earthquake mechanisms of the adriatic sea and western greece implications for the oceanic subduction continental collision transition summary we present 21 focal solutions magnitude 5 5 reliably computed by body wave modelling for the western hellenic arc from yugoslavia to the southern peloponnese mechanisms located within the aegean show normal faulting the t axis trending n s in the centre and parallel to the active boundary in the external part mechanisms associated with the keffalinia fault are consistent with dextral strike slip motion reverse mechanisms located along the active boundary are remarkably consistent and do not depend on the nature of the active boundary continental collision or oceanic subduction the consistency in azimuth of the slip vectors and of the gps velocity relative to africa all along the active boundary suggests that the deformation is related to the same motion the discrepancy between seismic energy release and the amount of shortening confirms that the continental collision is achieved by seismic slip on faults but the oceanic subduction is partially aseismic the northward decrease in velocity between continental collision and oceanic subduction suggests the continental collision to be a recent evolution of the active subduction

fault generated mountain fronts in southeast spain geomorphologic assessment of tectonic and seismic activity abstract tectonic activity of se spain is evaluated through the application of a general morphometric analysis over 17 different mountain fronts the selected fronts are distributed along the two most prominent crustal scale structures of the mediterranean sector of spain the eastern betic shear zone ebsz and the valencia trough geomorphic indexes used in this study are mountain front sinuosity index smf and valley floor width ratio vf this work is largely based on the smf vf regression analysis of the studied fronts together with previous available data from sw usa the development of mountain fronts in both different lithologies and tectonic contexts enabled characteristic morphometric signatures for different activity scenarios tectonic activity classes to be obtained this study thus indicates that variations of mountain front geomorphology triggered by different styles of faulting can be detected by morphometric analysis it is demonstrated that discrete uplift rates of 0 15 0 08 m ka are sufficient to keep relatively low smf values down to 1 4 in active fronts class 1 taking into account the reported uplift rates and preliminary palaeoseismic data for some of the class 1 studied fronts recurrence periods for surface rupture events can be theoretically bracketed for se spain recurrence periods for class 1 fronts could theoretically range between 10 000 and 12 500 years for maximum slip conditions and 1750 and 2600 years for minimum slip conditions inactive fronts class 3 develop under uplift rates down to 0 03 m ka and tested recurrence intervals for rupture events range between 25 000 and 50 000 years class 2 fronts of intermediate characteristics and activity display uplift rates between 0 07 and 0 03 m ka

the stratigraphic distribution of ni rich spinels in cretaceous tertiary boundary rocks at el kef tunisia caravaca spain and hole 761c leg 122 abstract ni rich spinels have been found throughhout the world at the cretaceous tertiary boundary these minerals have no counterparts in terrestrial rocks but have been observed in meteoroid ablation material and impact debris suggesting that the cretaceous tertiary boundary spinels result from an extraterrestrial event their stratigraphic distribution which has been observed at the cretaceous tertiary boundary sites of el kef tunisia caravaca spain and hole 761c odp leg 122 indian ocean are markedly different from site to site and are all much less extended than the ir anomalies regional differences in ni rich spinel distibution are entirely explained by a brief event recorded under different bioturbation conditions the wider stratigraphic dispersion of ir is attributed to postdepositional chemical processes at el kef the site which appears to be the least affected by bioturbation and which has the highest sedimentation rate the 1 2 mm thick ni rich spinel spike indicates that the deposition time did not exceed an upper limit of 100 years this upper limit is consistent only with the collision of an asteroid or a comet at the close of the cretaceous

210pb derived sediment accumulation and mixing rates for the washington continental slope abstract total sediment accumulation rates g yr in four canyons indenting the washington continental shelf are about twice those on the nearby open slope even though canyons comprise less than 40 of the depositional area of the entire slope this is because 210 pb derived sediment accumulation rates g cm 2 yr for astoria and quinault canyons are 3 4 times greater than those for willapa and grays canyons and intermediate open slope areas supporting the hypothesis that columbia river derived solids are preferentially transported to these two canyons quinault canyon currently appears to be accumulating solids at rates much greater than its low long term accumulation rate which is attributed to turbidity currents transporting solids down this canyon roughly every 500 years the following four different approaches all show that mixing may cause 210 pb derived sediment accumulation rates for slope and canyon sediments to be 2 3 times higher than true accumulation rates 1 comparison between accumulation rates calculated from 210 pb profiles with and without surface zones in which mixing has obviously affected 210 pb distributions 2 comparison between 210 pb derived and independently determined long term accumulation rates 3 comparison between 210 pb derived accumulation and modern columbia river discharge rates 4 comparison between two and three layer steady state one dimensional diffusion advection decay models mixing coefficients for surface sediments calculated using a one dimensional two layer vertical eddy diffusion model show large differences within the region with most in the 3 30 cm 2 yr range mixing rates are several times larger in canyon sediments from 0 2 1 1 km water depth probably due to physical reworking processes erroneously neglected mixing at depth of no more than 5 of that calculated for the surface mixed layer can cause the 2 3 fold calculated overestimation of true sediment accumulation rates and 2 4 fold calculated underestimation of true mixing coefficients

seasat altimetry and the south atlantic geoid 1 spectral analysis this paper presents a discussion of the spectral characteristics of geoid profiles derived from seasat alitmetry in the south atlantic individual profile spectra are computed and averaged in seven separate geodynamic provinces mid atlantic ridge flanks walvis and rio grande aseismic ridges and argentine and cape basins three distinct wavebands can be identified in most spectra for wavelengths shorter than 35 km the spectra are typical of white noise with a 7 cm rms amplitude typical of seasat altimeter measurement noise for wavelengths between 300 and 800 km our uppermost limit since original profiles are 1700 km long the spectra are in reasonable agreement with kaula s empirical rule and are compatible with a pratt thermal boundary layer compensation mechanism with an ill defined compensation depth of 30 60 km the paper centers on the description of the 35 300 km part of the spectra computation of an impedance for each province requires good knowledge of its bathymetry which is far from satisfactory as yet in the south atlantic we show that for wavelengths longer than 80 km the squared amplitude spectrum of bathymetry varies as the inverse of wave number we propose that this relationship might also hold at shorter wavelengths although it is not observed due to presently insufficient data using these spectral estimates and correcting for the mean depth of the topography we derive impedance actually response function estimates separately for each province the data are well accounted for by a regional compensation scheme based on elastic flexure models elastic thickness the best resolved parameter ranges from 2 to 5 km for the ridge and flanks and the crustal thickness from 4 to 13 km crustal thickness appears to be larger on the east flank demonstrating a general lack of symmetry between east and west in the south atlantic which appears to hold at all wavelengths and is also expressed in the bathymetry the rio grande rise involves low but nonzero elastic thickness and large crustal thickness 25 35 km in agreement with previously proposed models of local airy compensation the walvis ridge appears to imply a larger elastic thickness in excess of 8 km if the crustal thickness is less than 20 km which may be due to emplacement on older lithosphere therefore despite a lack of sufficient bathymetric control geoid data can be used at the scale of the entire south atlantic to provide reasonable information on thermomechanical compensation in the various provinces the spectral structure emphasizes the 35 300 km spectral window and should be used in constructing band pass filters that can separately enhance features related to plate kinematics or sublithospheric convection

seasat altimetry the north atlantic geoid and evaluation by shipborne subsatellite profiles a geological evaluation of geoid anomalies over the north atlantic is presented with emphasis on short 40 300 km wavelength undulations mapped by seasat radar altimetry long 3000 km and intermediate 300 3000 km wavelength undulations constrain subcrustal processes and are briefly reviewed portions of three seasat revolutions revs totaling 9300 km were followed by research ship which measured gravity magnetics topography and for a 800 km segment also seismic reflection data to form a ground truth data set for comparison to the altimetry the intermediate wavelength geoid the residual upon removal of a 14 14 long wavelength surface correlates with plate age slope 10 cm m y over cenozoic crust and major fracture zones appear as geoid steps a 3 5 to 5 m high over the bermuda rise may reflect thermal rejuvenation created within the plate 40 50 ma short wavelength geoid anomalies typically 10 50 cm in the open ocean were analyzed by high pass 200 or 400 km cutoff along track filtering and smoothing the vertical deflection computed from the seasat geoid compares well with one based on seismic reflection shipborne free air gravity except for a higher frequency cutoff correlates closely with geoid anomalies except near seamounts the principal contribution to geoid anomalies is fracture zone topography all major and many minor fracture zones fz s appear as geoid lineations particularly between the 15 20 and kane fz from the ridge axis to anomaly 34 the wsw trend of fz s between anomaly 21 and 34 is clearly expressed in the altimetry as is the smooth geoid over mid cretaceous smooth basement formed by fast spreading crustal ribbons 50 150 km wide of higher or lower geoid parallel fz trends some geoid lineations are oblique to both isochron and fz trends east of the puerto rico trench such anomalies may reflect compressional deformation within atlantic lithosphere

experimental tests for particle size dependent bioturbation in the deep ocean the potential for particle size dependent bioturbation rates was experimentally tested at 1 240 m in the santa catalina basin eastern pacific spherical glass bead tracers in five size classes 816 17 31 32 62 63 125 and 126 420 m were spread over the sediment surface and tube cored 997 d later downcore concentrations of glass beads were enumerated in each of the five size categories and page s l test was used to test the null hypothesis of equal vertical penetration of all size classes of tracer in all cores the null hypothesis was rejected finer tracers penetrated deeper into the sediment in two of the three cores vertical biodiffusivities were computed from concentration profiles of downcore tracers these also showed size dependence with biodiffusivities ranging from 1 cm2 yr for the 8 1 6 pm fraction to 0 1 cm2 yr for the 1 25 420 pm size class these data demonstrate that vertical bioturbation rates are particle size dependent in santa catalina basin the likely cause is preferential ingestion and downward transport of fine particles by deposit feeders

geomorphic constraints on surface uplift exhumation and plateau growth in the red river region yunnan province china field observations digital elevation model dem data and longitudinal profi le analysis reveal a perched low relief upland landscape in the red river region yunnan province china which correlates to an uplifted regional low relief landscape preserved over the eastern margin of the tibetan plateau as with other major rivers of the plateau margin the red river has deeply incised the lowrelief upland landscape which we interpret to be the remnants of a pre uplift or relict landscape we examine longitudinal river profi les for 97 tributaries of the red river most profi les consist of three segments separated by sharp knickpoints an upper lowgradient channel segment a steeper middle channel segment and a very steep lower channel segment upper channel segments correspond to the relict landscape and have not yet experienced river incision steeper middle and lower segments indicate onset of rapid two phase river incision on the basis of which changes in external forcings such as climate or uplift can be inferred in terms of two end member scenarios two phase incision could be the result of pulsed plateau growth in which relatively slow uplift during the fi rst phase is followed by rapid uplift during the second phase or it could refl ect adjustments of the main channel to changing climate conditions against the backdrop of steady plateau growth reconstruction of the paleo red river indicates 1400 m river incision 1400 1500 m surface uplift and a maximum of 750 m vertical displacement across the northern red river fault elevating the northern ailao shan range above the surrounding relict landscape on the basis of stratigraphic constraints incision along the red river likely began in pliocene time

