clay minerals as alteration products in basaltic volcaniclastic deposits of la palma canary islands spain clay minerals from several volcaniclastic environments including pyroclastic tuffs epiclastic lacustrine alluvial terraces marine fan delta and unconformity related paleosols in la palma canary islands were studied by xrd sem tem hrtem imaging and aem clay minerals and their assemblages allowed us to distinguish between primary volcaniclastic basaltic material produced directly by pyroclastic eruptions and epiclastic volcaniclastic material derived from erosion of pre existing volcanic rocks the clay fractions consist mainly of smectite with minor chlorite mica chlorite smectite mixed layers and talc phyllosilicates of the epiclastic units display wider compositional variations owing to wide variations in the mineralogical and chemical composition of the parent material most of the phyllosilicates mica corrensite talc and chlorite are inherited minerals derived from the erosion of the basement complex unit which had undergone hydrothermal alteration smectites of the epiclastic units are saponite and beidellite montmorillonite derived from the hydrothermal basement complex unit and from volcanic materials altered in the sedimentary environment conversely clay minerals of unconformity related paleosols are dominated by smectite composed of variable mixtures of saponite and beidellite which were formed by pedogenetic processes with later hydrothermal influence the mineralogical association in the pyroclastic unit is dominated by hydrothermally formed smectite beidellite montmorillonite zeolites and calcite this paper contributes to the differentiation between pyroclastic and epiclastic volcaniclastic rocks of several depositional settings in a basaltic volcanic complex by their clay minerals characterization

spatial arrangement of soil mantle in glacis de buenavista mexico as a product and record of landscape evolution abstract factors controlling spatial soil organization have recently attracted the attention of soil scientists because they can contribute to regional management of soil resources we present here a case study in the glacis de buenavista mexico an extended volcanic piedmont in order to develop an integral understanding of its soil cover as a product and at the same time as a record of the main stages of landscape evolution three phenomena were considered luvisol and vertisol type soils and pedosediments all of them analyzed in terms of their development degree clay content macro and micromorphology selective extractions of fe fe d fe o silicon si o and aluminum al o weathering index and clay mineralogy luvisols represented in the ahuatenco mexicapa and buenavista sections are located in the northern and central part of the area they are red clayey polygenetic soils that show strong weathering with high kaolinitic clay content and high weathering index values clay illuviation and reductomorphic processes combined with vertic features in some parts of the profiles vertisols dominate the central and southern portion of the glacis they exhibit cracking angular blocks with wedge like shapes slickensides and stress cutans the pedogenesis of the vertisol type is clearly associated with the presence of smectitic minerals in the clay fraction as a product of neoformation factors controlling this pedodiversity are relief which affects bioclimatic differentiation within the studied landsurface and defines the lateral redistribution of moisture and dissolved substances and time luvisols represent a longer pedogenetic phase that started in the late pleistocene according to the age of buried paleosols while vertisols mainly originated in the late holocene according to the age of buried organic horizons pedosediments are located in the central area of the glacis here past and present geomorphic processes interact to produce the greatest soil diversity the recent human induced erosion partly destroyed polycyclic luvisols and exposed ancient subsurface pedosedimentary strata at the same time it produced patches of unconsolidated pedosediments consisting mostly of redeposited luvisol materials

novel family of hexacyclic hopanoid alkanes c32c35 occurring in sediments and oils from anoxic paleoenvironments abstract four novel hexacyclic alkanes fairly common in crude oils and rock extracts from evaporitic series have been tentatively identified on the basis of gc ms data as c 32 c 33 c 34 and c 35 hexahydrobenzohopanes these structures only recorded in carbonate anhydrite sequences i e very anoxic paleoenvironments tend to concentrate when pristane to phytane ratios increase changes in their relative concentration to hopanes appear to be more related to variations in source and or environmental conditions than to maturity the ratio of the novel hexacylic c 35 hopane to c 35 hopane compared with other biomarker ratios suggests that hexacyclic alkanes and hopanes are byproducts of the same hopanoid precursors via different chemical reactions in addition the novel hexacyclic alkanes are bacterially resistant and may serve as a useful family to define the paleoenvironment viz very anoxic of the parent source rock of a drastically biodegraded oil

biomarker distributions in australian oils predominantly derived from terrigenous source material oils found in many australian sedimentary basins contain a relatively high input of terrigenous organic source material a study of a large number of these oils has permitted a number of biomarker distributions to be determined that appear to be characteristic for oils derived from terrigenous source material these features include the presence of sesquiterpanes absence of tricyclic terpanes relatively high concentrations of a c24 tetracyclic terpane predominance of c29 steranes presence of two unidentified c27 and c30 terpanes and virtual absence of 18 h oleanane the latter observation is significant since it appears that 18 h oleanane appears only in oils of tertiary age derived from terrigenous source material an attempt has also been made to compare the results for the australian oils with published results for oils derived from terrigenous source material in other parts of the world the number of reports in the literature for these oils is fairly limited but it appears that some of the observations for the australian oils can be extended to them this study is an initial attempt to devise a classification scheme that can be used to determine the origin of an oil unambiguously from biomarker parameters in order for this approach to be successful a relatively large number of biomarker parameters need to be assigned as characteristic of a particular type of source material

source dependent biomarker properties of five crude oils from the gulf of suez egypt abstract five crude oils from some producing wells in the southern part of the gulf of suez were characterized using a variety of organic geochemical parameters the results reveal significant differences within the oils from the gulf of suez basin that suggest two oil types and one mixed type type 1 oils from ras fanar and east zeit fields show a high relative abundance of gammacerane indicating a marine saline source depositional environment another related feature of these oils is the predominance of c 35 over c 34 17 h homohopanes type 2 oils from gama and amal 9 wells show oleanane indices over 20 indicating that they originated from an angiosperm rich tertiary source rock type 3 oil from amal 10 well has geochemical characteristics intermediate between those of types 1 and 2 this may reflect mixing of oils from the sources of both types 1 and 2 the geochemical characteristics of the oils vary sufficiently to suggest multiple sources the type 1 oils possess geochemical characteristics consistent with upper cretaceous brown limestone or lower eocene thebes formation carbonate source rocks type 2 oils are very similar in geochemical character to the lower miocene rudeis formation source rocks

