primary platinum mineralization in the nizhny tagil and kachkanar ultramafic complexes urals russia a genetic model for pge concentration in chromite rich zones the nizhny tagil uralian alaskan type ultramafic complex is composed of a dunite core with a rim of wehrlite and pyroxenite the dunite unit which has a uniform mineral composition olivine fo 89 8 92 1 avg 0 25 wt cao represents an accumulation of olivine and minor chromite from a mafic magma in an open system magma chamber after solidification of the dunite differentiation began with the formation of the wehrlite olivine fo 77 9 88 8 and pyroxenite corresponding to the closure of the magmatic system two main types of chromitite occurrence are observed in the dunite body small 100 5 cm scattered schlieren of chromite crystals within the ultramafic unit and much larger up to 100 5 m concentrations the chromite composition in both types is similar and uniform cr cr al fe 3 66 02 mg mg fe 2 49 05 and cr cr al fe 3 69 14 mg mg fe 2 49 81 respectively the larger concentrations of chromite include brecciated and net textured ore or massive veins that reflect the dynamic accumulation of chromite crystals in cavities along magma conduits inside the dunite body these cavities are analogous to small magma chambers within the consolidated part of the dunite body and similar to podiform chromitites in ophiolites were created by continuous feeding of magma to the system the platinum group element pge content of the chromite free facies of the dunite is relatively low pt being the only significant pge typically between 0 3 35 ppb but as much as 98 ppb in one sample in contrast both types of chromite occurrence are enriched in pge two pge mineralizing episodes are distinguished an ir ru rh os rich pt pd poor episode in which the platinum group minerals pgm are mainly ir alloys and a pt pd rich episode in which the pgm are mainly pt alloys i e pt 2 fe ni cu ptfeni 2 and tetraferroplatinum and tulameenite like compositions along with rare hollingworthite and an unidentified rhnias mineral the primary pgm have been affected locally by a serpentinization related low temperature alteration that is characterized by addition of copper with alteration to complex pt fe ni cu alloys of varied stoichiometry including tulameenite and platinian copper placer concentrations derived from the nizhny tagil complex have a slightly different assemblage of pgm with abundant isoferroplatinum the presence of gold commonly aggregating the pgm and unusual au sn and au pb alloys the kachkanar complex situated 120 km north of the nizhny tagil complex has essentially the same characteristics apart from a slightly different composition of the ultramafic cumulates suggesting that they were derived from a magma of different composition the pgm distribution also differs in that it contains more abundant isoferroplatinum than other pgm the high pt concentrations are the result of the affinity of platinum minerals for chromite and the mode of chromite deposit formation in the cavities in which chromite crystallized pgm tended to be incorporated in chromite or remained attached to chromite crystals to explain the very high concentrations of chromite associated pgm we define a cr factor which is the ratio of the mass of silicate magma to the mass of chromite in contact with the ascending magma where the cr is high i e a relatively low proportion of chromite in contact with a large amount of magma crystallizing the pt minerals the efficiency of the mechanical collection of pt minerals is at a maximum and the pt concentration i e amount of pt minerals will be high possible variations due to the collection of pge by a sulfide liquid have not been established a model is proposed whereby the observed chromite and associated pt mineralization can result from the normal magmatic evolution of the complex provided that a structural hydrodynamic trap is available to concentrate the chromite

influences of quaternary climatic changes on processes of soil development on desert loess deposits of the cima volcanic field california summary soils formed in loess are evidence of both relict and buried landscapes developed on pliocene to latest pleistocene basalt flows of the cima volcanic field in the eastern mojave desert california the characteristics of these soils change systematically and as functions of the age and surface morphology of the lava flow four distinct phases of soil development are recognized phase 1 weakly developed soils on flows less than 0 18 m y old phase 2 strongly developed soils with thick argillic horizons on 0 18 0 7 m y old flows phase 3 strongly developed soils with truncated argillic horizons massively impregnated by carbonate on 0 7 to 1 1 m y old flows and phase 4 degraded soils with petrocalcic rubble on pliocene flows a critical aspect of the development of stage 1 soils is the evolution of a vesicular a horizon which profoundly affects the infiltration characteristics of the loess parent materials laboratory studies show that secondary gypsum and possibly other salt accumulation probably occurred during the period of phase 1 soil development slight reddening of the interiors of peds from vesicular a horizons of phase 1 soils and presence of weakly developed b horizons indicates a slight degree of in situ chemical alteration however clay and fe oxide contents of these soils show that these constituents as well as carbonates and soluble salts are incorporated as eolian dust in contrast to phase 1 soils chemical and mineralogical analysis of argillic horizons of phase 2 soils indicate proportionally greater degrees of in situ chemical alteration these data the abundant clay films and the strong reddening in the thick argillic horizons suggest that phase 2 and phase 3 soils formed during long periods of time and periodically were subjected to leaching regimes more intense than those that now exist flow age data and soil stratigraphic evidence also indicate that several major loess deposition events occurred during the past 1 0 m y loess events are attributed to past changes in climate such as the pleistocene to holocene climatic change that periodically caused regional desiccation of pluvial lakes reduction of vegetational density and exposure of loose unconsolidated fine materials during times of warmer interglacial climates precipitation infiltrates to shallower depths than during glacial periods extensive saline playas which developed in the mojave desert during the holocene are a likely source of much of the carbonates and soluble salts that are accumulating at shallow depths both in phase 1 soils and in the formerly noncalcareous nongypsiferous argillic horizons of phase 2 and 3 soils

relative age dating of transported regolith and application to study of landform evolution in the appalachians abstract surficial deposits in the appalachians generally are thin discontinuous and difficult to date in the absence of numerical dates particularly for older deposits relative age indices based on degree of weathering and soil development have been used to distinguish and correlate deposits of different ages a favorite locale of relative age studies has been stream terraces where chronosequences have been developed to shed light on the relationship between time and weathering soil development the lack of applicable numerical dating techniques has led some researchers to establish relative chronosequences in which height of stream or fan terraces above modern river level arl serves as a proxy for time approximate incision rates can then be used to estimate numerical ages of the deposits relative age correlations between the weathering indices on the terraces and comparable indices on dated deposits on the coastal plain and in nearby glaciated regions suggest that ages so estimated are the right order of magnitude relative age indices show correlations with height arl that are as high as those with time perhaps because more data sets are available for relative chronosequences than for true chronosequences analogous relative age sequences can be established for alluvial fans and even for hillslope colluvium many weathering indices have been employed but weathering rind thickness on mafic to intermediate clasts has proved to be a particularly consistent and useful parameter in addition to showing how weathering and soil development progress over time relative age dating has shed light on the manner in which landforms evolve along some rivers for example the areal extent of old highly weathered alluvium far exceeds that of younger alluvium suggesting that formerly floodplains and low terraces were much more extensive than at present in addition the manner in which weathering indices on some river terrace sequences vary with height arl suggests that incision rate has changed through time relative age mapping of alluvial fans produces a map pattern of older and younger fan surfaces that allows the sequence of fan development to be inferred in one case suggesting a scenario different from those previously described for fans mapping also shows that the relative abundance of young intermediate and old fan surfaces varies greatly from one area to another several studies have demonstrated clustering of relative age values into a small number of groups suggesting temporal grouping and thus episodic deposition on fans regression of weathering rind thickness against height above modern drainageways of remnant fan surfaces in two areas suggests that fans are being incised more rapidly in one area than in another relative age of hillslope colluvium also aids geomorphic interpretation young brown colluvium is much more common than old red colluvium near the glacier border where red colluvium rarely occurs at the surface but typically is covered by brown colluvium probably mobilized during the late pleistocene distant from the ice margin however red colluvium is extensively exposed on interfluves relatively stable hillslopes can also be distinguished from active ones in this manner for example colluvium on hillslope noses is somewhat more weathered than that on hollow floors and sideslopes

rock weathering rates as functions of time the scarcity of documented numerical relations between rock weathering and time has led to a common assumption that rates of weathering are linear this assumption has been strengthened by studies that have calculated long term average rates however little theoretical or empirical evidence exists to support linear rates for most chemical weathering processes with the exception of congruent dissolution processes the few previous studies of rock weathering rates that contain quantitative documentation of the relation between chemical weathering and time suggest that the rates of most weathering processes decrease with time recent studies of weathering rinds on basaltic and andesitic stones in glacial deposits in the western united states also clearly demonstrate that rock weathering processes slow with time some weathering processes appear to conform to exponential functions of time such as the square root time function for hydration of volcanic glass which conforms to the theoretical predictions of diffusion kinetics however weathering of mineralogically heterogeneous rocks involves complex physical and chemical processes that generally can be expressed only empirically commonly by way of logarithmic time functions incongruent dissolution and other weathering processes produce residues which are commonly used as measures of weathering these residues appear to slow movement of water to unaltered material and impede chemical transport away from it if weathering residues impede weathering processes then rates of weathering and rates of residue production are inversely proportional to some function of the residue thickness this results in simple mathematical analogs for weathering that imply nonlinear time functions the rate of weathering becomes constant only when an equilibrium thickness of the residue is reached because weathering residues are relatively stable chemically and because physical removal of residues below the ground surface is slight many weathering features require considerable time to reach constant rates of change for weathering rinds on volcanic stones in the western united states this time is at least 0 5 my

