sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

evaluating the reliability of the stream tracer approach to characterize stream subsurface water exchange stream water was locally recharged into shallow groundwater flow paths that returned to the stream hyporheic exchange in st kevin gulch a rocky mountain stream in colorado contaminated by acid mine drainage two approaches were used to characterize hyporheic exchange sub reach scale measurement of hydraulic heads and hydraulic conductivity to compute streambed fluxes hydrometric approach and reachscale modeling of in stream solute tracer injections to determine characteristic length and timescales of exchange with storage zones stream tracer approach subsurface data were the standard of comparison used to evaluate the reliability of the stream tracer approach to characterize hyporheic exchange the reach averaged hyporheic exchange flux 1 5 ml s 1 m 1 determined by hydrometric methods was largest when stream base flow was low 10 l s 1 hyporheic exchange persisted when base flow was 10 fold higher decreasing by approximately 30 reliability of the stream tracer approach to detect hyporheic exchange was assessed using first order uncertainty analysis that considered model parameter sensitivity the stream tracer approach did not reliably characterize hyporheic exchange at high base flow the model was apparently more sensitive to exchange with surface water storage zones than with the hyporheic zone at low base flow the stream tracer approach reliably characterized exchange between the stream and gravel streambed timescale of hours but was relatively insensitive to slower exchange with deeper alluvium timescale of tens of hours that was detected by subsurface measurements the stream tracer approach was therefore not equally sensitive to all timescales of hyporheic exchange we conclude that while the stream tracer approach is an efficient means to characterize surface subsurface exchange future studies will need to more routinely consider decreasing sensitivities of tracer methods at higher base flow and a potential bias toward characterizing only a fast component of hyporheic exchange stream tracer models with multiple rate constants to consider both fast exchange with streambed gravel and slower exchange with deeper alluvium appear to be warranted

magnetic properties of sedimentary greigite fe3s4 an update greigite fe3s4 is an authigenic ferrimagnetic mineral that grows as a precursor to pyrite during early diagenetic sedimentary sulfate reduction it can also grow at any time when dissolved iron and sulfide are available during diagenesis greigite is important in paleomagnetic environmental biological biogeochemical tectonic and industrial processes much recent progress has been made in understanding its magnetic properties greigite is an inverse spinel and a collinear ferrimagnet with antiferromagnetic coupling between iron in octahedral and tetrahedral sites the crystallographic c axis is the easy axis of magnetization with magnetic properties dominated by magnetocrystalline anisotropy robust empirical estimates of the saturation magnetization anisotropy constant and exchange constant for greigite have been obtained recently for the first time and the first robust estimate of the low field magnetic susceptibility is reported here the curie temperature of greigite remains unknown but must exceed 350 c greigite lacks a low temperature magnetic transition on the basis of preliminary micromagnetic modeling the size range for stable single domain behavior is 17 200 nm for cubic crystals and 17 500 nm for octahedral crystals gradual variation in magnetic properties is observed through the pseudo single domain size range we systematically document the known magnetic properties of greigite at high ambient and low temperatures and with alternating and direct fields and illustrate how grain size variations affect magnetic properties recognition of this range of magnetic properties will aid identification and constrain interpretation of magnetic signals carried by greigite which is increasingly proving to be environmentally important and responsible for complex paleomagnetic records including widespread remagnetizations

south china sea surface water evolution over the last 12 myr a south north comparison from ocean drilling program sites 1143 and 1146 1 planktonic foraminifera pf from ocean drilling program odp sites 1143 and 1146 in the southern and northern south china sea scs respectively were quantitatively analyzed in order to reconstruct the sea surface environment over the last 12 myr the observed decrease in deep dwelling pf species after 10 ma at both sites is interpreted to reflect a depression of the upper water thermocline corresponding to the closure of the indonesian seaway around 11 9 ma this upper water column structure implies the intensification of equatorial pacific warm currents and the initial formation of the western pacific warm pool wpwp during the early late miocene the consistent pattern of south north thermocline evolution and the synchronous disappearance of globoquadrina dehiscens 9 8 ma at both sites 1143 and 1146 together imply that the entire scs was likely under the influence of the newly developed wpwp at 10 ma after 8 ma sea surface temperatures and thermocline variations evolved differently between the southern and northern scs the total deep dwelling pf fauna at site 1143 decreased gradually in abundance from 6 6 to 2 ma indicating a deepening of the thermocline in the southern scs in contrast deep dwelling pf species increased in abundance from 3 1 to 2 ma at site 1146 reflecting a shoaling of the thermocline in the northern scs this south north contrast reflects two major environmental regimes 1 the southern scs which has mainly been under the influence of the wpwp since the late late miocene and 2 the northern scs where effects of the east asian winter monsoon have prevailed especially since the late pliocene estimate of past sea surface temperatures ssts at site 1143 suggests a relatively stable and warm environment in the southern scs since about 2 5 ma with an increased influence of warm subsurface waters after the mid pleistocene transition 1 2 0 9 ma in the northern scs however a gradual decrease in winter sst recorded at site 1146 over the last 4 myr records east asian monsoon evolution especially the enhancement of the east asian winter monsoon between 3 1 and 2 ma

erosional response of south china to arc rifting and monsoonal strengthening a record from the south china sea abstract ocean drilling program sampling of the distal passive margin of south china at sites 1147 and 1148 has yielded clay rich hemipelagic sediments dating to 32 ma oligocene just prior to the onset of seafloor spreading in the south china sea the location of the drill sites offshore the pearl river suggests that this river or its predecessor may have been the source of the sediment in the basin which accounts for only 1 8 of the total neogene sediment in the asian marginal seas a mean erosion depth of 1 km over the current pearl river drainage basin is sufficient to account for the sediment volume on the margin two dimensional backstripping of across margin seismic profiles shows that sedimentation rates peaked during the middle miocene 11 16 ma and the pleistocene since 1 8 ma nd isotopic analysis of clays yielded nd values of 7 7 to 11 0 consistent with the south china block being the major source of sediment more positive nd values during and shortly after rifting compared to later sedimentation reflect preferential erosion at that time of more juvenile continental arc rocks exposed along the margin as the drainage basin developed and erosion shifted from within the rift to the continental interior nd values became more negative a rapid change in the clay mineralogy from smectite dominated to illite dominated at 15 5 ma synchronous with middle miocene rapid sedimentation mostly reflects a change to a wetter more erosive climate evidence that the elevation of the tibetan plateau and erosion in the western himalaya both peaked close to this time supports the suggestion that the asian monsoon became much more intense at that time much earlier than the 8 5 ma age commonly accepted

