the bristol mendip foreland thrust belt the thrusts and associated fold structures of the bristol mendip area are interpreted in terms of a thin skinned piggy back foreland thrust belt of variscan age with dominant northward transport strike normal balanced sections and compatible strike parallel sections have been constructed to illustrate the 3 d geometry of the linked thrust system north south shortening of c 20 km 40 is calculated from deformed and restored strike normal sections a thick and extensive thrust wedge of pre old red sandstone basement in the west of the area is responsible for culminations expressed at the surface as the mendip periclines uplifted culminations permit erosion to lower stratigraphic levels in the west and south of the area strike parallel sections and a hanging wall cut off map indicate that the majority of thrusts in the area are mainly oblique ramps rather than simple frontal and lateral ramps or flats the en echelon pattern of the mendip periclines may be related to the oblique ne climb of two of these thrusts the angle of frontal ramp climb through the dinantian stratigraphy is generally low and this explains the presence of numerous klippen of lower on upper carboniferous rocks whilst suggesting that certain thrust sheets were much more extensive than present outcrops indicate early pre thrusting movement on basement lineaments in the variscan foreland created uplifts angular unconformities and a predominance of n s structures in the north of the area

deep structure of the east mendip hills from gravity aeromagnetic and seismic reflection data beacon hill pericline is the most easterly pericline of the mendip hills whose folds and thrusts were formed during the variscan orogeny by earth movements directed from the south the silurian volcanic rocks making up the core of the pericline are shown to be responsible for the large linear magnetic anomalies present over eastern mendip magnetic anomalies within the radstock coalfield to the north however are related to volcanic horizons in the carboniferous limestone a three dimensional model shows the presence of silurian rocks beneath the spine of the eastern mendip hills seismic reflection sections are used to control two dimensional interpretations of potential field data from beacon hill pericline although the magnetic anomalies are adequately explained by the seismic model the gravity anomalies require the presence of an additional low density body beneath the pericline9s southern flank this body is interpreted as a thrust wedge of old red sandstone emplaced in its present position by a previously unrecognized post variscan normal fault the considerable lateral extent of the structure is demonstrated by the trend of the maxima of the horizontal gradient of the gravity anomalies

low temperature hydrothermal maturation of organic matter in sediments from the atlantis ii deep red sea abstract hydrocarbons and bulk organic matter of two sediment cores no 84 and 126 chain 61 cruise located within the atlantis ii deep have been analyzed although the brines overlying the coring areas were reported to be sterile microbial inputs and minor terrestrial sources represent the major sedimentary organic material this input is derived from the upper water column above the brines both steroid and triterpenoid hydrocarbons show that extensive acid catalyzed reactions are occurring in the sediments in comparison with other hydrothermal guaymas basin or intrusive systems cape verde rise the atlantis ii deep exhibits a lower degree of thermal maturation this is easily deduced from the elemental composition of the kerogens and the absence of polynuclear aromatic hydrocarbons of a pyrolytic origin in the bitumen the lack of carbon number preference among the n alkanes suggests especially in the case of the long chain homologs that the organic matter of atlantis ii deep sediments has undergone some degree of catagenesis however the yields of hydrocarbons are much lower than those observed in other hydrothermal areas the effect of lower temperature and poor source rock characteristics appear to be responsible for the differences

distribution and transport of hydrocarbons in surface sediments of the alaskan outer continental shelf abstract surface sediments from the outer continental shelf of alaska were analyzed for hydrocarbons as part of an environmental survey sponsored by noaa blm sediments were collected from the proposed oil lease areas of beaufort sea southeastern bering sea norton sound navarin basin gulf of alaska kodiak shelf and lower cook inlet data on normal and branched alkanes and di and triterpenoids from capillary gas chromatography gc and gas chromatography mass spectrometry gc ms indicate that the area displays little evidence of petroleum hydrocarbons i e seeps except at a few isolated stations beaufort sea sediments have the highest hydrocarbon budget whereas kodiak shelf sediments have the lowest the molecular markers of the hydrocarbons are of a mixed marine autochthonous and terrestrial allochthonous origin norton sound and cook inlet sediments contain the highest levels of terrigenous lipids and kodiak shelf the lowest the abundance of alkenes implies that relatively low oxidizing conditions exist in some of the depositional areas studied suggesting that extraneous petroleum hydrocarbons introduced into these sediments would be expected to have a relatively long residence time the distribution of polynuclear aromatic hydrocarbons pah is complex and shows a pyrolytic origin the data on perylene strongly favor the hypothesis that it is performed from terrigenous precursors and transported into the marine environment with no apparent in situ generation polynuclear aromatic hydrocarbons of diagenetic origin are probably dominant in gulf of alaska and kodiak shelf sediments two stations north of kalgin island in lower cook inlet and one in southeastern bering sea show typical weathered petroleum distribution of n alkanes and triterpenoids probable pathways of transport and fate of petroleum hydrocarbons in case of an oil spill are also briefly discussed

a seismic study of deep geological structure in the bristol channel area sw britain summary results from eight seismic refraction lines 35 90 km long in the bristol channel area are presented the data mostly land recordings of marine shots have been interpreted mainly by ray tracing and time term modelling upper layer velocities through palaeozoic rocks usually fall within the range 4 8 5 2 km s 1 below the carboniferous limestone with a normal velocity of 5 1 5 2 kms 1 the old red sandstone with a velocity of 4 7 4 8 kms 1 acts as a low velocity layer as do parts of the underlying lower palaeozoic succession in the central south wales bristol channel area and the mendips a 5 4 5 5 km s 1 refractor is correlated with a horizon at or near the top of the lower palaeozoic succession under the whole area except for north devon a 6 0 6 2 km s 1 basal refractor has been located and is correlated with precambrian crystalline basement rocks in general this refractor deepens southwards from a series of basement highs which existed before the major movements of the variscan orogeny in south wales resulting in a southerly thickening of the pre upper carboniferous supra basement sequence in north devon a 6 2 km s 1 refractor at shallow depth interpreted as a horizon in the devonian or lower palaeozoic succession overlies a deep reflector that may represent the precambrian crystalline basement

