evidence from u th dating against northern hemisphere forcing of the penultimate deglaciation milankovitch proposed that summer insolation at mid latitudes in the northern hemisphere directly causes the ice age climate cycles1 this would imply that times of ice sheet collapse should correspond to peaks in northern hemisphere june insolation but the penultimate deglaciation has proved controversial because june insolation peaks 127 kyr ago whereas several records of past climate suggest that change may have occurred up to 15 kyr earlier2 3 4 5 6 7 8 there is a clear signature of the penultimate deglaciation in marine oxygen isotope records but dating this event which is significantly before the 14c age range has not been possible here we date the penultimate deglaciation in a record from the bahamas using a new u th isochron technique after the necessary corrections for recoil mobility of 234u and 230th and a small age correction for sediment mixing the midpoint age for the penultimate deglaciation is determined to be 135 2 5 kyr ago this age is consistent with some coral based sea level estimates but it is difficult to reconcile with june northern hemisphere insolation as the trigger for the ice age cycles potential alternative driving mechanisms for the ice age cycles that are consistent with such an early date for the penultimate deglaciation are either the variability of the tropical ocean atmosphere system or changes in atmospheric co2 concentration controlled by a process in the southern hemisphere

uranium 234 anomalies in corals older than 150 000 years we present new precise u th ages of well preserved coral specimens collected from the island of barbados west indies and the atoll of mururoa french polynesia our new data confirm the ages attributed to oxygen isotope stage 7 in the framework of the milankovitch theory berger 1978 mar tinson et al 1987 by using thermal ionization mass spectrometry tims it is also possible to quantify precisely the 234u238u ratios in corals samples older than 150 kyr b p are shown to be characterized by significant excesses of 234u relative to the uranium isotopic composition expected if the corals grew in present day sea water assuming that the 230th ingrowth ages are accurate these anomalies translate into high initial 234u238u ratios about 1 2 at 200 kyr and up to 1 5 at about 450 kyr b p we propose that the anomalies result from both diagenetic addition and replacement of u and possibly from global changes in the 234u238u composition of sea water through time the 234u anomalies cast doubt on the accuracy of the classical 230th ingrowth dating method in old corals and in particular for the use of measured 234u238u ratios alone to date corals older than 150 kyr

u th he zircon and archaeological ages for a late prehistoric eruption in the salton trough california usa u th and u th he zircon geochronology redefines the timing of volcanic activity in the salton trough southern california usa the subaerial extension of the incipiently oceanic gulf of california u series disequilibrium corrected u th he zircon analyses for a granophyre ejecta clast from the red island rhyolite dome indicate an eruption age of 2480 470 a calendric dates between 0 and 940 before common era bce error at 95 confidence this eruption age is supported by u th zircon crystallization ages for two obsidian bearing lavas red island the host for the granophyre and obsidian butte a prehistoric quarry for obsidian that is widely distributed in southern california and northern mexico archaeological sites lavas and granophyre display overlapping zircon crystallization age distributions that support field and compositional evidence that they are cogenetic and contemporaneous the u th he eruption age is younger and significantly more precise than previous ages for these volcanoes and is the first indication that the eruption of obsidian flows coincided with human presence in the region a late prehistoric eruption age agrees with the absence of the obsidian butte lithic source among early prehistoric cultural artifacts previously attributed to submergence of the quarry location during hypothesized persistent flooding by ancient lake cahuilla

geological geophysical and thermal characteristics of the salton sea geothermal field california abstract the salton sea geothermal field is the largest water dominated geothermal field in the salton trough in southern california within the trough local zones of extension among active right stepping right lateral strike slip faults allow mantle derived magmas to intrude the sedimentary sequence the intrusions serve as heat sources to drive hydrothermal systems we can characterize the field in detail because we have an extensive geological and geophysical data base the sediments are relatively undeformed and can be divided into three categories as a function of depth 1 low permeability cap rock 2 upper reservoir rocks consisting of sandstones siltstones and shales that were subject to minor alterations and 3 lower reservoir rocks that were extensively altered because of the alteration inter granular porosity and permeability are reduced with depth field permeability is enhanced by renewable fractures i e fractures that can be reactivated by faulting or natural hydraulic fracturing subsequent to being sealed by mineral deposition in the central portion of the field temperature gradients are high near the surface and lower below 700 m surface gradients in this elliptically shaped region are fairly constant and define a thermal cap which does not necessarily correspond to the lithologic cap at the margin of the field a narrow transition region with a low near surface gradient and an increasing gradient at greater depths separates the high temperature resource from areas of normal regional gradient geophysical and geochemical evidence suggest that vertical convective motion in the reservoir beneath the thermal cap is confined to small units and small scale convection is superimposed on large scale lateral flow of pore fluid interpretation of magnetic resistivity and gravity anomalies help to establish the relationship between the inferred heat source the hydrothermal system and the observed alteration patterns a simple hydrothermal model is supported by interpreting the combined geological geophysical and thermal data in the model heat is transferred from an area of intrusion by lateral spreading of hot water in a reservoir beneath an impermeable cap rock

controls on the geomorphic expression and evolution of gryphons pools and caldera features at hydrothermal seeps in the salton sea geothermal field southern california abstract in the salton sea geothermal field in southern california expulsion of gas sediment and water creates unique geomorphic features similar to those seen on the surface of dormant mud volcanoes these include pools of water or highly fluid mud named mud pots and 0 5 to 2 5 m tall gryphons the features vary in size shape and type of eruptive activity and change form over time to evaluate controls on the surface morphology and evolution of these features we used repeated differential gps surveys observations of eruptive activity and measurements of erupted mud properties to document the physical characteristics and changes in the system over a 28 month period we find that the morphology of the gryphons is primarily a function of the mud expulsion style taller 1 5 m to 2 4 m gryphons form where narrower vents 5 cm to 15 cm diameter expel mud to the surface in discrete strombolian type eruptions caused by individual gas bubbles pushing mud up through the gryphon conduit and exploding at the surface smaller 0 6 m to 1 5 m gryphons form where wider vents allow a greater amount of gas to pass through which creates 0 25 to 1 m diameter mud craters that bubble continuously often from multiple points within the crater although viscous mud is required to create these positive topographic features variations in erupted mud temperature 30 c to 68 5 c density 1 44 g cm 3 to 1 59 g cm 3 and water content 36 to 44 between different gryphons did not correlate with gryphon size all the active gryphons experienced periods of growth and erosion over the study period due to changes in the degree of activity or small variations in the vent locations within the gryphons but the net change in height distributions over time was negligible pools directly adjacent to gryphon clusters are surficial features whose water level depends on seasonal rainfall and temperature isolated pools are also present and do not show similar response to seasonal changes suggesting that these pools are connected to the local groundwater system although changes in vent morphology and activity do occur the new data demonstrate that the system is steady state in terms of the height distribution of the gryphons and the location of the main seeps most of the gryphons occur in clusters that are surrounded by caldera like depressions that range from 10 to 25 m in diameter mud expelled from the gryphons is largely contained within the caldera depressions and we infer that subsidence of the calderas accounts for the lack of large scale build up of material in the surrounding area this study provides the first examination of the processes controlling the morphology of these features and the results may help to understand the dynamics and temporal evolution of gryphons which are found in both hydrothermal systems and on dormant mud volcanoes

bloedite sedimentation in a seasonally dry saline lake salada mediana spain abstract salt crusts covering the surface of the salada mediana a seasonally dry saline lake in northern spain consist predominantly of bloedite na2mg so4 2 4h2o microscopic features of the crust were investigated to understand processes of bloedite sedimentation this study was combined with satellite and airborne observations revealing asymmetrical concentric and parallel linear patterns related to wind action gypsum caso4 h2o and glauberite na2ca so4 2 in the calcareous sediments below the crust and abundant eugsterite na4ca so4 3 2h2o along the base of the crust largely formed at a different stage than bloedite the main part of the crust consists predominantly of coarse crystalline xenotopic hypidiotopic bloedite but fan like aggregates with downward widening radial aggregates surface layers with vertically aligned elongated crystals and partially epitaxial coatings occur as well the upper part of the crust is marked by a bloedite thenardite na2so4 association recording a change in brine composition that is not in agreement with results of modelling of local brine evolution a thin fine grained thenardite dominated surface formed in part by subaqueous settling of crystals but there are also indications for development by transformation of bloedite surface features include fan like bloedite aggregates with upward widening formed by bottom growth overall the salada mediana crusts record a complex history of bloedite and thenardite precipitation by various processes

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

pelagic sedimentation on an inactive gullied slope northwest providence channel bahamas abstract the southern flank of little bahama bank is a deep water carbonate slope into which a series of closely spaced canyons 10 200 m deep have been cut it is similar in morphology to many other slopes in the bahamas and these slopes are generally considered to be created by the erosion of downslope sediment gravity flows however little evidence for downslope sediment movement or associated erosion were found in the holocene or latest pleistocene sediments of the slope reported on here the sediments from water depths below 260 m consist of a uniform pelagic drape covering both the gullies and inter gully ridge tops high resolution seismic reflectors are not truncated along individual gully walls and the fine scale stratigraphy of the sediments recorded in glacial interglacial changes in the aragonite calcite ratio of the sediments is preserved in sediments from gullies and ridge tops it appears that for the last two to three glacial cycles there has been only minor downslope transport of sediment despite the gullied morphology erosion is not presently occurring on the slope

tims u series dating and stable isotopes of the last interglacial event in papua new guinea the extensive flight of uplifted reef terraces which occurs along the vitiaz strait on the northern flank of the huon peninsula in png papua new guinea contains a particularly good record of sea level changes in the last 250 ky the huon terraces were the target of an international expedition which took place in july august 1988 in particular we searched for suitable samples for u series dating in a reef complex designated as vii which is correlated with the last interglacial episode and high sea level stand this complex is composed of a barrier reef viib a lagoon and a fringing reef viia twelve corals from these terraces and two corals from the older reef complex viii were selected for analysis the petrography oxygen and carbon isotope compositions and magnesium and strontium concentrations were determined along with the concentrations and isotopic compositions of uranium and thorium 230 th 234 u ages of the corals with 99 aragonite having primary textures and which show u sr ratios around 0 4 10 3 and initial 234 u values close to that of present seawater appear to be reliable the most reliable ages from complex vii corals fall in two tight groups centered at 118 ky and 134 ky corals with 234 u t values higher than 160 and u sr ratios substantially lower than seawater are assumed to have undergone diagenetic alteration which appears to be common in this area the simplest model for sea level height for terrace vii is a continuous rise between 134 and 118 ky alternatively there may have been two periods of rapid sea level rise in contrast in the bahamas there is evidence that sea level remained rather constant over the time interval 132 to 120 ky the absence of ages between 132 and 120 ky in png could be the result of changes in the local tectonic uplift rates during that time or erosion that disrupted the continuous record in any event we find no basis for accepting a single brief time for the age of the last interglacial and applying this age as a precise chronometer for worldwide correlation or as a test of climatic models the older ages reported here precede the milankovitch solar insolation peak at 128 ky and the younger ages are 10 ky after this peak if the present high precision data are correct then it will be necessary to reassess the validity of the milankovitch theory of climatic changes the fundamental issue which must now be resolved is a means of identifying coral samples that have not been disturbed by diagenetic processes

