petrofacies of eocene sand injectites of the tumey giant injection complex california usa abstract the forearc succession of great valley group in central california provides some of the best examples of giant sand injection complexes in the world and is therefore considered valuable analogues for injectite systems in the subsurface several sand injection complexes are well described in the outcrop and subsurface however the petrographic characteristics of injectites are still poorly documented in this paper we present the results of an integrated study of field observations quantitative and qualitative sandstone petrography provenance and petrofacies analysis of the tumey giant injection complex tgic in order to understand its lithostratigraphy and petrological evolution and its impacts on reservoir petrofacies characteristics and fluid migration the tgic intrudes into a 450 m thick deep water succession of slope mudrocks and sandy channel fills of the kreyenhagen shale eocene forming an interconnected network of sandstone sills dykes and injection breccias the complex generated a horizontal and vertical plumbing system for fluid migration connecting isolated sandy channel fills among low permeability mudrocks the primary detrital composition diagenetic products microtextures and provenance signatures allowed for the definition and discrimination of depositional and intrusive petrofacies and their genetic relations petrofacies associations confirm that the gypsum cemented feldspathic litharenites from the kreyenhagen shale channel fills are the only source for the injection complex eodiagenetic compaction and extensive gypsum cementation reduced the primary porosity of the complex while telodiagenetic dissolution of autigenic constituents formed pervasive secondary porosity the underlying calcite cemented arkosic sandstones of the lodo and domengine formations acted as barriers for fluid flow aiding lateral fluid migration and overpressure buildup within the overlying kreyenhagen channel fills intense grain microfracturing occurred during sand remobilization and injection along with erosion of the host mudrocks this study has significance for the generation of reliable stratigraphic and petrological models for sand injection complex genesis and evolution that consequently can help the understanding and exploration of injectite complexes elsewhere

history and controls of subsidence in the late cretaceous tertiary great valley forearc basin california abstract analysis of the upper cretaceous tertiary fill of the great valley forearc basin of california reveals a complicated history of subsidence partitioned in time and space western oceanward parts of the basin record subsidence then uplift in apparent response to the angle and rate of descent of the underlying subducting plate specifically uplift in the forearc basin corresponds to the onset of the laramide orogeny and inferred low angles of subduction in contrast eastern arcward parts of the basin display subsidence histories suggestive of thermal contraction and compatible with continentward migration of sierran arc magmatism in the late cretaceous these results imply that subsidence histories of forearc basins are likely to be much more complicated and less predictable than those of rifted continental margins and foreland basins where single subsidence mechanisms predominate and time varying subduction is not an underlying controlling factor

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

sterane isomerisation and moretane hopane ratios in crude oils derived from tertiary source rocks the extent of sterane isomerisation reactions and the moretane hopane ratios of 234 crude oils taken world wide from a wide variety of source rocks of differing geological ages have been measured this data indicates that in 78 crude oils derived from tertiary source rocks sterane isomerisation reactions as determined by the 20s 20s 20r ration of the c29 5 h 14 h 17 h normal steranes and the c29 iso iso normal ratio iso 5 h 14 h 17 h are mainly incomplete and sometimes considerably so in addition the same crude oils have 17 h 21 h moretane 17 h 21 h hopane ratios which are significantly greater predominantly in the range 0 10 0 30 than those of crude oils derived from older mature source rocks mainly less than 0 1 this data for crude oils lends support to the hypothesis proposed by mackenzie and mckenzie 1983 for source rock extracts that the time temperature constraints of sterane isomerisation reactions are such that the time available for isomerisation in tertiary sediments is generally insufficient despite generation of crude oil at relatively high temperatures an alternative hypothesis is that the incomplete sterane isomerisation of tertiary crude oils may be due to generation of these crude oils from their deltaic land plant containing source rocks under low heating conditions a third hypothesis proposes that the tertiary crude oils may have picked up the incompletely isomerised steranes from immature sediments during migration although possible in particular instances such a mechanism does not appear to be generally applicable since in that case the phenomenon would then appear to be restricted to the tertiary the higher moretane hopane ratios of the tertiary crude oils could suggest that constraints similar to those applying in sterane isomerisation also operate in the conversion of moretane to 17 h hopane

