introduction to the special issue the formation and evolution of ceres occator crater abstract ceres the largest body in the asteroid belt was explored from orbit for the first time by the dawn mission the 92 km diameter occator crater contains bright regions or faculae which are one of the most remarkable discoveries of dawn s exploration of ceres a pit within the center of the crater contains both the cerealia facula and a central dome the vinalia faculae are located in the eastern crater floor occator s faculae are composed mostly of sodium carbonate and their single scattering albedo is the highest of any material on ceres surface the faculae do not occur in other impact craters on ceres and occator s extensive interior lobate materials are unusual understanding the driving forces behind the formation of occator crater and its faculae has the potential to lead us to a new understanding of the processes and conditions in ceres past and to possibly provide constraints about the present day internal state in this special issue we present a variety of investigations which use dawn data theoretical modeling and laboratory experiments to investigate occator crater and its faculae the results of these investigations are summarized and synthesized in the final paper of this collection herein we introduce ceres and the dawn mission and summarize the geophysical geological mineralogical and geochemical properties of ceres as derived from dawn data we also discuss the regional setting of occator crater and introduce occator crater itself

sulfur isotope evidence for widespread euxinia and a fluctuating oxycline in early to middle ordovician greenhouse oceans article i nfo despite marine geochemical records indicating widespread oxygenation of the biosphere in the terminal neoproterozoic era late cambrian records point to the persistence of deep water anoxia and potential for development of euxinic conditions the late cambrian spice steptoean positive carbon isotope excursion event however is a globally recognized chemostratigraphic marker that likely represents significant organic carbon burial and subsequent liberation of oxygen to the biosphere here we present high resolution carbon and sulfur isotope profiles from early to middle ordovician carbonate rocks from the argentine precordillera and western newfoundland to constrain oceanic redox conditions in the post spice world marine c isotope profiles record relatively stable behavior excursions b3 that is characteristic of greenhouse climates ma rine s isotope profiles record short term b10 6 yr rhythmic variation superimposed over a longer term

the end permian mass extinction a rapid volcanic co2 and ch4 climatic catastrophe abstract the end of the permian was a time of crisis that culminated in the earth s greatest mass extinction there is much speculation as to the cause for this catastrophe here we provide a full suite of high resolution and coeval geochemical results trace and rare earth elements carbon oxygen strontium and clumped isotopes reflecting ambient seawater chemistry and water quality parameters leading up to the end permian crisis preserved brachiopod low mg calcite based seawater chemistry supplemented by data from various localities documents a sequence of interrelated primary events such as coeval flows of siberian trap continental flood basalts and emission of carbon dioxide leading to warm and extreme greenhouse conditions with sea surface temperatures sst of 36 c for the late permian although anoxia has been advanced as a cause for the mass extinction most biotic and geochemical evidence suggest that it was briefly relevant during the early phase of the event and only in areas of upwelling but not a general cause instead we suggest that renewed and increased end permian siberian trap volcanic activity about 2000 years prior to the extinction event released massive amounts of carbon dioxide and coupled with thermogenic methane emissions triggered extreme global warming and increased continental weathering eventually these rapidly discharged greenhouse gas emissions less than 1000 years before the event ushered in a global hothouse period leading to extreme tropical ssts of 39 c and higher based on these sea surface temperatures atmospheric co 2 concentrations were about 1400 ppmv and 3000 ppmv for the late and end permian respectively leading up to the mass extinction there was a brief interruption of the global warming trend when sst dropped concurrent with a slight but significant recovery in biodiversity in the western tethys it is possible that emission of volcanic sulfate aerosols resulted in brief cooling just after the onset of intensified warming during the end of the permian after aerosol deposition global warming resumed and the biotic decline proceeded and was accompanied by suboxia in places of the surface ocean which culminated in the greatest mass extinction in earth history

effects of orientation on acoustic scattering from antarctic krill at 120 khz abstract backscattering measurements of 14 live individual antarctic krill euphausia superba were made at a frequency of 120 khz in a chilled insulated tank at the long marine laboratory in santa cruz ca individual animals were suspended in front of the transducers were only loosely constrained had substantial freedom to move and showed more or less random orientation one thousand echoes were collected per animal orientation data were recorded on video the acoustic data were analyzed and target strengths determined from each echo a method was developed for estimating the three dimensional orientation of the krill based on the video images and was applied to five of them giving their target strengths as functions of orientation scattering models based on a simplified distorted wave born approximation dwba method were developed for five animals and compared with the measurements both measured and modeled scattering patterns showed that 120 khz acoustic scattering levels are highly dependent on animal orientation use of these scattering patterns with orientation data from shipboard studies of e superba gave mean scattering levels approximately 12 db lower than peak levels these results underscore the need for better in situ behavioral data to properly interpret acoustic survey results a generic e superba dwba scattering model is proposed that is scalable by animal length with good orientation information this model could significantly improve the precision and accuracy of krill acoustic surveys

high resolution 87sr 86sr chemostratigraphy of the silurian implications for event correlation and strontium flux analyses of 87sr 86sr in silurian conodonts recovered from localities in north america and europe representing 13 of the 14 defined silurian conodont zones provide a high resolution record of seawater chemistry for the silurian period these data which are characterized by little or no scatter depict several high frequency cycles superimposed on a gradual longer term rise in 87sr 86sr for the silurian high frequency cycles have a duration of about one conodont zone and many correlate with sequence boundaries recognized around the world these data provide a much higher resolution image of secular changes in 87sr 86sr during the silurian and may require a rethinking of models of strontium isotope flux in marine basins

the ac 5 fejokoo quadrangle of ceres geologic map and geomorphological evidence for ground ice mediated surface processes abstract nasa s dawn spacecraft arrived at ceres on march 6 2015 and has been studying the dwarf planet through a series of successively lower orbits throughout these mission phases dawn obtained photographic mineralogical elemental abundance and gravity data ceres is the largest object in the asteroid belt with a mean diameter of 940 km the dawn science team conducted a geologic mapping campaign for ceres similar to the one that was implemented on the asteroid vesta dawn s previous target including production of a survey and high altitude mapping orbit hamo based global map and a series of 15 low altitude mapping orbit lamo based quadrangle maps in this paper we present the lamo based geologic map of the ac 5 fejokoo quadrangle 21 66 n and 270 360 e and discuss its implications the ac 5 quadrangle is primarily composed of ancient cratered terrain punctuated with several moderately fresh impact craters of geologic interest six large tholi that are possibly cryovolcanic in origin and an abundance of flows that well represent the full spectrum of mass wasting features observed on ceres the fejokoo quadrangle hosts the majority of oxo crater the site of the first spectroscopic detection of h2o ice on the surface of ceres the h2o detection is closely related to two distinctive morphological units interpreted as possible high water ice content landslides these observations and interpretations are consistent with ground ice mediated surface processes on ceres

the geology of the kerwan quadrangle of dwarf planet ceres investigating ceres oldest largest impact basin abstract we conducted a geologic mapping investigation of dawn spacecraft data to determine the geologic history of the kerwan impact basin region of dwarf planet ceres which is mostly located in the ac 7 kerwan quadrangle geological mapping was applied to dawn framing camera images from the low altitude mapping orbit lamo 35 m pixel and supplemented by digital terrain models and color images from the high altitude mapping orbit hamo 135 m pixel as well as preliminary visible and infrared spectrometer vir and gravity data the 284 km diameter kerwan impact basin is the oldest unequivocal impact crater on ceres and has a highly discontinuous polygonal degraded rim and contains a smooth unit that both fills the basin floor and surrounds the degraded rim to the west south and east although there are some subtle topographic features in the kerwan basin that could be interpreted as flow boundaries there is no indisputable evidence of cryovolcanic features in or around the basin however if such features existed they could be buried nevertheless all data point to impact induced melting of a cerean crust enriched in a volatile likely water ice to produce the kerwan smooth material subsequent geologic activity in this region includes emplacement of impact craters such as dantu which produced a variety of colorful deposits and rayed craters such as rao and cacaguat based on the crater size frequency distribution absolute model ages of the kerwan smooth material in and around the basin marking a minimum age for the kerwan basin our mapping defines this as the oldest boundary within the cerean geologic timescale separating the pre kerwanan and kerwanan periods at 1 3 ga lunar derived chronology model or 230 850 ma asteroid derived chronology model depending on strength of target material

construction of the cambrian and ordovician seawater 87sr 86sr curve abstract the estimated path of seawater 87 sr 86 sr during the cambrian and ordovician is based on 172 analyses the sample suite is largely from locations in oklahoma new york tennessee and texas where rocks of this age are widely exposed and well studied the oldest reliable samples examined in this study are of middle cambrian age and yield an 87 sr 86 sr near 0 70888 sw 19 the estimated ratio rises to near 0 70915 sw 8 in the lower upper cambrian the highest value during the phanerozoic and probably for all geologic time the estimated path drifts lower to near 0 70903 sw 4 at the cambrian ordovician boundary this further declines to near 0 70875 sw 32 at the end of the ibexian and reaches a value near 0 70821 sw 86 at the whiterockian mohawkian boundary the decline in the seawater 87 sr 86 sr continues into later mohawkian time to flatten abruptly near 0 70782 sw 125 this ratio is essentially constant through the latest ordovician the curve rises near to a ordovician silurian boundary value poorly constrained from our data near 0 70784 sw 123 the early paleozoic seawater curve shows the alternating dominance of continental and oceanic sources of sr continental sr dominated seawater from the beginning of the cambrian into late cambrian from that time as the cambrian transgression proceeded and radiogenic crystalline rocks were covered oceanic sr began to dominate sr from low ratio oceanic sources dominated through early mohawkian time an abrupt balance is struck between oceanic and continental sources to end the decline in the late ordovician and maintained until near the end of the ordovician the general curve shape follows the pattern suggested by proposed sealevel changes the rise and fall of seawater 87 sr 86 sr during the cambrian and ordovician characterized seawater variation during all the paleozoic

high resolution strontium isotope stratigraphy across the cambrian ordovician transition we have analyzed 214 fossil apatite samples from nine stratigraphic sections worldwide that cover the lower cambrian to lower ordovician for their strontium isotope ratios of these samples 180 from six sections that cover the cambrian ordovician transition 5 ma reveal how the extent of isotopic alteration can differ greatly according to lithology and sample type from three limestone sections 126 euconodont samples yield the most consistent 87sr 86sr ratios and are used in this article to constrain seawater 87sr 86sr across the cambrian ordovician boundary by contrast protoconodonts paraconodonts and inarticulate brachiopods are far less likely to retain a primary 87sr 86sr signature and appear to be of only limited value for chemostratigraphy seawater 87sr 86sr fell from maximum values for the phanerozoic of more than 0 7092 during the early late cambrian to 0 7090 by the earliest ordovician high resolution sampling has permitted the recognition of sinusoidal variations with a wavelength on the order of 1 ma that are superimposed on the overall fall in 87sr 86sr these variations may be caused by high order cycles in seawater 87sr 86sr or diagenetic alteration

