lithofacies analysis of colluvial sediments an aid in interpreting the recent history of quaternary normal faults in the basin and range province western united states inferring the frequency and magnitude of past earthquakes from the stratigraphy in exposures of normal faulted sediments is difficult because colluvial lithofacies assemblages adjacent to faults are complex similarities in facies assemblages adjacent to young fault scarps in arid to semiarid areas such as the basin and range province allow lithofacies to be grouped into two genetic architectural elements debris and wash elements upper and lower facies associations can commonly be recognized within each element a lithofacies code scheme similar to those used in the analysis of fluvial and glacial lithofacies sequences provides a concise way of illustrating lithofacies relations in fault exposures the source lithology of colluvial lithofacies is shown in the code and soil horizon symbols can be included the architecture of lithofacies assemblages near fault scarps in semiarid areas is explained by a model of colluvial sedimentation in response to a single surface faulting event analysis of lithofacies assemblages exposed in three trenches across normal faults in the eastern basin and range shows how the model can be used to interpret fault histories similar facies analysis methods may be useful in interpreting colluvial sequences formed by non tectonic processes

paleosol carbonates from the omo group isotopic records of local and regional environmental change in east africa abstract pliocene and pleistocene sedimentary rocks from the omo turkana basin in east africa are well known for fossil and archeological evidence of human evolution and provide a unique opportunity to study four million years of environmental change in a rift basin this study uses carbon and oxygen isotope ratios of pedogenic carbonates to examine environmental variability across 5000 km 2 within the omo turkana basin an expanded isotopic dataset including the first isotopic data on pedogenic carbonates from the shungura formation and new data from the nachukui and koobi fora formations is compared to published isotopic records from both the omo turkana basin and the lower awash basin ethiopia regionally the carbon isotope record indicates a steady increase of c 4 vegetation in floodplain environments for the past 4 million years the oxygen isotopic record indicates that the isotopic composition of rainfall was depleted in 18 o relative to today s waters and that both basins likely received more rainfall in the pliocene than today a shift to higher 18 o values in paleosol carbonate after 2 ma in the omo turkana basin but not in the lower awash basin suggests that the ecology and hydrology in these two rift basins were influenced by different climatic regimes in addition to regional trends pedogenic carbonates sampled from different parts of the basin show that the distribution of c 4 vegetation and soil water 18 o values varied with proximity to the axial river system and specifically that c 3 vegetation was more dominant in soils of the shungura formation compared with coeval sediments downstream in the nachukui and koobi fora formations this large isotopic dataset from pedogenic carbonates provides the opportunity to examine how terrestrial systems responded to global climate change during the last 4 million years from both local and regional perspectives the isotopic data indicate that local basin and climate dynamics strongly influenced the impact of large scale environmental change in east african rift basins

integrated seismic hazard analysis of the wasatch front utah we examined the combined effects of different sources that influence earthquake hazard of the populated wasatch front utah we first evaluated the fault stress interaction of the two largest historic earthquakes of the intermountain seismic belt isb the 1959 hebgen lake montana m s 7 5 and the 1983 borah peak idaho m s 7 3 earthquakes which experienced multisegment normal faulting ruptures estimates of the static stress change for these events revealed an increase in coulomb failure stress in areas of extended aftershocks these observations suggested that fault stress analysis is applicable in evaluating the spatial distribution of aftershocks after large normal faulting earthquakes in the same extensional stress regime of the eastern basin range including the wasatch front utah which encompasses the 370 km long wasatch fault and surrounding faults on the basis of this result we applied the modeling technique to the historically seismically quiescent wasatch fault and examined the relation between the pattern of stress change and the space time distribution of paleoearthquakes ages and locations of the wasatch fault paleoseismic data imply 17 single segment or 11 multisegment ruptures in the past 5 6 kyr we prefer the multisegment model because almost all of the large historical normal faulting earthquakes in the isb were multisegment fitting the along fault displacements by an analytic half ellipse function provides a first order distribution of the displacement over an entire rupture length and allows new estimates of fault slip rates and seismic moment with these data we also estimated the occurrence rate of m w 6 6 wasatch paleoearthquakes and showed that the rate was about three times higher than that inferred by the historical seismicity this result along with new information from a megatrench on the wasatch fault near salt lake city that revealed no scarp forming earthquakes between ca 9 0 and 15 5 ka suggests that large wasatch fault events in the past 5 6 kyr may be clustered the recurrence rate of large earthquakes estimated by the geodetic measured strain on the other hand is three to four times higher than that estimated by the long term fault slip rate this difference together with the observation of a low regional strain rate from historical seismicity suggests that cumulative aseismic deformation may be significant on the wasatch fault we also examined a major consideration for along strike segmentation namely how stress contagion could affect the probability of failure of adjacent faults including paleoearthquake derived fault slip rates global positioning system derived geodetic moment rates and the effect of stress contagion in the earthquake hazard estimation for a specific location in the salt lake valley revealed an increase in the annual frequency of peak ground acceleration 0 25 g by a factor of 1 4 4 0 and 5 4 respectively compared with that derived from historical seismicity only manuscript received 31 may 2001

pedogenic carbonate proxies for amount and seasonality of precipitation in paleosols the depth to carbonate nodular bk horizon in soils d in cm is correlated with mean annual precipitation p in mm so that bk horizons are deep in subhumid regions but shallow in semiarid regions previous quantifications of this relationship are unchanged by this new compilation of 807 soils p 137 24 6 45 d 0 013 d 2 where r 2 0 52 and standard error s e 147 mm in most north american postglacial soils the bk horizon is thin and well defined whereas in monsoonal tropical soils of pakistan and kenya the bk horizon is thick and diffuse data from 675 modern soils define the relationship between the thickness of soil with nodules t in cm and mean annual range of precipitation m in mm difference between monthly means of wettest and driest months m 0 79 t 13 71 where r 2 0 58 and s e 22 mm the relationship between carbonate nodule size s in cm and soil age a in ka is quantified by 9 radiocarbon dated soils from las cruces new mexico a 3 92 s 0 34 where r 2 0 57 and s e 1 8 k y these transfer functions are applied to reconstructing paleoclimatic change from paleocene eocene paleosols of the north horn formation and flagstaff limestone of axhandle canyon utah the terminal paleocene spike of warmth recorded by fossil plants in nearby wyoming was coincident with a brief peak in both mean annual precipitation and mean annual range of precipitation in utah

shallow erosion beneath turbidity currents and its impact on the architectural development of turbidite sheet systems erosion by turbidity currents changes the morphology of the sea floor the relief of the scoured surface may affect the dynamics of the flow and thereby the pattern of deposition this could in turn affect flow and deposition patterns in subsequent events this study investigates shallow centimetre to decimetre scale erosion beneath turbidite sheet sandstones of the oligocene macigno formation of north west italy where erosion and deposition are variably coupled at the bed scale in a net aggradational setting the research focus was on i the recognition of scour edges and erosive surfaces ii quantification of spatial differences in the amount of erosion and iii an investigation of how this differential erosion can be compensated by the deposits directly overlying the erosional surfaces where they can be observed scour edges commonly have sills of the overlying sandstone intruding beneath blocks and wings of the substrate that is being eroded a consequence of this de laminating scouring style is that erosional surfaces are bedding parallel when followed away from the scour edges giving the appearance of normal conformable bed bases despite their cryptic nature such bedding parallel scour surfaces can be recognized by comparing serial detailed sedimentary logs here 16 bed parallel scour surfaces were identified in a succession comprising 95 beds different styles of compensation by the overlying turbidite beds are defined based on differential sedimentation inside and outside of the scour relief it is found that differential erosion is on average under compensated by differential sedimentation in some cases the overlying deposits anti compensate being thinner at the location where more erosion has occurred unequal spatial distribution of differential erosion in the study area combines with sedimentary under compensation to result in a trend of accumulating section thickness differences over multiple beds in one ca 25 m thick package the maximum cumulative change in lateral gradient during some 20 events reached 0 17 before being reset by a single event this process can be interpreted either as a lobe compensation effect or as a scour enhancement effect depending on the orientation of the palaeohorizontal datum if allowed to proceed the latter process could force the system past a channellization threshold prompting a change from sheet to channelled architecture this type of shallow substrate scouring and differential deposition is likely to be an important process in the build up of sheet turbidite sandstone units and could play a major role in autocyclic adjustment of local sea floor gradients

the massive fossil humerus from the oldowan horizon of gombore i melka kunture ethiopia 1 39 ma abstract a well preserved distal portion of a left humerus was discovered in 1976 during excavations directed by j chavaillon at the gombore i site in the melka kunture area ethiopia the specimen labelled gombore ib 7594 formally melka kunture 3 or mk3 was found in situ within unit 2 of level b which is dated to 1 39 ma and includes a rich oldowan paleolithic assemblage although mk3 has never been described in detail it appeared in the literature several times and from a taxonomic point of view has been alternatively regarded as homo australopithecus or paranthropus according to our analysis mk3 exhibits a suite of features that fit the variability of the genus homo and does not display any clear australopithecus paranthropus affinity nevertheless mk3 adds a great deal of variability to the genus homo at least as far as the early pleistocene fossil record is concerned in particular our quantitative approach which combines traditional morphometric analyses and geometric morphometrics highlights traits that are uncommon among the plio pleistocene fossil record while affinities with mid to late pleistocene representatives of homo are observed in addition the large size of mk3 suggests that this humerus belonged to an individual whose body weight approached 90 kg far from the range of body size known for homo representatives in the early pleistocene and as big as those of extant humans or even gorillas we suggest that such peculiar features are of interest when regarded from an ecological perspective thus dimension and morphology of mk3 may be considered as an exaptation that became useful when early humans dispersed to high altitudes such as those of the upper awash basin on the ethiopian plateau at heights above 2000 m

chronostratigraphy and correlation of the plio pleistocene tephra layers of the konso formation southern main ethiopian rift ethiopia abstract the plio pleistocene konso formation is widely exposed in the konso area located at the southwestern end of the southern sector of the main ethiopian rift it is known for its rich acheulean archeological occurrences and abundant vertebrate fossils including those of a boisei and h erectus the formation also contains more than 30 tephra layers the lithologic characterization and major element compositions of discrete glass shards of these tephra combined with single crystal 40 ar 39 ar dating of seven tuffs have established the tephrostratigraphy and age range of the 200 m thick formation the succession at konso was deposited between approximately 1 9 and 1 4 ma and is divided into the sorobo turoha kayle and karat members in ascending stratigraphic order two of the konso tephra are correlative to the pliocene kbs and the early pleistocene chari tuffs of the omo turkana basin along the ethiopian and kenyan border this correlation enables precise time controlled comparisons of faunal and archeological remains between the two regions

