origin of formation waters of s e parts of the bohemian massif and the vienna basin abstract deep formation waters were sampled from boreholes on the s e slopes of the bohemian massif they are na cl hco 3 waters with tds in the range 6 52 g l 1 some of them are associated with gas and oil deposits the waters are rich in br and i and their dand 18 0 isotope compositions vary from 12 to 77 and 4 6 to 10 respectively the processes of concentration and dilution have been discussed based on deuterium and conservative element contents of the waters three regional groups can be identified in the plots br vs i and cl vs i the vienna basin samples vb southern s and northern n flanks of the bohemian massif bm the vb samples have as an end member brackish water with about 7 g l 1 cl about 40 marine component enriched in br and i this water has been later diluted by meteoric water of recent isotopic composition only 3 vb samples can be considered as derived from the dissolution of evaporites the salt content of the s and n end members is very close to or higher than sea water with an isotopic composition similar to the brackish water subaerial evaporation of diluted sea water is suggested as the process increasing salt content the evaporative enrichment of primary brackish solution can be estimated from extrapolation of cl vs i and br vs i plots to zero i about 25 mg l 1 br and 6 g l 1 cl for the southern flanks of the bm evaporated solutions were later diluted by meteoric waters with d in the range from 50 to 80 southern flanks and about 80 northern flanks

e i corrected paleolatitudes for the sedimentary rocks of the baja british columbia hypothesis paleomagnetic inclinations from sediments of the western terranes of canada are consistently too shallow for their reconstructed paleogeographic positions two contradicting explanations for these discrepancies are 1 terranes have been displaced northward with respect to the stable american craton by several thousands of kilometres between the late cretaceous 75 ma and the eocene 50 ma and 2 sedimentary inclination error has caused a shallow bias in the paleomagnetic directions here we apply the elongation inclination e i method to paleomagnetic data sets from sedimentary rocks of supposedly allochtonous terranes of western north america to correct for inclination flattening our results indicate that the paleomagnetic directions from the continental silverquick sediments 95 92 ma of southern british colombia are not seriously affected by inclination error because the magnetic signal most likely concerns a chemical remanent magnetisation crm in contrast the marine sediments of the nanaimo group 84 72 ma of vancouver island region appear seriously affected by inclination flattening f 0 7 and the e i corrected mean inclinations are about 98 steeper than the original data we arrive at corrected inclinations paleolatitudes of i 578 k 388n for the silverquick and i 558 k 368n for the nanaimo sediments our corrected paleolatitudes indicate that the canadian terranes were indeed located adjacent to the baja californian margin during the late cretaceous thus supporting the baja bc hypothesis d 2005 elsevier b v all rights reserved

neogene tectonic rotation of the santa ynez range western transverse ranges california suggested by paleomagnetic investigation of the monterey formation a paleomagnetic investigation was conducted on dolomite beds in the middle and upper miocene monterey formation in order to determine the timing and amount of post early miocene tectonic rotation experienced by the santa ynez range part of the western transverse ranges province of california five stratigraphic sections of the monterey formation exposed along the coastline west of santa barbara were extensively sampled the sections were correlated using tuff beds and ages were assigned to each dolomite bed on the basis of magnetostratigraphy and diatom biostratigraphy the dolomite beds possess stable primary remanent magnetic directions which pass fold tests and reversal tests and show a consistent decrease in magnetic declination with decreasing age rocks 14 8 to 15 8 m y old have a mean magnetic declination of 92 7 whereas rocks 8 to 11 m y old have a mean magnetic declination of 36 7 the consistent upsection decrease in magnetic declination within these stratigraphic sections is attributed to a rapid 56 10 clockwise rotation of the entire santa ynez range between 15 2 0 1 and 10 1 m y b p the mean magnetic declination of 36 7 in rocks 8 to 11 m y old is probably due to continued clockwise rotation of the santa ynez range during the plio pleistocene an early miocene palinspastic reconstruction is proposed in which the area of the presently east west trending santa ynez range is restored to an initially north south orientation

paleomagnetism of coastal california and baja california alternatives to large scale northward transport paleomagnetic data from the santa lucia orocopia sloa and baja borderland bba allochthons of coastal california and baja california have been interpreted to indicate up to 2500 km of post mid cretaceous northward transport of these regions with respect to interior north america however with neogene strike slip offsets taken into account geological interpretations correlate basement rocks of the coastal allochthons with continental basement rocks directly across the san andreas and related fault systems we have examined paleomagnetic data from sloa and bba and conclude that apparent discordances can be explained without large scale pre neogene tectonic transport three major observations are fundamental to this analysis 1 paleolatitudes derived from volcanic rocks of the jurassic eugenia formation of bba and coast range ophiolite of sloa are concordant when compared to revised jurassic reference paleomagnetic poles from interior north america 2 isotopic and paleobarometric data from the peninsula ranges batholith in southern california indicate that the batholith has been tilted northeast side up by an amount that can account for discordant paleomagnetic directions observed in plutonic rocks of the batholith without large scale northward transport 3 literal interpretation of the paleolatitudes determined from paleomagnetic directions in upper cretaceous and paleogene marine sedimentary rocks of sloa and bba requires north then south then north transport and a complex motion history between the two allochthons however concordant paleolatitudes are indicated by some sedimentary rocks while coeval or younger sedimentary rocks of the same allochthon have discordant paleolatitudes coupled with recent documentations of compaction shallowing of paleomagnetic inclination in other marine sedimentary rocks these inconsistencies suggest that paleolatitudes derived from most of the marine sedimentary rocks of sloa and bba are biased towards low paleolatitudes by compaction shallowing

rare earth elements as indicators of groundwater environment changes in a fractured rock system evidence from fracture filling calcite rare earth element ree abundances in core samples from precambrian crystalline rocks at the samkwang mine site provide evidence of the solution chemistry involved in precipitation of calcite on fractures the rock types collected in core samples are mainly banded gneisses with mineral assemblages dominated by biotite k feldspar quartz and plagioclase calcite chlorite muscovite and sericite occur as secondary minerals with calcite being the main filling material in fractures in general the core samples from 4 boreholes are enriched in light ree lree and depleted in heavy ree hree with negative eu anomalies however positive eu anomalies also occur at specific depths within 3 boreholes variation of chondrite normalized ree patterns results from the fracture filling calcite in core samples calcite fracture fillings provide a record of paleo hydrology where eu has been reduced and selectively concentrated in the solutions from which calcite has precipitated

seeping hydrocarbons and related carbonate mineralisations in sediments south of lihir island new ireland fore arc basin papua new guinea hydrocarbon gases have been sampled from both cold seeping and heat venting areas in the new ireland fore arc basin in the vicinity of lihir island highest concentrations of up to 10 l l ch4 with a 13cch4 value of 54 9 pdb have been measured in the deep ocean water within a long and narrow deep sea basin located between edison seamount and an uplifted structure named mussel cliff surface sediments of the seep area were covered with chemoautotrophic deep sea fauna such as calyptogena species and tube worms large authigenic calcite concretions occur in the sediments between 50 and 200 cm sediment depth the carbon isotopes of the carbonates in the concretions range from 15 to 40 pdb indicating a mixture of two co2 sources normal marine inorganic carbon fixed in biogenic shells and co2 from anaerobe bacterial oxidation processes of methane accordingly 14c ams dating suggests that authigenic calcite mineralisation incorporated relatively young carbon from methane oxidation in contrast the c1 c2 ratio of 234 and the 13cch4 value of 24 1 pdb in the hot hydrothermal vent of lihir harbour indicates a mixture of a major abiogenic carbon source for methane formation related to magmatism associated with lihir volcano the observed variable fluid characteristics within only 20 km distance between hot hydrothermal venting and the methane seeping deep sea area indicates highly variable heat flow situations and or sediment distributions which control the gas geochemical characteristics in the new ireland fore arc basin

composition and origin of natural gases accumulated in the polish and ukrainian parts of the carpathian region gaseous hydrocarbons noble gases carbon dioxide and nitrogen abstract ten natural gas samples associated and non associated with oil in the polish and ukrainian flysch carpathians and mesozoic basement of the carpathian foredeep were analysed for molecular and stable isotope compositions as follows 12 13c in ch4 c2h6 c3h8 and co2 1 2h in ch4 14 15n in n2 and 3 4he 20 21 22ne 36 38 40ar 84kr and 132xe in noble gases the gaseous hydrocarbons both in the silesian unit of the outer flysch carpathians and mesozoic basement are generally genetically related to thermogenic processes and occasionally to microbial carbon dioxide reduction these gases were mainly generated from mixed type ii iii kerogen during middle stage of the low temperature thermogenic processes gaseous hydrocarbons from starunia in the boryslav pokuttya unit were generated from type ii kerogen during middle stage of the low temperature thermogenic processes he is generally of crustal origin with more than 99 2 of radiogenic 4he but appreciable amount of 3he is probably derived from the upper mantle the 3he might have been derived from the pieniny klippen belt deep seated fault system or neogene and pleistocene andesitic and basaltic volcanism occurred in the eastern carpathian area nucleogenic 21ne and 22ne were analysed in all the samples the nucleogenic 21ne shows good correlation with radiogenic 4he with the production ratio of 4he 21ne 1 3 107 in the crust these isotopic values indicate a common source for these gases where both the nuclear reactions of decay and n are occurring concentrations of radiogenic 4he and 40ar and excess 21ne in the samples from the mesozoic basement are generally higher and more scattered compared with those in the silesian unit the larger concentrations of radiogenic and nucleogenic isotopes in the natural gases from the mesozoic basement is probably related to older geological formations than younger formations of the silesian unit carbon dioxide was generally generated during the thermal transformation of organic matter and occasionally during microbial processes nitrogen was mainly generated during thermal transformation of organic matter and also originated from atmosphere a least part of carbon dioxide and nitrogen may have been produced in crust

paleomagnetism of middle miocene volcanic rocks in the mojave sonora desert region of western arizona and southeastern california paleomagnetic directions have been obtained from 190 early to middle miocene 12 20 ma mafic volcanic flows in 16 mountain ranges in the mojave sonora desert region of western arizona and southeastern california these flows generally postdate early miocene tectonic deformation accommodated by low angle normal faults but predate high angle normal faulting in the region after detailed demagnetization experiments 179 flows yielded characteristic directions interpreted as original thermal remanent magnetizations trm because of the episodic nature of basaltic volcanism in this region the 179 flows yielded only 65 time distinct virtual geomagnetic poles vgps the angular dispersion of the 65 vgps is consistent with the angular dispersion expected for a data set that has adequately averaged geomagnetic secular variation the paleomagnetic pole calculated from the 65 cooling unit vgps is located at 85 5 n 108 9 within a 4 4 circle of 95 confidence this pole is statistically indistinguishable at 95 confidence from reference poles calculated from rocks of similar age in stable north america and from a paleomagnetic pole calculated from rocks of similar age in baja california the coincidence of paleomagnetic poles from the mojave sonora desert region with reference poles from the stable continental interior indicates that 1 significant vertical axis net tectonic rotations have not accompanied post middle miocene high angle normal faulting in this region 2 there has been no detectable post middle miocene latitudinal transport of the region and 3 long term nondipole components of the middle miocene geomagnetic field probably were no larger than those of the recent 0 5 ma geomagnetic field in contrast paleomagnetic data indicate vertical axis rotations of similar age rocks in the transverse ranges the eastern transverse ranges and the mojave block we speculate that a major structural discontinuity in the vicinity of the southeastward projection of the death valley fault zone separates western areas affected by vertical axis rotations from eastern areas that have not experienced such rotations

