geochemical evidence of secondary microbial methane from very slight biodegradation of undersaturated oils in a deep hot reservoir a rare finding of early mature undersaturated oils with low gas oil ratios enables us to document secondary microbial methane generation during very slight biodegradation in a deep hot reservoir in the ultradeep water of the gulf of mexico in three studied gas samples methane is enriched in 13 c 13 c is from 63 to 64 relative to pure thermogenic methane estimated 13 c is from 71 to 67 and pure primary microbial methane 13 c is 68 carbon dioxide in gases has 13 c values that negatively correlate with 13 c values of pure thermogenic methane methane is unusually enriched in heavy isotope 2 h relative to associated ethane some extracted oils are depleted in long chain alkyl aromatics these lines of geochemical evidence suggest anaerobic microbial degradation of oil and subsequent reduction of resulting carbon dioxide to methane although specific geobiological details of secondary microbial methane generation are unclear this process may be partially responsible for charging some of the largest gas and gas hydrate fields in the world

molecular and isotopic composition of free hydrocarbon gases from sicily italy 1 chemical and isotopic data have been used as geochemical tracers for a genetic characterization of hydrocarbon gases from a total of eleven manifestations located in eastern and central southern sicily italy the molecular analysis shows that almost all the samples are enriched in methane up to 93 2 vol with the exception of four gas samples collected around mt etna showing high mantle derived co2 content methane isotope signatures suggest that these are thermogenic gases or a mixture between thermogenic gases and microbial gases although samples from some mud volcanoes in southern sicily macalube di aragona show isotope signatures consistent with a mixing model between thermogenic and microbial by combining the molecular compositions c1 c2 c3 and the methane isotope ratios 13c1 such a process seems to be excluded therefore the occurrence of secondary post genetic processes should be invoked two main hypotheses have been considered the first hypothesis includes that the gas is produced by microbial activity and altered post genetically by microbial oxidation of methane while according to the second hypothesis thermogenic gas have modified their molecular ratios due to vertical migration

hydrothermal hydrocarbon gases in the sediments of the king george basin bransfield strait antarctica thermogenic hydrocarbons formed by the thermal alteration of organic matter are encountered in several piston core stations in the king george basin anatarctica these hemipelagic sediments are being deposited in an area of active hydrothermalism associated with the back arc spreading in the bransfield strait the lateral extent of sediments infiltrated by the hydrothermally influenced interstitial fluids is characterized by basalt diapirix intrusions and is delineated by an acoustically turbid zone in the sediments of the eastern part of the basin iron sulphide bearing veins and fractures cut across the sediment in several cores they appear to be conduits for flow of hydrothermally altered fluids these zones have the highest c2 and ethene contents the thermogenic hydrocarbons have molecular c1 c2 c3 ratios typically 50 and 13ch4 values between 38 and 48 indicating an organic source which has undergone strong thermal stress several sediment cores also have mixed gas signatures which indicate the presence of substantial amounts of bacterial gas predominantly methane hydrocarbon generation in the king george basin is thought to be a local phenomenon resulting from submarine volcanism with temperatures in the range 70 150 c there are no apparent seepages of hydrocarbons into the water column and it is not believed that significant accumulation of thermogenic hydrocarbons reside in the basin

early hettangian benthic planktonic coupling at doniford sw england palaeoenvironmental implications for the aftermath of the end triassic crisis abstract this paper presents a high resolution micropalaeontological study integrated with geochemical and sedimentological analyses of the triassic jurassic tr j transition at the doniford section sw england our analyses indicate the renewal of surface carbonate production in the blue lias formation early hettangian after the end triassic mass extinction based on the high abundance of surface carbonate producers schizosphaerellids which occurred in phase with development at sea floor of calcareous hyaline benthic foraminifers we deduce that a benthic pelagic coupling resulted in both the initial restoration of the biological carbonate pump and also a more efficient export production the presence of monospecific phytoplankton assemblages and benthic foraminiferal assemblages typical of poorly oxygenated environments suggest that the environmental stress continued after the end triassic maximal perturbation complete environmental recovery was prevented by a succession of alternating dysaerobic and anoxic phases that favoured the deposition of black shale sediments the hypothesis of a methane release mechanism as a trigger for the global carbon cycle perturbation and greenhouse conditions during the early jurassic is discounted based on evidence from the decoupled carbon isotope records of carbonate and organic matter apart from local control of a high amplitude sea level change across the tr j boundary the succession and nature of events at doniford are consistent with a scenario of global environmental and biotic changes triggered by the physical and chemical effects of the central atlantic magmatic province camp volcanism a super greenhouse climate in the aftermath of the end triassic mass extinction appears to be the results of the combination of the long term co2 accumulation in the atmosphere system due to the camp volcanic activity as well as the inefficiency of the biological pump due to reduced export production

mud volcano eruptions and earthquakes in the northern apennines and sicily italy abstract the relations between earthquakes and the eruption of mud volcanoes have been investigated at the pede apennine margin of the northern apennines and in sicily some of these volcanoes experienced eruptions or increased activity in connection with historical seismic events showing a good correlation with established thresholds of hydrological response liquefaction to earthquakes however the majority of eruptions have been documented to be independent of seismic activity being mud volcanoes often not activated even when the earthquakes were of suitable magnitude and the epicentre at the proper distance for the triggering this behaviour suggests that paroxysmal activity of mud volcanoes depends upon the reaching of a specific critical state dictated by internal fluid pressure and implies that the strain caused by the passage of seismic waves can activate only mud volcanoes in near critical conditions i e close to the eruption seismogenic faults such as the pede apennine thrust often structurally control the fluid reservoirs of mud volcanoes which are frequently located at the core of thrust related folds such an intimate link enables mud volcanoes to represent features potentially suitable for recording perturbations associated with the past and ongoing tectonic activity of the controlling fault system

