evaporitic and biosiliceous cyclic sedimentation in the miocene of the gulf of suez depositional and diagenetic aspects abstract the middle to late miocene evaporite bearing formations which outcrop along the gebel zeit and gems highs in the southwestern gulf of suez egypt consist of thick calcium sulphate beds rhythmically interbedded with marlstones siltstones and claystones containing various amounts of biogenic silica as well as pure diatomites the calcium sulphate beds are composed mainly of gypsum and anhydrite subaqueous crustallisation in subpermanent brine ponds of marine origin predominated during deposition of the selenite and laminated gypsum early diagenetic interstitial growth of nodular anhydrite occurred episodically when the water level dropped in response to increasing salinity associated with the precipitation of halite in the deeper troughs nevertheless most of the nodular facies resulted from the burial conversion of gypsum to anhydrite which has been sometimes rehydrated into gypsum a last phase of gypsum dehydration has occurred at the surface related to the present hot and dry climatic conditions the biosiliceous deposits contain either well preserved opal a or diagenetically altered opal ct clinoptilolite quartz and even clays diatom frustules such diagenetic changes are commonly described in the oceanic biosiliceous deposits the fossil content of these diatomitic layers implies shallow marine conditions on the shelves of highs induced by block faulting the cyclic succession of evaporited and biosiliceous deposits recorded the alternation of high sea level stands associated with high organic productivity probably enhanced by seasonal input of nutrients and low sea level stands associated with hypersaline conditions and evaporite deposition locally the sharp contact between the diatomites and gypsum argues for a rapid evolution of salinity towards high concentration up to gypsum saturation and more the formation of finely laminated diatomitic sediments is known to require either high organic productivity or anoxic conditions in bottom intermediate waters and eventually both processes in the gebel zeit and gemsa areas a local association of the biosiliceous sediments with diagenetic carbonates and native sulphur resulting from processes of bacterial sulphate reduction confirms that anoxic conditions occurred in the deep water body or in the sediments large amounts of organic compounds were involved in these diagenetic processes immature organic matter was consumed during an early diagenetic stage of transformation it is assumed that this organic matter was supplied either by the biosilica rich interbeds or the organic rich laminated carbonates the initial organic content of the biogenic deposits was impoverished as early as the first stages of sedimentation and diagenesis although a large part of the organic matter could have been destroyed by these early diagenetic processes and further oxidation in outcrops these sediments can be considered as potential source rocks in nearby less exposed sequences

crystallisation of nepheline syenite in a subvolcanic magma system tenerife canary islands abstract the late quaternary phonolitic pumice deposits of tenerife canary islands are the product of a periodically tapped periodically replenished zoned alkaline magma system nepheline syenite blocks occur as lithics in the deposits and provide solidified representatives of the phonolite magmas the blocks are considered to have crystallised in the roof zone of the active magma system at a depth of roughly 4 km beneath the las canadas caldera conversion of highly differentiated phonolitic magma to solid nepheline syenite was achieved between 770 and 680 c quenched glass of extreme composition in one erupted block provides a sample of the last interstitial liquid comparison of this sample with phonolitic pumice and with fully crystallised syenites allows reconstruction of the magmatic interstitial and subsolidus crystallisation histories of nepheline syenite phases represented by the phenocryst assemblage of the most differentiated phonolitic pumices sanidine sodalite nepheline na poor pyroxene biotite sphene and magnetite formed an initial crystal mush containing abundant trapped liquid on the walls of the magma chamber interstitial crystallisation involving the conversion of pyroxene to na rich compositions continued growth of felsic phases and partial to complete consumption of biotite sphene magnetite and apatite was accompanied by extreme sodium enrichment in the residual liquid stellate aegirine lavenite loparite and mn rich ilmenite are among the final products of magmatic crystallisation modification of feldspar primocrysts persisted into subsolidus conditions it is suggested that complete solidification of an open system alkaline magma chamber results in the formation of an alkaline alkaline ring complex

stable isotope anomalies in mediterranean pleistocene records oxygen and carbon isotope records of twelve mediterranean cores raised from west alboran sea to east off israel and of four atlantic cores raised from the western side of gibraltar and located respectively inside below and beyond the modern mediterranean outflow are compared to open ocean records of core 71 139c from the north atlantic and core v19 30 from the east pacific oxygen isotope stratigraphies can be established for deep mediterranean records and the major events of the last 150 ka are easily identifiable for instance the five substages of stage 5 or the 18 ka event stage 2 are identified but the 10 ka event younger dryas is only recorded by globigerina bulloides and benthic foraminifera suggesting that the cooling affected only winter sst 14c dates for the two terminations ia and ib of the last deglaciation which are recorded in sediment cores from areas with high sedimentation rates faro ridge alboran sea sicilian strait are in good agreement with the dates published for the same termination in atlantic cores an intermediate step however has been identified in some cores at 14 ka and divides termination ia into two phases oxygen isotope anomalies are recorded by the shallow water species globigerinoides ruber they correspond to 1 a higher amplitude glacial interglacial change in 18o values which exceeds that of the open ocean by 1 in the western basin and by 1 7 in the eastern basin 2 large isotopic depletions during the deposition of sapropel s1 s3 and s5 they are interpreted as the result of fresh water run off responsible for a strong dilution in the shallower layers of the east mediterranean waters the isotopic effect of this dilution averages 0 75 for sapropel s1 and 1 6 for sapropel s5 during the last glacial maximum the mediterranean still acted as a concentration basin and a gradient of 18o values similar to the modern one 0 75 existed from west to east in the deep waters apparently deep water temperatures were lower during the last glacial but the decrease did not exceed 4 c in the eastern basin major anomalies are also contained in the 13c records of g bulloides and benthic foraminifera the 13c records from surface intermediate and deep waters of the eastern basin and from intermediate and deep waters of the western basin are opposite to that of the open ocean during glacial time 13c values were higher in intermediate and deep waters of the whole mediterranean and also in surface water of the eastern basin at the same time the 13c gradient of surface to deep waters was low this gradient increased during the last deglaciation while 13c values of g bulloides and benthic foraminifera decreased this decrease interrupted at 10 ka may have been related to increased fresh water run off from the bordering contintents due to increased precipitation especially in the tropical belt the 13c depletion is clearly recorded in the levantine and deep water masses and can be traced westward in the mediterranean outflow oxygen and carbon isotope anomalies recorded simultaneously in the east mediterranean by the shallow water species globigerinoides ruber during sapropel deposition indicate that increased precipitation on the bordering continents and strong fresh water run off during the time of the last deglaciation may have caused a density stratification and deep stagnation in the eastern basin uncertainties arise from the fact that in the mixing model deglacial mediterranean waters are mixed with continental fresh waters the isotopic characteristics of which are not entirely understood although increased surface water production of biogenic material can not be excluded as a possible cause of 13c depletion it appears that the river discharge including the nile as well as black sea input are also plausible sources for the fresh water layering