formation processes of framboidal pyrite abstract pyrite framboid formation may be the result of four consecutive processes 1 nucleation and growth of initial iron monosulfide microcrystals 2 reaction of the microcrystals to greigite fe 3 s 4 3 aggregation of uniformly sized greigite microcrystals i e framboid growth and 4 replacement of greigite framboids by pyrite the uniform morphology uniform size range and ordering of the microcrystals in individual framboids as well as the range of observed framboid structures from irregular aggregates to densely packed spherical aggregates and polyframboids are consequences of these processes using dlvo theory derjaguin landau verwey and overbeek we have evaluated the stability of colloidal iron monosulfide suspensions with ionic strengths typical of marine and lacustrine waters in addition to van der waals attractive and double layer repulsive forces a term is included to account for the ferrimagnetic properties of greigite numerical models predict that magnetically saturated greigite particles 0 1 m in diameter will rapidly aggregate in either marine or fresh water the aggregation model is in agreement with the sequence of greigite formation followed by pyrite framboid formation established in a previous experimental study sweeney and kaplan 1973 and is consistent with the occurrence of framboids composed of other magnetic minerals e g greigite magnetite and magnesioferrite based on the temperature dependent magnetic properties of greigite and aging experiments in hydrothermal solutions this mechanism for framboid formation via precursor greigite could operate to temperatures of 200 c consistent with the occasional occurrence of pyrite framboids in the paragenesis of metalliferous ore deposits

increased contribution of terrigenous supply from taiwan to the northern south china sea since 3 ma seismic profiles provide evidence that there has been strong transport by deep water bottom currents and drift deposition on the northern slope of the south china sea earlier geochemical studies suggest that the drift sediments originated primarily from taiwan however the transport process history and origin of the deep water bottom deposition in the northern south china sea on both glacial interglacial and tectonic time scales remain unclear here we show new high resolution records of clay minerals grain size and mass accumulation rate mar of terrigenous materials from ocean drilling program odp site 1144 together with trace element concentrations in siliciclastic sediments from odp site 1146 combined with other published data we find that the primary source for sediments at odp sites 1144 1148 since 3 ma is from taiwan and not from pearl river as previously thought before 3 ma however sediment source to odp sites 1146 and 1148 was mainly from the pearl river increased contribution of terrigenous supply from taiwan to the northern south china sea since similar to 3 ma may be related to the formation of the taiwan orogen and strengthening of deep water bottom current transport in the northern south china sea variations in clay mineralogy and sedimentology at odp site 1144 located on a sediment drift shows strong glacial interglacial cyclicity this suggests that bottom current deposition is highly dependent on sea level fluctuations which control the terrigenous supply to the deep sea c 2010 elsevier b v all rights reserved

surface subsurface water interactions in an alluviated mountain stream channel data from an instream tracer experiment performed in north fork dry run shenandoah national park virginia illustrate that the transport of water and conservative solute in the stream is greatly influenced by interaction with water present in both the relatively shallow gravel bed and in the relatively deeper alluvial infill material the shape of concentration time curves from the field tracer experiment exhibit storage of tracer in the subsurface short term storage imposed by exchange with the gravel bed and long term storage by exchange with the deeper alluvial infill time series models fit the observed concentration data very well estimates of mixing volumes generated by the time series analysis indicate that a large volume of the gravel bed participates in rapid mixing with the surface stream at one point along the study reach a second order time series model is supported by the data suggesting two independent parallel flow paths observations of tracer in wells more than 10 m from the stream and the very extended recession of the tracer in the stream where it flows over a bedrock ledge support the contention that the deeper alluvium plays an important role in transient storage of solute in north fork dry run the work implies that physically based models to predict transport and storage in alluviated mountain catchments may have to account for interactions between the stream and large portions of its floodplain

geomagnetic paleointensity dating of south china sea sediments for the last 130 kyr relative paleointensity records from the northern south china sea northwest pacific ocean were studied in two gravity piston cores continuous mineral magnetic and paleomagnetic measurements were made using discrete sediment samples detailed rock magnetic parameters such as thermomagnetic and high field hysteresis data indicate that pseudo single domain magnetite in a narrow range of grain size and concentration is the main contributor to the remanent magnetization the uniform magnetic mineralogy meets the commonly accepted criteria for establishing relative paleointensity records the relative paleointensity rpi curves were constructed by normalizing the natural remanent magnetization nrm with isothermal remanent magnetization irm both in the 20 60 mt demagnetization state dating constraints have been provided by radiocarbon ages in the upper 400 cm of both cores furthermore we have correlated our paleointensity records with napis 75 s atlantic 1089 sint 200 and nopapis 250 to determine the chronological rpi framework for the south china sea scs pis although some temporal offsets of paleointensity features between the different records have been recognized their similar shape suggests that relative paleointensity on the 10 3 10 4 year scale is globally coherent and can provide an age framework for sediments independent of delta 18 o ages c 2009 elsevier b v all rights reserved

astronomical forcing of the east asian monsoon mirrored by the composition of pliocene south china sea sediments abstract high precision major and minor element records of pliocene core intervals from ocean drilling program odp site 1145 located in the northern part of the south china sea were generated at a 5 cm approximately 2 kyr resolution from the geochemical data distinct proxies those indicating changes in detrital matter provenance as well as those indicating productivity variations could be derived both the terrigenous input to the northern south china sea k si and variations in productivity ba al show a response to insolation forced monsoon variability while the fluvial input k si responds to changes in the summer monsoon productivity increases as documented by ba enrichments seem to reflect variations in winter monsoon intensity a stronger winter monsoon may have increased nutrient availability via dust input and or upwelling phenomena according to our geochemical proxy records summer and winter monsoons are approximately 180 out of phase this may imply forcing of the winter monsoon through southern hemisphere summer insolation maxima the k si ratio shows a linear correlation with the la90 1 0 5 northern hemisphere summer insolation record and has therefore been used to create an astronomical timescale for the investigated sediments of odp site 1145 carbonate contents and corresponding color reflectances display 41 and 100 kyr cycles we propose that these do not reflect glacial cycles but are rather the result of an interference signal of dilution by fluvial and eolian terrigenous material and carbonate production burial flux a sudden onset of gradual changes in sediment composition occurs after 3 0 ma this is also documented by an increase in sedimentation rates and may be caused by enhanced fluvial input from the pearl river due to intensified weathering rates on the asian continent this may be linked to tectonic processes around the himalayan tibetan complex and its consequences regarding land sea heating and atmospheric circulation

