holocene reef growth in torres strait the platform and fringing reefs of torres strait are morphologically similar to reefs of the northern great barrier reef to the south except that several are elongated in the direction of the strong tidal currents between the coral sea and the gulf of carpentaria surface and subsurface investigations and radiocarbon dating on yam warraber and hammond islands reveal that the initiation and mode of holocene reef growth reflect antecedent topography and sea level history on the granitic yam island fringing reefs have established in some places over a pleistocene limestone at about 6 m depth around 7000 years bp emergent holocene microatolls of porites sp indicate that the reefs have prograded seawards while sea level has fallen gradually from at least 0 8 m above present about 5800 years bp on the warraber island reef platform drilling near the centre indicated a pleistocene limestone foundation at a depth of about 6 m over which reefs established around 6700 years bp reef growth lagged behind that on yam island microatolls on the mature reef flat indicate that the reef reached sea level around 5300 years bp when the sea was around 0 8 1 0 m above present on the reef flat on the western side of hammond island bedrock was encountered at 7 8 m depth overlain by terrigenous mud a progradational reef sequence of only 1 2 m thickness has built seaward over these muds as sea level has fallen over the past 5800 years reef flat progradation on these reefs is interpreted to have occurred by a series of stepwise buildouts marked by lines of microatolls parallel to the reef crest marking individual coalescing coral heads detrital infill has occurred between these this pattern of reef progradation is consistent with the radiocarbon dating results from these reefs and with seismic investigations on the torres reefs

coccolithophore response to oceanographic changes in the equatorial atlantic during the last 200 000 years a deep sea core from the eastern equatorial atlantic meteor core 16772 1 21 s 11 58 w revealed strong primary productivity variations 70 230 gc m2 year based on the relative abundance of the deep living coccolithophore florisphaera profunda with productivity maxima following temperature minima during the last 200 000 years the response of the coccolithophore flora was investigated by relative and absolute abundance records of coccoliths the wind strength and the resulting equatorial upwelling intensity are thought to comprise the most important control of coccolith abundance and species composition which reflects the different abundance of coccolithophores living in the upper or lower photic zone relative abundances of the different species varies widely throughout the core although a wide range of species were present in the different samples three different taxa dominated the assemblage the lower photic zone species f profunda was the most abundant with a mean relative abundance of 49 4 throughout the core the upper photic zone flora were divided into three groups emiliania huxleyi together with small gephyrocapsa 3 m was the second most abundant species group mean 20 8 gephyrocapsa oceanica was the third most important species in the core and had a mean relative abundance of 16 8 all other species together represented a mean of 13 highest absolute abundance of coccoliths number gram sediment occurs in sediments deposited during periods of high sst mainly in warm isotope stages 1 and 5 the accumulation rates of coccoliths number cm2 ky show peaks in isotope stages 1 and 5 but also in some parts of cool isotope stages 4 and 6 high relative and absolute abundance of f profunda were found in warm isotope stages which suggests that a deep nutricline existed and that primary productivity was low absolute and relative abundance records of e huxleyi and small gephyrocapsa 3 m mainly showed higher values in sediments from warm periods the other upper photic zone coccolith species were generally more abundant during periods of low sst particularly in isotope stages 2 4 and 6 which were times of high primary productivity and a shallow nutricline this suggest that e huxleyi and small gephyrocapsa probably were able to live deeper in the water column than most other species during periods of low nutrient supply to the upper photic zone in summary the composition of the coccolith flora can be explained by the nutricline depth level with three different assemblages being recognized a deep photic zone assemblage consisting of f profunda a middle upper photic zone assemblage of e huxleyi and small gephyrocapsa and an upper photic zone assemblage consisting of all other species

sedimentary facies and holocene depositional processes of laura island majuro atoll article i nfo article history the depositional processesthat formed lauraisland majuroatoll marshall islands were reconstructed basedon a facies analysis of island sediments and spine ratios and radiocarbon ages of foraminifera sedimentary facies were analyzed from trenches and drill cores excavated on the island and its adjacent reef flat depositional ages were obtained using benthic foraminifera calcarina whose spines had not been abraded the facies were classified into two types gravelly and sandy the initial sediments of these sites consisted of gravelly facies in the lower horizon and sandy facies in the upper horizon their ages were approximately 2000 cal bp and coincident with the onset of a 1 1 m decline in regional relative sea level which enabled deposition of the gravelly facies half of the sand fraction of the sediment was composed of larger benthic foraminifera the spine ratioshowedthat theirsupply source on the reef flatwaslocated oceansideof theisland the supplysource appears to have been caused by the relative sea level fall this indicates that the studied island was formed by a relative reduction in wave energy and enhanced foraminiferal supply both of which were triggered by the late holocene relative sea level fall

atoll reef island formation and response to sea level change west island cocos keeling islands abstract reef islands around the margin of coral atolls generally comprise unconsolidated holocene sands and gravels overlying a reef flat or cemented conglomerate platform such islands have accreted within the last 3000 4000 years since sea level has reached a level close to present and the reef flat and conglomerate platform have formed island morphology consists of an oceanward ridge a less distinct lagoonward ridge and low lying central depression several alternative models of how such reef islands might have developed are examined in relation to chronology and sediment provenance particularly in the context of the cocos keeling islands where this issue has been debated since darwin visited the atoll which of these models appears most appropriate for an elongate reef island on the atoll margin is assessed using conventional radiocarbon dating of coral shingle and accelerator mass spectrometry ams radiocarbon dating of individual sand grains from pits across west island the dating results suggest that both coral clasts and individual grains of various components are generally reliable and replicable indicators of the chronology of island accumulation implying rapid transport of skeletal material after death of the contributing organisms across the reef flat zone and relatively little reworking the central part of west island appears to have formed first with oceanward accretion up until about 2000 years bp gradual oceanward accretion with lesser lagoonward extension has continued beyond 2000 years bp at the northern and southern ends of the island and a sequence of lagoonward recurving spits has formed adjacent to the inter island passage at the southern end of the island radiocarbon dating of fossil microatolls indicates a gradual fall of sea level over this period which appears to have had little effect on the pattern of island accretion

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

the characteristics and formation mechanism of a regional fault in shale strata insights from the middle upper yangtze china abstract shale is a type of fracture prone rock but few regional faults are observed in shale strata here we investigate a regional detachment fault in the middle upper yangtze muy to understand the formation mechanism of a special regional fault in shale strata based on a lithological mineralogical and mechanical study as well as semi quantitative model of displacement we found that the formation of this detachment fault is closely related to the lithological association and flexural slip processes the lithological association of this detachment fault is characterized by two thick competent layers separated by a thin weak interlayer at both the macroscopic and microscopic scales when these layers are folded the detachment fault zone is commonly present in a thin weak interlayer namely the wufeng formation at the macroscopic scale and primarily along interfaces in laminar siliceous shales lss and secondarily in k bentonite interlayers within the lss at the microscopic scale the regional fault zone is characterized by parallel to strata surfaces and abrupt contacts with the protolith the fabric of the fault core is obviously controlled by the flexural slip intensity and the number of slip events as well as their direction and structural position the natural shale gas obtained from well hd 1 has proven that this regional detachment fault in shale strata is not only a migration pathway for hydrocarbons but also acts as an adsorption state reservoir for free gas from other areas this regional detachment fault in shale strata is likely to advance the shale gas industry and to expand the exploration of conventional gas

evaluation of various satellite sensors for waterline extraction in a coral reef environment majuro atoll marshall islands abstract the ability of five satellite sensor bands ikonos band 4 terra aster bands 3 and 4 and landsat etm bands 4 and 5 was examined to extract the waterline at coral reef coasts majuro atoll marshall islands using different wavelength regions near infrared nir and shortwave infrared swir and different spatial resolutions 4 15 and 30 m after performing georeferencing and normalization of the images density slicing was used to extract the waterline comparisons of extracted waterline positions with ground level data for eight transects and global positioning system gps tracks of the island shorelines showed that nir bands were superior to swir bands because of the characteristics of the coral reef coasts including a lack of foam and suspended sediments which can affect the nir wavelength region if present and the presence of remnant water on reef flats during low tide which can affect the swir wavelength region a linear relationship was found between the estimation errors of waterline positions and the spatial resolutions of the nir sensors analysis on estimation errors and image costs showed that terra aster band 3 was the most cost effective sensor for extracting waterlines with reasonable accuracy the results serve as general guidelines for using satellite derived data to estimate intertidal topography and detect and monitor shorelines in coral reef environments

holocene sea level record on funafuti and potential impact of global warming on central pacific atolls geomorphic features inherited from the mid holocene glacio hydro isostatic sea level highstand that affected the central pacific region influence the susceptibility of atoll islets to potentially enhanced wave erosion associated with rise in sea level from global warming shoreline morphology on multiple islets of funafuti atoll in central tuvalu reflects a relative mid holocene sea level highstand 2 2 2 4 m above modern sea level typical islets are composed of unconsolidated post mid holocene sediment resting disconformably on cemented coral rubble formed beneath now emergent mid holocene reef flats exposed remnants of the lithified islet foundations serve as resistant buttresses protecting the flanks of atoll islets from wave attack islets lacking cemented mid holocene deposits as part of their internal structure are migratory sand cays with unstable shorelines any future sea level rise 0 75 m bringing high tide above the elevation of mid holocene low tide might trigger enhanced wave erosion of stable atoll islets by overtopping the indurated mid holocene reef platforms as analogous threshold relations are inferred for other central pacific atolls the risk of future inundation of island nations cannot be evaluated solely in terms of expected sea level rise with respect to gross islet elevations

sedimentary facies and depositional environment of the middle devonian geneseo formation of new york u s a abstract detailed facies characterization of the middle devonian geneseo formation in the northern appalachian basin nab shows a rich assembly of sedimentary features and textures that suggest shelfal mud deposition in a storm dominated shallow epeiric sea at the time of deposition acadian uplift supplied fine grained detritus from the east and stimulated delta growth as sediment was shed from the hinterland distribution of mudstone facies was controlled by a combination of autogenic processes and a general rise in sea level the vertical and lateral distribution of nine mudstone facies observed in this succession indicates an overall shallowing upwards trend westward progradation of catskill delta with multiple modes of sediment transport and deposition the water column became more oxygenated upsection as indicated by an increase in benthic fauna diversity e g leiorhynchus and orbiculoidea increasing bioturbation diversity e g chondrites palaeophycus planolites teichichnus thalassinoides and zoophycos and a decline of organic carbon content via oxidation and consumption physical and biological attributes of this mudstone dominated succession are used to reconstruct sedimentary processes and depositional conditions although a stratified basin model has previously been proposed for the geneseo formation observations made in this study do not support that interpretation collectively our observations indicate shelfal mud deposition above storm wave base in a relatively energetic environment with persistent lateral transport and advection by oscillatory flow wave induced currents river flood and storm wave generated offshore directed underflows as well as storm setup relaxation flows

