ostracod assemblages palaeoenvironment and cyclicity of purbeck type sediments of the munder formation lower cretaceous hils syncline n germany abstract berriasian marlstones in the upper part of the munder formation purbeck of the hils syncline have been regarded as freshwater deposits with minor brackish influence however similar to some marlstones of the english purbeck limestone group it remained unclear whether these deposits rich in non marine ostracods are lacustrine or marine lagoonal in origin facies analysis of the sediments revealed strikingly symmetric cycles composed of 1 red brown massive marlstones of distal alluvial plains 2 greenish grey bedded marlstones with microbial lamination of the supralittoral zone 3 dark grey charophyte marlstones and 4 light grey charophyte limestones with scattered porostromate oncoids of the eulittoral zone 5 poorly bedded light grey micritic limestones and 6 clayey marlstones of the sublittoral zone ostracod associations revealed by cluster analysis and associated microfossils indicate cyclic salinity changes coincident with lithofacies alternations a theriosynoecum association is restricted to eulittoral and shallow sublittoral lithofacies types and reflects freshwater to oligohaline conditions this association is accompanied by the freshwater gastropods gyraulus and provalvata as well as charophytes of the genera atopochara clavator and globator supralittoral marlstones are characterized by a mixed cypridea association composed of autochthonous cypridea of ephemeral freshwater pools and transported faunal elements increased salinities of miohaline to mesohaline conditions are indicated for sublittoral lithofacies types by a mantelliana association maximum flooding is indicated by the appearance of small foraminifera variations of monospecific ostracod stable isotope ratios coincide with the cyclic salinity fluctuations interpreted from ostracod assemblages along the section this correlation of lithofacies types and ostracod faunas implies that salinities increased with increasing water level and vice versa consequently a coupling of the water level of the hils basin to short term eustatic sea level changes must be assumed therefore the hils basin is interpreted as a marine embayment during the berriasian with freshwater spreading out on top of marine brackish water but not a lake a similar approach combining micropalaeontological and sedimentological evidence may help to distinguish between marginal marine sediments affected by cyclic sea level changes and lacustrine sediments displaying climatically driven cyclicity in the purbeck type area and elsewhere in europe

platinum mineralization in the kapalagulu intrusion western tanzania low grade copper and nickel mineralization was found near the eastern shore of lake tanganyika at kungwe bay in the early part of the twentieth century the mineralization occurs in harzburgite at the base of a layered gabbro complex known as the kapalagulu intrusion emplaced between the paleoproterozoic ubendian basement and overlying neoproterozoic itiaso group metasediments several mining and exploration companies continued the geophysical and drilling exploration for base metals throughout the last century culminating in the discovery of high grade platinum group element pge mineralization associated with chromitite and sulfide bearing harzburgite within the southeastern extension of the kapalagulu intrusion known as the lubalisi zone that is covered by a layer of nickel rich laterite regolith the poorly layered southeastern harzburgite forms part of the 1500 m thick lower ultramafic sequence and resembles a dike like body that flares upwards into a succession of well layered gabbroic rocks of the upper mafic sequence no pge mineralization has been found in the layered gabbro all the mineralization is associated with the chromite and sulfide rich harzburgite of the lower ultramafic sequence and the laterite regolith overlying the mineralized harzburgite the lubalisi zone harzburgite is underlain by basal dunite and overlain by an interval of layered harzburgite and troctolite and this ultramafic sequence is folded into a syncline that plunges towards the northwest that has been modified by major dolerite filled faults orientated subparallel to the fold axial surface extensive deep drilling in the lubalisi zone of the kapalagulu intrusion shows that the folded harzburgite can be subdivided into a lower feldspathic harzburgite a harzburgite containing chromitite seams and intervals of sulfide and chromite mineralization known as the main chromite sulfide succession mcss an overlying sulfide rich harzburgite and an upper feldspathic harzburgite impersistent stratiform pge mineralized horizons occur within the mcss harzburgite from which drill core samples were taken for platinum group mineral pgm characterization from two drill holes where the pge reefs reach the surface there is residual pge mineralization within the laterite regolith from which drill core samples were taken from various laterite lithological units for pgm characterization as the harzburgite pge reefs contain significant concentrations of both sulfide and chromite including chromitite seams they resemble the pge rich chromitite seams of the bushveld complex rather than the pge bearing main sulfide zone of the great dyke and main sulfide layer of the munni munni complex the dominant pd pgm in three pge reef samples varies ranging n 164 relative wt from bismuthides 63 bismuthtellurides 19 and tellurides 6 to tellurides 39 bismuthtellurides 24 stannides 14 and alloys 13 and to antimon arsenides 33 stannides 21 bismuthides 17 tellurides 13 and alloys 10 from 13 5 to 21 0 of the total pd occurs as a solid solution in pentlandite the three samples have similar pt pgm modal distributions n 172 relative wt the dominant pt mineral is sperrylite 79 58 and 47 followed by tellurides 15 17 21 alloys 2 1 1 and sulfides 2 1 0 comparison of pd pt ratios from assays to those calculated from minerals show that the data for the pt and pd pgm are very robust confirming the concentration methodology and characterization study of samples from a shallow drill hole penetrating the laterite regolith shows that the primary pd mineralization has not survived oxidation is mainly dispersed but some was reconstituted to form secondary minerals cabriite unnamed tellurides a selenide a pd te hg mineral alloys and pd bearing secondary sulfides millerite and heazlewoodite the primary pt minerals are more resistant to oxidation and dissolution especially sperrylite and isoferroplatinum but it is likely that other pt alloys tetraferroplatinum and tulameenite are of secondary origin after dissolution of pt tellurides

