gzhelian asselian palaeoaplysina microencruster reef community in the taishaku and akiyoshi limestones sw japan implications for late paleozoic reef evolution on mid panthalassan atolls abstract a palaeoaplysina microencruster reef community is recognized in the gzhelian asselian interval of the taishaku and akiyoshi limestones in sw japan which represent accreted panthalassan atoll carbonates in a reef core area of the atoll the alga palaeoaplysina acted as a framebuilder and was associated with various binders e g tubiphytes archaeolithoporella cystoporate bryozoans and microbialites and sediment bafflers such as fenestrate and cryptostomate bryozoans and phylloid algae in a subtidal environment of the back reef area palaeoaplysina and phylloid algae flourished as sediment bafflers a microbial community including tubiphytes and sessile foraminifers was predominant in a very shallow peritidal environment of the back reef area palaeoaplysina was distributed mainly along the northern margin of pangea and is regarded as a boreal element during gzhelian asselian time its distribution extended to the tropical or subtropical panthalassa ocean due to global cooling on the akiyoshi atolls the palaeoaplysina microencruster community was succeeded by a sponge microencruster community in the late early permian the timing of this biotic turnover is similar to that of a change in climate from icehouse to greenhouse conditions and coincides with superplume activity beneath the mid panthalassa ocean

late paleozoic glacial episodes in gondwanaland reflected in transgressive regressive depositional sequences in euramerica the late paleozoic glaciation of gondwanaland comprised two short episodes in the famennian i and visean ii confined to brazil and adjacent northwest africa and a long episode that started in the namurian iiia of eastern australia and bolivia argentina expanded to cover much of gondwanaland in the stephanian asselian iiib and collapsed in the early sakmarian iiic dropstones in eastern australia indicate that small ice centers lingered to the kazanian across the belt of low latitudes north of gondwanaland short ranging fossils in widespread shallow marine and paralic deposits indicate synchronous deposition of transgressive regressive sequences in different parts of euramerica these sequences correlate with glacial events in gondwanaland at three levels a four major regressions in euramerica in the famennian 1 visean 2 namurian 3 stephanian 4 and the tastubian transgression that preceded the sterlitamakian regression 5 also recorded in gondwanaland correlate with glacial episodes i ii and iiia iiib and iiic b the time interval of cyclothemic deposition in euramerica brigantian or latest visean to sterlitamakian correlates with that of glacial episode iii and c the dominant period of the euramerican cyclothems as estimated from the middle and late pennsylvanian deposits of the mid continent of north america and of the thickest known gondwanaland glacigenic sediment the earliest permian lyons group of western australia is 0 4 ma equivalent in turn to the long orbital eccentricity period of the quaternary ice age and the dominant period of fluctuation of the late miocene antarctic ice cap the three levels of correlations confirm wanless and shepard9s 1936 hypothesis that the late paleozoic cyclothems are controlled largely by sea level fluctuations related to the gondwanaland glaciation

activation of pacific mantle plumes during the carboniferous evidence from accretionary complexes in southwest japan the identification of ancient activity of large igneous provinces which may be surface manifestations of giant mantle plumes is of primary importance in understanding the evolution of the earth system because such major magmatic redistribution could have profound effects on the global environment the immobile trace element compositions of metamorphosed basaltic rocks called greenstones found in accretionary complexes of southwest japan suggest origins in accreted oceanic lavas at pacific hotspots rather than at mid oceanic ridges furthermore some of these greenstones have geochemical characteristics typical of hotspot lavas in the present superswell region of the south pacific ocean available age data show that the hotspot lavas formed at 350 300 ma greenstones with eruption ages identical to those in southwest japan are widely distributed in the circum pacific region these observations provide evidence for activity of a giant pacific mantle plume during the carboniferous the onset of such giant plume magmatism may have preceded that of the geomagnetic quiet zone