higher order gravitational potential gradients for geoscientific applications abstract gravity data have been applied for modelling and interpretation studies in geosciences this contribution reviews currently observable and foreseen gravity data represented by gradients of the gravitational potential functional models linking 3 d mass density distribution functions to potential gradients of up to the third order are formulated using volume integrals of the newtonian type with unitless kernel functions expressed both analytically and using infinite series of associated legendre functions spatial and spectral properties of the kernel functions are analysed and sensitivity of the gradients to particular mass density distributions is studied two particular mass density distribution models are used in numerical experiments a local 3 d mass density model representing shallow mass density variations and a global mass model represented by earth s upper sediments with lateral mass density variations computed values of the gradients demonstrate their different sensitivities to particular mass density distributions which change with an increasing distance of the gradients from gravitating masses third order gradients are particularly useful for studying near subsurface or shallow density structures such as caves caverns salt domes sediment basement morphology continental margins or buried fault systems that could be identified spatially more closely thus higher order gradients would offer an interesting tool for mass density mapping once their observability with the sufficient accuracy and resolution is realized

comparative sedimentology of shelf carbonates of the middle ordovician st paul group central appalachians abstract observations of present day environments are commonly used to aid in the interpretation of ancient sedimentary sequences this approach is used to determine the paleoclimate and depositional processes operating during formation of the limestones and dolostones of the lower middle ordovician st paul group row park and new market formations of maryland and southern pennsylvania a 200 m thick carbonate platform deposit within the group six facies defined by suites of sedimentary structures faunal assemblages and early diagenetic features are arranged in a large scale regressive transgressive sequence these consist of facies i lower burrowed peloidal facies facies ii burrowed skeletal facies facies iii lower laminated peloidal facies facies iv stromatolitic peloidal facies facies v upper laminated peloidal facies and facies vi upper burrowed peloidal facies a comparison of the st paul group deposits with those of the modern peritidal carbonate environments of shark bay western australia the abu dhabi and trucial coast areas of the persian gulf and andros island and the great bahama bank reveals 1 an overall similarity in features between the st paul group and the sediments of andros island and the great bahama bank and 2 a dissimilarity between those two deposits and the sediments of shark bay western australia and shoreline areas of the persian gulf for example the supratidal zones of the latter two typically contain evaporite minerals e g gypsum and anhydrite whereas the supratidal deposits of andros island and the st paul group are freshwater algal marsh and lake sediments the subtidal deposits of shark bay and the persian gulf generally are mechanically layered skeletal sand the subtidal deposits of the great bahama bank and the st paul group are bioturbated peloidal micrites the st paul group and the great bahama bank deposits are similar on a facies scale down to fine details observed microscopically bahamian modern analogs of the facies of the st paul group are for facies i shallow restricted bank and subtidal pond environments for facies ii a normal marine subtidal environment similar to the shoals which rim parts of the great bahama bank for facies iii and v tidal channel levee pond and marsh subenvironments of the channeled belt environment hardie and garrett 1977 for facies iv levee marsh and freshwater lake subenvironments of the interior of andros island and for the facies vi a semirestricted subtidal bank environment based on the features of the st paul group and by analogy with modern deposits the st paul group was deposited in a low energy rainy environment where deposition was controlled by storm processes many facies display penecontemporaneous marine cements and dissolution features

equatorial convergence of india and early cenozoic climate trends india s northward flight and collision with asia was a major driver of global tectonics in the cenozoic and we argue of atmospheric co2 concentration pco2 and thus global climate subduction of tethyan oceanic crust with a carpet of carbonate rich pelagic sediments deposited during transit beneath the high productivity equatorial belt resulted in a component flux of co2 delivery to the atmosphere capable to maintain high pco2 levels and warm climate conditions until the decarbonation factory shut down with the collision of greater india with asia at the early eocene climatic optimum at 50 ma at about this time the india continent and the highly weatherable deccan traps drifted into the equatorial humid belt where uptake of co2 by efficient silicate weathering further perturbed the delicate equilibrium between co2 input to and removal from the atmosphere toward progressively lower pco2 levels thus marking the onset of a cooling trend over the middle and late eocene that some suggest triggered the rapid expansion of antarctic ice sheets at around the eocene oligocene boundary

sr isotope evolution of seawater the role of tectonics we use a high resolution seawater sr isotopic evolution curve for the last 100 m y in conjunction with modern riverine sr flux measurements and also geologic tectonic and geochronological data to make the case for a close relationship between seawater sr isotopic composition and the india asia continental collision using a simple seawater sr budget model we begin by showing that the sr flux associated with alteration of seafloor basalts is too small and does not have the right time evolution to account for much of the seawater sr isotopic curve of the last 100 m y the flux of dissolved sr carried by rivers originating in the himalaya tibet region on the other hand is presently a significant fraction of the global sr budget we calculate how this riverine flux would have had to change with time in order to match the observed seawater sr isotopic curve and find that the riverine flux remains relatively constant prior to the collision of india with asia but then increases very significantly after collision we note that the period of most rapid change in seawater sr isotopic ratio from 20 ma to 15 ma is also a period of exceptionally high erosion in parts of the himalayas and the tibetan plateau as further evidence that sr derived from the collision of india with asia plays a major role in the sr isotopic evolution of seawater we show that the total amount erosion of the himalaya tibetan plateau since collision which we calculate separately represents a total amount of sr that is very nearly the same as the cumulative amount required by the sr isotopic change of seawater since collision the relationship between erosion and riverine sr flux allows us to use the sr isotopic evolution of seawater to reconstruct a history of erosion since collision and we find that the erosion rate accelerates with time since collision with the present having the largest rate when we apply the sr budget model to the entire phanerozoic using a new compilation of deformed continental area versus time we find that we can account for the large scale structure of the seawater sr isotopic curve but fail to reproduce several local maxima and minima especially in the period 100 300 ma the present high s7sr s6sr of seawater and similar highs in the devonian and cambrian do correlate with extensive deformation on the continents

the middle darriwilian ordovician δ13c excursion mdice discovered in the yangtze platform succession in china implications of its first recorded occurrences outside baltoscandia abstract the middle darriwilian 13 c excursion mdice one of the least known of the ordovician 13 c excursions has previously been recorded only from the middle ordovician of baltoscandia analysis of many recently collected limestone samples from the guniutan formation at two yangtze platform localities show elevated 13 c values in the same biostratigraphic interval microzarkodina ozarkodella conodont subzone as the mdice in baltoscandia which justifies identification of the chinese 13 c excursion as the mdice these occurrences which are in strata that show striking lithological and conodont faunal similarity to the swedish holen limestone and some coeval units in estonia indicate that the mdice the stratigraphically oldest of the named ordovician 13 c excursions is likely to have a world wide distribution and to have great potential for local and long range chemostratigraphic correlations

post hunnebergian ordovician carbon isotope trend in baltoscandia its environmental implications and some similarities with that of nevada abstract carbon isotope changes during post hunnebergian ordovician time were investigated as the corresponding sequence of rocks is stratigraphically nearly complete in baltoscandia an attempt was made to use it to elaborate the general pattern of carbon isotope changes in most of the ordovician complications caused by several local hiatuses condensed sections and facies changes were mitigated by the study of overlapping sections a total of 326 new whole rock analyses and published data from 18 drill cores and 4 outcrops in estonia latvia and sweden were considered the following positive carbon isotope events were observed 1 the mid darriwilian excursion peak 13c value 1 9 in the aseri stage 2 the mid caradoc excursion 2 2 in the uppermost part of the keila stage 3 the first late caradoc excursion 2 3 in the lower part of the rakvere stage 4 the second late caradoc excursion 2 4 in the upper part of the nabala stage 5 the early ashgill excursion 2 5 in the lowermost part of the pirgu stage 6 the mid ashgill excursion 2 0 in the upper part of the pirgu stage 7 the widely known large hirnantian excursion in estonia the peak value reaches 6 7 in the porkuni stage the study interval comprises a long 19 ma period characterized by low magnitude carbon isotope changes and a following much briefer 12 ma interval with often medium scale shifts and a major event at the end the latter interval reflects onset in the mid caradoc of a period of variable climate alternation of arid and humid episodes which ended with a serious cooling and glaciation the baltoscandian and north american nevada 13c trends are in general lines very similar providing good prospects for global chemostratigraphical correlation and understanding of role of oceanic processes in carbon cycling

carbon isotope δ13ccarb stratigraphy of the lower middle ordovician tremadocian darriwilian in the great basin western united states implications for global correlation abstract new stable carbon isotope data 13ccarb from lower middle ordovician tremadocian to darriwilian carbonate mudstone and wackestone rocks of the pogonip group are presented from two sections in the great basin region usa shingle pass east central nevada and the ibex area western utah the pogonip group is a succession of mixed carbonate and siliciclastic rocks that accumulated on a carbonate ramp under normal marine conditions during the late cambrian furongian to middle ordovician darriwilian the shingle pass and ibex area sections have been previously studied for their conodont biostratigraphy and contain a north american midcontinent conodont fauna that range from the cordylodus intermedius zone uppermost cambrian to the phragmodus polonicus zone darriwilian the 13c trend has four distinct characteristics recognized in both great basin sections 1 a drop in 13c from 1 at the base of the ordovician tremadocian to 0 7 2 a 1 to 2 positive 13c shift in the uppermost rossodus manitouensis zone during the late tremadocian 3 a gradual 13c increase from 2 to ca 0 during the end of the early ordovician floian and 4 a steady 13c decrease from 0 to 4 to 5 during middle ordovician dapingian darriwilian in the lower ordovician 13c trends reported here from the great basin are not consistent with a causal mechanism involving sea level change and the migration of isotopically distinct water bodies instead these lower ordovician isotope data most likely reflect primary seawater chemistry and changes in 13c on a global scale this interpretation is supported by the excellent correlation of 13c in the lower ordovician to other 13c trends reported from the sections in the argentine precordillera la silla and san juan formations and in western newfoundland st george and table head groups these correlations using 13c are consistent with published biostratigraphic data and provide an integrated and high resolution chemo biostratigraphic framework for the lower ordovician sedimentary record of the laurentian margin the middle ordovician portion of the 13c curves in the great basin represented by the kanosh and lehman formations shows significant isotopic depletion relative to the section in argentina thus although there is some indication that minima and maxima in the middle ordovician curves can be correlated the great basin sections show clear evidence of overprinting by local variables related to both diagenesis dolomitization and platform restriction

asteroid breakup linked to the great ordovician biodiversification event the great ordovician biodiversification event coincides 470 million years ago with the break up of a large asteroid and the resultant frequent bombardment of earth with asteroid fragments

