stratigraphy and remanence acquisition of a palaeomagnetic reversal in alluvial siwalik rocks of pakistan a high resolution record of a palaeomagnetic reversal is documented in miocene alluvial rocks of pakistan we examined lateral variability of lithostratigraphy and palaeomagnetic stratigraphy through the same palaeomagnetic reversal in six correlated sections each section contains one or more palaeomagnetic sites with directions between fully reversed and fully normal the position of the reversal illustrates local relief in the study area and the time transgressive nature of certain stratigraphic units variability in the thickness of the transitional interval indicates contemporaneous variability in sediment accumulation rates different characteristics of palaeomagnetic remanence are associated with the depositional and postdepositional history of these sediments variability in patterns of remanence behaviour is the basis for inferences about post depositional processes we discuss two magnetic parameters that express coherency of palaeomagnetic samples the maximum angle of deviation and the circular standard deviation of particular interest are samples with incoherent palaeomagnetic signals the incoherency of samples is inversely correlated with the thickness of the transitional interval a low rate of sediment accumulation suggested by a thin transitional interval may facilitate a prolonged period of remagnetization through pedogenic or hydrological processes alternatively transition intervals defined by coherent magnetization may be thin as a result of pedogenically induced incoherency

late miocene drying of central australia abstract a back to the future approach to climate change refines neogene records of paleoclimatic cooling and drying as future climate states for a warming world near alcoota station in central australia is a late miocene fossil mammal site for alcoota 10 ma and ongeva 8 ma local faunas the alcoota fauna includes the largest known land bird dromornis stirtoni and early diprotodontid kolopsis torus but the geologically younger ongeva fauna has a larger diprotodontid zygomaturus gilli these faunas are evolutionary predecessors of australian pleistocene megafauna calcareous paleosols recorded a marked turn toward aridity compared with underlying thick lateritic duricrusts which lack fossils laterites of likely middle miocene age are evidence of wet 1100 mm mean annual precipitation tropical 17 c mean annual temperature paleoclimates but these were deeply eroded and redeposited by the time of the late miocene mammals a succession of 19 paleosols of 5 pedotypes were recognized in the 19 m thick section with shallow calcareous nodule bk horizons as evidence of mean annual precipitation ranges from 100 to 400 mm and mean annual range of precipitation of 50 mm very similar to the modern climate of alcoota 296 mm precipitation with 56 mm difference between wet and dry month this was neither a rainforest nor monsoonal paleoclimate and vegetation inferred from paleosols was open woodland and gallery woodland similar to that of today central australia was not covered by monsoon rainforest during the late miocene and its paleoclimatic history of neogene desertification matches well that of other parts of the world

a linkage among pangean tectonism cyclic alluviation climate change and biologic turnover in the late triassic the record from the chinle formation southwestern united states abstract high precision geochronology provides unprecedented insights into the depositional history of the upper triassic chinle formation of the colorado plateau as well as its paleoenvironmental and paleobiological records the chinle succession exposed in the petrified forest national park pefo and vicinity arizona includes two large scale alluvial composite sequences although each composite sequence fines upward the upper composite sequence is more dominated by coarser grained deposits petrographic analysis of sandstone lithic content indicates an upward decrease in the proportion of volcanic rock fragments in each composite sequence paleocurrent indicators in the lower composite sequence suggest a variable paleoflow direction whereas northward paleoflow dominated the upper composite sequence the change in paleoflow appears to coincide with a reorganization of alluvial depositional processes and associated source terranes and precedes a rapid acceleration in basin subsidence climate proxy records from paleosol geochemistry indicate a gradual shift from humid to dry conditions across the transition between the lower and upper composite sequences and the adamanian revueltian biotic turnover composite sequence depositional reorganization climatic shift and biologic turnover in turn appear to coincide with episodes of magmatism recorded in triassic granitoid plutons presently exposed in southern california taken collectively these observations suggest that the late triassic depositional climatic and ecologic history at pefo may be related to emergence of the incipient cordilleran magmatic arc along the convergent western margin of pangea a new u pb date for the lower part of the chinle formation suggests that most or all of the formation was deposited in the norian stage

extreme element mobility during transformation of neoarchean ca 2 7ga pillow basalts to a paleoproterozoic ca 1 9ga paleosol schreiber beach ontario canada abstract this study reports petrographic major and trace element and oxygen isotopic data for a subaerial weathering profile at schreiber beach ontario canada the weathering profile developed on neoarchean ca 2 7 ga pillow basalts and is unconformably overlain by the paleoproterozoic ca 1 88 ga gunflint chert and basal conglomerates this stratigraphy suggests that the basalts were uplifted and subaerially weathered prior to deposition of the gunflint formation rocks at schreiber beach have been classified as pillow cores pillow rims hyaloclastites weathered red basalts and weathered brown to green basalts there are gradual textural mineralogical and geochemical transitions from unweathered basalts to intensely weathered hematite bearing basalts with stratigraphic height rocks at schreiber beach underwent seafloor hydrothermal alteration and greenschist facies regional metamorphism in the neoarchean following the subaerial weathering they were buried and re metamorphosed to greenschist facies in the paleoproterozoic given the preservation of primary igneous textures and trace element patterns in pillow cores they are used as a protolith to estimate element mobility during seafloor alteration metamorphism and subaerial weathering chloritized pillow rims and hyaloclastites are characterized by moderate losses or gains of major si ca na fe ti k and trace lile ree hfse and transition metals elements during neoarchean seafloor alteration alteration of these rocks at relatively low temperatures is indicated by enrichment in 18 o 18 o 10 4 to 12 7 relative to fresh basalt 5 5 subaerial weathering resulted in significant textural mineralogical e g hematite precipitation and geochemical variations in metamorphosed basalts causing additional redistribution of most major and trace elements and further enrichment in 18 o the highest 18 o values 16 1 to 17 1 occur at the silica rich base of the weathering profile many elements including lile ree and hfse are strongly enriched 100 or depleted up to 96 relative to their original abundances alkaline metasomatism which is a characteristic of precambrian paleosols is also evident at schreiber beach where extreme enrichment in k 280 to 1000 rb 390 to 660 and cs 1160 to 2560 occurs in the weathering profile

ichnology paleosols and palimpsests surfaces in the tinat member of the nuayyim formation unayzah group subsurface saudi arabia trace fossils and genetic stratigraphy in continental settings abstract the nuayyim formation of the unayzah group is widespread in subsurface central saudi arabia and constitutes a laterally variable stratigraphic unit with a complex mosaic of facies sedimentation for the tinat member took place majorly in a continental setting dominated by aeolian processes that resulted in dunes interdunes ephemeral stream deposits terminating with regional development of paleosols facies ichnofacies and palynological analysis suggest an arid to semi arid setting with biogenic activity in the form of continental fauna and plants in deposits associated with pedogenetical alteration in paleosol horizons therein burrowing exhibits elements of the scoyenia ichnofacies in beds with sparse to abundant bioturbation tectonic uplift and subaerial exposure resulted in the exhumation of previously buried substrates leading to the formation of burrowed palimpsests surfaces associated with paleosols at the end of unayzah deposition prior to the onset of the khuff formation progressive thermal updoming is interpreted to have occurred during the latest portion of the unayzah group sedimentation cycle in the arabian plate culminating in the regional pre khuff unconformity at the top of this megacycle recognized in this study by biogenically demarcated diastems ichnological and sedimentological observations outlined in this study are significant because they i refine existing interpretations of the paleoenvironmental history in the study area ii document diastems marking breaks in sedimentation and iii outline several soil forming cycles that allowed the establishment of a trace fossil suite with continental affinities thus demarcating the end of an entire sedimentation cycle the recognition and delineation of burrowed horizons associated with paleosols provides a tool to understand the tectono stratigraphic evolution of similar successions in the rock record

magnetic mineral assemblages in soils and paleosols as the basis for paleoprecipitation proxies a review of magnetic methods and challenges abstract magnetic iron oxide minerals principally magnetite maghemite hematite and goethite are formed in well drained soils in response to a suite of physical chemical and biological factors despite a wide range of complexity in the pedogenic processes that lead to magnetic mineral formation dissolution and transformation there are well documented empirical relationships between various magnetic mineral assemblages in soils with environmental and climatic conditions recently there has been an increase in the number of quantitative magnetic paleoprecipitation proxies that have been developed and there is great potential for magnetic methods to be used in the geologic record to develop reconstructions of past climates magnetic paleoprecipitation proxies have been widely utilized in quaternary or younger loess paleosol systems however they have yet to be utilized in the pre quaternary fossil record future studies of magnetic mineralogy of soils and paleosols should aim to explore non loessic modern soils and pre quaternary paleosols with more focus on understanding the interaction between magnetic mineral assemblages and soil moisture applications of existing and novel magnetic paleoprecipitation proxies in the fossil record should prove to be a valuable resource for paleoclimatologists

paleoproterozoic ca 1 9 ga megascopic life on land in western australia abstract controversial hairpin shaped trace fossils myxomitodes stirlingensis and discoid fossils cyclomedusa davidi are here reinterpreted in a reassessment of sedimentology and paleosols of the 1 9 0 1 ga stirling range formation of western australia paleosols in the stirling range formation were recognized from complex cracking patterns peds and cutans chemical and mineralogical zonation soil horizons and poikiloblastic crystals desert roses redox profiles of the paleosols are evidence of well drained profiles of a coastal plain under a low oxygen 433 116 ppmv and carbon dioxide 564 64 ppmv atmosphere gypsum pseudomorphs in paleosols that are deeply weathered chemically represent a persistence of acid sulfate weathering better known in archean paleosols before the great oxidation event at 2 45 ga chemical composition of the paleosols is evidence of a humid 1478 182 mm mean annual precipitation temperate 11 3 0 5 c mean annual temperature paleoclimate their paleoenvironmental setting was a coastal plain on a passive tectonic margin megafossils were found on paleosols of western red sandstones of the stirling range formation not in gray shales and sandstones of marine facies to the east trace fossils myxomitodes stirlingensis and discoid fossils are both found at the surface of well drained paleosols and so were not metazoan trails nor sea jellies myxomitodes was more likely a grex slug trail of soil slime molds and the cyclomedusa discoids were probably microbial colonies pervasive microfilamentous structures in the paleosol surface are additional evidence of paleoproterozoic microbial earth ecosystems

the soil skeleton as a tool for disentangling pedogenetic history a case study in tuscany central italy abstract in this paper we show that the study of the soil skeleton the 2 mm fraction can be useful for detecting the presence of paleosols and events that contributed to the development of the present soil mantle we studied profiles at four sites all formed on sandstone in tuscany central italy the bulk density porosity mineralogy organic c total nh4 n and effective cation exchange capacity ecec of the fine earth

chronostratigraphy and paleoclimatology of the lodeve basin france evidence for a pan tropical aridification event across the carboniferous permian boundary abstract paleosols preserved within the carboniferous permian succession of the lodeve basin massif central france change stratigraphically from histosols to calcic vertisols and calcisols to gypsic vertisols and ultimately back to calcic vertisols and calcisols new high precision u pb zircon ages ca idtims for tuff beds within the lodeve and adjacent graissessac basins significantly revise the chronostratigraphy of these and correlated permian terrestrial basins of eastern euramerica under the newly revised chronostratigraphy presented here these stratigraphic changes in morphology indicate a substantial drying of paleoenvironments across the carboniferous permian boundary with a trend toward progressively more arid and seasonal climates through most of the early permian this newly realized chronology provides a paleoenvironmental and paleoclimatic timeline for eastern tropical pangea that is contemporaneous with similar records in western pangea and suggests pan tropical progressive climate change toward aridity and seasonality occurred from the late carboniferous through early permian

