gypsum caves as indicators of climate driven river incision and aggradation in a rapidly uplifting region detailed geomorphological analysis has revealed that subhorizontal gypsum caves in the northern apennines italy cut across bedding planes these cave levels formed during cold periods with stable river beds and are coeval with fluvial terraces of rivers that flow perpendicular to the strike of bedding in gypsum monoclines when rivers entrench renewed cave formation occurs very rapidly resulting in the formation of a lower level river aggradation causes cave alluviation and upward dissolution paragenesis in passages nearest to the river beds the u th dating of calcite speleothems provides a minimum age for the formation of the cave passage in which they grew which in turn provides age control on cave levels the ages of all speleothems coincide with warmer and wetter periods when co 2 availability in the soils covering these gypsum areas was greater this climate driven speleogenetic model of epigenic gypsum caves in moderately to rapidly uplifting areas in temperate regions might be generally applicable to karst systems in different geological and climatic conditions

principles of early development of karst conduits under natural and man made conditions revealed by mathematical analysis of numerical models numerical models of the enlargement of primary fissures in limestone by calcite aggressive water show a complex behavior if the lengths of the fractures are large and hydraulic heads are low as is the case in nature dissolution rates at the exit of the channel determine its development by causing a slow increase of water flow which after a long gestation time by positive feedback accelerates dramatically within a short time span mathematical analysis of simplified approximations yields an analytical expression for the breakthrough time when this happens in excellent agreement with the results of a numerical model this expression quantifies the geometrical hydraulic and chemical parameters determining such karst processes if the lengths of the enlarging channels are small but hydraulic heads are high as is the case for artificial hydraulic structures such as dams it is the widening at the entrance of the flow path which determines the enlargement of the conduit within the lifetime of the dam this can cause serious water losses this can also be explained by mathematical analysis of simplified approximations which yield an analytical threshold condition from which the safety of a dam can be judged thus in both cases the dynamic processes of karstification are revealed to gain a deeper understanding of the early development of karst systems as a further important result one finds that minimum conditions below which karstification cannot develop do not exist

10be and 26al evidence for exceptionally low rates of australian bedrock erosion and the likely existence of pre pleistocene landscapes analysis of in situ produced 10be and 26al demonstrate that some australian inselbergs granitic domes are among the most stable geomorphic surfaces in the world eroding at rates as low as 0 6 m myr twenty isotopic analyses of ten samples suggest that the bare bedrock tops of these isolated granitic domes have been exposed to cosmic radiation for at least 0 5 myr and are eroding at a mean model rate less than 0 7 0 1 m myr n 6 isotopic analyses of samples collected from the top of mt wudinna little wudinna and yarwondutta rock are most consistent with continuous exposure during erosion on the other hand samples collected from the flanks of some domes and the tops of other domes have isotopic abundances suggestive of complex exposure histories including burial and reexposure these unique isotopic data provide the first quantitative information for evaluating longstanding but previously untested hypotheses regarding the antiquity and development of these enigmatic landforms and indicate that some eyre peninsula inselbergs are probably relict features of pre pleistocene landscapes

late quaternary chronostratigraphic framework of terraces and alluvium along the lower ohio river southwestern indiana and western kentucky usa abstract the lower ohio river valley is a terraced fluvial landscape that has been profoundly influenced by quaternary climate change and glaciation a modern quaternary chronostratigraphic framework was developed for the lower ohio river valley using optically stimulated luminescence osl dating and allostratigraphic mapping to gain insights into the nature of fluvial responses to glacial interglacial stadial interstadial transitions and holocene climate change river deposits t0 youngest to t7 oldest were mapped along a 75 km reach of the lower ohio river and were dated using 46 osl and 5 radiocarbon samples the examination of cores combined with osl and radiocarbon dating shows that fluvial sediments older than marine oxygen isotope stage mis 2 are present only in the subsurface aggradation during mis 6 illinoian glaciation filled the valley to within 7 m of the modern floodplain and by 114 ka mis 5e sangamon interglacial the ohio river had scoured the mis 6 sediments to 22 m below the modern floodplain surface there were no fluvial sediments in the valley with ages between mis 5e and the middle of mis 3 the mis 3 ages 39 ka and stratigraphic position of t5 deposits suggest the ohio river aggraded 8 14 m during mis 4 or mis 3 near the end of mis 3 the ohio river incised the mid last glacial mid wisconsinan deposits 10 m and began aggrading again by 30 ka aggradation continued into mis 2 with maximum mis 2 aggradation occurring before 21 ka which is coincident with the global last glacial maximum lgm as the ohio river adjusted to changing fluxes in sediment load and discharge following the lgm it formed a sequence of fill cut terraces in the mis 2 outwash that get progressively younger with decreasing elevation ranging in age from 21 ka to 13 ka from 14 ka to 13 ka the ohio river rapidly incised 3 m to form a new terrace and by 12 ka at the onset of the holocene the ohio river established a meandering channel pattern the river formed a broad floodplain surface from 12 ka to 6 ka and then incised 1 m and formed a fill cut terrace from 6 ka to 5 ka after 5 ka likely in response to mid holocene drought in north america the ohio river incised 5 m and by 4 ka the river began aggrading again the ohio river has aggraded 4 m since aggradation began at 4 ka the chronostratigraphic framework and reconstructed history developed here suggest that the lower ohio river is highly sensitive to glacial interglacial transitions and abrupt holocene climate change and responds rapidly to these allogenic forcings

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

soil profiles as indicators of mineral weathering rates and organic interactions for a pennsylvania diabase abstract basaltic bedrock dissolves quickly and its weathering rate is therefore important towards controlling the composition of natural waters soil formation and co 2 concentrations in the atmosphere despite its importance however few reports of basalt or diabase and gabbro weathering rates exist in the literature and most have been measured in laboratory dissolution experiments or based on watershed studies here using elemental profiles measured through regolith on a jurassic diabase dike in south central pennsylvania we calculate time integrated log dissolution rates mol m 2 s 1 of the primary minerals plagioclase 14 9 s 1 and augite 14 8 and of smectite 17 6 a secondary clay mineral formed in the soil characteristic patterns in elemental profiles are consistent with preserved signatures of corestone formation elemental and mineral signatures of the soils relative to the parent rock are compared to predictions from citrate containing basalt column dissolution experiments depletion of apatite and of al fe mn ti p y ni cr sc v ga cu zn and la are observed in the upper meter of the profile relative to the parent rock

pace of landscape evolution in the sierra nevada california revealed by cosmogenic dating of cave sediments we report 26 al 10 be based ages of sierra nevada caves that constrain detailed late pliocene and quaternary river incision his tories for five river canyons rapid incision of 0 2 mm yr from 2 7 to ca 1 5 ma slowed markedly to 0 03 mm yr thereafter likely reflecting the combined effects of a transient erosional re sponse to pliocene rock uplift and periodic mantling of riverbeds with glacially derived sediment in the late quaternary while 400 m of incision has occurred in the past 2 7 m y outpacing interfluve erosion and thereby increasing the local relief canyons as deep as 1 6 km existed prior to that time these new erosion rates strength en the case for tectonically driven late cenozoic uplift

origin and morphology of limestone caves limestone caves form along ground water paths of greatest discharge and solutional aggressiveness flow routes that acquire increasing discharge accelerate in growth while others languish with negligible growth as discharge increases a maximum rate of wall retreat is approached typically about 0 01 0 1 cm yr determined by chemical kinetics but nearly unaffected by further increase in discharge the time required to reach the maximum rate is nearly independent of kinetics and varies directly with flow distance and temperature and inversely with initial fracture width discharge gradient and pco2 most caves require 104 105 yr to reach traversable size their patterns depend on the mode of ground water recharge sinkhole recharge forms branching caves with tributaries that join downstream as higher order passages maze caves form where 1 steep gradients and great undersaturation allow many alternate paths to enlarge at similar rates or 2 discharge or renewal of undersaturation is uniform along many alternate routes flood water can form angular networks in fractured rock anastomotic mazes along low angle partings or sponge work where intergranular pores are dominant diffuse recharge also forms networks and spongework often aided by mixing of chemically different waters ramiform caves with sequential outward branches are formed mainly by rising thermal or h2s rich water dissolution rates in cooling water increase with discharge co2 content temperature and thermal gradient but only at thermal gradients of more than 0 01 c m can normal ground water co2 form caves without the aid of hypogenic acids or mixing artesian flow has no inherent tendency to form maze caves geologic structure and stratigraphy influence cave orientation and extent but alone they do not determine branch work versus maze character

