lateral extrusion of lower crust from under high topography in the isostatic limit where there is isostasy the rocks of the lower continental crust are subject to an effective lateral pressure gradient equal to the gradient of topographic load whether compensation is in crustal roots or in the mantle the result is a poiseuille flow planar channel flow in the weak lower crust which removes crust from under mountains and smooths and levels the topography assuming cubic power law creep the flux of crust is proportional to the third power of the topographic gradient to the usual arrhenius term to the tenth power of the absolute temperature of the lower crust and to the negative fifth power of the geothermal gradient the result is that any initial condition with an isolated high tends eventually toward a state where the topography is pancake shaped with a flat central plateau and steeper flanks spreading outward when adjacent pancakes merge most of the relief is eliminated flow may either roughen or smooth the moho depending on whether there are lateral density contrasts in the mantle lithosphere or not although it is difficult to find analytic solutions for this evolution it is easily simulated numerically using various published flow laws for plausible lower crustal rocks lateral extrusion is shown to be insignificant under the oceans marginally significant under shields and platforms important under elevated plains and dominant beneath high plateaus and or hot delaminated regions in particular the basin and range province of the western united states cannot maintain short wavelength 100 km moho relief of more than 1 km for times greater than 10 20 m y at most if the tibetan plateau of china has been delaminated as recently suggested then it may flatten even faster reducing 100 km wavelength topographic features to 200 m relief in no more than 0 03 0 13 m y and leaving only features with wavelengths over 400 km at the present therefore the lower crust of tibet may resemble a hydraulic reservoir as previously suggested because the flatness of the moho is self maintained in these regions information on past tectonics is continually lost and the present moho shape cannot be used to balance cross sections for times in the past the flatness of the moho today is not a constraint on the mechanisms of extension or shortening in these regions nor is it evidence for underplating by intrusions it also follows that very intense and inhomogeneous dilational strains may have occurred locally as in the metamorphic core complexes of the basin and range province

seasonal and interannual variation of coccolithophore fluxes and species composition in sediment traps north of gran canaria 29 n 15 w abstract coccolithophore flux variations in sediment traps of the time series station estoc european station for time series in the ocean canary islands located 60 nm north of gran canaria were recorded from april 1993 to december 1996 the 20 cup particle traps were deployed at 1000 and 3000 m below sea surface and sampling intervals ranged from eight days to three weeks coccolith and coccosphere fluxes at both trap depths were characterized by a strong seasonality at 1000 m maximum coccolith fluxes were reached during spring from march to april 1995 and from february to march 1996 highest coccolith fluxes of 4538 106 coccoliths m 2 d 1 occurred at the beginning of march 1996 whereas lowest values of 19 8 106 coccoliths m 2 d 1 were recorded in june 1994 total coccosphere fluxes were constantly low during most of the investigated time interval and showed only high values during the main sedimentation phases from january to march 1995 up to 6 2 106 spheres m 2 d 1 and in march 1996 36 4 106 spheres m 2 d 1 at 3000 m water depth the sedimentation pattern was rather similar to the pattern observed at 1000 m maximum coccolith and coccosphere fluxes were also reached during spring time in february 1994 8200 106 and 15 6 10 6 m 2 d 1 respectively and in march 1996 8114 106 and 32 3 10 6 m 2 d 1 respectively however total coccolith flux peaks at 3000 m were about 2 4 times higher compared to the upper traps probably due to horizontal advection from phytoplankton material from north of the study site this effect also influenced the coccolith caco3 flux estimates mean calculated coccolith caco3 fluxes ranged between 3 9 mg m 2 d 1 for the upper traps 1995 1996 and 9 9 mg m 2 d 1 for the lower traps 1996 coccoliths contributed for about 8 78 of the measured total caco3 fluxes the coccolithophore assemblages were dominated by emiliania huxleyi florisphaera profunda and gephyrocapsa ericsonii during the entire sampling period whereas all other species together generally contributed less than 40 to the total assemblages variability of species compositions at either trap depth was very low indicating similar seasonal flux patterns of the different species

core complex geometries and regional scale flow in the lower crust a simple flexural model that treats the lithosphere as a thin elastic plate overlying a fluid asthenosphere produces an excellent fit to the domal detachment fault geometries observed in typical core complexes of the basin and range province however this mode of isostatic compensation requires an unacceptably large reduction in local topographic elevation 3 5 km above core complex structures because topographic lows of this magnitude are not observed above core complexes today it requires mountain ranges 3 5 km higher than the surrounding areas to have existed at the site of each future core complex and requires these mountain ranges to have had large crustal roots that were subsequently uplifted to form a flat moho as the core complexes developed an alternate mode of isostatic compensation whereby compensation occurs primarily by regional scale flow of material within the lower crust beneath an elastic midcrust provides an equally good fit to the observed detachment fault geometries while requiring little reduction in local topographic elevation above developing core complex structures and providing an obvious means of maintaining a flat moho beneath these zones of upper crustal doming if this interpretation is correct then the effective elastic plate thickness below the basin and range province probably cannot exceed a maximum of about 4 km with a best guess estimate of about 0 5 to 1 km computation of the temperature structure associated with crustal flow during doming shows that an increase in temperature at the moho of about 100 c follows doming by several million years perhaps explaining the observed coincidence of core complexes with crustally derived igneous rocks subsequent cooling of the mid to lower crust beneath the core complex could result in freezing of the initially ductile lower crust within the core of the dome effectively locking the domal shape into the crust even after the detachment surface is cut by younger faults

mechanical basis for low angle normal faulting in the basin and range province low angle normal faults seem to violate the criterion that relates fault dip to stress orientation to explain such faults one must postulate a 45 rotation of principal stress directions at mid crustal depths which is difficult to understand on the basis of previous elastic crust models such a stress rotation is shown to be a natural consequence of a low viscosity lower crust

role of crustal flexure in initiation of low angle normal faults and implications for structural evolution of the basin and range province the mechanics of low angle normal faulting has proved difficult to establish despite clear geological evidence for the existence of such faults gently dipping shear stress trajectories are necessary for nucleation and propagation of low angle faults in a structurally isotropic medium such trajectories are not produced by simple horizontal extension but do arise in the presence of flexural stresses we model stress conditions in a cross section through the strong upper crust using airy stress functions for a two dimensional elastic medium numerical modeling indicates that high ratios of flexural stress to extensional stress produce conditions favorable for low angle normal fault initiation at intermediate depths in an elastic medium we propose that the gentle dip of cenozoic low angle normal faults in the basin and range province resulted from flexural stresses that were produced by isostatically uncompensated surface and especially moho relief resurgent mid cenozoic magmatism and the consequent reduction of the thermally dependent flexural strength of the mantle lithosphere transferred flexural stresses to the upper crust causing or promoting initiation of low angle normal faults temporal changes in structural style from dominantly low angle to dominantly high angle normal faulting may reflect reduction of the magnitude of flexural stresses in the upper crust due to flattening of the moho and cooling of the mantle lithosphere

listric normal faulting stress refraction and the state of stress in the gulf coast basin the close association of overpressured shales and the coincident flattening of listric normal faults has been noted and is usually explained in terms of gravity sliding models however incorporation of overpressure into mohr coulomb frictional faulting theory does not predict normal faults dipping at angles less than 45 even for very low coefficients of friction we suggest that low angle normal faults may form because of a rotation of the maximum principal stress away from vertical with depth such a rotation occurs if a significant contrast in viscosity exists between two adjacent strata such as a normally pressured sandstone and an underlying overpressured shale or evaporite the stress refraction model renders the presence of a preexisting fault plane or an extremely low coefficient of friction unnecessary to explain listric fault geometry and offers a failure mechanism in agreement with frictional faulting theory based on rheological arguments

