the influences of row grade ridge height and field slope on the seepage hydraulics of row sideslopes in contour ridge systems abstract seepage plays an important role in soil erosion in contour ridge systems seepage generated from subsurface flow causes hillslope instability by reducing the soil shear strength and mobilizing soil particles and can produce cave like features called seepage undercuts that can lead to contour failure as the main threat to contour plowing seepage results in large amounts of soil erosion due to row grade models used to predict seepage over a time series will provide a basis for modeling soil erosion resulting from seepage in contour ridging systems understanding seepage and its effects will advance our knowledge regarding seepage erosion mechanisms in contour ridge systems in this study 23 treatments were arranged using an orthogonal rotatable central composite design to model a seepage time series build a simple seepage prediction model and investigate the effects of row grade field slope and ridge height on seepage discharge most of the seepage discharge time series followed an s shaped curve the seepage discharge processes were fit by an exponential model with a determination coefficients r2 greater than 0 995 furthermore the physical meaning of the exponential model was consistent with the experimental results the seepage discharge continuously increased before the inflection point and then decreased finally the seepage discharge approached a steady value the maximum seepage discharge growth rate was achieved within 14 min and the seepage discharge became steady within 106 min second order polynomial regression models were used to determine the total and predicted steady seepage discharge using independent variables of row grade field slope and ridge height which produced r2 values of 0 66 p

europa s opposition surge in the near infrared interpreting disk integrated observations by cassini vims abstract near infrared observations of europa s disk integrated opposition surge by cassini vims first published in fig 4 of brown et al 2003 icarus 164 461 have now been modeled with the commonly used hapke photometric function the vims data set emphasizes observations at 16 solar phase angles from 0 4 to 0 6 the first time the 1 phase heart of europa s opposition surge has been observed this well in the near ir this data set also provides a unique opportunity to examine how the surge is affected by changes in wavelength and albedo at vims wavelengths of 0 91 1 73 and 2 25 m the geometric albedo of europa is 0 81 0 33 and 0 18 respectively despite this factor of four albedo range however the slope of europa s phase curve at 1 phase is similar at all three wavelengths to within the error bars and this common slope is similar to the phase coefficient seen in visible light observations of europa the two components of the opposition surge involving different models of the physical cause of the surge are the shadow hiding opposition effect shoe and the coherent backscatter opposition effect cboe because of sparse vims phase coverage it is not possible to constrain all the surge parameters at once in a hapke function that has both shoe and cboe accordingly we performed separate hapke fits for shoe only and cboe only surges at 2 25 m where vims data are somewhat noisy both types of surges can mimic the slope of the vims phase curve at 1 phase at 0 91 and 1 73 m however where vims data are cleaner cboe does a noticeably poorer job than shoe of matching the vims phase coefficient at 1 phase in particular the best cboe fit insists on having a steeper phase curve slope than the data this discrepancy suggests that europa s near ir opposition surge cannot be explained by cboe alone and must have a significant shoe component even at wavelengths where europa is bright

siderophile interelement variations in the cretaceous tertiary boundary sediments from caravaca spain a detailed profile of the siderophiles fe co ni pd re os ir pt and au from the cretaceous tertiary boundary at caravaca spain indicates that the major fractionation mechanisms are local redistribution reworking and diagenetic mobilization large fractions of the fe co and re and perhaps a small amount of pd and au appear to be terrestrially derived but nearly all of the ni os ir and pt must be derived from an extraterrestrial source only the basal layers at caravaca and stevns klint denmark are representative of the initial fallout and integrated ir fluences across entire sections can be misleading these suggest a concentration oft 120mg g projectile in the fallout and a global fluence of chondritic matter oft 140mg cm 2

selected plant microfossil records of the terminal cretaceous event in terrestrial rocks western north america abstract terrestrial or nonmarine rocks of western north america preserve a record of major disruption and permanent alteration of plant communities precisely at the k t boundary in the same rocks that preserve geochemical and mineralogical evidence of the terminal cretaceous impact event plant microfossil records from many localities show abrupt disappearance of pollen species plant extinctions closely associated with impact ejecta deposits containing iridium and shocked quartz localities discussed in detail in this review are starkville south clear creek north old raton pass and sugarite in the raton basin of colorado and new mexico west bijou in the denver basin colorado sussex in the powder river basin wyoming and pyramid butte and mud buttes in the williston basin north dakota

the structural evolution of active fault and fold systems in central otago new zealand evidence revealed by drainage patterns abstract central otago in new zealand is an area of active continental shortening in which a peneplain surface cut into schist has been deformed by folds which are developed above buried reverse faults we use the drainage patterns in this region to demonstrate various processes in fold and fault growth and interaction that would be difficult to identify by other means in particular we show 1 how simple asymmetric folds can develop into box folds 2 how apparently continuous ridges were formed by the coalescing of quite separate propagating fold and fault segments 3 evidence for the relative ages or relative uplift rates of adjacent structures and 4 evidence for the propagation direction of folds or faults as they grow the few quantitative estimates we obtain for fault propagation rates suggest an increase in length of 10 50 m per earthquake on faults about 20 km long these estimates are very uncertain but are similar in magnitude to an estimate made in nevada for a normal fault of similar size and are also similar to predicted estimates from theoretical growth models they raise the question of whether fault growth earthquake recurrence rates and climate change can interact to produce semi regular discrete features in an active landscape

