the relationship between shellbed type and sequence architecture examples from japan and new zealand abstract examples of lithology fossil content and taphonomic features of shellbeds and intervening less fossiliferous intervals are presented from four plio pleistocene successions shimosa group boso peninsula omma formation hokuriku area japan and okehu kai iwi and shakespeare groups in wanganui and the rangitikei group along the rangitikei river in new zealand as for pre pliocene 3rd and 4th order depositional sequences plio pleistocene 5th to 7th order depositional sequences contain a variety of shellbeds which are often associated with surfaces or intervals that are characterized by sedimentary condensation omission or erosion e g sequence boundaries ravinement surfaces downlap surfaces and condensed sections stratigraphic patterns of shellbed type tend to be similar and repetitive within a basin and a locality this demonstrates that a specific palaeogeography played an important role in determining the nature of shellbeds for example shellbeds formed in the context of toplap are common only in the shimosa group which was deposited in a moderately sheltered sea the palaeo tokyo bay toplap shellbeds are rare in other sequences formed in more open conditions despite the variability resulting from such basin characteristics common styles of shellbeds can be recognized that formed under conditions of marine onlap backlap downlap and toplap each type of shellbed has a characteristic fossil composition and taphonomy onlap and toplap shellbeds contain low diversity macrobenthic associations including glycymeris mercenaria paphies or other bivalves having robust shells which are often abraded or fragmented backlap shellbeds which are equivalent to the condensed section formed at the maximum transgression are characterized by dominance of epifaunal macrobenthos such as bryozoa brachiopoda pectinid and ostreid bivalves preserved in a slightly cemented glauconitic muddy matrix in contrast to fossils in such condensed sections the shell density and species diversity of downlap shellbed associations are rather low and in a few examples the macrobenthic association was buried rapidly in a lower unit of the highstand systems tract hst stratigraphically located above the condensed sections variations in the stratigraphic distribution of shellbed types are reflected in symmetrical and asymmetrical sequence architectures symmetrical sequences have roughly the same thickness of transgressive systems tracts tst and highstand systems tracts hst and have well segregated shellbeds that were formed during marine onlap and backlap asymmetrical cycles have very thin tsts and much thicker hsts and are characterized by the amalgamation of condensed onlap and backlap shellbeds such contrasting cycle architectures are interpreted to reflect inner symmetrical and outer asymmetrical shelf palaeodepositional settings the amalgamated onlap backlap shellbeds appear to be common in plio pleistocene sequences owing to the short duration of glacio eustatic sea level changes with dominant frequencies of 20 000 40 000 or 100 000 years shellbeds in the plio pleistocene are relatively simple and thin compared to those formed in ordinary third order depositional sequences infauna dominated benthic associations are generally more common than in third order cycles and epifaunal associations facilitated by taphonomic feedback on sediment starved shell gravel substrates occur only in the condensed section corresponding to maximum transgression in most plio pleistocene sequences

constraints on eustatic sea level changes during the mid pleistocene climate transition evidence from the japanese shallow marine sediment record abstract during the middle pleistocene the nature of glacial interglacial fluctuations changed from low amplitude and a periodicity of 41 ky to high amplitude and quasi periodic of 100 ky the origin of the mid pleistocene climate transition mpt is an unsolved mystery at present there is a debate about whether the initiation of the mpt was a gradual or an abrupt process this study investigated the process of initiation of the mpt from reconstructions of eustatic sea level changes as a proxy for global ice volume based on a reexamination of lithofacies and fossil occurrences from shallow marine sediments omma formation exposed on the west coast of japan the omma formation comprises 19 depositional sequences spanning marine isotope stages mis 56 21 3 reflecting sedimentation under alluvial plain to offshore conditions the data indicate that 1 sea level was lowest during mis 22 0 9 ma 2 sea level during mis 34 1 13 ma and mis 26 0 96 ma was lower than during any other glacial stage except for mis 22 and 3 sea level during mis 22 was at most 20 m lower than during mis 34 and 26 together these findings suggest that the initiation of the mpt was a gradual rather than abrupt process

