temporal spatial distribution and tectonic implications of the batholiths in the gaoligong tengliang yingjiang area western yunnan constraints from zircon u pb ages and hf isotopes abstract considerable progress has recently been made regarding temporal and spatial distribution of magmatism in the lhasa terrane however the eastward and southeastward correlation of these tibetan magmatic suites in western yunnan and burma remains poorly constrained this paper reports zircon u pb dating and hf isotopic compositions of granites in the gaoligong tengliang yingjiang area west yunnan it reveals three episodes of plutonism and more importantly a southwestward magmatic migration the gaoligong batholiths in the northeast were mainly emplaced during early cretaceous 126 121 ma and comprised predominantly s type granites with negative zircon ehf values ehf 2 12 the tengliang granites situated southwest of the gaoligong belt were emplaced in late cretaceous 68 76 ma and also displayed a strong peraluminous affinity and negative ehf 5 14 indicating a provenance from a proterozoic sedimentary source with little mantle contribution the youngest phase of magmatism 52 66 ma occurred in yingjiang southwestmost of the study area it is composed of s type granites ehf 2 12 in east yingjiang and i type granites ehf 4 6 in west yingjiang near the china burma border the late cretaceous early cenozoic plutons in the tengliang and yingjiang area are thus considered as the northern continuation of the late cretaceous magmatic arc west which comprises i type granites and andesitic rocks and of the belt of predominant s type granites east in burma thailand and malaysia such a chemical polarity of the dual i type and s type granites is strongly reminiscent of the northern american cordillera indicating a cordilleran style continental margin during the late cretaceous early cenozoic while the magmatic arc was related to eastward subduction of the neo tethys beneath the asian continent the s type granites represented the melting products of thickened crust in the hinterland in response to subduction induced decrease in lithospheric strength and compressive plate convergence forces and to a less degree to the collision between burma and sundaland blocks the gaoligong early cretaceous granites which bear strong similarities in lithology geochemistry and emplacement age to those in the northern magmatic belt in the lhasa terrane are also the magmatic expression of crustal thickening this crustal thickening may have stemmed from the collision between the lhasa block and the qiangtang block in late jurassic and early cretaceous the magmatism in western yunnan thus recorded a long term subduction of the neo tethyan plate enhanced by continental collisions at different time

pumpellyites and coexisting minerals in different low grade metamorphic facies of liguria italy pumpellyite from four phase assemblages pumpellyite epidote prehnite chlorite pumpellyite epidote actinolite chlorite pumpellyite epidote na amphibole chlorite together with common excess phases considered to be low variance in a cao mgo feo al2o3 fe2o3 na2o sio2 h2o system have been examined in areas which underwent metamorphism in the prehnite pumpellyite pumpellyite actinolite and low temperature blueschist facies respectively the analysed mineral assemblages are compared for nearly constant basaltic chemical composition at varying metamorphic grade and for varying chemical composition basic intermediate acidic at constant metamorphic conditions low temperature blueschist facies in the studied mineral assemblages coexisting phases approached near chemical equilibrium at constant basaltic bulk rock composition the mgo content of pumpellyite increases and the xfe3 of both pumpellyite and epidote decreases with increasing metamorphic grade the fe3 being preferentially concentrated in epidote both pumpellyite and epidote compositions vary with the bulk rock composition at isofacial conditions pumpellyite becomes progressively enriched in fe and depleted in mg from basic to intermediate and acidic bulk rock compositions the compositional comparison of pumpellyites from high variance 1 3 phases assemblages in various bulk rock compositions basic intermediate acidic rocks greywackes gabbros shows that the compositional fields of both pumpellyite and epidote are wide and variable broadly overlapping the compositional effects observed at varying metamorphic grade in low variance assemblages the intrinsic stability of both fe and al rich pumpellyites extends across the complete range of the considered metamorphic conditions element partitioning between coexisting phases is the main control on the mineral composition at different p t conditions

palaeomagnetic re investigation of early permian rift basalts from the baoshan block sw china constraints on the site of origin of the gondwana derived eastern cimmerian terranes a palaeomagnetic investigation was carried out on a series of rift basalts woniusi formation that accumulated on the baoshan block sw china in the early permian the aim being to provide quantitative palaeogeographical information on the eastern cimmerian terrane as it detached from eastern gondwana reliable data were obtained from four locations 28 individual cooling units and when combined with the findings of an earlier study three locations 19 sites indicate that breakup occurred at 41 9 s with errors 34 2 51 2 s using this information we fit baoshan against gondwana within a narrow longitudinal belt close to where northeast greater india and northwest australia were once in close proximity furthermore we suggest that sibumasu simao burma malyasia sumatra the largest of the eastern cimmerian blocks lay directly to the east offshore of australia qiangtang and lhasa almost certainly sat to the west off northern greater india se arabia but we are uncertain as to their exact configuration our findings are compared with several rather different models that have been published in recent years the new palaeomagnetic constraint highlights the flexibility authors currently have in reconstructing the region principally because of the overall lack of similar high quality data from the various blocks we explain how new data could resolve these ambiguities thereby offering more robust explanations for eastern gondwana s late palaeozoic development

intraplate extension prior to continental extrusion along the ailao shan red river shear zone left lateral movement of the ailao shan red river shear zone lends support to the hypothesis of continental extrusion resulting from the collision of india with asia our new observations from northwestern yunnan china and northwestern vietnam on different sides of the shear zone demonstrate that the sinistral offset was 600 km according to correlations of permian triassic flood basalt successions and late paleogene highly potassic mafic magmas we conclude that the shear was propagating on the south china continental margin and does not correspond to a suture between south china and indochina furthermore the highly potassic magmas were emplaced from ca 40 to 30 ma before the shear movement which was caused by the late oligocene to early miocene ca 27 22 ma extrusion activity this suggests that a late eocene to early oligocene intraplate extension possibly induced by delamination of thickened continental lithosphere took place in northwestern yunnan or eastern tibet as a response to the india asia collision this extension and sea floor spreading of the south china sea that began ca 30 ma could have accounted for the initiation of the ailao shan red river shear zone

paleomagnetic versus gps determined tectonic rotation around eastern himalayan syntaxis in east asia abstract northward indentation of the indian plate has brought about significant tectonic deformation into east asia a record of long term tectonic deformation in this area for the past 50 m yr particularly the vertical axis rotation is available through paleomagnetic data in order to depict rotational deformation in this area with respect to eurasia we compiled reliable paleomagnetic data sets from 79 localities distributed around eastern himalayan syntaxis in east asia this record delineates that a zone affected by clockwise rotational deformation extends from the southern tip of the chuan dian fragment to as far as the northwestern part of the indochina peninsula a limited zone that experienced a significant amount of clockwise rotation after an initial india asia collision is now located at 23 5 n 101 e far away from an area 27 5 n 95 5 e where an intense rotational motion has been viewed by a snapshot of gps measurements this discrepancy in clockwise rotated positions is attributed to southeastward extrusion of the tectonic blocks within east asia as a result of ongoing indentation of the indian plate a quantitative comparison between the gps and paleomagnetically determined clockwise rotation further suggests that following an initial india asia collision the crust at 30 n 94 e paleoposition was subjected to southeastward displacement together with clockwise rotation which eventually reached to present day position of 23 5 n 101 e implying a crustal displacement of about 1000 km during the past 50 m yr

miocene jiali faulting and its implications for tibetan tectonic evolution the karakoram jiali fault zone kjfz comprises a series of right lateral shear zones that southerly bound the eastward extrusion of northern tibet relative to india and stable eurasia here we present new 40 ar 39 ar age data from the puqu and parlung faults two easternmost branches of the jiali fault zone which indicate a main phase of the kjfz shearing from v18 to 12 ma thus the tibetan eastward extrusion bounded by principal strike slip fault zones started and was probably most active around the middle miocene an interval marked also by active east west extension in southern tibet the coincidence of these two tectonic events strongly suggests a common causal mechanism which is best explained as oblique convergence between india and asia under the framework of this mechanism the extension in southern tibet is not a proxy for the plateau uplift the kjfz activity was furthermore coincident with right lateral displacements along the gaoligong and sagaing faults in southeast asia this defines a miocene deformation record for the regional dextral accommodation zone that in response to the continuing india asia collision may have accounted for the initiation and prolonged history of clockwise rotation of the tibetan extrusion around the eastern himalayan syntaxis 2002 elsevier science b v all rights reserved

mass transport processes on amazon cone western equatorial atlantic three large mass transport deposits occur on the upper to middle amazon cone these slump debris flow complexes have been mapped from 3 5 khz echograms and cover approximately 75 000 sq km or about 10 of the cone the debris flows traveled down slopes with gradients as low as 1 90 to 1 165 0 3 to 0 6 for distances up to 300 km these deposits average 10 to 50 m in thickness and the total amount of sediments displaced may exceed 3 800 cu km the upslope parts of these complexes generally consist of hummocky slump or slide deposits which are commonly bounded by scarps of varying relief downslope from this zone of removal the deposits consist of thin the occurrence of such widespread mass movements on the amazon cone indicates that mass transport is probably an important sedimentation process on deep sea fans however most studies and models of modern deep sea fans have minimized or ignored the potential importance of mass transport processes in fan development we suggest that in the future both ancient and modern deep sea fans be more closely examined for mass transport deposits so that the importance of this process to overall fan development can be more accurately assessed

deep water density current deposits of delaware mountain group permian delaware basin texas and new mexico the guadalupian delaware mountain group is a 1 000 1 600 m 3 281 5 250 ft thick section of siltstone and sandstone deposited in a deep water density stratified basin surrounded by carbonate banks or reefs and broad shallow evaporite clastic shelves the most prevalent style of basinal deposition was suspension settling of silt laminated siltstone beds are laterally extensive and cover basin floor topographic irregularities and flat floored channels as much as 30 m 99 ft deep and 1 km or more wide channels can be observed in outcrop at the basin margin and can be inferred from closely spaced wells in the basin the channels are straight to slightly sinuous trend at high angles to the basin margin and extend at least 70 km 43 mi into the basin sandstone beds con ined to channels form numerous stratigraphic traps hydrocarbon sealing beds are provided by laminated organic siltstone which laterally can form the erosional margin where channels are cut into siltstone beds thick beds of very fine grained sandstones fill the channels these sandstones contain abundant large and small scale traction current produced stratification these sandy channel deposits generally lack texturally graded sedimentation units and show no regular vertical sequence of stratification types or bed thickness outcrop and subsurface evidence indicates delaware mountain group sediments were deposited by saline density currents dense saline water originated on evaporitic shelves and spilled across the carbonate rim down steep marginal slopes and into the basin basinal waters were density stratified denser flows moved along the basin floor cutting channels or depositing sand in existing channels less dense flows moved along density interfaces in the water column and carried silt size material far into the basin where it settled to the floor as thin alternating layers of detrital silt and organic debris little proximal to distal change occurred in the size or nature of the channels exploration predictions based on submarine fan models formed by turbidity currents would anticipate very d fferent proximal distal changes in sandstone geometry and facies