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

sedimentary stable isotope and micropaleontological records of paleoceanographic change in the messinian tripoli formation sicily italy abstract the tripoli formation 6 96 5 98 ma of the central sicilian basin provides a good record of the paleoceanographical changes that affected the mediterranean during the transition from slightly restricted conditions to the onset of the messinian salinity crisis the falconara gibliscemi section has been selected for an integrated approach at a high resolution scale using sedimentology stable isotopes of the carbonates and microfossils the sedimentary succession includes 46 precession controlled cycles resulting from the periodical increase in biosiliceous productivity diatomites that followed the deposition of marls and pinkish laminites which appear as sapropel type deposits induced by the oceanic fertilization by terrestrial nutrients during wet periods higher scale environmental changes are superimposed to this precession forced rhythmicity there is a general trend of increasing basin restriction from near marine conditions at the base of the tripoli to semi closed settings in its uppermost part which are the prelude of the salinity crisis this pattern reflects the hydrological response of the mediterranean to the progressive decrease of the atlantic inputs and an enhanced influence of the climate on depositional conditions however this evolution is not linear and shows successive phases of different duration during the first period until 6 71 ma open atlantic mediterranean exchanges maintained relatively stable marine conditions the second period 6 71 6 29 ma marks an important step in the basin restriction with a wider range of salinity fluctuations and an increased bottom stagnation the 6 71 ma event which is correlated at a mediterranean scale may have resulted from shallowing of the mediterranean gateway under a tectonic control this shallowing reduced the oceanic inputs resulting in an increased climatic constraint of the mediterranean hydrology during the third period 6 29 6 03 ma an increase of the surface water salinity resulted in stressful conditions for the marine microfauna the 6 29 ma change is a major step in the restriction that may be correlated with the intensification of the glaciation recorded in the atlantic which could have enhanced the effects of the tectonic closure the last two cycles 48 and 49 that underlie the calcare di base witnessed the rapid transition to a semi closed mediterranean setting characterized by large variations of salinity from diluted to hypersaline conditions under a dominant climatic control and by the nearly complete disappearance of the marine organisms long trend environmental changes recognized within the tripoli formation resulted from a complex set of interfering factors controlling the water fluxes exchanged between the mediterranean and the world ocean most of the rapid changes identified in falconara gibliscemi at 7 16 6 71 and 6 29 ma that occurred simultaneously in the western and eastern mediterranean were mainly controlled by the stepwise tectonic closure of the atlantic connections although a glacio eustatic overprint cannot be completely excluded

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

nile water as a cause of eastern mediterranean sapropel formation evidence for and against during the late pleistocene sapropels layers of organic carbon rich sediment formed throughout the entire eastern mediterranean basin in close association with glacial interglacial transitions the current theory for the mechanism of sapropel formation involves a density stratification of the water column due to the invasion of a large quantity of low saline water which resulted in oxygen depletion of the bottom waters most workers believe that this low salinity water was glacial meltwater that entered the mediterranean via the black sea and a series of interconnected glacial lakes but the suggestion also has been made that the freshwater originated from the nile river in this study the oxygen isotope values of planktonic foraminifera globigerinoides ruber have been examined in six gravity cores and one piston core from the southern levantine basin and compared with the oxygen isotope records ofg ruber from other areas of the eastern mediterranean this study deals mainly with the latest sapropel which was deposited approximately 7000 to 9000 years ago results indicate that nile discharge probably does reduce salinities somewhat in the immediate area surrounding the mouth of the nile but this water is rapidly mixed with the highly saline waters of the easternmost mediterranean using a mixing equation and surface water salinity limitations an approximate oxygen isotope balance of surface waters was calculated for the time of latest sapropel deposition this calculation shows that neither nile river discharge nor black sea input nor both together are large enough to account for the large scale oxygen isotope depletion associated with latest sapropel deposition in the eastern mediterranean this suggests that part of the isotopic change at termination i is probably due to increased surface water salinities during the last glacial maximum in addition evidence from the timing of sapropel 1 deposition and the dissolved oxygen balance indicates that deposition of the latest sapropel is associated with increased surface water production of biogenic material as much as three times higher than that of present day

