seasonal variability in the production of lower cretaceous calcareous nannoplankton the lower cretaceous munk marl bed in the central north sea area consists of alternating laminae of calcareous nannofossils and clayey material the lamination was most likely caused by seasonal variation in the production rate of calcareous nannofossils calcareous nannofossil deposition reflects short blooms many blooms were totally dominated by a single species and at least nine species occasionally monopolized the flora the production rate and mode of deposition is comparable to that of the modern black sea the munk marl bed contains a diverse marine calcareous nannofossil flora comprising 48 species the species composition exhibits changes that show similarities to the seasonal fluctuations in the modern atlantic ocean

a paleoslope model of late albian to early turonian foraminifera of the western atlantic margin and north atlantic basin abstract a paleoslope model of albian to turonian benthic foraminifera reveals seven successive biofacies which are associated with increasing paleodepth the paleoslope model indicates that the biofacies occupied inner neritic to abyssal environments of deposition 10 m to 3500 m water depth biofacies 1 and 2 characterize paleodepths of less than 60 m the biofacies contain abundant species of epistomina and gavelinella and exhibit a rapid stratigraphic alternation in response to local sea level change which considerably aids in the identification of depositional sequences species of globorotalites eggerellina and neobulimina characterize biofacies 3 which principally occurs between 60 m and 130 m paleodepth biofacies 3 is the only biofacies to occur in both the new jersey coastal plain and the baltimore canyon trough biofacies 4 is composed of species of gavelinella gyroidinoides and valvulineria and is abundant in outer neritic to middle bathyal paleodepths of 130 m to 600 m it is largely replaced by biofacies 5 during times of maximum flooding during sea level rise a diverse assemblage of species of lingulogavelinella and lenticulina characterize biofacies 5 paleodepths of 600 m to greater than 3500 m contain abundant species of osangularia pleurostomella praebulimina pseudopatellinella and quadrimorphina which define biofacies 6 and 7 in addition four biofacies of much more limited distribution are recognized biofacies 1 characterizes shallow water open marine paleoenvironments of the north atlantic and is composed of spirillinids and species of epistomina turonian dysaerobic environments are indicated by biofacies dsa and dsb which are composed mostly of agglutinated species dysaerobic environments expanded rapidly from middle bathyal to outer neritic depths in the early turonian on the western atlantic margin biofacies daa represents disturbed benthic environments and is dominated by species of psammosphaera and reophax biostratigraphy and species composition of the studied biofacies are similar to previously described european and south atlantic assemblages major speciation events occur among the genera gavelinella lingulogavelinella and valvulineria well defined neritic and bathyal biofacies formed during a rapid late albian species diversification concomitant with the first major cretaceous flooding of continental margins

rapid forearc uplift and subsidence caused by impinging bathymetric features examples from the new hebrides and solomon arcs 1 isotopically dated corals from the central new hebrides and new georgia island group solomon islands indicate that both forearcs underwent rapid late quaternary subsidence that was abruptly replaced by hundreds of meters of uplift at rates up to 8 mm yr while total plate convergence was only a few kilometers two mechanisms that might account for these rapid reversals in vertical motion include 1 a displacement mechanism in which the forearc is displaced upward by the volume of an object passing beneath on the subducting plate as the object moves deeper and vacates the base of the forearc the forearc subsides to near its original position and 2 a crustal shortening mechanism in which the forearc thickens and uplifts because of horizontal shortening when a large object impinges on the forearc and abruptly increases interplate coupling on the shallow end of the main thrust zone rapid subsidence follows when the impinging object is broken or otherwise decoupled shallow interplate coupling becomes weak and the uplifted forearc extends and subsides the displacement mechanism surely plays a role on timescales over which plates converge tens of kilometers but it fails to explain the geographic pattern short time frame and abruptness of the change from subsidence to uplift that we observe the crustal shortening mechanism is preferred because it allows the observed abrupt uplift when an object impinges on a forearc and causes locking of a shallow segment of the interplate thrust zone

isotopic evidence for early to mid cretaceous ocean temperature variability abstract stable isotopic measurements have been made on planktonic and benthic foraminifera of early to mid cretaceous early albian cenomanian age from dsdp site 463 located in the pacific ocean the degree of alteration of the foraminifera has been assessed through the application of scanning electron microscopy the oxygen isotope data support the view that during the cenomanian globigerine foraminifera such as the genus hedbergella inhabited near surface waters whilst the flattened keeled morphotypes lived deeper within the water column the carbon isotope data reveal a more complex pattern as the 13 c values from planktonic species essentially show a large overlap which is interpreted in terms of a weak 13 c gradient existing in the upper part of the ocean in contrast the oxygen isotope data from planktonic foraminifera from the late albian display no discernible depth stratification pattern and the 13 c data also show a large overlap of values indicative of a complete disruption of the upper part of the thermocline a relatively low surface to bottom water temperature gradient within the early middle albian part of the succession may reflect a well mixed ocean inferred cool ocean temperatures and or high salinities for the early albian may reflect increased oceanic poleward heat transport an increase in temperature and or decrease in salinity in the cenomanian suggests a reduction of the poleward heat flux promoting the build up of limited polar ice during this period of tropical warmth

oxygen isotopic composition of multiple species of planktonic foraminifera recorders of the modern photic zone temperature gradient abundances of 12 species of planktonic foraminifera collected in two plankton tows from the east tropical atlantic are compared to the chlorophyll content and the temperature of the sea water from which they were collected as expected from previous work in the tropics all dominant tropical species occur in greatest abundance within the photic zone many species occur in greatest abundances in the seasonal thermocline in association with the maximum chlorophyll concentration while a few algal symbiont bearing species occur in greatest abundance in the mixed layer the 18o measurements of planktonic foraminifera shells from core top sediment samples confirm the vertical stratification within the photic zone that is suggested by the relationship between hydrography and abundances found in the plankton tows and found in the statistical study by ravelo et al 1990 comparison between the measured 18o values of planktonic foraminifera with the predicted 18o profiles of the overlying water column at three core locations indicate that species abundances in the sediment record the seasonally integrated conditions of the photic zone and suggests that the abundance of a species in the sediment depends on whether the preferred ecological conditions of that species may be found within the photic zone of the overlying water column sometime during the year species which calcify below the photic zone have only trace relative abundances finally it appears that the total range of 18o values of the dominant species approximates the predicted annual 18o of calcite range in the upper 80 m of the water column

forcing mechanisms for mid cretaceous black shale formation evidence from the upper aptian and lower albian of the vocontian basin se france calcareous nannoplankton palynomorph benthic foraminifera and oxygen isotope records from the supraregionally distributed niveau paquier early albian age oceanic anoxic event 1b and regionally distributed niveau kilian late aptian age black shales in the vocontian basin se france exhibit variations that reflect paleoclimatic and paleoceanographic changes in the mid cretaceous low latitudes to quantify surface water productivity and temperature changes nutrient and temperature indices based on calcareous nannofossils were developed the nutrient index strongly varies in the precessional band whereas variations of the temperature index reflect eccentricity since polar ice caps were not present during the mid cretaceous these variations probably result from feedback mechanisms within a monsoonal climate system of the mid cretaceous low latitudes involving warm humid and cool dry cycles a model is proposed that explains the formation of mid cretaceous black shales through monsoonally driven changes in temperature and evaporation precipitation patterns the lower albian niveau paquier which has a supraregional distribution formed under extremely warm and humid conditions when monsoonal intensity was strongest bottom water ventilation in the vocontian basin was diminished probably due to increased precipitation and reduced evaporation in regions of deep water formation at low latitudes surface water productivity in the vocontian basin was controlled by the strength of monsoonal winds the upper aptian niveau kilian which has a regional distribution only formed under a less warm and humid climate than the niveau paquier low latitude deep water formation was reduced to a lesser extent and or on regional scale only the threshold for the formation of a supraregional black shale was not reached the intensity of increases in temperature and humidity controlled whether black shales developed on a regional or supraregional scale at least in the vocontian basin the increased preservation of organic matter at the sea floor was more significant in black shale formation than the role of enhanced productivity