a reappraisal of dolomite abundance and occurrence in the phanerozoic critical assessment of dolomite abundance throughout the phanerozoic suggests that most large scale dolomite has had an origin related to salinity elevated seawaters the distribution of such dolomite is not directly related to periods of major continental flooding but rather to periods when extensive peritidal sequences or large scale evaporite basins lagoons existed the development of such depositional systems is controlled largely by eustasy paleogeographic tectonic setting and paleoclimate extensive peritidal sequences are characteristic of mature passive margin carbonate platforms that formed during long periods of earth history generally devoid of major continental glaciation e g late precambrian through early paleozoic and mesozoic sea level fluctuations of relatively low amplitude during such periods allowed extensive cyclic peritidal dominated platforms to develop such platforms typically lack raised rims had depositional surfaces that stayed near sea level for tens of millions of years and show little evidence of major drops in sea level that would have exposed the shelf for long periods this would have allowed repeated replenishment of pore waters by mg rich marine fluids over very extensive supratidal surfaces also since the cycles are very thin the downward moving brines could penetrate several cycles on the inner platform causing massive dolomitization in contrast during major glacial periods e g middle to late mississippian to early permian and late cenozoic higher amplitude ice driven fluctuations in sea level led to extensive meteoric water flushing of shallow platforms but related dolomitization has been of minor significance under conditions of elevated mg ca ratio in hypersaline brines however large scale dolomitization could occur in response to the formation of extensive evaporite basins lagoons suitable climatic and paleogeographic tectonic conditions have allowed such dolomitization at various times during the phanerozoic regardless of specific styles of eustatic sea level change lack of massive dolomitization in holocene carbonates may be because neither extensive peritidal sequences nor large scale evaporite basins lagoons are prevalent in modern carbonate environments

dolomite abundance and stratigraphic age constraints on rates and mechanisms of phanerozoic dolostone formation increasing dolomite abundance with age relative to limestone has long been accepted as one of the general truisms of sedimentary geology a relationship which suggests that dolomitization is a cumulative process occurring slowly over the full burial history of a carbonate sequence however reevaluation of data in support of this assumption indicates that although relative dolomite abundances do change significantly throughout phanerozoic carbonate sequences no data set demonstrates any direct correlation between dolomite content and age whereas tabulation of available data does suggest greater amounts of dolomite formation during periods of continental flooding global mass balance calculations of potential magnesium sources also indicate that most dolomite has formed from marine or marine derived fluids at the earth9s surface this conclusion is indirectly supported by significant short term period scale changes in phanerozoic dolomite abundance a variation which would be more attenuated if dolomitization were dominantly a burial process dolomitization may be enhanced during times of global transgression higher atmospheric pco 2 and lower calcite saturation state in shallow marine settings

response of carboniferous permian mid oceanic seamount capping buildup to global cooling and sea level change akiyoshi japan abstract we discuss the response of a carboniferous permian mid oceanic atoll type carbonate buildup to global cooling and sea level fluctuation during gondwana glaciation our examination focused upon the stratigraphic distribution of emergence indicative diagenetic features as a proxy for sea level falls and we correlated their timing with hiatuses indicated by fusuline biostratigraphic discontinuities and the demise of warm adapted metazoan reef builders we examined the pennsylvanian moscovian to lower permian asselian shallow marine limestone succession ca 500 m thick of the akiyoshi limestone group southwest japan reconstructed as a mid oceanic seamount capping buildup in the panthalassan ocean the examined succession is dominated by atoll lagoon facies with subordinate coral chaetetes patch reefs and calci microbial mounds we have recognized several stratigraphic intervals less than 60 m thick in the examined succession in which emergence indicative diagenetic facies are concentrated these facies include the microcodium structure pendant cements recrystallization and algal casts each of the intervals occurs immediately below a fusuline zone boundary and represents a sea level fall event which lasted presumably 1 ma or less possibly reflecting the sea level fluctuation of third order cycles the emergence event in late kasimovian is the most prominent in the series of moscovian through asselian emergence events and resulted in a dissolution unconformity indicated by a fusuline biostratigraphic discontinuity we infer that many intercalations of less freshwater altered limestone in these stratigraphic intervals resulted from short lived emergence resubmergence episodes possibly due to the high frequency glacio eustyaic sea level fluctuation we also showed that the demise of warm adapted metazoan reef builders of corals and chaetetes happened nearly synchronously with the culmination of gondwana glaciation we hypothesize that the demise of these warm adapted reef builders is a biotic response of the akiyoshi buildup to the severe and prolonged global cooling during the pennsylvanian to early permian icehouse period the akiyoshi metazoan reef builders were replaced by calci microbes phylloid algae and calci sponges that exhibit an increasing significance during the lower to middle permian our results reveal the distinct sedimentary and biotic responses of a panthalassan atoll to global cooling and sea level fluctuation during gondwana glaciation in the southern hemisphere we conclude that carboniferous permian mid oceanic atoll stratigraphy has significant archival potential for recognizing the global palaeoclimatic change

