active strike slip faulting in el salvador central america several major earthquakes have affected el salvador central america during the past 100 yr as a consequence of oblique subduction of the cocos plate under the caribbean plate which is partitioned between trench orthogonal compression and strike slip deformation parallel to the volcanic arc focal mechanisms and the distribution of the most destructive earthquakes together with geomorphologic evidence suggest that this transcurrent component of motion may be accommodated by a major strike slip fault el salvador fault zone we present field geological structural and geomorphological data collected in central el salvador that allow the constraint of the kinematics and the quaternary activity of this major seismogenic strike slip fault system data suggest that the el salvador fault zone consists of at least two main e w fault segments san vicente and berlin segments with associated secondary synthetic wnw ese and antithetic nnw sse riedel shears and nw se tensional structures the two main fault segments overlap in a dextral en echelon style with the formation of an intervening pull apart basin our original geological and geomorphologic data suggest a late pleistocene holocene slip rate of 11 mm yr along the berlin segment in contrast with low historical seismicity the kinematics and rates of deformation suggested by our new data are consistent with models involving slip partitioning during oblique subduction and support the notion that a trench parallel component of motion between the caribbean and cocos plates is concentrated along e w dextral strike slip faults parallel to the volcanic arc

a newly recognized type of slickenside striation abstract this note summarizes current views on the origin of slickenside striations and points to the existence of a type of striation not readily explained by established genetic ideas such striations have been seen on fault surfaces in naturally deformed shale and in experimentally deformed paraffin wax they are defined by arrays of shallow slip parallel ridges and grooves of millimetric width and below on any given slip surface the ridges are as common as the grooves and display similar dimensions and profile shapes across any pair of slip surfaces in contact at the end of faulting ridges protruding from one surface fit into or nest with grooves on the other surface the origin of these features is not yet understood

organic geochemical characteristics and generating potential of source rocks from the lower middle jurassic coal bearing strata in the east junggar basin nw china abstract the junggar basin located in nw china is a large intracontinental superimposed basin samples were collected from the lower middle jurassic coal bearing strata of the eastern junggar basin and include mudstones carbargilites and coal the origin of organic matter thermal maturity paleoenvironment of sediment deposition and hydrocarbon potential of drill core samples was investigated organic geochemical analysis performed on 65 source rock samples indicates a wide range of toc values from 0 81 wt to 81 06 wt this study combined sedimentology biomarker organic petrography and stable carbon isotopic composition of kerogen and extracts analysis demonstrating the organic matter of the source rocks is derived from terrestrial higher plants with a minor contribution of aquatic algae and microbes rock eval data elemental composition of kerogen and odd over even normal alkane distribution reveal immaturity to low maturity with a humic type organic matter the source rocks were deposited in a freshwater oxic to sub oxic environment indicated by high pr ph ratios a predominance of c29 steranes low tricyclic terpanes and a low gammacerane index high dia regular c29 sterane ratios and moderate to high c29 c30 hopane ratios found in most samples are related to the presence of clay minerals based on the following parameters h c vs o c toc s1 s2 hydrogen index saturated hydrocarbons aromatic hydrocarbons and chloroform a we concluded that the samples collected from organic rich coal bearing strata may yield not only gas but also have the capability to generate and release liquid hydrocarbons

a new model for the emplacement of columbia river basalts as large inflated pahoehoe lava flow fields extensive flows of the columbia river basalt crb group in washington oregon and idaho are dominantly inflated compound pahoehoe sheet lavas early studies recognized that crb lavas are compound pahoehoe flows with textures suggesting low flow velocities but it was thought that the great thickness and extent of the major flows required very rapid emplacement as turbulent floods of lava over a period of days or weeks however small volume 1 km compound pahoehoe flows on kilauea hawai i demonstrate that such flows can thicken by at least an order of magnitude through gradual inflation and the same mechanism has been proposed for larger 10 20 km3 pahoehoe flows in iceland the vertical distribution of vesicles and other morphologic features within crb lava flows indicate that they grew similarly by inflation small pahoehoe lobes at the base and top of many crb pahoehoe lava flows indicate emplacement in a gradual piecemeal manner rather than as a single flood we propose that each thick crb sheet flow was active for months to years and that each group of flows produced by a single eruption a flow field was emplaced slowly over many years

biomarkers as proxies for plant inputs to peats an example from a sub boreal ombrotrophic bog lipid distributions in modern peat forming plants were determined and compared to biomarkers recovered from a ca 2800 year old peat deposited in a dutch ombrotrophic bog the peat section spans a well constrained shift in local hydrology and vegetation and potential molecular proxies for plant inputs were directly tested against the macrofossil record based on the analyses of modern plants low molecular weight lmw n alkanes c23 c25 and high molecular weight n alkanes c33 are proposed as potential biomarkers for sphagnum and non sphagnum inputs respectively consistent with this in the bargerveen peat core lmw n alkane abundances increase and hmw n alkane abundances decrease coincident with the shift to sphagnum dominated peat additional potential proxies include the abundances of c22 alkanedioic acid and phytenyl phytenoate as sphagnum indicators and the abundances of the triterpenoids taraxer 14 ene and taraxast 20 ene as biomarkers for ericaceae rootlets

seismic vp and vp vs structure of the geothermal area around tarutung north sumatra indonesia derived from local earthquake tomography abstract a passive seismic experiment with 42 short period stations was setup for 10 months from may 2011 within a 20 30 km radius covering the tarutung basin and the northern part of the sarulla graben along the seismically active sumatran fault north sumatra indonesia the objective of the project is to investigate the geothermal setting based on the vp and vp vs structures and the distribution of seismicity we recorded 2856 local earthquakes by at least 8 stations which were reduced to 809 events having gap angle less than 180 the initial earthquake locations were determined using simultaneous inversion for hypocenters and 1d velocity structure followed by 3d tomographic inversion the resulting seismicity distribution vp and vp vs structure reveal systematic differences between the tarutung basin and the sarulla graben the tarutung pull apart basin is characterized by a complex structure reflected by a broader distribution of seismicity compared with the very narrow rather vertical hypocenter distribution in the sarulla graben which was formed by fault perpendicular extension and not by pull apart tectonics high vp vs values near to the surface are imaged within the sarulla graben and northeast of the tarutung basin these features are interpreted as fluid bearing sediments with fracturing indicating potentially favorable conditions for geothermal exploitation the localized fluid flow northeast of tarutung could be explained by the releasing step over structure of the pull apart basin and resulting dilatational stress regime in this part of the basin heat sources are assumed to be located at greater depth in association with magmatic activities accompanying the subduction process and the heat is transported along the sumatran fault to shallow depth

pahoehoe transport as a correlated random walk 1 transport and emplacement of pahoehoe lava is often dominated by random influences such as budding small scale variations in topography degree of inflation and variations in how the skin cools stretches and cracks a random walk model is used to describe the transport of small pahoehoe lobes when random effects are a significant influence on emplacement we derive the stochastic formalism for random movements on a two dimensional grid our formulation features correlation and bias that determine the degree of randomness in the random walk of each parcel of lava qualitative and quantitative predictions of the random walk are compared with observations and data for pahoehoe lobes in hawaii the correlated random walk quantitatively describes lobe thickness transects whereas the uncorrelated random walk only reproduces the meandering of small filaments of a few toes correlation expresses momentum effects and a chain of memory from the flow front to the source of lava supply the correlated random walk features a channel forming regime that decays with distance from the source of lava supply the theory can also be interpreted in the context of a time dependent planar flow when many parcels of lava participate the overall shape of a one dimensional lobe has the appearance of a continuum wave the types of processes contained in this basic random walk model explain the multitude of concurrent or overriding features found in broad fields of toes the formalism can thus be extended to simulate large fields of emplaced pahoehoe in either terrestrial or planetary settings

