lack of evidence for enhanced preservation of sedimentary organic matter in the oxygen minimum of the gulf of california a test of the hypothesis that hydrogen rich organic matter accumulates preferentially in sediments under oxygen minima has been carried out by examining the composition of laminated and homogeneous diatomaceous sediments of the guaymas basin in the gulf of california the laminated sediments occur where an intense oxygen minimum intersects the slope around the margins of the basin above and below the depth of the oxygen minimum the sediments are homogenized by a burrowing infauna the two sediment types have very similar bulk chemical and mineral compositions and the organic matter is overwhelmingly marine the total organic carbon contents and rock eval parameters hydrogen and oxygen indices of the two sediment types are not significantly different whereas a road organic carbon maximum in the homogeneous sediments is centered at roughly 1200 m depth on the slope of the basin this maximum lies deeper than the core of the oxygen minimum thus both the concentration and the nature of the organic matter in the sediments of this highly productive marginal marine basin are not related to the concentration of dissolved oxygen in the bottom waters

chemostratigraphy of the jurassic system applications limitations and implications for palaeoceanography current chemostratigraphical studies of the jurassic system primarily involve the use of one sedimentary component marine organic carbon one divalent transition metal substituted in carbonate manganese and two isotopic tracers strontium isotope ratios 87 sr 86 sr and carbon isotope ratios 13 c carb and 13 c org in carbonate and in organic matter other parameters such as mg ca and sr ca ratios in calcite oxygen isotope ratios 18 o in carbonate sulphur isotope ratios 34 s in carbonate hosted sulphate nitrogen isotope ratios 15 n org in organic matter osmium isotope ratios 187 os 188 os in black shales and neodymium isotope ratios 143 nd 144 nd in various mineral phases are also useful but at present give poor resolution because the database is incomplete or compromised by various factors stratigraphical patterns in total organic carbon toc can be of either local or regional significance depending on the lateral extent of the former nutrient rich and productive water mass divalent manganese follows a similar pattern being concentrated most probably as a very early diagenetic phase only in oxygen depleted waters that typically underlie zones of elevated organic productivity shifts in mg ca and sr ca ratios on the time scale of ammonite subzones seem largely to reflect temperature changes strontium isotope ratios from pristine skeletal calcite provide a global signal 13 c values from carbonates with minimal diagenetic overprint potentially do the same although small spatial differences in palaeo water mass composition may have been locally significant oxygen isotope determinations on carbonate rocks and fossils generally yield values that are too scattered to be stratigraphically useful because they reflect palaeotemperature the evaporation precipitation balance in sea water and the impact of any diagenesis involving an aqueous phase nitrogen isotope ratios in organic matter reflect the chemistry of ancient water masses as affected by nitrate utilization and denitrification and the stratigraphical pattern of this parameter is more likely to correlate only on a regional basis neodymium isotope ratios in sea water are also water mass dependent and greatly affected by regional sources and oceanic current systems preliminary data on sulphur isotope ratios in carbonates and osmium isotope ratios in organic rich shales both potentially offering global correlation indicate that these tracers may be valuable although the records at present are not sufficiently well established to allow high resolution regional correlation in all cases biostratigraphically well dated reference sections against which the relevant geochemical data have been calibrated are required in the first instance to date studies on the stratigraphical distribution of organic carbon have been principally carried out in both northern boreal and southern tethyan europe carbon isotope stratigraphy has been undertaken primarily but not exclusively on bulk pelagic sediments from the alpine mediterranean or tethyan domain and strontium isotope stratigraphy has been undertaken largely on calcitic skeletal material belemnites and oysters from northern and southern europe in many sections including those containing ammonites multi parameter chemostratigraphy can give resolution that exceeds that attainable by classic biostratigraphical means strontium isotope ratios in skeletal calcite are a particularly powerful tool for illustrating changes in sedimentary rate and revealing gaps in the stratigraphical record