production and destruction control of biogenous sedimentation in the tropical atlantic 0 300 000 years b p late pleistocene signals of calcium carbonate organic carbon and opaline silica concentration and accumulation are documented in a series of cores from a zonal meridional depth transect in the equatorial atlantic ocean to reconstruct the regional sedimentary history spectral analysis reveals that maxima and minima in biogenous sedimentation occur with glacial interglacial cyclicity as a function of both 1 primary production at the sea surface modulated by orbitally forced variation in trade wind zonality and 2 destruction at the seafloor by variation in the chemical character of advected intermediate and deep water from high latitudes modulated by high latitude ice volume from these results a pattern emerges in which the relative proportion of signal variance from the productivity signal centered on the precessional 23 kyr band decreases while that of the destruction signal centered on the obliquity 41 kyr and eccentricity 100 kyr periods increases below 3600 m ocean depth

new model of reef island evolution maldives indian ocean a new model of reef island evolution based on detailed morphostratigraphic analysis and radiometric dating of three islands in south maalhosmadulu atoll maldives is presented islands initially formed on a foundation of lagoonal sediments between 5500 and 4500 yr b p when the reef surface was as much as 2 5 m below modern sea level islands accumulated rapidly during the following 1500 yr effectively reaching their current dimensions by 4000 yr b p since then the high circum island peripheral ridge has been subject to seasonal and longer term shoreline changes while the outer reef has grown upward reducing the energy window and confining the islands this new model has far reaching implications for island stability during a period of global warming and raised sea level which will partially reactivate the energy window although it is not expected to inhibit upward reef growth or compromise island stability

response of the inter tropical convergence zone to southern hemisphere cooling during upper ordovician glaciation stable isotope ratios of whole rock carbonates and faunas from three low latitude upper ordovician sections demonstrate a coherent pattern of shifting subtropical and tropical water masses and associated climate belts we suggest that tropical water beneath the inter tropical convergence zone 18o 10 to 15 was isotopically light reflecting high sea surface temperatures sst and reduced sea surface salinity sss subtropical water in both the northern and southern hemispheres is characterised by 18o values from 4 to 6 our interpretation is consistent with the published results from physical chemical modeling of ordovician seawater composition and climate models deriving absolute temperature and salinity values from ordovician 18ocarb data is problematic as they could reflect sst sss ice volume and potentially a variable diagenetic overprint and currently no independent constraints exist for any of these variables the itcz was positioned at 10 n of the equator during the early katian consistent with the likely position of the region of peak sea surface temperature sst during the late katian boda event the itcz moved across the equator to 10 s by analogy with the pliocene this resulted in a symmetrical distribution of sea surface currents about the equator this led to a net increase in heat flow towards the poles and lower latitudinal temperature gradients potentially explaining the migration of warm water faunas to higher southern latitudes during the boda event during the hirnantian the itcz shifted north of the equator resulting in a reduced poleward heat transport itcz position has been proposed as a likely forcing mechanism of neogene glaciation and the evidence from the ordovician suggests a discrete palaeo itcz whose position was controlled by solar insolation and latitudinal temperature gradients linked to ice volume changes and hadley cell dynamics we hypothesize that the position of the itcz was sensitive to the growing hirnantian ice sheet during the late ordovician we propose that latitudinal movement of the itcz during the late ordovician resulted in a major atmosphere ocean circulation re organization higher pco2 estimates for the ordovician caused more extreme changes in this circulation that were the likely primary cause of biotic mass extinction if the monsoon is considered an off equator itcz then we provide direct evidence of an ordovician monsoonal climate

high resolution facies analyses of mudstones implications for paleoenvironmental and sequence stratigraphic interpretations of offshore ancient mud dominated successions abstract the extent of lithofacies variability in fine grained sedimentary rocks is very poorly known in comparison to that present in coarser grained clastic and carbonate successions the absence of this information means that sediments present on continental shelves are rarely considered as integrated systems because fine grained facies such as shales are mostly excluded from sophisticated regional facies models to shed light upon lithofacies and grain size in shale dominated successions so that they can be incorporated into shelf wide depositional models the blackhawk formation of the mancos shale campanian age exposed in the book cliffs utah was investigated using combined field whole rock geochemical optical and electron optical methods these sediments show systematic grain size variations are intensely bioturbated and composed predominantly of detrital clays mainly dioctahedral micas quartz and feldspar with minor pyrite and organic matter they are organized into very thin 10 mm upward fining genetic beds they exhibit both systematic lateral 103 m scale and vertical 10 2 to 100 m scales lithofacies variability preferentially cemented units occur close to sequence boundaries unconformities these cemented units typically contain a very different detrital assemblage including significant quantities of chlorite from the rest of the succession and are located close to levels where there are marked stacking pattern discontinuities overall lithofacies variability is interpreted in terms of deposition occurring on an oxic continental shelf with the coarser grained facies being deposited in proximal settings offshore transition zone in contrast to the finer grained units that were deposited in more distal environments offshore zone storms are interpreted to have been the dominant mechanism dispersing the sediment once deposited the surface layers of the sediment were intensely reworked by burrowing organisms preferential preservation of ichnogenera from mid and lower tiers suggest that the depositional environment was energetic and erosion commonly removed the surface sediment layers prior to deposition of thin 10 2 m storm beds the larger scale 100 m upward coarsening units that are composed of stacked beds are interpreted to be parasequences preferential cementation at levels where large scale stacking patterns change is interpreted to occur at horizons where there were breaks in sediment accumulation and bacterial metabolic processes were able to supply sufficient solutes to fill uncompacted pore space with cement the presence of a very different detrital assemblage in these units suggests that winnowing occurred despite their relatively innocuous appearance in the field these surfaces are likely to be significant bypass surfaces over which sediment was delivered to the deeper parts of the basin during times of relative lowstand of sea level

porosity evolution of sandstones related to vitrinite reflectance abstract porosity of potential reservoir sandstones undergoes a complex multistage evolution or diagenesis during burial organic matter deposited in shales also changes during burial an irreversible process called thermal maturation measures of thermal maturation such as vitrinite reflectance r o are routinely available for subsurface samples so the question is can vitrinite reflectance be used to predict the evolutionary stage and quality of sandstone porosity prior to drilling no universal quantitative correlation between r o and sandstone porosity can exist for there are too many variables however r o can indicate the stage of sandstone porosity evolution the first stage is marked by progressive destruction of primary porosity and coincides with low levels of thermal maturation of kerogen up to an r o of 0 4 0 5 the second stage involves dissolution and flushing away of cements and detrital minerals by acid solutions to create secondary porosity the acids are produced by decarboxylation of kerogen in shales in the r o range of about 0 4 0 7 the third stage involves destruction of secondary porosity by cementation and compaction or ideally filling of secondary porosity by oil because the oil window begins at an r o of about 0 6 that is about where the third stage begins it continues until porosity and permeability are reduced to low noneconomic levels at which point the diagenetic evolution has reached porosity basement somewhere between r o 1 4 and 2 5 above r o 2 5 are unmistakable indications of incipient metamorphism in the sandstones because r o can be modeled and projected into undrilled parts of a basin it should be possible to predict the stage of porosity evolution of sandstones in advance of drilling a useful capability

mud rich density driven flows along an early ordovician storm dominated shoreline implications for shallow marine facies models abstract dynamic physical and biological seafloor processes shape the three dimensional stratal architecture of modern and ancient mud dominated continental shelves when evaluating a mudstone unit as a potential source reservoir or seal it is imperative to understand the physical biological and chemical seafloor processes that control mudstone depositional fabric and diagenesis this study presents sedimentological ichnological and geochemical data of exceptionally preserved mudstone originating from hyperpycnal and possible combined flow deposits in the lower ordovician tremadocian beach formation bell island group newfoundland seven mudstone facies are described based on textural compositional and ichnological characteristics mudstone deposits interpreted to originate from hyperpycnal flows are well cemented exhibit high chlorite illite ratios and contain sharp grain size changes commonly forming beds with tripartite subdivisions deposits of wave enhanced sediment gravity flows are in contrast poorly cemented illitic mudstone these mudstone facies exhibit decimeter thick wave or combined flow structures within siltstone and very fine sandstone beds as well as laterally discontinuous nonbioturbated mudstone layers beds of this facies have abundant mudstone on mudstone and mudstone on sandstone erosional contacts low organic carbon loading from the nonvegetated early paleozoic hinterland combined with a high reworking frequency on a shallow marine wave dominated shelf is inferred to have resulted in high remineralization efficiency and low preservation potential of reactive organic carbon burial efficiency and bioavailability of organic matter are considered to be the critical variables controlling infaunal colonization and bioturbation in mud dominated open coastline paleoenvironments this work demonstrates that ancient fine grained coastal systems are incompletely incorporated into sequence stratigraphic models owing to their atypical proximal to distal facies relationships it is proposed that the spatial organization of fine grained sediment and facies architecture in such systems are controlled by 1 frequency of sediment supply events 2 direction of mud transport 3 diagenetic reactivity of minerals and bioavailable organic carbon and 4 residence time of mineral grains and organic matter close to the sediment water interface

geochemistry of the extremely high thermal maturity longmaxi shale gas southern sichuan basin abstract the marine shale of the silurian longmaxi formation in southern sichuan basin china is characterized by its huge thickness 100 600 m high toc values 0 35 18 4 favorable types of organic matter i and ii1 high ro values 1 8 4 2 abundant brittle minerals average 56 3 and strong gas generation intensity particularly its bottom section which has toc 2 and thickness of 20 70 m has recently been a main target for shale gas exploration and development geochemical parameters of 13 gas samples from longmaxi shale from 10 wells were analyzed in this study wetness of the gas molar fraction of ethane through pentanes in total gaseous hydrocarbon is only 0 24 0 70 making the longmaxi shale gas among the driest in the world carbon isotopic compositions of the alkane gases from longmaxi shale are characterized by 13c1 13c2 13c3 with the most positive 13c1 values in the world a positive relationship was observed between its 13c1 and 13c2 values reflecting the extremely high thermal maturity of the source rock 2hch4 values range from 140 to 151 and the 2hc2h6 values range from 130 to 173 the hydrogen isotopic compositions were mainly characterized by 2hch4

late ordovician global warming the boda event there is substantial evidence for mid ashgillian global warming before the latest ordovician hirnantian glaciation as shown by the movement of previously lower latitude benthic faunas such as trilobites and brachiopods to progressively higher latitudes and by an increase in endemic faunas at low latitudes this is shown by faunal dynamics on several paleocontinents and endorsed by published evidence of warmer water sediments from gondwana and elsewhere we term this global warming the boda event