environmental significance of foraminiferal morphogroups in jurassic north sea deltas abstract the distribution of morphological groups of foraminifera has been analysed in toarcian and bajocian deposits of the northern north sea and the yorkshire coast the deposits are referred to prodeltaic lower delta front and interdistributary bay environments and contain mainly or entirely agglutinating assemblages of low to intermediate diversity a total of 33 agglutinating species are recognized in the studied material and these are arranged into eleven morphotypes composing seven subgroups and four morphogroups the categories are distinguished on the basis of main morphological features of the taxa combined with their life positions and micro habitats as inferred from modern analogues the prodelta deposits were formed in a normal saline and slightly stagnant depositional setting with foraminiferal faunas composed mainly of surficial and infaunal morphogroups the lower delta front and interdistributary bay sediments were deposited in shallow hyposaline waters strongly dominated by an epifaunal morphogroup with a partly phytal association a model of agglutinated morphotype distribution reveals increasing morphotype diversity and by inference ecological niche span from interdistributary bay through lower delta front to prodeltaic environments

an early albian arctic type ammonite arcthoplites from hokkaido northern japan and its paleobiogeographic and paleoclimatological implications abstract an early albian arctic type ammonite arcthoplites was discovered from the kamiji formation of the yezo group in the nakagawa area northern hokkaido northern japan this is the first reliable record of a hoplitid ammonite from japan and clearly indicates the distribution of an arctic fauna in the middle latitudes of the north pacific at that time synchronously with the appearance of this arctic type ammonite the tropical tethyan biota mesogean taxa disappeared from hokkaido and elsewhere in the northwest pacific these biogeographic changes suggest the existence of a cooling episode in the early albian north pacific

reconstructing past planktic foraminiferal habitats using stable isotope data a case history for mediterranean sapropel s5 abstract a high resolution stable o and c isotope study is undertaken on all planktic foraminiferal species that are reasonably continuous through an eemian sapropel s5 from the western side of the eastern mediterranean the data are considered within a context of high resolution isotope records for two further s5 sapropels from the central and easternmost sectors of the basin alkenone based sea surface temperature records for all three sapropels and planktic foraminiferal abundance records for the same sample sets through all three sapropels results are compared with similar data for holocene sapropel s1 the adopted approach allows distinction between species that are most suitable to assess overall changes in the climatic hydrographic state of the basin including depth related differentiations and the main seasonal developments and species that are most affected by variable biological controls or local regional and transient physico chemical forcings it is found that a priori assumptions about certain species palaeohabitats based on modern habitat observations may become biased when non analogue conditions develop in the case of mediterranean sapropel s5 these consisted of enhanced freshwater dilution elevated productivity shoaling of the pycnocline between intermediate and surface waters and stagnation of the subsurface circulation under these conditions some species are found to shift into habitat settings that differ considerably from those occupied today the present multiple species approach can identify such anomalous responses and thus offers a sound background for further shell chemistry investigations and quantitative interpretation of the isotopic profiles we capitalise on the latter potential and offer the first quantitative estimates of monsoon flooding into the mediterranean during the deposition of eemian sapropel s5

latest jurassic early cretaceous events and the late cimmerian unconformity in north sea area each of several regional or local unconformities may have been identified locally as the late cimmerian unconformity a supposed major break at the base of the valhall formation or roedby formation over most of the north sea the base of the valhall formation is isochronous and conformable with underlying sediments it is detected on seismic reflection profiles because it represents a widespread facies change marking the late ryazanian transgression most of the unconformities are of eustatic origin and the effects of eustatic sea level changes were never completely masked by local tectonics thus in the modeling of individual oil fields the possibility of sedimentary breaks occurring can be predicted in part by reference to regional or eustatic events modified journal abstract

tectonic erosion of the peruvian forearc lima basin by subduction and nazca ridge collision 1 subsidence of lima basin part of the peruvian forearc is controlled by tectonic erosion by the subducting nazca plate multichannel seismic reflection data coupled with age and paleowater depth constraints derived from ocean drilling program odp coring now allow the rates of erosion to be reconstructed through time in trenchward locations the forearc has experienced limited recent relative uplift 700 850 m likely due to preferential basal erosion under the center of lima basin long term subsidence driven by basal tectonic erosion dominates and is fastest closest to the trench since 47 ma eocene up to 148 km of the plate margin have been lost at an average rate of up to 3 1 km myr 1 appoximately 110 km of that total appears to be lost since 11 ma implying much faster average rates of trench retreat 10 km myr 1 since collision of the nazca ridge with the lima basin at 11 ma although there is no clear subsidence event at odp site 679 during the time at which nazca ridge was subducting beneath this part of the forearc 4 11 ma the more trenchward odp sites 682 and 688 show significant deepening after 11 ma indicating that subduction of the ridge accelerates tectonic erosion long term rates of crustal erosion in the region of lima basin are greater than estimates of regional arc magmatic productivity implying that such margins are net sinks of continental crust

surfaces with a long history the aptian top shu aiba formation unconformity sultanate of oman discontinuity surfaces in shallow marine carbonate successions may represent significant time gaps in the geological record of ancient epeiric neritic seas understanding the hidden geological information contained in major discontinuities is thus of key significance in palaeo environmental analysis sequence stratigraphy reconstructions of sea level change and basin evolution in the present paper the aptian top lower shu aiba formation discontinuity in the sultanate of oman is taken as a prominent example of a regionally extensive 100 000 km2 surface with a long up to 10 myr and complex geological history the top shu aiba discontinuity formed on the topographically elevated domain of the oman platform and represents in essence the late aptian time interval coeval carbonates in the intrashelf bab basin and oceanic rim indicate forced regression and sequence wise gradual down stepping available regional sedimentological sequence stratigraphic petrographic palaeontological and geochemical evidence from outcrops and cored wells in oman is summarized in part complemented by new data and reviewed in a process oriented context in the field the discontinuity is expressed as a low relief stained surface with evidence for a marine hardground stage being dominant indistinct features that indicate a transient meteoric precursor stage isotope shifts meteoric cements circumgranular cracks etc are present but their interpretation requires careful and detailed work this feature is remarkable as a series of relative sea level falls with amplitudes of up to several tens of metres from the early to late aptian boundary to the end of the aptian are reported from the middle east and elsewhere despite the palaeogeographic position of the study area in the tropical climate zone evidence of deep cutting karst features characteristic for many long term exposure surfaces worldwide is scarce acknowledging the fact that the modern world offers no genuine analogues for the lower aptian carbonate system in oman morphological similarities between actualistic wave eroded coastal terraces and the top shu aiba discontinuity are discussed critically this discussion may imply that during an exposure time of several million years the top shu aiba discontinuity experienced repeated stages of shallow flooding and emergence with each transgression removing portions of the underlying rock record the data shown here exemplify the complexity of hiatal surfaces in epeiric neritic carbonates and may serve as a case example for other major discontinuities