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

elemental mapping by dawn reveals exogenic h in vesta s regolith using dawn s gamma ray and neutron detector we tested models of vesta s evolution based on studies of howardite eucrite and diogenite hed meteorites global fe o and fe si ratios are consistent with hed compositions neutron measurements confirm that a thick diogenitic lower crust is exposed in the rheasilvia basin which is consistent with global magmatic differentiation vesta s regolith contains substantial amounts of hydrogen the highest hydrogen concentrations coincide with older low albedo regions near the equator where water ice is unstable the young rheasilvia basin contains the lowest concentrations these observations are consistent with gradual accumulation of hydrogen by infall of carbonaceous chondrites observed as clasts in some howardites and subsequent removal or burial of this material by large impacts

south china sea fluvial sediments an introduction the south china sea offers a special research opportunity for earth scientists because of its location and its well preserved terrigenous sediments wang and li 2009 as the largest one of the marginal seas separating asia from the pacific the south china sea functions as a natural laboratory for study of land sea interactions because of its unique source to sink record of fluvial sediments the south china sea receives more than 600 million tons of detrital sediments annually from numerous rivers including world s largest rivers such as the pearl the red and the mekong fig 1

effects of sediment transport and seepage direction on hydraulic properties at the sediment water interface of hyporheic settings summary relations between seepage flux and hydraulic properties are difficult to quantify in fluvial settings because of the difficulty in measuring these variables in situ tests conducted in a 1 5 m diameter by 1 5 m tall sediment filled tank indicate that hydraulic gradient increased and hydraulic conductivity k decreased following the onset of downward seepage but both parameters were little changed following the onset of upward seepage reductions in k during downward seepage were more pronounced when surface water current was sufficient to mobilize sediment on the bed averaged ratios of k determined during upward seepage to k determined during downward seepage k up k down through a sand and gravel bed increased from 1 4 to 1 7 with increasing surface water velocity and decreased to slightly greater than 1 when the sediment bed became fully mobile k up k down for tests conducted with a silt veneer on the bed surface was greater than 2 for all but the fastest surface water velocities substantial reductions in k also were associated with a silt floc that formed on the bed surface during and following test runs although the silt floc was typically less than 0 5 mm in thickness most of the hydraulic gradient was distributed across this thin layer k of the thin silt floc was reduced by two to three orders of magnitude relative to the underlying sediment directional bias in k and relation between k and surface water velocity require the presence or absence of a layer of lower k sediment at or near the bed surface without which no reduction in k and corresponding increase in hydraulic gradient can occur at the bed surface the lack of prior observation of the consistent bias in k associated with seepage direction is somewhat surprising given the numerous studies where k has been measured in fluvial settings but may be explained by the small value of the bias relative to the typical uncertainty associated with field determinations of k if shown to exist in field settings this bias and its relation to fluvial processes will be relevant to many studies conducted in hyporheic settings that require determination of fluxes across the sediment water interface

seven million years of wind and precipitation variability on the chinese loess plateau abstract recent studies of the eolian deposits in northern china have extended the east asian monsoon history back to the early miocene however the relative intensities of monsoonal winds and precipitation and the extent of their coupling prior to the pleistocene epoch remain poorly constrained mainly due to uncertainties in the interpretation of proxy indices generated from the mio pliocene red clay sequences here we reconstruct east asian monsoon oscillations over the past 7 ma using magnetic susceptibility and carbonate content as summer monsoon precipitation proxies and quartz grain size as a winter monsoon wind intensity index our results suggest that precipitation and wind intensity exhibited significant orbital scale variations prior to 4 2 ma followed by slightly damped variability between 4 2 and 2 75 ma subsequently east asian monsoon circulation experienced two large shifts at about 2 75 and 1 25 ma characterized by stepwise strengthening of glacial wind and interglacial precipitation a remarkable change in east asian monsoon seasonality occurred around 3 15 2 75 ma prior to 3 15 ma strong winds were positively correlated with high effective precipitation whereas after 2 75 ma strong winds were negatively correlated with heavy precipitation this shift was probably induced by a change from an insolation forced system to one strongly influenced by the combined effects of the phased uplift of the himalaya tibetan plateau and the simultaneous development of the northern hemisphere ice sheets

source to sink transport processes of fluvial sediments in the south china sea the south china sea offers an excellent case for studying source to sink transport processes of fluvial sediments among the global marginal seas this study synthesizes existing clay mineralogical and geochemical data from similar to 1500 samples from the seafloor and surrounding rivers deepwater mooring observation results and high resolution glacial cyclic clay mineralogy records from six high quality sediment cores source to sink sediment transport from the river mouth to the continental shelf and then to the abyssal basin is investigated at two time scales modern process and late quaternary glacial cycles the results firstly show the high diversity of clay mineralogical and geochemical compositions in riverbed surface sediments surrounding the south china sea e g dominant illite and chlorite in taiwan overwhelming majority of smectite in luzon dominant kaolinite in south china and similar amounts of the four clay mineral species in red and mekong river systems the formation of these fluvial sediments through chemical weathering in surrounding drainage systems is controlled principally by the east asian monsoon climate with warm temperature and high precipitation and subordinately by tectonic activity and specific lithological character the basin wide distribution of clay mineral assemblages combined with neodymium and strontium isotopic compositions reflects strong provenance control and differential settling effects the differential settling of kaolinite in slightly saline and proximal regions relative to smectite in more saline and distal regions is well demonstrated in the south china sea through combining clay mineralogical distributions on the seafloor with observed oceanic current systems the modern transport pathways can be well established e g in the northern south china sea illite and chlorite from taiwan are mainly carried by contour currents with the strong influence of mesoscale eddies high resolution sediment dynamic analysis for the late quaternary reveals different sediment transport patterns in the northern western and southern south china sea when the land sea configuration dramatically changed during glacial conditions in the north the terrigenous dispersal is mainly controlled by provenance supply and oceanic current transport in the west the clay mineral assemblage reflects variations of the prevailing surface current influenced by monsoon winds in the south the clay mineral input indicates intensive chemical weathering during interglacial periods and strengthened physical erosion during glacial periods the transport of terrigenous sediments since the last glaciation is quantitatively reconstructed through studying two deepwater sediment cores located in the northern south china sea the relative contributions from three provenances south china luzon and taiwan highlight their distinct variability over the last 28 ka implying that the southward shift of the inter tropical convergence zone itcz at 16 ka bp caused an increased sediment contribution from south china the intensified influence of the kuroshio current intrusion controls more efficient westward transport of luzon sediments and the stronger deepwater current transports taiwan sourced sediments further westward from the last glaciation to the holocene c 2015 elsevier b v all rights reserved