the mode and timing of windward reef island accretion in relation with holocene sea level change a case study from takapoto atoll french polynesia abstract takapoto atoll northern tuamotu islands french polynesia central pacific was selected as a test area to clarify the conditions of atoll island accretion in relation to mid to late holocene sea level changes surveys were conducted along two distinct cross island profiles on the windward coast of the atoll in addition the stratigraphy of an ocean facing islet was described from an excavation in order to reconstruct the successive island accretionary stages at both sites the basement of the atoll rims consists of conglomerate pavements on which lie shingle ridges reaching 4 m in elevation stratigraphic analysis of the excavated ridge reveals alternation of gravelly sand supported to gravel dominated sediments the chronology of island accretion is based on dating of 41 u th surface and excavated coral specimens ridge initiation occurred from about 1000 yr bp when sea level was close to its present position shingle deposits progressively prograded from the lagoon margins oceanwards and were partially cemented at their bases cementation may have increased the resistance of the islets to erosion as a result some island lands accumulated and have persisted over the last millennium the modern gross island morphology was acquired during the last 500 years this model can be considered to be of regional value for the northern tuamotu islands adjusted for local thermal subsidence hydroisostasy and or lithospheric flexure compared to some other indo pacific reef islands island initiation at takapoto appears to be have been delayed by 2 to 4 millennia probably in response to retardation in the reef catching up with mid holocene sea level dating of individual coarse grained coral clasts allowed the major wave surge events that have hit takapoto to be identified for the last millennium the use of gravels results in the identification of a greater number of medium energy surge impacts when compared with megaclast based records the frequency of storm events identified is consistent with that derived from historical observations severe storms have a very low frequency of occurrence one to two events per century on average

stem aem evidence for preservation of burial diagenetic fabrics in devonian shales implications for fluid rock interaction in cratonic basins u s a abstract fabrics microstructures and compositions of authigenic illite rich clays in devonian intracratonic basin shales were examined by x ray diffraction xrd scanning electron microscopy sem and scanning transmission electron analytical electron microscopy stem aem methods in order to relate the extent of clay diagenesis to the timing of mudstone system closure and to reconcile conflicting radiogenic and paleomagnetic ages obtained from these shales and associated limestones and bentonites authigenic illite in these devonian shales is similar to post transition illite rich mixed layer illite smectite i s in gulf coast and other young basin mudstones that have formed through replacement of detrital smectite or smectite rich i s without subsequent diagenetic modification the clay matrix is composed of subparallel intergrowths of illite rich crystals 30 200 a thick with low angle grain boundaries and defects at layer terminations contrast in some lattice fringe images is consistent with r1 r2 and r3 ordered mixed layer i s electron diffraction patterns indicate partially disordered 1md stacking sequences with significant turbostratic stacking and mixed layering the illite rich material is k and aldeficient and si enriched relative to ideal muscovite preservation of burial diagenetic authigenic mixed layer i s microstructures in these devonian shales implies that they have remained effectively closed systems following the smectite to illite transformation later alleghenian ca 300 ma tectonic or fluid flow events recorded by authigenic minerals in bentonites and carbonate lithologies throughout the u s midcontinent are apparently not recorded in these devonian shales preservation of diagenetic fabrics indicates that radiogenic isotope dating of cratonic basin shales should yield syndepositional to early burial diagenetic ages corresponding to the timing of i s authigenesis

pore characterization and shale facies analysis of the ordovician silurian transition of northern guizhou south china the controls of shale facies on pore distribution abstract the ordovician silurian wufeng longmaxi formations in the upper yangtze platform have been considered as the most promising shale play in china however few studies of detailed shale facies and their influence on pore distribution have been conducted therefore it is important to describe the heterogeneity of shale facies in detail and elucidate their relationship to pore networks and development seven distinct facies were identified on the basis of their characteristic physical biological and chemical attributes ion milled samples from all facies were examined with sem for identification of pore types point counting was used to quantify porosity four major pore types appear dominant framework pores phyllosilicate framework pf pores intrapores within inorganic grains and organic matter om pores due to variability in composition and depositional setting of the different facies pore networks are not uniform framework pores between detrital grains and pf pores are widespread in bioturbated claystones pores in black siliceous shales are dominated by framework pores supported by authigenic silica most of these are filled with kerogen bitumen that is host to foam and bubble type om pores intrapores within calcite or dolomite grains are common in fossiliferous mudstones and black dolomitic siltstones but are isolated and do not contribute to productive porosity in muddy siltstones pf pores are well developed within silty bands initial framework pores within silty beds or laminae however were subsequently cemented by calcite or destroyed by compaction as most of primary pf pores and primary frameworks pores are lost during compaction porosity is highly dependent on the population of framework pores between authigenic quartz grains secondary cracking of amorphous organic matter added porosity after initial infilling of porosity by oil and bitumen migration therefore porosity is mainly controlled by abundance of authigenic silica and toc in spite of differences of burial diagenesis among various facies understanding these main controls on porosity should be helpful to predict and find and more porous facies and have a significant impact on future gas exploration in the wufeng longmaxi formations

geohydrology of the laura fresh water lens majuro atoll a hydrogeochemical approach in small limestone islands the depositional history and subsequent chemical interactions between ground water and the aquifer host rock play critical roles in the occurrence movement and chemical quality of ground water the hydrogeochemistry of the laura fresh water lens majuro atoll marshall islands is an example of these relations laura is underlain by two principal hydrologic units the upper unit is a back reef marginal lagoonal deposit which formed during the holocene interglacial stage it is composed of moderately permeable carbonate sediments the lower hydrologic unit consists of highly permeable limestone that was subaerially exposed most likely during a pleistocene glacial lowstand similar stratification is found at bikini and enewetak atolls the upper hydrologic unit contains a calcium bicarbonate rich fresh water lens in which a potable fresh water nucleus as much as 14 m thick occurs on the lagoon side of the island storage in the fresh water nucleus ranged from 1 70 x 10 6 to 2 08 x 10 6 m 3 during 1984 1985 ground water occurrence and flow are governed by an asymmetric distribution of lithofacies about the longitudinal axis of the island and an abrupt increase in permeability at the contact between the upper and lower hydrologic units the highly permeable lower hydrologic unit contains sea water and truncates the fresh water sea water mixing zone the fresh water lens and associated fresh water sea water mixing zone are the site of continuously occurring diagenetic reactions that significantly affect the porosity and permeability of the aquifer non equilibrium dissolution precipitation reactions coupled with variations in co 2 input control the chemical evolution of laura ground water at the present rate of chemical weathering 465 m 3 of sediment are being dissolved and transported to the sea by ground water each year this dissolution results in an annual increase in porosity of 0 01 the primary factors controlling the occurrence and flow of ground water in the leeward reef islet of laura are 1 the depositional history of the upper hydrologic unit which has resulted in a greater accumulation of low permeability fine grained sediments beneath the lagoon side of the island and a high to low permeability coarse to fine grained sediment gradation between the ocean and lagoon and 2 the diagenetic history of the lower hydrologic unit which has resulted in a highly permeable basement

the record of late pleistocene biogenic sedimentation in the eastern tropical pacific ocean we have generated 300 kyr records of biogenic opal calcite and organic carbon corg for three cores in the eastern and central equatorial pacific ocean and have compared the records to determine whether common periods of biogenic sedimentation have occurred throughout the region we find that corg has been deposited in common pulses throughout the area while opal has a much more local pattern of variation calcite varies regionally but the record is shaped by superimposed dissolution and productivity processes the most intense corg peak occurs at 18 ka and can have greater than 2 times the holocene corg content other major corg peaks occur 150 ka and perhaps at 280 ka we have compared the corg record in one of the cores v19 28 to a model deepwater oxygen record developed from 13c data in the nearby v19 30 to test whether the corg record has been mostly shaped by degradation or by the rain of organic matter from the euphotic zone we found no coherence between the two records implying that the corg record is primarily a measure of productivity by comparing the opal calcite and corg records in v19 28 a core which is at or above the lysocline we found that both increased calcite and opal deposition matches high corg accumulation we also found however that the calcite and opal records were uncorrelated so that episodes of high opal deposition do not necessarily accumulate calcite rapidly we hypothesize that at least two different plankton communities have been dominant in the waters above this site one rich in opal secreting plankton and one more dominated by calcite producers the opal rich plankton community was dominant during the intervals 10 15 ka and 35 60 ka supplement data table 2 is available with entire articleon microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document p88001 2 50 payment must accompany order

patterns of sediment composition of jamaican fringing reef facies recent carbonate sediments from jamaican north coast fringing reefs were collected along three parallel traverses in the vicinity of discovery bay each traverse extended from near shore across the back reef reef crest and fore reef to a depth of 75 m relative abundances of the biotic constituents vary between sites reflecting general patterns of reef community composition the sediment is dominated by highly comminuted coral fragments 27 1 to 63 1 plates of the calcareous green alga halimedu 0 4 to 38 7 coralline algae 4 7 to 16 2 and the encrusting foraminiferan homotremu rubrum 0 7 to 9 5 with lesser amounts of other taxonomic groups non encrusting foraminifera 1 3 5 5 molluscs 1 4 7 0 echinoderms 0 9 5 0 coral fragments coralline algae and particles of homotrema rubrum dominate the sediments of the shallow portions of the fore reef 5 15 m whereas plates of hulimedu are most abundant in sediments from the back reef and deeper portions of the fore reef 2 24 m q mode cluster analysis using sediment constituent data resulted in the delineation of four reef biofacies over the depth range of this study 1 75 m

fabric anisotropy induced by primary depositional variations in the silt clay ratio in two fine grained slope fan complexes texas gulf coast and northern north sea article i nfo high resolution x ray texture goniometry hrxtg has been used to quantify the alignment anisotropy of phyllosilicate minerals in a series of diagenetically altered mudstone samples from the deep subsurface of the texas gulf coast and the northern north sea the sampled formations have undergone a simple burial history with no overprint of tectonic deformation that may have influenced the phyllosilicate orientation observations have been made in two constrained temperature windows 148 150 c north sea data and 169 210 c texas gulf coast wherein less than 20 smectite remains in the mixed layer phase illite smectite quantitative x ray powder diffraction xrpd shows quartz which is dominantly detrital and phyllosilicate content having an inverse relationship quantified illite smectite fabric intensity phyllosi licate alignments ranges from low alignment values of 2 42 m r d multiples of a random distribution to high alignment values 6 75 m r d and chlorite kaolinite ranges from 1 80 to 6 46 m r d we propose that the broad range of phyllosilicate fabric intensity observed reflects the range of quartz phyllosilicate ratios that are the imprint of depositional setting bedform truncation and initial grain size detrital quartz acts to disrupt fabric intensity by being non platy producing areas sheltered from effective stress pressure shadows and acting as a matrix support there is no evidence that bioturbation is a significant control on phyllosilicate alignment in these quartz phyllosilicate mixtures these findings have important implications for the role of grain scale alignment on seismic anisotropy in mudstone systems fabric intensity in post diagenetic samples can be predicted from 1 quartz content and 2 total clay content where

dissolution of marine shales and its influence on reservoir properties in the jiaoshiba area sichuan basin china abstract the dissolution of marine shales and its influence on reservoir physical properties was revealed based on shale samples from the ordovician silurian wufeng and longmaxi formations in the southeast of the sichuan basin china three kinds of gas storage spaces were formed by dissolution including intergranular dissolution interd pores intragranular dissolution intrad pores and dissolution microfractures dmf the diameters of the interd and intrad are 10 2 72 4 m and 0 13 1 52 m respectively the apertures of the dmf are between 0 5 and 11 2 m the dissolution effect resulted in a diagenetic environment for quartz cementation and a material basis for calcite veins the main controlling factors of the dissolution effect are the mineral constituent content in the matrix the amount of organic matter and the strata burial rate dissolution pores and fractures play important roles in shale gas enrichment and migration the porosity of shale reservoirs with dmf is twice the porosity of reservoirs without dmf and the spaces formed by dissolution pores and fractures are well connected a new model for shale gas flow in shale reservoirs was proposed which provides a new understanding for the connection between organic material pores and the results can be used for shale reservoirs worldwide

