palaeoclimatic and biotic changes during the aalenian middle jurassic at the southern laurasian seaway basque cantabrian basin northern spain the uppermost toarcian lowermost bajocian deposits have been studied in 10 sections located in the western part of the basque cantabrian basin northern spain the studied 276 successive recorded ammonite assemblages allowed detailed biostratigraphical subdivision and the correlation of the sections at the ammonite zone and subzone scale the foraminifers were studied in 96 samples and 55 diagenetically screened belemnite rostra were analyzed for c and o isotope facies and thickness distribution of the aalenian sediments suggest that deposition took place in a nearly symmetrical sub basin included into an intraplate shallow platform developed over continental crust on which flexure was the main control responsible for subsidence and basin evolution noteworthy negative 13cbel excursions coinciding with seawater temperature changes were recorded during the bradfordensis biochron around the concavum limitatum biochron boundary and around the aalenian bajocian boundary a close relationship between the changes in seawater temperature and the biotic changes observed in the foraminiferal and in the ammonoids assemblages has been evidenced during the comptum biochron the 18obel based palaeotemperature shows a remarkable cooling interval with an average seawater temperature of 15 7 c this cooling favoured the immigration of species of foraminifers that thrived in platforms with colder seawater temperatures located north of the basque cantabrian basin as a consequence a strong increase in the diversity of the foraminiferal assemblages 28 5 of first appearances occurred this interval also coincides with the highest ammonoid abundance recorded during the aalenian a notable increase in temperature with peak values up to 24 3 c was measured during the bradfordensis biochron this warming marks the beginning of progressive loss of foraminifer diversity and the decrease in the abundance of ammonoids however the increase in the relative abundances of some foraminiferal taxa such as the genus spirillina during the warming phase is remarkable some of the foraminiferal species that had their last occurrence during this interval seem to be immigrants from nw europe that arrived during the comptum cooling interval and that did not survive to rise of the seawater temperature another drop in temperature was recorded during the late gigantea and the early concavum biochrons coinciding with this cooling interval nearly 20 of the foraminiferal species disappeared while the ammonoid abundance increased a new and significant warming episode occurred during the latest aalenian limitatum biochron extending to the earliest bajocian discites biochron biotic response to this new t of 2 5 c is remarkable marking one of the most important crises of the aalenian more than 30 of the foraminiferal species disappeared and no new appearances were recorded ammonoids show a decrease in the specimen abundance during the limitatum discites warming preceding a drastic decrease in the species abundance the remarkable biotic changes linked to the variations of seawater temperature recorded in the basque cantabrian basin during the aalenian open the possibility that some of these faunal turnovers specially marked in the benthic foraminifers were of global extent and mainly forced by climate changes

diversity dynamics of early jurassic ostracods of the cordillera iberica spain and the re evaluation of the pliensbachian toarcian mass extinction the extinction and recovery of ostracoda at the pliensbachian toarcian p t boundary are analyzed based on a database of taxonomically revised pliensbachian to toarcian transition ostracod assemblages in contrast to earlier assertions the results of this study indicate that ostracod extinction rates were significant in comparison with other marine invertebrates an extinction rate of 54 has been calculated for upper pliensbachian ostracod species occurring in more than one section diversification took place in the latest pliensbachian spinatum zone and early toarcian tenuicostatum zone whereas diversity decrease occurred in the middle early toarcian strangewaysi subzone serpentinus zone this notable diversity decline in the early toarcian corresponds to a global mass extinction time whose peak has been documented in the tenuicostatum zone meanwhile the ostracod mass extinction occurred within the serpentinus zone and was followed by radiation and recovery in the succeeding bifrons zone s

response of middle jurassic benthic foraminiferal morphogroups to dysoxic anoxic conditions in the pieniny klippen basin polish carpathians abstract the distribution of foraminiferal morphological groups has been analyzed in upper aalenian lower bajocian black siltstones and mudstones of the pieniny klippen belt polish carpathians the deposits are assigned to middle neritic outer and upper bathyal zones represented by three succession and contain agglutinated and calcaeous foraminifera assemblages separate classifications of agglutinated and calcareous morphogroups are established and used for a palaeocological study the groups are distinguished on the basis of morphological features modes of life and feeding habits as inferred from modern analogues infaunal preferences of some foraminifera have been supported by comparison with other infaunal indicators such as trace fossil tiering and abundance of infaunal ostracods a new quantitative method to estimate dissolution of calcareous tests has been tested on the most common genus lenticulina it reveals a special survival strategy of this genus in suboxic muddy and flocculent substrate the distribution of morphogroups in comparison with other palaeoecological taphonomical and sedimentological indicators allows interpretations of organic input rate of sedimentation level of oxygenation position of the redox boundary and p h the studied deposits represent regional anoxic dysoxic event which occured within a semienclosed silled basin

