seismic stratigraphic reconstruction of plio quaternary depositional sequences on the continental shelf of korea strait abstract the korea strait is a seaway connecting the east sea with the east china sea the plio quaternary stratigraphy and sedimentation on the korea strait shelf was studied using a dense network of high resolution single channel seismic reflection profiles the shelf sequences above the acoustic basement consist of seven depositional sequences separated by erosional unconformities corresponding to falls in sea level individual sequences are characterized by well stratified and complex sigmoid oblique prograding reflection configurations reflecting a history of upbuilding and outbuilding in response to repetitive transgressive and regressive events driven by sea level changes during the regression to lowstand of sea level lowstand prograding wedges were formed seaward along the present shelf margin whereas during the highstand of sea level as in the present condition highstand deposits were deposited in the inner shelf along the coast however as the subsequent regression began the inner shelf highstand deposits were severely eroded out and or formed a condensed section volumetrically the forced regressive and lowstand systems tracts are the most important components of the korea strait consequently the plio quaternary sequence in this area consists of a succession of stacked progradational lowstand wedges mainly formed during the regression and lowstand of sea level

seismic stratigraphy of the southeastern black sea shelf from high resolution seismic records abstract high resolution seismic reflection profiles obtained from the shelves off the samsun and trabzon coasts southeastern black sea have revealed the existence of two distinct reflectors r and t reflector r forms the boundary between the upper depositional sequence a and the lower depositional sequence b seismo stratigraphically upper sequence a is characterized by stratified simple complex and lenticular seismic reflection configurations which imply changing depositional systems and or conditions changes of source and supply of sediments due to the relative change of sea level additionally the observed onlapping pattern within this sequence denotes rising of sea level during the last post glacial transgression the mounded seismic facies beyond the steep gradients on the shelf area of trabzon imply slump masses the lower depositional sequence b on the samsun and trabzon shelves is commonly characterized by chaotic reflection configurations which are interpreted either as strata deposited in a variable relatively high energy setting or as initially continous strata that have been deformed additionally the presence of some parallel subparallel reflections within this sequence denotes its stratified character the upper boundary of sequence b reflector r reflects a pre holocene unconformity probably caused by falling sea level at the time of the last glacial maximum additionally toplap termination at the upper boundary of sequence b indicates a stillstand of sea level at 91 m depth during the last glacial maximum based on borehole data sequence b is composed of consolidated sand and gravel admixtures in the samsun area and basalt agglomerate tuff series in the trabzon area reflector t forms the boundary of a zone of anomalous reflections acoustic turbidity at that are interpreted to represent gas in the sediments of the upper depositional sequence a the gas accumulations tend to occur in blanket and curtain forms depending on their appearances on seismic records

depositional history of quaternary sediments on the continental shelf off the southeastern coast of korea korea strait abstract the depositional history of quaternary sediments on the continental shelf off the southeastern coast of korea korea strait was investigated by means of analysing high resolution seismic profiles and sediment samples quaternary sediments up to 50 m thick overlie the irregular surface of the acoustic basement in the inner shelf the sedimentary column is comprised of two main sequences separated by a mid reflector which is interpreted as the pre holocene surface the holocene sequence reaching up to 30 m in thickness with a depocenter near the present river mouth is characterized by deposition in a prodelta environment while the upper pleistocene sequence represents deposition in deltaic or shallow water environments during the late glacial period most of the shelf was subaerially eroded and deposition took place only in the trough region the present location of marine built terraces indicates that the lowest position of sea level was about 130 m below its present level the subsequent postglacial transgression reworked pleistocene sediments to form a thin veneer of transgressive facies sea level rose rapidly in the early stages of the postglacial transgression and approached the present level at approximately 7000 5000 yrs b p recent sedimentation the holocene sequence probably began at that time

alkyldibenzofurans in terrestrial rocks influence of organic facies and maturation abstract dibenzofuran dbf dibenzothiophene dbt and phenanthrene phe have been determined along with their methyl derivatives mdbfs mdbts mps in coals carbonaceous shales and mudstones of lower cretaceous to upper carboniferous ages from the elmworth gas field canada and from the sakoa madagascar and ruhr coal germany basins the samples contained mainly terrestrial organic matter with thermal maturities in the 0 7 1 9 mean vitrinite reflectance rr range the pronounced predominance of mdbfs over mdbts in the sakoa samples is typical of plant debris deposited in lacustrine swamp environments onset of intense mdbf generation occurs at fairly low rank 0 77 rr as indicated by elevated concentrations of 50 120 g mdbfs g total organic carbon toc influences of lithology organic matter type and maturity on distributions of the target compounds were extracted from the molecular concentration data by multivariate statistical methods such as principal components analysis pca and fuzzy c means cluster analysis with nonlinear mapping nlm a specific source effect on 1 mdbt concentrations suggests that lichens contributed to the senescent coal forming forest in the sakoa coal basin alkyldibenzofurans hence are potential lichen biomarkers mdbfs can be used as maturity indicators only beyond 1 0 rr where ruhr coals displayed a distinct increase in the 1 4 mdbf ratio

dibenzothiophenes in solid bitumens use of molecular markers to trace paleo oil filling orientations in the lower cambrian reservoir of the moxi gaoshiti bulge sichuan basin southern china abstract the moxi gaoshiti mg bulge of the sichuan basin in southwestern china is unique because of its enormous gas field in old cambrian and proterozoic marine strata where oils in carbonate reservoirs have been nearly completely cracked to solid bitumen and natural gas because of high to post mature thermal maturity levels numerous solid bitumen bearing dolomites obtained from boreholes in the mg bulge provide an ideal opportunity to trace the major filling orientations for the lower cambrian paleo oil reservoirs biomarker analysis was conducted on solid bitumens through quantitative detection with gas chromatography mass spectrometry results show that all solid bitumen samples in the mg bulge exhibit similar compositions of molecular markers thereby implying that they belong to the same oil population and that paleo oils should be derived from the same source kitchen bed low pristane phytane and dibenzothiophene dbt phenanthrene ratios as well as the predominance of dbt among dbt dibenzofuran and fluorene are observed in the solid bitumen samples which suggest that related paleo oil reservoirs likely originated from a highly reducing marine shale environment all isopleth maps of the dbt concentrations 4 methyldbt 1 methyldbt 4 6 dimethyldbt 1 4 1 6 dimethyldbt dmdbt and 2 6 3 6 dmdbt 1 4 1 6 dmdbt ratios consistently indicate that the overall orientation of oil migration in the mg bulge is primarily from the west to east direction with the strongest filling point located at approximately the mx12 well the north to west direction is an additional filling orientation these indicators show that those paleo oils that had been cracked to pyrobitumens mainly originated from a source kitchen in the western part of the mg bulge a hydrocarbon source kitchen in the northern part of the mg bulge may also have developed but further research on this is needed the recognition of these solid bitumen molecular signatures particularly the consistent results using dbt concentrations and alkyl dbt thermal maturity indicators suggests a potential approach that can be applied to the study of paleo oil reservoirs

