seasonal variation in the flux of planktonic foraminifera time series sediment trap results from the panama basin abstract a mooring array with three automated sediment traps capable of collecting time series samples was deployed in the panama basin for one year beginning in december 1979 a series of six consecutive two month long samples was collected at each of three depths 890 2590 and 3560 m in order to examine seasonal variation in the flux of planktonic foraminifera and evaluate the contribution of foraminifera to the total carbonate flux the flux of the larger planktonic foraminifera 250 500 m and 500 1000 m is greatest during february march when upwelling is most intense in the panama basin in contrast the maximum flux of the smaller foraminifera 125 250 m is associated with a phytoplankton bloom during the summer months june through september this size dependent flux pattern appears to be a species specific effect the flux of the larger foraminifera is dominated by non spinose forms i e neogloboquadrina dutertrei and globorotalia theyeri while the flux of the smaller foraminifera consists predominantly of spinose species i e globigerinoides ruber g sacculifer and g conglobatus although the magnitude of the flux varied throughout the year the average weight of individual foraminiferal tests in different size fractions showed no seasonal variability with the exception of the june july period when there was a major coccolith bloom planktonic foraminifera greater than 125 m account for between 28 and 34 of the total carbonate flux at this location during the coccolith bloom planktonic foraminifera accounted for less than 2 of the total carbonate flux planktonic foraminifera in the 250 500 m size range are the most significant contributors to the overall particulate flux accounting for roughly 70 80 of the total foraminiferal fluxes measured at the three trap depths

cenozoic deformation of the tarim plate and the implications for mountain building in the tibetan plateau and the tian shan 1 the tarim basin in nw china developed as a complex foreland basin in the cenozoic in association with mountain building in the tibetan plateau to the south and the tian shan orogen to the north we reconstructed the cenozoic deformation history of the tarim basement by backstripping the sedimentary rocks two dimensional and three dimensional finite element models are then used to simulate the flexural deformation of the tarim basement in response to the sedimentary loads and additional tectonic loads associated with overthrusting of the surrounding mountain belts the results suggest that uplift of both the western kunlun shan and the tian shan orogens started during or before oligocene since the miocene mountain building accelerated in the western kunlun shan but showed segmented development in the tian shan the results also indicate reduced tectonic load along the altyn tagh fault since late miocene consistent with geological and geophysical evidence of the fault cutting the entire lithosphere and migrating southward during its cause of the cenozoic evolution

oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

trace metal signatures of eastern mediterranean sapropels abstract sapropel samples of pliocene to pleistocene age recovered during odp leg 160 from sites 964 ionian basin 969 mediterranean ridge 966 967 top and northern slope of the eratosthenes seamount south of cyprus and 968 cyprus margin were analysed for major and trace elements eastern mediterranean sapropels are characterized by high organic carbon and sulphur contents and by significant enrichments in several redox sensitive and or sulphide forming trace metals bi cd co cr cu mo ni re sb tl u v enrichment factors relative to average shale are comparable to those found in ctbe black shales the re content is extremely high in the sapropels studied with maximum values up to 1000 ng g re mo ratios averaging 2 7 10 3 are close to the seawater value high trace metal enrichments and re mo ratios close to the seawater value point to an anoxic water column during sapropel formation additionally enhanced ba concentrations in the sapropels support the assumption that bioproductivity was also high during these episodes trace metal signatures of sapropels originating from different drill sites on a transect across the eastern mediterranean are not only influenced by water depth but also by their location in the eastern mediterranean metal enrichments seem to be higher at the western sites compared with the eastern sites this probably reflects a change in the circulation pattern during periods of sapropel formation pliocene sapropels exhibit elevated trace metal contents in comparison with pleistocene examples therefore different palaeoceanographic conditions may have developed during the pleistocene compared with the pliocene altering palaeoceanography was probably controlled by climatic change which may be related to the onset of glaciation of the northern hemisphere decreasing summer precipitation throughout the late pliocene and the pleistocene may also have influenced sapropel deposition

organic rich layers in the metochia section gavdos greece evidence for a single mechanism of sapropel formation during the past 10 my abstract three well developed 10 ma old sapropels from the island of gavdos greece were selected for a detailed geochemical micropaleontological and sedimentological study the sapropels are characterized by a high organic carbon and a low carbonate content productivity was higher during sapropel formation as indicated by increased ba contents and higher percentages of the planktonic foraminiferal species neogloboquadrina acostaensis enrichment of mo and v in the sapropels indicates less oxygenated bottom water conditions which is supported by the flourishing of low oxygen tolerant benthic foraminifera variation in grainsize and the ti al ratio point to an alternating dominance of fluvial sapropels and eolian derived homogeneous intervals terrigenous clastics evidence for a local origin of the enhanced fluvial input comes from the gradual replacement of the sapropels by cyclic turbidite sequences which were fed by bed load type rivers the increased fluvial input during sapropel formation increased the sedimentation rate and caused the observed carbonate depletion the results obtained for the gavdos sapropels are consistent with those of previous studies of younger sapropels and related caco 3 cycles in the mediterranean the consistency in most of the geochemical and micropaleontological characteristics indicates that all sapropels and related layers are the result of a single mechanism for at least the past 10 my namely precession induced dry wet oscillations in the mediterranean climate still the effect of this mechanism on the intensity of surface water productivity dilution and diagenetic signals may differ from site to site depending on location depositional environment and intensity of the astronomical forcing

pliocene pleistocene vegetational and climatic evolution of the south central mediterranean abstract the vegetational history of the south central mediterranean clearly reflects the major global climatic changes of the last four million years a mediterranean type climate characterized by strong seasonality and a dry summer may have existed in this region during the early pliocene a short term climatic cooling at approximately 3 2 ma resulted in the temporary establishment of a humidity demanding flora the onset of major northern hemisphere glaciation at approximately 2 4 ma initiated an alternation between humid glacial and dry interglacial conditions vegetational differences between this region and the north west mediterranean indicate that distinct latitudinal climatic gradients probably existed in the mediterranean during the pliocene early pleistocene

