climate change during the early paleogene in the bogota basin colombia inferred from paleosol carbon isotope stratigraphy major oxides and environmental magnetism abstract paleosols in the bogota basin colombia record an increase in chemical weathering across the paleocene eocene p e transition rock magnetic properties and major element geochemistry exhibit an abrupt change in an interval identified as including the p e boundary as established by previously published biostratigraphy and a u pb date on volcanic zircons 56 2 1 6 ma during the stratigraphic interval that contains the p e transition magnetic susceptibility increases significantly with an order of magnitude higher concentration of magnetite maghemite and hematite the preponderance of pure stoichiometric magnetite in the paleosols of this interval indicates that the increase in magnetic susceptibility is due to changes in the rate of pedogenesis rather than an increase in the erosion of nearby volcanic rocks which would contribute titanomagnetite pedogenic structures preserved within the paleosols a lack of iron oxides as cement friability of the sandstones and previously published thermochronologic data are not consistent with burial diagenesis as an explanation for the origin of the magnetic mineral assemblage these enhanced pedogenesis and related chemical weathering is also confirmed by increases in the concentration of fe 2 o 3 and al 2 o 3 and loss on ignition values an increase in mean precipitation across this interval is inferred by the lack of carbonate nodules and a decrease in sio 2 in paleosols thus we hypothesize that there was an intensification of chemical weathering during the interval that contains the p e transition

sedimentology stratigraphy and paleoclimate at the late miocene coffee ranch fossil site in the texas panhandle abstract the late miocene coffee ranch fossil assemblage contains some of the earliest evidence of c4 herbivory in north america however little is known regarding the environmental setting associated with the fauna and a general lack of detailed paleoclimate data exists for the late miocene from the north american continental interior in this study the sedimentary environments stratigraphy geochronology and paleoclimate are interpreted for a series of outcrops of the late miocene ogallala formation in the texas panhandle that includes the coffee ranch locality updated magnetostratigraphy coupled with previously published geochronology indicates that all exposed strata were deposited over a 277 kyr interval within chron c3an 2n from 6 42 6 70 ma depositional environments include fluvial channels floodplain ponds floodplain paleosols eolian paleosols riverine tufa and reworked volcanic ash trunk and tributary fluvial channels are differentiated using channel dimensions sedimentary structures and bounding surface architecture and indicate seasonally variable discharge paleosols from nine pedofacies are described and preserve a spectrum of weakly developed entisols and weakly to moderately mature inceptisols and vertisols constitutive mass balance calculations reveal that mature paleosols formed along distinct pedogenic pathways calcic vertisols accumulated pedogenic carbonate and exhibited either net volumetric dilation or collapse as a result of mineral weathering in contrast non calcic vertisols show patterns of decalcification and variable degrees of volumetric dilation and collapse the presence of the paleosols described in this study requires paleoprecipitation between of 900 1150 mm yr approximately double modern values and a westward shift of the continental udic ustic soil moisture boundary by 400 km during the late miocene this finding suggests that climates in the southern midcontinent were not sufficiently arid to select for c4 photosynthetic pathways over c3 photosynthesis in the late miocene

magnetic hysteresis as a function of low temperature for deep sea basalts containing large titanomagnetite grains inference of domain state and controls on coercivity hysteresis loops to 1200 oe 95 ka m 1 are measured between 295 and 105 k for two deep sea basalts dsdp legs 34 and 37 containing large 200 m unexsolved titanomagnetite grains the curie points electron microprobe analyses and saturation magnetizations of the magnetic grains are the same as for synthetic titanomagnetite xfe2tio4 1 x fe3o4 with x 0 6 as temperature is lowered from 295 to 190 k coercive force hc slowly rises from 40 to 95 oe 3 2 to 7 6 ka m 1 approximately in proportion to the rise in the magnetostriction constant presumably hc is controlled by through internal stresses impeding domain wall motion as expected of multidomain grains the ratio of saturation remanence to saturation magnetization in 1200 oe 95 ka m 1 cycles jr js rises approximately in proportion to hc with a constant of proportionality consistent with titanomagnetite x 0 6 as temperature is lowered from 190 to 120 k hc rises rapidly to 400 oe 32 ka m 1 as a roughly linear function of the

origin of the absence of magnetic lineations in the yamato basin of the japan sea magnetic properties of mafic rocks from ocean drilling program hole 794 d we investigated magnetic properties of mafic rocks recovered from ocean drilling program hole 794 d in the yamato basin of the japan sea in contrast to other back arc basins in the western pacific lineated magnetic anomaly patterns have not been recognized in the yamato basin our objective is to clarify the reason for the absence of lineated magnetic anomalies by direct magnetic measurements of crustal rocks the dominant magnetic mineral of hole 794 d is titanomaghemite as commonly observed for typical oceanic basalts but the grain size is much larger greater than several tens of microns remanence properties i e low natural remanent magnetization intensities 1 5 a m low koenigsberger ratios 1 0 high viscous remanent magnetization and mixed magnetic polarities indicate that the mafic rocks cannot be a source of lineated magnetic anomalies while curie temperature saturation magnetization and susceptibility values are not significantly different from those of typical oceanic basalts magnetic properties related to stability are greatly reduced the large grain size of the mafic rocks from hole 794 d plays a primary role in differentiating the magnetic properties from those of typical oceanic basalts and is caused by the formation of sill sediment complexes beneath the yamato basin sill sediment complexes rather than extrusive basalts in typical oceanic crust are responsible for the absence of lineated magnetic anomalies in the yamato basin

an experimental study of magnetic viscosity in synthetic monodomain titanomaghemites implications for the magnetization of the ocean crust a study of magnetic viscosity in well characterized synthetic monodomain titanomaghemites of composition fe2 4ti0 6o4 is described it is found that the samples are capable of acquiring a viscous remanent magnetization vrm only when they are highly oxidized the same assembly does not show significant magnetic viscosity for 0 1 z 0 6 where z is the oxidation degree this is a result of their being in the thermally stable monodomain state with high anisotropies the observed increase in vrm for the highly oxidized material may be entirely due to the decrease in magnetic anisotropy a decrease in the total number of fe2 as a functin of oxidation results in a decrease in coercive force i e magnetic anisotropy of the initial monodomain titanomaghemites it is thought that the dramatic decrease in magnetic anisotropy at room temperature may be the main cause of the observed increase in vrm for the highly oxidized material finally we conclude that the ability of the magnetic layer of the ocean crust to acquire a vrm increases as the maghemitization degree increases

magnetic hysteresis properties of synthetic monodomain titanomaghemites titanomagnetites of near stoichiometric composition fe 2 4 al o 4 0 0 1 and 0 2 were oxidized in air to form compositions in the corresponding titanomaghemite system the magnetic hysteresis properties saturation magnetization isothermal remanence coercive force initial susceptibility were determined as a function of degree of oxidation in some cases being measured at elevated temperatures the titanomagnetites of the submarine crust are believed to become progressively maghemitized and the measured properties are related to the way in which the intensity and stability of an initially acquired thermoremanence will be modified during submarine weathering the results from the present monodomain synthetic analogues suggest that the intensity of remanence would fall by up to 50 during weathering this fall in intensity might be increased by a fraction of the grains becoming superparamagnetic although this was not so with the grain size range of the synthetics the stability of remanence would at first be increased by maghemitization and subsequently fall the rise in susceptibility with maghemitization would lead to an enhancement of the component of magnetization induced in an ambient field although the study probably simulates the compositions produced during submarine weathering the changes in microstructure e g due to grain cracking or heterogeneities in larger grains which may occur in nature are probably not reproduced in the synthetic analogues

late cretaceous paleosols as paleoclimate proxies of high latitude southern hemisphere mata amarilla formation patagonia argentina abstract although there is general consensus that a global greenhouse climate characterized the mid cretaceous details of the climate state of the mid cretaceous southern hemisphere are less clearly understood in particular continental paleoclimate reconstructions are scarce and exclusively derived from paleontological records using paleosol derived climofunction studies of the mid to upper cretaceous mata amarilla formation southern patagonia argentina we present a reconstruction of the mid cretaceous climate of southern south america our results indicate that at 60 south paleolatitude during the cenomanian santonian stages the climate was subtropical temperate warm 12 c 2 1 c and humid 1404 108 mm yr with marked rainfall seasonality these results are consistent with both previous estimations from the fossil floras of the mata amarilla formation and other units of the southern hemisphere and with the previous observations of the displacement of tropical and subtropical floras towards the poles in both hemispheres the data presented here show a more marked seasonality and slightly lower mean annual precipitation and mean annual temperature values than those recorded at the same paleolatitudes in the northern hemisphere

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

combining soil water balance and clumped isotopes to understand the nature and timing of pedogenic carbonate formation abstract pedogenic carbonate is an important archive for paleoclimate paleoecology and paleoelevation studies however it can form under seasonal environmental conditions that differ significantly from the mean growing season environment or mean annual conditions potentially complicating its use for proxy reconstructions the observed seasonal temperature is typically but not always biased high relative to mean annual air temperature mat to evaluate the annual timing of pedogenic carbonate formation ten different soils were sampled across the western united states sites were selected to span a variety of precipitation regimes and soil orders precipitation regimes ranged from arid sites mean annual precipitation map 50 cm dominated by summer precipitation pedogenic carbonate formation temperatures derived from clumped isotope measurements ranged between 6 and 22 c with most samples falling at or below mat clumped isotope temperatures were compared to monthly precipitation normals and modeled monthly values of evapotranspiration and soil water content results show that carbonate formation temperatures agree with the annual timing of soil water depletion suggesting soil moisture content is a primary control on the timing of pedogenic carbonate formation although the seasonal bias is a function of environmental factors that are difficult to reconstruct in paleo studies the use of other paleosol proxies can help to assess if changes in clumped isotope temperatures are a function of changes in air temperature or hydrology these results have important implications for the production of accurate paleoclimate and paleoelevation estimates