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

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

fracture network fluid pathways and paleostress at the tolhuaca geothermal field abstract in this study we examine the fracture network of the tolhuaca geothermal system located in the southern andean volcanic zone that may have acted as a pathway for migration and ascent of deep seated fluids under the far local stress field conditions of the area we collected the orientation slip data and mineralogical content of faults and veins recovered on a ca 1000 m deep borehole tol 1 located in the nw flank of the tolhuaca volcano tol 1 is a non oriented vertical borehole that recovered relatively young 1 axis 083 74 and a subhorizontal ns trending 3 axis 184 03 within the topmost 400 m of the borehole faults and veins are randomly oriented whereas below 400 m depth faults and veins show preferential ne to ew strikes and steep 50 dips the ew striking veins are compatible with the calculated local stress field whereas ne striking veins are compatible with the regional stress field the morphological elongation of volcanic centers alignments of flank vents and dikes orientation our results demonstrate that the paleomagnetic methodology proved to be reliable and it is useful to re orient vertical boreholes such as tol 1 furthermore our data show that the bulk transpressional regional stress field has local variations to a tensional stress field within the ne striking fault zone belonging to the liquine ofqui fault system favoring the activation of both nw and ne striking pre existent discontinuities especially the latter which are favorably oriented to open under the prevailing stress field the vertical 1 and ns trending subhorizontal 3 calculated in the tgs promote the activation of ew striking extensional veins and both ne and nw striking hybrid faults constituting a complex fluid pathway geometry of at least one kilometer depth

pahoehoe toe dimensions morphology and branching relationships at mauna ulu kilauea volcano hawai i pahoehoe toe dimensions morphology and branching relationships were analyzed in flows emplaced during 1972 at mauna ulu a satellitic shield on the east rift zone of kilauea volcano hawai i in order to characterize regions within flow fields dominated by networks of pahoehoe toes measurements of toe length width thickness and orientation were completed for 445 toes at 13 sites variations in site characteristics including slope substrate and position in the flow field allow an evaluation of the effects of such parameters on toe dimensions toe surface morphology ropy or smooth local flow lobe position interior or margin and connective relationships between toes were documented in the form of detailed toe maps these maps show the number of branches connecting a given toe to other toes in its local pahoehoe network and illustrate branching patterns statistical analyses of toe dimensions and comparisons of pahoehoe toe study sites and sub populations combined with field observations evaluation of toe maps and qualitative examination of toe dimension size distributions show the following a although there are significant variations at a given site toes typically have mean lengths 101 cm greater than mean widths 74 cm and mean widths greater than mean thicknesses 19 cm sites that have mean widths greater than mean lengths are those with lower slopes b where significant site to site variations in mean values of a given toe dimension were apparent these differences could not be directly related to site characteristics c ropy toes have significantly larger mean values of length width and number of branches than smooth toes and toes with three or more branches have greater lengths widths and thicknesses than toes with two or fewer branches suggesting concentration of flow in these toe types d the skewness of all size distributions of toe length and width to larger values suggests that toes are transitional to larger sheets and channels consistent with field observations and e two distinct types of branching patterns called monolayer and centrally ridged were observed in preserved pahoehoe flow lobes the significant variability in measured toe dimensions at mauna ulu suggests that toe dimensions are influenced by numerous locally defined random factors and that an approach based on stochastic methods can be used to model pahoehoe flow emplacement

correlation and migration studies of north central sumatra oils the central sumatra basin csb is a prolific petroleum producing basin and its petroleum systems have been extensively studied the widely occurring tertiary lacustrine shale brown shale has long been recognized as the main source rock for tens of billions of barrels of oil in place the oils produced from different fields display significant variation in source characteristics that have been attributed to variation in source facies despite this generalized recognition of the oil source the links between major oil accumulations and many possible source kitchens throughout the basin have not been established as detailed oil source correlation and oil migration routes are not well defined for continued exploration in the region detailed genetic grouping and migration routes of the oils were evaluated through geochemical characterization of numerous oils from various fields in the northern part of central sumatra biomarker and carbon isotopic data indicate that the oils are quite similar geochemically but form several genetic groups on the basis of subtle but persistent differences in source facies the groupings appear geographically meaningful and show association of the different oil groups with various troughs carbazole distributions show consistency in suggesting differences in relative migration distance among the oils within each genetic group by combining the oil grouping and carbazole distributions with geological data models of migration directions and pathways for oils in north central sumatra have been constructed

sunda strait and central sumatra fault sunda strait marks the limit between java trench frontal subduction and sumatra trench oblique subduction the right lateral central sumatra fault accommodates the oblique subduction it does not pass sunda strait but ends between sumatra and java in a complex pattern of dominantly normal faults associated with subsidence seismicity and volcanism we examine the implications of this phenomenon in sunda strait and in the adjacent fore arc basin and accretionary prism which underwent north south compression due to subduction as well as east west extension we propose that the strait is a consequence of the northwestward motion of the southwestern sumatra block along the central sumatra fault we also propose that the extensional zone in the sunda strait widens considerably to the southwest toward the trench and changes into a composite zone of deformation affected by strike slip as well as normal faulting

detailed fault structure of the tarutung pull apart basin in sumatra indonesia derived from local earthquake data abstract the tarutung basin is located at a right step over in the northern central segment of the dextral strike slip sumatran fault system sfs details of the fault structure along the tarutung basin are derived from the relocations of seismicity as well as from focal mechanism and structural geology the seismicity distribution derived by a 3d inversion for hypocenter relocation is clustered according to a fault like seismicity distribution the seismicity is relocated with a double difference technique hypodd involving the waveform cross correlations we used 46 904 and 3191 arrival differences obtained from catalogue data and cross correlation analysis respectively focal mechanisms of events were analyzed by applying a grid search method hash code although there is no significant shift of the hypocenters 10 8 m in average and centroids 167 m in average the application of the double difference relocation sharpens the earthquake distribution the earthquake lineation reflects the fault system the extensional duplex fault system and the negative flower structure within the tarutung basin the focal mechanisms of events at the edge of the basin are dominantly of strike slip type representing the dextral strike slip sumatran fault system the almost north south striking normal fault events along extensional zones beneath the basin correlate with the maximum principal stress direction which is the direction of the indo australian plate motion the extensional zones form an en echelon pattern indicated by the presence of strike slip faults striking ne sw to nw se events the detailed characteristics of the fault system derived from the seismological study are also corroborated by structural geology at the surface

one century of tectonic deformation along the sumatran fault from triangulation and global positioning system surveys an analysis combining historical triangulation and recent global positioning system gps survey measurements in west and north sumatra indonesia reveals a detailed slip history along the central part of the sumatran fault the arc parallel components of the combined velocity field are consistent with slip rates inferred from gps data ranging from 23 to 24 mm yr between 1 0 s and 1 3 n the sumatran fault appears to be characterized by deep locking depths of the order of 20 km and the occurrence of large mw 7 earthquakes the long term 1883 1993 strains show simple right lateral shear with rates similar to gps measured 1989 1993 strain rates coseismic deformation due to the 1892 tapanuli and 1926 padang panjang earthquakes estimated from triangulation measurements taken before and after the events indicates that the main shocks were significantly larger than previously reported the 1892 earthquake had a likely magnitude of mw 7 6 while the 1926 events appear to be comparable in size to the subsequent m 7 1943 events and an order of magnitude higher than previously reported