some recently developed landforms climatic implications abstract many landforms are geologically youthful most though by no means all are comparatively minor but several like gullies are widely distributed some are the work of processes that have been active over several centuries or a few millennia some may have formed under the influence of a single set of climatically induced processes but others are genetically more complex other recent landforms represent the culmination of processes that have long been active but which until recently had no surface expression yet others result from meteorological events acting on land surfaces rendered vulnerable by seperate in some instances clearly non climatic events even those forms which are climatically triggered are genetically complex and many are related to meteorological episodes rather than secular climatically induced processes the climatic interpretation of landforms is as complex in the short term as it is in the long

geochemical characteristics of water dissolved gases and implications on gas origin of sinian to cambrian reservoirs of anyue gas field in sichuan basin china abstract the anyue gas field is a supergiant gas field which was discovered recently in the sichuan basin china where the sinian dengying formation and the cambrian longwangmiao formation are principal gas reservoirs gas in the anyue field contains mainly methane 98 and a low content of heavy hydrocarbons with minor h 2 s component reservoirs commonly contain bitumen and produce formation water it is currently suggested that natural gas in the anyue field is derived from the secondary cracking of crude oil however carbon isotopic ratio of methane is significantly less negative than that of bitumen which contradicts the isotopic signature oil cracking process would predict besides this phenomenon also cannot be explained by the process of thermochemical sulphate reduction tsr because there is no remarkable correlation between the 13 c 1 values and h 2 s contents as suggested in previous studies both free gas and water dissolved gas from the anyue gas field were analyzed in this study for their stable isotopes results show that the 13 c 1 of the gas derived from the formation water is much less negative than that of free gas therefore it is inferred that the less negative 13 c 1 values in the free gas reservoir are attributable to addition of natural gas that is previously dissolved in formation water geological setting of the gas reservoirs in dengying and longwangmiao formations of the anyue gas field is favorable for the formation and preservation of water dissolved gas in addition both formations had experienced significant structural uplifting before the gas reservoirs were formed reduced temperature and pressure in the formations by geological uplifting could cause super saturation of methane in the formation water and as a consequence water dissolved methane gas could exsolve from water phase into gas phase therefore it is concluded that natural gas in the anyue field is a mixture of free gas and gas exsolved from the formation water as a result the carbon isotope of methane gas in the anyue field became less negative than that of a single free gas component would predict

seismic stratigraphy of the fault controlled submarine canyon valley system on the shelf and upper slope of anamur bay northeastern mediterranean sea abstract high resolution shallow seismic reflection uniboom and echosounding profiles obtained on the shelf and upper slope areas of anamur bay turkey northeastern mediterranean were studied together with previous data on the onshore geology of the area to investigate the origin and related seismic stratigraphy of the submarine anamur canyon it was found that the main axial trend of the submarine anamur canyon is aligned with the offshore projection of the n s orientated onshore anamur thrust fault of late cretaceous senonian to early tertiary age interpretation of the distinct reflection configurations observed on the seismic profiles reveals the presence of various seismic facies comparable with the depositional sequences resulting from the relative sea level changes during the late quaternary the acoustic basement probably miocene in age is overlain by a sedimentary column mainly plio quaternary which in turn can be divided into two major seismic sequences and 12 seismic facies that show considerable variations in both their lateral and horizontal extent a palaeo deltaic environment sequence i with its typical topset and foreset facies was recognized and the corresponding deposits are interpreted to be indications of coastal deltaic progradation during late pleistocene sea level highstands or during the early phases of the last major eustatic lowering reflections of sequence ii which includes nine distinct facies are marked by onlap configuration and are believed to be marine deposits of the flandrian transgression at least four transgressive cycles are evident from the seismic profiles at 70 90 60 45 and 40 m water depths the two sequences i and ii are now covered with the most recent facies

complex sedimentation of the holocene mud deposits in a ria type coastal area eastern korea strait abstract the innermost shelf of the eastern korea strait is a ria type coastal sea comprising islands intervening passageways and embayments a detailed analysis of high resolution 1 10 khz subbottom profiles and core sediments from this area reveals complicated depositional and distributional patterns of the holocene mud deposits related to complex topography with varying supply of the adjacent nakdong riverine sediments sediments from the nakdong river were bifurcated around gadeok island forming two proximal systems nakdong and western gadeok systems these proximal systems prograded offshore southward by active sediment supply from the nakdong river in the early stage suspended sediments passing through the nakdong system formed the distal gadeok waterway and eastern geoje systems in the area between the northern geoje and gadeok islands these distal systems show a northwestward onshore prograding tendency to jinhae bay the biggest bay in the vicinity of the nakdong estuary in which the jinhae bay system developed in the late stage a remarkable decrease of sediment supply from the nakdong river has caused retrograding geometry of the two proximal systems however the most distal jinhae bay system has continuously prograded bayward due to the persistent supply of sediments resuspended by strong tidal currents from nearby distal gadeok waterway and eastern geoje systems these complex depositional features indicate that topography has an important influence on depositional developments of the holocene mud deposits by controlling path and intensity of sediment dispersal and resuspension processes

the organic petrology of graptolites and maturity assessment of the wufeng longmaxi formations from chongqing china insights from reflectance cross plot analysis abstract the wufeng longmaxi formations ordovician silurian contain abundant graptolite bearing shales which have proven to be one of the most successful shale gas exploration targets in china and can provide an opportunity to study the organic petrology of graptolites organic petrology analysis has been conducted on these organic rich shales in order to depict the shape of graptolite reflectance indicating surface gris and their organic maturity granular and non granular graptolites have been observed in the studied sediments and non granular graptolites were the major graptolite species the strong positive correlation between the maximum reflectance rmax and bireflectance of graptolites indicates that the graptolites display stronger anisotropy with maturation a linear coalification path of graptolite fragments was observed in the studied sediments a remarkable decrease in the minimum reflectance rmin values of graptolites was observed when rmax exceeds 6 the samples with lower thermal maturity rmax 2 tend to be biaxial neutral whereas higher rank samples display biaxial negative characteristics the gris shape becomes more oblate with maturation the wufeng longmaxi shales from the southeastern chongqing and wuxi areas of the chongqing municipality china are post mature and in the dry gas zone whereas samples from the chengkou area of the chongqing municipality china are still in the oil window their different burial and thermal histories controlled their thermal maturity

fractionation of dibenzofurans during subsurface petroleum migration based on molecular dynamics simulation and reservoir geochemistry abstract dibenzofurans oxygen containing heterocyclic aromatics are ubiquitous in crude oils their geochemical implications in petroleum geochemistry have been studied in numerous previous publications here we present the distribution of dibenzofuran and its methylated homologues and calculate the polarity and solubility of methyldibenzofuran isomers based on the connolly surfaces and molecular dynamics simulation the results show that the geo chromatographic fractionation effect is evident due to absorption onto the water silica matrix carrier bed during the oil migration process two potential molecular indicators relative to dibenzofurans i e the total content of dibenzofurans and the relative abundances of 1 methyldibenzofuran to 4 methyldibenzofuran are proposed for tracing the oil migration orientation and filling pathways these two indicators were applied successfully in paleozoic marine carbonate and tertiary lacustrine sandstone reservoirs the variations of source input depositional environment and maturity for oils from same source bed kitchen appear to have no significant effect on these two indicators it suggested that these two dibenzofuran indicators are potentially effective molecular tracers for orientation and filling pathways in oil migration