compaction corrected inclinations from southern california cretaceous marine sedimentary rocks indicate no paleolatitudinal offset for the peninsular ranges terrane paleomagnetic data have been used extensively to delineate the terrane displacement and accretion history of the western margin of north america however the anomalously shallow paleomagnetic inclinations used to indicate large scale northward translation might be alternatively interpreted as due to postmagnetization tilting of batholithic rocks and compaction of marine sediments to understand the magnitude of burial compaction effects on the post cretaceous motion history of the peninsular ranges baja borderlands terrane a rock magnetic compaction and paleomagnetic study of the ladd formation and the point loma formation from southern california was conducted the anhysteretic anisotropy of remanence of the characteristic remanence carrying grains and individual magnetic grain anisotropy were used to correct the inclinations of each formation individual magnetic grain anisotropy was determined by both compaction experiments and redeposition of a magnetic separate in a dc magnetic field standard paleomagnetic studies of the units indicated that previous ladd formation results could be reproduced and a correction was made at the sample level we were unable to adequately reproduce earlier results of the point loma formation so the average remanence anisotropy was used to correct the previously reported mean direction the mean inclination of the ladd formation was conected from 46 95 8 to 58 95 4 and the mean inclination of the point loma formation was conected from 39 5 5 4 normal and 36 4 16 6 reversed to 56 0 5 1 normal and 53 0 16 7 reversed these results suggest that the peninsular ranges baja borderland terrane has been part of the western north america since the late cretaceous and that clay containing sedimentary rocks may typically experience from 10 to 15 of inclination shallowing due to burial compaction

free hydrocarbon gas gas hydrate and authigenic minerals in chemosynthetic communities of the northern gulf of mexico continental slope relation to microbial processes research submersibles and piston cores were used to sample two chemosynthetic communities in the gulf of mexico continental slope at 540 m water depth vent gas from the deep subsurface is the starting material from which other carbon pools are derived including gas hydrate free hydrocarbon gas in sediment and authigenic carbonate rock gas crystallizes as exposed mounds of structure ii gas hydrate and as massive vein fillings in hemipelagic mud venting rates from gas hydrate mounds periodically increase after the temperature of the bottom water increases gas hydrate decomposition is largely restricted to exposed hydrate and at shallow depth in sediment overall gas hydrate is accumulating not decomposing at study sites most free gas in sediment appears to be destroyed in situ by anaerobic microbial oxidation in chemosynthetic communities leading to sequestration of carbon as abundant authigenic carbonate rock depleted in 13c free methane is rapidly oxidized leaving residual methane enriched in 13c some in situ microbial co2 reduction occurs and methane depleted in 13c mixes with vent methane enriched in 13c the c2 c5 hydrocarbons of vent gas initially most depleted in 13c ethane isobutane isopentane are least affected by microbial oxidation whereas hydrocarbons initially enriched in 13c propane normal butane normal pentane are most affected anaerobic microbial oxidation of all c1 c5 hydrocarbon gases not only methane may be significant in chemosynthetic communities microbial processes contribute to the development and stability of chemosynthetic communities by providing required h2s anaerobic microbial processes lead to deposition of diagnostic authigenic minerals related to the carbon carbonate minerals and sulfur cycles pyrite elemental sulfur altering the seafloor seafloor cementation favors fauna such as chemosynthetic tubeworms and seep mussels by forming carbonate hardgrounds on an otherwise unfavorable mud dominated seafloor

mesozoic paleomagnetism and northward translation of the baja california peninsula paleomagnetic data from cretaceous igneous and sedimentary rocks of the peninsular ranges and continental borderland of the baja california peninsula yield an average pole position of 83 n 344 e a95 3 4 suggesting that the peninsula as a whole has moved northward 11 and rotated 32 clockwise with respect to the north american craton since cretaceous time only a small portion of this movement is due to the neogene opening of the gulf of california results from stratified rocks giving both positive and negative fold tests are included in the average cretaceous pole the rocks that fail fold tests have been deformed and remagnetized by nearby intrusives that are only slightly younger unconnected directions from these sites closely match corrected directions from sites where the fold tests are positive oceanic rocks were also sampled in the continental borderland from upper triassic and upper jurassic tectonostratigraphic terranes which are apparently allochthonous with respect to the western baja peninsula and each other these oceanic rocks show magnetizations indicating low paleolatitudes although the hemisphere of origin is presently unknown the cretaceous rocks of the baja california peninsula may have originally formed adjacent to the now truncated continental margin along the northern middle america trench northward transport of the peninsula probably occurred by transcurrent faulting associated with oblique subduction of the farallon plate beneath western north america between late cretaceous and late miocene time

changing redox conditions at cold seeps as revealed by authigenic carbonates from alaminos canyon northern gulf of mexico anaerobic oxidation of methane in anoxic sediments at cold seeps often leads to formation of authigenic carbonates close to the seafloor along continental margins recent work however indicated that the redox conditions in sediments may vary to some degree during seepage activity in order to shed new light on the extent of this variability authigenic carbonates from alaminos canyon lease block 645 of the northern gulf of mexico have been characterized by means of inorganic and organic geochemistry the carbonates were collected from seep deposits representing various seafloor morphologies including extensive pavements mounds fractured carbonate slabs surrounded by dense bivalve shells and vestimentiferan tubeworm colonies the deposits almost entirely consist of aragonite the 18o values of aragonite vary from 2 6 to 5 8 v pdb suggesting precipitation in slight disequilibrium with the surrounding pore fluids the 13c values of aragonite between 33 9 and 20 4 v pdb agree with variable amounts of carbonate derived from oxidation of thermogenic methane and crude oil methane was primarily oxidized in an anaerobic process as revealed by the presence of 13c depleted molecular fossils of methane oxidizing archaea 13c values as negative as 118 and sulfate reducing bacteria 13c values as negative as 97 the syntrophic partners in the anaerobic oxidation of methane the observed inventories of molecular fossils in the authigenic carbonates mirror those of known consortia of anaerobic methane oxidizing archaea anme and sulfate reducing bacteria namely the anme 2 desulfosarcina desulfococcus dss and anme 3 desulfobulbus dbb consortia in contrast the same carbonates exhibit shale normalized rare earth elements patterns that all display real negative ce anomalies ce ce 0 78 suggesting that at least temporarily oxic conditions prevailed the episodic occurrence of oxic conditions is confirmed by the presence of molecular fossils of aerobic methanotrophic bacteria including 4 methylcholesta 8 14 24 dien 3 ol and two bacteriohopanepolyols aminotetrol and aminotriol the 13c values of the biomarkers of aerobic methanotrophs are as negative as 58 and are consequently less 13c depleted than the molecular fossils of the prokaryotes performing anaerobic oxidation of methane a pattern in accord with culture experiments overall our results suggest that redox conditions at cold seeps are variable this variability probably reflects changes in seepage flux the combination of an inorganic and an organic geochemical approach used here is promising to better assess the variability and diversity of past fluid and gas expulsion at seeps

mineral forming and diagenetic processes related to tertiary hydrocarbon seepage at the bohemian massif outer western carpathians interface evidence from the hrabůvka quarry moravia czech republic v lomu hrab vka situovanem p i hranici ceskeho masivu reprezentovan m zvrasn n mi spodnokarbonsk mi siliciklastiky kulmske facie a terciernim sedimentarnim pokryvem zapadnich karpat tvo enem spodnobadensk mi siliciklastiky a vapnit mi jily byl v geologickem zaznamu zjist n fosilni v v r uhlovodik v clanku jsou prezentovany mineralogicke izotopove a geochemicke udaje a take data ze studia fluidnich inkluzi ktere umo nily vyhodnotit genezi dan ch hornin il a jejich fluid

mesozoic evolution of exotic terranes and marginal seas western north america abstract regional terrane analysis has been combined with a global evaluation of plate kinematics to produce a new tectonic model for the mesozoic evolution of western north america and its associated marginal seas the model employs a two tiered data reliability ranking system to resolve conflicts within data sets the lower tier of the ranking system involves the assignment of a numerical rank to paleomagnetic and or paleobiogeographic data based on each data set s reliability the upper tier of the ranking system places the paleomagnetic and paleobiogeographic data in perspective by assigning a relative order of importance to different types of data the most reliable data are considered to be departure rift and arrival collision times that are tightly constrained by independent data sets evidence of subduction and or strike slip motion also ranks high in the master ranking system paleomagnetic and vertebrate paleobiogeographic data come next in the hierarchy followed by invertebrate and floral paleobiogeographic data application of this approach to a case study the baja british columbia controversy has resulted in a coherent model for the entire region results derived from the application of this modelling approach to the problem of the mesozoic assembly of western north america suggest that its evolution may be modeled using a minimum of 57 large terranes oblique convergence may have been the dominant tectonic process along the western north american margin during the mesozoic causing large scale latitudinal transport of many exotic terranes the motions of the terranes produced a number of marginal seas yukonia etc that were short lived but important components of western margin tectonics a combination of collision events side swiping episodes and changes in plate kinematics led to the initiation of several regional tectonic upheavals including the nevadan and sevier orogenies

paleomagnetic evidence that the central block of salinia california is not a far traveled terrane new paleomagnetic results from late cretaceous 75 85 m y red beds on the central block of salinia indicate that salinia was located within 6 in latitude of its current cratonal north american position during the late cretaceous after correction for neogene san andreas fault transport the red beds formed as alluvial fan overbank deposits with hematite cement deposited directly on salinian granites in the la panza range paleomagnetic analysis shows two components of magnetization in the red beds a low blocking temperature present day overprint residing in goethite and a high blocking temperature 600 component residing in hematite the hematite magnetization is a chemical remanent magnetization which formed soon after deposition during pedogenesis the bedding corrected hematite remanence contains a magnetic polarity stratigraphy with antipodal normal and reversed directions twenty three class i sites 95 20 have an average hematite direction with inclination 54 4 and declination 18 2 95 6 1 after structural correction these paleomagnetic data suggest that salinia resided at about 35 n latitude during the late cretaceous within 6 of its current location adjacent to cratonal north america by contrast a summary of paleomagnetic data from the peninsular ranges terrane and the sur obispo terrane which are currently outboard of salinia shows northward transport of these terranes of 12 to 22 relative to their current locations in north america since the cretaceous the offsets increase systematically away from the craton with the most outboard sur obispo terrane which is composed of accretionary prism and distal forearc material showing the largest degree of northward translation