234u 238u mass spectrometry of corals how accurate is the uth age of the last interglacial period direct measurement of u and th by mass spectrometry recently provided a spectacular improvement in the precision of coral dating by the uth disequilibrium method 1 mass spectrometric data also provide a much better resolution for the examination of subtle diagenetic effects revealed by small variations of the 234u 238u ratio such perturbations may strongly affect the accuracy of the uth chronometer a compilation of all the corals analyzed to date by mass spectrometry shows that most of the corals from terraces of the last interglacial have initial 234u 238u ratios higher than present day seawater in contrast to modern holocene and last glacial corals some samples that have very high 234u 238u initial ratios up to 1 2 and high u concentrations up to 4 ppm were probably contaminated by continental groundwaters however even apparently pristine samples have 234u 238u initial ratios which are still slightly higher than present day seawater mean value 1 160 compared to 1 140 1 150 2 with little overlap between the two distributions this difference in the u initial ratio raises some uncertainty about the accuracy of the uth age determinations of these corals in spite of the fact that the 234u230th ages cluster in a narrow range between 122 and 133 kyr the data could also be interpreted as resulting from slight contamination of corals that are significantly older than 125 kyr two possible explanations may explain these data 1 all these samples may have been diagenetically altered since they all come from surface outcrops which have been directly exposed to precipitations or soil waters for 125 kyr in this case the true age of these corals remains uncertain depending on the timing of the alteration process i e initial late or continuous 2 the second possibility is that some of the differences in 234u 238u ratios measured in 125 kyr cold corals compared to modern seawater may be due to a higher 234u 238u ratio in seawater 125 kyr ago this could result from temporal variations in the weathering regimes of continental land masses

new 230th u and 14c ages from lake lahontan carbonates nevada usa and a discussion of the origin of initial thorium five sets of coeval lacustrine carbonate samples from pleistocene lake lahontan in western nevada were dated by both the ams 14c and 230th u isochron methods all five groups of samples were analyzed for u th isotopes by alpha spectrometry and one of the groups was additionally measured by thermal and secondary ionization mass spectrometry tims and sims for comparison the 14c ages were corrected to calendar years using the calibration curve recommended by bard et al 1992 without local reservoir correction on the 14c ages mean 230th u isochron ages of some sets are apparently older than their calendar corrected 14c ages by up to 2300 years modern carbon contamination of these carbonate samples through recrystallization or deposition of secondary calcite is likely to be responsible for part of the age discrepancies we explored additional biases associated with the isochron ages maybe produced by the presence of initial th coprecipitated from the lake water it can be shown that if dissolved hydrogenous th is directly incorporated into the pure carbonates then the three component mixing among 1 detrital th 2 hydrogenous th adsorbed on detritus and 3 hydrogenous th incorporated by the carbonate can introduce a positive age bias we have developed an approach to estimate the magnitude of this bias of the lake lahontan carbonates the preliminary estimates suggest a positive age bias of 1000 to 2000 years for two sets of the samples

variation in bioturbation with water depth on marine slopes a study on the little bahamas bank abstract reconstructing the paleoceanography of intermediate depth waters is dependent on sedimentary records preserved on marine slopes but knowledge of bioturbation processes in such slope environments is much poorer than for the deep sea in this study 210 pb profiles were measured for the upper 20 cm of sediment from five box cores taken on the slopes of the bahamas in water depths ranging from 400 to 1500 m these were compared with data from the bahamas bank tops and from elsewhere to assess the rate and depth of mixing in the slope environment excess 210 pb inventories are too high to explain by water column decay of 226 ra and are derived largely from atmospheric fallout down core 210 pb xs profiles show an upper zone where 210 pb xs activities decrease exponentially with depth suggesting uniform mixing and a lower zone with patchy 210 pb values reflecting isolated burrows in contrast to bank top sediment which shows 210 pb xs mixing to depths of 40 cm and mixing rates of 1000 cm2 kyr mixing of 210 pb on the slopes penetrates to only 8 cm with mixing rates of 210 pb derived mixing activity in ocean margin sediments diffusive versus nonlocal mixing j mar res 54 1207 1227 a simple model is used to assess the effects of mixing on typical bahamian slope sediments which have deposition rates and compositions which vary dramatically in response to sea level change proxy records such as 18 o are expected to be displaced by up to 0 8 kyr in bulk sediment and individual sediment constituents may be moved by up to 2 kyr relative to one another these mixing effects are reasonably small and may be safely ignored for some studies but for high resolution records or studies where precise age control is important bioturbation of slope sediments should be considered

spectral properties of halite rich mineral mixtures implications for middle infrared remote sensing of highly saline environments abstract middle infrared reflectance of minerals is often used to qualitatively predict their spectral emittance characteristics reflectance spectra of particulate minerals dispersed in a nonabsorbing material such as halite nacl can be very different from those of the isolated minerals and often resemble transmittance spectra to illustrate this behavior diffuse reflectance spectra 4 3 m 14 3 m of particulate samples of calcite gypsum quartz and montmorillonite in various mixtures with nacl are compared with reflectance and transmittance spectra of the pure minerals diffuse reflectance of a natural efflorescence associated with a sample of mojave desert playa material is also illustrated similarities in the spectra of the field sample and certain of the laboratory mixtures suggest that high concentrations of nacl could produce ambiguities for remotely sensed observations in certain saline environments however these preliminary laboratory measurements need supporting field studies to determine their significance in actual remote sensing situations

234u 238u ratios and230th ages for hateruma atoll corals implications for coral diagenesis and seawater234u 238u ratios published results for corals that are more than ca 50 ka old from for example barbados and vanuata often yield initial 234u 238u activity ratios that are significantly greater than 1 144 0 004 the value for modern seawater this study reports results for corals from hateruma atoll japan and investigates the effects of diagenesis on the initial 234u 238u ratios of the corals hateruma consists of over 95 reef material of less than 500 ka in age because groundwaters associated with recent carbonates tend not to have elevated 234u 238u ratios the scope for increasing the 234u 238u ratios of hateruma corals through groundwater interaction should be minimal the corals examined range from those which show no petrographic or x ray evidence for diagenetic alteration and are pristine to those containing secondary cements of either aragonite or high or low mg calcite these various phases have been mechanically separated and analysed in agreement with previous assertions the analyses of these separates demonstrates that the presence of calcite should be a cause for rejection of coral samples it is also shown that aragonite cement can form later than coral death and may bias estimates of age and initial 234u 238u ratios of the six pristine corals three have anomalous 230th 238u ratios requiring u loss and or230th addition the remaining fifteen of the eighteen total analyses reported here yield ages from 1 6 ka to 260 ka no evidence for an increase in 234u 238u ratios in past seawater from this period has been found the best estimates for 234u 238u ratios are close to the current seawater value

mineralogical characterization of microbial ferrihydrite and schwertmannite and non biogenic al sulfate precipitates from acid mine drainage in the donghae mine area korea the waters from abandoned coal mines and dumps contain high amounts of so4 al fe ca mg and mn they are precipitated in the stream bottom as oxides and or sulfates as brown or whitish flocculated biomats three types of biomats the reddish brown brownish yellow and white precipitates are found in the stream bottom of the donghae coal mine area in taebaek korea the biomats consist mainly of ferrihydrite with small amounts of goethite and schwertmannite with minor quartz and clay minerals and al sulfate the ferrihydrite and schwertmannite were directly precipitated from acid mine drainage amd containing high concentrations of fe and so4 goethite was transformed to ferrihydrite and or schwertmannite depending on ph values many spherical and rod shaped bacteria were observed from the reddish brown biomats the brownish yellow biomats are composed mainly of spherical type bacteria of 0 5 5 m in diameter the reddish brown and brownish yellow biomats show the characteristic shape of twisted stalks of gallionellaferruginea energy dispersive x ray spectrometer eds analysis of gallionellaferruginea in the reddish brown and brownish yellow biomats shows fe si ca al p s and fe si s al p ca in concentrations respectively

uranium series dating of fossil coral reefs extending the sea level record beyond the last glacial cycle abstract absolutely dated records of past sea level change are extremely important for understanding the advance and retreat of the large ice sheets when combined with other complementary climate archives and climate models such records offer the potential to gain an improved understanding of earth s natural climate cycles providing a firmer basis for assessing the role of anthropogenic effects such as greenhouse gas emissions in modifying climate the u series dating of fossil coral reefs has been widely utilized to provide absolutely dated records of past sea level change and numerous observations now exist for the past 130 000 years spanning the last glacial cycle despite this controversies still exist regarding the exact timing and character of sea level events within this time interval and extending the sea level history further back in time on the basis of robust and independent age constraints for older fossil reefs remains very elusive this is primarily due to a progressive loss in the resolution of the u series chronometer as one goes further back in time coupled to a lack of well preserved dateable coral in older fossil reefs to overcome these limitations the primary challenges are three fold first new analytical protocols are required to improve the resolution of the u series chronometer enhanced analytical precision must be coupled to accuracy through continued refinement of the u series decay constant determinations and via the implementation of rigorous inter laboratory calibration exercises second efforts should continue to be focussed on gaining an improved understanding of the mechanisms controlling open system exchange of the u series isotopes in fossil reef systems this will allow the number of reliable u series observations to be extended third alternative dateable archives of past sea level change must continue to be emphasized to further complement the coral reef database these limitations are discussed in the context of current developments that further advance the application of u series chronology to older fossil reef systems formed prior to the last glacial cycle

