depositional facies of a mud shoreface in suriname south america a mud analogue to sandy shallow marine deposits abstract immense volumes of argillaceous muds are being deposited along the world s longest continuous mud coastline which faces the open equatorial atlantic not only are these muds deposited in an environment normally associated with sand deposits but just as in sandstones sedimentary structures within these muds record the dynamic processes that deposited them this study investigates a 100 km long portion of the suriname coast utilizing cores bathymetric surveys and field observations from nearshore and innershelf environments using terminology borrowed from sand coastlines the innershelf nearshore of suriname is divided into transition zone shoreface foreshore and backshore the transition zone consists of a mix of offshore sands and shoreface muds shoreface and foreshore are subdivided into bank and interbank zones these zones are transitory because mud banks which make up the bank zones migrate westwardly mud banks are up to 5 m high 50 to 60 km long 10 to 20 km wide and oriented at oblique angles to the coastline these banks generally consist of fluid muds which are so fluid that they interact with surface waves causing them to be altered and damped banks are attached to the shoreline and commonly produce progradation of the coastline substrate within the interbank zone is more consolidat d than within the mud banks because of lack of wave dampening wave energies are relatively high within the interbank zone producing erosion of the shoreface and shoreline sand beaches are generally formed within the erosional interbank shoreline the vertical sedimentary sequence within the shoreface muds is a record of bank migration and other sedimentary processes present wave and current energies are recorded by scour and fill features discontinuity features micro cross laminations lenticular laminations and parallel to subparallel laminations laminations appear to be created by boundary layer shearing within fluid muds which are above wave base and made mobile by wave generated shore parallel currents large scale evidence for migration of the mud banks is westward dipping acoustical reflectors within the banks these reflectors which are over a kilometer apart mark the boundaries of annual migration events biogenic structures are generally absent within the fluid bank muds but are present within the more consolid ted interbank zone and associated with discontinuity features which are buried interbank surfaces migration and vertical stacking of mud banks are recorded by vertical sequences of massive and laminated muds which were deposited by mud banks and discontinuity features which were formed by interbank zones the coastal deposits of suriname are a mud analogue to nearshore and innershelf sand deposits transition zones of both mud and sand systems reflect a transition from offshore to shoreface processes and sediments both mud and sand shoreface foreshore systems reflect sediment input and wave current and tidal processes that act on them mud banks of suriname resemble linear sand ridges on the continental shelf of the eastern u s a in shape oblique orientation to the coastline and orientation with respect to dominant direction of transport processes the sequence of massive and laminated muds with discontinuity features resembles laminated to burrowed sequences found in ancient and recent nearshore and shallow marine sands

strong biological controls on sr ca ratios in aragonitic marine bivalve shells 1 it is well known that skeletal remains of carbonate secreting organisms can provide a wealth of information about past environments sr ca ratios have been successfully used as a temperature proxy in corals and sclerosponges previous work on aragonitic bivalve shells has not been conclusive but suggests a major control of growth rate on sr ca ratios as many studies have used bivalve growth rates to determine temperature we tested if sr ca ratios could predict temperature through its relationship with growth rate shells from the two species of clams from the same family veneroidea studied here saxidomus giganteus and mercenaria mercenaria show vastly different seasonal sr ca profiles a strong relationship between average annual sr ca ratios and annual growth rate was found in s giganteus shells from both washington r2 0 87 and alaska r2 0 64 usa but not in m mercenaria shells from north carolina usa furthermore the sr ca growth rate relationship was also evident upon a more detailed inspection of subannual growth rates in s giganteus r2 0 73 although there were significant positive correlations between sr ca ratios and temperature in s giganteus shells the correlations were weak 0 09 r2 0 27 and thus sr ca ratios cannot be used as a reliable temperature proxy in these species of aragonitic bivalves it is clear from this study that sr ca ratios are not under thermodynamic control in either clam species since thermodynamics predict a negative correlation between sr ca ratios and temperature in aragonite this points toward dominance of biological processes in the regulation of sr2 this is also reflected by the largely differing sr ca partition coefficients dsr in these shells dsr 0 25 when compared to inorganic coral and sclerosponge studies dsr 1 all of which show a negative dependence of sr ca on temperature we suggest that caution be taken when using sr ca in any biogenic aragonite as a temperature proxy when the dsr greatly deviates from one as this indicates the dominance of biological controls on sr ca ratios

holocene tsunamis in the southwestern bering sea russian far east and their tectonic implications the bering sea coast of kamchatka overlies a boundary between the proposed okhotsk and bering blocks or micro plates of the north american plate in the russian far east a history of tsunamis along this coast for the past 4000 yr indicates that the zone north of the kuril kamchatka subduction zone produces tsunamigenic earthquakes every few centuries such a record is consistent with convergence of the proposed okhotsk and bering blocks along the bering sea coast of kamchatka a tsunami deposit from the 1969 m w 7 7 ozernoi earthquake helps us interpret older tsunami deposits newly studied tephra layers from shiveluch volcano as well as previously established marker tephra layers in northern kamchatka provide age control for historic and prehistoric tsunami deposits based on 50 measured sections along 14 shoreline profiles tsunami deposit frequencies in the southwestern bering sea are about five per thousand years for tsunamis generated north of the kuril kamchatka trench

oceanography bathymetry and syndepositional tectonics of a precambrian intracratonic basin integrating sediments storms earthquakes and tsunamis in the belt supergroup helena formation ca 1 45 ga western north america abstract the carbonate dominated helena formation of the mesoproterozoic belt supergroup of western north america provides an instructive example of how a range of regional depositional and environmental characteristics of an ancient sea can be deduced on the basis of micron to metre scale features particularly revealing is the window opened by the presence of abundant molar tooth structure onto the paleoceanography paleobathymetry paleoclimate and tectonic regime of this intracratonic precambrian basin the facies hosting molar tooth structure is composed dominantly of lime mud with substantial subangular quartz and feldspar silt and clay derived from the western and southwestern side of the basin these are low energy tempestites deposited on a remarkably flat sea bottom at the limit of storm wave base at about 50 m sporadic domical stromatolite patch reefs confirm that the sea bottom was normally within the photic zone the ubiquity of molar tooth structure suggests frequent near field seismic activity during subsidence which generated ground motion sufficient to liquefy granular lime mud and terrigenous silt sporadic tsunamis from major submarine faults far to the west pounded the shallow water platform to the east tsunami off surge swept ooids and rounded coarse grained feldspathic quartz sand westward into deeper water and created strongly erosive currents that left gutter casts composed of lags of preferentially cemented molar tooth structure in otherwise relatively low energy facies mineralogical and geochemical evidence confirms that the belt basin was marine organic matter was essentially fully oxidized in the water column original high mg composition and cementation of lime mud in molar tooth structure indicate that calcite precipitated above the thermocline in supersaturated seawater under tropical conditions scattered bimineralic ooids in allochthonous grainstones indicate that shoals on the platform to the east were intermittently above a shallow aragonite compensation depth in warm water rare vestiges of halite and gypsum demonstrate occasional temporary salinity stratification for periods of up to a few years unaltered feldspar and mica grains point to a generally arid climate but the large volume of clay is suggestive of protracted weathering and transport

relative precipitation rates of aragonite and mg calcite from seawater temperature or carbonate ion control the temperature and degree of carbonate mineral supersaturation co3 2 ion concentration of seawater are the two most likely controlling variables on the compositions of recent marine carbonate cements the relative importance of these variables is difficult to assess in nature because they have similar trends with depth 0 1500 m and latitude in modern oceans we carried out laboratory experiments to investigate the relative growth rates of calcite mg calcite and aragonite in seawater as functions of both temperature 5 25 and 37 c and of carbonate ion concentration 2 5 to 15 times supersaturated with respect to calcite the precipitation rates of aragonite relative to those of calcite increase strongly with increasing temperature and are not affected greatly by changes in saturation state at 5 c calcite precipitation rates are nearly equivalent to those of aragonite regardless of the degree of saturation at both 25 and 37 c aragonite precipitation rates are much more rapid than those of calcite up to a factor of 4 except at very low saturation states calcite compositions vary from less than 5 mol mgco3 at 5 c to 14 mol mgco3 at 37 c our results suggest that the well documented shift toward precipitation of lower mol mg calcite and the decrease in abundance of aragonite cements with increasing oceanic depth and latitude can be attributed largely to lower temperatures

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

an integrated stratinomic model for the genesis and concentration of small shelly fossil style phosphatic microsteinkerns in not so exceptional conditions abstract carbonate fluorapatite filled millimeter scale microsteinkerns are a key element of the small shelly fossil ssf fauna generally associated with the late proterozoic cambrian the purported disappearance of these fossils and this style of phosphatic preservation during the cambrian stage 2 botomian extinction has been linked to changes in ocean chemistry and or changes to the physical environment due to the evolution of metazoans as well to the changing role of metazoans in the marine environment through a qualitative meta analysis of existing literature we document a broader temporal distribution for ssf style preservation than previously recognized we examine these occurrences for common patterns of depositional conditions and we offer a conceptual model for both the origin of the phosphatic microsteinkerns and their eventual concentration in certain sediments based on known biogeochemical diagenetic processes of authigenic calcium fluorapatite precipitation phosphogenesis and subsequent concentration of phosphatic sedimentary particles this polycyclic phosphogenic condensation ppc model makes predictions as to how and where this form of preservation might occur in cambrian and non cambrian marine strata alike

an oscillating trend in phanerozoic non skeletal carbonate mineralogy textural and compositional data on ancient ooids and cements suggest the existence of an oscillating phanerozoic temporal trend in non skeletal carbonate mineralogy the trend shows good correlation with eustatic climatic oscillations proposed by others the most likely mechanism appears to be plate tectonically influenced oscillations in pco2 the vapour pressure of co2 rather than change in oceanic mg ca ratio

plate boundary earthquakes and tsunamis of the past 5500 yr sixes river estuary southern oregon eleven plate boundary earthquakes over the past 5500 yr have left a stratigraphic signature in coastal wetland sediments at the lower sixes river valley in south coastal oregon within a 1 8 km2 abandoned meander valley 10 buried wetland soils record gradual and abrupt relative sea level changes back in time to 6000 yr ago an additional youngest buried soil at the mouth of the sixes river subsided during the a d 1700 cascadia earthquake multiple lines of evidence indicate that tectonic subsidence caused soil burial including permanent relative sea level rise following burial lateral continuity of buried soil horizons over hundreds of meters diatom assemblages showing that sea level rose abruptly at least 0 5 m and sand deposits on top of buried soils demonstrating coincidence of coseismic subsidence and tsunami inundation for at least two of the buried soils liquefaction of sediment accompanied subsidence the 11 soil burial events took place between 300 and 5400 yr ago yielding an average recurrence interval of plateboundary earthquakes of 510 yr comparing paleoseismic sites in southern washington and south coastal oregon with the sixes river site for the past 3500 yr indicates that the number and timing of recorded plate boundary earthquakes are not the same at all sites in particular a sixes earthquake at 2000 yr ago lacks a likely correlative in southern washington therefore unlike the a d 1700 cascadia earthquake some cascadia plate boundary earthquakes do not rupture the entire subduction zone from southern oregon to southern washington in the lower sixes river valley the upperplate cape blanco anticline deforms sediment of late pleistocene and holocene age directly above the subduction zone differential tectonic subsidence occurred during two of the plate boundary earthquakes when a blind upper plate reverse fault for which the cape blanco anticline is the surface fold slipped coseismically with rupture of the plate boundary during these two earthquakes sites 2 km from the anticline axis subsided 0 5 m more than sites 1 km from the axis