gondwanan deglaciation and opening of neotethys the al khlata and saiwan formations of interior oman abstract new stratigraphic petrographic and paleontological data from the lower permian of southeastern arabia help to elucidate the still debated timing of neotethys rifting and the climatic evolution following the gondwanan glaciation the transition from the al khlata to the saiwan formation here described in detail is interpreted to record continental break up and onset of neotethyan spreading between northern gondwana and the cimmerian terranes at mid sakmarian times as constrained by brachiopod assemblages the eastern oman arm of the neotethyan rift system instead failed and sea floor spreading of the indo madagascar trough was delayed until final fragmentation of gondwana in the late jurassic petrographic composition of lower permian sandstones documents a distinct change from transitional to dissected rift shoulder provenance and widespread exposure of granitoid basement rocks at a late syn rift to early post rift stage very abundant pore filling celestite at the al khlata saiwan transition may have precipitated from circulating brines related to remobilization of proterozoic salt due to rift tectonics the sharp base of the saiwan formation records a major transgression related to the onset of neotethyan spreading final deglaciation and consequent global sea level rise as indicated by ravinement surfaces associated with lag deposits with tree trunks reworked ferruginous pedogenic concretions and phosphate and by paleoecological analyses the basal bed of the saiwan formation is characterized by the pioneer pachycyrtella paleocommunity with pachycyrtella omanensis 85 suspension feeding rapid rates of reproduction and growth r strategy early maturity high mortality rates in the juveniles the more mature secondary ecological succession developed higher in the saiwan formation records maximum flooding and significant climatic amelioration the saiwan formation at the beginning of the late sakmarian finally sutures the irregular rift related topography in the rim basin of interior oman and records a shift towards warmer temperate conditions after the end of the gondwanan glaciation

sea level curve for pennsylvanian eustatic marine transgressive regressive depositional cycles along midcontinent outcrop belt north america at least 55 cycles of marine inundation and withdrawal are recognized in the mid desmoinesian to mid virgilian midcontinent outcrop sequence in north america they range from widespread major cycles classic cyclothems with deep water facies extending across the northern shelf through intermediate cycles persisting as marine horizons across the shelf to minor cycles developed on the lower shelf or as parts of major cycles biostratigraphic differentiation of the cycles should establish interbasinal correlation on a scale fine enough to allow evaluation of differential tectonics and sedimentation sequential groupings of cycles are more irregular than proposed megacyclothems or mesothems but they may be obscured by the distinctness of the major cyclothems estimates of cycle periods range from about 40 to 120 x 10 sup 3 yr for the minor cycles up to about 235 to 400 x 10 sup 3 yr for the major cyclothems the range for all cycles corresponds well to the range of periods of earth s orbital parameters that constitute the milankovitch insolation theory for the pleistocene ice ages and it further supports gondwanan glacial control for the pennsylvanian cycles even though the dominant period of the major pennsylvanian cyclothems is up to four times longer than the dominant 100 000 yr period inmore the pleistocene the shapes of both curves display rapid marine transgression rapid melting of ice caps and slow interrupted regression slow buildup of ice caps which suggest similar linkages between the climatic effects of the orbital parameters and ice cap formation and melting at the two different scales widely separated in time 28 references 3 figures less