magnetic effects of maghemitization of oceanic crust both theoretical considerations and available experimental results indicate that magnetic effects of maghemitization are strongly dependent on the grain size of the originally unoxidized titanomagnetite maghemitization of single domain titanomagnetite results in a decrease in coercivity an increase in susceptibility and a large decrease in q ratio maghemitization of multidomain titanomagnetite results in an increase in coercivity a decrease in susceptibility and no large changes in q ratio single domain titanomagnetite is probably resistant to the development of a chemical remanent magnetization crm whereas multidomain titanomagnetite can acquire a crm during maghemitization the behavior of pseudo single domain titanomagnetite which is the main carrier of remanence in submarine extrusive rocks is investigated by comparing the magnetic properties of the french american mid ocean undersea study famous less than 0 1 m y old and the leg 37 3 5 m y old pillow basalts recovered from the mid atlantic ridge near 37 n combining electron microprobe analyses curie temperature measurements and cell edge determinations we find that the famous rocks are already oxidized z 0 38 possibly as a result of some high temperature maghemitization during cooling of the magma comparison with the more highly oxidized z 0 7 leg 37 pillow basalts indicates that low temperature maghemitization of such rocks does not result in appreciable changes of coercivity and susceptibility although the q ratio does decrease and crm seems to be acquired such a crm could account for the anomalously low magnetic inclinations observed at most of the leg 37 sites

magnetic properties of variably oxidized pillow basalt in our study of changes in magnetic properties during low temperature oxidation of oceanic pillows we were able to essentially eliminate variations in grain size which plagued many previous studies this was accomplished by keeping the cores parallel to the outer glassy margin of the pillow while drilling the variably oxidized portions of the basalt curie temperature tc measurements indicated a large range in the degree of low temperature oxidation although most were in the early stages of maghemitization tc 300 c in samples with hysteresis parameters showing pseudo single domain behavior the natural remanent magnetization jnrm and susceptibility both decreased substantially with low temperature oxidation thus the koenigsberger ratio jnrm jinduced did not change the reduction in jnrm was mirrored by comparable decreases in saturation magnetization and saturation remanence low temperature oxidation also increased the bulk coercivity and the coercivity of remanence in the oxidized basalt relative to the less oxidized these later results are consistent with the theory that low temperature oxidation generally stabilizes the remanent magnetization of seafloor pillow basalts the increase in coercivity with oxidation in these pillow basalts contrasts will synthetic samples which show an overall decrease the behavior of natural samples reflects processes which occur during low temperature oxidation that do not normally occur in synthetic samples specifically the loss of iron from the grain and perhaps grain cracking

reply to comment on curie temperature and lattice constant reference contours for synthetic titanomaghemites by charles m keefer and peter n shive

chemical weathering of crystalline rocks in contrasting climatic conditions using geochemical proxies an overview abstract weathering profiles of granitoid rocks from the sila massif southern italy have been studied to characterize weathering processes that affect this area chemical weathering indices of the sila massif weathered granitoids were compared to those of different areas of the world characterized by different climates malaysia puerto rico georgia china nigeria colorado switzerland and sweden to decipher their weathering characteristics the geochemical indices show values of cia chemical index of alteration ranging from 55 to 97 ciw chemical index of weathering ranging from 60 to 100 pia plagioclase index of alteration ranging from 55 to 100 wip weathering index of parker ranging from 7 to 64 and rr ruxton ratio ranging from 2 14 to 3 96 all these geochemical proxies closely resemble each other and show variations mainly related to the different climatic and tectonic settings malaysia and puerto rico granitoids showing high cia values respectively 97 and 95 on average underwent very intensive chemical weathering alteration georgia china and nigeria showing medium high cia values respectively 86 90 and 92 on average underwent moderate intensive chemical weathering alteration southern italy and colorado granitoids showing medium low cia values 68 on average underwent moderate weak chemical weathering alteration whereas switzerland and sweden granitoids showing low cia values respectively 58 and 55 on average underwent weak chemical weathering alteration those values are mainly related to the climatic conditions in term of temperature and precipitation of each area cia vs climate histograms display a shift towards higher cia values with increasing of warm humidity tropical conditions whereas granitoids weathered under conditions inferred to be cold arid polar climate show lower cia values

paleopedology and geochemistry of late mississippian chesterian pennington formation paleosols at pound gap kentucky usa implications for high frequency climate variations abstract climate during the late mississippian late chesterian in the southern appalachian basin was characterized by alternating periods of aridity and humidity pennington formation paleosols at pound gap record climate and ecological changes for latest chesterian time ending at the mississippian pennsylvanian systemic boundary forty paleosols were identified described and assigned to seven pedotypes inferred soil orders considered as analogs include histosols entisols inceptisols alfisols and oxisols but are dominated by vertisols classification of an oxisol was determined by field and geochemical evidence of intense leaching and kaolinite dominated clay mineralogy field and micromorphologicial evidence suggests a polygenetic character of the vertisols resulting from changing soil drainage through time variations in soil drainage are quantified using proxy estimates of inferred soil processes such as base loss leaching lessivage and oxidation using the cia k proxy mean annual precipitation map estimates range from 519 to 1361 mm yr changes in map correspond with variation in inferred soil processes the flora of this time period in response to variations in precipitation and soil drainage also changes through time as evidenced by changes in abundance and depth of root traces reconstructed ecosystems range from sparse vegetative cover with shallow tabular root systems in early pennington soil development to dense deeply penetrating root systems suggestive of arborescent floral associations at the top of the succession approaching the mississippian pennsylvanian boundary this study provides greater resolution of changing climate and pedogenic processes than what is provided in previous studies of late mississippian climate and suggests that the documented variability in paleosol types and soil drainage might represent the record of high frequency climate changes likely associated with expansion and contraction of the paleo intertropical convergence zone itcz

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

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

climate and landscape reconstruction of the arroyo chijuillita member of the nacimiento formation san juan basin new mexico providing environmental context to early paleocene mammal evolution abstract the sedimentologic stratigraphic and paleopedologic attributes of a laterally continuous outcrop exposure of the basal portion of the lower paleocene arroyo chijuillita member of the nacimiento formation located in the bisti de na zin wilderness area was examined to provide paleoenvironmental context for the puercan north american land mammal age nalma terrestrial ecosystems of the san juan basin new mexico the studied outcrop spans the middle and late puercan pu2 pu3 nalma and thus is an ideal location to assess the potential causes of faunal turnover between pu2 and pu3 the stratal succession consists of fluvial channel and laterally continuous sandstone and associated fine grained floodplain deposits including paleosols that document variability in drainage and maturity quantitative and qualitative reconstructions of paleoclimate from paleosols supplemented by analyses of fossil floras indicate no change in climate through the studied interval further there is no evidence that regional tectonics relate to changes in depositional environments given the lack of evidence for climate change or regional tectonics and the characteristics of the fluvial facies and the paleosols across the study locality we interpret the spatial and temporal variability in paleopedologic and sedimentologic characteristics to be the result of autocyclic channel avulsion and migration additionally the stable climatic conditions and lack of tectonic influence between the pu2 and pu3 biozones suggest that mammalian turnover is unlikely to have been caused by extrinsic environmental changes i e climate or tectonics and is instead probably the result of rapid evolution following the k pg boundary and or competition from the migration of new mammalian species into the basin

rapid pleistocene desiccation and the future of africa s lake victoria abstract the effects of precipitation changes on tropical east african ecosystems and human populations is poorly understood due to the complex interplay between global and regional processes and missing data from key regions and time periods we generate a water budget model for lake victoria the largest tropical lake in the world the source of the white nile and a region that supports some of the densest human populations in africa that assesses the impact of changing climate on lake levels and the rate of lake level change model results demonstrate that significant changes in the size and volume of lake victoria are possible in response to changes in temperature precipitation and orbital forcing this modeling indicates that lake victoria can transition back and forth between modern lake levels and complete desiccation in centuries to a few millennia which is rapid enough to allow for two previously observed desiccation events between 14 18 ka during which time the lake drained and refilled twice combined observations from modeling and estimates of paleoprecipitation indicate that lake victoria was likely desiccated between 94 36 ka this dry interval partially overlaps the megadrought 140 70 ka identified in lakes malawi and tanganyika further south and the cooler drier conditions identified in the gulf of aden between 75 50 ka this prolonged desiccation was probably driven by eccentricity enhanced precession and high latitude forcing that affected the congo air boundary convergence using future climate projections our model also predicts that at current rates of temperature change and previous rates of lake level fall lake victoria could have no outlet to the white nile within 10 years and kenya could lose access to the lake in

rock magnetic signature of a miocene playa cycle in central asia and environmental implications the increased aridification of central asia during the miocene coincides in time with lake formations and the evolution of playa environments in the region however miocene continental climate dynamics and the forcing of aridification are still not well constrained neogene lacustrine mudflat deposits in the ili basin in southeast kazakhstan provide a well exposed paleoclimate archive here we present a detailed rock magnetic study of a middle miocene playa cycle deposited in a closed basin we use high resolution rock magnetic parameters lithological studies and geochemistry to reconstruct the playa environment and the depositional conditions the rock magnetic mineralogy of the playa cycle is controlled by hematite and two fine grained magnetite phases increased magnetic concentrations occur during dry mudflat conditions with a lower groundwater table and increased aridity the underlying processes controlling the observed variation in magnetic concentrations are a complex interplay of diagenetic processes during and after deposition the data support an authigenic origin of both magnetite phases one formed before and the other after sediment consolidation early diagenetic formation of fine grained magnetite by microbial activity is followed by post depositional formation of a secondary fine grained magnetite phase the rock magnetic results such as magnetic concentration dependent parameters arm sirm and s ratio indicate a sensitive record of ground water availability and aridity changes in the ili basin we suggest that they can serve as an effective proxy for detailed paleo environment reconstruction of playa evolution not only in the middle miocene ili basin but also in comparable floodplain playa lake settings

high frequency controls on alluvial successions an integrated sedimentological and palaeopedological approach to the plio pleistocene of argentina abstract plio pleistocene palaeosol bearing alluvial strata are continuously exposed along the marine cliffs of southeastern buenos aires province argentina the study interval was deposited by a mixed predominantly suspended load fluvial system outcrops are dominated by floodplain siltstones and mudstones that exhibit a cyclic alternation between calcic and vertic palaeosols this cyclicity is represented by meter scale alluvial cycles that show as a general trend a gradual increase in the proportion of channel fill deposits up section cyclic variations in palaeosols facies and architectural elements can be related to allogenic drivers such as climate and eustasy for the lower punta san andres alloformation the stratigraphic arrangement of the recognised palaeosols and the clay mineral distribution indicate that the palaeoclimate was subhumid average mean annual precipitation map 840 mm seasonal and temperate average mean annual temperature mat 7 85 c for at least 1 ma from ca 2 9 ma to ca 1 8 ma late pliocene early pleistocene with several intervals in which conditions became drier and probably colder even though climate was a major control on palaeosol development it is suggested here that it was not the main control on high frequency cycles variations in the orbital parameters more specifically in insolation were interpreted as having controlled the sedimentation and architectural evolution of the lower punta san andres alloformation depositional systems