magma sources for mesozoic anorogenic granites of the white mountain magma series new england usa the magma sources for granitic intrusions related to the mesozoic white mountain magma series in northern new england usa are addressed relying principally upon nd isotopes many of these anorogenic complexes lack significant volumes of exposed mafic lithologies and have been suspected of representing crustal melts sm nd and rb sr isotope systematics are used to evaluate magma sources for 18 felsic plutons with ages ranging from about 120 to 230 ma the possibility of crustal sources is further examined with analyses of representative older crust including paleozoic granitoids which serve as probes of the lower crust in the region multiple samples from two representative intrusions are used to address intrapluton initial isotopic heterogeneities and document significant yet restricted variations 1 in end overall mesozoic granite plutons range in end t from 4 2 to 2 3 with most 2 to 0 and in initial 87sr 86sr from 0 7031 to 0 709 the isotopic variations are roughly inversely correlated but are not obviously related to geologic geographic or age differences older igneous and metamorphic crust of the region has much lower nd isotope ratios with the most radiogenic paleozoic granitoid at end 180 ma of 2 8 these data suggest mid proterozoic separation of the crust in central northern new england moreover the bulk of the mesozoic granites cannot be explained as crustal melts but must have large mantle components the ranges of nd and sr isotopes are attributed to incorporation of crust by magmas derived from midly depleted mantle sources crustal input may reflect either magma mixing of crustal and mantle melts or crustal assimilation which is the favored interpretation the results indicate production of anorogenic granites from mantle derived mafic magmas

comment on non uniqueness and interpretation of the seawater 87sr 86sr curve by dave waltham and darren r grocke gca 70 2006 384 394

the central pit and dome at cerealia facula bright deposit and floor deposits in occator crater ceres morphology comparisons and formation abstract the prominent bright deposit cerealia facula ceres coincides with the central depression or central pit of the recently formed 92 km wide complex crater occator the central pit is 9 10 km wide and up to 1 km deep and is partially filled with a 700 m high 2 km wide dome the upper surface of the central dome is densely fractured but the flanks are not indicating that uplift of the dome surface occurred after the bright deposit was emplaced and primarily through uplift of the surface from below by laccolithic intrusion or volume expansion the pit is rimless except for two prominent massifs that flank it to the east and west this pit dome morphology bears a strong resemblance in morphology topography and dimensions to central pit craters observed on ganymede and callisto but is essentially absent on the similar sized ice rich moons of uranus saturn and pluto the lack of pit craters on midsize icy moons and the possible lack of central pit craters at the cold poles of ceres suggest that temperature is a significant controlling factor in central pit formation beyond the canonical inverse gravity scaling of complex crater transitions while renewed modeling will benefit from these new constraints the mapping of central pits on ceres including occator suggests that either the rheologically layered target model or more likely the melted central uplift model may be the most probable explanation for central pit formation on ceres lack of similar high resolution imaging on the galilean icy satellites precludes definitive evaluation of models there large volumes of lobate floor fill material at least 600 m thick in some places cover large areas of the southern and eastern floor of occator and small outcrops of this unit are found perched high on closed topographic depressions on the occator terrace zone and other higher areas of the crater floor the swirling and knobby surface textures of these lobate deposits are essentially indistinguishable from those on impact melt sheets on large lunar craters such as tycho these observations indicate that this unit is most likely an impact melt sheet formed from melted water ice admixed with unmelted particulate or dissolved phyllosilicates salts and or carbonates and large quantities of fragmented debris melt of ice phases within ceres crust is also supported by independent numerical models of impact at occator and would provide a ready source of fluids to promote hydrothermal deposition of the observed bright na carbonates on the surface of the central pit at occator if the deposit formed within a million years or so of impact the central dome finds analogs in salt domes on earth and pingos frost mounds on earth and mars which form by water and solute migration and freeze expansion later freezing of a central reservoir of volatiles beneath the central pit at occator or mobilization of ice or other phases during the cooling and refreezing process could explain the uplift of the central dome finally no changes were detected in the cerealia and vinalia facula bright deposits during the course of the prime dawn mapping mission placing additional constraints on their formation time and limits on ongoing activity

acoustically inferred zooplankton distribution in relation to hydrography west of the antarctic peninsula abstract the relationship between the distribution of zooplankton especially euphausiids euphausia and thysanoessa spp and hydrographic regimes of the western antarctic peninsula continental shelf in and around marguerite bay was studied as part of the southern ocean globec program surveys were conducted from the rvib n b palmer in austral fall april june and winter july august of 2001 acoustic video and environmental data were collected along 13 transect lines running across the shelf and perpendicular to the western antarctic peninsula coastline between 65 s and 70 s depth stratified net tows conducted at selected locations provided ground truthing for acoustic observations in fall acoustic volume backscattering strength at 120 khz was greatest in the southern reaches of the survey area and inside marguerite bay suggestive of high zooplankton and micronekton biomass in these regions vertically highest backscattering was in the 150 450 m depth range associated with modified circumpolar deep water cdw the two deep troughs that intersect the shelf break were characterized by reduced backscattering similar to levels observed off shelf and indicative of lower zooplankton biomass in recent intrusions of cdw onto the continental shelf estimates of dynamic height suggested that geostrophic circulation likely caused both along and across shelf transport of zooplankton by winter scattering had decreased by an order of magnitude 10 db in the upper 300 m of the water column in most areas and high backscattering levels were found primarily in a deep 300 m scattering layer present close to the bottom the seasonal decrease is potentially explained by advection of zooplankton vertical and horizontal movements and mortality predictions of expected backscattering levels based on net samples suggested that large euphausiids were the dominant source of backscattering only at very particular locations and depths and that copepods siphonophores and pteropods were more important in many locations

isostatic equilibrium in spherical coordinates and implications for crustal thickness on the moon mars enceladus and elsewhere miller institute for basic research in science at the university of california berkeley nasa gravity recovery and interior laboratory guest scientist program

strontium isotopic variations in jurassic and cretaceous seawater a high resolution seawater strontium isotope curve has been generated through the analysis of well dated and well preserved belemnites and oysters from the middle and upper jurassic and the lower cretaceous of great britain analysis of fe and mn concentrations in these fossils has yielded criteria for eliminating samples that are diagenetically altered the strontium isotope curve remains relatively flat through the aalenian and early bajocian rapidly descends through the late bajocian and bathonian and reaches a minimum in the callovian and oxfordian it then begins a rapid increase in the kimmeridgian and portlandian that continues through much of the early cretaceous the curve levels off in the barremian suddenly dips downwards in the aptian and recovers gradually through the albian the strontium isotopic variations are sufficiently large and the data are presented with sufficient stratigraphic detail to allow precise correlation to the classic ammonite zones and lithologic sections of great britain using the techniques of strontium isotope stratigraphy model results indicate that much of the variation in seawater 87sr86sr between 120 and 40 ma can be explained by changing the intensity of mid ocean ridge hydrothermal fluxes proportionally to estimated mid ocean ridge crustal generation rates it is also possible that the variations during the rest of the mesozoic and the permian are primarily reflections of changing hydrothermal inputs the model results have several important implications first they provide an example in which the variations in the strontium isotope curve are not necessarily driven by changes in fluvial inputs second they suggest that from at least the aptian through the eocene variations in continental weathering were minimal this heightens the importance of the rapid rise in seawater 87sr86sr beginning 40 ma as a significant transition to an extended period of increasing fluvial 87sr fluxes continuing to the present finally the results suggest that several documented short term excursions towards lower 87sr86sr in the latest triassic pliensbachian toarcian callovian oxfordian aptian albian and cenomanian turonian are interpretable as pulses of seafloor hydrothermal activity if so the strontium isotope record offers a means of constraining the timing duration and magnitude of known or proposed hydrothermal events in the geological record

did cooling oceans trigger ordovician biodiversification evidence from conodont thermometry the ordovician period long considered a supergreenhouse state saw one of the greatest radiations of life in earth9s history previous temperature estimates of up to 70 c have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time we present a very different global climate record determined by ion microprobe oxygen isotope analyses of early ordovician silurian conodonts this record shows a steady cooling trend through the early ordovician reaching modern equatorial temperatures that were sustained throughout the middle and late ordovician this favorable climate regime implies not only that the oxygen isotopic composition of ordovician seawater was similar to that of today but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period

a positive trend in seawater 87sr 86sr values over the early middle frasnian boundary late devonian recorded in well preserved conodont elements from the holy cross mountains poland abstract over the early middle frasnian boundary interval late devonian the oceans experienced major changes in global carbon cycling and nutrient dynamics with a prominent positive carbon isotope shift at the base of the palmatolepis punctata zone middle frasnian the aim of this study was to construct seawater 87 sr 86 sr ratio curves for the pa transitans pa hassi zonal interval using well preserved conodont apatite from two sections in the holy cross mountains south central poland the final curves suggest that seawater 87 sr 86 sr values were steady at 0 70794 0 70799 during the transitans zone but began to rise in the early punctata zone towards a value of 0 70814 in the late punctata zone an increase of 0 0002 the increase in seawater 87 sr 86 sr values over the early middle frasnian boundary appears to be the second of two prominent short term rises in 87 sr 86 sr values which led to an overall shift in values from a givetian plateau of between 0 70780 and 0 70785 to a late frasnian plateau of between 0 7080 and 0 7082 correlation with a regional positive 13 c anomaly and evidence for eutrophication in the marine environment suggests that the causes of these phenomena may be linked and that the positive 87 sr 86 sr shift was caused by an increase in the continental flux of sr to the oceans i e the weathering flux a possible explanation for an increase in the weathering flux is the denudation of a new acadian eovariscan orogen which would have been mostly weathered in the humid warm tropical equatorial region

bentonite geochronology marine geochemistry and the great ordovician biodiversification event gobe abstract attribution of ordovician climate forcing to explosive volcanism and the potential global importance of volcanism in ordovician biodiversification suggest the necessity of evaluating the relationships between k bentonite deposition and increasingly high resolution records of marine biogeochemical change globally ordovician strata preserve an extensive record of explosive volcanism including the widely recognized lower to middle ordovician famatina k bentonite suite in argentina and the upper ordovician millbrig deicke kinnekulle suite of north america and europe here we present high resolution id tims u pb zircon ages of k bentonites from measured sections of the san juan formation talacasto and cerro la chilca section of the argentine precordillera k bentonites from the argentine precordillera provide stratigraphically consistent i e younging upward ages that range from 473 45 0 70 ma to 469 53 0 62 ma and constrain the age of a low magnitude 2 globally recorded negative carbon isotope excursion evaluation of the timing of k bentonite deposition in the argentina precordillera relative to marine biostratigraphic and biogeochemical records provides insight into relationships between explosive volcanism and regional to global environmental change from a regional standpoint these ages provide critical direct evidence for a dapingian to earliest darriwilian age of the upper san juan formation at sampled localities these ages are consistent with carbon isotope data suggesting that the san juan formation in the region of its type section is coeval with only the base of the often correlated table head group of western newfoundland this data thus highlights the difficulties in using regional biostratigraphic data particularly within erosionally truncated or otherwise diachronous units to define the timeframe of carbon isotope chemostratigraphy new geochronological data also indicate that a discrete negative carbon isotope excursion within the san juan and table head formations is correlative to a globally recognized pre mdice negative excursion and indicates that this aspect of the marine carbon isotope record can be used as a discrete chronologic marker san juan formation bentonites however cannot be discretely correlated with observed environmentally significant changes in the middle ordovician marine geochemical records of carbon sulfur strontium or sea surface temperature these results suggest that the extent of volcanism represented by the famatina bentonite suite was insufficient to affect global surface environments and that the relationship between explosive volcanism and environmental change may not be straightforward as previously suggested