geomorphic analysis in areas of low rate neotectonic deformation south epirus greece as a case study abstract river morphology and the distribution of river deposits reliably reflect the neotectonic activity of a region in relation to rock resistance and climatic changes geomorphic indices have been used to identify landscape evolution and active faults particularly in areas of high rate tectonic deformation in areas of low rate deformation the influence of neotectonic activity on landscape evolution is less apparent although it is important the aim of this study is to examine the region of south epirus greece a region where the rates of active tectonic processes are low because rock resistance is low and the sediment supply is intense in this region the fault surfaces are either not well preserved or they are covered for the purposes of this paper geomorphic analysis including the drainage basin asymmetry factor the basin hypsometric curve and integral the valley floor width to height ratio longitudinal river profiles the stream length gradient index normalized by the graded river gradient and the mountain front sinuosity index was used to evaluate neotectonic activity and to identify covered potentially active faults in places where fault surfaces could be observed geological mapping and tectonic analysis were applied to determine the fault characteristics the first result of this work is that important active or potentially active faults extend for a significant distance into the alluvial plains of south epirus in this case study we considered that geomorphic indices constitute a valuable tool for identifying neotectonic activity in regions of low rate deformation furthermore geomorphic analysis reveals the location of covered fault structures contributes to evaluating fault capability and therefore to estimating seismotectonic hazard

microseimicity and strain pattern in northwestern greece during a 7 week microearthquake experiment conducted in epirus akarnania and the ionian islands of western greece we located approximately 600 earthquakes with magnitudes between 2 and 4 2 no event was deeper than 40 km the seismicity cannot be clearly associated with any single fault except the lixourion right lateral fault located west of the ionian islands focal mechanisms of about 100 earthquakes show for a narrow band of earthquakes located along the coast ene wsw shortening consistent with the surface tectonics farther east focal mechanisms show nnw sse extension beneath the foothills of the pindus mountains which is unrelated to surface faulting but is consistent with the presently subsiding basins this strain pattern is seen far north and south of the lixourion fault and is similar to the one observed in the peloponnese it suggests that a large scale mechanism is responsible for the recent geodynamics of both the northwestern and southwestern aegean

the mathematics of early diagenesis from worms to waves the changes that sediments undergo after deposition are collectively known as diagenesis diagenesis is not widely recognized as a source for mathematical ideas however the myriad processes responsible for these changes lead to a wide variety of mathematical models in fact most of the classical models and methods of applied mathematics emerge naturally from quantification of diagenesis for example small scale sediment mixing by bottom dwelling animals can be described by the diffusion equation the dissolution of biogenic opal in sediments leads to sets of coupled nonlinear ordinary differential equations and modeling organisms that eat at depth in the sediment and defecate at the surface suggests the one dimensional wave equation while the effect of waves on pore waters is governed by the two or three dimensional wave equation diagenetic modeling however is not restricted to classical methods diagenetic problems of concern to modern mathematics exist in abundance these include free boundary problems that predict the depth of biological mixing or the penetration of o2 into sediments algebraic differential equations that result from the fast reversible reactions that regulate ph in pore waters inverse calculations of input functions histories and the determination of the optimum choice in a hierarchy of possible diagenetic models this review highlights and explores these topics with the hope of encouraging further modeling and analysis of diagenetic phenomena

rapid bioturbation in equatorial pacific sediments evidence from excess 234th measurements in order to evaluate bioturbation in equatorial pacific sediments profiles of excess 234th were measured in cores collected during november and december 1992 at six abyssal sites along the jgofs equatorial pacific 140 w transect from 5 s to 9 n excess 234th half life 24 1 days was detected at all sites mean inventories ranged from a low of 0 25 dpm cm 2 at 9 n to a high of 2 6 dpm cm 2 at 2 n eddy diffusive models of the excess 234th profiles suggest that on 100 day timescales particle mixing is slow at 5 s and 2 s eddy diffusion coefficient db 0 4 cm2 year 1 faster at 0 and 2 n db 0 34 4 8 cm2 year 1 and fastest at 5 n db 4 7 11 cm2 year 1 at 9 n 234th is found almost entirely in the upper 5 mm of the seabed and db values are 0 1 cm2 year 1 db values generally increase as poc flux increases although the linear relationship r2 0 334 p 0 365 displays considerable scatter however if the only sites included in the regression are those where 234th profiles were measured in at least two core sets i e 0 2 n 5 n and 9 n the linear regression improves substantially r2 0 754 p 0 0012 these results suggest that measurements on a single core may not fully characterize the sediment mixing regime in a particular region and highlight the need for multiple samples from an individual site thorium 234 db values at 5 s 2 s and 9 n are in rough agreement with published db values calculated from the profiles of intermediate half life radioisotopes such as 210pb and 137cs in open ocean abyssal sediments however at 0 2 n and 5 n 234th db values are as much as an order of magnitude greater than published 210pb db values this phenomenon has been observed in other marine environments and may result from age dependent mixing non steady state mixing or a combination of the two processes particle mixing in cores collected at 5 s and 5 n appears to be best described as a largely eddy diffusive process however in cores collected at 2 s 0 2 n and 9 n non local mixing processes appear to affect 15 30 of the excess 234th inventory at these sites non local mixing appears to transport recently deposited material at least 3 4 cm below the sediment water interface within 100 days of its arrival at the seafloor the combination of rapid biodiffusive mixing and non local transport allows recently deposited reactive biogenic debris to be rapidly mixed into the seabed this may affect a wide range of diagenetic processes including oxygen consumption dissolution of biogenic debris and organic carbon remineralization models of early diagenesis in deep sea sediments may need to incorporate both non diffusive transport terms and rapid biodiffusive mixing of recently deposited particles

seafloor tectonic fabric from satellite altimetry abstract ocean floor structures with horizontal scales of 10 to a few hundred kilometers and vertical scales of 100 m or more generate sea surface gravity anomalies observable with satellite altimetry prior to 1990 altimeter data resolved only tectonic lineaments some seamounts and some aspects of mid ocean ridge structure new altimeter data available since mid 1995 resolve 10 km scale structures over nearly all the world s oceans these data are the basis of new global bathymetric maps and have been interpreted as exhibiting complexities in the sea floor spreading process including ridge jumps propagating rifts and variations in magma supply this chapter reviews the satellite altimetry technique and its resolution of tectonic structures gives examples of intriguing tectonic phenomena and shows that structures as small as abyssal hills are partially resolved a new result obtained here is that the amplitude of the fine scale 10 80 km roughness of old ocean floor is spreading rate dependent i

the tertiary geodynamical evolution of the aegean arc a paleomagnetic reconstruction abstract the paleomagnetic results obtained in the last 5 6 years from tertiary formations in the aegean domain indicate that the lower miocene arc was almost rectilinear with an e w trend and that its curvature has been acquired tectonically in two major phases during the middle miocene a first phase of deformation is characterized by rotations occurring at the two terminations of the arc clockwise in the west epirus anticlockwise in the east southeastern anatolia a second phase of rotation occurring in the last 5 ma about a pole situated in the southern adriatic sea has affected only the northwestern part the data also indicate that the antalya basin has not been involved in the geodynamical evolution of the arc so that the bey daglari represent its easternmost unit a more complex rotational pattern is observed in the internal zones the large rotations measured in evia 48 and skyros 26 probably occurred in the last 5 ma and result from rotation of fault bounded blocks in a shear zone connecting the north aegean trough to the external arc in the izmir region in the karaburun peninsula of western anatolia and in the island of lesbos significant counterclockwise clockwise or null rotations of coherent blocks have taken place during the neotectonic extensional regime furthermore the values of the inclination obtained from both sedimentary and volcanic oligo miocene formations are systematically shallower than expected on the basis of a geocentered dipole field this suggests that the entire studied area has undergone a northward drift of over 1000 km since the middle miocene

bias in foraminiferal multispecies reconstructions of paleohydrographic conditions caused by foraminiferal abundance variations and bioturbational mixing a model approach abstract a simple box model was applied to study the combined effect of bioturbation and foraminiferal abundance variations using synthetic isotope records constructed from the greenland oxygen isotope record gisp2 apart from the well known general smoothing of the signal the attenuation of peak heights and the up or downwards shift of the proxy records at intervals of changing abundance the modeling results draw attention to two effects of special importance to climatic reconstructions based on the comparison of proxy signals from two or more planktonic foraminifer species first the bioturbational mixing of tests out of abundance maxima and into over and underlying sediment can lead to the introduction of stratigraphic shifts between different species when species with opposing abundance patterns are used this shifting of the signals can easily result in apparent increases or decreases in the isotopic gradients between different species especially at intervals of rapidly changing climate conditions second in intervals with rapidly changing environmental conditions such as dansgaard oeschger cycles where species with different preferences often show opposing abundance patterns the mixing of foraminifer tests out of their respective abundance maxima can result in a general but artificial offset between the two species this offset then may disappear during intervals of slower variability these artifacts have the potential of seriously biasing any paleoceanographic and paleoclimatic reconstructions based on multispecies analysis where the studied species show opposing abundance patterns it is therefore highly recommended that species with as low abundance variations as possible or at least with similar abundance variations are used whenever multispecies reconstructions are attempted

reconstruction of the last deglaciation deconvolved records of δ18o profiles micropaleontological variations and accelerator mass spectrometric14c dating bioturbation acts as a low pass filter in displacing and reducing the amplitudes of stratigraphic signals this often leads to a loss of high frequency events in the stratigraphic record in addition when considering an isotopic signal 18o 14c measured in stratigraphic carriers such as foraminifera bioturbation and carrier abundance changes can create artifacts which may be falsely interpreted as leads or lags in the paleoclimatic record