the regional geology and evolution of the toba volcano tectonic depression indonesia the late quaternary toba volcano tectonic depression in the sunda arc is the largest resurgent cauldron in the world and lies in one of the largest ignimbrite fields the toba tuffs although composed of at least 3000 km 3 of acid tuffs spread over 20000 km 2 of mainland sumatra the greater part of the toba tuffs is believed to be a single ignimbrite cooling unit formed about 100 000 years ago the toba tuffs also include a 30000 year old airfall tuff which was erupted from a centre just n of the toba depression the toba depression developed through the same stages as other resurgent cauldrons it formed after lithification of the toba tuffs by collapse along regional faults crossing an eastwards bulge in the sumatran geanticline resurgent uplift raised lake sediments within the depression by about 500 m the uplift which was not confined to the depression was probably caused by continuing influx of magma and it is possible that the toba depression is still in the stage of post resurgence volcanism the eruption of the toba tuffs and of all post ignimbrite volcanism took place on the line of the western marginal fault of the depression this marginal fault once extended northwards offshore into a zone of miocene back arc rifting

strain partitioning during oblique plate convergence in northern sumatra geodetic and seismologic constraints and numerical modeling global positioning system gps measurements along the subduction zone of northern sumatra 2 s to 3 n reveal that the strain associated with the oblique convergence of the australian plate with eurasia is almost fully partitioned between trench normal contraction within the forearc and trench parallel shear strain within a few tens of kilometers of the sumatran fault kinematic analyses of interplate earthquake slip vectors provide slip rates on the sumatran fault within a few millimeters per year of gps and geologic rates giving us more confidence in the use of slip vectors for inferring slip partitioning elsewhere the inferred slip rate on the sumatran fault is 1 3 less than the full margin parallel component of plate motion an across forearc rotation in the slip vectors suggests that the missing arc parallel shear occurs seaward of the geodetic network between the forearc islands and the trench simple finite element models are used to explore the conditions under which the change in the principal strain rate directions between the forearc and the arc region can occur modeling suggests that neither a preexisting strike slip fault nor a zone of thermally induced lithospheric weakness in the overriding plate is needed for strain partitioning to occur in general forearc slivers form over the region of interplate coupling and are driven along strike by the basal shear a volcanic arc can help the partitioning process by localizing the margin parallel shear strain in the upper plate if its crust and mantle are weaker than its surroundings interplate slip vectors and geodetic results from sumatra together suggest that the highest coupling on the plate boundary occurs beneath and seaward of the forearc islands consistent with inferences about the rupture zones of great nineteenth century earthquakes there the sumatra example suggests that geodetic measurements of interseismic margin parallel shear strain at oblique convergent margins can be used to map the landward extent of the relatively high basal stress beneath the overriding plate if one can correct for strain localization caused by weak upper plate strike slip faults

source rock facies distribution predicted from oil geochemistry in the central sumatra basin indonesia the molecular and compound specific isotopic composition of the n alkanes in 30 oil samples from the central sumatra basin were analyzed with the purpose of determining facies variations of the source rock in this basin the oil samples were generated by the eocene oligocene lacustrine brown shale formation biomarkers in the oil samples indicate varying contributions from algal and terrigenous organic matter primarily under oxic or suboxic depositional conditions five source rock facies were identified based on the relative concentrations of n alkanes isoprenoids tricyclic terpanes and steranes the individual facies were also distinguished by the compound specific isotopic composition of the n alkanes source rock depositional environments vary from deep lacustrine shallow lacustrine and lacustrine saline to coal and mixed coal and lacustrine shale deep lacustrine facies predominate in the aman and bengkalis troughs whereas saline and shallow lacustrine facies predominate in the south aman and kiri troughs respectively oils derived from coal and mixed coal and lacustrine shale facies predominate in the northern part of the central sumatra basin in the tanjung medan and north of the balam grabens

productivity control on oil shale formation mae sot basin thailand abstract neogene oil shales from the freshwater lacustrine intermontane mae sot basin western thailand are examined in order to define a oil source rock potential b variations in molecular and isotopic geochemical characteristics and c the influence on source potential of organic matter productivity and preservation twelve samples spanning 7 m of section were examined using conventional isotopic molecular and organic petrographic methods of geochemical analysis temporal resolution is 2700 yr per sample because thermal maturity differences and fluid migration within the sample set are absent and organic matter type input variation is either minor or absent based on visual kerogen analysis we propose that organic matter differences among the samples are caused by variability in surface water productivity all samples are excellent potential source rocks vr 0 4 0 5 ro containing types i and ii organic matter modified van krevelen plot determination consisting of almost 100 fluorescent amorphous kerogen visual kerogen determination numerous diagnostic molecular markers and characteristics are present including perhydro carotene dammaranes norsterane s and novel distributions of tricyclic terpanes stable carbon isotope ratios of kerogens and extract fractions range over 5 and co vary with hydrogen index this covariance is attributed to temporal increases in surface water productivity leading to co2 limiting conditions and consequent increase in 13c of the organic matter in the photic zone during times of elevated productivity increased amounts of 13c enriched organic matter reached the water sediment interface thus times of greater productivity are accompanied by higher 13c and hydrogen index values with 13c related to productivity under co2 limiting conditions and hi related to the relative amount of the water column that was anoxic during deposition our findings suggest that in petroleum geochemical studies involving lacustrine source rocks 13c values must be used with caution as oil oil and oil source rock correlation parameters

oil source rock correlations limitations and recommendations a rigorous defensible and causal oil source rock correlation definitively ties an individual source rock sample to an individual crude oil using genetically based internally consistent parameter matches such a correlation is a relationship established between the two components which is consistent with all known chemical geochemical and geological information and meets three criteria a the relationship must be causal the oil must arise at least in part from the specified source rock s b chemical data used in the correlation must be comparable the elemental molecular and isotopic data derived from the source rock must be of the same type as that derived from the oil and c all available geological data must be supportive clear geological evidence must exist which allows the proposed source rock to have sourced the oil the three points of this definition are satisfied and the correlation is successful if we solve one analytical and three geological problems natural extraction of crude oil from its source rock i e expulsion differs mechanically and temporally from laboratory extraction leading to a correlation problem referred to as extraction differences and representing the single greatest analytical uncertainty in correlation efforts geologically three aspects confound oil source correlations occurrence of multiple source units and or source units at differing maturity levels lateral and vertical depositional variations in source unit s organic matter and lateral and vertical variation in reservoir unit s organic matter these concerns are overcome by taking five actions for each oil source correlation effort 1 select representative samples using statistically defensible methods 2 establish the inherent compositional variability laterally and temporally due to depositional and maturation processes in each prospective source unit 3 assess the extent of migration induced changes in oil composition including post migration changes such as in reservoir alteration 4 support each correlation with migration histories derived from 4d models 5 iterate correlation results with new data gathered from ongoing exploration efforts these five actions will a allow correlation success to be measured more objectively b establish risking parameters for direct use in basin assessment and c provide baseline criteria for use in assessing the reliability of oil source rock correlations although these approaches will improve conventional oil source rock correlation efforts ultimately they may not be needed if inversion methods become more reliable the ability to invert compositional data for crude oil i e predict the age lithology maturity and other characteristics of a source rock solely through chemical analysis of its expelled oil could eventually result in successful oil source rock correlations in which source rock analysis for oil source rock correlation purposes is less critical