seismic stratigraphy and sedimentation of magdalena fan southern colombian basin caribbean sea analysis of all available seismic data from the magdalena fan in the southern colombian basin caribbean sea allows subdivision of the sedimentary section into six seismic sequences units although sediments were deposited in the present day magdalena fan region since about late cretaceous terrigenous sedimentation became significant only in the late cenozoic during deposition of the upper three sequences associated with the uplifts of the andes these upper three sequences comprise the magdalena fan proper the uppermost sequence probably represents the last main phase of sedimentation subsequent to the major uplift of the andes in the pliocene the morphologic and shallow acoustic 3 5 khz characteristics of this fan unit are upper fan 1 60 1 110 gradients chann ls having well developed levees and several subbottom reflectors in all areas except in channels middle fan 1 110 1 200 gradients numerous channels with very subdued levees and several to few subbottom reflectors lower fan 1 250 gradients small channels relatively smooth sea floor and few or no subbottom reflectors the decrease in number of subbottom reflectors as well as in subbottom penetration downfan apparently results from increasing amounts of coarse grained sediments features in the form of regular hyperbolic echoes and sediment waves are very common in the upper middle and to some extent the lower fan although their heights gradually decrease downfan on multichannel seismic mcs records the upper fan exhibits conspicuous channel levee development and coalesc ng wedge shaped reflection patterns indicative of levee deposits the middle fan is characterized by the presence of chaotic and discontinuous reflection patterns which may have resulted from the presence of numerous channels and hyperbolic features and sediment waves of the type recorded on 3 5 khz records the lower fan region has relatively flat continuous reflections within the topmost seismic unit several episodes of sedimentation can be inferred from mcs records these episodes are probably related to uplifts in the source region lowered sea levels or shifting of the magdalena river delta in space and time subsequent to the major orogeny in middle pliocene a model of sedimentary processes proposed on the basis of the characteristics described visualizes a dominant role for channelized and overbank turbidity current deposition in the upper fan the influence of these currents decreases and that of the unchannelized currents increases downfan on the lower fan deposition by unchannelized turbidity sheet flows forms the dominant mode of sedimentation in addition slumping on the back sides of oversteepened levees and along broad fronts of the continental slope and other downslope mechanisms may also have influenced fan sedimentation significantly

magnetic effects of maghemitization of oceanic crust both theoretical considerations and available experimental results indicate that magnetic effects of maghemitization are strongly dependent on the grain size of the originally unoxidized titanomagnetite maghemitization of single domain titanomagnetite results in a decrease in coercivity an increase in susceptibility and a large decrease in q ratio maghemitization of multidomain titanomagnetite results in an increase in coercivity a decrease in susceptibility and no large changes in q ratio single domain titanomagnetite is probably resistant to the development of a chemical remanent magnetization crm whereas multidomain titanomagnetite can acquire a crm during maghemitization the behavior of pseudo single domain titanomagnetite which is the main carrier of remanence in submarine extrusive rocks is investigated by comparing the magnetic properties of the french american mid ocean undersea study famous less than 0 1 m y old and the leg 37 3 5 m y old pillow basalts recovered from the mid atlantic ridge near 37 n combining electron microprobe analyses curie temperature measurements and cell edge determinations we find that the famous rocks are already oxidized z 0 38 possibly as a result of some high temperature maghemitization during cooling of the magma comparison with the more highly oxidized z 0 7 leg 37 pillow basalts indicates that low temperature maghemitization of such rocks does not result in appreciable changes of coercivity and susceptibility although the q ratio does decrease and crm seems to be acquired such a crm could account for the anomalously low magnetic inclinations observed at most of the leg 37 sites

biodegradation of tar sand bitumens from the ardmore anadarko basins oklahoma ii correlation of oils tar sands and source rocks abstract in an earlier paper we reported the effects of biodegradation on tar sand bitumens from the southern part of the ardmore and anadarko basins in this paper we wish to describe geochemical correlations that have been made between the tar sand bitumens and oils produced from various formations in the pauls valley area 25 miles to the north it was determined that the tar sands were formed from a source similar to many of these oils whose reservoir ages ranged from ordovician to pennsylvanian the oils had been previously divided into two major groups on the basis of their biomarker distributions with one group 80 of the oils studied proposed to have been sourced from the woodford shale devonian and the other group from the viola limestone ordovician the tar sand bitumen oil correlation study based on hydrocarbon and porphyrin biomarker distributions and pyrolysis gas chromatography of asphaltenes has shown that the tar sand bitumen appears to be genetically related to the group of oils derived from the woodford shale and more specifically to those present in the oil creek formation ordovician of the anadarko basin

compositional variations of cretaceous pumpellyites along the western margin of south america and their relation to an extensional geodynamic setting pumpellyites in pervasively altered basic to intermediate rocks from three cretaceous andean volcanic sequences the colombian diabasic group the ecuadorian peruvian celica formation casma group and the chilean ocoite group were studied to test their compositional behaviour in relation to changes in geodynamic setting they occur mostly in assemblages of the prehnite pumpellyite facies filling amygdules and inside plagioclase phenocrysts a pumpellyites from the three geodynamic settings define three distinct compositional fields in afm space i those in the diabasic group plot closer to the fe corner ii those in the ocoite group plot closer to the al corner iii those in the celica formation casma group plot between and partly overlapping fields i and ii b pumpellyites in group i formed in t morb like k poor tholeiites high fe al affected by ocean floor metamorphism in an oceanic back arc basin pumpellyites in group ii generated in k rich calc alkaline low fe al to shoshonitic metabasites affected by burial metamorphism in an ensialic aborted marginal basin with moderate attenuation of the continental crust pumpellyites in group iii formed in basic and intermediate calc alkaline to tholeiitic rocks metamorphosed in ensialic marginal basins with various degrees of continental crust thinning from splitting to moderate attenuation a correlation between pumpellyite and host rock composition is suggested by these characteristics c pumpellyites in prehnite pumpellyite facies assemblages of some of the units studied plot inside higher and lower grade reference fields afm space corresponding to different geodynamic settings elsewhere this anomaly is attributed to the changing characteristics of the marginal basins at the south american margin and emphasizes the need to compare equal facies referred to equal settings

first global positioning system results in northern myanmar constant and localized slip rate along the sagaing fault we present the first recorded global positioning system gps data from myanmar measured at the northern tip of the sagaing fault this area is in a very complex geodynamic context where rigid and semirigid plates interact the 12 gps sites measured in 2005 and 2008 in northern myanmar show that the slip rate is 18 mm yr and is localized along a single active narrow fault trace 20 km wide the same rate was previously demonstrated and remeasured 500 km southward in central myanmar despite the geodynamic regional complexity induced by interaction between the sunda and india plates the burma microplate and the highly deformable eastern himalayan syntaxis the slip rate remains surprisingly constant along this fault however the modeled locking depth varies from 20 km in central myanmar to 5 km in the north

the pumpellyite actinolite and contiguous facies in part of the phyllite quartzite series central northern peloponnesus greece variations in assemblage and composition of the constituent minerals in basic and intermediate metavolcanics encountered in the zarouchla group of the phyllite quartzite series are consistent with a progressive sequence corresponding to temperature conditions estimated at 290 380 c minimum values under a total pressure greater than 3 5kbar and possibly as high as 5 kbar in the absence of more critical evidence the parageneses recorded in the metavolcanic rocks are interpreted as belonging to a prograde facies series from the lawsonite albitechlorite facies through the pumpellyite actinolite facies to the greenschist facies the present distribution of mineral assemblages does not show a simple increase of metamorphic grade in a given direction but is apparently related to the tectonic evolution of the metamorphic sequence

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

late cenozoic to recent transtensional deformation across the southern part of the gaoligong shear zone between the indian plate and se margin of the tibetan plateau and its tectonic origin abstract within the southeastern part of the tibetan plateau the gaoligong shan shear zone forms the boundary between the tengchong and baoshan blocks and is one of the main cenozoic strike slip fault systems of the eastern himalayan syntaxis the mountain ranges rise to a maximum elevation of 3623 m with a width of 20 km and a length of 400 km the core of the shear zone consists of a narrow belt of mylonitic rocks with right lateral strike slip fabrics formed during the northward movement of india relative to eurasia in oligocene and miocene time to the south the mountains decreases in elevation and end against the wanding fault the latter is one of a series of ne sw striking active left lateral strike slip faults within the southeastern part of the tibetan plateau the cause and timing for the change in elevation of the gaoligong shan is unknown but based on our recent structural and fission track geochronological work the decrease in elevation is the result of east west extension across the southern part of the gaoligong shear zone inferred from the late cenozoic and active normal faults along its eastern and western boundaries southward the eastern boundary fault system merges with a series of splays of the wanding strike slip fault while the western boundary fault system is bent into parallelism with the wanding fault this geometric relationship suggests that the normal faulting along the eastern and western boundary of the gaoligong shear zone was caused by transfer of the ne sw left lateral movement along the wanding fault into e w extension on faults to the northeast the resultant normal faulting caused the lowering of the topography in the southern part of the shear zone fission track data from 11 samples from the mylonitic rocks in the footwall of the ruili oblique slip fault left lateral thrust slip yielded ages between 8 4 and 0 9 ma coeval with volcanism within the jietou and mangbang basins the left lateral strike slip movement along the wanding and ruili faults is interpreted to have accommodated differential clockwise rotation of the gaoligong shear zone and its adjacent tectonic units during late cenozoic to recent time during the northward movement of the indian plate with respect to the southeastern margin of the tibetan plateau along the right lateral sagaing fault

origin and history of the oils in the lawton oil field southwestern oklahoma the lawton oil field is located on the wichita mountain uplift in southwestern oklahoma this study focused on addressing three problems related to the lawton oil field a what is are the source s of the oils b have the oils been subjected to alteration since emplacement and c what is the filling history of the field eighteen oils and one seep sample were collected and characterized by a variety of geochemical techniques including bulk composition biomarkers and stable carbon isotopes in order to address these questions source rocks in this region are absent following the pennsylvanian age wichita orogeny but biomarkers and stable isotopic data suggest the source of these oils is probably the woodford shale despite the fact that all of these oils were recovered from reservoirs at depths between 125 and 1 000 ft 38 and 305 m none of them appeared to be extensively biodegraded as manifested by the abundance of the complete range of n alkanes however the presence of 25 norhopanes in all eighteen samples suggests that these oils are mixtures of various proportions of degraded and non degraded or slightly degraded oils the seep sample and some oils have a relatively high abundance of the c32 22r hopanoic acid relative to the c31 22r hopanoic acid with the presence of these 22r hopanoic acids suggesting the oils have been degraded aerobically at some point in their history it was also noted that the concentration of the c31 22r hopanoic acid is higher in the shallower reservoirs than in the deeper reservoirs possibly indicating slightly higher levels of degradation in the shallower reservoirs compared to the deeper reservoirs a hydrocarbon accumulation model has been proposed for this field based on two main reservoir charging periods the initial charge of crude oil was biodegraded probably under anaerobic conditions the second charging period took place after or together with the uplift of the wichita mountains and subsidence of the southern part of the anadarko basin leading to deeper burial of the source rock and production of higher maturity oil which subsequently filled the reservoirs containing the degraded oil and may still be recharging these shallow reservoirs today

velocity field in asia inferred from quaternary fault slip rates and global positioning system observations we perform a joint inversion of quaternary strain rates and 238 global positioning system gps velocities in asia for a self consistent velocity field the reference frames for all geodetic velocity observations are determined in our inversion procedure india in moves relative to eurasia eu about a pole of rotation at 29 78 n 7 51 e 0 353 myr 1 which yields a velocity along the himalaya within india that is 73 76 of the magnitude of the in eu nuvel 1a velocity and a vector azimuth that is 8 10 clockwise of nuvel 1a in eu vector azimuth relative to eurasia south china moves at 9 11 mm yr in the direction 110 120 with a pole position 64 84 n 156 74 e 0 12 myr 1 amurian block motion has a pole position in a similar location but at a slower rate 64 61 n 158 23 e 0 077 myr 1 and most of the amurian eurasia motion is accommodated by extension across lake baikal tarim basin moves relative to eurasia about a pole of rotation at 39 24 n 98 2 e 0 539 myr 1 and 16 18 mm yr of shortening is accommodated across the west central tien shan there is distributed e w extension throughout both southern and north central tibet within southern tibet between the longitudes of 77 e to 92 e the deformation field accommodates 16 19 mm yr of e w extension we compare predicted seismic moment rates with those observed in this century in asia total observed seismic moment rates within the entire area of central and east asia 2 2 107 km2 in this century are 2 26 0 7 1020 n m yr 1 as compared with a predicted total rate of 2 03 0 066 1020 n m yr 1 comparisons between observed and predicted moment rates within 42 subregions reflect the generally unstable process of inferring long term seismic moment rates from a catalog of limited duration 94 years an observation period of 10 000 years would be required to reduce uncertainties in observed seismic moment rate to the same size as the uncertainties in model tectonic moment rates inferred from the joint inversion of gps and quaternary rates of strain we show that in general a better correlation with model tectonic moment rate is inferred from the seismicity catalog by considering the numbers of earthquakes above a cutoff magnitude mb 5 0 for the period january 1 1965 to january 1 1999