effects of the core shell structure on the magnetic properties of partially oxidized magnetite grains experimental and micromagnetic investigations the relationship between magnetic hysteresis parameters and the degree of oxidation of ultrafine magnetite particles is examined by both experimental measurements distributed particle assemblage with median grain size of 80 nm and standard deviation 0 43 and micromagnetic simulations single particles from 40 nm to 140 nm experimental results show that both coercivity bc and the ratio of saturation remanence to saturation magnetization mrs ms increase slowly as the oxidation parameter z increases from 0 to 0 9 thereafter both parameters decrease sharply as magnetite becomes completely oxidized to maghemite numerical simulations of hysteresis loop and microstructure using a micromagnetic model with a core shell geometry a stoichiometric core surrounded by an oxidized shell show three categories of behavior for magnetic grains during oxidation first the coercivity of sd particles decreases as oxidation proceeds but their remanence magnetization remains in a uniform state second for psd sized particles near the critical sd boundary 80 nm to 100 nm the initial vortex domain structure changes to a sd as oxidation occurs and returns to a vortex state upon complete maghemitization resulting in an initial rise and then fall of bc and mrs finally larger psd grains remain a vortex state throughout the maghemitization with less variations of bc and mrs the predicted magnetic properties exhibit good agreement with experimental observations and suggest that the domain arrangement is likely to be dominated by a core shell structure with strong exchange coupling at their interface overall the partially oxidized magnetite in sd psd range can reliably record palaeomagnetic signals

early oligocene paleosols of the dagshai formation india a record of the oldest tropical weathering in the himalayan foreland abstract this study reports paleopedological features of the fossil soils that formed during the earliest phase of continental sedimentation in the himalayan foreland the fluvial sequence of the dagshai formation 31 6 3 9 ma to 30 3 3 9 ma exposed along the koshaliya river nw himalaya contains four pedofacies named pedofacies a d of ferruginous paleosol sequences contained within overbank sediments the dagshai formation unconformably overlies the marine subathu formation pedofacies a consists of 3 4 well developed ferruginous paleosols overlain by gray sandstone beds pedofacies b d are marked by a progressive decrease in pedogenesis these paleosols occur as 0 5 m to 1 5 m thick bw bt btk bk bss horizons that are marked by extensive development of rhizoliths pedogenic carbonate and iron rich clay pedofeatures that correspond to modern entisols inceptisols alfisols and vertisols based on early oligocene paleogeographic position of the northward drifting indian plate it is inferred that these paleosols were formed at 18 n paleolatitude in the dagshai sub basin in the himalayan foreland micromorphology geochemical analyses weathering indices and stable isotope composition of paleosols indicate tropical climate paleoprecipitation of 947 1256 mm and paleotemperature of 25 c with an initial phase of monsoonal conditions during pedogenesis these paleoclimatic conditions favored c3 paleovegetation immediately after the transition from greenhouse to icehouse conditions

paleoenvironmental reconstruction of a paleosol catena the zinj archeological level olduvai gorge tanzania abstract paleosols record paleoclimatic processes in the earth s critical zone and are archives of ancient landscapes associated with archeological sites detailed field micromorphologic and bulk geochemical analysis of paleosols were conducted near four sites at olduvai gorge tanzania within the same stratigraphic horizon as the zinjanthropus paranthropus boisei archeological site paleosols are thin

a comparison of the magnetic properties of synthetic titanomaghemites and some oceanic basalts the variation of some magnetic properties of 1 synthetic titanomaghemites and 2 oceanic basalts from dsdp site 417 d as a function of grain size and oxidation is presented the synthesis of the initial titanomagnetite x 0 6 was carried out using controlled fugacity and self buffering techniques single phase titanomaghemites were produced by heating the titanomagnetite in air at low temperatures 350 c the magnetic properties studied on the synthetic titanomagnetite grain size 1 m show the following variations with increasing degrees of oxidation 0 z 0 6 1 curie temperature tc increases 2 saturation magnetization js at room temperature increases 3 js measured at 77 k decreases for z 0 3 and then increases for 0 3 z 0 6 4 bulk and remanent coercivities hc and hr increase slightly initially z 0 2 and then decrease at both room temperature and 77 k 5 susceptibility 0 decreases for z 0 3 and then increases 6 the magnetic viscosity acquisition and decay coefficients sa and sd increase and 7 the median destructive fields for an anhystretic remanent magnetization and a viscous remanent magnetization increase for z 0 3 and then decrease these magnetic data also suggest that the synthetic titanomaghemites are pseudo single domained psd and with increasing degrees of oxidation these psd grains become more sd like the basalt samples from site 417d are divided into fine grained pillow basalts and coarse grained massive flows most of the magnetic properties measured are distinctly different between these two groups the magnetic data indicate that the domain states of these basalts are probably psd although it is difficult to separate the effects of grain size and oxidation on the magnetic properties of these basalts it appears that grain size effects predominate a preliminary investigation of the magnetic viscosity of the synthetic and oceanic titanomaghemites suggests that a combination of thermally activated and diffusive magnetic viscosity is responsible for their viscous behavior finally we will discuss the roles of grain size and oxidation variation in oceanic basalts and their separate and combined effects on their magnetic behavior

biogeochemical characterization of a lithified paleosol implications for the interpretation of ancient critical zones abstract modern soils are characterized by an array of physical chemical mineralogical and biological laboratory analyses of samples taken from horizons of pedogenic profiles in contrast fossil soils paleosols are typically characterized from assays of whole rock molecular oxides because of sample lithification where element sources are unconstrained here we for the first time subject a lithified paleosol to an array of modern soil analytical techniques and new pedotransfer functions providing a glimpse into the colloidal world of an ancient critical zone as an analog to research conducted on a network of modern critical zones this methodology provides a framework for decoding a previously unknown archive of terrestrial biogeochemical information at multiple temporal and spatial scales application to a paleosol within an early paleocene critical zone reveals that many biogeochemical properties have been preserved since burial that are similar to modern clay rich vertisols the measured and calculated physical properties of this paleosol include clay content and mineralogy bulk density and water retention available water capacity and coefficient of linear extensibility shrink swell potential the chemical properties include cation exchange capacity exchangeable cations base saturation and exchangeable sodium percentage the solution properties electrical conductivity and ph seem reasonable but are interpreted with less confidence because of their greater vulnerability to alteration from fluid flow new pedotransfer functions to reconstruct pre burial organic carbon and nitrogen contents provide invaluable information of organically derived nutrient content the sum of the measured properties of the early paleocene paleosol in context of reconstructed regional environmental conditions indicate the presence of a mid successional hardwood forest in a humid climate with high water holding capacity high nutrient retention and rapid flux of elements through biogeochemical cycling

an experimental study of the intensity and stability of thermoremanent magnetization acquired by synthetic monodomain titanomagnetite substituted by aluminium summary titanomagnetites of composition fe2 4 al ti0 6o4 and fe2 6 al ti0 4o4 0 0 1 and 0 2 in both cases were prepared in the monodomain state by pulverization of sintered synthetic material in low fields the thermoremanence trm was found to be linear with inducing field and of high enough intensity to account for typical natural remanent magnetizations of fresh submarine basalts the higher field trm acquisition curves follow the neel model curve for an assemblage of non interacting identical particles in a general way only the differences being due to interactions or the range of particle blocking temperatures and volumes or other features of the samples not included in the model the unblocking temperatures of low field trm lie in a narrow range below the curie point the low field trm is very resistant to alternating field demagnetization and provides a very striking illustration of the strength of the trm mechanism in preserving a stable record of a weak magnetic field the result of a lowrie fuller test on the material is consistent with the monodomain state

quaternary glacial interglacial climate cycles in hawaii abstract the upper kilometer of the hawaiian scientific drilling program core consists of lavas that were emplaced subaerially burying paleosols these paleosols were preserved with minimal alteration and are used to construct a 330 kyr quaternary climate record within the temporal resolution of this record there appears to be a 100 kyr climate oscillation between cool dry and warm wet conditions indicating that tropical regions such as hawaii have responded to the same global climate forcings as have higher latitude areas during at least the past three glacial interglacial cycles it is also suggested that hawaiian climate may have become progressively warmer and wetter over the same period

refining the pedogenic carbonate atmospheric co2 proxy and application to miocene co2 abstract quantifying uncertainty is essential for any paleoenvironmental proxy recent work on propagating error through the equation used to determine atmospheric co 2 concentrations from paleosol carbonates yields conflicting results small magnitude uncertainty from gaussian error propagation contrasts with larger magnitude uncertainty from monte carlo error propagation the discrepancy is reconciled here by revising partial differential equations for the gaussian approach uncertainties calculated using the two approaches are compared and applied to miocene calcic paleosols monte carlo propagated errors are asymmetrical but otherwise agree with gaussian errors three methods for assigning soil respired co 2 concentrations s z to paleosols are also compared a revised calibration of depth to the bk horizon as a direct proxy for s z is presented and although it results in lower atmospheric co 2 concentrations than the original calibration it results in significantly higher calculated atmospheric co 2 than the use of mean annual precipitation as a proxy for s z or assigning s z values based on soil order averaging atmospheric co 2 concentrations calculated using soil order based s z values from 10 penecontemporaenous and independent paleosols will likely result in useful constraints on earth system sensitivity the improvement of proxies for s z is needed to increase the accuracy and precision and to resolve potential volatility in co 2 time series

vertisol genesis in a humid climate of the coastal plain of texas u s a numerous genetic studies of vertisols have been conducted using qualitative and semi quantitative methods across a broad range of climates however no detailed investigations exist on vertisols formed in humid climates using multiple pedogenic techniques on both a microlow ml and microhigh mh hence we sampled and characterized a ml and mh from a lake charles pedon mean annual rainfall 1090 mm mean annual temperature 20 c in the late pleistocene coastal plain beaumont formation of east texas according to the official series description the lake charles classifies as a fine smectitic hyperthermic typic hapludert with mollic and calcic diagnostic horizons coupled with field morphology and characterization data micromorphology and constituent mass balance interpretations were used to reconstruct the major pathway of pedogenesis in response to greater water recharge the ml contains darker colors more organic carbon greater depth of carbonate leaching and lower ph the proportion of oxalate extractable iron increases toward the surface and is in greater abundance in the ml than mh in contrast dithionite extractable iron increases with depth and has similar quantities in both the ml and mh the parent material and lower profiles contain asepic microfabric dominated by micaceous rich coarse clay and silt the asepic zone deep contains an abundance of soft carbonate masses and iron manganese segregations that appear to be forming contemporaneously with the presence of argillans substantiating clay translocation during the early history of soil formation sepic microfabric dominates the upper profiles of both the ml and mh in part from the transformation of biotite to smectite which is more pronounced in the microlow because of more intense weathering hard carbonate nodules and iron manganese concretions are abundant in the upper sepic zone and contain skelsepic microfabric suggesting that they are no longer growing dilation was the dominant strain force during pedogenesis from volume expansion in response to crack infills and shrink swell processes mass flux calculations indicate that total clay gains occurred in both the ml and mh during pedogenesis late pleistocene vertisols appear to approach steady state when forming in humid climates the soil mechanics model best explains the observed depth distribution of properties including slickensides with pedoturbation playing a secondary role in the genesis of these humid climate vertisols