compaction corrected paleomagnetic paleolatitudes for late cretaceous rudists along the cretaceous california margin evidence for less than 1500 km of post late cretaceous offset for baja british columbia the paleolatitudinal distribution of bivalve rudists has important significance for the baja british columbia baja bc hypothesis that western canadian superterranes from british columbia have been displaced 3000 km since cretaceous time rudists are not observed in baja bc sedimentary rocks yet they are common in late cretaceous strata in california and baja california which have the same paleomagnetically determined paleolatitudes approximately 25 n as baja bc rocks of late cretaceous age in order to resolve this contradiction and to delimit more exactly the southern paleolatitudes of baja bc paleomagnetic inclinations corrected for the effects of burial compaction were used to determine the paleolatitudinal distribution of rudists along the california margin compaction corrected paleomagnetic data from the peninsular ranges and salinia terranes indicate that rudists were restricted to paleolatitudes between 34 and 40 n evidence of coastal upwelling in the latest cretaceous marca shale may explain the northern limit of the rudist distribution these data suggest that baja bc was no farther south than 40 n in the late cretaceous thus limiting its post cretaceous displacement to less than 1500 km and that burial compaction has also affected the paleomagnetism of nanaimo group sedimentary rocks from vancouver island this result also helps resolve the conflict between paleomagnetic results which show 1500 km of post late cretaceous offset between the insular coast plutonic complex superterrane and the intermontane superterrane and geologic observations which can allow only tens of kilometers of offset between these terranes in the methow tyaughton basin

exotic terranes of western california numerous distinct geological terranes compose the north american cordillera1 there may be as many as 50 terranes in california alone2 critical to deciphering the history of cordilleran tectonic assembly is an understanding of the displacement history of individual terranes it is therefore important to know 1 whether a terrane has undergone significant motion with respect to the stable craton that is whether it is allochthonous or exotic 2 if so when relative motion started and stopped 3 from where an individual terrane originated and 4 the nature of interterrane movements we consider here the problem of determining whether the now juxtaposed salinian and stanley mountain terranes of california became amalgamated at or near their present position with respect to cratonic north america or if they collided at a considerable distance from their present positions and were later accreted to north america as a composite package the palaeomagnetic data that we present indicate that the latter was the case

remagnetization of cretaceous forearc strata on santa margarita and magdalena islands baja california sur implications for northward transport along the california margin paleomagnetic data for two sections of cretaceous forearc strata with different structural attitudes on santa margarita and magdalena islands in baja california sur mexico indicate that these rocks have been remagnetized probably during the late cenozoic the in situ paleomagnetic directions however are similar to data from other cretaceous rocks on peninsular california with unexpectedly shallow inclinations and easterly declinations these data have been interpreted as indicating either northward tectonic transport 10 15 of latitude and clockwise rotation 20 or compaction shallowing of magnetic inclinations in sedimentary rocks combined with southwestward tilting of plutonic rocks the available paleomagnetic data for cretaceous forearc strata in southern and baja california can be divided into three groups 1 sections with normal polarity magnetizations that fail fold tests and are remagnetized 2 sections with normal polarity magnetizations with no or inconclusive fold tests that may or may not be remagnetized and 3 sections with both normal and reversed polarity intervals where pervasive remagnetization has not occurred other rocks of the mesozoic great valley group coast range ophiolite and franciscan complex in california also have secondary magnetizations with directions similar to younger geomagnetic field directions although these widespread remagnetizations could have variable local causes we propose regional burial and uplift related to changes in subduction parameters as a possible explanation two episodes of remagnetization are apparent one in the late cretaceous and a second in the late cenozoic on the other hand the unremagnetized and apparently reliable data from sedimentary and plutonic rocks on the baja peninsula consistently indicate northward translation 14 3 and clockwise rotation 29 8 with respect to north america since the late cretaceous

kinematics of present crust and mantle flow in southern california in the southern california region published geologic studies of prehistoric fault offsets yield at least 81 rates of slip covering various periods of time chiefly since the opening of the gulf of california these rates together with the known geometries of active faults are used to constrain a hand fit block model for present horizontal velocity of the crust the assumptions employed are that these rates apply to the present that the blocks are internally rigid down to the greatest depth of earthquakes and that the over all pacific north american plate motion is correctly given by global models the resulting model fits 67 data within their uncertainties 10 more with a small discrepancy 1 mm yr and fails to accommodate only 4 data 2 of which are inconsistent with other data nominal precision is good 3 mm yr but accuracy and uniqueness are both suspect because many block boundaries are questionable despite its many local defects this model suggests four reliable regional conclusions first the rate of shortening on the south side of the transverse ranges varies from 6 to 14 mm yr increasing eastward which implies an unrecognized seismic hazard unless the motion is taken up by folding or fault creep second the pattern of block rotation rates is quite different from the pattern of rotations shown by tertiary paleomagnetic declinations which implies some major pliocene reorganization of blocks third the great bend left step of the plate boundary fault system in the transverse ranges appears to be straightening gradually by a 3 m y clockwise rotation relative to both plates finally if it is assumed that plate shortening has been occurring at this bend since the early pliocene and that crust and upper mantle velocities are similar then this model predicts mantle lithosphere downwelling to at least 250 km depth beneath the transverse ranges this prediction is consistent with upper mantle seismic velocity structure

diagenetic source of fluids causing the hydrothermal alteration of teschenites in the silesian unit outer western carpathians czech republic petroleum bearing vein mineralization from the střibrnik site calcite pyrite veinlets containing a small amount of quartz chlorite sphalerite and marcasite occur in teschenite which is situated within the lower cretaceous flysch siliciclastics of the silesian unit fluid inclusion study demonstrated the presence of a heterogeneous mixture of a low salinity aqueous solution and mature methane rich petroleum during precipitation of calcite and quartz the 13c values of methane and dissolved carbonate 34s values of pyrite and 18o values of parent hydrothermal solutions are all consistent with the external source of the fluid phase derived from diagenetically modified flysch sediments the vein formation occurred during an increase in both temperature from 80 c to 220 c and pressure 100 700 bar the observed discrepancy between the maximum fluid temperature and the regional burial temperature together with fluctuations in petroleum density and significant variations in chemical and isotopic compositions of fluids are interpreted in terms of episodic tectonically induced generation of the fluid phase related to deeper burial the observed ree patterns of hydrothermal calcite and pyrite can be attributed to increased concentrations of organic ligands in the fluid phase and or involvement of sorption desorption processes

new paleomagnetic rock magnetic and petrographic results from the valle group baja california mexico exploring the causes of anomalously shallow paleomagnetic inclinations 1 a detailed paleomagnetic rock magnetic and sedimentologic study was conducted on cenomanian age strata of the valle group at el campito baja california to examine the burial compaction effects on the paleomagnetic inclination of marine sedimentary rocks alternating field and thermal demagnetization isolated a characteristic remanence at 16 of 18 sites with a mean of dec 342 6 inc 19 1 and 95 3 4 the inclination is 38 7 shallower than that predicted by the reference paleopole for north america laboratory experiments indicate that compaction could account for only 7 5 of the inclination shallowing fold tests at different scales yield both positive and negative results making a tight constraint on the remanence s age impossible a primary postdepositional remanence is supported by bedding parallel foliations in the anisotropy of anhysteretic remanence fabric although primary anomalously shallow inclinations could indicate significant southerly then northerly paleolatitudinal offset a more likely scenario is a late cenozoic low temperature remagnetization which is suggested by alteration along the edges of some detrital silicate grains and a bimodal magnetic grain size distribution revealed by isothermal remanence data the synthesis of the data indicates that the vizcaino terrane was contiguous with the cordillera margin during remagnetization and underwent a subsequent 13 5 5 4 clockwise rotation we tentatively interpret that the remagnetization resulted from burial and or miocene volcanism which caused an acquisition of thermochemical remanent magnetization tcrm this study reveals a complicated remanence that resists easy interpretation and suggests caution in studies of similar rocks

plumbotectonic aspects of polymetallic vein mineralization in paleozoic sediments and proterozoic basement of moravia czech republic a regional isotopic study of pb and s in hydrothermal galenas and u pb and s in potential source rocks was carried out for part of moravia czech republic two major generations of veins syn variscan and post variscan are defined based on the pb isotope system together with structural constraints local structures and regional trends the pb isotopic compositions of galena plot in two distinct populations with outliers in 206pb 204pb 207pb 204pb space galena from veins hosted in greywackes provides a cluster with the lowest pb pb ratios 206pb 204pb 18 15 18 27 207pb 204pb 15 59 15 61 208pb 204pb 38 11 38 23 those hosted in both limestones and greywackes provide the second cluster 206pb 204pb 18 37 18 44 207pb 204pb 15 60 15 63 208pb 204pb 38 14 38 32 these clusters suggest model pb ages as early carboniferous and triassic jurassic the latter associated with mvt like deposits two samples from veins hosted in proterozoic rocks lie outside the two clusters in metagranitoid 206pb 204pb 18 55 207pb 204pb 15 64 208pb 204pb 38 29 and in orthogneiss 206pb 204pb 18 79 207pb 204pb 15 73 208pb 204pb 38 54 the results from these two samples suggest an interaction of mineralizing fluids with the radiogenic pb rich source basement the values of 34s suggest the paleozoic host rocks mostly 6 7 to 5 2 cdt as the source of s for hydrothermal sulfides mostly 4 8 to 2 5 cdt u pb data and pb isotope evolutionary curves indicate that late devonian and early carboniferous sediments especially siliciclastics are the general dominant contributor of pb for galena mineralization developed in sedimentary rocks plumbotectonic mixing occurred it is deduced only between the lower and the upper crust the latter involving proterozoic basement containing heterogeneous radiogenic pb without any significant input from the mantle it is concluded that in the moravo silesian and rhenohercynian zones including proximal districts in poland lead and sulfur have been mobilized from the adjacent rocks during multiple hydrothermal events in processes that are remarkably comparable in timing geochemistry of fluids and nature of sources

