global hydrocarbon seep carbonate precipitation correlates with deep water temperatures and eustatic sea level fluctuations since the late jurassic the anaerobic oxidation of methane aom in marine sediments most obviously at cold seeps is a major sink for this important greenhouse gas and is associated with the precipitation of carbonates the geological record of seep carbonates provides insights into the long term dynamics of this process since the late jurassic rates of seep carbonate precipitation have been high during times of low sea levels and cold deep water temperatures and vice versa one possibility is that sea level fall decreases the thickness of the methane hydrate stability zone in the sediment so that gas hydrates decompose in deeper sediments thereby increasing seepage and carbonate precipitation alternatively low deep water temperature facilitates gas hydrate formation on continental slopes and may thereby increase methane availability for aom performing consortia and associated carbonate precipitation these correlations and their potential causes may be of interest for the modelling of global carbon budgets and of past and future climates

tuffaceous marker horizons in the koobi fora region and the lower omo valley eight tuffs can now be correlated between the shungura formation in the lower omo valley ethiopia and the sediments in the koobi fora region kenya re evaluation of the stratigraphy shows that at least 475 m of sediment was deposited in the koobi fora region

diversity dynamics of early and middle jurassic brachiopods in the getic and danubian tectonic units of eastern serbia regional versus global patterns abstract quantitative assessment of regional diversity patterns reveals trajectories of faunal development on the basin scale and helps to understand its dependence on palaeoenvironmental changes global scale biotic evolution and major events in the history of the earth a total of 86 species 50 genera 18 families and 9 superfamilies of early and middle jurassic brachiopods are established in the getic and danubian tectonic units of eastern serbia compilation of their stratigraphic ranges allows analysis of their total diversity number of appearances and disappearances and turnovers in both units brachiopods radiated rapidly in the early pliensbachian then their diversity declined and these fossils disappeared a new radiation took place in the late bajocian and brachiopods remained diverse until the end of the bathonian they disappeared before the callovian in the getic unit and in the early callovian in the danubian unit the early pliensbachian radiation was significantly stronger than the late bajocian at the level of species the strength of these radiations was more or less comparable at higher taxonomic levels the strength of turnovers among brachiopods differed through geological time the composition of the middle jurassic brachiopod assemblages was more or less stable regional shoreline shifts basin depth changes palaeobiogeographical changes and plate tectonic re organizations were possible controls on regional patterns of brachiopod diversity dynamics however the latter also reflects some diversity patterns documented globally and in some other regions the bakony mountains the swiss jura mountains and the northern caucasus

quartz vein fabrics coupled to elevated fluid pressures in the stawell gold deposit south eastern australia shear and extensional veins formed during the reactivation of the magdala shear system at stawell in western victoria australia contribute to the formation of the auriferous central and basalt contact lodes within this shear system is a range of fault rocks accompanied by steep dipping 65 quartz rich laminated shear veins and relatively flat lying extensional veins both vein sets appear to have been a primary source for the host rock permeability during fluid flow in a regime of significant deviatoric stresses the macro and microstructures suggest that the dilatancy that produced mineralized veins formed under conditions of overpressure generated by fluid infiltration late in a tectonic regime a new microfabric analysis technique is used to investigate the quartz rich veins which allows rapid integration of the microstructure with the crystallographic preferred orientations cpos both the shear and extensional quartz veins have a random cpo with 120 dihedral angles between the quartz quartz grains which is typical of a metamorphic equilibrium microfabric the microstructures indicate that the quartz has undergone extensive grain adjustment in the solid state with grain shape and size affected by interfacial solution pressure solution effects these features are consistent with inferences from experimental rock deformation studies where grain boundary migration is enhanced in a water rich environment the onset of solution transfer processes pressure solution developed as the quartz microfabric stabilized and continued to modify the cpo and microstructure significantly it is concluded that grain growth and pressure solution are coupled diffusive mass transfer processes related to fluctuations in pore fluid pressures in a region undergoing deformation at near lithostatic pressures

morphological disparity of ammonoids and the mark of permian mass extinctions the taxonomic diversity of ammonoids in terms of the number of taxa preserved provides an incomplete picture of the extinction pattern during the permian because of a strongly biased fossil record the analysis of morphological disparity the variety of shell shapes is a powerful complementary tool for testing hypotheses about the selectivity of extinction and permits the recognition of three distinct patterns first a trend of decreasing disparity ranging for about 30 million years led to a minimum disparity immediately before the permian triassic boundary second the strongly selective capitanian crisis fits a model of background extinction driven by standard environmental changes third the end permian mass extinction operated as a random nonselective sorting of morphologies which is consistent with a catastrophic cause

testing the fossil record sampling proxies and scaling in the british triassic jurassic the quality of the fossil record varies immensely across taxa geographic regions environments and time intervals because much of this variation can be confounded when examining global patterns we present a detailed investigation of the british triassic and jurassic one of the most intensively studied pairs of systems in the world marine jurassic palaeodiversity is at least partly controlled by rock availability and accessibility the terrestrial record is patchier and effects of rock availability are overprinted by a stronger signal of sporadic preservation these results also fit a sea level driven common cause explanation as one would expect to see close correlation between rock availability and palaeodiversity in the marine realm but less so in the terrestrial formation counts and palaeodiversity do not correlate a surprising result given the number of earlier studies that have found close correlations however this study differs from most others in that formation counts and palaeodiversity metrics are derived from independent data sources and so within study redundancy is avoided the study confirms the complexity of rock fossil time series and the likelihood that the fossil record documents a complex mix of potential biological signal common cause signal and rock record and sampling bias it may be impossible to identify a useful simple sampling proxy for the fossil record that captures every bias and sampling error ironically when preservation is good sampling proxies representing rock availability such as outcrop area can be used to predict palaeodiversity but are ineffectual when the fossil record is patchy

organism substrate interactions and astrobiology potential models and methods abstract organism substrate interactions and their products biogenic structures are important biosignatures on earth this study discusses the application of ichnology the study of organism substrate interactions to the search for present and past life beyond earth three main questions are addressed 1 why to look for biogenic structures i e traces and ichnofabrics beyond earth 2 what biogenic structures to expect on other planets moons and asteroids 3 how to study extraterrestrial biogenic structures review of terrestrial evidence highlights a set of properties that make traces and ichnofabrics important for the search of potential extraterrestrial life trace fossils preserve the activity of soft bodied organisms biogenic structures are resilient to processes that obliterate other biosignatures i e mechanical and chemical degradation diagenesis tectonism and metamorphism traces are very visible biosignatures traces indicate environment and behaviour traces can be universal biosignatures i e biosignatures ideally suited for detecting any type of life a model of organism substrate interactions beyond earth is here proposed expected extraterrestrial traces are those that manifest behaviours that allow to maintain homeostasis excavations meandering traces and biodeposition structures most of the existing rovers and orbiters provide basic instruments for searching these traces it is here suggested that the search for extraterrestrial biogenic structures by rovers would also benefit from artificial adjustable lighting gpr lidar and drilling equipment with optical televiewer in this study open access databases of rover and orbiter imagery have been searched for traces and ichnofabrics but no unquestionable evidence of biogenic structures beyond earth has been found besides those produced by humans this sounds along the lines of the famous fermi paradox if the universe is teeming with aliens where are their traces results of this search show that habitable environments are not the only place to look for biogenic structures non habitable environments such as moons without atmosphere can favour the preservation of shallow tier traces the better preservation potential of traces compared to other biosignatures greatly widens the issue of planetary protection including the interaction between astronauts or vehicles and the substrate may produce disturbances although this study highlights a new direction of study with the tools and concepts of ichnology dialogue between the astrobiological and ichnological communities is needed to use its full potential and possibly answer one of the major questions of science does life exist beyond earth

origination and extinction through the phanerozoic a new approach abstract temporal patterns of origination and extinction are essential components of many paleontological studies but it has been difficult to obtain accurate rate estimates because the observed record of first and last appearances is distorted by the incompleteness of the fossil record here i analyze observed first and last appearances of marine animal and microfossil genera in a way that explicitly takes incompleteness and its variation into consideration this approach allows estimates of true rates of origination and extinction throughout the phanerozoic substantial support is provided for the proposition that most rate peaks in the raw data are real in the sense that they do not arise as a consequence of temporal variability in the overall quality of the fossil record even though the existence of rate anomalies is supported their timing is nevertheless open to question in many cases if one assumes that rates of origination and extinction are constant through a given stratigraphic interval then

exceptional fossil preservation during co2 greenhouse crises abstract exceptional fossil preservation may require not only exceptional places but exceptional times as demonstrated here by two distinct types of analysis first irregular stratigraphic spacing of horizons yielding articulated triassic fishes and cambrian trilobites is highly correlated in sequences in different parts of the world as if there were short temporal intervals of exceptional preservation globally second compilations of ages of well dated fossil localities show spikes of abundance which coincide with stage boundaries mass extinctions oceanic anoxic events carbon isotope anomalies spikes of high atmospheric carbon dioxide and transient warm wet paleoclimates exceptional fossil preservation may have been promoted during unusual times comparable with the present co 2 greenhouse crises of expanding marine dead zones oceanic acidification coral bleaching wetland eutrophication sea level rise ice cap melting and biotic invasions

