prediction of lithofacies and reservoir quality using well logs late cretaceous williams fork formation mamm creek field piceance basin colorado understanding the controls and distribution of reservoir quality is important for the economic success of tight gas reservoirs in which diagenesis interacts with primary depositional variations in environment and texture to exert a strong control on pore networks rock mechanical properties and natural fractures in the upper cretaceous williams fork formation of the piceance basin framework grain composition is a major control on compaction and the occurrence of authigenic phases alteration of volcanic grains in the upper williams fork led to grain coating clay precipitation ferroan dolomite cement is found only in the deeper marine influenced intervals in which dolostone fragments are present this study shows that careful petrographic assessment of lithofacies heterogeneity can be upscaled by correlation with log properties to yield tools for field scale reservoir quality prediction twelve lithofacies are identified based on sand grain populations cement types and clay matrix content sandstones of the highest reservoir quality are those with grain coating clays that inhibit quartz cementation these sandstones can be identified based on high density porosity log values sandstones with the poorest reservoir qualities are tightly cemented with carbonate and quartz cement or are rich in clay matrix carbonate cemented intervals are identified by low density porosity clay matrix rich samples have high gamma ray and low density porosity values the presence of abundant potassium feldspar in the upper intervals results in high gamma ray readings even in the clean clay matrix free sandstone

experimental determination of dynamic pore throat structure characteristics in a tight gas sandstone formation with consideration of effective stress abstract in this study a robust and pragmatic technique has been developed to experimentally quantify the dynamic characteristics of microscopic pore throat structure with consideration of effective stress in a tight gas sandstone formation more specifically porosity and permeability of highly heterogeneous core samples collected from a tight gas reservoir were measured and then thin section analysis as well as other analyses with the scanning electron microscopy and x ray diffraction techniques were performed to identify and classify the particle composition grain size clay minerals and pore and throat types subsequently pore throat structure such as its connectivity radius and size distributions were determined by conducting pressure controlled mercury injection and rate controlled mercury injection tests respectively in addition the nuclear magnetic resonance nmr technique is employed to examine effect of stress sensitivity on porosity and permeability as well as pore and throat radius under different pore pressures by decreasing the pore pressure from 30 0 to 1 0 mpa and the corresponding effective stress was increased from 0 to 29 0 mpa as such the pores and throats become smaller and the average proportion of volume controlled by nano scale throat with the radius less than 100 nm increased from 48 01 to 48 90 while the average volumetric proportion controlled by micron scale and submicron scale throats was decreased from 46 57 to 46 37 the shrinkage of pores and throats resulted in an average reduction for porosity and absolute permeability from 10 43 to 6 84 and from 0 01237 to 0 00501 md respectively moreover samples with a lower permeability showed more serious permeability damage illustrating that they experience a stronger stress sensitivity than those with a higher permeability

controls on reservoir quality of lower cretaceous tight sandstones in the laiyang sag jiaolai basin eastern china integrated sedimentologic diagenetic and microfracturing data abstract the jiaolai basin fig 1 is an under explored rift basin that has produced minor oil from lower cretaceous lacustrine deltaic sandstones the reservoir quality is highly heterogeneous and is an important exploratory unknown in the basin this study investigates how reservoir porosity and permeability vary with diagenetic minerals and burial history particularly the effects of fracturing on the diagenesis and reservoir deliverability the laiyang sandstones are tight reservoirs with low porosity and permeability

a model for fibrous illite nucleation and growth in sandstones we have developed a model for the formation of fibrous illite in sandstones where kaolinite is a primary reactant and potassium is derived from in situ k feldspar grain dissolution or imported into the model reference frame illite fiber nucleation and growth are modeled using arrhenius expressions that consider saturation state in addition to temperature and time nucleation occurs on pore walls and muscovite and detrital illite may be defined as energetically favorable substrates the model is integrated with other touchstone models to account for the influence of other diagenetic processes on surface area and reactant volumes and to provide input for permeability simulations we evaluated the illite model performance on two data sets 1 jurassic quartzose samples from offshore mid norway with maximum temperatures ranging from 108 to 173c 226 to 343f and 2 miocene lithic samples from offshore southeast asia that have maximum temperatures ranging from 157 to 182c 315 to 360f the model matches measured abundances of illite kaolinite and k feldspar in both data sets using identical kinetic parameters predicted k ar ages are consistent with available data given uncertainties associated with detrital contaminants although no illite particle size data are available from the analyzed samples modeled crystallite thicknesses from the norway data set are comparable to published measurements of 0 004 to 0 012 m from north sea samples with similar temperature histories

spectrum of pore types and networks in mudrocks and a descriptive classification for matrix related mudrock pores matrix related pore networks in mudrocks are composed of nanometer to micrometer size pores in shale gas systems these pores along with natural fractures form the flow path permeability network that allows flow of gas from the mudrock to induced fractures during production a pore classification consisting of three major matrix related pore types is presented that can be used to quantify matrix related pores and relate them to pore networks two pore types are associated with the mineral matrix the third pore type is associated with organic matter om fracture pores are not controlled by individual matrix particles and are not part of this classification pores associated with mineral particles can be subdivided into interparticle interp pores that are found between particles and crystals and intraparticle intrap pores that are located within particles organic matter pores are intrap pores located within om interparticle mineral pores have a higher probability of being part of an effective pore network than intrap mineral pores because they are more likely to be interconnected although they are intrap om pores are also likely to be part of an interconnected network because of the interconnectivity of om particles in unlithifed near surface muds pores consist of interp and intrap pores and as the muds are buried they compact and lithify during the compaction process a large number of interp and intrap pores are destroyed especially in ductile grain rich muds compaction can decrease the pore volume up to 88 by several kilometers of burial at the onset of hydrocarbon thermal maturation om pores are created in kerogen at depth dissolution of chemically unstable particles can create additional moldic intrap pores

focal mechanisms and stress variations in the caucasus and northeast turkey from constraints of regional waveforms abstract the continental collision between arabia and eurasia created large strike slip faults in turkey as well as mountains in the caucasus and the volcanic plateau between them in this study we use regional waveforms of a new seismic array deployed between 2008 and 2012 to constrain the focal mechanisms and depths of small to moderate sized earthquakes occurring in the western part of the central caucasus and northeast turkey the distribution of aftershocks and the twelve focal mechanisms involved in the sequence of the 2009 earthquake in racha are clearly a reactivation of a deeper segment of the 1991 m7 racha rupture zone the deeper segment is not well connected to the shallower decollement separating the basement and sedimentary basin the earthquakes we determined in northeastern turkey and southern georgia are related to the strike slip fault system we further combined all of the reliably determined focal mechanisms over the last 30 years to investigate the current stress status of the crust in three areas racha in the western greater caucasus javakheti near the lesser caucasus and in northeast turkey our results show that the directions of maximum compressional stress consistently fall within 2 to 14 n throughout the entire study region this appears to be controlled by the continental collision nonetheless the minimum compression switches from vertical in the greater caucasus to the east west direction in northeastern turkey due to the westward extrusion of the anatolia block which is driven partly by the hellenic subduction the transition of the stress field is close to the javakheti volcanic plateau in the lesser caucasus where the relative magnitude between the principal stresses appears to be strongly variable

change from late tertiary compression to quaternary extension in southern tibet during the india asia collision field studies in southern tibet show that subsequent to folding resulting from the india asia collision 50 40 ma reverse faults and backthrusts formed as a result of nne ssw and nnw sse trending compressions they affect conglomerates of oligocene miocene age and are probably contemporaneous with shearing on the himalayan main central thrust and folding of paleogene basins along the northern border of southern tibet 25 16 ma rift systems postdate compressional structures they were active during the pleistocene and probably during the pliocene 5 2 ma change from a compressional to an extensional regime in tibet probably occurred during the late miocene 10 5 ma this change is tentatively correlated with uplift inferred by chinese workers from paleogene to present day variations of the tibetan vegetation recent and active faulting in the high plateau results from a wnw ese striking extension this is in agreement with tibetan focal mechanisms the himalayan lowlands are subjected to a nne ssw trending compression as demonstrated by superficial deformations and seismicity therefore the horizontal maximum compressive stress trajectory is roughly parallel to india asia convergence hmax being 1 in the lowlands and 2 in the high plateau this change results from the increase of the vertical principal stress value due to the weight of the elevated mass zz is 3 in the lowlands and 1 in the high plateau thus the third principal stress axis is 2 in the lowlands and 3 in the high plateau allowing extension to occur in the wnw ese direction extensional tectonics are significantly different in southern and northern tibet southern tibet being constrained between the himalayan syntaxes the e w extensional principal deviatoric stress value 3 is of rather small magnitude and the n s trending 2 value is extensional as demonstrated by analysis of recent faults normal components prevail along all the azimuths in the field this favors formation of rift systems of large axial extension on the contrary north of the himalayan syntaxes northern tibet flows easily eastward the e w extensional principal deviatoric stress value 3 is of higher magnitude and the n s stress 2 is compressional as shown by inversion of focal mechanism data this favors strike slip components on faults which deviate from the n s direction as expressed in the field by shorter n s trending graben linked with normal strike slip faults these faults permit some n s shortening in northern tibet without thickening in response to india asia collision in high plateaus which are subjected to lateral compression such as the andean altiplano and tibet the extensional direction is basically controlled by the convergence direction being roughly orthogonal to the latter

new field and seismic data about the intraplate strike slip deformation in van region east anatolian plateau e turkey abstract the study area is the van earthquake region it is located in the western section of the east anatolian iranian plateau outside and to the east of the karliova triple junction based on the tectonic periods the rock units exposed in the study area are classified into two common categories these are the pre late pliocene paleotectonic units and the plio quaternary neotectonic units the paleotectonic units are composed of the yuksekova complex of campanian maastrichtian age and the kirkgecit formation of oligo miocene age the paleotectonic units are intensely deformed folded thrust to reverse faulted and converted into an imbricate stack the neotectonic units are composed of fluvio lacustrine sedimentary facies with volcanic interclations it is full of soft sedimentary structures such as deltaic structure slump fold sand dikes to sills and normal to reverse types of growth faults which imply to a sedimentation accompanied by both a volcanic activity and active tectonics originally the paleotectonic units are overlain with an angular unconformity by the nearly flat lying neotectonic units this angular unconformity and the big difference in the deformational patterns of both categories of rock units indicate an inversion in tectonic regime in late pliocene the new tectonic regime is the strike slip faulting dominated neotectonic regime it is governed by an approximately n s directed compression and composed of nw to ne trending strike slip faults n s trending oblique slip normal faults to fissures and the e w trending thrust to reverse faults most of thrust to reverse faults are inherited from the pre late pliocene paleotectonic regime some of them have reactivated and led to the occurrence of large and devastative earthquakes the last devastative seismic event is the 23 october 2011 tabanli van earthquake of mw 7 2 that caused 644 deaths and moderate to heavy damage of of structures 28 532 in van earthquake region the source of the tabanli earthquake is the everek erosional reverse fault in addition the tabanli earthquake is the largest seismic event occurred till now in turkey it was followed by a series over 6000 of small sized aftershocks and severeal moderate sized indepentent earthquakes of reverse normal and strike slip faulting origin both the field and new seismic data strongly reveal that the prominent tectonic regime in the east anatolian plateau is the strike slip neotectonic regime not the tensional tectonic regime as has been reported in some previous works the strike slip faulting and related deformation are confined into the upper shallowing part up to 40 km of the crust whilst the extensional deformations are the subcrustal processes and being taking place in a squashy zone at the depths of approximately 40 60 km

diagenetic history of tight sandstones and gas entrapment in the yulin gas field in the central area of the ordos basin china abstract the ordos basin is a large cratonic basin with an area of 250 000 km2 in central china upper paleozoic coals and shales serve as gas source rocks with peak generation and migration at the end of the early cretaceous recent exploration has verified the huge gas potential in the basin centered gas accumulation system bcgas however the mechanism for the gas accumulation is controversial with an integrated approach of thin section petrography ultra violet fluorescence microscopy fluid inclusion microthermometry raman microspectrometry scanning electron microscopy and x ray diffractometry we identified diagenetic trapping and evaluated the diagenetic history of sandstone reservoirs in the yulin gas field in the central area where structural stratigraphic and or sedimentary lithologic traps have not been found it was revealed that three phases of diagenesis and hydrocarbon charging occurred respectively in the late triassic late jurassic and at the end of the early cretaceous in the first two phases acidic water entered the reservoir and caused dissolution and cementation resulting in porosity increase however further subsidence and diagenesis including compaction and cementation markedly reduced the pore space at the end of the early cretaceous the bulk of the gas migrated into the tight reservoirs and the bcgas trap was formed in the updip portion of this system cementation continued to occur due to low gas saturation and has provided effective seals to retain gas for a longer period of time than water block in the bcgas the mechanism for the gas entrapment was changed from water block by capillary pressure in the bcgas to diagenetic sealing the diagenetic seals in the updip portion of the sand body were formed after gas charging which indicates that there is a large hydrocarbon exploration potential at the basin centered area

