valley fill alluviation during the little ice age ca a d 1400 1880 paria river basin and southern colorado plateau united states valley fill alluvium deposited from ca a d 1400 to 1880 is widespread in tributaries of the paria river and is largely coincident with the little ice age epoch of global climate variability previous work showed that alluvium of this age is a mappable stratigraphic unit in many of the larger alluvial valleys of the southern colorado plateau the alluvium is bounded by two disconformities resulting from prehistoric and historic arroyo cutting at ca a d 1200 1400 and 1860 1910 respectively the fill forms a terrace in the axial valleys of major through flowing streams this terrace and underlying deposits are continuous and interfinger with sediment in numerous small tributary valleys that head at the base of hillslopes of sparsely vegetated weakly consolidated bedrock suggesting that eroded bedrock was an important source of alluvium along with in channel and other sources paleoclimatic and high resolution paleoflood studies indicate that valley fill alluviation occurred during a long term decrease in the frequency of large destructive floods aggradation of the valleys ended about a d 1880 if not two decades earlier with the beginning of historic arroyo cutting this shift from deposition to valley entrenchment near the close of the little ice age generally coincided with the beginning of an episode of the largest floods in the preceding 400 500 yr which was probably caused by an increased recurrence and intensity of flood producing el nino events beginning at ca a d 1870

late quaternary arroyo formation and climate change in the american southwest arroyos entrenched ephemeral streams that form in desert environments first appeared in the arid and semiarid american southwest after 8000 14 c yr b p for at least 7 k y prior to that time climate vegetation and groundwater conditions were not conducive for arroyo formation along the floors of desert valleys after a hiatus in arroyo formation the frequency of arroyo cutting and filling increased dramatically after 4000 14 c yr b p the early holocene arroyos and increased frequency of arroyo incision after 4000 14 c yr b p are related to the establishment and changes in postglacial vegetation climate and groundwater conditions as a result arroyo sequences preserve a record of large scale climate change and small scale climatic perturbations that occurred during the holocene human modification of valley flood plains is an additional factor that contributed to mid nineteenth and early twentieth century arroyo cutting

late quaternary paleotemperatures derived from a speleothem from cango caves cape province south africa abstract an oxygen isotope temperature record over a large part of the past 30 000 yr has been obtained for the southern cape province of south africa by combining data on the isotopic composition of a stalagmite from a deep cave with that of a confined groundwater aquifer in the same region results show that temperatures during the last glacial maximum were on average about 6 c lower than those today with peaks up to 7 c lower a detailed analysis of the past 5000 yr suggests multiple fluctuations with generally lower temperatures 1 2 c around 4500 and 3000 yr b p the carbon isotopic composition of the stalagmite indicates significant vegetation changes between the late pleistocene and today and also during the second half of the holocene

stages in the life of a magnetic grain sediment source discrimination particle size effects and spatial variability in the south african karoo mineral magnetic properties are commonly used to trace the sources of river and lake sediments with the aim of identifying areas of a catchment experiencing the high rates of soil loss in some areas however there is poor understanding of how magnetic properties are able to discriminate between potential sediment sources the basis for mineral magnetic source discrimination between topsoils and subsurface material over different rock parent materials was investigated in the south african karoo the effects of particle size soil development alteration and diagenesis processes on the source discrimination were investigated good discrimination up to 100 correct discrimination was found between the sedimentary sources soils and subsurface and dolerite soils due to much higher concentrations of magnetic minerals in the dolerite there was little evidence of alterations to magnetic properties in subsurface sediments resulting in only a small ability of properties to differentiate between surface and subsurface sources it was found that during the development of topsoils there was a loss of high coercivity weakly magnetic grains and an enrichment in small superparamagnetic and stable single domain grains particle size was strongly related to magnetic properties with almost all of the secondary superparamagnetic and stable single domain grains created during soil formation being concentrated in the 125 m fractions the small ability of sediment to discriminate between surface and subsurface sources was based upon the dissolution of primarily fd and arm carrying grains in the 32 m fractions and to a lesser extent the 63 32 m fraction as a result it was recommended that source tracing with the 32 m fraction of soils and sediment should be treated separately from the 63 32 m and larger particle size fractions the relationships between particle size and magnetic properties were fairly consistent in all soil samples in each source group raising the possibility that reliable correction factors could be developed for each source group

comment on the bude formation sw england a three dimensional intra formational variscan imbricate stack by g e lloyd and n chinnery journal of structural geology 24 2002 1259 1280

alluvial terrace development and changing landscape connectivity in the great karoo south africa insights from the wilgerbosch river catchment sneeuberg dendritic channel networks in the wilgerbosch river catchment draining the south side of the sneeuberg south africa are deeply incised exposing terrace fills of varying thickness and extent channel long sections exhibit stepped profiles where resistant rock strata cross valley floors but are now partially or completely breached using a combination of aerial image analysis geomorphological mapping sedimentological investigations field logging grain size and magnetic susceptibility analyses and geochronology osl 14c this study demonstrates the patterns and controls on erosion and sedimentation and to a lesser extent the age structure of fills in two low order tributaries africanders kloof and wilgerbosch kloof and several reaches of the higher order wilgerbosch river a conceptual model of terrace development in relation to changing conditions of connectivity is presented valley headwaters are dominated by discontinuous palaeochannel and floodout sediments whilst in second to fourth order tributaries four sedimentologically and stratigraphically distinct terrace fills that exceed the scale and complexity of deposits on the northward side of the sneeuberg were identified and analysed the early part of this regional terrace succession highlights the importance of interactions between periglacial and fluvial activity on cut fill and pedogenesis around the time of the deglacial period terrace development is shown to have been a complex response to reconnection of the channel network with upland colluvial stores resulting in the valleys becoming choked with sediment this caused a rise in groundwater and formation of extensive calcretised rootmats on valley floors and slopes acting to blanket terraces 1 and 2 the thickness and longevity of this blanket is shown to restrict depth of incision in subsequent phases t3 t4 the deposits in these headwater valleys have until now been overlooked as a source of palaeoenvironmental information this study is the first to demonstrate the role and importance of changing connectivity in cut and fill phases that predate the late eighteenth century european incursion in the sneeuberg

ferrimagnetic iron sulfide formation and methane venting across the paleocene eocene thermal maximum in shallow marine sediments ancient west siberian sea

origin of ooidal ironstones in relation to warming events cretaceous eocene bakchar deposit south east western siberia abstract an integrated study involving petrographical mineralogical and geochemical investigations proposes the origin of the bakchar ironstone deposit by upward migration of a mixture of fe rich brine and hydrothermal fluid through marine sediments trace element concentrations of the ironstone deposits rule out continental derivation of fe while high ree concentrations indicate mixed hydrogeneous and hydrothermal source three main types of ironstone within the bakchar deposit are characterized by distinct mineralogical assemblage of authigenic minerals corresponding to oxic methanic and weakly sulfidic dysoxic conditions changing redox conditions of the depositional environment methane seepage in warm seawater and availability of iron influx possibly determined the final mineralogy of three varieties of ironstones the association of siderite with ferrimagnetic sulfides like greigite and pyrrhotite in type 1 ore indicate anaerobic oxidation of methane with limited bacterial sulfate reduction the ironstone deposits of narym kolpashevo and bakchar are contemporaneous with geological events like ocean anoxic event 3 oae 3 cretaceous paleogene k pg boundary and palaeocene eocene thermal maximum petm respectively all corresponding to warm seawater conditions