planktic foraminiferal sedimentation and the marine calcite budget 1 the vertical flux and sedimentation rate of planktic foraminiferal tests are quantified and a global planktic foraminiferal cac0 3 budget is presented test and calcite flux rates are calculated according to the distribution of species obtained from multinet and sediment trap samples modern planktic foraminiferal population dynamics are discussed as a prerequisite for the quantification of the calcite budget highlighting the importance of ecological autecological e g reproduction and biogeochemical conditions that determine the presence or absence of species to complete the open marine particulate caco 3 inventory the contribution of coccolithophores pteropods and calcareous dinophytes is discussed based on the studied regions the global planktic foraminiferal calcite flux rate at 100 m depth amounts to 1 3 3 2 gt yr 1 equivalent to 23 56 of the total open marine caco 3 flux the preservation of tests varies on a regional and temporal scale and is affected by local hydrography and dissolution during most of the year off peak periods many tests dissolve above 700 m water depth while settling through the water column with on average only 1 3 of the initially exported caco 3 reaching the deep seafloor pulsed flux events mass dumps of fast settling particles yield a major contribution of tests to the formation of deep sea sediments on average 25 of the initially produced planktic foraminiferal test cac0 3 settles on the seafloor the total planktic foraminiferal contribution of caco 3 to global surface sediments amounts to 0 36 0 88 gt yr 1 32 80 of the total deep marine calcite budget

detachment faults evidence for a low angle origin the origin of low angle normal faults or detachment faults mantling metamorphic core complexes in the southwestern united states remains controversial if sigma sub 1 is vertical during extension the formation of or even slip along such low angle normal faults is mechanically implausible no records exist of earthquakes on low angle normal faults in areas currently undergoing continental extension except from an area of actively forming core complexes in the solomon sea papua new guinea in light of such geophysical and mechanical arguments w r buck and b wernicke and g j axen proposed models in which detachment faults originate as high angle normal faults but rotate to low angles and become inactive as extension proceeds these models are inconsistent with critical field relations in several core complexes the rawhide fault an areally extensive detachment fault in western arizona propagated at close to its present subhorizontal orientation late in the tertiary extension of the region neither the wernicke and axen nor buck models predict such behavior in fact both models preclude the operation of low angle normal faults the authors recommend that alternative explanations or modifications of existing models are needed to explain the evidence that detachment faults form and operate with gentle dips

crustal structure of eastern nevada from cocorp deep seismic reflection data the western nevada segments of the cocorp 40 n deep seismic reflection survey of the north american cordillera reveal the geometry of structures of cenozoic and possibly earlier ages to travel times of 10 s corresponding to depths of 30 km the most striking feature of the data is a band of prominent reflections typically at traveltimes of 9 5 to 10 5 s that are present discontinuously across the entire data set few reflections are observed from beneath the base of this reflective zone which is interpreted as the crust mantle transition this reflection mono is inferred to be continuous across the survey area varying gradually in depth but without resolvable offsets it appears to have taken its present form or position during basin range crustal extension the middle to lower crust in much of the survey area is characterized by discontinuous reflections that are typically subhorizontal and locally dip gently west these reflections may represent intrusions or shear zones related to basin range or pre basin range extension but some are likely to be inherited from earlier compressional deformation reflections from the upper crust are interpreted as images of basin fill strata basin range normal faults and mesozoic and paleozoic thrusts related to back arc thrusting and accretion of oceanic and arc related rocks

structural features in a brittle ductile wax model of continental extension structural features produced during the rifting of continents depend on the layered rheological properties of the crust and lithosphere and in particular on the presence of any transitions between brittle and ductile behaviour1 here we use a wax model to explore the gross structural response of continental lithosphere under pure shear extension in the presence of a continuous brittle ductile transition the wax models were deformed under various boundary conditions to reflect a variety of different regions most notably the basin and range province of north america our experiments show the development of listric normal faults structures common to regions of continental extension we also observe the formation of distributed and discrete rifting and intrusion and occlusion of the upper brittle layer by the ductile lower layer the factor controlling deformation style in each case appears to be the relative thickness of the brittle and ductile layers although a relatively high rate of strain generally promotes discrete rifting

satellite and ship studies of coccolithophore production along a continental shelf edge each year since the coastal zone color scanner czcs 1 was launched on the nimbus 7 satellite in november 1978 extensive patches of water giving strong reflectance of visible light have been observed during the early summer along the outer margin of the north west european continental shelf between 45 and 60 n refs 2 3 various hypotheses including coccolithophores phytoplankton with external calcified plates or coccoliths were suggested to explain a comparable feature on landsat images for july 19774 to test these we report here observations made from french and uk research vessels in 1982 using unprocessed czcs images supplied by the university of dundee and centre de meteorologie spatiale in lannion to locate suitable sampling areas immediately before and during the cruise and atmospherically corrected data from the european space agency for subsequent analysis and calibration of the reflectance signals the high reflectance was found to be caused by a surface bloom of the widespread coccolithophore emiliania huxleyi lohm hay et mohler which also produced abundant detached coccoliths this finding is of relevance to recent work both on the ecology of coccolithophores5 including their importance in the sedimentation of biogenic carbon6 7 and lipids8 and in palaeoclimatic studies9 and on the development of reliable remote sensing techniques for the estimation of chlorophyll in oceanic waters10

calculation of coccolith volume and its use in calibration of carbonate flux estimates abstract estimates of coccolith volume help in determining total coccolith carbonate fluxes and the relative contributions of various coccolith species it is argued here that the best approach to deriving such coccolith volumes is to calculate shape factors k s for each species separately based on reconstruction of cross profiles and to determine mean sizes from measurement of size variation in the sample of interest then volume k s l 3 values of k s are given for the most important extant coccolith species based on reconstruction of cross sections followed by calculation of a volume of rotation using an iterative routine implemented in an image analysis package substantial errors ca 50 are inevitable in such calculations but the resultant data are nonetheless of value coccolith assemblages from north atlantic 47 n 20 w jgofs 1989 sediment trap samples are analysed as a test case calculated coccolith pic fluxes constitute 30 80 of the chemically determined total pic fluxes

the influence of lithogenic material on particulate inorganic carbon measurements of coccolithophores in the bay of biscay following earlier data suggesting a decoupling between coccolithophore abundance and its suggested proxy particulate inorganic carbon pic we investigated this relationship in the bay of biscay northwest european shelf between december 2009 and july 2010 coccolithophore abundance coccolith calcite and pic were determined in surface waters 5 m depth along a transect crossing the bay emiliania huxleyi was the most abundant species of coccolithophore and the main contributor of coccolith calcite 55 64 pic ranged from 0 07 to 11 7 mmol c m 3 and coccolith calcite from 0 002 to 0 27 mmol c m 3 total pic exceeded coccolith calcite in all samples with only 11 of the pic attributed to coccoliths coccolithophores alone could not account for the pic concentrations measured lithogenic particulate matter with calcite and dolomite components was observed in samples across the route and decoupled the relationship between pic and coccolithophore abundance presence of lithogenic material and mesozoic fossil coccoliths in the samples implies sediment resuspension these findings question the suitability of pic as a proxy for coccolithophore abundance and dynamics particularly on or near continental shelves where the resuspension and lateral transport of lithogenic calcite may decouple the potential relationship between pic and coccolithophores

