sedimentary facies and evolution in the qiantang river incised valley eastern china abstract this paper deals with the sedimentary facies and evolution of the qiantang river qr estuary and the characteristics and formation of the incised valley sequences and the related shallow biogenic gas reservoir on the basis of analysis of over 500 cores the result shows that since the last glaciation the late quaternary formation of the qr estuary area underwent three stages 1 deep cutting stage 2 rapid filling stage and 3 burial stage the fall of global sea level during the last glacial maximum enhanced the fluvial gradient and river cutting resulting in the formation of the large scale qr and taihu incised valleys with the interfluve being exposed to air on both flanks of the incised valley fluvial terraces at the elevations are present near the present qr estuarine mouth corresponding to 60 70 90 100 and 115 125 m burial depths the valleys were filled rapidly with fluvial sediments during the post glacial period with the rise of sea level the river mouth migrated to landward and backwater and retrogressive aggradation was enhanced the qr and taihu incised valleys are associated with an early filling and transgressive channel infilling sequence formation and a late filling and transgressive floodplain estuary formation subsequently the qr valley was buried under estuarine marine and estuarine sand bar sediments from bottom to top the incised valley successions can be grouped into four sedimentary facies river channel floodplain estuary estuary shallow marine and estuary sand bar the thickness of the river channel infilling deposits is controlled mainly by base level rising backwater retrogressive aggradation and neotectonism further localized thickening took place where deeper scour pools were present in the incised valley or fluvial terraces were formed during the fall of elative sea level during the deposition of the floodplain estuary facies the conditions of sea level rise tidal regime sediment supply and accommodation space were suitable for the development of a tidal ridge system the sand lenses associated with this facies may represent a tidal ridge system in the incised valley at the later stage when the estuarine sand bars were formed the sedimentary conditions were no longer favourable resulting in absence of sand ridge deposits biogenic gas is stored in the floodplain estuary sand lenses of the incised valleys the changjiang river provides the major sediment supply for the qr estuary sand bar and the qr carried sediments constitute only a small portion of the deposits

early to middle holocene rice cultivation in response to coastal environmental transitions along the south hangzhou bay of eastern china abstract south hangzhou bay shb in eastern china is one of the regions where agriculture began in the early holocene to better understand how farming based societies developed in this region we examined pollen charcoal foraminifera and grain size information of a well dated sediment core yj1503 in the yaojiang valley yjv pollen assemblages show that before 8600 cal yr bp pinus quercus juglans and pterocarya woodlands were dominant during ca 8600 8400 cal yr bp abundant foraminifera suggest a transient marine incursion although the former woodland species re established during 8400 7600 cal yr bp freshwater algae and dinoflagellates indicate a transition to brackish environments two peaks of charcoal at around 8200 and 7800 cal yr bp are possible early signs of human occupation that pre dated the hemudu culture after 7600 cal yr bp an increase of salt tolerant herbs including chenopodiaceae cyperaceae and poaceae

catastrophic tidal expansion in the bay of fundy canada tidal models for the bay of fundy canada site of the highest recorded modern tide show that tidal amplification began in the early holocene and by ca 5000 bp the range was almost 80 of the present range empirical data consisting of 146 sea level index points and other observations appear to contradict model results aggregated relative sea level data for chignecto bay and minas basin show that rapid tidal expansion began ca 3400 bp however if we separate these two geographically separate data sets evidence for this rapid late holocene tidal expansion is confined to minas basin we explain this singularity by positing a barrier at the mouth of minas basin at the minas passage that delayed tidal expansion with the rapid breakdown of this barrier and near instantaneous tidal expansion water temperature dropped tidal currents and turbidity increased and the form of the inner estuary was changed from lagoonal mesotidal to macrotidal we argue that the catastrophic breakdown of the barrier is

facies architecture and depositional model of a macrotidal incised valley succession qiantang river estuary eastern china and differences from other macrotidal systems filling of the modern coastal zone portion of the qiantang river qr in eastern china was initiated by marine inundation during the transgression after the last glacial maximum and has continued during the holocene sea level stillstand the early part of the fill is transgressive in character while the younger part is regressive this paper deals with the sedimentary facies surfaces architecture and depositional model of the qr incised valley fill based on the detailed analysis of the newly drilled core se2 and its correlation with more than 800 boreholes the incised valley deposits are grouped into five stacked facies amalgamated channel floodplain and channel paleo estuary offshore shallow marine and present day estuary a paleo estuary facies had never been identified before making these observations novel this facies is characterized by a sedimentary succession and sediment distribution that are distinct from those of the present day estuary because of a change in sediment supply from the sea floor beyond the estuary mouth it also contains large numbers of tidal channel sand bodies that are significant reservoirs for shallow biogenic gas since the last glaciation there have been three stages in the development of the qr incised valley fill sequence 1 a formation stage associated with sea level fall 2 a filling stage during the early transgression with rapid sea level rise and 3 a burial stage corresponding to the slowing of sea level rise and the onset of progradation this fill consists of four longitudinal segments each of which is distinguished by a distinct stratigraphic succession and different degrees of marine and fluvial influence the basal erosion surface and sidewalls of the incised valley the top of stiff clay on the interfluves and the top of falling stage fluvial terrace deposits compose the sequence boundary the initial flooding surface and maximum flooding surface are located within the amalgamated channel and offshore shallow marine sediments respectively these observations indicate that 1 relative sea level changes determine the stratal stacking patterns but local environmental factors such as physical processes accommodation sediment supply and coastal configuration control the nature of the facies surfaces and sediment distribution patterns and 2 the tripartite facies organization and wave ravinement surfaces typifying wave dominated or mixed energy wave and tide incised valley fills are absent in the macrotidal qr succession and the tidal ravinement and erosion surfaces of the macrotidal qr incised valley are more extensive and numerous than those of the wave dominated or mixed energy succession