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

coupled primary production benthic foraminiferal assemblage and sulfur diagenesis in organic rich sediments of the benguela upwelling system abstract episodically deposited dark organic rich pleistocene and late pliocene sediments from the lower continental slope off southwest africa reveal complex interactions between changes in primary production benthic foraminiferal assemblage and anaerobic microbial processes the organic rich layers contain diatom assemblages characteristic of intense seasonal coastal upwelling whereas stratigraphically adjacent sediments reflect pelagic primary production coastal upwelling dominated depositional intervals coincide with periods of enhanced carbon flux to the seafloor enhanced organic carbon export during dark layer deposition was accompanied by decreases in the diversity of benthic foraminifera to few opportunistic species adapted to high phytodetritus accumulation rates and low o 2 conditions in all sediments the sulfur isotopic composition of pyrite indicates redox cycling of sulfide close to the sediment water interface the sulfur isotopic evidence and the permanent presence of abundant low o 2 adapted benthic foraminifera throughout the organic rich layers suggest an oxygenated benthic environment efficient oxidation of sulfide and removal of sulfide by sulfidization of organic matter inhibited buildup of toxic hydrogen sulfide from bacterial sulfate reduction at the sediment water interface these data imply that in continental slope sediments underneath productive surface waters benthic dysoxic conditions are maintained by the lateral advection of dissolved oxygen to support a small but well adapted benthic community

a paleoceanographic model for the early evolutionary history of planktonic foraminifera the first major radiations of planktonic foraminifera occurred during the mid cretaceous however this period of great diversification was interrupted by two intervals of pronounced paleoceanographic paleoecologic change one during the latest aptian early albian and a second associated with the cenomanian turonian boudary both of these times corresponded with widespread organic carbon burial during intervals commonly referred to as oceanic anoxic events oae 1 and 2 respectively this synthesis focuses on the evolutionary history of aptian early cenomanian planktonic foraminifera and the relationship with oae 1 dynamic paleoceanographic changes controlled the course of planktonic foraminiferal evolution during the mid cretaceous heightened plate tectonic activity a major long term rise of global sea level and an overall increase of global temperatures characterized aptian albian time as proposed here the evolutionary history of aptian early cenomanian planktonic foraminifera was influenced most strongly by changes in the density structure and stability of the upper water column via changes in the sites and rates of water mass production through time and perhaps by subtle changes in oceanic productivity including trophic structure and shifts in productivity centers with rising sea level the creation and growth of epicontinental seas played a major role in regional climate change water mass production and water column structure epicontinental seas were also an important factor in creating vast new niche space and increased biotic diversity for many marine organisms the amplified seasonality and instability of epicontinental seas resulted in habitation of the upper water column by morphologically simple eurytopic planktonic foraminifera several new species of epicontinental sea dwelling planktonic foraminifera appeared during the mid cretaceous however much of the diversification of morphologic form took place in oceanic areas during times of oceanic stability and upper water column stratification during mid to late aptian and late albian time a decline in diversity and return to simple morphotypes occurred when oceanic stability was disrupted and the upper water column was poorly stratified during latest aptian early albian time

atlantic paleobathymetry paleoproductivity and paleocirculation in the late albian the benthic foraminiferal record spatial distribution patterns of benthic foraminifers in upper albian sediments from 25 dsdp odp sites and 31 onshore sections of the north and south atlantic ocean are used to generate paleobathymetric reconstructions and to identify areas of high primary production such as coastal and equatorial upwelling zones new paleobathymetric estimates are provided for dsdp odp sites and onshore locations that are not situated on oceanic crust paleobathymetric reconstructions indicate shallow water exchange between the north and south atlantic but show the existence of a deep water connection between the western and eastern tethys 2500 m through the gibraltar gateway strikingly there is no evidence for a strong latitudinal gradient in deep water benthic foraminiferal distribution during the late albian south atlantic assemblages show close affinity to north atlantic and tethyan assemblages exhibiting only a minor degree of provincialism biogeographic patterns reveal a distinct asymmetry in late albian paleoproductivity for the north atlantic as for the present day the eastern margins of the atlantic were generally more productive than the western margins and a belt of enhanced carbon aux export to the seafloor can be traced around the north african coast which probably corresponded to a zone of vigorous coastal upwelling by contrast assemblage composition in the south atlantic generally reflects mesotrophic to oligotrophic conditions benthic foraminiferal distribution patterns thus provide robust proxy data to test predictions from paleocirculation and paleobathymetric models for the mid cretaceous atlantic ocean and adjacent margins c 2001 elsevier science b v all rights reserved

testing the cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the turonian tropics on demerara rise glassy turonian foraminifera preserved in clay rich sediments from the western tropical atlantic yield the warmest equivalent 18o sea surface temperatures ssts yet reported for the entire cretaceous cenozoic we estimate turonian ssts that were at least as warm as conservative mean 30 c to significantly warmer warm mean 33 c than those in the region today however if independent evidence for high middle cretaceous pco2 is reliable and resulted in greater isotopic fractionation between seawater and calcite because of lower sea surface ph our conservative and warm sst estimates would be even higher 32 and 36 c respectively our new tropical ssts help reconcile geologic data with the predictions of general circulation models that incorporate high cretaceous pco2 and lend support to the hypothesis of a cretaceous greenhouse our data also strengthen the case for a turonian age for the cretaceous thermal maximum and highlight a 20 40 m y mismatch between peak cretaceous cenozoic global warmth and peak inferred tectonic co2 production we infer that this mismatch is either an artifact of a hidden turonian pulse in global ocean crust cycling or real evidence of the influence of some other factor on atmospheric co2 and or ssts a hidden pulse in crust cycling would explain the timing of peak cretaceous cenozoic sea level also turonian but other factors are needed to explain high frequency 10 100 k y instability in middle cretaceous ssts reported elsewhere

precessional forcing of nutricline dynamics in the equatorial atlantic climate control of nutricline depth in the equatorial atlantic can be monitored by variations in the abundance of the phytoplankton species florisphaera profunda a conceptual model based on in situ evidence associates high abundances of f profunda with a deep nutricline and low abundances with a shallow nutricline a 200 000 year record of f profunda relative abundances obtained from a deep sea core sited beneath the region of maximum equatorial divergence at 10 w has 52 percent of its variance centered on the 23 000 year precessional band cross spectral analysis between the signals of f profunda and sea surface temperature independently derived from zooplankton species shows their 23 000 year cycles to be coherent and nearly in phase abundance minima of f profunda coincide with times of december perihelion whereas abundance maxima coincide with june perihelion these relations indicate that nutricline dynamics in the divergence region of the equatorial atlantic are controlled by variations in the tropical easterlies forced by the precessional component of orbital insolation on time scales greater than 10 000 years