new estimates of displacement along the san andreas fault in central california based on paleobathymetry and paleogeography studies of depth related benthic foraminiferal biofacies permit the construction of paleobathymetric maps of the la honda and san joaquin basins of central california these maps support the hypothesis that the la honda and san joaquin basins were contiguous during the late oligocene and early miocene and subsequently were separated by about 320 330 km of right lateral displacement on the san andreas fault furthermore these estimates of displacement support the notion that right lateral slip occurred along the san andreas fault during the early miocene

the structural geometry and evolution of foreland thrust systems northern virginia seismic reflection data reveal that the structural geometry of the central appalachians of northern virginia consists of three distinct thrust systems each thrust system is characterized by a unique internal geometry the blue ridge thrust sheet is a composite thrust sheet composed primarily of imbricated precambrian crystalline rocks it over rode cambrian ordovician carbonates and formed a sheared basement cored fault bend fold thrusts within the sheet may be taconic and earliest alleghanian whereas final thrusting and emplacement of the sheet were probably slightly younger but still early alleghanian the north mountain thrust sheet is characterized by imbricated cambrian ordovician carbonates that are deformed into large amplitude mode ii fault bend folds and fault propagation folds rocks of this sheet were transported more than 60 km across a similar section of carbonates the leading edge of the north mountain thrust sheet was deformed into a fold with a mode ii fault bend fold geometry and was juxtaposed against middle paleozoic rocks the middle paleozoic rocks occur in a ramp across which displacement along the north mountain thrust was transferred to a higher detachment more than 60 km of cover rocks displaced during the emplacement of the north mountain thrust sheet either were transported across this ramp and thrust over a similar section in the western valley and ridge province or were backthrust above the sheet the timing for imbrication and emplacement of the north mountain thrust sheet is probably main phase alleghanian the lower carbonate duplex extends from beneath the blue ridge and north mountain thrust sheets westward across the western valley and ridge province the lower carbonate duplex is characterized by imbricated cambrian ordovician carbonates that form low amplitude fault bend folds this thrust system also probably formed during main phase alleghanian deformation

hydrocarbon sources and charge history in the southern slope region kuqa foreland basin northwestern china abstract numerous oil and condensate gas reservoirs have recently been discovered in the southern slope region of the kuqa foreland basin in the northern tarim basin northwestern china however their hydrocarbon sources and charge history are still unclear in this study oil source correlation was firstly used to ascertain the sources of oils in different tectonic belts the hydrocarbon charge history was then investigated using an integrated fluid inclusion analysis and basin modelling approach on the basis of a variety of oil source correlation geochemical parameters two distinct oil groups were delineated in this region group i including oils in the yaha and yingmai 7 tectonic belts while group ii comprising oils from the yangtake hongqi and yudong 2 tectonic belts and the ym 21 well oil source correlations show that group i oil is sourced from the upper triassic huangshanjie formation t 3 h while group ii oil is mainly sourced from the lower part of the middle jurassic qiakemake formation j 2 q both source rocks are located in the middle and northern parts of the kuqa foreland basin basin modelling shows that the t 3 h source rock began to generate early mature to mature oil at 34 ma and continued until around 3 ma the j 2 q source rock began to generate early mature to mature oil between after 34 ma and continued to 12 ma mainly in the central part of the j 2 q source rock oil migration modelling indicates that the t 3 h sourced oils did not accumulate in the southern slope region until 12 5 ma whereas the j 2 q sourced oils began to charge into the southern slope region around 5 3 ma coupled with fluid inclusion analysis the modelling shows that oils originated from the t 3 h source rock began to charge into the yaha tectonic belt as early as 6 ma and subsequently to the yingmai 7 tectonic belt which received its initial charge around 4 8 ma oils sourced from the lower j 2 q source rock began to charge into the yangtake tectonic belt around 4 ma and then into the yudong 2 tectonic belt around 3 7 ma oils first charged into the hongqi and ym 21 areas after 4 ma oils from the t 3 h and the lower j 2 q source rocks continued to charge into the southern slope region until 3 ma

