oil fields a source of heat flow data abstract a method of calculating terrestrial heat flow from oil fields is evaluated by reviewing its application to twelve petroliferous basins three of them in brazil and nine in indonesia in each well terrestrial heat flow was calculated by multiplying the temperature gradient obtained by commonly used procedures by the effective thermal conductivity the latter was calculated from quick thermal conductivity measurements on core samples by a transient hot wire method and from the lithologic log typically in each basin the conductivity of about 300 core specimens was measured and logs of 50 150 wells were examined in each formation penetrated by a well the total thickness of each rock type such as shale sandstone etc was determined from the composite lithologic log the harmonic mean of the thermal conductivity of a formation in the well was computed from these thicknesses and the average values of the conductivities of the rock types measured on cores collected from that formation the conductivity of the well is the harmonic mean of the conductivities of the formations the average precision of the determination of formation conductivity can be expressed as the 95 limits divided by the average value for twelve basins this measure of precision for formation conductivities averages 3 6 and the average precision of the conductivity of a basin is 2 0 on the same basis the precision of the determination of the temperature gradient in a basin averages 4 7 and that of the heat flow 5 8 expressing the variability of the geothermal quantities in a basin determined at discrete locations as the standard deviation divided by the average value we get for the mean variability in the twelve basins 6 7 for conductivity 15 0 for the gradient and 16 4 for the heat flow the variability must come in part from natural causes in general at the present level of accuracy no correlation between anomalous heat flow and the occurrence of oil in a basin was found values of thermal conductivity of sedimentary rocks and their variation with depth are useful in calculating paleotemperatures the magnitude of the mean heat flows of the basins is normal 63 mw m2 for the jurassic basins of the stable continental margin of brazil and somewhat elevated in the tertiary basins of indonesia north of the sunda trench subduction zone the values decreasing from 130 mw m2 in central sumatra to 70 mw m2 in eastern kalimantan future improvements in the procedures for determining conductivity might possibly bring out local anomalies in heat flow that might be caused by vertical seepage of water this would support the hydraulic theory of accumulation of oil and gas

using pebble lithology and roundness to interpret gravel provenance in piedmont fluvial systems of the rocky mountains usa abstract clast populations in piedmont fluvial systems are products of complex histories that complicate provenance interpretation although pebble counts of lithology are widely used the information provided by a pebble count has been filtered by a potentially large number of processes and circumstances counts of pebble lithology and roundness together offer more power than lithology alone for the interpretation of provenance in this study we analyze pebble counts of lithology and roundness in two contrasting fluvial systems of pleistocene age to see how provenance varies with drainage size the two systems are 1 a group of small high gradient incised streams that formed alluvial fans and terraces and 2 a piedmont river that formed terraces in response to climate driven cycles of aggradation and incision we first analyze the data from these systems within their geographic and geologic context after this is done we employ contingency table analysis to complete the interpretation of pebble provenance small tributary streams that drain rugged mountains on both sides of the santa cruz river southeast arizona deposited gravel in fan and terrace deposits of pleistocene age volcanic plutonic and to a lesser extent sedimentary rocks are the predominant pebble lithologies large contrasts in gravel lithology are evident among adjacent fans subangular to subrounded pebbles predominate contingency table analysis shows that hard volcanic rocks tend to remain angular and even though transport distances have been short soft tuff and sedimentary rocks tend to become rounded the wind river a major piedmont stream in wyoming drains rugged mountains surrounding the northwest part of the wind river basin under the influence of climate change and glaciation during the pleistocene the river deposited an extensive series of terrace gravels in contrast to santa cruz tributary gravel most of the wind river gravel is relatively homogenous in lithology and is rounded to well rounded detailed analysis reveals a multitude of sources in the headwaters and the basin itself but lithologies from these sources are combined downstream well rounded volcanic and recycled quartzite clasts were derived from the headwaters precambrian igneous and metamorphic clasts were brought down tributary valleys to the wind river by glaciers and sandstone was added where the river enters the wind river structural basin

extrusion tectonics of the okhotsk plate northeast asia based on focal mechanism geologic and lineament data faulting in the chersky range northeast asia changes from right lateral transpression between north america and eurasia to left lateral strike slip between north america and the okhotsk plate the location of the okhotsk eurasia boundary is poorly constrained available data suggest this boundary is right lateral the okhotsk plate is being compressed and extruded from between north america and eurasia resulting in high levels of microseismic activity along the southern flanks of the chersky range

imprint of the north american plate in siberia revealed by gps 1 gps observations in east siberia combined with global observations collected 1995 2002 place constraints on the geometry and motions of the eurasian north american and pacific plates in east asia by comparing velocities relative to eurasia and to north america we conclude that east siberia to the east of the cherskiy range belongs to the north american plate hypothesized for three decades but not proven because of uncertainties with the plate boundary arising from the ambiguous seismicity smaller plates in east asia such as okhotsk and amurian can neither be resolved nor excluded by the gps velocities

stochastic inversion of thermal data in a sedimentary basin resolving spatial variability summary the concept of spatial stochastic processes and the techniques of geostatistics and stochastic inversion are presented as a means for evaluating the spatial variability of thermal properties and temperature in sedimentary basins data from the uinta basin of ne utah are used to demonstrate the analysis bottom hole temperatures from oil and gas wells provide the best opportunity for a spatial analysis because of the large number and wide distribution of data errors in bottom hole temperatures are not too large to preclude their use and stochastic inversion provides an optimum method for removing random noise while retaining spatial resolution corrected bottom hole temperatures from 235 wells in the uinta basin are used to estimate a average geothermal gradient as a function of position in the basin and b temperature gradients in individual formations also as a function of position in the basin the latter analysis yields a high resolution estimate of temperature gradient and temperature throughout the basin the temperature field shows variations of up to 50 c at a depth of 4 km and is estimated to be accurate to better than 5 c this variation in temperature is consistent with conductive and advective mechanisms of heat transfer in a heterogeneous medium

chronology of pleistocene glacial advances in the central rocky mountains the distribution and ages of moraines in the wyoming type localities for pre pinedale rocky mountain glacial deposits are not well known through morphostratigraphic mapping river terrace longitudinal profile analysis and tephrochronology we place the age of sacagawea ridge moraines in the dinwoody lakes type area at about 660 ka outwash and river terrace deposits in the bull lake type area previously considered to be sacagawea ridge are actually older by one or two glacial cycles in the bull lake type locality 15 individual moraines are divided into 4 groups on the basis of relative age criteria using 36cl 10be cosmogenic dating of boulders the two older groups must be 130 ka the younger groups are given age ranges of 130 to 100 ka and 120 to 95 ka a terrace along wind river can be morphostratigraphically traced to the youngest of these moraine groups 36cl dating of boulders on the terrace provides an age range of 125 to 100 ka the combined relative age and cosmogenic nuclide chronology is consistent with previously published evidence from yellowstone national park demonstrating that mountain glaciers advanced not only prior to and during the later portion of marine isotope stage 6 but also during marine isotope stage 5d in contrast with some other areas of the rocky mountains we found no evidence for advances during marine isotope stage 4 at bull lake pinedale moraines that have a 36cl 10be age range of 23 to 16 ka suggest that glacial advances were limited to the later part of marine isotope stage 2 a river terrace that can be traced to these moraines has an age range of 23 to 16 ka a possible glacial advance during early marine isotope stage 2 is indicated by a river terrace whose age range is estimated by incision rate modeling at 46 to 28 ka but no moraines were identified along wind river there are eight terrace levels capped with outwash that are older than sacagawea ridge although the terraces are the record of early to middle pleistocene climatic cycles there are no correlative moraines preserved at the land surface