petrophysical characterization of oil bearing shales by low field nuclear magnetic resonance nmr abstract shales are important components of petroleum systems and it is necessary to reveal their petrophysical properties as reservoirs low field nuclear magnetic resonance nmr has proven to be a non invasive and effective technique for petrophysical characterization of sandstone carbonate and coal however little study has been done using this technique to systematically investigate the petrophysical properties of oil bearing shales which is essential for characterizing shale oil reservoirs in this study two sets of nmr measurements were performed to reveal the porosity permeability movable fluid volume and pore size distribution psd of oil bearing shales the results show the following 1 the nmr t2 spectrum strongly relates to the content of quartz and the amount of dissolution pores within shale three t2 spectrum peaks were identified by the relaxation times at 0 03 1 ms 1 20 ms and 20 ms corresponding to micropores 1000 nm respectively 2 by combining nmr with centrifugation both nmr porosity and movable porosity mp were calculated nmr porosity is well consistent with helium porosity and the mp values strongly relate to the development of mesopores in shales 3 based on the t2 spectrum an effective permeability model was proposed which can conveniently estimate the permeability of shales moreover two classical permeability models coates and sdr were also used to estimate shale permeability and the permeability values determined by these models agrees well with helium permeability 4 in combination with sem images analyses an nmr based psd was constructed that agrees well with the psd determined by sem the results demonstrate the applicability of nmr relaxation in a systematic investigation of the petrophysical properties of shales which has potential applications for geophysical logging in shale oil exploration

depositional and erosional coastal processes during the last postglacial sea level rise an example from the central tyrrhenian continental shelf italy abstract a transgressive systems tract tst deposit on the inner continental shelf of the south tuscany region central tyrrhenian sea italy formed during the last postglacial sea level rise its small scale stratigraphy has been detailed using high resolution seismic profiles gravity cores and grab samples the tst deposit overlies a lowstand unconformity shows a tabular geometry and comprises three internal architectures of beach facies 1 architecture a present on the outer sector of the study area is made up of only a reworked sand sheet 2 architecture b on the middle sector comprises palustrine bottom washover and the above mentioned reworked sand sheet and 13 architecture c on the inner sector represents the absence or scarcity of deposits reworked sand sheet ov r the unconformity because the lateral distribution of these vertical successions is not random but parallel to the coast each architecture represents an individual sedimentary stage during sea level rise however all architectures were formed via shoreface retreat in response to the landward migration of a beach complex over the unconformity during this migration the beach system was characterized by a source diastem located in the surf zone and by two sediment dispersal systems one moved the eroded sand over the flat back barrier palustrine area by storm washover while the other transported part of this sand to the lower shoreface forming a reworked sand sheet above the older and inactive source diastem ravinement surface the tst architectures originated from a transgressive succession of beach facies differentiated according to the intensity of shoreface retreat architecture a represents a low preservation potential of the original beach complex architecture b relatively high preservation and architecture c no preservation the intensity of erosion and the consequent preservation potential were totally controlled by antecedent topography

late quaternary transgressive deposits in a low gradient environmental setting korea strait shelf se korea abstract analysis of high resolution seismic profiles and sediment data from the korea strait shelf reveals that the late quaternary deposits in this area consist of five sedimentary units deposited during transgression phases of sea level changes between about 15 and 6 ka bp ancient beach shoreface complex unit p1 estuarine deposits unit p2 mid shelf sand sheet unit m1 sand ridge system unit m2 and inner shelf sand sheet unit m3 they are paralic and marine separated by a ravinement surface the lower paralic component below the ravinement surface consists of two sedimentary units p1 and p2 preserved from shoreface erosion the top surface of the paralic unit is truncated by a sharp erosional surface this surface is overlain by three sedimentary units m1 m2 and m3 which were produced by shoreface erosion that shifted landward during transgression the transgressive deposits in this area considering geometries and distribution patterns can be divided into three types i ii and iii type i overlying the lowstand systems tract is confined to the shelf margin and consists of a thick paralic unit p1 and a relatively thin marine unit m1 type ii on the mid shelf has no paralic component and the marine units m1 or m2 directly overly the sequence boundary type iii found in the inner shelf includes a thick paralic unit p2 and a thin marine unit m3 component it is completely covered by the highstand systems tract

shelf sequence and characteristic bounding surfaces in a wave dominated setting latest pleistocene holocene examples from northeast japan abstract this paper presents modern models for coastal to shelf sequences in a microtidal and wave dominated setting based on detailed analyses of latest pleistocene holocene sequences on the pacific side of northeast japan the latest pleistocene holocene sequences on the pacific side of northeast japan created in response to sea level changes for the last 30 kyr can be assigned to lowstand transgressive and highstand systems tracts related to sea level changes and show characteristic bounding surfaces and depositional systems these basically support the sequence architecture model of vail however transgression and regression occurred almost simultaneously with rise and fall of sea level in the study areas and so inflection points of sea level curves where the absolute slope or the rate of change is greatest are less significant for these high frequency sequences the characteristic bounding surfaces are a sequence boundary a transgressive surface which is the boundary between the lowstand and the transgressive systems tracts a ravinement surface which is found mainly in deposits of the transgressive systems tract and a maximum flooding surface which is the boundary between the transgressive and the highstand systems tracts the sequence boundary was created in response to falling sea level fluvial entrenchment shifted seaward with falling sea level therefore the boundary is a time transgressive unconformity and is not an isochronous boundary the transgressive surface is a nearby isochronous boundary that occurred when the shoreline had started to move landward from its maximum seaward excursion the ravinement surface is a diachronous surface created by shoreface erosion during transgression the shoreface erosion shifted landward with rising sea level and so the erosion surface created is time transgressive this surface is the most distinct bounding surface in the shelf sequence these characteristics of the bounding surfaces support and clarify the model of thorne and swift 1991 the transgressive systems tract on the shelf can be divided into two backstepping wedges separated by the ravinement surface the lower wedge consists of coastal plain and fluvial systems and the upper wedge is composed of transgressive sand and or sand ridges both the wedges show a backstepping depositional pattern which can be recognized in seismic records and cores these wedges correspond to the backstep backbarrier wedge and backstep shelf wedge of thorne and swift 1991 respectively

