elongated depressions associated with pockmarks in the western slope of the norwegian trench abstract terraces or elongated depressions have been surveyed in the western slope of the norwegian trench in origin the depressions seem to be closely related to the formation of pockmarks in the norwegian trench a study area d has been selected in the western slope for the description of the elongated depressions and their associated features an area of similar size e has also been selected in the norwegian trench in order to compare the recent geology of the two areas it is found that the elongated depressions probably are caused by a combination of shallow gas seepage the geometry of subsurface bedding and the action of bottom currents furthermore examples of faulting within soft silty unconsolidated clay is documented by use of deep towed boomer data the existence of such faults could explain how gas migrates through the upper layers

carbon isotope stratigraphy across the permian triassic boundary a review abstract the palaeozoic mesozoic transition is marked by distinct perturbations in the global carbon cycle resulting in a prominent negative carbon isotope excursion at the permian triassic p t boundary well known from a plethora of marine and continental sediments potential causes for this negative 13 c trend and their links to the latest permian mass extinction have been intensively debated in the literature in order to draw conclusions regarding causation a general 13 c curve was defined after consideration of all available datasets and with due reference to the biostratigraphic background the most important features of the p t carbon isotope trend are the following the 4 7 13 c decline lasting 500 000 years is gradual and began in the changhsingian at the stratigraphic level of the c bachmanni zone the decreasing trend is interrupted by a short term positive event that starts at about the latest permian low latitude marine main extinction event horizon eh indicating that the extinction itself cannot have caused the negative carbon isotope excursion after this short term positive excursion the 13 c decline continues to a first minimum at about the p t boundary a subsequent slight increase is followed by a second occasionally two peaked minimum in the lower and middle i isarcica zone the negative carbon isotope excursion was most likely a consequence of a combination of different causes that may include 1 direct and indirect effects of the siberian trap and contemporaneous volcanism and 2 anoxic deep waters occasionally reaching very shallow sea levels a sudden release of isotopically light methane from oceanic sediment piles or permafrost soils as a source for the negative carbon isotope trend is questionable at least for the time span a little below the eh and somewhat above the p t boundary

potential distribution of subsurface methane in the sediments of the eastern arabian sea and its possible implications high resolution shallow seismic reflection data obtained in the continental shelf sediments off western india from 10 n to 22 n reveal the characteristic anomalous seismic signatures in the form of acoustic maskings of methane rich horizons a conservative estimate of the potential subsurface methane in these gas charged sediments is of the order of 2 6 tg and its contribution to the atmosphere with an annual flux of 0 039 tg ch4 appears to be quite significant from our limited results coupled with worldwide reports it is concluded that the seepage of methane 8 to 65 tg through the seabed of the continental shelves worldwide cannot be ignored for the estimation of global oceanic flux of methane and its budget

the permian triassic transition in ocean island setting environmental disturbances and new high resolution carbon isotope record from the qiangtang basin nw china abstract the permian triassic boundary ptb events such as carbon isotope excursion volcanism and environmental disturbances are not well understood in an ocean island setting here we develop a new case study for the permian triassic transition in the qiangtang basin tibet by combining existing biostratigraphy new carbon isotope data sedimentological data u pb zircon age mineralogical and geochemical data these new data defined the permian triassic transition age as about 252 3 0 9 ma corresponding to the lowermost sea level a long term negative carbonate carbon isotope trend is present at the same stratigraphic level in different depositional environments strongly suggesting its global nature however our new ocean island setting is characterized by an abrupt shift in carbon isotope values across the level which is different from many chemostrtigraphic studies that show a gradual shift in carbon isotope values across the event horizon the most likely explanation for the abrupt shift in 13c values is a sedimentary hiatus at this level in the study section three stage climatic models through the ptb in the ocean island setting are identified stage 1 is characterized by a warm and humid climate with moderate chemical weathering while a hot and humid climate with intense chemical weathering dominates stage 2 the climate in stage 3 is a relatively hot and arid climatic condition with weak chemical weathering

martian north polar cap 1979 1980 a regression curve for the north polar cap of mars is extracted from the photographs obtained at kwasan observatory and at hida observatory during the 1979 1980 apparition the north polar cap was first observed at ls 26 and the latitude of the edge of the cap was about 66 n the retreat of the cap stopped until mars reached ls 57 when the cap started to shrink the edge reached a latitude around 80 n at ls 85 and then became almost stationary the roughly constant dimension of the north polar cap before mid spring appears to be a regular phenomenon but the onset time when the cap starts to shrink after the temporary stop appears to be different from year to year the measurements of the edge of the permanent cap showed an asymmetric shape in relation to the pole the cap extends farther to the south for longitudes near 0 than for those near 180 the shape of the permanent cap for ls 84 101 in 1980 agrees very well with that for ls 97 in 1972 obtained by mariner 9

carbon dioxide ice clouds snowfalls and baroclinic waves in the northern winter polar atmosphere of mars 1 the formation of co2 ice clouds in the northern winter polar atmosphere of mars and their relation to baroclinic planetary waves which dominate local dynamics are studied using a general circulation model the simulation shows that clouds are formed at altitudes of up to 40 km and their occurrence correlates to a large degree with the cold phases of transient planetary waves ice particles formed up to 20 km can reach the surface in the form of snowfall in certain longitude regions while in others these particles likely sublimate in the lower warmer atmospheric layers the simulation suggests that about a half of the seasonal ice cap is created by co2 snow while the remaining half by direct condensation on the surface thus the occurrences of ice clouds and rates of deposition are closely linked to traveling planetary waves indicating the possibility for the reliable forecasts of co2 snow storms citation kuroda t a s medvedev y kasaba and p hartogh 2013 carbon dioxide ice clouds snowfalls and baroclinic waves in the northern winter polar atmosphere of mars geophys res lett 40 1484 1488 doi 10 1002 grl 50326

regression of martian north polar cap 1990 1997 hubble space telescope observations abstract hubble space telescope imaging of mars from december 13 1990 through april 17 1997 has resulted in the synoptic monitoring of parts of four consecutive martian north polar cap regressional cycles spanningls 335 65 tols 144 56 the 1990 1993 observations were obtained with the wide field planetary camera 1 wfpc1 instrument while subsequent observations from 1994 to 1997 were obtained with the improved optics of the wide field planetary camera 2 wfpc2 mars observations were obtained from the ultraviolet 218 nm to the near infrared 1042 nm which has allowed us to constrain the effects of clouds and dust particulates on cap edge measurements hst observations of the polar cap regressions afterls 0 are fairly consistent from year to year with some variations possible beforels 0 the 1991 observations atls 35 25 andls 59 88 in the longitude range 270 280 possibly support a standstill in cap retreat at a latitude 70 n the standstill in cap retreat reported in previous years at a latitude 67 n was not observed in 1992 1997 comparison with previous ground based and spacecraft observations suggests that interannual variations may be significant they may be due to interannual atmospheric changes such as global dust storm activity lambert albedos of the north polar cap in red and violet bandpasses are similar to those reported before

methane related carbonate cements in pockmarks of the north sea abstract some pockmarks on the norwegian continental shelf contain patches of cemented sediment that can provide hardgrounds attractive to a variety of benthonic organisms detailed examination of a sandstone sample from a pockmark in norwegian block 25 7 in the north sea has revealed the presence of mg calcite and aragonite cements some of the latter forming botryoids all cement types are characterized by extremely light carbon isotopic compositions with a mean 13c value of 56 1 pdb which shows that the cements contain carbonate produced by oxidation of biogenic methane oxidation occurred in both the oxic and anoxic diagenetic zones trace amounts of interstitial methane mean 13c 40 8 and higher hydrocarbon gases up to c5 with a c1 cn ratio of 0 855 0 874 in the pockmark sediments indicate that some thermogenic methane may be mixed with the biogenic gas

intrabasin variability of the carbon isotope record across the permian triassic transition sverdrup basin arctic canada abstract a major late paleozoic depocentre the sverdrup basin canadian high arctic has been largely left out of the latest permian extinction debate as early workers presumed middle to late permian strata were absent basin scale sequence stratigraphic and chemostratigraphic correlations indicate late permian strata are only missing on the basin margins where they were removed by sub triassic erosion whereas continuous deposition is recorded in the basin centre the varying degree of sub triassic erosion has significant impact on the carbon isotope record across the latest permian extinction event where both the apparent rate and magnitude of carbon isotope shift vary as a function of basin position the intrabasin variability in apparent 13corg shift across the event is equivalent to that observed globally in contrast to the abrupt isotope shifts recorded on the basin margin similar to many records reported globally the basin centre section shows a systematic shift associated with the latest permian extinction the earth likely underwent a prolonged period of increasing environmental stress leading up to the event

the giant ruatoria debris avalanche on the northern hikurangi margin new zealand result of oblique seamount subduction despite convergent margins being unstable systems most reports of huge submarine slope failure have come from oceanic volcanoes and passive margins swath bathymetry and seismic profiles of the northern hikurangi subduction system new zealand show a tapering 65 30 km wide by 65 km deep margin indentation with a giant 3150 630 km3 blocky debris avalanche deposit projecting 40 km out across horizontal trench fill and a debris flow deposit projecting over 100 km slide blocks are well bedded up to 18 km across and 1 2 km high the largest being at the avalanche deposit s leading edge samples dredged from them are mainly miocene shelf calc mudstones similar to those outcropping around the indentation cores from cover beds suggest that failure occurred 170 40 ka possibly synchronously with a major extension collapse in the upper indentation however the northern part of the indentation is much older the steep straight northern wall is close to the direction of plate convergence and probably formed around 2 0 0 16 ma as a large seamount subducted leaving in its wake a deep groove obliquely across the margin and an unstable triangle of fractured rock in the 60 angle between groove and oversteepened margin front the triangle collapsed as a blocky avalanche leaving a scalloped southern wall and probably causing a large tsunami tentative calculations of compacted volumes suggest that the indentation is over 600 km3 larger than the avalanche supporting a two stage origin that includes subduction erosion since failure convergence has carried the deposits 9 km back toward the margin causing internal compression the eventual subduction accretion of the ruatoria avalanche explains the scarcity of such features on active margins and perhaps the nature of olistostromes in fold belts