estimating palaeo water depth from the physical rock record abstract palaeo water depth and its change with time is a key factor in environmental analysis and in sedimentology in general the literature published on this topic and on related subjects however is substantial albeit scattered within and between different communities geologists oceanographers engineers physicists etc here i focus on proxies for palaeo bathymetry as obtained from the physical rock record floral faunal and chemical evidence for palaeo water depth being equally important must be dealt with elsewhere an assessment of the main depth related parameters in actualistic settings is presented and their applicability to the fossil sedimentary record discussed the outcome reveals the full complexity of this topic there is for example no such thing as an average wave base depth applicable to a wide range of fossil case settings this because wave and current climates in general and particularly so in neritic and coastal settings are intriguingly complex furthermore observations from modern oceans are not a priori applicable to fossil ones acknowledging these problems and limitations critically evaluated quantitative proposals for depth indicative facies and features in the sedimentary record are presented and error bars discussed

comparative ecological analysis of the ostracod faunas from low and high polluted southwestern spanish estuaries a multivariate approach abstract the distribution and abundance of both living and total ostracod populations from the estuaries of the southwestern spanish coast are discussed a total of 68 species were obtained from 120 bottom samples collected in the channels channel margins and salt marshes four assemblages were recognized in this area a urocythereis oblonga assemblage with marine species well represented in sandy substrates located near the mouths b loxoconcha rhomboidea assemblage mainly developed in the quiet tidal channels conected with the main channels of the marine domains c loxoconcha elliptica assemblage enclosing the most cosmopolitan and euryhaline species very abundant in muddy sediments and low to moderate hydrodynamic conditions and d leptocythere porcellanea assemblage only observed in the clayey silty channel margins of the most protected ebb channels in these transitional environments very unfavorable conditions for the ostracod development were found in a the erosional channels and channel margins b most of the salt marsh samples with high subaerial exposure and c sectors with high metallic pollution levels and acidic waters

the platycopid signal deciphered responses of ostracod taxa to environmental change during the cenomanian turonian boundary event late cretaceous in se england abstract a multi proxy investigation of the cenomanian turonian boundary event ctbe near dover in southern england previously demonstrated that coincident with a major global positive carbon stable isotope excursion during oceanic anoxic event 2 oae 2 the diversity of nanoplankton dinoflagellates planktonic and benthonic foraminifera and ostracods was severely reduced this was attributed to decreasing levels of dissolved oxygen consequent on an intensification and expansion of the oceanic oxygen minimum zone omz into shelf seas in the case of the ostracods it was noted that as podocopid taxa became locally extinct platycopids became the dominant component of the fauna subsequently the platycopid signal hypothesis psh claimed that dominance of platycopids in ostracod assemblages could be regarded as a signal of dysaerobic conditions on the sea floor based on the premise that the filter feeding platycopids able to pass more water over their respiratory surface were better equipped than other benthonic ostracods to survive in water of reduced oxygen concentration the psh has been widely accepted and applied in palaeoenvironmental reconstructions of stratigraphic intervals ranging from the palaeozoic to the quaternary however the modern biological and ecological support claimed for the platycopid signal has been challenged platycopids are occasionally dominant in modern omzs but often they are not and in any case the same can be said about some podocopids apparently precise calibration scales published by some authors are not justified by available data furthermore platycopid signal indications of dysaerobic intervals in the english chalk succession often conflict with the evidence of macrofossils and trace fossils here we review old and new data from two ctbe sites in se england dover and eastbourne and advance an alternative interpretation of the platycopid signal based on the concept of the spread of oceanic oligotrophic conditions into the european chalk sea during oae2 we propose that ostracod assemblages overwhelmingly dominated by platycopids signify oligotrophy because living platycopids appear to be adapted to filter feed on nano and picoplankton which are predominant in oligotrophic conditions

