fast and slow spreading ridges structure and hydrothermal activity ultramafic topographic highs and ch4 output different parts of the world ridge system have quite different morphologies which reflect different constructional processes it appears that hydrothermal circulation at all spreading centers is an important exchange process between the ocean and the newly formed oceanic crust this hydrothermal circulation may vary according to morphology and crustal composition and may also affect ridge constructional processes the tag 26 n and snake pit 23 n hydrothermal sites on the mid atlantic ridge mar display mn ch4 ratios in overlying seawater similar to those of nonsedimented east pacific rise sites i e about 0 2 mol l in contrast large methane anomalies with very low mn ch4 ratios of 0 005 mol l are associated with ultramafic topographic highs near 15 n close to the axis and on ultramafic walls of the rift valley the association of ultramafic bodies and ch4 anomalies in seawater indicates active serpentinization processes ch4 is produced during serpentinization according to the fisher tropsch reaction charlou et al 1991 many ultramafic rock assemblages have been sampled on the mar away from fracture zones in particular by the deep sea drilling project changes of mechanical properties and of density of uplifted deep material in the accreting plate boundary zone caused by serpentinization may play an important role in the construction of slow spreading ridges

hydrothermal activity at the trans atlantic geotraverse hydrothermal field mid atlantic ridge crest at 26 n the first submersible observations of the only known active submarine hydrothermal field on a slow spreading oceanic ridge are incorporated with results of 10 prior years of investigation to derive an understanding of periodicity duration and varying intensity of hydrothermal activity at the trans atlantic geotraverse tag hydrothermal field on the mid atlantic ridge crest near latitude 26 n hydrothermal activity has persisted at this location for at least 1 106 years based on the distribution of hydrothermal and hydrogenous mineralization with respect to crustal age the hydrothermal activity has been cyclic multistage and episodic prior high temperature hydrothermal venting stages with a periodicity of the order of 1 104 years and duration of the order of 101 years are deduced from the estimated ages of discrete sedimentary layers anomalously enriched in cu fe and zn and correspond with the independently determined periodicity of volcanic eruptive cycles on the mid atlantic ridge the most recent episode of high temperature venting is inferred to have ceased in the recent past based on metal enrichment cu fe zn in the surficial sediment layer low temperature hydrothermal venting stages with a duration of the order of 1 104 years intervene between the short high temperature stages and produce stratiform deposits of layered and earthy manganese oxide iron oxide hydroxide and silicate bivalve like forms with the characteristics of vent clams in various stages of dissolution are identified on bottom photographs the fresh appearance of intact tubules composed of iron hydroxide that acted as vents on relict deposits conductive heat flow anomalies in the sediment column and the record of temperature anomalies and excess 3he in the near bottom water column suggest that the low temperature hydrothermal discharge is intermittent at individual vents on a time scale of years

a new fossil vent biota in the ballynoe barite deposit silvermines ireland evidence for intracratonic sea floor hydrothermal activity about 352 ma considerable controversy exists as to the timing of the important mississippian carbonate hosted irish type zn pb ba ag deposits the silvermines deposits have been defined as an end member of this style in that they have been interpreted to display textures indicative of sea floor deposition one of the strongest arguments in favor of this interpretation was the report of a hydrothermal vent field including pyritic chimneys in the ballynoe open pit barite deposit this paper adds to that body of evidence by describing a hydrothermal vent fauna from the same vent field consisting of a delicately pyritized worm tube hosted by massive pyrite and hematized filaments of apparent microbial origin the worm tube is remarkably similar to fossil worm tubes from modern and ancient volcanic hosted massive sulfide deposits and the filamentous microfossils have similarities to modern fe oxidizing bacteria we have found no correlation between the worm tube and normal mississippian fossils such as crinoids whose replacement by pyrite in the immediately underlying ballynoe footwall destroys original morphology the sulfur isotope composition of the worm tube and host pyrite is essentially identical to that of the vent field pyrite and the main sulfide ore stage of silvermines sulfides all having a mean value about 20 per mil indicating an open system bacteriogenic sulfide source these discoveries provide additional evidence for the exhalative nature of parts of the silvermines orebodies and imply that mineralization had begun in the irish ore field by the late tournaisian 352 ma

geomorphology of lake lisan terraces along the eastern coast of the dead sea jordan abstract lake lisan the lake that filled the jordan graben during the last glacial left behind a well developed sequence of erosional and depositional shore terraces in the south east of the current dead sea these terraces record a series of stillstands that were caused by small transgressions within an overall trend of falling lake levels the terraces were observed in places where they had not been identified previously the morphology of the terraces was investigated in six cross sections using differential gps altimetry the levels of the terraces range between 370 and 148 m a s l the high stand of lake lisan at 148 m correlates well with the high level of 150 m reported by bowman and gross bowman d gross t 1992 the highest stand of lake lisan 150 meters below msl israel journal of earth science 41 233 237 along the western coast of lake lisan the lake terraces are horizontal elongated and tectonically undisturbed and have a sub horizontal foreshore tread with an average slope of 8 2 and steep backshore cliff riser with an average slope of 17 7 the six cross sections show a good altitudinal correlation between their terraces moreover the terraces appear in undisturbed continuity on the aerial photos these morphological characteristics demonstrate that the retreat of the lake was a result of substantial climatic changes not of tectonic subsidence in situ stromatolites were found on most of the terraces reflecting a shallow water environment and emphasizing that these terraces are recessional well developed desert varnish and tafoni observed on blocks sitting on the terrace surfaces imply a long period of exposure and a low rate of post lacustrine erosion the formation of lisan terraces is constrained mainly by coastal slope water depth and underlying lithology the morphological analysis of these terraces allows identification of two kinds of pseudo terraces which were formed as a result of tread or riser destruction u th and osl dating allowed the dating of three events within the lake level curve more precisely the high level of 148 m occurred at 30 5 0 22 ka bp consistent with the heinrich event 3 and dansgaard oeschger stadial 5 the coldest period in the ngrip greenland ice core record the next lower terrace at 154 m was formed at 22 9 ka bp 0 29 and corresponds to the stadial 2c the final phase of the last high glacial the correlation between the lisan high stands and climatic stadials suggests that northern hemispheric cold periods led to periods with a more positive water balance in the near east at 10 0 8 ka bp lake lisan experienced a sharp drop to 200 m followed by a transgression between 9 5 to 7 ka bp

north sea rift system abstract the mesozoic north sea rift forms an integral part of the arctic north atlantic rift system rifting activity in the north sea commenced during the earliest triassic during the mid jurassic the central north sea underwent a temporary doming stage crustal extension peaked during the late jurassic earliest cretaceous abated subsequently and terminated altogether during the paleocene the saucer shaped cenozoic post rift basin straddles the axis of the viking and central grabens this speaks for the applicability of a depth dependent pure shear model rather than a simple shear model geophysical data indicate an important discrepancy between upper and lower crustal attenuation across the north sea rift suggesting that during rifting processes the mono discontinuity was seriously destabilized this requires a basic modification of currently favoured crustal stretching models

provenance of pliocene sediments and paleoenvironmental changes in the southern north sea region using samarium neodymium sm nd provenance ages and clay mineralogy abstract an 800 m thick sedimentary succession from the late pliocene north sea has been investigated on the provenance of the sediments and on changes of the source regions related to transport processes and climate changes the lower zanclean to piacenzian part of the succession from 1250 to 1050 m depth and the middle early gelasian part from 1100 to 700 m depth belong to one distributory system with at least two contributing source areas provenance ages calculated on basis of sm nd content indicate one old archean and one young

relict hydrothermal zones in the tag hydrothermal field mid atlantic ridge 26 n 45 w two relict hydrothermal zones were delineated between water depths of 3400 and 3500 m at the lower part of the east wall of the rift valley of the mid atlantic ridge in the tag hydrothermal field using a deep towed side scan sonar tow and a camera temperature tow along the northern 3 km of the wall and a submersible transect named the north and mir relict zones they are located about 4 km and 2 km northeast respectively of the known active high temperature sulfide mound between water depths of 3625 and 3670 m on the rift valley floor near the base of the east wall the north zone extends about 2 km along the northern end of the lower east wall the zone includes two moundlike features up to 30 m high by 200 m in diameter imaged by side scan sonar within a 2 km long line of discontinuous hydrothermal deposits comprising inactive toppled and standing chimneys layered material and patchy dark stains on sediment photographed by the camera temperature tow several other moundlike features were imaged with the side scan sonar outside of the photographic coverage the mir relict hydrothermal zone 2 km south of the north zone named after the mir submersible used to investigate it consists of three subzones 1 a 200 m wide area of diverse types of hydrothermal materials exposed by normal faulting at its western margin 2 a 400 m wide by 700 m long central area of discrete groups of toppled and standing inactive sulfide chimneys up to 25 m high on a substrate of red metalliferous sediment and carbonate lutite spires sampled on the highest chimneys are composed of coarse grained recrystallized sulfides dominated by pyrite and chalcopyrite which contain the first primary free gold grains 2 3 m diameter found at a hydrothermal site on a mid ocean ridge and 3 a 150 m wide hummocky area of layered hydrothermal material with the appearance of low temperature precipitates and carbonate lutite with patchy dark stains at its eastern margin the active sulfide mound the north zone and the mir zone are each located on the fractured western margins of gentle dome shaped areas of pillow flows typically 500 m in diameter interpreted as summits of volcanic centers that may have supplied heat to drive adjacent hydrothermal activity the distribution and size of the active and inactive hydrothermal zones of the tag field the chronology and the characteristics of relict samples recovered indicate a history of at least 100 103 years of high temperature hydrothermal episodes with multiple overprinting stages of mineralization accompanied by alteration

mid ocean ridges fine scale tectonic volcanic and hydrothermal processes within the plate boundary zone a first order model of spreading centers as idealized linear boundaries of crustal and lithospheric generation provides only a gross understanding of global scale plate kinematics as we attempt to understand the complexity of crustal and lithospheric structure of two thirds of the earth s surface it is becoming increasingly necessary to study the tectonic volcanic and hydro thermal processes within the spreading center plate boundary zone all ocean ic crust bears the imprint of these processes this review focuses on a few selected topics concernining the fine scale tectonics and geophysics of the active axial zone of mid ocean ridges with reference to associated volcanic and hydrothermal processes it draws heavily on recent studies that use deeply towed instrument packages multi beam bathymetric mapping ocean bottom instruments and alvin e g the famous amar rise and galapagos expeditions we begin with a review of the large scale structure of spreading centers we then take a close look at the axial neovolcanic zone and progress away from the axis through the active tectonic zones next we consider the characteristics of the axial magma chamber and associated hydrothermal actvity as well as the generation of magnetic anomaly stripes and their implications for crustal generation one of our findings is that the initial two dimensional model of volcanic and tectonic zones must be expanded upon to allow for variations