dynamics of iron and calcium carbonate redistribution and palaeohydrology in middle eocene alluvial paleosols of the southeast ebro basin margin catalonia northeast spain abstract paleosols in the alluvial middle eocene of the ebro basin exhibit both the redistribution of iron groundwater and surface water gley and calcium carbonate the hydrological dynamics are reconstructed through gley features and location of carbonate accumulation together these allow a sophisticated analysis of the seasonal palaeohydrology of ancient sedimentary environments this analysis is performed on paleosols developed in marginal and distal floodplain and delta plain deposits derived from the southeast ebro basin margin the most proximal part of the floodplain sediments had moderate mainly vadose calcite redistribution with surface water gleying and fairly deep groundwater the more distal sediments have stronger calcite redistribution both of vadose and surface water gley environments these were frequently overprinted by groundwater related calcite indicating shallow and fluctuating groundwater in the most distal alluvial sediments both calcite redistribution and further soil formation were weak while groundwater was shallow

pedogenesis and geochemical alteration of the picture gorge subgroup columbia river basalt oregon reddened clay rich horizons between basalt flows have historically been identified as baked zones or as zones of lateral groundwater movement the reddening has been attributed to thermal or chemical alteration of the permeable portion of the basalt flow many of these red horizons are instead paleosols that record significant hiatuses in basalt flow emplacement paleosols were identified in the field on the basis of features such as horizonation ped morphology and root traces terrestrial gastropods fossil plants and peats also occur locally plots of weathering indices such as base loss are consistent with a pedogenic origin for these horizons ca na mg fe 21 and p have been extensively lost from the a and bt horizons of the paleosols consistent with modern weathering patterns k and rb have been added to the upper portions of the profiles and lost in the lower portions of the profiles relative to the parent material with rb added disproportionately historically this pattern of enrichment has been cited as evidence of k metasomatism the apparent metasomatism can be explained using a new model in which there was extensive felsic volcanism contemporaneous with pedogenesis and k and rb were likely added by windborne ash the apparent discordance between k and rb contents of the paleosols can be explained by the presence of land plants because k is an important electrolyte and rb does not serve any major biological role this model could account for apparent k metasomatism in other paleosols following the advent of land plants and may be applicable to older paleosols as well

paleoclimatic records of late triassic paleosols from central ethiopia abstract the present study documents the major paleosols types within the lower adigrat sandstone in the blue nile basin of central ethiopia with the aim of unraveling the paleoclimatic signatures embedded in them the paleosols developed within an 80 m thick siliciclastic succession deposited in a mixed tide and wave dominated incised valley estuary during the late triassic based on down profile variations in pedogenic features three major paleosol types i e types i ii and iii were identified type i paleosols dominate the lower part of the section and are interpreted as moderately well drained argillic vertisols the dominant pedogenic process was shrinking and swelling of expandable clays i e smectite through repeated wetting and drying cycles the morphologies and the mineralogy of the paleosols provide persuasive evidence for pedogenesis under semi arid subtropical climatic conditions with pronounced wet dry seasonality highly fluctuating soil moisture regime and deep groundwater table the presence of a calcic bk horizon deep in the profiles is consistent with elevated soil moisture deficits and low to moderate mean annual precipitation map type ii paleosols interpreted to represent vertic gleysols are more common in the middle part of the section the pervasive gleying reflects poor soil drainage and a shallow groundwater table where the soil is waterlogged most of the year these paleosols suggest a humid tropical climate characterized by alternating wet dry seasonality but with more wet months per year the top of the unit is dominated by type iii paleosols that represent gleyed oxisols reflecting a more humid equatorial climate marked by wet seasons elevated annual soil moisture content and a high water table the presence of plinthite laterite is in agreement with a wet equatorial climate characterized by extensive chemical weathering and long periods of landscape stability the observed vertical progression in the major paleosol types from vertsols to gleysols and oxisols implies a systematic change in the number of wet months most probably in response to regional tectonics and long term climate change because the number of wet months is in part related to latitude and monsoonal climates the upward stratigraphic trend in paleosol orders is interpreted to signal the northward or equatorward migration of the blue nile basin and central ethiopia within pangea from dry subtropical low latitudes in the early late triassic carnian norian toward the humid wet equatorial possibly monsoonal paleoclimatic zone in the late triassic norian rhaetian

facies analysis of a probable large fluvial fan depositional system the upper triassic chinle formation at petrified forest national park arizona u s a abstract the upper triassic blue mesa member and the overlying sonsela member of the chinle formation consist of paleosol bearing alluvial strata whose characteristics vary markedly strata exposed within a 4 km2 study area at petrified forest national park were evaluated using sedimentologic stratigraphic paleopedologic and petrographic criteria to formulate potential depositional models that may account for varying alluvial deposition the study succession records a progressive up section increase in grain size increase in channel depth and width increase in lateral and vertical connectivity of channel deposits decrease in overbank preservation and crevasse splay and or sheetflood deposition and increase in overbank drainage mean annual precipitation from the calmag paleosol weathering proxy suggests precipitation averages approximately 1300 mm yr 1 3 m yr throughout the succession despite changing paleosol drainage these features are consistent with deposition in a progradational fluvial system such as a large fan or splay complex sediment accumulation rates in the study interval suggest decreased subsidence in the upper blue mesa member reduced rates of accommodation gain may have promoted progradation of the fluvial system an up section decrease in sandstone mineralogical maturity may be related to increasing sediment bypass in proximal fan positions or increased rates of erosion and sedimentation increasingly better drained paleosols are attributed to deposition in more upland positions during fan or avulsion complex progradation rather than changing climate

the distinction between ground water gley and surface water gley phenomena in tertiary paleosols of the ebro basin ne spain abstract in studies of paleosols the distinction iron segregation due to either surface water or ground water fluctuatins is hardly ever made recognition of subsequent hydromorphic phases is even more rare nevertheless such distinctions can be made and are very useful in determining the paleoenvironment in this study we demonstrate that subsequent stages of hydromorphism and their sequence can be recognized in paleogene paleosols of the ebro basin it appears that in these carbonate rich hydromorphic oils goethite iron segregations are due to ground water influence while hematitic segregations are due to surface water the preservation of original mineralogy in this case is due to absence of late diagenetic transformations the results contradict the thesis that red colours in such paleosols would be the result of the late diagenesis in the studied samples mottledcolour patterns frequently indicate fairly advanced soil formation although weathering of primary minerals is almost absent detailed study of colour patterns gives much additional information on the post depositional environment

greenhouse crises of the past 300 million years proxies of past co 2 and climate over the past 300 m y now reveal multiple global climate change events in unprecedented detail evidence for past co 2 spikes comes from expanded and refined data on stomatal index of fossil ginkgo and related leaves new evidence for synchronous climatic change comes from paleosols in montana utah and neighboring states each co 2 spike was coeval with unusually clayey red and decalcified paleosols which can be traced throughout the colorado plateau spikes in atmospheric co 2 also were coeval with increases in paleosol alkali depletion as an indication of high temperature and spikes in paleosol base depletion and depth to calcic horizons as indications of high precipitation in the colorado plateau times of warmer climate were also more humid perhaps due to greater moisture potential of warmer air seasonality of climate did not increase during warm wet spikes the mesozoic greenhouse was not persistently hot with cool spells but warm with hot flashes these data furnish power laws predicting the sensitivity and magnitude of change in mean annual temperature mat and mean annual precipitation map due to rising co 2 in a mid latitude mid continental region the magnitude of the coming anthropogenic greenhouse pales in comparison with past greenhouse spikes at times of global mass extinctions

pedosediments of karstic sinkholes in the eolianites of ne yucatan a record of late quaternary soil development geomorphic processes and landscape stability abstract the pedogenetic and geomorphic processes controlling soil development in tropical karstic landscapes are still poorly understood we have discovered and studied thick pedosediments in karst pockets developed in late pleistocene lithified calcareous dunes eolianites in the ne coast of the yucatan peninsula the morphological geochemical and mineralogical characteristics of the pocket fills were interpreted as a record of pedogenesis and geomorphic dynamics that shaped the soil mantle during the holocene sand fraction mineralogy and the zr ti ratio indicated a mixed origin of the soil parent material volcanic and granitic metamorphic components redeposited in the lithoral and coastal environments were identified within the soil matrix primary minerals were transformed by weathering and caused desilicification accumulation of clay hydroxy interlayered vermiculite and kaolinite and dithionite citrate bicarbonate extractable iron oxides fed reworked pedofeatures indicative of clay illuviation and redoximorphic processes were observed this set of processes points to a continuous phase of humid pedogenesis several thousand years long in the early middle holocene however the development of thick recalcified pedosediments in the pockets contrasting with the thin background rendzinas requires active soil redeposition during a late phase of geomorphic activity the available accelerator mass spectrometry ams radiocarbon date indicates that the switch of the erosion sedimentation processes could be related to ancient maya land use impact

regional paleoclimatic and stratigraphic implications of paleosols and fluvial overbank architecture in the morrison formation upper jurassic western interior usa abstract paleosols in the morrison formation upper jurassic from the western interior and colorado plateau regions occur in fluvial overbank and marginal lacustrine depositional facies associated with aggradational settings and at sequence bounding unconformities that mark divisions between major aggradational and degradational successions pedogenic features within these horizons preserve important contextual information about the local and regional paleoclimate and paleoenvironment in which the soils formed floodplain and lake margin paleosols show evidence that most of the morrison basin was characterized by a semi arid to tropical wet dry paleoclimate with fluctuating groundwater conditions a low precipitation to evaporation ratio and weak to moderately seasonal precipitation paleosol ichnofauna show evidence of a diverse and opportunistic flora and fauna that exploited changing conditions and existing nutrient and moisture regimes changes in paleosol type and degree of development over the basin indicate the overall regional paleoclimate was drier in the western and southern portions of the basin vertical trends indicate paleoclimatic conditions over the basin became steadily more humid through time laterally continuous well developed deeply weathered paleosols formed during times of little or no deposition and mark regional unconformities the paleosols at these sequence bounding unconformities serve as useful regional stratigraphic markers to trace genetic packages across the morrison depositional basin and to determine regional accommodation trends

evidence from paleosols for ecosystem changes across the cretaceous tertiary boundary in eastern montana ancient soils paleosols of the latest cretaceous hell creek formation are mildly calcareous have clayey subsurface bt horizons and exhibit abundant large root traces as is typical of forested soils in subhumid climates the fact that some of the paleosols are capped by thin impure coals is evidence for seasonally dry swamps the paleosol evidence thus supports published reconstructions based on fossil leaves pollen and vertebrates that this area was subtropical seasonally dry subhumid and forested mainly by angiosperms paleosols within the earliest tertiary paleocene tullock formation have thicker coaly surface o and a horizons and are more drab colored and less calcareous than paleosols of the hell creek formation these features are indications of waterlogging and of a humid climate large root traces and clayey subsurface bt horizons are evidence of swamp woodland and forest inferred base level and paleoclimate are compatible with evidence from fossil leaves and pollen that indicates more abundant deciduous early successional angiosperms and swamp conifers compared to those of late cretaceous time most of the paleosols have drab munsell hues and can be expected to preserve a reliable fossil record of pollen and other plant remains the carbonate content of the paleosols declines toward the top of the hell creek formation and the uppermost 3 m of the formation is noncalcareous because of this the decline in diversity and abundance of bone over this interval is interpreted as a taphonomic artifact evidence from paleosols supports paleobotani cal evidence for catastrophic change in ecosystems at the cretaceous tertiary boundary

