gas hydrates clathrates causing pore water freshening and oxygen isotope fractionation in deep water sedimentary sections of terrigenous continental margins the occurrence of gas hydrates in deep water sections of the continental margins predicted from anomalous acoustic reflectors on seismic profiles has been confirmed by recent deep sea drilling results on the pacific continental slope off guatemala gas hydrates were brought up for the first time from two holes 497 498a drilled during leg 67 of the dsdp in water depths of 2360 and 5500 m respectively the hydrates occur in organic matter rich pleistocene to miocene terrigenous sediments in the hydrate bearing zone a marked decrease in interstitial water chlorinities was observed starting at about 10 20 m subbottom depth pore waters at the bottom of the holes near 400 m subbottom have as little as half the chlorinity of seawater i e 9 similar but less pronounced trends were observed during previous legs of the dsdp in other hydrate prone segments of the continental margins where recharge of fresh water from the continent can be excluded e g leg 11 the crystallization of hydrates like ice excludes salt ions from the crystal structure during burial the dissolved salts are separated from the solids subsidence results in a downward motion of the solids including hydrates relative to the pore fluids thawing of hydrates during recovery releases fresh water which is remixed with the pore fluid not involved in hydrate formation the volume of the latter decreases downhole thus causing downward decreasing salinity chlorinity hydrate formation is responsible for oxygen isotope fractionation with18o enrichment in the hydrate explaining increasingly more positive 18o values in the pore fluids recovered after hydrate dissociation with depth

carbon isotope excursions and sea level change implications for the frasnian famennian biotic crisis new carbon and oxygen isotope data from carbonates spanning the frasnian famennian f f boundary in the guilin area south china show a broad positive 13 c rise and fall with sharp short lived negative 13 c events this pattern is comparable to that in europe and north america the integration of the isotope stratigraphy with high resolution sequence stratigraphy corroborates the onset of the positive 13 c excursion during a third order sea level fall in the latest frasnian this can best be explained through increased burial of c org during the sea level fall brought about by increased organic productivity caused by increased continent derived nutrient flux to the ocean due to enhanced weathering through the proliferation of land plants in the devonian this scenario would have resulted in anoxic and eutrophic conditions over epicontinental seas and blooms of cyanobacteria creating a highly stressful and fragile ecosystem for oligotrophic normal marine benthic organisms and leading to their massive decline the global third order sea level fall near the end of the frasnian may have led to gas hydrate dissociation giving the negative 13 c events and caused wild climatic fluctuations the subsequent short term events of sea level rise anoxia and eutrophication in the latest part of the f f transition would have placed additional environmental stresses on the already weakened biota leading to their further demise

method of estimating the amount of in situ gas hydrates in deep marine sediments abstract the bulk volume of gas hydrates in marine sediments can be estimated by measuring interval velocities and amplitude blanking of hydrated zones from true amplitude processed multichannel seismic reflection data in general neither velocity nor amplitude information is adequate to independently estimate hydrate concentration a method is proposed that uses amplitude blanking calibrated by interval velocity information to quantify hydrate concentrations in the blake ridge area of the us atlantic continental margin on the blake ridge blanking occurs in conjunction with relatively low interval velocities the model that best explains this relation linearly mixes two end member sediments hydrated and unhydrated sediment hydrate concentration in the hydrate end member can be calculated from a weighted equation that uses velocity estimated from the seismic data known properties of the pure hydrate and porosity inferred from a velocity porosity relationship amplitude blanking can be predicted as the proportions of hydrated and unhydrated sediment change across a reflection boundary our analysis of a small area near dsdp 533 indicates that the amount of gas hydrates is about 6 in total volume when the interval velocity is used as a criterion and about 9 5 when amplitude information is used this compares with a calculated value of about 8 derived from the only available measurement in dsdp 533

extensional tectonics of northwestern macedonia greece since the late miocene tectonic field studies in the florina ptolemais basin northwestern greece were carried out in an attempt to define the regional stress tensors in selected areas affected by neogene and quaternary faulting using recently proposed quantitative methods the analysis allows us to distinguish two extensional phases in the area a late miocene pliocene one with a ne sw average direction of extension and a pleistocene recent one with a nw se direction of extension we conclude that the principal stress axes 2 and 3 were interchanged in passing from one phase to the other these results are reasonably consistent with results of studies carried out in other parts of the aegean area especially the south aegean back arc domain

extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the paleocene isotopic records across the latest paleocene thermal maximum lptm indicate that bottom water temperature increased by more than 4 c during a brief time interval 104 years of the latest paleocene 55 6 ma there also was a coeval 2 to 3 excursion in the 13c of the ocean atmosphere inorganic carbon reservoir given the large mass of this reservoir a rapid 13c shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere however a direct consequence of warming bottom water temperature from 11 to 15 c over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic ch4 hydrate at locations with intermediate water depths in terms of the present day oceanic ch4 hydrate reservoir thermal dissociation of oceanic ch4 hydrate during the lptm could have released greater than 1 1 to 2 1 1018 g of carbon with a 13c of approximately 60 the release and subsequent oxidation of this amount of carbon is sufficient to explain a 2 to 3 excursion in 13c across the lptm fate of ch4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the lptm

paleoceanography a review for the gsa centennial the central problem of paleoceanography is the history of the circulation of the ocean although speculation about ancient oceanic circulation goes back to the past century the field of paleoceanography was founded in the 1950s as oxygen isotope studies suggested that oceanic deep waters were warmer in the past than they are today extensive coring of deep sea sediments by numerous expeditions after world war ii was followed by the ocean drilling programs providing a rich data base paleoceanographic interpretations have tried to explain the most obvious changes in sea floor sediments and their contained fossils changing paleotemperatures indicated by oxygen isotopes fluctuations in the calcium carbonate compensation depth accumulations of organic carbon rich sediments and the unexpected abundance of hiatuses in a setting which had been thought to be the ultimate sedimentary sink the result has been the intriguing discovery that although the positions and circulation of the major surface gyres is generally stable the deep circulation of the ocean may reverse on a variety of time scales it has been suggested that formation of north atlantic deep water which causes the uneven distribution of nutrients alkalinity and oxygen in the deep sea today may have been replaced by formation of north pacific deep water during the last deglaciation reversing the concentration gradients of nutrients alkalinity and oxygen on a longer time scale the present general circulation which is dominated by production of oxygen rich cold deep water in the subpolar regions today may have replaced a pre oligocene general circulation in which warm saline oxygen poor deep waters were formed in warm seas in the arid zones paleoceanography is still in its infancy many new clues to the history of the ocean are being discovered and many new ideas about conditions in the past are being developed the beginning of the next century should see continuing rapid growth and maturation in this exciting new field

abyssal circulation and benthic foraminiferal changes near the paleocene eocene boundary a major change in cenozoic deep sea benthic foraminifera occurred in the atlantic indian and pacific oceans near the paleocene eocene boundary benthic foraminiferal abundance changes began at about 61 5 ma at pacific deep sea drilling project dsdp site 577 a major extinction event followed at 58 57 ma between zones p6a and p6b and a series of first appearances continued until circa 55 5 ma zone p6c these faunal changes occurred during a 6 c warming of pacific bottom water and may indicate that the primary cause was changing temperature other potential causes of the faunal turnover include global changes in surface ocean productivity and changing bottom water source regions comparison of benthic and planktonic 13c records requires no change in the ratio of oceanic phosphorous to carbon during the late paleocene to early eocene which weakens the case for but does not disprove a change in surface ocean productivity at this time interbasinal comparisons of benthic foraminiferal 13c records document that water with high 13c values filled the cape basin during the late paleocene and possibly the early eocene circa 61 57 ma but apparently did not extend into the western basins of the atlantic this pattern suggests a supply of antarctic source water for the cape basin and possible tectonic isolation of the western atlantic basins during at least part of the late paleocene carbon isotope comparisons show that bottom water supply to the cape basin was reduced in the early eocene eolian grain size data suggest that a decrease in zonal wind intensity occurred at the end of the paleocene these late paleocene climatic changes bottom water warming and decreased wind intensity correspond with evidence for an important global tectonic reorganization and extensive subaerial volcanism which may have contributed to climatic warming through increased supply of co2