a direct link between the china loess and marine δ 18 o records aeolian flux to the north pacific most studies of quaternary climates conducted during the past 150 years have focused on glacial sequences and for the past 25 years marine sediments have provided significant further understanding of glacial and interglacial palaeoclimates an important goal of palaeoclimatology however to link the well known detailed continental records to marine records of similar resolution has yet to be realized the classic loess sequences of china provide an apparently continuous record of continental climate over the past 2 4 million years1 2 the oxygen isotope 18o timescale developed from the marine record3 gives us a global chrono stratigraphy of late pleistocene climates previously it has been suggested in studies of the aeolian component in pelagic sediments that it may be possible to link these two records directly by finding a suitable core from the north west pacific downwind from china4 5 here we report the results of such an effort for core v21 146 fig 1 and tie the last 500 000 years of the chinese loess soil sequence directly to the 18o timescale and in so doing refine the dating of regional loess and soil horizons

numerical verification of hyporheic zone depth estimation using streambed temperature summary the hyporheic zone is the active region of groundwater and surface water mixing and consequently through which the contaminants released to surface water are transferred to groundwater because of the high energy demand and expense associated with the remediation of contaminated groundwater it has become a matter of primary concern to find an efficient and cost effective way to restore the contaminated groundwater therefore delineating the hyporheic zone is of vital importance for the prevention and management of groundwater contamination this paper proposes a method to estimate the depth of the hyporheic zone using heat transfer analysis for a streambed in order to assess the adequacy of the proposed method the sensitivity of the results of heat transfer analyses to the hyporheic flux was evaluated due to the high sensitivity to the hyporheic zone depth the heat transfer analysis was determined to be appropriate to delineate the hyporheic zone depth the depth estimated from the heat transfer analysis was comparable with that from a conventional tracer test the proposed method has an advantage over existing methods of determining the hyporheic zone depth due to the fact that it only requires field temperature measurements

development of the east asian summer monsoon evidence from the sediment record in the south china sea since 8 5 ma 128 samples from ocean drilling program odp site 1143 in the southern south china sea were analyzed for grain size clay minerals biogenic opal content and quartz in order to reconstruct changes in east asian monsoon climate since 8 5 ma an abrupt change of terrigenous mass accumulation rate mar clay mineral assemblage median grain size and biogenic opal mar about 5 2 ma suggests that between 8 5 5 2 ma the source of terrigenous sediment was mainly in the region of surface uplift and basaltic volcanism in southern vietnam a simple model of east asian summer monsoon evolution was based on the clay feldspar ratio kaolinite chlorite ratio and biogenic opal mar the summer monsoon has two periods of maximum strength at 8 5 7 6 ma and 7 1 6 2 ma subsequently there was a relatively stable period at 6 2 3 5 ma continued intensification about 3 5 2 5 ma and gradually weakening after 2 5 ma since i ma the monsoon has intensified with remarkable high frequency and amplitude variability simultaneous increase in sedimentation rates at odp sites 1143 1146 and 1148 as well as in mar of terrigenous materials quartz feldspar and clay minerals at odp site 1143 at 3 5 2 5 ma may be the erosional response to both global climatic deterioration and the strengthening of the east asian summer monsoon after about 3 4 ma c 2006 elsevier b v all rights reserved

the polymict eucrites the polymict eucrites are a suite of about 14 polymict achondritic meteorites that contain at least 90 vol of eucritic material and are found both in antarctica and elsewhere they are part of a continuum of polymict breccias that includes howardites and polymict diogenites rare gas data suggest that some are gas rich regolith breccias the clasts contained in polymict eucrites sample a variety of lithologies from their parent body and include eucritic clasts alkali enriched eucrites pyroxene cumulate eucrites two pyroxene mafic rocks possibly feldspar cumulate eucrites diogenites fayalitic lithologies and a variety of other mineral clasts the eucritic clasts are probably samples of near surface lithologies on the parent body but the presence of two pyroxene mafic rocks is considered to be evidence of magmatic activity at pressures in excess of 1 kbar in the parent body partial melt models may explain some of the diversity among the clasts but cumulus processes are believed to have been important if pressures greater than 1 kbar are confirmed then the basaltic achondrite parent body bap must have a diameter in excess of 200 km the variety of lithologies suggests that not all basaltic achondrites are samples of igneous rocks formed by single stage melting of a chondritic asteroid but are instead samples of an evolved and diverse crust produced by serial magmatism

late cenozoic eolian deposition in the north pacific asian drying tibetan uplift and cooling of the northern hemisphere a newly constructed record of eolian dust accumulation from the central north pacific shows that dust deposition increased by an order of magnitude quite rapidly at 3 6 ma we associate this sudden drying with the uplift of at least the northern portion of the tibetan plateau shutting off the indian ocean moisture source to central and western china this ten fold increase in atmospheric dust loading appears to be associated with the 1 m y long shift toward heavy 18o values that occurred at 3 6 2 6 ma the dust grain size record of wind intensity begins its late cenozoic coarsening a million years before the drying event at 4 5 ma the northern hemisphere cooling that results in intensification of the subpolar westerly winds may have as its ultimate cause the drawdown of atmospheric co2 in the latest miocene and the early pliocene closing of the panamanian seaway