3 d anatomy of an active fault propagation fold a multidisciplinary case study from tsaishi western caucasus georgia abstract ongoing deformation processes combining fault propagation and folding are the cause of diffuse seismicity in many areas of the world a detailed understanding of the structural evolution of tectonically active folds is crucial for the evaluation of seismic hazard this paper proposes an integrated analysis of an active fold consisting in the development of a 3d model by combination of geomorphological observations field geological structural data and seismic reflection sections our case study is the tsaishi anticline located at the southwestern tip of the rioni basin uplifted area at the foothill of greater caucasus western georgia we recognized that the fold started to form since the beginning of the middle miocene although preliminary data suggest the possibility of initial local uplift in the oligocene folding process continues up to nowadays giving rise to a south vergent anticline as shown by upwarped late quaternary river deposits the fold backlimb is affected by three main back thrusts whereas at the foot of the forelimb a main north dipping thrust comes very close to the surface based on seismic sections here field data show the presence of a 13 km long fault scarp or fold scarp along the scarp is located the epicenter of the strongest earthquake to date the ms 6 0 tsaishi earthquake that struck the area in 1614 ce based on our results we propose that the overall structure can be classified as an active fault propagation fold the recognition of its very recent growing associated with a major underlying active fault represents also a major contribution to the seismic hazard assessment of this populated area

n alkane and pollen reconstruction of terrestrial climate and vegetation for n w africa over the last 160 kyr abstract proxy environmental records have been obtained for the last 160 kyr from the well studied odp site 658 ca 200 km west of cap blanc n w africa 20 5 n 18 35 w 2263 m water depth this collective assessment of several terrigenous proxies lithogenic fraction n alkane content and 13 c values and pollen counts provides a better understanding of the climate and vegetation history of the n w african hinterland the results indicate that for this site beneath the main dust pathway of the saharan air layer sal the dust flux increased during dry glacial periods but the amounts of pollen and n alkanes delivered were lower in accord with the decreased density of vegetation cover of their source areas the c 4 pollen was also very low but the heavy 13 c values of the n alkanes accorded with a mainly c 4 plant origin evidently the load of sal pollen was much reduced but not the sal wind strength

early paleogene evolution of terrestrial climate in the sw pacific southern new zealand 1 we present a long term record of terrestrial climate change for the early paleogene of the southern hemisphere that complements previously reported marine temperature records using the mbt cbt proxy based on the distribution of soil bacterial glycerol dialkyl glycerol tetraether lipids we reconstructed mean annual air temperature mat from the middle paleocene to middle eocene 62 42 ma for southern new zealand this record is consistent with temperature estimates derived from leaf fossils and palynology as well as previously published mbt cbt records which provides confidence in absolute temperature estimates our record indicates that through this interval temperatures were typically 5 c warmer than those of today at such latitudes with more pronounced warming during the early eocene climate optimum eeco 50 ma when mat was 20 c moreover the eeco mats are similar to those determined for antarctica with a weak high latitude terrestrial temperature gradient 5 c developing by the middle eocene we also document a short lived cooling episode in the early late paleocene when mat was comparable to present this record corroborates the trends documented by sea surface temperature sst proxies although absolute ssts are up to 6 c warmer than mats although the high calibration error of the mbt cbt proxy dictates caution the good match between our mat results and modeled temperatures supports the suggestion that sst records suffer from a warm summer bias particularly during times of peak warming

mapping of c4 plant input from north west africa into north east atlantic sediments abstract mapping the abundance of 13c in leaf wax components in surface sediments recovered from the seafloor off northwest africa 0 35 n reveals a clear pattern of 13c distribution indicating systematic changes in the proportions of terrestrial c3 and c4 plant input at 20 n latitude we find that isotopically enriched products characteristic of c4 plants account for more than 50 of the terrigenous inputs this signal extends westward beneath the path of the dust laden sahara air layer sal high c4 contributions apparently carried by january trade winds also extend far into the gulf of guinea similar distributions are obtained if summed pollen counts for the chenopodiaceae amaranthaceae and the poaceae are used as an independent c4 proxy we conclude that the specificity of the latitudinal distribution of vegetation in north west africa and the pathways of the wind systems trade winds and sal are responsible for the observed isotopic patterns observed in the surface sediments molecular isotopic maps on the marine sedimentary time horizons e g during the last glacial maximum are thus a robust tool for assessing the phytogeographic changes on the tropical and sub tropical continents which have important implications for the changes in climatic and atmospheric conditions

a case of post depositional aerobic degradation of terrestrial organic matter in turbidite deposits from the madeira abyssal plain abstract a set of oxidized and unoxidized sediment intervals from the f turbidite identified in two piston cores from the madeira abyssal plain map was analyzed for calcium carbonate total organic carbon toc total nitrogen tn stable carbon composition of toc 13c toc total hydrolyzable amino acids thaa total neutral sugars tsug lignin phenols lig two different lipid biomarkers of marine phytoplankton origin and vascular plantwax n alkanes and n acids comparison shows changes for all properties depicting the effect of post depositional aerobic oxidation the oxidation process re mineralized approximately 80 of the toc and approximately 60 of the tn in the original deposit and left the residual organic matter depleted in 13c by 1 7 2 9 thaa and tsug account for 10 or less of the toc in all samples leaving approximately 90 of the toc chemically unidentified thaa tsug lig marine phytoplankton biomarkers and plantwax n acids were lost from the oxidized deposit to an extent as great as that for toc two non protein amino acids alanine and aminobutyric acid and plant wax n alkanes displayed much less degradation 9 37 and concentrated 3 3 4 8 times relative to toc by the oxidation process these observations show that both marine and terrestrial components contribute to the re mineralized toc fraction a binary mixing approach was used to model quantitatively the change in 13c toc and plantwax n alkane concentration results suggest that terrestrial organic carbon contributes approximately 15 to the toc content of the original turbidite its abundance increases approximately 2 4 times as a consequence of the oxidation process and approximately 40 and 90 of the terrestrial and marine component of toc in the original turbidite respectively was destroyed by the oxidation process although selective preservation of terrestrial relative to marine organic carbon is a well documented phenomenon in sedimentary processes this study represents the first attempt to assess the sensitivity of terrestrial organic matter to oxidative degradation in a sedimentary environment

quaternary normal and reverse faulting and the state of stress in the central andes of south peru field studies in the andes of southern peru show that in the high andes and pacific lowlands quaternary and recent faults are normal this extensional tectonics postdates compressional deformations of pliocene early quaternary age in the sub andes the observed deformations are compressional they affect early quaternary deposits some of the faults separate quaternary deposits from the bedrock and thus are clearly of tectonic origin and not landslide effects striations on the fault planes indicate n s trending extension in the high andes and pacific lowlands the total amount of crustal stretching is small probably of the order of 1 during the last 1 2 m y in the sub andes folds and faults affecting neogene and early quaternary deposits result from n s shortening nevertheless it is supposed that this n s shortening is of early quaternary age the present day compression probably strikes e w judging from focal mechanisms in the sub andes of central peru southern bolivia and northwest argentina data from structural analysis of faults and from earthquake focal mechanisms allow us to surmise the state of stress in the andes of southern peru the high andes and pacific lowlands subjected to n s trending extension are bounded by two zones of e w trending compression the sub andes to the east and the contact between the convergent nazca and south america plates to the west in our model the maximum horizontal compressive stress trajectory hmax is roughly parallel with the e w convergence between the two plates hmax corresponds to 1 in the sub andes and to 2 in the high andes the latter situation is caused by the elevated mass of the high andes where zz the vertical stress is inferred to be 1 thus the third principal stress axis being orthogonal to the other two axes it is oriented n s allowing extension to occur in that direction on the other hand in the sub andes zz is 3 and horizontal e w shortening occurs the state of stress in the andean continental crust above the 30 dipping slab appears to be different from that in the andes of central peru situated above the flat subducting segment in this region compressional deformantion affect a wider part of the cordillera

stress tensor analysis of the 1998 1999 tectonic swarm of northern quito related to the volcanic swarm of guagua pichincha volcano ecuador the phreatic activity and the subsequent dacitic dome growth in 1998 1999 at guagua pichincha volcano ecuador were associated with two seismic swarms one located in the northern part of quito population 1 500 000 and another one just below the active volcano about 15 20 km sw from the first one quito swarm tectonic events have high frequencies from 1 to 10 15 hz we registered more than 3200 events among which 2354 events of 1 4 m l 4 2 between june 1998 and december 1999 at the 2 and 17 km depth the volcanic events below the guagua pichincha caldera have high from 1 to 10 15 hz and low less than 3 hz frequencies approximately 130 000 events were registered between september 1998 and december 1999 at the 2 4 and 3 5 km depth here we study the stress tensors of these two swarms deduced from the polarities of p first motions and compare them to the regional stress tensor deduced from cmt harvard focal mechanisms the quito swarm stress tensor is relatively close to the regional stress tensor the 1 axis was oriented n117 e close to the n102 e direction of the plate motion found by the gps measurement and 3 is nearly vertical the difference may be due to the action of the closely active guagua pichincha volcano the guagua pichincha stress tensor is very different from the regional tectonic one the 1 axis of the volcano is oriented n214 e almost perpendicular to the 1 of the swarm of quito and 3 is almost horizontal even if these two tensors are different they can be explained in a more general tectonic scheme the almost horizontal direction of 3 just below the volcano is compatible with an extensional horizontal direction that may be expected in the shallow extrados part of a compressional region and consistent with an opening of the top of the guagua pichincha volcano the movement of the fluids magma gas and or groundwater produced by the closely active guagua pichincha volcano seems to have an influence in the acceleration of the generation of seismic events

eolian transport of glycerol dialkyl glycerol tetraethers gdgts off northwest africa branched glycerol dialkyl glycerol tetraethers brgdgts of purportedly terrestrial origin are frequently detected in marine sediments even in remote ocean sites where no direct impact from land erosion via rivers takes place at these places the most likely explanation for the presence of brgdgts is in situ production or eolian transport but neither possibility has been demonstrated for the open ocean here we report the presence of isoprenoid iso and brgdgts in eight dust samples collected off northwest africa based on previous studies prevailing wind patterns bulk chemistry n alkane composition and isotopic signatures we show that northwest africa is the likely principal origin of the gdgts in the dust the concentrations of plant wax n alkanes in the dust are several orders of magnitude higher than those of gdgts and based on the distributions of these two compound classes we infer that they tag different carbon pools and sources of organic matter our finding demonstrates that brgdgts and isogdgts in marine sediments and wind derived deposits can have an eolian source consequently climate reconstruction may be attempted from wind derived deposits of brgdgts even in remote oceanic areas

a novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids we propose a novel tracer for terrestrial organic carbon in sediments based on the analysis of tetraether lipids using high performance liquid chromatography mass spectrometry hplc ms analysis of terrestrial soil and peats shows that branched tetraether lipids are predominant in terrestrial environments in contrast to crenarchaeol the characteristic membrane lipid of non thermophilic crenarchaeota which is especially abundant in the marine and lacustrine environment based on these findings an index was developed the so called branched and isoprenoid tetraether bit index based on the relative abundance of terrestrially derived tetraether lipids versus crenarchaeol this bit index was applied to surface sediments from the angola basin where it was shown to trace the outflow of the congo river furthermore analyses of particulate organic matter from the north sea showed relatively higher bit indices in water column particulate organic matter near large river inputs a survey of globally distributed marine and lacustrine surface sediments shows that the bit index in these environments correlates with the relative fluvial input of terrestrial organic material making this index generally applicable the new proxy allows the rapid assessment of the fluvial input of terrestrial organic material in immature sediments up to 100 ma old

sandstone reservoir quality prediction the state of the art joanna ajdukiewicz joined exxon production research company in 1980 she was reservoir quality assessment and prediction team lead there from 1991 to 1995 and at imperial oil research centre in calgary from 1995 to 1997 subsequently she has worked a variety of exploration company assignments in the north sea gulf of mexico and middle east her current interests are in predicting the distribution of early diagenetic controls on deep reservoir quality rob lander develops diagenetic models for geocosm llc he obtained his ph d in geology from the university of illinois in 1991 was a research geologist at exxon production research from 1991 to 1993 and worked for rogaland research and geologica as from 1993 to 2000 he is also a research fellow at the bureau of economic geology to guess is cheap to guess wrongly is expensive chinese proverb reservoir quality predictive models will be a useful element of risk analysis until remote sensing tools are invented that accurately measure effective porosity and permeability ahead of the bit this issue of the aapg bulletin highlights recent advances in a new generation of reservoir quality models that have successfully predicted porosity and permeability in diverse siliclastic reservoirs under many different burial conditions most previous attempts at predrill reservoir quality prediction have relied on empirical correlations or on first principle geochemical simulations that incorporate laboratory derived input parameters wood and byrnes 1994 the new reservoir quality models differ from previous approaches in that although incorporating theory inspired algorithms they include terms with values that are explicitly designed to be calibrated by and tested against data sets of high quality petrographic analyses that are linked to thermal and effective stress histories petrographic observations therefore provide essential constraints in these models on the types timing and rates of key geologic processes affecting sandstone pore systems this approach avoids the pitfalls inherent