biochronology paleoenvironments and stratigraphic sequences of the late albian middle eocene fore arc vizcaino basin western baja california mexico the vizcaino fore arc basin accumulated approximately 4 km 13 000 ft of upper albian middle eocene siliciclastic marine sedimentary rocks derived from the peninsular ranges in baja california data from eight exploratory wells document the micropaleontological content and lithological characteristics of these rocks the strata studied represent mostly neritic upper bathyal marine environments and overlie a basement composed of cretaceous granitic rocks or aptian albian volcaniclastic sedimentary rocks correlative with the alisitos formation we recognize four major depositional sequences within the basin that are related to the regional geology the basal albian turonian sequence 1 represents the initiation of fore arc basin sedimentation contains continental conglomerates that change to bathyal shales and correlates with the lower part of the valle group of the vizcaino peninsula sequence 2 is coniacian paleocene includes basal conglomeratic sandstones grading into maastrichtian bathyal shales and usually overlies a coniacian santonian unconformity sequence 2 is represented at the surface by the rosario group in northwestern baja california and the upper part of the valle group in the vizcaino peninsula sequence 3 is paleocene middle eocene represents continuity of fore arc sedimentation in neritic upper bathyal conditions is capped by a major unconformity and correlates with the sepultura and bateque formations to the north and south of the basin respectively the uppermost miocene pliocene sequence 4 is composed of marine sandstone siltstone unconformably overlying sequence 3 and is correlative with the tortugas formation that represents sedimentation after the end of subduction of the farallon plate beneath the north america plate

rare earth elements in cold seep carbonates from the niger delta abstract the circulation of methane rich fluids at cold seeps often leads to precipitation of authigenic carbonates mediated by microbial activity which can be used as archives of fluid seepage on continental margins in this study we have investigated the potential of using rare earth element ree concentrations in authigenic carbonates for tracing fluid sources and providing information on associated biogeochemical processes at cold seeps we have examined various chemical procedures for the analysis of ree in authigenic carbonates and present a robust method using dilute acetic acid solution that allows the extraction of ree from carbonate phases with reduced contamination from fe mn oxides and detrital minerals using this method we analysed a series of carbonate samples collected at various deep sea sites of active fluid seepage on the niger delta for their ree and trace element concentrations 13c and 18o values and 87sr 86sr isotope compositions we show that the ree composition of cold seep carbonates is controlled primarily by that of the fluid from which they have precipitated our results also suggest that significant ree fractionation can occur during carbonate precipitation which can be related to various degrees of ree complexation by organic versus carbonate ligands in response to changing pore water chemical composition for parameters such as carbonate alkalinity

magnetostratigraphy of displaced upper cretaceous strata in southern california a magnetostratigraphic study of upper cretaceous marine strata from the santa ana mountains in southern california has identified a campanian reversed magnetozone this reversed interval corresponding to marine magnetic anomaly 33 34 chron 33r of campanian age can be correlated with a campanian reversed magnetozone that has been reported from strata of the great valley sequence in central california the late cretaceous paleolatitude of the santa ana mountains is estimated from this study to be 26 6 n this is significantly different from the region9s expected cretaceous paleolatitude of 43 8 n as part of the north american stable craton and indicates that this region part of the peninsular ranges terrane was 1900 km farther south in cretaceous time relative to the stable craton

composition and origin of coalbed gases in the upper silesian and lublin basins poland abstract coalbed gases in the upper silesian coal basin uscb are highly variable in molecular and stable isotope composition geochemical indices and stable isotope ratios for coalbed gases from uscb vary within the following ranges ch4 c2h6 c3h8 hydrocarbon index from 122 to more than 10 000 cdmi carbon dioxide methane index cdmi co2 co2 ch4 100 from 0 0 to 21 0 13c ch4 from 79 9 to 44 5 d ch4 from 202 to 153 13c c2h6 from 24 6 to 22 3 13c c3h8 24 7 one sample and 13c co2 from 27 2 to 2 8 only two coalbed gases were collected from the lublin coal basin lcb geochemical indices and stable isotope ratios for these samples show the following values hydrocarbon index more than 10 000 cdmi 4 3 and 34 6 13c ch4 67 3 and 52 5 d ch4 201 one sample and 13c co2 13 7 and 11 9 methane higher gaseous hydrocarbons c2 to c5 and carbon dioxide occurring in the coalbed gases in both the uscb and the lcb were generated during the bituminous stage of the coalification process and probably during microbial reduction of carbon dioxide however depth related isotopic fractionation which has resulted from physical e g diffusion and adsorption desorption processes during gas migration cannot be neglected in both basins the coalification process lasted no longer than several ma and was completed at the end of the variscan orogeny at the turn of carboniferous and permian

methane seepages recorded in benthic foraminifera from miocene seep carbonates northern apennines italy abstract benthic foraminifera from seep carbonates and from enclosing non seep marls present within miocene formations in the northern apennines italy were investigated as proxies of methane seepage in the marine environment negative 13c values of benthic foraminifera from these seeps indicate unambiguously the local influence of co2 produced by microbial anaerobic methane oxidation on the benthic ecosystem calcareous species living within methane seeps display 13c values ranging from 9 04 to 25 74 pdb whereas in the coeval surrounding marls the same species display 13c values from 1 54 to 0 62 pdb different species cibicidoides kullenbergi c pachyderma siphonina rethiculata planulina wuellestorfi bolivina miocenica brizalina dilatata vulvulina pennatula and cibicides praecinctus in different seep carbonates indicate that benthic foraminifera independently of the taxa and of microhabitat preferences have more negative 13c values than those found in the enclosing marls therefore each species represents a potential proxy for past seafloor methane emissions in addition to the calcareous species the agglutinated species vulvulina pennatula displays 27 5 pdb in seep carbonates against 2 69 pdb in the enclosing marls this suggests that the species utilized strongly 13c depleted carbonate particles from authigenic carbonate precipitation during the mineralization of their tests

shifts in oxygen and carbon isotope signals in marine molluscs from the central paratethys europe around the lower middle miocene transition abstract stable isotope data of mollusc shells from two adjacent time slices karpatian badenian from the central paratethys were investigated to detect differences in environmental parameters and to depict shifts in the isotope signature of the paratethyan seawater around the early middle miocene transition altogether seventeen different gastropod species and one bivalve species from the karpatian korneuburg basin and the badenian northern alpine foreland basin were selected representatives of various ecological guilds yielded different isotope patterns especially in 13c reflecting different original habitats or nutrition although molluscs precipitate their shells in oxygen isotopic equilibrium we preferred to compare isotope data of shells of the same genus of the family turritellidae from the karpatian and badenian the badenian turritella shells from the northern alpine foreland basin yielded distinctly higher 18o and 13c values than the respective karpatian shells from the korneuburg basin as the main factors controlling 18o values in gastropod shells are temperature and 18o of the water during precipitation the differences between the oxygen isotope data of the two time slices can only be explained by these factors good independent palaeotemperature proxies exist for the early to middle miocene of central europe they do not indicate a significant temperature variation therefore different 18o values of the seawater in the different basins of the central paratethys must be responsible for the contrasting 18o values when calculated with commonly assumed 18o seawater values for the miocene badenian turritella shells indicate too cold temperatures these data clearly document the danger of palaeotemperature interpretations based solely on stable isotopes as smaller and marginal marine settings such as the paratethys sea can be seriously influenced by regional differences in the isotope composition of the seawater only a thorough consistent control by other climate proxies e g palaeoecology of molluscs as in this study allows a sensible interpretation

palaeolatitude drift history of displaced terranes in southern and baja california the delineation of microplate tectonic terranes1 which make up western north america the timing of their accretions to western north america and the identification of their original geological settings are all topics of debate2 3 the most recent addition to this family of terranes is the santa lucia orocopia allochthon4 5 sloa fig 1 which is made up of salinia6 7 and several other smaller terranes8 and is located in central and southern california this composite terrane amalgamated in the cretaceous and accreted to southern california by the early palaeogene4 5 we describe here new palaeomagnetic results from localities outboard from the sloa in southern california usa and baja california mexico these results are used to define a newly identified allochthonous terrane in southern and baja california peninsular ranges terrane9 prt which is outboard from the sloa estimate the prt s palaeolatitude drift history for the past 160 myr and infer its original geological setting prt and sloa palaeolatitude drift histories are then combined to produce a new perspective on the tectonic development of southern and baja california over the past 160 myr

microbial hydrocarbon gases in the witwatersrand basin south africa implications for the deep biosphere in this study compositions and 13c and 2h isotopic values of hydrocarbon gases from 5 mines in the witwatersrand basin south africa support the widespread occurrence of microbially produced methane in millions of years old fissure waters the presence of microbial methane is to a large extent controlled by the geologic formations in which the gases are found samples from the witwatersand supergroup have the largest microbial component based on 13c and 2h signatures and ch4 c2 values based on mixing between a microbial ch4 component and a more 13c enriched and 2h depleted c2 rich end member conservative estimates of the contribution of microbial ch4 to the gas samples range from 90 microbial ch4 at beatrix masimong and merriespruit to between 5 and 80 microbial ch4 at evander and 18 microbial ch4 at kloof the witwatersrand basin s history of thermal alteration of organic rich ancient sedimentary units suggests a thermogenic origin for this 13c enriched end member alternatively the potential for an abiogenic origin similar to hydrocarbon gases produced by water rock interaction at other precambrian shield mines is discussed microbial methane is predominantly found in paleo meteoric fissure waters with 18o and 2h values that fall on the meteoric waterline and have temperatures between 30 to 40 c in contrast fissure waters with a larger component of nonmicrobial hydrocarbon gases show a trend towards more enriched 18o and 2h values that fall well above the meteoric waterline and temperatures of 45 to 60 c the enrichment in 18o and 2h in these samples and their high salinity are similar to the isotopic and compositional characteristics of saline groundwaters and brines produced by water rock interaction at precambrian shield sites elsewhere the reported 100 ma ages of fissure waters from the witwatersrand and ventersdorp formations suggest that these microbial hydrocarbon gases are the product of in situ methanogenic communities in the deep subsurface of the witswaterand basin small subunit ribosomal rna genes were amplified using archaeal specific primer sets from dna extracts derived from several of these waters fissure waters with a high proportion of microbial methane also contained sequences resembling those of known methanogens

chemical and carbon isotopic evolution of hydrocarbons during prograde metamorphism from 100 c to 550 c case study in the liassic black shale formation of central swiss alps abstract hydrocarbon distributions and stable isotope ratios of carbonates 13ccar 18ocar kerogen 13cker extractable organic matter 13ceom and individual hydrocarbons of liassic black shale samples from a prograde metamorphic sequence in the swiss alps were used to identify the major organic reactions with increasing metamorphic grade the studied samples range from the diagenetic zone 17 n alkanes suggests the occurrence of cracking reactions of high molecular weight compounds the isotopically heavier up to 5 6 c 13 n alkanes with metamorphism suggests progressive thermal release of kerogen linked fatty acid precursors and degradation of n alkanes changes of the steroid and terpenoid distributions are clearly related to increasing metamorphic temperatures the absence of 18 h 22 29 30 trisnorneohopane ts the occurrence of 17 h trisnorhopane 17 h 21 h hopanes in the c29 to c31 range and 5 h 14 h 17 h 20r c27 c29 steranes in the low diagenetic samples the occurrence of specific hydrocarbons e g n alkylcyclopentanes cadalene hydrogenated aromatic compounds in metamorphic samples points to kerogen degradation reactions most probably occurring in the presence of water and under reducing conditions the changes of hydrocarbon distributions and carbon isotopic compositions of n alkanes related to metamorphism suggest that the organic geochemistry may help to evaluate the lowest grades of prograde metamorphism