regional patterns of bioturbation and iron and manganese reduction in the sediments of the southeastern bering sea regional patterns of iron fe and manganese mn reduction rates across the shelf and slope of the southeastern bering sea as well as the relative importance of these pathways in sedimentary organic matter remineralization were investigated during the spring and summer of 2009 reduction rates of fe and mn were calculated using depth pro les of solid phase iron and manganese oxide concentrations and bioturbation coef cients db determined from pro les of excess 234 th iron reduction was found to be a signi cant pathway for carbon mineralization across the shelf with an average rate of 1 74 mmol m 2 d 1 however fe reduction rates higher than 6 mmol m 2 d 1 were calculated and a signi cant regional pattern was observed with highest rates found on the northern shelf and dropping toward the south and offshore conversely mn oxide reduction was found to be of minor signi cance with low reduction rates in all regions averaging only 0 09 mmol m 2 d 1 across the shelf and accounting for no more than 5 of total carbon oxidation in any region these results indicate that fe oxide reduction is a signi cant pathway for carbon remineralization in the northern and middle shelf regions where organic matter deposition rates and benthic biomass are high additionally this work provides insight into the potential role of sedimentary iron reduction as a source of bioavailable fe in this region

australasian microtektites in a substrate a new constraint on ferromanganese crust accumulation rates abstract microtektites belonging to the australasian tektite strewn field are found in the substrate of a ferromanganese crust dredged from the central indian basin they are identified on their physical appearance geographic occurrence and chemical composition the ferromanganese crust has a thickness range of 6 17 mm and its chemistry and mineralogy indicate hydrogenic accretion because the australasian strewn field has an age of 0 77 ma this finding implies that the overlying fe mn crust has minimum accretion rates of 7 8 22 1 mm myr which are much higher than the average growth rates of hydrogenic crusts

assessing the global meltwater spike abstract l v worthington 1968 meteorological monographs 8 63 67 hypothesized that a low salinity lid covered the entire world ocean by deconvolving isotopic curves from the western equatorial pacific and equatorial atlantic w h berger r f johnson and j s killingley 1977 nature london 269 661 663 and w h berger 1978 deep sea research 25 473 480 reconstructed meltwater spikes similar to those actually observed in the gulf of mexico and thus apparently confirmed the worthington hypothesis it is shown that this conclusion is unwarranted the primary flaw in the reconstructed meltwater spikes is that the mixing intensity used in the deconvolution operation is overestimated as a result structure recorded in the mixed isotopic record becomes exaggerated in the attempt to restore the original unmixed record this structure can be attributed to variable ice volume decay during deglaciation effects of differential solution on planktonic foraminifera temporal changes in abundance of the foraminifera carrying the isotopic signal and analytical error an alternative geographic view to the global low salinity lid is offered a map showing portions of the ocean potentially affected by increased deglacial meltwater at middle and high latitudes and by increased precipitation induced runoff at low and middle latitudes

active tectonics in the sierra nevada betic cordillera se spain insights from geomorphic indexes and drainage pattern analysis article i nfo the sierra nevada of the central betic cordillera is a 3000 m high mountain range surrounded by neogene quaternary sedimentary basins having been uplifted since late miocene times the southern and western mountain fronts of the sierra nevada are fault bounded while the northern one is an unconformity between the neogene quaternary sediments of the guadix baza basin and the metamorphic rocks of the nevado filabride complex we have carried out a geomorphic study by examining drainage patterns and characteristics of mountain fronts in order to reveal areal variations and styles of rock uplift mountain front sinuosity smf area altitude relations hypsometric curves and valley floor entrenchment differ significantly between the northern western and southern mountain fronts the lack of important faults along the northern sierra nevada mountain front together with the elevated topographic position of the guadix baza basin average altitude is around 1100 m points to similar uplift of both geomorphic units sierra and basin in a single large scale crustal block the asymmetry factors show systematic asymmetries at both sides of the lanjaron river probably due to the presence of an active nne ssw oriented antiform in the western sierra nevada finally river profiles indicate maximal river entrenchment in the western part of the sierra nevada probably related to the uplift of the footwall of the padul niguelas fault system therefore our geomorphic analysis suggests that the western part of the sierra nevada is tectonically active by means of a combination of normal faults along the mountain front and nne ssw oriented active folds which in turn likely have a gravitational origin related to the exhumation of the footwall of the normal fault system

plutonium and210pb distributions in northeast atlantic sediments subsurface anomalies caused by non local mixing abstract the depth distributions of 210 pb and 239 240 pu measured in a suite of box cores collected from water depths of 4000 5000 m in the northeast atlantic ocean exhibit pronounced subsurface maxima caused by sediment reworking by benthic infauna small scale spatial heterogeneity in bioturbation rates is indicated by large differences in tracer profiles from duplicate cores separated only by a few centimeters 210 pb and 239 240 pu activity distributions from each subcore exhibit a high degree of correlation and most tracer profiles exhibit one or more subsurface maxima one dimensional biodiffusion analogue models do not adequately simulate the principal features of this data set however an inverse conveyer belt mixing model which simulates subsurface egestion or a functionally equivalent process of surficial material which is enriched both in organic debris and radioactive tracers can reproduce the subsurface tracer maxima single event and continuous subsurface egestion models have been formulated and solved for different feeding rates and background biodiffusive fields the single event model provides a better fit to the data and in particular ensures the observed high degree of correlation between the 210 pb and 239 240 pu activity profiles regardless of the different tracer input functions the most likely candidate responsible for subsurface tracer egestion is a large infaunal worm of the phylum sipunculida which dominates the biomass below a depth of 3 cm

the gravsat signal over tectonic features the range rate between two close gravitational satellites gravsat in low earth orbit has been evaluated over model tectonic features such as mountains and ranges fracture zones and trenches models are locally compensated and consist of both point mass dipoles and sheet mass dipoles masses and depths of compensation are chosen to approximate known gravity signatures the results show that for two satellites at 160 km altitude with 3 separation significant signal power 1 m s remains for most extended features at wavelengths less than 200 km furthermore there is strong sensitivity in the signal from these features to lateral and vertical changes of the order of 1 km and less in addition the signal of hidden geologic structures such as dikes salt domes and ore bodies may also stand above 1 m s for this low orbiting pair thus it may prove to be efficient to model the high frequency gravsat signal directly in terms of the parameters of tectonic topographic features and their compensation

palaeomagnetic results from southern albania and their significance for the geodynamic evolution of the dinarides albanides and hellenides abstract mesozoic and cenozoic rocks were studied in three tectonic units in southern albania the area belongs to the ionian zone outer albanides rock magnetic investigations comprising alternating field and thermal cleaning stepwise acquisition of isothermal remanent magnetization and hysteresis experiments were carried out they established magnetite and titanomagnetite as the main carriers of the natural remanent magnetization in the high field behaviour haematite and goethite can also be seen several fold tests on the site and on a regional scale indicate that the directions are characteristic these directions prove a general clockwise rotation of about 40 since the tortonian using all available palaeomagnetic data from albania individual movements of the different tectonic units within the inner and outer albanides can be deduced this is also valid for the albanian alps which are understood to be the southernmost part of the dinarides

comparison of different tracers and methods used to quantify bioturbation during a spring bloom 234 thorium luminophores and chlorophylla rates and types of particle bioturbation were measured before and during the 1993 phytoplankton spring bloom in long island sound u s a bioturbation rates were determined at intervals of 2 weeks using three independent tracers 234th chlorophyllaand luminophores that have different boundary conditions and reaction properties 234th t1 2 24 days is supplied continuously from overlying water the delivery of chlorophylla chl a a non conservative tracer of fresh organic matter having a known degradation rate tracks overlying water productivity and is characterized by non steady state pulses luminophores fluorescent particulate tracers were used in a series of manipulative pulse input experiments under bothin situand laboratory conditions sediment temperature varied from 0 4 to 15 8 c during the measurement period bioturbation was quantified by applying either steady or non steady state biodiffusive bioadvective models that take into account both diffusive transport db and vertical advective transport vb by conveyor belt feeders pulsed inputs of chl aand luminophores demonstrated rapid biogenic burial of surface sediment that was not resolved by234th there was discernible small scale spatial heterogeneity in mixing as indicated by large variations in bioturbation coefficients estimated in duplicate field or triplicate lab luminophore cores during the sampling period both types of biological sediment transport biodiffusive mixing and bioadvection were low dbranged from 0 001 0 04 cm2day 1andvb 0 00 0 05 cm day 1 biodiffusive mixing estimated fromin situtracer profiles increased lq2 3 during the pulsed organic matter input and temperature rise that characterized the bloom and post bloom period laboratory measurements of luminophores using three replicate cores from each sampling time also indicated a post bloom increase in biodiffusion with a possible transient peak enhancement lw4 about 40 days after the bloom there was an apparent short term relationship between fresh organic flux to the sea floor and elevated biodiffusion but the most consistent post bloom relationship is between mixing rate and temperature apparent activation energies 45 60 kj mol 1 bothin situand laboratory measurements also demonstrated that bioadvection coefficients increased 10 50 with chl ainput and rising temperature and correlated directly with specific changes in benthic community composition diffusive mixing coefficients calculated from the different tracers are of the same order of magnitude use of234th resulted in the lowest estimates of overall particle transport combined diffusive and advective multiple tracers and replication of mixing coefficient measurements are required for accurate quantification and resolution of bioturbation

formulation of the conceptual model for the tectonic geomorphological evolution of an area five main rivers of greece as a case study abstract this paper associates the tectonic conditions of five rivers integrated drainage networks in northwestern greece for the purpose of formulating the conceptual model of its tectonic and geomorphological evolution the applied methodology consisted in the synthesis of elements from the fields of tectonics and geomorphology using suitable software and gis techniques and the correlation of fault and drainage network trends by the use of rose diagrams to reveal the structures and tectonic events affecting the different orders of the branches and its evolution the relation between morphology tectonics and the development of the drainage network enabled comparison across different areas the grouping of rivers and the identification of areas influenced by the same geodynamic regime in northwestern greece two main groups of rivers were distinguished flowing across areas featuring different tectonic conditions while a transitional zone between them was defined the stages of the area s tectonic and geomorphological evolution were identified with highlighting the definitive impact of tectonic structures on the configuration of the river routes e g the petousi souli fault which forms a natural boundary in the centre of the study area and new elements were added in view of the aforementioned northwestern greece is an independent transitional area in the geodynamic regime of the entire eastern mediterranean notably the methodology applied to these rivers may also be used in other areas thus constituting a standard tool for investigating the geodynamic regime and evolution