sedimentary facies of the tide dominated paleo changjiang yangtze estuary during the last transgression abstract a large estuary was formed by marine inundation of the paleo changjiang yangtze incised valley during the transgression after the last glacial maximum this paper presents the sedimentary facies and architecture of the estuary fill based on the analysis of three sediment cores cm97 js98 and hq98 obtained from the present changjiang delta plain estuary fill deposits showing an upward fining succession were grouped into five depositional facies tidal river distributary channel muddy intertidal to subtidal flats transgressive lag and estuary front based on sedimentary textures lithology and physical sedimentary structures sand mud couplets are common in these deposits indicating that tides played a significant role in producing these sedimentary structures and that the estuary type was tide dominated some of the successive sand mud couplets probably recorded neap spring cycles as well as semidiurnal tidal cycles the nature of the estuary was very different from other representative tide dominated estuaries in sediment facies its distribution and sediment source for estuarine fill unlike the other estuaries that receive sediments mainly from the sea the paleo changjiang estuarine fill deposits were supplied largely from the river this difference would also have a great influence on the sedimentological and morphological component in the estuary the sediment distribution of the estuary showed fining seaward and estuary mouth sand bodies fed by marine source sand were absent the architecture model of tide dominated estuaries should be divided into two types by the degree of fluvial sediment supply the paleo changjiang estuary shows a good example for an estuary of large rivers

paleotidal regime in the changjiang yangtze estuary the east china sea and the yellow sea at 6 ka and 10 ka estimated from a numerical model abstract two dimensional paleotidal simulations were carried out to investigate the paleotides and paleotidal currents in the changjiang yangtze estuary the east china sea and the yellow sea calculations were made for 10 ka 6 ka and the present an age of 10 ka corresponds to a period during the last deglaciation when the sea level was about 45 m below its present level at that time the changjiang estuary extended southeastward to the east china sea for about 400 km the second period 6 ka coincides with the maximum holocene transgression in eastern china the paleotopography around the changjiang estuary was reconstructed for 10 ka and 6 ka using available borehole datasets to remove the holocene strata at 10 ka the spatial distribution of m2 tides was different from today no amphidrome was present in the yellow sea and the current velocity was generally larger on the continental shelf strength and ellipticity of the simulated tidal currents indicated that the northern part of the moribund tidal sand ridge system in the east china sea might have been formed at around this period on the other hand the tidal field at 6 ka was similar to that at present except for the region within and adjacent to the paleo changjiang estuary a radial tidal flow pattern was originated from the estuary mouth which seemed to have enhanced tides and tidal currents in the estuary

rapid onset of late paleozoic glaciation on gondwana evidence from upper mississippian strata of the midcontinent united states direct evidence of the late paleozoic glaciation of gondwana from glacial deposits suggests that geographically extensive continental glaciation began some time in the namurian late mississippian however the timing and characteristics of the onset of glaciation are poorly understood because of a lack of reliable paleontological control and reworking of initial glacial deposits by subsequent glacial advances indirect evidence of glaciation preserved in unconformity bounded low latitude ramp sequences in the illinois basin united states suggests that geographically extensive continental glaciation of gondwana actually began in the late visean an abrupt change from carbonate dominated sequences bounded by disconformities with little evidence of erosion to mixed carbonate siliciclastic sequences bounded by unconformities with deep incised valleys was likely produced by a three fold increase in the magnitude of eustatic sea level fluctuations the increase in the magnitude of sea level fluctuations was likely driven by an equally abrupt increase in ice volume and marks the onset of the geographically extensive late paleozoic glaciation of gondwana a possible explanation for the rapid onset of glaciation is the closing of the equatorial seaway between laurussia and gondwana closing of this seaway would have led to an abrupt change in oceanic and atmospheric circulation patterns that could have initiated major continental glaciation in the southern hemisphere