paleomagnetic study of cretaceous rocks from pu er western yunnan china evidence of internal deformation of the indochina block abstract cretaceous red sandstones and siltstones were collected at 31 sties for paleomagnetic investigation from the jingxing and nanxin formation around pu er 23 0 n 101 0 e western part of yunnan province china in order to examine quantitative amount of tectonic deformation of the simao terrane due to collision of india with asia after stepwise thermal demagnetization the high temperature component magnetization with unblocking temperature of around 680 c is isolated positive field tests show that the high temperature component magnetization from 25 sites is primary for the cretaceous formations a tilt corrected mean direction is d 59 9 i 45 2 with 95 5 1 corresponding to a paleopole at 35 8 n 173 1 e with a 95 5 6 comparison with cretaceous paleomagnetic pole of the whole china block indicates that amount of clockwise rotation in the pu er area is evaluated to be 46 9 with respect to the whole china block which is consistent with large amount of rotation in the mengla and jinggu areas 47 and 66 in the central part of the simao terrane clockwise rotation of the central part is larger by more than 20 compared to the yunlong and yongping areas of northern part of the simao terrane suggesting that the simao terrane experienced internal deformation the southward displacement of the pu er area expected from inclination data is 7 5 6 6 with respect to the chuan dian fragment which is a similar estimate to other areas in the simao terrane and the indochina block while the simao terrane displaced southward by 800 km together with clockwise rotation of 30 as a whole further clockwise rotation occurred in the central part

metamorphic gradients in burial metamorphosed vesicular lavas comparison of basalt and spilite in cretaceous basic flows from central chile partial spilitization of a 9 km thick pile of flood basalts with highly vesicular flow tops gave rise to patterns of secondary mineralogy at different scales a a local pattern of mineralogical variation from the almost unaltered bottom towards the altered top of each flow and b an overall pattern comparing flow tops throughout the pile with changes in mineralogical composition within a sequence of metamorphic zones and facies the local patterns mimic the trend of the overall pattern but are of opposite direction and telescoped thus a gradual ordering and andepletion of the secondary albite and increases in the fe al ratio of epidote and pumpellyite upwards within individual flows are comparable in range to corresponding overall changes downwards throughout several kilometres the mineralogical changes within the flows diminish in range towards the more altered deeper part of the pile

submarine fans and related depositional systems ii variability in reservoir architecture and wireline log character abstract the architecture and heterogeneity of deep marine clastic reservoir systems can be assessed at three scales at the macroscale lateral and vertical variations in the stacking patterns of submarine fans or fan complexes fundamentally affects the shape and scale of a reservoir and its trapping geometry at the mesoscale the distribution and type of architectural elements e g channel levees lobes sheet sands within the fan system have a major impact upon reservoir compartmentalisation and the distribution continuity and connectivity of sand shale bodies finally at the microscale the vertical and horizontal arrangement of reservoir and non reservoir facies and lithotypes defines flow units which fundamentally control fluid flow and production performance each type of submarine fan and related deep marine clastic reservoir system sand rich fans mixed sand mud ramps etc exhibits a predictable arrangement of architectural elements which form the basic building blocks of the system these features control reservoir architecture seismic expression and the geometry of sandbodies and non reservoir section a suite of reservoir architectural models is proposed for different deep marine clastic systems using unpublished and cited data from outcrop and subsurface studies these conceptual models are idealised simplifications which provide a preliminary framework for understanding broad scale reservoir archsitecture and wireline log character within contrasting types of fan and related systems the models are of value in the exploration for turbidite reservoirs by highlighting the risk on reservoir presence and distribution from an appreciation of the architectural style within appraisal and production they provide a basic framework from which an objective reservoir description can be made use of such conceptual analogue models for reservoir description will not adequately reflect the reality and individuality of a specific reservoir their use in understanding detailed reservoir complexity should therefore be approached with caution

the permian fusulinoidean faunas of the sibumasu and baoshan blocks their implications for the paleogeographic and paleoclimatologic reconstruction of the cimmerian continent abstract permian fusulinoidean faunas occur in mainly four stratigraphic levels in the baoshan block of west yunnan and the sibumasu block of southeast asia which constituted part of the eastern cimmerian continent the oldest fauna from the upper part of the dingjiazhai formation in the baoshan block consists of pseudofusulina eoparafusulina and a new boultoniid genus and is assignable to the yakhtashian artinskian the second one which occurs in the basal part of the ratburi limestone and its equivalent strata in the sibumasu block is represented by monodiexodina and is probably referable to the bolorian kungurian the third fauna composed of eopolydiexodina rugososchwagerina yangchienia chusenella jinzhangia and several other genera is dated to the murgabian wordian and occurs in the lower part of the shazipo and daaozi formations in the baoshan block and the main part of the ratburi limestone in the sibumasu block the youngest fauna of probably dzhulfian wuchiapingian age is found in the upper part of the ratburi limestone and contains nanlingella reichelina codonofusiella and a few staffellid genera a smaller foraminiferal genus shanita found from the upper part of the ratburi limestone and the upper part of the shazipo formation is also an important element of the foraminiferal assemblage near the midian dzhulfian capitanian wuchiapingian boundary in the baoshan and sibumasu blocks in the eastern cimmerian continent low generic diversity throughout the permian and the paucity of tethys characterizing neoschwagerinid and verbeekinid genera during middle permian time are two remarkable features of the permian fusulinoidean faunas in the cimmerian continent the generic diversity of permian fusulinoidean faunas in space and time gradually increases from the early permian to late middle permian as well as from the eastern cimmerian areas to western ones the temporal increase of the generic diversity can be explained by the northward drift of the cimmerian continent during permian time in contrast the lower generic diversity of the eastern cimmerian permian fusulinoidean faunas against western ones is possibly due to an oblique arrangement of the continent to paleolatitude thus the western cimmerian continent was more proximal to the tropical tethyan domain than its eastern part in addition the middle permian cimmerian paleobiogeographic region is likely to be subdivided into two subregions the western tethyan cimmerian and the eastern gondwanan cimmerian based on the distribution pattern of verbeekinid and neoschwagerinid fusulinoideans and overall generic diversity the scarce occurrence or total absence of these essentially tethys indicating fusulinoideans in the baoshan and sibumasu blocks suggests that the eastern cimmerian continent was still far from the equatoro tropical cathaysian domain and was probably in a warm temperate or subtropical zone until the end of the permian the eastern cimmerian areas finally migrated into a tropical zone by the late triassic judging from well developed carnian sponge coral buildups in the chaiburi formation in the sibumasu block

braided and meandering submarine fan channel deposits tesnus formation marathon basin west texas abstract exposures of predominantly mid fan channel deposits from the tesnus formation upper mississippian lower pennsylvanian of west texas provide an opportunity to examine possible meandering and braided deposits in a single submarine fan system within the tesnus six fan related sedimentary facies are recognized i amalgamated sandstone without vertical thickness trends ii amalgamated sandstone with thinning upward trends iii massive matrix rich sandstone iv interbedded sandstone and shale v chaotic sandstone and shale and vi black mudrock and chert the arrangement of sedimentary facies the nature of facies contacts and sandstone geometries differ significantly for braided versus meandering channel deposits sheet like braided channel deposits commonly exhibit a more random facies ordering and abrupt facies transitions whereas pod shaped meandering channel deposits commonly possess a more orderly arrangement of facies from base to top facies i vi in sequential order with gradual facies transitions the aforementioned differences in channel deposit characteristics are believed due primarily to variations in the migrational history of the braided abandonment and rapid shifting versus meandering gradual erosion and migration channel networks

kinematics and ar 40 ar 39 geochronology of the gaoligong and chongshan shear systems western yunnan china implications for early oligocene tectonic extrusion of se asia the gaoligong and chongshan shear systems glss and csss in western yunnan china have similar tectonic significance to the ailaoshan red river shear system asrrss during the cenozoic tectonic development of the southeastern tibetan syntaxis to better understand their kinematics and the cenozoic tectonic evolution of se asia this paper presents new kinematic and 40 ar 39 ar geochronological data for these shear systems all the structural and microstructural evidence indicate that the glss is a dextral strike slip shear system while the csss is a sinistral strike slip shear system and both were developed under amphibolite to greenschist grade conditions the 40 ar 39 ar dating of synkinematic minerals revealed that the strike slip shearing on the glss and csss at least began at 32ma possibly coeval with the onset of other major shear systems in se asia the latestage shearing on the glss and csss is dated at 27 29ma by the biotite 40 ar 39 ar ages consistent with that of the wang chao shear zone wcsz but 10ma earlier than that of the asrrss the dextral gaoligong shear zone within the glss may have separated the india plate from the indochina block during early oligocene combined with other data in western yunnan we propose that the baoshan southern indochina block escaped faster southeastward along the csss to the east and the glss to the west than the northern indochina block along the asrrss accompanying with the obliquely northward motion of the india plate during early oligocene 28 36ma during 28 17ma the northern indochina block was rotationally extruded along the asrrss relative to the south china block as a result of continuously impinging of the india plate

stability of ilmenite and titanomagnetite in the presence of carbon dioxide a thermodynamic evaluation the stability of ilmenite and titanomagnetite in the presence of co2 gas was evaluated thermodynamically ilmenite with a composition ilm90hm10 breaks down to the assemblage siderite hematite anatase below 270 c at 1 000 bars and below 300 c at 2 000 bars titanomagnetite with a composition usp50mt50 breaks down to the same assemblage below 345 c at 1 000 bars and below 385 c at 2 000 bars during the low grade metamorphism of basaltic rocks a co2 partial pressure of only a few hundreds bars is sufficient to alter ilmenite and titanomagnetite to the assemblage siderite hematite anatase

the central myanmar burma oil family composition and implications for source abstract geochemical characteristics of 31 miocene through eocene oils seeps an eocene coal and an eocene resin from the central myanmar burma basin system are examined the oils seeps vary widely in api gravity 8 52 sulfur concentration 26 3550 ppm 13 c 27 6 to 23 4 and molecular composition this variability is caused by varying amounts of biodegradation superimposed upon a single genetic oil family and the difference between aliphatic and aromatic hydrocarbon carbon isotope ratios i e 13 c arom 13 c aliph provides a useful gauge of the extent of biodegradation the projected geochemical characteristics of unaltered central myanmar oils are as follows a api gravity 35 37 b s 0 05 0 10 c 13 c aliph 27 8 to 27 6 d 24 ethylcholestanes are the dominant steranes and e 20s 24 ethyldiacholestane various bicadinanes and oleanane are present the ratio of 18 h 22 29 30 trisnorneohopane to 17 h 22 29 30 trisnorhopane t s t m is postulated as a maturity parameter and on this basis relative bicadinane concentration increases and the trans trans trans cis cis trans bicadinane ratio decreases with increasing thermal maturity in this oil set geologic arguments suggest a deep paleogene source for these oils two geochemical arguments that support this inference are a the occurrence of saturated and unsaturated c 15 and c 30 cadinane monomers and dimers in pyrolyzates of an eocene resin and the kerogen from an eocene coal and b identical compound specific carbon isotope ratios for selected isoprenoids and n alkanes in a typical central myanmar oil and the hydrous pyrolyzate expelled from an eocene coal we propose an eocene resinous shale coal source for these oils with the oldest eocene reservoirs filling first and the youngest miocene reservoirs filling last consistent with the observation that the least mature oils are present in the oldest reservoirs according to this model surface seepage and near surface oil could result from subsurface traps that are filled to spillpoint