paleoreconstruction by biological markers abstract during diagenesis and conversion of the original lipid fraction of biological systems to petroleum hydrocarbons the following four basic events needed for paleoreconstruction can be monitored by biological markets 1 sourcing 2 maturation 3 migration and 4 biodegradation actual cases of applying biological markers to petroleum exploration problems in different parts of the world are demonstrated cretaceous and phosphoria sourced oils in the wyoming thrust belt can clearly be distinguished from one another by high quality source fingerprinting of biomarker terpanes using gas chromatography mass spectrometry identification of recently discovered biological markers head to head isoprenoids allows subtle source differentiation between oils from sumatra the degree of crude oil maturation in basins from california alaska russia wyoming and louisiana can be assessed by specific novel biomarker ratios 20s 20r sterane epimers field evidence from such interpretation is confirmed by laboratory pyrolysis of the rock an example of immature sumatra rock is given extensive migration is documented by biomarkers in several oils the effect of biodegradation on biomarker steranes and terpanes is exemlified in a california basin all biological marker results are consistent with the geological setting and add a new dimension in assisting the petroleum explorationist toward paleo reconstruction

significance of coniferous rain forests and related organic matter in generating commercial quantities of oil gippsland basin australia contrary to the conventional belief that humic coal generates primarily gas 3 billion bbl of recoverable oil has been discovered in the humic coaly succession of the fluviodeltaic latrobe group upper cretaceous tertiary that serves as both the reservoir and the source for hydrocarbons in the offshore gippsland basin of southeastern australia evidence for generation of liquid hydrocarbons from the coaly succession includes 1 similarity of n alkane distribution in the oil and in the coal extracts 2 high wax content of oil up to 27 by weight 3 high ratio of pristane phytane in oil 5 6 and 4 dominance of c29 steranes in the oil in the gippsland basin coniferous rain forests dominated by kauri vegetation flourished in a raised bog setting present temperate climate and kauri vegetation of new zealand are considered to be the modern analog to the gippsland basin the coniferous vegetation provided large quantities of hydrogen rich exinite macerals such as cutinite and resinite with potential to generate oil high rainfall raised ground water level low oxygen high acidity and low nutrient conditions of a raised bog setting were suitable for preserving organic matter a comparison of gas chromatograms of oils in the gippsland basin with gas chromatograms of oils generated by hydrous pyrolysis in the laboratory from the immature source rocks suggests that the paraffinic fraction of the oil was derived from coal and the naphthenic fraction was derived chiefly from resin

emplacement of volcanic vents and geodynamics of central anatolia turkey abstract observations on synthetic aperture radar sar scenes of the european remote sensing ers satellite and digital elevation models dems complemented by field structural analysis permit a new understanding of relationships between tectonics and volcanism since the late miocene 10 ma in central anatolia volcanic edifices form elongate stratovolcanoes linear clusters and volcanic ridges they indicate emplacement on tension fractures and tail crack or horsetail features for instance the kara dag volcano is rooted on a tail crack which accommodates a horizontal left lateral throw component at a fault termination caldera complexes of cappadocia are associated with horsetail fault patterns the emplacement of volcanoes also benefits from larger scale tectonic structures the erciyes dag volcano is localized by the sultan saz releasing bend which opens along the sinistral strike slip ecemis fault deformation has been analysed from tension fractures which are perpendicular to the direction of extension and from field structural analysis on a regional scale the tectonic regime responsible for the distribution of volcanic vents in this area of convergence and lateral extrusion is not compression but extension the central taurus range is the thermally uplifted shoulder of the adana cilicia basin which is related to lithosphere thinning westward movements in the northwestern part of the studied area are influenced by the active back arc aegean extension situated to the west farther to the south the direction of motion turns southwest and south under the influence of the opening of the adana cilicia basin we interpreted that extension in the central anatolian plateau is related to crustal blocks moving above sub horizontal detachment surfaces located in the lower crust this is based on several facts the tuz golu fault zone is a within crust detachment the tuz golu basin does not affect the whole lithosphere because otherwise it would have been bordered by thermally uplifted shoulders movements change trend within a small 50 km region

lava flows are fractals we have conducted a preliminary investigation of the fractal nature of the plan view shapes of lava flows in hawaii based on field measurements and aerial photographs as well as in idaho and the galapagos islands using aerial photographs only our results indicate that the shapes of lava flow margins are fractals in other words lava flow shape is scale invariant at least within the range of scale measured 0 5m to 2 4km this observation has important implications for understanding the fluid dynamics of lava flows it suggests that nonlinear forces are operating in them because nonlinear systems frequently produce fractals furthermore a a and pahoehoe flows can be distinguished by their fractal dimensions d the majority of the a a flows we measured have d between 1 05 and 1 09 whereas the pahoehoe flows generally have higher d 1 14 1 23 we have extended our analysis to other planetary bodies by measuring flows from orbital images of venus mars and the moon all are fractal and have d consistent with the range of terrestrial a a and pahoehoe values combining the terrestrial and extraterrestrial data the fractal nature of lava flow outlines holds for over five orders of magnitude in scale 0 5m to 60km

tectonics of strike slip restraining and releasing bends restraining and releasing bends are common but enigmatic features of strike slip fault systems occurring in all crustal environments and at regional to microscopic scales of observation regional scale restraining bends are sites of mountain building transpressional deformation and basement exhumation whereas releasing bends are sites of topographic subsidence transtensional deformation basin sedimentation and possible volcanism and economic mineralization because restraining and releasing bends often occur as singular self contained domains of complex deformation they are appealing natural laboratories for earth scientists to study fault processes earthquake seismology active faulting and sedimentation fault and fluid flow relationships links between tectonics and topography tectonic and erosional controls on exhumation and tectonic geomorphology this volume addresses the tectonic complexity and diversity of strike slip restraining and releasing bends with 18 contributions divided into four thematic sections 1 a topical review of fault bends and their global distribution 2 bends sedimentary basins and earthquake hazards 3 restraining bends transpressional deformation and basement controls on development 4 releasing bends transtensional deformation and fluid flow

geochemistry of crude oils from eastern indonesia high resolution geochemistry shows genetic relationships among 27 crude oils from eastern indonesia and suggests the ages and paleoenvironments of their source rocks oils inferred to originate from tertiary and triassic jurassic source rocks in the study occur north and south of 2is latitude respectively twenty oils mainly from irian jaya and sulawesi originated from tertiary marine marlstone source rocks that contained type ii iii kerogen deposited under suboxic conditions probably the upper miocene klasafet formation these low sulfur oils show high oleanane c26 24 nordia cholestane and pristane phytane ratios and 13c rich carbon isotope compositions high oleanane and 24 nordiacholestane ratios are diagnostic of tertiary oils and source rocks these oils account for about 16 of the estimated ultimate recoverable reserves in eastern indonesia

is the slip rate variation on the great sumatran fault accommodated by fore arc stretching in oblique convergent subduction areas an obliquity increase should produce a slip rate increase on trench parallel strike slip faults and thus the fore arc platelet should be stretched along the great sumatran fault gsf that is associated with the oblique convergent sunda arc a northward increase of the gsf slip rate occurs parallel with the convergence obliquity transpressional back arc deformation accommodates part of the gsf slip rate variation while no significant fore arc stretching is observed the sumatran case shows that oblique convergence may be accommodated by deformation of a 500 km wide zone from the fore arc to the back arc domains