reasons for the low sedimentation and slow progradation in the pearl river delta southern china during the middle holocene abstract holocene sea level rise monsoonal discharge and human activity have been the main drivers for the evolutionary history of asian deltas in theory when sea level ceased to rise in around 7000 cal a bp deltas should have started to prograde seawards however previous studies revealed that the progradation of modern deltas was initially very slow and more importantly sediment accumulation within central deltaic basins was exceptionally low between 7000 and 4000 cal a bp in order to investigate the main reasons for such slow progradation and low sedimentation during the middle holocene this study reconstructed the sedimentary history of the head area of the pearl river delta the results show marine transgression from 9500 to 7500 cal a bp followed by marine regression starting from 7500 to 4000 cal a bp in response to sea level change during the latter period sedimentation was concentrated in the head area the amount of sediment entering the central basin was significantly reduced this limited amount of sediment was spread thinly across the wide deltaic basin a portion of it could have been transported out into the south china sea by the strong tidal currents resulting in an exceptionally low sedimentation in the central basin however in locations adjacent to former present islands locally supplied sediment helped sedimentation to continue from 7500 to 4000 cal a bp by about 4000 cal a bp the deltaic shoreline advanced into the central basin this period saw an increase of human activity that caused soil erosion and sediment supply leading to a marked increase in sedimentation rate active land reclamations also helped the acceleration of shoreline advance this sedimentary evolution model in the pearl river delta mirrors those of other deltas in the monsoonal asia

features and sealing mechanism of shallow biogenic gas in incised valley fills the qiantang river eastern china a case study abstract late quaternary shallow biogenic gas reservoirs have been discovered and exploited in the qiantang river qr estuary area eastern china the fall of global sea level during the last glacial maximum resulted in the formation of the qr incised valley from bottom to top the incised valley successions can be grouped into four sedimentary facies river channel facies floodplain estuarine facies estuarine shallow marine facies and estuarine sand bar facies all commercial biogenic gas pools occur in floodplain estuarine sand bodies of the qr incised valley and its branches the deeply incised valleys provided favorable conditions for the generation and accumulation of shallow biogenic gas the clay beds that serve as the direct cap beds of the gas pools are mostly restricted within the qr incised valley with burial depths ranging from 30 to 80 m remnant thicknesses of 10 30 m and porosities of 42 2 62 6 in contrast the mud beds cover the whole incised valley and occur as indirect cap beds with burial depths varying from 5 to 35 m thicknesses of 10 20 m and porosities of 50 6 53 9 the pore water pressures of clay and mud beds are higher than that of sand bodies and the difference can be as much as 0 48 mpa the pore water pressures of clay or mud beds can exceed the total pore water pressure and gas pressure of underlying sand reservoirs shallow biogenic gas can be completely sealed by the clay and mud beds which have higher pore water pressure the direct cap beds have better sealing ability than the indirect cap beds generally the pore water pressure dissipation time of clay and mud beds is conspicuously longer than that of sand beds this indicates that the clay and mud beds have worse permeability and better sealing ability than the sand beds however once the gas enters the sand lenses the pore water pressure cannot release efficiently

the effect of sea level climate and shelf physiography on the development of incised valley complexes a modern example from the east china sea abstract analysis of high resolution seismic reflection and sonar data from the east china sea ecs continental shelf reveals the presence of an extremely broad 330 km and deep maximum incision of 72 m incised valley complex whose development and subsequent fill is constrained to the end of the last glacial cycle 20 000 yr bp to present results from this study indicate that sea level change climate controlled discharge and sediment supply and shelf physiography were important factors in the development and subsequent fill of the ecs incised valley complex for example wet climatic conditions during the initial marine oxygen isotope stage mis 2 fall of sea level promoted fluvial erosion of the exposed shelf however the trend toward drier conditions during the mis 2 fall of sea level slowed the overall development of the incised valley complex to the point where only minor incision occurred during the maximum lowstand furthermore the low gradient morphology of the exposed outer shelf diminished the ability of fluvial systems to incise instead fluvial systems migrated laterally creating a shallow 300 km incised valley system on the outer shelf during the late mis 2 rise of sea level accommodation was generated within the flooded reaches of the valley complex however arid climatic conditions that prevailed at this time resulted in minor sediment delivery to the transgressive shoreline via the incised valley complex thus the upper part of the drowned lowstand fluvial deposits were exposed at the sea floor and reworked into a valley wide tidal bar and tidal sheet complex wetter climatic conditions during middle to late mis 1 resulted in abundant sediment delivery to the drowned parts of the valley complex estuary and buried lowstand fluvial deposits below the depth of tidal ravinement where they remained undisturbed current sequence stratigraphic models can be applied to the late quaternary stratigraphic secession of the ecs however these models are too simplistic because they rely largely on rates and directions of sea level change to explain stratal architectures although the extent and rate of sea level change is extremely important this study shows that high frequency climate change and shelf physiography also play important roles in the development of stratigraphic architectures these factors are particularly important for the development of incised valleys where they directly influence incised valley morphology and facies distributions