new insight into a subduction related orogen a reappraisal of the geotectonic framework and evolution of the japanese islands abstract the geotectonic framework and the evolutionary history of the japanese islands need revision in accordance with the various geophysical geological evidence gathered by new methodologies in the recent years including seismic tomography vibroseis ground breaking seismic experiments and detrital zircon chronology these investigations have addressed various themes such as 1 seismic profile of the crust and mantle beneath the japanese islands 2 high precision ages of the protoliths of high p t metamorphic rocks and 3 provenance of terrigenous clastics the results have led to a number of important findings including 1 detection of a large mass of slab around the mantle boundary layer suggesting the long term oceanic subduction beneath japan 2 confirmation of the subhorizontal piled nappe structure for the entire crust of japan 3 finding a new high p t metamorphosed accretionary complex unit that represents the youngest blueschist in japan 4 finding of the oldest early cambrian arc batholith and cover sediments and 5 the identification of plural arc batholiths which have already been erased from the surface based on a synthesis of these new data this article presents a re evaluation of the conventional geotectonic subdivision of the subduction related orogen in japan re definition of the elements and their mutual boundaries and re consideration of the geotectonic evolution of the japanese islands in particular the historical change in provenance suggests that proto japan has experienced large scale tectonic erosion in multiple stages and the corresponding large amounts of continental crust materials were subducted for understanding the orogenic growth of japan during the last ca 500 million years the significance of tectonic erosion coupled with continental contraction as well as the oceanward accretionary growth requires further attention

atoll stratigraphy as a record of sea level change problems and prospects stratigraphic hiatuses and solution unconformities in the subsurface of enewetak atoll northern marshall islands record periods of atoll emergence during low stands of sea level changes in sea level are also recorded in the atoll subsurface by variations in the rate of sediment accumulation relative to the subsidence rate of the underlying volcanic edifice past sea levels can be derived from atoll stratigraphy by correcting the present depth of dated subsurface horizons for thermal subsidence and lithospheric flexure since the time of deposition a correction for depositional paleodepth may also be necessary as a result of erosion and nondeposition during periods of emergence the history of sea level derived in this manner is discontinuous past sea levels derived from atoll stratigraphy can only be estimated to within 50 m relative to present sea level owing to uncertainties in the corrections for subsidence and flexure however the minimum magnitude of sea level falls estimated from stratigraphic hiatuses can be estimated to within 10 m owing to limited fossil based age resolution only long term sea level trends can be deduced from sediments dated by means of biostratigraphy based on the biostratigraphic ages of subsurface horizons at enewetak we can discern very little long term change in sea level from late eocene through late oligocene a rise to 110 m above present sea level in the early miocene a long term fall of 170 m through middle and late miocene time and a long term rise of 60 m from the end of the miocene to present resolution of the sea level history recorded beneath mid ocean atolls may be improved by determining the age of shallow marine carbonates by means of strontium isotope stratigraphy our interpretation of past sea levels based on 87sr 86sr chronostratigraphy from enewetak confirms the long term sea level trends inferred from biostratigraphic subsurface ages in addition we interpret three oligocene sea level falls with minimum magnitudes of 30 50 m at 35 33 30 and 25 ma and four miocene sea level falls greater than 30 95 m at 16 14 12 10 and 5 ma these estimates of the timing and magnitude of oligocene and miocene sea level changes derived from enewetak atoll stratigraphy are compared with sea level histories derived from continental margin stratigraphy and from ice volume changes inferred from deep sea foraminifera 18o records