sequence stratigraphy of the punta ballena member of the jama formation early pleistocene ecuador insights from integrated sedimentologic taphonomic and paleoecologic analysis of molluscan shell concentrations abstract early pleistocene strata are well exposed along the uplifted eastern margin of the esmeraldas caraquez basin particularly on the coastal cliff west of the city of jama a type locality for shallow marine quaternary sedimentary exposures on north central ecuador here at least 180 m of sediments accumulated in inner shelf to subaerial settings are present jama formation this paper is concerned with the middle stratigraphic unit of the jama formation the punta ballena member pbm integrated sedimentologic paleontologic and stratigraphic observations reveal that the pbm is composed of eight disconformity bounded depositional sequences hiatal shell concentrations which formed as a consequence of landward and seaward stratal attenuation are associated with sequence bounding and intrasequence surfaces together with sedimentologic characteristics these fossiliferous levels are important indicators of facies architecture and therefore are useful tools for interpreting sequence stratigraphy according to their taphonomic features and taxonomic composition the hiatal shell concentrations occurring within the pbm may be grouped into two main types each of which occupies a predictable stratigraphic position within the sequences current wave winnowed beds at the cycle base and community shell concentrations in a roughly mid cycle position current wave winnowed beds commonly underlain by thalassinoides burrows that penetrate to depths of as much as 1 5 m below ravinement surfaces are transported skeletal concentrations and formed through physical processes in shallow high energy environments they comprise a time averaged mixture of specimens having different ecologies and states of preservation and accumulated mainly under conditions of total passing of siliciclastic sediment i e terrigenous sediments are delivered to the site as suspended load but owing to the high environmental energy failed to accumulate community shell concentrations occur in sparsely fossiliferous intervals and result from reduced net sedimentation within low energy relatively deeper settings they are composed of matrix supported loosely clustered life oriented and little disturbed fossil assemblages but are packed in excess of likely living densities and are visually dominated by successive generations of the infaunal bivalve raeta undulata which colonized a slowly aggrading muddy seafloor the sedimentological and paleontological evidence presented here not only supports the results of previous studies which demonstrate the value of condensed shell concentrations in the identification of stratigraphically significant surfaces but also provides adds to the distinctive features of these shell beds

response of daily and annual shell growth patterns of the intertidal bivalve phacosoma japonicum to holocene coastal climate change in japan abstract it is well known that the latitudinal distribution of shallow marine mollusks around the japanese islands has changed episodically during the holocene in response to climate change however few studies have investigated the biotic response of individual species to holocene climate change at daily to annual scales of temporal resolution holocene shells of the venerid phacosoma japonicum recovered from various sites in japan preserve lunar daily and annual growth increments in the outer shell layer and hinge plate as also observed in modern shells sclerochronological analysis of 29 shells with known 14 c ages revealed that the life history traits e g length of the growth period and the mean lunar daily growth rate at a given age have changed markedly over the past 8000 years the intra annual patterns of lunar daily increments and shell oxygen isotope records of the fossil shells can be compared with those of modern specimens from various locations which are constrained by annual patterns of seawater temperature and summer autumn precipitation rates furthermore the temporal trends recorded in the fossil shells show a strong correlation with climate change in mid latitude parts of east asia over the past 8000 years indicating that p japonicum has changed its life history traits in response to holocene terrestrial and coastal climate change