chemostratigraphy of the jurassic system applications limitations and implications for palaeoceanography current chemostratigraphical studies of the jurassic system primarily involve the use of one sedimentary component marine organic carbon one divalent transition metal substituted in carbonate manganese and two isotopic tracers strontium isotope ratios 87 sr 86 sr and carbon isotope ratios 13 c carb and 13 c org in carbonate and in organic matter other parameters such as mg ca and sr ca ratios in calcite oxygen isotope ratios 18 o in carbonate sulphur isotope ratios 34 s in carbonate hosted sulphate nitrogen isotope ratios 15 n org in organic matter osmium isotope ratios 187 os 188 os in black shales and neodymium isotope ratios 143 nd 144 nd in various mineral phases are also useful but at present give poor resolution because the database is incomplete or compromised by various factors stratigraphical patterns in total organic carbon toc can be of either local or regional significance depending on the lateral extent of the former nutrient rich and productive water mass divalent manganese follows a similar pattern being concentrated most probably as a very early diagenetic phase only in oxygen depleted waters that typically underlie zones of elevated organic productivity shifts in mg ca and sr ca ratios on the time scale of ammonite subzones seem largely to reflect temperature changes strontium isotope ratios from pristine skeletal calcite provide a global signal 13 c values from carbonates with minimal diagenetic overprint potentially do the same although small spatial differences in palaeo water mass composition may have been locally significant oxygen isotope determinations on carbonate rocks and fossils generally yield values that are too scattered to be stratigraphically useful because they reflect palaeotemperature the evaporation precipitation balance in sea water and the impact of any diagenesis involving an aqueous phase nitrogen isotope ratios in organic matter reflect the chemistry of ancient water masses as affected by nitrate utilization and denitrification and the stratigraphical pattern of this parameter is more likely to correlate only on a regional basis neodymium isotope ratios in sea water are also water mass dependent and greatly affected by regional sources and oceanic current systems preliminary data on sulphur isotope ratios in carbonates and osmium isotope ratios in organic rich shales both potentially offering global correlation indicate that these tracers may be valuable although the records at present are not sufficiently well established to allow high resolution regional correlation in all cases biostratigraphically well dated reference sections against which the relevant geochemical data have been calibrated are required in the first instance to date studies on the stratigraphical distribution of organic carbon have been principally carried out in both northern boreal and southern tethyan europe carbon isotope stratigraphy has been undertaken primarily but not exclusively on bulk pelagic sediments from the alpine mediterranean or tethyan domain and strontium isotope stratigraphy has been undertaken largely on calcitic skeletal material belemnites and oysters from northern and southern europe in many sections including those containing ammonites multi parameter chemostratigraphy can give resolution that exceeds that attainable by classic biostratigraphical means strontium isotope ratios in skeletal calcite are a particularly powerful tool for illustrating changes in sedimentary rate and revealing gaps in the stratigraphical record

the early toarcian early jurassic and the cenomanian turonian late cretaceous mass extinctions similarities and contrasts abstract the early toarcian eto and cenomanian turonian c t mass extinctions are comparable from a wide range of scales and perspectives from a broad standpoint their similarities include virtually identical extinction intensity at the familial and generic levels widespread basinal facies deposited during sea level highstands an overall greenhouse climate and anoxia as an important causal mechanism the high resolution macroinvertebrate data analyzed here consisting of stratigraphic ranges diversity and abundance point to smaller scale similarities the two events resulted in significant ecological disruption and in both cases the biotic responses were very similar taxa inhabiting the upper water column were unaffected by anoxia and included ammonites and in the eto belemnites in addition epifaunal taxa adapted to low oxygen conditions such as the buchiids posidoniids and inoceramids flourished in the post extinction environment during the survival interval as conditions ameliorated the biota became more diverse and gradually began to resemble pre extinction biotas furthermore the 13c curves predict the end of the survival interval and suggest that the period characterized by carbon isotope excursions represent disrupted environmental conditions this points to the potential application of 13c as a tool for determining the repopulation modes and timing for other mass extinctions