geomorphology and natural hazards in karst areas a review 1 introductionsince human beings started to colonise the world slowly migrat ing in multiple directions from the african rift and ultimatelyreaching the southernmost territories of the americas they haveinteracted with the natural environment using its resources and suf fering from its hazardous processes survival of mankind was possiblethanks to its ability to adapt to an ever changing environment and itscapability to learn and communicate the new ndings from the ear liest times geomorphic features and processes were an essential partof social survival crozier et al 2011 in karst terrains caves wereused as shelters as well as burial and sacred places playing an instru mental role in the day to day struggle for survival especially duringthe ice ages fig 1 spectacular karst landmarks such as big cave en trances blue karst springs deep collapse sinkholes cenotes or rockarches just to name a few have often become part of the naturaland supernatural heritage of our ancestors in prehistoric times the human impact on the karst environmentwas very limited like the probability of properties and people beingdamaged by karst processes e g subsidence ooding both impactsandhazardsinkarstterrainshaveincreaseddramaticallyover thelasttwo centuries along with the exponential increase in population andour capability to modify the natural environment largely related tothe economic and technological development of the societies an in creasing number of scientists consider that humans are nowadaysthe most effective geomorphic agent and a prime factor in landscapeevolution zalasiewicz et al 2010 price et al 2011 in fact the for mal de nition of the anthropocene as a new epoch of the geologicaltime scale characterised by a signi cant and global human impact onthe earth s ecosystems is being debated at the present time around25 of the earth s population lives on or nearby karst areas ford andwilliams 2007 and the increasing exploitation of karst resources such as water and building material is leading to severe environmen tal impacts and unsustainable situations drew and hotzl 1999 gunn 2004 unfortunately the number of karst areas affected bywater pollution landscape degradation and other impacts is growingveryrapidly additionally thedamagecausedbyhazardouskarstpro cesses especially subsidence sinkholes beck 2003 waltham et al 2005 gutierrez et al 2008a will most likely keep on increasing exposed human elements augment and anthropogenic changes inthe karst systems frequently result in hazard enhancement karstgeomorphologists and hydrologists can play a decisive role in pre venting natural disasters in karst areas particularly those inducedby human activities dams with leakage and sinkhole problems milanovic 2000 cooper and gutierrez 2011 mines and tunnelsaffected by ooding and subsidence li and zhou 1999 autin 2002 casagrandeet al 2005 luchaetal 2008 high speedrailwaysbuilt in sinkhole prone areas guerrero et al 2008 or developmentof sinkholes at huge rates induced by lake level yechieli et al 2006 or water table sprynskyy et al 2009 declines the importance of properly managing karst areas and mitigatingthe detrimental effects caused by human activities on these inherentlysensitive environments has been boosted by a series of conferencesand projects since the early 1990s ford 1993 williams 1993 pariseet al 2008 2009 raising public awareness on the need to protectour endangered natural resources especially in developed countries has promoted the production of karst speci c environmental impactassessments veni 1999 recently severalapproacheshavebeenpro posedtoassessthedegreeofhuman induceddisturbanceinkarstareas van beynen and townsend 2005 calo and parise 2006 de waele 2009 north et al 2009 although these studies are essential for apropermanagementofthekarstresources theymaybefutileifnotfol lowed by adequate administrative decisions and regulations 2 karst geomorphology2 1 karst processeskarst is characterised by the predominance of rock dissolution overmechanical erosion and is typical of present temperate cold andwarm and tropical environments ford and williams 2007 in karstterrains surface and subsurface geomorphology and hydrology arelargely governed by dissolution of carbonate and or evaporite rocks in the most classical common situation surface waters acidi ed byco

an empirical stream power formulation for knickpoint retreat in appalachian plateau fluviokarst summary hydrologically abandoned caves on tributaries of the upper cumberland river tennessee usa record a wave of river incision that advanced up the drainage basin in the late pliocene and early pleistocene geomorphic and geologic evidence suggests that incision occurred as a migrating knickpoint generated by sudden base level lowering the passage of a knickpoint up the cumberland river tributaries was modeled as a perturbation to steady state incision according to the stream power law e kq m s n and tested using dated incision events recorded in cave sediments knickpoint migration rates generated by this model were 0 1 0 18 m yr over the entire stream network and 4 0 m yr for the mainstem cumberland river channel the ratio m n 0 79 was consistent with previously published parameters however the values of m 1 91 and n 2 39 were much higher than those reported in previous field studies these results suggest the stream power model may be used to model knickpoint migration in the study area provided values for the constants m and n are larger this may be due to the influence of fluviokarst where surface drainage is interrupted due to diversion into the underlying karst aquifer field measurements of channel and basin geometry in fluviokarstic tributaries to the upper cumberland river show 1 a stronger variance between channel slope and discharge 2 a nonlinear relationship between discharge and drainage area and 3 stream width to be nearly invariant as opposed to non karst watersheds because the stream power model relies heavily on the substitution of discharge for drainage area the behavior of channel incision and knickpoint migration in fluviokarst may differ substantially from that of non karst channels

erosion rates in and around shenandoah national park virginia determined using analysis of cosmogenic 10be we use cosmogenic 10be analysis of fluvial sediments and bedrock to estimate erosion rates 104 105 year timescale and to infer the distribution of post orogenic geomorphic processes in the blue ridge province in and around shenandoah national park virginia our sampling plan was designed to investigate relationships between erosion rate and lithology mean basin slope basin area and sediment grain size fifty nine samples were collected from a variety of basin sizes inferred erosion rates for the medium sand fraction of all fluvial samples from all lithologies range from 3 0 to 21 m my the area weighted mean erosion rate for single lithology basins in the park is 12 2 m my single lithology erosion rate ranges for fluvial samples are granite 7 0 to 20 m my metabasalt 3 8 to 21 m my quartzite 3 8 to 15 m my and siliciclastic rocks 5 2 to 15 m my multilithology basins erode at rates between 3 0 16 m my the shenandoah river basin 3305 km2 is eroding at 6 6 m my bedrock erosion rates range from 1 8 to 11 m my across all lithologies with a mean of 6 5 4 3 m my grain size specific 10be analysis of four samples showed no consistent trend of concentration with grain size cosmogenic analysis of bedrock and sediment from the shenandoah national park area allows us to speculate about why some parts of the appalachian mountains erode more slowly and some more rapidly overall it appears that steep drainage basins erode more rapidly than gently sloped basins climate and lithology may also influence basin scale rates of erosion as suggested by the difference in average erosion rates east and west of the divide and the difference between the erosion rates of quartzite and granite dominated basins data are conflicting in regards to the evolution of relief over time analyses made of exposed bedrock along ridgelines suggest that such rock is eroding either more slowly than adjacent drainage basins susquehanna river shenandoah national park region or at similar rates great smoky mountains providing a mechanism for growing relief at the scale of individual ridgelines however considering relief on a landscape or physiographic province scale by comparing erosion rates of the highlands versus the lowlands suggests that relief of the range as a whole is either steady or very slowly decreasing over multi millennial timescales the presence of significant erosion rate slope relationships negates a broad hackian view of the landscape because there is not uniform erosion across this landscape the aspect erosion rate and slope erosion rate relationships present in the shenandoah area suggest that the landscape is not fully adjusted to rock strength

dating plio pleistocene glacial sediments using the cosmic ray produced radionuclides 10be and 26al we use the cosmic ray produced radionuclides 26al and 10be to date plio pleistocene glacial sediment sequences these two nuclides are produced in quartz at a fixed ratio but have different decay constants if a sample is exposed at the surface for a time and then buried by overburden and thus removed from the cosmic ray flux the 26al 10be ratio is related to the duration of burial we first attempted to date pre wisconsinan tills by measuring 26al and 10be in fluvial sediments beneath them and applying the method of burial dating which previous authors have used to date river sediment carried into caves this method however requires simplifying assumptions about the 26al and 10be concentrations in the sediment at the time of burial we show that these assumptions are not valid for river sediment in glaciated regions 26al and 10be analyses of such sediment do not provide accurate ages for these tills although they do yield limiting ages in some cases we overcome this difficulty by instead measuring 26al and 10be in quartz from paleosols that are buried by tills we use a more general mathematical approach to determine the initial nuclide concentrations in the paleosol at the time it was buried as well as the duration of burial this technique provides a widely applicable improvement on other means of dating plio pleistocene terrestrial glacial sediments as well as a framework for applying cosmogenic nuclide dating techniques in complicated stratigraphic settings we apply it to pre wisconsinan glacial sediment sequences in southwest minnesota and eastern south dakota pre wisconsinan tills underlying the minnesota river valley were deposited 0 5 to 1 5 ma and tills beneath the prairie coteau in eastern south dakota and adjacent minnesota were deposited 1 to 2 ma

quantifying denudation rates on inselbergs in the central namib desert using in situ produced cosmogenic 10be and 26al in situ produced cosmogenic isotope concentrations in bedrock surfaces provide valuable estimates of site specific long term rates of denudation and provide constraints for numerical landscape evolution models measurements of cosmogenic sup 10 be and sup 26 al from graphite inselbergs in the arid to hyperarid central namib desert namibia indicate a mean rate of summit lowering of 5 07 1 1 m m y over the past ge 10 sup 5 yr the persistence of an arid climate in the region suggests that a similar rate may have prevailed for the past approximately 10 m y and possibly throughout much of the cenozoic some samples have complex exposure histories that can be explained by the mode of inselberg weathering and mass wasting the denudation rates estimated here are an order of magnitude higher than those reported for inselbergs in a significantly more humid environment in south australia this difference may largely be due to active salt weathering in the central namib as a result of high levels of coastal fog precipitation

pre wisconsin glacial stratigraphy of the central plains region in iowa nebraska kansas and missouri summary recent investigations have documented the presence of several tills and interglacial paleosols that were not recognized in the simple kansan aftonian nebraskan stratigraphic sequence also the single pearlette ash recognized by early workers now is known to be three different pearlette family ash beds of greatly contrasting ages the complexity of the stratigraphy as it is currently understood and the miscorrelations of early work necessitate abandonment of the archaic terms kansan aftonian and nebraskan in stratigraphic terminology continued use of those terms will only promote confusion of stratigraphic nomenclature and erroneous correlations of stratigraphic units the limited chronometric control available within the early and middle pleistocene stratigraphic sequence is provided directly by dating or by correlation of buried soils and volcanic ash beds and it is provided inferentially by interpretation of magnetic polarity data these controls provide at best a general time framework to begin a new synthesis of the quaternary history of the region new methods of dating are needed to facilitate long distance correlation of early and middle pleistocene deposits