rhodium distribution at the cretaceous tertiary boundary analysed by ultrasensitive laser photoionization the extraordinarily high concentrations of indium and other siderophiles found in cretaceous tertiary k t boundary deposits have been interpreted1 as a result of a large extraterrestrial body falling upon the earth causing mass extinction of the biota dominant in the cretaceous the existing alternative models of the cretaceous terminal event try to explain the anomaly of siderophile elements by their being concentrated through sedimentation or volcanic eruptions2 3 to understand the nature of the k t event it is important to establish the proportions of siderophiles and their isotopes in boundary deposits of that age especially the proportions of platinum group elements their concentrations in extraterrestrial material being high and occurring in ratios differing from those typical of terrestrial material here we present the first data on rhodium concentrations at the k t boundary in the sumbar sm 4 section turkmen ssr obtained by the ultrasensitive laser photoionization spectroscopy lapis technique4 5 the maximum rh concentration in the samples studied is 24 2 ng g 1the rh ir ratio is 0 34 0 06 which is close to the cosmic ratio of these elements the lapis technique is efficient and can be used for determining the concentrations of all siderophile elements and their isotopes in geological materials

terrestrial carbon and nitrogen isotopic ratios from cretaceous tertiary boundary nanodiamonds one hypothesis for the origin of the nanometer size diamonds found at the cretaceous tertiary k t boundary is that they are relict interstellar diamond grains carried by a postulated asteroid the 13 c 12 c and 15 n 14 n ratios of the diamonds from two sites in north america however show that the diamonds are two component mixtures differing in carbon and nitrogen isotopic composition and nitrogen abundance samples from a site from italy show no evidence for either diamond component all the isotopic signatures obtained from the k t boundary are material well distinguished from known meteoritic diamonds particularly the fine grain interstellar diamonds that are abundant in primitive chondrites the k t diamonds were most likely produced during the impact of the asteroid with earth or in a plasma resulting from the associated fireball

comparison of linear and nonlinear models for cohesive sediment detachment rill erosion hole erosion test and streambank erosion studies abstractcohesive sediment detachment is typically modeled for channels levees spillways earthen dams and internal erosion by using a linear excess shear stress approach however mechanistic nonlinear detachment models such as the wilson model have recently been proposed in the literature questions exist as to the appropriateness of nonlinear relationships between applied shear stress and the erosion rate therefore the objective of this research was to test the appropriateness of linear and nonlinear detachment models for cohesive sediment detachment using three data sets 1 rill erodibility studies across a limited range of applied shear stress 0 9 21 4 pa 2 hole erosion tests hets across a wide range of applied shear stress 12 6 62 0 pa and 3 streambank erodibility as quantified by jet erosion tests jets for the linear excess shear stress equation and the nonlinear wilson model across a small range of shear stress 1 4 pa the wilson model was also incorporated into the bank st

voyager photometry of europa abstract ninety voyager images ranging in phase angle from 3 to 143 and covering the spectral range from 0 34 to 0 58 m were analyzed to derive the photometric properties of europa at small phase angles the disk integrated phase curve is remarkable in that it shows little or no evidence of an opposition effect in agreement with earlier earth based observations by millis and thompson icarus 26 408 1975 the phase integral determined in the voyager clear filter centered near 0 47 m is 1 09 0 11 in good agreement with previous estimates based on radiometry the bolometric bond albedo is 0 62 0 14 the scattering properties of europa in general and of the two major terrain types bright plains and darker mottled terrain in particular cannot be represented by a lunar like photometric law however an equation which is a linear superposition of a lunar like scattering law and a lambert component provides an adequate simple representation of the scattering properties the plains are photometrically more homogeneous than the darker mottled terrain in the voyager clear filter the average normal reflectance is 0 71 for the plains on both the leading and trailing hemispheres for the darker mottled terrain the values are 0 60 on the leading hemisphere and 0 48 on the trailing one

galileo photometry of asteroid 243 ida galileo imaging observations over phase angles 19 5 to 109 8 are combined with near opposition earth based data to derive the photometric properties of ida to first order these properties are uniform over the surface and well modeled at 0 55 m by hapke parameters 0 0 22 h 0 020 b0 1 5 g 0 33 and 18 with corresponding geometric albedop 0 21 0 030 01and bond albedoab 0 081 0 0170 008 ida s photometric properties are more similar to those of average s asteroids p helfenstein and j veverka 1989 asteroids ii univ of arizona press tucson than are those of 951 gaspra two primary color units are identified on ida terrain a exhibits a spectrum with relatively shallower 1 m absorption and a relatively steeper red spectral slope than average ida while terrain b has a deeper 1 m absorption and a less steep red slope the average photometric properties of ida and terrain a are similar while those of terrain b differ mostly in having a slightly higher value of 0 0 22 versus 0 21 suggesting that terrain b consists of slightly brighter more transparent regolith particles galileo observations of ida s satellite dactyl over phase angles 19 5 to 47 6 suggest photometric characteristics similar to those of ida the major difference being dactyl s slightly lower albedo 0 20 compared to 0 21