reconstruction of the last deglaciation deconvolved records of δ18o profiles micropaleontological variations and accelerator mass spectrometric14c dating bioturbation acts as a low pass filter in displacing and reducing the amplitudes of stratigraphic signals this often leads to a loss of high frequency events in the stratigraphic record in addition when considering an isotopic signal 18o 14c measured in stratigraphic carriers such as foraminifera bioturbation and carrier abundance changes can create artifacts which may be falsely interpreted as leads or lags in the paleoclimatic record

surface mineral mapping at steamboat springs nevada usa with multi wavelength thermal infrared images abstract the purpose of this study was to evaluate the use of airborne multispectral and hyperspectral thermal infrared tir image data for mapping surface minerals characteristic of active geothermal systems tir image data from the master multispectral spectrometer and the sebass hyperspectral spectrometer were acquired over steamboat springs nevada usa in september 1999 spectral emissivity information was extracted from the data and used to generate mineral maps using the master data it was possible to map the extent of the active geothermal area as well as silica rich vs clay rich areas using the sebass data the same areas could be mapped and additionally the presence of several minerals including opal quartz alunite anorthite albite and kaolinite could be identified the sebass data also detected previously unidentified hydrous sulfate minerals tamarugite and alunogen forming around active fumaroles laboratory spectral data and xrd analyses of field samples confirmed the dominant mineral phases identified remotely the airborne field and laboratory data together with temperature anomaly and fumarole location data from other studies were synthesized and linked to the surface geology to determine the diagnostic surface mineral expression that could be mapped with tir remotely sensed data for future exploration for similar geothermal systems opaline sinter deposits are the most diagnostic surface expression of hot spring activity at steamboat springs because they represent areas of the recent geyser activity the differentiation between opal and chalcedony deposits and the identification of hydrous sulfate minerals forming around active fumaroles are also important because chalcedony represents ancient sinter deposits and hydrous sulfate minerals indicate locations of fumaroles that may be venting diffusely with no geyser activity the surface expression of the geothermal system at steamboat springs is small which emphasizes the need for high spatial resolution airborne imagers the 90 m pixels of aster tir data over the same area were only capable of resolving the area of past and recent sinter deposits together master multispectral tir data covered the entire area 12 km 2 at 5 m spatial resolution and were capable of defining the extent of the sinter deposits and zones of hydrothermally altered rocks the sebass image swath was too narrow 256 m to add significant spatial information to the overall map but the high spectral content identified several important minerals related to the local geology and the mineralogic surface expression of the geothermal system

shallow drilling in the salton sea region the thermal anomaly during two shallow thermal drilling programs thermal measurements were obtained in 56 shallow 76 2 m and one intermediate 457 3 m depth holes located both onshore and offshore along the southern margin of the salton sea in the imperial valley california these data complete the surficial coverage of the thermal anomaly revealing the shape and lateral extent of the hydrothermal system the thermal data show the region of high thermal gradients to extend only a short distance offshore to the north of the quaternary volcanic domes which are exposed along the southern shore of the salton sea the central thermal anomaly has an arcuate shape about 4 km wide and 12 km long across the center of the anomaly the transition zone between locations exhibiting high thermal gradients and those exhibiting regional thermal gradients is quite narrow thermal gradients rise from near regional 0 09 c m to extreme 0 83 c m in only 2 4 km the heat flow in the central part of the anomaly is greater than 600 mw m2 and in the two local anomalies exceeds 1200 mw m2 the shape of the thermal anomaly is asymmetric with respect to the line of volcanoes previously thought to represent the center of the field with its center line offset south of the volcanic buttes there is no broad thermal anomaly associated with the magnetic high that extends offshore to the northeast from the volcanic domes the salton sea thermal anomaly can be described as three nested thermal features superimposed on the regional salton trough heat flux a broad region of elevated conductive heat flow with constant temperature gradients of about 0 1 c m a central anomaly of high 0 4 c m near surface gradients observed through a conductive thermal cap underlain by a nearly isothermal zone of hydrothermal circulation and two local anomalies with shallow temperature gradients as high as 0 8 c m superimposed on the central geothermal system these observations of the thermal anomaly provide important constraints for models of the circulation of the hydrothermal system thermal budgets based on a simple model for this hydrothermal system indicate that the heat influx rate for local hot spots in the region may be large enough to account for the rate of heat flux from the entire salton trough

mass spectrometric 230th 234u 238u dating of the devils hole calcite vein the devils hole calcite vein contains a long term climatic record but requires accurate chronologic control for its interpretation mass spectrometric u series ages for samples from core dh 11 yielded 230 th ages with precisions ranging from less than 1 000 years 2 for samples younger than 140 ka thousands of years ago to less than 50 000 years for the oldest samples 566 ka the 234 u 238 u ages could be determined to a precision of 20 000 years for all ages calcite accumulated continuously from 566 ka until 60 ka at an average rate of 0 7 millimeter per 10 3 years the precise agreement between replicte analyses and the concordance of the 230 th 238 u 234 u 238 u ages for the oldest samples indicate that the dh 11 samples were closed systems and validate the dating technique in general

anhydrite diagenesis in a vegetated sabkha al khiran kuwait arabian gulf abstract in the al khiran sabkha supratidal anhydrite occurs in three distinct morphological forms a hair cream anhydrite which occurs exclusively in association with the halophyte halocnemum strobilaceum and b nodular laminated cottage cheese anhydrite which is associated with a bacterial cyanobacterial mat the former occurs as a massive layer up to 4 cm thick with the ahydrite initially pseudomorphing gypsum crystals while in the latter the layers are up to 7 cm thick and the anhydrite occurs as microcrystalline laths giving an aphanitic texture c sub aqueous anhydrite formed by the alteration of prismatic gypsum crystals growing in drainage channels on the death of the halophyte the gypsum g rlhar2 anhydrite a metastable equilibrium is upset and the hair cream anhydrite undergoes a reverse transformation to microcrystalline alabastrine secondary gypsum followed by gypcrust formation the above changes result in a series of characteristic diagenetic textures that were studied in detail by scanning electron microscopy sem the major diagenetic mechanism during the g rlhar2 a transformation is a dissolution reprecipitation process that is only partially controlled by physico chemical factors a climatic and biological influence also plays a significant role in this sometimes annual change depending on the rainfall intensity in contrast type b shows better preservation potential the intimate relationship between the plant and its soil water requirements results in a particular hydrodynamic behaviour of the capillary groundwater brines in the vadose zone hence it is inferred that the individual diagenetic stages are also correlatable with the changing hydrological conditions of the sabkha type c represents a rare occurrence in sabkhas and is more akin to some deeper water occurrences albeit on a very small scale anhydrite is always formed after a gypsum precursor and under predictable physico chemical conditions an average annual temperature of 30 c and brine chlorinity of 4 mol cl kg 1 although it is confined to the vegetated zone of the marine sabkha stable isotope analysis indicates a dominantly continental origin for the groundwaters and coexisting sulphate minerals on a regional scale the vegetated kuwait sabkhas appear to occupy a climatic position intermediate between the classic uae sabkhas and those of the mediterranean region al khiran is the northernmost limit of the evaporite belt containing anhydrite in the arabian gulf the palaeoclimatic and sedimentological implications of this distribution may be of potential value in the rock record

the 2010 m w 7 2 el mayor cucapah earthquake sequence baja california mexico and southernmost california usa active seismotectonics along the mexican pacific margin the el mayor cucapah earthquake sequence started with a few foreshocks in march 2010 and a second sequence of 15 foreshocks of m 2 up to m4 4 that occurred during the 24 h preceding the mainshock the foreshocks occurred along a north south trend near the mainshock epicenter the mw 7 2 mainshock on april 4 exhibited complex faulting possibly starting with a m6 normal faulting event followed 15 s later by the main event which included simultaneous normal and right lateral strike slip faulting the aftershock zone extends for 120 km from the south end of the elsinore fault zone north of the us mexico border almost to the northern tip of the gulf of california the waveform relocated aftershocks form two abutting clusters each about 50 km long as well as a 10 km north south aftershock zone just north of the epicenter of the mainshock even though the baja california data are included the magnitude of completeness and the hypocentral errors increase gradually with distance south of the international border the spatial distribution of large aftershocks is asymmetric with five m5 aftershocks located to the south of the mainshock and only one m5 7 aftershock but numerous smaller aftershocks to the north further the northwest aftershock cluster exhibits complex faulting on both northwest and northeast planes thus the aftershocks also express a complex pattern of stress release along strike the overall rate of decay of the aftershocks is similar to the rate of decay of a generic california aftershock sequence in addition some triggered seismicity was recorded along the elsinore and san jacinto faults to the north but significant northward migration of aftershocks has not occurred the synthesis of the el mayor cucapah sequence reveals transtensional regional tectonics including the westward growth of the mexicali valley and the transfer of pacific north america plate motion from the gulf of california in the south into the southernmost san andreas fault system to the north we propose that the location of the 2010 el mayor cucapah as well as the 1992 landers and 1999 hector mine earthquakes may have been controlled by the bends in the plate boundary