climatic and geochemical implications of archean pedogenic gypsum in the moodies group 3 2 ga barberton greenstone belt south africa abstract lithic sandstones of braided fluvial to supratidal facies in the paleoarchean moodies group 3 22 ga barberton greenstone belt south africa include several regionally traceable units with common to abundant in places rock forming nodular concretions of megaquartz pseudomorphs after gypsum barite and calcite concretionary accumulations are stratiform and commonly associated with aqueously reworked fine grained tuffaceous sediment of originally rhyodacitic composition and can grow to fist sized agglomerates in crusts tens of m in lateral extent weathering of tuffaceous material and feldspar delivered alkali cations such as ca ba and k while carbonates were likely supplied by silicate weathering of mafic to ultramafic volcanic rocks during exposure to a co2 rich atmosphere sulfate ions were partly delivered by oxidative pyrite dissolution which may have included microbial and abiotic disproportionation of volcanic s or so2 concretionary growth apparently took place under pedogenic to early diagenetic conditions within unconsolidated granular sediment in the vadose zone dominated by seasonal fluctuations of the groundwater level under evaporitic conditions the concretions likely represent the oldest terrestrial evaporites known to date and form part of the oldest known compound paleosols their formation and composition constrain the local occurrence of sulfate in the archean atmo and hydrosphere their interaction with the emerging biosphere archean weathering regime local climate and vadose zone hydrodynamics

polygenetic history of paleosols in middle upper pennsylvanian cyclothems of the illinois basin u s a part i characterization of paleosol types and interpretation of pedogenic processes abstract the morphology mineralogy and stratigraphic and lateral distribution of paleosols in pennsylvanian moscovian gzhelian atokan virgilian mixed marine and terrestrial coal bearing strata i e cyclothems in the illinois basin ib are presented in order to determine the dominant pedogenic processes within a cyclic sedimentary depositional framework paleosol morphologies range from weakly developed horizons with evidence of rooting and little to no pedogenic structure to horizons with well developed pedogenic slickensides angular blocky structure and carbonate nodules and tubules the majority of paleosols in strata from the basin interior preserve 1 low chroma gley colors 2 identifiable fossil plant organic matter that increases in abundance upward in the profiles toward the interpreted paleo surface and 3 calcite sphaerosiderite and pyrite cements and nodules in contrast paleosols in strata from the northern margin of the basin display high chroma colors and calcite cements and less fossil organic matter sphaerosiderite and pyrite cements these observations indicate that paleosols from the basin interior underwent a multi phase pedogenic and shallow burial history characterized by an initial better drained oxygenated stage under seasonal precipitation followed by a poorly drained reducing stage while paleosols from the northern margin of the basin experienced overall more oxygenated conditions throughout their pedogenic development x ray diffraction analysis of the 2 m size fraction of paleosol matrix in ib paleosols indicates a mineralogical composition dominated by kaolinite randomly interstratified r0 and ordered r1 illite smectite i s and subordinate amounts of chlorite these combined observational and mineralogical datasets indicate that significant changes in paleohydrology were largely responsible for the development of pennsylvanian soil profiles in the ib

mass balance reconstruction of a modern vertisol implications for interpreting the geochemistry and burial alteration of paleo vertisols abstract utilizing identical sampling and analytical techniques the morphological and chemical characteristics of a modern vertisol houston black series central texas can be directly compared with an upper mississippian paleo vertisol from the appalachian basin pennington formation east central tennessee mass balance reconstructions suggest retention of primary pedochemical patterns in the paleo vertisol including patterns of soil volume change strain and transport functions translocations of many major and trace elements retention of primary pedochemical patterns suggests that vertisols constitute nearly closed systems during burial diagenesis chemical and mineralogical changes associated with burial diagenesis of the paleo vertisol include oxidation of organic carbon oc illitization of smectites dehydration and recrystallization of fe mn oxyhydroxides and dolomitization of pedogenic calcite significant differences in the chemical behavior of gilgai microhigh and microlow pedons in modern vertisols have implications for interpretation of geochemical data obtained from paleo vertisols overall wetter soil conditions and variable redox potential under gilgai microlows promote greater depths of leaching and mobility of redox sensitive trace elements including co cr cu mn ni and v gilgai microhighs behave as evaporative wicks that draw moisture and soluble phases towards the soil surface resulting in precipitation of metal hydrosylate complexes and sulfates gypsum at the capillary fringe and shallower depths of leaching and fixation of trace elements paleoprecipitation estimates from paleosols based on the depth to the top of the pedogenic carbonate horizon should therefore utilize field petrographic and geochemical data for characterizing maximum depths of leaching loss or gain of exchangeable bases and calcification rather than relying solely upon field data

the sturgeon falls paleosol and the composition of the atmosphere 1 1 ga bp a paleosol is exposed along the north bank of the sturgeon river some 25 km sw of baraga michigan the paleosol was developed on hydrothermally altered keweenawan basalt and is overlain by the jacobsville sandstone textures mineralogy and chemical composition change gradually upwards from unweathered metabasalt through the paleosol to the contact of the paleosol with the jacobsville sandstone many of these changes are similar to those in modern soils developed on basaltic rocks however k has clearly been added to the paleosol probably by solutions which had equilibrated with k feldspar in the jacobsville sandstone the keweenawan basalt was oxidized quite extensively during its conversion to greenstone during weathering the remaining fe2 was oxidized to fe3 and was retained in the paleosol the composition of the parent greenstone and its change during weathering can be used to define an approximate lower limit to the ratio of the o2 pressure to the co2 pressure in the atmosphere during the formation of the paleosol formula see text free o2 must have been present in the atmosphere 1 1 ga ago but its partial pressure could have been 10 3 times lower than in the atmosphere today

physical compaction of vertic palaeosols implications for burial diagenesis and palaeo precipitation estimates burial compaction is one of several major obstacles to estimating palaeoprecipitation from depth to pedogenic carbonate in favourably preserved palaeosols palaeosols must be decompacted and the preburial depth to the pedogenic carbonate obtained vertic palaeosols may be particularly good candidates for palaeoprecipitation estimates because of their increased likelihood of preserving clastic dykes one of the best features for estimating burial compaction compaction estimates from clastic dykes and literature based depth of burial estimates suggest vertic palaeosols undergo significantly less burial compaction than may be commonly assumed late carboniferous vertic palaeosols buried to 2 5 3 0 km compacted to 93 of their original thickness in contrast clastic dykes in a nonpedogenic shale directly underlying one of the late carboniferous palaeosols records compaction to 70 of original thickness similarly obtained burial compaction and burial depth estimates for early carboniferous ordovician and proterozoic vertic palaeosols were used to test a burial compaction curve and equation specific to vertic palaeosols results suggest this vertic calibrated curve and equation can be used to estimate burial compaction for vertic palaeosols lacking clastic dykes but additional testing is needed naturally high bulk densities may have limited the compactibility of vertic palaeosols likewise high initial bulk density and an abundance of swelling clays may have severely limited the transmissivity of some vertic palaeosols as they passed from pedogenic to burial environments upon burial these vertic palaeosols may have behaved as closed systems which has implications for understanding their diagenetic modification additional efforts to understand burial compaction of vertic palaeosols also promises to improve our understanding of aquifer aquiclude and hydrocarbon reservoir seal relationships in sedimentary basins containing intercalated palaeosols

palaeosols and sequence stratigraphy of the lower permian abo member south central new mexico usa the relationship between palaeosols and sequence stratigraphy is tested in the lower permian abo member south central new mexico by comparing interfluve and fluvial terrace palaeosols with palaeosols that developed within lowstand fluvial deposits interfluve and fluvial terrace palaeosols consist of primary pedogenic features including vertical root traces vertic structures stage ii and iii pedogenic calcite and translocated clay argillans which are cross cut or replaced by low aluminium goethite gley colour mottling sparry calcite veins and ankerite the polygenetic character of the palaeosols is consistent with initial development for several thousand to tens of thousands of years on well drained interfluves or fluvial terraces followed by waterlogging due to invasion by a rising water table that locally may have been brackish in contrast lowstand fluvial sediment that filled incised valleys contains only rooted and vertic palaeosols whose immaturity resulted from high aggradation rates palaeosols similar to those in the abo member have been recognized in other ancient strata and when combined with highresolution correlation provide evidence for interpretation of sequencestratigraphic surfaces and systems tracts

reappraisal of a 2200 ma old paleosol near waterval onder south africa abstract a fossil soil paleosol about 2200 ma old in a deep roadcut between the towns of waterval boven and waterval onder transvaal here called the waterval onder clay paleosol was formerly reported to have formed on the hekpoort basalt it is here thought to have developed on a thick formerly at least 5 5 m upward fining and thinning sequence of sandstone siltstone and shale derived from pre existing soils on hekpoort basalt within the basal portion of the fluvial dwaal heuvel formation in contrast to paleosols developed on hekpoort basalt the waterval onder clay paleosol is little deformed lacks corestones and shows compositional variation and berthierine rich laminae interpreted as relict bedding the paleosol has a ridge and swale topography linear or wavy gilgai and a subsurface structure mukkara typical of modern vertisols since there is considerable relict bedding it probably formed over a short period of time less than 7000 years and was not self plowing to the extent seen in modern vertisols clastic dikes filled with sandstone from the overlying rocks are evidence that the profile was periodically dry to depths of at least 2 m more drab colored rocks below that may represent the level of permanent water table iron and manganese stain of layers and claystone granules within the surface horizon of the profile have some characteristics of modern rock varnish and could be taken as evidence for life in the soil the high ratio of ferric to ferrous iron near the surface of the paleosol together with evidence from clastic dikes that this horizon was not waterlogged is an indication of an oxidizing atmosphere although probably one in which oxygen was much less abundant than it is today the very low amounts of acid titratable bases in the shaly parent material of this paleosol and surficial loss of these bases within the paleosol appear to have been produced by decarbonation reactions comparable to those found today in soils of vascular land plants a likely source of weathering acid during the precambrian is an elevated abundance of atmospheric carbon dioxide considering these likely atmospheric differences together with the distribution of comparable modern vertisols and other geological evidence the climate under which this soil formed was probably semiarid to subhumid seasonally dry and temperate

on the origin of crevasse splay amalgamation in the huesca fluvial fan ebro basin spain implications for connectivity in low net to gross fluvial deposits abstract floodplain deposits are abundant in low gradient dryland river systems but their contribution to connected reservoir volumes has not yet been fully acknowledged due to their poor detectability with typical wireline log suites and relatively lower reservoir quality this study presents an analysis of stacked crevasse splays in the distal part of the miocene huesca fluvial fan ebro basin spain vertical stacking of crevasse splays implies local aggradation of the active channel belt lateral amalgamation of crevasse splays created an elevated rim around their feeder channel raising its bankfull height subsequent crevasse splays were deposited on top of their predecessors creating sand on sand contact through incision and further raising the active channel belt this process of channel belt super elevation repeated until an upstream avulsion occurred amalgamated crevasse splays constitute connected reservoir volumes up to 107 m3 despite their lower reservoir quality they effectively connect channel deposits in low net to gross fluvial stratigraphy and hence their contribution to producible volumes should be considered unswept intervals of amalgamated crevasse splays may constitute a secondary source of natural gas their interval thickness can serve as a proxy for feeder channel dimensions which can in turn be used to estimate the degree of stratigraphic connectivity