late messinian lago mare ostracod palaeoecology a correspondence analysis approach abstract in this paper two different italian late messinian lago mare ostracod assemblages dominated mainly by extinct paratethyan species have been analysed by means of detrended correspondence analysis dca the obtained plots have been compared and with the help of the limited autoecological data on similar living species and geochemical data on the sediments in which they were included the autoecology and synecology of the lago mare assemblages have been inferred in particular it seems reasonable to suppose that 1 assemblages made only by pointed candonids are typical of rather deep possibly less than one hundred meters of depth and freshwater oligohaline environments 2 assemblages mainly composed of leptocytheridae point to shallow probably few tens of meters of depth and mesohaline waters 3 diversified and even assemblages made both by pointed candonids and leptocytheridae are common in rather deep less than one hundred meters of depth but oligo low mesohaline environments 4 caspiocypris seems rather tolerant of brackish salinities but prefers shallow environments 5 tyrrhenocythere could be an indicator of shallow and fresh oligohaline waters 6 cyprideis is an indicator of shallow waters but can withstand a very wide salinity range

recent ostracoda from the laptev sea arctic siberia species assemblages and some environmental relationships ostracod assemblages from coretop sediments collected at 26 localities at different depths of the laptev sea shelf and upper continental slope were investigated for assemblage studies a total of 41 species belonging to 19 genera and 12 families have been identified three assemblages have been established that could be linked to environmental factors such as water depth bottom salinities water mass circulation and sea ice transportation the species rich and abundant assemblages of the western and central laptev sea were related to the atlantic waters occupying the upper continental slope these include relatively deep water forms that show clear affinities to north atlantic and arctic ocean assemblages cytheropteron biconvexa c testudo c simplex c nodosoalatum c inflatum c porterae krithe glacialis k minima pseudocythere caudata polycope punctata p orbicularis in the eastern middle shelf region the assemblage is comprised of acanthocythereis dunelmensis together with other normal marine species semicytherura complanata elofsonella concinna cluthia cluthae this assemblage seems connected to the winter flaw polynya which is believed to be the main area of sediment entrainment into sea ice the inner shelf assemblage of the southern laptev sea is dominated by shallow water euryhaline species paracyprideis pseudopunctillata and heterocyprideis sorbyana with admixture of the brackish water species roundstonia macchesneyi the unusual occurrence of a number of shallow water ostracod species on the upper continental slope may be explained by ice rafting which these ostracods are probably able to survive

northern north sea benthic ostracoda modern distribution and palaeoenvironmental significance the ostracod faunas of the northern north sea exhibit a depth related distribution that is controlled by substrate and hydrographic conditions four biofacies are defined on the basis of total live dead counts sandy substrates shallower than 110 m are characterized by robertsonites tuberculatus and cytheropteron latissimum these species are replaced by acanthocythereis dunelmensis and palmenella limicola on sandy muds in the fladen ground 110 150 m muellerina abyssicola dominates from 175 250 m in the norwegian channel giving way to krithe praetexta at greater depths on soft bottom substrates the results are compared with data from the skagerrak and the western european shelf area temperature ranges for the commonest taxa show that north sea faunas contain endemic western european species temperature range on average 2 20 c some southern species 5 26 c and taxa that range to high latitudes 2 to 14 c southern species are confined to the southern and western margins of the north sea