excavation induced microseismicity in the columnar jointed basalt of an underground hydropower station abstract large scale columnar jointed basalt cjb developments have had serious adverse effects on the stability of the project in progress to create the diversion tunnels at the baihetan hydropower station in china an in situ microseismic ms monitoring experiment was carried out to help understand the fracturing process in the cjb rock mass as a result of tunnel excavation ms monitoring performance accuracy of location estimation and system sensitivity is analyzed first then the spatiotemporal evolution of the ms activity associated with the baihetan cjb rock mass fractures along the tunnel axis and at the tunnel sidewalls during the entire excavation unloading process is obtained finally the forms and opportunities to deploy appropriate support are suggested according to the characteristics of the cjb microseismicity meanwhile the ms monitoring methods required for cjb or jointed hard rock engineering e g sensor types sensor spacing sensor array forms system protection and selection of analysis regions resulting from this exploration experiment are summarized

constraints on the timing of uplift of the yanshan fold and thrust belt north china this paper reports in situ u pb ages and hf isotopic data on detrital zircons from paleozoic to late mesozoic strata in the xishan area near beijing that provide important constraints on the evolution and paleogeography of the northern part of the north china craton ncc zircons from carboniferous to late mesozoic sandstones are characterized by three major groups of u pb ages 2 5 2 3 ga 1 9 1 7 ga and late phanerozoic ages the neoarchean and paleoproterozoic zircons and some phanerozoic zircons have negative ehf t values similar to igneous zircons from intrusive rocks known from the ncc indicating that the source of the sandstones was locally derived however late triassic to late jurassic 205 158 ma sandstones contain a group of phanerozoic zircons with positive ehf t values distinct from known igneous zircons in the ncc suggesting an exotic source the nearest potential source is the xing meng orogenic belt xmob to the north of the ncc where considerable amounts of juvenile crustal materials exist it is concluded that there are two sudden shifts in source provenances of the xishan sediments from the ncc before the late triassic to a mixed source from the ncc and xmob during the late triassic to late jurassic and then from the ncc again during the late jurassic 158 ma the first shift in source resulted from the exhumation and denudation of rocks due to uplift of the xmob which coincided with post collisional extension in the late triassic and intraplate extension of the ncc in the middle to late jurassic the second source shift resulted from the uplift of the yanshan fold and thrust belt thus constraining the timing of this to the late jurassic

the tectonic evolution of the north celtic sea and cardigan bay basins with special reference to basin inversion abstract the morphology and structural evolution of the north celtic sea basin ncsb and cardigan bay basin cbb are in large part controlled by reactivation of basement features of caledonian and possibly variscan origin from earliest triassic until maastrichtian times sedimentation was almost continuous initially in a rapidly subsiding rift system and finally in a progressive passive sag phase at the onset of the alpine orogeny both basins experienced spectacular inversion along readily identifiable axes the inversion takes the form of a compressive reactivation and reversal of the pre existing growth faults and a broad regional upwarping of the cretaceous depocentre the amount of inversion varies depending on the location within the basin but values in excess of 1000 m are possible by utilising regional seismic data the timing of inversion can be estimated as occurring between maastrichtian and eocene times which correlates with the so called laramide pulse of the alpine orogeny

evolution of a permian intraoceanic arc trench system in the solonker suture zone central asian orogenic belt china and mongolia abstract the identification of a fossil arc trench system from the ophiolite decorated solonker suture zone in the southernmost central asian orogenic belt caob enables us to constrain the timing of pre subduction extension ca 299 290 ma subduction initiation ca 294 280 ma ridge trench collision ca 281 273 ma and slab break off ca 255 248 ma in the permian a fraction of proto arc crust ca 45 km long up to 8 km wide is preserved as a volcanic plutonic sequence and is juxtaposed against a wide ca 30 80 km forearc melange this proto arc crust comprises two distinct magma series island arc tholeiite iat and mid ocean ridge basalt morb both of which have strong supra subduction zone ssz geochemical signatures zircons from a gabbro and a plagiogranite yielded weighted mean 206pb 238u ages of 284 0 4 0 and 288 0 6 0 ma the forearc melange consists of numerous ophiolite fragments and continental margin derived olistoliths blocks that predate the ophiolite the olistoliths are best represented by a gabbroic block 291 8 2 3 ma that contains granite xenoliths 312 6 1 8 and 313 6 3 1 ma other dated blocks include a trondhjemite 323 9 2 7 ma a gabbro 296 6 1 7 ma and a tonalite 294 9 2 4 ma small bodies of diabase andesite and diorite in the forearc melange exhibit a wide variety of geochemical signatures we dated zircons from an n morb like diabase 274 4 2 5 ma an e morb like diabase 252 5 2 3 ma a transitional sanukitoid adakite andesite 250 2 2 4 ma a sanukitoid high mg diorite 251 8 1 1 ma and an anorthosite 252 2 1 7 ma the n morb like diabase contains ca 301 394 ma zircon xenocrysts suggesting assimilation of trench sediments when a spreading ridge intersected a trench the other dated rocks simultaneously formed near the permian triassic boundary and captured abundant zircon xenocrysts ca 269 295 ma ca 301 495 ma and ca 923 2501 ma our new formation ages constrain a magmatic episode in response to slab break off beneath a fossil forearc in a young post collisional setting and the youngest xenocryst ages ca 269 273 ma may define the maximum depositional age of trench sediments