exhumational history of the north central pamir 1 the pamir plateau forms a prominent tectonic salient along the western end of the tibet tarim margin despite its tectonic significance relatively little is known about the timing of major cenozoic tectonic events in the pamir here we present new apatite and zircon u th he ages bulk rock geochemistry and al in hornblende barometry results from the karakul graben a prominent north south oriented rift basin located 50 km south of the main pamir thrust although cooling ages do not record the onset of extension graben bounding normal faults provide exposures of otherwise slowly eroding rocks which record two cenozoic thermal events existing geochronology and new results suggest that granitic rocks in the karakul region were shallowly emplaced cooled very quickly through 300 c and have experienced less than 10 km of exhumation since the late triassic a long period of relatively slow exhumation throughout much of the late mesozoic and cenozoic was punctuated by two periods of accelerated exhumation during the middle eocene 50 40 ma and early miocene 25 16 ma we interpret the first period of accelerated exhumation as a result of tectonic uplift and subsequent erosion due to the northward propagation of the india asia collision we attribute the second period of rapid exhumation to a renewed phase of tectonism and plateau uplift in the pamir perhaps related to a break off event along the down going indian plate at 25 ma or to the onset of slip along the nascent karakoram fault

nonlinear features of internal waves off baja california as observed from the seasat imaging radar the synthetic aperture radar sar on seasat has yielded well defined images of quasi periodic internal waves in the waters on the west side of baja california these waves occur in groupings separated by 15 23 km each group having 2 20 striations with wavelengths of the order of 300 m or longer they appear in water approximately 200 m deep shoreward of several banks at the continental shelf edge whose depths are as shallow as 15 m the wave surface signatures exhibit clear nonlinear features higher than linear group velocities and decreases in wavelength crest length and amplitude toward the rear of the packet environmental data for the area have been examined and these show a well developed mixed layer low winds and vigorous tidal action thus stratification wind speed tidal current and bottom topography apparently combine to establish proper conditions for tidal generation of internal waves the images have been analyzed from the standpoint of nonlinear wave theory and it is shown that the vertical displacement of an isopycnal surface can be estimated from a combination of sar imagery vertical density profiles and simple theoretical expressions numerical examples are given

laminated sediments from the vrica section calabria s italy evidence for plio pleistocene climatic change in the mediterranean region abstract six laminated sedimentary units laminites from the vrica section calabria southern italy have been analyzed geochemically and micropaleontologically to assess paleoclimatic conditions in this region during the transition from the pliocene to the pleistocene two laminites formed during the early pleistocene and one formed immediately below the pliocene pleistocene boundary all have a greater organic carbon content relative to the surrounding marls by contrast three late pliocene laminites exhibit no significant increase in organic carbon which indicates that the conditions associated with the formation of these three units were somewhat different than those associated with the formation of the three younger laminites stable isotope analyses of planktonic foraminifera from the laminites indicate that all of these units were formed during periods of decreased salinity concentrations in surface waters the laminites were formed as a result of basin anoxia brought on by increased surface water stratification during periods of high runoff the vrica planktonic foraminiferal census data indicates that the laminites contain a distinctive fauna which can be partially attributed to increased nutrient concentrations by contrast species assemblages within the marls seem to be primarily controlled by surface water temperatures through the use of polytopic vector analysis the foraminiferal census data can be simplified into five assemblages each of which reflects temperature salinity and or nutrient concentrations the nutrient dependent assemblage indicates an intensification in surface water productivity during periods of laminite formation during the later pliocene and early pleistocene while the temperature dependent assemblages indicate an overall cooling of surface water temperatures during the same period the results of the planktonic foraminiferal analyses support the concept of a regional cooling across the pliocene pleistocene boundary in the mediterranean in addition the results of this study indicate that these climatic changes resulted in differences in the nature of the laminites cooler climatic conditions during the latest pliocene and the early pleistocene favored the formation of laminites slightly richer in organic carbon and nitrogen because of increased organic carbon input or enhanced organic matter preservation the warmer climatic conditions of the late pliocene produced laminites relatively poor in organic carbon and nitrogen as a result of either decreased runoff or decreased organic matter preservation

late neogene laminated and opal rich facies from the mediterranean region geochemical evidence for mechanisms of formation abstract the mechanisms for the formation of laminated and opal rich sediments from southern italy bianco and vrica and southern sicily gela are investigated using a geochemical approach the vrica laminates are relatively rich in organic carbon while the gela laminites are not carbon nitrogen ratios carbon isotopic composition and lipid content of the organic matter at vrica indicate that the laminates represent periods of increased input of terrestrial organic matter and enhanced preservation based on oxygen isotopic studies of planktonic foraminifera a basin stratification model is presented to explain the formation of laminites at both vrica and gela biogenic silica and carbonate content and the carbon isotopic composition of benthic foraminifera suggest that the bianco diatomites represent periods of increased productivity the isotopic composition of planktonic foraminifera from bianco indicates that the increased productivity was a result of basin eutrophication brought on by continental runoff the low organic carbon content of the bianco diatomites is attributed to continuous bottom water ventilation the results of laminites studies indicate that they are not always rich in organic matter as generally assumed moreover the formation of organic rich laminites can be the result of enhanced preservation not increased productivity results from bianco indicate that preservation plays a primary role in controlling the organic carbon content of sediments

planktonic foraminifera of the northern indian ocean distribution and preservation in surface sediments in the northern indian ocean planktonic foraminiferal tests accumulate in a wide variety of surface water environments and depositional settings this variability enables us to isolate the effects that surface water ecology and differential dissolution have on the distribution of planktonic foraminifera from 251 geographically widespread surface sediment samples foraminiferal abundance varies from 0 to 104 whole foraminifera in the greater than 150 m fraction per gram dry sediment values 10 characterize the three deep basins of the equatorial indian ocean and the western bay of bengal foraminiferal tests are most abundant on carbonate covered ninety east and carlsberg ridges absolute abundance patterns are mainly controlled by non ecological processes variations in dissolution resistant species rsp with water depth reveal that the foraminiferal lysocline fl varies regionally the fl is deepest 3 800 m in the equatorial region rises abruptly to 3 300 m in the arabian sea and varies from 2 600 m to near 2 000 m moving northward in the bay of bengal deep samples with anomalously low rsp 30 suggest redeposition systematic geographic and depth related variation is observed for the 17 most abundant foraminiferal species dissolution resistant species g menardii g tumida g dutertrei p obliquiloculata generally exhibit a rapid and continuous increase in relative abundance at and below the fl susceptible species g ruber g bulloides g glutinata for example exhibit a rapid and continuous decrease in relative abundance at and below the fl moderately susceptible species g conglobatus g aequilateralis g conglomerata for example rapidly increase in abundance at the fl and systematically decrease with depth below the fl principal components analysis pca of faunal data from minimally dissolved 30 rsp samples reveals important ecologically related species intercorrelations the major biogeographic gradient is the negative covarying relationship between ag bulloides g glutinata species pair and a grouping ofg sacculifer g conglobatus g aequilateralis andg ruber pca of all samples demonstrates how differential dissolution alters this and other species relationships species groupings that incorporateg ruber g menardii andg dutertrei are particularly affected by dissolution comparison of average faunal data from minimally dissolved samples in the northern indian ocean with similar samples from other tropical regions suggests varying environmental factors produce distinct faunas within the tropical ocean for example g bulloides g falconensis andg hexagona are significantly more abundant in northern indian ocean surface sediments while such species asg ruber g sacculifer g dutertrei andp obliquiloculata dominate in other tropical regions