iridium enrichment in volcanic dust from blue ice fields antarctica and possible relevance to the k t boundary event abstract blue ice fields in antarctica well known as stranding zones of antarctic meteorites contain ice that is several tens to hundreds of thousand years old which records numerous events that have taken place since its formation among the most important structures on the ice fields are dust bands which are mostly of volcanic origin and consist of small volcanic glass shards and lithic fragments petrographic and chemical studies of a number of dust bands during earlier investigations have shown that significant ash layers are deposited at distances of up to several thousand kilometers from the source volcanoes samples of dust layers taken in the lewis cliff beardmore glacier area in antarctica analyzed in the course of this work for major and trace elements were identified as consisting of volcanic ash probably originating from the pleiades melbourne volcanic province northern victoria land some of these dust samples were found to contain iridium in concentrations of up to 7 5 ppb a positive correlation between ir and se as well as enrichments in as sb and other volcanogenic elements has been observed the dust samples investigated here have very small grain size consistent with the distance from the source volcanoes the small grain size of the dust suggests that the ir enrichment is a surface effect and was probably caused by condensation from a vapor phase this is the first time that significant ir enrichments have been found in volcanic dust which demonstrates that ir and possibly also other platinum group metals may be present in some volcanic ash deposits although this has been doubted by the proponents of the pure impact theory for the k t boundary event the results of this study suggest that the ir in the k t boundary clays is not necessarily of cosmic origin but alternatively may have originated from mantle reservoirs that were tapped during extensive volcanic eruptions which may been triggered by impact events

galileo observations of europa s opposition effect abstract during galileo s g7 orbit the solid state imaging ssi camera acquired pictures of the spacecraft shadow point on europa s surface as well as a comparison set of images showing the same geographic region at phase angle 5 coverage obtained at three spectral bandpasses vlt 0 41 m grn 0 56 m and 1mc 0 99 m at a spatial resolution of 404 m pixel shows a 162 220 km region of europa s surface located at 30 n 162 w we have used these images to measure the near opposition spectrophotometric behavior of four primary europan terrain materials ir bright icy material ir dark icy material dark lineament material and dark spot material the high spatial resolution of the g7 images reveal low albedo materials in dark spots that are among the darkest features 17 albedo at 0 56 m and 5 phase yet found on icy galilean satellites while material of comparable albedo is found on ganymede and callisto low albedo europan materials are much redder all europan surface materials exhibit an opposition effect however the strength of the effect as measured by the total increase in reflectance as phase angle decreases from 5 to 0 varies among terrains the opposition effects of ir bright icy and ir dark icy materials which dominate europa s surface are about 1 5 times larger than predicted from pre galileo studies low albedo materials in dark spots exhibit unusually intense opposition effects up to four times larger than bright icy europan terrains consistent with the presence of a strong shadow hiding opposition surge the strengths of the opposition surges among average europan terrains systematically vary with terrain albedo and can be explained in terms of the simultaneous contributions of shadow hiding and coherent backscatter to the total opposition effect coherent backscatter introduces a narrow angular contribution

measuring streambank erosion due to ground water seepage correlation to bank pore water pressure precipitation and stream stage limited information exists on one of the mechanisms governing sediment input to streams streambank erosion by ground water seepage the objective of this research was to demonstrate the importance of streambank composition and stratigraphy in controlling seepage flow and to quantify correlation of seepage flow erosion with precipitation stream stage and soil pore water pressure the streambank site was located in northern mississippi in the goodwin creek watershed soil samples from layers on the streambank face suggested less than an order of magnitude difference in vertical hydraulic conductivity ks with depth but differences between lateral ks of a concretion layer and the vertical ks of the underlying layers contributed to the propensity for lateral flow goodwin creek seeps were not similar to other seeps reported in the literature in that eroded sediment originated from layers underneath the primary seepage layer subsurface flow and sediment load quantified using 50 cm wide collection pans were dependent on the type of seep intermittent low flow lf seeps flow rates typically less than 0 05 l min 1 persistent high flow hf seeps average flow rate of 0 39 l min 1 and buried seeps which eroded unconsolidated bank material from previous bank failures the timing of lf seeps correlated to river stage and precipitation the hf seeps at goodwin creek began after rainfall events resulted in the adjacent streambank reaching near saturation i e soil pore water pressures greater than 5 kpa seep discharge from hf seeps reached a maximum of 1 0 l min 1 and sediment concentrations commonly approached 100 g l 1 buried seeps were intermittent but exhibited the most significant erosion rates 738 g min 1 and sediment concentrations 989 g l 1 in cases where perched water table conditions exist and persistent hf seeps occur seepage erosion and bank collapse of streambank sediment may be significant copyright 2007 john wiley sons ltd

impact production of co2 by the cretaceous tertiary extinction bolide and the resultant heating of the earth evidence at the cretaceous tertiary boundary suggests that the proposed extinction bolide struck a continental or shallow marine terrane this evidence includes shocked quartz and feldspar grains found in the boundary layer inherited from a range of rock types a high 87 sr 86 sr ratio in some planktonic fossils which could reflect continental derived sr ref 5 and evidence that the platinum group element rich clay layer is underlain at some localities by a deposit of possible tsunamic origin these observations and data demonstrate that sea level at the end of the cretaceous was 150 200 m higher than at present suggesting the possibility that the extinction bolide struck a shallow marine carbonate rich sedimentary section here we show that the impact of such a bolide 5km in radius onto a carbonate rich terrane would increase the co 2 content of the atmosphere by a factor of two to ten additional dissolution of co 2 from the ocean s photic zone could release much larger quantities of co 2 the impact induced release of co 2 by itself would enhance atmospheric greenhouse heating and give rise to a worldwide increase in temperature from 2 k to 10 k for periods of 10 4 to 10 5 years