the lowermost mississippi river a mixed bedrock alluvial channel in this study the distribution of channel bed sediment facies in the lowermost mississippi river is analysed using multibeam data complemented by sidescan sonar and compressed high intensity radar pulse seismic data as well as grab and core samples of bed material the channel bed is composed of a discontinuous layer of alluvial sediment and a relict substratum that is exposed on the channel bed and sidewalls the consolidated substratum is made up of latest pleistocene and early holocene fluvio deltaic deposits and is preferentially exposed in the deepest thalweg segments and on channel sidewalls in river bends the exposed substratum commonly displays a suite of erosional features including flutes that are quantitatively similar in form to those produced under known laboratory conditions a total of five bed facies are mapped three of which include modern alluvial deposits and two facies that are associated with the relict substratum a radius of curvature analysis applied to the mississippi river centreline demonstrates that the reach scale distribution of channel bed facies is related to river planform from a broader perspective the distribution of channel bed facies is related to channel sinuosity higher sinuosity promotes greater substratum exposure at the expense of alluvial sediment for example the ratio of alluvial cover to substratum is ca 1 5 1 for a 45 km segment of the river that has a sinuosity of 1 76 and this ratio increases to ca 3 1 for a 120 km segment of the river that has a sinuosity of 1 21 the exposed substratum is interpreted as bedrock and given the relative coverage of alluvial sediment in the channel the lowermost mississippi river can be classified as a mixed bedrock alluvial channel the analyses demonstrate that a mixed bedrock alluvial channel boundary can be associated with low gradient and sand bed rivers near their marine outlet

forced regressions in a sequence stratigraphic framework concepts examples and exploration significance sequence stratigraphic concepts suggest that stratal geometries develop and are largely controlled by changes in relative sea level on the shelf lowstand deposits which form during falls and subsequent stillstands of relative sea level can be recognized by the presence of an unconformity at the base the isolated and basinward position relative to the previous shoreline and the abrupt seaward translation of shallow water and shoreline facies into the basin across an unconformity surface this seaward translation of facies and shoreline regression in response to relative sea level lowering is termed a forced regression a forced regression is independent of variations of sediment flux and is in contrast with normal regressions that occur in response to excess sediment flux relative to space available on the shelf i e accommodation forced regressions commonly are associated with a zone of sedimentary bypass subaerial exposure and possible fluvial erosion between the newly formed and preceding shorelines certain shelf sands previously interpreted as offshore or mid shelf sand bodies thus can be reinterpreted as stranded lowstand shorelines associated with forced regressions this alternative interpretation has economic significance insofar as it suggests different subsurface correlations and reservoir geometries with the potential for development of new play types and enhanced recovery in o der fields examples of forced regression can be observed at a variety of scales and ages several such examples include the modern east coulee fan delta and the lower cretaceous viking formation in alberta canada the quaternary rhone delta and the quaternary hudson valley system

depositional model of a macrotidal estuary and floodplain south alligator river northern australia the south alligator river northern territory of australia has a macrotidal estuary tidal influence spring tidal range 5 6 m at the mouth extends 105 km up the channel it is dominated by freshwater in the wet season december april with a salt wedge near the mouth but is well mixed and becomes saline throughout the dry season the tidal channel can be divided into four different channel types an estuarine funnel a sinuous meandering segment a cuspate meandering segment in which the inside of bends are pointed and an upstream tidal channel the distribution of morphologically defined land classes and morphological units within each land class on the floodplain flanking the estuary differs from one channel type to another several stratigraphic and morphostratigraphic units have been recognized from drill holes on the coastal and deltaic estuarine plains and a model of development is proposed on the basis of extensive radiocarbon chronology and palynology the coastal plain has prograded with most rapid sedimentation between 5000 and 3000 yr bp a similar pattern of progradation is identified in the estuarine funnel in the sinuous segment of the estuary the channel has migrated laterally across the floodplain previous channel positions are indicated by palaeochannels and the meander tract is occupied by laminated channel sediments within the cuspate segment there are numerous sinuous palaeochannels on the plains in the upstream segment the channel and palaeochannels have long straight reaches with irregular bends and discontinuous levees and channel avulsion is indicated mangrove mud is a widespread stratigraphic unit throughout the plains the initial phase of development is a transgressive phase 8000 6800 yr bp when mangrove forests extended landwards into a pre existing valley as sea level rose as sea level stabilized the transgressive phase was followed by a widespread mangrove phase termed the big swamp 6800 5300 yr bp the mangrove forests disappeared from most of the plains as vertical accretion continued and were replaced by grass and sedge covered floodplains during the sinuous phase about 5300 2500 yr bp the channel migrated laterally and eroded the deltaicestuarine plain and deposited lateral accretion deposits laminated channel sediments part of the channel of the south alligator river has then progressed from sinuous to cuspate in form and erosion of river banks has occurred transgressive and big swamp phases occurred under rising and stabilizing sea level respectively later morphodynamic channel adjustments occurred under conditions of stable sea level the depositional model has direct application to other estuaries in northern australia and may be applied to other areas where sea level change has been similar