characterization of the hydrothermal system of the tinguiririca volcanic complex central chile using structural geology and passive seismic tomography abstract a structural characterization of the hydrothermal volcanic field associated with the tinguiririca volcanic complex had been performed by combining passive seismic tomography and structural geology this complex corresponds to a 20 km long succession of n25 e oriented of eruptive centers currently showing several thermal manifestations distributed throughout the area the structural behavior of this zone is controlled by the el fierro el diablo fault system corresponding to a high angle reverse faults of oligocene miocene age in this area a temporary seismic network with 16 short period stations was setup from january to april of 2010 in the context of the msc thesis of lira 2010 covering an area of 200 km 2 that corresponds with the hydrothermal field of tinguiririca volcanic complex tvc central chile southern central andes using p and s wave arrival times a 3d seismic velocity tomography was performed the preliminary locations of 2270 earthquakes have first been determined using an a priori 1d velocity model afterwards a joint inversion of both the 3d velocity model and final locations have been obtained high vp vs ratios are interpreted as zones with high hot fluid content and high fracturing meanwhile low vp vs anomalies could represent the magmatic reservoir and the conduit network associated to the fluid mobility based on structural information and thermal manifestations these anomalies have been interpreted in order to visualize the relation between local geology and the velocity model the volume associated with the magma reservoir and the fluid circulation network has been delimited using an iso value contour of vp vs equal to 1 70 the most prominent observed feature in the obtained model is a large v shaped low velocity anomaly extending along the entire study region and having the same vergency and orientation as the existing high angle inverse faults which corroborates that el fierro el diablo fault system represents the local control for fluid mobility this geometry coincides with surface hydrothermal manifestations and with available geochemical information of the area which allowed us to generate a conceptual model of fluid circulation in the volcanic hydrothermal system as well as define the location of the magmatic reservoir

mechanisms of petroleum accumulation in the bozhong sub basin bohai bay basin china part 1 origin and occurrence of crude oils the origin of the fourteen major oil fields in the bozhong sub basin bohai bay basin was studied based on the results of rock eval pyrolysis on more than 700 samples and biomarker analysis on 61 source rock samples and 87 oil samples the three possible source rock intervals have different biomarker assemblages and were deposited in different environments the third member of the oligocene dongying formation e3d3 32 8 30 3 ma in age is characterized mainly by high c19 c23 tricyclic terpane 0 75 high c24 tetracyclic terpane c26 tricyclic terpane 2 5 low gammacerane c30 hopane 0 15 and low 4 methyl steranes c29 steranes 0 15 ratios and was deposited in sub oxic to anoxic environments with significant terrigenous organic matter input the first e2s1 35 8 32 8 ma and third e2s3 43 0 38 0 ma members of the eocene shahejie formation have low c19 c23 tricyclic terpane and low c24 tetracyclic terpane c26 tricyclic terpane ratios and were deposited in anoxic environments with minor terrestrial organic matter input but have different abundances of 4 methyl steranes and gammacerane the hydrocarbon generating potential and biomarker associations of these three source rock intervals were controlled by tectonic evolution of the sub basin and climate changes three oil families derived from e2s3 e2s1 and e3d respectively and three types of mixed oils have been identified all large oil fields in the bozhong sub basin display considerable heterogeneities in biomarker compositions and originated from more than one source rock interval which suggests that mixing of oils derived from multiple source rock intervals or multiple generative kitchens and or focusing of oils originated from a large area of a generative kitchen is essential for the formation of large oil fields in the bozhong sub basin e2s3 and e2s1 derived oils experienced relatively long distance lateral migration and accumulated in traps away from the generative kitchen e3d3 derived oils had migrated short distances and accumulated in traps closer to the generative kitchen such a petroleum distribution pattern has important implications for future exploration there is considerable exploration potential for dongying derived oils in the bozhong sub basin and traps close to or within the generative kitchens have better chance to contain oils generated from the dongying formation

structural controls on a geothermal system in the tarutung basin north central sumatra abstract the sumatra fault system provides a unique geologic setting to evaluate the influence of structural controls on geothermal activity whereas most of the geothermal systems in indonesia are controlled by volcanic activity geothermal systems at the sumatra fault system might be controlled by faults and fractures exploration strategies for these geothermal systems need to be verified because the typical pattern of heat source and alteration clays are missing so that conventional exploration with magnetotelluric surveys might not provide sufficient data to delineate favorable settings for drilling we present field geological structural and geomorphological evidence combined with mapping of geothermal manifestations to allow constraints between fault dynamics and geothermal activity in the tarutung basin in north central sumatra our results indicate that the fault pattern in the tarutung basin is generated by a compressional stress direction acting at a high angle to the right lateral sumatra fault system nw se striking normal faults possibly related to negative flower structures and nnw sse to nne ssw oriented dilative riedel shears are preferential fluid pathways whereas ene wsw striking faults act as barriers in this system the dominant of geothermal manifestations at the eastern part of the basin indicates local extension due to clockwise block rotation in the sumatra fault system our results support the effort to integrate detailed field geological surveys to refined exploration strategies even in tropical areas where outcrops are limited

neotectonics of the sumatran fault indonesia the 1900 km long trench parallel sumatran fault accommodates a significant amount of the right lateral component of oblique convergence between the eurasian and indian australian plates from 10 n to 7 s our detailed map of the fault compiled from topographic maps and stereographic aerial photographs shows that unlike many other great strike slip faults the sumatran fault is highly segmented cross strike width of step overs between the 19 major subaerial segments is commonly many kilometers the influence of these step overs on historical seismic source dimensions suggests that the dimensions of future events will also be influenced by fault geometry geomorphic offsets along the fault range as high as 20 km and may represent the total offset across the fault if this is so other structures must have accommodated much of the dextral component of oblique convergence during the past few million years our analysis of stretching of the forearc region near the southern tip of sumatra constrains the combined dextral slip on the sumatran and mentawai faults to be no more than 100 km in the past few million years the shape and location of the sumatran fault and the active volcanic arc are highly correlated with the shape and character of the underlying subducting oceanic lithosphere nonetheless active volcanic centers of the sumatran volcanic arc have not influenced noticeably the geometry of the active sumatran fault on the basis of its geologic history and pattern of deformation we divide the sumatran plate margin into northern central and southern domains we support previous proposals that the geometry and character of the subducting investigator fracture zone are affecting the shape and evolution of the sumatran fault system within the central domain the southern domain is the most regular the sumatran fault there comprises six right stepping segments this pattern indicates that the overall trend of the fault deviates 4 clockwise from the slip vector between the two blocks it separates the regularity of this section and its association with the portion of the subduction zone that generated the giant m w 9 earthquake of 1833 suggest that a geometrically simple subducting slab results in both simple strike slip faulting and unusually large subduction earthquakes