comparison of vs30 using measured assigned and proxy values in three cities of northern greece abstract accurate vs30 estimates are increasingly important in seismically active areas due to their efficacy in site effect analysis for seismic hazard assessment as well as microzonation evaluation and shake maps development a comparison between different approaches for the time averaged shear wave velocity vs in the upper 30 m vs30 is presented in this study of vs30 a site to site or averaged zonation value technique comparison is assessed for proxy based and measured or assigned values respectively three urban areas of edessa grevena and xanthi in northern greece were selected for this study the merit of this selection was based on the historical seismicity geology and geomorphology of these areas this paper highlights the strong correlation between the proxy based approach and the assigned average values in zones of common geophysical and geotechnical characteristics within the frame of ec8 site characterization in addition on site by site comparison proxy based vs30 values agree with the ones derived from measured geophysical data with the exception of areas where shear wave velocity has a high rate increase with depth as well as in shallow bedrock above 30 m the proxy tends to underestimate the vs30 value higher disagreements are reported when stiffer formations are denoted through geotechnical mapping that are not clarified in the geological map

genesis of diamond a mantle saga a model for the genesis of natural diamond is presented based on the physical chemical and mineralogical properties and features of diamond optical studies suggest that individual diamonds have had complex growth histories in which growth and dissolution may have occurred growth was not always continuous nor did diamonds grow in necessarily similar chemical environments evidence for this is provided by variation in the nitrogen and trace element contents in diamonds as well as information from studies of the minerals included in diamond isotopic data suggest that diamonds formed from carbon whose sources varied isotopically the possibility exists that some diamonds may be products of recycled subducted carbon whereas others have formed from primordial material either through magmatic or metasomatic processes it is also likely that most diamonds formed in the archaean or proterozoic the cognate host rocks for diamond in the mantle were several but can be broadly grouped into eclogitic and ultramafic peridotitic however in mineralogic and chemical detail these rocks are quite diverse although diamond is commonly found in kimberlite and in lamproite at the earth s surface these two rocks are not genetically related to diamond formation instead they are the transporting vehicles in which diamond ascended rapidly from mantle depths to the crust

influence of gas hydrate morphology on the seismic velocities of sands this paper reports the results of a series of resonant column tests on specimens where gas hydrate has been formed in sands using an excess water technique in these specimens the amount of hydrate formed is restricted by the amount of gas in the specimen and with an excess of water being present in the pore space results of resonant column tests carried out to determine compressional and shear wave velocities suggest that gas hydrate formed in this way are frame supporting in contrast the behavior observed in sands where the hydrate is formed from finite water where the remaining pore space is saturated with methane gas termed in this paper the excess gas method exhibits a cementing behavior while tetrahydrofuran hydrate sands or where the hydrate is formed from dissolved methane within the pore water exhibit a pore filling behavior for hydrate saturations less than 40 for sands where the hydrate is formed using the excess water method much larger volumes of hydrate are required before a significant increase in shear wave velocity occurs although increases in compressional wave velocity are seen at lower hydrate contents these results suggest that hydrate interaction with the sediment is strongly dependent on morphology and that natural hydrate may exhibit contrasting seismic signatures depending upon the geological environment in which it forms

methane rich plumes on the carolina continental rise associations with gas hydrates seafloor venting of microbial gases occurs at 2167 m water depth over the blake ridge diapir gas rich plumes were identified acoustically in the water column up to 320 m above a pockmarked sea floor associated with active chemosynthetic biological communities plumes and venting fluids emanate from near a small fault that extends downward toward a dome in the bottom simulating reflector indicating that fluid and or gas migration is associated with gas hydrate bearing sediment below these plumes might be caused by gas bubbles or buoyant dumps of gas hydrate that float upward from the seafloor 18 refs 3 figs

paleogene stable isotope events the oxygen isotope record in paleogene benthic foraminifera shows that at the base of the paleogene the ocean deep waters had a temperature of about 10 c rising to about 12 c at the base of the eocene and cooling between 51 ma and 49 ma to about 9 c the most dramatic event occurred just after the eocene oligocene boundary at about 35 8 ma when ocean deep waters cooled by several degrees within 104 105 yr probably in association with temporary glaciation in the antarctic region another more intense glacial event in antarctica may have occurred later in the oligocene at about 31 ma and a third near the top of the oligocene at 24 ma in the marine carbon isotope record a very rapid negative excursion occurred precisely at the cretaceous tertiary boundary a recovery to unusually positive values in the late paleocene was followed by a second negative excursion close to the paleocene eocene boundary that was even more extreme in magnitude although it was not as rapid these major carbon isotope events permit very accurate stratigraphic correlation there are many other smaller features in the carbon isotope record that will also prove useful for this purpose

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

topographic slope as a proxy for seismic site conditions and amplification we describe a technique to derive first order site condition maps directly from topographic data for calibration we use global 30 arc sec topographic data and v s 30 measurements here v s 30 refers to the average shear velocity down to 30 m aggregated from several studies in the u s as well as in taiwan italy and australia v s 30 values are correlated against topographic slope to develop two sets of parameters for deriving v s 30 one for active tectonic regions where topographic relief is high and one for stable shields where topography is more subdued by taking the gradient of the topography and choosing ranges of slope that maximize the correlation with shallow shear velocity observations we can recover to first order many of the spatially varying features of sitecondition maps developed for california our site condition map for the low relief mississippi embayment also predicts the bulk of the v s 30 observations in that region despite rather low slope ranges we find that maps derived from the slope of the topography is often well correlated with other independently derived regional scale site condition maps but the latter maps vary in quality and continuity and subsequently also in their ability to match observed v s 30 measurements contained therein alternatively the slope based method provides a simple approach to uniform site condition mapping

evidence for sediment eruption on deep sea floor gulf of mexico a large crater has been discovered on the sea floor gulf of mexico in a water depth of 2176 meters deep tow high resolution imagery shows that the crater is cut into a low hill surrounded by near surface concentric faults approximately 2 million cubic meters of ejected sediment forms a peripheral debris field the low hill and faults may be related to mud diapirism or intrusion of gas hydrates into near surface sediments a recent eruption evacuated sediments from the crater apparently because of release of overpressured petrogenic gas

a terrain based site conditions map of california with implications for the contiguous united states abstract we present an approach based on geomorphometry to predict material properties and characterize site conditions using the v s 30 parameter time averaged shear wave velocity to a depth of 30 m our framework consists of an automated terrain classification scheme based on taxonomic criteria slope gradient local convexity and surface texture that systematically identifies 16 terrain types from 1 km spatial resolution 30 arcsec shuttle radar topography mission digital elevation models srtmdems using 853 v s 30 values from california we apply a simulation based statistical method to determine the mean v s 30 for each terrain type in california we then compare the v s 30 values with models based on individual proxies such as mapped surface geology and topographic slope and show that our systematic terrain based approach consistently performs better than semiempirical estimates based on individual proxies to further evaluate our model we apply our california based estimates to terrains of the contiguous united states comparisons of our estimates with 325 v s 30 measurements outside of california as well as estimates based on the topographic slope model indicate our method to be statistically robust and more accurate our approach thus provides an objective and robust method for extending estimates of v s 30 for regions where in situ measurements are sparse or not readily available

paleogene geochronology an integrated approach geochronology is the conceptual division of continuous time as measured geochronometry by the progression in an ordinal series of events this is best achieved by an approach which integrates four independent data sets magnetostratigraphy seafloor spreading magnetic lineation patterns biostratigraphy and isotopic ages this integrated approach results in an ordinal framework which can measure time with greater resolution though perhaps less accuracy than a radiometric approach alone a comparative analysis of two recently proposed paleogene geochronologic time scales is presented