transgressive systems tract development and incised valley fills within a quaternary estuary shelf system virginia inner shelf usa abstract high frequency quaternary glacioeustasy resulted in the incision of six moderate to high relief fluvial erosion surfaces beneath the virginia inner shelf and coastal zone along the updip edges of the atlantic continental margin fluvial valleys up to 5 km wide with up to 37 m of relief and thalweg depths of up to 72 m below modern mean sea level cut through underlying pleistocene and mio pliocene strata in response to drops in baselevel on the order of 100 m fluvially incised valleys were significantly modified during subsequent marine transgressions as fluvial drainage basins evolved into estuarine embayments ancestral generations of the chesapeake bay complex incised valley fill successions are bounded by or contain up to four stacked erosional surfaces basal fluvial erosion surface bay ravinement tidal ravinement and ebb flood channel base diastem in vertical succession these surfaces combined with the transgressive oceanic ravinement that generally caps incised valley fills control the lateral and vertical development of intervening seismic facies depositional systems transgressive stratigraphy characterizes the quaternary section beneath the virginia inner shelf where six depositional sequences sequences i vi are identified depositional sequences consist primarily of estuarine depositional systems subjacent to the transgressive oceanic ravinement and shoreface shelf depositional systems highstand systems tract coastal systems are thinly developed the quaternary section can be broadly subdivided into two parts the upper part contains sequences consisting predominantly of inner shelf facies whereas sequences in the lower part of the section consist predominantly of estuarine facies three styles of sequence preservation are identified style 1 represented by sequences vi and v is characterized by large estuarine systems ancestral generations of the chesapeake bay that are up to 40 m thick have hemicylindrical wedge geometries and occur within large coast oblique trending depressions paleo estuaries style 1 is dominated by fluvial through estuary mouth depositional systems seismic facies 1 4 style 2 sequence preservation represented by sequences iii and ii is dominantly an inner shelf and shoreface succession with a seaward thickening tabular wedge geometry that does not exceed 15 m in thickness these shoreface and inner shelf depositional systems of the upper transgressive systems tract seismic facies 9 and highstand systems tract seismic facies 7 and 11 are not associated with paleo estuaries style 3 sequence preservation is represented by sequence i the holocene sequence it consists of lower transgressive systems tract fluvial estuarine lagoonal and tidal inlet fill deposits seismic facies 1 6 and 8 overlain by upper transgressive systems tract shelf and shoreface sands seismic facies 9 style 3 has a crenulated wedge geometry and is thickest beneath and seaward of the modern chesapeake bay mouth it thins northward and landward onto late pleistocene interfluvial highs on the basinward side of the southern delmarva peninsula

major sinks of the changjiang yangtze river derived sediments in the east china sea during the late quaternary the east china sea ecs is a typical marginal sea located between the eurasian con tinentandwestpacificocean inthisstudy wereviewstate of the artresearchprogressonthepos sible sinks of the changjiang derived sediments in the ecs during the late quaternary the major sinks of these sediments in the ecs are on the outer shelf and the okinawa trough during the last glacial maximum corresponding to a lowstand of sea level during the deglacial marine transgres sion the gently dipping shelf was rapidly inundated and strong tides prevented fine sediment from deposition on the open shelf resulting in the development of a unique tidal sand ridge sys tem with sea level reaching the present situation and the modern marine environment being com pleted in the early holocene the changjiang sediments mostly accumulated in the river s estuary to build a large delta with only a fraction reaching the inner shelf and coastal embayments the late quaternary changes in monsoon climate induced river flux sea level and oceanic circulation primarily controlled the source to sink transport of the changjiang sediments in the ecs and fur ther determined the stratigraphic framework and sedimentary facies on the shelf

large scale liquefaction and fluidization in the cap chat melange quebec appalachians the cap chat melange crops out discontinuously for 200 km along the south shore of the st lawrence river in the gaspe peninsula it is located just south of logan s line the northern limit of the humber zone with the taconian foreland basin this melange is composed of dismembered rocks of the adjacent formations in particular the lower ordovician riviere ouelle and middle ordovician tourelle formations with lesser contributions by the middle ordovician des landes and the cambrian orignal formations blocks in the melange vary in size from a few centimetres to several kilometres with well preserved internal stratigraphy in the larger blocks the distribution of blocks is not uniform and the composition of the surrounding matrix changes with corresponding changes in block composition tectonic processes mostly extensional and compressional faulting are responsible for some of the chaotic aspects of the melange however the main mechanism was as follows i large scale liquefaction of the mudstone rich riviere ouelle formation ii sinking with consequent dismembering of the tourelle formation into this underlying weakened riviere ouelle formation and iii fluidization of the lowermost sand beds of the tourelle formation resulting in abundant sandstone sills and dikes in the riviere ouelle formation

coastal gia processes revealed by the early to middle holocene sea level history of east china abstract in order to examine relative sea level responses to the postglacial ice volume change and the glacio hydro isostatic adjustments gia this study investigated the inner part of the hangzhou bay east china a tectonically relatively stable far field location and reconstructed the early to middle holocene sea level history this investigation has established the elevational relationship between modern saltmarsh mudflat and tidal levels based on diatom analysis for sea level indicative meaning estimates produced 17 high quality sea level index points and simulated gia processes for the study site these results reveal that the relative sea level rose from 38 3 1 6 m in c 10 000 cal a bp to the present height by c 7000 cal a bp and the average rate of sea level rise decreased gradually from 19 6 2 6 mm a to 2 3 1 5 mm a during the 3000 years this period of sea level history was punctuated by two episodes of accelerated rise around 8200 and 7500 cal a bp the relative sea level rose to 0 8 1 4 m above msl by c 6500 cal a bp followed by a gradual fall back to the present height at 4500 cal a bp implying a different response to the potential additional ice melting between 7000 and 4000 cal a bp a comparison of the sea level histories between the inner and outer hangzhou bay indicates the coastal levering effect due to the marine inundation of the continental shelves a further comparison between sea level data from china and malay peninsula reveals different gia effects between the cathaysia yangtze blocks and the sundaland block