magnetic susceptibility of early paleozoic and precambrian paleosols abstract paleosols formed by weathering and plant colonization during breaks in eolian deposition of quaternary loesses are marked by enhanced magnetic susceptibility these paleosols can be recognized in the field from their soil structure and soil horizons but the most obvious and diagnostic feature of paleosols are root traces for paleosols of early paleozoic and precambrian age pre dating the evolution of rooted land plants root traces cannot be used as a diagnostic field criterion for recognizing paleosols surficial enhancement of magnetic susceptibility can be useful confirmation that some precambrian and early paleozoic rocks were paleosols unfortunately magnetic susceptibility enhancement of some paleosol profiles is compromised by burial gleization which reduces overall susceptibility values but especially susceptibility at the surface of the profile and produces a marked covariance of magnetic susceptibility with total iron content groundwater and surface water gleization during soil formation also depletes susceptibility over a wide range of iron content to give relatively flat depth functions of susceptibility in contrast well drained soils and paleosols have pronounced surficial susceptibility enhancement over a narrow range of iron content magnetic susceptibility peaks are useful supporting evidence for paleosols entirely red and oxidized but not for paleosols with common green gray reduction spots abundant organic matter iron manganese nodules or other evidence of gleization all known paleozoic and precambrian paleosols have susceptibility an order of magnitude less than in comparable quaternary paleosols and soils so that quaternary magnetic susceptibility climofunctions and chronofunctions cannot yet be applied to paleozoic and precambrian paleosols although their susceptibility values are comparable with those of modern gleyed soils paleozoic and precambrian paleosols maintain a depth function of surficial enhancement of susceptibility as well as red color deeply penetrating cracks and other features of well drained soils burial recrystallization of fine grained magnetite and maghemite may have compromised the magnitude of their susceptibility peaks alternatively they may not have been as biologically active in susceptibility enhancing microbes as modern soils

middle moscovian climate of eastern equatorial pangea recorded in paleosols and fluvial architecture abstract fluvial architecture in conjunction with the morphology petrographical mineralogical and geochemical composition of intercalated paleosols of the middle moscovian upper radnice member of the continental kladno rakovnik basin czech republic were studied in order to decipher climatic signals in the eastern pangea region during the late paleozoic ice age analysis of architectural elements reveals vertical changes from strongly amalgamated channel fills of bedload dominated braided streams to isolated ribbon like meandering channel fills in mud dominated floodplain strata the resulting large scale fining upward cycles separated by laterally widespread bounding surfaces are interpreted as having been formed in response to allocyclic processes driven by variable intensities of precipitation which affected the density of vegetation cover across the landscape and in turn the amount and character of sediment supply bedload dominated parts of the cycles were deposited during periods of low water tables and sparse vegetation whereas periods of maximum precipitation resulted in higher water tables and a greater density of vegetation cover which in turn stabilized the floodplains and fixed streams to narrow meandering anastomosing channels in mud dominated floodplain strata associated paleosols resemble modern vertisols which form under seasonal precipitation in modern settings however coeval formation of inertinite rich peat represented by histosols and gleyed low chroma vertisols in the stratigraphically lowest paleosol succession occurred under overlapping marginal conditions for the climatically different types of soils i e under a seasonal climate where precipitation exceeds evapotranspiration for 6 to 8 months out of the year mean annual precipitation calculated from the geochemistry of b horizons of vertisols calmag proxy varies between 1815 and 1730 mm yr

eocene paleosols on king george island maritime antarctica macromorphology micromorphology and mineralogy abstract we investigated the origin of reddish layers between basalt flows in an early eocene volcanic succession in king george island maritime antarctica previous studies in the area classified these layers as regolith surfaces baked zones and paleosols but the properties of these layers and the reasons for their classification are not clarified since the early eocene epoch was one of the warmest phases on earth during the cenozoic a proper investigation of these layers is crucial to obtain additional regional information about the paleoenvironment the focus of this study is on three profiles located in the admiralty bay on king george island they were classified as paleosols based on field micromorphological and mineralogical properties main soil forming processes identified by micromorphological analyses were clay neoformation pedo bioturbation and a weak redoximorphosis the occurrence of plant residues in all profiles was a reliable indicator that these soils formed a land surface during the early eocene abundant weathered volcanic glass and pyroclasts may indicate andosolization although the main diagnostic features for andosols which are the presence of nanocrystalline minerals and organic matter accumulation were not detected or only in small amounts respectively the long term burial of the paleosol could be a reason for lacking of these diagnostic features clay minerals associated with moderately weathered volcanic soils smectite were detected in the x ray diffraction analysis a predominantly reddish colour of most of the soil horizons is given by hematite confirmed by the determination of pedogenic oxides nevertheless rubification was not solely a result of pedogenesis but also of reddening of oxyhydroxides by dehydration during diagenesis other diagenetic processes were burial compaction loss of organic matter and induration in the horizons directly buried by a basalt flow voids were filled by zeolite crystals an effect related to lava cooling another possible diagenetic effect was the geochemical rejuvenation and homogenization of the profiles despite the occurrence of these features the results are in agreement with previous studies indicating a humid temperate paleoclimate for king george island during the early eocene

rb sr evidence for punctuated illite smectite diagenesis in the oligocene frio formation texas gulf coast the size fractions of a suite of upper oligocene frio formation shale samples taken from below 10 500 ft in a well on the texas gulf coast fall on a rb sr isochron corresponding to an age of 23 6 0 8 m y the isochron shows an initial 87 sr 86 sr ratio of 0 7088 0 0004 this suggests that regularly interstratified illite smectite simultaneously equilibrated soon after burial over a range of burial depths at 7 000 8 000 ft shallower than at present oxygen isotope values for these clays are also consistent with equilibration under shallower burial conditions such a pattern conflicts with the prevailing idea of a gradual illitization of smectite with progressive burial a new model of episodic or punctuated diagenesis is proposed whereby sudden diagenesis is initiated by a change in pore water chemistry clay reaction occurs over a range of temperature at this time such that the deeper clays are transformed completely to 80 illite and the shallow clays are transformed less completely subsequent pore water chemical changes inhibit further clay reaction and the mineralogic gradient and the isotopic signature formed at 23 6 m y b p are frozen in seven to eight thousand feet of additional post oligocene burial has not resulted in the creation of younger illite smectite consequently there is no evidence that illite smectite diagenesis is currently taking place in the frio formation

model for k bentonite formation evidence from zoned k bentonites in the disturbed belt montana thirty four k bentonites from the marias river formation upper cretaceous in the montana disturbed belt have been studied in detail a 2 5 m thick k bentonite is zoned mineralogically and chemically the upper and lower contacts of the bed being more illitic and k rich than the middle of the bentonite k ar dates of illite smectite separated from the bed are also zoned yielding older ages at the contacts than at the center a model for the formation of k bentonites enclosed by k rich shale is presented in which k bentonites form from smectite bentonites during a thermal event t 100 200 c potassium is derived from mineralogic breakdown probably mica and k feldspar in the shale and migrates by diffusion into the bentonite

quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols abstract paleosols fossil soils are preserved throughout the geologic record in depositional settings ranging from alluvial systems to between basalt flows until recently paleosols were studied using primarily qualitative methods in recent years paleopedology has shifted from a largely qualitative field based on comparisons with modern analogues to an increasingly quantitative endeavor some of this change has been a result of applying existing techniques to new materials but many of the innovations have been the result of applying new techniques to new materials including thermodynamic modeling of soil formation isotope geochemistry and applications of empirical relationships derived from modern soils a variety of semi quantitative and quantitative tools has been developed to examine past weathering and pedogenesis and to reconstruct both paleoenvironmental and paleoclimatic conditions at the time that the paleosols formed though it is often not possible to achieve the same temporal resolution as with marine records for paleoclimatic reconstructions proxies based on paleosols are potentially a much more direct means of making paleoclimatic reconstructions because soils form at the earth s surface in direct contact with the atmospheric and climatic conditions at the time of their formation paleoclimatic and environmental properties that may be reconstructed using the new proxies include provenance weathering intensity mean annual precipitation and temperature during pedogenesis nutrient fluxes into and out of the paleosols the atmospheric composition of important gases including co2 and o2 the moisture balance during pedogenesis the soil gas composition reconstructed vegetative covering and paleo altitude

metamorphic alteration of a precambrian 2 2 ga paleosol from south africa revealed by backscattered electron imaging abstract like many precambrian paleosols the 2200 ma old waterval onder clay has been metamorphosed to the greenschist facies of regional metamorphism the extent of metamorphic alteration of the fine grained uppermost horizons of the paleosol is assessed here using optical and backscattered electron microscopy in hand specimens and under low power optical examination the paleosol shows surficial lamination cumulic horizon of soil terminology rounded clasts coated with opaque sesquioxides manganoferriargillans cracks defining a fitted breccia of blocks that were evidently soft in places blocky angular peds cracks filled with multiple generations of material from above illuviation argillans and zones of unusually highly birefringent clay climobimasepic plasmic fabric with backscattered electron microscopy however at a resolution of less than about 10 m the fine structure of originally colloidal parts of the paleosol mangans argillans matrix and plasma separations is shown to be extensively recrystallized to illite and berthierine original soil structure has been obscured at this resolution by crystal growth at random across original microscopic discontinuities preferred orientation of metamorphic crystals can still be seen along what are presumed to be highly birefringent zones of oriented clay similar to those in modern soils but the matrix itself shows random clusters of crystals suggestive of an advanced stage of illitization by ostwald ripening the style of recrystallization of laminae in the surface horizon is similar to that seen lower in the profile where recrystallized beds are thicker and coarser grained thus the paleosol probably formed on an upward thinning and fining sequence of sandstone and shale rather than on basalt on this assumption the profile has gained iron compared with its shaly parent material rather than lost iron compared with basalt this may be an indication of greater oxygenation of the atmosphere than previously thought possible microbial traces can be seen in thin section but because of pervasive recrystallization these remain dubiofossils

paleosols in devonian red beds from northwest china and their paleoclimatic characteristics abstract paleosols have been discovered in the late devonian famennian shaliushui formation near pingchuan city gansu province china and are recognized by evidence of root traces soil horizons and soil structures root traces are remnants of substantial woody plants reaching deeply within profiles as clayey infills and as drab haloed root traces soil horizons include thick layers of large calcareous nodules bk horizon and subsurface accumulations of clay bt horizon and slickensided claystone vertic bw horizon soil structures include blocky peds and calcareous nodules the nodules and drab haloed root traces formed syndepostionally during the late devonian because they were also observed in clasts of paleosol and nodules in fluvial conglomerates interbedded with the paleosols analyses for rb sr and ba sr ratios and magnetic susceptibility measurements confirm that the more strongly developed paleosols with larger calcareous nodules and higher clay content are also more chemically differentiated and have higher magnetic susceptibility under semi arid climates this suite of paleosols is evidence of semi arid to sub humid highly seasonal climate under dry woodlands and shrublands paleosols of the shaliushui formation are a potentially valuable archive of late devonian palaeoclimates of northwest china

an integrative physical mineralogical and ichnological approach to characterize underfilled lake basins fil mancuso adriana cecilia consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet mendoza instituto argentino de nivologia glaciologia y ciencias ambientales provincia de mendoza instituto argentino de nivologia glaciologia y ciencias ambientales universidad nacional de cuyo instituto argentino de nivologia glaciologia y ciencias ambientales argentina

three dimensional swelling of clay lumps the disposal of large volumes of clay lumps obtained from underground construction activities and seabed dredging is a problem in a highly built up environment such as singapore the use of such clay lumps for reclamation of land is an environment friendly proposition the clay lumps when placed under water will undergo three dimensional swelling calculation of the degree of swelling is important for making decisions on when to place surcharge and in what quantity on top of the fill for closing the inter lump voids this paper reports the results of experimental and numerical studies that were carried out to understand the swelling behaviour of clay lumps when placed under water experimental results were compared with finite element method results using linear and non linear elastic models the study shows that the suction present in the lumps increases initially before dissipation suggesting the presence of the cryer mandel effect during three dimensional swelling the importance of simulating co