reduction of the hyporheic zone volume due to the stream aquifer interaction 1 pore water in stream sediments is continuously exchanged with the surface water from the overlying stream this exchange of water and solutes that occurs across the stream sediment interface plays an important role for fluvial ecology because of the unique biochemical conditions rich biodiversity and high rates of metabolism while many studies have observed the extent of the hyporheic zone to be modified by changes in the level of the groundwater table the actual importance of this interaction is still difficult to quantify here we focus on the case of bedform induced hyporheic exchange to show how the the volume of hyporheic sediments that receive water from the stream is significantly reduced by the upwelling of subsurface water a simple scaling relationship for the assessment of maximum depth of the hyporheic zone is proposed by relating hyporheic flow to the groundwater discharge in an aquifer with given hydraulic properties and head difference between the stream and the aquifer

a model for the origin of basaltic achondrites based on the yamato 7308 howardite the y 7308 howardite comprises a variety of lithic clasts and mineral fragments the mg mg fe atomic ratios of the pyroxenes in diogenitic clasts eucritic clasts and fayalite hedenbergite tridymite plagioclase clasts vary continuously from 0 76 to less than 0 30 olivine fragments in the matrix have a wide range of mg mg fe ratios from 0 88 to 0 71 this continuum of chemical compositions for olivine and pyroxene is explained by the fractional crystallization of a primary magma the composition of a liquid produced by removing olivine and pyroxene from the primary magma is almost identical to that of eucrites and the solidification of this liquid on the surface of a magma ocean might have formed a eucrite crust on the parent body a source material of carbonaceous or ll chondrite like composition may produce the hed howardites eucrites diogenites magma by partial or batch melting the volatile components such as alkalis sulfur oxides etc may have been lost and reduction of feo and fe203 components to fe metals also may have taken place prior to and or during the formation and crystallization of the hed magma

oligocene miocene magnetic stratigraphy carried by biogenic magnetite at sites u1334 and u1335 equatorial pacific ocean 1 sediments from the equatorial pacific ocean at the integrated ocean drilling program sites u1334 and u1335 record reliable magnetic polarity stratigraphies back to 26 5 ma late oligocene at sedimentation rates usually in the 5 20 m myr range putative polarity subchrons that do not appear in current polarity timescales occur within chrons c5acr c5adn and c5bn 1r at site u1335 and within chrons c6aar 2r c6br c7ar and c8n 1n at site u1334 subchron c5dr 1n 17 5 ma is recorded at both sites supporting its apparent recording in the south atlantic ocean and has an estimated duration of 40 kyr the oligocene miocene calcareous oozes have magnetizations carried by submicron magnetite as indicated by thermal demagnetization of magnetic remanences the anhysteretic remanence to susceptibility ratio and magnetic hysteresis parameters transmission electron microscopy of magnetic separates indicates the presence of low titanium iron oxide magnetite grains with size 50 100 nm and shape similar to modern and fossil bacterial magnetite supporting other evidence that biogenic submicron magnetite is the principal remanence carrier in these sediments in the equatorial pacific ocean low organic carbon burial arrests microbial pore water sulfate reduction thereby aiding preservation of bacterial magnetite

a magma ocean on vesta core formation and petrogenesis of eucrites and diogenites abstract available evidence strongly suggests that the hed howardite eucrite diogenite meteorites are samples of asteroid 4 vesta abundances of the moderately siderophile elements ni co mo w and p in the hed mantle indicate that the parent body may have been completely molten during its early history during cooling of a chondritic composition magma ocean equilibrium crystallization is fostered by the suspension of crystals in a convecting magma ocean until the crystal fraction reaches a critical value near 0 80 when the convective system freezes and melts segregate from crystals by gravitational forces the extruded liquids are similar in composition to main group and stannern trend eucrites and the last pyroxenes to precipitate out of this ocean before convective lockup span the compositional range of the diogenites subsequent fractional crystallization of a main group eucrite liquid which has been isolated as a body of magma produces the nuevo laredo trend and the cumulate eucrites the predicted cumulate mineral compositions are in close agreement with phase compositions analyzed in the cumulate eucrites thus eucrites and diogenites are shown to have formed as part of a simple and continuous crystallization sequence starting with a magma ocean environment on an asteroidal size parent body that is consistent with vesta

last glacial maximum in china comparison between land and sea abstract as a result of the sea level drop at the last glacial maximum about 100 120 m in the south china sea and 130 150 m in the east china sea the size and configurations of the china seas changed greatly the east china sea with the yellow sea and bohai gulf was reduced into an elongated trough while the south china sea became a semi enclosed gulf due to the southern shift of the polar front in the north pacific and the reorganization of the surface current system the winter temperature in the south china sea was 6 10 c colder and the seasonality was much stronger than it is now the reduced sea area and thus the increased distance to the coast together with the declined sea surface temperature led to intensified aridity on the land the enhanced eolian processes related to the intensification of the winter monsoon caused an expansion of the loess deposition area reaching the southeastern part of china to the south of the yangtze river and off the modern sea coast vegetation zones greatly shifted to the southeast in north china deserts and steppes were much more extensive than they are now and the modern areas of warm temperate broad leaved forests were occupied by steppes or woodland in south china the deciduous broadleaved forests were developed in areas now covered by evergreen forests and the monsoon rain forest completely disappeared the changes in the climate on land and the configurations of seas altered the sediment supply and sedimentation rate in the china seas giving rise to the atlantic type late quaternary caco3 curve there

east asian monsoon evolution since the late miocene from the south china sea abstract the south china sea scs has become a global focus for paleoclimatic and paleoceanographic studies due to its location which makes it highly sensitive to the east asian monsoon and to pacific ocean changes we present here a refined magnetostratigraphy for the last 6 5 ma for hole u1431d which was recovered during iodp expedition 349 in the central scs magnetic analyses demonstrate that magnetite is the dominant magnetic carrier except for within a greigite bearing layer at 130 5 132 0 meters below sea floor the greigite layer coincides with the timing of intensification of northern hemisphere glaciation and records an oceanographic response to this event environmental magnetic results indicate that the east asian summer and winter monsoon were stable from 6 5 to 5 ma the summer monsoon intensified at 5 ma and then weakened gradually since 3 8 ma in contrast the winter monsoon weakened at 5 ma and has then been enhanced since 3 8 ma and more stable from 0 6 ma spectral analysis indicates that the east asian summer monsoon was driven directly by low latitude insolation changes before 3 2 ma and that it has been affected by both low latitude insolation and high latitude ice volume changes since 3 2 ma