sedimentary response to milankovitch type climatic oscillations and formation of sediment undulations evidence from a shallow shelf setting at gela basin on the sicilian continental margin abstract a multi proxy chronological framework along with sequence stratigraphic interpretations unveils composite milankovitch cyclicity in the sedimentary records of the last glacial interglacial cycle at ne gela basin on the sicilian continental margin chronostratigraphic data including foraminifera based eco biostratigraphy and 18 o records tephrochronological markers and 14 c ams radiometric datings was derived from the shallow shelf drill sites geob14403 54 6 m recovery and geob14414 27 5 m collected with both gravity and drilled mebo cores in 193 m and 146 m water depth respectively the recovered intervals record marine isotope stages and substages mis from mis 5 to mis 1 thus comprising major stratigraphic parts of the progradational deposits that form the last 100 ka depositional sequence calibration of shelf sedimentary units with borehole stratigraphies indicates the impact of higher frequency 20 ka sea level cycles punctuating this 100 ka cycle this becomes most evident in the alternation of thick interstadial highstand hst wedges and thinner glacial forced regression fsst units mirroring seaward shifts in coastal progradation albeit their relatively short lived depositional phase these subordinate hst units form the bulk of the 100 ka depositional sequence two mechanisms are proposed that likely account for enhanced sediment accumulation ratios sar of up to 200 cm ka during these intervals 1 intensified activity of deep and intermediate levantine intermediate water liw associated to the drowning of mediterranean shelves and 2 amplified sediment flux along the flooded shelf in response to hyperpycnal plumes that generate through extreme precipitation events during overall arid conditions equally the latter mechanism is thought to be at the origin of undulated features resolved in the acoustic records of mis 5 interstadials which bear a striking resemblance to modern equivalents forming on late holocene prodeltas of other mediterranean shallow shelf settings

changes in depositional systems and sequences in response to basin evolution in a rifted and inverted basin an example from the neogene niigata shin etsu basin northern fossa magna central japan abstract the niigata shin etsu basin which occurs along the eastern margin of the sea of japan was generated in middle miocene time as a failed rift basin in relation to the backarc opening of the japan arc and was converted to a compressional basin in late miocene time the basin filling succession can be divided into four tectonostratigraphic units stages based on characteristics of depositional systems depositional sequences tectonic subsidence rate and sediment supply these units coincide in time with major tectonic events during backarc rifting and subsequent basin inversion unit i 16 13 5 ma represents a syn rift stage characterized by rapid basin subsidence the rate of accommodation exceeded the rate of accumulation resulting in a retrogradational stacking pattern of muddy slope to basin floor systems unit ii 13 5 6 5 ma represents a post rift thermal subsidence stage the rate of accommodation nearly equaled the rate of accumulation resulting in an aggradational stacking pattern of five third order depositional sequences mainly comprising submarine fan turbidite systems affected by supply of coarse clastics unit iii 6 5 1 ma represents the basin inversion stage showing no subsidence or uplift the accumulation rate exceeded the rate of accommodation resulting in rapid progradation of depositional sequences composed of slope shelf shallow marine delta and fluvial systems unit iv 1 ma present represents an intense compressional stress field sedimentation has been restricted to a synclinal area due to syndepositional folding and uplift changes in basin subsidence rate and sediment supply resulting from tectonics and climate change in the basin and the provenance strongly affected characteristics of the depositional systems and sequences the change in basin subsidence also created a basinwide depositional cycle whereas eustasy affected relative sea level changes created higher order depositional sequences during relatively stable phases of tectonics

origin of ureilites inferred from a sims oxygen isotopic and trace element study of clasts in the dar al gani 319 polymict ureilite secondary ion mass spectrometer sims oxygen isotope analyses were performed on 24 clasts representing 9 clast types in the dar al gani dag 319 polymict ureilite with precisions better than 1 olivine rich clasts with typical ureilitic textures and mineral compositions have oxygen isotopic compositions that are identical to those of the monomict ureilites and plot along the ccam carbonaceous chondrite anhydrous mineral line other igneous clasts including plagioclase bearing clasts also plot along the ccam line indicating that they were derived from the ureilite parent body upb thus we suggest that some of the plagioclase bearing clasts in the polymict ureilites represent the missing basaltic component produced by partial melting on the upb trace element concentrations mg k sc ti v cr mn fe co ni cu rb sr and ba in ureilitic plagioclase and glass from 13 clasts were obtained by using the sims high mass resolution method the trace element contents of the plagioclase generally show monotonic variations with anorthite content mol that are consistent with partial melting and fractional crystallization incompatible trace element concentrations k ti and ba are low and variable for plagioclase with an 40 indicating that the parental magmas for some clasts were derived from a depleted source we performed partial melt modeling for ci and cm precursor compositions and compared the results to the observed trace element k ba and sr abundances in the plagioclase our results indicate that 1 the upb evolved from a alkali rich carbonaceous chondritic precursor 2 parent melts of porphyritic clasts could have formed by 5 20 equilibrium partial melting and subsequent fractional crystallization and 3 parent melts of the incompatible trace element depleted clasts could be derived from fractional melting where low degree 10 partial melts were repeatedly extracted from their solid sources thus both the oxygen isotopic and trace element compositions of the plagioclase bearing clasts in dag 319 suggest that the upb underwent localized low degree partial melting events the partial melts could have been repeatedly extracted from the precursor resulting in the formation of the olivine pigeonite monomict ureilites as the final residue