provenance of lower paleogene strata in the huerfano basin implications for uplift of the wet mountains colorado u s a abstract sedimentary basins throughout the western interior of north america preserve a record of late cretaceous through latest eocene sedimentation derived from flanking laramide uplifts and sevier hinterland in northern and western basins the strata contain a well documented record of laramide style exhumation however the tectonic histories of more southerly basins such as the huerfano basin studied herein are comparatively poorly known despite being key for understanding the spatiotemporal evolution of laramide tectonism in this study we address this issue with a comprehensive analysis of provenance for the poison canyon cuchara and huerfano formations in the huerfano basin south central colorado u s a as part of our provenance analysis we characterized gravel clast composition petrographic compositions of sandstone bodies n 31 thin sections and u pb detrital zircon age spectra n 848 age determinations from fluvial sandstone units in each of the three formations the results are used to construct a new unroofing and source history for the sediments in the basin that contradicts previous hypotheses diagnostic zircon peaks at 516 517 ma 1423 1430 ma and 1678 1687 ma show that sediment delivered to the huerfano basin did not originate in the san luis highlands or the incipient sangre de cristo mountains but from the precambrian crystalline core and associated cambrian plutons of the wet mountains which were exposed by the time laramide deposition began in the basin there are no detected provenance shifts upsection indicating a largely stable or lithologically uniform sediment source from the paleocene through at least 51 ma this suggests that the major changes recorded in the rock record were more likely related to variations in tectonic and climatic conditions rather than changes in lithology of the rocks being eroded

basement control of tertiary intrusions and associated mineral deposits along tijeras canoncito fault system new mexico a major zone of basement anisotropy in central new mexico the tijeras canoncito fault system has been episodically active since precambrian time and has formed shears in precambrian rocks open fractures for fissure filling and breccias with open spaces for mineral deposition tertiary plutons emplaced along this zone of crustal weakness were the sources of mineralizing solutions provided heat for hydrothermal systems and may have remobilized mineral deposits from precambrian basement rocks recurrent movement along the faults was important in ore genesis as emplacement of intrusions was followed by further fault movement to create open spaces for mineral deposition

temperatures and depth dependent heat flow in western north sea bottom hole temperatures and lithologic information from 167 released wells between 52 and 58 n in the british sector of the north sea have been studied and measurements of thermal conductivity have been conducted on many samples from all the main stratigraphic units although large errors may be associated with the temperature information it is sufficiently reliable to establish that heat flow is not conserved with depth over much of the western north sea in the central graben and anglo dutch basin heat flow in the upper 1 2 km 3 300 6 600 ft is around 50 mw m 2 increasing downward to about 100 mw m 2 farther west on the mid north sea high and on the east midlands shelf the situation is reversed with shallow heat flows of about 80 mw m 2 decreasing downward to about 50 mw m 2 these variations are not readily explained either by heat flow refraction or by tectonic activity they are most probably attributable to the deep and continuing circulation of water the circulation may well be on a very large scale and must be largely fault controlled

new physical evidence of the role of stream capture in active retreat of the blue ridge escarpment southern appalachians abstract the blue ridge escarpment of the southern appalachian mountains is a striking and rugged topographic feature of the ancient passive margin of eastern north america the crest of the escarpment generally coincides with an asymmetric regional drainage divide separating steep streams of the escarpment face from low gradient streams of the blue ridge upland recent exhumation and erosion rate studies suggest that the escarpment has evolved by inland erosional retreat but the mechanism timing and magnitude of retreat remain poorly understood longitudinal stream profiles and slope drainage area relationships of several upland basins draining the divide have led to the identification of 14 previously unknown fluvial terrace deposits preserved at the escarpment crest these relict terraces and the associated beheaded drainages indicate the role of large stream capture events in producing ongoing escarpment retreat through landward divide migration and subsequent topographic adjustment terrace location and preservation suggest that rectilinear drainage patterns and divide asymmetry generate discrete high order captures and episodes of rapid localized retreat that collectively produce slower evolution of the escarpment at large while overall retreat magnitude and rate remain unknown roundness of terrace alluvium suggests that the most recent captures have locally produced tens of kilometers of retreat within the limited preservation lifetime of the deposits in contrast with recent numerical modeling and cosmogenic studies these data show the potential for stream capture and divide migration to sustain passive margin escarpment evolution long after the cessation of rifting the fluvial record of divide retreat preserved atop the blue ridge escarpment suggests the potential for using field methods to better constrain the histories of younger taller and potentially more dynamic passive margin escarpments

conductive heat flux in vc 1 and the thermal regime of valles caldera jemez mountains new mexico over 5 of heat in the western united states is lost through quaternary silicic volcanic centers including the valles caldera in north central new mexico these centers are the sites of major hydrothermal activity and upper crustal metamorphism metasomatism and mineralization producing associated geothermal resources we present new heat flow data from valles caldera core hole 1 vc 1 drilled in the southwestern margin of the valles caldera thermal conductivities were measured on 55 segments of core from vc 1 waxed and wrapped to preserve fluids these values were combined with temperature gradient data to calculate heat flow above 335 m which is probably unsaturated heat flow is 247 16 mw m 2 the only deep temperature information available is from an uncalibrated commercial log made 19 months after drilling gradients derived from uncalibrated temperature logs and conductivities are inversely correlated between 335 and 737 m indicating a conductive thermal regime and component heat fluxes over three depth intervals 335 539 m 549 628 m and 628 737 m are in excellent agreement with each other with an average of 504 15 mw m 2 temperature logs to 518 m depth with well calibrated temperature sensors result in a revised heat flow of 463 15 mw m we use shallow thermal gradient data from 75 other sites in and around the caldera to interpret the thermal regime at the vc 1 site a critical review of published thermal conductivity data from the valles caldera yields an average thermal conductivity of 1 w m 1 k 1 for the near surface tuffaceous material and we assume that shallow gradient values c km 1 are approximately numerically equal to heat flow mw m 2 heat loss from the caldera is asymmetrically distributed with higher values 400 mw m 2 or higher concentrated in the west southwestern quadrant of the caldera this quadrant also contains the main drainage from the caldera and the youngest volcanism associated with the caldera we interpret the shallow thermal gradient data and the thermal regime at vc 1 to indicate a long lived hydrothermal and magmatic system in the southwestern valles caldera that has been maintained through the generation of shallow magma bodies during the long postcollapse history of the caldera high heat flow at the vc 1 site is interpreted to result from hot water circulating below the base of the core hole and we attribute the lower heat flow in the unsaturated zone to hydrologic recharge

interseismic coupling and asperity distribution along the kamchatka subduction zone 1 gps measurements of interseismic horizontal surface velocities reveal the degree of kinematic coupling of the plate boundary thrust along the kamchatka subduction zone from about 51 degrees to 57 degrees n latitude inversions for the distribution of aseismic slip rate along the similar to 15 degrees nw dipping underthrust suggest a nonslipping plate interface in southern kamchatka above similar to 50 km depth along the segment that ruptured in the m w 9 1952 earthquake north of similar to 53 degrees n the subduction interface experiences significant aseismic slip consistent with the lower seismic moment release in m 8 5 earthquakes along this portion of the subduction zone the gps velocities are consistent with a boundary element forward model in which historic earthquake rupture zones are represented as locked asperities surrounded by a zero shear stress subduction interface loaded by plate convergence models in which the complete rupture zones of historic earthquakes are considered locked greatly overpredict the degree of kinematic coupling reducing the area of the locked model asperities to the central 25 area of historic rupture zones fits the data well suggesting that large earthquakes involve small fully locked core asperities surrounded by conditionally stable portions of the plate interface areas of low aseismic slip rate appear to be roughly correlated with areas of low isostatic gravity anomalies over offshore forearc basins while less coupled portions of the kamchatka subduction zone coincide with high gravity anomalies offshore of two peninsulas possibly related to the subduction of the emperor meji seamount chain and the kruzenstern fracture zone