sub millimeter heterogeneity of yttrium and chromium during growth of semi pelitic garnet x ray maps of yttrium and chromium in two garnets from a semipelitic schist from central nepal reveal parallel spiraling bands of high and low concentration 10 30 m wide this zoning mimics similar concentration bands defined by foliation in the matrix outside the garnets the garnets apparently incorporated the matrix zoning intact during growth at conditions up to lower amphibolite facies these observations and interpretations indicate that yand cr concentrations remained heterogeneous at the scale of tens of micrometers during breakdown of matrix minerals and growth of garnet this conclusion extends results of previous work which showed that y and cr do not homogenize at the centimeter to millimeter scale during metamorphism to amphibolite facies the width of the concentration bands in the garnets places a constraint on the maximum effective intracrystalline diffusion coefficient for both y and cr in garnet of about 10 21 cm 2 s for peak metamorphic conditions of about 9 kbar at 5708c different concentrations of yand cr at different positions around the rim of each garnet indicate disequilibrium for these elements between garnet and matrix phases the presence of an internal foliation defined by the yand cr concentration bands rules out pre kinematic garnet growth most useful in conjunction with other indicators zoning of these elements in garnet is thus a tool for deciphering the relative timing of deformation and garnet growth

geomorphological palaeoenvironments of the sneeuberg range great karoo south africa sedimentary sequences within headwater valleys on the landward side of the great escarpment of south africa are elucidated and their significance as indicators of environmental change is assessed this study focuses on the sneeuberg range the most prominent mountain range in the semi arid central great karoo valley fills of a hitherto unrecognised complexity and of a greater age than any previously recorded in the central great karoo are reported three phases of deposition spanning the late pleistocene up to the present are documented from sites where gully erosion has incised the valley fills the earliest depositional phase is represented by deeply weathered calcretised gravel deposits which probably were emplaced by debris flow and fluvial processes in the form of a fan these deposits subsequently were buried by finer grained largely unconsolidated sediment with much of this emplacement occurring during the holocene there is evidence for phases of landscape stability and instability within this facies finally sheetwash has removed fine grained sediments from valley flanks and has deposited it either on valley bottoms or in presently active gullies this process appears to be ongoing and is the subject of current investigation the sedimentary deposits are interpreted as representing a wide range of palaeoenvironmental conditions that have prevailed within the central great karoo since the penultimate glaciation copyright 2003 john wiley sons ltd

processes of arroyo filling in northern new mexico usa we documented arroyo evolution at the tree trench and arroyo scales along the lower rio puerco and chaco wash in northern new mexico usa we excavated 29 buried living woody plants and used burial signatures in their annual rings to date stratigraphy in four trenches across the arroyos then we reconstructed the history of arroyo evolution by combining trench data with arroyo scale information from aerial imagery light detection and ranging lidar longitudinal profiles and repeat surveys of cross sections burial signatures in annual rings of salt cedar and willow dated sedimentary beds greater than 30 cm thick with annual precision along both arroyos incision occurred until the 1930s in association with extreme high flows and subsequent filling involved vegetation development channel narrowing increased sinuosity and finally vertical aggradation a strongly depositional sediment transport regime interacted with floodplain shrubs to produce a characteristic narrow trapezoidal channel the 55 km study reach along the rio puerco demonstrated upstream progression of arroyo widening and filling but not of arroyo incision channel narrowing or floodplain vegetation development we conclude that the occurrence of upstream progression within large basins like the rio puerco makes precise synchrony across basins impossible arroyo wall retreat is now mostly limited to locations where meanders impinge on the arroyo wall forming hairpin bends for which entry to and exit from the wall are stationary average annual sediment storage within the rio puerco study reach between 1955 and 2005 was 4 8 10 5 t yr 16 of the average annual suspended sediment yield and 24 of the long term bedrock denudation rate at this rate the arroyo would fill in 310 yr

climate and ephemeral stream processes twentieth century geomorphology and alluvial stratigraphy of the little colorado river arizona during the first 40 years of the twentieth century erosion was the dominant geomorphic process affecting the morphology of the little colorado river channel the discharge regimen was one of frequent large floods and high annual discharge that created a wide sandy channel free of vegetation in the 1940s and early 1950s average annual precipitation declined reducing annual discharge to about 57 of that of the preceding period as well as reducing the frequency of large floods the channel adjusted to the new hydrologic regimen by reducing its width parts of the channel were frequently dry and riparian vegetation primarily nonnative salt cedar became established on the higher channel surfaces precipitation and discharge thereafter increased and aggradation by overbank deposition was the primary geomorphic process as indicated by accretion of 2 to 5 m of flood plain alluvium between 1952 and 1978 events of 1980 however suggest that the flood plain has ceased to accrete although climate has not fluctuated the flood plain has probably reached a critical height above the channel beyond which further accretion is unlikely under the existing discharge regimen the recent history of the little colorado broadly suggests that flood plain development was initiated by climatically induced hydrologic fluctuations flood plain deposits in the stratigraphic column of such ephemeral streams may record repeated adjustments to altered hydrologic conditions

early diagenesis of inner shelf phosphorite and iron silicate minerals lower cretaceous of the orpheus graben southeastern canada implications for the origin of chlorite rims wells in the orpheus graben encountered the most proximal part of the deltaic lower cretaceous rocks of the scotian basin more distal sandstones are important gas reservoir rocks with good reservoir quality where fe rich chlorite chamosite rims on framework grains have inhibited quartz cementation cutting samples from the orpheus graben show the presence of fe rich sheet silicates berthierine or chamosite and early diagenetic phosphorite these minerals were analyzed by electron microprobe and their textures were mapped with backscattered electron images studies in the north sea have shown a relationship between high phosphorus and the presence of good chlorite rims in reservoir rocks the mineralization of pore water phosphorus instead of its return to seawater is favored by fe rich sediments and sorption on iron oxides during shallow sea floor diagenesis the fe ti and p contents are uncommonly high in scotian basin shales compared with global average shale compositions the uncommon occurrence of inner shelf phosphorite in this study is interpreted to be a consequence of the same high fe content of the sediment that also favors the formation of fe rich sheet silicates in rapidly deposited deltaic sandstones of the offshore reservoirs the dominance of type 3 kerogen led to sulfate depletion occurring at depths of tens of meters and a corresponding great thickness for overlying eh oxidation potential controlled diagenetic zones the thick fe reduction zone allowed the formation of early diagenetic berthierine which on burial formed the chamosite rims that resulted in the improved reservoir quality in sandstones the distribution of phosphorus minerals may be an indicator of conditions suitable for berthierine formation

anastomosing channels and arroyo development on the nogoa river central queensland australia abstract it is widely accepted that european settlement in australia has had a major impact on river channels for many parts of australia records are available which permit the history of channel changes to be reconstructed over most of the post settlement period in this paper the history of changes on part of the nogoa river in central queensland is described from the first european contact until the present the river channel at this site has changed from an anastomosing pattern to a single large channel arroyo there is evidence to suggest that such changes have occurred also in the past but an unusual feature of the present incision phase is that incision is synchronous throughout the region this may have been triggered by the introduction of cattle which naturally congregate in the moister valley bottoms in this otherwise dry environment the changes observed here reflect those reported for the semiarid regions of the usa a linking factor appears to be hydrological behaviour characterised by high levels of variability in the annual flood series which appears to render such streams more sensitive to disturbance than those with less variable flood behaviour

recent landscape history in arid western new south wales australia a model for regional change accelerated erosion by wind and water has taken place in arid western new south wales australia since the introduction of domestic and feral herbivores by europeans in the nineteenth century this action led to widespread soil loss by sheetwash rilling gullying and aeolian deflation upland creek systems formerly comprising shallow sinuous channels are now entrenched into alluvial fills on the valley floor radiocarbon dating of charcoal from aboriginal cooking pits exposed by this erosion indicates that the current phase of incision of the valley floor has occurred since grazing of domestic animals began about 140 years ago stratigraphic evidence is presented which suggests that this type of incision gullying or arroyo cutting in the valley floor may not have occurred before within the 20 000 year sedimentary history of the valley fills studied channel enlargement and knickpoint retreat initiated by these changes is ongoing and the implications of this for land and heritage management in the region are discussed a conceptual model is presented which summarises the hydrogeomorphic changes which have occurred in upland catchments in the region as a result of changes in landcover