late quaternary deltaic lowstand wedges on the rhone continental shelf france abstract shallow seismic profiles on the rhone continental shelf have shown the existence of stacked progradational lowstand wedges on the outer shelf accumulated during late quaternary glacioeustatic lowstands the wedges are bounded by sharp to erosional sequence boundaries and onlap onto the middle shelf the thickness of individual wedges attains 50 meters at the shelf edge where they are sheared by slumping the wedges exhibit well developed progradational clinoforms episodically interrupted by internal unconformities on which there is a downward shift of the succeeding clinoforms these represent small scale in the order of a few meters falls in sea level during the quaternary eustatic cycles the durations of the stable highstand conditions appear to have been too brief to permit the regressive highstand tract to prograde to the outer shelf therefore the shelf edge builds up entirely with lowstand wedges

stratral architectures of late quaternary regressive transgressive cycles in the roussillon shelf sw gulf of lions france abstract a seismic and sequence stratigraphy scheme of the southwestern area of the gulf of lions shelf nw mediterranean basin is presented through the analysis of high resolution seismic profiles obtained with a minisparker system and calibrated with published seismic and core data of the adjacent languedoc area the observed stratigraphic architecture records the repetition of four regressive transgressive cycles which constitute high frequency depositional sequences dss regressive intervals dominate the generation of shelf sedimentary architecture within regressive intervals the identification of progressively shallower clinoforms from proximal to distal in a downdip direction constitutes a strong indicator of the occurrence of forced regressions this stratigraphic pattern documents the preservation of potential sand prone reservoirs encased within widespread regressive wedges and directly connected with organic matter rich muds as distally there is no sharp basal contact between the two the unusual preservation of pre last glacial maximum transgressive deposits is attributed to the combined influence of previous shelf topography and dominant wave regime the most significant transgressions were recorded by shallow water deposits in distal middle and proximal locations distal and proximal deposits develop over relatively steep surfaces which caused slower transgressions and favoured the generation of wave dominated coastal deposits in contrast middle deposits show moderate development over a smooth shelf profile as a consequence of rapid shoreline translation the analysis of spatial changes of regressive transgressive cycles provided important information about the nature of shelf processes and about the relative significance of regressive versus transgressive intervals within each individual ds whose development was led by recent high frequency sea level cycles dominance of 120 ka cycles would imply that transgressive deposits represent a partial record of glacial interglacial transgressions dominance of 20 ka cycles is not favoured by the fact that the preservation of quaternary deposits is apparently limited on the shelf

pyrobitumen in south china organic petrology chemical composition and geological significance abstract pyrobitumen has been discovered in the dolostone reservoir of the central sichuan basin southwest china accumulates coevally with hydrothermal minerals in pores the pyrobitumen has strong anisotropy with an evolutionary sequence from mosaic to a fibrous texture a similar sequence of anisotropy has also been observed in mesophase pitch during the process of coking coal reflectance of the pyrobitumen shows a positive correlation with anisotropic evolution and increasing depth hopane and sterane biomarkers are abundant in extracts of highly anisotropic pyrobitumen with smooth rough hyperplastic surface and honeycomb micropores methylpyrene and methylchrysene maturity indicators and the reflectance values of pyrobitumen show a positive linear correlation in cambrian samples but show random correlation in sinian samples fluid inclusion microthermometry of hydrothermal minerals together with the burial and heat flow history of the reservoir indicate an abrupt thermal event that may have impacted the generation and evolution of pyrobitumen this appears to be confirmed by the reflectance values of pyrobitumen in the source rock and reservoir the pyrobitumen in source rock was less heated by the hydrothermal fluid due to its poor porosity and have lower reflectance values however the pyrobitumen in weathering crust reservoir was more heated by the hydrothermal fluid and have higher reflectance values because the reservoir rocks have higher porosity the occurrence and characteristics of pyrobitumen indicate an in situ pyrolysis of oil which was triggered by an abrupt thermal event in the reservoir the reconstruction of burial history and heat flow as well as the hydrothermal fluid minerals of the dolomite reservoir all indicate the thermal event of the sichuan basin might correlate with the emei mantle plume in late permian

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

organic geochemical characteristics and accumulation of the organic matter in the jurassic to cretaceous sediments of the saihantala sag erlian basin china abstract the organic petrology and organic geochemistry of jurassic to cretaceous hydrocarbon source rocks from the saihantala sag the erlian basin have been analyzed to determine their geochemical characteristics hydrocarbon potential and organic matter accumulation the mudstones of the alatanheli formation j1 2al the aershan formation k1ba the lower tengger member k1bt1 and the upper tengger member k1bt2 and the saihantala formation k1bs contain variable total organic carbon concentrations and organic matter type the observed macerals in the j1 2al k1ba k1bt1 and k1bt2 mudstones are sapropelinites including lamalginites mineral bituminous groundmasses and rare telalginites vitrinites and inertinites in order of abundance whereas vitrinites and inertinites are the predominant macerals in the k1bs mudstones the vitrinite reflectances are lower than 0 7 in the studied samples suggestive of their low organic maturity which is consistent with the strong yellow fluorescence of the lamalginites and telalginites low tmax values the presence of 17 h 21 h hopanes and hop 17 21 enes and aliphatic and aromatic thermal maturity parameters the studied samples were mainly deposited under anoxic saline lake environments the major biological sources in the j1 2al k1ba k1bt1 and k1bt2 mudstones are bacteria and algae whereas higher plants are the more important biological source in the k1bs mudstones as indicated by biomarkers and maceral contents the j1 2al k1ba k1bt1 and k1bt2 mudstones mainly have more capacity to generate oil than gas whereas the k1bs mudstones are mainly gas prone despite the low thermal maturity of the studied mudstones abundant oil has been found in the southeast of the saihantala sag with mature source rocks the nature of their generated products was due to their different formation mechanisms of organic matter accumulation the organic matter accumulation in the j1 2al k1ba k1bt1 and k1bt2 mudstones was controlled by the high primary productivity and anoxic conditions whereas the formation of the k1bs organic rich sediments was mainly related with a high influx of higher plants

late quaternary transgressive and highstand systems tracts in the northern east china sea mid shelf abstract analysis of very high resolution 3 5 khz seismic profiles and sediment data from the northern east china sea mid shelf region reveals that the sedimentary sequence above the acoustic basement consists of five late quaternary sedimentary units comprising transgressive and highstand systems tracts formed after the last glacial maximum the transgressive systems tract includes four units 1 incised valley fill unit i 2 transgressive estuarine deltaic complex unit ii 3 transgressive sand sheet unit iii and 4 tidal sand ridge unit iv the lower two units units i and ii representing a paralic environment consist of sediment preserved from shoreface erosion the upper units units iii and iv corresponding to a marine environment consist of sediments produced through shoreface erosion during the holocene transgression a ravinement surface separates the lower and the upper units the highstand systems tract is composed of a distal mud patch unit v derived from the huanghe and changjiang rivers in china dispersal and deposition of this modern mud are largely controlled by the regional circulation pattern and sediment supply

seismic stratigraphic framework of the continental shelf offshore delmarva u s a implications for mid atlantic bight evolution since the pliocene abstract understanding how past coastal systems have evolved is critical to predicting future coastal change using over 12 000 trackline kilometers of recently collected co located multi channel boomer sparker and chirp seismic reflection profile data integrated with previously collected borehole and vibracore data we define the upper