soil geomorphic research a selective overview abstract much soil geomorphologic research involves tracking the development of soils with time otherwise known as soil chronosequences most of these have been undertaken on landforms underlain by quaternary depsits of varying ages in general there is a predictable variation in both soil horizon sequence and amounts of constituents such as clay fe and caco 3 with time the rate at which these constituents accumulate in the soil is a function of parent material bioclimate and atmospheric dust influx and because of the latter soils in aridic regions can form at rapid rates profile properties can be used to estimate the ages of deposits and faulting events but the error on the estimated age can be 50 or greater the position of salt accumulations in soil profiles is one of the best indications of climatic change and these can be modelled to compare with various climatic parameters present and past profile characteristics due to pedogenic thresholds however can mimic those due to climatic change so close dating is necessary to differentiate the effects of both soil geomorphic data are essential to understand the origin of ancient paleosols in the sedimentary rock records but a major problem still is one of recognition of these features as soils and to separate the effects of pedogenesis from those of diagenesis

sources of spatial complexity in two coastal plain soil landscapes abstract the spatial pattern of soils and soil properties in soil landscapes is considered here as a function of 1 systematic variation along catenas or associated with spatial patterns of soil forming factors and 2 local pseudo random variations associated with local disturbances or small unobserved variations in soil forming factors the problem is approached at two study sites in the u s atlantic coastal plain using algebraic graph theory and the spectral radius of the soil adjacency matrix as a measure of complexity the matrix is constructed based on the observed spatial contiguity of soil taxa and soil factor sequences sfs are defined for each site based on systematic soil variation associated with variations in parent material topography sandy surface thicknesses and secondary podzolization the spectral radii of the networks described by the adjacency graphs are compared to those associated with the maximum for a graph of the same size and the maximum associated with control entirely by variations in soil forming factors at the clayroot study site which is entirely cropland complexity of the adjacency matrix is less than the maximum that could be accounted for by the four identified sfs due to redundant information in the sfs the littlefield site by contrast has a spectral radius greater than here where about half the site is forested the contingent variation is likely associated with effects of individual trees on soil morphology the utility of the adjacency analysis is in identifying whether soil heterogeneity is likely associated with sfs or with contingent factors not captured in sfs

influence of late quaternary climatic changes on geomorphic and pedogenic processes on a desert piedmont eastern mojave desert california radiocarbon dating of late quaternary deposits and shorelines of lake mojave and cation ratio numerical age dating of stone pavements dorn 1984 on the adjacent soda mountains piedmont provide age constraints for alluvial and eolian deposits these deposits are associated with climatically controlled stands of lake mojave during the past 15 000 yr six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and piedmont surfaces as well as on soil geomorphic data all but one of these stratigraphic units were deposited in response to time transgressive climatic changes beginning approximately 10 000 yr ago increased eolian flux rates occurred in response to the lowering of lake mojave and a consequent increase in fine sediment availability increased rates of deposition of eolian fines and associated salts influenced pedogenesis stone pavement development and runoff infiltration relations by 1 enhancing mechanical weathering of fan surfaces and hillslopes and 2 forming clay and silt rich surface horizons which decrease infiltration changes in alluvial fan source areas from hillslopes to piedmonts during the holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less permeable soils inferred increased in early to middle holocene monsoonal activity resulted in high magnitude paleo sheetflood events on older fan pavements this runoff triggered piedmont dissection which in turn caused increased sediment availability along channel walls thus runoff infiltration changes during the late quaternary have occurred in response to eolian deposition of fines pedogenesis increased sheetflood activity in the holocene and vegetational changes which are related to many complicated linkages among climatic change lake fluctuations and eolian hillslope and alluvial fan processes

relative age relationships of debris flow deposits in the southern blue ridge north carolina abstract periods of increased landscape instability in the southern blue ridge were assessed with relative ages of three sequences of debris flow deposits the sequences consist of a series of lobate deposits that are expressed as step like landforms on the floors of host valleys data were collected at three sites from soil pits on the toe and apex of debris flow deposits relative ages were obtained by qualitatively and statistically examining data on clast weathering soil color clay content and iron species consistent results among the indicators of relative age demonstrate that they have utility in warm to temperate humid environments at each site the topographically highest debris flow deposits are slightly older than those at lower elevations one deposit at each of the three sites has a relative age that is very similar to that of one deposit at the other sites this similarity in age indicates that an external factor such as extreme precipitation accounts for the formation of debris flows at approximately the same time in the geological past one of the sites however also has deposits that are clearly younger than the deposits at the other sites which indicates that intrinsic factors also affect the formation of debris flows in the region

petrology of the motaghairat mafic ultramafic complex eastern desert egypt a high mg post collisional extension related layered intrusion abstract the geodynamic settings of the precambrian mafic ultramafic complexes in the eastern desert of egypt have important bearing on understanding the geotectonic evolution of the arabian nubian shield we present a detailed petrological study on a layered mafic ultramafic intrusion that is located at the contact between the precambrian continental crust and the miocene red sea oceanic crust the motaghairat layered intrusion consists of basal lherzolite orthopyroxenite troctolite olivine gabbro and anorthosite on the top variations in modal mineralogy and mineral chemistry along with the chemical composition of these units suggest their derivation from a common high mg tholeiitic parent melt through fractional crystallization processes the parental magma was derived from a metasomatised mantle source the primitive mantle normalized patterns of the calculated melts exhibit enrichment in u relative to th and ba relative lree which indicate that the enriched lithospheric mantle source was metasomatised by fluids derived from a subducted oceanic crust rather than by a sediment melt geological and petrological evidences suggest that the layered motaghairat intrusion was emplaced during post orogenic extension following subduction break off and lithospheric delamination after the collision between the amalgamated island arc terranes and the saharan metacraton the heat source required to melt the metasomatised lithospheric mantle was derived from the upwelling of hot asthenosphere after the subduction break off

periglacial wedges and the late pleistocene environment of wyoming s intermontane basins abstract nonsorted polygons in the uppermost 2 to 3 m beneath pleistocene surfaces indicate permafrost at 1340 m and higher elevations in the intermontane and piedmont plains of wyoming during the wisconsin and perhaps earlier glacial maxima the polygons as much as 10 m in diameter are delineated by wedges that vary in depths range from narrow to moderately flared forms and deform host materials the wedges have silty fine to medium sand matrices largely eolian with pebbles or clasts from hosts of gravel or bedrock some wedges may reflect seasonal cracking in a periglacial active zone but most are either permafrost sand wedge relics or less commonly ice wedge casts alternative explanations are rejected largely because similar features are apparently lacking in the lower and warmer plains from eastern colorado southward the wedges suggest an arid windy periglacial environment whose mean annual temperatures are conservatively estimated as some 10 to 13 c colder than those at present although late wisconsin early holocene floral and faunal evidence indicates lowered montane biotic zones the eolian and periglacial features indicate a lack of extensive forest cover on the basin floors in conjunction with vertebrate fossil associations of grazing and tundra animals the wedges may provide a parallel line of evidence for a former periglacial steppe or steppe tundra in the wyoming basins

estimating ages of late quaternary stream terraces from analysis of weathering rinds and soils rates of growth of rock weathering rinds and rates of changes of soil morphologic and chemical properties that are calibrated at sites of known ages produce powerful tools for estimating ages of geomorphic surfaces particularly when materials datable by conventional methods are not widespread sequences of latest quaternary stream terraces from the south island of new zealand are ideally suited for application of these calibrated age techniques because climate and source materials for terrace deposits are internally consistent within two regions west land and marlborough modal and mean thicknesses of weathering rinds formed in surface cobbles of torlesse graywacke provide age estimates for latest pleistocene and holocene stream terraces in marlborough with uncertainties estimated at 5 to 40 modal rind thickness of subsurface cobbles provides age estimates for latest quaternary westland sites with uncertainties of 10 to more than 50 few dated soils are available to constrain rates of soil development in westland and marlborough furthermore soils were sampled from only one pedon on each surface morphologic data however provide least squares age estimates for westland sites with uncertainties typically greater than 100 and the calibration data can further bracket likely soil ages to less than 50 uncertainty the regression data from marlborough are less reliable but profile index ratios help bracket ages to at least 50 distributions of oxalate extractable fe and ai and total major element concentrations allow age estimates for westland and marlborough soils with uncertainties estimated at 15 to 50 despite these uncertainties the three techniques combine to provide age estimates with the high resolution needed to examine details of fault slip rates or stream downcutting the calibration data and weathering rates used herein are applicable only to the new zealand region studied although similar calibrated age techniques should provide high resolution dating in many other regions such techniques are particularly useful when multiple approaches are available to provide independent cross checks

dynamic pedogenesis new views on some key soil concepts and a model for interpreting quaternary soils abstract inasmuch as soils are open systems and rarely if ever achieve equilibrium with their environments it is philosophically sound to view all soils as expressing varying levels of polygenesis as that term has been redefined soil genesis and resultant morphology may then be viewed in a comprehensive framework of soil evolution that consists of two linked pathways one developmental and the other regressive that reflect interactions of both exogenous and endogenous vectors vectors are factors processes and conditions of pedogenesis following this philosophy a model of pedogenesis is framed in an evolutional paradigm that emphasizes the integrated effects of dynamic and passive pedogenic vectors in directing pathways and in controlling rates of soil genesis through time the dynamic vectors include energy and mass fluxes frequencies of soil wetting and drying water table dynamics organisms feedback processes and pedoturbation the passive vectors include parent materials soil chemical environment stability of geomorphic surfaces and various evolved soil properties and conditions accessions both sets of vectors vary spatially and the dynamic vectors more so than passive vectors fluctuate through time the model is expressed as s f d p dd dt dd dt where s is the state of the soil or degree of profile evolution d is the set of dynamic vectors p is the set of passive vectors and dd dt and dp dt denote change through time t the model helps explain the apparent minimal development and regressed character of some old soils and the rapid and strong development of some young ones