geology and formation mechanism of late quaternary shallow biogenic gas reservoirs in the hangzhou bay area eastern china late quaternary shallow biogenic gas reservoirs have recently been discovered and exploited in the coastal hangzhou bay area northern zhejiang province eastern china the river in this area strongly incised the underlying old beds during a period of glacial maximum which resulted in the formation of the qiantangjiang and the taihu incised valleys these incised valleys were filled with fluvial sediments and buried by marine sediments during the postglacial period late quaternary strata of the incised valley area are composed of four sedimentary facies in ascending order fluvial floor facies iv flood plain facies iii sublittoral marine bay facies ii and estuarine facies i all commercial gas fields occur in flood plain sand bodies of incised valleys the bodies are buried 3060 m 98197 ft deep and are 3 07 0 m 9 823 ft thick with a maximum thickness of more than 10 m 33 ft they are surrounded by impermeable clays rapid deposition of overlying sublittoral marine bay sediments supplied not only abundant gas sources but also good preservation conditions the main hydrocarbon sources are dark gray clays of the flood plain facies and gray muds of the sublittoral marine bay facies sediments of both facies have organic carbon content generally more than 0 4 shallow biogenic gas fields and deep gas fields require vastly different drilling and completion techniques drilling and completion costs are much lower for the biogenic gas fields quaternary incised valleys and flood plains other than hongzhou bay in coastal areas of eastern china are promising targets of further exploration for shallow biogenic gas

middle holocene coastal environment and the rise of the liangzhu city complex on the yangtze delta china abstract the large prehistoric city of liangzhu and its associated earthen dike emerged on the yangtze delta coast after two millennia of occupation in this area by scattered communities details of its development have been widely discussed in the literature our results reveal that the city was selectively built at the head of an embayment backed by hills with close access to food freshwater and timber and with protection from coastal hazards radiocarbon and optically stimulated luminescence osl dating shows that it was built around 4 8 4 5 ka and the earthen dike was constructed a little later at 4 1 ka during this time saltwater wetlands were changing to freshwater in response to rapid coastal progradation as the postglacial sea level rise stabilized this facilitated rice farming and furthered the development of the city with elaborate city planning the younger large scale earthen dike and artificial ponds possibly suggest increasing demand for flood mitigation and irrigation

exploration methods for late quaternary shallow biogenic gas reservoirs in the hangzhou bay area eastern china commercial accumulations of shallow biogenic gas have been widely found in the world the successful development and exploitation of shallow gas is dependent on using suitable technology to effectively prospect for this kind of resource shallow biogenic gas reservoirs buried less than 120 m 393 7 ft have been discovered and successfully exploited in the hangzhou bay area northern zhejiang province eastern china in this study we describe the methods used for the exploration of shallow gas including cone penetration test cpt shallow shear wave seismic data soil gas radon analysis microbiological prospecting and electromagnetic surveying the cpt is effective in helping to determine stratigraphic divisions and correlations especially reservoir identification dense cpts are useful for both the preliminary exploration and enlarging a known gas field shallow shear wave seismic profiles identify the top surface of a gas bearing sand bed which shows a strong reflecting boundary the reflection will sharply decline where the gas bearing sand body pinches out thus a gas bearing sand body can be outlined the area of gas reservoirs can further be determined by high soil gas radon content over the boundary of the gas accumulation methane consuming bacteria can act as an indicator for the presence of methane within the gas bearing area electromagnetic methods can aid in determining whether there is gas in the sand bodies and in determining the thickness of the gas layer

late quaternary evolution of the yellow east china sea tidal regime and its impacts on sediments dispersal and seafloor morphology the evolution of a tidal current field in the yellow sea and east china sea yecs in response to the sea level rise since the last glacial maximum lgm was investigated using a two dimensional tidal model with special attention to changes in the sedimentary environment of the continental shelf region it was found that tidal currents on the yecs shelf have generally been semi diurnal throughout the post glacial stages with f ratio index of diurnal inequality and s2 m2 ratio index of spring neap cycle remaining similar to present on the other hand the spatial distribution of the tidal bottom stress associated with m2 and m4 tidal currents changed greatly during the transgression as the sea level rose two core regions showing high bottom stress values migrated shoreward from cheju island toward the west coast of korea and along the retreat path of the paleo changjiang estuary distribution of extremely intense tidal bottom stress suggested that intense tidal reworking may have occurred at sea levels from 90 to 45 m in the southeast yellow sea and at 75 to 60 m off the paleo changjiang estuary the latter of which agreed with the timing of a large terrigenous organic c flux observed on the shelf slope distribution of slightly weaker bottom stress indicated that the sand ridges off the changjiang estuary and in the southeast yellow sea also might have formed at during those periods on the other hand when the sea level was between 45 and 15 m the tidal bottom stress was generally not strong enough to invoke significant reworking even though the stress intensity may be stronger than present correlation with modern and relict sedimentary features suggested that the tidal process have played a significant role on the reworking and deposition of sediments on the yecs shelf

