tectonic interactions between india and arabia since the jurassic reconstructed from marine geophysics ophiolite geology and seismic tomography gondwana breakup since the jurassic and the northward motion of india toward eurasia were associated with formation of ocean basins and ophiolite obduction between and onto the indian and arabian margins here we reconcile marine geophysical data from preserved oceanic basins with the age and location of ophiolites in nw india and se arabia and seismic tomography of the mantle below the nw indian ocean the north somali and proto owen basins formed due to 160 133 ma n s extension between india and somalia subsequent convergence destroyed part of this crust simultaneous with the uplift of the masirah ophiolites most of the preserved crust in the owen basin may have formed between 84 and 74 ma whereas the mascarene and the amirante basins accommodated motion between india and madagascar east africa between 85 and circa 60 ma and 75 and circa 66 ma respectively between circa 84 and 45 ma oblique arabia india convergence culminated in ophiolite obduction onto se arabia and nw india and formed the carlsberg slab in the lower mantle below the nw indian ocean the nne ssw oriented slab may explain the anomalous bathymetry in the nw indian ocean and may be considered a paleolongitudinal constraint for absolute plate motion nw india asia collision occurred at circa 20 ma deforming the sulaiman ranges or at 30 ma if the hindu kush slab north of the afghan block reflects intra asian subduction our study highlights that the nw india ophiolites have no relationship with india asia motion or collision but result from relative india africa arabia motions instead key points we present a new tectonic model for the evolution of nw indian ocean subducted slab under the carlsberg ridge resulted from arabia india convergence

a climatic trigger for a major oligo miocene unconformity in the himalayan foreland basin 1 subsidence in foreland basins is modulated by the size of the flexural load the elastic thickness of the foreland lithosphere the nature of the sedimentary fill and the rate of convergence basal forebulge unconformities are well known from these basins but here we focus on a major unconformity in the himalayan foreland which removed much of the oligocene lower miocene this is a critical time in the himalaya because it spans the period of initial rapid exhumation of high grade metamorphic rocks and the start of motion on the main central thrust we show that the synchronous timing of unconformity and rapid greater himalayan exhumation may be explained by the same trigger enhanced erosion we estimate that accelerating erosion between 24 and 20 ma would have removed 1 5 km more rock from the greater himalaya than would have been the case had erosion remained at the slower paleogene rates during this time erosion must have temporarily exceeded rock uplift rates by transferring rock from the himalaya to the indian ocean the load is reduced and the indian plate is flexed less so that the depth of the foreland basin shallows to a new equilibrium state we use a flexural model to estimate that erosional unloading could have caused uplift of 400 500 m of the basin at the range front extending 70 150 km into the basin intensification of the asian summer monsoon around the oligo miocene boundary 24 ma is the most likely trigger of the stronger erosion similar unconformities are seen at 15 16 ma and in the pleistocene also linked to faster erosion at these times

arc magmatism witnessed by detrital zircon u pb geochronology hf isotopes and provenance analysis of late cretaceous miocene sandstones of onshore western makran se iran the present work aims to contribute to the cenozoic tectonic setting of the western part of the makran accretionary wedge in se iran we determine the provenance of both deep marine turbiditic and deltaic shelf late cretaceous miocene sandstones describe the sandstone modal framework and heavy minerals and report a new geochronological and isotopic study including 2307 detrital zircons u pb ages and 204 in situ hf isotopic analyses modal sandstone framework compositions indicate that a magmatic arc and recycled accreted sediments were the main sources of eocene oligocene and miocene sandstones cr spinel and heavy mineral assemblages indicate ultramafic rocks likely ophiolitic mantle as a subsidiary source detrital zircon u pb ages cluster in five main age groups 1 neoproterozoic grains suggesting a continental crust provenance within the central iran blocks 2 jurassic grains with hf isotopic compositions of continental crust suggesting a rifting related magmatic provenance 3 late cretaceous and 4 eocene grains with hf isotopic compositions typical of continental crust and non depleted mantle suggesting a continental magmatic arc provenance and 5 early miocene grains the new u pb age and hf isotopic ratios correspond to those obtained in the east iranian makran they fit tectonic reconstructions with middle jurassic intracontinental rift early cretaceous to eocene subduction below central iran forming a continental arc to the north of makran and closure of the related oceanic in the paleogene erosional products of the corresponding magmatic arc are found in the makran basin our data disprove that provenance characteristics of the makran sedimentary rocks are consistent with derivation from the himalayan sources

discovery of the palaeo indus delta fan complex the indus river carries sediments from the western himalaya and deposits some of these as channel and floodplain sediments or molasse the rest of its load forms the indus delta at the margin of the indian ocean the indus delta passes some of its sediments to be deposited as indus submarine fan turbidites thus as elsewhere himalayan molasse delta and fan deposition are related hi tune and space however when we examine fluvial and marine age range data of the older indus deposits in terms of this sedimentary assemblage a major portion of its marine record is missing the oldest known molasse along the indus suture zone and hi the foredeep are middle eocene and late palaeocene hi age respectively a recent synthesis of sedimentation in the northern indian ocean however shows that turbidite sedimentation started around early miocene in the modern indus fan and even later in the bengal fan where are the palaeogene indus delta and fan sediments we suggest herein that these are preserved as the palaeogene siliciclastic khojak formation hi the katawaz basin and eastern makran the modern indus river is 2900 km long coumes kolla 1984 and has 30 000 m 3 s 1 discharge milliman et al 1984 in summer fig 1 twice that of the mississippi river the annual suspended sediment load wells coleman 1984 varies between 395 and 435 x 10 3 t almost equal to that of the mississippi the existence of the middle eocene to middle miocene indus molasse along the

geochemistry of sediments of the ganges alluvial plains evidence of large scale sediment recycling the himalaya an amalgamation of different lithotectonic units brought together during and even before the himalayan orogeny has been subjected to various phases of denudation since the palaeogene sediments derived by erosion of these lithotectonic units in different proportions were delivered to the himalayan foreland the nature and proportions of sediments from various lithotectonic units delivered to the foreland varied in response to the prevailing tectonic and climatic conditions during the orogeny the geochemistry of sediments collected from floodplain river channels and reworked aeolian sediments from the delhi and moradabad areas of the ganges plain of the foreland basin indicates that they were derived from moderately weathered sedimentary sources further the results also suggest that the sediments are not subjected to any significant post depositional chemical weathering high tectonic instability in the source area and the geomorphology and cycles of aggradation and degradation in fluvial regimes in the ganges plain do not favor much chemical weathering homogenization of various lithotectonic units of the himalaya through several episodes of sedimentary reworking is shown by the rare earth elements ree geochemistry of the sediments the predominant source for the homogeneous sediments is likely the high himalayan crystalline or the tertiary sub himalayan sediments again the later was derived from high himalayan crystalline if so the ganges alluvial plain is geochemically a quaternary extension of tertiary sub himalaya the average composition of lithologies subjected to erosion in the himalaya appears to be better represented by the alluvial mud present in the plain

zircon hf isotopic constraints on the sources of the indus molasse ladakh himalaya india 1 india asia collision has resulted in the largest orogenic event on earth since at least 500 ma and this has had a profound influence on the drainage patterns of asia on the asian monsoon climate on global oceanography as well as on faunal extinctions despite this importance understanding of the paleogene evolution of this system is limited u pb and lu hf isotopic analyses of detrital zircons from the clastic sedimentary rocks of the indus molasse located within the indus suture of the ladakh himalaya india show that most have mesozoic cenozoic ages and juvenile hf isotopic compositions this suggests that the main source of these sediments is the transhimalayan batholith with minor flux from the lhasa karakoram terrane and indian plate the lower indus molasse chogdo formation is inferred to have been deposited at 60 49 ma whereas the upper choksti formation was deposited later than 45 41 ma and contains a greater contribution from the lhasa terrane the transhimalayan batholith was eroded throughout indus molasse sedimentation but increasing exhumation of lhasa karakoram terrane indicates its progressive uplift after initial collision and requires formation of apaleo indus river shortly after collision

provenance of cenozoic sedimentary rocks from the sulaiman fold and thrust belt pakistan implications for the palaeogeography of the indus drainage system abstract the provenance of middle eocene to early miocene sedimentary rocks cropping out in the sulaiman fold and thrust belt has been determined examining the mineralogy bulk rock major and trace elements and nd sr isotopes the older 50 30 ma deposits are characterized by a mixed orogenic provenance with a major contribution from the karakorum and the tethyan belt c 80 as the 50 30 ma deposits have a provenance distinct from that of coeval subathu khojak and ghazij shallow marine formations of india and pakistan we propose that they were deposited as a distinct delta system that once fed the palaeo indus fan we document a major change in provenance that occurred before the early late oligocene transition at c 30 ma this change in provenance is marked by the appearance of chlorite and monazite and a shift toward more radiogenic nd sr isotopic compositions we interpret this change as the result of the exhumation and erosion of the proto higher himalaya the 30 15 ma sampled rocks are characterized by a major contribution from the tethyan belt and the higher himalayan crystallines 70 90 and a subordinate contribution 10 30 from the karakorum ophiolitic suture and trans himalaya as the end 0 values of our 30 15 ma samples are similar to those of the palaeo indus fan deposits we suggest that the 30 15 ma sedimentary rocks of the sulaiman fold and thrust belt were the fluvial onshore record of the indus fan other coeval deposits of india and pakistan recorded similar increasing exhumation of the higher himalaya range so that we postulate that these sedimentary rocks all derived from the palaeo indus drainage basin this would suggest that the modern indus drainage basin is no younger than 30 ma

diagenesis and the formation of authigenic illite rich i s crystals in gulf coast shales tem study of clay separates abstract shale samples ranging in depth from 305 m to 3658 m miocene to late cretaceous from a single well in dewitt county texas were examined by x ray diffraction xrd scanning transmission electron microscopy stem and analytical electron microscopy aem techniques to detail the mineralogical textural and chemical changes during diagenesis xrd data suggest that from the surface down to 2134 m illite smectite i s is 50 illite aem data show that this smectite rich i s contains more k than na or ca suggesting that at least some k exchange with pore fluids occurred well before the transition to illite rich i s and implying a lesser role for detrital k feldspar and mica in the transition in addition direct stem aem observations of separates show that these smectite rich amples contain equidimensional euhedral authigenic illite rich i s crystallites at depths as shallow as 610 m electron diffraction yields single crystal patterns however such crystallites are rare compared with common anhedral flakes electron diffraction patterns for anhedral masses show powder rings indicating random orientation of layers al si ratios for anhedral material imply a smectite like high si content for tetrahedral sites al si ratios for the euhedral crystallites suggest an illite like lower si content for tetrahedral sites between 2134 m and 2438 m 83 to 88 c the smectite to illite s i transition abruptly occurs such that at 2438 m and deeper the i s content remains constant at 75 90 illite direct stem aem observations of separates of these illite ich samples show abundant equidimensional euhedral authigenic illite rich i s crystals electron diffraction shows single crystal patterns xrd data show that mixed layer i s is dominantly r1 ordered we interpret these data to suggest that initially anhedral smectite rich material is dominant with significant k in exchangeable cation positions rare illite rich i s crystals form in the early stages of diagenesis in gulf coast pelitic rocks during the abrupt s i transition the original random orientation of smectite layers is lost and a coherent arrangement of illite packets is formed the s i transition proceeds by dissolution of smectite rich material and utilization at least in part of exchangeable k to develop abundant euhedral dominantly r1 ordered illite rich i s crystals the development of illite rich i s crystals proceeds via an ostwald step rule process dissolution of metastable smectite rich i s and growth of abundant euhedral r1 ordered metastable illite ri h i s crystals

estimation of kerogen porosity in source rocks as a function of thermal transformation example from the mowry shale in the powder river basin of wyoming evaluations of porosity relevant to hydrocarbon storage capacity in kerogen rich mudrocks i e source rocks have thus far been plagued with ambiguity in large part because conventional core and petrophysical techniques were not designed for this rock type the growing recognition of an intraparticle organic nanopore system that is related to thermal maturity is beginning to clarify this ambiguity this mode of porosity likely evolved with the thermal transformation of labile kerogen and probably neither depends nor interacts except perhaps chemically with previously assumed matrix or mineral porosity that is dominated by bound water and that may be largely irrelevant to hydrocarbon storage capacity in these rocks to address this newly recognized and important nonmatrix kerogen pore system that is arguably the dominant hydrocarbon storage and mobility network in these rocks we introduce a relatively simple kinetic model that describes porosity development within kerogen as a function of thermal maturation kerogen porosity development is estimated within the upper albian mowry shale in the powder river basin of wyoming to illustrate the approach relevant storage capacity is considered to have evolved with thermal decomposition of organic matter during catagenesis where we estimate that kerogen porosity does not typically exceed 3 of bulk rock volume modeled oil in place estimates are comparable to residual oil estimates from pyrolysis data s1 at lower maturities but exceed pyrolytic s1 yields at higher maturities we hypothesize therefore that a subsurface kinetic porosity model might represent a means to account for s1 losses at surface conditions and to circumvent difficulties surrounding estimations of expulsion efficiencies that are inherent to more traditional mass balance calculations