geophysical and geochemical evidence for subsurface hydrocarbon leakage in the bering sea alaska abstract geophysical and geochemical surveys were conducted on the bering sea shelf to investigate whether hydrocarbons found in the surficial sediment particularly in association with certain geophysical events indicate the presence and nature of more deeply reservoired oil and gas deposits surface sediment samples were obtained at 1000 sites where high resolution seismic data indicated the presence of gas seepage and or surface faulting in addition sites for background measurements were occupied away from areas of gas seepage results of the geophysical survey show seismic wipeout zones to be present throughout the bering sea shelf sediment samples obtained within the shallow wipeout zones confirm that these features are caused by gas in addition compositional and isotopic analyses indicate that the gas is of biogenic and thermogenic origins the thermogenic leakage appears to be related to localized faulting and shallow structuring the high resolution seismic data therefore provide an excellent tool for locating leakage points thereby enhancing the opportunity of finding migrated thermogenic hydrocarbons in surficial sediments an examination of vertical variability shows the hydrocarbon concentrations to be strongly related to various processes occurring in the surficial sediments core samples must be taken from below the zone of maximum disturbance to obtain unaltered hydrocarbon samples

quaternary tectonics in the gulf of patras western greece abstract air gun seismic and 3 5 khz profiling data from the gulf of patras western greece show that it is occupied by a small asymmetric graben with several geometric similarities to the larger scale graben in the gulf of corinth to the east major listric faulting characterizes the southern flank of the graben whilst the northern flank represents an associated rollover structure affected by antithetic and synthetic faulting the present phase of subsidence is of holocene age but buried growth faults suggest earlier subsidence in the gulf the average rate of subsidence through the holocene is estimated to be 10 mm year the gulf of patras graben together with the gulf of corinth graben and the megara basin represent a continuous system of wnw ese trending grabens in a broad zone of intense seismicity within the aegean domain individual grabens are offset and are interconnected by ne sw trending fault systems

changes in the global carbon cycle occurred as two episodes during the permian triassic crisis coeval records of ocean atmosphere and terrestrial change are crucial to understanding the pattern and causes of global mass extinction across the permian triassic boundary ptb however relationships among changes in different settings remain largely unclear primarily due to the challenges associated with the correlation among disparate records here we compare marine carbon isotopic records with marine and terrestrial environmental and biotic events recorded in sediments from the meishan ptb section of south china time scaled carbonate carbon isotopes exhibit two gradual major shifts across the ptb at meishan and these are duplicable elsewhere around the tethys ocean the two shifts are associated with two episodes of enhanced terrestrial weathering indicated by an increased abundance of 13 c enriched moretanes relative to hopanes and an elevated abundance of black carbon fragments key marine events previously reported for the ptb including photic zone euxinia faunal mass extinction and cyanobacterial expansion also occur as two episodes coinciding with both of the progressive shifts to negative 13 c values and enhanced weathering the temporal sequence of the duplicable events suggests that the biotic crisis was a consequence of prolonged and episodic changes in the marine and continental systems and argues against an extraterrestrial impact as the main cause

initial assessment of the carbon emission rate and climatic consequences during the end permian mass extinction numerous lines of geochemical and stable isotopic evidence indicate that the end permian mass extinction was accompanied by abrupt climate change induced by co2 addition catastrophic end permian siberian volcanism may have released a large amount of co2 into the atmosphere and pushed the earth s system beyond a critical threshold causing the mass extinction however the injection rate total amount and source of co2 are largely unknown we conducted a suite of simulations using the recently published carbon isotope records and u pb ages from meishan section in zhejiang province china an earth system model of intermediate complexity cgenie http www genie ac uk was used to extract the pattern of co2 release needed to replicate the observed carbon isotope excursion across the permian triassic boundary this analysis leads us to suggest that the source of co2 must have been significantly heavier than typical biogenic or thermogenic methane to explain the significant warming that occurred during and after the extinction event nevertheless as with the paleocene eocene thermal maximum end permian rates of co2 addition were likely small compared with modern fossil fuel burning but considerably more protracted such that the likely total co2 emitted significantly exceeded the modern fossil fuel reserves peak emission rates corresponded to the onset of the maximum extinction interval consistent with carbon cycle disruption including volcanogenic co2 induced warming and perhaps ocean acidification as a trigger for the end permian mass extinction

winter and spring evolution of northern seasonal deposits on mars from omega on mars express the omega visible near infrared imaging spectrometer on mars express has observed the retreat of the northern seasonal deposits during martian year 27 28 from the period of maximum extension close to the northern winter solstice to the end of the retreat at l s 95 we present the temporal and spatial distributions of both co 2 and h 2o ices and propose a scenario that describes the winter and spring evolution of the northern seasonal deposits during winter the co 2 rich condensates are initially transparent and could be in slab form a water ice annulus surrounds the sublimating co 2 ice extending over 6 of latitude at l s 320 decreasing to 2 at l s 350 and gradually increasing to 4 5 at l s 50 this annulus first consists of thin frost as observed by the viking lander 2 and is then overlaid by h 2o grains trapped in the co 2 rich ice layer and released during co 2 sublimation by l s 50 h 2o ice spectrally dominates most of the deposits in order to hide the still several tens of centimeters thick co 2 ice layer in central areas of the cap we propose the buildup of an optically thick top layer of h 2o ice from ice grains previously embedded in the co 2 ice and by cold trapping of water vapor from the sublimating water ice annulus the co 2 ice signature locally reappears between l s 50 and 70 what emerges from our observations is a very active surface atmosphere water cycle these data provide additional constraints to the general circulation models simulating the martian climate copyright 2011 by the american geophysical union

fjord water circulation patterns and dysoxic anoxic conditions in a mediterranean semi enclosed embayment in the amvrakikos gulf greece abstract oceanographic research in the amvrakikos gulf in western greece a semi enclosed embayment isolated from the ionian sea by a narrow shallow sill has shown that it is characterised by a fjord like oceanographic regime the gulf is characterised by a well stratified two layer structure in the water column made up of a surface layer and a bottom layer that are separated by a strong pycnocline at the entrance over the sill there is a brackish water outflow in the surface water and a saline water inflow in the near bed region this morphology and water circulation pattern makes the amvrakikos gulf the only mediterranean sea fjord the investigations have also shown that the surface layer is well oxygenated whereas in the pycnocline the dissolved oxygen do declines sharply and finally attains a value of zero thus dividing the water column into oxic dysoxic and anoxic environments at the dysoxic anoxic interface at a depth of approximately 35 m a sharp redox cline develops with eh values between 0 and 120 mv occurring above and values between 0 and 250 mv occurring below where oxic and anoxic biochemical processes prevail respectively on the seafloor underneath the anoxic waters a black silt layer and a white mat cover resembling beggiatoa like cells are formed the dysoxic anoxic conditions appeared during the last 20 to 30 years and have been caused by the excessive use of fertilisers the increase in animal stocks intensive fish farming and domestic effluents the inflicted dysoxia anoxia has resulted in habitat loss on the seafloor over an area that makes up just over 50 of the total gulf area and approximately 28 of the total water volume furthermore anoxia is also considered to have been responsible for the sudden fish mortality which occurred in aquaculture rafts in the gulf in february 2008 therefore anoxic conditions can be considered to be a potential hazard to the ecosystem and to the present thriving fishing and mariculture industry in the gulf

timing of the permian triassic biotic crisis implications from new zircon u pb age data and their limitations abstract the most profound biotic crisis in the earth s history causing the near extinction of both terrestrial and marine life occurred at the end of the permian period about 253 myr ago and marks the paleozoic mesozoic era boundary the cause of this event is still a matter of vigorous debate with both brief and catastrophic as well as gradual mechanisms having been proposed similar to a recent landmark study this study uses the u pb method on zircons from the uppermost permian lowermost triassic ash fall deposits at meishan zhejiang province se china in order to examine time and rate constraints for these events the results of both this study and previous work show that for these ash layers the effects of pb loss are combined with varying amounts and sources of inheritance resulting in an age scatter which prohibits the extraction of a statistically robust age in many cases though the effects of pb loss on the zircons analyzed in this study were reduced by leaching the grains in hydrofluoric acid as opposed to commonly applied air abrasion prior to analysis the presence within a single ash layer of multiple generations of older xenocrysts in many cases only slightly older than the depositional age has made quantitative interpretation even more difficult when these combined phenomena bias individual zircon ages by less than a percent they are extremely difficult to deconvolute and if multi grain analyses are used can become impossible to recognize because of the resulting age averaging monte carlo simulations using actual measurements of individual zircon crystals show that age excursions due to pb loss and xenocrystic contamination for the meishan bentonites are easily homogenized to the point of undetectability when replicate analyses of multi grain zircon samples are compared thus this study uses only high precision analyses of single crystals whether from our work or that of previous studies three main conclusions have emerged first our data require a significant increase in the age of the permian triassic boundary by more than 2 myr compared to the previous study which shifts the age to a value older than 253 ma second neither our data nor those from previous work can confirm or negate the possibility of a very abrupt biotic crisis third even large suites of very high quality single zircon u pb analyses for these tuffs cannot in most cases yield objective reliable and robust dates with accuracies at the sub myr level though the temptation to perform arbitrary selection of subsets of the analyses for that purpose is almost irresistible the last conclusion is not an indictment of zircon u pb dating in general other rocks and other zircon populations can and do behave very differently and further technical advances will likely improve our ability to prepare grains or sub grains of adequately enhanced quality for analysis consequently the results of the present study strongly suggest that for problems requiring time scale accuracy inferences from zircon u pb dating must be based on sufficiently large suites of single crystal or crystal domain high precision analyses