pematang sihapas petroleum system of central sumatra abstract the pematang sihapas petroleum system of central sumatra is one of the most important lacustrine oil systems in southeast asia the brown shale formation lacustrine of the pematang group has generated 60 109 barrels of oil sihapas early miocene sandstones are the principal reservoirs of this system giant fields e g minas and duri having sihapas marine sandstone reservoirs occur principally along the eastern margins of sub basins smaller fields having pematang nonmarine sandstone reservoirs are confined to the deeper troughs the pematang group was deposited in a series of small grabens it exhibits a tripartite stratal architecture basal lower red bed fluvial alluvial unit medial brown shale lacustrine unit and upper upper red bed fluvial alluvial unit the upper red bed unit is the main pematang reservoir source rock attributes of the brown shale are highly variable pyrolysis yields of samples containing 1 0 wt toc range up to 120 mg hc g rock with a mean of 25 3 mg hc g rock the oil proneness of the kerogen also varies the more oil prone portions of the unit appear in the upper portion of the stratigraphic unit and in the fully lacustrine facies i e poor source rock development occurred in lake margin deltaic and fan delta facies geochemical differences also exist among the different sub basins the pematang group is disconformably overlain by the menggala formation basal transgressive unit of sihapas group menggala strata consist of well sorted quartzose to subarkosic sandstones having an average porosity of 20 and an average permeability of 1500 md menggala sandstones are the most prolific hydrocarbon reservoirs in central sumatra many of the oil fields in central sumatra are associated with paleohighs drag folds and post mid miocene inversion hydrocarbon generation was initiated during the miocene and continues currently in some parts of the basin

middle eocene paleohydrology of the dongying depression in eastern china from sedimentological and geochemical signatures of lacustrine mudstone previous understanding that stratigraphic variability in lacustrine sequences is primarily caused by depositional processes governed by regional tectonics and climatic change remains to be tested on microscopic scale here we study the upper fourth member es4u of the eocene shahejie formation the major source rock of the dongying depression eastern china in order to understand stratigraphic heterogeneity and tectonic and climate controls on depositional processes in lacustrine mudstone our study integrates core descriptions microscopic observations and studies of mineralogy toc and chemical weathering proxies of cia and ln al2o3 na2o from two full bore cores and correlation of gamma ray logs from six wells across the depression we identified four major lithofacies including the interbedded evaporite and mudstone deposited in a shallow salt lake the silt bearing clay rich mudstone deposited in a pro delta environment within a shallow open lake the laminated calcareous mudstone deposited in a deep stratified meromictic lake with frequent earthquake activities and the massive calcareous mudstone deposited in a shallow and oxygenated lake the es4u member changed from the interbedded evaporite and mudstone dominated lithofacies association to silt bearing clay rich mudstone dominated lithofacies association and then laminated calcareous mudstone dominated lithofacies association suggesting basin wide changes in depositional processes lake level lake water chemistry and paleohydrology we suggest that these changes reflect balance between sediment and water supply and potential accommodation of the lake basin which were governed by paleoclimate in the lake drainage and extensional tectonics we infer that during the deposition of the es4u member the lake basin evolved from an underfilled lake basin with salty lake water under arid climate to a shallow balanced fill lake basin when climate became humid then to a deep balanced fill basin with stratified bottom lake water when climate became more humid and the basin was deepened by tectonic activity this study demonstrates that climate and tectonics both control paleolimnological changes and depositional processes of lacustrine mudstone

the sipoholon geothermal field and adjacent geothermal systems along the north central sumatra fault belt indonesia reviews on geochemistry tectonics and natural heat loss abstract the sipoholon system in the tarutung basin is one of five geothermal systems associated with a c 100 km stretch of the sumatra fault system sfs in north central sumatra indonesia that exhibits parallel sets of dextral strike slip faults associated with seismic activity characteristics of discharged thermal fluids differ significantly between the systems the gas rich sipoholon field transfers only c 19 mw heat by ca so4 hco3 springs with sio2 fluid equilibria pointing to temperatures of 50 80 c at intermediate depths most of its thermal springs t in contrast all four thermal systems in the sarulla block concession to the southeast of the sipoholon field are convective high temperature systems that transfer significant heat to the surface fumaroles steaming ground thermal springs hot pools and thermal lakes discharge at least 50 mw heat at three of the four prospects where the temperatures of springs and fumaroles often reach boiling point many hot springs of the sarulla block systems discharge dominantly na hco3 cl type waters with partially equilibrated cation compositions a result of fluid rock equilibration and mixing processes sio2 fluid equilibria indicate 130 to c 200 c with cation geothermometers pointing to a high reservoir temperature 200 260 c for all four systems this was confirmed by the first deep exploratory wells drilled c 20 years ago in three prospects that encountered t 250 c at bottom hole 1 5 km depth the structural setting of the five geothermal fields is complex at tarutung it is associated with the narrow tarutung basin filled with volcanic debris and ash the basin exhibits a partly exposed dextral strike slip fault along its ne margin and can be interpreted in terms of a trans tensional pull apart basin two of the adjacent sarulla block systems are associated with large volcanic debris basins namora i langit and silangkitang that exhibit half graben structures in profiles normal to two large active faults of the sumatra fault system sfs the other two systems donotasik and sibualbuali are hosted by an elongated graben structure parallel and within the sfs and by a stratovolcano respectively

studying travertines for neotectonics investigations middle late pleistocene syn tectonic travertine deposition at serre di rapolano northern apennines italy middle late pleistocene tectonic activity has been inferred through studies on travertine deposits exposed in a tract of the hinterland northern apennines a detailed study on the relationships between tectonics and travertine deposition coupled with 230th 234u age determination of travertines at cava oliviera quarry located close to serre di rapolano village southern tuscany northern apennines allowed us to recognise pleistocene faults whose activity has been referred to 157 24 ka at least travertine deposition was tectonically controlled by wsw ene striking oblique and normal faults associated to a main fault named as the violante fault this structure dissected a regional normal fault known as the rapolano fault early middle pliocene in age which bounded the eastern side of the pliocene siena basin and gave rise to space accommodation for clayey and sandy marine sediments hydrothermal circulation and related travertine deposition was favoured by the damaging enhancement due to the fault fault intersection tectonic activity has been also documented by deformation recorded by travertines which suggest a main tectonic event between 64 5 and 40 5 ka the tectonic activity described for the study area agrees with the quaternary tectonic evolution documented in the surrounding areas e g mt amiata and mt vulsini as well as the tyrrhenian margin of the central apennines indicating that a widespread tectonic activity affected the inner part of the apennines until the latest quaternary

compound specific stable carbon isotope analysis as a tool for correlating coal sourced oils and interbedded shale sourced oils in coal measures an example from turpan basin north western china molecular geochemical methods have shown that it is often diacult to diaerentiate between coal and interbedded shale sourced oils even though coals and interbedded shales may exhibit considerable organic influx variation e g land plant vs algal organic matter due to the changes of depositional setting however compound specific stable carbon isotopic compositions are sensitive to the source input variations typically specific molecules are more depleted in 13 c with increasing content of aqueous biota this hypothesis is examined and exemplified by comparing the stable carbon isotopic ratios of n alkanes from source rock extracts and related oils of the turpan basin northwestern china stable carbon isotopic values of n alkanes extracted from coals and interbedded shales show that d 13 c values of n alkanes with less than 20 carbon atoms vary only slightly however there are dramatic changes in the isotopic compositions of higher molecular weight n alkanes furthermore n alkanes from coal extracts are enriched in 13 c relative to that of interbedded shales with excursions up to 2 3 this comparison enables the diaerentiation of coal and interbedded shale sourced oils and provides information useful in assessing the hydrocarbon system of a basin 2000 elsevier science ltd all rights reserved