tectonic and geologic evolution of the espanola basin rio grande rift structure rate of extension and relation to the state of stress in the western united states abstract the espanola basin of the rio grande rift began as a broad crustal downwarp in latest oligocene time most of the basin is 2 3 km deep but localized faulting allowed accumulation of up to 5 km of sedimentary fill in a central sub basin the localized early faulting ended before filling of the central espanola basin was completed about 10 m y ago movement on faults that define the present western margin of the espanola basin began 10 m y ago jemez mountain volcanism in the western espanola basin also began at about this same time west tilting of up to 30 occurred due to movement along pervasive n trending intrabasin faults about 7 5 m y ago in conjunction with continued movement along the western border faults volcanism continued after this tilting forming many of the large volcanic constructs of the jemez mountains regional uplift of the entire northern rio grande rift began 7 m y ago movement on the pajarito fault zone began about 5 m y ago and continues to the present this fault zone defines the western margin of the velarde graben a narrow central sub basin where recent movement has been concentrated some volcanism also has occurred within the southern velarde graben total extension across the espanola basin since 26 m y ago is estimated to have been 5 5 km roughly 10 or between 3 5 and 8 km assuming high angle planar faulting the 0 2 mm yr averaged long term rate of extension has been separated into three periods of activity 1 1 0 14 mm yr from 26 to 10 m y ago 2 2 0 5 mm yr from 10 to 5 m y ago 3 3 0 14 mm yr from 5 m y ago to present a change in least principal stress direction from wsw ene to wnw ese that occurred throughout the western united states about 10 m y ago coincides with a roughly 3 5 times increase in the rate of extension preferential development and movement of n to ne trending normal faults and a few degrees of clockwise rotation of rocks in the western espanola basin similar to the espanola basin initial basins of the southern rio grande rift were broad downwarps and rifting was greatly accelerated after 10 m y ago accelerated uplift of the northern rio grande rift also occurred at about this time indicating that activity in the entire rio grande rift was modulated by this change in extension direction 10 m y ago that appears related to pacific north american plate interactions this modulation coupled with major faulting 10 m y ago preceding uplift 7 m y ago in the espanola basin suggest a passive rifting process for the rio grande rift whereby stresses due to plate interactions elsewhere cause faulting in the lithosphere which leads to the development of a passive asthenospheric uplift furthermore the roughly 20 m y pre uplift history of sediment accumulation in basins of the central and southern rift and the inherited character trend and geometry of the rio grande rift as a whole are also more consistent with a passive rifting process

geothermal studies in the san juan basin and the four corners area of the colorado plateau i terrestrial heat flow measurements abstract twenty five new heat flow measurements are presented for the san juan basin and the four corners area of the colorado plateau in the southwestern united states temperature gradients at most sites are calculated from temperature logs at depths between 1 km and 2 km resulting heat flow values appear to be locally less variable than shallower data these new data develop smooth uniform trends consistent with the regional geology as such it is reasonable to suggest that these data may be somewhat less influenced by near surface perturbations to heat flow than are shallower data in the area i e local hydrologie movement weathered conductivity samples topographic variations and paleoclimate effects heat flow increases going from the four corners area into the northern san juan basin a trend consistent with other geophysical studies heat flow also increases as the san juan basin is traversed south to north approaching the san juan volcanic field this observation suggests a unique thermal anomaly associated with the san juan volcanics heat flow in areas of the san juan basin quite away from extensive volcanics is 70 mw m 2 suggesting a small but statistically valid difference between regional heat flow in the non volcanic regions of the san juan basin and in some of the other non volcanic regions of the colorado plateau where the mean heat flow is 65 mw m 2 again this conclusion seems consistent with other geophysical data

analysis of sediment from steps in a small catchment in the polish carpathians in relation to the transition zone between the hillslope and fluvial system abstract an investigation to determine the transition zone between the hillslope system and the fluvial system in connection with the degree of differentiation of sediment located upstream and downstream of log steps ls and boulder steps bs was undertaken in the channel of a stream located in a small mountain catchment area in the silesian beskidy mts polish carpathians a stream channel into which large wood was introduced artificially several years ago granulometric analyses of 41 samples taken from upstream 21 and downstream 20 of steps were performed to analyze the effectiveness of log steps and boulder steps in the differentiation of mineral sediment it was demonstrated that log steps have a significant impact on the functioning of the channel by shaping its longitudinal profile and affecting the transport of mineral material whereas boulder steps retain less sediment showing the beneficial effects of artificial creation of log steps in mountain stream channels results of granulometric analyses suggested the location of the theoretical transition zone between the hillslope system and the fluvial system suggesting the location and range of this zone in small mountain catchment areas can change depending on the intensity and range of slope processes in the longitudinal profile of the channel

mixed geothermal and shallow meteoric origin of opal and calcite beds in pliocene lower pleistocene axial fluvial strata southern rio grande rift rincon hills new mexico u s a abstract exposed in upper pliocene fluvial strata in the eastern rincon hills and adjacent jornada del muerto basin southern rio grande rift new mexico usa are five laterally continuous beds 0 2 to 1 0 m thick of opal ct which straddle the east rincon hills normal fault four of these opal beds change basinward over 1 km or less to white friable lithofeldspathic sand with opal glaebules and then to microcrystalline calcite the opal and calcite generally replaced fine sand at shallow depths although two beds locally precipitated from standing water 87sr 86sr values 0 71301 to 0 71724 of the opal beds are consistent with precipitation from an advecting high temperature geothermal fluid that flowed through bedrock and or from a high temperature geothermal fluid derived from a deep crustal source carbon and oxygen isotopic values 13cpdb 7 1 to 0 6 18opdb 9 1 to 5 6 of the calcite beds lie between and overlap those of paleozoic carbonate and pliocene paleosol calcite suggesting precipitation from a mixture of a high temperature geothermal fluid that interacted with paleozoic carbonates and shallow meteoric groundwater for which paleosol calcite is a proxy the geothermal fluids are interpreted to have upwelled along the east rincon hills fault flowed laterally at or just below the surface and precipitated opal in response to rapid cooling and evaporation downflow precipitation of opal glaebules occurred as a result of decreasing silica concentrations and perhaps by mixing with shallow meteoric groundwater from which calcite precipitated probably by co2 degassing

terrestrial heat flow estimates from petroleum bottom hole temperature data in the colorado plateau and the eastern basin and range province preliminary heat flow estimates were calculated for 32 sites in the colorado plateau the eastern basin and range province and the middle rocky mountains at 23 of these sites the heat flow estimates are believed to have merit the heat flow estimates often agree with nearby measurements and correlate reasonably well with interpretations from other geophysical techniques the mean of the heat flow estimates hi the northern colorado plateau interior 66 to 69 mwm 2 is within 5 or 18 of the mean of deep or shallow heat flow measurements respectively estimates in the peripheral areas of the plateau in the san juan basin agree with higher heat flow measurements at sites approaching the san juan volcanic field estimates along the western periphery of the colorado plateau are higher than in the interior and therefore suggest an anomalously shallow mantle asthenosphere extending 50 km under the plateau this is consistent with previous studies above average basin and range heat flows are estimated in the eastern basin and range province 99 102 mwm 2 and this concurs with a high energy flux zone proposed for the area the transition from high to low heat flow estimates between the eastern basin and range province and the middle rocky mountains seems to occur over a small distance 36 km the narrow heat flow transition implies shallow thermal sources in proximity to the basin and range middle rocky mountains transition this may correspond to a shallow crustal low velocity zone previously interpreted along the transition

estimation of formation temperature from borehole measurements summary a new numerical method is described for modelling the thermal disturbance around a borehole and a comparison is made with the commonly used line source model the numerical model generally gives an estimate of the equilibrium formation temperature which is up to about 20 per cent higher than the horner plot method the relaxation of the borehole temperature is sensitive to the contrast between the thermal properties of the drilling fluid and of the surrounding rock as well as to the disturbance time the importance of vertical temperature gradients and fluid motion both free convection in the borehole and flow in the formation is also examined it is found that vertical temperature gradients are unlikely to be important provided temperatures are measured more than 10 borehole radii above the bottom convective heat transfer can be important under some drilling conditions