timing and mechanisms of surface and intermediate water circulation changes in the nordic seas over the last 10 000 cal years a view from the north iceland shelf abstract the north iceland shelf bears essential components of the present surface and intermediate circulation of the northern north atlantic instrumental and historical data give evidence of the sensitivity of this domain to broad regional scale oceanic and atmospheric anomalies our investigation of the paleohydrological variability off northern iceland throughout the last 10 000 cal yr suggests that atmospheric forcing alone through combined changes in strength of the wind stress curl and sea level atmospheric pressure pattern over the nordic seas is sufficient to explain the recorded changes in origins and dynamics of surface and intermediate water masses our biotic proxies coccoliths and benthic foraminifera were extracted from a giant piston core md99 2269 collected in a shelf trough where sediment accumulated at an excess rate of 2 m kyr the mid holocene from 6 5 to 3 5 cal kyr bp was a time of peaked carbonate production and subsequent sedimentation and strong water column stratification with a thick layer of cold fresh arctic surface water overlapping an enhanced flow of irminger atlantic intermediate water applying conditions triggering present time carbonate plankton blooms in the studied area we infer that a lowered cyclonic activity associated with decreased winter storms and reduced production of arctic intermediate water in the iceland sea were conductive of the recorded mid holocene water column structure the opposite situation warm atlantic surface water low vertically integrated inflow of irminger water abutment of arctic intermediate water in deep shelf troughs characterized the early holocene as well as a shorter late holocene period centred at 2 cal kyr bp the little ice age ca 0 2 0 6 cal kyr bp and a short event at around 3 cal kyr bp stand as times of extreme advection of polar waters and extended sea ice development a comparison of the recorded long term holocene evolution of water column structure off northern iceland with climate and hydrological changes in the north eastern atlantic suggests that the strength of atlantic inflow into the nordic seas was subjected to a balance between the irminger and the norwegian branches this balance is thought to be mostly related to changes in the intensity and location of westerly winds and associated atmospheric pressure gradients in the north atlantic

modeling carbonate microfacies in the context of high frequency dynamic relative sea level and environmental changes discussion i would like to clear up some misconceptions stated by spence and tucker 1999 regarding steinhauff and walker 1995 and make some positive comments about the approach they used to document and interpret a mesozoic carbonate example from france spence and tucker 1999 explain that systems tracts described using standard microfacies e g wilson 1975 flugel 1982 fail to take into account gradual changes in the water depths occurring through changes in relative sea level they cite steinhauff and walker 1995 as an example illustrating the shortcomings of using microfacies to correlate a carbonate succession misconceptions readers are liable to draw three misleading conclusions after reading spence and tucker 1999 1 steinhauff and walker 1995 somehow misused ternary plots in characterizing the rocks that they studied spence and tucker 1999 p 948 describe how ternary plots may unwittingly break down compositional relays into a series of static temporal pin points implying that meaningful boundaries exist between individual

coccolithophorids on the continental slope of the bay of biscay production transport and contribution to mass fluxes abstract coccoliths collected by sediment traps deployed on the slope of the bay of biscay northeastern atlantic from june 1990 to august 1991 were examined to determine their contribution to the transport of carbonate on a mid latitude continental margin they also were used as tracers of particle transfer processes on this slope two traps located at 1900 m respectively at 2300 mooring site 1 and 3000 m mooring site 2 water depths provided high resolution 4 7 days time series samples covering a 14 month period at ms2 and a 3 month period at ms1 coccoliths from 28 species were identified over the course of the experiment among which emiliania huxleyi was always dominant relative abundance range 59 93 total coccoliths number fluxes were high but variable ranging from 390 106 to 1610 106 coccoliths m 2 day 1 at ms1 and from 58 106 to 1500 106 coccoliths m 2 day 1 at ms2 the time weighted mean flux calculated for the whole experiment at ms2 was 499 106 coccoliths m 2 day 1 estimate of coccoliths minimal contribution to total carbonate flux at 1900 m depth averaged 12 which represented a weighted mean flux of 7 3 mg m 2 day 1 2 7 g m 2 yr 1 lateral transport of coccoliths resuspended from shelf and or upper slope sediments seems to be the dominant transfer process to depth on this northeastern atlantic slope nevertheless the clear seasonal succession observed in the species composition implies that the deposition resuspension transport sequence is rapid presumably less than a few months several short and unsmoothed signals directly issued from coccoliths bloom events also were recorded in our traps a result that indicates rapid settling rates the overall coccolith sedimentation processes appear as being quite diversified but quantitative and qualitative analyses of aggregates collected by the traps suggest that they are important carriers of coccoliths in this margin environment

how normal faulting and sedimentation interact to produce listric fault profiles and stratigraphic wedges abstract in a series of scale experiments we generated listric normal faults by extending models composed of colored sand layers deposited at regular time intervals throughout deformation during syntectonic sedimentation progressive bulk extension along a single set of faults caused domino type tilting of fault blocks underlying tilted faults propagated upwards with constant dips into newly sedimented layers hence fault profiles become progressively more listric tilting of the free surface resulted in asymmetrical depressions and in fan shaped deposits stepwise or continuous geometric models of domino tilting and synchronous sedimentation yield the same structural and stratigraphic features as observed in the sand models the continuous geometric model shows that a critical parameter governing fault curvature is the ratio r between rates of bulk strain and sedimentation both types of models reveal that synchronous sedimentation and bulk extension are capable by themselves of generating listric normal faults

slope transport of suspended particulate matter on the aquitanian margin of the bay of biscay abstract spatial and temporal characteristics of the water masses and the dispersion of the suspended particulate matter were investigated using current meter hydrographic and nephelometric observations gathered during the ecofer experiment 1989 1991 in the cap ferret canyon on the aquitanian margin of the bay of biscay while characteristics of the deep water masses were stable from one year to another large hydrographic change in the upper 500 m related to winter renewal induced by poleward advection of warm and saline water along the continental slope the slope circulation and seasonal eddy activity appear as important dynamical mechanisms that control the entrainment and the dispersion of the suspended particulate matter from the neritic domain to the deep ocean a predominantly northward along slope current with occasional reversal characterizes this circulation the nephelometric structures also showed seasonal changes in the overall suspended particulate matter content but recurrent features such as the presence of intermediate nepheloid layers at the shelf break depth and various depths along the slope 500 1000 and 2000 m were observed these nepheloid layers extended off the slope to about 10 30 km but especially laterally along the slope their presence indicated that suspended particulate matter exchanges between the shelf and the slope occurred mainly in the head of the canyon and along the southern open slope the intermediate nepheloid layers around 500 m depth detached from the slope particularly in regions where the bottom slope is close to critical for the m2 internal tide

effects of acidification and primary production on coccolith weight implications for carbonate transfer from the surface to the deep ocean 1 the coccolithophores are not only an important group of oceanic primary producers they are also one of the main carbonate producers in the ocean because the calcium carbonate plates coccoliths secreted by these unicellular algae are so small and light a few picograms each they cannot be directly weighed with the result that very little is known about the effect of primary production and dissolution on the coccoliths using a new method that allows a rapid estimate of the weight of discrete coccoliths we analyzed the effect of dissolution the results of two acidification experiments using cultured and fossil coccoliths indicate that acidification does not change significantly the weight and size of coccoliths on the basis of these experiments we identify four parameters for identifying the effects of dissolution on a coccolith assemblage these parameters were applied in samples from two sediment trap time series taken at the same tropical atlantic site eumeli but separated by 2000 m water depth there was no evidence of increased dissolution with water depth between 250 and 2500 m this is indicative of the absence of dissolution of coccoliths between the photic zone and the lysocline other studies have identified supra lysoclinal dissolution and we propose that most of this takes place in the photic zone and possibly in the guts of grazers most of the coccolith weight changes observed over the duration of trap deployment were related to the occurrence of two coccolithophore blooms which resulted in significant increases in average coccolith weight of the dominant coccolithophore species during the blooms changes in growth rate and cell density appear to have a significant effect on the weight of coccoliths to test this observation we cultured e huxleyi at different p and n concentrations this test confirmed that coccoliths weigh more when coccolithophore production is highest an important consequence for the carbon pump is that during higher primary production events the coccoliths will increase the ballasting of the aggregates in which they are carried to the seafloor increasing the rate and amount of organic matter sequestered into the deep sea