jiulong methane reef microbial mediation of seep carbonates in the south china sea chemoherm carbonates as well as numerous other types of methane seep carbonates were discovered in 2004 along the passive margin of the northern south china sea lithologically the carbonates are micritic containing peloids clasts and clam fragments some are highly brecciated with aragonite layers of varying thicknesses lining fractures and voids dissolution and replacement is common mineralogically the carbonates are dominated by high magnesium calcites hmc and aragonite some hmcs with mgco3 contents of between 30 38 mol extreme hmc occur in association with minor amounts of dolomite all of the carbonates are strongly depleted in 13c with a range from 35 7 to 57 5 pdb and enriched in 18o 4 0 to 5 3 pdb abundant microbial rods and filaments were recognized within the carbonate matrix as well as aragonite cements likely fossils of chemosynthetic microbes involved in carbonate formation the microbial structures are intimately associated with mineral grains some carbonate mineral grains resemble microbes the isotope characteristics the fabrics the microbial structure and the mineralogies are diagnostic of carbonates derived from anaerobic oxidation of methane mediated by microbes from the succession of hmcs extreme hmc and dolomite in layered tubular carbonates combined with the presence of microbial structure and diagenetic fabric we suggest that extreme hmc may eventually transform into dolomites our results add to the worldwide record of seep carbonates and establish for the first time the exact locations and seafloor morphology where such carbonates formed in the south china sea characteristics of the complex fabric demonstrate how seep carbonates may be used as archives recording multiple fluid regimes dissolution and early transformation events

organic geochemical study and genetic correlation of natural gas oil and menilite source rocks in the area between san and stryi rivers polish and ukrainian carpathians abstract we studied the source rocks and petroleum accumulations in the carpathian mountains of the polish ukrainian border area between the san and stryi rivers a total of 108 oligocene menilite formation rock samples 12 oil and 15 gas samples accumulated in the oligocene reservoirs and one oil and gas sample from an upper cretaceous reservoir were analysed the aim of this study was to evaluate the petroleum potential of the menilite formation in this area and to evaluate potential genetic correlations between source rock and petroleum the menilite formation represents a prolific source rock with toc content ranging from 2 to 7 wt locally exceeding 20 wt algal type ii and mixed type ii iii kerogens dominate but sometimes type iii kerogen and rarely type i kerogen occur thermal maturity of the oligocene menilite formation increases from outer to inner tectonic units from the immature in the boryslav pokuttya and skole units to the overmature in the southern parts of silesian and dukla units as a consequence petroleum potential decreases in the same order geochemical analyses reveal that oil and gas generation and migration processes within the carpathian flysch succession are complicated all analysed oils were generated from the menilite formation during early and peak stages of the oil window associated gas is of low temperature thermogenic origin sometimes containing an admixture of microbial gas high temperature thermogenic gas occurs only in the polish part of the silesian unit

isotopic compositions of diagenetic dolomites in the tortonian marls of the western mediterranean margins evidence of past gas hydrate formation and dissociation abstract previous studies in the lorca basin s e spain sediment geol 2002 have shown that the diagenetic dolomitic concretions from the tortonian marls are related to the past occurrence of gas hydrates which were rapidly dissociated when the sea level dropped during the messinian salinity crisis these conclusions were based on the oxygen and carbon isotopic compositions of these dolomites which indicated that the carbonate diagenesis occurred either in 13 c rich 18 o poor solutions as it is typical in gas hydrate systems or in 13 c poor 18 o rich solutions generated during gas hydrate decomposition we have recently discovered similar dolomitic nodules in other tortonian marly successions from s e spain and northern morocco the oxygen and carbon isotopic compositions of the diagenetic dolomites from these areas in spain and morocco are very similar to those from the lorca basin this demonstrates that the dolomitic nodules from the tortonian marls of the betic and rifian basins were all related to the same diagenetic environments where pore fluids were modified by gas hydrate formation dissociation processes these overall observations in s e spain and northern morocco suggest that the dissociation of gas hydrates during the messinian salinity crisis was not a local phenomenon but corresponded to a major event which affected both sides of the western mediterranean margins it might have been initiated during the first major restriction step that started around 6 7 ma in the mediterranean sea and probably climaxed at 5 9 ma when the mediterranean sea level dropped by more than 1000 m during the salt deposition stage

paleomagnetic and geologic data indicating 2500 km of northward displacement for the salinian and related terranes california results of a pair of paleomagnetic studies of sedimentary rocks in the salinian terrane of westernmost california indicate a northward displacement of about 2500 km since cretaceous time stratigraphic relations suggest that the salinian terrane became amalgamated with several others by the late cretaceous and all underwent the same northward translation this composite terrane allochthon became sutured to cratonal north america by early tertiary time one paleomagnetic study involved upper cretaceous turbidites of the pigeon point formation fine grained thin bedded turbidites yielded the most reliable results whereas medium to coarse grained sandstones are not always stably magnetized contorted layers resulting from soft sediment deformation usually gave directional results parallel to those of undeformed sedimentary layers thereby implying a postdepositional remanence process there is no indication of inclination error or other processes affecting the fidelity of the remanent magnetization paleomagnetic results from four separate locations in the pigeon point formation gave positive fold tests and mean inclination values near 36 a mean geomagnetic latitude calculated from these results is 21 2 5 3 much more southerly than the value of 46 5 2 3 calculated for pigeon point using paleomagnetic pole data from late cretaceous rocks from cratonic north america declination values are not antipodal for normal and reversed polarity sites analysis of depositional current directions from sandstone beds of the same outcrops shows that the difference is the result of neogene rotations of small crustal blocks adjacent to the san gregorio fault in a sequence of paleocene turbidites that crop out at point san pedro four sample localities yielded positive fold tests with mean inclination values near 40 declination values however were spread over a range between 230 and 320 comparison with depositional current directions from the same outcrops indicates clockwise rotations related to neogene right slip on the pilarcitos fault the mean geomagnetic latitude calculated for the point san pedro sediments is 24 5 4 0 and is more southerly than the 43 3 2 5 latitude expected for that location for the salinian terrane and the west coast of cratonic north america absolute rates of latitudinal motion were 8 5 cm yr northward and 3 cm yr southward respectively

late cretaceous intra arc thrusting in southern california thick zones of mylonitic rock are exposed in or between a number of the suspect crystalline terranes in the transverse ranges and eastern peninsular ranges of southern california after palinspastic reconstruction of strike slip displacements along neogene faults in the region the mylonite zones appear in a semicontinuous belt several hundred kilometers long mylonitic deformation in these areas is of a similar style and age lineation trends in the mylonitic rocks are closely aligned when palinspastic reconstruction takes into account the block rotations in the region and the sense of shear is consistently west directed the mylonite zones appear to have formed concurrently in a major midcrustal thrust system that juxtaposed the basement terranes during the late cretaceous a kinematic model is proposed in which a west directed ductile thrust zone along the eastern side of the peninsular ranges is offset by a sinistral tear fault or lateral thrust ramp along the southern margin of the san gabriel mountains from a ductile thrust underlying crystalline basement terranes to the north this model requires the suspect basement rocks of the peninsular and transverse ranges to be linked tectonically by the latest cretaceous this late cretaceous thrust system also appears to continue directly into autochthonous basement rocks in the san bernardino mountains the late cretaceous westward displacement of basement rocks in the transverse ranges relative to the northern end of the peninsular ranges batholith is mirrored by similar tectonic movement around the southern end of the sierra nevada batholith it is argued here that a formerly continuous batholithic belt was breached by ductile west directed thrusting during the late cretaceous between the two still recognizable batholiths the salinia terrane represents the westernmost portion of this westward escaping arc segment and would have been established as a crustal salient by the latest cretaceous this model implies that the basement terranes involved in this thrusting episode are parautochthonous fragments of a cretaceous continental arc and refutes suggestions that they have been accreted in the cenozoic

cold seep deposits of beauvoisin oxfordian southeastern france and marmorito miocene northern italy microbially induced authigenic carbonates the relation of two well known ancient carbonate deposits to hydrocarbon seepage was confirmed by this study archaea are found to be associated with the formation of oxfordian seep carbonates from beauvoisin and with a miocene limestone from marmorito tube worm limestone carbonates formed due to a mediation by archaea exhibit extremely positive or extremely negative 13ccarbonate values respectively highly positive values 15 reflect the use of 13c enriched co2 produced by methanogenesis low 13c values of the marmorito carbonates 30 indicate the oxidation of seepage derived hydrocarbons likewise the 13c content of specific tail to tail linked isoprenoids biomarkers for archaea was found to be strikingly depleted in these samples as low as 115 the isotopic signatures corroborate that archaea were involved in the cycling of seepage derived organic carbon at the ancient localities another miocene limestone marmorito limestone shows a strong imprint of methanotrophic bacteria as indicated by 13c values of carbonate as low as 40 and biomarker evidence epifluorescence microscopy and field emission scanning electron microscopy revealed that bacterial biofilms were involved in carbonate aggregation in addition to lucinid bivalves previously reported from both localities we infer that sponges from beauvoisin and tube worms from marmorito depended on chemosynthesis as well low 13c values of nodules related to sponge taphonomy 27 indicate that sponges might have been linked to an enhanced hydrocarbon oxidation tube worm fossils from marmorito closely resemble chemosynthetic pogonophoran tube worms from recent cold seeps and are embedded in isotopically light carbonate 13c 30