vertical and lateral collapses on tenerife canary islands and other volcanic ocean islands recent studies demonstrate that tenerife has undergone large lateral collapses this has led to the suggestion that the las canadas caldera one of the best exposed calderas in the world is the result of lateral collapse we have tested this idea using the available structural stratigraphic volcanological and geochronological data we conclude that the las canadas caldera is the result of a complex sequence of vertical collapse events associated with a long history of phonolitic explosive activity in the central part of tenerife our results indicate however that vertical collapses may have played a major role in triggering lateral collapses we propose that the association of vertical and lateral collapse events such as inferred for tenerife can also explain similar sequences of events interpreted to have affected other large volcanic ocean islands

experiments on rift zone evolution in unstable volcanic edifices large ocean island volcanoes frequently develop productive rift zones located close to unstable flanks and sites of older major sector collapses flank deformation is often caused by slip along a decollement within or underneath the volcanic edifice we studied how such a stressed volcanic flank may bias the rift zone development the influence of basal lubrication and lateral flank creep on rift development and rift migration is still poorly constrained by field evidence here our analog experiments provide new insights we injected colored water into gelatin cones and found systematic orientations of hydro fractures dikes propagating through the cones at the base of the cone diverse friction conditions were simulated by variation of the basal creep conditions we modeled radial dike swarms collinear rift zones and three armed rift systems it is illustrated that a single outward creeping flank is sufficient to modify the entire rift architecture of a volcano the experiments highlight the general unsteadiness of dike swarms and that the distribution and alteration of weak substratum may become a major player in shaping a volcano s architecture

volcanic and morphological evolution of la gomera canary islands based on new k ar ages and magnetic stratigraphy implications for oceanic island evolution the spatial and chronological evolution of canary islands volcanism is due to eastward progression of the slow moving african plate over a mantle plume la gomera is located between the western shield stage islands 12 ma with 23 k ar ages and palaeomagnetic data we can constrain the timing of the main subaerial volcanic phases of la gomera the shield volcano c 9 4 8 0 ma the postshield peripheral lava flows c 7 4 5 0 ma the postshield horizontal lava flows c 5 4 4 3 ma and late intra canyon lava flows c 1 9 ma the horizontal lava flows fill a 10 km wide depression formed by a giant landslide garajonay the entire structure of la gomera is in relief inversion declining volcanic construction rates from the shield to the postshield stages are correlated with increasing erosion rates whereas the period of volcanic quiescence hiatus has low erosion rates the succession and duration of the hotspot volcanic stages in the canary islands are compared with those in the hawaiian islands thus underlining differences between slow moving and fast moving plate settings

eruptive and structural history of teide volcano and rift zones of tenerife canary islands the teide and pico viejo stratocones and the northwest and northeast rifts are products of the latest eruptive phase of the island of tenerife initiated with the lateral collapse of its northern flank that formed the las canadas caldera and the icod la guancha valley ca 200 ka the eruptive and structural evolution of this volcanic complex has been reconstructed after detailed geological mapping and radioisotopic dating of the significant eruptive events a set of 54 new 14 c and k ar ages provides precise age control of the recent eruptive history of tenerife particularly teide volcano the third highest volcanic feature on earth 3718 m above sea level 7 km high and unique in terms of its intraplate setting the development of the teide pico viejo volcanoes may be related to the activity of the northwest and northeast rifts volcanic and intrusive activity along both rift zones may have played an important role in activating the gravitational landslide and in the subsequent growth nested within the collapse embayment of an increasingly higher central volcano with progressively differentiated magmas the coeval growth of the central volcano with sustained activity along the rifts led to a clear bimodal distribution in composition of eruptive products with the basaltic eruptions in the distal part of the rifts and phonolitic and more explosive eruptions in the central area where the differentiated stratocones developed current volcanic hazard in tenerife is considered to be moderate because eruptive frequency is low explosivity is modest and the eruptive activity of the teide stratocone seems to have declined over the past 30 k y with only one eruption in this period 1150 yr b p

40ar 39ar stratigraphy of pyroclastic units from the canadas volcanic edifice tenerife canary islands and their bearing on the structural evolution many felsic pyroclastic units of various types are exposed in different sectors of tenerife new 40ar 39ar determinations allow them to be placed more precisely in the general volcano stratigraphic succession according to geographic distribution stratigraphic position and isotopic ages four main pyroclastic phases may be identified the first san juan de la rambla phase 2 1 ma is only known in the north of tenerife in the tigaiga massif the second adeje phase 1 8 1 5 ma is most completely developed in the southwest of the island but occasionally occurs in the other sectors the third las americas phase 1 ma is only presently known in the southern region the fourth bandas del sur phase 0 7 0 15 ma is essentially exposed in the southeast sector the results of this work emphasise the complexity of the pre 1 ma eruptive history of tenerife and underline the fact that explosive volcanic activity has taken place for at least the last 2 ma vertical collapse structures have developed as a result of pyroclastic flow activity and these may be as old as 1 6 1 8 ma therefore much older than generally considered the precise location of calderas is difficult to ascertain as a result of the repeated lateral flank collapse during the construction of the canadas volcano