segmentation and supercycles a catalog of earthquake rupture patterns from the sumatran sunda megathrust and other well studied faults worldwide abstract after more than 100 years of earthquake research earthquake forecasting which relies on knowledge of past fault rupture patterns has become the foundation for societal defense against seismic natural disasters a concept that has come into focus more recently is that rupture segmentation and cyclicity can be complex and that a characteristic earthquake model is too simple to adequately describe much of fault behavior nevertheless recognizable patterns in earthquake recurrence emerge from long high resolution spatially distributed chronologies researchers now seek to discover the maximum minimum and typical rupture areas the distribution variability and spatial applicability of recurrence intervals and patterns of earthquake clustering in space and time the term supercycle has been used to describe repeating longer periods of elastic strain accumulation and release that involve multiple fault ruptures however this term has become very broadly applied lumping together several distinct phenomena that likely have disparate underlying causes we divide earthquake cycle behavior into four major classes that have different implications for seismic hazard and fault mechanics 1 quasi periodic similar ruptures 2 clustered similar ruptures 3 clustered complementary ruptures rupture cascades and 4 superimposed cycles segmentation is likewise an ambiguous term we identify master segments and asperities as defined by barriers to fault rupture these barriers may be persistent rarely or never traversed frequent occasionally traversed or ephemeral changing location from cycle to cycle we compile a catalog of the historical and paleoseismic evidence that currently exists for each of these types of behavior on major well studied faults worldwide due to the unique level of paleoseismic and paleogeodetic detail provided by the coral microatoll technique the sumatran sunda megathrust provides one of the most complete records over multiple earthquake rupture cycles long historical records of earthquakes along the south american and japanese subduction zones are also vital contributors to our catalog along with additional data compiled from subduction zones in cascadia alaska and middle america as well as the north anatolian and dead sea strike slip faults in the middle east we find that persistent and frequent barriers rupture cascades superimposed cycles and quasi periodic similar ruptures are common features of most major faults clustered similar ruptures do not appear to be common but broad overlap zones between neighboring segments do occur barrier regions accommodate slip through reduced interseismic coupling slow slip events and or smaller more localized ruptures and are frequently associated with structural features such as subducting seafloor relief or fault trace discontinuities this catalog of observations provides a basis for exploring and modeling root causes of rupture segmentation and cycle behavior we expect that researchers will recognize similar behavior styles on other major faults around the world

long term 17 ma turbidite record of the timing and frequency of large flank collapses of the canary islands volcaniclastic turbidites on the madeira abyssal plain provide a record of large volume volcanic island flank collapses from the canary islands this long term record spans 17 ma and comprises 125 volcaniclastic beds determining the timing provenance and volumes of these turbidites provides key information about the occurrence of mass wasting from the canary islands especially the western islands of tenerife la palma and el hierro these turbidite records demonstrate that landslides often coincide with protracted periods of volcanic edifice growth suggesting that loading of the volcanic edifices may be a key preconditioning factor for landslide triggers furthermore the last large volume failures from tenerife coincide with explosive volcanism at the end of eruptive cycles many large volume canary island landslides also occurred during periods of warmer and wetter climates associated with sea level rise and subsequent highstand however these turbidites are not serially dependent and any association with climate or sea level change is not statistically significant

diaphyseal cross sectional geometry of near eastern middle palaeolithic humans the tibia external osteometric assessments of near eastern middle palaeolithic human tibial diaphyseal robusticity have been used to argue for significant differences in locomotor loading regimes between late archaic and early modern humans from the middle palaeolithic of that region reassessment of tibial diaphyseal strength using cross sectional geometry of their shafts scaled against biomechanically appropriate measures of body mass and beam length reveals no significant difference between the near eastern late archaic human and qafzeh skhul early modern human samples this is in agreement with other assessments of their comparative levels of locomotor strength and endurance indicating similar levels of summed loads upon their lower limbs once body mass and beam length are appropriately incorporated into the analysis at the same time there are no systematic differences in either relative cortical area within cross sections or the biomechanically relevant distribution of bone indicated by perpendicular second moments of area between these samples what emerges from a consideration of appropriately scaled measures of strength of these nemp tibiae however precise the estimates employed is that contrary to previous assessments there are no grounds for inferring a significant change in locomotor activity levels or patterns between late archaic and early modern humans in the near eastern middle palaeolithic

holocene surface rupture history of an active forearc fault redefines seismic hazard in southwestern british columbia canada author s morell kd regalla c amos c bennett s leonard l graham a reedy t levson v telka a

onset of submarine debris flow deposition far from original giant landslide submarine landslides can generate sediment laden flows whose scale is impressive individual flow deposits have been mapped that extend for 1 500 km offshore from northwest africa these are the longest run out sediment density flow deposits yet documented on earth this contribution analyses one of these deposits which contains ten times the mass of sediment transported annually by all of the world s rivers understanding how this type of submarine flow evolves is a significant problem because they are extremely difficult to monitor directly previous work has shown how progressive disintegration of landslide blocks can generate debris flow the deposit of which extends downslope from the original landslide we provide evidence that submarine flows can produce giant debris flow deposits that start several hundred kilometres from the original landslide encased within deposits of a more dilute flow type called turbidity current very little sediment was deposited across the intervening large expanse of sea floor where the flow was locally very erosive sediment deposition was finally triggered by a remarkably small but abrupt decrease in sea floor gradient from 0 05 degrees to 0 01 degrees this debris flow was probably generated by flow transformation from the decelerating turbidity current the alternative is that non channelized debris flow left almost no trace of its passage across one hundred kilometres of flat 0 2 degrees to 0 05 degrees sea floor our work shows that initially well mixed and highly erosive submarine flows can produce extensive debris flow deposits beyond subtle slope breaks located far out in the deep ocean

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

δ18o in mollusk shells from pliocene lake hadar and modern ethiopian lakes implications for history of the ethiopian monsoon abstract two of the five lacustrine intervals in the largely fluvial hadar formation afar ethiopia occur in the sidi hakoma member deposited 3 4 3 2 ma in a perspective of the 18o of 11 modern ethiopian lakes and their shells the 18o of the hadar fossil shells provide a snapshot of the nature of ancient lake hadar and ethiopia s climate in the pliocene ethiopia s modern lakes both in the rift and on the western plateau are fed by drainage of plateau rain with its well established barely negative 18osmow of 1 3 except for the man made lake koka reservoir all other ethiopian lakes are isotopically quite positive ranging from 5 4 to 16 0 indicating how significant evaporation is in their water budget shells from lakes with extant mollusk populations are mostly in isotopic equilibrium with the 18o and temperature of their lake water the upper transgressive interval in the sidi hakoma member is the largest one in the formation beginning at its base with the gastropod beds beach deposits mollusks from shell beds other than the gastropod beds show more positive and more variable 18o between shells with internal variations within shells as much as 7 at these times the site must have been underlain by a shallow partially isolated embayment of lake hadar which underwent rapid expansions and then contractions by evaporation within the few year lifetimes of the individual mollusks the results from the gastropod beds are of most significance for interpreting the overall paleoclimate at hadar their uniformly negative 18opdb shell values that average 6 7 represent a much less evaporated stage of lake hadar when its 18osmow was 8 lower than the spectrum of modern lakes in ethiopia and indeed even 3 or more lower than average modern plateau rain to explain such negative values we hypothesize that the atlantic derived air mass component to the ethiopian monsoon was persistently strengthened during pliocene summers which intensified the amount and the negative isotopic character of rainfall onto both the afar and the ethiopian plateaus that drained to lake hadar a similar phenomenon characterized the brief periodic pluvial episodes of the quaternary including the latest in the early holocene known as the african humid period in contrast to the hot semi desert steppe conditions of today s western afar the diverse abundant terrestrial fossil fauna at hadar including the early hominid australopithecus afarensis is explained by the wetter and probably cooler summers that persisted throughout the late pliocene

modification of wave cut and faulting controlled landforms from a casual observation that the form of degraded fault scarps resembles the error function this investigation proceeds through an elementary diffusion equation representation of landform evolution to the application of the resulting equations to the modern topography of scarplike landforms the morphologic observations can be analyzed either in the form of one or more cross strike elevation profiles or in the form of the slope offset plot a point plot of maximum scarp slope versus scarp offset working with either or both of these data representations for nine geologic structures which range in age from 3 to 400 ka b p and in offset from 1 to 50 m we apply analytical solutions for the vertical initial value scarp the vertical continuous offset scarp and the finite slope initial value scarp the model calculations are intrinsically ambiguous yielding as the final answer only the product t in the case of the initial value problem or the product a 1 in the case of the repeated faulting problem here t is the age of a single scarp forming event 2a is the vertical slip rate and is the mass diffusivity a single profile across three sea cliffs along the santa cruz california coast is analyzed as three separate initial value problems a reasonably constrained age for the sea cliff standing above the highway 1 platform returns 11 gkg 1 gkg 1 m2 ka with this we can date the two older sea cliffs in fact we do the converse age estimates for these two older sea cliffs based on a uniform rate of uplift both yield the same as for the lower sea cliff we treat a single profile of the raymond fault in pasadena san marino in terms of the repeated faulting problem for it the uplift rate of r crook and others yields 16 gkg the very substantial preexisting offset across the raymond fault must have been buried leveled some 230 ka b p when the modern topography began to form our analysis of the lake bonneville shoreline scarps reveals a dependence of t on 2a suggestive of nonlinear modification processes this appearance is treated with the finite slope initial value scarp model to determine 1 1 gkg for the lake bonneville shoreline scarps the suggestion of m n machette that approximately 100 000 year old meter high scarps are unobservable in weakly consolidated alluvial terranes of the basin and range and rio grande rift valley provinces can be formulated as 1 gkg the coincidence between this inequality and the lake bonneville shoreline is striking and it suggests that the value of 1 gkg may be generally applicable as a good first approximation to the modification of alluvial terranes within the semiarid regions of the western united states the lake bonneville shoreline is the basis for dating four sets of fault scarps in west central utah the drum mountains fault scarps can be modeled in several different circumstances but the most likely interpretation is that these fault scarps formed as the result of a single episode of normal faulting 3 6 to 5 7 ka b p the younger age is associated with quite low initial slope angles 25 the other three sets of fault scarps show no evidence for finite initial value slopes fault scarps along the eastern base of the fish springs range are very young 3 ka b p we estimate the age of fault scarps along the western flank of the oquirrh mountains to be 32 ka b p which meets the weak geologic constraint that they be older than the lake bonneville shoreline fault scarps along the northeastern margin of the sheeprock mountains are even older 53 ka b p an intriguing consequence of our single event analysis of these scarps is that an 11 5 m offset occurred in a single earthquake

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

frequency and timing of landslide triggered turbidity currents within the agadir basin offshore nw africa are there associations with climate change sea level change and slope sedimentation rates abstract older sequence stratigraphic models suggested that submarine landslide and turbidite activities are greatest during sea level lowstands however growing evidence indicates that many turbidite systems are also active during sea level transgressions and highstands the moroccan turbidite system comprises three depocentres of which agadir basin is closest to the moroccan slope and canary archipelago the very large volumes of sediment transported by individual sediment flows in this system suggest that they are triggered by landslides extensive core coverage and dating control for the agadir basin deposits have provided an excellent opportunity to derive accurate records of turbidite and associated landslide frequency for the last 600 ka previous studies in the more distal madeira abyssal plain depocentre have indicated that large volume 50 km 3 turbidites occurred at oxygen isotope stage ois boundaries this study of agadir basin confirms that two major turbidites beds a5 and a12 occurred during glacial interglacial transitions associated with ois4 and ois6 however this association is based on just two examples and two other large volume turbidites beds a7 and a11 did not occur at a stage boundary the main conclusion of this study is that 90 of turbidites and landslides occurred during rising and high sea level which represents 40 of the total time during the last 600 ka only 10 of the turbidites and landslides occurred during glacials 40 of the time with a paucity of turbidites and landslides at peak glacial lowstands a comparison to sediment accumulation rates in the source area of the turbidite suggests that landslides did not occur preferentially during periods of more rapid sedimentation rate although sedimentation rates in this area only varied from 4 to 6 g cm 2 ka 1