comment on magnetostratigraphic study of the kuche depression tarim basin and cenozoic uplift of the tian shan range western china baochun huang john d a piper shoutao peng tao liu zhong li qingchen wang rixiang zhu earth planet sci lett 2006 doi 10 1016 j epsl 2006 09 020 abstract the recent publication of magnetostratigraphic study of the kuche depression tarim basin and cenozoic uplift of the tian shan range western china by b c huang j d a piper s t peng t liu z li q c wang r x zhu earth planet sci lett 2006 doi 10 1016 j epsl 2006 09 020 discusses the cenozoic uplift history of the tianshan mountains by studying the magnetostratigraphy of paleogene to neogene continental sediments from two sections located in the kuche basin at the northern edge of the tarim basin to support their conclusion they reinterpreted a magnetostratigraphic study of the yaha section which lies 10 km south of their sections we previously published j charreau s gilder y chen s dominguez j p avouac s sen m jolivet y li and w wang magnetostratigraphy of the yaha section tarim basin china 11 ma acceleration in erosion and uplift of the tianshan mountains geology 34 3 2006 181 184 here 1 we argue that the interpretations of the sedimentation rate changes they proposed for the kuche sections are partially invalid 2 we disagree with their reinterpretation of the age of the yaha section and 3 we think that the way they interpret their ams data is incorrect

oligocene clockwise rotations along the eastern pamir tectonic and paleogeographic implications despite the importance of the pamir range in controlling asian paleoenvironments and land sea paleogeography its tectonic evolution remains poorly constrained in time and space hindering its potential for understanding deep to surface processes we provide here new constraints on vertical axis tectonic rotations from the southwest tarim basin along the eastern flank of the pamir arcuate range based on paleomagnetic results two well dated eocene to oligocene sections previously analyzed using biostratigraphy and magnetostratigraphy yield consistently clockwise rotations of 21 6 4 2 in 41 to 36 ma strata then 17 1 6 5 in 33 to 28 ma strata at the aertashi section and 14 2 11 5 in 41 to 40 ma strata at the kezi section combined with a regional review of existing paleomagnetic studies these results indicate that most of the clockwise rotations along the eastern pamir occurred during oligocene times and did not extend systematically and regionally into the tarim basin in contrast on the western flank of the pamir tectonic rotations in cretaceous to neogene strata are regionally extensive and systematically counterclockwise throughout the afghan tajik basin this timing and pattern of rotations is consistent with paleogeographic reconstructions of the regional sea retreat out of central asia and supports a two stage kinematic model 1 symmetric rotations of either flanks of the pamir arcuate range until oligocene times followed by 2 continued rotations on its western flank associated with radial thrusting and along the eastern flank no further rotations due to decoupled transfer slip starting in the early miocene

late pliocene to early pleistocene astronomically forced sea surface productivity and temperature variations in the mediterranean abstract principal component analysis of late pliocene to early pleistocene planktonic foraminiferal abundances from the mediterranean yielded two significant components which represent first order approximations for sea surface productivity and temperature this interpretation is confirmed by the good fit between the score plots and sea surface productivity and sea surface temperature proxy records based on selected eutrophic and temperature sensitive species using present day habitat characteristics spectral analysis revealed significant peaks in the orbital frequency bands of the spectrum suggesting that variations in sea surface productivity and temperature are controlled by the quasi periodic variations in the earth s orbit precession forced variations are reflected primarily in sea surface productivity and to a lesser degree in sea surface temperature maxima in sea surface productivity and temperature in this frequency band occurred at times of sapropel formation the sea surface productivity maxima can be explained by an increased input of river borne nutrients and by the shoaling of the pycnocline and the associated intensification of the deep chlorophyll maximum dcm layer precession forced variations in sea surface temperature are not related to glacial cycles since this frequency component is almost completely absent in ice volume proxy records for this time interval sapropel bound sea surface temperature maxima presumably reflect periods of maximum insolation during the northern hemisphere summer the contrasting winter signal corresponds to minimum insolation values which may be reflected by peak abundances ofgloborotalia inflata obliquity forced variations are reflected primarily in sea surface temperature and not in sea surface productivity these temperature fluctuations correspond with ice volume changes registered in the oxygen isotope record at the north atlantic dsdp site 607 this shows that obliquity forced sea surface temperature variations in the mediterranean are primarily driven by glacial cycles

geological evidence against large scale pre holocene offsets along the karakoram fault implications for the limited extrusion of the tibetan plateau two end member models proposed to accommodate the convergence between india and asia north of the himalaya are 1 homogeneous crustal thickening of the tibetan plateau and 2 continental escape or extrusion of tibet and southeast asia away from the indenting indian plate foremost among the arguments supporting the latter would be large scale 1000 km offsets and high present day slip rates along the major strike slip faults bounding the postulated extruding crust notably the altyn tagh fault along the northern margin of tibet and the karakoram fault along the sw margin satellite photographic interpretation and field mapping in the karakoram mountains in pakistan the nubra siachen area of north ladakh and the pamirs in xinjiang show that although the karakoram fault is extremely active today geological offsets along the right lateral fault are probably less than 120 km the 21 0 5 ma baltoro monzogranite leucogranite batholith has been rotated clockwise about a vertical axis 35 40 into nw se alignment parallel with the karakoram fault east of the siachen glacier with a maximum offset of 90 km across the fault the bangong shyok suture zone similarly has a dextral offset of 85 km the course of the indus river which was antecedent to the rise of the ladakh karakoram and himalayan ranges has been offset dextrally by 120 km south of pangong lake if present day slip rates approximately 32 mm yr avouac and tapponnier 1993 are correct only 4 ma are required to obtain a 120 km offset there is no geological evidence for any larger scale pre holocene offsets and it is suggested that the karakoram fault cannot have accommodated major eastward lateral motion of tibetan crust the fault has also exerted little or no influence on surface topographic uplift cutting obliquely across the highest peaks of the karakoram dextral motion along the central part of the karakoram fault has been transferred in the north to the rangkul murghab and karasu transpressional faults in the central pamir north of tashkurgan the karakoram fault shows mainly normal motion around the kongur and mustagh ata gneiss domes metamorphic core complexes and the extensional muji graben minor dextral displacement has occurred along the shiquanhe fault but this motion cannot be linked to the jiale fault of east tibet the southern end of the karakoram fault merges with the indus yarlung suture zone near mount kailas and does not cut across the himalaya the lack of large scale geological offsets along the karakoram fault together with its very recent initiation 5 or 4 ma suggests that it is related to the pliocene quaternary northward indentation of the pamir and not to any long term extrusion of tibetan crust following the indian collision