premetamorphic lateritisation in proterozoic metabasites of rogaland sw norway heterogeneous layers of granulite facies metamorphic basites of the proterozoic supracrustal faurefjell formation in rogaland s w norway display an extreme chemical variation within a single layer the bulk chemical composition gradually changes from approximately basaltic in basic granulites to alumina iron rich in granofelses component ratios and composition volume relations indicate open system chemical reactions mainly involving the extraction of silica apparent enrichment in fe ti p al zr ni co zn y nb hf and ree and variations in resulting metamorphic mineral assemblages are related to premetamorphic progressive lateritisation of a basaltic protolith the weathering generated a continuous chemical suite from sio2 48 wt fe2o3 10 wt and al2o3 19 wt in the basic granulites to 14 wt 40 wt and 25 wt in the fe al granofelses metasomatism during diagenesis and during very high grade metamorphism 1200 900 ma further perturbed the concentrations of relatively mobile elements ca mg k rb sr ba na and li in the laterites without affecting the transition metal ratios in particular the ree did not fractionate differentially during the supracrustal and metasomatic alteration

chemistry and mineralogy of precambrian paleosols at the base of the dominion and pongola groups transvaal south africa abstract we have studied alteration zones found between sedimentary rocks of the lowest proterozoic dominion and archean pongola groups and underlying granitic rocks transvaal south africa the alteration zones have a transitional lower boundary primary igneous minerals are gradually destroyed upward toward the contact with overlying sedimentary rocks ca mg na p and mn are progressively lost upwards in the zone the chemical and mineralogical variations and available stratigraphic evidence are all consistent with the interpretation that these zones are paleosols formed by precambrian weathering 2 8 3 0 ga ago after formation the paleosols underwent metasomatism and metamorphism sericite now present in the paleosols was probably formed by low temperature potassium metasomatism of original clays andalusite in the pre pongola paleosol was probably formed by metamorphism of original clays in impermeable zones which prevented groundwater flow and potassium metasomatism the dominion paleosol was investigated at three localities the effects of weathering were similar at the three sites except for the behavior of iron one site lost about 20 of iron whereas the other sites lost 75 and 80 of initial iron content the differences in iron loss may be due to variation in soil ventilation and diffusion of atmospheric gases as a function of grain size and topography variations in iron loss may be used to place some constraints on the composition of the precambrian atmosphere given constraints imposed by dominion paleosols overlying uraniferous conglomerates requirements for chemical weathering and the greenhouse effect and possible presence of non diffusing photochemical oxidants the partial pressures of oxygen and carbon dioxide gases probably are in the ranges po1 0 02 to 0 5 pal present atmospheric level and pco2 5 to 30 pal

petrography and geochemistry of a 2000 2200 ma old hematitic paleo alteration profile on ongeluk basalt of the transvaal supergroup griqualand west south africa abstract a 4 m thick paleo alteration profile thought to represent one of the oldest known ferruginized hematitic paleoweathering zones is described from a depth of 720 m in a drill core on the farm drakenstein 263 some 20 km northwest of hotazel in griqualand west south africa the paleo alteration profile is developed on 2240 57 ma ongeluk basalt along the angular unconformity that separates transvaal strata from 2070 95 ma basal red beds of the olifantshoek group basaltic ongeluk lava was subjected to greenschist facies metamorphism represented by a mineral assemblage of fe pumpellyite chlorite albite and quartz before paleosol development the subsequent paleo alteration is characterized by concentration of fe2o3 in the form of hematite iron rich chlorite and abundant sericite the abundance of sericite results in a large excess of k2o relative to the amount of al2o3 that could have been derived from weathering of the parent basalt the origin of the excess potassium is problematical and could have been derived from basin water groundwater or metamorphic fluids field relationships favour introduction from basin water during deposition of overlying olifantshoek red beds elements such as sodium calcium and magnesium were leached from the alteration profile whereas ree became concentrated within it the most interesting aspect of the ree distribution is the preferred concentration of the lighter lanthanides la and nd in the middle part of the alteration profile relative to heavy ree and the development of a marked negative ce anomaly in the paleo weathered material hydrothermal vein alteration took place after deposition of the overlying olifantshoek red beds

chromium isotope fractionation during oxidative weathering implications from the study of a paleoproterozoic ca 1 9ga paleosol schreiber beach ontario canada abstract this study reports detailed stable cr sm nd and rb sr isotope data for a ca 1 9 ga old subaerial weathering profile at schreiber beach ontario canada from which detailed major and trace element signatures and 18 o values were previously reported the weathering profile developed on neoarchean 2 7 ga pillow basalts and is unconformably overlain by the paleoproterozoic 1 88 ga gunflint chert and basal conglomerates this stratigraphy suggests that the basalts were uplifted and subaerially weathered prior to deposition of the gunflint formation the aim was to investigate the behaviour of chromium during ancient weathering processes and to contribute to the question whether or not stable isotope fractionation accompanied the release of chromium from the weathering rocks at times when atmospheric oxygen was supposedly high enough in a period following the great oxygenation event goe 2 45 ga ago and prior to the deposition of the gunflint cherts at 1 82 ga these iron rich cherts belong to one of the last regionally extensive banded iron formations bifs deposited before the 1 billion year long mesoproterozoic period during which a drastic change in ocean chemistry prevented deposition of bifs the gradual textural mineralogical and geochemical changes from unweathered basalts to strongly weathered hematite bearing basalts with increasing stratigraphic height are associated with shifts in the chromium isotope compositions the 53 cr value of unweathered pillow basalt cores 0 19 0 02 2 is within the range of mantle inventory values whereas weathered brown to green basalts soils exhibiting up to 30 lower cr concentrations compared to unweathered pillow cores are isotopically lighter 53 cr 0 35 0 11 in contrast red hematite rich basalts and hyaloclastites underlying the brown to green basaltic soils with the highest 18 o enrichment in the profile are isotopically heavier 53 cr 0 05 0 15 rb sr isotope data of weathered basalts define a correlation line with a slope corresponding to an age of 1574 24 ma mswd 13 which we interpret to reflect a diagenetic event accompanied by alkaline metasomatism during subsidence burial of the gunflint basin the non correlation of k enrichment factors with 53 cr 18 o and other major and trace elements in the weathered rocks indicates that alkaline metasomatism did not affect the geochemical signatures produced during in situ subaerial weathering instead correlations between 53 cr and 18 o and between 53 cr ce ce u and v indicate coupled mobilization of the redox sensitive elements during oxidative processes and their partial re deposition at depth from high 18 o freshwaters partial re precipitation of heavy cr at depth can be explained on the basis of the weak positive correlation between 53 cr and fe enrichment factors it is seen as a consequence of the reduction of mobile cr vi and co precipitation as mixed fe iii cr iii oxhydroxides during contemporaneous oxidation of the fe 2 bearing groundwaters at depth a process similar to the one governing the deposition of most precambrian bifs redistribution of certain elements during the weathering process in this case rees is furthermore indicated by a correlation line in a sm nd isochron diagram defined by the schreiber beach data with a slope corresponding to an age of 1 93 0 19 ga mswd 26 an age which is compatible with the direct geological constraints for the timing of the paleosol formation at this locality an oxidative atmosphere at 1 9 ga as implied by the results from the schreiber profile is furthermore supported by positively fractioned cr isotopes 53 cr from 0 06 to 0 39 recorded in the iron rich gunflint cherts directly above the palaeo weathered horizons at schreiber beach these values are interpreted to stem from a positively fractionated shallow seawater chromium composition at 1 88 ga potentially reflecting a continental run off characterized by positive 53 cr and are in accordance with cr isotope signatures in worldwide bifs including the gunflint iron formation our results show the potential of cr isotope studies on ancient paleosols to untangle the presence of oxidative weathering processes making this isotope system a viable and important tracer for the reconstruction of surface oxygenation in earth s history

a vertic paleosol at the archean proterozoic contact from the singhbhum orissa craton eastern india abstract we report on an inferred paleoproterozoic soil horizon from the singhbhum orissa craton near keonjhargarh orissa eastern india which preserves vertic vertisol like features the 2 10 m thick white shale consists of quartz muscovite pyrophyllite interpreted as a paleosol overlies 3 32 ga granite and is covered by pre 2 0 ga sandstones kolhan group deposited in marginal marine environments the paleosol passes downwards through a partly altered granite saprolith zone to fresh granite abundant pedogenic slickensides ped structures gilgai topography reddish stain on ped surfaces and sepic plasmic microfabric in the paleosol were probably related to shrink and swell processes driven by marked seasonal precipitation in a well drained landscape an observed decrease of alkali elements and an increase of silica alumina and cia values from granite to paleosol together with relatively constant ti al ratios suggest in situ weathering of granite protolith however a paleo vertisol necessitates a mafic parent rock either directly igneous or reworked through alluvium the c 2 25 ga malangtoli jagannathpur basaltic rocks are relatively widespread and close to the inferred paleosol occurrences and provide a logical solution geochemistry of the highly depleted paleosol in contrast particularly when applying the isochon method strongly supports a granitic parent the apparent conundrum can possibly be solved through repeated alluvial reworking of both granitic and mafic detritus and accumulation of weathered material with varying proportions of these two components yet enough smectitic clays 30 to form a paleo vertisol this pre 2 0 ga weathering event in the singhbhum craton is consistent with a global scenario of paleoproterozoic weathering which followed an extended global glaciation and thus has the potential to contribute to understanding of pre 2 0 ga amalgamation of regional and global cratonic blocks

sequence stratigraphic context of extensive basin margin evaporites middle jurassic gypsum spring formation wyoming u s a abstract ancient marine evaporites are commonly far more extensive than any known modern evaporite system this is true not only for basin central saline giants but also for evaporites that occur in basin margin settings and the origin of these basin margin systems is unclear extensive basin margin evaporites of the middle jurassic gypsum spring formation are well exposed along the eastern flank of the bighorn basin in wyoming usa and a facies and sequence stratigraphic analysis was undertaken to understand the origin of these evaporites and associated deposits the gypsum spring formation was deposited on a northwestward dipping mixed evaporate carbonate siliciclastic ramp with facies and depositional environments that include distal ooid shoal grainstone open marine shallow subtidal peloidal skeletal wackestone to packstone restricted shallow subtidal laminated lime mudstone peritidal dolostone and microbialite as well as red mudstone and gypsum deposited on mud flats sabkhas and salinas three depositional sequences are present with the j 1 j 1a and j 1b sequence boundaries characterized locally by chert pebble lags silicified horizons and iron rich paleosols evaporites accumulated in a basin margin position with 1 6 m beds of gypsum forming in salinas and sabkhas and nodular anhydrite and gypsum forming in red mudstones deposited on sabkhas and mud flats the limited lateral extent of salina type gypsum beds and the variable number of these beds among the exposures indicates substantial autocyclic control on the formation of salinas salinas are well developed in the tst of the j 1 sequence and sabkhas and mud flats are well developed in the j 1 hst the j 1a hst and the j 1b tst the great lateral extent of the gypsum spring evaporites reflects the original expanse of the depositional environment in which they formed and is not the result of diachroneity of a narrow evaporite precipitating belt such as the modern day coastal sabkhas of the trucial coast the great lateral extent of gypsum spring evaporites suggests that they were precipitated mainly from continental brines on an expansive desert mudflat