the distribution and geochemistry of platinum group elements as event markers in the phanerozoic abstract the discovery of the platinum group element pge enrichment in the cretaceous tertiary k t boundary impact layer popularized the use of pges as geochemical event markers and prompted an explosion of interest in these elements whose geochemical behavior is poorly understood instead of concentrating on the more easily analyzed pges e g iridium many studies now include the entire group analytical methods have been improved to the point where small samples 5 g can be analyzed confidently at the sub ppb level allowing the determination of the distribution of pges in the oceans atmosphere and biosphere the presence or absence of a pge anomaly is often used as a criterion for determining whether an event horizon is impact related however to date only the k t boundary yields a distinct pge anomaly with positive interelement correlations and solar interelement ratios terrestrial sources such as volcanic emissions are also being investigated as potential contributors to pge anomalies at other phanerozoic event horizons primary signatures e g interelement ratios characteristic of the pge source may be altered during various high and or low temperature processes for example fractionation during impact melting vaporization condensation remobilization redistribution and diagenesis can obscure original signatures and make determination of the pge source difficult future research might be directed towards establishing the behavior of the pges during such processes

modeling the formation of the k pg boundary layer abstract in this paper we investigate the formation of the cretaceous paleogene k pg boundary layer through numerical modeling the k pg layer is widely agreed to be composed of meteoritic material and target rock from the chicxulub impact site that has been ejected around the globe and mixed with local material during final deposition the observed composition and thickness of the k pg boundary layer changes with azimuth and distance from the impact site we have run a suite of numerical simulations to investigate whether we can replicate the observational data with a focus on the distal k pg layer and the impact glasses at proximal sites such as beloc haiti previous models of the k pg ejecta have assumed an initial velocity distribution and tracked the ejecta to its final destination here we attempt to model the entire process from impact to the arrival of the ejecta around the globe our models replicate the observed ejecta thickness at proximal sites and the modeled ejecta is composed of sediments and silicate basement rocks in agreement with observational data models that use a 45 impact angle are able to replicate the total ejecta and iridium volume at distal sites and the majority of the ejecta is composed of meteorite and target sediments sub vertical impacts generate too little iridium and oblique impacts of 30 degrees generate too much however in contrast to observations models that involve ballistic transport of ejecta lead to ejecta thickness decreasing with increasing distance and are unable to transport shocked minerals quartz and zircon from the chicxulub basement rocks around the globe we suggest that much of the k pg ejecta is transported non ballistically and that the most plausible mechanism is through re distribution from a hot expanding atmosphere the results are important for future investigations of the environmental effects of the chicxulub impact

new method for the measurement of osmium isotopes applied to a new zealand cretaceous tertiary boundary shale the determination of osmium content and isotopic abundances in geological materials has received increasing attention in recent years following the proposal of alvarez et al 1 that mass extinctions at the end of the cretaceous period were caused by the impact of a large 10km meteorite which left anomalously high iridium levels as a geochemical signature in the boundary shales here we report a new and simple method for measuring osmium in geological materials involving fusion of the sample with sodium peroxide distillation of the osmium as the tetroxide using perchloric acid extraction into chloroform and absorption of the chloroform extract onto graphite powder before instrumental neutron activation analysis in a variant of this technique the chloroform extract is back extracted into an aqueous phase and the osmium isotopes are determined by plasma source mass spectrometry icpms we have used this method on the woodside creek new zealand cretaceous tertiary boundary clay and have obtained the first osmium content 6g ng g 1 for this material the 187os 186os ratio is 1 12 0 16 showing a typical non crustal signature this combined distillation extraction icpms method will prove to be useful for measuring osmium isotopes in other geological materials

the distribution of some platinum group elements in the ug 2 chromitite layer of the bushveld complex samples representing consecutive 2 cm thick slabs of a drill core through the ug 2 chromitite layer were analyzed for platinum group elements the results when plotted against height reveal an interesting pattern with sequences that follow exponential curves of the type y zx k where y equals the concentration of the element in samples taken at a distance x from the base of the layer and z is a constant the data fit the curves with correlation coefficients of better than 0 90 and levels of significance less than 0 1 percent which shows that the fit cannot be due to chance but that a process following or approximating an exponential equation must have been involved the most probable such process is fractionation according to the rayleigh law it is postulated that these sequences that follow the rayleigh law formed by bottom crystallization when the magma was in motion calculations indicate that the elements supplied to the site of crystallization were withdrawn from a surprisingly small thickness of magma and that their supply was not limited by diffusion between the sequences that follow the rayleigh law are sequences that probably crystallized from stagnant magma so that the supply of elements to the site of crystallization was diffusion controlled in these sequences the ratios between the different platinum group elements change progressively it is argued that these results reveal that the platinum group minerals crystallized very early in ug 2 layer type deposits and show a pattern of element behavior conforming closely with that of a classical compatible element which has a very large bulk distribution coefficient therefore the well known processes of enrichment applicable to such elements during processes of melting and crystallization could have been operative this one example is not sufficient to disclaim the possibility that platinum group elements can also behave like incompatible elements under different conditions as is assumed by many authors in this field

sediment detachment and transport processes associated with internal erosion of soil pipes subsurface flow can be an important process in gully erosion through its impact on decreasing soil cohesion and erosion resistance as soil water content or pressure increases and more directly by the effects of seepage forces on particle detachment and piping the development of perched water tables in duplex soils fosters lateral flow that can result in seepage at the surface of hillslopes and or formation of soil pipes by internal erosion of lateral preferential flow paths continued internal erosion of soil pipes can lead to gullies dam and levee failures however the processes involved in particle and aggregate detachment from soil pipe walls and transport processes within soil pipes have not been well studied or documented this paper reviews the limited research on sediment detachment and transport in macropores and soil pipes and applies the knowledge learned from the much more extensive studies conducted on streams and industrial pipes to hydrogeologic conditions of soil pipes knowledge gaps are identified and recommendations are made for future research on sediment detachment and transport in soil pipes

