comparative studies of the kinetic parameters of various algaenans and kerogens via open system pyrolyses abstract kinetic parameters were determined for the first time via open system pyrolyses on algaenans highly resistant biomacromolecules that are selectively preserved during kerogen formation isolated from extant microalgae parallel studies were also carried out on 10 kerogens exhibiting with one exception a low level of maturity these kerogens included samples chiefly derived from the selective preservation of the above algaenans and samples mainly or almost exclusively derived from the natural vulcanization pathway important differences in activation energy e a distributions were observed between the four algaenans investigated and correlated with their chemical structures the kerogens predominantly derived from algaenan selective preservation pula alginite ne 70 and bj 248 torbanites rundle oil shale also exhibited pronounced differences in e a distributions these distributions provided i information on the diversity of the source materials and ii reflected the occurrence of important differences in chemical structures and thermal behaviour between three of the tested kerogens even though they are all classified as low maturity type i the kimmeridge clay samples and the lorca oil shale showed broad e a distributions shifted to low energies when compared with the above algaenans and kerogens such shifts reflect an important or even almost exclusive for some of these kerogens contribution of materials originating from sulphur incorporation into various lipids during early diagenesis finally the kinetic data derived for the nine low maturity fossil samples were extrapolated to a very low geological heating rate of 3 c ma 1 and the generation rate curves and cumulative yield curves thus obtained were compared

magma chamber scale liquid immiscibility in the siberian traps represented by melt pools in native iron magma unmixing i e separation of a homogeneous silicate melt into two or more liquids is responsible for sudden changes in the evolution of common melts element fractionation and potential formation of orthomagmatic ore deposits although immiscible phases are a common phenomenon in the mesostasis of many tholeiitic basalts evidence of unmixing in intrusive rocks is more difficult to record because of the transient nature of immiscibility during decompression cooling and crystallization in this paper we document a clear case of liquid immiscibility in an intrusive body of tholeiitic gabbro in the siberian large igneous province using textures and compositions of millimeter sized silicate melt pools in native iron the native iron crystallized from a metallic iron liquid which originated as disseminated globules during reduction of the basaltic magma upon interaction with coal bearing sedimentary rocks in the siberian craton the silicate melts entrapped and armored by the native iron are composed of two types of globules that represent the aluminosilicate 60 77 wt sio2 and silica poor fe ti ca p rich in wt sio2 15 46 feo 15 22 tio2 2 7 cao 11 27 p2o5 5 30 conjugate liquids different proportions and the correlated compositions of these globules in individual melt pools suggest a continuously evolving environment of magmatic immiscibility during magma cooling these natural immiscible melts correspond extremely well to the conjugate liquids experimentally produced in common basaltic compositions at 1025 c our results show that immiscibility can occur at large scale in magma chambers and can be instrumental in generating felsic magmas and fe ti ca p rich melts in the continental igneous provinces

braided fluvial to marine transition the basal lower cambrian wood canyon formation southern marble mountains mojave desert california abstract the lower cambrian wood canyon formation recognized over a 39 000 km2 belt through the southern great basin and mojave desert was examined in the southern marble mountains eastern mojave desert southeastern california there it crops out as a well exposed 90 130 m thick feldspathic sandstone nonconformably overlying proterozoic basement previous investigators have suggested a tide dominated nearshore shallow marine origin for the entire unit in the eastern mojave based on broad scale stratigraphic trends and localized fossil occurrences in the upper member of the formation in contrast to a regional approach the present study uses a detailed lithofacies analysis in a smaller study area to suggest that a fluvial to marine transition occurs within these strata the middle and upper members of the wood canyon formation are recognized in the southern marble mountains and are divisible into six distinct lithofacies that possess gradational contacts where exposed cross stratified sandstone facies a mediumpebble conglomerate facies b planar stratified sandstone facies c sandstone and thin mudstone facies d mudstone with intercalated sandstone facies e and horizontally laminated siltstone facies f facies a d contained within the middle member comprise the bulk of wood canyon sediments and record the depositional characteristics of a transition zone from a distal alluvial braid plain to a tidally influenced fluvial dominated braid delta complex cross stratification in the braid plain sediments displays a strongly unimodal pal ocurrent pattern suggestive of downstream migrating sinuous crested megaripples braid delta sediments however show a more dispersed paleocurrent pattern and contain a sparse trace fossil assemblage a change from fluvial dominated to marine dominated processes is recorded in upper member rocks facies e and f facies e contains many of the traits characteristic of a low to mid tidal flat sequence such as coarsely interlayered bedding flaser and lenticular bedding microripple marks and locally abundant rusophycus and planolites trace fossils facies f which dominantly consists of horizontally laminated siltstone is interpreted as the product of an estuarine lagoon that developed behind and within a discontinuous barrier of stranded braid bars