rapid warming and ostracods mass extinction at the lower toarcian jurassic of central spain abstract here we present the results of the study of two lower toarcian carbonate sections located in the iberian range of central spain analyses of stable isotope on belemnite calcite allowed calculation of seawater palaeotemperature variations which were compared with the stratigraphical distribution of ostracods these organisms are particularly sensitive to ratios of temperature and salinity variations and hence are good indicators of climate changes from a cooling interval with seawater temperatures of 13 2 c recorded at the pliensbachian toarcian transition seawater temperature began to rise in the lowermost toarcian tenuicostatum zone reaching average temperatures between 14 6 c and 16 3 c during the time of deposition of this zone coinciding with this seawater warming up to 85 of the ostracods species progressively disappeared during a period of approximately 300 kyr marking the extinction interval the extinction boundary located around the tenuicostatum serpentinum zonal boundary coincides with a marked increase in temperature in the serpentinum zone on which average seawater temperatures of 22 c have been calculated warming continued through part of the middle toarcian bifrons zone reaching average temperatures of 24 7 c readjustment of the ostracod population allowed recovery of these faunas in the upper serpentinum zone although the extinction of a major ostracod group the healdioids was also recorded the correlation between mass extinction and warming infers a causal relationship comparison of the results with the records of stable isotopes in belemnites and in bulk carbonates as well as toc and facies analysis suggests that the anoxia linked to the early toarcian oceanic anoxic event was not the main responsible for the ostracod mass extinction

ostracoda and palaeo oxygen levels with particular reference to the upper cretaceous of east anglia abstract it has been shown that the percentage of platycopina the sole remaining group of filter feeding ostracoda since the global extinction of the metacopina in the lower toarcian making up a fossil ostracod fauna can be used as a measure of dissolved oxygen in past oceans high levels of platycopids indicate low oxygen and vice versa a new scale is introduced here based mainly on the environmental oxygen levels of modern oceans and their equivalent percentages of living platycopids in order to evaluate the palaeo oxygen levels of the upper chalk in east anglia the effects of varying oxygen concentrations on the overall simple species diversity of the ostracoda is also shown to have important palaeoenvironmental implications the study is based on 79 samples from the santonian to lower maastrichtian of the trunch borehole and 126 samples from outcrops in suffolk and norfolk ranging from the coniacian to lower maastrichtian the coniacian is shown to have been a time of low to very low oxygen except for its upper part that was much better ventilated the santonian and lower campanian were low to very low in their dissolved oxygen while the upper campanian and particularly the lower maastrichtian had much higher oxygen levels notwithstanding these general trends oxygen levels appear to have fluctuated rapidly throughout the interval during times of both generally low and high oxygenation these variations in oxygenation are thought to have been associated with the oxygen minimum zone and its migrations onto the continental shelf and subsequent retreat to the continental slope this in turn is related to sea level fluctuations and this together with the potential for the application of this technique to sequence stratigraphy are discussed

the ages of the kabanga north and kapalagulu intrusions western tanzania a reconnaissance study the kabanga north and kapalagulu intrusions form part of a 500 km belt of intrusions within the kibaran orogenic belt of central africa some of the intrusions within the belt host important ore deposits notably ni sulfides at kabanga and ni laterites at musongati and kapalagulu despite the economic significance of the intrusions their ages have remained unclear here we present shrimp ii u pb zircon ages interpreted as magmatic ages of crystallization for the kabanga north intrusion 1403 14 ma and for the kapalagulu intrusion 1392 26 ma these data along with other geochronological and petrological data support a model of a broadly coeval and cogenetic suite of mafic ultramafic intrusions throughout the kibaran orogenic belt from northwest tanzania through burundi and possibly as far south as the democratic republic of congo

geochemistry and mineralogy of platinum group elements at hartley platinum mine zimbabwe the main sulfide zone msz is the most prominent layer of the great dyke layered intrusion carrying economic platinum group element pge mineralization at the hartley platinum mine the msz is up to some meters thick and is composed of a basal pge rich subzone which overlaps slightly with a base metal sulfide rich subzone on top based on the degree of sulfide mineralization and pge ratios the subzones can be further divided into geochemically distinct layers stratigraphically upwards the msz displays metal profiles characterized by increasing cu ni pt pd and ppge ipge ratios accompanied by a general element decoupling in the order pd pt base metals more specifically ipge pd pt ni cu co s sulfides au te bi the fine structure of the msz is regarded to reflect primary magmatic features of consecutive batches of sulfide accumulation concomitant scavenging of pge and fractionation sulfide deposition was followed by a second limited subsolidus stage of pge redistribution mineralogically most of the pd and rh is hosted in pentlandite whereas pt is dominantly present in the form of discrete platinum group minerals pgm within the msz sequence sperrylite is present throughout the pge subzone of the msz cooperite braggite occur mainly in its basal part and the pt pd bismuthotellurides concentrate at the top these findings indicate that a large proportion of the pge primarily concentrated in sulfide under magmatic conditions was redistributed in the subsolidus stage and formed discrete pgm with available reactant partners chemical gradients and magmatic hydrothermal fluids probably led to small scale redistribution of pge within the msz