characterization of transport in an acidic and metal rich mountain stream based on a lithium tracer injection and simulations of transient storage physical parameters characterizing solute transport in the snake river an acidic and metal rich mountain stream near montezuma colorado were variable along a 5 2 km study reach stream cross sectional area and volumetric inflow each varied by a factor of 3 because of transient storage the residence time of injected tracers in the snake river was longer than would be calculated by consideration of convective travel time alone distributed inflows along the stream were a significant source of in stream chemical variations these transport characteristics of the snake river were established on the basis of the assumption of lithium as an ideally conservative tracer and use of simulations of advection dispersion and transient storage evaluations of the validity of this combined tracer and simulation approach lend confidence to the estimation of the physical transport parameters but further development is warranted for methods of onsite transport experimentation in hydrologically complex chemically reactive environments

chemical composition of the howardite parent body deduced from kapoeta primary mafic magmas chemical data are presented for three mafic clasts extracted from the kapoeta howardite bulk compositions and petrologic observations suggest that two of these lithic clasts represent olivine plagioclase bearing orthopyroxenites chondrite relative refractory lil abundances of two of the clasts are inferred to represent primary mg rich magmas produced by extensive 70 partial melting of a source composition indistinguishable from the silicate fraction of average ch cl ordinary chondrites with the exception of the depletion of the alkalis na and k by a factor of 13 1 in the source composition a metal free and volatile depleted kapoeta parent body kpb is subsequently deduced and is shown to compare very well with other similarly derived achondrite parent body apb and howardite parent body hpb estimates but not to parent body estimates derived from inferences based on eucrite phase equilibrium studies other implications suggest that the kpb is heterogeneous with respect to fe mg ratios

deepwater overflow through luzon strait 1 this study examines water property distributions in the deep south china sea and adjoining pacific ocean using all available hydrographic data our analysis reveals that below about 1500 m there is a persistent baroclinic pressure gradient driving flow from the pacific into the south china sea through luzon strait applying hydraulic theory with assumptions of zero potential vorticity and flat bottom to the luzon strait yields a transport estimate of 2 5 sv 1 sv 106 m3 s 1 some implications of this result include 1 a residence time of less than 30 years in the deep south china sea 2 a mean diapycnal diffusivity as large as 10 3 m2 s 1 and 3 an abyssal upwelling rate of about 3 10 6 m s 1 these quantities are consistent with residence times based on oxygen consumption rates the fact that all of the inflowing water must warm up before leaving the basin implies that this marginal sea contributes to the water mass transformations that drive the meridional overturning circulation in the north pacific density distributions within the south china sea basin suggest a cyclonic deep boundary current system as might be expected for an overflow driven abyssal circulation

isotopic paleoceanography of the caribbean and east pacific role of panama uplift in late neogene time comparisons of carbon isotopic data on benthic foraminifera from deep sea drilling project sites 502 western caribbean and 503 eastern pacific indicate that the difference between the atlantic and the pacific in the per mil enrichment in carbon 13 of total dissolved carbon dioxide increased about 6 million years ago and again 3 million years ago when the difference reached the modern level 1 per mil comparisons of planktonic foraminiferal oxygen isotopic data for the caribbean and the pacific suggest that the salinity of caribbean surface waters began increasing 4 million years ago possibly in response to shoaling of the panama isthmus these results suggest that modern circulation patterns in the caribbean and eastern pacific developed by 3 million years ago in concert with changing tectonic climatic and biogeographic patterns

magnesium oxide iron oxide mass balance constraints and a more detailed model for the relationship between eucrites and diogenites according to a currently popular model for petrogenesis on the howardite eucrite and diogenite hed parent asteroid the diogenites are not comagmatic with most eucrites but instead formed in separate orthopyroxenite dominated plutons this model can be tested for consistency with mass balance for mgo and feo assuming the overall diogenite diogenite eucrite ratio d of the parent asteroid is at least comparable to the average d for the eucrite diogenite dominated howardite regolith breccias average mg mgo mgo feo is much lower for eucrites especially noncumulate eucrites than for diogenites unless the diogenite parent magmas eventually produced a large proportion of low mg residual basalt and gabbro rbg the implied initial magma s mg is vastly higher than that of any noncumulate eucrite starting from a source previously depleted by putative primary eucrite genesis melt mg can be estimated as a function of the exchange reaction kd and degree of melting using several very conservative assumptions e g assuming that the total mgo feo concentration is nearly the same in the nascent melt as in the residual solids the degree of melting required to yield a melt with mg high enough to satisfy mass balance without implying an rbg component that accounts for 50 of all eucrites is an implausibly high 60 80 wt the separate orthopyroxenitic plutons sop model also seems inconsistent with the uniform density of melts across the diogenite eucrite compositional spectrum 2 77 2 82 g cm3 which implies that diogenitic magmas should have been as capable as eucrites of extruding to form lavas this difficulty cannot be reduced by simply assuming that later formed magmas were systematically both more plutonic and more mgo rich than earlier ones because the plutonic cumulate eucrites equilibrated with melts systematically lower in mg than noncumulate eucrites conceivably the bulk mg of the asteroid s silicate system was increased between primary melt eucrite genesis and sop diogenite genesis by graphite fueled reduction of feo however the graphite oxidation process generates a huge proportion of gas which would have enhanced the buoyancy of the nascent diogenite parent magmas thus exacerbating the difficulty of achieving the implied high degrees of partial melting to avoid these difficulties but still form most eucrites as rapidly cooled extrusives i propose the nerd noncumulate eucrites as extruded residua of diogenites model in this model the diogenites form as early cumulates from a large magma system probably a global magma ocean that yields a large proportion of eucritic melt as residuum this residual melt zone undergoes relatively little crystallization during a period when it is episodically tapped to produce extrusions dikes and sills of rapidly cooled noncumulate eucrites slight 5 10 porosity in the nascent eucritic crust keeps it marginally buoyant over the residual melt zone the common thermal metamorphism of noncumulate eucrites results from baking by superjacent flows during the episodic venting of the melt zone the nerd model s greatest advantage is that it does not require implausibly high degrees of localized melting in the mature stages of igneous evolution of the hed asteroid