the khazzan gas accumulation a giant combination trap in the cambrian barik sandstone member sultanate of oman implications for cambrian petroleum systems and reservoirs khazzan is a giant tight gas accumulation located in northern oman the accumulation is associated with cambrian barik sandstone member reservoirs in a semiregional combination stratigraphic structural trap this article outlines the background to the discovery of khazzan and describes our understanding of its geology and petroleum systems and the study work used to support screening appraisal and development strategies for the khazzan accumulation the stratigraphic element of the trap is associated with a northerly thinning and transition of continental fluvial braid plain and shoreface sandstones into offshore mud rocks the structural element of the trap formed as a result of the compactional drape of these reservoir units and the later structuring associated with an underlying long lived intrabasin high the integration of multiple correlation techniques well log correlation recognition of changes in core facies and ichnofacies and magnetostratigraphy has helped to define an intrareservoir correlation framework for the barik sandstone member with a resolution of approximately less than or equal to 1 m y allowing detailed insights into stratigraphic and areal controls on hydrocarbon compositional variations trapping mechanisms reservoirs and reservoir connectivity fluvial sandstones within the khazzan stratigraphic pinch out form better reservoirs the stratigraphic framework developed indicates that these fluvial units are associated with discrete geographically extensive progradation events the association of production with discrete reservoir levels and areas allows a robust semipredictive regional model for targeting better reservoirs and highlights a scope for an additional intra barik stratigraphic trapping potential regionally enhanced reservoir quality within the more productive reservoirs is attributed to depositional and possibly hydrocarbon charge controls on secondary porosity and it is complex subtle crest to flank compositional variations in hydrocarbon type across the gas accumulation hint at complex hydrocarbon charge and mixing between two structural domains and petroleum systems before and during barik deposition john millson holds a b sc honors geology degree and a ph d from aston university in birmingham united kingdom and the university of wales abersytwyth joining the oil industry as a petroleum geologist in 1985 he has worked in the united kingdom nigeria netherlands and oman with some 11 years of working on various aspects of the geology of oman his main interests include tectonostratigraphy and unconventional hydrocarbon resources jamie quin is a geologist for statoil hydro since joining the oil industry in 2001 he has worked on assets in oman for badley ashton and associates libya for repsol ypf and norway statoil he holds a b sc degree from the university of glasgow an m sc degree from royal holloway university of london and a ph d from trinity college dublin erdem idiz is currently a global exploration adviser for exploration new ventures with shell international exploration and production in the netherlands he received his m sc degree in geology 1981 and ph d in geochemistry 1987 from the university of california los angeles ucla after a postdoctorate at the institut francais du petrole he joined shell in 1988 working in research and applications as a geochemist and basin modeler in the netherlands germany and canada his research interests are petroleum systems analysis biomarkers and stable isotopes peter turner holds degrees from cardiff and leicester universities and was a reader in earth sciences at the university of birmingham in the united kingdom from 1988 to 2006 where he was head of the petroleum geoscience group his research includes paleomagnetism sedimentology and hydrocarbon reservoirs and since retiring from university life he has worked as a full time consultant focusing on exploration in north and west africa and china no details available

trace elements in magnetite from massive iron oxide apatite deposits indicate a combined formation by igneous and magmatic hydrothermal processes iron oxide apatite ioa deposits are an important source of iron and other elements e g ree p u ag and co vital to modern society however their formation including the namesake kiruna type ioa deposit sweden remains controversial working hypotheses include a purely magmatic origin involving separation of an fe p rich volatile rich oxide melt from a si rich silicate melt and precipitation of magnetite from an aqueous ore fluid which is either of magmatic hydrothermal or non magmatic surface or metamorphic origin in this study we focus on the geochemistry of magnetite from the cretaceous kiruna type los colorados ioa deposit 350 mt fe located in the northern chilean iron belt los colorados has experienced minimal hydrothermal alteration that commonly obscures primary features in ioa deposits laser ablation inductively coupled plasma mass spectroscopy la icp ms transects and electron probe micro analyzer epma wavelength dispersive x ray wdx spectrometry mapping demonstrate distinct chemical zoning in magnetite grains wherein cores are enriched in ti al mn and mg the concentrations of these trace elements in magnetite cores are consistent with igneous magnetite crystallized from a silicate melt whereas magnetite rims show a pronounced depletion in these elements consistent with magnetite grown from an fe rich magmatic hydrothermal aqueous fluid further magnetite grains contain polycrystalline inclusions that re homogenize at magmatic temperatures 850 c smaller inclusions 500 ppm concentrations

early generation characteristics of a sulfur rich monterey kerogen this paper documents the critical role of organic sulfur in the early formation of bitumen and oil from a sulfur rich kerogen from the miocene monterey formation in california monterey kerogen commonly contains abundant chemically bound sulfur 8 14 wt which appears responsible for early low temperature generation of heavy sulfur rich petroleum due to the lower energy required to break carbon sulfur bonds compared to carbon carbon bonds hydrous pyrolysis was used to simulate the natural generation of petroleum from a sulfur rich type ii kerogen from the phosphatic member of the monterey shale the amount and distribution of sulfur in the kerogen bitumen and expelled oil generated at various temperatures indicate that 1 initial bitumen and oil generation is directly related to cleavage of weak sulfur linkages and 2 most of the expelled oil is formed by decomposition of bitumen and not directly from the kerogen finally comparison of hydrous pyrolysis results with other type ii kerogens suggests that the temperature of peak bitumen generation is inversely related to the heteroatom content primarily sulfur of the kerogen low temperature bitumen generation is an important exploration concept because kerogen rich in sulfur can generate producible oil at thermal maturities significantly below conventionally accepted values furthermore established relationships between thermal maturity sulfur content and other oil properties such as api gravity can be used to rank exploration prospects

relative sea level changes and the development of a cambrian transgression the lower cambrian in northwest scotland is one example of a lower palaeozoic orthoquartzite carbonate succession deposited on a slowly subsiding peneplained precambrian basement during a period of relative sea level rise this particular setting led to the development of a very wide low gradient shelf which was extremely sensitive to minor sea level changes the basal quartz arenite section lower member pipe rock is a transgressive tide dominated systems tract but lacks a systematic parasequence architecture because of three factors a fluvial sediment flux was insufficient to induce shoreline progradation accommodation space was limited during sea level falls which are commonly expressed by widespread erosional surfaces and sediment yield to the shelf by transgressive reworking was a major contributor towards the preserved stratigraphy the storm dominated fucoid beds represent a condensed section and also show the effects of rapid and widespread facies belt oscillations because of the low shelf gradient an overlying highstand systems tract is also lacking partly due to the absence of a large fluvial sediment yield and also due to lowstand and transgressive reworking an erosively based tidal sandsheet at the top of the fucoid beds interpreted to be a lowstand systems tract therefore rests directly on the condensed section of the underlying sequence this was in turn reworked into linear tidal sandbanks salterella grit during slow sea level rise prior to the next major transgression the limited accommodation space therefore introduced a preservational bias towards deepening upward trends on a parasequence and sequence scale the oscillations in facies belts episodic subareal exposure and the potential to remove substantial portions of systems tracts suggests that lower palaeozoic orthoquartzite successions may exhibit regular and abrupt vertical shifts in depositional environment which given their subtle lithological character may require detailed analysis to identify such successions may also display incomplete development of several components of transgressive regressive sequence architecture