last glacial fire regime variability in western france inferred from microcharcoal preserved in core md04 2845 bay of biscay abstract high resolution multiproxy analysis microcharcoal pollen organic carbon neogloboquadrina pachyderma s ice rafted debris of the deep sea record md04 2845 bay of biscay provides new insights for understanding mechanisms of fire regime variability of the last glacial period in western france fire regime of western france closely follows dansgaard oeschger climatic variability and presents the same pattern than that of southwestern iberia namely low fire regime associated with open vegetation during stadials including heinrich events and high fire regime associated with open forest during interstadials this supports a regional climatic control on fire regime for western europe through fuel availability for the last glacial period additionally each of heinrich events 6 5 and 4 is characterised by three episodes of fire regime with a high regime bracketed by lower fire regime episodes related to vegetational succession and complex environmental condition changes

fluxes and budget of on the continental margin of the bay of biscay northeastern atlantic abstract as part of the ecofer experiment ecomarge program jgofs france concentrations of the natural radionuclide 210 pb were measured in particulate matter collected by sediment traps deployed for a 14 month period june 1990 august 1991 on two mooring lines within the cap ferret canyon on the french continental slope of the bay of biscay northeastern atlantic 210 pb concentrations range 63 218 dpm g 1 and fluxes range 0 1 11 2 dpm cm 2 yr 1 displayed typical gradients increasing with depth at both mooring sites also at equivalent trap depths 210 pb activities were systematically higher on the deep slope mooring 3000 m compared to the shallow one 2300 m fluxes of 210 pb generally decreased seaward and exhibited temporal variations but with no marked seasonal trend essentially matching variations in total mass flux various correlations between 210 pb activities and major constituents of trapped particles were examined 210 pb activities were independent of the particle composition indicating that in this area scavenging of this nuclide from the water column was not directly tied to the quality of settling particles the 210 pb budget as determined by the balance of local supply flux and fluxes to sediment traps and sediments implies important lateral inputs to both mooring sites 65 89 of the flux measured by traps a feature typical of continental margin environments on the basis of annual mean 210 pb activity in traps of the two mooring sites two particle sources are hypothesized the first source located in shallow waters of the shelf and upper slope supplies the entire slope region the second source probably composed of resuspended particles from upper slope sediments feeds essentially the upper and intermediate slope region maximum sedimentation rates determined on seven box cores decreased with bottom depth from 0 3 to 0 4 cm yr 1 at the canyon heads down to 0 06 cm yr 1 at 3000 m a good agreement was observed at both mooring sites between 210 pb fluxes registered by the near bottom traps and excess 210 pb inventories within the underlying sediments suggesting that nuclide fluxes measured by traps during this experiment are representative of fluxes on a longer time scale 10 100 yr nevertheless total mass fluxes measured by traps were 3 4 times lower than 210 pb determined sediment accumulation rates a discrepancy that may be more apparent than real given the possible errors in the latter due to bioturbation

modern coccolithophore and carbonate sedimentation along a productivity gradient in the canary islands region seasonal export production and surface accumulation rates abstract coccolithophores one of the main primary and carbonate producers in the surface waters of the canary islands region were investigated to quantify coccolith and coccolith carbonate export fluxes and to determine possible trends in species composition related to different productivity conditions present day fluxes were compared to the long term records of coccolith and carbonate accumulation in holocene sediments underneath the mooring locations coccolithophore flux variations in sediment traps at three stations along an e w transect at approximately 29 n from the upwelling influenced north west african shelf region to the open ocean were recorded from january to september 1997 total coccolith fluxes along the studied transect were highly seasonal with pronounced sedimentation events occurring in february upper traps and march deep traps related to the winter phytoplankton bloom in surface waters while total coccolith flux rates and fluxes of different species at the two oceanic sites lp and estoc were comparable mean 6 4 and 5 4 10 8 coccoliths m 2 d 1 fluxes increased significantly towards the shallower site ebc mean 13 7 10 8 coccoliths m 2 d 1 this gradient points to increased productivity in surface waters at the near shore station probably associated with nutrient rich upwelling filaments detaching from the coast and or the easternmost islands additionally a strong influence of laterally advected coccolith rich material was demonstrated for the deeper sediment traps at the two offshore sites resulting in an increase of mean daily coccolith fluxes by a factor 3 lp and by a factor 2 estoc respectively estimated coccolith carbonate fluxes along the transect were 2 8 g m 2 ebc and 1 2 1 3 g m 2 estoc lp in the upper traps representing 31 33 of the total annual carbonate flux the coccolith carbonate supply was higher in the deeper traps with 63 at lp and 44 at estoc respectively average holocene coccolith and coccolith carbonate accumulation rates derived from surface samples at the mooring locations generally confirm the sediment trap results discrepancies mainly result from near bottom and down slope particle transfer processes which especially influence the site closer to the shelf dissolution processes are likely to affect primarily the deep sediments at the oligotrophic site lp the diverse subtropical coccolithophore assemblages were quite similar in all sediment trap samples from the three mooring sites with three species emiliania huxleyi florisphaera profunda gephyrocapsa ericsonii contributing significantly to the assemblage despite the good correspondence between the assemblage compositions along the transect some trends towards the upwelling influenced site ebc could be observed whereas all gephyrocapsa species mainly g ericsonii respond positively to higher productivity conditions at the near shore station calcidiscus leptoporus and the deep photic zone species f profunda increased in mean relative abundances towards the two offshore sites pointing to a preference for the more stable oligotrophic conditions of the subtropical gyre

rift structure of the northern mississippi embayment from the analysis of gravity and magnetic data gravity and magnetic data have been simultaneously inverted to derive a crustal model of the northern mississippi embayment which is compatible with geologic and seismic refraction data the results indicate that this region is a site of a late precambrian early paleozoic rift system an anomalously dense layer is present at the base of the crust and thickens beneath a broad northeast trending graben that formed during the initial phases of rifting the thickest part of anomalous crust occurs beneath the region of greatest seismic activity which lies within the geographic limits of the graben it is suggested from this correlation that strain accumulates within the anomalous crust layer which acts as an inhomogeneity in a relatively homogeneous lithosphere based on the results of this study and previous geophysical studies the complex tectonic evolution of the upper mississippi embayment since late precambrian time is rift formation possibly along a pre existing shear zone graben development in cambrian time reactivations in permian and cretaceous time and subsequent formation of the present mississippi embayment and fault zones with large influences from rift structures