clockwise rotation of the red river fault inferred from paleomagnetic study of cretaceous rocks in the shan thai malay block of western yunnan china more than 150 samples were collected at 23 sites from the lower cretaceous jingxing formation near the city of yongping 25 5 n 99 5 e which is located on the west side of the red river fault sixteen sites have characteristic directions with a high temperature component above 500 c the high temperature component of magnetization from twelve sites is of pre fold origin and reveals clockwise deflection in declination d 42 0 i 51 1 and 95 15 7 the easterly declination of more than 40 at yongping is consistent with the cretaceous paleomagnetic direction d 45 of chuxiong 25 n 101 5 e which is located on the east side of the red river fault both areas were subjected to about 25 clockwise rotation with respect to the eastern part of the yangtze block since cretaceous time we conclude that the red river fault was rotated through25 16 with respect to the eastern part of the yangtze block associated with rotation of the yongping and chuxiong areas removal of the rotation from the red river fault indicates that the latter and the jinsha suture formed a straight line along n55 w s55 e within the asian continent from vietnam to the tibetan plateau in the present coordinate system during the cretaceous the linear feature of the red river fault and jinsha suture was probably deformed to the present curved shape as a result of collision of the indian continent with the asian continent

a braided distributary system on the orinoco deep sea fan abstract a long range side scan sonar gloria survey has been made of part of the orinoco deep sea fan that abuts against the deformation front of the barbados outer ridge i e in a pre orogenic setting immediately east of the deformation front sinuous channels up to 65 m deep and 3 km wide extend downslope and become very shallow a few metres or less deep and branch into a pattern that resembles stream braiding near the foot of the slope here there is a possible suprafan lobe and an almost flat perched sediment pond dammed by a buried basement ridge in this locality many of the acoustic contrasts on the sonographs are primarily due to differences in sediment type and small scale roughness rather than to variations in slope angle possible debris flows aligned along some of the braided channels have been identified from high resolution profiles this braided system of shallow channels then converges into a single channel that overtops the dam because of their braided nature the internal structure of the resulting deposits is likely to be complex these deposits should eventually be incorporated into the barbados ridge complex in contrast to this pre orogenic setting gloria sonographs also suggest that some orinoco sediment moves down along synclinical axes of folds on the barbados ridge complex i e in a syn orogenic setting

crustal channel flows 1 numerical models with applications to the tectonics of the himalayan tibetan orogen 1 plane strain thermal mechanical numerical models are used to examine the development of midcrustal channel flows in large hot orogens in the models radioactive self heating reduces the viscosity of tectonically thickened crust and increases its susceptibility to large scale horizontal flow channels can be exhumed and exposed by denudation focused on the high relief transition between plateau and foreland we interpret the himalaya to have evolved in this manner channel flows are poorly developed if the channel has a ductile rheology based on wet quartz flow laws and well developed if there is an additional reduction in viscosity to 1019 pa s this reduction occurs from 700 c to 750 c in the models and is attributed to a small percentage of in situ partial melt melt weakening model ht1 provides an internally consistent explanation for the tectonic evolution of many features of the himalayan tibetan orogenic system erosional exhumation exposes the migmatitic channel equivalent to the greater himalayan sequence ghs between coeval normal and thrust sense ductile shear zones corresponding to the south tibetan detachment and the main central thrust systems outward flow of unstable upper crust rotates these shears to low dip angles in the model both the ghs and the lesser himalayan sequence are derived from indian crust with the latter from much farther south similar models exhibit a range of tectonic styles including the formation of domes resembling north himalayan gneiss domes model results are relatively insensitive to channel heterogeneities and to variations in the behavior of the mantle lithosphere beneath the model plateau

biodegradation of tar sand bitumens from the ardmore and anadarko basins carter county oklahoma abstract a series of tar sand bitumens collected from a single shallow well in the ardmore basin carter county oklahoma has been characterized by various geochemical techniques particular emphasis has been placed on determination of variations in biomarker distributions both hydrocarbons and porphyrins as a function of biodegradation the tar sand bitumens have been severely biodegraded and most of the n alkanes low molecular weight cycloalkanes isoprenoid alkanes c27 c29 steranes light aromatics and sulfur compounds have been removed in addition the hopane distributions have been altered to differing degress with the pseudohomolugoues above c30decreasing in concentration prior to the c20 21 the triaromatic steroid hydrocarbons were also altered with preferential removal of 20r epimers c20 21 and c27 28 diasterane and c30 sterane distributions appear to be relatively unaffected by biodegradation the high resistance of tricyclic terpanes the c24 tetracyclic terpane and monoaromatic steroid hydrocarbons to biodegradation indicate that the distributions of these compounds are well suited to serve as correlation parameters in heavily altered samples it was also observed in this study that the main ring structure of the porphyrin molecule was not affected by these very high levels of biodegradation previously hypothesized changes in porphyrin structure due to biodegradation have included n alkyl side chain cleavage and possible conversion from dpep to etio type porphyrins an investigation has also been made with an active seep collected from sulphur in the anadarko basin oklahoma and the results show that the relative rate of biodegradation of various classes of biomarkers differs between these two locations although it was proposed that the original oil responsible for these two seeps is derived from the same source rock formation

northwest trending middle cenozoic left lateral faults in southern yunnan china and their tectonic significance abstract the northwest striking jianshui qujiang and chuxiong faults and probably the zhongdian fault south china show evidence for different amounts of middle cenozoic pre pliocene and post early paleogene left lateral displacement that range from 6 to 25 km the age and orientation of the left lateral faults suggest that the faults are related to a regional deformational event associated with important left lateral shear on the ailao shan shear zone which lies 50 70 km to the south identification of these faults extends left lateral shear during this deformational event farther to the northeast than previously recognized unlike the ailao shan shear zone these faults do not appear to be part of a through going nw trending shear zone these faults are interpreted to be the northernmost part of a nw trending boundary whose main structure the left lateral ailao shan shear zone forms a broad zone of mylonitic rocks bounding a crustal fragment that rotated clockwise around the eastern himalayan syntaxis following middle cenozoic left lateral displacement only the jianshui and qujiang faults exhibited a reversal of displacement in post miocene time this reversal is interpreted to be the result of counterclockwise rotation within the broad n s striking left lateral xiaojiang fault zone none of the post miocene displacement on these two faults appears to be related to post miocene right lateral displacement on the red river fault system the chuxiong fault may have reversed its early left lateral displacement but evidence from surface geology for young and active right lateral displacement is not clear the zhongdian fault appears to have undergone only left lateral displacement some of which may be middle cenozoic in age and some post miocene in age active displacement on the zhongdian fault is interpreted to mark the eastern boundary for a small crustal fragment that rotates clockwise around the eastern himalayan syntaxis

paleomagnetic study of cretaceous rocks from the yangtze block central yunnan china implications for the india asia collision abstract more than 200 samples for this study were collected at 30 sites from the cretaceous matoushan and puchanghe formations around the city of chuxiong 25 n 101 5 e twenty four sites have characteristic directions with a high temperature component above 350 c paleomagnetic directions from 21 sites of the cretaceous formations reveal clockwise deflection in declination d 44 6 i 41 3 and 95 10 7 the reliability of the direction is ascertained through a positive fold test and the presence of normal and reversed polarities comparison with paleomagnetic data from other areas indicates that the chuxiong area was rotated clockwise through26 17 with respect to the eastern part of the yangtze block whereas it was subjected to more than 44 of clockwise rotation with respect to the neighboring blocks of lhasa 56 21 and western sichuan 44 16 since cretaceous time the clockwise rotation of chuxiong is a reflection of rotational motion of the large region including the southeastern qiangtang terrane and the jinsha suture red river fault paleomagnetic data and tectonic features suggest that the rotation occurred prior to the folding in the central yunnan province probably during the paleogene this large rotation is a spectacular example of the deformation in the southeastern part of the asian continent due to the collision of india

quaternary development of channels levees and lobes on middle laurentian fan seismic reflection profiles from the middle laurentian fan show that the western fan valley has an abrupt eastward leftward hook at its terminus the right hand levee of this valley has been built across an older depositional surface in which numerous south trending channels developed before the abrupt bend formed this older channeled surface probably represents a complex depositional lobe deposit eastward deflection of turbidity current flow occurred after debris flow or slide deposits partly obstructed the valley near its termination or after aggradation of the lobe deposits this deflection produced an abrupt change in the valley trend through time the eastward growing part of the levee has migrated northward toward the axis of the channel this northward migrati n confines turbidity current flow against the levee of another valley immediately upfan this study documents progradation of muddy facies over sandy lobes thus providing conditions for an effective seal for any hydrocarbons accumulated in the lobe sands updip migration of hydrocarbons through valley fill sands that are contiguous with the lobes could be blocked locally by thick debris flow units or by fine grained turbidite fill in abandoned channels

petroleum geochemistry of oil and gas from barbados implications for distribution of cretaceous source rocks and regional petroleum prospectivity petroleum produced from the barbados accretionary prism at woodbourne field on barbados is interpreted as generated from cretaceous marine shale deposited under normal salinity and dysoxic conditions rather than from a tertiary source rock as previously proposed barbados oils correlate with some oils from eastern venezuela and trinidad that are positively correlated to extracts from upper cretaceous la luna like source rocks three distinct groups of barbados oils are recognized based on thermal maturity suggesting petroleum generation occurred at multiple levels within the barbados accretionary prism biodegradation is the most significant process affecting barbados oils resulting in increased sulfur content and decreased api gravity barbados gases are interpreted as thermogenic having been co generated with oil and show mixing with biogenic gas is limited gas biodegradation occurred in two samples collected from shallow reservoirs at the woodbourne field the presence of cretaceous source rocks within the barbados accretionary prism suggests that greater petroleum potential exists regionally and perhaps further southeast along the passive margin of south america likewise confirmation of a cretaceous source rock indicates petroleum potential exists within the barbados accretionary prism in reservoirs that are deeper than those from woodbourne field

paleomagnetic analysis of eastern tibet implications for the collisional and amalgamation history of the three rivers region sw china abstract a comparative analysis of paleolatitudes and latitudinal displacements was undertaken for the south china simao baoshan shan thai indochina qiangtang lhasa and himalayan blocks by using available paleomagnetic data to determine the collisional and amalgamation history of the main blocks in the three rivers region western yunnan the results show that 1 the simao block is a south china derived block 2 the baoshan and shan thai blocks were subjected to rapid northward drift during the period from late carboniferous to late permian 3 the baoshan block collided with the simao block in the late permian and continued to drift rapidly northwards together with the south china and shan thai blocks until the late triassic 4 the paleo tethys separating the baoshan and simao blocks was possibly opened in the early silurian 5 the meso tethys ranged in age from early permian time to early cretaceous time and reached its greatest width of about 42 latitude in the late triassic