isotopic composition of waters from ethiopia and kenya insights into moisture sources for eastern africa 1 oxygen and deuterium isotopic values of meteoric waters from ethiopia are unusually high when compared to waters from other high elevation settings in africa and worldwide these high values are well documented however the climatic processes responsible for the isotopic anomalies in ethiopian waters have not been thoroughly investigated we use isotopic data from waters and remote data products to demonstrate how different moisture sources affect the distribution of stable isotopes in waters from eastern africa oxygen and deuterium stable isotopic data from 349 surface and near surface groundwaters indicate isotopic distinctions between waters in ethiopia and kenya and confirm the anomalous nature of ethiopian waters remote data products from the tropical rainfall measuring mission trmm and national centers for environmental prediction ncep reanalysis project show strong westerly and southwesterly components to low level winds during precipitation events in western and central ethiopia this is in contrast to the easterly and southeasterly winds that bring rainfall to kenya and southeastern ethiopia large regions of high equivalent potential temperatures e at low levels over the sudd and the congo basin demonstrate the potential for these areas as sources of moisture and convective instability the combination of wind direction data from ethiopia and e distribution in africa indicates that transpired moisture from the sudd and the congo basin is likely responsible for the high isotopic values of rainfall in ethiopia

high temperature environments of human evolution in east africa based on bond ordering in paleosol carbonates many important hominid bearing fossil localities in east africa are in regions that are extremely hot and dry although humans are well adapted to such conditions it has been inferred that east african environments were cooler or more wooded during the pliocene and pleistocene when this region was a central stage of human evolution here we show that the turkana basin kenya today one of the hottest places on earth has been continually hot during the past 4 million years the distribution of 13c 18o bonds in paleosol carbonates indicates that soil temperatures during periods of carbonate formation were typically above 30 c and often in excess of 35 c similar soil temperatures are observed today in the turkana basin and reflect high air temperatures combined with solar heating of the soil surface these results are specific to periods of soil carbonate formation and we suggest that such periods composed a large fraction of integrated time in the turkana basin if correct this interpretation has implications for human thermophysiology and implies a long standing human association with marginal environments

composition and provenance of turbidite sands late quaternary madeira abyssal plain abstract late quaternary sediments from the madeira abyssal plain map consist of metre thick fine grained distal turbidites separated by centimetre thick layers of pelagic clay marl and or ooze three major compositional groups of turbidites have been defined by previous work volcanic organic rich and calcareous the coarse to medium grained sand fraction from the basal parts of the volcanic turbidites is predominantly composed of volcanic glass pumice and foraminifera whereas heavy mineral and plagioclase feldspar grains plus basalt and trachyte clasts become more abundant in the overlying fine grained sands and silts the bases of organic rich turbidites consist of fine grained sands and silts which are rich in foraminifera quartz and alkali feldspar grains and altered lithic clasts calcareous turbidites have bases composed of medium to fine grained foraminiferal sand devoid of terrigenous coarse grained material new mineralogical data are used to define grain assemblages in the sand silt fraction from these turbidite groups these assemblages are comparable to mineral assemblages from alkali olivine basalts trachybasalts to trachyandesites and trachytes phonolites on the azores canary islands and madeira and with sediments from the continental margin of northwestern africa volcanic glass chemistry however distinguishes the canary islands as the principal island provenance of the volcaniclastic sands volcaniclastic material probably originated either from reactivation of basic volcanism on tenerife and gran canaria in the quaternary or during the development of the western islands of la palma and hierro 5 ma recent trachytic and phonolitic material was derived from the more fractionated volcanic complexes on the central and eastern islands of the canary islands tenerife gran canaria fuerteventura and lanzarote organic rich turbidites consist of two mineralogical subgroups which originated from two distinct source areas along the continental margin of northwestern africa 1 north of the canaries off morocco 2 south of the canaries off senegal differences in the mineralogy between source areas reflect geographical variations in the weathering of continental granitic rocks which were subsequently transported off shore mainly by aeolian processes calcareous turbidites were derived from the great meteor cruiser seamount chain west of the map

a mass balance approach to basin sedimentation constraints on the recent history of the turkana basin abstract the turkana basin provides some excellent examples of mass balance constraints on recent basin history high sedimentation rates in the basin imply that major river captures occurred in the recent geologic past the chemistry of the lake is that to be expected for a relatively deep closed basin alkaline lake after several thousand years mass balance in the water budget shows that major changes in lake levels over a short time interval can only result from catastrophic events

stratigraphic placement and age of modern humans from kibish ethiopia in 1967 the kibish formation in southern ethiopia yielded hominid cranial remains identified as early anatomically modern humans assigned to homo sapiens however the provenance and age of the fossils have been much debated here we confirm that the omo i and omo ii hominid fossils are from similar stratigraphic levels in member i of the kibish formation despite the view that omo i is more modern in appearance than omo ii 40ar 39ar ages on feldspar crystals from pumice clasts within a tuff in member i below the hominid levels place an older limit of 198 14 kyr weighted mean age 196 2 kyr on the hominids a younger age limit of 104 7 kyr is provided by feldspars from pumice clasts in a member iii tuff geological evidence indicates rapid deposition of each member of the kibish formation isotopic ages on the kibish formation correspond to ages of mediterranean sapropels which reflect increased flow of the nile river and necessarily increased flow of the omo river thus the 40ar 39ar age measurements together with the sapropel correlations indicate that the hominid fossils have an age close to the older limit our preferred estimate of the age of the kibish hominids is 195 5 kyr making them the earliest well dated anatomically modern humans yet described

vertisol genesis in a humid climate of the coastal plain of texas u s a numerous genetic studies of vertisols have been conducted using qualitative and semi quantitative methods across a broad range of climates however no detailed investigations exist on vertisols formed in humid climates using multiple pedogenic techniques on both a microlow ml and microhigh mh hence we sampled and characterized a ml and mh from a lake charles pedon mean annual rainfall 1090 mm mean annual temperature 20 c in the late pleistocene coastal plain beaumont formation of east texas according to the official series description the lake charles classifies as a fine smectitic hyperthermic typic hapludert with mollic and calcic diagnostic horizons coupled with field morphology and characterization data micromorphology and constituent mass balance interpretations were used to reconstruct the major pathway of pedogenesis in response to greater water recharge the ml contains darker colors more organic carbon greater depth of carbonate leaching and lower ph the proportion of oxalate extractable iron increases toward the surface and is in greater abundance in the ml than mh in contrast dithionite extractable iron increases with depth and has similar quantities in both the ml and mh the parent material and lower profiles contain asepic microfabric dominated by micaceous rich coarse clay and silt the asepic zone deep contains an abundance of soft carbonate masses and iron manganese segregations that appear to be forming contemporaneously with the presence of argillans substantiating clay translocation during the early history of soil formation sepic microfabric dominates the upper profiles of both the ml and mh in part from the transformation of biotite to smectite which is more pronounced in the microlow because of more intense weathering hard carbonate nodules and iron manganese concretions are abundant in the upper sepic zone and contain skelsepic microfabric suggesting that they are no longer growing dilation was the dominant strain force during pedogenesis from volume expansion in response to crack infills and shrink swell processes mass flux calculations indicate that total clay gains occurred in both the ml and mh during pedogenesis late pleistocene vertisols appear to approach steady state when forming in humid climates the soil mechanics model best explains the observed depth distribution of properties including slickensides with pedoturbation playing a secondary role in the genesis of these humid climate vertisols

coulomb stress evolution in a diffuse plate boundary 1400 years of earthquakes in eastern california and western nevada usa diffuse plate boundaries are characterized by deformation distributed over a wide area in a complex network of active faults and by relatively low strain rates these characteristics make it difficult to understand the spatial and temporal distribution of seismicity the area east of the sierra nevada between longitudes 121 degrees w and 116 degrees w is part of a diffuse plate boundary at least 17 major surface rupturing earthquakes have happened here in the last 1400 years our purpose is to determine whether these events influence each other or whether they are randomly distributed in time and space we model the evolution of coseismic and postseismic coulomb failure stress changes delta cfs produced by these earthquakes and we also model interseismic stresses on the entire fault network our results show that 80 of the earthquake ruptures are located in areas of combined coseismic and postseismic delta cfs 0 2 bar this relationship is robust as shown by the control tests that we carried out using random earthquake sequences we also show that the fish lake valley pyramid lake and honey lake faults have accumulated 45 37 and 27 bars respectively of total delta cfs i e coseismic postseismic interseismic in the last 1400 years such values are comparable to the average stress drop in a major earthquake and these three faults may be therefore close to failure

the lifecycle of mid ocean ridge seamounts and their prodigious flank collapses abstract volcanic seamounts are spectacular bathymetric features representing undersea mountains comparable in size to volcanic islands they are often sites of active volcanism represent major marine habitats and contain potentially globally significant commodities of trace metals however we know comparatively little about how they form the extent of their volcanic lifecycle and what risks they pose from periodic flank collapse here we study a uniquely extensive 43 myr record of volcaniclastic and calciclastic turbidites accumulated on the madeira abyssal plain in the ne atlantic which originate from large submarine landslides from the adjacent great meteor cruiser seamount complex on the flanks of the mid atlantic ridge these turbidites present the first long term temporal record of the recurrence magnitude and emplacement mechanism of seamount flank collapses from a single seamount complex throughout its lifecycle landslides from the great meteor cruiser seamount complex are comparable size to those from the canary islands with average volumes of 30 40 km3 but can be as large as 130 km3 comparable to many volcanic island landslides these seamount landslides were predominantly multi stage failures similar to those form neighbouring volcanic islands but in contrast occurred preferentially during sea level lowstands we show that volcanic seamounts above mantle plumes have long protracted lifecycles and that substantial flank failures are capable of occurring at all stages of development temporal change in turbidite composition has for the first time enabled reconstruction of the inception around 43 45 myrs ago ascension taking around 20 25 myrs emergence after 30 myrs and later recession last 9 myrs cessation in volcanism last 4 myrs and subsidence of the seamounts from 2 myrs onwards these seamounts above a mantle plume have taken around 26 myrs to emergence above sea level from inception while their volcanic island contemporaries only took 2 to 5 myrs here we use the history of turbidites derived from landslides from the seamounts to show how the seamounts developed and suffered mass wasting during their life cycles

surface faulting accompanying the borah peak earthquake and segmentation of the lost river fault central idaho on the morning of 28 october 1983 the ms 7 3 borah peak earthquake struck central idaho and formed a y shaped zone of surface faults that is divided into a southern a western and a northern section the total length of the surface faults is 36 4 3 1 km and the maximum net throw is 2 5 to 2 7 m the near surface net slip direction determined from the rakes of striations in colluvium averaged 0 17 m of sinistral slip for 1 00 m of dip slip the 20 8 km long southern section is the main zone of surface faulting and coincides with the thousand springs segment of the lost river fault it has the largest amount of net throw most complex rupture patterns and best evidence of sinistral slip the surface faults include zones of ground breakage as much as 140 m wide en echelon scarps with synthetic and antithetic displacements and individual scarps that are nearly 5 m high the 14 2 km long western section diverges away from the lost river fault near the northern end of the southern section the net throw on this section is generally less than 0 5 m but locally is as much as 1 6 m the new ruptures are poorly developed across the crest and north flank of the willow creek hills they are mostly downhill facing arcuate scars perhaps incipient landslides that may overlie a deeper zone of tectonic movement the northern section at least 7 9 km long is on the warm spring segment of the lost river fault and has a maximum net throw of about 1 m the pattern of surface faulting on this section is simple compared to the other sections a 4 7 km long gap in 1983 surface faults separates the northern and southern sections but contains an older scarp of late pleistocene age geologic seismologic and geodetic data from the earthquake suggest that barriers confined the primary coseismic rupture to the thousand springs segment of the fault the rupture propagated unilaterally to the northwest from a hypocenter near the southeastern end of the segment the southeastern boundary of the segment is marked by an abrupt bend in the range front a 4 km long gap in late quaternary scarps and transverse faults of eocene age that intersect the lost river fault the northwestern boundary of the thousand springs segment is at the junction of the willow creek hills and the lost river fault here the southern and western sections of surface faults diverge and there is a gap in the 1983 scarps during the first few weeks after the main shock the large magnitude and large stress drop aftershocks clustered near this barrier later aftershocks were mainly northwest of the barrier on the warm spring and challis segments and showed that strain adjustments eventually affected the entire northern part of the lost river fault fault scarp morphology and the bedrock geology suggest that the boundary between the thousand springs and warm spring segments has probably ruptured less frequently and had less net slip during much of the late cenozoic than the interior of the adjacent segments the 1983 faulting shows that although segment boundaries can stop or deflect primary ruptures secondary surface faulting can occur on adjacent segments of the main fault a late pleistocene scarp in the 1983 gap suggests that infrequent earthquakes perhaps larger than the 1983 event might break through a segment boundary and thus release strain on two adjacent segments