late pliocene early pleistocene paleoceanographic evolution of the sea of japan abstract the stratigraphic distribution and abundance of molluscs and planktonic foraminifera within a sixth order 41 kyr depositional sequence of the early pleistocene omma formation in central japan provide several important information on the sea of japan since 2 5 ma the sea possibly experienced three substages in the paleoceanographic history since then during substage i 2 5 1 71 ma oxygen isotope stage 60 59 cold northern surface water prevailed due to the closure of the sea s southern entrance during substage ii 1 71 1 52 ma stage 51 the warm tsushima current flowed into the sea from the south during interglacial highstands during substage iii 1 52 0 ma isolation of the sea of japan was reinforced by narrowing and or shallowing of the northern entrance these changes were caused by some local tectonic movements that affected topography of the southern and northern straits inflow of the tsushima current resulted in migration of warm water organisms into the sea of japan during interglacial stages and acted as a barrier to the migration of terrestrial organisms between east asia and japanese islands

sequence response to syndepositional regional uplift insights from high resolution sequence stratigraphy of late early pleistocene strata periadriatic basin central italy abstract this paper deals with the depositional sequences that occur within the uppermost part of the plio pleistocene periadriatic basin fill in the southern marche region central italy the succession is an early pleistocene easterly dipping clastic wedge showing an overall shallowing trend from slope clays to shallow marine and non marine deposits comprising two major sequences namely qmb and qmc analysis has provided new insights into i the nature of sedimentary facies and facies associations occurring within the upper part of qmb and qmc ii the gradual contact within qmb between regressive littoral deposits rld and underlying deep marine blue clays iii the composite origin of the emilian surface which is a widespread erosional unconformity separating qmb from qmc iv the cyclothemic pattern of qmc composed of downstepping small scale depositional sequences v the role played by synsedimentary uplift on the stacking pattern of small scale sequences and their internal architecture up to three small scale depositional sequences have been recognised within qmc qmc1 qmc2 and qmc3 they are up to 50 m thick and defined by previously unrecorded lower rank regionally extensive surfaces facies organization indicates that as a rule in ascending stratigraphic order each small scale sequence may includes a distinctive basal unconformity surface that can be traced from incised valleys to associated interfluves an incised valley fill a transgressive surface of marine erosion a transgressive systems tract a highstand systems tract a regressive surface of marine erosion and an attached falling stage systems tract in proximal positions the small scale sequences are dominated by transgressive and highstand systems tracts with incised valley fills and falling stage systems tracts absent or volumetrically much less significant in relatively basinward locations where the regressive surfaces of marine erosion converge with the lower sequence boundary the falling stage systems tract may represent the entire depositional sequence high frequency sequences display a distinctive stacking pattern and form a tectonically induced forced regressive sequence set underlain by a composite tectonically enhanced regressive surface of marine erosion formed by the lateral connection of lower rank sequence boundaries