the impact of calcareous nannofossils on the pelagic carbonate accumulation across the jurassic cretaceous boundary abstract calcareous nannofossils were important producers of pelagic carbonates in mesozoic oceans in order to better understand the origin of mesozoic pelagic carbonates we studied upper jurassic to lower cretaceous sediments in the central atlantic ocean dsdp sites 105 367 534a with respect to their content of calcareous nannofossils the interval under investigation is characterized by a significant increase in the deposition of carbonate rich sediments a trend that goes along with the rapid radiation of calcareous nannofossils the assemblage composition and the size variation of common taxa were analyzed and subsequently the contribution of this phytoplankton group to the pelagic carbonate accumulation was calculated results reveal two long term changes of the nannofossil assemblage composition 1 the early tithonian coccolith assemblages are of low diversity watznaueria spp cyclagelosphaera spp zeugrhabdotus spp whilst the mid to late tithonian assemblage is dominated by nannoliths conusphaera mexicana polycostella beckmannii nannoconus spp and large sized watznaueria 2 the early berriasian is characterized by a shift from the late tithonian nannolith rich assemblage to a highly diverse coccolith assemblage morphometric studies of the placolith genus watznaueria show for all three dsdp sites large sized forms of this genus in the mid and late tithonian followed by a decrease of up to 2 m for the mean size in the earliest berriasian at dsdp site 105 the studied nannolith taxa show an increase in size during the mid tithonian to berriasian interval the records of both nannofossil carbonate estimates and the measured bulk rock carbonate reveal two periods of increase in the nannofossil carbonate record of dsdp site 105 a first significant increase of the carbonate accumulation is observed in the mid and late tithonian probably caused by mass occurrences of strongly calcified taxa c mexicana p beckmannii nannoconus spp watznaueria cf manivitae this interval is here named nannofossil calcification event nce the second carbonate maximum in the late berriasian is related to a rise in absolute abundances of nannofossils this peak is amplified by an overall increase of the sedimentation rate the calculated accumulation rates of nannofossils nannofossil carbonate and bulk rock carbonate for the late berriasian are on the same scale as values from recent ocean surface sediments a comparison of nannofossil carbonate values with the bulk rock carbonate content shows that on average only 27 of the total carbonate can be explained by our nannofossil carbonate estimates this discrepancy is most likely caused by the high amount of unidentifiable micrite and fragments of calcareous nannofossils other factors contributing to the error are possible inaccuracies in the determination of absolute abundances and nannofossil volume calculations the nce occurs during a long term sea level fall dry climate and presumed low pco 2 levels a decline in abundance of strongly calcified nannofossils coincides with the opening of the pacific atlantic seaway via central america which may have had a substantial impact on the palaeoceanographic situation in the central atlantic ocean these changes are here considered to have at least partly caused the shifts in abundance size and assemblage composition of calcareous nannofossils observed across the jurassic cretaceous boundary interval

stable oxygen and carbon isotopes of live benthic foraminifera from the bay of biscay microhabitat impact and seasonal variability we determined the stable oxygen and carbon isotopic composition of live rose bengal stained benthic foraminifera n150 am size fraction of seven taxa sampled along a downslope transect between 140 to 2000 m water depth in the bay of biscay at the five stations hoeglundina elegans cibicidoides pachydermus uvigerina peregrina uvigerina mediterranea preferentially occupy shallow infaunal niches whereas melonis barleeanus and uvigerina elongatastriata occupy an intermediate infaunal microhabitat and globobulimina spp live in a deep infaunal niche close to the zero oxygen boundary when compared with d 18 o values of calcite formed in equilibrium with bottom waters u peregrina forms its test in close equilibrium with bottom water d 18 o all other foraminiferal taxa calcify with a constant offset to calculated equilibrium calcite there is no systematic relationship between the foraminiferal microhabitat depth and the dd 18 o between foraminiferal and equilibrium calcite we calculated correcting factors for the various taxa which are needed for constructing multispecies based oxygen isotope records in paleoceanographic studies of the study area the d 13 c values of foraminiferal taxa investigated in this study do neither record bottom water d 13 cdic in a 1 1 relationship nor with a constant offset but appear to be mainly controlled by microhabitat effects the increase of d 13 c values of shallow infaunal taxa with increasing water depth reflects the decrease of the exported flux of organic carbon along the bathymetric transect and early diagenetic processes in the surface sediment this is particularly the case for the shallow infaunal u peregrina the d 13 c values of deep infaunal globobulimina spp are much less dependent on the exported organic matter flux we suggest that the dd 13 c between u peregrina and globobulimina spp can shed light on the various pathways of past degradation of organic detritus in the benthic environments at a station in 550 m water depth where periodic eutrophication of sediment surface niches was demonstrated previously we performed a two year seasonal survey of the isotopic composition of foraminiferal faunas no marked seasonal changes of the stable carbon isotopic composition of shallow intermediate and deep infaunal foraminiferal taxa were observed thus the d 13 c values of foraminiferal individuals belonging to the n150 am fraction may result from rather long term calcification processes lasting for several weeks or months which limit the impact of ephemeral 12 c enrichment of shallow infaunal niches on the isotope chemistry of adult individuals during eutrophic periods only highly opportunistic taxa reproducing or calcifying during

low angle normal faults and seismicity a review although large low angle normal faults in the continental crust are widely recognized doubts persist that they either initiate or slip at shallow dips 30 because 1 global compilations of normal fault focal mechanisms show only a small fraction of events with either nodal plane dipping less than 30 and 2 andersonian fault mechanics predict that normal faults dipping less than 30 cannot slip geological reconstructions thermochronology paleomagnetic studies and seismic reflection profiles mainly published in the last 5 years reinforce the view that active low angle normal faulting in the brittle crust is widespread underscoring the paradox of the seismicity data for dip slip faults large enough to break the entire brittle layer during earthquakes m w 6 5 consideration of their surface area and efficiency in accommodating extension as a function of dip suggests average recurrence intervals of earthquakes r tan assuming stress drop rigidity modulus and thickness of the seismogenic layer do not vary systematically with dip if the global distribution of fault dip normalized to total fault length is uniform the global recurrence of earthquakes as a function of dip is shown to be r tan sin this relationship predicts that the frequency of earthquakes with nodal planes dipping between 30 and 60 will exceed those with planes shallower than 30 by a factor of 10 in good agreement with continental seismicity assuming major normal faults dipping more than 60 are relatively uncommon revision of andersonian fault mechanics to include rotation of the stress axes with depth perhaps as a result of deep crustal shear against the brittle layer would explain both the common occurrence of low angle faults and the lack of large faults dipping more than 60 if correct this resolution of the paradox may indicate significant seismic hazard from large low angle normal faults

sinking of coccolith carbonate and potential contribution to organic carbon ballasting in the deep ocean abstract there exists a great need to better understand the controls on organic carbon sequestration to the deep sea by virtue of its role in modulating atmospheric co 2 concentrations recent studies suggest that organic fluxes to the oceanic interior are higher in regions dominated by carbonate sedimentation thus also concluding that relatively heavy carbonate particles are an effective mineral ballast for organic carbon caco 3 production in the pelagic ocean is mainly mediated by foraminifera and coccolithophores but the precise role of these carbonate producers as mineral ballast for organic carbon in the ocean has not yet been tested here we evaluate sediment trap flux data from an array of 13 moorings 15 traps situated in diverse conditions and with global coverage all for organic carbon flux calculated coccolith carbonate flux and fine fraction flux when available discrepancies are recorded between the amount of carbonate fine fraction and calculated coccolith carbonate and there is the need to determine the origin of the unknown caco 3 in the fine fraction the coccolith carbonate flux magnitude is determined not only by the coccolith flux number but also by the carbonate mass of the key species for example very abundant coccolithophore species such as emiliania huxleyi have a very low species specific carbonate mass and are therefore of lower carbonate flux significance than expected intuitively among the main coccolith carbonate species contributors in our sediment trap sites are calcidiscus leptoporus and helicosphaera carteri in that these are all relatively massive compared to their numerical abundances we observed generally positive correlations between calculated coccolith carbonate and organic carbon daily fluxes suggesting that on a global basis there is a ballasting mechanism at work seemingly most efficiently with c leptoporus in the carbonate dominated north atlantic a fairly constant global relationship between annual fluxes of calculated coccolith carbonate and organic carbon implies some uniformity in the pic poc rain ratio however improvements in coccolith carbonate estimation are needed to not only understand this ratio currently but also to help understand future sequestration of organic carbon to the oceanic interior