gas charged sediments in the aegean and ionian seas greece abstract during the last fifteen years marine seismic surveys in the aegean and ionian seas have revealed numerous acoustic anomalies i e acoustic turbid zones gas pockets gas plumes enhanced reflectors columnar disturbances wipe outs and meso to micro morphological features such as pockmarks domes mud volcanoes and elongated depressions these are attributed to the presence of gas in sediment interstices the gas charged sediments are found in pleistocene and present day fjord like environments pleistocene and present day deltaic environments lakes and open sea environments the gas found in the quaternary fjord like and deltaic depositional environments is assumed to be of biogenic origin the gas found in the pre quaternary open sea environments is associated with faulting and salt doming and may therefore be of thermogenic origin although the sediment grain size is favourable for the formation of pockmarks the lack of them is probably due to the high seismicity which characterises these regions

triggers of permo triassic boundary mass extinction in south china the siberian traps or paleo tethys ignimbrite flare up abstract assessment of the synchroneity between the siberian traps and the permo triassic boundary ptb mass extinction has led to the proposition that the siberian flood volcanism was responsible for the severest biotic crisis in the phanerozoic however recent studies suggest that the siberian traps may have postdated the main extinction horizon in this paper we demonstrate using stratigraphy a time and intensity coincidence between ptb volcanic ash and the main extinction horizon geochemistry of the ptb volcanic ashes in five sections in south china indicates that they were derived from continental magmatic arc zircons extracted from the ptb volcanic ashes have negative e hf t 12 9 to 2 0 and 18 o 6 8 to 10 9 consistent with an acidic volcanism and a crustal derived origin and therefore exclude a genetic link between the ptb mass extinction and the siberian traps on the basis of spatial variation in the number of the ptb volcanic ash layers and the thickness of the ash layers in south china we propose that the ptb volcanic ash may be related to paleo tethys continental arc magmatism in the kunlun area ignimbrite flare up related to rapid plate subduction during the final assemblage of the pangea super continent may have generated a volcanic winter which eventually triggered the collapse of ecosystem and ultimately mass extinction at the end of the permian the siberian traps may have been responsible for a greenhouse effect and so have been responsible for both a second pulse of the extinction event and early triassic ecological evolution

modern sedimentation in the n w aegean sea abstract the area under investigation is located within 22 45 to 23 45 e and from 39 15 to 40 15 n sedimentological bathymetric and shallow geophysical data were collected from here during the 7 78 cruise of r r s shackleton twenty seven sea bed surface samples were collected using a day grab from different environments these were analysed for grain size distribution carbonate content and clay mineralogy on the basis of the bathymetric and shallow geophysical data the area has been classified into five major physiographic environments according to their bathymetry and topography 1 shelf thermaicon plateau 2 slope 3 marginal plateau 4 the canyon system and valleys and 5 sporades basin based on the sedimentological analyses the surface sediments have been classified into four major provinces as follows 1 province 1 shelf muds 2 province 2 muddy sands 3 province 3 outer margin muds and 4 province 4 outer shelf shelf break it is concluded that modern sedimentation in the n w aegean sea is dominated by the terrigenous river inputs and by the circulation of both high and low salinity masses

deep water hydrocarbon seeps in guaymas basin gulf of california abstract acoustically discovered hydrocarbon seeps along a transform fault zone on the sonoran margin of guaymas basin and in the southern trough of guaymas basin were examined and sampled during dives of dsv alvin seepage of methane and heavier hydrocarbons occurs through shallow pockmarks along the eroding crest of a steep anticline 1600 m below sea level extensive ledges of aragonite crop out around the rims of the pockmarks isotopic analysis indicates that carbonate precipitation is a result of methane oxidation seepage zones within the pockmarks support dense communities of calyptogena half buried in the mud tubeworms lamellibracheae sp have colonized many of the aragonite outcrops though the margin site is only a few kilometers from a high temperature sulfide precipitating and petroleum discharging vent system at a nearby center its structural setting is more akin to pockmarks described from continental shelves and its chemosynthetic fauna is more like that around low temperature seeps on other continental slopes and margins e g oregon u s a and japan the seep in the southern trough is a condensate type petroleum c 1 c 40 and rises as a plume from a young vent mound system about 2000 m below sea level

gas seepage and assumed mud diapirism in the italian central adriatic sea abstract an assemblage of acoustic and topographical features recorded on high resolution 3 5 khz sub bottom profiler records are discussed a close relationship between locally elevated sea bed mounds or ridges and the several acoustic features is found in the adriatic sea off ortona italy these features include acoustically turbid or opaque zones assumed to represent gas charged sediments acoustically transparent sediments assumed to represent sediments with relatively high pressured pore water free of large gas bubbles acoustic fountains assumed to represent 1 2 m wide sediment columns of relatively high pressured pore water where the gas charged pore water may migrate vertically through the sediment acoustic voids assumed to be up to 50 m wide sediment zones near the sea bed containing high pressured gas charged pore water finely layered sediments assumed to represent sediments with sharp density contrasts caused by varying gas concentrations a function of grain size and stagnant pore water gas seepage to the water column originating at the acoustic voids the positive topographical sea bed features are assumed to represent sediment clay diapiric structures the mechanism of diapir formation and its association with the gas charged sediments and gas seepages is discussed diapirism is assumed to result when plastic clay near the sea bed is charged with gas migrating from below bubbles forming and concentrating in the plastic clay causes local density reversals whereby the clay flows upwards due to buoyancy thus forming the elevated topographical features and the associated gas seepages

yearly comparisons of the martian polar caps 1999 2003 mars orbiter camera observations abstract the mars global surveyor mars orbiter camera wide angle cameras were used to obtain images of the north and south seasonal and residual polar caps between 1999 and 2003 wide angle red camera images were used in assembling mosaics of the north and south polar recessions and regression rates were measured and compared there are small variations in the north polar recession between 2000 and 2002 especially between l s 7 and l s 50 however there is no evidence for the plateau in the recession curves that has been observed in some prior years the south polar recession changes very little from year to year and the 2001 dust storm had little if any effect on the average cap recession that year albedo values of the geographic north pole were measured using wide angle red and blue camera images and the residual south polar cap configuration was compared between the three years observed by moc the albedo of the geographic north pole generally varies between 0 5 and 0 6 as measured from moc wide angle red camera images there were only minor variations near the edges of the residual south polar cap between the three years examined

sedimentation processes in a tectonically active environment the kerkyra kefalonia submarine valley system ne ionian sea the kerkyra kefalonia valley system is the northwestern extension of the hellenic arc trench system representing the collision zone of the apulian platform and the hellenides the system is distinguished by two different physiographic regions the northern part u shaped and oriented nnw sse with relatively gentle slopes and a wide floor and the southern part oriented ne sw v shaped and with much steeper side walls and a narrow floor both parts are formed tectonically with the former coinciding with a collision zone and the latter being the morphometric expression of the kefalonia strike slip fault sediments recovered in the piston cores from the region consist of fine grained material deposited by a variety of sedimentation processes such as gravity driven mass movements associated with seismic activity i e slumping sliding debris flows grain flows turbidites seismoturbidites and to a lesser extent by hemipelagic deposition measured near bed currents and their associated shear stresses indicate resuspension of the material mainly within the northern part of the valley sub bottom acoustic seismic profiling data reveal various sedimentary provinces related to different mechanisms of sediment accumulation i the eastern margin of the apulian platform with hemipelagic sedimentation together with possible advection of suspensates from the adriatic in response localised to seabed erosion ii the western hellenic margin with down slope episodic sliding and slumping induced primarily by earthquake activity together with an input from hemipelagic settling iii the collision zone coinciding with the northern part of the kerkyra kefalonia valley system with deposition mostly from resuspension the occurrence of local mass gravity flows and the advection of some material from the north and iv the kefalonia strike slip fault region where mass gravity flows are the dominant mechanisms related to erosion deposition from resuspension overall sedimentation within the tectonically active kerkyra kefalonia valley system is characterised by the coupling of the mass gravity driven flows which are the predominant mechanisms with the near bed current regime related with resuspension phenomena and the advection of suspensates these latter mechanisms is likely more pronounced during the winter period when dense water masses formed in the adriatic inflowing into the ionian sea

characteristics of pockmarks in the norwegian trench a 3 km wide corridor across the norwegian trench was surveyed in detail with high resolution side scan sonar and subbottom profiler boomer in order to study pockmarks the pockmarks in the norwegian trench are dish shaped depressions found in the soft silty clays they range from 2 m to 300 m in diameter and appear with a maximum density of 40 50 per km2 lineated depressions and strings of small pockmarks were discovered the strings are generally composed of individual pockmarks 10 15 m in diameter each string can be up to 400 m long some medium sized pockmarks 40 50 m in diameter were found in groups often associated with a large parental pockmark the deep towed subbottom profiler records indicated columnar disturbances fountains in the sediments below some of the pockmarks these fountains are interpreted as vents or fissures through which gas or liquids migrate buried pockmarks and anomalies interpreted as boulders possibly gas bubbles trapped in the substrata were also found the recordings bear evidence of gas or liquid migration originating from layers lying beneath the soft clay sequence a large hydrocarbon gas reservoir has recently been found during exploration drilling in the immediate vicinity of the studied pockmark area pockmarks may be indicators of deep lying gas or oil reservoirs and therefore prove interesting features in relation to hydrocarbon prospecting

significance of mud volcanism 1 mud volcanism and diapirism have puzzled geoscientists for 2 centuries they have been described onshore and offshore in many places on earth and although they occur in various tectonic settings the majority of the features known to date are located in compressional tectonic scenarios this paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described mud volcanoes show variable geometry up to tens of kilometers in diameter and several hundred meters in height and a great diversity regarding the origin of the fluid and solid phases gas predominantly methane water and mud may be mobilized at subbottom depth of only a few meters but in places can originate from several kilometers depth with minor crustal or mantle input the possible contribution of mud extrusion to global budgets both from quiescent fluid emission and from the extrusive processes themselves is important in regions where mud volcanoes are abundant such as the collision zones between africa and eurasia fluid flux through mud extrusion exceeds the compaction driven pore fluid expulsion of the accretionary wedge also quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and hence to greenhouse climate