ostracod diversity and sea level changes in the late cretaceous of southern england abstract the available data of ostracod ranges for the cenomanian campanian and maastrichtian stages of the late cretaceous of the northern part of the anglo paris basin were examined and combined with new data from the turonian santonian and coniacian stages a new cumulative species diversity curve is presented for the ostracoda of the late cretaceous of britain the results obtained challenge the method of chronoecologic charts to determine sea level from diversity when a more complete data set is applied and compared with published sea level curves the result is the inverse of that previously predicted by employing chronoecologic charts a model is presented of changing sea levels in s e england from the cenomanian through to the santonian which integrates the new diversity data with published sea level changes and curves of stable isotopes of oxygen and carbon in the earliest cenomanian low diversity is associated with a deeper water depositional environment and warmer temperatures the mid cenomanian diversity maximum corresponds to a regressive trough and cooler water over the cenomanian turonian boundary interval the diversity minimum is correlated with global sea level and temperature maxima the proportion of ostracods possessing eye tubercles falls to a minimum over this period after the diversity crash the cenomanian fauna was replaced by the new turonian fauna east west migrations into the anglo paris basin were facilitated by the sea level rise overcoming marginal basin highs the pattern seen in the mid cenomanian is also present at the turonian coniacian boundary interval that of high diversity corresponding with a regressive trough on a long term regressive trend with cooling conditions the model for this northern part of the anglo paris basin then associates high diversity with regressive cooler conditions and low diversity with deeper and warmer water

high sea surface temperatures during the early aptian oceanic anoxic event 1a in the boreal realm the early aptian was characterized by the widespread occurrence of anoxia in the oceans known as oceanic anoxic event oae 1a intense degassing from submarine volcanic plateaus presumably resulted in high atmospheric co2 concentrations culminating in greenhouse conditions oae 1a can therefore be considered as a past natural experiment important to understand the future evolution of our climate paleotemperature estimates for oae 1a are however predominantly based on bulk oxygen isotopes which are susceptible to diagenetic overprinting while tex86 paleotemperature estimates are limited in number or derived from stratigraphically poorly constrained sections here we reconstructed for the first time sea surface water temperatures ssts based on the tex86 paleothermometer from an oae 1a section from the middle northern latitudes 39 n paleolatitude we find a sst rise starting prior to oae 1a and reaching a maximum during the event with ssts of 31 34 c 4 9 c higher than those of older hauterivian lower aptian sediments from the same sedimentary basin the end of oae 1a is marked by relatively lower ssts of 30 c these observations are supported by belemnite based oxygen isotope d18obel data and calcareous nannofossils our integrated data set clearly indicates that super greenhouse conditions prevailed during oae 1a at northern latitudes ssts are similar to those estimated for coeval low latitudinal sites suggesting that an equable warm climate with reduced latitudinal gradients characterized the early aptian

contrasting mineralogical and processing potential of two mineralization types in the platinum group element and ni bearing kapalagulu intrusion western tanzania abstract the kapalagulu layered ultramafic and mafic intrusion is emplaced between the paleoproterozoic ubendian basement and overlying neoproterozoic itiaso group metasedimentary rocks located near the western shore of lake tanganyika high grade platinum group element pge mineralization 1 6 g t pt pd au is associated with chromitite and sulfide bearing harzburgite within the southeastern extension of the intrusion known as the lubalisi zone which is covered by a layer of nickel rich 0 2 2 ni laterite regolith that contains linear areas of pge mineralization in the lubalisi zone the mineralization may be divided into several significant geometallurgical domains a high grade pge mineralization 1 6 g t pt pd au associated with stratiform pge reefs and chromitite seams within a harzburgite unit b high grade pge mineralization up to 12 g t pt pd au associated with small bodies and veins of nickel massive sulfide within harzburgite below pge bearing reefs and chromitite seams c low grade pge mineralization 0 1 0 5 g t pt pd au associated with a sulfide mineralized harzburgite unit above the pge bearing reefs d laterite style residual pge mineralization 0 2 4 g t pt pd au associated with chromite concentrations in the saprolite and overlying red clay horizons of the laterite regolith and e supergene ni associated with the saprock and overlying saprolite clay mineralogical study of three samples from the pge reef consisting of high grade pge chromitite and harzburgite indicate that this mineralization will give a good metallurgical response to conventional grinding and floatation due to the relatively coarse grained nature of the pgm p80 from 37 to 52 m association with base metal sulfides and unaltered gangue minerals wilhelmij and cabri 2016 in contrast mineralogical and metallurgical study of the ni and pge mineralized laterite indicate that it cannot be processed using conventional mineral processing techniques but that a hydrometallurgical route should be used to recover the base and precious metals because any process is very much deposit controlled significant metallurgical and geometallurgical testing of mineralized samples as well as pilot plant testing will be required to arrive at feasibility studies

