geochemistry and sedimentology of the lower silurian longmaxi mudstone in southwestern china implications for depositional controls on organic matter accumulation abstract spatial and temporal changes of lithofacies and abundance of organic matter in mudstones control distribution of prospective unconventional petroleum reservoirs in a sedimentary basin lithofacies characterization is an essential prerequisite to understanding of organic matter accumulation depositional processes and water column chemistry this research combines geochemical analyses and detailed sedimentologic observations in order to investigate the depositional controls on organic matter abundance in the prolific black mudstone of the long 1 member of the lower silurian longmaxi formation in southwestern china six primary lithofacies deposited at variable marine water depths and under differing water column chemistry were identified from an 83 m long core based on microscopic observations of sediment texture and structure and biota and analyses of total organic carbon toc content mineralogy and trace element abundances our results show that toc content is well correlated to biogenic quartz content and the non detrital components of v u mo ni and cu suggesting the accumulation of organic matter in the studied mudstone was controlled by high paleoproductivity and anoxic water conditions the good correlations also suggest that the abundant organic matter was produced by algal blooms which are typically associated with radiolarian thrive because of the symbiotic relationship between algal and radiolarian the low mo toc ratios of the three lithofacies formed in deep anoxic environments were similar to the ratios of modern sediments deposited in anoxic euxinic environments suggesting moderate basin restriction during deposition the mudstone in the lower longmaxi formation may be part of the globally abundant organic rich mudstones of early silurian age whose depositional mechanism have yet to be fully explored the distribution of lithofacies in the studied interval shows an overall trend from deep water to shallow water depositional environments we developed a detailed depositional model to interpret the evolution of depositional environments of the lower longmaxi formation this study provides an example to how better characterize unconventional hydrocarbon systems through coupling of rigorous geochemical and sedimentological analysis

the composition and its impact on the methane sorption of lacustrine shales from the upper triassic yanchang formation ordos basin china abstract the organic geochemistry mineralogy and methane sorption of lacustrine shales of the upper triassic yanchang formation collected from the south eastern ordos basin were investigated to characterize them and clarify the effects of shale composition on their sorbed gas capacity these yanchang shales have recently been selected as a target area for shale gas exploration in typical terrestrial strata in china the two main sections of these shales containing type ii organic matters chang 7 and chang 9 have relatively high total organic carbon content toc of 2 10 the two shales also have similar mineralogies mainly comprising quartz clay minerals and feldspars both the chang 7 and chang 9 shales are generally in the oil window chang 9 is slightly more mature than chang 7 higher methane sorption capacity was observed for chang 9 than for chang 7 shales determined on a dried basis at 50 c methane sorption measurements were further performed on three samples from which the residual bitumen had been extracted and their corresponding kerogen fractions to gain insight into the effects of shale composition on methane sorption this was significantly higher in solvent extracted samples than in raw samples indicating that residual bitumen largely restricts methane sorption on such shales a positive correlation between the amount of clay minerals and methane sorption capacity of bulk rocks was evident suggesting that clay mineral content is relevant to methane sorption this result was also supported by the much higher methane sorption capacity of solvent extracted shales compared to the extracted kerogen from those shales when measured sorption data was normalized to toc values the effects of both residual bitumen and clay mineral on the methane sorption of bulk rocks have complicated the evaluation of methane sorption on organic matter in these mature shales

origin distribution and alteration of asphalts at chapopote knoll southern gulf of mexico abstract following the discovery of asphalt volcanism in the campeche knolls a research cruise was carried out in 2006 to unravel the nature of the asphalt deposits at chapopote the novel results support the concept that the asphalt deposits at the seafloor in 3000 m of water depth originate from the seepage of heavy petroleum with a density slightly greater than water the released petroleum forms characteristic flow structures at the seafloor with surfaces that are ropy or rough similar to magmatic lava flows the surface structures indicate that the viscosity of the heavy petroleum rapidly increases after extrusion due to loss of volatiles consequently the heavy petroleum forms the observed asphalt deposit and solidifies detailed survey with a remotely operated vehicle revealed that the asphalts are subject to sequential alterations e g volume reduction leading to the formation of visible cracks in the asphalt surface followed by fragmentation of the entire deposit while relatively fresh asphalt samples were gooey and sticky older fragmented pieces were found to be brittle without residual stickiness furthermore there is evidence for petroleum seepage from below the asphalt deposits leading to local up doming and sometimes to whip shaped extrusions extensive mapping by tv guided tools of chapopote asphalt volcano indicates that the main asphalt deposits occur at the south western rim that borders a central crater like depression the most recent asphalt deposit at chapopote is the main asphalt field covering an area of 2000 m2 asphalt volcanism is distinct from oil and gas seepage previously described in the gulf of mexico and elsewhere because it is characterized by episodic intrusions of semi solid hydrocarbons that spread laterally over a substantial area and produce structures with significant vertical relief as chapopote occurs at the crest of a salt structure it is inferred that asphalt volcanism is a secondary result of salt tectonism

stable carbon isotopes of coal derived gases sourced from the mesozoic coal measures in china coal derived large scale gas fields derived from the mesozoic coal measures in china are mainly distributed in the middle lower jurassic coal measures in the tarim junggar and turpan hami basins in northwest china and the upper triassic xujiahe formation coal measure in sichuan basin central china in 2011 the annual production was 21 6 109 m3 and the proved geological reserves were 2485 109 m3 accounting for 21 and 30 of the total in china respectively based on analyses of gas composition and stable carbon isotopes ratios of 203 samples and stable carbon isotopes of 102 co2 samples the following conclusions were made a based on diagnostic plots using the stable carbon isotopic and molecular composition of gas samples alkane gas from the mesozoic coal measures in china is shown to be coal derived b according to the 13c2 vs c2h6 plot of a great number of oil derived and coal derived gases in china it is concluded that gases with 13c2 28 5 are coal derived and those with 13c2 28 5 are oil derived in most cases c among the natural gases from the mesozoic coal measures in china primary coal derived gases with normal carbon isotopic distribution pattern among the c1 c4 alkanes i e 13c1 13c2 13c3 13c4 are dominant d carbon isotopic pattern reversal mainly results from the mixing of coal derived gases having different maturities but the same source and secondly from microbial oxidation of propane e g mu 3 and mu 4 wells in the gumudi gas field junggar basin e co2 in the coal derived gases from the mesozoic coal measures in china has both biogenic and abiogenic origins the biogenic origin is dominant and the abiogenic co2 is mainly found in the kuqa depression in the tarim basin and western sichuan basin f isotopic differences between heavy hydrocarbon gases and methane become less with increasing maturity

mesozoic cenozoic tectonic relationships between the kuqa subbasin and tian shan northwest china constraints from depositional records abstract stratigraphic profiles in the kuqa subbasin located along the southern flank of the tian shan northwest china display similar mesozoic cenozoic evolutionary sequences of compositional maturity exist in conglomerate clasts sandstone framework grains and detrital heavy minerals the similarity of these time series profiles resulted from orogenesis and intracontinental deformation of the provenance area the ancestral tian shan mineralogical maturities of conglomerates and sandstones increase from triassic to middle jurassic and decrease from upper jurassic lower cretaceous to tertiary this trend parallels a similar decrease in maturity in detrital heavy minerals zircon rutile and tourmaline dominate in middle upper triassic to middle jurassic sandstone whereas unstable hornblende and pyroxene dominate the heavy mineral suites in the tertiary especially in miocene and pliocene strata these compositional trends are coeval with gradual southward migration of alluvial depositional fronts and depositional depocenters from cretaceous to miocene since the pliocene large scale southward migration of alluvial depositional systems occurred while depositional depocenters migrated northward based on the mesozoic cenozoic depositional records the tectonic evolution of the tian shan kuqa subbasin may be divided into five phases 1 in early triassic following compression and uplift since permian gravelly braided river alluvial plain depositional systems developing in the kuqa subbasin characterized by sands of mixed orogenic provenance type derived from the ancestral tian shan 2 from middle triassic to middle jurassic sediment composition of the kuqa subbasin reflects arc orogen and mixed orogenic sand types with extensive planation of the ancestral tian shan and the development of relatively stable coal bearing depositional environments 3 renewed compression uplift of the tian shan occurred in late mesozoic especially in cretaceous with most detrital modes of the kuqa subbasin indicating provenance attributes akin to the south tian shan 4 further intensive compression uplift and probably southward basinward propagation of the south tian shan occurred during miocene and 5 supracrustal gravity gliding and collapse occurred in the tian shan kuqa subbasin probably due to intensive deep compression with rejuvenated uplift and probable southward basinward structural propagation of the south tian shan developing since pliocene observed changes in sediment composition and depositional environment since pliocene time were also controlled by frequent and abrupt climate changes in addition to intensive uplift of the tian shan moreover all depositional records in the kuqa subbasin seem to reflect west to east differences in provenance along the tian shan probably indicating greater exhumation depth in the western tian shan than that in the eastern tian shan since early cretaceous

structure of the makran subduction zone from wide angle and reflection seismic data abstract makran is one of the largest accretionary wedges on the globe formed by the convergence between the eurasian and the arabian plates it is characterised by an extremely high sediment input of 7 km and a shallow subduction angle we present seismic velocity models from four wide angle seismic lines that image the wedge sediments and the subducted oceanic crust three strike lines show complex but rather one dimensional structures where the observed seismic phases have been studied with the reflectivity method a 160 km long dip line was surveyed coincident with a mcs line collected by cambridge university in 1986 prestack depth migration of this data with the new wide angle velocities shows improved images compared to earlier results interpretation of the wide angle and the mcs data indicates that a decollement is developed along a bright reflector within the turbiditic sequence more than 3 km of sediment bypasses the first accretionary ridges underthrusting and is transported to greater depth this might help to explain the sparse earthquake activity associated with subduction here in the strike lines low velocity layers occur landward of the deformation front in zones where active thrusting or underplating takes place the oceanic crust is characterised by a strong velocity contrast between layer ii and layer iii

geochemical facies analysis of fine grained siliciclastics using th u zr rb and zr rb sr ratios abstract abundance of the trace elements zr rb sr th and u may provide insight into the sedimentological origin of fine grained siliciclastic sediments provided that the units are derived from similar source areas as demonstrated here with suites of the fine grained jurassic and cretaceous rocks from the barents sea and svalbard zr rb ratios can be interpreted to indicate grain size variations while zr rb sr values reflect variations in the siliciclastic versus carbonate contents the th u ratio can be applied as an indicator of the redox conditions in 3d plots such as presented here the interplay between these geochemical factors can be interpreted in terms of the sedimentological evolution of the depositional basin the geochemical facies analyses show that similar depositional conditions existed on the jurassic shelf in the two studied localities the succeeding prodeltaic cretaceous beds were generally coarser grained and deposited in ventilated depositional conditions

heterogeneity of the lower silurian longmaxi marine shale in the southeast sichuan basin of china this study characterizes the vertical heterogeneity of the lower silurian longmaxi marine shale in the southeast sichuan basin based on core description thin sections observation geological chemistry data interrogation and qemscan image analysis lithofacies associations mineralogy graptolite species occurrence rock fabrics as well as toc total organic carbon and gas content change noticeably and regularly in the lower silurian longmaxi marine shale within sequence stratigraphic framework lithofacies associations mainly include in situ graptolite rich and siliceous shale in the transgressive systems tract tst micro offsite graptolite rich shale and shale interbedded with siltstone laminaes in the early highstand systems tract ehst and micro offsite graptolite rich and carbonate rich shale in the late highstand systems tract lhst the tst has a greater abundance of diplogratus than ehst and lhst and has a lesser level of monograptus which is conversely higher in the ehst and lhst the tst shale is silica rich while the lhst shale is generally clay rich the ehst shale is more balanced in its silica and clay content than the tst and lhst are the sedimentary structure and fabric of shale shows that shale is homogenous in the tst with laminaes well developed in the ehst but decreasing in the lhst toc and gas content are highest in the tst and decrease upward the tst with high toc high gas content high brittle minerals silica rich and anoxic suboxic to dysoxic sedimentary environment is the most potential shale gas target interval in the study area our research also shows that the toc mainly controls shale gas accumulation and that the redox conditions mainly control the preservation of organic matter the silica also plays a significant role in shale gas content due to its contribution to hydraulic fracturing finally the study proposes a depositional and heterogeneity model for the lower silurian longmaxi marine shale in the study area

atmospheric weathering of scandinavian alum shales and the fractionation of c n and s isotopes abstract subaerial exposure and oxidation of organic carbon c org rich rocks is believed to be a key mechanism for the recycling of buried c and s back to earth s surface importantly processes coupled to microbial c org oxidation are expected to shift new biomass 13 c org composition towards more negative values relative to source however there is scarcity of information directly relating rock chemistry to oxidative weathering and shifting 13 c org at the rock atmosphere interface this is particularly pertinent to the sulfidic c org rich alum shale units of the baltoscandian basin believed to constitute a strong source of metal contaminants to the natural environment following subaerial exposure and weathering consistent with independent support we show that atmospheric oxidation of the sulfidic c org rich alum shale sequence of the cambrian devonian baltoscandian basin induces intense acid rock drainage at the expense of progressive oxidation of fe sulfides sulfide oxidation takes priority over microbial organic matter decomposition enabling quantitative massive erosion of c org without producing a 13 c shift between acid rock drainage precipitates and shale moreover 13 c enrichment in inorganic carbon of precipitates does not support microbial c org oxidation as the predominant mechanism of rock weathering upon exposure instead a 34 s 34 s shale 34 s precipitates 0 accompanied by elevated s levels and the ubiquitous deposition of acid rock drainage sulfate minerals in deposited efflorescent precipitates relative to shales provide strong evidence for quantitative mass oxidation of shale sulfide minerals as the source of acidity for chemical weathering slight 15 n depletion in the new surface precipitates relative to shale coincides with dramatic loss of n from shales collectively the results point to pyrite oxidation as a major driver of alum black shale weathering at the rock atmosphere interface indicating that quantitative mass release of c org n s and key metals to the environment is a response to intense sulfide oxidation consequently large scale acidic weathering of the sulfide rich alum shale units is suggested to influence the fate and redistribution of the isotopes of c n and s from shale to the immediate environment