the fate of coccoliths at 48 n 21 w northeastern atlantic abstract as part of the joint global ocean flux study program jgofs north atlantic bloom experiment nabe coccolithophore fluxes were recorded over one year period from april 1989 to april 1990 three vertically moored sediment traps synchronized on a 14 day interval were deployed at 48 n 21 w at three water depths at 1 2 and 3 7 km sea floor at 4 4 km we present the results on the vertical variability of coccolith and coccosphere fluxes through the water column calcium carbonate was the largest component of the total mass flux followed by particulate organic matter and opal coccolith and coccosphere seasonal fluxes followed the seasonality of the biogeochemical particle fluxes at all three depths with maxima occurring during the spring particle bloom the decrease in correlation between coccosphere and coccolith fluxes with depth from r 0 98 at 1 km depth to 0 60 at 3 7 km depth documents that disaggregation of the coccospheres occurs during settling in the deeper part of the water column between 1 and 3 7 km water depth annual coccosphere and coccolith fluxes were 1 5 108 and 0 9 10 11 m 2 year 1 respectively at 1 km depth or 3 1 108 and 1 4 10 11 m 2 year 1 including the spring 1990 episode for the 3 7 km trap the corresponding values were 0 5 108 and 1 1 1011 0 6 108 and 1 1 1011 including the partially recorded spring 1990 episode the slight increase in coccolith numbers with water depth can be explained by coccosphere disintegration and lateral influx nevertheless selective dissolution of delicate coccolith species from 1 to 3 7 km water depth occurs e g relative abundances of oolithothus fragilis coccoliths decrease from 3 at 1 km to less than 0 5 at 3 7 km water depth emiliania huxleyi gephyrocapsa muellerae calcidiscus leptoporus and coccolithus pelagicus constitute from 65 at 1 km depth to 95 at 3 7 km depth of the total coccolith assemblages the same four coccolith taxa dominate the fossil assemblages in the underlying surface sediments selective dissolution continues in the sediments most notably the abundance of the solution resistant species c leptoporus increases from 10 to 15 in the trap samples to 15 40 in the sediments annual flux of calcium carbonate in sediment trap samples accounts for about 60 of the total annual mass flux with the coccolith fraction m being about 45 of the annual carbonate flux mean value of 41 at 1 km and 50 at 3 7 km water depth the correlation between the m caco 3 and the calculated coccolithophore and calcisphere caco3 fluxes decreases with depth r 0 92 at 1 km and r 0 86 at 3 7 km indicating that partial dissolution and fragmentation of the delicate less calcified coccolithophore and planktic foraminifera species occurs during settling this fine fragmentation of biogenic caco3 can contribute to the m fraction causing the decrease of correlation with the calculated caco3 fluxes being based only on the flux of intact coccoliths and calcispheres

coccolithophore fluxes from sediment traps in the northeastern arabian sea off pakistan abstract we investigated coccolithophore fluxes from four sediment traps located in the northeastern arabian sea at the continental slope of pakistan two moorings wpt and ept western isastern pakomin trap consisting of one and two sediment traps were deployed at water depths of about 500 m and 1500 m they collected settling particles from october 1993 to february 1994 and from may 1995 to february 1996 at intervals of 22 and 24 days respectively a longer sampling was prevented probably due to high sedimentation events which occluded the trap cones both areas were characterised by a strong seasonality in coccolith fluxes high fluxes were recorded with up to 2000 10 6 coccoliths m 2 d 1 in the early sw summer monsoon and up to 5400 10 6 coccoliths m 2 d 1 in the early ne winter monsoon generally coccosphere fluxes exhibited a similar trend but were some orders of magnitude lower than coccolith fluxes twenty seven taxa were identified in this study all well to moderately well preserved and with a small range of diversity the species composition was dominated by gephyrocapsa oceanica florisphaera profunda and emiliania huxleyi making up about 70 of the assemblages during the sw summer monsoon high productivity in the surface waters of the eastern arabian sea may be linked to the upwelling system off oman apparently nutrient rich surface water derived from the southwestern upwelling areas off oman with high standing stocks were carried into this area by northeast flowing currents in contrast during the ne winter monsoon the locally observed high coccolithophore production is hypothesised to respond to local injections of nutrient rich deep water into the surface water due to sea surface cooling leading to convection consequently fluxes during the winter monsoon were in the same range as during the summer monsoon

reconstructing calcification in ancient coccolithophores individual coccolith weight and morphology of coccolithus pelagicus sensu lato we have adapted an existing method to estimate coccolith calcite weight using birefringence beaufort 2005 to suit the large coccoliths of coccolithus pelagicus which are only partially birefringent under cross polarised light microscopy fossil and sediment trap material from the south tasman rise region of the southern ocean was used for calibration and validation our approach was tested with only the coccolith central area ca considered for measurement to avoid relying on the less robust proximal shields thus our results are relative and intend to quantify intra specific variations in volumetric calcite weight expressed as a weight index wi our results were overall consistent with mass estimation based on distal shield lengths however the wi approach clearly has the advantage in exploring allometric scaling between coccolith size and weight as well as in measuring the degree of calcification in similarly sized morphotypes combining wi and morphometry data distal shield length dsl we demonstrate subtle but statistically significant changes in shape and thus calcification degree both within and between the tested coccolithus populations most strikingly it appears that modern coccolithus populations in the southern ocean are on average more heavily calcified than their fossil counterparts

modeling carbonate microfacies in the context of high frequency dynamic relative sea level and environmental changes sequence stratigraphic models are used to interpret stratal architecture and key stratal bounding surfaces in ancient carbonate platforms within the context of changing accommodation space during third order relative sea level cycles however individual systems tracts are still described using standard microfacies that give a snapshot of limestone composition but they do not take into account gradual changes in the marine environment resulting from variations in water depth during the cycle of relative sea level change water depth is the single most significant collective control on a wide range of environ mental gradients affecting carbonate sediment composition during dy namic relative sea level fluctuations stratigraphic changes in carbonate sediment composition are characterized by systematic shifts in the rel ative importance of different limestone component grain types forming temporal continuums or relays relays are detected using computer optimized jaccard s similarity coefficient matrices to analyze presence absence compositional data individual relays between grain types may link together samples that are generically unrelated to one another but are nevertheless genetically related to deposition during the same uni directional dynamic environmental gradient a stratigraphic relay identified within the basal beds of the mid cretaceous urgonian carbonate platform succession of se france re cords unidirectional environmental gradients linked to changing water depth characteristic of a transgressive systems tract periods of static water depth such as the keep up phase of a late highstand systems tract at the top of the urgonian carbonate platform succession are characterized by fixed compositional assemblages stratigraphic breaks between individual compositional relays and assemblages occur at in flections in changing water depth marking the boundaries between individual systems tracts and sequences currently identified using stra tal geometries and key stratal surfaces the use of relays to model microfacies and identify individual system tracts and sequence boundaries has several advantages over existing methods this approach can be used where key stratal surfaces are difficult to distinguish such as in planar and concordantly bedded inner platform settings and in arid depositional environments where physical evidence of subaerial platform exposure such as karstification is poorly developed the technique can also be used to determine the genetic significance of unconformities preserved in outcrop or core within a sequence stratigraphic context by differentiating unconfor mities formed at the extremes of relative sea level cycles from those formed by other abrupt acyclical environmental changes

nannofossil carbonate fluxes during the early cretaceous phytoplankton response to nutrification episodes atmospheric co2 and anoxia 1 greenhouse episodes during the valanginian and aptian correlate with major perturbations in the c cycle and in marine ecosystems carbonate crises and widespread deposition of corg rich black shales quantitative analyses of nannofossil micrite were conducted on continuous pelagic sections from the southern alps northern italy where high resolution integrated stratigraphy allows precise dating of early cretaceous geological events rock forming calcareous nannofloras were quantified in smear slides and thin sections to obtain relative and absolute abundances and paleofluxes that are interpreted as the response of calcareous phytoplankton to global changes in the ocean atmosphere system increased rates of volcanism during the formation of ontong java and manihiki plateaus and the parana etendeka large igneous province lip are proposed to have caused the geological responses associated with early aptian oceanic anoxic event oae 1a and the valanginian event respectively calcareous nannofloras reacted to the new conditions of higher pco2 and fertility by drastically reducing calcification the valanginian event is marked by a 65 reduction in nannofossil paleofluxes that would correspond to a 2 3 times increase in pco2 during formation of the parana endenteka lip a 90 reduction in nannofossil paleofluxes which occurred in a 1 5 myr long interval leading into oae1a is interpreted as the result of a 3 6 times increase in pco2 produced by emplacement of the giant ontong java and manihiki plateaus high pco2 was balanced back by an accelerated biological pump during the valanginian episode but not during oae1a suggesting persisting high levels of pco2 in the late aptian and or the inability of calcareous phytoplankton to absorb excess pco2 above threshold values