thermal cracking of kerogen in open and closed systems determination of kinetic parameters and stoichiometric coefficients for oil and gas generation abstract the purpose of the study is to compare artificial maturation of kerogens representative of the main types of organic matter kerogen types i ii ii s and iii in open and anhydrous closed pyrolysis systems the generated compounds are fractionated according to their thermal stability into six chemical classes c 1 c 2 c 5 c 6 c 14 c 15 saturates c 15 aromatics and nsos which include resins and asphaltenes in both systems primary cracking of kerogen can be described by two main reactions oil generation together with early gas generation followed by late gas production mass balances obtained in the two pyrolysis systems are reasonably similar although some secondary cracking of the nsos and underestimation of methane potential due to incomplete pyrolysis may occur in the open system kinetic parameters of thermal cracking are derived from experiments in the open system using an optimization procedure which determines a unique frequency factor and a weight distribution of chemical classes for a discrete series of activation energies the resultant frequency factors are checked with those obtained for specific molecular tracers such as n c 12 and n c 24 alkanes generated from kerogens in open and closed systems under isothermal conditions the results show that using a unique frequency factor as determined by optimization is correct for type i ii and ii s kerogens this factor is more questionable however when the distribution of activation energies is very broad such as for type iii coals based on this study a strategy for determination of kinetic parameters on any new source rock sample is proposed

shallow drilling in the salton sea region the thermal anomaly during two shallow thermal drilling programs thermal measurements were obtained in 56 shallow 76 2 m and one intermediate 457 3 m depth holes located both onshore and offshore along the southern margin of the salton sea in the imperial valley california these data complete the surficial coverage of the thermal anomaly revealing the shape and lateral extent of the hydrothermal system the thermal data show the region of high thermal gradients to extend only a short distance offshore to the north of the quaternary volcanic domes which are exposed along the southern shore of the salton sea the central thermal anomaly has an arcuate shape about 4 km wide and 12 km long across the center of the anomaly the transition zone between locations exhibiting high thermal gradients and those exhibiting regional thermal gradients is quite narrow thermal gradients rise from near regional 0 09 c m to extreme 0 83 c m in only 2 4 km the heat flow in the central part of the anomaly is greater than 600 mw m2 and in the two local anomalies exceeds 1200 mw m2 the shape of the thermal anomaly is asymmetric with respect to the line of volcanoes previously thought to represent the center of the field with its center line offset south of the volcanic buttes there is no broad thermal anomaly associated with the magnetic high that extends offshore to the northeast from the volcanic domes the salton sea thermal anomaly can be described as three nested thermal features superimposed on the regional salton trough heat flux a broad region of elevated conductive heat flow with constant temperature gradients of about 0 1 c m a central anomaly of high 0 4 c m near surface gradients observed through a conductive thermal cap underlain by a nearly isothermal zone of hydrothermal circulation and two local anomalies with shallow temperature gradients as high as 0 8 c m superimposed on the central geothermal system these observations of the thermal anomaly provide important constraints for models of the circulation of the hydrothermal system thermal budgets based on a simple model for this hydrothermal system indicate that the heat influx rate for local hot spots in the region may be large enough to account for the rate of heat flux from the entire salton trough

origin of granulite terranes and the formation of the lowermost continental crust differences in composition and pressures of equilibration between exposed regional granulite terranes and suites of granulite xenoliths of crustal origin indicate that granulite terranes do not represent exhumed lowermost crust as had been thought but rather middle and lower middle crustal levels application of well calibrated barometers indicate that exposed granulites record equilibration pressures of 0 6 to 0 8 gigapascal 20 to 30 kilometers depth of burial whereas granulite xenoliths which also tend to be more mafic record pressures of at least 1 0 to 1 5 gigapascals 35 to 50 kilometers depth of burial thickening of the crust by the crystallization of mafic magmas at the crust mantle boundary may account for both the formation of regional granulite terranes at shallower depths and the formation of deep seated mafic crust represented by many xenolith suites

