calibrating the end permian mass extinction the end permian mass extinction was the most severe biodiversity crisis in earth history to better constrain the timing and ultimately the causes of this event we collected a suite of geochronologic isotopic and biostratigraphic data on several well preserved sedimentary sections in south china high precision u pb dating reveals that the extinction peak occurred just before 252 28 0 08 million years ago after a decline of 2 per mil in 13c over 90 000 years and coincided with a 13c excursion of 5 that is estimated to have lasted 20 000 years the extinction interval was less than 200 000 years and synchronous in marine and terrestrial realms associated charcoal rich and soot bearing layers indicate widespread wildfires on land a massive release of thermogenic carbon dioxide and or methane may have caused the catastrophic extinction

the terrestrial permian triassic boundary event bed is a nonevent comment we welcome the fact that gastaldo et al 2009 1 have been continuing research in the karoo of south africa those of us who have worked there know how important new research in this area is if we are to ever understand the causes of the permian triassic mass extinction on land however here

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

changing fluvial environments across the permian triassic boundary in the karoo basin south africa and possible causes of tetrapod extinctions abstract the karoo supergroup is a 12 km thick succession of sedimentary rocks that accumulated in a large intracratonic retroarc foreland basin in southwestern gondwana the strata record 100 million years of almost continuous sediment accumulation from the permo carboniferous 300 ma through to the early jurassic 190 ma under a range of climatic regimes and within several tectonically controlled sub basins alluvial sediments dominate the succession from the late permian onwards fossils of synapsid reptiles and early dinosaurs are sufficiently common to be used in a ten fold biostratigraphic subdivision of these strata the permian triassic boundary in the karoo succession is marked by a major extinction of the herbivorous dicynodonts which co incides with a rapid change in fluvial facies this study uses field observations of the sedimentary facies palaeosols and in situ fossils of well exposed p tr boundary sequences in the southern karoo basin to provide evidence of environmental changes that may have caused the tetrapod extinctions in the main karoo basin below the p tr boundary sequence the sediments comprise drab greenish grey mudrocks with a few thick 3 12 m multistoried laterally accreted fine grained sandstone bodies the mudrocks host hydromorphic palaeosols with palustrine carbonate horizons and mostly disarticulated skeletal remains of dicynodon assemblage zone fauna above a transition zone of approximately 20 m thickness these strata change into reddish brown mudrocks with numerous thin 0 5 5 m ribbon sandstone bodies and more continuous sheet sandstones calcic palaeosols with rhizocretions nodular horizons and pervasive calcareous encrustation of articulated skeletons of lystrosaurus and associated fauna of the lystrosaurus assemblage zone within a 20 m thick interval of the transitional strata fossils of dicynodon and lystrosaurus occur together the facies transition that co incides with the latest permian dicynodont extinction is interpreted as a change in fluvial style from meandering to low sinuosity channels with general drying of the floodplain habitats and redistribution of vegetation belts the horsetails in particular became significantly reduced in areal distribution the changes in fluvial style in the karoo basin at the end of the permian were triggered by a pulse of thrusting in the southerly source area dated at 247 ma 2 ma which brought about rapid progradation of a large sandy braided fan system the katberg sandstone fm into the central parts of the basin a concomitant basinward migration of depositional environments allowed the lystrosaurus communities that were adapted to dry floodplains to colonise the entire basin to the detriment of most of the wet floodplain dicynodon fauna that lived there

fungal abundance spike and the permian triassic boundary in the karoo supergroup south africa the most severe mass extinction of marine species and terrestrial vertebrates and plants is associated with the permian triassic boundary 251 ma the extinction interval is also marked by the disappearance of most late permian gymnosperm palynomorphs at a layer containing solely the abundant remains of fungi this fungal spike apparently represents widespread devastation of arboreous vegetation stratigraphic and palynological study of the carlton heights section in the southern karoo basin of south africa revealed a 1 m thick fungal spike zone that occurs simultaneously with the last appearance of typically late permian gymnosperm pollen the plant extinction and fungal spike zone are found above the last occurrence of late permian mammal like reptiles of the dicynodont zone at other karoo sections using the fungal event as a time line in marine and non marine sections allows placement of the marine extinctions and the extinction of terrestrial plants and reptiles within a brief crisis interval of less than about 40 000 years at the end of the permian

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

an autochthonous glossopterid flora with latest permian palynomorphs and its depositional setting in the dicynodon assemblage zone of the southern karoo basin south africa article i nfo the discovery of a plant fossil assemblage situated 70 m below the vertebrate defined permian triassic boundary allows for the characterization of part of the late permian landscape in the southern karoo basin the megafloral and microfloral assemblages are preserved in association with an o horizon above a weakly developed palaeosol exposed in both new and old wapadsberg pass eastern cape province south africa stable isotope geochemical evidence indicates that pedogenesis occurred under conditions of a high regional water table and the palaeosol was entombed by overbank or avulsion deposits in an aggradational landscape that includes tuffite the low diversity macroflora contains gymnospermous glossopteris and sphenopsid phyllotheca trizygia elements that include vegetative axial leaf and reproductive strobilar remains glossopteris leaves are microphyllous and may reflect the taxon s physiological response to purported climate perturbation or wetland edaphic conditions and exhibit a range of plant animal interactions palynological residues contain sphenophyllalean cuticles and the microfloral assemblage is consistent with a low diversity glossoperid dominated woodland with a sphenopsid understory extrabasinal elements include representa tives of peltasperms alisporites corystosperms falcisporites and conifers lueckisporites pollen conforming to lunatisporites pellucidus is present in the assemblage and is considered an indicator taxon for the latest permian to early triassic when compared to palynological assemblage zones in australia the wapadsberg pass flora is assigned a late changhsingian age and therefore represents the youngest autochthonous glossopteris dominated flora to be reported from gondwana these results extend a palynostratigraphic framework across the southern hemisphere that complements other zonations presently applied to the karoo basin succession

simple method for calculating reach averaged bed load transport abstracta simple and robust method is proposed for calculating reach averaged bed load transport in sand and gravel bed rivers with no calibration the data required are the bed surface d50 and d84 measured with the nontruncated pebble count technique the slope the width and the flow depth or discharge the method is illustrated by comparison with bed load samples measured in 15 river reaches

summit erosion rates deduced from 10be implications for relief production in the central appalachians we have measured erosion rates using 10 be from bare bedrock surfaces exposed at high elevations at dolly sods west virginia a classic appalachian paleoperiglacial plateau the mean erosion rate from nine samples is 5 7 m m y signifi cantly lower than previously estimated periglacial erosion rates in this region measured bare bedrock erosion rates likely represent the rate at which the highest portions of this broad upland are being lowered fluvial incision rates measured in the region over similar time scales are 2 times faster suggesting relief is increasing in this portion of the appalachians this observation of increasing relief is inconsistent with prior work suggesting that the central appalachian landscape is in dynamic equilibrium or currently decreasing in relief we hypothesize that late cenozoic climate change has accelerated fl uvial incision rates creating a disequilibrium landscape with growing relief with hillslopes undergoing adjustment to increased fl uvial incision rates

new physical evidence of the role of stream capture in active retreat of the blue ridge escarpment southern appalachians abstract the blue ridge escarpment of the southern appalachian mountains is a striking and rugged topographic feature of the ancient passive margin of eastern north america the crest of the escarpment generally coincides with an asymmetric regional drainage divide separating steep streams of the escarpment face from low gradient streams of the blue ridge upland recent exhumation and erosion rate studies suggest that the escarpment has evolved by inland erosional retreat but the mechanism timing and magnitude of retreat remain poorly understood longitudinal stream profiles and slope drainage area relationships of several upland basins draining the divide have led to the identification of 14 previously unknown fluvial terrace deposits preserved at the escarpment crest these relict terraces and the associated beheaded drainages indicate the role of large stream capture events in producing ongoing escarpment retreat through landward divide migration and subsequent topographic adjustment terrace location and preservation suggest that rectilinear drainage patterns and divide asymmetry generate discrete high order captures and episodes of rapid localized retreat that collectively produce slower evolution of the escarpment at large while overall retreat magnitude and rate remain unknown roundness of terrace alluvium suggests that the most recent captures have locally produced tens of kilometers of retreat within the limited preservation lifetime of the deposits in contrast with recent numerical modeling and cosmogenic studies these data show the potential for stream capture and divide migration to sustain passive margin escarpment evolution long after the cessation of rifting the fluvial record of divide retreat preserved atop the blue ridge escarpment suggests the potential for using field methods to better constrain the histories of younger taller and potentially more dynamic passive margin escarpments

a playa deposit of pre yellow sands age upper rotliegend weissliegend in the permian of northeast england abstract a complexly interbedded thin succession of sandstone siltstone and mudstone beneath the permian yellow sands formation upper rotliegend weissliegend was cored in a borehole 11 km off the coast of northeast england the cored strata rest unconformably on fissured westphalian b mudstone and mainly comprise low dipping fine to coarse grained grey sandstone with unevenly spaced thinner dark red to grey mudstone beds and laminae most of the sandstone beds are moderately to poorly sorted fine to very fine grained subarkoses with some sublitharenites and are weakly to strongly cemented by dolomite predominant kaolinite and illite sedimentary structures include subhorizontal plane to wavy lamination ripple lamination salt ridges and soft sediment deformation the siltstones and mudstones are more uniform in lithology and primary thickness they contain sandstone filled desiccation cracks mudstone saucers and narrow sandstone dykes traces of possible former evaporite minerals are concentrated in the sandstones by comparison with modem desert depositional environments these strata are interpreted as the deposits of a playa occupying a depression on a stony deflationary desert surface on a rock pediment or peneplain flanking the ancestral pennines the floor of the depression which probably lay in the capillary fringe just above the contemporary water table was periodically flooded so as to form a shallow playa lake comparable successions beneath the yellow sands have not been recorded from surface exposures in northeast england but mudstone beds at this stratigraphical level have been recorded in four other cored offshore boreholes and are presumed to be of similar origin to those described in this study the stratigraphical position of these deposits suggests that they may be of pre yellow sands age and coeval with or younger than the basal permian breccia palynological analysis of mudstone samples from the core reveal the presence of plant material and indeterminate pyrite invested possibly indigenous bisaccate pollen indicative of a vegetated hinterland with deposition occurring within a reducing possibly sulphide rich environment

the terrestrial permian triassic boundary event bed is a nonevent a unique isochronous interval in the karoo basin south africa previously has been interpreted to postdate vertebrate extinction at the permian triassic boundary in the bethulie area lootsberg pass and elsewhere it is demonstrated that the laminated beds or laminites in the bethulie region are stratigraphically indistinct the heterolithic interval exposed on the heldenmoed farm is 8 m below the bethel farm section

new geochemical and palaeontological data from the permian triassic boundary in the south african karoo basin test the synchronicity of terrestrial and marine extinctions abstract the end permian mass extinction epme is widely recognised as the largest mass extinction in phanerozoic history in marine strata the main extinction event is well constrained and has been radiometrically dated to an interval of some 60 kyr approximately 251 9 million years ago however the age and duration of the epme in the terrestrial realm as well as its possible synchronicity with that of the marine realm is debated here we shed light on issues pertaining to the identification and position of the terrestrial epme in southern africa using recently collected sedimentological facies sequences palaeontological biostratigraphic ranges geochemical stable isotope analyses and detrital zircon id tims data from a new site in the xhariep district of the south african karoo basin we demonstrate that the permian triassic boundary sequence containing evidence for phased tetrapod extinctions is time equivalent with the marine extinction we conclude that the terrestrial epme recorded in the karoo may be regarded as essentially synchronous with the epme currently defined in the marine realm and was likely the result of the same volcanically induced atmospheric disturbances this study describes the first single vertical succession of vertebrate and plant fossils that span the terrestrial permian triassic boundary that are also well constrained both by relative stable isotopes and absolute detrital zircon geochronology dating methods