effect of moisture and temperature conditions on the decay rate of a purple mudstone in southwestern china soil formation and geomorphology are primarily influenced by the rock decay which in turn is strongly determined by moisture and temperature conditions however it remains unclear whether rock decay is dominated by thermal stresses or by hydration disintegration and there is little information on mudstone decay rate in southwestern china this study hypothesized that rock decay is dominated by hydration mechanism and focused on the physical decay characteristics of typical purple mudstones using a combination of field and laboratory based experiments the bedrock of a penglaizhen group j 3 p in yanting county sichuan province southwestern china was exposed and covered with nylon fabric in situ soil depths of 10 20 40 and 60 cm were laid on this nylon fabric in 2003 and the decay rate the quantity of clastic particles 2 mm that were decayed from the bedrock in t km 2 yr 1 under the nylon fabric was measured both in 2005 and 2009 in addition fresh mudstones sampled from the matoushan group k 2 m the tuodian group j 3 t and the lufeng group j 1 l in yuanmou county shuangbai county and lufeng county of yunnan province southwestern china respectively were subjected to alternating applications of moisture temperature and their interaction seven treatments in the laboratory and their decay ratios the mass of decayed rock of 2 mm clastic particles to sampled rock mass in percent were measured in 2010 in the field the decay rate of the bedrock showed a significant p 0 05 positive relationship with both the daily moisture and temperature variation at the interface between the soil and bedrock in the laboratory results showed that the effect of moisture variation but not temperature alternation on rock decay was apparent suggesting that purple rock decay is dominated by hydration mechanism freezing thawing in particular affects the sampled rocks because it causes more spalling and fracturing the j 3 t rock had the highest decay ratio because it had the highest clay mineral content and porosity of the three rock types hierarchical clustering analysis suggested that the variation of moisture content and h2o phase solid or liquid within rock plays a key role in rock decay processes both field and laboratory studies consistently showed that the alteration of wetting drying and freezing thawing as well as moisture content substantially influenced rock decay c 2012 elsevier b v all rights reserved

geophysical evidence concerning the southern boundary of the london platform beneath the hog s back surrey the results of a gravity survey have been interpreted with seismic reflection and borehole data to show that a major change in the structure of the upper crust underlies the hog s back w of guildford surrey the pre mesozoic basement beneath the thin mesozoic succession n of the hog s back is of a lower density than that underlying the thick mesozoic succession to the s this lower density basement was probably the principal cause of the relative stability of the london platform during the mesozoic era the sourthern boundary of the london platform may have been initiated by variscan thrusting with subsequent reversal of displacement or may be inherited from an older crustal lineament

extension tectonics in the wessex basin southern england the permian to cretaceous tectonic evolution of the wessex basin was controlled by horizontal tensional and vertical isostatic forces within the lithosphere the gross morphologies of its constituent structures were governed by the location of variscan thrust and wrench faults in the upper and middle crust which suffered extensional reactivation in tensional stress fields oriented approximately nw se several episodes of crustal extension can be resolved in early permian early triassic early jurassic and late jurassic early cretaceous times these were characterized by the rapid subsidence of fault bounded basins and commonly by erosion of adjacent upfaulted blocks superimposed upon the fault controlled subsidence dominant during periods of fault quiescence and becoming increasingly important with time a component of regional subsidence is considered to have a thermal origin this suggests that crustal extension was accompanied by some form of not necessarily uniform lithospheric thinning subsidence analyses assuming local airey isostasy give cumulative crustal extension factors of 20 28 beneath the grabens a more reasonable assumption of regional airey compensation indicates basinwide crustal extension of 13 17 which is consistent with birps offshore deep seismic reflection data

mesozoic reactivation of variscan thrusting in the bristol channel area uk new seismic reflection data from the bristol channel area provide direct evidence of a major variscan thrust in the palaeozoic basement beneath the mesozoic bristol channel syncline the thrust has an average southerly dip of about 25 and it rises into the major fault the central bristol channel fault zone cbcfz at the northern margin of the bristol channel syncline the cbcfz is attributed to reactivation in extension of the variscan thrust probably during the early cretaceous there is no evidence for major synsedimentary movement on the cbcfz and the bristol channel syncline does not represent a rollover structure section restoration suggests that the cbcfz has cut up through a previously tilted sequence of triassic and jurassic strata pervasive nnw sse cross faults are interpreted as original variscan transfer faults that have been reactivated in the mesozoic and tertiary

hydrocarbons in the sediments of port valdez alaska consequences of five years permitted discharge abstract hydrocarbons have been investigated in the sediments of port valdez alaska after three to five years of oil terminal operation with a routine daily discharge of 170 kg of petroleum residue in an otherwise undeveloped area surficial benthic sediments 0 5 cm and core segments down to 30 cm have been analyzed information about total hydrocarbons unresolved complex mixture normal alkanes pristane phytane hopanes and polycyclic aromatic hydrocarbons indicates that petroleum biogenic hydrocarbons and combustion derived aromatic hydrocarbons are present in sediments around the terminal at concentrations up to 218 g g 1 dry sediment the vertical horizontal and temporal distributions of anthropogenic hydrocarbons indicate that most of the sedimentary hydrocarbon accumulation has occurred within 1 km of the terminal a simple calculation suggests that less than 3 of the total oil discharged during routine operations of the terminal has entered the sediments of port valdez for comparison sediment hydrocarbon accumulation associated with a nearby small boat harbor was also examined