reassessment of the basal sauk supersequence boundary across the laurentian craton margin hinge zone southeastern california abstractin the death valley and mojave desert regions of southeastern california the contact separating the lower and middle members of the wood canyon formation wcf is currently interpreted as a regional scale unconformity coincident with the base of the sauk sequence regional mapping of this surface however reveals a nonconformable contact with underlying crystalline basement in cratonic settings and a relatively conformable contact atop a northwest thickening wedge of off craton strata that is capped by the lower member of the wcf consistent with an unconformity the progressive loss of three carbonate units within the lower member of the wcf has been attributed to incision by the base of the middle member wcf however fossil evidence and correlation based on carbon isotope compositions of each lower member wcf dolostone unit reject top down erosion to describe their loss and overall cratonward thinning results from multiple detailed measured stratigraphic sections of a conglomerate at the b

early cambrian metazoans in fluvial environments evidence of the non marine cambrian radiation davies and gibling 2012 1 raise concerns that sediments hosting trace fossils in the early cambrian middle member of the wood canyon formation which we have interpreted as fluvial may be marine in origin they suggest that in the absence of body fossils or specific minerals it may not be

marine to fluvial transition proterozoic upper rewa sandstone maihar india abstract the proterozoic upper rewa sandstone in central india is generally interpreted as entirely marine a detailed study in maihar madhya pradesh however reveals upward transition from marine to fluvial through a mixed facies association also bearing eolian imprints facies associations differ in stratal geometry and arrangement palaeocurrent direction and pattern as well as in grain size and sorting the fine grained marine association is dominated by tidal sheet deposits with characteristic rhythmic changes in thickness and style of cross stratification and their packages as well as local evidence of current reversals subordinate beach deposits are also present the major palaeocurrent direction is highly consistent and westward the coarse grained often granule rich sandstones of the fluvial association are embodied by four facies correlatable with flow stages and relative bed shear these braided stream deposits are preserved in vertical stacks of tabular sandbodies in response mainly to basin subsidence the palaeocurrent pattern is unimodal and northwestward but its dispersion covers 180 the rocks are poorly sorted and at places incorporate sand clasts although they are virtually mud free and mineralogically mature as in two other associations the medium to fine grained sandstones at the intermediate interval between the marine and fluvial associations are of distinct lensoid geometry they incorporate representatives from the previous two associations as well as translatent strata interdune erg deposits and possibly aeolian cross strata consequently the palaeocurrent pattern is polymodal with a spread over 270 an overall coarsening up trend in the fluvial part and thinning up trend in the tidal part imply progradation in spite of evidence of basin subsidence a high rate of sediment discharge from a perennial river system in a humid climate is suggested

rise in seawater sulphate concentration associated with the paleoproterozoic positive carbon isotope excursion evidence from sulphate evaporites in the 2 2 2 1 gyr shallow marine lucknow formation south africa past oceanic sulphate concentration is important for under standing how the oceansredox state responded to atmospheric oxygen levels the absence of extensive marine sulphate evaporites before 1 2 gyr probably reflects low seawater sulphate and or higher carbonate concentrations sulphate evaporites formed locally during the 2 22 2 06 gyr lomagundi positive d 13 c excursion however the 2 2 2 1 gyr lucknow formation south africa provides the first direct evidence for seawater sulphate precipitation on a carbonate platform with open ocean access and limited terrestrial input these marginal marine deposits contain evidence for evaporite molds pseudomorphs after selenite gypsum and solid inclusions of ca sulphate in quartz carbon and sulphur isotope data match the global record and indicate a marine source of the evaporitic brines the apparent precipitation of gypsum before halite requires 2 5 mm l 1 sulphate concentration higher than cur rent estimates for the paleoproterozoic during the lomagundi event which postdates the 2 32 gyr initial rise in atmospheric oxygen seawater sulphate concentration rose from archean values of 200 lm l 1 but dropped subsequently because of higher pyrite burial rates and a lower oceanic redox state

submarine thermal springs associated with young volcanoes the teahitia vents society islands pacific ocean abstract hydrothermal solutions were sampled close to two summits of teahitia a submarine volcano from the southern extension of the society volcanic chain the temperatures measured within two vents were 30 c the vent solutions have a ph value around 5 3 and are enriched in fe mn si ba li and rees relative to ambiant seawater but show only a small decrease in mg and so4 concentrations the lowest measured 87sr 86sr is 0 70867 while the end is identical to those of the surrounding alkali basalt 2 5 the vent solutions from teahitia have chemical characteristics similar to pele s vents loihi seamount another mid plate volcano the exact temperature of seawater basalt interaction is difficult to constrain however the absence of positive eu anomaly in the fluids the particles and in the hydrothermal deposits from teahitia seems to exclude the participation of a high temperature component comparable as those involved in mid ocean ridge axis vents

predicting the generation of heavy oils in carbonate evaporitic environments using pyrolysis methods abstract a series of low maturity kerogen and asphaltene samples of a sulphur rich mediterranean carbonate source rock sequence as well as two associated oil samples were analysed by different pyrolysis methods the source rock was characterised by the occurrence of four different lithotypes three of which possessed source potential elemental analysis revealed that each source lithofacies contained a distinct kerogen type comprising type i s for shale intercalations type ii s in the laminated lithofacies and low sulphur type ii in the pure carbonate portions of the source rock pyrolysis gas chromatography using coupled fid and hecd detectors provided a more detailed insight into kerogen asphaltene composition than afforded by rock eval pyrolysis bulk kinetic analysis demonstrated that asphaltenes and type i s kerogens were the most labile species present in the source rocks type ii s kerogens often quoted as the major source of heavy oils were the most stable of the sulphur rich organic matter types the occurrence of various kerogen types with differing stabilities in the carbonate source rock analysed as determined by bulk pyrolysis fid implies that peak hydrocarbon generation in the source rock sequence is not confined to a single temperature but rather to a relatively large temperature range of roughly 20 c combination of bulk hydrocarbon generation kinetics and a multistep pyrolysis approach demonstrated that for carbonate evaporitic environments it is necessary to differentiate between early and late maturity products this is because the lower energies 46 49 kcal mol which may be attributed to s c bond cleavage reactions are empirically of greater importance especially in view of the fact that they may represent the main generation stage under natural conditions