the stability of sulfate and hydrated sulfate minerals near ambient conditions and their significance in environmental and planetary sciences abstract sulfate and hydrated sulfate minerals are abundant and ubiquitous on the surface of the earth and also on other planets and their satellites the humidity buffer technique has been applied to study the stability of some of these minerals at 0 1 mpa in terms of temperature relative humidity space on the basis of hydration dehydration reversal experiments updated phase relations in the binary system mgso 4 h 2 o are presented as an example to show how reliable thermodynamic data for these minerals could be obtained based on these experimental results and thermodynamic principles this approach has been applied to sulfate and hydrated sulfate minerals of other metals including fe both ferrous and ferric zn ni co cd and cu metal sulfate salts play important roles in the cycling of metals and sulfate in terrestrial systems and the number of phases extends well beyond the simple sulfate salts that have thus far been investigated experimentally the oxidation of sulfide minerals particularly pyrite is a common process that initiates the formation of efflorescent metal sulfate minerals also the overall abundance of iron bearing sulfate salts in nature reflects the fact that the weathering of pyrite or pyrrhotite is the ultimate source for many of these phases many aspects of their environmental significance are reviewed particularly in acute effects to aquatic ecosystems related to the dissolution of sulfate salts during rain storms or snow melt events hydrous mg ca and fe sulfates were identified on mars with wide distribution and very large quantities at many locations on the basis of spectroscopic observations from orbital remote sensing and surface explorations by rovers however many of these findings do not reveal the detailed information on the degree of hydration that is essential for rigorous interpretation of the hydrologic history of mars laboratory experiments on stability fields reactions pathways and reaction rates of hydrous sulfates likely to be found on mars enhance our understanding of the degrees of hydration of various sulfates that should currently exist on mars at various seasons and locations and during various atmospheric pressure and obliquity periods two sets of systematic experiments were described one on hydrous mg sulfates and the other on hydrous fe 3 sulfates also their implications to mars sulfates mineralogy were discussed

mud volcanoes the most important pathway for degassing deeply buried sediments abstract this paper discusses the nature of the phenomenon of mud volcanism with respect to degassing of deeply buried sediments mud volcanoes are defined as geological structures and their main elements are described based on the nature of activity mud volcanoes are grouped in to three main types and the relationship between each type and corresponding morphological expression is discussed the presented up to date data of the world geographical distribution of mud volcanoes show that they approximate to 1800 individuals a detail overview of geological environments in which they occur helps to deduce some necessary conditions for mud volcano formation the basic mechanisms of mud volcano formation are discussed specifically the fluid pressure hypothesis and some triggering events are identified the most common investigation approach and some criteria for recognizing of a submarine mud volcano on side scan sonar records and seismic sections are given mud volcanism in the mediterranean ridge an accretionary complex and black sea abyssal plane a back ark basin with tectonic regime of extension are described as case studies to show variety in morphology and common factors in development of mud volcanoes the manifestation of continuous gas migration through mud volcanoes is clarified and the attempt made to quantify the gas release shows that mud volcanoes are one of the significant natural sources of atmospheric methane emitting a total amount of about 10 3 to 12 6 tg annually

glacial interglacial differences in circulation and carbon cycling within the upper western north atlantic we investigated glacial interglacial changes in the circulation and carbon cycling in the western north atlantic subtropical gyre using hydrographic data and downcore records of the stable isotopic compositions of individual shells of bahamian benthic foraminifera potential temperature salinity depth relations show that modern thermocline 200 1000 m and deep 1000 2000 m waters in the providence channels bahamas originate in the sargasso sea and are typical of the subtropical gyre gradients in the stable isotopic compositions of late holocene planulina and cibicidoides species from the bank margins 400 to 1500 m depth reflect temperature nutrient and isotopic gradients of modern subtropical gyre waters the difference between the 18o of glacial maximum and late holocene foraminifera is 2 1 for the upper 900 m of the water column and 1 6 for deeper waters indicating that these waters were 4 c and 2 c cooler respectively during glacial time the glacial temperature gradient dt dz was similar to today while the base of the thermocline was 100 m shallower these results differ significantly from our earlier results from multiple shell 18o analyses which implied upper thermocline waters were only 1 c cooler and dt dz was greater during the glacial maximum the difference occurs because bioturbation adversely affects multiple shell analyses of glacial aged samples from shallow water depths at all depths above 1500 m foraminiferal 13c are greater during the glacial maximum than the late holocene by at least 0 1 to 0 2 as much as 0 6 in the lower thermocline indicating that nutrient concentrations throughout the thermocline were reduced and there was no oxygen minimum zone during the glacial maximum this suggests greater more uniform ventilation of the thermocline results of single and multiple shell 13c analyses of glacial age foraminifera compare favorably because samples most affected by mixing correspond to water depths where the glacial interglacial change of 13c was small cooler upper ocean waters during the glacial maximum reflect cooler temperatures at the ocean surface where isopycnal surfaces outcrop including large areas of the subtropical ocean a shallower thermocline base is consistent with southward migration of the northern edge of the subtropical gyre or increased mode water production enhanced thermocline ventilation is consistent with more vigorous winds and all isopycnal surfaces outcropping in the area of ekman downwelling

uranium series dating of marine and lacustrine carbonates of the possible uranium series dating schemes the most important and most widely applied to marine carbonates is 230th dating with 231pa dating playing an increasingly important role for this reason this review will focus on these two methods 230th dating also referred to as u th dating or 238u 234u 230th dating involves calculating ages from radioactive decay and ingrowth relationships among 238u 234u and 230th 232th is also typically measured as a long lived essentially stable index isotope over the time scales relevant to 230th dating at present 230th dating can in principle be used to date materials as young as 3 years and in excess of 600 000 years edwards et al 1987a 1993 edwards 1988 see stirling et al 2001 for an example of dating corals in excess of 600 000 years old 231pa dating also referred to as u pa dating involves calculating ages from the ingrowth of 231pa from its grandparent 235u at present 231pa dating can be used to date materials as young as 10 years and as old 250 000 years edwards et al 1997 230th dating covers all of the 231pa time range and more with somewhat higher precision and is therefore the method of choice if a single method is applied however the combination of 231pa and 230th dating is of great importance in assessing possible diagenetic mobilization of the pertinent nuclides and thereby the accuracy of the ages allegre 1964 ku 1968 even if the primary age exceeds the 250 000 year limit of 231pa dating the combined methods can be used to assess the degree to which the samples have remained closed over the past 250 000 years e g edwards et al 1997 thus

development and growth of recently exposed fumarole fields near mullet island imperial county california abstract new field observations aerial surveys lidar measurements and laboratory studies of mud samples 2006 to 2012 are reported of several formerly submerged fumarole complexes that are presently undergoing surface exposure as the salton sea level drops some remain submerged as of this writing 2012 the fumarole fields range in area from 1000 to 50 000 m2 they consist of hundreds of warm to boiling hot gryphons mud volcanoes salses mud pots and countless active gas vents unusually shaped mud volcanoes in the form of vertical tubes with central vents were observed in many places since exposure began in 2007 the surface morphology has changed dramatically with a trend toward more and growing gryphons larger mud pots and the development of sulfur vents chemical analysis of mud from several gryphons revealed the presence of the ammoniated sulfate minerals boussingaultite and lecontite among other more common sulfates with other geothermal features the fumaroles define a well defined lineament marking the trace of a probable fault a model for the development of gryphon morphology is presented

remotely sensed ammonia emission from fumarolic vents associated with a hydrothermally active fault in the salton sea geothermal field california 1 airborne hyperspectral imaging surveys were conducted over a geothermally active region straddling the southeastern shore of the salton sea in southern california the imagery was acquired across the 7 6 13 5 m longwave infrared region with a ground sample distance of approximately 1 m prominent thermal hot spots associated with fumaroles along a known fault line were observed to coincide with emission of free ammonia presumed to originate from geothermally induced pyrolytic decomposition of nitrogenous compounds that permeate the lake water sediment and adjacent agricultural terrain it is shown that the inferred fluxes of ammonia constitute a significant fraction 10 25 of the total atmospheric ammonia burden assessed for the salton sea environs and represent a previously unreported source for that locale

assessing subsidence rates and paleo water depths for tahiti reefs using u th chronology of altered corals we present uranium thorium chronology fora 102 m core through a pleistocene reef at tahiti french polynesia sampled during iodp expedition 310 tahiti sea level we employ total and partial dissolution procedures on the older coral samples to investigate the diagenetic overprint of the uranium thorium system although alteration of the u th system cannot be robustly corrected diagenetic trends in the u th data combined with sea level and subsidence constraints for the growth of the corals enables the age of critical samples to be constrained to marine isotope stage 9 we use the ages of the corals together with o based sea level histories to provide maximum constraints on possible paleo water depths these depth constraints are then compared to independent depth estimates based on algal and foraminiferal assemblages microbioerosion patterns and sedimentary facies confirming the accuracy of these paleo water depth estimates we also use the fact that corals could not have grown above sea level to place a maximum constraint on the subsidence rate of tahiti to be 0 39 m ka with the most likely rate being close to the existing minimum estimate of 0 25 m ka

alteration and remelting of nascent oceanic crust during continental rupture evidence from zircon geochemistry of rhyolites and xenoliths from the salton trough california abstract rhyolite lavas and xenoliths from the salton sea geothermal field southern california provide insights into crustal compositions and processes during continental rupture and incipient formation of oceanic crust salton buttes rhyolite lavas contain xenoliths that include granophyres fine grained altered rhyolites felsite and amphibole bearing basalts zircon is present in lavas and xenoliths surprisingly even in the basaltic xenoliths where it occurs in plagioclase rich regions interpreted as pockets of crystallized partial melt zircons in the xenoliths are exclusively late pleistocene holocene in age and lack evidence for inheritance u th isochron ages are 20 5 1 2 1 2 ka granophyres 18 3 3 5 3 6 ka felsite 30 1 12 4 14 1 ka and 9 2 6 6 7 0 ka basalts all errors 1 the dominant zircon population in the rhyolite lavas yielded u th ages between 18 and 10 ka with few pre quaternary xenocrysts present 18ozircon values are lower than typical crustal basement values thus ruling out rhyolite genesis by melting of continental crust moreover 18ozircon values are 0 5 1 0 lower than compositions achievable by zircon crystallization from residual melt in equilibrium with unaltered mid ocean ridge basalt suggesting that basaltic crust and silicic plutons in the subsurface of the salton sea geothermal field isotopically exchanged with meteoric waters this is evidence for deep reaching hydrothermal circulation and indicates rhyolite genesis by episodic remelting of altered basalts instead of fractional crystallization of unaltered basaltic magma

