genesis of the late eocene bedded halite in the qaidam basin and its implication for paleoclimate in east asia abstract it has long been suggested that the eocene climate in east asia was characterized by three latitudinally distributed zones one middle arid zone and two humid zones to its north and south the middle arid zone was firstly proposed based on the widespread red beds and evaporites in a nww trending zone of china however this long standing model has recently been challenged by increasing doubts about the effectiveness of these arid climate indicators the qaidam basin as one of the eocene evaporites bearing basins in china can be studied to test whether the bedded evaporites can validly indicate arid climate over 300 m halite beds have been found in the late eocene upper xiaganchaigou uxg formation in a local saline center shizigou area of the qaidam basin its coexistence with source rocks and limited distribution together with the absence of red beds make it difficult to explain the halite genesis with the conventional climatic controlled playa model based on stratigraphic correlation lithological and mineralogical observation and oxygen carbon and chlorine isotopic analysis we identify several characteristics about the shizigou saline center 1 undulated lake floor 2 shallow water 3 limited hydrothermal impact 4 evaporation induced precipitation 5 high eolian influence and 6 fluctuated climate background according to these investigations we suggest a new model for the genesis of the bedded halite in the qaidam basin the tectonic climatic model the key point for this model is that the undulated topography caused by tectonic activity and the fluctuated climate together leaded to the hydrological isolation of the shizigou area the shizigou area was isolated from the larger brackish qaidam paleolake for independent evaporation during arid climate stage while connected with it during humid climate stage causing alternatively water influx and evaporation and inducing the occurrence of interbedded halite and source rocks thus the widespread bedded halite in the eocene strata over china may indicate fluctuated rather than arid climate in east asia

sediment dispersal and quantitative stratigraphic architecture across an ancient shelf two large 200 to 300 km near continuous outcrop transects and extensive well log data ca 2800 wells allow analysis of sedimentological characteristics and stratigraphic architecture across a large area ca 60 000 km2 of the latest santonian to middle campanian shelf along the western margin of the western interior seaway in eastern utah and western colorado usa genetically linked depositional systems are mapped at high chronostratigraphic resolution ca 0 1 to 0 5 ma within their sequence stratigraphic context in the lower part of the studied interval sediment was dispersed via wave dominated deltaic systems with a compound clinoform geomorphology in which an inner wave dominated shoreface clinoform was separated by a muddy subaqueous topset from an outer clinoform containing sand poor gravity flow deposits these strata are characterized by relatively steep net regressive shoreline trajectories 0 1 with concave landward geometries narrow nearshore belts of storm reworked sandstones 2 to 22 km wide offshore mudstone belts 250 km and relatively high sediment accumulation rates ca 0 27 mm year 1 the middle and upper parts of the studied interval also contain wave dominated shorefaces but coeval offshore mudstones enclose abundant isolated tide influenced sandstones that were transported sub parallel to the regional palaeoshoreline by basinal hydrodynamic tidal circulation these strata are characterized by relatively shallow net regressive shoreline trajectories 190 km and relatively low sediment accumulation rates ca 0 11 mm year 1 the change in shelfal sediment dispersal and stratigraphic architecture from i compound clinoform deltas characterized by across shelf sediment transport to ii wave dominated shorelines with isolated tide influenced sandbodies characterized by along shelf sediment transport is interpreted as reflecting increased interaction with the hydrodynamic regime in the seaway as successive shelfal depositional systems advanced out of a sheltered embayment utah bight this advance was driven by a decreasing tectonic subsidence rate which also suppressed autogenic controls on stratigraphic architecture

soft sediment deformation in upper proterozoic torridonian sandstones applecross formation at torridon northwest scotland abstract the applecross formation upper proterozoic torridon group northwest scotland was deposited as planar laminated and cross bedded coarse sands in braided streams soft sediment deformation is described from a 97 m thick study section most of which comprises contorted stratification the main structures are cusps and complex recumbent folded cross bedding formed by water escape during fluidization four assemblages of structures are recognized deformation as isolated structures in an otherwise undeformed unit may have been triggered by fluid turbulence discrete and chaotic units record widespread liquefaction and fluidization respectively of the most recently deposited sediment deformation may have been triggered by upwelling groundwater multilayer complexes formed when water escape from a buried layer generated fluidization in the overlying sediment this may have been triggered by seismically induced liquefaction some parts of the succession were disturbed on separate occasions by different processes sediment laden currents are unlikely to have been a major trigger for deformation it is concluded that specific soft sediment deformation structures result from the combination of driving forces deformation mechanism and initial geometry assemblages of structures relate to the timing of deformation and are of more value in identifying the trigger for deformation

sedimentary structures tentatively attributed to seismic events abstract fingerprints of earthquakes in the sedimentary record are as yet difficult to identify this is particularly true for failure phenomena dewatering slumping fault graded and turbidite structures that could have been triggered also by other kinds of energy input other promising candidates are strange biostratinomic features convex down stacking of shells current orientation in wave ripple accumulations as well as certain preservational features found in geosynclinal pelagic limestones but in every case verification of the seismic origin is still needed

volcaniclastic sediments process interaction and depositional setting of the mio pliocene miura group se japan abstract the mid miocene to early pliocene 14 3 ma miura group exposed on the miura and boso peninsulas around tokyo bay in southern honshu comprises at least a 2 km thick succession of volcaniclastic sediments these accumulated in a forearc basin or basins on the eastern side of a proto izu bonin arc prior to and during accretion of the miura block onto the honshu arc and its subsequent dextral transcurrent eduction the basin fill shows a complex admixture of facies that result from multiple processes which operated on a relatively shallow slope basin the main facies groups include dark coloured mostly coarse grained scoriaceous beds pale coloured muddy silty pumiceous bioturbated sediment yellowish and whitish coloured tuffaceous horizons and chaotic slump debris flow and injection units many of the facies and beds in the older misaki formation can be readily interpreted as the result of a direct pyroclastic fall through the air and water b downslope resedimentation via turbidity currents and related processes in some cases derived from subaqueous base surge pyroclastic flow or vertical density currents c hemipelagic settling commonly under the influence of thermohaline bottom currents in other cases composite beds are believed to result from the interaction of these processes in more complex events the younger hasse formation is dominated by more shallow water marine currents and storm events and in parts by fluvial or proximal fan delta processes the distribution of these different facies illustrates the evolution and shallowing of the miura boso forearc basins during accretion and emplacement

hiatal duration of correlative sequence boundaries from oligocene pliocene mixed carbonate siliciclastic sediments of the south florida platform abstract sequence boundaries defined by regional unconformities in mixed carbonate siliciclastic sediments have a variable duration from the margin to the interior of the florida platform factors controlling the timing and duration of these unconformities include a combination of global eustatic and regional mechanisms sediment supply current intensification integrated chronostratigraphies developed from a transect of continuous cores in the south central interior to the southern margin of the florida platform show an increase in duration of the hiatal gaps along correlative sequence boundaries toward the platform edge two sequence boundaries are correlated across the south florida platform and mark formation contacts the lower sequence boundary sb a marks the suwannee limestone arcadia formation contact and is of significantly less duration in the platform interior southwest peninsular florida 2 0 m y than at the south platform margin middle florida keys 8 1 m y the hiatal gap along the upper sequence boundary sb b marking the arcadia formation overlain by miocene pliocene sediments that vary in age and composition regionally records the same increase from the central part of the platform southwest florida arcadia fm peace river fm 1 6 m y to the south platform edge lower florida keys arcadia fm stock island fm 11 5 m y eustatic fluctuations affected the relative sedimentation rates of the mixed sediments in the platform interior and at the margin most notably the large eustatic fall at the end of the early oligocene terminated carbonate deposition of the suwannee limestone sb a sediment accumulation on the platform interior was more temporally continuous than at the margin because of greater siliciclastic input from the north the strengthening of marine currents beginning in the middle miocene limited sediment accumulation across the southern platform margin sb b and possibly caused erosion of the margin carbonates increasing the duration of the hiatal gap on top of the arcadia formation