a rapid method for magnetic granulometry with applications to environmental studies we have developed a rapid method of characterizing the fine scale variation sub micron to hundreds of microns m in the grain size of magnetite in long sediment cores this method is a new rock magnetic tool and can be readily applied to the following disciplines 1 environmental studies 2 hydrology 3 petrology and 4 geomagnetism the method consists of a comparative plot of the depth variation of two magnetic parameters the first parameter low field less than 0 1 millitesla mt or 1 oe susceptibility in a steady field is plotted on the abscissa the second parameter anhysteretic remanent magnetization arm imparted by a smoothly decreasing af of peak value 100 mt 1 000 oe in the presence of a weak steady field 0 01 0 1 mt or 0 1 1 oe is plotted on the ordinate for a sediment column in which the magnetic mineral is magnetite a plot of the two magnetic parameters shows transitions in the average magnetic grain size with depth as clearly discernible changes in the slope of a regression line fit to the individual points arm

a study of the tex86 paleothermometer in the water column and sediments of the santa barbara basin california 1 particulate organic matter collected during a 2 year period as part of an ongoing sediment trap study and a high resolution sediment record from 1850 to 1987 a d from the santa barbara basin were analyzed for tex86 a temperature proxy based on marine crenarchaeotal membrane lipids highest fluxes of crenarchaeotal lipids in the water column were found in may june 1996 and from october 1996 to january 1997 and in general showed a good correlation with mass fluxes tex86 reconstructed temperatures from the sediment trap series ranged from 8 to 11 c and were usually substantially lower than sea surface temperatures sst indicating that unlike in previous studies the tex86 corresponds to subsurface temperatures likely between 100 and 150 m tex86 temperature variations observed in trap samples were not coupled to changes in sst or deep water temperatures and only to some degree with crenarchaeotal lipid fluxes this suggests that a complex combination of different depth origins and seasonal growth periods of crenarchaeota contributed to the variations in tex86 signal during the annual cycle tex86 temperatures in the two sediment cores studied 8 13 c were also substantially lower than those of instrumental sst records 14 17 5 c confirming that tex86 records a subsurface temperature signal in the santa barbara basin this result highlights the importance of performing calibration studies using sediment traps and core tops before applying the tex86 temperature proxy in a given study area

ostracod response to habitat change in an early aptian shelf sea abstract changes in ostracod assemblage composition from the lower aptian of the lower saxony basin germany are investigated to estimate their potential as proxies for palaeoenvironmental habitat changes in an epicontinental setting the studied palaeoenvironmental factors include oxygen depletion increasing temperatures during oae 1a and an increasing water depth caused by the supra regionally recorded early aptian transgression in the late early aptian a distinct short term decrease of water depth is inferred five ostracod associations are recognized two are characterized by a unique composition of species and three are unique by dominance of certain species the stratigraphic record is unique for one association all other associations are exclusively occurring in short intervals of the section but are co occurring with the sub and superjacent ostracod association we observe a change from veeniacythereis acrocythere dolocythere dominated to cytherella dominated associations initiating well before oae 1a and ending slightly before the upper limit of oae 1a most likely triggered by increasing temperatures and affected by increasing water depth changing water depth proved to be the most important factor affecting the successive appearance of ostracod associations moreover ostracod associations change in dominance from cytherella to pontocyprella schuleridea and finally to neocythere dominated faunas parallel to an increasing water depth a re establishment of palaeoenvironmental conditions typical for the veeniacythereis dolocythere dominated association gave rise to a saxocythere batavocythere dominated replacement association although ostracods are very sensitive organisms with respect to oxygen deficiency the oxygen depletion during oae 1a was not a major factor for changing ostracod associations during black shale deposition ostracods vanished completely a recognized change in associations started before the anoxic period and ended afterwards high resolution ostracod studies appeared to be a very powerful proxy for changing water depth temperature and oxygenation in early cretaceous epicontinental settings like the lower saxony basin