plate tectonics and island arcs the plate tectonic concepts that developed rapidly in the late l960s made possible the understanding of island arcs before that time mobilistic concepts evolved slowly hindered particularly in the united states by an obstructionist geoscience establishment the volcanic belts of island arcs form about 100 km above subducting plates convergent plate boundaries evolve complexly with time and at any one time vary greatly along their lengths seismicity defines positions but not trajectories of descending slabs which sink more steeply than they dip and are overridden by advancing upper plates subduction occurs beneath only one side at a time of an internally rigid plate and the common regime in an overriding plate behind a surficial accretionary wedge is extensional except where a collision is underway back arc basin lithosphere is built behind or by migrating island arcs which lengthen and increase their curvatures a collision can involve two active arcs in which case intervening lithosphere sinks beneath both of them or an active margin and a passive one either type of collision generally is followed by the breaking through of new subduction beneath the composite mass of light crust from a new trench on the outside of the aggregate conversely a new subduction system commonly is a by product of collision a strip of back arc basin crust is in many cases left attached to the aggregate in front of the new trench and becomes the basement for a fore arc basin the leading edge of which is raised as melange is stuffed under it sedimentation in trenches is predominantly longitudinal and can be from distant sources accretionary wedges are dynamic being thickened at both toes and bottoms by tectonic accretion and thinned by gravitational forward flow melange is largely a product of tectonic imbrication and flowage driven by these conflicting processes not of submarine sliding high pressure metamorphic rocks form beneath overriding plates not within wedges in front of them arc magmas incorporate much material from the lithosphere through which they rise and vary correspondingly with the evolving composition of that lithosphere arc crust is inflated into geanticlines by intrusive rocks and thermal expansion submarine island arc volcanic rocks are widely spilitized with na enrichment and ca depletion by hydrothermal reaction with sea water the lower crust of mature island arcs consists of granulite facies rocks of mafic intermediate and felsic intermediate compositions the mohorovicic discontinuity may be primarily a constructional boundary representing the shallow limit off crystallization of voluminous rocks of ultramafic composition or plagioclase free mineralogy

partial melting of apatite bearing charnockite granulite and diorite melt compositions restite mineralogy and petrologic implications melting experiments p 6 9 kbar t 850 950 c nno 02 hm were done on mafic to felsic charnockites a dioritic gneiss and a felsic garnet granulite all common rock types in the grenville basement of eastern north america a graphite bearing granulite gneiss did not melt water h2o 0 60 to 2 0 wt is bound in low grade retrograde metamorphic minerals and is consumed during the earliest stages of melting most melts are water undersaturated melt compositions range from metaluminous silicic granodiorite diorite starting composition to peraluminous or weakly metaluminous granites all others in general liquids become more feldspathic less silicic and less peraluminous and are enriched in feo mgo and tio2 with increasing temperature residual feldspar mineralogy controls the cao k2o and na2o contents of the partial melts and the behavior of these elements can be used particularly if the degree of source melting can be ascertained to infer some aspects of the feldspar mineralogy of the source k feldspar a common restite phase in the charnockite and granulite but not the diorite should control the behavior of ba and possibly eu in these systems and yield signatures of these elements that can distinguish source regions and in some cases bulk versus melt assimilation apatite a common restite phase is enriched in rare earth elements ree especially middle ree retention of apatite in the restite will result in steep light ree enriched patterns for melts derived from the diorite and charnockites