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

earthquake recurrence and magnitude and seismic deformation of the northwestern okhotsk plate northeast russia 1 recorded seismicity from the northwestern okhotsk plate northeast asia is currently insufficient to account for the predicted slip rates along its boundaries due to plate tectonics however the magnitude frequency relationship for earthquakes from the region suggests that larger earthquakes are possible in the future and that events of mw 7 5 which should occur every 100 350 years would account for almost all the slip of the plate along its boundaries due to eurasia north america convergence we use models for seismic slip distribution along the bounding faults of okhotsk to conclude that relatively little aseismic strain release is occurring and that larger future earthquakes are likely in the region our models broadly support the idea of a single okhotsk plate with the large majority of tectonic strain released along its boundaries

subsurface evidence for the sudden integration of the salt river across the internally drained basin and range province arizona usa abstract the dynamics of river systems are most easily studied by observing their present geomorphology exposed at earth s surface however the bulk of these often long lived transportation and depositional systems is mostly buried at depth and hidden from view accessing these subsurface archives is often not possible the phoenix basin of arizona usa with its rich collection of water well drilling information offers a unique opportunity clast assemblages of sand and gravel deposits contained in subsurface drill cuttings enable estimates of sediment provenance and importantly reveal changes of provenance over time this study represents more than a decade of drill cuttings analysis and presents a method for evaluating the depositional history of how the phoenix basin developed a large external river system that crossed a long lived internally drained basin this configuration developed after basin and range faulting and extension had ceased allowing the basin to fill to capacity with sediment when placed in the context of a series of new isopach maps of the subsurface ancestral salt river deposits our clast assemblage analysis supports the conclusion that the salt and verde rivers appeared suddenly in the geologic record the ancestral salt river deposits and other nearby streams crossing the basin each possess a unique clast assemblage that can be used to fingerprint sediments with similar sources we use these observations to draw conclusions about the age and origin of these streams used in conjunction with other types of analyses such as cosmogenic burial dating and detrital zircon analyses determining clast assemblages of drill cuttings in the context of mapping these assemblages is a powerful new method for estimating the source of sediment and for understanding how the phoenix basin and basins in general fill with sediment this information is of value in modeling both basin development and groundwater resources in similar contexts in arizona and elsewhere

reinterpretation of the cedar ridge section wind river range wyoming implications for the glacial chronology of the rocky mountains the cedar ridge stratigraphic section in the escarpment north of bull lake wind river range wyoming may be the most significant section of quaternary sediments in the rocky mountains this section contains a thick sequence of bull lake till but its greater significance is as the type section or a reference section for the deposits of three pre bull lake glaciations washakie point oldest cedar ridge and sacagawea ridge reference section type section at dinwoody lakes however after reexamining the tills lake sediments and buried soils in this section we conclude that the stratigraphic record is best interpreted as the result of two glaciations not the four of previous investigations buried soils are especially useful in deciphering the stratigraphy of this section through the contrast between well developed interglacial soils and weakly developed interstadial soils we conclude that only the bull lake and sacagawea ridge glaciations are represented by deposits in the cedar ridge section deposits formerly called cedar ridge are reinterpreted as representing an early stade of the sacagawea ridge glaciation a paleomagnetic study reveals that all the sediments have normal polarity and thus are probably younger than the brunhes matuyama boundary of ca 770 ka although the deposits of the cedar ridge section have been correlated with moraines and terraces this procedure should be done only by direct tracing or with the use of all available dating control the best record of quaternary glaciations in the area however is in the river terraces of glacial outwash origin in the wind river basin not the moraines and stratigraphic sections along the mountain front

can the okhotsk plate be discriminated from the north american plate the plate geometry in northeast asia has been a long standing question with a major issue being whether the sea of okhotsk and northern japanese islands are better regarded as part of the north american plate or as a separate okhotsk plate this question has been difficult to resolve because earthquake slip vectors along the kuril and japan trenches are consistent with either pacific north america or pacific okhotsk plate motion to circumvent this difficulty we also use slip vectors of earthquakes along sakhalin island and the eastern margin of the japan sea and compare them to the predicted eurasia okhotsk and eurasia north america motions for a model with a separate okhotsk plate we invert 10 eurasia okhotsk and 255 pacific okhotsk slip vectors with pacific north america and eurasia north america nuvel 1 data alternatively for a model without an okhotsk plate those eurasia okhotsk and pacific okhotsk data are regarded as eurasia north america and pacific north america data respectively the model with an okhotsk plate fits the data better than one in which this region is treated as part of the north american plate because the improved fit exceeds that expected purely from the additional plate the data indicate that the okhotsk plate can be resolved from the north american plate the motions on the okhotsk plate s boundaries predicted by the best fitting euler vectors are generally consistent with the recent tectonics the eurasia okhotsk pole is located at northernmost sakhalin island and predicts right lateral strike slip motion on the nne striking fault plane of the may 27 1995 neftegorsk earthquake consistent with the centroid moment tensor focal mechanism and the surface faulting along the northern boundary of the okhotsk plate the north america okhotsk euler vector predicts left lateral strike slip consistent with the observed focal mechanisms on the nw boundary of the okhotsk plate the eurasia okhotsk euler vector predicts e w extension discordant with the limited focal mechanisms and geological data this misfit may imply that another plate is necessary west of the magadan region in southeast siberia but this possibility is hard to confirm without further data such as might be obtained from space based geodesy

inversion of bottom hole temperature data the pineview field utah wyoming thrust belt the present day temperature field in a sedimentary basin is a constraint on the maturation of hydro carbons this temperature field may be estimated by inverting corrected bottom hole temperature bht data thirty two bhts from the pineview oil field are corrected for drilling disturbances by a horner plot and inverted for the geothermal gradient in nine formations both least squares l2 norm and uniform l1 norm inversions are used the l1 norm is found to be more robust for the pineview data the inversion removes random error from the corrected bht data by partitioning scatter between noise associated with the bht measurement and correction processes and local variations in the geothermal gradient three hundred thermal conductivity and density measurements on drill cuttings are used together with formation density logs to estimate the in situ thermal conductivity of six of the nine formations the thermal conductivity estimates are used in a finite element model to evaluate 2 d conductive heat r

estimates of terrestrial heat flow in northern chihuahua mexico based upon petroleum bottom hole temperatures bottom hole temperature data from deep petroleum tests are used in conjunction with estimated and measured thermal conductivity values to estimate heat flows at 12 sites in northern chihuahua the errors and uncertainties associated with these estimates and measurements are discussed from these heat flow estimates several geothermal regions are proposed which appear reasonable in terms of data statistics and the geologic environments in northeastern chihuahua an area of considerable tectonic activity with no cenozoic volcanic activity the heat flow mean is 73 mw m 2 westward in north central chihuahua the heat flow values become 85 mw m 2 farther westward in northwestern chihuahua heat flows 105 mw m 2 are estimated however there is only a modest probability that mean heat flow values for northwestern and north central chihuahua differ very high heat flows 250 mw m 2 and low heat flows 2 are not observed in north central or in northwestern chihuahua the deep temperature data may be removed from the effects of hydrothermal activity in sediments and along faults which can cause very high or low values it may also be possible that potential magma sources in the crust of the study area are not as young and hot as the sources associated with the volcanics along the rio grande rift in new mexico although heat flows of 105 mw m 2 do suggest crustal magmatic sources additional geophysical data will be needed to consider these possibilities