volcanic evolution of the island of tenerife canary islands in the light of new k ar data new age determinations from tenerife together with those previously published 93 in all provide a fairly comprehensive picture of the volcanic evolution of the island the oldest volcanic series with ages starting in the late miocene are formed mainly by basalts with some trachytes and phonolites which appear in anaga teno and roque del conde massifs in anaga ne three volcanic cycles occurred one older than 6 5 ma a second one between 6 5 and 4 5 ma with a possible gap between 5 4 and 4 8 ma and a late cycle around 3 6 ma in teno nw after some undated units the activity took place between 6 7 and 4 5 ma with two main series separated by a possible pause between 6 2 and 5 6 ma in the zone of roque del conde s the ages are scattered between 11 6 and 3 5 ma between 3 3 and 1 9 ma the whole island underwent a period of volcanic quiescence and erosion the large canadas volcano made up of basalts trachytes and phonolites was built essentially between 1 9 and 0 2 ma to the ne of this central volcano linking it with anaga is a chain of basaltic emission centers with a peak of activity around 0 8 ma the canadas caldera had several collapse phases associated with large ignimbrite emissions there were at least an older phase more than 1 ma old on the western part of the volcano and a younger one less than 0 6 ma old in the eastern side the two large valleys of guimar and la orotava were formed by large landslides less than 0 8 ma ago and probably before 0 6 ma ago the present canadas caldera was formed by another landslide less than 0 2 ma ago this caldera was later filled by the huge teide volcano which has been active even in historic times during the same period a series of small volcanoes erupted at scattered locations throughout the island the average eruptive rate in tenerife was 0 3 km3 ka with relatively small variations for the different eruptive periods this island and la gomera represent a model of growth by discontinuous pulses of volcanic activity separated by gaps often coinciding with episodes of destruction of the edifices and sometimes extended for several million years the neighbouring gran canaria on the other hand had an initial rapid shield building phase during which more than 90 of the island was built and a series of smaller pulses at a much later period a comparison between these three central islands indicates that the previously postulated westward displacement in time of a gap in the volcanic activity is valid only as a first approximation several gaps are present on each island overlapping in time and not clearly supporting either of the models proposed to explain the evolution of the canaries

the plio quaternary volcanic evolution of gran canaria based on new k ar ages and magnetostratigraphy the combined use of radiometric dating 51 new unspiked k ar ages magnetostratigraphy and field geology establishes a new time framework for the last two stages of the volcanic evolution of gran canaria most of the dated samples have ages coherent with their stratigraphic positions and magnetic polarities our new set of data extends the end of the roque nublo rn group one of the main posterosive stages of gran canaria which started about 4 9 ma ago to ages as young as 2 87 ma this is about 0 7 ma younger than previously thought moreover the dating of samples collected in well defined stratigraphic sequences supports the contemporaneity of the early stages of the post roque nublo group and the vanishing activity of the roque nublo stratovolcano between 3 7 and 2 9 ma the multiple lateral collapses of the roque nublo stratovolcano occurred during this period between 3 5 and 3 1 ma which corresponds to a main period of volcanic quiescence after 2 9 ma the effusive activity propagated along a well defined nw se rift until about 1 5 ma shifting progressively from a rifting propagation to platform forming lavas thereafter the activity is very disperse and belongs to the brunhes period with most of it before 500 ka

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

implications for the early shield stage evolution of tenerife from k ar ages and magnetic stratigraphy abstract the combined use of field geology radioisotopic dating and magnetic stratigraphy applied to the old shield volcanoes of tenerife provides a reliable time framework for the early shield stage evolution of the island the greater part of this new set of ages obtained from sequences of lava flows is in agreement with the astronomical polarity time scale this approach illustrates that previous k ar data collected without a comprehensive stratigraphy should be viewed with caution and in some cases discarded altogether the shield volcanoes of tenerife encompass a relatively small number of magnetozones an observation consistent with the relatively short periods of growth shown by the new ages 1 2 my the island was constructed by the aggregation of three successive shields the roque del conde central shield between about 11 9 and 8 9 ma and the teno 6 2 5 6 ma and anaga 4 9 3 9 ma volcanoes this new oldest subaerial age of tenerife fits with the others obtained in the canaries in a clear west to east monotonous age progression one of the main restrictions for hotspot related island chains

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

stratigraphy of the bandas del sur formation an extracaldera record of quaternary phonolitic explosive eruptions from the las canadas edifice tenerife canary islands explosive volcanism has dominated the large phonolitic shield volcano of tenerife the las canadas edifice for the last 1 5 m y pyroclastic deposits of the bandas del sur formation are exposed along the southern flanks and record the last two of at least three long term cycles of caldera forming explosive eruptions each cycle began with flank fissure eruptions of alkali basalt lava followed by minor eruptions of basanite to phonotephrite lavas minor phonotephritic to phonolitic lava effusions also occurred on the flanks of the edifice during the latter stages of the second explosive cycle non welded plinian fall deposits and ignimbrites are the dominant explosive products preserved on the southern flanks of these a significant volume has been dispersed offshore many pyroclastic units of the second explosive cycle exhibit compositional zonation banded pumice occurs in most units of the third youngest explosive cycle and ignimbrites typically contain mixed phenocryst assemblages indicating the role of magma mixing mingling prior to eruption at least four major eruptions of the third cycle began with phreatomagmatic activity producing lithic poor accretionary lapilli bearing fallout and or surge deposits the repeated brief phase of phreatomagmatism at the onset of these eruptions is interpreted as reflecting an exhaustive water supply probably a small caldera lake that was periodically established during the third cycle accidental syenite becomes an increasingly important lithic clast type in ignimbrites up sequence and is interpreted as recording the progressive development of a plutonic complex beneath the summit caldera successive eruptions during each explosive cycle increased in volume with the largest eruption occurring at the end of the cycle more than ten major explosive eruptions vented moderately large volumes 1 ges 10 km 3 of phonolitic magma during the last two cycles culminating each explosive cycle was the emplacement of relatively large volume 5 10 km 3 ignimbrites with coarse vent derived lithic breccias interpreted to record a major phase of caldera collapse in the extracaldera record explosive cycles are separated by 0 2 m y periods of non explosive activity repose periods were characterized by erosion remobilization of pyroclastic deposits by discharge events and pedogenesis the current period of non explosive activity is characterized by the construction of the teide pico viejo stratovolcanic complex within the summit caldera this suggests that eruptive hiatuses in the extracaldera record may reflect effusive activity and stratovolcano or shield building phases within the summit caldera alternating effusive and explosive cycles have thus been important in the volcanic evolution of the las canadas edifice