practical determination of critical shear stress in cohesive soils abstractin comparison to sand and gravel cohesive soils and clays in particular present significant challenges when critical entrainment thresholds and erosion rates are to be determined for a p

seepage caused tension failures and erosion undercutting of hillslopes summary seepage has been suggested as an important factor in gully and river bank erosion this study investigated the underlying mechanisms of instability by seepage in laboratory studies a 25 cm tall 50 cm wide and 20 cm long soil block with a focused inflow reservoir was constructed to investigate seepage gradient forces and the three dimensional nature of seepage particle mobilization i e seepage erosion and undercutting experiments included sand and loamy sand soil blocks packed at prescribed bulk densities 1 30 1 70 mg m 3 and with an outflow face at various angles 90 75 and 60 constant heads of 15 25 and 35 cm were imposed on the soil to induce flow a laser scanner was utilized to obtain the three dimensional coordinates of the bank and undercut surfaces at approximately 15 30 s intervals the bulk density of the two different soil types controlled which seepage failure mechanism occurred 1 tension or pop out failures due to the seepage force exceeding the soil shear strength which was being concurrently reduced by increased soil pore water pressure or 2 particle entrainment in the seepage flow particle mobilization bank undercutting and bank collapse when the initial seepage force gradient was less than the resistance of the soil block for cases experiencing particle mobilization and undercutting seepage erosion initiated as unimodal i e concentrated at one point or as multimodal i e initiating at several locations across the bank face and this result was largely controlled by the bank angle a five parameter gaussian function was fitted to the measured three dimensional undercut shapes to derive parameters for the maximum depth of undercutting position of the center of the peak and the vertical and lateral spreads of the undercut the parameters of this distribution can be useful in the development of improved sediment transport functions and the incorporation of this failure mechanism into hillslope stability models

mineralogic evidence for an impact event at the cretaceous tertiary boundary a thin claystone layer found in nonmarine rocks at the palynological cretaceous tertiary boundary in eastern montana contains an anomalously high value of iridium the nonclay fraction is mostly quartz with minor feldspar and some of these grains display planar features these planar features are related to specific crystallographic directions in the quartz lattice the shocked quartz grains also exhibit asterism and have lowered refractive indices all these mineralogical features are characteristic of shock metamorphism and are compelling evidence that the shocked grains are the product of a high velocity impact between a large extraterrestrial body and the earth the shocked minerals represent silicic target material injected into the stratosphere by the impact of the projectile

reevaluation of siderophile element abundances and ratios across the cretaceous paleogene k pg boundary implications for the nature of the projectile abstract the discovery over 30 years ago at gubbio italy and caravaca spain of an enrichment in the concentrations of iridium ir and the other platinum group elements pge by up to four orders of magnitude irmax 0 10 87 ng g compared to average continental crustal background levels remains one of the most important discoveries in the earth sciences since then similar anomalies have been detected in more than 120 cretaceous paleogene k pg boundary sites worldwide highly elevated ir and other siderophile element abundances in roughly chondritic ratios are considered strong indicators for the presence of a meteoritic contribution in impact related lithologies melt rocks impact ejecta material etc delivered when an extraterrestrial object strikes earth the presented work adds 113 unpublished pge analyses of 38 k pg sections worldwide to the existing literature the analytical protocol relied on for this purpose consisted of a combination of a nickel sulfide fire assay pre concentration technique and subsequent trace metal determination via inductively coupled plasma mass spectrometry icp ms through repeated determination of key siderophile elements i e cr co ni and pge the importance of sampling nugget effects and analytical methodologies applied becomes more apparent even more critically these analytical effects are superimposed by the local syn and post depositional conditions that have affected the pristine meteoritic signature of the k pg impactor including potential fractionation during vaporization and condensation dissimilar pge carrier phases terrestrial pge input sedimentation rate reworking diagenesis bioturbation and chemical diffusion while chondrite normalized pge patterns of individual sites appear relatively flat i e chondritic strong variations in siderophile element content and inter element ratios exist between k pg locations inter laboratory measurements and replicate analyses hampering a precise projectile identification using highly siderophile elements only when considering improved databases of siderophile element concentrations in meteorites in combination with linear regression analysis to calculate inter element ratios from a large suite of ejecta deposit sites the nature of the k pg projectile can be resolved application of this methodology to an extensive data set of continental and marine sites very proximal to distal to the chicxulub impact structure supports a carbonaceous chondritic impactor type cm or co

the cretaceous tertiary transition the fossil sequences from cores across the cretaceous tertiary boundary show a range of transition times and transition time intervals depending on the fossil indicators and the location of the site these variations together with the pattern of iridium distribution with depth at some sites differences in total amounts of iridium variations in noble metal abundances normalized to extraterrestrial concentrations the depositional effects that might be expected in a reducing environment and the clay mineralogy of the boundary layer clays put into question the interpretation that an extraterrestrial event was the cause of the faunal changes and the iridium anomaly in the vicinity of the cretaceous tertiary transition it seems more likely that an explanation for the changes during the transition will come from continued examination of the great variety of terrestrial events that took place at that time including extensive volcanism major regression of the sea from the land geochemical changes and paleoclimatic and paleoceanographic changes

shocked quartz in the cretaceous tertiary boundary clays evidence for a global distribution shocked quartz grains displaying planar features were isolated from cretaceous tertiary boundary clays at five sites in europe a core from the north central pacific ocean and a site in new zealand at all of these sites the planar features in the shocked quartz can be indexed to rational crystallographic planes of the quartz lattice the grains display streaking indicative of shock in x ray diffraction photographs and also show reduced refractive indices these characteristic features of shocked quartz at several sites worldwide confirm that an impact event at the cretaceous tertiary boundary distributed ejecta products in an earth girdling dust cloud as postulated by the alvarez impact hypothesis