microseismicity stress and fracture in the coso geothermal field california abstract microseismicity stress and fracture in the coso geothermal field are investigated using seismicity focal mechanisms and stress analysis comparison of hypocenters of microearthquakes with locations of development wells indicates that microseismic activity has increased since the commencement of fluid injection and circulation microearthquakes in the geothermal field are proposed as indicators of shear fracturing associated with fluid injection and circulation along major pre existing fractures high seismicity zones are associated with the main fluid flow paths within the geothermal system calculated stress patterns from focal mechanisms provide direct evidence for the boundary between significantly different stress regimes within the coso geothermal field microseismicity in the coso geothermal field is spatially but not temporally related to regional seismicity extending southeast of the field the spatial distribution of these events defines a northwest trending seismic fracture zone consistent with a previously defined northwest striking zone the abrupt decrease of seismicity below this fracture zone may provide seismic evidence for the existence of a brittle and ductile transition zone at shallow depth beneath the coso geothermal field

a study of the hydrocarbon distribution and lower cretaceous greensand prospectivity in blocks 48 15 48 17 48 18 and 48 19 north celtic sea basin

a revised sea level curve for the early jurassic a comparison is undertaken of three different methods of eustatic sea level analysis 1 shallowing and deepening transgressive events inferred from the facies sequence 2 changes through time in the areal spread of epicontinental seas 3 seismic stratigraphy the results of these methods are compared mainly with reference to the lower jurassic new data are brought forward from several continents in a stage by stage study and it is concluded that thelias was characterized by interrupted sea level rise with no major regressions both the transgressions and regressions were relatively rapid with the major transgressions associated with widespread anoxic bottom waters estimates of the net amount of sea level rise through early jurassic time range from 75 m to 110 m

nitrogen isotope evidence for water mass denitrification during the early toarcian jurassic oceanic anoxic event bulk sedimentary nitrogen isotope 15ntot data have been generated from lower jurassic black carbon rich shales in the british isles and northern italy deposited during the early toarcian oceanic anoxic event a pronounced positive 15ntot excursion through the exaratum subzone of the falciferum zone defined by characteristic ammonites in the british isles broadly correlates with a relative maximum in weight percent total organic carbon and in some sections with a negative 13corg excursion upwelling of a deoxygenated water mass that had undergone partial denitrification is the likely explanation for relative enrichment of 15ntot and parallels may be drawn with quaternary sediments of the arabian sea gulf of california and northwest mexican margin the development of early toarcian suboxic water masses and consequent partial denitrification is attributed to increases in organic productivity approximately coincident phenomena include the following a relative climatic optimum realignment of major oceanic current systems and a possible release of methane gas hydrates from continental margin sediments early in the history of the oceanic anoxic event

stratigraphy of the triassic lower jurassic and middle jurassic aalenian from the fastnet basin offshore south west ireland abstract the stratigraphy of the triassic lower jurassic and middle jurassic aalenian of the fastnet basin is described the sequence has been divided using wireline log criteria six rock units are recognized in the triassic and 12 in the lower jurassic and middle jurassic aalenian none of these major rock units shows any significant diachroneity apparent breaks in the sequence due to unconformities or condensed sections have been identified within or bounding three of the rock units the liassic limestone liassic marl and liassic sandstone dating is provided by both microfaunas and microfloras extracted from ditch cuttings and sidewall cores the ages of the triassic rock units are mainly determined by correlation with dateable sequences in the north celtic sea basin whereas the jurassic rock units yielded abundant short ranging microfossils