geochemistry of selected oils and rocks from the central portion of the west siberian basin russia six analyzed oils produced from middle jurassic to upper cretaceous strata in the middle ob region of the west siberian basin show biomarker and stable carbon isotope compositions indicating an origin from the upper jurassic bazhenov formation the chemical compositions of these oils are representative of more than 85 of the reserves in west siberia kontorovich et al 1975 bazhenov sourced oil in cenomanian strata in the van egan field underwent biodegradation in the reservoir resulting in a low api gravity an altered homohopane distribution and the appearance of 25 norhopanes without alteration of the steranes high api gravity oil from the salym field has surpassed the peak of the oil window consistent with abnormally high temperatures and pressures in the bazhenov source rock from which it is produced the remaining oils are very similar including samples from valanginian and bathonian callovian intervals in a sequence of stacked reservoirs in the fedorov field bazhenov rock samples from the study area contain abundant oil prone marine organic matter preserved under anoxic conditions organic matter in a bazhenov core from the pokachev 58 well was compared with the oils because it is thermally mature and shows total organic carbon toc 13 8 wt and hydrogen index values hi 489 mg hc g toc representative of the average for the formation 10 7 wt for 840 samples 420 mg hc g toc for 75 samples other rocks in the middle ob region are far less likely to have generated these oils than the bazhenov formation no prospective source rocks older than middle jurassic were available geochemical analyses indicate a lack of thermally mature hauterivian or younger source rocks in the study area core samples from the lower cretaceous frolov formation either are thermally immature hauterivian or show little oil generative potential berriasian valanginian the upper jurassic vasyugan formation shows lower oil generative potential than the bazhenov formation the average toc for vasyugan rocks is 3 20 wt 240 samples average atomic h c ratios for vasyugan and bazhenov kerogens are 0 90 10 samples and 1 13 25 samples respectively the vasyugan formation cannot be excluded as a source rock because insufficient sample was available for biomarker analysis core from the lower to middle jurassic tyumen formation in the yemyegov 15 well was compared with the oils because it is thermally mature and shows toc and hi values 2 78 wt and 137 mg hc g toc respectively indicating slightly more favorable oil generative characteristics than the average for the formation 2 75 wt for 720 samples 95 mg hc g toc for 25 samples the core contains terrigenous gas prone organic matter that shows no relationship with the analyzed oils

an early india asia contact paleomagnetic constraints from ninetyeast ridge odp leg 121 new paleomagnetic results from sedimentary rock and basement of the ninetyeast ridge ocean drilling program leg 121 sites 756 758 detail the northward movement of the indian plate for the past 80 m y analysis of the combined paleolatitude age profile indicates a distinct reduction in india9s northward movement rate at 55 ma interpreted as completion of suturing of greater india and asia india9s northward motion slowed from 18 19 5 cm yr to 4 5 cm yr for the location of site 758 comparison of this profile with paleomagnetic data from the wider himalayan region indicates that initial contact between northwestern greater india and southern asia was already established by cretaceous tertiary time this supports a possible causal link between the india asia convergence and the deccan traps extrusion

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

low temperature magnetic behavior of titanomagnetites titanium substitution has a significant effect on the temperature dependence 5 300 k of low temperature saturation remanence and of initial susceptibility in synthetic and natural titanomagnetite fe3 xtixo4 0 x 0 4 and electronic and lattice relaxation phenomena over the entire titanomagnetite compositional range these features produce diagnostic magnetic behavior useful for titanomagnetite identification in natural samples moreover the apparent similarities between the thermal decay of low temperature remanence of titanomagnetite with pyrrhotite pure magnetite and superparamagnetic phases can lead to complications in interpreting low temperature remanence data when titanomagnetite is present

biodegradation scales applications and limitations abstract biodegradation schemes based on the sequential removal of hydrocarbons are commonly applied to indicate the level of degradation that a petroleum accumulation may have experienced but inconsistent patterns of degradation are typically seen if large data sets are examined and oil mixing greatly complicates any attempt at seeking a globally consistent biodegradation scheme in the athabasca oil sands province degradation of steranes diasteranes and hopanes can occur simultaneously along with the formation of 25 norhopanes highlighting the difficulties towards assigning a degradation level to reflect the degree of compositional alteration experienced by a heavy oil or bitumen in addition the aromatic hydrocarbons such as the methyl phenanthrene isomers show differential susceptibility to degradation whilst the 9 methylphenanthrene 9 mp may show selective resistance to degradation compared to 1 methylphenanthrene 1 mp we have also seen that 9 mp may be removed prior to 1 mp in some cases both 9 mp and 1 mp may be strongly removed in comparison with the 3 and 2 methylphenanthrenes the complex interplay of charge history reservoir environment e g presence absence of water legs and extent and mass transport mechanics of the basal biodegradation reaction zone are most likely to have led to the many and varied petroleum compositions that are a feature of the athabasca tar sands and many other degraded oil provinces

fluvial features in the deep sea new insights from the glacigenic submarine drainage system of the northwest atlantic mid ocean channel in the labrador sea abstract side scan sonar imagery and seismic profiles from the submarine drainage system of the northwest atlantic mid ocean channel namoc of the labrador sea reveal the presence of a variety of fluvial features in the deep sea the analogies extend from meso scale features to the basin wide drainage pattern at basin scale the namoc submarine drainage system consists of downslope converging tributary canyons on the slope and yazoo type tributary channels joining a central trunk channel on the basin floor in detail the following fluvial features have been observed in namoc and its tributaries meandering and braided channels and talwegs point bars some with meso scale bedforms terraces wash over fans submarine hanging valleys and chute pools and levee gullying and slumping some of these features are new and have not been recognised before in the deep sea others have not been documented in comparable detail previously although the similarity of deep sea turbidite depositional features with fluvial features has long been recognised in the literature fundamental differences exist between turbidite and fluvial facies associations the most noticeable of which is the lateral juxtaposition of a meandering deep sea channel and a submarine braidplain the latter has only been established for a glacigenic submarine drainage system the analogy with fluvial processes may be used in the quantification of flow processes of large scale natural turbidity currents

oxide sulphide relationships in sodalite bearing metasomatites of the epembe swartbooisdrif alkaline province north west namibia the south eastern part of kunene intrusive complex kic namibia angola is host to volumetrically significant and economically important concentrations of sodalite in the area around swartbooisdrif north west namibia the mineralisation was formed by metasomatic exchange with carbonatites of the epembe swartbooisdrif alkaline province this process led to the breakdown of ore minerals initially present in various rock types of the kic and caused the formation of new opaque phases in the sodalite bearing metasomatites a detailed investigation of textures and chemical compositions of the fe ti oxides and sulphides has allowed evaluation of the complex ore forming processes related to the polyphase magmatic and metasomatic history of the sodalite deposit the predominant opaque phases in the various rock types of the kic are ilmenite and titano magnetite which are highly concentrated in the so called magnetite plugs it is clear from the textural evidence that most of the ilmenite and titano magnetite although of orthomagmatic origin recrystallised under subsolidus conditions conformably their respective chemical compositions and phase relations represented in the system feo 1 2fe2o3 tio2 point to re equilibration at temperatures below 600 c ilmenite and titano magnetite were affected by later deformation and decomposed by various reactions related to or outlasting the metasomatic process oxidation of ilmenite led to the formation of symplectitic aggregates of rutile and secondary magnetite carbonatisation of the fe ti oxides produced rutile and the siderite and rhodochrosite components in ankerite pyrite in part together with rutile and secondary magnetite was formed by sulphidation of the fe ti oxides conspicuous aggregates of granular or lamellar intergrowths of pyrite with hematite and or magnetite are interpreted as products of contemporaneous sulphidation and oxidation of former igneous pyrrhotite rarely observed pyrrhotite with pentlandite lamellae is probably not an igneous relic but was formed during the metasomatic event smaller amounts of chalcopyrite bornite digenite chalcocite galena ferroan siegenite millerite and polydymite testify to different cooling stages during or after metasomatism applying the phase relations in the simplified system fe co ni s o we were able to reconstruct a semi quantitative t f s2 f o2 path for the ore forming processes

microbial degradation of aromatic components of crude oils a comparison of laboratory and field observations abstract small aliquots of crude oil brent north sea were incubated aerobically for periods of up to 14 days with an inoculum of recent sediment the saturated and aromatic hydrocarbon components were then isolated and the latter were compared by capillary gas chromatography with similar fractions isolated from four oils from the barrow sub basin of western australia which had experienced different degrees of biodegradation biodegradation of the aromatic hydrocarbons of brent oil produced a series of altered oils whose compositions were comparable to those of the naturally reservoir degraded oils compounds such as naphthalene phenanthrene and alkylated homologues of these hydrocarbons were oxidised but individual isomers were oxidised to different extents

pumpellyite bearing rocks in central sweden and extent of host rock alteration as a control of pumpellyite composition metamorphic assemblages and mineral compositions in basic to intermediate volcanic rocks of two precambrian units the sub jotnian and jotnian in the dala region central sweden reveal a history comprising two metamorphic episodes the sub jotnian rocks were metamorphosed during a first episode the metamorphic grade ranges from prehnite pumpellyite facies in a displaced block with sub jotnian lava occurring in the border zone of a major impact structure to pumpellyite actinolite facies and to greenschist facies in the lower part of the unit the unconformably overlying jotnian rocks were metamorphosed to prehnite pumpellyite facies during a subsequent episode which also left its imprint in the sub jotnian basement two other jotnian sequences in central sweden are in the same facies

effect of water washing on crude oil compositions crude oils from venezuela oklahoma and new mexico were water washed in the laboratory at temperatures from room temperature to 80 c and with water salinities from 0 to 300 000 mg l in experiments lasting from 7 to 338 hours the effects of water washing were determined by gas chromatographic and gas chromatography mass spectrometric analysis of the residual oil these experiments show that water washing is particularly effective for the c15 fraction and hydrocarbons are removed in the sequence aromatics then n alkanes then naphthenes in the c15 fraction no loss of pristane phytane steranes or terpanes occurs but some aromatics and sulfur compounds especially dibenzothiophene are depleted although water washing reduces api gravity water washing is unlikely to produce tar layers the effects of water washing were simulated with a numerical model based on the equation of diffusion predicted oil water ratios were in good agreement with the experimental values for the light ends and the model suggests that water washing is very fast in the subsurface comparison of oils that appeared to have been water washed in nature with the equivalent unwashed oils showed the expected compositional trends water washing is probably the dominant process affecting crude oil composition in the subsurface when water flows past oils under conditions where bacterial degradation is precluded by temperature 80 c or by lack of dissolved oxygen and the temperatures are too low for thermal cracking

timing of india asia collision geological biostratigraphic and palaeomagnetic constraints 1 a range of ages have been proposed for the timing of india asia collision the range to some extent reflects different definitions of collision and methods used to date it in this paper we discuss three approaches that have been used to constrain the time of collision the time of cessation of marine facies the time of the first arrival of asian detritus on the indian plate and the determination of the relative positions of india and asia through time in the qumiba sedimentary section located south of the yarlung tsangpo suture in tibet a previous work has dated marine facies at middle to late eocene by far the youngest marine sediments recorded in the region by contrast our biostratigraphic data indicate the youngest marine facies preserved at this locality are 50 6 52 8 ma in broad agreement with the timing of cessation of marine facies elsewhere throughout the region double dating of detrital zircons from this formation by u pb and fission track methods indicates an asian contribution to the rocks thus documenting the time of arrival of asian material onto the indian plate at this time and hence constraining the time of india asia collision our reconstruction of the positions of india and asia by using a compilation of published palaeomagnetic data indicates initial contact between the continents in the early eocene we conclude the paper with a discussion on the viability of a recent assertion that collision between india and asia could not have occurred prior to 35 ma

deep sea fan deposits in the macigno formation middle upper oligocene of the gordana valley northern apennines italy abstract facies characteristics are described for a 2300 m thick turbidite succession of the macigno formation middle upper oligocene which crops out as a continuously exposed section in the gordana valley northern apennines in the study area the macigno formation consists of two sandy members separated by a shaly member the sandy members contain lithic associations characteristic of submarine fan deposits and form distinct fan complexes the middle shaly member represents a period of basin starvation three main facies associations are recognized in the macigno fan deposits fan fringe outer fan lobe and braided midfan facies associations the fan fringe deposits consist of monotonous or small scale cyclically arranged thin bedded turbidites the outer fan lobe deposits are composed of medium to very thick bedded classical turbidites internally organized in thickening upward cycles with minor intercalations of thin bedded sandstone beds two distinct types of outer fan lobe deposits distal and proximal are recognized on the basis of rock type internal organization and vertical facies relationships the midfan deposits consist of amalgamated massive sandstone and pebbly sandstone which display repeated thinning upward cycles the three main facies associations are superposed t define major thickening and coarsening upward cycles reflecting distinct episodes of fan progradation the relationships between the facies associations of the macigno deposits and the existing models of submarine fan sedimentation are discussed after the deposition of the fan complexes fan sedimentation in this part of the basin was replaced by movements of allochthonous units heralded by large olistostromes