a tale of shales the relative roles of production decomposition and dilution in the accumulation of organic rich strata middle upper devonian appalachian basin abstract a new consensus on the processes responsible for organic carbon burial in ancient epeiric seas has emerged more firmly grounded in the uniformitarian framework of modern oceanography and biogeochemistry this consensus recognizes the interdependent roles of sedimentation primary production and microbial metabolism in favor of earlier end member models e g production vs preservation in this study one of the classic stratigraphic sequences upon which the preservation end member was based is re interpreted in light of this new consensus the study employs an extensive new sedimentological biogeochemical database from cores drilled in western new york the database spans over 500 m and 15 my of devonian deposition in the appalachian basin and provides a framework for comparative study of organic matter burial the major conclusions are 1 few organic rich units were deposited under pervasive anoxic sulfidic water columns 2 establishment and breakdown of seasonal thermoclines on annual or longer timescales were the predominant mode of stratification and 3 under such conditions remineralization of bio limiting nutrients may have played a key role in organic matter burial by creating a eutrophication pump this pump may have augmented an already rising nutrient inventory such that productivity levels exceeded the threshold required for development of suboxic to anoxic conditions in sediments and episodically in bottom waters a final conclusion asserts that the master variable for organic matter accumulation was relative sea level change which exerted influence on clastic dilution preservation and production processes sea level rise events led to sediment starvation and organic carbon concentration in distal basin sediments as well as to decreased effectiveness of seasonal mixing and thus longer build up intervals for remineralized nutrients episodic mixing of nutrient enriched bottom waters led to enhanced production ultimately increased clastic sediment delivery and water column mixing during relative sea level fall diluted surface sediment organic content such that respiratory demand could be met by increased oxygen supply thus terminating deposition of strata enriched in organic carbon

sedimentary association of alternated mudstones and tight sandstones in china s oil and gas bearing basins and its natural gas accumulation abstract oil and gas resources are abundant in china s continental sedimentary basins where the main task of exploration has been finding oil for many years in recent years however new discoveries of large scale natural gas have been successively obtained the natural gas mainly exists in the sedimentary association of alternated mudstones and tight sandstones and is dominantly low permeability tight sand gas through the in depth study on gas reservoir analysis diagenetic evolution source rock distribution and hydrocarbon generating behavior natural gas generation and accumulation it is concluded that during the major subsiding stage of large scale lake basins the multicyclic subsiding process of the lake surface controls the development of high quality source rocks the wide distribution of sands and the superimposition of the two types of rocks in the vertical direction the lacustrine muddy source rocks are developed including mud shale carbonaceous mudstone and coal bed which are in the medium high evolution stage and produce mainly gas and the gas generation intensity is high through the analysis of the subsidence evolution processes of the carboniferous permian systems transitional marine continental facies in the ordos basin and the triassic xujiahe formation continental facies in the sichuan basin it is concluded that the widely distributed sandbodies of delta facies although with tight properties are interbedded with source rocks and easy to accumulate natural gases the natural gas is migrated and accumulated within small distance and is characterized by large area accumulation because of the strong hydrocarbon generation capacity big thickness and stable distribution of the underlying mud shale the potential of gas resources should not be underestimated the geocyclicity of china s continental sedimentary basins controls the sedimentary association of alternated mudstones and tight sandstones resulting in superimposed accumulations of shale gas and tight sand gas

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

geochemistry of shales from the archean 3 0 ga buhwa greenstone belt zimbabwe implications for provenance and source area weathering abstract phyllites from the archean 3 0 ga buhwa greenstone belt zimbabwe were deposited on a stable cratonic platform analyses of the phyllites generally define a single geochemical group based on major and trace element abundances the phyllites are strongly depleted in cao na2o and sr with respect to average archean upper crust by contrast k2o ba and rb are enriched several times relative to average archean upper crust reflecting basin scale k metasomatism transition metals are somewhat depleted whereas high field strength elements are typically enriched relative to average archean upper crust samples generally have fractionated lree patterns average cen smn 2 4 with small negative eu anomalies average eu eu 0 78 and generally flat hrees average gdn ybn 1 3 such geochemical characteristics suggest that the source dominantly consisted of tonalite with less common occurrences mafic volcanic rocks and granite mixing calculations which massbalance the rees and th sc suggest 70 tonalite 15 mafic volcanic rocks and 15 granite as possible proportions for the source of the phyllites a nearby early archean 3 5 ga continental nucleus preserves similar lithologies and is the probable source intense chemical weathering of the source terrane is indicated by premetasomatized chemical index of alteration values of 95 100 nearly complete depletion of cao and na2o and high al2o3 na2o ratios fine grained sediments of comparable age and presumed tectonic setting elsewhere in southern africa show similar geochemical characteristics implying that source area compositions and weathering intensities were similar these mature platformal deposits suggest a tectonically stable environment where intense chemical weathering took place at 3 0 ga across southern africa

controls on organic matter accumulation in the triassic chang 7 lacustrine shale of the ordos basin central china abstract the triassic chang 7 formation is a rich lacustrine source rock in the ordos basin central china petrographic and geochemical analyses were performed in order to research the mechanism of organic matter om enrichment in the chang 7 shales bulk geochemical data indicate that the om rich shales were formed in a fresh and brackish water which is not usually the case for high toc total organic carbon content sediments therefore there must be some special conditions favorable for om enrichment in chang 7 shales petrography and element geochemistry show that the chang 7 om rich shales are abundant in om enriched laminae framboidal pyrites collophanes and some elements including iron fe diphosphorus pentoxide p2o5 copper cu vanadium v molybdenum mo and uranium u high bio productivity algae blooming and anoxic depositional environments are critical for om enrichment as the organic carbon contents increase the fe p2o5 cu v mo and u element contents increase as well and the ratios of u th and v v ni are growing many geochemical data demonstrate that the water was oxic while the environment under the sediment water interface was anoxic as a result of a high organic supply that sufficiently consumed oxygen taking into account the geological settings and our previous studies we propose that the frequent volcanic events and hydrothermal activity caused by the collision of the north china landmass with the yangtze landmass and consequential formation of the qingling mountains had a significant role in the om enrichment in the fresh and brackish lacustrine shales deposition of volcanic ash into aqueous environments might lead to the increase of some key nutrients such as fe and p2o5 which might enhance primary bio productivity new evidence for hydrothermal activity the reddingite was demonstrated in this study not only can the hydrothermal activity provide elements necessary for life but is also favorable for formation of anoxic settings the deposition of the chang 7 lacustrine om rich shales can be explained using the high bio productivity driven model which is related to volcanic events and hydrothermal activity as a consequence of regional tectonic movements an anoxic depositional setting is beneficial for om preservation and slow sedimentation rates in the deep lacustrine environments are favorable for om enrichment

geological and morphological setting of 2778 methane seeps in the dnepr paleo delta northwestern black sea abstract the dnepr paleo delta area in the nw black sea is characterized by an abundant presence of methane seeps during the expeditions of may june 2003 and 2004 within the eu funded crimea project detailed multibeam seismic and hydro acoustic water column investigations were carried out to study the relation between the spatial distribution of methane seeps sea floor morphology and sub surface structures 2778 new methane seeps were detected on echosounding records in an area of 1540 km 2 all seeps are located in the transition zone between the continental shelf and slope in water depths of 66 to 825 m the integration of the different geophysical datasets clearly indicates that methane seeps are not randomly distributed in this area but are concentrated in specific locations the depth limit for the majority of the detected seeps is 725 m water depth which corresponds more or less with the stability limit for pure methane hydrate at the ambient bottom temperature 8 9 c in this part of the black sea this suggests that where gas hydrates are stable they play the role of buffer for the upward migration of methane gas and thus prevent seepage of methane bubbles into the water column higher up on the margin gas seeps are widespread but accurate mapping illustrates that seeps occur preferentially in association with particular morphological and sub surface features on the shelf the highest concentration of seeps is found in elongated depressions pockmarks above the margins of filled channels on the continental slope where no pockmarks have been observed seepage occurs along crests of sedimentary ridges there seepage is focussed by a parallel stratified sediment cover that thins out towards the ridge crests on the slope seepage also appears in the vicinity of canyons bottom flanks and margins or near the scarps of submarine landslides where mass wasting breaches the fine grained sediment cover that acts as a stratigraphic seal the seismic data show the presence of a distinct gas front which has been used to map the depth of the free gas within the sea floor sediments the depth of this gas front is variable and locally domes up to the sea floor where the gas front approaches the seafloor gas bubbles were detected in the water column a regional map of the sub surface depth of the gas front emphasises this gas front versus seep relationship the integration of all data sets indicates that the spatial distribution of methane seeps in the dnepr paleo delta is mainly controlled by the gas hydrate stability zone as well as by stratigraphic and sedimentary factors

a numerical study on the effects of taiwan topography on a convective line during the mei yu season abstract during the morning hours on 23 may 2002 a convective line associated with a mei yu front brought heavy rainfall along the coast of central taiwan under favorable synoptic conditions of warm air advection and large convective available potential energy cape of over 3000 m2 s 2 doppler radar observations indicated that deep convection was organized into a linear shape with a northeast southwest orientation along the front about 70 km offshore from taiwan over the northern taiwan strait the system then moved toward taiwan at a slow speed of about 4 m s 1 in the present study the effects of taiwan topography on this convective line and subsequent rainfall distribution were investigated through numerical modeling using the nagoya university cloud resolving storm simulator cress at a 2 km horizontal grid size experiments with different terrain heights of taiwan including full terrain ftrn half terrain htrn and no terrain ntrn were performed the control run using full terrain and co

distribution and height of methane bubble plumes on the cascadia margin characterized by acoustic imaging submersible investigations of the cascadia accretionary complex have identified localized venting of methane gas bubbles in association with gas hydrate occurrence acoustic profiles of these bubble plumes in the water column in the vicinity of hydrate ridge offshore oregon provide new constraints on the spatial distribution of these gas vents and the fate of the gas in the water column the gas vent sites remained active over the span of two years but varied dramatically on time scales of a few hours all plumes emanated from local topographic highs near the summit of ridge structures the acoustic images of the bubble plumes in the water column disappear at water depths between 500 to 460 m independent of the seafloor depth this coincides with the predicted depth of the gas hydrate stability boundary of 510 to 490 m suggesting that the presence of a hydrate skin on the bubble surface prevents them from rapid dissolution the upper limit of the acoustic bubble plumes at 460 m suggests that dissolution of the residual bubbles is relatively rapid above the hydrate stability zone

influence of paleoenvironmental factors on preservation of organic matter in middle cretaceous greenhorn formation pueblo colorado sedimentological and geochemical studies of the upper cretaceous hartland shale and overlying bridge creek limestone members of the greenhorn formation reveal close associations between abundance of current induced sedimentary structures extent of bioturbation and type of preserved organic matter abundant hydrogen rich organic matter 4 5 wt and low sulfur to organic carbon ratios are characteristic of the laminated facies which lack current induced sedimentary structures sparse hydrogen poor organic matter 0 1 0 5 wt and relatively high sulfur to organic carbon ratios are characteristic of the bioturbated facies which contain numerous sedimentary structures indicative of currents the concentration of oxygen in the benthic environment and the degree of bio urbation of the sediment apparently were determined principally by the rate that oxygen was supplied advectively by currents rather than by the rate of oxygen consumption by decomposition thus paleoclimatic and paleo oceanographic factors that influenced mixing and current strength in the water column profoundly affected the amount and type of organic matter preserved in these units it is proposed that episodes of high river discharge lead to density stratification of the water column and in turn to quiescent oxygen depleted bottom water and high preservation of organic matter thus accounting for the intermittent widespread deposition of organic rich strata during maximum transgression and depth of the greenhorn sea the lateral association of voluminous deltaic deposits with dee water black shales in other elongate or restricted marine basins may have causes similar to those envisioned for the hartland shale and bridge creek limestone members

a detrital heavy mineral viewpoint on sediment provenance and tropical weathering in se asia abstract understanding heavy mineral preservation is important for interpreting generation pathways provenance and geochemistry of sediments despite this many assumptions about heavy mineral stability are based on ancient strata and few studies consider modern sediments particularly those in tectonically active tropical areas such as se asia we report new heavy mineral data on 69 river sand samples from the malay peninsula and sumatra in which one aim was to find provenance indicators specific to these areas identifications were performed using optical microscopy and confirmed with sem eds in the malay peninsula heavy minerals record granitic and contact metamorphic provenance variable amounts of zircon tourmaline hornblende andalusite epidote monazite rutile and titanite and minor amounts of pyroxene apatite anatase garnet diaspore colourless spinel cassiterite and allanite are typical of this source area the composition of assemblages from sumatra indicates contributions from two major sources the modern volcanic arc i and the basement ii abundant pyroxene particularly hypersthene up to 70 is diagnostic of the volcanic arc source vesuvianite garnet andalusite tourmaline chrome spinel rutile anatase and corundum are present only in small amounts