fires at the k t boundary carbon at the sumbar turkmenia site abstract we have measured carbon at the marine k t boundary site sm 4 at the sumbar river in turkmenia ussr which has an undisturbed ir profile and the largest known ir anomaly 580 ng cm 2 twenty samples ranging from 100 to 100 cm were analyzed to determine the concentration and 13 c of elemental carbon and kerogen using a cr 2 o 7 oxidation method wolbach and anders 1989 to resolve these components the samples were unusually complex containing 3 kerogen components of distinctive ir spectra and half lives in cr 2 o 7 200 100 and 60 h in addition to soot and charcoal from the k t fire the elemental c has 13 c 25 96 0 6 l o close to the mean for 11 k t sites 25 8 0 6 11 mg cm 2 the first of the 2 kerogen components 13 c 22 8 which dominates in the cretaceous appears to come from detrital carbonaceous shale the second 13 c 27 7 o occurs only in the boundary clay and may come from land plant material swept to sea or phytoplankton grown in the presence of excess light co 2 from fires on land the great thickness of the boundary clay 10 5 cm permits determination of the compositional profiles with unprecedented spatial resolution ir and shocked quartz both representing impact ejecta rise sharply at the boundary peak in the basal layer and then decline soot and total elemental c show a similar spike in the basal layer but then rise rather than fall peaking at 7 cm apparently fires started before the basal layer had settled implying that ignition and spreading of major fires became possible if not immediately then very soon after the impact there is no basis for claims by hansen et al 1987 that k t carbon black first occurs 3 5 m below the danish k t boundary and has 13 c of 27 4 to 27 8 o reexamination of a sample from nye klov shows that these authors confused kerogen with carbon black

paleoenvironmental significance of clay mineral associations at the cretaceous tertiary passage abstract the clay mineral stratigraphy at the cretaceous tertiary transition is considered by the study of new sections walvis ridge maud rise central italy northern tunisia which are compared with results of previous investigations increased contents of smectite and or kaolinite or substrate derived species e g illite group depending on the areas investigated are observed near the boundary these diversified modifications indicate increased erosion and predominance of local detrital supply including that of volcanic rocks over general related causes most probably these modifications of clay mineral associations express a major geodynamic disruption characterized by tectonic instability and sea level drop those events began prior to the cretaceous tertiary boundary i e prior to the major iridium anomaly recorded in sediments this could explain why a catastrophic event at the cretaceous tertiary boundary is hardly evidenced in the clay sedimentological record which is extremely sensitive to the global changes in the earth s terrestrial environment

the manson impact structure 40ar 39ar age and its distal impact ejecta in the pierre shale in southeastern south dakota the 40 ar 39 ar ages of a sanidine clast from a melt matrix breccia of the manson iowa impact structure mis indicate that the mis formed 73 8 0 3 million years ago ma and is not coincident with the cretaceous tertiary boundary 64 43 0 05 ma the mis sanidine is 9 million years older than 40 ar 39 ar age spectra of mis shock metamorphosed microcline and melt matrix breccia interpreted earlier to be 64 to 65 ma grains of shock metamorphosed quartz feldspar and zircon were found in the crow creek member upper campanian at a biostratigraphic level constrained by radiometric ages in the pierre shale of south dakota that are consistent with the 40 ar 39 ar age of 73 8 0 3 ma for mis reported herein

the opposition surge and photopolarimetry of fresh and coated basalts abstract we present polarization phase curve measurements and analysis for three basalt samples fresh dark red varnished and dark gray varnished each sample displays a prominent opposition surge countering the widely held notion that only particulate surfaces and not bare rock will display this phenomenon the most likely cause of the opposition surge is coherent backscattering but the width of the surge suggests that other mechanisms may also contribute the photopolarimetric properties of the samples especially the negative branch parameters are most comparable to those of c class asteroids

terrestrial impact structures impact structures are the dominant landform on planets that have retained portions of their earliest crust the present surface of the earth however has comparatively few recognized impact structures this is due to its relative youthfulness and the dynamic nature of the terrestrial geosphere both of which serve to obscure and remove the impact record although not generally viewed as an important terrestrial as opposed to planetary geologic process the role of impact in earth evolution is now receiving mounting consideration for example large scale impact events may have been responsible for such phenomena as the formation of the earth s moon and certain mass extinctions in the biologic record the importance of the terrestrial impact record is greater than the relatively small number of known structures would indicate impact is a highly transient high energy event it is inherently difficult to study through experimentation because of the problem of scale in addition sophisticated finite element code calculations of impact cratering are gen erally limited to relatively early time phenomena as a result of high com putational costs terrestrial impact structures provide the only ground truth against which computational and experimental results can be com pared these structures provide information on aspects of the third dimen sion the preand postimpact distribution of target lithologies and the nature of the lithologic and mineralogic changes produced by the passage of a shock wave they also provide data for cratering rate estimates and in some cases on the nature of the impacting body in this review emphasis is placed on the nature of terrestrial impact structures the criteria for their identification and their contribution to