constraints on the geometries of structures within the sedimentary rocks at the cajon pass scientific drillsite california an analysis of downhole geophysical logs and their relation to surface geological data constrain the structure in the first 700 m of the cajon pass scientific drillhole several angular folds mapped in a small canyon 150 m to the southeast of the drillsite are associated with a steep northeast dipping reverse fault at depth this fault is inferred to cut the scientific drillhole in basement at 700 m and to intercept a nearby oil exploration well arkoma federal 1 26 within the sediments at 350 m the folds mapped at the surface are thought to have developed in late miocene to early pliocene time during the squaw peak thrusting event the inferred reverse fault offsets the sediment basement contact 180 m between the two holes

early jurassic mass extinction a global long term event the end pliensbachian extinction event 187 ma has been interpreted either as one of 10 global periodically recurring mass extinctions of the past 250 m y or as a minor localized european event elevated levels of family extinction spanned five ammonite zones during the late pliensbachian and the early toarcian an interval of 7 5 m y and were distributed unequally in the boreal tethyan and austral realms detailed sampling of invertebrate macrofaunas through complete expanded sequences in northwest europe shows that most species extinctions occurred in the early toarcian following a regional anoxic event the early jurassic mass extinction event took place over a long time scale and it was global in extent

diversity dynamics of bajocian middle jurassic ammonites and transgressions regressions in the caucasian sea northern neo tethys ocean a case high resolution test of probable dependence abstract ammonites commonly occur in the bajocian deposits of the greater caucasus basin from where 180 species and 52 genera are reported this back arc basin was located on the northern neo tethyan margin embraced by the caucasian sea an evaluation of diversity patterns for 7 bajocian ammonite zones documents high diversity in the beginning middle and end of the stage with a maximum in the humphriesianum zone and two diversity minima the mid early bajocian impoverishment of ammonite assemblages was caused by both an increase in the rate of disappearance and a decrease in the rate of appearance whereas the only latter was responsible for the mid late bajocian diversity drop an analysis of dominating facies types in the greater caucasus basin documents that the total diversity rose during regressions and fell during transgressions shoreline shifts corresponded better with changes in the number of appearances and worse with those of disappearances a comparison of results from this study with those obtained in the betic cordillera does not clarify the observed dependence changes in the exterior connections of the caucasian sea its depth and oxygen depletion of its waters are unlikely explanations of the regionally documented coincidence of ammonite diversity dynamics and transgressions regressions

elemental and mineralogical analyses using geochemical logs from the cajon pass scientific drillhole california and their preliminary comparison with core analyses estimates of elemental and mineralogical abundances from geochemical logs are compared to preliminary chemical and modal analyses from cores in the cajon pass scientific drillhole accuracies of log computed weight percent oxide and mineralogy determinations range from 10 to 30

cold seep and oxygen minimum zone associated sources of margin heterogeneity affect benthic assemblages diversity and nutrition at the cascadian margin ne pacific ocean abstract hydrate ridge hr located on the northeastern pacific margin off oregon is characterized by the presence of outcropping hydrates and active methane seepage additionally permanent low oxygen conditions overlay the benthic realm this study evaluated the relative influence of both seepage and oxygen minima as sources of habitat heterogeneity and potential stress inducing features on the bathyal metazoan benthos primarily nematodes at three different seep and non seep hr locations exposed to decreasing bottom water oxygen concentrations with increasing water depth the nematode seep communities at hr exhibited low diversity with dominance of only one or two genera daptonema and metadesmolaimus elevated average individual biomass and 13c evidence for strong dependance on chemosynthesis derived carbon resembling deep sea seeps worldwide although the hr seep habitats harbored a distinct nematode community like in other known seep communities they differed from deep sea seeps in well oxygenated waters based on that they shared the dominant genera with the surrounding non seep sediments overlain by oxygen deficient bottom water the homogenizing effect of the oxygen minimum zone on the seep nematode assemblages and surrounding sediments was constant with increasing water depth and concomitant greater oxygen deficiency resulting in a loss of habitat heterogeneity