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

heterogeneity of intergranular intraparticle and organic pores in longmaxi shale in sichuan basin south china evidence from sem digital images and fractal and multifractal geometries abstract previous studies have determined many types of pores in shale such as organic pores inorganic pores and microfractures in this study pores are classified as intergranular intraparticle and organic pores based on the location of their occurrence the heterogeneities of the three pore types and their effects on the occurrence of shale gas which is of utmost practical importance for shale gas exploration and development are discussed in this study the three types of pores are quantitatively characterized using fractal and multifractal methods the mean fractal dimension and mean width of the multifractal spectrum of these pores are found to be different i e 1 5985 and 1 665 for intraparticle pores 1 5869 and 1 475 for intergranular pores and 1 6 and 1 3725 for organic pores intraparticle pores have the highest heterogeneity intergranular pores have intermediate heterogeneity and organic pores have the lowest heterogeneity sem images show that organic pores have good connectivity homogeneous distribution and small range of aperture change but have the lowest heterogeneity even where pores are abundant thus they provide the largest shale gas occurrence space in contrast intergranular pores are less abundant have lower connectivity and have higher heterogeneity than organic pores thereby providing a relatively smaller shale gas occurrence space finally intraparticle pores are the least abundant and possess the poorest connectivity largest range of aperture change and highest heterogeneity of the three pore types thereby providing the smallest shale gas occurrence space we conclude that organic pores are crucial to the occurrence of shale gas and can provide a new index for the evaluation of shale gas exploration and development

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

a morphodynamic model of reef island development on atolls abstract reef islands on the rims of atolls are deposits of unconsolidated reef sediment that have accumulated as a result of sediment transportation processes reef islands appear especially vulnerable to changing environmental conditions particularly regarding the impact of sea level rise the morphodynamic processes involved in the development of these landforms however are poorly understood and difficult to observe over long time periods several conceptual models of reef island development have been proposed that offer insights into reef island behaviour particularly where these models can be implemented in a computational framework this paper presents an aggregated scale behaviour oriented model that simulates sediment accumulation on an atoll rim a requirement of the behaviour based modeling approach is that the model parameters need to be determined for each application of the model an inversion algorithm is used to estimate values for model parameters including the maximum volume of the island and the sediment production rate the model provides a framework for experimentation with modes of island development links sediment production to the observed morphology of the reef island and quantifies the limits to reef island development

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

early diagenetic pyrite morphology in a mudstone dominated succession the lower jurassic cleveland ironstone formation eastern england abstract diagenetic pyrite in the mudstones and ironstones of the lower jurassic cleveland ironstone formation of eastern england exhibits two distinct morphologies framboidal pyrite commonly associated with organic matter and euhedral pyrite associated with detrital clay pellets these two morphologies are mutually exclusive in occurrence framboidal pyrite is present in clay rich mudstones ooidal ironstones apatite rich units and some silt rich mudstones euhedral pyrite is present in silt rich and sand rich mudstones 34s isotopic analysis of six samples of pyrite suggests that both types of pyrite morphology precipitated during early diagenesis from porewaters with open access to overlying sea water although both probably acted as sites for continued pyrite precipitation during burial it is proposed that framboidal pyrite precipitated from iron dominated porewaters at sites of sulfide supply i e in the region of organic matter as a result of bacterial sulfate reduction where locally sulfide production rates were high enough for porewaters to reach supersaturation with respect to fes euhedral pyrite also precipitated from iron dominated porewaters but sulfide production rates from organic matter was such that fes saturation was not reached at the sites of sulfide production instead euhedral pyrite was precipitated directly from porewater when fes2 saturation was reached the control over pyrite morphology was probably the amount and reactivity of the organic matter within the deposited sediments the sand rich mudstones contained less reactive organic matter due to clastic dilution and deposition in shallower environments with o2 rich bottom waters the ironstones and apatite rich units were deposited under very low sedimentation rates and as a result organic matter contents were very low and iron reduction dominated early diagenesis which inhibited sulfate reduction the presence of minor framboidal pyrite within these units however suggests that sulfide reduction took place in micro environments during early diagenesis

comparative molecular biomarker assessment of phytoplankton paleoproductivity for the last 160 kyr off cap blanc nw africa abstract we report high resolution molecular abundance data for alkenones dinosterol long chain diols and n alkanols from odp site 658 20 45 n 18 35 w 2263 m water depth these data are compared with previously reported data for toc chlorins opal and long chain n alkanes the contents and mass accumulation rates mars of chlorins are used as total phytoplankton productivity proxies while the contents and mars of opal dinosterol alkenones and diols are used as productivity proxies for diatoms dinoflagellates haptophytes and eustigmatophytes diatoms respectively five high productivity intervals hpis are identified two at the glacial interglacial transition boundaries of 132 122 and 15 8 ka two within the warmer periods of mis 3 50 30 ka and the late holocene 4 0 ka and one within the glacial period of mis 4 67 60 ka productivity was lowest during both the penultimate glacial maximum of mis 6 150 140 ka and the last glacial maximum 22 18 ka as revealed by both the total phytoplankton and individual phytoplankton productivity indicators phytoplankton community structure changed significantly over the last 160 kyr the termination i ii hpis were characterized by higher opal content possibly reflecting increased diatom contributions to total productivity eustigmatophyte diatom and haptophyte contributions were higher during mis 5 but decreased toward the holocene dinosterol revealed an opposite trend with the highest contribution in the holocene we ascribe such changes in phytoplankton communities to the effects brought about by the varying amounts and nature of nutrient inputs contributed regionally by eolian dusts river influxes ocean currents and upwelling water masses

incremental accretion of a sandy reef island over the past 3000 years indicated by component specific radiocarbon dating 1 low lying reef islands appear particularly threatened by anticipated sea level rise and determining how they formed and whether they are continuing to accumulate sediment is essential for their sustainable management depositional chronology of warraber island a small sand cay in torres strait australia is re examined based on ams radiocarbon dating of specific skeletal components whereas radiometric dating of bulk sand samples indicated one or more discrete phases of mid late holocene deposition component specific ams radiocarbon dating of sand grains indicates sustained incremental growth over the past 3000 years ages on gastropods that lived on the reef flat around the island indicate continuing sediment production and island progradation in contrast to bulk ages and other components produced at greater distances growth of sand cays depends on the rate and pattern of sediment supply which are functions of the local ecology of the surrounding reef and reef flat and hydrodynamic constraints

hydrographic and current observations on the continental slope and shelf of the western equatorial atlantic abstract hydrographic and current profiling data from december 1980 and current meter data obtained between september 1980 and november 1981 from the continental slope and shelf of the western equatorial atlantic between 2 and 7 n are used to describe the character of the north brazil coastal current nbcc system hydrographic data and the profiling results show that the nbcc has three distinct branches during the boreal fall in the near surface a strong current flows northwestward parallel to the coast at least as far as 6 n current speed within the near surface nbcc over a one year period were between 75 and 250 cm s 1 while the transport in december 1980 was between 15 and 20 106 m3 s 1 there was a southeastward near surface flow farther offshore which appears to be the return of the nbcc the ultimate destination of which is the north equatorial countercurrent offshore of the southeastward flow was a portion of a low salinity lens of amazon water the waters within and below the thermocline

global variations of surface ocean productivity in low and mid latitudes influence on co2 reservoirs of the deep ocean and atmosphere during the last 21 000 years based on detailed reconstructions of global distribution patterns both paleoproductivity and the benthic 13c record of co2 which is dissolved in the deep ocean strongly differed between the last glacial maximum and the holocene with the onset of termination i about 15 000 years ago the new export production of low and mid latitude upwelling cells started to decline by more than 2 4 gt carbon year this reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric co2 as recorded in ice cores and with a slight delay of more than 1000 years to a large scale gradual co2 depletion of the deep ocean by about 650 gt c this estimate is based on an average increase in benthic 13c by 0 4 0 5 the decrease in new production also matches a clear 13c depletion of organic matter possibly recording an end of extreme nutrient utilization in upwelling cells as shown by sarnthein et al 1987 the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades which in turn was linked via a shrinking extent of sea ice to a massive increase in high latitude insolation i e to orbital forcing as primary cause

silica diagenesis in the lower paleozoic wufeng and longmaxi formations in the sichuan basin south china implications for reservoir properties and paleoproductivity abstract silica diagenesis is one of the most important aspects of black shale diagenesis and critically controls the reservoirs properties of black shales three stratigraphic sections of the wufeng and longmaxi formations in the sichuan basin along a proximal to distal transect were investigated to study quartz types and their silica sources as well as their influences on reservoirs properties including rock mechanical properties and porosity preservation six types of quartz including detrital quartz recrystallized radiolaria siliceous fossil fragments microcrystalline quartz quartz overgrowth and hydrothermal quartz veins were identified based on their occurrences and morphologies under the petrographic microscope and scanning electron microscope and cathodoluminescence color and intensity original biogenic silica now exists as recrystallized radiolaria and microcrystalline silica in the mudstone matrix and follows systematic distribution patterns both laterally and stratigraphically the biological origin of this silica component is supported by the presence of recrystallized radiolaria with preserved spines preservation of ghosts of the central capsule serrated edges reflecting the spherical lattices of the outer shell and in addition preserved sponge spicules a further source of silica for microcrystalline quartz formation was silica released in the course of clay mineral smectite to illite transformation the different types of quartz make different contributions to the reservoir properties of shales with microcrystalline quartz having the most important impact microcrystalline quartz enhances the rock mechanical properties of shales and protects initial porosity from mechanical compaction through a rigid framework of interconnected diagenetic silica grains pores between microcrystalline quartz grains are shielded from complete mechanical compaction and provide space for accumulation of bitumen and oil later in burial history subsequently these pore filling organic matter develop secondary organic nanopores at higher thermal maturity although biogenic silica content has been used as a paleoproductivity proxy the method used to calculate it is based on questionable assumptions and model parameters need to be fine tuned for a given shale succession on the basis of petrographic observations in addition the commonly observed positive correlation between total organic carbon toc and biogenic silica is invalid for very low sedimentation rates and extremely high concentrations of biogenic silica from low to extremely high biogenic silica content in organic rich sediments a parabolic relationship between toc and biogenic silica should be common