pterosaur diversity untangling the influence of sampling biases lagerstatten and genuine biodiversity signals abstract pterosaurs were a diverse and successful group of mesozoic reptiles with an evolutionary history that extended for approximately 145 myr recent attempts to understand species richness trajectories for pterosaurs have led to them becoming a focal group for ongoing debate about the importance of sampling biases in determining observed species richness patterns in the vertebrate fossil record here we reanalyse pterosaur species richness through time and make statistical comparisons to proxies for pterosaur fossil record sampling and global terrestrial tetrapod sampling using several approaches including generalised least squares multiple regression models moreover we make quantitative comparisons between species richness and morphological diversity disparity sampling of the pterosaur fossil record shows substantial temporal heterogeneity with cretaceous pterosaur records more commonly recovered from terrestrial environments and with sampling proxies for cretaceous pterosaurs closely tracking global sampling proxies for terrestrial tetrapods the similarities between pterosaur based and global sampling proxies for cretaceous data call into question the hypothesis that observed correlations between pterosaur sampling proxies and pterosaur species richness result from mere redundancy multiple regression modelling supports the hypothesis that much of the variation present in pterosaur palaeobiodiversity curves results from a combination of the presence or absence of lagerstatten sites of exceptional preservation and a background sampling signal that may reflect temporal variation in fossiliferous sedimentary rock despite these evident strong biases in the pterosaur record it seems plausible that both species richness and disparity peaked relatively late in the evolutionary history of pterosaurs during the late jurassic early cretaceous although an absence of pterosaur bearing terrestrial lagerstatten in the late triassic early jurassic fossil record means that caution is required it is possible that a late peak in diversity may reflect the ecological radiation of pterodactyloid pterosaurs from the late jurassic onwards which has been linked to increased terrestrial locomotory abilities and ecological niche occupancy and relaxed constraints upon body size evolution

assessing sampling of the fossil record in a geographically and stratigraphically constrained dataset the chalk group of hampshire southern uk taphonomic geological and sampling processes have been cited as biasing richness measurements in the fossil record and sampling proxies have been widely used to assess this however the link between sampling and taxonomic richness is poorly understood and there has been much debate on the equivalence and relevance of proxies we approach this question by combining both historical and novel data a historical fossil occurrence dataset with uniquely high spatial resolution from the upper cretaceous chalk group of hampshire uk and a newly compiled 3d geological model that maps subsurface extent the geological model provides rock volumes and these are compared with exposure and outcrop area sampling proxies that have often been conflated in previous studies the extent to which exposure area true rock availability has changed over research time is also tested we find a trend of low cenomanian to high turonian to campanian raw richness which correlates with and is possibly driven by the number of specimens found after sampling standardization an unexpected mid turonian peak diversity is recovered and sampling standardized genus richness is best predicted by rock volume suggesting a species area or genus area effect additionally total exposure area has changed over time but relative exposure remains the same supplementary materials a locality list abundance matrix and all correlation and modelling results are available at https doi org 10 6084 m9 figshare c 3592208

current and historical perspectives on the completeness of the fossil record of pelycosaurian grade synapsids abstract understanding of the early evolution of tetrapods may have been influenced by the effects of geological and anthropogenic sampling biases as suggested by previous studies here we make a thorough assessment of how these and other biases affect the record of pelycosaurian grade synapsids a group of tetrapods that dominated the terrestrial realm during the late carboniferous and early permian modified versions of the character and skeletal completeness metrics are used to assess the completeness of the known specimens while a recently published supertree of basal synapsids is tested for congruence between the stratigraphic and phylogenetic hypotheses a historical analysis is also applied to the record in order to show how the biases in the study of this group over the past centuries may have influenced the current record the results show that the completeness of basal synapsid specimens shows very little variation throughout the early permian a peak in skeletal and character completeness metric values in the middle permian wordian is attributed to exceptional preservation of the mezen fauna a significant negative correlation is found between the skeletal completeness metric and a taxic diversity curve of pelycosaurs implying a tendency to name many species based on poor material the lack of correlation between the character completeness metric and diversity is attributed to the history of discovery in the group the majority of pelycosaur species were named between the 1930s and 1960s when character based assignments were secondary to size location and stratigraphy a strong correspondence between the phylogeny and stratigraphy implies a reliable phylogenetic hypothesis but the low relative completeness index score suggests that a great deal of the fossil record is missing while the relative completeness index has improved over the past century the rate of improvement has slowed in the last two decades and the slowing rate of discovery of new species suggests that the limit of what the fossil record of pelycosaurs has to offer is being approached a consistent shape of diversity curves over the past century implies that the same biases which affected the record in the past are still affecting it now this study highlights the need for sampling correction methods to be employed in studies of early synapsids

no gap in the middle permian record of terrestrial vertebrates during the permian tetrapods showed a major transition from basal synapsid dominated faunas in the first half to therapsid dominated faunas in the second the transition was significant in marking the beginning of richer and more complex communities a precursor to modern terrestrial ecosystems this changeover may have been gradual or abrupt but its study has been complicated by the postulated occurrence of a substantial hiatus in the fossil record termed olson9s gap which obscured the nature of the turnover new evidence from redating of key tetrapod bearing units of the american southwest and european russia confirms that there is no gap in the fossil record of permian tetrapods indeed evidence for substantial sampling bias in the permian tetrapod fossil record as a whole is queried

mesozoic mammaliaform diversity the effect of sampling corrections on reconstructions of evolutionary dynamics abstract recent years have witnessed an explosion of new fossil discoveries and analyses documenting the unappreciated ecological and morphological diversity of mesozoic mammaliaformes in contrast the taxonomic diversity dynamics through the first 165 million years of mammal evolution have not yet been rigorously analysed leaving patterns of diversification during this important period open to conjecture here we present a comprehensive statistical analysis of global mammaliaform diversity spanning from the late triassic appearance of mammaliaforms 230 million years ago hereafter mya to the end cretaceous mass extinction 66 mya we analysed 691 occurrences representing 367 genera and 550 species in standard time bins of approximately 10 million years in duration significant correlations between diversity and sampling proxies suggest sampling biases in the mammaliaform fossil record shareholder quorum subsampling and model based approaches were used to mediate these biases after applying these methods the following patterns were supported low standing diversity during the late triassic early jurassic evolution of early mammaliaformes e g morganucodonts was followed by high standing diversity during the late jurassic due primarily to the diversification of eutriconodonta multituberculata and cladotheria this peak was followed by a fall in diversity during the middle of the hauterivian barremian interval suggesting that extinctions typically associated with the jurassic cretaceous boundary may instead have occurred later during the early cretaceous standing diversity recovered through several fluctuations during the mid cretaceous approximately barremian to albian leading to a second peak in the campanian that reflects the diversification of key clades including therians analyses of geographically restricted datasets illustrate a significant spatial heterogeneity in sampling with several intervals dominated by north american occurrences uneven sampling effort and geographic heterogeneities in the fossil record are significant factors affecting reconstructions of mesozoic mammaliaform diversity and correcting these biases can markedly alter observed patterns and their interpretation

a survey of palaeontological sampling biases in fishes based on the phanerozoic record of great britain fishes represent more than half of all living vertebrate species but patterns of fish diversity remain little explored in the fossil record a compendium of fossil occurrences from great britain was assembled in order to address a series of questions concerning the palaeontological record of fishes there are broad similarities between british richness trajectories and those compiled from global data including an initial peak in the mid palaeozoic devonian or carboniferous depending on the compilation with a late palaeozoic trough followed by a sharp rise in diversity in the late cretaceous and paleogene the british dataset is too small to reveal any significant differences in richness between time bins using subsampling but a modelling approach based on sampling and geological proxies consistently shows lower than predicted richness in the silurian devonian and higher than predicted richness in the late cretaceous and eocene this positive excursion is robust to the exclusion of data from the early eocene london clay lagerstatte chondrichthyans sharks rays and ratfishes and osteichthyans ray finned and lobe finned fishes show contrasting relationships with geological and sampling proxies possibly reflecting different taphonomic profiles or idiosyncratic variation in the relative proportion of freshwater and marine deposits over the british phanerozoic

beach orientation bar morphology and the concentration of metalliferous placer deposits a case study lake turkana n kenya the concentration of metalliferous particles in migrating swash bars is shown to depend upon processes controlled by the cross sectional shape of the bar a sand spit provides two shorelines each with a different pattern of wind waves and each characterized consistently by bars of different shape where the wave period is low the bar is dune like and its crest is set asymmetrically landward of the centre line where the wave period is high the bar is tabular with a crest set just at the swash limit and on the lakeward side of the centre line these differences in shape are important to the concentrating process it is shown that swash dominated dune like forms produce concentrations of metalliferous grains that average only 13 the tabular bar form on the other hand effects a significantly higher concentration of 21 through a hydrodynamic sorting process that is governed by limited swash overspill onto the landward slope concentrations of 90 are reached at specific positions confirmation of the concentrating process is obtained from detailed microstratigraphic interpretation of the contemporary bar while the ancient bars of abandoned shorelines add supporting evidence clear cut differences in placer concentration allow several diagnostic parameters to be identified for reconnaissance exploration these include shore line orientation wave pattern and bar cross sectional morphology which can be combined with the reconstruction of abandoned shorelines using remote sensing imagery to provide a resource evaluation

impacts of global warming on permo triassic terrestrial ecosystems geologists and palaeontologists have expressed mixed views about the effects of the end permian mass extinction on continental habitats and on terrestrial life current work suggests that the effects on land were substantial with massive erosion following the stripping of vegetation associated with long term aridification and short term bursts of warming and acid rain wildfires at the permo triassic boundary contributed to the removal of forests and the prolonged absence of forests from the earth s surface for up to 10 myr these physical crises on land impinged on the oceans suggesting tight interlocking of terrestrial and marine crises levels of extinction on land may well have been as high as in the sea and this is certainly the case for tetrapods the mass extinction seems to have been less profound for plants and insects but it is hard at present to disentangle issues of data quality from reductions in abundance and diversity several killing agents have been proposed and of these tetrapods may have succumbed primarily to acid rain mass wasting and aridification plants may have been more affected by the sudden effects of heating and wildfires and the crisis for insects has yet to be explored