comparison of soils in midwestern united states and western europe with the interglacial record abstract paleosols that formed primarily before the last glaciation cannot be adequately explained by a model of holocene like interglacial periods of about 10 000 yr in length which has been inferred from the marine 18 o 16 o record geological and palynological evidence from terrestrial midlatitude sites suggests that temperate conditions conducive to soil formation existed for periods greatly in excess of 10 000 yr during the middle and late pleistocene available data on soils formed during this interval from western europe and midwestern united states are best explained by relatively long interglaciations or the development of composite soils over a number of temperate periods climatic contrasts between the interglaciations appear to have been overemphasized widespread assumptions regarding greater warmth in interglaciations prior to the present one are generally unproven in the absence of precise dating progress in relating paleosols to fragmentary local records of quaternary climatic changes will be achieved by detailed analytical techniques such as soil micromorphology

chronology and rates of faulting of ventura river terraces california new evidence concerning the chronology of four late pleistocene terraces of the ventura river near oak view california that are vertically offset and tilted by reverse and reverse flexural slip faults provides a means of estimating rates of fault movement and downcutting by the ventura river radiocarbon ages of charcoal contained within terrace deposits date two of the terraces correlation of soils that have developed on terrace deposits and extrapolation of the rate of vertical displacement of the arroyo parida santa ana fault not a flexural slip fault date the others resulting age estimates for the four main late pleistocene terraces are qt5b 30 000 qt6a 38 000 qt6b 54 000 and qt6c 92 000 yr b p vertical slip rates on flexural slip faults range from 0 3 to 1 1 mm yr and apparently are related to the rate form and mechanics of folding of the north limb of the ayers creek canada larga syncline average rates of downcutting of the ventura river for several intervals during the late pleistocene estimated from the chronology and relative elevation of river terraces north of the arroyo panda santa ana fault upstream from the zone of faulting vary from 0 5 to 1 3 mm yr the range in rates probably reflects variations in local uplift as well as adjustments to changing eustatic sea level climatic conditions and or regional deformation of the western transverse ranges the average rate of downcutting of the ventura river north of the zone of flexural slip faulting is 0 8 mm yr compared with 1 2 to 2 2 mm yr in the deformation zone immediately to the south this apparently indicates that during tectonic deformation there is an approximate balance between the rate of uplift due to faulting and folding and the rate of downcutting by the fluvial system

using melt inclusions to determine parent magma compositions of layered intrusions application to the greenhills complex new zealand a platinum group minerals bearing island arc intrusion the permian greenhills complex of southland new zealand is a small ultramafic to mafic layered intrusion that hosts primary magmatic platinum group minerals pgms as inclusions in cumulus chromian spinel grains we have determined the major and trace element chemistry of the parent magmas of the complex using the composition of rehomogenized melt inclusions trapped in cumulus spinel grains from dunite these melt inclusions have compositions similar to those of primitive ankaramite dikes that cut the complex verifying that our data are representative of the parent melt chemistry these magmas have high mgo and cao and are enriched in pb sr and large ion lithophile elements compared to high field strength and rare earth elements we suggest that the parent magmas to the complex were primitive low k island arc tholeiite basalts that formed by high degrees of melting of a spinel peridotite source the platinum group element contents of such magmas are expected to be very high therefore the primary pgms at greenhills are suggested to have precipitated directly from the melt following differentiation and cooling in a shallow magma chamber

holocene erosion sedimentation and stratigraphy at raven fork southern blue ridge mountains usa holocene colluvial and alluvial stratigraphy and a radiocarbon chronology are presented for the valley of the lower three kilometers of raven fork a mountain stream draining 194 km 2 of high relief 1 3 km terrain of the southern blue ridge mountains in western north carolina usa which is in a region that lacks good chronological data lower hillslopes alluvial colluvial fans alluvial bottomlands first terrace and floodplain and the modern stream channel are landforms described with respect to soils stratigraphy and sedimentary structures standard methods for subsurface investigations core holes excavation units exposures are used in conjunction with extensive archeological excavations and cultural chronologies radiocarbon ages from each landform are used to calculate long term average rates of sedimentation results indicate that the first half of the holocene experienced somewhat more rapid rates of hillslope sedimentation 0 3 to 1 1 mm yr than the last half of the holocene 0 1 0 2 mm yr on footslopes toeslopes and alluvial colluvial fans prior to historic time we suggest that these subtle differences in the rates of sedimentation were driven by changes in global paleoclimate that favored a high frequency of heavy rainfall including tropical storms and or severe thunderstorms and more and possibly larger floods during the first half of the holocene prehistoric rates of vertical accretion on the first terrace t1 ranged from 0 1 to 0 8 mm yr between about 10 000 and 3000 calendar years ago and incision below t1 formed the late holocene floodplain beginning at about 6000 years ago we suggest that this incision is linked to a reduction in the supply of sediment and a reduction in the magnitude of floods historical rates of sedimentation on all parts of the depositional landscape 2 0 2 7 mm yr on hillslopes and fans and 5 8 6 5 mm yr on floodplains were about an order of magnitude greater than prehistoric rates we attribute these rates to human impacts such as timber harvest and land clearing which caused accelerated erosion we attribute the abundance of fine grained sediment in streams of the southern blue ridge province which is atypical in many mountain streams around the world to the regionally widespread mantle of saprolite as a source of sediment to the fluvial system holocene sedimentation on all depositional landforms in the valley led to sedimentary burial of archeological materials which highlights the need to consider site burial on lower hillslopes and terraces for evaluation of the cultural resources in the southern blue ridge mountains these findings show that the entrenched condition of the raven fork channel was inherited from the middle holocene and can be considered a natural state for this mountain stream casting doubt on the negative connotation that is often assigned to entrenched channels

soil development in till of various ages in northeastern pennsylvania abstract eleven well drained soils formed in till parent materials of varying ages in northeastern pennsylvania were studied to determine changes in the soils with time four profiles three lackawanna and one bath were formed in woodfordian till 15 000 yr b p and two leck kill were formed in altonian till 28 000 75 000 yr b p in these soils the extractable iron oxide extractable aluminum oxide and kaolinite contents increase with age as do the total clay and fine total clay ratio with increasing age the maximum accumulation of these constituents is found deeper in the profile the extractable silicon oxide distribution is constant with depth but it decreases in overall amount with time gibbsite is found only in small amounts in the a horizon of altonian soils but occurs throughout the profile of pre wisconsinan soils although only in small amounts in general differences were found in these soils which separated them into three groups representing varying degrees of soil development a regression equation was derived to predict the age of soils formed from the altonian till based on a clay accumulation index value for soils of known woodfordian and holocene ages the equation log y 1 80 0 992 log x best fit the data with an r 2 value of 0 913 using this equation a mean age of 41 000 yr was calculated for the altonian soils this date was used to derive a second equation to predict ages for pre wisconsinan soils the equation with the highest r 2 value 0 934 was log y 1 81 0 998 log x dates for soils developed in the white deer till and the laurelton till of the pre wisconsinan stage were calculated to be 86 000 and 91 000 yr b p respectively these dates fall within ages estimated for the sangamon interglaciation and thus would appear to be too young for pre sangamonian materials the probable reason for the too young age is that the c horizon material of the pre wisconsinan soils was weathered and did not provide an accurate estimate of clay accumulation for the prediction equation

soil forming intervals caused by eolian sediment pulses in the lahontan basin northwestern nevada we have studied a series of toyeh post isotope stage 2 eolian dust fall was the source of fines and salts in these soils apparently this influx was concentrated during two brief intervals or pulses one during the holocene and one during the previous isotope stage 5 interpluvial leaching during the sehoo pluvial removed salts from churchill soils carbonate and soluble salts now observed in the churchill soils represent a toyeh overprint on the churchill profile these pulses of fine sediment and accompanying salts are tantamount to the soil forming intervals that morrison described in the lahontan area episodic eolian dustfall provides fine particles of silicates calcite and soluble salts that infiltrate into the clast supported alluvial piedmont sediments several hundred playas exist in the basin and range each providing directional dust contributions that influence local and regional soil development we counsel caution in assuming constant gradual development of soil properties without due consideration of paleoenvironmental influences on soil forming factors

reinterpretation of the exposed record of the last two cycles of lake bonneville western united states a substantially modified history of the last two cycles of lake bonneville is proposed the bonneville lake cycle began prior to 26 000 yr b p the lake reached the bonneville shoreline about 16 000 yr b p poor dating control limits our knowledge of the timing of subsequent events lake level was maintained at the bonneville shoreline until about 15 000 yr b p or somewhat later when catastrophic downcutting of the outlet caused a rapid drop of 100 m the provo shoreline was formed as rates of isostatic uplift due to this unloading slowed by 13 000 yr b p the lake had fallen below the provo level and reached one close to that of great salt lake by 11 000 yr b p deposits of the little valley lake cycle are identified by their position below a marked unconformity and by amino acid ratios of their fossil gastropods the maximum level of the little valley lake was well below the bonneville shoreline based on degree of soil development and other evidence the little valley lake cycle may be equivalent in age to marine oxygenisotope stage 6 the proposed lake history has climatic implications for the region first because the fluctuations of lake bonneville and lake lahontan during the last cycle of each were apparently out of phase there may have been significant local differences in the timing and character of late pleistocene climate changes in the great basin second although the bonneville and little valley lake cycles were broadly synchronous with maximum episodes of glaciation environmental conditions necessary to generate large lakes did not exist during early wisconsin time