climatically forced organic carbon burial in equatorial atlantic and pacific oceans over the past ten years sedimentary geochemists have noted that climate changes associated with pleistocene glaciations have had a pronounced effect on the rate of organic carbon burial found in the tropical oceans1 4 in particular two to five times higher organic carbon accumulation rates have been observed for the 18 kyr bp glacial maximum than for the holocene in several short sediment cores from both oceans see fig 1 here i present 300 kyr time series for organic carbon mass accumulation rate from four sediment cores two each from the equatorial pacific and atlantic and show that orbital forcing of global climate has strongly affected the rate of organic carbon burial in the equatorial oceans

pore structures of different types of shales and shale gas exploration of the ordovician wufeng and silurian longmaxi successions in the eastern sichuan basin south china abstract shales from ordovician wufeng and silurian longmaxi groups in the sichuan basin were analyzed by using the field emission scanning electron microscopy helium pycnometry and low pressure gas adsorption experiments there are mainly three lithofacies in the studied shale reservoirs clay rich siliceous shale s 3 argillaceous siliceous mixed shale m 2 and silica rich argillaceous shale lithofacies cm 1 the organic rich s 3 shales have the highest porosity averaging 5 4 the largest pore volume averaging 0 024 ml g and the highest specific surface area averaging 21 6 m2 g organic matter om pores contribute 62 6 to the porosity of s 3 shales m 2 shales have the moderate pore structure with porosity averaging 4 3 pore volume averaging 0 019 ml g and specific surface area averaging 16 7 m2 g organic matter and clay minerals contribute 49 5 and 36 8 to the porosity of m 2 shales respectively the cm 1 shales have the lowest porosity averaging 4 1 the smallest pore volume averaging 0 017 ml g and the lowest specific surface area averaging 15 6 m2 g the organic lean cm 1 shales are dominated by clay mineral pores clay minerals contribute 56 to the porosity of cm 1 shales om pores are well developed in the s 3 shale lithofacies while most of om pores are destroyed or compacted in cm 1 shale lithofacies the effect of compaction on porosity of cm 1 shales is stronger than that of m 2 and s 3 shales because of the highest clay minerals content and the lowest siliceous minerals content considering the pore spaces and hydraulic fracturing operation the s 3 shales is more suitable to shale gas exploration than m 2 and cm 1 shales certainly the m 2 and cm 1 shales also have certain amounts of hydrocarbon storage capacity and could be considered as the candidate targets for shale gas exploitation

astronomic timescale for the pliocene atlantic δ18o and dust flux records of ocean drilling program site 659 high resolution benthic oxygen isotope and dust flux records from ocean drilling program site 659 have been analyzed to extend the astronomically calibrated isotope timescale for the atlantic from 2 85 ma back to 5 ma spectral analysis of the 18o record indicates that the 41 kyr period of earth s orbital obliquity dominates the pliocene record this is shown to be true regardless of fundamental changes in the earth s climate during the pliocene however the cycles of sahelian aridity fluctuations indicate a shift in spectral character near 3 ma from the early pliocene to 3 ma the periodicities were dominantly precessional 19 and 23 kyr and remained strong until 1 5 ma subsequent to 3 ma the variance at the obliquity period 41 kyr increased the timescale tuned to precession suggests that the pliocene was longer than previously estimated by more than 0 5 m y

geologic time series from deep sea sediments time scales and distortion by bioturbation abstract in order to evaluate the time and frequency domain characteristics of geologic time series obtained from deep sea sediments two important problems must be considered first an accurate time scale must be established for the sediment records to be studied an accurate time scale is a basic requirement for such techniques as spectral and cross spectral analysis secondly the distortion of a geologic time series by sedimentation processes such as bioturbation must be considered if inferences are to be made about the mechanisms controlling climatic and oceanographic processes reflected in the geologic record recently it has been suggested that the periodic components in paleoclimatic records which can be related to variations in the earth s orbital parameters can be used as a means for providing very detailed control for late pleistocene sediment sections a time scale is estimated by tuning an individual frequency component in a climate record to an orbital parameter the tuning procedure commonly uses the technique of bandpass filtering which removes all frequency components except the one equivalent to an orbital parameter and then adjusting the geologic time scale so that the filtered record and orbital record align since bandpass filtering will produce a periodic record from any data set a question is raised as to the circularity of this tuning approach a series of numerical experiments using synthetic time series are used to determine if the tuning of a geologic record artificially induces improved correlation and increased periodic character in a climatic record these experiments indicate that the tuning does not artificially induce these effects thus it is suggested that the careful use of orbital tuning provides a powerful means of defining a geologic time scale the degree to which bioturbation distorts a paleoclimatic record is studied by comparing the spectra of oxygen isotopic records obtained from cores with sedimentation rates ranging from 1 to 12 cm 1000 yr 1 it is shown that the systematic change in the variance spectra of these records that is predicted by models of bioturbation cannot be observed for sedimentation rates greater than 2 cm 1000 yr 1 this can be explained in part if bioturbation is a function of sedimentation rates if this is the case then bioturbation must proceed to depth of tens to hundreds of centimeters however it seems likely that the degree to which bioturbation alters the climate signal preserved in deep sea sediment cores has been overestimated

carboxylic acid anions in formation waters san joaquin basin and louisiana gulf coast u s a implications for clastic diagenesis abstract carboxylic acid anions caa in formation waters are of interest to studies of clastic diagenesis because of their ability to buffer formation water eh and ph and thus substantially contribute to controls on carbonate mineral stability and their ability to complex and transport al and si from the site of aluminosilicate mineral dissolution during diagenesis carboxylic acid anions are also extremely important to the aqueous geochemistry of ca fe mn pb and zn some formation waters from sedimentary basins contain high concentrations of caas the analyses of 20 formation waters from the san joaquin basin california and 20 formation waters from the louisiana gulf coast basin presented in this study show concentrations as high as 8100 ppm monofunctional and 370 ppm difunctional cca by comparison previously reported analyses indicate monofunctional caa occir in concentrations up to 10 000 ppm and difunctional caa may occur in concentrations up to 2610 ppm analyses of drilling muds and scale soaps presented in this study show that few if any difunctional caa in the study area can be attributed to contamination from these sources additionally aqueous extracts of crude oils contain both mono and difunctional acid anions as do the aqueous and petroleum phases of hydrous pyrolysates previously unreported dissolution experiments equilibrium computer simulations and hydrous pyrolysis experiments support those already published and suggest that caa are generated during thermal maturation of kerogen and expelled from the shale along oil wet microfractures upon entering the water wet sandstone pore the hydrophilic caa partition into the aqueous phase organic inorganic reactions may occur which from caa metal complexes because the complexes are hydrophobic they partition in the petroleum phase where present carboxylic acid anions are of great importance to clastic diagenesis over the temperature range in which they dominate fluid alkalinity certainly no other viable mechanism has been advanced which adequately explains the observed aluminosilicate mineral dissolution with subsequent mass transfer of a1 as well as the carbonate mineral diagenetic successions observed in sand shale systems world wide the utility of modeling these observations of organic inorganic diagenesis is limited only by the ability to model the concentration and distribution of caa through space and time

spatial and temporal variations in wave characteristics across a reef platform warraber island torres strait australia a field experiment was conducted at warraber island torres strait australia to investigate spatial and temporal variations in wave characteristics and energy across a mesotidal coral reef platform measurements of water depth were obtained using five pressure sensors deployed across a 2 7 km section of reef flat from july 3 5 2001 the reef surface was uneven and consisted of an outer reef flat a central reef flat depression an inner reef ramp a palaeo reef surface and the shoreline water levels decreased landward across the platform with tide ranges at the shoreline being almost 50 lower than at the outer reef flat rising and falling tides were characterised by a bimodal energy distribution with both short period 0 3 s and wind 3 8 s waves present higher water levels were dominated by wind waves the highest waves occurred at high tides associated with nocturnal tidal cycles with hs decreasing from 0 5 to 0 2 m from the outer reef flat to the shoreline wave energy at swell 8 20 s and infragravity 20 s frequencies was negligible across the reef platform although there was evidence of wave groups at higher water levels reef geometry and changes in water level determine the magnitude of wave energy on the reef platform up to 85 95 of incident wave energy is attenuated by the central reef flat depression at high and low tide respectively and strong linear relationships exist between hs and h at all locations both wave height and wave type are strongly depth dependent critical reef rim depths required to produce hs of a given size vary spatially across the reef rim due to variations in reef topography a distinct depth related threshold exists at which short period and wind wave dominance reverses over a 14 day spring neap tidal cycle the time of occurrence of wave action diminishes across the reef platform to the shoreline larger waves hs 0 2 m occur for only 9 of time at the outer reef flat and for less than 0 5 over the remaining reef platform this implies that on mesotidal reef platforms sediment entrainment and transport are severely constrained under normal wave energy conditions and significant change is likely restricted to extreme events

grain assemblages and strong diagenetic overprinting in siliceous mudrocks barnett shale mississippian fort worth basin texas porosity permeability and total organic carbon toc in a heterogeneous suite of 21 high maturity samples vitrinite reflectance 1 52 2 15 from the barnett shale in the eastern fort worth basin display few correlations with parameters of rock texture fabric and composition these factors being mostly obscured by the effects of a protracted history of diagenesis diagenesis in these rocks includes mechanical and chemical modifications that occurred across a wide range of burial conditions compaction and cementation have mostly destroyed primary intergranular porosity the porosity average 5 vol by gas research institute helium porosimetry and pore size 8 nm median pore throat diameter are reduced to a degree such that pores are difficult to detect even by imaging ar ion milled surfaces with a field emission scanning electron microscope the existing porosity that can be imaged is mostly secondary and is localized dominantly within organic particulate debris and solid bitumen the grain assemblage is highly modified by replacement a weak pattern of correlation survives between bulk rock properties and the ratio of extrabasinal to intrabasinal sources of siliciclastic debris higher porosity permeability and toc are observed in samples representing the extreme end members of mixing between extrabasinal siliciclastic sediment and intrabasinal derived biosiliceous debris reservoir quality in these rocks is neither more strongly nor more simply related to variations in primary texture and composition because the interrelationships between texture and composition are complex and importantly the diagenetic overprint is too strong