biogeochemistry and natural attenuation of nitrate in groundwater at an explosives test facility an interdisciplinary study was conducted to characterize the distribution and fate of no3 in groundwater at lawrence livermore national laboratory llnl site 300 a high explosives test facility in the semi arid altamont hills of california site 300 groundwater contains no3 concentrations ranging from 200 mg no3 l several lines of evidence strongly suggest that denitrification is naturally attenuating no3 in the confined o2 depleted region of the bedrock aquifer under study tnbs2 a both no3 and dissolved o2 do concentrations in groundwater decrease dramatically as groundwater flows from unconfined to confined aquifer conditions b stable isotope signatures i e 15n and 18o of groundwater no3 indicate a trend of isotopic enrichment that is characteristic of denitrification and c dissolved n2 gas the product of denitrification was highly elevated in no3 depleted groundwater in the confined region of the tnbs2 aquifer long term no3 concentrations were relatively high and constant in recharge area monitoring wells typically 70 100 mg no3 l and relatively low and constant in the downgradient confined region typically 0 1 3 mg no3 l suggesting a balance between rates of no3 loading and removal by denitrification chemolithoautotrophic denitrification with pyrite as the electron donor is plausible in the tnbs2 aquifer based on the low dissolved organic c concentrations 1 5 mg l that could not support heterotrophic denitrification the common occurrence of disseminated pyrite in the aquifer and the trend of increasing so2 4 as groundwater flows from aerobic unconfined to anoxic confined aquifer conditions nitrate sources were investigated by experimentally determining the 15n and 18o signatures of no3 from three potential anthropogenic sources of no3 at site 300 ba no3 2 mock explosive hno3 and photolysis of the explosive rdx hexahydro 1 3 5 trinitro 1 3 5 triazine the isotopic signatures of these potential no3 sources were markedly different than those of no3 in tnbs2 groundwater samples suggesting that other sources must contribute significantly to the no3 loading at site 300 in particular no3 and no2 resulting from rdx photolysis reflected dramatically depleted 15n ca 7 4 and 18o ca 25 7 values

investigating the history of east asian monsoon and climate during the last glacial interglacial period 0 140 000 years mineralogy and geochemistry of odp sites 1143 and 1144 south china sea abstract monsoon climate is an important component of the global climatic system a comprehensive understanding of its variability over glacial interglacial time scales as well as of its effects on the continent and in the ocean is required to decipher links between climate continental weathering and productivity a detailed multiproxy study including bulk and clay mineralogy grain size analysis phosphorus geochemistry sedex extraction organic matter characterization and nitrogen stable isotopes was carried out on samples from odp sites 1143 and 1144 leg 184 south china sea covering the past 140 000 years we tentatively reconstruct the complex sedimentation and climatic history of the region during the last glacial interglacial cycle when sea level variations linked to the growth and melting of ice caps interact with monsoon variability during interglacial periods of high sea level summer monsoon was strong and humid and warm climate characterized the adjacent continent and islands clay minerals bear signals of chemical weathering during these intervals high calcite and reactive phosphorus mass accumulation rates mars indicate high productivity especially in the southern region of the basin during glacial intervals strong winter monsoon provided enhanced detrital input from the continent as indicated by high detrital mar glacial low sea level resulted in erosion of sediments from the exposed sunda shelf to the south and clay mineral variations indicate that warm and humid conditions still prevailed in the southern tropical areas enhanced supply of nutrients from the continent both by river and eolian input maintained high primary productivity reduced circulation during these periods possibly induced active remobilization of nutrients such as phosphorus from the sediments intense and short cold periods recorded during glacial and interglacial stages correlate with loess records in china and marine climatic records in the north atlantic confirming a teleconnection between low and high latitude climate variability

climatic and tectonic controls on weathering in south china and indochina peninsula clay mineralogical and geochemical investigations from the pearl red and mekong drainage basins 1 results of clay mineralogy major element geochemistry and sr and nd isotopes in 93 argillaceous samples collected from drainage basins of the pearl red and mekong rivers reveal different degrees of chemical weathering in southeast asia despite similar climate conditions across these regions the kaolinite illite ratio illite chemistry index and illite crystallinity can be used as indicators of chemical weathering intensity these mineralogical proxies combined with the k2o na2o cao molar ratio chemical index of alteration cia and weathering trends observed from major element results indicate intensive silicate weathering in the pearl river basin moderate to intensive in the mekong river basin and moderate in the red river basin although a significant modification of epsilon nd 0 values in our riverine sediments during chemical weathering and transport is unlikely sr 87 sr 86 ratios are controlled by various states of chemical weathering of high sr minerals such as plagioclase rich in na and ca with a linear decrease trend from the pearl mekong to red river basins our results suggest that it is not the warm climate with heavy monsoon precipitation but tectonics playing the most significant role in controlling weathering and erosion processes in south china and indochina peninsula strong physical erosion caused by tectonic activities and river incision along the eastern margin of the tibetan plateau and along the red river fault system is responsible for high contents of primary minerals in the lowlands of red and mekong river basins

analysis of solute transport in a divergent flow tracer test with scale dependent dispersion it has been known for many years that dispersivities increase with solute displacement distance in a subsurface the increase of dispersivities with solute travel distance results from significant variation in hydraulic properties of porous media and was identified in the literature as scale dependent dispersion in this study laplace transformed analytical solutions to advection dispersion equations in cylindrical coordinates are derived for interpreting a divergent flow tracer test with a constant dispersivity and with a linear scale dependent dispersivity breakthrough curves obtained using the scale dependent dispersivity model are compared to breakthrough curves obtained from the constant dispersivity model to illustrate the salient features of scale dependent dispersion in a divergent flow tracer test the analytical results reveal that the breakthrough curves at the specific location for the constant dispersivity model can produce the same shape as those from the scale dependent dispersivity model this correspondence in curve shape between these two models occurs when the local dispersivity at an observation well in the scale dependent dispersivity model is 1 3 times greater than the constant dispersivity in the constant dispersivity model to confirm this finding a set of previously reported data is interpreted using both the scale dependent dispersivity model and the constant dispersivity model to distinguish the differences in scale dependence of estimated dispersivity from these two models the analytical result reveals that previously reported dispersivity distance ratios from the constant dispersivity model should be revised by multiplying these values by a factor of 1 3 for the scale dependent dispersion model if the dispersion process is more accurately characterized by scale dependent dispersion copyright 2007 john wiley sons ltd