structural characteristics of shallowly buried accretionary prism rapidly uplifted neogene accreted sediments on the miura boso peninsula central japan 1 the upper miocene misaki and nishizaki formations on the miura and boso peninsulas in central japan preserve the deformation features of an off scraped accretionary prism the spatial distribution geometry and style of accretion related deformation with paleotemperature and burial depth estimation are elucidated in this study the deformation structures and textures are similar to those of modern accretionary prisms the low maximum paleotemperature 50 c and high preserved porosity of the sediments 30 50 imply a maximum burial depth of less than 1000 m on the basis of the mode of deformation this off scraped body is divided into an imbricate thrust a thrust unit and an upper coherent unit in ascending order the imbricate thrust corresponds to a branch from the basal decollement zone and is subdivided into a brecciated zone a main gouge zone and a shear band zone the thrust unit hosts a concentration of thrust systems that form various orders of duplex structures while the upper coherent unit is characterized by gravitational instability and earthquake induced deformation without thrust faulting the duplex distribution shear strain and fluid migration associated with the off scraping processes are clearly localized within the imbricate thrust and thrust unit this accretion related deformation occurred before lithification of the sediment and under high fluid pressure induced by shear deformation thickening of the sedimentary sequence and earthquake induced liquefaction these processes are inferred to control the effect on the mode of deformation and the location of thrusting during early deformation of the accretionary prism

paleogeographic reconstruction of the eocene idaho river north american cordillera eocene lake gosiute in southwestern wyo ming was progressively fi lled in by volcani clastic sediment between 49 6 and 47 0 ma the source of this material has long been thought to have been the absaroka volcanic province immediately north of the greater green river basin lead isotope compositions of sandstone from this interval however are consistent with derivation from the challis volcanic fi eld the 40 ar 39 ar ages of single de trital k feldspar crystals from greater green river basin sandstones are nearly identical to 40 ar 39 ar eruptive ages for volcanic rocks of the challis volcanic fi eld 49 8 45 5 ma but we also identify mesozoic and proterozoic crystals that are consistent with cooling ages for rocks that were likely exposed in the idaho segment of the north american cordillera during the eocene most of these rocks are traversed by or are up gradient of a major eocene paleovalley in central idaho the sud den appearance of challis derived sediment in the greater green river basin indicates that a major river here named the idaho river connected the interior of the north american cordillera to the greater green river basin this connection requires 500 km to reach from central idaho to the greater green river ba sin the idaho river probably carried detritus that was stripped from distant uplifted moun tains above the active challis volcanic fi eld as far south as the piceance creek basin suggest ing a total length of at least 1000 km middle eocene metamorphic core complexes in the northern cordillera likely produced a major highland in the headwaters of the idaho river which generated river systems that drained both eastward into the wyoming foreland and westward into the oregon coast ranges

mixing of siliciclastic and carbonate sediments in shallow shelf environments the inhibiting effect that siliciclastic material has on carbonate secreting organisms has lead to the generalization that sediments composed of mixtures of carbonate and siliciclastic material should rarely form however many modern and ancient shelf deposits contain a spectrum of sediments that are of mixed composition the processes responsible for this mixing can be grouped into four categories 1 punctuated mixing where sporadic storms and other extreme periodic events transfer sediments from one depositional environment to another 2 facies mixing where sediments are mixed along the diffuse boundaries between contrasting facies 3 in situ mixing where the carbonate fraction consists of the autochthonous or parautochthonous death assemblages of calcareous organisms that accumulated on or within siliciclastic substrates and 4 source mixing where admixtures are formed by the uplift and erosion of nearby carbonate source terranes the allochemical constituents of mixed sediments are both coralgal and foram mollusc in composition the foram mollusc assemblage is the most common because of the effects of increased turbidity unstable substrates and the clogging of filter feeding mechanisms associated with a siliciclastic influx

sequence stratigraphy in lacustrine basins a model for part of the green river formation eocene southwest uinta basin utah u s a abstract in the middle green river formation of central nine mile canyon uinta basin utah several lacustrine dominated intervals 10 m thick comprise aggradational carbonate parasequence sets and a progradational clastic parasequence maximum flooding surfaces are best identified within profundal oil shale that caps some of the clastic parasequences these lacustrine transgressive systems tracts therefore exhibit parasequence stacking patterns unlike typical marine sequences two types of sequence boundary are identified type a sequence boundaries display evidence for a basinward shift in facies across a regionally mappable surface that is an angular or rarely parallel unconformity and they typically juxtapose amalgamated braided fluvial channel sandstone late lowstand systems tract onto the profundal oil shale they also bound depositional sequences that show a distinct asymmetry being dominated by transgressive systems tracts 5 80 m thick highstand systems tracts are less than 4 m thick and may be removed completely by erosion on overlying sequence boundaries other surfaces satisfy only some of the standard criteria of sequence boundaries and are termed type b sequence boundaries type a sequence boundaries mark pronounced base level falls following times when the uinta lake had merged with a lake in an adjacent basin to form a much deeper lake such merging permitted the establishment of a new threshold at higher elevation following lake level balancing type b sequence boundaries are interpreted as marking base level falls from a barely merged lake or a lake that had an outflow over a 200 m stratigraphic thickness type a sequence boundaries are more common upsection indicating that with time a pluvial climate became more pronounced or that the adjacent lake was more easily filled type a sequence boundaries also become angular rather than parallel unconformities upsection suggesting increased tilting of the basin margin over time

quantifying the oldest tidal record the 3 2 ga moodies group barberton greenstone belt south africa the 3 2 ga moodies group in the barberton greenstone belt south africa contains the oldest preserved record of tides the tidal record is preserved in a tidal sand wave deposit in the lower moodies group as bundles of sandstone foresets separated by mudstone drapes detailed analysis of rhythmic foreset bundles permits quantification of the tidal record and reveals a hierarchy of diurnal fortnightly and monthly tidal periodicities thick thin pairs of foreset bundles reflect deposition from semidiurnal dominant and subordinate flood tidal currents respectively cyclic variations in foreset bundle thicknesses record longer period changes in strength of the dominant semidiurnal tidal currents consistent with neap spring neap tidal cyclicity alternating thicker and thinner neap spring neap cycles are comparable to anomalistic perigean apogean tidal signatures this quantitative record of tides in the middle archean moodies group represents by 2 2 b y the oldest such documentation tidal cyclicity recognized in the moodies sand wave deposit is comparable to that recorded in modern tidal settings and identified in the carboniferous rock record and is most compatible with a lunar orbital shape similar to that existing today

new constraints on methane fluxes and rates of anaerobic methane oxidation in a gulf of mexico brine pool via in situ mass spectrometry abstract deep sea biogeochemical cycles are in general poorly understood owing to the difficulties of making measurements in situ recovering samples with minimal perturbation and in many cases coping with high spatial and temporal heterogeneity in particular biogeochemical fluxes of volatiles such as methane remain largely unconstrained because of the difficulties with accurate quantification in situ and the patchiness of point sources such as seeps and brine pools to better constrain biogeochemical fluxes and cycling we have developed a deep sea in situ mass spectrometer isms to enable high resolution quantification of volatiles in situ here we report direct measurements of methane concentrations made in a gulf of mexico brine pool located at a depth of over 2300 m concentrations of up to 33 mm methane were observed within the brine pool whereas concentrations in the water directly above were three orders of magnitude lower these direct measurements enabled us to make the first accurate estimates of the diffusive flux from a brine pool calculated to be 1 1 0 2 mol m 2 yr 1 integrated rate measurements of aerobic methane oxidation in the water column overlying the brine pool were 320 mol m 2 yr 1 accounting at most for just 0 03 of the diffusive methane flux from the brine pool calculated rates of anaerobic methane oxidation were 600 1200 m yr 1 one to two orders of magnitude higher than previously published values of aom in anoxic fluids these findings suggest that brine pools are enormous point sources of methane in the deep sea and may in aggregate have a pronounced impact on the global marine methane cycle