10be distribution in soils from merced river terraces california abstract the distribution and residence time of cosmogenic 10 be in clay rich soil horizons is fundamental to understanding and modelling the migration of 10 be on terrestrial sediments and in groundwater solutions we have analyzed seven profiles of clay rich soils developed from terrace sediments of the merced river california the terraces and soils of increasing age are used to compare the 10 be inventory with a simple model of accumulation decay and erosion the data show that the distribution of 10 be varies with soil horizon clay content that the residence time of 10 be in these horizons exceeds 10 5 years and that to a rough approximation the inventory of 10 be in a thoroughly sampled soil profile fits the equation n q em 1 e where q is delivery rate e is erosion rate m is the concentration of 10 be in the eroding surface layer is the decay constant and t is the age of the depositional unit from which the soil has developed the general applicability of this model is uncertain and warrants further testing in well calibrated terrace sequences

pedogenic gradients for iron and aluminum accumulation and phosphorus depletion in arctic and alpine soils as a function of time and climate pedogenically significant chemical extracts of iron aluminum and phosphorus are related mainly to time in chronosequences from baffin island canadian arctic the alpine sierra nevada and wind river range western united states the alpine khumbu glacier area himalaya nepal and the alpine southern alps new zealand based on the accumulation index for fe and al and the depletion index for p in each region the following ranking of chemical pedogenic development is obtained southern alps khumbu glacier area wind river range sierra nevada coastal baffin island inland baffin island the ranking mainly follows regional climate with the greatest accumulation and depletion to the warmest and wettest environment and the least accumulation and depletion in the coldest and driest environment

soil chronosequence of brasstown creek blue ridge mountains usa abstract a chronosequence of soils on alluvial terraces in the appalachian highlands of the southeastern united states is identified by simple methods of quantitative soil morphology and chemical analysis the chronosequence is from brasstown creek a 5th order stream draining 65 km 2 of the blue ridge mountains of north georgia the portion of the valley studied is about 1 km wide and contains five quaternary terrace remnants radiocarbon dates show that the floodplain t0 is late holocene and includes historical post ca 1830 a d sediment and the four older terraces t1 t5 are pre holocene the floodplain soils are either entisols in historical sediment or buried inceptisols with weak bw horizons in late holocene to protohistoric sediment the lowest terrace t1 is terminal pleistocene in age and its soils have bt horizons that are about 0 9 m thick 10yr 4 5 to 10yr 5 4 in colour and contain 25 to 35 clay soils on terraces older than t1 become progressively redder and contain more clay with increasing age culminating with 2 5yr hues and 40 to 52 clay in the bt horizon of t5 percent clay in bt horizons rubification indices iron oxide contents and element ratios progressively change with age of the terraces but other morphological properties ph and individual element concentrations are of less use as chronosequence variables

soil chronosequence studies in temperate to subtropical low latitude low relief terrain with data from the eastern united states the coastal plain of the eastern united states is a low latitude low altitude low relief terrain composed primarily of gently dipping marine and marginal marine sediments that range in age from cretaceous to quaternary population density of the area is moderate and most of the population is concentrated along the coast inland of the coast agriculture including growing trees for pulp is the dominant economy in this region soils have developed along two different pathways one pathway is dominated by the dissolution and movement of oxyhydroxides and the accumulation of organic matter the other by the accumulation of clays and oxyhydroxyides and the adsorption or oxidation of organic matter the first pathway has resulted in the formation of spodosols the second in the development of ultisols no clearly distinguishable age trends have been identified in the spodosols but the properties of ultisols can be measured to quantify surface material alteration through time ultisols are therefore suited to order of magnitude chronostratigraphic interpretations potentially data derived through the study of ultisols can be used to develop models that predict how surface processes will change due to continued weathering and pedogenesis or as the result of climate change

weathering instability and landscape evolution abstract the argument in this paper is that the fundamental control on landscape evolution in erosional landscapes is weathering the possibility of and evidence for instability in weathering at four scales is examined the four scales are concerned with weathering processes allocation of weathered products the interrelations of weathering and denudation and the topographic and isostatic responses to weathering limited denudation the regolith hillslope landscape unit and landscape scales respectively the stability conditions for each model and the circumstances under which the models themselves are relevant are used to identify scale related domains of stability and instability at the regolith scale the interactions among weathering rates resistance and moisture are unstable but there are circumstances over long timescales and where weathering is well advanced under which the instability is irrelevant at the hillslope scale the system is stable when denudation is transport rather than weathering limited and where no renewal of exposure via regolith stripping occurs at the level of landscape units the stability model is based entirely on the mutual reinforcements of weathering and erosion while this should generally lead to instability the model would be stable where other external controls of both weathering and erosion rates are stronger than the weathering erosion feedbacks at the broadest landscape scale the inclusion of isostatic responses destabilizes erosion topography uplift relationships thus if the spatial or temporal scale is such that isostatic responses are not relevant the system may be stable essentially instability is prevalent at local spatial scales at all but the longest timescales stability at intermediate spatial scales is contingent on whether weathering erosion feedbacks are strong or weak with stability being more likely at shorter and less likely at longer timescales at the broadest spatial scales instability is likely although stability may be present at intermediate temporal scales if weathering erosion feedbacks are weak the distinction is important because stability is associated with convergent evolution whereby the effects of initial variations or disturbances are reduced over time as the landscape converges toward a stable equilibrium state instability by contrast indicates divergent evolution increasing differentiation over time and the persistence and growth of disturbance effects and initial variations

multiple paleosols in pre wisconsinan drift northwestern montana and southwestern alberta summary varying numbers of strongly developed paleosols occur on and between multiple pre wisconsinan diamict mostly till units which cap interfluves east of waterton glacier parks southwestern alberta and northwestern montana investigation of stratigraphy morphology and genesis of the paleosols permits subdivision of quaternary deposits and estimation of the length and climatic characteristics of pre wisconsinan interglacials stratigraphic relations indicate at least five soils in five tills on saint mary ridge and mokowan butte up to three soils in four tills on two medicine ridge two soils in two tills on milk river ridge and one soil in one till on cloudy ridge ages of diamicts probably range from late pliocene to kansan or early illinoian because the paleosol till sequences on mokowan butte and saint mary ridges are not correlative more than five pre late illinoian depositional and soil forming episodes are probably represented in the region paleosols generally include 1 to 5 m thick reddish leached clay rich argillic horizons overlying leached cambic or calcic horizons or indurated calcretes 4 to 15 m thick morphological chemical and mineralogical properties of paleosols resemble those of paleudalfs and paleustalfs suggesting the soils formed over long periods 0 02 to 2 68 ma under climates which were significantly warmer by at least 6 degrees c and moister than today s

soil catenas on pinedale and bull lake moraines willow lake wind river mountains wyoming abstract soils in coarse grained tills on pinedale about 20 000 years old and bull lake about 140 000 years old moraines show significant variaton with slope position and age soils on the pinedale moraine are mostly non calcareous typic cryoborolls with a bw c profiles that thicken considerably downslope these soils are weakly developed due to their youth and to the unstable steep up to 24 highly convexo concave slopes soils on the bull lake moraine are mostly argic cryoborolls with a bt c profiles these soils are more strongly developed than soils at similar positions on the pinedale moraine because the bull lake moraine is older and has less steep up to 16 more gently curved slopes the soils on the bull lake moraine contain more clay a higher proportion of pedogenic clay more weathered stones and more free sesquioxides erosion and dry conditions at the convex summit and shoulder sites on the bull lake moraine have resulted in thin soils with minimal argillic horizons these soils are only slightly more strongly developed than soils at analogous sites on the much younger pinedale moraine in contrast at the concave sites in downslope positions the soils on the bull lake moraine are much more strongly developed than analogous soils on the pinedale moraine slow deposition of weathered material probably transported by creep has acted concurrently with pedogenesis to form soils with thick homogeneous argillic horizons the relationship between hillslope curvature and soil properties on both moraines is shown by significant correlations between soil properties and the second derivative of the hillslope profile this relationship is probably due primarily to the interaction of soil formation and soil creep

soil geomorphology present dilemmas and future challenges abstract understanding the manner in which landscapes change is still a major challenge for geomorphologists recent work has shown quite convincingly that landscape evolution occurs during relatively short periods of intense adjustment followed by longer periods of stability the challenge is to determine the way in which such change occurs and the factors which control the changes this paper by using a number of specific examples from a variety of environments suggests that many of these issues may be resolved by adopting an integrative approach involving soil information as well as geomorphological concepts

the ferguson lake deposit an example of ni cu co pge mineralization emplaced in a back arc basin setting the world s largest ni cu platinum group element pge deposits are dominantly hosted by ultramafic rocks within continental extensional settings e g raglan voisey s bay resulting in a focus