graptolite derived organic matter in the wufeng longmaxi formations upper ordovician lower silurian of southeastern chongqing china implications for gas shale evaluation abstract the organic rich shales of the wufeng longmaxi formations ordovician silurian are one of the most important hydrocarbon source rocks and shale gas exploration targets in china graptolites are abundant in these shales but their contribution to the dispersed organic matter om has been overlooked this lack of attention could seriously affect the evaluation of om type om maturity hydrocarbon generation potential reservoir characteristics and gas content of these shales optical microscope and focused ion beam scanning electron microscope fib sem techniques were employed to describe the optical characteristics and micro nanopores of the graptolites to determine the contribution of the graptolites and to evaluate the thermal maturity of the wufeng longmaxi formations non granular graptolites which show a stronger anisotropy and higher reflectance under polarized light than the granular graptolites were primarily observed in these sediments graptolites account for 20 93 of the dispersed om in the wufeng longmaxi formations and the level of their contribution has been attributed to the radiation of graptolites at the late ordovician kaptian and the recovery of graptolites at the early silurian rhuddanian the bireflectance values of the non granular graptolites fall between 2 22 and 4 32 indicating a behavior similar to biaxial anthracitic vitrinite the equivalent vitrinite reflectance eqvro values of the sediments in the wufeng longmaxi formations calculated from the mean maximum reflectance of non granular graptolite fall in the range of 3 08 4 29 and these values have a precision that is greater than in previous studies on the wufeng longmaxi formations abundant organic pores were observed in the non granular graptolites and they are aligned parallel to the fusellar layers of the graptolites this indicates that the fusellar layers of non granular graptolites controlled the development and distribution of organic pores such abundant organic pores played a significant role in the accumulation of shale gas in the wufeng longmaxi formations of the upper yangtze platform

specific surface area and pore size distribution in clays and shales one of the biggest challenges in estimating the elastic transport and storage properties of shales has been a lack of understanding of their complete pore structure the shale matrix is predominantly composed of micropores pores less than 2 nm diameter and mesopores pores with 2 50 nm diameter these small pores in the shale matrix are mainly associated with clay minerals and organic matter and comprehending the controls of these clays and organic matter on the pore size distribution is critical to understand the shale pore network historically mercury intrusion techniques are used for pore size analysis of conventional reservoirs however for unconventional shale reservoirs very high pressures 414 mpa 60 000 psi would be required for mercury to access the full pore structure which has potential pitfalls current instrumental limitations do not allow reliable measurement of significant portions of the total pore volume in shales nitrogen gas adsorption techniques can be used to characterize materials dominated by micro and mesopores 2 50 nm a limitation of this technique is that it fails to measure large pores diameter 200 nm we use a nitrogen gas adsorption technique to study the micro and mesopores in shales and clays and compare the results from conventional mercury porosimetry techniques our results on pure clay minerals and natural shales show that i they have a multiscale pore structure at different dimensions ii fine mesopores with a characteristic 3 nm pore size obtained with n2 gas adsorption are associated with an illite smectite group of clays but not with kaolinite iii compaction results in a decrease of pore volume and a reduction of pore size in the inter aggregate macropores of the illitesmectite clays while the fine intra tachoid mesopores are shielded from compaction iv for natural shales mineralogy controls the pore size distributions for shales and the presence of micropores and fine mesopores in natural shales can be correlated with the dominance of the illite smectite type of clays in the rock our assessment of incompressible 3 nm sized pores associated with illite smectite clays provides an important building block for their mineral modulus

cenozoic history of the himalayan bengal system sand composition in the bengal basin bangladesh stratigraphic sequences preserved in the bengal basin provide detrital information that documents a significantly older history of the eastern himalaya than that available from ocean drilling program and deep sea drilling project cores recovered from the bengal fan the bengal basin formed as a result of the himalayan collision is located at the juncture of the indian craton to the west the shillong massif and the himalayan belt to the north and the indo burman ranges to the east modal analyses of eocene and oligocene sandstones of the cherra kopili and barail formations document compositions that are dominated by subangular monocrystalline quartz grains with scarce to no feldspar grains and few lithic fragments cherra and kopili qt 99 f 1 l 0 barail qt 90 f 3 l 7 qt total quartz f feldspar l lithic fragments these compositions are similar to sands derived from the indian craton suggesting that they underwent intense chemical weathering likely in a source with low relief and considerable transport himalayan tectonism during this time was probably significantly more distant from the bengal basin than at present sandstones of the miocene surma group bhuban and boka bil formations are rich in feldspar grains argillite and very low grade metamorphic lithic fragments bhuban qt 66 f 15 l 19 boka bil qt 57 f 23 l 20 relative to older sandstones suggesting onset of uplift and erosional unroofing in the eastern himalaya and initiation of stream systems supplying orogenic detritus to the bengal basin sands of the upper miocene to pliocene tipam group and the pliocene pleistocene dupi tila sandstone contain abundant argillitic and low to medium grade metamorphic lithic fragments and feldspar grains tipam qt 61 f 19 l 19 dupi tila qt 70 f 13 l 17 suggesting continued orogenic unroofing these younger sands are rich in potassium feldspar p f 0 30 0 20 relative to plagioclase p rich bhuban and boka bil sandstones p f 0 66 and 0 48 suggesting a granitic source probably the miocene leucogranites of the high himalayan crystalline terrane these results document for the first time contrasts in orogenic history recorded in the bengal system vs western himalayan foreland basins sands deposited in the bengal basin are generally more quartzose and less lithic than those from the western himalayan foreland basins and pre miocene strata in the bengal system show little to no evidence of orogenic activity in part this probably reflects west to east progression of the himalayan collision but it probably also results from sedimentary systems propagating southward ahead of the advancing mountain belt as it has been consuming the remnant ocean basin trapped between the indian craton and the burmese block

kinematic evolution of andean fold thrust structures along the boundary between the eastern cordillera and middle magdalena valley basin colombia 1 surface and subsurface data support a kinematic reconstruction of cenozoic fold thrust deformation along the eastern cordillera magdalena valley transition in colombia the la salina fault lsf marks the boundary between west vergent eastern cordillera structures and hinterland deposits of the middle magdalena valley basin apatite fission track and u th he thermochronological results for the west directed lsf reveal initial hanging wall exhumation during middle eocene early oligocene 45 30 ma shortening renewed exhumation in the early middle miocene 18 12 ma and accelerated late miocene pliocene 12 3 ma exhumation vitrinite reflectance data suggest maximum burial of 4 6 km helping constrain cenozoic basin architecture mapping of the lsf reveals hanging wall cretaceous eocene rocks in a broad anticline syncline pair with limited faulting and footwall eocene quaternary basin fill in a complex series of tight thrust related folds limited displacement along the westernmost frontal thrust suggests that shortening is largely accommodated by east directed thrusting within a broader triangle zone of a passive roof duplex and probable minor strike slip deformation in the preferred kinematic restoration the most recent phase of shortening to transpressional deformation represents out of sequence reactivation of the lsf consistent with irregular crosscutting relationships among footwall structures earliest exhumation by 45 30 ma in the eastern cordillera fold thrust belt is correlated with increased sedimentary lithic fragments and high compositional maturity in sandstones of the adjacent magdalena valley basin exhumation since 15 ma coincided with decreased compositional maturity and elevated accumulation rates for the real group the compositional provenance shifts are attributed to westward advance of fold thrust deformation into the proximal eastern segments of the magdalena valley basin

centennial scale variability of the british ice sheet implications for climate forcing and atlantic meridional overturning circulation during the last deglaciation evidence from paleoclimatic archives suggests that earth s climate experienced rapid temperature changes associated with pronounced interhemispheric asymmetry during the last glacial period explanations for these climate excursions have converged on nonlinear interactions between ice sheets and the ocean s thermohaline circulation but the driving mechanism remains to be identified here we use multidecadal marine records of faunal oxygen isotope and sediment proxies from the northeast atlantic proximal to the western margins of the last glacial british ice sheet bis to document the coupling between ice sheet dynamics ocean circulation and insolation changes the core data reveal successions of short lived 80 100 years high amplitude ice rafted debris ird events that were initiated up to 2000 years before the deposition of detrital carbonate during heinrich events he 1 and 2 progressive disintegration of the bis 19 16 kyr before present b p occurred in response to abrupt ocean climate warmings that impinged on the northeast atlantic during the early deglaciation peak ird deposition recurs at 180 220 year intervals plausibly involving repeated breakup of glacial tidewater margins and fringing marine ice shelves the early deglaciation culminated in a major meltwater pulse at 16 3 kyr b p followed by another discharge associated with he1 some 300 years after we conclude that temperature changes related to external forcing and marine heat transport caused a rapid response of the bis and possibly other margins of the eurasian ice sheet massive but short lived meltwater surges influenced the atlantic meridional overturning circulation thereby contributing to north atlantic climate variability and bipolar climatic asymmetry

high pressure methane and carbon dioxide sorption on coal and shale samples from the parana basin brazil abstract an experimental study has been conducted to assess the potential for coalbed methane production and carbon dioxide storage in coals carbonaceous shales and source rocks in the parana basin in brazil high pressure sorption tests with methane and carbon dioxide were performed on coal and carbonaceous shales from the santa terezinha coalfield and samples from two principal petroleum source rocks measured excess sorption capacities ranged from 0 03 to 0 47 mmol g for methane and 0 14 to 0 81 mmol g for carbon dioxide showing a decrease with decreasing organic matter content linear regression lines for methane sorption capacity vs toc extrapolated to approximately zero whereas for carbon dioxide the intercept of the regression line indicated a residual sorption capacity of 0 2 mmol g on the mineral matter present day gas contents of coals collected from the first cbm well in the santa terezinha coalfield correspond to 13 38 of the measured maximum sorption capacities carbon dioxide sorption capacities exceed methane sorption capacities by a factor of 1 9 to 6 9 for these coals free sorption capacities of the under saturated coals in combination with preferential sorption of carbon dioxide could favour co 2 enhanced methane recovery and co 2 storage in coals and shales of the study area based upon the calculated coal reserves gas contents and measured sorption capacities a total storage potential of 15 4 gt co 2 was estimated for an area of 20 40 km 2 in the santa terezinha coal field assuming a combined co 2 enhanced coalbed methane ecbm production and co 2 storage operation to fully evaluate the potential for carbon dioxide storage and coalbed methane production further studies are required to assess producibility of methane and efficiency of long term co 2 storage in the study area

the importance of shale composition and pore structure upon gas storage potential of shale gas reservoirs abstract the effect of shale composition and fabric upon pore structure and ch 4 sorption is investigated for potential shale gas reservoirs in the western canadian sedimentary basin wcsb devonian mississippian d m and jurassic shales have complex heterogeneous pore volume distributions as identified by low pressure co 2 and n 2 sorption and high pressure hg porosimetry thermally mature d m shales 1 6 2 5 vro have dubinin radushkevich d r co 2 micropore volumes ranging between 0 3 and 1 2 cc 100 g and n 2 bet surface areas of 5 31 m 2 g jurassic shales which are invariably of lower thermal maturity ranging from 0 9 to 1 3 vro than d m shales have smaller d r co 2 micropore volumes and n 2 bet surface areas typically in the range of 0 23 0 63 cc 100 g co 2 and 1 9 m 2 g n 2 high pressure ch 4 isotherms on dried and moisture equilibrated shales show a general increase of gas sorption with total organic carbon toc content methane sorption in d m shales increases with increasing toc and micropore volume indicating that microporosity associated with the organic fraction is a primary control upon ch 4 sorption sorption capacities for jurassic shales however can be in part unrelated to micropore volume the large sorbed gas capacities of organic rich jurassic shales independent of surface area imply a portion of ch 4 is stored by solution in matrix bituminite solute ch 4 is not an important contributor to gas storage in d m shales structural transformation of d m organic matter has occurred during thermal diagenesis creating and or opening up microporosity onto which gas can sorb as such d m shales sorb more ch 4 per weight percent wt toc than jurassic shales inorganic material influences modal pore size total porosity and sorption characteristics of shales clay minerals are capable of sorbing gas to their internal structure the amount of which is dependent on clay type illite and montmorillonite have co 2 micropore volumes of 0 78 and 0 79 cc 100 g n 2 bet surface areas of 25 and 30 m 2 g and sorb 2 9 and 2 1 cc g of ch 4 respectively dry basis a reflection of microporosity between irregular surfaces of clay platelets and possibly related to the size of the clay crystals themselves mercury porosimetry analyses show that total porosities are larger in clay rich shales compared to silica rich shales due to open porosity associated with the aluminosilicate fraction clay rich sediments low si al ratios have unimodal pore size distributions

petrology and provenance of cenozoic sand from the indus cone and the arabian basin dsdp sites 221 222 and 224 abstract the closing of the remnant ocean basin between india and asia has produced the uplifted gneissic sedimentary and metasedimentary terrane of the western himalayas sediment derived from this source is presently being deposited in the submarmefan and basin plain complex of the indus cone and arabian abyssal plain the location of dsdp sites 221 222 and 224 point counts of 15 cenozoic sand samples from these sites have mean qfl percentages of 43 30 27 the plagioclase total feldspar mean is 0 66 lithic types are dominated by quartz mica tectonite argillite shale polycrystalline carbonate and other sedimentary and metasedimentary varieties volcanic grains present are mainly felsic these sands resemble those of the bengal and nicobar fans which were also derived from the himalayas these plus other sands derived from collision orogenic belts have a distinctive signature p f close to 0 66 lv l low 0 10 or less and q dominant with f and l subequal