latest pleistocene glacial chronology of the uinta mountains support for moisture driven asynchrony of the last deglaciation abstract recent estimates of the timing of the last glaciation in the southern and western uinta mountains of northeastern utah suggest that the start of ice retreat and the climate driven regression of pluvial lake bonneville both occurred at approximately 16 cal ka to further explore the possible climatic relationship of uinta mountain glaciers and the lake and to add to the glacial chronology of the rocky mountains we assembled a range wide chronology of latest pleistocene terminal moraines based on seventy four cosmogenic 10be surface exposure ages from seven glacial valleys new cosmogenic exposure ages from moraines in three northern and eastern valleys of the uinta mountains indicate that glaciers in these parts of the range began retreating at 22 20 ka whereas previously reported cosmogenic exposure ages from four southern and western valleys indicate that ice retreat began there between 18 and 16 5 ka this spatial asynchrony in the start of the last deglaciation was accompanied by a 400 m east to west decline in glacier equilibrium line altitudes across the uinta mountains when considered together these two lines of evidence support the hypothesis that lake bonneville influenced the mass balance of glaciers in southern and western valleys of the range but had a lesser impact on glaciers located farther east regional scale variability in the timing of latest pleistocene deglaciation in the rocky mountains may also reflect changing precipitation patterns thereby highlighting the importance of precipitation controls on the mass balance of pleistocene mountain glaciers

different tdm ch4 hydrothermal plume signatures tag site at 26 n and serpentinized ultrabasic diapir at 15 05 n on the mid atlantic ridge as a part of the 1988 noaa vents program ch4 and mn tracers were used to identify and compare hydrothermal plumes found above the tag field 26 n and in the rift valley at 15 n close to the eastern intersection of the ridge axis with the 15 20 n fracture zone at the mid atlantic ridge mar active hydrothermal venting was confirmed at tag based on elevated concentrations of total dissolved mn tdm up to 30 nmol kg high ch4 concentrations up to 200 nl l and elevated nephelometry signals plumes of a different composition were identified at 15 n with high ch4 concentrations up to 400 nl l low total dissolved mn concentrations tdm 1 nmol kg and no significant nephelometry signal the different properties of these tracers and the different tracer ratios can be used to deduce vent fluid characteristics and compare one hydrothermal area to another tdm ch4 and nephel ch4 ratios at tag are of the same order of magnitude as those observed at other spreading axis hydrothermal fields at 15 n the low tdm ch4 ratio provides evidence of fluid circulation into ultrabasic rocks and offers a potentially useful and single method of exploring for hydrothermal activity associated with serpentinization mantle degassing through hydrothermal activity associated with serpentinization is an important process with respect to chemical and thermal exchanges between the upper mantle and the ocean different ratios of hydrothermal tracers i e tdm ch4 provide a useful framework for identifying subseafloor processes along mid oceanic ridges

isotope paleoecology of episodic mid to late holocene bison population expansions in the southern plains u s a abstract we used a xad purified ams radiocarbon method to date 62 bison specimens from different contexts on the very southern extent of the great plains of north america to produce a precise chronology of bison population expansions spanning the last 6000 years sixty one of these samples provide stable carbon and nitrogen isotope data indicating relative temperature and moisture conditions during intervals defined by the presence of bison within this time span this chronology indicates climatic conditions favorable to bison were present in the greater central texas area including the uplifted edwards plateau and extending to the coastal plain during periods from 5955 to 5815 3290 to 3130 2700 to 2150 and 650 to 530 cal bp however isotope results suggest climatic conditions differed for each period the earliest calf creek period was characterized by cool but dry conditions the later late archaic 1 2 periods were increasingly warmer and wetter and the latest toyah period was cooler and drier than the late archaic periods but warmer and wetter than calf creek both the calf creek and toyah periods had higher variability within these overall trends comparison with regional records suggests that these periods represent variation within generally cool dry climates human adaptive response to increased bison availability resulted in significant cultural changes across all four periods

tropical climates at the last glacial maximum a new synthesis of terrestrial palaeoclimate data i vegetation lake levels and geochemistry palaeodata in synthesis form are needed as benchmarks for the palaeoclimate modelling intercomparison project pmip advances since the last synthesis of terrestrial palaeodata from the last glacial maximum lgm call for a new evaluation especially of data from the tropics here pollen plant macrofossil lake level noble gas from groundwater and delta 18 o from speleothems data are compiled for 18 2 ka c 14 32 degrees n 33 degrees s the reliability of the data was evaluated using explicit criteria and some types of data were re analysed using consistent methods in order to derive a set of mutually consistent palaeoclimate estimates of mean temperature of the coldest month mtco mean annual temperature mat plant available moisture pam and runoff p e cold month temperature mat anomalies from plant data range from 1 to 2 k near sea level in indonesia and the s pacific through 6 to 8 k at many high elevation sites to 8 to 15k in s china and the se usa mat anomalies from groundwater or speleothems seem more uniform 4 to 6 k but the data are as yet sparse a clear divergence between mat and cold month estimates from the same region is seen only in the se usa where cold air advection is expected to have enhanced cooling in winter regression of all cold month anomalies against site elevation yielded an estimated average cooling of 2 5 to 3 k at modern sea level increasing to approximate to 6 k by 3000m how ever neotropical sites showed larger than the average sea level cooling 5 to 6 k and a non significant elevation effect whereas w and s pacific sites showed much less sea level cooling 1 k and a stronger elevation effect these findings support the inference that tropical sea surface temperatures ssts were lower than the climap estimates but they limit the plausible average tropical sea surface cooling and they support the existence of climap like geographic patterns in sst anomalies trends of pam and lake levels indicate wet lgm conditions in the w usa and at the highest elevations with generally dry conditions elsewhere these results suggest a colder than present ocean surface producing a weaker hydrological cycle more arid continents and arguably steeper than present terrestrial lapse rates such linkages are supported by recent observations on freezing level height and tropical ssts moreover simulations of greenhouse and lgm climates point to several possible feedback processes by which low level temperature anomalies might be amplified aloft

late quaternary vegetation history of rough canyon south central new mexico usa abstract south central new mexico usa at the junction of the rocky mountains high plains and chihuahuan desert is one of the better known regions in the late quaternary of north america plant macrofossils and pollen from a packrat midden series in rough canyon new mexico allows refinement of plant distributions and paleoclimates in this transitional area since full glacial times from 17 000 to 12 000 14c yr bp pinus edulis juniperus scopulorum woodlands dominated limestone substrates between 1800 and 1490 m with pseudotsuga menziesii and other mixed conifer species restricted to shady north facing slopes juniperus deppeana the dominant juniper today above 2000 m in southern new mexico is conspicuously absent from glacial middens and must have been displaced south of the us mexico border the minimum climatic conditions for p edulis j scopulorum woodlands are ca 20 wetter and 3 5 5 c cooler july mean maximum temperatures than the modern climate at rough canyon holocene warming drying may have started as early as 12 000 14c yr bp with the extirpation of j scopulorum from rough canyon and was completed by at least 10 54014c yr bp the record for arrivals of some desert species is confounded by traces of pollen and macrofossils in some of the glacial middens which could signify either earliest occurrence or temporal mixing contamination of assemblages ams 14c dating can discriminate between early arrival and contamination in midden macrofossils but not in pollen ams dates show that choisya dumosa presently near its northern cold limits at rough canyon endured late glacial winters possibly as clonal populations some larrea tridentata leaves and pollen occur in middens dominated by conifers and oaks no longer at the site an ams date of 3205 14c yr bp on larrea leaves from one midden indicates contamination evidence for some macrofossil contamination however does not rule out the possibility that pollen of desert elements e g larrea prosopis in late glacial early holocene middens indicates their presence in the tularosa basin well ahead of their local appearance in rough canyon finally the increasing dominance of desert elements after 5000 14c yr bp in the rough canyon series and elsewhere in the northern chihuahuan desert could reflect slow postglacial migration from the south and or progressive encroachment with gradual stripping of soils formed during the last glacial period

spatial variability of late quaternary paleoclimates in the western united states abstract paleoclimatic interpretation of proxy data is complicated sometimes by the appearance of heterogeneous patterns of climatic responses across networks of sites modern climate analogues for the western united states similar to those patterns of atmospheric circulation of 18 000 and 9000 yr b p were examined in order to explain such patterns of spatial heterogeneity modern analogues were defined by comparing modern atmospheric circulation patterns with those simulated by general circulation models maps of temperature and precipitation anomalies of the modern analogues reveal patterns of spatial heterogeneity which resemble the patterns of effective moisture compiled from paleoclimatic data january 1957 was found to be a reasonable 18 000 yr b p analogue and it features isolated areas of increased wetness in the northern great basin and increased dryness in the northwest interior analogues for 9000 yr b p from a composite of 11 augusts display patterns of spatial heterogeneity of effective moisture over most of the mountainous areas the analogues suggest that spatial heterogeneity of climate is the rule rather than the exception over much of the western united states with the climatic anomalies at any particular time representing the outcome of the mediation of large scale atmospheric circulation controls by smaller scale topographic features

hydrothermal circulation serpentinization and degassing at a rift valley fracture zone intersection mid atlantic ridge near 15 n 45 w a hydrothermal system characterized by high ratios of methane to both manganese and suspended particulate matter was detected in seawater sampled at the eastern intersection of the rift valley of the mid atlantic ridge with the fifteen twenty fracture zone this finding contrasts with low ratios in black smoker type hydrothermal systems that occur within spreading segments near bottom water sampling coordinated with seabeam bathymetry and camera temperature tows detected the highest concentrations of methane at fault zones in rocks with the appearance of altered ultramafic units in a large dome that forms part of the inside corner high at the intersection the distinct chemical signatures of the two types of hydrothermal systems are inferred to be controlled by different circulation pathways related to reaction of seawater primarily with ultramafic rocks at intersections of spreading segments with fracture zones but with mafic rocks within spreading segments

the effects of late quaternary climate and pco2 change on c4 plant abundance in the south central united states the late quaternary was a time of substantial environmental change with the past 70 000 years exhibiting global changes in climate atmospheric composition and terrestrial floral and faunal assemblages we use isotopic data and couple climate and vegetation models to assess the balance between c3 and c4 vegetation in texas during this period the carbon isotope composition of fossil bison mammoth and horse tooth enamel is used as a proxy for c3 versus c4 plant consumption and indicates that c4 plant biomass remained above 55 through most of texas from prior to the last glacial maximum lgm into the holocene these data also reveal that horses did not feed exclusively on herbaceous plants consequently isotopic data from horses are not reliable indicators of the c3 c4 balance in grassland biomes estimates of c4 percentages from coupled climate vegetation models illuminate the relative roles of climate and atmospheric carbon dioxide co2 concentrations in shaping the regional c4 signal c4 percentages estimated using observed modern climate vegetation relationships and late quaternary climate variables simulated by a global climate model are much lower than those indicated by carbon isotope values from fossils when the effect of atmospheric co2 concentration on the competitive balance between c3 and c4 plants is included in the numerical experiment however estimated c4 percentages show better agreement with isotopic estimates from late quaternary mammals and soils this result suggests that low atmospheric co2 levels played a role in the observed persistence of c4 plants throughout the late quaternary