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

submarine landslide identified in md179 cores off joetsu area eastern margin of the sea of japan abstract gas hydrate is exposed on the sea floor and is buried in shallow sediments in the off joetsu area at the eastern margin of the sea of japan sediment cores recovered from topographic highs of the joetsu knoll and umitaka spur show pockmarks and mounds formed by gas hydrate dissociation but those from the un named ridge have no such topographic features all topographic highs and pockmarks mainly comprise bioturbated layers interbedded with thinly laminated tl layers which are common sea of japan sediments recovered sediments are however mostly disturbed by submarine landslides showing tilted horizons faults slump folds and breccia except that from the un named ridge the timing of events is well constrained by identification of the number of tl layers in some sediment cores landslides occurred both during the cold glacial period of the late mis3 to the last glacial maximum lgm and during the warm interglacial period of the post lgm all were caused by the explosive rise of gas hydrate formed at very shallow depths of the sea bottom by the supply of gas from the depth of the gas hydrate stability zone through gas chimney passages developed under the pockmarks seismic activity demands consideration as a factor because the off joetsu area is tectonically active

ice core record of atmospheric methane changes relevance to climatic changes and possible gas hydrate sources the antarctic and greenland ice contains an almost direct record of past atmospheric ch4 the record over the last 200 years reveals a spectacular 150 increase of the ch4 atmospheric mixing ratio since pre industrial times at the scale of a glacial interglacial cycle the record shows a remarkable correlation with climatic changes with high low ch4 levels during warm cold periods a striking feature of the glacial interglacial ch4 record is the presence of large and abrupt at the scale of a century or less changes during the last glaciation and glacial interglacial transition the classical interpretation for the origin of ch4 changes prior to the industrial era involves mainly the wetland source in the context of gas hydrates the question is to know whether the past ice core record contains fingerprints of catastrophic hydrate release chr we currently conclude that the available record shows no evidence for chr but additional ice core analyses are necessary to reach a more definitive conclusion

on the unusual characteristics of the diamonds from letseng la terae kimberlites lesotho abstract the letseng la terae kimberlites are situated 3100 m above sea level in the maloti mountains of lesotho southern africa the principal economic bodies are two late cretaceous low grade 1 3 5 carats hundred ton cpht kimberlite pipes that host high value diamonds realising us 2000 2500 carat ct in 2008 terms locally the larger kimberlite body is referred to as the main pipe 17 2 ha and the smaller one is called the satellite pipe 5 2 ha these pipes and their associated eluvial and proximal alluvial deposits are renowned for yielding large d colour gem quality diamonds including 100 carat ct stones earlier artisanal effort 1959 1977 and formal mining 1977 1982 produced 335 000 carats cts including the 601 ct lesotho brown in 1968 in 2003 letseng diamonds limited re commenced mining operations and had produced 265 000 cts by the end of july 2008 including 24 100 ct diamonds the largest of which was the 603 ct lesotho promise we report here on the unusual characteristics of the letseng diamond population that include i 75 gem quality that is more commonly associated with alluvial diamond deposits ii large average stone size of ca 1 carat stone ct stn that is also more typical of certain alluvial diamond placers iii high yielding rounded to flattened irregular resorbed dodecahedral shapes main pipe 67 and satellite pipe 87 with subordinate dodecahedral macle main pipe 32 and satellite pipe 12 and broken ca 1 forms in both pipes the octahedral component is virtually absent iv economically favourable colour mix ca 33 white colour diamonds in both pipes v abundance of nitrogen free d colour type iia diamonds that dominate the internationally recognised special stone size fraction which covers all diamonds larger than 10 8 cts main pipe 32 and satellite pipe 51 during 2008 these larger special diamonds commanded prices in excess of us 15 000 ct contributing ca 75 of the revenue generated by the letseng mine furthermore of the 24 100 ct diamonds recovered between november 2003 and july 2008 18 75 were type iia d colour diamonds that also fetched prices mostly in excess of us 25 000 ct therefore the type iia diamonds boost significantly the revenue per unit measure in this case the us ton of the letseng la terae pipes making these low grade kimberlites economic to mine

u th isotope constraints on gas hydrate and pockmark dynamics at the niger delta margin abstract the application of uranium thorium dating methods to authigenic carbonates provides unique constraints on the temporal evolution of methane seeps at ocean margins in this study we report u th isotope measurements for carbonate breccias collected from within a hydrate bearing pockmark located at the niger delta margin these concretions were extracted from a carbonate rich layer in the upper two meters of a sediment core n2 ks 44 1200 m water depth well above the present day sulphate methane transition zone about 3 m depth and the presence of gas hydrates in the sediment the stratigraphy of core n2 ks 44 was established by tuning its downcore al ti profile to a well dated nearby reference core and carbonate 230 th u ages were calculated using isochron methods our results indicate that a major event of aragonite precipitation occurred between about 13 and 2 5 ka at the studied location comparison of sediment accumulation rates at both core n2 ks 44 and the nearby reference site suggests that the initial stage of carbonate precipitation between 13 and 10 ka was associated with sediment winnowing probably related to intense fluid seepage in contrast our data indicate that sedimentation rates rapidly increased within the pockmark after 7 ka in agreement with the presence of carbonate breccias exhibiting u th ages older than their corresponding stratigraphic age this observation would suggest that sediment reworking took place after that time possibly caused by erosion of the surrounding sediment within the pockmark we hypothesize that the period of carbonate formation between 13 and 2 5 ka was related to an upward migration of gas hydrate reservoirs to the near seafloor environment after this pulse of enhanced fluid flow the diminution of methane fluxes at the base of the local gas hydrate occurrence zone would have led to hydrate dissolution in sub surface sediments and pockmark formation thereby explaining the progressive increase in sedimentation rates the absence of recent carbonate concretions and the deepening of the sulphate methane transition zone at site n2 ks 44 inferred from pore water data overall these results provide further constraints about the relationship between gas hydrate dynamics and the evolution of pockmarks at ocean margins through time