discovery of oil bitumen co existing with solid bitumen in the lower cambrian longwangmiao giant gas reservoir sichuan basin southwestern china implications for hydrocarbon accumulation process abstract natural gas in the recently discovered lower cambrian longwangmiao giant gas reservoir of the sichuan basin in southwestern china has been considered to be from oil cracking and sourced from the underlying lower cambrian qiongzhusi shales similar to the underlying neoproterozoic dengying giant gas reservoir however geological considerations and differences in geochemistry between the longwangmiao and dengying gases bitumens imply different scenarios organic petrology geochemistry and trace element analyses of widely occurring bitumen were conducted to evaluate this hypothesis results show the coexistence of solid bitumen and oil bitumen in this reservoir for the first time which implies a new hydrocarbon accumulation process and associated exploration strategies the two types of bitumen were termed type a solid bitumen and type b oil bitumen which were sourced from the lower cambrian qiongzhusi formation shale and the lower silurian longmaxi shale respectively the type a solid bitumen shows little fluorescence and its color under plane polarized light is almost black this indicates that the type a solid bitumen is likely of high maturity it typically occurs in dissolution pores and accounts for approximately 90 of all bitumen in the reservoir in contrast the type b oil bitumen is brown black in color under plane polarized light and yellow green under fluorescence light indicating that it is mature it occurs in the residual spaces of the solid bitumen and represents approximately 10 of the total bitumen content this suggests that type a bitumen charged the reservoir earlier than did the type b bitumen during the indosinian epoch of the triassic oil generated from the mature qiongzhusi formation migrated into the longwangmiao and dengying reservoirs following this the dengying reservoir reached the temperature threshold for oil cracking since the late cretaceous and it is suggested that oil could have started to crack to gas which is the critical moment for the gas formation however the longwangmiao oils had not been cracked at this stage because the reservoir temperature had not reached the threshold later during the himalayan epoch the gas in the dengying reservoir as well as some kerogen cracking gas from the qiongzhusi shales migrated into the longwangmiao reservoir along faults gas gravity drainage and phase separation took place in the longwangmiao reservoir forming the type a solid bitumen and giant gas accumulation later oil generated from the longmaxi shales migrated into the longwangmiao reservoir forming the type b oil bitumen the case here is an example of a multi stage oil and gas accumulation future exploration targets should include middle upper cambrian reservoir rocks

giant gas discovery in the precambrian deeply buried reservoirs in the sichuan basin china implications for gas exploration in old cratonic basins abstract an estimated trillions of cubic meters of natural gas have recently been discovered in the sinian dolomite reservoirs in the sichuan basin china the 20 26 m thick reservoirs were found in deep structural lithologic traps of 5000 5500 m deep the sinian gas is thought to have been derived mainly from the sinian source rocks and partly from the cambrian source rocks the gas is thermally matured with a dryness ratio c1 c1 4 of 0 997 0 9998 c2h6 content

geo chromatographic fractionation effect of methyldibenzofuran in dolomite reservoirs and its application in tracing oil filling pathways in the sichuan basin abstract dibenzofuran and its methyl substituted homologues are the important oxygen containing polycyclic aromatic compounds in crude oils the ratio of 1 4 methyldibenzofuran has been successfully used in sandstone reservoir tracing oil migration orientation here we focus on the geo chromatographic fractionation effect of methyldibenzofuran mdbf in dolomite reservoirs we calculated the charge density differences between 1 methyldibenzofuran 1 mdbf and 4 methyldibenzofuran 4 mdbf based on density functional theory the e i n between mdbf isomers and dolomite 104 surface was also calculated according to molecular dynamics simulation the result show that comparing with the 4 mdbf there is strong interaction between 1 mdbf and dolomite 104 surface leading the ratio of 1 mdbf and 4 mdbf increase with the migration distance there is no significant correlation between bitumen reflectance and the ratio of 1 mdbf and 4 mdbf in our samples in addition molecular simulation results show that the mdbf isomers are thermodynamically stable and dissociation of ph ch3 is difficult to occur under geological condition all these demonstrate that 1 mdbf and 4 mdbf can be survived after oil cracking to gas and pyrobitumen therefore in theory the ratio of 1 4 methyldibenzofuran is also regarded as an index for oil migration orientation in dolomite reservoir gas chromatography mass spectrometry results show that mdbfs occur at relatively higher abundance in the bitumens of the ediacaran dengying formation z2dn4 and cambrian longwangmiao formation 1l in the sichuan basin the ratio of 1 4 methyldibenzofuran has been successfully used to trace the crude oil filling pathway in the z2dn4 and 1l dolomite reservoir in the sichuan basin in this study two preferential filling orientations i e from west to east and from north to south for paleo oil have been identified in the contour maps of 1 4 methyldibenzofuran in the z2dn4 and 1l which is consistent with the geological background

quaternary high resolution seismic sequence based on instantaneous phase of single channel seismic data in the south yellow sea china abstracts the south yellow sea sys is a semi closed epicontinental sea with a dense network of seismic reflection profiles preserving favorable depositional strata single channel seismic has been one of the primary technical methods used to study the characteristics of regional strata sediment since the neogene period based on two cores csdp 1 and qc2 and single channel seismic data obtained from continental shelf of the sys in 2013 we present analysis on sequence stratum and evolution environment for the quaternary around cores csdp 1 and qc2 in the middle and western sea areas of south yellow sea identification of instantaneous phase demonstrates more plentiful strata information instantaneous phase of marine deposits is seen to continue with horizontal level in most parts except the areas with some clay and clay silts continental units feature poor layering in instantaneous phase profile along with the two cores the result suggests that marine sedimentary time for the core csdp 1 was longer than that for the core qc2 since 700 ka and it may mean the existence of four regressions paleo shoreline lay between cores csdp 1 and qc2 during 700 460 ka 289 270 ka 75 29 ka and 13 1 10 3 ka different subsidence and climate comprehensively drove the evolution of sedimentation during the quaternary in sys

relation of sequence stratigraphy to modern sedimentary environments one method of testing the concept of sequence stratigraphy is to compare it to quaternary sediments in which chronology stratigraphic relations and facies geometry are more clearly understood than in older rocks rapid deposition rates during quaternary glacial eustatic cycles in large deltaic depocenters generate sequences comparable to those in the ancient stratigraphic record in the northern gulf of mexico the late wisconsinan holocene mississippi river has deposited a type 1 sequence that includes lowstand transgressive and high stand systems tracts characteristics of modern mississippi river sedimentary environments support the methodology used in sequence analysis but the short time taken for sequence generation here raises important questions about sequence time scales correlation and driving mechanisms