a compaction correction for the paleomagnetism of the cretaceous pigeon point formation of california the paleomagnetism of the cretaceous pigeon point formation turbidites was reexamined to determine whether the 25 of southerly paleolatitudinal offset originally observed champion et al 1984 for these rocks was all or in part due to compaction shallowing of their paleomagnetic inclination the study consisted of two parts 1 a standard paleomagnetic study including detailed thermal and alternating field demagnetization was conducted on oriented cores collected at pigeon point approximately 50 km south of san francisco california the results of this study were combined with the alternating field demagnetized results for samples provided by d champion from the initial pigeon point paleomagnetic study the combined data set has a mean direction for pigeon point i 41 6 d 346 9 similar to that originally obtained by champion et al 1984 2 material from the pigeon point formation was disaggregated given a laboratory analog of a postdepositional remanence and compacted to pressures as high as 0 13 mpa which caused volume losses up to 53 the laboratory compacted samples were alternating field demagnetized and their magnetic inclination and anisotropy of anhysteretic remanence were both measured these data were used to derive correction curves following jackson et al 1991 which describe the specific relationship between remanence anisotropy and inclination shallowing for the pigeon point formation two correction curves were determined one assuming that the magnetic particle orientation distribution experienced a prolate deformation after remanence acquisition and one assuming an oblate deformation these two different corrections were necessary because the anisotropy of anhysteretic remanence indicates a composite fabric due to both a prelithification technically caused lineation and a burial compaction foliation the anisotropy of anhysteretic remanence measured for each paleomagnetic sample and the correction curves determined from the laboratory compaction experiments indicate that the inclination of the pigeon point formation has been shallowed by burial compaction the compaction corrected pigeon point mean directions assuming either a prolate i 53 1 d 347 2 or an oblate i 49 8 d 346 8 deformation suggest only 13 to 16 of southerly paleolatitudinal offset for the pigeon point formation in the cretaceous not the 25 originally observed champion et al 1984 the resulting paleolatitude for the pigeon point formation could indicate that salinia served as a link between the cratonic sierra nevada arc to the north and the peninsula ranges baja borderlands allochthon to the south alternatively our results suggesting a 10 compaction inclination shallowing for the pigeon point turbidites may indicate that many of the paleomagnetic studies placing the peninsula ranges baja borderlands 15 to the south of north america in the cretaceous and tertiary may have suffered from a similar effect and that the allochthon has been nearly in place since the cretaceous

origin of methane in quartz crystals from the tertiary accretionary wedge and fore arc basin of the western carpathians abstract quartz crystals from mineralised joints of the carpathian flysch contain fluid inclusions covering the compositional range from gaseous ch4 co2 c2 mixture through ch4 saturated oil to ch4 saturated aqueous solution the c isotope composition of ch4 extracted from the fluid inclusions 31 and 36 v pdb is indicative of a thermogenic dry gas released from overmature rocks although the maturation level of the surrounding flysch corresponds to a wet gas generating zone trapping pt conditions for the ch4 bearing fluids range between 130 and 205 c and 0 5 and 3 7 kbar the fluid inclusion derived crystallisation temperatures are inconsistent with the vitrinite reflectance data strongly fluctuating fluid pressures during growth of the quartz crystals indicate the existence of a crack seal mechanism with recurrent hydrostatic and lithostatic regimes fluid pressures exceeding the lithostatic load have been recorded in the dukla nappe the overpressures have been generated by fluid volume increase due to thermal decomposition of oil and kerogen to ch4 and pyrobitumen occurrence of oil and condensate in the ch4 bearing inclusion fluids trapped at temperatures considerably above oil window suggest a short termed transient post orogenic heating rather than a prolonged heating related to burial the thermal event giving rise to the quartz crystallisation has been coincidental with regional collapse and uplift of the western carpathians

fluid inclusions in sedimentary and diagenetic systems abstract some of the major problems in sedimentary geology can be solved by using fluid inclusions in sedimentary and diagenetic minerals important fluids in the sedimentary realm include atmospheric gases fresh water of meteoric origin lake water seawater mixed water evaporated water formation waters deep in basins oil and natural gas preserving a record of the distribution and composition of these fluids from the past should contribute significantly to studies of paleoclimate and global change research is essential for improving understanding of diagenetic systems and provides useful information in petroleum geology applications of fluid inclusions to sedimentary systems are not without their complexities some fluid inclusions exposed to natural conditions of increasing temperature may be altered by thermal reequilibration which results in stretching or leakage and refilling of some fluid inclusions similarly overheating in the laboratory can also cause reequilibration of fluid inclusions so fluid inclusions from the sedimentary realm must be handled carefully and protected from overheating natural overheating of fluid inclusions must be evaluated through analysis of the most finely discriminated events of fluid inclusion entrapment fluid inclusion assemblages fia consistency in homogenization temperatures within a fluid inclusion assemblage consisting of variably sized and shaped inclusions is the hallmark of a data set that has not been altered through thermal reequilibration in contrast fluid inclusion assemblages yielding variable data may have been altered through thermal reequilibration if a fluid inclusion assemblage has not been altered by thermal reequilibration its fluid inclusions may be useful as geothermometers for low and high temperature systems or useful as geobarometers applicable throughout the sedimentary realm if a fluid inclusion assemblage has been altered partially by thermal reequilibration techniques for distinguishing between altered and unaltered fluid inclusions may be applied in studies of global change fluid inclusions can be used as sensitive indicators of paleotemperature of surface environments fluid inclusions also preserve microsamples of ancient seawater and atmosphere the analysis of which could figure prominently into discussions of past changes in chemistry of the atmosphere and oceans in petroleum geology fluid inclusions have proven to be useful indicators of migration pathways of hydrocarbons they can delineate the evolution of the chemistry of hydrocarbons and they remain important in understanding the thermal history of basins and relating fluid migration events to evolution of reservoir systems in studies of diagenesis fluid inclusions can be the most definitive record most diagenetic systems are closely linked to temperature and salinity of the fluid thus fluid inclusions are sensitive indicators of diagenetic environments

combined tectonic sediment supply driven cycles in a lower carboniferous deep marine foreland basin moravice formation czech republic the lower carboniferous moravian silesian culm basin mscb represents the easternmost part of the rhenohercynian system of collision related deep water foreland basins culm facies the upper visean moravice formation mf of the mscb shows a distinct cyclic stratigraphic arrangement two major asymmetric megacycles bounded by basal sequence boundary each about 500 to 900 m thick have been revealed the megacycles start with 50 to 250 m thick basal segments of erosive channels overbank successions and slope apron deposits interpreted as lowstand turbidite systems up section they pass into hundred metre thick fine grained low efficiency turbidite systems palaeocurrent data show two prominent directions basin axis parallel ssw nne directions which are abundant in the whole mf and basin axis perpendicular to oblique w e to nw se directions which tend to be confined to the basal parts of the megacycles or channel lobe transition systems in their upper parts based on the facies characteristics palaeocurrent data sandstone composition data and trace fossil distribution data we suggest a combined tectonics sediment supply driven model for the mf basin fill periods of increased tectonic activity resulted in slope oversteepening probably combined with increased rate of lateral w e sediment supply into the basin producing the basal sequence boundary and the subsequent lowstand turbidite systems during subsequent periods of tectonic quiescence the system was filled mainly from a distant southern point source producing the thick low efficiency turbidite systems consistently with the previous models our own sediment composition data indicate a progressively increasing sediment input from high grade metamorphic and magmatic sources up section most probably related to an uplift in the source area and progressive unroofing of its structurally deeper crustal parts the first occurrence of the cruziana nereites ichnofacies in sand rich turbidite systems in the youngest parts of the mf go el to go spi zone supported by rapidly increasing quartz concentrations in sandstones is thought to indicate a transition from generally underfilled to generally overfilled phase in evolution of the mscb basin this transition may be linked to the onset of upper visean phase of northward basin fill progradation assumed by previous authors

geological geochemical and microbial processes at the hydrate bearing hakon mosby mud volcano a review abstract submarine mud volcanoes are point sources of fluid expulsion and oases of active geological geochemical and microbial processes in the deep ocean the results of multidisciplinary investigations at the hakon mosby mud volcano hmmv in the norwegian sea at 1250 m water depth are reviewed in this paper seafloor morphology lithotypes geochemical and biological processes at the hmmv are concentrically zoned the zonation is controlled by ejection of sediment water and gases mainly methane accompanied by high heat flow in the mud volcano crater a structural gas hydrate accumulation is associated with the hmmv gas hydrate is abundant only in a relatively narrow zone where optimal conditions low temperature and high gas concentration exist for gas hydrate crystallization authigenic minerals bacterial mats and chemosynthetic communities typical of cold seep environments are present rapid anaerobic sulfate dependant oxidation of methane is thought to be mediated by a consortium of methanogens and sulfate reducing bacteria although methane is oxidized in sediments at high rates a significant portion of this gas may escape into the ocean mainly as diffuse flux in the water column methane is rapidly dissolved and oxidized this observation supports the hypothesis that gas flux from deep water mud volcanoes contributes to the oceanic carbon pool but not to the atmosphere the hmmv represents an important natural laboratory and provides insight to processes at the interface of methane rich sediments and cold bottom water in the deep ocean future studies may best focus on accurate direct measurements of gas flux and quantification of the biogeochemical cycling of major chemical elements in shallow sediment

anatomy of seep carbonates ancient examples from the miocene of the northern apennines italy ancient hydrocarbon seep carbonates of miocene age have been reported from marine sedimentary successions of the northern apennines in the form of irregularly shaped micritic masses containing abundant fossil remains of oligotypic assemblages they are recognized by their peculiar biological sedimentological and geochemical features and represent an excellent on land example of carbonate bodies interpreted as the remains of ancient cold seeps in the apenninic chain the abundance and the extent of the outcrops provide a rare opportunity to study the geometry facies distribution and internal structures of fossil methane derived carbonates the present study reports an integrated view of the sedimentology mineral paragenesis and geochemistry of these seep carbonates in two different tectono sedimentary settings foredeep and satellite basins the main result of this study is the recognition of 17 facies in the investigated seepcarbonates the detailed facies and microfacies analysis led to the identification of different structures which occur in welldefined parts of the carbonate masses the recurring and broadly similar stratigraphy and facies association from the two considered geological environments is diagnostic of the different stages of seep carbonate formation and evolution d 2005 elsevier b v all rights reserved

carbon stable isotopic composition of benthic foraminifera from pliocene cold methane seeps cascadia accretionary margin abstract cold methane seep carbonates preserve the distinctive carbon stable isotope signatures of their ambient porewaters thus facilitating the identification of methane sources and fluid migration pathways this study employs an isotopic indicator from microfossils in a diffuse fossil seep for the recognition and characterization of methane seepage in the rock record benthic foraminifera from the pliocene quinault formation western washington state are plentiful and provide a temporal link between modern and more ancient seeps stable carbon isotope analyses of individual foraminiferal tests revealed a clear distinction between seep and non seep foraminifera infaunal species globobulimina pacifica and nonion basispinatum collected from seep samples exhibited 13 c values that were highly variable and often strongly depleted values ranged from 33 1 to 55 3 pdb in g pacifica and from 2 1 to 42 9 pdb in n basispinatum the epifaunal species cibicidoides mckannai though less depleted also showed considerable variability with 13 c values ranging from 1 7 to 3 1 pdb in contrast non seep specimens were much more enriched and less variable non seep specimens of n basispinatum displayed 13 c values clustering between 0 5 and 1 5 pdb while non seep specimens of c mckannai yielded a range of 1 1 to 1 8 pdb sem analyses and oxygen isotope values of foraminiferal tests indicated minimal diagenetic alteration 13 c values from authigenic blebs small nodules with wispy indistinct boundaries ranged from 8 7 to 38 4 pdb by combining these inorganic carbonate data with the foraminiferal values the association of seep specific bivalves and the present day leakage of thermogenic methane from the nearby garfield gas mound we conclude that these foraminifera precipitated their tests in the presence of methane derived carbon thus they record pore water 13 c depletion and syn depositional fluid flow pathways near the sediment water interface in a seep system active 3 4 mya and continuing onshore and offshore today the range and degree of 13 c depletion in the pliocene microfossils is due to the heterogeneity of seepage caused by different methane sources i e thermogenic and biogenic the tortuosity of fluid migration pathways reaching the seafloor sediments and mixing of seep fluids with dissolved inorganic carbon dic and marine organic carbon