diversity patterns of the vascular plant group zosterophyllopsida in relation to devonian paleogeography abstract the zosterophyllopsida originated in the silurian and became prominent vascular components of early devonian floras worldwide an updated dataset of zosterophyllopsids at species level is analyzed to compare the taxic composition of five putative paleophytogeographic units laurussia siberia northwestern gondwana kazakhstan and northeastern gondwana i e australia china and the shan thai block the high level of endemicity shown by each unit confirms the phytogeographic differentiation and the occurrence of geographical barriers preventing massive floral exchanges between the corresponding regions for the late silurian early devonian time interval statistical analyses conducted on the three largest datasets those corresponding to laurussia siberia and northeastern gondwana indicate that the diversity dynamics of the group followed the same pattern in these regions almost all taxic diversity measures show that specific diversity was greatest in the middle and late pragian diversity dropped significantly thereafter however residual diversity reveals genuine regional patterns from this we show that the radiation of the zosterophyllopsida may have stopped earlier in northeastern gondwana and siberia than laurussia we propose that the onset of these extinctions resulted from the competitive replacement of the zosterophyllopsids by increasingly diversified lycopsids and basal euphyllophytes whose evolution could have been favored by external factors

cosmogenic nuclide age constraints on middle stone age lithics from niassa mozambique abstract the late phases of the middle stone age msa in the east african rift system ears are known for their evolutionary shifts and association with bottlenecks transcontinental expansion and climatic fluctuations the chronology of msa sites contemporaneous with these eco demographic upheavals is uncertain because of the scarcity of datable sites and the poor understanding of their depositional and erosional histories we apply terrestrial cosmogenic nuclide dating in a stratigraphic section with a complex exposure history to the study of the luchamange beds a widespread sedimentological unit underlying msa sites from the shores of lake niassa mozambican ears we use an innovative approach which may be applicable elsewhere to calculate their age using a monte carlo based bayesian model that links depth profiles of 26al and 10be and uses other geomorphic and cosmogenic nuclide age constraints on episodic erosion and burial the age of the basal luchamange beds is 42 77 15 ka and the msa occupation on top is 29 3 11 ka these dates suggest temporal overlap between msa and the earliest later stone age and diversity in cultural manifestations at the end of the msa

phanerozoic transgressions and regressions on the continents a quantitative approach based on areas flooded by the sea and areas of marine and continental deposition

geological and anthropogenic controls on the sampling of the terrestrial fossil record a case study from the dinosauria dinosaurs provide excellent opportunities to examine the impact of sampling biases on the palaeodiversity of terrestrial organisms the stratigraphical and geographical ranges of 847 dinosaurian species are analysed for palaeodiversity patterns and compared to several sampling metrics the observed diversity of dinosaurs theropoda sauropodomorpha and ornithischia are positively correlated with sampling at global and regional scales sampling metrics for the same region correlate with each other suggesting that different metrics often capture the same signal regional sampling metrics perform well as explanations for regional diversity patterns but correlations with global diversity are weaker residual diversity estimates indicate that sauropodomorphs diversified during the late triassic but major increases in the diversity of theropods and ornithischians did not occur until the early jurassic diversity increased during the jurassic but many groups underwent extinction during the late jurassic or at the jurassic cretaceous boundary although a recovery occurred during the cretaceous only sauropodomorphs display a long term upward trend the campanian maastrichtian diversity peak is largely a sampling artefact there is little evidence for a gradualistic decrease in diversity prior to the end cretaceous mass extinction except for ornithischians and when such decreases do occur they are small relative to those experienced earlier in dinosaur evolution the geological society of london 2011

variability of particle size characteristics of sheetwash sediments and fluvial suspended sediment in a small semiarid catchment kenya abstract the variability of particle size characteristics for sheetwash sediments and fluvial suspended sediments are presented data for three representative storm events are described for a small 0 30 km2 erodible semiarid catchment suspended sediment output per event ranged from 340 to 810 t km 2 ninety eight percent of the suspended sediment was less than 63 m and was supplied from remobilization of stored colluvium discharge and particle size class relationships were complex for individual storm events but were best described by third order polynomial functions results of a one way analysis of variance showed that concentrations of total suspended sediment silt and sand varied significantly between storm events temporal variation of clay concentration in runoff were not significant suggesting that a single hillslope source area contributed to the channel subsystem the mean grain size and sorting of sheetwash sediments were significantly different from fluvial suspended sediment for individual storm events sheetwash sediments were coarser and more poorly sorted than fluvial suspended sediments enrichment ratios indicated selective erosion and transport of silt and clay and preferential deposition of sands

vertebrate diversity across the end permian mass extinction separating biological and geological signals abstract this study examines regional diversity patterns of permian triassic terrestrial vertebrates of the south african karoo basin and the russian fore ural region previous studies clearly established that the diversity patterns of synapsids the dominant terrestrial tetrapods of their time are significantly biased by heterogeneity in the permian triassic terrestrial rock record this conclusion was based on a positive correlation between taxonomic diversity estimates tdes and varying sampling proxies 1 number of formations and 2 outcrop area recently these proxies have been criticized to be non independent variables or problematic for other reasons and 3 number of localities or 4 number of specimens have been suggest as more reliable proxies in the present study i test the relevance of the latter proxies 2 4 with respect to vertebrate diversity in south africa and russia on these regional scales log transformed and generalized differenced tdes of vertebrates at varying taxonomic levels are with few exceptions not significantly correlated with the various sampling proxies 2 4 for the complete time series after eliminating the impact of the end permian extinction event by excluding the earliest triassic time intervals selected vertebrate tdes in south africa and russia show statistically significant strong positive correlations with outcrop area number of localities and number of specimens diversity residuals resulting from modeled diversity estimates exhibit clade specific patterns with little support for a mid permian end guadalupian event but strong support for a severe end permian extinction the results imply that although vertebrate diversity patterns in south africa and russia are at least partially biased by the permian triassic terrestrial rock record they still preserve genuine biological signals finally it is important to note that outcrop area represents a valid and useful sampling proxy at the regional scale of the south african karoo basin and that it should be used in concert with other sampling proxies such as the number of localities and specimens that accurately capture various aspects of sampling in a given study area as it has been performed in the present study

macrostratigraphy of north america abstract the geological record is a three dimensional mosaic of gap bound rock bodies that at any given scale of temporal resolution were emplaced more or less continuously at any geographic location the irregular alternation of processes responsible for the formation and destruction of rock bodies results in the preservation of hiatus bound rock packages that have a distinct time of first occurrence base or oldest portion a time of last occurrence top or youngest portion and a suite of defining characters e g lithologies thickness fossils etc many important aspects of the geologic record can be quantified by compiling the stratigraphic ranges of such gap bound rock packages these include the quantity and spatial and temporal distribution of preserved rock rates of rock formation sequence stratigraphic architecture and area weighted rates of expansion and contraction erosional truncation of rock emplacement settings this approach to characterizing the rock record is scalable per

mass extinctions and sea level changes abstract review of sea level changes during the big five mass extinctions and several lesser extinction events reveals that the majority coincide with large eustatic inflexions the degree of certainty with which these eustatic oscillations are known varies considerably thus the late ordovician and end cretaceous extinctions are associated with unequivocal major regressions demonstrated from numerous widespread regions in contrast the multiple high frequency sea level changes reported for the frasnian famennian crisis based on the supposed depth preferences of conodont taxa have little support from sequence stratigraphic analyses which reveals the interval to be one of highstand the end permian mass extinction has long been related to a severe first order lowstand of sea level newell n d 1967 revolutions in the history of life geol soc am spec pap 89 63 91 based primarily on the widespread absence of latest permian ammonoid markers but field evidence reveals that the interval coincides with a major transgression newell s hypothesis that marine extinctions are related to shelf habitat loss during severe regression remains tenable for the end guadalupian and end triassic extinction events but not for other crises rapid high amplitude regressive transgressive couplets are the most frequently observed eustatic changes at times of mass extinction with the majority of extinctions occurring during the transgressive pulse when anoxic bottom waters often became extensive the ultimate cause of the sea level changes is generally unclear a glacioeustatic driving mechanism can only be convincingly demonstrated for the end ordovician and end devonian events at other times it is speculated that they may relate to the widespread regional doming and subsequent collapse caused by the impingement of superplumes and ultimate eruption on the base of the lithosphere

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

determinants of extinction in the fossil record the causes of mass extinctions and the nature of biological selectivity at extinction events are central questions in palaeobiology it has long been recognized however that the amount of sedimentary rock available for sampling may bias perceptions of biodiversity1 2 3 4 5 6 7 and estimates of taxonomic rates of evolution5 6 7 8 this problem has been particularly noted with respect to the principal mass extinctions5 6 7 8 9 10 11 12 here we use a new compilation of the amount of exposed marine sedimentary rock to predict how the observed fossil record of extinction would appear if the time series of true extinction rates were in fact smooth many features of the highly variable record of apparent extinction rates within marine animals can be predicted on the basis of temporal variation in the amount of exposed rock although this result is consistent with the possibility that a common geological cause determines both true extinction rates and the amount of exposed rock it also supports the hypothesis that much of the observed short term volatility in extinction rates is an artefact of variability in the stratigraphic record

mesozoic echinoid diversity in portugal investigating fossil record quality and environmental constraints on a regional scale several analyses of diversity through geological time use global synoptic databases and this practice often makes it difficult to distinguish true signals in changing diversity from regional scale sampling and or geological artefacts here we investigate how echinoid diversity changed through the mesozoic of the lusitanian basin in portugal based on a comprehensive revised database and seek to distinguish biological signal from geological or environmental constraints the observed diversity pattern is far from having a defined trend showing many fluctuations that appear to be linked with gaps in the geological record this study revealed that independently of the method used whether correlation tests or model fitting the diversity signal is not completely explained by the studied sampling proxies among the different proxies marine facies variation in combination with outcrop area best explains the palaeodiversity curve