tidal bedding and tidal cyclicities within the intertidal sediments of a microtidal estuary dyfi river estuary west wales u k abstract in the microtidal dyfi river estuary west wales the characteristic sedimentary structure within the intertidal sediments is tidal bedding this consists of sand mud couplets by means of thickness measurements and detailed observations the following conclusions can be drawn 1 the thicknesses of and structures in both mud layer and sand layer of each couplet vary systematically downward in the studied cores and trenching profiles variations are mainly due to differences in the current speed and tidal range between tides to difference of individual neap spring tides and to the possible effect of filtering of currents due to being in the intertidal zone 2 the patterns of sand mud couplet thickness variations reflect two main types of tidal cyclicities diurnal inequality and the neap spring neap tidal cycle which is in turn related to the lunar cycle 3 the mud layer of each couplet represents deposition from suspension at times of tidal slack no ebb slack water period during low tide in the intertidal zone thus no ebb mud deposition during low water whilst the sand layer is deposited by asymmetrical bidirectional tidal currents in either the ebb or flood half of a tidal cycle 4 the tidal regime derived from these variation patterns is characterized by a mixed predominantly semi diurnal form which is comparable with the present tidal regime 5 finally it can be concluded that tidal bedding patterns are the structural expressions of tidal cyclicity

stratigraphic and structural relationships between meso cenozoic lagonegro basin and coeval carbonate platforms in southern apennines italy abstract stratigraphic studies and facies analysis integrated with a new geological and structural survey of the meso cenozoic units outcropping in the campania lucania apennines southern italy allowed us to restore the palaeogeographic pattern and the tectonic evolution of the chain during oligo miocene times the southern apennines are a n150 striking and ne verging fold and thrust belt mainly derived from the deformation of the african apulian passive margin four wide belts with different features have been recognized in the chain area from east to west the following units outcrop a successions characterized by basinal to marginal facies ranging in age from cretaceous to miocene tectonically lying on plio pleistocene foredeep deposits b successions characterized by shallow water basinal and shelf margin facies ranging in age from middle triassic to miocene lagonegro units overthrust on the previous ones c triassic to miocene carbonate platform successions apenninic platform units overthrust on the lagonegro units d jurassic cretaceous to miocene deep water successions ophiolite bearing or internal units and associated siliciclastic wedges outcropping along the tyrrhenian belt and the calabria lucania boundary overthrust on the apenninic platform units all these units tectonically lie on the buried apulian platform which is covered at least in the eastern sector of the chain by pliocene to pleistocene foredeep deposits stratigraphic patterns of the cretaceous to lower miocene lagonegro successions are coherent with the platform margin ones calcareous clastics of the lagonegro basin are in fact supplied by an adjacent western platform as inferred by several sedimentological evidences slump and palaeocurrent directions and decreasing grain size towards the depocentre of the basin tectonic relationships among the different units of the chain with particular emphasis on the lagonegro and apenninic platform units of the lucanian segment are shown by means of both regional and detailed geological cross sections the lagonegro units constantly underlie the carbonate units originating from detachment and thrusting of the western platform and overlie the eastern i e apulian platform the lagonegro units show a strong lateral variability of map scale structures dome and basin folds are in fact largely observable in the lucanian apennine further the belt is widely affected by plio quaternary strike slip and extensional faults yet excluding the brittle deformation due to quaternary faulting the complexity of structural styles seems to result from the neogene refolding of more ancient structures produced by oligo miocene intraplate deformation this hypothesis is supported by two independent lines of evidence the first is the recognition of unconformities between the lower miocene numidian sandstone and the underlying lagonegro successions at least in the southwestern sectors the second is that the internal i e western platform remains undeformed until the early miocene both stratigraphic and structural data suggest an external position of the meso cenozoic lagonegro basin with regard to the coeval apenninic platform

basin evolution in the arc arc izu collision zone mio pliocene miura group central japan a comparative study of the present collision zone between the izu bonin ridge island arc with mainland japan honshu arc and the mio pliocene of onshore se japan suggests that arc arc collision processes and the resulting stratigraphic successions may be repetitious and predictable arc arc collision has led to the incremental accretion of segments of delaminated izu bonin arc crust onto the honshu arc associated with the sequential southward migration in jumps of the plate boundary and trench prior to accretion of a segment of izu bonin arc crust the leading edge underwent uplift to generate an approximately trench parallel topographic high the zenisu ridge being the present example with the hayama mineoka uplift zone as a mio pliocene example the ridge separated a northern trench or trough from a southern intra oceanic arc basin during collision accretion the trench received both honshu arc derived terrigenous and izu bonin arc derived volcaniclastic sediments whereas the arc basin tended to receive only arc deposits during the final stages of accretion the arc basin began to receive ever increasing volumes of terrigenous honshu arc derived detritus fed through basement controlled canyons the accretionary process was accompanied by intense deformation and the residual deep marine basin was then infilled above an angular unconformity

architectural complexity of a carbonate transgressive systems tract induced by basement physiography three dimensional exposure of the plio pleistocene calcarenite di gravina formation around matera horst italy permits analysis of the architecture and internal complexities of carbonate sedimentary bodies around a palaeoisland spatial organization of the different lithosomes along with their skeletal composition sedimentary structures and bedding patterns helps decipher the key factors that controlled platform architecture and distribution of heterogeneities basement physiography type and loci of carbonate production bottom currents and changes in accommodation relative sea level changes resulted from high frequency glacioeustatic cycles that punctuated an overall tectonically induced transgression topographic relief fragmentation of the limestone basement and wave energy controlled lithoclastic supply basement physiography and relative sea level changes determined the area available for carbonate producing biotas and thus the amount and type of skeletal sediments on the moderately dipping south western margin waves and associated currents re distributed the lithoclasts derived from coastal abrasion bioclasts mostly derived from epiphytic seaweed production in the shoreface infralittoral prisms resulted from downdip transport progradation and longshore transport which controlled along strike continuity of the prisms where basement continuity was interrupted at the margin of the palaeoisland a lithoclastic fan was deposited from dumping sediments carried by shore parallel currents fan shaped skeletal bodies coalesced to form an apron on the steeper northern side of the palaeoisland when a structural platform was flooded and epiphytic carbonates were shed red algae contribution depended on the available oligophotic area which in turn was controlled by high frequency sea level cycles basement physiography and apron aggradation the internal architecture of this apron resembles a low stand wedge but it accumulated during transgression deeper water contour parallel currents formed a lithosome at the foot of the structural relief interpreted as drift deposits it is composed of shallow water benthonic skeletal components planktonic foraminifera and some limeclasts

tidal rhythmites in a deep sea environment an example from mio pliocene misaki formation miura peninsula japan abstract the mio pliocene misaki formation miura peninsula japan is characterized by alternation of mafic scoriaceous pebbly sandstone pumiceous sandstone and siltstone and mudstone formed in a fore arc basin in an arc arc collisional zone the qualitative as well as quantitative evidences of tide during the misaki sedimentation in the jogashima area miura peninsula are presented here the lunar synodic period of 28 days lunar month extracted from the misaki tidal rhythmite agrees well with the published miocene tidal rhythmite data the couplet series of the misaki tidal rhythmite however is often interrupted by downslope resedimentation via turbidity currents intense penecontemporaneous deformation and bioturbation association of deep sea turbidites mass flow deposits and tidal rhythmite suggest misaki sedimentation in the miura peninsula took place in a submarine canyon setting

disobedient sediments can feedback on their transportation deposition and geomorphology abstract most sediments are obedient to the winds waves and currents which direct their transportation and deposition it has long been recognized however that the grain size and or grain kind of sediments can feedback on the processes of their own transportation deposition and geomorphology as well as that of succeeding deposits this note is to review three examples of marine sediments in which a single grain size or grain kind produces multiple feedbacks tidal bars of holocene ooid sands on great bahama bank are an example of multiple feedbacks of one grain kind on tidal currents wave action and accumulations these feedbacks are responsible for the distinctive pattern of elongated bars and channels which in turn amplify tidal currents the near constant movement of grains on the shallow bars and in the channels is where pellet nuclei are coated to form ooids thus the development and growth of bars feeds back to produce more ooids regional encrinites which consist predominantly of the disarticulated highly porous skeletons of crinoids are common from ordovician to jurassic during blooms of these filter feeders the resulting grains which are equivalent to quartz grains a tenth of their size can be entrained by currents as low as a knot ca 0 5 m s the resulting mobile substrate deters other invertebrates taphonomic feedback and results in the prevalence of layering produced by traction transport of low velocity the belt of mud extending for some 1600 km between the amazon and orinocco rivers is a special example of the feedback of mud on depositional processes sedimentary structures and geomorphology of the accumulations the clay rich mud from the amazon produces fluid mud which dampens and transforms wave action from the open sea to promote its own accumulation in giant bars in the inner shelf and shoreline with a variety of familiar laminations the result is a wedge of mud rich deposits some 24 m thick and 30 km wide capped with cheniers of sand which has prograded seaward in some 6000 years