seismic and geochemical evidence for shallow gas in sediment on navarin continental margin bering sea marine seismic studies coupled with geochemical investigations demonstrate that hydrocarbon gases are ubiquitous in the near surface 250 m or 820 ft depth sediment of the navarin continental margin in the northern bering sea three types of acoustic anomalies appear to be related to the presence of gas in the sediment these anomalies are most prevalent in the northern half of the navarin basin acoustic anomalies attributed to gas hydrates and to diagenetic boundaries are present on seismic records of the lower slope between navarinsky and zhemchug canyons hydrocarbon gases methane through butanes are common in the surface 5 m or 17 ft depth sediment of the navarin continental margin methane the most abundant hydrocarbon gas is present in amounts ranging from 84 000 to 1 l l of wet sediment these concentrations are two to three orders of magnitude greater than the other hydrocarbon gases the highest concentrations of methane greater than 1 000 l l were measured in sediment of navarinsky canyon and over the central part of the navarin basin the source of methane is mainly biogenic but the hydrocarbon gas compositions in 17 of 141 cores suggest the presence of thermogenic gas most of these 17 cores are from the continental slope at water depths greater than 150 m 490 ft no direct correlation could be found between acoustic anomalies and gas concentrations in the sediment this lack of correlation is probably due to the limited penetration of the gravity corer and the spotty distribution of hydrocarbon concentrations

permian triassic boundary interval in the middle east iran and n oman progressive environmental change from detailed carbonate carbon isotope marine curve and sedimentary evolution abstract the end permian negative 13c excursion is well known but its cause and chronology are still in question in an attempt to decipher the timing and reasons for this strong decrease we established high resolution sedimentological biostratigraphical and carbonate carbon isotopic studies in four sections in iran abadeh shareeza zal and djulfa and two in oman wadi sahtan the position of the sections on two different margins of the neotethys has allowed us to distinguish between local and global signals this high resolution chemostratigraphy tested for isochrony on the basis of an updated high resolution conodont and ammonoid biostratigraphy allows the discrimination of nine successive isotopic events ie 0 8 for the permian triassic boundary interval ptbi the negative excursion of the ptbi has been separated into four distinct parts a first drop ie 0 occurs in the late wuchiapingian with an amplitude of around 1 3 a second decrease begins ie 1 2 at the base of the dzhulfites ammonoid beds changhsingian and continues gradually until the extinction event top jolfensis conodont interval without important second order variations its amplitude varies between 1 5 and 2 8 and its duration has been estimated around 2 2 ma revealing a non catastrophic phenomenon the lower meishanensis praeparvus conodont zone records stationary to slightly increasing values ie 3 the interval of the curve after the extinction event between the upper meishanensis praeparvus zone and the base of the i isarcica zone records numerous second order variations ie 4 7 its amplitude is of 1 2 3 1 these second order variations are correlatable in iran but with some uncertainty with oman poor correlation of these small peaks with others published sections might be due to a higher sensitivity to local perturbations and a lower buffer capacity of the whole ocean we assume that the processes leading to the extinction event also caused the isotopic decrease before the extinction level with a maximal amplitude of only 2 8 this allows consideration of some possible mechanisms that were rejected as unrealistic to cause a 4 6 excursion

martian north polar cap recession 2000 mars orbiter camera observations abstract the wide angle cameras of the mars orbiter camera moc on the mars global surveyor have recorded the 2000 recession of the seasonal co 2 cap in the north polar region from l s 330 to 90 in stark contrast to the asymmetric behavior of the south seasonal cap the seasonal north cap remains relatively circular and uniform until mid spring when the retreat reaches the circum polar dune field which is the one major nonuniformity in the cap the recession of cap edge latitude versus areocentric longitude l s is very well represented as a linear function until late spring there is no evidence for the plateau or standstill in the recession curve that has been observed in some prior years the lambert albedo of the seasonal frost deposits in the north polar region demonstrates the increase with insolation first observed by paige in 1985 increasing to approximately 0 57 at l s 40 the north polar cap near solstice visually appears smaller than that observed by moc at the start of mapping in 1999 but later images acquired in summer show the residual cap returning to its more usual shape the most likely explanation for these changes in albedo is precipitation and subsequent removal of dust on the cap as a result of frequent dust storms near the cap edge

association of 34s depleted pyrite layers with negative carbonate δ13c excursions at the permian triassic boundary evidence for upwelling of sulfidic deep ocean water masses 1 a marine permian triassic boundary ptb section at nhi tao vietnam contains a series of at least 9 pyritic horizons characterized by concurrent decreases in pyrite s 34spy and carbonate c isotopic compositions 13ccarb the first and largest of the events that precipitated these pyritic horizons was coincident with the late permian mass extinction while subsequent events were generally smaller and occurred at quasiperiodic intervals of 20 to 30 ka a near complete lack of organic carbon to drive bacterial sulfate reduction in sediment pore waters among other considerations argues against a diagenetic control for these relationships rather the covariant patterns documented herein are most easily explained as the product of recurrent upwelling of anoxic deep ocean waters containing 34s depleted hydrogen sulfide and 13c depleted dissolved inorganic carbon the sulfide 34s record of the study section represents a mixture of a small amount of isotopically heavy authigenic pyrite formed via in situ bacterial sulfate reduction with a generally larger quantity of isotopically light syngenetic pyrite precipitated within the water column during upwelling episodes although upwelling of toxic deepwaters has been invoked in earlier studies as a mechanism for the late permian marine mass extinction this is the first study to 1 document patterns of pyrite 13ccarb covariation that strongly support upwelling as a major process at the ptb and 2 provide evidence of multiple quasiperiodic upwelling events that may reflect reinvigoration of global ocean overturn following a prolonged interval of late permian deep ocean stagnation

offshore and onshore seepage of thermogenic gas at katakolo bay western greece abstract considerable seepage of natural gas occurs throughout the katakolo bay both at sea and on land along the ionian coast of peloponnesus western greece explosive levels of ch4 and toxic concentrations of h2s accumulating in the ground pose a severe hazard for humans and tourist infrastructures a wide offshore and onshore gas survey including marine remote sensing underwater exploration by a towed instrumented system compositional and isotopic analyses and flux measurements of gas allowed us to assess that a gas seepage takes place along two main normal faults b offshore side scan sonographs recorded at least 823 gas bubble plumes over an area of 94 200 m2 at depths ranging from 5 5 to 16 m c offshore and onshore seeps release the same type of thermogenic gas 13cch4 34 to 36 d offshore gas showed increased stable carbon isotopic ratio of co2 and propane which suggests enhanced biodegradation of hydrocarbons e isotopic data combined with thermogenic gas generation modeling and maturity plots suggest that the gas is related to a deep petroleum system with jurassic carbonate reservoirs triassic source rocks and triassic evaporites f h2s 34s 2 4 is produced by thermochemical sulfate reduction in deep anhydrites in contact with hydrocarbon rich carbonates g due to the shallow depth more than 90 of ch4 released at the seabed enters the atmosphere consistent with theoretical bubble dissolution models with a mean plume output of 0 12 kg d 1 total offshore ch4 output was estimated in the range of 33 to 120 t y 1 and h in the onshore area at least 50 gas vents in the harbor and a large seep on the adjacent faros hill emit in total about 89 t ch4 y 1 katakolo results to be one of the biggest thermogenic gas seepage zones in europe

mass extinctions and sea level changes abstract review of sea level changes during the big five mass extinctions and several lesser extinction events reveals that the majority coincide with large eustatic inflexions the degree of certainty with which these eustatic oscillations are known varies considerably thus the late ordovician and end cretaceous extinctions are associated with unequivocal major regressions demonstrated from numerous widespread regions in contrast the multiple high frequency sea level changes reported for the frasnian famennian crisis based on the supposed depth preferences of conodont taxa have little support from sequence stratigraphic analyses which reveals the interval to be one of highstand the end permian mass extinction has long been related to a severe first order lowstand of sea level newell n d 1967 revolutions in the history of life geol soc am spec pap 89 63 91 based primarily on the widespread absence of latest permian ammonoid markers but field evidence reveals that the interval coincides with a major transgression newell s hypothesis that marine extinctions are related to shelf habitat loss during severe regression remains tenable for the end guadalupian and end triassic extinction events but not for other crises rapid high amplitude regressive transgressive couplets are the most frequently observed eustatic changes at times of mass extinction with the majority of extinctions occurring during the transgressive pulse when anoxic bottom waters often became extensive the ultimate cause of the sea level changes is generally unclear a glacioeustatic driving mechanism can only be convincingly demonstrated for the end ordovician and end devonian events at other times it is speculated that they may relate to the widespread regional doming and subsequent collapse caused by the impingement of superplumes and ultimate eruption on the base of the lithosphere

triassic continental subduction in central tibet and mediterranean style closure of the paleo tethys ocean the qiangtang metamorphic belt qmb in central tibet is one of the largest and most recently documented high pressure hp to near ultrahigh pressure near uhp belts on earth lu hf ages of eclogite and blueschist facies rocks within the qmb are 244 223 ma indistinguishable from the age of uhp metamorphism in the qinling dabie orogen results of a u pb detrital zircon study suggest that protoliths of the qmb include upper paleozoic qiangtang continental margin strata and sandstones that were derived from a paleozoic arc terrane that developed within the paleo tethys ocean to the north we attribute qmb hp metamorphism to continental collision between the qiangtang terrane and a paleo tethys arc terrane this collision and the coeval south china north china collision may have slowed convergence between laurasia and gondwana derived terranes and initiated mediterranean style rollback and backarc basin development within much of the remnant paleo tethys ocean realm