intergranular pressure solution in four quartzose sandstones abstract cathodoluminescence petrography and scanning electron microscopy reveal that several geologic variables significantly influenced intergranular pressure solution and quartz cementation in the bromide ordovician oklahoma upper minnelusa permian wyoming nugget jurassic utah and tuscarora silurian pennsylvania sandstones a linear relationship exists between mean grain size and intergranular pressure solution with finer grained samples having experienced more intergranular pressure solution than coarser grained ones samples that display pervasive illite grain coatings have also experienced more intergranular pressure solution than those with no or poorly developed grain coatings sorting and limited framework grain compositional variability have exerted little influence o intergranular pressure solution silica budgets indicate that in the bromide upper minnelusa and nugget sandstones more quartz has been dissolved by intergranular pressure solution than is present as cement these sandstones have exported silica during burial diagenesis in the tuscarora the amount of quartz dissolved by intergranular pressure solution is about equal to the amount of quartz cement present implying approximate mass balance however petrographic evidence suggests that most of the quartz cement in at least three of these sandstones predates most intergranular pressure solution implying that they acted as silica importers during shallow diagenesis and silica exporters during deeper diagenesis intergranular pressure solution has played varying roles in determining the ultimate porosity of these four sandstones in the nugget intergranular pressure solution was the single most important diagenetic process that influenced porosity evolution in the bromide intergranular pressure solution was slightly more important than mechanical compaction and considerably more important than cementation in the tuscarora intergranular pressure solution was slightly more important than mechanical compaction and of about equal importance to quartz cementation in the upper minnelusa intergranular pressure solution was less important than both mechanical compaction and gypsum anhydrite cementation

evaluating the use of weathering indices for determining mean annual precipitation in the ancient stratigraphic record abstract different quantitative methods have been developed to determine paleo rainfall using paleosols of particular interest are methods that use bulk geochemistry to calculate a weathering index and from that mean annual precipitation twenty three paleosols that formed during a time of significant climate change the paleocene eocene thermal maximum petm were analyzed to evaluate the relative merits of two geochemical proxies that have been developed for estimating paleoprecipitation one depends on the chemical index of alteration without potash cia k and the other uses the calmag weathering index which depends on cao and mgo the paleosols are located in the paleogene fort union and willwood formations in the bighorn basin wy morphologic differences among the paleosols indicate that they formed under varied soil moisture conditions a morphology index was developed from pedogenic features that are sensitive to soil drainage and thus to rainfall to assess that variability quantitative mean annual precipitation map values were calculated for each paleosol using the cia k index and the calmag index which was developed specifically for vertisols those results were compared to the morphology index for 23 paleosols the results indicate that increases and decreases in map calculated from both methods correlate relatively well to changes in the soil morphology index however the results from the calmag weathering index show a stronger correlation the results suggest that the calmag proxy provides a more robust map estimate for vertisols in addition to comparing map estimates to the soil morphology index we compared the map values to paleorainfall estimates determined from paleofloras at the same stratigraphic levels as three of the paleosols that comparison confirms that the calmag method is reliable for reconstructing map from ancient vertisols the results also show that in the bighorn basin vertisols with a b horizon

carbon isotope fractionation during decomposition of organic matter in soils and paleosols implications for paleoecological interpretations of paleosols abstract stable isotope ratios reported as 13c of organic carbon preserved in paleosols have potential utility as a valuable paleoecological indicator if the isotopic composition of paleobiomass is preserved in the paleosol organic carbon without fractionation however soil organic matter is in a constant state of decomposition in an open system and frequently decomposes further during alteration after burial of the paleosol during this decomposition kinetic fractionation of 13c 12c in an open system results in concentration of 13c in the residual organic matter preserved in the soil and paleosol this paper summarizes studies of modern soils which show that this 13c enrichment follows a rayleigh distillation process whereby the 13c 12c ratio is a function of the natural logarithm of the fraction of remaining soil organic carbon leaving soil organic carbon 13c enriched by up to 6 with respect to the original biomass if the fraction of original biomass carbon remaining during these decomposition processes deviates significantly from 1 the soil organic carbon can be 13c enriched by several per mil and thus not a good paleoecological indicator of the 13c value of the original biomass therefore effective paleoecological studies of 13c preserved in paleosol organic carbon must therefore demonstrate that the measured concentration of organic carbon in the paleosol is near its maximum concentration during soil formation or that the paleosol organic matter does not include the 13c enriched products of microbial decomposition suggestions are made for interpreting the effects of carbon isotope fractionation of organic matter and for materials and methods most useful for paleoecological studies from bulk paleosol organic carbon

fluvial sedimentology and revised stratigraphy of the triassic flagstone bench formation northern prince charles mountains east antarctica the flagstone bench formation ranges in age from earliest triassic to norian late triassic and is exposed in the beaver lake area of the northern prince charles mountains this sandstone dominated formation rests conformably on the bainmedart coal measures and represents the upper part of the permian triassic amery group it is divisible into three members the ritchie jetty and mckelvey members in ascending order nine sedimentary facies assignable to three facies associations major channel crevasse fan and flood basin deposits are recognized within the formation ritchie member sedimentation took place during a transition from consistently hygric to seasonally dry conditions and the unit comprises sandstone dominated sheet like channel deposits interspersed with few thin mottled haematite rich flood basin siltstones deposition took place under fluctuating discharge conditions chiefly within the channel tracts of axially northwesterly northeasterly flowing low sinuosity braided rivers the jetty member shows a gross upward fining profile dominated in the lower part by poorly sorted pebbly sandstones and in the upper part by ferruginous mudcracked siltstones mottled palaeosols calcrete and thin massive sandstone sheets this unit reflects deposition of easterly directed alluvial fans and extensive flood basin silt under a semi arid climatic regime the upper triassic sandstone dominated mckelvey member shows a return to axial drainage along the lambert graben with sedimentation occurring primarily within low sinuosity braided channel tracts under wetter climatic conditions

the proterozoic thelon paleosol northwest territories canada abstract beneath the 1 72 ga thelon formation in the northwestern part of the canadian shield an unmetamorphosed and undeformed paleosol is preserved on a variety of paleoproterozoic and archean protoliths this paper documents the paleosol referred to as the thelon paleosol in four localities where it developed on leucocratic schist gneiss and granite the thelon paleosol is characterized by these ascending changes from fresh protolith through paleosol to the unconformity a saprolitic disruption of the protolith resulting in ped and ferran formation b reddening of the paleosol as a consequence of hematitization c increase in dissolution of feldspar plagioclase alkali feldspar increase in the degree of iron oxidation in biotite chlorite and garnet and an increase in the abundance of neoform kaolinite illite and hematite cement d a loss of tio2 fe2o3 total feo mno mgo cao na2o k2o p2o5 u zr rb sr ba e a gain of fe2o3 and f an increase in cia values the fabric of the parent material appears to be the only soil forming factor that locally influenced paleosol development in comparison to thin profiles developed on massive relatively impervious protoliths thick profiles have developed on metamorphic protoliths in which the fabric has allowed deeper penetration of paleoweathering fluids the behaviour of iron in the profiles particularly profile 2 with a granite protolith and an increase in hematite towards the top of the profiles suggests that the thelon paleosol formed under an oxidizing atmosphere subsequent deposition of quartzose conglomerate and sandstone of the thelon formation has caused compaction of the thelon paleosol and this compaction probably was responsible for the formation of stylocumulates in the paleosol during diagenesis of the thelon formation the influx of diagenetic fluids into the paleosol produced veinlets of quartz and hematite a newly recognized microcrystalline hydrated alumino phosphate sulphate mineral and widespread pseudomorphs of illite after pedogenic vermiform kaolinite

terrestrial paleoenvironmental reconstructions indicate transient peak warming during the early eocene climatic optimum major changes in climate and ecology occurred during the early eocene climatic optimum sometime between 52 and 50 ma recent work suggests that the timing and duration of the event are characterized by different responses in the marine and terrestrial realms and that traditional causal mechanisms may not adequately explain such differences we applied high resolution paleopedology geochemical analysis and phytolith biostratigraphy techniques to paleosol suites within the well described wind river formation of western wyoming usa this multiproxy record indicates a short 1 m y peak period of carbon isotopic enrichment up to 2 higher and elevated pco2 high temperatures up to 8 c higher increased precipitation up to 500 mm yr 1 higher and shifts in fl oral composition up to 10 terrestrial climatic and ecological changes of this kind during the early eocene climatic optimum are consistent with changes in contemporaneous records that have been ascribed to high atmospheric pco2 but a transient peak interval suggests that the cause of high atmospheric pco2 during the early eocene was likely not increased volcanism or decreased silicate weathering which operate on longer timescales instead terrestrial records from across western north america agree that early eocene climatic optimum changes may have been caused by other sources such as a combination of increased ventilation of oceanic carbon and increased petroleum generation in sedimentary basins the climatic and environmental changes exhibited by this and other north american terrestrial records also defi ne a pattern of regional response that is relevant for understanding the impacts of global climate change events

profiles of elemental concentrations in precambrian paleosols on basaltic and granitic parent materials abstract profiles of elemental concentrations are interpreted for four precambrian paleosols two developed on basalt and two on granodiorite all four paleosols appear to be the erosional remnants of originally thick soil saprolite regoliths the granitic paleosols are in south africa where they underlie the 2 9 3 0 ga pongola supergroup and the 2 8 2 9 ga dominion reef conglomerate one of the basaltic paleosols also occurs in south africa where it caps the ventersdorp basalt and underlies the 2 3 ga black reef quartzite the other basaltic paleosol underlies sandstone of the 2 7 ga timiskaming group in the abitibi belt of the canadian shield all four paleosols exhibit pronounced upward loss of sodium but no consistent loss of the heavier alkali elements rubidium and cesium iron decreases upward above iron rich basaltic parent rocks but there is no consistent loss of iron above iron poor granitic parents the rare earth elements are less fractionated than during intensive modern weathering uranium locally has been fractionated from thorium possibly due to oxidative dissolution during precambrian weathering

a review of apatites iron and manganese minerals and their roles as indicators of biological activity in black shales abstract biological contribution to the formation of minerals has become more than a descriptive area in geological thought and research mechanisms of specific mineral accumulation and deposition in oceancs lakes and even desert environment are studied using interdisciplinary approaches and applied in the interpretation of earth processes phosphorus iron and manganese are and probably were essential elements in life forms the common minerals of these elements apatite and magnetite for example can be found in a variety of sedimentary environments both ancient and modern where they could be useful indicator minerals to interpret geologic environments the crystal morphological structural and chemical including isotopic attributes of these usually fine grained minerals can be compared with bulk chemical and stratigraphic information to augment our understanding of the mechanisms of formation and diagenesis in sediments such as black shales

diagenetic reddening of early eocene paleosols on king george island antarctica abstract the objective of this study was to determine if the early eocene paleosols on king george island maritime antarctica have acquired their reddish color during the paleopedogenesis by burial diagenesis and or by heating of a covering lava flow we used micromorphology diffuse reflectance spectroscopy x ray diffraction and mineral magnetic properties to identify the iron oxides in these paleosols these are weakly moderately developed paleosols formed on a basaltic tephra under a cool humid paleoclimate therefore prone to ferrihydrite and goethite rather than hematite formation however the iron oxide assembly was dominated by maghemite and hematite nevertheless the large grain size and high crystallinity of hematites suggested they are rather diagenetic than pedogenic the clustering content and distribution of hematites finely dispersed on the groundmass coating replacing primary minerals and as mottles and or nodules rather than their crystal size were responsible for the color differences these properties were likely the result of past pedogenesis processes forming originally ferrihydrite linked with paleodrainage conditions heating by the covering lava flow affected the magnetic properties of two profiles but without affecting their color taken together all these results suggest that the burial reddening took place by dehydration and transformation of ferrihydrite to hematite our findings highlight the importance of detailed mineralogical analysis to identify iron oxides present in reddish paleosols because identification based solely on morphology e g yellowish color gradual horizon transitions can lead to misinterpretation of paleoenvironmental conditions

influence of provenance and preservation on the carbon isotope variations of dispersed organic matter in ancient floodplain sediments 1 carbon isotope ratios of bulk organic matter in sedimentary rocks 13cdom are a potential source of paleoenvironmental information in terrestrial stratigraphic sequences however insufficient understanding of the range of depositional and post depositional controls on 13cdom values makes interpretations of these data difficult here we evaluate the effects of organic matter om provenance and preservation on 13cdom using records spanning the paleocene eocene thermal maximum petm in the bighorn basin wyoming usa as a case study we sampled sedimentary rocks spanning the petm in two well studied locations polecat bench pb and highway 16 hw16 in the bighorn basin independent carbon isotope records from biomarkers and pedogenic carbonates at these sites suggest that local shifts in plant and soil 13c values associated with the petm cie were broadly similar and were characterized by an abrupt 5 decrease followed by a plateau and a eventual return to pre petm 13c values the 13cdom records from both sites differ significantly from these reference curves in both amplitude of change and in preserving high frequency isotopic fluctuations and large isotopic anomalies superimposed on the general pattern of isotopic change through the cie for each location we separated organo mineral fractions mom concentrated macerals from 20 stratigraphic levels and analyzed the carbon isotope ratio 13c of each fraction at both sites the 13c of the fine and coarse mom differ significantly from each other and from 13cdom concentration weighted mixing of these isotopically distinct om fractions explains high resolution 13cdom fluctuations but does not explain the large isotopic anomalies observed at both sites at hw16 we identified two thermally and isotopically distinct populations of macerals interpreted as being indigenous and recycled om at this site one over total organic carbon 1 toc values correlate with 13cdom for pre petm and petm strata and both relationships converge toward the 13c of recycled om for low toc at pb macerals display homogeneous thermal maturity but the proportion of isotopically distinct vitrinite and liptinite varies between facies relationships between 1 toc and 13cdom are also present within specific stratigraphic intervals at pb but values do not converge on a single isotopic value across the sampled interval these observations are consistent with variable mixing of om fractions having different provenance mixing of exotic recycled om at hw16 and locally reworked om at pb with indigenous fresh om at both sites and explain the large anomalies observed in the 13cdom records at both sites our findings raise questions about the assumption that om in ancient sediments is indigenous and dominantly records 13c variations of local plants

petrography and diagenesis of silcrete from the kalahari basin and cape coastal zone southern africa abstract silcrete is widely distributed in southern africa and occurs both in genetic association with deeply weathered bedrock weathering profile type and as a significant component of the cenozoic kalahari beds where it has formed through silicification of a variety of continental deposits nonweathering profile type silcrete fabrics are classified into four major types gs grain supported skeletal quartz grains in contact f floating skeletal grains floating in matrix m matrix skeletal grains 5 of volume and c conglomeratic detrital component containing pebbles f and m fabric types are subdivided on the presence absence of glaebules replacement by silica of a precursor matrix can account for the development of all four fabric types but at least some gs and c fabr c silcretes have formed by passive silica precipitation in packing voids glaebules and colloform features predominantly composed of concentrations of anatase and iron oxide are common in weathering profile silcretes but their precise origin is uncertain authigenic silica is present as megaquartz microquartz length slow and length fast chalcedony predominantly in void fills cryptocrystalline silica and opal ct depending on the silica and ionic concentrations of pore waters ph and host sediment characteristics diagnostic petrographic features including glaebules colloform structures and chalcedonic vugh fills may be used in conjunction with geochemical data and sedimentary associations to interpret silcretes in the stratigraphic record with respect to weathering profile types formed in humid low ph environments or nonweathering profile types formed in high ph semiarid to arid environments

middle triassic paleosols and paleoclimate of antarctica abstract the lashly formation in the allan hills of southern victoria land antarctica is now at a latitude of 76 s and during the middle triassic was at least 70 s the combined evidence of fossil roots and soils indicates a paleoclimate unusual for such a high latitude temperate paleotemperature is indicated by roots logs and leaves of woody plants and the degree of chemical weathering and clay formation within the paleosols paleosols of the lashly formation are more like soils of southern sweden than those of either finland or southern europe silt infiltration structures around root traces and in cracks within the paleosols are evidence for a seasonally snowy climate but there is no evidence of ice wedges or other permafrost features in the paleosols other evidence of climatic seasonality includes well defined growth rings in fossil wood and abscission scars at the base of fossil leaves diverse broadleaf plants and noncalcareous paleosols indicate a humid climate with mean annual precipitation of about 1200 mm such a wet climate is anomalous for the interior of the supercontinent of pangea and such a warm and mildly seasonal climate is anomalous for such high latitudes this paleoclimatic anomaly may be a lingering effect of global greenhouse initiated at the permian triassic boundary paleoclimatic variables calculated here may be useful for recalibrating global paleoclimatic models for the middle triassic

ecosystem response to soil biogeochemical behavior during the late cretaceous and early paleocene within the western interior of north america paleosol properties are routinely characterized by whole rock geochemistry compromising the interpretation of important biogeochemical information in deep time as a consequence we employ a new pedotransfer function approach to the characterization of paleosols and apply this methodology to late cretaceous campanian and maastrichtian and early paleocene danian landscapes from the dawson creek study area of the western interior to 1 reconstruct collodially based physical and chemical soil properties and 2 assess climate and soil biogeochemical controls on evolving terrestrial ecosystems nine paleoseries i e pedotypes characterize the range of soil properties within the fluvial stratigraphic succession which includes entisols inceptisols and vertisols all soils had optimal water holding potential as inferred from low bulk densities whereas poorly drained and colonizing landscapes likely suffered from poor aeration during seasonal water logging even with high water holding capacity maastrichtian soils experienced seasonal moisture stress because of lower rainfall than campanian and danian soils fertility levels were sufficient for the growth of most plants judging from high cation exchange capacity and base saturation negligible aluminum toxicities because of nonacid ph and limited salinity and sodicity from relatively low exchangeable sodium and soluble salts in solution unlike warm temperate and forested paleosols with neutral ph from the campanian and danian subtropical and alkaline paleosols from the maastrichtian apparently supported a woodland plant formation adapted to low availability of iron and manganese which were fixed with calcium in carbonate and low availability of phosphorous because it formed insoluble compounds with iron and manganese carbon nitrogen phosphorous and sulfur cycling through microbially mediated mineralization of soil organic matter was limited from low litter inputs in both early and midsuccessional ecosystems particularly in woodland soils results do not reveal demonstrable changes in soil characteristics through the k t transition

weathering characteristics of interflow volcanic boles from mandla lobe eastern deccan volcanic province abstract the deccan volcanism straddling the cretaceous paleogene boundary resulted into one of the most extensive continental flood basalts in the western and central peninsular india the interflow sedimentary units boles often cited as paleosols are the rare archives of paleoenvironmental conditions existed during successive lava flows a debate on the origin of boles as true paleosols exists therefore in order to trace out regional extent of such conditions pedogenic non pedogenic in the context of their paleoenvironmental significance during the deccan volcanism we studied here mineral magnetic characteristics of 36 color differentiated bole beds from the mandla lobe in the eastern deccan volcanic province edvp classified into four types gray yellow brown and red based on their munsell notations the gray yellow and brown boles show dominantly ferrimagnetic composition chiefly magnetite and titanomagnetite while red boles characterize mixed ferri and antiferromagnetic mainly hematite mineralogy the granulometric domain parameters suggest larger single domain sd and the multidomain md ferrimagnets in the majority of cases whereas superparamagnetic sp particles with frequency dependent susceptibility fd 2 6 to 20 3 10 8 m 3 kg 1 are limited to the few red and brown boles only the significant presence of primary parent magnetic minerals i e coarse sd md titanomagnetite and magnetite in the majority of boles depict incipient to moderate weathering owing to limited time intervals during successive eruptions the combination of hematite and sp particles present only in the few red and brown boles depicts baking effect rather than pedogenesis the comparison of magnetic properties of boles from edvp and western deccan volcanic province wdvp shows significant differences in the concentration of sp ferrimagnetic particles and hematite attributed to variable weathering intensity duration and heating related alterations from the upper flows both edvp and wdvp boles indicate similar first order paleoenvironmental conditions without any major pedogenesis that can be regionally correlated

extensive middle miocene weathering interpreted from a well preserved paleosol cricket flat oregon usa abstract the high resolution marine isotope climate record indicates pronounced global cooling during the langhian 16 13 8 ma beginning with the warm middle miocene climatic optimum and ending with significant antarctic ice sheet expansion and the transition to icehouse conditions however the timing and rate of cooling during the langhian are uncertain terrestrial paleoclimate data from this interval is sparse and sometimes conflicting in particular there are gaps in the terrestrial record in the pacific northwest during the late langhian and early serravallian between about 14 5 and 12 5 ma new terrestrial paleoclimate data from this time and region could help reconcile these conflicting records paleosols are particularly useful for reconstructing paleoenvironment because the rate and style of pedogenesis are primarily a function of surface environmental conditions however complete and well preserved paleosols are uncommon most soils form in erosive environments that are not preserved or in environments such as floodplains that accumulate in small increments the resulting cumulic soils are usually thin weakly developed and subject to diagenetic overprinting from subsequent soils the paleosol at cricket flat in northeastern oregon is an unusually complete and well preserved paleosol from a middle miocene volcanic sequence in the powder river volcanic field an olivine basalt flow buried the paleosol at approximately 13 8 0 6 ma based on three 40ar 39ar dates on the basalt we described the cricket flat paleosol and used its physical and chemical profile and micromorphology to assess pedogenesis the cricket flat paleosol is an ultisol like paleosol chemically consistent with a high degree of weathering temperature and rainfall proxies suggest that cricket flat received 1120 180 mm precipitation year 1 and experienced a mean annual temperature of 14 5 2 1 c during the formation of the paleosol significantly warmer and wetter than today this suggests slower cooling after the middle miocene climatic optimum than is seen in the existing paleosol record

core concepts of paleopedology abstract the current renaissance of scientific interest in paleosols has brought a variety of views and approaches to paleopedology two main approaches have emerged for the description and labelling of paleosols geosols are ancient land surfaces consisting of laterally connected suites of paleosols used for stratigraphic subdivision of sedimentary deposits pedotypes are individual kinds of paleosols named after localities like geosols pedotypes are used for mapping and describing individual profiles usually for the purpose of paleoenvironmental interpretation both pedotypes and geosols are field based labels for which genetic or interpretive considerations are at a minimum they can be interpreted using at least three distinct approaches taxonomic uniformitarianism is based on the assumption that a paleosol is formed in a similar environment to a surface soil of the same type the factor function approach interprets specific aspects of paleoenvironments from measured features of paleosols by comparison with paleoenvironmentally related variation of that feature in surface soils finally the process model approach seeks to recreate soil forming processes mathematically with input from measurable features of paleosols each approach has limitations such as the need for proxy features to classify paleosols in systems designed for surface soils the attainment of similar appearance of a paleosol by different pathways and the mathematical uncertainty of model assumptions the approaches of classification experimentation and modelling are not unique to paleopedology being widespread among other sciences fundamental to paleopedology however are the concepts of profiles and soilscapes of the past

biogenic overgrowth on detrital pyrite in ca 3 2 ga archean paleosols regionally traceable paleosols in the lower moodies group of the barberton greenstone belt ca 3 22 ga northeastern south africa and swaziland contain locally abundant silicified nodules originally composed of pedogenic carbonates and sulfates interbedded with heavy mineral laminae dominated by pyrite pyrite grains show rounded detrital cores and secondary idiomorphic rims with trace element concentrations and 34 s ratios clearly different from those of the cores while cores have low co and ni concentrations and high co ni ratios rims show as much as 5 5 wt of these elements and low co ni ratios reflecting the weathering of nearby ultramafic rocks in situ sulfur isotope analyses of pyrite cores show 34 s vcdt vienna canyon diablo troilite values between 5 and 5 while the rims show 34 s vcdt values between 20 and 24 5 suggesting biogenic fractionation of sulfur the close spatial association and microtextural evidence for nearly contemporaneous formation of the pedogenic sulfate nodules and the secondary pyrite rims suggests microbial processing of sulfur in the paleosols which provided reduced and 34 s depleted sulfur for the growth of authigenic pyrite this indicates that vadose zone soil forming processes in the archean involved not only physical and chemical modification of moist unconsolidated sediment in a terrestrial environment but also already included its microbiological modification

distinguishing climate in the soil record using chemical trends in a vertisol climosequence from the texas coast prairie and application to interpreting paleozoic paleosols in the appalachian basin u s a a suite of vertisols clay rich soils with high shrink swell potential were examined across a climosequence climatic transect in twelve soil pits from the coast prairie of texas in order to determine if mean annual precipitation map exerts a control on the chemistry of these soils and if the observed chemical trends are useful for interpreting paleoclimate records of paleovertisols in the geologic record the precipitation regime of the climosequence spans a range between 144 and 86 cm year with moisture regimes classified as udic udic ustic ustic and aridic ustic in a general northeast to southwest direction other soil forming factors such as soil age 35 40 ka parent material fluviodeltaic beaumont formation of late pleistocene age landscape low relief coastal plain and vegetation prairie or mixed woody shrubs are relatively constant across the climosequence climate sensitive chemical proxies of map identified include dithionite citrate extractable fe fedith acid oxalate extractable fe feoxal caco3 equivalent caco3equiv s and ammonium acetate extractable na k and mg naacet kacet and mgacet respectively which vary across the climosequence because of differences in effective depths of leaching and intensity of wetting and drying cycles these standard usda wet chemical climate proxies are related to bulk oxide or element chemistry of soils and paleosols measured using xrf which supports the use of geochemical climate proxies for interpreting the paleoclimate records of paleovertisols application of the chemical index of alteration minus potash cia k geochemical climofunction to late mississippian paleosols from the appalachian basin of the eastern u s demonstrates evidence for a shift from a lower to a higher map paleoclimate that is consistent with previous paleoclimate models and with observed morphological changes in the paleosols we advocate actualistic research using bulk chemistry of soils and paleosols as a means of obtaining soil information useful for interpreting paleosols in the geological record

geology of precambrian paleosols at the base of the huronian supergroup elliot lake ontario canada abstract detailed examination of two new profiles through the denison series paleosol and one new profile through a pronto series paleosol in the elliot lake area lend fresh insight into atmospheric and hydrogeologic environmental conditions of precambrian earth these are reassessed with reference to the results of previous studies as true indigenous paleosols of polygenetic character virtually all of the criteria grandstaff et al 1986 for identification of paleosols are met the paleosols bear strong mineralogical and chemical similarities despite derivation from different parent materials and sampling at locations distant from each other there has evidently been a common reaction to weathering processes peculiar to the early proterozoic diagenetic and metamorphic events mask to a considerable extent the role played by environmental and hydrologic conditions in the development of the paleosols in the denison greenstone derived paleosol clay formed from amphibole feldspar and chlorite is altered to sericite increased quartz content is due to residual concentration and to secondary development in granodiorite derived paleosol quartz and sericite are generally more abundant quartz is relatively concentrated toward the top of the profile the paleosols are thus primarily sericite quartz and chlorite assemblages rutile and leucoxene are accessory minerals profiles of elemental chemistry show the most drastic changes in concentration at the base in transition to bedrock magnesia and lime are leached from all profiles as in modern soils although in common with most precambrian paleosols potash accumulated total fe is strongly depleted from the profiles except just above the bedrock contact with granodiorite a condition attributed to mobilization of fe from the paleosol to a position directly over relatively impermeable parent rock use of holland s method of establishing oxygenation from paleosols indicates that in terms of fe content parent material of granodiorite derived paleosol should produce a reduced fe paleosol the oxygen demand of this rock was greater than granite owing to an abundant ferromagnesian content two fossil eluvial horizons marked by high chlorite and a dramatic decrease in sericite content are recognized in the denison paleosol their existence shows that although initial stages of weathering may have occurred under water saturated conditions conditions were probably more arid than supposed by previous workers particularly during the later stages of development of the paleosol although fe enriched the eluvial horizons are drastically depleted in potash al and th removal of al 2 o 3 negates normalization of chemical analyses of paleosols to al 2 o 3 for purposes of constant volume calculations th associated with sericite in the profiles increases at the contact with the overlying matinenda formation in association with rutile and leucoxene owing to interaction with diagenetic u bearing fluids from overlying sediments rutile and leucoxene originate from parent rocks and are a late stage form of mineralization these titaniferous phases indirectly contributed to the local dominance of brannerite type orc through diagenetic processes of mineralization involving the pronto reaction paleotopographic greenstone highs are related to local anomalously high concentrations of heavy minerals in the brannerite rich orc this involves hydraulic deposition of heavy minerals in the lee of crescent shaped greenstone highs with subsequent diagenetic upgrading granodiorite derived paleosol contains 5 10 times more au than the denison paleosol and is modestly enriched above background a slight decrease in au content upward evident in all profiles is an artefact of erosion of the top of the paleosols

paleosols as indicators of paleoenvironment and paleoclimate paleosols are ancient soils that have been incorporated into the geological record soils form in response to interactions among the lithosphere hydrosphere biosphere and atmosphere so paleosols potentially record physical biological and chemical information about past conditions near earth s surface as a result paleosols are an important resource for terrestrial environmental and climatic reconstructions long standing paleosol research topics include morphology classification and clay mineralogy all of which provide information about pedogenic processes and local paleoenvironments paleosols are also used to infer processes involved in the development of stratigraphic architecture and basin evolution recent paleosol research has introduced semiquantitative and quantitative measures for environmental and chronometric reconstructions that provide insight into major regional to global changes in temperature precipitation and atmospheric pco2 these new proxies focus on morphological and chemi

the nature and origin of gleyed polygenetic paleosols in the loess covered glacial drift plain of northern missouri usa abstract at four study sites in northern missouri the farmdale and sangamon paleosols which are developed in loess are welded to the underlying yarmouth paleosol developed in till upon initial examination however they appear to be a single thick continuous gleyed horizon gleysol along flat tabular drainage divides this welded solum is gleyed and is identical in all respects with the historical definition of gumbotil the solum may exceed 4 m in thickness but has little discernable horizonization the profiles are nearly homogeneous containing approximately 50 clay throughout most of the solum of which 70 80 are expandable clay minerals variations in texture clay mineralogy and weathering indices are typical of a welded solum which forms a complex polygenetic profile the base of the solum retains abundant slickensided joints and upon exposure it rapidly develops shrink swell features typical of vertisols this behavior coupled with the remarkable homogeneity within the solum indicates that these soils underwent significant mixing primarily by pedoturbation a characteristic of modern vertisols

late miocene advent of tall grassland paleosols in oregon abstract paleosols in the late miocene rattlesnake formation reveal three successive paleoclimatic regimens that can be dated using cumulative paleosol development prior to the radiometrically dated rattlesnake ash flow tuff 7 05 ma the basal rattlesnake formation ca 7 5 7 3 ma has a suite of weakly calcareous paleosols indicating subhumid paleoclimate 800 1000 mm mean annual precipitation or map and seasonal waterlogging a shift at ca 7 3 ma to semi arid paleoclimate map 500 850 is indicated by paleosols with calcic horizons at depths of 105 85 cm a second shift at ca 7 2 ma ushered in an assemblage of soils with shallow 36 53 cm calcic horizons indicating semi arid conditions map 200 600 mm not much different from today along with the climatic shifts documented by the paleosols there also are substantial changes in alluvial architecture and paleotopography the lower rattlesnake formation ca 7 5 7 2 ma was deposited by a stream flowing northeast in an ancestral john day valley the upper part of the formation ca 7 2 7 1 ma was deposited within large alluvial fans shed from the growing anticline of picture gorge basalt to the north stepwise changes in former vegetation can also be interpreted from paleosols the basal rattlesnake formation 7 5 7 3 ma has a suite of paleosols with root traces clay skins and manganese nodules like those of riparian woodland and seasonally waterlogged riparian meadow the succeeding paleoclimatic sequence 7 3 7 2 ma includes the earliest known mollic paleosols with deep 50 cm calcareous nodules interpreted as former soils of tall grassland also found are manganese stained paleosols of seasonally waterlogged meadows and weakly developed paleosols of early successional riparian vegetation a later paleoclimatic sequence 7 2 7 1 ma includes desert shrubland paleosols as well as paleosols of early successional riparian vegetation fossil bones and teeth found in many paleosols indicate coeval changes in mammalian faunas the major shift from woodland to grassland at ca 7 3 ma introduced into this area tall grassland ecosystems including large cursorial horses and pronghorns aridification continued with the shift to shrubland ca 7 2 ma early hemphillian which corresponds to continent wide mass extinction of most remaining browsing mammals from the clarendonian chronofauna

preserved stable isotopic signature of subaerial diagenesis in the mescal limestone central arizona implications for the timing of a terrestrial plant cover discussion and reply reply

floodplain palaeosols of the cenomanian dunvegan formation alberta and british columbia canada micromorphology pedogenic processes and palaeoenvironmental implications

late oligocene early miocene paleosols of distal fluvial systems ebro basin spain abstract the study of paleosols can be a vital tool in the paleoenvironmental interpretation of continental deposits because their physical and chemical characteristics are a reflection of variations in aspects of soil formation changes in paleosol characteristics can be used to determine the architecture and nature of parent material paleosol maturity topography climate and soil forming organisms including vegetation cover on the ancient floodplain and can be utilized to recreate a palaeocatena furthermore paleosols can provide quantitative data on paleoclimate where other sources such as organic matter and pedogenic carbonate are absent late oligocene early miocene strata exposed in the ebro basin spain have been identified as proximal alluvial fan fluvial and lacustrine continental facies in parts of the distal fluvial system pedogenically altered channel and overbank deposits interfinger with ephemeral lacustrine facies three main paleosol types developed in these sediments and have been described and compared to modern soils entisol like early successional soils inceptisol like young soils and alfisol like open woodland soils paleoenvironmental reconstructions suggest a mosaic of ecotypes with areas of open woodland composed of shrubs herbs and small trees and other plants of low stature and with each ecotype being controlled primarily by fluctuating paleohydrological conditions from field observations and geochemical analysis the climate was found to be humid continental mean annual temperature mat 10 14 c 4 c mean annual precipitation map 450 830 mm yr 1 200 mm yr 1 these results indicate that climatic conditions were wetter than the present day ebro basin mat 14 c map 320 mm yr 1 and differ from previous interpretations of an arid to semi arid environment based on sedimentological criteria alone

ediacaran gaskiers glaciation of newfoundland reconsidered newly discovered palaeosols in the gaskiers formation of newfoundland provide a new perspective on its palaeoenvironment and are evidence that it was not a deep submarine tillite nor an anoxic deep sea floor nor a cap carbonate from extreme geochemical perturbation of the global ocean discovery of oxidized palaeosols and re evaluation of sedimentary facies and stratigraphic relationships now suggest reinterpretation as a coastal plain with glacial moraines in the forearc basin of a continental volcanic arc like modern japan ediacaran palaeosols of the gaskiers formation lack large root traces but show soil profile differentiation clay enrichment and depletion of alkali and alkaline earth elements at the expense of feldspar and rock fragments and diagnostic soil structures blocky peds argillans sepic plasmic fabric these palaeosols are evidence of a humid temperate climate and marked marine regression accompanying the gaskiers glaciation of the early ediacaran 580 ma geochemical weathering trends in the palaeosols especially phosphorus depletion are characteristic of biologically active soils ediacaran microbial earth ecoystems may have been responsible for filamentous disruption of bedding in the palaeosols