understanding geomorphic responses to environmental change a 19 000 year case study from semi arid central texas usa understanding the impact of past climatic changes on landscape stability is crucial in order to predict and mitigate the effects of future changes however in arid and semi arid environments reconstructions are often hampered by a poor understanding of the relationship between sediment deposition and climate we present here data from central texas a region that is sensitive to environmental change but has received relatively little attention the study integrates a chronology of 29 optically stimulated luminescence osl ages from six sedimentary sites in a range of depositional contexts with a 19 000 a climate record derived from pollen extracted from the adjacent boriack bog by comparing the two records we aimed to assess the relationship between climate change and geomorphic activity data show that extensive aeolian and colluvial deposition occurred during the mid to late holocene with sedimentation generally increasing during more arid phases however a number of depositional events on slopes were associated with moister episodes and sediment was also deposited in a summit setting immediately after phases of increased precipitation linkages between climate change and geomorphic response were therefore complex being controlled by both sediment supply and transport energy the climatic fluctuations identified in the boriack bog record highlight the sensitivity of central texas to environmental change while disparities in conditions recorded between it and other palaeoenvironmental sites in the southern usa emphasise the need for further work in order to enhance understanding of landscape sedimentary response to climate copyright c 2010 john wiley sons ltd

the internal structure of fault zones in basaltic sequences abstract normal faults in basalt along mid ocean ridges and continental rifts play a major role in the formation of topography advection of fluids and the dynamics of biosphere however almost nothing is known of the internal structure of volcanic growth faults at depth where many key processes take place in this paper we present the results of scaled model experiments validated against outcrop studies of a volcanic growth fault system on hawai i the analogue model uses cohesive hemihydrate powder with carefully characterized physical properties a cohesion of 62 pa friction angle of 0 71 and tensile strength of 33 pa imply a length scaling ratio of 1 5000 50 000 between the model and the upper part of extending oceanic crust with a basalt column above a normal fault time lapse imagery high resolution particle image velocimetry and field observations show ground flexure in an initial elastic stage before subvertical mode i fissures propagate from the surface downwards some of the mode i fractures become inactive while others develop into massively dilatant normal faults the dominant processes within the faults are brecciation block rotation and gravitational transport of fragments along the fault maintaining meter sized cavities to a depth of several hundred meters even when these volcanic growth faults are resurfaced a pervasive dilatancy persist within the system if circulating seawater provides a sufficient oxygen supply the large cavities in normal faults at mid ocean ridges could harbour large ocean floor life forms to several hundred meters depth

variations in flow and transport in thick desert vadose zones in response to paleoclimatic forcing 0 90 kyr field measurements modeling and uncertainties 1 an understanding of unsaturated flow and potential recharge in interdrainage semiarid and arid regions is critical for quantification of water resources and contaminant transport we evaluated system response to paleoclimatic forcing using water potential and cl profiles and modeling of nonisothermal liquid and vapor flow and cl transport at semiarid high plains texas and arid chihuahuan desert texas amargosa desert nevada sites infiltration in response to current climatic forcing is restricted to the shallow 0 3 3 m subsurface subsurface cl accumulations correspond to time periods of 9 90 kyr bulge shaped cl profiles generally represent accumulation during the holocene 9 16 kyr lower cl concentrations at depth reflect higher water fluxes 0 04 8 4 mm yr during the pleistocene and earlier times low water potentials and upward gradients indicate current drying conditions nonisothermal liquid and vapor flow simulations indicate that upward flow for at least 1 2 kyr in the high plains and for 12 16 kyr at the chihuahuan and amargosa desert sites is required to reproduce measured upward water potential gradients and that recharge is negligible 0 1 mm yr in these interdrainage areas index terms 1809 hydrology desertification 1815 hydrology erosion and sedimentation 1833 hydrology hydroclimatology keywords paleoclimate chloride mass balance unsaturated zone unsaturated flow modeling

short duration holocene lakes in the mojave river drainage basin southern california stratigraphic sedimentologic and pedologic studies of beach ridge and lacustrine deposits indicate that up to five times during the holocene shallow lakes covered silver lake playa in southeastern california for periods of years to decades the two youngest lacustrine events at about 390 90 yr b p and 3620 70 yr b p coincide with the early and late neoglacial episodes of north america increasing evidence in recent years from other nonglaciated areas leads us to conclude that the effects of these climatic episodes were much more widespread than previously thought the climate during these episodes was characterized by an increased frequency of winter storms in the southwestern united states causing wetter conditions that affected diverse hyperarid environments in the mojave desert and adjacent regions we propose that this wide areal coverage was caused by large scale winter atmospheric circulation patterns which are probably related to changes in sea surface temperatures and oceanic circulation in the eastern north pacific ocean

early jurassic hydrothermal vent community from the franciscan complex san rafael mountains california the figueroa massive sulfide deposit located in franciscan complex rocks in the san rafael mountains of california preserves the only known jurassic hydrothermal vent fossils the figueroa fossil assemblage is specimen rich but of low diversity and comprises in order of decreasing abundance vestimentiferan worm tubes the rhynchonellid brachiopod anarhynchia cf gabbi and a species of nododelphinulid gastropod the figueroa fossil organisms lived at a deep water high temperature vent site located on a mid ocean ridge or seamount at an equatorial latitude the fossil vent site was then translated northwestward by the motion of the farallon plate and was subsequently accreted to its present location an iron silica exhalite bed the probable lateral equivalent of the figueroa deposit contains abundant filamentous microfossils with two distinct morphologies and probably represents a lower temperature diffuse flow environment the figueroa fossil community was subject to the same environmental conditions as modern vent communities but it is unique among modern and other fossil vent communities in having rhynchonellid brachiopods

young volcanism and related hydrothermal activity at 5 s on the slow spreading southern mid atlantic ridge the effect of volcanic activity on submarine hydrothermal systems has been well documented along fast and intermediate spreading centers but not from slow spreading ridges indeed volcanic eruptions are expected to be rare on slow spreading axes here we report the presence of hydrothermal venting associated with extremely fresh lava flows at an elevated apparently magmatically robust segment center on the slow spreading southern mid atlantic ridge near 5 s three high temperature vent fields have been recognized so far over a strike length of less than 2 km with two fields venting phase separated vapor type fluids exit temperatures at one of the fields reach up to 407 c at conditions of the critical point of seawater the highest temperatures ever recorded from the seafloor fluid and vent field characteristics show a large variability between the vent fields a variation that is not expected within such a limited area we conclude from mineralogical investigations of hydrothermal precipitates that vent fluid compositions have evolved recently from relatively oxidizing to more reducing conditions a shift that could also be related to renewed magmatic activity in the area current high exit temperatures reducing conditions low silica contents and high hydrogen contents in the fluids of two vent sites are consistent with a shallow magmatic source probably related to a young volcanic eruption event nearby in which basaltic magma is actively crystallizing this is the first reported evidence for direct magmatic hydrothermal interaction on a slow spreading mid ocean ridge

evidence from western north america for rapid shifts in climate during the last glacial maximum the estancia basin in southwestern united states contains evidence for strong and rapid pulsations in the supply of moisture brought into the region during the last ice age the pulses were recorded during episodes of stream discharge that spread plumes of fresh water laden with quartz sand over the saline lake the largest pulses in stream discharge lasted only a few decades were organized into cycles that were spaced approximately 200 to 250 and 2000 years apart and were of sufficient magnitude to freshen and maintain the lake at its maximum recorded elevation

fossil clams from a serpentinite hosted sedimented vent field near the active smoker complex rainbow mar 36 13 n insight into the biogeography of vent fauna hydrothermal circulation at ultramafic hosted sites supports a large variety of high and low temperature hydrothermal vents and associated ecosystems the discovery of abundant fossil vesicomyid and thyasirid shell accumulations at the ridge crest approximately 2 5 km east of the active rainbow vent field on the mid atlantic ridge mar 36 degrees 13 n increased our knowledge regarding the diversity of vent communities at slow spreading ridges bivalve molluscs of the family vesicomyidae were represented by the genus phreagena here we present the first record of this genus in the atlantic ocean this second vesicomyid species known from the mar phreagena sp was found to be associated with a thyasira species that is affiliated with t southwardae at the logatchev vent field on the mar and with t vulcolutre in the gulf of cadiz these two clams have close relationships with seep taxa along the continental margin and were likely associated with sedimented vent fields delta o 18 and delta c 13 analyses of the shells suggested that the burrowing bivalve thyasira could incorporate isotopically light carbon derived from the oxidation of methane in the sediment while the signature of phreagena sp shells denoted a different carbonate source c 14 dating of the shells denoted that the hydrothermal activity in the rainbow area began at least similar to 25 5 kyr bp which is similar to the model of the hydrothermal vent field distribution that was proposed for the logatchev hydrothermal site the results provide new insight regarding the diversity of chemosynthetic fauna on the mar over geologic time ultramafic hosted on axis sedimented vent fields extend the range of habitats for chemosynthetic communities underlying the need to further explore the geology of these types of environments on slow spreading ridges and to determine their role in the ecology of deep sea vent communities

late quaternary lacustrine history and paleoclimatic significance of pluvial lake cochise southeastern arizona abstract during the latest quaternary freshwater pluvial lakes intermittently formed in the topographically closed willcox basin arizona a lacustrine sequence of six separate high stands of lake cochise is documented by stratigraphic studies 19 radiocarbon ages and supplementary evidence two stands of pluvial lake cochise older than 14 000 yr b p reached elevations above 1290 m the prominent 1274 m shoreline of lake cochise which circumscribes the basin was largely created during a high stand between 13 750 and 13 400 yr b p during the holocene water filled the willcox basin three times to an elevation slightly below the crest of the 1274 m shoreline this occurred once during the early holocene around or before 8900 yr b p and twice during the later part of the middle holocene since the middle holocene only shallow ephemeral lakes have occupied the deflated central portion of ancient lake cochise a depression known as the willcox playa the lacustrine sequence of lake cochise provides an independent evaluation of late quaternary paleoclimatic reconstructions for southern arizona and the american southwest

timing and extent of late quaternary paleolakes in the trans pecos closed basin west texas and south central new mexico abstract the trans pecos closed basin is a hydrographically closed region covering 20 000 km 2 centered on salt basin 160 km east of el paso texas geomorphic and limnetic evidence have been used to identify four major highstands for lake king during the last glacial maximum lgm additional geomorphic features from a second recently identified paleolake lake sacramento have been found in the beargrass subbasin a nested subbasin approximately 75 km northwest of salt basin radiocarbon ages of the organic material in lake king sediments date four abrupt climate changes and rapid lacustrine transgressions during the lgm with a quasi periodicity of 2000 yr geomorphic evidence in the beargrass subbasin identifies lake cycles contemporaneous with those in lake king the dates for these transgressions correlate with the dates of freshening events identified by researchers in paleolake basins elsewhere in new mexico the quasi periodicity of the events approximates that of dansgaard oeschger events identified from greenland ice cores the contemporaneity of the trans pecos transgressions with transgressive events in other basins in the region suggests that paleolakes in the region were in phase with respect to abrupt climate changes during the latter stages of the lgm