mud volcanoes at the front of the makran accretionary complex pakistan abstract conical mounds 1 1 5 km in diameter and up to 65 m high were mapped at the foot of the active makran continental margin the mounds developed seaward of the accretionary front in a relatively planar zone where the beginning of build up of tectonic pressure initiates deformation based on shallow high resolution 4 khz sediment echosounding the sedimentary sequence in this area is generally well stratified as indicated by closely spaced horizontal reflections however in the vicinity of the mounds the sediment is characterised by many acoustically transparent zones which are 100 300 m in diameter and cut near vertically through the horizontal reflectors two sediment cores from the top of the largest cone and a neighbouring acoustically transparent zone reveal small scale post depositional deformation in a stratified sequence and methane concentrations up to 40 000 ng g this deformation and disruption of potential reflectors provides a clue to explain the acoustic transparency we interpret it as caused by the rise of charged fluids and mud leading initially to the slight disturbance of the generally good acoustic reflectors and eventually to the formation of conical mud mounds mud volcanoes mcs data showing a buried mound in an analogous structural position support the idea of tectonically induced mud fluid expulsion seaward of the accretionary front

depositional environment and organic matter accumulation of upper ordovician lower silurian marine shale in the upper yangtze platform south china abstract the main controlling factors of organic matter accumulation in the upper ordovician wufeng lower silurian longmaxi formations are complex and remain highly controversial this study investigates the vertical variation of total organic carbon toc content as well as major and trace element concentrations of four ordovician silurian transition sections from the upper yangtze platform of south china to reconstruct the paleoenvironment of these deposits and to improve our understanding of those factors that have influenced organic matter accumulation in these deposits the residual toc content of the wufeng formation averages 3 2 and ranges from 0 12 to 6 0 the overlying lower longmaxi formation displays higher toc content avg 4 4 followed upsection by consistent and lower values that average 1 6 in the upper longmaxi formation the concentration and covariation of redox sensitive trace elements mo u and v suggest that organic rich intervals of the wufeng formation accumulated under predominantly anoxic conditions organic rich horizons of the lower longmaxi formation were deposited under strongly anoxic to euxinic conditions whereas organic poor intervals of the upper longmaxi formation accumulated under suboxic conditions positive correlations between redox proxies and toc contents suggest that organic matter accumulation was predominantly controlled by preservation barium excess ba xs values indicate high paleoproductivity throughout the entire depositional sequence with an increase in the lower longmaxi formation increased productivity may have been induced by enhanced p recycling as evidenced by elevated c org p tot ratios mo u covariation and mo toc values reveal that the wufeng formation was deposited under extremely restricted conditions whereas the longmaxi formation accumulated under moderately restricted conditions during the late ordovician the extremely restricted nature of ocean circulation on the upper yangtze platform in tandem with enhanced stratification of the water column promoted anoxic conditions favorable for the preservation of organic matter during early silurian time organic matter accumulation was principally controlled by changes in sea level which affected terrigenous flux redox conditions and the degree of nutrition recycling

acoustically detected hydrocarbon plumes rising from 2 km depths in guaymas basin gulf of california plumes extending nearly 1000 m from the 1500 2000 m deep seafloor of guaymas basin were detected from below the 23 5 khz inverted echo sounder of the scripps deep two vehicle individual sound reflectors bubbles or drops rise at approximately 17 cm s in one plume the deep tow side scan records provide more information on the plumes structure at the altitude of the vehicle 75 m where some form multiple side scan targets one 20 m across near bottom 4 khz profiles show that plumes overlie young fault traces associated with extensional faulting at the basin s spreading centers of outcrops of tilted beds beside strike slip faults we infer from analysis of the deep tow observations field relationships and knowledge of the geology of this basin that the plumes are made of light hydrocarbons perhaps mainly methane that emanate from seabed seeps one of the acoustically detected plumes was at a spreading axis hydrothermal field which has many buoyant acoustically transparent thermal plumes some of which are rich in dissolved hydrocarbons

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

paleoenvironmental reconstruction of the coal and oil shale bearing interval in the lower cretaceous muling formation laoheishan basin northeast china abstract the laoheishan basin in northeast china has been filled with lower cretaceous coal and oil shale bearing sediments the basin fill includes from base to top alluvial conglomerate lower member of muling formation fan delta sediments interbedded with coal and oil prone mudstone denominated as oil shale layers in the upper member of muling formation and volcaniclastic rocks dongshan formation in the present study the maturity of organic matter oil shale quality and paleoenvironment of the coal and oil shale accumulation are investigated based on macro and micropetrographic data proximate and ultimate analyses bulk geochemical parameters biomarkers analysis and stable isotope geochemistry in the laoheishan basin both coal and oil shale layers are derived from land plant organic matter this contrast the oil shale of this basin from oil shale coal intercalations in fault related basins in which oil shale has been found to be of algal origin the coal is sub bituminous in rank hydrogen rich and oil prone the oil shale is of low medium grade and the relatively low oil yield may relate to the abundant resinite and sporinite because of their lower generation potential compared with alginite accumulation of the high ash coal commenced in low lying mire drowned during frequent floodings subsequently high ash low sulfur coal was deposited in a stable low lying mire under oxic conditions and limited bacterial activity afterwards the mire was drowned and formed a freshwater dysoxic to oxic shallow lake in which oil shale layers accumulated finally the depositional environment returned to low lying mire but probably with a brackish influence as indicated by elevated sulfur contents in the uppermost samples petrography and biomarker based proxies indicate that gymnosperms dominated the paleovegetation of the mire accompanied by variable amounts of herbaceous plants such as ferns

depositional models for fine grained sediment in the western hellenic trench eastern mediterranean sediment in tectonically active topographically restricted settings of the western hellenic arc eastern mediterranean consists primarily of clayey silt and silty clay failure of metastable sediment temporarily stored on relatively steep slopes is triggered by earthquake tremors and eustatic oscillations redeposition of these materials by gravitative transport has resulted in markedly different lithofacies from site to site most piston cores include three late quaternary stratigraphic units that can be correlated with sections in other parts of the eastern mediterranean numerous radiocarbon age determinations enhance the correlation seven fine grained sediment types are identified in cores from eight distinct depositional environments some muds are closely related to specific environments slump and debris flow deposits on slope and high relief environments or to time well laminated mud during the latest pleistocene mid holocene or to both uniform and faintly laminated muds restricted to trench basins turbiditic and hemipelagic muds are common throughout the study area mud distribution patterns correlate closely with calculated sedimentation rates we propose two depositional models for these sediments the first emphasizes downslope transformations resulting in progressively reduced flow concentration during transport from slump and debris flow turbidity current low density turbidity current or turbid layer mechanisms the distal end member deposits settling from low concentration flows are thick rapidly emplaced fine grained uniform muds closely associated with faintly laminated muds these were ponded in flat trench basin plains planktonic and terrigenous fractions in the turbiditic finely laminated and uniform muds record mixing of materials of gravitative and suspension origin during redeposition this sequence prevails under conditions of minimal stratification of water masses as characterized by the present mediterranean in the second model developed for conditions of well developed water mass stratification well laminated rather than uniform mud prevails as the end product of low concentration flows these very finely laminated and graded muds record particle by particle settling from detached turbid layers concentrated along density interfaces they include material from turbid layers complemented by the normal rain of pelagic material stratification barriers resulted in region wide distribution of such deposits in both slope and trench environments

origin and enrichment factors of natural gas from the lower silurian songkan formation in northern guizhou province south china abstract the northern guizhou area located near the southwestern margin of the yangtze block and south of the sichuan basin is a promising area for shale gas exploration and development the discovery of a natural gas accumulation in the lower silurian songkan formation in the study area is the first discovery of natural gas in this stratum in china marking an exciting breakthrough in natural gas exploration in northern guizhou area this paper presents an investigation of this accumulation using gas geochemistry including gas composition carbon and hydrogen isotopes in context with geological information available for the study area our results indicate that the natural gas accumulation in songkan formation is probably sourced from the lower silurian wufeng longmaxi shale the 13 c ch 4 values range from 33 9 to 33 2 the 13 c c 2 h 6 values range from 37 0 to 36 2 and the 2 h ch 4 values range from 157 to 144 these results indicate that the gases are of thermogenic origin and are oil derived furthermore isotopic rollovers seen in the natural gas is similar to that seen in the natural gas from the local wufeng longmaxi shale which is identified as carbon exchange at high temperature the 13 c co 2 values range from 20 8 to 17 1 suggesting that carbon dioxide was mainly generated by thermogenic processes the fracture investigation indicates that the large development of horizontal fractures in calcareous mudstone is one of the reasons for the high yield of natural gas in songkan formation the petrophysical parameters suggest that limestone with low porosity and permeability effectively prevents natural gas escaping and seals natural gas into calcareous mudstone with horizontal fractures

unconventional shale gas systems the mississippian barnett shale of north central texas as one model for thermogenic shale gas assessment shale gas resource plays can be distinguished by gas type and system characteristics the newark east gas field located in the fort worth basin texas is defined by thermogenic gas production from low porosity and low permeability barnett shale the barnett shale gas system a self contained source reservoir system has generated large amounts of gas in the key productive areas because of various characteristics and processes including 1 excellent original organic richness and generation potential 2 primary and secondary cracking of kerogen and retained oil respectively 3 retention of oil for cracking to gas by adsorption 4 porosity resulting from organic matter decomposition and 5 brittle mineralogical composition the calculated total gas in place gip based on estimated ultimate recovery that is based on production profiles and operator estimates is about 204 bcf section 5 78 10 9 m 3 1 73 10 4 m 3 we estimate that the barnett shale has a total generation potential of about 609 bbl of oil equivalent ac ft or the equivalent of 3657 mcf ac ft 84 0 m 3 m 3 assuming a thickness of 350 ft 107 m and only sufficient hydrogen for partial cracking of retained oil to gas a total generation potential of 820 bcf section is estimated of this potential approximately 60 was expelled and the balance was retained for secondary cracking of oil to gas if sufficient thermal maturity was reached gas storage capacity of the barnett shale at typical reservoir pressure volume and temperature conditions and 6 porosity shows a maximum storage capacity of 540 mcf ac ft or 159 scf ton

mesozoic sedimentary evolution of the northwest sichuan basin implication for continued clockwise rotation of the south china block we present new sedimentary data integrated into a regional mesozoic stratigraphic framework to provide a detailed picture of spatio temporal variations in deposition and depocenter migration of the northwest sichuan basin the mesozoic sedimentary evolution is utilized to interpret basin subsidence history and to unravel coeval basin margin tectonics the northwest sichuan basin together with the songpan ganzi terrane behaved as a passive margin south of the qinling paleo tethys from late paleozoic to early middle triassic times and then evolved into a peripheral foreland basin in response to collision of the north and south china blocks since the late middle triassic coeval with strong north south contraction of the songpan ganzi terrane in the late triassic sinistral transpressional deformation of the longmen shan belt led to flexural subsidence of the adjacent western sichuan basin renewed basin margin fold thrust activity triggered recurrence of flexural subsidence of the northwest sichuan basin since the middle jurassic with the depocenter eventually shifting to the northwestern corner of the basin in the early cretaceous sedimentary evolution of the northwest sichuan basin and the basin margin deformation imply that the south china block had been rotating clockwise relative to the north china block throughout the mesozoic with an interim period of early jurassic tectonic quiescence a model is advanced that invokes clockwise rotation of the south china block as a driver for tectonic evolution of both the basin and adjoining structural belts and provides an explanation for several salient features that are otherwise puzzling

organic geochemical characteristics and depositional setting of paleogene oil shale mudstone and sandstone from onshore penyu basin chenor pahang malaysia abstract the eastern chenor pahang area of the penyu basin contains an untapped potential in part due to poor knowledge of its organic facies characteristics the sedimentary succession of eastern chenor pahang area is dominated by fine to coarse grained sandstone occurring in association with oil shale and mudstone in a predominantly fining upward sequence detailed geochemical and petrographic characterization was carried out on oil shale and mudstone samples to evaluate the origin and type of organic matter om as well as the paleoenvironmental conditions and organic richness of the paleogene sedimentary succession the facies are only enriched in total organic carbon toc potential hydrocarbon yield s2 and extractible organic matter eom the types of organic matter are important index reflecting the potential of the source rock s based on elemental ratios the analyzed samples are shown to contain types i and ii kerogens this finding is supported by the high hydrogen index hi of 300 mg hc g toc and the presence of abundant liptinitic materials biomarker signatures n alkanes n c25 high c29 c30 17 h hopane ratios 0 8 3 3 and high c29 steranes 49 78 low total sulfur and v v ni ratio suggest a predominantly terrestrial source input with some contribution from aquatic microorganisms as indicated by the common occurrence of amorphous organic matter combining this results with n alkane patterns kerogen types and organic petrography predominance of c29 sterane probably indicates a contribution of aquatic organisms such as green and brown algae consistent with botrycoccus braunii race a and pediastrum contribution and some influence of higher plants om integration of biomarker studies with bulk geochemical and petrographic analysis suggests that the analyzed samples were deposited under suboxic conditions in a fresh water lacustrine environment this finding is corroborated by the ratios of pristane phytane v ni and sr br high bioproductivity and a stratified fresh water column with suboxic bottom water condition enhanced om preservation in the analyzed mudstone and shale facies the high om content in these samples maybe related to the fine grained matrix of the mud rocks and the paleoclimate in the area

natural marine seepage blowout contribution to atmospheric methane the release of methane sequestered within deep sea methane hydrates is postulated as a mechanism for abrupt climate change however whether emitted seabed methane reaches the atmosphere is debatable we observed methane emissions for a blowout from a shallow 22 m hydrocarbon seep the emission from the blowout was determined from atmospheric plume measurements simulations suggest a 1 1 gas loss to dissolution compared to 10 loss for a typical low flux bubble plume transfer to the atmosphere primarily was enhanced by the rapid upwelling flows induced by the massive discharge this mechanism could allow methane suddenly released from deeper 250 m waters to contribute significantly to atmospheric methane budgets copyright 2006 by the american geophysical union