slurry extrusion on ceres from a convective mud bearing mantle ceres is a 940 km diameter dwarf planet that is predominantly composed of silicates and water ice in ceres partially differentiated interior extrusive processes have led to the emplacement on its surface of domes with heights of kilometres here we report the analysis of a gravity anomaly detected by the dawn spacecraft which is associated with the geologically recent dome ahuna mons by modelling the anomaly with a mass concentration method we determine that the subsurface structure includes a regional mantle uplift which we interpret as a plume this structure is the probable source of fluids forming ahuna mons and together with constraints from the dome s morphology indicates a rheological regime corresponding to a slurry of brine and solid particles we propose that the properties of such a solid liquid mixture can explain the viscous relaxation and the mineralogy of the dome the presence of a plume and of slurry material indicate recent convection in a mud bearing mantle the inferred slurry extrusion on ceres differs from the water dominated cryovolcanism of icy satellites and so reveals compositional and rheological diversity in extrusive phenomena on planetary surfaces ahuna mons dome on ceres formed by extrusion of a mixture of brine and solids sourced from a muddy mantle plume according to numerical modelling of slurry rheology and a gravity anomaly found by the dawn mission

strontium and carbon isotope stratigraphy of the llandovery early silurian implications for tectonics and weathering abstract a high resolution 87sr 86sr curve and paired 13c carbonate organic data set is generated for the llandovery series from the ikla drill core in estonia a 13c carbonate curve is also presented from the pancake range in nevada observed 87sr 86sr values in the ikla drill core are at a minimum in the early llandovery rhuddanian stage 0 7079 to 0 7080 and then trend to more radiogenic ratios in the basal part of the telychian stage an 87sr 86sr high near 0 7084 is observed in the telychian at the top of the studied section the range of values is in general agreement with the data from previous sample sets of brachiopods and conodonts recovered from localities in north america and europe that record a rising trend in the 87sr 86sr ratio throughout the llandovery from approximately 0 7080 to 0 7084 the major increase in the 87sr 86sr ratio during the late llandovery may be due to weathering of radiogenic source rocks that were uplifted during early silurian continent continent collisions the sr rise potentially coincides with the occurrence of an unusually thick sequence of k bentonite beds representing large magnitude ash falls in the early telychian a previously documented negative 13c excursion in marine carbonates in the lower telychian interval of the ikla core is quasi synchronous with the increase in 87sr 86sr our new organic matter 13c data from the ikla core confirm that this negative 13c carbonate excursion is not a result of diagenesis furthermore a negative 13c excursion in carbonates from the early telychian portion of the pancake range section in nevada seems to confirm the global scope of this carbon cycle perturbation

depositional sequences and palaeoceanographic change in the ordovician of the siberian craton abstract nine major depositional sequences separated by regional unconformities are recognized in the ordovician of the siberian craton these sequences are typically characterized by an absence of lowstand systems tracts relatively thin transgressive systems tracts and somewhat thicker shallowing upward highstand systems tracts the most prominent unconformities marking forced regressions are associated with the base of the baykit depositional sequence early darriwilian and the top of the ordovician across the former the tropical type carbonate factory was terminated and siliciclastic sediments baykit sandstone were deposited these changes in lithology inferably correspond to tectonic events along the western margin of the siberian continent with major flooding events during the volgino kirensk kudrino and mangazeya depositional sequences phosphatization became much more widespread and carbonate rock compositions shift from tropical type to temperate type this lithological shift is due to a combination of upwelling of cool water increased nutrient influx and increased water turbidity major transgressions marked by widespread black shales and or deep water marine red bed facies occurred during the volgino kirensk kudrino late darriwilian mangazeya early sandbian and kety middle katian depositional sequences the ordovician depositional sequences of the siberian craton can be tentatively correlated with those developed in the baltica palaeocontinent which suggests that most of them were controlled mainly by eustasy the pattern of long term lithological changes in the ordovician of the siberian craton and our established sea level curve demonstrate more similarities with north america than with baltica

an improved jpl mars gravity field and orientation from mars orbiter and lander tracking data abstract the mars gravity field resolution is mostly determined by the lower altitude mars reconnaissance orbiter mro tracking data with nearly four years of additional mro and mars odyssey tracking data since the last jpl released gravity field mro110c and lander tracking from the mer opportunity rover the gravity field and orientation of mars have been improved the new field mro120d extends the maximum spherical harmonic degree slightly to 120 improves the determination of the higher degree coefficients as demonstrated by improved correlation with topography and reduces the uncertainty in the corresponding mars orientation parameters by up to a factor of two versus previously combined gravity and orientation solutions the new precession solution is 7608 3 2 1 mas yr and is consistent with previous results but with a reduced uncertainty by 40 the love number solution k2 0 169 0 006 also shows a similar result to previous studies

gravity field expansion in ellipsoidal harmonic and polyhedral internal representations applied to vesta abstract a 20th degree ellipsoidal harmonic gravity field of vesta is determined by processing radiometric doppler and range data from the dawn mission the gravity field shows sensitivity up to degree 18 and the coefficients are globally determined on average to degree 15 gravity anomalies are mapped to the brillouin ellipsoid 304 289 247 km which is a substantially closer fit to the surface than the reference ellipsoid 290 290 265 km used to map the conventional spherical harmonic series especially near the poles two models of internal structure are subsequently explored in which density variations are permitted in the uppermost layer i e crust in order to explain vesta s local gravitational signature these models include the case of a two layer model with an average crustal thickness of 55 5 km and a three layer model with an average crustal thickness of 22 4 km for both two layer and three layer scenarios the bouguer gravity anomaly is minimized for a crustal density of 2970 kg m 3 the remaining bouguer anomalies can be explained by lateral crustal density variation of 2310 3440 kg m 3 and 2660 3240 kg m 3 for the 22 4 km and 55 5 km crustal thickness models respectively the general trend of the estimated lateral crustal densities for the two cases is very similar with a wider range for the 22 4 km case due to a thinner crust this indicates that a thick crust e g 55 5 km would be more favorable for minimizing the range of lateral crustal density variations consideration of independent geochemical and petrological constraints suggests that a three layer model is a more appropriate representation of vesta s internal structure despite the fact that two layer models provide a satisfactory fit to gravity data alone in detail it is found that densities derived from gravity data assuming three layer models and those derived from the howardite eucrite diogenite meteorites and estimates of plausible bulk vesta composition show an excellent level of mutual consistency

gravitational and topographic isotropy of the earth moon mars and venus the internal structures and surface shapes of the terrestrial planets are expected to be dominantiy isotropic we attempt to test this hypothesis by developing a criterion for recognizing statistical isotropy of spherical scalar fields and applying that test to the nonhydrostatic components of the gravitational and topographic fields of the earth moon mars and venus the criterion for topographic or geoidal surfaces is that the directional variance should be independent of azimuth that is the mean square east west slopes should be equal to the mean square north south slopes all four planets generally pass the criteria with a few minor exceptions most of the exceptions are likely to be artifacts of the current generation of planetary gravity and topography models rather than real features of the planets of the several broad band departures from isotropy which we found the only one likely to be real is the tendency for the earth s gravity and topography to have only 80 as much variance in a north south direction as in an east west direction

the great ordovician biodiversification event gobe the palaeoecological dimension abstract the great ordovician biodiversification event gobe saw a spectacular increase in marine biodiversity at all taxonomic levels largely within the phyla established much earlier during the so called cambrian explosion the diversification was probably the result of a combination of several geological and biological processes and the positive feedbacks resulting from them the present paper reviews the palaeoecological dimension of the gobe it involved major increases in s and biodiversity largely associated with the rise of the paleozoic evolutionary fauna dominated by suspension feeders and involving a greater occupation of ecospace and more complex ecological structures in the ecological evolutionary units p1 and p2 in the benthos these include more complex food webs than those of the cambrian greater tiering especially above the sediment water interface and the development of guild structures indicating increased competition between taxa for particular resources the ordovician is characterized by a profound change in reef composition with a switch from microbial dominated reefs in the early and middle ordovician to metazoan dominated reefs in the late ordovician increases in complexity of deep water trace fossil assemblages began in the early ordovician and mark the increasing exploitation in that environment and the development of hardgrounds permitted bioerosion and encrusting strategies together with the appearance of cryptic communities within the water column the gobe involved a significant increase in the diversity of the phytoplankton and the development of a diverse zooplankton including planktotrophic larvae from a range of invertebrate clades this revolution in the plankton enabled the establishment of a diverse fauna of pelagic vertebrates molluscs and arthropods and promoted the rise of suspension feeders in the benthos an escalation amongst predators and thus community evolution may also have been a major driver of biodiversification

87sr 86sr record of permian seawater abstract a population of 169 permian articulate brachiopod shells was analysed for their 87 sr 86 sr ratios 51 of these characterised as well preserved and stratigraphically well defined are utilized for delineation of the permian seawater strontium isotope trend the 87 sr 86 sr curve shows values of about 0 7080 in the lowermost permian asselian followed by a gradual decline to 0 70685 in the capitanian and a minor rise in the dzhulfian and lower dorashamian to values of 0 70715 just below the permian triassic boundary the early permian decrease in the strontium isotope curve that commences in the early sakmarian is coincident with the advancing deglaciation of the gondwana and with the increased aridity in large parts of the pangaea these factors may have led to a reduced continental weathering of rb rich silicate rocks and thus to the decline in seawater 87 sr 86 sr starting with the artinskian the opening of the neotethys and the associated widespread basaltic volcanism supplied low radiogenic strontium to seawater from an enhanced hydrothermal flux in the capitanian basaltic volcanism in the entire palaeotethys ceased and this may have been the reason for a slightly more radiogenic seawater isotopic composition during the lopingian higher input of riverine sr due to expansion of humid areas may have been a contributory factor

evidence for a small 0 000 030 but resolvable increase in seawater 87sr 86sr ratios across the cretaceous tertiary boundary previous studies of 87 sr 86 sr patterns across the cretaceous tertiary k t boundary have generated inconsistent results analyses of samples from ocean drilling program hole 1049c provide better taphonomic and diagenetic control than has been previously achieved and indicate 1 that there was a rapid increase of 0 000 030 in seawater 87 sr 86 sr ratios across the k t boundary 2 that post k t cretaceous foraminifera at this site are reworked and 3 that subtle diagenetic overprinting affects the basal 15 cm of the danian ooze these conclusions are consistent with the asteroid impact hypothesis reworking rather than survivorship confirms nearly complete extinction of cretaceous tethyan planktic foraminifera the 87 sr 86 sr excursion can be explained by enhanced continental weathering perhaps related to acid rain in the aftermath of the k t impact