the response of benthic foraminifera to productivity cycles in the eastern equatorial pacific faunal and geochemical constraints on glacial bottom water oxygen levels the stage 2 glacial maximum in eastern equatorial pacific ocean sediments is characterized by a pronounced increase in the organic carbon content which has been attributed either to increased upwelling and higher production along the equatorial divergence during the last glacial period or to enhanced preservation as a consequence of a lower concentration of dissolved o2 in glacial bottom water several lines of evidence are presented based on data from two gravity cores collected from the central panama basin which support the former interpretation first both the abundance and the size of benthic foraminifera of the genus uvigerina increase in stage 2 coincident with the increase in organic carbon concentration most probably because of the greater availability of organic detritus during the glacial period the increase in foraminiferal size and associated greater requirement of oxygen for respiration argues against the probability that oxygen was substantially depleted in the upper centimeter where uvigerina spp are thought to live second the number of meiofaunal faecal pellets increases markedly during the stage 2 maximum indicating a more populous and active infauna which again argues against oxygen depletion third there is no significant decrease in the iodine organic carbon i corg ratio in the stage 2 sediments because iodine is depleted relative to carbon in anoxic basins but enriched in association with organic matter in oxic environments the absence of a depletion in the i corg ratio in stage 2 is evidence that bottom water remained oxygen replete during the last glacial fourth molybdenum is not enriched in sediments deposited in stage 2 the presence of anoxic or dysaerobic bottom water or shallow pore waters during that time would have been recorded by the addition of mo to the sediments via coprecipitation with authigenic iron sulphides the combined faunal and geochemical data are consistent with the notion that panama basin deep waters remained oxygen replete during the last glacial maximum it is concluded that the late stage 2 carbon enrichment in the eastern equatorial pacific more probably reflects higher productivity rather than enhanced preservation

depth dependent carbonate dissolution changes in the eastern north atlantic during the last 170 000 years abstract previous studies have shown that dissolution increased in the north atlantic during glacial 13o stages 2 4 and 6 the relative intensity of the events is similar in cores between 3000 4600 m with the stage 4 event being the most intense canary basin cores deeper than 4600 m show a different pattern of dissolution itensity for example stage 6 dissolution was more intense than stage 4 the divergent dissolution patterns at depths 4600 m may indicate the presence of a discrete water mass at abyssal depths during some glacial episodes an analysis of stage 6 records in different parts of the atlantic suggests that the water mass at that time may have been the antarctic bottom water

key species of hermatypic coral for reef formation in the northwest pacific during holocene sea level change abstract cores from holocene reefs provided a growth history and species level identification of corals and demonstrated the most important reef builders during the formation stage this knowledge is important to determine a principle for reef formation and to provide preservation plans in the near future a biological and sedimentological study of sediment cores recovered from the palau islands and yoron island northwest pacific revealed four major facies corymbose acropora arborescent acropora massive porites and detritus species level observations show that arborescent acropora a muricata and a intermedia contributed to reef growth under low to moderate energy conditions whereas corymbose and tabular acropora a digitifera a hyacinthus and a robusta a abrotanoides and i palifera were key species for reef formation under high energy conditions during holocene sea level rise and the ensuing period of sea level stability once sea level had stabilized massive porites became restricted to areas subjected to low energy turbid conditions these key species are successful corals because the ecological strategy is rapid growth determinate growth a high degree of colony integration strongly resistant to wave action and rapid local dispersion via fragmentation moreover the western boundary current kuroshio flows along the reefs in the northwest pacific and it is easy for key species to distribute throughout the region during the period of holocene sea level rise and stabilization these features are a principle for reef formation during sea level changes these key species played a significant role in holocene reef formation in the northwest pacific however coral mortality caused by climate change has recently been widely reported moreover the decrease in key species abundance in present day reefs has been more severe than that in any other species these geological findings have important implications regarding the appropriate use of coral transplantation and decisions regarding the optimal location and size of marine protected areas

regional depositional changes and their controls on carbon and sulfur cycling across the ordovician silurian boundary northwestern guizhou south china abstract the controls of regional depositional environment on stable isotope records spanning the ordovician silurian boundary on the yangtze platform have seldom been investigated the objectives of this study include reconstruction of regional depositional settings and assessment of how sedimentary processes may have influenced carbon and sulfur isotopic fractionation seven shale facies have been recognized in the wufeng longmaxi interval from two locations completely bioturbated claystone of the basal wufeng formation accumulated on a shallow oxygenated muddy shelf overlying faintly banded black siliceous shale suggests deposition under deep anoxic conditions interrupted by episodes of dysoxia muddy fossiliferous facies of the guanyinqiao formation reflects a glacial sea level lowstand setting and the observed proximal to distal heterogeneity of facies matrix supports shallowing in the proximal area overlying faintly banded black shale of the longmaxi formation tells of a post glacial transgression the carbonaceous deposits are overlain by banded gray and dark gray muddy siltstones and suggest a shoaling upward trend the shallow water facies display relatively heavier 13 c org values whereas deep water facies are characterized by lower 13 c org values discrepancies between hirnantian positive 13 c org excursions in proximal and distal areas probably reflect spatial gradient in seawater 13 c dic induced by glacioeustasy deposits accumulated under oxic and physically dynamic conditions display strong positive 34 s sulfide excursions perhaps a consequence of diagenetic sulfate reduction occurred at some depth below the sediment water interface and removed from the sulfate pool of overlying water column negative relationship between 34 s sulfide and toc indicates that redox conditions and physical reworking of sediment at the sediment water interface controlled the rate of microbial sulfate reduction and sulfur isotope fractionation overall co variation of lithofacies and isotopic records suggests that local heterogeneity of seawater chemistry and sedimentary dynamics may exert partial controls on biogeochemical processes and amplify the magnitude of the hirnantian isotopic excursions in the proximal area

impacts of eustasy and hydro isostasy on the evolution and landforms of pacific atolls consideration of eustatic and hydro isostatic effects on late quaternary sea levels in the tropical pacific ocean indicates that the configuration of modern atolls with emergent annular reef flats is a transient morphology not developed until post mid holocene time annular atoll reefs perched atop carbonate platforms which cap buried volcanic edifices are underlain by 8 28 m of holocene limestone disconformably overlying a substratum of last interglacial or older limestone comparable thicknesses 9 23 m of holocene sediment are present beneath atoll lagoons that are uniformly 85 m deep during glacio eustatic drawdowns in global sea level by 120 125 m carbonate platforms of modern atoll provinces rose abruptly from the sea as clusters of subaerial limestone plateaus flanked by steep cliffs modern analogues are provided by emergent atolls uplifted on the flexural arches of trench forebulges slow subsidence coupled with karstic erosion of emergent atolls during the last glaciation lowered the surfaces of last interglacial reef edifices by the amounts needed to provide accommodation space for holocene reef growth during the postglacial eustatic rise in sea level modern atoll reef caps began to grow after 9 ka when rising holocene sea level overtopped degraded remnants of interglacial reefs but remained submerged until carbonate buildups approached sea level in mid holocene time 6 4 ka classic atoll morphology with circlets of multiple islets dotting annular reefs formed in combination with late holocene hydro isostatic drawdown in tropical pacific sea level in response to equatorial ocean siphoning a facet of global isostatic adjustment gia to deglaciation early holocene eustatic rise in sea level and late holocene hydro isostatic decline in sea level combined to produce a regionally variable mid holocene highstand in tropical pacific sea level that stood 1 0 2 6 m above modern sea level cemented mid holocene paleoreef flats now stranded well above sea level serve as resistant foundations for non migratory pinned islets that were not present along atoll rims until after the local crossover date when ambient high tide level first fell below mid holocene low tide level existing atoll landforms have a time depth generally 1 2 ka

insolation cycles as a major control of equatorial indian ocean primary production analysis of a continuous sedimentary record taken in the maldives indicates that strong primary production fluctuations 70 to 390 grams of carbon per square meter per year have occurred in the equatorial indian ocean during the past 910 000 years the record of primary production is coherent and in phase with the february equatorial insolation whereas it shows diverse phase behavior with 18o depending on the orbital frequency eccentricity obliquity or precession examined these observations imply a direct control of productivity in the equatorial oceanic system by insolation in the equatorial indian ocean productivity is driven by the wind intensity of westerlies which is related to the southern oscillation therefore it is suggested that a precession forcing on the southern oscillation is responsible for the observed paleoproductivity dynamics

origin and characterization of eagle ford pore networks in the south texas upper cretaceous shelf abstract recent studies have shown that the loss of primary pores and the development of secondary pores in mudrocks are primarily controlled by burial diagenesis of the mineral matrix and thermal maturation of organic matter om however the lack of quantitative data on nanometer to micrometer scale rock properties has limited the ability to define and predict petrophysical properties and fluid flow in these fine grained rocks to upscale these rock properties quantitative data are needed at multiple scales representative eagle ford group samples were collected from continuous cores taken from two adjacent oil producing wells in karnes county texas to investigate small scale variations in mineralogy diagenesis and pore type point count and pore tracing methods were used to systematically quantify pore types and determine the size and shape of the identified pores the two cores from the eagle ford are dominated by modified mineral pores although secondary om pores in migrated petroleum bitumen are also important the mineral pore network includes 1 primary mineral pores originally saturated with formation water and 2 modified mineral pores containing migrated petroleum bitumen and or residual oil the om pore network includes 1 primary om pores and 2 secondary om pores including relatively large less abundant om bubble pores and relatively small more abundant om spongy pores the abundance of om spongy pores correlates positively with total organic carbon toc content and that of mineral pores weakly correlates with the volume of quartz plus feldspar studied samples have similar thermal maturities although samples from one deeper core are slightly more mature than the other except for thermal maturation the strong micrometer scale heterogeneity of rock components and properties texture fabric mineralogy and toc impacts the abundance distribution and type of pores this micrometer scale heterogeneity in porosity and pore networks would in turn significantly impact matrix permeability

geochemical evolution of organic rich shales with increasing maturity a stxm and tem study of the posidonia shale lower toarcian northern germany hydrocarbon generation and retention processes occurring within gas shales as a response to increases in thermal maturation are still poorly constrained while efforts have been directed at unravelling the resource potential composition and textures of these economically important unconventional systems their spatial variability in chemistry and structure is still poorly documented at the sub micrometer scale here we have characterized samples of the lower toarcian posidonia shale samples from northern germany at varying stages of thermal maturation using a combination of compositional organic geochemistry and spectromicroscopy techniques including synchrotron based scanning transmission x ray microscopy stxm we document geochemical and mineralogical heterogeneities down to the nanometer scale within the investigated samples as a function of their level of thermal maturity in particular authigenic albite crystals containing nanometric halite inclusions have been documented within the investigated mature and overmature samples the presence of such tracers of palaeobrine carbonate interactions supports a maturation scenario for the lower toarcian posidonia shale intimately related to ascending brine fluids rather than a maturation scenario solely resulting from high heat flows in addition various types of asphaltene and nso rich bitumen have been detected within the same samples very likely genetically derived from thermally degraded organic precursors furthermore the formation of nanoporous pyrobitumen has been inferred for samples of gas window maturity likely resulting from the formation of gaseous hydrocarbons by providing in situ insights into the fate of bitumen and pyrobitumen as a response to the thermal evolution of the macromolecular structure of kerogen the results reported here constitute an important step towards better constraining hydrocarbon generation processes during natural shale gas maturation