mechanistic detachment rate model to predict soil erodibility due to fluvial and seepage forces abstractthe erosion rate of cohesive soils is typically computed using an excess shear stress model based on the applied fluvial shear stress however no mechanistic approaches are available for incorporating additional forces such as groundwater seepage into the excess shear stress model parameters seepage forces are known to be significant contributors to streambank erosion and failure the objective of this research was to incorporate seepage forces into a mechanistic fundamental detachment rate model to improve the predictions of the erosion rate of cohesive soils the new detachment model which is referred to as the modified wilson model was based on two modified dimensional soil parameters b0 and b1 that included seepage forces due to localized groundwater flow the proposed model provided a general framework for studying the impact of soil properties fluid characteristics and seepage forces on cohesive soil erodibility equations were presented for deriving the material parameters from bot

magnetostratigraphy and biostratigraphy of cretaceous tertiary continental deposits ager basin province of lerida spain abstract at fontllonga northeast spain province of lerida a nearly continuous outcrop covers the stratigraphic interval from the maastrichtian to the thanetian in continental deposits magnetostratigraphy of the section was determined from 72 samples the magnetic polarity sequence was satisfactorily correlated with chrons 32r to 26r top of lower maastrichtian to lower thanetian chron 29r in which the k t boundary occurs is unambiguously recognizable considering the biostratigraphic data charophyte ostracod palynomorph the k t boundary occurs in the uppermost part of the microchara cristata subzone which includes late cretaceous and early palaeocene species this subzone is interpreted as an interval of crisis following the late maastrichtian extinctions and preceeding the palaeocene radiation no ir rich horizon has been yet found in this section the stratigraphic position of the last dinosaur remains found in the chron 31n interval leaves open the question of a causal link between the extinction of cretaceous reptiles and the k t event

multispectral photometry of the moon and absolute calibration of the clementine uv vis camera abstract we present a multispectral photometric study of the moon between solar phase angles of 0 and 85 using clementine images obtained between 0 4 and 1 0 m we produce a comprehensive study of the lunar surface containing the following results 1 empirical photometric functions for the spectral range and viewing and illumination geometries mentioned 2 photometric modeling that derives the physical properties of the upper regolith and includes a detailed study of the causes for the lunar opposition surge 3 an absolute calibration of the clementine uv vis camera the calibration procedure given on the clementine calibration web site produces reflectances relative to a halon standard and further appear significantly higher than those seen in groundbased observations by comparing clementine observations with prior groundbased observations of 15 sites on the moon we have determined a good absolute calibration of the clementine uv vis camera a correction factor of 0 532 has been determined to convert the web site www planetary brown edu clementine calibration html reflectances to absolute values from the calibrated data we calculate empirical phase functions useful for performing photometric corrections to observations of the moon between solar phase angles of 0 and 85 and in the spectral range 0 4 to 1 0 m finally the calibrated data is used to fit a version of hapke s photometric model modified to incorporate a new formulation developed in this paper of the lunar opposition surge which includes coherent backscatter recent studies of the lunar opposition effect have yielded contradictory results as to the mechanism responsible shadow hiding coherent backscatter or both we find that most of the surge can be explained by shadow hiding with a halfwidth of 8 however for the brightest regions the highlands at 0 75 1 0 m a small additional narrow component halfwidth of

soil properties controlling seepage erosion contributions to streambank failure the majority of sediment leaving catchments may be from streambank failure seepage erosion of unconsolidated sand above a restrictive layer is an important erosion process in incised streams that leads to streambank failure by undercutting banks the objective of this study was to determine the impact of soil properties on seepage erosion and the resulting streambank failure seepage flow and sediment concentrations were measured in situ at eight locations along the banks of a deeply incised stream in northern mississippi using field observations as a guide the soil profile conditions of a shallow 45 cm streambank consisting of 30 cm of topsoil a 10 cm conductive layer and a 5 cm restrictive layer were mimicked in laboratory lysimeter experiments to quantify the hydrologic properties controlling seepage erosion and bank failure under a 40 cm head the time to flow initiation and the flow rate were linearly related to the slope of the restrictive layer seepage erosion began within minutes of flow initiation and resulted in substantial 3 to 34 cm undercutting of the bank sediment concentrations of seeps were as high as 660 g l 1in situ and 4500 g l 1 in the lysimeters sediment concentrations were related to the layer slope thereby indicating the importance of detailed site characterization the usda ars streambank stability model demonstrated the increase in instability of banks due to undercutting by seepage erosion but failed to account for the sediment loss due to sapping for stable banks and overestimated the sediment loads for failed banks published in 2006 by john wiley sons ltd

testing the hapke photometric model improved inversion and the porosity correction abstract in conjunction with a companion paper shepard m k helfenstein p 2011 icarus submitted for publication we derive test and apply a detailed approach for visualizing the phase angle dependence of light scattering in particulate soils from both whole disk and disk resolved observations to reduce the number of model parameters and provide stronger constraints on model fits we combine hapke s hapke b 2008 icarus 195 918 926 recent correction for effects of porosity with his hapke b 1986 icarus 67 264 280 model of the shadow hiding opposition effect we further develop our method as a tool for least squares fitting of hapke s model to photometric data finally we present an improved method for estimating uncertainties in retrieved values of hapke model parameters we perform a preliminary test of the model on spectrogoniometric measurements from three selected laboratory samples from shepard and helfenstein shepard m k helfenstein p 2007 j geophys res 112 e03001 17 our preliminary suite of test samples is too small and selective to permit the drawing of general conclusions however our results suggest that hapke s porosity correction improves the fidelity of fits to samples composed of low and moderate albedo particles and may allow for more reliable retrieval of porosity estimates in these materials however we find preliminary evidence that in high albedo surfaces the effects of porosity may be difficult to detect