the mercury gravity field orientation love number and ephemeris from the messenger radiometric tracking data abstract the mercury gravity field spin pole axis rotation period love number and ephemeris have been determined using the complete four years of messenger tracking data from march 2011 to april 2015 the pole location and obliquity 1 99 0 12 arcmin is consistent with previous determinations since messenger was in a highly elliptical orbit with periapsis in the far northern hemisphere the gravity resolution over the surface of mercury varies greatly from harmonic degree n 12 at the south pole to n 154 in a small region near the north pole which was covered with exceptionally low periapsis data near the end of mission the gravity field mess160a is determined to n 160 and shows notable improvement in the correlation with topography three different constraint methods are used to generate the gravity field the nominal method is a kaula power law of 5 10 5 n2 to constraint the coefficients one alternate constraint uses surface acceleration measurements which only constrains the unobserved portion of the gravity field the other constraint method sets the gravity uncertainties using the harmonic spectrum of the gravity derived from topography the mercury tidal love number solution k2 0 53 0 03 is larger than previous results but within suggested error bounds in addition the technique for estimating the mercury ephemeris is discussed

geochemistry of cambro ordovician arbuckle limestone oklahoma implications for diagenetic δ18o alteration and secular δ13c and variation abstract isotopic analyses of 227 limestone samples from the cambro ordovician arbuckle group oklahoma document slow secular changes in the chemistry of the limestones from late cambrian to early ordovician the 18o values of the limestones increase from 10 to 7 pdb 13c values decrease from 0 to 2 pdb and 87 sr 86 sr ratios decrease from 0 7091 to 0 7088 the light 18o values suggest that all arbuckle limestones underwent diagenetic alteration probably caused by meteoric water recharged during the development of the overlying pre middle ordovician unconformity the gradual 18o increase from late cambrian to early ordovician reflects reduced 18o depletion with decreasing burial temperature during alteration although the presence of additional primary secular 18o variation cannot be ruled out the 13c and 87 sr 86 sr variations in accord with 13c and 87 sr 86 sr variations in the literature represent primary secular variations the variations indicate that the 13c value and 87 sr 86 sr ratio of early paleozoic surface seawater decreased from late cambrian to early ordovician the 13c variation during this time period seems to correlate with sea level variation specifically during sea level fall an increase in the rate of oxidation of organic matter caused 13c depletion of inorganic bicarbonate in seawater as a result early ordovician carbonates probably deposited during the regression stage of the latest precambrian to latest early ordovician cycle became 13c depleted relative to late cambrian carbonates the decrease of seawater 87 sr 86 sr ratio from late cambrian to early ordovician may have resulted from decreased riverine sr input caused by decreased rate of continental weathering

strontium isotope stratigraphy potential resolution and event correlation abstract a new generation 87sr 86sr isotope curve for the phanerozoic seawater based on a compilation of 3635 stratigraphically well defined and well preserved skeletal components results in a substantially narrower band with some discrepancies if compared to the curve of burke et al 1982 which is based mostly on whole rock samples the results obtained from low mg calcite shells foraminifers belemnites brachiopods and oysters are mostly superior to those from phosphatic skeletal components such as conodonts even if the latter are exceptionally well preserved cai 1 5 at this stage the phanerozoic data set based on fossils is patchy for the cambrian upper ordovician lower devonian and upper carboniferous triassic intervals the major practical constraint that precludes delineation of an unequivocal sr isotope curve for the phanerozoic seawater is the uncertainty in the assignment of absolute ages to the samples as a result the curve is in reality a band this is a reflection of the limitations of biostratigraphy and geochronology that are inherited by any derivative correlation and dating technique including isotope stratigraphy it is therefore unlikely that in the near future the sr isotope stratigraphy will surpass the resolution capability of biostratigraphy as a global correlation tool on the other hand if complemented by lithostratigraphy it is potentially a valuable tool for correlation of sequences on intrabasinal and regional scales taking into account the above limitations careful consideration must be given to assignment of higher order isotope peaks to specific events within a biozone and to the use of such events as a global correlation tool

carbon sulfur oxygen and strontium isotope records organic geochemistry and biostratigraphy across the permian triassic boundary in abadeh iran pelagic deposits at abadeh represent a complete biostratigraphic record across the permian triassic boundary ptb the presumed water depth during deposition of these sediments was between 60 and 90 m similar to other permian triassic boundary sections the succession at abadeh is characterised by a negative carbon isotope shift of approximately 4 the values start to decrease in the lower c changxingensis c deflecta s l zone reach 0 12 v pdb in the uppermost permian just below the ptb remain low to the early i isarcica zone 0 32 and increase subsequently in the upper i isarcica zone for the time interval of the ptb negative carbon isotope excursion between the c iranica and the i isarcica zones no correlation exists between the 13ccarb and the 18ocarb the above observations argue against the conclusion of heydari et al 2001 that the carbon isotope event at the p t transition is an alteration artefact and not a global signal the decrease in 13ccarb is accompanied by a 5 and potentially up to 10 increase in 34ssss together these features are thought to reflect a complex global event notably the development of widespread anoxic oceans with anoxic bottom layers rising onto the shelves for the carbon isotope drop other factors such as the collapse of ocean primary productivity may also have played a role the 87sr 86sr ratios of dzhulfian seawater show only a minor increase from 0 70705 to 0 70710 reaching 0 70720 in the dorashamian the increase becomes steeper in the early triassic reaching 0 70754 in the n dieneri zone the rise of the strontium isotope values is thought to be related to enhanced continental weathering under humid climatic conditions in the uppermost permian c meishanensis h praeparvus zone and the lack of a dense land vegetation in the early triassic prior to the spathian upper olenekian

radiogenic isotopes systematics and applications to earth surface processes and chemical stratigraphy radiogenic isotopes have wide application to chemical stratigraphy geochronology provenance studies and studies of temporal changes in earth surface processes this paper briefly reviews the principles of radiogenic isotope geochemistry and the distribution of a number of elements of interest in the environment and then uses this information to explore the range of applications to chemical stratigraphy and other fundamental subjects of sedimentary geology many of these applications center on the reconstruction of secular variations in paleoseawater isotope signals these seawater isotope curves can be used for stratigraphic correlation and to assess changes through earth history in processes such as tectonic uplift climate change biogeochemical cycling ocean circulation crustal growth and surface water evolution understanding the modern biogeochemical cycle of the element isotope system of interest is essential for gaining the maximum information regarding the operation of ancient cycles the main sources of uncertainty for reconstructing seawater isotope curves involve diagenetic alteration sample impurities and errors in age assignments rigorous sample selection criteria and pretreatment methods are keys to reconstructing the most accurate seawater isotope curves applications are discussed for the rb sr sm nd la ce lu hf re os u th pb k ar and cosmogenic isotope systems d 2003 elsevier b v all rights reserved

improved chronostratigraphic reference curve of late neogene seawater 87sr 86sr we present a reference curve of seawater 87 sr 86 sr variation through the past 7 m y based on 455 samples of planktonic foraminifera from ocean drilling program odp site 758 in the indian ocean this single site curve is superior to extant curves because of several features 1 a continuous sedimentary section free of disturbances 2 a well determined and precise chronostratigraphy that is calibrated to numeric age on the basis of continuous magnetostratigraphy and a refined astronomical time scale 3 a high temporal resolution sample interval averages 15 ka 4 an improved analytical reproducibility and 5 a uniformly high sample quality the gross structure of the site 758 curve is generally similar to that observed in previous work but the increased temporal resolution and decreased analytical scatter of the curve provide improved chronostratigraphic resolution at the 95 confidence level uncertainties on age estimates range from 0 60 m y in the lower pleistocene and upper miocene to 2 03 m y in the middle pliocene moreover this detailed record identifies two periods of steplike increases in seawater 87 sr 86 sr 6 10 to 5 80 ma and 1 46 to 1 13 ma that are characterized by rates of change of 150 10 6 m y these features if verified at other sites indicate abrupt changes in the sr mass balance of the ocean and may be used as precise event markers in late neogene marine sections

oxygen and strontium isotopes as provenance indicators of fish at archaeological sites the case study of sagalassos sw turkey abstract in this paper we investigate the potential use of oxygen and strontium isotope ratios 18 o p and 87 sr 86 sr measured in archaeological fish enamel as provenance indicators 18 o p and 87 sr 86 sr were measured in a suite of archaeological carp remains recovered from the anatolian townsite of sagalassos dated to the early byzantine period ad 450 650 and compared to that of modern fish river and lake waters from the anatolian region we used sequential leaches in weak acetic acid to remove diagenetic sr from fossil tooth enamel monitoring the effectiveness of this approach by measuring the sr ca ratios of the leachates via an isotope dilution thermal ionization mass spectrometry method id tims 18 o p values mostly excluded a riverine origin 87 sr 86 sr ratios of one fish overlapped with the 87 sr 86 sr signatures of two lakes in the anatolian region and at least one lake golcuk could be removed as a candidate owing to a very distinctive 87 sr 86 sr signature not found in any of the fish remains most of the tooth samples analyzed could not be assigned a precise geographical origin since the 87 sr 86 sr ratios measured in enamel did not match that of any of the local lakes selected as potential origin this result suggests that carp may have originated from lakes that have not yet been sampled although this conclusion is not supported by other archaeological evidence alternatively the lack of correspondence between lakes and fish sr isotope ratios highlights several possible sources of uncertainties including spatial heterogeneity in 87 sr 86 sr ratio within a lake the contribution of dietary strontium to the 87 sr 86 sr ratio of fish tooth enamel and post mortem alteration of the tooth sr isotope signal during fossilization in spite of the high precision of the strontium isotope analyses and the wide range of variation in the surface waters of the anatolian lakes and rivers this method may remain limited to distinguishing between lakes situated in regions of bedrock of very distinct age and geology until these sources of uncertainty are more fully investigated

improved parametrization of antarctic krill target strength models there are historical discrepancies between empirical observations of antarctic krill target strength and predictions using theoretical scattering models these differences are addressed through improved understanding of key model parameters the scattering process was modeled using the distorted wave born approximation representing the shape of the animal as a bent and tapered cylinder recently published length based regressions were used to constrain the sound speed and density contrasts between the animal and the surrounding seawater rather than the earlier approach of using single values for all lengths to constrain the parameter governing the orientation of the animal relative to the incident acoustic wave direct measurements of the orientation of krill in situ were made with a video plankton recorder in contrast to previous indirect and aquarium based observations krill were observed to orient themselves mostly horizontally averaging predicted scattering over the measured distribution of orie