the stratigraphic and geochemical record of playa cycles monitoring a pangaean monsoon like system triassic middle keuper s germany abstract the combination of high resolution stratigraphy with high resolution geochemistry allowed monitoring the cyclicity of a playa system in two dimensions time and space the playa cycles of the middle upper triassic steinmergel keuper located in southern germany were studied both in terms of lateral facies shift variations and long term cyclic patterns the lateral variation was expressed by investigating a time equivalent transect that spanned the kieselsandstein horizon within a 130 km distance from marginal to mid playa position whereas the long term cyclic pattern was investigated in core malschenberg where a time record of ca 5 106 years was encountered mudstone dolomite cycles with dolomites representing the wet and mudstones the dry phases reflect cyclic playa lake level changes indicating varying intensities of monsoon like circulation moisture transport from the tethys ocean into the german basin is implied by 18o depletion trends of isochronous dolomite beds from the margin to mid playa position suggesting dominantly rayleigh like circulation patterns distinct covariance of 18o 13c is used as indicator of lake level stands the k al curve with inverse covariation compared to 18o reflects fluctuating weathering conditions on the fan and the vindelician high a hierarchic cycle stacking pattern composed of metre scale to tens of metre cycles is interpreted to be a result of changing pangaean monsoon like intensities in the milankovitch frequency band spectral analysis shows that the power spectra are dominated by precession and eccentricity

pattern of vertebrate extinctions across an event bed at the permian triassic boundary in the karoo basin of south africa the extinction of vertebrates around the time of the permian triassic boundary has long been regarded as a gradual event occurring over millions of years our new field investigations of fluvial strata in the central and southern karoo basin of south africa have revealed the presence of an event bed coinciding with a mass extinction of terrestrial fauna and flora the bed is in a sedimentary sequence that is marked by a reddening of flood plain mud rocks and a change from high to low sinuosity river channel systems here we show that the pattern of vertebrate taxa disappearing below this boundary and the subsequent appearance of new taxa above the boundary are consistent with a relatively sudden possibly catastrophic event perhaps of 50 000 yr duration or less

denudation and retreat of the serra do mar escarpment in southern brazil derived from in situ produced 10be concentration in river sediment the serra do mar escarpment located along the southeastern coast of brazil is a high elevation passive margin escarpment this escarpment evolved from the denudation of granites migmatites and gneisses the granites outcrop in the form of a ridge along the escarpment crest due to its differential erosion sugarloaf hills from the surrounding lithologies several studies suggest that the passive margin escarpments are actively retreating toward the interior of the continent however no prior study has calculated the long term denudation rates of serra do mar to test this hypothesis in this study we measured the in situ produced 10be concentration in fluvial sediments to quantify the catchment wide long term denudation rates of the serra do mar escarpment in southern brazil we sampled the fluvial sediments from ten watersheds that drain both sides of the escarpment the average long term denudation rate of the oceanic side is between 2 1 and 2 6 fold higher than the rate of the continental side 26 04 1 88 mm ka 1 integrating over between 15 8 ka 1 and 46 6 ka 1 and 11 10 0 37 mm ka 1 integrating over between 52 9 ka 1 and 85 4 ka 1 respectively these rates indicate that the coastal base level is controlling the escarpment retreat toward the continental high lands which is consistent with observations made at other high elevation passive margins around the globe the results also demonstrate the differential erosion along the serra do mar escarpment in southern brazil during the quaternary where drainages over granites had lower average denudation rates in comparison with those over migmatites and gneisses moreover the results demonstrate that the ocean facing catchments have been eroded more intensely than those facing the continent the results also reveal that drainage over the granites decreases the average denudation rates of the ocean facing catchments and the sugarloaf hills therefore are natural barriers that slowly retreat once they are exhumed copyright 2013 john wiley sons ltd

climate variations and the appalachians from the late paleozoic to the present results from model simulations abstract a series of climate model simulations are utilized to examine the climate evolution of the appalachians from the carboniferous to the present through consideration of large scale changes in paleogeography and potential variations in carbon dioxide on long time scales the model simulations predict considerable variations in temperature and precipitation through time in addition a number of shorter time scale phenomena may influence the climatic record of the appalachians in particular milankovitch orbital variations can produce rhythmic climate and weathering particular geographic configurations since the carboniferous tend to promote sensitivity to orbital variations although far from comprehensive the model simulations provide independent predictions of climate which can be utilized to investigate the evolution of the appalachians deductively

a geophysical study of the earth s crust in central virginia implications for appalachian crustal structure a regional seismic reflection line i 64 across the virginia piedmont has provided a stacked section suitable for an integrated interpretation of geophysical data in the region a highly reflective upper crust an allochthonous blue ridge province underlying thrust sheets including the blue ridge master decollement and a basal decollement at a depth of about 9 km 3 s are confirmed on the seismic data immediately east of the blue ridge province appalachian structures plunge to as much as 12 km 4 s depth the evington group hardware terrane and chopawamsic metavolcanic rocks carolina terrane crop out in the piedmont province and numerous eastward dipping reflections originate from these rocks in the subsurface these eastward dipping reflectors overlie a gently west dipping 10 15 highly reflective zone that varies in depth from 1 5 s 4 5 km beneath the goochland terrane to 4 s 12 km beneath the rocks of the evington group some of the overlying eastward dipping reflections apparently root in this zone the zone may include decollement surfaces along which the overlying rocks were transported relatively few reflections originate from within autochthonous grenville basement at the western end of the profile the goochland granulite terrane is interpreted to be a westward thrust nappe structure that has overridden a portion of the chopawamsic metavolcanic rocks a broad zone of east dipping 20 45 reflections bounds the goochland terrane on the east these reflections may originate from deformation zones and continue to moho depths they appear to be correlative with similar events seen on other appalachian lines the pervasiveness of the zone of east dipping events on other seismic reflection lines and the continuity of the adjacent piedmont gravity high suggest continuity of crustal features along the length of the appalachians a major conclusion of this study is that crustal thinning is responsible for the main components of the gravity field in virginia that is the appalachian gravity gradient and the piedmont gravity high the crust thins from about 52 km beneath the appalachian mountains to about 35 km beneath richmond virginia and then rethickens by up to 10 km beneath the zone of east dipping reflections mylonites east of richmond the i 64 seismic data also contain a sequence of reflections at about 9 12 s indicative of lower crustal layering the base of this zone of reflections coincides almost exactly with the mohorovicic discontinuity interpreted from earlier refraction work the layering extends about 70 km west from richmond virginia and is interpreted as a lower crustal transition zone that is believed to persist across most of virginia

tracing hillslope sediment production and transport with in situ and meteoric 10be 1 we use in situ produced and meteoric 10be analyzed in soils from 28 pits on four hillcrest parallel transects along a 14 hillslope in the great smoky mountains north carolina as tracers of soil production and transport we rely upon amalgamation both to investigate and smooth spatial variability in 10be concentrations lidar indicates that the hillslope is topographically complex and that soil is moved downslope diffusively until it encounters the ephemeral channel network and is rapidly exported in situ produced 10be measured in depth profiles indicates that over millennial timescales soils are mixed above the soil saprolite boundary in contrast meteoric 10be concentrations increase with depth and are correlated to concurrent increases of dithionite extractable al and ph observations explained by similar al and be mobility in the soil the concentrations of both meteoric and in situ produced 10be increase downslope proportional to the maximum soil particle path length the data suggest virtual downslope soil velocities of 1 1 1 7 cm yr 1 in a well mixed active transport layer 60 cm thick the thickness of this transport layer is constant downslope and depends on the rooting depth and consequent root wad thickness of downed trees on the slope both of which reflect depth to the soil saprolite boundary both meteoric and in situ produced 10be suggest that soil production is balanced by surface denudation at rates between 10 and 13 m myr 1 soil residence times on the slope range from 21 to 33 kyr based on the meteoric 10be inventories major element geochemical analysis suggests little if any elemental loss during soil transport downslope

impacts of global warming on permo triassic terrestrial ecosystems geologists and palaeontologists have expressed mixed views about the effects of the end permian mass extinction on continental habitats and on terrestrial life current work suggests that the effects on land were substantial with massive erosion following the stripping of vegetation associated with long term aridification and short term bursts of warming and acid rain wildfires at the permo triassic boundary contributed to the removal of forests and the prolonged absence of forests from the earth s surface for up to 10 myr these physical crises on land impinged on the oceans suggesting tight interlocking of terrestrial and marine crises levels of extinction on land may well have been as high as in the sea and this is certainly the case for tetrapods the mass extinction seems to have been less profound for plants and insects but it is hard at present to disentangle issues of data quality from reductions in abundance and diversity several killing agents have been proposed and of these tetrapods may have succumbed primarily to acid rain mass wasting and aridification plants may have been more affected by the sudden effects of heating and wildfires and the crisis for insects has yet to be explored

implications of the shear stress river incision model for the timescale of postorogenic decay of topography 1 the reason for the survival of mountainous topography in ancient orogenic belts is a long standing problem in geomorphology and geodynamics we explore the geomorphologic controls on the timescale for the postorogenic decay of topography to address the question of whether there is a viable geomorphologic explanation for the persistence of topography in ancient orogenic belts or whether alternative geodynamic explanations must be sought using both approximate analytical solutions and numerical simulations we show that the standard detachment limited stream power river incision model predicts for reasonable initial topographies relatively short postorogenic decay times of 1 10 myr additional layers of complexity are introduced to this simplest model including isostasy and flexural strength a transition to transport limited conditions during decline and the incorporation of the combined effects of a critical threshold for erosion and the stochastic variability of flood magnitudes each of these additional factors acts to lengthen the decay timescale pure airy isostatic rebound of a thick crustal root results in decay times that are at most a factor of 6 longer than the detachment limited result the transition to transport limited conditions involves partial protection of the bed by a thin layer of alluvium which inhibits erosion and therefore increases decay times by a factor of 2 3 in our analysis finally including critical shear stress results increases decay time by approximately a factor of 20 for the parameter values in our example calculation more importantly however a significant portion of topography remains after predicted lowering rates have dropped to values less than measured rates of denudation in weathering limited low relief environments thus a model combining isostasy a transition to transport limited conditions and a critical shear stress for erosion could account for the presence of residual topography for hundreds of million years all three of these factors can be expected to play a role in natural settings

pattern and tempo of great escarpment erosion extensive geological geophysical structural and geochronological data suggest that the locations of great escarpments bordering passive margins are exceptionally stable and are probably determined by crustal structure together the data do not support the established paradigm of ongoing significant and parallel escarpment retreat rather thermochronologic data and sedimentary sequences in ocean basins suggest that initial tectonically controlled rift escarpments undergo rapid and significant erosion only during the earliest stages of seafloor spreading development of stable passive margin escarpments follows this period of intense erosion escarpments increase in sinuosity as embayments retreat more rapidly than interfluves measurements of 24 escarpments suggest that sinuosity and the rate at which it increases depends upon the location of maximum uplift the geometry of the preescarpment drainage system and margin age all data suggest that the location of passive margin escarpments does not change significantly over time