late paleocene to eocene paleoceanography of the equatorial pacific ocean stable isotopes recorded at ocean drilling program site 865 allison guyot an expanded and largely complete upper paleocene to upper eocene section was recovered from the pelagic cap overlying allison guyot mid pacific mountains at ocean drilling program odp site 865 18o26 n 179o33 w paleodepth 1300 1500 m reconstructions show that the site was within a few degrees of the equator during the paleogene because no other paleogene sections have been recovered in the pacific ocean at such a low latitude site 865 provides a unique record of equatorial pacific paleoceanography detailed stable isotopic investigations were conducted on three planktonic foraminiferal taxa species of acarinina morozovella and subbotina we studied benthic foraminiferal isotopes at much lower resolution on species of cibicidoides and lenticulina nuttallides truernpyi and gavelinella beccariiformis because of their exceptional rarity the 5180 and 513c stratigraphies from site 865 are generally similar to those derived from other paleocene and eocene sections the planktonic foraminiferal records at site 865 however include significantly less short term single sample variability than those from higher latitude sites indicating that this tropical oligotrophic location had a comparatively stable water column structure with a deep mixed layer and less seasonal variability low amplitude 0 1 0 8 o oscillations on timescales of 250 000 to 300 000 years correlate between the 513c records of all planktonic taxa and may represent fluctuations in the mixing intensity of surface waters peak sea surface temperatures of 24o 25oc occurred in the earliest eocene followed by a rapid cooling of 3 6oc in the late early eocene temperatures remained cool and stable through the middle eocene in the late eocene surface water temperatures decreased further vertical temperature gradients decreased dramatically in the late paleocene and were relatively constant through much of the eocene but increased markedly in the late eocene intermediate waters warmed through the late paleocene reaching a maximum temperature of 10oc in the early eocene cooling in the middle and late eocene paralleled that of surface waters with latest eocene temperatures below 5oc extinction patterns of benthic foraminifera in the latest paleocene were similar to those observed at other pacific sites and were coeval with a short term very rapid negative excursion in 513c values in planktonic and benthic taxa as at other sites during this excursion benthic foraminiferal 5180 values decreased markedly indicating warming of 4 to 6oc for tropical intermediate waters while planktonic taxa show slight warming 1 oc followed by 2oc of cooling convergence of 5180 values of planktonic and benthic foraminifera suggests that thermal gradients in the water column in this tropical location collapsed during the excursion these data are consistent with the hypothesis that equatorial pacific surface waters were a potential source of warm higher salinity waters which filled portions of the deep ocean in the latest paleocene oxygen isotopic data indicate that equator to high southern latitude sea surface thermal gradients decreased to as little as 4oc at the peak of the excursion suggesting some fundamental change in global heat transport

correlation between isotope records in marine and continental carbon reservoirs near the palaeocene eocene boundary changes in the isotope content of the large marine carbon reservoir can force shifts in that of the smaller carbon pools in the atmosphere and on land the carbon isotope compositions of marine carbonate sediments from the late palaeocene vary considerably exhibiting a sudden decrease close to the palaeocene eocene boundary which coincides with deep sea benthic extinctions1 and with changes in ocean circulation here we report that these fluctuations in the marine carbon isotope record are closely tracked by the terrestrial records provided by palaeosol carbonates and mammalian tooth enamel in using palaeosol carbonates to reconstruct the co2 content of the ancient atmosphere2 isotope shifts of this sort will have to be taken into account the sharp decrease in 13c 12c ratios in the late palaeocene provides a datum for precise correlation of marine and continental records and suggests that abrupt climate warming at this time may have played an important role in the evolution of land mammals

origin of bottom simulating reflectors geophysical evidence from the cascadia accretionary prism vertical seismic profile vsp data from two drill sites on the cascadia margin show low velocity zones indicative of free gas be neath a bottom simulating reflector bsr offshore oregon at ocean drilling program odp site 892 velocities drop from an average of 1750 m s above the bsr to less than 1250 m s below it sonic logs confirm that seismic velocity in the sediments adjacent to the borehole is less than that of water for at least 50 m beneath the depth of the bsr at this site similarly at odp site 889 offshore vancouver velocities range from 1700 to 1900 m s in the 100 m above the bsr and drop abruptly to 1520 m s in the 15 m just beneath it the low velocities observed beneath the bsr are strong evidence for the presence of 1 5 free gas by volume the bsr at these two sites results from the contact between gas free sediments containing a small quantity of hydrate above the bsr and a low velocity free gas zone beneath it although the bsr is associated with the base of the hydrate stability field hydrate appears to account for relatively little of the velocity contrast that produces the bsr velocity above the bsr at site 889 is only about 100 m s greater than that expected for sediments of similar porosity sediments above the bsr at site 892 appear to have normal velocity for their porosity and may contain little hydrate

increased continental margin slumping frequency during sea level lowstands above gas hydrate bearing sediments we present sup 14 c data on sediment samples from cores of the upper 7 m of the sediment column overlying a major continental rise gas hydrate field on the southern carolina rise and inner blake ridge offshore the southeastern united states the data show that glacial age sediments are underrepresented in the cores the observation is consistent with a previously predicted association between sea level lowstands and increased frequency of sea floor slumping on continental margins containing gas hydrates 26 refs 3 figs

role of naturally occurring gas hydrates in sediment transport naturally occurring gas hydrates have the potential to store enormous volumes of both gas and water in semi solid form in ocean bottom sediments and then to release that gas and water when the hydrate s equilibrium conditions are disturbed therefore hydrates provide a potential mechanism for transporting large volumes of sediments under the combined low bottom water temperatures and moderate hydrostatic pressures that exist over most of the continental slopes and all of the continental rises and abyssal plains hydrocarbon gases at or near saturation in the interstitial waters of the near bottom sediments will form hydrates the gas can either be autochthonous microbially produced gas or allochthonous catagenic gas from deeper sediments equilibrium conditions that stabilize hydrated sediments may be disturbed for example by continued sedimentation or by lowering of sea level in either case some of the solid gas water matrix decomposes released gas and water volume exceeds the volume occupied by the hydrate so the internal pressure rises drastically if large volumes of hydrate are decomposed part of the once rigid sediment is converted to a gas and water rich relatively low density mud when the internal pressure due to the presence of the compressed gas or to buoyancy is sufficiently high the overlying sediment may be lifted and or breached and the less dense gas cut mud may break through such hydrate related phenomena can cause mud diapirs mud volcanos mud slides or turbidite flows depending on s diment configuration and bottom topography

developing a map of geologically defined site condition categories for california consideration of site conditions is a vital step in analyzing and predicting earthquake ground motion the importance of amplification by soil conditions has long been recognized but though many seismic instrument sites have been characterized by their geologic conditions there has been no consistent simple classification applied to all sites as classification of sites by shear wave velocity has become more common the need to go back and provide a simple uniform classification for all stations has become apparent within the pacific earthquake engineering research center s next generation attenuation equation project developers of attenuation equations recognized the need to consider site conditions and asked that the california geological survey provide site conditions information for all stations that have recorded earthquake ground motion in california to provide these estimates we sorted the available shear wave velocity data by geologic unit generalized the geologic units and prepared a map so that we could use the extent of the map units to transfer the velocity characteristics from the sites where they were measured to sites on the same or similar materials this new map is different from the california geological survey preliminary site conditions map of california in that 19 geologically defined categories are used rather than national earthquake hazards reduction program categories although this map does not yet cover all of california when completed it may provide a basis for more precise consideration of site conditions in ground motion calculations

deep sea erosional unconformity in the southeastern gulf of mexico multichannel seismic data and deep sea drilling project dsdp well information reveal a prominent erosional unconformity in the deep southeastern gulf of mexico corresponding to a 44 to 38 5 m y b p hiatus middle to late eocene at dsdp site 540 leg 77 the unconformity was apparently produced by the bottom effects of wind driven surface currents paleo florida current and gravitational mass movements capable of scouring the slope intensification of these sedimentary processes may have been related to global cooling and a reported drop in sea level in the late eocene but it may also have been part of a complex global response to a postulated paleogene meteorite impact

brown diamonds and high pressure high temperature treatment abstract much progress has been made in recent years towards greater understanding of the various point and extended defects that give rise to colour in diamond and how such defects can be modified via treatment to change a diamond s colour such fundamental understanding has been vital in providing reliable means for gemmological laboratories to identify treated diamonds and ensure maintenance of consumer confidence in diamond the application of high pressure high temperature treatment to remove a brown colour component has prompted significant research recently into the cause of brown colour this article reviews progress to date and the evidence that indicates that clusters of around 60 vacancies are the defects responsible for the absorption causing brown colour the general principles and techniques applied to the detection of diamonds subjected to high pressure high temperature treatment are also discussed detailed comparison between photoluminescence spectra from treated and untreated diamonds is vital in the identification of type iia diamonds whilst absorption features provide a robust means of identification for type i diamonds a detection scheme based on the shape of the platelet related infrared absorption is presented