sedimentary signatures and processes during marine bolide impacts a review abstract studies of submarine impact craters resulting from impacts of comets or asteroids demonstrate that the presence of water and the physical properties of target rocks have a major influence on sedimentary processes associated with meteorite impacts this results in difference in sedimentary signature of bolide impacts in marine environments compared to subaerial impact craters in subaerial impacts the targets are commonly hard rocks frequently of igneous and or metamorphic origin whereas in submarine impacts the targets are mostly unconsolidated or poorly lithified sediments or sedimentary rocks with high volumes of pore water such differences result in variability in crater morphology and in sedimentary processes inside and outside the impact area impacts in shallow water marine neritic environments produced craters with low or absent rims and wide and shallow brims as characterize by both the montagnais on the scotian shelf the mjolnir in the barents sea 45 and 40 km in diameter respectively and the chesapeake bay 90 km in diameter lack of elevated rims is thought to be the result of current reworking and resurge of the water back into the excavated cavity as the water in the crater is vaporized during this process resurge gullies can be cut across the rim while mass and debris flows turbidites and other gravity deposits are produced as results of tsunami and crater wall and central high collapse during and after the crater excavation stage such deposits are found both within and outside the crater structure the only difference between gravity deposits triggered by an impact or other rare events such as earthquakes is the admixture of various melt particles and possible enrichments in iridium in the former impacts near the shelf edge may cause partial collapse of the continental margin as shown by the montagnais and chicxulub impacts some of the gravity and debris flows generated by margin collapse may be channelized with final deposits up to several hundred meters thick extending for hundreds of kilometers from the impact site other impact features such as shatter cones tektites spherules and ni spinels shocked quartz isotropication and partial melts are common to both submarine and subaerial impacts theoretical calculations of the destructive forces of mega tsunami waves triggered by meteorite impact in the ocean greatly exceed those based on geologic evidence a dearth of gigantic tsunami evidence for the chicxulub impact outside of the gulf of mexico where from theoretical modelling the maximum near bottom orbital velocity of water flow crossing the deep north atlantic basin should have been 1 m s could be the result of the mitigating effect of the bathymetry of surrounding area causing wave diffraction and interference calculated maximum horizontal orbital velocity near the seafloor at the shelf for the montagnais impact is 22 m s for a 200 m high wave 5 5 m s for a 50 m high wave at 500 km decreasing to 0 5 m s at 1000 km strong enough to scour the deep ocean bottom and produce distinct erosion surfaces and disconformities in marine sedimentary record however lack of cores across impact horizon prevents confirmation of occurrence of such bottom water flows

late cambrian missing link in macroborer evolution preserved in intraclasts abstract macroborings are known to be rare to absent in middle to late cambrian successions the time interval between the end early cambrian archaeocyath extinction and the advent of new boring organisms during the mid late ordovician the ordovician bioerosion revolution the occurrence of macroborings was controlled mainly by hard substrate availability archaeocyath reefs and hardgrounds provided synsedimentarily lithified substrates during the early cambrian and ordovician respectively in this study we report bioerosion structures from micritic intraclasts of flat pebble conglomerates in the hwajeol formation furongian taebaeksan basin korea two types of macroborings trypanites and cf gastrochaenolites are recognized both of which penetrate micritic clasts and are filled with bioclastic grainstone matrix several lines of evidence including the sharp boundaries and unaltered shapes of macroborings as well as the occurrence of macroborings penetrating the coating of iron and or manganese oxide coated micritic clasts indicate that these macroborings formed after the cementation of micritic substrates the hwajeol macroborings would have formed on micritic clasts and or hardgrounds that were eroded and formed flat pebbles the presence of bioerosion structures within clasts of the hwajeol flat pebble conglomerates supports a previous hypothesis that macroborers survived in hardgrounds during the middle to late cambrian after the extinction of archaeocyath reefs in addition the hwajeol cf gastrochaenolites is the earliest of its kind implying that there could be more kinds of macroborings hidden within cambrian flat pebble conglomerates

earthquake magnitude frequency epicentral distance and soft sediment deformation in sedimentary basins abstract empirical equations available for earthquake magnitude frequency and the maximum epicentral distance of liquefied sites versus magnitude are combined with the characteristic instantaneous sediment deposition rate at a station in a sedimentary basin to form a model for the local stratigraphic frequency of earthquake induced soft sediment deformation structures both the style of sedimentation and the characteristics of the earthquake source combine to determine the pattern of incidence of the structures in a basin the model is probably most directly applicable to the geodynamic interpretation of fluvial basins in which substantial volumes of readily liquefied sands accumulate at high local short term rates

tsunamis in a stormy sea middle cambrian inner shelf limestones of western argentina abstract coarse grained strata deposited on continental shelves and epeiric seas in some tens of meters water depth are conventionally ascribed simply to storms of varying intensity which interrupted the settling out of suspended mud surprisingly the possibility of tsunamis is virtually never evaluated even though they might indeed should have been common in many regions portions of the middle cambrian la laja formation of the argentine precordillera formed in such a submerged epeiric platform or shelf they comprise a suite of three limestone facies variably argillaceous burrowed mudstone bioclastic grainstone and intraclastic conglomerate composed of pieces of mudstone including cemented haloes around burrows sporadically developed eocrinoid meadows and trilobite populations are recorded respectively by disarticulated ossicles and usually broken sclerites the latter indicate that generally exoskeletons became fragmented by repeated bottom turbulence hence the mudstones and grainstones show that before stabilization by calcite cementation which began beneath the sediment water interface and away from burrow margins physical reworking of the surface sediment by storms was so frequent that it did not leave a specific signature of individual events by contrast scattered lenticular beds of intraclastic conglomerate were due to anomalous brief episodes of deep scour and strong oscillatory flow from powerful wave action these conglomerates then escaped subsequent reworking because they are abruptly interbedded and encased within uniform mudstone and there are no stratigraphic patterns allochthonous material or unconformities to indicate sea level fluctuation the events that created the conglomerates were more likely tsunamis not storms they could have been unleashed by faulting elsewhere on the shelf or rifting beyond the shelf margin to the present day west to southwest those originating in the rift basin may have been diffracted by marginal shoals and attenuated by the shallowness of the platform which caused the waves to break some distance offshore in any case the study area was not affected by backwash recognition of tsunami laid beds urges a reexamination of the standard tempestite paradigm with its use of coarse grained strata as a simple measure of storm frequency and intensity

petrology chemistry and texture of modern river sands amazon river system key idea following the spirit of p d krynine the sands of the world s largest tropical river system are studied to reveal much about the general origin of sand and sandstone thin section and chemical study of 95 sand samples from the amazon river system in brazil peru ecuador and colombia a river system with great contrasts in climate and rock types reveals that sands derived from the andes are lithic arenites whereas sands derived from precambrian terrains are much richer in quartz as are sands in rivers draining tertiary molasse sand becomes more mature downstream along the main stem of the amazon solimoes maranon so that a sample analyzed at the mouth does not accurately reflect headwater composition dilution by quartz rich tributaries and quartz rich tertiary outcrops possible differential elimination of rock fragments and even possible weathering on the modern flood plain of the amazon contribute to enhanced maturity downstream we speculate that although data on modern large subarti

isotopic evidence for the paleoenvironmental evolution of the mesoproterozoic helena formation belt supergroup montana usa high resolution isotopic and geochemical data constrain long debated marine vs lacustrine depositional models for the helena formation a carbonate unit within the mesoproterozoic belt supergroup montana paired carbon and oxygen isotope and minor element analyses of microsamples from a diverse array of petrographic components effectively distinguish between primary and secondary isotopic signatures 13c values reflecting primary depositional conditions increase progressively from an average of 0 near the base of the helena formation to an average of 1 4 near the top over a stratigraphic thickness of 100 200 m because the base of this 1 6 shift coincides with a basin wide facies change marked by the appearance of stromatolitic units and an increased occurrence of features indicative of evaporative conditions and subaerial exposure the shift toward more positive 13c values is interpreted to reflect an increase in biologic productivity coupled with increasingly evaporative conditions in the eastern part of the belt basin 13c values from the lower part of the helena formation are similar to those from other marine carbonates of similar age and suggest that the belt basin was marine during deposition of the helena formation taken as a whole these relations suggest that helena sediments were deposited in a shallow marine basin that was increasingly isolated from the open mesoproterozoic ocean original 13o values have been retained only in syndepositional and early diagenetic intergranular cements in oolitic grainstones that occur in the upper part of the helena formation the most positive 13o values derived from these cements 6 1 pdb are up to 3 higher than previous estimates for the 13o value of mesoproterozoic marine calcite however because these phases are associated with facies deposited under restricted marine conditions interpretation of 13o values from these cements with regard to the composition of the open mesoproterozoic ocean awaits study of additional coeval marine carbonate successions

numerical modelling of tsunami propagation with implications for sedimentation in ancient epicontinental seas the lower jurassic laurasian seaway abstract tsunamis are frequent events in modern marine environments but evidence of their passing in subtidal ancient epicontinental sea deposits is elusive it has been suggested that this is due to mis identification or poor preservation potential herein a numerical modelling approach is used to show that tsunami propagation in one large ancient epicontinental sea was hindered by the damping effect of shallow bathymetries and reflection refraction and diffraction from emergent landmasses the imperial college ocean model icom is used for this study and is first validated against data from the sumatra andaman tsunami of december 2004 a palaeobathymetric dataset is then presented for the hettangian lower jurassic laurasian seaway with idealised tsunami sources situated on the continental shelf and within the adjacent oceanic basin results show that tsunamis forced from within ocean basins adjacent to the epicontinental sea are rapidly attenuated over the continental slope and fail to propagate great distances onto the shelf similarly the sedimentological effect of tsunamis forced from within the epicontinental sea is also restricted it is concluded that tsunami deposits in ancient epicontinental seas are most likely to occur in relative proximity to the source region and this must contribute to their scarcity in the geological record

recent morphodynamics of alpine lakes in southern carpathian mountains using high resolution optical imagery abstract this study reveals for the first time the surface area evolution of glacial lakes in the romanian carpathians over 47 years the research also advances our understanding of the potential of satellite based remote sensing techniques to monitor the geomorphologic evolution of 27 rock basins into glacial lakes in the retezat mountains southern romanian carpathians these mountains host most of the glacial lakes in romania including both the widest and deepest glacial lakes using high precision orthorectification and co registration techniques the surface area extension and reduction of 27 shallow water bodies ranging in size from 0 10 to 9 14 ha were analyzed over two time intervals 1968 2007 and 2007 2014 the total surface area increased only by 1 between 1968 and 2014 with over half of the growth occurring during the last 7 years of the study period analysis of the surface area extension and reduction revealed that catchment aspect catchment size lake elevation land cover topography and lake depth are the main environmental factors controlling the present state of the glacial lakes in the central part of the retezat mountains the results suggest that the different behavior of glacial lakes within the north facing valleys compared with the evolution of the lakes settled in southern exposed valleys is mainly due to climatic and geomorphologic particularities of the opposing slopes on the northern side the lakes are slowly decreasing due to more intense geomorphologic activity of both the erosivity of precipitations and periglacial processes e g gelifraction mass wasting and permafrost degradation high altitude lakes generally are increasing because of the longer duration of the ice cover and the smaller amounts of sediment yielded by the nature of the soil or lack thereof and vegetation cover in the alpine area lakes with small catchments show the highest variability displaying significant changes whereas shallow lakes are the most prone to horizontal and vertical silting these controls which regulate changes in lake basin sizes provide baseline information on current trends in the evolution of romanian carpathian alpine lakes the methodology applied here could be widely applicable to other similar environments with widespread implications for understanding the global effects of climate change on alpine lakes