geological constraints on the precambrian history of earth s rotation and the moon s orbit over the past decade the analysis of sedimentary cyclic rhythmites of tidal origin i e stacked thin beds or laminae usually of sandstone siltstone and mudstone that display periodic variations in thickness reflecting a strong tidal influence on sedimentation has provided information on earth s paleorotation and the evolving lunar orbit for precambrian time before 540 ma depositional environments of tidal rhythmites range from estuarine to tidal delta with a wave protected distal ebb tidal delta setting being particularly favorable for the deposition and preservation of long detailed rhythmite records the potential sediment load of nearshore tidal currents and the effectiveness of the tide as an agent of sediment entrainment and deposition are related directly to tidal range or maximum tidal height and consequent current speed hence the thickness of successive laminae deposited by tidal currents can be a proxy tidal record with paleotidal and paleorotational values being determined by analysis of measured records of lamina and cycle thickness the validity of the findings can be investigated by testing the primary observed values for internal self consistency through application of the laws of celestial mechanics paleotidal and paleorotational values provided by late neoproterozoic 620 ma tidal rhythmites in south australia are validated by these tests and indicate 13 1 0 1 synodic lunar months yr 400 7 solar days yr a length of day of 21 9 0 4 h and a relative earth moon distance a a0 of 0 965 0 005 the mean rate of lunar recession since that time is 2 17 0 31 cm yr which is little more than half the present rate of lunar recession of 3 82 0 07 cm yr obtained by lunar laser ranging the late neoproterozoic data militate against significant overall change in earth s moment of inertia and radius at least since 620 ma cyclicity displayed by paleoproterozoic 2450 ma banded iron formation in western australia may record tidal influences on the discharge and or dispersal of submarine hydrothermal plumes and suggests 14 5 0 5 synodic months yr and a a0 0 906 0 029 the combined rhythmite data give a mean rate of lunar recession of 1 24 0 71 cm yr during most of the proterozoic 2450 620 ma suggesting that a close approach of the moon did not occur during earlier time concentrated study of precambrian tidal rhythmites promises to illuminate the evolving dynamics of the early earth moon system and may permit the lunar orbit to be traced back to near the time of the moon s origin

scales of spatial variability for surface ocean pco2 in the gulf of alaska and bering sea toward a sampling strategy twenty four near exact repeat tracks over a 48 month period of ocean surface pco2 data from the north pacific offer an uprecedented opportunity to examine the space scales of pco2 in this region because previous basin scale studies of air sea carbon flux have shown that the field of pco2 air sea disequilibrium largely controls the field of flux and atmospheric pco2 is relatively constant knowing how to sample pco2 in seawater is a crucial element of the design of a basin scale carbon flux observing system unbiased within 3 atm along track means for pco2 can be obtained from measurements made every 40 km hourly for a ship traveling 20 knots we find distinctly different characteristics of spatial variability in two open ocean regions the bering sea and the gulf of alaska the first zero crossing of the mean spatial autocorrelation function is 1 5 longitude in the bering sea and 3 5 in the gulf of alaska when the cruise data are linearly detrended to remove the larger scale field there is a strong seasonal variation in the zero crossing with shorter scales in the summer in near shore waters there is extreme variability often with very small space scales and very large cruise to cruise differences neither the mean nor variability statistics from a single ship cruise data set appear likely to produce reliable information for designing an observing system

deep marine tidal bottom currents and their reworked sands in modern and ancient submarine canyons abstract submarine canyons provide a unique setting for tidal processes to operate from shallow marine to deep marine environments in modern canyons current meter measurements at varying water depths 46 4200 m show a close correlation between the timing of up and down canyon currents and the timing of semi diurnal tides these tidal bottom currents in submarine canyons commonly attain maximum velocities of 25 50 cm s based on core and outcrop studies of modern and ancient deep marine deposits it is proposed here that sand mud rhythmites double mud layers climbing ripples mud draped ripples alternation of parallel and cross laminae sigmoidal cross bedding with mud drapes internal erosional surfaces lenticular bedding and flaser bedding can be used to interpret deposits of deep marine tidal currents this approach is an alternative to the conventional approach in which most deep water traction structures e g climbing ripples and cross bedding would be attributed to deposition from turbidity currents underwater photographs show active mass flows i e slides slumps grain flows and debris flows in modern canyons box cores taken from modern submarine canyons e g la jolla california and conventional cores and outcrops of ancient canyon fill facies oua iboe pliocene nigeria and the annot sandstone eocene oligocene se france contain deposits of both tidal processes and mass flows this facies association in the rock record can be used as a criterion for recognizing submarine canyon settings in a channel mouth environment deep marine tidal deposits are likely to develop elongate bars that are aligned parallel to the channel axis within the channel whereas turbidites are more likely to develop depositional lobes that are aligned perpendicular to channel axis turbidite depositional lobes are much larger than the channel width whereas tidal sand bars are much smaller than the channel width therefore the wrong use of a turbidite lobe model with sheet geometry in lieu of a tidal bar model with bar geometry will result in an unrealistic overestimation of sandstone reservoirs in deep water exploration

modeling of cyclic tidal rhythmites based on a range of diurnal to semidiurnal tidal station data abstract where individual tides deposit appreciable accumulations of sediment cyclic tidal rhythmites can form that exhibit semimonthly tidal cyclicities a number of modern analogs and ancient counterparts indicate the importance of such features for paleoenvironmental analyses in this study predicted high low tidal station data are used to simulate current speeds which in turn are used to simulate sedimentation of tidal rhythmites this modeling has been done to depict the patterns encoded in cyclic tidal rhythmites in order to delineate the spectrum of different tidal regimes the simulations are based upon a series of macrotidal diurnal to semidiurnal tidal systems depending upon thresholds of relative tidal current speed only portions of semimonthly tidal cycles will be preserved within cyclic tidal rhythmites

lithofacies stable isotopic composition and stratigraphic evolution of microbial and associated carbonates green river formation eocene piceance basin colorado lacustrine carbonates of the eocene green river formation crop out on the western margin of the piceance basin and the eastern margin of the uinta basin in western colorado this area allows tracing of vertical and horizontal facies variation over hundreds of meters limestone beds consist of littoral to sublittoral lithofacies bioclastic and oolitic grainstones oolitic wackestone intraclastic rudstone stromatolites and thrombolites facies form upward deepening cycles that start with sharp based grainstones and packstones followed by stromatolites or thrombolites and capped by fine grained stromatolites and or oil shale deposits the vertical succession of carbonate deposits correlates with evolutionary lake stages the succession starts with grainstone deposits rich in ostracods and gastropods that correspond to an initial freshwater lake thrombolites capped by laminated stromatolites or coarse agglutinated stromatolites correlate with a higher salinity transitional lake deepening upward cycles as much as 5 m 16 ft thick of thrombolites agglutinated stromatolites and fine grained stromatolites occur in the highly fluctuating lake the upper section is dominated by laminated stromatolites that correspond to a rising lake stable isotope 18o and 13c values covary and range from 8 to 0 8 and 3 to 5 respectively the 18o values indicate carbonate precipitating water evolved from fresh to saline and became less saline in the upper green river negative excursions of 13c values correspond to lake level rises and positive excursions of 13c values occur during lake level falls syndepositional to burial diagenesis modified carbonate porosity early dissolution is followed by burial compaction and fracturing compaction and late calcite cements occluded primary and secondary porosity

sedimentary processes in the great lakes sediments in the great lakes are subject to four general categories of processes input transport deposition and postdepositional alteration sedimentary input is from coastal erosion 64 riverine input 26 atmospheric transport 3 and several lesser sources 7 once in the lake sediments are transported to their place of deposition along the bottom and or in suspension depending upon grain size and density the rate of deposition in the great lakes is variable and ranges from zero in some areas to over 6000 g m sup 2 yr sup 1 in the eastern basin of lake erie after deposition sediments undergo bioturbation dissolution of carbonate and opal remobilization of many metals followed by reprecipitation within the surficial oxidized layer and degradation of organic compounds