isotopic evidence for chemosynthesis based nutrition of macrobenthos the lightness of being at pacific methane seeps the importance of chemosynthetic nutritional pathways was examined for macrofaunal invertebrates 300 mm from methane seeps in the gulf of alaska 4 413 4 443 m on the oregon margin 590 m and on the northern california slope eel river margin 520 m by use of natural abundance stable isotopic data seep macrofauna exhibited lighter d 13 c and d 15 n values than those in nonseep sediments but isotopic signatures varied among seep sites macrofaunal isotopic signatures indicated chemosynthetically fixed carbon sources with a significant contribution from methane derived carbon mdc in macrofauna from sediments of pogonophoran fields averaged 13

diversity dynamics and mass extinctions of the early middle jurassic foraminifers a record from the northwestern caucasus abstract the early middle jurassic foraminiferal assemblages of the northwestern caucasus including a total of 315 species and 68 genera were analysed to establish the principal diversity patterns at substage level of resolution an overall conclusion is that the number of species varied significantly in contrast to the number of genera the most diversified were late sinemurian pliensbachian late toarcian early aalenian and late bajocian assemblages significant diversity drops have been documented in the early toarcian and in the middle aalenian the first of them corresponds to the well known mass extinction which regionally was initiated in the pliensbachian and terminated when rapid late toarcian diversification began the second event could be considered as a regional evidence of a new mass extinction that appeared in the middle aalenian and was most likely associated with the aalenian bajocian regional anoxic event also recorded in the carpathian part of the western tethys the most intense foraminiferal turnovers took place in the toarcian and in the middle aalenian early bajocian the lazarus effect in spite of its high value has not much influenced the estimation of principal diversity trends

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 recovery and radiation of early jurassic ammonoids morphologic versus palaeobiogeographical patterns abstract the recovery and radiation of the early jurassic ammonoid morphospace as represented by nine morphologic groups identified in an earlier study are traced through the first 36 subzones of the hettangian to domerian time interval a quantitative survey of the dispersion of 436 species over 15 palaeogeographical areas reveals seven palaeobiogeographical patterns each corresponding to an exclusive set of species exhibiting similar characteristics in terms of distribution and abundance this study combines morphologic chronostratigraphical and palaeobiogeographical data in an attempt to investigate possible connections between morphologic recovery and radiation patterns and the history of ammonoid distribution on a global scale two out of nine morphologic groups are found to be prevalent in a single palaeobiogeographical pattern through the major part of the studied time interval and a single morphologic group prevails in all the marine areas considered during domerian times all the other relationships identified are less tightly constrained in space and time and indicate loose ties over more limited periods and narrower distributions the present results suggest that such complex relationships can be deciphered more successfully by using analytical palaeobiogeographical patterns as proposed here rather than classical palaeobiogeographical units biochores

lithostratigraphy determined from discriminant analysis of geochemical well logs from the cajon pass scientific drillhole california geochemical well logs recorded in the cajon pass scientific drillhole provide an estimate of the elemental concentrations of si al fe ca k th ti s and the hree gd the continuous geochemical profiles were used to define a lithostratigraphy in the cystalline basement from 501 to 1 829 m the interval between the faulted top of basement and a thrust fault at 689 m consists of six alternating slivers of granite and granodiorite interlayered granitic and granodioritic units were then encountered to another fault at 1290 m whereas gneisses of granitic to tonalitic composition were logged in the basal portion of the hole linear discriminant analysis of major element chemistry as well as variations in gd th ti and s were used to demonstrate that each of the major lithostratigraphic units is chemically distinct different trace element signatures and variable degrees of metamorphism indicate a complex thermal and hydrological history for the basement rocks encountered in the cajon pass well

