 10 to 80 hz band surface noise in the western united states was much higher than in kazakhstan but downhole noise levels in both regions were similar and greatly reduced compared to surface noise we suspect that this is due to differences in surface vault quality between the two sets of stations

a geological map of the southern deccan traps india and its structural implications a geological map of an area of over 125 000 km 2 within the southern deccan traps india is presented which is based upon variations in the basalt geochemistry it represents a synthesis of new data and earlier work the use of large data sets has allowed stratigraphic boundaries to be established with greater accuracy over a much larger area than before the geochemical sections demonstrate that the southward overstepping stratigraphic style encountered along the ghats ridge has an essentially north to south polarity and that there appears to be detectable overstep in an east to west sense however the stratigraphy defines a pronounced coastward dipping monoclinal flexure across the western ghats ridge between 16 n and 18 n the data are consistent with two models of eruption the first considers the deccan eruptive focus to have been fixed throughout the volcanic episode producing an essentially annular flow pattern the second considers the flow pattern to have been generated from a southerly migrating eruptive centre resulting from the northerly drift of india over a fixed hotspot both hypotheses are consistent with recent quantitative models which suggest that rapid and voluminous flood basalt eruptions are the result of continental rifting events associated with plume generated thermal 9highs9 until a causal link between established plume hotspot trails and impact sites can be satisfactorily demonstrated we find it unnecessary to invoke a cataclysmic impact event as an explanation for the deccan eruptions

earth motion caused by local atmospheric pressure changes summary observations have been made of the local atmospheric pressure field and the long period seismic noise fields both on the surface of the earth and in a mine at a depth of 183 metres the observations show that during windy intervals and in the period range 20 100 s there is a strong correlation between local atmospheric pressure changes and the noise recorded by a vertical seismograph located on the surface in contrast over the same range of periods there is no correlation between the seismic noise recorded in the mine and local atmospheric pressure changes except during the passage of acoustic waves it is shown that the noise in this pass band is not due to the buoyant response of the seismograph but is caused by the motion of the earth responding to atmospheric pressure changes

new palaeomagnetic data from the mahabaleshwar plateau deccan flood basalt province india implications for the volcanostratigraphic architecture of continental flood basalt provinces abstract new magnetostratigraphic data from seven western ghats sections in the deccan volcanic province are presented these are combined with an established geochemically defined stratigraphy and volcanological logs to provide a correlated chronological eruptive framework we identify two magnetic polarities in five of the sections and these are assigned to chrons 29r and 29n importantly the reversal boundary represents an identifiable isochronous surface within the volcanic pile this surface occurs at different elevations as does the altitude of the geochemically defined formation boundary i e ambenali mahabaleshwar fms which defines a second isochronous surface inspection reveals significant differences in the number and thickness of lava units preserved between these two surfaces this indicates that there was significant local topography c 80 m across deccan volcanic province lava fields during their development an interpretation consistent with topographies observed across modern and historical examples e g hawaii iceland these data also indicate that the geochemical stratigraphies of continental flood basalt provinces can mask local and sub regional detail in lava stacking patterns when applied at smaller spatial scales 2 10 4 m finally transitional r n directions preserved in some eruptive units place constraints upon the rates of eruption and indicate c 2 ka periods of volcanic repose

high frequency seismic noise at lajitas texas a preliminary analysis of high frequency 1 to 20 hz ambient seismic noise at a very quiet site in southwest texas is presented at frequencies greater than 1 hz the displacement noise power decreases at a rate between f 4 and f 5 the ambient seismic noise is also characterized by persistent narrow band peaks f 0 2 hz of unknown origin the noise appears to be propagating at phase velocities 2 5 to 4 km sec or greater which suggests higher mode surface or body waves estimates of coherence and degree of polarization of three component array data indicate that the high frequency ambient noise is relatively well organized over distances of at least 600 to 700 m for a single component but is relatively unorganized in a three component sense a principal result of this preliminary analysis is that the use of three component high frequency 1 to 20 hz arrays at very quiet sites coupled with three component processors may result in substantial improvement of the thresholds for detection and discrimination of weak seismic events