long term studies of land degradation in the sneeuberg uplands eastern karoo south africa a synthesis for the past 15 yr the sneeuberg uplands in the eastern karoo south africa have been a focus for research on land degradation by the above authors and other colleagues earlier work in the karoo emphasised vegetation change whereas we concentrate on physical changes to the landscape at the small catchment scale e g bare degraded areas badlands and gully donga systems analysis of sedimentation in farm dams allows for reconstruction of environmental histories using 210pb 137cs geochemical and mineral magnetic properties of the sediments erosion rates on badlands are monitored using arrays of erosion pins sediment source tracing within small catchments points to the importance of hillslope sources and the relative erosional inactivity of gully systems sediment supply from hillslope and colluvial sources is maintained by high rates of weathering on mudstones and sandstones current degradation should be viewed in the context of a c 200 yr history of overgrazing by european style stock farming and limited areas of former cultivation in the valleys grazing pressures are now much reduced but the loss of soils and vegetation suggests that landscape recovery will require several decades additional drivers of past degradation are likely to have been periods of drought and fire natural and managed and a gradual increase in both rainfall intensity and the frequency of extreme rainfall events the future of the degraded sneeuberg landscape will depend on future farming practices desirable options include more sustainable livestock practices adoption of wildlife farming and other more benign regimes involving mixes of agriculture tourism and wildlife protection together with landscape rehabilitation measures

hydrological response of a dryland ephemeral river to southern african climatic variability during the last millennium a long term flood record from the buffels river the largest ephemeral river of nw south africa 9250 km2 was reconstructed based on interpretation of palaeoflood documentary and instrumental rainfall data palaeoflood data were obtained at three study reaches with preserved sedimentary evidence indicating at least 25 large floods during the last 700 yr geochronological control for the palaeoflood record was provided by radiocarbon and optically stimulated luminescence osl dating annual resolution was obtained since the 19th century using the overlapping documentary and instrumental records large floods coincided in the past within three main hydroclimatic settings 1 periods of regular large flood occurrence 1 large flood 30 yr under wetter and cooler prevailing climatic conditions ad 1600 1800 2 decreasing occurrence of large floods 1 large flood 100 yr during warmer conditions e g ad 1425 1600 and after 1925 and 3 periods of high frequency of large floods 4 5 large floods in 20 30 yr coinciding with wetter conditions of decadal duration namely at ad 1390 1425 1800 1825 and 1915 1925 these decadal scale periods of the highest flood frequency seem to correspond in time with changes in atmospheric circulation patterns as inferred when comparing their onset and distribution with temperature proxies in southern africa

the recent history of erosion and sedimentation on the southern tablelands of southeastern australia sediment flux dominated by channel incision abstract as in other regions colonised from europe within the last few centuries australia s vegetation and soils have been dramatically changed by clearing cropping and grazing in southeastern australia particularly on the southern tablelands the impacts of european settlement are clearly manifested by channel incision by using stratigraphic and documentary evidence in conjunction with aerial photographs sediment budgets for the post settlement period have been constructed to define the fluxes and stores of sediment for each of the major geomorphic components of the 136 km2 catchment of jerrabomberra creek near canberra using these budgets and some plausible assumptions it has been possible to approximate the history of both the sediment delivery ratio and sediment yield for this catchment while the quantities estimated in this analysis are approximations the trends through time are credible sediment yield increased rapidly to a peak after european settlement and has returned to a level between the peak and the pre european value the delivery ratio has followed a similar trend the most general conclusion to emerge is that in this landscape both the total sediment flux and the sediment yield of the catchment have been dominated by channel erosion this result is contrary to the findings in many parts of the world where sheet and rill erosion dominates the fluxes the soil conservation implication of these results is clear to control off site effects of erosion the focus must be on the channels

occurrence and origin of minerals in a chamosite bearing coal of late permian age zhaotong yunnan china the minerals found in the no 5 coal late permian from the zhaotong coalfield yunnan province southwestern china have been examined and found to consist mainly of kaolinite pyrite chamosite quartz and calcite with trace amounts of illite and mixed layer illite smectite the proportion of chamosite in clay minerals ranges from 32 to 56 wt with an average of 46 wt chamosite is distributed not only in collodetrinite but also occurs as cell fillings in fusinite semifusinite and telinite the high content and mode of occurrence of chamosite in this mine indicate its formation by interaction of kaolinite with fe mg rich fluids during early diagenesis except for a minor amount of terrigenous quartz most quartz is of authigenic origin and formed from kaolinite desilication the calcite content of the no 5 coal is 1 4 6 3 with an average of 3 and is distributed in collodetrinite and as cell fillings of coal forming plants calcite originated from seawater invasion during peat accumulation pyrite occurs in several ways as massive framboidal isolated enhedral anhedral and euhedral forms in addition the presence of a large amount of pyritized red algae provides strong evidence of seawater invasion during peat accumulation the red algae may have played an important role in the enrichment of sulfur in the coal the characteristic assemblage of minerals in this mine resulted from a unique basinal environment in which the mineral matter was derived from a basaltic source region volcanic activity and seawater transgression during coal formation

discontinuous ephemeral streams abstract many ephemeral streams in western north america flowed over smooth valley floors before transformation from shallow discontinuous channels into deep arroyos these inherently unstable streams of semiarid regions are sensitive to short term climatic changes and to human impacts because hillslopes supply abundant sediment to infrequent large streamflow events discontinuous ephemeral streams appear to be constantly changing as they alternate between two primary modes of operation either aggradation or degradation may become dominant attainment of equilibrium conditions is brief disequilibrium is promoted by channel entrenchment that causes the fall of local base level and by deposition of channel fans that causes the rise of local base level these opposing base level processes in adjacent reaches are maintained by self enhancing feedback mechanisms the threshold between erosion and deposition is crossed when aggradational or degradational reaches shift upstream or downstream extension of entrenched reaches into channel fans tends to create continuous arroyos upvalley migration of fan apexes tends to create depositional valley floors with few stream channels less than 100 years is required for arroyo cutting but more than 500 years is required for complete aggradation of entrenched stream channels and valley floors discontinuous ephemeral streams have a repetitive sequence of streamflow characteristics that is as distinctive as sequences of meander bends or braided gravel bars in perennial rivers the sequence changes from degradation to aggradation headcuts concentrate sheetflow a single trunk channel conveys flow to the apex of a channel fan braided distributary channels end in an area of diverging sheetflow and converging sheetflow drains to headcuts the sequence is repeated at intervals ranging from 15 m for small streams to more than 10 km for large streams lithologic controls on the response of discontinuous ephemeral streams include 1 amount and size of sediment yielded from hillslopes 2 infiltration capacity of valley floor alluvium that influences both the unit stream power available for upstream headcut migration and the attenuation of flashy streamflow events by riparian vegetation in sheetflow reaches and 3 cohesiveness of alluvium which affects headcut and streambank morphology and rates of arroyo extension downcutting and widening initiation of arroyo cutting may be too complex to be attributed to a single cause such as change in mean annual precipitation or grazing by livestock but is most likely associated with a decrease in density of protective plant cover on hillsides and along valley floors relatively larger unit stream power makes downstream reaches more susceptible to initial entrenchment during floods than headwaters reaches and favors persistent arroyos entrenchment continues until an equilibrium longitudinal profile is briefly attained then channel widening occurs streambanks are undercut and aggradation begins

the bude formation sw england a three dimensional intra formational variscan imbricate stack abstract the deformation of the upper carboniferous bude formation sw england is re interpreted in terms of a sedimentary multilayer sequence which represents a compromise between mechanically competent and mechanically incompetent behaviour the chevron folding that characterises the sandstone shale multilayer sequence is shown to be only a part of a more complex regional scale polyphase deformational history that developed at high structural levels in the late variscan orogeny the major tectonic features are thrust faults which are responsible for the imbrication of the original sedimentary pile six distinct thrust sheets are recognised in the 5 km coastal section studied northerly directed thrusts pre date chevron folding whilst structurally necessary southerly propagating back thrusts both pre and post date folding where they post date folding they impose a southerly shear onto the rocks leading to modification of existing folds the significance of these thrust structures has previously been ignored due to their tendency to develop parallel to bedding and to be overprinted by flexural slip features during chevron folding a model is presented that views the bude formation as a three dimensional intra formational imbricate stack which is at any single locality an instantaneous representation of an orogenic front propagating into its own foreland basin