high resolution seismic study as a tool for sequence stratigraphic evidence of high frequency sea level changes latest pleistocene holocene example from the korea strait abstract sequence stratigraphic analysis of high resolution seismic reflection profiles and sediment data reveals that the latest pleistocene holocene deposits in the korea strait shelf off the southeastern korean peninsula form a high frequency sequence consisting of a set of lowstand transgressive and highstand systems tracts that corresponds to a fifth order 20 kyr sea level cycle eight depositional systems each with different seismic facies constitute the systems tracts the lowstand systems tract consisting of sandy mud forms a deltaic wedge that pinches out updip near or at the relict shelf edge the transgressive systems tract consisting mainly of sands includes six depositional systems 1 inner shelf transgressive layer 2 transgressive estuarine deltaic complex 3 transgressive sand ridge 4 mid shelf transgressive layer 5 incised channel fill and 6 beach shoreface complex although the transgressive systems tract is widely distributed it is much thinner than the lowstand and highstand systems tracts the highstand systems tract is composed of a prodelta shelf complex consisting almost exclusively of holocene muds the distribution and geometry of the systems tracts in the latest pleistocene holocene sequence in the korea strait shelf is different from that of vail s model in that 1 the lowstand systems tract consists only of the lowstand deltaic wedge which forms an elongated sediment body along the paleoshelf edge and 2 the highstand systems tract is completely confined to the inner shelf and forms a nearshore belt parallel to the coastline high frequency 20 kyr high amplitude magnitude of about 130 m sea level change together with strong currents flowing northeastward along the southeastern coast of the korean peninsula and varying sediment supply have resulted in this rather unusual stratigraphic architecture

organic geochemistry of marine source rocks and pyrobitumen containing reservoir rocks of the sichuan basin and neighbouring areas sw china abstract three bitumen fractions were obtained and systematically analysed for the terpane and sterane composition from 30 paleozoic source rocks and 64 bitumen containing reservoir rocks within the upper sinian lower cambrian lower silurian middle carboniferous upper permian and lower triassic strata in the sichuan basin and neighbouring areas china these bitumen fractions include extractable oils bitumen i oil bearing fluid inclusions and or closely associated components with the kerogen or pyrobitumen mineral matrix released during kerogen or pyrobitumen isolation and demineralization bitumen ii and bound compounds within the kerogen or pyrobitumen released by confined pyrolysis bitumen iii in addition atomic h c and o c ratios and carbon isotopic compositions of kerogen and pyrobitumen from some of the samples were measured geochemical results and geological information suggest that 1 in the central sichuan basin hydrocarbon gases in reservoirs within the fourth section of the upper sinian dengying formation were derived from both the lower cambrian and upper sinian source rocks and 2 in the eastern sichuan basin hydrocarbon gases in middle carboniferous huanglong formation reservoirs were mainly derived from lower silurian source rocks while those in upper permian and lower triassic reservoirs were mainly derived from both upper permian and lower silurian marine source rocks for both the source and reservoir rocks bitumen iii fractions generally show relatively lower maturity near the peak oil generation stage while the other two bitumen fractions show very high maturities based on terpane and sterane distributions tricyclic terpanes evolved from the distribution pattern c20 c23 finally to c20 c21 c23 during severe thermal stress the concentration of c30 diahopane in bitumen iii the bound components released from confined pyrolysis is substantially lower than in the other two bitumen fractions for four terrigenous upper permian source rocks demonstrating that this compound originated from free hopanoid precursors rather than hopanoids bound to the kerogen

sequence stratigraphy and depositional setting of the tiber delta integration of high resolution seismics well logs and archeological data abstract using archeological evidence radiocarbon data well logs and high resolution seismic profiles we applied sequence stratigraphic analysis to sediments deposited during the last glacio eustatic cycle on the tyrrhenian continental margin embracing the tiber river months these sediments form a high frequency sequence of fifth order that has developed over the last 20 000 yr since the last lowstand hereafter referred to as the tiber depositional sequence tds the tds is still evolving and lies on a type 1 sequence boundary that has been identified both on the shelf and below the present delta plain this sequence consists of lowstand transgressive and highstand systems tracts the lowstand deposits are not present on the shelf but are found on the continental slope where they constitute the last progradation set of the continental margin a network of gullies active when the river mouth was at the shelf break is present within the lowstand deposits the transgressive systems tract tst deposits lie directly on the basal unconformity landwards the tst is represented by a retrogradational parasequence set of fluvial coastal barrier lagoon and lagoonal delta facies seaward on the shelf these parasequences merge into a seismically transparent deposit that forms a condensed section the flooding surfaces that bound the parasequences are marked by peat layers that were dated by 14c the radiometric ages were used to draw a carve of sea level rise for the last 11 000 yr the top of the transgressive systems tract maximum flooding surface is represented by the last peat layer which was formed about 4700 5000 yr bp and buried 4 5 m below the present upper delta plain the highstand systems tract is made up of deposits of the present tiber wave dominated delta i e upper and lower delta plain delta front and prodelta slope the aligned beach ridges mark the position of the prograding coastline which for the last 2500 yr can be dated by archeological and historical data the recent very fast progradation of the tiber delta during the last 500 years is consistent with historical data on floods of the city of rome and the suspended load of the tiber river

stratigraphic organization of late pleistocene deposits of the western part of the golfe du lion shelf languedoc shelf western mediterranean sea using high resolution seismic and core data detailed analysis of shallow penetration single channel seismic data integrated with piston core data reveals that the stratigraphic architecture on the rhone shelf of the western mediterranean sea is characterized by a complex stratigraphy comprising both the regressive and transgressive parts of late pleistocene depositional sequences several cycles of deposition are observed and are interpreted to be associated with fourth or possibly fifth order cycles of relative change of sea level the regressive parts of the sequence are inferred to have been deposited either during late highstand or during periods of relative fall of sea level these deposits are characterized in some instances by discrete downstepping wedges and internal downward shift surfaces however in other instances this evidence is not present the transgressive parts of the depositional sequences are characterized by backstepping wedges and isolated sand bars in general these types of deposits are more common on the western part of the rhone shelf and are largely absent on the extreme eastern part of the shelf the transgressive deposits seem to be preferentially preserved at both inner and outer shelf locations and less so in the middle shelf the exception to this is the area near the rhone delta depocenter where transgressive deposits are observed across the entire shelf key surfaces separating stratigraphic units include ravinement surfaces downlap surfaces and subaerially formed erosional surfaces these stratal discontinuity surfaces constitute the basis for analysis of the stratigraphic architecture this area is dominated by seismic reflection geometries suggesting a high energy depositional environment relatively steeply dipping seismic reflections bounded by horizontal to irregular erosional surfaces characterize most of the upper pleistocene section in this area the high energy seismic facies correspond to three types of deposits 1 thick regressive sands of lobate delta front origin 2 retrogradational beach barriers overlying the regressive wedge on the outer to middle shelf and 3 late transgressive beach sands and ridges observed at the inner shelf the stratigraphic complexity illustrated here is likely analogous to similar although commonly undetected complexity that characterizes petroleum fields in shallow shelf settings a variety of geomorphic elements have been interpreted here these include transgressive sand bars wave dominated distributary mouth bars recurved spits isolated shelf edge shoreface beaches and distributary channels these elements are consistent with an interpretation of a depositional environment characterized by wave dominated delta deposition the morphology of the delta in the eastern part of the shelf i e near the depocenter seems to be consistent from the outer to inner shelf location suggesting that the position of the shoreline relative to the shelf edge and the presence of submerged shelf outboard of the shoreline had only minor impact on deltaic deposition moreover climatic change and changes of fluvial discharge that likely characterized this area during the end page 119 late pleistocene similarly had only minor effect on delta morphology