the armenian earthquake of 1988 december 7 faulting and folding neotectonics and palaeoseismicity summary the spitak earthquake of 1988 december 7 is the first well documented event directly associated with surface breaks in the transcaucasian regions of the ussr the earthquake was located within the ese wnw oriented pambak sevan thrust and fold zone corresponding to the southern front of the lesser caucasus the mechanism of the earthquake is consistent with the nearly ns compressive tectonics due to the active continental collision between the arabian block and the russian platform the rupture is composed by several branches two of which reach the surface the first branch oriented n140 begins near the village of alavar has a length of 11 km and disappears at about 4 km se of spitak it consists of a right lateral en echelon system of strike slip faults with a maximum offset of 50 cm the second branch is the main one and breaks for about 8 km between spitak and gekhasar with a general orientation n120 showing reverse faulting dipping to the north with a right lateral component surface ruptures between gekhasar and spitak show either a narrow band of pressure ridges in alluvial deposits and soil or a fault scarp in the bed rocks when soil is absent maximum displacements observed between spitak and gekhasar attain 160 cm of vertical motion and 90 cm of horizontal dextral offset the displacement also varies within this branch showing finer segmentation few secondary deformations are observed some normal faults near gekhasar correspond to the collapse of the uplifted block an anticline fold oriented parallel to the fault scarp and situated along its northwestern prolongation emphasizes the regional compressive tectonics landslides were activated on its flanks a 200 m long reverse fault break observed along the hinge of a secondary fold suggests the occurrence of a blind thrust at depth and that the hidden branches which continue the main central segment towards the nw are associated to surface folding therefore the total length of the fault and fold zone is about 40 km in agreement with the rupture length and seismic moment obtained on the basis of surface wave modelling well developed uplifted terraces in the northern block and subsiding valleys in the southern block indicate past quaternary activity in the fault region palaeoseismological evidence of ancient earthquakes has been recognized in trenches across the spitak fault one old event occurred between 17 000 years bp and the beginning of the formation of present day soil

the role of fluid pressure and diagenetic cements for porosity preservation in triassic fluvial reservoirs of the central graben north sea anomalously high porosities and permeabilities are commonly found in the fluvial channel sandstone facies of the triassic skagerrak formation in the central north sea at burial depths greater than 3200 m 10 499 ft from which hydrocarbons are currently being produced the aim of our study was to improve understanding of sandstone diagenesis in the skagerrak formation to help predict whether the facies with high porosity may be found at even greater depths the skagerrak sandstones comprise fine to medium grained arkosic to lithic arkosic arenites we have used scanning electron microscopy petrographic analysis pressure history modeling and core analysis to assess the timing of growth and origin of mineral cements with generation and the impact of high fluid pressure on reservoir quality our interpretation is that the anomalously high porosities in the skagerrak sandstones were maintained by a history of overpressure generation and maintenance from the late triassic onward in combination with early microquartz cementation and subsequent precipitation of robust chlorite grain coats increasing salinity of pore fluids during burial diagenesis led to pore filling halite cements in sustained phreatic conditions the halite pore filling cements removed most of the remaining porosity and limited the precipitation of other diagenetic phases fluid flow associated with the migration of hydrocarbons during the neogene is inferred to have dissolved the halite locally dissolution of halite cements in the channel sands has given rise to megapores and porosities of as much as 35 at current production depths

incorporating capillary pressure pore throat aperture radii height above free water table and winland r35 values on pickett plots methods are presented for incorporating capillary pressure pore throat aperture radii height above the free water table and winland r 35 values on pickett plots the techniques involve the use of log log plots of effective porosity vs resistivity combined with empirical equations for calculating capillary pressure written as a function of permeability porosity and water saturation i show that a crossplot of porosity vs true resistivity in some cases apparent resistivity or true resistivity affected by a shale group should result in a straight line for intervals with constant capillary pressure and constant pore throat aperture radii key advantages of the proposed methods are 1 the capillary pressure at any point on the pickett plot is consistent with porosity permeability and water saturation at that particular point 2 the value of r w does not have to be known in advance provided that the reservoir contains some water bearing intervals and 3 core data are not essential although it is strongly recommended to have cores to properly calibrate the equations presented in this article if capillary pressures from cores are available it is possible to estimate the value of r w even if there are not water bearing intervals in the reservoir pore throat aperture radii r 35 values computed using the empirically derived winland equation compare reasonably well with pore throat aperture radii r p35 calculated from techniques presented in this article this is significant because the data sets used to establish these empirical equations come from different areas different reservoirs and different lithologies and were evaluated independently at different times a mathematical relationship is developed between winland r 35 values and the pore throat aperture r p35 presented in this article the methods are illustrated using two case histories the first one is a gulf coast high porosity sand shale sequence the second is a limestone oil reservoir from the lansing kansas city formation the integration of permeability capillary pressures pore size classes and geometry of the pores on a log log graph of porosity vs resistivity makes the pickett plot one of the most formidable formation evaluation tools yet devised roberto aguilera is president of servipetrol ltd in calgary canada he has an undergraduate degree in petroleum engineering from the universidad de america in bogota colombia and a master s degree and ph d in petroleum engineering from the colorado school of mines he was an aapg instructor on the subject of naturally fractured reservoirs from 1984 through 1996 he received the outstanding service award from the petroleum society of the canadian institute of mining metallurgy and petroleum engineers cim in 1994 he is a distinguished author of the journal of canadian petroleum technology 1993 and 1999 and a society of petroleum engineers distinguished lecturer on the topic naturally fractured reservoirs for the 2000 2001 season he has developed various methods that have been published in leading journals of the oil industry he has authored and been a contributor to various books including naturally fractured reservoirs pennwell 1980 and 1995 the technology of artificial lift methods pennwell 1984 horizontal wells gulf publishing 1991 and determination of oil and gas reserves petroleum society of cim monograph 1 1994

complex deformation in the caucasus region revealed by ambient noise seismic tomography abstract cross correlation of 3years of ambient seismic noise recorded at 35 seismic stations deployed in caucasus region yields hundreds of short period surface wave phase speed dispersion curves on inter station paths we inverted these measurements using two techniques to construct tomographic images of the principal geological units of caucasus high resolution isotropic and azimuthally anisotropic phase velocity maps at periods between 5 and 20s and shear velocity tomographic maps between 5 and 30km are generated the resulting maps show a velocity dichotomy between the caucasus region and the surrounding that is interpreted in term of changes in crustal thickness there is also a strong dichotomy in the anisotropic pattern between the eastern part and the western part of the caucasus this difference in both amplitudes and directions of the 2 anisotropy is linked to the tectonic regime changes in the region these observations suggest a good correlation between the tomographic models and the geology of the region it was also possible to identify the early stage of the indentation of the arabian plate into the eurasian plate as well as to detect the possible magma chamber responsible for the javakheti highland

how does the pore throat size control the reservoir quality and oiliness of tight sandstones the case of the lower cretaceous quantou formation in the southern songliao basin china abstract pore throat size is a very crucial factor controlling the reservoir quality and oiliness of tight sandstones which primarily affects rock properties such as permeability and drainage capillary pressure however the wide range of size makes it difficult to understand their distribution characteristics as well as the specific controls on reservoir quality and oiliness in order to better understand about pore throat size distribution petrographic scanning electron microscopy sem pressure controlled mercury injection pmi rate controlled mercury injection rmi quantitative grain fluorescence qgf and environmental scanning electron microscopy esem investigations under laboratory pressure conditions were performed on a suite of tight reservoir from the fourth member of the lower cretaceous quantou formation k 1 q 4 in the southern songliao basin china the sandstones in this study showed different types of pore structures intergranular pores dissolution pores pores within clay aggregates and even some pores related to micro fractures the pore throat sizes vary from nano to micro scale the pmi technique views the pore throat size ranging from 0 001 m to 63 m and revealed that the pore throats with radius larger than 1 0 m are rare and the pore throat size distribution curves show evident fluctuations rmi measurements indicated that the pore size distribution characteristics of the samples with different porosity and permeability values look similar the throat size and pore throat radius ratio distribution curves had however significant differences the overall pore throat size distribution of the k 1 q 4 tight sandstones was obtained with the combination of the pmi and rmi methods the permeability is mainly contributed by a small part of larger pore throats less than 30 and the ratio of the smaller pore throats in the samples increases with decreasing permeability although smaller pore throats have negligible contribution on reservoir flow potential they are very significant for the reservoir storage capacity the pore throats with average radius larger than 1 0 m mainly exist in reservoirs with permeability higher than 0 1md when the permeability is lower than 0 1md the sandstones are mainly dominated by pore throats with average radius from 0 1 m to 1 0 m the ratio of different sized pore throats controls the permeability of the tight sandstone reservoirs in different ways we suggest that splitting or organizing key parameters defining permeability systematically into different classes or functions can enhance the ability of formulating predictive models about permeability in tight sandstone reservoirs the pmi combined with qgf analyses indicate that oil emplacement mainly occurred in the pore throats with radius larger than about 0 25 0 3 m this result is supported by the remnant oil micro occurrence evidence observed by sem and esem

active faulting and natural hazards in armenia eastern turkey and northwestern iran active fault zones of armenia se turkey and nw iran present a diverse set of interrelated natural hazards three regional case studies in this cross border zone are examined to show how earthquakes interact with other hazards to increase the risk of natural disaster in northern armenia a combination of several natural and man made phenomena earthquakes landslides and unstable dams with toxic wastes along the pambak sevan sunik fault pssf zone lowers from 0 4 to 0 2 0 3g the maximum permissible level mpl of seismic hazard that may induce disastrous destruction and loss of life in the adjacent vanadzor depression in the ararat depression a large active fault bounded pull apart basin at the junction of borders of armenia turkey iran and azerbaijan an earthquake in 1840 was accompanied by an eruption of ararat volcano lahars landslides floods soil subsidence and liquefaction the case study demonstrates that natural hazards that are secondary with respect to earthquakes may considerably increase the damage and the casualties and increase the risk associated with the seismic impact the north tabriz gailatu fault system poses a high seismic hazard to the border areas of nw iran eastern turkey nakhichevan azerbaijan and southern armenia right lateral strike slip motions along the north tabriz fault have given rise to strong earthquakes which threaten the city of tabriz with its population of 1 2 million the examples illustrate how the concentration of natural hazards in active fault zones increases the risk associated with strong earthquakes in armenia eastern turkey and nw iran this generally occurs across the junctions of international borders hence the transboundary character of active faults requires transboundary cooperation in the study and mitigation of the natural risk

selective organic matter preservation in burn down turbidites on the madeira abyssal plain 1 oxidized intervals of five organic rich madeira abyssal plain map turbidites deposited during the miocene pliocene and pleistocene all displayed comparable major loss of total organic carbon toc 84 3 1 accompanied by a negative isotopic 13c shift ranging from 0 3 to 2 9 major but significantly lower loss of total nitrogen ntot 61 7 1 also occurred leading to a decrease in toc relative to ntot c ntot and a 1 3 to 2 7 ntot isotopic 15n shift compound specific isotopic measurements on plant wax n alkanes indicate the terrestrial organic component in the unoxidized deposits is 13c enriched owing to significant c4 contribution selective preservation of terrestrial relative to marine organic carbon could account for the 13c behavior of toc upon oxidation but only if a 13c depleted component of the bulk terrestrial signal is selectively preserved in the process although the c ntot decrease and positive 15n shift seems inconsistent with selective terrestrial organic preservation results from analysis of a modern eolian dust sample collected in the vicinity indicate these observations are compatible regardless of the specific explanation for these isotopic observations however our findings provide evidence that paleoreconstruction of properties such as pco2 using the 13c of toc is a goal fraught with uncertainty whether or not the marine sedimentary record considered is contaminated with significant terrestrial input nonetheless despite major and selective loss of both marine and terrestrial components as a consequence of postdepositional oxidation intensive organic geochemical proxies such as the alkenone unsaturation index u37k appear resistant to change and thereby retain their paleoceanographic promise