aliphatic hydrocarbons in surface sediments from the north queensland coast and great barrier reef effects of tropical cyclone winifred abstract aliphatic hydrocarbons were determined in inner shelf and reef lagoon surface sediments off the north queensland coast near innisfail in february 1986 immediately after tropical cyclone winifred passed through the region causing severe rainfall runoff and disturbance of bottom sediments lagoon sediments from feather gilbey and potter reefs 25 50 km offshore were characterized by a suite of c 15 c 25 n alkanes and alkenes derived predominantly from algal sources terrestrial hydrocarbons were not present in contrast inner shelf sediments contained relatively large amounts of terrestrial derived c 25 c 33 n alkanes which decreased in concentration with distance from the coast inner shelf sediments collected after the cyclone also contained a suite of petroleum derived hydrocarbons the concentrations of terrestrial derived hydrocarbons increased in samples collected from the inner shelf after the cyclone however the distribution of terrestrial hydrocarbons was largely confined to the inner shelf after the cyclone and only occurred in trace concentrations in midshelf sediments these results indicate that cyclone related outwelling of suspended sediments and presumably nutrients from rivers was confined to the inner shelf and did not reach the reef zone the post cyclone phytoplankton bloom was probably caused by resuspension of bottom sediments and release of porewater nutrients rather than advection of river plumes to the offshore reefs

weathering profile of non welded ignimbrite and the water infiltration behavior within it in relation to the generation of shallow landslides the mechanism underlying rain induced shallow landslides of non welded ignimbrite is found to be a special type of weathering profile and the behavior of water infiltrating through that profile according to our study of ito ignimbrite in southern kyushu japan rhyolitic volcanic glass the primary component of ignimbrite is first hydrated and dissolved forming halloysite halloysite near ground surface is then transported through the ignimbrite by infiltrating water and becomes clogged in interstices to form clay bands suction monitoring across a weathering profile indicated that downward infiltration of water is disrupted once by a zone of less permeable clay bands and again at the weathering front this disruption at the front is caused by a capillary barrier effect caused by the structure where finer weathered material overlies coarser fresh material this results in a well defined weathering front particularly beneath a slope where water flux is parallel to the front whereas the front is transitional beneath a ridge top where the front is nearly horizontal and the water flux is normal to the front infiltrating water from rain increases the weight of weathered material and decreases the suction within the material which is the final trigger of a shallow landslide of non welded ignimbrite long term weathering which proceeds on the order of years provides slide material

structure of blackdown pericline mendip hills from gravity and seismic data blackdown pericline is the western pericline of the mendip hills which were formed during the variscan orogeny at the end of the carboniferous unlike the more easterly periclines blackdown pericline has no associated magnetic anomaly indicating the absence of the silurian volcanic rocks responsible for the anomaly in eastern mendip the gravity field of blackdown pericline cannot be adequately modelled by the known geology of the mendip hills and requires the presence of an anomalously dense body at shallow depth the geometry of the body is inferred from a seismic reflection profile and is interpreted as a wedge of precambrian basement rocks its high density and negligible susceptibility may indicate an amphibolitic composition three models involving variscan thrusting and post variscan listric normal faulting are presented in explanation of the presence of the wedge the anomalous body is shown to be laterally continuous to west and east a linear negative gravity anomaly to the north of blackdown pericline is interpreted to be caused by a small occurrence of coal measures which have not before been described from this area

latitudinal change of normal paraffin composition in the northwest pacific sediments abstract we analyzed normal saturated paraffins n paraffins in 70 surface sediments in the northwest pacific to examine the spatial distribution of organic materials all sediments show bimodal n paraffin abundance patterns against carbon number with maxima at c 16 and c 31 indicating that n paraffins in marine sediments are a mixture of long chain n paraffins from land based higher plant waxes and short ones from marine organisms we observed in this study a significant change of carbon preference index cpi from 2 5 in low latitudes to 4 5 in mid high latitudes around 19 25 n the following influences are discussed as the cause of cpi offset between low and mid high latitudes 1 meteorological conditions 2 n paraffin composition of higher land plants 3 contribution of petroleum components and 4 mixing ratio of higher land plants and marine organisms however none of them can be the possible cause of the cpi offset because n paraffin content and composition vary significantly according to the species of a bacterium difference of the species of bacterial communities between low and mid high latitudes may be a possible reason for the cpi offset found in sediment from the northwest pacific

hydrocarbon geochemistry in surface sediments of alaskan outer continental shelf part 1 c15 hydrocarbons the c15 hydrocarbons in 220 surface sediments from the outer continental shelf of alaska were analyzed as part of an environmental survey supervised by national oceanic and atmospheric administration and bureau of land management gas chromatography and gas chromatography mass spectrometry were employed for the identification of organic compounds in the bitumen extracts surface sediments from one station in southeastern bering sea and two stations in lower cook inlet display n alkanes and triterpenoid distribution typical of weathered petroleum major faulting in the vicinity of the southeastern bering sea station may account for the leakage of petroleum from subsurface reservoir rocks oil production in upper cook inlet or a hitherto unrecorded seep in the rea could contribute petroleum hydrocarbons to the sediments from the two stations in lower cook inlet apart from these stations there is little evidence of near surface petroleum seeps in the sites investigated

mechanism and effect of chemical weathering of sedimentary rocks the mineralogy geochemistry and physical and mechanical properties of rocks from four weathering profiles of miocene to pleistocene mudstones and sandstones in japan showed that chemical weathering of sedimentary rocks is characterized by sequential reaction between percolating groundwater and rock forming minerals pyrite a common mineral contained in sedimentary rocks is especially important in these sequential reactions pyrite is oxidized by oxygen coming from the ground surface and sulfuric acid is generated at the base of the oxidized zone the sulfuric acid in turn dissolves rock forming materials to make a dissolved zone if the fluxes of oxygen and water are in the same direction sulfuric acid generated at the oxidation front migrates farther and forms a dissolved zone if these fluxes are in opposite directions the oxidized and dissolved zones are not differentiated rocks in the dissolved zone are caused to deteriorate by the acid leaching and are acidic if buffering minerals such as calcite and zeolite are absent in the oxidized zone sandstone is strengthened because of cementation by iron oxide or hydroxide while mudstone is weakened because it has greater clay fractions and larger specific surface areas than sandstone

impact of weathering on macro mechanical properties of chalk local pillar scale study of two underground quarries in the paris basin abstract in order to investigate the causes of underground collapse and aid the development of prevention strategies we conducted a detailed study of the physico mechanical behaviour and ageing of chalk in underground quarries in the parisian basin france core samples were drilled horizontally from pillars at two sites the saint martin le n ud underground dolomitic chalk quarry oise france and the estreux underground glauconitic chalk quarry nord france uniaxial tests were performed on dry and saturated cylindrical specimens extracted perpendicularly to the cores at regular distances along their lengths the cores were drilled horizontally from the edge to the centre of the pillars measurements of both physical and mechanical properties were made the dolomitic chalk saint martin le n ud exhibits variations in mechanical and physical properties with horizontal pillar depth and both density and compressive strength appear to increase outwards from the core to the wall of the pillar the opposite of what would be expected from a purely mechanical point of view scanning electronic microscope sem analysis revealed progressive degradation and increasing homogeneity of the grains from the edge to the inside of the pillar at the pillar wall the crystal faces are well defined almost euhedral and the grains are of variable size in contrast crystals in the inner part of the pillar are finer grained and anhedral with highly degraded edges in addition video logging of the pillar revealed a greater number of fractures in the centre of the pillar than at its edge in physico mechanical tests and sem analysis performed on the estreux glauconitic chalk no significant variation was observed between the pillar wall and the pillar core however dissolution marks were observed along the entire length of the half pillar core

crustal structure beneath southern england from deep seismic reflection profiles seismic reflection events from recently acquired profiles in southern england are interpreted in terms of stratigraphic and structural interfaces between rock units in particular evidence is brought forward that a series of reflection events dipping between 22 and 27 with azimuth averaging 160 represents 2 major thrust zones occurring in the variscan floor beneath mesozoic cover a geological model based upon borehole information and regional geological considerations is presented the tentative recognition of crystalline basement overlain and overstepped by late proterozoic rocks of variable thickness suggests that basement in this area was unstable from late precambrian times the mesozoic structural evolution can be related to tectonic re activation of major concealed thrust zones in the palaeozoic 9basement9

squeezing rock conditions at an igneous contact zone in the taloun tunnels tehran shomal freeway iran a case study squeezing rock conditions at the contact zone of an andesitic basaltic body and tuff country rocks in the taloun tunnels were investigated and analyzed evaluation of the rock mass properties illustrates the fact that they were significantly reduced at the contact zone especially when wet detailed monitoring and measurements of tunnel wall convergence at the contact zone in the taloun service tunnel during the 10 months following excavation and installation of initial support prior to installation of heavy support showed greater than 3 of the normalized tunnel closure this confirms moderate squeezing conditions at the contact zone the measured displacement was even higher than that of the fault zone in which deformation was decreased during the first month and eventually stabilized similarly numerical modeling of the deformation at the contact zone not only confirmed a higher value of the tunnel convergence but also demonstrated the reduction of in situ stress and development of plastic zones across the contact zone these data are also believed to account for the squeezing condition at the contact zone it is expected that this condition will be significantly increased in the main road tunnels due to the fact that these tunnels are twice as wide as the service tunnel therefore proper and timely support must be applied numerical analysis of the support at the contact zone showed that the stress due to bending moment is greater than that of the axial forces on the lining this calls for certain support measures in the form of permanent lining and two layers of steel bars to compensate for the tensile stress exertion on the lining

hydrocarbon geochemistry of the puget sound region ii sedimentary diterpenoid steroid and triterpenoid hydrocarbons cyclic components of the aliphatic hydrocarbon mixtures extracted from puget sound sediment cores include a suite of c19 and c20 diterpenoid hydrocarbons of which fichtelite sandaracopimaradiene and isopimaradiene have been identified although apparently also derived from vascular plants these diterpenoid hydrocarbons have relative abundances distinctly different from the co existing plant wax n alkane suite five c27 c28 and c29 diasteranes and four c29 c30 and c31 17 h 21 h hopanes occur in relatively constant proportion as components of a highly weathered fossil hydrocarbon assemblage these chromatographically resolved cycloalkanes along with the strongly covarying unresolved complex mixture have been introduced to puget sound sediments from adjacent urban centres at increasing levels over the last 100 yr in the absence of any major oil spill naturally occurring triterpenoid hydrocarbons including hop 22 29 ene diploptene are also present a new group of c30 polyenes has been detected which contains compounds apparently structurally related to a co existing bicyclic c25 diene and to c20 and c25 acyclic multibranched hydrocarbons described in a previous paper barrick et al 1980

probing deep weathering in the shale hills critical zone observatory pennsylvania usa the hypothesis of nested chemical reaction fronts in the subsurface weathering is both an acid base and a redox reaction in which rocks are titrated by meteoric carbon dioxide co2 and oxygen o2 in general the depths of these weathering reactions are unknown to determine such depths cuttings of rose hill shale were investigated from one borehole from the ridge and four boreholes from the valley at the susquehanna shale hills observatory ssho pyrite concentrations are insignificant to depths of 23 m under the ridge and 8 9 m under the valley likewise carbonate concentrations are insignificant to 22 and 2 m respectively in addition a 5 6 m thick fractured layer directly beneath the land surface shows evidence for loss of illite chlorite and feldspar under the valley secondary carbonates may have precipited the limited number of boreholes and the tight folding make it impossible to prove that depth variations result from weathering instead of chemical heterogeneity within the parent shale however carbonate depletion coincides with the winter water table observed at 20 m ridge and 2 m depth valley it would be fortuitous if carbonate containing strata are found under ridge and valley only beneath the water table furthermore pyrite and carbonate react quickly and many deep reaction fronts for these minerals are described in the literature we propose that deep transport of o2 initiates weathering at ssho and many other localities because pyrite commonly oxidizes autocatalytically to acidify porewaters and open porosity according to this hypothesis the mineral distributions at ssho are nested reaction fronts that overprint protolith stratigraphy the fronts are hypothesized to lie subparallel to the land surface because o2 diffuses to the water table and causes oxidative dissolution of pyrite pyrite derived sulfuric acid h2so4 plus co2 also dissolve carbonates above the water table to understand how reaction fronts record long term coupling between erosion and weathering will require intensive mapping of the subsurface copyright 2013 john wiley sons ltd

alkane and pah biomarkers as tracers of terrigenous organic carbon in arctic ocean sediments abstract we present the first sedimentary biomarker study encompassing the entire arctic ocean a large data set of organic markers for terrigenous petroleum and combustion inputs alkanes hopanes and steranes parent and alkyl polycyclic aromatic hydrocarbons pahs is examined for patterns in space and time using principal components analysis pca and partial least squares pls biomarker patterns reveal the central arctic ocean basin sediments to be compositionally distinct from those of the mackenzie river beaufort sea and barents sea but similar to those of the laptev sea pah distributions reflected in pah ratios and pca projections demonstrate that arctic ocean sediment is dominated by natural inputs to the extent that anthropogenic combustion pahs are not significant we find only modest changes between the glacial and post glacial sediments for atmospherically transported hydrocarbon biomarkers while particle associated biomarkers were captured strongly at basin edges during the glacial period and much more evenly transported across basins during the post glacial period the orders of magnitude decreases in particle associated petrogenic alkanes and pahs in central basins during glacial times coupled with the uniformity of most petrogenic biomarker parameters for most basin and shelf locations reflect a massive reduction in ice transport that makes the margins the most likely source of petrogenic material for the pleistocene holocene central arctic basins the proximity of large coal deposits of various maturity levels along the lena river the overlap in pah and biomarker composition of the laptev sea and surficial sediments from the central arctic ocean and the location of the laptev sea at the origin of the main transpolar drift all point to eroded coals from the lena river laptev sea as the likely source of petrogenic hydrocarbons to the central arctic ocean the ubiquitous presence of allochthonous coal in arctic ocean surface sediments provides a major constraint on the use of petrogenic biomarkers to infer the presence of subsurface petroleum reserves

comparative study of sterols in shelf and slope sediments off northeastern taiwan abstract bottom sediments and suspended matter from the shelf and slope areas off northeastern taiwan were analyzed for sterol n alkanol and n alkane compositions the algal sterols cholesterol ratios mean 1 were 1 00 0 31 n 7 for the shelf sediments 3 29 0 61 n 7 for the slope sediments and 1 54 0 19 n 3 for the suspended matter the much higher proportion of cholesterol in the shelf sediments is most likely derived from mollusks in the relict sediments an additional sterol source for the shelf sediments probably is suspended matter in the water column although the shelf has no apparent sedimentation results from phytol and n alkanols suggest recent inputs of lipids from the water column to the shelf the stanol stenol ratios are lower for the older shelf sediments than for the younger slope sediments

normal paraffins in shales as an indicator of depositional environment abstract normal paraffin compositions were determined for marine sediments from coastal and pelagic environments and for shales in the jurassic cretaceous bedded chert sequence from the franciscan terrane western north america the pelagic sediments and shales from a lower horizon of the bedded chert sequence are characterized by short chained n paraffins the coastal sediments and shales from the upper horizon show high abundance of n paraffins especially for long chained ones and a strong odd carbon predominence the comparison of n paraffin compositions of shales with those of marine sediments suggests that the bedded chert sequence had deposited in continuous environments from pelagic to coastal this inference is in harmony with that based on the major minor and rare earth element compositions the result suggests that shales in the franciscan bedded chert sequence preserve well the normal paraffin signals acquired at the deposition and demonstrates that the normal paraffin composition can be a useful indicator of sedimentary environment

hydrocarbon geochemistry in surface sediments of alaskan outer continental shelf part 2 distribution of hydrocarbon gases the distribution of c1 to c4 hydrocarbon gases in surficial sediments from the alaskan continental shelf was determined as part of a regional environmental survey sponsored by national oceanic and atmospheric administration and bureau of land management noaa blm methane ethane ethene propane propene n butane and iso butane were observed in low concentrations 0 1 10 ppb as weight gas to dry weight sediment in nearly all of the 190 sediment samples examined with methane exceeding c2 to c4 hydrocarbons in abundance by about a factor of 10 no gasoline range c5 to c8 hydrocarbons were detected above blank levels ethene was found generally to be more abundant than ethane while propane was slightl more abundant than propene the correlation between these hydrocarbons suggests a common possibly biogenic origin sediments from norton sound have anomalously high methane concentrations probably as a result of biological methanogenesis in subsurface organic rich peat layers most of the regions sampled showed median values of the c1 c2 c3 ratio of 20 the generally low c1 concentrations probably resulted from the selective loss of c1 by biologic oxidation or ebullition from the surface sediments no major c2 to c4 hydrocarbon anomalies were discovered however at some stations in kachemak bay kodiak shelf and norton sound anomalously high c3 c3 1 ratios indicated the poss ble presence of thermogenic gases at depth

durability of soft rocks in eocene flysch formation dalmatia croatia abstract the mechanical weathering of marl in the form of disintegration of intact material caused by repeated drying and wetting also known as slaking is an important factor affecting the durability and stability of cuts in soft rocks and eocene flysch formations dalmatia croatia it is often valued and used in rock classification as a slake durability index sdi an index property recommended by the international society for rock mechanics and american society for testing and materials it was observed that the results of conventional laboratory tests on marl samples using two slaking cycles are not always in accordance with the appearance of the samples after testing highly fragmented rock material in spite of the high resistance durability result based on the retained sample mass depending on factors such as porosity hydraulic conductivity and mineralogical composition the effects of weathering might sometimes not be obvious within two cycles which suggested that durability classification is not suitable for all soft rock types in order to determine the additional criteria that would reduce the uncertainty of standardised durability testing in soft rocks both the standard and modified tests of durability as well as a series of additional index tests carbonate content dry density water absorption porosity and point load strength index were conducted on 70 samples of marl several variants of the sdi were analysed with various numbers of cycles cycle times and combinations thereof to emphasise the differences between various types of marl a variant of loss slake index was introduced and determined using 30 samples based on the results obtained according to the degradation type observed after the slaking the samples were grouped into three groups based on the presented results a classification with the defined criteria for high medium and low durability has been suggested for the purpose of a durability analysis of the cuts in marls

origins of hydrocarbons in bering sea sediments i aliphatic hydrocarbons and fluorescence abstract sixty three samples from thirteen gravity cores were analyzed by gc fid qualitative gc ms and fluorescence spectroscopy to determine the concentration distribution and sources of hydrocarbons in bering sea sediments aliphatic hydrocarbons and fluorescence associated with aromatic compounds were detected in sediments at all locations the sediments contain variable amounts of marine biological debris terrigenous plant biowaxes recycled continental material petroleum and combustion derived hydrocarbons hydrocarbon concentrations were low and similar to previous reports from the alaskan outer continental shelf average ucm and total n alkanes varied from 10 7 to 73 3 and 2 6 to 4 6 g g respectively olefins of a presumed biological origin were widely distributed throughout bering sea sediments the presence of a complete suite of normal alkanes isoprenoids an unresolved complex mixture alkylated pahs and mature biological markers suggest that locations in the western and southern bering sea are contaminated with petroleum this petroleum may be derived from natural seepage recycled mature continental material autochthonous exposed immature mature sediments and or deposition of water column tarballs the petroleum at one southern bering sea location is typical of a condensate and is significantly different from that observed at western bering sea locations vertical distributions and the presence of significant amounts of volatile hydrocarbons suggest that petroleum seepage is a likely source of contamination at these locations

a study of the organic matter in tunisian phosphates series relevance to phosphorite genesis in the gafsa basin tunisia abstract in the gafsa basin tunisia peloidal fracolite is interbedded with shales limestones and rocks of intermediate lithology the rocks were deposited in an epicontinental sea and have been buried no more than 500 m the organic matter they contain is therefore thermally immature and in all units derived mainly from marine plankton particularly dinoflagellates the organic matter in the phosphorite units is composed predominantly of humic acids ha which are essentially located within the pellets these pellets are surrounded by an outer matrix in which the organic matter is similar to the kerogen comprised in the shally strata alternating with the phosphorite and limestone beds during weathering the content of the organic matter assocciated with the matrix decreases more rapidly than that of the organic matter entrapped within the pellets geochemical and palynological study of the organic matter in interbedded rocks of different lithology shale limestone phosphorite suggest that the shales were deposited in a reducing environment the limestones in one that was oxic whilst the phosphorites were formed in a redox environment inermediate between the two the interpretation of the data presented in this paper is that the genesis of shales phosphate and some carbonate beds excluding coquinas did not result from the deposition of initially sharply differentiated sediments but resulted from differences in diagenesis of sediments initially containing planktonic organic matter associated with clay and carbonate minerals

geochemistry of c25 and c30 biogenic alkenes in sediments of the narragansett bay estuary abstract the distributions of a series of structurally related c 25 and c 30 biogenic alkenes in sediments of the narragansett bay estuary have been determined the suite of alkenes detected differs both quantitatively and qualitatively from those previously reported in other estuanne and coastal regions four c 25 mono and dienes and one c 30 diene comprise 73 91 of the total alkenes in all surface upper 2 5 5 cm sediments analyzed however significant geographic variations exist in the relative abundance of these five compounds throughout the estuary a comparison of alkene concentrations with 13 c of the bulk sedimentary organic matter has shown that the geographic variations of some alkenes reflect the distribution of marine organic matter suggesting a marine source for these compounds the distributions of other alkenes are not similarly correlated in particular concentrations of the c 30 diene are relatively constant and exhibit no dependence on the origin of organic matter in these sediments this distribution implies an in situ production of this alkene throughout the estuary analysis of several sediment cores reveals that alkene concentrations are generally highest at the surface and decrease to low constant values within the upper 25 cm an exception is the subsurface concentration of one c 25 diene which exhibits an increase at the same depth in two separate upper bay cores

chemical evidence of differential particle dispersal in the southern washington coastal environment aliphatic hydrocarbons cupric oxide oxidation products of lignin and polycyclic aromatic hydrocarbons pah were analyzed by capillary gas chromatography in sediments from the southern washington continental shelf and slope the concentration of diploptene relative to plantwax n alkanes increased systematically in surface sediments with distance offshore along east west transects of the study area and remained constant in surface sediments along the midshelf silt deposit analogous trends were also observed for the concentration of cinnamyl phenols relative to vanillyl phenols and total methylphenanthrenes relative to phenanthrene these changes in sedimentary composition are evidence that diploptene from some terrestrial source lignin characteristic of non woody vascular plant tissue and a fossil organic material contained within weathered rock debris disperse across the washington continental shelf and slope in geographic patterns distinct from that for other river derived chemically related materials the compositional variations are explained by the particulate associations of the land derived chemicals and differential hydraulic dispersion of their respective carrier particles after discharge at the mouth of the columbia river

overview of the recent sediment hydrocarbon geochemistry of atlantic and gulf coast outer continental shelf environments abstract an overview of the hydrocarbon geochemistry of recent marine sediments from the u s atlantic and gulf of mexico outer continental shelf ocs regions is presented hydrocarbon levels along the atlantic ocs are fairly uniform ranging between in the north atlantic eastern gulf south texas gulf and coastal louisiana sediments a linear relationship exists between total hydrocarbon and total organic carbon concentrations indicating that each area consists of a geochemical province defined by a source input or depositional regime specific to the region the use of trace parameter bulk parameter ratios such as total hydrocarbon or individual pah concentrations total organic carbon content in defining such provinces and thus in serving as a basis for evaluating variations in source inputs as part of future surveys is demonstrated this approach views the hydrocarbon content and composition of atlantic and gulf coast ocs sediments as points on a spectrum defined by input types sources and deposition patterns sedimentation and erosion which conceptually link all the regions into a unified system

weathering of valle ricca stiff and jointed clay abstract the study proposes a weathering model of pliocene pleistocene stiff and jointed blue grey clay transforming into yellow clay physical mineralogical chemical and textural changes as well as the weathering profile were investigated in a quarry of central italy based on geological records and inferences these changes are likely to have occurred within a time span of about 50 000 years bp upon overburden stress unloading and in a stress regime that is locally controlled by suction weathering propagated into the clay at a rate of about 0 3 mm year and was enhanced by the enlargement of the pre existing tectonic discontinuities and by the formation of new joints a mass loss of about 22 25 wt was calculated considering fe and p as immobile elements the individual oxides contribute to mass loss in the following order sio2 cao co2 al2o3 mgo k2o s na2o tio2 mno the fe2o3 fe2o3 feo ratio varies from 9 29 in the blue grey clay to 75 82 in the yellow one oxidation and or dissolution of 7 a fe2 bearing clay minerals mica like minerals and calcite and parallel increase of smectite and fe hydroxides play a critical role in the chemical changes and explain the higher plasticity of the yellow clay with respect to the blue grey one the role of water during the weathering process was inferred to occur in cyclical steps 1 seepage of meteoric water 2 dissemination of highly oxidizing meteoric water 3 triggering of oxidation and dissolution of minerals 4 water evaporation 5 partial migration of the elements contained in the aqueous solution and consequent deposition of minerals in the joints

chemical weathering mechanisms and their effects on engineering properties of soft sandstone and conglomerate cemented by zeolite in a mountainous area abstract sandstone and conglomerate cemented by zeolite crystals in a humid mountainous area in japan are weathered and also weakened or strengthened by chemical interaction with percolating water that was originally in equilibrium with the atmosphere near the ground surface carbonic acid generated by the dissolution of carbon dioxide from the atmosphere and biological activity in the soil dissolves zeolite and thereby weakens the rocks at the oxidation front the base of the oxidized zone oxygen from the atmosphere reacts with pyrite in the rock to form sulfuric acid and iron oxide and or hydroxide the iron oxide and or hydroxide precipitates on zeolite surfaces and strengthens the rocks by cementing the grains to each other beneath the oxidation front and extending to the dissolution front sulfuric acid migrates downward dissolves zeolite and thus weakens the rocks this weathering mechanism and the resulting changes in mechanical properties of rocks generally are to be expected in marine sandstone and conglomerate with small amounts of clay in the matrix because the most common cementing mineral is carbonate which is also easily dissolved by acid and further because pyrite is a common rock forming mineral in marine sedimentary rocks the effects of chemical weathering on the mechanical properties of sandstone and conglomerate are different from those of mudstone because the latter contains much larger amounts of clay minerals the cementation of constituent grains by iron oxide and or hydroxide is inhibited by clay minerals because clay minerals have high specific surface areas and also because large amounts of iron can be incorporated in the minerals

volatile c1c7 organic compounds in an anoxic sediment core from the pettaquamscutt river rhode island u s a abstract surface sediments from an anoxic marine environment the upper basin of the pettaquamscutt river rhode island were analyzed for volatile organic compounds in the c 1 c 7 range the compounds identified included methane ethane alkenes c 2 c 5 carbon disulfide cyclopentane 3 methylpentane methylfuran aldehydes and ketones ethane methylfuran and most of the aldehydes and ketones showed maxima at the sediment water interface methane levels were very high 10 100 times greater than observed in most other surface sediments examined in this laboratory

possible variscan thrusting beneath the somerton anticline somerset vibroseis seismic data were acquired by goal petroleum plc during 1982 in the vicinity of the somerton anticline somerset these data show the simple form of the anticline but in addition show a southward dipping discontinuous seismic event beneath gravity modelling demonstrates that this event may be correlated with an e w trending gravity gradient which can be followed for approximately 150 km the dipping seismic event may represent a variscan thrust plane which dips to the ssw in contrast to similar planes seen to the east which dip to the sse the variation in dip seen between these postulated thrust planes may explain the curvature of structural trends seen within and to the east of the mendip hills the polden hills fault runs sub parallel to the proposed thrust plane beneath the somerton anticline and may be linked to a mesozoic reactivation of the postulated thrust

