sequence stratigraphy of the neoproterozoic infra krol formation and krol group lesser himalaya india a bstract a sequence stratigraphic study of terrigenous and carbonate rocks of the infra krol formation and krol group in the lesser himalaya fold and thrust belt of northern india was undertaken as part of a broader investigation of the significance of carbon isotope data in neoproterozoic successions eight regional stratigraphic discontinuities were traced over a distance of nearly 300 km and interpretations were anchored in a series of local studies involving the mapping of key beds and the measurement of closely spaced sections three of the regional surfaces are interpreted as sequence boundaries on the basis of 1 locally developed incised valleys 60 m deep 2 paleokarstic depressions with 50 m of mappable relief 3 subaerial dissolution and weathering products breccias and calcrete filling vertical fissures dikes cavities and shallow de pressions in underlying carbonate rocks and 4 small scale evidence for sub aerial exposure at an erosion surface the remaining five discontinuities are regional flooding surfaces identified on the basis of either facies changes with an abrupt upward deepening across the surface or transitions in facies stacking patterns typically from forestepping to backstepping a glacio eustatic origin is permitted although not required for the three sequence boundaries but no evidence has been found for marked lowering of sea level at other horizons a mismatch between the stratigraphic location of sequence boundaries and car bon isotope minima suggests that local diagenetic alteration or oceanographic phenomena unrelated to glaciation may be in part responsible for observed isotopic variation and that small ice sheets may have existed during apparently nonglacial times without producing either cap carbonates or negative carbon isotope excursions

anomalies in global carbon cycling and extinction at the triassic jurassic boundary evidence from a marine c isotope record this study investigates whether the end triassic biotic crisis was coupled with a perturbation of the marine c isotope budget the marine c isotope signature serves as a proxy of the marine carbon reservoir and ultimately of the global c cycle a continuous shallow water marine limestone succession from the western southern alps bergamasc alps northern italy provides information on the end triassic biotic crisis and on the evolution of the marine carbon reservoir across the triassic jurassic t j boundary the established carbonate c isotope curve is marked by a negative c isotope pulse coinciding with the disappearance of the end triassic benthic faunal assemblage and a widespread rhaetian carbonate platform drowning event the negative spike is followed by a positive c isotope excursion starting at the palynological t j transition the negative c isotope pulse may have resulted from the sudden release of gas hydrates the positive isotope excursion records a global change in organic carbon burial rates probably in response to elevated atmospheric co2 levels at a time of massive volcanic activity in the central atlantic magmatic province high co2 levels were responsible for the end triassic biocalcification crisis carbonate platform collapse and possibly the sudden release of methane from gas hydrate

changing climate changing process implications for salt transportation and weathering within building sandstones in the uk salt weathering is a crucial process that brings about a change in stone from the scale of landscapes to stone outcrops and natural building stone facades it is acknowledged that salt weathering is controlled by fluctuations in temperature and moisture where repeated oscillations in these parameters can cause re crystallisation hydration de hydration of salts bringing about stone surface loss in the form of for example granular disaggregation scaling and multiple flaking however this traditional view of how salt weathering proceeds may need to be re evaluated in the light of current and future climatic trends indeed there is considerable scope for the investigation of consequences of climate change on geomorphological processes in general building on contemporary research on the deep wetting of natural building stones it is proposed that as stone may be wetter for longer ion diffusion may become a more prominent mechanism for the mixing of molecular constituents and a shift in focus from physical damage to chemical change is suggested data from ion diffusion cell experiments are presented for three different sandstone types demonstrating that salts may diffuse through porous stone relatively rapidly in comparison to for example dense concrete pore water from stones undergoing diffusion experiments was extracted and analysed factors controlling ion diffusion relating to time of wetness within stones are discussed continued saturation connectivity of pores mineralogy behaviour of salts sedimentary structure and potential changes in system dynamics as a result of climate change are addressed system inputs may change in terms of increased moisture input translating into a greater depth of wetting front salts are likely to be stored differently in stones with salt being in solution for longer periods during prolonged winter wetness this has myriad implications in terms of the movement of ions by diffusion and the potential for chemical change in the stone especially in more mobile constituents leading to a weakening of the stone matrix grain boundary cementing the output may be mobilisation and precipitation of elements leading to for example uneven cementing in the stone this reduced strength of the stone or compromised ability of the stone to absorb stress is likely to make crystallisation a more efficacious mechanism of decay when it does occur thus a delay in the onset of crystallisation while stonework is wet does not preclude exaggerated or accelerated material loss when it finally happens