oceanic methane layers the hydrocarbon seep bubble deposition hypothesis bubble plumes from hydrocarbon seeps drive upwelling flows in the water column that can disappear if the bubbles dissolve this may lead to formation of a layer enriched in gases and substances transported by the bubbles a process we term bubble deposition a review of observed dissolved methane layers in the north sea showed their existence in an area of active seeping pockmarks at a height of 20 30 m above the sea bed well below the thermocline to test the bubble deposition hypothesis rising seep bubbles were simulated numerically the model predicted a dissolution depth consistent with the observed methane layer for 2700 m radius bubbles the model also predicted that bubbles smaller than 3400 m dissolved subsurface decreasing to 2000 m for a 10 cm s 1 upwelling flow we speculate that this layer may be attractive to marine organisms although north sea seeps are not oily this mechanism also applies to oily bubbles from hydrocarbon seeps or a leaking undersea gas oil pipeline thus bubble deposition can create a subsurface oil layer which rises far slower than either the bubble stream or droplets entrained in the stream

sulige field in the ordos basin geological setting field discovery and tight gas reservoirs abstract the sulige gas field in central ordos basin is one of the largest gas fields in china with about 860 7 billion cubic meters bcm of proven gas reserve this field covers an area of about 500 km 2 with largely tight clastic reservoirs the upper carboniferous lower permian deltaic sandstones and upper permian lacustrine mudstones deposited in a stable cratonic tectonic setting form an effective petroleum system that is favorable for gas accumulation in large scale stratigraphic lithologic traps based on wire line log response drilling stem test and core data a generalized classification system was developed for the gas reservoirs of the sulige field thus type i and ii rocks are capable of gas production without natural and or artificial fracturing type iii rocks are capable of gas production after artificial fracturing and type iv rocks are too tight to produce at commercial rates even with artificial fracturing the discovery of the sulige field not only adds large gas reserve in the ordos basin but strongly indicates the overlook potential of both tight sandstone reservoir rock and relatively porous and permeable sweet spots in it

a compositional classification for grain assemblages in fine grained sediments and sedimentary rocks reply abstract a tripartite compositional classification is proposed for sediments and sedimentary rocks that have grain assemblages with greater than 50 percent of a weight or volume of particles smaller than 62 5 m 4 phi tarl terrigenous argillaceous contains a grain assemblage dominated by more than 75 percent of particles of extrabasinal derivation including grains derived from continental weathering and also volcanogenic debris carl calcareous argillaceous contains less than 75 percent of particles of extrabasinal derivation debris and among its intrabasinal grains contains a preponderance of biogenic carbonate particles including carbonate aggregates sarl siliceous argillaceous contains less than 75 percent of particles of extrabasinal derivation and contains a preponderance of biogenic siliceous particles over carbonate grains these three classes of fine grained particulate sediments and rocks effectively separate materials that have distinct depositional settings and systematic contrasts in organic matter content and minor grain types in the subsurface the grain assemblages that define these classes follow contrasting and predictable diagenetic pathways that have significant implications for the evolution of bulk rock properties and thus assigning a fine grained rock to one of these classes is an important first step for predicting its economic and engineering qualities for purposes of description these three class names can be joined to modifier terms denoting rock texture more precise compositional divisions specific grain types of notable importance and diagenetic features

detailed facies analysis of the upper cretaceous tununk shale member henry mountains region utah implications for mudstone depositional models in epicontinental seas abstract lower middle turonian strata of the tununk shale member of the greater mancos shale were deposited along the western margin of the cretaceous western interior seaway during the greenhorn second order sea level cycle in order to examine depositional controls on facies development in this mudstone rich succession this study delineates temporal and spatial relationships in a process sedimentologic based approach the 3 dimensional expression of mudstone facies associations and their stratal architecture is assessed through a fully integrative physical and biologic characterization as exposed in outcrops in south central utah sedimentologic characteristics from the millimeter to kilometer scale are documented in order to fully address the complex nature of sediment transport mechanisms observed in this shelf muddy environment the resulting facies model developed from this characterization consists of a stack of four lithofacies packages including 1 carbonate bearing silty and sandy mudstone cssm 2 silt bearing calcareous mudstone scm 3 carbonate bearing silty mudstone to muddy siltstone cms and 4 non calcareous silty and sandy mudstone ssm spatial and temporal variations in lithofacies type and sedimentary facies characteristics indicate that the depositional environments of the tununk shale shifted in response to the 2nd order greenhorn transgressive regressive sea level cycle during this eustatic event the tununk shows a characteristic vertical shift from distal middle shelf to outer shelf cssm to scm facies then from outer shelf to inner shelf environment scm to cms and to ssm facies shifting depositional environments as well as changes in dominant paleocurrent direction throughout this succession indicate multiple source areas and transport mechanisms i e longshore currents offshore directed underflows storm reworking this study provides a rare documentation of the greenhorn cycle as exposed across the entire shelf setting high resolution mapping of genetically related packages facilitate the development of process based depositional models that can be utilized for lateral correlations into the equivalent foredeep strata of the cretaceous interior

characterization of depositional conditions for lacustrine oil shales in the eocene jijuntun formation fushun basin ne china abstract the strike slip fushun basin hosts a lacustrine oil shale interval of ca 50 300 m in the eocene lutetian jijuntun formation the oil shale deposits consist of the lower lean oil shale unit losu and the upper rich oil shale unit rosu in outcrop areas the identified depositional cycles of ca 8 10 m and 5 8 m in thickness record the stacking of massive and non laminated oil shales in the losu and fine and coarse laminated oil shales in the rosu respectively depositional conditions in the paleo jijuntun lakes were synoptically reconstructed based on sedimentary features trace element and organic geochemical proxies oxic to suboxic fresh water conditions were prevailing in the paleo jijuntun lakes during deposition of the losu and then evolved into oxygen deficient fresh to mildly brackish water conditions during deposition of the rosu as revealed by the concentrations of redox and salinity sensitive trace elements e g v ni v cr ni co and sr ba ratios and boron content in the oil shales warm to cool and humid to arid climate represented by e g sr cu and rb sr ratios could result in the deepening of water column from ca 20 30 m to ca 100 m and saline stratification superposed on pre existing thermal stratification in the paleo jijuntun lakes a systematical decrease approximately one order of magnitude in the concentrations of most trace elements except for boron and co in the coaly oil shale in the lowermost losu relative to those in the other oil shales in the jijuntun formation indicates the significant change of organic matter om input from higher plant especially coaly materials to aquatic plankton this is partly consistent with the variations of om input from terrestrial higher plant and aquatic organisms type ii kerogen in the losu to lacustrine algae type i kerogen in the rosu as revealed by biomarkers the slight to significant enrichment or depletion of few trace elements i e mn and mo in these immature to low mature oil shale deposits may be associated with low to moderate productivities of aquatic plankton and or incompletely oxygen free conditions in the paleo jijuntun lakes

mineralogical and geochemical compositions of late permian coals and host rocks from the guxu coalfield sichuan province china with emphasis on enrichment of rare metals abstract this paper reports the geochemical and mineralogical compositions of the late permian no 25 coal semi anthracite and its host rocks roof and floor strata from the guxu gulin xuyong coalfield sichuan province china the coal is characterized by medium sulfur content average 2 73 and has an average ash yield of 20 95 in contrast to other late permian coals from southwestern china that are enriched in sc v cr co ni and cu the no 25 coal does not contain an abundance of these transition elements but is rich in lithophile elements be y nb zr hf and u the elevated concentrations of trace elements in the no 25 coal were probably derived from the felsic intermediate rocks at the top of the emeishan basalt sequence rather than from the emeishan mafic basalts the floor strata of the no 25 coal can be divided into two sub sections the upper sub section of the sequence immediately below the no 25 coal consists of material with a felsic intermediate composition probably derived from terrigenous sources and the lower sub section is composed of mafic tuff the terrigenous mineral matter in the no 25 coal appears to have the same sediment source region as the upper sub section of the floor strata based on their similar geochemical compositions the roof strata of the no 25 coal are more quartzose and were probably derived from a different sediment source region the mineral matter in the coal is dominated by kaolinite and to a lesser extent calcite and pyrite the roof and floor strata each have quite different mineralogy with kaolinite dominant in the latter and illite kaolinite and quartz in the former pyrite contents are variable both in the coal and in the host rocks the floor strata and the coal have been affected by hydrothermal solutions leading to the enrichment of rare earth elements and yttrium rey nb ta zr hf and u the rey in the coal and floor strata as well as the nb ta zr hf and u in the floor strata represent potentially economic rare metal resources

multiple controls on the paleoenvironment of the early cambrian marine black shales in the sichuan basin sw china geochemical and organic carbon isotopic evidence abstract in order to understand the paleoenvironment of the early cambrian black shale deposition in the western part of the yangtze block geochemical and organic carbon isotopic studies have been performed on two wells that have drilled through the qiongzhusi formation in the central and southeastern parts of sichuan basin it shows that the lowest part of the qiongzhusi formation has high toc abundance while the middle and upper parts display relative low toc content redox sensitive element mo and trace elemental redox indices e g ni co v cr u th and v v ni suggest that the high toc layers were deposited under anoxic conditions whereas the low toc layers under relatively dysoxic oxic conditions the relationship of the enrichment factors of mo and u further shows a transition from suboxic low toc layers to euxinic high toc layers on the basis of the mo toc relationship the qiongzhusi formation black shales were deposited in a basin under moderately restricted conditions organic carbon isotopes display temporal variations in the qiongzhusi formation with a positive excursion of 13 c org values in the lower part and a continuous positive shift in the middle and upper parts all these geochemical and isotopic criteria indicate a paleoenvironmental change from bottom anoxic to middle and upper dysoxic oxic conditions for the qiongzhusi formation black shales the correlation of organic carbon isotopic data for the lower cambrian black shales in different regions of the yangtze block shows consistent positive excursion of 13 c org values in the lower part for each section this excursion can be ascribed to the widespread early cambrian transgression in the yangtze block under which black shales were deposited

the fluvial and lacustrine sedimentary systems and stratigraphic correlation in the upper triassic xujiahe formation in sichuan basin china the calcarenites and siliciclastic sandstones in the upper triassic xujiahe formation are key targets of the unconventional gas exploration in sichuan basin to resolve the long debated stratigraphic correlation of the interfingering lithostratigraphic members between the different exploration blocks a facies classification scheme integrating sedimentary structures in borehole images bhi and lithology from wireline logs is calibrated in the cored wells and extrapolated into the noncored wells three major sedimentary systems are recognized in xujiahe by mapping the facies trends and paleocurrent directions in the coarse grained sediments one system may dominate over the others at different times and or locations in the foreland basin in response to the orogenic movements in the surrounding mountains the longmen shan in the northwest of the study area is the main source provenance for the carbonate conglomerates and calcarenites meanwhile the systems in the northeast and southeast deposited the sandstone wedges alternating lacustrine swamp and fluvial sediments are penetrated in both proximal and distal areas in the basin although there is no indication of a basinwide lake in the xujiahe period abundant sandy shale breccia conglomerates containing large shale breccias plant materials and contorted shale blocks in association with thick foreset bedded sandstones suggest subaqueous gravity flows possibly because of the collapse of a multistoried delta front characterization of these dynamic sedimentary systems through multidisciplinary interpretation of the seismic data cores bhi and wireline logs is not only fundamental to the sedimentary analysis but also the exploration strategy in the areas with optimal juxtaposition of reservoir sandstones and coaly source rocks

active mud volcanoes on and offshore eastern makran pakistan to study the activity source and driving force of the venting of fluidized mud in the coastal makran we carried out reconnaissance surveys of two active onshore mud volcano fields chandragup and jebel u ghurab and of a newly born march 1999 offshore mud volcano malan island all studied on and offshore mud volcanoes line up along one southwest northeast trending structural lineament the axis of the dhak anticline isotopic data point to a bacterial origin of the gas mainly methane mixed benthic foraminiferal faunas and calcareous nannofloras suggest that the source level of the extruded mud is at a sub surface depth of 2 3 km observed mud discharge varied between 0 and 1 4 m3 h 1 and gas discharge rates between negligible amounts to 1 m3 s 1 mud temperatures in the crater lake of chandragup i are near ambient temperatures they rise slightly 1 5 c during episodes of modest mud outflow an area of 160 000 m3 of soft mud was vigorously extruded from the sea floor at a water depth of 10 m within days after 15 march 1999 forming malan island the island was destroyed within a few months after its birth by deep reaching wave action during the sw monsoon this was possibly aided by local subsidence of the mud volcano structure due to the volume loss following rapid degassing and mud extrusion

geochemistry of the sinian cambrian gas system in the sichuan basin china abstract based on the outcrops core samples drilling cuttings seismic and geochemical data natural gases of the sinian cambrian gas system were derived from four sets of over mature high quality source rocks the cambrian qiongzhusi source rock is sapropelic with toc of 1 94 ro eq of 1 83 3 90 and a thickness of 140 m on average the sinian 620 541 ma doushantuo source rock is sapropelic with toc of 1 69 ro eq of 2 08 3 83 and a thickness of 11 m on average the 3rd member of the dengying fm is also sapropelic with toc of 1 43 ro eq of 3 16 3 21 and a thickness of 13 m on average the 2nd and 4th members of the dengying fm are dominated by algal dolomite with toc of exhibiting 0 39 ro eq of 1 97 3 46 and a thickness of 246 m on average most of the 13c2 values are lower than 28 and gas dryness is 99 indicating that the natural gas is oil derived with high maturity the high contents of isoparaffins and cycloparaffin suggest that natural gas in the sinian cambrian reservoir was originated from secondary oil cracking the cambrian longwangmiao gas was mainly derived from the cambrian qiongzhusi source rock and the gas within the sinian dengying formation mainly originated from the three sinian source rock layers the area with gas generation intensity superimposed the four sets of source rocks exceeding 6 109 m3 km2 covered 80 of the sichuan basin the proved reserves exceed 1 0 1012 m3 in the sinian cambrian gas system and the accumulated gas resource in the sinian cambrian gas system might exceed 5 1012 m3