erosional equilibrium and disequilibrium in the sierra nevada inferred from cosmogenic 26al and 10be in alluvial sediment we used cosmogenic 26 al and 10 be in stream sediment to measure landscape scale erosion rates for topographically diverse catchments at seven sierra nevada sites at three sites erosion rates and hillslope gradients are strongly correlated increasing with proximity to fault scarps and river canyons which appear to have accelerated local base level lowering rates and thus increased catchment erosion rates by up to 15 fold at four other sites far from fault scarps and river canyons erosion rates are much more uniform and less sensitive to average hillslope gradient our measurements show that contrasts in landscape erosion rates cannot be inferred from hillslope gradients alone because landscapes can evolve toward a state of erosional equilibrium in which steep and gentle slopes erode at similar rates

is the vertebrate defined permian triassic boundary in the karoo basin south africa the terrestrial expression of the end permian marine event the end permian extinction records the greatest ecological catastrophe in earth history the vertebrate fossil record in the karoo basin south africa has been used for more than a century as the standard for understanding turnover in terrestrial ecosystems recently claimed to be in synchrony with the marine crisis workers assumed that systematic turnover at the dicynodon assemblage zone boundary followed by the appearance of new taxa directly above the base of the lystrosaurus assemblage zone is the continental expression of the end permian event and recovery to test this hypothesis we present the first highprecision age on strata close to the inferred permian triassic boundary a u pb isotope dilution thermal ionization mass spectrometry zircon age of 253 48 0 15 ma early changhsingian is from a silicified ash layer 60 m below the current vertebrate defined boundary at old lootsberg pass southern south africa this section yields newly discovered plants and vertebrates and is dominated by a normal polarity signature our collective data suggest that the dicynodon lystrosaurus assemblage zone boundary is stratigraphically higher than currently reported and older than the marine extinction event therefore the turnover in vertebrate taxa at this biozone boundary probably does not represent the biological expression of the terrestrial end permian mass extinction the actual permian triassic boundary in the karoo basin is either higher in the katberg formation or is not preserved the currently accepted model of the terrestrial ecosystem response to the crisis both in this basin and its extension globally requires reevaluation

reply to discussion of permian triassic vertebrate footprints from south africa ichnotaxonomy producers and biostratigraphy through two major faunal crises by marchetti l klein h buchwitz m ronchi a smith r m h deklerk w j sciscio l and groenewald g h 2019 abstract our recent comprehensive review of the permian early triassic tetrapod tracksites from south africa includes a revision of the ichnotaxonomy and the incorporation of a large quantity of new material the paper also discusses in light of the revised ichnotaxonomy and palaeontology of several sites trackmaker attribution and the biostratigraphy of permian early triassic tetrapod tracks precise information about the fossiliferous localities was provided where possible and when sites were relocated three footprint associations were described fa i iii and highlight their potential stratigraphic value the youngest fa iii was recognized at four different localities and is likely induan in age a recent comment by gastaldo and neveling 2019 regarded one of these fa iii localities the bethel tracksite which received criticism for its unclear geographic placement and its stratigraphic position further comments included a discussion of the possible palaeoecological interpretation of this tracksite in replying to these queries we provided more precise geographic and stratigraphic information confirming the occurrence of this tracksite 15 m above the faunal transition which we consider to be currently coinciding with the permian triassic boundary ptb palaeoecological inferences are herein further clarified

sedimentary facies and environmental ichnology of a permian playa lake complex in western argentina abstract a moderately diverse arthropod ichnofauna occurs in permian ephemeral lacustrine deposits of the paganzo basin that crop out at bordo atravesado cuesta de miranda western argentina sedimentary successions are interpreted as having accumulated in a playa lake complex deposits include three sedimentary facies a laminated siltstone and mudstone b current rippled cross laminated very fine grained sandstone and c climbing and wave rippled cross laminated fine grained sandstone deposited by sheet floods under wave influence in the playa lake complex analysis of facies sequences suggests that repeated vertical facies associations result from transgressive regressive episodes of variable time spans the bordo atravesado ichnofauna includes cruziana problematica diplocraterion isp cf diplopodichnus biformis kouphichnium isp merostomichnites aicunai mirandaichnium famatinense monomorphichnus lineatus palaeophycus tubularis umfolozia sinuosa and umfolozia cf u longula the assemblage is largely dominated by arthropod trackways and represents an example of the scoyenia ichnofacies trace fossils are mostly preserved as hypichnial ridges on the soles of facies c beds being comparatively rare in facies a and b ichnofossil preservation was linked to rapid influx of sand via sheet floods entering into the lake four taphonomic variants types 1 4 are recognized each determined by substrate consistency and time averaging type 1 is recorded by the presence of low density assemblages consisting of poorly defined trackways which suggests that arthropods crawled in soft probably slightly subaqueous substrates type 2 is represented by low to moderate density suites that include sharply defined trackways commonly associated with mud cracks suggesting that the tracemakers inhabited a firm desiccated lacustrine substrate type 3 displays features of types 1 and 2 and represents palimpsestic bedding surfaces resulting from the overprint of terrestrial ichnocoenoses over previously formed softground suites type 4 differs from type 2 only in that assemblages display a high density of traces recorded by numerous superimposed trackways which suggests a major time gap of subaerial exposure before sheet flood entrance therefore type 4 surfaces are mostly interpreted as track imprinted omission surfaces

paleomagnetic constraints on the permian triassic boundary in terrestrial strata of the karoo supergroup south africa implications for causes of the end permian extinction event the closure of the palaeozoic witnessed the greatest biotic crisis in earth history surprisingly little is known about the effects and timing of the terrestrial counterpart of the well described end permian mass extinction from known marine successions worldwide in the present study reliable paleomagnetic results were obtained from a pt boundary section in the terrestrial karoo basin of south africa permo triassic aged mudstones from a locality in the eastern cape province yielded two magnetic chrons reverse followed by normal with the boundary possibly close to the reversal this extends to results from a previous study thereby jointly identifying a r n r polarity pattern for this boundary interval the ptb interval is constrained below the red mudstones of the beaufort group at the present locality and within reverse magnetised green mudstone implying a diachronic relation between the marine and terrestrial end permian mass extinction events

global climate perturbations during the permo triassic mass extinctions recorded by continental tetrapods from south africa several studies of the marine sedimentary record have documented the evolution of global climate during the permo triassic mass extinction by contrast the continental records have been less exploited due to the scarcity of continuous sections from the latest permian into the early triassic the south african karoo basin exposes one of the most continuous geological successions of this time interval thus offering the possibility to reconstruct climate variations in southern laurasia from the middle permian to middle triassic interval both air temperature and humidity variations were estimated using stable oxygen 18op and carbon 13cc isotope compositions of vertebrate apatite significant fluctuations in both 18op and 13cc values mimic those of marine records and suggest that stable isotope compositions recorded in vertebrate apatite reflect global climate evolution in terms of air temperature oxygen isotopes show an abrupt increase of about 8 c toward the end of the wuchiapingian this occurred during a slight cooling trend from the capitanian to the permo triassic boundary ptb at the end of the permian an intense and fast warming of 16 c occurred and kept increasing during the olenekian these thermal fluctuations may be related to the emeishan south china and siberian volcanic paroxysms that took place at the end of the capitanian and at the end of the permian respectively vertebrate apatite 13cc partly reflects the important fluctuations of the atmospheric 13c values the differences with marine curves being likely due to the evolution of local humidity both the oxygen and carbon isotope compositions indicate that the ptb was followed by a warm and arid phase that lasted 6 ma before temperatures decreased during the late anisian toward that of the end permian environmental fluctuations occurring around the ptb that affected both continental and marine realms with similar magnitude likely originated from volcanism and methane release

high precision temporal calibration of late permian vertebrate biostratigraphy u pb zircon constraints from the karoo supergroup south africa therapsid and other tetrapod fossils from the south african karoo supergroup provide the most detailed and best studied terrestrial vertebrate record of the middle and late permian the resulting biostratigraphic scheme has global applicability establishing a temporal framework for these faunas has proven difficult magnetostratigraphy has been hampered by a jurassic overprint and intercorrelation with permian marine sequences has been equivocal here we report u pb zircon isotope dilution thermal ionization mass spectrometry id tims dates for five volcanic ashes interbedded with fossils from the pristerognathus tropidostoma and cistecephalus vertebrate biozones of the beaufort group this temporal framework allows correlation to marine zonations and improves understanding of rates of faunal evolution and patterns of basin evolution our results identify no correlative vertebrate extinctions in the karoo supergroup to the marine end guadalupian mass extinction and raise the question of whether there is any record of a terrestrial extinction related to the emeishan large igneous province

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

classification of paleosols despite increased interest in paleosols during the past decade no satisfactory classification is in current use presented here is a largely descriptive classification system that utilizes those pedogenic features that have the highest preservation potential in the rock record emphasized in the classification are morphological and mineralogical features that are easily recognizable in the field and through the petrographic microscope the classification is based on evaluation of the relative prominence in a paleosol of six pedogenic features or processes organic matter content horizonation redox conditions in situ mineral alteration illuviation of insoluble minerals compounds and accumulation of soluble minerals the most prominent of these six features processes provides the key to classifying a paleosol into one of nine orders four of the order names are borrowed from soil taxonomy histosol spodosol oxisol vertisol whereas the other five order names are presented here for the first time calcisol gypsisol gleysol argillisol protosol the orders may be preceded by one or more subordinate modifiers that describe other important features of the paleosol the classification is relatively easy to apply to the rock record and should enhance communication and aid in the standardization of terminology

anatomy of a mass extinction sedimentological and taphonomic evidence for drought induced die offs at the permo triassic boundary in the main karoo basin south africa abstract the southern part of the karoo basin of south africa contains a near complete stratigraphic record of the permo triassic boundary ptb isotope and magneto stratigraphy confirm that these predominantly fluvial strata are approximately the same age as zircon dated marine ptb sections 252 mya by august 2013 our team had found 579 in situ vertebrate fossils mostly of the clade therapsida in ptb exposures at three widely separated locations in the southern karoo basin biostratigraphic ranges of the various taxa found in each of the sections reveal three separate phases of die off within the same roughly 75 metre thick stratigraphic interval displaying the same sequence of sedimentary facies interpreted as indicative of climatic drying increased seasonality and the onset of an unpredictable monsoon type rainfall regime the three phases of an inferred ecologically stepped mass extinction are phase 1 45 m 30 m below ptb datum brought on by lowered watertables which led to loss of shallow rooting groundcover in the more elevated proximal floodplain areas and the disappearance of the smaller groundcover grazing herbivorous dicynodonts and their attendant small carnivores phase 2 20 0 m below ptb datum is the main extinction that occurs in massive maroon grey mudrock culminating in an event bed of laminated reddish brown siltstone mudstone couplets this facies reflects progressively unreliable rainfall leading to vegetation loss in proximal and distal floodplain areas the larger tree browsing herbivores and their attendant carnivores are confined to watercourses before finally disappearing phase 3 25 30 m above ptb datum occurs in massive maroon siltstone facies with evidence of climatic aridity including the accumulation of mummified carcasses buried by windblown dust all of the surviving permian taxa disappear within 30 m of the ptb temporal resolution based on accretion rates and pedogenic maturity of each stratigraphic section reveals that phase 1 and phase 2 die offs lasted 21 000 and 33 000 years separated by a short period of 7000 years where no disappearances are recorded and this was followed by 50 000 years of stasis for the final extinction phase lasting only 8000 years that removed all the permian survivor taxa we propose that the recorded disappearances are real rather than preferential preservation failure and that they represent drought induced die offs moving progressively up the food chain as the terrestrial ecosystem collapsed the latter mostly likely caused by volcanogenic greenhouse gas emissions and rapid global warming