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

effects of weathering on nickel and vanadyl porphyrins of a lower toarcian shale of the paris basin the effects of weathering on the organic matter within a narrow sediment interval from surficial to 10 m depth belonging to the lower toarcian shales of the paris basin were studied at a molecular level among the compositional changes observed the most striking feature is a severe breakdown of the metalloporphyrins ni and vo at the surface as evidenced by quantitative data in addition this degradation of the geoporphyrins is accompanied by substantial modification of their composition with preferential degradation of porphyrins with exocyclic rings over polyalkylporphyrins these quantitative and qualitative changes are thought to result from exposure of the sediment to weathering conditions more specifically abiotic oxidation is likely to be the main weathering process responsible for this superficial alteration of the sedimentary porphyrins this is particularly suggested by oxidation experiments carried out on a mixture of sedimentary nickel and vanadyl porphyrins where oxidation of the former complexes occurs at a faster rate thus geoporphyrins may be used as molecular indicators to evaluate the degree of oxidation of weathered geological samples containing this kind of molecule

characterization of petroleum source rocks and shales by pyrolysis gas chromatography mass spectrometry multiple ion detection abstract a number of organic rich shales and potential source rocks from australia and alaska have been examined by pyrolysis gaschromatography mass spectrometry multiple ion detection attempts have been made to observe variations in the distributions of biomarkers released from the samples by pyrolysis particular emphasis has been placed on the release of pentacyclic triterpanes to evaluate whether or not a one step pyrolysis method can be used to determine relative maturity of the samples immature shales are observed to produce c27 and c29 hopenes not present at higher levels of maturity as well as number of hopanes and moretanes variations in the distributions of alkylbenzenes alkanes alkenes sesquiterpenoids and diterpenoids can also be monitored during the pyrolysis reaction and provide information on the nature of the source material in the samples

pumpellyite from zeolite facies metabasites of the horokanai ophiolite in the kamuikotan zone hokkaido japan pumpellyite occures in zeolite facies metabasites of the horokanai ophiolite in the kamuikotan zone hokkaido japan filling veins or amygdules replacing igneous plagioclase or clinopyroxene or olivine and occupying the matrix its composition and pleochroism vary greatly even within a single sample but appear to be related to its mode of occurrence thus the most al rich pumpellyite with pale green to green pleochroism develops in pseudomorphs after plagioclase whereas the most fe rich variety with deep green to brown pleochroism occurs in the matrix in low grade metamorphic rocks which commonly contain relict minerals chemical equilibrium is attained only locally this results in the correlation of the composition of pumpellyite with its mode of occurrence such as the precursor phases which are replaced by pumpellyite on the other hand among pumpellyites occurring in similar mode and coexisting with ca zeolite laumontite or wairakite epidote chlorite and quartz the al content tends to be enriched in the wairakite bearing metabasites over the laumontite bearing metabasites it follows that the composition of pumpellyite is also dependent upon the temperature of metamorphism

origin and migration pathway of biodegraded oils pooled in multiple reservoirs of the chepaizi uplift junggar basin nw china insights from geochemical characterization and chemometrics methods abstract the chepaizi uplift possesses three sets of oil bearing reservoirs six sets of source intervals multiple episodes of hydrocarbon charging and variable physical properties of crude oils in this study based on geochemical characterization source intervals and the biodegradation rank of the crude oils four oil populations named as group a b c and d d1 d2 were defined the combined results of q cluster analysis qca and discriminant analysis da indicate that group a occurred mainly in lower neogene shawan formation n1s in the western chepaizi uplift and were primarily derived from the middle lower jurassic xishanyao badaowan sangonghe formations j2x j1b j1s and a little of paleogene anjihaihe formation e2 3a of the sikeshu sag group b occurred essentially in upper carboniferous xibeikulasi formation c2x of the western chepaizi and originated mainly from the j1b mudstone of the shawan sag in addition the crude oils of group c occurred mainly in the lower cretaceous tugulu group k1tg of the eastern chepaizi and were primarily derived from carboniferous sourced oil from the chepaizi uplift the crude oils of groups d d1 and d2 are mixed with permian p1f and p2w of shawan sag and carboniferous sourced oil from the chepaizi uplift based on the reconstruction of the migration history the oils of group a in the n1s formation of western chepaizi migrated predominantly from the south sikeshu sag to the north and northeast with wells su1 2 and c27 as the initial filling points the oils of group b in the n1s formation of the western chepaizi travelled predominantly from the southeast shawan sag to the north and northwest the oils of group d1 in the c2x formation of eastern chepaizi migrated mainly from the northeast and southeast shawan sag to the west with well p661 as the initial filling point wells sm011 and c64 are the initial filling points of the k1tg group in the hongche fault belt crude oils of group c in the k1tg group travelled predominantly from the southeast shawan sag and northeast to the west into the eastern chepaizi and from well p68 to the southwest according to the paleo oil preferential filling orientations and paleogeomorphology some favourable targets for petroleum exploration of the chepaizi uplift are forecast in this study

internal crustal deformation in the northern part of shan thai block new evidence from paleomagnetic results of cretaceous and paleogene redbeds in order to describe the internal deformation of the northeast part of the shan thai block resulting from the penetration of the indian plate into asia a paleomagnetic study was carried out on the cretaceous and paleogene strata in the southern part of the simao terrane high temperature magnetic components with unblocking temperatures around 680 degrees c were isolated and positive fold test shows its primary nature of magnetization the tilt corrected site mean directions of the lower cretaceous and upper cretaceous from the menglun area are d s 46 2 degrees i s 45 9 degrees k 11 0 alpha 95 10 6 degrees and d s 33 2 degrees i s 30 9 degrees k 68 4 alpha 95 8 2 degrees respectively the site mean directions of the upper cretaceous and lower paleogene for the mengban area are d s 50 5 degrees i s 31 0 degrees k 207 6 alpha 95 6 4 degrees and d s 43 5 degrees i s 23 0 degrees k 26 1 alpha 95 13 4 degrees respectively the results of the lower cretaceous and upper paleogene from the mengla area are d s 46 9 degrees i s 42 2 degrees k 27 3 alpha 95 7 7 degrees and d s 41 8 degrees i s 23 8 degrees k 38 9 degrees alpha 95 5 8 degrees respectively in comparison with previous paleomagnetic data of the simao terrane the rotational deformation can be divided into four stages the cretaceous and paleocene sediments of the simao terrane experienced intensive folding before the early oligocene during the early oligocene to early miocene the shan thai and indochina blocks experienced southeastward extrusion with similar to 20 degrees clockwise rotation relative to the south china block during the middle to late miocene the shan thai blocks experienced more 15 degrees clockwise rotation since the late miocene the activity of strike slip faults surrounding the simao terrane enhanced the internal differential rotations of the terrane these deformation processes finally resulted in a complex internal deformation of the simao terrane c 2013 elsevier b v all rights reserved

hydrothermal alumina rich clays and boehmite on the gorda ridge abstract hydrothermal alteration of basalt on the northern gorda ridge produced an alteration crust up to 1mm thick that can be divided into two layers based on mineralogy an inner layer next to the basalt surface is an al rich interlayered smectite chlorite similar to high temperature al rich clays recovered from the east pacific rise 21 n with minor quartz zeolite phillipsite and relict plagioclase an exterior layer of boehmite alo oh and minor anatase results from severe leaching of the underlying clays the alteration crust is progressively enriched in al ti v and cr from interior to exterior by residual weathering the presence of boehmite and absence of a silica rich phase in the exterior of the crust indicates the hydrothermal fluids were silica undersaturated or silica was maintained in solution by extremely acidic fluids this constitutes the first reporting of boehmite as a major alteration mineral in a mid ocean ridge hydrothermal environment

pumpellyite in low grade metamorphic rocks from ligurian and lucanian apennines maritime alps and calabria italy in the ligurian apennines and the brianzonese area of the maritime alps northern italy and in the lucanian apennines and calabria southern italy pumpellyite formed during the alpine metamorphism is widespread in terranes of late paleozoic to miocene age particularly in mafic ophiolites tethyan ophiolites of jurassic early cretaceous age pumpellyite developed under variable metamorphic conditions which include zeolite prehnite pumpellyite pumpellyite actinolite lawsonite albite and blueschist facies pumpellyite from rocks belonging to all these facies was studied in 30 specimens of different chemistry derived mostly from ophiolitic basalt and gabbro but also from gneiss amphibolite and greywacke protoliths microprobe data give evidence of strong compositional variations of pumpellyite the ranges are extreme for al and fetot al2o3 18 74 30 91 feotot 0 46 12 71 to a lesser extent for mg mgo 0 58 4 00 with a reciprocal variation of al and fetot which suggests that most fe is fe3 pumpellyite compositions can be related with the metamorphic conditions particularly an increase of the al fetot ratio with increasing pressure but larger compositional variation for each facies in the al fetot mg diagram than those previously described was recognized particularly the compositions of pumpellyite from the pumpellyite actinolite and blueschist fades assemblages extend towards higher fetot contents moreover pumpellyites of the lawsonite albite facies rocks result to be more aluminous than in blueschist facies such relations appear to be inconsistent with that expected by the effects of pressure on the al content as the rocks are generally incompletely re equilibrated their bulk chemistry is not an important factor of pumpellyite composition in fact the correlations of al fetot and mg are low the local environment of crystallization more evidently the composition of the precursor minerals seems to be a major controlling factor the observed topologic relations indicate that either the nature of the precursor mineral or the presence of relict phases have a great influence on the pumpellyite composition the observed variations within individual specimens as well as the interspecimen ones can be explained by small scale inhomogeneities and in some cases by differences in the activity of o2 it can be therefore concluded that the composition of pumpellyite often reflects disequilibrium crystallization and cannot be generally used as an indicator of metamorphic conditions

sedimentologic development of a late oligocene miocene forearc embayment valdivia basin complex southern chile abstract deposition of tertiary sediments in the southeastern part of the valdivia basin commenced during the late oligocene with the rapid incision of rivers draining the palaeo coastal range alluvial fans developing along the steep valley flanks joined gravelly braided streams transporting bedload to the coast tectonic and eustatic stability lasting into the early miocene subsequently allowed lateral erosion of the valley flanks and the development of extensive fluvial and estuarine peat swamps this stable period was interrupted briefly by a volcanic eruption at 23 5 ma shortly after 23 ma rapid uplift caused by an acceleration in plate convergence resulted in renewed erosion of the landscape as reflected in the deposition of coarse river gravels basin subsidence and marine transgression proceeding up the river valleys subsequently formed still deep embayments occasionally disturbed by debris flows and turbidity currents originating on the steep wooded valley flanks at the upper limits of the inlets bayhead deltas tidal flats and beaches existed in some areas fan deltas prograded into the embayments as reflected in the interfingering relationship between conglomerates and marine mudrocks in the deeper parts of the embayments the frequency of debris flows and turbidity currents increased markedly during periods of relative sea level lowstand the landscape was eventually inundated by continued subsidence and marine transgression which lasted until a possibly eustatic sea level fall in the early tortonian