c25 and c30 biogenic alkenes in sediments and detritus of a new england salt marsh as part of a geochemical study of c25 and c30 biogenic alkenes in estuarine environments distributions of these compounds in detritus and sediments collected from a new england salt marsh round swamp on conanicut island in narragansett bay rhode island have been determined the alkene assemblages detected consisting primarily of four acyclic c25 dienes and trienes and a c30 bicyclic diene qualitatively resemble those previously reported for other sediments in which anoxic conditions were prevalent these similarities exist despite significant differences in the principal sources of sedimentary organic matter suggesting that the occurrence of these specific alkenes is more likely associated with an in situ process common to anoxic environments than with a direct input from a specific source size fractionation 840 m and 840 m to 1 2 m of marsh detritus revealed that the larger size fraction consisting primarily of decaying spartina debris contains significant amounts of alkenes this result together with alkene subsurface profiles which show high surface concentrations decreasing to near background levels by 20 cm suggest that anaerobic bacteria are mediating in situ production of these compounds previous studies of bacterial hydrocarbons have not reported the presence of these c25 and c30 alkenes although similar compounds have been isolated from several species of methanogenic bacteria however attempts to induce alkene synthesis by decomposing spartina anaerobically in the laboratory were unsuccessful in light of this result the exact source of alkenes in marsh sediments remains uncertain the absence from marsh sediments of other c25 alkenes whose sedimentary distributions had been previously correlated with the presence of marine planktonic organic matter implies the existence of different origins for structurally related constituents of this hydrocarbon series

a mechanism of chemical weathering of mudstone in a mountainous area abstract the chemical weathering of marine mudstone in humid mountainous areas of japan is dominated by the oxidation of pyrite a common mineral in marine sedimentary rocks this process occurs at the oxidation front that is the base of the oxidized zone and sulfuric acid is formed chlorite is transformed into smectite due to the oxidizing and acidic conditions as sulfuric acid migrates downward from the oxidation front minerals are dissolved and components are leached out from the underlying dissolved zone whose lower boundary is the dissolution front the oxidation and dissolution fronts migrate downward as weathering progresses in mountainous areas

weathering rate of mudstone and tuff on old unlined tunnel walls abstract the mechanisms and rate of weathering of soft sedimentary rocks exposed along unlined tunnel walls were investigated using mineralogical chemical and physical methods tunneling occurred several decades ago within the kakinokidai formation middle pleistocene and the kiwada formation lower pleistocene of the kazusa group of chiba prefecture as well as within the fukuda formation miocene of saitama prefecture in japan since then the walls of the tunnels have been desiccated by ventilation sulfuric acid has been generated by pyrite oxidation calcite and glass have been dissolved by sulfuric acid and gypsum has crystallized on the surface of the tunnel walls the oxidized zone was formed on the surface of the walls by the weathering the formation of this zone and weathering rates determined as rates of movement of the oxidation fronts in the vadose zone are explained by the diffusion of oxygen from the surface of the tunnel walls the relationship between the depth of the oxidation front lcm and the number of years since excavation tyear was expressed by l r oxi t the roxi values from the tunnels ranged among 5 for the middle pleistocene sandy mudstone 2 4 for the middle pleistocene mudstone 0 3 for the lower pleistocene mudstone and 1 3 for the miocene tuff roxi depends on the diffusion coefficients of oxygen and the chemical composition of rocks the diffusion coefficients of oxygen de calculated using the roxi and chemical compositions of the four kinds of rock above were 10 5 cm2 s 10 7 10 5 cm2 s 5 10 8 cm2 s and 4 10 7 3 10 6 cm2 s respectively depending on the air permeabilities of the rocks that correlate closely with the coefficient of water permeabilities k the relationship for the mudstone was log de cm2 s 0 91 log k cm s 0 71 the values of de for the tuff were smaller than for the mudstone due to the smaller air porosities of 0 01 0 04

gypsum growth induced by pyrite oxidation jeopardises the conservation of fossil specimens an example from the xiaheyan entomofauna late carboniferous china abstract the destruction and damage of fossils in palaeontological collections through pyrite fes2 oxidation is a major and well known issue in this paper we investigate the impact of this reaction on the conservation of xiaheyan fossil entomofauna tupo formation late carboniferous ningxia china through three steps first we examined and characterised the elemental and mineralogical composition of newly excavated specimens of museum specimens and of weathering products at the outcrop using sem edx raman microspectroscopy and xrd second in order to determine the potential reactivity of newly excavated fossils we performed artificial ageing experiments a technique recently applied in palaeontology that can offer valuable insights into long term conservation of fossils finally we designed and applied a protocol aiming at forcing the formation of gypsum outside the fossils so as to preserve the fossil integrity namely crystallisation pits our data demonstrate that the depositional environment at xiaheyan was rich in sulphur and devoid of oxygen with perhaps oxygen rich microenvironments which led respectively to the precipitation of framboidal pyrite and of primary iron oxyhydroxides the further chemical palaeo weathering led to an extensive oxidation of pyrite in the outcrop resulting in the precipitation of secondary iron oxyhydroxides and of jarosite and gypsum both sulphates the low abundance of iron oxyhydroxides and the poor diversity of sulphates compared to analogous localities indicate a distinct weathering scenario with a persistence of acidic water and an extensive leaching leading to the maintenance of only insoluble sulphates despite the extensive in situ pyrite oxidation artificial ageing experiments demonstrated a remaining weak degradation potential gypsum a calcium sulphate is the near exclusive efflorescence to develop within artificially aged fossils contrary to the most commonly encountered efflorescence on pyritised fossils namely iron sulphate this instance can be attributed to the complete mobilisation of iron through iron oxyhydroxide precipitation and the availability of calcium ions induced by the dissolution of calcium carbonates present on xiaheyan outcrops during palaeo weathering unfortunately the recourse to crystallisation pits failed to prompt gypsum crystallisation we further suggest preventive storage conditions and prospects for investigation on the gypsum precipitation process at work notably the role of organic compounds