sulfate mineralogy of fumaroles in the salton sea geothermal field imperial county california abstract the salton trough lies in the transition between the san andreas fault and oblique spreading centers and transform faults in the gulf of california the salton sea geothermal field is the northernmost expression of those spreading centers in 2007 two ammonia emitting fumarole fields that had been submerged beneath the salton sea were exposed for the first time in nearly 50 years as the sea level continued to drop these fields have developed a number of boiling pools mud pots gryphons and a unique suite of ammonium sulfate minerals these have been studied over time with long wave infrared remote sensing coupled with ground truth surveys backed by laboratory analyses of the minerals many vents lie at the center of concentric rings of mineralization with systematic occurrence of different minerals from center to edge three semi concentric zones fumarole transition and evaporite have been defined with respect to ammonia emitting vents and bubbling pools the scale of these zones range from several meters localized around individual vents to that of the fumarole fields as a whole the fumarole zone is closest to the vents and locally contains cavernous sulfur crystals and significant deposits of gypsum mascagnite boussingaultite and other ammonium sulfates the transition zone comprises a dark brown surficial band of inconspicuous sodium nitrate underlain by anhydrite bassanite that is thought to have formed by ammonia oxidizing microbes interacting with the ammonium sulfates of the outer fumarole zone the evaporite zone is the outermost and contains blodite thenardite and glauberite which are typical of the sulfates associated with the shoreline of the salton sea remote sensing has shown that the mineral zones have remained relatively stable from 2013 to 2017 with minor variations depending on rainfall temperature and levels of agricultural runoff

speleothem evidence for late holocene climate variability and floods in southern greece abstract we present stable isotope data 18o 13c from a detrital rich stalagmite from kapsia cave the peloponnese greece the cave is rich in archeological remains and there are reasons to believe that flooding of the cave has directly affected humans using the cave using a combination of u th and 14c dating to constrain a site specific correction factor for 232th 238u detrital molar ratio a linear age model was constructed the age model shows that the stalagmite grew during the period from ca 950 bc to ca ad 830 the stable oxygen record from kapsia indicates cyclical changes of close to 500 yr in precipitation amount with rapid shifts towards wetter conditions followed by slowly developing aridity superimposed on this signal wetter conditions are inferred around 850 700 500 and 400 100 bc and around ad 160 300 and ad 770 and driest conditions are inferred to have occurred around 450 bc ad 100 150 and ad 650 detrital horizons in the stalagmite indicate that three major floods took place in the cave at 500 bc 70 bc and ad 450 the stable carbon isotope record reflects changes in biological activity being a result of both climate and human activities

protactinium 231 dating of carbonates by thermal ionization mass spectrometry implications for quaternary climate change measurement of protactinium 231 231pa in carbonates by thermal ionization mass spectroscopy yields 231pa ages that are more than 10 times more precise than those determined by decay counting carbonates between 10 and 250 000 years old can now be dated with 231pa methods barbados corals that have identical 231pa and thorium 230 230th ages indicate that the timing of sea level change over parts of the last glacial cycle is consistent with the predictions of the astronomical theory two devils hole calcite subsamples record identical 231pa and 230th ages suggesting that the chronology of this climate record is accurate

a northern lead in the orbital band north south phasing of ice age events abstract re analysis of existing data sets shows that they are fully consistent with northern insolation control of ice age cycles and do not provide strong support for alternate models invoking tropical or southern controls the coldest time of the last 100 ka in central greenland was nearly synchronous with the minimum in summer insolation about 24 ka bp thousand years before 1950 approximately one third of the total termination i warming since then was achieved over the almost 10 ka before the abrupt warming into the bolling which some workers have interpreted as the start of the warming southern warming as recorded in the byrd station antarctica ice isotopic record lagged northern warming co2 rise was roughly synchronous with southern warming methane rise may have been delayed a little as was sea level rise and the change in the isotopic composition of atmospheric oxygen was delayed significantly the data for the extrema just before termination ii are consistent with occurrence of the same phasing as for termination i but with somewhat different progression of the two terminations once initiated perhaps because of differences in the forcing

processes controlling water and hydrocarbon composition in seeps from the salton sea geothermal system california usa water mud gas and petroleum bearing seeps are part of the salton sea geothermal system ssgs in southern california seeps in the davis schrimpf seep fi eld 14 000 m 2 show considerable variations in water temperature ph density and solute content water rich springs have low densities 98 vol halogen geochemistry of the waters indicates that mixing of deep and shallow waters occurs and that near surface dissolution of halite may overprint the original fl uid compositions carbon isotopic analyses suggest that hydrocarbon seep gases have a thermogenic origin this hypothesis is supported by the presence of petroleum in a water dominated spring composed of 53 saturated compounds 35 aromatics and 12 polar compounds the abundance of polyaromatic hydrocarbons and immature biomarkers suggests a hydrothermal formation of the petroleum making the ssgs a relevant analogue to less accessible hydrothermal seep systems e g the guaymas basin in the gulf of california

high precision u series dating of last interglacial events by mass spectrometry houtman abrolhos islands western australia the houtman abrolhos islands situated at the western passive margin of the australian continent consist of a series of shelf edge coral reefs the central platforms of the reefs are late pleistocene in age and are generally some 3 5 m above present sea level the uppermost part of the last interglacial reefs normally has an upward shallowing sequence consisting of coral framestone coralline algal bindstone and skeletal grainstone to rudstone this sequence represents deposition in water depths of less than 2 m and provides a good indicator of sea level high precision mass spectrometric dates of corals from the abrolhos reefs including dates obtained from drill cores arological isotopic and stratigraphic criteria are established for the selection of suitable samples for dating and for assessing the reliability of dates using the screened dates and the stratigraphic evidence the timing and character of the sea level variations of the last interglacial in the abrolhos region are examined the data show that sea level of the last interglacial in the abrolhos was 4 m below its present height by ca 134 ka bp and probably reached about 2 m above present height at ca 133 ka bp the exact time at which sea level reached its peak 6 m above present sea level cannot be determined from our data but it is clear that the sea level high stand of the last interglacial lasted until ca 116 ka bp and that for much of the last interglacial sea level at the abrolhos was at a height of about 4 m above its present level

sodium sulphate deposits of neogene age the kirmir formation beypazari basin turkey the evaporite member of the kirmir formation was deposited in shallow lacustrine environments during the upper miocene the most soluble minerals of this member can be currently observed in the cayirhan mine the evaporite member which is composed of secondary gypsum at outcrop can be subdivided into a bedded lower unit and a massive upper unit in the bedded lower unit most of the gypsum throughout the basin can be identified as having been transformed from glauberite in the glauberite layers of the cayirhan mine some glauberite textures clear glauberite suggest a primary subaqueous free precipitation on a depositional floor more common however are the glauberite textures indicating an interstitial growth within a clayey magnesitic matrix in the thenardite layers accompanying the glauberite in the cayirhan mine some disruption structures can be assigned to synsedimentary dissolution these structures together with the textures of the thenardite suggest that the original sodium sulphate was mirabilite thenardite being a secondary phase which formed during early to moderate burial diagenesis the massive upper unit in which evidence of sodium bearing minerals is absent is characterized by laminated to banded gypsum and nodular gypsum in the marginal areas of the evaporitic basin whereas thick clast supported gypsum breccias prevail in the northern deeper part of the basin the brecciation of these calcium sulphate layers occurred as a result of synsedimentary gravitative slumping under tectonic control although the sulphur isotopic values d 34 s of the sulphates of the kirmir formation suggest a marine derived brine supply the oxygen isotopic values d 18 o and the strontium ratios 87 sr 86 sr do not support such a supply the origin of the mother brines the glauberite genesis the depositional model of the sodium sulphates and the salinity evolution are discussed d 2002 elsevier science b v all rights reserved

infrared stealthy surfaces why tes and themis may miss some substantial mineral deposits on mars and implications for remote sensing of planetary surfaces 1 infrared spectral observations have yielded many important insights into the nature of mars however spectral effects tied to surface roughness and particle size can make mineral deposits substantially more difficult to detect and identify than is generally known including for current investigations the effects hold for mars and other planets but here we focus on the impact on the exploration of mars laboratory spectra of pure smooth surfaced minerals have previously been used to conclude that the 1996 global surveyor thermal emission spectrometer tes and the 2001 mars odyssey thermal emission imaging system themis will detect a mineral deposit that covers 10 of a pixel those laboratory spectra have formed the foundation for modeling and interpretations of tes themis data and for development of the 2003 mars rover minites here for the first time we compare tes themis foundation data to laboratory field and unique airborne spectra of rough surfaces we demonstrate that substantial well crystalline regional mineral deposits including rock outcrops can be 100 exposed and remain undetected at the sensitivity of tes themis we then detail the physics which apply to all geologic materials previous studies have demonstrated the complicating physical effects for solids versus particulates for a range of minerals including oxides sulfates carbonates and each of the seven silicate classes we identify three cases of spectral behavior that can impact interpretations in case 1 physical effects cause a target to be undetectable by a given infrared instrument infrared stealthy in case 2 variations in spectral contrast mimic abundance variations which confounds abundance mapping in case 3 alteration of the spectral band shape impacts compositional interpretations optically smooth materials will be well represented in tes themis minites identifications conversely if a material forms an optically rough surface or sufficiently small particles on mars then it will be comparatively underrepresented or missed surface roughness occurs on three broad scales and roughness at the grain scale can be a primary variable in whether a mineral is detectable nondetection of certain key minerals e g carbonates can significantly impact geologic and climatic interpretations and landing site selection the tes themis detection threshold may be 10 coverage on the basis of specific laboratory samples but for field measurements that prediction represents an idealized lower bound interpretations built on nondetection should be revisited after defining the uncertainties in detection capabilities for specific instruments as applied to expected mineral surface textures on mars including at the grain scale the impact on future measurement strategies including minites should also be assessed