joint application of satellite remote sensing ground penetrating radar gpr and resistivity techniques for targeting ground water in fractured ophiolites of south andaman island india the ophiolitic complex of the study area oriented in n s direction having moderate to steep slopes of the topography and characterized by strong heterogeneity repetitive deformations and multiple intrusions ophiolites of the study area encompass the major groundwater bearing zones generally these formations have shallower fractured aquifers of a thickness 30 45 m and sometimes due to deep tensile fractures the thickness of aquifer exceeds more than 60 m with a considerable groundwater yield a joint venture of satellite remote sensing geoelectrical resistivity and ground penetrating radar gpr techniques has been used to assess the groundwater potential of the fractured ophiolites the interpreted resistivity inversion model and gpr results were incorporated with borehole lithologs for their subsurface properties and structural variations the integration of using multiple techniques has increased the accuracy of interpretation and thus conflated results significantly rendered the existence of weathered and fractured zone having hydrogeological importance based on the parameters viz geoelectrical properties of layers reflection configuration thickness of weathered and fractured aquifer zone a typical aquifer model for the study area that contains various layers and subtle structural variation has been developed further the derived integrated geophysical data also detail on various lithological characteristics and advances the understanding about aquifer systems of fractured ophiolites and the distribution of groundwater in fractures

geochemical comparison of fluid inclusion and present day oil accumulations in the papuan foreland evidence for previously unrecognised petroleum source rocks abstract petroleum production in papua new guinea is limited to the papuan fold belt present day oil accumulations in fields such as iagifu hedinia and gobe are thought to be mainly derived from clay rich jurassic marine source rocks containing terrestrially derived organic matter that were deposited under oxic conditions in this study other generative source rocks in the papuan foreland are indicated using fluid inclusion fi oil data from three wildcat wells koko 1 bujon 1 and kimu 1 which were drilled on the bosavi arch detailed organic geochemistry of these fi oils and associated free oils or oil stains suggests that none of these were generated from the aforementioned jurassic source rocks instead at least three different generative source rocks are indicated firstly a marine probably late cretaceous or younger source rock deposited under reducing conditions is indicated by the bujon 1 fi oil this source rock had a moderate contribution from higher plant organic matter including oleanane and or lupane the bujon 1 fi oil has similarities with fi oils from the iagifu 7x and p nyang 2x wells in the papuan fold belt secondly an algal dominated lacustrine source rock is indicated by the biodegraded koko 1 rft crude oil the unbiodegraded fi oil from koko 1 and the bujon 1 oil stains from the toro and imburu formations these lacustrine oils have high abundances of tricyclic terpanes pregnane homopregnane and gammacerane contain carotane and have high c26 c25 tricyclic terpane ratios the source of the lacustrine oils is inferred to contain moderate amounts of terrestrial organic matter indicated by a dominance of c29 steranes and abundant aromatic higher plant biomarkers and could be gypsiferous shales embedded in oligocene miocene carbonates or triassic age sediments deposited on igneous basement during early rifting associated with the break up of gondwana the kimu 1 fi oil was generated from a mature marine suboxic source rock but has a different geochemical composition to free oil from a similar interval which was derived from a carbonate rich source rock none of the fi oils correlate well with oil families previously described in papua new guinea accordingly the oils recovered from fis in this part of the papuan basin support the presence of laterally varying source rock compositions and qualities and indicate that there are opportunities to develop new charge models for features across the papuan foreland furthermore koko 1 bujon 1 and kimu 1 fi oils have different geochemical compositions compared to the associated free oils or oil stains indicating that each of these localities has a multi phase charge history further work to lower exploration risk in the papuan foreland should be directed to understanding the distribution maturity and expulsion history of these newly recognised potential source rocks

geochemical and biological marker assessment of depositional environments using brazilian offshore oils abstract a combined geochemical and molecular characterization of a wide selection of oils from the major brazilian offshore basins has been undertaken the elemental sulphur nickel and vanadium and bulk oapi and 13c properties of each sample been considered together with its molecular composition determined using liquid and gas chromatography and quantitative biological marker investigations using gas chromatography mass spectrometry for alkanes the results reveal significant differences in the chemical features of the various oils which enable them to be divided into five groups the distinction of the groups appears to reflect differences in the depositional environment of the source rocks of the oils each group is correlated tentatively with source rocks laid down in a specific depositional regime namely lacustrine freshwater lacustrine saline water marine evaporitic marine carbonate or marine deltaic the diagnostic features that allow this classification are the relative abundance and carbon number distributions of n alkanes pristane phytane ratios sulphur nickel and vanadium contents carbon isotope data the absolute concentrations of hopanes and steranes and their abundance relative to 4 methylsteranes and also the occurrence and abundance of several specific biological markers including 18 h oleanane gammacerane carotane tricyclic terpanes higher acyclic isoprenoids 28 30 bisnorhopane and 25 28 30 trisnorhopane this investigation shows the value of a combined geochemical and molecular approach in the assessment of the palaeoenvironment of deposition of the source rocks which gave rise to the oils

hydrothermal alteration of a seamount complex on la palma canary islands implications for metamorphism in accreted terranes the hydrothermal metamorphism of a sequence of pliocene age seamount extrusive and volcaniclastic rocks on la palma canary islands is characterized by a relatively complete low pressure high temperature facies series encompassing the zeolite prehnite pumpellyite and greenschist facies the observed mineral zonations imply metamorphic gradients of 200 300 c km the metamorphism of the seamount at least in its core region is distinct from ocean floor metamorphism the former is characterized by a serially continuous facies series encompassing zeolite prehnite pumpellyite and greenschist assemblages and the latter by a discontinuous metamorphic gradient in which prehnite pumpellyite assemblages are absent these metamorphic features presumably reflecting fundamental thermal tectonic differences between extending oceanic crust at mid oceanic ridges vs the more static crust underlying seamount volcanoes should aid in the recognition of incoherent fragments of seamount metamorphic rocks within accreted terranes which typically have undergone subsequent higher pressure temperature regional metamorphism albeit to comparable grades