the quaternary pyroclastic succession of southeast tenerife canary islands explosive eruptions related caldera subsidence and sector collapse a much revised quaternary stratigraphy is presented for ignimbrites and pumice fall deposits of the bandas del sur in southern tenerife new ar 41 ar 39 data obtained for the arico granadilla fasnia poris la caleta and abrigo formations are presented allowing correlation with previously dated offshore marine ashfall layers and volcaniclastic sediments we also provide a minimum age of 287 7 ka for a major sector collapse event at the gaimar valley the bandas del sur succession includes more than seven widespread ignimbrite sheets that have similar characteristics including widespread basal plinian layers predominantly phonolite composition ignimbrites with similar extensive geographic distributions thin condensed veneers with abundant diffuse bedding and complex lateral and vertical grading patterns lateral gradations into localized massive facies within palaeo wadis and widespread lithic breccia layers that probably record caldera forming eruptions each ignimbrite sheet records substantial bypassing of pyroclastic material into the ocean the succession indicates that las canadas volcano underwent a series of major explosive eruptions each starting with a plinian phase followed by emplacement of ignimbrites and thin ash layers some of coignimbrite origin several of the ignimbrite sheets are compositionally zoned and contain subordinate mafic pumices and banded pumices indicative of magma mingling immediately prior to eruption because passage of each pyroclastic density current was characterized by phases of non deposition and erosion the entire course of each eruption is incompletely recorded at any one location accounting for some previously perceived differences between the units because each current passed into the ocean estimating eruption volumes is virtually impossible nevertheless the consistent widespread distributions and the presence of lithic breccias within most of the ignimbrite sheets suggest that at least seven caldera collapse eruptions are recorded in the bandas del sur succession and probably formed a complex nested collapse structure detailed field relationships show that extensive ignimbrite sheets e g the arico poris and la caleta formations relate to previously unrecognized caldera collapse events we envisage that the evolution of the nested las cahadas caldera is more complex than previously thought and involved a protracted history of successive ignimbrite related caldera collapse events and large sector collapse events interspersed with edifice building phases

sedimentary and diagenetic markers of the restriction in a marine basin the lorca basin se spain during the messinian abstract the lorca basin southeastern spain is part of a chain of small marginal neogene basins located in the structurally active betic area the upper miocene messinian sequence is composed of a thick diatomite bearing series tripoli unit overlain by the main evaporites analogous to the classical succession that records the main events during the salinity crisis in the mediterranean region the shallow restricted conditions of this region amplified the sedimentary responses to local and global forcings an integrated approach using sedimentology micropalaeontology stable isotope geochemistry and organic geochemistry has been applied to the tortonian messinian succession of the lorca basin in order to obtain a continuous record of the environmental changes the sediments record two major events which affected the whole mediterranean 1 high levels of productivity that led to the formation of the diatomite bearing deposits in the early messinian tripoli and 2 the messinian salinity crisis with its two major stages represented by the halite and gypsum units both mainly precipitated from marine derived brines the rapid reflooding of the mediterranean by normal marine waters at the base of the pliocene did not reach the lorca basin nor other basins of this part of the betic area instead continental sediments were deposited as a consequence of the regional uplift of se iberia which started close to the messinian pliocene boundary the most prominent feature of this basin concerns the record of its restriction by the time of the deposition of the tripoli unit which led to intercalations of precursor evaporitic layers consisting of ca sulphate deposited in sub aqueous and sabkha conditions interbedded with diatomites this alternation of evaporites and diatomites proves that the lorca basin was periodically restricted and reflooded by marine waters a possible cause for this being relative sea level fluctuations in the mediterranean this strengthens evidence of diachronism that suggests that the onset of the first messinian evaporitic deposition was not synchronous but was dependent on bathymetry and local tectonics high productivity during the early messinian in this basin is demonstrated by the thick deposits of diatomites however stagnation episodes may have occurred during this interval as suggested by the preservation of high amounts of organic matter organic rich shales and the extent of bacterial sulphate reduction which apparently occurred during early diagenesis the formation of organo sulphur compounds replacement of sulphates by carbonates and the high levels of elemental sulphur are by products of diagenetic processes occurring in a restricted hypersaline environment

geochemical studies of the recent sapropel and associated sediment from the hellenic outer ridge eastern mediterranean sea i mineralogy and chemical composition abstract the mineralogy major and minor element geochemistry and the accumulation rate of a single kastenlot core from the eastern mediterranean is reported the sapropel is similar mineralogically and in its major element composition to the associated marl ooze and calcareous clay it differs from these sediments in having higher concentrations of ba cr cu mo ni sr and zn and lower concentrations of mn the enrichments are explained by increased fertility ba organic matter or sulphide association cr cu mo ni and zn and the presence of aragonitic pteropods sr the organic material has a marine origin based on the carbon isotopic value 13 c 20 and c n ratio 10 the sapropel accumulated 3 to 5 times faster than the associated sediments in this particular core the evidence is consistent with the formation of this sapropel by an increased flux of carbon to the sea floor this would have been caused by increased marine primary production in the eastern mediterranean during periods of reversed circulation brought about by high post glacial runoff primarily from northern africa the additional carbon flux would have lowered the oxygen levels of the bottom waters but it is not known whether anoxic conditions ensued or whether they would have been necessary to preserve the deposited carbon