tearing and breaking off of subducted slabs as the result of collision of the panama arc indenter with northwestern south america we present two regional lithospheric cross sections that illustrate eastward and southeastward dipping subducted slabs to depths of 315 km beneath the surface of colombia in northwestern south america these cross sectional interpretations are based on relocated earthquake hypocentral solutions models supported on gravity and magnetic regional data and coda q q c tomography the method of tomographic imaging based on spatial inversion of the coda wave has advantages of providing information on the lateral variations of the anelastic properties and thermal structure of the lithospheric system mapping of earthquake defined benioff zones combined with tomographic imaging reveals the presence of an 240 km long east west striking slab tear named here the caldas tear the proposed caldas tear separates a zone of shallow 20 30 dipping southeastward subduction in the area of colombia adjacent to panama and the caribbean sea which is not associated with subduction related volcanism from an area of steeper 30 40 dipping slab adjacent to the eastern pacific ocean that is associated with an active north south chain of active arc volcanoes we propose that the caldas slab tear separating these two distinct subducted slabs originally formed as the southern boundary of the panama indenter an extinct island arc that began subducting beneath northwestern south america about 12 ma the area south of the panama indenter is miocene oceanic crust of the nazca plate which subducts eastward beneath northwestern south america at normal angles and melts to form a north south trending active volcanic arc in addition to the formation of the caldas tear we propose that impedance of the thicker crustal area of the panama arc indenter over the past 12 ma may have led to down dip break off of previously subducted oceanic crust that is marked by an extremely concentrated and active earthquake swarm of intermediate depth earthquakes beneath east central colombia

soil fertility and slope processes in the western cumberland escarpment of kentucky influences on the development of horticulture in the eastern woodlands the archaeological record of dry rockshelters in the red river valley of eastern kentucky contains botanical remains of several weedy annual seed bearing plants that point to the independent development of agriculture during the late archaic and early woodland period the objective of this study is to gather quantitative data through the chemical and physical analysis of soils collected within a valley transect to gain insights into landscape processes and soil fertility that may have played a role in the early development of plant domestication and the location of garden plots in relation to rock shelter sites in the upper cumberland plateau region of eastern kentucky soils on upland benches formed in limestones have soil fertility values that are comparable to fertile floodplain soils upslope outcrops of calcareous bedrock are contributing basic cations to these bench soils additionally in comparison to other landscape positions these upland soils have high levels of organic carbon available p and greater c n ratios soil morphology radiocarbon dates and archaeological evidence indicate that many of the numerous earthflows and debris flows within the region are early to middle holocene in age these slides were likely generated by mid holocene climatic shifts in which the frequency and intensity of summer precipitation increased across the southeastern united states these slope failures may have contributed to the development of plant domestication by creating forest canopy gaps and disturbed soils in which weedy plants thrived

iron oxides and clay minerals within profiles as indicators of soil age in northern italy abstract nine profiles representing the alfisol inceptisol and entisol orders were sampled on three terraces forming a chronosequence total iron dithionite extractable iron and oxalate extractable iron were determined for all horizons of all profiles and the clay mineralogy for horizons of three profiles the percentage of total fe fet extracted by dithionite fed increased with age of terraces as did the difference between fed and feo oxalate extractable analysis of variance anova of the horizon data showed that the ratios fed fet and fed feo fet were closely related to the ages of the terraces clay minerals were also related to terrace ages with 2 1 minerals dominant in the profiles on the youngest and mixed layer minerals and kaolinite more abundant in profiles on the older terraces

rates and processes of soil development on quaternary terraces in cajon pass california field and laboratory analyses of soils on 11 well dated fluvial terraces spanning the past 0 5 m y demonstrate that a threshold governs changes in several morphological and chemical characteristics of increasingly older soils correlations with respect to time among iron species soil morphology and soil silt and clay demonstrate that the chronosequence at cajon pass reflects primarily an evolutionary largely time dependent trend and does not reflect differences in external factors such as climate most of the soil development on holocene terraces of the cajon pass area is due to physical incorporation of eolian dust and organic material into initially very permeable gravels this process decreases soil permeability and is conducive for an increase in the magnitude of chemical weathering latest pleistocene and older pleistocene soils have developed clay and authigenic iron oxide rich b horizons at the expense of organic matter rich a horizons and color b horizons as the extent of chemical weathering has increased this conversion of the soil from a noncolloidal system to a much more colloidal system takes place over a relatively short period of time 4 000 yr and is herein defined as a type of pedologic threshold in the cajon pass area the attainment of the threshold and subsequent development of the argillic b horizon of soils on latest pleistocene terraces occurred during the holocene thus the absence of argillic horizons in soils on holocene terraces is attributable to simply their younger age rather than to the pleistocene to holocene climatic change the threshold is a function of several variables including influx rate of eolian dust and initial soil permeability therefore the time required to attain the threshold will vary in chronose quences characterized by geomorphic or geographic settings that are different from conditions found in cajon pass

distribution of calcium carbonate in desert soils a model a model that describes the distribution of calcium carbonate in desert soils as a function of dust flux time climate and other soil forming factors shows which factors most strongly influence the accumulation of carbonate and can be used to evaluate carbonate based soil age estimates or paleoclimatic reconstructions models for late holocene soils have produced carbonate distributions that are very similar to those of well dated soils in new mexico and southern california these results suggest that 1 present climate is a fair representation of late holocene climate 2 carbonate dust flux can be approximated by its holocene rate and 3 changes in climate and or dust flux at the end of the pleistocene effected profound and complex changes in soil carbonate distributions both higher carbonate dust flux and greater effective precipitation are required during the latest pleistocene early holocene to explain carbonate distributions in latest pleistocene soils 21 refs 4 figs 1 tab

factors controlling 13c contents of sedimentary organic compounds principles and evidence the carbon isotopic composition of any naturally synthesized organic compound depends on 1 the carbon source utilized 2 isotope effects associated with assimilation of carbon by the producing organism 3 isotope effects associated with metabolism and biosynthesis and 4 cellular carbon budgets these factors are reviewed and quantitative considerations summarized particularly with regard to active and passive modes of carbon assimilation by phytoplankton and the existence of discernible regularities in isotope effects associated with lipid biosynthesis it is concluded that n alkyl lipids are in general depleted in 13c by about 1 5 relative to polyisoprenoid lipids produced by the same organism the effects of biological reworking on isotopic compositions of organic carbon are examined and it is suggested that enrichment of 13c in sedimentary organic carbon may result from loss of ch4 from zooplanktonic gut communities isotopic methods for estimation of ancient co2 levels are considered and a hyperbolic form favored for the relationship between concentrations of dissolved co2 and isotopic fractionation

inherited vs acquired complexity in east texas weathering profiles complexity in weathering profiles may reflect variability in the parent material and or complex feedback relationships within regolith weathering systems because regolith formation modifies or destroys the parent material it is difficult to determine the extent to which variability in the weathering profile is inherited as opposed to created by the weathering processes the state probability function spf designed to model the spatial pattern of transitions in system states is applied to complex weathering profiles formed in glauconitic materials in east texas to address this issue the weathering profile is remarkably complex with units ranging from unweathered parent material to highly modified weathering products similar to those found in the bt horizons of the overlying rhodic paleudalf there is a very general vertical sequence with more weathered material near the top and less weathered material near the bottom however the pattern is quite irregular highly weathered units are found everywhere except at the base of the study section and much less developed units are found throughout though the spf indicates a high degree of spatial complexity the value never approaches or exceeds that which would be expected in a random vertical sequence of weathering horizons variation inherited from the parent material would produce spf values greater than that for a random sequence the complex patterns in the east texas regolith are thus attributable primarily to feedbacks within the weathering system and indicate that the complexity is dominantly acquired whatever anisotropy there may have been in the parent material has been magnified and overprinted by complex interactions within the weathering system

periglacial geomorphology of the appalachian highlands and interior highlands south of the glacial border a review abstract many features reported in the appalachian region have been assigned a paleoperiglacial origin based on field relationships and their similarities with analogs active in present day actuoperiglacial environments these forms include but are not limited to sorted and nonsorted varieties of patterned ground grezes litees block fields block slopes and block streams cryoplanation terraces and hillslope and river terrace landscapes although very small scale features generally less than 1 m in plan or section dimension and some larger forms on steep hillslopes are known to be at least sporadically active today the large scale features discussed here are interpreted as either inactive or truly fossil periglacial phenomena thus they hav implications for paleoclimatic reconstruction and significance as indicators of relative landscape stability since the time s of their development this paper briefly reviews the historical dimension of early researchs work present selected examples of recent results and gives authors conclusions

platinum group elements as petrological indicators in mafic ultramafic complexes of the central and southern urals preliminary results abstract platinum group elements pge and gold were analyzed by icp ms after the ni sulphide fire assay pre concentration step in 44 rocks from 5 orogenic mafic ultramafic massifs of the central and southern urals they comprise a ring zoned ural alaskan type bodies of the pt bearing belt kachkanar tagil uktus and b lherzolite harzburgite complexes overlain by layered wehrlite gabbro and diorite nurali mindyak supposed to be ophiolite type suites total pge and au contents are generally higher in ural alaskan type complexes compared with lherzolite harzburgite complexes mantle normalized pge patterns range from nearly unfractionated in the dunites pd ir 0 57 3 68 to mildly and strongly fractionated in wehrlite clinopyroxenite and gabbro pd ir 9 1 187 exceptionally high values of pd ir 761 2622 are observed in amphibole rich lithologies at kachkanar possibly indicating a relationship between fractionation of the less refractory pd and increased fluid activity in the parental magma pronounced positive pt anomalies up to 20 times the mantle estimate distinguishes the ural alaskan type dunites and progressively reduces in pyroxenites and gabbros in the lherzolite harzburgite complexes of mindyak and nurali layered wehrlites and pyroxenites as well as rocks from the gabbro diorite units have fractionated pge patterns pd ir 2 94 92 39 and positive pt anomaly as in the ural alaskan complexes conversely the pt anomaly is negative in the peridotites and increases from lherzolites and harzburgites to dunites similarly to residual mantle from alpine type orogenic massifs the pd ir 0 71 3 7 is higher than in ophiolites and resembles that of lherzolite massifs of the western mediterranean representing sub continental mantle variation of the pt anomaly versus pd ir in ural alaskan type complexes and in the layered sequences overlaying lherzolite harzburgite mantle suites is consistent with magmatic fractionation in which pt behaves as a compatible element it reflects a progressive depletion by partial melting in mantle peridotites the pt becoming incompatible in the last stage of melting in which pt poor residual dunites are formed the positive pt anomaly in ural alaskan type complexes is striking and would appear as a distinctive feature of the parent magma probably inherited from its mantle source