releasing the sequence stratigraphy paradigm overview and perspectives sequence stratigraphy arose as a paradigm in stratigraphy after the integration of the descriptive seismic method introduced by exxon researchers in the 1970s with genetic concepts linking seismic attributes to sedimentary dynamics since then the sequence stratigraphy model underwent significant modification owing to the increasing scenarios of application each with its own practical requirements this led to the fragmentation of the original model into a plethora of sub methods and the flourishing of redundant notions and terminology reviewers striving to preserve the unity and fitness of sequence stratigraphy systematically weakened the central assumption by which it stood as a novelty and a paradigm the relevance of relative sea level cycles in shaping strata sequentially in contrast to this attitude the value of a model explicitly relying on the upholding control of sea level is herein reconsidered based on the marine record of quaternary climate driven sea level cycles traditionally conceived as exceptionally short lived and extraordinary events in the history of the earth these cycles are documented worldwide on modern continental margins providing convincing evidence of how sea level fluctuations actually shape sequences

sequence stratigraphy seismic profiles and cores of pleistocene deposits on the rhone continental shelf abstract high resolution seismic profiles on the rhone deltaic shelf has shown the existence of a complex of pleistocene superimposed prograding wedges interrupted by a major incised valley system cutting across the shelf the individual wedges are interpreted from internal geometry and coring data as prograding shoreface deposits accumulated during periods of relative sea level lowering punctuated by small scale relative sea level falls or forced regressions they are related to 5th order glacio eustatic cycles and are stacked to form a composite 4th order sequence radiocarbon dating tandetron ams of the upper wedge to 40 ka bp indicates a stratigraphic hiatus across the shelf corresponding to the glacial maximum lowstand at the end of the wurmian cycle isotopic stage 2 during which sea level had dropped to 120 m below present sea level seaward tilting of the wedge boundaries indicate that the shelf has been subjected to differential subsidence that provides the necessary accommodation space for deposits to accumulate on the mid outer shelf the seaward tilting results from a cumulative effect of sediment and hydrostatic loading tectonism is also expressed by a westward shore parallel tilting in the area east of the incised valleys the amount of tilting the stacking pattern of the wedges and the location of incised valleys are structurally controlled by the alpine orogen which dips westward under the rhone margin the tectonic component interacts with glacio eustatic sea level fluctuations and accounts for the partition of the shelf into two areas with specific features separated by the rhone incised valleys

catastrophic soil erosion during the end permian biotic crisis organic geochemical analyses of sedimentary organic matter from a marine permian triassic transition sequence in northeastern italy reveal a significant influx of land derived diagenetic products of polysaccharides this unique event reflects massive soil erosion resulting from destruction of land vegetation due to volcanogenic disturbance of atmospheric chemistry the excessive supply of soil materials to the oceans provides a direct link between terrestrial and marine ecological crises suggesting that ecosystem collapse on land could have contributed to the end permian marine extinctions

stratigraphic architecture and spatio temporal variability of high frequency milankovitch depositional cycles on modern continental margins an overview abstract this study is a review of quaternary milankovitch cycles as recorded on modern continental shelves worldwide on the background of the many existing examples we focus on selected case studies from mediterranean adriatic and tyrrhenian seas and atlantic gulfs of mexico and cadiz margins that represent general and peculiar characters of middle upper pleistocene sequences forming under the control of composite 100 and 20 ka milankovitch cycles the most pervasive stratigraphic pattern displayed by shelf deposits is referred to the 100 ka sea level cycle and consists of fairly uniform depositional sequences mostly composed by regressive deposits forming during the falling limb of the sea level curve these are generally classified as falling stage systems tract fsst and display a regressive facies architecture reflecting the dominant control of sea level on many margins fsst units may show slight though significant differences with respect to highstand systems tract hst and lowstand systems tract lst regressive units more closely reflecting environmental changes and the local variability of depositional systems in contrast with the theoretical and overall scale independent model developed to predict composite stratigraphic cycles and sequences the middle upper pleistocene stratigraphic record from numerous shelf settings shows a subdued signature of the higher frequency 20 ka milankovitch cyclicity however when detectable the 20 ka architectural pattern is characterized by a relatively greater spatial and temporal variability compared to 100 ka sequences this fact likely reflects the increasing importance of factors controlling the depositional environment e g seafloor morphology oceanographic regime sediment input and dispersal etc with respect to sea level change during the shorter intervals encompassed by 20 ka cycles on this basis two end member cases have been distinguished depending on the generation or not of high frequency sequence boundaries a prerequisite to qualify the higher frequency motifs as depositional sequences these two end members are comprehensive of the highly variable patterns displayed by middle upper pleistocene shelf sequences which in turn reflect the interplay between the geological setting the dominant sea level control and the effective response of sedimentary systems the variable stratigraphic patterns of milankovitch cycles represent conceptual and practical constraints as to the classification of high frequency quaternary sequences under the general schemes of the standard sequence stratigraphy model

late quaternary inner shelf deposits in response to late pleistocene holocene sea level changes nakdong river se korea abstract the high resolution seismic profiles from the inner shelf off the nakdong river in se korea can be directly correlated with the lithologic characteristics in the borehole data these correlations offer an opportunity to document the evolution of the inner shelf deposits with sediment supplies in response to the late quaternary sea level changes the inner shelf sequence in this area consists of four sedimentary units which comprise a set of lowstand transgressive and highstand systems tracts deposited since the last glacial maximum incised channel fill su1 estuary su2 sand veneer su3 and subaqueous delta su4 the lowermost unit su1 which overlies the sequence boundary is interpreted as fluvial deposits formed during the last glacial period and the early stage of transgression and belongs to the lowstand to transgressive systems tract the lower middle unit su2 lying below the ravinement surface represents a paralic component that consists of estuarine sandy mud or muddy sand developed between approximately 13 and 8 cal ka bp whereas the upper middle unit su3 above the ravinement surface corresponds to a marine component that consists of sand veneer produced by the shelf erosion during the ensuing sea level rise these two units su2 and su3 belong to the transgressive deposits the uppermost unit su4 regarded as the highstand systems tract formed the nakdong subaqueous delta including the proximal and distal systems developed after the highstand sea level at approximately 6 cal ka bp the lateral transition from the proximal to distal facies suggests a prograding delta system in the nakdong river