paleomagnetism of cretaceous red beds from tadzhikistan and cenozoic deformation due to india eurasia collision abstract we have carried out structural and paleomagnetic studies in the tadzhik depression in order to evaluate the main features of the alpine tectonics of this area about 340 cores from 43 sites of lower cretaceous red beds were sampled from four different localities in the basin and adjacent ranges a well defined component of magnetization a of normal polarity with high unblocking temperatures up to 650 670 c was isolated from all the sites another component of magnetization b with unblocking temperatures between 650 and 680 c was isolated from only fifteen sites this component is bipolar the fold test is positive for both components we believe that component a was acquired during the cretaceous long interval of normal polarity comparison with eurasian reference data shows significant counterclockwise rotation of a locality close to the pamir wedge r 51 5 and another counterclockwise rotation from the inner part of the basin r 15 5 no significant rotations are observed at the two other localities on the periphery of the tadzhik basin

modeling the evolution of continental subduction processes in the pamir hindu kush region several geological and geophysical studies suggest the presence of two converging subduction zones in the western syntaxis of the india eurasia collision zone with steep northward subduction of indian lithosphere beneath the hindu kush and southward subduction of asian lithosphere under the pamir we investigate the geometry and the timing of these subduction processes seismic tomography images are used to constrain the geometry of the two slabs under the pamir and the hindu kush by measuring the tomographically inferred length of the indian slab under the hindu kush region and by comparison with paleomagnetic reconstructions we estimate that the process of indian slab break off most likely occurred at the early stage of the collision at ca 44 48 ma we infer that after slab break off western india continued its northward motion until its northern boundary reached the present hindu kush region where it began to subduct we estimate an age for the initiation of subduction in this region of about 8 ma we apply 2d thermo kinematic and rheological numerical modeling to compute the temperature distribution and brittle field along two vertical sections across the hindu kush and pamir regions for the hindu kush we introduce parameters reproducing fast and near vertical subduction whereas in the pamir region we use the results from published studies to reproduce slower subduction modeling results indicate that faster subduction under the hindu kush results in a deeper brittle region which is consistent with observed deeper seismicity than in the pamir region

atlantic mediterranean water exchange during the late neocene the nature of water exchange between the mediterranean and the atlantic is examined for three time periods during the late neogene in order to assess the impact of flow patterns between these basins on bottom water conditions in the oceans the large volume of carbonates and evaporites deposited in the mediterranean during the messinian salinity crisis appears to have caused the open ocean to become more undersaturated in calcium carbonate resulting in increased dissolution of deep sea carbonates during the latest miocene during the earliest pliocene an estuarine type of flow existed between the atlantic and mediterranean waters entered the mediterranean at depth and flowed out at the surface benthic foraminiferal stable isotopic evidence from the north atlantic indicates that north atlantic deep water nadw was produced throughout the early pliocene and that the absence of saline mediterranean outflow did not have a significant effect on bottom water production eustatic lowering of sea level during the last glacial maximum 18 000 years b p reduced water exchange between the atlantic and the mediterranean as a result salinities in the mediterranean increased substantially but it seems unlikely that diminished nadw production during the last glacial episode can be attributed to a reduction in mediterranean outflow

vertical distribution and isotopic fractionation of living planktonic foraminifera from the panama basin a model1 2 which explains the vertical and seasonal distribution of planktonic foraminifera was developed using data from the western north atlantic and is comprised of three tenets 1 the conditions in the photic zone upper 80 100 m exclusively dictate planktonic foraminifera species composition and abundance throughout the water column 2 species are vertically stratified within the photic zone according to their temperature preference depth distribution according to temperature preference has been proposed by several authors3 based on isotope analyses of sediments due to seasonal temperature variations seasonal variations in the 18o composition of seawater and species specific isotope fractionation rigorous proof of this hypothesis cannot be provided from sediment analyses alone 3 the chlorophyll maximum is a major food source zone which is preferentially exploited by foraminifera our data from the panama basin which are presented here are confirmation of this model the panama basin in the eastern equatorial pacific which has a shallow and steep thermocline was sampled for living planktonic foraminifera a multiple opening closing net and environmental sensing system mocness 4 was used to collect 13 sets of eight vertically stratified oblique samples we report here the quantitative distribution and stable isotopic composition of planktonic foraminifera from four mocness tows taken over 5 days during august 1979 rv knorr cruise 73 at 5 20 n 8 50 w each tow consisted of eight samples which integrated 12 5 m intervals from 0 to 100 m for moc 126 25 m intervals from 0 to 200 m for moc 127 100 150 m intervals from 0 to 1 000 m on moc 128 and 250 m intervals from 0 to 2 000 m on moc 131

the crotone series a synthesis and new data the crotone series is undoubtedly the best studied early pleistocene succession in the world its matchless location and sedimentary conditions contribute to optimal achievements in biostratigraphy magnetostratigraphy cyclostratigraphy and finally chronology robust stratigraphic correlations are established between the semaforo and vrica areas thanks to field surveys a cored borehole and ash mineralogy and geochemistry the crotone series covers the time interval from 2 47 to 1 21 ma and displays 30 complete glacial interglacial cycles from mis 97 to mis 37 insolation cycles are recorded from i 236 to i 116 by combining lithology sapropels and palynology amorphous organic matter and abundance in pollen grains of riparian trees two indices of anoxic condition development and runoff intensity respectively the understanding of early pleistocene glacial interglacial pollen records is clarified as the response of vegetation to the strong interaction between precession and obliquity has been analysed along several successive climatic cycles modern pollen records from the rhone mouth shed light on the conditions of deposition of the sapropels contributing to specify their intensity and duration c 2010 elsevier ltd and inqua all rights reserved