generation accumulation and resource potential of biogenic gas biogenic gas is generated at low temperatures by decomposition of organic matter by anaerobic microorganisms more than 20 of the world s discovered gas reserves are of biogenic origin a higher percentage of gases of predominantly biogenic origin will be discovered in the future biogenic gas is an important target for exploration because it occurs in geologically predictable circumstances and in areally widespread large quantities at shallow depths in rapidly accumulating marine sediments a succession of microbial ecosystems leads to the generation of biogenic gas after oxygen is consumed by aerobic respiration sulfate reduction becomes the dominant form of respiration methane generation and accumulation become dominant only after sulfate in sediment pore water is depleted the most important mechanism of methane generation in marine sediments is the reduction of co2 by hydrogen electrons produced by the anaerobic oxidation of organic matter co2 is the product of either metabolic decarboxylation or chemical decarboxylation at slightly higher temperatures the factors that control the level of methane production after sediment burial are anoxic environment sulfate deficient environment low temperatu e availability of organic matter and sufficient space the timing of these factors is such that most biogenic gas is generated prior to burial depths of 1 000 m in marine sediments most of the biogenic gas formed can be retained in solution in the interstitial pore waters because of higher methane solubility at the higher hydrostatic pressures due to the weight of the overlying water column under certain conditions of high pressures and or low temperatures biogenic methane combines with water to form gas hydrates biogenic gas usually can be distinguished from thermogenic gas by chemical and isotopic analyses the hydrocarbon fraction of biogenic gas consists predominantly of methane the presence of as much as 2 of heavier hydrocarbons can be attributed to admixture of minor thermogenic gas due to low temperature degradation of organic matter the amounts of hydrocarbon components other than methane generally are proportional to temperature age and organic matter content of the sediments biogenic methane is enriched in the light isotope 12c dgr13c1 lighter than 55 ppt owing to kinetic isotope fractionation by methanogens the variations in isotopic composition of biogenic methane are controlled primarily by dgr13c of the original co2 substrate which reflects the net isotopic effect of both addition and removal of co2 the methane isotopic composition also can be affected by mixing of isotopically heavier thermogenic gas the possible complicating factors require that geologic chemical and isotopic evidence be considered in attempts to interpret the origin of gas accumulations accumulations of biogenic gas have been discovered in canada germany italy japan trinidad the united states and ussr in cretaceous and younger rocks at less than 3 350 m of burial and in marine and nonmarine rocks other gas accumulations of biogenic origin have undoubtedly been discovered however data that permit their recognition are not available

downstream fining in large sand bed rivers abstract downstream fining of bed sediments is a well known phenomenon in gravel bed rivers but also occurs in large sand bed rivers the underlying processes however are not necessarily the same due to the difference in sediment mobility grain size distribution width and geographical setting downstream fining studies focusing on large sand bed rivers are scarce nevertheless in this paper the processes that affect downstream fining in gravel bed rivers are reviewed and it is evaluated to what extent they are relevant for large sand bed rivers furthermore several new downstream fining processes are discussed ending in a conceptual model of downstream fining in large sand bed rivers in deriving the conceptual model downstream fining processes are divided into three categories abrasion selective transport and sediment addition extraction abrasion rates in large sand bed rivers are small due to the durable lithologies the small grain size the high degree of rounding the dominance of grinding as abrasion process and the dominant suspended transport mode of the bed sediment only in the upstream part of large sand bed rivers abrasion rates may be somewhat higher selective transport rates in large sand bed rivers everywhere overrun abrasion rates but are small compared to selective transport rates in gravel bed rivers because the unimodal sediments in sand bed rivers exhibit stronger hiding exposure effects during threshold of motion conditions but especially because many sand bed rivers though not all are in state of fully mobilised transport making differences in threshold of motion between coarse and fine grains relatively unimportant selective transport in these rivers is probably mainly the result of the presence of suspended load transport in combination with the effects of dune and perhaps bend sorting which are all processes that act on a relatively large scale within sand bed rivers the degree of selective transport probably decreases downstream due to the change in mixture bimodality and sorting efficiency there are indications that coarse grains may sometimes even be more mobile than fine grains in the downstream part of sand bed rivers note that in contrast to abrasion selective transport only produces a stable downstream fining pattern if the river profile is concave generally a stronger profile concavity leads to a higher aggradation rate and a stronger downstream fining trend sediment addition and extraction processes can obscure the effects of abrasion and selective transport in sand bed rivers overbank sedimentation for instance may significantly decrease the downstream fining rate in large sand bed rivers because especially fine grains are removed from the bed dredging can also strongly affect the downstream fining trend depending on the volume and the grain size of the sediment involved meander migration may cause a nett loss of coarse grains from the channel in aggrading circumstances increasing the downstream fining rate river bifurcations can cause a discontinuity in the downstream fining pattern because bend sorting upstream of the bifurcation causes the river branch that originates in the outer bend of the main channel to be much coarser than the other branch all these addition and extraction processes not only have a direct effect on the grain size composition of the river bed but also indirectly influence downstream fining by their effect on the longitudinal bed profile other sediment addition and extraction processes such as tributary confluences non alluvial sediment sources and dumping are less common in large sand bed rivers but can locally have a great effect a full determination of the relative importance of all downstream fining processes in large sand bed rivers requires extensive field measurements the construction of detailed fractionwise sediment balances and the development of numerical downstream fining models that incorporate all processes described above