mineralogy geochemistry and the origin of high phosphorus oolitic iron ores of aswan egypt abstract the coniacian santonian high phosphorus oolitic iron ore at aswan area is one of the major iron ore deposits in egypt however there are no reports on its geochemistry which includes trace and rare earth elements evaluation texture mineralogy and origin of phosphorus that represents the main impurity in these ore deposits have not been discussed in previous studies in this investigation iron ores from three localities were subjected to petrographic mineralogical and geochemical analyses the aswan oolitic iron ores consist of uniform size ooids with snowball like texture and tangentially arranged laminae of hematite and chamosite the ores also possess detrital quartz apatite and fine grained ferruginous chamosite groundmass in addition to fe 2 o 3 the studied iron ores show relatively high contents of sio 2 and al 2 o 3 due to the abundance of quartz and chamosite p 2 o 5 ranges from 0 3 to 3 4 wt showing strong positive correlation with cao and suggesting the occurrence of p mainly as apatite x ray diffraction analysis confirmed the occurrence of this apatite as hydroxyapatite under the optical microscope and scanning electron microscope hydroxyapatite occurred as massive and structureless grains of undefined outlines and variable size 5 150 m inside the ooids and or in the ferruginous groundmass among trace elements v ba sr co zr y ni zn and cu occurred in relatively high concentrations 62 240 ppm in comparison to other trace elements most of these trace elements exhibit positive correlations with sio 2 al 2 o 3 and tio 2 suggesting their occurrence in the detrital fraction which includes the clay minerals ree ranges between 129 5 and 617 ppm with strong positive correlations with p 2 o 5 indicating the occurrence of ree in the apatite chondrite normalized ree patterns showed lree enrichment over hree la yb n 2 3 5 4 and negative eu anomalies eu eu 0 75 0 89 the oolitic texture of the studied ores forms as direct precipitation of iron rich minerals from sea water in open space near the sediment water interface by accretion of feo sio 2 and al 2 o 3 around suspended solid particles such as quartz and parts of broken ooliths the fairly uniform size of the ooids reflects sorting due to the current action the geochemistry of major and trace elements in the ores reflects their hydrogenous origin the oolitic iron ores of the timsha formation represent a transgressive phase of the tethys into southern egypt during the coniacian santonian between the non marine turonian abu agag and santonian campanian um barmil formations the abundance of detrital quartz positive correlations between trace elements and tio 2 and al 2 o 3 and the abundance mudstone intervals within the iron ores supports the detrital source of fe this prediction is due to the weathering of adjacent land masses from cambrian to late cretaceous the texture of the apatite and the ree patterns which occurs entirely in the apatite exhibits a pattern similar to those in the granite thus suggesting a detrital origin of the hydroxyapatite that was probably derived from the precambrian igneous rocks determining the mode of occurrence and grain size of hydroxyapatite assists in the maximum utilization of both physical and biological separation of apatite from the aswan iron ores and hence encourages the use of these ores as raw materials in the iron making industry

ammonite faunal turnover tracing sea level changes during the jurassic betic cordillera southern spain ammonite faunal turnover has been used to trace changes in sea level during the jurassic in the betic cordillera southern spain i e westernmost tethys major turnovers recorded in the jurassic succession are interpreted as extinction phenomena and as appearance diversification and radiation bioevents of the various ammonite associations they are explained as being due to falls and rises in sea level respectively the ten most abrupt diversification and radiation bioevents have been detected in the ammonite associations associated with pelagic jurassic sedimentary rocks all of these bioevents can be linked with sea level rises most coinciding with the eustatic increases of the same age expressed in the eustatic curves of hallam and haq et al the relative sea level falls including eustatic ones coinciding with extinctions are recorded as stratigraphic breaks and stratigraphic condensation phenomena in the betic jurassic succession the seven most significant extinction events recognized in the betic jurassic are also largely attributable to eustatic falls we conclude that the proposed faunal turnover curve is predominantly the expression of global changes in sea level and it can be considered as a basis for plotting a jurassic eustatic curve

paleomagnetism of the cambrian moore hollow group texas evidence for a primary magnetization carried by detrital magnetite petrographic and paleomagnetic studies of the cambrian moore hollow group texas establish the presence of three magnetic minerals and several components of magnetization hematite is the dominant carrier of the magnetic remanence in most samples and is primarily a diagenetic replacement of preexisting fe bearing phases hematite dominant samples have characteristic directions which range from shallow easterly to shallow southerly this distribution suggests multiple components of magnetization acquired at various times in the paleozoic the paleopole obtained for an unmineralized breccia 135 7 e 15 4 n represents either a chemical remanent magnetization of middle ordovician to early silurian age or a vector addition of two or more cambrian through silurian components mineralized breccias at the silver creek mississippi valley type deposit yield a permian direction 117 0 e 51 6 n because hematite in this deposit predates mineralization the permian age represents a maximum age for the mineralization at silver creek many samples contain goethite as a replacement of fe dolomite glauconite and pyrite the direction of magnetization carried by goethite is near the present geomagnetic field or in a minority of samples antipodal to it rounded ti magnetite was identified by sem in magnetic extracts from siliciclastic poor facies irm acquisition and thermal demagnetization confirms the presence of magnetite in these samples some samples contain an apparent modern viscous remanent magnetization the dominant component 72 samples 10 sites has a site mean declination of 93 8 and inclination of 14 5 with an 95 8 5 corresponding to a pole position at 163 0 e 0 6 s the presence of detrital magnetite polarity changes lack of evidence for prolonged burial and the proximity of this pole position to other late precambrian cambrian poles suggest that this component of magnetization indeed reflects the late cambrian paleopole for cratonic north america

geochemistry of some gases in hydrothermal fluids from the southern juan de fuca ridge five samples of hydrothermal fluids from two vent areas on the southern juan de fuca ridge were analyzed for dissolved gases concentrations in the end member hydrothermal fluid of h2 270 527 mol kg ch4 82 118 mol kg and co2 3920 4460 mol kg are well above values in ambient seawater and are similar to concentrations reported for other ridge crest hydrothermal systems the carbon isotopic ratios of the ch4 13c 17 8 to 20 8 and co2 13c 3 6 to 4 7 suggest that at least some of the ch4 and co2 in the fluids is basalt derived the range of 13c values for the basalt derived co2 is 6 8 to 9 7 calculated by assuming conservation of recharge co2 during hydrothermal circulation apparent temperatures of equilibration between the ch4 and the basalt derived co2 range from 640 c to 750 c small amounts of ethane c2h6 ch4 0 9 10 3 2 2 10 3 propane and butane detected in the samples may also have formed in the basalt one sample of almost pure 95 5 hydrothermal fluid contained a significant fraction up to 63 and 74 respectively of the recharge ar and n2 this suggests that the fluid has not undergone extensive vapor liquid phase separation

segmentation and configuration of subducted lithosphere in italy an important control on thrust belt and foredeep basin evolution the apennine foredeep basin system located on continental crust consists of four roughly parallel basin segments each containing a flexural outer rise and an inner trough that deepens continuously toward the thrust belt flexural modeling of subsidence data across the basin indicates that this foredeep basin results mainly from deep subsurface loads acting on the subducted slab from within the subduction zone rather than from the topographic load of the apennine mountains the geometry of the four basin segments observed within the apennine foredeep is thus inferred to reflect subduction of segmented lithosphere where each lithospheric segment corresponds to a segment of the foredeep basin beneath the basin and in the foreland the lithosphere is continuous segmentation occurs only at depth beneath the thrust belt this pattern olf segmentation of the subducted lithosphere at depth is reflected in the large scale geometry of the outer part of the apennine thrust belt and appears to control it similarly the pattern of segmentation also appears to control the position of the eastern limit of back arc type extension in western italy these relations strongly suggest a genetic relation between subduction zone processes foredeep basin geometry and thrust belt evolution in which the configuration of the subducted lithosphere largely controls the large scale surface deformation observed in the apennine system