age of initiation of the india asia collision in the east central himalaya abstract we document the stratigraphy and provenance of the lower tertiary terrigenous sections in the zhepure shan region of the tethyan himalaya southern tibet using petrographic and geochemical whole rock and single grain techniques the cretaceous early tertiary shelf deposits of shallow marine carbonates and siliciclastics of the former indian passive margin near the western end of the zhepure shan are conformably overlain by lower tertiary clastic rocks sandstones in the jidula formation paleocene mostly contain monocrystalline quartz grains of cratonic origin in contrast significant amounts of immature framework grains with a distinct ophiolitic and volcanic arc influence are present in the youxia early eocene and shenkeza post early eocene formations major trace and rare earth element concentrations in both sandstones and shales complement the petrographic data and indicate that the source of the jidula formation consisted primarily of quartzose basement rocks probably of indian con

organic matter clay mineral intergranular pores in the lower cambrian lujiaping shale in the north eastern part of the upper yangtze area china a possible microscopic mechanism for gas preservation abstract gas shales with a high gas content were encountered in the lower cambrian lujiaping formation in the northeast part of the upper yangtze area china in this area the tectonic condition is complex and the organic matter is over matured so conventional oil and gas exploration have not previously been considered during a recent shale gas exploration canister desorbed gas contents of more than 1 m 3 t were detected from 490 to 825 m depth with a maximum value of 3 18 m 3 t at 762 m hence to understand the mechanism of preservation of the gas is important the gas shales have a total organic carbon toc content of between 0 44 and 6 91 and vitrinite like macerals reflectance r o between 3 3 and 4 3 with type ii kerogen the porosity of 22 gas shale samples ranges between 0 4 and 2 29 and their permeability is between 6 9 10 5 and 3 8 10 1 md to investigate the shale s pore structure and its relation to gas storage behavior we studied the microscopic mechanism of gas preservation using a combination of pore characterization techniques including focused ion beam scanning electron microscope fib sem imaging and comparison of gas sorption and free gas storage capacity folding thrusting and subsequent rapid uplifting movements occurred after most of the dry gas had been originally generated and the present gas is a mixture originated from the cracking of liquid hydrocarbons at high maturity and kerogen pyrolysis in the early hydrocarbon generation phase sem observations combined with low temperature gas adsorption and mercury injection capillary pressure analyses show that pores within the organic matter or the mineral particles in the lujiaping shale are rare while the nanometer sized pores 1 4 nm between organic matter and clay mineral particles especially in cleavage domains are greatly developed thus the gas in these shales is mainly adsorbed gas due to the limited free gas storage space this is unlike most other shale gas reservoirs pores within the organic matter and pores between or within mineral particles are dominant moreover the desorbed gas content correlates well with toc content and the microporous and mesoporous specific surface area determined by low temperature co 2 and n 2 respectively suggesting that the nanometer sized pores associated with the organic matter make up the fundamental storage space for this shale the calculations based on fib sem observation showed that the nanometer sized intergranular pores have large specific surface areas with their small pore throat diameters resulting in high capillary pressure these characteristics have contributed to the preservation of shale gas in this complex tectonic area

geochemical constraints on the origin and volume of gas in the new albany shale devonian mississippian eastern illinois basin this study involved analyses of kerogen petrography gas desorption geochemistry microporosity and mesoporosity of the new albany shale devonian mississippian in the eastern part of the illinois basin specifically detailed core analysis from two locations one in owen county indiana and one in pike county indiana has been conducted the gas content in the locations studied was primarily dependent on total organic carbon content and the micropore volume of the shales gas origin was assessed using stable isotope geochemistry measured and modeled vitrinite reflectance values were compared depth of burial and formation water salinity dictated different dominant origins of the gas in place in the two locations studied in detail the shallower owen county location 415 433 m 1362 1421 ft deep contained significant additions of microbial methane whereas the pike county location 832 860 m 2730 2822 ft deep was characterized exclusively by thermogenic gas despite differences in the gas origin the total gas in both locations was similar reaching up to 2 1 cm3 g 66 scf ton lower thermogenic gas content in the shallower location lower maturity and higher loss of gas related to uplift and leakage via relaxed fractures was compensated for by the additional generation of microbial methane which was stimulated by an influx of glacial melt water inducing brine dilution and microbial inoculation the characteristics of the shale of the maquoketa group ordovician in the pike county location are briefly discussed to provide a comparison to the new albany shale

locating earliest records of orogenesis in western himalaya evidence from paleogene sediments in the iranian makran region and pakistan katawaz basin a combination of sediment petrography detrital zircon u pb and fission track dating is used to show that provenance of the paleogene sedimentary rocks exposed in the makran region of southern iran and the katawaz basin of pakistan is consistent with a source from the nascent western himalaya and associated magmatic arc results from this important archive show that paleogene erosion was focused mainly on the arc and northern indian margin and in contrast to the east central himalaya we have not detected widespread rapid exhumation indicative of strong forcing by climate driven erosion at that time

climate correlations between greenland and antarctica during the past 100 000 years the ice cores recovered from central greenland by the grip1 2 and gisp23 projects record 22 interstadial warm events during the part of the last glaciation spanning 20 105 kyr before present the ice core from vostok east antarctica records nine interstadials during this period4 5 here we explore links between greenland and antarctic climate during the last glaciation using a high resolution chronology derived by correlating oxygen isotope data for trapped o2 in the gisp2 and vostok cores we find that interstadials occurred in east antarctica whenever those in greenland lasted longer than 2 000 years our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and antarctica ice older than 115 kyr in the gisp2 core shows rapid variations in the 18o of o2 that have no counterpart in the vostok record the age depth relationship and thus the climate record in this part of the gisp2 core appears to be significantly disturbed

compositional suites of terrigenous deep sea sands of the present continental margins the compositional variability shown by sands of present continental margins was determined through conventional microscopic techniques this allowed the establishment of a descriptive classification of deep sea terrigenous sands based on a restricted number of commonly used parameters the fundamental sand types include 1 qf suite sands in which quartzose and or feldspathic grains predominate carbonate l bearing sands on average richer in lithics occur within this suite 2 ql suite in which quartzose and or lithic grains predominate little compositional diversification is apparent within this suite 3 fl suite in which lithic and or feldspathic grains predominate two compositional members can be identified based on the k feldspar plagioclase ratio 4 lv suite consists of sands in which volcanic grains largely dominate the lithic types vitric and serpentine sands occur within this suite the suites are related to distinct source area types defined as follows 1 cratonic block 2 sedimentary orogenic belt 3 volcanic orogenic belt 4 volcanic arc some sands cannot be easily assigned to a single compositional suite because petrologic parameters overlap with an adjacent suite such critical compositions are commonly arkosic using roundness of the framework components it is possible to define a category identified as matured sands which are greatly enriched in resistates

zircon u pb and hf isotopic constraints on the onset time of india asia collision the time of initial collision between india and asia has been extremely controversial despite the fact that it is vital to constraining the orogenesis and subsequent evolution of the himalayas and tibetan plateau here we report u pb and hf isotope analysis of detrital zircons from two principal foreland basins that is the sangdanlin and gyangze basins respectively in the western and central parts of southern tibet our data suggest that asian derived clastic sediments started contributing to sedimentation on the indian continental margin earlier than generally thought at 60 ma in both basins near the yarlung zangbo suture zone in southern tibet no evidence for the existence of an intra oceanic arc within the neotethys is observed we conclude that 60 ma can be used to constrain the onset time of the india asia collision at least in central tibet after this initial collision closure of the neotethys propagated both westward and eastward with the final closure occurring at 50 and 45 ma in northwestern and eastern himalayas respectively our conclusion differs significantly from the previous view that the india asia collision may have started in northwestern himalaya and propagated eastward with diachronous suturing

early middle miocene paleodrainage and tectonics in the pakistan himalaya the 18 14 ma kamlial formation himalayan foreland basin sedimentary rocks in the chinji village region potwar plateau pakistan are characterized by 1 lithofacies indicative of deposition by a large river 2 a dominant magmatic arc provenance completely unlike the recycled orogen foreland basin deposits stratigraphically below above or coeval with these rocks and 3 subordinate contribution from a rapidly exhuming source interpreted as either the nanga parbat haramosh massif or the southern margin of the asian crust the start of kamlial formation deposition at this locality at 18 ma marks a major break with the older murree formation rocks which were deposited by rivers draining predominantly the himalayan thrust stack south of the arc we interpret this change as the result of diversion of the paleo indus river to its present position which crosses the kohistan arc and himalayas and debouches into the foreland if the rapidly exhuming subordinate source region were the nanga parbat haramosh massif then initiation of its uplift would have resulted in significant arc detritus to the basin as the overlying arc carapace was exhumed as the carapace was progressively breached arc material would have become a less substantial component of detritus to the basin consistent with the reported petrography of the overlying siwalik deposits

large scale sediment underplating in the makran accretionary prism southwest pakistan field relations in the emergent part of the makran accretionary prism show that a mid miocene to early pliocene slope and shelf sedimentary sequence was deposited directly on abyssal plain turbidites without any detectable stratigraphic or structural discordance sedimentological evidence for rapid shoaling however indicates that the underlying sediment column was tectonically thickened by a factor of between two and three during this period this can be explained by large scale underthrusting and underplating of sediment a mode of accretion that is also favored by mass balance considerations the visible deformation in the coastal makran occurred when the region was 70 100 km north of the contemporary prism front

development of organic porosity in the woodford shale with increasing thermal maturity abstract using a combination of focused ion beam milling and scanning electron microscopy we describe the evolution of secondary organic porosity in eight woodford shale late devonian early mississippian samples with mean random vitrinite reflectance values ranging from 0 51 ro to 6 36 ro organic porosity was observed to be absent in samples with vitrinite reflectance values of up to 0 90 ro with the first appearance of secondary pores starting with the 1 23 ro sample porosity in the organic matter was unexpectedly absent in a sample with a vitrinite reflectance of 2 00 ro however organic pores were again found in samples with higher thermal maturities porosity when present did not appear to be uniformly distributed among the organic matter that was within less than a micron of each other suggesting important differences in composition of the organic matter thin regions of organic matter were observed between grains raising the possibility that small amounts of the deposited organic matter were compacted between grains to form thin layers and or the structures are part of the secondary organic matter interpreted to be post oil bitumen which was left behind as a residue during oil migration through the shale some regions of porous organic matter appeared to be grain protected whereas others did not which indicates that these non protected porous organic regions may be stress supporting with porosity intact under in situ reservoir conditions these observations suggest that thermal maturity alone is insufficient to predict porosity development in organic shales and other factors such as organic matter composition complicate porosity development

organic matter hosted pore system marcellus formation devonian pennsylvania the marcellus formation of pennsylvania represents an outstanding example of an organic matter om hosted pore system most pores detectable by field emission scanning electron microscopy fe sem are associated with om instead of mineral matrix in the two wells studied here total organic carbon toc content is a stronger control on om hosted porosity than is thermal maturity the two study wells span a maturity from late wet gas vitrinite reflectance ro 1 0 to dry gas ro 2 1 samples with a toc less than 5 5 wt display a positive correlation between toc and porosity but samples with a toc greater than 5 5 wt display little or no increase in porosity with a further increasing toc in a subset of samples 14 across a range of toc 2 3 13 6 wt the pore volume detectable by fe sem is a small fraction of total porosity ranging from 2 to 32 of the helium porosity importantly the fe sem visible porosity in om decreases significantly with increasing toc diminishing from 30 of om volume to less than 1 of om volume across the range of toc the morphology and size of om hosted pores also vary systematically with toc the interpretation of this anticorrelation between om content and sem visible pores remains uncertain samples with the lowest om porosity higher toc may represent gas expulsion pore collapse that was more complete as a consequence of greater om connectivity and framework compaction whereas samples with higher om porosity lower toc correspond to rigid mineral frameworks that inhibited compactional expulsion of methane filled bubbles alternatively higher toc samples may contain om low initial hydrogen index relatively unreactive that is less prone to development of fe sem detectable pores in this interpretation om type controlled by sequence stratigraphic position is a factor in determining pore size distribution

lithofacies depositional environments regional biostratigraphy and age of the chitarwata formation in the bugti hills balochistan pakistan abstract the oligocene early miocene chitarwata formation records a critical interval of terrestrial sedimentation that predates the siwalik deposits on the potwar plateau of north central pakistan this oligocene early miocene time interval has long been considered as lacking in the entire indo pakistan region the chitarwata formation is widely exposed in the sulaiman range but has never been described in detail in the sulaiman lobe where the famous fossiliferous strata called bugti bone beds have been known for over a century and half the chitarwata formation represents coastal delta at the base and plain and fluvial environments at the top lithofacies and sedimentary structures of the chitarwata formation in the bugti area are described in detail and show a clearly distinct lithologic pattern different from that reported from the zinda pir area the chitarwata formation also records an important transition in the evolution of the drainage systems in the area during the late paleogene and early neogene this transition from the west flowing paleo indus fluvial system to the development of the ancestral indus drainage system may explain the numerous hiatuses that characterize the chitarwata formation the abundance of fossil mammals from the chitarwata and overlying vihowa formation in the bugti hills provides critical biochronologic information that sheds new light on biostratigraphic correlation with the zinda pir area and for the entire sulaiman range