paleoenvironmental reconstruction of jurassic dinosaur habitats of the vega formation asturias spain jurassic aged strata of asturias spain contain trace fossils including sauropod theropod and ornithopod dinosaur footprints but their paleoenvironmental context has been relatively unstudied a coastally exposed continuous section at playa de vega shows a clear transition from the marine middle jurassic rodiles formation to the terrestrial upper jurassic vega formation within the 100 m of vega formation stratigraphy that was logged there four distinct types of paleosols were identified 1 entisols 2 inceptisols 3 vertisols and 4 composite or cumulative paleosols the paleosol types and their features indicate a floodplain depositional setting with short stature shrubby vegetation theropod and ornithopod tracks have been identified at the base of the section indicating that a dinosaurian fauna was present at playa de vega during the jurassic results from well characterized climofunctions based on modern soils and paleosol b horizon chemical composition of the inceptisols and vertisols yield mean annual precipitation estimates of 400 980 mm yr 1 and mean annual temperature estimates of 8 15 c the presence of vertisols with both evidence for shrink and swell behavior and dispersed pedogenic carbonate is consistent with a strongly seasonal precipitation regime the 13 c analyses of pedogenic carbonates yield values that range from 7 09 to 8 88 relative to vienna peedee belemnite vpdb and indicate carbon dioxide levels about six times pre industrial levels consistent with previous results the asturian vertebrate track assemblage is remarkably similar to that of the morrison formation western united states but it has greater overall richness the pattern is reversed for body fossils the reconstructed paleoenvironmental and paleoclimatic conditions indicate similar depositional settings in both places but with a cooler wetter more seasonal environment in asturias the greater seasonality indicated by the vega formation relative to the morrison formation may explain the observed differences in richness

thermomagnetic investigations of titanomagnetite in submarine basalts evidence for differential maghemitization abstract initial susceptibility k coercive force h c remanent coercive force h rc and saturation induced and remanent magnetizations j s and j rs have been measured at a series of 10 12 temperature steps between ambient temperature and 340 c for three selected fine or coarse grained submarine basalts ranging in age from the present to 30 ma possible magneto chemical changes which could have been induced by the successive heatings were checked through repeated measurements at room temperature which showed that no significant changes of the hysteresis parameters occurred below the 300 c temperature step average curie points are between 110 and 170 c but a quite large dispersion of curie points exists in a single rock sometimes over 400 c at room temperature the bulk of magnetic oxides consist either of multidomain md grains in the two coarse grained rocks dolerites or of small pseudosingle domain psd particles in the fine grained rock a pillow basalt the temperature dependence of coercivity of the oldest coarse grained rocks is surprisingly different from that of synthetic titanomagnetites coercivity is found to increase at intermediate temperatures with a maximum in the range 250 300 c in the most spectacular example h c rises from 28 to 75 oe and h rc from 67 to 200 oe when temperature rises from 20 to 235 c correlatively j rs j s increases to 0 3 indicating the presence of small psd grains the youngest pillow basalt sample displays similar although faint evidence of the presence of grains finer and with higher curie points than the bulk of the titanomagnetite population this thermal behaviour of submarine basalts is interpreted as the result of differential maghemitization within a single rock the finest grains being more rapidly and more completely oxidized at low temperature in our 3 ma old coarse grained sample the average oxidation index z is only 0 3 average curie point 110 c while the finest grains are completely maghemitized z 1 with a curie point of the order of 450 c

alluvial response to the paleocene eocene thermal maximum climatic event polecat bench wyoming u s a abstract the stratigraphic interval spanning the paleocene eocene thermal maximum in the northern bighorn basin wyoming shows changes in the alluvial record that can be tied to a high resolution climate record the complexity and stratigraphic spacing of paleosols change through the study section comparison to the climate record reconstructed from paleosols indicates the changes correspond to paleocene eocene thermal maximum climatic fluctuations in particular the middle of the section contains thick welded paleosols and thin avulsion deposits that link to times of well drained floodplains and lower mean annual precipitation stratigraphic intervals below and above the main part of the paleocene eocene thermal maximum interval correspond to times of less well drained floodplains and higher mean annual precipitation these strata contain thinner paleosols and thick avulsion deposits differences in paleosol complexity and spacing suggest that sediment flux to the depositional site varied in response to precipitation fluctuations associated with the paleocene eocene thermal maximum welded paleosols and thin avulsion deposits indicate reduced floodplain accretion during deposition of the middle of the paleocene eocene thermal maximum intervals with widely spaced paleosols indicate more rapid accretion we hypothesize that drier episodes associated with warming caused reduced vegetation in source areas and promoted erosion and increased sediment yield because precipitation was reduced much of that sediment was stored in upstream reaches of the fluvial system rather than moving to the depositional basin welded paleosols formed because of diminished sediment supply to the basin with a return to wetter conditions during the recovery phase of the paleocene eocene thermal maximum upstream water flux increased stored sediment moved to the basin and vertically spaced thinner paleosols developed the results demonstrate how vertical sections of alluvial paleosols can provide information on how climate fluctuated through time and how the fluvial system responded to climate change

paleopedologic and paleohydrologic records of precipitation seasonality from early pennsylvanian underclay paleosols u s a underclays in the crooked fork group lower pennsylvanian atokan langsettian in eastern tennessee u s a are paleosols associated with fourth order depositional sequences that record changing paleohydrologic conditions during their formation climate changes possibly milankovitch driven resulted in evolution of soil landscapes from well drained seasonally wet floodplains and delta plains dominated by vertic vertisol like paleosols to very poorly drained everwet swamps dominated by sideritic gley paleosols coals paleohistosols cap most underclays and record peat swamp development during everwet conditions followed by marine submergence pedogenic slickensides and angular blocky ped structures in conjunction with illuviated clay pore fillings and sepic plasmic microfabric indicate an initial better drained phase of paleosol development stage i gley overprinting characterized by drab low chroma paleosol colors fe reduction in upper portions of paleosols sideritic rhizocretions sphaerosiderite and pyrite nodules extensive leaching and translocation of alkali and alkaline earth elements and kaolinitization of smectites and hydroxy interlayer vermiculite hiv indicate a later poorly drained stage of paleosol development characterized by saturated conditions moderate to low eh and low ph stage ii as well as peat swamp development lastly burial and juxtaposition of marine facies on top of terrestrial deposits terminated paleosol and peat development stage iii paleosols likely formed under conditions of marked seasonality of rainfall judging from both modern analog systems in sumatra and pennsylvanian paleoclimate models the chemical index of alteration without potash cia k was used as a proxy for atokan paleoprecipitation estimated as 1300 mm yr this estimate is comparable with mean annual precipitation map in modern tropical to subtropical rainy environments

reconstructing a high paleolatitude mesozoic paleoenvironment from a truncated and deeply buried regolith norwegian north sea abstract the paleoregolith in this study was unconformably overlain by lower cretaceous valanginian marine deposits of the asgard formation and buried below two kilometers of sediments on the utsira high norwegian north sea the upwards intensification of chemical alteration manifested in the replacement of feldspars by clays leaching of base cations and reduced mechanical rock strength in addition to the presence of terrestrial biotitic features suggested weathering during subaerial exposure of the utsira high during the mesozoic the paleoregolith can be divided into three weathering facies altered coherent rock saprock and saprolite whereas the absence of true soil horizons suggested erosional truncation of the regolith before burial possible remnants of the eroded soil were identified as pedogenic mud aggregates in the overlying asgard formation bearing similar compositional characteristics as the saprolite clay mineralogy bulk geochemical composition micromorphology and depth of biotic features were used to reconstruct the paleoenvironmental conditions that prevailed during the formation of the regolith in the mesozoic north sea our results point to a regolith formation under periodically water restricted conditions promoting the co existence of interstratified illite smectite beidellite and kaolinite deep presence of endomycorrhizae the fungal extension of the root structure and precipitation of iron oxide nodules application of recently developed geochemical climofunctions indicated that the regolith formed in a mesic 10 12 c and subhumid 1157 1406 mm yr environment and under strongly acidic soil conditions ph 5 2 5 6

consequences of the maghemitization on the magnetic properties of submarine basalts synthesis of previous works and results concerning basement rocks from mainly d s d p legs 51 and 52 abstract this study attempts to point out the effects of low temperature oxidation on the magnetic properties of oceanic basalts to evidence the maghemitization effect in terms of chemical change alone we tried to keep constant both the concentration and the grain size of the magnetic minerals this study bears essentially on basaltic samples drilled at site 417a and 417d during the d s d p legs 51 and 52 but also includes other available data the concentration changes were neutralized either by counting the magnetic oxides with a microscope or by normalizing a magnetic parameter to another one which similarly varies upon maghemitization for the grain size we selected magnetic criteria that seem the best to represent the magnetic domain state configuration of the titanomagnetite thus we chose to work with constant ranges of both h cr h c and j rs j s values the magnetic minerals at site 417a and 417d are titanomagnetites displaying varying maghemitization degrees but whose original composition varies little around x 0 55 including a roughly constant amount of minor elements al 0 08 and mg 0 04 ions per formula unit therefore it was assumed that the curie temperature rise reliably represents the maghemitization increase the main results are the following ones the saturation induced magnetization j s continuously decreases by a factor of two to three during maghemitization consequently this process can actually be considered to be the main cause of the decrease in the magnetic anomalies amplitude when going away from the sea floor spreading axes the other magnetic parameters are grain size dependent and appear to evolve in a roughly opposite way in the fine grained sd psd and in the coarse grained psd md basalts the initial susceptibility first slightly decreases then increases in the former case while continuously decreasing in the latter the evolution of the coercive force parameters is opposite to the susceptibility s in both groups these results are in general good agreement with theoretical predictions and for the fine grained basalts with results obtained from synthetic substituted sd titanomaghemites however contrary to expectations we did not find any change in the magnetic viscosity with maghemitization it seems rather that the viscosity is mainly controlled by the magnetic domain structure and microstructures in the titanomagnetites being generally negligible in the fine grained basalts pillows and significant in the doleritic basalts this study shows that even if maghemitization slightly alters the reliability of fine grained basalts as palaeomagnetic recorders these rocks still remain the main source of the oceanic magnetic anomalies alternatively due to their significant magnetic viscosity the doleritic basalts contribute little to the anomaly pattern whatever their maghemitization degree

the sedimentology paleoenvironment and diagenesis of the asencio formation of western uruguay abstract the uppermost sandstones of the asencio formation of southwestern uruguay are characterized by a striking iron rich geochemical overprint which has been interpreted as paleopedogenic in origin among the notable features of the asencio is the extension of the overprint into tubes that extend several meters into the underlying mercedes formation field observations and geochemical analyses of the asencio formation and its parent lithologies from four localities around uruguay allow the identification of the asencio overprint as a ferricrete displaying a number of the features typically associated with ferricrete formation iron and aluminum enrichment conversion of labile minerals to kaolinite vermiform pseudoconglomeratic and mottled textures and loss of bulk density in comparison to the unmodified parent the nature and uniformity of the geochemical profiles through the asencio formation suggests that this paleopedogenic modification occurred during a single phase of intense tropical weathering on a stable land surface possibly over a geologically short time period paleoenvironmental proxies suggest this weathering could have occurred at temperatures around 18 c with about 1500 mm of precipitation although these proxies are not developed for paleosols lacking a strong bt horizon like the asencio no existing hypotheses can satisfactorily explain the nature of the tubes extending from the base of the asencio formation nor do any of the observed features aid in the dating of the asencio

constraining paleohydrologic change during the paleocene eocene thermal maximum in the continental interior of north america abstract quantifying the relationship between carbon cycle perturbations and the hydrologic cycle in the geologic past is crucial to accurately modeling how future anthropogenic carbon emissions and resulting radiative forcing might affect the hydrologic cycle interpreting changes in proxy records for insight into paleohydrologic change is complex and documented records of paleohydrologic response to past global warming are rare we use the relationship between two independent proxy records the stable isotope ratios of hydrogen in n alkanes and oxygen in tooth enamel of coryphodon to examine paleohydrologic change in the continental interior of north america during the paleocene eocene thermal maximum petm hyperthermal 56 ma the coryphodon 18o record allows us to infer shifts in surface water isotope values through time by applying an empirical relationship between tooth enamel and precipitation 18o values precipitation 18o values increase by 4 during the petm but n alkane hydrogen isotope ratios show no directional change during the petm we explore multiple hypotheses that could explain the differences between the isotope records including a change in apparent fractionation as a result of plant community change a shift in the slope of the local meteoric water line a change in the season of rainfall or a shift in the season of lipid production we model the changes that would be required to reconcile the isotope records for each hypothesis and evaluate the likelihood of each of the scenarios we posit that the most likely hypothesis for the observed differences between the isotope records is a change in either the season of rainfall or the season of lipid production during the petm

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

the chemical index of alteration cia as a proxy for climate change during glacial interglacial transitions in earth history abstract the glacial interglacial transitions of ice ages are associated with large rapid changes in climate which potentially can be reconstructed from stratigraphic profiles of the chemical index of alteration cia here we present a case study based on high resolution cia profiles of neoproterozoic glacial deposits from south china paleolatitude 30 n as a record of the climate transition at the termination of the sturtian glaciation 663 ma drillcore zk2115 gaodi deposit exhibits a progressive upsection increase in mean cia over a 50 m interval from 58 range 52 65 note all ranges are given as 16th 84th percentiles in the synglacial upper tiesi ao formation to 67 range 64 69 in the deglacial basal datangpo formation cap carbonates and to 68 range 66 70 in the postglacial datangpo formation black shales a coeval section from the lijiawan deposit also exhibits an increasing cia trend upsection within shallow water mn carbonate facies these cia patterns show no relationship to lithology and are interpreted to reflect climatic warming and intensified chemical weathering during the sturtian deglaciation similar large increases in postglacial cia values are seen in paleoproterozoic and late paleozoic successions and at least moderate increases in cia values are recorded during warm stages of the late quaternary e g the bolling allerod and holocene relative to the cold stages e g the last glacial maximum and younger dryas the rapidity of cia changes in quaternary systems 1 to 10 kyr suggests that weathering intensity may have changed at similarly rapid rates in more poorly dated deep time glacial successions with potential implications for snowball versus slushball models of cryogenian glaciations these examples show that cia can be a robust proxy for climate changes i e enhanced chemical weathering intensity during glacial interglacial transitions of both ancient and recent ice ages

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

magnetic state of 10 40 ma old ocean basalts and its implications for natural remanent magnetization abstract the natural remanent magnetization nrm of ocean basalts giving rise to the pattern of marine magnetic anomalies is known to be of comparatively low intensity for about 20 ma old oceanic crust the aim of this study is to detect possible peculiarities in the rock magnetic properties of ocean basalts of this age and to establish a link between magnetomineralogy rock magnetic parameters and the low nrm intensity ocean basalts covering ages from 0 7 to 135 ma were selected for rock magnetic experiments and their room temperature hysteresis parameters curie temperature and temperature dependence of saturation magnetization ms t was determined and complemented by reflected light microscopy the majority of samples is magnetically dominated by titanomagnetite and titanomaghemite with increasing oxidation state with age for these a strong dependence of hysteresis parameters on the age of the samples is found the samples have a minimum in saturation magnetization and a maximum in magnetic stability in the age interval ranging from approximately 10 to 40 ma coinciding with the age interval of low nrm intensity the observed change in saturation magnetization is in the same order as that for the nrm intensity a further peculiarity of the titanomaghemites from this age interval is the shape of their ms t curves which display a maximum above room temperature neel p type and sometimes a self reversal of magnetization below room temperature neel n type these special rock magnetic properties can be explained by titanomagnetite low temperature oxidation and highly oxidized titanomaghemites in the age interval 10 40 ma a corresponding measurement of the nrm at elevated temperature allows to identify a maximum in nrm intensity above room temperature for the samples in that age interval this provides evidence that the nrm is equally carried by titanomaghemites and that the low nrm intensities for about 20 ma old ocean basalts are caused consequently by the low saturation magnetization of these titanomaghemites

paleosols trace fossils and precipitation estimates of the uppermost triassic strata in northern new mexico abstract this study provides a detailed pedogenic evaluation of two upper triassic late norian through rhaetian stratigraphic intervals in new mexico in order to assess the climate and ecology of the latest triassic which ended in a mass extinction the two study areas are located in north central and east central new mexico and are separated by 200 km each section contains abundant paleosols of varying maturity with features that reflect an arid to semiarid climate there is little pedogenic variation throughout the strata at each location and a typical paleosol profile is about 1 m thick and has an ab bw bk bc horizon succession bkm bss bssk or bssg horizons are present in some paleosols micromorphological features suggest dominantly well drained sola e g abundant carbonate nodules illuviated clay with minor periods of moist or saturated conditions e g femn concretions femn coatings and hypocoatings sepic plasmic fabrics trace fossils are abundant in these strata and are dominated by taenidium serpentinum and root traces depth to carbonate functions estimate that mean annual precipitation was between 200 and 450 95 mm relative to location 1 eastern new mexico location 2 north central new mexico produced higher paleo precipitation estimates and has stronger and more abundant sepic plasmic fabrics in thin sections the presence of a gleyed paleosol camborygma eumnkenomos and slickensides at location 2 also suggests conditions wetter than at location 1 taxonomically all of the paleosols in this study appear to be entisols or aridisols and can be grouped into seven representative pedotypes of varying maturity by comparing these paleosols to modern soils this study demonstrates that the late triassic western interior during the late norian to rhaetian was arid to semiarid and supported a desert shrub environment that had localized and periodic moist or saturated soil conditions

eustatic control on alluvial sequence stratigraphy a possible example from the cretaceous tertiary transition of the tornillo basin big bend national park west texas u s a paleosol bearing alluvial strata of latest cretaceous and earliest tertiary age are continuously exposed along dawson creek in big bend national park west texas u s a and exhibit a three tier hierarchy of depositional cyclicity meter scale fluvial aggradational cycles facs occur as fining upward successions that are gradation ally overlain by paleosols or are sharply overlain by the coarser grained base of the succeeding fac without an intervening paleosol facs stack into decameter scale fluvial aggradational cycle sets fac sets that also fine upward and from base to top contain either a grad ual upsection increase in soil maturity and soil drainage or a somewhat symmetrical pattern of increasing and decreasing paleosol maturity longer period trends of fac thickness lithologic proportions paleosol maturity and paleosol drainage indicate that two complete and two partial hectometer scale fluvial sequences occur within the study in terval from base to top each sequence is characterized by an asym metric increase and decrease in fac thickness a decrease in the pro portion of sand prone fluvial facies an increase in paleosol maturity and better paleosol drainage whereas facs and fac sets are interpreted to record cyclic epi sodes of channel avulsion and stability and longer term avulsive chan nel drift within the alluvial valley respectively fluvial sequences may coincide with third order sea level changes within the north american western interior seaway as such the cretaceous tertiary k t transition within the tornillo basin may provide an example of me gascale stratigraphic cyclicity that is controlled by eustatic sea level within a fully fluvial succession thickening and thinning successions of facs record a third order period of accelerating transgressive equivalent and decelerating highstand equivalent base level rise and subsequent base level fall falling stage to lowstand equivalent se quence boundaries are placed at the sharp inflection between thinning and thickening facs sand prone facies and immature more poorly drained paleosols are associated with the transgressive equivalent por tion of each sequence and mudrock dominated overbank facies and their associated mature well drained paleosols are associated with the highstand and falling stage equivalent

coupled co2 climate response during the early eocene climatic optimum abstract the early eocene climatic optimum eeco has been characterized as a prolonged warm event indicated by increased atmospheric pco 2 temperatures precipitation and biological turnover a new paleoenvironmental reconstruction using integrated pedological geochemical and isotopic data from the green river basin green river great divide region provides a high resolution record of environmental and climatic change throughout the eeco our reconstruction indicates that this region and likely much of the margin of paleolake gosiute was a stable fluvially controlled floodplain environment with evidence of large scale continuous soil development and features comparable with modern alfisols temperate forest soils regional climate data from multiple proxies indicates that the period was warm temperate and semi arid to sub humid with a peak interval from about 51 5 50 9 ma that exhibits significantly warmer 7 c and wetter 750 mm yr 1 conditions resulting in major changes to the local weathering regime isotopic analyses also indicate a rapid increase to high atmospheric pco 2 values 1700 ppmv and a shift in the 13 c composition of pedogenic carbonates during this peak interval that appear to define and provide a cause for this significant regional response to global climatic change the new data when combined with foraminiferal 13 c records are consistent with co 2 ventilation from a deep marine reservoir source this multi proxy reconstruction suggests that the eeco may have had a superimposed peak of climatic and ecological change on land

reconstruction of a pleistocene paleocatena using micromorphology and geochemistry of lake margin paleo vertisols olduvai gorge tanzania abstract olduvai gorge tanzania contains a rich record of pleistocene paleoclimate and paleoenvironment as well as an abundance of paleontological and archaeological data the 2 2 ma of volcaniclastic infill can be divided into time slices using dated tuffs sediments were deposited in a semi arid closed rift basin containing a shallow saline alkaline lake until 1 75 ma four trenches in uppermost bed i sample a 20 ka time slice between ng eju tuff base 1 818 0 006 ma and tuff if top 1 803 0 002 ma they form a 1 km transect of the lake margin flat that contains both stacked and cumulative paleosols that are interpreted as a heterogeneous paleocatena closer to the lake paleosols are thinner vertically stacked and separated by thin tuffs or tufa further from the lake margin there is additional volcaniclastic input and paleosols are thicker and cumulative macroscale and micromorphological features identify these clay rich paleosols as paleo vertisols abundant pedogenic slickensides and a variety of ped shapes were observed in the field as well as micro ped structures and stress cutans in thin section although weakly developed these paleo vertisols also have distinct horizons defined by soil color changes differing ped shapes and bulk geochemistry and are indicative of monsoonal precipitation seasonality paleosols and parent materials were analyzed for bulk geochemistry of major rare and trace elements geochemical proxies reveal changing hydrology not definitively identifiable in the field or micromorphology molecular weathering ratios show increased weathering and mass balance calculations indicate greater translocations positive and negative through time lower soil moisture due to a drier climate likely created better drained conditions allowing for increased pedogenesis the records of femn oxides and zeolites precipitated in rhizoliths are further evidence for changing redox conditions and water chemistry redox sensitive elements such as fe and mn were mobilized during saturated soil conditions and precipitated during drier conditions as the hydrology changed due to increased aridity zeolites precipitated as rhizoliths due to capillary rise and evaporative pumping of saline alkaline water the fluctuating hydrology identified in the paleo vertisols deposited between 1 79 and 1 81 ma is indicative of a precession cycle and consistent with records from olduvai gorge and throughout east africa this 20 ka time slice of the 2 ma drying trend identified in africa coincides with the first hominin migrations out of africa at 1 8 ma and suggests that hominins were living in a water stressed environment with annual precipitation seasonality and large variations in precipitation due to precession

palaeoclimatic and site specific conditions in the early permian fossil forest of chemnitz sedimentological geochemical and palaeobotanical evidence abstract as significant indicators of deep time palaeoclimate a number of new palaeontological pedological and geochemical characteristics are provided for the chemnitz fossil lagerstatte to depict more precisely its environmental conditions for the first time several lines of evidence indicate that this fossil forest instantaneously preserved by volcanic deposits once received an annual precipitation of around 800 1100 mm but grew on a nearly unweathered palaeosol although the composition of this rich and diverse t0 assemblage suggests a hygrophilous dense and multi aged vegetation dominated by conservative lineages the habitat was affected by environmental disturbances and pronounced seasonality repeated changes in local moisture availability are suggested by geochemical proxies the co occurrence to intergrowth of calcic and ferric glaebules in the palaeosol and developmental traits of perennial vegetational elements specific substrate adaptation is reflected by different root systems and cyclic growth interruptions recorded in the stems branches and roots of long lived woody plants many differentially adapted terrestrial animals complete the more comprehensive reconstruction of a late sakmarian ecosystem and its climatic and preservational controls albeit spatially confined this diverse in situ record may contribute to understand wetland dryland dynamics of sub tropical northern hemisphere pangaea

paleosols and paleoenvironments of the early miocene deposits near karungu lake victoria kenya abstract a 50 m thick stratigraphic section at ngira near karungu on the shore of lake victoria in western kenya documents the early miocene paleoenvironments of the area the basal ngira paleosol is a 7 6 m thick oxisolic vertisol that formed during a prolonged period of pedogenesis it began as a smectite dominated vertisol that was later overprinted through polypedogenesis to become a kaolinitic paleosol highly depleted of all base cations with abundant fe concentrations and depletions and complexly variegated color mottle patterns that reflect extensive ferruginization paleoenvironmental reconstructions using bulk geochemistry indicate warm and wet conditions during development of the ngira paleosol that probably supported a tropical seasonal forest on a stable upland surface for 10s to 100s of thousands of years following this long lived stable landscape rapid subsidence perhaps associated with slip on a high angle fault associated with the onset or progression of the nyanza rift and or the development and eruptive history of the nearby kisingiri volcano buried the paleosol and formed a nascent lake basin that experienced multiple transgressions and regressions during one interval of regression fluvial sandstones and conglomerates were deposited along with fluvio lacustrine sandstones and claystones that include weakly developed paleosols these weakly developed paleosols indicate a relatively dry paleoenvironment with seasonal precipitation and probably a shrubland bushland or riparian forest habitat important terrestrial and aquatic vertebrate fossils are primarily preserved within fluvial and fluvio lacustrine deposits indicating that the terrestrial karungu fauna lived in a relatively dry and open habitat this study demonstrates polypedogenesis and inferences regarding onset of abrupt tectonic activity in the early miocene in equatorial eastern africa and emphasizes the contrasts between landscape stability of the ngira paleosol and the poorly developed soils in the fluvio lacustrine facies

variations in magnetization intensity and low temperature titanomagnetite oxidation of ocean floor basalts the remanent magnetization of the oceanic crust exhibits a systematic long term variation which correlates with the amplitudes of marine magnetic anomalies after a sharp initial decrease of natural remanent magnetization intensity a minimum is reached at 20myr followed by a gradual increase up to ages of 120 myr the progressive sea floor alteration of the magnetic minerals carrying the crustal magnetism is proposed as a cause for this behaviour

examining the spatial consistency of palaeosol proxies implications for palaeoclimatic and palaeoenvironmental reconstructions in terrestrial sedimentary basins terrestrial sediments are a significant archive of past conditions and the critical zone in particular is important for understanding past and ongoing interactions between the atmosphere biosphere and lithosphere understanding the details of a palaeolandscape or palaeocatena record can greatly improve palaeoenvironmental descriptions and palaeoclimate reconstructions during crucial time periods in the past this article presents multi proxy data including palaeosol descriptions major element geochemistry magnetic composition and stable isotope geochemistry from an early eocene palaeosol transect which show distinct trends in palaeosol features and geochemistry across the landscape particularly in terms of the differences between a horizon and b horizon samples a horizon geochemical and physical features are highly variable and reflect other not strictly pedogenic controls whereas b horizon composition is extremely consistent given that most palaeoclimatic or palaeoenvironmental proxies based on palaeosols use b horizon features these results highlight the robustness of those proxies at the same time the difference between a horizons and b horizons and the variability within a horizons of the same palaeosol in different geomorphic settings underscores the importance of palaeosol description detailed sampling and a multi proxy approach to produce both precise and accurate reconstructions of past environments and climates using terrestrial sedimentary records

new constraints on using paleosols to reconstruct atmospheric pco2 ecosystem and climatic changes due to anthro po genic emissions of co 2 are of increasing importance to society one way to predict these changes in the future is to study warming events in the geologic past the main control of earth s temperature over geologic time is the concentration of atmospheric co 2 however the precise relationship between co 2 and temperature is not fully understood therefore it is essential to be able to quantify atmospheric co 2 concentrations in the geologic past especially at times of rapid climate change analogous to current atmospheric changes one widely applied proxy relates the carbon isotopic composition of pedogenic carbonates to atmospheric pco 2 but one of the key variables soil respired co 2 s z is not well constrained this study presents a new proxy where soil respired co 2 is related to mean annual precipitation map by the following equation s z 5 67 map 269 9 r 2 0 59 se 681 ppm this proxy validated for modern atmospheric pco 2 levels constrains the primary source of uncertainty in the soil carbonate paleobarometer we apply this proxy to make atmospheric pco 2 reconstructions for examples from the cenozoic mesozoic and paleozoic and calculate co 2 estimates that are in better agreement with estimates from other independent proxies and model results than previous pedogenic carbonate reconstructions the implications of the uncertainties attributed to pedogenic carbonate paleobarometry as well as guidelines for using this method are discussed by making individual measurements rather than assumptions for each isotopic value and combining those analyses with an s z estimate for each paleosol considered using our new proxy described herein we can obtain increased precision for atmospheric pco 2 reconstructions

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

multi proxy paleosol evidence for middle and late triassic climate trends in eastern utah abstract prior investigations suggest that alluvial lowlands of pangea in the southwestern u s a during the middle to late triassic experienced an arid to semiarid climate with significant seasonality our investigation finds evidence for a global pluvial episode from paleosols in the middle to late triassic section of eastern utah multi proxy paleosol evidence is used to quantify rainfall amounts ambient temperatures and atmospheric co 2 concentrations and infer associated plant formations related to ecosystem persistence rainfall estimates are derived from geochemical molecular weathering ratios temperature and atmospheric co 2 levels from stable oxygen and carbon isotopes of pedogenic carbonate respectively and ecosystem reconstruction by a combination of climate indexes and paleosol characteristics eight pedotypes were identified and include poorly drained aquic entisols fisher well drained non aquic entisols salt valley calcic aridisols castle valley calcic inceptisols moab cambic ute and calcic la sal vertisols dystric inceptisols kokopeli and argillic alfisols slickrock the middle triassic moenkopi formation anisian was dominated by castle valley paleosols with mean annual rainfall between 300 and 400 mm and mean annual temperature between 13 and 23 c mesic to hyperthermic based on these climate indexes and root traces the associated plant formation was most likely desert shrub or dry woodland the lower chinle formation carnian contains a succession of ute and la sal paleosols that changed up section to kokopeli fisher and slickrock paleosols in accordance with geochemical and isotopic signatures from these pedotypes rainfall amounts initially increased to between 700 and 900 mm and then to between 1300 and 1400 mm temperatures estimated from the la sal paleosol are approximately 18 c thermic at this time the lower chinle marks a transition from dry woodland to open forest that appears to correlate with the formation of the petrified forest member in arizona the upper chinle formation carnian norian reveals a return to semiarid to subhumid conditions and the formation of castle valley moab and salt valley paleosols all of which appear to have supported desert shrub or dry woodlands rainfall amounts decreased to between 400 and 600 mm with temperatures eventually increasing to 29 c hyperthermic using the paleosol isotopic barometer atmospheric co 2 estimates generally correlate with other proxy for the triassic the well developed alfisols and noncalcareous inceptisols identified during the carnian of the lower chinle correlate with a previously identified global pluvial episode based on sedimentological and marine isotopic evidence possibly in response to rifting of pangea it should not be assumed that the middle to late triassic in continental alluvial lowlands supported a uniform semiarid to arid climate with strong seasonality

paleoenvironmental and paleoclimatic reconstruction of cretaceous aptian cenomanian terrestrial formations of texas and oklahoma using phyllosilicates abstract clay mineralogy chemistry and stable oxygen and hydrogen isotope compositions of 11 phyllosilicate samples from cretaceous paleosol profiles were determined in order to evaluate early to late cretaceous paleoenvironments and paleoclimates around north central texas and southern oklahoma samples consist of mineralogical mixtures of illite smectite and kaolinite samples from the albian antlers formation in southern oklahoma and the cenomanian woodbine formation are dominated by kaolinite while the remaining samples are dominated by smectite and illite major element compositions of paleosol matrix materials are used to calculate calmag weathering values that range from 31 to 84 and correspond to cretaceous paleoprecipitation estimates ranging from 270 to 1490 mm yr paleosol phyllosilicate hydrogen and oxygen stable isotope values range from 50 to 67 to 18 5 to 21 7 respectively and in conjunction with their respective mineral and chemical compositions correspond to in situ soil crystallization temperatures ranging from 26 3 c to 31 c paleoprecipitation trends exhibit two marked increases in precipitation from the early to late cretaceous in the albian antlers formation and cenomanian woodbine formation stratigraphic intervals with phyllosilicates that yield cooler temperature estimates coincide with stratigraphic intervals with markedly higher precipitation estimates based on calmag values importantly cool high precipitation intervals correlate with periods of extensive shallow seas upon the north american craton comparison of cretaceous temperature precipitation and meteoric water estimates to modern analogs supports the presence of climates similar to modern tropical climates during the cretaceous at subtropical or temperate paleolatitudes in what is now texas and oklahoma consistent with general circulation models and energy balance models suggesting a pervading cretaceous greenhouse

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

new weathering index improves paleorainfall estimates from vertisols vertisols are clayey shrink swell soils that are widely recognized in the rock record thus generating the need to better understand the dynamics of elemental concentrations on the development of weathering indexes for climate interpretations we assessed the weathering performance of the four major base forming oxides cao mgo na 2 o k 2 o along a modern vertisol climosequence spanning a strong precipitation gradient and discovered that the concentration of bulk soil cao and mgo yields the strongest correlation to mean annual precipitation map based on this fi nding we introduce the calmag weathering index defi ned as al 2 o 3 al 2 o 3 cao mgo 100 which improves rainfall estimates for vertisols relative to the wellestablished cia k chemical index of alteration minus potassium weathering index rather than documenting the hydrolysis of weatherable minerals common in many other soil orders in vertisols calmag principally tracks the fl ux of calcium and magnesium sourced from calcium carbonate detrital clay and exchangeable ca 2 and mg 2 application to two mesozoic paleosols reveals that in drier climates cia k yields higher map estimates than calmag but that the reverse is true in wetter climates this work improves paleorainfall estimates from vertisols and suggests that a family of weathering indexes is needed for different paleosol types

early holocene paleosols at the southwestern ramlat as sab atayn desert margin new climate proxies for southern arabia abstract the ramlat as sab atayn desert margin near ma rib yemen displays well preserved early holocene paleosols which are documented by ams 14 c and soil data mollusc shells in bwk and bwkb horizons are dated to the period between 12 5 and 9 5 ka cal bp the buried soils above ahb and abwkb horizons indicate a period of soil formation mainly between 8 8 and 8 3 ka cal bp between 8 3 and 6 7 ka cal bp more weakly developed soils occur and those only locally in contrast to the paleosols sandy cover sediments c horizons without considerable signs of pedogenesis appear due to increasing aridity wind activity and sheet wash after 8 3 ka cal bp these results indicate an arid climate and the formation of cover sediments at the desert margin of yemen in the rain shadow of the yemen highlands after the main period of soil formation which ended around 8 3 ka cal bp at the latest at 6 7 ka cal bp calculating from geochemical data a palaeoprecipitation of about 400 to 600 mm a 1 235 mm a 1 from 12 5 to 8 3 ka bp is proposed accordingly after 8 3 ka cal bp the summer position of the itcz and the associated monsoon rain belt carrying rain to northeastern yemen is assumed not to go beyond 15 n in its whole amplitude

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

vertisol carbonate properties in relation to mean annual precipitation implications for paleoprecipitation estimates abstract previous publications combining the properties of multiple soil orders show that depth to carbonate dtc increases systematically between 350 and 1000 mm of mean annual precipitation map we hypothesize that carbonate in vertisols clay rich shrink swell soils respond differently to water flux than other soil orders because of lower permeability to test this hypothesis we compiled soil description and characterization data from multiple published sources across a late pleistocene climosequence of the coast prairie of texas to assess the relationship between map 700 1400 mm and dtc the dtc of carbonate nodules represents an index of accumulation and the dtc of calcium carbonate equivalent total carbonate 2 0 mm diam an index of leaching the dtc for 1 2 and 5 abundances were assessed using regression analysis the r2 values were highest for the dtc of 2 nodules and of 1 calcium carbonate equivalent in vertisol microlows surprisingly relatively high r2 values were calculated

thick dyke emplacement and internal flow a structural and magnetic fabric study of the deep seated dolerite dyke of foum zguid southern morocco 1 knowledge on forced magma injection and magma flow in dykes is crucial for the understanding of how magmas migrate through the crust to the earth s surface because many questions still persist we used the long thick and deep seated foum zguid dyke morocco to investigate dyke emplacement and internal flow by means of magnetic methods structural analysis petrography and scanning electron microscopy we also investigated how the host rocks accommodated the intrusion regarding internal flow 1 important variations of the rock magnetic properties and magnetic fabric occur with distance from dyke wall 2 anisotropy of anhysteretic remanent magnetization reveals that anisotropy of magnetic susceptibility ams results mainly from the superposition of subfabrics with distinct coercivities and that the imbrication between magnetic foliation and dyke plane is more reliable to deduce flow than the orientation of the ams maximum principal axis and 3 a dominant upward flow near the margins can be inferred the magnetic fabric closest to the dyke wall likely records magma flow best due to fast cooling whereas in the core the magnetic properties have been affected by high temperature exsolution and metasomatic effects due to slow cooling regarding dyke emplacement this study shows that the thick forceful intrusion induced deformation by homogeneous flattening and or folding of the host sedimentary strata dewatering related to heat as recorded by thick quartz veins bordering the dyke in some localities may have also helped accommodating dyke intrusion the spatial arrangement of quartz veins and their geometrical relationship with the dyke indicate a preintrusive to synintrusive sinistral component of strike slip

mesozoic intracontinental underthrust in the se margin of the north china block insights from the xu huai thrust and fold belt the xu huai thrust and fold belt located in the southeastern margin of the north china block consists mainly of thrust and folded pre mesozoic strata its geodynamic evolution and tectonic setting are topics of long debate this paper provides new evidence from geological mapping structural analysis and making balance cross sections with restoration of cross sections results suggest that this belt was subjected to two phase deformation including an early phase regional scale nw ward thrust and fold and a late phase extension followed by the emplacement of dioritic monzodioritic porphyrites dated at 131 135 ma and locally strike slip shearing according to the mapping field observations and drill hole data three structural units were distinguished namely 1 the pre neoproterozoic crystalline basement in the eastern segment 2 the nappe unit or the thrust and fold zone in the central segment which is composed of neoproterozoic to ordovician carbonate rocks and carboniferous permian coal bearing rocks about 2600 m thick and 3 the western frontal zone a major decollement fault has also been identified in the base of the nappe unit on which dozen meter to km scale thrust and fold bodies were commonly developed all pre mesozoic depositional sequences were involved into a widespread thrust and fold event six uncompetent rock layers with biostratigraphic ages nanjing university 1996 have been recognized and each uncompetent rock layer occurred mainly in the top of the footwall playing an important role in the development of the xu huai thrust and fold belt geometry of the major decollement fault suggests that the nappe unit of this belt was rooted in its eastern side near the tan lu fault zone two geological cross sections were chosen for structural balancing and restoration from the balanced cross sections ramp flat and imbricated faults as well as fault related folds were identified a shortening of 20 6 29 6 km was obtained from restoration of balanced sections corresponding to a shortening rate of 43 6 46 4 this shortening deformation was likely related to the se ward intracontinental underthrust of the north china block beneath the south china block during the mesozoic

modification of the magnetic mineralogy in basalts due to fluid rock interactions in a high temperature geothermal system krafla iceland summary active high temperature 150 c geothermal areas like the krafla caldera ne iceland often show distinct magnetic lows in aeromagnetic anomaly maps suggesting a destruction of magnetic minerals by hydrothermal activity the main alteration processes in such an environment are low temperature oxidation 350 c maghemitization and fluid rock interactions we investigated the rock magnetic properties natural remanent magnetization nrm magnetic susceptibility and their temperature and field variation and the mineralogy using x ray diffraction microscopic methods and electron microprobe analyses of two drill cores kh1 and kh3 from the rim of the krafla caldera the drill cores have distinctly lower nrm values average 3 a m 1 compared to younger surface basalts average 20 a m 1 along with a large variation in magnetic susceptibility 1 3 10 7 4 9 10 5 m3 kg 1 the secondary mineral assemblage sulphides sphene rutile and chlorite indicates an alteration within the chlorite smectite zone for both cores without depth zoning optical miscroscopy in combination with the bitter technique and backscatter electron microscopy along with the thermomagnetic analyses allow distinguishing two different magnetomineralogical groups of titanomaghemite 1 titanomaghemite with intermediate titanium concentration and probably high vacancy concentration and 2 titanomaghemite with low titanium concentration and low vacancy concentration the mineral assemblages textures and magnetic properties deduced from the mentioned magnetic measurements indicate two stage transformation mechanism 1 dissolution of titanium at low ph under oxidizing conditions the ulvospinel component of titanomagnetite and ilmenite forms rutile or sphene and fe2 migrates out of the spinel lattice forming titanomaghemite 2 formation of pyrite and dissolution of remaining titanomaghemite under reducing and acidic conditions the latter mechanism produces ghost textures all titanomaghemite is transformed and only their former grain shapes are preserved with only paramagnetic minerals left and ferrimagnetic minerals nearly dissolved this mechanism could explain the significant magnetization loss which is seen in many local magnetic anomaly lows within the oceanic crust and volcanic islands like iceland or hawaii the production of nanoporous textures in titanomaghemites is suggested as a mechanism for the enhancement of the magnetic susceptibility values related to the hydrothermal alteration of krafla

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

alteration and dissolution of fine grained magnetite and its effects on magnetization of the ocean floor abstract scanning and transmission electron microscopy stem of ocean floor pillow basalts with ages between 0 and 70 ma reveals progressive alteration of submicrometer titanomagnetite to phases such as goethite and clays in contrast larger titanomagnetite grains 1 m oxidize to titanomaghemite without apparent change in crystal morphology rock magnetic experiments are consistent with a selective removal of the submicrometer grains as the basalts age and show good correlations between the ranges of grain sizes observed by stem and those indicated by hysteresis properties remanence contributions from the larger pseudo single domain and multi domain titanium iron oxides are inferred to decrease only slightly as the ocean floor becomes older whereas the overall remanence decays with age as the substantial contribution from stable single domain titanomagnetite grains diminishes greatly due to their alteration to other phases although more work on many more samples is required to verify our conclusions the current data imply that this alteration is one of the reasons that amplitudes of marine magnetic anomalies diminish with age over time scales of tens of millions of years

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

nrm intensity of altered oceanic basalts across the mar 21 n 0 1 5 ma a record of geomagnetic palaeointensity variations summary during cruise tammar may 1996 of r v nadir and submersible nautile 66 basaltic rock samples were collected along two long cross sections encompassing the oceanic crust between 0 and 1 5 myr at the centre of the mid atlantic ridge segment located at 21 n this dense sampling provides a means to investigate natural remanent magnetization nrm variability with age using rock magnetic studies high field and k t experiments palaeofield intensity determinations by the original thellier method together with the good geophysical and geological knowledge of this peculiar segment nrm intensities range from 1 3 to 25 4 a m 1 but do not display any rapid exponential decay with age as expected despite the scatter they seem to present short wavelength variations consistent on both flanks of the two lines because of the relative uniformity in grain size i e single domain sd ulvospinel content i e x 0 6 and amount of magnetic minerals in tammar samples the observed across axis nrm intensity variations may be due either to oxidation degree variations or to geomagnetic field intensity changes curie temperatures display no increase towards the flanks nor a clear relationship with nrm intensities suggesting that oxidation degree is not the major process controlling the nrm variations half of the collected samples either fresh or highly altered provide good quality palaeointensity determinations depending on the alteration degree of samples two major types of nrm trm diagrams are observed for relatively fresh materials only one line segment and the major part of nrm is used for field intensity calculations for moderately or highly altered specimens two line segments are observed with the first most probably corresponding to thermal demagnetization of the original remanence and the second to the product resulting from chemical modification i e inversion despite the difference in the amount of nrm that can be thermally demagnetized samples of similar age but of different non stoichiometric degree give coincident palaeofield strengths palaeofield values from 15 to 62 t i e vadm from 3 4 to 13 6 1022 a m2 are in good agreement with the global palaeointensity database and display coherent short wavelength undulations with age consistent assuming a 1 km wide neo volcanic zone and steady symmetrical spreading with the relative palaeointensity record deduced from sediment core analysis guyodo valet 1999 comparison between nrm and field intensity variations with age reveals a remarkable coincidence between both signals suggesting that the nrm intensities are more sensitive to the field intensity than to the alteration degree these observations suggest that magnetic particles are titanomaghemites generated during the initial magma cooling and storing a durable record of the geomagnetic field intensity the type of remanence is either 1 a chemical remanent magnetization that closely mimics the properties of the initial nrm or 2 a thermoremanent magnetization the maghemitization precedes the trm acquisition or 3 a mixture of both

effects of weathering on single domain magnetite in early pliocene marine marls rock magnetic parameters are often used to recognize variations in the original magnetic mineralogy and for normalizing purposes in palaeointensity studies incipient weathering however is shown to have a profound but partly reversible influence on the rock magnetic properties of the marls of the early pliocene trubi formation in southern sicily italy the remanence in the marls resides in single domain sd magnetite grains but the remanent coercive force hcr shows a strong variation and most values observed are anomalously high hcr range 36 188 mt the enhanced coercivities are attributed to stress in the magnetite grains induced by surface oxidation at low temperature upon heating to 150 c a reduction of coercivities occurs that can be explained by a stress reduction as a result of a reduction of fe2 gradient due to a higher diffusion rate at elevated temperature after heating to 150 c coercivities are quite uniform throughout the outcrop and the values are characteristic of sd magnetite hcr range 30 38 mt the bulk susceptibility increases by 4 24 per cent and the isothermal remanent magnetization irm decreases by 5 11 per cent the increase in anhysteretic remanent magnetization arm is large 20 242 per cent the magnitude of the changes is related to the degree of weathering another effect of heating the marl samples to 150 c is a substantial reduction of the coercivities of the secondary overprint in the natural remanent magnetization after heating separation of the secondary and primary components by alternating field demagnetization is more efficient the usual difficulties of thermal demagnetization above 300 c may thus be avoided by a combination of moderate heating to 150 c and subsequent alternating field demagnetization

magnetic properties of variably serpentinized abyssal peridotites we have compiled new and published data on the magnetic properties of 245 serpentinized abyssal peridotites from seven deep sea drilling project and ocean drilling program sites the magnetic susceptibility k of these samples does not increase linearly with the degree of serpentinization s instead k remains modest in partially serpentinized samples s 75 peridotites in the oceanic crust moderately serpentinized peridotites s 75 have nrm values 5 a m and k 0 05 si low temperature oxidation of magnetite is found to lower the nrm and k values of seafloor samples and of cataclastically deformed drilled samples

a new paleothermometer for forest paleosols and its implications for cenozoic climate climate is a primary control on the chemical composition of paleosols making them a potentially extensive archive applicable to problems ranging from paleoclimate reconstruction to paleoaltimetry however the development of an effective widely applicable paleosol temperature proxy has remained elusive this is attributable to the fact that various soil orders behave differently due to their respective physical and chemical properties therefore by focusing on an individual order or a subset of the 12 soil orders whose members exhibit similar process behavior a better constrained paleothermometer can be constructed soil chemistry data were compiled for 158 modern soils in order to derive a new paleosol paleothermometry relationship between mean annual temperature and a paleosol weathering index pwi that is based on the relative loss of major cations na mg k ca from soil b horizons the new paleothermometer can be applied to clay rich paleosols that originally formed under forest vegetation including inceptisols alfisols and ultisols and halves the uncertainty relative to previous approaches a case study using cenozoic paleosols from oregon united states shows that paleotemperatures produced with this new proxy compare favorably with paleobotanical temperature estimates global climatic events are also evident in the oregon paleosol record including a 2 8 c drop across the eocene oligocene transition comparable to marine records and a neogene peak temperature during the mid miocene climatic optimum

a volcanomagnetic observation on mount st helens washington total magnetic fields were recorded at five sites on mt st helens between 23 october and 11 november 1981 an interval which included an extrusive dome building eruption of the volcano two of the magnetometers located in the volcano s crater measured reversible magnetic changes which correspond to fluctuations in tilt measured nearby however the relationship is highly nonlinear electric fields were measured on the east flank of the volcano near its summit to search for electrokinetic effects they show no correlation with the magnetic changes and in the long term are uncorrelated with eruptive activity our favored interpretation of the magnetic changes is that they result from stress induced changes in the magnetization of the volcano magnetic field values returned to pre anomaly values this reversibility rules out pressure induced magnetization as the dominant mechanism and places an upper limit of 300 bars on the stress changes the limited spatial extent of the magnetic anomaly field places the source of stress at shallow depth beneath the crater floor consistent with models based on strain data

the magnetism and microstructure of pulverized titanomagnetite fe2 4ti0 6o4 the effect of annealing maghemitization and inversion abstract titanomagnetite fe 2 4 ti 0 6 o 4 pulverized in a ball mill to make the material readily maghemitize on the laboratory time scale has been used as an analogue for the magnetic mineral of submarine basalts the ball milling in addition to reducing particle size produces an internal nanocrystalline structure annealing at high enough temperature 600 c 800 c removes the nanocrystalline structure but the titanomagnetite crystals carry a relic of ball milling induced non stoichiometry which contributes to magnetic strain anisotropy despite this complication the coercive force of the annealed material is close to the average coercive force of pillow basalts and should provide an improved synthetic analogue for laboratory studies inspired by the magnetism and mineralogy of the submarine crust the nanocrystalline structure persists in maghemitized pulverized titanomagnetite and the magnetization process parameters are consistent with an increasing importance of thermal fluctuations as maghemitization proceeds in the transformations produced by annealing maghemitization and inversion the spinel component immediately post transformation has composition and or concentration inherited from the pre transformation spinel and does not correspond to equilibrium later re equilibration of the coexisting phases accelerated in the laboratory by elevated temperature leads to diminution of the spinel component in favour of more stable phases unlike the inversion of maghemite to haematite the inversion product of titanomaghemite is not a unique assemblage of phases

palaeomagnetism of the teschenitic rocks lower cretaceous in the outer western carpathians of poland constraints for tectonic rotations in the silesian unit summary results of palaeomagnetic investigations of the lower cretaceous teschenitic rocks in the silesian unit of the outer western carpathians in poland bring evidence for pre folding magnetization of these rocks the mixed polarity component reveals inclinations between 56 and 69 which might be either of cretaceous or tertiary age apparently positive results of fold and contact tests in some localities and presence of pyrhotite in the contact aureole suggest that magnetization is primary although a neogene or earlier remagnetization cannot be totally excluded since inclination only test between localities gives syn folding results higher palaeoinclinations 66 69 correlate with a younger variety of teschenitic rocks dated for 122 120 ma while lower inclinations 56 60 with an older variety 138 133 ma this would support relatively high palaeolatitudes for the southern margin of the eurasian plate in the late part of the early cretaceous and relatively quick northward drift of the plate in this epoch together with the silesian basin at its southern margin declinations are similar to the cretaceous tertiary palaeodeclinations of stable europe in the eastern part of the studied area but rotated ca 14 70 counter clockwise in the western part this indicates together with older results from czech and slovakian sectors of the silesian unit a change in the rotation pattern from counter clockwise to clockwise at the meridian of 19 e the rotations took place before the final collision of the outer carpathians nappe stack with the european foreland