the possible role of benthic microbial mats during the formation of carbonaceous shales in shallow mid proterozoic basins a considerable portion of the upper member of the mid proterozoic newland formation meagher county montana consists of carbonaceous silty shales striped shale facies this type of shale facies is common in proterozoic basins and is host to several major base metal deposits the striped shales were deposited in a subtidal setting basinward of carbonates characterized by cryptalgal laminites mudcracks and flat pebble conglomerates the carbonaceous silty shales are considered remnants of benthic microbial mats irregular internal laminae patterns of particle trapping mechanical deformation during penecontemporaneous soft sediment deformation and filamentous microbiota provide evidence for this interpretation the dolomitic clayey shale contains graded silt clay couplets and these are interpreted as storm layers modern subtidal microbial mats can only survive under special conditions but in the proterozoic it is suggested that benthic microbial mats colonized the shallow seafloor during periods of low sediment input leading to the formation of carbonaceous shales

syneresis cracks subaqueous shrinkage in argillaceous sediments caused by earthquake induced dewatering abstract syneresis cracks often confused with subaerial desiccation phenomena are traditionally ascribed to subaqueous shrinkage whereby salinity changes caused deflocculation of clay this and other previously proposed mechanisms fail to account for their occurrence in low energy typically non evaporitic facies stratigraphically sporadic distribution intrastratal formation under shallow burial depths variation in morphology degree of contraction generation of sedimentary dikelets as crack fills and deformation of dikelets and enclosing layers instead it is suggested that ground motion from strong synsedimentary earthquakes caused argillaceous sediments to dewater interbedded sands and silts to be almost simultaneously liquefied and injected into the resulting fissures and then these dikelets to be distorted comparative rarity of syneresis cracks in phanerozoic versus precambrian marine strata is considered to be primarily an evolutionary consequence of theological changes caused by increased organic binding of clay flocs in the water column greater input of organic matter into the sediment and the diversification of sediment dwelling bacteria and meiofauna in phanerozoic deposits

leaving no stone unturned the feedback between increased biotic diversity and early diagenesis during the ordovician ordovician change in the nature of seafloor carbonates saw rapid decline of previously widespread flat pebble conglomerates and the palaeozoic peak abundance of hardgrounds the effective disappearance of flat pebble conglomerates widely attributed to physical disruption of substrate by bioturbation is reinterpreted as reflecting increased depth of carbonate precipitation below the taphonomically active zone such that early lithified carbonates were less frequently reworked by scour with deeper more stable zones of cementation exhumed limestones formed hardgrounds whose mid ordovician acme supported rapid increase in epizoan diversity further deepening of cementation to below normal scour accompanied post ordovician decline in submarine hardgrounds supplementary materials database for figure 2 is available at http www geolsoc org uk sup18896

a possible tsunami deposit around the jurassic cretaceous boundary in the boulonnais area northern france abstract an unusual succession of facies locally deposited around the jurassic cretaceous boundary in the boulonnais northern france is attributed to a tsunami event by comparison with recent tsunami deposits this sedimentary succession includes basal erosion with reworked lithified blocks soft sediment deformations an erosional conglomerate overlain by wood fragments and clays containing continental and marine fossils in one setting and conglomerate with mixed fauna in an other setting the tsunami probably affected the coast of the boulonnais area of the london brabant massif the origin of the event is unknown it was most probably triggered by an earthquake but other origins such as volcanic eruptions a giant landslide or even the impact of an extraterrestrial bolide into the ocean may also be considered

possible seismic origin of molar tooth structures in neoproterozoic carbonate ramp deposits north china the xinmincun formation forms the uppermost unit of a thick neoproterozoic section which accumulated near the east margin of the north china block and is overlain by two thin nearshore to continental formations below fossiliferous lower cambrian sediments although tectonically deformed sedimentary structures are preserved undeformed on cleavage parallel surfaces and an 80 m section has been reconstructed by correlation across minor folds and faults in the golden stone beach area 50 km ne of the city of dalian southern liaoning province the measured section shows 65 m of storm dominated deposits consisting of alternations of micrites and sharp based graded intraclastic grainstone beds tempestites some with rudaceous commonly erosional or guttered bases the top 15 m of section shows three alternations of similar subtidal lithofacies with partly to completely dolomitized peritidal deposits laminated sometimes fenestral and desiccated micrite beds and intraclastic rudite and grainstone beds tempestite beds become thinner and less abundant upwards towards a muddy upper shoreface zone this environment was characterized in part by the occurrence of micrite with thin or streaky lamination probable storm resuspended sediment interbedded tempestites numerous erosion surfaces and evidence of liquidization and sediment slumping into hollows molar tooth structures are widespread in micrite beds of the xinmincun formation and are present in lesser abundance in tempestites and liquefied channel fills originally the structures were sub vertical cracks 1 20 cm long tapering upwards and downwards subsequently they became filled with microspar cement and buckled rigidly during compaction of surrounding sediment during burial evidence of repeated episodes of cracking presence of brecciated cracks and localization of cracking within beds together with variable degree of development and variation of preferential alignment in plan indicates a mechanical origin crack generation may have been by seismic surface waves generated by movement along faults defining either the basin s margins or its internal structure or possibly by wave action during storms a seismic origin for molar tooth structure is consistent with other neoproterozoic occurrences their preferential occurrence in precambrian deposits arises from the relative rigidity of micritic sediment at this time related to lack of bioturbation incipient cementation and possibly microbial binding

facies and origin of shales from the mid proterozoic newland formation belt basin montana usa shales constitute more than 60 of the world s sediments yet while facies models for sandstones and carbonates are at a high level of sophistication the study of shales has clearly lagged behind in the mid proterozoic newland formation six major shale facies types deposited in nearshore to basinal environments are distinguished on the basis of bedding characteristics textural features and the proportions of silt clay and carbonate textural features of these shale types are related to sedimentary environments as deduced from associated lithologies the shales are undisturbed by bioturbation and their textural and sedimentary characteristics reflect subaqueous growth of microbial mats erosion and deposition by storms deposition of flocculated vs dispersed clays continuous slow background sedimentation winnowing by waves or currents and subaerial exposure

cirque form and development in romania allometry and the buzzsaw hypothesis abstract a complete inventory of the 631 glacial cirques in romania and adjacent ukraine shows that they are scale specific and develop allometrically extending in length more rapidly than they deepen shape changes with size horizontal dimensions are around 700 m vertical around 300 m on each quantitative measure they form a single unimodal population with limited variation in size on a logarithmic scale cirque axial gradients 15 33 are appropriate to occupation by rotationally flowing glaciers lake basins are more common 26 on granitic rocks compared with 10 6 of all cirques geology also affects vertical dimensions and gradients the relation between subjective five grades and objective measures of cirque development is shown by an r 2 of 62 when grade is predicted from maximum gradient minimum gradient and plan closure cirques larger in horizontal dimensions have better grades cirque floors cover around 28 of cirque map area larger cirques and nested inner and outer cirques are common in ranges that rose well above the snowline and are associated with more extensive more symmetrical glaciation and more cols in size and shape romanian cirques are similar to those in england and wales they are similar in some respects to those in part of the british columbia coast mountains except for smaller vertical dimensions they may have developed only in the last few glaciations mountain ranges can be ranked by degree of glacial modification and symmetry of glaciations the buzzsaw hypothesis is applicable only in the cores of the higher ranges elsewhere summit surfaces that are essentially preglacial survive

influence of mg2 on the kinetics of calcite precipitation and calcite crystal morphology abstract the kinetics of calcite growth in the presence of mg2 has been studied by both a ph free drift method and by visual observation our experiments show that the calcite growth rate is reduced by the presence of mg2 the higher the mg ca ratio in the solution the lower the growth rate in a caco3 supersaturated solution the inhibition of calcite growth by the presence of mg2 is caused by mg2 being incorporated into the original calcite seed surfaces and developing new crystal surfaces the mg2 distribution on the calcite surfaces is not uniform as there is likely to be different mg2 densities on the newly developed surfaces than on the original surfaces of the calcite seeds this causes the calcite crystal morphology to change the significance of creating error in using the initial rate data rather than the equilibrium rate data for the prediction of the calcite precipitation kinetics is discussed

sr mg ratios of modern marine calcite empirical indicators of ocean chemistry and precipitation rate holocene biotic and abiotic marine calcite have a similar range of mg contents 0 to 22 and 4 to 21 mol mgco3 respectively yet biotic calcite has sr2 concentrations that are consistently 1250 ppm higher than those of abiotic calcite as in laboratory experiments a positive linear relation is observed between dsr and calcite mg content this produces two distinct linear trends on a plot of sr2 vs mg2 concentrations principal axes of variation for both trends have similar slopes yet distinctly different sr2 concentration intercepts biotic y 0 024x 1298 r2 0 70 abiotic y 0 027x 47 r2 0 77 the similar slopes of these trends reflect the constancy of mgca and srca ratios of modern seawater equations describing the dependence of dsr on calcite mg content are derived from both trends biotic dsr 3 16 x 10t 6 ppm mg 0 169 abiotic dsr 3 52 x 10 6 ppm mg 0 0062 characterization of sr mg trends for holocene materials allows comparison with analogous trends from ancient samples to estimate relative changes in seawater mgca and srca ratios the relatively high sr contents of biotic calcite result from rapid precipitation rates associated with shell accretion in marine organisms calcites precipitated from seawater in laboratory experiments have dsr values that are similar to those of biotic marine calcite suggesting that both precipitate at approximately the same rate our estimates of surface area normalized precipitation rates in planktonic and benthonic foraminifera are comparable to those of seeded ph stat experiments we conclude that the dsr values for biotic and experimental marine calcite are kinetically controlled whereas the lower precipitation rates of abiotic marine calcite yield dsr values that approximate equilibrium conditions experimentally derived equations describing the relation between dsr and calcite precipitation rate indicate that the offset in sr content between biotic and abiotic calcite is the result of abiotic precipitation rates that are two to five orders of magnitude lower than those of biotic precipitates however observations of naturally occurring marine cements suggest that the five order of magnitude offset best represents natural system processes