sedimentology stratigraphy and tectonic implications of a paleo proterozoic continental extensional basin the el sherana edith river groups northern territory australia the ca 1 83 ga el sherana edith river basin of northern territory australia contains terrestrial sedimentary and volcanic rocks deposited during continental extension or transtension braid pl

sequence stratigraphy of the taebaek group cambrian ordovician mideast korea abstract this study focuses on the sequence stratigraphic implications of the taebaek group cambrian ordovician a mixed carbonate siliciclastic sequence ca 1200 m thick in the mideastern part of the korean peninsula the group contains 11 lithologic units formations that can be partitioned into four packages supersequences i iv each package comprises alternation of siliciclastic and carbonate successions corresponding to the second order sequence supersequence formed in a period of 10 100 m y supersequence i jangsan myeonsan myobong and daegi fms represents the initial inundation and subsequent drowning during the late early to middle middle cambrian it experienced the drowning between the middle and late middle cambrian forming type 3 sequence boundary supersequence ii sesong and hwajeol fms was formed by prolonged marine flooding during the late middle and late cambrian it was terminated by a large supply of siliciclastics due to the rejuvenation of the drainage basin and the subsequent shallowing at the cambrian ordovician boundary type 2 sequence boundary supersequence iii dongjeom dumugol and makgol fms comprises the lowstand coarse grained siliciclastics transgressive shale by marine flooding and shallow platform carbonates by highstand progradation in the early ordovician following the large scale eustatic fall of sea level in the earliest middle ordovician supersequence iv jigunsan and duwibong fms formed on the subaerial exposure surface type 1 sequence boundary by resumed marine flooding in the middle ordovician this study provides basis for basin scale correlation with the coeval sequences in northeastern china

provenance of quartzite clasts in the eocene oligocene sespe formation paleogeographic implications for southern california and the ancestral colorado river quartzite clasts in fluvial sespe formation conglomerates of the santa monica mountains were compared petrographically with potential source rocks in the basin and range and transition zone provinces to determine their provenance modal analysis indicates that sespe orthoquartzite clasts are mainly quartzofeldspathic and derived from source rocks with craton interior provenance such clasts were probably derived from stirling quartzite and wood canyon formation sources in the northern mojave desert the mazatzal peak quartzite of central arizona is the probable source of quartzolithic orthoquartzite clasts containing abundant detrital jasper grains sespe metaquartzite clasts are mainly from sources in the southern mojave desert but some may be from the yavapai terrane of central arizona the dual provenance of orthoquartzite clasts suggests that the sespe paleoriver was a bifurcating system tapping both mojave desert and sonora desert sources after compensating for neogene displacement along the san andreas fault a paleogeographic reconstruction shows that there is a general spatial coincidence between sespe and other cenozoic paleodelta deposits around los angeles that contain exotic clasts and the inferred location of the mouth of the colorado river assuming that it existed during the eocene thus the colorado river may be much older than previously thought as old as late paleocene and perhaps was once part of an ancient fluvial connection with the mojave desert interior

yttrium and rare earth elements in fluids from various deep sea hydrothermal systems rare earth element ree and yttrium y concentrations were measured in fluids collected from deep sea hydrothermal systems including the mid atlantic ridge mar i e menez gwen lucky strike tag and snakepit the east pacific rise epr i e 13 n and 17 19 s and the lau vai lili and manus vienna woods pacmanus desmos back arc basins bab in the south west pacific in most fluids y is trivalent and behaves like ho chondrite normalized y ree y reen concentrations of fluids from mar epr and two bab sites i e vai lili and vienna woods showed common patterns with lree enrichment and positive eu anomalies ree analysis of plagioclase collected at lucky strike strengthens the idea that fluid ree contents are controlled by plagioclase phenocrysts other processes however such as ree complexation by ligands cl f so42 secondary phase precipitation and phase separation modify ree distributions in deep sea hydrothermal fluids ree speciation calculations suggest that aqueous ree are mainly complexed by cl ions in hot acidic fluids from deep sea hydrothermal systems ree concentrations in the fluid phases are therefore influenced by temperature ph and duration of rock fluid interaction unusual y reen patterns found in the pacmanus fluids are characterized by depleted lree and a positive eu anomaly the demos fluid sample shows a flat y reen pattern which increases regularly from lree to hree with no eu anomaly these manus basin fluids also have an unusual major element chemistry with relatively high mg so4 h2s and f contents which may be due to the incorporation of magmatic fluids into heated seawater during hydrothermal circulation ree distribution in pacmanus fluids may stem from a subseafloor barite precipitation and the ree in demos fluids are likely influenced by the presence of sulfate ions

tempestite frequency curves a key to late ordovician and early silurian subsidence sea level change and orbital forcing in the anticosti foreland basin quebec canada following partial closure of the northern iapetus ocean along the newfoundland segment of the st lawrence promontory subsidence along the anticosti platform was influenced by residual thermal subsidence renewed tectonic loading by thrust sheets to the south and sediment loading basement subsidence calculated by removing the effects of sediment loading was between 2 and 5 cm ka in the caradocian increasing to 8 6 cm ka in the pusgillian and cautleyan and reaching a maximum of 17 7 cm ka in the rawtheyan during deposition of the princeton lake and vaureal formations a marked decline in subsidence beginning in the hirnantian and continuing into the early silurian may reflect decoupling of thrust loads to the south although a further stage of thrust loading may have occurred in the aeronian during deposition of the lower part of the jupiter formation storm frequency curves produced using tempestite abundance thickness and grain size through more than a kilometre of carbonate strata on antico