flow resistance and sediment transport by concentrated overland flow in a grassland valley abstract flow resistance and sediment transport data are needed from well vegetated humid environments to evaluate surface wash erosion and channel incision by overland flow in humid environments runoff in valley floors can reach depths of several centimetres but erosion is often limited by dense grass cover intense grazing reduces grass cover but the impacts of this on sediment transport processes are poorly understood we conducted flume experiments in a grassed valley of coastal california to investigate flow resistance and sediment yield under natural conditions and with progressive clipping of grass cover flow resistance has a laminar like relationship with reynolds number but we attribute this to very low velocity beneath submerged stems and not to the state of flow the sediment transport relations provide support for the concept of a threshold shear stress below which erosion is effectively prevented by surface resistance shear stress partitioning suggests that on a densely grassed surface over 90 of flow resistance is exerted on plant stems this effectively prevents sediment transport at boundary shear stresses as high as 1000 1800 dyn cm2 complete clipping of the grass cover reduces the critical shear stress for sediment transport to 11 38 of that under natural conditions continued surface wash erosion and channel initiation are prevented however by strong soil cohesion provided by a dense root mat even with reduction of root density boundary shear stresses of at least 250 430 dyn cm2 are required for channel incision

a 3000 year high resolution stalagmitebased record of palaeoclimate for northeastern south africa high resolution stable isotope variations and growth structure analyses of the last three millennia of a 6600 year stalagmite record at cold air cave makapansgat valley south africa are presented growth layers which are measurable over the last 250 years are shown to be annual the correlation between the width of growth layers and precipitation is strongly positive changes in 18o and 13c are positively correlated and inversely correlated to changes in the colour of the growth layers in the stalagmite variations in colour are directly correlated with mean annual temperature dark colouration is the product of increased temperature and mobilization of organic matter from the soil and is associated with wetter summers and enhanced growth of c4 grasses darker colouring and enriched 18o and 13c reflect a warmer wetter environment whereas lighter colouring and depleted isotopic values are indicative of cooler drier conditions the dominant episode in the 3000 year record is the cool dry 500 year

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

late holocene sediment storage in canyons of the colorado plateau field surveys of ten drainage basins 10 to 1 790 km2 in area in the colorado plateau utah and arizona and repeat photography of 156 fluvial environments providing comparative evidence spanning up to 114 yr reveal that two stratigraphic units characterize the alluvial materials on valley floors an older unit deposited generally between 1250 a d 200 yr and 1880 a d 20 yr was dissected by arroyo development by the early twentieth century a younger unit was deposited generally during the period after approximately 1943 5 yr rates of sedimentation in the 1943 1980 period were almost twice the rates in the 1250 1880 period channel storage rates during the two periods of sedimentation are related to drainage basin area by a power function similar to functions relating slope sediment production and sediment yield to drainage basin area storage rates in the 1943 1980 period were about 50 of the rates of slope sediment production the amount of sediment stored in the two units exhibits a definable spatial pattern source streams with basin areas upstream 10 000 km2 alternatively stored or evacuated moderate amounts of sediment in response to upstream evacuations of sediment from the colorado plateau riparian vegetation change and hydro climatic changes in mountain watersheds outside the plateau region

iron rich carbonate tidal deposits angepena formation south australia a redox stratified cryogenian basin abstract the cryogenian angepena formation ca 650 ma of south australia records deposition in a peritidal environment equivalent to and landward of the balcanoona reef complex and offers valuable insights into shallow marine chemistry during the nonglacial interlude between two global ice ages the sedimentary facies comprise an iron rich marine red bed succession and include red mudcracked dolomitic shales tepee dolostone crossbedded intraclastic ooid grainstone and tepee related sheet cavities with marine cements these facies are interpreted to have been deposited in a cryogenian tidal flat to subtidal setting that is laterally equivalent to the reefal and back reef environments of the balcanoona formation marine cements from this environment are characterized by well preserved non and bright cathodoluminescent zoning and strong negative to slightly positive cerium ce anomalies ce ce we suggest that the angepena formation is indicative of intermittent synsedimentary iron oxide precipitation in an oxidized peritidal environment in an otherwise strongly ferruginous and anoxic oceanic setting large negative ce anomalies develop over a narrower depth range when compared to modern oxic marine settings highlighting the importance of dissolved mn and fe concentrations in controlling the magnitude of the negative ce anomalies overall coupled sedimentological and geochemical evidence suggest a neoproterozoic shallow marine system at the interface of an oxidizing atmosphere and an anoxic ferruginous marine system

mineralogical and compositional characteristics of late permian coals from an area of high lung cancer rate in xuan wei yunnan china occurrence and origin of quartz and chamosite abstract some townships in xuan wei county yunnan province have one of the highest lung cancer mortality rates in china and the epidemic disease in the area has generally been attributed to the polycyclic aromatic hydrocarbons pahs released from domestic coal burning however the cancer causing culprit is not settled as tian tian l 2005 coal combustion emissions and lung cancer in xuan wei china ph d thesis university of california berkeley found nanometer quartz in these coals soot emissions and lung cancer tissues we have conducted mineralogical and geochemical studies of the coals from xuan wei for the purpose of shedding light on the minerals which may be related to the epidemic lung cancer in this paper abundances modes of occurrence and origins of minerals and elements in the coals from two mines in xuan wei have been studied using optical microscope low temperature ashing x ray diffraction analysis scanning electron microscope equipped with energy dispersive x ray spectrometer and inductively coupled plasma mass spectrometry the minerals in the coals are mainly composed of quartz chamosite kaolinite and calcite the particle size of quartz is rather small mostly less than 20 m and it is of authigenic origin chamosite occurs mainly as cell fillings the occurrence of quartz and chamosite indicates that they were derived from the hydrothermal fluids epigenetic calcite is derived from calcic fluids kaolinite is derived mainly from sediment source region of kangdian oldland to the west of coal basin the composition of xuan wei coal is high in sio2 fe2o3 tio2 cao mno v co ni cu and zn the high sio2 content is attributed to quartz and the fe2o3 content to chamosite the high mn and low mg contents in the coal indicate the inputs of hydrothermal fluids cao occurs mainly in epigenetic calcite elements ti co ni cu zn and rare earth elements were derived from the basaltic rocks at sediment source region

sedimentology and oceanography of early ordovician ironstone bell island newfoundland ferruginous seawater and upwelling in the rheic ocean abstract the bell island and wabana groups together comprise a ca 150 m thick succession of interbedded clastic and chemical sedimentary rocks composed of eight distinct lithofacies that accumulated along the northern margin of the rheic ocean lithofacies stacking patterns indicate that deposition occurred during a marine transgression with superimposed small scale sea level fluctuations producing at least six parasequences parasequences containing ironstone are 10 to 20 m thick and composed of hummocky cross stratified sandstone interbedded with organic rich mudstone and phosphatic fe silicate bearing siltstone which is overlain by hematitic granular ironstone capped by an erosive flooding surface this lithofacies association is interpreted to record the deposition of upwelling related ironstone on a storm dominated shelf the close relationship between fe silicates and phosphorite typical of upwelling systems suggests that fe was delivered from deep anoxic nutrient rich seawater that also stimulated high surface productivities the result was the precipitation of authigenic sedimentary apatite in anoxic organic rich sediments that accumulated near the upwelling front the gradual advection of fe rich waters away from the upwelling front initiated precipitation of fe silicate coated grains and cements in suboxic pore waters iron pumped into shallower environments through advection and fe redox cycling is interpreted to have precipitated fe oxyhydr oxide grains in sediment of the oxygenated middle shelf these coated grains were subsequently concentrated by fairweather and storm currents on the shoreface to create granular economic fe deposits we challenge conventional models of paleozoic ironstone deposition that rely on a continental source of fe by proposing a hydrothermal source that supplied fe2 to the shelf through upwelling it also highlights the potential connection between the delivery of anoxic ferruginous seawater to the margins of the rheic ocean and the early ordovician extinctions that punctuated the beginning of the great ordovician biodiversification event