mediterranean quaternary sapropels an immediate response of the african monsoon to variation of insolation abstract in the subsurface of the east mediterranean sea eleven discrete basin wide organic rich black sapropels were deposited during the last 465 000 years they are dated by oxygen isotopic chronostratigraphy the most recent sapropel has been shown to be the consequence of heavy nile river summer floods due to increased monsoonal summer precipitation over ethiopia and not of scandinavian ice sheet meltwater influx into the east mediterranean sea as was previously believed while most sapropels were deposited during interglacials two thick sapropels formed during glacial periods as shown by their position in the oxygen isotopic stratigraphy and by their pollen record in core rc9 181 the new evidence presented here is that the sapropel sequence in this core including the two glacial sapropels correlates on a one to one basis with the highest values of an index of insolation on top of the atmosphere the concept of this index derives from an analysis of the african monsoon process the index variation is computed for the last 465 000 years from the caloric northern summer insolation in the tropical latitudes controlled by variations of the earth s orbital parameters it is conjectured that this index might be linked through the climate system to the monsoonal precipitation which in africa produces the nile river summer flood

geochemistry of coeval marine sediments in mediterranean odp cores and a land section implications for sapropel formation models abstract the geochemistry of eastern mediterranean sediments from the early pleistocene insolation cycle i 156 was studied in the vrica land section calabria italy and in odp sites 967 eratosthenes seamount and 969 mediterranean ridge the odp sediments are rich in carbonates and contain a sapropel with up to 20 organic carbon whereas the vrica sediments are rich in clays and contain a laminite with up to 1 organic carbon processes that affect land sections but not odp sediments partly account for these differences more desiccation and compaction of the land sections resulted in higher dry bulk densities subsurface weathering caused oxidation in sediments surrounding porous ash layers resulting in lower organic carbon and total nitrogen contents and lower c n ratios and organic carbon isotopic values around those ash layers subaerial weathering only resulted in further desiccation and higher na and k contents at the outcrop surface because of evaporation other geochemical differences between the odp cores and the land section are interpreted in terms of different settings the vrica sediments have been deposited closer to land in shallower water with a higher sedimentation rate and in a more western part of the mediterranean than the investigated odp sediments thus aluminium contents and organic carbon accumulation rates are higher terrestrial and redox sensitive element to aluminium ratios as well as barium contents are lower and organic carbon isotopic values are more negative in the sediments of vrica than in the odp cores the formation of a laminite enriched in organic carbon at vrica versus laminated sapropels at the odp sites can however be explained by one model combining both higher productivity and better preservation during precession minima the occurrence of an interval enriched in organic carbon around the anoxic laminite provides support for the hypothesis that anoxia is caused when a certain productivity threshold is exceeded the inferred duration of the laminite is shorter than that of the sapropels indicating that anoxia may have lasted longer in deep water or in more eastern parts of the eastern mediterranean than in shallow environments or in the western part of the eastern mediterranean this investigation shows that marine sediments in land sections may be directly comparable with their equivalents in marine cores this presented comparison of organic rich sediments in the well constrained setting of the mediterranean neogene will enhance our understanding of older black shales in marine cores and land sections

tectonic history of the altyn tagh fault system in northern tibet inferred from cenozoic sedimentation the active left slip altyn tagh fault defines the northern edge of the tibetan plateau to determine its deformation history we conducted integrated research on cenozoic stratigraphic sections in the southern part of the tarim basin fission track ages of detrital apatites existing biostratigraphic data and magnetostratigraphic analysis were used to establish chronostratigraphy whereas composition of sandstone and coarse clastic sedimentary rocks was used to determine the unroofing history of the source region much of the detrital grains in our measured sections can be correlated with uplifted sides of major thrusts or transpressional faults implying a temporal link between sedimentation and deformation the results of our studies together with existing stratigraphic data from the qaidam basin and the hexi corridor suggest that crustal thickening in northern tibet began prior to 46 ma for the western kunlun shan thrust belt at ca 49 ma for the qimen tagh and north qaidam thrust systems bounding the north and south margins of the qaidam basin and prior to ca 33 ma for the nan shan thrust belt these ages suggest that deformation front reached northern tibet only 10 5 m y after the initial collision of india with asia at 65 55 ma because the aforementioned thrust systems are either termination structures or branching faults of the altyn tagh left slip system the altyn tagh fault must have been active since ca 49 ma the altyn tagh range between the tarim basin and the altyn tagh fault has been a long lived topographic high since at least the early oligocene or possibly late eocene this range has shed sediments into both the tarim and qaidam basins while being offset by the altyn tagh fault its continuous motion has made the range act as a sliding door which eventually closed the outlets of westward flowing drainages in the qaidam basin this process has caused large amounts of oligocene miocene sediments to be trapped in the qaidam basin the estimated total slip of 470 70 km and the initiation age of 49 ma yield an average slip rate along the altyn tagh fault of 9 2 mm yr remarkably similar to the rates determined by gps global positioning system surveys this result implies that geologic deformation rates are steady state over millions of years during continental collision

on the origin of upper miocene sapropelites a case study from the faneromeni section crete greece for the first time results of an integrated geochemical and micropalaeontological study of upper miocene sapropelites in a land based section in the mediterranean are presented three sapropelites and adjacent homogeneous intervals in the cretan faneromeni section have been investigated in detail the chemical and foraminiferal characteristics were found to be markedly similar to those of plio pleistocene sapropelites as the physiography and climate of the late miocene mediterranean were not fundamentally different from those of today our preferred model for late miocene sapropelite formation is similar to the one recently developed for plio pleistocene sapropelites increased seasonality and freshwater input during northern hemisphere summer insolation maxima triggered high export production and oxygen consumption rates which in combination with a concomitant decrease in deep water formation rate resulted in the observed high organic matter content of the sapropelites

after the deluge mediterranean stagnation and sapropel formation in an east mediterranean marine core the upper sapropel begins soon after the start of a global event a very heavy precipitation which occurred in the equatorial latitudes during the late glacial early holocene this heavy precipitation in africa channelled by the nile river across 35 of latitude produced a low salinity surface layer in the east mediterranean in this confined basin with high bottom salinity the steep salinity gradient stratified the water column the stagnant bottom waters triggered the sapropel formation cretaceous sapropels in the tropical oceans may result from the same chain of events in warm humid climates with contrasting wet and dry seasonal rhythm

weathering processes on the rock surface in natural outcrops the case of an ancient marble quarry belevi turkey weathering and mineralogical processes observed in a marble quarry in turkey are compared with similar processes occurring on monument surfaces patina formations microstromatolitic microlaminated monolayered as well as destructive processes mainly biopitting and bioerosion are associated with microbial colonisation of the rock surfaces and one influenced by microclimatic conditions patina stratification is independent of substrate rock but is affected by the position and orientation of rock surfaces the different layers formed by mineralisation processes may reflect the seasonality of climatic events and the consequent colonisation bio deteriorative processes take place mainly when the climatic conditions cause the organisms to live below the surface