predicted and measured petrophysical and geochemical characteristics of the egret member oil source rock jeanne d arc basin offshore eastern canada abstract the log r wireline log technique has been used to predict high vertical resolution geochemical profiles for 17 well penetrations of the upper jurassic egret member source rock of the jeanne d arc basin offshore newfoundland the predictions are compared with rock eval data obtained from the same interval high resolution comparison of the computed total organic carbon toc curves with gamma ray logs implies that the source rock layers in the egret member are mainly shale claystone and the non source rock layers are limestone marl to the south and siltstone sandstone to the north these comparisons also indicate that in the mature area some coarse grained non source rock layers are filled with hydrocarbons implying primary migration of oil gas using the average computed toc value the thickness of the egret member and the average formation density the mass of organic carbon was calculated at 19 well locations and regional variations examined areas with a great mass of organic carbon were identified the present mass of organic carbon is primarily related to the amount of organic matter being deposited and preserved but the expulsion of oil gas may also exert a control using 1 wt as the lower limit for a source rock it was observed that the percentage of non source rock in the egret member is generally higher in immature wells lom 7 than in mature wells probably as a result of hydrocarbon migration expulsion after maturation

a fluid inclusion study of cement and vein minerals from the celtic sea basins offshore ireland abstract fluid inclusion petrography and microthermometry have been carried out on jurassic sandstone cements quartz calcite and dolomite and later fracture filling calcite quartz veins from the north celtic sea and the fastnet basins fluid inclusions in the sandstone cements are small 1 8 m monophase liquid only or liquid rich two phase liquid vapour aqueous inclusions all display irregular to elliptical morphologies the two phase aqueous inclusions homogenise to the liquid phase between 60 122 c and have salinities ranging from 7 0 16 0 wt nacl equivalent indicating precipitation of the cements by moderate salinity waters in contrast the veins host both aqueous and petroleum inclusions the aqueous inclusions are liquid rich two phase liquid vapour inclusions 2 30 m long that are typically primary and show irregular and negative crystal shape morphologies their homogenisation temperatures to liquid range from 50 145 c and salinities from 6 20 wt nacl equivalent indicating broadly similar salinities coupled with a wider range of minimum trapping temperatures to those recorded from the cements yellow brown two phase liquid vapour petroleum inclusions are hosted by vein calcite from several wells in the central north celtic sea basin some of these inclusions appear to be primary and all are spatially associated with the aqueous inclusions the two phase liquid vapour petroleum inclusions homogenise mostly to the liquid between 50 130 c petroleum inclusions in the vein calcites indicate that petroleum was transported via fractures at a late stage through the jurassic and cretaceous strata of the celtic sea basins and apparently not through the sandstone matrix

provenance and tectonic settings of the late paleozoic sandstones in central inner mongolia ne china constraints on the evolution of the southeastern central asian orogenic belt abstract late paleozoic sedimentary strata outcrop extensively in central inner mongolia and are a key to understanding the tectonic evolution of the southeastern central orogenic belt a combined analysis of petrography whole rock major and trace element and nd isotope is carried out on representative sandstones from the late paleozoic sedimentary strata 420 270 ma the sandstones are mainly wackes and litharenites in lithology with low sio2 al2o3 of 2 85 9 47 averagely 5 22 and poor textural and compositional maturities implying short sediment transportation between the depositional basins and provenances the trace element compositions are generally comparable to that of the average upper continent crust ucc with negatively sloping chondrite normalized rare earth element distribution patterns la yb n 3 43 11 averagely 6 94 and flat ucc normalized trace element distribution patterns the nd isotopic compositions show great variation nd t 5 01 to 5 35 with depositional time of the sandstones and coincide well with the arc magmatic phases in central inner mongolia the geochemical signatures of the sandstones indicate that the dominant provenances are intermediate to felsic arc magmatic rocks that have ages approximating the deposition although old recycled sediments may have made a minor contribution an active continental arc setting during the late paleozoic in central inner mongolia controlled by the northward subduction of the paleo asian oceanic slab was the most likely depositional tectonic setting of the sandstones this active continental arc setting continued to at least 270 ma implying that the final closure of the paleo asian ocean along the solonker suture zone most likely occurred sometime during the late permian to early triassic the northward subduction of the paleo asian ocean is likely of west pacific style in which the present day baolidao arc has a close genetic link with the south mongolian microcontinent and likely the former originally formed as the arc margin of the latter