three deep resource plays in the san joaquin valley compared with the bakken formation a continuous oil accumulation is one that is pervasive throughout a large area and is not affected by natural hydrodynamic influences three source rocks in the san joaquin valley of california are actively producing hydrocarbons and represent potential continuous oil accumulations the monterey kreyenhagen and moreno formations the energy information administration announced in 2014 that there are potentially 15 billion bbl of recoverable oil in the monterey formation in california spiking huge interest such a resource would make the monterey by far the largest continuous oil accumulation in north america this number has since been reduced dramatically to 600 million bbl of oil for the state and 21 million bbl of oil within the san joaquin valley in this study the subsurface character of the bakken formation of north dakota is compared with the three source rocks in the san joaquin valley at oil window depths to characterize these reservoirs hundreds of well logs core descriptions and mud logs were studied a technique to rank character of oil show data was developed in which interesting possibly interesting or not interesting wells were located on thermal maturity maps interesting wells have significant oil shows whereas not interesting wells have minor or no shows in the bakken formation the character of the oil show correlates with well productivity applying this same classification to the san joaquin valley source rocks leads to a more disappointing conclusion although there are oil shows in the source rocks of the san joaquin valley at oil window depths suggesting the presence of a continuous oil accumulation the distribution of shows is both laterally and vertically heterogeneous and not predictable moreover recent attempts to produce from source rocks at these depths have not been economically successful we conclude that the three source rocks in the san joaquin valley represent heterogeneous and discontinuous oil accumulations at oil window depths in the subsurface likely there are billions of barrels of oil in these discontinuous oil accumulations source rocks in the bakken are rated as world class source rocks in the san joaquin valley are good to excellent quality however the quality of the oil shows in the san joaquin valley appears poorer than the bakken formation it is possible that effective drainage between the source rocks and the up dip reservoirs has left large volumes of the source rocks at oil window depths with only residual oil saturation complex structural and stratigraphic architecture heterogeneity and continuity create issues of predictability for optimal areas to target rapid rates of subsidence over the past few million years and accompanying thrusting and folding resulted in a complex subsurface pressure regime the lack of clear hydraulic fracture targets analogous to the middle bakken further complicates drilling decisions and likely deliverability in addition the oil windows in the san joaquin valley are significantly deeper than the bakken formation which would result in substantially higher well cost recent drilling results support this study and suggest that heterogeneous and discontinuous oil accumulations in the san joaquin are unlikely to become economic without dramatic changes in technology

organic geochemical characterisation of depositional palaeoenvironments of source rocks and oils in brazilian marginal basins abstract an investigation of bulk isotopic and molecular features of a wide selection of source rocks and oils from brazilian marginal basins ranging from lower cretaceous to tertiary in age provides a number of organic geochemical criteria that characterise and distinguish their depositional palaeo environments the methods employed include evaluation of organic carbon contents rock eval pyrolysis vitrinite reflectance measurements determination of carbon isotope ratios elemental and visual kerogen analysis assessment of oils and solvent extracts by liquid and gas chromatography and quantitative biological marker investigations using gc ms for aliphatic hydrocarbons and uv vis spectrophotometry for metalloporphyrins selected data were evaluated using principal component analysis the results enable the recognition and differentiation of seven depositional regimes lacustrine freshwater lacustrine saline water marine evaporitic marine carbonate marine deltaic marine highly anoxic with a predominance of calcareous mudstone lithology and marine anoxic with predominance of siliciclastic lithology diagnostic features in the biological markers from these depositional environments include the carbon number distributions of n alkanes pristane phytane ratios absolute concentrations of carotane higher acyclic isoprenoids c 30 hopane and steranes and the abundance of the latter relative to 4 methylsteranes the occurrence and abundance of particular biological markers such as gammacerane tricyclic and tetracyclic terpanes 18 h oleanane 28 30 bisnorhopane and 25 28 30 trisnorhopane and the relative abundances of nickel and vanadyl porphyrins

integrating strike slip tectonism with three dimensional basin and petroleum system analysis of the salinas basin california the salinas basin is a strike slip basin in central california with stratigraphy dominantly composed of miocene monterey formation despite a long history of oil production aspects of petroleum system development in the basin remain poorly understood of the seven main oil fields one san ardo field has produced more than 500 million bbl of oil or 99 of all oil found in the basin the evolution of this basin was profoundly influenced by strike slip movement on the rinconada fault which bisected the depocenter beginning circa 15 ma to address the influence of strike slip motion on petroleum system development we constructed a three dimensional 3 d basin and petroleum system model that incorporates strike slip displacement seismic reflection profiles from a 3 d survey reveal four main tectonic stages that correspond to events in petroleum system evolution petroleum generation from type ii kerogen source rock began circa 11 ma approximately 4 m y after strike slip faulting began to offset a once contiguous sedimentary depocenter two separate petroleum provinces an eastern one and a western one developed and the fault zone likely was a conduit for petroleum if nonsealing most accumulated petroleum was derived from the eastern pod of active source rock because of greater sedimentary burial east of the fault our model roughly replicates the skewed distribution in oil field size factors controlling field size distribution include trap size and connectivity to source