independent active microplate tectonics of northeast asia from gps velocities and block modeling 1 independent okhotsk and amurian microplate motions are tested using velocities from 123 gps sites 80 from within the proposed okh and amu plate boundaries used to constrain the plate kinematics of northeast asia a block modeling approach is used to incorporate both rigid block rotation and near boundary elastic strain accumulation effects in a formal inversion of the gps velocities models include scenarios with and without independent okh and amu plate motion our modeling favors scenarios with independent okh and amu motion based on the application of f test statistics the independent okh plate rotates 0 231 deg myr clockwise with respect to north america about a pole located north of sakhalin the modeled amu plate rotates 0 298 deg myr counterclockwise with respect to nam about a pole located west of the magadan region the plate motion parameters of the independent plates are consistent with the kinematics inferred from earthquake focal mechanism solutions along their boundaries

estimates of terrestrial heat flow from deep petroleum tests along the rio grande rift in central and southern new mexico twenty six new estimates of heat flow are calculated for the albuquerque belen basin and the basins of the southern rio grande rift in new mexico from these and previous data the following heat flow patterns may be suggested the regional or background heat flow in the albuquerque belen basin is 77 mw m 2 there is also a ne sw trend of higher heat flow 92 110 mw m 2 across the region in the southern rio grande rift between socorro and las cruces the regional heat flow appears to be 95 mw m 2 in this region there are also higher heat flows 117 135 mw m 2 at widely scattered sites south of las cruces near the international border between mexico and the united states preliminary and perhaps suspect data suggest the possibility of a transition to the intermediate heat flows previously estimated at sites throughout much of northeastern chihuahua mexico regional heat flow values in the albuquerque belen basin and in the basins of the southern rio grande rift are consistent with but do not constrain simple models of crustal thinning higher heat flows in these two areas are thought to be caused by hydrothermal fluids largely groundwaters but possibly magma in some areas transporting heat upward along crustal fracture zones

possible influences of thermal stresses on basin and range faulting reasonable if not conclusive arguments may be made for the heating and subsequent cooling of the basin and range province during middle and late cenozoic time it is proposed that thermal stresses developed during this time and played a role in the formation of basin and range structure the analysis depends upon physical models which are surely a simplification of the actual heating and or cooling occurring in geological environments where rock failure and faulting are influenced by regional tectonic stresses the rock fabric and previously induced zones of weakness nevertheless the one dimensional models which represent crustal heating by means of an increase of temperature at depth and crustal cooling in concert with overall lithospheric cooling allow an appreciation that thermal stresses developing more or less contemporaneously with heating or cooling events are of sufficient magnitude to be considered important contributions to rock failure the thermal stresses are oriented in a manner generally consistent with observed faulting across the basin and range province it is therefore suggested that thermal stresses may have combined with regional tectonic stresses to help promote the structures observed in the basin and range province

thermal histories and hydrocarbon generation example from utah wyoming thrust belt the thermal history of the utah wyoming thrust belt in the vicinity of the pineview oil and gas field is studied with a detailed thermal model the model incorporates a heterogeneous thermal conductivity structure radioactive heat generation in the crust sediment compaction variable basal heat flow through time and thermal effects of sedimentation erosion and thrust faulting the analysis is constrained by 206 corrected bottom hole temperatures 660 thermal conductivity measurements and 10 new vitrinite reflectance measurements present surface heat flow in this part of the utah wyoming thrust belt is estimated to be 60 8 mw m2 surface heat flow in the late cretaceous about 70 ma is inferred to have been 38 8 mw m2 from an lysis of vitrinite reflectance data about half of the apparent difference between ancient and present surface heat flow may be attributed to transient thermal effects of sedimentation erosion and thrusting the hypothesis of a constant background thermal state in this part of the thrust belt for the last 70 m y may not be ruled out however thermal history simulations in which the background thermal state changes through time better match constraints imposed by estimated present surface heat flow and vitrinite reflectance data application of the thermal history analysis to hydrocarbon generation is illustrated with a kinetic model of organic maturation oil and gas at the pineview field may have been generated in two stages first stage just before and during thrusting and the second stage during cenozoic warming

an integrated global model of present day plate motions and plate boundary deformation summary in this paper we present a global model gsrm 1 of both horizontal velocities on the earth s surface and horizontal strain rates for almost all deforming plate boundary zones a model strain rate field is obtained jointly with a global velocity field in the process of solving for a global velocity gradient tensor field in our model we perform a least squares fit between model velocities and observed geodetic velocities as well as between model strain rates and observed geological strain rates model velocities and strain rates are interpolated over a spherical earth using bi cubic bessel splines we include 3000 geodetic velocities from 50 different mostly published studies geological strain rates are obtained for central asia only and they are inferred from quaternary fault slip rates for all areas where no geological information is included a priori constraints are placed on the style and direction but not magnitude of the model strain rate field these constraints are taken from a seismic strain rate field inferred from normalized focal mechanisms of shallow earthquakes we present a global solution of the second invariant of the model strain rate field as well as strain rate solutions for a few selected plate boundary zones generally the strain rate tensor field is consistent with geological and seismological data with the assumption of plate rigidity for all areas other than the plate boundary zones we also present relative angular velocities for most plate pairs we find that in general there is a good agreement between the present day plate motions we obtain and longterm plate motions but a few significant differences exist the rotation rates for the indian arabian and nubian plates relative to eurasia are 30 13 and 50 per cent slower than the nuvel1a estimate respectively and the rotation rate for the nazca plate relative to south america is 17 per cent slower on the other hand caribbean north america motion is 76 per cent faster than the nuvel 1a estimate while crustal blocks in the india eurasia collision zone move significantly and self consistently with respect to bounding plates only a very small motion is predicted between the nubian and somalian plates by integrating plate boundary zone deformation with the traditional modelling of angular velocities of rigid plates we have obtained a model that has already been proven valuable in for instance redefining a no net rotation model of surface motions and by confirming a global correlation between seismicity rates and tectonic moment rates along subduction zones and within zones of continental deformation

tethyan collision forces and the stress field of the eurasian plate resistive forces along convergent plate boundaries have a major impact on surface deformation most visibly at collisional plate boundaries although quantification of these forces is key to understanding the evolution and present state of mountain belts they remain highly uncertain due to the complexity of plate boundary structures and rheologies in previous studies of the eurasian plate we have analysed the balance of plate boundary forces tractions resulting from lithosphere mantle coupling and intraplate variations in topography and density structure this yielded a range of acceptable force distributions in this study we investigate to which extent the observed present day stress field provides further constraints on the distribution of forces we address the dynamics of the eurasian plate as a whole this enables us to base our analysis on mechanical equilibrium of a tectonic plate and to evaluate all forces as part of an internally consistent set of forces driving and deforming eurasia we incorporate tractions from convective mantle flow modelling in a lithospheric model in which edge and lithospheric body forces are modelled explicitly and compute resulting stresses in a homogeneous elastic thin shell intraplate stress observations used are from the world stress map project eurasia s stress field turns out to be particularly sensitive to the distribution of collision forces on the plate s southern margin and to a much lesser extent to lithospheric density structure and tractions from mantle flow stress observations require collision forces on the india eurasia boundary of 7 0 10 5 tn m 1 and on the arabia eurasia boundary of 1 3 2 7 tn m 1 implication of mechanical equilibrium of the plate is that forces on the contacts with the african and australian plates amount to 1 0 2 5 and 0 1 3 tn m 1 respectively we use our results to assess the validity of the classical view that the mean elevation of an orogenic plateau can be taken as a measure of the magnitude of the compressive in this case collision related forces involved for both the tibetan and the iranian plateaus two plateaus with significantly different average elevations we find that the horizontal force derived from the excess gravitational potential energy collapse force is in balance with the collision force