sedimentology of the paleoproterozoic kungarra formation turee creek group western australia a conformable record of the transition from early to modern earth abstract this paper presents the first detailed sedimentological analysis of the paleoproterozoic kungarra formation the lowermost of three formations comprising the turee creek group in western australia which was deposited across the rise in atmospheric oxygen the great oxidation event or goe and the transition from early to modern earth the data show that the kungarra formation has a gradational conformable lower contact with underlying banded iron formation of the hamersley group and predominantly comprises an upward shallowing succession from deepwater shales and siltstones through rippled fine grained sandstones and stromatolitic carbonates to tidal flat deposits that immediately underlie coastal fluvial deposits of the overlying koolbye formation at the base of the kungarra formation is a gradual transition from alternating units of magnetic green shale and thin units of banded iron formation that pass upsection to units of non magnetic shale and ferruginous chert and grey chert reflecting a gradual loss of iron from the world s oceans accompanying the rise of atmospheric oxygen a falling stage systems tract is recognised above this transition in the hardey syncline area capped by stromatolitic carbonates and a period of exposure marked by an erosional unconformity and carbonate beachrock two glacio eustatic cycles are recognised within the middle to upper parts of the kungarra formation each of which is marked by the rapid onset of falling systems tracts and characterised by falling systems tracts during and following diamictite deposition stratigraphic data are used to infer a depobasin filled by a sediment wedge prograding from southeast to northwest in contrast to previous models of a north northeastward deepening foreland basin the lack of seismites or internal unconformities within the formation precludes a foredeep setting rather deposition is interpreted as having occurred within an intracratonic basin with detritus sourced from erosion of uplifted bedrock to the southeast

growth processes and melange formation in the southern apennines accretionary wedge abstract the southern apennines owe their present geometry to the subduction of an apulian continental lithospheric slab and are thus best interpreted as an accretionary wedge southward the apenninic thrust front branches on to the still active ionian wedge which is related to the present calabro sicilian subduction the interpretation of conventional seismic reflection profiles and exploration wells combined with geologic field studies biostratigraphy and structural geology provide constraints for a geodynamic model for the post messinian growth of the apenninic prism our model for the apennines is a good analogy for submerged oceanic accretionary prisms in both instances features such as out of sequence thrusts underplating and duplexes are viewed as processes to explain the thickening of accretionary wedges syntectonic terrigenous deposits have accumulated in the synclines developed above the flats of pliocene thrust faults these depocenters represent piggy back basins younger accretion at the eastern border of the accretionary wedge has led to a progressive uplifting and tilting of the already emplaced thrust sheets including a continous westward migration of the depocenters in the piggy back basins during pliocene and early quaternary times a contrary west to east migration of the depocenters locally occurred where preexisting flats of pliocene thrust faults have been refolded rather than only being rotated dewatering processes and effects of overpressures on undercompacted sediment deformations can also be studied in the southern apennines melanges and broken formations form an important component of the trench apparently restricted to the base of tectonic nappes listric normal faults are a major structural element which preserves in combination with the erosion of topographic highs and resedimentation in the piggy back basins a uniform geometric shape critical taper for the prism the age and location of these distensive or gravitational effects are also discussed

soft sediment deformation produced by tides in a meizoseismic area turnagain arm alaska turnagain arm is a semidiurnal hypertidal estuary in southeastern alaska with a recorded tidal range of 9 m contorted bedding and flow rolls preserved in tidal sediments within the estuary have previously been interpreted as resulting from the mw 9 2 great alaskan earthquake of 1964 horizons of flow rolls between undeformed beds in sediments and rock strata have been used to infer ancient earthquakes in other areas although many types of soft sediment deformation structures can be formed by earthquakes observations of sedimentation on tidal flats in the inner parts of turnagain arm in the summers of 2003 and 2004 show that a wide range of soft sediment deformation structures similar to those inferred to have been formed by earthquakes can form in macrotidal estuaries in the absence of seismic shock during sedimentation rate measurements in 2004 soft sediment deformation structures were recorded that formed during one day s tide either in response to overpressurization of tidal flats during rapid tidal drawdown or by shear stress exerted on the bed by the passage of a 1 8 m tidal bore structures consisted of flow rolls dish structures flames and small dewatering pipes in a bed 17 cm thick in the future if the flow rolls in turnagain arm were found in isolated outcrops across an area 11 km in length in an estuary known to have been influenced by large magnitude earthquakes would they be interpreted as seismites these examples show that caution is needed when using horizons of flow rolls to infer paleoseismicity in estuarine deposits because many of the mechanisms tidal flux tidal bores slumping flooding that can cause deformation in rapidly deposited unconsolidated silts and sands are orders of magnitude more common than great earthquakes

collision of the izu arc with honshu and the effects of oblique subduction in the miura boso peninsulas abstract collision of the izu arc in central japan is discussed with a focus on its tectonic effects to the east of the arc in the miura boso peninsulas of honshu the tectonics are the combination of the following events philippine sea plate spreading in the late oligocene to early miocene opening of the sea of japan in the middle miocene obduction of ophiolitic rocks in the northeasternmost corner of the philippine sea plate and forearc sedimentation between the honshu and izu arcs oblique subduction has shifted the plate boundary from northeast to southwest from the present mineoka tectonic belt through the miura fold belt to the sagami trough since the miocene remarkable right lateral transpressional deformation occurred throughout this period of the oblique collision and subduction

synorogenic evolution of large scale drainage patterns isotope paleohydrology of sequential laramide basins in the past decade we and others have compiled an extensive dataset of o c and sr isotope stratigraphies from sedimentary basins throughout the paleogene north american cordillera in this study we present new results from the piceance creek basin of northwest colorado which record the evolving hydrology of the eocene green river lake system we then place the new data in the context of the broader cordilleran dataset and summarize implications for understanding the synorogenic evolution of large scale drainage patterns the combined data reflect 1 a period of throughgoing foreland rivers heading in the sevier fold and thrust belt and flowing east 2 ponding of freshwater lakes in the foredeep as laramide uplifts blocked drainage 3 hydrologic closure that led to both intensive evaporation in the terminal sink of the piceance creek basin and integration of catchments over length scales 1000 km 4 infilling of basin accommodation by southward migrating magmatism in distal catchments leading to the freshening and demise of intraforeland lakes that also stepped south over time

structural evolution of the lucanian apennines southern italy abstract in this paper we present a study of an entire segment of the southern apennines of italy extending from the pollino mountain range to the south to the agri valley to the north in which all the units of the chain are represented combining regional information with detailed structural data obtained from the different tectonic units forming the orogenic belt the structure as well as the tectonic evolution of this portion of the orogenic belt are proposed the overall architecture of this segment of the southern apennines mountain chain represents the result of a complete orogenic cycle in which oceanic subduction syn collisional and post collisional events are well recorded structurally this segment of the orogenic belt exhibits two distinct structural levels separated by a major detachment surface the sole thrust of the accretionary wedge that occur at the surface in the allochthonous nappes and at depth in the adria continental margin the upper level is characterized by an imbricated fan system affecting the allochthonous terranes emplaced during oceanic subduction and the first stages of continent continent collision the lower level is represented by a duplex geometry that has developed in the post collisional stage during evolution of the foreland migrating thrust system involving the carbonate platform basin system of the adria block during the last stages of the mountain building process when the foreland thrust migration was locked by the thickening of the colliding continental crusts the southern apennines were thus affected by a severe strike slip tectonics that dissects the entire mountain belt deeply modifying the previous thrust geometry