constraints from deep crustal structure on long term landform development of the british isles and eastern united states abstract it is assumed that some major landforms not easily explained by surface geology could be controlled by deep crustal properties the concept was first applied in the british isles and then to the u s atlantic provinces both regions were affected by similar orogenies in late precambrian paleozoic times and presently belong to the passive margins of the north atlantic ocean in both areas the pattern of rifting was greatly influenced by preexisting tectonic fabric of the continental crust in the british isles pre mesozoic structures are cut obliquely by the atlantic margin while in the u s border the present margin is nearly parallel to the paleozoic sutures the british isles were affected by differential block tectonics during the tertiary examples are given of regional scale landforms linked with crustal hinges recent data confirm the great heterogeneity of the crust beneath the british isles each crustal unit has its own isostatic response according to the state of stress and its own dynamic equilibrium between rock resistance erosion processes and uplift rate in the atlantic provinces of the united states the regional physiographic framework is simpler but allochthonous terranes thrust westward over the grenville basement and shelf sediments have buried some major discontinuities in the deep crust reverse faults associated with the nw se compressional stressfield are numerous but cannot explain regional scale landforms like the blue ridge escarpment above the piedmont rock control is not the direct cause of the escarpment the blue ridge from reaches its highest relief where discontinuities in the deep crust interfere with surficial geological features ocean to continent creep processes are suggested to explain the sustained uplift of the appalachian highlands and the relatively stable position of the mountainous front since middle mesozoic times

altered river morphology in south africa related to the permian triassic extinction the permian triassic transition in the karoo basin of south africa was characterized by a rapid and apparently basin wide change from meandering to braided river systems as evidenced by preserved sedimentary facies this radical changeover in river morphology is consistent with geomorphic consequences stemming from a rapid and major die off of rooted plant life in the basin evidence from correlative nonmarine strata elsewhere in the world containing fluvial permian triassic boundary sections suggests that a catastrophic terrestrial die off of vegetation was a global event producing a marked increase in sediment yield as well as contributing to the global 13 c excursion across the permian triassic boundary

strong rocks sustain ancient postorogenic topography in southern africa the cape mountains of southern africa exhibit an alpine like topography in conjunction with some of the lowest denudation rates in the world this presents an exception to the often cited coupling of topography and denudation rates and suggests that steep slopes alone are not sufficient to incite the high denudation rates with which they are commonly associated within the cape mountains slope angles are often in excess of 30 degrees and relief frequently exceeds 1 km yet be 10 based catchment averaged denudation rates vary between 2 32 0 29 m m y and 7 95 0 90 m m y we attribute the maintenance of rugged topography and suppression of denudation rates primarily to the presence of physically robust and chemically inert quartzites that constitute the backbone of the mountains be 10 based bedrock denudation rates on the interfluves of the mountains vary between 1 98 0 23 m m y and 4 61 0 53 m m y the close agreement between the rates of catchment averaged and interfluve denudation indicates topography in steady state these low denudation rates in conjunction with the suggestion of geomorphic stability are in agreement with the low denudation rates 20 m m y estimated for southern africa during the late cenozoic by means of cosmogenic nuclide thermochronology and offshore sedimentation analyses accumulatively these data suggest that the coastal hinterland of the subcontinent may have experienced relative tectonic stability throughout the cenozoic

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

low rates of bedrock outcrop erosion in the central appalachian mountains inferred from in situ 10be bedrock outcrops are common on central appalachian mountain ridgelines because these ridgelines define watersheds the rate at which they erode influences the pace of landscape evolution to estimate ridgeline erosion rates we sampled 72 quartz bearing outcrops from the potomac and susquehanna river basins and measured in situ produced 10 be ridgeline erosion rates average 9 1 m m y 1 median 6 m m y 1 similar to 10 be derived rates previously reported for the region the range of erosion rates we calculated reflects the wide distribution of samples we collected and the likely inclusion of outcrops affected by episodic loss of thick slabs and periglacial activity outcrops on main ridgelines erode slower than those on mountainside spur ridges because ridgelines are less likely to be covered by soil which reduces the production rate of 10 be and increases the erosion rate of rock ridgeline outcrops erode slower than drainage basins in the susquehanna and potomac river watersheds suggesting a landscape in disequilibrium erosion rates are more similar for outcrops meters to tens of meters apart than those at greater distances yet semivariogram analysis suggests that outcrop erosion rates in the same physiographic province are similar even though they are hundreds of kilometers apart this similarity may reflect underlying lithological and or structural properties common to each physiographic province average 10 be derived outcrop erosion rates are similar to denudation rates determined by other means sediment flux fission track thermochronology u th he dating indicating that the pace of landscape evolution in the central appalachian mountains is slow and has been since post triassic rifting events

apatite u th he age constraints on the development of the great escarpment on the southeastern australian passive margin the southeast australian margin like other high elevation passive margins is characterised by a steep escarpment that separates a dissected coastal plain from a low relief inland plateau quantitative constraints on the generation of escarpments can be provided by apatite u th he ages here we use a coast perpendicular traverse across the coastal lowlands escarpment and plateau to test the three prevailing models of se australian escarpment formation namely retreat into a downwarped rift shoulder escarpment retreat and down wearing on high elevation rift shoulder with flexural rebound apatites from the coastal plain have he ages of between 87 and 112 ma suggesting that the coastal lowlands developed very rapidly after rifting and continental break up at 85 100 ma the he age data are inconsistent with the erosion of a downwarped rift margin and cannot be explained by a constant post break up rate of lateral escarpment retreat across the coastal plain or by constant down wearing the data require either rapid escarpment retreat or rapid in place excavation of the escarpment soon after break up in response to rifting and the lowering of base levels on the margin of the new continent at break up followed by a period of landscape stability and low erosion combined with the existing apatite fission track record the he data are consistent with erosion of 3 4 km within a maximum of 28 myr of break up at a minimum vertical erosion rate of 130 m myr 1 along the coast the rapid denudation period across the coastal plain in this region took less than 48 myr from the coast to the escarpment base which corresponds to an average vertical erosion rate of 45 m myr 1 this is equivalent to a mean escarpment retreat rate of 5 10 km myr 1 apatite he ages from the plateau 183 247 ma indicate that the highlands remained stable throughout continental break up experiencing average erosion rates of less than 10 m myr 1 since the late palaeozoic early mesozoic

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

slow rates of rock surface erosion and sediment production across the namib desert and escarpment southern africa slow erosion has characterized the namib desert the namibian escarpment and the adjacent namibian highlands over the pleistocene paired analyses n 66 of in situ produced 10be and 26al in quartz bearing samples of bedrock primarily from inselbergs of sediment from dry river and stream channels and of clasts from desert surfaces reveal large inventories of these cosmogenic nuclides indicating significant landscape stability over at least the past million years bedrock samples n 47 collected in three transects from the coast across the escarpment and into the highlands show no spatial pattern in elevation normalized nuclide abundance despite a difference in mean annual precipitation map between sample sites at the coast map 400 mm yr 1 average model erosion rates inland of the escarpment 3 2 1 5 n 9 are indistinguishable from average rates seaward of the escarpment 3 6 1 9 n 38 indicating that rock on the pedimented coastal plain is eroding at the same rate as rock in the highlands sediment samples n 3 from small streams suggest that the landscape as a whole is eroding more rapidly than the bedrock outcrops and that a basin in the steep escarpment zone is eroding several times faster 16 m my 1 than either a basin in the highlands 5 m my 1 or a basin in the coastal plain 8 m my 1 data from large rivers n 4 constrain erosion rates averaged over 105 yrs and 104 to 105 km2 between 3 and 9 m my 1 small quartz clasts n 12 collected from four desert surfaces record extraordinarily long variable and in some cases complex exposure histories simple 10be model ages are as high as 1 8 my some minimum total histories considering both 10be and 26al and including both burial and exposure exceed 2 7 my as a group the namibian cosmogenic data do not support the model of significant and on going escarpment retreat the similarity of erosion rates calculated from 10be analysis of fluvial sediments and longer term 107 yr average mass removal rates estimated by others using fission track analysis of rock suggests that namibian erosion rates have reached a steady state and are changing little over time at outcrop scales the concordance of 10be and 26al in most bedrock samples suggests that the model of steady uniform bedrock erosion is valid there is no indication of intermittent burial shedding of thick rock slabs or stripping of previous cover at an intermediate scale a transect of bedrock samples north of gobabeb demonstrates that the northern boundary of the massive namib sand sea has been steady and unshifting similarly low cosmogenically estimated erosion rates across west and central namibia suggest that the landscape is in geomorphic steady state its overall appearance changing only slowly through time

late cenozoic flexural deformation of the middle u s atlantic passive margin despite the century long recognition of regional epeirogeny along the middle atlantic passive margin relatively few studies have focused on understanding postrift uplift mechanisms here we demonstrate that epeirogenic uplift of the central appalachian piedmont and subsidence of the salisbury embayment represent first order flexural isostatic processes driven by continental denudation and offshore deposition our results show that regional epeirogenic processes present on all atlantic type passive margins are best resolved by specific stratigraphic and geomorphic relationships rather than topography a simple one dimensional geodynamic model constrained by well dated baltimore canyon trough coastal plain and lower susquehanna river piedmont stratigraphy simulates flexural deformation of the u s atlantic margin the model represents the passive margin lithosphere as a uniformly thick elastic plate without horizontal compressive stresses that deforms flexurally under the stress of strike averaged vertically applied line loads model results illustrate a complex interaction among margin stratigraphy and geomorphology the isostatic response to denudational and depositional processes and the modulating influence of exogenic forces such as eustasy the current elevation with respect to modern sea level of fluvial terraces and correlative coastal plain deposits or unconformities is successfully predicted through the synthesis of paleotopography eustatic change and margin flexure results suggest that the middle u s atlantic margin landward of east coast magnetic anomaly is underlain by lithosphere with an average elastic thickness of 40 km flexural rigidity d 4 1023 n m the margin experiences an average long term denudation rate of approximately 10 m m y and the piedmont has been flexurally upwarped between 35 and 130 meters in the last 15 m y long term isostatic continental uplift resulting from denudation and basin subsidence resulting from sediment loading are accommodated primarily by a convex up flexural hinge physiographically represented by the fall zone our results elucidate an inherent danger in using topography alone to constrain late stage passive margin deformation mechanisms only through careful synthesis of field stratigraphic and geomorphic elements such as fluvial terraces coastal plain deposits and offshore stratigraphy can age control be extended from the offshore depositional setting to the erosionally dominated continent this study demonstrates that despite a relatively subdued topography the middle u s atlantic margin experiences progressive flexural isostatic deformation similar to that proposed for high relief margins characterized by great escarpments thus margin topographic diversity remains a function of other factors such as lithospheric composition and or structure supracrustal stratigraphy and structure degree of drainage integration drainage divide migration and climate