cyclic changes in turonian to coniacian planktic foraminiferal assemblages from the tropical atlantic ocean abstract abundance patterns of planktic and benthic foraminifera from a tropical atlantic drill site ocean drilling program site 1259 demerara rise suriname margin display a pronounced 400 kyr cyclicity uninterrupted throughout our 87 8 92 ma record between two clearly distinguishable assemblages 1 a pelagic foraminifer fauna which represents a deep oxygen minimum zone and 2 another assemblage representing a shallow oxygen minimum zone where the foraminifer fauna is dominated by a higher diversity population of mostly small clavate and biserial species common in epicontinental seas the cyclic changes in the long eccentricity band 400 kyr between these two assemblages are proposed to reflect changes in the mean latitudinal position of the intertropical convergence zone itcz associated fluctuations in precipitation and trade wind strength may have influenced the upwelling regime at demerara rise leading to the observed cyclicity of planktic foraminiferal assemblages the severe turonian to coniacian paleoclimatic and paleoceanographic changes in the atlantic ocean e g gateway opening cooling and glaciation however seem to have no influence on the composition of tropical planktic foraminiferal faunas there is no apparent relationship between foraminifer abundances and a major deflection in the stable isotope record interpreted elsewhere as a sign of the growth and decay of a large polar ice sheet

formation of the late aptian niveau fallot black shales in the vocontian basin se france evidence from foraminifera palynomorphs and stable isotopes abstract we present paleoceanographic models for the formation of the marlstone facies and the most prominent black shale intervals of the late aptian niveau fallot black shale succession from the vocontian basin se france in the lower part of the succession the composition of benthic foraminiferal assemblages of the niveau fallot 2 and 2 black shales suggests an enhanced burial of organic matter due to more eutrophic conditions and resulting low oxygen conditions at the seafloor in the upper part of the succession including niveau fallot 3 and 4 a third order sea level fall indicated by a decrease in the stable carbon isotope values may have resulted in a reduced water mass exchange between the vocontian basin and the western tethyan ocean this may have led to dysoxic conditions at the seafloor of the vocontian basin and may have favored the formation of organic rich sediments as shown by benthic foraminiferal assemblages decreased evaporation however is proposed as the most important mechanism causing a restriction of deep water formation within the basin which finally led to the formation of the niveau fallot 3 and 4 black shales based on our investigations the formation of the niveau fallot black shales was caused by different factors the most prominent ones include sea level fluctuations increasing productivity and changes in precipitation and evaporation rates furthermore niveau fallot 3 can probably be correlated with the thalmann black shale event in california and a dark horizon at the mazagan plateau dsdp site 545

coseismic and long term vertical displacement due to back arc shortening central vanuatu offshore and onshore data following the mw 7 5 26 november 1999 ambrym earthquake 1 this paper presents a combined analysis of data collected both onshore and offshore in the epicentral region of the mw 7 5 26 november 1999 ambrym earthquake this offshore event occurred at the southern end of the back arc thrust belt of the vanuatu subduction zone east of the island of ambrym and resulted in permanent uplift of the eastern tip of the island the data presented include 1 interpretation of older seismic lines across the tectonic front 2 compilation of aftershock sequences 3 postseismic bathymetry from multibeam surveys 4 measurements of permanent coseismic ground motion using desiccated red algae uplifted beaches and uplifted coral colonies and 5 dating of raised corals exposed along the coastal cliff the active scarp of the main fault appears 13 km east of the eastern tip of ambrym 40 km long 2 km depth 950 m maximum step uplift rates of 3 5 4 mm yr for the past 8000 years are calculated by dating raised corals this leads to a longer seismic recurrence interval of 375 years for events similar to that of 1999 assuming no interseismic subsidence postseismic ground motion was monitored using stainless steel marks set at three sites along the uplifted coast in january 2000 no significant motion could be recorded during the 2 years following the event but slight subsidence cannot be ruled out finally our results confirm that the back arc belt of central vanuatu is an active tectonic crustal wedge propagating eastward that accommodates more shortening than the vanuatu subduction zone to the west

the barremian aptian turnover of biota in northwestern europe evidence from belemnites abstract neocomian valanginian barremian and gault aptian albian are lithostratigraphic terms used in the last century to divide the sub chalk cretaceous of northern europe the division is based on significant palaeoceanographic and palaeogeographic changes in the early aptian these changes are linked to a major turnover of marine floras and faunas which occurred simultaneously in the boreal realm the tethys and the indo pacific ocean various floral and faunal elements became extinct in the aptian both in the tethys and in the boreal realm while on the other hand new genera and species evolved marked changes in the diversification rate were observed for organisms with a different mode of life plankton nekton benthos apart from calcareous nannofossils foraminifera and ammonites this turnover also occurs in belemnites and the suborder belemnitina was completely replaced by the suborder belemnopseina the northwestern european barremian is characterised by the very successful belemnite family oxyteuthididae belemnitina which was completely replaced by the genus neohibolites belemnopseina in early aptian times this aptian turnover which is expressed by a homogenisation of marine floras and faunas is best explained by significant palaeoceanographic changes occurring in the early aptian the sea floor spreading rate which increased at the barremian aptian boundary significantly peaked in the late early aptian a mantle plume in the pacific possibly caused an additional production of oceanic crust both processes caused a major sea level rise this in turn resulted in a major change of the palaeoceanographic setting and restricted marginal seas like the northwestern european basins in barremian times became drowned the more open oceanic setting of the aptian enabled cosmopolitan floras and faunas to spread worldwide the aptian saw the radiation of planktonic foraminifera which played only a minor role in pre aptian times these palaeoceanographic changes from restricted marginal seas to a more homogeneous pelagic setting are considered to be the main cause for the significant changes in the composition of belemnite faunas

influence of oceanic anoxic events on the evolution of mid cretaceous radiolaria in the north atlantic and western tethys abstract mid cretaceous aptian turonian extinction radiation events of radiolaria from the north atlantic and western tethys are summarized in relation to oceanic anoxic events oae from investigations of radiolarian faunas black shales and stable carbon isotopes extinction and radiation events of radiolaria can be observed from the late early aptian the earliest albian the latest albian and the cenomanian turonian boundary these events correlate well with organic carbon rich sediments that contain type ii kerogen and show positive 13c excursions they correspond to the oceanic anoxic events oae in the early aptian oae 1a selli level early albian oae 1b late albian oae 1d and latest cenomanian oae 2 bonarelli level detailed investigations of the two most significant events the selli and the bonarelli level in the umbria marche basin of central italy show that extinctions coincide with the first occurrence of marine black shales type ii kerogen and the most prominent rise of 13corg values stepwise extinctions and continuous radiations precede and follow the events similar patterns are evident for the oae 1b and 1d black shales dominated by terrestrial organic matter type iii kerogen e g oae 1c are not characterized by isotopic excursions or by radiolarian extinction radiation events contemporaneous drowning events documented from carbonate platforms around the investigated basins provide a link to a model where flooding of lowlands and leaching of nutrients during a relative rise of sea level lead to an increased productivity and an expansion of the oxygen minimum zone omz because of the loss of deep habitats deeper dwelling forms become extinct shallower dwelling radiolarians survive a narrowing of the omz during highstands and relative sea level falls together with a coupled decrease of the nutrient supply leads to the development of new niches and therefore to radiation

insolation cycles as a major control of equatorial indian ocean primary production analysis of a continuous sedimentary record taken in the maldives indicates that strong primary production fluctuations 70 to 390 grams of carbon per square meter per year have occurred in the equatorial indian ocean during the past 910 000 years the record of primary production is coherent and in phase with the february equatorial insolation whereas it shows diverse phase behavior with 18o depending on the orbital frequency eccentricity obliquity or precession examined these observations imply a direct control of productivity in the equatorial oceanic system by insolation in the equatorial indian ocean productivity is driven by the wind intensity of westerlies which is related to the southern oscillation therefore it is suggested that a precession forcing on the southern oscillation is responsible for the observed paleoproductivity dynamics