the short term fate of fresh algal carbon in continental slope sediments emplacement of a tracer mixture containing 13c labeled green algae on the sea floor of the continental slope offshore of cape hatteras north carolina elicited a rapid response over 1 5 d from the dense benthic community certain deposit feeding annelids e g scalibregma injlatum and aricidea quadrilobata became heavily labeled with 13c as a result of ingestion of the algae 13c labeled organic matter was transported to a depth of at least 4 5 cm into the seabed during the 1 5 d period presumably as a consequence of a feedingassociated activity nonlocal transport produced subsurface peaks in organic 13c at 2 3 cm dissolved inorganic 13c produced by the oxidation of the labeled algae penetrated to lo cm depth the transport of highly reactive organic matter from the sediment surface at initial velocities 1 3 cm d l is expected to be an important control of subsurface benthic processes in slope environments characterized by abundant macrofaunal populations anaerobic processes which are enhanced on the cape hatteras slope relative to adjacent areas may be promoted by the rapid injection of reactive material into subsurface sediments the transport in turn is a consequence of the dense infaunal populations that are supported by the rapid deposition of organic carbon in this region

attenuation of millennial scale events by bioturbation in marine sediments the discovery of large millennial scale oscillations 1 10 kyr period in climate records from ice cores and marine sediments in the north atlantic has motivated the search to understand their cause and evaluate the geographic extent of this variability one uncertainty in comparing marine geologic records of millennial scale variability is the extent to which mixing of sediment by organisms at the seafloor bioturbation may attenuate millennial scale events in the stratigraphic record evidence of attenuation of millennial variability can be found in cores with sedimentation rates in the range of 5 15 cm kyr modeling the attenuation of a hypothetical input time series similar to gisp2 using a moderate level of mixing provides estimates of attenuation as a function of sedimentation rate the amplitude of a 4 kyr duration event is reduced by 50 for sedimentation rates10 cm kyr and reduced by 20 for sedimentation rates of 20 cm kyr minimal attenuation 5 is achieved only when the sedimentation rate exceeds 50 cm kyr for a 4 kyr duration event and 70 cm kyr for a 2 kyr duration event the intensity of mixing plays a role in determining how much attenuation occurs the amplitude of a 4 kyr duration event in a 10 cm kyr core is reduced by 75 under strong mixing or reduced by 25 under weak mixing this study indicates that the original amplitude of dansgaard oeschger do millennial scale events observed during the last glacial may be twice the observed amplitude for cores with sedimentation rates 10 20 cm kyr that have experienced moderate bioturbation regional comparisons of the amplitude of millennial scale variability will require cores with weak mixing or sedimentation rates exceeding 50 cm kyr in order to avoid biased estimates of the amplitude of millennial scale 4 kyr duration variability

mixing sedimentation rates and age dating for sediment cores abstract analytic solutions to the advection diffusion equation useful as a guide for the interpretation of mixing sedimentation rate and age dating effects in sediment cores have been derived various simplified mixing models appropriate to 14 c and 210 pb measurements have been considered the emphasis has been on a discussion of the various interrelations and dependencies among the mixing coefficient sedimentation rate and radioactive decay constant parameters in determining the 14 c and 210 pb concentrations as a function of depth porosity variations within the sediment column are also considered and the transformed advection diffusion equation including porosity effects is derived

is burial velocity a master parameter for bioturbation abstract the intensity of biological mixing in a marine sediment is widely believed to be related to the flux of labile organic matter at the same time this flux has been shown to be strongly correlated to the burial velocity one would then expect a significant correlation between biological mixing coefficient d b and burial velocity a nonlinear regression of existing data with a power law eqns 2 and 3 of the text produces a statistically significant correlation the statistical significance of the regression in no way implies causation and in fact it accounts for only about 22 of the total variance in the dataset thus reducing its physical significance a number of additional processes contribute to the large observed variance including timing of mixing events temporal and spatial heterogeneity differences in temporal scales sampling artifacts and specific particle associations with due care the d b relationship may prove useful in defining the likely range of d b values in a particular environment a similar analysis of the tracer identified surface mixed depth shows that it is essentially independent of burial velocity with a worldwide mean of 9 8 4 5 cm depth of mixing is probably more closely related to the energetic costs of deep burrowing

internal structure and evolution of the late quaternary sequence in a shallow embayment the amvrakikos gulf nw greece abstract the late quaternary stratigraphic pattern of the amvrakikos gulf in the eastern mediterranean has been studied on the basis of the analysis of high resolution seismic profiles and short sediment cores lowstand transgressive and highstand systems tracts have been identified that are configured in a major depositional sequence of a fifth order sea level cycle during the last glaciation when the sea level was lowered by 55 m relative to its present position ca 50 ka bp the amvrakikos gulf was probably emerged giving rise to a subaerial erosion and fluvial incision in the western shallow part of the gulf and b development of a paleo lake in the eastern deepest domain until the early phase of the post glacial transgression ca 11 50 ka bp a paleo river characterized by a dense network of v shaped valleys was draining the western part of the gulf and flowing into the ionian sea in the isolated eastern part lowstand lacustrine deposits deltaic and prodeltaic units accumulated within the paleo lake at the latter stage of the last post glacial transgression ca 11 ka bp seawater entered the gulf and the transgressive systems tract was deposited consisting of incised channel fills beach shoreface deposits and delta prodelta wedges buried terraces have been identified also within this transgressive tract that reveal a step like sea level rise since ca 6 ka bp when the sea level reached its present day position a distal prodeltaic unit has been deposited and overlain by prograding deltaic wedges the spatial distribution of these wedges provides evidence of a continuous shifting of the river mouths during holocene the recent sedimentation patterns are related to the terrigenous inputs primarily from the arachthos river located in the northeastern part of the gulf and secondarily from the louros river located in the northwestern part

paleomagnetic reconstruction of the cenozoic evolution of the eastern mediterranean abstract a total of 113 paleomagnetic sites were sampled along an anatolian s n transect from the arabian platform the hatay region the eastern taurides the kirsehir block the sivas basin and the eastern pontides reliable characteristic remanent paleomagnetic directions were retrieved from 37 of these sites spanning in time from paleocene to miocene in a general way declinations are westerly deviated and inclinations are shallower than the geocentered dipole value at the present latitudes when combined with previously published results these data indicate that a large scale counterclockwise rotation of anatolia of some 25 has occurred since the miocene assuming that the pole of rotation of anatolia with respect to europe has remained constant in time at the location given by macclusky et al j geophys res 105 2000 5695 on the basis of the geodetic data this rotation implies that a large westward displacement 500 km at the average latitude of 40 has taken place assuming that the rotation was initiated by the arabia europe collision about 12 ma ago this corresponds to an average displacement of about 40 mm year together with previous results from the western part of the aegean arc these results indicate that the main trends of the cenozoic evolution of the eastern mediterranean appear to consist of two post early miocene rotations of opposite senses a clockwise rotation of the western part of the aegean tectonophysics 146 1988 183 around a pole situated in northern albania and a counterclockwise rotation around the pole given by mcclusky et al j geophys res 105 2000 5695 comparison with gps data suggest that both rotations are still active today

a model for particle selective transport of tracers in sediments with conveyor belt deposit feeders conveyor belt deposit feeding organisms prevalent in both marine and freshwater systems have a profound effect on sediment properties and transport processes these organisms ingest sediments over a range of depths while depositing gut contents from tails protruding above the sediment surface this action results in particle selective transfer of buried materials to the sediment surface and imposes an accelerated rate of sediment and pore water burial within the feeding zone most previous efforts to combine sediment diagenesis with the effects of biogenic reworking characterize mixing as exclusively diffusive and ignore such major advective effects here a model is developed based on fundamental diagenetic equations for transport and reaction for the distribution of tracers in accumulating sediments subject to compaction and diffusive as well as advective redistribution by benthic organisms conveyor belt cb feeding is characterized as a first order process with a depth dependent rate constant which is either localized gaussian or distributed integrated gaussian biogenic diffusivity of bulk sediments is allowed these alternative depth dependences as well the model assumes simple linear adsorption of the tracer between solid and solution phases and uses a time dependent flux at x 0 which is a combination of that originating externally and the depth integrated contributions from feeding particle selectivity is introduced by applying mass conservation separately to transport of the tracer and bulk sediments properties of the model are illustrated for tracers in nondispersive systems strongly bound to sediment solids cb recycling gives rise to transient reflections on passage of a tracer pulse through the zone of bioturbation reflections readily disappear in the presence of various integrative processes the system time resolution is defined in terms of the downward propagation of dual tracer pulses and shown to be systematically degraded by intensified feeding and selective transport a simple expression is developed for estimating the magnitude of particle selective changes in steady state surface concentrations in terms of the particle selectivity factor and the efficiency of sediment reworking unrecognized particle selectivity can lead to false inferences about changes in the rate of delivery of tracers to sediments selective cb recycling can cause a tracer such as 210pb to be retained largely within the bioturbation zone so that relatively little activity reaches the region of sediment useful for geochronological interpretation increased selectivity accentuates the sensitivity of the profile to details of the reworking process the model applied to previous studies of cb deposit feeders in tracer labeled freshwater microcosms shows the need to include particle diffusion as well as advection in the treatment of cb transport

chemical profiles in k t boundary section of meghalaya india cometary asteroidal or volcanic abstract the cretaceous tertiary boundary ktb exposed as a 1 5 cm thick limonitic layer in the um sohryngkew river basin in meghalaya is marked by enhanced concentrations of ir co ni os fe zn sb by factors of 4 to 1200 and ree by factors of 1 7 to 5 compared to the cretaceous shales ir concentration is generally 10 in 2 m thick broad band around the ktb abruptly reaching a peak concentration of 12 1 ng g 1 within the limonitic layer the os ir ratio at the ktb is 0 37 but in the adjacent shales it is 1 8 suggesting that the sources of these elements in the peak and the broad band may be different cretaceous planktonic foraminifera and dynocysts start disappearing before the ir rich limonitic layer was deposited but several diminutive cretaceous foraminifera survive after this layer the observations indicate that the extinctions are confined to a short span of time but are probably not as abrupt as anticipated by the asteroidal impact hypothesis the chemical data are discussed in terms of cometary asteroidal and volcanic hypotheses the profiles of ir and os ir can be understood in the frame work of a model of cometary impact in which cometary debris falls onto the earth preceding and succeeding the fall of the cometary nucleus

quantitative analysis of relative tectonic activity in the sarvestan area central zagros iran neotectonics is a major factor controlling landform development in tectonically active regions and it has significantly affected fluvial systems and mountain front landscapes in the sarvestan area of the central zagros iran the area is located along the simply folded belt of the zagros and is an outcome of the sw ne oriented tectonic conversion that initiated in the late cretaceous and strengthened during the early miocene due to the collision of the arabian and eurasian plates to assess tectonic activities in the area we analyzed geomorphic indices the stream gradient index sl drainage basin asymmetry af hypsometric integral hi valley floor width valley height ratio vf drainage basin shape bs and mountain front sinuosity j these indices were combined to yield the relative active tectonics index iat using geographic information systems gis based on iat values the study area was divided into four parts class 1 very high relative tectonic activity 1 0 in area class 2 high 20 0 class 3 moderate 67 0 and class 4 low 12 0 the results are consistent with field observations on landforms and geology