a major drop in seawater 87sr 86sr during the middle ordovician darriwilian links to volcanism and climate a large drop in seawater 87 sr 86 sr during the middle ordovician was among the most rapid in the entire phanerozoic new 87 sr 86 sr measurements from nevada indicate that the rapid shift began in the pygodus serra conodont zone of the upper darriwilian stage we use a numerical model to explore the hypothesis that volcanic weathering provided the flux of nonradiogenic sr to the oceans a close balance between volcanic outgassing and co 2 consumption from weathering produced steady p co 2 levels and climate through the middle katian consistent with recent ordovician paleotemperature estimates in the late katian outgassing was reduced while volcanic weathering continued and resulted in a cooling episode leading into the well known end ordovician glaciation

the strontium isotopic composition of ordovician and silurian brachiopods and conodonts relationships to geological events and implications for coeval seawater utilized for strontium isotope measurements the results document a gradual decrease in 87 sr 86 sr from 0 7091 to 0 7087 from tremadoc to llandeilo a sharp decline to 0 7078 during the late llandeilo early caradoc little change during caradoc and the ashgil and a steady rise to 0 7087 through the silurian these long term 10 7 yr variations with magnitudes in the range of 10 23 are interpreted to be controlled primarily by continental collisional tectonics and its associated erosion and weathering the gradual decrease in 87 sr 86 sr ratio during the early ordovician may record the reduction in uplift and weathering rates due to waning of the pan african orogenies the rapid decline near the llandeilo caradoc boundary suggests a strong hydrothermal flux likely due to increased sea floor spreading and a possible superplume event the latter may have caused the prominent transgressive phase the largest in the phanerozoic which would have muted continental flux input although the caradoc was the main interval for the taconic orogeny its impact on the sr continental flux may have been delayed until the early llandovery this effect complemented by reworking of glacial deposits near the ordovician silurian boundary and enhanced by phases of the silurian salinic orogeny may have combined to give the progressive increase in the strontium isotope ratio through the silurian the scale and directionality of these changes makes the strontium isotope curve valuable for dating and correlation purposes copyright 1998 elsevier science ltd

potential anomalies on a sphere applications to the thickness of the lunar crust a new technique for calculating potential anomalies on a sphere due to finite amplitude relief has been developed we show that by raising the topography to the nth power and expanding this field into spherical harmonics potential anomalies due to topography on spherical density interfaces can be computed to arbitrary precision using a filter for downward continuing the bouguer anomaly we have computed a variety of crustal thickness maps for the moon assuming both a homogeneous as well as a dual layered crust the crustal thickness maps for the homogeneous model give plausible results but this model is not consistent with the seismic data petrologic evidence and geoid to topography ratios all of which suggest some form of crustal stratification several dual layered models were investigated and it was found that only models with both upper and lower crustal thickness variations could satisfy the gravity and topography data these models predict that the entire upper crust has been excavated beneath the major nearside multiring basins additionally significant amounts of lower crustal material was excavated from these basins especially beneath crisium this model also predicts that mantle material should not have been excavated during the south pole aitken basin forming event and that lower crustal material should be exposed at the surface in this basin

middle and upper ordovician carbon isotope chemostratigraphy in baltoscandia a correlation standard and clues to environmental history abstract the baltoscandian epeiric sea was characterised by relatively slow but continuous carbonate deposition from the middle ordovician up to the silurian relatively good preservation of ordovician and silurian carbonate rocks in baltoscandia makes this region unique for chemostratigraphical and palaeoenvironmental studies previous palaeozoic carbon isotope studies have revealed isotopic events in different lithologies over the baltoscandian palaeobasin and some of them on different palaeocontinents we propose a composite carbon isotope curve for the baltoscandian region a new subdivision of the middle and upper ordovician succession into seventeen chemostratigraphic zones and an improved nomenclature of isotopic excursions based on analyses of 13 c carb data from 25 drillcore and outcrop sections of estonia latvia and sweden the composite carbon isotope curve is compared with biostratigraphical data on conodont and chitinozoan distribution the katian hirnantian interval with highly fluctuating isotopic values shows climatic cyclicity of about two million years in baltoscandia no abrupt changes occur in the dapingian sandbian part of the baltoscandian isotope curve but the mid darriwilian excursion nearly coincides with the onset of cooler temperatures similar to modern like equatorial sea surface temperatures and related global biodiversification increase suggesting a climatic background for this event

harmonic and statistical analyses of the gravity and topography of vesta abstract we examine the gravity and topography of the asteroid 4 vesta as recently revealed by the dawn mission the observed gravity is highly correlated with the observed topography and suggests little lateral variation in density the variance spectra of both gravity and topography follow power laws which are very similar to those seen for the moon mars venus and earth a significant way in which vesta differs from these larger silicate bodies is that both gravity and topography are significantly anisotropic with more north south variation than east west variation rapid rotation plausibly contributes to this anisotropy but only at harmonic degree two the remainder of the anisotropy appears related to the large impacts which formed the rheasilvia and veneneia basins we note that as usual gravitational inverse problems are non unique while the observed gravity and topography of vesta do not preclude existence of a metallic core they certainly do not require it

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

the strontium isotopic composition of brigantian late dinantian seawater abstract strontium isotopic determinations of different fossiliferous biominerals from brigantian late dinantian carbonates in northern england reveal that many are affected by diagenetic overprinting of their original 87 sr 86 sr ratios only pristine non luminescent articulate brachiopod shell material can be used to gain reliable estimates of carboniferous and by deduction palaeozoic ocean chemistries conodonts are found to be the only type of phosphatic biomineral capable of preserving original palaeoseawater chemistries however this only applies to specimens subjected to minimal burial temperatures other phosphatic biominerals are conclusively shown to be readily susceptible to diagenetic overprinting of original sr isotopic ratios a brigantian strontium curve compiled from pristine brachiopod calcite shows a relatively complex evolution with time but it can be resolved into two separate components operating on different time scales a cyclic sinusoidally shaped component with a frequency of 1 ma appears to fluctuate about a longer term more gradual linear increase in the brigantian seawater isotopic composition

sr and nd isotopes at the prmian triassic boundary a record of climate change abstract we present a detailed curve of seawater 87sr 86sr for the middle permian to triassic based on analyses of conodonts from overlapping sections in the u s a pakistan correlated using conodont biostratigraphy the isotope ratio decreased in the middle permian at an average rate of 0 000062 ma 1 reached a minimum in the capitanian 257 258 ma and increased in the late permian at an average rate of 0 000097 ma 1 the late permian rate of increase was roughly two and a half times greater than the average increase over the past 40 ma and approximately equal to the highest cenozoic rates which occurred over much shorter time intervals modeling results suggest that decreasing middle permian 87sr 86sr ratios were driven by changes in the riverine sr flux to the oceans while increasing ratios in the late permian triassic are attributed to both increased riverine 87sr 86sr and flux the reduced middle permian riverine flux coincides with extreme continental aridity associated with the formation of pangea and recorded by massive evaporite deposits in addition mountains in the equatorial region of pangea may have created a rain shadow thereby minimizing precipitation in regions that currently contribute the bulk of chemical weathering products to the ocean increasing riverine 87sr 86sr in the late permian is suggested by the observation that 143nd 144nd values decrease at the same time however the source of radiogenic sr is not known frequently cited mechanisms for increasing 87sr 86sr in runoff such as glaciations and continent to continent collisions coincide instead with decreasing seawater 87sr 86sr in the middle permian one possible source may have been deep erosion into older orogens associated with a dramatic increase in chemical weathering in the late permian the cause of enhanced weathering appears to have been increased levels of atmospheric co2 with associated global warming and increased humidity proposed sources of co2 include dissociation of gas hydrates and oxidation of organic matter during extreme sea level regression as well as volcanic emissions from siberian traps eruptions continental floral and faunal distributions are consistent with this interpretation as are oceanic 13c patterns and variations in shallow water sediment lithologies

constraints on ceres internal structure and evolution from its shape and gravity measured by the dawn spacecraft ceres is the largest body in the asteroid belt with a radius of approximately 470 km in part due to its large mass ceres more closely approaches hydrostatic equilibrium than major asteroids pre dawn mission shape observations of ceres revealed a shape consistent with a hydrostatic ellipsoid of revolution the dawn spacecraft framing camera has been imaging ceres since march 2015 which has led to high resolution shape models of the dwarf planet while the gravity field has been globally determined to a spherical harmonic degree 14 equivalent to a spatial wavelength of 211 km and locally to 18 a wavelength of 164 km we use these shape and gravity models to constrain ceres internal structure we find a negative correlation and admittance between topography and gravity at degree 2 and order 2 low admittances between spherical harmonic degrees 3 and 16 are well explained by airy isostatic compensation mechanism different models of isostasy give crustal densities between 1 200 and 1 400 kg m3 with our preferred model giving a crustal density of 1 287 70 87 kg m3 the mantle density is constrained to be 2 434 5 8 kg m3 we compute isostatic gravity anomaly and find evidence for mascon like structures in the two biggest basins the topographic power spectrum of ceres and its latitude dependence suggest that viscous relaxation occurred at the long wavelengths 246 km our density constraints combined with finite element modeling of viscous relaxation suggests that the rheology and density of the shallow surface are most consistent with a rock ice salt and clathrate mixture

calibration of a conodont apatite based ordovician 87sr 86sr curve to biostratigraphy and geochronology implications for stratigraphic resolution the ordovician 87 sr 86 sr isotope seawater curve is well established and shows a decreasing trend until the mid katian however uncertainties in calibration of this curve to biostratigraphy and geochronology have made it diffi cult to determine how the rates of 87 sr 86 sr decrease may have varied which has implications for both the stratigraphic resolution possible using sr isotope stratigraphy and efforts to model the effects of ordovician geologic events we measured 87 sr 86 sr in conodont apatite in north american ordovician sections that are well studied for conodont biostratigraphy primarily in nevada oklahoma the appalachian region and ohio valley our results indicate that conodont apatite may provide an accurate medium for sr isotope stratigraphy and strengthen previous reports that point toward a signifi cant increase in the rate of fall in seawater 87 sr 86 sr during the middle ordovician darriwilian stage our 87 sr 86 sr results suggest that sr isotope stratigraphy will be most useful as a high resolution tool for global correlation in the mid darriwilian to mid sandbian when the maximum rate of fall in sr