rifted margin source rock deposition a carbon isotope and biomarker study of a west african lower cretaceous lacustrine section lower cretaceous passive margin sections penetrated in wells peripheral to the deep basinal development of pre salt sediments of the liawenda ponta vermelha troughs in the lower congo coastal basin revealed sustained source potential kerogen type kinetic ea a and carbon isotopic data plus rock extract biomarker signatures confirmed large systematic organofacies variations within these rift phase sediments an inverse correlation between 25 28 30 trisnorhopane and gammacerane abundances suggested three major depositional regimes reflecting salinity and water depth control 13c depleted basal sediments showing strong gammacerane 4 methyl sterane signatures were segregated by a major isotopic excursion this event represented the transition between saline playa lake to deeper water stratified conditions supporting a high level of anoxia for these intermediate sediments sterane and tricyclic diterpane abundances plus sterane hopane ratios had marine connotations and could be interpreted as the result of intermittent marine incursions fore shadowing irreversible oceanic ingression a resurgence of gammacerane abundance in the uppermost sediments typified littoral shallow marine depositional conditions recognition of a possible non ubiquity in lacustrine depositional conditions during the opening of a rifted margin provides further insight into the complexity and attendant controls on hydrocarbon generation in such habitats

hydrocarbon source rock potential in the southwestern gulf of suez graben insights from organic geochemistry and palynofacies studies on well samples from the ras el bahar oilfield abstract palynological and biomarker characteristics of organic facies recovered from cretaceous miocene well samples in the ras el bahar oilfield southwest gulf of suez and their correlation with lithologies environments of deposition and thermal maturity have provided a sound basis for determining their source potential for hydrocarbons in addition to palynofacies analysis toc rock eval pyrolysis kerogen concentrates bitumen extraction carbon isotopes and saturated and aromatic biomarkers enable qualitative and quantitative assessments of sedimentary organic matter to be made the results obtained from rock eval pyrolysis and molecular biomarker data indicate that most of the samples come from horizons that have fair to good hydrocarbon generation potential in the study area the upper cretaceous paleocene lower eocene samples contain mostly type ii to type iii organic matter with the capability of generating oil and gas the sediments concerned accumulated in dysoxic anoxic marine environments by contrast the miocene rocks yielded mainly type iii and type ii iii organic matter with mainly gas generating potential these rocks reflect deposition in a marine environment into which there was significant terrigenous input three palynofacies types have been recognized the first a consists of type iii gas prone kerogen and is typical of the early middle miocene belayim kareem and upper rudeis formations the second b has mixed oil and gas features and characterizes the remainder of the rudeis formation the third association c is dominated by amorphous organic matter classified as borderline type ii oil prone kerogen and is typical of the matulla turonian santonian and wata turonian formations rock eval t max pi hopane and sterane biomarkers consistently indicate an immature to early mature stage of thermal maturity for the whole of the studied succession

phyllosilicates in hydrothermally altered basalts from dsdp hole 504b leg 83 a tem and aem study phyllosilicates occurring as replacements of olivine clinopyroxene and interstitial materials and as veins or fracture fillings in hydrothermally altered basalts from dsdp hole 504b leg 83 have been studied using transmission and analytical electron microscopy the parageneses of phyllosilicates generally change systematically with depth and with the degree of alteration which in turn is related to permeability of basalts saponite and some mixed layer chlorite smectite are the dominant phyllosilicates at the top of the transition zone chlorite corrensite and mixed layer chlorite corrensite occur mainly in the lower transition zone and upper levels of the sheeted dike zone chlorite talc and mixed layer talc chlorite are the major phyllosilicates in the sheeted dike zone although replacement of talc or ohvine by saponite is observed the phyllosilicates consist of parallel or subparallel discrete packets of coherent layers with packet thicknesses generally ranging from 100 a to a few hundred a the packets of saponite layers are much smaller or less well defined than those of chlorite corrensite and talc indicating poorer crystal linity of saponite by contrast chlorite and talc from the lower transition zone and the sheeted dike zone occur in packets up to thousands of a thick the si si al ratio of these trioctahedral phyllosilicates increases and fe fe mg decreases in the order chlorite corrensite saponite and talc these relations reflect optimal solid solution consistent with minimum misfit of articulated octahedral and tetrahedral sheets variations in composition of hydrothermal fluids and precursor minerals especially in si si al and fe fe mg ratios are thus important factors in controlling the parageneses of phyllosilicates the phyllosilicates are generally well crystallized discrete phases rather than mixed layered phases where they have been affected by relatively high fluid rock ratios as in high permeability basalts in veins or areas adjacent to veins intense alteration in basalts with high permeability indicating high fluid rock ratios is characterized by pervasive albitization and zeolitization minimal alteration in the basalts without significant albitization and zeolitization is characterized by the occurrence of saponite mixed layer chlorite smectite in the low temperature alteration zone and mixed layer chlorite corrensite or mixed layer talc chlorite in the high temperature alteration zone textural non equilibrium for phyllosilicates is represented by mixed layering and poorly defined packets of partially incoherent layers the approach to textural equilibrium was controlled largely by the availability of fluid or permeability