natural remanent magnetization acquisition in bioturbated sediment general theory and implications for relative paleointensity reconstructions we present a general theory for the acquisition of natural remanent magnetizations nrm in sediment under the influence of a magnetic torques b randomizing torques and c torques resulting from interaction forces dynamic equilibrium between a and b in the water column and at the sediment water interface generates a detrital remanent magnetization drm while much stronger randomizing torques may be provided by bioturbation inside the mixed layer these generate a so called mixed remanent magnetization mrm which is stabilized by mechanical interaction forces during the time required to cross the surface mixed layer drm is lost and mrm is acquired at a rate that depends on bioturbation intensity both processes are governed by a mrm lock in function the final nrm intensity is controlled mainly by a single parameter that is defined as the product of rotational diffusion and mixed layer thickness divided by sedimentation rate this parameter defines three regimes 1 slow mixing 10 with mrm acquisition and full drm randomization and 3 intermediate mixing because the acquisition efficiency of drm is larger than that of mrm nrm intensity is particularly sensitive to in case of mixed regimes generating variable nrm acquisition efficiencies this model explains 1 lock in delays that can be matched with empirical reconstructions from paleomagnetic records 2 the existence of small lock in depths that lead to drm preservation 3 specific nrm acquisition efficiencies of magnetofossil rich sediments and 4 some relative paleointensity artifacts

terminal cretaceous environmental events the geologic record of terminal cretaceous environmental events indicates that iridium and other associated elements were not deposited instantaneously but during a time interval spanning some 10 000 to 100 000 years the available geologic evidence favors a mantle rather than meteoritic origin for these elements these results are in accord with the scenario of a series of intense eruptive volcanic events occurring during a relatively short geologic time interval and not with the scenario of a single large asteroid impact event

a generalized stochastic approach to particle dispersal in soils and sediments abstract we explore a generalized stochastic description for the dispersal of particles in soils and sediments the model is based on the continuous time random walk ctrw which enables a very general description of particle mixing due to biological activity a community of burrowing organisms is characterized by a bioturbation fingerprint that consists of two probability distributions the jump length distribution describes the distance a particle travels within a given bioturbation event the waiting time distribution describes the time interval a particle waits at a given location in between two bioturbation events our stochastic analysis provides insight on the applicability of the widely used biodiffusion model which forms the asymptotic limit of the ctrw model this asymptotic behaviour of diffusion is always reached independent of the shape of bioturbation fingerprint provided that the waiting time distribution has a finite mean and the jump length distribution has a finite variance the biodiffusion coefficient can be decomposed as the variance of the jump length distribution over the mean of the waiting time distribution since the variance enables a squared weighing of the jump distance long range displacements will contribute more to the mixing intensity d b than short range displacements therefore large macrofauna will contribute disproportionately to the mixing intensity relative to their abundance as they displace particles over longer distances than smaller organisms finally we review the potential for bioturbation of so called anomalous transport models where either the mean of the waiting time distribution or the variance of the jump length distribution becomes infinite

roughness of the marine geoid from seasat altimetry the geographical variability of short wavelength geoid power spectra geoid roughness has been mapped for the world s oceans between latitudes 72 deg n and 72 deg s a spectral analysis of seasat altimeter data reduced to sea surface heights has been performed at 2 min intervals for 15 consecutive days of the 3 day repeat orbit the geoid roughness represented by these spectra for wavelengths shorter than about 220 km is separated from the total sea height variance and is displayed in the form of a global contour map the global average geoid roughness is 32 cm rms varying from a high in excess of 2 m rms near deep ocean trenches to a low of 2 cm rms in the southeast pacific near the east pacific rise this average value agrees well with previous estimates based on gravimetry and geos 3 altimetry in general the smoothest areas in the marine geoid overlie relatively young sea floor adjacent mid ocean spreading centers where even short wavelength topographic variations tend to be isostatically compensated

tectonic geomorphology of the red rock fault insights into segmentation and landscape evolution of a developing range front normal fault the red rock fault an active normal fault in southwest montana is reevaluated for fault segmentation using a multiproxy approach field characterization of soils coupled with radiocarbon ages in offset hanging wall fans and terraces constrain the rupture history at a number of locations along strike these data are coupled with morphometric analysis of dated alluvial fan deposits and adjacent 2nd and 3rd order footwall drainage basins to further constrain fault kinematics and segmentation morphometric analysis of the big sheep creek catchment which drains a large area of the footwall range provides a control on the spatial extent offault influence on footwall topography three fault segments are recognized by this study compared with the two segments recognized previously data from offset alluvial surfaces were synthesized with hanging wall fan and footwall drainage basin data to demonstrate a southward increase in displacement along the red rock fault since at least the latest pleistocene at a maximum rate of 1 5 mm yr red rock ruptures were mainly confined to segments suggesting a fault behaving as several discrete slip surfaces however simultaneous rupture of adjacent segments during one event indicates some fault zone coalescence a youthful red rock fault is supported by the absence of tectonic influences on footwall topography and is consistent with an eastward progression of normal fault development along the northern arm of the yellowstone hot spot q 2005 elsevier ltd all rights reserved

tilting neotectonics of the guadiamar drainage basin sw spain the guadiamar river ows from the southern iberian massif to the guadalquivir foreland basin sw spain its drainage basin displays asymmetries in the stream network the arrangement of alluvial terraces and the con guration of the trunk river valley the stream network asymmetry was studied using morphometric measures of transverse topographic sym metry asymmetry factor and drainage basin shape the alluvial terraces were studied through the lithologic logs of more than a hundred boreholes and eld mapping the morphometric methods demonstrate a regional tectonic tilting toward the sse causing both the migration of the guadiamar river toward the east and the migration of the guadiamar tributaries toward the southwest as a consequence of the guadiamar river migration an asymmetric valley developed with a steep eastern margin caused by river dissection and a gentle western margin where the main alluvial deposits are found the ages obtained using the 14c analysis of samples from several alluvial deposits show that the river migration and thus tilting has occurred during the holocene as well as earlier in the quaternary this interpretation revises the guadiamar longitudinal fault assumed by previous studies copyright 2003 john wiley sons ltd

biological pumping upwards of the coarse fraction of deep sea sediments abstract in a restricted part of an area intensively sampled by box coring approximately 50 samples from a 2 4 km rectangle a stiff muddy glacial gravel till is encountered at a depth of 30 40 cm x radiographs of the upper 15 to 20 cm of the cores reveal gravel in overlying foraminiferal mud only from the area where there is the deeper till layer the localization strongly suggests that the material in the top of the cores has its source in the deeper layer i postulate that burrowing organisms move gravel upward by pushing aside the particles that are too large to be eaten because the strength of the enclosing mud decreases upwards the gravel particles move preferentially upward the upward decrease in shear strength of he sediment is rapid at an interface occurring 4 cm below the surface on average thus hydrostatic pressures of 20 to 200 g cm2 exerted by vermiform burrowing animals act within an environment of asymmetrical sediment property permitting an asymmetrical response to the uniformly directed body pressure this asymmetrical response a pumping mechanism affecting material that does not pass through the gut is contrasted with the mixing of finer sediments that are eaten and excreted documented by many other workers dimensional arguments suggest the flux of material is related to the ratio of biological mixing rate to sedimentation rate the mechanism is also applicable to maintenance of mn nodules and their nuclei at the surface if macrofossils have behaved like gravel some s ell beds may have been generated and some stratigraphic anomalies caused by this means

patterns of quaternary uplift of the corinth rift southern border n peloponnese greece revealed by fluvial landscape morphometry abstract the rift of corinth is a world class example of young active rifting and as such is an ideal natural laboratory of continental extension however though much investigated for two decades several aspects of the mechanisms at work are still poorly understood the aim of this paper is a detailed morphometric study of the fluvial landscape response to the tectonic uplift of the rift southern shoulder in order to reconstruct the rift s quaternary evolution with special attention to timing location and intensity of uplift episodes based on the use of a large set of catchment and long profile metrics complemented by the new r sr integrative approach of the regional drainage network we identified three distinct episodes of uplift of the northern peloponnese coastal tract of which the intermediate one dated around 0 35 0 4 ma is only recorded in the topography of the central part of the rift shoulder and the youngest one appears to have propagated from east to west over the last 10 20 ka while net uplift remained minimum in the eastern part of the study area during the whole quaternary it shows a clear maximum in the central part of the rift shoulder since 0 4 ma and an eastward shift of this maximum in recent times maximum uplift rates calculated from the morphometric data are of 1 05 and 2 5 mm year 1 for the mid middle pleistocene and holocene uplift episodes respectively the morphometric evidence reveals an onshore uplift history remarkably consistent with the rift evolution reconstructed from other data sets in the long term it shows a stable pattern of maximum activity in the central part of the rift confirming previous conclusions about the absence of rift propagation in the short term it sheds light on a possible e w migration of the zone of recent uplift suggesting that in the near future fault activity and seismic hazard might concentrate in the heliki aegion area at the western tip of this uplift wave

transition matrix model of bioturbation and radionuclide diagenesis bioturbation rates in muddy sediments are thought to be due primarily to the reworking activities of benthic deposit feeders however current mathematical models of bioturbation do not explicitly link rates of particle mixing with realistic biological reworking mechanisms to address this problem i present a transition matrix model of bioturbation that quantitatively links the reworking activities of individual organisms and community level particlemixing rates solutions to the model are presented for two kinds of tracers particle reactive radionuclides with a constant input flux and conservative tracers added to the sediment as a pulse the model was used to predict the vertical profiles of excess 234 th and 210 pb in the field the model parameters were determined from benthic community structure data model predictions were then compared to measured profiles of these tracers on the basis of this comparison i inferred that maldanid polychaetes at the study site were collecting sediment at the sedimentwater interface and depositing it at depth this transport mechanism had a large effect on the predicted tracer profiles a sensitivity analysis of the model indicated that deposit feeding by the two most abundant species mediomastus ambiseta and nucula annulata was the most important process determining the burial rate of the tracers the model results also indicated that the combined effects of deposit feeding and sedimentation were sufficient to determine the vertical distributions of excess 234