late pleistocene holocene sediments on the spanish continental shelves model for very high resolution sequence stratigraphy abstract sequence stratigraphy analysis of high resolution seismic profiles geopulse uniboom and 3 5 khz of late pleistocene holocene sediments has been carried out on five sectors of the spanish continental margin four types of depositional settings are distinguished in these sectors 1 low subsident ramps alboran margin cadiz gulf 2 high subsident 2m kyr ramps alicante valencia 3 ria type morphology on the atlantic passive margin ria de muros and 4 fault scarp morphology systems with subsidence balearic margin a type 1 sequence is interpreted in all these sectors being composed of lowstand systems tract transgressive systems tract and highstand systems tract this conforms to the basic concepts of sequence stratigraphy and each systems tract correlates with a particular part of the last eustatic hemicycle characteristic shelf features such as terraces terraces with beach deposits and progradational sediment wedges evidence a complex stacking of lesser sub sequences in all the systems tracts which must be related to very short period sea level stillstands and fall we propose a very high resolution sequence stratigraphy model in which the last sea level hemicycle is punctuated by p cycles 4500 years which give rise to the neo glacial events h cycles 2200 950 years and c cycles 500 50 years these cycles interact with each other thus establishing the placing of the high and low sea levels this attention to detail 1 explains sedimentary evolution on both the shelf and upper slope during late pleistocene holocene time 2 illustrates some departures from the classical sequence stratigraphy model and 3 also demonstrates that the late pleistocene holocene eustatic curve is not one simple transgression but is modulated by three differing period cycle groups below the milankovitch band our model is delimited by fluctuating sea level during pleistocene holocene times such features should be identifiable on any continental margin however localized features occur due to subsidence and continental shelf morphology which determ ine the location and depth of sedimentary bodies generated in each eustatic cycle

geometry lateral variation and preservation of downlapping regressive shelf deposits eastern tyrrhenian sea margin italy abstract the shelf of the eastern tyrrhenian sea margin changes substantially in width shelf break depth and sea floor steepness over relatively short distances largely owing to pronounced lateral changes in subsurface geologic structure remnants of late pleistocene prograded coastal deposits are locally preserved on the middle and outer parts of the shelf we recognize two major controls on the distribution lateral extent thickness and preservation potential of these prograded deposits first prograded downlapping deposits formed only where the physiographic shelf break was deeper than the lowstand shoreline thus providing accommodation space for the lowstand deposits second the proximity and relative size of sediment sources and the local coastal dispersal system apparently infl enced the geometry of the deposit midshelf and shelf margin bodies composed of seaward steepening downlapping reflectors were deposited as thin to thick continuous prograding sheets over an irregular eroded shelf surface and onto the shelf edge during the latest fall and lowstand of sea level decreased sedimentation at the end of this lowstand resulted in net erosion during sea level rise shoreface erosion created a major marine erosional ravinement surface landward of the 120 m isobath and much of the downlapping deposits were removed preservation of these downlapping deposits is largely a function of their thickness thick continuous deposits are common on the shelf edge whereas on the midshelf only thin remnants are preserved locally where depressions or morphologic steps were present in the shelf surface

evolution of late quaternary deposits on the inner shelf of the south sea of korea abstract high resolution 3 5 khz seismic profiles and sediment samples were analysed to delineate the shallow seismic stratigraphy of late quaternary deposits in the central part of the korean south sea the stratigraphy above the acoustic basement is represented by three distinct sedimentary sequences separated by erosional boundaries the upper sequence a has an acoustically semi transparent signature usually without distinct internal reflectors and overlies the flat lying mid reflector r the sediments in this sequence consist of bioturbated terrigenous mud derived mainly from the seomijin river they have developed during the last 5000 yrs and have an accumulate rate of 10 40 cm 100 yrs reflector r represents the postglacial transgressive layer formed during the last stage of the holocene sea level rise approximately between 7000 yrs b p and 5000 yrs b p the middle sedimentary sequence b below r shows parallel to subparallel internal reflectors and prograding clinoforms that have formed largely during the last glacial period the top of this sequence displays various erosional channels and transparent fills produced by subaerial and fluvial erosion of the pre existing shelf the submerged channels indicate the existence of a paleochannel system presumambly the extension of the paleo seomijin river during the sea level lowstand the lower sequence c has an irregular erosional upper surface and an acoustically transparent subbottom it is interpreted as the erosional remnants of earlier pleistocene sediments formed in shallow water environments

late quaternary lowstand wedges on the shelf margin and trough region of the korea strait abstract high resolution sparker profiles collected from the korea strait reveal a distinct pattern of stacked progradational sedimentary wedges on the shelf margin and trough region these sedimentary wedges comprise a succession of three distinct units a lower b middle c upper unit bounded by erosional unconformities and their internal structures show well stratified complex sigmoid oblique types the isopach map shows that the wedges thicken seaward and their landward limit is in about 100 120 m water depth according to the internal structure distribution pattern and radiocarbon dates these sedimentary wedges are interpreted to have been formed during the glacioeustatic sea level lowstands multiple falls of sea level during the late quaternary coupled with high sediment discharge from the paleo nakdong river system resulted in the formation of thick lowstand wedges three intervals of wedge building are recorded the youngest one unit c is interpreted to mark the last glacial period while the middle one unit b represents the lowstand period before the last interstadial

evolution and chronology of late pleistocene shelf perched lowstand wedges in the korea strait abstract detailed interpretation of high resolution seismic profiles from the korea strait has shown the existence of a complex of three stacked sedimentary sequences on the outer shelf the individual sequences consisting of prograding wedge are interpreted from internal structure and sediment data as a shelf perched lowstand wedge system related to alternating episodes of successive regression and transgression although the entire sequences have not been fully dated it is believed that the sequences were deposited during late pleistocene sea level lowstands repeated falls of sea level isotopic stages 8 6 and 2 resulted in the formation of lowstand sedimentary sequences during subsequent episodes of sea level rise isotopic stages 8 7 6 5 and 2 1 the sequences were reworked and draped by thin transgressive sands

very high resolution seismics as a tool for sequence stratigraphy applied to outcrop scale examples from eastern tyrrhenian margin holocene pleistocene deposits three eastern tyrrhenian continental margin areas with very different depositional and tectonic settings were analyzed using single channel very high resolution reflection seismics coupled with sea floor sampling fourth and fifth order depositional sequences derived from quaternary glacio eustatic processes are now buried at shallow depths within the continental shelf the sequences have been reconstructed in detail with great lateral continuity the tectonic setting did not influence the development of high order sequences which are probably synchronous at a global scale within these sequences it has been possible to recognize all the systems tracts hypothesized by sequence stratigraphy models confirming that this method does not depend upon time or scale the geom try of depositional sequences is strongly dependent on sedimentation rate i e on the distance from sources local factors such as transport pattern variations caused by sea level changes paleotopography of the transgressed surface characteristics of feeding hydrographic nets and interactions with bioconstructions must be considered because they play an important role in the geometrical development of depositional sequences in high order depositional sequences lowstand systems tracts are volumetrically predominant highstand and transgressive systems tracts seem to be linked to point sources because they have a three dimensional 3 d geometry on the contrary lowstand systems tracts are related to linear sources parallel to the shelf break they cause the progradation of the whole margin so that they form the margin structure almost entirely