source rock potential and paleoenvironment of the miocene rudeis and kareem formations gulf of suez egypt an integrated palynofacies and organic geochemical approach abstract a study on source rock characterization and paleoenvironmental interpretation has been carried out on a relatively thick miocene sedimentary succession from three wells gh 404 2a gh 420 1 sa e6a in the southern gulf of suez egypt the compilation of detailed optical investigations including palynofacies analysis spore coloration index sci vitrinite reflectance vrr and source rock geochemical data enables a detailed evaluation of organic matter om richness kerogen type and thermal maturation level despite their high content of calcium carbonate up to 52 the studied sediments yielded sufficient palynologic residue for a detailed palynofacies and organic petrographic study the palynomorph content comprises mainly marine components essentially dinoflagellate cysts and accessorily microforaminiferal linings while terrestrial derived material is relatively rare persistent occurrence of amorphous organic matter aom indicates that dysoxic to anoxic conditions prevailed throughout the deposition of the investigated sediments the main objective of this study is to combine organic geochemical and palynological data in an attempt to assess the source rock potential of the rudeis and kareem formations in the gulf of suez these data in addition also allow for the reconstruction of the depositional environment the present investigation employs multimode microscopic methods using transmitted white light along with incident light fluorescence microscopy for the first time geochemical and petrographic analyses performed on bulk rock samples and palynological residues demonstrate that both the rudeis formation and the kareem formation are mainly of kerogen type iii or mixed type ii iii independent thermal maturation specific parameters such as rock eval tmax vrr and sci indicate an immature to early mature stage palynofacies analyses combined with organic geochemical data indicate that the rudeis formation was deposited under shallow to open marine conditions whereas the overlying kareem formation was formed mainly in an open marine setting

the origin and implications of clay minerals from yellowknife bay gale crater mars the mars science laboratory msl rover curiosity has documented a section of fluvio lacustrine strata at yellowknife bay ykb an embayment on the floor of gale crater approximately 500 m east of the bradbury landing site x ray diffraction xrd data and evolved gas analysis ega data from the chemin and sam instruments show that two powdered mudstone samples named john klein and cumberland drilled from the sheepbed member of this succession contain up to 20 wt clay minerals a trioctahedral smectite likely a ferrian saponite is the only clay mineral phase detected in these samples smectites of the two samples exhibit different 001 spacing under the low partial pressures of h2o inside the chemin instrument relative humidity 1 smectite interlayers in john klein collapsed sometime between clay mineral formation and the time of analysis to a basal spacing of 10 a but largely remain open in the cumberland sample with a basal spacing of 13 2 a partial intercalation of cumberland smectites by metal hydroxyl groups a common process in certain pedogenic and lacustrine settings on earth is our favored explanation for these differences the relatively low abundances of olivine and enriched levels of magnetite in the sheepbed mudstone when compared with regional basalt compositions derived from orbital data suggest that clay minerals formed with magnetite in situ via aqueous alteration of olivine mass balance calculations are permissive of such a reaction moreover the sheepbed mudstone mineral assemblage is consistent with minimal inputs of detrital clay minerals from the crater walls and rim early diagenetic fabrics suggest clay mineral formation prior to lithification thermodynamic modeling indicates that the production of authigenic magnetite and saponite at surficial temperatures requires a moderate supply of oxidants allowing circum neutral ph the kinetics of olivine alteration suggest the presence of fluids for thousands to hundreds of thousands of years mineralogical evidence of the persistence of benign aqueous conditions at ykb for extended periods indicates a potentially habitable environment where life could establish itself mediated oxidation of fe 2 in olivine to fe 3 in mag

constructive and destructive episodes in the building of a young oceanic island la palma canary islands and genesis of the caldera de taburiente the results of new field observations 23 new k ar determinations and sixteen previously published determinations provide the basis for the reconstruction of the subaerial volcanic history of the island of la palma after the seamount activity represented by the materials of the basal complex an eruptive phase between 2 0 and 1 3 ma formed a large shield a period of volcanic quiescence followed until around 1 ma during which a large lateral collapse partly destroyed the former edifice between 1 05 and 0 7 ma activity was renewed in the shield and a n s ridge was built in the southern part of the island around 0 7 ma two new large lateral collapses affected the western part of both edifices and they were followed by eruptions between 0 71 and 0 65 ma which built a new edifice that partly filled the depressions thus created the caldera de taburiente constitutes the eroded remnants of the depression formed in the northern shield from 0 65 ma to present activity has been restricted to the n s ridge which has continued to grow southwards there was a general n s migration of volcanic activity with time but in the shield the trend was northwest to southeast eruptive rates seem to have been fairly constant during the different eruptive phases considered between 0 15 and 0 37 km3 ka a very similar succession of constructive and destructive episodes has been obtained for the neighboring island of hierro but in this case the activity started around 0 8 ma and eruptive rates were about 0 5 km3 ka

hydrothermal alteration in research drill hole y 2 lower geyser basin yellowstone national park wyoming y 2 a u s geological survey research diamond drill hole in lower geyser basin yellowstone national park was drilled to a depth of 157 4 meters the hole penetrated interbedded siliceous sinter and travertiae to 10 2 m glacial sediments of the pinedale glaciation interlayered with pumiceous tufffrom 10 2 to 31 7 m and rhyolitic lavas of the elephant back flow of the central plateau member and the mallard lake member of the pleistocene plateau rhyolite from 31 7 to 157 4 m hydrothermal alteration is pervasive in most of the nearly continuous drill core rhyolitic glass has been extensively altered to clay and zeolite minerals intermediate heulandite clinoptilolite mordenite montmorillonite mixed layer illite montmorillonite and illite in addition to quartz and adularia numerous veins vugs and fractures in the core contain these and other minerals silica minerals opal b cristobalite a cristobalite and chalcedony zeolites analcime wairakite dachiardite laumontite and yugawaralite carbonates calcite and siderite clay kaolinite and chlorite oxides hematite goethite manganite cryptomelane pyrolusite and groutite and sulfldes pyrrhotite and pyrite along with minor aegirine fluorite truscottite and portlandite interbedded travertine and siliceous sinter in the upper part of the drill core indicate that two distinct types of thermal water are responsible for precipitation of the surficial deposits and further that the water regime has alternated between the two thermal waters more than once since the end of the pinedale glaciation 10 000 years b p alternation of zones of calcium rich and sodium and potassium rich hydrothermal minerals also suggests that the water chemistry in this drill hole varies with depth

later stages of volcanic evolution of la palma canary islands rift evolution giant landslides and the genesis of the caldera de taburiente the islands of la palma and el hierro form the western end of the hotspot induced canary islands chain both islands are at present in the earliest and fastest shield building stage of growth and show many similarities with the hawaiian islands la palma shows two very distinct phases of volcanic construction 1 a pliocene submarine volcanic and intrusive series interpreted as an uplifted seamount at least 1500 m above present sea level and 2 a subaerial volcanic series erupted in the past 2 m y taburiente volcano initially formed the northern part of the island and then extended to the south forming a ridge cumbre nueva ridge that was partially destroyed about 560 ka by a giant lateral collapse the cumbre nueva collapse possibly involving 180 200 km 3 of subaerial volcanic material the northwest boundary of the cumbre nueva collapse formed a vertical scarp that enlarged by headward erosion formed the spectacular depression of caldera de taburiente cumbre vieja volcano a north south elongated rift forms the southern half of la palma and constitutes its last stage of growth including all eruptive activity in the past 125 k y detailed field observations mapping and high precision radiometric dating have allowed reconstruction of the growth and structural changes of the cumbre vieja volcano interactions between eruption rates coastal erosion and glacio eustatic sea level change allow stratigraphic subdivision of the edifice the structure of the volcano has been controlled for most of its history by a rift system with a clearly dominant north south and less distinct north east and north west volcanic rift zones the rift reorganization of the volcano to a single north south rift since 7 ka and the opening of faults during the 1949 eruption probably reflect increasing instability of the west flank of the volcano

mineralogical and geo chemical characterization of a diapiric formation in the north of spain abstract we have selected seven profiles located in a diapiric formation in the north of spain the profiles have been analyzed for the mineralogy and the chemical composition of original materials soils developed above them and clay fractions three soils formed on basic rock of volcanic origin ophite and rich in alterable minerals three others formed on clay marl and one soil formed on gypsiferous marl plagioclases pyroxenes vermiculites and biotites are the main minerals found in the soil samples and ophitic rocks biotite smectite chlorite and interstratified chlorite vermiculite make up the predominant mineralogical association in the clay fraction of the soils calcite biotite and on top of all chlorite are the main minerals in the marls and the soils developed on them with gypsum predominant in the gypsiferous marl the mineralogy of its clay fraction is comprised mainly of chlorite and biotite the variations in content of al2o3 tio2 and na2o in the ophites are considered to be associated with the differences in the evolution of the pyroxenes the variability of the chemical composition of the keuper sediments and the soils is attributed more to the chaotic disposition of the triassic materials in the formation of the diapir than to intense chemical weathering the low concentrations of silica iron and aluminum extractable with ammonium oxalate indicate the low proportion of non crystalline products fundamentally it is the semiarid conditions in the study zone together with the processes of extrusion and hydrothermal activity affecting the formation of the diapir that are responsible for the genesis of the minerals

eocene paleosols on king george island maritime antarctica macromorphology micromorphology and mineralogy abstract we investigated the origin of reddish layers between basalt flows in an early eocene volcanic succession in king george island maritime antarctica previous studies in the area classified these layers as regolith surfaces baked zones and paleosols but the properties of these layers and the reasons for their classification are not clarified since the early eocene epoch was one of the warmest phases on earth during the cenozoic a proper investigation of these layers is crucial to obtain additional regional information about the paleoenvironment the focus of this study is on three profiles located in the admiralty bay on king george island they were classified as paleosols based on field micromorphological and mineralogical properties main soil forming processes identified by micromorphological analyses were clay neoformation pedo bioturbation and a weak redoximorphosis the occurrence of plant residues in all profiles was a reliable indicator that these soils formed a land surface during the early eocene abundant weathered volcanic glass and pyroclasts may indicate andosolization although the main diagnostic features for andosols which are the presence of nanocrystalline minerals and organic matter accumulation were not detected or only in small amounts respectively the long term burial of the paleosol could be a reason for lacking of these diagnostic features clay minerals associated with moderately weathered volcanic soils smectite were detected in the x ray diffraction analysis a predominantly reddish colour of most of the soil horizons is given by hematite confirmed by the determination of pedogenic oxides nevertheless rubification was not solely a result of pedogenesis but also of reddening of oxyhydroxides by dehydration during diagenesis other diagenetic processes were burial compaction loss of organic matter and induration in the horizons directly buried by a basalt flow voids were filled by zeolite crystals an effect related to lava cooling another possible diagenetic effect was the geochemical rejuvenation and homogenization of the profiles despite the occurrence of these features the results are in agreement with previous studies indicating a humid temperate paleoclimate for king george island during the early eocene

calc silicate mineralization in active geothermal systems detailed study of the calc silicate mineralogy in the cerro prieto geothermal system was used to demonstrate examples for thermodynamic evaluation of phase relations among minerals of variable composition and to calculate the chemical characteristics of hydrothermal solutions compatible with the observed calc silicate assemblages in general there is a close correlation between calculated and observed fluid compositions calculated fugacities of o 2 at about 320 degrees c in the cerro prieto geothermal system are about five orders of magnitude less than those at the nearby salton sea geothermal system this observation is consistent with the occurrence of fe super 3 rich epidotes and andradite garnets in the latter system and the presence of prehnite at cerro prieto modified journal abstract

miocene biofacies development and geological history of the gulf of suez egypt abstract miocene sediments of the gulf of suez were deposited in a rapidly subsiding rift which became active during late oligocene and early pliocene tectonic episodes complex lithological variations associated with the variable submarine structure commonly preclude detailed correlation of drilled subsurface successions thick middle to late miocene evaporites and their geometry obscure seismic interpretation of prospective sub evaporitic early and middle miocene sequences the thick miocene sediments are believed to have significantly furnished the source as well as the reservoirs and seals for the oil discovered in the gulf of suez over four billion barrels of oil have been established as recoverable reserves in miocene reservoirs a new gulf wide detailed correlation scheme is established based upon a series of newly defined microfaunal assemblage zones these zones are based on holistic analysis of microfauna utilizing planktonic and benthonic foraminifera diatoms otoliths and pteropods dating by planktonic foraminifera and calcareous nannofossils indicates the zones are isochronous vertical and lateral variations in assemblage characteristics have been identified mapped and are concluded to be the results of vertical and lateral differences in salinity water depth water clarity lithological variation and oxygen availability the correlative applicability of this scheme within the gulf of suez provides potential for it to serve as a reference for drilled sequences in the red sea where thicker evaporite sequences make sub evaporitic stratigraphic correlation even more difficult owing to the greater seismic attenuation isochronous palaeoenvironmental variations are detected utilizing the zonation scheme both within the gulf of suez and the red sea region which will assist in the correlation and mapping of stratigraphic sequences of hydrocabon potential detection confirmation and the degree of displacement of faults is also improved by the application of the scheme

diversity and origin of quartz cements in continental carbonates example from the lower cretaceous rift deposits of the south atlantic margin abstract silica precipitation in continental carbonates is a common process occurring during sedimentation and diagenesis the lower cretaceous rift deposits of the south atlantic equatorial margin which are intensively explored by petroleum companies provide good examples of such silicifications in carbonates exhibiting a wide diversity of petrographic habit of early to late quartz cements in order to understand the palaeoenvironmental and diagenetic conditions leading to this diversity we integrated detailed petrography of diagenetic sequences and quartz habit with 18oquartz measurements by sims of individual cements observed in samples from the offshore and onshore basins of the west african margin the petrographic description highlights the omnipresence of early fibrous microquartz cements exhibiting either length fast or length slow habit in addition to laminated microquartz and micro or mega quartz forms amongst the isotopic analysis the 18oquartz data show that length slow cements are generally strongly enriched in 18o 18oquartz ranging from 31 to 37 smow whereas length fast forms show less elevated values 25 c and

characteristics and alteration origins of matrix minerals in volcaniclastic kimberlite of the muskox pipe nunavut canada abstract the matrix of volcaniclastic kimberlite vk from the muskox pipe northern slave province nunavut canada is interpreted to represent an overprint of an original clastic matrix muskox vk is subdivided into three different matrix mineral assemblages that reflect differences in the proportions of original primary matrix constituents temperature of formation and nature of the altering fluids using whole rock x ray fluorescence xrf whole rock x ray diffraction xrd microprobe analyses back scatter electron bse imaging petrography and core logging we find that most matrix minerals serpentine phlogopite chlorite saponite monticellite fe ti oxides and calcite lack either primary igneous or primary clastic textures the mineralogy and textures are most consistent with formation through alteration overprinting of an original clastic matrix that form by retrograde reactions as the deposit cools or in the case of calcite by precipitation from ca bearing fluids into a secondary porosity the first mineral assemblage consists largely of serpentine phlogopite calcite fe ti oxides and monticellite and occurs in vk with relatively fresh framework clasts alteration reactions driven by deuteric fluids derived from the juvenile constituents promote the crystallisation of minerals that indicate relatively high temperatures of formation 400 c lower temperature minerals are not present because permeability was occluded before the deposit cooled to low temperatures thus shielding the facies from further interaction with fluids the other two matrix mineral assemblages consist largely of serpentine phlogopite calcite diopside and chlorite they form in vk that contains more country rock which may have caused the deposit to be cooler upon emplacement most framework components are completely altered suggesting that larger volumes of fluids drove the alteration reactions these fluids were likely of meteoric provenance and became heated by the volcaniclastic debris when they percolated into the vk infill most alteration reactions ceased at temperatures 200 c as indicated by the absence or paucity of lower temperature phases in most samples such as saponite recognition that muskox vk contains an original clastic matrix is a necessary first step for evaluating the textural configuration which is important for reconstructing the physical processes responsible for the formation of the deposit

sedimentological evidence for early miocene fault reactivation in the gulf of suez the sedimentary response to early miocene fault reactivation and marginal uplift in the gulf of suez is strikingly evident within the gemsa half graben this mid rudeis event occurred in the late burdigalian 16 5 ma approximately 8 m y after the onset of rifting in outcrop complicated lateral facies transitions reflect the change from a ramped margin to a structurally controlled depositional environment angular unconformities and truncation mark this event atop marginal tilt block crests distal downlapping sequences are present in adjacent topographic lows that acted as sand depocenters channels draining the rift margins acted as point sources for basinward alluvial fan development sand ratio isopach maps reveal the presence of four active upper rudeis formation fan systems within the gemsa half graben

the history of intrusive activity on the island of la palma canary islands abstract the island of la palma located in the northwest of the canary archipelago consists of two main geological units 1 the subaerial extrusive coberta series covers most of the island and consists of alkali basaltic lavas phonolitic plugs and pyroclastic rocks erupted between 1 61 ma and the recent 2 the basement complex is exposed in the barranco de las angustias and the caldera de taburiente and consists of the submarine intrusive and extrusive seamount series and a basal plutonic complex alkali basaltic dikes of different ages and orientations intruded in both units three groups of dikes and sills can be distinguished based on their field relationships petrography geochemistry and ages the oldest group i represent the feeder dikes to the seamount series intruded between 2 9 and 4 0 ma b p they were originally steep with a n05 w strike and perpendicular to the originally nearly flat bedding of the layered seamount series subsequent to emplacement group i dikes and the extrusives of the seamount series were rotated into their present orientation group ii sills intruded parallel to the bedding of the seamount series 45 230 are coeval with or younger than group i but older than the erosional unconformity separating the coberta and the basement complex i e 1 6 ma 50 vol of the volcanic edifice of the la palma seamount and highlight the importance of intrusive processes for island growth intrusions into central oceanic volcanoes like la palma may result in an uplift and rotation of more than 30 km 3 by up to 45

corrensite and mixed layer chlorite corrensite in metabasalt from northern taiwan tem aem empa xrd and optical studies many chloritic minerals in low grade metamorphic or hydrothermally altered mafic rocks exhibit abnormal optical properties expand slightly upon glycolation expandable chlorite and or have excess alvi relative to aliv as well as significant ca k and na contents chloritic minerals with these properties fill vesicles and interstitial void space in low grade metabasalt from northern taiwan and have been studied with a combination of tem aem empa xrd and optical microscopy the chloritic minerals include corrensite which is an ordered 1 1 mixed layer chlorite smectite and expandable chlorite which is shown to be a mixed layer chlorite corrensite corrensite and some mixed layer chlorite corrensite occur as rims of vesicles and other cavities while later formed mixed layer chlorite corrensite occupies the vesicle cores the tem observations show that the mixed layer chlorite corrensite has ca 20 and the corrensite has ca 50 expandable smectite like layers consistent with xrd observations and with their abnormal optical properties the aem analyses show that high si and ca contents high alvi aliv and low fevi fe mg vi ratios of chlorites are correlated with interstratification of corrensite or smectite like layers in chlorite the aem analyses obtained from 200 500 a thick packets of nearly pure corrensite or chlorite layers always show that corrensite has low aliv siiv and low fevi fe mg vi while chlorite has high aliv siiv and high fevi fe mg vi this implies that the trioctahedral smectite like component of corrensite has significantly lower aliv siiv and fevi fe mg vi the ratios of fevi fe mg vi and aliv siiv thus decrease in the order chlorite corrensite smectite the proportions of corrensite or smectite like layers relative to chlorite layers in low grade rocks are inferred to be controlled principally by fe mg ratio in the fluid or the bulk rock and by temperature compositional variations of chlorites in low grade rocks which appear to correlate with temperature or metamorphic grade more likely reflect variable proportions of mixed layered components the assemblages of trioctahedral phyllosilicates tend to occur as intergrown discrete phases such as chlorite corrensite corrensite smectite or chlorite corrensite smectite a model for the corrensite crystal structure suggests that corrensite should be treated as a unique phase rather than as a 1 1 ordered mixed layer chlorite smectite

dehydration of dioctahedral aluminous phyllosilicates thermodynamic modelling and implications for thermobarometric estimates we propose a solid solution model for dioctahedral aluminous phyllosilicates accounting for the main compositional variations including hydration observed in natural smectites interlayered illite smectite illites and phengites from diagenetic to high grade metamorphic conditions the suggested formalism involves dehydrated micas and hydrated pyrophyllite like thermodynamic end members with these end members the equilibrium conditions of quartz water k bearing mica like phyllosilicates of fixed 2 1 composition are represented by a line in p t space along which the interlayer water content varies the relevant thermodynamic properties required for the calculation of equilibrium conditions were derived using a set of 250 natural data of known maximal temperature and pressure conditions which covers a range between 25 c and few mpa to 800 c and 5 gpa the temperatures calculated at fixed pressure with our model are in fair agreement with those reported in the literature for the 250 natural data at low temperature and pressure the amount of interlayer water in k deficient phengite and illite is predicted to reach 100 of the apparent vacancies which is consistent with previous values reported in the literature although the amount of interlayer water is predicted to decrease with pressure and temperature it is calculated to be significant in k deficient phengite from lt hp pelites metamorphosed at about 350 c 10 kbar the presence of molecular water in the interlayer site of such phengites has been confirmed by ftir mapping its implications for p t estimates are discussed

the smectite to chlorite transition in a fossil seamount hydrothermal system the basement complex of la palma canary islands the hydrothermal metamorphism of a sequence of pliocene aged seamount extrusive and volcanoclastic rocks on la palma includes a relatively complete low p t facies series encompassing the zeolite prehnite pumpellyite and greenschist facies the observed mineral zonations imply metamorphic gradients of 200 300 c km 1 the transition from smectite to chlorite in the la palma seamount series is characterized by discontinuous steps between discrete smectite corrensite and chlorite which occur ubiquitously as vesicles and to a much lesser extent vein in fillings trioctahedral smectites mg fe mg 0 4 0 75 occur with palagonite and na ca zeolites such as analcime and a thompsonite natrolite solid solution corrensite mg fe mg 0 5 0 65 first appears at stratigraphic depths closely corresponding to the disappearance of analcime and first appearance of pumpellyite discrete chlorite mg fe mg 0 4 0 6 becomes the dominant layer silicate mineral coincident with the appearance of epidote and andraditic garnet within the stratigraphic section there is some overlap in the distribution of the three discrete layer silicate phases although random interstratifications of these phases have not been observed although smectite occurs as both low and high charge forms the la palma corrensite is a compositionally restricted 1 1 mixture of low charge trioctahedral smectite and chlorite electron microprobe analyses of coarse grained corrensite yield structural formulae close to ideal values based on 50 negative charge recalculations calcium average 0 20 cations formula unit is the dominant interlayer cation with lesser mg k and na the absence of randomly interlayered chlorite smectite in the la palma seamount series may reflect high time integrated fluid fluxes through the seamount sequence this is consistent with the ubiquity of high variance metamorphic mineral assemblages and the general absence of relict igneous minerals in these samples

diagenetic history and reservoir quality of tight sandstones a case study from shiqianfeng sandstones in upper permian of dongpu depression bohai bay basin eastern china abstract the upper permian shiqianfeng sandstones located in the dongpu depression bohai bay basin china are fluvio lacustrine deposits and have high content of pore filling volcanic dust average 7 93 vol this study focuses on diagenetic processes and reservoir quality of the tight sandstones based on different lithofacies an integrated approach such as core observation x ray diffraction scanning electron microscopy cathode luminescence stable isotope analysis of carbon and oxygen compositions electron microprobe analysis and fluid inclusion analysis were utilized the tight sandstones consist of subarkose and lithic subarkose and have undergone significant diagenetic events including compaction quartz cementation carbonate cementation mainly calcite and ferrocalcite and formation of authigenic clay minerals i e chlorite rims kaolinite and mixed layer illite smectite the volcanic dust altered with increase of burial depth resulting in the production of abundant silicic materials and depletion of metallic ions i e fe 2 mg 2 ca 2 and mn 2 this process formed subhedral micro quartz pore filling authigenic quartz smectite and chlorite rims during the early diagenetic stage early phase carbonate cements calcite ferrocalcite occurred in several samples they were also influenced by volcanic dust alteration resulting in intrusive of fe 2 and high contents of mn 2 average 12 5 mol further alteration of volcanic dust at the mesogenetic stage can result in cementation of kaolinite and euhedral micro quartz quartz overgrowth developed because of smectite to illite reactions and the alteration of volcanic dust late phase carbonate cements dolomite and ankerite are rare the present low porosity average 6 17 vol and permeability average 0 198 md of the shiqianfeng sandstones mainly resulted from intense compaction diverse cementation and pore filling of volcanic dust as strong hydrodynamic conditions of pore water modification of reservoir quality in the conglomeratic sandstone and gritstone lithofacies mainly distribute in braided channel occurred by alteration of volcanic dust thick braided channel at the high structural position should be the focal point for the future exploration

application of biological markers in the recognition of the geochemical characteristics of some crude oils from abu gharadig basin north western desert egypt abstract the objective of this study is to establish the relationship between the hydrocarbons recovered from the abu gharadig basin and middle jurassic khatatba formation as well as the previously established upper cretaceous abu roash f member a suite of fourteen crude oil and condensate samples from the mesozoic reservoirs jurassic cretaceous of the abu gharadig basin western desert egypt was analyzed and geochemically compared with extracts from source rocks of the middle jurassic khatatba formation and the upper cretaceous abu roash f member based on molecular indicators of organic source input depositional environment and age diagnostic biomarkers at least two petroleum systems operate in the abu gharadig basin those derived from late cretaceous marine shales and jurassic early cretaceous non marine organic rich shales as source rocks and possibly a third system appears to be a mixture of them both the correlation of some abu gharadig oils to a late cretaceous source establishes a petroleum system involving these marine cretaceous source rocks

effects of source thermal maturity and biodegradation on the distribution and isomerization of homohopanes in petroleum abstract the distributions of c31 c35 17 21 h homohopanes in marine petroleums can be used to describe redox conditions in the source rock depositional environment for example high c35 homohopane indices c35 c31 c35 are typical of petroleums generated from source rocks deposited under anoxic marine conditions where the c35 backbone of the precursor bacteriohopanetetrol is preferentially preserved homohopane distributions have been used to distinguish petroleums from different organic facies of the same source rock homohopane distributions are altered by secondary processes for example the c35 homohopane index decreases with increasing api gravity and thermal maturity of related oils from the monterey formation offshore california similar decreases in the homohopane index are observed for expelled oils from monterey source rock during hydrous pyrolysis biodegradation can result in selective loss of high or low molecular weight homologs apparently depending on the bacterial population in the reservoir bacterial demethylation of homohopanes appears necessary to explain 25 norhopanes in at least one biodegraded oil hydrous pyrolysis studies of the phosphatic and siliceous members in the monterey formation show that identical heating conditions result in different homohopane c 22 epimer ratios furthermore a reversal in the trend of the epimer ratio at high experimental temperatures is observed for the phosphatic but not for the siliceous lithology this could be caused by the combined effects of isomerization and differential thermal destruction of epimers at high temperatures possibly mediated by rock mineralogy

neogene tectonic and stratigraphic events in the gulf of suez rift area egypt abstract the gulf of suez neogene syn rift section contains at least five datable intra basinal unconformities or stratigraphie hiatuses these events and associated changes in sedimentary sequences seen in the basin can be related to changes in suez rift subsidence miocene eustasy and the tectonic effects of adjacent red sea and dead sea rifting the first hiatus spans oligocene to earliest miocene time and separates syn rift from pre rift strata throughout the region this erosional event resulted from regional emergence during the oligocene and the initiation of suez rifting a second hiatus from 21 19 ma separates the poorly dated shallow marine nukhul formation of aquitanian to early burdigalian age from the overlying upper bathyal shales of the middle burdigalian to langhian nn3 5 rudeis formation this hiatus resulted from both a brief lowstand in early burdigalian sea level and increased suez rift related tectonism this event climaxed with the rapid tectonic subsidence that established deep marine conditions by 19 ma a third major event occurs within the rudeis at 17 ma nn4 n7 and marks the initiation of uplift of i he rift shoulders and margins and decelerated subsidence or even minor uplift in the axial trough hiatuses are seen over paleohighs e g tilted fault blocks whereas coarse elastics are deposited in more basinal areas in submarine fans and as turbidites a fourth unconformity at 14 ma separates the middle miocene kareem formation from overlying anhydrites and open marine shales of the belayim formation minor tectonic uplift throughout the suez region resulted from this event and a sill was established between the mediterranean and suez basins allowing cyclic anhydrite marl deposition from 14 to 11 ma this post kareem event may be the sedimentary response to initiation of movement along the dead sea aqaba transform a sharp drop in sea level at 11 ma restricted the suez basin even more and marked the initiation of massive halite precipitation in the central and southern suez well south of the sill area a final major neogene event occurs at the miocene pliocene boundary and is marked by a major unconformity caused by tectonic uplift this tectonic pulse is related to initiation of red sea sea floor spreading and acceleration of sinistral motion along the dead sea aqaba transform at 5 ma this event establishes the marine connection with the red sea and the sedimentary environments seen in the gulf of suez today