diagenesis of a tight gas sand reservoir upper cretaceous mesaverde group piceance basin colorado abstract the upper cretaceous mesaverde group in the piceance basin western colorado contains thick sections of low porosity low permeability sandstones that are reservoirs for large accumulations of hydrocarbon gas the mesaverde sandstones are lithic arkoses and feldspathic litharenites containing quartz plagioclase variable k feldspar chert and volcanic rock fragments important diagenetic processes that have affected the sandstones include compaction dissolution of feldspar and or alteration to clay precipitation of carbonate and quartz cements precipitation of illite and alteration of detrital clays mixed layer illite smectite porosity is relatively constant a decrease in primary porosity downward is approximately balanced by an increase in secondary porosity with significant microporosity in authigenic and diagenetic clays k feldspar is almost completely absent below 5500 feet 1675 m fibrous illite is relatively abundant above this depth and variable in abundance below the k ar ages of the clays increase with depth from 40 m y at the top of the sampled section to 55 m y at the base indicating illitization of a precursor smectite at approximately the 100 c isotherm samples with abundant fibrous illite have relatively smaller age values mass balance calculations indicate that dissolution of k feldspar illitization of smectite and precipitation of fibrous illite were coupled these reactions suggest the transport of dissolved potassium upward hundreds of feet 100 300 m in the section possibly associated with water driven vertically by the migration of gas

distributions of branched gdgts in soils and lake sediments from western uganda implications for a lacustrine paleothermometer bacterially produced branched glycerol dialkyl glycerol tetraethers gdgts are ubiquitous in soils and lake sediments and can potentially be used to reconstruct past temperatures in lakes however it is still unclear if these compounds are derived from eroded soils or if they are produced in situ to better understand environmental controls on the distributions of these compounds and the sources of branched gdgts to lake sediments we compare branched gdgt distributions and concentrations in lake sediments and catchment soils within a 3600 m altitudinal transect in western uganda reconstructed mean annual air temperature maat determined from the degree of methylation mbt and cyclisation cbt of branched gdgts in soils decreases with increasing altitude as is expected from the air temperature gradient in our transect however we observe significant offsets between observed and reconstructed temperatures in soils from wet high elevation soils but not in most dry low elevation soils branched gdgt distributions differ significantly between lake sediments and soils at all elevations with greater differences at low elevations than at high elevations these data support previous hypotheses that branched gdgts are produced in situ in lakes and suggest that the abundance of water in soil environments may play a role in controlling the distribution of branched gdgts while branched gdgts in lacustrine sediments can be used to reconstruct temporal temperature variations in lakes we urge caution in utilizing this proxy in lacustrine systems with high soil loadings especially if there is evidence of changing clastic fluxes through time

geodynamics seismicity and seismic hazards of the caucasus abstract being a part of ongoing continental collision between the arabian and eurasian plates the caucasus region is a remarkable site of moderate to strong seismicity where devastating earthquakes caused significant losses of lives and livelihood in this article we survey geology and geodynamics of the caucasus and its surroundings magmatism and heat flow active tectonics and tectonic stresses caused by the collision and shortening gravity and density models and overview recent geodetic studies related to regional movements the tectonic development of the caucasus region in the mesozoic cenozoic times as well as the underlying dynamics controlling its development are complicated processes it is clear that the collision is responsible for a topographic uplift inversion and for the formation of the fold and thrust belts of the greater and lesser caucasus tectonic deformations in the region is influenced by the wedge shaped rigid arabian block indenting into the relatively mobile region and producing near n s compressional stress and seismicity in the caucasus regional seismicity is analysed with an attention to sub crustal seismicity under the northern foothills of the greater caucasus which origin is unclear whether the seismicity associated with a descending oceanic crust or thinned continental crust recent seismic tomography studies are in favour of the detachment of a lithospheric root beneath the lesser and greater caucasus the knowledge of geodynamics seismicity and stress regime in the caucasus region assists in an assessment of seismic hazard and risk we look finally at existing gaps in the current knowledge and identify the problems which may improve our understanding of the regional evolution active tectonics geodynamics shallow and deeper seismicity and surface manifestations of the lithosphere dynamics among the gaps are those related to uncertainties in regional geodynamic and tectonic evolution e g continental collision and associated shortening and exhumation lithosphere structure deformation and strain stress partitioning and to the lack of comprehensive datasets e g regional seismic catalogues seismic gravity and geodetic surveys

gps derived strain rate field within the boundary zones of the eurasian african and arabian plates we use the gps velocity field 1988 1998 for eastern mediterranean and asia minor to determine the crustal deformation strain rate field in an area bounded by 35 n and 43 n and 20 e and 48 e we calculate the normal and shear strain rate components associated with the major faults and compare these qualitatively with seismological data uncertainties in the calculation of the strain rates reach 50 nstrain yr 1 in sparsely observed parts of anatolia whereas we estimate errors 20 nstrain yr 1 in the aegean and marmara regions the largest compressional strain rate components in the eastern part of the study area occur along the greater caucasus mountain front reaching 70 nstrain yr 1 1 nstrain yr 1 0 0317 10 15 s 1 the north anatolian fault zone is the clearest feature in the shear strain rate field it is expressed as a pronounced dextral strike slip fault zone reaching rates of up to 170 nstrain yr 1 this holds true also for the izmit area where the august 17 1999 earthquake occurred central anatolia is almost strain free whereas extension prevails in western anatolia the principal axes of extension vary around the n s direction with strain rates of up to 85 nstrain yr 1 these extensional areas coincide with graben features and normal faulting earthquakes the central and southwestern aegean sea is strain free with values far below 40 nstrain yr 1 the seismic cluster around the dodekanissa islands southeastern aegean sea coincides with nw se oriented extension attaining strain rates of up to 90 nstrain yr 1 this area of extension also exhibits recent active volcanism the entire hellenic arc shows compressional strain rates perpendicular to the arc the pliny strabo troughs along the eastern segment of the arc show left lateral shear strain rates reaching 80 nstrain yr 1 significant extension is found in central greece with a nne ssw oriented maximum of 120 nstrain yr 1 centered around the gulf of corinthos the kephalonia fault zone in nw greece is a distinct dextral fault zone separating apulia from the rapidly moving aegean microplate right lateral shear strain rates reach 150 nstrain yr 1

glacial interglacial contrast in mbt cbt proxies in the south china sea implications for marine production of branched gdgts and continental teleconnection abstract two proxies derived from branched glycerol dialkyl glycerol tetraethers br gdgts the methylation index of branched tetraethers mbt and the cyclization ratio of branched tetraethers cbt are often used to reconstruct paleo mean annual air temperature maat and soil ph based on the premise that br gdgts in the marine environment are mainly of terrigenous origin however mounting evidence indicates that br gdgts can be produced in situ in oceanic settings which may affect maat reconstruction and the use of other related paleoenvironmental proxies we have determined br gdgt distributions in a sedimentary core md05 2896 7 from the southern south china sea which provided high resolution profiles of mbt and cbt indices as well as the branched and isoprenoid tetraether bit index bit varied systematically with glacial interglacial cycles reaching much lower

decoupled warming and monsoon precipitation in east asia over the last deglaciation our understanding of the continental climate development in east asia is mainly based on loess paleosol sequences and summer monsoon precipitation reconstructions based on oxygen isotopes delta o 18 of stalagmites from several chinese caves based on these records it is thought that east asian summer monsoon easm precipitation generally follows northern hemisphere nh summer insolation however not much is known about the magnitude and timing of deglacial warming on the east asian continent in this study we reconstruct continental air temperatures for central china covering the last 34 000 yr based on the distribution of fossil branched tetraether membrane lipids of soil bacteria in a loess paleosol sequence from the mangshan loess plateau the results indicate that air temperature varied in phase with nh summer insolation and that the onset of deglacial warming at similar to 19 kyr bp is parallel in timing with other continental records from e g antarctica southern africa and south america the air temperature increased from is c at the onset of the warming to a maximum of 27 degrees c in the early holocene similar to 12 kyr bp in agreement with the temperature increase inferred from e g pollen and phytolith data and permafrost limits in central china comparison of the tetraether membrane lipid derived temperature record with loess paleosol proxy records and stalagmite 5180 records shows that the strengthening of easm precipitation lagged that of deglacial warming by ca 3 kyr moreover intense soil formation in the loess deposits caused by substantial increases in summer monsoon precipitation only started around 12 kyr bp ca 7 kyr lag our results thus show that the intensification of easm precipitation unambiguously lagged deglacial warming and nh summer insolation and may contribute to a better understanding of the mechanisms controlling ice age terminations

determination of static and dynamic characteristics of microscopic pore throat structure in a tight oil bearing sandstone formation in this study an integrated and practical framework has been developed to quantify the static and dynamic characteristics of microscopic pore throat structure in a tight oil bearing sandstone formation experimentally thin sections were prepared out of core samples collected from a tight formation while corresponding analyses were respectively performed by using the scanning electron microscopy sem and x ray diffraction xrd techniques in addition to pore types and clay minerals the size fraction and distribution of grains were identified and classified pore and throat size distributions were then determined by using pressure controlled mercury injection pmi and rate controlled mercury injection rmi respectively to quantify the changes in microscopic pore throat structure after brine flow tests subsequently displacement experiments of waterflooding and surfactant flooding were performed to determine the upper and lower cutoff value of the movable throat radius rock grains primarily containing fine sand and silt are found to possess complex compositions while both intergranular pores and intragranular dissolution pores are dominant nano throats may have developed in a tight formation due to small radii of pores and throats compared to the pore size distribution throat radius is found to be reduced by 13 9 after brine flow tests while the cutoff value of movable throat can be decreased to 0 019 m from 0 033 m by using a surfactant

curie point depth geothermal gradient and heat flow estimation and geothermal anomaly exploration from integrated analysis of aeromagnetic and gravity data on the sabalan area nw iran prospecting the geothermal resources in northwest of iran conducted in 1975 revealed several promising areas and introduced the sabalan geothermal field as a priority for further studies the sabalan mt representing the sabalan geothermal field is a large stratovolcano which consists of an extensive central edifice built on a probable tectonic horst of underlying intrusive and effusive volcanic rocks in this study curie point depth cpd geothermal gradient and heat flow map were constituted from spectral analysis of the aeromagnetic data for the nw of iran the top of the geothermal resource i e the thickness of the overburden was evaluated by applying the euler deconvolution method on the residual gravity data the thickness of the geothermal resource was calculated by subtracting the euler depths obtained from the cpds in the geothermal anomalous region the geothermal anomalous region was defined by the heat flow value greater than 150 mw m2 cpds in the investigated area are found between 8 8 km in the sabalan geothermal field and 14 1 in the northeast the results showed that the geothermal gradient is higher than 62 c km and the heat flow is higher than 152 mw m2 for the geothermal manifestation region the thickness of the geothermal resource was also estimated to vary between 5 4 and 9 1 km these results are consistent with the drilling and other geological information findings indicate that the cdps agree with earthquake distribution and the type of thermal spring is related to the depth of the top of the geothermal resource

oil charging model and controlling factors revealed by an online nuclear magnetic resonance nmr system abstract it is very difficult to simulate the charging process of crude oil under experimental conditions due to the low porosity and permeability of tight sandstone however simulations are important for revealing the mechanism of formation of tight oil and the oil water distribution characteristics as well as for enhancing the oil recovery efficiency in this study we established a new method called nuclear magnetic resonance coupling displacement nmr dp to simulate the tight oil charging process online the nmr dp method has the advantages of high precision velocity recyclability and the ability to reflect the distribution of fluids in the micropores of a tight rock we conducted a simulation experiment involving the charging of crude oil into eight sandstone samples from gaotaizi in the qijia longhupao area of the songliao basin the results of this experiment were combined with those of microscopic measurements conducted on the pore structure i e nuclear magnetic resonance nitrogen adsorption high pressure and rate controlled mercury injections and micron computed tomography in this way we clarified the charging process and its controlling factors e g physical properties and wettability and established a tight oil charging model the results indicate that the oil charging saturation was controlled by several factors including the charging pressure physical properties pore throat structure and mineral composition of the rock a smaller radius of the pore throat corresponded to a lower oil charging saturation and higher starting pressure gradient the lower the content of clay and carbonate minerals and the higher the content of feldspar mineral the higher the oil saturation oil mainly occurred in the larger pores while residual water mainly occurred in the smaller pores the charging process was divided into four stages an exponential rapid growth stage a logarithmic slow growth stage a linear slow growth stage and a quasi stationary stage the method established in this paper is expected to be helpful for analyzing the distribution law of oil and water in tight sandstone areas thereby aiding in the prediction of sweet spots and development of tight oil