strontium isotope stratigraphy of the middle devonian brachiopods and conodonts a set of 145 strontium isotope ratios based on skeletal components of emsian to frasnian age reveals a detailed structure of the seawater 87sr 86sr curve that can ultimately serve as a tool for high resolution isotope stratigraphy in the devonian brachiopod and conodont samples were collected in the eifel region of germany the area around the global stratotype for the middle devonian with an apparent average temporal resolution in the 105 y range preservation of the brachiopod shell material has been assessed by optical microscopy sem and cathodoluminescence and only the better preserved internal secondary layer of the shell has been utilized for strontium isotope measurements the 87sr 86sr curve shows a short decline from 0 7081 to 0 7078 through the late emsian followed by short term fluctuations with an amplitude of up to 10 4 around a mean of 0 7078 during the eifelian and givetian and a rise from late givetian into the late devonian the above high frequency oscillations and spikes are likely a reflection of condensed sedimentary records due to erosional and nondepositional events but a direct confirmation for such a scenario can be claimed only for the latest eifelian otomari event insufficient stratigraphic resolution precludes testing for the other events and isotopic spikes conodont skeletal elements even if well preserved at cai 2 5 yielded results that are mostly enriched in radiogenic 87sr if compared to coeval brachiopods although this enrichment is usually within the 10 5 range conodonts despite their superior stratigraphic resolution should be utilized only as a material of second choice in cases where brachiopods are rare or absent

a revised 87sr 86sr curve for the silurian implications for global ocean chemistry and the silurian timescale abstractrecent recalibration of the silurian timescale and improved global chronostratigraphic correlation of silurian strata significantly altered the silurian 87sr 86sr curve and the temporal extent of available data whereas previous silurian 87sr 86sr composites showed a generally monotonic increase throughout the silurian revisions to the silurian timescale now require a major increase in the rate of change in 87sr 86sr at or near the onset of the gorstian age of the ludlow epoch similarly improved chronostratigraphic correlations between silurian outcrops on anticosti island canada and gotland sweden indicate that the middle part of the telychian age which is roughly 10 15 of the total duration of the silurian period is undersampled and underrepresented in silurian 87sr 86sr composites a revised silurian 87sr 86sr curve based on 241 new and published analyses confirms the significant increase in the rate of change of 87sr 86sr toward more radiogenic values near the base of the ludlow ser

sr c and o isotope geochemistry of ordovician brachiopods a major isotopic event around the middle late ordovician transition here we present sr c and o isotope curves for ordovician marine calcite based on analyses of 206 calcitic brachiopods from 10 localities worldwide these are the first ordovician wide isotope curves that can be placed within the newly emerging global biostratigraphic framework a total of 182 brachiopods were selected for c and o isotope analysis and 122 were selected for sr isotope analysis seawater 87sr 86sr decreased from 0 7090 to 0 7078 during the ordovician with a major quite rapid fall around the middle late ordovician transition most probably caused by a combination of low continental erosion rates and increased submarine hydrothermal exchange rates mean 18o values increase from 10 to 3 through the ordovician with an additional short lived increase of 2 to 3 during the latest ordovician due to glaciation although diagenetic alteration may have lowered 18o in some samples particularly those from the lower ordovician maximum 18o values which are less likely to be altered increase by more than 3 through the ordovician in both our data and literature data we consider that this long term rise in calcite 18o records the effect of decreasing tropical seawater temperatures across the middle late ordovician transition superimposed on seawater 18o that was steadily increasing from 3 standard mean ocean water smow by contrast 13c variation seems to have been relatively modest during most of the ordovician with the exception of the globally documented but short lived latest ordovician 13c excursion up to 7 nevertheless an underlying trend in mean 13c can be discerned changing from moderately negative values in the early ordovician to moderately positive values by the latest ordovician these new isotopic data confirm a major reorganization of ocean chemistry and the surface environment around 465 to 455 ma the juxtaposition of the greatest recorded swings in phanerozoic seawater 87sr 86sr and 18o at the same time as one of the largest marine transgressions in phanerozoic earth history suggests a causal link between tectonic and climatic change and emphasizes an endogenic control on the o isotope budget during the early paleozoic better isotopic and biostratigraphic constraints are still required if we are to understand the true significance of these changes we recommend that future work on ordovician isotope stratigraphy focus on this outstanding middle late ordovician event

characterizing and navigating small bodies with imaging data recent advances in the characterization of small body surfaces with stereophotoclinometry are discussed the principal data output is an ensemble of landmark maps l maps high resolution topography albedo maps of varying resolution that tile the surface of the body because they can have a resolution comparable to the best images and can be located on a global reference frame to high accuracy l maps provide a significant improvement in discriminatory power for studies of small bodies ranging from regolith processes to interior structure these techniques are now being used to map larger bodies such as the moon and mercury l maps are combined to produce a standard global topography model gtm with about 1 57 million vectors and having a wide variety of applications they can also be combined to produce high resolution topography maps that describe local areas with much greater detail than the gtm when combined with nominal predictions from other data sources and available data from other instruments such as lidar or radar solutions for the spacecraft position and camera pointing are the most accurate available examples are drawn from studies of phobos eros and itokawa including surface characterization gravity analysis spacecraft navigation and incorporation of lidar or radar data this work has important implications for potential future missions such as deep interior and the level of navigation and science that can be achieved

strontium isotopic composition of mid cretaceous seawater the 87sr 86sr ratio in fish teeth separated from mid cretaceous marl and black shale from the northeastern apennines and venetian alps italy define three periods of low 87sr 86sr ratio at 121 to 124 million years ago ma 110 to 115 ma and 89 to 91 ma the 87sr 86sr excursions correspond to oceanic anoxic events represented by the livello selli livello 113 livello urbino and livello bonarelli black shale marker beds and probably reflect an increase in the low 87sr 86sr hydrothermal strontium flux associated with the emplacement of the ontong java and kerguelen plateaus 120 to 110 ma and the caribbean plateau 89 to 91 ma the modeled flux is consistent with the volumes and eruption rates of the oceanic plateaus but is far smaller than expected from the proposed cretaceous crustal production rates of 50 to 100 percent greater than modern

strontium isotope systematics of conodonts middle devonian eifel mountains germany abstract the eifel mountains lithological profile the stratotype for the middle devonian was densely sampled for conodonts to delineate the sr isotopic evolution of coeval sea water the 87sr 86sr curve obtained shows oscillations around a mean of about 0 7078 that have a frequency in the 105 106 yr range and an amplitude in the 10 5 10 4 range these oscillations mimic those obtained on coeval brachiopods diener et al 1996 but are shifted into more radiogenic domains by up to 10 4 model calculations suggest that the shift is due to partial 30 40 early diagenetic equilibration of conodonts with their enclosing bulk rock matrix the reality of partial recrystallisation is supported by visible neoformed blocky apatite crystals on the surface of the conodonts despite their otherwise apparently excellent preservation with cai values of 1 5 2 5 we therefore suggest that studies anticipating use of conodonts as a recorder of paleoceanographic events should be confined to specimens embedded in a relatively clean matrix such as pure limestone even these results should be cross checked by comparison with data on coeval low mg shells such as brachiopods or belemnites

darriwilian middle ordovician delta c 13 carb chemostratigraphy in the precordillera of argentina documentation of the middle darriwilian isotope carbon excursion mdice and its use for intercontinental correlation although documented from estonia latvia sweden eastern north america and china the middle ordovician darriwilian positive delta c 13 excursion known as the mdice has previously not been recognized with certainty in south america the most promising region in south america for detailed middle ordovician carbon isotope research is the precordillera of western argentina where there are many excellent exposures of biostratigraphically well dated carbonate successions spaning the tremadocian through sandbian stratigraphic interval for this project we collected numerous isotope and conodont samples from the middle darriwilian las chacritas and aguaditas formations at their type localities which yielded important biostratigraphic data as well as informative delta c 13 carb values in the e pseudoplanus zone in the upper half of the las chacritas formation there is a relatively modest but distinct delta c 13 carb excursion because its stratigraphic position and magnitude closely agree with the mdice in other parts of the world we recognize it as the first firm record of this excursion in south america the fact that the delta c 13 carb curve from the las aguaditas formation shows no such excursion is due to the existence of a stratigraphic gap between the lower and middle members of this formation that cuts out the excursion interval the precordilleran mdice is used for detailed long range correlations with successions in baltoscandia newfoundland and china illustrating the usefulness of also this delta c 13 carb excursion as a global stratigraphic tool a recent proposal of a greatly extended chronostratigraphic range of the table head group on newfoundland is rejected based on well established biostratigraphic evidence c 2013 elsevier b v all rights reserved less

radiogenic isotope composition of carboniferous seawater from north american epicontinental seas abstract abundant marine sedimentary deposits accumulated in the epeiric seas of north america during the carboniferous period 359 299 ma when the earth s climate shifted from a global greenhouse to icehouse geochemical records extracted from these deposits are often assumed to reflect global ocean processes and are increasingly being used to infer relationships between tectonism carbon cycling and climate change we analyzed radiogenic isotopes sr nd in biogenic apatite along a north american transect to constrain the degree of coupling between the epicontinental seas and the open ocean in many samples the primary sr signal is altered however the original nd isotopic composition of the biogenic apatite seems to be preserved the end t values range from 8 6 to 4 5 in the us midcontinent basins and from 11 4 to 5 7 at arrow canyon nevada usa indicating the development of an east west geochemical gradient throughout the pennsylvanian this apparent decoupling of the epicontinental seas from the open ocean was established by the latest mississippian thus circulation of waters between epicontinental seaways of western us and the basins to the east and south was periodically restricted shifts toward unradiogenic nd at arrow canyon seem to correspond with glacio eustatic changes across the mid carboniferous boundary these end t variations may have been caused by changes in weathering rates sources marine circulation or a combination of both

ordovician and silurian sea water chemistry sea level and climate a synopsis following the cambrian explosion and the appearance in the fossil record of most animal phyla associated with a range of new body plans the ordovician and silurian periods witnessed three subsequent major biotic events the great ordovician biodiversification event the end ordovician extinction the first animal extinction and second largest of the five mass extinctions of the phanerozoic and the early silurian postextinction recovery there are currently no simple explanations for these three major events combined extrinsic geological and intrinsic biological factors probably drove the biodiversifications and radiations and the appearance and disappearance of marine habitats have to be analysed in the frame of changing palaeogeography palaeoclimate and sea water chemistry the present paper reviews the relationships of the three biotic events to chemical and physical processes occurring in the ocean and atmosphere during the ordovician and silurian including sea level changes geochemical proxies 13c 18o 87sr 86sr of the ocean waters and the evolution of the atmosphere oxygen and carbon dioxide content less

precise timing of the late ordovician sandbian super eruptions and associated environmental biological and climatological events two of the largest known eruptions in the phanerozoic produced the ordovician millbrig k bentonite of north america and the kinnekulle k bentonite of scandinavia which have been previously suggested to be coeval the millbrig k bentonite from kentucky usa and the kinnekulle k bentonite from bornholm denmark yielded chemical abrasion thermal ionization mass spectrometry u pb zircon dates of 452 86 0 29 and 454 41 0 17 ma 2 analytical uncertainty respectively thus showing significant age differences contrary to what is generally held these data and four additional newly dated k bentonites directly establish the first radioisotopic age constraints for the ordovician katian sandbian global stage boundary refine global stratigraphic correlations date associated chemostratigraphic events and suggest an alternative volcanic climate hypothesis for the late ordovician supplementary material u pb radioisotopic data table and analytical methods are available at www geolsoc org uk sup18636