origin of ooidal ironstones in relation to warming events cretaceous eocene bakchar deposit south east western siberia abstract an integrated study involving petrographical mineralogical and geochemical investigations proposes the origin of the bakchar ironstone deposit by upward migration of a mixture of fe rich brine and hydrothermal fluid through marine sediments trace element concentrations of the ironstone deposits rule out continental derivation of fe while high ree concentrations indicate mixed hydrogeneous and hydrothermal source three main types of ironstone within the bakchar deposit are characterized by distinct mineralogical assemblage of authigenic minerals corresponding to oxic methanic and weakly sulfidic dysoxic conditions changing redox conditions of the depositional environment methane seepage in warm seawater and availability of iron influx possibly determined the final mineralogy of three varieties of ironstones the association of siderite with ferrimagnetic sulfides like greigite and pyrrhotite in type 1 ore indicate anaerobic oxidation of methane with limited bacterial sulfate reduction the ironstone deposits of narym kolpashevo and bakchar are contemporaneous with geological events like ocean anoxic event 3 oae 3 cretaceous paleogene k pg boundary and palaeocene eocene thermal maximum petm respectively all corresponding to warm seawater conditions

active faulting and seismicity along the siculo calabrian rift zone southern italy abstract southern italy is dominated by extensional tectonics that in the calabrian arc and eastern sicily produced the development of the siculo calabrian rift zone scrz this zone is represented by a 370 km long fault belt consisting of 10 to 50 km long distinct fault segments which extend both offshore and on land being also responsible of the crustal seismicity of this region the geological and morphological observations indicate that the active normal faults of the scrz are characterized by throw rates ranging from 0 7 to 3 1 mm a they accommodate an almost uniform horizontal extension rate of about 3 0 mm a along a wnw ese regional extension direction based on our field observations and following empirical relationships between magnitude and surface rupture length connections between large crustal earthquakes and distinct fault segments of the scrz have been also tentatively tested our data indicate moreover that the magnitudes m of the historical and instrumental earthquakes are consistent with the estimated values and that the geometry and kinematics of the fault segments and the related different crustal features of the scrz control the different seismic behaviours of adjacent portions of the active rift zone

fluid migration and origin of a mud volcano in the northern apennines italy the role of deeply rooted normal faults introductionsurface seeps of gas oil and salinewaters areconsideredtobeindicatorsof deep seated hydrocarbon accumu lationandhavebeenused forover60years as a guide to hydrocarbonprospectivity a wide spectrum ofseepages belongs to di erent geologi cal settings e g camerlenghi etal 1992 1995 thrasher etal 1996 schulz etal 1997 kopf etal 1998 graue 2000 spectacular seepagescan be found in basins with highsedimentation rates that generateoverpressureandmuddiapirism gu liev and feyzullayev 1996 up dipcarrier beds and active tectonic fea tures act as channels for subsurface uidandlocalizesurfaceemissionsuptotens orevenahundred kilometresfrom the reservoir thrasher etal 1996 during migration the domi nant mechanism that changeshydrocarbon composition is phasepartitioning migration of hydrocar bons is then largely the result ofbuoyancy of the free phase formedduringthisprocess matthews 1996 eventually thegeologyofthebasinisthe key to interpreting complicated uidmigrationpathways manystud ies simply focus on the oil and gascomponents of the migrating uidrather than on the characteristics ofthewaterandmudthatareassociatedwithhydrocarbonmigrationandalsoextruded by spontaneous seeps eventhough water is invoked as beingresponsibleforatleastlighthydrocar bon removal klusman and saaed 1996 watersofdi erentprovenancecontributetotheascending uidsandtheir geochemical characteristics canhelp in understanding their evolutionduring diagenesis and migration e g white 1965 hanor 1987 holyshandto th 1996 thispaperpresentssomeanalytical data from a spontaneoussurface seep bearing saline water mud gas and oil at the foothills ofthe northern apennines the aimsare i to provide some insight intothedepthandoriginofthe uidsandthe nature of the seepage pathway and ii tode nethelossofsubsurface uids accumulation related to thegeologicalpattern geological setting and structuralcontrol of the regnano mudvolcanoin the external portion of the nor thern apennines spontaneous uidemissions are distributed along twobelts borgia etal 1986 nanni andvivalda 1999 minissaleetal 2000 the rst belt stretches along the poplainfoothills whilethesecondoneisinternal and runs nearly parallel tothe main apenninic divide fig 1 theregnanomudvolcanoconsistsofmud breccias and mud ows spread ing over an area of 0 5km

a new estimate of global methane flux from onshore and shallow submarine mud volcanoes to the atmosphere a new estimate of global methane emission into the atmosphere from mud volcanoes mvs on land and shallow seafloor is presented the estimate considered a lower limit is based on 1 new direct measurements of flux including both venting of methane and diffuse microseepage around craters and vents and 2 a classification of mv sizes in terms of area km2 based on a compilation of data from 120 mvs the methane flux to the atmosphere is conservatively estimated between 6 and 9 mt y 1 this emission from mvs is 3 6 of the natural methane sources and is comparable with ocean and hydrate sources officially considered in the atmospheric methane budget the total geologic source including mvs seepage from seafloor microseepage in hydrocarbon prone areas and geothermal sources would amount to 35 45 mt y 1 the authors believe it is time to add this parameter in the intergovernmental panel on climate change official tables of atmospheric methane sources

fluid geochemical transect in the northern apennines central northern italy fluid genesis and migration and tectonic implications chemical and isotopic characteristics of natural gas and thermal water discharges from the western back arc tyrrhenian sea across the apennine thrust belt to the po valley and adriatic coast foredeep basins in the northern apennines central northern italy reveal a large scale fluid motion in the upper crust both vertically and horizontally on the basis of gas compositions two different domains of rising fluids have been distinguished 1 co2 rich he poor 3he 4he high domain in the western peri tyrrhenian extensional sector 2 ch4 rich he rich 3he 4he low domain in the eastern adriatic compressional sector such gases rising from various depths are crossed by a huge lateral n2 rich water flow in the peri tyrrhenian sector of ca so4 hco3 meteoric derived waters that move in a regional wide aquifer hosted in a quite thick mesozoic carbonate series morphologically the co2 vents consist of mud basins with high gas rate emission where the rising fluids move upwards through diatremes on the other hand ch4 emissions seep out from typical mud volcanoes with a reduced gas flow rate where the fluid motion is likely related to saline diapir extrusions and the methane is mostly carried to the surface by the associated mud the two rising mechanisms described locate southwest and northeast of the apennine watershed respectively from a seismic point of view the ch4 domain in the thrust belt and foredeep areas is characterized by a large number of earthquakes indirectly pointing to a different rheological behavior of the terrains with respect to the more internal peri tyrrhenian area owing to the quite high thermal gradient of the latter the boundary of the brittle ductile crust in the peri tyrrhenian sector can be located at a 10 km shallow depth although the presence of several post orogenic basins would suggest widespread extensional tectonics in all areas west of the apennine watershed those located in the easternmost part display gas vents with typical crustal 3he 4he ratios as this ratio is very sensitive to deep fluids rising from the mantle we hypothesize that such basins at the foot of the apennines are not due to tensive stress as suggested by their morphological shape they are piggy back thrust top basins developed and evolved in a still acting compressive tectonic regime