the paleogeographic significance of aquilapollenites occurrence in pakistan abstract the occurrence of the genus aquilapollenites in upper cretaceous and neogene sediments of northwestern pakistan is reported here aquilapollenites amplus aquilapollenites reductus and aquilapollenites sp occur in the maastrichtian palynomorph assemblage from an outcrop sample of the mir ali section northern waziristan aquilapollenites medeis in the neogene murgha faqir zai formation of the pishin basin balochistan is considered a reworked cretaceous specimen the upper cretaceous sediments of the asian plate on the tethys margin are considered to be the source of aquilapollenites spp in these samples

ice sheet variability around the north atlantic ocean during the last deglaciation millennial scale variability in the flux of ice rafted detritus to north atlantic sediments during the last glacial period has been interpreted to reflect a climate forced increase in the discharge of icebergs from ice sheet margins surrounding the northern north atlantic ocean 1 but the relationship between ice sheet variability and climate change is not clear as both the sources of ice rafted detritus and the ice marginal processes are varied and complex 2 4 terrestrial records are helpful in unravelling this complexity because they can demonstrate the scale of ice sheet oscillations and whether the ice sheet or sector was advancing or retreating with respect to climate change here we constrain the age and anatomy of a prominent readvance of the british ice sheet in the northern irish sea region at similar to 14 14 c kyr bp similar to 16 4 calendar kyr bp the analysis indicates that the british ice sheet participated in an iceberg discharge episode known as heinrich event 1 comparison with other terrestrial and marine ice sheet records suggests that the dynamic collapse of the laurentide ice sheet beginning at 14 6 15 0 c 14 kyr bp1 4 similar to 17 2 17 6 calendar kyr bp 5 initiated varied responses from other ice sheet margins around the northern north atlantic region these observations support the argument that the release of icebergs and meltwater during heinrich event 1 disrupted the north atlantic thermohaline circulation 6 8 leading to a delay or reversal of deglaciation of the northern hemisphere and at least as far south as 40 degrees s for two to three thousand years 5 9 10 suggesting a climate forcing and response similar to that of the ensuing younger dryas cold snap 11 12

provenance of the lower tertiary murree redbeds hazara kashmir syntaxis pakistan and initial rising of the himalayas abstract the murree supergroup of northern pakistan is represented by an over 6 km thick succession of deltaic redbeds and intercalated impure foraminiferal limestones of latest palcocene to middle eocene ilerdian to lutetian age cropping out in the northern part of the hazara syntaxis and by redbeds of younger age early middle eocene to early miocene cropping out in the southern part of the syntaxis rawalpindi area the quartzolithic composition of the murree redbeds testifies to a collision orogen provenance detritus was derived from a suture belt including thrust sheets of metasedimentary and subordinately sedimentary rocks volcanic or volcaniclastic rocks and ophiolites phyllite rock fragments are most common in the ilerdian sandstones whereas volcanic and carbonate rock fragments are more abundant in the lutetian sandstones minor quantities of chert and serpentineschist indicating contribution from uplifted subduction complex sources as well as siltstone shale and limestone grains are invariably present detrital modes of sandstones and southwestward progradation of tertiary clastic wedges both testify to provenance from the proto himalayan chain located to the north and uplifted since the very first stages of the india asia continental collision at the end of the paleocene the coeval chulung la redbeds of the tethys himalaya instead consisting of volcanic and subordinate ophiolitic detritus testify to exclusive provenance from the obducting trans himalayan are trench system this major petrographic difference may be accounted for by the different structural setting of the chulung la piggy back and murree foreland basins these two distinct collisional basins have been separated probably since the onset of collision by a fold thrust belt beginning to rise in the position occupied today by the high and lesser himalayan structural domains throughout the murree supergroup main petrographic parameters do not vary greatly and volcanic sedimentary low grade metasedimentary and ophiolitic detritus persisted until the early miocene indicating slow progressive growth of the chain only during the middle miocene when the highly metamorphosed rocks of the high himalaya were carried southward along the main central thrust mct the mountain range began to rise to dramatic heights and huge amounts of detritus started to feed the siwalik foreland basin sandstones and the remnant ocean turbidites of the indus and bengal fans

unroofing history of the eastern himalaya and the indo burman ranges heavy mineral study of cenozoic sediments from the bengal basin bangladesh abstract upper eocene to neogene fill of the bengal basin provides an earlier unroofing history of the eastern himalaya and indo burman ranges than that provided by drilling of the bengal fan and analysis of heavy minerals in these sequences provides useful provenance constraints quartzose sandstones of the eocene kopili and oligocene barail formations contain only 0 2 heavy minerals comprising abundant opaque minerals and stable minerals such as tourmaline garnet rutile and zircon this assemblage suggests sediment sources dominated by low to intermediate grade metamorphic silicic igneous and metasedimentary rocks the low heavy mineral content and abundance of stable minerals suggest intense chemical weathering these sediments may have been derived in part from incipient uplifts of the proto himalaya and or the indo burman ranges but a more likely source is the indian craton immediately to the west miocene sandstones of the surma group contain more abundant and more diverse heavy mineral assemblages than oligocene sandstones these include abundant opaque minerals and garnet mostly almandine and moderate to minor amounts of tourmaline kyanite zircon calcic amphibole rutile chlorite zoisite staurolite epidote sillimanite and clinopyroxene indicating a broad range of mostly metamorphic source rocks upper strata of the surma group also contain abundant blue green amphibole orthopyroxene and sparse chromite suggesting exhumation of arc and ophiolitic rocks sands and sandstones from the upper miocene to pliocene tipam group and the pliocene to pleistocene dupi tila formation contain assemblages similar to those of the underlying miocene sandstones along with more abundant orthopyroxene and sillimanite in dupi tila sands temporal variations in heavy mineral assemblages in the bengal basin suggest that orogenic detritus first appears in the eastern himalayan foredeep much later early miocene than in the western part of the foredeep eocene the appearance of high pressure phases in upper miocene strata reflects continued unroofing of deeper crustal metamorphic and silicic to ultramafic plutonic rocks

the innuitian ice sheet configuration dynamics and chronology abstract portrayal of north american ice cover during the last glacial maximum is dominated by the laurentide ice sheet leaving little detail for the adjacent innuitian ice sheet iis four decades of geological fieldwork across the queen elizabeth islands now warrant specific treatment of the iis including its chronology configuration dynamics and retreat this reconstruction is relevant to the sedimentary history of the arctic ocean and to high latitude climate forcing the iis was composed of both an alpine and lowland sector the advance of the alpine sector occurred as recently as 19 14 c ka bp geological evidence configures outflow from alpine and lowland divides that produced several palaeo ice streams one extending northwestward across the canadian arctic archipelago to the polar continental shelf retreat of the iis commenced along its southwest margin 11 6 14 c ka bp however most of the ice sheet remained on the continental shelf during the younger dryas by 10 14 c ka bp marine based ice experienced widespread calving through the western and central archipelago in response to holocene warming and ongoing eustatic sea level rise the sea penetrated the eastern archipelago by 8 5 14 c ka bp gutting the alpine sector of the iis regional isobases record the glacioisostatic signature of the ice sheet and are congruent with the primary geological evidence the delayed buildup of the iis was out of phase with the growth of the laurentide ice sheet that occasioned climatic and glacio eustatic forcing in the innuitian region recent modelling experiments reinforce the hypothesis that growth of the laurentide ice sheet culminated in a split jet stream that temporarily favoured augmented precipitation and growth of the iis

the detrital record of orogenesis a review of approaches and techniques used in the himalayan sedimentary basins the sediment archive of material eroded from an active tectonic region and stored in adjacent basins can provide a valuable record of hinterland tectonism especially when information in the source region itself is obscured by later metamorphism or removed by tectonism or erosion using the sediment record to document tectonism is a well established approach but more recently there has been a burgeoning of the number of isotopic techniques which can be applied to detrital material in particular single grain analyses thus the scope for application of detrital studies to a number of different tectonic problems has widened considerably in this review the example of sediments eroded from the himalayan orogen and preserved in the suture zone basin foreland basin remnant ocean basins and deep sea fans is used to illustrate the approach techniques as diverse as petrography heavy mineral xrf and sr nd studies single grain dating by ar ar u pb and fission track methodologies and single grain sm nd and pb isotopic analyses are described the paper documents how the sediment record can be used to determine the thermal and tectonic evolution of the orogen constrain mechanisms of continental deformation exhumation rates and palaeodrainage

the effect of water saturation on methane breakthrough pressure an experimental study on the carboniferous shales from the eastern qaidam basin china abstract breakthrough pressure plays an important role in shale gas flow mining and caprock evaluation a series of breakthrough experiments were conducted under different water saturation conditions for four shales taken from the carboniferous hoit taria formation in the eastern qaidam basin china to investigate the influence of water saturation on breakthrough pressure relevant geochemical tests mineral composition clay content total organic carbon thermal maturity and vitrinite reflectance and micro structural characteristics of micro pores were also conducted breakthrough pressures under at least five different water saturations from 0 to 100 were obtained and relationship between breakthrough pressure and water saturation was fitted for each sample we found that breakthrough pressure increases exponentially with water saturation the decrease in effective pore diameter caused by both the bound water films and the swelling of the clay minerals resulted in the increase in the breakthrough pressure after water saturation reached about 60 breakthrough pressure increased rapidly from connectivity reduction caused by the sealing off of smaller pores and partial water saturation of the macropores by analyzing the correlation between breakthrough pressure and pore structure characteristics breakthrough pressure is inversely related to porosity and is primarily affected by macropores because macropores consist of many microfractures with lengths up to dozens of micrometers they determine the porosity and then affect the connectivity of the rock correlation analysis between the mineral compositions and breakthrough pressure showed that toc content exhibits a positive correlation with breakthrough pressure but neither quartz content nor the clay mineral content exhibits a correlation by combining this information with field emission scanning electron microscope results we found that microfractures are easily created where the toc total organic carbon is concentrated and these microfractures substantially contribute to the number of macropores however dissolution pores in the quartz and clay minerals are rare therefore the correlation between toc content and breakthrough pressure primarily results from the microfractures this study provides practical information for further studies of shale gas migration as well as shale gas mining and caprock evaluation

celtic sea linear tidal sand ridges the irish sea ice stream and the fleuve manche palaeotidal modelling of a transitional passive margin depositional system abstract the linear tidal sand ridges ltsr of the celtic sea constitute the largest examples of their bedform type on earth previous sedimentological and seismic stratigraphic interpretation suggests that the ltsr are moribund tidally remobilised sediments representing the transgressive systems tract this interpretation is supported by two dimensional finite difference model reconstructions of the m 2 tide forced using the output from a glacial isostatic adjustment model to derive palaeotopography and a global ocean model to derive the tides on the ocean boundary used here to reconstruct peak bed stress vectors for the celtic sea for timesteps covering the transgression since the last glacial maximum last 21 ka these data are coupled with interpretation of recent published observations on the outer shelf depocentres of the fleuve manche and the irish sea ice stream isis to confirm that the ltsr distribution is consistent with modelled sand transport paths during transgression the main phase of ltsr growth was between 20 cal ka and 12 cal ka ridge axis orientations reflect the final phase of ltsr construction around 12 cal ka with some later growth of the most southerly ltsr as late as 10 cal ka ltsr growth was from the sw across the shelf towards the ne strong tidal pumping of sediments into slope canyon heads on the outer shelf occurred between 20 cal ka and 12 cal ka contributing to turbidite activity and the growth of the celtic and armorican deep sea fans it is proposed that 1 the fleuve manche shelfal estuary delta and the irish sea ice stream isis shelf fan were the main sediment depocentres supplying the growing ltsr 2 the lack of sediments available in the western channel limited ltsr growth in this area and that the easterly termination of the ltsr in this sector results from sediment starvation and 3 the northeasterly termination in the celtic sea sector is a function of declining peak bed stresses rather than sediment starvation the celtic sea margin represents a passive margin depositional system transitional between true glacial ice stream trough mouth fan systems to the north and the fluvial canyon systems characteristic of the margin to the south this interpretation therefore complements studies of macroscale sedimentation linked to glaciation on the continental margins of the north atlantic