change in the thickness of the warm tsushima current at the initiation of its flow into the sea of japan abstract the initiation of flow of the warm tsushima current created significant changes in quaternary paleoceanography and ecosystems in the continental shelf of the japanese islands in the sea of japan in order to understand the behavior of the current at the initiation of its flow we reconstruct the change in the relative thickness of the current during the initiation of flow based on combining planktonic and shallow water molluscan fossil analyses of the early pleistocene omma formation in central japan the result indicates that warm water planktonic foraminifera and cold water molluscs coexisted during about 2300 2400 years just after the initiation of the intrusion of the tsushima current migration of a warm water molluscan fauna to the shelf occurred shortly after the local extinction of cold water molluscs this means that the rate of increase in thickness of the tsushima current during the initiation of flow was faster than that of the sea level rise using deep sea core records and modern biogeographic data the rates of the former and latter are calculated to be 17 2 8 9 m per 1000 years and 1 9 1 1 m per 1000 years respectively because bottom water change might lag behind surface water change during a rapid climatic change in all shallow water combining planktonic and benthic fossil analyses is necessary to reconstruct shallow paleoceanography

quaternary time scale for the ontong java plateau milankovitch template for ocean drilling program site 806 a 2 m y oxygen isotope record of globigerinoides sacculifer from the ontong java plateau based on cores from ocean drilling program leg 130 is dated by matching variations to an orbital template the procedure allows us to present the most complete quaternary record available for the western equatorial pacific the template generating algorithm describes a balance between growth and melting of ice following basic milankovitch theory ice growth is taken as constant while melting is taken to depend on summer insolation current ice mass and average past ice mass template settings must be changed once between 1 and 1 2 ma to reflect a major shift in climate template fits are strikingly good over much of the record and can be used to detect and fill gaps from core breaks and other disturbances one result of template dating is an exact age for the brunhes matuyama magnetic reversal boundary at 790 5 ka as well as several other precise dates 900 ka for the middle pleistocene climate shift 1070 1240 and 1450 ka for isotope stages 31 37 and 47 respectively sedi mentation rates fluctuate between 18 and 28 m m y a ca 400 ka cycle being the most prominent major anomalies arise within the transitional regime 1 2 to 1 ma the origin of the cycles is unknown we propose productivity variations in the western equatorial pacific

cyclic changes in lithofacies and molluscan content in the early pleistocene omma formation central japan related to the 41 000 year orbital obliquity abstract eleven cyclothems based on change in sedimentary facies and molluscan fossil associations are identified in the middle part of the omma formation early pleistocene in kanazawa central japan the systematic change in the molluscan fossil associations within individual cycles indicates that the oceanic conditions changed in parallel with water depth fluctuations such that an increase in water depth corresponds to a marine climatic warming these changes in water depth and oceanic conditions exactly coincides with the oxygen isotope fluctuations reported for deep sea sediments the cyclothems identified here in the omma formation can be explained best as the result of glacio eustasy with a period of the 41 000 years which corresponds to the period of orbital obliquity

reconstruction of the thickness of the tsushima current in the sea of japan during the quaternary from molluscan fossils abstract the present distribution of the benthic fauna in the sea of japan reveals that the thickness of the warm tsushima current is about 150 m because cold water elements are found in bottom faunas in the underlying cold intermediate water below this depth identification of such cold water taxa from quaternary molluscan assemblages makes it possible to estimate the thickness of the tsushima current in the past in order to determine the depth and nature of the cold water fauna living below the warm surface current molluscan and planktonic faunas were analyzed from the omma formation which comprises at least 14 superposed cyclothems corresponding to oxygen isotope stages 50 to 22 based on faunal analyses one molluscan association that lived below the warm tsushima current was identified from the horizon equivalent to stage 47 about 1 45 ma the depth of the upper limit of the association that is the thickness of the tsushima current was estimated using sedimentary structures and oxygen isotope records from deep sea cores the result show that the thickness of the current was less than two thirds that of today