a dynamic biodegradation model suggested by petroleum compositional gradients within reservoir columns from the liaohe basin ne china abstract a suite of petroleum reservoir extracts from the liaohe basin ne china was analyzed to investigate the effects and controls of biodegradation on petroleum composition systematic changes seen as marked gradients in petroleum bulk composition component concentrations and molecular indicators have been observed in two biodegraded oil columns in the es3 column 1700 1850 m biodegradation has removed substantial amounts of normal and isoprenoid alkanes more severe biodegradation occurs in the shallower es1 column 1500 1650 m with both steranes and hopanes being partially removed temperature has an overall control on biodegradation in the two columns a lower reservoir temperature leading to a higher degree of biodegradation however observed variation in the degree of biodegradation in the es3 column at different sites is controlled by water leg size with a higher level of degradation being associated with a thicker water leg the supply of nutrients from the water leg is thought to have a significant impact upon the degree of biodegradation in addition to water leg size nutrient supply the compositional gradients also are controlled by the relative rate of mixing of fresh oil charge gradients can only be conserved in biodegraded petroleum columns if the rate of diffusive mixing is similar to or lower than the rate at which the hydrocarbons are removed a biodegradation model is proposed that couples geochemical and geological factors to provide a coherent approach for assessing the impact of degradation on petroleum our geochemical study indicates that biodegradation occurs mainly within a narrow region at or near the base of the oil column the stable compositional gradients are produced after an initial induction period involving diffusive transport of alkanes to the oil water contact owc and diffusion of biodegradation products such as 25 norhopanes and other metabolites away from the reaction site the mixing of continuously charged oil with residential biodegraded oil by diffusion may be considered as one of the most important factors controlling the biodegradation process the conceptual model illustrates all of these processes and opens the possibility of model driven prediction of oil properties and sweetspot location in reservoirs

pumpellyites in two low grade metamorphic terranes north of newcastle nsw australia microprobe analyses of pumpellyites from rocks of variable chemistry formed under similar metamorphic conditions in two palaeozoic low grade metamorphic terranes show that they have an extreme range in composition feo 0 9 22 96 and that fe2 mg2 and fe3 al3 are the dominant substitutions a less extreme variation in composition of pumpellyites has been noted in samples taken from a metamorphosed differentiated metadolerite on an a1 fe mg diagram these pumpellyites extend through the fields of high pressure to low pressure terranes indicating that pumpellyite compositions should be used with caution when determining metamorphic conditions

a geochemical investigation of crude oils and source rocks from biyang basin china abstract china has a number of petroliferous lacustrine sedimentary basins of varying salinity and age mainly eocene a geochemical investigation has been undertaken on several oils and source rocks from the eocene lacustrine biyang basin the distributions of n alkanes isoprenoids steranes and terpanes have been studied and used to characterize the sedimentary environment of deposition maturity biodegradation and undertake possible correlations the ratios of c 30 hopane gammacerane 4 methyl steranes regular steranes steranes hopanes c 21 tricyclic c 30 hopane are proposed to be indicative of the depositional environment whereas s carotane appears to be a source related indicator the geochemical data obtained in this study suggest that the major source rocks in the biyang basin were deposited in a saline hypersaline depositional environment

the base of slope carbonate breccia system of ceuse tithonian s e france occurrence of progradational stratification in the head plug of coarse granular flow deposits abstract once interpreted as a deep water canyon infilling and later as some kind of tempestite deposit the tithonian breccias of ceuse are here reinterpreted as a small lobe deposit emplaced at the mouth of a gully cutting into a slope between two deep water terraces in the eastern part of the subalpine basin the breccias belong to two basic categories mostly grain supported and occasionally mud supported spectacular large scale oblique geometries apparent lateral accretions are observed in the grain supported breccias both within the infilling of the lower feeder channel and in the updip part of the lobe detailed analyses of these geometries show that they correspond to progradational features both laterally and in a more distal position on the lobe these progradational bodies evolve into a pile of unsorted massive breccias sometimes showing a crude even stratification we thus propose a depositional model for the grain supported breccias linking the two facies as follows the deposition of a gravity flow begins at the toe of slope mouth of the tributary gully by a progradational head which evolves downslope and laterally to a splay of massive or crudely stratified breccia the internal oblique stratification flattens distally over a distance of a few kilometres elementary beds pile up in morphological compensation to build the 100 m thick breccia body of ceuse because the breccias are derived from the gravity reworking of deep water nodular carbonates there is no sand sized material available in the depositional system or only a little probably produced through an erosive clast grain diminution process during transport this explains why the thick breccia beds pass quickly eastward to thin bedded mud turbidites

chrome spinels in gabbro wehrlite intrusions of the pechenga area kola peninsula russia emphasis on alteration features abstract chrome spinels are common accessory minerals of the pechenga ultramafic rocks in nw russia varying in metamorphic grade from sub greenschist to amphibolite facies magmatic chrome spinels can be grouped into two main types spinel 1 which crystallized first is represented by al ti chromite it occurs mainly as inclusions in olivine and rather less commonly enclosed within interstitial minerals spinel 2 crystallized after spinel 1 and has composition varying from ti rich chromite to ti rich chrome magnetite spinel 2 occurs in the interstitial spaces between olivine crystals and enclosed within intercumulus silicates zoned crystals with spinel 1 in the core overgrown by spinel 2 are also common cr poor titanomagnetite occurring in pyroxenites and gabbro apparently represents further evolution of spinel 2 phases metamorphic chrome spinels are represented by ferritchromit and cr magnetite which are the dominant chrome spinel phases in the amphibolite facies rocks the continuous trend of the magmatic chrome spinels composition is indicative of their intensive post cumulus alteration by reaction with evolving intercumulus liquid this reaction led to depletion of the earlier crystallized chrome spinels in mg cr and al and their enrichment in ti and fe 3 oxidation exsolution of ilmenite from ti rich chrome spinels is another common process of post crystallization alterations serpentinization of olivine led to formation of magnetite which overgrew and cut chrome spinel grains low temperature hydrothermal processes in particular talc carbonate alterations could cause a local loss of ti and further redistribution of mg mn and zn prograde metamorphic reactions led to formation of ferritchromit and magnetite replacing primary chrome spinels another common process affecting ti rich chrome spinels is a prograde metamorphic recrystallization of exsolved ilmenite which changes from submicron lamellae through a regular grid of coarse ilmenite crystals and further to their irregular blebs and rims metamorphism of epidote amphibolite and amphibolite facies has led to the liberation of most of the elements metamorphically liberated cr was captured by antigorite

self reversal of remanent magnetization in basalts due to partially oxidized titanomagnetites summary a range of basaltic samples from olby france and vogelsberg germany displaying the phenomenon of partial and complete self reversal was studied in order to decipher the physical mechanism responsible for self reversed magnetic remanence in basalts microscopic observations and rock magnetic measurements show titanomagnetite to be the carrier of remanence due to low temperature oxidation the titanomagnetites are present in two magnetic phases forming close side by side phase assemblages the ore grains consist of a non oxidized magnetically soft titanomagnetite part with curie temperatures between 140 and 300 c and a magnetically hard low temperature oxidized part with curie temperatures between 410 and 590 c magnetic force microscopy observations present evidence that the oxidation process does not only influence the curie temperatures and thus the blocking temperature spectrum but also the domain configuration during acquisition of a thermoremanence the two phases are magnetically coupled leading to a remanent magnetization of the low curie temperature phase which is antiparallel to the applied external magnetic field computational modelling of the remanence acquisition process explains the coupling of the two phases by magnetostatic interaction as the observed partial oxidation of ore grains is not uncommon in subaerial basalts partial and complete self reversal is probably a frequently occurring phenomenon nevertheless it remains unnoticed in most cases as it cannot be detected by the standard stepwise thermal demagnetization technique despite the complex remanence properties our investigations indicate that the upper part of the blocking temperature spectrum still carries reliable palaeodirectional information

permian tectonic framework and palaeogeography of se asia abstract the principal continental lithospheric terranes now comprising se asia and that existed in the permian are the south china indochina super terrane and the sibumasu simao west burma and sw borneo semitau terranes the simao terrane is here regarded a separate terrane derived from south china by back arc spreading in the lower carboniferous rather than as an extension of indochina the main palaeo tethys ocean in thailand is identified as being represented by the chiang mai and sra kaeo sutures and the eastern boundary of the sibumasu terrane is thus interpreted to lie farther west in thailand than previously inferred the nan uttaradit suture is interpreted as representing a marginal back arc basin and contiguous with the ailaoshan and jinshajiang sutures in sw china the south china indochina super terrane and the simao terrane were located within the palaeo tethys in equatorial latitudes during the permian where they together with north china exhibit cathaysian floras and faunas the sibumasu terrane was located on the nw australian margin of gondwana until the sakmarian major shifts in faunal affinities from gondwana province faunas to an independent sibumasu province and then to assimilation into the cathaysian province records the separation and rapid northward drift of sibumasu after the late sakmarian the principal permian palaeogeographic models for the region are assessed for internal consistencies and conflicts

paleomagnetic results from the upper carboniferous of the shan thai malay block of western yunnan china the upper carboniferous basaltic woniusi formation was sampled at 21 sites from two limbs of a syncline near baoshan city 25 2 n 99 3 e and from a monocline near yongde county 23 9 n 99 2 e for paleomagnetic study the study area is generally thought to be part of the shan thai malay microplate thermal demagnetization reveals a single polarity characteristic remanent magnetization chrm which is carried by both magnetite and hematite with the former being the dominant mineral in basalt and the latter being the principal carrier in associated tuffaceous basalt and sandstone the tilt corrected formation mean from baoshan d 209 2 i 61 0 95 6 7 confirms the results reported by previous workers and a positive fold test constrains the chrm acquisition to be prefolding the paleomagnetic inclinations determined from this study are similar to that derived from the devonian rocks from the same area by other workers indicating a paleolatitude of about 42 for the baoshan area during the devono carboniferous time the paleomagnetic declinations however present a large difference between the two sampling localities for the upper carboniferous as well as between the sampling sites for the devonian and for the upper carboniferous the paleo declination difference can be partly explained by the apparent polar wander of gondwana if the shan thai malay microplate was rigidly attached to gondwanaland during this time interval the large part of it has to be ascribed to tectonic rotations between the sampling sites this fact suggests that extreme caution should be exerted when trying to establish an apparent polar wander path for and to reconstruct the paleo geographic position of the shan thai malay microplate

intraplate deformation of the indian subcontinent 1 while deformation at the earth s surface primarily occurs along tectonic plate boundaries major earthquakes have shaken regions deep within continental interiors three of the largest m 7 5 historic intraplate earthquakes occurred within the indian subcontinent suggesting the possibility of significant intraplate deformation we consider surface velocities determined from new gps data collected at 29 continuous gps stations and 41 survey mode gps stations in india between 1995 and 2007 to find a north south shortening rate of 0 3 0 05 nanostrain yr 1 which may be accommodated by 2 1 mm yr of more localized convergence across central india southward motions at 4 7 mm yr of sites on the shillong plateau in northeast india reflect rapid shortening and high earthquake hazard associated with active thrust faults bounding the plateau the width and magnitude of the elastic strain accumulation field across the himalaya varies little from 76 90 longitude but the strain is more broadly distributed and convergence rates are higher along the eastern 200 km of the range