a 23 myr magnetostratigraphic time framework for site 1148 odp leg 184 in south china sea and its geological implications abstract the ocean drilling program odp leg 184 recovered a continuous sedimentary sequence since miocene at site 1148 in the northern south china sea scs which provided a unique record for better understanding the tectonic environmental and climatic evolution of the scs in this study we report a detailed paleomagnetic study on 881 discrete samples from the upper 460 m cores of hole 1148a through stepwise alternating field demagnetization af or thermal demagnetization td rock magnetic results from isothermal remanent magnetization irm acquisition temperature dependence magnetic susceptibility t and hysteresis loop parameters of representative samples indicate that the main magnetic mineral is low coercivity pseudo single domain magnetite the characteristic remanent magnetization chrm with moderate downward or upward inclinations was identified after removing a low stability drilling induced remanence with steep downward inclinations a new 23 myr magnetostratigraphic time framework was established by correlating the magnetic polarity sequence to the geomagnetic polarity time scale 2012 gpts 2012 ogg 2012 in combination with biostratigraphic data the mean sediment accumulation rates for lithostratigraphic units v and iv unit iii and lower unit ii upper unit ii unit ib and unit ia are calculated as 20 8 m myr 15 17 m myr 24 18 m myr 17 07 m myr and 49 01 m myr respectively

effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation the late cenozoic closure of the seaway between the north andsouth american continents is thought to have caused extensive changes in ocean circulation and northern hemisphere climate1 2 but the timing and consequences of the emergence of the isthmus of panama which closed the seaway remain controversial1 2 3 4 5 here we present stable isotope and carbonate sand fraction records from caribbean sediments which when compared to atlantic and pacific palaeoceanographic records indicate that the closure caused a marked reorganization of ocean circulation starting 4 6 million years ago shallowing of the seaway intensified the gulf stream and introduced warm and saline water masses to high northern latitudes these changes strengthened deep water formation in the labrador sea over the next million years as indicated by an increased deep water ventilation and carbonate preservation in the caribbean sea and favoured early pliocene warming of the northern hemisphere the evaporative cooling of surface waters during north atlantic deep water formation would have introduced moisture to the northern hemisphere although the pronounced intensification of northern hemisphere glaciation between 3 1 and 2 5 million years ago substantially lagged the full development of north atlantic deep water formation we propose that the increased atmospheric moisture content was a necessary precondition for ice sheet growth which was then triggered by the incremental changes in the earth s orbital obliquity

in situ quantification of spatial and temporal variability of hyporheic exchange in static and mobile gravel bed rivers seepage meters modified for use in flowing water were used to directly measure rates of exchange between surface and subsurface water in a gravel and cobble bed river in western pennsylvania usa allegheny river qmean 190 m3 s and a sand and gravel bed river in colorado usa south platte river qmean 9 7 m3 s study reaches at the allegheny river were located downstream from a dam the bed was stable with moss algae and river grass present in many locations median seepage was 0 28 m d and seepage was highly variable among measurement locations upward and downward seepage greatly exceeded the median seepage rate ranging from 2 26 upward to 3 76 downward m d at the south platte river site substantial local scale bed topography as well as mobile bedforms resulted in spatial and temporal variability in seepage greatly in exceedence of the median groundwater discharge rate of 0 24 m d both upward and downward seepage were recorded along every transect across the river with rates ranging from 2 37 to 3 40 m d despite a stable bed which commonly facilitates clogging by fine grained or organic sediments seepage rates at the allegheny river were not reduced relative to those at the south platte river seepage rate and direction depended primarily on measurement position relative to local and meso scale bed topography at both rivers hydraulic gradients were small at nearly all seepage measurement locations and commonly were not a good indicator of seepage rate or direction therefore measuring hydraulic gradient and hydraulic conductivity at in stream piezometers may be misleading if used to determine seepage flux across the sediment water interface such a method assumes that flow between the well screen and sediment water interface is vertical which appears to be a poor assumption in coarse grained hyporheic settings copyright 2011 john wiley sons ltd

the kapoeta howardite implications for the regolith evolution of the howardite eucrite diogenite parent body a large hand sample and numerous polished thin sections made from the hand sample of the ka poeta howardite and its many diverse lithic clasts were studied in detail by optical microscopy and electron microprobe techniques in an attempt to understand the surface processes that operated on the howardite eucrite diogenite hed parent body most likely the asteroid 4 vesta four unique unusually large clasts designated a mafic breccia b granoblastic eucrite d howardite and h melt coated breccia were se lected for detailed study modal analysis mineral microprobe analysis and noble gas measurements petro graphic studies reveal that kapoeta consists of a fine grained matrix made mostly of minute pyroxene and plagioclase fragments into which are embedded numerous different lithic and mineral clasts of highly vari able sizes the lithic clasts include pyroxene plagioclase eucrite orthopyroxenite diogenite howardite impact melt metal sulfide rich and carbonaceous chondrite clasts the howardite clasts include examples of lithic clasts that constitute breccias within breccias suggesting that at least two regolith generations are represented in the kapoeta sample we studied the clast assemblage suggests that repeated shock lithifica tion was an important process during regolith evolution noble gas analyses of clast samples fall into two populations a solar gas rich clasts h rim only and d and b clasts a and b which are essentially free of solar gases the concentrations of solar noble gases in the two matrix samples differ by a factor of 40 it appears that clast d is a true regolith breccia within the kapoeta howardite breccia within breccia while clast h is a regolith breccia that has been significantly impact reworked our data indicate that the kapoeta howardite is an extraordinarily heterogeneous rock in modal mineral and lithic clast abundances grain size distributions solar wind noble gas concentrations and cosmic ray exposure ages these results illustrate the repetitive nature of impact comminution and lithification in the regolith of the hed parent body