controls on sedimentation in distal margin palaeovalleys in the early tertiary alpine foreland basin south eastern france the influence of palaeodrainage characteristics palaeogeography and tectonic setting are rarely considered as controls on stratigraphic organization in palaeovalley or incised valley systems this study is an examination of the influence of source region vs downstream base level controls on the sedimentary architecture of a set of bedrock confined palaeovalleys developed along the distal margin of the alpine foreland basin in south eastern france three distinct facies associations are observed within the palaeovalley fills fluvial facies association a is mainly dominated by poorly sorted highly disorganized clast to matrix supported cobble to boulder conglomerates that are interpreted as streamflood deposits facies association b comprises mainly yellow siltstones and is interpreted as recording deposition in an estuarine basin environment estuarine marine facies association c comprises interstratified estuarine siltstones and clean well sorted washover sandstones the sedimentary characteristics of the valley fill successions are related to the proximity of depositional sites to sediment source areas palaeovalleys located proximal to structurally controlled basement palaeohighs are entirely dominated by coarse fluvial streamflood deposits in contrast distal palaeovalley segments which are located several kilometres downstream contain successions showing upward transition from coarse fluvial facies into estuarine central basin fines and finally into estuarine marginal marine facies facies distributions suggest that the fluvial deposits form wedge shaped downstream thinning sediment bodies whereas the estuarine deposits form an upstream thinning wedge the vertical stacking of fluvial to estuarine to marginal marine depositional environments records the fluvial aggradation and subsequent transgression of relatively small bedrock confined river valleys which drained a rugged upland terrain facies geometries suggest that a fluvial sediment wedge initially prograded downvalley in response to high bed load sediment yields subsequently palaeovalleys became drowned during the passage of a marine transgression with the establishment of estuarine conditions initial fluvial aggradation and subsequent marine flooding of the palaeovalleys is a consequence of the interaction of high local rates of sediment supply and relative sea level rise driven by flexural subsidence of the basin

quantitative analysis of the stratigraphic architecture of incised valley fills a global comparison of quaternary systems abstract facies models of the internal fills of incised valleys developed in shelf and coastal settings during cycles of relative sea level change are largely conceptual descriptive and qualitative in form moreover they are commonly bespoke to individual examples here a database driven quantitative statistical analysis of 87 late quaternary incised valley fills ivfs has been undertaken to assess the general validity and predictive value of classical facies models for ivfs and to investigate the relative importance of possible controls on their stratigraphic organization based on datasets from the published literature stored in a sedimentological database the geometry and proportion of systems tracts and of architectural elements of different hierarchies within ivfs are quantified these variables were analysed to assess how they vary in relation to parameters that represent potential controlling factors relative sea level stage continental margin type drainage basin area valley geometry basin physiography and shoreline hydrodynamics the stratigraphic organization of the studied coastal plain ivfs is generally consistent with that represented in facies models the primary control being the rate and magnitude of relative sea level change however results from this study demonstrate significant variability in the stratigraphic architectures of ivfs which is not accounted for by existing models variations in the facies architecture of coastal plain and cross shelf valley fills can be attributed to controls other than sea level and expressed in relationships with continental margin type basin physiography catchment area river system size and shoreline hydrodynamics the following primary findings arise from this research i compared to their counterparts on passive margins coastal plain ivfs hosted on active margins contain on average a higher proportion of fluvial deposits and a lower proportion of central basin estuarine deposits estuarine deposits tend however to be thicker this suggests a control on ivf stratigraphic architecture exerted by distinct characteristics of the tectonic setting of the host continental margins notably basin physiography rates and mode of sediment supply and nature of sediment load ii the thickness and proportion of lowstand systems tract are positively correlated with coastal plain ivf dimensions likely reflecting the role of drainage basin area in dictating the scale of the fluvial systems that carved and infilled the valleys iii positive correlations are observed between the thickness of fluvial deposits bayhead delta deposits and central basin estuarine deposits versus coastal plain ivf dimensions and valley catchment area this suggests a control exerted by the river system scale on sediment supply rates and on the accommodation determined by valley size iv positive correlations between the thickness and proportion of barrier complex deposits within cross shelf ivfs versus mean shelf gradient indicate that the geometry of the shelf might control the establishment and preservation of barrier island environments in incised valleys located on the shelf v correlations between the width of coastal plain ivfs and present day mean tidal range at the shoreline indicate that tidal dynamics may contribute to the widening of the incised valleys positive correlation is observed between the proportion of tide dominated elements in highstand ivf deposits and ivf width suggesting possible effects of interplays between hydrodynamic conditions and the geometry of incised valleys on their infills this study highlights the complexity of the internal fills of incised valleys which must be considered when attempting the application of facies models of ivfs to rock record interpretations or as predictive tools in subsurface studies