methane seepage effects on biodiversity and biological traits of macrofauna inhabiting authigenic carbonates abstract authigenic carbonate rocks at methane seeps are recognized as hosting diverse and abundant invertebrate assemblages with potential forcing from fluid seepage and hydrography mensurative studies of carbonate macrofauna 0 3 mm at hydrate ridge or revealed little effect of water depth and overlying oxygenation at 600 m and 800 m but a large influence of seepage activity on density taxonomic composition diversity and biological traits feeding lifestyle motility size and calcification rocks exposed to active seepage had 3 4 higher total macrofaunal densities than under inactive conditions assemblages exhibited higher species richness and reduced evenness greater dominance under active seepage than inactive conditions but no difference in h or rarefaction diversity actively seeping sites were characterized by errant motile bacterial grazing small and medium sized heavily calcified species whereas inactive sites exhibited a greater diversity of feeding modes and more burrowers sessile large and lightly calcified species active rocks supported more exogonid syllidae ampharetid and cirratulid polychaetes provannid snails pyropeltid limpets nemerteans and sponges whereas inactive rocks supported higher densities of ophiuroids isopods gammarid amphipods hydroids typosyllis syllidae and tanaids transplant experiments in which rocks were transferred between active and inactive sites at hydrate ridge north 600 m revealed that assemblages respond within 13 months to increase or cessation of seepage taking on the feeding size and calcification characteristics of the background fauna at the new site lifestyles and motility patterns shifted more slowly as the sessile attached species did not track seepage as quickly provannid snails and pyropeltid limpets rapidly colonized rocks transplanted to active sites and disappeared when transplanted to inactive sites given the known variability of fluid fluxes and rapid community response a mosaic of communities changing in space and time is hypothesized to generate the relatively high species diversity at methane seeps

stable isotope signatures and methane use by new zealand cold seep benthos the carbon isotopic composition of seep faunal tissue represents a time integrated view of the interaction between biology and the biogeochemical gradients within the environment here we provide an initial description of carbon and nitrogen stable isotope signatures of dominant symbiont bearing megafauna and heterotrophic mega and macrofauna from 10 methane seep sites on the continental margin of the north island of new zealand 662 1201 m water depth isotopic signatures suggest that sulfide oxidation supports symbiont bearing taxa including solemyid and vesicomyid bivalves and methanotrophic symbionts are present in the seep mussel bathymodiolus sp multiple species of frenulata siboglinidae are present and have a range of isotopic values that are indicative of both thiotroph and methanotroph based nutrition isotopic composition of the tubeworm lamellibrachia sp varied by 23 3 among individuals although there was no consistent difference among sites variation in methane use by heterotrophic fauna appears to reflect the availability of hard vs soft substrate macrofauna on hard substrates had high 13c signatures reflecting consumption of photosynthetic derived organic matter two unique biotic assemblages were discovered to be fueled largely by methane a hard substrate multi phyla sponge associated community inhabiting the sponge pseudosuberites sp and a soft sediment assemblage dominated by ampharetid polychaetes isotope signatures yield estimates of 38 100 and 6 100 methane derived carbon in sponge associates and ampharetid bed macrofauna respectively these estimates are comparable to those made for deeper methane seeps at the florida escarpment 3290 m and kodiak alaska seeps 4445 m the overall high use of methane as a carbon source by both symbiont bearing and heterotrophic fauna suggests that new zealand methane seeps are an ideal model system to study the interaction among metazoans bacteria archaea and their resulting effect on methane cycles

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

marine faunal realms of the mesozoic review and revision under the new guidelines for biogeographic classification and nomenclature consensus among the friends of paleobiogeography produced tentative guidelines to the classification and nomenclature of marine biogeographic units i e biochores based on these loose rules the present paper is a critical review of all published mesozoic marine realms subrealms and superrealms formerly called climatic belts biochores are defined by the overall endemism within geographic and time envelopes that include choro and chrono types without consideration of facies or climate the hierarchy of ranks or tiers is superrealm realm subrealm province subprovince only ranks in italics are obligatory region is informal these ranks scale with endemism geographic range and persistence in time biochores are named geographically following nomenclatural guidelines not strict rules of synonymy and homonymy with priority beginning with uhlig s paper of 1911 uhlig s two climatic belts are tentatively accepted as optional top ranking superrealms for times of exceptional global endemism available names for them are euroboreal or panboreal new and tethys panthalassa the validity of the 29 existing names for realm group biochores realms subrealms and superrealms in the marine mesozoic is discussed 19 names are rejected for a variety of reasons including synonymy homonymy and usefulness the most important realm group biochores are arctic and boreal atlantic in the boreal euroboreal realm or superrealm and tethyan mediterran caucasian indo pacific jurassic early cretaceous and austral middle late cretaceous in the tethys panthalassa superrealm