exposed coasts vs sheltered bays contrast between new zealand and japan in the molluscan record of temperature change in plio pleistocene cyclothems abstract cyclothems in the omma formation on the japan sea coast of central honshu each contains two ecostratigraphic datums the appearance and disappearance datums of warm water molluscs cold water molluscs occur both below in early tst and above in late hst and possibly rst warm water ones which occur in late tst and early hst in contrast no new zealand cyclothems in the main plio pleistocene basins contain both cold and warm water faunas in one cycle cyclothems in the petane group central hawke s bay and in the castlecliff section wanganui basin contain entirely eurythermal and warm water molluscs throughout cyclothems in south wairarapa have entirely eurythermal and cold water molluscs throughout the subantarctic zygochlamys delicatula fauna even in hsts of some cycles this contrast demonstrates the importance of exposure of the deposition site to strong coastal currents for the maximum faunal expression of temperature change the omma formation was deposited in an open site on the japan sea coast where currents transported larvae of a wide variety of molluscs northwards and southwards in response to temperature oscillations the main new zealand cyclothemic successions were deposited in large embayments sheltered from the influence of coastal currents the maximum faunal expression within one cyclothem of plio pleistocene temperature change can be expected in only those few deposition sites that satisfy the optimum requirements deposition of reasonably complete sequences at least tsts hsts and rsts preserved in an exposed coastal site influenced by strong currents from both the north and south on the inner shelf in the temperate regions between ca 30 and 60 north and south near the north south oriented coast of a large continent

sequence stratigraphy of sixth order 41 k y pliocene pleistocene cyclothems wanganui basin new zealand a case for the regressive systems tract this study is based on a late pliocene and early pleistocene approximately 2 6 1 7 ma succession about 1 km thick of 20 sixth order 41 k y duration cyclothems of shelf origin exposed in the rangitikei river valley in the eastern part of wanganui basin the cyclothems correlate with 18 o isotope stages 100 58 and each 41 k y glacialinterglacial stage couplet is represented by an individual depositional sequence comprising transgressive highstand and regressive systems tracts unlike most examples inferred from the stratigraphic record these systems tracts were deposited during phases of known sea level cycles indicated by the contemporary oxygen isotope ice volume curve because of the high rate of subsidence of wanganui basin glacioeustatic sea level falls during most cycles were not of sufficient magnitude to expose the outer shelf thus the rangitikei section provides an exceptional example of regressive strata deposited landward of the contemporary shelf break simple one dimensional modeling shows that moderate to high rates of basin subsidence 1 2 mm yr and low rates of sedimentation 0 2 mm yr during transgressions combined to produce an accommodation surplus at the relative highstand this surplus accommodation was infilled during the late highstand and ensuing fall partly by aggradational highstand systems tract shelf siltstone and chiefly by strongly progradational shoreface sediments of the regressive systems tract rangitikei regressive systems tracts are distinguished from forced regressive systems tracts sensu hunt and tucker 1992 by their different stratal geometry by definition forced regressive systems tracts display an erosional contact with the underlying highstand systems tracts and typically occur as a series of downstepped disjunct shoreline wedges stranded on the shelf and or slope in contrast regressive systems tracts exhibit a gradational lower contact above which parasequences are stacked in a strongly progradational pattern terminated by the superjacent sequence boundary cyclothems display two types of motif termed rangitikei dt depositional transgression and rangitikei nt nondepositional transgression which include the following architectural elements in ascending stratigraphic order 1 a basal sequence boundary that is coincident with either the transgressive surface of erosion which displays small scale up to 50 cm erosional relief and may be penetrated by the ichnofossil ophiomorpha or its deeper water correlative conformity 2 either a thick 5 30 m transgressive systems tract comprising a deepening upward nearshore to inner shelf mixed carbonate siliciclastic lithofacies succession depositional transgression or a thin 2 m transgressive systems tract comprising condensed fossiliferous facies deposited on the sediment starved offshore shelf nondepositional transgression 3 a sharp downlap surface separating condensed fossiliferous facies of the transgressive systems tract from terrigenous siltstone of the superjacent highstand systems tract 4 a highstand systems tract comprising a 10 20 m thick interval of aggradational shelf siltstone and 5 a thick up to 45 m progradational inner shelf to shoreface lithofacies assemblage ascribed to the regressive systems tract condensed shell beds are associated with intrasequence and sequence bounding discontinuities and together with the sedimentological and stratal characteristics of the sequences are important indicators of stratigraphic architecture four types of shell bed are associated with surfaces formed by four different types of stratal termination onlap backlap downlap and flooding surface shell beds cf kidwell 1991 are associated respectively with the transgressive surface of erosion apparent truncation at the top of the transgressive systems tract the downlap surface and local marine flooding surfaces a fifth shell bed type termed a compound shell bed forms in offshore environments where the downlap surface converges with the sequence boundary and elements of both the downlap and the backlap shell beds become mixed or superposed the shell beds mark zones of stratal attenuation and can be used as surrogates for seismic discontinuities when applying sequence stratigraphic concepts at outcrop scale