sedimentary geology and stromatolites of the middle proterozoic belt supergroup glacier national park montana abstract the belt supergroup is a thick dominantly fine grained sequence of middle proterozoic strata occurring in western montana northern idaho and parts of washington state alberta and british columbia the sequence in glacier national park is located along the northeastern part of present exposures of the belt supergroup it is 2 9 km thick extremely well exposed and for the most part structurally simple although it was subjected to lowermost greenschist facies metamorphism primary sedimentary structures are exceptionally well preserved subtidal intertidal alluvial and possibly deltaic depositional environments appear to be represented in the belt sequence in glacier national park the lowermost unit the altyn limestone is not entirely exposed in the park a partial section 150 m thick consists of impure dolostones deposited largely in shallow subtidal and intertidal settings this carbonate unit is overlain by terrigenous strata of the appekunny and grinnell argillites the appekunny argillite is 700 m thick consists largely of green colored fine grained terrigenous material and appears to have been deposited predominantly in offshore and or deltaic settings the overlying grinnell argillite is 605 m thick and consists of red colored terrigenous material deposited largely on an alluvial plain the overlying siyeh limestone is 780 m thick and consists largely of impure dolostones and dolomitic limestones deposited in shallow subtidal and intertidal settings overlying the siyeh limestone is the 385 m thick snowslip formation which consists of slightly dolomitic predominantly fine grained terrigenous strata deposited largely in intertidal settings the overlying shepard formation is not exposed in its entirety in the central part of glacier national park a 270 m thick section which excludes the uppermost part of the formation consists of impure dolostones and argillites and appears to have been deposited in subtidal and intertidal settings stromatolites are abundant diverse and well preserved in glacier national park with mound shaped forms and columnar forms of the group baicalia occurring in the altyn limestone and siyeh limestone and mound shaped stromatolite like structures occurring in the snowslip and shepard formations particularly prominent is a 24 32 m thick stromatolite unit in the upper siyeh limestone which contains baicalia and conophyton and appears to represent a prograding stromatolite reef with baicalia originating in a moderate energy reef front setting and conophyton originating in a lower energy back reef setting individual units in these cycles can be correlated for 90 km many of the conophyton in these cycles are inclined probably as a result of gentle wave action and the direction of inclination is relatively constant for 90 km with the axes trending sw ssw and plunging 30 60 sw

silurian carbonate high energy deposits of potential tsunami origin distinguishing lateral redeposition and time averaging using carbon isotope chemostratigraphy abstract stable carbon isotope curves are used as a precise stratigraphic tool in the paleozoic even though they are commonly based on shallow water carbonate record characterized by low stratigraphic completeness identification of episodes of large scale redeposition and erosion may improve 13ccarb based correlations here a series of at least three episodes of high energy onshore redeposition are described from the makarivka member new unit of the ustya formation from the homerian middle silurian of podolia ukraine the makarivka member is emplaced within a tidal flat succession its most prominent part is divided into a lower polymictic conglomerate of sand to boulder sized clasts representing a range of subtidal facies and an upper heterolithic unit composed of grainstone and mudstone laminae the aim of the study is to identify the mechanism of deposition of the allochthonous conglomeratic material in this member based on analogies with recent tsunami deposits the conglomerate is interpreted to reflect the strongest landward directed current in the tsunami run up phase and the heterolith alternating high density landward currents stagnant intervals allowing mud and land derived debris to settle and backwash flows the tsunamite was deposited during an interval of decreasing isotopic values of the mulde excursion a global 13c excursion reaching 5 2 in the studied sections clast redeposition in an interval characterized by rapidly changing 13ccarb offers the opportunity to evaluate the degree of temporal and spatial averaging caused by the tsunami the clasts in the polymictic conglomerate show scattered 13ccarb values 0 3 to 2 1 compared to homogenous 1 3 to 1 6 values in the matrix the presence of clasts characterized by low 13ccarb values is explained by their decrease with bathymetry rather than erosion of pre excursion strata whereas high values characterize material entrained from the sea floor and strata directly underlying the tsunamite close 1 3 and 1 5 average 13ccarb values suggest that the matrix of the conglomerate is potentially a product of clast grinding

carbonate platform dominated by peloidal sands lower ordovician la silla formation of the eastern precordillera san juan argentina the lower ordovician la silla formation of the precordillera of west central argentina is part of the west facing early palaeozoic tropical carbonate platform succession that comprises the core of the cuyania terrane up to 360 m thick it is exposed in several thrust sheets over a distance of some 250 km along and across depositional strike over a palinspastically unrestored distance of about 35 km la silla formation is a strikingly pure limestone with subordinate finely crystalline dolomite and rare chert it accumulated on a more or less uniformly subsiding passive margin copious precipitation of microcrystalline calcite probably influenced by microbial activity to varying degrees led to the generation of peloids ooids and aggregates of these grains as well as small amounts of lime mud intraclasts stromatolites and thrombolites rare bioclasts are limited mostly to scattered gastropods and trilobite sclerites bioturbation is present locally the array of carbonate rock types is grouped into eight recurring lithofacies in order of decreasing abundance i peloidal grainstone ii laminated dolostone iii intraclastic rudstone iv microbial laminite v peloidal packstone vi ooidal grainstone vii thrombolite boundstone and viii mudstone these facies represent sediments that formed solely in a shallow subtidal marine environment with no evidence of restricted conditions hypersalinity or subaerial exposure no events of eustatic sea level change are recorded by far the dominant facies is grainstone composed of well sorted fine sand sized peloids and peloidal aggregates in homogeneous tabular to gently undulating medium to thick beds cross lamination is scarce clusters of sub metre sized microbial patch reefs developed sporadically the shallow platform is envisaged to have been covered by extensive peloidal sand flats and low relief banks and little lime mud was generated the setting was probably microtidal and may not have been affected by strong trade winds it was washed by frequent relatively gentle wave action but without experiencing powerful storms in the middle member anomalous lenses of intraclastic rudstone and laminated dolostone occur as graded beds overlying sharply downcut scoured surfaces up to 20 cm deep these are interpreted to indicate a phase when accretion was punctuated occasionally by tsunamis generated from rift faulting seaward of the platform margin the remarkably uniform peloidal grainstone composition over a broad area shows that given the appropriate combination of climate environmental and ecological factors large portions of some early palaeozoic platforms were dominated by grainy sediment and remained under well agitated conditions within fair weather wave base without distinct lateral facies differentiation or tidal flat aggradation

syntectonic sedimentation in the proterozoic upper belt supergroup northwestern montana deepening environments in the proterozoic libby formation record a tectonically induced style of sedimentation distinctly different from that of older belt rocks facies associations and sedimentary structures indicate that deposition in the lower libby formation occurred above fair weather wave base thick widespread hummocky cross stratified quartzite in the upper libby formation lacks the association of shallow water features present in the lower libby formation suggesting that upper libby deposition occurred below fair weather wave base and above storm wave base independent evidence for tectonism during deposition of the belt supergroup exists but is plagued by poor age control the angular unconformity that occurs between libby equivalent rocks and the overlying windermere supergroup indicates tectonic activity between deposition of the belt purcell and windermere supergroups the interpreted subsidence or rise in basin water level combined with newly uplifted source areas as recorded in the upper libby formation and garnet range formation could have been an early manifestation of movements that produced this unconformity

assessment of permafrost conditions in the highest mountains of the balkan peninsula abstract the proposed research addresses the problem of permafrost occurrence for the first time in the highest mountains of the balkan peninsula the likely unlikely presence of ice rich permafrost in 13 rock glaciers in the rila and pirin mountains was investigated using thermal measurements e g ground surface temperature monitoring measurements of the bottom temperature of snow cover and late summer alpine spring water temperature measurements and ground penetrating radar surveys based on the thermal records intact rock glaciers appear likely above 2450 m on north facing slopes where incoming solar radiation is small and the pronounced shadow effect of the ridges allow an extended duration of snow cover thermal results revealed that the coarse blocks influence the near surface energy exchange fluxes confirming the significant influence of the cooling effect of high porosity unconsolidated debris deposits the intense ground overcooling during the early winter is mainly the result of temperature driven air convection whereas in late winter the low thermal conductivity of the porous boulder mantle below a thick snow cover can cause ground cooling furthermore the reduced insolation below the late lying snow patches prevents the ground from heating up during the warm season at most of the sites the winter equilibrium temperatures are lower than 3 c and the mean annual ground surface temperatures are negative or close to 0 c ground penetrating radar gpr measurements detected permafrost occurrence in three rock glaciers underneath a thick active layer 4 10 m forthcoming research on this topic is needed to evaluate more carefully the importance of local conditions for permafrost preservation

flat pebble conglomerate its multiple origins and relationship to metre scale depositional cycles carbonate flat pebble conglomerate is an important component of precambrian to lower palaeozoic strata but its origins remain enigmatic the upper cambrian to lower ordovician strata of the snowy range formation in northern wyoming and southern montana contain abundant flat pebble conglomerate beds in shallow water cyclic and non cyclic strata several origins of flat pebble conglomerate are inferred for these strata in one case all stages of development of flat pebble conglomerate are captured within stormdominated shoreface deposits of hummocky cross stratified hcs fine carbonate grainstone a variety of synsedimentary deformation structures records the transition from mildly deformed in situ stratification to buckled beds of partially disarticulated bedding to fully developed flat pebble conglomerate these features resulted from failure of a shoreface and subsequent brittle and ductile deformation of compacted to early cemented deposits failure was induced by either storm or seismic waves and many beds failed along discrete slide scar surfaces centimetre scale laminae within thick amalgamated hcs beds were planes of weakness that led to the development of platy clasts within partly disarticulated and rotated bedding of the buckled beds in some cases buckled masses accelerated downslope until they exceeded their internal friction completely disarticulated into clasts and transformed into a mass flow of individual cm to dm scale clasts this transition was accompanied by the addition of sand sized echinoderm rich debris from local sources which slightly lowered friction by reducing clast clast interactions the resulting dominantly horizontal clast orientations suggest transport by dense viscous flow dominated by laminar shear these flows generally came to rest on the lower shoreface although in some cases they continued a limited distance beyond fairweather wave base and were interbedded with shale and grainstone beds the clasts in these beds show no evidence of extensive reworking i e not well rounded or condensation i e no rinds or coatings a second type of flat pebble conglomerate bed occurs at the top of upward coarsening metre scale cycles the flat pebble conglomerate beds cap these shoaling cycles and represent either lowstand deposits or in some cases may represent transgressive lags the clasts are well rounded display borings and have iron rich coatings the matrix to these beds locally includes glauconite these beds were considerably reworked and represent condensed deposits thrombolites occur above the flat pebble beds and record microbial growth before initial transgression at the cycle boundaries a third

chemical model for the origin of minor limestone shale cycles by anaerobic methane oxidation chemical and isotopic studies of jurassic carbonate concretions indicate an origin by anaerobic methane oxidation concretion growth occurred within the top 1 m of sediment in a thin zone where methane was consumed to stimulate a late rejuvenated phase of sulfate reduction similar chemical and isotopic characteristics are shown by diagenetic carbonate in several limestone shale sequences and an origin by anaerobic methane oxidation is proposed for these sequences also the evolution of isolated concretions into diagenetic limestones depends on the extent of and depth variations in carbonate supersaturation arising from anaerobic methane oxidation and the persistence of a reduced sedimentation rate or a depositional hiatus diagenetic limestones formed in this way can often be recognized by their association with a later pyrite phase that is more abundant and has more positive sup 34 s values than the adjacent shales