migration and evolution patterns of floras and faunas in marine early cretaceous sediments of nw europe the distribution and migration patterns of marine nannofloras and faunas in the early cretaceous berriasian aptian of nw europe are described boreal nannofloras and faunas dominate in the latest berriasian the early valanginian the mid late valanginian the late early hauterivian and the mid late hauterivian sea level highstands linked to warming enabled tethyan nannofloras and faunas to spread into nw europe during three intervals 1 in the earliest late valanginian 2 in the latest valanginian and earliest hauterivian and 3 in short influxes in the late hauterivian culminating in the latest hauterivian during the barremian regression the palaeoceanography of nw europe changed totally from a marginal sea to a restricted basin this oceanographic setting allowed the evolution of endemic nannofloras and faunas a major sea level rise caused by increased sea floor spreading changed the palaeoceanographic situation significantly in the aptian due to widespread oceanic conditions nannofloras and faunas became homogenised and cosmopolitan nevertheless the peak of the transgression was again linked to a widespread influx of tethyan nannofloras and faunas in the mid late aptian nutfieldiensis zone the dispersal and evolution patterns of the nannofloras and faunas in the early cretaceous were mainly controlled by the suitability of sea ways regressions transgressions and temperature planktonic benthic and nectonic organisms reacted in similar ways their distribution pattern differs however significantly due to different modes of life

coseismic coastal uplift and coralline algae record in northern chile the 1995 antofagasta earthquake case coralline algae that may be predominant in the upper part of the infralittoral zone along rocky shorelines proved to be a useful indicator of rapid coastal uplift as these encrusting algae cannot survive desiccation even for short periods at low tide they can provide estimates of positive vertical motions like those which may accompany seismic events the desiccation of a fringe of the algal encrustment at the base of the intertidal area infralittoral fringe combined with effects of solar radiation rapidly kills the organisms this mortality results in a conspicuous alteration of the pigmentation from pink beige reddish to white after the july 30 1995 antofagasta earthquake mw 8 1 in northern chile such a white fringe appeared in some parts of the bay of antofagasta and surroundings the width of the dead algae fringe varied from 0 to more than 1 8 m the widest observed widths are related to local parameters exposition to wave splash geometric disposition that account for an amplification of the width of the dead algae fringe and must be identified thus a careful study of each locality led us to determine the extent of the coastal areas that had been uplifted and to reconstruct with a precision of the order of 2 cm the amount of the vertical deformation along the antofagasta bay and southern mejillones peninsula it was thus shown that the coastline bordering the town of antofagasta suffered practically no coseismic uplift while areas to the south and to the west of antofagasta bay proved to have been uplifted by as much as 25 and 40 cm respectively the maximum uplift 80 cm was seen at the southwestern tip of the peninsula of mejillones these precise reconstructions are of great help for the calibration of geodetic studies performed independently and for the modelling of the coseismic deformation at a regional scale

the barremian and aptian stepwise development of the oceanic anoxic event 1a oae 1a crisis integrated benthic and planktic high resolution palaeoecology along the gorgo a cerbara stratotype section umbria marche basin italy abstract the barremian and aptian were times of global plate reconfiguration and profound changes in the ocean climate system culminating in the worldwide deposition of lower aptian black shale layers oae 1a based on high resolution lithostratigraphic and micropaleontological analyses precursor conditions and timing of the anoxia are here reconstructed along a 33 06 m thick section in the proposed barremian aptian boundary gssp stratotype at gorgo a cerbara umbria marche basin italy a non uniform history of benthic foraminiferal diversification is interrupted by the selli level oae 1a and by three turnover points for both benthic and planktic organisms each highlighted by prominent breaks in lithology and outcrop morphology the first two points at 1 1 myr and 20 50 kyr prior to the onset of the oae 1a correspond respectively to the nannoconid bathypelagic calcareous nannofossils decline and crisis events and separate a pelagic limestone chert claystone lithological cycles of the uppermost maiolica formation showing frequencies reminiscent of orbital eccentricity and containing an oligotrophic barremian benthic and planktic assemblage dominated by k selected nannoconids and rhizammina b greenish grey cherty marls of the lowermost marne a fucoidi formation associated to declining sedimentation rates and eutrophic early aptian assemblages dominated by radiolarians and lituolid benthic foraminifera and c anoxic radiolarites and shales of the carbonate free selli level high magnitude and frequency assemblage fluctuations occur between the nannoconid crisis 25 cm below the lowermost oae 1a black shale layer and the selli level base with suggestions of bottom water acidification at 800 kyr after the oae 1a end a third turnover point in the basal reddish member of the marne a fucoidi highlights middle aptian assemblages characterized by a bloom of early macroperforate planktic foraminifera hedbergella spp and appearances of new benthic species marking a shift towards better oxygenation oae 1a oxygen and pelagic carbonate factory crises are here suggested to have been step wise and linked to global warming conditions

recent benthic foraminiferal associations and ecology of the scotia sea and argentine basin abstract we investigated 88 surface sediment samples taken with a multiple corer from the southwestern south atlantic ocean for their live rose bengal stained and dead benthic foraminiferal content using q mode principal component analysis six live and six dead associations are differentiated live and dead association distributions correspond fairly well differences are mainly caused by downslope transport and selective test destruction in addition four potential fossil associations are calculated from the dead data set after removal of non fossilizable species these potential fossil associations are expected to be useful for paleoceanographic reconstructions environments are described in detail for the live and potential fossil associations and for selected species along the upper argentine continental slope strong bottom currents control the occurrence of live dead and potential fossil angulogerina angulosa associations here particles of a high organic carbon flux rate remain suspended below this high energy environment live dead and potential fossil uvigerina peregrina dominated associations correlate with enhanced sediment organic carbon content and still high organic carbon flux rates the live a angulosa and u peregrina associations correlate with high standing crops furthermore live and dead epistominella exigua nuttallides umbonifer associations were separated dominance of a nuttallides umbonifer potential fossil association relates to coverage by antarctic bottom water aabw and lower circumpolar deep water lcdw above the calcite compensation depth ccd three associations of mainly agglutinated foraminifera occur in sediments bathed mainly by aabw or cdw a reophax difflugiformis association was found in mud rich and diatomaceous sediments below the ccd a psammosphaera fusca association occurs in coarse sediments poor in organic carbon while a cribrostomoides subglobosus ammobaculites agglutinans association covers a more variable environmental range with mud contents exceeding 30 one single eggerella bradyi martinottiella communis association poor in both species and individuals remains from the agglutinated associations below the ccd if only preservable species are considered for calculation