highly heterogeneous precambrian basement under the central deccan traps india direct evidence from xenoliths in dykes abstract crustal or mantle xenoliths are not common in evolved tholeiitic flood basalts that cover huge areas of the precambrian shields yet the occasional occurrences provide the most direct and unequivocal evidence on basement composition few xenolith occurrences are known from the deccan traps india and inferences about the deccan basement have necessarily depended on geophysical studies and geochemistry of deccan lavas and intrusions here we report two basalt dykes rajmane and talwade dykes from the central deccan traps that are extremely rich in crustal xenoliths of great lithological variety gneisses quartzites granite mylonite felsic granulite carbonate rock tuff because the dykes are parallel and only 4 km apart and only a few kilometres long the xenoliths provide clear evidence for high small scale lithological heterogeneity and strong tectonic deformation in the precambrian indian crust beneath measured 87sr 86sr ratios in the xenoliths range from 0 70935 carbonate to 0 78479 granite mylonite the rajmane dyke sampled away from any of the xenoliths shows a present day 87sr 86sr ratio of 0 70465 and initial at 66 ma ratio of 0 70445 the dyke is subalkalic and fairly evolved mg no 44 1 and broadly similar in its sr isotopic and elemental composition to some of the lavas of the mahabaleshwar formation the xenoliths are comparable lithologically and geochemically to basement rocks from the archaean dharwar craton forming much of southern india as several lines of evidence suggest the dharwar craton may extend at least 350 400 km north under the deccan lava cover this is significant for precambrian crustal evolution of india besides continental reconstructions

lithofacies analysis of basic lava flows of the parana igneous province in the south hinge of torres syncline southern brazil abstract the parana igneous province records the volcanism of the earlier cretaceous that preceded the fragmentation of the gondwana supercontinent historically investigations of these rocks prioritized the acquisition of geochemical and isotopic data considering the volcanic pile as a monotonous succession of tabular flows this work provides a detailed analysis of the emplacement conditions of these basic volcanic rocks applying the facies analysis method integrated to petrographic and geochemical data the torres syncline is a nw se tectonic structure located in southern brazil where a thick sequence of the parana etendeka volcanic rocks is well preserved this study was performed in the south hinge of the syncline where the basaltic lava flows are divided into three lithofacies associations early compound pahoehoe early simple pahoehoe and late simple rubbly the first lavas that erupted were more primitive compound pahoehoe flow fields composed of olivine basalts with higher mgo contents and covered the sandstones of the botucatu formation the emplacement of compound pahoehoe flow fields is possibly related to intermittent low effusion rates whereas the emplacement of simple pahoehoe is related to sustained low effusion rates with continuous supply the thick simple rubbly lavas are associated with high effusion rates and were formed during the main phase of volcanism in the area the absence of paleosoils between the lavas and lithofacies associations suggests that the successive emplacement of the lava flows occurred in a relatively short time gap geochemically the lithofacies associations are low tio2 and belong to gramado magma type the lavas of the south hinge of the torres syncline have a similar evolution when compared to other continental basaltic provinces with earlier compound flows at the base and thicker simple flows in the upper portions

origin of deccan trap lavas evidence from combined trace element and sr nd and pb isotope studies abstract geochemical and isotope results are presented from a new study of the most southern basalts in the deccan trap india three chemical formations are recognised two of which can be correlated with the established stratigraphy in mahabaleshwar and imply a regional southerly dip of 0 06 over a distance of 250 km in detail sr isotope variations within the ambenali and mahabaleshwar formations can be shown to reflect three distinct end members which provide new constraints for petrogenetic models pb isotope data for selected basalts exhibit a wide range with 206 pb 204 pb 16 87 22 45 and a linear correlation on a pb pb diagram the least contaminated ambenali basalts plot within the pb array and interaction with mantle lithosphere involves a shift to less radiogenic pb whereas contamination with crust is characterised by more radiogenic pb unlike the karoo and parana continental flood basalt provinces only four flow units within the southern deccan appear to contain a significant contribution from mantle lithosphere the mahabaleshwar and ambenali formation basalts exhibit a striking negative pb sr isotope trend which is presently regarded as one of the features of interaction with shallow level lithospheric mantle it further suggests that basalts from the walvis ridge kerguelen and ninetyeast ridge all remobilised such shallow level material and that the deccan basalts which were not affected by crustal contamination reflect interaction between asthenospheric material similar to t type morb but related to the reunion hotspot and continental mantle lithosphere of the indian plate

interferometric assessment of clamping quality of borehole geophones borehole arrays are often preferred over surface installations for hydraulic fracture monitoring of deep experiments due to their proximity to the treatment zone borehole geophone strings are typically clamped to the observation wellbore wall using electromechanical or magnetic devices in order for them to be in close contact with the surrounding formations and record the background noise and propagating wavefields related to the microseismic experiments this contact needs to be maintained throughout the recording time we have used seismic interferometry to assess the clamping quality of borehole geophone arrays we determined that the characteristics of the retrieved crosscorrelation functions between a reference receiver and other receivers in an array are indicative of the clamping quality of the former geophone to the borehole wall we have also defined the concept of separation frequency or emergence frequency as the frequency below which direct body waves propagating along the receiver line are clearly observed on the crosscorrelation gathers the crosscorrelation gathers associated with poorly clamped geophones show predominantly tube waves or incoherent waveforms body waves only emerge below very low separation frequencies the crosscorrelation gathers of relatively better coupled geophones on the other hand have higher separation frequencies we have applied this method to four different borehole microseismic data sets labeled here as a b c and d of which data set d was previously known to suffer from some clamping issues data sets b and c with inferred better coupling had separation frequencies of approximately 60 hz whereas the other two data sets are characterized by lower separation frequencies 15 hz for data set a and 20 hz for data set d suggesting relatively poorer coupling