where are the missing faults in translated terranes abstract a central dilemma in understanding terranes that have translated long distances is that modern plate tectonics and paleomagnetic studies indicate translations of thousands of kilometers while the faults along which the terranes moved these great distances are not found relations long known from geology and from recent studies of modern transform plate boundaries suggest that preserving strike slip faults that record 1000 km scale translations is unlikely and therefore in many cases paleomagnetism may be our only reliable indicator of how far terranes translated four reasons are explored here for why large offset strike slip faults are likely to be missing in translated terranes 1 strike slip faults in continents commonly are partially or wholly destroyed or reactivated only 400 500 km of over 1000 km of offset on cretaceous early tertiary strike slip faults in northern british columbia are accounted for in southern british columbia the missing strike slip faults probably continued south into the hinterland of the rocky mountain thrust belt as oblique thrust faults much like the modern alpine marlborough fault system of new zealand the major strike slip faults in southeastern british columbia were obliterated by eocene extensional faulting uplift and erosion 2 offsets of 1000 km scale are likely to occur on many anastomosing faults with offsets of 100 km scale many of which are left behind and not found in the translated terrane the greater san andreas plate boundary has accumulated 1200 km of transform motion that is distributed on numerous faults from the offshore borderland to eastern california there is a narrow terrane in the offshore borderland of california that has moved 1200 km relative to north america but no single fault has nearly that much offset 3 major faults in narrow oceans formed by oblique divergent plate boundaries have a low potential for preservation for example the deep dense oceanic crust of the gulf of california where the major transform faults of the oblique rift lie has a low potential for preservation in contrast baja california is currently a continental terrane that has translated 300 km relative to north america along the plate boundary in the gulf of california because of the relative buoyancy of continental crust baja california is likely to be preserved in any future accretion event 4 faults in the margins of oblique divergent plate boundaries are dominantly normal faults and not strike slip faults there is little strike slip faulting in central baja california even though the plate boundary has a rift angle of only 20 recent field data and modeling show that at 0 20 strike slip faults will dominate the secondary faults surprisingly at 20 to 35 there are both strike slip and normal faults and at 35 45 there are few or no strike slip faults even though the relative motion of these types of oblique rifts is dominated by transcurrent motion over extensional motion

fluid circulation and formation of minerals and bitumens in the sedimentary rocks of the outer carpathians based on studies on the quartz calcite organic matter association abstract different methods have been used to examine minerals and or solid bitumens in three adjacent carpathian regions of poland ukraine and slovakia the minerals fill smaller and larger veins and cavities where they occur either together or separately they usually co occur with the solid bitumens all 13cpdb values measured for calcite lie in a relatively wide interval between 6 25 and 1 54 while most values fall into the narrower interval from below 0 to about 3 the general range of calcite 18o results for the whole studied region is between 17 13 and 25 23 vsmow or from about 11 to 5 vpdb while the majority of these values are between 20 0 and 23 5 vsmow 10 53 and 8 00 pdb respectively 18ovsmow results for quartz vary between 23 2 and 27 6 the carbonate percentage determined in some samples falls between from 90 caco3 while the toc values changes from 0 09 to over 70 the aliphatic fraction predominates in all studied samples mainly in bitumens and oils the composition of the aliphatic fraction is relatively homogeneous and points to a strong aliphatic oil like paraffin character of the bitumens such a composition is characteristic of the carpathian oils and different from the rocks studied that contain the higher percentage of a polar fraction the content of the aliphatic fraction in bitumens is only slightly higher than that in two oils used for comparison the distribution of n alkanes is variable in rocks solid bitumens as well as inclusions in quartz and calcite two groups of bitumens may be distinguished those with a predominance of long chain n alkanes in the c25 c27 interval in some cases from c23 c25 and without or with a very low concentration of short chain n alkanes in the interval of c14 c21 show also a high content of isoprenoids i e of pristane pr and phytane ph in all but one bitumen samples pr predominates over ph the second group comprises oils and rock samples with a characteristic predominance of short chain n alkanes in the interval from c13 c19 and a low percentage of the long chain n alkanes from the n c27 n c33 interval pristane and phytane exhibit a concentration comparable to that of c17 and c18 n alkanes with a pr predominance over ph due to high maturity only small amounts of the most stable compounds from the hopane group have been observed in the samples also oleanane in one case among the aromatic hydrocarbons phenanthrene and its methyl and dimethyl derivatives are dominant in bitumens source rocks and inclusions in calcite and quartz occurrence of cyclohexylbenzene and its alkyl derivatives as well as cyclohexylfluorenes in solid bitumens suggest that they formed from oil accumulations under the influence of relatively high temperatures in oxidizing conditions homogenization temperatures for aqueous brine inclusions in quartz within the dukla and silesian units polish and ukrainian segments are between 125 and 183 9 c while salinities are low in the interval of 0 2 5 5 wt nacl eq the inclusions in calcite homogenize at higher temperatures of almost 200 c and the brine displays higher salinity than the fluid in the quartz two quartz generations may be distinguished by inclusion and isotope characteristics and the macroscopic diversity oil inclusions homogenize at 95 c one phase inclusions in quartz contain methane co2 and nitrogen in variable proportions

methane derived authigenic carbonates from active hydrocarbon seeps of the st lawrence estuary canada abstract nearly 2000 pockmarks with diameters ranging from a few tens of meters up to 700 m are present on the seafloor of the st lawrence estuary in eastern canada coring of some pockmarks resulted in the recovery of various sized and shaped carbonate concretions in a predominantly silty mud matrix petrographic and geochemical data on four authigenic carbonate concretions are reported as well as data from shell material in the unconsolidated sediment video observations and echo sounder images indicate that the sampled pockmarks are actively gas venting the video images show significant look alike microbial mats in areas where gas is venting the carbonate concretions are primarily made up of carbonate cements with varying percentage of shell fragments micrite particles and fine grained clastics orthorhombic crystal morphology and diagenetic fabrics including isopachous layers and botryoids characterize the aragonite cement oxygen isotopes ratios for the cement crusts do not record any thermal anomaly at the site of precipitation with 18 o vpdb ratios 3 in equilibrium with cold 5 c deep marine waters whereas significant negative 13 c vpdb ratios 9 9 to 33 5 for cement and shell material within concretions indicate that the carbonates largely derive from the microbial oxidation of methane the 13 c vpdb ratios of aragonite shells 2 7 to 5 6 taken from unconsolidated sediments at some distance from the concretions vents show variable dilution of hco 3 with negative 13 c vpdb ratios derived from microbial oxidation of methane with isotopically normal 0 marine bicarbonate these results are in agreement with other lines of evidence suggesting that pockmarks formed through the recent and still active release of gas from a reservoir within the paleozoic sedimentary succession

evidence for intense ree scavenging at cold seeps from the niger delta margin for many trace elements continental margins are the location of intense exchange processes between sediment and seawater which control their distribution in the water column but have yet to be fully understood in this study we have investigated the impact of fluid seepage at cold seeps on the marine cycle of neodymium we determined dissolved and total dissolvable td concentrations for ree and well established tracers of fluid seepage ch4 tdfe tdmn and nd isotopic compositions in seawater samples collected above cold seeps and a reference site i e away from any fluid venting area from the niger delta margin we also analyzed cold seep authigenic phases and various core top sediment fractions pore water detrital component easily leachable phases uncleaned foraminifera recovered near the hydrocast stations methane tdfe and tdmn concentrations clearly indicate active fluid venting at the studied seeps with plumes rising up to about 100 m above the seafloor depth profiles show pronounced ree enrichments in the non filtered samples td concentrations within plumes whereas filtered samples dissolved concentrations exhibit slight ree depletion in plumes relative to the overlying water column and display typical seawater ree patterns these results suggest that the net flux of ree emitted into seawater at cold seeps is controlled by the presence of particulate phases most probably fe mn oxyhydroxides associated to resuspended sediments at the reference site however our data reveal significant enrichment for dissolved ree in bottom waters that clearly relates to diffusive benthic fluxes from surface sediments neodymium isotopic ratios measured in the water column range from end 15 7 to 10 4 evidence that the end values for antarctic intermediate waters aaiw differed from those reported for the same water mass at open ocean settings shows that sediment water interactions take place in the gulf of guinea at each site however the bottom water end signature generally differs from that for cold seep minerals easily leachable sediment phases and detrital fractions from local sediments ruling out the possibility that seepage of methane rich fluids and sediment dissolution act as a substantial source of dissolved nd to seawater in the gulf of guinea taken together our data hence suggest that co precipitation of fe mn oxyhydroxide phases in sub surface sediments leads to quantitative scavenging of dissolved ree at cold seeps preventing their emission into bottom waters most probably it is likely that diffusion from suboxic surface sediments dominates the exchange processes affecting the marine nd cycle at the niger delta margin

abiogenic fischer tropsch synthesis of hydrocarbons in alkaline igneous rocks fluid inclusion textural and isotopic evidence from the lovozero complex n w russia a detailed fluid inclusion study has been carried out on the hydrocarbon bearing fluids found in the peralkaline complex lovozero petrographic microthermometric laser raman and bulk gas data are presented and discussed in context with previously published data from lovozero and similar hydrocarbon bearing alkaline complexes in order to further understand the processes which have generated these hydrocarbons ch4 dominated inclusions have been identified in all lovozero samples they occur predominantly as secondary inclusions trapped along cleavage planes and healed fractures together with rare h2o dominant inclusions they are consistently observed in close association with either arfvedsonite crystals partially replaced by aegirine aegirine crystals or areas of zeolitization the majority of inclusions consist of a low density fluid with ch4 homogenisation temperatures between 25 and 120 c those in near surface hand specimens contain ch4 h2 up to 40 mol higher hydrocarbons however inclusions in borehole samples contain ch4 higher hydrocarbons h2 indicating that at depth higher hydrocarbons are more likely to form estimated entrapment temperatures and pressures for these inclusions are 350 c and 0 2 0 7 kbar a population of high density liquid ch4 dominant inclusions have also been recorded mainly in the borehole samples homogenising between 78 and 99 c these consist of pure ch4 trapped between 1 2 and 2 1 kbar and may represent an early ch4 bearing fluid overprinted by the low density population the microthermometric and laser raman data are in agreement with bulk gas data which have recorded significant concentrations of h2 and higher hydrocarbons up to c6h12 in these samples these data combined with published isotopic data for the gases ch4 c2h6 h2 he and ar indicate that these hydrocarbons have an abiogenic crustal origin and were generated during postmagmatic low temperature alteration reactions of the mineral assemblage this would suggest that these data favour a model for formation of hydrocarbons through fischer tropsch type reactions involving an early co2 rich fluid and h2 derived from alteration reactions this is in contrast to the late magmatic model suggested for the formation of hydrocarbons in the similar peralkaline intrusion ilimaussaq at temperatures between 400 and 500 c