characterization of eocene lacustrine source rocks and their oils in the beibuwan basin offshore south china sea two hundred twenty five rock samples and thirty seven oil samples from the beibuwan basin south china sea were analyzed with geochemical and organic petrological techniques to evaluate the eocene lacustrine source rocks and investigate controls on their properties and the distribution of different oil families in the basin two types of organic facies are recognized in the liushagang ls formation the first organic facies is algal dominated and mainly occurs in the organic rich laminated mudstones of the middle member of the ls ls 2 that were deposited in an anoxic stratified medium deep lake environment it is geochemically identified by its high abundance of c30 4 methylsteranes and heavy 13c values in the range of 22 4 to 27 5 the organic matter in this organic facies comprises type i and ii1 kerogens with its macerals dominated by fluorescent amorphous organic matter aom and exinites indicating a highly oil prone character the second organic facies is of terrestrial algal origin and is mainly identified in the non laminated mudstones of the upper ls 1 and lower ls 3 members of the liushagang formation that were deposited in shallow dysoxic weakly stratified fresh water environments source rocks of the second organic facies mainly contain type ii1 ii2 kerogens with mixed macerals of aom internites and vitrinites it is geochemically differentiated from the algal dominated organic facies by its relatively low abundance of c30 4 methylsteranes and lighter 13c values in the range of 27 20 to 28 67 three oil groups are identified by their biomarkers and stable carbon isotopes the first two groups a and b are probably end members of two major oil families a and b that correspond to the algal dominated organic facies and algal terrestrial organic facies respectively most of the discovered oils belong to group a oils that are characterized by a high abundance of c30 4 methylsteranes and heavy 13c values and show a good correlation with the algal dominated organic facies in ls 2 group b oils are found only within the ls 1 and ls 3 reservoirs and they are recognized by their relatively low content of c30 4 methylsteranes and lighter 13c values showing a close relation to the algal terrestrial source facies within the ls 1 and ls 3members respectively group c oils display intermediate biomarker features and stable carbon isotope values and are interpreted to be a mixture of group a and b oils the oil source correlation reveals a strong control of organic facies on the geographic distribution of oil groups or oil fields in the basin

self organizing maps in geothermal exploration a new approach for understanding geochemical processes and fluid evolution understanding geochemical processes is an important part of geothermal exploration to get information about the source and evolution of geothermal fluids however in most cases knowledge of fluid properties is based on few parameters determined in samples from the shallow subsurface this study presents a new approach that allows to conclude from the combination of a variety of these data on processes occurring at depth in a geothermal reservoir the neural network clustering technique called self organizing maps soms successfully distinguished two different geothermal settings based on a hydrochemical database and disclosed the source evolution and flow pathways of geothermal fluids scatter plots as shown in this study are appropriate presentations of element concentrations and the chemical interaction of water and rock at depth one geological setting presented here is marked by fault dominated fluid pathways and minor influence of volcanic affected fluids with high concentrations of hco3 ca and sr the second is a magmatically dominated setting showing strong alteration features in volcanic rocks and accommodates acidic fluids with high so4 and si concentrations former studies i e giggenbach 1988 suggested cl hco3 and so4 to be generally the most important elements for understanding hydrochemical processes in geothermal reservoirs their relation has been widely used to classify different water types in geothermal fields however this study showed that non standard elements are at least of same importance to reveal different fluid types in geothermal systems therefore this study is an extended water classification approach using som for element correlations som have been proven to be a successful method for analyzing even relatively small hydrochemical datasets in geothermal applications

the initial cooling of pahoehoe flow lobes in this paper we describe a new thermal model for the initial cooling of pahoehoe lava flows the accurate modeling of this initial cooling is important for understanding the formation of the distinctive surface textures on pahoehoe lava flows as well as being the first step in modeling such key pahoehoe emplacement processes as lava flow inflation and lava tube formation this model is constructed from the physical phenomena observed to control the initial cooling of pahoehoe flows and is not an empirical fit to field data we find that the only significant processes are a heat loss by thermal radiation b heat loss by atmospheric convection c heat transport within the flow by conduction with temperature and porosity dependent thermal properties and d the release of latent heat during crystallization the numerical model is better able to reproduce field measurements made in hawai i between 1989 and 1993 than other published thermal models by adjusting one parameter at a time the effect of each of the input parameters on the cooling rate was determined we show that a the surfaces of porous flows cool more quickly than the surfaces of dense flows b the surface cooling is very sensitive to the efficiency of atmospheric convective cooling and c changes in the glass forming tendency of the lava may have observable petrographic and thermal signatures these model results provide a quantitative explanation for the recently observed relationship between the surface cooling rate of pahoehoe lobes and the porosity of those lobes jones 1992 1993 the predicted sensitivity of cooling to atmospheric convection suggests a simple field experiment for verification and the model provides a tool to begin studies of the dynamic crystallization of real lavas future versions of the model can also be made applicable to extraterrestrial submarine silicic and pyroclastic flows

travitonics using travertines in active fault studies abstract late quaternary travertines deposited from hot springs can reveal much about the neotectonic attributes and histories of structures on the basis of field studies in the aegean region turkey and greece the northern apennines italy and the basin and range province usa we conclude that the following relationships are of predictive value i travertine deposits are preferentially located along fracture traces either immediately above extensional fissures or in the hanging walls of normal faults ii the locations of many travertine fissure ridge deposits coincide with step over zones relay ramps between fault segments networks of intersecting tensional fissures reflecting the complex strains experienced in such settings are probably responsible for enhancing hydrothermal flow iii the morphology of travertine deposits overlying extensional fissures is controlled by the rheology of the underlying materials tufa cones towers pinnacles form on former and present lake floors where fissures underlie unconsolidated sediments whereas fissure ridges develop where fissures cut bedrocks at the surface iv fissure ridges comprise outwardly dipping bedded travertine flanking a central tensional fissure filled by vertically banded travertines fissures can be used to infer local stretching directions v where there are travertines datable by the u series method it is possible to calculate time averaged dilation and lateral propagation rates for individual fissures vi most fissures cutting fissure ridges comprise self similar angular segments with fractal dimensions in the range 1 00 1 12 the properties of bedded travertine combined with stress perturbations at fissure tips probably being responsible for such similar fractal dimensions being inferred from such a wide range of locations fissures gradually increasing in width with depth are products of continuous fracture dilation in contrast to those that form during episodic dilation which display stepped increases of width with depth vii travertine deposited from springs along fault zones accumulate in terraced mounds sited down slope of the spring line viii many post depositional fractures cutting travertine deposits are locally oriented at right angles to deposit margins and ix systematic joints in travertines are restricted to those parts of eroded sheet deposits that have been exhumed

stress change and effective friction coefficient along the sumatra andaman sagaing fault system after the 26 december 2004 m w 9 2 and the 28 march 2005 m w 8 7 earthquakes the 2004 aceh and 2005 nias events are the two greatest earthquakes of the past 40 years with a total rupture of 1700 km long and a coseismic slip reaching up to 25 m these two earthquakes have caused large stress perturbations which significantly altered seismic activity in the sumatra andaman region using both detailed mapping of failure planes and various slip distributions we calculate this stress change along the sumatra andaman sagaing fault system from central sumatra to southern myanmar the static coulomb stress change delta cff and the observed seismic activity are in very good agreement with a coulomb index similar to 20 greater than the one obtained for random events compared to previous studies this high coulomb index confirms two important issues on the use of static stress change criterion unsuited to study near field aftershocks and only relevant for aftershocks analysis on large and mature faults at a time scale of several months the calculated delta cff distribution suggests that the 2004 and 2005 earthquakes inhibit failure on the north andaman rift and on the sagaing fault while failure is encouraged along the transform andaman zone the central andaman rift the west andaman fault the sumatra fault system and the offshore thrust faults west of sumatra island the maximum value of similar to 15 20 bar 1 5 2 mpa for delta cff is reached in the northern part of the sumatra fault system this high value together with the lack of major earthquake in the last 170 years result in a high seismic hazard for this region our results are also consistent with temporal evolution of both earthquakes location and focal mechanism prior to and after the events in particular we explain the occurrence and the mechanism of seismic swarms observed in the central andaman rift and along the west andaman fault finally our calculations reveal that the seismicity in the andaman rift zone can only be explained if mu 0 5 this result leads to two end member models one with a constant and high fault friction and one with spatial variations for which friction may depend on either the nature of the lithosphere oceanic versus continental or the fault type