effects of composition and pore structure on the reservoir gas capacity of carboniferous shale from qaidam basin china abstract shale adsorption and breakthrough pressure are important indicators of shale gas development and key factors in evaluating the reservoir capacities of shales in this study geochemical tests pore structure tests methane adsorption tests and breakthrough pressure tests were conducted on shales from the carboniferous hurleg formation in eastern qaidam basin the effects of the shale compositions and pore structures on the adsorption and breakthrough pressures were studied and the reservoir capacities of the shales were evaluated by analyzing the shale adsorptions and sealing effects the results indicate that the organic carbon content was only one of factors in affecting the adsorption capacity of the shale samples while the effect of the clay minerals was limited based on the positive correlation between the adsorption capacity and specific surface area of the shale the specific surface area of the micropores can be used as an indicator to determine the adsorption capacity of shale the micro fracturing of brittle minerals such as quartz create a primary path for shale gas breakthrough whereas the expansion of clay minerals with water greatly increases the breakthrough pressure in the shale samples methane adsorption tests showed that maximum methane adsorption for shale samples z045 and s039 was 0 107 and 0 09655 mmol g respectively the breakthrough pressure was 39 36 mpa for sample s039 maintained for 13 days throughout the experiment however no breakthrough was observed in sample z045 when subjected to an injected pressure of 40 mpa for 26 days this indicates that sample z045 corresponding to a depth of 846 24 m exhibited higher adsorption capacity and a better reservoir sealing effect than sample s039 498 4 m depth this study provides useful information for future studies of qaidam basin shale gas exploration and development and for evaluation of shale quality

stratigraphic evidence for an early collision between northwest india and asia the collision of india with asia1 had a profound influence on late cretaceous and cenozoic oceanography2 climate3 fauna extinctions4 and the motion of at least some of the earth s litho spheric plates5 as the collision ended a period of rapid indo asian convergence6 a precise knowledge of its timing when the crust of the neo tethys ocean was completely subducted7 at some point along the plate boundary is important for understanding its wider consequences but current estimates of the collision age range from 65 to 38 myr before present6 8 11 here we report the results of extensive biostratigraphic analyses from waziristan and kurram in northwest pakistan which show that accretionary prism and trench strata were first thrust onto the northwest indian passive margin after 66 myr but before 55 5 myr after this time volcanic arc fragments the accretionary prism trench material and imbricates of the north indian slope were raised to shallow water depths and overlapped by upper palaeocene shallow water carbonates and shales12 14 indicative of post collision thrusting in this region finally both the suture and the indian craton were overlapped by continuous unconformable upper lower eocene shallow marine strata demonstrating that suturing was complete by 49 myr

microdistribution and mobility of water in gas shale a theoretical and experimental study abstract multiphase adsorbed and free liquid water that is accumulated in shale matrix pores i e pore water substantially affects the storage and transport of gas in shale traditionally used macroscopic parameters e g initial irreducible mobile and clay bound water saturations are not sufficient to describe the microdistribution characteristics and mobility of pore water in the complex porous shale matrix in this paper a new classification was proposed in which the pore water is composed of adsorbed and free parts of which the latter is subdivided into capillary bound and mobile water the components of pore water have the following features during the centrifugation process a adsorbed water is essentially immobile while free water is potentially mobile b capillary bound water is gradually transformed into mobile water with increased centrifugal pressure difference and c the maximum mobile water amount is numerically equal to the free water amount based on the classification an effective technique which integrates centrifugation water imbibition and low temperature nitrogen adsorption methods with the modified li s adsorption ratio equation 2018 was established to quantitatively evaluate the microdistribution characteristics adsorbed and free amounts and their ratios and the mobility mobile amount potential and capacity of pore water in marine shales from the southern sichuan basin in china furthermore the mechanism of controlling the microdistribution and mobility of pore water is analyzed with respect to the microscopic pore structure characteristics and material compositions of shales the primary results demonstrate that 1 adsorbed and free water amounts obtained by centrifugation tests range from 5 145 to 31 282 mg g adsorbed and from 7 880 to 49 751 mg g free the weight ratio of adsorbed water is 0 268 0 629 2 the mobile potential and mobile capacity of pore water are represented by the free water amount and mid value pressure difference respectively a positive relationship between these two parameters occurs in the studied shales 3 pore microstructure characteristics of shale mainly impact the microdistribution and mobility of pore water in the shale matrix the adsorbed water amount is closely associated with the specific surface area of pores while the free and mobile water amounts are controlled by the pore volume the ratios of adsorbed and free water depend on the size and morphology of pores for certain state parameters the mobile ratio is impacted by pore complexity which indicates that as the complexity increases the mobile ratio decreases the study provides significant insight into the microdistribution and mobility of pore water in gas shale matrix

bib sem characterization of pore space morphology and distribution in postmature to overmature samples from the haynesville and bossier shales abstract four haynesville shale and four bossier shale samples were investigated using a combination of scanning electron microscopy sem and broad ion beam bib polishing this approach enables the microstructure and porosity to be studied down to the mesopore size r in the haynesville shale to 1 79 2 26 vr r in the bossier shale this variety within the samples enabled us to study controls on the porosity distribution in these shales visible pores exist as intraparticle pores mainly in carbonate grains and pyrite framboids and as interparticle pores mainly in the clay rich matrix pores in organic matter show a characteristic porosity with respect to the type of organic matter which mainly consists of mixtures of amorphous organic matter and minerals organic laminae and discrete macerals a clear positive trend of organic matter porosity with maturity was found pore sizes are power law distributed in the range of 4 4 m to at least 36 nm in equivalent diameter the differences in power law exponents suggest that a more grain supported coarse grained matrix may prevent pores from mechanical compaction porosities measured in the bib cross sections were significantly lower in comparison to porosities obtained by mercury intrusion porosimetry mip this difference is mainly attributed to the different resolution achieved with bib sem and mip and type of pore network extrapolation of pore size distributions psds enables the bib sem porosity to be estimated down to the resolution of the mip and thus to upscale microstructural observation at the confined space of the bib sem method to bulk porosity measurement these inferred porosities are in good agreement with the mip determined porosities which underpins the assumption that pores segmented in bib sem mosaics are representative of the mip methodology

growth dynamics and deglaciation of the last british irish ice sheet the deep sea ice rafted detritus record the evolution and dynamics of the last british irish ice sheet biis have hitherto largely been reconstructed from onshore and shallow marine glacial geological and geomorphological data this reconstruction has been problematic because these sequences and data are spatially and temporally incomplete and fragmentary in order to enhance biis reconstruction we present a compilation of new and previously published ice rafted detritus ird flux and concentration data from high resolution sediment cores recovered from the ne atlantic deep sea continental slope adjacent to the last biis these cores are situated adjacent to the full latitudinal extent of the last biis and cover marine isotope stages mis 2 and 3 age models are based on radiocarbon dating and graphical tuning of abundances of the polar planktonic foraminifera neogloboquadrina pachyderma sinistral nps to the greenland gisp2 ice core record multiple ird fingerprinting techniques indicate that at the selected locations most ird are sourced from adjacent biis ice streams except in the centre of heinrich h layers in which ird shows a prominent laurentide ice sheet provenance ird flux data are interpreted with reference to a conceptual model explaining the relations between flux north atlantic hydrography and ice dynamics both positive and rapid negative mass balance can cause increases and prominent peaks in ird flux first order interpretation of the ird record indicates the timing of the presence of the biis with an actively calving marine margin the records show a coherent latitudinal but partly phased signal during mis 3 and 2 published data indicate that the last biis initiated during the mis 5 4 cooling transition renewed growth just before h5 46 ka was succeeded by very strong millennial scale variability apparently corresponding with dansgaard oeschger do cycles closely coupled to millennial scale climate variability in the north atlantic region involving latitudinal migration of the north atlantic polar front this indicates that the previously defined precursor events are not uniquely associated with h events but are part of the millennial scale variability major growth of the ice sheet occurred after 29 ka with the barra ice stream attaining a shelf edge position and generating turbiditic flows on the barra donegal fan at 27 ka the ice sheet reached its maximum extent at h2 24 ka earlier than interpreted in previous studies rapid retreat initially characterised by peak ird flux during greenland interstadial 2 23 ka was followed by readvance between 22 and 16 ka readvance during h1 was only characterised by biis ice streams draining central dome s of the ice sheet and was followed by rapid deglaciation and ice exhaustion the evidence for a calving margin and ird supply from the biis during greenland stadial 1 younger dryas event is equivocal the timing of the initiation maximum extent deglacial and readvance phases of the biis interpreted from the ird flux record is strongly supported by recent independent data from both the irish sea and north sea sectors of the ice sheet

influence factors and an evaluation method about breakthrough pressure of carbonate rocks an experimental study on the ordovician of carbonate rock from the kalpin area tarim basin china abstract there are many oil and gas fields around the world that are sealed by tight carbonate caprocks compared with gypsum rocks and shales tight carbonate caprocks are characterized by brittleness and ease of structural fracturing and dissolving in acidic groundwater the breakthrough pressure bp is a significant indicator that indicates the sealing capacity of the caprocks therefore we conducted a series of experiments including effective porosity permeability casting thin sections bp mineral composition microstructural characteristics and clay minerals contents on carbonate samples from ordovician system in the kalpin area tarim basin china to research factors that affect the bp of carbonate caprocks according to the experimental data analysis the bp deceases with macropore proportions and increases with proportions of micropore and mesopore volume due to the large macropore proportion and low clay content

shale characteristics in the southeastern ordos basin china implications for hydrocarbon accumulation conditions and the potential of continental shales abstract continental shales in china are generally characterised by low thermal maturity and high clay content characteristics that are significantly different from those of marine shales documented in the usa and elsewhere whether such continental shales have commercial hydrocarbon potential as marine shale in the usa is a question for the china petroleum industry recently vertical drills in the lacustrine shales in the yanchang formation produced an average of two to five tons of oil and 1000 3000 m3 of gas per day by reservoir hydraulic fracturing which demonstrates that the continental shales can also achieve viable hydrocarbon production shale and gas samples collected from the chang 7 c7 and chang 9 c9 members yanchang formation in the southeastern ordos basin were examined for geochemical petrologic and gas content analysis the results show that the c7 and c9 members developed a huge volume of organic rich shales with 2 4 wt toc in the deep or semideep lacustrine characterised primarily by type ii kerogen with a relatively low thermal maturity and a vitrinite reflectance ranging from 0 5 to 1 5 ro which decreases from west to east the hydrocarbon product varies with the thermal maturity in the southwestern corner the gas content measured by canister desorption equals 1 15 3 49 m3 t rock and the gas absorption capacity ranges from 3 to 5 m3 t rock whereas in the eastern part the gas content is low and oil production is 1 4 m3 day on average nanometre scale pores and micro fractures are well developed all of this indicates that the continental shales in the southeastern ordos basin might have huge shale hydrocarbon resources however the clay content of the continental shales of c7 and c9 ranging from 40 to 60 of the bulk mineral content are much higher than for gas produced in marine shales which might lead to significant challenges for successful development

composition and origin of volcanic ash zones in late quaternary sediments from the reykjanes ridge evidence for ash fallout and ice rafting abstract seven quaternary volcanic ash zones including the well known ash zones az i and az ii have been investigated in five well dated sediment cores from the reykjanes ridge between 59 and 60 n the zones were defined on their geochemical composition morphological variation of the particles and stratigraphic position the ash zones az i and az ii show a mixture of colorless bubble wall shards and brown blocky glasses whereas ash zones vz 1 to 5 are composed of dark to light brown volcanic glasses ranging in shape and texture from blocky nonvesicular shards to highly vesicular pumiceous types the dark brown glass shards of ash zones vz 1 to 5 represent subalkalic and low k subalkalic basaltic series geochemical correlation of the ash zones with possible source areas indicates that they all derived from iceland the colorless shards in az i and az ii are of rhyolitic composition the eastern volcanic zone on iceland is the most important source with abundant volcaniclastics being produced by subaerial subglacial eruptions and secondary erosion of volcanic rocks explosive volcanism on iceland is manifested by marine ash layers az i and az ii most of the volcaniclastic zones vz 1 to 5 coincide chronologically with peak abundances of coarse ice rafted material ird indicating that most of this volcanic glass was incorporated into the icelandic ice sheet and released to the ocean by iceberg calving and subsequent melting however two layers in vz 1 and vz 5 have no correlatives in the ird record suggesting that they were probably transported by local sediment gravity flows from this we must infer that most of the ice rafting episodes bearing volcanic particles as observed in sediments from reykjanes ridge monitor glacier fluctuations on iceland

characterizing the shale gas resource potential of devonian mississippian strata in the western canada sedimentary basin application of an integrated formation evaluation devonian mississippian strata in the northwestern region of the western canada sedimentary basin wcsb were investigated for shale gas potential in the subsurface thermally mature strata of the besa river horn river muskwa and fort simpson formations attain thicknesses of more than 1 km 0 6 mi encompassing an area of approximately 125 000 km2 48 300 mi2 and represent an enormous potential gas resource total gas capacity estimates range between 60 and 600 bcf section of particular exploration interest are shales and mudrocks of the horn river formation including the laterally equivalent lower besa river mudrocks muskwa formation and upper besa river formation which yield total organic carbon toc contents of up to 5 7 wt fort simpson shales seldom have toc contents above 1 wt horn river and muskwa formations have excellent shale gas potential in a region between longitudes 122w and 123w and latitudes 59n and 60n national topographic system nts 94o08 to 94o15 in this area which covers an areal extent of 6250 km2 2404 mi2 average toc contents are higher 3 wt as determined by wire line log calibrations and have a stratal thickness of more than 200 m 656 ft gas capacities are estimated to be between 100 and 240 bcf section and possibly greater than 400 tcf gas in place a substantial percentage of the gas capacity is free gas caused by high reservoir temperatures and pressures muskwa shales have adsorbed gas capacities ranging between 0 3 and 0 5 cm3 g 9 6 16 scf t at reservoir temperatures of 60 80c 140 176f whereas besa river mudrocks and shales have low adsorbed gas capacities of less than 0 01 cm3 g 0 32 scf t liard basin region because reservoir temperatures exceed 130c 266f potential free gas capacities range from 1 2 to 9 5 cm3 g 38 4 to 304 scf t when total pore volumes 0 4 6 9 are saturated with gas the mineralogy has a major influence on total gas capacity carbonate rich samples indicative of adjacent carbonate platform and embayment successions commonly have lower organic carbon content and porosity and corresponding lower gas capacity 1 toc and 1 porosity seaward of the carbonate slave point edge muskwa and lower besa river mudrocks can be both silica and toc rich up to 92 quartz and 5 wt toc and most favorable for shale gas reservoir exploration because of possible fracture enhancement of the brittle organic and siliceous rich facies however an inverse relation between silica and porosity in some regions implies that zones with the best propensity for fracture completion may not provide optimal gas capacity and a balance between favorable reservoir characteristics needs to be sought