the influence of hydrothermal fluid composition and advection rates on black smoker chimney mineralogy insights from modeling transport and reaction abstract a detailed study of black smoker chimneys was carried out by drawing together mineralogical observations and measured fluid compositions the modeling technique which establishes a link between vent fluid chemistry and vent deposit mineralogy is used to examine the influence of the physical environment on transport across short length scales centimeters which are subject to steep thermal 350 c and chemical gradients and to predict saturation states of minerals as functions of position within chimney walls owing to short length scales steep gradients and constancy of bounding fluid compositions concentration profiles are controlled by transport the effect of reaction rates on profiles is assumed to be negligible precipitation at points within the chimney wall is thus kinetically controlled local equilibrium does not apply and precipitation must be suppressed when calculating distributions of species and saturation states of minerals model calculations are performed in a series of four steps the first is speciation of measured fluid compositions at in situ temperature and pressure conditions results of calculations are plotted on stability diagrams of log fo2 log f s2 and log fo2 log a fe 2 a cu 2 to examine how closely the predicted saturation states fit with observations of minerals coexisting with the hydrothermal fluid at the vent sites the second step is calculation of heat and mass transport across the chimney wall the third is speciation of the pore fluid compositions calculated to exist in the wall subsequent to transport and the fourth is comparison of calculated mineral saturation states to observations of naturally occurring chimney samples application of the modeling technique to five vent sites which exhibit distinct fluid compositions allows reproduction of observed mineralogy model results demonstrate the sensitivity of geochemical processes to the physical environment porosity tortuosity permeability mineral composition to rates of advection of seawater inward or hydrothermal fluid outward across chimney walls and to endmember fluid composition

high frequency sequence stratigraphy of upper cenozoic deposits in the central and southeastern north sea areas abstract during late cenozoic times southwestward prograding deposits filled in the central and southern part of the epicontinental north sea basin the ringkobing fyn high acted as a topographical high partly separating the central and southeastern north sea into two embayments which were connected towards the west by a deeper seaway located in the central graben area the stratal geometry deduced from seismic sections indicates different basin physiography subsidence rates and sediment influx between the two embayments eustatic sea level cycles of several frequencies interacted with low subsidence rates in the southern embayment to generate composite relative sea level cycles each composed of relative sea level cycles of higher frequencies forty five upper cenozoic sequences are identified in the southern embayment whereas only 21 sequences are recognized in the northern embayment major hiati and intervals of starved sedimentation may therefore be present in the northern embayment the sequences stack into nine composite sequences each reflecting a depositional cycle representing lowstand succeeded by transgressive highstand conditions in general a composite sequence is characterized by a period of increasing sediment accumulation rates

the shoreline preservation index as a relative age dating tool for late pleistocene shorelines an example from the bonneville basin u s a this paper evaluates the utility of the shoreline preservation index s p i for estimating the age of late pleistocene palaeolake shorelines the relative influence of various factors on shoreline preservation and whether shoreline preservation varies significantly with shoreline aspect sampled shorelines from the 3300 km2 study area which includes the skull tule and puddle valley portions of the lake bonneville basin range in age from approximately 26 to 12 ka their total s p i values range from 23 to 69 per cent average 46 per cent and do not vary significantly with shoreline aspect the data from skull and tule valleys where studied shorelines are of known age are analysed first in order to determine if there are statistically significant associations between variables representing shoreline preservation age degree of geomorphic development and duration of subaerial exposure pairwise correlation is then repeated using observations from all three valleys in order to determine how data from the puddle valley shorelines whose hypothesized ages are not supported by radiocarbon analyses affect the results results show that s p i is useful as a relative age dating tool that the postulated ages of the puddle valley shorelines are ordinally correct and that geomorphic development is not an important influence on the preservation of these late pleistocene shorelines the relative importance of shoreline age and the relative unimportance of duration of subaerial exposure with respect to shoreline preservation suggest that subaqueous processes play a more substantial role in shoreline obliteration than is generally suggested

evidence for younger dryas global climate oscillation and human response in the american southwest whether or not abrupt younger dryas climate change affected regional paleoenvironments and late pleistocene hunter gatherer populations is an important topic in the archaeology of the american southwest this paper reviews multiple age resolved proxy evidence to gauge the magnitude and direction of younger dryas chronozone ydc environmental changes in different settings and systems there is no record of ydc pluvial lake highstands in arizona or new mexico but there are impressive records of vegetation faunal stable isotope and geomorphological change coincident with the ydc these correlate with important adaptive changes in human hunting and land use as revealed in the analysis of the spatiotemporal distribution of late pleistocene hunting technologies clovis and folsom projectile point distributions do not support extant models of paleoenvironmental conditions in these interpretations significant cultural changes that coincide with the ydc include the clovis to folsom transition the demise of mammoth hunting and the development of a highly successful emphasis on bison increased regionalization and the abandonment of the northwestern chihuahuan and the sonoran deserts by mobile big game hunters

pluvial lakes in the great basin of the western united states a view from the outcrop abstract paleo lakes in the western united states provide geomorphic and hydrologic records of climate and drainage basin change at multiple time scales extending back to the miocene recent reviews and studies of paleo lake records have focused on interpretations of proxies in lake sediment cores from the northern and central parts of the great basin in this review emphasis is placed on equally important studies of lake history during the past 30 years that were derived from outcrop exposures and geomorphology in some cases combined with cores outcrop and core records have different strengths and weaknesses that must be recognized and exploited in the interpretation of paleohydrology and paleoclimate outcrops and landforms can yield direct evidence of lake level facies changes that record details of lake level fluctuations and geologic events such as catastrophic floods drainage basin changes and isostatic rebound cores can potentially yield continuous records when sampled in stable parts of lake basins and can provide proxies for changes in lake level water temperature and chemistry and ecological conditions in the surrounding landscape however proxies such as stable isotopes may be influenced by several competing factors the relative effects of which may be difficult to assess and interpretations may be confounded by geologic events within the drainage basin that were unrecorded or not recognized in a core the best evidence for documenting absolute lake level changes lies within the shore nearshore and deltaic sediments that were deposited across piedmonts and at the mouths of streams as lake level rose and fell we review the different shorezone environments and resulting deposits used in such reconstructions and discuss potential estimation errors lake level studies based on deposits and landforms have provided paleohydrologic records ranging from general changes during the past million years to centennial scale details of fluctuations during the late pleistocene and holocene outcrop studies have documented the integration histories of several important drainage basins including the humboldt amargosa owens and mojave river systems that have evolved since the miocene within the active tectonic setting of the great basin these histories have influenced lake levels in terminal basins many pre late pleistocene lakes in the western great basin were significantly larger and record wetter conditions than the youngest lakes outcrop based lake level data provide important checks on core based proxy interpretations we discuss four such comparisons in some cases such as for lakes owens and manix outcrop and core data synthesis yields stronger and more complete records in other cases such as for bonneville and lahontan conflicts point toward reconsideration of confounding factors in interpretation of core based proxies

out of the tropics the pacific great basin lakes and late pleistocene water cycle in the western united states the water cycle in the western united states changed dramatically over glacial cycles in the past 20 000 years higher precipitation caused desert lakes to form which have since dried out higher glacial precipitation has been hypothesized to result from a southward shift of pacific winter storm tracks we compared pacific ocean data to lake levels from the interior west and found that great basin lake high stands are older than coastal wet periods at the same latitude westerly storms were not the source of high precipitation instead air masses from the tropical pacific were transported northward bringing more precipitation into the great basin when coastal california was still dry the changing climate during the deglaciation altered precipitation source regions and strongly affected the regional water cycle

serpentinized ultramafics and hydrothermal activity at the mid atlantic ridge crest near 15 n the initial occurrence of serpentinized ultramafic rocks at the nontransform intersection of a wall of a rift valley with the wall of a fracture zone is described from a site at the fifteen twenty fracture zone the ultramafics crop out in block faulted terrain on the upper portion of the eastern intersection between the rift valley and fracture zone walls in water depths between 2910 and 3300 m they comprise cumulate harzburgites pyroxenites iherzolites and wehrlites as well as gabbronorites olivine gabbronorites gabbropegmatites and alteration products including serpentinites bastite serpentinites and asbestos the ti zr y relations and relatively constant zr ti ratio in basalts recovered with the ultramafic rocks indicate a cogenetic relation from a common magmatic source that has undergone a late stage differentiation in the lower crust ongoing hydrothermal activity is indicated by chemical anomalies 3he mn in the near bottom water at the ultramafic outcrop the upwelling hydrothermal circulation apparently follows crust penetrating faults that may have controlled the diapiric ascent of the serpentinites and that continue to tap degassing magma and or mantle the observations presented indicate that ultramafic cumulates form beneath the rift valley adjacent to long offset 100 km ridge ridge transform faults where they are serpentinized by hydrothermal processes within the initial 1 106 years of generation of lithosphere at a slow spreading axis the corners formed by the intersections of the walls of a rift valley with both the transform rt corner and the nontransform rn corner portions of these fracture zones are principal loci of diapiric emplacement of serpentinized ultramafics

a continuous high resolution record of late pleistocene climate variability from the estancia basin new mexico lake sediments that accumulated in the estancia basin central new mexico provide a detailed record of submillennial latest pleistocene climatic oscillations sedimentologic biologic and geochemical proxies for changes in salinity and lake level were used to identify episodes of wet and dry climate that occurred between 24 and 12 k y b p as dated by 14c by means of accelerator mass spectrometry from shoreline and basin center deposits these dates determine the timing and duration of the episodes of wet and dry climate the lake expanded and contracted repeatedly during the last glacial maximum and fluctuated near its highest elevation several times during the interval ca 20 to 15 k y b p a pronounced lowstand lasting 1 k y occurred between ca 15 and 14 k y b p followed by two more highstands of the lake between ca 14 and 12 5 k y b p desiccation of the perennial lake after 12 k y b p was followed by a final poorly dated highstand at ca 10 k y b p the record of lake level fluctuations from the estancia basin provides a high resolution record of changes in water budget in a basin the comparatively simple physiography and hydrogeology of which ensured a direct response to the strong climatic fluctuations that occurred during the last glacial maximum and termination

deep sea and shallow water hydrothermal vent communities two different phenomena hydrothermal vent communities from 76 areas lying at depths from 0 to 4100 m were split into two groups bdeepq and bshallow waterq based on the occurrence of vent obligate restricted to hydrothermal vents taxa of a high rank genus and family the two groups were then compared based on a large set of environmental faunistic and community parameters the degree of obligacy of fauna sharply changes at the depth of approximately 200 m in 21 shallow water areas located at depths b200 m vent obligate taxa are absent or their taxonomic rank does not exceed a species the total number of vent obligate species in shallow water is 8 and their obligacy is uncertain data from 55 areas lying at depths from 200 to 4100 m indicate there are ca 400 obligate species in 47 of these areas obligate vent taxa of the genus or the family rank are present obligate taxa of the genus rank appear at 200 m depth and of the family rank at 386 m the depth ca 200 m corresponds well with differences in community structure and composition and environmental parameters deep sea n200 m hydrothermal communities differ from shallow water ones b200 m in a much higher ratio of vent obligate taxa deep sea vent communities are also distinguished by the lack of diatom and algae bacterial mats phytoplankton lower species richness the development of large sulphide structures higher role of active vents in structuring communities in space replication of a set of dominant taxa in communities within large regions reproduced through the succession at newly formed vent fields more pronounced concentric and vertical zonality higher biomass of macrofauna the important role of symbiotrophic forms dominating the biomass the ratio of species with a bpointq species range endemic to small areas is higher in the deep sea there are no significant differences between the vent and non vent biogeography both in shallow waters and the deep ocean modern deep sea hydrothermal vent communities have a longer evolutionary history than their shallow water counterparts to explain major differences between deep and shallow water hot vent communities evolutionary processes need to be analysed over long geological periods and within global vertical zones it is suggested that the proportion of organic matter derived from chemosynthesis and photosynthesis plays a crucial role in evolution when calculated for global zones this proportion increases with depth to a certain critical level that separates deep and shallow water hot vent communities and fauna vertical zonation in the distribution of obligate taxa in hydrothermal vent communities indicates that this level is reached at approximately 200 m depth