back arc convection model for columbia river basalt genesis abstract genesis of the columbia river basalt group crbg may be accounted for by the progressive thermal erosion of an attenuated heterogenous subcontinental lithosphere scl by back arc convection behind the cascade arc assembly of the source components of the crbg began during the early mesozoic when slices of former oceanic lithosphere were isolated below terranes accreted to the continental margin subsequent lithospheric shearing accompanying northward translation of the terranes allowed the injection of small degree partial melts from the asthenosphere which solidified in the scl as pyroxenite veins the scl source of the crbg underwent a further episode of shearing accompanied by attenuation during the eocene and oligocene when it was caught between contrasting right lateral terrane translation and e w extension regimes in the northern cordillera and basin and range province respectively the attenuation resulted in the raising of the geotherm close to that of the pyroxenite and iherzolite solidi melting was triggered by back arc convection behind the cascade arc the pyroxenite was the first component mobilised constituting the principal source of the imnaha formation continued back arc convection resulted in the failure of the scl and the generation of the voluminous grande ronde formation from pyroxenite and the surrounding scl the change to wanapum volcanism marks the stage of exhaustion of in situ sources and their replacement with a combination of proterozoic scl from the east and asthenospheric material by back arc convection the saddle mountains formation was derived entirely from proterozoic scl small magma volumes resulted in a susceptibility to local contamination such that the distinct isotopic arrays of the saddle mountains formation comprise three mixing lines and do not have any age significance

onset of the mid cretaceous greenhouse in the barremian aptian igneous events and the biological sedimentary and geochemical responses basalts and biostratigraphy dated at 125 120 ma from the ontong java and manihiki plateaus in the western pacific evidence the largest volcanic event in earth history in at least the past 160 m y the intervening nova canton trough rifted at about 121 118 ma and a number of guyots and seamounts formed concurrently or slightly later geological events that probably were responses to these volcanic tectonic events occurred in the following chronostratigraphic order biotic fluctuations began at about 122 5 ma at about 122 0 ma 87sr 86sr began to decline slowly metal concentrations of co mn pb yb and cu in sediments peaked at about 121 5 121 2 ma changes in planktonic communities and sedimentation culminated in a nannoconid crisis just prior to 120 5 ma and in the selli black shale oae la at about 120 5 119 5 ma a sharp drop in 13c occurred at the beginning of the selli event and rebounded into a longer positive excursion that reached a peak after the selli event at about 119 5 118 5 ma at 120 5 ma 87sr 86sr declined rapidly and reached a minimum at about 116 113 ma we speculate that the intensity of these latter responses suggests a corresponding peak in volcanic tectonic activity at about 121 119 ma

development of the gulf of guayaquil ecuador during the quaternary as an effect of the north andean block tectonic escape 1 interpretation of industrial multichannel seismic profiles and well data are used to identify the main tectonic features of the gulf of guayaquil gg area these include two e w trending major detachments the posorja and the jambeli detachment systems which represent half grabens with oppositely dipping detachments to the south and to the north respectively the ne sw trending puna santa clara fault system developed as a transfer fault system between the posorja and the jambeli detachments the esperanza and the jambeli basins exhibit 3 4 km of sediment that accumulated during the past 1 6 1 8 myr the puna santa clara fault system bounds the esperanza and the jambeli basins evidencing that the evolution of these basins is tightly controlled by the two detachments at depth to the west the n s trending domito fault system bounding the posorja detachment system and the esperanza basin to the west acted as a transfer zone between the shelf area and the continental slope the pliocene series show no significant variations in thickness throughout the gulf of guayaquil area suggesting that no important tectonic deformation occurred from 5 2 to 1 8 1 6 ma the major period of tectonic deformation in the gulf of guayaquil area occurred during the pleistocene times three main tectonic steps are identified from early pleistocene to 180 ka major subsidence occurred along the esperanza and jambeli basins from 180 to 140 ka most of the gulf of guayaquil area was above sea level during the isotope substage 6 low stand from 140 ka to present tectonic activity is restricted along the normal faults bounding the esperanza basin the tenguel fault and the puna santa clara and domito fault systems a n s trending tensional stress regime characterizes the pleistocene times throughout the northward drifting of the north andean block is proposed to control the tectonic evolution and associated subsidence of the gulf of guayaquil area it is also accepted that the collision of the carnegie ridge with the trench axis has to play a major role in controlling the north andean block northward drift because the carnegie ridge subduction is possibly an ongoing process which began prior to the pliocene we postulate the along strike morphology of the ridge at the origin of interplate coupling variations the subduction of an along strike positive relief of the ridge is proposed at the origin of the major tectonic reorganization of the gg area occurring at 1 8 1 6 ma

eocene oil shales from jordan paleoenvironmental implications from reworked microfossils abstract reworked microfossils common in paleogene sediments in jordan are here used to reconstruct the depositional environment the reworked taxa which include both calcareous nannofossils and foraminifera of cretaceous and paleocene age were found in eocene oil shales the potential provenance of the reworked material and the underlying processes of the reworking are discussed we differentiate between a subaerial erosion of exposed hinterland strata and a submarine abrasion of sediments a total of 73 smear slides have been prepared to identify calcareous nannofossils another fifteen samples were analyzed for foraminifera the allochthonous calcareous nannofossil and foraminifera taxa can be linked to a lithified source which was eroded and transported with both calcitic lithic fragments and organic matter multiple factors controlling the transport of the reworked taxa during the time of deposition have been investigated for the jordanian oil shales climate changes are thought to be the cause for changes in the abundance patterns and in the composition of the reworked taxa the input of common autochthonous components during arid phases and more allochthonous sediment particles during humid periods filled the eocene sink a fall in relative sea level perhaps in combination with increased storm activity caused a transport of reworked material to deeper parts of the azraq hamza sub basin the relative sea level changes in turn were related to syndepositional movements redefining the shape of the azraq hamza sub basin and its internal fault block architecture

benthic foraminifera off west africa 1 n to 32 s do live assemblages from the topmost sediment reliably record environmental variability abstract recent benthic foraminifera 125 m were investigated from multicorer samples on a latitudinal transect of 20 stations between 1 n and 32 s along the upper slope off west africa samples were selected from a narrow water depth interval between 1200 and 1500 m so that changes in water masses are minimized but changes in surface productivity are important and the only significant environmental variable live rose bengal stained benthic foraminifera were counted from the surface sediment down to a maximum of 12 cm dead foraminifera were investigated in the top 5 cm of the sediment only five live and five dead benthic foraminiferal assemblages were identified using q mode principal component analysis matching distinct primary productivity provinces characterized by different systems of seasonal and permanent upwelling differences in seasonality quantity and quality of food supply are the main controlling parameters on species composition and distribution of the benthic foraminiferal faunas to test the sensitivity of foraminiferal studies based on the uppermost centimeter of sediment only a comparative q mode principal component analysis was conducted on live and dead foraminiferal data from the top 1 cm of sediment it has been demonstrated that on the upper slope off west africa most of the environmental signals as recorded by species composition and distribution of the total live and dead assemblages i e including live and dead foraminifera from the surface sediment down to 12 cm and 5 cm respectively can be extracted from the assemblages in the top centimeter of sediment only on the contrary subsurface abundance maxima of live foraminifera and dissolution of empty tests strongly bias quantitative approaches based on the calculation of standing stocks and foraminiferal numbers in the topmost centimeter