how did thin submarine debris flows carry boulder sized intraclasts for remarkable distances across low gradients to the far reaches of the mississippi fan submarine density flows dominate sediment transport into many parts of the ocean and form submarine fans which are some of the largest sediment accumulations on earth previous studies often assumed that the distal fringes of submarine fans would be dominated by extensive sheet like deposits from dilute and expanded turbidity currents because only turbidity currents would transport large volumes of sediment for long distances across such low gradients deposits with a remarkable frondlike shape occur at the furthest fringe of the mississippi submarine fan understanding the emplacement process of these deposits is important because their frondlike shape suggests deposition from debris flows rather than turbidity currents previous analyses concluded that these deposits comprise a complex arrangement of thin interbedded turbidity current and debris flow deposits here we propose a different internal geometry for the frondlike deposits intervals previously described as in place turbidites are interpreted to be clasts within a single debrite interval that is 1 to 2 m thick this debrite interval is underlain by clean sand the debrite interval could have been emplaced by multiple debris flows or one event comprising multiple pulses clasts in the debrite interval are much bigger than previously thought including boulders with diameters that can exceed 50 cm we show that thin 2 m and extremely fluidal debris flows could have carried these boulders across gradients of only 0 06 to the fringes of one of the world s largest submarine fans without hydroplaning this long transport distance could occur if the density of the clasts was less than that of the surrounding debris flow emplacement of the basal clean sand layer appears closely linked to debris flow deposition because the clean sand layer pinches out in a location similar to that of the overlying debrite we therefore suggest that the basal clean sand most likely settled out from the overlying debris flows and that the clean sand is not a fore running turbidity current deposit shearing at the base of a mud rich debris flow would most likely produce a muddy basal sand interval rather than the clean sand that is observed this basal sand interval is therefore less likely to be a record of a lubricating layer with high pore fluid pressure on which the debris flows moved this study shows how thin and highly mobile debris flows can redistribute large volumes of sediment including bouldersized clasts long distances into the deep ocean across remarkably low gradients

anatomy of turbidites and linked debrites based on long distance 120 x 30 km bed correlation marnoso arenacea formation northern apennines italy much of our understanding of submarine sediment laden density flows that transport very large volumes ca 1 to 100 km3 of sediment into the deep ocean comes from careful analysis of their deposits direct monitoring of these destructive and relatively inaccessible and infrequent flows is problematic in order to understand how submarine sediment laden density flows evolve in space and time lateral changes within individual flow deposits need to be documented the geometry of beds and lithofacies intervals can be used to test existing depositional models and to assess the validity of experimental and numerical modelling of submarine flow events this study of the miocene marnoso arenacea formation italy provides the most extensive correlation of individual turbidity current and submarine debris flow deposits yet achieved in any ancient sequence one hundred and nine sections were logged through a ca 30 m thick interval of time equivalent strata between the contessa mega bed and an overlying columbine marker bed correlations extend for 120 km along the axis of the foreland basin in a direction parallel to flow and for 30 km across the foredeep outcrop as a result of post depositional thrust faulting and shortening this represents an across flow distance of over 60 km at the time of deposition the correlation of beds containing thick 40 cm sandstone intervals are documented almost all thick beds extend across the entire outcrop area most becoming thinly bedded 40 cm in distal sections palaeocurrent directions for flow deposits are sub parallel and indicate confinement by the lateral margins of the elongate foredeep flows were able to traverse the basin in opposing directions suggesting a basin plain with a very low gradient small fractional changes in stratal thickness define several depocentres on either side of the verghereto high area the extensive bed continuity and limited evidence for flow defection suggest that intrabasinal bathymetric relief was subtle substantially less than the thickness of flows thick beds contain two distinct types of sandstone ungraded mud rich sandstone intervals record evidence of en masse debrite deposition graded mud poor sandstone intervals are inferred to result from progressive grain by grain turbidite deposition clast rich muddy sandstone intervals pinch out abruptly in downflow and crossflow directions in a fashion consistent with en masse debrite deposition the tapered shape of mud poor sandstone intervals is consistent with an origin through progressive grain by grain turbidite deposition most correlated beds comprise both turbidite and debrite sandstone intervals intrabed transitions from exclusive turbidite sandstone to turbidite sandstone overlain by debrite sandstone are common in the downflow and crossflow directions this spatial arrangement suggests either i bypass of an initial debris flow past proximal sections ii localized input of debris flows away from available sections or iii generation of debris flows by transformation of turbidity currents on the basin plain because of seafloor erosion and or abrupt flow deceleration a single submarine flow event can comprise multiple flow phases and deposit a bed with complex lateral changes between mud rich and mud poor sandstone

carbon isotope ratio of cenozoic co2 a comparative evaluation of available geochemical proxies 1 the carbon isotope ratio 13c of plant material is commonly used to reconstruct the relative distribution of c3 and c4 plants in ancient ecosystems however such estimates depend on the 13c of atmospheric co2 13cco2 at the time which likely varied throughout earth history for this study we use benthic and planktonic 13c and 18o records to reconstruct a long term record of cenozoic 13cco2 confidence intervals for 13cco2 values are assigned after careful consideration of equilibrium and non equilibrium isotope effects and processes as well as resolution of the data we find that benthic foraminifera better constrain 13cco2 compared to planktonic foraminiferal records which are influenced by photosymbiotes depth of production seasonal variability and preservation furthermore sensitivity analyses designed to quantify the effects of temperature uncertainty and diagenesis on benthic foraminifera 13c and 18o values indicate that these factors act to offset one another our reconstruction suggests that cenozoic 13cco2 averaged 6 1 0 6 1 while only 11 2 million of the last 65 5 million years correspond to the pre industrial value of 6 5 with 90 confidence here 13cco2 also displays significant variations throughout the record at times departing from the pre industrial value by more than 2 thus the observed variability in 13cco2 should be considered in isotopic reconstructions of ancient terrestrial plant ecosystems especially during the late and middle miocene times of presumed c4 grassland expansion

estimating surface rupture length and magnitude of paleoearthquakes from point measurements of rupture displacement we present a method to estimate paleomagnitude and rupture extent from measurements of displacement at a single point on a fault the variability of historic ruptures is summarized in a histogram of normalized slip then scaled to give the probability of finding a given displacement within a rupture for any magnitude considered the histogram can be inverted assuming any magnitude earthquake is as likely as another yielding probability density functions of magnitude and rupture length for any given displacement measurement to improve these distributions we include a term to account for the probability that the earthquake would cause ground rupture and two alternative distributions of earthquake magnitude the gutenberg richter magnitude distribution predicts shorter rupture lengths and smaller magnitudes than does a uniform distribution where any magnitude earthquake is considered equally likely longer ruptures and larger magnitudes than the uniform model are predicted by an alternative magnitude distribution designed to return site average displacement this model is a generalization of the characteristic earthquake model and reasonably describes paleoseismic findings on the southern san andreas fault where slip is accommodated by average displacements of a few meters and earthquake recurrence times of 100 250 years our results should increase the value of paleoseismic displacement measurements for hazard assessment in particular they quantify probability estimates of earthquake magnitude and rupture length where point observations of rupture displacement are available and so can contribute to probabilistic seismic hazard analyses online material rupture profiles used to sample rupture variability

terrigenous fe input and biogenic sedimentation in the glacial and interglacial equatorial pacific ocean many ocean regions important to the global carbon budget including the equatorial pacific ocean have low chlorophyll concentrations despite high levels of conventional nutrients iron may instead be the limiting nutrient and elevated input of terrigenous fe during windy glacial episodes has been hypothesized to stimulate oceanic productivity through time and thus regulate the oceanic and atmospheric co2 balance to test whether particulate fe input is related to the accumulation of biogenic matter in one important low chlorophyll high nutrient area that is the equatorial pacific ocean we present results from a suite of sediment cores that collectively record biogenic deposition through the last six glacial interglacial cycles 600 000 years our data set includes new chemical data on total fe terrigenous and biogenic components in three cores as well as previously published mineralogic records of coljan input to the region chemical spectral and stratigraphic analysis indicates that 1 terrigenous input to the region shows no consistent pattern of either glacial or interglacial maxima 2 the accumulation of particulate fe is closely related to the accumulation of terrigenous matter linear r 2 0 81 0 98 3 there are no coherent spectral relationships between fe input and glacial periodicity i e 5180 in any of the orbital frequency bands 4 the linear and cross spectral correlations between fe or coljan input and caco3 concentration are most commonly the strongest observed relationships between fe and any biogenic component yet indicate a largely inverse pattern with higher fe being associated with low caco3 5 there is no consistent linear r 2 correlation or spectral coherence between the accumulation of fe and that of caco3 corg or opal thus in total there is no relationship between terrigenous fe input and sedimentary sequestering of carbon additionally although we cannot specifically address the potential for changes in solubility of the terrigenous fraction that may be driven by a terrigenous compositional change the fe ti ratio which monitors first order mineralogic changes records only slight variations that also are linearly and spectrally unrelated to glacial periodicity the bulk fe flux and the accumulation of any biogenic component finally we find that the paleoceanographic flux of fe is several order of magnitudes larger than modem observations of coljan fe input suggesting that the long term importance of fe input by dust storms which deliver fe on the order of the sedimentary burial may be underestimated the removal of particulate terrigenous fe from the recently discovered source within the equatorial undercurrent however remains unquanfified and may also prove significant

expansion of c4 grasses in the late miocene of northern pakistan evidence from stable isotopes in paleosols stable isotopic clay mineralogic and bulk chemical analyses were conducted on paleosols of the neogene siwalik sections in northern pakistan in order to reconstruct floodplain environments over the past 17 ma the stable carbon isotopic composition of soil carbonate mean 13c pdb 10 2 and associated organic matter mean 13c pdb 24 1 in paleosols representing 17 7 3 ma reveal that floodplain vegetation was dominated by c3 plants at 7 3 ma a shift toward more positive carbon isotopic values began signaling the gradual expansion of c4 grasses onto the floodplain from 6 ma to present carbon isotopic values for paleosol carbonate mean 13c pdb 0 6 and organic matter mean 13c pdb 14 4 are uniformly enriched in 13c indicating the presence of nearly pure c4 grassland the scarcity of kaolinite and abundance of smectite and pedogenic carbonate in most paleosols suggest that rainfall in the region remained 1 0 1 25 m yr or less for the entire 17 ma of record paleosols in the lower portion of the section lack organic a horizons but have reddish b horizons often containing secondary iron oxide nodules leaching depths of soil carbonate in these older paleosols are typically greater than those in the plio pleistocene part of the section where organic a horizons are common and b horizons are markedly more yellow the combined evidence suggests that the mature paleosols in the pre 7 3 ma part of the record are dominantly calcareous alfisols or mollisols that once underlay nearly pure c3 vegetation perhaps trees and shrubs while calcareous mollisols underlying c4 grassland dominate the upper part of the record the carbon and oxygen isotopic trends in the paleosol record in pakistan are also evident in the diet of fossil mammals and in paleosols from nepal thus demonstrating that these paleoenvironmental changes in floodplain vegetation may be continent wide local effects such as the development or intensification of the asian monsoon driven by uplift of the tibetan plateau may have led to the expansion of c4 grasses if however the expansion of c4 grasses proves globally synchronous then a larger scale cause such as a marked decrease in co2 may be the driving mechanism