stromatolites and associated facies in shallowing upward cycles from the middle proterozoic altyn formation of glacier national park montana abstract the approximately 1450 ma old altyn formation is the oldest stratigraphic unit exposed in glacier national park montana the lower part of the formation informally called member a contains at least 17 shallowing upward cycles with an average cycle thickness of 4 2 m each cycle rests on an erosional surface and has subtidal quartz microcline dolarenites in the basal part the subtidal rocks pass upward into stratiform stromatolites interbedded with dolarenites similar to those in the basal layers the stromatolites formed on tidal flats during calm periods and the dolarenites were transported from subtidal areas to the tidal flats by storm driven waves and currents domal and columnar stromatolites grew in relatively higher energy conditions particularly in tidal channels in the lower tidal flats the upper parts of some cycles have sparse dolarenites and are dominated by stratiform stromatolites desiccation features and complete dolomitization of subtidal and intertidal carbonate sediments occur in member a many cycles within this member contain evidence of the diagenetic formation of gypsum and anhydrite in sediments deposited in subtidal and intertidal zones the carbonate sediments in each cycle accumulated up to sea level causing progradation of tidal flats into a shallow subtidal area this led to the development of a supratidal zone analogous to a modern sabkha member a is overlain by quartz microcline dolarenites of informal member b which were deposited in subtidal environments informal member c overlies member b and contains shallowing upward cycles similar to those of member a but with an average cycle thickness of 2 5 m member c cycles also differ in containing mud cracked shales and terrigenous arenites these terrigenous sediments were derived by mechanical weathering in the source area they were transported into the supratidal and upper intertidal zones during flash flooding the change from member a to member b represents an overall transgressive trend this was followed by an overall regression giving the change from member b to member c the repeated shallowing upward cycles are due to smaller transgression progradation events that were superimposed on these larger trends the altyn formation was deposited in an epicontinental basin each shallowing upward cycle was produced by sediment aggradation and progradation following rapid subsidence resulting from vertical tectonic activity the paleoclimate was arid with occasional storms flooding the tidal flats with subtidal sediments and the upper tidal flats with terrestrial sediments such a paleoclimate is consistent with the subtropical to tropical paleolatitudes indicated by paleomagnetic data for the altyn formation depositional area

nd evidence for proterozoic crustal development in the belt purcell supergroup a knowledge of the chemical and isotopic characteristics of the continents as they existed in the past is essential to an understanding of their evolution1 7 vestiges of these characteristics remain in the sedimentary record for example the character and crustal residence age4 of ancient continental crust has been deduced from the sm nd isotopic patterns of clastic sediments that have survived to the present day4 6 8 we report here sm nd isotopic measurements from the belt purcell supergroup of western north america which form the first detailed isotopic investigation of a major proterozoic sedimentary succession the belt purcell has many features also seen in the detrital load of the world s major contemporary rivers including exceptionally homogeneous 147sm 144nd and 143nd 144nd ratios and a small range of crustal residence ages mantle additions to the continental crust seem to have been relatively minor since the middle proterozoic

a note on the preservation of offshore tsunami deposits abstract in this contribution we explore the preservation potential of offshore tsunami deposits the application of linear wave theory and flat bottom conditions allows a simplified representation of the physical environment in such an environment it is possible to compute the boundary water depth below which the influence of storm waves on tsunami deposits is negligible the majority of the tsunami deposits described in the literature were deposited onshore where the tsunami wave is transformed into bores and rollers these deposits differ from tsunami sediments of the deeper shelf where the water sediment interaction corresponds more to wave influences we define the boundary depth db as the depth below which tsunami deposits cannot be reworked due to storm waves this is based on the assumption that the wave base coincides with the seabed if the wave base is below the bed a reworking of bed sediments occurs if it is above no energy is transferred to the bottom as an example we use tide gauge records at pointe de la rue seychelles and ca 50 km offshore from brisbane australia at a water depth of 70 m to derive the major wave parameters of the sumatra tsunami and a category 1 cyclone that occurred from 4 6 march 2004 in brisbane the brisbane storm wave reached the maximum wave height of 14 3 m wave periods varied between 6 s and 14 s and the computed maximum wavelength was 237 m the largest height of the sumatra tsunami was 3 01 m periods of between 24 min and 61 min were computed for the time between two subsequent peaks the combination of our hydrodynamic considerations with information from a simplified hjulstrom sundborg diagram implies that the most powerful storm and tsunami waves produce conditions near and at the sea bed that allow the transport of sediment grains from decimeters to meters in diameter that means a sandy tsunami deposit in the area of the brisbane tide gauge would be reworked by storm waves assuming the highest wave amplitude during the 2004 march storm at brisbane as such a boundary wave the water depth below which preservation of tsunami deposits is most likely is greater than 65 m

influences of temperature and mg ca ratio on caco3 precipitates from seawater the mg ca ratio at which the calcium carbonate mineral that has pseudohomogeneously precipitated from seawater changes from calcite to aragonite was experimentally determined as a function of temperature results indicate a dramatic change in the critical mg ca ratio over a relatively small temperature range for example in normal seawater with a mg ca of 5 1 the critical temperature is 6 3 c at a temperature of 25 c however mg ca must be less than 1 4 0 1 for calcite to form these data indicate that paleoclimatic conditions at the time of carbonate deposition must be considered when attempting to make inferences about variation in other factors such as paleo p co 2 p pressure and paleo mg ca ratios that may control carbonate mineral formation by abiotic processes however the inverse relation between inferred global paleoclimatic conditions and the dominant type of caco 3 polymorph being abiotically deposited i e warm conditions and low mg calcite versus cool conditions and aragonite suggest that substantial changes must have taken place in ocean chemistry over phanerozoic time

southern carpathian rock glaciers inventory distribution and environmental controlling factors abstract rock glaciers are valuable diagnostic landforms indicating permafrost creeping during their genesis and activity based on the analysis of high quality air orthophoto and field work a first polygon based inventory of rock glaciers from the southern carpathians has been elaborated in total 306 rock glaciers were included in the inventory comprising 79 debris and 227 talus rock glaciers most of these landforms were classified as relict 258 while only 48 covering 2 81 km 2 were considered intact the size of rock glaciers considered as a proxy for past environmental conditions and the relationships with the predictor variables lithology aspect contributing area geographic coordinates elevation and slope range were analysed using bivariate statistics analysis of variance anova and various post hoc tests the statistical analysis revealed that the rock glaciers occurring in the highest mountain ranges in areas composed of granites and granodiorites are considerably larger than the others because their duration of activity is greater strong dependences between rock glacier size and other topographic attributes contributing area aspect and slope range were also confirmed the rock glacier distribution in the southern carpathians is clearly controlled by topography lithology and debris availability the abundance of rock glaciers increases with altitude but their size decreases slightly in mountain units where granites and granodiorites predominate retezat and par ng mountains the density of rock glaciers and the mean specific area covered by these spectacular landforms are considerably higher than in other areas the higher continentality effects of the southern carpathians enabled the formation of rock glaciers at substantially lower elevations than in the alps the mean altitude of intact rock glaciers front which could be used as a morphological indicator of discontinuous permafrost is located at 2088 m

the giant pacific oyster crassostrea gigas as a modern analog for fossil ostreoids isotopic ca o c and elemental mg ca sr ca mn ca proxies 1 modern analogs are an essential part of palaeoclimate studies because they provide the basis for the understanding of geochemical signatures of fossils ostreoids are common in many sedimentary sequences and because of their fast growth high temporal resolution sampling of past seasonal variability is possible here two shell structures of modern giant pacific oysters crassostrea gigas the chalky substance and foliate layers have been sampled for trace element distributions mg sr mn and stable isotope variability c o ca oxygen isotopes exhibit a clear seasonal signature mean carbon isotope values of different oysters agree within 0 1 but ontogenic variability is complicated by shell growth patterns and potential small vital effects the calcium isotope ratios are found to be constant throughout ontogeny within analytical precision at a value of 44 40ca 0 68 0 16 2 sd srm 915a which is consistent with other bivalve species calcium isotope ratios in oyster shell material might thus be a possible proxy for palaeo seawater calcium isotope ratios element ca ratios are significantly higher in the chalky substance than in the foliate layers and especially high sr ca and mn ca ratios are observed for the first growth season of the oysters mg ca ratios in the chalky substance show a negative correlation with 18o values compatible with a temperature dependence whereas this correlation is absent in the foliate layers seasonal changes of sr ca are controlled by metabolic processes whereas for mn ca an additional environmental control is evident

sedimentation earthquakes and tsunamis in a shallow muddy epeiric sea grinnell formation belt supergroup ca 1 45 ga western north america

sequence sequence stratigraphy sea level changes and depositional systems in the cambro ordovician of the north china carbonate platform abstract the cambro ordovician strata in north china were deposited over a very extensive craton extending some 1500 km east west and 1000 km north south the dominantly shallow water carbonate succession reaches up to 2000 m in thickness and two megasequences transgressive regressive cycles can be distinguished lower cambrian through lower ordovician strata and middle through upper ordovician strata separated by a major palaeokarst the first megasequence consists of nine sequences which are generally 50 150 m in thickness the lower cambrian sediments consist of phosphorites and phosphatic sandstones deposited during the flooding of the craton carbonates mudrocks and evaporites were deposited in the early cambrian under an arid climate laying the foundation for the subsequent long period of shallow water carbonate deposition which lasted some 70 m y the middle and lower upper cambrian sequences consist predominantly of mudrocks and storm deposits tempestites in the lower part and oolitic grainstones and tidal flat lime mudstones in the upper part these represent outer mid and mid inner ramp depositional systems respectively of the transgressive and highstand systems tracts these sequences have strong similarities with the grand cycles in the cambro ordovician successions of north america in the upper cambrian there is a distinctive unit of glauconitic purple red mudstone several metres thick which is interpreted as the deposits of the maximum flooding of the first megasequence in the upper cambrian there was a phase of tilting of the north china carbonate platform to the north and storm deposits especially intraclastic conglomerates and hummocky cross stratified grainstones packstones were very common at this time also common in upper middle and lower upper cambrian strata are stromatolitic thrombolitic bioherms several metres in diameter the upper upper cambrian through lower ordovician strata are dominantly fine grained limestones and dolomites deposited in shallow subtidal and inter to supra tidal environments on a low energy epeiric sea platform this part of the succession is the regressive part of the first megasequence so that overall the platform shows an evolution from platform initiation to platform foundation to a ramp depositional system and then an extensive epeiric platform on a small scale the succession is composed of metre scale shallowing upward cycles parasequences arranged into cycle sets of 10 30 m thick the middle upper ordovician megasequence consists mostly of shallow water carbonates with several thick evaporite units minor palaeokarsts and palaeosoils separate the sequences which are composed of metre scale cycles regional uplift affected the north china platform in the ordovician and sedimentation did not resume until the carboniferous there is a good correlation of the two transgressive regressive megasequences described here with the global 2nd order relative sea level curve for the cambro ordovician

aragonite saturation state dynamics in a coastal upwelling zone 1 coastal upwelling zones may be at enhanced risk from ocean acidification as upwelling brings low aragonite saturation state ar waters to the surface that are further suppressed by anthropogenic co2 ar was calculated with ph pco2 and salinity derived alkalinity time series data from autonomous ph and pco2 instruments moored on the oregon shelf and shelf break during different seasons from 2007 to 2011 surface ar values ranged between 0 66 0 04 and 3 9 0 04 compared to an estimated pre industrial range of 1 0 0 1 to 4 7 0 1 upwelling of high co2 water and subsequent removal of co2 by phytoplankton imparts a dynamic range to ar from 1 0 to 4 0 between spring and autumn freshwater input also suppresses saturation states during the spring winter ar is less variable than during other seasons and is controlled primarily by mixing of the water column