temperature variability over africa during the last 2000 years a growing number of proxy historical and instrumental data sets are now available from continental africa through which past variations in temperature can be assessed this paper co authored by m

fluvial responses to land use changes and climatic variations within the drury creek watershed southern illinois abstract fluvial responses to climatic variation and anglo american settlement were documented for the drury creek watershed southern illinois by examining stratigraphic geomorphic climatic and historical data regional analyses of long term precipitation records document a period of decreasing mean annual precipitation from 1904 to about 1945 and an increasing trend in annual precipitation from 1952 to the present the period between 1945 and 1951 experienced a large number of intense storms that resulted in high annual precipitation totals statistical relationships illustrate that changes in precipitation totals are transferred to the hydrologic system as fluctuations in stream discharge historical records of southern illinois show that a maximum period of settlement and deforestation occurred between the 1860s and 1920s this era ended in the 1940s when large tracts of land were revegetated in an attempt to curtail erosion which had caused extensive upland degradation in response to hillslope erosion at least two meters of fine grained sediments were deposited on valley floors average sedimentation rates determined using decdrochronologic techniques are estimated to be 2 11 cm yr for the period between 1890 and 1988 rates that are 1 to 2 orders of magnitude greater than pre settlement values calculated for other areas of the midwest however botanical data suggest that aggradation was episodic possibly occurring during three periods characterized by greater annual precipitation since the 1940s sedimentation rates have declined reduced rates of sedimentation are related to an episode of channel entrenchment that reduced overbank flooding entrenchment coincided with a period of 1 reduced sediment yields associated with watershed revegetation and the introduction of soil conservation practices and 2 intense storm activity that resulted in long periods of high discharge as a result of channel incision and hillslope erosion newly exposed bedrock in upstream areas currently provides a source of gravel load to the channels the distribution of coarse bedload material along tributary streams combined with downstream decreases in width depth ratios and tractive force estimates suggest that channels in the drury creek watershed are slowly adjusting their configuration to transport coarse bedload material the fluvial response to the increased influx of coarse sediment began more than 45 years ago and continues today

sand ramps as palaeoenvironmental archives integrating general principles and regional contexts through reanalysis of the klipkraal sands south africa abstract sand ramps occur on a continuum of topographically controlled landforms ranging from purely aeolian features climbing falling dunes to talus cones and alluvial fans sand ramps have been identified as potentially important palaeoenvironmental archives in dryland regions that possess relatively few quaternary proxy records their utility however requires not only good age control of depositional phases but clear identification of process regimes determined through morphological and sedimentological analyses with several recent studies indicating the complexities of palaeoenvironmental interpretations and the controls of ramp development bateman et al 2012 rowell et al 2018 klipkraal sands is a sand ramp on the north eastern margin of the semi arid karoo that has been important for inferences of the extent of southern african late quaternary aeolian activity thomas et al 2002 we reanalyse this feature in the light of both its significance and other recent studies that have inferred extensive southern african lgm aeolian activity telfer et al 2012 2014 new sedimentological data and twelve osl dates indicate the klipkraal sands formed episodically between 100 0 14 ka rather than accumulating rapidly while sedimentological data question the aeolian affinities of the bulk of the feature therefore klipkraal is reinterpreted as showing no particular affinity to the lgm with sediments locally sourced with a significant colluvial component only the upper historical sediments can be clearly interpreted as aeolian deposits a complex interplay of processes is suggested for which a meaningful palaeoenvironmental interpretation cannot be easily defined this implies that the local geomorphic processes and controls operating on sand ramps need to be established before they can be fully utilised as palaeoenvironmental archives with implications for their interpretation worldwide

how old are the gullies dongas of the sneeuberg uplands eastern karoo south africa abstract the sneeuberg uplands in the eastern karoo are wetter than lowland sites with 400 mm of rainfall for over 150 years until recently they have been overgrazed largely by sheep the landscape consists of badlands less degraded areas and networks of gullies occupying the valley floors and hillside depressions these gullies have been relatively stable since at least 1945 the age of the gullies is controversial but various authors have speculated that they result from european incursion from the late 18th century onwards reconsideration of the relationship between vlei wetland deposits in the valley bottoms and gullies suggest that the gullies must post date late holocene development of vlei conditions incision by gullies would have resulted in a drying out of wetlands which occurred later and allowed cultivation of many valley bottoms for wheat and fodder crops gullies may have developed from deliberate attempts to drain wetlands for agriculture they are also likely to have formed from wagon tracks and a changed hydrology resulting from overgrazing and vegetation degradation on valley bottoms and hillslopes in other parts of south africa it has been suggested that gullies result from climatic impacts including instability in the little ice age this study should be seen in the context of an on going global debate about the role of climate and human mismanagement of the natural landscape

a record of rapid holocene climate change preserved in hyrax middens from southwestern africa the discovery of sensitive paleoenvironmental proxies contained within fossilized rock hyrax middens from the margin of the central namib desert africa is providing unprecedented insight into the region s environmental history high resolution stable carbon and nitrogen isotope records spanning 0 11 700 cal calibrated yr b p indicate phases of relatively humid conditions from 8700 7500 6900 6700 5600 4900 and 4200 3500 cal yr b p with a period of marked aridity occurring from 3500 until ca 300 cal yr b p transitions between these phases appear to have occurred very rapidly often within 200 years of particular importance are 1 the observed relationship between regional aridifi cation and the decline in northern hemisphere insolation across the holocene and 2 the signifi cance of suborbital scale variations in climate that covary strongly with fl uctuations in solar forcing together these elements call for a fundamental reexamination of the role of orbital forcing on tropical african systems and a reconsideration of what factors drive climate change in the region the quality and resolution of these data far surpass any other evidence available from the region and the continued development of this unique archive promises to revolutionize paleoenvironmental studies in southern africa

from black and white to colour in the silurian abstract ironstones and iron rich limestones regularly occur as components of time specific intervals of the palaeozoic as well as in younger times brett et al 2012 this issue silurian sediments deposited at high latitudes along the peri gondwana border are characterized by black and white limestone and graptolitic shale sequences those in the carnic alps southern austria additionally contain colourful pink to red limestones and ironstones laminated structures such as the ferruginous coatings around skeletal fragments mostly trilobites and some cephalopods and echinoderms and stromatolitic features along discontinuity surfaces display dark red green white and brownish colours due to the presence of goethite magnetite hematite chamosite calcite and subordinate apatite confocal laser raman microscopy and complementary microscopic analysis of these ferruginous laminated structures document the presence of carbonaceous matter associated with fossilized microbial structures in the form of stromatolites filaments and coccoids suggesting a microbial role in the colouring of the silurian world of the carnic alps iron concentrations up to 30 that of matrix and surrounding non ferruginous rocks suggest blooms of iron microbe activity in response to the time specific occurrence of chemically charged sea water during global biotic events

climate controls on late pleistocene landscape evolution of the okhombe valley kwazulu natal south africa hillslopes in central and western parts of kwazulu natal south africa are often mantled by colluvial sediments of the masotcheni formation these sediments have accreted in response to several cycles of deposition pedogenesis and incomplete erosion climatic controls on these cycles are incompletely known results from fieldwork micromorphology stable carbon isotope analysis and optically stimulated luminescence dating of masotcheni formation sediments from okhombe valley in the drakensberg foothills are combined deposition in the area had at least 11 phases starting before 42 ka and ending before 0 17 ka the first six deposits from before 42 ka to after 29 ka resulted from the interplay between slope processes and fluvial redistribution under cold conditions solifluction was the most important slope process no deposits have been found from the last glacial maximum arguably because this period was too dry the last five deposits from about 11 ka to before 0 17 ka resulted from fluvial redistribution of upslope material and older deposits under increasing precipitation current extreme gully erosion in the masotcheni formation indicates a lack of available upslope material leaving downslope deposits as the only sediment source for fluvial redistribution this model for landscape response to climate change may be able to explain how climate controlled landscape processes in other masotcheni formation sites in kwazulu natal in the research area and elsewhere this proposition may be tested with numerical landscape evolution models

a 13 year record of erosion on badland sites in the karoo south africa land degradation in south africa has been of concern for more than 100 years with both climate change and inappropriate land management overgrazing being proposed as primary drivers however there are few quantitative studies of degradation and in particular few of erosion by water badlands taken here to be the landform which results from extreme erosion have been notably neglected we report on 13 consecutive years of erosion pin measurements of badland erosion on 10 study sites in the sneeuberg uplands of the eastern karoo in south africa the study sites are on holocene colluvium which mantles footslopes they have been subject to overgrazing for at least 100 years c 1850 1950 currently they are lightly grazed by sheep the area receives about 500 mm rainfall per year the sites are remote with only informal farmer operated daily raingauges nearby the nearest subdaily raingauge is c 55 km distant also we report on an analysis of the erosion pin data which focuses on establishing the origins and context of the badlands including the relationship between study sites and adjacent valley bottom gully systems compare erosion rates on our study sites with rates determined by erosion pins on other badland sites and discuss the implications of these erosion rates for landscape development and off site impacts net erosion rates on the study sites are relatively high compared with global badland rates and range from 3 1 to 8 5 mm yr 1 which may be extrapolated to 53 to 145 t ha yr 1 using a measured bulk density of 1 7 g cm 3 however comparisons with badland sites elsewhere are difficult because of different measuring methodologies lithologies climate and dominant processes erosion rates on the study sites are strongly influenced by rainfall amounts and in particular by daily rainfall events which exceed 10 mm this is the threshold intensity at which runoff has been observed to commence on badlands of significance but of lesser influence is weathering mainly by wetting and drying this prepares bare surfaces for erosion however questions remain regarding the role of site characteristics and of processes at each site in determining between site differences in erosion rate crude extrapolation of current rates of erosion in conjunction with depths of incision into the badlands suggests that badland development started around 200 years ago probably as a response to the introduction of european style stock farming which resulted in overgrazing we assume but cannot quantify the additional influence of periods of drought and burning in the erosional history of the area intermittent connection of these badlands to valley bottom gullies and therefore to small farm dams and ultimately to large water storage reservoirs increases their impact on local water resources

genesis of unusual lithologies associated with the late middle devonian taghanic biocrisis in the type taghanic succession of new york state and pennsylvania abstract the middle devonian late middle givetian tully formation in new york state is the type regional expression of the global taghanic biocrisis it is marked by anomalous development of massive to rhythmically bedded micritic limestone deposits within a vastly thicker acadian foreland basin clastic succession lower medial tully carbonates record the incursion of tropical old world realm owr taxa tully fauna and the outage of the long standing higher diversity cooler water endemic eastern americas realm ear biota hamilton fauna succeeding tully strata record a return of the hamilton fauna followed by its demise due both to replacement by the lower diversity cosmopolitan genesee fauna and by the overspread of widespread anoxic bottom conditions coupled with the onset of drastically increased sediment input following tully group deposition massive micritic limestones yielding modest diversity tully fauna assemblages are particularly characteristic of the lower medial tully succession on the western new york tully platform these are coeval with nearly barren ribbon limestone and siltstone deposits in the adjacent new berlin east central new york and central pennsylvania basins these depocenters trapped terrigenous sediment and helped to create sediment starved conditions on the platform anomalous tully carbonate deposition is believed to be coincident with strong super estuarine water mass stratification in offshore tully shelf and basin settings where a warmer denser more saline water mass flowed northward shoreward across the study area beneath a counter flow of oxygenated river influenced surface water dysoxic conditions would have developed below the pycnocline favoring the tully fauna incursion precipitation of carbonate mud and possibly promoting the formation of ooidal chamosite at least five thin 1 30 cm thick mappable beds of black ooidal chamosite are observed in taghanic shelf margin slope and basin deposits these beds are typically intensely bioturbated variably rich in associated siderite contain corroded low diversity fossil assemblages and are regionally associated with condensed lag deposits above unconformities work by others suggests that chamosite formation occurs under minimally reducing post oxic interstitial conditions which are followed in turn by more strongly reducing conditions which allow for variable siderite and pyrite formation terrestrial pedogenic alteration of silicates by evolving land plant communities under warm humid conditions led to an increased supply of kaolinite as well as iron oxides and hydroxides that served as precursors to chamosite formation in the new berlin basin the transgressive top hamilton base taghanic succession is marked by a succession of diastems associated with basin deepening and upward increasing chamosite occurrence in dysoxic facies occurrence of ooidal chamosite in upper medial tully platform deposits smyrna bed may reflect water mass stratification and extreme sediment starvation at the shelf margin eastward spectral transformation of sparsely fossiliferous smyrna ooidal chamosite in the western new berlin basin into richly fossiliferous non chamositic equivalent neritic deposits east of that basin suggests that the counter flow of oxygen and nutrient rich lower salinity water had blocked the denser restricted water layer from advancing over the eastern tully clastic shelf closer to shore

chamosite siderite and the environmental conditions of their formation in chamosite type phanerozoic ooidal ironstones abstract two characteristic ironstone minerals occurring in chamosite type ironstone deposits were investigated these are the minerals of the chlorite and the carbonate series the samples are from 31 localities and 8 countries czech republic france germany united kingdom egypt nigeria and usa these deposits are identical to those presented by mucke and farshad mucke a farshad f in press whole rock and mineralogical composition of phanerozoic ooidal ironstones comparison and differentiation of subtypes ore geology reviews with ordovician to late cretaceous ages electron microprobe analyses of 197 carbonates and 64 chlorites were carried out the analytical points of the carbonates in a magnesite calcite siderite rhodochrosite 100 mol diagram are distributed within a limited area close to the siderite end member the area can be subdivided into two fields 1 the carbonates of the ordovician ironstones of the welsh prague and thuringian basins have high siderite concentrations 87 1 to 90 6 mol magnesite contents from 6 7 to 8 3 mol and calcite concentrations from 1 6 to 2 4 mol in the ordovician ironstone of krusna hora prague basin the siderite concentrations are lower 78 3 mol and those of magnesite 15 6 mol and calcite 5 7 mol are higher 2 the carbonates of the other ironstones jurassic to late cretaceous have lower siderite 72 5 to 79 mol and higher magnesite 12 6 to 15 7 mol and calcite 6 9 to 12 2 mol contents the average values of the rhodochrosite end member lie in the range between 0 13 and 2 31 mol and the siderite rhodochrosite ratio 158 on average the analytical points of the chlorite analyses are presented in the fetot mg alvi 100 atom diagram one field containing exclusively chlorites with green internal reflections can be subdivided into two areas one area contains the chlorites of the ordovician ironstones consisting of 62 8 to 77 7 atom fetot 17 5 to 30 9 atom alvi and 4 1 to 7 4 atom mg and the other those of the jurassic to late cretaceous ironstones consisting of 55 7 to 62 5 atom fetot 26 to 33 8 atom alvi and 9 to 13 atom mg the second field contains altered chlorites of ferruginized ironstones aswan and red mountain formation these chlorites present brown internal reflections and have compositions 34 9 to 46 7 atom fetot 24 8 to 42 2 atom alvi and 16 0 to 28 5 atom mg that do not reflect the original diagenetic environment within the al al fe mg mg mg fe atom diagram the chlorite analyses are concentrated in a limited field which is distinctly separated from chlorites formed in other environments the occurrence of carbonate and chlorite both with slightly varying compositions dominated by their iron end members which occur characteristically in association with framboidal pyrite and organic matter are indications that three prerequisites for the formation of the ironstones are comparable in narrow limits these are 1 the composition of the protoliths 2 the depositional environment of the protoliths and their rates of deposition and 3 the environmental conditions that occurred during the lithification of the protoliths due to submarine diagenesis the protoliths consist of mixtures of kaolinite fe3 oxide hydroxide and organic matter the depositional environments are marine basins in which fully marine conditions occur and thus the availability of mg and ca not contained in the protoliths exists the rates of deposition control the amount of mg in the chloritess and that of mg and ca in the carbonatess and the environmental conditions during submarine diagenesis depend on the availability of organic matter creating reducing conditions due to bacterial oxidation the resulting conditions are reducing and depending on the amount of organic matter pass successively from post oxic formation of chamosite and authigenic rice grain shaped siderite via sulphidic formation of framboidal pyrite into methanic formation of abundant xenomorphic siderite that replaces chamosite

mineralogy and geochemistry of the coals from the karmozd and kiasar coal mines mazandaran province iran abstract the karmozd and kiasar mines are two major coal producing areas in the central alborz coal bearing field northern iran this study focused on the mineralogy and geochemistry with respect to the mode of occurrence of elements in feed coals and element partitioning during coal preparation the low sulfur content in the coal seams indicates a non marine origin i e deposition in lacustrine and swamp environments detrital minerals in the coal seams are quartz feldspar albite and orthoclase mica muscovite and biotite amphibole hornblende and kaolinite authigenic minerals include pyrite calcite and chlorite the contents of most elements are within the general worldwide ranges with the exceptions of mn co and cr in some coal seams correlation coefficients between elements and the ash yield identified four separate groups of elements the sequential extraction results indicate that al na k zn cu and co principally occur in the silicates whereas pb and cr mainly occur in the organic fraction calcium and mg display strong affinities to the carbonate phase while cd mainly occurs in the water soluble and organic fractions the calculated removability index shows that the coal cleaning method in zirab not only removes mineral matter and pyritic sulfur but also reduces the content of most inorganic elements

modern alluvial history of the paria rver drainage basin southern utah abstract stream channels in the paria river basin were eroded and partially refilled between 1883 and 1980 basin wide erosion began in 1883 channels were fully entrenched and widened by 1890 this erosion occurred during the well documented period of arroyo cutting in the southwest photographs of the paria river channel taken between 1918 and 1940 show that the channel did not have a floodplain and remained wide and deep until the early 1940s a thin bar

holocene flood histories in south western usa harden t macklin m g baker v r 2010 holocene flood histories in south western usa earth surface processes and landforms 35 6 707 716 sponsorship aberystwyth university university of arizona

late ordovician ice marginal processes and sea level change from the north gondwana platform evidence from the valongo anticline northern portugal abstract in the valongo anticline northern portugal the upper ordovician age sobrido formation records glacioeustatic sea level changes and glacially influenced depositional environments on the north gondwana platform associated with the hirnantian glaciation new stratigraphic data from the sobrido formation taking into account lateral facies variations not exposed in the type section allow for a better understanding of hirnantian glacial sedimentary processes sea level changes and palaeogeography the lower member of the sobrido formation is composed of quartzites alternating with siltstones and mudstones the transition to the upper member is most commonly an erosional contact marked by a ferruginous horizon the lowermost part of the upper member contains a thinly laminated and rhythmically bedded mudstone that is capped by a thin mm scale shelly bed and overlain by massive diamictites laterally conglomerate beds that have erosion bases are rhythmically interbedded with slates and diamictites that sometimes contain outsized mudstone clasts the uppermost part of the upper member is very variable in thickness laterally and contains massive to laminated diamictite beds intercalated with quartzites conglomerates and slates massive diamictites commonly exhibit thin horizons with fe oxides and occasionally manganese phosphate and oolitic chamosite the lower member of the sobrido formation is interpreted as ice proximal outwash that is transitional laterally to subaqueous ice contact fans formed by debris and mass flows erosion followed by chemical weathering of the lower member and variably within the lowermost part of the upper member is interpreted as a response to sea level fluctuations and development of spatially variable anoxic conditions and groundwater migration within isolated marine basins facies within the upper member of the sobrido formation are interpreted as ice distal laminated diamictites and ice proximal deposits massive diamictites quartzites and conglomerates groove casts and hummocky cross stratification within quartzite beds suggest deposition in a shallow shelf setting the upper ordovician lower silurian transition is locally marked by a ferruginous horizon black basal quartzites are interpreted to record development of an erosional unconformity during silurian sea level rise in other areas a chloritoid layer indicates proximity to dry land these palaeoenvironmental interpretations suggest dynamic changes in sedimentary and geochemical processes in response to sea level and related palaeogeographic changes during the upper ordovician and transitional to the lower silurian on the north gondwana platform

a tenfold increase in the orange river mean holocene mud flux implications for soil erosion in south africa soil erosion poses a major threat to sustainable agriculture in southern africa but is difficult to quantify one measure of soil erosion is the sediment flux of rivers the orange river is the principal source of sediment to the western margin of south africa with an estimated mean mud flux over the last 11 500 years the holocene epoch of 5 1 3 2 7 4 million metric tons year mt yr a total of 43 gigatons gt 10 15 g representing 72 of the holocene mud flux has accumulated on the shelf in the orange river prodelta and mudbelt a clayey fine silt deposit focused on the inner to middle shelf only 8 5 gt of the mud flux occurs in holocene calcareous ooze on the slope comparison of the clay to mud ratio of offshore deposits with orange river suspended sediment and catchment soils indicates that 20 11 gt of the holocene mud flux has been lost as clay beyond the margin the orange river mud flux prior to the building of large dams 1930 1969 is ten times greater than the mean holocene mud flux and is reconciled with estimates of soil erosion within the catchment a tenfold increase in the orange river mud flux implies up to a hundredfold increase in total soil erosion depending on the extent of mud storage over periods of decades to centuries within the catchment erosion has shifted from areas of high relief and rainfall of the drakensberg escarpment during the holocene to intensely cultivated lands of low relief having moderate to high rainfall in the eastern catchment and to a lesser extent grazing areas of the southern orange river catchment

late holocene alluvial history of the cuyama river california usa dryland river deposits are archives of past changes in fluvial system form and process chronostratigraphic reconstruction of the late holocene alluvial history of the cuyama river in west central california reveals past spatial and temporal variation in dryland channel form and process the modern cuyama river consists of a wide braided reach in the upper drainage basin a narrower arroyo reach in the middle of the drainage basin and a bedrock canyon reach in the lower drainage basin that drains to the santa maria coastal plain along the arroyo reach late holocene stratigraphy is well exposed and is the focus of this study between ca 1700 and 350 yr b p two widespread deposits of tabular bedded clay silt and fine sand were deposited separated by a buried soil formed between 950 and 700 yr b p channel incision occurred between 550 and 350 yr b p next deposition of massive to bedded sands occurred in a pattern alternating between poorly confined deposition on top of older deposits onto the broad valley floor and channelized deposition along the valley axis inset into older deposits the superposed deposits now underlie the main valley terrace and the valley axis deposits are preserved as inset fill terraces historical arroyo cutting then formed a 65 km long arroyo ca 150 yr b p based on correlation to regional paleoclimate records channel aggradation occurred during periods of relative aridity and low peak discharge events while wet periods possibly floods after drought led to fluvial incision these cycles are superimposed on a transition from a wide silt and fine sand dominated fluvial system to a modern narrow sand and gravel dominated arroyo channel the relationship between times of fluvial process change and climate change in cuyama valley bears considerable similarity to other well studied dryland rivers in the southwestern united states however the complex sedimentology and geometry of preserved fluvial deposits suggest that a wider range of fluvial modes occurred along the cuyama river than has been reported in simpler cut and fill dominated channels elsewhere these spatial and sedimentological complexities underscore the need to link fluvial deposits and their bounding unconformities along a channel in order to fully understand the spatial and temporal evolution of ancient fluvial systems