recent advances in fine particle magnetism implications for paleomagnetism it is becoming increasingly obvious in paleomagnetism that the older practice of using large numbers of samples to improve statistical measures of accuracy is often not adequate to reveal the signal of greatest geological importance blanket demagnetization treatments are now largely outdated except for the most ideally behaved samples a rapidly vanishing phenomenon in many locales variations in characteristic remanent directions between neighboring and supposedly contemporaneous but lithogically distinct rock units can no longer be simply treated as noise we now recognize that such differences may actually reflect rock magnetic effects rather than such factors as the short term behavior of the geomagnetic field or local variations in structure multiple overprints often the result of moderate reheating and or chemical alteration can result in an uncertain relationship between the timing of emplacement and the acquisition of remanence in the past rocks which presented such problems could often be avoided in favor of more straightforward units much of that geological cream has been skimmed however further progress in many areas particularly the determination of the apw path and reversal stratigraphy in the paleozoic will require a better understanding of magnetization processes in order to resolve the above mentioned problems and produce accurate and reliable results

palaeobiogeography and the ordovician and mesozoic cenozoic biotic radiations curves of taxonomic diversity through geological time consistently show major evolutionary radiations during the ordovician period and from the mid mesozoic to the present day both intervals were characterized by marked biotic provincialism reflecting episodes of major continental break up and global tectonism and their later histories featured steep global climatic gradients the ordovician radiation can be recognized at a wide spectrum of taxonomic levels from species to class and the biogeographical patterns associated with the radiation of individual clades reflect a complex combination of plate distribution tectonic activity sedimentary environment sea level rise and ultimately glaciation the true scale of the mid mesozoic cenozoic biotic radiation is currently a topic of intense debate but there is no doubt that it affected plants and animals in both the marine and terrestrial realms the role of land bridges and ocean gateways in controlling the for mation of biodiversity patterns has been a persistent theme in mesozoic cenozoic bio geography and a complex set of neogene tectonic events probably aided the development of both latitudinal and longitudinal provinces during the cenozoic the present volume highlights some of the successes across a spectrum of approaches to unravelling the ordovician and mesozoic cenozoic radiations within the context of palaeobiogeography

new insights into magma dynamics during last two eruptions of mount etna as inferred by geochemical monitoring from 2002 to 2005 two distinct eruptive events characterize the volcanic activity at mount etna during the 2002 to 2005 period we identified signals of magma ascent preceding these eruptions by geochemical monitoring of both chemical composition and he isotope ratio of gas emissions from five locations in the peripheral area of the volcano the geochemical signals are interpreted using the models proposed by caracausi et al 2003a 2003b and allow identification of episodes of magma ascent and estimation of the pressures of degassing magma as observed for the 2001 eruption caracausi et al 2003b magma ascent probably triggered the onset of the 2002 2003 eruption and minor events of magma ascent were observed between may and december 2003 in contrast to the previous two eruptions the 2004 2005 eruption was not preceded by significant geochemical signals of volcanic unrest suggesting that this eruption was mainly triggered by the failure of the upper portion of the volcanic edifice under the magmatic hydrostatic pressure in the conduits high 3he 4he ratio revealed new volatile rich magma accumulation the 2002 2003 eruption was preceded by a much shorter period of new magma accumulation from deep levels of the feeding system few minor signals of magma migration were detected at some of the sites during the months preceding the 2004 2005 eruption suggesting that the degassed 3he depleted magma resident in the volcanic conduits was not replaced by new volatile rich magma this is in agreement with the lack of explosive activity during the 2004 2005 eruption and with petrologic observations that the parent magma probably erupted in 2000 and 2001 new geochemical signals of magma ascent from the deep reservoir have been identified since june 2005 indicating that the volcanic activity of mount etna is evolving toward new pre eruptive conditions

origin of oils in po basin northern italy abstract the crude oils of the po basin are characterized by means of different analytical techniques capillary gc of the saturated and aromatic hydrocarbons carbon isotopic composition of the fractions capillary gc ms of the steranes and terpanes v and ni content the geochemical data allow to sharply discern three main genetic groups one in the pedelpine area malossa group and two in the pedeapennine area cortemaggiore and cavone groups furthermore two other oils are distinguished one in the pedealpine area gaggiano slightly different from the malossa group and one in the pedeapennine area bagnolo peculiar for its terpane distribution extract of rock samples from units which show the best source rock characteristics were also studied in order to establish oil source rock correlations the riva di solto argilite triassic was found to be the primary source for the malossa oil group the marnoso arenacea tertiary is recognized as the source rock for the cortemaggiore oil group the presence of oleanane in both oil and rock extract was a key point for the conclusive evidence for the source of this oil for the cavone group a triassic carbonate a sulfur rich kerogen is inferred as the probable source rock the meride limestone triassic is the source rock for the gaggiano oil whereas for the bagnolo oil a possible tertiary origin is suggested this case history provides another record of the occurrence of oleanane in oils generated by tertiary source rocks containing organic matter of continental origin

jurassic planktonic foraminifera from the united kingdom unequivocal planktonic foraminifera have been discovered in oxfordian strata from dorset and scotland these assemblages are in part coeval with previously reported occurrences of planktonic taxa in the oxfordian of normandy and seine maritime france three species are now reported from the united kingdom for the first time globuligerina oxfordiana grigelis 1958 haeuslerina helvetojurassica haeusler 1881 and compactogerina sp cf c stellapolaris grigelis 1977 there appears to be a close relationship between the distribution of these planktonic taxa in the uk and a marked sea level highstand

magnetic properties of oolitic iron ore on bell island newfoundland abstract magnetic properties of samples from bell island sedimentary rocks have been studied x ray analysis indicates that the main magnetic mineral is hematite in all samples the other iron bearing minerals identified are siderite and chamosite microscope observations of thin sections suggest that the rocks consist of oolitic hematite in a matrix of siderite or calcite the intensity of natural remanent magnetization nrm varies in the range of 0 03 0 4 a m 1 depending on the percentage of hematite the thermal demagnetization curves of nrm show in some cases a sharp increase in magnetization at temperatures in the range 500 600 c the peaks that occur in these demagnetization curves are due to a chemical change of siderite during repeated laboratory heating x ray analysis confirmed that the newly formed material is magnetite since the original nrm has been masked by the new intergrown material this would result in a serious error in the determination of paleomagnetic pole positions the samples showing this behaviour were not considered for paleomagnetic study the samples containing oolitic hematite in a calcite matrix exhibit very high stability of nrm including directional stability until almost 670 c for these samples a virtual pole position based on n 6 samples 32 specimens demagnetized to 665 c is 34 n 114 e not far from published ordovician poles for the north american craton