monitoring migration rates of an active subarctic dune field using optical imagery we developed a novel method to quantify subtle rates of landscape evolution using two satellite imaging systems with different viewing angles and spectral sensitivities we selected the slowly migrating high latitude subarctic great kobuk sand dunes gksd kobuk valley national park alaska usa for our study the cosi corr technique was used for precise orthorectification co registration and subpixel correlation of satellite data aster visible near infrared vnir and spot panchromatic images with a 5 year temporal separation were correlated to measure the horizontal velocity of the gksd to reduce correlation noise aster vnir bands were linearly mixed to match the spot panchromatic band and raw correlation measurements were projected onto a local robust migration direction to estimate unbiased velocity magnitudes the results show that the most likely migration rate for the gksd ranges from 0 5 to 1 5 m year with peak velocities up to 3 8 m year and uncertainty of approximately 0 16 m year the unprecedented ability to measure slow migration rates including those that may occur over a relatively short time interval illustrates the value of this method to reliably detect and monitor subtle ground movements including dune migration glacier flow mass movements and other small scale processes

styles of early diagenesis and the preservation potential of onshore tsunami deposits a re survey of isla mocha central chile 2 years after the february 27 2010 maule tsunami abstract the style of early diagenesis and preservation of onshore tsunami deposits are poorly constrained only tsunami surveys and subsequent re surveys can fill this information gap here we present the results of a first re survey in 2012 on isla mocha following the original survey in 2010 in the wake of the february 27 2010 maule earthquake and tsunami in central chile as a result of this tsunami a large number of boulders consisting of clay rich fine sandstones representing the miocene age bedrock of the island had been transferred from the tidal to shallow subtidal zone onto the coastal plain coarse clastic sediment mixtures of pebbles granules and sand entrained at coastal plain terraces and transported up to the maximum runup position c 600 m from the coast by the inflow had been left behind as extensive backflow blankets on the lower coastal plain in 2012 vegetation had covered the 2010 tsunami deposits sediment beyond 200 m from the coast had been removed by a combination of surface processes and grazing cattle grain size distributions of the preserved sediment show an increase of the sand fraction at the expense of the coarser grain sizes boulders show patterns resembling mud cracks on the surface and evidence of disintegration into smaller fragments and sand veneers of dried algae documenting the derivation of the boulders from the tidal zones had flaked off partly or completely from most rock surfaces at the northern wind facing coast of the island a c 130 m long and 1 2 m high beach ridge had accumulated most likely from reworked tsunami sediment boulders deposited by tsunamis are commonly assigned a high preservation potential we demonstrate for the first time that such boulders may in fact disintegrate rapidly and disappear from the record over short geological time scales given a lithology susceptible to weathering the degree of modification to the lsla mocha tsunami boulders and deposits strongly questions the applicability of inverse models using paleotsunami deposit thickness and grain size distributions to infer parameters and magnitudes of the causative tsunamis inverse models would consequently underestimate tsunami flow parameters and may result in the inference of erroneous transport modes and event magnitudes our study gives strong evidence in support of re survey studies following the deposition of tsunami sediments by tracing and quantifying the changes affecting them

upper cambrian carbonate platform evolution elvinia and taenicephalus zones pterocephaliid ptychaspid biomere boundary northwestern wyoming abstract the pterocephaliid ptychaspid biomere boundary is an upper cambrian extinction horizon that can be used to correlate mixed carbonate siliciclastic strata in northwestern wyoming the biomere boundary is defined by the change between the elvinia and taenicephalus zones of the standard north american trilobite zonation it is also signaled chemostratigraphically by a positive trend in carbon isotope ratios thus both biostratigraphic horizons and carbon isotope data are used to constrain the position of the biomere boundary in northwestern wyoming study of 21 stratigraphic sections reveals the presence of distinct facies belts for the middle and upper elvinia zone and lower taenicephalus zone these are interpreted to reflect deposition in three distinct paleoenvironments 1 oolitic shoal 2 intrashelf basin and 3 inner platform margin following a major hiatus in sedimentation in wyoming during much of pterocephaliid biomere time a healthy shallow water carbonate factory was reestablished during elvinia zone time this produced abundant deposits of oolitic and skeletal packstone in the shoal environment and an areally extensive thrombolite boundstone facies in the intrashelf basin setting approximately coincident with the biomere boundary extinction event irvingella major time ooid production was terminated and the thrombolites were drowned the correlation of this major change in the pattern of sedimentation allows for the recognition of parts of two depositional sequences in the study area this drowning event sequence boundary may also be coeval with the accumulation of transported shallow water carbonate deposits in an inner platform margin environment during early taenicephalus zone time sedimentation rates were apparently reduced and the entire study area is marked by thin concentrations of trilobite and brachiopod shells the nonskeletal carbonate factory was never reestablished in the former shoal environment where thick successions of homogeneous lime mud accumulated during the rest of taenicephalus zone time flat pebble conglomerate and shale accumulated in the storm influenced intrashelf basin during this time sea level change and changes in seawater chemistry likely both played roles in the drowning event across the elvinia taenicephalus boundary a positive trend in carbon isotope values across the pterocephaliid ptychaspid biomere boundary is observed in the six sections analyzed this is consistent with previous studies that indicated that the mass extinction occurs within a regional shift towards positive values and this may reflect the development of low oxygen conditions on the shelf the global significance of these isotopic trends changes in relative sea level and the mass extinction has not been confirmed although recent study of the extinction event at the base of the pterocephaliid biomere has revealed a similar trend towards positive carbon isotope values that is worldwide

scale of tsunami generated sedimentary structures in deep water to date no attempt has been made to explore possible constraints on maximum water depths for tsunami generated sedimentary structures of various sediment grain sizes in terms of estimated wavelength and amplitude of potential bedforms this paper explores some possible quantitative limits on threshold velocities for sediment movement at specified water depths assuming airy wave theory which treats tsunami waves as shallow water small amplitude long wavelength waves such a treatment suggests that the passage of tsunami waves is unlikely to entrain sediment coarser than line sand to coarse silt in water depths in excess of 200 mm although fraught with theoretical difficulties and a lack of observations of modern sedimentary bedforms attributable to known tsunamis this paper is presented to stimulate debate rather than provide definitive answers

the intensity duration and severity of low aragonite saturation state events on the california continental shelf 1 ocean acidification will progress in an episodic manner yet this has rarely been considered here we investigate how the intensity duration and severity of episodic low aragonite saturation state events along the california continental shelf have changed since 1750 and how they might change up to 2050 under the a2 scenario from the special report on emissions scenarios by the intergovernmental panel on climate change our model based results suggest that between 1750 and 2010 aragonite undersaturation events along the shelf have quadrupled in their number and lengthened in duration but that even larger changes are bound to occur within the next 20 to 40 years undersaturation will become very likely the norm near the seafloor by 2030 and if atmospheric co2 increases beyond 500 ppm this layer will become permanently undersaturated combined with a fourfold increase in intensity the resulting increase in severity of low aragonite saturation state events will substantially affect the viability of calcifying organisms and will alter ecosystem structure

late pleistocene glacial chronology of the pietrele valley retezat mountains southern carpathians constrained by 10be exposure ages and pedological investigations abstract the southern carpathians are located in the transition zone between mediterranean and continental climates and constituted the major areas of ice accumulation in the carpathians during pleistocene glaciations an absolute glacial chronology had not yet been established in this study we constrain the glacial history of the pietrele valley in the retezat mountains located in the southern carpathians and find that the timing of the late wurmian glacial advance is asynchronous to global climate records likely reflecting changes in moisture availability in the area the former ice extent of two major glacial advances m1 or lolaia glacial advance and m2 or capra judele glacial advance in the valley was reconstructed based on mapping and surveying of glacial features field relations and different pedological weathering indicators of till imply that the m1 glacial advance occurred well before the global last glacial maximum lgm its deposition during the penultimate glaciation is unlikely no boulders suitable for exposure dating were found on m1 moraines seventeen exposure ages show that the moraines of the maximum late wurmian m2 glacial advance were abandoned around 16 1 1 6 ka another late glacial advance m3 or stevia advance occurred during the younger dryas chron as constrained by two exposure ages we suggest that the glacial advance that occurred during the time of the global lgm was less extensive than the m2 glacial advance and the deposits were overrun by the lateglacial m2 glacier as we found no field evidence of glacial deposits between the m1 and the m2 moraines we explain this obvious asynchronity of the local late wurmian ice extent with that of global records of ice accumulation with increased aridity in the carpathians during the global lgm due to a lower sea level the reconstructed late pleistocene equilibrium line altitude ela shows a distinct increase in the trend from the alps and the bavarian forest to the carpathians in comparison to the modern ela this finding supports the high aridity in the study area during the late pleistocene two distinct lateglacial moraines were deposited during times of reported colder and wetter climatic conditions around the north atlantic heinrich events h0 and h1

storms versus tsunamis dynamic interplay of sedimentary diagenetic and tectonic processes in the cambrian of montana the upper cambrian deadwood formation of north central montana is composed mainly of fine grained calcareous sandstone and intercalated silty shale and contains scattered intraclastic flat pebble conglomerate these rocks typical of many mixed carbonate siliciclastic subtidal shelf successions of proterozoic through early ordovician age are distal storm deposits in which the conglomerates are conventionally thought to record occasional very high energy events that scoured incipiently cemented layers in the deadwood formation most sandstone beds have a linear to crudely reticulate pattern of vertical cracks filled with injected silt and clay the cracks exhibit a consistent northwest southeast trend and are very shallow burial deformation structures caused by the passage of seismic waves possibly originating from strong earthquakes in idaho most conglomerates are composed of angular to subangular sandstone intraclasts the polygonal plan view of which is similar in outline to the areas between cracks in the sandstones the deformation implied by the cracks sporadic distribution of conglomerates high degree of scouring indicated and angularity of the intraclasts argue that rather than storms the conglomerates were generated by occasional tsunamis the sweep of these tsunamis across the shallow intracratonic sea created extraordinarily strong oscillating bottom currents at the deeper reaches of storm wave base tsunamites are therefore identified with confidence virtually for the first time in shallow subtidal shelf deposits

climatic implications of cirque distribution in the romanian carpathians palaeowind directions during glacial periods the many glacial cirques in the mountains of romania indicate the distribution of former glacier sources related to former climates as well as to topography in the transylvanian alps southern carpathians cirque floors rise eastward at 0 714 m km 1 and cirque aspects tend ene confirming the importance of winds from some westerly direction there is a contrast between two neighbouring ranges the fa ga ras where the favoured aspect of cirques is ene and the iezer where the tendency is stronger and to nne this can be explained by the iezer mountains being sheltered by the fa ga ras which implies precipitation bearing winds from north of west at times of mountain glaciation palaeoglaciation levels also suggest winds from north of west which is consistent with aeolian evidence from pleistocene dunes yardangs and loess features in the plains of hungary and south western romania in northern romania including ukrainian maramures the influence of west winds was important but sufficient only to give a northeastward tendency in cirque aspects this gave stronger asymmetry than in the transylvanian alps as the northward solar radiation incidence tendency in these marginally glaciated mountains was less diluted by wind effects cirque floors in northern romania are lower also in northeast facing cirques in general cirque aspects result from several factors and the mean tendency is not downwind but is displaced from poleward by wind and by minor effects copyright 2010 john wiley sons ltd