constraining kimberlite geology through integration of geophysical geological and geochemical methods a case study of the mothae kimberlite northern lesotho abstract the cretaceous mothae kimberlite is located in northern lesotho on the southeast margin of the kaapvaal craton historical work suggests that mothae has a low average diamond grade of 3 cpht and the economic viability therefore depends on the presence of large high quality and thus value diamonds as does that of the nearby letseng diamond mine defining such a diamond population requires a very large and representative bulk sample the near surface geology of the mothae kimberlite was investigated using ground geophysical surveys pit mapping petrography measurements of the mantle components and whole rock compositions integration of data from these different approaches clearly defines the outline of the kimberlite at the surface and permits definition with varying confidence levels of at least six geologically distinct domains within the body the domains are defined primarily on the basis of variations in the relative abundances of certain mantle derived minerals extracted from exploratory pit samples supported to varying extents by geophysically defined zones variations in kimberlite type established petrographically and variations in whole rock composition the domains are interpreted to reflect the presence of multiple phases of volcaniclastic kimberlite each with a potentially different diamond content the map of the near surface geology constructed on the basis of the work described in this paper provides a valuable framework for planning of further drilling and sampling work aimed at constraining the diamond resource at mothae this study illustrates the value of an integrated multidisciplinary approach to understanding the geology of a complex kimberlite body during the early stages of evaluation

spatially correlated multiscale vs30 mapping and a case study of the suzhou site abstract the average shear wave velocity in the first 30 m of subsoil vs30 is a key indicator of site response affecting the ground motion amplification for many earthquake engineering applications mapping of vs30 over a large region is commonly done through proxy based models correlating vs30 with geological or topographic information in this paper a multiscale random field based framework is presented and applied to mapping vs30 over extended areas this framework accounts for spatial variations of vs30 values across different length scales and is able to adaptively refine around areas of high interest while maintaining consistent description of spatial dependence in the case study site suzhou city a total of 309 shear wave velocity measurements are compiled and used to calculate vs30 values from which the statistical and spatial parameters for the random field model are inferred usgs topography based vs30 data are also collected and used as secondary information to improve the accuracy of predictions the random field models are coupled with monte carlo simulations to obtain a multiscale vs30 map and its associated uncertainties at the suzhou site the new vs30 map is then applied to site classification and amplification factor characterization in the studied region to demonstrate its applications

late devonian carbon isotope stratigraphy and sea level fluctuations canning basin western australia the upper devonian reef complexes of the canning basin contain some of the world s best exposed continuous stratigraphic sections through the frasnian famennian boundary the facies distribution and composition of these reef complexes record interactions among sea level changes sediment supply ocean chemistry and paleoecology changes in relative sea level produced spatial shifts in reef platform development and regional changes in sediment supply that can be correlated across facies boundaries using a combination of sequence stratigraphy biostratigraphy and carbon isotope stratigraphy during the lowstand interval below the frasnian famennian boundary the reef margin advanced down the reef slope in shallow water environments and siliciclastics locally dominated in the marginal slope environment compilation of a broad late frasnian to early famennian sequence stratigraphic framework for the canning basin demonstrates that transgressive intervals correlate to positive carbon isotopic excursions within the basin these isotopic shifts also can be correlated to time equivalent positive carbon isotopic excursions reported from transgressive intervals in europe thus the late frasnian transgressions in the canning basin were primarily eustatic rather than tectonic in origin and positive carbon isotopic signatures of the kellwasser horizons are globally correlative c 2002 elsevier science b v all rights reserved

global change at the paleocene eocene boundary climatic and evolutionary consequences of tectonic events rea d k zachos j c owen r m and gingerich p d 1990 global change at the paleocene eocene boundary climatic and evolutionary consequences of tectonic events palaeogeogr palaeoclimatol palaeoecol 79 117 128 events of the paleocene eocene boundary provide the clearest example to date of how a tectonic event may have global climatic consequences recent advances permit well constrained stratigraphic determination of several events that occurred at that boundary in chron c24r a many fold increase in sea floor hydrothermal activity a global warming a reduction in the intensity of atmospheric circulation a conversion to salinity driven deep ocean circulation a marked lightening of oceanic 313c values extinction and evolution of both benthic foraminifera and land mammals and important plate boundary reorganizations including the outpouring of the east greenland volcanics and the initiation of the oceanic rift between norway and greenland we hypothesize that enhanced sea floor hydrothermal activity occasioned by global tectonism resulted in a flooding of the atmosphere with coz causing a reduced pole to equator temperature gradient and increased evaporation at low latitudes increased formation of warm salty probably low nutrient waters coupled with the warm temperatures at high latitudes occasioned a salinity driven rather than temperature driven deep water circulation this newly evolved ocean circulation pattern changed the apportionment of global heat transport from the atmosphere to the ocean with concomitant changes in the circulation intensity of both reduced intensity of atmospheric circulation resulted in lower oceanic biological productivity and enhanced seasonality of climate on the continents a major extinction event among benthic foraminifera was probably a response to the new low nutrient and chemically changed bottom waters and endemism following rapid evolution and dispersal of mammalian orders may have been in response to the new continental climate regime

a laboratory investigation into the seismic velocities of methane gas hydrate bearing sand remote seismic methods which measure the compressional wave p wave velocity vp and shear wave s wave velocity vs can be used to assess the distribution and concentration of marine gas hydrates in situ however interpreting seismic data requires an understanding of the seismic properties of hydrate bearing sediments which has proved problematic because of difficulties in recovering intact hydrate bearing sediment samples and in performing valid laboratory tests therefore a dedicated gas hydrate resonant column ghrc was developed to allow pressure and temperature conditions suitable for hydrate formation to be applied to a specimen with subsequent measurement of both vp and vs made at frequencies and strains relevant to marine seismic investigations thirteen sand specimens containing differing amounts of evenly dispersed hydrate were tested the results show a bipartite relationship between velocities and hydrate pore saturation with a marked transition between 3 and 5 hydrate pore saturation for both vp and vs this suggests that methane hydrate initially cements sand grain contacts then infills the pore space these results show in detail for the first time using a resonant column how hydrate cementation affects elastic wave properties in quartz sand this information is valuable for validating theoretical models relating seismic wave propagation in marine sediments to hydrate pore saturation

potential impact on climate of the exploitation of methane hydrate deposits offshore abstract considerable attention has focussed on methane hydrates as a potential energy resource but much less on the potential environmental problems of exploiting these deposits in fact methane hydrate deposits represent a dynamic system formed as a result of the continuous migration of methane gas along fracture systems any exploitation of methane hydrates offshore will perforce take place in these unstable systems and could lead to the large scale release of ch 4 under unfavourable circumstances however most of this ch 4 would be oxidized to co 2 within the water column under steady state conditions only under exceptional circumstances would large scale release of ch 4 into the atmosphere take place the impact of exploiting these deposits offshore on global climate may therefore be limited provided serious efforts are made to minimize environmental impacts at present prospects for the commercial exploitation of methane hydrates are in their infancy considerable ingenuity will be required to satisfy the requirements of safe operating conditions mitigation of environmental hazards and commercial viability the need to exercise caution before attempting to exploit these deposits is emphasized