evolution and dynamics of a fold thrust belt the sulaiman range of pakistan we present observations and models of the sulaiman range of western pakistan that shed new light on the evolution and deformation of fold thrust belts earthquake source inversions show that the seismic deformation in the range is concentrated in the thick pile of sediments overlying the underthrusting lithosphere of the indian subcontinent the slip vectors of the earthquakes vary in strike around the margin of the range in tandem with the shape of the topography suggesting that gravitational driving forces arising from the topography play an important role in governing the deformation of the region numerical models suggest that the active deformation and the extreme plan view curvature of the range are governed by the presence of weak sediments in a pre existing basin on the underthrusting indian plate these sediments affect the stress state in the over riding mountain range and allow for the rapid propagation of the nose of the range and the development of extreme curvature and laterally varying surface gradients

radiocarbon constraints on the age of the maximum advance of the british irish ice sheet in the celtic sea reconstructions of the british irish ice sheet biis during the last glacial maximum lgm in the celtic sea and southern ireland have been hampered by a paucity of well dated stratigraphic records as a result the timing of the last advance of the largest outlet of the biis the irish sea ice stream to its maximum limit in the celtic sea has been variously proposed as being pre last glaciation early devensian and lgm the irish sea till was deposited by the irish sea ice stream during its last advance into the celtic sea we present 26 stratigraphically well constrained new ams radiocarbon dates on glacially transported marine shells from the irish sea till in southern ireland which constrain the maximum age of this advance the youngest of these dates indicate that the biis advanced to its overall maximum limit in the celtic sea after 26 000 20 000 14c yr bp thus during the last glaciation the most extensive phase of biis growth therefore appears to have occurred during the lgm at least along the celtic sea and irish margins these data further demonstrate that the uppermost inland glacial tills from the area of supposed older drift in southern ireland a region previously regarded as having been unglaciated during the lgm also date from the last glaciation thus most of southern ireland was ice covered at the lgm advance of the biis to its maximum southern limit in the celtic sea may have been a short lived glaciodynamic response facilitated by subglacial bed conditions rather than a steady state response to climate forcing alone

investigations on the methane sorption capacity of marine shales from sichuan basin china abstract high pressure methane sorption isotherms measured at 30 50 and 80 c and pressure up to 20 mpa were measured on lower silurian marine shales from sichuan basin of china the effect of total organic carbon content temperature thermal maturity mineral composition and pore structure on methane sorption capacity has been investigated a linear combination approach has been developed to predict the langmuir sorption capacity of shales based on the mass fractions of their organic and inorganic components this information can be used to estimate the in situ sorption capacity of shale layers as a function of burial depth formation pressure and temperature and composition methane sorption capacity of the dry shales shows a positive relationship with toc and specific surface area the langmuir pressure decreases with increasing maturity but the toc normalized langmuir sorption capacity of over mature shales also decreases with increasing thermal maturity this may be related to the carbonization of highly over mature organic matter for the samples investigated approximately 16 3 46 7 average 28 6 of the methane sorption can be attributed to clay minerals and 46 5 81 5 to average 67 6 organic matter in these shales respectively using the linear combination approach the calculated langmuir sorption capacity function matches the measured values reasonably methane sorption capacity computed as a function of depth for a mean hydrostatic pressure gradient of 0 01 mpa m and a geothermal gradient of 0 03 c m shows a rapid increase and reaches a maximum between 900 and 1800 m followed by a slow decrease with increasing depth at shallow burial depths 900 1800 m sorption capacity is controlled by the geothermal gradient higher geothermal gradients result in a steeper decline of sorption capacity

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

sandstone petrology and provenance of the siwalik group northwestern pakistan and western southeastern nepal abstract the siwalik group consists of a neogene sedimentary succession 5 8 km thick deposited as the himalayan foreland basin developed following collision between the indian and eurasian continents it consists of fluvial deposits composed of shale siltstone and sandstone in the lower part and thick sandstone and conglomerate in the upper part this paper presents new petrologic data on the sandstone composition of two coeval petrofacies of siwalik group in two areas the potwar plateau of northwestern pakistan and the surai khola and bakiya khola localities of western and southeastern nepal in both regions detrital modes reflect a collisional orogen provenance petrologic parameters indicate derivation from mid crustal rocks and overlying sedimentary strata ascribed to different tectonostratigraphic units of the high himalaya and tibetan zone the siwalik sandstones of the potwar plateau nw pakistan are composed of low to medium grade metamorphic and sedimentary detritus and subordinately of ophiolitic and volcanic detritus abundant metamorphic detritus consists of phyllite fine grained schist lithics and coarse grained gneiss derived from the high and or lesser himalaya sedimentary detritus is represented by abundant limestone radiolarian chert siltstone shale very fine grained quartzarenite and other sandstone grains the siliciclastic grains probably were eroded from older terrigenous sequences belonging to the tethys himalayan and lesser himalayan zones uplifted during the india eurasia collision ophiolitic volcanic lithic grains and radiolarian chert reflect a provenance from the indus suture and tran himalayan belt the sandstones of western and southeastern nepal surai khola and bakiya khola sections have higher quartz and lower feldspar contents than those of northwestern pakistan and contain sedimentaclastic western nepal and metamorphiclastic sandstones southeastern nepal comparison of the data presented here with previous work on pre and post siwalik sandstones of the himalaya range and of the remnant ocean basins along both sides of the indian peninsula also derived from the himalayan suture belt suggests abundant quartzolithic detritus from the eocene to the present varying proportions of lithic populations in time are related to rapid uplift of the himalayas and intense unroofing of sedimentary metasedimentary and deeper terranes

progressive reduction in ne atlantic intermediate water ventilation prior to heinrich events response to nw european ice sheet instabilities we present high resolution benthic 13c records from intermediate water depth core site md01 2461 1153 m water depth from the porcupine seabight ne atlantic spanning 43 to 8 kyr b p at an average proxy time step of 160 56 years this core provides information on the linkage between records from the portuguese margin and high latitude north atlantic basin allowing additional insights into north atlantic thermohaline circulation thc variability during millennial scale climatic events of the last glacial together these records document both discrete and progressive reductions in glacial north atlantic intermediate water gnaiw formation preceding heinrich h events 1 2 and 4 recorded through the apparent interchange of glacial northern and southern sourced intermediate water signatures along the european margin close coupling of nw european ice sheet nweis instability and gnaiw formation is observed through transient advances of scw along the european margin concurrent with pulses of ice rafted debris and meltwater release into the ne atlantic between 27 and 16 kyr b p when the nweis was at maximum extent and proximal to last glacial maximum convection zones in the open north atlantic it is such nweis instability and meltwater forcing that may have triggered reduced north atlantic thc prior to collapse of the laurentide ice sheet at h1 and h2 precursory reduction in gnaiw formation prior to h4 may also be inferred however limited nweis ice volume prior to h4 and convection occurring in the norwegian greenland sea require that if a meltwater trigger is invoked as appears to be the case at h1 and h2 the source of meltwater prior to h4 is elsewhere likely higher latitude ice sheets clarification of the sequencing and likely mechanisms of precursory decrease of the north atlantic thc support theories of h event initiation relating to ice shelf growth during cold periods associated with reduced north atlantic thc and subsequent ablation through subsurface warming and sea level rise associated with further reductions in meridional overturning

the organic matter distribution and methane capacity of the lower cretaceous strata of northeastern british columbia canada abstract the methane sorption capacity of a succession of sandstone siltstone shale and coal from the lower cretaceous fort st john group of northeastern british columbia was investigated average organic matter om content for all formations is 2 3 wt with a minimum of 0 6 wt and maximum of 10 1 wt the methane sorption capacity ranges between 0 19 and 2 74 cm3 g at 6 mpa and at 30 c total gas capacity free and sorbed gas ranges between 2 2 and 16 6 cm3 g at 6 mpa micropore volumes range between 0 43 and 1 69 cm3 100 g a positive correlation exists between the om content micropore volume and the methane capacity of shales shales with high methane capacities have either high contents of inertodetrinite or vitrinite moisture content shows a positive relationship with om content micropore volume and methane capacity the negative relationship between moisture and surface area derived from n2 adsorption suggests the moisture is located within the microporosity of the om and also explains the positive relationship between methane capacity and moisture the high inertodetrinite and vitrinite contents correlate with sea level regressions that delivered terrestrial om from coastal plains located south of the study area into the basin

sandstone detrital modes in the makran accretionary wedge southwest pakistan implications for tectonic setting and long distance turbidite transportation detrital modes of early miocene to early pliocene sandstones from the makran accretionary wedge in southwest pakistan show a mainly quartzolithic composition with an evolution from the transitional recycled to quartzose recycled the lithic types however indicate two distinct petrofacies accreted abyssal plain turbidites have qp11lvm27lsm62 and lm39lv27ls34 showing a predominant supply from sedimentary and metasedimentary source terranes whereas slope and shelf facies sediments deposited on the accretionary wedge have qp7lvm47lsm47 and lm22lv48ls30 due to an increase of volcanic detritus the detrital modes of the abyssal plain sediments suggest a recycled orogenic source probably the himalayan collision zone the facies and longitudinal dispersal pattern suggest deposition in an oligo miocene analogue of the present indus fan the sediment must have been transported across strike parallel to the transform structure linking the makran wedge to the himalayas chaman ornach nal fault system and fed into the fan at the western end of the subduction zone the detrital modes also show an increase in volcanic detritus with time lv l 0 27 for the early miocene abyssal plain sediments to 0 47 for the slope sequences this may have been derived from late mesozoic volcanic terrains in northern baluchistan or the ladakh himalayas or more probably from the early to middle miocene andesitic volcanic centre in the northern makran

multidecadal ocean variability and nw european ice sheet surges during the last deglaciation a multiproxy paleoceanographic record from the atlantic margin off the british isles reveals in unprecedented detail discharges of icebergs and meltwater in response to sea surface temperature increases across the last deglaciation we observe the earliest signal of deglaciation as a moderate elevation of sea surface temperatures that commenced with a weakly developed thermocline and the presence of highly ventilated intermediate waters in the rockall trough this warming pulse triggered a series of multidecadal ice rafted debris peaks that culminated with a major meltwater discharge at 17 500 years before present related to ice sheet disintegration across the nw european region the impact of meltwater caused a progressive reduction in deep water ventilation and a sea surface cooling phase that preceded the collapse of the laurentide ice sheet during heinrich event 1 by 500 1000 years a similar sequence of rapid ocean ice sheet interaction across the european continental margin is identified during the bolling allerod to younger dryas transition the strategic location of our sediment core suggests a sensitive and rapid response of ice sheets in nw europe to transient increases in thermohaline heat transport

porosity of devonian and mississippian new albany shale across a maturation gradient insights from organic petrology gas adsorption and mercury intrusion the evolution of porosity in shales with increasing maturity was examined in a suite of five new albany shale samples spanning a maturity range from immature vitrinite reflectance ro 0 35 to postmature ro 1 41 devonian to lower mississippian new albany shale samples from the illinois basin used in this study contain marine type ii kerogen having total organic carbon contents from 1 2 to 13 0 wt organic petrology co2 and n2 low pressure adsorption and mercury intrusion capillary pressure techniques were used to quantify pore volumes pore sizes and pore size distributions increasing maturity of the new albany shale is paralleled by many changes in the characteristics of porosity the total porosity of 9 1 vol in immature new albany shale decreases to 1 5 vol in the late mature sample whereas total pore volumes decrease from 0 0365 to 0 0059 cm3 g in the same sequence reversing the trend at even higher maturity the postmature new albany shale exhibits higher porosity and larger total pore volumes compared to the late mature sample with increasing maturity changes in total porosity and total pore volumes are accompanied by changes in pore size distributions and relative proportions of micropores mesopores and macropores porosity related variances are directly related to differences in the amount and character of the organic matter and mineralogical composition but maturity exerts the dominant control upon these characteristics we conclude that organic matter transformation due to hydrocarbon generation and migration is a pivotal cause of the observed porosity differences