genetic classification of petroleum systems our genetic classification of petroleum systems is founded on a simple working nomenclature that consists of combining qualifiers from each of the following three categories 1 charge factor supercharged normally charged or undercharged 2 migration drainage style vertically drained or laterally drained and 3 entrapment style high impedance or low impedance the charge factor is estimated on the basis of the richness and volumetrics of mature source rocks the source potential index spi which combines source rock richness and thickness into a single parameter is a convenient shortcut for comparing the petroleum potential of diverse source rocks containing dissimilar kerogen types and for rapidly estimating regional charging capacity in extensively explored basins a positive correlation exists between the magnitude of spi and basin wide petroleum reserves the migration drainage style is determined from the structural and stratigraphic framework of a basin vertical migration drainage which occurs mainly through faults and fracture systems breaching a seal is characteristic of petroleum systems contained within rift basins deltaic sequences salt dome provinces wrench basins and fold and thrust belts in contrast lateral migration drainage is dominant wherever stratigraphically continuous seal reservoir doublets extend over a very large area in a tectonically stable province e g commonly foreland or intracratonic platform basins recognition of the dominant migration style helps to predict the location of zones of petroleum occurrence in relation to the hydrocarbon kitchens the entrapment style which is also dependent on the structural framework and the presence and effectiveness of seals describes the degree of resistance i e impedance working against dispersion of the petroleum charge application of these working concepts should help to significantly reduce geologic risk particularly in new ventures type exploration

hydrothermal activity on the reykjanes ridge the steinaholl vent field at 63 06 n we have completed a systematic survey for hydrothermal activity along the reykjanes ridge from 57 45 n to 63 09 n shipboard determinations of total dissolvable mn tdmn and dissolved si ch4 and h2 have revealed evidence for only one site of hydrothermal activity along this section of ridge crest the steinaholl vent field at 63 06 n 1 our measurements confirm this site to be a stable hydrothermal convection cell of at least two years duration the site is situated in just 250 350 m of seawater and unlike deeper sited vent fields e g tag 3650 m 26 n mar is notable for the formation of bubble rich plumes which have been imaged using a high frequency 38 khz echo sounder high dissolved gas concentrations of up to 18 nmol l ch4 and 30 nmol l h2 coincide with these bubble rich plumes the steinaholl plume is also characterised by high total dissolvable mn tdmn anomalies up to 60 nmol l and dissolved si anomalies 2 mol l yielding molar tdmn ch4 and tdmn si ratios of 3 5 and 0 03 respectively directly comparable to the tag hydrothermal plume the absence of any indication of hydrothermal activity along the remainder of the reykjanes ridge is intriguing between 11 n and 40 n on the mid atlantic ridge previous studies have revealed evidence for hydrothermally active sites approximately every 150 km for the 300 km of ridge crest studied in detail here 750 km total only one site has been found thus despite its proximity to the iceland hot spot the incidence of hydrothermal activity along this section of ridge crest appears to be only 20 50 of that measured elsewhere along the slow spreading mid atlantic ridge

new age data for mid atlantic ridge hydrothermal sites tag and snakepit chronology revisited the chronologies of tag and snakepit hydrothermal fields have been established using 210pb pb 230th 234u and 14c dating at the tag field a mn oxide record indicative of low temperature events began at least 125 000 years and possibly 140 000 years ago with maximum intensities at 15 000 7000 and 4000 years before present high temperature events giving rise to sulfide deposits began about 100 000 years ago and have been intermittent to the present day a presently active site has experienced intermittent pulses of activity every 4000 to 6000 years over the past 20 000 years decrease in activity is often marked by low temperature aragonite precipitation in chimney conduits at 4000 7000 and 9000 years ago after a period of quiescence lasting about 4000 years this site was reactivated about 50 years ago the snakepit field is much younger and no sulfides older than 4000 years have been recovered relict sulfide deposits are dated between 2000 and 4000 years old indicating this site was active during a quiescent period at tag reactivation of snakepit took place about 80 years ago and is presently concurrent with that of tag comparison with hydrothermal sites on the east pacific rise suggests that on slow spreading ridges the major fracture systems focussing the hydrothermal discharge can be reactivated at intervals and new deposits precipitated on top of older ones while on faster spreading ridges each pulse of activity is separated in space and time resulting in discrete deposits

drilling the snake pit hydrothermal sulfide deposit on the mid atlantic ridge lat 23 sup 0 22 n a major high temperature hydrothermal area has been discovered in the mid atlantic ridge rift valley about 25 km south of the kane fracture zone the vent field consists of a wide area 40 000 m sup 2 of dark hydrothermal deposits numerous sulfide chimneys and mounds some up to 11 m high and high temperature black smoker vents ten shallow holes the first ever drilled in an active submarine hydrothermal area recovered friable unconsolidated fe cu fe and zn sulfides and several large fragments of massive sulfide mainly chalcopyrite from the locally thick 13 m hydrothermal deposits the vents are also associated with an unusual biological community of smaller more mobile organisms than reported from the east pacific rise

late pleistocene paleohydrology near the boundary of the sonoran and chihuahuan deserts southeastern arizona usa abstract ground water discharge gwd deposits form in arid environments as water tables rise and approach or breach the ground surface during periods of enhanced effective precipitation where preserved these deposits contain information on the timing and elevation of past ground water fluctuations here we report on the investigation of a series of gwd deposits that are exposed in discontinuous outcrops along a 150 km stretch of the san pedro valley in southeastern arizona near the boundary of the sonoran and chihuahuan deserts chronologic isotopic geochemical faunal assemblage ostracodes and gastropods and sedimentological evidence collectively suggest that the elevation of the regional water table in the valley rose in response to a change in climate 50 ka ago and remained relatively high for the next 35 ka before falling during the bolling allerod warm period rebounding briefly during the younger dryas cold event and falling again at the onset of the holocene the timing of these hydrologic changes coincides closely with variations in 18o values of calcite from a nearby speleothem to the west and changes in lake levels at pluvial lake cochise to the east thus in southeastern arizona the assumption that changes in climate are reflected in all aspects of the hydrologic cycle of a region simultaneously is validated the timing of these changes also broadly coincides with variations in the gisp2 18o record which supports the hypothesis that atmospheric teleconnections existed between the north atlantic and the deserts of the american southwest during the late pleistocene

greenland ice core studies abstract greenland deep ice cores represent continuous sequences of deposits spanning the last up to several hundred thousand years isotopes and impurities in the ice reveal a broad spectrum of information on past environmental conditions in the north atlantic region for example climatic changes in terms of surface temperature and annual precipitation turbidity and chemical composition of the atmosphere including its co 2 concentration volcanic activity and its climatic impact and cosmic radiation flux changes in the past one of the fundamental parameters in ice core studies is the isotopic composition of the ice for example the 18 o concentration on the relative scale which varies in phase with the temperature of snow formation the seasonal variations allow identification of annual layers in the core and hence absolute dating back to at least 8000 yrs b p with some reservations smoothed records may be interpreted in terms of climatic temperature changes cp fig 1 which shows profiles along two deep ice cores from dye 3 southeast greenland and camp century northwest greenland the latter spans all of the last glaciation and the preceding interglacial eem the time scale in units of 10 3 yrs b p has been derived by comparison of the most predominant features with their analogues in sea sediment cores dansgaard et al 1982 the dramatic shifts in times of full glacial severity seem to recur with a quasi periodicity of 2550 yrs perhaps caused by abrupt changes of the north atlantic sea ice cover spectral data analysis by the maximum entropy method shows similar but greatly damped oscillations in the well dated post glacial part of the camp century record in antiphase with independent estimates on world wide degree of glaciation dansgaard et al 1984 figure 2 left shows the deepest 340 m of the dye 3 profile plotted on a linear depth scale the very deepest 25 m of ice is silty and the s are higher than in holocene ice indicating a time of deposition with unusually high temperature of formation probably the eemian interglacial however the record is hardly continuous that far back in time fig 2 middle shows some of the oscillations in detail and fig 2 right gives further details of three representative shifts along with a dust concentration profile increasing towards left the dust is probably brought to greenland mainly from distant areas covered by loss the dust content changes less abrupt than and not at exactly the same depth which indicates that the measured shifts are not due to temporal discontinuities in the ice core the general antiphase between dust content and suggests higher storminess in times of lower s the circles are co 2 concentrations in air inclusions in the ice but it is still doubtful if they can be interpreted in terms of past atmospheric co 2 concentrations hammer et al 1980 great volcanic eruptions inject acid gases into the stratosphere particularly sulphuric gases which are spread all over the hemisphere under oxydation the strong acids re enter the troposphere and are subsequently washed out by precipitation causing acid layers in the ice sheets hence acidity profiles along the holocene part of the ice cores reveal violent volcanic activity in the northern hemisphere and comparison with the profiles suggest a substantial cooling impact on the climate hammer et al 1980

interstadial climatic cycles a link between western north america and greenland during the interval 33 6 to 26 1 ka searles lake in southeastern california went through six major cycles of expansion and contraction a comparison of u th ages for these events with the chronologies for quasi cyclic interstadial episodes in the ice core from summit greenland suggests that the episodes of low water at searles lake are synchronous with the interstadial episodes at summit the two phenomena may be linked by variations in the strength of the global hydrological cycle driven by oscillations in the atlantic ocean thermohaline circulation

hydrothermal vents near a mantle hot spot the lucky strike vent field at 37 n on the mid atlantic ridge the lucky strike hydrothermal field occurs in the summit basin of a large seamount that forms the shallow center of a 65 km long ridge segment near 37 n on the mid atlantic ridge the depth and chemistry of the ridge segment are influenced by the azores hot spot and this hydrothermal field is the first atlantic site found on crust that is dominated by a hot spot signature multiple hydrothermal vents occur over an area of at least 300 m by 700 m vent morphologies range from flanges and chimneys with temperatures of 200 212 c to black smoker chimneys with temperatures up to 333 c cooler fluids from northern vents have higher chlorinities and lower gas volumes while hotter southern fluids have chlorinities 20 below seawater with higher gas volumes suggesting phase separation has influenced their compositions all gas volumes in fluids are higher than those at tag and snake pit hydrothermal fields black smokers exhibit their typical mineralogy except that barite is a major mineral particularly at lower temperature sites which contrasts with previously investigated atlantic sites the fluid chemistry distribution of the relict sulfide deposits on the seamount summit in the areas investigated using dsv alvin and contact relationships between active vent sites and surrounding basaltic and sulfide substrate suggest that the hydrothermal system has a long history and may have recently been rejuvenated fauna at the lucky strike vent sites are dominated by a new species of mussel and include the first reported sea urchins the lucky strike biological community differs considerably from other vent fauna at the species level and appears to be a new biogeographic province the lucky strike field helps to constrain how variations in the basaltic substrate influence the composition of hydrothermal fluids and solids because basalt compositions at lucky strike are 10 30 times enriched in incompatible elements compared to other atlantic hydrothermal sites such as tag snake pit and broken spur the incompatible element