the erosion response to quaternary climate change quantified using uranium isotopes and in situ produced cosmogenic nuclides abstract studying how catchment erosion has responded to past climate change can help us better understand not only how landscape evolution operates but also predict the consequences of future climate change on soil resource availability recent years have seen the development of tools that allow a quantitative assessment of past changes in catchment erosion this work reviews the principles of the application of in situ produced cosmogenic nuclides and uranium isotopes to quantifying past erosion rates results highlight the role of periglacial processes and mass wasting in dictating how catchment erosion responds to climatic variability at the 10 kyr scale at the million year scale it is more difficult to untangle the role of climate and tectonics a strong coupling exists at the 10 kyr to 100 kyr scales between climatic cycles and the transfer time of regolith from source to sink this coupling reflects changes in sediment source that are either set by changes in vegetation cover at the catchment scale or by the storage of sediments on continental shelves at a larger scale although further analytical developments are required for these tools to reach their full potential existing works suggest that in the near future they will provide unprecedented quantitative insights on how soil and fluvial systems adapt to external perturbations climatic tectonic and or anthropic

karst landscape evolution in the littoral area of the bay of biscay north iberian peninsula the western pyrenean area contains extensive karst areas however their genesis and development are still mostly unknown in this work we make a general description of the karst landscape in different karst areas 1 rasa type 2 cone type karst and 3 alpine type karst the first two types are present in the littoral area where geomorphological evolution mostly depends on sea level and climatic changes we focused our study in two karst areas of the littoral cone type karst we correlate different caves created from different stable water table levels three representative caves are studied in detail studying their stratigraphic record based on allostratigraphy finally we dated the different phases of speleothem formation in the three caves using all this information we defined four stable paleowater table levels at 50 150 220 and 350 m asl controlled by sea level changes and isostatic uplift events the lowest level is the youngest with an age of c 1 ma we discovered that the interior of the three caves display very similar endokarst allostratigraphic sequences characterized firstly by an erosion phase a fluvio karst input flowstone speleothem formation and finally dripping speleothem formation the chronological data shows a correlation between these phases and pleistocene climatic phases the erosion phase is related to the falling sea level fluviokarst detrital input is related to cold glacial stages and the formation of speleothems is related to the warmest interglacial moments and high sea level periods

reconstructing past climates using carbon isotopes from fulvic acids in cave sediments little is known about the potential of organic substances found within cave sediments to provide useful reconstructions of past climatic changes here we present a study of the carbon isotopes of fulvic acids extracted from sediments from a cave in west central florida fulvic acids are the most contemporaneous representation of soil humic substances derived from vegetation growing above the cave radiocarbon dating of these sediments constrains their depositional period to be late holocene the range of the fulvic acid 13c record shows the dominance of c3 vegetation during this period but with changes in abundance and the shifting presence of c4 plants the 13c values record both the little ice age and medieval climate anomaly which produce drier and wetter conditions for florida respectively our conclusion that the stable carbon isotopic values of the cave sediment record as a proxy for vegetation change as driven by variability in precipitation is strongly supported by a comparison with the 13c and 18o values of two uranium series dated speleothems from this part of florida with both being proxies for precipitation change

climate change in southern illinois usa based on the age and δ13c of organic matter in cave sediments abstract matrix supported diamicton and uniform to laminated silty fine grained sediment deposited from about 42 500 to 27 600 cal yr b p under slackwater conditions nearly filled two caves in southwestern illinois at some point most of the sediment was flushed from the caves and from about 22 700 to 4000 cal yr b p floods deposited a drape of sandy and silty sediment on remnant slackwater successions cobbly alluvium and bedrock especially from 7700 to 4000 cal yr b p clay mineral analyses of the slackwater cave sediment reveal a provenance of chiefly petersburg silt a smectite and illite rich proglacial lacustrine unit present in the overlying illinois episode glacial succession today remnants of the ancient subterranean slackwater deposits nearly fill several secondary passages and in at least two locations cover a cobble mantled strath terrace 1 3 to 1 5 m above active stream channels slumping and sinkhole formation appear to have been important mechanisms for deposition of the ancient subterranean deposits slumping of these surficial deposits and associated vegetation can occur along the flanks of sinkholes in addition to sinkhole formation and enter caves however the finer organics some of them comminuted during transport into the caves become part of the cave alluvium this finer organic fraction is the modern analog of the humified organic matter disseminated in slackwater sediment dated in this investigation by radiocarbon methods twenty four 14c ages on humified organic matter provide chronologic control the 13c values of the organic matter reflect the proportion of c4 type to c3 type vegetation growing in and around swallets and sinkholes at the time of redeposition drought tolerant c4 type vegetation was more prevalent relative to c3 type vegetation from 42 500 to 31 200 cal yr b p compared to conditions from 28 800 cal yr b p to the present the 13c values are consistent with the results from other investigations of speleothems and organic matter from loessial paleosols

a 200 kyr record of cosmogenic radionuclide production rate and geomagnetic field intensity from 10be in globally stacked deep sea sediments the reconstruction of geomagnetic field intensity variations during the last 200 kyr from paleomagnetic data is at present the subject of numerous studies and major debate there is currently no generally accepted record here we present a global stacked record of 230thex normalized 10be deposition in marine sediments representing relative variations in 10be production rate which are translated into field intensity variations the record shows major periods during which the field intensity was between 10 and 40 of the present day value namely 30 42 60 75 85 110 and 180 192 kyr b p our results are compared to independently derived paleomagnetic studies and th u calibrations of 14c dates on corals during most of the observed period the geomagnetic field intensity was weaker than today resulting in an overall 30 reduced value for the last 200 kyr

dramatic increase in late cenozoic alpine erosion rates recorded by cave sediment in the southern rocky mountains abstract apparent increases in sedimentation rates during the past 5 ma have been inferred at sites around the globe to document increased terrestrial erosion rates but direct erosion rate records spanning this period are sparse modern and paleo erosion rates for a small alpine catchment 3108 m above sea level in the southern rocky mountains are measured using the cosmogenic radionuclides crns 10be and 26al in cave sediment bedrock on the overlying landscape surface and coarse bedload in a modern fluvial drainage the unique setting of the marble mountain cave system allows the inherited erosion rates to be interpreted as basin averaged erosion rates resulting in the first crn based erosion rate record from the rocky mountains spanning 5 myr pliocene erosion rates derived from the oldest cave sample 4 9 0 4 ma for the landscape above the cave are 4 9 1 1 m myr 1 mid pleistocene erosion rates are nearly an order of magnitude higher 33 1 2 7 to 41 3 3 9 m myr 1 and modern erosion rates are similar due to the effects of snow shielding these erosion rate estimates are likely higher than actual rates by 10 15 the most likely explanation for this dramatic increase in erosion rates which likely occurred shortly before 1 2 ma is an increase in the effectiveness of periglacial weathering processes at high elevations related to a cooler and wetter climate during the pleistocene providing support for the hypothesis that changes in late cenozoic climate are responsible for increased continental erosion

estimating erosion rates and exposure ages with 36cl produced by neutron activation the isotopic composition of water soluble cl extracted from mineral grains in granitic rocks appears to reflect the relative age of debris flow fan surfaces and the erosion rate of bedrock outcrops our data indicate that some granitic landforms are stable landscape elements eroding on the order of meters to tens of meters per million years samples collected from debris flow fan surfaces of three distinct relative ages show the expected increase of model age with time but the 36cl exposure ages for boulders on any particular surface vary by a factor of more than five the method we used for extracting cl was designed to isolate the 35cl n 36cl production pathway and to simplify the chemical preparation of samples such isolation from fluid inclusions allows direct interpretation of measured 36cl cl ratios but requires a model to predict the thermal neutron production and absorption profile below the rock surface using such a model we find good agreement between measured and predicted 36cl cl for eight samples collected below the ground surface as well as consistency between several groups of samples collected near one another using elemental abundance data for 129 granitic rocks we modeled 36cl cl supported by radiogenic neutrons and find that it varies from 4 to 125 10 15 mean 21 18 1 however from the surface to a depth of 10 m thermal neutrons resulting from muon interactions have the potential to generate more 36cl than do radiogenic neutrons the production of 36cl in the subsurface has important implications for surface exposure dating of young low altitude samples collected from moraines and debris flow or alluvial fans especially at ages where erosion of the boulder surface is significant or where the source area for boulders is at altitudes much higher than the landform to be dated

estimates of the rate of regolith production using and from an alpine hillslope abstract the production of regolith is a fundamental geomorphic process because most surface processes transport only unconsolidated material we use concentrations of the cosmogenic radionuclides crns 10 be and 26 al in regolith and bedrock to deduce the rate of production of regolith on an alpine hillslope in the wind river range wy these calculations are based on a theoretical model which we develop here this model shows that it is important to consider dissolution of regolith in regolith production and in basin averaged erosion rate studies rates of production of regolith are uniform along the hillslope and the mean rates for the entire hillslope deduced from 10 be and 26 al are 14 3 4 0 and 13 0 4 0 m ma 1 respectively rates of production of regolith deduced from 10 be concentrations in regolith mantled bedrock support the rates deduced from regolith concentrations in the alpine environment examined here the rate of production of regolith beneath 90 cm of regolith is nearly twice as fast as the average rate of production of regolith on bare rock surfaces which small et al small e e anderson r s repka j l finkel r 1997 erosion rates of alpine bedrock summit surfaces deduced from in situ 10 be and 26 al earth and planetary science letters 150 413 425 previously documented rock mantled with regolith probably weathers more rapidly than bare rock because the water required for frost weathering is limited on bare rock surfaces because the hillslope examined here is convex with constant curvature and regolith production and thickness are uniform down the slope the regolith volume flux must be proportional to the local slope of the hillside therefore our results are consistent with gilbert s gilbert g k 1909 the convexity of hilltops journal of geology 17 344 350 steady state hillslope hypothesis if tor height and the difference between rates of weathering on bare and regolith mantled rock provide a fair estimate of the age of summit flats steady state hillslope conditions have been attained in less than several million years