oceanographic and geophysical applications of satellite altimetry since the last quadrennial report new satellite altimeter data have not been generally available nevertheless important progress has been made from analyses of geos 3 and seasat data the marine gravity field has been determined to an extraordinary resolution and accuracy and important solid earth geophysical interpretations made in the area of oceanography statistical estimates of the variability of dynamic topography have been published methods for incorporating altimeter data into numerical models have been developed and applied and tentative but interesting determinations of the mean circulation have been made in addition altimeter waveform analysis has made it possible to use altimeter data to determine elevations of major ice fields finally important new insights into the nature of satellite ephemeris error and its influence on altimetrically derived sea surface topography have been achieved

a simple model of flow sediment organism interaction abstract previous models of organism sediment interaction have been limited primarily to eddy diffusion type mixing while such models are useful in interpreting some stratigraphic records they cannot be expected to provide mechanistic insights into the diversity of interactions among sedimentary processes organism activities and boundary layer flows to provide a more general formulation capable of dealing with all three types of processes in concert a simple discrete time markov model is generated this version of the model deals explicitly only with particulate and not liquid phases the initial formulation is a two compartment ergodic model of deposit feeding particle selection by deposit feeders results in incorporation of the selected particles into fecal pellets and fecal pellet disaggregation completes the cycle particles which are more strongly selected or which are incorporated into more robust pellets thus spend more time and reach higher relative concentration in the fecal pellet compartment the next level of complexity is achieved by adding burial from the free sediment non fecal pellet compartment this model predicts that particles which are more strongly selected or incorporated into more robust fecal pellets will have greater residence times in surficial sediments both pellets and free sediments before they become part of the stratigraphic record and will therefore achieve higher concentrations in surficial sediments than will less preferred particles the full flow sediment organism system is reached by adding the potential for lateral advection of particles the probability of such advection is allowed to differ between pellets and free sediments increasing selection and robustness of fecal pellets then can either increase or decrease relative concentration and residence time of a given particle type in surficial sediments the model thus provides a means of explaining differences in stratigraphic patterns among materials deposited simultaneously it also suggests that deposit feeder selection may increase the average age i e time since initial deposition of surficial sediments by maintaining preferred particle types near the surface selection may likewise control the texture of surficial sediments in a manner which is easily confused with purely physical sorting parameters which require careful measurement in testing these simple predictions are selectivity by deposit feeders probability of selection rate of fecal pellet breakdown under realistically simulated conditions probability of pelletal disaggregation differential erodibilities of pellets versus free sediments relative probabilities of lateral advection and rates of burial of free sediments versus pelletized sediments probabilities of burial

210pb derived sediment accumulation and mixing rates for the greater puget sound region abstract recent sediment accumulation rates of 46 1200 mg cm2 yr are calculated from excess 210pb activity profiles in 44 sediment cores from 27 sites in the greater puget sound region rates calculated for nine stations in the deeper waters of central puget sound average 480 mg cm2 yr and are greatest between seattle and tacoma near the southern end of this region the standard error of this mean is 113 mg cm 2 yr magnitudes and geographic trends of 210pb derived accumulation rates agree with limited data on sediment inputs and transport paths their accuracy is further supported by several independent approaches including comparison with particle fluxes collected in year long series of sediment trap deployments at two sites accumulation rates are calculated assuming no mixing beneath surface mixed layers of 2 22 cm sediment mixing coefficients in these surface layers average at least 43 cm2 yr four times greater than those reported in open washington coast sediments the difference is attributed to the greater benthic biomass in puget sound sediments particle residence times in surface mixed layers vary from 1 5 to 68 years and introduce corresponding uncertainties in ages of horizons beneath the mixed layers for most of this region these residence times will cause a 20 30 year time lag in achieving an equivalent response of surface sediment chemical concentrations to changes in concentrations in freshly depositing particles for constituents whose stability and phase associations resemble those of 210pb these time lags limit the ability of sediment chemistry monitoring programs to recognize recent changes in composition and fluxes of chemicals to sediments recent fluxes calculated from the product of surface sediment chemical concentration and accumulation rates will be inaccurate for chemicals if their input concentrations have changed in the last 20 30 years

a model for 137cs and other tracers in lake sediments considering particle size and the inverse solution abstract a numerical model for the time dependent behavior of particle associated tracers in sediments has been developed the model is based on the advection diffusion equation for a tracer and includes a sediment density that increases with depth as a modified power function and a diffusion coefficient that follows a half gaussian function versus depth with maximal diffusivity at the sediment water interface the solution procedure is based on finite elements or finite differences the density function is developed from soil mechanics concepts and includes mixing effects through a young s modulus that is increased in the top layer according to a half gaussian function the new density function provides a better fit to 15 out of 17 sediment cores from lake michigan than a frequently used exponential expression the tracer model provides an excellent fit for the 137cs distributions in all of the 17 lake michigan cores that were investigated our fit to the 137cs profile of a southern lake michigan core that has been examined by others is significantly better than previous fits particularly near the top of the core from two different forms of the governing equation for a tracer and the resultant fits to experimental data it appears that 137cs is associated with colloidal and 210pb with settling particles a previously developed time domain method to extract the historical input record of a tracer from its sedimentary profile influenced by mixing has been further improved by including m depth and n time intervals where m n and by fitting the influx to a polynomial the improved method is demonstrated for the cd input to a northern lake michigan core nlm84b although the time resolution obtained 5 yr is better than the previous resolution 15 yr it is clear that the method needs to undergo further development in order to decrease the error of the reconstructed influx and particularly to avoid negative fluxes

assessment of relative active tectonics southwest border of the sierra nevada southern spain abstract we present a new method for evaluating relative active tectonics based on geomorphic indices useful in evaluating morphology and topography indices used include stream length gradient index sl drainage basin asymmetry af hypsometric integral hi ratio of valley floor width to valley height vf index of drainage basin shape bs and index of mountain front sinuosity smf results from the analysis are accumulated and expressed as an index of relative active tectonics iat which we divide into four classes from relatively low to highest tectonic activity the study area along the southwest border of the sierra nevada in southern spain is an ideal location to test the concept of an index to predict relative tectonic activity on a basis of area rather than a single valley or mountain front the study area has variable rates of active tectonics resulting from the collision of africa with europe that has produced linear east west anticlinal forms as well as extension with variable vertical rates of normal faulting to about 0 5 m ky we test the hypothesis that areas of known relatively high rates of active tectonics are associated with indicatives values of iat

time series measurements of macrobenthos abundance and sediment bioturbation intensity on a flood dominated shelf abstract four 70 m stations on the continental shelf offshore from the eel river northern california were occupied at roughly four month intervals between february 1995 and march 1998 and in august 1999 at each of the stations profiles of excess 234 th were used to quantify sediment bioturbation intensity in addition at two of the stations macrofaunal abundance species composition and functional groupings were quantified during the study period the eel river displayed a range of hydrological conditions with historically significant floods in january 1995 and january 1997 return periods of 15 and 40 y respectively relatively low flows during the winters of 1995 1996 and 1998 1999 and an el nino year characterized by moderate but frequent discharges in 1997 1998 the january 1995 and 1997 floods deposited 3 7 cm of fine grained high porosity sediment with high c n ratios and a terrestrial organic carbon signature at the study sites the following general questions are addressed herein 1 how do macrofaunal abundance species composition and functional groupings vary over time 2 does the sediment deposition following the january 1997 flood constitute a major disturbance to the eel shelf macrobenthos 3 how does sediment bioturbation intensity vary in time space and what are the main factors controlling this variation the eel shelf macrofauna is strongly dominated by subsurface deposit feeding polychaetes with anomalously low abundances of surface deposit feeders and virtually no suspension feeders among the community dominants the abundance data revealed a clear seasonal pattern with peak density 4 5 10 4 m 2 in the fall and a factor of two lower density in the late winter spring 2 10 4 m 2 within this seasonal context there was little evidence for extraordinary mortality caused by the january 1997 flood in that overall wintertime mortality and the mortality of most community dominants during a year 1995 1996 when there was no flood deposition were comparable to the mortality observed following the january 1997 flood in contrast the depth distribution of the macrofauna revealed a distinctive post flood pattern whereby a majority 55 70 of individuals were temporarily found at depths 4 cm this pattern suggests an active response by the resident fauna to sediment deposition and supports the idea that the floods did not cause a widespread disturbance although there may not be clear evidence for short term flood effects the overall species composition and functional groupings do imply that the sedimentary environment high sediment accumulation rates and abundant terrestrial organic matter has had a long term influence on the eel shelf macrofauna model fits to 75 profiles of excess 234 th show that in general the data are consistent with a steady state biodiffusive model the resultant mixing intensities ranged from 3 to 325 cm 2 y 1 with averages standard deviation of 35 33 24 19 37 35 and22 9 cm 2 y 1 at stations c70 i70 l70 and o70 respectively the average biodiffusivity for all stations and times was 29 25 cm 2 y 1 n 62 due to the large amount of variability which is consistent with other continental margin studies it was not possible to detect significant spatial or temporal variability although there is a hint of higher mixing intensities during the late summer early fall the period of maximal carbon flux to the seabed correlations between total macrofaunal abundance and mixing intensity are notably poor whereas a slightly better correlation r 2 0 22 was obtained between the abundance of large animals and bioturbation intensity by explicitly considering organic carbon flux or some measure of seabed food resources and the abundance of larger organisms it may be possible to predict bioturbation intensity better in future studies although the pervasive small scale variability detected on the eel river shelf warrants in depth theoretical and experimental consideration

determination of mixing parameters from tracer distributions in deep sea sediment cores abstract computer optimization and approximate analytical procedures are developed for the determination of the depth of bioturbation mixing d and the mixing coefficient d for instantaneous tracer inputs the methods have been applied to observations of microtektites volcanic ash and pumice in sixteen deep sea sediment cores the values for d are well determined generally with confidence intervals of a few centimeters or less and with an average value of d 11 cm for the sixteen cores the values for d are determined to first figure accuracy at best with values of around 10 cm 2 ka 1 or greater

particle age distributions and o2 exposure times timescales in bioturbated sediments 1 a stochastic particle tracking approach is used to compute particulate age distributions and oxygen exposure times oets in bioturbated marine sediments simulations representative of abyssal plain continental slope and continental shelf sediments indicate that within the mixed zone the variability in particle age is of the same order of magnitude as the average age itself this spreading of particle age by bioturbation complicates the interpretation of sedimentary archives the results further show that average and median ages of particle bound constituents undergoing decay during early diagenesis deviate from those of inert tracers similarly oets depend on the biological mixing and biogeochemical reactivity of particulate constituents hence ratios of the o2 penetration depth lo2 and the linear sedimentation rate may not offer reliable measures of actual oets taking into account biodiffusional particle mixing and preferential degradation of organic matter under oxygenated conditions the stochastic model predicts a global inverse relationship between the burial efficiency and the oet of organic carbon in ocean sediments the relationship however differs significantly from that proposed by hartnett et al 1998 who used o2 penetration depths divided by linear sedimentation rates lo2 to estimate oets