multiple origins of methane in the earth methane occurrences in the earth s crust are predominantly of biogenic origin i e their ultimate source is biologically formed organic matter methane can also form through inorganic reactions and is consequently termed abiogenic biogenic methanes can either form through bacterial or thermogenic processes bacterial processes follow a co2 reduction and or fermentation pathway the fermentation processes are quantitatively more important in recent fresh sediments and swamps methane formed by co2 reduction however is most common in older sediments and commercial gasfields temperature organic substrate and age may be the major factors controlling the relative importance of the two pathways stable isotope concentrations in thermogenic methanes seem to be controlled by the extent of conversion of organic matter the timing of gas expulsion and trapping the different character of methane in individual sedimentary basins may be a result of the geologic history geothermal methanes are most likely derived from pyrolysis of organic matter abiogenic methane occurs in hydrothermal vents and ophiolite complexes inorganic reactions either surficial or deep seated are the likely source of such methanes a uniform mantle origin of methane is not supported by the observed isotope variations in naturally occurring methanes

paleomagnetic reexamination of the lower ordovician wabana and bell island groups of the avalon peninsula of newfoundland the wabana and bell island groups of the avalon peninsula of newfoundland contain oolitic hematite beds of early ordovician age dipping 11 north northwest twenty one oolitic hematite samples from nine sites were thermally demagnetized in 10 or 11 steps to 660 or 680 c at 450 c 15 samples from six sites define a stable magnetization direction d 21 2 i 12 5 k 137 95 5 7 with respect to bedding the remaining six samples failed to attain the stable end point five of them because of growth of much magnetite which probably resulted from breakdown of siderite during thermal demagnetization the paleopole for the wabana bell island groups lies at 33 n 102 e dm 5 8 dp 3 0 it is compared with other early paleozoic paleopoles from cratonic north america and the avalon zone and its significance for the iapetus ocean is discussed

mount etna geochemical signals of magma ascent and unusually extensive plumbing system fiveyearsofgasmonitoringfromselectedsitessuggestthatmtetna splumbingsystemismuchmoreextensivethanpreviously reported it extends at least 40 km sw from thevolcano s boundary along the ne sw regional fault whereit discharges about 200 tons day of gas containing heliumwith mantle type isotopic composition synchronousvariations of

geochemistry of gases and waters discharged by the mud volcanoes at paterno mt etna italy approximately 20 km south of mt etna craters at the contact between volcanic and sedimentary formations three mud volcanoes discharge co2 rich gases and na cl brines the compositions of gas and liquid phases indicate that they are fed by a hydrothermal system for which temperatures of 100 150 c were estimated by means of both gas and solute geothermometry the hydrothermal system may be associated with co2 rich groundwaters over a large area extending from the central part of etna to the mud volcanoes numerous data on the he ch4 co2 composition of the gases of the three manifestations sampled over the past 5 years indicate clearly that variations are due to separation processes of a co2 rich gas phase from the liquid the effects of these processes have to be taken into account in the interpretation of the monitoring data collected for the geochemical surveillance of etna volcano

the search for the origin of the planktic foraminifera planktic foraminifera are an extremely abundant important and successful group of marine protists they are particularly useful in reconstructing past environments and for biostratigraphic dating despite their importance the origin of the group is uncertain previous work has suggested that they evolved from a benthic ancestor during the triassic or perhaps the mid jurassic bajocian but a reason for their origination has remained unclear here we present evidence from the toarcian early jurassic of nw europe that the origin of the planktic foraminifera may have been one of the results of the early toarcian oceanic anoxic event this event appears to have been associated with a massive dissociation of gas hydrates and other perhaps related water chemistry changes

massive dissociation of gas hydrate during a jurassic oceanic anoxic event in the jurassic period the early toarcian oceanic anoxic event about 183 million years ago is associated with exceptionally high rates of organic carbon burial high palaeotemperatures and significant mass extinction heavy carbon isotope compositions in rocks and fossils of this age have been linked to the global burial of organic carbon which is isotopically light in contrast examples of light carbon isotope values from marine organic matter of early toarcian age have been explained principally in terms of localized upwelling of bottom water enriched in 12c versus 13c refs 1 2 5 6 here however we report carbon isotope analyses of fossil wood which demonstrate that isotopically light carbon dominated all the upper oceanic biospheric and atmospheric carbon reservoirs and that this occurred despite the enhanced burial of organic carbon we propose that as has been suggested for the late palaeocene thermal maximum some 55 million years ago the observed patterns were produced by voluminous and extremely rapid release of methane from gas hydrate contained in marine continental margin sediments

origin of light hydrocarbons in gases from mud volcanoes and ch4 rich emissions abstract this paper presents new chemical data of hydrocarbon rich gases discharged from mud volcanoes and ch4 rich emissions located in different areas of italy northern apennines and sicily the determination of c5 c10 alkanes cyclics and aromatics was carried out by gc ms while the main gas species and c1 c4 hydrocarbons were analyzed by gc tdc and gc fid respectively methane is by far the most abundant component of all the investigated gas emissions with the exception of part of those discharging close to mt etna volcano which are co2 rich the gas samples collected from the emilia apennine and sicily show d ch4 and 13c ch4 values typical of thermogenic gases most gases from the romagna apennine discharge methane with a biogenic isotopic signature non methane hydrocarbons of biogenic gases are almost exclusively c2 c4 alkanes with minor amounts fraction of mol mol of c4 compounds including few aromatics and cyclics likely deriving from minor thermogenic contribution not evidenced by the 13c ch4 and d ch4 values the etnean gases whose r ra and 13c co2 values indicate a strong contribution from a hydrothermal fluid source related to the nearby volcanic system show a significant enrichment of aromatics compounds up to 36 of the non methane organic gas fraction which is likely produced by catalytic reforming processes such as dehydrocyclization of alkanes the thermogenic gases from the apennines and southwestern sicily are characterized by the presence of more than 20 different cyclic compounds with concentrations up to several mol mol cyclic compounds are likely formed by i thermal cracking and ii uncompleted aromatization of alkanes occurring at depth 3 km and temperatures not exceeding 120 150 c