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

erosional dynamics flexural isostasy and long lived escarpments a numerical modeling study erosional escarpments are common features of high elevation rifted continents fission track data suggest that these escarpments form by base level lowering and or marginal uplift during rifting followed by lateral retreat of an erosion front across tens to hundreds of kilometers previous modeling studies have shown that this characteristic pattern of denudation can have a profound impact upon marginal isostatic uplift and the evolution of offshore sedimentary basins yet at present there is only a rudimentary understanding of the geomorphic mechanisms capable of driving such prolonged escarpment retreat in this study we present a nonlinear two dimensional landscape evolution model that is used to assess the necessary and sufficient conditions for long term retreat of a rift generated escarpment the model represents topography as a grid of cells with drainage networks evolving as water flows across the grid in the direction of steepest descent the model accounts for sediment production by weathering fluvial sediment transport bedrock channel erosion and hillslope sediment transport by diffusive mechanisms and by mass failure numerical experiments presented explore the effects of different combinations of erosion processes and of dynamic coupling between denudation and flexural isostatic uplift model results suggest that the necessary and sufficient conditions for long term escarpment retreat are 1 incising bedrock channels in which the erosion rate increases with increasing drainage area so that the channels steepen and propagate headward 2 a low rate of sediment production relative to sediment transport efficiency which promotes relief generating processes over diffusive ones 3 high continental elevation which allows greater freedom for fluvial dissection and 4 any process including flexural isostatic uplift that helps to maintain a drainage divide near an escarpment crest flexural isostatic uplift also facilitates escarpment retreat by elevating topography in the vicinity of an eroding escarpment thereby increasing channel gradients and accelerating erosion which in turn generates additional isostatic uplift of all the above conditions high continental elevation is common to most rift margin escarpments and may ultimately be the most important factor

spatial variability of 10be derived erosion rates across the southern peninsular indian escarpment a key to landscape evolution across passive margins abstract the persistence of significant topography in ancient tectonically inactive orogenic belts remains one of the outstanding questions in geomorphology in southern peninsular india the impressive topographic relief of the western ghat mountains in tectonic quiescence since at least ca 65 ma has raised important questions concerning the long term mechanism of topographic evolution quantifying the distribution of erosion in space and time is critical to understanding landscape evolution although the long term erosion rates are reasonably well known the short term erosion rates and the relative importance of factors controlling erosion in southern peninsular india are less well constrained we present a new suite of catchment averaged and local erosion rates using in situ produced 10be concentrations in river sediments and exposed bedrock samples in southern peninsular india catchment averaged erosion rates vary from 9 6 0 8 m ma 1 in the highlands to 114 3 13 8 m ma 1 on the escarpment side bedrock erosion rates range from 2 4 0 2 m ma 1 in the ridge top to 143 4 25 4 m ma 1 in active channel beds of the highlands catchment averaged erosion rates derived from the across escarpment westward draining catchments are significantly higher than those derived from the eastward draining over highland catchments the difference indicates that long term down wearing of the highland proceeds at lower rates than in the escarpment zones catchment averaged erosion rates are moderately correlated with mean hillslope angles and local relief whereas they are strongly correlated with catchment averaged channel steepness index this suggests that topographic steepness is the major control on the spatial variability of erosion while strong rainfall gradient is of minor importance in this area 10be derived average erosion rates in highlands are consistent with previous long term erosion rate estimated from thermochronometry these results collectively point to large scale steady state topography only decaying slowly with time steady state likely reflects the balance between erosion and isostatically driven uplift of the southern peninsular india

early triassic aggradational and degradational landscapes of the karoo basin and evidence for climate oscillation following the p tr event the lower triassic katberg formation beaufort group karoo supergroup in south africa is a fine grained arenaceous unit deposited under ephemeral bedload dominated fluvial conditions and previously interpreted as representing a continuous stratigraphic record its genesis was linked directly to the end paleozoic extinction event and was considered to exhibit the results of a trend towards aridification the present study documents the lowermost katberg formation exposed at carlton heights northern cape province to test the aridification hypothesis four lithofacies vary in both vertical and lateral relationships with feldspathic sandstone dominating the stratigraphy pisolith size nodular conglomerate consists of pedogenically derived carbonate nodules originally precipitated within aridisols none of which are either exposed or reported from the formation rather the only evidence of extreme aridification is found within channel lag barform and overbank deposits marking landscape degradation landscape aggradation is characterized by two feldspathic sandstone geometries where 1 medium bedded planar bedded or ripple laminated sheet sandstone is interpreted as ephemeral sheetflood deposits and 2 thick bedded cross laminated multi lateral lenticular sandstone is interpreted as associated with deeper sand bed braided anabranching systems overbank fines consist of polyphase siltstone paleosols in which bioturbated inceptisols were overprinted by gleysols wherein large pedogenic carbonate nodules precipitated under a high regional water table evidence exists for periodic drying in these wet regimes but no evidence exists for extreme aridity hence the lowermost katberg formation superficially exhibits only an aggradational sedimentological record but significant diastems exist as evidenced by the concentration of aridisol precipitates at the base of each degradational cycle a model for the early triassic in this part of the karoo basin is presented wherein this record is interpreted as a function of climate oscillations rather than either episodic uplift in the cape fold belt or any ecosystem response to the end permian extinction

evidence of transient topographic disequilibrium in a landward passive margin river system knickpoints and paleo landscapes of the new river basin southern appalachians the upper new river basin of the southern appalachian mountains a major tributary of the modern ohio river represents the unglaciated headwaters of the tertiary teays river system of eastern north america dating of relict fluvial gravels have suggested that new river incision may be outpacing lowering of the surrounding uplands but physical evidence of transient topographic disequilibrium has yet to be identified we use focused topographic analysis of the upper new river basin to delineate a perched low relief paleo landscape that is experiencing transgressive dissection due to incision by the new river and its tributaries accelerated incision has decoupled hillslopes from the drainage network generating knickpoints which represent the boundary between remnants of the paleo landscape and actively adjusting topography downstream steepening of hillslopes downstream of knickpoints suggests dynamic headward migration which along with knickpoint occurrence throughout the drainage network is inconsistent with the development of fixed stream profile convexities atop strike extensive geologic contacts in the absence of tectonic forcing we favor a climatically forced drop in external base level as driver of the incision pattern we observe plio pleistocene glacial damming and diversion of the teays river to form the modern ohio river lowered regional base level for the study area potentially forcing the paleo landscape developed during the teays era to adjust to the modern drainage pattern the upper new river may therefore represent the potential for glacially driven drainage rearrangement to drive transient topographic evolution hundreds of kilometers away from the ice margin long after the disappearance of ice sheets copyright 2013 john wiley sons ltd

denudation rates for the southern drakensberg escarpment se africa derived from in situ produced cosmogenic 36c1 initial results cosmogenic 36 c1 concentrations in basalt samples from the drakensberg escarpment on the se african passive margin give quantitative estimates of denudation and scarp retreat rates over the 10 4 10 6 year timespan addressed by these data the calculated escarpment retreat rate has been 50 95 m ma 1 and the average summit denudation rate 6 m ma 1 the scarp retreat rate is an order of magnitude less than previously suggested the rate of summit lowering is sufficient to prevent the long term intact survival of erosion cycle surfaces formed in the mesozoic that were previously inferred for this region

erosion of a granite inselberg gross spitzkoppe namib desert abstract namibia with its passive margin setting long term tectonic stability and long lasting arid climate is a typical granitic landscape characterized by numerous dominating inselbergs the namib has been the focus of quantitative studies on the overall rates of bedrock exhumation escarpment retreat and sediment generation transport and deposition results from these studies indicate steady bedrock erosion rates ranging between 1 and 5 mm kyr 1 over the last 105 106 yr this rate was determined from samples collected mostly from small inselbergs with low relief how fast the large and classic inselbergs which dominate the namib desert landscape erode generate sediment and contribute to the overall sediment supply has yet to be systematically examined we document erosion rates of the gross spitzkoppe gs one of the largest inselbergs in the namib desert namibia based on measured concentrations of 10be in samples collected from bedrock boulders and surface grus the results suggest a slow lowering rate 1 2 mm kyr 1 while the overall slope processes deliver sediment to the base of the cliff with 5 6 105 atoms g 1 quartz this concentration is equivalent to an average erosion rate of 8 mm kyr 1 2 3 times faster than the bedrock lowering rate thus the inselberg has been eroding by cliff retreat the concentration of cosmogenic isotopes in slope sediment is controlled by exposure time on the slope weathering of exposed bedrock and weathering of subsurface bedrock sediment continues to accumulate cosmogenic isotopes while being transported on the flat pediments surrounding the inselberg within 1 2 km from the base of the gs the concentration doubles to 10 105 atoms g 1 quartz the increase is achieved by dosing due to exposure and mixing with highly dosed sediment eroded from near subsurface bedrock from this area grus is transported through a network of low gradient channels to the atlantic ocean 100 km away cosmogenic isotope concentration in sediment increases to 30 105 atoms of 10be g 1 quartz which is 3 4 times higher than that measured in the grus close to the gs and is controlled by the erosion rate of stable bedrock throughout the entire drainage basin dosing due to exposure during transport obviously contributes to the overall measured concentration in the sediment as it approaches the ocean

discussion of permian triassic vertebrate footprints from south africa ichnotaxonomy producers and biostratigraphy through two major faunal crises by marchetti l klein h buchwitz m ronchi a smith r m h deklerk w j sciscio l and groenewald g h 2019 abstract a newly devised tripartite subdivision of the karoo basin south africa is based on a number of vertebrate trackways spanning the middle permian wordian capitanian to lower triassic reportedly induan rocks of the beaufort formation the youngest footprint assemblage fa iii is reported to occur in the lowermost triassic rocks of the palingkloof member one collection site from which seven trackways are reported bethel farm is a classic south african locality where some authors place the end permian extinction event and coincidentally the vertebrate based terrestrial permian triassic boundary published gps coordinates for the bethel farm site though indicate that these trackways originate from exposures of the burgersdorp formation near the town of aliwal north outcrops here are assigned to the cynognathus assemblage zone and indicate a middle triassic age assignment in addition we caution the use of any small temporally or spatially restricted dataset which is of severely limited utility in making broad generalizations about paleoenvironmental or paleoecological interpretations

a geomagnetic polarity timescale for the permian calibrated to stage boundaries the reverse polarity kiaman superchron has strong evidence for at least three or prob ably four normal magnetochrons during the early permian normal magnetochrons are during the early asselian base ci1r 1n at 297 94 0 33 ma late artinskian ci2n at 281 24 2 3 ma mid kungurian ci3n at 275 86 2 0 ma and roadian ci3r an at 269 54 1 6 ma the mixed polarity illawarra superchron begins in the early wordian at 266 66 0 76 ma the wordian capitanian interval is biased to normal polarity but the basal wuchiapingian begins the beginning of a significant reverse polarity magnetochron lp0r with an overlying mixed polarity interval through the later lopingian no significant magnetostratigraphic data gaps exist in the permian geomagnetic polarity record the early cisuralian magnetochrons are calibrated to a succession of fusulinid zones the later cisuralian and guadalupian to a conodont and fusulinid biostratigraphy and lopingian magnetochrons to conodont zonations age calibration of the magnetochrons is obtained through a bayesian approach using 35 radiometric dates and 95 confidence intervals on the ages and chron durations are obtained the dating control points are most numerous in the gzhelian asselian wordian and changhsingian intervals this significant advance should provide a framework for better correlation and dating of the marine and non marine permian