innovative methods for flow unit and pore structure analyses in a tight siltstone and shale gas reservoir tight gas reservoirs are notoriously difficult to characterize routine methods developed for conventional reservoirs are not appropriate for tight gas reservoirs in this article we investigate the use of nonroutine methods to characterize permeability heterogeneity and pore structure of a tight gas reservoir for use in flow unit identification profile permeability is used to characterize fine scale 1 in 2 5 cm vertical heterogeneity in a tight gas core more than 500 measurements were made profile permeability although useful for characterizing heterogeneity will not provide in situ estimates of permeability furthermore the scale of measurement is much smaller than log scale pulse decay permeability measurements collected on core plugs under confining pressure were used to correct the profile permeability measurements to in situ stress conditions and 13 point averages of profile permeability were used to relate to log derived porosity measurements finally n2 adsorption a new method for tight gas was used to estimate the pore size distribution of several tight gas samples a unimodal or bimodal distribution was observed for the samples with the larger peak corresponding to the dominant pore throat size as confirmed by independent methods furthermore the adsorption desorption hysteresis loop shape was used to interpret the dominant pore shape as slot shaped pores which is typical of many tight gas reservoirs the n2 adsorption method provides rapid analysis and does not suffer from some of the same limitations of hg injection in the future we hope that the n2 adsorption method may prove useful for flow unit characterization based on dominant pore size of fine grained siltstone shale tight gas reservoirs

spatial heterogeneity of sources of branched tetraethers in shelf systems the geochemistry of tetraethers in the berau river delta kalimantan indonesia abstract the bulk organic matter composition total organic carbon toc content and 13ctoc and composition of isoprenoid and branched glycerol dialkyl glycerol tetraethers gdgt in surface sediments from 43 stations in the berau river delta east kalimantan indonesia including two coast shelf transects and stations within the river mouth were examined to reveal the spatial heterogeneity in these parameters in order to assess the impact of a tropical river loaded with suspended matter on the sedimentary organic matter in the shelf system the high resolution study showed that despite the extensive transport of eroded soil material by the river to the sea terrestrial organic matter and brgdgts are only deposited on a relatively small part of the shelf the concentrations of brgdgts are highest up to 120 g g 1 toc in sediments deposited in and close to the mouth of the berau river and their distribution indicates that they represent a mixture of soil derived and river in situ produced brgdgts crenarchaeol concentrations reach 700 g g 1 toc in sediments deposited on the outer shelf due to thaumarchaeotal production in shelf waters this results in a strong gradient 0 93 0 03 in the bit index with high values in the river mouth and low values on the shelf the decline in the bit index is caused by both decreasing concentrations of the brgdgts and increasing concentrations of crenarchaeol the bit index shows a highly significant but non linear relationship with 13ctoc on the shelf in the area not under the direct influence of the berau river cyclic brgdgts become relatively dominant most probably due to in situ production in the alkaline pore waters of the surface sediments the spatial heterogeneity of sources of brgdgts on the berau shelf complicates the use of brgdgts as temperature proxies application of the global soil calibration to sedimentary mixtures of brgdgts in the river influenced area of the shelf results in a severe underestimation of mean annual air temperature mat by 6 c this is due to the mixed origin of the brgdgts which are not only derived from soil erosion but likely also from riverine production as has been observed for other river systems comparison of the berau shelf other shelf systems indicates that in situ production of brgdgts in shelf sediments is a widespread phenomenon that is especially pronounced at water depths of ca 50 300 m it is hypothesized that this is so because benthic in situ production of heterotrophic brgdgt producing bacteria is fueled by the higher delivery of fresh organic matter to these sediments as the consequence of higher primary productivity in shelf waters and a decreased mineralization due to the relatively short settling times of particles on the shelf for palaeoclimatic studies of marine shelf sediments the application of brgdgts as proxies is severely complicated by the heterogeneity of sources of brgdgts comparison of the brgdgt composition of soils with those of shelf sediments may assist in deciding if sedimentary brgdgts are predominantly derived from soil erosion several methods to do so are discussed

the evolution of pore scale fluid saturation in low permeability sandstone reservoirs in many tight gas basins of the western united states distinguishing between productive and non productive low permeability sandstones and predicting relative amounts of gas and water production is difficult comparison of gas shows calculated water saturations and saturation height profiles between gas productive and non productive sandstones of equal reservoir quality all appear similar capillary pressure derived height functions are difficult to apply and classic rock typing procedures lack the predictive capability that is common to more traditional reservoirs basin reconstructions suggest the timing of petroleum charge and migration preceded maximum burial and uplift this initial charge was likely a primary drainage displacement with reservoir porosity greater by a factor of 2 3 relative to values found today and permeability greater by 1 3 orders of magnitude these reservoir systems became low permeability following initial charge reflecting continued diagenesis throughout burial subsequent uplift and erosion with burial decreasing pore volume caused water saturations and gas columns to increase during uplift and erosion gas columns adjusted to changing structural configuration in some cases this led to gas accumulations being leaked and spilled in other cases structural readjustment resulted in capillary imbibition and in some cases secondary or higher order drainage and imbibition within trapped accumulations gas expansion upon uplift further increased gas columns in cases where gas columns were spilled or within migration pathways imbibition led to residual or near residual water saturations conventional formation evaluation is fundamentally rooted in concepts associated with primary drainage displacement tight gas reservoirs that have experienced late uplift following an earlier phase of charge are unlikely to be characterized by primary drainage and are much more likely to be characterized by imbibition or secondary or higher order drainage and possibly imbibition the hysteresis between primary drainage and imbibition or secondary or higher order drainage and imbibition in tight gas reservoirs is significant and unlike many more traditional reservoirs does not tend to converge on a narrow range of values estimates of water saturation are scalar values and do not contain information that allows the saturation history and displacement direction to be deciphered recognition that reservoirs are unlikely to be in primary drainage equilibrium is a fundamental paradigm shift that impacts petroleum evaluation at all scales ranging from basin potential to completion decisions within a given well although this paper is written from the perspective of tight gas petroleum systems the principles are equally applicable to low permeability oil reservoirs

constraints on the sources of branched tetraether membrane lipids in distal marine sediments abstract branched glycerol dialkyl glycerol tetraethers brgdgts are membrane lipids produced by soil bacteria and occur in near coastal marine sediments as a result of soil organic matter input their abundance relative to marine derived crenarchaeol quantified in the bit index generally decreases offshore however in distal marine sediments low relative amounts of brgdgts can often still be observed sedimentary in situ production as well as dust input have been suggested as potential though as yet not well constrained sources in this study brgdgt distributions in dust were examined and compared with those in distal marine sediments dust was sampled along the equatorial west african coast and brgdgts were detected in most of the samples albeit in low abundance their degree of methylation and cyclisation expressed in the mbt methylation index of branched tetraethers and dc degree of cyclisation indices respectively were comparable with those for african soils their presumed source comparison of dc index values for brgdgts in global soils congo deep sea river fan sediments and dust with those of distal marine sediments clearly showed however that distal marine sediments had significantly higher values this distinctive distribution is suggestive of sedimentary in situ production as a source of brgdgts in marine sediments rather than dust input the presence of in situ produced brgdgts in marine sediments means that caution should be exercised when applying the mbt cbt palaeothermometer to sediments with low bit index values i e

partitioning of strike slip and convergent motion between eurasia and arabia in eastern turkey and the caucasus the plate motion model nuvel 1 de mets et al 1990 predicts a strongly oblique component to the convergence between arabia and eurasia at the longitude of the caucasus earthquake focal mechanisms suggest that this oblique convergence is partitioned into pure right lateral strike slip motion in eastern turkey and pure shortening by thrusting in the greater caucasus such partitioning offers an explanation for the apparent eastward continuation of the right lateral faulting of the north anatolian fault from turkey into iran from a summation of seismic moment tensors between 1911 and 1991 it appears that most of the right lateral strike slip motion in eastern turkey is accommodated by faulting in large earthquakes while most of the shortening in the caucasus appears to occur aseismically

a paleomagnetic and paleointensity study on pleistocene and pliocene basaltic flows from the djavakheti highland southern georgia caucasus abstract new paleomagnetic rock magnetic and paleointensity results obtained on samples from 23 basaltic lava flows belonging to four different flow sequences mashavera kvemo orozmani zemo karabulaki and diliska of pleistocene and pliocene age from the eastern djavakheti highland in southern georgia are presented radiometric dating of these sequences yields ages between 1 8 and 2 18 ma for mashavera 2 07 and 2 58 ma for zemo karabulakhi and 2 12 and 3 27 for diliska no radiometric ages are available for the kvemo orozmani sequence which is considered to be coeval to the mashavera sequence rock magnetic experiments including measurement of thermomagnetic hysteresis and irm acquisition curves suggest low ti titanomagnetite as main carrier of remanence although a lower curie temperature component was also observed in several cases reversible and non reversible curves were recorded in thermomagnetic experiments paleomagnetic analysis generally indicated the presence of a single component mainly in the mashavera sequence but also two more or less superimposed components in some other cases in 21 sites a characteristic component could be determined and all except one were characterised by normal polarity directions flows from the mashavera sequence had a rather steep inclination 73 1 nevertheless a mean paleomagnetic direction of all four sequences is obtained d 8 5 i 60 8 n 4 95 11 7 k 62 7 which agrees with the plio quaternary directions obtained in previous studies in georgia the paleomagnetic pole obtained latitude 82 1 longitude 118 2 a 95 8 0 k 240 7 agrees with the pole values of both the 0 ma and the 5 ma windows of the synthetic eurasian polar wander path from besse and courtillot 2002 in order to analyse the behaviour of secular variation the scatter of paleosecular variation of virtual geomagnetic poles of both the mashavera flow and all 18 studied flows of pleistocene age was calculated it could be observed that both data sets seem to fit well the expected scatter at latitude 41 n paleointensity experiments were carried out with the coe modification of the thellier method twenty five out of 84 samples 30 provided reliable paleointensity results these successful results were mainly obtained in the mashavera sequence most flows yielded paleointensity results in the 30 45 t range in accordance with expected pliocene to present day intensities two flows however located near the top of the mashavera sequence yield high paleointensity values around 60 t anomalous paleointensity results in the upper lying mashavera flows together with the steep inclinations observed in that sequence could perhaps signal the near onset of the olduvai matuyama reversal

seasonal effects of water temperature and dissolved oxygen on the isogdgt proxy tex86 in a mediterranean oligotrophic lake abstract to appraise the application of isoprenoid glycerol dialkyl glycerol tetraethers isogdgts as paleoclimate proxies in small lakes we investigated the effect of seasonal variability in temperature and dissolved oxygen concentration do on the gdgt contents and its proxy in the water column of an oligotrophic karst lake in the catalan pre pyrenees lake montcortes from october 2013 to november 2014 we collected suspended particulate matter spm monthly at three depths and retrieved the sediment from a trap located at 20 m below the lake surface the gdgt contents in the spm and sediment trap presented a marked seasonal variation showing the highest values in summer and autumn in addition the isogdgt proxy tex86 in spm and sediment trap showed a marked seasonal variability which matched the temperatures of the upper water column and fit the published global trend between tex86 and mean annual lake surface temperature lst however in the hypolimnion where oxygen was depleted for most of the study period we found that tex86 co varied with do this further confirms previous claims with seasonal field data that the sedimentary tex86 lst signal may be confounded by do conditions consequently the application of tex86 to estimate lst should be carefully appraised in environments with depleted do conditions

the caucasus an actual example of the initial stages of continental collision abstract a field study of the neotectonics of the georgian caucasus is combined with geophysical geodetic and geological information in order to obtain a mechanical model of actual deformation the analysis of satellite photos together with topographical and geological maps shows that the great caucasus is bisected by a nne trending sinistral strike slip fault zone the western great caucasus is thrusted to the south over the rioni basin while on the other hand its northern flank is a monocline that descends gently into the russian platform active volcanism is present from elbruz to kazbeg the eastern great caucasus is limited by thrusts to the north and to the south and intermediate structures are disposed in a fan like shape no recent volcanism is observed the eastern limit of the chain is a nnw trending dextral strike slip fault zone seismicity from a local network illustrates the activity of the thrusts and gives evidence for the strike slip faults microtectonic data confirm the recent activity and the sinistral character of the borjomi kazbeg strike slip fault the strike slip faults bordering the eastern caucasus may be seen as the limits of a plastic wedge in front of the arabian plate at an early stage of continental collision

active stress field and fault kinematics of the greater caucasus abstract this work contributes to depict the current seismicity fault kinematics and state of stress in the greater caucasus territories of georgia azerbaijan and russia we merged and homogenized data from different earthquake catalogues relocated 1000 seismic events created a database of 366 selected focal mechanism solutions 239 of which are new and performed a formal stress inversion preferential alignments of crustal earthquake foci indicate that most seismic areas are located along the southern margin of the belt and in the north eastern sector this is consistent with the presence of dominant active wnw ese faults parallel to the mountain range in the entire greater caucasus a dominant nne ssw oriented greatest principal stress 1 controls the over all occurrence of earthquakes of minor and major magnitude main earthquakes are characterized by a vertical least principal stress 3 corresponding to reverse kinematics reverse slip is more common along the southwestern and north eastern foothills of the greater caucasus although in these areas there are also scattered strike slip events this suggests the presence of local stress fields with horizontal 1 and 3 in the central southern part of the mountain belt in correspondence of the local collision between the lesser and the greater caucasus 1 rotates to nnw sse the strike slip events instead dominate along the southern flank of the central eastern mountain range this is interpreted as the effect of the collision that promotes eastward escape of the tectonic blocks located to the east