osl dating and gpr mapping of palaeotsunami inundation a 4000 year history of indian ocean tsunamis as recorded in sri lanka to evaluate and mitigate tsunami hazard as long as possible records of inundations and dates of past events are needed coastal sediments deposited by tsunamis tsunamites can potentially provide this information however of the three key elements needed for reconstruction of palaeotsunamis identification of sediments dating and finding the inundation distance the latter remains the most difficult the existing methods for estimating the extent of a palaeotsunami inundation rely on extensive excavation which is not always possible here by analysing tsunamites from sri lanka identified using sedimentological and paleontological characteristics we show that their internal dielectric properties differ significantly from surrounding sediments the significant difference in the value of dielectric constant of the otherwise almost indistinguishable sediments is due to higher water content of tsunamites the contrasts were found to be sharp and not to erode over thousands of years they cause sizeable electromagnetic wave reflections from tsunamite sediments which permit the use of ground penetrating radar gpr to trace their extent and morphology in this study of the 2004 boxing day indian ocean tsunami we use gpr in two locations in sri lanka to trace four identified major palaeotsunami deposits for at least 400 m inland investigation inland was constrained by inaccessible security zones the subsurface extent of tsunamites not available without extensive excavation provides a good proxy for inundation the deposits were dated using the established method of optically stimulated luminescence osl this dating partly corroborated by available historical records and independent studies contributes to the global picture of tsunami hazard in the indian ocean the proposed method of combined gpr osl based reconstruction of palaeotsunami deposits enables estimates of inundation recurrence and therefore tsunami hazard for any sandy coast with identifiable tsunamite deposits the method could be also used for anchoring and synchronizing chronologies of ancient civilisations adjacent to the ocean shores

rock glacier dynamics in southern carpathian mountains from high resolution optical and multi temporal sar satellite imagery the dynamics of rock glaciers in marginal periglacial environments are poorly understood especially in eastern europe where the enhanced continentality produces a distinct pattern of periglacial phenomena multi temporal image analysis of high resolution optical and radar satellite imagery of the southern carpathian mountains romania revealed the small dynamic nature and a slow geomorphologic evolution of rock glaciers over a 46 yr period of record 1968 2014 nine rock glaciers located in glacial cirques and troughs within the central area of retezat mountain were included in this study overall the estimated displacement rates are extremely low i e a few cm year compared with other active rock glaciers from all over the world despite their relative attenuated activity it appears that judele valea rea and pietrele are still active rock glaciers but in an evident disequilibrium imbalance with the actual climate these findings document the lowest altitude and easternmost active rock glaciers at this latitude from europe quantitative investigations were concentrated on pietrele rock glacier subject of recent field campaigns optical data analysis indicated a slight acceleration of the horizontal velocities at the surface of pietrele rock glacier in recent years this acceleration appears to be caused by an increase in the temperature of permafrost resulting from an evident warming of external air temperature radar data analysis suggested seasonal variability of surface motion with higher deformation in autumn whereas in early summer or spring the deformation is negligible overall the results obtained with cross correlation analysis interferometric synthetic aperture radar insar coherence analysis and small baseline subset sbas multitemporal interferometry are consistent displaying similar deformation patterns with the highest creep rates located in the southern and western portions of the glacier these findings are supported by thermal and geophysical measurements which suggest the probable presence of permafrost within these areas the observed displacements were interpreted as permafrost creep and their very low velocity rates suggest the deforming frozen layers are very thin these results provide i baseline information and decadal scale trends and a ii strategy for future monitoring of the health and integrity of the rock glacier environment in the carpathian mountains

estimates of large magnitude late cambrian earthquakes from seismogenic soft sediment deformation structures central rocky mountains a variety of unusual early post depositional deformation structures exist in grainstone and flat pebble conglomerate beds of upper cambrian strata western colorado including slide scarps thrusted beds irregular blocks and internally deformed beds thrusted beds up to tens of centimetres thick record thrust movement of a part of a bed onto itself along a moderate to steeply inclined 15 to 40 ramp locally producing hanging wall lenses with fault bend geometries thrust plane orientations are widely distributed and in some cases nearly oppositely oriented in close proximity indicating that they did not form as failures acted upon by gravity forces irregular bedded to internally deformed blocks are isolated on generally flat upper bedding surfaces these features represent parts of beds that detached moved up onto and some distances across the laterally adjacent undisturbed bed surfaces deformation of thin intervals of mud on the ocean floor by moving blocks rules out the possibility of storm induced deformation because the mud was not eroded by high shear stresses that would accompany the extremely large forces required to produce and move the blocks finally internally deformed beds are characterized by large blocks fitted fabrics of highly irregular fragments and contorted lamination which represent heterogeneous deformation such as brecciation and liquefaction the deformation structures were produced by earthquakes linked to the reactivation of mesoproterozoic crustal scale shear zones in the central rockies during the late cambrian analysis of the deformation structures indicates very large body forces and calculated earthquake generated ground motion velocities of ca 1 6 m sec 1 these correspond to moment magnitudes of ca 7 0 or more and a mercalli intensity of x these are the only known magnitude estimates of phanerozoic other than quaternary large intensity earthquakes for the rocky mountain region and they are as large as or larger than previous estimates of proterozoic earthquakes along these major shear zones of the central rockies

sedimentology of the december 26 2004 sumatra tsunami deposits in eastern india tamil nadu and kenya the december 26 2004 sumatra tsunami caused severe damage at the coasts of the indian ocean we report results of a sedimentological study of tsunami run up parameters and the sediments laid down by the tsunami at the coast of tamil nadu india and between malindi and lamu kenya in india evidence of three tsunami waves is preserved on the beaches in the form of characteristic debris accumulations we measured the maximum run up distance at 580 m and the maximum run up height at 4 85 m flow depth over land was at least 3 5 m the tsunami deposited an up to 30 cm thick blanket of moderately well to well sorted coarse and medium sand that overlies older beach deposits or soil with an erosional unconformity the sand sheet thins inland without a decrease of grain size the deposits consist frequently of three layers the lower one may be cross bedded with foresets dipping landward and indicating deposition during run up the overlying two sand layers are graded or parallel laminated without indicators of current directions thus it remains undecided whether they formed during run up or return flow thin dark laminae rich in heavy minerals frequently mark the contacts between successive layers benthic foraminifera indicate an entrainment of sediment by the tsunami from water depths less than ca 30 m water depth on the indian shelf these depths are present at distances of up to 5 km from the coast in kenya only one wave is recorded which attained a run up height of 3 m at a run up distance of ca 35 m from the tidal water line at the time of the tsunami impact only one layer of fine sand was deposited by the tsunami it consists predominantly of heavy minerals supplied to the sea by a nearby river the sand layer thins landward with a minor decrease in grain size benthic foraminifera indicate an entrainment of sediment by the tsunami from water depths less than ca 30 m water depth reaching down potentially to ca 80 m the presence of only one tsunami related sediment layer in kenya but three in india reflects the impact of only one wave at the coast of kenya as opposed to several in india grain size distributions in the indian and kenyan deposits are mostly normal to slightly positively skewed and indicate that the detritus was entrained by the tsunami from well sorted pre tsunami deposits in nearshore swash zone and beach environments

shallow marine tsunami deposits in teluk banten nw java indonesia generated by the 1883 krakatau eruption teluk banten tb is a tropical shallow marine embayment with coral reef islands close to the krakatau volcanic complex the 1883 krakatau eruption generated a tsunami which had a devastating effect on the neighboring coastal areas the effects of the 1883 krakatau eruption and the associated tsunami on the bottom sediments in tb are assessed using textural compositional and 210 pb geochronological data an important diagnostic criterion consists of the occurrence of tephra conform descriptions of the 1883 eruption tephra the tsunamite consists of a sandy layer with abundant reworked shell and other carbonate fragments coarse components in the tsunamite consist of locally derived material eroded from the seabed land derived components are incorporated in the tsunamite only in close proximity to the coast the tsunamite is thickest in localized areas of the central part of the bay along the northern open sea facing slope of tb the tsunamite is relatively thin 6 7 cm thick but well preserved as little postdepositional modifications have occurred in the eastern bay area recent erosion since the redirection of the ciujung river in the 1920s has removed the krakatau tsunamite along the west coast of tb the only signature of the 1883 krakatau eruption consists of tephra and evidence for a high energy event is lacking presumably the western area was sheltered from the tsunami wave coming from the northwest at the shallower stations with low accumulation rates the tephra has been thoroughly mixed by bioturbation 2003 elsevier science b v all rights reserved

strong kinetic effects on sr ca ratios in the calcitic bivalve pecten maximus although sr ca ratios in abiogenic calcite are strongly controlled by precipitation rates such a kinetic effect has never been demonstrated in calcitic bivalve shells therefore we report sr ca ratios together with daily growth rates in the calcitic shells of four individuals of the bivalve pecten maximus age class i ratios of sr ca were found to be variable among individuals that grew at the same location illustrating that vital effects dominate over environmental controls although daily growth rate was correlated with shell sr ca ratios it explained only half of the sr ca variations however daily shell surface area increment an estimation of the total quantity of carbonate precipitated for a given time explained 74 of the sr ca variability in the shells of p maximus this proves for the first time in a calcitic bivalve that shell sr ca partitioning is mainly controlled by kinetic effects the sr ca ratio should therefore be tested as a potential proxy of calcification rate in modern or fossil calcitic biocarbonates

seismites in the mesoproterozoic altyn formation belt supergroup montana a test for tectonic control of peritidal carbonate cyclicity the mesoproterozoic altyn formation of western montana contains abundant seismites that record the physical state of the sediment at the time of earthquake induced ground motion earthquakes were likely generated by normal faulting during subsidence because part of the altyn is composed of cyclic upward shallowing peritidal carbonates it may afford an opportunity to test whether spasmodic subsidence provides a viable mechanism for the episodic generation of the requisite accommodation space at cycle tops no stratigraphic relation between the seismites and peritidal cycles is perceived however so it appears that this process may not be a control of cyclicity

stratigraphic control of rare earth pattern types in mid proterozoic sediments of the belt supergroup montana u s a implications for basin analysis abstract within sediments of the helena embayment an eastern extension of the mid proterozoic belt basin montana u s a three different types of ree patterns were identified the lower part of the investigated sequence chamberlain shale and lower newland formation is a uniform shale interval which accumulated during a period of tectonic quiescence the ree patterns of these shales normalized to nasc are either flat or lree enriched lacking eu deficiencies the superjacent unit newland transition zone contains variable amounts of feldspathic sandstone it indicates rejuvenation of the hinterland and regression the uppermost unit upper newland formation consists of alternating packages of carbonates and shales ree patterns in shales of the newland transition zone and upper newland formation have negative eu anomalies this drastic change of ree patterns was observed in all stratigraphic sections the source rocks of the beltian sequence were probably dominated by granitoid gneisses and migmatites and rocks of this composition show negative eu anomalies against nasc in many other places the observed negative eu anomalies in the shales were probably inherited from the source rocks however the patterns of the chamberlain shale and the lower newland formation are not as easy to explain because the source rocks seem not to have changed during deposition of the beltian sequence perhaps more intense chemical weathering during chamberlain shale lower newland time obscured the negative eu anomalies in the residual clays adsorption of lree s on clays during transport may have caused the lree enriched patterns a change in tectonic regime and weathering intensity coincides with the stratigraphic distribution of the different ree pattern types thus stratigraphically controlled ree pattern distribution in a sedimentary basin may help to establish quasi time lines and may allow monitoring of tectonic pulses and of weathering conditions in the hinterland