soft sediment deformation structures in the mio pliocene misaki formation within alternating deep sea clays and volcanic ashes miura peninsula japan abstract the mio pliocene misaki formation of the miura group miura peninsula japan shows an extremely wide variety of soft sediment deformation structures the most common deformation structures are load casts and associated flame structures dish and pillar structures synsedimentary faults multilobated convolutions chaotic deformation structures sedimentary veins and dykes and large scale slides and slump scars the formation which accumulated in a deep sea environment 2000 3000 m is well exposed in and around jogashima it consists of relative thin commonly dm scale alternations of deep marine fine grained sediments and volcanic ejecta that are as a rule coarse grained since the formation represents fore arc deposits of the izu bonin and the honsu arc collision zone it might be expected that tectonic activity also played a role as a trigger of the soft sediment deformation structures that abound in these sediments this is indicated indeed by the abundance of soft sediment deformations over large lateral distances that occur in numerous beds that are sandwiched between undeformed beds on the basis of their characteristics and the geological context these layers can be explained satisfactorily only by assuming deformation triggered by seismicity which must be related to the izu bonin and honsu arc collision the layers thus form deep marine seismites

tidal rhythmites in offshore shale a case study from the palaeoproterozoic chaibasa shale eastern india and implications abstract tidal rhythmites have been documented from modern continental shelves and distal offshore settings in significant contrast to their modern counterparts sedimentological studies of ancient tidal rhythmites formed in distal offshore settings and quantification of tidal rhythms encoded therein are however scarce this paper presents sedimentological analysis of vertically accreted tidal rhythmites from the palaeoproterozoic chaibasa shale facies in india and quantification of their tidal rhythms the facies characteristics of the chaibasa shale coupled with harmonic analysis of the laminae thicknesses of the sandstone inter layers corroborate a distal shelf palaeogeography for the generation of the vertically accreted tidal rhythmites the latter are the distal counterparts of laterally accreted tidal bundle deposits well preserved within the shallow marine chaibasa sandstones the number of lunar days in a synodic month 23 estimated from the chaibasa shale facies is however considerably lower than that estimated from the chaibasa sandstone facies 32 suggesting that the tidal record encoded from the chaibasa shale facies is incomplete

cross stratified calcarenites from new zealand subaqueous dunes in a cool water oligo miocene seaway cross bedded cool water bioclastic limestones of the te kuiti group on the north island of new zealand are composed primarily of bryozoans echinoderms and benthic foraminifers their prominent large scale unidirectional cross stratification is interpreted as produced by migrating subaqueous dunes on the floor of a 50 100 km wide north east trending seaway in water depths of 40 60 m these dunes are thought to have developed in response to strong seaway parallel tidal currents combined with a north east directed set up or oceanic current cross stratification is organized into four hierarchical levels 1 cross lamination 2 first order sets 3 second order sets and 4 cross stratified successions the levels are based on increasing degrees of internal complexity distinct attributes such as internal organization cross set thickness foreset shape and lower bounding surface shape are used to describe and interpret the cross stratification all these attributes are here integrated in a new and expanded classification of unidirectional cross stratification that emphasizes flow and bedform dynamics rather than overall set shape individual cross stratified successions are interpreted to have formed by dunes with varying sinuosity superposition and flow history under conditions of different current strength but constant sediment production horizontally bedded successions are the result of robust active dune fields that grew during times of vigorous sediment transport formset successions were produced from large compound dunes and are the expression of languid and decaying dune fields that developed during times of decreasing sediment transport these decaying dunes were gradually smothered by continuously and locally produced bioclastic sediment formset cross stratified successions are most likely to develop in carbonates where the sediment is produced in place than in terrigenous clastics where the sediment is imported

implication for the two stage layer parallel faults in the context of the izu forearc collision zone examples from the miura accretionary prism central japan abstract the southern tip of the miura peninsula central japan exposes nice outcrops of forearc sediment accreted to another forearc which occurred during a series of izu arc collision with the honshu arc neogene deep marine volcaniclastic sedimentary sequences the misaki formation show many types of faulting and folding associated with layer parallel faults besides many imbricate thrusts of the main deformation stage the layer parallel faults are divided into two stages one is related to northwestward gravity driven slump deposits the other is southeastward thrust faulting and the both are associated with many layer duplications with liquefaction of sediments the slumping is commonly developed in the upper part of the sequence in the surface of the down going slab before accretion whereas the thrusting is dominant in the lower part within the toe of the accretionary prism probably along the decollement zones in the prism thus the misaki formation represents a good example of deformation just before and after shallow forearc accretion in the arc collision zone

sedimentological consequences of arc arc collision an example from mio pliocene miura group japan abstract this paper presents brief sedimentological inventory of the misaki and the overlying hasse formation constituting the miura group based on observations made at jogashima island miura peninsula and infers the nature of the stratigraphic transition from tectonic viewpoint the lower part of the misaki formation is made of very coarse to coarse grained scoriaceous normally graded sandstones fine grained sandstones siltstones and mudstones and indicates a deep sea submarine canyon depositional setting there is no evidence of storm reworking shallow marine processes in the lower parts of the misaki formation at least in the jogashima island as suggested by stow et al 1998 however the upper part of the misaki succession formed in a shallow marine depositional setting the overlying hasse formation characterized by brownish coloured very coarse to coarse grained large scale trough cross stratified very poorly sorted sandstones very poorly sorted polymictic and matrix dominated mass flow conglomerates with siltstone fine grained sandstone clasts derived from the underlying misaki formation and occasional reverse grading in significant contrast to the underlying misaki formation the hasse formation lacks very fine grained sandstone siltstone mudstone facies unlike the tholeiitic basalt composition of the lapilli and pebbles of the misaki sandstone beds the scoriaceous lapilli and pumiceous beds of the hasse formation are of calc alkaline composition the hasse sedimentation probably took place in much shallower paleogeography compared to the underlying misaki formation most probably in an alluvial fan braided fluvial setting the misaki hasse stratigraphic contact is very sharp and erosional and represents a subaerial unconformity i e depositional sequence boundary our sedimentological data from the jogashima island clearly indicate progressive shallowing of the depositional setting during the terminal phase of the misaki sedimentation and much abrupt shallowing across the misaki hasse transition possibly as a consequence of ongoing collision between the izu bonin and honshu arcs

implications of lunar orbital periodicity from the chaibasa tidal rhythmite india of late paleoproterozoic age harmonic analysis of the sandstone foreset laminae thickness series from the chaibasa tidal rhythmite india clearly shows that a normal semidiurnal tidal system with synodic month of 32 lunar days was in effect during the late paleoproterozoic 2100 1600 ma the minimum number of solar days in a lunar sidereal month was 31 published quantitative tidal rhythmite data of others in combination with data derived from the chaibasa tidal rhythmite indicate long term stability of the lunar orbit and progressive increase in the earth moon distance during the proterozoic

structural styles in the frontal zones of the southern apennines italy an example from the molise district structural interpretation of available geological and geophysical data from the molise area southern italy demonstrates that the frontal zones of this sector of the apennines are characterized by a threefold zoneography defined by distinct structural styles resolved geometry of both pellicular and deep seated structures and their relationships constrain possible reconstructions for the undeformed pre miocene southeastern margin of the afro adriatic continent and its neogene deformation history identification of peculiar structural associations in the foreland foredeep complex and reinterpretation of relevant stratigraphic data suggest that deformation in this sector of the apennines has already reached the most external apulian domains and is possibly migrating at present toward the currently active adriatic foredeep of the molisan thrust system

late pleistocene silty tidal rhythmites in the macrotidal flat between youngjong and yongyou islands west coast of korea abstract late pleistocene silty tidal rhythmites developed in the macrotidal flat between youngjong and yongyou islands demonstrate hierarchical tidal cycles ranging from daily to monthly variations associated with synodic tropical and anomalistic cycles on the basis of rhythmicities and textural composition the rhythmites were likely deposited in an upper intertidal flat under a mixed dominantly semi diurnal tidal regime the rhythmites showing gradational contact with overlying cryoturbated silty facies indicating subaerial exposure and subsequent weathering during the last glacial maximum represent the tidal environment during the last highstand or ensuing regression phase of sea level in the late pleistocene