tectonic depositional and diagenetic history of monterey formation miocene central san joaquin basin california the miocene monterey formation in the central san joaquin basin of california consists of biogenic siliceous rocks with a significant terrigenous clastic component correlation of electric logs in conjunction with analysis of outcrop sections core samples and paleontologic data suggests that deposition of the monterey was controlled by an interplay of basin geometry san andreas related tectonics fluctuations in sea level and changes in climate the basin is bounded on the east by the sierran magmatic arc complex and on the west by the san andreas fault during the late saucesian through early mohnian 20 10 ma the basin was reshaped by tectonism related to the migrating mendocino triple junction creating a broad gently sloping shelf to the east that cut off the supply of clastics to the central basin with the subsequent evolution of the san andreas fault the salinian block was emplaced along the western basin margin restricting the seaway and permitting low oxygen nutrient rich waters to occupy the basin as a result laminated organic rich fine grained pelagic to hemipelagic sediments of the monterey formation were deposited a warmer climate during saucesian through luisian time with less intensive upwelling le to more calcareous less siliceous sedimentation a cooling trend during late miocene time 10 5 ma increased upwelling activity diatom productivity in the water column and deposition of diatomaceous debris although turbidites accumulated on the basin floor and terrigenous clastics were deposited on the eastern shelf relatively undiluted diatomaceous deposits developed on outer shelves and slopes atop anticlinal banks generated by wrench tectonism and in some areas of the basin floor a mid mohnian eustatic sea level rise caused fine grained deposition to extend onto the eastern shelf slightly later a mid late mohnian period of exceptionally cool temperatures resulted in the most extensive development of upwelling related siliceous sediments throughout the basin with diagenesis these deposits formed the siliceous shales and porcelanites of the monterey formation high sedimentation rates coincident with a eustatic drop in sea level led to clastic progradation in latest miocene time as the basin filled analysis of organic matter from cores of the monterey formation shows that kerogen type reflects overall sedimentation trends samples from northern and eastern areas contain abundant terrestrial organic matter whereas samples from western areas mostly contain marine kerogens source potential is thus strongly influenced by geographic locality as well as lithology maturity of kerogen was assessed using vitrinite reflectance thermal alteration indices and pyrolysis techniques the latter two appear to be the more reliable indicators of organic matter maturity in the monterey formation of the san joaquin valley although much of the monterey formation in the study area may be thermally immature portions are probably generating hydrocarbons today in deep synclinal areas

3 d numerical modelling of methane hydrate accumulations using petromod highlights petromod is the 1st basin modelling software including methane hydrate simulation the gas hydrate module includes physical thermodynamic and kinetic properties petromod simulates the evolution over time of the ghsz petromod includes a kinetic for the organic matter degradation at low temperature abstract within the german gas hydrate initiative sugar a new 2 d 3 d module simulating the biogenic generation of methane from organic matter and the formation of gas hydrates has been developed and included in the petroleum systems modelling software package petromod typically petromod simulates the thermogenic generation of multiple hydrocarbon components oil and gas their migration through geological strata finally predicting oil and gas accumulations in suitable reservoir formations we have extended petromod to simulate gas hydrate accumulations in marine and permafrost environments by the implementation of algorithms describing 1 the physical thermodynamic and kinetic properties of gas hydrates and 2 a kinetic continuum model for the microbially mediated low temperature degradation of particulate organic carbon in sediments additionally the temporal and spatial resolutions of petromod were increased in order to simulate processes on time scales of hundreds of years and within decimetres of spatial extension in order to validate the abilities of the new hydrate module we present here results of a theoretical layer cake model the simulation runs predict the spatial distribution and evolution in time of the gas hydrate stability field the generation and migration of thermogenic and biogenic methane gas and its accumulation as gas hydrates