increase of human over natural erosion rates in tropical highlands constrained by cosmogenic nuclides we quantify the difference between the human caused sediment yield and the natural rates of soil production and bedrock erosion in a now largely deforested tropical highland the present day rate of soil loss in the upper mahaweli catchment sri lanka is calculated by using suspended river load fluxes these data provide spatially averaged sediment yields of 130 2100 t km 2 yr 1 local rates of soil loss from agricultural plots on hillslopes are as high as 7000 t km 2 yr 1 by comparison natural rates of sediment generation as determined by measuring cosmogenic 1 0 be in quartz from sediments and soils are only 13 30 t km 2 yr 1 the natural rates presented here provide a benchmark against which recent erosion rates determined by various sediment gauging techniques can be referenced in the sri lankan highlands these results suggest that soil is now being lost 10 100 times faster from agriculturally utilized areas than it is being produced

determination of predevelopment denudation rates of an agricultural watershed cayaguas river puerto rico using in situ produced 10be in river borne quartz accurate estimates of watershed denudation absent anthropogenic effects are required to develop strategies for mitigating accelerated physical erosion resulting from human activities to model global geochemical cycles and to examine interactions among climate weathering and uplift we present a simple approach to estimate predevelopment denudation rates using in situ produced cosmogenic 10be in fluvial sediments denudation processes in an agricultural watershed cayaguas river basin puerto rico and a matched undisturbed watershed icacos river basin were compared using 10be concentrations in quartz for various size fractions of bed material the coarse fractions in both watersheds bear the imprint of long subsurface residence times fine material from old shallow soils contributes little however to the present day sediment output of the cayaguas this confirms the recent and presumably anthropogenic origin of the modern high denudation rate in the cayaguas basin and suggests that pre agricultural erosional conditions were comparable to those of the present day icacos

the terrestrial permian triassic boundary event is a nonevent reply we are pleased to reply to ward et al 2012 1 about the stratigraphic record of the karoo basin where the terrestrial ecosystem response to the end permian extinction is recorded the present extinction model envisions a marine and terrestrial response coupling the permian triassic boundary

mountain erosion over 10 yr 10 k y and 10 m y time scales we used cosmogenic 10 be to measure erosion rates over 10 k y time scales at 32 idaho mountain catchments ranging from small experimental watersheds 0 2 km 2 t o large river basins 35 000 km 2 these long term sediment yields are on average 17 times higher than stream sediment fluxes measured over 10 84 yr but are consistent with 10 m y erosion rates measured by apatite fission tracks our results imply that conventional sediment yield measurements even those made over decades can greatly underestimate long term average rates of sediment delivery and thus overestimate the life spans of engineered reservoirs our observations also suggest that sediment delivery from mountainous terrain is extremely episodic sporadically subjecting mountain stream ecosystems to extensive disturbance

disruption of playa lacustrine depositional systems at the permo triassic boundary evidence from vyazniki and gorokhovets on the russian platform abstract permo triassic sections at vyazniki and gorokhovets provide evidence on terrestrial events at or close to the permo triassic boundary the time of the largest ever mass extinction the sedimentary succession records the overrun of a muddy playa lacustrine depositional system by major channel belts transporting sand grade sediments biostratigraphy of sections at vyazniki and gorokhovets zhukov ravine shows that this event occurred either at the very end of the permian or 8 m above in the sections the timing and nature of this event which records increased sediment flux from the ural mountains is closely comparable with that from the southern uralian foreland basin the vyazniki and gorokhovets sections are 800 km from the mountain front and in a separate depositional basin which strengthens the case that increased sediment flux from the urals at the permo triassic boundary is related to devegetation of upland catchments increasing sediment yield and a switch toward low frequency but high magnitude discharge events increasing sediment delivery the interbedding of fluvial and aeolian deposits provides further evidence for climatic instability and extremes in the early triassic supplementary material detailed reports on the ostracodes and fossil fish remains from the zhukov ravine sections are available at http www geolsoc org uk sup18402

a multidisciplinary approach to review the vertical and lateral facies relationships of the purported vertebrate defined terrestrial permian triassic boundary interval at bethulie karoo basin south africa abstract the stratigraphic section at bethulie south africa is reported to contain the vertebrate defined permian triassic boundary succession in the terrestrial realm of the karoo basin the model of vertebrate turnover from the daptocephalus to lystrosaurus assemblage zones tightly constrains the boundary sequence to a short stratigraphic interval where siltstone color begins to change from greenish gray to grayish red the latter color interpreted to be a consequence of aridification the biological response to this facies change has been termed the great dying and the sedimentary rocks that are preserved are ascribed to a playa lake depositional setting this drying event is believed to be contemporaneous across the basin although previous studies have shown that the facies appears at multiple horizons at all purported permian triassic boundary sections in the basin here we report results of a multidisciplinary effort to characterize the vertebrate assemblage zone boundary interval exposed at bethulie using the lithostratigraphic petrographic geochemical and rock magnetic properties of these rocks in this stratigraphic succession at its type location the 3 m thick assemblage zone boundary interval is distinguished by thick beds of greenish gray greenish gray mottled to grayish red and grayish red siltstone all of which change facies characteristics laterally along strike specifically about 220 m to the southeast of the type section sediments lose all grayish red coloration whereas the interval becomes laminated to the northwest petrographically most siltstone is homogenized with few burrows and small scale cross bedded structures with mudchips there are no gypsiferous or calcareous beds nor is there evidence of disturbed structures authigenic breccia or pseudomorphs associated with dessication mean elemental composition of both greenish gray and grayish red beds are indistinguishable geochemically and both are dominated by illite and chlorite clay species mossbauer spectroscopic analyses reveal the presence of a small concentration of fine grained hematite in the grayish red siltstone with its presence mainly found as coatings on clay minerals rock magnetic experiments isothermal remanent magnetization acquisition and backfield dc demagnetization magnetic hysteresis susceptibility vs temperature yield data that demonstrate no essential differences between the different colored siltstones and both lithologies host mangnetite maghematite and hematite our results do not support the previous interpretation that this inferred permian triassic boundary interval represents the onset of playa lake deposits under conditions of aridification rather our evidence supports the existence of a wet landscape at what is considered the daptocephalus lystrosaurus assemblage zone boundary

quantifying passive margin denudation and landscape development using a combined fission track thermochronology and cosmogenic isotope analysis approach abstract a new approach to empirically constraining numerical models of denudation and landscape development across passive continental margins is presented involving a combination of apatite fission track thermochronology and cosmogenic isotope analysis this integrated strategy is applied to the namibian sector of the south west african margin where the conventional landscape evolution model of inland retreat of an escarpment initiated at the coast at break up implies a mean rate of retreat of 1 km ma 1 the thermochronological and cosmogenic isotope data are incompatible with a simple escarpment retreat model since they show that denudation rates oceanward of the present escarpment position have been low 1 since the end of the eocene and the estimated rate of escarpment retreat has been only 10 m ma 1 this low rate of retreat is however consistent with numerical landscape evolution models where the escarpment is pinned at an inland drainage divide

siltstones across the daptocephalus dicynodon and lystrosaurus assemblage zones karoo basin south africa show no evidence for aridification abstract changes in the record of vertebrate assemblage zones in the karoo basin south africa serve as a model for the response of terrestrial ecosystems to the end permian biotic crisis vertebrate turnover from the daptocephalus to lystrosaurus assemblage zone is believed to have begun with the appearance of subtle siltstone color variance and is coeval with a unique laminated lithofacies both of which are interpreted by other workers to represent evidence for an aridification trend the laminated facies consists of interbedded greenish gray and dark reddish gray siltstone with coloration of the latter reported as a function of an increasing eolian component the current study combines stratigraphy petrography geochemistry and rock magnetic properties of an interlaminated succession and lateral equivalents at old lootsberg pass in the eastern cape province to determine whether such subtle color variance is a function of aridification and hence climate change siltstones were evaluated from intervals both below and above a pedogenic nodule bearing feldspathic wacke that is physically correlated over a 0 5 km distance the lower succession consists of interbedded greenish gray sensu latu and reddish gray sensu latu siltstone in which undisturbed and minimally disturbed primary sedimentary along with few secondary biogenic structures are interpreted to represent deposition in an abandoned channel fill complex massive greenish gray and dark reddish gray siltstone above the channel complex demonstrate that coloration is variable across laterally equivalent strata both lithologies were assessed using x ray fluorescence x ray diffraction mossbauer spectroscopy scanning electron microscopy with eds and bulk magnetic susceptibility stepwise acquisition of an isothermal remanent magnetization irm and backfield direct field demagnetization our data indicate that there is no statistically significant difference in major element concentrations between lithologies and that subtle color difference is a function of the presence of fine lystrosaurus assemblage zone was not arid in contrast the landscape was wet that allowed for the continued growth of a permian age flora under conditions of high water table that experienced temporal fluxes in the hydrological regime promoting spatial color modification of sediment

abrupt and gradual extinction among late permian land vertebrates in the karoo basin south africa the karoo basin of south africa exposes a succession of upper permian to lower triassic terrestrial strata containing abundant terrestrial vertebrate fossils paleomagnetic magnetostratigraphic and carbon isotope data allow sections to be correlated across the basin with this stratigraphy the vertebrate fossil data show a gradual extinction in the upper permian punctuated by an enhanced extinction pulse at the permian triassic boundary interval particularly among the dicynodont therapsids coinciding with negative carbon isotope anomalies

p and s wave tomography of the mantle beneath the united states mantle seismic structure beneath the united states spanning from the active western plate margin to the passive eastern margin was imaged with teleseismic p and s wave traveltime tomography including usarray data up to may 2014 to mitigate artifacts from crustal structure 5 40 s rayleigh wave phase velocities were used to create a 3 d starting model major features of the final p and s models include two distinct low velocity anomalies at depths of 60 300 km beneath the central and northern appalachians and passive margin the central appalachian low velocity anomaly coincides with eocene basaltic magmatism and the northern anomaly is located along the cretaceous track of the great meteor hot spot at depths of 300 700 km beneath the central and eastern u s large high velocity anomalies are inferred to be remnants of the farallon slab that subducted prior to 40 ma during the laramide orogeny

late quaternary paleoclimates and biotic responses in eastern north america and the western north atlantic ocean abstract broad scale late quaternary paleoclimatic changes are interpreted from palynological records across eastern north america and from assemblages of marine foraminifera in the western north atlantic ocean quantitative reconstructions of past dominance for major tree taxa at eight fossil pollen sites located south of the maximum glacial extent in the southeastern united states illustrate dramatic responses of tree populations to climatic change during the transition from pleistocene to holocene conditions a series of maps depicting changes in inferred boundaries of predominant airmasses during the late quaternary are based upon paleoclimatic interpretation of paleovegetation maps for eastern north america and climap maps of winter sea surface temperatures for the western north atlantic ocean in the eastern united states at 18 000 b p strong zonal circulation resulted in a fixed position of the atmospheric polar frontal zone along 33 n latitude the pacific airmass extended from 33 n latitude north to the southern margin of the laurentide ice sheet with the maritime tropical airmass dominating south of 33 n across the gulf coastal plain the gulf of mexico and the equatorial atlantic ocean the oceanic polar frontal zone extended northeastward from cape hatteras to 37 n in the western north atlantic ocean late glacial climatic amelioration was first reflected in vegetational changes south of the laurentide ice sheet beginning at 16 500 b p late glacial weakening in zonal atmospheric flow resulted in the penetration of the maritime tropical airmass farther to the north during the summer season increased summer warmth and rain produced substantial melting of the southern flank of the laurentide ice sheet the early holocene interval from 12 500 to 8 000 b p bracketed the time of maximum seasonality of solar radiation ca 11 000 b p during the early holocene enhanced meridional air flows resulted in increased seasonality of temperatures by 10 000 b p the oceanic polar frontal zone was displaced northward from the gulf stream anomalously cold maritime climatic conditions persisted along the central atlantic coast reflecting the position of the cold marine labrador current between the atlantic seaboard and the gulf stream during the mid holocene or hypsithermal interval from 8 000 to 4 000 b p prevailing westerlies expanded the midcontinental region of warmth and aridity for the last 4 000 years the modern climatic regime has been characterized by increased meridional flow