the architecture of precambrian high energy tidal channel deposits an example from the lyell land group eleonore bay supergroup northeast greenland abstract within the 2 5 km thick late proterozoic lyell land group of the eleonore bay supergroup in east greenland numerous successions of stacked sheet sandstone bodies 10 70 m thick occur each succession consists of several 5 50 m thick multistorey sand sheets separated from each other by 0 2 2 m thick heterolithic mudstone or sandstone beds individual sand sheets are 0 2 3 0 m thick they have highly erosive lower contacts show a rough fining upward trend and are capped by a thin mudstone veneer containing desiccation cracks dominant sedimentary structures within the sand sheets are sets of planar cross bedding showing a range of characteristic tidal features such as successive bundles of foresets herringbone cross stratification ebb and flood caps and numerous reactivation surfaces horizontal lamination is abundant and may in some instances comprise more than half of the structures within a sand sheet the sand sheets represent high energy tidal channels with the multistorey sand sheets constituting larger tidal channel complexes the heterolithic beds represent mixed tidal flat sediment deposited during periods of tidal channel complex abandonment probably caused by channel aggradation and changing drainage patterns the tidal channels were wide shallow and very sandy with a very poorly developed channel morphology caused by lack of fine grained sediments and vegetation most likely they evolved within a meso to microtidal sandy back barrier setting where the channels migrated swiftly across tidal flats and reworked most interchannel sediment an architecture was developed consisting of stacked sand sheets interbedded with rare heterolithic mudstone beds the model presented incorporates sedimentary parameters and processes characteristic of a pre vegetative landscape and it has no direct modern analogue

fluid inclusion and stable isotope study of the esfordi apatite magnetite deposit central iran a reply sir we are pleased that our recent paper in economic geology jami et al 2007 presenting the geologic setting a description of the mineralization fluid inclusion and o isotope analyses of the esfordi p fe oxide deposit in central iran has been of interest to aftabi and his colleagues aftabi et al 2009 the opportunity to discuss further some aspects of our paper is appreciated including support for a hydrothermal dominated depositional model for esfordi aftabi et al 2009 focus their comments on the question of the affinity of the esfordi p fe oxide deposit in particular they argue that esfordi and by inference other diverse fe oxide deposits within the bafq district of central iran should be considered rapitan type banded iron formations i e bif klein 2005 rather than kiruna type hitzman 2000 in discussing our results and conclusions in the light of previous work particularly forster and jafarzadeh 1994 aftabi et al 2009 have misconstrued our interpretation of some of the textural and isotopic data as providing support for an orthomagmatic model for the esfordi p fe oxide deposit based on the structure relationships between mineralization and host rocks fluid inclusion and isotopic data we concluded that esfordi exhibits strong evidence of hydrothermal origin though we did not preclude some component of precursor orthomagmatic processes in formation of the p fe mineralisation it is noted that some examples of the kiruna end member of the continuum of fe oxide deposits discussed by hitzman 2000 are controversial particularly in regard to their evolution sillitoe and burrows 2002 henriquez et al 2003 we have shown that esfordi has a number of features typical of the kiruna type deposits and does not exhibit features consistent with an affinity to rapitan type fe oxide deposits this evidence will be discussed briefly with further data

early cambrian metazoans in fluvial environments evidence of the non marine cambrian radiation comment kennedy and droser 2011 1 proposed that the colonization of non marine depositional environments occurred much earlier than previously thought prior sedimentological interpretation of the trace fossil bearing succession of the middle member of the wood canyon formation diehl 1979 2 fedo

sedimentology and sequence stratigraphy of neoproterozoic and cambrian units across a craton margin hinge zone southeastern california and implications for the early evolution of the cordilleran margin abstract neoproterozoic basal cambrian strata exposed in eastern california represent the deposits of a craton margin hinge zone that formed in response to the fragmentation of the neoproterozoic supercontinent rodinia one unresolved question regarding the late neoproterozoic stratigraphy in the southwestern united states has been the interpretation of paleotectonic affinity for rocks deposited above the glaciogenic kingston peak formation of central concern has been attempts to identify the position in this stratigraphy where rift related sediments give way to passive margin deposits subsidence analyses suggest that rifting occurred near the start of the cambrian perhaps coincident with the feldspathic middle member wood canyon formation it rests on a disconformity that represents the base of the sauk supersequence and would likely represent the break up unconformity in subsidence analysis models middle member wood canyon and overlying lower middle cambrian strata extend far into the craton detailed sedimentary facies and sequence stratigraphic analysis of post kingston peak pre middle wood canyon rocks indicate that depositional facies in this succession distal alluvial through shallow subtidal are similar to units deposited on the stable craton further these pre sauk units which can be divided into multiple principally eustatically driven depositional sequences are correlated across long distances and even lap onto the edge of the stable craton we suggest the kingston peak formation is the principal rift generated deposit and the overlying thick predominantly siliciclastic section represents the basal deposits of the cordilleran passive margin kingston peak strata consist of thick coarse diamictites interbedded with turbidites such facies are unique in the overall stratigraphy but are similar to other known rift deposits although the age of the kingston peak formation is not well constrained and may be as young as 590 ma it may correlate with the rapitan sturtian glaciation 720 ma which would place middle wood canyon strata some 150 ma younger than the start of rifting

architectural elements from lower proterozoic braid delta and high energy tidal flat deposits in the magaliesberg formation transvaal supergroup south africa abstract three architectural elements are identified in the lower proterozoic magaliesberg formation pretoria group transvaal supergroup of the kaapvaal craton south africa 1 medium to coarse grained sandstone sheets 2 fine to medium grained sandstone sheets and 3 mudrock elements both sandstone sheet elements are characterised by horizontal lamination and planar cross bedding with lesser trough cross bedding channel fills and wave ripples as well as minor desiccated mudrock partings double crested and flat topped ripples due to the local unimodal palaeocurrent patterns in the medium to coarse grained sandstone sheets they are interpreted as ephemeral braid delta deposits which were subjected to minor marine reworking the predominantly bimodal to polymodal palaeocurrent trends in the fine to medium grained sandstone sheets are inferred to reflect high energy macrotidal processes and more complete reworking of braid delta sands the suspension deposits of mudrocks point to either braid delta channel abandonment or uppermost tidal flat sedimentation the depositional model comprises ephemeral braid delta systems which debouched into a high energy peritidal environment around the margins of a shallow epeiric sea on the kaapvaal craton braid delta and tidal channel dynamics are inferred to have been similar fine material in the magaliesberg formation peritidal complexes indicates that extensive aeolian removal of clay does not seem applicable to this example of the early proterozoic

negligible microbial matground influence on pre vegetation river functioning evidence from the ediacaran lower cambrian series rouge france supported by shell international exploration and production b v under research framework agreement pt38181

modeling oil generation with time temperature index graphs based on the arrhenius equation the time and depth of oil generation from petroleum source rocks containing type ii kerogens can be determined using time temperature index tti graphs based on the arrhenius equation activation energies e and frequency factors a used in the arrhenius equation were obtained from hydrous pyrolysis experiments on rock samples in which the kerogens represent the range of type ii kerogen compositions encountered in most petroleum basins the e and a values obtained were used to construct graphs that define the beginning and end of oil generation for most type ii kerogens having chemical compositions in the range of these standards activation energies of these standard kerogens vary inversely with their sulfur content the kerogen with the highest sulfur content had the lowest e value and was the fastest in generating oil whereas the kerogen with the lowest sulfur content had the highest e value and was the slowest in generating oil these standard kerogens were designated as types iia b c and d on the basis of decreasing sulfur content and corresponding increasing time temperature requirements for generating oil the summation tti arr values determined graphically with these type ii kerogen standards in two basin models were compared with a computer calculation using 2000 increments the graphical method came within 3 of the computer calculation as type ii kerogens are the major oil generators in the world these graphs should have wide application in making preliminary evaluations of the depth of the oil window in exploration areas

immiscible iron and silica rich melts and magnetite geochemistry at the el laco volcano northern chile evidence for a magmatic origin for the magnetite deposits abstract the pliocene el laco volcano northern chile hosts a large iron oxide deposit that occurs as stratiform bodies with underlying feeder zones dykes hosted by hydrothermally altered andesite lava flows phenocrysts in the andesite hosting the mineralization have abundant melt inclusions displaying strong evidence for melt immiscibility most of the pyroxene and the plagioclase phenocrysts contain abundant fe rich melt inclusions with low ti magnetite pyroxene apatite and minor anhydrite the glassy groundmass of these melt inclusions is chemically similar to sub alkaline rhyolitic rocks e g 70 sio 2 si al k na rich large resorbed plagioclase phenocrysts also host another group of melt inclusions with a similar silica rich groundmass but hosting evenly distributed immiscible and complex fe rich spheroidal globules that are enriched in ti p mg ca and s these immiscible globules and the ti poor magnetite daughter crystals in the melt inclusions in pyroxene phenocrysts are thought to be the parental iron oxide melt liquid after which their coalescence leads to the formation of magnetite melts from which the magnetite that formed the el laco iron oxide deposits crystallized and were emplaced the mineralogy and chemistry of these melt inclusions tracks the chemical evolution of the fe ox melts and supports a magmatic origin for the el laco magnetite this is mainly recognized by the continuum of compositions between volcanic separate immiscible fe oxide melts and magnetite ores the trace element composition of the fe rich melt inclusions and of the magnetite in the host andesite and the ore bodies reveals a systematic depletion in most of the elements that are compatible in magnetite the ti content of the magnetite also records the separation and crystallization of the iron rich melt typically the magnetite in the orebodies and the melt inclusions is ti poor compared with titanomagnetite found in the andesite groundmass and that hosted by the hydrothermally altered andesite that is interpreted as being attributed to its crystallization under oxidizing and sulfur rich conditions the cause of this unusual chemical behaviour is probably due to the mechanism s governing the crystallization of the iron rich melt including the temperature changes in chemistry prior to eruption and an increase in the redox conditions of the silicate melt magma oxidation facilitates the prevalence of ferric iron and formation of ti poor magnetite preventing the incorporation of ti in the exsolving iron rich melt the likely reason for the formation of these large ti poor magnetite deposits is likely the contamination of the parental andesitic magma by oxidized crustal rocks and concomitant crystallization of magnetite under oxidizing conditions something that had a significant impact on the elemental distribution

reply to discussion by a aftabi and s mohseni on combined igneous and hydrothermal source for the kiruna type bafq magnetite apatite deposits in central iran trace element and oxygen isotope studies of magnetite by mehdipour ghazi et al ore geology reviews 105 2019 590 604 abstract in this reply we emphasize on some geological and geochemical evidence that indicate most of the studied deposits choghart chadormalu and sechahun have magmatic origin and they are not related to bif deposits as declared by aftabi and mohseni 2019 field studies reveal the existence of at least three types of iron mineralization in the posht e badam block 1 stratiform fe oxide ologist sublayers within the neoproterozoic meta sedimentary units 2 iron lenses within the early cambrian volcano sedimentary unit and 3 massive magnetite deposits we assume that studies by aftabi and mohseni 2019 were focused on iron deposits mainly belonging to type 2 iron mineralization above we proposed contamination of primary silicate magma with older units similar to ediacaran bands of magnetite reported by aftabi and mohseni 2019 that include iron phosphor and sodium which were responsible for triggering immiscibility of fe rich melt from silicate magma and formation of the studied massive iron deposits

stratigraphic investigations of carbon isotope anomalies and neoproterozoic ice ages in death valley california an unusual richness of biogeochemical events is recorded in neoproterozoic cambrian strata of the death valley region california united states eight negative carbon isotope d13c excursions are found in carbonate units between 1 08 ga and the precambrian cambrian boundary four of these excursions occur in carbonates that contain textural features similar to those found globally in postglacial cap carbonates including one or more of the following laminite with rollup structures apparent tube rocks seafloor precipitates and sheet crack cements however only two of these units the sourdough limestone member of the kingston peak formation and the noonday dolomite rest directly upon glacial strata the basal beck spring dolomite and the rainstorm member of the johnnie formation each contain negative excursions and cap carbonate like lithofacies but do not rest on known glacial deposits if the negative d13c excursions are assumed to record depositional processes two equally interesting hypotheses are possible 1 the death valley succession records four glacial pulses in neoproterozoic time but glacial units are not preserved at two stratigraphic levels 2 alternatively other global oceanographic processes can cause negative excursions and cap carbonate like facies in addition to or independent of glaciation

depositional and tectonic setting of the archean moodies group barberton greenstone belt south africa the 3 22 3 10 ga old moodies group uppermost unit of the swaziland supergroup in the barberton greenstone belt bgb is the oldest exposed well preserved quartz rich sedimentary sequence on earth it is preserved in structurally separate blocks in a heavily deformed fold and thrust belt north of the inyoka fault moodies strata reach up to 3700 m in thickness detailed mapping correlation of measured sections and systematic analysis of paleocurrents show that the lower moodies group north of the inyoka fault forms a deepening and fining upward sequence from a basal alluvial conglomerate through braided fluvial tidal and deltaic sandstones to offshore sandy shelf deposits the basal conglomerate and overlying fluvial facies were derived from the north and include abundant detritus eroded from underlying fig tree group dacitic volcanic rocks shoreline parallel transport and extensive reworking dominate overlying deltaic tidal and marine facies the lithologies and arrangement of moodies group facies sandstone petrology the unconformable relationship between moodies strata and older deformed rocks presence of at least one syndepositional normal fault and presence of basaltic flow rocks and airfall fall tuffs interbedded with the terrestrial strata collectively suggest that the lower moodies group was deposited in one or more intramontane basins in an extensional setting thinner moodies sections south of the inyoka fault generally less than 1000 m thick may be correlative with the basal moodies group north of the inyoka fault and were probably deposited in separate basins a northerly derived southward thinning fan delta conglomerate in the upper part of the moodies group in the central bgb overlies lower strata with an angular unconformity this and associated upper moodies conglomerates mark the beginning of basin shortening by south to southeast directed thrust faulting along the northern margin of the bgb and suggest that the upper moodies group was deposited in a foreland basin timing orientation and style of shortening suggest that this deformation eventually incorporated most of the bgb into a major fold and thrust belt

a marine to fluvial transition in the paleoproterozoic koolbye formation turee creek group western australia abstract although no unambiguous biogenic criteria exist to discriminate precambrian shallow marine successions from fluvial deposits physical sedimentological evidence including an association of primary sedimentary structures and textures stratigraphic position and comparison with phanerozoic and modern examples has been found useful in identifying these deposit types our high resolution sedimentary facies analysis coupled with new mapping clearly indicates shallow marine to beach aeolian to fluvial sedimentation in the paleoproterozoic koolbye formation of the turee creek group western australia a falling stage systems tract within the koolbye formation has been documented our sedimentary facies analysis in combination with sedimentological analysis of the underlying kungarra formation indicates development of at least three falling stage systems tracts within the turee creek group across the rise of atmospheric oxygen the great oxidation event

combined igneous and hydrothermal source for the kiruna type bafq magnetite apatite deposit in central iran trace element and oxygen isotope studies of magnetite abstract the main deposits of the bafq district choghart se chahun and chadormalou deposits are magnetite apatite ore bodies with early cambrian age hosted by early cambrian volcano sedimentary rocks showing lava flow structure with miarolitic cavities and occasional brecciation the texture and geochemistry trace elements and o isotope of the studied magnetite crystals show three types of magnetite with different proportions in different parts of the district and the deposits these are primary ignious magnetite and high temperature hydrothermal magnetite in the massive parts of the deposits and foam like magnetite in the veins or in the fractures of the massive part the lack of zonation high ti fe ratios and 18o values 2 than the massive magnetites the magmatic origin for the main part of the ores in the bafq is more plausible contamination of the primary magmas of the bafq magmatic rocks with crustal phosphorus and evaporate units was the major agent for triggering iron rich melt immiscibility from the original magma concentration of volatiles in the iron rich melt involving in crystallization of the primary magnetite and nucleation of the aqueous fluid bubbles on magnetite surfaces led to ascending the buoyant fluid bubble magnetite aggregates this caused continuation of the magmatic magnetite microlites growth from the iron rich magmatic hydrothermal fluid and formed high temperature hydrothermal magnetite formation of hypersaline fluid due to crystallization of iron rich melt at shallow depth led to crystallization of titanite and th u ree bearing minerals and sodic calcic alteration related to magnetite mineralization microscopic evidence replacement of magnetite by hematite and filling of fractures of thorite by magnetite show that degassing continued at shallow depth which led to re crystallization of the primary magnetites and formation of the foam like magnetites

sedimentology of a lacustrine fan delta system miocene horse camp formation nevada usa a 1600 m thick succession of the miocene horse camp formation member 2 exposed in east central nevada records predominantly terrigenous clastic deposition in subaerial and subaqueous fan delta environments and nearshore and offshore lacustrine environments these four depositional environments are distinguished by particular associations of individual facies 14 defined facies subaerial and subaqueous fan delta facies associations include ungraded matrix and clast supported conglomerate normally graded matrix and clast supported conglomerate ungraded and normally graded sandstone and massive to poorly laminated mudstone subaqueous fan delta deposits typically have dewatering structures distorted bedding and interbedded mudstone the subaerial fan delta environment was characterized by debris flows hyperconcentrated flows and minor sheetfloods the subaqueous fan delta environment by debris flows high and low density turbidity currents and suspension fallout the nearshore lacustrine facies association provides examples of deposits and processes rarely documented in lacustrine environments high energy oscillatory wave currents probably related to a large fetch reworked grains as large as 2 cm into horizontally stratified sand and gravel offshore directed currents produced uncommonly large typically 1 2 m thick trough cross stratified sandstone in addition stromatolitic carbonate interbedded with stratified coarse sandstone and conglomerate suggests a dynamic environment characterized by episodic terrigenous clastic deposition under high energy conditions alternating with periods of carbonate precipitation under reduced energy conditions massive and normally graded sandstone and massive to poorly laminated mudstone characterize the offshore lacustrine facies association and record deposition by turbidity currents and suspension fallout a depositional model constructed for the horse camp formation member 2 precludes the existence of all four depositional environments at any particular time rather phases characterized by deposition in subaerial fan nearshore lacustrine and offshore lacustrine environments alternated with phases of subaerial fan delta subaqueous fan delta and offshore lacustrine deposition this model suggests that high energy nearshore currents due to deep water along the lake margin reworked sediment of the fan edge thus preventing development of a subaqueous fan delta environment and promoting development of a well defined nearshore lacustrine environment low energy nearshore currents induced by shallow water along the