c isotopic stratification in a neoproterozoic postglacial ocean we report c isotopic data from the cap carbonate overlying the terminal proterozoic nantuo diamictites in south china the c isotopic measurements reveal a large c isotopic gradient of 3 along paleoenvironmental transect from shelf to deep basinal sedimentary facies the c isotopic stratification may attribute to the effect of biological pumping in a postglacial ocean our results confirm that the sea level rise was rapid and that atmospheric co2 was significantly high immediately following deglaciation

cambrian ordovician depositional sequences in the middle east a perspective from turkey abstract in southern turkey taurus chain or taurides and southeastern turkey border folds of the arabian plate nearly complete cambrian to ordovician successions are preserved four major sedimentary sequences are defined according to the main transgressive events and the subsequent shelf progradations these sequences allow us to link the turkish mostly distal lower palaeozoic detritals to the more proximal arabian formations in spite of contrasting facies the lower palaeozoic development is outlined through four successive steps defined in southern turkey 1 initiation of a cratonic platform regime terreneuvian i e earliest cambrian depositional sequence 1 with fluviatile conglomerates and red bed sediments associated with volcanics 2 development of a stable marine platform late terreneuvian to early ordovician depositional sequences 2 and 3 including widespread but diachronous middle cambrian carbonates and subsequent storm dominated detritals 3 tectonic instability middle ordovician leading to a new palaeogeography on the gondwana platform with the differentiation of a sag basin bedinan qasim depocenter lower part of depositional sequence 4 and 4 glaciation latest ordovician upper part of depositional sequence 4 identified by glaciomarine deposits forming the hirnantian glacial record this thick 2000 m detrital succession records a first order long term subsidence driven cambrian to ordovician transgressive trend and includes second order sequences reflecting interactions between global eustasy and tectonic instability on a larger scale the identification of recurrent sequence stratigraphic features with similar trends in the cambrian ordovician successions on the arabian platform implies that a former location of the taurus domain cannot be situated in the present day eastern mediterranean area but should lie directly north of the arabian platform this location places southern turkey at the junction between the north african segment of the gondwana siliciclastic shelf to the west present day coordinates and the eastern arabian segment in good agreement with mixed faunal signatures from both areas primary control of the tectonostratigraphic development of southern turkey during the lower palaeozoic may be a forced evolution from arc platform to rift drift transitions cordilleran model that has migrated progressively eastwards from the avalonian domain along the northern gondwana margin to the arabian domain throughout the lower palaeozoic

salt weathering simulations under hot desert conditions agents of enlightenment or perpetuators of preconceptions because of access difficulties and inhospitable environmental conditions our understanding of rock weathering in hot deserts has been strongly influenced by laboratory simulations however a risk exists that results may come to owe more to experimental design than to actual environmental conditions experienced at the atmosphere rock surface interface this was especially true in early salt weathering simulations that seemingly sought to reinforce the orthodoxy of a physically dominated weathering environment driven by extremely high absolute temperatures and large diurnal temperature ranges however improvements in environmental sensors over the last 20 years have established the complexity of desert climates and the importance of microclimatic controls and allowed considerable refinement of experimental design this overview evaluates the implications of recent simulation studies and presents new information on possible fatigue effects of differential thermal expansion of salts and the salt weathering of test blocks under compressive loading in doing so it demonstrates how physical rock properties change during experimentation the importance of short term surface temperature fluctuations distinctions between the weathering of unconfined debris and larger rock surfaces the importance of moisture and salt applications that replicate their availability in deserts the importance of rock thermal properties in controlling their weathering response in environments dominated by radiative heating and cooling and the overall complexity of weathering regimes

effects of direct and indirect heating on the validity of rock weathering simulation studies and durability tests rock surface and subsurface temperature responses in samples exposed to direct heating insolation under natural hot desert conditions reveal considerable variability between lithologies related to differences in thermal properties especially albedo and thermal conductivity however when the same samples are heated indirectly by air in an oven based environmental cabinet lithological differences in temperature response disappear and all samples attain temperatures similar to the air temperature within the cabinet rates and patterns of rock decay produced in such environmental cabinets may not therefore reflect those encountered under natural conditions where breakdown is related to micro environmental conditions at the rock air interface and where rock temperature is one of the most important controlling factors in addition to implications for assessment of weathering effectiveness use of only indirect forms of heating affects the determination of comparative rock durability because all rock types are cycled through the same temperature regimes because temperature exerts such a major control on rock breakdown through its control on physical and chemical weathering processes all significant factors influencing it must be included in the design of weathering simulations and durability tests

