interferometric daylight seismic imaging summary claerbout s daylight imaging concept is generalized to a theory of interferometric seismic imaging ii interferometric seismic imaging is defined to be any algorithm that inverts correlated seismic data for the reflectivity or source distribution as examples we show that ii can image reflectivity distributions by migrating ghost reflections in passive seismic data and generalizes the receiver function imaging method used by seismologists interferometric seismic imaging can also migrate free surface multiples in common depth point cdp data and image source distributions from passive seismic data both synthetic and field data examples are used to illustrate the different possibilities of ii the key advantage of ii is that it can image source locations or reflectivity distributions from passive seismic data where the source position or wavelet is unknown in some cases it can mitigate defocusing errors as a result of statics or an incorrect migration velocity the main drawback with ii is that severe migration artefacts can be created by partial focusing of virtual multiples

glacial to holocene changes in the surface and deep waters of the northeast indian ocean abstract stable carbon and oxygen isotopic investigations are carried out on planktonic and benthic foraminifera from an ams dated sediment core of the northeast indian ocean neio to infer glacial to holocene changes in surface and deep waters the chronology of this gravity core sk157 14 water depth 3306 m lat 5 11 n long 90 05 e was established using six ams radiocarbon ages and oxygen isotope stratigraphy variations in 18 o and 13 c values of planktonic globigerinoides ruber and benthic foraminifera cibicidoides spp are suggestive of large changes in the surface and deep water characteristics during the last 60 ka the 18 o pl values in core sk157 14 are significantly higher compared to the sediment cores in the northern bay of bengal and the andaman sea because of the diminished influence of riverine fresh water fluxes large variations in planktonic 18 o pl are noticed during the marine isotopic stage mis 3 1 and 3 3 glacial to holocene 18 o pl amplitude 1 8 is consistent with other published oxygen isotope records from the nearby locations maximum enrichment in 18 o pl occurs at 24 19 and the minimum during 7 6 ka bp spectral analysis of planktonic 18 o pl time series suggests a teleconnection between surface water 18 o and north atlantic climate oscillations benthic foraminiferal 18 o ben values indicate deep water cooling of 1 5 c during the last glacial maximum the 13 c ben values are generally higher for the holocene foraminifera suggesting greater contribution from the north atlantic deep water nadw however glacial benthic foraminifera are characterized by lower 13 c ben values highly depleted 13 c ben values during the 60 50 21 17 and 13 11 ka bp intervals suggest decrease contribution from the north atlantic deep water nadw and increase influx from the southern ocean deep water sodw in addition oxidation of organic matter and ageing of the deep water may have contributed in the pronounced decrease in 13 c ben during the glacial intervals

elimination of the overburden response from multicomponent source and receiver seismic data with source designature and decomposition into pp ps sp and ss wave responses this paper shows that betti s reciprocity theorem gives an integral equation procedure to eliminate from the physical multicomponent source multicomponent receiver seismic measurements the effect of the physical source radiation pattern and the response of the physical overburden that is the medium above the receiver plane the physical multicomponent sources are assumed to be orthogonally aligned anywhere above the multicomponent receiver depth level other than the position of the sources no source characteristics are required the method denoted the betti designature elastic demultiple has the following additional characteristics it preserves primary amplitudes while eliminating all waves scattered from the overburden it requires no knowledge of the medium below the receiver level it requires no knowledge of the medium above the receiver level it requires information only of the local density and elastic wave propagation velocities at the receiver level to decompose the physical seismic meas

worldwide initiation of holocene marine deltas by deceleration of sea level rise radiocarbon dated deltaic sequences of holocene age from different parts of the world began to accumulate within a restricted time range from about 8500 to 6500 years ago evaluation of major delta processes indicates that deceleration in sea level rise was the key factor in holocene delta formation within many deltas there is as much as a 2000 year age range between basal deposits in seaward and landward cores this age difference records the progressive landward migration of near mean sea level depositional environments during the lower to mid holocene establishment of a chronostratigraphic framework for holocene delta development provides a fundamental global baseline for distinguishing sea level change from vertical land motion by tectonism and isostasy and for evaluating rates of future marine incursion into low lying deltas

finite difference modeling experiments for seismic interferometry in passive seismic interferometry new reflection data can be retrieved by crosscorrelating recorded noise data the quality of the retrieved reflection data is among others dependent on the duration and number of passive sources present during the recording time the source distribution and the source strength to investigate these relations we set up several numerical modeling studies to carry out the modeling in a feasible time we design a finite difference algorithm for the simulation of long duration passive seismic measurements of band limited noise signatures in the subsurface novel features of the algorithm include the modeling of thousands of randomly placed sources during one modeling run the modeling experiments explore the dependency relation between the retrieved reflections and source signature length source positions number of sources and source amplitude variations from these experiments we observed that the positions of the passive sources and the length of the source signals are of direct influence on the quality of the retrieved reflections random amplitude variations among source signals do not seem to have a big impact on the retrieved reflections

adaptive decomposition of multicomponent ocean bottom seismic data into downgoing and upgoing p and s waves with wavefield decomposition the recorded wavefield at a certain depth level can be separated into upgoing and downgoing wavefields as well as into p and s waves the medium parameters at the considered depth level e g just below the ocean bottom need to be known in order to be able to do a decomposition in general these parameters are unknown and in addition measurement related issues such as geophone coupling and crosstalk between the different components need to be dealt with in order to apply decomposition to field data an adaptive five stage decomposition scheme was developed in which these issues are addressed in this study the adaptive decomposition scheme is tested on a data example with a relatively shallow water depth 120 m consisting recordings from of a full line of ocean bottom receivers although some of the individual stages in the decomposition scheme are more difficult to apply because of stronger interference between events compared to data acquired over deeper water

elastic interferometry for ocean bottom cable data theory and examples elastic imaging from ocean bottom cable obc data can be challenging because it requires the prior estimation of both compressional wave p wave and shearwave s wave velocity fields seismic interferometry is an attractive technique for processing obc data because it performs model independent redatuming retrieving pseudo sources at positions of the receivers the purpose of this study is to investigate multicomponent applications of interferometry for processing obc data this translates into using interferometry to retrieve pseudo source data on the sea bed not only for multiple suppression but for obtaining p converted p to s wave ps wave and possibly pure mode s waves we discuss scattering based elastic interferometry with synthetic and field obc datasets conventional and scattering based interferometry integrands computed from a synthetic are compared to show that the latter yields little anti causal response a four component 4c pseudo source response retrieves pure mode s reflections as well at p and ps reflections pseudo source responses observed in obc data are related to p wave conversions at the seabed rather than to true horizontal or vertical point forces from a gulf of mexico obc data set diagonal components from a ninecomponent pseudo source response demonstrate that the p wave to s wave velocity ratio v p v s at the sea bed is an important factor in the conversion of p to s for obtaining the pure mode s wave reflections

evaluation of elastodynamic interferometric redatuming a synthetic study on salt dome flank imaging summary the recent introduction of novel redatuming techniques based on the principles of timereversed acoustics and source receiver reciprocity has allowed seismic measurements collected on one datum to be extrapolated to another datum under favourable conditions this process can approximately remove the complicated overburden structures without any velocity information we introduce an elastic redatuming scheme for walkaway vertical seismic profiles wvsps based on these principles using p and s wave potentials which are derived from the spatial derivatives of the measured wavefields additional field acquisition is utilized to directly measure these derivatives we test our elastic redatuming scheme on data simulated with an elastic finite difference algorithm the elastodynamic green s functions between multicomponent receivers in a borehole are then extracted from data recorded using multicomponent p and s wave sources at the surface the wavefields are redatumed as four parts two related to the p wave potential and another two related to the s wave potential these parts are migrated separately and form four independent images of the salt dome flank providing a more complete elastic description of the subsurface

the melting history of the late pleistocene antarctic ice sheet spatial and temporal variations in the sea levels of the past 20 000 years around the globe place constraints on the melting history of the major late pleistocene ice sheets the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9 000 6 000 years ago when it may have lagged behind minor melting of the antarctic ice sheet continued throughout the holocene

geochemical and sedimentological characteristics of surface sediments from ashtamudi estuary southern india implications for provenance and modern sedimentary dynamics geochemical and end member mixing analyses emma of the grain size distribution were conducted on recent surface sediments from ashtamudi estuary southern india to investigate the hydrodynamic factors that influence the depositional processes in the region the complex interplay between the natural fluvial and marine and anthropogenic influences on the ashtamudi estuary have been delineated based on the inter relationships between geochemical elements and the end members em derived from the grain size parameters si al and fe are the major elements in the sediment of ashtamudi estuary constituting 26 47 9 21 and 8 14 respectively four grain size end members were identified with dominant modes of 7 em1 6 em2 4 5 em3 and 3 3 em4 corresponding to fine silt medium silt coarse silt and fine sand respectively the high contributions of al fe cr and ni combined with the em1 and em2 in the upstream of the estuary indicated that the fine grained sediments were derived from the fluvial inputs into the basin the marine tidal influenced lower estuary is characterised by high concentrations of si ti ca sr and coarse fraction end member em3 the elemental concentration of cu zn and co along with em4 shows higher values along the shore region suggesting human interventions in the basin this integrated geochemical analysis and emma provide advancement in the knowledge of the transportation mechanisms and regional sediment dynamics from the estuarine system in southern india

cyanobacteria and testate amoeba as potential proxies for holocene hydrological changes and climate variability evidence from tropical coastal lowlands of sw india cyanobacteria and thecamoebians are the two major constituents of non pollen palynomorphs npp found in the palynological preparations the former is well represented in the sediment archives while the latter has restricted occurrence in the holocene sequence apart from the conventional organic matter of pollen and spores well preserved morphotypes of gleotrichia and rivularia are the best forms of cyanobacteria found in almost all the studied profiles and their abundance towards early to middle holocene coincides with the heavy rainfall and wet climate conditions during the holocene climate optimum hco contrary to cyanobacterial diversity thecamoebians are restricted to late holocene in most of the studied profiles and their occurrence is correlated with the prevailing dry and stressful environmental conditions the major elements of thecamoebians identified belong to arcellaceans centropyxids and cucurbitella types abundance of centropyxids and arcellaceans in varapuzha west kadungallur koonamavu pachcha and ernakulam indicates low humidity and low precipitation however the relative abundance of centropyxids in mid holocene at ernakulam and koonamavu reflects the early colonization of this type competing with the cyanobacteria whereas arcellaceans are essentially confined to late holocene dominance of cyanobacteria and its proliferation is directly related to freshwater influx of the rainfall as well as the local hydrological regimes associated with the active aquifers controlled by the geomorphological features of the region in which the wetland system sustained considering the signatures of cyanobacteria and thecamoebians observed in the sediment archives their occurrence in the wetlands during the holocene corresponds to the hydrodynamic regimes brought in by the freshwater influx as a result of monsoon variability the well preserved cyanobacterial signatures in sediment archives of kerala coast and their scarcity or even absence elsewhere along the west coast of india indicates that they are exclusively adapted to the wetland habitats where the hydrodynamic regimes are regularly controlled by fresh water influx in the form of extended rainy days of the monsoon system

evidence for two pre flandrian palaeosols in buchan north east scotland evidence is presented for the existence of two distinct pre flandrian palaeosols at a single site kirkhill quarry in buchan north east scotland this is the first such site reported from scotland and it is possible that the two palaeosols represent interglacial episodes which are equivalent in age to last interglacial compare with ipswichian and the penultimate interglacial compare with hoxnian a combination so far unknown in the british isles the stratigraphy also demonstrates that the part of the buchan plateau under study may have been glaciated on at least three separate occasions

data driven adaptive decomposition of multicomponent seabed recordings dual sensor hydrophone and three component geophone data recorded on the seafloor allow the elastic wavefield to be decomposed into its upgoing and downgoing p and s wave components most decomposition algorithms require accurate knowledge of the elastic properties of the seafloor in the vicinity of the receivers and properly calibrated sensors in order for the data to be a faithful vector representation of the ground motion we present a multistep adaptive decomposition scheme that provides the necessary information directly from the data by imposing constraints on intermediate decomposition results the proposed scheme requires no a priori information and only a minimal amount of user defined input thus allowing multicomponent data to be decomposed in an automated data driven fashion the performance of the technique is illustrated using seabed data acquired in the north sea with prototype single sensors multicomponent geophones individually sampled realistic seafloor properties and sensor calibration operators are obtained and elastic decomposition of the calibrated data generally yields good results dominant water layer reverberations are successfully attenuated and primary reflections are substantially enhanced in the computed upgoing p wave potential just below the seafloor in contrast the result for the upgoing s wave potential is somewhat less convincing although the energy of water layer multiples is substantially reduced notable amounts of undesired multiple energy remain in this section after decomposition particularly at high offsets these imperfections may point to inaccuracies in the parametrization of the seafloor or remaining inaccuracies in the vector fidelity of the horizontal geophone recordings nevertheless the results obtained with the extended data driven decomposition scheme are at least comparable to previously published results

seismic and electromagnetic controlled source interferometry in dissipative media abstract seismic interferometry deals with the generation of new seismic responses by crosscorrelating existing ones one of the main assumptions underlying most interferometry methods is that the medium is lossless we develop an interferometry by deconvolution approach which circumvents this assumption the proposed method applies not only to seismic waves but to any type of diffusion and or wave field in a dissipative medium this opens the way to applying interferometry to controlled source electromagnetic csem data interferometry by deconvolution replaces the overburden by a homogeneous half space thereby solving the shallow sea problem for csem applications we demonstrate this at the hand of numerically modeled csem data

remote sensing of hydrocarbon layers by seabed logging sbl results from a cruise offshore angola detecting and assessing hydrocarbon reservoirs without the need to drill test wells is of major importance to the petroleum industry seismic methods have traditionally been used in this context but the results can be ambiguous another approach is to use electromagnetic sounding methods that exploit the resistivity differences between a reservoir containing highly resistive hydrocarbons and one saturated with conductive saline fluids modeling presented by eidesmo et al 2002 demonstrates that by using seabed logging sbl a special application of frequency domain controlled source electromagnetic csem sounding the existence or otherwise of hydrocarbon bearing layers can be determined and their lateral extent and boundaries can be quantified such information provides valuable complementary constraints on reservoir geometry and characteristics obtained by seismic surveying

fluvio sedimentary response of the monsoon fed indian rivers to late pleistocene holocene changes in monsoon strength reconstruction based on existing 14c dates abstract the primary objective of the present study is to identify major phases of alluviation in the indian region since the abrupt deglacial intensification of the monsoon 15 cal ka bp on the basis of analysis of 68 radiocarbon dates from two major hydro geomorphic regions of india the central ganga basin cgb and the deccan peninsula dp the recognition of main phases of alluviation and incision has been achieved by evaluating the temporal distribution and clustering of the radiocarbon dates from alluvial sequences the clusters were detected on the basis of the interpretation of the summed probability distribution plots derived by using oxcal version 4 0 1 and calpal version may 2006 software packages the summed probability plots reveal that periods of alluviation in the cgb represented by three clusters 13 9 12 3 11 9 11 2 and 9 8 9 0 cal ka bp occur roughly before the onset of early holocene monsoon optimum phase two other clusters occur in the intervals 3 6 2 8 and 1 1 0 9 cal ka bp the peak monsoon period generally lacks clusters of radiocarbon dates implying fluvial erosion and channel incision this period also shows clustering of radiocarbon dates of the abandoned channels in comparison 14c dates from dp alluvial units form clusters at 16 4 14 12 8 11 2 10 8 8 9 8 1 6 7 and 5 1 3 9 cal ka bp indicating an association with the deglacial early holocene humid phase alluviation in the dp appears to have continued more or less uninterrupted till the middle of the holocene epoch the beginning and end of the discernible gap in the radiocarbon dates of cgb 9 0 3 6 cal ka broadly corresponds with the two well established short term events of the holocene 8 2 and 4 2 ka cal bp in comparison the prominent gap of dp radiocarbon dates 3 9 2 1 ka cal bp approximately begins with the 4 2 ka cal bp short term event onset of aridity and ends with the 2 0 ka cal bp enhanced monsoon event notwithstanding the inter regional differences in the fluvio sedimentary response in the india region the clusters of radiocarbon dates indicate that the century to millennium scale variations in fluvial activity in the indian subcontinent were intimately linked to long term fluctuations in the monsoon strength during the late quaternary

mis 5a and mis 3 relatively high sea level stands on the hatay samandag coast eastern mediterranean turkey abstract the coastal belt of hatay samandag in the east mediterranean is marked by the intersection of the african arabian and eurasian anatolian platelet plates where several quaternary shorelines related to relative sea level changes can be seen above the current sea level in this study the most common and best preserved high sea level markers of the marine isotope stage mis 5 and mis 3 shorelines were dated for the first time using the mollusc based electron spin resonance esr method as a result of this research the age of the late mis 5 and mis 3 sea level highstands in the eastern mediterranean the elevation of the corresponding shoreline at samandag coast and the vertical component of the late quaternary tectonic movements which has an impact on shoreline were determined the shorelines at 48 43 m elevations between cevlik and samandag at 58 6 m in tekebasi and at 21 m at keldag have been dated to approximately 72 ka and therefore are correlated with mis 5a the shoreline at 40 39 m elevations between cevlik and samandag has been dated to approximately 53 ka and therefore is correlated with mis 3 according to the position of the mis 5a shorelines the uplift rate over the last 72 ka was 0 88 mm y between cevlik and samandag 1 08 mm y in tekebasi and 0 56 mm y in keldag yielding a 0 84 mm y average this rather fast uplift appears to be related to the vertical component of the strike slip active faults in the samandag antakya fault zone

pollen inferred late glacial and holocene climate in southern balkans lake maliq abstract high temporal resolution analysis of pollen records from lake maliq albania provides quantitative estimates of monthly temperature and precipitation changes since the last deglaciation the climate parameters were estimated using the best modern analogue technique with an updated modern pollen climate database composed of 2748 surface samples the record shows two main cooling phases in the maliq area the oldest and younger dryas and a cooling event around 8200 years which suggests that the forcing factors driving climate variations in the north atlantic area since the last glacial period also extended their influence into the mediterranean area the oldest and younger dryas are also characterized by an arid climate and a change in the seasonality of precipitation the summer precipitation tends to be greater during the cooling phases than during the temperate periods the holocene climate is relatively stable and the values of each parameter reach their modern levels except for an arid event between 8300 and 8100 cal bp

late quaternary evolution of ashtamudi sasthamkotta lake systems of kerala south west india abstract sedimentological and palynological analysis of two borehole samples collected from the confluence of kallada river with the ashtamudi lake in the south west coast of india have been addressed while ascertaining the late quaternary evolution of the two borehole samples the one collected from pangod 9 03 n 76 42 e reveals a fining upward sequence with medium to coarse sand 3 05 m at base organic carbon rich silt and fine sand dominated sediments 2 m at the middle and yellowish brown muddy sediments 3 2 m at the top the middle layer embeds a suite of partly carbonized sub fossil logs of wet evergreen to semi evergreen vegetation the palynoflora of this layer reveals that the depositional site is within the tidal limit and deposition occurred under high precipitation and atmospheric humidity the similarity in 14 c dates of a wood at 5 m bgl 7490 90 yrs bp and the embedding sediments 7480 80 yrs bp indicate quick burial of the riparian vegetation the west kallada borehole 9 30 n 76 37 e reveals middle to late holocene sequence of clayey silt 6250 110 yrs bp 3880 80 yrs bp and sand resting unconformably over greyish white clayey sand with pebbles and granules derived from laterite provenance palynological analysis shows that the holocene sedimentation took place under marine nearly marine environment and later changed to brackish water and finally to freshwater environment marine transgression 6000 yrs bp coupled with heavy rainfall in the hinterlands was responsible for faster sedimentation in the region the heavy mineral contents especially opaques garnet and sillimanite in the sediment samples of the study area as well as the bathymetric configuration of the ashtamudi sasthamkotta and chelupola lakes reiterate the fact that these lakes have been evolved from an embayment consequent to incomplete partial silting up during early to middle holocene higher sea levels and also under high rainfall of the holocene climatic optimum of around 10 000 7000 yrs bp