productivity and paleoclimatic controls on source rock character in the aman trough north central sumatra indonesia abstract the central sumatra basin csb is a prolific oil producing basin in indonesia where a single source rock has been identified the brown shale formation of the paleogene pematang group despite the presence of a single source rock the oils in the central sumatra basin and particularly in the aman trough exhibit variable molecular and isotopic compositions previously described as reflective of lateral facies variations within the source rock analyses by gas chromatography gc gas chromatography mass spectrometry gc ms and gas chromatography isotope ratio mass spectrometry gc irms of 15 oil samples from the aman trough allowed identification of vertical and lateral facies changes within the brown shale formation as well as paleoproductivity and paleoclimatic changes that took place during deposition of this prolific source rock the molecular and isotopic data indicate the source rock for these oils was deposited in a fresh to brackish water stratified lake in which co 2 limiting conditions prevailed compound specific isotopic data also indicate that changes in paleoclimatic conditions possibly associated with the eocene oligocene paleoclimatic transition had an effect on the geochemical composition of the source rock in the aman trough

geochemistry grouping and origins of crude oils in the western pearl river mouth basin offshore south china sea abstract thirty seven crude oils and 20 source rocks were selected for detailed molecular geochemical and isotopic analyses in order to establish the genetic relationships between the discovered oils and various petroleum source facies in the western pearl river basin offshore south china sea four groups of oils were identified the group i oils distributed in the southwestern wc19 1 field of wenchang b sag are characterized by high abundance of 4 methyl steranes relative to regular steranes low abundance of bicadinanes and high 13 c values showing good correlation with the medium deep lacustrine source facies in the wenchang formation the group ii oils represent the majority of the discovered oil reserves in the study area including those from the qionghai uplift and the northeast block of the wc19 1 oil field these oils have moderate concentrations of c 30 4 methylsteranes abundant bicadinanes and low 13 c values and correlate well with the shallow lake source facies of the wenchang formation in the wenchang b and a sags the group iii oils found in the wenchang a sag and surrounding areas are devoid of c 30 4 methylsteranes with abundant bicadinanes and similar 13 c values to those of the group ii oils these characteristics show close affinity with the coal bearing sequence in the enping formation thus suggesting a coaly source for these oils the group iv oils found only in the wc8 3 field display intermediate chemical compositions between the group ii and group iii oils most likely from mixed sources in the wenchang a sag these oil source genetic relationships suggest dominantly short distance oil migration and thus strong source facies controls on the geographic distribution of oil and gas fields within the western pearl river mouth basin

the tectonic framework of the sumatran subduction zone the great aceh andaman earthquake of december 26 2004 and its tragic consequences brought the sumatran region and its active tectonics into the world s focus the plate tectonic setting of sumatra has been as it is today for tens of millions of years and catastrophic geologic events have likely been plentiful the immaturity of our understanding of great earthquakes and other types of geologic hazards contributed to the surprise regarding the location of the 2004 earthquake the timing however is probably best understood simply in terms of the inevitability of the infrequent events that shape the course of geologic progress our best hope is to improve understanding of the processes involved and decrease our vulnerability to them

stratigraphy of the toba tuffs and the evolution of the toba caldera complex sumatra indonesia during the past 1 2 m y a magma chamber of batholithic proportions has developed under the 100 by 30 km toba caldera complex four separate eruptions have occurred from vents within the present collapse structure which formed from eruption of the 2800 km3 youngest toba tuff ytt at 74 ka eruption of the three older toba tuffs alternated from calderas situated in northern and southern portions of the present caldera the northern caldera apparently developed upon a large andesitic stratovolcano the calderas associated with the three older tuffs are obscured by caldera collapse and resurgence resulting from eruption of the ytt samosir island and the uluan block are two sides of a single resurgent dome that has resurged since eruption of the ytt samosir island is composed of thick ytt caldera fill whereas the uluan block consists mainly of the oldest toba tuff ott in the past 74000 years lava domes have been extruded on samosir island and along the caldera s western ring fracture this part of the ring fracture is the site of the only current activity at toba updoming and fumarolic activity the toba eruptions document the growth of the laterally continuous magma body which eventually erupted the ytt repose periods between the four toba tuffs range between 0 34 and 0 43 m y and give insights into pluton emplacement and magmatic evolution at toba

radiometric ages and paleomagnetism of the sigura gura formation upper part of the toba tuffs in sumatra indonesia abstract a radiometric age determination by means of k ar and fission track method was carried out on the sigura gura formation upper part of the toba tuffs in sumatra indonesia the results are as follows 1 k ar age 0 96 0 15 ma 2 fission track ages by re etched method of external crystal surface are 1 11 0 12 and 1 11 0 14 ma 3 fission track ages by external detector method of crystal surface are 0 87 0 09 and 0 86 0 10 ma 4 the paleomagnetic polarity of the sigura gura formation is reversed so this reversed polarity surely belongs to the matuyama reversed epoch though it was previously correlated with the blake event in the brunhes normal epoch 5 the ash flow deposit which was the uppermost part of the sigura gura formation shows the youngest fission track age 0 03 0 01 ma in previous and this works so this must be a different unit called the porsea formation which overlies the sigura gura formation 6 the porsea formation may be a product of the same volcanic activity which erupted the toba ash layer identified in the deep sea sediments at about 0 075 ma ago 7 in addition six fission track age values were obtained from the younger toba tuffs of toba volcanic complex they are dated at 0 62 0 1 ma

ambient seismic noise tomography reveals a hidden caldera and its relation to the tarutung pull apart basin at the sumatran fault zone indonesia abstract we analyzed the noise recordings of a short period seismic network to derive a shallow crustal s wave velocity model at the sumatra fault in northern sumatra indonesia by correlating the noise of 40 seismic stations recording for 9 months we could recover rayleigh waves from vertical component recordings with sufficient signal to noise ratio group velocities of the rayleigh waves could be determined in the period range from 0 71 to 4 4 s these group velocities were used to invert for 2d group velocity maps at specific periods finally the derived group velocity maps were inverted for a 3d s wave velocity model this model shows a region of a strong velocity decrease off the great sumatran fault zone at the northeastern margin of the young tarutung pull apart basin this observed low velocity block coincides with a caldera like morphological feature which is interpreted as the surface expression of a hidden volcanic caldera considering the surface manifestations of geothermal activity around this anomaly we conclude that the caldera is still acting as a heat source on the other hand the weak morphological expression at the surface indicates a certain age of the caldera which might be older than the tarutung pull apart basin the findings provide important constraints on general concepts for the formation of pull apart basins along the sumatran fault and their relation to volcanism