evidence of subsurface anaerobic biodegradation of hydrocarbons and potential secondary methanogenesis in terrestrial mud volcanoes abstract the assessment of gas origin in mud volcanoes and related petroleum systems must consider post genetic processes which may alter the original molecular and isotopic composition of reservoir gas beyond eventual molecular and isotopic fractionation due to gas migration and microbial oxidation investigated in previous studies we now demonstrate that mud volcanoes can show signals of anaerobic biodegradation of natural gas and oil in the subsurface a large set of gas geochemical data from more than 150 terrestrial mud volcanoes worldwide has been examined due to the very low amount of c 2 in mud volcanoes isotopic ratios of ethane propane and butane generally the best tracers of anaerobic biodegradation are only available in a few cases however it is observed that 13 c enriched propane is always associated with positive 13 c co2 values which are known indicators of secondary methanogenesis following anaerobic biodegradation of petroleum data from carbon isotopic ratio of co 2 are available for 134 onshore mud volcanoes from 9 countries azerbaijan georgia ukraine russia turkmenistan trinidad italy japan and taiwan exactly 50 of mud volcanoes all releasing thermogenic or mixed methane show at least one sample with 13 c co2 5 pdb thermogenic ch 4 associated with positive carbon isotopic ratio of co 2 generally maintains its 13 c enriched signature which is therefore not perturbed by the lighter secondary microbial gas there is however high variability in the 13 c co2 values within the same mud volcanoes so that positive 13 c co2 values can be found in some vents and not in others or not continuously in the same vent this can be due to high sensitivity of 13 c co2 to gas water rock interactions or to the presence of differently biodegraded seepage systems in the same mud volcano however finding a positive 13 c co2 value should be considered highly indicative of anaerobic biodegradation and further analyses should be made especially if mud volcanoes are to be used as pathfinders of the conditions indicative of subsurface hydrocarbon accumulations in unexplored areas

early jurassic north atlantic sea surface temperatures from tex86 palaeothermometry early jurassic marine palaeotemperatures have been typically quantified by oxygen isotope palaeothermometry of benthic and nektonic carbonate and phosphatic macrofossils however records of early jurassic sea surface temperatures that can be directly compared with general circulation model simulations of past climates are currently unavailable the tex86 sea surface temperature proxy is based upon the relative abundance of glycerol dialkyl glycerol tetraethers preserved in organic carbon bearing sediments this proxy has been used extensively on cretaceous and cenozoic materials and in one study on middle and upper jurassic sediments here tex86 is applied for the first time to lower jurassic sinemurian pliensbachian sediments cored at deep sea drilling project site 547 in the north atlantic the abundance of glycerol dialkyl glycerol tetraethers in these sediments is very low despite biomarker and rock eval data suggesting that thermal maturity is generally low sea floor oxygenation and a high input of reworked terrestrially sourced organic matter may explain the low concentrations for samples from which it was possible to quantify the relative abundance of glycerol dialkyl glycerol tetraethers tex86 values range from 0 78 to 0 88 equating to sea surface temperatures in excess of 28 c these temperatures are broadly comparable with new general circulation model simulations of the sinemurian and pliensbachian stages and support the general view of a predominantly warm climate the new proxy data suggest that under favourable geological conditions it is possible to extend the record of tex86 based sea surface temperatures back into the early jurassic

rockmagnetic properties of fine grained natural low temperature haematite with reference to remanence acquisition mechanisms in red beds summary grain size dependence of some remanent magnetic properties of a natural low temperature haematite is reported the haematite was obtained from a gossan in montarnu france and upgraded by magnetic separation seven grain size fractions were prepared ranging from 10 down to 0 25 m by means of microprecision sieving and centrifuging the haematite has an average crystallite size of 60 nm and contains minor contents of si al and h2o its unit cell dimensions are very close to those of ideal haematite the magnetic properties of the haematite are strongly dependent on its thermal history for the original unheated haematite fractions the isothermal saturation remanence jrs decreases with grain size the remanent coercive force hcr remanent acquisition coercive force hcr and median destructive field of the saturation remanence h1 2i are maximal in the 1 0 0 5 m fraction this grain size range can be understood as the sd threshold size in analogy with ferrimagnetic minerals jrs hcr x xin is a useful grain size indicator lowtemperature cycling of jrs shows identical behaviour for all fractions the remanence decreases slightly and shows no sharp morin transition after annealing the haematite fractions at 700 c jrs is considerably reduced relative to the original haematite predominantly due to removal of the defect moment both hcr and hcr have increased and their maximal values are shifted to the 2 1 1 0 m fraction all fractions show a much sharper morin transition during low temperature cycling of jrs due to crystallite enlargement trm decreases with grain size the different rock magnetic properties before and after annealing might provide a basis for the discrimination in sediments between a haematite drm with a high temperature origin and a haematite crm which has a low temperature origin two natural red beds one with a crm and one with a drm associated with high temperature haematite broadly show the expected differences in coercivity and in annealing behaviour although a full account of all aspects of the observed behaviour can not yet be given

a crustal seismic profile across sicily abstract a crustal reflection seismic profile more than 100 km long was recorded across central sicily from the tyrrhenian shore to the sicily channel to understand the deep structures and the collision mechanisms between europe and africa and the subsequent geodynamic evolution the profile was acquired using explosive sources and 240 active channels recorded by a sercel 408 xl 24 bits a d converter with a 12 km spread and a 24 fold coverage the data were processed following a non conventional procedure in order to preserve the relative amplitudes of the reflections and to better investigate the sicily deep structures down to the moho the main highlighted structures are the dramatic flexure of the iblean crust the huge deeper than expected trough of caltanissetta consisting of deep seated thrusts and nappes and the imbricate thrust system of rigid bodies characterizing the northern maghrebian chain we designed an ad hoc acquisition and processing in order to highlight these main geological features in the seismic stacked section moreover the deepest parts of the caltanissetta trough are imaged for the first time and its bottom is now fixed at more than 7 s twt the giant crustal wedge flexuring the iblean foreland and the moho geometries are examinated

thermal alteration of the magnetic mineralogy in ferruginous rocks the northampton ironstone contains the paramagnetic minerals siderite and berthierine and a trace of the ferrimagnetic mineral magnetite the magnetic fabric of this sedimentary rock as defined by the anisotropy of magnetic susceptibility is controlled by bedding compaction but is inverse i e the maximum susceptibility axes are normal to the bedding plane this inverse fabric is attributed to the dominating presence of siderite the rocks were incrementally heated to 600 c and the magnetic fabric was measured at room temperature and at near liquid nitrogen temperature after each heating step cooling the samples in liquid nitrogen enhances the paramagnetic contribution to the magnetic fabric after heating the samples above 250 c the room temperature magnetic fabric became normal with the minimum susceptibility axes perpendicular to the bedding plane the low temperature magnetic fabric remains inverse until the samples are heated to about 500 c after heating to higher temperatures a normal fabric was observed at both room temperature and low temperature rock magnetic evidence shows that magnetite is created during the heating the start of mineralogical changes in the rock was detected by electron spin resonance spectroscopy powder x ray diffraction and acquisition of isothermal remanence berthierine starts to break down at approximately 250 c and is totally oxidized by 500 c the creation of magnetite in the heating experiments corresponds with this mineralogical change the change in the room temperature magnetic fabric is associated with the decomposition of berthierine part of which alters to magnetite the new magnetite phase has a normal magnetic fabric which overprints the inverse magnetic fabric of siderite