quantification of gas bubble emissions from submarine hydrocarbon seeps at the makran continental margin offshore pakistan 1 evidence for twelve sites with gas bubble emissions causing hydroacoustic anomalies in 18 khz echosounder records flares was obtained at the convergent makran continental margin the hydroacoustic anomalies originating from hydrocarbon seeps at water depths between 575 and 2870 m disappeared after rising up to 2000 m in the water column dives with the remotely operated vehicle quest 4000 m revealed that several individual bubble vents contributed to one hydroacoustic anomaly analyzed gas samples suggest that bubbles were mainly composed of methane of microbial origin bubble size distributions and rise velocities were determined and the volume flux was estimated by counting the emitted bubbles and using their average volume we found that a low volume flux flare 1 at 575 mbsl 90 ml min caused a weak hydroacoustic signal in echograms whereas high volume fluxes flare 2 at 1027 mbsl 1590 ml min flare 5 c at 2870 mbsl 760 ml min caused strong anomalies the total methane bubble flux in the study area was estimated by multiplying the average methane flux causing a strong hydroacoustic anomaly in the echosounder record with the total number of equivalent anomalies an order of magnitude estimate further considers the temporal variability of some of the flares assuming a constant flux over time and allows a large range of uncertainty inherent to the method our results on the fate of bubbles and the order of magnitude estimate suggest that all of the 40 32 106 mol methane emitted per year within the gas hydrate stability zone remain in the deep ocean

sequence stratigraphic architectures and sand body distribution in cenozoic rifted lacustrine basins east china cenozoic rifted lacustrine basins in east china display three main basin types 1 basins with steeply dipping boundary fault whose hanging walls tilt along pivot points 2 basins with listric boundary faults whose hanging walls bend along flexural bending points and 3 basins formed by earlier extensional rifting with later strike slip movement superimposed the sequence development is intimately linked to the tectonic movements in the area where second order sequences are regionally correlatable from basin to basin and relate to the large scale tectonic movements in the region third order sequences are related to local tectonic activity and are correlatable within basins between subbasins and sometimes between neighboring basins detailed sequence stratigraphic analysis and mapping of depositional systems demonstrate that sand body distribution patterns are related to sequence stratigraphic frameworks for the three kinds of basins the positions of pivot point zones flexural bend zones and strike slip faults plus the syndepositional faults all control the distribution of depositional systems systems tract and sand bodies these controlling factors can be attributed to different structural and stratigraphic features that change the accommodation structural elements include boundary faults syndepositional faults and abrupt changes in dip stratigraphic controls include preexisting surfaces with local channelization paleobathymetric lows and onlap onto clinoform slopes the lowstand sand bodies deposited at the downdip end of these controlling factors constitute the current and future exploration targets for conventional reservoirs

hydroacoustic methodology for detection localization and quantification of gas bubbles rising from the seafloor at gas seeps from the eastern black sea 1 detailed acoustic investigation of bubble streams rising from the seafloor were conducted during r v meteor cruise m72 3a at a deep submarine hydrocarbon seep environment the area is located offshore georgia eastern part of the black sea at a water depth between 840 m and 870 m the sediment echosounder parasound ds 3 p70 was used for detecting bubbles in the water column that causes strong backscatter in the echographs flares employing the swath echsounder kongsberg em710 flares in the water column were mapped along the entire swath width of approximately 1000 m at high spatial resolution the exact location of the flares could be extracted manually subsequently the horizontally looking sonar kongsberg digital telemetry ms1000 mounted on a remotely operated vehicle rov was utilized to quantify the flux of bubbles a model was developed that is based on the principle of finding the acoustic mass in order to quantify the bubble flux at various seeps the acoustic approach from the backscatter data of the rov sonar resulted in bubble fluxes in the range of 0 01 to 5 5 l min corresponding to 0 037 to 20 5 mol ch4 min at in situ conditions 850 m water depth 9 c independent flux estimations using a funnel shaped device showed that the acoustic model consistently produced lower values but the offset is less than 12 furthermore the deviation decreased with increasing flux rates a field of bubble streams was scanned three times from different directions in order to reveal the reproducibility of the method flux estimations yielded consistent fluxes of about 2 l min 7 4 mol ch4 min with variations of less than 10 although gas emissions have been found at many sites at the seafloor in a range of geological settings the amount of escaping gas is still largely unknown with this study presenting a novel method of quantifying bubble fluxes employing a horizontally looking sonar system it is intended to contribute to the global effort of better constraining bubble fluxes at deep sea settings

preparation of polished thin sections from poorly consolidated regolith and sediment materials abstract good quality polished thin sections can be prepared from poorly consolidated wet fragile and friable regolith and sediment materials in a standard earth science thin section laboratory with only minor additional equipment materials are dried over an acetone bath impregnated with a polyester resin mix and cut and polished using minor modifications of standard hard rock thin sectioning equipment and techniques the sections produced are suitable for both optical and electron microscopy and electron probe microanalysis

pore characteristic responses to categories of depositional microfacies of delta lacustrine tight reservoirs in the upper triassic yanchang formation ordos basin nw china abstract primary depositional variations interact with diagenetic modifications to exert strong control on pore networks in tight hydrocarbon reservoirs however the linkage between pore characteristics and depositional microfacies remains enigmatic which restricts the prediction of high quality reservoir distributions the continental tight reservoirs of the yanchang formation in the ordos basin are targeted to clarify and estimate the sensitivity of pore characteristics to depositional microfacies a multi methodical approach utilizing petrographic assessments logging evaluations digital imaging analyses and high pressure mercury intrusion experiments enables us to reveal the high microheterogeneity of pore types pore size distribution and pore fractal features the results identified the microfacies including distributary channels dcs mouth bars mbs interdistributary bays ibs sheet sands sss turbidite fans tfs shallow lacustrine mudstones slms and semi deep lacustrine mudstones sdlms from the chang 8 to chang 6 members dominated by residual intergranular pores and microfractures the main storage spaces of the dc and mb microfacies are within mesopores which provide 62 92 and 81 of the total pore volume respectively however the micropores that are mainly composed of clay intercrystalline pores and feldspar dissolved pores provide 55 70 52 62 and 53 80 of the total pore volume for the ib slm and sdlm microfacies respectively in addition the pore fractal dimension results indicate that the mesoporous structure of the argillaceous microfacies ib slm and sdlm is more heterogeneous than that of the arenaceous microfacies dc mb and tf therefore the dominant reservoir spaces of the different depositional microfacies are distributed over diverse pore radius ranges and the varying degrees of mesoporous development are a crucial factor affecting the reservoir capacity moreover the fractal dimensions have a significant negative correlation with pore volume in the meso micropore range characterized by lower pore sorting coefficients broader skewness and more abundant rigid siliceous grains the arenaceous microfacies with lower fractal dimensions and higher pore volume have better reservoir capacity than argillaceous microfacies that are rich in ductile minerals microscopic observations show that the muddier reservoirs of interdistributary bays and lacustrine mudstones are more susceptible to pore filling chlorite and illite which can deteriorate the reservoir quality these results indicate that the controlling effect of depositional microfacies on pore characteristics is fundamentally caused by differences in mineralogical composition and depositional texture and these results could provide new insights into the mechanisms of microfacies controls on reservoir quality

interaction between accretionary thrust faulting and slope sedimentation at the frontal makran accretionary prism and its implications for hydrocarbon fluid seepage 1 using high resolution seismic profiles and other geophysical data collected during r v meteor cruise m74 2 we investigate the distribution patterns of shallow sediments their structure and deformation processes and their role in the migration accumulation and seepage of hydrocarbon rich fluids here we show that rapid syn kinematic sedimentation at the frontal makran accretionary prism provides a mechanism by which emerging imbricated thrust packets override the footwall at the seafloor without significant mass wasting and destruction of fault related anticline in the hanging wall these anticlines may rise high above the seafloor to form plate boundary parallel ridges and distinguish from simple thrust blocks seen at convergent margins elsewhere with the fast burial of many thrust faults by the syn kinematic sediments anticlinal growth structures form in these syn kinematic sediments by continuous thrust activity the anticlinal structures preserved within the cores of the ridges or formed from these syn kinematic sediments act as structural traps for migrating hydrocarbon rich fluids above which fluid escape structures are generated leading to seafloor seeps most of the discovered hydrocarbon seeps around sixth ridge are sourced from these traps despite the compressional environment and the rapid syn kinematic sedimentation rates shallow subsurface of the frontal makran is a normally pressured regime in which the buoyancy of hydrocarbons may account for the fluid migration in this important respect the makran accretionary prism differs from many other convergent margins and accretionary prisms where fluid flow is largely driven by tectonically induced overpressure

sedimentary characteristics of thick layer lacustrine beach bars in the cenozoic banqiao sag of the bohai bay basin east china abstract lacustrine beach bar reservoirs have become important exploration targets in the bohai bay basin in china especially in the banqiao sag within the huanghua depression where some typical thick layer beach bar reservoirs have been discovered recently the average single layer thickness of the beach bar sand bodies in the second member of the paleogene shahejie formation within the sag is greater than 10 m and the cumulative thickness of these sands reach up to 100 m the second member of the shahejie formation in the banqiao sag consists of a third order sequence of three systems tracts a lowstand systems tract a transgressive systems tract and a highstand systems tract beach bar sand bodies were deposited widely in the sag in the lowstand systems tract but were less deposited in the other systems tracts the sedimentary characteristics distribution patterns and formation mechanisms of the beach bar sand bodies in the lowstand systems tract of the second member of the shahejie formation were systemically studied using cores wireline logs and 3d seismic data the beach bar was divided into five sedimentary microfacies namely sandy bar centre sandy bar flank interbar deposit coastal beach and infralittoral beach based on the integrated analysis of the paleostructure and sedimentary environment it was inferred that the thick layer beach bars in this area resulted from the combination and joint control of the sediment source system hydrodynamic environment lake level variations and contemporaneous fault activity firstly the sands in the braided river delta of the beidagang buried hill structural belt served as the provenance that provided the material basis for the beach bars in the banqiao sag secondly the wave effects in the gentle slope belt controlled the scale and distribution of the beach bars under the control of waves various sedimentary microfacies were regularly distributed in particular the continuous activity of the contemporaneous dazhangtuo fault contributed to the formation of the thick layer beach bars in the banqiao sag the contemporaneous fault controlled the allocation of the sediments providing abundant sands in the downthrown side of the fault in addition there was a constant high energy hydrodynamic environment near the fault plane where the sand bodies experienced long term reworking by waves and gradually formed beach bars with large thickness the activity of the contemporaneous fault increased the accommodation space in the lowstand systems tract of the second member of the shahejie formation which resulted in continuous sand deposition and provided the necessary conditions for forming the thick layer beach bars

provenance of tertiary sandstone in the northern qaidam basin northeastern tibetan plateau integration of framework petrography heavy mineral analysis and mineral chemistry abstract an exceptionally thick cenozoic sedimentary succession has developed in the qaidam basin of the northeastern tibetan plateau the provenance remains enigmatic thus more precise investigations are needed an integrated study of sandstone framework petrography heavy mineral analysis and mineral chemistry was adopted to perform provenance analysis of the tertiary sandstones in the northern qaidam basin no individual method exists that can provide comprehensive provenance interpretations on spatial and temporal variations based on three types of data three depositional areas can be distinguished sandstones of area a exhibit relatively high abundances of quartz garnet and zircon as well as relatively high textural maturity implying long distance sources multi composition garnets and tourmalines reveal derivations of metasedimentary rocks and intermediate acidic igneous rocks sandstones of area b are rich in metamorphic lithic fragments epidote and garnet a dominance of fe rich garnets with low mg low mn and variable ca contents and dravites demonstrates predominant derivation of metasedimentary rocks therefore the north qaidam and south qilian terranes are potential source areas for these two depositional areas additionally high metamorphic heavy mineral abundances in the upper formations imply increasing contributions of these two metamorphic belts during the tertiary tectonic uplift however sandstones of area c are characterized by relatively high abundances of feldspar igneous heavy minerals and high fe mn garnet which suggest a main source of igneous rocks the altun and qilian mountains are potential source regions furthermore increasing amounts of feldspar and igneous heavy minerals in the upper formations indicate a significant presence of igneous parent rocks which are most likely a response to the multi stage uplift events in the altun mountains since the early eocene

geochemistry of archean shales from the witwatersrand supergroup south africa source area weathering and provenance with a few exceptions shales from the archean witwatersrand supergroup 2800 ma in south africa are depleted in na ca lile ree and hfse compared to phanerozoic shales cr co and ni are enriched in all witwatersrand shales and fe and mg are high in shales from the west rand groups wrg and lower central rand group crg shales from the crg and uppermost wrg are enriched in na al lile ree hfse and transition metals relative to shales from the lower wrg chondrite normalized ree patterns for all witwatersrand shales are enriched in light ree and exhibit small to moderate negative eu anomalies a positive correlation of ree and al2o3 contents in the shales suggests that ree are contained principally in clay minerals relative to shales from the crg shales from the wrg exhibit depletions of na ca and sr a feature probably reflecting intense chemical weathering of their source rocks cia indices in witwatersrand shales are variable chiefly 70 98 even within the same shale unit such variations reflect chiefly variable climatic zones or rates of tectonic uplift in source areas with perhaps some contribution from provenance and element remobilization during metamorphism compared to present day upper continental crust all but the orange grove roodepoort and k8 shales appear to have been derived from continental sources depleted in lile ree and hfse and enriched in transition metals computer mixing models based on six relatively immobile elements th hf yb la sc co and four source rocks indicate that the relative proportions of granite basalt and komatiite increased with time in sediment source areas at the expense of tonalite the contributions of basalt and komatiite appear to reach a maximum during deposition of the booysens shale and granite during deposition of the k8 shales and possibly during deposition of the orange grove shales