recent and long term behavior of the brawley fault zone imperial valley california an escalation in slip rate the brawley fault zone bfz and the brawley seismic zone constitute the principal transfer zone accommodating strain between the san andreas and im perial faults in southernmost california the bfz ruptured along with the imperial fault in the 1940 mw 6 9 and the 1979 mw 6 4 earthquakes although in each case only minor slip apparently occurred on the bfz several other episodes of slip and creep have been documented on the bfz historically until this study it has been unclear whether the past few decades reflect average behavior of the fault two trenches were opened and a series of auger holes were bored across three strands of the bfz at harris road to compare the amount of slip observed historically with the displacements observed in the paleoseismic record evidence is presented across the westernmost strand of the bfz and across the entire bfz at harris road to show that both the average vertical slip rate observed in modern times since 1970 and the vertical creep rate excluding coseismic slip observed during the 1970s are sig nificantly higher than the long term average across the westernmost strand the long term vertical rate is 1 2 1 5 0 5 mm yr and the average rate since about a d 1710 is determined to be no greater than 2 0 mm yr in contrast the average vertical rate between 1970 and 2004 across that strand was at least 4 3 mm yr and the 1970s vertical aseismic creep rate was 10 mm yr likewise across the entire bfz the long term vertical rate is 2 8 4 1 1 4 mm yr whereas the rate between 1970 and 2004 was at least 7 2 mm yr and the 1970s aseismic creep rate was 10 mm yr the long term strike slip rate cannot be determined across any strands of the bfz but may be significant in contrast to the commonly accepted higher sedimentation rates inferred for the entire imperial valley we find that the average sedimentation rate on the downthrown side of the bfz adjacent to mesquite basin in the millennium preceding the onset of agricultural influences was at most 3 5 mm yr finally a creep event occurred on the bfz during our study in 2002 and is documented herein online material appendices 1 and 2 trench logs and color versions of figures 7 8 and 10

duration and structure of the past four interglaciations reanalysis and additional dating of the devils hole 18o paleotemperature record confirm that the last interglaciation in the great basin the continental analog of marine isotopic substage 5e lasted 22 000 yr consistent with the vostok paleotemperature record which suggests a duration of 19 000 yr for this event in antarctica the three preceding interglaciations in the devils hole record analogs of marine isotopic substages 7e 9c and 11c range from 20 000 to 26 000 yr in duration a 20 000 yr duration for the last interglaciation is consistent with tims uranium series dated sea level high stands thus the widely held view that interglaciations were of 11 000 to 13 000 yr duration and constituted only about 10 of mid to late pleistocene climatic cycles needs reexamination the warmest portion of each interglaciation in the devils hole time series is marked by a 18o plateau signifying apparent climatic stability for periods of 10 000 to 15 000 yr duration

the last interglacial ocean the final effort of the climap project was a study of the last interglaciation a time of minimum ice volume some 122 000 yr ago coincident with the substage 5e oxygen isotopic minimum based on detailed oxygen isotope analyses and biotic census counts in 52 cores across the world ocean last interglacial sea surface temperatures sst were compared with those today there are small sst departures in the mid latitude north atlantic warmer and the gulf of mexico cooler the eastern boundary currents of the south atlantic and pacific oceans are marked by large sst anomalies in individual cores but their interpretations are precluded by no analog problems and by discordancies among estimates from different biotic groups in general the last interglacial ocean was not significantly different from the modern ocean the relative sequencing of ice decay versus oceanic warming on the stage 6 5 oxygen isotopic transition and of ice growth versus oceanic cooling on the stage 5e 5d transition was also studied in most of the southern hemisphere the oceanic response marked by the biotic census counts preceded led the global ice volume response marked by the oxygen isotope signal by several thousand years the reverse pattern is evident in the north atlantic ocean and the gulf of mexico where the oceanic response lagged that of global ice volume by several thousand years as a result the very warm temperatures associated with the last interglaciation were regionally diachronous by several thousand years these regional lead lag relationships agree with those observed on other transitions and in long term phase relationships they cannot be explained simply as artifacts of bioturbational translations of the original signals

sulfate minerals in evaporite deposits evaporite deposits preserve a wealth of information on earth s past surface conditions the deposits are sensitive indicators of depositional environment and climate recorded in a wide variety of mechanically and chemically produced sedimentary structures and fabrics unique to evaporite deposits is the record they carry of the hydrochemistry of surface waters including seawater sulfate minerals are important components in understanding the hydrochemistry of ancient surface waters sedimentological aspects of evaporite deposits were compiled by melvin 1991 in the compilation sedimentology specific to ca bearing sulfates was described by warren 1991 lowenstein and hardie 1985 handford 1991 and smoot and lowenstein 1991 discussed the sedimentology of evaporites in general these general principles can be applied specifically to the sulfate minerals in evaporite deposits sedimentological aspects of sulfate minerals in evaporite deposits are not discussed here for this information the reader is referred to the above references hardie et al 1985 and spencer and lowenstein 1988 discussed the petrography of evaporites and the interpretation of fabrics of evaporite minerals examples of petrographic aspects of sulfate minerals in evaporites are presented here along with references specific to the sulfate minerals for a more complete understanding of these aspects the reader is referred to the above references the major focus of this chapter is on the chemical aspects of the common sulfate minerals that occur in evaporite deposits the discussion begins with an explanation of the concept of chemical divides and the determination of evaporation paths and the evolution of brines in accordance with mineral solubility and the composition of dilute inflow waters determination of the precipitation pathways of the more soluble salts is more complex examples of sulfate mineral assemblages in evaporation systems calculated via thermochemical modelling are given for both marine and non marine systems the mineralogy of evaporite deposits is

timing and duration of the last interglacial evidence for a restricted interval of widespread coral reef growth abstract we report new mass spectrometric u series ages for eight last interglacial fossil reefs along the continental margin of western australia corals were selected in growth position from localities that are characterized by apparently low levels of diagenesis and relative tectonic stability so that the fossil reefs provide critical information on last interglacial sea levels without requiring corrections for tectonic movements in addition we have improved the constraint on the timing of onset of reef growth by recovering drill core coral from the base of the reefs uranium and thorium isotopes were measured with high levels of precision leading to improvements in age resolution and allowing samples which have undergone diagenetic exchange of uranium and thorium to be more easily identified and discarded these data supplement our previous results for rottnest island and leander point leading to more than seventy mass spectrometric u series ages from which constraints can be placed on the timing duration and character of the last interglacial sea level highstand reliable ages show that reef growth started contemporaneously at 128 1 ka along the entire western australian coastline while relative sea levels were at least 3 m above the present level because western australia is located far from the former penultimate glacial maximum ice sheets and are not significantly effected by glacial unloading these data constrain the timing of onset of the last interglacial period to 128 1 ka assuming reef growth started soon after sea level approached interglacial levels a unique regressive reef sequence at mangrove bay constrains the timing of termination of the last interglacial period to 116 1 ka the major episode of reef building however both globally and locally along the western australian coast is restricted to a very narrow interval occurring from 128 ka and 121 ka suggesting that global ocean surface temperatures were warm and or sea levels were stable enough to allow prolific reef growth only during the earlier part of the last interglacial

use of uranium thorium dating to determine past 14c reservoir effects in lakes examples from antarctica the chronologies of many lacustrine records suffer from radiocarbon reservoir effects due to the presence of dissolved dead carbon or to slow air water exchange here we use the tims uranium thorium disequilibrium method in conjunction with ams radiocarbon dating to determine the age of lacustrine carbonates and to quantify the past radiocarbon reservoir effect in two antarctic lakes with differing characteristics by correcting a single sample u th age for detrital contamination a 14 c offset of v18 000 yr was obtained for carbonates from the former grounding line of the ross sea ice sheet in glacial lake trowbridge this large reservoir effect is believed to result from the direct input of old co2 from glacial meltwater in the second example an isochron approach on coeval samples formed at the bottom of lake vida now exposed due to lower lake level yielded an age of 9550 340 yr b p and a radiocarbon reservoir age of 3600 yr this offset was probably the result of lack of aeration due to perennial ice cover and or strong density stratification this evidence for long term isolation of the lake bottom indicates another level of hardship for life in the dry valley lacustrine environment an environment studied as an analogue for extreme periods of earth history as well as for exobiological implications the success of the u th technique on these two examples indicates that tims u th dating will be of widespread use in dating the important climate information recorded in the dry valleys both within and beyond the 14 c age range fl 2001 elsevier science b v all rights reserved

experiments on the indentation process during cryptodome intrusions new insights into mount st helens deformation scaled experiments were carried out to study the deformation of a volcanic edifice by forcible intrusion of a cryptodome as the magma analogue is injected vertically into a sand cone asymmetric deformation is caused by the formation of a curved major shear fault which dips inward from one side of the cone to the opposite edge of the intrusion the path of the ascending silicone deviates to follow the trajectory of the fault and a lateral bulge grows slowly from the footwall of the fault the oblique push makes the bulge migrate outward causing extension upslope to form an asymmetric graben in the hanging wall of the major shear fault we suggest that the pattern of internal deformation within mount st helens prior to the may 18 1980 eruption was similar to that observed in our scaled models

tectonic evolution of the salton sea inferred from seismic reflection data the salton sea is an evolving pull apart basin located between the san andreas and imperial faults in southern california seismic and geological data reveal a rapidly subsiding southern sub basin that is bounded by a hinge zone to the north and northwest dipping normal faults to the south oblique extension across strike slip faults causes subsidence and leads to the formation of pull apart basins such as the salton sea in southern california the formation of these basins has generally been studied using laboratory experiments or numerical models1 2 3 4 here we combine seismic reflection data and geological observations from the salton sea to understand the evolution of this nascent pull apart basin our data reveal the presence of a northeast trending hinge zone that separates the sea into northern and southern sub basins differential subsidence 10 mm yr 1 in the southern sub basin suggests the existence of northwest dipping basin bounding faults near the southern shoreline which may control the spatial distribution of young volcanism rotated and truncated strata north of the hinge zone suggest that the onset of extension associated with this pull apart basin began after 0 5 million years ago we suggest that slip is partitioned spatially and temporally into vertical and horizontal domains in the salton sea in contrast to previous models based on historical seismicity patterns5 the rapid subsidence and fault architecture that we document in the southern part of the sea are consistent with experimental models for pull apart basins1