comparative sequence stratigraphy and structural styles of the slyne trough and hebrides basin the slyne trough to the west of ireland is divided into three sections north central and south the south and central sub basins are separated by a seismic dead zone along the line of the clew bay disturbance the central and north sub basins are separated by a zone transferring the fault bounding the main basin from the western margin in the central sub basin to the eastern margin in the north sub basin five stratigraphic sequences from the slyne trough which span the rhaetian to middle jurassic are recognized in the 27 13 1 well and they are compared to the equivalent sequences in the hebrides basin the late jurassic hebridean sequences are expected in the deeper parts of the central slyne trough the slyne trough and hebrides basin sediments are mainly tectonically controlled although major eustatic events in the early toarcian and late bathonian are recognized

petroleum geochemistry of the lower and middle jurassic in atlantic margin basins of ireland and the uk potential hydrocarbon source rocks of lower and middle jurassic age have been reported from outcrop shallow boreholes and exploration wells in atlantic margin basins of the uk hebrides west of shetlands and flanking the ne rockall trough and recently in the continuation of this trend offshore ireland slyne erris and porcupine basins previously these organic rich mudrocks were considered to be of little economic importance due largely to their perceived limited areal distribution and low maturity however recent geochemical studies of oils and shales from exploration drilling of these basins shows the lower and middle jurassic to have considerable potential as effective hydrocarbon source rocks supplanting the late jurassic early cretaceous kimmeridge clay formation equivalents as the only viable oil source rock in the region flanking the atlantic margin in the irish and uk sectors rich oil source potential occurs in two transgressive mudrock cycles of lower jurassic age these are the sinemurian pliensbachian interval and the overlying toarcian section present in basins such as the solan minch hebrides slyne north celtic sea st george s channel and central english channel the middle jurassic source rocks have a more limited areal distribution and occur in the faroe shetland solan west lewis west flannan hebrides slyne and north porcupine basins with oil source potential in regressive marginal marine to lacustrine facies mudrocks geochemical studies were undertaken on mudrocks from the lower and middle jurassic sections in atlantic margin basins outcrop shallow borehole core and exploration well cores and cuttings samples and on oils from drill stem test and shows core and cuttings extracts detailed analyses using gc gc ms and carbon isotopes allowed both characterization of the source rocks and oil to source correlation biomarker and carbon isotope studies of oils from the faroe shetland basin foinaven and schiehallion fields the porcupine basin connemara accumulation the wessex basin wytch farm and kimmeridge oil fields and wells in the slyne basin show strong correlations to the various source rock developments in the lower and middle jurassic the mixed biodegraded foinaven and schiehallion oils have a major waxy component and correlate with lacustrine middle jurassic source rocks in the solan and west lewis west flannan basins middle jurassic sourcing of the connemara oils is also suggested while oils in the slyne basin appear to have been largely sourced by the lower jurassic pabba shale formation oils in the wessex basin wytch farm and kimmeridge appear to have been sourced by hettangian sinemurian mudrocks and those in the north celtic sea basin by toarcian source rocks the results from this study in combination with previously published data show that rich effective oil prone source rocks occur in both the lower and middle jurassic of the atlantic margin basins offshore ireland and the uk these source rocks can be correlated with indigenous oils indicating the existence of a previously under evaluated petroleum system

seismicity associated with the 1995 1996 eruptions of ruapehu volcano new zealand narrative and insights into physical processes abstract seismicity associated with the 1995 1996 eruptions of ruapehu reflects processes associated with the intrusion of magma to shallow depth in the volcanic edifice its subsequent eruption and changes in the volcanic plumbing system resulting from the eruptions the sequence consisted of two distinct periods of eruptive activity the first lasting from september 17 1995 until late october or early november 1995 and the second from june 16 1996 until late july 1996 immediately prior to and during the early stages of the 1995 eruptions seismicity was similar to that recorded at ruapehu during the previous 25 years with the exception of the occurrence between september 17 and 25 1995 of sub 1 hz tremor which is thought to represent magmatic intrusion in early october a new pattern of seismicity was established with the disappearance of the 2 hz tremor resonator source and a change to wideband 2 10 hz tremor and wideband volcanic earthquakes this change coincided with the ejection of the last vestiges of crater lake and the change in eruptive style from phreatomagmatic to magmatic seismicity associated with the 1996 eruptions was very similar to that which accompanied the later part of the 1995 activity implying the same eruption processes and that no significant changes had occurred in the volcanic plumbing system during the intervening period geochemical geodetic and seismic precursors to the 1995 eruptions were both minor and inconsistent highlighting the difficulty in forecasting these eruptions furthermore deep volcano tectonic earthquakes were extremely rare throughout the 1995 and 1996 eruptive sequences suggesting that stresses associated with magmatic intrusion were minor this most likely resulted from the existence of either an open or a ductile pathway from the deep magma source to the surface prior to the eruptions and because the volume of magma intruded and subsequently erupted was relatively small 3