response of the marine infauna to triassic jurassic environmental change ichnological data from southern england abstract the trace fossil record through the triassic jurassic boundary interval is examined at three sites in central and southern england st audrie s bay somerset pinhay bay devon and long itchington warwickshire the lower pre planorbis beds of the blue lias formation record low ichnotaxonomic diversity low bioturbation intensity small burrow diameters and an absence of deep tier bioturbation the stepwise reappearance of ichnotaxa following this interval is similar at the three sites suggesting similar rates of recovery in the benthic marine ecosystem and highlighting the potential contribution of these trace fossils to stratigraphic correlation mass extinction in the late triassic is increasingly linked to the emplacement of the central atlantic magmatic province camp timing of the onset of camp volcanism in the uk is currently imperfectly known but potentially occurred within either the westbury formation or the lilstock formation if the onset of camp was within the lilstock formation the modestly diverse trace fossil assemblage of the langport member of the lilstock formation suggests that emplacement of camp had little lasting effect on the marine benthos in central and southern england the decline in benthic activity recorded in the pre planorbis beds appears to be unrelated to the onset of camp and any associated environmental change it is more likely related to an episode of marine anoxia an episode of marine anoxia also provides a suitable causal mechanism for the reduction of infaunal tiering

palaeoclimate environmental factors and bird body size a multivariable analysis of avian fossil preservation abstract for this study we abstracted data on 693 avian fossil specimens from 398 publications to determine preservation biases in the avian fossil record our results show that dissociated wing and leg bones are the most commonly preserved avian skeletal elements and they are preferentially preserved in environments of high erosion and reworking potential notably continental shelf marine environments using bivariate descriptive displays and multivariable regression analyses we investigated the trends and associations between well preserved avian specimens i e fully or partially articulated and a variety of taphonomic factors including depositional environment body size and palaeoclimate the regression model shows that well preserved specimens are independently associated with depositional environments of low reworking potential commensurate with low energy systems warm and humid climates and smaller bird body size our results also indicate that fossils of smaller birds are less common than those of larger birds but they are more often well preserved bivariate analyses revealed that five times as many articulated specimens are found in warm and humid climates as in cool or dry climates and this association persists in the multivariable regression model warm climates the strongest predictor of better skeletal preservation may be underestimated as a source of taphonomic bias in the avian fossil record possibly because of the indirect nature of climate effects rapid burial events such as volcanic ash accumulations and mudflows are recognised for their influence on preservation but climate related storm events may be more important to avian taphonomy than previously understood our analyses indicate that geologic processes leading to high quality preservation of avian fossils are closely associated with climate additional studies based both on fossils and modern taphonomic experiments with improved collection of climate related data are needed to advance our understanding of avian taphonomy

palaeoecology of the late triassic extinction event in the sw uk a high resolution palaeoecological study of the shelly invertebrate macrofauna across two marine triassic jurassic boundary sections in the uk st audrie9s bay and lavernock point is presented loss of taxonomic richness occurs in the upper westbury formation to lower lilstock formation late rhaetian but if sample size is taken into account there is little convincing evidence of a catastrophic marine extinction there is however good evidence for significant palaeoecological change in the benthic marine ecosystem at this time the immediate post event recovery interval in the upper lilstock formation is characterized by assemblages of low abundance low diversity high dominance and low evenness body sizes of taxa that survived the event and originated afterwards were low until the later hettangian recovery to higher abundance higher diversity and higher evenness is recorded in the psiloceras planorbis zone recovery of the benthic ecosystem in the aftermath of the late triassic event was disrupted by marine anoxia and shows additional similarities to the much slower recovery that followed the late permian event the pattern of body size changes recorded in the shelly fossil record closely matches that of the trace fossil record shell thickness trends do not support a biocalcification crisis during the late triassic biotic event

extinction trajectories of benthic organisms across the triassic jurassic boundary abstract we analysed diversity and abundance patterns of benthic organisms across the triassic jurassic t j boundary based on the paleobiology database pbdb which compiles palaeontological collection data on a global scale while sepkoski s sepkoski j j jr 2002 a compendium of fossil marine animal genera bulletins of american paleontology 363 1 563 compendium on the stratigraphic ranges of marine animal genera suggests that the dominant macrobenthic groups of the late triassic experienced significant extinctions prior to the t j boundary a significant end triassic extinction peak is evident from pbdb s data this rhaetian extinction peak is found in both an analysis of the raw data of stratigraphic ranges and a sample standardized analysis of occurrence data 41 of all mesobenthic and macrobenthic genera crossing the norian rhaetian boundary became extinct within the rhaetian although this rate suffices to characterize the end triassic extinction as a true mass extinction against a middle triassic to middle jurassic background significantly reduced rhaetian origination rates add to the strong diversity depletion in the earliest jurassic as for other mass extinctions evidence for selective extinction is meagre when the analysis is limited to the boundary interval alone and when focused on taxonomic and ecological characteristics of individual genera when taxa are separated by environmental preferences however several determinants of extinction risk become evident suggesting that reef dwellers had a significantly higher extinction risk than level bottom dwellers taxa with an inshore preference were more strongly affected than offshore taxa taxa preferring carbonate substrates were more strongly hit than taxa preferring siliciclastic substrates and taxa preferentially inhabiting low latitudes had higher extinction rates than taxa more common at intermediate and high latitudes much of this selectivity is not independent and also seen in the intervals of background extinctions suggesting that the end triassic mass extinction represents an intensification of background extinctions but not a qualitatively different macroevolutionary regime one possible exception is related to preferences for depositional environments suggesting a selective rhaetian extinction in reefs and inshore settings

environmental determinants and ecologic selectivity of benthic faunas from nearshore to bathyal zones in the end permian mass extinction brachiopod evidence from south china abstract in south china the changhsingian brachiopods are extraordinarily abundant and diverse comprising 447 species in 143 genera they were widespread in nearshore shallow sea reef carbonate platform shelf basin and bathyal zones brachiopod attachment modes were also highly diversified and include burrowing body cementation pedicle attaching on substratum body spines anchoring on substratum pedicle attaching on objects and clasping spines anchoring on other objects they suffered the species and genus extinction rates of 91 5 and 86 respectively in the first episode of the end permian mass extinction and further species and genus extinction rates of 84 2 and 80 0 respectively in the second crisis for the permian triassic p tr brachiopods there were 1 selective extinction of the normal shallow marine dwellers relative to these inhabiting deep sea or marginal seas and 2 among the normal shallow marine habitats selective extinction of reef dwellers relative to non reef forms ecologically the body cementation forms suffered much higher extinction rates than other lifestyle elements in contrast both the burrowing and clasping spine anchoring forms had much lower extinction rates than other lifestyle elements although the reef and bathyal dwellers partly survived the first extinction event they migrated to other habitats to survive the crisis the estimation of extinction rates based on the single episode mass extinction pattern cannot reveal precisely the extinction severity of brachiopod faunas over the p tr transition brachiopod diversity changes support the two stage mass extinction pattern near the p tr boundary

the fossil record and spatial structuring of environments and biodiversity in the cenozoic of new zealand there is increasing evidence to suggest that drivers of bias in the fossil record have also affected actual biodiversity history so that controls of artefact and true pattern are confounded here we examine the role of spatial structuring of the environment as one component of this common cause hypothesis our results are based on sampling standardized analyses of the postmiddle eocene record of shelf molluscs from new zealand we find that spatial structuring of the environment directly influenced the quality of the fossil record contrary to our expectations however we find no evidence to suggest that spatial structuring of the environment was a strong or direct driver of taxic rates net diversity or spatial structuring in mollusc faunas at the scale of analysis stage to stage variation in sampling standardized diversity over the past 40 ma exhibits two superficially independent dynamics a changes in net diversity were associated primarily with changes in origination rate and b an unknown common cause related extinction rate to the quality of the fossil record and indirectly to spatial structuring of the environment we suggest that tectonic drivers manifest as second order sequence stratigraphic cycles are likely to have been a key element of this common cause our perceptions of biodiversity history are influenced strongly by secular biases in the quality of the fossil record e g raup 1976 peters foote 2001 many authors have argued against a literal reading of the record and various techniques to minimize the impacts of sampling biases have been developed e g connolly miller 2001 foote 2003 alroy 2010 in addition however a number of studies have proposed that the relationship between sampling biases and diversity dynamics may be complex these studies have suggested that there are latent common cause factors such as plate tectonics and sea level change which have affected simultaneously the quality of the fossil record and true macroevolutionary history e g newell 1952 sepkoski 1976 smith 2001 peters foote 2002 foote 2003 peters 2005 2006a wall et al 2009 demonstrating potential common causes separating their effects from simple preservation and sampling biases and interpreting them mechanistically are challenging problems that must be solved if palaeobiologists are to resolve true patterns and processes of macroevolutionary change through geological time the aim of the present paper is to examine the role of spatial structuring of the environment and of biodiversity in driving both macroevolutionary dynamics and biases in the fossil record fig 1 specifically we are interested in the extent to which partitioning of marine environments may have influenced biodiversity and the preservation of that diversity in part the study is founded on the expectation that the geographical range and evolution extinction dynamics of organisms occupying a particular habitat will be related to the area and fragmentation of that habitat e g rosenzweig 1995 maurer nott 1998 at the same time we anticipate that the quality of the marine fossil record will be influenced by for example the areal extent and distribution of depositional v non depositional or erosional environments factors that are also likely to affect habitat fragmentation and diversity to test the role of spatial structuring in the common cause hypothesis we use the exemplary well studied and relatively complete fossil record of post middle eocene level bottom shelf molluscs from new zealand e g crampton et al 2003 2006a this record is approximately from mcgowan a j smith a b eds comparing the geological and fossil records implications for biodiversity studies geological society london special publications 358 105 122 doi 10 1144 sp358 8 0305 8719 11 15 00 the geological society of london 2011 40 complete at the species level for the neogene as estimated using two very different approaches cooper et al 2006 crampton et al 2006a in this paper therefore we derive an index for spatial heterogeneity of the environment and adapt established indices of spatial differentiation in the new zealand cenozoic mollusc fauna we then compare time series of these measures to time series of sampling probability a proxy for the quality of the fossil record and sampling standardized estimates of overall species richness origination rate and extinction rate all analyses and computations reported here were undertaken using r r development core team 2010 materials and methods