permian climate development in the northern peri tethys area the lodeve basin french massif central compared in a european and global context abstract the lodeve basin which contains an exceptional long and nearly uninterrupted profile of early to late permian continental red beds is well correlated to the other european permocarboniferous basins together they cover the time span from the late pennsylvanian to the permian triassic boundary although these basins were placed within the equatorial belt for the whole permian several climatic changes are recorded in the sediments terrestrial sedimentation is governed by the interaction of climate and tectonics as well as by volcanism to a variable degree therefore small scale climatic variations of the milankovitch band are hardly discernable and if so they could not be correlated between different basins indeed larger scale climatic shifts could be identified it is shown that the shift from the carboniferous icehouse to the mesozoic warmhouse was a multi stage process this global warming resulted in a general aridisation of northern pangea indicated by outspreading playa and sabkha red beds aeolianites and evaporites several short phases of increased humidity interrupted this trend indicated by wet red beds lake sediments and coal deposits in central and southern europe these wet periods are traceable within the late stephanian lower rotliegend gzhelian asselian topmost lower rotliegend asselian sakmarian upper rotliegend i late artinskian early kungurian and upper rotliegend ii zechstein wuchiapingian the aridisation of the northern pangea which accelerated near the sakmarian artinskian transition is attributed to a reorganisation of the major ocean currents cold water currents along the western flank of the pangea indicated by the permian chert event blocks moisture transport from west onto the continent during roadian and wordian the onset of an additional cold water current along the cimmerian continents blocks moisture transport from the east both phenomena together are responsible for the maximum of aridity at the early to middle permian transition additionally the equatorial climate has been affected by an increasing seasonality within the late pennsylvanian and permian caused by the wide shifting of the zone of inter tropical convergence itc over the equator based on a new reconstruction of the pangean assembly in this paper climatic changes in the permian are interpreted and causes of the arid humid arid shifts are examined phases of higher humidity are often related to events of global impact like the waxing and waning of the gondwanan glaciation obtained in the south african karoo basin dwyka group but also regional events had strong climatic influence the zechstein transgression in the northern and southern permian basin as well as the bellerophon transgression of the southern alps caused the wet phase in the wuchiapingian

significance of different modes of rhizolith preservation to interpreting paleoenvironmental and paleohydrologic settings examples from paleogene paleosols bighorn basin wyoming u s a abstract different modes of preservation of root traces rhizoliths provide information on soil moisture regimes in alluvial paleosols in the paleogene fort union and willwood formations of the bighorn basin wyoming u s a this paper links different styles of rhizolith preservation to paleosols whose other pedogenic attributes provide information on ancient soil drainage consequently the paleodrainage significance of different rhizolith preservation patterns is established more confidently rhizoliths consisting of elongate gray mottles rhizohaloes with red rims are common in relatively well drained red paleosols the gray zones are depleted of iron fe whereas the color of the rims indicates hematite accumulation these features are typical of surface water gley processes that caused fe and manganese mn to move from the root channel outward to the soil matrix calcareous rhizocretions either calcareous tubular concretions or micro accumulations of carbonate within gray rhizotubules are also common in moderately well drained red paleosols more poorly drained purple paleosols also have rhizoliths consisting of fe depletion zones however the rhizohaloes are surrounded by yellow brown goethite rims rather than red hematitic rims in many paleosols the red and yellow brown accumulation rims were partly removed by continued depletion producing abundant irregular shaped mottles the nature of the rhizohalo and the color of the fe oxide rim provide information about the intensity of gleying that a paleosol underwent the poorly drained paleosols also show rhizoliths preserved as goethite accumulations contained within gray depletion zones indicating movement of reduced fe from the matrix towards the root channel probably as a result of groundwater gley processes the goethite accumulations are intermingled locally with lignite representing preservation of the root organic material some rhizoliths are preserved as tube shaped concentrations of small 0 1 0 2 mm diameter black spheres whose color indicates a mix of mn and fe oxides these are most common in paleosols with low chroma gray matrix colors indicating very poor drainage the very poorly drained paleosols also show rhizoliths preserved in jarosite which is an oxidation product of pyrite careful observational and geochemical analysis of rhizoliths which are common in continental deposits can help produce a clearer and more thorough interpretation of ancient drainage conditions information about degree of ancient soil wetness or moisture is important for understanding past climatic conditions and for reconstructing terrestrial paleolandscapes

estimating rates of denudation using cosmogenic isotope abundances in sediment we propose as a testable hypothesis a basin scale approach for interpreting the abundance of in situ produced cosmogenic isotopes an approach which considers explicitly both the isotope and sediment flux through a drainage basin unlike most existing models which are appropriate for evaluating in situ produced cosmogenic isotope abundance at discrete points on earth s surface our model is designed for interpreting isotope abundance in sediment because sediment is a mixture of materials in favourable cases derived from throughout a drainage basin we suggest that measured isotope abundances may reflect spatially averaged rates of erosion we investigate the assumptions and behaviour of our model and conclude that it could provide geomorphologists with a relatively simple means by which to constrain the rate of landscape evolution if a basin is in isotopic steady state and if sampled sediments are well mixed

geodynamic and geomorphic evolution of the permo triassic appalachian mountains abstract the basic topography of a steady state accretionary mountain range is a function of the critical taper of the accretionary wedge which in turn depends upon the convergence flux at the toe internal rock strength basal slope and erosion rate off the top it is possible to obtain a first order estimate of this topography for ancient mountain ranges by constraining these parameters using sediment thicknesses in adjacent flexurally produced sedimentary basins here we apply the technique to the early permian central appalachians by first obtaining the steady state mass of the wedge from a flexural loading model of beaumont and others then the equations of a critically tapered wedge are solved using a monte carlo method of parameter selection those solutions that match the observed mass of the wedge suggest that the early permian appalachians possessed a central andean topography with average relief of from 3 5 4 5 km and width of 250 300 km

vertebrate extinction across permian triassic boundary in karoo basin south africa distinct assemblages of paleosols above and below the permian triassic boundary in the karoo basin of south africa are evidence for reorganization of ecosystems following this greatest of all mass extinctions the permian triassic boundary is recognized from the last appearance of dicynodon and from a series of negative excursions in the isotopic composition of carbon within therapsid tusks pedogenic carbonate nodules and organic matter the boundary is also marked by laminated beds with very weakly developed paleosols a change from purple 10r to brownish red 2 5yr paleosols and a thin 10 cm claystone breccia of reworked soil clasts paleoclimatic changes include a shift from arid and highly seasonal paleoclimate inferred from diffuse and shallow calcareous nodules in permian paleosols to semiarid and less seasonal paleoclimate inferred from deep and well focused calcic horizons in triassic paleosols an earliest triassic shift to warmer and wetter paleoclimate is also indicated by increased chemical weathering abundance of lycopsids and diversity of labyrinthodonts permian paleosols have root traces comparable to those of open shrubland and riparian woodland whereas triassic paleosols have root traces and profile forms like soils of open woodland this is a significant paleoenvironmental change but not as dramatic a change as would be expected from the devastating extinctions of 88 of fossil vertebrate genera latest permian therapsid reptiles were diverse and ecologically specialized in contrast the principal earliest triassic therapsid lystrosaurus was a burrower with no specific habitat preference its short internal nares barrel chest and high neural spines would have given it greater aerobic scope than preexisting therapsids and may have been an advantage under conditions of hypercapnia and hypoxia these adaptations and associated ecosystem changes are compatible with widespread vertebrate mortality by acidosis and pulmonary edema in a post apocalyptic greenhouse created by the voluminous release of methane from shallow marine and permafrost clathrates

latest permian paleosols from wapadsberg pass south africa implications for changhsingian climate terrestrial settings preceding the endpermian crisis are reported to trend toward increasingly dry and arid conditions resulting in landscape change and a shift in fl architectures and regimes much of the latest permian changhsingian stratigraphic record in the karoo basin south africa consists of paleosols which record the physical conditions across time and space preboundary sequences at wapadsberg pass eastern cape province provide insight into the climate regime that infl uenced paleosol formation at that time a high resolution sedimentological and geochemical study of two stacked aggradational paleosols in conjunction with stable isotope geochemical characterization of paleosol carbonate cemented concretions over a 90 m section at this locality demonstrates that these landscapes were predominantly wetland terrains without a demonstrable trend in increasing drying up to the permian triassic boundary as defi ned by vertebrates in the area two paleosols examined 70 m below the permian triassic boundary are identifi ed as protosols and the former soil air interface of each is marked by an autochthonous forestfl oor litter in which canopy leaves of glossopteris and groundcover plants of trizygia are preserved molecular weathering ratios e g base loss clayeyness chemical index of alteration minus potassium cia k etc determined from these horizons are indicative of immature soil development under watersaturated conditions assuming that paleosol matrix concentrations of trace elements are indicative of permian soil solution chemistries high concentrations of ni cu ba and cr may have been growth stress factors that may account for the small glossopterid leaf size in the megafl oras in contrast to current models that implicate stress in response to climate change stable isotope 18 o and 13 c values are presented for micritic and microspar 20 m calcite cements from carbonate nodules collected at 15 horizons through a 90 m stratigraphic interval up to and including the permian triassic boundary these isotopic ratios exhibit dissimilar trends no clear trend exists in 18 o peedee belemnite pdb values range from 14 7 to 21 8 in contrast a trend exists in 13 c values where carbonate cements almost certainly precipitated under well drained conditions in an interval that is 60 m below the permiantriassic boundary 5 3 while 13 c values as low as 16 9 indicative of water logged conditions begin 90 m below and continue up to the permian triassic boundary hence no evidence is found for a preboundary trend toward increasing aridity at this locality the fi rst estimates of the latest permian atmospheric pco2 from paleosols based on coexisting calcite and organic matter 13 c values from paleosols that developed under well drained conditions provide a range of values from 900 to 1900 and 500 to 1300 ppmv respectively which are signifi cantly lower than the latest early permian when terrestrial biome replacement is documented to have occurred