variations in noise and signal levels in a pair of deep boreholes near amarillo texas to better understand the depth dependence of improvements in signal to noise ratio for borehole seismic data we have collected and analyzed a data set recorded from a pair of high fidelity broadband 1 to 80 hz seismometers sited in two closely separated deep boreholes near amarillo texas the total decrease surface to 1951 m in minimum noise level is up to 30 db the total decrease in maximum noise level is up to 35 db and the range of noise values maximum to minimum at a given depth decreases from 30 to 10 db the majority of the noise reduction occurs within the first few hundred meters below the surface but the decrease continues with depth and there is no indication that even lower noise levels do not exist below our deepest recording depth 1951 m cultural work day noise prominent during normal working hours from 0 to 40 hz is observed at all depths suggesting a strong body wave component wind generated 15 to 60 hz noise is strongest at the surface and is observed as deep as 367 m without a properly shielded hole with the addition of shielding to reduce the coupling between the borehole casing and or cable with the wind wind generated noise above 40 hz can be eliminated at 367 m events with near vertical propagation paths and signal power above 1 hz show signal strength decreasing uphole with a steady winnowing of high frequencies that can be fit by a simple frequency independent q of 35 5 8 for the material between 1951 and 367 m

paleontological view of the ages of the deccan traps the cretaceous tertiary boundary and the india asia collision volcanism in the deccan traps of india occurred over at most three magnetic chrons centered on a main reversed chron paleontological data indicate that this reversed chron must coincide with 29r which contains the cretaceous tertiary k t boundary recent 40 ar 39 ar data may therefore provide one of the best estimates of the absolute age of the k t boundary 65 7 2 0 ma moreover the eurasian character of k t boundary terrestrial faunas in india suggests that this was also close to the time of india asia collision this is significantly earlier than generally recognized and implies about 4000 km of continental shortening in the collision zone probably absorbed jointly by crustal thickening and strike slip extrusion

mapping the sub trappean mesozoic sediments in the western part of narmada tapti region of deccan volcanic province india abstract deccan traps spread over large parts of south west and central india possibly hiding underneath sediments with hydrocarbon potential here we present the results of seismic refraction and wide angle reflection experiments along three profiles and analyze them together the results from all other refraction profiles executed earlier in the western part of narmada tapti region of the deccan volcanic province dvp we employ travel time modelling to derive the granitic basement configuration including the overlying trap and sub trappean sediment thickness if any travel time skips and amplitude decay in the first arrival refraction data are indicative of the presence of low velocity sediments mesozoic which are the low velocity zones lvz underneath the traps reflection data from the top of lvz and basement along with the basement refraction data have been used to derive the mesozoic sediment thickness in the middle and eastern parts of the study region between narmada and tapti the mesozoic sediment thickness varies between 0 5 and 2 0 km and reaches more than 2 5 km south of sendhwa between narmada and tapti rivers thick mesozoic sediments in the eastern parts are also accompanied by thick traps the mesozoic sediments along the present three profiles may not be much prospective in terms of its thickness except inside the cambay basin where the subtrappean sediment thickness is about 1000 1500 m in the eastern part of the study area the deepest section 4 km has thick 2 km mesozoic sediments but with almost equally thick deccan trap cover results of the present study provide important inputs for future planning for hydrocarbon exploration in this region

emplacement history and inflation evidence of a long basaltic lava flow located in southern payenia volcanic province argentina abstract the el corcovo lava flow from the huanul shield volcano in the southern mendoza province central western argentina traveled a distance of 70 km and covered a minimum area of 415 km 2 the flow emplacement was controlled both by extrinsic e g topography and intrinsic e g lava supply rate lava physicochemical characteristics factors the distal portion of the lava flow reached the colorado river valley in la pampa province where it spread and then was confined by earlier river channels cross sections through the flow surveyed at several localities show two vesicular layers surrounding a dense central section where vesicles are absent or clustered in sheet shaped and cylindrical shaped structures lavas of the el corcovo flow are alkaline basalts with low values of viscosity the morphological and structural characteristics of the flow and the presence of landforms associated with lava accumulation are the evidence of inflation this process involved the formation of a tabular sheet flow up to 4 m of thick with a large areal extent in the proximal sectors while at terminal sectors frontal lobes reached inflation values up to 10 m the numerous swelling structures present at these portions of the flow suggest the movement of lava in lava tubes we propose that this aspect and the low viscosity of the lava allowed the flow travel to a great distance on a gentle slope relief