a biomarker perspective on dust productivity and sea surface temperature in the pacific sector of the southern ocean abstract in this study we present a new multiproxy data set of terrigenous input marine productivity and sea surface temperature sst from 52 surface sediment samples collected along e w transects in the pacific sector of the southern ocean allochthonous terrigenous input was characterized by the distribution of plant wax n alkanes and soil derived branched glycerol dialkyl glycerol tetraethers brgdgts 230th normalized burial of both compound groups were highest close to the potential sources in australia and new zealand and are strongly related to lithogenic contents 232th indicating common sources and transport detection of both long chain n alkanes and brgdgts at the most remote sites in the open ocean strongly suggests a primarily eolian transport mechanism to at least 110 w i e by prevailing westerly winds two independent organic sst proxies were used the u 37 k based on alkenones and the tex86 based on isoprenoid gdgts both u 37 k and tex86 indices show robust relationships with temperature over a temperature range between 0 5 and 20 c likely implying different seasonal and regional imprints on the temperature signal alkenone based temperature estimates best reflect modern summer sst in the study area when using the polar calibration of sikes et al 1997 in contrast tex86 derived temperatures may reflect a subsurface signal rather than surface 230th normalized burial of alkenones is highest close to the subtropical front and is positively related to the deposition of lithogenic material throughout the study area in contrast highest isogdgt burial south of the antarctic polar front may be largely controlled by diatom blooms and thus high opal fluxes during austral summer

hydromechanical controls on the spatiotemporal patterns of injection induced seismicity in different fault architecture implication for 2013 2014 azle earthquakes

the influence of variations in illite morphology on the permeability of middle jurassic brent group sandstones cormorant field uk north sea abstract sem examination of core samples from brent group sandstones in the cormorant field reveals that critical point drying preserves delicate illite morphologies that are damaged during air drying this damage may lead to an increase in permeability as defined by the drying effect air permeability air dried air permeability critical point dried the cormorant reservoir sandstones contain four illite morphologies early diagenetic pore lining illite formed before hydrocarbon emplacement and occurs ubiquitously pore bridging illite blooming illite and illite that replaces kaolinite all formed later and occur preferentially at or below the oil water contact damage to these late illites causes an average drying effect of 3 5 and explains why measured permeabilities predict higher water injection rates than occur in the field comparison with data from other reservoirs reveals that the drying effect is influenced by variations in illite particle dimensions as well as illite morphology tem shadowing techniques reveal that illite particle sizes describe a trend from small particles in reservoirs with large drying effects to large particles in reservoirs with small drying effects these size variations probably reflect differing illite growth rates permeability in illite bearing sandstones thus reflects not only the amount of illite present but also the size of the individual particles and their morphology

the spitak armenia earthquake of 7 december 1988 field observations seismology and tectonics the epicentre of the destructive earthquake that devastated northern armenia the strongest in the region since historical times is located within the lesser caucasus a mountain country subjected to north south compression by the push of the arabian plate a french soviet field expedition studied surface breaks and aftershock activity the fault scarp could be followed for 13 kilometres and showed a reverse dislocation of 1 6 metres aftershocks are shallower than 13 kilometres and delimit a ruptured surface of about 300km2

active tectonics of the alpine himalayan belt between western turkey and pakistan summary over 80 new fault plane solutions combined with satellite imagery as well as both modern and historical observations of earthquake faulting are used to investigate the active tectonics of the middle east between western turkey and pakistan the deformation of the western part of this region is dominated by the movement of continental material laterally away from the lake van region in eastern turkey this movement helps to avoid crustal thickening in the van region and allows some of the shortening between arabia and eurasia to be taken up by the thrusting of continental material over oceanic type basement in the southern caspian mediterranean makran and black sea thus central turkey bounded by the north and east anatolian strike slip faults is moving west from the van region and overrides the eastern mediterranean at two intermediate depth seismic zones one extending between antalya bay and southern cyprus and the other further west in the hellenic trench the motion of northern iran eastwards from the van region is achieved mainly by a conjugate system of strike slip faults and leads to the low angle thrusting of iran over the southern caspian sea the seismicity of the caucasus shows predominantly shortening perpendicular to the regional strike but there is also some minor elongation along the strike of the belt as the causcasus overrides the caspian and black seas the deformation of the eastern part of this region is dominated by the shortening of iran against the stable borders of turkmenistan and afghanistan the north east direction of compression seen in zagros is also seen in north east iran and the kopet dag where the shortening is taken up by a combination of strike slip and thrust faulting large structural as well as palaeomagnetic rotations are likely to have occurred in ne iran as a result of this style of deformation north south strike slip faults in southern iran allow some movement of material away from the collision zone in ne iran towards the makran subduction zone where genuinely intermediate depth seismicity is seen within this broad deforming belt large areas such as central turkey nw iran azerbaijan central iran and the southern caspian appear to be almost aseismic and therefore to behave as relatively rigid blocks surrounded by active belts 200 300 km wide the motion of these blocks can usefully be described by poles of rotation the poles presented in this paper predict motions consistent with those observed and also predict the opening of the gulf of iskenderun ne of cyprus the change within the zagros mountains from strike slip faulting in the nw to intense thrusting in the se and the relatively feeble seismicity in se iran baluchistan this description also explains why the north south structures along the iran afghanistan border do not cut the east west ranges of the makran within the active belts surrounding the relatively aseismic blocks a continuum approach is needed for a description of the deformation even though motions at the surface may be concentrated on faults the evolution of fault systems within the active zones is controlled by geometric constraints such as the requirement that simultaneously active faults do not in general intersect many of the active processes discussed in this paper particularly large scale rotations and lateral movement along the regional strike are likely to have caused substantial complexities in older mountain belts and should be accounted for in any reconstructions of them

cenozoic recent tectonics and uplift in the greater caucasus a perspective from azerbaijan the greater caucasus is europe s highest mountain belt and results from the inversion of the greater caucasus back arc type basin due to the collision of arabia and eurasia the orogenic processes that led to the present mountain chain started in the early cenozoic accelerated during the plio pleistocene and are still active as shown from present gps studies and earthquake distribution the greater caucasus is a doubly verging fold and thrust belt with a pro and a retro wedge actively propagating into the foreland sedimentary basin of the kura to the south and the terek to the north respectively based on tectonic geomorphology active and abandoned thrust fronts the mountain range can be subdivided into several zones with different uplift amounts and rates with very heterogeneous strain partitioning the central part of the mountain range defined by the main caucasus thrust to the south and backthrusts to the north forms a triangular shape zone showing the highest uplift and fastest rates and is due to thrusting over a steep tectonic ramp system at depth the meridional orogenic in front of the greater caucasus in azerbaijan lies at the foothills of the lesser caucasus to the south of the kura foreland basin

modes rates and geomorphological consequences of active tectonics in the marmara region nw turkey a critical overview based on seismotectonic field observations abstract the marmara region is a tectonically active belt in northwestern turkey where field evidence of the collusion escape and strike slip tectonics is manifested the effect of tectonics on the modification of coastal and morphological features of nw turkey is although extensive relatively unknown and rarely appreciated active tectonics in the region has normal and reverse forms of dip slip namely uplift and subsidence and strike slip as is plainly demonstrated by the 1999 marmara earthquake sequence along the north anatolian fault naf these tectonic effects are presently related to the geometry of the naf the mode of lateral movement along it and proximity to the fault the 1999 earthquakes provided data indicating that over a return period of about 250 years seismotectonic strike slip movements recur up to 5 m and dip slip movements up to 2 6 m suggesting the rate of tectonics along the naf in the marmara region is on the order of 20 mm a for strike slip and 10 mm a for dip slip movements these rates are sufficiently large to form during the late quaternary prominent features of the landscape in the marmara region

sources and distributions of branched and isoprenoid tetraether lipids on the amazon shelf and fan implications for the use of gdgt based proxies in marine sediments branched glycerol dialkyl glycerol tetraethers brgdgts in river fan sediments have been used successfully to reconstruct mean annual air temperature maat and soil ph of the congo river drainage basin however in a previous study of amazon deep sea fan sediments the reconstructed maats were ca 10 c colder than the actual maat of the amazon basin in this study we investigated this apparent offset by comparing the concentrations and distributions of brgdgts in amazon river suspended particulate matter spm and sediments to those in marine spm and surface sediments the riverine brgdgt input was evident from the elevated brgdgt concentrations in marine spm and surface sediments close to the river mouth the distributions of brgdgts in marine spm and sediments varied widely but generally showed a higher relative abundance of methylated and cyclic brgdgts than those in the river since this difference in brgdgt distribution was also found in intact polar lipid ipl derived brgdgts which were more recently produced the change in the marine brgdgt distribution was most likely due to marine in situ production consequently the maats calculated based on the methylation of branched tetraethers mbt and the cyclisation of branched tetraethers cbt were lower and the cbt derived ph values were higher than those of the amazon basin however spm and sediments from stations close to the river mouth still showed mbt cbt values that were similar to those of the river therefore we recommend caution when applying the mbt cbt proxy it should only be used in sediment cores that were under high river influence the influence of riverine derived isoprenoid gdgt isogdgt on the isogdgt based tex86 temperature proxy was also examined in marine spm and sediments an input of riverine isogdgts from the amazon river was apparent but its influence on the marine tex86 was minor since the tex86 of spm in the amazon river was similar to that in the marine spm and sediments

geometry segmentation and stress regime of the spitak armenia earthquake from the analysis of the aftershock sequence summary the aftershock sequence of the spitak earthquake as recorded by a dense portable network deployed around the source region is analysed in order to obtain a precise description of the mechanics of the rupture a collection of 708 well recorded events corresponding to a period of about two weeks is studied their hypocentres are accurately located and their focal mechanisms are calculated individually as well as by a joint procedure that permits us to estimate the stress regime the epicentral distribution of these aftershocks indicates that the fault at depth extends well beyond the surface rupture towards the west and northwest neotectonic and seismic observations permit us to identify five segments broken during the earthquake the southeastern one oriented n140 corresponds to the surface ruptures along the alavar right lateral shear fault the main surface ruptures between spitak and gekhasar correlate well with aftershocks showing a n120 trending fault surface dipping 50 to the ne and acting as a thrust with a right lateral component two similar segments towards the west are offset and hidden under active folds a fifth segment towards the nw corresponds to a right lateral blind shear fault buried in depth in the vicinity of the large pambak sevan fault 14 vertical sections across the fault including focal mechanisms illustrate these features a relocation of the main shock and aftershocks for the period before the installation of the portable network confirms the spatial extent of the seismicity the foreshock the main shock and the strongest aftershock 4min 20s after the main shock have approximately the same epicentre thus the rupture started at the crossing of the pambak sevan and alavar faults and propagated bilateraly from there although the seismic moment associated to the alavar branch is only about one sixth of the total moment the stress regime is one of triaxial compression with a a axis oriented n344 the same orientation is given by the microtectonic observations made on the central segment of the surface ruptures a result that agrees with previous estimates for the georgian caucasus

changes in the tectonic regime above a subduction zone of andean type the andes of peru and bolivia during the pliocene pleistocene this paper adresses the changes in the tectonic regime in the peruvian and bolivian andes that have occurred since the upper miocene when the present day elevation of the cordillera above sea level has been almost reached the stress patterns are deduced essentially from a field study of fault kinematics and a numerical inversion of the slip vector data measured on the fault planes the cuzco fault system in southern peru is chosen as an example to illustrate the methodology used in this region striations on both active and holocene faults are in agreement with a n s extension but faults affecting early pleistocene deposits exhibit two families of striations the younger results from the previous n s extension the older involving reverse motions results from either an e w or a n s compression faults affecting pliocene formations often show an oldest family of striations resulting from a ne sw or an e w trending extension thus three tectonic regimes are demonstrated which are also supported by regional unconformities and sedimentological data 1 a pliocene extensional regime 2 a lower pleistocene compressional regime and 3 a mid pleistocene present day extensional regime similar analyses conducted in the pacific and sub andean lowlands allow sketching of the successive pliocene pleistocene stress patterns in the central andes the quaternary and present day stress pattern is characterized by a n s extension in the high andes and in the pacific lowlands and by an e w compression in the sub andean lowlands and at the contact between the nazca and south american plates this stress pattern is interpreted at a large wavelength 100 km as an effect of compensated topography this model supposes that the vertical lithospheric stress zz increases with the topography the crustal thickness and the low density mantle beneath and that the lithospheric maximum compressional horizontal stress hmax trending e w roughly parallel to the convergence is fairly constant on both edges of the andes the tectonics being compressional zz is 3 and hmax is 1 in the high andes zz becomes 1 then the e w trending hmax is 2 and hmin trending n s is 3 allowing extension to occur in this direction the pliocene stress pattern was characterized by a ne sw or an e w trending extension in the high andes in the pacific lowlands and possibly in the sub andean lowlands this stress pattern was clearly different from the present day one because the e w trending stress was hmin this required a weak push or eventually tractional boundary forces acting on the south american lithosphere it is suggested that this might result from a strong slab pull due to a long steeply dipping slab which decreased the value of the xx stress transmitted to the overriding plate the early pleistocene state of stress was compressional since the elevation of the andes had not markedly decreased during this period this required an increase of the e w trending stress value this resulted from a strong coupling between the two lithospheric plates possibly due to a rupture of a long slab under its own weight other spatial changes in the stress pattern are related to the particular situation of the forearc to the subduction of the buoyant nazca ridge and to the different dips of the slab extension in the high andes is of small magnitude of the order of 1 during the last 1 2 m y in a few basins it may have attained 40 during the pliocene 5 3 m y

active inversion tectonics simple shear folding and back thrusting at rioni basin georgia abstract the rioni basin located between the greater and lesser caucasus in georgia is an outstanding example of ongoing inversion tectonics marine and continental deposits of cretaceous neogene age have been locally uplifted since the end of miocene the uplifted area totals 1300 km 2 and plio quaternary river deposits have been raised up to 200 m above the surrounding plains inversion tectonics has been accompanied by the development of south vergent asymmetrical folds and strike slip faults along the border of the uplifted area the folds have locally an en echelon geometry and microtectonic data indicate rotation of the paleostress direction over time suggesting simple shear deformation in the interiors of the uplifted area there are gentle symmetrical folds and one main active south dipping reverse fault corresponding to a backthrust morphostructural evidence as well as the tilting of quaternary strata the offset of quaternary alluvial deposits and the presence of crustal seismic activity indicate that compressional tectonics is still active the combination of field data with seismic reflection sections shows that inversion tectonics took place through a series of north dipping blind thrusts and a wedge with passive back thrusting uplift and contraction are more developed along the eastern part of the study area suggesting the westward propagation of the closure of the transcaucasian depression

increased dust deposition in the pacific southern ocean during glacial periods dust deposition in the southern ocean constitutes a critical modulator of past global climate variability but how it has varied temporally and geographically is underdetermined here we present data sets of glacial interglacial dust supply cycles from the largest southern ocean sector the polar south pacific indicating three times higher dust deposition during glacial periods than during interglacials for the past million years although the most likely dust source for the south pacific is australia and new zealand the glacial interglacial pattern and timing of lithogenic sediment deposition is similar to dust records from antarctica and the south atlantic dominated by patagonian sources these similarities imply large scale common climate forcings such as latitudinal shifts of the southern westerlies and regionally enhanced glaciogenic dust mobilization in new zealand and patagonia

stress tensor and fault plane solutions for a population of earthquakes an algorithm for the simultaneous estimation of the orientation and shape of the stress tensor and the individual fault plane solutions for a population of earthquakes is studied it corresponds to a synthesis of the methods used by brillinger et al 1980 to obtain focal mechanisms and by armijo and cisternas 1978 for stress tensor analysis in microtectonics the input data are the polarities of the p arrival and take off angles for the set of source station pairs the method distinguishes in general which one of the nodal planes corresponds to the fault and gives the direction of the slip the application to the aftershock sequence of the 1980 arudy earthquake western pyrenees shows that the observations may be explained by a single stress tensor producing a n32 e extension with a likelihood of 95 per cent

latitudinal distribution of terrestrial lipid biomarkers and n alkane compound specific stable carbon isotope ratios in the atmosphere over the western pacific and southern ocean abstract we investigated the latitudinal changes in atmospheric transport of organic matter to the western pacific and southern ocean 27 58 n 64 70 s molecular distributions of lipid compound classes homologous series of c15 to c35 n alkanes c8 to c34 n alkanoic acids c12 to c30 n alkanols and compound specific stable isotopes 13c of c29 and c31 n alkanes were measured in marine aerosol filter samples collected during a cruise by the r v hakuho maru the geographical source areas for each sample were estimated from air mass back trajectory computations concentrations of tc and lipid compound classes were several orders of magnitude lower than observations from urban sites in asia a stronger signature of terrestrial higher plant inputs was apparent in three samples collected under conditions of strong terrestrial winds unresolved complex mixtures ucm showed increasing values in the north pacific highlighting the influence of the plume of polluted air exported from east asia n alkane average chain length acl distribution had two clusters with samples showing a relation to latitude between 28 n and 47 s highest acl values in the tropics whilst a subset of southern samples had anomalously high acl values compound specific carbon isotopic analysis of the c29 25 6 to 34 5 and c31 n alkanes 28 3 to 37 revealed heavier 13c values in the northern latitudes with a transition to lighter values in the southern ocean by comparing the isotopic measurements with back trajectory analysis it was generally possible to discriminate between different source areas the terrestrial vegetation source for a subset of the southernmost southern ocean is enigmatic the back trajectories indicate eastern antarctica as the only intercepted terrestrial source area these samples may represent a southern hemisphere background of well mixed and very long range transported higher plant organic material

branched glycerol dialkyl glycerol tetraethers in pleistocene loess paleosol sequences three case studies abstract branched glycerol dialkyl glycerol tetraethers branched gdgts are membrane lipids presumably derived from anaerobic heterotrophic soil bacteria empirical studies have shown that the composition of branched gdgts in topsoils varies in degree of cyclization and methylation expressed as cbt and mbt i e cyclization and methylation index of branched tetraethers depending on soil ph and mean annual air temperature mat here we present results from three case studies namely three well studied loess paleosol sequences lpss in which we measured the branched gdgts in order to test the applicability of these biomarkers for paleoclimate reconstruction the results show that major disagreements exist between expectations based on available stratigraphic pedological and geochemical data on the one hand and gdgt derived reconstructions on the other hand caution is therefore advised when interpreting the respective indices in lps studies we discuss several potential directions for future research i some of the target peaks in the hplc chromatograms consist of multiple unidentified compounds this needs to be addressed by way of improved component separation identification and new calibration studies ii factors other than mat and soil ph that could affect membrane composition should be further investigated e g nutrient availability and redox conditions as well as seasonality and changes in bacterial communities iii gdgts may be produced in non negligible amounts at depth and thus overprint the original in situ signal a concern that could be termed growth depth effect iv gdgts should also be analyzed in dust source regions and contemporaneous eolian sediments in order to address a potential redeposition effect

the middle eocene climatic optimum meco a multiproxy record of paleoceanographic changes in the southeast atlantic odp site 1263 walvis ridge the middle eocene climatic optimum meco 40 ma was a transient period of global warming that interrupted the secular cenozoic cooling trend we investigated the paleoceanographic paleoenvironmental and paleoecological repercussions of the meco in the southeast atlantic subtropical gyre ocean drilling program site 1263 tex86 and 18o records support an 4 c increase in surface and deepwater temperatures during the meco there is no long term negative carbon isotope excursion cie associated with the early warming consistent with other sites and there is no short term negative cie 50 kyr during the peak of the meco in contrast to what has been observed at some sites this lack of a cie during the peak of the meco at site 1263 could be due to poor sediment recovery or geographic heterogeneity of the 13c signal benthic and planktic foraminiferal mass accumulation rates markedly declined during meco indicating a reduction of planktic foraminiferal production and export productivity vertical 13c gradients do not indicate major changes in water column stratification and there is no biomarker or micropaleontological evidence that hypoxia developed we suggest that temperature dependency of metabolic rates could explain the observed decrease in foraminiferal productivity during warming the kinetics of biochemical reactions increase with temperature more so for heterotrophs than for autotrophs steady warming during meco may have enhanced heterotroph i e foraminiferal metabolic rates so that they required more nutrients these additional nutrients were not available because of the oligotrophic conditions in the region and the lesser response of primary producers to warming the combination of warming and heterotroph starvation altered pelagic food webs increased water column recycling of organic carbon and decreased the amount of organic carbon available to the benthos

the impact of diagenesis on the heterogeneity of sandstone reservoirs a review of the role of depositional facies and sequence stratigraphy diagenesis exerts a strong control on the quality and heterogeneity of most clastic reservoirs variations in the distribution of diagenetic alterations usually accentuate the variations in depositional porosity and permeability linking the types and distribution of diagenetic processes to the depositional facies and sequence stratigraphic framework of clastic successions provides a powerful tool to predict the distribution of diagenetic alterations controlling quality and heterogeneity the heterogeneity patterns of sandstone reservoirs which determine the volumes flow rates and recovery of hydrocarbons are controlled by geometry and internal structures of sand bodies grain size sorting degree of bioturbation provenance and by the types volumes and distribution of diagenetic alterations variations in the pathways of diagenetic evolution are linked to 1 depositional facies hence pore water chemistry depositional porosity and permeability types and amounts of intrabasinal grains and extent of bioturbation 2 detrital sand composition 3 rate of deposition controlling residence time of sediments at specific near surface geochemical conditions and 4 burial thermal history of the basin the amounts and types of intrabasinal grains are also controlled by changes in the relative sea level and therefore can be predicted in the context of sequence stratigraphy particularly in paralic and shallow marine environments changes in the relative sea level exert significant control on the types and extent of near surface shallow burial diagenetic alterations which in turn influence the pathways of burial diagenetic and reservoir quality evolution of clastic reservoirs carbonate cementation is more extensive in transgressive systems tract tst sandstones particularly below parasequence boundaries transgressive surface and maximum flooding surface because of the abundance of carbonate bioclasts and organic matter bioturbation and prolonged residence time of the sediments at and immediately below the sea floor caused by low sedimentation rates which also enhance the formation of glaucony eogenetic grain coating berthierine odinite and smectite formed mostly in tst and early highstand systems tract deltaic and estuarine sandstones are transformed into ferrous chlorite during mesodiagenesis helping preserve reservoir quality through the inhibition of quartz cementation the infiltration of grain coating smectitic clays is more extensive in braided than in meandering fluvial sandstones forming flow barriers in braided amalgamated reservoirs and may either help preserve porosity during burial because of quartz overgrowth inhibition or reduce it by enhancing intergranular pressure dissolution diagenetic modifications along sequence boundaries are characterized by considerable dissolution and kaolinization of feldspars micas and mud intraclasts under wet and warm climates whereas a semiarid climate may lead to the formation of calcrete dolocrete cemented layers turbidite sandstones are typically cemented by carbonate along the contacts with interbedded mudrocks or carbonate mudstones and marls as well as along layers of concentration of carbonate bioclasts and intraclasts commonly hybrid carbonate turbidite arenites are pervasively cemented proximal massive turbidites normally show only scattered spherical or ovoid carbonate concretions improved geologic models based on the connections among diagenesis depositional facies and sequence stratigraphic surfaces and intervals may not only contribute to optimized production through the design of appropriate simulation models for improved or enhanced oil recovery strategies as well as for co2 geologic sequestration but also support more effective hydrocarbon exploration through reservoir quality prediction

composition age and provenance of organic matter in nw african dust over the atlantic ocean 1 eolian dust deposited on a meteorology buoy over the boreal winter and spring of 1992 1993 in the northeast atlantic off northwest africa 18 n 22 w afforded sufficient material for detailed assessment of its biogeochemical characteristics and provenance the sample was subjected to microscopic examination and bulk elemental isotopic black carbon and molecular lignin lipid analyses the bulk elemental composition and organic carbon oc content 1 02 dry weight establishes the dust s origin as continental upper crust and is typical of dusts that emanate from west africa these data are in accord with the extensive satellite imagery documenting the transit of dust clouds from the sahara and sahel regions e g nasa toms aerosol index microscopic examination reveals that charcoal like particles from vegetation fires black carbon bc are the most abundant morphologically distinct organic components accelerator mass spectrometry ams 14c analysis yields conventional 14c ages for bulk oc of 1260 40 years and bc of 2070 35 years taken together with corresponding stable carbon isotopic compositions 13c 18 9 and 15 1 respectively these results suggest the presence of biomass and burning residues derived from predominantly c4 vegetation that accumulated in soils over the late holocene molecular level measurements are also consistent with this scenario for example lignin derived phenols in the dustfall sample indicate a significant contribution of angiosperm grass type tissue the altered nature of the lignin suggests storage as residues in soils solvent extractable lipid constituents include a marked leaf wax type component with a molecular and stable carbon isotopic composition similar to those observed in surface marine sediments in this region the hydrocarbon fraction contained some diesel type contamination but the n alkanes c23 c33 retained a prominent odd even distribution with 13c ranging from 26 7 to 28 5 the suite of even carbon numbered n alkanols c22 c32 is 14c dated at 647 150 years with 13c values ranging from 23 9 to 30 4 the long chain n alkanoic acids c22 c32 exhibited 13c values ranging from 22 6 to 27 4 these waxes are evidently a mixed signal derived from contemporary c3 and c4 vegetation and from ablated soils and desiccated lake sediments of middle to late holocene age this molecular approach shows promise as a tool for continental paleoenvironmental assessment particularly with respect to past vegetation cover regional aridity and wind systems