petrogenesis of greenstones from the mino tamba belt sw japan evidence for an accreted permian oceanic plateau abstract permian greenstones in the jurassic mino tamba accretionary complex southwest japan are divided into three distinct series on the basis of their geological occurrence mineralogy and geochemistry a low ti series lts is associated with lower permian chert and limestone and is the most voluminous of the three series the lts shows slightly more enriched geochemical and isotopic characteristics than morb a transition series ts is mainly associated with lower permian chert and has more enriched geochemical signatures than morb its isotopic characteristics are divided into enriched and depleted types a high ti series hts occurs as sills and hyaloclastites within middle permian chert and as dikes intruding the ts some hts rocks have high mgo contents the hts is characterized by enrichment in incompatible trace elements and an isotopic composition comparable to himu type basalt the geochemistry of the voluminous lts is similar to that of the oceanic basalt series of the kerguelen plateau suggesting production by partial melting of a shallow mantle plume head below thick oceanic lithosphere in early permian time we infer that the ts formed simultaneously at the margins of the mantle plume head in contrast the hts may have resulted from partial melting of a deep mantle plume tail in middle permian time permian greenstones in the mino tamba belt may have thus formed by superplume activity in an intra oceanic setting given the presence of two known contemporary continental flood basalt provinces siberia and emeishan and some accreted oceanic plateau basalts the vast magmatism of the mino tamba oceanic plateau suggests a large scale superplume pulse in permian time accretion of oceanic plateaux may have played an important role in the growth of continental margins and island arcs in japan and elsewhere in the circum pacific region

paleoreef maps evaluation of a comprehensive database on phanerozoic reefs to get a better understanding of controls on reef development through time we created a comprehensive database on phanerozoic reefs the database currently comprises 2470 reefs and contains information about geographic position paleoposition age reef type dimensions environmental setting paleontological and petrographical features and reservoir quality of each buildup reef data were analyzed in two qualitatively different ways the first type of analysis was by visualization of paleogeographic reef distribution maps five examples late devonian early permian late triassic late jurassic middle miocene are presented to show the potential of paleoreef maps for paleogeographic and paleoclimatological reconstructions the second type of analysis was a numerical processing of coded reef characteristics to realize major trends in reef evolution and properties of reef carbonates the analysis of paleolatitudinal reef distributions through time shows pronounced asymmetries in some time slices probably related to climatic asymmetries rather than controlled by plate tectonic evolution alone the dominance of particular reef builders through time suggests that there are seven cycles of phanerozoic reef development first curves for the phanerozoic distribution of bioerosion in reefs bathymetric setting and debris potential of reefs are presented the observed pattern in the temporal and spatial distribution of reefs with reservoir quality may assist in hydrocarbon exploration statistical tests on the dependencies of reefal reservoir quality suggest that large size high debris potential low paleolatitude high amount of marine aragonite cement and a platform shelf edge setting favor reservoir quality reefal reservoirs are significantly enhanced in times of high evaporite sedimentation elevated burial of organic carbon low oceanic crust production low atmospheric co2 content and cool paleoclimate as well as when they are present in aragonite oceans

depositional evolution of lower permian palaeoaplysina build ups kapp duner formation bjornoya arctic norway abstract the lower permian kapp duner formation on bjornoya includes an approximately 45 m thick palaeoaplysina build up complex this complex is composed of stacked cycles of thin 0 1 m thick restricted shelf mudstones and thicker palaeoaplysina wackestone to boundstone capped by subaerial exposure surfaces in the lower part of the complex the build ups are tabular and laterally more widespread than the lenticular build ups found in the upper part of the complex the depositional cycles most likely formed in response to fourth order glacio eustatic fluctuations in sea level while the history of the build up complex is controlled by longer term third order fluctuations in relative sea level the position of the build up complex is structurally controlled

stable isotope signatures associated with palaeosols pennsylvanian holder formation new mexico the holder formation pennsylvanian virgilian of southern new mexico usa consists of limestones interbedded with siliciclastics it was deposited during times of glacio eustatic sea level change and was exposed subaerially during multiple sea level lowstands microcomponents and whole rock samples of limestones were analysed for 13c and 18o values to examine the method of whole rock isotopic analysis for detecting subaerial exposure events and to determine the diagenetic processes acting during subaerial exposure whole rock isotopic shifts are not consistently present across petrographically identified subaerial exposure surfaces apparently whole rock isotopic shifts do not result from wholesale replacement of the host sediment during soil formation however the isotopic shifts are present in calcareous soil precipitated microcomponents such as rhizoliths laminated crusts and soil precipitated cements the components are heterogeneous in isotopic composition but converge on a meteoric calcite line at about 18o 5 5 these microcomponents are heterogeneous in distribution and may either dominate or be a minor constituent of the whole rock at a single stratigraphic horizon without petrographic selection of palaeosol components the detection of whole rock isotopic shifts may depend on the selection or chance sampling of a rock containing abundant microcomponents precipitated in a soil environment only minor whole rock isotopic shifts come from those rocks bearing no evidence of exposure and bearing lithological characteristics suggesting subaerial exposure was unlikely