estimating the rock volume bias in paleobiodiversity studies to interpret changes in biodiversity through geological time it is necessary first to correct for biases in sampling effort related to variations in the exposure of rocks and recovery of fossils with age data from new zealand indicate that outcrop area is likely to be a reliable proxy of rock volume in both stable cratonic regions where the paleobiodiversity record is strongly correlated with relative sea level and on tectonically active margins in contrast another potential proxy the number of rock formations is a poor predictor of outcrop area or sampling effort in the new zealand case

synchronous compression and extension in east gondwana tectonic controls on world class gold deposits at 440 ma the collision of a seamount or microcontinental block with an arc may produce complex strain distributions and changes in the tectono magmatic setting slab rollback and associated upwelling of asthenosphere occurred ca 440 ma near the margin of east gondwana in response to subduction zone lock up following arc collision ca 455 ma world class porphyry copper gold deposits e g cadia formed in the backarc during extension and magmatism associated with slab rollback upwelling of the asthenosphere also provided the heat engine for generation of hydrothermal fluids the result was elevated fluid pressures and compressional brittle deformation associated with orogenic gold mineralization e g bendigo inboard of the east gondwana margin

the ties linking rock and fossil records and why they are important for palaeobiodiversity studies a correlation exists between the quality of the rock record and the diversity of fossils recorded from that rock record but what drives that correlation and how consistent that correlation is across different environments remain to be determined palaeontologists wishing to investigate past diversity patterns need to first address issues of geological bias in their data the fossil record provides the only empirical evidence of how life has diversified over geological time but it needs to be interpreted with caution for many years the history of diversity was estimated simply by summing up the numbers of taxa species genera families palaeontologists have recorded from successive geological time intervals or extrapolated from their first and last occurrences in the geological record this time series approach led to what is now a classic view of how diversity has changed over time sepkoski et al 1981 benton 1995 sepkoski 1997 such counts take the fossil record at face value or assume that biases or errors are randomly distributed in such a way that the overall effect is negligible we now realize that this is only a first crude approximation that may be subject to a number of strong biases that arise because of the nature of the sedimentary rock record time series analysis requires that sampling be carefully controlled for best results ideally data should be collected so that sampling from each time interval is uniform or at least sampled fairly using the shareholder quorum subsampling method alroy 2010 otherwise apparent changes in diversity may arise for spurious reasons for example because a a time intervals being sampled are of variable duration longer time intervals 1 4 more recorded diversity or b a time interval has been more intensively sampled more localities specimens habitats formations sampled 1 4 more recorded diversity while for a biological survey it is easy to plan a sampling strategy that will give approximately equal effort and coverage for observations palaeontologists are faced with a much more difficult task firstly the time bins they work with are irregular and highly variable in their duration for example the durations of one of the most widely used time scales has intervals spanning two orders of magnitude gradstein et al 2004 secondly and much more critically palaeontologists are collecting from an already incomplete and highly biased set of rocks which in turn skew the range of taxa and habitats that can be sampled zuschin et al 2011 bluntly put we cannot sample what is not preserved in the rock record although phylogenetic and molecular approaches can attempt to compensate pol norrell 2006 bininda emonds et al 2007 wills 2007 o connor et al 2011 so while it may be possible to standardize for sampling effort from the rock record that remains those rocks might provide a far from uniform sample of the sediments and palaeoenvironments that were originally present palaeontologists cannot therefore assume uniform sampling of the fossil record and must try to assess how the rock record they have to work with has affected their ability to sample evenly and then develop methods that compensate appropriately for this variation in recent years therefore palaeobiodiversity studies have become more probabilistic in their approach concerned with establishing confidence limits around estimates that try to correct for uneven sampling alroy et al 2001 2008 and testing empirical patterns against model predictions foote 2001 smith mcgowan 2007 mcgowan smith 2008 if we are to improve our estimates of biodiversity over time then sampling parameters need to be better quantified and we need to better understand the complex interrelationship between rock and fossil records this is no simple task and requires a more systematic approach to recording culture as well as better documentation of the variables benton et al 2011 figure 1 summarizes the problem as we see it palaeontologists estimate past diversity from remains preserved in the rock record as with any from mcgowan a j smith a b eds comparing the geological and fossil records implications for biodiversity studies geological society london special publications 358 1 7 doi 10 1144 sp358 1 0305 8719 11 15 00 the geological society of london 2011 biological survey variation of sampling effort of the surviving rock record needs to be factored out but this rock record has already passed through a geological filter that has altered and distorted not only the rock area that survives to sample but also the proportions of facies and the preservational quality of its fossil record were this geological filter to remain approximately constant over time there would be little problem of interpreting the biological signal however it is far from uniform with amounts of rock to sample proportions of facies represented by those rocks and preservation potential all varying from one time interval to the next to interpret observed changes in sampled biodiversity estimates correctly we must therefore first understand the role of the geological filter variability of the rock and fossil records

depressed rates of origination and extinction during the late paleozoic ice age a new state for the global marine ecosystem rates of origination and extinction for marine animal genera dropped to low levels in latest mississippian time immediately after massive glaciers formed in the southern hemisphere and a second order mass extinction occurred evolutionary turnover and diversity remained low for 50 m y shifting markedly upward precisely when extensive glaciation ended in early permian time all diverse taxa with good fossil records experienced low rates of origination and extinction during this major ice age such sluggish rates would be predicted for faunas of shallow seas on or adjacent to a heavily glaciated supercontinent such as pangea where cool and highly seasonal thermal regimes should dictate that species have broad ecological niches widespread geographic distributions and large and relatively stable populations

the first half of tetrapod evolution sampling proxies and fossil record quality abstract the first half of tetrapod evolution witnessed substantial diversification of the clade and several major turnovers and mass extinctions in the time since their origin more than 380 myr ago to the beginning of the middle jurassic 175 myr ago tetrapods apparently diversified fitfully reaching their highest level in the middle permian and showing major diversity declines in the late moscovian early permian wordian lower wuchiapingian end permian lower anisian lower ladinian late triassic lower norian to upper rhaetian end triassic and early jurassic upper sinemurian lower pliensbachian of these diversity drops only the end permian and end triassic correspond to recognised mass extinctions and the late moscovian and early norian drops to other previously identified environmental crises the remainder could be real extinction or turnover events or partially artefacts of biased sampling there are strong correlations between formation counts and tetrapod palaeodiversity suggesting a sampling component in the raw data but the covariation is not uniform through the whole time span being poor from devonian to middle permian and better from late permian to early jurassic there is limited evidence for covariation between the tetrapod palaeodiversity time series and other putative sampling metrics such as specimen completeness numbers of publications map areas gap bounded sedimentary units rock volumes formations and fossil collections modelling by multiple correlations shows that formation count is generally the best explanatory model either on its own or combined with other sampling time series however it is not clear that formation count is independent of the palaeodiversity time series because rises and falls in both signals could reflect variations in original diversity or in preservation or in sampling

comparison of taxonomic diversity strontium isotope and sea level patterns sepkoski s compendium of 28 730 marine genera was analyzed with a view toward comparing taxonomic diversity strontium isotope stratigraphy and sea level changes the fossil record analyses discriminated between origination extinction and pass through genera and collectively delineated changes in number of genera with time at the largely stratigraphic stage level with notable exceptions of the cretaceous and tertiary taxonomic diversity generally paralleled both strontium isotope stratigraphy and sea level changes sampling bias was suggested in the tertiary where an increase in genera numbers toward the recent opposed the downward trends of both strontium isotope and sea level curves the removal of all recent genera from the sepkoski database confirmed the bias in producing complimentary downward trends in all curves regression analysis of taxonomic diversity with respect to sea level extent and time duration explained 82 of the variability of the remaining data sea level fluctuations are not always accompanied by significant changes in taxonomic diversity but strontium isotope analyses offers the potential of constraining the extent to which the magnitude of changes are associated with time duration

cascading trend of early paleozoic marine radiations paused by late ordovician extinctions the greatest relative changes in marine biodiversity accumulation occurred during the early paleozoic the precision of temporal constraints on these changes is crude hampering our understanding of their timing duration and links to causal mechanisms we match fossil occurrence data to their lithostratigraphical ranges in the paleobiology database and correlate this inferred taxon range to a constructed set of biostratigraphically defined high resolution time slices in addition we apply capture recapture modeling approaches to calculate a biodiversity curve that also considers taphonomy and sampling biases with four times better resolution of previous estimates our method reveals a stepwise biodiversity increase with distinct cambrian and ordovician radiation events that are clearly separated by a 50 million year long period of slow biodiversity accumulation the ordovician radiation is confined to a 15 million year phase after which the late ordovician extinctions lowered generic richness and further delayed a biodiversity rebound by at least 35 million years based on a first differences approach on potential abiotic drivers controlling richness we find an overall correlation with oxygen levels with temperature also exhibiting a coordinated trend once equatorial sea surface temperatures fell to present day levels during the middle ordovician darriwilian age contrary to the traditional view of the late ordovician extinctions our study suggests a protracted crisis interval linked to intense volcanism during the middle late ordovician katian age as richness levels did not return to prior levels during the silurian a time of continental amalgamation we further argue that plate tectonics exerted an overarching control on biodiversity accumulation

marine diversity through the phanerozoic problems and prospects the fossil record provides direct evidence of how diversity has changed over time but cannot be taken at face value diversity curves constructed from counting taxa in the rock record are seriously biased by unevenness of geographical and stratigraphical sampling effort inequality in the rock record available for sampling and inconsistent taxonomic practice sample standardization removes some bias but does not overcome more general incompleteness problems modelling that accounts for potential biases is a newer approach but needs accurate estimates of rock record and consistent taxonomic data uncertainty remains over whether the steep rise in diversity over the last 100 ma is real or reflects sampling bias the repeated rise and fall of marine diversity over time correlates closely with the areal extent of sedimentary deposits and independent estimates of the quality of the fossil record implying a common driving factor namely tectonically mediated sea level change however whether changes in diversity are primarily biological in origin or reflect sampling artefact remains contentious there is a distinct possibility that many of the apparent rises and falls in diversity over the phanerozoic including most of the mass extinctions arise either partially or entirely from rock record bias

using remote sensing and a geographic information system to quantify rock exposure area in england and wales implications for paleodiversity studies rock outcrop area and number of sedimentary formations have been widely used as sampling proxies in paleodiversity studies and have often been found to correlate with apparent paleodiversity however rock exposure area is a better proxy for the amount of sedimentary rock available for study than the widely used measures of outcrop area i e map area or number of formations with the use of remote sensing and a geographic information system gis it is possible to quantify rock exposure area accurately on a regional scale rock exposure area does not correlate well with either outcrop area or number of sedimentary formations and the proportion of rock exposed in different areas can vary considerably with proximity to the coast bedrock age lithology land use and elevation therefore this suggests that the correlation of paleodiversity and rock volume estimates is best explained by a common cause hypothesis rather than a geologic sampling bias hypothesis gis methods offer an efficient and accurate method of quantifying regional sedimentary rock exposure and may provide a helpful approach to assessing rock record bias on patterns in the fossil record

a comparison of orogenic gold mineralisation in central victoria aus western south island nz and nova scotia can implications for variations in the endowment of palaeozoic metamorphic terrains abstract the palaeozoic western lachlan orogen in victoria se australia the buller terrane western south island new zealand and the meguma terrane nova scotia canada are remarkably similar in regard to their geological age and history structural make up and the setting and formation of orogenic lode and disseminated style gold deposits within these fold belts a comprehensive review of the principal characteristics of orogenic gold deposits in each of the three historically important gold provinces illustrates the many similarities but it also reveals several major geological structural tectonic geochemical and geochronological differences that may account for the disparity in contained gold and overall endowment between the three fold belts aspects that stand out as potentially playing a critical role in the generation of a phanerozoic world class orogenic gold province include 1 the presence of a hydrated oceanic character substrate that can provide a fertile source rock for both fluids and metals 2 asthenospheric thermal input to trigger and sustain crustal devolatilisation and melting 3 the existence of a number of near vertical deep seated faults 4 substantial transcurrent movement and 5 evolution of an accretionary subduction system that promotes development of an extensive fore arc system with prolonged fluid generation and circulation quantification of these controlling factors provide a significantly improved understanding of the processes that control the genesis of orogenic gold deposits and also have the potential to enable discrimination between more and less gold favourable orogens and parts of orogens

covariation in macrostratigraphic and macroevolutionary patterns in the marine record of north america students of earth history have long recog nized the correlation between the quantity of preserved sedimentary rock and the diversity of life recorded as fossils but paleontologists have yet to determine whether this pattern refl ects a causal relationship or a unidirec tional sampling bias in fossil data imposed by preserved rock quantity distinguishing between these two alternatives has been com plicated by the fact that many of the basic patterns of paleontologic and lithologic co variation have yet to be quantifi ed rigorously here we present the fi rst analyses of the co variation between the macrostratigraphic and macroevolutionary histories of north america based on geographically and tem porally explicit co occurrences of rocks and fossils the analyses use independent quan titative summaries of the stratigraphic and fossil records by integrating the paleobiology database paleodb and macrostrat a mac rostratigraphy database for north america which allows a more direct comparison of the stratigraphic and biological histories of the continent than has heretofore been possible within the macrostrat database the rock re cord is divided into discrete packages of sedi ment that are bound by hiatuses resolvable at the stage level using per interval per pack age rates of sediment package initiation and truncation and genus fi rst and last appear ances herein regional origination and extinc tion we fia substantially stronger positive correlation between sediments and biology for extinction like parameters than we do for origination like parameters four of the largest coincident pulses of regional extinc tion and sediment truncation occur during the widely recognized end ordovician late permian end triassic and end cretaceous mass extinction intervals a further compari son of the global ranges of north american genera to north american macrostratigra phy indicates that the regional and global extinction of genera are more likely to oc cur in the same stage than are global and regional originations together these results suggest that our general understanding of biodiversity dynamics from the fossil record may not be strongly biased by the preserva tion of sediments and leaves open the pos sibility that certain large perturbations to the earth system are responsible for major changes of state in both the sedimentary and biological systems

foraminiferal zonation of late paleozoic depositional sequences from the later part of the devonian through the permian calcareous foraminifers became abundant and evolved rapidly this rapid evolution of taxa forms the basis of a detailed zonation through the carboniferous and permian comparison of this evolutionary history of foraminifers their biostratigraphic zonation and the depositional sequences in which they occur suggests that sea level events in late paleozoic depositional history contributed significantly in subdividing a fairly continuous evolutionary record into a succession of about 75 identifiable foraminiferal zones during a 100 125 myr time span although variable in terms of duration and vertical occurrences the more completely recorded high stand intervals give brief histories of the foraminiferal evolutionary record and are sandwiched between the poorly recorded or unrecorded low stand intervals many of the individual foraminiferal zones are confined to a single depositional sequence the late paleozoic carbonate foraminiferal fossil record as with the rest of the fossil record is strongly affected by sediment deposition nondeposition as a result of major changes in sea level this incomplete fossil record is the result of repeated depositional breaks because of the way that depositional sequences form it is not possible to ascribe macromutations punctuated evolution or punctuated gradualism as the cause of this evolutionary pattern of the shelf carbonate fossil record this pattern is distinctive and we refer to it as sequence evolution and sequence extinction in the later part of the middle permian and in the late permian the fossil record clearly illustrates that a series of faunal losses through sequence extinctions progressively exceeded faunal replacements and new species through sequence evolution but not a mass extinction as is commonly ascribed to the end of the permian period most permian faunas became extinct in the interval of 8 to 4 million years before the end of the late permian

fossil crocodilians as indicators of late cretaceous and cenozoic climates implications for using palaeontological data in reconstructing palaeoclimate abstract that the earth s climate has cooled over the last 100 million years has been recognized since the early nineteenth century the transition from the hot house world of the cretaceous a time interval without significant polar icesheets to the ice house world in which we now live today the dynamics process responsible for this change are being examined using computer models especially general circulation models gcm s through such work our understanding of the dynamics of the earth system improves and our ability to predict future trends is enhanced but the success of modelling experiments can only be assessed by comparing results with observations the pattern which for palaeoclimate are drawn exclusively from the geological record palaeoclimate interpreted from geological data is invariably based on analogy with the recent the validity of which depends on corroboration from multiple lines of evidence this requires the compilation and investigation of large global datasets of well constrained geological climate proxies this study uses the palaeodistribution of fossil crocodilians to examine the spatial distribution of palaeoclimate during this transition fossil crocodilians have a relatively good fossil record and are climatically limited in the recent they also provide a manageable global dataset with which to investigate other issues that impinge on the use of geologic data for reconstructing palaeoclimate taphonomy sampling effects time averaging tectonics and for fossils palaeobiogeography and evolution as such this study provides a possible template for examining other climate proxies in order to validate and hone palaeoclimatic interpretations an analysis of modern crocodilians indicates that temperature is the principal influence on their global distribution with the coldest month mean temperature cmm of 5 5 c marking the minimum thermal limit for the group corresponding today to a minimum mean annual temperature mat of 14 2 c the duration of warmth during the year partly indicated by the mean annual range of temperature mart is also important as this affects early juvenile development and survival the presence of standing water provides an essential thermal buffer against temperature extremes by analogy the palaeodistribution of fossil crocodilians suggests the following during the late cretaceous and early palaeogene mat s in excess of 14 2 c cmm s 5 5 c permeated throughout mid latitudes and coastal regions in high latitudes during the oligocene the restriction of fossil crocodilians to low latitudes suggests high latitude cooling as indicated by numerous other lines of evidence coeval restriction of crocodilians to coastal regions in mid latitude north america and much of asia consistent with increased seasonality and aridification in continental interiors may reflect local orographic changes as well as global climate change during the miocene fossil crocodilians return to the great plains of north america but do not reoccupy the continental interior of asia by the pliocene crocodilians are again restricted to low latitudes and coastal regions in mid latitudes coincident with further high latitude cooling and aridification and cooling of mid latitude continental interiors minor distributional changes during the holocene may reflect human effects

application of mineral equilibria modeling to constrain t and x co2 conditions during the evolution of the magdala gold deposit stawell victoria australia mineral equilibria modeling involving solid solution calculations has been combined with mineral assemblage information from the alteration zones associated with gold mineralization to determine the t and xco2 conditions for the formation of the magdala gold deposit at stawell victoria australia economic gold mineralization is primarily hosted within the stilpnomelane alteration zone of the stawell facies that is adjacent to the magdala basalt evolution of the magdala gold deposit involved at least three fluid infiltration events 1 a co2 bearing fluid during the d2 deformation event produced carbonate spots throughout the chlorite zone 2 a co2 s k bearing fluid accompanied the d3 4ab deformation and produced a muscovite zone and siderite rims on ankerite and 3 a co2 k s au bearing fluid during the d4c deformation event produced the stilpnomelane zone of the stawell facies the proximal and distal alteration zones within the magdala basalt and the main economic gold mineralization mineral equilibria modeling constrains the temperature of formation of the magdala deposit to t 345 390 c at 3kbar substantially lower than indicated by other previous classical thermobarometry methods furthermore this method has allowed the characterization of the mineralizing fluid and constrained its composition to xco2 0 08 at 3kbar the timing and composition of the mineralizing fluids are similar to that of metamorphic fluid generated from devolatilization of a greenstone pile with peak of metamorphism occurring earlier and at deeper levels in the crust

hiatus distributions and mass extinctions at the cretaceous tertiary boundary much disagreement over the interpretation of data bearing on various cretaceous tertiary k t extinction scenarios results from a failure to view these data within their appropriate stratigraphic context combined biostratigraphic and chronostratigraphic analyses of k t boundary sequences have revealed systematic differences in patterns of sediment accumulation within continental shelf and deep sea depositional settings although virtually all deep sea boundary sequences are marked by intervals of nondeposition or hiatus formation during the latest cretaceous and earliest tertiary many continental shelf slope sequences appear to be temporally complete over this same interval this differential pattern of sediment accumulation can be related to the latest maastrichtian earliest danian sea level rise during which deep sea sediment accumulation rates would be expected to drop as the locus of sediment deposition migrated across the continental shelf our data suggest that the abrupt shifts in carbon isotope abundances single peak ir anomalies and apparently instantaneous mass extinctions of marine plankton which are routinely reported from deep sea k t boundary sequences and used to support a causal relation between late cretaceous bolide impacts and k t mass extinctions may be artifacts of a temporally incomplete or extremely condensed deep sea stratigraphic record

permian triassic boundary interval as a model for forcing marine ecosystem collapse by long term atmospheric oxygen drop ecological traits of reefs across the permian triassic boundary interval coincide with a modeled decline of atmospheric oxygen throughout the permian period selective extinction and recovery patterns within the reef system are observed both at the end of the middle permian end guadalupian and at the permian triassic boundary the end guadalupian event selectively affected corals and broke down the cool water carbonate factory sponges however were largely unaffected and bloomed in reefs toward the end of the permian the end permian total destruction of the metazoan reef system only left behind poorly diverse microbial communities the temporal reef patterns are thus similar to spatial patterns of modern benthic communities approaching oxygen minimum zones this observation suggests that a decline in oxygen concentrations was at least partly involved in the destruction of reefs even where there is no direct evidence of oceanic anoxia

quantifying the deep sea rock and fossil record bias using coccolithophores while many studies show a correlation between observed taxonomic richness and various measures of geological sampling all have been based on the same record of terrestrial and marine sediments collected from the land here we present the first analyses of how rock and fossil records vary in the deep sea we have developed a novel database of species occurrences of coccolithophores sampled during major drilling programs of the north atlantic including the mediterranean and caribbean our sampling proxy the number of deep sea sites sampled perhaps the most direct measure of sampling used so far shows an exponential rise towards the recent over the same period species richness has grown in an approximately linear fashion but genus level richness shows a sharp initial increase followed by a much slower decline however correlations between both richness measures and sampling are extremely strong and a model assuming true diversity to be constant accurately predicts much of observed richness we conclude that the deep sea fossil record like its land based counterpart bears a rock record bias the geological society of london 2011

lazarus taxa and fossil abundance at times of biotic crisis mass extinctions are often followed by intervals in which taxa disappear from the fossil record only to reappear again later this lazarus effect is often attributed to a poor quality fossil record or migration to refuges testing these alternatives with examples from the end permian and late triassic extinctions reveals that there is no link with the abundance of fossiliferous sites and the proportion of lazarus taxa nor are missing taxa encountered in potential refuges therefore the abundance of lazarus taxa in the aftermath of these extinctions is probably a reflection of the extreme rarity of organisms at this time

evolution of desert colluvial boulder slopes abstract we employed rhyolite domes formed during the past million years in eastern california to study the evolution of boulder dominated slopes the slopes studied are steep from 25 to 35 and are made of coarse boulder sized blocks these slopes include well varnished vertically oriented colluvial deposits that appear similar to relict periglacial stone stripes in this case they are the result of ongoing desert slope processes such deposits are common throughout the arid southwestern us but their morphometric character fabric and rates of formation have not been assessed systematically basic field and isotopic dating methods are combined with two relatively new surface dating techniques cosmogenic chlorine 36 and rock varnish microlaminae to produce a detailed million year long slope development history with broad implications for geomorphic theory grain size grain shape grain angularity and slope deposit area do not change significantly from genesis to 0 5 ma trends in the data change markedly after that time a geomorphic threshold occurs between 0 5 and 1 ma as indicated by significant changes in all parameters but grain orientation data on going erosion over the million year continuum is evidenced by active debris flow features by terminal pleistocene ages of microlaminae on all deposits and by 36cl ages that are progressively younger than potassium argon ages for slope genesis

drawing a line in the sand identifying and characterizing boundaries in the geological record the identification and characterization of boundaries is a fundamental activity in geoscience spatial and temporal boundaries are rarely sharp but are more usually zones of transition which may have variable characteristics the examination of palynological and micropalaeontological data is often crucial for the delineation of geological boundaries especially for the definition of global boundary stratotype sections and points gssps the sixteen papers in this volume highlight many productive methodological approaches to boundary identification this essay reviews the theoretical background to boundary identification in geology and provides the contextual perspective for the subsequent papers much of geoscience has to do with classification of organisms of rocks or of processes inevitably classification devolves into an exercise in drawing boundaries putting a limit on what is included and what is not in the geological record this exercise takes place in three dimensions with space and time interacting to produce a plethora of boundaries and boundary definitions although conventionally on stratigraphic charts for example temporal boundaries are often shown as sharp lines in reality they are rarely so similarly spatial boundaries on maps are seldom as abrupt as they are drawn process boundaries are yet more subtle and usually less clear indeed even to speak of a boundary is contentious since boundaries come in many forms and types boundaries are more often intervals or spaces of transition leaving plenty of room for argument over their placement perhaps for this reason some of the more truculent and long lasting debates in geology have been over the positioning and identification of boundaries drawing a line in the sand may seem a simple exercise but turns out to be fraught with complexities boundary definitions in geoscience the criteria for identifying chronostratigraphic biostratigraphic and lithostratigraphic units are outlined in rules set up by international agreement such as the international stratigraphic guide salvador 1994 or guidelines such as the north american stratigraphic code north american commission on stratigraphic nomenclature 1983 or the stratigraphic procedure rawson et al 2002 the demarcation of boundaries is generally a consequence of the identification of units rather than the other way round historically the identification of boundaries has often arisen from the practical exigencies of geological mapping the need to produce visual representations of geology primarily based on sections or surface exposures boundaries therefore were often synonymous with the limits of mappable units that were generally field identified on the basis of lithology this approach gave rise to the designation of body stratotypes a methodology that proved limiting for the subdivision of geological time because of gaps in the rock record harland et al 1990 modern geochronology emphasizes boundaries especially lower stage boundaries rather than units as fundamental for subdivision and correlation remane 2003 under the auspices of the international commission on stratigraphy ics various subcommissions have been established to examine the placement of particularly critical temporal boundaries in the geological record see list in gradstein ogg 2003 considerable effort has been devoted to the establishment of global boundary stratotype sections and points gssps with more than 40 defined so far gradstein et al undated for each boundary a type section and a specific 3b2 version number 7 51a w may 2 2001 jobsin m11251 00c geo introduction 3d date 27 10 04 time 11 48am page 1 of 10 m11251 the geological society tradespools frome somerset from beaudoin a b head m j eds 2004 the palynology and micropalaeontology of boundaries geological society london special publications 230 1 10 0305 8719 04 15 the geological society of

cretaceous tetrapod fossil record sampling and faunal turnover implications for biogeography and the rise of modern clades we use newly compiled data on global occurrences of cretaceous lepidosaurs mammals and crocodylomorphs and existing data on dinosaurs to investigate faunal turnover and fossil record heterogeneity statistically significant relationships between many clade specific fossil record sampling proxies within major continental areas e g european mammal bearing formations suggest that temporal patterns of fossil record sampling intensity of the most abundant tetrapod clades are similar to each other with a few exceptions that might reflect clade specific facies preferences or differences in worker effort especially in poorly sampled regions such as gondwana however the absence of strong statistical relationships between tetrapod sampling proxies from different continental areas suggests that there is no unified global sampling signal for terrestrial tetrapods the cretaceous witnessed substantial faunal turnover and the rise of many advanced clades that today dominate terrestrial faunas despite strong spatiotemporal heterogeneity in sampling of the cretaceous tetrapod record it is clear that this transition occurred in a spatiotemporally staggered fashion thus it cannot be attributed to a temporally localised early late cretaceous cenomanian turonian extinction event many advanced clades including eutherian mammals iguanian and gekkotan squamates and the main cryptodiran turtle crown clades first appeared or first attained high fossil diversities in asia however relatively poor sampling and dating of middle cretaceous terrestrial deposits means that hypotheses of asian rather than laurasian diversifications remain tentative differences between gondwanan and laurasian faunas became progressively greater during the cretaceous and although many gondwanan clades survived the end cretaceous extinction event these only survive to the present as relictual populations with narrow geographic ranges e g monotremes and rhynchocephalians

ecological disruption precedes mass extinction mass extinctions are dramatic features of the fossil record in which extinction risk is substantially elevated above background levels although extinction risk varies markedly over geologic time as well as geographically it was particularly elevated and global in extent during the so called big five events the late ordovician late devonian end permian end triassic and end cretaceous 1 these events were originally recognized by variations in extinction rate in marine animal families and their importance remains in analyses at the genus level and that account for variable preservation over geologic time 2 3 increasing attention has concentrated on understanding the ecological effects of mass extinction and other lesser but still significant extinction episodes 4 10 in pnas sheets et al 11 document the ecological changes in marine planktonic communities not only during but preceding the late ordovician 447 444 ma mass extinction

paleoproterozoic turbidite hosted gold deposits of the ashanti gold belt ghana west africa comparative analysis of turbidite hosted gold deposits and an updated genetic model abstract the paleoproterozoic gold deposits of the ashanti gold belt ghana occur mainly as auriferous quartz veins in graphitic shears proximal to contacts between deformed and metamorphosed turbidites and tholeiitic volcanics alternately block faulted tarkwaian sediments they are suggested in this article to belong to that class of gold deposits recognized as turbidite hosted hence evidence from previous investigations of turbidite hosted and turbidite associated gold deposits occurring in circumstances roughly similar to the ashanti deposits are used where relevant to produce an updated genetic model for the latter given the relatively significant amounts of graphite associated with the major ashanti deposits the role of non carbonate carbon is assessed in the light of conclusions reached by work on other turbidite hosted and turbidite associated gold belts conclusions as to the origins of mineralizing fluids and temporary repositories of gold auriferous interflow sediments reached by work on these other belts are also analysed a concept of the tectonic development of the ashanti belt kumasi basin area introduced in this article is deemed to be critical to the origin of the ashanti gold deposits it encompasses the role of non carbonate carbon turbidites and the primary sources and secondary repositories of au and as in the genesis of the major ashanti gold deposits it examines the significance of the intimate relationship between calc alkaline volcanism and the basin sediments the occurrences of felsic metasandstones in transition zone sediments and ttg granitic material and fragments of chemical sediments in turbidites all of which are incompatible with one or the other of existing concepts of tectonic development in the area

gold mineralization under cover in southeast australia a review of an exploration initiative for stawell type deposits abstract exploration for orogenic stawell type deposits in the northern extension of the stawell zone under the tertiary murray basin sediments in southeastern australia has produced the discovery of at least two new deposits at wildwood and kewell previous research on the stawell gold deposit has highlighted the importance of litho facies structural evolution and hydrothermal alteration in the localization of fluid flow at the time of mineralization application of geophysical tools including magnetic and gravity surveys at both regional and more detailed scales delineated a number of significant coincident magnetic and gravity anomalies which upon further investigation through aircore drilling proved to be basalt subsequent drilling on the margins of the wildwood and kewell basaltic domes delineated areas of prospective litho facies hydrothermal alteration quartz veins and mineralization akin to that found in the stawell deposit analysis of multi element geochemistry revealed significant gains in fe in the transition from unaltered to altered unmineralized 1 ppm au altered host rock magnetic remanence properties of the various lithologies within the stawell zone showed that high fluid flow can result in the precipitation of sulfides with fixed stable remanent magnetization the orientation of which may not be parallel to the present day magnetic field whereas zones of low fluid flow have soft magnetization that can be easily modified the implication of variation in remanence orientation for exploration is that regional aeromagnetic anomalies which have opposite polarities may coincide with zones of high fluid flow and are potential target areas for mineralization

marine diversity in the geological record and its relationship to surviving bedrock area lithofacies diversity and original marine shelf area biological principles suggest that recorded species diversity should increase as sampled area and habitat diversity increase however the interactions between earth system drivers of these physical quantities their representation in the preserved rock record and fossil species counts are debated we tracked marine bedrock area lithofacies diversity and echinoid species diversity through an 80 m y sea level cycle as recorded in the cretaceous of the united kingdom to test these relationships relative completeness of the rock record rises during transgression but drops rapidly at maximum flooding and continues to fall during highstand lithofacies diversity peaks during transgression but drops sharply as maximum flooding is reached whereas bedrock area peaks at maximum flooding then declines progressively through the highstand interval as a result of post cretaceous erosion both bedrock area and number of lithofacies units correlate with species diversity but species diversity is predicted best by the two combined there are no simple relationships between bedrock area and lithofacies diversity or the original area of marine sediments and range of habitats that once existed these variables are strongly shaped by stratigraphic architecture while the geological record left by a major sea level cycle accurately captures the biological evolution of local communities it is incomplete and systematically biased in its coverage of environments and communities erosional truncation of sediment packages and species ranges in the later stages of sea level cycles explains the reported asymmetric relationship between macroevolution and macrostratigraphy

the magdala lode system stawell southeastern australia structural style and relationship to gold mineralization to gold mineralization across the western lachlan fold belt

palaeoclimate and palaeoenvironmental responses in the western mediterranean over the last 140 ka evidence from mallorca spain climatic change in the western mediterranean basin over the last 140 ka has been investigated from sediment and soil sequences along the coast of the northeastern part of mallorca spain palaeoclimate and palaeoenvironments are reconstructed from sediment and soil structures marine and terrestrial molluscan fauna grain size distributions mineral magnetics sediment and soil chemistry sem and oxygen isotope values dating is by osl and amino acid geochronometry along with marine molluscan faunal assemblages all oxygen isotope stages and substages from ois 6 to 1 are recorded mean annual temperatures m a t of c 19 2 c for the climatic optimum of the last interglacial compare with c 17 3 c for the present and are associated with high sea level extensive woodland and stable soils although wide temperature ranges are detected during this stage with values as low as c 10 3 c through ois 5d to 5a m a t fluctuated from 8 2 c to 17 9 c low sea level open vegetation effective river activity and aeolian sand and dust deposition characterize 5d and 5b while relatively high sea level and soil development on stable landscapes dominate ois 5c and 5a ois 4 is represented by m a t of c 4 9 c with aeolian sand and loess deposition limited river activity and weak soil development loess deposition persisted into ois 3 but at this time the m a t was c 13 c and with higher humidity and vegetation growth during the lgm ois 2 m a t was c 8 1 c and effective river slope and aeolian processes along with associated with limited vegetation cover were responsible for the most extensive changes in the landscape major rates of change occur during periods of climatic deterioration when the high levels of geomorphic energy were imposed on a landscape undergoing a breakdown of vegetation cover

completeness of the fossil record and the validity of sampling proxies a case study from the triassic of england and wales many studies have highlighted correlations between palaeodiversity and sampling proxies these correlations have been interpreted as evidence for bias common cause or redundancy between signals here we compare a number of sampling proxies representing sedimentary rock volume rock accessibility and worker effort with palaeodiversity through the predominantly terrestrial triassic system in england and wales we find that proxies for sedimentary rock volume and accessibility do not correlate with palaeodiversity until the removal of facies related preservational and palaeoecological factors this indicates that a weak sampling signal may be present but the effects of changing palaeoenvironments are far more important at the regional scale significant correlations between worker effort and palaeodiversity are detected although this is likely to be a result of the preferential sampling of formations already known to be rich in fossils the fact that there is little evidence for sedimentary rock bias in the fossil record of the triassic of england and wales suggests that either 1 sampling bias is not a major source of error at the regional scale or 2 sampling proxies are inadequate representations of geological and human sampling bias supplementary material correlation test results and raw time series data from the study are available at www geolsoc org uk sup18567

sea level variations and the quality of the continental fossil record theoretical and empirical studies suggest that sea level change was a fundamental parameter determining the distribution of fossil marine organisms although a similar relationship is generally assumed for the continental fossil record this intuition remains speculative quantitative evidence reveals no correlation between sea level variations and the distribution of continental tetrapods in the late jurassic eocene interval the quality of the continental fossil record depends on many more factors than just eustatic changes

integrated record of ludlow upper silurian oceanic geobioevents coordination of changes in conodont and brachiopod faunas and stable isotopes abstract the ludlow epoch silurian was marked by several globally recognized but mechanistically poorly understood biotic events the most pronounced of them was the lau event which strongly decimated conodont graptolite and brachiopod faunas additionally this event coincides with the largest positive stable carbon isotopic anomaly in the whole phanerozoic as well as the resurgence of the so called anachronistic microbial facies that were frequently encountered during survival episodes of the major mass extinction events in this contribution based on the analysis of the outer shelf facies succession milaiciai 103 core from the lithuanian part of the silurian baltic basin as integrated quantitative record of conodont brachiopod and 13 c changes across most of the ludlow is presented the succession was subdivided into four conodont zones that served as a stratigraphic framework for analyzing the 13 c and palaeoecological trends the depth constrained cluster analysis revealed successions of three statistically distinct conodont and six statistically distinct brachiopod assemblages that replace each other near the change points in the stable carbon isotopic curve the application of a newly developed mathematical technique based on the analysis of recurrence patterns of the fossil assemblages revealed that both conodonts and brachiopods are represented by highly time specific assemblages in the aftermath of the lau event o snajdri interval zone the anomalous interval is confined to the transgressive and highstand phases of the 3rd order post lau transgression the discussed interval is coeval with the extensive development of stromatolitic communities in the nearshore environments around the world the results allow for the first time to quantify the profound ecosystem wide geobiological impact of the mid ludfordian event that lasted up to the latest ludfordian

suspended sediment discharge from snowmelt ikushunbetsu river hokkaido japan department of geophysics faculty of science hokkaido university ni ows kita ku sapporo 060 japan received 3 march 1995 accepted 17 december 1995 abstract sediment discharge generated from snowmelt was observed in the ilmshunbetsu river hokkaldo japan drainage basin area 60 km 2 in april may 1992 and april 1993 continuous records of water discharge q and suspended sediment concentration c indicated synchronous temporal variations at a station on the riverbank and a downstream increase in sediment discharge q q c between two stations along a river channel the sediment suspended over 90 of water depth consisted of more than 95 wt of silt 3 91 d 62 5 m and clay d 3 91 zm sources of the fine suspended sediment were identified by comparing grain size distributions of riverbed and side gorge slope sediment samples being supplemented by mineralogical analysis it is concluded that the sediment discharge is generated by the fluvial erosion of weathered soils which are accumulated on side gorge slopes from the collapse of the top soil and the amount of sediment eroded per unit area per unit time is approximately proportional to the fluvial shear stress