interpretation procedures for the determination of sediment parameters from time dependent flux inputs abstract a formulation for the effects of a time dependent input flux to a sedimentation system consisting of a diffusive layer underlain by a non diffusive medium has been developed the intent is to provide interpretation procedures for the determination of sedimentation rate diffusion coefficient and mixed layer thickness from observed tracer concentrations they have been applied for illustrative purposes to published137cs and239 240pu measurements

the influence of porosity gradients on mixing coefficients in sediments the surface layer of aquatic sediments is a zone characterized by both porosity gradients and intensive mixing in the standard approach porosity gradients are ignored when estimating mixing intensity here model formulations with both constant and varying porosity are contrasted to estimate mixing coefficients db from tracer depth profiles complementing the well known exponential solution of the constant porosity model we present a general solution to the variable porosity model in terms of hypergeometric functions when using these models in a forward way the tracer activities predicted by the variable porosity model are higher than those generated by the constant porosity model similarly when inverse modelling db values estimated by the variable porosity model are systematically higher than those derived from the constant porosity model still differences in db values remain relatively small when applying both mixing models to excess 210pb data profiles from slope sediments a maximal difference of 30 is obtained between db values the average deviation being 16 a systematic exploration of parameter space predicts a maximal underestimation of 60 when deriving db values from the constant porosity mixing model given the uncertainty imposed by other model assumptions underlying the diffusive mixing model the influence of porosity gradients on db values must be classified as rather modest hence the current mixing coefficient database is not biased by the constant porosity approximation

marine tectonics processes at mid ocean ridges the use of multibeam echo sounders and various side looking sonar systems has greatly increased our knowledge and understanding of mid ocean ridge mor processes since the last iugg review on mid ocean ridge research macdonald 1983 the extensive use of swath mapping tools such as sea beam deep tow seamarc i and ii the application of multichannel seismic reflection techniques to the detection of axial magma chambers and the use of satellite data in the study of oceanic lithosphere have rejuvenated marine tectonics and have generated and stimulated a large number of important contributions this review will focus on what we feel were the major developments in marine tectonics with an emphasis on mid ocean ridges in the last four years certain topics such as marine seismicity and satellite studies are only briefly mentionned for reference and will be covered in greater detail in other reviews because of the exponential growth in the number of publications related to mors during 1982 1986 only a few references pertinent to each of the major research topics will be quoted in the text as examples but the reader will find an extensive bibliography at the end of the text references published prior to 1982 were added only where appropriate

extraction of the m2 ocean tide from seasat altimeter data summary three complementary methods for the extraction of the m2 ocean tide using seasat altimetry are presented and compared the first method that developed by cartwright alcock which provides point measurements of the tide at the crossovers of the seasa t repeat orbit ground track has been applied to a study of the tide in tropical ocean areas the other two methods involve spatial expansions of m2 in terms of either surface spherical harmonics in the case of the method developed by mazzega or platzman normal modes of the world ocean the results obtained by each method from only one month of seasat data reproduce many features of the tide represented in recent tidal models and promise well for satellite altimetry as a future source of tidal knowledge

tectonic geomorphology of the easternmost extension of the gulf of corinth beotia central greece the easternmost sector of the gulf of corinth the beotia area in central greece is an area with active normal faults located between the two major rift structures of central greece the gulf of corinth and the north gulf of evia these active normal faults include wnw to e w and ne to ene trending faults affect the landscape and generate basin and range topography within the beotia we study four normal fault zones and drainage basin geometry in the easternmost sector of the gulf of corinth to document the impact of active tectonics on the landscape evolution fault and drainage geometry are investigated based on detailed field mapping and high resolution digital elevation models tectonic geomorphic analysis using several parameters of active tectonics provides information concerning the relative tectonic activity and fault growth in order to detect areas of lateral stream migration that could indicate recent tectonic activity the transverse topographic symmetry factor and the asymmetry factor are used to analyse drainage basin geometry in six large drainage basins and a drainage domain covering the study area our results show that vertical motions and tilting associated with normal faulting influence the drainage geometry and its development values of stream gradient indices sl are relatively high close to the fault traces of the studied fault zones suggesting high activity mountain front sinuosity smf mean values along the fault zones ranges from 1 08 to 1 26 valley floor width to valley height ratios vf mean values along the studied fault zones range between 0 5 and 1 6 drainage basin shape bs mean values along the fault zones range from 1 08 to 3 54 all these geomorphic parameters and geomorphological data suggest that the analyzed normal faults are highly active lateral fault growth was likely produced by primarily eastward propagation with the wnw to e w trending faults being the relatively more active structures

m2 ocean tide at cobb seamount from seasat altimeter data seasat altimetry reduced to sea surface heights and harmonically analyzed at the frequencies of the dominant tidal components provides a direct measurement of m2 ocean tide parameters near cobb seamount in the northeast pacific comparison of these altimetric tide parameters with those determined from a bottom pressure gauge located on the summit of cobb seamount shows fair agreement in amplitude 43 cm versus 81 cm and good agreement in greenwich phase angle 243 versus 242 degrees the precision of the altimeter solution is estimated at 8 cm in amplitude and 10 degrees in phase angle

preserving the palaeoenvironmental record in drylands bioturbation and its significance for luminescence derived chronologies luminescence osl dating has revolutionised the understanding of late pleistocene dryland activity however one of the key assumptions for this sort of palaeoenvironmental work is that sedimentary sequences have been preserved intact enabling their use as proxy indicators of past changes this relies on stabilisation or burial soon after deposition and a mechanism to prevent any subsequent re mobilisation as well as a dating technique osl especially at the single grain level can be used to gain an insight into post depositional processes that may distort or invalidate the palaeoenvironmental record of geological sediment sequences this paper explores the possible impact of bioturbation the movement of sediment by flora and fauna on luminescence derived chronologies from quaternary sedimentary deposits in texas and florida usa which have both independent radiocarbon chronologies and archaeological evidence these sites clearly illustrate the ability of bioturbation to rejuvenate ancient weathered sandy bedrock and or to alter depositional stratigraphies through the processes of exhumation and sub surface mixing of sediment the use of multiple osl replicate measurements is advocated as a strategy for checking for bioturbated sediment where significant osl heterogeneity is found caution should be taken with the derived osl ages and further measurements at the single grain level are recommended observations from the linear dunes of the kalahari show them to have no bedding structure and to have osl heterogeneity similar to that shown from the bioturbated texan and florida sites the kalahari linear dunes could have therefore undergone hitherto undetected post depositional sediment disturbance which would have implications for the established osl chronology for the region

the april 2007 earthquake swarm near lake trichonis and implications for active tectonics in western greece abstract we investigate the properties of the april 2007 earthquake swarm mw 5 2 which occurred at the vicinity of lake trichonis western greece first we relocated the earthquakes using p and s wave arrivals to the stations of the hellenic unified seismic network husn and then we applied moment tensor inversion to regional broad band waveforms to obtain the focal mechanisms of the strongest events of the 2007 swarm the relocated epicentres cluster along the eastern banks of the lake and follow a distinct nnw ese trend the previous strong sequence close to lake trichonis occurred in june december 1975 we applied teleseismic body waveform inversion to obtain the focal mechanism solution of the strongest earthquake of this sequence i e the 31 december 1975 mw 6 0 event our results indicate that a the 31 december 1975 mw 6 0 event was produced by a nw se normal fault dipping to the ne with considerable sinistral strike slip component we relocated its epicentre i using phase data reported to isc and its coordinates are 38 486 n 21 661 e ii using the available macroseismic data and the coordinates of the macroseismic epicentre are 38 49 n 21 63 e close to the strongly affected village of kato makrinou b the earthquakes of the 2007 swarm indicate a nnw sse strike for the activated main structure parallel to the eastern banks of lake trichonis dipping to the ne and characterized by mainly normal faulting occasionally combined with sinistral strike slip component the 2007 earthquake swarm did not rupture the well documented e w striking trichonis normal fault that bounds the southern flank of the lake but on the contrary it is due to rupture of a nw se normal fault that strikes at a 45 angle to the trichonis fault the left lateral component of faulting is mapped for the first time to the north of the gulf of patras which was previously regarded as the boundary for strike slip motions in western greece this result signifies the importance of further investigations to unravel in detail the tectonics of this region

seismicity and seismotectonics in epirus western greece results from a microearthquake survey during a twelve month passive tomography experiment in epirus in northwestern greece a total of 1368 microearthquakes were located the most accu rately located events and focal mechanisms are used here to understand the seismo tectonics of the area the seismicity shows a clear association with the main previously defined deformation zones a total of 434 well defined focal mechanisms were also used for the determination of the stress pattern in the area the computed stress field pattern is quite complex close to the surface and almost homogeneous at depths below 15 km for these depths the stress field is purely compressional in a west southwest direction whereas for shallow depths it is transpressional or even extensional for some smaller areas the abrupt change in the stress pattern which occurs as depth increases suggests the existence of a detachment surface which is provided by the evaporites that have intruded into the upper layers through the thrust zones the presence of the evaporites and their lateral extent is mapped by the seismicity distribution and con firmed by seismic tomography based on the findings we estimate a possible total evaporite thickness of almost 10 km at least for the central part of the study area such a result is important for the oil exploration efforts that have just started in epirus

microearthquake seismicity and active tectonics of northwestern greece we carried out a microearthquake survey lasting for six weeks in northwest greece using 18 portable seismograph stations to examine a region in which normal and thrust faulting have been reported in close proximity to one another with this array we located 148 events and determined fault plane solutions for eight events using only rays radiated upwards the seismicity of the region is diffuse with events extending to depths of nearly 30 km and there is a minimum in activity near a depth of 15 km the fault plane solutions exhibit a wide spectrum of fault types and orientations and are not consistent with simple zones of shortening or extension neither tractions applied to the edges or bottom of the region nor deviatoric stresses that compensate for lateral variations in crustal thickness can account for the variety of fault plane solutions we think that the complicated behavior is a manifestation of inhomogeneous deformation due at least in part to a pre existing complicated juxtaposition of structures and formations

early organic diagenesis the significance of progressive subsurface oxidation fronts in pelagic sediments abstract porewater and solid phase geochemical data at two contrasting ne atlantic stations are reported station 10552 on the cape verde abyssal plain is a site of slow pelagic accumulation ca 0 4 cm kyr 1 molecular oxygen is present in the sediment column to at least 2 m and probably much deeper labile organic carbon is almost totally consumed in the upper few centimetres of the sediment by contrast at station 10554 on the madeira abyssal plain the pelagic sequence has been interrupted by the occasional deposition of organic rich turbidites porewater oxygen and nitrate profiles show that subsurface organic metabolism of the organic carbon associated with the uppermost turbidite layer is a significant fraction of the overall metabolism in the sediment column this metabolism occurs at a relatively thin reaction front which progresses deeper into the turbidite with time this phenomenon exerts a controlling influence on the present nutrient profile and redox succession in a less extreme form substrate distributions of this latter type are not uncommon in atlantic sediments a model has been developed which is controlled by both oxygen and nitrate data this model permits a vertical profile of metabolic activity to be derived and also gives estimates of the reaction rate constants and solid phase mixing rates at these two contrasting stations about 30 of the total activity at station 10554 is located within the turbidite at the deepening reaction front this is a non steady state condition in fact it is found that the integrated metabolic activity at the two stations is not dissimilar ca 1 2 10 13 moles cm 2 sec 1 the striking differences in redox profile are therefore primarily attributable to differences in the distribution of metabolic activity within the column

mechanisms and models of iridium anomaly shape across the cretaceous paleogene boundary article i nfo the interpretation of the cretaceous paleogene k pg iridium anomaly and other impact ejecta as the result of a single large asteroid impact has been the subject of much debate in part due to the distribution of impact markers beyond the narrow confines of the k pg boundary sedimentary layer here we revisit the hypothesized processes leading to the shape of k pg iridium profiles including geochemical remobilization and or diffusion prolonged deposition volcanism multiple impacts and sediment mixing using evidence from the literature and modeling of one north pacific site we find that sediment mixing of a single impact event provides the most parsimonious mechanism for iridium profile shape in open ocean oxic sediments while the increase in background iridium bracketing the boundary likely has a volcanic origin in some past studies a sediment mixing mechanism for iridium profile shape was ruled out based on an overly simplified set of expectations for the effect of sediment mixing on markers of geologically instantaneous events thus we introduce and use a lagrangian sediment mixing model to illustrate the theoretical effects of mixing on records of rapid events the sediment mixing origin for iridium anomaly shape the correspondence in mixing extent between iridium and microfossils and the fit of sediment mixing models to an empirical iridium profile indicate that iridium may provide a better tracer of mixing than previously proposed k pg mixing tracers such as ni spinels

nonlinear parameter estimation for sediment cores abstract nonlinear parameter estimation techniques are applied to three distinctly different sediment cores for which concentrations of tracers with steady and time dependent flux inputs are available the mathematical model employed consists of a diffusive upper layer of finite depth underlain by a semi infinite nondiffusive medium confidence regions and intervals are reported for sedimentation rate diffusion coefficient and mixed layer depth based on ordinary least squares criteria for each tracer conflicting estimates are resolved using a weighted least squares procedure which combines observations of the individual tracers and exploits their strengths and weaknesses

tertiary geodynamical evolution of northwestern greece paleomagnetic results abstract paleomagnetic results have been obtained from 29 sites sampled in lower to upper oligocene flysch sections of the ionian zone in northwestern greece they indicate a clockwise rotation of about 45 of the entire region a comparison with previously published results relative to both younger and older formations shows that this rotation has occurred in two phases of comparable amplitude one during middle miocene and the other during pliocene and quaternary separated by a period of at least 7 ma during which no significant rotation has occurred no major rotation has occurred during the entire paleocene and eocene stages this large measured rotation implies a horizontal displacement of at least 100 km in epirus possible mechanisms involving a rotation of the nappe sheets rotation of the basement or a combination of the two are discussed the two phases of paleomagnetic rotation can be correlated with the tertiary and quaternary calc alkaline volcanic activity in the aegean sea a palinspastic reconstruction shows that the orientation of the major structures now striking n155 was almost east west in the middle miocene at the epoch of their formation

statistical re analysis for size dependency in deep sea mixing using the data of ruddiman et al we tested the implicit assumption that biogenic mixing intensity dbslb within a deposit is independent of particle size a conservative friedman rank sums test and the multiple comparison test for it were used to compare the downcore dispersion of several size fractions 11 500 m of volcanic ash in three of the seven cores analyzed the null hypothesis of size independent mixing was rejected fisher s method of compounding independent probabilities forced rejection of the hypothesis of size independent mixing overall p 0 001 i e when all the data for the seven cores were considered together mixing is size dependent with finer fractions being more intensely mixed the likely cause is size selective feeding by infauna the importance of the observed differences in stratigraphy among size fractions must be evaluated against the resolution required to address the problem at hand

palaeomagnetic evidence from pelagic limestones for clockwise rotation of the ionian zone western greece abstract on the basis of a pilot study of all the major carbonate lithologies in the ionian zone of western greece the upper part of the upper senonian to upper eocene microbreccious limestones formation was selected as the most suitable facies for a detailed regional palaeomagnetic study the 51 sites sampled are situated on flanks of anticlines or monoclines which post date the acquisition of the characteristic remanent magnetization the regional folding occurred during post late eocene emplacement of nappe sheets which had undergone decollement on triassic evaporitic horizons the palaeomagnetic directions after correction for deviations of local fold axis orientation have a regional significance after this correction the mean palaeodeclination is about 35 e relative to the geographic pole with respect to the early tertiary african pole position these palaeodeclinations indicate an apparent 38 clockwise rotation of the nappe sheets the palaeoinclinations support a palaeogeographic model locating the carbonate sediments of the ionian zone on the northeastern margin of the adriatic promontory of the african plate the total rotation implied by the palaeodeclination data is possibly due to a combination of two different mechanisms 1 1 rotation of the nappe sheets during overthrust and emplacement during the main mid miocene compressional phase of deformation 2 2 rotation of the ionian zone basement and nappes associated with extension in the aegean basin during the last 13 m y

fine scale distributions of porosity and particulate excess210pb organic carbon and caco3 in surface sediments of the deep equatorial pacific abstract sediment samples were recovered from the central equatorial pacific ocean sectioned at 1 mm intervals and analyzed for porosity organic carbon excess210pb and caco3 steep porosity gradients were measured in the upper 1 cm of the sediment column with extremely high values observed near the sediment surface similarly particulate organic carbon contents are highest at the sediment surface decrease sharply in the upper 1 cm and are relatively constant between 1 and 5 cm caco3 values on the other hand are lowest at the sediment surface and increase to a constant value below 5 10 mm depth at the carbonate ooze sites excess210pb is present throughout the upper 5 cm of the sediments suggesting relatively rapid particle mixing rates however extremely high excess210pb activities 100 dpm g are observed at the sediment surface with sharp gradients present in the upper 1 cm which would suggest slow rates of mixing this apparent contradiction along with the major features of the caco3 and particulate organic carbon profiles can be explained by a particle selective feeding mechanism in which organic carbon excess210pb enriched particles are preferentially maintained at the sediment surface via ingestion and defecation by benthic organisms

morphotectonic records of neotectonic activity in the vicinity of north almora thrust zone central kumaun himalaya abstract the landform development and valley floor morphology of active regions is significantly controlled by tectonic processes in the present study the upper catchments of kosi and gagas river valleys have been investigated with special emphasis on aggradational landforms to explain the spatial and temporal variability of aggradation incision in response to tectonic activity during the late quaternary and holocene in central kumaun himalaya major tectonic elements such as the north almora thrust nat rasiyari fault rf and gagas fault gf are considered to be controlling the development of landforms in the region the valleys have preserved debris flow terraces bedrock strath terraces and fluviolacustrine terraces that provide signatures of tectonic activity morphostratigraphy of the terraces reveals that the oldest landforms are preserved in the hanging wall block of the nat rf and along the gf reconstructions based on morphostratigraphy through the application of optical chronology suggests multiple phases of fluvial aggradation in the upper catchment of the kosi and gagas rivers that were initiated around 34 ka the youngest phase of aggradation is dated to be around early to mid holocene 7 1 ka based on terrace morphology four major phases of enhanced uplift have been estimated during 34 15 8 7 and 3 ka the older uplift event dated to be around 34 ka is represented uplift along gf which accommodated onset of valley fill aggradation in gagas valley the 15 8 ka event represents uplift along rf which led to the generation of debris flow from adjacent hillslopes the 7 ka event represents uplift of a hanging wall block of the nat and deposition of debris flow terraces however the youngest 3 ka event represents enhanced uplift which is responsible for the incision of the older valley fill sediments and bedrock following this a phase of accelerated incision erosion owing to an increase in uplift rate occurred as evident from the strath terraces between 7 and 1 ka

geomorphic response of coastal streams to low intermediate and high rates of uplift medocino triple junction region northern california analysis of three dimensional morphological properties of 24 coastal drainage basins that have evolved in areas of low 3 m 1 000 yr rates of uplift near the mendocino triple junction mtj coastal northern california identified channel gradients as the best indicator of tectonism in the landscape lower order tributaries best reflect tectonically controlled differences the largest streams examined of third order are able to adjust to most base level change and maintain their profile form whereas lower order streams farther upstream tend to accumulate the effects of net base level fall and have steepest profiles in the areas of highest uplift rates variations in steepness of first order channel gradients indicate that 1 high uplift rates in the wake of the mtj have existed for at least 73 000 yr and 2 differential tilt of the region to the north and south of the current locus of highest uplift rate is occurring in association with regional uplift although first order streams are excellent indicators of areas of both high uplift rates and regional differential tilting they are less useful in distinguishing between areas of low and intermediate uplift rate analysis of the longitudinal profile of the main trunk stream of ten of the 24 drainage basins using the stream gradient index was more useful to categorize broadly the uplift rates and to distinguish between streams in low and intermediate uplift rate areas although the hypotheses tested herein do not identify the exact mechanism off uplift in the mtj region they do indicate that the nature of deformation is most likely regional tilt rather than crustal shortening with localized compressional folding and thrust faulting they also indicate that geomorphic responses trail in the wake of the uplift rate response caused by development of a slab window beneath the north american plate 1 maximum uplift rates occur 9 km south of the northern boundary of the slab window 2 maximum mean first order channel gradient occurs 16 km south of the northern edge of the slab window and 3 maximum drainage basin relief occurs 20 km south of the northern edge of the slab window associated lag times between passage of the southern edge of the subducted gorda plate slab and geomorphic responses are 160 000 yr for maximum uplift rates 290 000 yr for maximum channel gradients and 370 000 yr for maximum relief