helium and methane measurements in hydrothermal fluids from the mid atlantic ridge the snake pit site at 23 n methane and helium isotopes concentrations have been measured in hydrothermal fluids of black smoker vents at the snake pit area mar 23 n as part of the hydrosnake cruise with the submersible nautile the samples contain large quantities of helium and methane with endmember values of 4 6 10 5 cm3 stp g for helium and 1 38 10 3 cm3 stp g for methane the helium isotopic ratio 3he 4he is 8 4 times the atmospheric ratio these values are strikingly similar to those already obtained on the east pacific rise the ch4 3he ratio is also quite similar ch4 3he 2 6 106 suggesting a non biogenic origin of this gas in the fluids assuming that the range of variation of the 3he concentration data obtained so far from various tectonic settings is close to the genuine range of values encountered on mid ocean ridges the global mass flow involved in the hydrothermal circulation at the ridge s axis is estimated between 1000 and 3000 m3 of water sec leading to a residence time of the global ocean with respect to the hydrothermal circulation between 15 and 45 million years this estimate implies that in addition to the individual vents smokers there is an extensive diffuse circulation of hydrothermal fluids along the ridges in agreement with recent observations concerning heat budgets at hydrothermal sites in the eastern pacific

growth of bivalves at deep sea hydrothermal vents along the galapagos rift direct measurements of shell growth of an unclassified mussel from active hydrothermal vents along the galapagos rift reveal growth rates of approxmately 1 centimeter per year for mature specimens the largest mussel collected with shell length of 18 4 centimeters was estimated to be 19 7 years old at the time of sampling recorded growth rates are among the highest documented for deep sea species

3d seismic geomorphology of a large plio pleistocene delta bright spots and contourites in the southern north sea abstract regional 2d seismic interpretation has been integrated with high resolution 3d interpretation in dutch offshore blocks a f in the southern north sea 17 horizons mmu s1 s4 s4 1 s4 2 s5 s5 1 s6 s13 and 14 seismic units were interpreted expanding upon studies by kuhlmann and wong 2008 the study presents detailed and extensive twt structure and thickness maps of key depositional units allowing paleogeographic reconstructions detailed analysis of incisional scour marks and hypothesised iceberg scours and constructional features contourites identified initially by bright spots on seismic data linked to bottom currents was undertaken paleo paleographic reconstructions of water depth emphasise the role of hypothesised tidally generated contour currents in the late stage deltaic infill of an epicontinental basin north sea

a novel eye in eyeless shrimp from hydrothermal vents of the mid atlantic ridge rimicaris exoculata1 is a shrimp that swarms over high temperature 350 c sulphide chimneys at mid atlantic ridge hydrothermal fields 3 600 m 1 7 this shrimp lacks an externally differentiated eye1 having instead a pair of large organs within the cephalothorax immediately beneath the dorsal surface of the transparent carapace connected by large nerve tracts to the supraesophageal ganglion these organs contain a visual pigment with an absorption spectrum characteristic of rhodopsin ultra structural evidence for degraded rhabdomeral material suggests the presence of photoreceptors no image forming optics are associated with the organs we interpret these organs as being eyes adapted for detection of low level illumination and suggest that they evolved in response to a source of radiation associated with the environment of hydrothermal vents

hydrocarbon plumbing systems above the snohvit gas field structural control and implications for thermogenic methane leakage in the hammerfest basin sw barents sea abstract based on the analysis of the high resolution 3d seismic data from the sw barents sea we study the hydrocarbon plumbing system above the snohvit and albatross gas field to investigate the geo morphological manifestation and the dynamics of leakage from the reservoir fluid and gas escape to the seafloor is manifested in this area as mega pockmarks 1 2 km wide large pockmarks

diking young volcanism and diffuse hydrothermal activity on the southern mid atlantic ridge the lilliput field at 9 33 s detailed exploration with remotely operated and autonomous deep submergence vehicles has revealed at 9 degrees 33 s the presence of the southernmost active hydrothermal field known so far on the mid atlantic ridge the size of the hydrothermal field which we have named lilliput is about 1000 m x 250 m it lies in a water depth of 1500 m on a ridge segment segment a3 with considerably thickened crust of 11 km four relatively small diffuse vent sites occur on a large young estimated 100 years old lava flow partly covering the flow with hydrothermal fe oxide hydroxide sediments based on homogeneous major element compositions of ca 25 lava samples this flow covers an area of at least 5 km x 0 6 km the lava flow erupted from a series of parallel fissures at the western edge of the flow and a volcanic ridge consisting of up to 30 m high pillow mounds the volcanic ridge probably represents the surface expression of an underlying dike which fed the flow several drained lava pond structures were observed within the flow but only one shows hydrothermal activity the hydrothermal venting and precipitation of abundant fe oxyhydroxides appear to be related to the young diking and eruption event and the four different hydrothermally active sites of the lilliput field lie along and almost equidistant from the eastern flank of the supposed dike although a hydrothermal plume some 500 m above the seafloor was found in two consecutive years 2005 and 2006 no high temperature venting associated with lilliput has been found in agreement with findings at other ridges with thick crust such as reykjanes high magma supply rate and frequent diking and eruption events may lead to hot hydrothermal vents being rare in slow spreading segments with thick crust whereas diffuse venting is abundant interestingly the fauna at the lilliput vents largely consists of small and apparently juvenile mussels bathymodiolus sp and did not show any signs of growth during the four years of continuing observations possibly reflecting pulsing hydrothermal activity

paleoclimatic and paleoceanographic conditions leading to development of sapropel layer s1 in the aegean sea abstract sapropel s1 occurs as 25 35 cm thick black weakly laminated muds in aegean sea cores s1 was deposited between 9600 and 6400 yr b p during a period of isotopically depleted and relatively cool surface waters micro faunal and floral data indicate a major reduction in surface waters salinity during the deposition of s1 and oxygen isotopic data show a northerly fresh water source relatively light 13 c org and high pollen spore concentrations in s1 suggest increased influx of terrestrial organic carbon probably supplied by major rivers draining into the northern aegean sea benthic foraminifera indicate high nutrient low oxygen bottom waters for s1 and together with silt sized hematite and manganese coatings suggest that during the deposition of s1 surface sediments were oxic visual and xrd evidence of pyrite in s1 together with enrichments in s cu zn as ni cr and fe suggest that subsurface conditions were sufficiently reducing for so 4 2 reduction to occur probably by diffusion from surface oxic into subsurface anoxic sediments palynomorphs in s1 show large increases in terrestrial pollen and spores with the floral assemblage indicating significant influx from northern european rivers and minor african components associated with increased summer monsoonal rain abundance of dinoflagellates and amorphogen suggests some increase in primary productivity in response to increased influx of humic compounds however there is no evidence of upwelling the clay fraction in s1 shows notable decreases in smectite and kaolinite and reciprocal increases in illite and chlorite the combined data suggested that the evolution of s1 in the aegean sea largely resulted from stagnation of the surface waters during the final disintegration of the continental ice sheets rather than an increase in primary productivity and higher preservation of organic carbon on the sea floor

pliocene paleoenvironment evolution as interpreted from 3d seismic data in the southern north sea dutch offshore sector a high resolution 3d seismic survey from the dutch offshore sector has been interpreted and subsequently correlated with existing regional seismo stratigraphic concepts derived from conventional 2d seismic data sets the interpreted 13 seismic units have been related to a newly established chrono stratigraphic framework kuhlmann et al 2006a b chronostratigraphy of late neogene sediments in the southern north sea basin and paleoenvironmental interpretations palaeogeography palaeoclimatology palaeoecology 239 426 455 integrated chronostratigraphy of the pliocene pleistocene interval and its relation to the regional stratigraphical stages in the southern north sea region netherlands journal of geosciences geologie en mijnbouw 85 1 19 35 resulting in up dated age control for the seismic units the generation of amplitude maps time slices and isopach maps from the 3d seismic data enabled detailed spatial and temporal reconstruction regarding the paleoenvironmental and climatological development as depicted by kuhlmann et al 2006a chronostratigraphy of late neogene sediments in the southern north sea basin and paleoenvironmental interpretations palaeogeography palaeoclimatology palaeoecology 239 426 455 the lowermost seismic units s1 s4 comprise condensed middle miocene to piacencian sediments deposited under warm open marine conditions these sediments show a uniform seismic facies of low amplitude reflectors the boundary of seismic unit s4 s5 around 2 6 ma delineates a shift towards generally colder climate conditions that are connected to the onset of northern hemisphere glaciation seismic unit s5 includes alternations of warmer and colder periods during warmer periods bottom currents generated elongated structures 2 5 4 km long 300 500 m wide on the horizon display these layers show as well shallow gas accumulations with a more regional extent and are related to coarser grained sediments sealed by clayey sediments of the cold phases a homogenous seismic facies is characteristic for the colder periods within seismic units s6 and s7 internal fore set structures display the regressional trend related to the cooling of this interval seismic units s8 s11 display a pattern of unoriented lineaments which was probably caused by icebergs drifting into the north sea and souring the sea floor this finding is in accordance with the shallow marine arctic conditions of this interval within these units a bright spot of 3 by 7 km in size is interpreted to result from shallow gas accumulation related to a grounded iceberg this feature represents another more local area of gas accumulation that is closely related to iceberg activity within the study area the uppermost seismic units s12 and s13 belong to a fluvial paralic paleo environment that is characterised by aggradational seismic reflectors pleistocene glacial valleys were recognised in the upper 200 m below sea floor 2007 elsevier ltd all rights reserved

fluid flow features in hydrocarbon plumbing systems what do they tell us about the basin evolution abstract fluid flow features such as sandstone intrusions mud volcano systems and pockmarks represent well known geological structures generated due to flow of fluids in the subsurface however the integration of fluid flow features in quantitative and qualitative basin analysis is still in its infancy this study presents a review and a qualitative integration of fluid flow features in basin analysis of the danish north sea area and of salt mini basins offshore angola based on results from six case studies focusing on the detection mapping and evaluation of features related to focused fluid flow in these areas in the study the diversity of seismically imaged fluid flow features in hydrocarbon plumbing systems is reviewed and their utility is demonstrated this is done by focusing on the aspects of fluid flow related features that can be integrated into basin analysis studies and how these may help us increase the understanding of basin evolution and to achieve the major goals of basin analysis such as understanding the depositional and tectonic context of the basin and the presence and extent of hydrocarbons particularly concerning the determination of fluid flow timing triggers sources and routes fluid flow features represent a major but underused tool in basin analysis