a paleoclimatic and paleoatmospheric record from peatlands accumulating during the cretaceous paleogene boundary event western interior basin canada petrological and 13 c analyses were undertaken on contiguous specimens of coal and intercalated minor organic rich clastic sediments collected from coal seams spanning the cretaceous paleogene boundary in the alberta and saskatchewan portions of the western interior basin the generally high smectite content of the coal suggests that the original mires were largely small disconnected and rheotrophic readily receiving abundant waterborne detrital clastic material of largely volcanic origin nevertheless using the distinctive claystone that marks the cretaceous paleogene boundary as a regional datum it is possible to correlate cycles in the vitrinite and inertinite composition of the coals over 500 km estimates of peat accumulation rates suggest that the cycles in vitrinite and inertinite composition represent regional cyclic fluctuations in wildfire and oxidation of the peatlands and overlying canopy at a frequency of hundreds to thousands of years the likely causes of these fluctuations were cyclic regional scale changes in temperature the cretaceous paleogene boundary event occurred early during a phase of gradually increasing temperature and or decreasing rainfall but peak wildfire and desiccation of peat occurred up to 14 000 yr later than the cretaceous paleogene boundary and the mires did not experience significant water stress in the immediate aftermath of the extinction event a persistent 1 5 3 0 negative 13 c excursion occurs across the cretaceous paleogene boundary but it cannot be readily separated from four further negative excursions later in the earliest danian the negative carbon isotope excursion linked to the cretaceous paleogene boundary began a few hundred years before the event itself and recovery occurred within 21 k y and possibly in as little as just a few thousand years consistent with recently calibrated shallow marine 13 c records hence the atmospheric and surface ocean carbon pools were coupled at this time the absence of evidence for catastrophic change in the climatic regime at the time of the cretaceous paleogene extinction in these mires supports the notion that the negative shift in atmospheric 13 c was brought about by changes in the 13 c composition of the surface ocean this is consistent with the greater magnitude of extinction experienced by marine fauna relative to the terrestrial realm

understanding mass fluvial erosion along a bank profile using peep technology for quantifying retreat lengths and identifying event timing this study provides fundamental examination of mass fluvial erosion along a stream bank by identifying event timing quantifying retreat lengths and providing ranges of incipient shear stress for hydraulically driven erosion mass fluvial erosion is defined here as the detachment of thin soil layers or conglomerates from the bank face under higher hydraulic shear stresses relative to surface fluvial erosion or the entrainment of individual grains or aggregates under lower hydraulic shear stresses we explore the relationship between the two regimes in a representative us midwestern stream with semi cohesive bank soils namely clear creek ia photo electronic erosion pins peeps provide for the first time in situ measurements of mass fluvial erosion retreat lengths during a season the peeps were installed at identical locations where surface fluvial erosion measurements exist for identifying the transition point between the two regimes this transition is postulated to occur when the applied shear stress surpasses a second threshold namely the critical shear stress for mass fluvial erosion we hypothesize that the regimes are intricately related and surface fluvial erosion can facilitate mass fluvial erosion selective entrainment of unbound exposed mostly silt sized particles at low shear stresses over sand sized sediment can armor the bank surface limiting the removal of the underlying soil the armoring here is enhanced by cementation from the presence of optimal levels of sand and clay select studies show that fluvial erosion strength can increase several fold when appropriate amounts of sand and clay are mixed and cement together hence soil layers or conglomerates are entrained with higher flows the critical shear stress for mass fluvial erosion was found to be an order of magnitude higher than that of surface fluvial erosion and proceeded with higher approximately 2 4 times erodibility the results were well represented by a mechanistic detachment model that captures the two regimes copyright 2017 john wiley sons ltd

pdf orientations in shocked quartz grains around the chicxulub crater we measured 852 sets of planar deformation features pdfs in shocked quartz grains in impactite samples of the yaxcopoil yax 1 core and from 4 cretaceous tertiary k t boundary deposits the monaca the cacarajcara and the pealver formations in cuba and dsdp site 536 within 800 km of the chicxulub crater in order to investigate variations of pdf orientations in the proximity of the crater orientations of pdfs show a broad distribution with peaks at 1013 1012 and 1112 plus r z 1011 orientations with minor c 0001 s 1121 t 2241 plus x 5161 and m 1010 plus a 11 20 orientations planar deformation features with c 0001 orientation are relatively more abundant in the proximity of the chicxulub crater than in distal sitessuch as north america the pacific ocean and europe this feature indicates that in the proximity ofthe crater part of the shocked quartz grains in the k t boundary deposits were derived from the lowshock pressure zones moreover the orientations of pdfs with 1122 plus r z 1011 are high in our studied sites and frequencies of these orientations decrease with increasing distance from the crater on the other hand absence of c 0001 and the rare occurrence of pdfs with 1122 plus r z 1011 orientations in the sample from the yax 1 core that was taken at the top of the impactite layer of the chicxulub crater suggests that the sampling horizon that reflects a certain cratering stage is also an important factor for variations in shocked quartz

the chicxulub impact event and its environmental consequences at the cretaceous tertiary boundary abstract an impact mass extinction hypothesis for the cretaceous tertiary k t boundary transition has been confirmed with multiple lines of evidence beginning with the discovery of impact derived ir in k t boundary sediments and culminating in the discovery of the chicxulub impact crater likewise a link between the chicxulub impact crater and k t boundary sediments has been confirmed with multiple lines of evidence including stratigraphic petrological geochemical and isotopic data the environmental effects of the chicxulub impact event were global in their extent largely because of the interaction of ejected impact debris with the atmosphere the environmental consequences of the chicxulub impact event and their association with the k t boundary mass extinction event indicate that impact cratering processes can affect both the geologic and biologic evolution of our planet