chemical and isotopic evidence for sources of fluids in a mud volcano field seaward of the barbados accretionary wedge chemical isotopic and heat budgets are controlled by fluid flow and venting at convergent margins fluids vent from accretionary complex sediments via numerous pathways including mud volcanoes which are common at the barbados convergent margin chemical and isotopic compositions of fluids collected from four mud volcanoes located east of the barbados deformation front at 13 50 n indicate venting is sufficiently rapid to prevent diffusion from seawater in sediments surrounding the mud volcanoes the rate of nonfocused fluid flow is 0 26 cm yr although this rate is 3 orders of magnitude slower than the flow from the mud volcanoes significantly more fluid vents from the sediments surrounding the mud volcanoes than from the restricted areas of rapid flow from the volcanoes chloride concentrations are depleted to a minimum of 211 mm 45 of seawater value primarily by mixing diagenetically altered pore fluids with an 18o enriched fresh water released from the dissociation of methane hydrate this reaction is accompanied by the release of sufficient methane to form a free gas phase and initiate eruption of the mud volcanoes the geochemical compositions of the diagenetically altered pore fluids reflect the interplay between five major reactions 1 clay mineral dehydration which releases h2o and influences a range of chemical and isotopic compositions 2 organic matter regeneration which increases alkalinity nh4 and br and decreases so42 concentrations 3 cation exchange with clay minerals which increases na and decreases nh4 concentrations 4 carbonate recrystallization and precipitation which decrease ca2 but increase sr2 concentrations and 5 conversion of volcanic ash to clay minerals which utilizes h2o and decreases mg2 concentrations the geochemistry of the pore fluids suggests that these reactions occurred at temperatures ranging from 75 to 115 c thus at the regional geothermal gradients of 27 to 40 c km these temperatures indicate that the source regions are at 2 to 4 5 km depth

organic geochemistry of recent marine sediments from the nansha sea china recent marine sediments from two cores collected on the continental slope of the nansha sea china have been analyzed for organic matter content n alkane and isoprenoid hydrocarbons fatty acids n alkanols and sterols the organic carbon contents of the two sediment cores average 0 7 and 0 53 respectively and are higher than those of other sedimentary environments in this region the distributions of various lipid compounds indicate that most of the sedimentary organic matter in the two cores is derived from marine plankton and bacteria with land derived organic matter present in relatively small amounts the decrease in relative abundances of shorter chain lipids n alkanes n fatty acids and n alkanols with depth is evident as is the biochemical conversion of stenols to stanols in some samples the low pristane phytane ratios may result primarily from microbial activity and reflect the occurrence of significant diagenetic alteration of organic matter in the two cores

the early evolution and palaeobiogeography of mesozoic planktonic foraminifera this is a digitised version of a thesis that was deposited in the university library if you are the author and you have a query about this item please contact pearl admin pearladmin plymouth ac uk

genetic characterization of natural gases natural gases can be characterized genetically using four properties c2 concentration carbon and hydrogen isotope variations in methane and carbon isotope variation in ethane three diagrams for genetic characterization of gases have been designed in which the carbon isotopic composition of methane is correlated with the other parameters in these diagrams compositional fields have been defined for primary gases biogenic thermogenic associated and thermogenic nonassociated and for gases which result from mixing of these gases these fields are strictly empirical and comprise compositional variations found in about 500 natural gases the isotopic and compositional variations in natural gases can be described in terms of 1 processes during formation of the gases such as bacterial fermentation or maturation of organic matter and 2 processes during secondary migration mixing of primary gases is an important and common process migration of gases predominantly affects the c2 concentration whereas the isotopic properties of gaseous hydrocarbons primarily remain unchanged allowing an assessment of the origin of migrated gases and properties of their source rocks the formation of gas from humic organic matter and coals is not yet clear from published data the diagrams use data from various basins and areas interstitial gases from the gulf of california are entirely of bacterial origin traces of thermogenic gases are formed only in the vicinity of dolerite sills gases in the south german molasse basin and in the vienna basin are of bacterial mixed and thermogenic origins data from the north italian po basin provide examples for genetic characterization of migrated gases

boron rich mud volcanoes of the black sea region modern analogues to ancient sea floor tourmalinites associated with sullivan type pb zn deposits large submarine mud volcanoes in the abyssal part of the black sea south of the crimean peninsula are similar in many respects to synsedimentary mud volcanoes in the mesoproterozoic belt purcell basin one of the belt purcell mud volcanoes directly underlies the giant sullivan pb zn ag deposit in southeastern british columbia footwall rocks to the sullivan deposit comprise variably tourmalinized siltstone conglomerate and related fragmental rock local thin pyrrhotite rich and spessartine quartz beds are interpreted as fe and fe mn exhalites respectively analogous fe and mn rich sediments occur near the abyssal black sea mud volcanoes massive pyrite crusts and associated carbonate chimneys discovered in relatively shallow waters 200 m depth west of the crimean peninsula indicate an active sea floor hydrothermal system subaerial mud volcanoes on the kerch and taman peninsulas 100 km north of the abyssal mud volcanoes contain saline thermal waters that locally have very high b contents to 915 mg l these data suggest that tourmalinites might be forming in or near submarine black sea mud volcanoes where potential may also exist for sullivan type pb zn mineralization

water rock interaction in tertiary sandstones san joaquin basin california u s a diagenetic controls on water composition three water types are recognized among petroleum associated waters of the southern san joaquin basin 1 meteoric water 2 diagenetically modified connate water and 3 mixed meteoric modified connate water the diagenetically modified connate marine water can be further subdivided into three types 1 fully mg depleted mg 1 mole of the sum of na k ca and mg 2 partially mg depleted and 3 ca enriched enrichment in ca which is the sharpest chemical divide found for the diagenetically modified connate water is the result of feldspar albitization the ca enriched waters are also rich in total dissolved al up to 6 mg l 1 and exhibit lighter 18o values than other diagenetically modified connate waters the total dissolved al abundance in these waters may be due to the presence of organic complexing agents simple and aromatic organic acids and phenolics the lighter 18o values are probably due to both albitization and the lack of substantial clay diagenesis illitization of smectite