a comparison of biomarker records of northeast african vegetation from lacustrine and marine sediments ca 3 40 ma integrated terrestrial and marine records of northeast african vegetation are needed to provide long high resolution records of environmental variability with established links to specific terrestrial environments in this study we compare records of terrestrial vegetation preserved in marine sediments in the gulf of aden deep sea drilling project dsdp site 231 and an outcrop of lacustrine sediments in the turkana basin kenya part of the east african rift system we analyzed higher plant biomarkers in sediments from both deposits of known equivalent age corresponding to a ca 50 100 ka humid interval prior to the b tulu bor eruption ca 3 40 ma when the lokochot lake occupied part of the turkana basin molecular abundance distributions indicate that long chain n alkanoic acids in marine sediments are the most reliable proxy for terrestrial vegetation carbon preference index cpi 4 5 with more cautious interpretation needed for n alkanes and lacustrine archives marine sediments record carbon isotopic variability in terrestrial biomarkers of 2 3 roughly equivalent to 20 variability in the c3 c4 vegetation contribution the proportion of c4 vegetation apparently increased at times of low terrigenous dust input terrestrial sediments reveal much larger 2 10 shifts in n alkanoic acid d 13 c values however molecular abundance and isotopic composition suggest that microbial sources may also contribute fatty acids contaminating the lacustrine sedimentary record of terrestrial vegetation 2007 elsevier ltd all rights reserved

biomarker records of late neogene changes in northeast african vegetation open savannah grasslands dominated by c4 plants became a significant component of northeast african vegetation during the late neogene we present molecule specific carbon isotopic mea surements of terrestrial plant biomarkers preserved in marine sed iments off northeast africa that allow reconstruction of orbital scale vegetation changes in short time windows over the past 9 4 m y the biomarker data show large amplitude vegetation vari ability as early as 3 8 ma with the greatest c4 expansion occurring after 3 4 ma we sampled orbital scale oscillations of up to 5 almost as large as the observed late neogene range of 7 sug gesting that large and repeated oscillations between more open and more closed landscapes were an important aspect of northeast af rican vegetation change during the past 4 m y

turbidite record of frequency and source of large volume 100 km3 canary island landslides in the last 1 5 ma implications for landslide triggers and geohazards during the last two decades numerous studies have focused on resolving the landslide histories of the canary islands issues surrounding the preservation and dating of onshore and proximal submarine landslide deposits precludes accurate determination of event ages however submarine landslides often disaggregate and generate sediment gravity flows volcaniclastic turbidites sampled from madeira abyssal plain piston cores represent a record of eight large volume failures from the western canary islands in the last 1 5 ma during this time there is a mean recurrence rate of 200 ka while the islands of el hierro and tenerife have individual landslide recurrences of 500 ka and 330 ka respectively deposits from the 15 ka el golfo landslide from el hierro and 165 ka icod landslide from tenerife are examined this study also identifies potential deposits associated with the orotava 535 ka guimar 850 ka and rogues de garcia landslides 1 2 ma from tenerife el julan 540 ka and el tinor 1 05 ma landslides from el hierro and the cumbre nueva landslide 485 ka from la palma seven of eight landslides occurred during major deglaciations or subsequent interglacial periods which represent 55 of the time however all of the studied landslides occur during or at the end of periods of protracted island volcanism which generally represent 60 of the island histories although climate may precondition failures it is suggested that volcanism presents a more viable preconditioning and trigger mechanism for canary island landslides

provenance and pathways of late quaternary turbidites in the deep water agadir basin northwest african margin a series of individual turbidites correlated over distances 100 km are present in the recent fill of the agadir basin offshore northwest africa the aim here is to unravel multiple turbidite source areas and flow pathways and show how turbidite provenance studies contribute to interpretation of flow processes agadir basin turbidites are sourced from four main areas with the majority originating from the siliciclastic morocco shelf their sand mud distribution is strongly controlled by flow sediment volume with relatively low volume flows dying out within the agadir basin and large volume flows bypassing significant sediment volumes to basins further downslope two large volume volcaniclastic turbidites are attributed to a canary islands landslide source while several small mud dominated turbidites are interpreted to be locally sourced from hemipelagic draped seamounts e g turbidite ab10 finally turbidite ab1 1 ka is only present in the western agadir basin and is linked to recent re activation of the sahara slide headwall the muddy suspension clouds of three large volume flows all linked to large scale landslides have covered huge areas of seafloor and flowed along or even slightly upslope for long distances it is proposed that northeastwards flowing bottom currents have aided transport of these dilute flow fractions into and across the agadir basin

paleoseismic evidence of characteristic slip on the western segment of the north anatolian fault turkey we have conducted a paleoseismic investigation of serial fault rupture at one site along the 110 km rupture of the north anatolian fault that produced the mw 7 4 earthquake of 17 august 1999 the benefit of using a recent rupture to compare serial ruptures lies in the fact that the location magnitude and slip vector of the most recent event are all very well documented we wished to determine whether or not the previous few ruptures of the fault were similar to the recent one we chose a site at a step over between two major strike slip traces where the principal fault is a normal fault our two excavations across the 1999 rupture reveal fluvial sands and gravels with two colluvial wedges related to previous earthquakes each wedge is about 0 8 m thick considering the processes of collapse and subsequent diffusion that are responsible for the formation of a colluvial wedge we suggest that the two paleoscarps were similar in height to the 1999 scarp this similarity supports the concept of characteristic slip at least for this location along the fault accelerator mass spectrometry ams radiocarbon dates of 16 charcoal samples are consistent with the interpretation that these two paleoscarps formed during large historical events in 1509 and 1719 if this is correct the most recent three ruptures at the site have occurred at 210 and 280 year intervals

calibration of xrf core scanners for quantitative geochemical logging of sediment cores theory and application abstract on line analysis of split sediment cores by xrf core scanners has become increasingly popular in the past decade because it allows nondestructive extraction of near continuous records of element intensities from sediment cores with a minimum of analytical effort a disadvantage of xrf core scanning relative to conventional geochemical analysis is the problematic conversion of core scanner output to element concentrations the main reason for this long standing problem is the poorly constrained measurement geometry attributable to inhomogeneity of the specimens e g variable water content and grain size distribution irregularities of the split core surface and in some setups spatial variations in thickness of an adhesive pore water film which forms directly below a protective foil covering the core surface we propose a log ratio calibration model for xrf core scanners derived from a combination of xrf spectrometry theory principles of compositional data analysis and empirical evidence the log ratio calibration model provides accurate and precise predictions of sediment composition element concentrations from xrf core scanner output with a limited number of parameters namely 2 d 1 where d equals the number of chemical elements whose concentrations are to be estimated the model can accommodate the inherent non linearity of the relation between relative intensities and concentrations which is apparent from the fact that it provides unbiased estimates an immediate corollary of our results is that log ratios of element intensities which are related to log ratios of element abundances by a simple linear transformation provide the most easily interpretable signals of relative changes in chemical composition consistent use of log ratios of element intensities or concentrations should minimise the risk of drawing erroneous conclusions from geochemical proxies the relative standard deviation precision of predicted element concentrations in core geob7920 is less than 2 stochastic simulations indicate that this level of precision can be attained with 40 randomly selected calibration specimens improved control over input errors and development of robust goodness of fit statistics allows xrf core scanning to be developed into a rigorous quantitative measurement technology the log ratio calibration equation derived in this study may be adapted to inter laboratory and inter instrument calibration as well

fault segmentation new concepts from the wasatch fault zone utah usa the question of whether structural segment boundaries along multisegment normal faults such as the wasatch fault zone wfz act as persistent barriers to rupture is critical to seismic hazard analyses we synthesized late holocene paleoseismic data from 20 trench sites along the central wfz to evaluate earthquake rupture length and fault segmentation for the youngest 3 ka and best constrained earthquakes differences in earthquake timing across prominent primary segment boundaries especially for the most recent earthquakes on the north central wfz are consistent with segment controlled ruptures however broadly constrained earthquake times dissimilar event times along the segments the presence of smaller scale subsegment boundaries and areas of complex faulting permit partial segment and multisegment e g spillover ruptures that are shorter 20 40 km or longer 60 100 km than the primary segment lengths 35 59 km we report a segmented wfz model that includes 24 earthquakes since 7 ka and yields mean estimates of recurrence 1 1 1 3 kyr and vertical slip rate 1 3 2 0 mm yr for the segments however additional rupture scenarios that include segment boundary spatial uncertainties floating earthquakes and multisegment ruptures are necessary to fully address epistemic uncertainties in rupture length we compare the central wfz to paleoseismic and historical surface ruptures in the basin and range province and central italian apennines and conclude that displacement profiles have limited value for assessing the persistence of segment boundaries but can aid in interpreting prehistoric spillover ruptures our comparison also suggests that the probabilities of shorter and longer ruptures on the wfz need to be investigated

unusually low rates of slip on the santa rosa range fault zone northern nevada the santa rosa range fault zone srrfz is one of the most topographically prominent normal fault systems in the northern basin and range province of the western united states it has been assigned high rates of vertical slip by others and has been identified as a possible site of the future extension of the central nevada seismic belt cnsb we use detailed trench mapping and luminescence dating to estimate displacements and timing of the last several large magnitude paleoearthquakes on the southern part of the srrfz at a trench site near orovada nevada coseismic vertical displacements ranged from 1 to 2 8 m for each of the last four events luminescence ages provide time limits for the last three events of 125 155 ka 90 108 ka and 11 16 ka these data yield recurrence intervals of 17 65 k y and 74 97 k y and an elapsed time of 11 16 k y since the youngest event slip rate determinations at the orovada site are complicated by multiple fault strands but rates calculated from a variety of data are surprisingly low 0 01 0 16 mm yr given the topographic prominence of the santa rosa range a lack of compelling patterns in a comparison of paleoseismic parameters indicate that the srrfz is no more likely a location for a large magnitude earthquake than previously identified seismic gaps or along faults that lie directly north of the cnsb

sedimentological and geochemical evidence for multistage failure of volcanic island landslides a case study from icod landslide on north tenerife canary islands 1 volcanic island landslides can pose a significant geohazard through landslide generated tsunamis however a lack of direct observations means that factors influencing tsunamigenic potential of landslides remain poorly constrained the study of distal turbidites generated from past landslides can provide useful insights into key aspects of the landslide dynamics and emplacement process such as total event volume and whether landslides occurred as single or multiple events the northern flank of tenerife has undergone multiple landslide events the most recent being the icod landslide dated at 165 ka the icod landslide generated a turbidite with a deposit volume of 210 km3 covering 355 000 km2of seafloor off northwest africa the icod turbidite architecture displays a stacked sequence of seven normally graded sand and mud intervals named subunits sbu1 7 evidence from subunit bulk geochemistry volume basal grain size volcanic glass composition and sand mineralogy combined with petrophysical and geophysical data suggests that the subunit facies represents multistage retrogressive failure of the icod landslide the basal subunits sbu1 3 indicate that the first three stages of the landslide had a submarine component whereas the upper subunits sbu4 7 originated above sea level the presence of thin non bioturbated mud intervals between subunit sands suggests a likely time interval of at least several days between each stage of failure these results have important implications for tsunamigenesis from such landslides as multistage retrogressive failures separated by several days and with both a submarine and subaerial component will have markedly lower tsunamigenic potential than a single block failure