10be and 26al production rates deduced from an instantaneous event within the dendro calibration curve the landslide of kofels otz valley austria surface exposure dating requires the knowledge of cosmogenic nuclide production rates when determining time integrated production rates the exposure ages of the calibration samples need to be accurately known the landslide of kofels austria is very well suited for this purpose it is the largest landslide in the crystalline alps of austria dating back to 7800 100 years bc ams 14c dating of buried wood which is well within the 14c dendro calibration curve exposed quartz veins were sampled from the tops of large boulders from the toe of the landslide for analysis of 10be and 26al to calculate sea level high geomagnetic latitude 60 open sky radionuclide production rates corrections were applied for altitude and latitude for shielding by surrounding mountains for sample geometry vegetation and snow cover and for sample thickness the production rates for an exposure age of 10 000 years are 5 75 0 24 10be atoms yr g sio2 and 37 4 1 9 26al atoms yr g sio2 a 26al 10be ratio of 6 52 0 43 can be calculated the influence of the geomagnetic field on these production rates has been estimated using two different geomagnetic field records our production rates should be a good approximation for the use of surface exposure dating between about 5000 and 13 000 years bp

complex exposure histories of chert clasts in the late pleistocene shorelines of lake lisan southern israel activities of 26 al and 10 be in five chert clasts sampled from two beach ridges of late pleistocene lake lisan precursor of the dead sea in southern israel indicate low rates of chert bedrock erosion and complex exposure burial and by inference transport histories the chert clasts were derived from the senonian mishash formation a chert bearing chalk which is widely exposed in the nahal zin drainage basin the drainage system that supplied most of the material to the beach ridges simple exposure ages assuming only exposure at the beach ridge sampling sites range from 35 to 354 ky using the ratio 26 al 10 be total clast histories range from 0 46 to 4 3 my unrelated to the clasts current position and exposure period on the late pleistocene beach ridges 160 177 m below sea level optically stimulated luminescence dating of fine sediments from the same and nearby beach ridges yielded ages of 20 0 s 1 4 ka and 36 1 s 3 3 ka these ages are supported by the degree of soil development on the beach ridges and correspond well with previously determined ages of lake lisan which suggest that the lake reached its highest stand around 27 000 cal years bp if the clasts were exposed only once and than buried beyond the range of significant cosmogenic nuclide production then the minimum initial exposure and the total burial times before delivery to the beach ridge are in the ranges 50 1300 ky and 390 3130 ky respectively alternatively the initial cosmogenic dosing could have occurred during steady erosion of the source bedrock back calculating such rates of rock erosion suggests values between 0 4 and 12 m my 1 t he relatively long burial periods indicate extended sediment storage as colluvium on slopes and or as alluvial deposits in river terraces some clasts may have been stored for long periods in abandoned pliocene and early pleistocene routes of nahal zin to the mediterranean before being transported again back into the nahal zin drainage system and washed on to the shores of lake lisan during the late pleistocene copyright 2003 john wiley sons ltd

late quaternary paleoecology and paleoenvironments of the central mississippi alluvial valley a radiocarbon dated sediment core from powers fort swale located in the western lowlands of southeastern missouri provides sedimentological and palynological evidence for dynamic changes in fluvial regime and vegetation in the central mississippi alluvial valley during the late pleistocene and holocene intervals during the late wisconsinan glacial maximum glacial meltwater carried by the mississippi river maintained active braided streams sand grains in full glacial and late glacial sediments of powers fort swale show evidence of reworking by eolian activity with late pleistocene formation of sand dunes continuing until 11 600 yr b p within the western lowlands the sedimentological sequence indicates a progressive stepwise loss of glacial meltwater and coarse sediment supply during the late glacial interval resulting in abandonment of braided stream terraces the initial partial diversion of mississippi river flow occurred in the late glacial interval possibly as early as 16 300 yr b p as the mississippi river shifted from the western lowlands through the bell city oran gap in crowleys ridge and into the eastern lowlands by 14 500 yr b p the complete diversion of meltwater through this gap coincided with a change in the powers fort sediment core from a spruce dominated to an oak dominated pollen assemblage at 11 500 yr b p sedimentological changes reflected a changeover to a meandering river regime the transition to pollen assemblages characteristic of holocene temperate swamp forest occurred at 9500 yr b p

biostratigraphic techniques for analyzing benthic biofacies stratigraphic condensation and key surface identification pliocene and pleistocene sediments northern green canyon and ewing bank offshore louisiana northern gulf of mexico the northern deep gulf of mexico is a geologically complex province consisting of neogene intraslope minibasins created by sediment loading onto and evacuation of allochthonous salt sedimentary fill in the minibasins consists of bathyal turbidite systems with highly variable facies distribution in this paper we present three biostratigraphic techniques developed to increase our understanding of the geologic evolution of the northern green canyon and ewing bank lease areas the first two techniques address the nature of stratigraphic condensation in minibasins and the relative areal extent of the condensed sections the third technique uses benthic foraminifers to improve the stratigraphic knowledge of the area 1 the first technique is concerned with sediment accumulation plots from wells helping to identify possible areas of condensation based on variations in the rate of accumulation by displaying several wells together the areal extent of the condensed section can be identified and the causes for the condensation can be evaluated 2 the second technique addresses condensation within one minibasin during a 2 5 m y interval relative abundance values are plotted from a series of wells at selected time surfaces and tied to seismic horizons that are correlated throughout the basin this allows plotting a series of maps that show how stratigraphic condensation changes throughout a basin 3 the third technique develops benthic biofacies maps that more accurately reflect the highly irregular paleobathymetry of the slope at the time of deposition these maps were created by plotting the benthic biofacies of the sediments recovered from a well at the stratigraphic extinction of 29 selected planktonic foraminifer and calcareous nannoplankton species the maps are integrated with lithostratigraphic and structural palinspastic reconstructions the resulting maps are interpreted to more accurately reflect benthic biofacies of the continental slope at specific geological times during the pliocene and pleistocene

north american glacial meltwater history for the past 2 3 m y oxygen isotope evidence from the gulf of mexico a high resolution 18 o record from the northeastern gulf of mexico ocean drilling program leg 100 hole 625b provides a history of surface waters for the past 5 35 m y negative 18 o anomalies between 0 3 and 3 0 in planktic foraminifera beginning at 2 30 ma can only have resulted from the discharge of isotopically light glacial meltwater from the mississippi river meltwater anomalies implicate either the periodic presence of north american mid latitude glacial ice since the late pliocene or a drainage system very different from that of the present

cosmogenic dating of fluvial terraces fremont river utah absolute dating of river terraces can yield long term incision rates clarify the role of climate in setting times of aggradation and incision and establish the rates of pedogenic processes while surface exposure dating using cosmogenic 10be and 26al would seem to be an ideal dating method the surfaces are composed of individual clasts each with its own complex history of exposure and burial the stochastic nature of burial depth and hence in nuclide production in these clasts during exhumation and fluvial transport and during post depositional stirring results in great variability in clast nuclide concentrations we present a method for dealing with the problem of pre depositional inheritance of cosmogenic nuclides we generate samples by amalgamating many individual clasts in order to average over their widely different exposure histories depth profiles of such amalgamated samples allow us to constrain the mean inheritance to test for the possible importance of stirring and to estimate the age of the surface working with samples from terraces of the fremont river we demonstrate that samples amalgamated from 30 clasts represent well the mean concentration depth profiles show the expected shifted exponential concentration profile that we attribute to the sum of uniform mean inheritance and depth dependent post depositional nuclide production that the depth dependent parts of the profiles are exponential argues against significant post depositional displacement of clasts within the deposit our technique yields 10be age estimates of 60 9 102 16 and 151 24 ka for the three highest terraces corresponding to isotope stages 4 5d and 6 respectively the mean inheritance is similar from terrace to terrace and would correspond to an error of 30 40 ka if not taken into account the inheritance likely reflects primarily the mean exhumation rates in the headwaters of order 30 m ma

relationships between fluvial evolution and karstification related to climatic tectonic and eustatic forcing in temperate regions this paper reviews the diversity of relationships between river evolution and karstogenesis it also underlines the fundamental role of numerical dating methods e g cosmogenic nuclides applied to sedimentary sequences in tiered cave passages as they have provided new insights into these complex interactions although karst terrain is widespread worldwide we focus on european karst catchments where the sedimentary records are especially well preserved we review the recent dating of fluvial sediments and speleothems to examine the timing of karstification incision and deposition in cave levels the most complete alluvial records occur in tectonically uplifted high mountains where some of the oldest sediment fills date to the miocene evidence indicates that not only uplift but also climatic conditions and fluvial dynamics e g knickpoint retreat increased channel flow and or sediment load and stream piracies can play a major role in speleogenesis and geomorphological evolution in evaporite rocks speleogenesis is characterized by rapid dissolution and subsidence in european catchments gypsum cave development largely occurred during cold climate periods while limestone caves formed during warm interglacial or interstadial phases our synthesis is used to propose four models of fluvial and karst evolution and highlight perspectives for further research

steady 10be derived paleoerosion rates across the plio pleistocene climate transition fish creek vallecito basin california rates of erosion over time provide a valuable tool for gauging tectonic and climatic drivers of landscape evolution here we measure 10be archived in quartz sediment from the fish creek vallecito basin to resolve a time series of catchment averaged erosion rates and to test the hypothesis that aridity and increased climate variation after ca 3 ma led to an increase in erosion rates in this semi arid ice free setting the fish creek vallecito basin located east of the peninsular ranges in southern california is an ideal setting to derive a plio pleistocene paleo erosion rate record the basin has a rapid sediment accumulation rate a detailed magnetostratigraphic age record and its stratigraphy has been exposed through recent rapid uplift and erosion a well defined source region of uniform lithology and low erosion rate provides a high reproducible 10be signal we find that paleo erosion rates were remarkably consistent between 1 and 4 ma averaging 38 24 m myr 2 modern catchment averaged erosion rates are similar to the paleo erosion rates the uniformity of erosion over the past 4 myr indicates the landscape was not significantly affected by late pliocene global climate change nor was it affected by a local long term increase in aridity