insulating effect of coals and black shales in the appalachian basin western pennsylvania sedimentary rocks rich in organic matter often have lower thermal conductivities than other rock types as a result of this natural insulating effect temperature gradients in carbonaceous strata may become elevated even under conditions of low to average heat flow causing underlying rocks to reach higher temperatures and higher thermal maturities than would otherwise occur this hypothesis was tested by determining the weighted average thermal conductivity of a carboniferous coal bearing section from the conemaugh group of the appalachian basin coals from the sampled section yielded low thermal conductivity values of 0 2 0 15 wm 1 k 1 when measured with a needle probe apparatus measurements of other carbonaceous units also showed low thermal conductivity values 0 9 0 05 wm 1 k 1 for black shales and 1 2 0 20 wm 1 k 1 for dark gray shales relative abundances of all measured lithologies were estimated from a 288 well database these abundances yielded an average conductivity of 1 6 wm 1 k 1 for the entire conemaugh group geothermal gradients for the conemaugh group estimated from thermal conductivity and heat flow data range from 38 to 47 mk m 1 in good agreement with gradients estimated from the actual thermal maturity of coals the additional temperature increment contributed to underlying rocks by this insulating effect may help explain the anomalous thermal maturity of the appalachian basin reducing the need to call upon excessive burial or higher values of heat flow in the past

morphostratigraphy and provenance of plio pleistocene terraces in the south eastern alpine foreland the mislinja and upper savinja valleys northern slovenia

using precision temperature logs to estimate horizontal and vertical groundwater flow components a new method of estimating the horizontal and vertical specific discharge components of groundwater flow from precision subsurface temperature measurements is presented plotting the vertical temperature gradient as a function of both z and t and then fitting a plane to the data can provide coefficients from which the vertical and horizontal groundwater specific discharge components may be estimated alternatively by considering the vertical component of groundwater to be zero it is shown that quadric or cubic fits to temperature data provide coefficients from which horizontal groundwater flow may be estimated these expressions along with expressions previously derived to estimate only vertical only horizontal or both vertical and horizontal flow components are fitted to observational data from four sites and five flow zones it is learned for these examples using an available fitting program that although many of the expressions fit the observational data very well statistically those expressions which incorporate both the vertical and horizontal flow components of specific discharge must generally be constrained so that resulting parameters will provide flow estimates consistent in direction and heat transfer with available piezometer data and or the fundamental curvature of the temperature log expressions incorporating only x or only z can sometimes yield estimates quite different from the estimates obtained from the expressions incorporating both x and z it is concluded that an estimate of the horizontal and vertical flow components requires both consideration of the flow calculations along with available piezometric data and the fundamental curvature of the temperature log

current deformation rates and extrusion of the northwestern okhotsk plate northeast russia 1 northeast asia is a region of broad deformation resulting from the convergence of the eurasian eu and north american na plates part of this convergence has been suggested to be relieved by the extrusion and deformation of the okhotsk plate ok three models for the deformation of the seismically active northwestern corner of the okhotsk plate based on different modes of deformation partitioning are calculated and compared to observations from gps seismicity and geology the results suggest that this region is being extruded southeastward and deforming internally by a mixture of pure contraction smooth extrusion and rigid extrusion calculated extrusion rates are 3 5 5 mm yr comparable to estimates from geologic data and internal deformation rates are 3 0 10 9 yr 1 internal deformation may be only partially accommodated by seismicity but the short time span of seismic data leaves this subject to large uncertainty

heat flow in the utah wyoming thrust belt from analysis of bottom hole temperature data measured in oil and gas wells bottom hole temperature bht data from oil and gas wells represent a large albeit low quality data base for heat flow determinations a method for analyzing bht data sets that directly addresses the problem of noise in the data is presented and illustrated by application to 303 bhts from the anschutz ranch ar cave creek cc and anschutz ranch east are oil gas fields in the utah wyoming thrust belt located in the middle rocky mountain physiographic province of the western united states correction of raw bht data by means of a horner plot yields 81 corrected bhts an additional 90 bhts not suitable for a horner correction are corrected by means of a new bht correction which may be applied to any single bht for which a depth and time of measurement are known the average geothermal gradient at both ar cc and are is found to be 23 c km although an average gradient analysis fails to explain scatter in the data analysis of corrected bhts through inversion of a layered earth model yields estimates of formation thermal gradients and temperature fields at ar cc and are that are stable and unique with an average precision of 2 to 3 c thermal conductivity measurements were made on 360 drill cutting samples representing 14 thrust belt formations in situ conductivity is estimated using porosity from calibrated well logs heat flow is estimated by comparing temperature calculated by a two dimensional finite element model with temperature estimated from analysis of bht data analysis of bht data from the ar cc area yields an estimated regional heat flow of 60 mw m2 8 mw m2 a similar analysis at are results in an estimate of 58 mw m2 8 mw m2 these estimates are close to values determined for the wyoming basin and the central colorado plateau and imply that a thermal transition from the middle rocky mountains to elevated heat flow characteristic of the basin and range province 80 to 90 mw m2 must take place within 50 km

clearing observed pgr in grace data aimed at global viscosity inversion weighted mass trends technique 1 the time variable gravity field shows the effects of large present day mass variations associated with hydrological phenomena and melting ice sheets resulting in a shaded post glacial rebound pgr signal a meaningful viscosity inversion based on a global scale comparison of grace data and pgr predictions is thus hard to obtain we derive a weighted surface mass distribution in water equivalent starting from an initial guess which portrays the secular effects of present day phenomena the gravity field it generates is then carefully removed from grace data resulting in a gravity pattern where the effects of pgr are clearer and ready to be compared with the predictions on the basis of viscoelastic stratified earth models and different pleistocene deglaciation models we show that the quality of a global preliminary viscosity inversion greatly improves

contingency table analysis of pebble lithology and roundness a case study of huangshui river china and comparison to rivers in the rocky mountains usa abstract contingency table analysis of pebble lithology and roundness is an effective way to identify the source terrane of a drainage basin and to distinguish changes in basin size piracy tectonism and other events first the analysis to terrace gravel deposited by the huangshui river northeastern tibet plateau china shows statistically contrasting pebble populations for the oldest terrace t7 dadongling 1 2 ma and the youngest terraces t0 t3 0 15 ma two fluvial processes are considered to explain the contrast in correlation between lithology and roundness in t7 gravel versus t0 t3 gravel 1 reworking of t7 gravel into t0 t3 gravel and 2 growth in the size of the river basin between t7 and t0 t3 times we favor growth in basin size as the dominant process from comparison of pebble counts and contingency tables second comparison of results from huangshui river of china to three piedmont streams of the rocky mountains usa highlights major differences in source terrane and history like rocky mountain piedmont gravel from colorado examples the huangshui gravels show a preference observed versus expected frequency for rounded granite but unlike rocky mountain gravel huangshui gravel shows a preference for angular quartzite and for rounded sandstone in conclusion contrasting behavior of lithologies during transport not always apparent in raw pebble counts is readily analyzed using contingency tables to identify the provenance of individual lithologies including recycled clasts results of the analysis may help unravel river history including changes in basin size and lithology

analysis of temperatures in sedimentary basins the michigan basin we develop an analytical and numerical methodology for the analysis of large bottom hole temperature bht data sets from sedimentary basins and test the methodology using temperature stratigraphic and lithologic data from 411 boreholes in the michigan basin least squares estimates of temperature gradients in the formations and lithologies present are calculated as solutions to a large system of linear equations at each borehole the temperature difference between the bottom and top of the hole is represented as a sum of temperature increments through the various formations or lithologies penetrated by the borehole quadratic programming techniques enable bounds to be placed on the gradient solutions in order to suppress or exclude improbable gradient estimates numerical experiments with synthetic data reveal that the estimates of temperature gradients for a given formation or lithology are sensitive to the degree of representation of that unit well represented units have more stable gradient estima