stratigraphical and palynological appraisal of the late quaternary mangrove deposits of the west coast of india the organic deposits derived from the mangrove swamps form reliable stratigraphic markers within the late quaternary sequence of kerala konkan basin three generations of such deposits have been identified the older one is dated to around 43 000 40 000 14c yr b p with a few dates beyond the range of radiocarbon the younger ones date from the middle holocene to latest pleistocene 10 760 4540 14c yr b p and the late holocene 4000 14c yr b p pollen analyses confirm that the deposits are mostly derived from the mangrove vegetation peat accumulation during the period 40 000 28 000 14c yr b p can be correlated with the excess rainfall 40 100 greater than modern values of the asian summer monsoon the low occurrence of mangrove between 22 000 and 18 000 14c yr b p can be attributed to the prevailing aridity and or reduced precipitation associated worldwide with last glacial maximum because exposure surfaces and ferruginous layers are commonly found in intervals representing this period the high rainfall of 11 000 4000 14c yr b p is found to be the most significant as the mangrove reached an optimum growth around 11 000 14c yr b p but with periods of punctuated weaker monsoons from the present and previous studies it has been observed that after about 5000 or 4000 14c yr b p the monsoons became gradually reduced leading to drying up of many of the marginal marine mangrove ecosystems a case study of hadi profile provided an insight to the relevance of magnetic susceptibility to record the ecological shift in late holocene

late holocene flooding history of a tropical river in western india in response to southwest monsoon fluctuations a multi proxy study from lower narmada valley abstract a multi proxy study on the sediments from lower narmada valley western india records large flooding events and high sediment influx linked to southwest monsoon variations during late holocene on the basis of proxy data and chronology of preserved sediments three major environmental perturbations at 1809 1487 and 1187 cal bp have been identified that corroborate well with the regional fluctuations in southwest monsoon variability a phase of dominant marine influence between 2185 and 1809 cal bp is inferred based on the presence of marine palynomorphs mangrove pollen and amorphous organic matter and is coincident with the phase of weak monsoon in the region a transition from marine marsh environment to a phase of high fluvial influx occurred around 1809 cal bp the fluvial influence is inferred based on the replacement of amorphous organic matter with structured organic matter presence of fresh water algae decrease in the 13c values and dominance of kaolinite clay the fluvial regime stabilized between 1487 and 1187 cal bp as recorded in the overbank sediments palynomorphs and geochemical indices and sedimentation occurred under a highly oxidizing and high energy condition with long distance transport of sediments the later incision of the sediment sequence which post dates 1187 cal bp can be attributed to enhanced precipitation the response of the lower narmada valley to short term southwest monsoon fluctuations is manifest in the shifting deposition environments and a major role of terrestrial sediment influx variability is surmised leading to relative sea level variations in this part of the indian subcontinent a temporal and process based interplay between flooding periods and sediment discharge in river systems and tidal conditions is suggested for the tropical estuarine environments

experimental quantification of the seismoelectric transfer function and its dependence on conductivity and saturation in loose sand under certain circumstances seismic propagation within porous media may be associated to a conversion of mechanical into electromagnetical energy known as a seismoelectromagnetic phenomemon the propagation of fast compressional p waves is more specifically associated to manifestations of a seismoelectric field linked to fluid flow within the pores the analysis of seismoelectric phenomena which requires combining the theory of electrokinetics to biot s theory of poroelasticity provides us with a transfer function noted e u that links the coseismic seismoelectric field e to the seismic acceleration u in order to measure the transfer function we have developed an experimental set up enabling seismoelectric laboratory observation in unconsolidated quartz sand within the kilohertz range the investigation focused on the impact of fluid conductivity and water saturation over the coseismic seismoelectric field during the experiment special attention was given to the accuracy of electric field measurements we concluded that in order to obtain a reliable estimate of the electric field amplitude the dipole from which the potential differences are measured should be of much smaller length than the wavelength of the propagating seismic field time lapse monitoring of the seismic velocities and seismoelectric transfer functions were performed during imbibition and drainage experiments in all cases the quantitative analysis of the seismoelectric transfer function e u was in good agreement with theoretical predictions while investigating saturation variations from the residual water saturation to full saturation we showed that the e u ratio undergoes a switch in polarity at a particular saturation s also implying a sign change of the filtration traducing a reversal of the relative fluid displacement with respect to the frame this sign change at critical saturation s stresses a particular behaviour of the poroelastic medium the dropping of the coseismic electric field to zero traduces the absence of relative pore fluid displacements representative of a biot dynamically compatible medium we concluded from our experimental study in loose sand that measurements of the coseismic seismoelectric coupling may provide information on fluid distribution within the pores and that the reversal of the seismoelectric field may be used as an indicator of the dynamically compatible state of the medium