a quantitative comparison of soil development in four climatic regimes abstract a new quantitative soil development index based on field data has been applied to chronosequences formed under different climatic regimes the four soil chronosequences developed primarily on sandy deposits have some numeric age control and are located in xeric inland merced calif xeric coastal ventura calif aridic las cruces n mex and udic susquehanna valley pa soil moisture regimes to quantify field properties points are assigned for developmental increases in soil properties in comparison to the parent material currently ten soil field properties are quantified and normalized for each horizon in a given chronosequence including two new properties for carbonate rich soils in addition to the eight properties previously defined when individual properties or the combined indexes are plotted as a function of numeric age rates of soil development can be compared in different climates the results demonstrate that 1 the soil development index can be applied to very different soil types 2 many field properties develop systematically in different climatic regimes 3 certain properties appear to have similar rates of development in different climates and 4 the profile index that combines different field properties increases significantly with age and appears to develop at similar rates in different climates the soil development index can serve as a preliminary guide to soil age where other age control is lacking and can be used to correlate deposits of different geographical and climatic regions

influences of eolian and pedogenic processes on the origin and evolution of desert pavements well developed desert pavements are present above eolian deposits that mantle flows of the cima volcanic field located in the mojave desert california soil stratigraphic data and geochemical data demonstrate that eolian and pedogenic processes play major roles in the evolution of these pavements eolian dust 1 accelerates mechanical fragmentation of flow rock providing the source material for pavements and 2 accumulates slowly below basaltic colluvium in flow depressions eventually promoting development of cumulate soils below the evolving stone pavement an increase in dust flux during the holocene has raised ancient pleistocene pavements as much as 20 cm above the former land surface the results of our studies demonstrate for the first time that most desert pavements do not form by deflation by overland flow or by upward migration of stones through a slowly formed clayey argillic horizon desert pavements are born and maintained at the surface

a soil chronosequence on quaternary marine terraces san clemente island california a soil chronosequence on marine terraces was examined on san clemente island california in an arid mediterranean climate in order to see which soil properties differ most systematically with time ages of the geomorphic surfaces were determined by radiocarbon uranium series and amino acid racemization techniques and range from 1 000 000 yrs soils on surfaces 200 000 yrs old are vertisols or alfisols with vertic properties such as slickensides and cracks and they exhibit both prismatic and angular blocky sphenoidal or only angular blocky structure solum thickness increases linearly with age of geomorphic surface clay soluble salts ald smectite mica ratios in the clay fraction and quartz plagioclase ratios in the silt fraction when expressed as profile summations show increases with age of geomorphic surface the best fit regression equations are linear with the exception of ald which is best expressed as a power function important soilforming processes appear to be alteration of mica to smectite accumulation at depth of soluble salts derived from marine aerosols possibly additions of eolian materials clay illuviation in the younger soils and pedoturbation in the older soils the observations reported here allow the following conclusions to be drawn about soils in this environment 1 certain soil properties which show distinct trends with time can be used for relative age dating in geomorphic and stratigraphic studies 2 soils have not reached a steady state condition with respect to many of their properties and 3 alfisols and mollisols with natric b horizons may be precursors to vertisols

loess stratigraphy in central china abstract the loess deposits in central china record world wide climate changes of the last 2 5 ma numerous climatic oscillations are marked by alternating loess and soil units with continuous coverage of the matuyama and brunhes epochs magnetic susceptibility of the deposits correlates closely with the oxygen isotope record of the deep sea sediments and provides an independent measure of climate and time the key marker bed of the chinese loess sequence is the paleosol s5 the time equivalent of the mid brunhes oxygen isotope stages 13 14 and 15 it marks a prolonged interval of warm humid climate lasting from approximately 615 to 470 thousand years ago several episodes of river downcutting coincide with deposition of the exceptionally thick loess units l1 oceanic oxygen isotope stages 2 to 4 l2 stage 6 l5 stage 12 l6 stage 16 l9 stage 22 l15 stage 38 about 1 15 ma and ws4 about 2 3 ma these erosional events are interpreted as a result of episodic uplift of the loess plateau the deposition of the earliest loess layers between 2 5 and 2 3 ma ago marks a first order shift from warm and humid environments toward harsh continental steppes comparable to those of the middle and late pleistocene little if any lithologic or paleontologic changes were noted within or above the olduvai magnetozone so that the proposed plio pleistocene boundary at approximately 1 65 ma has no lithostratigraphic and biostratigraphic representation in the chinese loess series comparison with the deep sea drilling program core 552a in the north atlantic and with the santerno river section near bologna shows that the occurrence of the earliest loess in china coincides with the timing of the first significant ice rafting in the north atlantic and with the appearance of cold water foraminifers in the marine deposits of northern italy an extension of the stage system of the oxygen isotope signal extended back to the gauss matuyama boundary is proposed

the evolution of holocene reg gravelly soils in deserts abstract reg soil is an aridisol developed upon a stable alluvial surface composed of sand to coarse gravel the objectives of the present study were 1 to examine the initial evolution of reg soil properties with time 2 to assess and explain the rates of development of different properties 3 to establish the suitability of different soil properties for relative age dating the time dependent soil properties examined were 1 mechanical weathering of surficial rocks and desert pavement evolution 2 chemical and biological weathering of surficial rocks 3 the thickness of soil profiles and soil horizons 4 soil texture in the different horizons 5 salts and gypsum distribution and concentration in different soil horizons 6 degree of mechanical weathering of gravel in c horizons fifteen successive surfaces of the nahal wadi ze elim sequence of alluvial fans were selected for study dead sea region israel under an extremely arid climate the sequence is of holocene age 14 000 years b p to recent the main conclusions are 1 reg soils develop rather fast in several 10 3 years since their initiation however the various soil properties developed at different rates 2 the rates of change of three soil properties decrease with time these are the texture in different horizons change in added airborne and rain washed dust salinity within the soil profile change in added salts and gypsum and the amount of mechanically shattered rocks 3 soil thickness is established rather rapidly young and older holocene soil have practically the same depth surficial weathering rates appear to remain fairly constant with time 4 in coarse gravel the evolution of reg soils is dependent on added fines and salts of airborne origin and the resultant changing hydrologic regime in the soil profile the run off infiltration ratio changes as more fines and salts are added to the soil profile and as desert pavement develops 5 surficial features and fine clay in the soil profile may be used for approximate dating of otherwise undatable holocene alluvial surfaces salts and gypsum content should be cautiously used in a rather general way

platinum group element geochemistry of intraplate basalts from the aleppo plateau nw syria early middle miocene intraplate basalts from the aleppo plateau nw syria have been analysed for their platinum group elements pges they contain extremely low pge abundances comparable with most alkali basalts such as those from hawaii and mid ocean ridge basalts the low abundances together with high pd ir pt ir ni ir cu pd y pt and cu zr are consistent with sulphide fractionation which likely occurred during partial melting and melt extraction within the mantle some of the basalts are too depleted in pges to be explained solely by partial melting of a primitive mantle like source such ultra low pge abundances however are possible if the source contains some mafic lithologies many of the basalts also exhibit suprachondritic pd pt ratios of up to an order of magnitude higher than primitive mantle and chondrite an increase too high to be attributable to fractionation of spinel and silicate minerals alone the elevated pd pt associated with a decrease in pt but not ir and ru are also inconsistent with removal of pt bearing pge minerals or alloys which should have concurrently lowered pt ir and ru in contrast melting of a metasomatized source comprising sulphides whose pt and to a lesser extent rh were selectively mobilized through interaction with silicate melts may provide an explanation

weathering and soil development on fan surfaces as a function of height above modern drainageways roan mountain north carolina abstract a relative age chronosequence has been established for fan surfaces on the west and south piedmont slopes of roan mountain north carolina based on measurements of weathering and soil development indices at 20 sites in addition to standard soil properties measurements were made of amphibolite clast weathering rind thickness maximum surface boulder size and mean size and sorting of a 10 kg whole sediment sample from the c horizon soils lacking bt horizons occur only at high altitudes at or near the heads of young fans excepting these locations the youngest fan surfaces have soils with bt horizons generally less than 60 cm thick hues of 10 7 5yr maximum clay contents less than 35 percent rind thicknesses less than 1 2 mm and maximum boulder diameters of 1 2 m soils of the oldest fan surfaces have bt horizons 75 200 cm thick hues of 5 2 5yr rind thicknesses of 6 14 mm maximum clay contents of 40 60 percent and maximum boulder diameters less than 0 75 m although the youngest fan surfaces are close to the level of modern drainageways the oldest stand as much as 20 m above these drainageways and are obviously relict features an index of fan height above modern drainageways was devised that combines height above lateral drainageways with height above the main stream of the valley into which the fan debouches many weathering and soil development properties correlate significantly with this height index including weathering rind thickness r 0 86 munsell hue 0 65 maximum percent clay 0 59 graphic mean phi units of whole sediment particle size analysis 0 54 maximum boulder diameter 0 52 maximum percent free iron in b horizon 0 50 and thickness of bt horizon 0 49 a soil weathering soil development index using these parameters shows a 0 82 correlation coefficient with the height index a cluster analysis shows that the 20 sites can be placed into three distinct groups suggesting that the formation of fan surfaces may be episodic on long time scales a comparison of the fan map with a county soils map shows that the oldest fan surface is fairly consistently mapped as dillsboro series but that the younger fan surfaces show no consistent relationship to soils mapping