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

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

age and duration of the matuyama brunhes geomagnetic polarity reversal from 40ar39ar incremental heating analyses of lavas abstract constraints on the timing of geomagnetic polarity reversals have come mainly from k ar or more recently 40 ar 39 ar age determinations of lavas or their k rich phenocrysts that erupted prior or subsequent to particular geomagnetic events we have obtained 40 ar 39 ar isochron ages using incremental heating techniques on groundmass separates phenocryst poor whole rock samples or plagioclase from eight basaltic to andesitic lavas that erupted during the matuyama brunhes m b polarity transition at four geographically dispersed sites these eight lavas range from 784 6 7 1 ka to 770 8 5 2 ka 1 errors the weighted mean 778 7 1 9 ka gives a high precision age that is remarkably consistent with revised astronomical age estimates for the m b polarity transition 6 12 13 despite uncertainties in absolute calibration of 40 ar 39 ar ages relative to mineral standards used as neutron fluence monitors our age determinations are consistent with five other 40 ar 39 ar studies focused on the m b transition these results confirm that the earlier k ar based geomagnetic polarity time scale underestimated the age of the m b reversal by about 6 none of the eight isochron ages are distinguishable from one another at the 95 confidence level however we are tantalizingly close to testing for the duration of this reversal one lava at the base of a sequence of transitionally magnetized flows in chile and the uppermost lava in a similar sequence on maui are only just indistinguishable in age at the 95 confidence level and preserve different magnetic orientations we suggest that the 12 kyr difference in age represents an upper limit for the duration of the reversal and is similar to the period of low magnetic field intensity associated with records of the m b reversal from deep sea sediment cores together with the short duration 2 kyr of the directional reversal observed in several different marine sediment sections our data suggest that reversal of the field s direction could have occurred at slightly different times depending on the position of the recording site

stratigraphy structure and volcanic evolution of the pico teide pico viejo formation tenerife canary islands abstract the structure and volcanic stratigraphy of the pico teide pico viejo pt pv formation deriving from the basanite phonolite stratovolcanoes pt and pv and numerous flank vent systems are documented in detail based on new field and photogeologic mapping geomorphologic analysis borehole data and petrological and geochemical findings results provide insight into the structure and evolution of the pt pv magma system and the long term cyclic evolution of tenerife s post shield volcanic complex the pt pv formation comprises products of central volcanism mainly emplaced into the las canadas caldera lcc and contemporaneous products from adjacent rifts pt pv central volcanic products become more differentiated up section with felsic lavas dominating the recent output of the system this is attributed to the evolution of a shallow magma reservoir beneath pt that was emplaced early in the pt pv cycle on the intra caldera segment of tenerife s post shield rift system the rift axis has been the focus of pt pv intrusive and eruptive activity and has controlled the location of the stratocones the current geometry of the rifts reflects a major structural reorganisation defining the start of the pt pv cycle at 0 18 ma namely the truncation of the north side of the lcc lce by the giant icod landslide the internal stratigraphy of the pt pv formation suggests that pt developed early with pv developing as a satellite vent activity has since alternated between pt and pv due to episodes of vent blockage or chamber sealing these processes have allowed significant volumes of phonolitic magmas to develop and accumulate within the pt chamber which have vented through radial dike systems during tumescence episodes and from the rift system which has permitted lateral magma transport the pt pv magma system is a potentially hazardous source of future felsic eruptive activity on tenerife

late neogene changes of paleoclimate and paleoproductivity off northwest africa d s d p site 397 abstract the sediment record of site 397 may provide information about both the causes of changes in coastal productivity in the northeast atlantic and the history of climate in northwest africa during the late neogene this study concentrates on the drastic climatic reversal near 2 4 m y b p near 3 2 m y b p a distinct increase of accumulation rates of terrigenous matter and higher paleo trade wind speeds may suggest increased aridity of the northwest african continent this change was followed by higher paleoproductivity of coastal waters off northwest africa high paleoproductivity may be caused by both fluvial nutrient supply and or upwelling during the beginning and the end of inter glacial times river discharge was dominant whereas during phases of glacial maximum stronger fertility of increased coastal upwelling became more important

benthic foraminiferal δ13c and accumulation rates of organic carbon uvigerina peregrina group and cibicidoides wuellerstorfi the glacial to interglacial 13c records of the benthic foraminifera cibicidoides wuellerstorfi and the uvigerina peregrina group from deep sea cores cannot be adjusted by a generally valid constant the 13c values of the u peregrina group largely correlate with the accumulation rates of organic carbon suggesting a local habitat effect those of c wuellerstorfi vary independently with respect to the carbon flux and record fluctuations in the 13c of the ambient bottom water isotopic composition

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

a sediment nutrient oxygen feedback responsible for productivity variations in late miocene sapropel sequences of the western mediterranean abstract cyclic sediments observed throughout the mediterranean during the late miocene have been related to precessional forcing of ocean stratification individual couplets typically 2 m thick sequences of sapropels and diatom rich marls can be reliably traced from western spain to crete and were formed in restricted marginal basins micropaleontological evidence indicates paradoxically that the organic carbon rich sapropels were formed under low productivity conditions marked by surface water stratification and deep anoxia whereas the diatom rich marls were formed under high productivity conditions marked by upwelling here we present geochemical evidence mainly from detailed phosphorus determinations and paleo redox proxies indicating that a sediment nutrient oxygen feedback herein dubbed the sno effect is in part responsible for driving the observed productivity variations during stratification anoxic conditions in these basins cause the release of the limiting nutrient phosphorus from reducible oxide phases in the sediments basin stagnation causes the buildup of phosphorus below the photic zone subsequent overturn driven by precessionally driven winds injects phosphorus rich bottom waters into the photic zone the biotic response to this overturn is high productivity in marls directly overlying the sapropels culminating in diatom mat formation exhaustion of the stored excess phosphorus results in lower productivity marls which grade back into sapropels due to lower wind stresses and the return of stagnant basin conditions these findings indicate that the sno effect may in part be responsible for precessional scale productivity variations observed in parts of the mediterranean and perhaps present in other restricted ocean basins like the miocene monterey formation and the modern santa barbara basin