the late triassic rift related volcanic rocks from eastern qiangtang northern tibet china age and tectonic implications abstract the late triassic nadi kangri volcanic rocks with nearly ew trending outcrops within the qiangtang basin northern xizang tibet china are composed mainly of acid tuff dacite rhyolite and minor basic volcanic rocks there exists a significant depositional hiatus between the nadi kangri volcanic rocks and underlying strata therefore the nadi kangri volcanic rocks represent a new evolution history of the mesozoic qiangtang basin the magma emplacement age of the nadi kangri volcanic rocks in the geladaindong area is 220 4 2 3 ma representing the onset of the mesozoic qiangtang basin the nadi kangri basalts have high nb zr 0 049 0 058 ta hf 0 12 0 15 and zr y 4 95 6 01 ratios in the tectonic discrimination diagrams such as zr vs zr y and th hf vs ta hf the nadi kangri basaltic rocks mostly plot in the within plate setting field the geological background and the geochemical characteristics suggest that the nadi kangri volcanic rocks were formed in a continental rift setting

neotectonic evolution of northwestern continental greece the post miocene sedimentary and structural evolution of nw continental greece changes from west to east

carbon sulfur oxygen and strontium isotope records organic geochemistry and biostratigraphy across the permian triassic boundary in abadeh iran pelagic deposits at abadeh represent a complete biostratigraphic record across the permian triassic boundary ptb the presumed water depth during deposition of these sediments was between 60 and 90 m similar to other permian triassic boundary sections the succession at abadeh is characterised by a negative carbon isotope shift of approximately 4 the values start to decrease in the lower c changxingensis c deflecta s l zone reach 0 12 v pdb in the uppermost permian just below the ptb remain low to the early i isarcica zone 0 32 and increase subsequently in the upper i isarcica zone for the time interval of the ptb negative carbon isotope excursion between the c iranica and the i isarcica zones no correlation exists between the 13ccarb and the 18ocarb the above observations argue against the conclusion of heydari et al 2001 that the carbon isotope event at the p t transition is an alteration artefact and not a global signal the decrease in 13ccarb is accompanied by a 5 and potentially up to 10 increase in 34ssss together these features are thought to reflect a complex global event notably the development of widespread anoxic oceans with anoxic bottom layers rising onto the shelves for the carbon isotope drop other factors such as the collapse of ocean primary productivity may also have played a role the 87sr 86sr ratios of dzhulfian seawater show only a minor increase from 0 70705 to 0 70710 reaching 0 70720 in the dorashamian the increase becomes steeper in the early triassic reaching 0 70754 in the n dieneri zone the rise of the strontium isotope values is thought to be related to enhanced continental weathering under humid climatic conditions in the uppermost permian c meishanensis h praeparvus zone and the lack of a dense land vegetation in the early triassic prior to the spathian upper olenekian

martian north polar hazes and surface ice results from the viking survey completion mission viking infrared observations of the martian north polar regions taken during the 1979 1980 viking survey completion mission have been used to determine the location and nature of the retreating polar cap edge and of an accompanying atmospheric ice haze the haze is composed of water ice and its visible opacity is approximately unity equivalent to 1 2 precipitable microns of water ice during the polar cap retreat aerocentric longitude ls 340 60 the haze is nearly always present and extends from at most a few degrees south of the polar cap edge to an undetermined distance over the cap interior the transition from ice free ground to a predominantly ice covered surface at the cap edge spans 5 10 of latitude the ability of the viking infrared observations to distinguish haze from surface condensate yields a more accurate seasonal regression for the polar cap than can be determined from visual images generally the infrared observations presented here yield a regression similar to those determined from earth based and or spacecraft visual data for the same and for previous northern springs however there are differences concerning details of the cap retreat the thermal data indicate that the martian seasonal polar cap did extend south of 60 n during this particular late winter and that the midspring resumption of the cap retreat occurs at ls 50

geophysical evidence for gas geohazards off iskenderun bay se turkey abstract high resolution seafloor and sub surface data were acquired as part of a site survey in iskenderun bay se turkey to characterize the geohazards at the location of the proposed drilling site a 3 km 3 km geophysical study reveals a pockmark field which trends ne and nne similar to the trend of major fault systems in the area the pockmarks with an average diameter of 35 m reach their highest density in the northern part of the detailed survey area with 13 features km2 acoustic anomalies in the seismic records acoustic turbidity blanking enhanced reflectors below the proposed drilling site indicated potential shallow gas beneath it the local seismic anomalies amplitude and frequency parallel to stratigraphy were assigned a low gas risk as a result of the active neotectonics in the area the pockmark field presented a potential hazard for drilling at the original location the geohazard study resulted in moving the proposed drilling site eastward to an area of fewer pockmarks less sub surface seismic anomalies and thus a location interpreted as a lower geohazard environment

rapid and synchronous collapse of marine and terrestrial ecosystems during the end permian biotic crisis a newly studied permian triassic p tr boundary section in jameson land east greenland contains an abundant and well preserved marine fauna as well as terrestrial palynomorphs for the first time it is possible to compare the biotic crises of the marine and terrestrial realms using the same samples from the same section the sediments record a negative excursion in 13 c carb values of 8 9 and in 13 c org values of 10 11 the presence of the conodont hindeodus parvus combined with the 13 c carb record enables correlation with the proposed global stratotype section at meishan this shows that the greenland section is the most expanded p tr section known collapse of the marine and terrestrial ecosystems took between 10 and 60 k y it took a further few hundred thousand years for the final disappearance of permian floral elements collapse of the terrestrial and marine ecosystems began at the same stratigraphic level and preceded the sharp negative excursion in the 13 c record

methane and hydrogen sulfide seepage in the northwest peloponnesus petroliferous basin greece origin and geohazard gas seepages along the ionian coast of the northwestern peloponnesus greece at killini katakolo and kaiafas reflect deep hydrocarbon generation processes and represent a real hazard for humans and buildings methane microseepage gas concentration in offshore and onshore vents and gas dissolved in water springs including the isotopic analysis of methane have shown that the seeps are caused by thermogenic methane that had accumulated in mesozoic limestone and had migrated upward through faults or zones of weakness induced by salt diapirism a link between local seismicity and salt tectonics is suggested by the analyses of hypocenter distribution methane acts as a carrier gas for hydrogen sulfide produced by thermal sulfate reduction and or thermal decomposition of sulfur compounds in kerogen or oil methane seeps in potentially explosive amounts and hydrogen sulfide is over the levels necessary to induce toxicological diseases and lethal effects

the wuchiapingian changhsingian boundary upper permian at meishan of changxing county south china abstract section d at meishan changxing county in the zhejiang province china has been extensively studied in various aspects of the stratigraphy during the past 20 years it was ratified by the international union of geological sciences iugs as the global standard stratotype section and point gssp for the permian triassic boundary in 2000 and is also a potential stratotype for the wuchiapingian changhsingian boundary however the contact relationship between the longtan wuchiapingian and changxing chainghsingian formations has been a controversial subject for years recent studies on section c about 300 m west of section d at meishan confirm a complete depositional succession around the boundary and suggest that the proposed boundary level the fad of clarkina wangi within the lineage from c longicuspidata to c wangi is consistent with the first appearance of the index changhsingian fusulinid palaeofusulina sinensis and tapashanitid ammonoids

evolution of oceanic redox conditions during the permo triassic transition evidence from deepwater radiolarian facies abstract the 90 biodiversity loss among marine invertebrate species during the end permian mass extinction the most severe phanerozoic biocrisis has been attributed to widespread oceanic anoxia superanoxia recent studies of the lithofacies inorganic geochemistry and biomarkers of permian triassic boundary ptb sections have yielded an inferred pattern of oceanic redox changes that is complex and sometimes inconsistent in this contribution we review the ecology of radiolarians an important microzooplankton group during the permo triassic transition and consider its implications for contemporaneous changes in paleoceanographic conditions our analysis shows that 1 late permian radiolarian faunas were cosmopolitan with different orders having specific depth preferences i e albaillellarians favoring deeper waters and spherical forms entactinarians and spumellarians shallower waters 2 deep water taxa declined earlier than shallow water taxa 3 many paleozoic type taxa survived into the early triassic but went extinct during a second crisis in the dienerian dead clade walking followed by the appearance or expansion of mesozoic type taxa during the olenekian and 4 the survival of paleozoic type taxa during the early triassic was greater at higher paleolatitudes than in the tropics these observations are consistent with a first order redox control on radiolarian faunal distributions specifically a shallowing and poleward expansion of the oceanic oxygen minimum zone during the ptb crisis the consequent adaptation of some deepwater taxa to shallower environments resulted in early triassic radiolarian faunas in continental basins becoming more similar to those in pelagic settings enhanced survival of paleozoic type taxa in high latitude regions indicates that the main stressor on permo triassic radiolarian communities was reduced oceanic oxygen levels stronger in the tropics rather than climatic warming stronger at the poles

tracking mid to late holocene depositional environments by applying sedimentological palaeontological and geochemical proxies amvrakikos coastal lagoon sediments western greece mediterranean sea abstract this study presents sedimentological palaeontological geochemical mineralogical and organic petrography data from a 30 m deep core representing a mid to late holocene lagoonal depositional environment of a coastal area of amvrakikos gulf western greece three horizons were dated using 14c the sedimentological palaeontological and geochemical interpretations of the lagoonal sediments reveal three major lithological units deposited between around 5200 and 1600 bp the upper lithological unit extended to a depth of 11 20 m the middle from 11 20 to 21 30 m and the lower one from 21 30 to 30 00 m a mean rate of sedimentation of 5 7 mm y and a maximum rate of 12 6 mm y were estimated the mineralogical analysis and the magnetic susceptibility of the core points to a constant sediment source supply the mid to late holocene depositional environment mainly reflects inundation by the braid plain of the arachthos and secondarily by the louros river the reconstruction of the depositional environments corresponds to a shallow marine and deltaic brackish lagoon and specifically to an environment proximal to river supply the high rates of sedimentation as well as the interpretation of depositional environments indicate that the coastal sedimentological processes during the mid to late holocene were mainly controlled by the progradation of river deltas moreover the geochemical proxies the recovered molluscs and the microfauna as well as the organic petrography analyses indicate periods of dysoxic and hypoxic conditions these holocene dysoxic and hypoxic events indicate that the recent dystrophic crises in the amvrakikos gulf are not only the result of human activities but also the contribution of natural processes