an isotopic study of a fluvial lacustrine sequence the plio pleistocene koobi fora sequence east africa stable isotopic analyses of plio pleistocene and modern sediments in the fluvial lacustrine system occupying the turkana basin east africa provide constraints on the paleoenvironmental and diagenetic histories of the pliocene through the recent sediments in the basin the 13c values for carbonates in lacustrine sediments range from 15 to 22 relative to pdb depending on the varying proportions of co2 from the atmospheric reservoir and from various metabolic sources the 18o values of carbonates in lacustrine sediments indicate that the isotopic composition of paleolake water varied by over 10 from the pliocene to the present the 13c values for pedogenic carbonates record paleoccologic variations and suggest that c4 plants did not become well established in the preserved depositional parts of the basin until about 1 8 myr ago the 18o values pedogenic carbonates suggest a range of over 10 for the isotopic composition of soil water during this interval they also suggest a period of major climatic instability from about 3 4 to 3 1 myr and at about 1 8 myr together the 13c and 18o values of pedogenic carbonates indicate that the present conditions are as arid and hot as any that had prevailed during deposition of these plio pleistocene sediments

correlation frequency of emplacement and source directions of megaturbidites on the madeira abyssal plain abstract this paper describes the sediments of the whole madeira abyssal plain including the madcap area to the south previous studies have centred on the central sub basin which occupies most of the plain and which has become one of the most studied areas of seafloor the plain is made up of a series of large turbidites separated by thin pelagic layers which can be used to provide a high resolution stratigraphy back to about 750 000 years many of the turbidites were deposited close to oxygen isotope stage boundaries suggesting a strong relationship to sea level climate change although the exact initiation mechanism for the flows is not known data from the northern and southern extensions of the plain shows the effects of different entry points for the four main turbidite groups volcanic rich turbidites enter from the ne and e calcareous turbidites from the w one group of organic rich turbidites enters from the se and one group from the ne and e different turbidite sources operate for limited periods before switching to one of the other source areas it is very rare for two sources to provide turbidites at the same isotope stage boundary

a 1 2 myr record of isotopic changes in a late pliocene rift lake ethiopia the hadar fluvio lacustrine formation ethiopia contains an original hominid fossil australopithecus afarensis and an abundant vertebrate faunal assemblage1 2 the formation3 4 consists of a 150 300 m thick sequence of fine to coarse detrital sediments originating from the ethiopian plateau escarpment with some interbedded pyroclastic layers the three lower members of the formation were formed in a lacustrine environment which was occasionally interrupted by fluvial drainage the upper member is quite distinct and formed as an alluvial fan delta this sedimentary sequence was deposited at the end of the pliocene between 3 9 and 2 7 myr as indicated by magnetostratigraphy5 the palaeomagnetic record spans the gilbert gauss transition period k ar dating6 7 and biostratigraphy8 we consider here the oxygen and carbon isotope variations observed throughout the formation and their palaeo hydrological implications

geochemical tracers of northern portuguese estuarine sediments on the shelf the northern portuguese coastal zone is drained by large iberian rivers along which there is intensive industrial agricultural and urban activity offshore of the two main river basins of the douro and minho two fine grained sedimentary formations can be characterised a geochemical study of this sediment cover has been performed focussing in particular on the fine deposits and the adjacent estuaries the chemical composition of superficial sediments collected from the northern portuguese shelf and from the river basins of the minho and douro rivers was determined for major minor and trace elements the rare earth elements ree composition was also determined in selected samples statistical analyses of these data for the shelf sediments allow us to identify elements with similar behaviours and the different sediment types along the shelf and to evaluate of their origins downcore profiles of the chemical composition of the fine sediments reveal no evidence for changes induced by recent human activities to assess the influence of the rivers on the fine sedimentary formations the elemental distribution patterns of selected sediments have been compared with the estuarine sediments lithogenic elements composition normalised to al and the shale normalised ree distributions showed there are similarities between the douro river sediments and the sediment composition of the douro and galicia mud patches however the galicia mud field showed no relationship in its chemical composition to sediments derived from the minho river nor was any evidence for heavy metal contamination originating from the douro estuary detected in anthropogenic element al ratios in the shelf sediments this may be because of processes associated with resuspension complexation and bioturbation that occur during sediment transport and deposition nevertheless the douro river seems to be the main continental source of fine sediments being deposited on the northern portuguese shelf

displacement and geometrical characteristics of earthquake surface ruptures issues and implications for seismic hazard analysis and the process of earthquake rupture there now exist about three dozen historical earthquakes for which in vestigators have constructed maps of earthquake rupture traces accompanied by de scriptions of the coseismic slip observed along the fault strike the maps and slip distributions are compiled here to place observational bounds on aspects of seismic hazard analysis and fault mechanics analysis leads to an initial statistical basis to predict the end points of rupture and the amount of surface slip expected at sites along the strike during earthquakes on mapped faults the observations also give support to the ideas that there exists a process zone or volume of about 3 4 km in dimension at the fronts of large laterally propagating earthquake ruptures within which stress changes may be sufficient to trigger slip on adjacent faults and that the ultimate length of earthquake ruptures is controlled primarily by the geometrical complexity of fault traces and variations in accumulated stress levels along faults that arise due to the location of past earthquakes to this may be added the observation that the form of earthquake surface slip distributions is better described by asymmetric rather than symmetric curve forms and that earthquake epicenters do not appear to correlate in any systematic manner to regions of maximum surface slip observed along strike online material maps of surface ruptures digitized values and curve fits to surface slip distributions and notes and references for tables 1 and 2

paleoseismic results from the alpine site wasatch fault zone timing and displacement data for six holocene earthquakes at the salt lake city provo segment boundary

the spatial and temporal distribution of grain size breaks in turbidites grain size breaks are surfaces where abrupt changes in grain size occur vertically within deposits grain size breaks are common features in turbidites around the world including ancient and modern systems despite their widespread occurrence grain size breaks have been regarded as exceptional and not included within idealized models of turbidity current deposition this study uses ca 100 shallow sediment cores from the moroccan turbidite system to map out five turbidite beds for distances in excess of 2000 km the vertical and spatial distributions of grain size breaks within these beds are examined five different types of grain size break are found type i in proximal areas between coarse sand and finer grained structureless sand type ii in proximal areas between inversely graded sand overlain by finer sand type iii in proximal areas between sand overlain by ripple cross laminated finer sand type iv throughout the system between clean sand and mud and type v in distal areas between mud rich debrite sand and mud this article interprets types i and v as being generated by sharp vertical concentration boundaries controlled by sediment and clay concentrations within the flows whilst types ii and iii are interpreted as products of spatial temporal fluctuations in flow capacity type iv are interpreted as the product of fluid mud layers which hinder the settling of non cohesive grains and bypasses them down slope decelerating suspensions with sufficient clay will always form cohesive layers near to bed promoting the generation of type iv grain size breaks this may explain why type iv grain size breaks are widespread in all five turbidites examined and are commonplace within turbidite sequences studied elsewhere therefore type iv grain size breaks should be understood as the norm not the exception and regarded as a typical feature within turbidite beds

determination of turbidity current erosional characteristics from reworked coccolith assemblages canary basin north east atlantic turbidites contain mixtures of sediments of various ages these sediments can include both material that was eroded to form the initial turbidity current plus additions derived from erosion of the sea floor during transport it has been possible to interpret the age range of sediments incorporated into individual turbidites from the madeira abyssal plain by examining the proportions of microfossil coccolith species that they contain the pelagic record of coccoliths is well known for the quaternary period and shows a succession of dominant species or acmes each lasting a few tens of thousand years hence erosion of sediment representing more than a few tens of thousand years will produce coccolith mixtures not seen in the pelagic record but dependent upon the age range of the sediments that were eroded this age range can be estimated by comparison with synthetic ratios of coccolith species created by combining ratios of species from successively older layers in the pelagic record these can then be compared with the ratios found in individual turbidites until a match is found the results show age ranges of 54 500 kyr for the sediment mixture in seven turbidites from the madeira abyssal plain since the volumes of these turbidites are also known and accumulation rates in their source areas can be estimated it is possible to determine both the thickness and the area of the eroded sediment mass that generated the turbidity current minimum depths of erosion on the north west african continental margin vary from 8 to 50 m and minimum areas eroded from 1600 to 5800 km2 none of the turbidites examined contains a significant excess of surface sediment suggesting that once formed the turbidity currents that transported them were virtually non erosional and that they travelled several hundred kilometres in this state

the northwest african slope apron a modern analogue for deep water systems with complex seafloor topography the northwest african slope apron is an interesting modern analogue for deep water systems with complex seafloor topography a sediment process map of the northwest african continental margin illustrates the relative roles of different sedimentary processes acting across the entire margin fine grained pelagic and hemipelagic sedimentation is dominant across a large area of the margin and is considered to result from background sedimentary processes alongslope bottom currents smooth and mould the seafloor sediments and produce bedforms such as erosional furrows sediment waves and contourite drifts downslope gravity flows debris avalanches debris flows and turbidity currents are infrequent but important events on the margin and are the dominant processes shaping the morphology of the slope and rise the overall distribution of sedimentary facies and morphological elements on the northwest african margin is characteristic of a fine grained clastic slope apron however the presence of numerous volcanic islands and seamounts along the margin leads to a more complex distribution of sedimentary facies than is accounted for by slope apron models in particular the distribution and thickness of turbidite sands are controlled by the location of the break of slope which is itself controlled by the pre existing submarine topography

generic along strike segmentation of afar normal faults east africa implications on fault growth and stress heterogeneity on seismogenic fault planes understanding how natural faults are segmented along their length can provide useful insights into fault growth processes stress distribution on fault planes and earthquake dynamics we use cumulative displacement profiles to analyze the two largest scales of segmentation of 900 normal faults in afar east africa we build upon a prior study by manighetti et al 2009 and develop a new signal processing method aimed at recovering the number position displacement and length of both the major i e longest and the subordinate secondary segments within the faults regardless of their length age geographic location total displacement and slip rate 90 of the faults contain two to five major segments whereas more than 70 of these major segments are divided into two to four secondary segments in each hierarchical rank of fault segmentation most segments have a similar proportional length whereas the number of segments slightly decreases with fault structural maturity the along strike segmentation of the afar faults is thus generic at its two largest scales we summarize published fault segment data on 42 normal reverse and strike slip faults worldwide and find a similar number two to five of major and secondary segments across the population we suggest a fault growth scenario that might account for the generic large scale segmentation of faults the observation of a generic segmentation suggests that seismogenic fault planes are punctuated with a deterministic number of large stress concentrations which are likely to control the initiation arrest and hence extent and magnitude of earthquake ruptures