controls on stable strontium isotope fractionation in coccolithophores with implications for the marine sr cycle abstract the controls on stable sr isotope fractionation into the calcite produced by the coccolithophore species emiliania huxleyi coccolithus pelagicus spp braarudii and gephyrocapsa oceanica are investigated each species has been cultured under controlled laboratory conditions at a range of temperatures 10 25 c to test the potential of 88 86 sr as a proxy for growth rate and or sea surface temperature coccolithophores are one of the most abundant pelagic calcifiers since sr substitutes to some degree for ca in their calcite coccoliths coccolithophores represent a significant output of sr from seawater potentially influencing the 88 86 sr mass balance in the modern oceans the coccoliths are investigated for their 88 86 sr sr ca and 18 o measured as function of temperature as temperature is increased all species show a negative stable sr isotopic fractionation related to a temperature controlled growth rate we infer the shift of 88 86 sr to lighter values as indicative of a kinetic control on the isotope fractionation revealing the potential of 88 86 sr as a proxy for growth rate which in these experiments is primarily dictated by temperature the results from these experiments indicate that coccolithophore calcite incorporates sr with a very light 88 86 sr isotope composition as low as 0

coccolithophore export production species composition and coccolith caco3 fluxes in the ne atlantic and abstract coccolithophores were examined in two sediment traps deployed for one year april 1989 to april 1990 at approximately 1 km water depth in the subtropical ne atlantic at 34 n 21 w station nabe 34 and in the temperate ne atlantic 48 n 21 w station nabe 48 as part of the jgofs north atlantic bloom experiment nabe at both stations maximum coccolith and coccosphere fluxes were recorded during local spring bloom periods the average coccolith and coccosphere fluxes at nabe 34 were 1 12 10 9 m 2 d 1 and 4 90 10 6 m 2 d 1 respectively at this station coccoliths from 51 taxa were identified a marked seasonal change was noticed in relative abundances of emiliania huxleyi and deep photic zone species e huxleyi dominated during spring while in late autumn the coccolith assemblage was dominated by florisphaera profunda and the coccosphere assemblage by g flabellatus and algirosphaera spp emiliania huxleyi was the most abundant species in the overall coccolith and coccosphere assemblages with 69 and 64 respectively at nabe 48 the average daily fluxes were significantly lower with 3 88 10 8 coccoliths m 2 d 1 and 8 45 10 5 coccospheres m 2 d 1 and only 36 taxa were recorded in the trap samples emiliania huxleyi was the dominant species in the coccolith assemblage throughout the year with 72 and showed maximum fluxes during spring 1990 coccolithus pelagicus exhibited a distinct seasonal pattern with maximum fluxes in early june 1989 probably related to the development of a mesoscale cyclonic eddy in the vicinity of the trap site holococcolithophore fluxes were highest during maximum sea surface temperatures in summer the coccosphere assemblage was dominated by gephyrocapsa spp syracosphaera spp and e huxleyi estimated caco3 fluxes of coccoliths coccospheres and calcareous dinophytes were compared with the caco3 content in the fine m fraction the annual mass estimated caco3 flux of coccoliths and coccospheres was 5 1 g m 2 yr at nabe 34 and 2 7 g m 2 yr at nabe 48 and that of calcareous dinophytes 0 9 and 0 1 g m 2 yr respectively these summed mass estimated values contributed on average only 55 at nabe 34 and 60 at nabe 48 to the fine fraction caco3

coccolithophore export production during the 1997 1998 el nino event in santa barbara basin california the response of coccolithophore export production to non el nino and el nino conditions was monitored during a two year period 26 march 1996 3 april 1998 in the centre of the santa barbara basin 34 14 n 120 02 w california borderland during the 1997 1998 el nino the seasonal cycle of the surface water conditions was altered by the presence of a relatively warm low nutrient and low salinity water mass throughout the studied period the total mass flux is dominated by lithogenic components with terrigenous input being highest during el nino period although the annual biogenic sediment fluxes were largely dominated by silica with diatoms as the major contributor to the opal flux the coccolith flux was high during the entire studied period during winter 1998 carbonate fluxes were unusually high for this time of the year moreover a strong positive correlation between organic carbon and opal flux indicates that siliceous phytoplankton production is the most important factor controlling organic carbon flux in the santa barbara basin a positive correlation between carbonate and organic carbon fluxes existed indeed during the final phase of el nino when the correlation between organic carbon and opal fluxes is poor the sinking coccolithophore assemblage was dominated by emiliania huxleyi followed by florisphaera profunda umbilicosphaera sibogae gephyrocapsa oceanica helicosphaera carteri gephyrocapsa muellerae and calcidiscus leptoporus the intensification of el nino 1997 1998 conditions altered the typical hydrographic structure of the santa barbara basin weakening the spring upwelling as reflected by reduced diatom fluxes in contrast the coccolith flux was relatively high during el nino particularly for the tropical species g oceanica that showed a pronounced increase in its flux when the spring upwelling was reduced under el nino conditions in addition we have found that this species has a strong correlation with nitrite phosphate and iron availability in surface water

export production of coccolithophores in an upwelling region results from san pedro basin southern california borderlands a seven month long time series sediment trap project was carried out in san pedro basin southern california borderlands in order to evaluate the response of calcareous nannoplankton to seasonal hydrographic changes this region is periodically influenced by upwelling particularly during the spring and early summer the highest fluxes of both whole coccospheres and individual coccoliths occurred during winter january february a period when the fluxes of diatoms and planktic foraminifera were low the highest coccolithophore fluxes were recorded in the mid february with 860 106 coccoliths m 2 day 1 8 106 whole coccospheres m 2 day 1 and 80 mg of coccolith carbonate m 2 day 1 coccolith carbonate fluxes in january and february account for most of the total carbonate fluxes measured during this period the season of maximum coccolithophore production in this region winter is correlated with weak stratification of the upper water column low total primary production low nutrient contents and low temperatures emiliania huxleyi and florisphaera profunda are the two most abundant species in this region while e huxleyi displays no distinct seasonal changes in flux f profunda shows a clear preference for cold low nutrient water conditions and low light levels helicosphaera spp flux is positively correlated to the total coccosphere fluxes and is indicative of high coccolithophore productivity