light hydrocarbons in hydrothermal and magmatic fumaroles hints of catalytic and thermal reactions volcanic gaseous mixtures emitted from active volcanoes frequently show variable amounts of saturated alkanes unsaturated alkenes and aromatic volatile hydrocarbons three major patterns of distributions can be recognized apparently related to the chemical physical environment of formation of the gas exhalations alkane rich low temperature gas emissions from recently active volcanic areas aromatic rich hydrothermal manifestations and alkene rich magmatic fumaroles on active volcanoes thermodynamic data together with theoretical and practical findings from the petroleum industry point to two main types of reactions occurring in these volcanic environments cracking and reforming cracking processes mainly caused by thermal effects occur when hydrocarbon bearing hydrothermal fluids enter and mix with a hot and dry rapidly rising magmatic gas phase the most probable products are light alkenes with carbon numbers decreasing with increasing reaction temperatures the presence of aromatic species in hydrothermal fluids can be linked to reforming processes catalysed by several possible agents such as smectites and zeolites generally present in the hydrothermally altered volcanic terranes and facilitated by long residence times in a hydrothermal envelope

late cenozoic subduction complex of sicily abstract besides remnants of hercynian deformations in the peloritani nappe and of pre oligocene alpine structures in the troiani nappe most compressive structures observed in the sicilian accretionary wedge result from the late cenozoic tortonian to present continental subduction of the apulia iblei block and are thus synchronous with distensive structures related to the opening of the tyrrhenian sea syntectonic deposits fill southward migrating foredeeps in a sequential fashion and the dating of these deposits helps to constrain the timing of deformation similarly plio quaternary sediments eroded from the accreted units rest on top of the allochthon in either compressive piggy back depressions or extensional basins the age and configuration of these overlap deposits constrain our reconstructions of the subsurface geometry of the underlying peri tyrrhenian detachment faults or s verging thrust faults post depositional erosion normal faulting and syntectonic filling of basins contribute to maintaining the critical taper of the prism whose geometry is continuously altered owing to frontal accretion underplating and isostatic uplift

paleomagnetism of early cambrian redbeds on cape breton island nova scotia results are reported from steeply dipping red sandstones collected at nine sites 45 samples of the lower cambrian morrison river and maccodrum formations on southeast cape breton island which forms part of the avalon terrane demagnetization studies indicate minimal overlap of stability spectra in thermal alternating field and chemical treatments a stable component hematite with high unblocking temperatures 680 c is dominant at all sites its mean direction corrected for geologic tilt is d 281 i 32 k 97 giving a paleomagnetic pole pole m at 20 n 146 w dp dm 3 6 the corresponding in situ direction is d 147 i 59 k 97 with a pole m at 2 s 39 w dp dm 6 8 poles m and m were compared with published paleozoic poles for the avalon zone and cratonic north america to test whether the magnetization originated before or after the taconic ordovician folding it could have been acquired during deposition or early diagenesis early to middle cambrian in whic

an oxygen minimum palaeoceanographic signal from early toarcian cavity fills moderately deep marine toarcian sedimentary rocks of the medianes nappe alpine front ranges switzerland comprise calcarenites and lime mudstones they were deposited under storm and fairweather conditions in the dysaerobic zone near the storm wave base these remnants of the northern margin of the tethyan ocean show facies where primary sediment 9deep water9 stromatolitic micrite was reworked during early diagenesis stromatactis like cavities were formed by carbonate dissolution near the sediment water interface suboxic early diagenetic conditions are indicated by corroded pyrite and newly formed glauconitic oncoids carbon and oxygen stable isotope data indicate cavity stabilization and cementation above the sulphate reducing zone oceanographic conditions during the time of cavity development are reconstructed from the carbon and oxygen isotope composition of cavity cements of bulk sediment and of associated ammonites 13 c values of up to 4 are related to the oceanic anoxic event of the early toarcian and oxygen isotope values from cements and ammonites define a shallow toarcian thermocline

organic and inorganic geochemistry of low temperature gas discharges at the baia di levante beach vulcano island italy abstract discharge from subaereal and submarine gas vents of the baia di levante beach gases from the vulcano island were sampled for major and trace gas components in may and november 1995 chemical compositions and equilibrium calculations suggest three different groups of co 2 rich gas emissions depending on their distance from the la fossa crater 1 gas vents close to the faraglione area are characterised by high h 2 s contents high calculated equilibrium temperatures based on inorganic species and relatively high proportion of alkene compounds 2 gas vents close to vulcanello are characterised by low calculated equilibrium temperatures and low amounts of alkenes and 3 pontile sample has the highest equilibrium co 2 pressure up to 68 bars which may account for the observed absence of benzene the relative large variability of h 2 s in the baia di levante beach gas discharge may be attributed to either different interactions between iron sulphides and weakly acid waters or catalytic effect of elemental sulphur on the de hydrogenation of cyclo hexane thermodynamic calculations suggest that the main inorganic species and ch 4 may have re equilibrated at relatively shallow depth 10 200 m b s l and 30 600 m b s l for a lithostatic and hydrostatic pressure respectively the slow kinetics of reactions in the c n h 2 n c n h 2 n 2 systems with respect to that of ch 4 co co 2 may explain the observed propene propane ratios which can only be reached at reaction temperatures of 300 350 c this low speed of reactions can also explain the observed disequilibrium of c1 c4 alkanes

palinspastic restoration and paleogeographic reconstruction of the peri tyrrhenian area during the neogene abstract this paper presents the results of research carried out on the paleogeographic and geodynamic post collisional evolution of the peri tyrrhenian area from the southern alps to sicily during this post collisional evolution a back arc area thrust belt foredeep system developed in which the following tectono sedimentary zones can be distinguished from the external to the internal ones the foreland zone connected to the foredeep through a slope generally controlled by normal faults the foredeep an assymmetric depression with strong subsidence related to the compressional activity of the thrust zone the chain whose outward migration from the late oligocene onward was discontinuus with important stages of crisis partially connected to the mechanical response of different crustal thicknesses existing in the foreland the discontinuous satellite basins developed within the thrust belt the back arc basins developed in the inner part of the chain where the superposition of the extensional tectonics over previous compressional domains causes the fragmentation of the thrust belt leading to its destruction according to this model seven palinspatic maps are discussed regarding the following time intervals late oligocene 25 24 m y burdigalian 22 20 m y langhian 17 16 m y serravallin 15 13 m y tortonian 10 9 m y late messinian 5 5 5 3 m y and early pliocene 5 3 4 6 m y during five of these time intervals significant geodynamic modifications occurred in the whole peri tyrrhenian area leading to paleogeographic changes in any case the geodynamic evolution of the whole area seems clearly controlled by the activity of important bundles of tectonic lines transversal to the chain which in the same time interval in the outermost part of the thrust belt separated areas with different values of shortening and in tthe most internal zones separated segments having different amount of extension these tectonic lines certainly have a crustal significance and have probably acted along previous formed discontinuities