holocene climatic vicissitudes and sea level changes in the south western coast of india appraisal of stable isotopes and palynology abstract the southern kerala coast in sw india has experienced dramatic changes in climate and sea level during holocene these changes are apparently well preserved in the sedimentary archives of the estuarine basins that are entrenched on the uplifted neogene deposits here we report the sedimentary processes palaeoclimate and sea level records decoded from two borehole cores puthenthuruthu and munrothuruthu borehole cores retrieved respectively from the marine and fluvial ends of the second largest estuarine basin in sw india the ashtamudi estuary using sedimentology palynology and stable isotopes as the major proxies the heavy rainfall event at the latter half of early holocene 6117 101 bp is reflected well in the isotopic signatures of the puthenthuruthu borehole core the higher level of lighter isotopes of oxygen and carbon at 10 15 m below ground level is a clear indication of freshwater influx from the hinterland due to intensified monsoon activity this in turn was responsible for the development of bay head delta in the fluvial end of the estuary during early middle holocene period palynological contents below the level indicate a facies change as freshwater and terrestrial elements dominate over marine contents further the occurrence of desmids shows the marine facies is being gradually replaced by freshwater to continental facies this was followed by the deposition of littoral sands as flood tide islands within the estuarine basin the palynological investigations of sediments with radiocarbon age of 4350 90 bp in the munrothuruthu borehole core show a dry phase with high saline depositional environment in the beginning which is followed by influx of freshwater as indicated by the higher content of lighter isotopes of carbon and oxygen in the calcareous nodules algal pisolites embedded in the sediments the occurrence of pteridophytic spores and a few pollen of cullenia in the palynological preparations in the upper half of the silt and clay dominated intervening layers reiterate this view

the use of oxygen isotope variation in shells of estuarine mollusks as a quantitative record of seasonal and annual colorado river discharge abstract we describe a new method for the calculation of river flow that uses the oxygen isotope composition of bivalve mollusk shells that grew in the river water seawater mixing zone of the colorado river estuary sclerochronological techniques are used to identify tidally induced fortnight scale bundles of daily growth increments within shell cross sections these fortnightly markers are used to establish a chronology for samples taken for 18 o analysis a composite seasonal 18 o profile derived from five shells that grew in the absence of river water flow is used as a baseline against which profiles of river influenced shells are compared because this comparison is between matched fortnights within a year the temperature of shell growth is likely to be very similar the difference in 18 o between the river influenced shell and the no flow composite shell therefore represents the change in the 18 o of the water due to the presence of river water in the mixing zone the river water end member is also determined within a fortnightly context so that the change in the 18 o of mixing zone water can be used to calculate the relative proportions of seawater and fresh water the fresh water end member is calculated from the 18 o of bivalves alive prior to the emplacement of dams and water diversions on the colorado river the marine end member is based on direct measurements of the 18 o of northern gulf of california water during times of no colorado river flow the system has been calibrated to absolute flow amounts using recent releases of known volume and rate

integration of electromagnetic and seismic data to assess residual gas risk in the toe thrust belt of deepwater niger delta during the last couple of years drilling activities in the deepwater thrust belt play of nigeria figure 1 have shown mixed results with some wells finding pay but others coming across low saturation gas and or brine sands in this frontier exploration context shell nigeria e p co snepco has been particularly successful in a number of toe thrust prospects where the key risk is trap integrity related to both earlier thrust faults and later extensional faults

signatures of late quaternary land sea interactions and landform dynamics along southern kerala coast sw india abstract the kerala coast displays a spectrum of varied geomorphic features that are evolved as a function of late quaternary land sea interaction the southern kerala coast south of achankovil shear zone asz has been characterised by cliffed coast with entrenched estuarine basins pocket beaches promontories older and younger strand plains etc that are evolved as a result of the transgressive regressive phases to which the coast has been subjected during the late quaternary period in spite of having varied geomorphic features lacuna in comprehending the evolutionary phases of the coastal landform features is the primary impediment that bolstered us to unravel the late quaternary land sea interactions and landform changes of the coast between thottapally and vizhinjam moreover the last two centuries are known to have been witnessing many natural as well as human induced environmental perturbations in the area the present study attempts to reconstruct t he late quaternary landform dynamics based on the satellite data while the last century changes were extracted from the digital shoreline analysis system dsas the evidences based on geomorphic variations suggest that the present study area hosts two distinct paleo coastlines 1 coincides with the eastern boundary of the older strand plains accreted during late pleistocene and 2 marks the boundary between older and younger strand plains accreted during early middle holocene a sector wise analysis reveals that the northern half of the study area is characterised by many coast perpendicular estuarine basins with well developed bay head deltas in its fluvial end and flood tide islands near the estuarine mouth on the contrary the southern half is characterised by pocket beaches and coast parallel backwater bodies developed during the regressive phases of the sea a high resolution study of the shoreline changes during the period 1920 2018 reveals that the younger strandlines are vulnerable to severe coastal erosion and shoreline retreat at many places compared to coastal accretion the study stresses the imminent need for continuous monitoring and implementation of site specific mitigation measures for the conservation and management of this coast known for its outstanding natural beauty and strategic beach placer deposits