paleocurrent and fabric analyses of the imbricated fluvial gravel deposits in huangshui valley the northeastern tibetan plateau china abstract gravel deposits on fluvial terraces contain a wealth of information about the paleofluvial system in this study flow direction and provenance were determined by systematic counts of more than 2000 clasts of imbricated gravel deposits in the xining region northeastern tibetan plateau china these gravel deposits range in age from the modern huangshui riverbed to miocene aged deposits overlain by eolian sediments our major objectives were not only to collect first hand field data on the fluvial gravel sediments of the xining region but also to the reconstruct the evolution of the fluvial system these data may offer valuable information about uplift of the northeastern tibetan plateau during the late cenozoic era reconstructed flow directions of the higher and lower gravel deposits imply that the river underwent a flow reversal of approximately 130 180 in addition the lithological compositions in the higher gravel deposits differ significantly from the lower terraces suggesting that the source areas changed at the same time eolian stratigraphy overlying the gravel deposits and paleomagnetic age determination indicate that this change occurred sometime between 1 55 ma and 1 2 ma we suggest that tectonic activity could explain the dramatic changes in flow direction and lithological composition during this time period therefore this study provides a new scenario of fluvial response to tectonic uplift a reversal of flow direction in addition field observation and statistical analyses reveal a strong relationship between rock type size and roundness of clasts

heat flow in the presence of topography numerical analysis of data ensembles we present a method of estimating subsurface temperatures and true regional heat flow in the presence of perturbing topography variable surface temperature and subsurface thermal conductivity contrasts the method involves solution of the steady state three dimensional heat conduction equation by finite difference numerical techniques the topography is represented by an irregular upper boundary and the variable surface temperature as a boundary condition along the irregular upper surface internal structural configurations and conductivity contrasts are easily accommodated the principal variable input into the system is the deep basal unperturbed heat flow the best value of heat flow is obtained by minimizing in a least squares sense the differences between observed and calculated temperatures temperature observations commonly are distributed irregularly in the near surface perturbed environment in multiple vertical or inclined boreholes tunnels and or mine galleries the method is particul

long term controls on continental scale bedrock river terrace deposition from integrated clast and heavy mineral assemblage analysis an example from the lower orange river namibia abstract establishing relationships between the long term landscape evolution of drainage basins and the fill of sedimentary basins benefits from analysis of bedrock river terrace deposits these fragmented detrital archives help to constrain changes in river system character and provenance during sediment transfer from continents source to oceans sink thick diamondiferous gravel terrace deposits along the lower orange river southern namibia provide a rare opportunity to investigate controls on the incision history of a continental scale bedrock river clast assemblage and heavy mineral data from seven localities permit detailed characterisation of the lower orange river gravel terrace deposits two distinct fining upward gravel terrace deposits are recognised primarily based on mapped stratigraphic relationships cross cutting relationships and strath and terrace top elevations and secondarily on the proportion of exotic clasts referred to as proto orange river deposits and meso orange river deposits the older early to middle miocene proto orange river gravels are thick up to 50 m and characterised by a dominance of karoo supergroup shale and sandstone clasts whereas the younger plio pleistocene meso orange river gravels 6 23 m thick are characterised by more banded iron formation clasts mapping of the downstepping terraces indicates that the proto gravels were deposited by a higher sinuosity river and are strongly discordant to the modern orange river course whereas the meso deposits were deposited by a lower sinuosity river the heavy minerals present in both units comprise magnetite garnet amphibole epidote and ilmenite with rare titanite and zircon grains the concentration of amphibole epidote in the heavy minerals fraction increases from the proto to the meso deposits the decrease in incision depths recorded by deposit thicknesses above strath terraces and the differences in clast character size and roundness and type between the two units are ascribed to a more powerful river system during proto orange river time rather than reworking of older deposits changes in provenance or climatic variations in addition from proto to meso orange river times there was an increase in the proportion of sediments supplied from local bedrock sources including amphibole epidote in the heavy mineral assemblages derived from the namaqua metamorphic complex this integrated study demonstrates that clast assemblages are not a proxy for the character of the matrix and vice versa because they are influenced by the interplay of different controls therefore an integrated approach is needed to improve prediction of placer mineral deposits in river gravels and their distribution in coeval deposits downstream

two stage evolution of the altyn tagh fault during the cenozoic new insight from provenance analysis of a geological section in nw qaidam basin nw china introductionthe 1600 km long active altyn taghfault atf de nes the northern edgeof the tibetan plateau links thewestern kunlun eastern kunlun andqilian orogenic belts fig 1a and gures prominently in constrainingthe timing mechanism and stress dis sipation of the tibetan uplift e g yinand harrison 2000 tapponnier etal 2001 cowgill et al 2003 aspectof its cenozoic evolution has beenattracting hot debate zhou and gra ham 1996 yue and liou 1999 yinet al 2002 liu et al 2007 and akey issue is the initiation of left slipmovement on the fault which wasconsidered to occur i during lateeocene early oligocene evidenced bythermochronology in the altynmountain chen et al 2001 andsedimentology adjacent to the fault meng et al 2001 yue et al 2001 ritts et al 2004 or ii since middlemiocene through structural analysisin the qaidam basin yuan et al 2008 wang et al 2010 apatite s sion track result along the atf wanet al 2001 chen et al 2002 andcomprehensive analysis of the north ern tibetan plateau burch el et al 1989 wang 1997 meyer et al 1998 yin et al 2002 argued a much earlierinitiation age 49 ma of the westernand central segments of the atf butwith questionable proofs ritts et al 2004 two factors probably lead tothis uncertainty i the atf is toolarge to allow us to nd an appropri ate proxy deciphering accurately itsevolution and ii most extant studiesshare a bias that the atf has beenalways a left slip fault during thecenozoic which we regard as a mis understanding in this paper provenance analysis has beenproved e ective on revealing theuplifting history of mountains andevolution of major faults e g lindseyet al 2007 miao et al 2008 linet al 2009 marsaglia et al 2010 the qaidam basin is the largest sed imentary basin inside the tibetan pla teau and accumulated thick terrestrialsediments during the cenozoic rieseret al 2006 making itself an idealplace for deciphering the uplift andpropagation of the plateau yin et al 2007 2008 as it is bounded by theatf to the northwest fig 1b itssedimentation has possibly been tiedto the development of this large scaleintracontinentalfault fewworkshavebeen done on this subject due to thetough geographic conditions in thispaper we investigated a geologicalsection spanning eocene pliocene inthe nw qaidam basin and analysedin detail provenance of the sediments we link the result to cenozoic evolu tion of the atf and try to illustrate together with some other evidences that the atf was used to be a basalshear zone before its initiation of left slip since middle miocene which rec onciles the two contrasting viewpointson the cenozoic initiation of the atfabovementioned geological settingthe study section is seated at thesouthern side of the atf and incisesthe western limb of the nw trendingganchaigou anticline bounded to thenorth by a north directed reversefault a branch fault of the atf fig 1c the cenozoic strata are wellexposed in the section including thexiaganchaigou xg shangganchai gou sg xiayoushashan xy shangyoushashan sy and shizigou szg formations in an ascendingorder the xg formation consists of redmudstone siltstone and sandstoneattaining bed thickness of 0 2 1 m interbedded with conglomerate andpebble sandstone layers 10 20 cmthick figs 2 and 3a the stratumeven comprises more than 100 mthick calcareous mudstones in theupper part in the drillhole chaishen 3 about 6 km east of the sectionabstract