26al 10be 21ne burial dating abstract cosmogenic nuclide burial dating relies on a pair of cosmic ray produced nuclides that are produced in the same rock or mineral target at a fixed ratio but have different half lives for example 26 al and 10 be are produced in quartz at 26 al 10 be 6 75 1 if a sample of quartz is exposed at the surface for a time 26 al and 10 be concentrations reflect this ratio if it is then buried below the penetration depth of cosmic rays production stops and both nuclides decay the half life of 26 al is half that of 10 be so the 26 al 10 be ratio decreases over time and can be used to date the burial event because quartz derived from surface erosion and then buried by sediment accumulation is common the method is widely applicable for dating plio pleistocene clastic sediments all terrestrial applications of burial dating so far have used the 26 al 10 be pair here we show that coupling cosmogenic 21 ne which is also produced in quartz with 26 al or 10 be should improve upon both the age range and accuracy of 26 al 10 be burial dating we establish the feasibility of this approach by 21 ne measurements at two sites that have already been dated using 26 al 10 be burial dating burial ages from all three nuclide pairs agree at both sites which shows that currently accepted values for decay constants and production ratios are internally consistent thus it is possible at present to increase the useful range of cosmogenic nuclide burial dating by incorporating 21 ne fully realizing the potential improvements in accuracy would benefit from additional estimates of 21 ne 26 al and 21 ne 10 be production ratios that are independent of the 26 al and 10 be decay constants

quaternary downcutting rate of the new river virginia measured from differential decay of cosmogenic 26al and 10be in cave deposited alluvium the concentrations of the cosmogenic radionuclides sup 26 al and sup 10 be in quartz can be used to date sediment burial here we use sup 26 al and sup 10 be in cave deposited river sediment to infer the time of sediment emplacement sediment burial dates from a vertical sequence of caves along the new river constrain its quaternary downcutting rate to 27 3 4 5 m m y and may provide evidence of regional tectonic tilt 32 refs 3 figs 1 tab

crustal and uppermost mantle structure beneath the continental rifting area of the gulf of suez from earthquake tomography abstract suez rift is one of the active seismic zones in the northward continuation of the red sea as indicated by recent earthquake records from the egyptian national seismological network ensn we present a new model of p and s wave velocities in the crust and uppermost mantle beneath the gulf of suez and surrounding areas including the northern portion of the red sea using the records from 94 seismic stations we analyzed 66 000 p and 17 000 s wave arrival times from 9700 events the travel time tomography inversion was performed using the iterative lotos code the spatial resolutions of the derived models were assessed using several synthetic tests the most prominent anomaly is a sharp high velocity anomaly beneath the red sea which is observed in both the p and s models at all depth intervals we interpret this anomaly to be oceanic crust that was formed through extension associated with a dispersed system of spreading centers beneath the gulf of suez the upper and middle crusts appear to be strongly heterogeneous and are dominated by low velocity anomalies indicative of the continental nature of the crusts in contrast at a depth of 30 km we observe a prominent high velocity anomaly along gulf of suez which is interpreted to be the result of crustal thinning associated with extension between the sinai block and the african plate the thickness of the crust beneath the rift is estimated to be approximately 25 km whereas that in the surrounding areas appears to be 30 35 km in the northwestern part of the area we observe a low velocity zone in the middle and lower crusts that coincide with intense seismicity and a well developed system of recent faults on the surface this region may mark a possible area of northward propagation of the suez rift zone

erosion of an ancient mountain range the great smoky mountains north carolina and tennessee analysis of 10be and 26al in bedrock n 10 colluvium n 5 including grain size splits and alluvial sediments n 59 including grain size splits coupled with field observations and gis analysis suggest that erosion rates in the great smoky mountains are controlled by subsurface bedrock erosion and diffusive slope processes the results indicate rapid alluvial transport minimal alluvial storage and suggest that most of the cosmogenic nuclide inventory in sediments is accumulated while they are eroding from bedrock and traveling down hill slopes spatially homogeneous erosion rates of 25 30 mm ky 1 are calculated throughout the great smoky mountains using measured concentrations of cosmogenic 10be and 26al in quartz separated from alluvial sediment 10be and 26al concentrations in sediments collected from headwater tributaries that have no upstream samples n 18 are consistent with an average erosion rate of 28 8 mm ky 1 similar to that of the outlet rivers n 16 24 6 mm ky 1 which carry most of the sediment out of the mountain range grain size specific analysis of 6 alluvial sediment samples shows higher nuclide concentrations in smaller grain sizes than in larger ones the difference in concentrations arises from the large elevation distribution of the source of the smaller grains compared with the narrow and relatively low source elevation of the large grains large sandstone clasts disaggregate into sand size grains rapidly during weathering and downslope transport thus only clasts from the lower parts of slopes reach the streams 26al 10be ratios do not suggest significant burial periods for our samples however alluvial samples have lower 26al 10be ratios than bedrock and colluvial samples a trend consistent with a longer integrated cosmic ray exposure history that includes periods of burial during down slope transport the results confirm some of the basic ideas embedded in davis geographic cycle model such as the reduction of relief through slope processes and of hack s dynamic equilibrium model such as the similarity of erosion rates across different lithologies comparing cosmogenic nuclide data with other measured and calculated erosion rates for the appalachians we conclude that rates of erosion integrated over varying time periods from decades to a hundred million years are similar the result of equilibrium between erosion and isostatic uplift in the southern appalachian mountains

dating of pliocene colorado river sediments implications for cosmogenic burial dating and the evolution of the lower colorado river we applied cosmogenic 26 al 10 be burial dating to sedimentary deposits of the ancestral colorado river we compared cosmogenic burial ages of sediments to the age of an independently well dated overlying basalt flow at one site and also applied cosmogenic burial dating to sediments with less precise independent age constraints all dated gravels yielded old ages that suggest several episodes of sediment burial over the past 5 3 m y comparison of burial ages to the overlying 4 4 ma basalt yielded good agreement and suggests that under the most favorable conditions cosmogenic burial dating can extend back 4 5 m y in contrast results from other sites with more broadly independent age constraints highlight the complexities inherent in burial dating these complexities arise from unknown and complicated burial histories insufficient shielding postburial production of cosmogenic isotopes by muons and unknown initial 26 al 10 be ratios nevertheless and in spite of the large range of burial ages and large uncertainties we identify samples that provide reasonable burial age constraints on the depositional history of sediment along the lower ancestral colorado river these samples suggest possible sediment deposition and burial at ca 5 3 4 7 and 3 6 ma our calculated basinwide erosion rate for sediment transported by the modern colorado river 187 mm k y 1 is higher than the modern erosion rates inferred from the historic sediment load 80 100 mm k y 1 in contrast basinwide paleo erosion rates calculated from pliocene sediments are all under 40 mm k y 1 the comparatively lower denudation rates calculated for the pliocene sediment samples are surprising given that the sampled time intervals include significant pliocene aggradation and may include much incision of the grand canyon and its tributaries this conflict may arise from extensive storage of sediment along the route of the colorado river slower paleobedrock erosion or the inclusion of sediments that were derived preferentially from higher elevations in the watershed

neogene rejuvenation of central appalachian topography evidence for differential rock uplift from stream profiles and erosion rates abstract the persistence of topography within ancient orogens remains one of the outstanding questions in landscape evolution in the eastern north american appalachians this question is manifest in the outstanding problem of whether topographic relief is in a quasi equilibrium state decaying slowly over many millennia or whether relief has increased during the late cenozoic here we present quantitative geomorphic data from the nonglaciated portion of the susquehanna river drainage basin that provide insight into these end member models analysis of channel profiles draining upland catchments in the northern valley and ridge appalachian plateau blue ridge and piedmont provinces reveals that a large number of streams have well defined knickpoints clustered at 300 600 m elevation but not systematically associated with transitions from weak to resistant substrate cosmogenic 10 be inventories of modern stream sediment indicate that erosion rates are spatially variable ranging from 5 30 m myr above knickpoints to 50 100 m myr below knickpoints overall channel gradients normalized for drainage area scale linearly with catchment averaged erosion rates collectively regionally consistent spatial relationships among erosion rate channel steepness and knickpoints reveal an ongoing wave of transient channel adjustment to a change in relative base level reconstructions of relict channel profiles above knickpoints suggest that higher rates of incision are associated with 100 150 m of relative base level fall that accompanied epierogenic rock uplift rather than a change to a more erosive climate or drainage reorganization channel response timescales imply that the onset of relative base level change predates 3 5 ma and may have begun as early as 15 ma we suggest that adjustment of the channel network was likely driven by changes in mantle dynamics along the eastern seaboard of north america during the neogene

rock to sediment slope to sea with 10be rates of landscape change abstract measurements of cosmogenic nuclides predominately 10be allow new insights into the ways in which and the rates at which sediment is generated transported and deposited over timescales ranging from 103 to 106 years samples from rock exposures are used to estimate erosion rates at points on the landscape whereas samples of fluvial sediment provide estimates of basin scale rates of denudation integrated over 104 km2 nuclide data show that hilltop bare rock outcrops erode more slowly than basins as a whole suggesting the potential for relief to increase over time as well drained outcrops grow higher more elaborate experiments and interpretive models provide insight into the distribution of hillslope processes including the bedrock to soil conversion rate which appears to increase under shallow soil cover and then decrease under deeper soils changes in average nuclide activity down slopes can be used to estimate grain speed over millennia suggesting for example that sediment o