paleoenvironmental interpretation of lake margin deposits using δ13c and δ18o results from early pleistocene carbonate rhizoliths olduvai gorge tanzania isotope analyses of lake margin rhizoliths from paleo lake olduvai ca 1 75 ma form the basis of a new model proposed here for interpreting stable isotope values of phreatic rhizolith carbonates average 18o and 13c values from rhizoliths formed in transgressive lacustrine waxy claystones are relatively low low 18o averages 5 5 reflect meteoric water values consistent with increased precipitation during wet periods that would increase the outflow of fresh water from subsurface seeps and shift a brackish groundwater zone lakeward low 13c averages 4 1 could indicate little atmospheric exchange high plant decay and or increased groundwater low 13c flow higher averages in 18o 3 6 and 13c 2 0 occur during dry periods and lake regressions earthy claystones when hydraulic head is reduced the lake recedes and water within the wetlands is subjected to intense evaporation and gas exchange with the atmosphere the isotope ratios of the rhizoliths from lowermost bed ii change in response to groundwater hydrology on milankovitch time scales but the isotopes also provide evidence of shorter term decadal to centennial scale climate fluctuations the orbitally driven climate changes are recorded faithfully by lithologic variations and stable isotope patterns

multivariate statistical and multiproxy constraints on earthquake triggered sediment remobilization processes in the central japan trench understanding the impact of earthquakes on subaqueous environments is key for submarine paleoseismological investigations seeking to provide long term records of past earthquakes for this purpose event deposits e g turbidites are among others identified and stratigraphically correlated over broad areas to test for synchronous occurrence of gravity flows hence detailed spatiotemporal petrographic and geochemical fingerprints of such deposits are required to advance the knowledge about sediment source and the underlying remobilization processes induced by past earthquakes in this study we develop for the first time in paleoseismology a multivariate statistical approach using x ray fluorescence core scanning magnetic susceptibility and wet bulk density data that allow to test confirm and enhance the previous visual and lithostratigraphic correlation across two isolated basins in the central japan trench the statistical correlation is further confirmed by petrographic heavy grain analysis of the turbidites and additionally combined with our novel erosion model based on previously reported bulk organic carbon 14c dates we find surficial sediment remobilization a process whereby strong seismic shaking remobilizes the uppermost few centimeters of surficial slope sediment to be a predominant remobilization process which partly initiates deeper sediment remobilization downslope during strong earthquakes at the japan trench these findings shed new light on source to sink transport processes in hadal trenches during earthquakes and help to assess the completeness of the turbidite paleoseismic record our results further suggest that shallow buried tephra on the slope might significantly influence sediment remobilization and the geochemical and petrographic fingerprints of the resulting event deposits

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

turbidite depositional architecture across three interconnected deep water basins on the north west african margin the moroccan turbidite system mts on the north west african margin extends 1500 km from the head of the agadir canyon to the madeira abyssal plain making it one of the longest turbidite systems in the world the mts consists of three interconnected deep water basins the seine abyssal plain sap the agadir basin and the madeira abyssal plain map connected by a network of distributary channels excellent core control has enabled individual turbidites to be correlated between all three basins giving a detailed insight into the turbidite depositional architecture of a system with multiple source areas and complex morphology large volume 100 km3 turbidites sourced from the morocco shelf show a relatively simple architecture in the madeira and seine abyssal plains sandy bases form distinct lobes or wedges that thin rapidly away from the basin margin and are overlain by ponded basin wide muds however in the agadir basin the turbidite fill is more complex owing to a combination of multiple source areas and large variations in turbidite volume a single very large turbidity current 200 300 km3 of sediment deposited most of its sandy load within the agadir basin but still had sufficient energy to carry most of the mud fraction 500 km further downslope to the map large turbidity currents 100 150 km3 of sediment deposit most of their sand and mud fraction within the agadir basin but also transport some of their load westwards to the map small turbidity currents 35 km3 of sediment are wholly confined within the agadir basin and their deposits pinch out on the basin floor turbidity currents flowing beyond the agadir basin pass through a large distributary channel system individual turbidites correlated across this channel system show major variations in the mineralogy of the sand fraction whereas the geochemistry and micropalaeontology of the mud fraction remain very similar this is interpreted as evidence for separation of the flow with a sand rich erosive basal layer confined within the channel system overlain by an unconfined layer of suspended mud large volume turbidites within the mts were deposited at oxygen isotope stage boundaries during periods of rapid sea level change and do not appear to be specifically connected to sea level lowstands or highstands this contrasts with the classic fan model which suggests that most turbidites are deposited during lowstands of sea level in addition the three largest turbidites on the map were deposited during the largest fluctuations in sea level suggesting a link between the volume of sediment input and the magnitude of sea level change

temperature and carbonate ion effects on mg ca and sr ca ratios in benthic foraminifera aragonitic species hoeglundina elegans received 16 march 2005 revised 20 june 2005 accepted 3 november 2005 published 21 february 2006 1 core top samples from atlantic little bahama banks lbb and pacific hawaii and indonesia depth transects have been analyzed in order to assess the influence of bottom water temperature bwt and aragonite saturation levels on mg ca and sr ca ratios in the aragonitic benthic foraminifer hoeglundina elegans both the mg ca and sr ca ratios in h elegans tests show a general decrease with increasing water depth although at each site the decreasing trends are consistent with the in situ temperature profile mg ca and sr ca ratios in lbb are substantially higher than in indonesia and hawaii at comparable water depths with a greater difference observed with increasing water depth because we find no significant difference between results obtained on live and dead specimens we propose that these differences are due to primary effects on the metal uptake during test formation evaluation of the water column properties at each site suggests that in situ co3 ion concentrations play an important role in determining the h elegans mg ca and sr ca ratios the co3 ion effect is limited however only to aragonite saturation levels dco3 aragonite below 15 mmol kg 1 above this level temperature exerts a dominant effect accordingly we propose that mg ca and sr ca in h elegans tests can be used to reconstruct thermocline temperatures only in waters oversaturated with respect to the mineral aragonite using the following relationships mg ca 0 034 0 002 bwt 0 96 0 03 and sr ca 0 060 0 002 bwt 1 53 0 03 for dco3 aragonite 1 5mmol kg 1 the standard error associated with these equations is about 1 1 c reconstruction of deeper water temperatures is complicated because in undersaturated waters changes in mg ca and sr ca ratios reflect a combination of changes in co3 and bwt overall we find that sr ca rather than mg ca in h elegans may be a more accurate proxy for reconstructing paleotemperatures

extensional reactivation of thrust faults accompanied by coseismic surface rupture southwestern wyoming and north central utah extensional reactivation of thrust faults north of the uinta mountains in utah and wyoming is accompanied by quaternary surface faulting tilting and monoclinal folding the 40 km long bear river fault zone consists of down to the west right stepping en echelon scarps each about 3 0 to 3 5 km in length striking n20 w to n20 e scarp derived colluvial deposits record two holocene surface ruptures with net vertical tectonic displacements ranging from 5 m per event west 1989 in press radiocarbon ages indicate surface faulting events occurred at about 4 6 ka and 2 4 ka the length of surface rupture and net slip per event in the bear river fault zone imply a seismic potential comparable to the lost river fault hebgen lake fault and the wasatch fault zone a late quaternary normal scarp is also coincident with the leading edge of the absaroka thrust fault 7 2 km west of the bear river fault zone scarp derived colluvial deposits record one surface faulting event over a length of at least 5 0 km the age of surface rupture is coeval with the bear river fault zone 2 4 ka normal faults displacing pleistocene surfaces deposits and tectonic tilt indicate that the hogsback thrust east of the bear river fault zone was reactivated in a normal sense but now may be inactive due to subsequent development of the bear river fault zone cumulative normal throw of 200 m on the hogsback fault may be responsible for postulated tectonic separation of the bear river and green river drainage basins neotectonic deformation results from east west extension superposed on the hogsback and absaroka thrust plates extensional reactivation of thrust faults caused propagation of new normal faults over stress points particularly at the hogsback ramp to flat transition and at the thrust leading edges the ages of surface rupture and cumulative throws indicate normal reactivation of the hogsback and absaroka thrusts and propagation of the intervening bear river fault zone proceeded from east to west opposite initial development of the thrusts in late cretaceous to paleocene time normally reactivated thrust faults and propagation of listric normal faults accompanied by surface rupture have significant implications for the tectonic seismogenic development of the eastern basin and range transition zone

new techniques in sediment core analysis an introduction marine sediment cores are the fundamental data source for information on seabed character depositional history and environmental change they provide raw data for a wide range of research including studies of global climate change palaeoceanography slope stability oil exploration pollution assessment and control and sea floor surveys for laying cables pipelines and siting of sea floor structures during the last three decades a varied suite of new technologies have been developed to analyse cores often non destructively to produce high quality closely spaced co located downcore measurements characterizing sediment physical properties geochemistry and composition in unprecedented detail distributions of a variety of palaeoenvironmentally significant proxies can now be logged at decadal and in some cases even annual or subannual scales allowing detailed insights into the history of climate and associated environmental change these advances have had a profound effect on many aspects of the earth sciences particularly palaeoceanography in this paper we review recent advances in analytical and logging technology and their application to the analysis of sediment cores developments in providing access to core data and associated datasets and data mining technology in order to integrate and interpret new and legacy datasets within the wider context of sea floor studies are also discussed despite the great advances in this field however challenges remain particularly in the development of standard measurement and calibration methodologies and in the development of data analysis methods new data visualization tools and techniques need to be developed to optimize the interpretation process and maximize scientific value amplified collaboration environments and tools are needed in order to capitalize on our analysis and interpretation capability of large multi parameter datasets sophisticated yet simple to use searchable internet databases with universal access and secure long term funding and data products resulting in user defined data mining query and display so far pioneered in the usa and australia provide robust models for efficient and effective core data stewardship

environmental dose rates and radioactive disequilibrium from some australian luminescence dating sites abstract determination of geological archaeological ages by luminescence dating requires the measurement of the rate of delivery of radiation dose from the sample and its environment for all age determinations it is necessary to assess whether the dose rate has been constant during the time that the dose has been accumulating and to make allowance for it if it was not we report here results from a number of australian sites to illustrate the information that can be found about element concentrations about their distribution and about dose rates tests for radioactive disequilibrium form part of these measurements such tests take the form of comparison of independent measurements of dose rates and or individual elements in general there is little or no evidence for disequilibrium in aeolian dune systems even when the age of the system exceeds 500 ka however disequilibrium has been found in several sites subject to wet conditions

palaeoseismicity of the oquirrh fault utah from shallow seismic tomography the magnitude and frequency of normal fault palaeoearthquakes are usually determined by trenching studies that ascertain the size and number of colluvial wedges along the fault such information can be invaluable in predicting the seismic hazard and potential for a future earthquake in that region digging trenches across normal faults however is environmentally intrusive expensive and limited in the penetration depth to overcome these problems we propose the use of 3 d seismic tomography as a means to identify the shapes and sizes of colluvial wedges along normal faults as an example 2 d and 3 d seismic surveys were conducted across the oquirrh fault utah with the purpose of imaging the normal fault structure to a depth of about 10 m results show that the 3 d tomogram clearly delineates the fault zone and a colluvial wedge both of which correlate extremely well with the geological cross section interpreted from an adjacent trench the thickness of the colluvial wedge image is used in conjunction with a seismic section to compute an estimate of a 6 8 moment magnitude earthquake for the most recent event on this fault which is in close agreement with the 7 0 estimate based on a nearby trenching study these tomographic results demonstrate for the first time that seismic imaging methods can be used in some cases to estimate unambiguously the shapes of colluvial wedges and the sizes of prehistoric earthquakes thus seismic tomography has the possibility of providing cheaper deeper and wider but less resolved images of fault systems than the intrusive excavation of trenches across faults