chronology of expansion and contraction of four great basin lake systems during the past 35 000 years abstract during the past 35 000 years lake bonneville lake russell and lake searles underwent a major period of lake level change the lakes were at moderate levels or dry at the beginning of the period and seem to have achieved highstands between about 15 000 and 13 500 yr b p the rise of lake lahontan was gradual but not continuous in part because of topographic constraints intrabasin spill lake lahontan also had an oscillation in lake level at 15 500 yr b p radiocarbon age estimations for materials that were deposited in the lake basins indicate that lake bonneville rose more or less gradually from 32 000 yr b p and had major oscillations in level between 23 000 and 21 000 yr b p and between 15 250 and 14 500 yr b p lake russell and lake searles had several major oscillations in lake level between 35 000 and 14 000 yr b p the timing and exact magnitude of the oscillations are difficult to decipher but both lakes may have achieved multiple highstand states all four lakes may have had nearly synchronous recessions between about 14 000 and 13 500 yr b p after the recessions the lakes seem to have temporarily stabilized or experienced a minor increase in size between about 11 500 and 10 000 yr b p these data provide circumstantial evidence that the younger dryas event affected climate on at least a hemispheric scale during the holocene the four lakes remained at low levels and small oscillations in lake level occurred an important aspect of the lake level data is the accompanying expansion of lake surface area at the time of the last highstand lake bonneville and lake lahontan had surface areas about 10 times larger than their mean historical reconstructed areas whereas lake russell and lake searles had surface areas about 5 times larger than their mean historical reconstructed areas differences in the records of effective wetness may have been due to the locations of the basins relative to the position of the jetstream or they may have resulted from lake atmosphere feedback processes

evaluating escarpment evolution and bedrock erosion rates in the western guadalupe mountains west texas and new mexico abstract the guadalupe mountains tower above surrounding plains and basins in western texas and southeast new mexico although this mountain range is extensively studied for the permian stratigraphy related to the petroleum reservoirs in the adjacent delaware basin little is known about the geomorphic history the western escarpment in particular rises abruptly from the salt basin to the west of the range and guadalupe peak rises 1600 m above the surrounding landscape this study investigates how geologic processes create and maintain the steep profile of the escarpment on the western boundary of the guadalupe mountain range in situ produced cosmogenic nuclides were used to quantify erosion rates across the steep western front of the range to assess how tectonic climatic and lithologic forces influence the escarpment profile erosion rates range from 1 to 73 m myr faster erosion rates in the southern area of the escarpment coincide with more frequently mapped faults higher elevations at the top of the rim and locations with colder temperatures and higher precipitation topographic profiles across the western escarpment surfaces indicate greater retreat from the original positions of fault surfaces at the north end of the mountain range faster erosion rates in the mountain range are linked to greater uplift and more recent activity in the southern end of the guadalupe mountains

black smokers massive sulphides and vent biota at the mid atlantic ridge the discovery of black smokers massive sulphides and vent biota in the rift valley of the mid atlantic ridge demonstrates that this assemblage of hydrothermal phenomena is not limited to intermediate to fast spreading oceanic ridges hydrothermal exchange processes may thus be important at the ridges which extend through the atlantic ocean and western indian ocean comprising more than half of the 55 000 km global length of seafloor spreading centres

stratigraphy of the rotliegend group in the danish part of the northern permian basin north sea a stratigraphic study of the rotliegend offshore denmark has resulted in a coherent lithostratigraphic framework and a better understanding of the mid permian evolution of the eastern northern permian basin the rotliegend group is subdivided into the karl formation composed of syn rift volcanics and volcaniclastic sediments and the younger post rift auk formation dominated by aeolian and fluvial sandstones radiometric age data based on k ar dating of plagioclase from the karl formation volcanics combined with previously published age data suggests that volcanism took place during two separate events 276 281 ma and 261 269 ma both events post date the lower rotliegend volcanism 288 300 ma in the southern permian basin suggesting that the northern permian basin was formed during a later tectonic event the main volcanic event in the northern permian basin was broadly coeval with volcanic activity in the altmark area of ne germany reflecting simultaneous rifting and onset of upper rotliegend 2 sedimentation in the northern and southern permian basins

the development and seismic expression of synsedimentary features within the chalk of southern england seismic reflection data acquired onshore to the north of bournemouth southern england image clearly a series of prominent concave up troughs or depressions and concave down mounded structures within the white chalk subgroup the chalk lithostratigraphy in the area of study is established from borehole geophysical log correlations these correlations then provide calibration of the seismic reflection data indicating that the structures are concentrated at levels between the lewes nodular chalk formation and tarrant chalk member and towards the base of the portsdown chalk formation onlap downlap and truncation of reflectors are observed with the most dramatic features forming a stacked series directly overlying faulting of jurassic strata similar stratal geometries have been described from comparable levels in the chalk of the north sea and in outcrop in britain and france to many they represent channels formed by submarine erosion and redeposition of the chalk during relative sea level falls linked to tectonics we also interpret a number of apparently incisive structures and slumped infill sequences described here as being of primary syndepositional origin the slumping and the close association of these features with underlying faults and proximity to nearby major crustal faults may be indicative of submarine erosion of the chalk caused by sea level changes linked to syndepositional fault movements however evidence of toplap downlap pairs is also suggestive of more aggradational mounding or laterally migrating surfaces or facies belts the presence of any such structures implies rapid lateral variations in the chalk that would have implications not only for aquifer management and future storage schemes but also during the processing of seismic reflection data and general studies and correlations of the chalk across southern britain

sequential vertical gas charge into multilayered sequences controlled by central conduits four sets of stacked amplitude anomalies are described from a three dimensional seismic survey acquired in block a of the dutch north sea the amplitude anomalies aas have a subcircular planform and within each set they are stacked vertically they have a high degree of spatial overlap in the vertical succession these sets of aas are interpreted as vertical anomaly clusters vacs composed of five to seven major aas each seismic interpretation of the vacs and quantitative analysis of the reservoir intervals reveal that the vacs are gas bearing silt rich reservoirs hosted in the upper section of the upper north sea group a mixed clastic succession of pliocene to pleistocene age novel analysis based on the geometry of the individual anomalies reveals that these are likely to be the result of a gas migration process characterized by sequential upward gas charge into reservoir units and that the flow across the seals separating these reservoirs is controlled by central regions of focused fluid flow these regions function as seal bypass systems and are most likely formed by hydraulic fracturing

building the crust at the mid atlantic ridge the morphology of the sea floor at mid ocean ridge spreading centres provides a key to understanding how ocean crust is constructed images of the axial zone of the slow spreading mid atlantic ridge obtained at a range of spatial scales show that crustal construction is complex and highly variable reflecting an underlying three dimensional variability in magmatic tectonic and hydrothermal processes

seismic characteristics of fluid escape pipes in sedimentary basins implications for pipe genesis abstract fluid escape pipes were first documented from 3d seismic data over a decade ago and have subsequently been identified in many petroliferous basins worldwide they are characterized on seismic data by vertical to sub vertical zones of reduced reflection continuity that have a columnar geometry in three dimensions the upper terminations of these pipes commonly coincide with pockmarks or palaeo pockmarks signifying a close connection of pipe formation with a high flux fluid expulsion process dimensions range from tens to hundreds of metres in diameter and hundreds to over a thousand metres in height and the slenderness ratio defined as height diameter ranges from 0 8 to over 20 pipes are frequently associated with sub vertical clustering of amplitude anomalies on seismic data related either to the presence of free gas or to cementation linked to the passage of hydrocarbons three mechanisms have been suggested to explain pipe genesis 1 hydraulic fracturing 2 erosional fluidisation and 3 capillary invasion we suggest a further two possible mechanisms in the form of localised collapse by volume loss and synsedimentary flow localisation we review all five mechanisms and conclude that it is unlikely that a single mechanism applies but that combinations of these processes may all occur in particular contexts fluid escape pipes may be far more widespread that currently appreciated and they may play a critical role in secondary hydrocarbon migration and in providing leakage pathways for trapped hydrocarbons through overlying seals

geochronology of tag and snakepit hydrothermal fields mid atlantic ridge witness to a long and complex hydrothermal history geochronological studies of a large number of precipitates from the tag hydrothermal field and of few samples from snakepit hydrothermal field of the mid atlantic ridge show intermittent repeated hydrothermal events at both sites 210pb pb and 230th 234u measurements of sulfides iron and manganese oxides and 14c measurements of carbonates combined with observations of hydrothermal events recorded as discrete layers in sediment cores provide the basis for unravelling the temporal history of the fields the tag field shows intermittent activity over the past 120 000 years as evidenced by ages of low temperature mn oxides the presently active black smoker mound first formed about 40 000 50 000 years ago with precipitation of massive sulfides it has had intermittent pulsed high temperature activity every 5000 6000 years over the past 20 000 years which may reflect renewed magmatic activity at the ridge axis fluid flow is focussed at the mound site by structural and tectonic control suggested by the intersection of n s ridge parallel lystric normal faults and an e w transform fault periods of inactivity are marked by covering of the mound with pelagic carbonate ooze which is probably partially dissolved and reprecipitated as aragonite at the end of each high temperature event the snakepit field had an initial event about 4000 years ago probably shortly after the eruption of the volcanic ridge on which it sits a recent renewal still presently active was probably initiated by recent fissuring of the volcanic pile

biogeographic implications of a packrat midden sequence from the sacramento mountains south central new mexico abstract thirteen packrat neotoma spp and two porcupine erethizon dorsatum middens from 1555 to 1690 m elevation from the sacramento mountains new mexico provide an 18 000 yr vegetation record in the northern chiuahuan desert the vegetation sequence is a mesic wisconsin fullglacial 18 000 16 000 yr b p pinyon juniper oak woodland a xeric early holocene ca 11 000 8000 yr b p juniper oak woodland a middle holocene ca 8000 4000 yr b p desert grassland and a late holocene ca 4000 yr b p to present chihuahuan desertscrub the frequency of spring freezes and summer droughts in the late wisconsin probably set the northern limits of pinus edulis and juniperus monosperma at about 34 n or 6 south of today s limit rising summer tempratures in the early holocene eliminated pinyon and other mesic woodland plants from the desert lowlands and allowed the woodland to move upslope at this time pinyon juniper woodland and pine forest dominated by pinus ponderosa probably began their spectacular holocene expansions to the north continued warming in the middle holocene led to very warm summers with strong monsoons relatively dry cold winters and widespread desert grasslands desertscrub communities in the northern chihuahuan desert did not develop until the late holocene when the biseasonal rainfall shifted slightly back toward the winter catastrophic winter freezes decreased and droughts in all seasons increased the creosote bush desertscrub corridor across the continental divide between the chihuahuan and sonoran deserts was probably connected for the first time since the last interglaciation

chronostratigraphy of late neogene sediments in the southern north sea basin and paleoenvironmental interpretations a chronostratigraphic framework has been established for upper neogene sediments from the northern netherlands offshore sector southern north sea data of dinoflagellate cysts pollen and foraminifers from eight boreholes are integrated and the resulting biostratigraphic events are connected to an additionally retrieved paleomagnetic record the sedimentary succession comprises at the base late to middle miocene sediments and spans the piacenzian to gelasian stages from 3 6 to 1 8 ma including the paleomagnetic gauss matuyama boundary and the olduvai subchron sedimentation rates vary between 30 cm kyr in the lower part of the succession and reach up to 84 cm kyr in the upper part these rates are high enough to record short paleomagnetic events and for the first time the presence of the so called x event has been recorded and dated at around 2 44 ma in a sedimentary setting the name north sea event is proposed here the paleoclimatic and paleoenvironmental information pictures the onset of northern hemisphere glaciation and the subsequent intensification of glacial conditions with its impact on the north sea sea region the paleoenvironmental changes are characterised by a stepwise development and five successive intervals are distinguished during the first interval a warm climate and an open marine setting prevailed the second interval is characterised by dominantly cold climatic conditions with occasional warmer periods during the third interval the environment became restricted marine and a stable freshwater layering occurred which facilitated the development of sea ice in the shallow sea within the fourth interval extreme cold arctic conditions were predominant and shallowing continued the fifth interval shows fluvial to deltaic paralic conditions from then on facies differences from the nearby delta system overruled the basin wide signals at the studied location 2006 elsevier b v all rights reserved