climatic and biotic upheavals following the end permian mass extinction the recovery from the end permian mass extinction was slow and prolonged a temperature reconstruction shows that further biotic crises during the recovery were associated with extreme warmth

late quaternary evolution of the gulf of patras greece tectonism deltaic sedimentation and sea level change abstract the gulf of patras is an actively subsiding late cenozoic graben in western greece that receives deltaic sediment from the large acheloos and evinos rivers the late quaternary sedimentation history of the gulf is interpreted from 3 5 khz profiles numerous short cores and airgun seismic profiles a widespread unconformity represents the isotopic stage 2 marine lowstand when the gulf was subaerially exposed subsequent deltaic progradation and associated coastal transgression was greatest during the 13 10 5 ka slowdown in sea level rise and the period of stable sea level since the mid holocene switching of delta distributaries can be related to the known evolution of the subaerial parts of the deltas the stage 2 unconformity provides a datum for quantitative determination of rates of subsidence the central graben is subsiding at rates of 3 5 mm yr rates in the northern part of the gulf average 1 2 mm yr this is consistent with a listric faulting model for the origin of the modern patras graben

initiation of gas hydrate pockmark in deep water nigeria geo mechanical analysis and modelling abstract a review of recent literature shows that two geomorphologically different types of pockmarks contribute to gas seepage at the seafloor type 1 pockmarks are defined as seafloor craters associated to fluid seepage and are the most classical type referred to as pockmarks in the literature in contrast type 2 pockmarks reveal a complex seafloor morphology that may result from the formation decomposition of gas hydrates in underlying sedimentary layers interpretation of very high resolution seismic data sedimentological analyses and geotechnical measurements acquired from the eastern niger submarine delta reveal that type 2 pockmarks are associated to the presence at depth of a conical body of massive gas hydrates based on acquired data theoretical analysis and numerical modelling it was possible to propose a novel geo mechanical mechanism controlling the irregular seafloor deformations associated to type 2 pockmark and to show that pockmark shapes and sizes are directly linked to the initial growth and distribution of sub seafloor gas hydrates the study illustrates the role of gas hydrates formation in the fracturation deformation of the subsurface sediment and the formation of type 2 pockmarks

stable isotopes of carbon from basaltic rocks and their possible relation to atmospheric isotope excursions abstract repeated short time negative excursions from the general trend of organic carbon isotopes occur at and shortly after the permo triassic and cretaceous tertiary mass extinctions the cause of these excursions is unexplained since an extinction event can only explain one excursion at each boundary at the p t boundary one negative excursion occurs shortly before the boundary proper followed by one at the boundary followed by several excursions that can be correlated in both marine and terrestrial environments over larger geographical distances also at the k t boundary negative excursions in organic carbon which can be correlated occur after the boundary in both marine and terrestrial settings as both mass extinctions occurred contemporaneously with major continental flood basalts the present study focuses on the possible effect of eruption of flood basalts on the atmospheric carbon isotopic budget the carbon isotopic compositions of forty different basalts from the time span of albian to the recent and predominantly continental flood were measured the isotopic composition of the co2 gas released by basalts is generally accepted as being rather heavy 5 pdb based on observations from hawaii this is in strong contrast to the observed values in this study which showed that the gas released had an average isotopic value of around 23 pdb acid digestion by hf left a residue of elemental carbon with isotopic values in the range of 24 to almost 28 pdb this corresponds to the carbon released during stepped heating experiments in the temperature range from 200 to 600 c since basalt in a molten state has a temperature of 600 c and since the most negative carbon i e the elemental carbon is released below that temperature it suggests that the most isotopically negative component is not present as elemental carbon above temperatures of 600 c in view of the recorded isotopic composition of 24 for gas collected at a temperature between 700 and 800 c from mauna loa it seems that the generally assumed 5 is unrepresentative for flood basalts it is therefore possible that high intensity volcanic episodes have caused the repeated negative excursions it is further suggested that the short time non secular isotopic variation pattern of organic carbon through time may be a record of volcanic activity the episodic nature of volcanism precludes it from being causally related to the secular variations elemental carbon from four different kimberlites yielded carbon isotopic values similar to those from basalts it is suggested that the boudouard reaction 2co c co2 may be responsible for the formation of the elemental carbon

martian north polar cap 1996 1997 abstract in order to investigate the interannual variability of the regression of the martian north polar cap the regression of the martian north polar cap during the 1996 1997 apparition is examined utilizing measurements with ccd images the regression of the north polar cap in 1996 1997 as determined from our measurements is in excellent agreement with concurrent observations using the hubble space telescope the regression of the north polar cap in 1996 1997 seems to be a little faster than the mean regression or the regression in 1979 1980 after l s 51 but seems to be similar to those in 1946 1948 1950 1972 1977 1978 and 1994 1995

two episodes of environmental change at the permian triassic boundary of the gssp section meishan abstract high resolution stratigraphic records through the permian triassic boundary ptb interval of the global stratotype section and point gssp at meishan zhejiang province china reveal that the ptb crisis was not a single abrupt catastrophe a bed by bed analysis of environmental and biotic changes makes clear that the crisis can be resolved into two discrete episodes each consisting of three stages a unstably oscillating conditions b peak crisis conditions and c ameliorating conditions the first crisis episode commenced in bed 23 peaked in beds 24e 26 and ameliorated in beds 27 and 28 while the second crisis episode commenced in bed 29 peaked in beds 34 38 and ameliorated in beds 39 and higher the macroscopic mass extinctions happened not at the beginning nor the end of each cycle but at times when the crisis or perturbation of environments began these extinction events do not show detectable feedbacks to concurrent environmental changes in each episode cyanobacteria proliferation postdated the macroscopic extinction while proliferation of green sulfur bacteria predated the environmental crisis causational analysis between environmental and microbial changes show that geomicrobial functional groups exercised pronounced effects on the marine c n s cycles and ocean redox conditions during the ptb crisis it is possible thus that the microbial crises played an important role in strengthening or evening triggering the environmental crisis

seasonal recession of mars south polar cap in 1986 photographs of mars obtained during the 1986 opposition of the planet have been used to derive the regression curve for the south polar cap between ls 190 and ls 255 the 1986 regression appears to have been unexceptional until after ls 230 when it becomes retarded relative to the normal established by the 1971 and 1977 regressions a study of the data as a function of the filter used suggests that circumpolar clouds were present in early spring unlike the case in the 1977 recession

the end permian regression in south china and its implication on mass extinction abstract records of more than 20 permian triassic boundary ptb sections from south china show that widespread end permian regression took place in whole south china timing of the low ebb of this regression was pinpointed to the clarkina meishanensis and hindeodus changxingensis zones biostratigraphic and paleogeographic studies at conodont zonation level reveal that the yangtze carbonate platform and isolated small carbonate platforms in the hunan guizhou guangxi hgg basin experienced sedimentary hiatus during these two zones which lasted about 50 100 kya meanwhile the basinal areas namely the northern marginal basin of yangtze platform and the hunan guizhou guangxi basin have continuous conodont zonation with silicious and ashbed deposits the basinal areas show two negative 13c shifts during the ptb interval from clarkina yini zone to isarcicella isarcica zone while on the platforms there is usually only one negative shift because the early shift at c meishanensis zone was lost during hiatus the end permian regression and successive rapid transgression taking place at the ptb casted important effects to the pattern and process of the ptb mass extinction the depositional hiatus hitherto underestimated will necessitate reassessment of some interpretations on the causes and results of that extinction

latest permian to early triassic basin to shelf anoxia in the sverdrup basin arctic canada a combined sequence stratigraphic and geochemical study of the latest permian extinction event in nw pangea provides new insight into the onset and extension of basin anoxia onto the adjacent shallow shelf the latest permian transgression in the sverdrup basin of arctic canada initiated prior to onset of deep water anoxia and continued past the latest permian extinction event deep water anoxia initiated after the shelf was flooded in mid to late changhsingian time requiring a much more rapid and much greater vertical rise in the chemocline than that associated with relative sea level supporting the chemocline upward excursion model our work also extends evidence of global euxinc conditions to nw pangea euxinic conditions developed just prior to the main extinction event and we suggest that this was associated with a significant pyrite rain out event which stripped bio essential nutrients from anoxic seawater prior to the main disruption of the global carbon cycle as recorded by shifts in the carbon isotope record

catastrophic soil erosion during the end permian biotic crisis organic geochemical analyses of sedimentary organic matter from a marine permian triassic transition sequence in northeastern italy reveal a significant influx of land derived diagenetic products of polysaccharides this unique event reflects massive soil erosion resulting from destruction of land vegetation due to volcanogenic disturbance of atmospheric chemistry the excessive supply of soil materials to the oceans provides a direct link between terrestrial and marine ecological crises suggesting that ecosystem collapse on land could have contributed to the end permian marine extinctions

gas induced erosion features in the north sea pockmarks are prominent features on the seafloor at two main regions of the north sea the south fladen area and the norwegian trench the pockmarks vary in size from 5 m across to about 150 m and in depth from 1 m to about 20 m some of the features consist of several very small unit pockmarks these are probably gas induced erosion features and found only in soft finegrained marine and glaciomarine sediments they are probably caused by shallow or deep seated gas or fluid release through the seabed whereby the finest particles are thrown into suspension and redistributed by nearbottom currents on the north sea plateau a small pockmarked area has recently been found a close relationship exists here between mobile gas in the upper sediments faulting in the soft sediments and the morphology of the seabed other morphological features in the north sea such as coast parallel depressions and elongated depressions or terraces are also interpreted here as gas induced erosion products this applies yet again to the mottled seabed features which appear as patches of high reflectivity on side scan sonar records from the north sea plateau they correspond to shallow seabed depressions on the deep towed boomer records judging from reported observations from several shallow seas world wide volatile transport through the seabed is probably quite common and several morphological features are undoubtably induced by this process several erosion features of similar origin are probably common also in deep ocean basins

recent gravitative mass movements in a highly tectonically active arc system the hellenic arc abstract the hellenic arc system is located within one of the world s most seismically active areas and has experienced extreme tectonism throughout tertiary and quaternary times this paper discusses the various types of gravitative mass movements that have been detected and examines their causative factors in environments of high tectonic and seismic activity the areas surveyed are the sporadhes and corinth grabens in the back arc basin the zante cephalonia shelf on the inner slope of the hellenic trench and the kythera ridge in the outer island arc the various types of gravitative mass movements that have been documented include i sliding of large masses with no or only slight internal deformation ii sliding of masses with disintegration of the sediment fabric to debris flows and iii slow downslope creep the mass movements are associated with fault escarpments delta fronts and well stratified slopes with slope gradients ranging from 2 to 40 earthquakes seem to be the main mechanism initiating mass movement but other mechanisms such as increasing topographic gradient gas in the sediment pores and heavy rain can also independently trigger and or contribute to the initiation of mass movements

the permian triassic boundary at nhi tao vietnam evidence for recurrent influx of sulfidic watermasses to a shallow marine carbonate platform the permian triassic boundary at nhi tao cao bang province vietnam was sampled in a 7 5 m thick outcrop section at high resolution 5 cm intervals for chemostratigraphic and magnetic susceptibility analysis the section consists entirely of slightly argillaceous limestone representing shallow marine facies of the jinxi platform one of several large carbonate platforms within the nanpanjiang basin located on the southern margin of the south china craton upper permian strata beds 1 7 are mainly dark gray cherty fossiliferous wackestones and packstones containing a diverse open marine fauna whereas uppermost permian and lower triassic strata beds 9 and higher are medium gray calcimicrobial framestones containing rare macrofossils these facies are separated by a 12 cm thick oolitic pisolitic grainstone bed 8 that coincides with the disappearance of most late permian faunal elements as well as with the first appearance of various geochemical anomalies that continue into the lower triassic part of the section this late permian event horizon is characterized by 1 an abrupt decline in total organic carbon to near zero values 2 the onset of a sustained decline in carbonate 13c and 3 the first of eight concentration peaks in pyrite sulfur significantly each sulfide peak is associated with lower pyrite 34s values as well as with the onset of a negative carbonate 13c excursion or the acceleration of an excursion already in progress these chemostratigraphic relationships are consistent with multiple episodes of upwelling of sulfidic 34s and 13c depleted deep ocean waters onto the jinxi platform the first upwelling event was the most intense and caused a drastic reduction in primary productivity and the demise of the late permian fauna subsequent episodes were less intense but may have contributed to a delay in recovery of early triassic marine ecosystems a ten fold increase in magnetic susceptibility in bed 9 may record the influx of fine detrital particles following destruction of terrestrial ecosystems and massive soil erosion the terrestrial signal of the end permian catastrophe thus follows the marine signal with a 12 cm lag which may reflect the time of transit of soil derived particles across the nanpanjiang basin suggesting that the marine and terrestrial crises in the nhi tao region occurred more or less synchronously these observations suggest a model in which renewal of global ocean overturn followed a prolonged interval of deep ocean stagnation during the late permian with upwelling intensity modulated by short term 20 kyr climate cyclicity

evidence for shallow hydrocarbons offshore northern santa cruz county california geologic notes analyses of high resolution seismic reflection profiles and hydrocarbon samples indicate that natural hydrocarbon seepage is occurring along the san gregorio and monterey bay fault zones offshore northern santa cruz county california a variety of anomalous seismic reflection features such as water column anomalies subsurface amplitude anomalies bright spots and seismic smears wipeouts has been observed and mapped more than 100 water column anomalies probable gas seeps occur in the study area of approximately 270 mi2 700 km2 many of these seismic anomalies are associated with subsurface geologic structures which suggests hydrocarbon migration from depth samples of natural gas collected from a shallow coastal water well contain 74 to 91 methane 7 to 23 nitrogen 2 carbon dioxide and 1 ethane the methane appears to be thermogenic in origin having dgr13c values of 29 51 to 32 55 pmil pdb rock dredges from 2 300 ft 700 m of water in ascension submarine canyon have also recovered oil saturated sandstones further suggesting the seepage of hydrocarbons we interpret the shallow occurrence of most of these hydrocarbons to be the result of migration from depth along active faults within the san gregorio and monterey bay fault zones

ostracods crustacea through permian triassic events abstract through geological times the main turnover of marine ostracod group occurred at the permian triassic boundary ptb when the palaeozoic world gave way to meso cenozoic world as quite all the groups ostracods intensively suffered of the end palaeozoic events but they have the particularity to pass the ptb and to be present in quite all marine environments we have studied the ostracod assemblages from the best preserved marine permian triassic sections through the world these sections are for most of them located along the palaeo tethys margins south china block and tibet r p china bukk mountains hungary dolomites italy taurus mountains turkey and elbourz mountains iran these areas present different environmental settings from very shallow water to deep shelf the biostratigraphy is well constrained by the presence of conodont index in deep environment from external shelf to slope all the permian ostracods disappear slightly before the ptb and are absent from the early triassic the last representatives of palaeopsychrospheric forms occur in the early anisian on the platforms during the late permian the ostracods are abundant and highly diversified everywhere along peri tethyan margins the typical palaeozoic forms are mixed with the very first meso cenozoic representatives the specific extinction rates in the latest permian vary from 74 to 100 during the earliest triassic two different settings have to be considered with or without microbialitic deposits the development of microbialites gives favorable ecological conditions to ostracods during the griesbachian the fauna is composed of both new comers and surviving palaeozoic forms the reduction of size is frequently observed this interval is called survival stage during the dienerian and the smithian the fauna are very scarce and poor these two substages represent the maximum of poverty for the ostracod fauna may be due to the development of anoxia on the platforms during the spathian occurs the beginning of the true recovery the very last palaeozoic representatives are found in the earliest anisian which is the radiation stage of ostracod fauna with typical new comers the interval of palaeozoic meso cenozoic ostracod turnover is quite long about 15 my

martian south polar cap boundary 1971 and 1973 data abstract international planetary patrol photographs of mars obtained during the 1971 and 1973 apparitions have been used to produce regression curves for the martian south polar cap for those years useful data span the range in areocentric longitude l s 186 261 in 1971 and l s 255 301 in 1973 these regression curves are compared to the 1977 regression curve obtained from viking observations and to the results of 1956 observations there is remarkable consistency between the 1971 ipp and 1977 viking data points and the 1973 regression does not appear to have differed significantly from those of 1971 or 1977

seafloor gas seeps triggered by a northern california earthquake abstract a series of marine surveys using high resolution seismic reflection and side scan sonar profiling was conducted on the klamath river delta from 1977 to 1985 in november 1980 near the middle of this 8 year time period a major earthquake magnitude 7 occurred in the area the earthquake caused liquefaction of shelf deposits off the klamath river and while mapping the sediment failures we observed an inordinate number of gas vents and acoustic anomalies in the sediment gas charging and water column gas clouds our analyses indicate that a change in gas seepage occurred after the earthquake there was a marked increase in gas abundance immediately after the earthquake a gradual decrease over the next year and stabilization at pre earthquake gas levels within five years or less the acoustic anomalies were observed in pre quaternary rocks as well as in surficial holocene deposits and gas seeps overlay truncated anticlines faults and syncline exposures thus the gas released may have been in part thermogenic in origin a large area 20 km 2 on the delta failed during the earthquake and the abundance of gas seeps and craters in the area suggests that sediment degassing may have been an important process contributing to failure

telescopic observations of mars 1996 1997 results of the marswatch program abstract during the 1996 1997 apparition of mars marswatch and the international mars patrol imp of the mars section of the association of lunar and planetary observers alpo received 2750 observations from 70 observers in 14 countries approximately 40 of these observations are ccd images many of which were obtained through filters covering a spectral range from 330 to 820 nm in addition a large number of high quality visual observations were performed through standard color filters permitting more accurate assessments of surface and atmospheric phenomena the apparition coverage extended through 249 11 to 260 of areocentric longitude l s permitting monitoring of the northern hemisphere spring summer autumn meterological activity north polar cap npc behavior and albedo feature alterations there were few significant changes in albedo feature morphology during the 1996 1997 apparition the north polar cap rift the rima tenuis which had been observed and imaged during each aphelic apparition since 1980 was not observed perhaps due to a slowing in the npc regression after 80 l s the incidence of discrete clouds orographic and localized was higher than that predicted on the basis of the alpo imp s martian meteorology study that spanned 14 previous apparitions from 1964 to 1993 discrete clouds were more numerous than in 1993 or 1995 peaking in late northern spring 30 l s earlier than predicted the syrtis blue cloud was extensively observed and imaged between 66 and 115 l s the rate of occurrence of limb clouds was significantly lower than predicted for a given subseason their peak incidence occurred after aphelion but their frequency decreased rapidly after 105 l s nearly two martian seasons earlier than observed during previous apparitions limb hazes bright in blue and ultraviolet light were more numerous and conspicuous throughout the northern summer as predicted from the meteorology study arctic clouds increased in number around aphelion and were often large and bright during early northern summer a variable north polar hood was observed after 160 l s we find clear evidence for the existence of extensive equatorial cloud bands which became numerous between 50 and 120 l s peaking in early northern summer 105 l s and often merging into bright limb clouds these bands were more frequent and prominent in 1996 1997 than during the 1993 or 1995 apparitions and were extensively imaged in blue and ultraviolet light by both groundbased observers and by the hst