chemical diversity and origin of precambrian charnockitic rocks of the central pedlar massif grenvillian blue ridge terrane virginia abstract middle proterozoic rocks of the pedlar massif are comprised of varied charnockitic and granulitic lithologies representing 1150 1000 ma grenvillian metamorphic and igneous events in the central appalachians of virginia chemically and mineralogically diverse units include metaluminous to peraluminous charnockites enderbites jotunites and granulite gneisses ranging in sio2 from 47 to 79 wt relative to bulk continental crust typical charnockites are enriched by 3 6 in rb k ba lree zr and hf less enriched in ta sr p and hree and depleted in cs th ti and sc although low sio2 members have relatively high ti and p and some high sio2 units are depleted in k rb and ba the pedlar river charnockite suite prcs vesuvius megacrystic charnockite vmc nellysford granulite gneiss ngg and the lady slipper granulite gneiss lsgg exhibit common chemical signatures and trends notably evident in uniform lree enriched patterns with variable eu anomalies which reflect their derivation from a mixed protolith of volcanics and reworked volcaniclastic sediments dated at 1130 1150 ma pedlar river charnockites represent portions of deep seated granulite gneisses that were mobilized by granulite facies dehydration melting and emplaced en masse as plutons into overlying and surrounding gneisses during the grenville episode divergent ree patterns in the prcs are attributed to crystallization of quartz feldspar garnet or hree compatible mafic and accessory phases leading to complementary chemical signatures in mafic and felsic layers depletion of cs throughout the pedlar massif is attributed to its incompatibility with major mineral phases during either protolith evolution or granulite facies dehydration while dispersions in k rb sr ba and eu are due to the relative proportions of the major phases quartz k feldspar plagioclase and biotite mobility of insoluble trace elements zr hf ta and th require partial melting and crystallization of accessory mineral phases whereas sc cr and ree mobility depends on the proportions of pyroxene and garnet several leucocharnockites and other felsic rocks of the prcs show markedly elevated th values ranging from 10 to 83 ppm which complement depleted th in typical prcs units these charnockitic rocks represent low degree partial melts 1 5 from normal prcs or ngg protoliths to produce high silica magmas which separated from the main charnockitic body

laboratory measurements on turbulent pressure fluctuations in and above gravel beds the statistics of pressure fluctuations above and within three types of porous granular beds such as in gravel bed streams rivers and man made canals are investigated by data gained via laboratory flume experiments the flow conditions examined include a diversity of hydrodynamic loads that increase up to the point where single grains are moving from time to time without causing severe modification to the bed texture and the related positions of the pressure sensors analysis is performed by means of histograms and spectral techniques and vertical intensity profiles two simplified equations are found that describe the vertical decrease for the standard deviation of the measured fluctuations indicating drag and lift respectively nondimensionalized by the mean bed shear stress the former fluctuation is described by a crude linear fit whereas the latter clearly shows that the lift intensity decreases exponentially in the porous bed with a decay distance of one to two times the equivalent grain roughness within the subsurface layer the standard deviation reaches a nonzero constant mainly dominated by long wave pressure fields that are convected in the outer flow these findings can be used in future sediment transport models that use force balance approaches to determine incipient motion conditions

alleghanian episode of k bentonite illitization in the southern appalachian basin mixed layer illite smectite i s from middle ordovician potassium k bentonites was found to be uniformly illitic throughout the southern appalachian basin regardless of variable depths of burial of the k bentonites the k ar ages of illitization are narrowly confined between 272 and 303 ma late pennsylvanian to early permian this suggests that illitization was a short lived episode coincident with and prompted by the alleghanian orogeny the illitization is explainable by the fluid expulsion hypothesis recently proposed by others e g oliver hot saline fluids were flushed to the basin edges from the deeply buried part of the foreland basin during the orogeny these fluids are thought to be effective agents of illitization some of our k bentonite samples are stratigraphically and geographically close to mississippi valley type lead zinc deposits suggesting a similar mode of origin rapid illitization of shales in a fashion similar to that observed for the bentonites should have led to high pore water pressures that enabled them to act as ideal decollements during alleghanian thin skinned deformation