rates of erosion and topographic evolution of the sierra nevada california inferred from cosmogenic26al and10be concentrations concentrations of cosmogenic 26 al and 10 be in cave sediments and bedrock surfaces combined with studies of landscape morphology elucidate the topographic history of the southern sierra nevada over the past 5 ma caves dated by 26 al 10 be in buried sediments reveal that river incision rates were moderate to slow between c 5 and 3 ma 0 07 mm a 1 accelerated between 3 and 1 5 ma c 0 3 mm a 1 and then have subsequently become much slower c 0 02 mm a 1 although the onset of accelerated incision coincides in time with both postulated pliocene tectonism and pronounced global climate change we argue that it primarily represents the response to a discrete tectonic event between 3 and 5 ma dated cave positions reveal that prior to 3 ma river canyons displayed up to 1 6 km of local relief suggesting that pliocene rock uplift elevated pre existing topography renewed incision beginning c 3 ma deepened canyons by up to 400 m creating narrow inner gorges tributary streams exhibit strong convexities indicating that the transient erosional response to pliocene uplift has not yet propagated into upland surfaces concentrations of 26 al and 10 be in bare bedrock show that upland surfaces are eroding at slow rates of c 0 01 mm a 1 over the past c 3 ma upland surfaces eroded slowly while adjacent rivers incised rapidly increasing local relief although relief production probably drove at least modest crestal uplift considerable prepliocene relief and low spatially averaged erosion rates suggest that climatically driven rock uplift is not sufficient to explain all uplift implied by tilted markers at the western edge of the range despite the recent pulse of erosion spatially averaged erosion rates are low and have probably acted to preserve the broad topographic form of the sierra nevada throughout much of the late cenozoic copyright 2005 john wiley sons ltd

steady erosion rates in the himalayas through late cenozoic climatic changes sediment accumulation rates and thermal trackers suggest a substantial and global increase in erosion rates over the past few million years that increase is commonly associated with the impact of the northern hemisphere glaciation but methodological biases have led researchers to debate this hypothesis here we test whether himalayan erosion rates increased by measuring beryllium 10 10be in the sediment of the bengal bay seabed sediment originated from rocks that produced 10be under the impact of cosmic rays during erosion near surface thus the 10be concentrations indicate erosion rates the 10be concentration of the bengal bay sediment depends on the contributions of the ganga and brahmaputra rivers their sediments have distinct 10be concentrations because of distinct elevations and erosion in their drainage basins variable contributions could thus complicate erosion rate calculation we traced these contributions by a provenance study using the strontium sr and neodymium nd isotopic sediment compositions within uncertainties of 30 our reconstructed past erosion rates show no long term increase for the past six million years this stability suggests that climatic changes during the late cenozoic have an undetectable impact on the erosion patterns in the himalayas at least on the ten thousand to million year timescales accounted for by our dataset long term himalayan erosion rates remained stable through the global climatic changes of the past six million years according to the cosmogenic nuclide composition of terrestrial sediments recovered from the bay of bengal

10be analysis of a quaternary weathering profile in the virginia piedmont samples from a residual weathering profile in the virginia piedmont have been analyzed for cosmogenic 10be concentrations are highest in clay rich soil and decrease exponentially to a depth of about 15 m despite uncertainties about the processes by which 10be may be intercepted before entering the solum and eroded after incorporation a minimum age may be calculated for the regolith this calculation is based on the delivery rate of 10be and its decay rate and suggests that this residual profile developed during a period no shorter than 8 105 yr the calculated minimum age may be within a factor of 2 of maximum age estimates based on surface lowering by erosion and on the rate of rock weathering to saprolite the vertical distribution of 10be in the profile could result from a steady state balance of deposition weathering radioactive decay and erosion

palynological evidence for late miocene pliocene and early pleistocene climate changes in the middle u s atlantic coastal plain abstract palynomorph assemblages from eight geologic formations in the middle atlantic coastal plain ranging in age from latest miocene to early pleistocene have been interpreted in terms of terrestrial paleoclimates the data suggest that a warm temperate to subtropical climate warmer than at present prevailed at the close of the miocene and the beginning of the pliocene at that time there was little or no temperature gradient within the study area 36 30 to 39 n this warm period was followed by a warm temperate interval in virginia and north carolina with temperatures probably not very different from those of today although a slight warming trend probably occurred during the deposition of the colerain beach member of the chowan river formation a definite cool interval is indicated by the presence of spruce pollen in the bacons castle formation of virginia this interval is interpreted to have begun about 2 3 2 4 ma or possibly slightly later simultaneous with the cooling that has been recorded in deep sea cores of the north atlantic ocean and in the pre tiglian of western europe this was followed by a warmer than present period that may be correlated with the tiglian of the latest pliocene finally palynological data from the cape may formation of new jersey suggest that a warm temperate warmer than at present climate prevailed during the early pleistocene

climate driven unsteady denudation and sediment flux in a high relief unglaciated catchment fan using 26al and 10be panamint valley california abstract environmental changes within erosional catchments of sediment routing systems are predicted to modulate sediment transfer dynamics however empirical and numerical models that predict such phenomena are difficult to test in natural systems over multi millennial timescales tectonic boundary conditions and climate history in the panamint range california are relatively well constrained by existing low temperature thermochronology and regional multi proxy paleoclimate studies respectively catchment fan systems present there minimize sediment storage and recycling offering an excellent natural laboratory to test models of climate sedimentary dynamics we used stratigraphic characterization and cosmogenic radionuclides crns 26al and 10be in the pleasant canyon complex pcc a linked catchment fan system to examine the effects of pleistocene high magnitude high frequency climate change on crn derived denudation rates and sediment flux in a high relief unglaciated catchment fan system calculated 26al 10be burial ages from 13 samples collected in an 180 m thick outcropping stratigraphic succession range from ca 1 55 0 22 ma in basal strata to ca 0 36 0 18 0 52 0 20 ma within the uppermost part of the succession the mean long term crn derived paleodenudation rate 36 8 mm kyr 1 is higher than the modern rate of 24 0 6 mm kyr from pleasant canyon and paleodenudation rates during the middle pleistocene display some high frequency variability in the high end up to 54 10 mm kyr the highest crn derived denudation rates are associated with stratigraphic evidence for increased precipitation during glacial pluvial events after the middle pleistocene transition post ca 0 75 ma suggesting 100 kyr milankovitch periodicity could drive the observed variability we investigated the potential for non equilibrium sedimentary processes i e increased landslides or sediment storage recycling to influence apparent paleodenudation rates end member mixing models suggest that a mixture of 50 low crn concentration sediment from landslides is required to produce the largest observed increase in paleodenudation rate the overall pattern of crn derived burial ages paleodenudation rates and stratigraphic facies suggests milankovitch timescale climate transitions drive variability in catchment denudation rates and sediment flux or alternatively that climate transitions affect sedimentary process regimes that result in measurable variability of crn concentrations in unglaciated catchment fan systems

the use of in situ produced cosmogenic radionuclides in glaciology and glacial geomorphology the usefulness of in situ produced cosmogenic radionuclides in constraining glacial chronologies through exposure age dating has been demonstrated in numerous studies however an understanding of cosmogenic radionuclide techniques and their uncertainties opens up a wide range of other potential applications in glaciology and glacial geomorphology recently developed applications include estimation of spatial and temporal variations in the depth of glacial erosion from cosmogenic radionuclide inheritance which provides important constraints on process based erosion models and burial dating which can provide chronological control for glacial advances and the onset of till deposition an interesting new application currently at the level of theoretical model development concerns the unraveling of complex exposure and burial histories overall in situ produced cosmogenic radionuclide techniques provide a means with which to constrain a wide range of ice sheet and glacial models over time scales of a thousand to a few million years

insights into wasatch fault vertical slip rates using the age of sediments in timpanogos cave utah abstract timpanogos cave located near the wasatch fault is about 357 m above the american fork river fluvial cave sediments and an interbedded carbonate flowstone yield a paleomagnetic and u th depositional age of 350 to 780 ka fault vertical slip rates inferred from calculated river downcutting rates range between 1 02 and 0 46 mm yr 1 these slip rates are in the range of the 0 12 ma wasatch range exhumation rate 0 5 0 7 mm yr 1 suggesting that the long term vertical slip rate remained stable through mid pleistocene time however the late pleistocene 0 250 ka decelerated slip rate 0 2 0 3 mm yr 1 and the accelerated holocene slip rate 1 2 mm yr 1 are consistent with episodic fault activity assuming that the late pleistocene vertical slip rate represents an episodic slowing of fault movement and the long term 0 12 ma average vertical slip rate including the late pleistocene and holocene should be 0 6 mm yr 1 there is a net late pleistocene vertical slip deficit of 50 75 m the holocene and late pleistocene slip rates may be typical for episodes of accelerated and slowed fault movement respectively the calculated late pleistocene slip deficit may mean that the current accelerated wasatch fault slip rate will extend well into the future