a new model for atmospheric oxygen over phanerozoic time a mathematical model has been constructed that enables calculation of the level of atmospheric o2 over the past 570 my from rates of burial and weathering of organic carbon c and pyrite sulfur s burial rates as a function of time are calculated from an assumed constant worldwide clastic sedimentation rate and the relative abundance and c and s contents of the three rock types marine sandstones and shales coal basin sediments and other non marine clastics red beds arkoses by our model values of o2 versus time using a constant total sedimentation rate agree with those for variable sedimentation derived from present day rock abundances and estimates of erosional losses since deposition this agreement is the result of our reliance on the idea that any increase in total worldwide sediment burial with consequently faster burial of c and s and greater o2 production must be accompanied by a corresponding increase in erosion and increased exposure of c and s on the continents to o2 consumption via weathering it is the redistribution of sediment between the three different rock types and not total sedimentation rate that is important in o2 control to add stability to the system negative feedback against excessive o2 fluctuation was provided in the modeling by the geologically reasonable assignment of higher weathering rates to younger rocks resulting in rapid recycling of c and s we did not use direct o2 negative feedback on either weathering of c and s or burial of c because weathering rates are assumed to be limited by uplift and erosion and the burial rate of c limited by the rate of sediment deposition the latter assumption is the result of modern sediment studies which show that marine organic matter burial occurs mainly in oxygenated shallow water and is limited by the rate of supply of nutrients to the oceans by rivers results of the modeling indicate that atmospheric o2 probably has varied appreciably over phanerozoic time during the late carboniferous and permian periods o2 was higher than previously because of the rise of vascular land plants and the widespread burial of organic matter in vast coal swamps a large decrease in o2 during the late permian was due probably to the drying up of the coal swamps and deposition of a large proportion of total sediment in c and s free continental red beds sensitivity study shows that major parameters affecting results are the mean c concentration in coal basins and the relative sizes of the reservoirs of young rapidly recycled versus old rocks less sensitivity was found for changes over time in total land area undergoing weathering and the use of direct o2 negative feedback on marine carbon burial good agreement for rates of c burial calculated via our model and via independent models which are based on the use of stable carbon isotopes indicates that the dominant factor that has brought about changes in atmospheric o2 level and the isotopic composition of dissolved inorganic carbon in seawater over phanerozoic time is sedimentation and not weathering or higher temperature phenomena such as basalt seawater reaction

ocean nutrient distribution and oxygenation limits on the formation of warm saline bottom water over the past 91 m y it has been proposed that deep water formation in the oceans would be quite different during geologic intervals with reduced equator to pole temperature gradients salinity rather than temperature differences might drive the deep ocean circulation saline water would tend to form at subtropical latitudes where evaporation exceeds precipitation we point out a likely consequence of warm saline bottom water formation on ocean chemistry the tendency to drive the ocean toward anoxia this effect is not due to the previously noted lower oxygen solubility with increasing ocean temperature but rather to the increased efficiency with which plankton will extract nutrients from convecting waters at low latitudes the present ocean nutrient content is sufficient to induce deep water anoxia if circulation were to change yet anoxia is rare in the paleoceanographic record a simple ocean chemical model makes explicit the tradeoffs between mean ocean nutrient content and circulation parameters that will satisfy the geologic observations of an oxygenated ocean since the mid cretaceous barring decreases of ocean phosphate on the order of 30 50 deep water formation at high latitudes was a major source of ocean ventilation in the warmer past

characterization of hydrocarbon gas within the stratigraphic interval of gas hydrate stability on the north slope of alaska u s a abstract in the kuparuk river unit 2d 15 well on the north slope of alaska a 60 m thick stratigraphic interval that lies within the theoretical pressure temperature field of gas hydrate stability is inferred to contain methane hydrates this inference is based on interpretations from well logs 1 release of methane during drilling as indicated by the mud log 2 an increase in acoustic velocity on the sonic log and 3 an increase of electrical resistivity on the electric logs our objective was to determine the composition and source of the gas within the shallow gas hydrate bearing interval based on analyses of cutting gas headspace gas from canned drill cuttings collected from within the gas hydrate bearing interval of this well has an average methane to ethane plus propane c1 c2 c 3 ratio of about 7000 and an average methane 13c value of 46 relative to the pdb standard these compositions are compared with those obtained at one well located to the north of 2d 15 along depositional strike and one down dip well to the northeast in the well located on depositional strike kuparuk river unit 3k 9 gas compositions are similar to those found at 2d 15 at the down dip well prudhoe bay unit r 1 the c1 c2 c3 ratios are lower 700 and the methane 13c is heavier 33 we conclude that the methane within the stratigraphic interval of gas hydrate stability comes from two sources in situ microbial gas and migrated thermogenic gas the thermal component is greatest at prudhoe bay up dip to the west the thermogenic component decreases and microbial gas assumes more importance

hirnantian sea level changes in the baltoscandian basin a review abstract correlation of hirnantian sections of the baltoscandian basin reveals four major transgressive regressive sea level cycles related to waxing and waning of ice sheets at high southern hemisphere paleolatitudes the correlation between stratigraphic members in estonia and latvia shows transgressions regressions in the first half of the hirnantian when sea level fluctuated between shallow and deep shelves during the second half of the hirnantian the sea regressed into the former deep shelf leaving north estonia as a mainland after that the sea retreated to the central baltoscandian basin and the whole baltic shelf stayed subaerial this final regression brought the coastline to the vicinity of scania in the west and of lublin basin in the east in the latest hirnantian during ice cap melting sea level began to ascend the baltic shelf submerged again in the early silurian this transgression of latest hirnantian earliest silurian indicates fast melting of ice in gondwanan ice sheets we are proposing that the destabilisation of great amount of gas hydrates due to diminishing of water column pressure during the last deepest regression acted as a trigger for rapid warming of climate the ascertainment of sea level changes presumes correlations between different parts of the baltoscandian basin comparison of published data on stratigraphy lithology faunal finds chemical elements and stable carbon isotopes was the ground for tracking hirnantian changes

combined vertical incidence and wide angle seismic study of a gas hydrate zone blake ridge wide angle ocean bottom seismic data and single channel seismic reflection data were collected in june 1992 over an area where gas hydrates are thought to be extensive on blake ridge offshore south carolina wide angle reflections were observed on four woods hole oceanographic institution ocean bottom hydrophones at offsets up to 15 km results from traveltime inversion show that the bottom simulating reflector bsr that marks the base of the hydrate stability field lies 400 500 m below the seafloor and is overlain by a 200 to 300 m thick layer of average velocity 1 9 km s 1 there is no evidence for significant lateral velocity variation associated with lateral changes in bsr character ray tracing calculations show that the observation of the bsr out to large offsets 7 km constrains the maximum vertical velocity gradient to about 0 5 s 1 amplitude versus offset avo analysis was performed for ranges up to about 6 km and incidence angles of more than 70 the high amplitude of the bsr in the normal incidence data can be explained by two models both of which include a strong negative impedance contrast the hydrate wedge model and the free gas layer model synthetic seismogram calculation for the wedge model using the reflectivity method shows a strong increase in the bsr amplitudes at offsets between 3 and 5 km because of postcritical reflections and diving waves within the wedge this amplitude increase is clearly not observed in the data which shows only a relatively modest increase in amplitude with offset this observation agrees better with the calculated avo for the gas layer model the lack of a distinct reflection from the base of the gas layer implies that the gas layer is not thicker than 25 m and or that the base of the gas layer is a gradational boundary