high resolution shallow seismic identification of gas escape features in the sediments of loch tay scotland tectonic and microbiological associations high resolution seismic reflection profiles 3 5 khz have revealed the presence of extensive interstitial gas accumulation within the sedimentary sequences of loch tay scotland as identified by acoustic turbidity masking the seismic stratigraphy within the central section of the loch in the deepest water area directly above the zone of the seismically active loch tay fault focused flows of gas through the sediment pile to the loch bed via chimneys and pockmarks together with gas seeps within the water column have been identified microbiological observations indicate that the gas is biogenic ch4 produced by both chemoautotrophic which use co2 as a source of carbon and h2 as a source of energy and aceticlastic species which use acetate as a source of carbon and energy of methanogens in the fine grained organic rich deposits that have been focused into the zone of accumulation in the deep central part of the loch the spatial distribution of the gas escape features suggests that earthquake movements along the loch tay fault are responsible for facilitating focused gas escape in this part of the loch by the creation of new pathways and conduits through the sediment pile along which gas can migrate upwards and exit into the water column relict pockmarks and associated chimneys identified in the seismic records indicate that gas escape has been taking place since pleistocene times though the precise timings cannot be ascertained this is the first time that such features have been reported from a lake in the uk

major perturbation of ocean chemistry and a strangelove ocean after the end permian mass extinction the severe mass extinction of marine and terrestrial organisms at the end of the permian period c 251 ma was accompanied by a rapid 1 ma decrease in sedimentary burial of organic carbon in the early triassic

characteristics of claystones across the terrestrial permian triassic boundary evidence from the chahe section western guizhou south china abstract x ray diffraction xrd scanning electronic microscopy sem and x ray fluorescence spectroscopy xfs studies were undertaken for claystones and or mudstones from the chahe section a terrestrial permian triassic boundary tptb section our results indicate that the compositions of claystones in the permian triassic boundary ptb interval beds 66f 68 outlined by biostratigraphy are different from claystones and or mudstones found either below or above the interval of the same section the clay minerals in the claystones of the ptb interval are mainly composed of illite montmorillonite interlayers with a few montmorillonites and chlorites the other claystones and or mudstones underlying and overlying the ptb consist of chlorites and or kaolinites some authigenic clastic minerals such as hexagonal dipyramid quartz and zircons are only found in claystones in the ptb interval from the chahe section and some marine ptb sections in western guizhou and eastern yunnan southwestern china in addition some elements are present in abnormal concentrations in the claystones of the ptb interval as well most important is that we found no spherules in all the claystones studied indicating no evidence of an extraterrestrial impact during the permian triassic transition the particular characteristics of the tptb claystones at the chahe section indicate their volcanic origin and thus provide a reliable auxiliary event marker for high resolution demarcation of the tptb in south china they are also indicative in the marine ptb claystones in south china thus the ptb claystones can be used as auxiliary markers for high resolution correlation of the ptb from marine facies to land in south china when direct fossil evidence in the ptb sequence is lacking

the impacts of sea level changes during latest pleistocene and holocene times on the morphology of the ionian and aegean seas se alpine europe abstract the tentative coastline configuration in the ionian and aegean seas in three late pleistocene holocene time slices is given based on the global eustatic sea level curve in combination with local geological and geoarcheological data at lowstand stage 2 21 500 cal yr bp years before present sea level 120 m extensive shelves existed in the northern aegean sea and to a second degree in the eastern aegean sea and in the northern and central parts of the ionian sea many islands were connected with each other and with the mainland a great part of the periphery of gulfs that have an entrance less than 120 m deep was subaerially exposed while in their central parts lakes were formed at 11 500 cal yr bp sea level 60 m the exposed shelf was much restricted most of the gulfs were overflowed by the advancing sea and only a few islands were still connected with the mainland finally at 8000 cal yr bp and onward the sea initially intruded the lowlands and the gulfs but the subsequent sediment input by the rivers regressed the sea to its present position thus many human settlements and old cities that were maritime during hellenistic or older times are now a few to tens of kilometers inland

biogeochemical evidence for euxinic oceans and ecological disturbance presaging the end permian mass extinction event article i nfo the permian triassic boundary event at 252 2 ma marks the largest extinction of marine fauna in the phanerozoic and there is a wide consensus that the extinction coincided with an intense oceanic anoxic event thestratotypeofthechanghsingianstage preciselyconstrainedbytheptbglobalstratotypesectionandpoint gssp and the gssp for the wuchiapingian changhsingian boundary both at meishan in southern china is well documented in respect to geochronology and the pattern of extinction here we report secular trends in bulk isotopic parameters and lipid biomarkers in a core spanning 214 m of stratigraphic section across the ptb and through the entire changhsingian interval our analysis of these data viewed in the context of relative sea level change and strontium isotopes reveals distinct shifts in paleoenvironmental conditions and profound changes in plankton ecology well before and following the biological extinction event specifically patterns of steroids and triterpenoids indicate a marine plankton community that was heavily dominated by bacteria during the late wuchiapingian middle changhsingian and early griesbachian stages secular trends in aromatic hydrocarbons diagnostic for anoxygenic green sulphur bacteria chlorobiaceae identify periods when euxinic conditions extended into the photic zone during the entire changhsingian stage here also the 15

onset of biotic and environmental recovery from the end permian mass extinction within 1 2 million years a case study of the lower triassic of the meishan section south china abstract paleontological sedimentary and geochemical data obtained from the lower triassic strata of the meishan section south china suggest that onset of biotic recovery coincided with amelioration of paleoceanographic conditions and an increase in ocean productivity the griesbachian meishanorhynchia association from meishan indicates biotic recovery between the recovery stages 1 and 2 both the initial biotic recovery and palaeoceanic environmental amelioration occurred within 1 2 myr after the end permian mass extinction in the late griesbachian

sedimentary evolution of the continental early middle triassic canizar formation central spain implications for life recovery after the permian triassic crisis the permian triassic transition p t was marked by important geochemical perturbations and the largest known life crisis consequences of this event as oxygen depleted conditions and the unusual behavior of the carbon cycle were prolonged during the early triassic interval delaying the recovery of life in both terrestrial and marine ecosystems studies on lower triassic sediments of continental origin as in the case of western europe are especially problematic due to the scarcity of fossils and absence of precise dating the canizar fm is an early middle triassic unit of continental origin of the se iberian ranges e spain a detailed sedimentary study of this unit allows a shedding of light on some unresolved problems of the continental deposits of this age the top of this unit is dated as early anisian by means of a pollen association while the age of its base is here estimated as late smithian or smithian spathian transition different facies associations and architectural elements have been defined in this unit in the western and central parts of the basin this unit shows sedimentary characteristics of fluvial deposits with locally intercalated aeolian sediments while in the eastern part there is an alternation of both aeolian and fluvial deposits sedimentary structures also indicate changes in the climate conditions mainly from arid to semiarid two marked arid periods when well preserved aeolian sediments developed during early middle spathian and spathian anisian transition they alternated with two semiarid but more humid periods during the late spathian and early anisian these conditions basically correspond with the general arid and very arid conditions described for central western european plate during the same period of time the ateca montalban high in the northern border of the study basin must have represented an important topographic barrier in the western tethys separating aeolian dominated areas to the n and ne from fluvial dominated areas to the south the canizar fm has been subdivided into six members a f separated by seven 1 7 major bounding surfaces mbs these surfaces are well recognized laterally over hundred of km and they represent 104 105 my mbs 5 is considered to be of late spathian age and it is a clear indication of tectonic activity represented by a mild unconformity this event represents a change in the sedimentary characteristics reactivation of the unit and from here to the top of the unit are found the first signals of biotic recovery represented by tetrapod footprints plants roots and bioturbation all of these characteristics and the estimated age represented by the mbs 5 event permit this surface to be related to the coeval hardegsen unconformity of central western europe these first signals of biotic recovery can thus be related to an increased oxygen supply due to the new created paleogeographical corridors in the context of this tectonic activity these biotic signals occurred 5 my after the permian triassic limit crisis a similar delay as occurred in other coeval and neighboring basins

a high resolution approach in the recent sedimentation processes at the head of zakynthos canyon western greece the recent sedimentation processes at the head of zakynthos canyon in western greece have been re examined using a dense grid of high resolution seismic reflection profiles and sediment cores the current survey has revealed three new sediment sources that contribute considerably to the filling of the canyon floor that were not detected in previous surveys these sediment sources are a a string of five large pockmarks and b a large slide both along the north killini shelf and c a canyon arcoudi canyon dissecting the central killini shelf slope furthermore the erosional depositional area which was found to lie at the centre of the canyon floor extends downslope and seems to be actively receiving material mainly from the killini side three potential salt diapir locations were found and steeper slope gradients were proved to border the canyon head in contrast to the results of the older surveys mass movements affect almost the entire part of the slopes bounding the canyon head and can be distinguished in slides mass flows and turbidity currents the subbottom structure of the canyon floor confirms this evidence since it is constructed of alternating mass flow and turbidity current deposits the sedimentation processes are obviously affected by the high seismicity of the area although salt diapirism and associated high slope inclinations ascending gas from deeper sedimentary layers and homoclinal stratification seem to be dominant contributing factors sediment sources are classified according to their priority in the filling of the canyon floor

a pockmark field in the patras gulf greece and its activation during the 14 7 93 seismic event abstract during a recent oceanographical geophysical survey carried out in the southeastern part of the gulf of patras in western greece for the construction of an outfall an active pockmark field was found the pockmark field was formed in soft layered holocene silts the pockmarks are associated with acoustic anomalies attributed to gas charged sediments the pockmarks vary in size and shape from 25 to 250 m in diameter and from 0 5 to 15 m in depth and are among the largest and deepest observed in the world on july 14th 1993 during the survey a major earthquake of magnitude 5 4 on the richter scale occurred in the area during the 24 hour period prior to the earthquake the bottom water temperature anomalously increased on three occasions whilst for a few days after the earthquake it was noted that the majority of the pockmarks were venting gas bublles it is considered that the three abrupt sea water temperature increases were probably the result of upward migrating high temperature gas bubbles in the water column it is further suggested that the earthquake was the triggering mechanism and that the gas expulsion was caused by the reduction in the pore volume in the sediments resulting from changes in the stress regime prior to the earthquake therefore it can be suggested that in seismic areas adjacent to pockmark fields earthquake prediction may be achieved by monitoring the water temperature and or the rate of gas venting in the pockmark field our analysis indicates that the pockmark field in the patras gulf has formed slowly during the holocene by continuous gas venting which is periodically being interrupted by short duration events of enhanced gas seepage triggered by earthquakes