passive seismic monitoring of mine scale geothermal activity a trial at lihir open pit mine the lihir open pit mine in papua new guinea is located inside an old volcano where geothermal activity is strongly present outbursts of hot water and steam into the mining areas were a major safety concern passive seismic monitoring was carried out at the mine to investigate whether the geothermal activities could be detected and located using microseismic techniques in a mining environment in this trial sixteen triaxial geophones which can withstand temperature up to 200 c were used and installed in four deep boreholes inside the pit the microseismic events were discriminated using the sta lta triggering criterion during 6 weeks of monitoring more than 17 000 events were recorded approximately 12 of the events showed harmonic vibration characteristics similar to those observed in other geothermal and volcanic areas suggesting that the geothermal activity inside the pit was captured by the microseismic monitoring system more than 75 of the events present both p and s waves and they were interpreted to be associated with rock fracturing due to stress release near the bottom of the pit many geothermal type events were located in areas where shear events occurred implying that the detected geothermal events were not far from the mining area below the pit and they may also be associated with mining the borehole installation of the geophones significantly reduced the interference of mining noise and achieved good observation of the seismic events however equipment installation requires great attention as the geophones may be destroyed due to unexpected rising temperature within the boreholes

volcanic tremors at etna a model for hydraulic origin spectral analysis of volcanic tremors at etna reveals 2 characteristic features 1 the escaping vapor and gas streams drive the magma in random turbulent motion generating a seismic wave emission according toa f n exp m f k wherea amplitude f frequency n m k parameters 2 sudden transients in the boundary conditions of the piping system generate hydraulic pressure pulses which in the seismogram appear as wave packages their monochromatic frequency content suggests that their origin is associated with strong resonance phenomena it is conclusive that volcanic eruptions may be distinguished and classified according to different eigenfrequencies of the fissure and pipe network involved in the volcanic activity furthermore positions of active dykes may be traced following the amplitude distributions associated with pronounced spectral lines in the tremor spectra

composition and weathering conditions of paleoproterozoic upper crust of bundelkhand craton central india records from geochemistry of clastic sediments of 1 9ga gwalior group abstract the 1 9 ga gwalior group represents one of the major paleoproterozoic depositional basin of bundelkhand craton and is comprised of 1 km thick unmetamorphosed and undeformed sedimentary succession with basal clastic sequence of sandstone shale association par formation and an upper chemogenic bif rich sequence morar formation the geochemical examinations of the basal clastic rocks are the subject of present study the compositional maturity and extreme quartz enrichment in sandstones of gwalior group suggest slow upliftment and high in situ weathering of basement terrains in a stable platformal setting these clastic sediments are characterized by strong depletion of mobile constituents like ca sr and na high plagioclase index of alteration pia values and strong positive correlation between al 2 o 3 and tio 2 indicating severe weathering of upper crust positive correlation between feo t and tio 2 suggests fe retention in paleoweathering profiles and is attributed to oxygenated atmosphere post depositional potash metasomatism is indicated in a cn k systematics of these sediments and k enrichment from near zero to as high as 38 is inferred with most of the shale samples show 30 extraneous k 2 o additions depleted transition element ni cr co sc contents elevated large ion lithophile element lile k rb ba th light rare earth elements lree contents fractionated rare earth element ree patterns strong negative eu anomalies in these sediments point toward k rich intracrustal granitic source component steeper ree patterns avg la yb n 12 57 compared to basement granites and conspicuous depletion of y over other liles in auc normalized spidergram also suggest a heavy rare earth element hree depleted ttg source component minor contribution from tholeiitic mafic rock is evidenced from th sc sc la sc sc th systematics and positive correlation of transition elements with feo t and tio 2 mixing calculations on the ree data suggest that upper continental crust of bundelkhand craton was constituted of 40 granite 40 ttg and 20 mafic rocks this is in contrast with the present day composition of bundelkhand granite gneiss complex bggc that contains 90 high k granite the data suggest unroofing of granite batholiths by means of erosion and upliftment of supracrustal ttg cover