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

age distribution of cinder cones within the bandas del sur formation southern tenerife canary islands the quaternary bandas del sur formation in the south of tenerife comprises a complex sequence of pyroclastic rocks and lavas in contrast to the nw and ne rift zone on tenerife the s rift zone comprises a number of characteristics with respect to the morphological features eruption cyclicity and the geochemistry of the volcanic deposits various flank eruptions of the las canadas volcano associated with basaltic lavas and the formation of cinder cones within the bandas del sur are important volcanic units for understanding the explosive volcanic cycles during the pleistocene on tenerife a number of palaeomagnetic studies as well as major and trace element geochemistry and two radio isotope dates k ar have been carried out on prominent cinder cones in order to discover their stratigraphic position combining our results with previous k ar data the cones and lavas can be subdivided into three stratigraphic units the first unit contains cinder cones with reverse magnetization and y nb ratios between 0 37 and 0 41 cinder cones which belong to the second unit show normal magnetization and y nb ratios of c 0 948 0 779 ma and 0 323 0 300 ma these units define volcanic cycles ending in violent plinian eruptions the third and youngest unit possibly marks the beginning of a further volcanic cycle that started c 0 095 ma ago

age of the plio pleistocene boundary in the vrica section southern italy new palaeomagnetic data from the proposed plio pleistocene boundary stratotype section vrica section southern italy are presented here in order to improve the correlation of these sediments to the magnetic polarity time scale if the interpretation preferred here is correct the boundary falls above the olduvai normal subchron at approximately 1 6 myr

temporary repopulation by low oxygen tolerant benthic foraminifera within an upper pliocene sapropel evidence for the role of oxygen depletion in the formation of sapropels foraminiferal study of a continuous set of samples across the upper pliocene c2 sapropel singa section southern italy revealed an interval containing substantial numbers of benthic foraminifera bound by sediments in which benthic foraminifera are absent the absence of benthic foraminifera is indicative of anoxic conditions the interval with benthic foraminifera contains an association that is strongly dominated by the species bulimina marginata which is tolerant to low oxygen concentrations the bottom water oxygenation did not improve sufficiently to allow development of a more diverse benthic foraminfferal fauna or the return of intensively burrowing organisms variations in the planktic foraminiferal fauna and in the stable isotope records suggest that a surface water cooling preceded the benthic repopulation a warming seems to have coincided with the return to bottom anoxia the planktic productivity markers globigerina bulloides and neogloboquadrina show minor variations across the repopulated interval the benthic repopulation which reflects improved bottom water oxygenation was probably favored by enhanced dense water formation in response to general cooling of the surface waters

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

calcareous plankton biostratigraphy and biochronology of the pliocene lower pleistocene succession of the capo rossello area sicily abstract in the first part of this paper we present the calcareous nannofossil biostratigraphy of the capo rossello section sicily which suggests that a sedimentary gap exists at the contact between the trubi and the overlying monte narbone formation close to the top of the proposed zanclean stratotype this suggestion is supported by the planktonic foraminiferal results and field observations in contrast the transition from the trubi to the monte narbone formation is well exposed gradational and biostratigraphically continuous in the nearby section of punta piccola a composite of the capo rossello and punta piccola sections serves as a good biostratigraphic reference for the pliocene of the mediterranean in a second part of this paper we have attempted to update the mediterranean pliocene time framework by integrating all of the available biostratigraphic biochronologic chronostratigraphic paleomagnetic and radiometric data

the late quaternary diego hernandez formation tenerife volcanology of a complex cycle of voluminous explosive phonolitic eruptions abstract the diego hernandez formation dhf 600 ca 180 ka represents the products of the most recent complete cycle of phonolitic explosive volcanism on tenerife canary islands spain we provide a revised and detailed stratigraphy new 40ar 39ar and u th he age determinations for major eruptive units a summary of new chemical data and an overview of the key characteristics of the cycle including volume estimates dispersal patterns eruption styles phreatomagmatic influences and caldera collapse episodes the complex stratigraphy of the dhf is divided into 20 named members each representing a major eruption as well as numerous unnamed members of limited present day exposure the major eruptions are represented by the fortaleza 370 ka roque 347 ka 3 km3 aldea 319 ka 3 km3 fasnia 309 ka 13 km3 poris 268 ka 3 5 km3 arafo 4 km3 caleta 223 ka 3 5 km3 and abrigo between 196 and 171 ka 20 km3 members the aldea fasnia and poris members consist of highly complex successions of plinian fall surge and flow deposits and several of the eruptions produced widespread and internally complex ignimbrite sheets phreatomagmatism occurred most frequently in the opening phase of the eruptions but also recurred repeatedly throughout many of the sequences inferred sources of water include a shallow caldera lake and groundwater and intermittent phreatomagmatic activity was an important influence on eruption style another important factor was conduit and vent instability which frequently loaded the eruption column with dense lithic debris and occasionally triggered column collapse and ignimbrite formation most of the major dhf eruptions were triggered by injection of mafic magma into existing phonolitic magma bodies two phonolitic magma types were available for eruption during the lifetime of the dhf but each was dominant at different times the results presented here support a caldera collapse rather than a landslide model for the origin of the las canadas caldera although the evolution of the caldera is evidently more complex and incremental than first thought

submarine push moraine formation during the early fennoscandian ice sheet deglaciation abstract the glacial history in the topographically confined paleo ice stream drainage route of vestfjorden north norway was analysed based on bathymetric data high resolution seismology and 14 c ams dated gravity cores the inner part of the fjord is characterised by axial parallel mega scale lineations whereas the outer part is dominated by two marginal morainal bank systems the vaeroy inner and rost outer marginal moraine systems comprise several transverse zigzag shaped ridges seismic records show thrusted and folded sediment blocks within the ridges the landforms are inferred to reflect basal processes and the transition from warm based inner fjord to cold based outer fjord conditions i e fast flow followed by basal freeze on sediment deformation and morainal bank formation the moraines formed during the final part of two paleo ice sheet re advances 14 c ams dating indicates a maximum age of 13 7 14 c ka bp 16 2 cal ka bp for the rost system whereas the vaeroy system is inferred to be slightly older than 12 5 14 c ka bp 14 5 cal ka bp this demonstrates that the northern part of the fennoscandian ice sheet behaved in a much more dynamic way during the early deglaciation than previously assumed

stratigraphy structure and geochronology of the las canadas caldera tenerife canary islands after a long period of subaerial fissure fed extrusions of basaltic magmas 12 to 3 ma volcanic activity was then concentrated in the central part of tenerife phonolitic magma chambers formed and a central volcanic complex was constructed the las canadas edifice the formation of a large depression the las canadas caldera truncated the top of the edifice the active twin strato cones teide pico viejo are sited in this depression the history of the las canadas caldera and edifice are established from stratigraphy geochronology k ar dates and volcanological studies two different groups are recognized separated by a major unconformity the lower group is dated at 2 to 3 ma and includes the products of several volcanic centres which together represent several cycles the upper group ranges from 1 56 to 0 17 ma and includes three different formations representing three long term 100 to 300 ka volcanic cycles the periods of dormancy between each formation were of 120 to 250 ka duration the las canadas caldera is a multicyclic caldera which formed over the period 1 18 0 17 ma each cycle of activity represented by a formation culminated in caldera collapse which affected different sectors of the las canadas edifice geological observation and geochronology support an origin by collapse into a magma chamber the minimum volume of pyroclastic ejecta is substantially greater than the present caldera depression volume 45 km3 but approaches the inferred volume of the original caldera depression 140 km3 after the formation of the caldera sector collapses could also occur at the northern flank of the volcano causing the disappearance of the northern side of the caldera wall

review and new aspects concerning the formation of eastern mediterranean sapropels abstract in this paper it is proposed that the formation of eastern mediterranean sapropels occurred in an anti estuarine type of circulation which was to some degree weakened relative to the present in response to reduction of the eastern mediterranean excess of evaporation over freshwater input this reduction of excess evaporation would have been imposed by intensifications of 1 the indian ocean summer sw monsoon influencing the eastern mediterranean via increased nile discharge and 2 the system of mediterranean depressions an element of the westerly atlantic system causing increased precipitation and decreased evaporation both the indian ocean summer monsoon and the westerly atlantic system would be intensified in response to the occurrence of distinct minima in the cycle of precession it is demonstrated that reduced excess evaporation whether or not coinciding with global phases of deglaciation would lead to reduction of surface water salinities in the eastern mediterranean causing isolation of previously formed high salinity cooler deep water thus mixing was severely reduced possibly even restricted to eddy diffusion with only occasional convective events that because of the existing density gradient hardly ever would reach the deepest parts of the basin the consequently diminished oxygen advection down from a few hundred meters in the water column favoured preservation of the sinking organic matter this would however suffice only to enable the formation of sapropels with low organic carbon contents the high organic carbon contents observed in various sapropels are argued to reflect superimposed increases of export production the described scenario accounts for previously reported 1 increases of organic carbon content with increasing depth of deposition within individual sapropels and 2 asymmetrical sequences of sapropel deposition characterized by gradual build up and rather abrupt ending it is furthermore in agreement with 3 isotopic and faunal reconstructions of the history of exchange transports through both the strait of sicily and the strait of gibraltar and 4 faunal and floral reflections of the presence or absence of a distinct deep chlorophyll maximum with its associated increases in export production indicating the presence or absence of a shallow pycnocline within the euphotic layer moreover the described scenario 5 is in no way conflicting with the reports of sapropels in the western mediterranean and 6 seems to be endorsed by occasionally intercalated intervals suggestive of somewhat improved oxygenation amidst anoxic benthic desert levels a situation that has been observed in a few quaternary and pliocene sapropels

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

the formation of eastern mediterranean sapropels abstract sapropel formation in the eastern mediterranean is explained by an oceanographic approach it is suggested that sapropels are not only a consequence of eustatic sea level changes as earlier proposed by olausson a model which is widely accepted but rather a result of a very sensitive reaction of the eastern mediterranean to any small climatic amelioration present day aeration of the deep eastern mediterranean basin results from circulation of oxygen rich deep water originating mainly in the adriatic assuming present day conditions a climatic amelioration towards more humid and warmer conditions leading to an increase of the water temperature in the adriatic basin by 0 7 c or to a decrease of its salinity by only 0 2 will cause stratification of water masses and enhance sapropel formation