rapid and selective clast weathering on an alluvial fan eastern karoo south africa abstract a small alluvial fan formed on the surface of a dry infilled dam in january 2010 as a result of a high magnitude rainfall and flood event gravel and boulder size clasts in the fan comprised dolerite mudstones and fine grained sandstones within a month of formation some mudstone gravels had disintegrated due to weathering processes the fan was investigated four years later and the weathering of different lithologies was categorised and quantified almost half of the weathered clasts were completely weathered forming small heaps or spreads of particles

paleoenvironmental significance of aluminum phosphate sulfate minerals in the upper cretaceous ooidal ironstones e ne aswan area southern egypt aluminum phosphate sulfate aps minerals are present as small disseminated crystals in the upper cretaceous shallow marine ooidal ironstones e ne aswan area southern egypt their association with the ironstones is considered as a proxy of subaerial weathering and post diagenetic meteoric water alteration the mineralogical composition of the ooidal ironstones was investigated by optical and scanning electron microscopes x ray diffraction fourier transform infrared and raman spectroscopy the ooidal ironstones are composed mainly of ooids and groundmass both of which consist of a mixture of detrital quartz and diagenetic fluorapatite chamosite and pyrite mineral assemblages these mineral assemblages are destabilized under acidic and oxidizing continental conditions these conditions resulted from the oxidation of pyrite and probably organic matter under warm and humid tropical climate followed the santonian sea regression and subaerial exposure these pedogenic conditions promoted corrosion of quartz dissolution of chamosite and apatite and hydrolysis of feldspars of the nearby exposed granitoids the released si al and sr from quartz chamosite and feldspars fe and s from pyrite and p ca and light rare earth elements lree from apatite are reprecipitated as hematite kaolinite apatite and aps minerals from the pore fluids or along fractures the paragenetic sequence and textural relationships of this post diagenetic mineral assemblage indicate that hematite was formed by replacement of chamosite followed by formation of a secondary generation of pore filling chlorapatite and aps minerals and finally the precipitation of kaolinite in the remaining pore spaces the formation of aps minerals and chlorapatite is simultaneous but aps minerals are stable at shallow depths under acidic to neutral ph conditions whereas chlorapatite is stable under alkaline ph conditions alkaline conditions were maintained at greater depths when the infiltrated acidic fluids reacted with chamosite the aps minerals display a homogeneous chemical composition in all ironstone locations in aswan area corresponding to a solid solution between crandallite caal3 po4 2 oh 5 h2o goyazite sral3 po4 2 oh 5 h2o svanbergite sral3 po4 so4 oh 6 and woodhouseite caal3 po4 so4 oh 6 end members the variations in the aps mineral chemistry ab3 xo4 2 oh 6 are essentially due to variable substitutions of sr and lree for ca at the a site and limited s for p at the x site the spatial distribution of aps minerals and their composition in the ooidal ironstones of aswan area permitted to consider them as good tracers of physicochemical and paleoenvironmental changes in particular those associated with subaerial exposure and pedogenesis the post diagenetic phosphatization and kaolinization of the aswan ironstones decrease their economic potentiality thus understanding paragenetic sequence and textural relationships is essential for the iron ore beneficiation

provenance and tectonic implications of the 3 28 3 23 ga fig tree group central barberton greenstone belt south africa abstract sedimentary rocks provide a valuable record of non uniformitarian paleoarchean tectonic processes the rocks of the 3 28 3 23 ga mapepe formation mark the initiation of orogenesis in the barberton greenstone belt south africa however reconstruction of the mapepe basin s is challenging because the rocks occur in fault bounded structural belts that are characterized by lateral heterogeneity and whose correlation remains uncertain we have studied the petrography geochemistry and detrital zircon geochronology from outcrop and drill core samples from two adjacent structural belts the manzimnyama syncline and the eastern barite valley area to evaluate the timing of basin formation correlate between these two adjacent areas and provide constraints on the character of tectonic uplift in the eastern barite valley area sedimentation was initiated at about 3260 ma the section includes a lower deep water unit of mainly mudstone overlain by a shoaling upward sequence of fan delta sandstone and conglomerate the sandstone throughout the formation was derived by erosion of local uplifts of the underlying greenstone belt sequence except at the top of the section where sedimentation was dominated by dacitic volcaniclastic sediments dated at 3239 ma in contrast rocks of the mapepe formation in the manzimnyama syncline area 1 2 km south of the eastern barite valley area record the initiation of sedimentation at about 3277 ma with deposition of a rhyolitic tuffaceous unit followed by persistent deep water sedimentation of banded iron formation banded ferruginous chert and turbiditic sandstone siliciclastic sediments are immature and were derived by erosion of older supracrustal greenstone belt rocks no fig tree age volcanism younger than 3260 ma is recorded in this belt overall mapepe sedimentary rocks record the formation of numerous local uplifts of underlying supracrustal rocks with periodic volcanic activity and the dispersal of debris to form mainly small fan deltas flanked by deep water systems the contrasting ages lithologies depositional settings and provenance of the sedimentary rocks in the now adjacent eastern barite valley and manzimnyama syncline belts suggest that they were deposited in either different parts of a large complex fig tree basin or represent separate basins that have been juxtaposed during post fig tree tectonism and shortening

development of badlands and gullies in the sneeuberg great karoo south africa abstract the study aims to examine the origin and development of land degradation with particular emphasis on badland and gully systems in the sneeuberg uplands of the great karoo this is an area of semiarid extensive stock farming where land degradation in the form of rill and gully erosion has accompanied the replacement of grassland by shrub vegetation species diversity has declined and ground cover has been reduced leading to a positive feedback loop which exacerbates the degradation many foot slopes developed in shales clays and colluvium have extensive incipient badland development with closely spaced gullying up to 1 5 m deep in valley bottom and valley side depression locations gullies up to 8 m deep have developed usually cut to bedrock through valley fills of mainly holocene colluvium both badlands and gullies appear to have developed since european settlement and to be part of the same hydrological system with extensive areas of bare ground badlands feeding water to incising gullies experiments using simulated rainfall throw some light on current processes badland areas are active under high frequency low magnitude rainfall events major gullies are likely to be the result of occasional high magnitude events but these have not been observed overgrazing in the past is the most likely cause of the degradation

palustrine wetland formation during the mis 3 interstadial implications for preserved alluvial records in the south african karoo abstract dryland alluvial successions across interior south africa are a focus of pedosedimentary research because they provide insights into past hydrogeomorphic changes and improve our understanding of allogenic and autogenic controls on fluvial system behaviour this paper focuses on an alluvial succession preserved within the wilgerbosch river on the great escarpment south africa the pedosedimentary architecture of a calcretized palaeosol formed within an abandoned mis 3 51 39 ka floodplain was investigated using grain size micromorphological xrd and mineral magnetic analyses the primary controls on pedogenesis are inferred and the impacts of their products on subsequent landscape development outlined the biologically dominated calcrete micromorphology is consistent with the rhizogenic calcrete variety which together with xrd grain size and soil magnetic data provides evidence for a palustrine palaeowetland system palustrine wetland systems have been documented across interior south africa but the formation of rhizogenic calcretes in association with these systems has to our knowledge not been reported previously we interpret these palaeowetlands to have resulted from basin wide hydrogeomorphic adjustments rather than localised discontinuous channel and floodout processes magnetic enhancement of the soil column overlying the calcrete compared to the overlying floodplain deposits is indicative of moister climate conditions at 51 ka relative to 39 ka we hypothesise that the longevity of geomorphic quiescence coupled with relatively moist climate conditions in early mis 3 resulted in enhanced soil caco3 accumulation the resultant cementation of this abandoned floodplain deposit accounts for an alluvial record that is dominated by older rather than younger e g holocene deposits despite the narrow valley context