florisphaera profunda a possible nannoplankton indicator of late quaternary changes in sea water turbidity at the northwestern margin of the pacific three piston cores from the ryukyu trench slope northwestern margin of the pacific ocean contain nearly continuous paleoceanographic records of the last 320 165 and 105 kyr ages of the cores are constrained by planktic 18o stratigraphy and roughly substantiated by the presence of two calcareous nannofossil events spectral analysis of the changes in relative abundance offlorisphaera profunda a nannoplankton species presently living in the lower euphotic zone reveals a maximum power at 0 01 cycles kyr corresponding to the 100 kyr cycle of orbital eccentricity much lower power is observed at the 23 kyr precessional band this differs from the equatorial atlantic ocean variations which show dominant power in the 23 kyr precessional band in the changes off profunda abundances molfino and mcintyre 1990a besides our cores were taken outside the equatorial divergence zone we also show a rather close relationship betweenf profunda abundance and sea water transparency secchi depth in the present northwest pacific based on data from 204 sites of surface sediment samples because sea water transparency is primarily affected by bio productivity change in open ocean stratigraphic changes off profunda abundances in our cores seem to have been caused by productivity change as well pointed out by molfino and mcintyre 1990a b a mechanism proposed by them for its change however is not applied to our cases due to differences in spectral analysis results and in geographic situation alternatively we suggest that geographic change of the northwestern margin of the pacific during the late quaternary causedf profunda abundance change through the sea water turbidity change which has been affected not only by bio productivity but also by land origin particles supply

planktic foraminifera from the mid cretaceous barremian early albian of the north sea basin palaeoecological and palaeoceanographic implications abstract a marine cretaceous succession barremian albian of a cored borehole bgs 81 40 located in the central north sea basin has been examined with respect to its planktic and benthic foraminiferal content as well as for calcareous nannofossils the distribution patterns of foraminifera and calcareous nannofossils allow for a two fold division of the investigated interval 1 the barremian earliest aptian interval which reflects a marine temporary restricted setting this is indicated by sporadic occurrences of planktic foraminifera with very rare planispiral forms suggesting short term connections of the boreal and tethyan realms the benthic foraminiferal assemblages indicate aerobic sometimes dysaerobic bottom water conditions high abundances of nannoconids in the barremian suggest enhanced stratification and or warm oligotrophic surface water 2 the late aptian early albian interval which was characterised by an open oceanic environment with cool and aerobic surface water conditions planktic foraminifera are more abundant and diverse than in the lower interval trochospiral hedbergellids dominate the foraminiferal assemblages the episodic occurrences of planispiral clavate and trochospiral flattened planktic morphotypes indicate the existence of a seaway between the boreal and the tethyan realms aerobic to dysaerobic bottom water conditions are suggested by the composition of the benthic foraminiferal assemblages high abundances of cool water taxa within the calcareous nannofossil assemblages indicate a cooling trend across the latest aptian and earliest albian

reconstruction of short term palaeoceanographic changes during the formation of the late albian niveau breistroffer black shales oceanic anoxic event 1d se france the niveau breistroffer black shale succession in the vocontian basin se france is the regional equivalent of the widely distributed late albian oceanic anoxic event 1d the studied black shale rich interval at the col de palluel section is 6 28 m thick and comprises four black shale units with up to 2 5 wt total organic carbon toc intercalated with marlstones calcareous nannofossil palynomorph planktic foraminifera and stable isotopic data from the niveau breistroffer succession suggest that short term climate changes influenced its deposition with relatively warm and humid climate during black shale formation in comparison with relatively cool and dry climatic conditions during marlstone deposition an increase in the terrigenous marine ratio of palynomorphs indicates enhanced humidity and higher runoff during black shale formation a nutrient index based on calcareous nannofossils and the abundance pattern of small 63 125 m hedbergellid foraminifera show short term changes in the productivity of the surface water surface water productivity was reduced during black shale formation and increased during marlstone deposition a calcareous nannofossil temperature index and bulk rock oxygen isotope data indicate relative temperature changes with warmer surface waters for black shale samples at these times warm humid climate and reduced surface water productivity were accompanied by greater abundances of subsurface dwelling calcareous nannofossils nannoconids and planktic foraminifera rotaliporids these taxa presumably indicate more stratified surface water conditions we suggest that the formation of the niveau breistroffer black shales occurred during orbitally induced increase in monsoonal activity that led to increasing humidity during periods of black shale formation this in turn caused a decrease in low latitude deep water formation and probably an increase in surface water stratification the combination of these two mechanisms caused depleted o 2 concentrations in the bottom water that increased the preservation potential of organic matter

correlating environmental changes during early albian oceanic anoxic event 1b using benthic foraminiferal paleoecology abstract the nature and consequences of mid cretaceous oceanic anoxic events oaes are the subject of ongoing debate and recent studies have shown that different scenarios are needed to explain each of these events nevertheless similarities between the different oaes can be observed here we have reconstructed paleoenvironmental changes during the early albian oae 1b using benthic foraminiferal distributions and lithologies in three sections from different basins and paleowater depths eutrophic conditions as indicated by the presence of infaunal as well as opportunistic genera such as gyroidinoides pseudobolivina pleurostomella and bolivinitids prevailed before and during the oae and led to dysoxic to anoxic conditions dysoxia was most intense in the bathyal sections but also occurred in the outer shelf where more heterogeneous patterns of foraminiferal distributions are believed to reflect fluctuations of the upper boundary of an oxygen minimum zone a change from eutrophic to mesotrophic conditions caused the termination of oae 1b and opportunistic benthic foraminifera e g pseudobolivina pleurostomella were the first to subsequently repopulate the bathyal sea floor repopulation occurred rapidly in the shallow settings and gradually in the deeper sites where a normal diverse pre event fauna was established a few tens of thousands of years after oae 1b

tectonic record of strain buildup and abrupt coseismic stress release across the northwestern peru coastal plain shelf and continental slope during the past 200 kyr 200 kyr both segments uplifted at high rates of 10 to 20 mm yr 1 through tectonic pulses coeval with the eustatic deglacial sea level rises of isotope stage 1 and warm isotope substage 5e respectively the uplift and related extensive emersion of the coastal plain require high coupling along the subduction zone and or underplating at depth offshore industry acquired reflection seismic lines combined with em12 bathymetric data allow us to investigate the tectonic regime and deformation of the continental margin and shelf major dipping seaward detachments control the long term subsidence of this area these main tectonic features define a tectonic segmentation the talara paita and sechura segments are identified from north to south no clear tectonic correlation in time exists between the onshore and the continental margin segmentations or in space either the longterm subsidence of the offshore indicative of subduction erosion working at depth requires low coupling along the subduction channel at depth the distribution of permanent deformation along the northern peru forearc area includes long term uplift along the coastal plain and long term subsidence along the continental margin the neutral line being located within the 10 km seaward from the present coastline an extensive sequence of raised marine cliffs and associated notches evidences that the most recent uplift step 20 23 ka to present along the cabo blanco segment is related to a sequence of major earthquakes we infer that eustacy exerts important feedback coupling to the seismogenic behavior of the north peru subduction zone we speculate that during sea level fall pore fluid pressure diminishes along the subduction channel inducing a possible seaward migration of the locked zone i e migration of the updip limit reaching a maximum by the end of the eustatic low stand during eustatic sea level rise pore fluid pressure increases along the subduction channel this in turn is capable of weakening the previously locked zone along the plate interface beginning an earthquake sequence earth s orbital variations are a potential external cause that may control the physical processes at work along plate interface