depth time correction of petroleum bottom hole temperatures in the po plain italy we have analyzed a wide set of time temperature data from petroleum wells in two areas of the po plain italy and propose empirical temperature corrections for mud circulation formation thermal parameters and the temperature dependence of thermal conductivity are taken into account analyses show that formation equilibrium temperatures computed with the horner method compare well with those obtained by the cooper and jones method which gives on average temperatures lower by only 2 c for shut in times less than 10 hours the corrected temperatures compared with temperatures measured during drillstem tests show that the proposed corrections are relatively accurate the two data sets give coherent results and the inferred average geothermal gradient is 21 5 mk m in the apenninic buried arc area and 25 2 mk m in the south piedmont basin pedealpine homocline area the horner slope data as a function of depth are then fitted with a second order polynomial and depthtime correction equations are calibrated for the two areas finally we propose an empirical function for the estimate of the mud circulation time which is often unavailable

evaluating a 2d image based computerized approach for measuring riverine pebble roundness abstract the geometrical characteristics of pebbles are important features to study transport pathways sedimentary history depositional environments abrasion processes or to target sediment sources both the shape and roundness of pebbles can be described by a still growing number of metrics in 2d and 3d or by visual charts despite new developments existing tools remain proprietary and no pebble roundness toolbox has been available widely within the scientific community the toolbox developed by roussillon et al 2009 automatically computes the size shape and roundness indexes of pebbles from their 2d maximal projection plans using a digital camera this toolbox operates using 2d pictures taken of pebbles placed on a one square meter red board allowing data collection to be quickly and efficiently acquired at a large scale now that the toolbox is freely available for download 1 an evaluation is needed to help end users sample process and interpret the data we first assess the influence of pebble position and of the resolution and enhancement of pictures and errors associated with the sampling size second we run experimental flume tests of roundness trends that confirm the great potential of the toolbox for river geomorphic diagnoses as well as for targeting sediment sources we also validate the correlation between roundness metric trends and particle abrasion

determination of thermal properties and formation temperature from borehole thermal recovery data thermal recovery in boreholes cooled by circulation of drilling mud has been modeled for estimating formation temperature and thermal conductivity coupled with a finite element simulation of heat conduction inverse modeling for the desired parameters starts with a genetic algorithm that feeds initial estimates of model parameters to an iterative quasi linear inversion scheme in addition to using the rms misfit between the computed and observed borehole temperatures the results are assessed by comparing or constraining the model formation temperature with a value obtained conventionally from an asymptotic temperature time relation for a steady line source the model conductivity is further evaluated for equality with a conductivity value which is estimated through simulation of heat exchange between the formation and circulating mud test results on synthetic data and two sets of highly noisy borehole data from lake baikal in russia indicate that the two equality criteria in temperature and conductivi

influence of overthrusting on maturation of hydrocarbons in phosphoria formation wyoming idaho utah overthrust belt geochemical analyses were performed on 11 phosphoria formation samples collected throughout the wyoming idaho utah overthrust belt maturation models incorporating the thermal effects of thrust faulting with lopatin s techniques were then used to interpret these geochemical data in particular four of the sample sites were selected for detailed thermal modeling these four sites include one sample site in an area unaffected by thrusting two sites located in the hanging walls of major thrusts and one site in the footwall of the darby thrust the detailed thermal modeling shows overthrusting did affect the thermal history of the phosphoria formation the effect of thrusting was to cool the overriding sheet and warm the sediments being overridden thus the hanging wall samples had a different post thrusting thermal history than the footwall sample cooling of the hanging wall slowed post thrusting maturation in the two thrust sheet samples in contrast the footwall sample was exposed to higher temperatures after thrusting and the maturation process was accelerated results of this study indicate that tectonism influences the thermal history of the rocks and should be included in any reliable source rock evaluation program involving overthrust strata a simple evaluation based only on the thickness of the overburden in general will not be sufficient to explain fully the maturation data in the absence of actual geochemical information such as ro tai or cai the models described in this paper appear to be sufficiently accurate to give a reasonable estimate of thermal maturity of a potential source bed

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

geothermal studies in the san juan basin and the four corners area of the colorado plateau ii steady state models of the thermal source of the san juan volcanic field abstract the increase of heat flow approaching the san juan volcanic field depicts a smooth profile having a relatively large half width perhaps 50 100 km one may suggest thermal sources creating the observed anomaly at equivalent depths under or in proximity to the san juan volcanic field although the cause of the increased heat flow approaching the san juan field may be in part associated with more regional southern rocky mountain tectonics geologic heat flow and seismic data support the idea of a separate thermal source associated with the san juan volcanic field it can be shown that cooling and solidification of very deep magma bodies to 75 km provide less heat than required by the observed anomaly replenishment of the thermal source causing the heat flow anomaly is postulated this replenishment is approximated in a limiting case by developing finite difference steady state models the best models are consistent with a plume which rises from depths of at least 100 km to depths as shallow as 35 km whose edge is about 10 km south of durango

estimation of the thermal conductivity anisotropy of rock with application to the determination of terrestrial heat flow a moderately large data set of mostly sedimentary and metamorphic rocks compiled from the literature shows an inverse correlation between thermal conductivity anisotropy and thermal conductivity perpendicular to bedding the empirical relationship can be represented by a simple two component end member mixing model one end member is anisotropic x z 2 5 and has a relatively low thermal conductivity perpendicular to bedding z 1 w m k the other end member is isotropic and has a relatively high thermal conductivity perpendicular to bedding 4 w m k the proposed model may be used to derive a correction for anisotropic effects observed during thermal conductivity measurements on mixtures of randomly oriented aggregates although the accuracy and reliability of a universal correction procedure remain to be determined the proposed correction scheme should enhance our ability to estimate accurately heat flow in sedimentary basins where generally only borehole cuttings are available for thermal conductivity measurements

shear wave structure of the upper crust of the albuquerque belen basin from rayleigh wave phase velocities fundamental mode rayleigh wave phase velocities have been obtained for the albuquerque belen basin of the rio grande rift source and instrumental characteristics limited useful data to the period band 6 12 s inversion of the phase velocity data yielded a model for the shear velocity of the upper 20 km of the basin the model contains two velocity inversions one near a depth of 6 km the other near 18 km the velocity inversion near 18 km is attributed to the effects of a midcrustal magma body known from previous studies the cause of the low velocity zone near 6 km is not known but it may be caused by an upper crustal magma body the average of the velocities for the upper crustal model presented here ave 3 33 km s is comparable to those reported in previous studies

global tectonics and space geodesy much of the success of plate tectonics can be attributed to the near rigidity of tectonic plates and the availability of data that describe the rates and directions of motion across narrow plate boundaries m 1 to 60 kilometers wide nonetheless many plate boundaries in both continental and oceanic lithosphere are not narrow but are hundreds to thousands of kilometers wide wide plate boundary zones cover m 15 percent of earth s surface area space geodesy which includes very long baseline radio interferometry satellite laser ranging and the global positioning system is providing the accurate long distance measurements needed to estimate the present motion across and within wide plate boundary zones space geodetic data show that plate velocities averaged over years are remarkably similar to velocities averaged over millions of years

quartzite selection in fluvial deposits the n12 level of roca dels bous middle palaeolithic southeastern pyrenees abstract the exploitation of rocks from secondary deposits is attested widely in the european middle palaeolithic however few studies have focused on analysing the implications derived from the management of these deposits the fluvial terraces near the mousterian site of roca dels bous have been sampled to determine their lithological composition and cobble morphology comparison with artefacts recovered from level n12 indicate selection patterns in the fluvial deposits of black quartzite as well as preferential management of blanks with specific morphological and volumetric characteristics this approach reveals behaviours involved in the acquisition transport transformation and discard of stone tools necessary for neanderthal subsistence and indicates interest in the study of secondary deposits and local raw materials in middle palaeolithic contexts