structural and depositional evidence for repeated ice marginal oscillation along the eastern margin of the late devensian irish sea ice stream abstract late devensian glacigenic sediments and landforms along the north west coast of wales document the advance and subsequent retreat of the eastern margin of an irish sea ice stream that met coalesced and ultimately uncoupled from ice radiating outwards from the adjacent welsh ice cap centred over snowdonia across the boundary between the two former ice masses is a set of sediment landform assemblages that reflect rapidly changing erosional and depositional conditions during ice interaction from the inner part of the ice stream the assemblages range outwards from a subglacial depositional assemblage characterised by drumlin swarms through a subglacial erosional assemblage marked by prominent bedrock scours and large subglacial rock channels through an ice marginal assemblage identified by closely spaced glaciotectonised push moraines and intervening marginal sandur troughs into a freely expanding proglacial sandur and lacustrine delta assemblage the ice marginal assemblage provides evidence for numerous oscillatory episodes during retreat and at least 20 ice marginal limits can be identified at least 11 of these display multiple criteria for identifying readvance and in the ideal case is characterised by a moraine form built by localised tectonic stacking of diamict to the rear fronted by a clastic wedge of ice front alluvial fan gravel and intercalated flow till the distribution of sediment landform assemblages suggests a highly dynamic convergent ice stream flow pattern with high ice velocity a sharply delineated lateral shear margin pervasive ice marginal glaciotectonic deformation and a tightly focused ice marginal sediment delivery system all signature characteristics of contemporary ice streams

the paleogene record of himalayan erosion bengal basin bangladesh a knowledge of himalayan erosion history is critical to understanding crustal deformation processes and the proposed link between the orogen s erosion and changes in both global climate and ocean geochemistry the most commonly quoted age of india asia collision is 50 ma yet the record of paleogene himalayan erosion is scant either absent or of low age resolution we apply biostratigraphic petrographic geochemical isotopic and seismic techniques to paleogene rocks of the bengal basin bangladesh of previously disputed age and provenance our data show that the first major input of sands into the basin in the 1 km thick deltaic barail formation occurred at 38 ma our biostratigraphic and isotopic mineral ages date the barail formation as spanning late eocene to early miocene and the provenance data are consistent with its derivation from the himalaya but inconsistent with indian cratonic or burman margin sources detrital mineral lag times show that exhumation of the orogen was rapid by 38 ma the identification of sediments shed from the rapidly exhuming southern flanks of the eastern central himalaya at 38 ma provides a well dated accessible sediment record 17 myr older than the previously described 21 ma sediments in the foreland basin in nepal discovery of himalayan detritus in the bengal basin from 38 ma 1 resolves the puzzling discrepancy between the lack of erosional evidence for paleogene crustal thickening that is recorded in the hinterland 2 invalidates those previously proposed evidences of diachronous collision which were based on the tenet that himalayan derived sediments were deposited earlier in the west than the east 3 enables models of himalayan exhumation e g by mid crustal channel flow to be revised to reflect vigorous erosion and rapid exhumation by 38 ma and 4 provides evidence that rapid erosion in the himalaya was coincident with the marked rise in marine 87sr 86sr values since 40 ma whether 38 ma represents the actual initial onset of vigorous erosion from the southern flanks of the east central himalaya or whether older material was deposited elsewhere remains an open question

sandstone petrology and geochemistry of the oligocene early miocene panjgur formation makran accretionary wedge southwest pakistan implications for provenance weathering and tectonic setting abstract the oligocene early miocene panjgur formation is comprised of submarine fan and abyssal plain turbidites deposited within the makran subduction complex sandstones of the formation are litharenite to feldspathic litharenite petrographic data indicates a quartzose recycled provenance dominated by plutonic and metamorphic fragments major elements concentrations reveal a moderate level of mineralogical maturity and high values of chemical proxy of alteration cpa 88 29 coupled with a high th u ratio 9 37 which reveals intense weathering in the source area the zr nb y and th concentrations are comparable to upper continental crust ucc values and trends in th cr th co and cr zr ratios support contribution from a felsic source however enrichment in ni and cr reinforced by trends in ni co cr v v ni and y ni ratios reveals mixing of the felsic source with mafic ultramafic source terrains tectonic discrimination plots suggest continental arc to active continental margin setting this study supports the katawaz delta panjgur submarine fan model and upholds the initial southward transport of predominantly felsic detritus from the himalayan orogenic belt controlled by the chaman ornach nal transform fault system this study further adds that the bela muslimbagh ophiolites associated melanges and the west pakistan fold thrust belt from the east and the chagai raskoh volcanic arc from the west were also concurrently shedding mafic ultramafic detritus to the basin and that the depositional system in the makran region turned westward roughly parallel to the present active margin of the makran accretionary wedge

the characteristics of coal reservoir pores and coal facies in liulin district hedong coal field of china the composition rank coal facies and coal pore structure characteristics of 15 coal samples were investigated systemically using methods of lithotype analysis maceral analysis proximate analysis mercury porosimetry analysis and nitrogen adsorption analysis these samples were directly collected from the working faces of no 4 8 9 seams in liulin district eastern margin ordos basin china four types of paleoenvironment including a wet forest swamp an intergradation forest swamp a drained forest swamp and a fresh water peat swamp were distinguished by lithotype and merceral analysis an r cluster analysis was performed to demonstrate the correlations between the coal facies and the pore structures the results showed that coal rank is the primary factor affecting the development of micropores and transition pores whereas coal facies control the development of seepage pores in similar coalification conditions especially in a local district and in a seam this work suggests that the vertical variations observed in coal properties macerals vitrinite reflectance mineral matters porosity bet specific area pore size distributions and pores connectivity were controlled by groundwater level fluctuations indicated by variations in the ground water index gwi in the ancient mires due to different accommodation and peat accumulation rates comparison of the porosity characteristics of various coal reservoirs developed in various coal facies indicates that wet forest swamp facies is favorable to the formation of a coalbed methane reservoir because of reasonable pore structure and good connectivity intergradation forest swamp facies rank the second and drained forest swamp facies are less advantageous

mesozoic ophiolites sutures and arge scale tectonic movements in afghanistan abstract the tectonic history of afghanistan appears to be the result of successive accretion of fragments of gondwana to the active margin of laurasia since the end of the paleozoic the margin in afghanistan lies along the present herat and panjshir faults south of hindu kush swings around the central pamirs and can presumably be traced along the present western altyn tagh and kunlun faults in tibet north of this boundary paleozoic rocks have been deformed in the upper paleozoic whereas south of it there is no trace of the hercynian orogeny the first collision of gondwanian fragments with laurasia probably occurred in the early mesozoic along the hindu kush and kunlun to the south ophiolites along the panjao and pangong nu chiang sutures respectively in central afghanistan and central tibet testify for another suturing event in the upper jurassic or lower cretaceous the indus tsangpo suture between india and tibet corresponds in eastern afghanistan to two ophiolite subbelts near kabul and khost both ophiolite complexes have been emplaced between maestrichtian and lower eocene by choking of two northward dipping subduction zones after complete contact between the indian and asian continents was achieved presumably in the end of eocene the penetration of india into asia caused large scale intra continental shortening a large part of the shortening was accommodated by strike slip faulting along mesozoic and more ancient sutures central afghanistan in particular was extruded to the west along the herat suture by the protrusion of the pamir wedge it subsequently collided with the lut block

newly discovered paleogene deltaic sequence in katawaz basin pakistan and its tectonic implications in the katawaz basin pakistan the deltaic and turbidite facies of the khojak formation are the paleogene analogue of the modern indus river emptying into the arabian sea to form the indus delta fan system facies identified include upper continental slope to prodelta distal to proximal distributary mouth bar distributary channel interdistributary bay estuary fluvial channel natural levee and flood plains of lower and upper delta plains the proposed model is a fluvial dominated wave modified delta that axially fed khojak submarine fan turbidites exposed in the southwestern part of the basin these sediments were eroded from the early himalayan orogenic highlands and transported southwestward down the axis of the katawaz remnant ocean basin

paleogeographic and paleotectonic evolution of the himalayan range as reflected by detrital modes of tertiary sandstones and modern sands indus transect india and pakistan detrital modes of sandstones derived from the himalayan suture belt record the history of the mountain range since initial collision between india and asia which began in latest paleocene time tertiary clastic wedges deposited in fore arc foreland and remnant ocean basins and exposed along the indus transect from northernmost india to the arabian sea represent the best opportunity to study sedimentary responses to successive tectonic events during continental collision quartzose continental block and feldspatholithic magmatic arc sandstones were deposited respectively on the passive indian tethys himalayan succession and active asian indus group continental margins during late cretaceous paleocene time closure of the neotethys was marked by sudden arrival of volcanic and ophiolitic detritus on the passive continental margin of the indian plate during deposition of sediments dated at foraminiferal zones p6 pakistan to p8 india starting in early eocene time deposition of chulung la formation and murree supergroup volcanic and ophiolitic to metasedimentary detritus was accumulated in rapidly subsiding piggy back and foreland basins homogeneous petrographic composition within the eocene lower miocene murree supergroup with only slight progressive increase of detrital feldspars suggests erosion of largely supracrustal rocks involved in thrusting in the north in middle miocene time marked enrichment in medium to high grade metamorphic detritus in foreland sandstones siwalik group reflects rapid uplift of a warm wedge of indian crust which was carried southward along the main central thrust this major paleogeographic change was recorded also by quartzolithic remnant ocean turbidites which were fed great distances along transverse fracture zones and later accreted in the coastal makran subduction complex panjgur association and makran group recycled orogen detritus derived from the elevated himalayan chain is still accumulating today in the indus fan enrichment in feldspars with respect to ancient sandstones reflects deep erosion levels into mid crustal rocks along the core of the growing orogen

the effect of moisture on the methane adsorption capacity of shales a study case in the eastern qaidam basin in china this study investigated the effects of moisture on high pressure methane adsorption in carboniferous shales from the qaidam basin china the shale characteristics including the organic inorganic compositions and pore structure volume and surface distribution were obtained using various techniques gibbs adsorption measurements were performed over a pressure range up to 6 mpa and temperatures of 308 15 k on dry samples and moisture equilibrated samples to analyze the correlations between organic inorganic matter pore structure and moisture content on the methane sorption capacity compared to dry samples the sorption capacity of wet samples 0 44 2 52 of water content is reduced from 19 7 5 3 to 36 1 6 1 langmuir fitting is conducted to investigate moisture dependent variations of adsorbed methane density langmuir pressure and volume by combining the pore volume and surface distribution analyses our observations suggested that the main competition sites for ch4 h2o covered pores of approximately 2 7 nm whereas the effective sites for methane and water were predominantly distributed within smaller 10 nm respectively regarding the compositional correlations the impact of moisture on the amount of adsorbed methane shows a roughly linearly decreasing trend with increasing toc content ranging from 0 62 to 2 88 whereas the correlation between the moisture effect and various inorganic components is more complicated further fitting results indicate that illite smectite mixed formations are closely related to the methane capacity whereas the illite content show an evident connection to the pore structural volume and surface variations in the presence of moisture

active tectonic deformation of the western indian plate boundary a case study from the chaman fault system abstract collision of the eurasian and indian plates has resulted in two spatially offset subduction zones the makran subduction zone to the south and the himalayan convergent margin to the north these zones are linked by a system of left lateral strike slip faults known as the chaman fault system 1200 km which spans along western pakistan although this is one of the greatest strike slip faults yet temporal and spatial variation in displacement has not been adequately defined along this fault system this study conducted geomorphic and geodetic investigations along the chaman fault in a search for evidence of spatial variations in motion four study areas were selected over the span of the chaman fault 1 tarnak rud area over the tarnak rud valley 2 spinatizha area over the spinatizha mountain range 3 nushki area over the nushki basin and 4 kharan area over the northern tip of the central makran mountains remote sensing data allowed for in depth mapping of different components and faults within the kohjak group wind and water gap pairs along with offset rivers were identified using high resolution imagery and digital elevation models to show displacement for the four study areas the mountain front sinuosity ratio valley height to width ratio and the stream length gradient index were calculated and used to determine the relative tectonic activity of each area these geomorphic indices suggest that the kharan area is the most active and the tarnak rud area is the least active gps data were processed into a stable indian plate reference frame and analyzed fault parallel velocity versus fault normal distance yielded a 8 10 mm yr displacement rate along the chaman fault just north of the spinatizha area insar data were also integrated to assess displacement rates along the fault system geodetic data support that ultra slow earthquakes similar to those that strike along other major strike slip faults such as the san andreas fault system are possible along the northern segments of the chaman fault zone geomorphic data suggest that the chaman fault along southern part is not very active now but may have gone through high tectonic activity in the past

the effects of pore structure on wettability and methane adsorption capability of longmaxi formation shale from the southern sichuan basin in china the lower silurian longmaxi formation shale in the sichuan basin is one of the most promising shale gas plays in china pore structure has a significant impact on hydrocarbon migration within shales this study conducts systematic experiments to analyze the pore structure wettability and methane adsorption capacity of the longmaxi formation shale samples from the southern sichuan basin the pore size distributions obtained from n2 adsorption high pressure mercury intrusion porosimetry and statistical analysis of representative field emission scanning electron microscopy photographs of organic matter om are compared to evaluate the contribution of om pores to total pore spaces shale wettability was determined by contact angle measurements and spontaneous imbibition experiments the results reveal that these samples could be divided into three wettability categories more water wet samples z1 more oil wet samples z4 and intermediate wet samples z2 and z3 although samples z1 and z4 have similar total organic carbon toc contents om pores within sample z4 have a larger average pore size and occupy a greater proportion of the total pore spaces compared with sample z1 whereas inorganic pores contribute more to the total pore spaces of sample z1 sample z4 has a larger methane adsorption capacity than sample z1 with a higher brunauer emmett teller bet surface area which may be caused by the difference in their om pore types samples z2 and z3 with less toc content have lower porosities and bet surface areas as well as lower methane adsorption capacities consequently the pore structure significantly affects the wettability and methane adsorption capacity of the longmaxi shale