upper jurassic lowermost cretaceous marine shale source rocks farsund formation north sea kerogen composition and quality and the adverse effect of oil based mud contamination on organic geochemical analyses abstract the jude 1 well is located in the central part of the danish central graben north sea and was drilled into immature black shales of the upper jurassic lowermost farsund formation a world class marine source rock the well was drilled with oil based drilling mud obm the lithofacies consists of argillaceous shale calcareous shale and dolomite stringers as confirmed by cuttings and core a core was taken in the upper part of the formation at the beginning of a hot argillaceous shale interval characterized by elevated toc and hi values cuttings and core samples were investigated to unravel kerogen composition source rock quality and the contamination effect of obm on organic geochemical analyses the organic facies of the source rocks corresponds to type ii kerogen or organofacies b sensu pepper and corvi 1995 considerable fluctuations in hi values through the farsund formation reflect pronounced variations in source rock quality although a faint lamination of the shales and overall high toc contents testify to prevailing oxygen deficient depositional conditions preventing significant bioturbation and reworking of the sediment and organic matter petrography of core samples reveals a relatively homogenous sapropelic kerogen composition dominated by a groundmass of yellowish fluorescing amorphous organic matter and liptodetrinite intimately associated with the mineral matrix telalginite is less abundant but tasmanites and in particular leiosphaerida type telalginites were observed minor but varying amounts of detrital terrigenous macerals suggest a considerable distance to land areas and thus limited supply of land plant derived organic matter the argillaceous shale lithofacies generally is more oil prone and organic rich than the more gas prone calcareous shale facies the uppermost section includes the hot argillaceous shales which together with two deeper argillaceous shale intervals are highly organic rich and oil prone average toc of the hot argillaceous shales is 7 wt and hi reaches 500 mg hc g toc the total ultimate expulsion potential uep of the over 853 m 2799 ft thick farsund formation is 142 mmboe km2 results from non contaminated samples are thus consistent with the farsund formation being a world class highly oil prone marine source rock the predicted oil composition corresponds to paraffinic low wax oils the adverse effect of obm contamination on geochemical analyses is demonstrated by rock eval data and measured bulk kinetics of contaminated core samples the measured kinetics has a considerable proportion of low activation energies related to obm contamination which is also supported by high production indices further gas chromatograms of the saturated fraction of extracts from contaminated cores clearly show evidence of obm in the nc11 nc14 range rock eval s2 peaks have a shoulder showing that the low ea peaks result from carry over from the s1 peak caused by the obm contamination as a consequence hydrogen index values are increased

turbine tent measurements of marine hydrocarbon seeps on subhourly timescales 1 three turbine seep tents simultaneously measured marine seep gas fluxes with high time resolution 0 2 s at multiple locations tents were inverted polyvinyl cones 2 m diameter 1 m tall and weighted on their lower skirt edges rising gas bubbles induce vertical fluid motions which were measured by laboratory calibrated turbines in chimneys on top of the tents initial deployment was at an active seep area in the coal oil point seep field in the santa barbara channel california the three tents simultaneously collected data for continuous time periods of 2 hours in both the morning and afternoon seabed temperature and pressure were acquired every 3 s over the same time periods as the flux measurements from a conductivity temperature depth ctd mounted on one tent results strongly suggest that oceanic swell had a significant forcing effect on the flux at a subhourly timescale there was an inverse relationship between effect of swell height on the flux and flux swells from 1 to 4 m height and periodicities of 7 and 12 s caused variations of 1 to 4 from the average flux proposed mechanisms to explain the observations are diffusion with surrounding sediments termed gas charging swell induced changes in fracture size termed fracture forcing and swell induced vent activation deactivation termed pore activation on the basis of the seep frequency response we propose pore activation was dominant

geochemical characteristics of marine and terrestrial shale gas in china abstract although the annual production of shale gas in china was 13 10 8 m 3 in 2014 a systematic study on geochemical and isotopic characteristics of these unconventional gases has not been well addressed in the present study almost all shale gas samples available in china including marine shale gas from the wufeng longmaxi formation in the sichuan basin o 3 w s 1 l and terrestrial shale gas from chang 7 member t 3 y 7 in the ordos basin were collected and analyzed for their geochemical and isotopic compositions the shale gas from the wufeng longmaxi shale is dry gas with an average methane content of 98 38 and records a highest content of ch 4 in the world 99 59 which is consistent with the very high thermal maturity levels of the gas shales that have equivalent vitrinite reflectance eqvro values between 2 4 and 3 6 the 13 c 1 values are correspondingly heavy and record a heaviest 13 c 1 values 26 7 for the shale gases found in the world as well the average values of 13 c 1 13 c 2 and 13 c 3 for the wufeng longmaxi shale gas are 31 3 35 6 and 47 2 respectively displaying a complete carbon isotopic reversal i e 13 c 1 13 c 2 13 c 3 2 h ch4 and 2 h c2h6 has an average value of 148 and 173 respectively also yielding a hydrogen isotopic reversal i e 2 h ch4 2 h c2h6 the chang 7 shale has an average toc content of 13 81 with vitrinite reflectance vro values between 0 7 and 1 2 the chang 7 shale gas is wet gas with an average methane content of 84 90 and is rich in heavy gaseous hydrocarbons c 2 c 5 the respective values of 13 c 1 13 c 2 and 13 c 3 are 48 7 36 4 and 31 3 displaying a positive carbon isotopic distribution pattern i e 13 c 1 13 c 2 13 c 3 the average 2 h ch4 2 h c2h6 and 2 h c3h8 values are 256 244 and 188 respectively and are characterized by a positive distribution pattern i e 2 h ch4 2 h c2h6 2 h c3h8 the differences in gas wetness and carbon and hydrogen isotopic distribution patterns between the shale gases from the wufeng longmaxi and chang 7 shale are attributed to variations in thermal maturity levels co 2 is present in low content in both the wufeng longmaxi and chang 7 shale gases mostly less than 1 13 c values for the co 2 in the wufeng longmaxi formation are between 8 9 and 9 2 indicating an inorganic origin from the cracking of carbonate mineral in the shales under high temperatures in contrast 13 c values of the co 2 in the chang 7 shale gas range from 8 2 to 22 7 indicating an organic origin from the thermal degradation of organic matter helium in both the wufeng longmaxi and chang 7 shale gases is dominantly of curst origin in terms of their r ra ratios that vary from 0 01 to 0 08 positive carbon isotopic distribution pattern is typical of primitive thermogenic gas however it can be converted into complete or partial carbon isotopic reversal patterns due to secondary alteration the causes that yield carbon isotopic reversal include 1 mixing of gases with the same source but different thermal maturity levels 2 secondary cracking of oil or wet gas 3 formation water involved reactions 4 gas diffusion and 5 carbon isotope exchange between alkane gases at high temperature among them carbon isotopic exchange between alkane gases at high temperature is a key factor nine plots have been drawn based on the shale gases from china usa and canada among them the plot of 13 c 2 versus wetness demonstrates a lying s shape with two inflection points on the gas wetness axis the wetness value of 1 4 represents a critical point from pyrolytic gas primary cracking gas to cracking gas secondary cracking gas and whereas the wetness value of 6 marks the end of oil generation on the diagram of wetness versus 13 c shale gases with wetness values greater than 1 6 are characterized by positive carbon isotopic distribution pattern whereas a complete or partial carbon isotopic reversals are observed for shale gases with wetness values less than 1 6

morphotectonics and mechanics of the central makran accretionary wedge off pakistan abstract swath bathymetry images and 3 5 khz data acquired during rv sonne cruise 123 in autumn 1997 are the base for analysing the morphology and deformation styles of the huge makran accretionary wedge the continental slope off pakistan is characterised by three morphological provinces a the lower slope is built of a sequence of imbricate thrust slices which form long and narrow accretionary ridges with flanks locally as steep as 20 and between 10 and 20 on average while the regional slope is only 1 2 b the nearly flat mid slope terrace is present in the central east part of the margin narrows significantly towards the east and is absent east of 63 45 and c the upper slope up to the shelf has a regionally uniform slope as steep as about 8 and comprises a very rough topography with many gullies and canyons and evidence for mass wasting two meandering canyons crossing the entire margin down to the abyssal plain at about 63 15 63 30 can be correlated with onshore rivers they have been formed by episodic erosion through turbidity flows and are characterised by erosional and depositional portions sinuosity of the canyons is exclusively caused by the accretionary ridges functioning as obstacles for flow to be directly downhill application of coulomb rheology to the frontal part of the makran wedge implies that the mid level decollement is intrinsically extraordinary weak with a great strength contrast to the overlying sediments comparison with nankai cascadia and the western mediterranean ridge reveals new insights in the parameters controlling the shape of an accretionary wedge and the role of a mid level decollement

climate and tectonic driven deposition of sandwiched continental shale units new insights from petrology geochemistry and integrated provenance analyses the western sichuan subsiding basin southwest china abstract how the depositional setting efficiently governs the characteristic sandwiched continental shale units remains uncertain which restricts an integrated assessment of organic rich fluvio lacustrine shale reservoirs and accurate estimation of potential natural gas resources here we present new results from petrological observations element geochemical fingerprinting and integrated analyses of heavy mineral basinal subsidence history and sandstone stratum ratio on typical and terrigenous sandwiched like depositional systems of the targeted upper triassic xujiahe formation in the western sichuan subsiding bain southwest china in view of the representative and environment sensitive indices we suggest that passive continental margin and continental island arc dominated by granite to granodiorite source are the major tectonic settings of the provenance and both a more warm humid climate characterized by intensified chemical weathering conditions and a calm tectonically quiescent setting are identified as two major drivers forcing the accumulation and preservation of organic matter in organic rich continental shale units finally a comprehensive depositional model is established for providing new insights into the linkage between palaeoclimatic conditions tectonic pulses and terrigenous clastic sedimentation both the cyclic palaeoclimate fluctuations and episodic tectonic activities are believed to have exerted a very considerable force on development of the unique sandwiched like stratigraphic framework and the coupling interactions between the tectono climatic evolution and fine grained sedimentation are thus also stressed

sediment compaction and fluid migration in the makran accretionary prism the makran continental margin in the gulf of oman forms the seaward extremity of an accretionary sediment prism which extends several hundred kilometers inland a recently acquired multichannel seismic reflection profile shot across the margin imaged the structure of the prism in greater detail than was previously possible and allowed us to investigate the relationship between deformation and pore fluid motion in the region velocity analyses of the common midpoint gathers reveal a marked change in velocity structure at the toe of the accretionary wedge as seen in previous sonobuoy wide angle data accreted sediments show significantly higher vertical velocity gradients than those of sediments entering the prism this change is interpreted as due to porosity reduction as pore fluids are squeezed out of the compacting sediment a prominent bottom simulating reflector appears 500 800 m beneath the sea bed several lines of evidence suggest that this reflector represents the base of a gas hydrate zone underlain by widespread free gas which may be exsolved from pore water migrating from deep within the sediment pile up permeable fault planes imaged in the profile the hydrate reflector appears to shallow in the region of some faults suggesting a temperature anomaly due to the presence of warm pore fluids a heat flow profile derived from the depth of the hydrate reflector does not show the expected landward decrease as the sediment pile thickens simple thermal modeling suggests that advective heat flow within the prism may explain this anomaly the inferred presence of overpressured pore fluids in the makran suggests that accreted sediments have a low permeability the seismic evidence suggests a two stage compaction process with rapid initial dewatering through intergranular permeability as sediment enters the prism followed by a buildup of pore pressure as the permeability decreases and fluid migration is restricted to fault zones

provenance of deep water reservoir sandstones from the jubarte oil field campos basin eastern brazilian margin the provenance of the maastrichtian deep water reservoir sandstones from the jubarte oil field campos basin eastern brazil was studied using an integrated approach that included quantitative petrography conventional heavy mineral analysis garnet mineral chemistry and zircon geochronology the reservoirs are predominantly coarse poorly sorted sandstones with feldspathic composition derived from uplifted basement terrains the fourth and fifth order depositional sequences analyzed show no major variations in composition or in provenance through time however variations in apatite tourmaline presents potential to be used as a parameter for sandstone correlation within the field the composition of heavy minerals indicates derivation from high temperature and low to medium pressure aluminous metapelitic rocks from granites and subordinate mafic rocks derived from the cabo frio tectonic domain and the oriental terrain of ribeira orogen characterizing a supply route from sw to ne the low ztr index as well as the absence of low grade stable heavy minerals and of metasedimentary rock fragments suggest that by the end of cretaceous all supracrustal low grade terrains had already been totally eroded and that plutonic infracrustal rocks were exposed similarly to the present situation the integration of the compositional and textural aspects suggests a tectonically active source area located relatively close to the basin the active tectonic uplift of the basement terrains provided a large volume of coarse poorly sorted sediments carried directly from mountain streams and alluvial fans to deep water the high frequency shifts in apatite tourmaline values support a direct derivation of the deep water sandstones from adjacent alluvial systems with short but differential exposure to weathering the voluminous deposition of such coarse grained and immature turbidites under the general transgressive conditions of the maastrichtian indicates a tectonic rather than eustatic control on their deposition with important implications for the exploration of similar reservoirs in campos basin and in similar basins of eastern brazilian margin