microbially originated wrinkle structures on sandstone and their stratigraphic context palaeoproterozoic koldaha shale central india abstract wrinkle structures on sandstone beds are abundant and present in diverse forms in the palaeoproterozoic koldaha shale vindhyan basin central india the inferred palaeogeography of sedimentation ranges from offshore marine to terrestrial the wrinkled sandstones belonging to the relatively deeper marine part good preservation of ultramicroscopic microbial elements within these sandstones strongly supports a microbial mat origin of the wrinkles which was facilitated by development of an oxygen depleted condition immediately beneath the sediment water interface as depicted in early pyrite growth later impermeable shale encasing the sandstone beds arrested further scope for destruction of the microbial elements trapping of fine detritus by microbial filaments is documented by the invariable occurrence of a silty clay veneer on the wrinkled surfaces and by its characteristic texture wrinkle morphology has been classified and an attempt has been made to understand the origin of each of the varieties and to visualize the processes that acted upon the microbial mats to produce the wrinkle structures in their specific palaeogeographic context the general palaeogeographic bias in occurrence of the sandy wrinkles is well reflected in their concentration in the lower part of the highstand systems tracts hst s one superposed above the other comprising the koldaha shale the smaller scale palaeogeographic control is indicated by compartmentalization of two wrinkle varieties in the upper and the basal intervals of the hst s and overlapping occurrence of other varieties in the medial interval with apparent preference for either the upper or the lower levels

the paleoenvironmental distribution of phanerozoic wrinkle structures abstract wrinkle structures are microbially induced sedimentary structures that are known to have formed in ancient marine siliciclastic environments this study reviews the sedimentary context and paleoenvironmental distribution of these sedimentary structures throughout three distinct intervals of the phanerozoic the cambrian the post cambrian paleozoic and the lower triassic during these times wrinkle structures are found primarily within two sedimentary environments storm dominated subtidal environments and the intertidal zone subtidal occurrences of wrinkle structures during the post ordovician phanerozoic only appear to occur during intervals of environmental stress while earlier examples from the cambrian and lowermost ordovician likely formed prior to significant increases in extent and depth of bioturbation that hallmark most of the phanerozoic intertidal examples occur regardless of severe environmental stress and may have formed under low levels of bioturbation due to inherent vagaries of a marginal marine setting these environmental preferences appear to be conservative throughout the phanerozoic and may very well extend throughout earth s history

covariance of structural and stratigraphic trends evidence for anticlockwise rotation within the walker lane belt death valley region california and nevada large magnitude relative rotations of range scale structural blocks are inferred to be products of crustal extension in the death valley region in california and nevada reconstructions of the extended terrain restore pre tertiary contractile structures with currently diverse trends into a relatively simple north northeast trending thrust belt we interpret trends of major contractile structures throughout the death valley region as characteristically discordant to and thus geometrically independent from stratigraphic trends we compare trends of pre tertiary contractile structures with paleoflow orientations in lower cambrian strata throughout the extended terrain significant differences between mean paleoflow orientations are consistent in magnitude and sense with differences observed in the structural trends available evidence does not support interpretation of paleoflow data from apparently rotated areas as representing an original paleogeography distinct from that of adjacent areas facies variations are present within the contractile structures we interpret the strong covariance throughout the study area between structural and paleoflow trends of diverse orientations as evidence for vertical axis rotations combined rotation estimates from these data indicate clockwise rotations of 85 12 for bare mountain and 73 24 for the striped hills but anticlockwise rotations of 30 35 and 87 29 respectively for the northern and southern grapevine mountains such large rotations of opposite sense may be related to north south shortening accommodated by conjugate strike slip faults during large magnitude extension in the death valley region but are difficult to explain as products of regional dextral shear within the southern walker lane belt

reply to discussion by sadegh mohseni and alijan aftabi of significance of apatite ree depletion and monazite inclusions in the brecciated se chahun iron oxide apatite deposit bafq district iran insights from paragenesis and geochemistry by bonyadi z davidson g j mehrabi b meffre s ghazban f chemical geology 281 2011 253 269

precambrian cambrian transition death valley united states the death valley region contains one of the best exposed and often visited precambrian cambrian successions in the world but the chronostratigraphic framework necessary for understanding the critical biologic and geologic events recorded in these sections has been inadequate the recent discovery of treptichnus phycodes pedum within the uppermost parasequence of the lower member of the wood canyon formation allows correlation of the precambrian cambrian boundary to this region and provides a necessary global tie point for the death valley section new carbon isotope chemostratigraphic profiles bracket this biostratigraphic datum and record the classic negative carbon isotope excursion at the boundary for the first time biostratigraphic chemostratigraphic and lithostratigraphic information from pretrilobite strata in this region can be directly compared with similar data from other key sections that record the precursors of the cambrian explosion few precambrian cambrian boundary sections contain both the facies restricted boundary fossil t pedum and carbon isotope data as found in death valley thus the death valley succession provides a critical link toward our understanding of the correlation between siliciclastic dominated and carbonate dominated precambrian cambrian transition sections