deep sea habitat heterogeneity influence on meiofaunal communities in the gulf of guinea to estimate the degree of spatial heterogeneity of benthic deep sea communities we carried out a multiple scale from m s to 200 km investigation in the congo angola margins equatorial west african margin 3150 4800 m in which we examined the metazoan meiofauna at a variety of habitats along the congo channel system and in the associated cold seep we investigate the structure density vertical distribution patterns in the sediment and biomass of meiofaunal communities in the gulf of guinea and how they are controlled by hydrologic and biogeochemical processes the meiofaunal communities in the gulf of guinea were shaped by heterogeneous conditions on the margin and reflect the multiple scale spatial variability that corresponds with the different identified habitats the two control sites located at 100 km away from the canyon were inhabited by very dense and the most diverse meiobenthic communities similar meiobenthic communities inhabited the transition zone between the canyon and the cold seep sites located along the congo channel were obviously affected by the local high velocity bottom currents and unstable sedimentary conditions in this active submarine system extremely low meiobenthic densities and very low proportions in the most surficial sediment layers provided evidence for recently highly disturbed sediments at these sites the remote operated vehicle rov victor 6000 provided images of the cold seep showing a patchy distribution of several types of patchy distributed megafaunal communities dominated by three key symbiotic taxa mytilidae vesicomyidae and siboglinidae these cold seep sediments were colonised by a unique meiobenthic community characterised by a high small scale m s patchiness low species richness and the prominent dominance of two large sized nematode species sabatieria mortenseni which is a cosmopolitan nematode known from littoral habitats and an undescribed desmodora species the high individual body weight of s mortenseni and its dominance at the cold seep site resulted in a significantly higher nematode biomass at the seep compared to the surrounding sites in addition the vertical nematode profiles with maximum proportions in subsurficial layers points to a chemosynthesis based meiobenthic community in this cold seep in contrast to the phytodetritus based communities at the control sites and at the transition zone

food web structure of seep sediment macrobenthos from the gulf of mexico abstract the slope environment of the gulf of mexico gom supports dense communities of seep megafaunal invertebrates that rely on endosymbiotic bacteria for nutrition seep sediments also contain smaller macrofaunal invertebrates whose nutritional pathways are not well understood using stable isotope analysis we investigate the utilization of chemosynthetically fixed and methane derived organic matter by macrofauna biological sampling was conducted in three lower slope gom seep environs green canyon gc852 1428 m atwater valley at340 2230 m and alaminos canyon ac601 2384 m infaunal 13 c and 15 n exhibited a broad range of values most infauna appeared to be heterotrophic although several taxa had very light 15 n and 13 c values indicating possible reliance on chemoautotrophic symbioses the lightest 13 c and 15 n values were observed in nematodes 13 c 54 6 0 1 15 n 6 1 0 2 and one gastropod 13 c 54 1 15 n 1 1 from green canyon mixing model results indicated that sulfur oxidizing beggiatoa may be an important food source for seep infauna the rate of utilization ranged from 60 to 100 at green canyon and atwater valley the overall range in isotope values was similar across the three sites suggesting that biogeochemical processes may be very similar in these geographically distinct areas

early and mid jurassic molluscan biogeography and the establishment of the central atlantic seaway abstract a new analysis of lower and middle jurassic bivalve faunas of western north america and the southern andes in comparison to europe supported by evidence from other molluscs throws further light on the establishment of a central atlantic epicontinental seaway prior to the formation of a true oceanic strait between eastern north america and africa south america some restriction to free communication persisted until the early callovian but there was an episode of relatively free intermigration in the toarcian to early bajocian time interval which is associated with major rise of sea level one of the most significant consequences of this event was a spread into northwest europe of taxa which were previously confined to the pacific margins to occupy niches vacated as a result of an early toarcian extinction event

the early toarcian jurassic anoxic event stratigraphic sedimentary and geochemical evidence detailed paleogeographic studies in the southern alps suggest that an oxygen minimum model is appropriate for interpreting conditions on tethyan continental margins advection of manganese in this low oxygen layer may explain the local occurrence of carbonate ores of this element carbon sulfur and iron sulfur ratios although showing considerable scatter suggest that bottom waters at this time were locally euxinic containing free hydrogen sulfide this oceanic anoxic event was preceded by significant faunal turnover of ammonites in tethys and accompanied by widespread extinction of benthos in northern europe in response to the lateral spread of anoxic bottom waters during transgression similar changes may be recognized in other parts of the world other anoxic events may have taken place during the jurassic but documentation is as yet meagre furthermore models for such phenomena remain largely speculative although upwelling and increased planktonic productivity commencing in pre toarcian time are favored for the falciferum zone event documented here from author