a basin modeling and organic geochemistry study in the vallecitos syncline san joaquin basin california abstract the vallecitos syncline is a westerly structural extension of the san joaquin basin the vallecitos oil field comprised of eight separate areas that produce from cretaceous and paleogene reservoirs accounted for 5 4 mmb of oil and 5 6 bcf associated of gas through 2010 however exploration for oil and gas in the vallecitos area is challenging due to structural complexity and limited data the purpose of this study is to evaluate whether source rocks are actively generating petroleum in the vallecitos syncline and to improve our understanding of burial history and timing of hydrocarbon generation we conducted biomarker analysis on twenty two oil samples from the vallecitos syncline source related biomarkers show two genetic groups of oil which originated from two different source rocks these results differ from earlier published interpretations in which the kreyenhagen formation is the only source rock in the vallecitos syncline and suggest that the cretaceous moreno formation in the syncline also is an active source rock stratigraphic evidence and modeling suggest that late cenozoic episodes of erosion due to folding and uplift removed significant overburden on the flanks of the syncline to better understand the petroleum systems and clarify the total active source rocks in the area 2d burial histories were generated through the vallecitos syncline a published cross section through the deepest part of the syncline was selected to conduct thermal history basin evolution and migration analyses the 2d model results indicate that the lower kreyenhagen formation has various maturities within the formation at different locations in the present day syncline the basal part of the kreyenhagen formation is in the dry gas window and maturity decreases away from the central part to the flanks it remains immature along shallow portions of the present day flanks in contrast the basal part of the moreno formation achieved extremely high maturity past the gas generation zone but is in the oil generation zone on the flanks of the syncline at shallow depth all of our geochemical and 2d model results suggest that there are two active source rocks in the vallecitos syncline accordingly we propose that there are two active petroleum systems in the vallecitos syncline

distributed shear rotation and partitioned strain along the san andreas fault central california folds commonly form along transform fault systems in the san andreas strike slip fault two mechanisms of folding have been described that are regarded as incompatible 1 wrench tectonics or distributed shear and 2 strain partitioning shortening being perpendicular to the fault the compatibility and relative importance of these two mechanisms are not well understood in part because folds are the result of lengthy deformation this paper synthesizes paleomagnetic data sedimentary thickness maps fault patterns and seismic reflection profiling data along the san andreas transform fault system that indicate a 20 30 clockwise map view reorientation of pliocene en echelon folds to their present position subparallel to the san andreas fault the folds continue to develop today as a result of shortening perpendicular to the fault folds apparently rotated with continuing strain in the wrench zone and with increasing shortening across the shear zone rotation likely occurred when changing pacific plate motions increased the component of convergence across the fault system this field example documents deformation by these two different mechanisms in the same fold belt which has broad implications for interpreting other fold belts formed in similar settings the geologic record suggests that the opposing theories of wrench deformation and strain partitioned shortening perpendicular to the fault are both important and compatible processes that act at different times and places

oil families and mixed oil of the north central west siberian basin russia the recognition correlation and quantification of oil mixtures remain challenging in petroleum system studies most prolific basins have multiple source rocks that generate petroleum over wide ranges of maturity compound specific isotopic analyses of alkanes csia a and diamondoids csia d are very effective for determining hydrocarbon mixtures quantitative diamondoid analysis qda and csia d provide a unique advantage for source correlation of thermally altered liquids or condensates and for condensate mixtures with black oil biomarker fingerprints qda and various csia methods were applied to 37 oil and condensate samples to investigate the existence of deep sources and to identify and deconvolute cosourced oil mixtures the data were used to unravel the components of mixed oil having widely diverse levels of maturity in the north central west siberian basin three oil families and their locations are recognized in the basin one of the families appears to be composed of oil mixtures derived from two end member families that originated from the upper jurassic bazhenov and lower to middle jurassic tyumen source rocks our results suggest that a significant part of the gas in the giant gas fields of north central western siberia e g urengoi and yamburg is of thermogenic origin the source of this thermal gas which was formerly assigned to various source origins was determined to be the tyumen formation some samples in the basin also show mixtures of noncracked bazhenov oil with cracked tyumen condensate the area where prevalent oil cracking has occurred was determined from qda