correlating shelf carbonate evolutive phases with fluid expulsion episodes in the foredeep miocene northern apennines italy abstract in the miocene of the northern apennines of italy evolutionary phases of shallow water carbonates in wedge top basins are coeval with methane rich fluid expulsion episodes in the inner foredeep we identified four main correlative events primarily controlled by synsedimentary tectonics sediment input and climate cooling 1 a burdigalian tectonic phase determined the onset of shelfal sedimentation in wedge top areas and is correlated with an important episode of fluid expulsion in marly sediments of the inner foredeep croce di moggiona seep carbonates 2 the decrease of shelfal carbonate production and the increase of detrital input in the early langhian correspond with a second important episode of seep carbonate precipitation in the inner foredeep castagno d andrea 3 the demise of the carbonate shelf and the coeval expulsion of methane rich fluids in the inner foredeep vicchio and m citerna seep carbonates at the langhian serravallian boundary approximate the mi3b cooling event the lower temperatures associated with increased siliciclastic weathering led to the crisis of shallow water carbonate production whereas the pressure drop due to the eustatic fall may have triggered the gas charged fluid expulsion 4 the tectonic related uplift of frontal sectors of the wedge top basin led to the wide erosion of the burdigalian langhian carbonates and caused the precipitation of authigenic seep carbonates deruta seep both in the slope and the adjacent foredeep

the end of the ice age methane gas hydrates may have contributed to the rapid rise in atmospheric ch4 co2 and global temperatures at the end of the last major glaciation about 13 500 years ago given suitable orbital conditions and insolation at high latitude a small triggering event such as the release of one or more arctic gas pools may have initiated massive release of methane from hydrate under ice and in permafrost the consequent greenhouse warming would have provided strong positive feedback amplifying emission this warming driven by ch4 may have induced the release of co2 from the oceans to the biosphere stabilizing the interglacial carbon cycle

balancing the deglacial global carbon budget the hydrate factor abstract the discovery that methane from dissociation of gas hydrates could be an important factor in the global carbon cycle resolves the major discrepancy in estimates of the increase of terrestrial biomass from the last glacial period to the present carbon isotope budgeting using the marine carbon isotopic record results in an estimate centered around 500 gtc whereas palaeovegetation reconstruction with biosphere models gives averages around 1000 gtc the discrepancy may be resolved by considering release of isotopically light methane through destabilization of gas hydrates this provides a unique means of estimating the contribution of gas hydrates to the deglacial rise in atmospheric methane a release of 120 gtc methane makes a biospheric carbon transfer of 1000 gtc compatible with the marine carbon isotope data this however represents less than 30 of the enhanced atmospheric methane production between 18 and 8 ka observed in ice cores supporting the theory that glacial interglacial variations in atmospheric methane were driven primarily by changes in the extent of tropical and temperate wetlands and not by methane release from clathrates by balancing the deglacial carbon budget we demonstrate that global carbon models will have to incorporate glacial interglacial vegetation shifts of at least 1000 gtc which many currently find difficult

compilation of a local vs profile database and its application for inference of vs30 from geologic and terrain based proxies abstract the time averaged shear wave velocity in the upper 30 m of a site v s 30 is commonly used for ground motion prediction when measured velocities are unavailable v s 30 is estimated from proxy based relationships developed for application on global or local scales we describe the development of a local relationship for greece which begins with compilation of a profile database pdb from published sources and engineering reports the pdb contains 314 sites 238 have profile depths 30 m and 59 are within 100 m of accelerographs we find existing relations for extrapolating a time averaged velocity for depths less than 30 m to v s 30 to overpredict v s 30 we present equations for these extrapolations we then compile proxies for pdb sites including terrain type surface geology and surface gradients at 30 and 3 arcsec resolution from radar derived digital elevation models dems when checked against ground survey data we find ground elevations from 3 arcsec dems to be more accurate relative to survey data than alternative 30 9 and 1 arcsec dems drawing upon expert opinion we develop geologic categories based on age gradation and depositional environment and assign such categories to pdb sites we find an existing 30 arcsec gradient based global model to be biased relative to local v s 30 data for gradients 0 05 m m bias relative to a california model is also found for four of the eight well populated geomorphic categories and new local values are provided we find statistically significant effects of the 3 arcsec gradient on v s 30 for quaternary and tertiary materials but no gradient effect for those from the mesozoic among quaternary sediments holocene mapped quaternary age unspecified and mixed fine gradation materials exhibit consistent v s 30 gradient trends whereas pleistocene and coarse gradation sediments have faster velocities for the study region we recommend use of the modified terrain and geology based methods in combination for proxy based v s 30 estimation online material profile database spreadsheet and figures of elevation residuals

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

seafloor nuclear magnetic resonance assay of methane hydrate in sediment and rock 1 proton nuclear magnetic resonance nmr of liquid water can be used to indirectly detect and assay methane hydrate in opaque earth materials it is also potentially useful for quantifying pore size control of hydrate formation and for estimating in situ hydraulic permeability of hydrate affected earth formations the method is quantitative nondestructive and volumetrically averaging over a spatially selected region in the first controlled validation of this measurement we have used nmr to measure changes in the liquid water content of sediment and rock resulting from methane hydrate formation hydrates were artificially formed at the seafloor by introducing methane into tubes containing sediments or rock saturated with seawater after several weeks the samples were visited by a remotely operated vehicle on which nmr equipment was mounted reduction of the nmr signal indicated hydrate had formed in the sample within a well defined measurement volume hydrate content determined by nmr quantitatively predicted the volume of methane gas evolved during subsequent dissociation

methane hydrate and free gas on the blake ridge from vertical seismic profiling seismic velocities measured in three drill holes through a gas hydrate deposit on the blake ridge offshore south carolina indicate that substantial free gas exists to at least 250 meters beneath the bottom simulating reflection bsr both methane hydrate and free gas exist even where a clear bsr is absent the low reflectance or blanking above the bsr is caused by lithologic homogeneity of the sediments rather than by hydrate cementation the average methane hydrate saturation above the bsr is relatively low 5 to 7 percent of porosity which suggests that earlier global estimates of methane in hydrates may be too high by as much as a factor of 3

sem based quantitative mineralogical analysis of peridotite kimberlite and concentrate abstract quantitative automated mineralogy is the acquisition of mineralogical and textural data by scanning electron microscopy based energy dispersive analytical methods the technique is used in the metals and energy resource extraction industries to provide accurate mineral characterization information over large data sets we have employed this method to three projects related to diamonds mantle peridotite kimberlite and garnet concentrate the first example assesses the metasomatic clinopyroxene phlogopite modal mineralogy in peridotite xenoliths from premier cullinan south africa understanding mantle mineral variability can be coupled with measureable mineral properties to develop mantle geophysical and geochemical models the second example compares kimberlites from letseng satellite pipe lesotho and ngamiland botswana to assess the variability of kimberlite mineralogy kimberlite domains can be identified on a micro scale with potential to understand parameters such as hardness and grindability or to identify kimberlite clusters with discrete mineral assemblages the third example applies mineral compositional variability in garnet concentrate samples as a possible tool for evaluating exploration projects application of garnet definitions to concentrates through digitally grouping grains into discrete populations results in improved understanding of large sample populations and hence diamond prospectivity quantitative mineralogy applied to diamond related projects utilizes the principles of geometallurgy in evaluating large data sets for greater understanding of the variability of mantle materials

a geostatistical approach to mapping site response spectral amplifications article if quantitative estimates of the seismic properties do not exist at a location of interest then the site response spectral amplifications must be estimated from data collected at other locations currently the most common approach employs correlations of site class with maps of surficial geology analogously correlations of site class with topographic slope can be employed where the surficial geology is unknown our goal is to identify and validate a method to estimate site response with greater spatial resolution and accuracy for regions where additional effort is warranted this method consists of three components region specific data collection a spatial model for interpolating seismic properties and a theoretical method for computing spectral amplifications from the interpolated seismic properties we consider three spatial interpolation schemes correlations with surficial geology termed the geologic trend gt ordinary kriging ok and kriging with a trend kt we estimate the spectral amplifications from seismic properties using the square root of impedance method thereby linking the frequency dependent spectral amplifications to the depth dependent seismic properties thus the range of periods for which this method is applicable is limited by the depth of exploration a dense survey of near surface s wave slowness ss throughout kobe japan shows that the geostatistical methods give more accurate estimates of ss than the topographic slope and gt methods and the ok and kt methods perform equally well we prefer the kt model because it can be seamlessly integrated with geologic maps that cover larger regions empirical spectral amplifications show that the region specific data achieve more accurate estimates of observed median short period amplifications than the topographic slope method