preservation of seawater sr and nd isotopes in fossil fish teeth bad news and good news abstract we analyzed 87sr 86sr ratios in foraminifera pore fluids and fish teeth for samples ranging in age from eocene to pleistocene from four ocean drilling program sites distributed around the globe site 1090 in the cape basin of the southern ocean site 757 on the ninetyeast ridge in the indian ocean site 807 on the ontong java plateau in the western equatorial pacific and site 689 on the maud rise in the southern ocean sr isotopic ratios for dated foraminifera consistently plot on the global seawater sr isotope curve for sites 1090 757 and 807 sr isotopic values of the pore fluids are generally less radiogenic than contemporaneous seawater values as are values for fossil fish teeth in contrast pore fluid 87sr 86sr values at site 689 are more radiogenic than contemporaneous seawater and the corresponding fish teeth also record more radiogenic values thus sr isotopic values preserved in fossil fish teeth are consistently altered in the direction of the pore fluid values furthermore there is a correlation between the magnitude of the offset between the pore fluids and the seawater curve and the associated offset between the fish teeth and the seawater curve these data suggest that the hydroxyfluorapatite of the fossil fish teeth continues to recrystallize and exchange sr with its surroundings during burial and diagenesis therefore sr chemostratigraphy can be used to determine rough ages for fossil fish teeth in these cores but cannot be used to fine tune age models in contrast to the sr isotopic system our nd concentration data combined with published isotopic and rare earth element data suggest that fish teeth acquire nd during early diagenesis while they are still in direct contact with seawater the concentrations of nd acquired at this stage are extremely high relative to the concentrations in surrounding pore fluids as a result nd isotopes are not altered during burial and later diagenesis therefore fossil fish teeth from a variety of marine environments preserve a reliable and robust record of deep seawater nd isotopic compositions from the time of deposition

high resolution shape model of ceres from stereophotoclinometry using dawn imaging data abstract we present a high resolution global shape model of ceres determined using the stereophotoclinometry technique developed at the jet propulsion laboratory by processing dawn s framing camera data acquired during approach to post low altitude mapping orbit lamo phases of the mission a total of about 38 000 images were processed with pixel resolutions ranging from 35 6 km pixel to 35 m pixel and the final global shape model was produced with 100 m grid spacing the final spc derived topography was computed relative to the 482 km 482 km 446 km mean ellipsoid which ranges from 7 3 km to 9 5 km for the purpose of validation we performed various error analyses to assess and quantify realistic uncertainties in the derived topography such as dividing the data into different subsets and re computing the entire topography based on these studies we show that the average total height error of the final global topography model is 10 2 m and 88 9 of the surface has the total height error below 20 m we also provide improved estimates of several physical parameters of ceres the resulting gm estimate is 62 62905 0 00035 km3 s2 or the mass value of 938 392 0 005 1018 kg the volume estimate is 434 13 0 50 106 km3 with a volumetric mean radius of 469 72 km combined with the mass estimate the resulting bulk density is 2161 6 2 5 kg m3 other improved parameters include the pole right ascension 0 291 42763 0 0002 pole declination 0 66 76033 0 0002 and prime meridian and rotation rate of w0 170 309 0 011 and dw dt 952 1532635 0 000002 deg day respectively also for geophysical and geological studies we provide spherical harmonic coefficients and a gravitational slope map derived from the global shape model

true polar wander of ceres due to heterogeneous crustal density ceres is the largest body in the main asteroid belt it was recently explored by the dawn mission to uncover strong similarities with other icy bodies the morphological features observed on the surface of ceres indicate a relatively wide range of water ice concentrations leading us to investigate the magnitude and distribution of crustal density heterogeneities and to consider whether they could have caused a reorientation of ceres here we present three independent and corroborating lines of evidence for the true polar wander of ceres thanks to the global gravity inversion approach applied to the shape and gravity data of ceres we find crustal density heterogeneities up to approximately 0 3 g cm 3 with a prominent positive density anomaly aligned with the equator in the region of ahuna mons the topography shows the remnants of an equatorial ridge compatible with the position of the palaeo equator and indicates that ceres reoriented by approximately 36 with the palaeo pole following an indirect path to the current pole of ceres the tectonic patterns generated by the true polar wander are in close agreement with the location and orientation of the samhain catenae and uhola catenae crustal fractures these results highlight the complex interior structure and richness of processes taking place in ceres scale icy bodies the dwarf planet ceres may have reoriented in the past due to a heterogeneously dense crust a scenario consistent with gravity and topographic data and the distribution of crustal fractures

long lived glaciation in the late ordovician isotopic and sequence stratigraphic evidence from western laurentia the timing and causes of the transition to an icehouse climate in the late ordovician are controversial results of an integrated 13c and sequence stratigraphic analysis in nevada show that in the late ordovician chatfieldian stage mid caradoc a positive 13c excursion in the upper part of the copenhagen formation was closely followed by a regressive event evidenced within the prominent eureka quartzite the chatfieldian 13c excursion is known globally and interpreted to record enhanced organic carbon burial which lowered atmospheric p co2 to levels near the threshold for ice buildup in the ordovician greenhouse climate the subsequent regressive event in central nevada previously interpreted as part of a regional tectonic adjustment is here attributed in part to sea level drawdown from the initiation of continental glaciation on gondwana this drop in sea level which may have contributed to further cooling through a reduction in poleward heat transport and a lowering of p co2 by suppressing shelf carbonate production signals the transition to a late ordovician icehouse climate 10 m y before the widespread hirnantian glacial maximum at the end of the ordovician

the interior structure of ceres as revealed by surface topography abstract ceres the largest body in the asteroid belt 940 km diameter provides a unique opportunity to study the interior structure of a volatile rich dwarf planet variations in a planetary body s subsurface rheology and density affect the rate of topographic relaxation preferential attenuation of long wavelength topography 150 km on ceres suggests that the viscosity of its crust decreases with increasing depth we present finite element fe geodynamical simulations of ceres to identify the internal structures and compositions that best reproduce its topography as observed by the nasa dawn mission we infer that ceres has a mechanically strong crust with maximum effective viscosity 10 25 pa s combined with density constraints this rheology suggests a crustal composition of carbonates or phyllosilicates water ice and at least 30 volume percent vol low density high strength phases most consistent with salt and or clathrate hydrates the inference of these crustal materials supports the past existence of a global ocean consistent with the observed surface composition meanwhile we infer that the uppermost 60 km of the silicate rich mantle is mechanically weak with viscosity 21 pa s suggesting the presence of liquid pore fluids in this region and a low temperature history that avoided igneous differentiation due to late accretion or efficient heat loss through hydrothermal processes

mars high resolution gravity fields from mro mars seasonal gravity and other dynamical parameters abstract with 2 years of tracking data collection from the mro spacecraft there is noticeable improvement in the high frequency portion of the spherical harmonic mars gravity field the new jpl mars gravity fields mro110b and mro110b2 show resolution near degree 90 additional years of mgs and mars odyssey tracking data result in improvement for the seasonal j 3 gravity changes which compares well to global circulation models and odyssey neutron data and mars rotation and precession 7594 10 mas year once atmospheric dust is accounted for in the spacecraft solar pressure model solutions for mars solar tide are consistent between data sets and show slightly larger values k2 0 164 0 009 after correction for atmospheric tide compared to previous results further constraining core models an additional 4 years of mars range data improves the mars ephemeris determines 21 asteroid masses and bounds solar mass loss dgmsun dt

strontium isotope evolution of late permian and triassic seawater the 87sr 86sr values based on brachiopods and conodonts define a nearly continuous record for the late permian and triassic intervals minor gaps in measurements exist only for the uppermost brahmanian lower part of the upper olenekian and middle norian and only sparse data are available for the late permian these 219 measurements include 67 brachiopods and 114 conodont samples from the tethyan realm as well as 37 brachiopods and one conodont sample from the mid european middle triassic muschelkalk sea the late permian lower triassic interval is characterized by a steep 1 3 10 3 rise from 0 7070 at the base of the dzhulfian to 0 7082 in the late olenekian a rate of change comparable to that in the cenozoic in the mid triassic anisian and ladinian the isotope values fall to 0 7075 followed again by a rise to 0 7081 in the middle late norian the 87sr 86sr values decline again in the late norian sevatian and rhaetian to 0 7076 the sharp rise in the 87sr 86sr values during the late permian early triassic was coincident with widespread clastic sedimentation because of the paucity of tectonic uplifts the enhanced erosion may have been due to intermittent humid phases during mainly an arid interval coupled with the absence of a dense protective land plant cover following the mass extinction during the latest permian the apex of the 87sr 86sr curve at the olenekian anisian boundary coincides with cessation of the large scale clastic sedimentation and also marks the final recovery of land vegetation as indicated by the renewed onset of coal formation in the middle triassic the rising 87sr 86sr values from the middle carnian to the late norian coincide with the uplift and erosion of the cimmeride indosinian orogens marking the closure of the palaeotethys the subsequent rhaetian decline that continues into jurassic pliensbachian toarcian boundary on the other hand coincides with the opening of the vardar ocean and its eastern continuation in the izmir ankara ophiolitic belt samples from the upper muschelkalk are more radiogenic than the global trend this may reflect separation of the basin from the open ocean due to strong meteoric influx from a large land mass in the north the germanic basin became increasing brackish up section in the north and east but because of the high evaporation rates the salt content was not much reduced in the southern and central basin where a rich but increasingly endemic marine fauna survived

the ceres gravity field spin pole rotation period and orbit from the dawn radiometric tracking and optical data abstract ceres gravity field and rotational parameters have been precisely measured using 1 5 years of radiometric doppler and range data and optical landmark tracking from the dawn spacecraft in orbit about the dwarf planet as was the case with dawn at vesta the gravity field orientation parameters landmark locations and ceres orbit are jointly estimated in a global solution even though dawn s radio science investigation at ceres was complicated by additional thrusting for attitude control the resulting spherical harmonic gravity field has a half wavelength resolution of up to 82 km degree 18 near the equator which is similar harmonic resolution to that of vesta the gravity field is consistent with airy isostatic compensation and this model assumption limits ceres crustal density to be between 1200 and 1600 kg m 3 for two layer and three layer models with mean crustal thickness between 27 and 43 km the compensation depth is determined using admittance between gravity and gravity from topography and is superior to admittance between gravity and topography the gravitational mass of ceres is determined to better than 0 002 gm ceres 62 62736 0 00040 km 3 s 2 the spin pole location is improved by 10 over previous results with right ascension 291 427 and declination 66 760 uncertainty less than 0 001 and the rotation rate is improved by 100 over previous determinations from hubble space telescope hst images ceres heliocentric orbit has also been improved with about 17 months of precision range measurements reducing ephemeris uncertainties to about 10 m during the dawn timeframe