reconstructing nutricline dynamics of mid cretaceous oceans evidence from calcareous nannofossils from the niveau paquier black shale se france abstract a high resolution calcareous nannofossil record is presented from the lower albian niveau paquier black shale from the vocontian basin se france the niveau paquier black shale represents the regional equivalent of the supraregionally distributed oceanic anoxic event 1b oae 1b to reconstruct surface water fertility a nutrient index based on zeugrhabdotus erectus discorhabdus rotatorius high fertility indicators and watznaueria barnesae low fertility indicator was established using principal component analysis in addition the distribution of nannoconus spp and absolute abundances of coccoliths coccoliths per gram were used for reconstructing nutricline dynamics of the surface waters high surface water fertility coincides with low percentages of nannoconids and vice versa moreover high percentages of nannoconids correlate with low absolute abundances of all other coccoliths based on the observed nannoplankton distribution pattern and a suggested similarity in ecological requirements between nannoconids and the modern taxon florisphaera profunda a model is proposed that couples nannoconid abundances with dynamics of the nutricline time series analyses of the nutrient index show fluctuations within the precessional band the precession controlled fluctuations of the surface water fertility may represent a monsoonal signal with the nutrient supply in the surface waters depending on the strength of monsoonal activity during periods of enhanced monsoonal activity which were characterized by humid conditions and stronger winds mixing of the upper water column was enhanced during that time the abundance of nannoconids decreased as a consequence of enhanced wind stress that improved vertical mixing and led to an entrainment of nutrients into the surface waters this resulted in an increase of primary production during periods of reduced monsoonal activity marked by drier conditions and reduced wind stress the surface waters were depleted in nutrients as a result of a deep nutricline and a reduced nutrient supply to the upper photic zone in a stratified water column percentages of nannoconids increased according to the mechanisms outlined above fluctuations of the nutrient index and nannoconid percentages have been used as a proxy for reconstructing the physical structure of mid cretaceous oceans steered by precession forced monsoonal activity the results of the study show that the formation of the lower albian oae 1b from the vocontian basin occurred under strongly fluctuating surface waters fertility

nannofossils and superplumes the early aptian nannoconid crisis a group of calcareous nannoplankton named nannoconids experienced a crisis in the early aptian and recovered only later in the late aptian after a period of virtual absence although no extinctions occurred the widespread nature of the nannoconid crisis suggests a global causal factor this crisis is recorded within the chiastozygus litterarius nannofossil and globigerinelloides blowi planktonic foraminiferal zones postdates magnetic chronozone m0 by approximately 300 kyr and precedes the oceanic anoxic subevent 1a and associated 13c anomaly by some 40 100 kyr selective dissolution and anoxia cannot explain the crisis because nannoconids are dissolution resistant forms and their crisis clearly precedes the deposition of anoxic sediments at least 1 m y prior to the nannoconid crisis the onset of a nannoplankton speciation event may be the response of nannofloras to a major rise in relative sea level the nannoconid crisis seems to be synchronous with the early aptian volcanic eruptions in the pacific ocean hence calcareous nannoplankton were severely affected by the superplume volcanic episode the coccolithophorid bloom nannoconid crisis was possibly induced by the excessive co2 levels in the atmosphere and or caused by changes in nutrient content of oceanic surface waters fertility was enhanced by rapid turnover of nutrients due to the abnormal volcanic activity and accelerated transfer of nutrients from the continents into the oceans under warm and humid conditions of the mid cretaceous greenhouse climate the nannoconid crisis may represent a competition between phytoplankton groups for nutrients or more likely competition between different calcareous nannoplankton the biologic affinity and mode of life of nannoconus are unknown because there is no modern analog of this genus however comparison of lower cretaceous nannofossil assemblages with modern nannoplankton cummunities suggests that nannoconids like extant florisphaera profunda possibly inhabited the lower photic zone concentrations of nutrients in the upper euphotic zone may have triggered blooms of coccolithophorids and nannoconid depletion this model implies that the nannoconid crisis is the result of an abrupt major change in the structure of surface waters caused directly or indirectly by the superplume the adjustments of the biosphere to the new paleoceanographic and climatic conditions required some 40 100 kyr before changing into abnormally high primary productivity and deposition of organic carbon rich sediments with dinoflagellates outcompeting nannoplankton

palaeobiogeography of early cretaceous berriasian barremian calcareous nannoplankton in order to assess early cretaceous nannoplankton biogeography we studied a series of sites which provide a north south transect across the atlantic ocean supplemented by sections from the north sea basin barents sea falkland plateau weddell sea antarctica argo abyssal plain nw of australia and neuquen basin argentina quantitative assemblage data were gathered from each site for seven time slices within the berriasian to barremian interval each horizon being determined by a nannofossil datum trends in species relative abundance and measures of diversity evenness and richness provide revealing biogeographic information a broad low to mid palaeolatitude zone 50 degrees n 50 degrees s is flanked in both northern and southern hemispheres by distinct high palaeolatitude zones major changes in assemblage abundance and composition occur across a sharp biogeographic front at around 50 degrees n and s palaeolatitude high palaeolatitude assemblages are lower in species richness and diversity and characterised by the presence of abundant typically bipolar taxa e g crucibiscutum salebrosum a less distinct biogeographic boundary at similar to 40 degrees n is distinguished by the presence absence of rarer but biogeographically significant taxa many of which have previously been assigned to boreal or tethyan provinces continental shelf sites are characterised by lower diversity assemblages with common to dominant diagnostic taxa which vary with palaeolatitude nannoconus and micrantholithus at low palaeolatitudes and biscutum constans and zeugrhabdotus spp at higher palaeolatitudes the latter two taxa are considered to be indicative of elevated surface water fertility and the former two may have been similarly adapted the genus watznoueria is ubiquitously dominant giving the populations an unevenness which appears to be a common feature throughout coccolithophore history c 2000 published by elsevier science b v all rights reserved

early cretaceous calcareous nannofossils from high latitudes implications for palaeobiogeography and palaeoclimate abstract in order to better understand the palaeoceanography and palaeoclimate of the early cretaceous nannofossil data have been obtained from high latitudinal sites from offshore mid norway and from the barents sea no consistent nannofossil data are yet available for early cretaceous high latitudes which should more clearly reflect possible palaeoclimatic changes as recorded in fluctuations of diversity and abundance existing data from france italy romania poland and nw europe germany north sea england have been complemented by material from higher latitudes in order to record the arctic boreal nannofossil assemblages 400 samples from the norwegian shelf and the barents sea have been analysed sixty samples covering the berriasian barremian interval yielded calcareous nannofossils these are derived from cores between 63 and 73 n of present day latitudes the nannofossil assemblages recorded are generally of a low diversity and characterized by abundant watznaueria barnesae and crucibiscutum salebrosum whereas biscutum constans is less common c salebrosum rare or absent at low latitudes is extremely common in the norwegian samples it shows a bipolar distribution especially during valanginian hauterivian times in the early valanginian a distinctive latitudinal gradient in the abundance of c salebrosum impoverished in low latitudes and abundant in high latitudes possibly reflects latitudinal differences in temperature restricted palaeoceanographic settings caused by a sea level lowstand may have amplified these thermal gradients palaeoclimatically this implies the existence of climatic belts throughout parts of the early cretaceous early valanginian hauterivian resulting from considerable temperature gradients from north to south the palaeobiogeographic patterns discussed resulted in the formation of distinctive latitudinally bound nannofossil zones which to a certain extent are similar to those of modern oceans the palaeobiogeographic patterns described support the idea of an ice house phase for the early valanginian and disagree with the suggestion of a globally warm equable climate during that time