predictive models for sandstone diagenesis abstract factors governing the evolutionary path that sandstone and shale sequences follow during burial diagenesis include provenance and depositionally controlled compositional and textural elements near surface redox reactions organic inorganic interactions within the zone of intermediate burial diagenesis deep diagenetic reactions which include abiotic thermal sulfate reduction carbonate mineral alteration and quartz cementation and the potential for meteoric influx and renewal of near surface processes due to uplift exposure and or base level fluctuation as a consequence the use of thermal exposure indicators to describe the extent of diagenesis such as r0 or time temperature history indicators such as tti must be used with caution though useful in predicting general trends in porosity loss due to simple compaction they have little utility in making forward predictions of anomalously high porosity e g preserved and or enhanced porosity or anomalously low porosity a more useful approach whereby the processes controlling porosity evolution are evaluated in terms of the depositional hydrologic burial and thermal histories is presented here

imaging pores in sedimentary rocks foundation of porosity prediction abstract this review examines the history and current practice of technologies for imaging of pores in sedimentary rocks pores are that portion of the rock volume occupied by components of relative mobility such as water of various salinities microbial life petroleum liquids gases and supercritical fluids through a rock s history the contained pores evolve as the primary detrital assemblage responds chemically and mechanically to changing conditions in the subsurface description and classification of pores based upon their paragenesis depends upon inspection by imaging that allows the pores to be seen and interpreted in the context of historical processes responsible for formation of the pore walls since the late 1960s sample preparation and imaging methodologies that clarified our understanding of pores in their correct historical context have been at the root of important advances in prediction of porosity and related bulk properties in the subsurface these older approaches are now joined by new technologies that serve current efforts to extend predictive capabilities to nm scale pores in the fine grained low permeability rocks that dominate in the deeper parts of sedimentary basins and indeed in the sedimentary record as a whole placing the smallest pores into their proper paragenetic context presents a challenge in the quest to develop predictive models for porosity evolution in fine grained rocks

revisiting late holocene sea level change from the gilbert islands kiribati west central pacific ocean new coral microatoll data allow presenting an updated late holocene sea level curve for the gilbert islands of kiribati examination of build up elevation and spatial distribution of microatolls along with radiocarbon age data from coral samples suggest an approximately 1 m sea level high stand possibly lasting from 3500 to 1900 cal yr bp our sea level curve which is similar to the one reported from the marshall islands is a baseline to reconstruct the evolution of reef flats and reef islands in addition it provides important contextual data to infer human settlement on islands in the west central pacific

diagenetic origin of quartz silt in mudstones and implications for silica cycling mudstone the most abundant sedimentary rock type1 composed primarily of clay or silt sized particles contains most of the quartz found in sedimentary rocks2 these quartz grains which are chemically and mechanically resistant and therefore preserve their characteristics well have long been considered to be derived from the continental crust1 here we analyse quartz silt from black shales in the eastern usa dating back to the late devonian period about 370 million years ago using backscattered electron and cathodoluminescence imaging and measure oxygen isotopes with an ion probe our results indicate that up to 100 of the quartz silt in our samples does not originate from the continental crust instead it appears to have precipitated early in diagenesis in algal cysts and other pore spaces3 with silica derived from the dissolution of opaline skeletons of planktonic organisms such as radiolaria and diatoms transformation of early diatoms into in situ quartz silt might explain the time gap between the earliest fossil occurrences of diatoms about 120 myr ago4 and molecular evidence for a much earlier appearance between 266 or even 500 myr ago5 6 moreover if many other mudstone successions show similarly high proportions of in situ precipitated rather than detrital quartz silt the sedimentary record in mudstones may have been misinterpreted in the past with consequences for our estimates of palaeoproductivity as well as our perceptions of the dynamics and magnitude of global biogeochemical cycling of silica

facies patterns and geography of the yangtze region south china through the ordovician and silurian transition abstract lithofacies and biofacies changes through the ordovician and silurian transition on the yangtze platform are coincident with stepwise mass extinctions recovery events global sea level changes and regional palaeogeographic configurations facies patterns through three intervals the late mid ashgill hirnantian and early rhuddanian indicate that black shale occupied most of the yangtze platform region during the late mid ashgill and early rhuddanian while the hirnantian possesses more diverse facies types the black shale was replaced by carbonate facies during the hirnantian coincident with a global sea level low stand biofacies changes from the late mid ashgill graptolitic to the hirnantian shelly facies were apparently signalled by gradual and diachronous existence of a mixed facies the manosia facies in the yangtze region however the biofacies change was abrupt from the hirnantian to the early rhuddanian when graptolitic facies occupied most areas on the yangtze platform leaving only a very narrow limited belt of shelly facies along the southern margin of the platform in northern guizhou the early rhuddanian unified biofacies pattern is a result of a global sea level rise which may be synchronized with a recovery bioevent of graptolites after hirnantian mass extinction

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

the durability of bioclastic sediments and implications for coral reef deposit formation the generation and composition of carbonate sediment within tropical carbonate settings is controlled by the skeletal production of caco3 in conjunction with physical biological and chemical processes which act to break down and disperse skeletal remains using the results of detailed tumbling barrel experiments this paper discusses the role the physical durability of common constituents of reef sediment plays in the composition of coral reef deposits the durability of the skeletal remains of six reef sediment constituents was determined experimentally using tumbling barrels results indicate that constituent durability varies considerably amongst common reef sediment constituents calcareous algae halimeda was the least durable constituent tested followed by larger benthic foraminifera baculogypsina sphaerulata and marginopora vertebralis and the pelecypod fragum fragum two species of branching coral acropora sarmentosa and acropora nasuta were found to be the most resistant to physical destruction these findings provide increased power to interpret reef and island deposits and the potential role skeletal durability plays in the retention of constituent skeletons within coral reef associated sedimentary systems

anatomy of a modern coral reef flat a recorder of storms and uplift in the late holocene abstract cores from kabira reef ishigaki island southwest japan reveal the internal structure and temporal changes in sedimentary process of a complete coral reef flat the reef crest caught up with sea level at about 4000 yr bp since then it expanded oceanward and the reef pavement has grown landward the backreef structure is composed of bioclasts derived from the reef framework of all the bioclasts corals and coralline algae are most abundant coral fragments coarser than 3 0 o have dominated the backreef sediments since about 2000 yr bp benthic foraminiferal tests first occurred at about 4000 yr bp and their abundance increased significantly starting around 2000 yr bp shallowing of the reef crest is also indicated by the presence of the shallow water benthic foraminifera baculogypsina sphaerulata tests after 2000 yr bp the date 2000 yr bp is coincident with tectonic uplift at kabira reef kawana 1989 we consider this uplift to have caused a relative sea level fall that aided the deposition of coral fragments transported from the reef pavement by storms the relative sea level fall also caused subaerial exposure of the reef crest during low tides and the transition of reef building organisms from corals to shallow water species of benthic foraminifera resulting in a change noticeable in the constituents of backreef sediments the results of this study suggest that the coral reef flat and especially the backreef can be a faithful recorder of relative sea level changes

exploring carbonate reef flat hydrodynamics and potential formation and growth mechanisms for motu abstract atolls which develop as reef building coral platforms extend to near sea level typically consist of a shallow reef flat encircling a central lagoon often sub aerial islets known as motu or reef islands consisting of sand gravel and coral detritus can be found perched atop the reef flat here we use hydrodynamic numerical modeling xbeach to better understand the role of waves and wave driven currents on the reef flat and the processes driving motu formation and evolution by differing representative reef flat geometry e g width and water depth we investigate the effects of varying wave climate on hydrodynamics and resultant bed shear stresses across the reef flat model results suggest that as a reef flat shallows bed shear increases then after passing a critical value decreases again using these results we hypothesize that reef flats should attain a critical water depth just at the threshold for sediment mobilization resulting in a constant depth reef flat in both abrasional and depositional settings as reef flats widen prograding into the back reef lagoon shear stress decreases across the flat with a minimum in shear stress arising approximately midway on the reef flat motu formation would be expected to initiate at this mid flat nucleation site either from a storm when coarse sediment is mobilized and deposited or gradually as the reef flat widens a mid flat deposit need not be subaerial to form a motu sediment piled shallower than the critical depth would continue to accumulate once a motu is present reef flat shear stress directions reverse and the motu shoreline should prograde seawards until reaching a relatively narrow critical reef flat width 200 m together these results suggest that reef flats and motu spatially self organize through a series of morphodynamic feedbacks

muddy prodeltaic hyperpycnites in the lower genesee group of central new york usa implications for mud transport in epicontinental seas abstract recent studies of marine continental shelves show that hyperpycnal flows are responsible for offshore transport of large volumes of sediment detailed facies analysis and petrography of the lower genesee group in the northern appalachian basin nab shows a wealth of sedimentary textures and fabrics that indicate mud deposition by lateral transport across and along the shelf under energetic conditions intervals of silt rich mudstones and muddy siltstones with internal scours diffuse stratification soft sediment deformation normal and inverse lamina set grading and a reduced intensity and diversity of bioturbation occur in multiple facies types and interrupt what appears to be the overall background sedimentation these intervals and their sedimentary features are interpreted as products of high density fluvial discharge events which generated turbulent flows that carried fine grained clastics several tens of kilometers offshore from the paleoshoreline recognizing these sediments as products of river flood and storm wave generated offshore directed underflows challenges previous depositional models for organic rich mudstones in the lower genesee succession which call for clastic starvation and suspension settling of clay and silt in a deep stratified basin rapid deposition of fine grained intervals from hyperpycnal plumes in a setting favoring preservation of organic rich mudstones calls for a reappraisal of the depositional setting of not only the genesee group but also of comparable mudstone successions in the appalachian basin and elsewhere

deep circulation of the north atlantic over the last 200 000 years geochemical evidence variations in the cadmium calcium ratio of north atlantic deep water are recorded in the fossil shells of benthic foraminifera the oceanic distribution of cadmium is similar to that of the nutrients hence the cadmium calcium ratio in shells records temporal variations in nutrient distributions data from a north atlantic sediment core show that over the past 200 000 years there has been a continuous supply of nutrient depleted waters into the deep north atlantic the intensity of this source relative to nutrient enriched southern waters diminished by about a factor of 2 during severe glaciations this evidence combined with carbon isotope data indicates that the continental carbon inventory may have been less variable than previously suggested

pore types in the barnett and woodford gas shales contribution to understanding gas storage and migration pathways in fine grained rocks the identification of organoporosity microscale and nanoscale pores within organic matter in shales its importance to storage and perhaps transfer of gas molecules through shales and methods for gathering three dimensional images of the pores such as by argon ion milling and or field emission scanning electron microscopy have all been well documented and discussed for unconventional gas shales however other types of pores exist within shales that can be important to storage and migration of gas and oil and other technologies are available for their identification and imaging the different pore types found in the barnett and woodford shales are described and classified in this article scanning electron microscopy revealed the presence of porous floccules in both the barnett and woodford shales which appear similar to laboratory produced floccules and to those in other ancient shales published experimental and observational studies indicate that floccules are hydraulically equivalent to coarser grains and are transported by traction processes current induced microsedimentary structures and textures within the barnett and woodford shales as well as the preserved floccules suggest such processes were active during transport and deposition pore spaces between the floccules are open and can provide storage space as well as permeability pathways for gas molecules through the shales pores are also found within organic matter that occurs both as discrete particles and as adsorbed coatings around clay grains in the shale they are referred to here as organopores porous fecal pellets are also common in the barnett shale preserved fossil fragments such as organic walled spores and inorganic sponge spicules have hollow central chambers which may remain partially or completely open even after burial intraparticle pores occur between grains of various minerals e g pyrite framboids microchannels within shale matrix which may be the bounding surfaces of scours or microsedimentary structures may also provide permeability pathways for hydrocarbon migration mircrofractures are also common and their initiation might be related to mineral crystal structure when present in sufficient quantity these pore types offer potential gas and oil molecule storage spaces and permeability pathways through the shales