geochronology of late pleistocene to holocene speleothemsfrom central texas implications for regional paleoclimate a detailed chronology for four stalagmites from three central texas caves separated by as much as 130 km provides a 71 000 yr record of temporal changes in hydrology and climate mass spectrometric 238 u230 th and 235 u231 pa analyses have yielded 53 ages the accuracy of the ages and the closedsystem behavior of the speleothems are indicated by interlaboratory comparisons concordance of 230 th and 231 pa ages and the result that all ages are in correct stratigraphic order over the past 71 000 yr the stalagmites have similar growth histories with alternating periods of relatively rapid and slow growth the growth rates vary over more than two orders of magnitude and there were three periods of rapid growth 71 60 ka 39 33 ka and 24 12 ka these growth rate shifts correspond in part with global glacial interglacial climatic shifts paleontological evidence indicates that around the last glacial maximum 20 ka climate in central texas was cooler and wetter than at present this wetter interval corresponds with the most recent period of increased growth rates in the speleothems which is consistent with conditions necessary for speleothem growth the temporal shift in wetness has been proposed to result

decadal to millennial scale solar forcing of last glacial maximum climate in the estancia basin of central new mexico abstract lacustrine sediments from the estancia basin of central new mexico reveal decadal to millennial oscillations in the volume of lake estancia during last glacial maximum lgm time lgm sediments consist of authigenic carbonates detrital clastics delivered to the lake in stream flow pulses and evaporites that precipitated in mudflats exposed during lake lowstands and were subsequently blown into the lake variations in sediment mineralogy thus reflect changes in hydrologic balance and were quantified using rietveld analysis of x ray diffraction traces radiocarbon dates on ostracode valve calcite allowed the construction of mineralogical time series for the interval 23 600 to 18 300 ka which were subjected to spectral analysis using redfit schulz and mudelsee 2002 dominant periods of 900 375 and 265 yr are similar to cycles in holocene 14 c production reported for a variety of tree ring records suggesting that the lake estancia sediments record variations in solar activity during lgm time a prominent spectral peak with a period of 88 yr appears to reflect the solar gleissberg cycle and may help along with the 265 yr cycle to explain an ongoing mystery about how lake estancia was able to undergo abrupt expansions without overflowing its drainage basin

influence of seep emission on the non symbiont bearing fauna and vagrant species at an active giant pockmark in the gulf of guinea congo angola margin detailed surveying with an rov found that a dense and diverse cold seep community colonises a giant pockmark located at 3200 m depth 8 km north from the deep congo channel several types of assemblages either dominated by mytilidae and vesicomyidae bivalves or siboglinidae polychaetes are distributed on the 800 m diameter active area the site is characterised by a most active central zone in a depression with abundant carbonate concretions and high methane fluxes where high density clusters of mussels and siboglinids dominate in contrast the peripheral zones display large fields of dead and live vesicomyids on soft sediment with a lower mean density and lower methane concentration in seawater the associated megafauna includes alvinocarididae shrimps echinoids holothurians of the family synaptidae several species of gastropods two species of galatheids and zoarcidae and ophidiidae fishes multivariate analyses of video transect data show that the distribution of these major megafauna species at the pockmark scale is influenced by the habitat heterogeneity due to fluid or gas emission occurrence of hydrates substratum variability and by the presence of large symbiont bearing species several assemblages dominated either by mytilids vesicomyids or siboglinids have been sampled for megafauna densities and biomass estimations and stable isotope measurements 13c and 15n of dominant species and food sources the highest estimates of megafauna densities have been obtained in mytilid beds according to their stable isotopes values non symbiont bearing species mainly rely on chemosynthesis originated carbon either as primary consumers of chemoautotrophic microorganisms or at higher trophic level recycling organic matter or relying on bivalve and tubeworm production most of them likely feed on different sources like shrimps but differences according to habitat have been evidenced carbon and nitrogen isotope ratios of galatheids and benthic or benthopelagic fishes captured by trawls at increasing distances from the pockmark provide evidence of the high variability in the proportion of chemosynthesis originated carbon in their diet from 15 to 38 according to the species captured as far as 4 km to the site

origin of a toarcian manganese carbonate silicate deposit from the križna unit tatra mountains poland abstract a mn bearing sequence of the kri na unit in the western tatra mountains occurs locally between shallow water crinoidal tempestites lower toarcian and pelagic red nodular limestones middle toarcian aalenian the mn bearing sequence forms a lens shaped body up to 2 m thick extending for a few hundred meters it consists of several distinctive facies fe rich layer 15 cm thick jasperite up to 0 5 m thick x ray amorphous mn oxide layer 10 cm thick shale 510 cm thick and mn rich bed up to 1 1 m thick minerals in the mn rich bed such as braunite caryopilite mn bearing calcite and rhodochrosite are distributed in two distinctive zones carbonate and silicate dominated the most important geochemical characteristics of these deposits are high mn contents up to 62 8 wt mno low concentrations of transitional elements co ni cu

hydrothermal methane venting between 12 n and 26 n along the mid atlantic ridge hydrographic surveys along the mid atlantic ridge mar between 12 n and 26 n carried out from 1984 to 1990 show a variable pattern of ch4 rich water column plumes the vertical distribution of ch4 at stations located every 20 40 km is presented along this 1200 km long section of the mar ch4 venting is clearly demonstrated ch4 enriched fluids rise from vents as plumes spreading is confined to the axial valley due to the topography of the mar ch4 contents from 45 nmol to 675 nmol kg are measured in the buoyant plumes above the two active hydrothermal sites mark 23 n tag 26 n known at present whereas ch4 anomalies up to 3 6 nmol kg are typically observed in plumes emitted either on the inner floor on the walls and or at the top of the rift mountains along the studied ridge section ch4 concentrations 45 mol to 144 mol kg in mark and tag vent fluids are of the same order of magnitude as those found in the east pacific rise fluids even though ch4 is known to be unstable with respect to oxidation by dissolved oxygen and in spite of its microbial oxidation in plumes these results confirm ch4 to be a good indicator to track hydrothermal plumes and to map the variation of hydrothermal activity along mid oceanic ridges moreover between 12 and 26 n along the mar ch4 results show that while hydrothermal activity is present everywhere along the ridge it is predominant near fracture zones fz kane fz 15 20 n fz comparison of ch4 tracer with total dissolvable manganese tdm tracer in plumes allows us to differentiate subseafloor hydrothermal processes the high tdm ch4 found above tag and mark areas is indicative of basalt seawater interaction while at 15 n the low tdm ch4 provides evidence of fluid circulation in ultrabasic rocks ch4 data confirm the association between mantle degassing hydrothermal activity and serpentinization along this 12 26 n section of the mid atlantic ridge

a 164 ka record of environmental change in the american southwest from a carlsbad cavern speleothem abstract a horizontal core 2 8 m in length drilled from the georgia giant column in carlsbad cavern provides climate information for the last 164 ka forty six alpha spectrometric u series ages determined at intervals of 7 6 cm along the core indicate five periods of deposition and five hiatuses the longest from 136 to 110 ka variations in growth rate 0 to 70 mm ka in the abundance of aragonite chalcedony and fe bearing phases and in 13c indicate that glacial intervals of the last 164 ka ois 6 4 and 2 were much wetter than today as were the colder substages 5d and 5b of ois 5 by contrast during the two warmest periods of the past 164 ka namely ois 5e and 1 there was no deposition on either side of the speleothem suggesting conditions as dry or drier than today the record from carlsbad parallels data from many other sites in the southwestern usa and northern mexico and data from marine sediments and ice cores demonstrating the extent to which ice sheet fluctuations influenced conditions in southern new mexico detailed correlation of 13c values in the georgia giant which range from 6 6 to 0 9 relative to pdb with distant speleothem records and with data from ice cores further documents the linkage of southwestern climate with global scale extent of glaciation values of 18o in the georgia giant core range from 9 7 to 4 7 relative to pdb and average 6 6 18o depleted carbonate in the georgia giant during ois 6 at a time when the world s oceans were enriched in 18o suggests that precipitation during cold intervals was brought largely by pacific air masses in fall winter and spring as a result of the southward displacement of the polar jet stream by the growth of the laurentide ice sheet termination ii marking the end of the penultimate glaciation is well defined in the core s 18o data analytical uncertainties in the radiometric ages do not preclude a start of termination ii as late as 128 ka as suggested by specmap data however data from the georgia giant core are more compatible with an earlier start like that obtained from devils hole and vostok data raising the possibility that early warming was widespread in the u s southwest region by 145 ka

origin of terrestrial gypsum dunes implications for martian gypsum rich dunes of olympia undae abstract the estancia white sands guadalupe and cuatrocienegas dune fields are among the largest known aeolian gypsum sand dune accumulations on earth and occupy closed drainage basins within the rio grande rift high sedimentation rates of lacustrine gypsum occur in topographic depressions within the closed basins the gypsum accumulations result from long term complex interaction between tectonism climate and a hydrologic cycle that involves geochemical recycling of sulfur from older sedimentary rocks flanking and underlying the basins gypsum precipitation in lacustrine environments is strongly controlled by local groundwater bedrock interaction the ranges of 34s values per mil vs vcdt for gypsum sand in the white sands dune field 12 1 to 13 9 guadalupe dune field 10 2 to 12 5 and cuatrocienegas dune field 14 6 to 15 9 indicate that the main sources of dissolved sulfate are evaporite strata of lower permian middle permian and cretaceous ages respectively a spatial increase of 34s values across the white sands dune field in the direction of prevailing winds matches well with a stratigraphically upward increase of 34s values recorded in lake otero an ancient lake in the basin strata this finding supports previous suggestions that white sands dune field evolved as a result of the step wise deflation of previously stored sediments in lake otero the modern gypsum dune fields are primarily wet eolian systems in which dune accumulation is controlled by a near surface groundwater table which promotes early cementation of the dune accumulations early cementation in the interdune surfaces and to a lesser degree on the dune surfaces reduces the amount of sand available for transport and slows rates of dune migration based on an average migration rate of 2 m year the time needed for a dune at white sands to migrate the downwind distance of the dune field is approximately 6500 years which matches well with other estimates of the initiation of the dune field at approximately 7000 years ago and indicates that white sands likely evolved as a wet aeolian system as on earth gypsum rich dune fields apparently are rare on mars gypsum has been identified only within the olympia undae dune field which encircles a portion of the martian north polar residual ice cap analogous to terrestrial gypsum dunes the gypsum within the olympia undae gypsum rich dunes might have originated from transport and deposition via aeolian processes in this model gypsum rich source sediment could have been formed by confined groundwater or surface water activity and later transported by the wind any subsequent gypsum precipitation in the source area could have been initiated by episodic melting of the martian polar ice cap it is likely that the gypsum was deposited in the olympia undae dunes after the main deflation events that led to formation of the siliciclastic components of the dune field