the record of tidal cycles in mixed silici bioclastic deposits examples from small plio pleistocene peripheral basins of the microtidal central mediterranean sea the pliocene pleistocene peripheral marine basins of the mediterranean sea in southern italy from basilicata and western calabria to northern and eastern sicily represent tectonically formed coastal embayments and narrow straits here units of cross stratified mixed silici bioclastic sand 25 to 80 m thick record strong tidal currents the central mediterranean sea has had a microtidal range of ca 35 cm and the local amplification of the tidal wave is attributed to tides enhanced in some of the bays and to the out of phase reversal of the tidal prism in narrow straits linking the tyrrhenian and ionian basins the siliciclastic sediment was generated by local bedrock erosion whereas the bioclastic sediment was derived from the contemporaneous foramol type cool water carbonate factories the cross strata sets represent small to medium sized 10 to 60 cm thick two dimensional dunes with mainly unidirectional foreset dip directions these tidalites differ from the classical tidal rhythmites deposited in mud bearing siliciclastic environments firstly the foreset strata lack mud drapes and instead show segregation of siliciclastic and bioclastic sand into alternating strata secondly the thickness variation of the successive silici bioclastic strata couplets measured over accretion intervals of 2 to 3 m and analysed statistically reveal only the shortest term diurnal and semi diurnal tidal cycles thirdly the record of diurnal and semi diurnal tidal cycles is included within the pattern of neap spring cycles differences between these sediments and classical tidal rhythmites are attributed to the specific palaeogeographic setting of a microtidal sea with the tidal currents locally enhanced in peripheral basins it is suggested that this particular facies of mud free silici bioclastic arenite rhythmites in the stratigraphic record might indicate a specific type of depositional sub tidal environment of straits and embayments and the shortest term tidal cycles

small scale heterogeneity of dissolved gas concentrations in marine continental shelf waters 1 marine continental shelf waters are known to contribute significantly to the global air sea fluxes of many gases biogeochemical cycles in these regions are highly dynamic and it is thus often difficult to fully resolve the spatial and temporal distribution of gases in the upper water column high frequency real time gas measurements with a membrane inlet mass spectrometer mims reveal significant small scale heterogeneity in the distribution of co2 o2 ar ratios and dimethylsulfide dms in continental shelf waters of the eastern subarctic pacific ocean and bering sea decorrelation length scales for the gas distributions ranged from 15 to 25 km with significant variability observed on subkilometer spatial scales in the case of dms a number of rapid excursions were observed over distances that would be difficult to resolve with conventional methods across most of the sampling transects co2 and o2 ar ratios were correlated suggesting that biological processes dominated the cycling of these gases in contrast dms concentrations were generally uncoupled from co2 and o2 ar although concentrations often did change sharply across hydrographic and productivity fronts the results presented here suggest that previous field studies may have underestimated the true spatial variability of dissolved gases dms in particular in surface waters of highly dynamic marine systems high frequency gas measurements have significant promise for unraveling complex biogeochemical cycles in these regions

characteristics and variability of the inner front of the southeastern bering sea the inner front of the southeastern bering sea shows marked spatial variability in frontal characteristics created by regional differences in forcing mechanisms differences in forcing mechanisms sea ice advance retreat and storm strength and timing and early spring water properties result in strong interannual variability in biological chemical and physical features near the front we have developed a simple model based on surface heat flux and water column mixing to explain the existence of cold belts cont shelf res 19 14 1999 1833 associated with such fronts hydrography fluorescence and nutrient observations show that pumping of nutrients into the euphotic zone occurs and this can prolong primary production at the inner front the effectiveness of this process depends on two factors the existence of a reservoir of nutrients in the lower layer on the middle shelf and the occurrence of sufficient wind and tidal energy to mix the water column

calcarenite and sapropel deposition in the mediterranean pliocene shallow and deep water record of astronomically driven climatic events introductionsapropelformationinthemediterra nean basin during the pliocene andquaternary has been widely debated the time and phase relationship ofsapropels to astronomic cycles hasbeen established and a high reso lution sapropel based astronomictime scale has been reconstructedfor mediterranean neogene deposits e g hilgen 1991 lourens etal 1996 hilgenetal 1999 sapropels provide a deep water basin wide record of astronomicallydriven climatic events they occur asindividualcyclesthatcanbecorrelatedtoprecessionalminima 19 23kyr orassmall andlarge scaleclusters 100 400kyr withmoredevelopedindivid ualsapropels correspondingtoeccen tricity maxima obliquity 41kyr controls the thin thick pattern ofcyclicity e g lourens etal 1996 pliocene large scale sapropel clustersfollowmajorcoolingeventsreferredtoas the forerunners of the quaternarynorthern hemisphere glaciation keigwin 1987 raymo etal 1989 tiedemann etal 1994 rio et al 1997 these events dated at 3 1 2 7and 2 1ma are recorded in themediterranean basins by importantmicro and macrofaunal turnovers monegattiandra 2001 palaeoceanographic events relatedto sapropel formation have usuallybeen studied from a deep water per spective theirshallow waterrecordisless well known the stratigraphicarchitectureofplioceneshallow waterdepositsoftheapennine maghrebianbasins is frequently characterized bythe rhythmic alternation of coarse grained calcarenites and siliciclasticmudstones our observations suggestthat calcarenites are not randomlydistributed in the stratigraphic col umn but they occur in well de nedtimeslicesstartingfrom3 1ma theycanbetracedthroughdi erentgeody namicsettings suggestinganin uenceof climatic and or eustatic forcing individual calcarenites occur in clus tershavingthesameageaslong termsapropelclusters thiscorrelationsug gests that tightly linked factors con trolledtheformationofbothdeposits this paper documents the large scale 10

reliability of lunar orbital periods extracted from ancient cyclic tidal rhythmites abstract ancient tidal periods extracted from the geologic record are useful to constrain and calibrate theoretical models of the evolution of the earth moon system analysis of rocks that contain such tidal periodicities termed cyclic rhythmites have tended to concentrate on long series and have focused on the more obvious periods for example neap spring periods have been the most widely discussed such information can be reliably extracted from bedform thickness series measured within laterally accreted tidal bundles and vertically accreted tidal laminae other lunar orbital data is also encoded in cyclic rhythmites however this additional information has been much less extensively applied to earth moon models herein short segments of well formed cyclic rhythmites are examined to determine how reliably the various tidal periods can be extracted via harmonic analysis rhythmite series analyzed here exhibit well formed neap spring tidal periods and also exhibit a prominent fortnightly inequality or a variation in the height of successive spring tides this inequality is related to the elliptical nature of the lunar orbit anomalistic month and it is demonstrated that this period can also be reliably extracted from cyclic rhythmites tropical periods which reflect the changing lunar declination that occurs during a tropical month have also been reported from cyclic rhythmites unlike synodic and anomalistic periods the apparent tropical periods extracted from some cyclic rhythmites do not always accurately correspond to the expected values in only a few cases can this period be reliably extracted from short segments of cyclic tidal rhythmite data this period is commonly only poorly encoded in rhythmites because 1 it tends to be masked by higher amplitude synodic periods and 2 it is not well expressed within predominantly semidiurnal tidal systems samples selected from the proterozoic and phanerozoic tend to be more common during specific intervals of geologic time these intervals were characterized by glacio eustatic flux and in some cases by unique continental configurations understanding these basic controls on rhythmite occurrences should aid in the discovery of additional examples

fine grained sediment transport and sorting by tidal exchange in xiangshan bay zhejiang china abstract during the winter of 1983 25 h measurements of current speed flow direction water depth and suspended sediment concentration were carried out at six stations located in the inlet section of xiangshan bay during spring and neap tides an analysis of the data obtained shows that tidal exchange in the form of either vertical residual circulation or bay mouth water mixing is responsible for the observed net landward movement of suspended sediment though the ebb currents are stronger than the flood currents in the inlet the analysis suggests also that the tidal exchange processes in combination with the settling behaviour of the suspended sediments and the morphological features of the inlet section lead to marked sorting of the fine grained sediments with the clayey material predominating in the inner part of the bay and the silty material in the outer part

recent and active tectonics in the calabrian arc southern italy normal faulting which has developed since the middle pleistocene with an overall ese wnw extension is the dominant mode of deformation which has characterized the calabrian arc up to the present quaternary normal faults extend for a total length of about 180 km along the inner side of the arc the different normal fault segments which during the pleistocene controlled the evolution of the main marine sedimentary basins are varying in length from 10 to 20 km and have fault escarpments showing a very young morphology which define the fronts of the major mountain ranges of the arc the morphological features of the fault escarpments suggest slip rates of 0 8 1 1 mm yr for the last 700 k y and values of 0 6 0 9 mm yr for the last 120 k y indicating a uniform rate of faulting since the middle pleistocene crustal seismicity and the mesoseismic areas of historical large events 6 5 m 7 1 which occurred in the calabrian arc are located within a narrow belt along the hanging walls of the quaternary normal fault segments this suggests that the normal faults which dissect the inner side of the calabrian arc may be seismically active