overflow dynamics and bottom water formation in the western ross sea influence of tides 1 the tidal impact on overflow dynamics and bottom water production in the western ross sea is studied with the finite element ocean model which allows embedding a mesh with 0 5 km resolution in a coarse resolution 30 km setup without nesting the simulated overflow properties inside and downstream of the western ross sea are described the overflow exhibits pronounced variability at both daily and spring neap tidal time scales in the western ross sea tides increase mixing over both the outer shelf and upper slope there plume jets are shaped by tidal currents at a bathymetric bend west of the drygalski trough mouth descending rapidly and supplying the bottom water a fraction of shelf water remains over the shelf and propagates westward from the ross sea but it does not contribute significantly to bottom water formation because of energetic mixing over the upper slope compared to a simulation without tidal forcing tides with the major k1 and o1 constituents increase the outflow rate over the continental slope off cape adare by about 70 a set of sensitivity experiments show that the rate of bottom water production is not a monotonic function of the tidal currents amplitude tidal forcing with intermediate strength leads to the most efficient bottom water formation

black pebble occurrence and genesis in holocene carbonate sediments florida keys bahamas and tunisia abstract black carbonate lithoclasts along with blackened peloids ooids skeletal fragments and entire limestone beds are found in the shallow subtidal intertidal and supratidal zones of modern and ancient carbonate environments they are often associated with pedogenic features such as root traces or caliche the blackening is due to impregnation of the sediment by dissolved colloidal or finely particulate organic substances in an anoxic and alkaline environment or microenvironment the organic matter is derived from decayed algae and or decayed or burnt higher terrestrial plants iron sulfides contribute to the blackening especially in samples containing algal matter a complex interplay of adsorption of organic matter on carbonate crystal surfaces neomorphism and microcrystalline cementation in the vadose or freshwater phreatic zones is thought to fix the organic matter and make the black coloration relatively resistant to oxidation black pebbles form through reworking of the preferentially cemented and blackened sediment by coastal erosion they are mostly relics because the less consolidated host sediment is washed away black pebbles may thus be valuable indicators of ancient coastal and terrestrial environments

ancient helictites and the formation of vadose crystal silt in upper jurassic carbonates southern germany abstract speleothems and vadose crystal silt are effective indications for karstification processes in the fossil record upper jurassic limestones in southern germany that have undergone vadose diagenesis contain on crystal margins and tips of coarse bladed calcites numerous fibrous calcite crystals formed by abnormal growth conditions and internal sediment within fractures and vugs fibrous calcite crystals grew as crusts in fence and mesh like arrangements fibrous crystals which have a length width ratio of greater than 1 10 are made up of stacked subcrystals composed of an alternation of hexagonal prisms and rhombohedra they exhibit a central to somewhat eccentric capillary electron probe microanalysis shows low mg calcite mineralogy with negligible amounts of fe mn and sr as well as disseminated clay and metal hydroxide impurities stable isotope data show relatively 13c enriched and 18o depleted values 13c 2o oo pdb 18o 6o oo pdb suggesting a meteoric environment and co2 degassing as the main process of formation fibrous calcite crystals form from capillary fluids that are highly supersaturated with respect to calcium carbonate contaminated with alien mineral impurities the abnormal growth pattern is suggested to be substrate controlled and attributed to mineral impurities that produce numerous crystallization nuclei fibrous calcite crystals are comparable to helictites of the filiform type that are reported only from quaternary caves nevertheless the diagenetic sequence and oxygen isotope data suggest a late cretaceous to early tertiary age for their formation the internal sediment consists exclusively of silt size fragments of fibrous crystals and therefore is comparable to vadose crystal silt crystal silt is generated by the erosion of fibrous crystals both by vadose seepage and air currents this study is the first observation of ancient helictites and related vadose crystal silt documenting the close relationship between pore ceiling vadose cements and the generation of crystal silt