geochemistry of paleozoic marine oils from the tarim basin nw china part 4 paleobiodegradation and oil charge mixing abstract fifty three oil samples from paleozoic marine reservoirs of the tarim basin were analyzed by gc fid and gc ms to elucidate the influence of biodegradation and mixing on molecular compositions biodegradation has a major impact on many classes of compounds but the ultimate compositions and physical properties of the oil are influenced strongly by mixing with late oil charge subsequent to the process of biodegradation almost all samples display biodegradation signatures characterized by variable size of the unresolved complex mixture ucm and variable amounts of 25 norhopanes 25 nhs and 17 nortricyclic terpanes 17 nts the ubiquitous occurrence of n alkanes suggests that the petroleum accumulated in these fields is mainly a mixture of previously biodegraded oils with later migrated fresh oils the unaltered late charge of oil which has commingled with the initial biodegraded charge gives the wide range of oil gravities and asphaltene contents observed most commonly used maturity and depositional environment diagnostic parameters in the saturated hydrocarbon fraction are affected by biodegradation based on the intensity of 25 nhs and 17 nts oils from the tabei uplift appear to have experienced a much greater degree of biodegradation than those from the tazhong uplift however we caution against the simplistic use of molecular indicators to define a specific level of biodegradation in this case study as it may be somewhat misleading for physical property prediction a wide range of estimated maturity values from different components provides an important clue for multiple charge and mixing interpretations the relationship between the absolute concentrations of compound class and peak hump ratios of the samples can potentially qualitatively differentiate the pulse of inputs to the mixed oils the positive correlation between the concentrations of a given compound class and peak hump ratios may suggest that that class of compounds is most likely derived from the late charge after biodegradation while the negative correlation may indicate compounds largely inherited from the early charge before biodegradation some compounds show almost no correlation between their concentrations and peak hump ratios implying more similar intensity of charge inherited from early pulse and amalgamated from later pulses in some extremely biodegraded cases where ucm hump can also be diminished not in present case study the correlation between compound class concentrations and peak hump ratios will be more complicated

a new petrogenetic grid for low grade metabasites abstract we have used internally consistent thermodynamic data to present calculated phase equilibria for the system na2o cao mgo al2o3 sio2 h2o ncmash in the range 0 500 c and 0 1 10 kbar involving the phases anorthite glaucophane grossular heulandite jadeite laumontite lawsonite paragonite prehnite pumpellyite stilbite tremolite wairakite zoisite with excess albite clinochlore quartz and pure water average activity terms derived from published mineral chemical data were included for clinochlore glaucophane prehnite pumpellyite tremolite and zoisite the new petrogenetic grid delineates stability fields and parageneses of common index minerals in zeolite prehniteactinolite prehnite pumpellyite pumpellyite actinolite blueschist and greenschist facies metabasites the stability fields of mineral assemblages containing prehnite pumpellyite epidote actinolite albite chlorite quartz were analysed in some detail using activity data calculated from five specific samples for example the prehnite actinolite facies covers a p t field ranging from about 220 to 320 c at pressures below 4 5 kbar the transition from the prehnite actinolite and pumpellyite actinolite to greenschist facies occurs at about 250 300 c at 1 3 kbar and at about 250 350 c at 3 8 kbar p t fields of individual facies overlap considerably due to variations in chemical composition

antimony in rutile as a pathfinder for orogenic gold deposits abstract in our study we explore the applicability of rutile as a pathfinder for orogenic gold deposits which are an important source of this metal worldwide we analysed rutile associated with orogenic au deposits from three different precambrian terranes the capricorn orogen the barberton greenstone belt and the ashanti belt all of which formed under greenschist conditions and share similarities in the style of mineralisation microtextural evidence from scanning electron microscopy and electron back scatter diffraction indicates that rutile formed during the main deformation and alteration stage in these rocks and is therefore related to mineralisation we used electron microprobe and laser ablation icp ms to investigate the trace element compositions of rutile and we compared our results to other gold deposits we find that hydrothermal rutile from gold deposits contains certain trace element characteristics in particular high sb concentrations up to 1500 ppm in au deposits of the capricorn orogen that are distinct from rutile from non mineralised rocks of various petrogenetic origin other elements such as w and sn are found to be more enriched in rutile from other rock types namely felsic magmatic rocks and hydrothermal veins and are therefore not diagnostic of au mineralisation in this type of deposits we also find that the presence of sub m scale inclusions in particular zr si th bearing phases sulfide minerals and native au can severely affect analyses of this type of rutile and compromise the applicability of zr in rutile geothermometry

tertiary paleomagnetic data from northwestern yunnan china further evidence for large clockwise rotation of the indochina block and its tectonic implications abstract eocene red sandstones were collected at 15 sites for paleomagnetic study from two areas lanping and yunlong of the western part of yunnan province china in the northern part of indochina the high temperature magnetization component with an unblocking temperature of around 680 c is isolated after stepwise thermal demagnetization characteristic directions from nine accepted sites reveal a positive fold test at the 99 confidence limit indicating that the high temperature magnetization component is possibly of eocene age a tilt corrected mean direction from nine accepted sites is d 266 1 i 39 8 with 95 11 2 corresponding to a paleopole at 14 5 n 169 7 e with a95 10 9 a comparison with previously reported tertiary paleomagnetic data indicates that the lanping basin of the northern part of the indochina block rotated clockwise through 91 15 with respect to the yangtze craton this large magnitude clockwise rotation is probably caused by the superimposition of regional and local rotations our previous middle cretaceous paleomagnetic results from the yunlong area indicate that about 40 of clockwise rotation out of 90 is explained by tectonic rotation due to a relatively rigid body rotation of the simao terrane during indentation of india the remaining component of rotation is probably ascribed to further eocene post eocene rotational motion of the tectonically independent small blocks within the lanping basin associated with fault movement

subaqueous sediment gravity flow deposits practical criteria for their field description and classification a new method for the description and classification of subaqueous sediment gravity flow deposits is proposed the classification scheme employs a convenient letter code and divides deposits individual beds into descriptive categories of two hierarchical levels facies and subfacies facies as the higher rank categories are distinguished chiefly on the basis of sediment type i e bed grain size texture a total of 13 facies have been distinguished g gravel gs gravel sand couplet gys gravelly sand s sand sm sand mud couplet ms mud sand couplet tm silt mud couplet mt mud silt couplet m mud mys muddy sand sym sandy mud myg muddy gravel gym gravelly mud subfacies as the lower rank categories are distinguished within the individual facies on the basis of the bed s internal structures the number of subfacies is unlimited and their labelling code includes particular facies symbols see above preceded by lower case letters denoting specific sedimentary structures and their vertical arrangement subfacies thus refer to the bed s intervals or divisions which are labelled as follows m massive unstratified and ungraded g graded unstratified and graded s plane stratified x cross stratified 1 parallel and or cross laminated q liquefied for example subfacies gsg graded to plane stratified gravel are gravel beds that have a lower graded interval and an upper plane stratified interval subfacies xg cross stratified gravel are gravel beds that are cross stratified throughout subfacies sls plane stratified to laminated sand are sand beds that have a lower plane stratified interval and an upper laminated parallel and or cross laminated interval

progradational patterns at the head of single units of base of slope submarine granular flow deposits conglomerats des gâs coniacian se france upper cretaceous conglomerates sandstones and calcarenites outcropping in the glandage syncline les gas gorge belong to two superimposed turbidite systems the first being the shortest about two hundred metres thick five kilometres wide and a mere ten kilometres long both onlap a sw ne oriented palaeoslope created by faulting in the latest turonian on the southern edge of the vercors carbonate platform the first system is coniacian in age the second probably campanian this study deals only with the first system which comprises in stratigraphic order classical sandstone turbidites clast supported conglomerates and coarse grained cross bedded sandy calcarenites the transition between the last two lithologies is progressive allowing the mechanisms responsible for apparent lateral accretions found pervasively in both the conglomerates and the calcarenites to be understood here cross bedding is not the result of changes in the direction of accretion in lateral bars or in oblique infillings of sinuous channels as is often suggested in other similar deep water carbonate systems each event bed comprises a prograding conglomeratic head plug blanketed in continuous sedimentation by forward spreading bioclastic calcarenites the superimposition of such mixed beds gives rise to a low angle cross stratification an unusual feature for a system interpreted as a base of slope apron conglomerates were probably deposited through a granular flow mechanism at a strong hydraulic jump at the base of the slope associated calcarenites show supercritical flow features the undulating transverse architecture of its large head onlapping the paleoslope suggests it is a multi apex apron the sandstone conglomerate calcarenite succession of the depositional sequence is interpreted as overall transgressive after the late turonian tectonic phase that led to the exposure of the vercors carbonate platform updip

structure kinematics and ages of transpression during strain partitioning in the chongshan shear zone western yunnan china abstract the chongshan shear zone extends from the eastern himalayan syntaxis to the lincang granitic pluton in yunnan province china the structure and kinematics show that the shear zone comprises mainly of mylonitic gneiss migmatite and schist with a dextral dominated strike slip motion in an n s trending northern segment and a sinistral strike slip shear in nw se trending middle and southern segments both were developed under a bulk regional scale sinistral transpression shrimp and la icpms u pb and 40 ar 39 ar dating reveal two tertiary magmatic events along the zone followed by younger sinistral strike slip shear the eocene magmatic event c 55 38 ma followed by metamorphism at c 36 ma happened before the strike slip motion the strike slip shear along the zone began c 32 ma which generated shear heating from 32 to 22 ma the 40 ar 39 ar ages of syn kinematic micas range from 19 to 14 ma and indicate that the strike slip shear continued to this time with coeval transpressional exhumation and uplift of the metamorphic rocks along the biluoxueshan chongshan chain the chongshan zone is thus a cenozoic shear zone which was contemporaneous with motion on the left lateral ailao shan red river shear zone and the right lateral gaoligong shear zone and should be important in accommodating the northwards movement of india during collision during oligocene to miocene times the continental block that was extruded between the ailao shan red river and gaoligong shear zones was dismembered into at least two major fragments by the chongshan shear zone

biodegradation of 25 norhopanes in a liaohe basin ne china oil reservoir a suite of reservoir cores in an oil column from the shuguang oil field liaohe basin ne china was characterized geochemically to investigate the behaviour of 25 norhopanes nhs during biodegradation the extracted bitumens show similar organofacies type and maturity levels with biodegradation as the primary control on compositional variation all bitumens suffered severe biodegradation influence which removed all regular steranes and most of the pentacyclic terpanes leaving nhs as dominant components in total ion chromatograms of the saturated hydrocarbon fraction however the nhs are not the endpoint of hopane destruction they are biodegraded as well biodegradation of nhs can be illustrated by significant depletion in their concentrations and systematic variation in ratios of resistant to vulnerable components throughout the oil column the biodegradation sequence is somewhat similar to normal pentacyclic terpanes among the nh series 18 25 30 bisnorneohopane is the most recalcitrant to biodegradation the 18 22 25 29 30 tetranorneohopane is more resistant to biodegradation than 17 22 25 29 30 tetranorhopane and 34nhs are more resistant than other nhs degradation of nhs provides a new angle to understanding the complicated inter relationships in subsurface biodegraded reservoirs

the direction correction tilt test an all purpose tilt fold test for paleomagnetic studies abstract the tilt or fold test in paleomagnetism is used to infer whether paleomagnetic remanence was acquired before or after tectonic tilting while several tilt test formulations have been proposed none fully satisfies the requirements of statistical validity applicability to all bedding geometries and ease of use this paper introduces the direction correction dc test which examines the relationship between the paleomagnetic site mean directions and their corresponding bedding tilt corrections the dc test is similar to mcfadden s correlation test because both test whether or not the site directions contain information about the bedding tilts however the dc test gives greater weight to sites with greater counter bedding the dc test is similar to watson s numerical tilt tests because they determine the degree of untilting which gives optimal concentration of site directions however the dc test uses analytical rather than numerical methods graphical output aids the researcher in recognizing problem sites using both real and simulated data the dc test is demonstrated to be more discriminating than other tilt test formulations for all bedding geometries the simulations show that the power of the tilt test is inversely proportional to the 95 confidence interval 95 of the overall mean as a rule of thumb paleomagnetists should attempt to sample sufficient sites to obtain an 95 less than 1 6 of the bedding attitude difference