rare earth element geochemistry of australian paleozoic graywackes and mudrocks provenance and tectonic control abstract in the paleozoic graywackes of eastern australia there is an increase in the total abundance of rare earth elements ree a light to heavy ree ratio and a decrease in the chondrite normalized eu anomaly with the increase in sio2 al2o3 and k2o na2o ratios this is due to the change in the dominant source rocks from andesite to dacite to granite gneiss and sedimentary rocks similarly an increase in total ree and a decrease in eu anomaly is also seen in the associated mudrocks with the increase in total clay content this correlation in paleozoic sedimentary rocks suggests that the ree characteristics of terrigenous sedimentary rocks reflect the depositional tectonic setting of the basin the oceanic island arc type graywackes are characterised by their lower total ree abundance only slight enrichment of lree over hree and the absence of a negative eu anomaly on chondrite normalised plots the continental island arc type graywackes are discriminated by their higher ree abundance and la yb ratio the presence of a small negative eu anomaly on the chondrite normalised plots and the significant enrichment of eu compared to paas post archean average australian shale the sedimentary rocks deposited on andean type active continental margins passive margins platform and cratonic basins are all characterised by the high enrichment of lree over hree and the presence of a pronounced negative eu anomaly on chondrite normalised plots and can not be discriminated from each other by ree patterns alone

a new toc rock eval and carbon isotope record of lower jurassic source rocks from the slyne basin offshore ireland abstract this paper presents an integrated assessment of total organic carbon rock eval pyrolysis carbonate 13 c and 18 o and total organic carbon 13 c record of upper sinemurian aalenian age from the slyne basin well 18 25 1 offshore ireland total organic carbon up to 5 2 wt and rock eval pyrolysis data highlights the portree shale formation equivalent lower middle toarcian as a mature t max 440 c source rock dominated by type ii kerogens this interval is more than 90 m thick in a previously unexplored paleogeographical domain regarding stable carbon isotopes the 13 c record shows positive values during the upper sinemurian a negative trend followed by a minor positive trend during the uppermost sinemurian lower pliensbachian a negative trend during the lowermost lower toarcian and then the return to more positive 13 c values despite the biostratigraphic uncertainty the coarse resolution of the dataset and the complex assessment of diagenetic effects we suggest that the 13 c record of the studied well records the raricostatum zone positive cie the sinemurian pliensbachian boundary event and the negative cie associated with the t oae the t oae positive cie is not clearly defined in the obtained dataset the slight post t oae negative cie recovery to more positive values and the continuation of a relatively high organic content is coeval with a regional organic matter preservation interval observed in several northern european locations these new datasets and their interpretation add to the understanding of the paleoenvironmental dynamics during the early middle jurassic in the northern european domain and opens new possibilities for hydrocarbon exploration in ireland s offshore

development of small gas fields in the kinsale head area a number of potential development prospects have been identified in the area of the kinsale head gas field in the celtic sea using the recent development of the ballycotton gas field as a model this paper discusses how similar fields might be developed as satellites of the existing production platforms the ballycotton gas field was discovered in march 1989 by an exploration well drilled in block 48 20 by the western pacesetter iv a further two wells confirmed the extent of the gas accumulation see taber et al 1995 the field is located approximately 25 miles off the coast of cork and 8 miles north of the kinsale head gas field fig 1 which up to that time was ireland s only producing gas field colley et al 1981 the existence of gas processing facilities relatively close to the discovery well was a major factor in determining the technical and commercial viability of the ballycotton gas field owing to the relatively small size of the field and the predicted initial flow rate of over 50 mmscfd which could be obtained from the primary lower cretaceous a sandstone reservoir it was decided to tie the discovery well 48 20 2 back to one of the kinsale head platforms this was made possible by means of sub sea completion techniques whereby the necessary production equipment is installed underwater at the well site and the well is remotely controlled from a mother platform which also processes the gas this obviates the need for a permanent platform or a floating production system both