thermal infrared remote sensing and kirchhoff s law 1 laboratory measurements by the end of this century the earth observing system eos will provide worldwide thermal infrared multispectral images of the earth presenting geologists with a new kind of remote sensing data for interpretation thus it has become essential to understand the spectral emittance behavior of terrestrial surface materials perhaps the most fundamental question to be answereed is the extent to which such materials follow kirchhoff s law epsilon 1 r under laboratory and field conditions especially when a sample displays a thermal gradient we present the first rigorous quantitative comparison of directional and hemispherical reflectance and directional emittance of rock and soil samples in the laboratory with thermal gradients induced by heating them from below and allowing them to radiate to a colder background the results show that only an extemeley low density sample composed of fine particles sifted into a fairy castle structure displays a thermal gradient steep enough within the infrared skin depth to cause significant 6 departure from kirchhoff s law there is no detectable effect on the more normal terrestrial samples such as soils and rocks measured in the laboratory even when semitransparent coatings are involved thus both emittance and reflectance measurements can be used to calculate sample emissivity for most terrestrial surface materieals however the effect on kirchhoffian behavior of different field environments which may induce a steeper thermal gradient in particulate samples has yet to be determined and some low density surface materials like newly fallen snow frost and efflorescent salts on playas have yet to be measured in emittance

fluid flow through carbonate platforms constraints from 234u 238u and cl in bahamas pore waters the geometry timing and rate of fluid flow through carbonate margins and platforms is not well constrained in this study we use u concentrations and isotope ratios measured on small volumes of pore water from bahamas slope sediment coupled with existing chlorinity data to place constraints on the fluid flow in this region and by implication other carbonate platforms these data also allow an assessment of the behaviour of u isotopes in an unusually well constrained water rock system we report pore water u concentrations which are controlled by dissolution of high u organic material at shallow depths in the sediment and by reduction of u to its insoluble 4c state at greater depths the dominant process influencing pore water 234 u 238 u is alpha recoil in holocene sediments the increase of pore water 234 u 238 u due to recoil provides an estimate of the horizontal flow rate of 11 cm year but with considerable uncertainty at depths in the sediment where conditions are reducing features in the u concentration and 234 u 238 u profiles are offset from one another which constrains the effective diffusivity for u in these sediments to be1 2 10 8 cm 2 s 1 at depths between the holocene and these reducing sediments pore water 234 u 238 u values are unusually low due to a recent increase in the dissolution rate of grain surfaces this suggests a strengthening of fluid flow probably due to the flooding of the banks at the last deglaciation and the re initiation of thermally driven venting of fluid on the bank top and accompanying recharge on the slopes interpretation of existing chlorinity data in the light of this change in flow rate constrain the recent horizontal flow rate to be 10 6 3 4 cm year estimates of flow rate from 234 u 238 u and cl are therefore in agreement and suggest flow rates close to those predicted by thermally driven models of fluid flow this agreement supports the idea that flow within the bahamas banks is mostly thermally driven and suggests that flow rates on the order of 10 cm year are typical for carbonate platforms where such flow occurs 1999 elsevier science b v all rights reserved

dating open systems by the 238 u 234 u 230 th method application to quaternary reef terraces abstract the sedimentation conditions and diagenetic processes of biogenic and inorganic carbonates are such that the assumptions of a closed system evolution and the absence of initial th invoked in classical 238 u 234 u 230 th dating methods are very often not fulfilled for such material this problem is of interest for all studies requiring accurate dating of corals or aragonite rich sediments as in palaeoclimatology or neotectonics extending the approach of henderson and slowey nature 404 2000 61 66 we propose a consistent model that takes into account possible initial 230 th excess and where continuous selective redistribution gain or loss of 234 u 234 th and 230 th is controlled by recoil processes this model applied to quaternary marine terraces in barbados marie galante lesser antilles arc and pacific islands is able to explain the large scatter in isotopic compositions observed in the series of cogenetic corals or sediments we show that recoil processes generally tend to increase the 234 u 238 u and 230 th 234 u ratios with time leading to an overestimation of the apparent ages calculated using classical methods on the basis of simple assumptions identical marine initial 234 u 238 u 0 and 230 th 232 th 0 ratios we propose a method for calculating a best estimate of the age of cogenetic series our model offers an alternative way to date old reef terraces where corals are almost systematically altered and where classical dating methods do not apply it may also explain the apparent variations of the 234 u 238 u seawater initial ratio estimated from corals formed in the last 300 ka and the apparent uncoupling between sea level highstands and high latitude northern hemisphere summer insolation our set of equations can be applied to all weathering processes where the mobility of u series isotopes is controlled by recoil

direct u th dating of marine sediments from the two most recent interglacial periods a knowledge of the age of marine sediments is necessary to determine the timing of events and rates of processes in the marine realm and the relationships among marine and other climatically sensitive records the establishment of an accurate chronology for pleistocene marine sediments beyond the range of radiocarbon dating approximately the past 45 kyr has therefore been a goal of palaeoceanographers for decades early attempts1 2 based on measurements of the radionuclides 230th and 231pa were beset with problems and subsequent studies focused on tying fluctuations in marine sediment oxygen isotope records to events such as the formation of coral reef terraces and changes in the earth s magnetic polarity3 4 and tuning the resultant chronologies to the earth s orbitally driven insolation variations5 8 but these chronologies especially the age and duration of the last interglacial period have been challenged by several studies9 12 raising questions about the fundamental cause of pleistocene climate fluctuations here we report the direct u th dating of aragonite rich marine sediments from the bahamas and present an accurately dated marine oxygen isotope record for the last two interglacials we obtain dates of 120 127 kyr bp for the last interglacial and 189 190 kyr bp for the late stage 7 interglacial these dates are in accord with the general theory of orbitally forced climate fluctuations and demonstrate the potential of our direct dating approach for developing an absolute chronology for the pleistocene marine oxygen isotope record

rapid fluctuations in sea level recorded at huon peninsula during the penultimate deglaciation about 140 000 years ago the breakup of large continental ice sheets initiated the last interglacial period sea level rose and peaked around 135 000 years ago about 14 meters below present levels a record of last interglacial sea levels between 116 000 years to 136 000 years ago is preserved at reef vii of the uplifted coral terraces of huon peninsula in papua new guinea however corals from a cave situated about 90 meters below the crest of reef vii are 130 000 2000 years old and appear to have grown in conditions that were 6 c cooler than those at present these observations imply a drop in sea level of 60 to 80 meters after 130 000 years sea level began rising again in response to the major insolation maximum at 126 000 to 128 000 years ago the early about 140 000 years ago start of the penultimate deglaciation well before the peak in insolation is consistent with the devils hole chronology

the timing of high sea levels over the past 200 000 years the 230 th ages and 234 u 238 u ratios were determined for barbados corals that grew during periods of high sea level within the last 200 000 years the similarity of the initial 234 u 238 u ratios of some of the corals to the modern marine value suggests that these samples are pristine and that the marine 234 u 238 u ratio 83 000 and 200 000 years ago was within 2 per mil of the modern value the accuracies of the 230 th ages are evaluated on the basis of the 234 u 238 u values and a model of the behavior of uranium and thorium isotopes during diagenesis for the last three interglacial and two intervening interstadial periods sea level peaked at or after peaks in summer insolation in the northern hemisphere this overall pattern supports the idea that glacial interglacial cycles are caused by changes in earth9s orbital geometry the sea level drop at the end of the penultimate interglacial the last interglacial and a subsequent interstadial period lagged behind the decrease in insolation by 5 000 to 10 000 years

exploration of geothermal systems using hyperspectral thermal infrared remote sensing abstract visible near infrared vnir short wave infrared swir and thermal infrared tir remote sensing has long been used for geothermal exploration specific focus on the tir region 8 12 m has resulted in major rock forming mineral classes being identified and their areal percentages to be more easily mapped due in part to the linear mixing behavior of tir emission to understand the mineral compositional and thermal distribution of active geothermal surfaces systems hyperspectral tir data from the spatially enhanced broadband array spectrograph system sebass airborne sensor were acquired over the salton sea ca geothermal fields by the aerospace corporation on march 26 2009 and april 6 2010 sebass collects 128 wavelength channels at 1 m spatial resolution such high resolution data are rarely available for this type of scientific analysis and enabled the identification of rare mineral assemblages associated with the geothermally active areas one surface unit with a unique spectrum believed to be a magnesium sulfate of unknown hydration state was identified for the first time in the sebass data the abundance and distribution of this mineral varied between 2009 and 2010 likely due to the precipitation conditions data obtained by the sebass sensor were also regressed to the 32 channel spectral resolution of the mineral and gas identifier magi airborne sensor in order to test sensitivity limits at this lower spectral resolution all surface minerals were still effectively identified and therefore validated data at magi resolution are still very effective for accurate surface compositional mapping a similar approach used at active geothermal areas in other semi arid regions around the world has the potential to better characterize transient mineralogy identify indicators minerals understand the influence of surface and ground water and ultimately to locate new geothermal targets for future exploration furthermore new mineral and gas identification magi data serve as an excellent precursor for future spaceborne tir data such as the system proposed for the hyperspectral infrared imager hyspiri instrument