evolution of the coastal wetland systems of sw india during the holocene evidence from marine and terrestrial archives of kollam coast kerala abstract kerala coast in southwest india is endowed with an interlacing network of wetlands evolved during the late quaternary the wetlands in the southern part of kerala especially around kollam district show antecedent characteristics and are incised on the neogene sediments these wetlands include 20 0 35 0 m thick deposits of holocene sediments containing good archives of landform evolution and climate changes holocene sedimentation was initiated at about 8920 110 bp and is represented mainly by sub fossil wood peat or carbonaceous clays subsequent deposition of brackish water to marine sediments occurred in the middle holocene the proposed evolutionary model reveals that many wetland bodies including sasthamkotta lake chelupola lake chittumalachira lake and kotta lake were evolved from the proto estuarine basins the upper arms of the pre holocene ashtamudi and paravur estuaries were cut off due to progradation of alluvial sediments during the holocene climatic optimum

environmental significance of carbon and oxygen isotope ratios of banded corals from lakshadweep india abstract the stable isotope ratios 18o and 13c of the coral porites compressa from the lakshadweep islands eastern arabian sea preserve environmental parameters related to monsoon induced upwelling the oxygen isotopic ratios in p compressa record the seasonal drop in sea surface temperature sst during the monsoon season an earlier calibration of the coralline 18o with observed changes in sst is used to estimate past sst changes and to evaluate the relationship with upwelling and rainfall the seasonal variations in carbon isotope ratios seem to be controlled by photosynthesis of the algal symbiont which in turn is modulated by monsoon activities sedimentation sediment suspension water current and turbidity both 18o and 13c in this species do reflect the monsoon clearly

investigating the dynamical behavior of the intertropical convergence zone since the last glacial maximum based on terrestrial and marine sedimentary records abstract the intertropical convergence zone itcz is an integral component of the earth s climate system it plays important roles in monsoon precipitation transport of chemical tracers between the hemispheres enso variability etc the itcz is characterized by seasonal movement that stays several degrees north of the equator during the boreal summer and a few degrees south of the equator during the boreal winter the seasonal movement across the hemisphere is driven by seasonal changes in insolation apart from seasonal migration itcz also moves in longer timescales that is governed by the orbital motion of the earth as well as by the internal dynamics of the earth s ocean atmospheric variability proxy records indicate the mean position of the itcz of the indian ocean sector was somewhat different relative to its estimated position considering solar insolation variability in orbital time scale in this paper we investigate the movement of the itcz that occurred in millennium time scales and discuss its implications mainly on south asian monsoon variabilities the study relies on proxy data the isotopic analysis of foraminifera and speleothem one of the important implications of this study is that the indian summer monsoon rainfall which is undergoing a slow decreasing trend for the last several decades is expected to experience a reverse trend in a few decades

decomposition of electromagnetic fields into upgoing and downgoing components this paper gives a unified treatment of electromagnetic em field decomposition into upgoing and downgoing components forconductiveandnonconductivemedia wheretheelectromagneticdataaremeasuredonaplaneinwhichtheelectricpermittivity magneticpermeability andelectricalconductivityareknown constants with respect to space and time above and below the plane of measurement the medium can be arbitrarily inhomogeneousandanisotropic in particular the proposed decomposition theory applies to marine em low frequency data acquired for hydrocarbon mapping where the upgoing components of the recordedfield guided and refracted from the reservoir that are of interest for the interpretation the direct source field the refracted airwave induced by the source the reflected field from the sea surface and most magnetotelluric noise traveling downward just below the seabed are field components that are considered to be noise in electromagneticmeasurements the viability and validity of the decomposition method is demonstrated using modeled and real marine em data also termed seabed logging sbl data the synthetic data are simulated in a model that is fairly representative of the geologic area wheretherealsblwerecollected theresultsfromthesynthetic data study therefore are used to assist in the interpretation of the realdatafromanareawith320 mwaterdepthaboveaknowngas province offshore norway the effect of the airwave is seen clearly in measured data after field decomposition just below the seabed the upgoing component of the recorded electric field has almost linear phase indicating that most of the effect of the airwavecomponenthasbeenremoved

the free surface assumption for marine data driven demultiple methods in the past integral formulations for marine data driven demultiple methods have been derived from reciprocity theorems two fundamental assumptions in these derivations were that the sea surface is flat and has a known reflection coefficient often taken to be minus one in this paper we show that for dual sensor data these assumptions can be relaxed the sea surface has to obey the same conditions as any other reflecting boundary in the subsurface it must be constant in time but shape and reflection strength can vary in space for both surface related multiple elimination and multiple attenuation by multi dimensional deconvolution we derive integral equations that depend only on the measured pressure and particle velocity fields finally we show there is an intimate connection between the integral equations for the methods

monitoring changes in velocity and q using non physical arrivals in seismic interferometry application of seismic interferometry to records from receivers at the earth s surface from sources in wells retrieves the reflection response measured at the receivers as if from virtual sources located also at the surface when the wavefields experience intrinsic losses during propagation non physical arrivals ghosts would appear in the retrieved result these ghosts appear due to waves that reflect inside a subsurface layer thus a ghost contains information about the seismic properties of the specific layer we show how such ghosts can be used to monitor layer specific changes in the velocity and intrinsic losses in the subsurface we show how to identify the ghosts using numerical modelling results from a vertical well and how to estimate the layer specific velocity and quality factor changes using numerical modelling results from a horizontal well as well as ultrasonic s wave laboratory data