glacial sequence near mccall idaho weathering rinds soil development morphology and other relative age criteria abstract the sequence of glacial deposits near mccall idaho previously assigned to the pinedale and bull lake glaciations contains deposits of four different ages these ages are defined by multiple relative age criteria including weathering rinds soil development surface rock weathering morainal morphology and loess stratigraphy the thickness of weathering rinds on basaltic clasts is statistically representative and reproducible and can be used to estimate numerical ages following in order of decreasing relation to age are soil development surface rock weathering and moraine morphology the glacial deposits near mccall appear to correspond to times of high worldwide ice volume indicated by the marine oxygen isotope record pilgrim cove and mccall deposits both assigned to the pinedale glaciation are late wisconsin in age perhaps 14 000 and 20 000 years respectively they represent a rare case in which deposits of pinedale age can be separated by relative age data timber ridge deposits assigned to the bull lake glaciation have subdued but well preserved morainal morphology relative age data indicate that they are pre wisconsin in age probably about 140 000 150 000 years old although we cannot exclude an older age williams creek deposits are clearly distinct from and intermediate in age between mccall and timber ridge deposits weathering rinds and the inferred ages of the other deposits suggest an early wisconsin age for williams creek deposits

changes in the content and composition of pedogenic iron oxyhydroxides in a chronosequence of soils in southern california abstract studies of the pedogenic iron oxyhydroxides in suites of latest holocene to middle pleistocene soils formed on fluvial deposits of the transverse ranges southern california indicate that the content and composition of iron oxyhydroxide change in a systematic manner analysis of total secondary free iron oxides dithionite extractable fe 2 o 3 d and ferrihydrite oxalate extractable fe 2 o 3 o shows that 1 a single logarithmic model y a b log x or double logarithmic model log y a b log x where y is the total mass of pedogenic fe oxides g cm 2 soil column and x is soil age describes the rate of increase in fe 2 o 3 d with time 2 the fe 2 o 3 d content correlates linearly with soil reddening and clay content 3 the fe 2 o 3 o fe 2 o 3 d ratio which indicates the degree of fe oxide crystallinity is moderately high to very high 0 22 0 58 in middle holocene to latest pleistocene soils and progressively decreases to less than 0 10 in older soils 4 the value of the fe 2 o 3 o fe 2 o 3 d ratio also appears to be infuenced by climate and 5 temporal changes in fe oxide content and mineralogy are accompanied by related systematic changes in clay mineralogy and organic matter content these relationships are attributed to a soil environment that must initially favor ferrihydrite precipitation and or organic matter fe complexation subsequent transformation to hematite causes increasingly intense reddening and a concomitant decrease in the fe 2 o 3 o fe 2 o 3 d ratio the results demonstrate that iron oxide analysis is useful for numerical age studies of noncalcic soils and shows potential as an indicator of paleoclimates

climatic implications of alternating clay and carbonate formation in semiarid soils of south central montana abstract evidence for climatic change is found in petrographic thin sections from soils formed on glaciofluvial deposits of rock creek and the lower clarks fork montana these soils presently in a semiarid climate range from late pliocene to holocene in age and have undergone periodic fluctuations in soil moisture caused by climatic changes in the lower parts of soil b horizons accretion of illuvial layers of clay argillans occurs mainly during wet glacial climatic periods whereas carbonate precipitates mainly during dry interglacial climatic periods thin section studies of the argillan and carbonate layers show that 1 post pinedale soils that have formed only in the present interglacial climate contain areas of secondary carbonate unrelated to argillans 2 soils formed on outwash of successively older glaciations contain proportionately more alternating layers of argillans and carbonate and 3 the maximum number and sequence of layers in a soil correspond to the number of local cycles of glacial outwash deposition and subsequent stream incision that followed the beginning of soil formation these cycles are inferred to correspond to local glacial interglacial fluctuations the correspondence between the microscopic record and the glacial outwash record for rock creek suggests that some of the climatic changes seen in the marine oxygen isotope record did not strongly affect the study area

boulder streams debris fans and pleistocene climate change in the blue ridge mountains of central virginia the west slope of the blue ridge mountains in central virginia is a polygenetic landscape containing interglacial and periglacial features this paper proposes a general model relating the distribution and origin of hillslope and toeslope quaternary landforms to climatically influenced geomorphic processes two generations of interglacial debris fans in the study area differ in their degree of soil development and clast weathering boulder streams which clog debris flow chutes for the upper debris fans are interpreted as solifluction features formed during successive periglacial episodes growth of the boulder streams and associated talus slopes can influence the magnitude and frequency of debris flows and fan formation during interglacials

morphological and chemical characteristics of soil catenas on pinedale and bull lake moraine slopes in the salmon river mountains idaho abstract morphological and chemical properties of soils developed on moraines of granitic composition and forested with lodgepole pine in bear valley idaho change significantly with age and slope position soil development on pinedale and bull lake moraine slopes of similar curvature and steepness was assessed at the summits shoulders backslopes and footslopes of both catenas and at the toeslope of the bull lake catena many soil properties show trends in development with both age and slope position these properties include clay content clay film development color plagioclase weathering and dithionite citrate extractable iron fed the degree of development of all these properties is greater on the bull lake catena relative to that on the pinedale catena this trend reflects increased soil development with age on both catenas development of soil properties is commonly highest at the footslope or toeslope sites and minimum at the backslope site downslope changes are attributed to both colluviation and pedogenic processes including sorting of sediments during downslope transport greater accumulation of eolian materials transported to downslope sites by surface processes and greater in situ weathering of mineral grains at the footslope and toeslope sites

neoarchean convergent margin ni cu mineralization axis lake and nickel king ni cu deposits in the south rae craton of the canadian shield abstract the southern portion of the rae craton in the canadian shield is host to multiple ca 2 63 ga ni cu rich metamorphosed mafic intrusions with noritic noritic anorthositic and pyroxenitic compositions including those hosting the undeveloped axis lake and nickel king deposits found in northern saskatchewan and southeast northwest territories in order to understand the setting of these intrusions and their concomitant mineralization we investigated their geochemical and isotopic characteristics mineralized intrusions at axis lake and nickel king are metamorphosed up to granulite facies with local partial melting the intrusions preserve whole rock major element geochemistry consistent with a sub alkaline basaltic composition e g sio2 46 54 wt tio2 the nd isotope values of the axis lake intrusion ndt2630 0 3 to 2 1 are more juvenile and closer to the depleted mantle value relative to those of the nickel king deposit ndt2630 2 4 to 0 4 this agrees with their also distinctive th yb and nb yb distributions suggesting oceanic and continental arc like settings respectively the axis lake and nickel king nd isotope compositions are indistinguishable from other arc like 2 61 to 2 58 ga mafic to felsic intrusions and volcanic rocks recognized in the rae craton and the neighboring chesterfield block the age spatial distribution and geochemistry of the studied intrusions coincide with the initial stages of a recently defined 2 63 2 60 ga continental arc the roots of which are found in the south rae craton our data indicate that neoarchean intrusions with an arc like geochemistry may be a significant exploration target in the rae craton this broadens possible host suites beyond the established paleoproterozoic rift related rocks most commonly considered as the prime target for ni cu pge mineralization

local topography and erosion rate control regolith thickness along a ridgeline in the sierra nevada california the ridgelines of mountain ranges are a source of geomorphic information unadulterated by the arrival of sediment from upslope studies along ridgecrests therefore can help identify and isolate the controls on important regolith properties such as thickness and texture a 1 5 km section of ridgeline in the sierra nevada ca with a tenfold decrease in erosion rate inferred from ridgetop convexity provided an opportunity to conduct a high resolution survey of regolith properties and investigate their controls we found that regolith along the most quickly eroding section of the ridge was the rockiest and had the lowest clay concentrations furthermore a general increase in regolith thickness with a slowing of erosion rate was accompanied by an increase in biomass changes in vegetation community broader ridgeline profiles and an apparent increase in total available moisture the greatest source of variation in regolith thickness at the 10 100 m scale however was the local topography along the ridgeline with the deepest regolith in the saddles and the thinnest on the knobs because regolith in the saddles had higher surface soil moisture than the knobs we conclude that the hydrological conditions primarily driven by local topography i e rapid vs slow drainage and water storage potential provide the fundamental controls on regolith thickness through feedbacks incorporating physical weathering by the biota and chemical weathering moreover because the ridgeline saddles are the uppermost extensions of first order valleys we propose that the fluvial network affects regolith properties in the furthest reaches of the watershed

suggested terminology for quaternary dating methods abstract classification of quaternary dating methods should be based on the level of quantitative information and the degree of confidence contained in the age estimates produced by the dating methods we recommend the use of the terms numerical age calibrated age relative age and correlated age to describe these levels we also classify dating methods by type into sideral isotopic radiogenic chemical and biological geomorphic and correlation methods the use of absolute is inappropriate for most dating methods and should be replaced by numerical the use of date should be minimized in favor of age or age estimate we recommend use of the abbreviations ka and ma for most ages calender dates can be used where appropriate and yr b p can be used for radiocarbon ages