differentiating the effect of episodic tectonism and eustatic sea level fluctuations in foreland basins filled by alluvial fans and axial deltaic systems insights from a three dimensional stratigraphic forward model many studies of foreland basins have recognized a hierarchical organization in the stacking of sequences deposited by axial deltaic and alluvial fan systems the hierarchy is often explained in terms of the competing control of eustasy and pulsed tectonic subsidence and the different frequencies at which these processes operate unravelling the relative contributions of tectonic and eustatic controls on the sequence stacking pattern is a fundamental question in foreland basin analysis yet this is difficult because of the lack of independent stratigraphic evidence in this study a three dimensional numerical model is presented which aids in the interpretation of alluvial successions in foreland basins filled by transverse and axial depositional systems under conditions of variable tectonism and eustatic sea level change the tectono sedimentary model is capable of simulating the hierarchical stratigraphic response to both eustatic and tectonic forcing and is of higher resolution than previous models of foreland basin filling numerical results indicate that the onset of tectonic activity is reflected by rapid retrogradation of both depositional systems and by widespread flooding and onlap of carbonate sediments syntectonic fluvial patterns on the axial deltaic plain are dominated by bifurcating channels swiftly relocating in response to the general rise in relative sea level induced by flexural subsidence the resulting surface morphology of the axial delta is convex upwards syntectonic eustatic sea level fluctuations result in parasequence scale packages of retrograding and prograding fan and delta sediments bounded by minor flooding surfaces and type 2 sequence boundaries incised channels are rare within the syntectonic parasequences and are formed only during phases of tectonic quiescence when eustatic falls are no longer compensated by the subsidence component in the rise in relative sea level suites of amalgamating axial channels corresponding to multiple eustatic falls delineate the resulting type 1 unconformities coarse grained incised channel fills are found in the zone between the alluvial fan fringes and the convex upward body of the axial delta as the axial streams tend to migrate towards this zone of maximum accommodation

trace elements as palaeoenvironmental markers in strongly mature hydrocarbon source rocks the cretaceous la luna formation of venezuela abstract the late cretaceous la luna formation is the main hydrocarbon source rock formation in venezuela in the lake maracaibo area the formation shows a steep maturation gradient affecting sedimentary organic matter om and clay minerals related to local burial history and thrusting events the influence of the gradient is examined through geochemical organic and inorganic and mineralogical investigations carried out on samples from five cored boreholes in the maracaibo basin the analytical procedure comprises rock eval pyrolysis vitrinite reflectance measurement palynofacies observation major and trace element content determination performed on bulk rock samples or after a sequential leach protocol dop calculation and the examination and analysis of clay mineral assemblages the maturation gradient seems to have had no effect upon the distribution of the trace elements referred to as proxy indicators for palaeodepositional conditions of om rich sediments ba p v mo ni co cu cd cr and mn consequently trace elements appear to be reliable palaeoenvironmental markers they indicate that during the la luna fm deposition the water column must have had variable conditions with high primary production near the surface and the correlative development of euxinic conditions at the bottom this provides further arguments for an upwelling system affecting the northern platform of south america during late cretaceous time the relative scarcity of reactive iron in the depositional environment must have taken an active part in a process involving sulphur and acting on the environmental conditions as well as on om vulcanisation this process favours aliphatic om storage and may be relevant for many other om rich facies or hydrocarbon source rocks

controls on facies distribution and stratigraphic preservation in the ganges brahmaputra delta sequence abundant sediment supply and accommodation space in the bengal basin have led to the development of a major late quaternary delta sequence this sequence has formed in a tectonically active setting and represents an important example of a high energy marine and fluvial high yield continental margin deposit recent studies have detailed the delta s stratigraphy and development noting that tectonics and sediment supply control the ganges brahmaputra more significantly than in many other delta systems these ideas are developed here through a discussion of the effects that spatial and temporal variations in tectonics and sediment supply have had on deltaic processes and sequence character unique and differing stratigraphies are found within thedeltasystem suchthatfine grainedsedimentpreservationisfavoredinareasofactivetectonicprocessessuchasfolding block faulting and subsidence coarse grained deposits dominate the stratigraphy under the control of high energy fluvial processes and mixed fine coarse stratigraphies are found in areas dominantly influenced by eustatic sea level change overlaid upon these spatially varying stratigraphic patterns are temporal patterns related to episodic events e g earthquakes and rivers avulsions and long termchangesinclimate andsediment supply modelingisalsousedtoinvestigatethe influenceofavariable sedimentsupply on sequence character results show that the timing and magnitude of sediment input relative to sea level rise is a significant control on the subaerial extent of the delta and the relative dominance of alluvial and marine facies within the sequence d 2002 elsevier science b v all rights reserved

trace element behavior and redox facies in core shales of upper pennsylvanian kansas type cyclothems the black shale submember of core shales of pennsylvanian kansas type cyclothems is highly enriched in redox sensitive trace elements tes relative to the overlying gray shale submember as well as to many other modern and ancient organic rich deposits controls on trace element behavior in the black shale can be inferred from trace element enrichment factors efs relative to gray shale and the relationship of tes to total organic carbon toc most tes conformed to one of two patterns 1 mo u v zn and pb exhibited moderate efs and strong covariation with toc in samples having 10 wt toc and 2 cu ni cr and co exhibited low efs and moderate to strong covariation with toc in all samples these patterns are inferred to represent different responses to benthic redox conditions the first pattern is characteristic of tes of strong euxinic affinity i e those taken up in solid solution by fe sulfide or involved in other reactions catalyzed by free h2s and resident mainly in authigenic phases whereas the second pattern is characteristic of tes of weak euxinic affinity i e those not strongly influenced by the presence of free h2s and resident mainly in the organic carbon or detrital fractions of the sediment these inferences allowed development of a multiproxy technique for assessing redox facies in black shale samples euxinic conditions were considered to have existed if at least two of four redox indicator trace elements mo u v zn showed euxinic levels of enrichment and nonsulfidic anoxic conditions were inferred otherwise the validity of the procedure is indicated by 1 agreement among all four redox indicators for a large majority of samples 69 of 185 2 among samples yielding a mixed redox signal a systematic sequence of te enrichment v zn mo u and 3 for tes of weak euxinic affinity reduced variance among samples representing each redox facies sequential enrichment may be a response to differential redox thresholds for accumulation e g v or postdepositional remobilization of trace elements e g u and may provide a basis for finer assessment of redox conditions in low oxygen paleoenvironments than permitted by simple classification schemes the multiproxy procedure for redox facies analysis developed in this study is likely to be more reliable than widely used single proxy indicators based on trace elements e g mo authigenic u or v v ni or c s fe systematics e g s toc or dop d 2004 elsevier b v all rights reserved

authigenic carbonates derived from oxidized methane vented from the makran accretionary prism off pakistan we report the first discovery and sampling of a methane hydrogen sulfide rich cold seep from the makran accretionary prism off pakistan arabian sea a variety of cm to m scale pockmarks and gas seepage structures were identified from underwater tv photo sled profiles crossing the oxygen minimum zone omz related to highresolution seismic parasound records from the seeps isotopically light bacterially formed methane is emanating that is partly oxidized to hco3 in the bacterial sulfate reduction zone this results in the precipitation of irregular dark gray to black crusts of indurated authigenic carbonates mainly cryptocrystalline magnesian calcite and ca rich dolomite near the sediment seawater interface within the omz downcore the crusts grade into hemipelagic carbonate poor silty clays with transitional lithologies in between similar to the pockmark carbonates from the oregon margin and in the north sea the authigenic carbonates are extremely depleted in 13c 13ccarbonate 40 this suggests that they were derived from bacterial methane 13cmethane 77 8 that was oxidized under anaerobic conditions the authigenic carbonates are associated with white fluffy mats of chemoautotrophic h2s oxidizing bacteria small pockmarks appear to be concentrated at small scale escarpments suggesting focussed fault controlled pore fluid expulsion due to the tectonic dewatering and degassing of the accretionary prism whereas diffuse discharge of pore fluids is inferred from the widespread occurrence of tiny gas bubble tubes

elements and phosphorus minerals in the middle jurassic inertinite rich coals of the muli coalfield on the tibetan plateau abstract the content modes of occurrence and origin of elements and phosphorus minerals in the jurassic coals of the muli coalfield on the tibetan plateau were investigated using optical microscopy field emission scanning electron microscopy in conjunction with energy dispersive x ray spectrometry x ray powder diffraction x ray fluorescence spectrometry and inductively coupled plasma mass spectrometry the muli coals l1 and l2 coals are of high volatile a bituminous to medium volatile bituminous rank characterized by low sulfur contents and are generally dominated by the inertinite group macerals predominantly semifusinite and fusinite the l1 coal contains abundant apatite 7 9 on average on an organic matter free basis and alumino phosphate minerals of goyazite gorceixite crandallite group 4 9 on average and accordingly the concentrations of elements f 253 g g on average p 2349 g g sr 526 g g and ba 790 g g are elevated as compared with common world hard coals the deposition of phosphorous bearing minerals in the muli coals was not derived from volcanic input penetration of ca and al rich solutions release of phosphorus from organic matter during plant decay and an appropriate sedimentary environment such as low ph low water table for peat and oxidizing conditions were critical factors in deposition of the phosphorus minerals

pore characteristics of lacustrine shale within the oil window in the upper triassic yanchang formation southeastern ordos basin china abstract organic matter om rich shale in the yanchang formation is recognized as a promising hybrid shale oil shale gas system in lacustrine strata in china being mainly in the oil window both the type and distribution of the pores in the shale have been affected by several factors including petroleum expulsion and retention mineral and organic composition and compaction to obtain a better understanding of the factors controlling om pore development 10 core samples were selected with various om content from the chang 7 and chang 9 members of the yanchang formation for pore characterization the investigation combined microscopic observation both of thin sections and ion milled surfaces of samples with low pressure carbon dioxide and nitrogen adsorption and bulk porosity measurements with the main emphasis being on om associated pores the selected samples generally have relatively low total porosity with the pores being poorly connected most pore types found in marine shales were present the size of porous om is usually small mostly measuring several hundreds of nanometers to a few micrometers which suggest a general compaction effect on pore development the pore development is related to different petroleum expulsion processes shale with very porous om was a very important feature the om coexisting with fluorescent lipitinites was present in a cross linked nanofiber structure possibly related to altered extracellular polymeric substances eps by compaction and maturation various om types that varied in both size and shape did not contain any visible pores e g woody relics migrated solid bitumen and om laminae in close association with clay minerals unusually low meso and macropore volume in the sample with the highest total organic carbon toc content was confirmed by the predominance of om laminae without visible pores however abundant micropores were indicated by co 2 adsorption analysis meso and macropores in this sample had probably not developed due to a significant compaction effect due to the small numbers of studied samples these om pore characteristics need to be viewed with caution

geochemistry of the miocene oil shale hancili formation in the cankiri corum basin central turkey implications for paleoclimate conditions source area weathering provenance and tectonic setting abstract the geochemistry of oil shale units of hancili formation in the cankiri corum basin central turkey was studied using various chemical analyses the mineralogical composition of the samples were preliminarily investigated using pearson s correlation coefficients of selected elements indicating that the samples contain abundant clay minerals as well as k feldspar and carbonate the k 2 o al 2 o 3 and sio 2 al 2 o 3 ratios indicate that the major proportion of clay minerals is composed of smectite si al ti k na and fe reside in clay minerals while ca mg and mn are mostly associated with carbonates e g calcite and dolomite and phosphorous p is present as apatite the total ree content of the oil shale range from 19 to 113 ppm the chondrite normalized patterns of the oil shale show lree enrichments hree deficits negative eu anomalies and negligible ce anomalies in general major trace and rare earth element abundances suggest that the studied oil shale in the cankiri corum basin are mainly from the intermediate rocks mixed with small amounts of basic rocks and that their source rocks are mostly deposited in the continental collision setting the ree geochemistry of the oil shale suggests that these samples were derived from a consistent terrigenous source and the eu anomaly was inherited from the source rocks the paleoclimate index c value varies between 0 07 and 1 22 reflecting a generally semi arid to humid conditions in addition rb sr 0 22 and sr cu 9 09 ratios support the idea that warm and humid conditions prevailed during deposition of the hancili formation sr ba ratios 0 54 3 7 of the studied samples suggest a paleoenvironment with variable salinity the co variation among this factor and paleoclimate indicators suggest that variations in climatic conditions exerted a primary control on salinity the substantially low c value and rb sr ratio and significantly high ratios of sr cu and sr ba and also elevated carbonate content of four samples indicate that these samples were deposited during hot and arid periods and that the paleoclimate controlled the terrigenous sediment flux to the lake basin the chemical index of alteration cia a cn k ternary diagram and high th u ratios indicate that the parent rocks of the oil shale experienced moderate chemical weathering steady state

dynamics of the gas flux from shallow gas hydrate deposits interaction between oily hydrate bubbles and the oceanic environment decomposition of methane hydrates on the continental margins is a potentially significant source of atmospheric methane but the input depends upon the poorly understood fate of the hydrocarbon bubbles rising from the sea floor during a field trip to the gulf of mexico three different seepages were imaged and analyzed three different imaging techniques were tried side front and back illumination of which back illumination produced the best results the images were analyzed and the size dependent bubble distribution mass flux and rise speeds determined the total observed gas flux was 62 3 10 3 mol s 1 primarily methane of which a single vent produced seven times the next largest vent of this major vent 50 of the bubble mass was contained in the largest bubbles r 5500 m the vertical velocities demonstrated that these bubbles were heavily contaminated with oil which was also corroborated by bubble shape and oscillation observations

a review of anomalous rare earth elements and yttrium in coal abstract coal deposits have attracted much attention in recent years as promising alternative raw sources for rare earth elements and yttrium rey not only because the rey concentrations in many coals or coal ashes are equal to or higher than those found in conventional types of rey ores but also because of the world wide demand for rey in recent years has been greater than supply in addition to anomalies of enrichment or depletion of light medium and heavy rey in coal deposits normalized to upper continental crust post archean australian shale or north american shale composite anomalies of redox sensitive ce and eu and in some cases of non redox sensitive la gd and y could be used as geochemical indicators of the sediment source region sedimentary environment tectonic evolution and post depositional history of coal deposits factors controlling rey anomalies in coal deposits include the geochemistry of terrigenous source rocks ingress of hydrothermal fluids influence of marine environments percolating natural waters volcanic ashes and sedimentary environments of peat formation additionally the smoothness of a normalized rey distribution pattern provides a simple but reliable basis for testing the quality of rey chemical analyses for coal and other sedimentary rocks