on the relation between seismic interferometry and the simultaneous source method summary in seismic interferometry the response to a virtual source is created from responses to sequential transient or simultaneous noise sources in the simultaneous source method overlapping responses to sources with small time delays are recorded seismic interferometry and the simultaneous source method are related in this paper we make this relation explicit by discussing deblending as a form of seismic interferometry by multidimensional deconvolution

mid holocene sea level highstand along the southeast coast of china various sea level curves have been proposed for the coast of china in the past two decades these sea level curves indicate a complex history of holocene sea level and so the debate on whether or not a higher mid holocene sea level highstand exists in the coast of china has continued this paper aims to re examine the holocene sea level history for the low latitude part of the china coast between 18 n and 32 n by re assessing all the sea level data available from the east to south coasts and separating them according to geological settings in order to examine the influences of global and local factors the reconstructed sea level histories from different coastal sectors of the china coast reveal a certain degree of variability in the timing and height of mid holocene sea level highstand within large river deltas the mid holocene sea level highstand occurred earlier by almost 1000 years than that from other coastal sites the highstand from large river deltas appears also lower in altitude a few metres below the present day sea level due probably to the local factors of subsidence and sediment consolidation in geologically stable coastal sites the highstand is recorded at the same altitude as the present day sea level a 1 2 m higher highstand is found from sites where tectonic uplift is observed

the upper parana river brazil geomorphology sedimentology and paleoclimatology this study involves the geomorphological sedimentological and paleoclimatological aspects of the upper parana river at porto rico state of parana brazil the alluvial plain is composed of a braided system main channel with island and sandy bars and an anastomosing system involving secondary channels tributaries and a complex of swamps pools and natural levees river discharge in its upper course varies from 8400 to 13 000 m3 s minimum of 2550 m3 s and maximum of 33 740 m3 s solid discharge reaches 27 106 tons year for suspended sediments and 3 106 tons year for load sediments through echobathymetric survey bed forms were grouped in ripples megaripples dunes and sand waves a detailed study of the sedimentology heavy minerals and facies architecture was applied to the two major geomorphic provinces and their subenvironments channel province with sand bar and bed form deposits and overbank province with natural levee flood basin crevasse and island deposits palynological preliminary studies show that during the late pleistocene the area was dominated by grassland and savannas under drier climatic conditions since the beginning of the holocene there has been a generalized transition to a humid phase and the present broadleaf forest occupies the area some hypotheses can be formulated for the evolution of the area 1 the first order architectural element channel ch was generated during the pleistocene associated with climatic changes and tectonism the alluvial valley was filled up by alluvial colluvial deposits at the end of the pleistocene channel deposits present 40 ka bp 2 tectonism and climatic changes atlantic climatic optimum generated a new valley bottom 5 8 m below the former level and a wide meandering plain was built up 4000 4500 bp 3 a recent fluvial system created a new terrace 3 m above the normal water level

green s functions extraction and surface wave tomography from microseisms in southern california we use crosscorrelations of seismic noise data from 151 stations in southern california to extract the group velocities of surface waves between the station pairs for the purpose of determining the surface wave velocity structure we developed an automated procedure for estimating the green s functions and subsequent tomographic inversion from the 11 325 station pairs based on the characteristics of the noise field we eliminate specific events by a procedure that does not introduce any spurious spectral distortion in the band of interest 0 05 0 2 hz further we only used the emerging arrival structure above a threshold signal to noise ratio the result is that mostly station pairs with their axes oriented toward the sea are used consistent with the noise having a microseism origin finally it is the time derivative of the correlation function that is actually related to the green s function the emergence of the time domain green s function is proportional to the square root of the recording time and inversely proportional to the square root of the distance between stations the tomographic inversion yields a surface wave velocity map that compares favorably with more conventional and elaborate experimental procedures

cyanobacteria as potential biomarkers of hydrological changes in the late quaternary sediments of south kerala sedimentary basin india abstract cyanobacteria tolerate extreme hydrological regimes and their mucilaginous filaments account for binding and preservation of delicate structures as the hydrological set up is controlled by rainfall they serve as biomarkers to distinguish palaeoenvironmental scenario and ecological shifts ranging from late pleistocene to early holocene 40 ka 2 5 ka in the studied boreholes of the south kerala basin ayiramthengu panavally and west kallada the accrued cyanobacteria microflora is unique as it has different morphotypes of rivularia sp and gloeotrichia sp at varying levels in the sediment profiles probably reflecting the signatures of hydrological modifications associated with the development of wetland system the response of cyanobacteria is similar in panavally and ayiramthengu from early to late holocene with short signals of pauses probably relating to aberrations in precipitation however the late pleistocene and late holocene periods show a poor record of cyanobacteria reflecting decline in rainfall and prevalence of long spell of dry phase from early holocene to middle holocene the turnover of cyanobacteria has been prolific which may be due to the holocene optimum rainfall relatively larger size and better carbonised and smaller size and lighter coloured morphotypes are correlated with such hydrological modifications as a result of high and low rainfall respectively during the early holocene and late holocene as the cyanobacteria have the potential for adaptation and stabilization of numerous specialized eco and morphotypes in time and space they provided additional palaeodata as good biomarkers of climatic change