the sequence of local recolonization of warm water marine molluscan species during a deglacial warming climate phase a case study from the early pleistocene of the sea of japan abstract changes in the fossil assemblage of offshore molluscs within each sixth order 41 kyr depositional sequence of the early pleistocene omma formation document repeated recolonizations of warm water species into the sea of japan each recolonization started as soon as the warm tsushima current began to flow in the sea of japan during a deglaciation and subsequent interglacial period here we examined in detail the stratigraphic distribution of six selected significant warm water species and calculated confidence intervals for their first local appearances in a total of 10 deglaciations using continuously sampled data they were subdivided into two groups based on the chronological order of their first appearance during warming phases comparison of geological with biogeographic data reveals that these migration patterns are not always consistent with the modern geographic distributions of the species these results show that fossil records may anticipate how the assemblage of local species would change in response to climate warming

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

glaucony and carbonate grains as indicators of the condensed section omma formation japan the fifth order depositional sequences of the early pleistocene omma formation exposed along the japan sea coast of central japan were formed by glacial eustasy during oxygen isotope stages 50 to 28 in each depositional sequence two ecostratigraphic datums are always present the appearance and disappearance datums of warm water molluscan species these datums are independent of sequence stratigraphic concepts because the establishment of them is based on immigration events of molluscan species associated with glacio eustatic sea level changes determination of time planes shows that the appearance datum seems to occur near the midpoint of sea level rise on the glacial to interglacial shift in deep sea d 18 o records in order to evaluate the significance of the condensed section in sequence stratigraphy and also to facilitate its recognition this study examines the stratigraphic relationship of the condensed section indicators glaucony and carbonate grains with respect to the position of the ecostratigraphic datums in depositional sequences of the omma formation the results show that the maximum concentration of carbonate grains is a more reliable maximum flooding surface indicator than the concentration of glaucony the combination of indicators of condensed section and ecostratigraphic datums represented by incursion epiboles enables the boundary between transgressive and highstand systems tracts to be recognized in the inner shelf parts of depositional sequences moreover truncation of ecostratigraphic datums during sea level falls demonstrates significant erosion at the sequence boundaries integration of climatic palaeoecology and sequence stratigraphy permits a level of correlational precision of the order of a few thousands of years 1998 elsevier science b v all rights reserved

constraints on the timing of systems tract development with respect to sixth order 41 ka sea level changes an example from the pleistocene omma formation sea of japan abstract the middle part of the omma formation exposed along the sea of japan coast in central japan comprises 11 sixth order 41 ka depositional sequences that were deposited in the inner to outer shelf environments and accumulated during oxygen isotope stages 50 to 28 warm water planktonic foraminifera intruded into the sea of japan during interglacial periods and were extirpated in the following glacial period the stratigraphic distribution of these microfossils provides datum that allows the timing of systems tract formation and the degree of truncation at the superjacent ravinement surface to be constrained the disappearance datum of warm water planktonic foraminifera demonstrates unequivocally that the regressive systems tract was deposited during falling sea level sixth order cyclothems of the omma formation include the following architectural elements in ascending stratigraphic order 1 a basal sequence boundary that is superposed on the ravinement surface 2 a transgressive systems tract 2 5 m thick consisting of a basal shell bed 0 3 m thick a condensed onlap shell bed and overlying fine to very fine grained sandstone 3 a maximum flooding horizon that coincides with the horizon that has the maximum concentration of sand size biogenic grains 4 a highstand systems tract 2 3 m thick consisting of fine grained sandstone and sandy siltstone and 5 a resgressive systems tract