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

faunal responses to oxygen gradients on the pakistan margin a comparison of foraminiferans macrofauna and megafauna the pakistan margin is characterised by a strong mid water oxygen minimum zone omz that intercepts the seabed at bathyal depths 150 1300 m we investigated whether faunal abundance and diversity trends were similar among protists foraminiferans and gromiids metazoan macrofauna and megafauna along a transect 140 1850 m water depth across the omz during the 2003 intermonsoon march may and late post monsoon august october seasons all groups exhibited some drop in abundance in the omz core 250 500 m water depth o2 0 10 0 13 ml l 1 4 46 5 80 m but to differing degrees densities of foraminiferans 63 m were slightly depressed at 300 m peaked at 738 m and were much lower at deeper stations foraminiferans 300 m were the overwhelmingly dominant macrofaunal organisms in the omz core macrofaunal metazoans reached maximum densities at 140 m depth with additional peaks at 850 940 and 1850 m where foraminiferans were less abundant the polychaete linopherus sp was responsible for a macrofaunal biomass peak at 950 m apart from large swimming animals fish and natant decapods metazoan megafauna were absent between 300 and 900 m o2 0 2 ml l 1 8 92 m the progressively deeper abundance peaks for foraminiferans 63 m linopherus sp and ophiuroids probably represent lower omz boundary edge effects and suggest a link between body size and tolerance of hypoxia macro and megafaunal organisms collected between 800 and 1100 m were dominated by a succession of different taxa indicating that the lower part of the omz is also a region of rapid faunal change species diversity was depressed in all groups in the omz core but this was much more pronounced for macrofauna and megafauna than for foraminiferans oxygen levels strongly influenced the taxonomic composition of all faunal groups calcareous foraminiferans dominated the seasonally and permanently hypoxic sites 136 300 m agglutinated foraminiferans were relatively more abundant at deeper stations where oxygen concentrations were 0 13 ml l 1 5 80 m polychaetes were the main macrofaunal taxon within the omz calcareous macrofauna and megafauna molluscs and echinoderms were rare or absent where oxygen levels were lowest the rarity of larger animals between 300 and 700 m on the pakistan margin compared with the abundant macrofauna in the omz core off oman is the most notable contrast between the two sides of the arabian sea this difference probably reflects the slightly higher oxygen levels and better food quality on the western side

nitrogen cycling in a deep ocean margin sediment sagami bay japan on the basis of in situ no microprofiles and chamber incubations complemented by laboratory based assessments of anammox and denitrification we evaluate the nitrogen turnover of an ocean margin sediment at 1450 m water depth in situ no profiles horizontally separated by 12 mm reflected highly variable no penetration depths no consumption rates and nitrification on average the turnover time of the pore water no pool was 0 2 d net release of nh z during mineralization 0 95 mmol m 22 d21 sustained a net efflux of ammonia 53 nitrification 24 and anammox activity 23 the sediment had a relatively high in situ net influx of no 1 44 mmol m22 d21 that balanced the n2 production as assessed by onboard tracer experiments n2 production was attributed to prokaryotic denitrification 59 anammox 37 and foraminifera based denitrification 4 anammox thereby represented an important nutrient sink but the n2 production was dominated by denitrification despite the fact that no stored inside foraminifera represented 80 of the total benthic no pool the slow intracellular no turnover that on average sustained foraminifera metabolism for 12 52 d contributed only to a minor extent to the overall n2 production the microbial activity in the surface sediment is a net nutrient sink of 1 1 mmol n m 22 d 21 which aligns with many studies performed in coastal and shelf environments continental margin areas can act as significant n sinks and play an important role in regional n budgets