isotope signatures associated with early meteoric diagenesis the environments in which carbonate diagenesis proceeds have been documented in previous studies of holocene and late pleistocene sediments and limestones on barbados west indies variations in the carbon and oxygen isotopic composition of limestones produced during early freshwater diagenesis have been observed in this study to occur in specific patterns six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework 1 the subaerial exposure surface is characterized by strongly 12c enriched limestones 13c compositions of underlying limestones grow progressively heavier with increasing depth 2 the subaerial exposure surface may also be marked by slight 18o enrichment 3 an abrupt shift in 18o values may differentiate sediments above the exposure surface from those below 4 sediments altered in the marine meteoric mixing zone may be characterized by positive covariance between their 18o and 13c compositions 5 the vadose phreatic boundary may be marked by a sharp increase in 13c values in the seaward portions of a fresh groundwater system and 6 samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of 18o and a wide range of 13c compositions analysis of samples from five palaeozoic and mesozoic formations which contained petrographic evidence of early freshwater diagenesis showed that isotope patterns similar to those observed in barbados limestones have been preserved in rocks as old as mississippian these isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks they might be used to identify limestones diagenetically altered in meteoric environments to identify mixing zone cements and dolomites and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations

paleogeographic reconstruction of accreted oceanic rocks akiyoshi southwest japan the depositional setting of an accreted oceanic rock succession of limestone chert and greenstone is reconstructed by using the stratigraphy age and lithologic features in the akiyoshi terrane southwest japan stratigraphic and radiolarian paleontological results identify four coeval oceanic rock units ranging in age from late early carboniferous to late middle permian sediments on the top the upper flank the lower flank and the foot of the seamount and on the surrounding ocean floor are represented by reef limestone detrital limestone with spicular chert spicular chert with displaced limestone and radiolaria bearing chert respectively all units rest on greenstone radiolaria bearing chert is interpreted as a more distal facies than spicular chert these rocks are interpreted as sediments deposited on and around a basaltic seamount formed in an open ocean realm that had no input of terrigenous materials

facies stacking patterns in high frequency sequences influenced by long term sea level change on a permian panthalassan oceanic atoll an example from the akiyoshi limestone sw japan abstract detailed core examination of middle permian guadalupian lagoonal successions of mid panthalassan atoll carbonates akiyoshi limestone revealed distinct stratigraphic variation of facies and sequence stacking patterns the long term sea level change reconstructed from the atoll stratigraphy of the akiyoshi includes a bolorian to midian gentle sea level fall punctuated by a short lived murgabian sea level rise these sea levels can be regarded as eustasy judging from the monotonous subsidence of the akiyoshi atoll and its good correspondence with the sea level curves of other areas two sequence types are defined sequence type a consisting of shoal to lagoon grainstone occurred in low accommodation during the sea level highstand to falling stages of the late murgabian to midian this sequence type is bounded by two successive subaerial exposure surfaces and exhibits the uneven but generally low 13c values throughout the section in contrast sequence type b occurred in increasing accommodation during the sea level rise of the early murgabian this sequence type represents a composite sequence comprising parasequences and consists of various types of facies such as peritidal lime mudstone lagoonal packstone and boundstone and shoal grainstone sequence type b is characterized by consistently high 13c values except for the negative shift immediately below the sequence top surface these lines of evidence demonstrated that long term eustatic sea level change obviously controls the variations of sequence types in atoll carbonates