mechanisms to explain the elemental composition of the initial aragonite shell of larval oysters calcifying organisms face increasing stress from the changing carbonate chemistry of an acidifying ocean particularly bivalve larvae that live in upwelling regions of the world such as the coastal and estuarine waters of oregon usa arguably the first and most significant developmental hurdle faced by larval oysters is formation of their initial prodissoconch i pdi shell upon which further ontological development depends we measured the minor metal compositions sr ca mg ca of this aragonitic pdi shell and of post pdi larval crassostrea gigas shell as well as the water they were reared in over 20 days for a may and an august cohort in 2011 during which time there was no period of carbonate under saturation after testing various methods we successfully isolated the shell from organic tissue using a 5 active chlorine bleach solution elemental compositions sr mg c n of the shells post treatment showed that shell sr ca ranged from 1 55 to 1 82 mmol mol mg ca from 0 60 to 1 11 mmol mol similar to the few comparable published data for larval oyster aragonite compositions we compare these data in light of possible biomineralization mechanisms an amorphous calcium carbonate acc path an intercellular path and a direct from seawater path to shell formation via biologically induced inorganic precipitation of aragonite the last option provides a mechanistic explanation for 1 the accelerated precipitation rates of biogenic calcification in the absence of a calcifying fluid 2 consistently elevated precipitation rates at varying ambient water saturation states and 3 the high ca selectivity of the early larval calcification despite rapid precipitation rates

impact of sample pretreatment on the measured element concentrations in the bivalve arctica islandica correlating metal to calcium me ca ratios of marine biogenic carbonates such as bivalve shells to environmental parameters has led to contradictory results biogenic carbonates represent complex composites of organic and inorganic phases some elements are incorporated preferentially into organic phases and others are incorporated into inorganic phases chemical sample pretreatment to remove the organic matrix prior to trace element analysis may increase the applicability of the investigated proxy relationship though its efficiency and side effects remain questionable we treated inorganic calcium carbonate and bivalve shell powder arctica islandica with eight different chemical treatments including h2o2 naoh naocl and acetone and analyzed the effects on 1 me ca ratios sr ca mg ca ba ca and mn ca 2 organic matter n content and 3 mineralogical composition of the calcium carbonate the different treatments 1 cause element and treatment specific changes of me ca ratios 2 vary in their efficiency to remove organic matter and 3 can even alter the phase composition of the calcium carbonate e g formation of ca oh 2 during naoh treatment among all examined treatments there were none without any side effects in addition certain me ca changes we observed upon chemical treatment contradict our expectations that lattice bound elements sr and ba should not be affected whereas non lattice bound elements mg and mn should decrease upon removal of the organic matrix for instance we observe that naocl treatment did not alter sr ca ratios but caused unexpected changes of the mg ca ratios the latter demonstrates that the buildup of complex biogenic composites like the shell of arctica islandica are still poorly understood

molar tooth structure in proterozoic carbonate rocks origin from synsedimentary earthquakes and implications for the nature and evolution of basins and marine sediment proterozoic argillaceous lime mudstones commonly contain molar tooth structure a curious synsedimentary feature consisting of crumpled generally vertically oriented veins filled with calcite microspar long enigmatic these veins are interpreted here as earthquake induced deformation structures a model is proposed whereby violent ground motion caused shrinkage dewatering and fissuring of the colloidal sea floor sediment of clay and lime mud a slurry of equant particles of lime mud segregated from the clay platelets trapped in the matrix was expelled into these voids the host bed underwent as much as 80 compaction as well as shear causing the lime mud filled fissures to be ptygmatically folded and shingled both vertically and horizontally and in places pulled apart this lime mud lithified rapidly by high mg calcite grain growth such that subsequent earthquakes shattered the folded veins in the belt basin of western north america tsunamis from different events created currents that transported ooids and coarse sand from shoals into deeper water and scoured deeply into the now consolidated sediment leaving behind a lag of vein fragments molar tooth structure is a signature of basin tectonism recorded specifically in argillaceous lime mudstones deposited in low energy settings above the thermocline in supersaturated marine water syneresis cracks are the counterpart in terrigenous facies in that silt and sand were injected into the shrinkage fissures this process points to the importance of seismically induced compaction under negligible burial smectite might have made up a significant proportion of the sediment making it more conducive to shrinkage the absence of molar tooth structure in phanerozoic strata is ascribed mainly to changes in sediment rheology brought about by increased organic binding due to diversification of the microbiota

tsunami deposits in holocene bay mud in southern kanto region pacific coast of central japan abstract tsunami have probably deposited sand sheets that are intercalated in holocene bay floor mud exposed on the boso and miura peninsulas facing the convergent boundary of the pacific philippine sea and eurasian plates we have identified seven sand sheets at four drowned valleys and correlated these by 137 radiocarbon dates of shells and wood the sheets consist of poorly sorted muddy sand and well sorted sand layers in fining upward sequences containing abundant transported shells rip up clasts and wood fragments the sheets erosionally overlie bioturbated bay floor mud that contains molluscan shells in life position most of the sheets are less than 20 cm thick and rarely more than 50 cm thick some molluscan shells are older in these layers than in underlying mud both landward and seaward paleocurrents are shown in a few cases by imbrication of shells and by low angle wedge shaped lamination at least five of the sand sheets contain molluscan fossils derived from rocky coasts or shore platforms although they intercalated in mud deposited within bays at depths of 10 15 m two other sand sheets are dominated by open seashore ostracode assemblages although they were deposited in the brackish inner bay and muddy central bay five of the layers may correlate with emergences recorded by nearby holocene marine terraces these correlations suggest that great earthquakes triggered the inferred tsunami the tsunami occurred at intervals of 300 2000 years beginning about 10 000 years ago

calcitic aragonitic and mixed calcitic aragonitic ooids from the mid proterozoic belt supergroup montana a great variety of ooid types occurs within the siyeh and snowslip formations of the mid proterozoic belt supergroup montana cortical layers are inferred to have been composed either of calcite in a radial concentric or radial with dark rays fabric or aragonite in a radial or concentric fabric the calcitic cortical layers record their original fabrics but the originally aragonitic cortical layers have been replaced by calcite in a range of textures and by quartz and dolomite some formerly aragonitic cortical layers are replaced by calcite spar which contains relics of the original cortical structure others consist of calcite spar without inclusions or columnar calcite which grew radially from the nucleus commonly a calcitic ooid some ooids were wholly composed of calcite others were of aragonite but two phase ooids were common mostly consisting of an inner calcitic part and an outer aragonitic part probable microdolomite inclusions suggest a high mg content of the calcitic cortical layers the depositional environment of these oolites was probably analogous to baffin bay texas where a similar range of ooid types is forming today

geomorphic evolution of a storm dominated carbonate ramp c 549 ma nama group namibia the well exposed hoogland member c 549 ma of the northern nama group kuibis subgroup namibia represents a storm dominated carbonate ramp developed in a foreland basin of terminal proterozoic age the ramp displays facies gradients involving updip grainstones which pass downdip into broad spatially extensive tracts of microbial laminites and finely laminated mudstones deposited above and below storm wave base trough cross bedded coarse grainstones are shown to transit downdip into finer grained calcarenites irregular microbial laminites and mottled laminites siliciclastic siltstones and shales were deposited further downdip platform growth was terminated through smothering by orogen derived siliciclastic deposits ramp morphology was controlled by several different processes which acted across many orders of magnitude millimetres to kilometres including in situ growth of mats and reefs scouring by wave produced currents and transport and infilling of coarse grained carbonates and fine grained carbonates and clastics at the smallest scale roughening of the sea floor through heterogeneous trapping and binding by microbial mats was balanced by smoothing of the sea floor through accumulation of loose sediment to fill the topographic lows within the upward propagating mat at the next scale up parasequence development involved roughening of the sea floor through shoal growth and grainstone progradation balanced by sea floor smoothing through shale infilling of resulting downdip accommodation as well as the metre scale topographic depressions within the mosaic of shoal water facies at even larger sequence platform scales roughening of the sea floor occurred through aggradation and progradation of thick carbonates balanced by infilling of the foreland basin with orogen derived siliciclastic sediments at all scales a net balance was achieved between sea floor roughening and sea floor smoothing to maintain a more or less constant ramp profile

sedimentology of rocky shorelines 3 hydrodynamics of megaclast emplacement and transport on a shore platform oahu hawaii abstract megaclasts of well cemented coralgal limestone have been emplaced onto a shore platform by large waves on the north shore of oahu hi emplacement and movements of the largest ca 96 ton megaclast have been dated using aerial photographs hydrodynamic forces at the low submerged shoreline cliff are computed using design wave characteristics based on linear wave theory and experimental results considering the local wave climate and near shore bottom topography force exerted by a tsunami has been estimated based on the 1946 aleutian tsunami the computed forces are evaluated in terms of the initial fracturing along a given failure plane that is required in order for the detachment to occur the analysis shows that tsunami as well as large swell waves are capable of quarrying the megaclast provided that sufficient initial fracturing is present dislodgement and emplacement most likely occurred in a sequence during impact of a single wave on the shoreline cliff swell waves however are seldom capable of emplacing large blocks onto the platform due to their rapid disintegration after breaking so that most blocks quarried from the cliff edge fall back onto the submarine terrace emplacement of large boulders seems to require extreme sea waves with periods longer than storms or north pacific swells usually produce transport mechanisms on the shore platform vary depending on megaclast shape sliding is a common mechanism of transport for larger and irregular megaclasts whereas somewhat smaller and platy megaclasts are occasionally found in overturned positions

neoproterozoic tsunamiite upper bhander sandstone central india abstract this paper addresses a distinctive event bedset encased by coastal erg margin deposits at a preferred stratigraphic level near the base of the neoproterozoic upper bhander sandstone in central india the bedset is composed of couplets of sandstone beds that exhibit incisive amalgamation although they differ in geometry structures at soles within and at tops of beds vertical grain size variation as well as palaeocurrent pattern and direction the wide extent of the bedset is evident from several exposures spread over a distance of more than 50 km roughly in strike parallel direction flow and depositional dynamics interpreted from the coupled event beds are more consistent with a tsunami origin than alternative palaeogeography compatible models of climate induced storm flash flood or accentuated tide deposits a palaeotsunamiite model is thus discussed with separate incoming and outgoing components considering the overall depositional setting to be an epeiric sea coast in an intracratonic sag basin the relevant bedset is inferred to reflect the record of a teletsunamiite it would also be one of the very few precambrian tsunamiites known so far exceptional preservation of this possible tsunamiite was facilitated by sheltered deposition behind the backshore zone and the berm as well as by rapid burial by wind deflated sands and advancing aeolian dunes