geochemical signatures preserved in sediments of the semaforo and vrica sections calabria italy and their relations with variations of the sedimentary regime abstract the well known semaforo and vrica sections in calabria italy represent a sequence of homogeneous marls with intercalations of laminated marls these marine sediments are of pliocene to pleistocene age and were originally deposited at a water depth of about 500 m the homogeneous marls have been deposited under oxic conditions the laminated marls under oxygen poor or anoxic conditions samples collected from present day outcrops of the homogeneous and laminated marls were analyzed for major minor and trace elements the laminated marls have a lower caco3 content as compared to the homogeneous marls which is primarily caused by dilution through increased input from land in the case of one semaforo and all but one vrica laminates the caco3 contents could have been diminished further by conversion into gypsum which was formed after oxidation of pyrite variations in the organic carbon corg content of the marls are probably caused by changes in sedimentation rates the small average corg enrichment in the laminates may be attributed to better preservation under euxinic conditions the high cl content of some samples is probably caused by evaporation of porewater from the sampled outcrops the profiles of the al ti fe k mg and p contents of the terrigenous components are practically equal throughout the sections the laminateshave systematically lower na zr and mn contents the lower na and zr contents indicate changes in the sedimentation regime whereas the lower mn content can be attributed to reductive dissolution under suboxic to anoxic conditions in comparison with the homogeneous marls the laminates are relatively enriched in redox sensitive and or chalcophile trace elements in the decreasing order mo cd sb se u cu v ni cr syn sedimentary or early diagenetic hydrogenous enrichment from overlying seawater is the only plausible explanation for their enrichment for most of these trace elements the enrichment is more pronounced when the laminates were deposited during bottom water anoxia a condition inferred from the presence of pyrite derived gypsum for reasons not understood two trace elements behave in opposite fashion laminated marls are depleted in as and zn relative to the homogeneous marls

concentration of crustal displacement along a weak altyn tagh fault evidence from paleomagnetism of the northern tibetan plateau 1 like many regional structures in the northern tibetan plateau the tula syncline changes strike by 40 from nw se to nearly ew as it approaches the altyn tagh fault from the south to test whether this strike curvature is due to oroclinal bending we analyzed paleomagnetic samples from 109 sites collected from late jurassic to paleogene red sedimentary strata of the tula syncline fold and reversal tests suggest a primary origin for the characteristic remanent magnetization from nine sites in the eastern half and 41 sites in the western half of the syncline the observed 13 3 8 8 declination difference between the two halves of the tula syncline is far less than the 40 difference predicted for oroclinal bending instead the arc shape of the syncline is an original configuration produced by transport above an arcuate thrust ramp along with paleomagnetic data from the northern qaidam basin these results from the tula syncline indicate that crustal displacement between the tarim basin and the northern tibetan plateau is accommodated by strike slip motion on the altyn tagh fault rather than distributed shear within the northern tibetan plateau

paleomagnetic constraints on neotectonic deformation in the kashi depression of the western tarim basin nw china a paleomagnetic study is reported of eocene to pliocene formations from the kashi depression which aims to constrain the pattern of neotectonic deformation within the western sector of the tarim basin in northwest china with the exception of pliocene specimens from one locality east kulukeqiati which show large within site mean variations in declination most sites from five sampled formations yield well grouped characteristic remanent magnetizations and positive fold tests and are of probable post depositional detrital origin first order consistency of paleomagnetic results from a range of rock ages and localities demonstrates that only small inter locational vertical axis rotation has occurred here and indicates that the kashi depression is decoupled from the remainder of tarim to the east and has behaved as a quasi rigid block which has rotated by 20 30 counterclockwise relative to eurasia and north china since the late pliocene the crustal scale talas ferghana fault cuts the tian shan and meets the kashi depression in the region immediately to the northwest of the study region and we find no paleomagnetic evidence for differential rotations to suggest that this fault zone extends southwards across the kashi depression to link with the north pamir thrust fault nptf instead we argue that the southern extension of this zone is a transform orogen junction with southward motion of the eastern wall accommodated by southward thrusting at the margins of the south tian shan and the tarim basin we propose that dextral transpression around the margins of the crustal block incorporating the kashi depression was responsible for the contrasting amounts of thrusting on the nptf in the southwest and the south tian shan thrust fault in the north extensive evidence for neotectonism in the bordering zones of this block as well as some paleomagnetic evidence from low unblocking temperature components indicates that the deformation produced by block rotation is ongoing

a model of estuarine circulation in the pliocene mediterranean based on new ostracod evidence the recent discovery of the psychrospheric ostracod agrenocythere pliocenica seguenza in zanclean marls of eastern crete1 expands the reach of early pliocene deep oceanic circulation far into the eastern mediterranean current models of pliocene water mass circulation though allowing for the atlantic psychrosphere to flow freely into the western basin consider the eastern basin as being largely stagnant2 3 i propose here a new model of estuarine circulation affecting both west and east mediterranean this circulation was associated with increased atmospheric humidity and driven by upwelling the model is compatible with organic rich sedimentation in parts of the eastern mediterranean and does not imply an excessively deep or wide connection with the atlantic

stable isotopic constraints on the tectonic topographic and climatic evolution of the northern margin of the tibetan plateau abstract this study presents oxygen and carbon isotopic records from lacustrine paleosol alluvial and fluvial carbonate sampled in thirteen cenozoic sedimentary sections that span the northern margin of the tibetan plateau isotopic analyses of 1475 carbonate samples yield 18 o values that range from 13 1 to 38 9 smow and 13 c values range from 11 5 to 3 7 pdb based on these analyses we see two isotopic trends regionally we interpret a paleogene decrease in average oxygen isotope values to result from an increase in the mean elevation of the study region s drainages as they tapped waters from a growing tibetan plateau to the south of the study area we interpret a neogene increase in both carbon and oxygen isotope values to result from the initiation of local mountain building in the study area and the withdrawal of marine waters which increased basin isolation aridity and temperatures the timing of inferred initiation of uplift in this region is consistent with structural thermochronological and sedimentological evidence for a tectonic transition in the early and middle miocene from accommodation of india eurasia convergence through extrusion along the altyn tagh fault to accommodation of convergence through active shortening and mountain building in this region this study also supports tectonic models for the differential uplift of the tibetan plateau in that mountain building in this study region significantly postdates estimates for the attainment of high elevation from isotopic studies of the central tibetan plateau

precession related sapropelites of the messinian sorbas basin south spain paleoenvironmental significance abstract the sorbas basin southern spain is a narrow and elongated basin located in the betic corridor that formed the northern connection between the atlantic and the paleomediterranean during the late miocene in the centre of the basin about 120 m of well preserved cyclic marine sediments crop out ranging in age from 7 2 to 6 myr these cycles make up the abad member and are an excellent example of precession control over sedimentation in the upper part of the sequence upper abad member the cycles include organic rich laminated brown marls sapropelites alternating with homogeneous marls displaying diatomite layers the om rich laminated marls are the westernmost sapropelites of the mediterranean this paper is a geochemical mineralogical sedimentological and micropaleontological analysis of three cycles with sapropelites the data enable us to distinguish two main climatic scenarios the climate which dominated each of these scenarios regulated the sedimentology and the physico chemistry of the water column resulting in the sapropelite homogeneous marl cyclic alternations the sapropelites developed during a climate characterised by a long period of temperate and humid conditions that occur at times of precession minima these climatic conditions changed progressively to a subarid and drier weather during which homogeneous sediments were deposited the changes between these scenarios were gradual as expected from precession dynamics our data suggest that the change from the subarid to the humid climate transition from homogeneous marls to laminated sapropelites took place at a faster rate or at least was recorded more rapidly by the sediments than the transition from the humid interval to the sub arid period

cyclic variations in the chemical composition of eastern mediterranean pliocene sediments a key for understanding sapropel formation abstract two pliocene mediterranean sediment cores from ocean drilling program odp leg 160 sites 964 pisano plateau ionian basin and 967 lower northern slope of eratosthenes seamount south of cyprus have been analyzed for major and minor elements si ti al fe mg ca k ba cr ni v zn zr by x ray fluorescence analysis at a depth resolution of 3 to 4 cm a total of 430 samples core 964c 9h comprises five sapropels with up to 9 7 total organic carbon toc one 2 5 m thick turbidite and a 50 cm segment of a second turbidite whereas core 967b 9h contains eight sapropels with toc contents of up to 6 7 cyclic variations in carbonate content and detrital matter composition are evident at both sites at site 964 pisano plateau terrigenous detrital matter chemistry reflects periods of stronger saharan dust input higher si al and zr al ratios alternating with fluvial input from the northern borderlands higher mg al ratios cyclicity is not well expressed at this location because turbidites and winnowing occur site 967 eratosthenes seamount sediments are strongly influenced by discharge from the nile river during humid periods low k al and mg al ratios at site 967 sapropels occur only during periods of enhanced nile discharge with correspondingly lower si al ti al mg al k al and zr al ratios accumulation rates of carbonate and terrigenous detrital matter were 30 lower during such episodes because of the reduction in eolian input and carbonate production and or carbonate dissolution periodical ba enrichments which are not only seen in the sapropels but in every k al minimum document the association of enhanced bioproductivity and sapropel formation as calculated from excess ba concentrations productivity increased by up to a factor of five during intervals of intensified nile runoff fluviatile discharge seems to be responsible for an enhanced input of nutrients and suspended matter containing low mg al and k al ratios based on organic carbon concentrations episodes of sapropel formation lasted at least from 1000 to 4000 years at site 964 and from 2000 to 6000 years at site 967 periods of enhanced bio productivity as defined by ba enrichments lasted from 8000 to 12 000 years at site 967 episodes of high river discharge and corresponding nutrient input as well as conditions of sapropel formation seem to have lasted longer in the eastern part of the basin site 967 than at the pisano plateau site 964

magnetochronology of the upper cenozoic strata in the southwestern chinese tian shan rates of pleistocene folding and thrusting abstract the southwestern chinese tian shan of central asia is an actively deforming part of the indian asian collision system paleomagnetic investigations of two plio pleistocene terrestrial successions provide the first detailed magnetostratigraphy for the upper cenozoic strata in this region paleomagnetic samples were collected from 358 sites within the atushi formation and xiyu formation across the atushi talanghe anticline near atushi thermal demagnetization behavior reversal and fold tests of paleomagnetic stability indicate that the characteristic remanence directions were acquired before tilting and folding of the strata a composite magnetostratigraphic section for this sequence correlates with the mammoth subchron to the jaramillo subchron between 3 3 and 1 07 myr of the geomagnetic polarity timescale of cande and kent j geophys res 100 1995 6093 6095 the mean declination 349 3 in the boguzihe section indicates a counterclockwise vertical axis rotation 11 2 during the past 1 4 myr the conglomeratic xiyu formation is time transgressive along its progradational contact with the underlying atushi formation across a map distance of 6 km the basal contact ranges from less than 1 0 myr in the ganhangou section to 1 9 myr in the boguzihe section to the southwest and to 2 8 myr on the northwest limb of the anticline northeastward lateral propagation and growth of the atushi talanghe anticline initiated at 1 4 myr in the boguzihe and 1 2 myr in the ganhangou the cross section in the boguzihe provides a conservative maximum estimate of shortening rate of 3 3 4 4 mm yr and uplift rate of 3 mm yr this rate represents about half of the geodetically determined shortening rate between the northern tarim basin and the kyrgyz tian shan wang et al acta seismol sin 22 2000 263 270 reiger et al earth planet sci lett 191 2001 157 165 during fold growth over the past 1 4 myr the crest of the atushi talanghe anticline eroded at an average rate of 2 6 2 7 mm yr

global plate motion frames toward a unified model 1 plate tectonics constitutes our primary framework for understanding how the earth works over geological timescales high resolution mapping of relative plate motions based on marine geophysical data has followed the discovery of geomagnetic reversals mid ocean ridges transform faults and seafloor spreading cementing the plate tectonic paradigm however so called absolute plate motions describing how the fragments of the outer shell of the earth have moved relative to a reference system such as the earth s mantle are still poorly understood accurate absolute plate motion models are essential surface boundary conditions for mantle convection models as well as for understanding past ocean circulation and climate as continent ocean distributions change with time a fundamental problem with deciphering absolute plate motions is that the earth s rotation axis and the averaged magnetic dipole axis are not necessarily fixed to the mantle reference system absolute plate motion models based on volcanic hot spot tracks are largely confined to the last 130 ma and ideally would require knowledge about the motions within the convecting mantle in contrast models based on paleomagnetic data reflect plate motion relative to the magnetic dipole axis for most of earth s history but cannot provide paleolongitudes because of the axial symmetry of the earth s magnetic dipole field we analyze four different reference frames paleomagnetic african fixed hot spot african moving hot spot and global moving hot spot discuss their uncertainties and develop a unifying approach for connecting a hot spot track system and a paleomagnetic absolute plate reference system into a hybrid model for the time period from the assembly of pangea 320 ma to the present for the last 100 ma we use a moving hot spot reference frame that takes mantle convection into account and we connect this to a pre 100 ma global paleomagnetic frame adjusted 5 in longitude to smooth the reference frame transition using plate driving force arguments and the mapping of reconstructed large igneous provinces to core mantle boundary topography we argue that continental paleolongitudes can be constrained with reasonable confidence

late cenozoic tectonic development of the intramontane alai valley pamir tien shan region central asia an example of intracontinental deformation due to the indo eurasia collision 1 the pamir indentor of the northwestern himalayan syntaxis is a first order feature demonstrating partly the northward extent of deformation due to the cenozoic indo eurasia collision the alai valley of kyrgyzstan at the northern end of the indentor is a strategically positioned e w trending intramontane basin that constrains the timing and extent of crustal deformation in this area of the collision zone to quantify the convergence accommodated across the alai valley during the late cenozoic we collected structural and stratigraphic field data reviewed existing soviet literature and analyzed migrated seismic reflection profiles to construct and restore two regional sections crosscutting the basin our study suggests that the development progressive closure and conversion of this formerly marine basin into a terrestrial intramontane basin result from two main deformation events 1 distributed north south contraction took place during the late oligocene early miocene accommodated one third to half of the total shortening and was followed by the formation of a regional erosion surface and 2 n s shortening resumed in the mid miocene and continues today during this second episode the thrust front migrated southward localized along the trans alai ranges and failed to reactivate earlier neogene structures horizontal shortening of about 35 across the alai valley implies relatively low strain rates and displacement rates of about 4 18 4 69 10 16 s 1 and 0 66 0 78 mm yr 1 respectively for the last 25 myr our study confirms other regional observations indicating that contractional deformation occurred far in the interior of the asian continent as early as the late oligocene

geometry of the pamir hindu kush intermediate depth earthquake zone from local seismic data 1 we present new seismicity images based on a two year seismic deployment in the pamir and sw tien shan a total of 9532 earthquakes were detected located and rigorously assessed in a multistage automatic procedure utilizing state of the art picking algorithms waveform cross correlation and multi event relocation the obtained catalog provides new information on crustal seismicity and reveals the geometry and internal structure of the pamir hindu kush intermediate depth seismic zone with improved detail and resolution the relocated seismicity clearly defines at least two distinct planes one beneath the pamir and the other beneath the hindu kush separated by a gap across which strike and dip directions change abruptly the pamir seismic zone forms a thin approximately 10 km width curviplanar arc that strikes east west and dips south at its eastern end and then progressively turns by 90 to reach a north south strike and a due eastward dip at its southwestern termination pamir deep seismicity outlines several streaks at depths between 70 and 240 km with the deepest events occurring at its southwestern end intermediate depth earthquakes are clearly separated from shallow crustal seismicity which is confined to the uppermost 20 25 km the hindu kush seismic zone extends from 40 to 250 km depth and generally strikes east west yet bends northeast toward the pamir at its eastern end it may be divided vertically into upper and lower parts separated by a gap at approximately 150 km depth in the upper part events form a plane that is 15 25 km thick in cross section and dips sub vertically north to northwest seismic activity is more virile in the lower part where several distinct clusters form a complex pattern of sub parallel planes the observed geometry could be reconciled either with a model of two sided subduction of eurasian and previously underthrusted indian continental lithosphere or by a purely eurasian origin of both pamir and hindu kush seismic zones which necessitates a contortion and oversteepening of the latter

new cretaceous paleomagnetic poles from the tarim basin northwestern china most paleomagnetic studies of the tarim have been focused on the paleozoic with little data published for mesozoic rocks however the ancient configuration of this part of asia has been affected by the indian eurasian collision during the second french chinese karakorum expedition from kashkar to kunjerab in the autumn of 1990 we sampled about 500 cores from 53 sites of upper and lower cretaceous red sandstones from three areas near uytak yingjisha and wuqia 38 5 39 5 n 75 76 5 8 isothermal remanent magnetization acquisition indicates the presence of minerals with high magnetic coercivity stepwise thermal demagnetization confirms that hematite is the dominant carrier and allowed the separation of low temperature components ltc 600 c in most samples the mean direction of ltcs is aligned with that of the present earth field normal and reversed polarities have been found for the htcs of each age group htcs show positive fold tests for at least one sub study where the attitudes of bedding were sufficiently different to allow the test to be performed more important the four sub studies from yingjisha and wuqia give fully compatible results results from the uytak area show a wide dispersion in declinations as could be expected from the rather severe deformation and proximity to major thrust and strike slip faults data obtained in the kuche area from northern tarim by li and co workers and in southern junggar by chen and co workers are statistically identical to the new data from yingjisha and wuqia data from paicheng in northern tarim appear to have been subject to local rotation excluding those sites which appear from paleomagnetic study to have been significantly rotated we calculated a mean cretaceous pole for the tarim basin at 69 1 n 223 88 ass 3 5 n 5 this result indicates that the total post cretaceous rotation of tarim relative to junggar and to eurasia has been negligible 2 6 6 1 and 0 4 4 6 respectively continental shortening and rotation between tarim and junggar within the tien shan are not resolved by paleomagnetism although the values obtained 400 t 600 km 3 6 are compatible with tectonic models of the range a major discrepancy warranting further geological investigation is that between the tarim and north china block poles which would imply some 1400 1060 km of north south relative displacement

origin of the plio pleistocene vrica laminites organic geochemical evidence meyers p a 1993 origin of the plio pleistocene vrica laminites organic geochemical evidence mar geol 115 117 127 organic geochemical properties of samples from lower pleistocene laminite layer h at vrica calabria have been examined for evidence of the origin of these dark colored sediments the laminite samples are geochemically distinct from the surrounding gray marly clays they contain less caco 3 and more toc have higher c n ratios and lower 613c values and their hydrocarbon contents indicate larger proportions of land derived organic matter the vrica taminites appear to have originated principally as a consequence of enhanced runoff of land derived organic matter and clastic sediments from nearby land areas during episodes of wetter regional climate freshening of surface waters by the runoff created salinity stratification of the water column diminished availability of oxygen in near bottom waters and improved preservation of organic matter marine productivity was probably also enhanced but not as much as is evident for pelagic sapropels in the eastern mediterranean