rates and patterns of late cenozoic denudation in the northernmost atlantic coastal plain and piedmont topography of a 2800 km 2 section of the u s atlantic coastal plain and piedmont is reconstructed at five times from the late miocene to the holocene the reconstructions are based on mapping of fluvial colluvial and marginal marine deposits that are dated by radiocarbon palynostratigraphy and correlation to adjacent glacial and marine units denudation rates and patterns are calculated by subtracting successive topographies with 60 m horizontal resolution and 6 m vertical resolution the overall late miocene to holocene denudation rate of 10 m m y is similar to other estimates of long term denudation in the region the overall rate resolves spatially into a wide range of local rates varying from a minimum of 0 2 m m y on residual uplands to as high as 600 m m y in glacially rerouted stream channels the distribution of local rates shows that denudation is accomplished by stream incision in response to long term glacio eustatic decline followed by slope retreat into residual uplands from the incised channels slope retreat replaces the uplands with pediments and straths pediment landforms and sediments and observation of modern scarps and valley heads indicate that groundwater seepage from the base of residual uplands is an important mechanism of slope retreat this process is self limiting because as the volume of residual upland is reduced seepage diminishes and slope retreat slows until small residuals undergo little or no further reduction thus relict topography is preserved even as most of the landscape actively erodes

a signature of transience in bedrock river incision rates over timescales of 10 4 10 7 years measured rates of river incision into bedrock are commonly interpreted as proxies for rates of rock uplift see refs 1 and 2 for example and indices of the strength of climatic forcing of erosion over time see refs 3 and 4 for example this approach implicitly assumes that river incision rates are in equilibrium with external forcings over a wide range of timescales here we directly test this assumption by examining the temporal scaling of bedrock river incision from 155 independent measurements of river incision compiled from 14 sites of these sites 11 exhibit a negative power law dependence of bedrock river incision rate on measurement interval a relationship that is apparent over timescales of 10 4 10 7 years and is independent of tectonic and geomorphic setting thus like rates of sediment accumulation rates of river incision into bedrock exhibit non steady state behaviour even over very long measurement intervals non steady state behaviour can be explained by episodic hiatuses in river incision triggered by alluvial deposition if such hiatuses have a heavy tailed length distribution regardless of its cause the dependence of incision rate on measurement interval complicates efforts to infer tectonic or climatic forcing from changes in rates of river incision over time or from comparison of rates computed over different timescales

the initiation of northern hemisphere glaciation for well over a century scientists have speculated that variations in the atmospheric concentration of radiatively important trace gases such as carbon dioxide could control the earth s climate e g arrhenius 1 896 recent observations of significant glacial interglacial variation in atmo spheric co2 in ice cores put this idea on a firm observational as well as theoretical footing e g barnola et ai1 987 in this century as atmospheric co2 levels creep steadily upwards in response to the burning of fossil fuels and forests the specter of manmade global climate change looms before us ipcc 1990 a possibility that has heightened interest in the natural variability of climate in the past in particular the 3 c warming pre dicted for the next century has stimulated interest in past warm climates such as the middle pliocene around 3 0 million years ma ago an interval that has often been invoked as a greenhouse world budyko et al 1985 in this paper the climate transition from the warm mid pliocene around 3 2 ma to the onset of northern hemisphere ice ages around 2 4 ma is examined evidence for the initiation of significant northern hemisphere glaciation is examined as well as how this event affected climate around the globe while the cause of individual glacial interglacial oscillations is tied to milankovitch variations in the earth s orbit around the sun e g imbrie et ai 1 992 these insolation changes cannot account for the long term cooling trend which culminated in northern hemisphere glaciation in the final section of this paper mechanisms of long term climate change

beryllium 10 concentrations in the hyper arid soils in the atacama desert chile implications for arid soil formation rates and el nino driven changes in pliocene precipitation abstract meteoric 10be concentrations in soil were measured to understand the mechanism timescale and climatic dependence of soil formation in the hyper arid atacama desert the observed systematic decline of soil 10be concentrations with depth has been reproduced using a simple model that assumes soil matrix including 10be builds up as layers over time while 10be decays in situ this suggests a mechanism of soil accumulation via atmospheric deposition which is in agreement with stable isotopic evidence the model estimates an age of 6 6 0 4 ma for the total soil profile small discrepancies between the model and observations are likely mainly due to changes in precipitation rates that can impact 10be delivery rates and 10be movement within the profile interpreted in this way the 10be data suggest drying in the atacama after 4 7 ma and returning to an insignificant wet period at 1 ma which was possibly connected to el nino or la nina like climate change

a first attempt to date the original deckenschotter of penck and bruckner with cosmogenic nuclides abstract in the classical area of alpine quaternary stratigraphy bavaria germany a succession of four gravel spreads that are separated from each other by valley incision was recognized by penck and bruckner 1909 die alpen im eiszeitalter tauchnitz leipzig 1199p the two older gravel terraces attributed to glaciations named gunzian and mindelian have so far not been dated recent advances in the use of cosmogenic nuclides allow the burial age determination of sediments the method uses the different decay of the two nuclides 26al and 10be to date the time since a deposit was shielded from further radiation a depth profile makes it possible to model ages for surface sediments that are not shielded completely this paper discusses the various constraints that must be addressed in order to date surface sediments and it presents the ages obtained 2 35 ma for gunzian 0 68 ma for mindelian these dates are in good agreement with measurements of tectonic displacement and development of catchments the results confirm that the burial age determination method is basically feasible for such terraces

denudation rates determined from the accumulation of in situ produced 10be in the luquillo experimental forest puerto rico we present a simple method for estimation of long term mean denudation rates using in situ produced cosmogenic 10be in fluvial sediments procedures are discussed to account for the effects of soil bioturbation mass wasting and attenuation of cosmic rays by biomass and by local topography our analyses of 10be in quartz from bedrock outcrops soils mass wasting sites and riverine sediment from the icacos river basin in the luquillo experimental forest puerto rico are used to characterize denudation for major landform elements in that basin the 10be concentration of a discharge weighted average of size classes of river sediment corresponds to a long term average denudation of 43 m ma 1 consistent with mass balance results

mid pleistocene cosmogenic minimum age limits for pre wisconsinan glacial surfaces in southwestern minnesota and southern baffin island a multiple nuclide approach abstract paired 10 be and 26 al analyses n 14 indicate that pre wisconsinan glaciated bedrock surfaces near the northern baffin island and southern minnesota paleo margins of the laurentide ice sheet have long and complex histories of cosmic ray exposure including significant periods of partial or complete shielding from cosmic rays using the ratio 26 al 10 be we calculate that striated outcrops of sioux quartzite in southwestern minnesota southern margin were last overrun by ice at least 500 000 years ago weathered bedrock tors on the once glaciated uplands of baffin island northern margin are eroding no faster than 1 1 m myr 1 the equivalent of at least 450 000 years of surface and near surface exposure our data demonstrate that exposure ages and erosion rates calculated from single nuclides can underestimate surface stability dramatically because any intermittent burial and the resultant lowering of nuclide production rates and nuclide abundances will remain undetected

magnetostratigraphy of sediments in mammoth cave kentucky clastic sediment deposits found within the caves of mammoth cave national park have yielded a magnetostratigraphic pattern of magnetic polarity reversals which indicates that they were deposited over a range of at least 1 million and most likely 2 million years

spatially averaged long term erosion rates measured from in situ produced cosmogenic nuclides in alluvial sediment spatially averaged erosion rates of small catchments can be accurately inferred from the concentrations of cosmogenic nuclides in stream sediment here we test this technique at two catchments by comparing erosion rates inferred from cosmogenic nuclides with rates of alluvial fan deposition over the past 16 000 years these two independent estimates agree within one standard error demonstrating that cosmogenic nuclide signatures of stream sediment can be used to measure spatially averaged long term erosion rates using this technique we show that long term erosion rates are an exponential function of average hillslope gradient at these sites

the development of iron crust lateritic systems in burkina faso west africa examined with in situ produced cosmogenic nuclides we have investigated the development of iron crust laterites on the stable west african craton in northern burkina faso using cosmogenic radionuclides produced in situ in quartz veins and pebbles lateritic soils develop in tectonically stable slowly eroding tropical environments and are a major component of the earth s surface to examine processes affecting laterite formation we determined 10be and 26al in samples of quartz from three sites representing two sequential and connected iron crust laterite systems results from outcropping quartz veins suggest that the mean erosion rate in this region is about 3 8 m myr 1 in addition data from quartz cobbles and pebbles incorporated in iron crusts demonstrate that depth dependent distributions of these nuclides may be used to distinguish surfaces undergoing burial from those undergoing erosive loss results from sections of the lowland lateritic system are consistent with mean accumulation rates of a few metres per million years quartz cobbles presently at depths of a few metres in a paleochannel filled with rapidly deposited fluvial colluvial material have10be distributions that suggest that the lowland lateritic surface may have formed during an erosive episode presumably associated with a wetter climate roughly 300 kyr bp these results illustrate the practicality and the potential of the use of in situ produced cosmogenic nuclides for understanding the history of formation of laterites and for differentiating between systems formed through in situ chemical weathering and mechanical transport

holocene dune sourced alluvial fans in the nebraska sand hills abstract the large stabilized dunes of the nebraska sand hills are in a phase of degradation the deposition of small scale alluvial fans composed of well sorted fine to medium grained sand occurs when sand is transported via gullies on the lee side of large barchanoid ridge dunes during infrequent intense summer rain storms 5 cm h the hydraulic conductivity of the dune sand itself is too high to allow hortonian overland flow but organically bound mats and crusts on the surface of the dunes help to impede infiltration secondary eolian bed forms at the crests of the dunes focus shallow groundwater and overland flow that erodes gullies internally alluvial fans are dominated by laminated sands interpreted as sheetflood deposits depositional couplets of structureless bottom and laminated top sands may form from a combination of hyperconcentrated flow and sheetflood thickness of deposits varies with storm intensity and sediment supply in the gullies the alluvial fans are holocene in age and gully initiation may have begun at the onset of a wetter climate when vegetation was less dense than at present water laid sandstones associated with large scale eolian cross strata have been recognized in precambrian devonian and cretaceous sequences the alluvial fans from the sand hills may provide a new modern analogue for interpreting these ancient sandstones

geologic controls on bedrock channel width in large slowly eroding catchments case study of the new river in eastern north america abstract we have investigated the geologic controls on hydraulic geometry of bedrock rivers using a single large catchment the new river from a stable tectonic setting with variable resistant lithology but spatially stable climate our survey of channel width at 0 5 km spacing along 572 km of the river shows major variation that only roughly fits the expected scaling relationships between width drainage area and slope considerable variations in width including steps in trends and large spikes relate to physiogeologic boundaries that the river passes through a large fraction 15 of the river s length classifies as bedrock reach showing that it behaves more like a bedrock river than an alluvial river unlike established trends the channel is wider in bedrock than in alluvium field observations show that aspect ratio width to depth is not constant but fluctuates systematically with width from wide shallow reaches to narrower deeper reaches our observations of bedrock properties suggest that susceptibility to fluvial plucking versus abrasion may control this anomalous channel morphology one end member form with aspect ratio as high as 500 which we term the incision plain is associated with very closely spaced discontinuities 10 cm in otherwise hard rock we propose that the closely spaced discontinuities enable efficient plucking that leads to widening by lateral erosion this morphology locally occurs in other passive margin rivers and may be a fundamental fluvial form that is similar to but the inverse of slot canyons the other end member which we term channel neck is narrower and deeper with complex flow paths through blocky bedrock this form occurs where discontinuity spacing is longer 0 5 m and erosion is abrasion dominated these results imply that changes in channel width do not necessarily reflect variations in uplift rate but instead may result from complex response to bedrock properties

a statistical framework to quantify spatial variation in channel gradients using the integral method of channel profile analysis 1 we present a statistical technique for analyzing longitudinal channel profiles our technique is based on the integral approach to channel analysis drainage area is integrated over flow distance to produce a transformed coordinate which has dimensions of length assuming that profile geometry is conditioned by the stream power law defined as e kamsn where e is erosion rate k is erodibility a is drainage area s is channel gradient and m and n are constants the slope of a transformed profile in elevation space should reflect the ratio of erosion rate to channel erodibility raised to a power 1 n this quantity is often referred to as the channel steepness and represents channel slope normalized for drainage area our technique tests all possible contiguous segments in the channel network to identify the most likely locations where channel steepness changes and also identifies the most likely m n ratio the technique identifies locations where either erodibility or erosion rates are most likely to be changing tests on a simulated landscape demonstrate that the technique can accurately retrieve both the m n ratio and the correct number and location of segments eroding at different rates where model assumptions apply tests on natural landscapes illustrate how the method can distinguish between spurious channel convexities due to incorrect selection of the m n ratio from those which are candidates for changing erodibility or erosion rates we also show how given erosion or uplift rate constraints the method can be used to constrain the slope exponent n

biological energy in landscape evolution traditional conceptual models of landscape evolution view topography as an outcome of endogenic forces uplift working against exogenic forces of denudation the energy considerations of these concepts have focused on the conversion of the potential energy of landscape relief to kinetic energy the concept of the biosphere as a planetary membrane for capturing and converting solar energy coupled with the critical geomorphic role of biota call for a consideration of biotic contributions to geomorphic work a review of estimates of global rates of kinetic energy of denudation and uplift and net primary production npp indicates that the energy density of npp is on average three to seven orders of magnitude greater than the others if even a tiny fraction of npp is geologically significant then the biological subsidy to the energy of landscape evolution must be considered on a par with that of geophysical and geochemical phenomena a case study in eastern kentucky shows that even if only 0 1 percent of npp is geomorphically significant it still far exceeds the energy inputs from uplift and conversion of potential to kinetic energy by denudation this is unlikely to be unique though the relative importance of biological and geophysical processes must obviously vary with climate tectonic setting and other factors results indicate that particularly where biological activity is significant geomorphic work performed by biota may be greater than that associated with endogenic processes and with the kinetic energy of denudation

distinction between epigenic and hypogenic maze caves abstract certain caves formed by dissolution of bedrock have maze patterns composed of closed loops in which many intersecting fractures or pores have enlarged simultaneously their origin can be epigenic by shallow circulation of meteoric groundwater or hypogenic by rising groundwater or production of deep seated solutional aggressiveness epigenic mazes form by diffuse infiltration through a permeable insoluble caprock or by floodwater supplied by sinking streams most hypogenic caves involve deep sources of aggressiveness transverse hypogenic cave origin is a recently proposed concept in which groundwater of mainly meteoric origin rises across strata in the distal portions of large flow systems to form mazes in soluble rock sandwiched between permeable but insoluble strata the distinction between maze types is debated and is usually based on examination of diagnostic cave features and relation of caves to their regional setting in this paper the principles of mass transfer are applied to clarify the limits of each model to show how cave origin is related to groundwater discharge dissolution rate and time the results show that diffuse infiltration and floodwater can each form maze caves at geologically feasible rates typically within 500 ka transverse hypogenic mazes in limestone to enlarge significantly within 1 ma require an unusually high permeability of the non carbonate beds generally 10 4 cm s large discharge and calcite saturation no greater than 90 which is rare in deep diffuse flow in sedimentary rocks deep sources of aggressiveness are usually required the origin of caves by transverse hypogenic flow is much more favorable in evaporite rocks than in carbonate rocks

numerical ages for plio pleistocene glacial sediment sequences by 26al 10be dating of quartz in buried paleosols abstract we describe a method for dating plio pleistocene sediments by analysing 26 al and 10 be in quartz from buried paleosols the method amounts to a generalization of the technique of burial dating which has previously been used to date river sands deposited in caves as well as fluvial terraces we a measure nuclide concentrations at multiple depths in the paleosol b use the geologic context of the sample to construct an exposure burial history an exposure model that can be used to predict the nuclide concentrations in the samples as a function of whatever unknown parameters are of geological interest e g the ages of geologic units and then c find the parameters in the exposure model that result in the best fit between predicted and observed nuclide concentrations we apply the method to a paleosol developed on the uppermost till in eastern nebraska which is buried by several middle to late pleistocene loess units the ages of some of which are known independently the lowest loess unit whose age was not previously known was deposited 0 58 0 12 ma and the till was emplaced 0 65 0 14 ma which agrees with existing age constraints from paleomagnetic measurements and the position of the lava creek ash in the regional stratigraphy the most important source of uncertainty in these age determinations is the analytical uncertainty in 26 al and 10 be measurements uncertainties in either the nuclide production rates or the geologic model are comparatively unimportant

pliocene pleistocene incision of the green river kentucky determined from radioactive decay of cosmogenic 26al and 10be in mammoth cave sediments cosmogenic 26al and 10be in sediments washed into mammoth cave kentucky record the history of 3 5 m y of water table position governed by incision and aggradation of the green river a tributary of the ohio river upper levels of the cave formed during a period of slow river incision and were later filled with sediment due to river aggradation at 2 3 2 4 ma a brief surge of river incision ca 2 ma was followed by river stability and cave passage formation at a lower level rapid incision through 15 m of bedrock ca 1 5 ma was prompted by repositioning of the ohio river to its present course along an ice sheet margin renewed incision ca 1 2 ma and aggradation at 0 7 0 8 ma correlate with major ice advances in the ohio river basin measurements of 26al and 10be also indicate that sandstone capped uplands have maintained slow erosion rates of 2 7 m m y for the past 3 5 m y despite accelerated pleistocene river incision rates of 30 m m y

paleoflood events recorded by speleothems in caves speleothems are usually composed of thin layers of calcite or aragonite however cemented detrital materials interlayered between laminae of speleothemic carbonate have been also observed in many caves flowstones comprising discontinuous carbonate layers form due to flowing water films while flood events introduce fluviokarstic sediments in caves that on occasion are recorded as clayey layers inside flowstones and stalagmites this record provides a potential means of understanding the frequency of palaeofloods using cave records in this work we investigate the origin of this type of detrital deposit in el soplao cave northern spain the age of the lowest aragonite layer of a flowstone reveals that the earliest flood period occurred before 500 ka though most of the flowstone formed between 422 69 43 ka and 400 66 42 ka this suggests that the cave was periodically affected by palaeoflood events that introduced detrital sediments from the surface as a result of occasional extreme rainfall events especially at around 400 ka the mineralogical data enable an evolutionary model for this flowstone to be generated based on the alternation of flood events with laminar flows and carbonate layers precipitation that can be extrapolated to other caves in which detrital sediments inside speleothems have been found copyright 2014 john wiley sons ltd

the source of gypsum in mammoth cave kentucky mammoth cave kentucky usa is the world9s longest human navigable cave system gypsum caso 4 2h 2 o crystals line many dry passages of the limestone cave and the source of sulfur for the gypsum remains uncertain previous workers have suggested sulfate from pyrite oxidation mississippian aged sulfate evaporites and pleistocene soil sulfate as possible sulfur sources we use sulfur isotopes 34 s to constrain the gypsum sulfur source by comparing the 34 s values of different possible sources to that of gypsum throughout the cave 34 s gypsum values n 106 from 12 different locations within the mammoth cave system are along a continuum of 34 s values from 12 0 to 12 8 with little variability along the crystal growth axis or between samples within the same cave chamber neither sulfur from coeval sedimentary evaporites i e gypsum anhydrite nor from formations overlying the cave is required to explain the 34 s gypsum data rather the range of pyrite 34 s in strata immediately surrounding the cave is sufficient to generate the spectrum of observed 34 s gypsum modern water 34 s so 4 values are similar to the host formation 34 s pyrite suggesting that oxidized pyrite from the host formation continues to be a major sulfur source to this day together these observations strongly suggest a significant local source of sulfur for mammoth cave gypsum the majority 66 100 of which is derived from the oxidation of pyrite in strata adjacent to the cave