eustatic sea level change at the mid pleistocene climate transition new evidence from the shallow marine sediment record of japan abstract based on the excellent sedimentary record we have identified five depositional sequences in the upper part of the omma formation exposed along the japan sea coast of central japan the base of this stratigraphic section is placed just below the top of the jaramillo subchron and the top is located below the brunhes matuyama boundary biostratigraphy supports the interpretation that the lower three sequences correlate with marine oxygen isotope stages mis 28 26 26 24 and 24 22 respectively we have reconstructed a eustatic sea level curve from analyses of sedimentary facies fossil molluscs basin subsidence and sediment accumulation the resulting sea level curve shows that mean eustatic sea level dropped between 1 0 and 0 9 ma and that sea level was lowest at mis 22 which has the heaviest 18o value between mis 28 and 22 the total fall in mean sea level is inferred to be 20 30 m this independent sea level record demonstrates that ice sheet volume rapidly increased at the mid pleistocene climate transition mpt and culminated in mis 22 as inferred from the 18o record the upper two depositional sequences imply the contribution of precession to changes in ice sheet volume would have arisen in mis 21 just after the mpt

ocean change around greenland under a warming climate the impact of climate warming on the ocean near greenland is investigated with a high resolution coupled global climate model the ocean around greenland exhibits a strong warming in response to a four times increase of present day atmospheric co 2 levels the signal is intensified in the intermediate layer and regionally strongest in the greenland sea the projected changes in temperature are driven by changes affecting the large scale ocean circulation rather than changes of the local atmospheric heat forcing the ocean conditions examined here provide a background for the water masses in contact with the outlet glaciers around the greenland coast the future warming of the warm subtropical origin layer could thus lead to enhanced ice sheet melting although the signal could be mitigated by other effects including an enhanced stratification of the surface fresh layer applying a simple parameterization to estimate the change in melt rate along the greenland coast we find that ice sheet melting increases everywhere in response to the change in water mass properties although the melt rate changes show large variations in space the largest melting acceleration is found on the east coast between fram strait and denmark strait where both the parameterization applied to present day conditions and observations suggest moderate melting up to now these model results caution that the greenland ice sheet mass balance should be monitored everywhere and not only where melting occurs at the moment

sequence concepts at seismic and outcrop scale the distinction between physical and conceptual stratigraphic surfaces abstract the sequence stratigraphic terms maximum flooding surface and downlap surface as currently applied are ambiguous examples of these intra sequence surfaces are summarised from high frequency mid pleistocene sequences and from a cretaceous recent seismic megasequence both from new zealand at any one locality a mid pleistocene sequence contains up to four stratal discontinuities in ascending order the sequence boundary ravinement surface local flooding surface and downlap surface these physical surfaces which occur in outcrop are regionally diachronous and should be differentiated from theoretical isochronous horizons such as the time of maximum flooding horizon corresponding to maximum shoreline transgression and the time of peak eustatic or local relative sea level horizons corresponding to the highpoint of the eustatic and relative sea level cycles respectively in seismic studies the boundary between the transgressive and highstand systems tracts is usually located at the downlap surface on the basis of a major thermo tectonic sea level cycle in the canterbury basin it is shown that the downlap surface is not a single regional surface and that the change in slope associated with toes of successive prograding clinoforms rises in stratigraphic height basinwards the downlap surface therefore does not usually coincide with the maximum flooding horizon in plio pleistocene cyclothems a discrete unit the mid cycle shellbed straddles the contact between the transgressive and highstand systems tracts this unit might be classified within its own systems tract the condensed section systems tract csst alternatively the position of the boundary between the transgressive and highstand systems tracts can remain unspecified or unknowable