temperature control on the incorporation of magnesium strontium fluorine and cadmium into benthic foraminiferal shells from little bahama bank prospects for thermocline paleoceanography surface sediments from little bahama bank lbb intersecting the subtropical thermocline were used to assess the influence of temperature on the incorporation of mg sr f and cd into shells of benthic foraminifera samples were obtained from twelve cores along the southern slope of lbb covering a temperature range of 18 4 5 c between 301 and 1585 m we studied the composition of ten calcitic and one aragonitic species which are often used in paleochemical reconstructions mg ca ratios decrease with increasing water depth in all benthic species both with calcitic and aragonitic mineralogy showing a strong correlation with water temperature similar decrease is seen in sr ca but with no correlation with temperature none of the benthic species studied here exhibits a depth or temperature related change in f ca similar trends are observed when using an ocean wide dataset which includes shallow and deep core tops 300 5000 m we suggest that temperature is the primary control on the mg content of benthic foraminifera based on inorganic precipitation experiments and thermodynamic considerations presented here a 30 40 decrease in the mg distribution coefficient in calcite may be expected as a result of a temperature change from 25 c to 5 c which is about half the observed change in lbb a calibration curve applied to c pachyderma data from core tops along the slope of little bahama bank suggests that water temperature may be inferred from mg ca ratios with an uncertainty of about 0 8 c therefore the mg content of benthic foraminifera may provide a new independent temperature proxy for studying shallow waters paleoceanography the linear decrease in sr ca with increasing depth is not correlated with temperature the trend is constant from the ocean surface down to 5 km suggesting that pressure related effects on the calcification process are a more likely explanation than post depositional dissolution mg ca ratios in aragonitic shells of h elegans covary with temperature in accord with recent observations from corals in contrast the sr and f chemistry of h elegans is very different than that of corals and inorganically precipitated aragonites the disparities between the elemental composition of biogenic and inorganic phases and the large intergeneric and interspecific differences observed both in planktonic and benthic foraminifera implicate temperature related physiological processes in regulating the coprecipitation of elements in foraminiferal shells our work demonstrates that cd ca ratios of shallow calcitic species reflect the vertical distribution of nutrients no significant influence of temperature on the partitioning of cd into the shells was found our data extend the previous deep water calibration boyle 1992 thereby allowing for the reconstruction of the nutrient chemistry of shallow thermocline waters

the wister mud pot lineament southeastward extension or abandoned strand of the san andreas fault we present the results of a survey of mud pots in the wister unit of the imperial wildlife area thirty three mud pots pot clusters or related geothermal vents hundreds of pots in all were identified and most were found to cluster along a northwest trending line that is more or less coincident with the postulated sand hills fault an extrapolation of the trace of the san andreas fault southeastward from its accepted terminus north of bombay beach very nearly coincides with the mud pot lineament and may represent a surface manifestation of the san andreas fault southeast of the salton sea additionally a recent survey of vents near mullet island in the salton sea revealed eight areas along a northwest striking line where gas was bubbling up through the water and in two cases hot mud and water were being violently ejected

u th dating of carbonate platform and slope sediments absolute chronology of marine sediment beyond the 14c age range provides a test for models of climate change and has many other applications u th techniques have been used for such chronology by dating corals but extending these techniques to marine sediment is complicated by the presence of significant initial 230th both in detrital material and scavenged from seawater in this study we investigate four methods of solving the initial 230th problem for a particular type of marine sediment the aragonite rich sediments of carbonate platforms and slopes bulk sediment u th analyses can be corrected for initial th to yield ages with 2 to 3 kyr precision for highstand periods when sediment aragonite contents are particularly high uncertainty on the corrections causes inadequate precision for sediment from other periods however removal of scavenged th before analysis would enable a dramatic increase in this precision but has not proved successful despite a range of chemical leach approaches using heavy liquids to separate the various carbonate minerals found in bahamas sediment enables an isochron approach to correct for initial th but the presence of initial th from two sources requires correction or removal of one source of initial th before the other is deconvolved by the isochron quantitative removal of detrital material before isochron analysis proves a successful approach such isochron data demonstrate that although sediment remains closed to u th on a centimetre scale nuclides are moved from grain to grain by recoil such intergrain exchange is expected to be observed in all sediments containing mineral grains with different u concentrations measured 234u 238u allows the recoil movement to be corrected and results in isochron ages with precision sometimes as low as 3 kyr the accuracy of this approach has been proved by dating samples within the 14c age range sediments spanning the penultimate deglaciation have also been dated after a small correction for bioturbation the age for this event is found to be 135 2 3 5 ka this date is 8 kyr before the peak in northern hemisphere insolation and suggests that deglaciation is initiated by a mechanism in the southern hemisphere or tropics this isochron approach shows considerable promise for dating of sediments older than this event which will provide further information about the timing and mechanisms of global climate change

first use of an airborne thermal infrared hyperspectral scanner for compositional mapping in may 1999 the airborne thermal infrared hyperspectral imaging system spatially enhanced broadband array spectrograph system sebass was flown over mormon mesa nv to provide the first test of such a system for geological mapping several types of carbonate deposits were identified using the 11 25 m band however massive calcrete outcrops exhibited weak spectral contrast which was confirmed by field and laboratory measurements because the weathered calcrete surface appeared relatively smooth in hand specimen this weak spectral contrast was unexpected here we show that microscopic roughness not readily apparent to the eye has introduced both a cavity effect and volume scattering to reduce spectral contrast the macroroughness of crevices and cobbles may also have a significant cavity effect the diminished spectral contrast is important because it places higher signal to noise ratio snr requirements for spectroscopic detection and identification this effect should be factored into instrumentation planning and interpretations especially interpretations without benefit of ground truth sebass had the required high snr and spectral resolution to allow us to demonstrate for the first time the ability of an airborne hyperspectral thermal infrared scanner to detect and identify spectrally subtle materials

the aster spectral library version 2 0 abstract the advanced spaceborne thermal emission reflection radiometer aster on nasa s terra platform has been widely used in geological and other science studies in support of aster studies a library of natural and man made materials was compiled as the aster spectral library v1 2 and made available from http speclib jpl nasa gov the library is a collection of contributions in a standard format with ancillary data from the jet propulsion laboratory jpl johns hopkins university jhu and the united states geological survey usgs a new version of the library v2 0 is now available online or via cd which includes major additions to the mineral and rock spectra the aster library provides a comprehensive collection of over 2300 spectra of a wide variety of materials covering the wavelength range 0 4 15 4 m

pleistocene sea levels and tectonic uplift based on dating of corals from sumba island indonesia we collected and dated fossil corals from the uplifted reef tracts of sumba island mass spectrometry tims and ams was used to obtain reliable and precise radiochronological results it is possible to identify outcrops corresponding to major sea level high stands isotope stage 1 starting at 7 1 kyr bp 5a c a 86 kyr bp 5c c a 105 kyr bp 5e between 119 and 132 kyr bp and 9 c a 305 kyr bp the radiochronological data are thus broadly consistent with the timing of sea level fluctuations predicted by the astronomical theory of paleoclimates comparison with similar data from other terrace sequences and from benthic 18o records indicates that the average tectonic uplift rate at cape laundi sumba is on the order of 0 2 0 5m kyr the lowest values 0 3m kyr lead to the build up of polycyclic topographic terraces in which it is possible to find corals grown during different interstadial or even interglacial times

uranium series chronology and environmental applications of speleothems an increasing number of scientists recognize the value of speleothems1 as often extremely well preserved archives of information about past climate vegetation hydrology sea level nuclide migration water rock interaction landscape evolution tectonics and human action well constrained data are required to document past changes reconstruct past patterns and predict future responses of the earth system at a wide range of spatial and temporal scales speleothems are particularly useful in this regard because they can be found in many locations of the globe sampled at high resolution and reliably dated using high precision uranium series techniques speleothems are bodies of mineral material formed in caves as the result of chemical precipitation from groundwater flowing or dripping in a cave most speleothems are composed of calcite formed by slow degassing of co2 from supersaturated groundwater but aragonite and gypsum forms are also common particularly near cave entrances where evaporative effects are important a host of different speleothem types decorate the walls ceilings and floors of caves and their mineralogy and morphology is a function of fluid flow and chemistry of waters feeding a particular location as well as the ambient conditions temperature chemistry light in the air or water filled void subaerial forms include the familiar stalagmites stalactites draperies flowstones subaqueous forms include rimstone pools rafts mammillary calcite wall coatings and dog tooth spar for an extensive review of the types of speleothem that have been observed see hill and forti 1997 speleothems are used in a multitude of ways to explore past environmental conditions perhaps the most fundamental of which is their very presence or absence deposition of speleothems relies on sufficient water supply and soil co2 to enable dissolution and transport of reactants in the vadose zone to underlying caves in arid or glacial times conditions may not have been favorable for speleothem formation

relations of ammonium minerals at several hydrothermal systems in the western u s abstract ammonium bound to silicate and sulfate minerals has recently been located at several major hydrothermal systems in the western u s utilizing newly discovered near infrared spectral properties knowledge of the origin and mineralogic relations of ammonium minerals at known hydrothermal systems is critical for the proper interpretation of remote sensing data and for testing of possible links to mineralization submicroscopic analysis of ammonium minerals from two mercury and gold bearing hot springs deposits at ivanhoe nevada and mclaughlin california shows that the ammonium feldspar buddingtonite occurs as fine grained euhedral crystals coating larger sulfide and quartz crystals ammonium feldspar seems to precipitate relatively late in the crystallization sequence and shows evidence for replacement of nh4 by k or other monovalent cations some buddingtonite is observed in close association with mercury but not with gold ammonioalunite is found in a variety of isolated crystal forms at both deposits nitrogen isotopic values for ammonium bearing minerals show a 14 range in composition precluding assignment of a specific provenance to the nitrogen the correlations of nitrogen isotopic values with depth and ammonium content suggest some loss of nitrogen in the oxidizing supergene environment possibly as a metastable mineral the high ammonium content in these hydrothermal systems the close association to mercury and the small crystal size of the ammonium bearing minerals all suggest that ammonium may be transported in a late stage vapor phase or as an organic volatile such a process could lead to the formation of a non carbonaceous organic aureole above a buried geothermal source the discovery of a 10 km outcrop of ammonium minerals confirms that significant substitution of ammonium in minerals is possible over an extensive area and that remote sensing is a feasible means to detect such aureoles

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr