effect of organic carbon flux and dissolved oxygen on the benthic foraminiferal oxygen index bfoi variations in oceanic primary productivity flux of organic carbon to the sediments and dissolved oxygen levels in the water column are thought to be important in the control of benthic foraminiferal test size wall thickness morphology and species composition of assemblages by many foraminiferal paleontologists aspects of these processes should be reflected by the benthic foraminiferal oxygen index bfoi based on these foraminiferal characteristics however analyses indicate that the bfoi correlates most strongly with dissolved oxygen levels in overlying water r2 0 81 weakly with oceanic primary productivity r2 0 55 and weakly with organic carbon flux to the sediments r2 0 51 although both dissolved oxygen and organic carbon flux are main controlling factors for benthic foraminiferal assemblages the bfoi is a useful indicator extracted from benthic foraminiferal assemblages for estimating the condition of dissolved oxygen in cretaceous and cenozoic oceans

on the hellenic subduction zone and the geodynamic evolution of crete since the late middle miocene abstract in recent syntheses of the geodynamic evolution of the aegean area the hellenic subduction zone and in particular its initiation plays a central role two basic aspects of the recent comprehensive model put forward by le pichon angelier and co workers are a initiation of subduction along the hellenic arc is inferred to have taken place approximately 13 ma ago whereas several others have suggested approximately 5 ma and b migration of the trench system to the south southwest giving rise to an extensional regime in the back arc region which led to general subsidence and formation of the present day aegean sea new data on the structure of the upper mantle underneath the aegean area indicate that the former aspect requires modification the seismic velocity structure indicating a northward dipping slab down to a depth of at least 600 km and the depth distribution of earthquake hypocenters can not be reconciled with straightforward initiation of subduction approximately 13 ma ago estimates of about 5 ma for the time of initiation of the present subduction zone are even more difficult to reconcile assuming 400 km as an upper bound for the effect of stretching of the aegean sea and of other processes contributing to the separation of crete from the eurasian mainland we arrive at an age for the hellenic subduction zone of at least 26 ma as to aspect b geological data of crete lend strong support to the idea that on crete compressional tectonics is of much greater importance than current models imply combining geophysical and geological data we propose a modification of the tectonic evolution for the cretan segment of the hellenic arc whereas the basic process of extension caused by a migrating trench system roll back in a land locked basin remains a very useful and sound concept the tectonics of the margins of a region subject to stretching in this case crete may be more complicated than hitherto thought in our model the documented fragmentation of crete into several basins which started about 12 ma ago is not attributed to initiation of subduction but to inception of the roll back process compressional tectonics on crete is taken to be associated with deformation of the crust resulting from the overall tensional stress regime

u pb single zircon ages and geochemistry of metagranitoid rocks in the cycladic blueschists evia island implications for the triassic tectonic setting of greece abstract u pb zircon geochronology geochemical and microstructural analyses were carried out to a metagranitoid suite exposed in the blueschist unit of the attic cycladic zone on evia island concordant zircons from three metagranitoid samples yielded id tims u pb single grain ages of 234 1 2 ma 232 1 ma and 214 0 7 ma which are interpreted to constrain the intrusion of the igneous protolith in late triassic times these age data in combination with previously published early middle triassic protolith ages of meta igneous rocks from other greek islands support magmatic activity in the cycladic area throughout the triassic major and trace element whole rock analyses reveal that the granitic protolith of the evia metagranitoid suite is of a type affinity implying triassic magmatism in an extensional setting along the northern gondwanan margin rather than back arc extension above a subduction zone subsequent alpine subduction and related high pressure metamorphism led to pervasive non coaxial fabrics of the evia metagranitoid which indicate top to the e se shearing this alpine deformation took place under ductile viscous conditions at temperatures close to 450 500 c and differential stresses of 65 15 10 mpa

the age of the tortonian messinian boundary the tortonian messinian boundary is marked by the first occurrence datum fod of globorotalia conomiozea which is found all over crete in open marine marls with good palaeomagnetic properties within the framework of the miomar project the previously studied sections of langereis et al 1 have been extended and partly resampled here we present new magnetostratigraphic and biostratigraphic results from sections on eastern crete faneromeni central crete kastelli and western crete potamida and skouloudhiana supplemented by cyclostratigraphic data the recently developed geomagnetic polarity time scale ck92 of cande and kent 2 allows an unambiguous correlation of the polarity sequences on crete the fod of g conomiozea occurs in the reversed interval of anomaly c3bn lr this leads to a new age determination of 6 92 ma for the tortonian messinian boundary and a duration of 1 76 myr for the messinian a slightly modified version of ck92 if we use more recent age estimates provides an age of 7 10 ma and a duration of 1 78 myr respectively bipartite sedimentary cycles are distinctly present in the cretan sections studied assuming that these cycles are precession induced and using an average periodicity of 21 7 kyr enables us to independently estimate the duration of the successive individual polarity zones the astronomically derived durations of the cretan polarity zones are in good agreement with ck92 but are approximately 10 shorter

the importance of the oxygen minimum zone and sediment geochemistry in the distribution of recent benthic foraminifera in the northwest indian ocean abstract the relationship between the distribution of benthic foraminifera and sediment type and depositional environment in the arabian sea is discussed the benthic foraminiferal fauna were sampled in nineteen recent surface sediment samples and geochemical variables of the sediment of the same samples were measured the water depths for the box core samples varies from 440 to 4040 m a total of 103 species and six species complexes were identified the geochemical properties were found to correspond well to the sediment type and depositional environment and six different sediment depositional environment types could be distinguished analysis of the benthic foraminiferal fauna reveals specific faunal assemblages that are closely related to these sediment depositional environment types

subduction and the depth of convection in the mediterranean mantle 1 we tie together geological data paleotectonic reconstruction plate motion and tomographic analysis to unravel the history of subduction and back arc extension of the eastern and central mediterranean in these two regions extensional processes started contemporaneously around 30 myr ago but with marked differences in the eastern region the aegean basin opened slowly 1 cm yr behind a shallow dipping slab 40 45 the corresponding high velocity anomaly extends inside the upper mantle and can be also followed in the midmantle down to a depth of at least 1500 km its descent into the midmantle initiated most probably during the late cretaceous and the trench moved northeastward following the path of the eurasian plate and under the persistent push of the african plate conversely in the central mediterranean region subduction initiated later and the motion of the subducting slab is confined to the upper mantle causing punctuated and rapid episodes of back arc extension provencal and tyrrhenian basins behind a slab that dips steeply 75 we explore the causes that control how the slab subducted and interacted with the lower more viscous part of the mantle

recent benthic foraminifera from the continental margin of northwest africa community structure and distribution abstract sediment grab samples were collected at 107 locations along the continental margin of northwest africa these samples form a series of depth transects between the straits of gibraltar and dakar senegal the greater than 250 m size fraction was retained for a census of both the live and dead foraminifera after deleting trace occurrences jaccard and correlation coefficient based cluster analyses were performed to decipher the community structure for this margin the geographic distribution of the four major faunal provinces recognized is conventional in that for both the live and dead assemblages three are related to depth upper slope and shelf middle slope and lower slope and continental rise the biotopes and thanatotopes within these provinces are strongly restricted along vertical or latitudinal boundaries when the data are analysed using jaccard coefficients dendrograms constructed from correlation coefficients emphasize depth related faunal communities dominant species such as cibicides lobatulus trifarina fornasinii planulina ariminensis uvigerina finisterrensis and c wuellerstorfi are generally distributed within a definite depth range along this margin and strongly influence the correlation coefficient based dendrograms other distributions are clearly not depth related but correspond to various environmental variables for example cancris auriculus coarse substrate bolivina subaenariensis oxygen minimum cibicidoides kullenbergi and hoeglundina elegans low organic carbon uvigerina peregrina is also a notable exception to depth dependence in that this dominant species and the province it represents are generally confined to the continental slope south of cape blanc its preference for that region may arise from the high organic carbon and fine grain size of the sediment there from low salinity of the bottom water or from other unknown variables the most important vertical faunal boundary occurs between cape barbas and cape blanc between 22 and 21 n latitude in contrast the canary island ridge intersects the continental margin at a saddle depth of about 1500 m but that physiographic barrier has little effect on provincialism of the deep water benthic foraminifera

hydrocarbon prospectivity in the hellenic trench system organic geochemistry and source rock potential of upper miocene lower pliocene successions in the eastern crete island greece results of the current and already published studies suggest that the tortonian in age deposits could serve a major source rocks for both oil and gas beneath the messinian evaporites in the hellenic trench system additionally the strong terrestrial input in pliocene deposits could lead to the production of biogenic gas similar to the po basin in adriatic sea italy in the current study fourteen samples from late miocene faneromeni section and twelve samples from the early pliocene makrilia section in eastern crete were collected in order to evaluate their hydrocarbon generation potential for this purpose rock eval analysis and characterization of the organic matter were performed the results document a clear distinction between the two sections faneromeni section contains organic matter of kerogen type iii whereas the makrilia section contains organic matter of kerogen type iv the hi toc plot diagram in both sections indicates poor oil generating potential with the exception of several samples showing fair to good gas and oil potential although thermal maturities of the samples from the two successions are similar according to the t max values samples from faneromeni succession exhibit higher hydrogen index values indicating a better quality of organic matter in terms of hydrocarbon generation very low obtained concentrations of bitumen mg g of rock as well as the predominance of nso compounds compared to the saturates and aromatics indicate low maturation level the n alkanes profiles exhibit a bimodal distribution indicating a mixed origin marine and terrestrial of the organic matter in both areas terrestrial organic matter input is more pronounced in makrilia section the analysis of saturated biomarkers indicates that faneromeni deposits were accumulated under constant organic matter input in an environment influenced by cyclic changes from marine to lagoon origin and vice versa faneromeni section corresponds to a restricted basin during tortonian with quick and often sea level fluctuations just before the messinian crisis while makrilia section represents a very restricted intramontane basin with strong terrestrial influence

closure of the paleotethys in the external hellenides constraints from u pb ages of magmatic and detrital zircons crete abstract paleotethys was a highly mobile oceanic realm pinching into the supercontinent pangea between gondwana and eurasia in the late paleozoic early mesozoic published paleotethyan reconstructions reveal that the time of paleotethys closure and the position of its suture are highly debated we present new magmatic and detrital zircon ages separated from pre alpine basement and permian to triassic cover rocks exposed in the external hellenides of crete these age data reveal variscan and cimmerian docking of microplates along the southern margin of laurasia and help to constrain the time of paleotethys closure 46 of detrital zircons from quartzite in the variscan basement are pennsylvanian with concordant ages at 321 2 ma 310 3 ma and 300 3 ma the basement is unconformably overlain by arc related volcanics of the tyros unit magmatic zircons of which yielded a concordant u pb zircon age at 285 2 ma thus the metasediments of the basement interpreted as former trench sediments were deposited metamorphosed and exhumed in latest carboniferous to early permian times 302 283 ma magmatic activity during this late variscan phase is also indicated by igneous boulders within olenekian meta conglomerates of the tyros unit which yielded concordant u pb zircon ages at 291 2 and 310 2 ma the late variscan orogenic phase is attributed to the collision of the gondwana derived southern minoan terrane smt with laurasia subsequent to northward subduction of paleotethys lithosphere and visean collision of the northern minoan terrane nmt magmatic activity ceased during the late permian but revived in the lower triassic as is indicated by felsic volcanics 249 2 ma concordant u pb zircon and by detrital zircons 242 3 240 5 ma 237 3 ma concordant u pb zircon of the tyros unit at the same time the variscan chain was exhumed and removed as is shown by the detritus in the lower to middle triassic tyros sediments which includes high grade metamorphic rocks and detrital zircons with u pb ages ranging from 280 to 335 ma a significant change in the detrital components occurred in the ladinian when the variscan basement with its permo triassic cover was thrust on top of clastic sediments today represented by the phyllite quartzite unit s str the phyllite quartzite unit s str shows cadomian and older but no variscan detritus because of its position along the northern margin of the cimmerian ribbon continent thus in the eastern mediterranean paleotethys was closed during the ladinian and the related suture in the external hellenides is situated between the variscan basement active margin in the north and the phyllite quartzite unit s str passive margin in the south carnian crustal extension led to subsidence of the variscan cimmerian chain most parts of which merged below sea level this is the reason why 90 of the detritus of the carnian tyros beds are not related to the variscan but to the cadomian and grenvillian basement of the e gondwana derived cimmerian ribbon continent

tertiary palaeogeography and tectonostratigraphic evolution of the northern and southern peri tethys platforms and the intermediate domains of the african eurasian convergent plate boundary zone abstract the increasing effects of african eurasian convergence during the tertiary resulted in the uplift and emergence of the northern and southern peri tethys platforms palaeogeographic maps covering six selected time slices including the middle eocene late early oligocene late early miocene early middle miocene early late miocene and middle to late pliocene illustrate that environmental and depositional differentiations on the northern platform and along the bordering domains of the convergence zone were more pronounced than on the southern platform and its adjacent areas the tectonic evolution of the northern platform included an overall eastward directed trend in the onset of basin uplift and emergence which started at about the eocene oligocene transition at 34 ma tectonostratigraphic analyses indicate a striking contemporaneity of the events which defined the temporal and spatial development of both the domains of the convergent plate boundary zone and the bordering platforms five episodes of major regional change in palaeogeographic and tectonic setting are distinguished they occurred in the late eocene 37 34 ma early late oligocene 30 27 ma latest early to earliest middle miocene 17 15 ma early late miocene 9 8 ma and late early to early middle pliocene 4 3 ma these episodes encompassed changes which were most probably induced by geodynamic events primarily related to the relative motions of the african arabian and eurasian plates in turn the plate motions are assumed to have triggered discrete steps in the regional kinematics and geodynamics that governed the palaeogeographic evolution of the peri tethys platforms and the intermediate domains of the african eurasian plate boundary zone

benthic foraminifer palaeoecology of the late quaternary continental outer shelf of a landlocked marine basin in central aegean sea greece abstract north evoikos gulf greece constitutes a landlocked epicontinental and semi enclosed basin connected to the central west aegean sea through a strait probably not allowing full exchange of intermediate and deep water masses benthic foraminifer analyses were carried out on a late quaternary core from the outer shelf of the basin with the aim of tracing palaeoceanographic changes the benthic foraminifer species percentage per sample was used to calculate two main biological proxies the benthic foraminifer oxygen index bfoi and benthic foraminifer high productivity bfhp proxy estimated by grouping benthic foraminifer taxa which are known to flourish under high corg flux the estimated values of bfhp and bfoi were controlled mainly by the abundance of bolivinid species which are generally considered as opportunistic and shallow infaunal species tolerant to low oxygen conditions the statistical analysis q mode cluster analysis singled out four time intervals each characterized by certain levels of oxygenation and food availability time interval 1 8513 8300 cal bp is characterized by a mixed fauna of oxyphilic taxa and taxa that live in suboxic environment indicating the existence of a relatively eutrophic system with a well oxygenated sediment water interface time interval 2 8300 8100 cal bp records a deterioration of conditions on sea floor testified by significant oxygen and biotic diversity decrease benthic foraminifer composition in time interval 3 8100 7000 cal bp depicts environmental conditions still highly variable yet with faunal indication of more stable conditions than during the previous interval finally the benthic foraminifer assemblage of time interval 4 7000 3500 cal bp is related to the high food supply and good bottom circulation the data suggest a strong linkage between the quantity and quality of the organic matter supplies and the diversity and composition of the benthic foraminifer faunas moreover this study clearly demonstrates that vertical tectonic movements need to be taken into account when reconstructing the late quaternary palaeoceanography of this region

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

anatomy of the antarctic circumpolar current volume transports through drake passage the 20 year october 1992 to august 2013 observation based volume transport time series of the antarctic circumpolar current acc through drake passage dp across the jason altimeter track 104 is analyzed to better understand the acc transport variability and its potential causes the time series of three transport components total tt barotropic bt and baroclinic bc referenced to 3000 m present energetic intraseasonal fluctuations with a salient spectral peak at 50 and 36 days with the largest least variance being associated with the bt bc component low frequency variations are much less energetic with a significant variance limited to the annual and biannual timescales and show a nonstationary intermittent link with the southern annular mode and the nino 3 4 index for interannual timescales the region around 57 s in the yaghan basin appears to be a strategic point for a practical monitoring of the acc transport as the whole track tt is significantly correlated with the local tt r 5 0 53 and bt r 5 0 69 around 57 s these local bt and tt variations are associated with a well defined tripole pattern in altimetric sea level anomaly sla there is evidence that the tripole pattern associated with bt is locally generated when the bc associated mesoscale slas which have propagated eastward from an upstream area of dp cross the shackleton fracture zone to penetrate into the yaghan basin barotropic basin modes excited within the yaghan basin are discussed as a plausible mechanism for the observed energy containing intra seasonal spectral peaks found in the transport variability

miocene high pressure metamorphism in the cyclades and crete aegean sea greece evidence for large magnitude displacement on the cretan detachment the cyclades in the backarc region of the present hellenic subduction zone are known for widespread late cretaceous to eocene high pressure metamorphism in the cycladic blueschist unit we report 40 ar 39 ar and rb sr phengite ages of 24 21 ma for high pressure metamorphism 8 10 kbar 350 400 c in the lowest tectonic unit in the cyclades the basal unit which structurally underlies the cycladic blueschist unit the basal unit is correlated with the tripolitza unit of the external hellenides in the forearc region of the hellenic subduction zone the tripolitza unit is unmetamorphosed on crete where it is separated from the underlying high pressure 8 10 kbar 300 400 c plattenkalk and phyllite quartzite units by the extensional cretan detachment the age for high pressure metamorphism in the latter units is similar to our age for the basal unit in the cyclades because pressure temperature conditions in the plattenkalk and phyllite quartzite units on crete and the basal unit in the cyclades are also similar they must have been in close proximity in the early miocene hellenic subduction zone a palinspastic reconstruction suggests a subsequent displacement of 100 km on the cretan detachment this is one of the greatest displacement magnitudes ever reported from detachment faults because of this large offset the cretan detachment was an efficient agent for exhuming high pressure rocks

the tectonic development of the hellenic arc and the sea of crete a synthesis abstract we use field analyses together with interpretation of aerial photographs orbital imagery and sea beam data to define more accurately the geometry of fault systems in the hellenic arc the tectonics of the area are dominated by extensional processes related to normal faulting we then use sea beam data previous oceanographic studies and extrapolation of field analyses on surrounding islands to describe the fault pattern of the cretan sea basin which is found consistent with the land fault pattern the mechanisms of the late neogene and quaternary deformation of the central and southern aegean region are analysed in terms of stress trajectories as revealed by field studies of fault populations we then examine the subsidence of the sea of crete in terms of a model of uniform stretching of the lithosphere the opening of the sea of crete was cylindrical and did not result in bending of crete this leads us to modify the southern portion of an earlier kinematic reconstruction of aegea in agreement with recent paleomagnetic results the implications of the opening of the sea of crete on the tectonic evolution of the straits to the west and east of crete are discussed finally the uplift of the outer arc is explained by underplating due to subduction

late carboniferous plutonism within the pre alpine basement of the external hellenides kithira greece evidence from u pb zircon dating in memory of theodor doutsos for his invaluable contribution to the understanding of geology of greece u pb zircon dating of three granitic orthogneisses sampled from kithira island sw greece provide the first reliable evidence for carboniferous plutonism within the pre alpine basement of the external hellenides concordant zircons from two samples yielded ages at 324 2 ma and 323 3 ma whereas the third sample yielded a lower intercept age at 320 1 2 ma the concordant ages are interpreted to date the emplacement of the igneous protolith ages of inherited zircons of two orthogneisses range from 2 5 to 2 4 ga indicating late archaean early proterozoic crustal components in combination with published ages for other aegean metagranitoids the new u pb ages provide additional evidence of a temporally restricted period of plutonism in the pre alpine aegean region from 325 to 300 ma comparing the post neoproterozoic evolution of the investigated basement with that of the cycladic and pelagonian basements and of the continental massifs of ne greece and turkey we argue that all these crustal blocks were part of the gondwana derived cimmerian terrane based on the spatial and temporal distribution of late carboniferous aegean plutonism we suggest that this period of magmatic events results from the southward subduction of palaeotethys beneath the marginal fragments of northern gondwana

source rock potential of middle cretaceous rocks in southwestern montana the middle cretaceous in southwestern montana is composed of a marine and nonmarine succession of predominantly clastic rocks that were deposited along the western margin of the western interior seaway in places middle cretaceous rocks contain appreciable total organic carbon toc such as 5 59 for the mowry shale and 8 11 for the frontier formation in the madison range most samples however exhibit less than 1 0 toc the genetic or hydrocarbon potential s1 s2 of all the samples analyzed except one yield less than 1 mg hc g rock strongly indicating poor potential for generating commercial amounts of hydrocarbons out of 51 samples analyzed only one a thermopolis shale sample from the snowcrest range showed a moderate petroleum potenti l of 3 1 mg hc g rock most of the middle cretaceous samples are thermally immature to marginally mature with vitrinite reflectance ranging from about 0 4 to 0 6 r0 maturity is high in the pioneer mountains where vitrinite reflectance averages 3 4 r0 and at big sky montana where vitrinite reflectance averages 2 5 r0 at both localities high r0 values are due to local heat sources such as the pioneer batholith in the pioneer mountains

anoxic basins of the eastern mediterranean an overview it is well known that the mediterranean sea underwent several episodes of basin wide stagnation in the plio pleistocene but extant anoxic basins were first discovered between 1983 and 1984 in the strabo trench and in the southwestern slopes of the mediterranean ridge facing the sirte abyssal plain since then several expeditions were carried out to investigate the geology and physiography of the basins as well as the physical and chemical characters of the water column although the geodynamic settings of the tyro and bannock basins are quite different they are very deep closed and filled by dense salty cold brines whose presence is attributed to submarine dissolution of messinian evaporites bannock basin is interpreted as a collapse basin with a complex configuration central domes and several satellite basins most of which are anoxic unlike the tyro basin it is characterized by precipitation of gypsum occurring as euhedral crystals within the sediments and dredged along the steep wall bordering the main basin to the east the interface separating normal seawater from the brines corresponds to a well defined pycnocline with a density contrast of approximately 20 where strong bacterial activity seems to occur and a sudden decrease in transmittance is recorded studies on the water column document drastic changes of all the various parameters measured o2 h2s ca po4 ba across the interface sediments deposited beneath the brines are anoxic this kind of geologically induced anoxia is persistent and diachronous in contrast with the isochronous episodic repetitive and climatically induced anoxia recorded in the same area of the eastern mediterranean

the pindos fold and thrust belt greece inversion kinematics of a passive continental margin continuous exposure in the pindos mountain chain greece and the detailed stratigraphic measurements in the area enable us to construct eight balanced cross sections across the pindos fold and thrust belt pftb and to approach quantitatively some parameters which controlled foreland evolution the 160 km wide passive continental margin of the apulian continent in greece was progressively shortened from east to west at rates of 6 mm year between the early oligocene and late eocene from the rear to the frontal part of the wedge fault bend folds duplexes and imbricates were formed while strain was partitioned into faulting 34 layer parallel shortening 23 and buckling 9 foreland subsidence and internal deformation of the orogenic wedge are strongly affected by two parameters of equal importance the thrust load of the overthrusted microcontinents and the rigidity of the underthrusted apulian passive margin changes in the thickness of the pre orogenic sediments and reactivated transform faults induced salients during the lower miocene the orogenic wedge in the peloponnese suffered additional uplift and westward gravitational gliding induced by the intracontinental subduction of the palaeozoic rift zone of the phyllite quartzite series which was reactivated and returned to the earth s surface during the hellenic orogeny

geochemistry of upper miocene lower pliocene source rocks in the hellenic fold and thrust belt zakynthos island ionian sea western greece abstract the southwestern margin of the hellenic fold and thrust belt situated along the southern edge of the dinarides albanides hellenides continental convergent zone has been studied in terms of its hydrocarbon generating potential the upper miocene lower pliocene tortonian to zanclean clastic sedimentary succession at zakynthos island provides an excellent opportunity to evaluate the source rock potential of such a system twenty seven mudstone samples were analyzed using organic geochemical techniques such as rock eval pyrolysis bitumen extraction open column chromatography and gas chromatography mass spectrometry the obtained data indicate that the sedimentary sequence contains units with sufficient organic material of good enough quality to be considered as potential source rocks the input of terrestrial organic material and associated gaseous generating potential is indicated by 1 rock eval pyrolytic yields and calculated values of hydrogen and oxygen indices 2 n alkane distribution with dominant long chain components 3 high terrigenous to aquatic organic material ratios 4 odd to even predominance values 5 low sulfur content and 6 occurrence of gammacerane the kerogen is immature as evidenced by 1 t max and production index values 2 odd to even predominance values 3 low diasterane to sterane and pr ph ratios 4 low 20s 20s 20r and sterane ratios and 5 presence of gammacerane

deep sea ecosystem variability of the aegean sea during the past 22 kyr as revealed by benthic foraminifera abstract specific responses of the regional deep sea ecosystems to climatic and oceanographic processes during the last 22 kyr are revealed by benthic foraminiferal faunas from two cores in the northern and southern aegean sea under glacial boundary conditions high diversity benthic foraminiferal faunas and elevated benthic foraminiferal numbers indicate enhanced organic matter availability and well ventilated deep water masses in the whole aegean sea the glacial termination is accompanied by significant fluctuations in productivity and deep water ventilation in the northern aegean sea meltwater inflow from mountain glaciers during the bolling allerod warm period resulted in a restriction of local deep water formation as mirrored by a dominance of bolivinids during the deposition of sapropel s1 drops in benthic foraminiferal number and diversity are more significant in the southern aegean sea when compared to the north this suggests the persistence of local deep water formation in the northern aegean sea during s1 deposition in addition faunal fluctuations within s1 at both sites suggest the repeated influence of short term cooling events on the re ventilation and re colonization of aegean deep sea ecosystems during the middle and late holocene benthic foraminiferal faunas document the establishment of oligotrophic and well ventilated conditions in the southern aegean sea the corresponding faunas from the northern aegean sea reflect generally mesotrophic conditions and variable deep water oxygenation during the entire holocene the deep sea ecosystems of this region responded very sensitively to short term changes in humidity and temperature these abrupt climate changes controlled the inflow of nutrients from rivers and the black sea and the formation of local deep water masses

the cassini vims archive of titan from browse products to global infrared color maps abstract we have analyzed the complete visual and infrared mapping spectrometer vims data archive of titan our objective is to build global surface cartographic products by combining all the data gathered during the 127 targeted flybys of titan into synthetic global maps interpolated on a grid at 32 pixels per degree 1 4 km pixel at the equator in seven infrared spectral atmospheric windows multispectral summary images have been computed for each single vims cube in order to rapidly identify their scientific content and assess their quality these summary images are made available to the community on a public website vims univ nantes fr the global mapping work faced several challenges due to the strong absorbing and scattering effects of the atmosphere coupled to the changing observing conditions linked to the orbital tour of the cassini mission we determined a surface photometric function which accounts for variations in incidence emergence and phase angles and which is able to mitigate brightness variations linked to the viewing geometry of the flybys the atmospheric contribution has been reduced using the subtraction of the methane absorption band wings considered as proxies for atmospheric haze scattering we present a new global three color composite map of band ratios red 1 59 1 27 m green 2 03 1 27 m blue 1 27 1 08 m which has also been empirically corrected from an airmass the solar photon path length through the atmosphere dependence this map provides a detailed global color view of titan s surface partially corrected from the atmosphere and gives a global insight of the spectral variability with the equatorial dunes fields appearing in brownish tones and several occurrences of bluish tones localized in areas such as sinlap menvra and selk craters this kind of spectral map can serve as a basis for further regional studies and comparisons with radiative transfer outputs such as surface albedos and other additional data sets acquired by the cassini radar radar and imaging science subsystem iss instruments

tectonics of the hellenic trench a synthesis of sea beam and submersible observations abstract detailed bathymetric investigations were performed in four zones of the hellenic trench system in 1978 using the multi narrow beam echo sounder sea beam on r v jean charcot in 1979 a field study using the 3000 m submersible cyana was conducted in three of the four sites covered by sea beam we summarize here the principal tectonic results of these studies and publish the corresponding sea beam maps it is shown that compressional structures affect the sedimentary cover of the outer wall and trench whereas extensional tectonics is present on the inner wall in addition there is evidence that most of the upper sedimentary cover is not subducted but rather piles up in front of the trench to form the mediterranean ridge we suggest that the surface limit of the zone of mechanical decoupling occurs near the base of the inner wall we show that the gross structure of the trench as well as the strain pattern observed is controlled by the kinematics of subduction and we discuss its evolution since its initiation about 13 m y ago

active faulting on the island of crete greece in order to characterize and quantify the middle late quaternary and ongoing deformation within the southern aegean forearc we analyse the major tectonic structures affecting the island of crete and its offshore the normal faults typically consist of 4 30 km long dipslip segments locally organised in more complex fault zones they separate carbonate and or metamorphic massifs in the footwall block from loose to poorly consolidated alluvial and colluvial materials within the hangingwall all these faults show clear evidences of recent re activations and trend parallel to two principal directions wnw ese and nne ssw based on all available data for both onland and offshore structures morphological and structural mapping satellite imagery and airphotographs remote sensing as well as the analysis of seismic profiles and the investigation of marine terraces and holocene raised notches along the island coasts for each fault we estimate and constrain some of the principal seismotectonic parameters and particularly the fault kinematics the cumulative amount of slip and the slip rate following simple assumptions and empirical relationships maximum expected magnitudes and mean recurrence periods are also suggested summing up the contribution to crustal extension provided by the two major fault sets we calculate both arc normal and arcparallel long term strain rates the occurrence of slightly deeper and more external low angle thrust planes associated with the incipient continental collision occurring in western crete is also analysed although these contractional structures can generate stronger seismic events m 7 5 they are probably much rarer and thus providing a minor contribution to the overall morphotectonic evolution of the island and the forearc a comparison of our geologicallybased results with those obtained from gps measurements show a good agreement therefore suggesting that the present day crustal deformation is probably active since middle quaternary and mainly related to the seismic activity of upper crustal normal faults characterized by frequent shallow 20 km moderate to strong seismic events seldom alternating with stronger earthquakes occurring along blind low angle thrust planes probably ramping from a deeper aseismic detachment ca 25 km this apparently contradicting co existence of juxtaposed upper tensional and lower compressional tectonic regimes is in agreement with the geodynamics of the region characterised by continental collision with nubia and the aegean mantle wedging

deepwater fold and thrust belt classification tectonics structure and hydrocarbon prospectivity a review abstract deepwater fold and thrust belts dwftbs are classified into near field stress driven type 1 systems confined to the sedimentary section and type 2 systems deformed by either far field stresses alone or mixed near and far field stresses dwftbs can occur at all stages of the wilson cycle up to early stage continent continent collision type 1 systems have either weak shale or salt detachments they occur predominantly on passive margins but can also be found in convergent related areas such as the mediterranean and n borneo examples include the niger and nile deltas the west coast of africa and the gulf of mexico type 2 systems are subdivided on a tectonic setting basis into continent convergence zones and active margin dwftbs continent convergence zones cover dwftbs developed during continent arc or continent continent collision and those in a deepwater intracontinental setting e g w sulawesi makassar straits active margins include accretionary prisms and transform margins the greatest variability in dwftb structural style occurs between salt and shale detachments and not between tectonic settings changes in fold amplitude and wavelength appear to be more related to thickness of the sedimentary section than to dwftb type in comparison with shale salt detachment dwftbs display a lower critical wedge taper more detachment folds long and episodic duration of deformation and more variation in vergence structures unique to salt include canopies and nappes accretionary prisms also standout from other dwftbs due to their relatively long continuous duration rapid offshore propagation of the thrust front and large amount of shortening in terms of petroleum systems many similar issues affect all dwftbs these include the oceanward decrease in heat flow offshore increase in age of mature source rock and causes of trap failure e g leaky oblique and frontal thrust faults breach of top seal by fluid pipes one major difference between type 1 and type 2 systems is reservoir rock high quality continent derived quartz rich sandstones are generally prevalent in type 1 systems more diagenetically reactive minerals derived from igneous and ophiolitic sources are commonly present in type 2 systems or many are simply poor in well developed turbidite sandstone units however some type 2 systems particularly those adjacent to active orogenic belts are partially sourced by high quality continent derived sandstones e g nw borneo s caspian sea columbus basin in some cases very high rates of deposition in accretionary prisms adjacent to orogenic belts coupled with uplift due to collision results in accretionary prism related fold belts that pass laterally from sub aerial to deepwater conditions e g s caspian sea indo burma ranges the six major hydrocarbon producing regions of dwftbs worldwide gulf of mexico niger delta nw borneo brazil west africa s caspian sea stand out as differing from most other dwftbs in certain fundamental ways particularly the very large volume of sediment deposited in the basins and or the great thickness and extent of salt or overpressured shale sdetachments

late neogene to quaternary contractional structures in crete greece abstract based on geological and tectonic investigations carried out along an n s coast to coast transect across central crete southern aegean greece new meso and macro structural data mainly collected from neogene quaternary deposits are presented and discussed the occurrence of large scale folds and thrusts together with diffuse minor contractional structures as well as the overall geometry of the fault bounded sedimentary basins document the persistence of a tortonian early pleistocene contractional regime characterized by an nnw sse to nne ssw shortening direction and affecting the upper crust this contractional event s was associated with the ongoing hellenic subduction and caused the development of a southwards migrating out of sequence thrust system consisting of both reactivated inherited structures and new ones the new data emphasize the importance and the extent of this contractional event intervening between the early middle miocene exhumation phase and the still active upper crustal extensional regime that was resumed in the island only during pleistocene when the region was affected by diffuse normal faulting while the contractional event was likely due to a stronger coupling along the overall subduction system the onset of the new extensional stress conditions was probably related to a sudden southwards jump of the basal detachment along the lithospheric african subduction that caused a general stress release in the uppermost crust