impact of long term climate change and sea level fluctuation on mississippian to permian mid oceanic atoll sedimentation akiyoshi limestone group japan abstract to understand the impacts of long term climatic episodes and sea level changes on mid oceanic atoll sedimentation the stratigraphic changes of litho and bio facies and stratigraphic levels of freshwater diagenetic alteration and biostratigraphic discontinuity of the akiyoshi limestone group upper visean to upper capitanian were reviewed this group records approximately 70 million years of atoll sedimentation in a mid oceanic realm of the panthalassa ocean which developed nearly synchronously with the late paleozoic gondwana glaciation the entire succession of the akiyoshi limestone group was divided into four facies associations skeletal oolitic grainstone muddy limestone muddy limestone skeletal grainstone and reefal limestone associations skeletal oolitic grainstone and reefal limestone associations upper visean to bashkirian are characterized by an abundance of oolite and crinoidal grainstone and reef facies of warm adapted metazoan reef builders corals chaetetes and bryozoans respectively characteristics of skeletal oolitic grainstone and reefal limestone associations indicate their deposition in a warm climate with elevated sea level muddy limestone association moscovian to kasimovian records the demise of the warm adapted metazoan reef builders and frequent emergence events of the buildup many geochemical data support the significant drop in temperature during moscovian through kasimovian time these depositional and biotic events of muddy limestone association indicate that its sedimentation was strongly affected by cool climate and generally low sea level muddy limestone skeletal grainstone association is characterized by an upward increasing significance of calcimicrobes calcareous algae and calcisponges the succession records less frequent emergence events than that of muddy limestone association ii these characters reflect a warming climate and sea level rise in gzhelian to capitanian time the climate episodes and sea level changes interpreted from the akiyoshi limestone group generally correspond to the global trend of mississippian to permian long term climatic change and sea level fluctuation related to the major glacial events of gondwana glaciation the late visean to bashkirian warm climate and elevated sea levels moscovian to kasimovian cooling and sea level lowering and gzhelian to capitanian warming and sea level rise recorded in the akiyoshi buildup are comparable to the global climate model and sea level fluctuation which contain early to middle mississippian pre glacial warm climate and highstands middle to late pennsylvanian cooling and related glacio eustatic sea level fluctuation at the culmination of gondwana glaciation and early to middle permian global warming and sea level rise due to the retreat of gondwana ice sheets akiyoshi atoll sedimentation was most significantly affected pennsylvanian global cooling and related sea level lowering but their impact was short lived the onset of the cooling and frequent emergence events in the akiyoshi buildup occurred delayed approximately 10 millions years later than that of comparable episodes on the pangean shelves the post glacial warming in the akiyoshi buildup started at least several millions of years earlier than in epicontinental seas of the pangea this phenomenon may be due to the palaeoposition of the akiyoshi buildup in a mid oceanic realm of the panthalassa ocean

origin and significance of isotope shifts in pennsylvanian carbonates asturias nw spain abstract the primary variability of the composition and properties of seawater is much greater in the shallow coastal zones than in the main body of ocean water an inadequate understanding of this variability as well as different diagenetic environments severely limit the interpretation of the stable isotope record of shoalwater carbonates in order to investigate this primary and diagenetic variability along a bashkirian moscovian platform to basin transect 13c and 18o analyses have been performed on more than 1000 matrix micrite carbonate cement and brachiopod shell samples in isotope analysis these different carbonate materials tend to complement each other inasmuch as they have different advantages and shortcomings the resulting data reveal spatial trends in 13c and 18o signatures from platform top lower values to basin higher values in the case of 13c from pristine brachiopods this trend can be explained by the long residence time aging of platform top water masses in the case of brachiopod 18o this variance is interpreted to reflect temperature differences between warm surface and colder bottom water separated by a permanent thermocline at about 150 to 200 m beneath the shelf break micrite and marine cement isotopic values from the platform interior were reset lowered during pervasive early meteoric diagenesis in contrast micrite and marine cement isotopic values from the outer platform slope and basin show higher values close to the assumed pennsylvanian seawater isotopic composition this implies that isotopic data from shoalwater carbonates including pristine brachiopod shells might not necessarily reflect paleoceanographic trends of the open ocean water masses because of changes in coastal water mass isotope signature and interaction with early meteoric fluids