eocene atmospheric co2 from the nahcolite proxy estimates of the atmospheric concentration of co 2 co 2 atm for the hothouse climate of the early eocene climatic optimum eeco vary for different proxies extensive beds of the mineral nahcolite nahco 3 in evaporite deposits of the green river formation piceance creek basin colorado usa previously established co 2 atm for the eeco to be 1125 ppm by volume ppm here we present experimental data that revise the sodium carbonate mineral equilibria as a function of co 2 and temperature co precipitation of nahcolite and halite nacl now establishes a well constrained lower co 2 atm limit of 680 ppm for the eeco paleotemperature estimates from leaf fossils and fluid inclusions in halite suggest an upper limit for co 2 atm in the eeco from the nahcolite proxy of 1260 ppm these data support a causal connection between elevated co 2 atm and early eocene global warmth but at significantly lower co 2 atm than previously thought which suggests that ancient climates on earth may have been more sensitive to a doubling of co 2 atm than is currently assumed

pliocene pleistocene sequences bounded by subaerial unconformities within foramol ramp calcarenites and mixed deposits salento se italy nine discrete metre scale sequences of early pliocene to middle pleistocene age were deposited in the small novoli graben salento peninsula puglia s italy they consist of carbonate and mixed carbonate siliciclastic sediments deposited on a slowly subsiding foreland ramp skeletal concentrations and intervening less fossiliferous intervals have been examined to provide information on major environmental parameters and infer the dynamics of their changes taphonomic and palaeoecological analyses indicate that storm induced waves and currents reduced sediment input and settling behaviour of components were the main factors controlling the features of the various shellbed types the concentrations were formed below fair weather wave base in low stress inner to outer shelf environments and are often associated with surfaces or intervals that are characterized by sedimentary condensation vertical change in the fossil content within individual cycles indicates water depth changes that were parallel to climatic fluctuations hence may result from glacio eustatic sea level changes most sequences are bounded by subaerial karstic unconformities because of the regional setting of low subsidence rate the record of the relative sea level fluctuations is incomplete episodes of subaerial exposure and concomitant effects of vadose diagenesis are documented by i diagenetic changes leading to hardening of unconformity horizons ii local subvertical solution pits developed in the vadose zone below unconformity surfaces iii networks of polygonal cracks below unconformities and iv infilling of solution pits and polygonal cracks with vadose silt and marine sediment inwashed during transgressions following the subaerial stages lower sequences are characterized by tighter cementation and significant increase in moldic and vuggy porosity due to superimposition of the diagenetic effects of repeated high amplitude sea level fluctuations

lacustrine varve formation through time abstract studies using sediment traps in lakes reveal that the seasonal flux of sediment regulates both the composition and timing of deposition of materials that reach the bottoms of lakes if the bottom waters of a lake are partly or totally anoxic the seasonally deposited materials are preserved as annual groupings of laminae varves common components that form individual laminae consist of allochthonous clastic material derived from the drainage basin precipitated carbonate minerals diatom frustules iron rich and manganese rich flocs autochthonous organic detritus and autochthonous and allochthonous materials resuspended from the bottom the style of varving has changed over geologic time reflecting changes in biologic evolution and types of materials available precipitated iron rich laminations were common in the middle precambrian graded sets of clastic organic laminations persisted through the precambrian prior to the evolution of bioturbating benthic organisms glaciolacustrine varves appear to have retained their distinctive character through time carbonate rich varves occurred sporadically in the precambrian and phanerozoic with the exception of diatoms major components of modern lacustrine varves were present through the paleozoic and mesozoic and yet varves are rare in strata of these ages and may have accumulated in marine to brackish water environments diatoms were introduced into lacustrine systems in early tertiary time and are common components of varves from then on diatom laminae combined with a greater chance for geologic preservation of younger lake deposits have increased the number of geologically young occurrences of varved sediments however seasonal associations of modern varve components and the processes they represent are present in ancient deposits and provide clues to the interpretation of ancient environments

stratigraphic evidence for a deep eocene lake uinta piceance creek basin colorado relief on a prograding clastic complex is used to estimate the water depth of eocene lake uinta in the piceance creek basin of western colorado relief of as much as 412 in is present today on the complex postdepositional compaction can account for only about 100 m of this relief therefore the remaining 312 m appear to represent paleorelief on the floor of lake uinta the lake was apparently more than 300 m deep authigenic saline minerals were precipitated in the unlithified sediments of the deeper areas of the lake suggesting that at least the lower part of the water column was highly saline the evidence presented here indicates that the deep stratified lake model is more appropriate than the more generally accepted shallow or playa lake model for lake uinta

geochemical and sm nd isotopic characteristics of the late archaean palaeoproterozoic dhanjori and chaibasa metasedimentary rocks singhbhum craton e india implications for provenance and contemporary basin tectonics abstract in significant contrast to other cratonic blocks of india the singhbhum cratonic successions record continuous depositional record from the palaeoarchaean to mesoproterozoic although the sedimentary facies characteristics and mode of stratigraphic sequence building of the dhanjori and chaibasa formations are well known sedimentary geochemistry provenance and tectonic milieu of deposition of these two formations are hitherto unknown the current manuscript presents geochemical and sm nd isotopic data from the dhanjori and chaibasa formations for the first time and combine previous sedimentological data with the goal to expand the framework for understanding the depositional and tectonic setting of these two formations the sm nd isotopic data for the chaibasa clastics is unambiguous with respect to provenance average nd t 2 2 ga 0 8 1 0 and average nd model age tdm 2 51 0 08 ga with average 147 sm 144 nd ratios 0 1114 0 0041 for phyllites and quartzites indicate an extremely homogeneous source signature consistent with a late archaean juvenile crustal provenance possibly a dominantly upper crustal provenance the sm nd isotopic data from the older dhanjori formation also indicate broadly similar provenance as comparable lithologies in the younger chaibasa formation our sm nd isotopic data is entirely consistent with the previous sedimentological data and confirms a terrestrial rift dominated tectonic setting for the dhanjori formation proximal sources poorly mixed provenance and a marginal marine to offshore setting for the more homogeneous nd isotopic signature of the chaibasa formation distal sources well mixed provenance

palinspastic restoration and paleogeographic reconstruction of the peri tyrrhenian area during the neogene abstract this paper presents the results of research carried out on the paleogeographic and geodynamic post collisional evolution of the peri tyrrhenian area from the southern alps to sicily during this post collisional evolution a back arc area thrust belt foredeep system developed in which the following tectono sedimentary zones can be distinguished from the external to the internal ones the foreland zone connected to the foredeep through a slope generally controlled by normal faults the foredeep an assymmetric depression with strong subsidence related to the compressional activity of the thrust zone the chain whose outward migration from the late oligocene onward was discontinuus with important stages of crisis partially connected to the mechanical response of different crustal thicknesses existing in the foreland the discontinuous satellite basins developed within the thrust belt the back arc basins developed in the inner part of the chain where the superposition of the extensional tectonics over previous compressional domains causes the fragmentation of the thrust belt leading to its destruction according to this model seven palinspatic maps are discussed regarding the following time intervals late oligocene 25 24 m y burdigalian 22 20 m y langhian 17 16 m y serravallin 15 13 m y tortonian 10 9 m y late messinian 5 5 5 3 m y and early pliocene 5 3 4 6 m y during five of these time intervals significant geodynamic modifications occurred in the whole peri tyrrhenian area leading to paleogeographic changes in any case the geodynamic evolution of the whole area seems clearly controlled by the activity of important bundles of tectonic lines transversal to the chain which in the same time interval in the outermost part of the thrust belt separated areas with different values of shortening and in tthe most internal zones separated segments having different amount of extension these tectonic lines certainly have a crustal significance and have probably acted along previous formed discontinuities