detrital fine grained sediment contribution from taiwan to the northern south china sea and its relation to regional ocean circulation article i nfo results of clay mineralogy in 140 samples collected in major rivers and lakes in southwestern taiwan and on the seafloor off taiwan in the northeastern south china sea scs combined with clay mineral records of the pearl river drainage basin rivers in luzon and the south china shelf and slope are used to semi quantitatively evaluate the detrital fine grained sediment contribution of taiwan to the northern scs the clay mineral assemblage of the taiwan sourced sediments consists dominantly of illite average 56 and chlorite 41 with very scarce kaolinite and smectite their respective distribution from the rivers and lakes to the seafloor off taiwan does not show obvious basin wide differences linear correlations of illite chemistry index with illite crystallinity and of illite crystallinity with kaolinite present two end members of provenances the pearl river and taiwan for the south china shelf and slope assuming that kaolinite in the northern scs is provided completely from the pearl river the contribution of taiwan in clay minerals is evaluated as 29 to the south china shelf and 23 to the south china slope respectively accordingly the contribution of the pearl river to the south china shelf and slope is 52 and 31 respectively the luzon arc accounts for the rest of clay mineral components for the northern scs mainly by providing smectite the bashi strait crossed branches of the southward deep north pacific deep water and the northward surface kuroshio current in the western pacific may transport taiwan sourced suspended sediments westwards to the northern scs

linked sequence stratigraphy and tectonics in the sichuan continental foreland basin upper triassic xujiahe formation southwest china abstract intracontinental subduction of the south china block below the north china block in the late triassic resulted in formation of the transpressional sichuan foreland basin on the south china block the upper triassic xujiahe formation was deposited in this basin and consists of an eastward tapering wedge of predominantly continental siliciclastic sedimentary rocks that are up to 3 5 km thick in the western foredeep depocenter and thin onto the forebulge and into backbulge depocenters five facies associations a e make up the xujiahe formation and these are interpreted respectively as alluvial fan transverse and longitudinal braided river meandering river overbank or shallow lacustrine and deltaic deposits this study establishes a sequence stratigraphic framework for the xujiahe formation which is subdivided into four sequences sq1 2 3 and 4 sequence boundaries are recognized on the basis of facies tract dislocations and associated fluvial rejuvenation and incision and systems tracts are identified based on their constituent facies associations and changes in architectural style and sediment body geometries typical sequences consist of early to late transgressive systems tract deposits related to a progressive increase in accommodation and represented by facies associations a b and c that grade upwards into facies association d regionally extensive and vertically stacked coal seams define maximum accommodation and are overlain by early highstand systems tract deposits represented by facies associations d e and c late highstand systems tract deposits are rare because of erosion below sequence boundaries sequence development in the xujiahe formation is attributed to active and quiescent phases of thrust loading events and is closely related to the tectonic evolution of the basin the sichuan basin experienced three periods of thrust loading and lithospheric flexure sq1 lower sq2 and sq3 two periods of stress relaxation and basin widening upper sq 2 and sq3 and one phase of isostatic rebound sq4 paleogeographic reconstruction of the sichuan basin in the late triassic indicates that the longmen mountains to the west consisting of metamorphic sedimentary and pre neoproterozoic basement granitoid rocks was the major source of sediment to the foredeep depocenter subordinate sediment sources were the xuefeng mountains to the east to backbulge depocenters and the micang mountains to the northwest during the late history of the basin this study has demonstrated the viability of sequence stratigraphic analysis in continental successions in a foreland basin and the influence of thrust loading on sequence development

molecular and isotopic partitioning of low molecular weight hydrocarbons during migration and gas hydrate precipitation in deposits of a high flux seepage site detailed knowledge of the extent of post genetic modifications affecting shallow submarine hydrocarbons fueled from the deep subsurface is fundamental for evaluating source and reservoir properties we investigated gases from a submarine high flux seepage site in the anoxic eastern black sea in order to elucidate molecular and isotopic alterations of low molecular weight hydrocarbons lmwhc associated with upward migration through the sediment and precipitation of shallow gas hydrates for this near surface sediment pressure cores and free gas venting from the seafloor were collected using autoclave technology at the batumi seep area at 845 m water depth within the gas hydrate stability zone vent gas gas from pressure core degassing and from hydrate dissociation were strongly dominated by methane 99 85 mol of c1 c4 co2 molecular ratios of lmwhc c1 c2 c3 1000 and stable isotopic compositions of methane 13c 53 5 v pdb d h around 175 smow indicated predominant microbial methane formation c1 c2 ratios and stable isotopic compositions of lmwhc distinguished three gas types prevailing in the seepage area vent gas discharged into bottom waters was depleted in methane by 0 03 mol c1 c4 co2 relative to the other gas types and the virtual lack of 14c ch4 indicated a negligible input of methane from degradation of fresh organic matter of all gas types analyzed vent gas was least affected by molecular fractionation thus its origin from the deep subsurface rather than from decomposing hydrates in near surface sediments is likely as a result of the anaerobic oxidation of methane lmwhc in pressure cores in top sediments included smaller methane fractions 0 03 mol c1 c4 co2 than gas released from pressure cores of more deeply buried sediments where the fraction of methane was maximal due to its preferential incorporation in hydrate lattices no indications for stable carbon isotopic fractionations of methane during hydrate crystallization from vent gas were found enrichments of 14c ch4 1 4 pmc in short cores relative to lower abundances max 0 6 pmc in gas from long cores and gas hydrates substantiates recent methanogenesis utilizing modern organic matter deposited in top sediments of this high flux hydrocarbon seep area

implications of elemental concentrations for provenance redox conditions and metamorphic studies of shales and limestones near pueblo co usa abstract major element and some trace element compositions including the ree of shales carbonate rich shales and limestones of late cretaceous age have been analyzed at two outcrops near pueblo co elemental ratios that are characteristic of the provenance of terrigenous debris that are the least variable with changing percent acid insoluble residue vs percent calcite are th cr la co la lu cn and eu eu the ce ce la sc and la cr ratios however are only constant when greater than 30 of a sample is composed of acid insoluble residue at less than 30 acid insoluble residue these elemental ratios increase markedly the th co and th sc ratios are fairly constant from nearly 0 to about 60 acid insoluble residue above 60 residue these ratios increase due to the high concentration of th in the graneros to hartland shales at everhart ranch the average of the th co th sc th cr la co la sc and la cr ratios are similar to those of the mcs mid continent shales and paas post archean australian shales thus these carbonate rich to carbonate poor rocks analyzed in this study contain terrigenous debris that has been derived from granitoids similar to those that supplied debris to the mcs and paas the ce ce ratios are lower and the mn mn log mn sample mn shales fe sample fe shales values are more positive in the more calcite rich bridge creek and ft hays limestones than in the other units suggesting that they formed in an oxidizing environment the ce ce are the highest and the mn values are the most negative in the graneros to hartland shales suggesting that they formed under more reducing conditions the elemental concentration of one sample relative to that of another sample over a few meters distance usually vary in small amounts e g medians of the ratios of the same elements between adjacent samples ranges from 1 06 to 1 70 however the ratio of elemental concentrations between adjacent samples can sometimes be quite large the least variation of elemental ratios between adjacent samples often occurs within the more carbonate poor shales the greatest variation occurs within the limestones thus trying to decipher local movement of elements due to metamorphism in similar carbonate shale limestone sequences should be done cautiously since local elemental variation due to sedimentary processes can be large

the geochemical characteristics and factors controlling the organic matter accumulation of the late ordovician early silurian black shale in the upper yangtze basin south china abstract organic rich black shale of the upper yangtze basin from the late ordovician and early silurian is considered an excellent source rock in south china the formation and preservation conditions of this resource are revealed by its geochemical characteristics in this study geochemical indices including redox indices v v ni v cr v sc and ni co and primary productivity indices p ti and ba al and paleoclimate clastic flux and sedimentary rate analyses are presented to investigate the accumulation mechanism of organic matter redox indices suggest that a stagnant anoxic environment predominated in the upper yangtze basin during accumulation of wufeng and longmaxi formations in contrast ventilated and oxygenated marine conditions pervaded the upper yangtze basin during deposition of linxiang and guanyinqiao formations the concentrations of v and u demonstrate that accumulation of organic matter was mainly controlled by redox conditions besides such factors as clastic fluxes fresh water inflows or a mixed deposition with a rapid sedimentary rate cannot be ignored due to their influences on organic matter enrichment and preservation however weak co variance relationship of toc content and productivity proxies including p ti and ba al demonstrates that the accumulation of organic matter was not controlled by primary productivity results of the present study suggest a depositional model that stresses the importance of tectonic movements and glacial events on the accumulation and preservation of organic matter the model shows that the upper yangtze basin was a semi restricted basin system influenced by the isolation of xuefeng but also it implies that oxygen depleted bottom water of the basin favored the accumulation and preservation of sedimentary organic matter resulting in the formation of organic rich black shale

development of tectonic cyclothems in rift pull apart and foreland basins sedimentary response to episodic tectonism the thickest part of asymmetric rift pull apart and foreland basin fills commonly consists of large scale hundreds to thousands of metres thick tectonically generated cyclothems of fine grained marine lacustrine or longitudinal fluvial deposits and coarse grained transverse braid plain or alluvial fan deposits the appearance of coarse clastics in these basin fills is typically noted as the time of tectonically rejuvenated source area uplift based on the conceptual tie between relief and coarse grain size and on the application of the davis theory of landform development we propose the opposite interpretation that the commencement of fine grained sedimentation above coarse grained deposits in a tectonic cyclothem is the best indicator of renewed tectonic activity this reinterpretation is more consistent with 1 modern examples 2 the consideration of source area and sedimentary basin geomorphology 3 the disparity between the reaction rates of the various environments to subsidence 4 the disparity between the rates of tectonic uplift and erosion and 5 the controls on elastic wedge progradation in our model extensive coarse grained clastic wedge progradation is an indicator of tectonically quiescent phases

structural and geochronological constraints on the mesozoic cenozoic tectonic evolution of the longmen shan thrust belt eastern tibetan plateau 1 the longmen shan thrust belt in the eastern margin of the tibetan plateau underwent deformation of d1 associated with the late triassic collision between the north and south china blocks followed by deformation of d2 and d3 related to the eastward growth of the tibetan plateau the d1 is marked by moderately tight folds f1 spaced cleavage s1 mineral lineation l1 multistage reactivated faults and top to the south thrusting this deformation initiated before 237 ma and ended at 208 ma the 193 159 ma d2 deformation is top to the southeast directed and normal ductile in nature and was associated with the formation of half graben basins the mesozoic deformation of the longmen shan belt was related to the subduction of the paleo tethys oceanic lithosphere followed by the south china block underneath the songpan ganze terrane the d1 was produced in the pro side of the overriding songpan ganze plate most probably driven by slab corner flow above the retreating south china block the d2 and extensional songpan ganze turbidite basin were produced by roll back and migration of the overriding plate above the retreating subduction zone this model for the deformation from d1 to d2 is similar to a mediterranean style model the d3 is characterized by se ward thrusting with stepwise migration of rapid denudation and dextral strike slip faulting during the late cretaceous to present therefore the longmen shan thrust belt involved mesozoic compressional and extensional events that were overprinted by the late cretaceous to cenozoic compressional event

source rock potential and depositional environment of upper cretaceous sedimentary rocks abu gharadig basin western desert egypt an integrated palynological organic and inorganic geochemical study abstract the abu gharadig basin in the northern part of the western desert egypt is among the most important petroleum provinces in egypt here cenomanian to santonian rocks of bahariya formation and abu roash a g members from the gpt 3 well were investigated for their depositional environment kerogen quality petroleum generation potential and thermal maturity by geochemical petrological and palynological methods the sediments of the bahariya and abu roash formations excluding the abu roash f member represent variable shallow marine environments with poor preservation of marine organic matter whereas there is an excellent preservation in the abu roash f member the basal part of this member is characterized by anoxic carbonate rich depositional conditions high toc values up to 7 high hi up to 700 mghc gtoc and liptinite dominated organic matter depletion of iron leads to sulfur incorporation into organic matter which is reflected in high thiophene benzene ratios above sediments are enriched in terrestrial elements fe ti as well as k and mn this pattern and the occurrence of the fresh brackish water algae botryococcus suggests a regression phase during deposition the upper part of the abu roash f member is again characterized by fully marine suboxic conditions and a lower thiophene benzene ratio the source rock section demonstrates lower thermal maturity compared to the above and below sections based on all microscopic pyrolysis and biomarker data this indicates thermal maturity retardation suppression most likely due to a different organic facies and early diagenetic transformation of kerogen as indicated by the geochemical and palynological data the source rock heterogeneity indicates a relatively shallow marine environment where the changes in bottom water conditions are very sensitive to sea level fluctuations residual oil characterization reveals two reservoir compartments which are in the abu roash d and c members the abu roash f source rocks are compared with time equivalent sediments in the tarfaya basin in morocco which represent more distal settings the more proximal group a is characterized by s fe ratios between 0 57 and 0 67 indicating suboxic conditions it has toc and hi values not exceeding 4 and 600 mghc gtoc respectively at variable caco3 contents the more distal tarfaya sediments group b have higher toc and hi as well as high organic sulfur contents group a is higher in terrigenous element concentrations the tmax of immature source rocks ranges from 410 to 415 c in organic sulfur rich samples and from 420 to 430 c in organic sulfur poor samples revealing an important impact of organic facies on maturity parameters furthermore there is an inverse relationship between s fe and al2o3 toc which might become an important tool in paleoenvironmental reconstructions as well as petroleum source rock studies