characterization of gas shale pore systems by porosimetry pycnometry surface area and field emission scanning electron microscopy transmission electron microscopy image analyses examples from the barnett woodford haynesville marcellus and doig units the nanometer scaled pore systems of gas shale reservoirs were investigated from the barnett marcellus woodford and haynesville gas shales in the united states and the doig formation of northeastern british columbia canada the purpose of this article is to provide awareness of the nature and variability in pore structures within gas shales and not to provide a representative evaluation on the previously mentioned north american reservoirs to understand the pore system of these rocks the total porosity pore size distribution surface area organic geochemistry mineralogy and image analyses by electron microscopy were performed total porosity from helium pycnometry ranges between 2 5 and 6 6 total organic carbon content ranges between 0 7 and 6 8 wt and vitrinite reflectance measured between 1 45 and 2 37 the gas shales in the united states are clay and quartz rich with the doig formation samples being quartz and carbonate rich and clay poor higher porosity samples have higher values because of a greater abundance of mesopores compared with lower porosity samples with decreasing total porosity micropore volumes relatively increase whereas the sum of mesopores and macropore volumes decrease focused ion beam milling field emission scanning electron microscopy and transmission electron microscopy provide high resolution 5 nm images of pore distribution and geometries image analysis provides a visual appreciation of pore systems in gas shale reservoirs but is not a statistically valid method to evaluate gas shale reservoirs macropores and mesopores are observed as either intergranular porosity or are confined to kerogen rich aggregates and show no preferred orientation or align parallel with the laminae of the shale networks of mesopores are observed to connect with the larger macropores within the kerogen rich aggregates

detrital zircon and provenance analysis of late cretaceous miocene onshore iranian makran strata implications for the tectonic setting a multidisciplinary provenance study including sandstone framework heavy mineral analysis in situ u pb dating of detrital zircon and hf isotopic ratio analysis of dated zircons was undertaken on late cretaceous miocene deep marine turbiditic and deltaic sandstones of makran accretionary wedge se iran to determine their sedimentary provenance and tectonic setting sandstone framework modes reveal both magmatic arc rocks as a source of late cretaceous oligocene detritus and recycling of miocene sandstones heavy mineral assemblages cr spinel and blue amphibole indicate ophiolite and high pressure low temperature metamorphic rocks blueschists as a supplementary provenance in total 2931 laser ablation inductively coupled plasma mass spectrometry icp ms u pb detrital zircon ages on 21 sandstone samples yielded three major age peaks at ca 167 ma 88 7 ma and 48 9 ma also 241 in situ hf isotope analyses of dated zircons provide evidence for dominantly igneous source rocks two main detrital zircon ages are identified 1 abundant middle jurassic grains with hf isotopic compositions of continental crust suggesting a rifting related magmatic provenance and 2 late cretaceous eocene grains with hf isotopic compositions of continental crust and nondepleted mantle suggesting a continental magmatic arc provenance this change in provenance is attributed to the late cretaceous convergence between arabia and eurasia

zooming in on heinrich layers theories explaining the origin of the abrupt massive discharges of ice rafted detritus ird into the glacial north atlantic the heinrich layers hls generally point to the laurentide ice sheet as the sole source of these events until it was found that the irds also originated from icelandic and european ice sheets bond and lotti 1995 snoeckx et al 1999 grousset et al 2000 this apparent contradiction must be reconciled as it raises fundamental questions about the mechanism s of hl origin we have analyzed two 12 cm thick hls in an ultrahigh resolution mode 1 2 century intervals in a mid atlantic ridge piston core the 18o record n pachyderma left coiling reveals strong excursions induced by the melting of the icebergs these excursions are associated with a strong decrease in the amount of planktic foraminafersand with a 3 c cooling of the surface waters counts of coarse detrital grains reveal that ird are deposited according to a typical sequence 1 volcanic glass 2 quartz and feldspars 3 detrital carbonate that implies a chronology in the melting of the differentpan atlantic ice sheets sr and nd isotopic composition confirm that in both heinrich layers h1 and h2 precursor ird came from first europe iceland followed then by laurentide derived ird an internal cyclicity can be identified during h1 and h2 about four to six major abrupt discharges occurred roughly on a century timescale the 13c and 15n records reveal that dominant inputs of continent derived organic matter are associated with ird within the hls hiding the plankton productivity signal

a preliminary study on the pore characterization of lower silurian black shales in the chuandong thrust fold belt southwestern china using low pressure n2 adsorption and fe sem methods although lower silurian black shales within and around the sichuan basin have received renewed attention during the past few years because of their potential prospectivity for shale gas studies associated with shale gas reservoir evaluation are still rare in this study eight black shale core samples were collected from a well drilled recently in the chuandong thrust fold belt southwestern china and their geochemistry and pore structures were investigated using low pressure n2 adsorption analysis and field emission scanning electron microscopy fe sem observations the results show that the black shales have total organic carbon toc values ranging from 1 01 to 3 98 and their equivalent vitrinite reflectance values are in the range of 2 84 3 05 both mineral matrix and organic matter pores are well developed with pore sizes ranging from several to several hundred nanometers the total porosity for the eight samples ranges from 2 60 to 4 74 and the percentages of organic matter pores are estimated to be in the range of 31 62 the total surface area ranges from 5 06 m2 g to 19 32 m2 g and the micropore 2 nm surface area estimated by the t plot method ranges from 3 13 m2 g to 9 27 m2 g the toc values have positive relationships with the total porosity total surface area and the micropore 2 nm volume and surface area indicating toc may be an effective parameter for shale gas reservoir evaluation in the studied area

detrital modes and provenance of the paleogene khojak formation in pakistan implications for early himalayan orogeny and unroofing different tectonic settings have characteristic detrital modes and sediment dispersal patterns detrital modes and sediment dispersal patterns of the siliciclastic khojak formation in the katawaz basin pakistan suggest that its sand was derived from the early himalayan orogen and longitudinally transported to the katawaz remnant ocean where it was deposited as a delta submarine fan complex modal analysis of the khojak formation suggests composition that is dominated by subangular quartz with abundant lithic fragments and minor feldspar i e qt 60 f 9 l 31 qt total quartz f feldspar l lithic fragments the predominance of quartz sedimentary and low grade metamorphic lithic fragments suggests early derivation from a collision orogen scarcity of detrital feldspar and volcanic lithic fragments precludes a magmatic arc as the main source the decrease in monocrystalline quartz concomitant increase in total lithic percentages and relative abundance of low grade metamorphic lithic fragments from the bottom to the top of the khojak formation reflect progressive erosional history of the early himalaya this history is part of a previously known major unroofing trend collectively depicted by the detrital modes of the murree formation siwalik group and the modern indus fan in the indian ocean these detrital modes are also related in time and space

high resolution evidence for linkages between nw european ice sheet instability and atlantic meridional overturning circulation published studies show that ice rafted debris ird deposition preceding heinrich h events h1 and h2 in the ne atlantic was derived from the nw european ice sheets nweis possibly offering clues about ice sheet sensitivity and stability and the mechanisms that caused periodic collapse of the laurentide ice sheet lis we present detailed lithological and geochemical records including radiogenic isotope fingerprinting of ird deposits from core md01 2461 proximal to the last glacial british ice sheet bis demonstrating persistent instability of the bis with significant destabilisation occurring 1 5 1 9 kyr prior to both h1 and h2 dated at 16 9 and 24 1 kyr bp respectively in the ne atlantic paired mg ca and 18o data from the surface dwelling globigerina bulloides and subsurface dwelling neogloboquadrina pachyderma sinistral are used to determine late glacial variability of temperature salinity and stratification of the upper water column a picture emerges that the bis was in a continuing state of readjustment and never fully reached steady state increased sea surface temperatures appear to have triggered the episode of nweis instability preceding h1 it seems most probable that the so called precursor events were not linked to the h events however if response to a common thermal forcing is considered an increased response time of the lis up to 2 kyr longer than the nweis may be inferred negative salinity excursions of up to 2 6 indicate significant incursions of melt water associated with peaks in nweis instability decreased surface density led to a more stable stratification of the upper water column and is associated with reduced ventilation of intermediate waters recorded in depleted epibenthic 13c cibicidoides wuellerstorfi we suggest that instability and meltwater forcing of the nweis temporarily weakened atlantic meridional overturning circulation allowing transient advance of southern sourced waters to this site prior to h events 1 and 2

a time slice approach to the history of cenozoic sedimentation in the indian ocean abstract results from drilling at over 100 sites have been combined with a new plate tectonic model to produce a series of palinspastic maps which represent snap shots of the changing patterns of sediment accumulation in the indian ocean through the cenozoic the maps clearly delineate the main sedimentary depocenters and show how the sedimentary record has responded on an oceanwide scale to major changes in paleogeography tectonics paleocirculation and or climate paleogene sediment accumulation rates were generally low with significant accumulation in only limited areas suggesting weak ocean circulation and stable well stratified conditions by contrast the vigorous thermohaline circulation of the neogene resulted in substantial widespread sedimentation accumulation rates were generally high and displayed a wide range of values following rapid growth of the east antarctic ice sheet in the mid miocene carbonate sedimentation has been progressively restricted to the shallow ridges and plateaus of the western indian ocean but accumulates there with locally high rates the link between tectonics and terrigenous sedimentation is exemplified by the major deep sea fans off east africa zambezi fan and india indus and bengal fans which developed in response to uplift and erosion beginning in late oligocene time in the east african rift system and the himalayas respectively although maps from only five widely spaced times are shown the methodology is such that a continuous series of maps at intervals as close as 1 m y can readily be generated ultimately the combination of such time slice maps with the results of detailed time series studies will provide a powerful tool for understanding past oceanic environments

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

sedimentology of the indus group ladakh northern india implications for the timing of initiation of the palaeo indus river the upper reaches of the indus river form a longitudinal network that drains a large portion of the western himalaya it plays an important role as a sediment routing system feeding the indus delta and submarine fan and has played a controlling role in the denudational history of the western himalaya given the rivers long term significance its timing of initiation remains poorly constrained the facies palaeocurrents and provenance of the post early eocene indus group preserved along the upper reaches of the modern indus reveal a history of fluvial deltaic and deep water sedimentation in an intermontane basin dominated by internal drainage hence the indus group is not considered to represent the deposits of a palaeo indus river as previously thought illite crystallinity values and apatite fission track dating of the indus group suggest that the succession was buried to temperatures of 155 280 c and that unroofing started in early miocene times and proceeded at 0 1 0 4 mm a 1 to the present the youngest sedimentary rocks preserved along the indus basin are early miocene in age from the tectonostratigraphically equivalent deposits around kargil to the west of the study area the transition from sediment accumulation to erosional unroofing in early miocene times coincides with accelerated regional unroofing of the high himalayas to the south and the initiation of the indus delta submarine fan to the west differential uplift between the northward thrusting of the zanskar and indus sedimentary succession against the undeformed ladakh batholith provides a mechanism for post early miocene initiation of a major longitudinal river hence early miocene times is believed to represent the earliest possible age of initiation of the palaeo indus river following this course

nd and sr isotope characteristics of quaternary indo gangetic plain sediments source distinctiveness in different geographic regions and its geological significance quaternary sediments of the himalayan foreland basin known also as the indo gangetic plains have been studied for their sr and nd isotope geochemistry to constrain their sources and to infer their geological significance the data show a large variation in the sr 87 sr 86 values and relatively a minor variation in the epsilon nd 0 values for compositionally homogeneous sediments sediments of the ganga yamuna and satluj systems have high sr 87 sr 86 0 75 and low epsilon nd 0 16 all relative to the previous group suggesting their derivation from the sub himalayan sediments including tertiary subathu formation the subathu was likely derived from the indus tsangpo suture zone basaltic volcanics and tibetan sedimentary series the thar desert ghaggar river sediments are isotopically similar to those of the indus plain indicating a shared provenance either immediate or ultimate the exposed sediments of the incised yamuna river at kalpi in the ganga yamuna plains were derived from peninsular india these southern ganga yamuna plain sediments are isotopically similar to the thar desert ghaggar river sediments although the juvenile components of their provenance differ the vindhyans deccan traps and indus tsangpo suture zone volcanics respectively in the southern ganga plain the peninsular wedge of sediments could be present at depths below about 12 m interbedded or mixed with himalayan sediments the isotope geochemistry of sediments also shows that the earliest influx of the himalayan sediments to the ganga yamuna interfluve occurred around 68 70 ka this indicates that the yamuna river has been flowing in the region at least since the late pleistocene the dynamic relationship between the yamuna and chambal rivers in the region negates the idea of yamuna being a tributary of ghaggar saraswati river system during the harappan time 3500 to 1900 bc