evolution of reg soils in southern israel and sinai abstract reg soils mostly camborthids and gypsiorthids cover some 15 of the negev and sinai deserts analytical data of seven profiles on depositional surfaces of increasing age in the negev show clear relationships between ages of surfaces and soil profile features exemplified in the development of the cambic salic and gypsic horizons the youngest soil a coarse desert alluvium soil typic torriorthent of dry wadi beds up to a few thousand years old has little profile differentiation and is generally non saline or slightly saline on the higher terraces connected with the lisan formation about 70 000 12 000 years b p clear profile differentiation and the beginning of development of cambic horizons can be discerned evident in their colour textural p differences the soils are already saline and somewhat gypsiferous both soils are not yet defined as regs because of their negligible or restricted profile differentiation reg soils on the older and higher geomorphic surfaces in the arava rift valley several hundred thousand years old have well differentiated profiles with cambic salic and gypsic horizons below their stony desert pavements typical reg soils have light coloured vesicular horizons over mellow very pale brown loam frequently with laminar structure almost completely stone free layers the reddish brown loamy to clay loam b horizons are very saline and show intensive salt weathering of gravels gypsic and petrogypsic horizons occur at depth such reg soils represent the stable surfaces and soils of deserts and were developed over a long period of desert weathering

hillslope response to knickpoint migration in the southern appalachians implications for the evolution of post orogenic landscapes the southern appalachians represent a landscape characterized by locally high topographic relief steep slopes and frequent mass movement in the absence of significant tectonic forcing for at least the last 200 ma the fundamental processes responsible for landscape evolution in a post orogenic landscape remain enigmatic the non glaciated cullasaja river basin of south western north carolina with uniform lithology frequent debris flows and the availability of high resolution airborne lidar dems is an ideal natural setting to study landscape evolution in a post orogenic landscape through the lens of hillslope channel coupling this investigation is limited to channels with upslope contributing areas 2 7 km2 a conservative estimate of the transition from fluvial to debris flow dominated channel processes values of normalized hypsometry hypsometric integral and mean slope vs elevation are used for 14 tributary basins and the cullasaja basin as a whole to characterize landscape evolution following upstream knickpoint migration results highlight the existence of a transient spatial relationship between knickpoints present along the fluvial network of the cullasaja basin and adjacent hillslopes metrics of topography relief slope gradient and hillslope activity landslide frequency exhibit significant downstream increases below the current position of major knickpoints the transient effect of knickpoint driven channel incision on basin hillslopes is captured by measuring the relief mean slope steepness and mass movement frequency of tributary basins and comparing these results with the distance from major knickpoints along the cullasaja river a conceptual model of area elevation and slope distributions is presented that may be representative of post orogenic landscape evolution in analogous geologic settings importantly the model explains how knickpoint migration and channel hillslope coupling is an important factor in tectonically inactive i e post orogenic orogens for the maintenance of significant relief steep slopes and weathering limited hillslopes copyright 2011 john wiley sons ltd

holocene and late pleistocene slip rates on the san andreas fault in yucaipa california using displaced alluvial fan deposits and soil chronology we derived slip rates on the san andreas fault from displacement of alluvial fans and from approximate dating of the fans by the degree of soil development distinctive red purple sedimentary rocks of the miocene potato sandstone exposed on yucaipa ridge in the san bernardino mountains were transported down wilson creek and shed across the modern trace of the san andreas fault soils developed in alluvial fan deposits contain red purple clasts of the potato sandstone and are progressively more developed toward the north west as a result of fault displacement we used soil development to estimate the ages of these alluvial fans and underlying deposits using dated soils from cajon pass and from the central valley of california we estimated ages of wilson creek deposits using a statistical method of maximum likelihood these methods also utilize monte carlo simulations of larger data populations and account for soil variability uncertainty of calibration dates and the limited number of soils described and sampled resulting age estimates have considerable as much as 80 uncertainty resulting largely from quality of calibration dates slip rates for three time intervals were obtained by restoring the medial axis of each displaced fan to wilson creek maximum slip rates were also obtained by restoring the westernmost extent of each fan to wilson creek best estimate rates averaged to the present for 0 to 14 000 yr are 14 to 25 mm yr for 0 to 30 000 yr 22 to 34 mm yr and for 0 to 65 000 or 90 000 yr 12 to 16 mm yr maximum rates averaged to present for 0 to 14 000 yr are as high as 65 mm yr older rates are as high as 80 mm yr when holocene rates are accounted for actual or incremental slip rates for the interval 30 000 to 65 000 or 90 000 yr b p are probably 6 to 13 mm yr these data tentatively suggest that slip rates on the modern trace have increased during the late quaternary uncertainties in slip and age data however allow for rates to have been nearly constant or even decreasing toward the present

field based and spectral indicators for soil erosion mapping in semi arid mediterranean environments coastal cordillera of central chile the coastal cordillera of central chile is naturally sensitive to soil erosion due to moderate to steep slopes intense winter rains when the vegetation cover is scarce and deeply weathered granitic rocks in 1965 60 per cent of its surface was moderately to very severely eroded today this process is still largely active but no data are currently available to evaluate the real extent distribution and severity of soil degradation on a regional scale this information is vital to support efficient soil conservation plans a multi scale approach was implemented to produce regional land degradation maps based on remote sensing technologies fieldwork has shown that the surface colour or redness and the density of coarse fragments are pertinent erosion indicators to describe a typical sequence of soil degradation in the context of mediterranean soil developed on granitic materials and micaschists field radiometric experiments concluded that both factors influence the reflectance of natural surfaces and can be modelled using radiometric indices accessible from most satellites operating in the optical domain i e redness index and brightness index finally the radiometric indices were successfully applied to spot images to produce land degradation maps only broad classes of erosion status were discriminated and the detection of the degradation processes was only possible when most of the fertile layer had already been removed this technology provides decision making information required to develop regional soil conservation plans and to prioritize actions between catchment areas especially in vast inter tropical regions where spatialized data are not always readily available copyright 2006 john wiley sons ltd

progressive and regressive pedogenesis and complex soil evolution abstract the simultaneous operation of regressive and progressive pedogenetic pathways raises the possibility that soil evolution may exhibit patterns far richer and more complex than increasing development over time this possibility is explored via a numerical model incorporating the relative rates of progressive and regressive pedogenesis and feedbacks between these rates and the degree of soil development this model may exhibit deterministic chaos and sensitive dependence on initial conditions with realistic parameter values variations in profile development in a region of the north carolina coastal plain where soil forming factors are relatively constant is consistent with deterministic chaos chaotic soil evolution suggests that soil development may reflect the interplay between progressive and regressive soil forming processes in addition to or instead of the age of a surface or deposit the former may produce a state of development which is unique to a particular time sensitively dependent on the unknown initial conditions and not simply related to age soils and their genetic signatures as indicators of relative ages and quaternary environments may need to be reinterpreted in this light

sedimentologic and geomorphic variations in storm generated alluvial fans howgill fells northwest england in june 1982 a storm with a return period greater than 100 yr but lasting less than 2 5 hr destabilized hillslopes and produced a suite of geomorphologically and sedimentologically diverse alluvial fans thirteen major fans were deposited at the tributary junctions between small 2 catchments and two north flowing headwater streams of the river lune northwest england storm generated fans spread over or became inset into older stable fans and produced localized vertical accretion of as much as 3 m and lateral accretion of as much as 100 m sedimentary processes operating during deposition involved debris flow transitional flow and streamflow six facies types are recognized on the basis of depositional topography sedimentary texture and fabric and matrix content viscous debris flow d1 dilute debris flow d2 transitional flow t1 fluvial bars and lobes s1 s2 and fluvial sheet gravels s3 regionally streamflow deposition prevails over debris flow deposition and type s3 facies has the greatest areal extent temporal and spatial variations in facies deposition during the storm however resulted from water sediment ratio variations fan deposition involved an early phase of debris flow to transitional flow due to large inputs of sediment from hillslope failures this was followed by a systematic change to more dilute conditions resulting in streamflow deposition and eventually in channel incision a significant amount of geomorphic work and complex variations in sedimentary processes during the storm resulted in part from extensive overland flow and hillslope destabilization discriminant analyses indicate that catchment size channel gradient and percentage of area eroded during the storm controlled whether debris flow or streamflow facies dominated a fan sequence smaller steeper catchments had a greater percentage of the area yielding sediment and are dominanted by debris flows whereas larger catchments produced more runoff resulting in dilution and streamflow the results indicate that the facies sequences and fan entrenchment in the howgill fells which are typically considered products of longer term climatic change or tectonics in other localities are here primarily affected by thresholds related to catchment geomorphology by the type of sediment available and by the position within the storm cell

geochemistry of platinum group elements of the zoned ultramafic alto condoto complex northwest colombia the alto condoto complex dated at 20 ma is a zoned ultramafic intrusion with a magmatic rock sequence ranging from dunite to hornblendite the different petrographic units are cumulates formed by fractional crystallization processes parts of the central dunite are anomalously enriched in ptfe alloys and to a minor degree in iros alloys all other lithologic units of the complex display normal fractionation trends of platinum group elements pge with a general increase of total pge from wehrlite to horn blende clinopyroxenite and hornblendite this normal trend is best described by increasing pd and decreasing ir abundances the controlling factor for pge mineralization in zoned ultramafic complexes is probably an effective ptfe alloy precipitation during the crystallization of olivine this may be initiated by rapid tectonic movements causing pressure decrease and overheating of the magma with pge alloy formation as a result of the f sub o 2 shift during olivine crystallization