bottom current controlled sedimentation and mass wasting in the northwestern sea of okhotsk abstract quaternary sedimentation in the northwestern sea of okhotsk where tidal and thermohaline currents are active was studied using 8443 km of high resolution air gun profiles from four cruises it is characterized by 1 bottom current controlled processes which lead to widespread deposition of contourite drifts and sediment waves on the north okhotsk continental margin and the northernmost sakhalin slope as well as to erosion and sediment reworking on the northern sakhalin shelf 2 mass wasting triggered probably by shallow earthquakes by gas hydrate instability during sea level lowstands leading to slumps and debris flows in the western derugin basin 3 deposition of the fluvial load of the river amur which results in sediment drift bodies and prograding lowstand wedges during glacial periods and to contourite drifts and a fan during interglacial times and 4 ice rafted detritus and hemipelagic sedimentation interrupted by episodic turbidity current activity especially in the derugin basin and its northern eastern and southern flanks

late holocene foraminifera of blake ridge diapir assemblage variation and stable isotope record in gas hydrate bearing sediments abstract the presence of gas hydrates on the blake ridge diapir northeastern atlantic ocean offers an opportunity to study the impact of methane seepage on the ecology and geochemistry of benthic foraminifera in the late holocene three push cores covering a time span of 1000 yrs were retrieved from three distinct microhabitats at the top of the diapir at a water depth of 2150 m i sediments away from seepage control core ii sediments overlain by clusters of methanotrophic and thiotrophic bivalves and iii chemoautotrophic microbial mats the foraminiferal assemblages at the two seep sites are marked by a reduction in benthic foraminiferal species diversity coupled with a near absence of agglutinated species however an opportunistic population rise in ch4 or h2s tolerant calcareous species e g globocassidulina subglobosa and cassidulina laevigata that utilize the abundant trophic resources at the seeps has led to an increase in the overall assemblage density there the 18o and 13c values of three species of benthic foraminifera gyroidinoides laevigatus globocassidulina subglobosa and uvigerina peregrina and the planktonic species globorotalia menardii were acquired from all three cores the benthic species from methane seeps yield 13c values of 0 1 to 4 2 vpdb that are distinctly more 13c depleted relative to the 13c of 0 4 to 1 0 vpdb at the control off seep site the species from a mussel bed site exhibit more negative 13c values than those from microbial mats possibly reflecting different food sources and higher rate of anaerobic oxidation of methane the positive 13c values in the paired planktonic species suggest that authigenic carbonate precipitation did not overprint the observed 13c depletions hence the probable cause of negative 13c of benthic foraminifera is primary calcification from dissolved inorganic carbon dic containing mixed carbon fractions from a highly 13c depleted microbially oxidized methane and b a seawater source

diamonds exploration mines and marketing abstract the beauty value and mystique of exceptional quality diamonds such as the 603 carat lesotho promise recovered from the letseng mine in 2006 help to drive a multi billion dollar diamond exploration mining and marketing industry that operates in some 45 countries across the globe five countries botswana russia canada south africa and angola account for 83 by value and 65 by weight of annual diamond production which is mainly produced by four major companies de beers alrosa rio tinto and bhp billiton bhpb which together account for 78 by value and 72 by weight of annual diamond production for 2007 during the last twelve years 16 new diamond mines commenced production and 4 re opened in addition 11 projects are in advanced evaluation and may begin operations within the next five years exploration for diamondiferous kimberlites was still energetic up to the last quarter of 2008 with most work carried out in canada angola democratic republic of the congo drc and botswana many kimberlites were discovered but no new economic deposits were outlined as a result of this work except for the discovery and possible development of the bunder project by rio tinto in india exploration methods have benefitted greatly from improved techniques of high resolution geophysical aerial surveying new research into the geochemistry of indicator minerals and further insights into the formation of diamonds and the relation to tectonic structural events in the crust and mantle recent trends in diamond marketing indicate that prices for rough diamonds and polished goods were still rising up to the last quarter of 2008 and subsequently abruptly sank in line with the worldwide financial crisis most analysts predict that prices will rise again in the long term as the gap between supply and demand will widen because no new economic diamond discoveries have been made recently the disparity between high rough and polished prices and low share prices of publicly traded diamond companies may be due to investors losing patience with the slow pace or absence of new promising discoveries and switching into shares of base metals and fertilizers for agriculture potash and phosphates

glacioeustatic fluctuations the mechanism linking stable isotope events and sequence stratigraphy from the early oligocene to middle miocene one of the most difficult challenges of sequence stratigraphy is the establishment of synchronism between events observed in widely separated basins problems arise because the resolution of the best stratigraphic methods is not good enough to establish the synchronism of similar aged events on a global scale unless a common mechanism affecting global eustasy is assumed such as variations in the ice volume there is no a priori reason to expect that sequences of similar age in widely separated basins are indeed synchronous the stable oxygen isotope composition of marine carbonates is a proxy for sea level which has been underutilized in sequence stratigraphy identification of isotope events is based on d sup 18 o data from dsdp and odp sites 522 529 563 608 and 747 drilled in the atlantic and indian oceans these records were used to define oligocene and miocene oxygen isotope zones in addition we present isotope data from petrobras well a drilled in the campos basin brazil ages of isotope events correspond well with the ages of sequence boundaries and maximum flooding surfaces because of the good correlation between the isotope and sequence stratigraphic records we reconfirm that ice volume change is the common mechanism driving sea level fluctuations from the oligocenemore to present less

natural gas hydrates in the rio grande cone brazil a new province in the western south atlantic the rio grande cone is a large scale fanlike feature in the continental slope of the pelotas basin southern brazil where ubiquitous world class bottom simulating reflectors bsrs are readily observed in seismic records with the purpose of searching for natural gas hydrate deposits in the cone area four oceanographic cruises were carried out between may 2011 and july 2013 leading to the discovery of two pockmark fields active faults and gas hydrates in shallow sediments multichannel seismic multibeam echo sounder side scan sonar and sub bottom profiler records were used to map the shallow section and select sites for piston core sampling gas hydrates were recovered in several piston cores within muddy sediments collected inside pockmarks displaying high backscatter in the multibeam and side scan sonar data we present two representative piston cores where numerous levels of gas hydrates occur along with degassing features authigenic carbonate and soupy sediments gas dissociated from gas hydrate samples is dominantly methane 99 78 with minor quantities of ethane the chemical and isotopic compositions of the gas strongly suggest a biogenic origin for the analyzed samples these new findings are regarded as strong enough evidence to consider the rio grande cone as a new gas hydrate province

evidence for late jurassic release of methane from gas hydrate four late jurassic carbonate successions deposited in the tethys atlantic ocean record a negative carbon isotope excursion of at least 2 the excursion is present in both organic and carbonate carbon records and is comparable in magnitude and duration to isotopic changes during the late paleocene thermal maximum our results indicate that during the late jurassic long considered a warm greenhouse time additional greenhouse gas was input to the atmosphere by a sudden release of methane from buried gas hydrate a potential triggering mechanism may have been the opening of an oceanic gateway through the early atlantic between the ancient tethys and pacific oceans