climatic control of turbidite deposition on the madeira abyssal plain studies of sedimentation in the southwestern part of the madeira abyssal plain have revealed sequences of turbidites correlatable over thousands of square kilometres turbidites are sediments transported by turbidity currents and represent rapidly accumulated sedimentary units1 in this case in the distal part of the flow they are very fine grained and homogeneous occasionally with silty bases individual turbidites are separated by thin pelagic units which alternate from oozes to pelagic clays a stratigraphy for these pelagic units has been produced from combining coccolith distributions and lithological changes which enables comparison to cores containing only pelagic sediments from outside the turbidite province these comparisons show that turbidity currents cause no significant erosion in the area the major turbidites occur between lithological alternations which reflect global climate changes associated with glaciations and related eustatic sea level fluctuations turbidites have been linked with eustacy on previous occasions but only with low stands of sea level2 3 our work shows that turbidites are more likely to occur during regressions and transgressions rather than in the quiet periods between

near synchronous and delayed initiation of long run out submarine sediment flows from a record breaking river flood offshore taiwan subsea fiber optic telecommunication cables can break under fast sediment flows that travel 100s of kilometers through the deep ocean in response to earthquakes and submarine landslides similar flows are inferred to form from major river floods whose sediment laden waters plunge and travel along the seabed however the complex initiation of flood related flows and their hazard potential have not been observed until now here we use cable fault data from the gaoping canyon manila trench off taiwan to show that a major river flood formed during typhoon morakot 2009 generated two long run out destructive sediment flows one during peak flood and the other 3 days later the latter flow was more damaging with speeds and run out similar to that of landslide triggered turbidity currents formed in the same catchment if the second flow was due to remobilized canyon sediment it occurred during low earthquake mw 2 0 activity suggesting other triggering mechanisms

from coseismic offsets to fault block mountains in the basin and range extensional province of the western united states coseismic offsets under the influence of gravity display predominantly subsidence of the basin side fault hanging wall with comparatively little or no uplift of the mountainside fault footwall a few decades later geodetic measurements gps and interferometric synthetic aperture radar insar show broad 100 km aseismic uplift symmetrically spanning the fault zone finally after millions of years and hundreds of fault offsets the mountain blocks display large uplift and tilting over a breadth of only about 10 km these sparse but robust observations pose a problem in that the coesismic uplifts of the footwall are small and inadequate to raise the mountain blocks to address this paradox we develop finite element models subjected to extensional and gravitational forces to study time varying deformation associated with normal faulting stretching the model under gravity demonstrates that asymmetric slip via collapse of the hanging wall is a natural consequence of coseismic deformation focused flow in the upper mantle imposed by deformation of the lower crust localizes uplift which is predicted to take place within one to two decades after each large earthquake thus the best preserved topographic signature of earthquakes is expected to occur early in the postseismic period

calculating erosion by deep sea turbidity currents during initiation and flow turbidity currents transport massive amounts of sediment from continental margins to the deep sea individual flows can catastrophically remove and redeposit as turbidites many hundreds of cubic kilometres of material1 2 with the larger events reaching the bottom of the continental slope to form the abyssal plains3 here we show that the age range of sediments in individual turbidites can be used directly to estimate both the thickness of failed sediment in the source region even when its exact location is unknown and the extent to which the turbidity current caused erosion of the sea bed our method involves the comparison of the abundance ratios of microfossil coccolith species in turbidites with those in the ocean margin sediments of the source region analysis of a recently emplaced turbidite on the madeira abyssal plain shows that it contains a mixture of sediments with an age range of about 200 000 years equivalent to the failure of a block of sediment about 15 m deep radiocarbon dating and coccolith ratios show that the turbidite contains only about 12 of recent near surface sediment indicating that this turbidity current caused surprisingly little erosion en route

estimating prehistoric earthquake magnitude from point measurements of surface rupture abstract we have developed a method for estimating the magnitude of prehistoric earthquakes using displacement data that usually can be collected from paleoseismic investigations this method is necessary because essentially all current magnitude estimates for prehistoric events rely on determining the total length of coseismic surface rupture which is rarely measurable or rely on segmentation scenarios for which uncertainties cannot be quantified although surface rupture length is a better predictor of magnitude than displacement for historic earthquakes paleoseismic investigations are better at providing measurements of the amount of displacement at a site along a fault the key to our method is to incorporate the variability in displacement observed in 14 modern events which allows a formal uncertainty in magnitude to be assigned to prehistoric ruptures we show how multiple measurements along a preserved fraction of a rupture can be combined to reduce the uncertainty in the estimate of magnitude our analysis shows that uncertainty asymptotically approaches the natural variability of ruptures so 5 to 10 displacement measurements are sufficient to characterize paleomagnitude we conclude that sampling of scarps with lengths of even 10 of the original rupture can provide magnitude values that reasonably estimate the earthquake tests of the method using randomly sampled data from the 1992 m w 7 3 landers and 1954 m s 6 8 dixie valley earthquakes provide close approximations of the actual magnitudes

ground penetrating radar investigation of active faults along the dead sea transform and implications for seismic hazards within the city of aqaba jordan abstract ground penetrating radar gpr was used in an effort to locate a major active fault that traverses aqaba city jordan measurements over an exposed trenched cross fault outside of the city identify a radar signature consisting of linear events and horizontal offset flexured reflectors both showing a geometric correlation with two known faults at a control site the asymmetric linear events are consistent with dipping planar reflectors matching the known direction of dip of the faults however other observations regarding this radar signature render the mechanism generating these events more complex and uncertain gpr measurements in aqaba city were limited to vacant lots seven gpr profiles were conducted approximately perpendicular to the assumed strike of the fault zone based on regional geological evidence a radar response very similar to that obtained over the cross fault was observed on five of the profiles in aqaba city although the response is weaker than that obtained at the control site the positions of the identified responses form a near straight line with a strike of 45 although subsurface verification of the fault by trenching within the city is needed the geophysical evidence for fault zone location is strong the location of the interpreted fault zone relative to emergency services military bases commercial properties and residential areas is defined to within a few meters this study has significant implications for seismic hazard analysis in this tectonically active and heavily populated region

african climate change and faunal evolution during the pliocene pleistocene abstract environmental theories of african faunal evolution state that important evolutionary changes during the pliocene pleistocene interval the last ca 5 3 million years were mediated by changes in african climate or shifts in climate variability marine sediment sequences demonstrate that subtropical african climate periodically oscillated between markedly wetter and drier conditions paced by earth orbital variations with evidence for step like 0 2 ma increases in african climate variability and aridity near 2 8 ma 1 7 ma and 1 0 ma coincident with the onset and intensification of high latitude glacial cycles analysis of the best dated and most complete african mammal fossil databases indicates african faunal assemblage and perhaps speciation changes during the pliocene pleistocene suggesting more varied and open habitats at 2 9 2 4 ma and after 1 8 ma these intervals correspond to key junctures in early hominid evolution including the emergence of our genus homo pliocene pleistocene shifts in african climate vegetation and faunal assemblages thus appear to be roughly contemporary although detailed comparisons are hampered by sampling gaps dating uncertainties and preservational biases in the fossil record further study of possible relations between african faunal and climatic change will benefit from the accelerating pace of important new fossil discoveries emerging molecular biomarker methods for reconstructing african paleovegetation changes tephra correlations between terrestrial and marine sequences as well as continuing collaborations between the paleoclimatic and paleoanthropological communities

rupture of the pitaycachi fault in the 1887 mw 7 5 sonora mexico earthquake southern basin and range province rupture kinematics and epicenter inferred from rupture branching patterns during the 3 may 1887 mw 7 5 sonora earthquake surface rupture end to end length 101 8 km an array of three north south striking basin and range province faults from north to south pitaycachi teras and otates slipped sequentially along the western margin of the sierra madre occidental plateau this detailed field survey of the 1887 earthquake rupture zone along the pitaycachi fault includes mapping the rupture scarp and measurements of surface deformation the surface rupture has an endpoint to endpoint length of 41 0 km dips 70 w and is characterized by normal left lateral extension the maximum surface offset is 487 cm and the mean offset 260 cm the rupture trace shows a complex pattern of second order segmentation however this segmentation is not expressed in the 1887 along rupture surface offset profile which indicates that the secondary segments are linked at depth into a single coherent fault surface the pitaycachi surface rupture shows a well developed bipolar branching pattern suggesting that the rupture originated in its central part where the polarity of the rupture bifurcations changes most likely the rupture first propagated bilaterally along the pitaycachi fault the southern rupture front likely jumped across a step over to the teras fault and from there across a major relay zone to the otates fault branching probably resulted from the lateral propagation of the rupture after breaching the seismogenic part of the crust given that the much shorter ruptures of the otates and teras segments did not develop branches

reevaluation of holocene faulting at the kaysville site weber segment of the wasatch fault zone utah the 1978 kaysville utah trench excavated by swan and others 1980 across a large graben of the weber segment of the wasatch fault zone was reexcavated in 1988 to reevaluate the timing and nature of holocene faulting relogging of the trench reveals evidence for five or six faulting events younger than the provo phase of lake bonneville circa 13 000 14c years b p geometric reconstruction of net vertical offset in the last three events suggests a variation in coseismic vertical displacement at this site ranging from a net of 1 4 3 4 m per event the three latest faulting events occurred at shortly before 0 6 0 8 ka 2 8 0 7 ka and circa 3 8 7 9 ka earlier events cannot be directly dated because older graben fill sediments yielded thermoluminescence ages older than the time of deposition and some scarp derived colluvial wedges beneath the trench floor were not exposed the two younger faulting events we recognize at kaysville correlate reasonably well with faulting events on the same segment 25 km north near east ogden utah at circa 0 8 1 2 ka and 2 5 3 0 ka forman and others 1991 whereas the earlier kaysville event is significantly older than the earliest 3 5 4 0 ka event dated at east ogden the 3 5 4 0 ka ground rupture recognized at east ogden may have died out at a subsegment boundary between the two trench sites within the 61 km long weber segment

identifying and quantifying erosion beneath the deposits of long runout turbidity currents along their pathway variations between the geochemical compositions coccolith species compositions and the physical properties of turbidite muds and their underlying hemipelagites can be used to understand the erosive nature of sediment gravity flows large volume submarine landslides on the nw moroccan continental margin produce long runout turbidity currents capable of traversing hundreds to thousands of kilometres across the adjacent moroccan turbidite system mts these turbidity currents are responsible for turbidites that are among the largest volume most aerially extensive and longest runout deposits recorded these resulting turbidite beds can be correlated over distances of 1800 km across the full 250 000 km2 area of the mts due to the ability to trace these individual flow deposits throughout the mts large volume beds a5 a7 a11 a12 and a15 can be shown to be erosive upon debouching agadir canyon whilst smaller volume flows were not erosive these aforementioned large volume flows have been capable of eroding up to 15 km3 of material in the canyon mouth equating to as much as 50 of the later deposit volume evidence suggests individual flows erode up to 4 5 m of sediment within scours in the mouth of agadir canyon however these scours are 8 0 m deep indicating that several flows contribute to forming the scours in a series of cut and fill episodes several flows including beds a5 a7 a11 and a12 were also erosive in agadir basin up to 210 km from the canyon the present study indicates that large volume flows a5 a7 and a12 are also erosive within the channel lobe transition zone within the proximal madeira abyssal plain after exiting the madeira channels over 800 km from agadir canyon studying the deposits of these flows and their compositional changes along their entire pathway has provided invaluable information of whether the flows are erosive where this erosion takes place and to what extent they erode the seafloor there are also broader implications towards gaining information about flow processes at the bed interface calculating basin sediment budgets and better understanding discontinuous stratigraphy in distal turbidite systems