constraining landscape development of the sri lankan escarpment with cosmogenic nuclides in river sediment escarpments are prominent morphological features along high elevation passive margins recent studies integrating geomorphology thermochronology and cosmogenic nuclide based denudation rate estimates suggest a rapid phase of denudation immediately after the earliest stages of seafloor spreading and subsequent slow denudation rates since to constrain the geomorphic evolution of passive margins we have examined the development of the sri lankan escarpment cosmogenic nuclide data on river sediment along a north south transect across the southern escarpment reveal that the landscape is eroding ten times more rapidly in the escarpment zone 26 to 71 mm kyr 1 than in the high elevation plateau above it and in the lowland plain beneath it 2 6 to 6 2 mm kyr 1 unlike these low denudation rate areas the escarpment denudation is strongly and linearly hill slope dependent this shows that denudation and retreat are tightly interlinked within the escarpment which suggests that the escarpment is evolving by rift parallel retreat rather than by escarpment downwearing supporting evidence is provided by the morphology of rivers draining the escarpment zone these have steep bedrock channels which show sharp and prominent knickpoints along their longitudinal profiles it appears that fluvial processes are driving escarpment retreat as rivers migrate headwards were they incise into the high elevation plateau however the average catchment wide denudation rates of the escarpment zone are low compared to the denudation rates that are estimated for constant escarpment retreat since rifting in common with other escarpments worldwide causes for this slow down can be tectonic change related to flexural bending of the lithosphere climate change that would vary the degree of precipitation focused into the escarpment or the decrease in the contributing catchment area which would reduce the stream power available for fluvial erosion c 2006 elsevier b v all rights reserved

stratigraphic classification of ancient lakes balancing tectonic and climatic controls lakes and lake deposits present two fundamental paradoxes 1 modern lakes are vastly complicated but the rock records of lakes are relatively simple extensive observations reveal three distinct facies associations of common and widespread occurrence these are referred to here as fluvial lacustrine fluctuating profundal and evaporative facies associations 2 most explanations of modern and ancient lakes attribute their nature to climate but neither modern lake parameters lake size depth and salinity nor the character of ancient lake strata thickness extent lithology correlate with measured or inferred climatic humidity we propose that it is the relative balance of rates of potential accommodation mostly tectonic with sediment water fill mostly a function of climate that controls lake occurrence distribution and character lake basins may be termed overfilled balanced fill or underfilled depending on the balance between these rates we conclude that climate and tectonics exert coequal influence on lake deposits at both mesoscales 1 m to hundreds of meters and macroscales hundreds to thousands of meters

permian tetrapod extinction events abstract four substantial tetrapod extinctions have been identified during the permian but only one of these is an apparent mass extinction analyses of global compilations of the family level diversity of permian tetrapods have been confounded by incorrect and compiled correlations instead analyzing diversity patterns at the genus level in best sections identifies only one apparent mass extinction of permian tetrapods much evolutionary turnover took place among tetrapods during the latter part of the early permian and had been identified as a single mass extinction at the artinskian kungurian boundary however the only stratigraphically dense tetrapod record of the late early permian from the southwestern usa indicates a succession of extinctions spread out from redtankian through littlecrontonian kungurian time not a single mass extinction olson s gap remains a hiatus in the global record of permian tetrapods equivalent to part of the kungurian roadian across the gap eupelycosaur dominated assemblages were replaced by therapsid dominated assemblages but the claim that this is associated with a mass extinction olson s extinction has been based on compressing all of the extinctions of the redtankian littlecrotonian and olson s gap into one event recognition of olson s gap does not preclude the possibility of an extinction at the early middle permian boundary olson s extinction however the gap in the tetrapod fossil record makes it impossible to establish the magnitude precise timing and structure of the extinctions that took place across olson s gap the only permian mass extinction of tetrapods is the dinocephalian extinction event during the gamkan near the end of the guadalupian which saw the total extinction of dinocephalians and major diversity drop in therocephalians in the karoo basin of south africa this extinction is the loss of at least 64 of generic diversity the changeover from dinocephalian assemblages to assemblages without dinocephalians in other parts of permian pangea suggests that the dinocephalian extinction event was a global event the late permian tetrapod extinctions are older than the end permian marine extinctions furthermore the magnitude of the diversity drop and ecological severity of the end permian tetrapod extinctions have been greatly overstated best sections analysis in the karoo basin indicates a stepwise late permian tetrapod extinction during deposition of the upper dicynodon assemblage zone that took at least 250 000 and perhaps more than a million years the culmination of this stepwise extinction across the highest occurrence of dicynodon boundary of platbergian and lootsbergian land vertebrate faunachrons is a loss of genera not much above an inferred background extinction rate of permian tetrapod genera and resembles the amount of turnover seen at several other boundaries of permian and triassic land vertebrate faunachrons the case for coeval land plant insect and tetrapod extinctions during the permian is a weak one the first coeval marine and nonmarine mass extinctions of the phanerozoic were likely the end guadalupian extinction climate change notably greenhouse climates may have driven permian tetrapod extinctions but that hypothesized relationship needs better documentation

rates of erosion and landscape change along the blue ridge escarpment southern appalachian mountains estimated from in situ cosmogenic 10be the blue ridge escarpment located within the southern appalachian mountains of virginia and north carolina forms a distinct steep boundary between the lower elevation piedmont and higher elevation blue ridge physiographic provinces to understand better the rate at which this landform and the adjacent landscape are changing we measured cosmogenic beryllium 10 10be in quartz separated from sediment samples n 50 collected in 32 streams and from three exposed bedrock outcrops along four transects normal to the escarpment allowing us to calculate erosion rates integrated over 104 105 years these basin averaged erosion rates 5 4 49 m myr 1 are consistent with those measured elsewhere in the southern appalachain mountains and show a positive relationship between erosion rate and average basin slope erosion rates show no relationship with basin size or relative position of the brevard fault zone a fundamental structural element of the region the cosmogenic isotopic data when considered along with the distribution of average basin slopes in each physiographic province suggest that the escarpment is eroding on average more rapidly than the blue ridge uplands which are eroding more rapidly than the piedmont lowlands this difference in erosion rates by geomorphic setting suggests that the elevation difference between the uplands and lowlands adjacent to the escarpment is being reduced but at extremely slow rates copyright 2016 john wiley sons ltd

permo triassic fluvial systems in the southeastern karoo basin south africa abstract a prominent clastic wedge of latest permian to early triassic age katberg sandstone prograded northwestwards into the main karoo basin from a southerly source area as a sedimentary response to renewed tectonism associated with the cape fold belt proximal to distal relationships within this clastic wedge and its relationships with underlying and overlying formations reveal a variety of stream types which reflect changing tectonic and climatic conditions towards the close of permian times the depositional area of the southeastern karoo basin was crossed by meandering river channels cutting through earlier formed floodplain deposits balfour formation tectonic rejuvenation of the source area in early triassic times led to steeper gradients and a sharp increase in the supply of coarser grained detritus as a result alluvial fans developed in areas adjacent to the source terrane and the river channels became braided depositing only sands katberg sandstone with muds and silts being carried down into the most distal parts of the floodplain burgersdorp formation subsequent denudation of the source area gradually reduced slopes and allowed the source ward shift of the distal facies until it eventually overstepped the earlier formed braided stream deposits accompanying the changes in tectonic conditions was a change in climatic which also influenced stream type the late permian to early triassic period records a general change to warmer climatic conditions following the widespread glaciation of the early to middle permian thus the lowest beaufort group sediments were probably deposited in warm temperate to humid conditions with later deposits being laid down under an increasingly arid regime

palaeoenvironments and palaeotectonics of the arid to hyperarid intracontinental latest permian late triassic solway basin u k abstract the late permian to late triassic sediments of the solway basin consist of an originally flat lying laterally persistent and consistent succession of mature dominantly fine grained red clastics laid down in part of a very large intracontinental basin the complete absence of body or trace fossils or palaeosols indicates a very arid hyperarid depositional environment for most of the sediments at the base of the succession thin regolith breccias and sandstones rest unconformably on basement and early permian rift clastics overlying gypsiferous red silty mudstones very fine sandstones and thick gypsum were deposited in either a playa lake or in a hypersaline estuary and their margins these pass upwards into thick bedded multi storied fine to very fine grained red quartzo felspathic and sublithic arenites in which even medium sand is rare despite channels with clay pebbles up to 30 cm in diameter above thick trough cross bedded and parallel laminated fine grained aeolian sandstones deposited in extensive barchanoid dune complexes pass up into very thick multicoloured mudstones and gypsum deposited in marginal marine or lacustrine sabkha environments the latter pass up into marine lower jurassic shales and limestones thirteen non marine clastic lithofacies are arranged into five main lithofacies associations whose facies architecture is reconstructed where possible by analysis of large exposures the five associations can be compared with the desert pavement arid ephemeral stream sabkha saline lake and aeolian sand dune environments of the arid to hyperarid areas of existing intracontinental basins such as lake eyre and lake chad the accommodation space in such basins is controlled by gradual tectonic subsidence moderated by large fluctuations in shallow lake extent caused by climatic change and local variation and this promotes a large scale layer cake stratigraphy as exemplified in the solway basin here the dominant fine grained mature sandstones above the local basal reg breccias suggest water reworking of wind transported sediment as in the northern part of the lake chad basin growth faulting occurs in places in the solway basin caused by underlying evaporite movement but these faults did not significantly affect pre late triassic sedimentation and did not expose pre permian units above the basal breccias there is no evidence of post early permian rifting anywhere during deposition of the late permian to middle triassic british succession although the succession is often interpreted with a rift basin model the arid to hyperarid palaeoclimate changed little during deposition of the solway basin succession in contrast to lakes eyre and chad and this is attributed to tectonic and palaeolatitude stability unlike the later mesozoic cenozoic only limited plate movements took place during the triassic in western europe palaeolatitude changed little and the solway basin remained in the northern latitudinal desert belt from early to mid triassic times however the influence of the early triassic impoverished biota on environmental interpretations needs further study

δ13c values of carbonate nodules across the permian triassic boundary in the karoo supergroup south africa reflect a stinking sulfurous swamp not atmospheric co2 abstract paleosol macromorphology petrography and stable isotope geochemistry of carbonate nodules from permo triassic p t boundary strata of the central karoo basin south africa are presented in order to evaluate their utility as geochemical archives of permian triassic paleoatmospheric chemistry and their potential to provide a terrestrial carbon isotope chemostratigraphy for correlation with contemporaneous global marine 13 c records paleosol morphologies across p t boundary strata of the central karoo basin indicate the region was a poorly drained seasonally to continuously flooded bottomland radiaxial calcite microspar and micrite microtextures are observed in the calcite nodules associated with p t paleosol profiles micritic calcite is typical of soil carbonate that forms in well drained soils characterized by open system gaseous diffusion between the soil and global atmosphere whereas more coarsely crystalline textures and radiaxial calcite are more typical of crystallization in phreatic environments with limited gaseous diffusion between the soil and global atmosphere in this regard only those nodules composed of micritic calcite can be considered as a potentially reliable source of proxy information for paleoatmospheric 13 c values across the p t boundary the 13 c values of all carbonate nodules from two overlapping measured sections near carlton heights south africa range from 24 4 to 1 8 whereas micritic calcite nodule 13 c values range from 7 0 to 21 3 comparison of calcite 13 c values with penecontemporaneous organic matter 13 c values indicate that calcite 13 c values 13 c values rather these more negative carbonate nodule 13 c values likely reflect calcite crystallization under poorly drained swampy conditions characterized by a semi closed chemical system that evolved independently of earth s troposphere therefore previously reported negative carbon isotope shift s measured from carbonate nodules in the karoo basin p t strata do not provide a record of atmospheric 13 c and probably do not provide a viable carbon isotope stratigraphy that can be realistically correlated with global p t marine carbon isotope stratigraphies