equatorial origin for lower jurassic radiolarian chert in the franciscan complex san rafael mountains southern california lower jurassic radiolarian chert sampled at two localities in the san rafael mountains of southern california 20 km north of santa barbara contains four components of remanent magnetization components a b and b are inferred to represent uplift miocene volcanism and subduction accretion overprint magnetizations respectively the fourth component c isolated between 580 and 680 c shows a magnetic polarity stratigraphy and is interpreted as a primary magnetization acquired by the chert during or soon after deposition both sequences are late pliensbachian to middle toarcian in age and an average paleolatitude calculated from all tilt corrected c components is 1 3 north or south this result is consistent with deposition of the cherts beneath the equatorial zone of high biologic productivity and is similar to initial paleolatitudes determined for chert blocks in northern california and mexico this result supports our model in which deep water franciscan type cherts were deposited on the farallon plate as it moved eastward beneath the equatorial productivity high were accreted to the continental margin at low paleolatitudes and were subsequently distributed northward by strike slip faulting associated with movements of the kula farallon and pacific plates upper cretaceous turbidites of the cachuma formation were sampled at agua caliente canyon to determine a constraining paleolatitude for accretion of the jurassic chert sequences these apparently unaltered rocks however were found to be completely overprinted by the a component of magnetization similar in situ directions and demagnetization behaviors observed in samples of other upper cretaceous turbidite sequences in southern and baja california imply that these rocks might also give unreliable results

correction of inclination shallowing and its tectonic implications the cretaceous perforada formation baja california abstract a paleomagnetic and magnetic fabric study of the aptian to albian perforada formation the oldest sedimentary unit of the cretaceous valle group was conducted to determine whether the perforada inclination had been shallowed by burial compaction and to correct the inclination for any shallowing the perforada formation is located on the vizcaino terrane of the vizcaino peninsula of west central baja california an accurate paleolatitude will indicate whether the vizcaino terrane is far travelled eighty eight specimens from 43 independently oriented hand samples and cores were collected from 11 sites a small 10 m fold was sampled in order to constrain the age of the magnetization with a fold test thermal and alternating field demagnetization was able to isolate characteristic magnetizations for most samples maximum unblocking temperatures near 580 c indicate that magnetite is the magnetic carrier the characteristic magnetization passes the fold test at the 99 confidence level anisotropy of anhysteretic remanence aar and anisotropy of magnetic susceptibility ams measurements show that five sites had well developed bedding parallel foliations while four sites had poorly developed aar fabrics but foliated ams fabrics the remaining two sites had poorly developed foliations for both ams and aar the mean inclination i 35 6 of the five sites with well developed aar foliations is 13 7 shallower than the mean inclination i 49 3 of the two sites with poorly developed aar and ams fabrics when the inclinations of the sites with well developed aar foliations are corrected using an individual particle anisotropy of 1 5 determined from magnetic extract epoxy samples dried in 30 50 mt dc magnetic fields the corrected mean inclination i 50 1 is indistinguishable from the mean inclination of the sites with poorly developed aar fabrics a corrected formation mean direction for the perforada formation d 311 8 i 47 0 95 9 3 indicates a 33 5 11 1 counterclockwise rotation and 5 6 7 7 of post cretaceous northward motion after 3 of neogene fault motion has been removed these results indicate that the vizcaino terrane has moved little with respect to the peninsular ranges terrane and cratonic north america since the cretaceous

sources of cam3 temperature bias during northern winter from diagnostic study of the temperature bias equation the community atmosphere model version 3 cam3 temperature simulation bias is examined in this paper we compare cam3 output with european centre for medium range weather forecasts ecmwf 40 year reanalysis era 40 data we formulate a time mean temperature bias equation then evaluate each term in the equation our focus is on the northern hemisphere winter time we group the temperature equation terms into these categories linear advection terms nonlinear advection terms transient eddy terms and diabatic heating and find that linear advection and diabatic bias are the largest the nonlinear terms velocity bias advection of temperature bias are much smaller than each of the other groups of terms at all levels except near the surface linear advection terms have dipolar pattern in the atlantic negative nw of positive which reflects the shift of the cam3 model north atlantic storm track nast into europe especially in the upper troposphere opposite sign dipolar structure occurs over alaska positive and the north pacific storm track negative the transient advection terms in middle latitudes are larger in the upper troposphere and generally positive along the atlantic storm track along the north pacific storm track npst the transient terms are negative in the mid and lower troposphere over much of the npst positive in upper troposphere the diabatic heating bias has large values in the tropics along the intertropical convergence zone icz and along the midlatitude storm tracks during this time of year the icz is mainly in the southern hemisphere but cam3 emphasizes an icz like heating in the northern hemisphere of the atlantic and pacific oceans cam3 tends to have a weaker icz especially in the atlantic in midlatitudes we find large bias in heating by precipitation and vertically averaged net radiation over the nast europe and the middle east

the south pacific convergence zone spcz a review abstract the circulation features associated with the south pacific convergence zone spcz and its accompanying cloud band are reviewed and discussed the paper focuses on the following topics location structure and characteristics of the spcz theories and observations concerning its existence the significance and scope of the spcz in global scale circulation patterns quasi periodic changes in its location and strength and synoptic scale features within its regional influence e g cyclones subtropical jets it concludes with some challenging problems for the future

simple shear of southern california during neogene time suggested by paleomagnetic declinations we have studied the paleomagnetism of various neogene age rocks in southern california as a means of determining the amounts of oligocene and younger tectonic rotation and translation which has occurred in this region our results suggest that fully 25 of this area in particular the transverse ranges has undergone extreme clockwise rotation work in southeastern california implies that 40 of clockwise rotation has occurred here although paleomagnetic declinations adjacent to a major right lateral fault are apparently rotated over 200 the crustal block bounded by the san gabriel and san andreas fault has undergone a net clockwise rotation of 35 although the data here can be interpreted to show that an original early miocene rotation of about 50 was followed by a late miocene or pliocene counterclockwise rotation of 15 paleomagnetic results from the offshore islands suggests that san clemente santa barbara and san nicolas islands have not rotated but santa catalina has undergone about 90 of clockwise rotation all of the northern channel islands including anacapa santa cruz santa rosa and san miguel are implied to have rotated 70 or 80 clockwise this result is also found for the santa monica mountains east of anacapa island in the santa ynez range north of the channel islands paleomagnetic study of the monterey formation also indicates large clockwise rotations of near 90 these data also suggest that the santa maria basin is not rotated and that the north boundary of the rotated region is the santa ynez river fault stratigraphic control on the paleomagnetic data from the monterey formation implies that the rotation began about 16 m y ago and may be continuing today in the western region paleomagnetic inclination data from our study show that the northern channel islands in particular may have translated 15 northward since middle miocene time however equally valid interpretations of these same data are that the low inclinations are due to the combined effects of erroneous structural corrections non dipole magnetic field behavior and right offset on the san andreas fault system palinspastic reconstruction of southern california regions for the early miocene implies that parts of the transverse ranges structures were once aligned with north trending extensional structures in the southwestern united states we propose that pacific american plate interactions both rifted the continental crust to create this pattern and rotated the western most structures within a dextral simple shear zone which had a half width of about 400 km

clockwise rotation and implications for northward drift of the western transverse ranges from paleomagnetism of the piuma member sespe formation near malibu california 1 new paleomagnetic results from mid tertiary sedimentary beds in the santa monica mountains reinforce the evidence for large scale rotation of the western transverse ranges and anisotropy measurements indicate that compaction induced inclination flattening may resolve a long standing controversy regarding the original paleolatitude of the rotated block previously published paleomagnetic data indicate that post oligocene rotation amounts to 70 110 clockwise affecting the channel islands santa monica mountains and santa ynez mountains the sespe formation near malibu consists of a lower member dominated by nonmarine sandstone and conglomerate and an upper section the piuma member which consists of gray red sandstone and mudstone interbedded with minor tuff and limestone beds the piuma member has a paleomagnetic pole at 36 6 n 326 7 e a95min 5 0 a95max 9 6 obtained by thermal demagnetization of 34 oriented cores from oligocene and early miocene beds after correcting for plunge of the geologic structure the data are consistent with significant clockwise rotation 77 7 of the region relative to stable north america rotation of the western transverse ranges is generally viewed as a consequence of pacific north american plate interactions after 28 ma when east west subduction gave way to northwest transform motion in southern california inclinations from the piuma study indicate a paleolatitude anomaly of 11 7 and are consistent with a mean northward drift that exceeds generally accepted san andreas fault displacement by a factor of 3 however sedimentary inclination error may accentuate the anomaly anisotropy of isothermal remanent magnetization indicates inclination flattening of approximately 8 and correction for the effect reduces the paleolatitude anomaly to 5 3 5 8 compaction may explain the inclination flattening in these sedimentary rocks but the process does not adequately explain lower than expected inclinations found in previous studies of miocene volcanic rocks of the western transverse ranges

rare earth elements of seep carbonates indication for redox variations and microbiological processes at modern seep sites at marine seeps methane is microbially oxidized resulting in the precipitation of carbonates close to the seafloor methane oxidation leads to sulfate depletion in sediment pore water which induces a change in redox conditions rare earth element ree patterns of authigenic carbonate phases collected from modern seeps of the gulf of mexico the black sea and the congo fan were analyzed different carbonate minerals including aragonite and calcite with different crystal habits have been selected for analysis total ree content sigma ree of seep carbonates varies widely from 0 1 ppm to 42 5 ppm but a common trend is that the sigma ree in microcrystalline phases is higher than that of the associated later phases including micospar sparite and blocky cement suggesting that sigma ree may be a function of diagenesis the shale normalized ree patterns of the seep carbonates often show different ce anomalies even in samples from a specific site suggesting that the formation conditions of seep carbonates are variable and complex overall our results show that apart from anoxic oxic conditions are at least temporarily common in seep environments c 2012 elsevier ltd all rights reserved