recognizing exposure drowning and missed beats platform interior to platform margin sequence stratigraphy of middle ordovician limestones east tennessee stratigraphic sequences in a middle ordovician platform interior carbonate succession steinhauff and walker in press are correlated to the platform margin surfaces of subaerial exposure are correlated among seven stratigraphic sections four from the platform succession and three from platform margin rocks surfaces of subaerial exposure define stratigraphic sequences within a carbonate succession that shows little evidence of cyclicity in the field interpretation of carbonate facies geometry is based on outcrop observation petrographic and geochemical analysis of samples and consideration of paleobathymetric curves in the platform succession most sequences are bounded by exposure surfaces but in more continuously subtidal areas periods of shallowing and drowning are discerned in bathymetric curves on the basis of multiple lines of evidence exposure surfaces are evidenced by subjacent meteoric cements or other features indicating exposure such as truncated marine cements vuggy porosity with vadose silt and pendant cements or mud cracks at some localities a marked shallowing event correlates to exposure elsewhere in subtidal sediments drowning is indicated by the lack of shallow water physical sedimentary features and water depth curves based on multiple lines of evidence including the presence of red algae thin shelled eyeless trilobites delicate arborescent bryozoa and deposit feeding organisms evidence for drowning unconformity is in some cases provided by cephalopod rich black to blood red limestone beds rich in iron and manganese oxides and occasionally by corroded surfaces encrusted with these minerals we have referred to the succession as apparently noncyclic because evidence for exposure and shallowing is subtle and is not always observable in the field nonetheless these strata show fourth order subsequences that can be grouped into third order sequences by the existence of pronounced and less pronounced exposure surfaces pronounced surfaces of exposure are those that overlie fenestral mudstones that contain exposure features such as crystal silt and calcite cement in vugs lined by reddish crusts and are truncated by deeper water lithologies for example seven pronounced surfaces of subaerial exposure define six third order sequences 10 50 m thick on the platform near thorn hill tennessee within the lower four third order subsequences 19 less pronounced surfaces showing fewer exposure features are present in approximately 400 m of section these surfaces define fourth order subsequences that are correlative from place to place in the platform succession many but not all of these platform fourth order subsequences can be correlated to the platform margin also some fourth order subsequences are present only at the platform edge fifth order meter scale packages or parasequences are present within these fourth order sequences but are not correlative over wide areas as are the other sequences most are probably the result of migration of lateral environments geometries unlike those of siliciclastic sequences result where condensed sections or deepening events are followed by exposure in this carbonate succession the sequences defined here constitute shallowing upward packages that are then a type of cycle these are used to construct modified fischer plots for both the platform interior and platform margin stratigraphic successions surfaces of subaerial exposure are correlated from the platform to the platform margin by matching pronounced exposure surfaces and deepening events shown in water depth curves for the platform with pronounced exposure surfaces and deepening or shallowing events at the platform margin this analysis provides several possible solutions the most conservative of which suggests that some sequences or cycle beats are missing beats are missed in three ways 1 sea level remains near the platform margin causing deposition to be restricted to that area 2 tectonic uplift exposes the platform interior but not platform margin areas until subsidence allows resubmergence and 3 drowning carries platform margin areas to depths precluding carbonate deposition there though sediment does accumulate on the platform in cases 1 and 2 the missed beats would be on the platform but in case 3 they would be at the platform margin

population dynamics of living planktic foraminifers in the hemipelagic southeastern bay of biscay abstract population dynamics of planktic foraminifer species are discussed in relation to environmental factors across the continental slope onto the shelf of the southeastern bay of biscay along a bathymetric transect from 2000 m to 145 m water depth 154 vertical plankton tows were obtained during different seasons on five cruises between june 2006 and july 2008 the distribution of live specimens 100 m sampled at distinct intervals down to 700 m water depth is compared to changes in temperature salinity and chlorophyll a concentration the overall seasonal variability and depth distribution of species in the hemipelagic southeastern bay of biscay has been similar to open ocean faunas in the pelagic north atlantic each species examined occurred at considerable variability in habitat depth and seasonal distribution the vertical distribution of planktic foraminifer species was mainly driven by the depth of the deep chlorophyll maximum dcm and hence linked to the development of the thermocline the seasonal variation of river discharge could have had differential effects on the distribution of planktic foraminifers and may have inhibited or triggered the production of species low standing stocks at onshore stations in spring and high standing stocks in july both in low saline waters indicate that salinity in itself did not control the distribution of planktic foraminifers instead factors which co vary with salinity such as turbidity and organic matter possibly affected the distribution of planktic foraminifers on a species specific scale in general the distribution of planktic foraminifer species on a seasonal vertical and regional scale along the offshore onshore transect was related to surface water salinity and turbidity and to the availability of food

coccolithophore export production in guaymas basin gulf of california response to climate forcing abstract the flux and taxonomic composition of coccolithophores has been determined for sediment trap samples collected over a two year period from guaymas basin central gulf of california the gulf of california is a subtropical marginal sea with exceptionally high rates of primary productivity the annual biogenic sediment fluxes are largely dominated by silica with diatoms as the major contributor to the opal flux for the july 1990 through november 1992 study period the total coccolithophore export production in guaymas varied in response to the strength of el nino southern oscillation enso coccolithophore production follows the general surface primary productivity pattern with relatively high fluxes from late fall to late winter and low production in the summer when the water column is highly stratified and nutrient depleted high fluxes of up to 10 9 coccoliths m 2 day 1 and 3 10 6 coccospheres m 2 day 1 indicate that coccolithophores are an important component of the phytoplankton population in guaymas basin the intensification of enso conditions during 1992 altered the typical hydrography of the gulf of california by increasing sst and reducing the strength of spring upwelling this is reflected in reduced opal and diatom fluxes during this period conversely these more oligotrophic conditions resulted in higher total coccolithophore fluxes during spring and summer 1992 gephyrocapsa oceanica is present in the gulf throughout the study period but is dominant during weak or non enso times emiliania huxleyi and to a lesser degree florisphaera profunda are abundant during strong enso periods two major coccolithophore signals are indicative of strong enso conditions and could be used as paleo enso indicators in the gulf of california a the switch in dominance between g oceanica and e huxleyi and b high abundances of the deep dwelling species f profunda the abundance of this latter species shows a strong inverse relationship with opal fluxes a comparison of the annual coccolith flux with coccolith accumulation rates in the surface sediments indicates that only about 10 20 of the coccolith export production is preserved in the anoxic sediments of guaymas basin this very low level of preservation is probably due to bacterial processes on the sea floor which cause acidification of the bottom waters at the sediment water interface coccolith accumulation rates are higher in surface sediments from the western coast of the central gulf suggesting both higher coccolithophore production and better preservation in this region probably associated with lower diatom production tintinnids which agglutinate coccoliths are strongly selective for both coccolith size and species

origin of regional rooted low angle normal faults a mechanical model and its tectonic implications rooted listric low angle normal faults 20 of regional extent have been recognized widely in the past few years in the north american cordillera and elsewhere the low angle geometry of these crustal scale normal faults conflicts with anderson s 1942 classic theory of faulting in that theory the orientations of principal stresses are assumed to be vertical and horizontal the predicted dip angle of normal faults is about 60 rather than 20 or less recent geological and geophysical studies in the mid tertiary extensional terrane of southeastern california and western arizona suggest that thick mylonitic gneisses in the lower plates of low angle detachment faults may represent unidirectionally sheared laminar flow in and below the midcrust directed ductile flow possibly related to the gravitational spreading of thickened lower crust may induce a shearing traction on the horizontal or subhorizontal base of the brittle upper crust thus the orientations of the principal stresses can no longer be vertical and horizontal at this interface a simple elastic model incorporates the effect of basal shearing due to gravitational spreading on stress distributions in an elastic upper crust this model shows that parallel belts of compression and extension can be produced if a shearing traction acting on the base of the elastic upper crust is considered in particular appropriate stress conditions for the formation of regional low angle normal faults 20 can be produced by the superposition of two stress fields a basal shear stress field induced by the basal shear traction and a contractional stress field in which the horizontal deviatoric stress is compressional and the vertical gradient of the horizontal normal stress component is constant this superposed stress field may represent a tectonic setting where a stress field with compressional deviatoric stress induced by plate subduction or convergence is superposed on a basal shear stress field induced by gravitational spreading of thickened lower crust these results may explain both puzzling parallel belts of extension and compression and the occurrence of major low angle normal faults in some orogenic systems

the origin of large local uplift in extensional regions large localized uplift is commonly observed in continental regions undergoing extension these observations can be modelled by planar high angle normal faulting of an elastic upper crust overlying an inviscid lower crust isostasy provides the necessary driving force the model quantifies the role of flexural rigidity density variations in the crust and erosion and deposition of sediment