distributional variations in marine crenarchaeotal membrane lipids a new tool for reconstructing ancient sea water temperatures it has recently been shown that membrane lipids of marine crenarchaeota a ubiquitous and abundant component of plankton occur in relatively high concentrations in recent and ancient sediments in this study we investigated the environmental controls on the relative distribution of these lipids in surface sediments we especially focussed on temperature as it is known from the thermophilic genetic relatives of marine crenarchaetoa that the composition of their membrane strongly depends on growth temperature indeed a significant linear correlation r2 0 92 is found between the number of cyclopentane rings in sedimentary membrane lipids derived from marine crenarchaeota and the annual mean sea surface temperatures this suggests that the mechanism of physical adaptation of their membrane compositions to temperature is identical to that of their thermophilic relatives in turn archaeal lipid distributions in sediments may thus allow the reconstruction of sea water temperatures of ancient marine environments

comparison of instrumental and gdgt based estimates of sea surface and air temperatures from the skagerrak sea surface temperatures ssts and annual mean air temperatures mats are estimated for the last 200 years from glycerol dialkyl glycerol tetraethers gdgts proxies in a marine sediment core from the skagerrak off southern norway the reconstructed values compare well with annual ssts and summer air temperatures obtained from composite regional instrumental records the results provide further confidence in the application of proxies based on gdgts to estimate past temperatures

paleostress analysis of a gigantic gravitational mass movement in active tectonic setting the qoshadagh slope failure ahar nw iran abstract for better understanding of the dynamics of large slope failures the slope scale stress field reconstructions are eligible a new approach of paleostress analysis of large gravitational mass movements based on the multiple inverse method in 9d space and processed by a non commercial code mark2010 is demonstrated on the case of a gigantic gravitational slope failure in active tectonic setting at mount qoshadagh in nw iran the entire slope failure represents a very deep seated gravitational slope deformation with relatively short displacement roto translational base and an estimated volume of about 83 110 km3 which is of the last glacial age this gigantic slope failure has developed in an active tectonic setting along the qoshadagh fault system or called south ahar fault which caused fast uplift of the entire mountain range of qoshadagh and it was probably seismically triggered using this paleostress approach we were able to distinguish the mass movement stress phase of nw compression in the rockslide s zone of compression and nw se extension in the upper part from a variety of other 8 regional tectonic and 2 subsequent gravitational phases maximum principal stress of the slope failure phase was in its compression zone sub parallel to the estimated displacement vector in the head it was sub vertical the paleostress analysis has been proved as a useful tool for reconstructing the stress field evolution of large slope failures

source parameters of large earthquakes in the east anatolian fault zone turkey summary the east anatolian fault zone accommodates most of the motion between the arabian plate and the apparently little deforming interior of central turkey the direction of overall slip across this zone is crucial to the determination of the slip rate on the north anatolian fault we use long period p and sn waveforms to determine the source parameters of the four largest earthquakes that occurred in or near the east anatolian fault zone in the last 35 years only one of these actually involved left lateral strike slip motion on a ne sw fault but the other three and the nearby 1975 lice earthquake all had steeply dipping nodal planes with a nnw strike if these were the auxiliary planes then all the earthquakes had a slip vector direction within about 10 of 063 if this direction represents the arabia turkey motion then the slip rate on the north anatolian fault must be in the range 31 to 48 mm yr with a probable value of 38 mm yr and the overall slip rate across the east anatolian fault zone must be about 29mmyr with a range of 25

active tectonics in the lesser caucasus coexistence of compressive and extensional structures detailed spot image analysis which completed field data and a microseismicity study was done on the central caucasian mountain belt georgia armenia and eastern turkey north of the front of the arabian collision in order to clarify the relationships between compression extension and volcanism in fact this region is characterized by relatively complex active tectonics associating both n s compressive e w thrusts and folds and e w extensional n s normal faults and dikes structures accompanied by considerable neogene to quaternary volcanism and ne sw left lateral and nw se right lateral strike slip faults these different structures are all intricately imbricated and can be observed at different scales the general layout implies an important variation in the stress state for instance this passes from a n s compression in the spitak earthquake fault zone to an e w extension at the aboul samsar volcanic axis these results agree well with the n s convergence between arabia and eurasia and the e w lateral expulsion of the anatolian and iranian blocks a detailed cartographic network of active structures was drawn and their kinematic relationships were specified in places recent offsets on strike slip faults were estimated at about 500 to 1000 m suitable sites for future determination of fault velocity displacements were also selected this study shows that some strike slip faults behave partly like faults which transform the e w extension of the n s striking normal faults into a n s compression along the e w thrusts one of the characteristics of this region is the continuous important volcanic activity at least from the jurassic until now this persistence evidences a lithospheric thinning which remained in spite of the recent arabian eurasian collision because of the e w extension linked to the opposite lateral expulsion of the anatolian and iranian blocks this geodynamic evolution can explain the juxtaposition and superimposition of volcanic structures and thrusts in a general compressive context

provenance of present day eolian dust collected off nw africa 1 atmospheric dust samples collected along a transect off the west african coast have been investigated for their physical grain size distribution mineralogical and chemical major elements composition on the basis of these data the samples were grouped into sets of samples that most likely originated from the same source area in addition shipboard collected atmospheric meteorological data modeled 4 day back trajectories for each sampling day and location and total ozone mapping spectrometer aerosol index data for the time period of dust collection february march 1998 were combined and used to reconstruct the sources of the groups of dust samples on the basis of these data we were able to determine the provenance of the various dust samples it appears that the bulk of the wind blown sediments that are deposited in the proximal equatorial atlantic ocean are transported in the lower level 900 hpa ne trade wind layer which is a very dominant feature north of the intertropical convergence zone itcz however south of the surface expression of the itcz down to 5 s where surface winds are southwesterly we still collected sediments that originated from the north and east carried there by the ne trade wind layer as well as by easterly winds from higher altitudes the fact that the size of the wind blown dust depends not only on the wind strength of the transporting agent but also on the distance to the source hampers a direct comparison of the dust s size distributions and measured wind strengths however a comparison between eolian dust and terrigenous sediments collected in three submarine sediment traps off the west coast of nw africa shows that knowledge of the composition of eolian dust is a prerequisite for the interpretation of paleorecords obtained from sediment cores in the equatorial atlantic

on the features of the geodynamo following reversals or excursions by absolute geomagnetic paleointensity data we carried out a thellier paleointensity study of a 3 6 million year pliocene geomagnetic excursion recorded in a lava flow succession from southern georgia lesser caucasus previous paleomagnetic study phys earth planet int 96 1996 41 revealed that several consecutive lava flows record an intermediate polarity direction at the base of the section followed by a thick reverse polarity zone samples of 71 from 26 flows from both polarity zones were pre selected for paleointensity experiments because of their low viscosity index stable remanent magnetisation and close to reversible continuous thermomagnetic curves altogether 54 samples from 21 flows yielded reliable paleointensity estimates the mean paleointensity of the intermediate field is 7 8 2 4t three flows the stable polarity paleointensity is higher with a mean 24 2 8 2t 15 flows which corresponds to a mean virtual dipole moment vdm of 4 6 1 8 10 22 am 2 this value is significantly lower than the average pliocene geomagnetic dipole moment and post intermediate dipole moments recorded in volcanic sequences at hawaii 4 ma and steens mountain 16 2 ma however our results are quite similar to the post intermediate field recorded in iceland during the gauss matuyama reversal these results suggest that the regime of the geodynamo following reversals or excursions may vary significantly from one case to the next without any apparent systematic features 2001 elsevier science b v all rights reserved

the state of stress in an overriding plate situated above a flat slab the andes of central peru in the andes of central peru that are situated above a flat dipping slab analysis of both structural data collected in the field and available focal mechanisms show that the quaternary and recent state of stress is characterized by n s trending extension in the western cordillera and along the pacific coast whereas e w trending compression prevails in the sub andean lowlands and at the contact between the nazca and south american plates the eastern cordillera deformations suggest an intermediate state of stress i e strike slip faulting characterized by e w trending compression and n s trending extension thus major fault zones striking nw se i e parallel to the central peruvian andes are normal with a sinistral component in the western cordillera e g cordillera bianca and reverse sinistral in the eastern cordillera e g cordillera de huaytapallana this state of stress displays similarities with that of southern peru and may be also interpreted as an effect of compensated high topography in this model the vertical stress zz increases with the topography and hmax is considered as fairly constant trending e w roughly parallel to the convergence on both edges of the andes tectonics being compressional zz is 3 and hmax is 1 in the high andes zz becomes 1 then hmax is 2 allowing hmin striking n s to be 3 along the pacific coast tectonics is not compressional as expected and a nearly neutral state of stress may be due to a topographical effect related to the nearby deep peru chile trench however a conspicuous difference occurs in the andes of central peru in respect to the southern peru andes compressional strike slip tectonics is observed in the eastern cordillera indeed the mean elevation of the eastern cordillera is 3 7 km whereas that of the western cordillera is 4 2 km allowing an intermediate state of stress to occur therefore in central peru a lower mean andean topography and a stronger coupling consequence of the flat subduction seems to explain that compressional tectonics is distributed in a more widespread area than in southern peru superficial deformations related to the subduction of the aseismic nazca ridge are restricted to the coastal domain opposite to this ridge they support the fact that submarine topography of large extension may subduct without producing compressional deformation in the overriding plate which can be reminiscent of a collisional setting

source settling and degradation of branched glycerol dialkyl glycerol tetraethers in the marine water column abstract branched glycerol dialkyl glycerol tetraethers branched gdgts are commonly found in distal marine sediments however their presence in the water column source and delivery process are not fully understood in this study we examined seasonal and depth variation in the flux of branched gdgts in sinking particles and underlying sediment at 39 n 147 e in the mid latitude nw pacific from november 1997 to august 1999 branched gdgts showed synchronous variation in their sinking flux at different depths and the variation was similar to that of lithogenic material of eolian dust origin their degrees of cyclization and methylation were nearly constant and bear some resemblance to those of alkaline soils this suggests that westerly winds transport branched gdgts to the study site via the atmosphere from continental asia the sinking flux of branched gdgts was higher in 1999 than in 1998 presumably reflecting changes in the migration path of asian dust in response to the el nino southern oscillation synchronous variation in branched gdgt concentrations at different depths implies rapid vertical transport of branched gdgts to deep water with a sinking velocity exceeding 260 m d 1 the sinking flux of the branched gdgts decreased with increasing depth but the rate of decrease was much smaller than those of other compounds the preservation efficiency of branched gdgts was 3 5 6 4 of surface inputs at the water sediment interface which is much higher than those of isoprenoid gdgts 1 0 1 3 and other compounds the branched and isoprenoid tetraether bit index values were extremely low i e

co seismic stress transfer and magnitude frequency distribution due to the 2012 varzaqan ahar earthquake doublets m w 6 5 and 6 4 nw iran abstract the coulomb stress changes imparted by the 2012 varzaqan ahar earthquake doublets to the surrounding area have been examined and correlated with the spatial distribution of the aftershocks the stress changes due to the first main shock show that the western half of the south ahar fault the southeastern half of the magnetic lineament ml1 the northeastern end of the ml2 the entire length of the ml3 a large part of the ml4 and the northeastern half of the ml5 were brought closer to failure whereas the entire length of the khajeh fault a part of the north tabriz fault the western half of the ml1 a large part of the ml2 the northwestern end of the ml4 and the southwestern half of the ml5 were moved away from failure along the length of the ml1 some aftershocks were clustered in the southeastern and central sections while around the western section there is no earthquake clustering the epicentral distributions of the aftershocks exhibit that most of the events were concentrated in the increased coulomb stress zones the b value distributions in the map view and in the cross sectional view have been investigated the map view shows that the low b value regions e g the north northwest east northeast and southeast of the main shock are in good agreement with the positive coulomb stress change zones the cross sectional view indicates that the high b value regions correlate with the areas of high co seismic slip release therefore surrounding the hypocenter and the western end of the first main shock fault have high b values more slip and positive stress drop while the central sections of the fault have low b values less slip and negative stress drop