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

reef island accretion and soil development on makin kiribati central pacific the late holocene accretionary history of reef islands on makin the northernmost table reef of the gilbert atoll chain western kiribati has been reconstructed based on conventional radiocarbon dating of coral shingle and bulk sand samples and ams radiocarbon dating of individual grains makin is geomorphologically and sedimentologically simple comprising one main island with only a minor residual lagoon and composed of sand dominated by the reef flat foraminifera calcarina spengleri amphistegina lobifera and baculogypsina sphaerulata deposition commenced in mid platform around 2500 years ago in situ fossil coral heliopora dated at 2400 80 years bp indicates that sea level was 0 4 0 5 m above present at that time progradation occurred progressively to westward at a relatively constant rate of 200 300 m ka 1 however progradation was interrupted on the eastern side by lagoon encapsulation around 1400 years ago the soil and vegetation characteristics are uniform over most of the reef islands as a result of clearance and the planting and maintenance of coconuts and do not reflect reef island depositional history remnant stands of pisonia forest with an associated phosphatic soil are not related to any particular geomorphological feature or period of deposition the reef islands are continuing to accrete as a result of production of foraminifera on the reef flat

dimethylsulfide production variations over the past 200 k y in the equatorial atlantic a first estimate dimethylsulfide dms released from phytoplankton produces cloud condensation nuclei in the marine troposphere thereby providing a climate regulating mechanism by increasing cloud albedo a 200 k y long sedimentary record from the equatorial atlantic of dms producing phytoplankton suggests that dms production increased during the glacial stages thus potentially working to further cool the glacial world important factors limiting the operation of this possible feedback mechanism for planetary cooling may be the strength of trade winds and the availability of fine iron rich dust needed to fertilize growth of dms producers

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

eco geomorphic processes that maintain a small coral reef island ballast island in the ryukyu islands japan abstract landform changes in ballast island a small coral reef island in the ryukyu islands were investigated by remote sensing analysis and a field survey the area of the island almost doubled after a mass coral bleaching event in 1998 coral branches generated by the mass mortality and broken by waves were delivered and stocked on a reef flat and accumulated to expand the area of the island in 2012 high waves generated by typhoons also changed the island s topography overall the island moved in the downdrift direction of the higher waves waves impacting both sides of the island piled up a large volume of coral gravels above the high tide level eco geomorphic processes including a supply of calcareous materials from the corals on the same reef especially during stormy wave conditions were key factors in maintaining the dynamic topographic features of this small coral reef island

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

predominance of stratified anoxic yangtze sea interrupted by short term oxygenation during the ordo silurian transition abstract the ordo silurian transition was a critical interval in geological history during which profound biotic climatic and oceanic changes occurred in order to explore the oceanic palaeoredox changes multiple geochemical proxies including ratios of s c fehr fet fep fehr and dop values are presented here from three sections wangjiawan western hubei sanjiaguan northern hunan and nanbazi northern guizhou across the ordo silurian boundary on the yangtze platform these palaeoredox data indicate a predominance of stratified anoxic ferruginous ocean on the yangtze block during this transition which was interrupted by a brief episode of oceanic oxygenation in the early hirnantian this oxygenation temporally coinciding with the end ordovician glaciation and global glacio eustatic sea level fall likely resulted from enhanced circulation of polar cold dense oxygen rich water onto the low latitude shelf the prior and subsequent longer term episodes of anoxic ocean particularly the later one which started in the late hirnantian occurred in parallel with the rapid climatic warming and sea level rise which could have slowed down oceanic circulation thereby enhancing oceanic stratification anoxia and organic preservation oceanic redox changes together with rapid climatic and sea level fluctuations were likely responsible for the stepwise massive demise of the ordo silurian biotic crisis

morphology genesis and distribution of nanometer scale pores in siliceous mudstones of the mississippian barnett shale research on mudrock attributes has increased dramatically since shale gas systems have become commercial hydrocarbon production targets one of the most significant research questions now being asked focuses on the nature of the pore system in these mudrocks our work on siliceous mudstones from the mississippian barnett shale of the fort worth basin texas shows that the pores in these rocks are dominantly nanometer in scale nanopores we used scanning electron microscopy to characterize barnett pores from a number of cores and have imaged pores as small as 5 nm key to our success in imaging these nanopores is the use of ar ion beam milling this methodology provides flat surfaces that lack topography related to differential hardness and are fundamental for high magnification imaging nanopores are observed in three main modes of occurrence most pores are found in grains of organic matter as intraparticle pores many of these grains contain hundreds of pores intraparticle organic nanopores most commonly have irregular bubblelike elliptical cross sections and range between 5 and 750 nm with the median nanopore size for all grains being approximately 100 nm internal porosities of up to 20 2 have been measured for whole grains of organic matter based on point count data from scanning electron microscopy analysis these nanopores in the organic matter are the predominant pore type in the barnett mudstones and they are related to thermal maturation nanopores are also found in bedding parallel wispy organic rich laminae as intraparticle pores in organic grains and as interparticle pores between organic matter but this mode is not common although less abundant nanopores are also locally present in fine grained matrix areas unassociated with organic matter and as nano to microintercrystalline pores in pyrite framboids intraparticle organic nanopores and pyrite framboid intercrystalline pores contribute to gas storage in barnett mudstones we postulate that permeability pathways within the barnett mudstones are along bedding parallel layers of organic matter or a mesh network of organic matter flakes because this material contains the most pores

late quaternary carbonate sedimentation at the sierra leone rise eastern equatorial atlantic ocean abstract in the eastern equatorial atlantic ocean changes in the concentration of carbonate in late quaternary sediments resulted from reduced production of carbonate in surface waters and increased dilution with non carbonate sediments during glacial maxima during glacial stages production of carbonate in surface water measured as its accumulation rate in shallow undissolved cores decreased by one half the glacial accumulation rate of non carbonate components increased 1 5 to 4 times over holocene values the greatest increases occurred in the deepest cores carbonate dissolution during stages 2 3 and 4 increased the proportion of foraminiferal fragments and decreased the accumulation rate of susceptible species in the deep sites in shallow sites slightly increased dissolution can be detected during stage 3 while greatly increased dissolution occurred during stage 4 bathymetric profiles of foraminiferal fragmentation and accumulation document a shoaling of the foraminiferal lysocline by 1000 m during glacial isotopic stages we present a mass balance model of sediment accumulation for carbonate and insoluble components and from this model we estimate the rate of downslope transport and dissolution of carbonate at the sierra leone rise our results show that during stage 4 the rate of carbonate loss to dissolution was greater than the rate observed today or during other interglacial stages the calculated rates of dissolution for stages 2 and 3 are not significantly different from those calculated for stage 1

nano scale pore structure and fractal dimension of organic rich wufeng longmaxi shale from jiaoshiba area sichuan basin investigations using fe sem gas adsorption and helium pycnometry abstract much attention have been recently paid to the upper ordovician wufeng shale o3w and lower silurian longmaxi shale s1l in the jiaoshiba area of sichuan basin which is now the largest producing shale gas field in china field emission scanning electron microscopy fe sem low pressure gas n2 and co2 adsorption helium pycnometry x ray diffraction and geochemical analyses were performed to investigate the pore structure and fractal dimension of the pores in o3w s1l shale formation in the jiaoshiba area fe sem images show that organic matter om pores are dominant in the organic rich samples and these pores are often irregular bubble like elliptical and faveolate in shape while in organic poor samples limited and isolated interparticle interp intraparticle intrap and om pores are observed reversed s shaped isotherms obtained from nitrogen adsorption are type and hysteresis loops indicate that the shape of micropore in the samples is slit or plate like bet surface areas and total pore volume vary from 12 2 to 27 1 m2 g and from 1 8 10 2 to 2 9 10 2 cm3 g with an average of 19 5 m2 g and 2 3 10 2 cm3 g respectively adsorption volume from both n2 and co2 adsorption increases with respect to toc contents porosities obtained from helium porosimetry are comparable with these from gas co2 and n2 adsorption in o3w s1l shale however porosity determined by quantitative fe sem analysis is much smaller which is mainly related to limited resolution and the small areas of investigation based on the frenkel halsey hill fhh model of low pressure n2 adsorption fractal dimensions of the pores varied from 2 737 to 2 823 relationships between pore structure parameters and toc content mineral composition and fractal dimension reveal that the fractal dimension is mainly associated with micropores samples with higher toc content higher quartz content and lower clay content tend to contain more heterogeneous micropores resulting in higher fractal dimensions and more complicated pore structure in shales therefore fractal dimension is an effective parameter to reflect the complexity of pore structure and the degree of micropore development in o3w s1l shale

late pleistocene paleoclimatology of the central equatorial pacific flux patterns of biogenic sediments high resolution records of the concentration and mass accumulation rate mar or flux of biogenic sediments from core rc11 210 in the central equatorial pacific are compared for the entire late pleistocene the fluxes of calcium carbonate and organic carbon correlate well the opal flux pattern shows no direct correlation with the other two rather opal flux maxima correlate with slopes of i e both precede and follow the organic carbon and carbonate mar peaks organic carbon and calcite therefore may both be better indicators of past productivity than opal which is an indicator of transition at this location we interpret the sequence low biogenic fluxes high opal fluxes high carbonate carbon and opal fluxes as representing the transition from low to high sea surface biological productivity the phase relationships for eccentricity of the biogenic sedimentation records were compared to those of other climatic indications including the oxygen isotope record of ice volume the ice core co2 record the pacific 13c record the deep nutrient cd ca record and the eolian grain size record of wind intensity we find that starting from maximum ice volume phase angle of 0 the phase relationships of the 100 000 year periodicity show in the first quadrant maximum wind intensity 30 and maximum calcite and carbon flux 45 occurring first followed by maximum opal flux 75 and then maximum deep nutrients 95 minimum pacific 13c occurs at a phase angle of 155 the maximum co2 in the vostok record and minimum ice volume is at 180 thus in the eccentricity climate cycle glacial conditions lead to stronger wind driven circulation which enhances productivity which in turn results in enhanced oceanic and atmospheric carbon dioxide and minimum ice volume

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr