relations between relative changes in sea level and climate shifts pennsylvanian permian mixed carbonate siliciclastic strata western united states study of pennsylvanian virgilian permian wolfcampian strata of the western united states parts of idaho utah new mexico and kansas reveals complex relations between relative changes in sea level and shifts in climate relative falls in sea level are indicated by subaerial exposure of subtidal sediments and fluvial incision through subtidal sediments changes in the character of pedogenesis and sediment transport deposition and supply and the variable distribution of climatically sensitive lithofacies within cyclothems are interpreted to reflect shifts in climate during deposition of each cyclothem the majority of stratal relationships documented herein from a number of long term climatic sedimentologic and shelf settings are consistent with a hypothesis that relative highs in sea level are accompanied by more seasonal conditions whereas relative lows are characteristically more arid uncommon deviations are present however and may be due to 1 shoaling caused by sedimentation or tectonic uplift independent of a eustatic climatic signal 2 complex sedimentologic or geomorphic responses to climate change 3 leads lags or thresholds in either glacial advance and retreat or the climatic response to such changes this study shows that coupled climatic shifts and changes in sea level exert a pronounced but varied influence on stratigraphic architecture in depositional settings across late paleozoic ramps the proposed climatically enhanced cyclic and reciprocal sedimentation model predicts that during a single eustatic fall updip areas have features indicating a more seasonal or humid climate that are overlain or overprinted by characteristics suggesting more arid climate in downdip areas that were not subaerially exposed until the late stages of a eustatic fall only more arid climatic features are represented in the terrestrial or subaerial exposure features

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

caco3 dissolution in california continental margin sediments the influence of organic matter remineralization in situ benthic flux chamber and oxygen microelectrode and shipboard porewater results have been used to quantify sea floor dissolution of caco3 on the continental rise adjacent to central california usa the porewater distributions and benthic fluxes of o2 no3 ta ca2 13c and tic are interpreted using a numerical simulation of organic matter remineralization and caco3 dissolution in marine sediments the processes considered in the simulation include organic matter oxidation by o2 no3 and so42 caco3 dissolution and precipitation hs and nh4 oxidation and sediment mixing and sediment accumulation calculated benthic fluxes of o2 no3 ta tic 13c and ca2 porewater concentrations of o2 no3 and nh4 and sediment distributions of organic carbon caco3 excess 210pb and 14c agree well with the measurements benthic fluxes of alkalinity and inferred caco3 dissolution rates cannot be explained on the basis of dissolution driven solely by bottom water undersaturation if the influence of metabolically produced co2 is included benthic fluxes are fully reconciled however this is in agreement with benthic chamber ca2 and 13c results that independently imply substantial caco3 dissolution in these sediments the above observations are in contrast to those reported by jahnke et al 1994 for the west african continental rise and the western equatorial pacific where 1 g diagenetic models predict dissolution fluxes larger than observed with benthic flux chambers we conclude that the extent of metabolic caco3 dissolution may vary regionally numerous factors such as the depth of metabolic co2 production and caco3 dissolution kinetics are known or predicted to influence metabolic dissolution among the factors that should be considered in reconciling these observations are l the extent to which sulfate reduction and reoxidation reactions may influence acid base properties in surface sediments and 2 the total sedimentary caco3 content of the sites that may influence porewater acidity through surface exchange reactions at the mineral surface

the influence of organic matter diagenesis on caco3 dissolution at the deep sea floor abstract in situ benthic flux chamber measurements were performed at seafloor locations in the atlantic and pacific oceans where the bottomwaters were supersaturated approximately saturated and undersaturated with respect to calcite there was no evidence of significant dissolution at or above the saturation horizon below the saturation horizon however significant benthic fluxes of titration alkalinity and calcium out of the sediments were observed indicating appreciable dissolution where observed the rate of dissolution is consistent with a rate expression of reaction order 4 5 and a rate constant in the range of 0 05 to 0 5 per day a numerical simulation was constructed to represent organic matter and caco3 diagenesis at the seafloor at the supersaturated and near saturation sites the model over predicts the influence of metabolically produced co2 on the extent of caco3 dissolution it is possible that these results can be reconciled by a better understanding and parameterization of organic matter mineralization and porewater transport processes in surface sediments the primary factors to be considered include 1 the oxidation state of the carbon being oxidized 2 the vertical distribution of oxidation rates including the role of doc in sediment remineralization 3 the influence of nondiffusive transport of near surface porewaters and 4 the influence of episodic depositional events on organic and inorganic carbon cycling

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

the global ocean flux of particulate organic carbon areal distribution and magnitude the magnitude and distribution of the particulate organic carbon poc rain rate to the seafloor in the atlantic pacific and indian ocean basins between 61 n and 61 s has been estimated from benthic oxygen flux estimates for water depths 1000 m only the calculation utilizes the extensive data sets of sedimentary organic carbon caco3 and accumulation rate to extrapolate between individual benthic flux measurement sites using an empirically derived correlation between the seafloor oxygen flux and these parameters the poc flux through the 1000 m depth horizon was then estimated from published correlations between sediment trap determined fluxes and water depth total oxygen utilization in the deep ocean is estimated to be 1 2 1014 mol o2 yr 1 a value that agrees well with previous estimates which were based on surface water primary productivity sediment trap and depth relationships and with deep water respiration rates estimated from apparant oxygen utilization aou 14c relationships on the basis of the derived global ocean flux distribution it is concluded that 1 dissolved organic carbon doc inputs are not required to account for estimated deep water respiration rates 2 the majority of the poc input to the deep ocean occurs within 30 of the equator 3 the proportion of primary production that reaches the deep sea does not vary greatly with latitude 4 gyre and continental margin regions contribute roughly equally to the deep poc flux with a relatively minor contribution from the equatorial divergence region 5 of the estimated 7 2 1013 mol c yr 1 of poc that sinks below the 1000 m depth horizon 45 3 3 1013 mol c yr 1 reaches the seafloor where it is oxidized 6 when normalized to basin area average deep flux rates in the atlantic and pacific are similar while highest rates are observed in the indian ocean and 7 the results can be fully reconciled only if the benthic flux of doc is significantly less than the benthic o2 flux

microbial and meiofaunal abundance redox potential ph and shear strength profiles in deep sea pacific sediments vertical profiles of microbial and meiofaunal abundances and of redox potential ph water content and shear strength have been measured in sediment subcores from seven box cores collected in the southern central pacific and the findings have been related to potential effects on pelagic fluxes and sedimentation microbial and meiofaunal abundance decreased exponentially with sediment depth micro organisms were found throughout the depth of the core to 40 cm meiofauna were only present in the top 5 cm to 10 cm meiofaunal metazoans decreased more rapidly than foraminiferans redox potential was always positive decreased below the surface and often rose again deeper in the sediment ph showed no clear cut trend with depth shear strength increased with sediment depth and showed occasional anomalous fluctuations water content decreased progressively downwards with the widest scatter in the top 5 10 cm the most important implications of these results for the water column above are likely to be biologically mediated organic mineralization and nutrient regeneration into the water column and biodeposition of heavy metals and the binding of particulates at and above the sediment water interface by extracellular polymeric material which will in turn lead to differential patterns of sedimentation

sampling the oxygen minimum zone off pakistan glacial interglacial variations of anoxia and productivity preliminary results sonne 90 cruise during cruise sonne 90 the well developed oxygen minimum zone omz in the northeastern arabian sea was sampled in great detail to study surface ocean productivity and organic carbon accumulation preservation during the last hundred to hundred thousands of years nearly anoxic conditions on and below the seafloor are indicated by the lack of macrobenthos and nekton absence of bioturbation high marine organic carbon accumulation and preservation of laminated sediments between about 300 and 1000 m water depth on the steep continental slope this pattern approximately coincides with the zone of extremely low o2 concentrations presently observed in the water column accumulation of organic material on the deeper slope near the lower boundary of the omz is enhanced by downslope transport downcore we observe a complex alternation of dark colored laminated and light colored homogeneous facies in general laminated organic carbon rich intervals were deposited under suboxic bottom water and enhanced productivity conditions mainly during warm stages e g bolling allerod and holocene from 8000 yrs b p to recent the homogeneous bioturbated intervals indicate normal bottom water oxygen levels and reduced productivity during or just after cold stages e g terminations ia and b and younger dryas the striking facies similarities of the sedimentary record in cores collected from different areas and water depths suggest a unique pattern of late pleistocene corg accumulation in the northeastern arabian sea which depends mainly on regional surface ocean productivity and intermediate water oxygenation however the sedimentary record is also influenced by variations in sediment supply from the makran and karachi shelf and from indus river discharge during rapid sea level changes

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

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

biological modifiers of marine benthic seascapes their role as ecosystem engineers benthic organisms in marine ecosystems modify the environment on different spatial and temporal scales these modifications many of which are initially at a microscale are likely to have large scale effects on benthic seascapes this is especially so if the species are ecosystem engineers most species of infaunal and epifaunal invertebrates and macrophytes contribute at a geophysical or geochemical level microorganisms also play a key but currently neglected role in the intertidal and immediately sublittoral zone algae and seagrasses and mussels in mussel beds have received considerable attention a substantial fossil record also exists mathematical modelling of these systems is still in its infancy although several sophisticated mathematical tools have been applied the effects of bioturbation and of microorganisms have been less studied and little is known about the activities of benthic organisms in the deep sea this paper addresses all these effects and places them in the context of large scale benthic seascapes and of the extensive literature on species defined as ecosystem engineers in the sea

chemical evolution of mid ocean ridge hot springs abstract chemical analyses yielding elemental concentrations of major and minor elements of four hot springs on the east pacific rise at 21 n and 10 hot springs from the southern trough of the guaymas basin gulf of california provide a basis for thermodynamic modeling of conductive cooling of the hydrothermal endmembers mixing of the hydrothermal endmember with seawater and reaction of an epr type fluid with sediment of bulk chemical composition corresponding to unaltered sediment from dsdp hole 477 in the guaymas basin results of the calculations indicate that conductive cooling of endmember fluids within closed chimneys and conduits accounts for the solution composition of one vent on the east pacific rise and several vents in guaymas basin mixing of the hydrothermal fluids with seawater yields a prediction of mineral assemblages closely approximating those observed in samples of chimneys from the east pacific rise and drill cores in guaymas basin the hypothesis that guaymas basin hydrothermal fluids result from interaction of an epr type fluid with sediment cover in guaymas basin is supported by calculations which predict an increase in ph to a value similar to guaymas basin fluids an order of magnitude decrease in metal concentrations and an excellent agreement between predicted mineral assemblages as a function of extent of interaction with sediment and observed mineral assemblage distribution with depth

trace fossils as a paleoceanographic tool evidence from late quaternary sediments of the southwestern iberian margin biogenic structures in late quaternary sediments from the southwestern iberian continental slope were studied by using x ray images from two cores from 580 and 1750 m water depth eight different ichnocoenoses were observed indistinct bioturbation planolites dominated thalassinoides dominated chondrites dominated planolites and thalassinoides dominated pyritized microburrows such as trichichnus and mycellia dominated chondrites trichichnus and mycellia dominated and zoophycos variations of the ichnocoenoses within the cores show a striking correlation with climatically induced changes in the hydrographical regime i e current strength and bathymetric position of the mediterranean outflow water mow comparison of the response of the ichnocoenoses to changes in bottom water conditions and substrate between the two cores studied indicate that bottom water oxygenation and enrichment of particulate organic matter at the base of the mow layer are the primary factors controlling the ichnocoenoses the traces even recorded short term climatic changes such as the younger dryas cold event the spatial and temporal distribution patterns are in good agreement with earlier models of the mow history which gives reason to see a refinement of trace fossils as a complementary tool for paleoceanographical studies

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

uniformity and diversity in the composition of mineralizing fluids from hydrothermal vents on the southern juan de fuca ridge abundances of li ni k rb ca sr ba mn fe zn and si have been determined in fluid samples from seven vents located in three areas on the southern juan de fuca ridge the hydrothermal component estimated from the mg contents of the samples ranges from 7 to 76 concentrations of fe and si among the other elements in acid stabilized solutions appear to be generally representative of the parental hydrothermal fluids but some zn determinations and most ba values appear to be too low thermodynamic calculations indicate that the acidified samples remain supersaturated with respect to silica barite and pyrite unacidified samples are supersaturated in addition with respect to zns fes and many silicate phases within the constraints of limited sampling there appear to be differences in fluid compositions both within and between the three vent areas some uniform differences in the elemental abundances predicted for hydrothermal end member fluids might be due to inmixing of fresh seawater at depth in the hydrothermal system the juan de fuca hydrothermal fluids contain more fe but otherwise have relative elemental abundances fairly similar to those in 13 sup 0 n east pacific rise fluids albeit at higher levels in contrast fluids from 21more sup 0 n east pacific rise and galapagos have lower k rb and much lower sr and na abundances these compositional features probably result from interaction of these fluids with a different mineral assemblage possibly more mature greenstone copyright american geophysical union 1987 less

chemistry of hydrothermal solutions from the southern juan de fuca ridge fluids from three vent fields on the southern juan de fuca ridge were sampled in september 1984 using the dsrv alvin the fluids are uniquely high in both chloride which ranges up to twice the seawater value and in metal content simple vapor liquid phase separation could not have produced both the high chlorinity and gas concentrations observed in these fluids the cause of the elevated chlorinity can not be uniquely identified but may be the result of either or a combination of two processes 1 subsurface formation of a degassed brine and subsequent mixing of a small amount of this brine with a hydrothermal seawater which has not undergone a phase separation and 2 dissolution of a chloride rich phase combined with a possible small loss of gas during sampling procedures although measured temperatures were all less than 300 sup 0 c quartz geothermometry suggests that the fluids have equilibrated at greater than 340 sup 0 c quartz geobarometry is also in agreement with geophysical estimates of depth to the local magma chamber copyright american geophysical union 1987

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

formation of massive sulfide deposits on oceanic ridge crests incremental reaction models for mixing between hydrothermal solutions and seawater equilibrium path calculations have been used to model mixing between hot 350 c hydrothermal solutions and ambient seawater in an attempt to simulate mineral precipitation at seafloor vents these calculations predict temperatures of precipitation paragenetic sequence of minerals and chemical composition of chimney deposits associated with vents on the seafloor at 21 n epr assuming sulfate sulfide disequilibrium during mixing the paragenetic sequence revealed is chalcopyrite anhydrite pyrrhotite pyrite sphalerite graphite and barite when sulfate sulfide equilibria is permitted during mixing however reduction of small amounts of sulfate results in early precipitation of pyrite and a sequence of cu rich sulfide minerals chalcopyrite bornite chalcocite covellite this sequence is analogous to that observed in thin chimney walls the calculations indicate that sulfide mineral precipitation occurs in response to both cooling and change in composition of the hydrothermal solutions as a result of mixing varying the amount of mixing with respect to temperature simulating conductive heating of seawater prior to mixing results in only minor variations in the sequence and abundance of precipitated phases anhydrite precipitation during mixing occurs early which is consistent with formation of an anhydrite leading edge of chimney structures similarly extrapolation of warm spring data from galapagos to zero so4 concentration suggests anhydrite formation due to mixing with seawater beneath the seafloor most likely below the level of reactive calcareous sediments subsequent interaction of the mixed hydrothermal solution with those sediments results in elevated and variable ca concentrations estimated for end member solutions from the galapagos precipitation of mg hydroxide sulfate hydrate in the walls of the vent chimneys at 21 n epr occurs as a result of conductive heating of ambient seawater with only very minor amounts of mixing in contrast precipitation of amorphous silica in the vents must be due to conductive cooling of the hydrothermal solutions thus incremental reaction calculations demonstrate that reactions occurring in and associated with venting ridge crest hydrothermal solutions can be effectively modeled using the thermodynamic data and reaction modeling codes available today departures from equilibrium required to accurately model the mixing process are easily accommodated and consistent with data from the vents and vent forming materials

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

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

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

major and minor metal composition of three distinct solid material fractions associated with juan de fuca hydrothermal fluids northeast pacific and calculation of dilution fluid samples abstract three distinct types of solid material are associated with each sample of the hydrothermal fluid that was collected from the vents of the southern juan de fuca ridge the solid materials appear to be representative of deposits on ocean floors near mid ocean ridges and interpretation of the chemistry of the hydrothermal solutions requires understanding of them sr isotopic evidence indicates that at least two and probably all three of these solid materials were removed from the solution with which they are associated by precipitation or adsorption this occurred after the pure hydrothermal fluid was diluted and thoroughly mixed with ambient seawater the three types of solid materials are respectively a coarse zn and fe rich material with small amounts of na and ca a finer material also rich in zn and fe but with alkali and alkaline earth metals and a scum composed of ba or zn with either considerable fe or si and sr mineral identification is uncertain because of uncertain anion composition only in the cases of ba and zn were metal masses greater in solid materials than in the associated fluids for all other metals measured masses in fluids dwarf those in solids the fluids themselves contain greater concentrations of all metals measured except mg than seawater we discuss in detail the relative merits of two methods of determining the mixing proportions of pure hydrothermal solution and seawater in the fluids one based on sr isotopes and another previously used method based on mg concentrations comparison of solute concentrations in the several samples shows that degree of dilution of pure hydrothermal solutions by seawater and amounts of original solutes that were removed from it as solid materials are not related there is no clear evidence that appreciable amounts of solid materials were not conserved lost either during or prior to sample collection

metals and isotopes in juan de fuca ridge hydrothermal fluids and their associated solid materials the 87sr 86sr ratio of the hydrothermal solution hts 0 7034 is larger than that of basalt 0 7025 at the southern vent field of the juan de fuca ridge sjfr both the sr isotopic ratio for hts and the water rock interaction ratio lie between those at two sites farther south on the east pacific rise 13 n and 21 n these parameters may be closely related to subsurface temperatures and rates of magma ascent and to extent of faulting and surface areas of the frameworks of the hydrothermal systems for these three pacific ocean sites there is no steady geographical progression of these measured parameters nor of reported spreading rate with increasing latitude northward pb and nd isotopic measurements are uniform for all samples from the sjfr ranging only from 18 43 to 18 58 for 206pb 204pb fluids and associated solids and centering near 0 5131 for 143nd 144nd only fluids measured values for basalts and sulfides from the site have similar values relatively high 206pb 204pb values at the sjfr suggest the potential for the existence of an anomalous radiogenic heat source in the underlying mantle material a nd sm mass ratio of about 5 suggests that the system of the sjfr like those at 13 n and 21 n may be light rare earth element enriched the availability of three types of solid material associated with each fluid sample has provided an opportunity to study chemical distribution between fluids and solids sr isotopic compositions provide strong evidence that at least two of the types of solids are precipitates from their individually associated fluids for most metals measured the masses in the fluids were greater than the masses in solid materials however some metals or the solids that contain them may not have been conserved fractions possibly being lost during sampling or earlier a sr isotopic method of determining extent of seawater dilution of the fluid samples yields different results from the traditionally used method based on mg concentrations perhaps due to differing degrees of precipitation of the two metals

continental drift and phanerozoic carbonate accumulation in shallow shelf and deep marine settings knowledge of past rates of transfer of rock forming materials among the principal geologic reservoirs is central to understanding causes and magnitudes of change in earth surface processes over phanerozoic time to determine typical rates of global sediment cycling we compiled information on area volume and lithology of shallow water sediments by epoch for both terrigenous clastics and marine carbonates data on amounts of surviving continental terrigenous rock as opposed to deep oceanic and including terrestrial marginal marine and marine deposits exhibit positive age area trends wherein greatest areas and volumes of conglomerate sandstone and shale are represented by younger sequences global volumes of terrigenous clastic sediment yield a mean cycling rate of 0 00124 m yr similar to that determined for eurasian 0 00127 north american 0 00058 a b ronov 0 00352 t d cook and a w bally african 0 0017 and south american 0 0021 clastic sequences surficial erosion results in the mean destruction of 0 124 of terrigenous rock volume per million years of reservoir age in contrast surviving epicratonic and shelf margin carbonate sequences yield negative cycling rates of about 0 164 m yr surviving areas and volumes increase with sequence age that is the amount of limestone and dolostone preserved in shallow water settings increases back in time to maximal areal extents in the middle and upper cambrian mass age data on terrigenous clastic successions indicate generally constant rates of crustal erosion over phanerozoic time decrease in size of the shallow marine carbonate reservoir forward in time therefore suggests generally invariant rates of global limestone accumulation and a shift in sites of accumulation from shallow cratonic to deep oceanic settings over much of the past 540 m yr causes of this eon scale depositional translocation of carbonate sediment from shallowto deep marine settings cannot be satisfactorily linked to either changes in global sea level or the evolution of carbonate producing plankton because neither exhibits a pattern of unidirectional change in position or abundance since the early phanerozoic however tabulation of long term variation in areas of continental shelves from paleogeographic maps reveals a generally uniform decrease in low latitude 30 platform area with decreasing age over most of the phanerozoic moreover rate of change of low latitude shelf area km 2 m yr is almost exactly

bioturbation in deep sea pacific sediments bioturbation structures have been recorded in sediment cores from 5000 m to 5300 m water depth collected from the pacific ocean using subcores from spade box cores shear strength and eh profiles were also taken the results have been related to pelagic fluxes and sedimentation bioturba tion structures consist of holes and chambers of various sizes running vertically and horizontally whose abundance size and shapes have been measured values did not decrease exponentially with sediment depth but end abruptly at depths ranging from 30 cm to 45 cm in many instances there were subsurface peaks of vertical and horizontal burrows there was also evidence of lateral galleries large deep in filled burrows were observed these consisted of light and dark brown sediment having different shear strengths eh profiles showed that the sediment was aerobic with slightly lower values near the sediment surface possibly associated with meiofaunal and bacterial activity the most important implications of this work for pelagic processes are likely to be increased transfer of dissolved and particulate material between the sediment and the water column due to the physical network of burrows within the sediment and increased surface roughness caused by burrow openings mucus binding of particulates and faecal pelletization are also likely to be important all of these effects will be most noticeable at high burrow densities

chinese loess record of monsoon climate during the last glacial interglacial cycle the thick loess paleosol succession of central china contains a detailed record of changes in east asian monsoon climate since the late miocene epoch the alternating loess paleosol stratigraphy closely resembles the marine oxygen isotope record implying that episodic dust deposition and pedogenesis are in phase with global ice volume fluctuations and controlled by variations in solar radiation reaching the land surface deposits equivalent to marine isotope stages mis 5 through 1 have been dated by 14c 10be luminescence and magnetic susceptibility and grain size models malan loess mis 4 2 decreases in thickness southeastward from 30 m in the western loess plateau to 5 m east of xi an downwind asian dust is found in japan the north pacific ocean and the greenland ice sheet where it has a chemical signature that points to a primary source in western china during glacial times the mean dust flux in the central loess plateau reached 0 35 mm year whereas in interglacial times it fell to 0 1 mm year times of high dust influx and reduced soil development coincided with strengthened winter monsoon conditions which are inferred from variations in loess grain size times of decreased dust accumulation and strong pedogenesis marked by high values of magnetic susceptibility represent times of strengthened summer monsoon conditions high frequency fluctuations in dust influx during deposition of the malan loess include peaks that likely correlate with north atlantic heinrich events the younger dryas oscillation is recorded in chinese eolian and organic deposits by a shift from cool humid late glacial conditions to cold and dry conditions followed by a return to milder humid climate at the beginning of the holocene warm moist climate associated with a strong summer monsoon characterized the first half of the holocene epoch when a widespread paleosol complex developed on the loess plateau increased dust deposition during the middle to late holocene marked a shift to cooler drier conditions

biogeomorphological implications of microscale interactions between sediment geotechnics and marine benthos a review abstract at the foundations of biogeomorphological processes in the sea lie interactions between the activities of marine benthic animals and the geotechnical properties of their sedimentary environments the potential significance of these interactions which take place at a microscale level of millimetres to metres for the large scale geomorphology of the seabed has rarely been appreciated in the context of this review large scale is defined as greater than 50 m to hundreds of kilometres the present review addresses this link drawing examples from a wide range of marine environments including estuaries the intertidal zone continental shelves and slopes and the deep sea it firstly considers sediment stabilisation slope failure sediment mixing biodeposition sediment compaction and hydrodynamic effects this is followed by a consideration of two extremes of the ecological pyramid the effects of marine meiofauna and marine vertebrates the final section draws attention to the central role of faunal mucus and extracellular polymeric material ecpm in many of the microscale interactions that we describe the implications of these microscale biological processes and features are discussed in terms of their influence on and control of the large scale geomorphology of the seabed

authigenic carbonates derived from oxidized methane vented from the makran accretionary prism off pakistan we report the first discovery and sampling of a methane hydrogen sulfide rich cold seep from the makran accretionary prism off pakistan arabian sea a variety of cm to m scale pockmarks and gas seepage structures were identified from underwater tv photo sled profiles crossing the oxygen minimum zone omz related to highresolution seismic parasound records from the seeps isotopically light bacterially formed methane is emanating that is partly oxidized to hco3 in the bacterial sulfate reduction zone this results in the precipitation of irregular dark gray to black crusts of indurated authigenic carbonates mainly cryptocrystalline magnesian calcite and ca rich dolomite near the sediment seawater interface within the omz downcore the crusts grade into hemipelagic carbonate poor silty clays with transitional lithologies in between similar to the pockmark carbonates from the oregon margin and in the north sea the authigenic carbonates are extremely depleted in 13c 13ccarbonate 40 this suggests that they were derived from bacterial methane 13cmethane 77 8 that was oxidized under anaerobic conditions the authigenic carbonates are associated with white fluffy mats of chemoautotrophic h2s oxidizing bacteria small pockmarks appear to be concentrated at small scale escarpments suggesting focussed fault controlled pore fluid expulsion due to the tectonic dewatering and degassing of the accretionary prism whereas diffuse discharge of pore fluids is inferred from the widespread occurrence of tiny gas bubble tubes

two abyssal sites in the southern ocean influenced by different organic matter inputs environmental characterization and preliminary observations on the benthic foraminifera abstract the abundance and diversity of the deep sea benthos are intimately linked to inputs of organic matter from the euphotic zone however it is often difficult to isolate the influence of surface productivity on benthic ecosystems from other environmental factors to this end two abyssal sites 4200 m water depth located under contrasting productivity regimes around the crozet plateau in the indian ocean sector of the southern ocean were sampled during the austral summer of 2004 2005 one site m5 east of the crozet isles was located beneath an area where there was an enduring seasonal phytoplankton bloom the second site m6 was located in an oligotrophic high nutrient low chlorophyll hnlc region to the south of the islands organic fluxes to the seafloor at these sites are thought to reflect the overlying productivities so that the benthic environment to the east of the islands was more eutrophic than at the southerly station all other environmental variables were similar at the two sites which are located just 460 km apart the concentrations of chlorophyll a and total organic carbon in the surficial sediments were significantly greater at the relatively eutrophic site east of the islands m5 than at the southerly site m6 total nitrogen however was similar at both sites significantly higher phytopigment concentrations were observed in the surficial sediments at the eutrophic site in particular the concentration of chlorophyll a was 3 times greater than at the southern site although the freshness of the labile component as measured by chlorophyll a to pheophorbide ratio was not different between sites these results confirm that fluxes of organic matter to the seafloor were higher at the site located beneath the bloom region this was reflected in the abundance and diversity of live stained and dead benthic foraminifera 125 m which were greater at the eutrophic site the species composition of the dead foraminiferal assemblages were similar at both sites however and were dominated by nuttallides umbonifera pullenia bulloides and melonis pompiloides an exception was the phytodetritus species epistominella exigua which was more abundant at the eutrophic site indicating a larger seasonal component to the export under the bloom region differences in the organic matter input regimes at the two sites appear to influence the abundance and diversity but not the overall species composition of the foraminiferal assemblages

a 225 kyr record of dust supply paleoproductivity and the oxygen minimum zone from the murray ridge northern arabian sea abstract analysis of a 15 m long sediment core recovered from the murray ridge northern arabian sea reveals a 225 000 year record of climate induced variations in surface water productivity mid water ventilation and dust input in the northern arabian sea productivity and dust input records closely resemble those from the owen ridge and oman margin also the phase lag of 10 kyr between maximum productivity and precession minimum is in phase with the summer monsoon upwelling record from the owen ridge and the oman margin this implies that the productivity variations in the northern arabian sea during the last 225 kyr are primarily controlled by changes in the indian ocean summer monsoon the winter monsoon obviously played a minor role in the productivity history of the northern arabian sea another result from this study is that the mg al record from the murray ridge nicely documents the post glacial flooding of the persian gulf which is the main glacial source for dolomite dust in this region finally it is concluded that the intensity of the omz co varies with surface water productivity being weak during periods of reduced summer monsoon especially during glacial periods

benthic biological and biogeochemical patterns and processes across an oxygen minimum zone pakistan margin ne arabian sea abstract oxygen minimum zones omzs impinging on continental margins present sharp gradients ideal for testing environmental factors thought to influence c cycling and other benthic processes and for identifying the roles that biota play in these processes here we introduce the objectives and initial results of a multinational research program designed to address the influences of water depth the omz 150 1300 m and organic matter om availability on benthic communities and processes across the pakistan margin of the arabian sea hydrologic sediment and faunal characterizations were combined with in situ and shipboard experiments to quantify and compare biogeochemical processes and fluxes om burial efficiency and the contributions of benthic communities across the omz in this introductory paper we briefly review previous related work in the arabian sea building the rationale for integrative biogeochemical and ecological process studies this is followed by a summary of individual volume contributions and a brief synthesis of results five primary stations were studied at 140 300 940 1200 and 1850 m water depth with sampling in march may intermonsoon and august october late to postmonsoon 2003 taken together the contributed papers demonstrate distinct cross margin gradients not only in oxygenation and sediment om content but in benthic community structure and function including microbial processes the extent of bioturbation and faunal roles in c cycling hydrographic studies demonstrated changes in the intensity and extent of the omz during the sw monsoon with a shoaling of the upper omz boundary that engulfed the previously oxygenated 140 m site oxygen profiling and microbial process rate determinations demonstrated dramatic differences in oxygen penetration and consumption across the margin and in the relative importance of anaerobic processes but surprisingly little seasonal change a broad maximum in sediment om content occurred on the upper slope roughly coincident with the omz but the otherwise poor correlation with bottom water oxygen concentrations indicated that other factors are important in determining sediment om distributions downcore profiles generally showed little clear evidence of in situ om alteration and there was little sign of om enrichment resulting from the southwest monsoon in sediments collected in the late to postmonsoon sampling this is interpreted to be due to rapid cycling of labile om organic geochemical studies confirmed that sediment om is overwhelmingly of marine origin across the margin but also that it is heavily altered with only small changes in degradation state across the omz more negative stable c isotopic compositions in surficial sediments at hypoxic sites within the omz core are attributed to a chemosynthetic bacterial imprint dramatic changes in benthic community structure occurred across the lower omz transition apparently related to om availability and quality as well as to do concentrations high resolution sampling biomarkers and isotope tracer studies revealed that oxygen availability appears to exert threshold type controls on benthic community structure and early faunal c processing biomarker studies also provided evidence of faunal influence on sediment om composition together the results offer strong evidence that benthic fauna at sites across the margin play important roles in the early cycling of sediment om through differential feeding and bioturbation activities

contrasting patterns and connections of rock and biotic diversity in the marine and non marine fossil records of north america abstract macrostratigraphy uses packages of continuous sedimentation that are bound by hiatuses of non deposition erosion or alternations between environments lithologies to characterize spatiotemporal patterns of sedimentation previous work has linked the macrostratigraphy of marine shelf environments to many different macroevolutionary patterns in the marine animal fossil record here we use an improved macrostratigraphic database for north america combined with fossil occurrence data in the paleobiology database to show that macroevolutionary and macrostratigraphic patterns are correlated more strongly in marine environments than in non marine environments we also test the hypothesis that the temporal distribution of lithological diversity measured as evenness similar to ecological evenness based on the number of lithostratigraphic units with a given lithologic type within each time interval has a relationship to genus level taxonomic diversity in both the marine and non marine realms uneven sampling of lithologies and their corresponding depositional environments can bias our perception of taxonomic diversity by causing taxa from poorly sampled environments to be underrepresented in the fossil record our results show a negative correlation between lithologic evenness and marine vertebrate generic richness less even sampling of lithologies corresponds to a higher observed taxonomic richness and no correlation with lithologic evenness and non marine diversity measures this suggests a difference in the relationship between biologic and sedimentary processes at work in the marine and non marine realms and possibly differences in the magnitude of the bias imposed by the rock record on the underlying biologic patterns

paleocene and eocene kaolinite distribution in the south atlantic and southern ocean antarctic climatic and paleoceanographic implications abstract clay mineral associations of paleocene and eocene age have been examined in six drilled sequences from the southern south atlantic and southern ocean these sites are located to provide three depth transects across intermediate water masses widespread abundance of pedogenic smectite at all locations suggests globally warm climates and alternating wet and dry seasons on the adjacent continental margins including antarctica as was the case during the late cretaceous remarkably kaolinite is observed only in paleocene eocene sediments at the highest latitudes of these sites and must have originated from antarctica the restriction of kaolinite to the antarctic region is inferred to have resulted from especially higher rainfall there during the paleocene eocene relative to the lower latitude areas examined this inferred high rainfall is considered to have resulted from globally warm temperatures that increased poleward latent heat transport compensating for a strong heat deficit in the antarctic region relative to the tropics kaolinite was not observed in the latest cretaceous maastrichtian sediments of maud rise antarctica kaolinite first appears in the clay mineralogical assemblages in the earliest paleocene 64 to 64 5 ma at a time of relatively cool intermediate waters and before a warming trend of surface waters currents at intermediate water depths transported fine terrigenous sediments from the antarctica during the latest paleocene and early eocene 59 to 52 ma at a time when the oxygen isotopic strongly in east antarctica during the latest paleocene and early eocene 59 to 59 ma at a time when the oxygen isotopic data indicate maximum warmth of surface and intermediate waters of the southern ocean these are interpreted to reflect a paleocene maximum of antarctic rainfall this development peaked at 57 3 m close to the paleocene eocene boundary a time of maximum warmth based on oxygen isotopic data increased illite content and associated chlorite and random mixed layer clays at the end of the middle eocene 41 ma suggest local development of poorly weathered soils on antarctica favored by a cooling of the southern ocean coeval extension of kaolinite into shallower water depths and similar clay mineral associations in shallower and deeper sites indicate the development of cooler conditions led to an increasing influence of antarctic environments upon intermediate water masses at high latitudes

a critical evaluation of depositional parameters controlling the variability of organic carbon in arabian sea sediments abstract organic carbon distribution in the surficial sediments of the arabian sea to some extent mirrors the surface productivity being both high in the peripheral portions and low in the central region suggesting that the productivity is a primary source of organic matter however a critical examination reveals that the organic enrichment on the slope of the indian margin is two to four higher max 16 71 than on the slope of the arabian peninsula max 7 54 while the productivity in the former region is three to four times lower than the latter this observation suggests that the influence of productivity on organic enrichment is of secondary importance high concentrations 4 of organic carbon exactly coincide with the oxygen minimum zone 150 1500 m water depth evidently reflecting the crucial role played by the anoxic bottom waters in the preservation of organic carbon incidently the organic rich band along the western indian slope is wide long and highly concentrated as compared to that of the slope of the arabian peninsula and no organic enrichment is found on other continental slopes of the arabian sea although an equally intense oxygen minima impinge on the floor of the slope such a variability of organic carbon on the slopes is attributed to various geological parameters such as texture of sediments rates of fine terrigenous sediment deposition shelf width slope gradient bottom currents and adsorption capacity of individual clay minerals all these observations suggest that the productivity is not an ultimate control for the organic enrichment of bottom sediments but it is the bottom water anoxia in conjunction with various depositional parameters which determine the degree of preservation

bioturbation geochemistry and geotechnics of sediments affected by the oxygen minimum zone on the oman continental slope and abyssal plain arabian sea abstract we investigate the way the oxygen minimum zone omz alters interactions between bioturbation and sediment geochemistry and geotechnical properties sediments are compared within and below the omz on the oman continental slope and adjacent abyssal plain during the post monsoonal autumn season quantitative measurements were made of eh and ph of total organic matter tom and carbonate of water content and shear strength and of bioturbation structures in vertical profiles of subcores taken from spade box core samples the omz stations had distinctively low redox conditions and high carbonate content and different geotechnical properties and different bioturbation structures than stations below the omz on the abyssal plain these differences are related to the degree of anoxia and to water depth within the omz eh ph and carbonate increased with water depth and tom and water content decreased we also noted the presence of subsurface sediment heterogeneity on the continental slope within the omz in the omz eh water content and bioturbation decreased with increasing sediment depth there was a slight decrease in ph in the top 5 cm at all stations shear strength nearly always increased with increasing sediment depth at each water depth correlations show down core trends in these parameters while across all water depths correlations were significant at deeper sediment depths 20 30 cm an eh ph diagram identified two water depth groupings 391 1008 and 1265 3396 m cluster analysis showed the upper and lower sediment depths form separate clusters the break occurring at 4 7 5 cm while there are also distinct clusters related to water depth we relate our results to bottom water oxygen concentrations reported by other investigators and to regional scale geochemical processes

variations in bioturbation across the oxygen minimum zone in the northwest arabian sea abstract oxygen minimum zones are expected to alter substantially the nature rates and depths of bioturbation along continental margins yet these effects remain poorly studied using excess 210 pb profiles sediment x radiography and box core samples for macrofauna we examined bioturbation processes at six stations 400 700 850 1000 1250 and 3400 m deep along a transect across the oxygen minimum zone omz on the oman margin bottom water oxygen concentrations ranged from 0 13 ml l 1 at 400 m to 2 99 ml l 1 at 3400 m 210 pb mixed layer depth and bioturbation intensity db exhibited high within station variance and means did not differ significantly among stations however the mean mixed layer depth 4 6 cm for pooled omz stations 400 1000 m depths 0 13 0 27 ml l 1 bottom water oxygen was half that for stations from similar water depths along well oxygenated atlantic and pacific slopes 11 1 cm suggesting that oxygen stress reduced 210 pb mixing depth on the oman margin modal burrow diameter and the diversity of burrow types at a station were highly correlated with bottom water oxygen concentration from the edge to the core of the oman omz spearman s rho 0 89 p 0 02 suggesting that these parameters are useful proxies for bottom water oxygen concentrations under dysaerobic conditions in contrast neither the maximum diameter and nor the maximum penetration depth of open burrows exhibited oxygen related patterns along the transect reduced 210 pb mixing depth within the oman margin omz appeared to result from a predominance of surface deposit feeders and tube builders within this zone rather than from simple changes in horizontal or vertical distributions of macrofaunal abundance or biomass the number of burrow types per station was highly correlated with macrofaunal species diversity suggesting that burrow diversity may be a good proxy for species diversity in paleo dysaerobic assemblages we conclude that bottom water oxygen concentrations of 0 13 0 27 ml l 1 substantially alter a number of bioturbation parameters of importance to diagenetic and biofacies models for continental margins

micro scale geotechnical variability in continental slope and abyssal sediments influenced by the oxygen minimum zone in the arabian sea abstract we describe a new micro scale method of measuring the penetration resistance of the surficial layers of slope and abyssal plain sediments within and below the omz on the oman continental slope the micro scale load resistance penetrometer mlrp continuously measures the penetration resistance q of a cylindrical probe driven at constant velocity into cores of sediment recovered by sub coring box core samples measurements are recorded at 0 8 mm depth intervals into the sediment by an automated data acquisition system these provide continuous depth profiles of penetration resistance q and its variability qr in surficial sediments 0 100 mm the results represent the first published application of this technique to slope and abyssal plain sediments the q data divide the stations into shallow omz somz stations 391 854 m deep omz domz stations 987 1285 m and abyssal non omz anomz stations 3392 3396 m one station 688 m was anomalous penetration resistance q was positively related to shear strength and inversely related to water content but not to bioturbation measured as burrow numbers relaxation and pull out data were obtained from three stations three patterns of qr were observed consisting of well confined data data containing large negative and positive spikes and data showing a progressive down core increase in spikes four additional measures of q variability were defined which show statistically significant relationships with burrow numbers an increase in bioturbation estimated by burrow numbers is associated with a decrease in micro scale variability in q this is related to the activity of burrowing macrofauna our results are discussed in the context of biogeotechnical modifications of sedimentary environments