daytime rock surface temperature variability and its implications for mechanical rock weathering tenerife canary islands summary summer and winter rock surface temperature measurements are presented from three sites along an altitudinal gradient significant between and within site variability is recognised related to insolation cloud cover and air temperature differences maritime influences and time of year the variability argues against the use of a single rock temperature regime to characterise hot desertic environments in for example weathering simulation studies superimposed upon diurnal patterns of heating and cooling are numerous short 3 15 minutes and medium term 1 2 hours fluctuations related to wind speed and cloud cover variations rates of surface temperature change are very high during these fluctuations 3 c minute and it is proposed that they may enhance the operation of a number of mechanical rock weathering mechanisms

facies stratigraphy and evolution of a middle ediacaran carbonate ramp khufai formation sultanate of oman the khufai formation is the oldest carbonate platform of the cryogenian to lowermost cambrian huqf supergroup a stratigraphic characterization of this unit includes detailed facies descriptions a sequence stratigraphic interpretation and evaluation of lateral heterogeneity and overall ramp evolution the khufai formation comprises one and one half depositional sequences with a maximum flooding interval near the base of the formation and a sequence boundary within the upper peritidal facies most of the deposition occurred during highstand progradation of a carbonate ramp facies tracts include outer ramp and midramp mudstones and wackestones ramp crest grainstone shoal deposits and extensive inner ramp microbially dominated peritidal deposits outcrops in the oman mountains are deep water deposits including turbiditic grainstone and wackestone interbedded with siliciclastic rich siltstone and crinkly laminite facies patterns and parasequence composition are variable both laterally across the outcrop area and vertically through time because of a combination of ramp morphology siliciclastic supply and possible syndepositional faulting the lithostratigraphic boundary between the khufai formation and the overlying shuram formation is gradational and represents significant flooding of the carbonate platform the stratigraphic characterization presented here along with the identification of key facies and diagenetic features will help further future exploration and production of hydrocarbons from the khufai formation

a simple theoretical approach to the thermal expansion mechanism of salt weathering abstract the traditional plate theory in solid mechanics is used to estimate the thermal stress caused by a superficial salt layer on a rock substrate this preliminary investigation theoretically demonstrates that the thermal expansion of superficial salt layers is difficult to result in rock breakdown during the process of salt weathering

selective weathering of cross bedded layers forming shelters and small caves on akopan tepui venezuela field laboratory and experimental evidence about diagenesis and weathering of the mataui formation arenites roraima supergroup middle proterozoic abstract south american table top mountains tepuis are formed by quartzites and sandstones of mataui formation belonging to the roraima supergroup lower to middle proterozoic field observations in the northern part of akopan tepui in venezuela revealed that unlike the beds with flat bedding the cross bedded layers are commonly affected by selective weathering expressed by depressions shelters and even small caves all the arenites are fine grained most of them are likely of aeolian origin hardness measurements confirmed that the cross bedded layers are softer than the flat bedded or structureless beds occurring above and below them petrographic analysis showed that the rocks are mostly fine grained quartzites to quartz sandstones with original sand grains overgrown by syntaxial quartz cement and bearing signs of compaction manifested by local pressure solution some intergranular spaces are filled by newly formed phyllosilicates paragonite locally intergrown with muscovite in the overlying beds no porosity was observed by microscopic study and under sem whereas in the underlying rocks signs of slight weathering and etching of phyllosilicates was observed together with locally widened spaces along the grain to grain boundaries the samples from cross bedded layers display weathering the degree of which depends on the present access of flowing water where water has periodical access to the arenite it shows dissolution of quartz cement arenization together with complete leaching and removal of the phyllosilicates due to lateritization the intergranular spaces are considerably widened and quartz grains bear signs of strong skeletal etching and pitting samples from the sites where the water access ceased show mostly leaching of phyllosilicates with weak skeletal dissolution of quartz grains without pitting to imitate the origin of structures observed in the field experimental modelling was performed using artificially layered and compacted fine grained sands on which sodium silicate solution was dripped during soaking downward preferential penetration of the solution along the cross bedding laminae funnel flow was observed in the cross bedded layer the resulting structures display good lithification of horizontally layered sands and relatively poorer lithification of the cross bedded sediment between them showing triangular shaped overhangs and shelters which mimic those on the akopan tepui differential weathering of otherwise petrologically very similar arenites indicates that there had to be a difference in the initial porosity in the time of the rock denudation a preserved porosity in the cross bedded layers was necessary for the water rock contact to perform dissolution

some guidelines in reconstructing ancient sea conditions from wave ripplemarks abstract the collection of substantial field data on wave ripple mark spacing wavelength steepness grain size and symmetry index from the miocene burdigalian sandstones of western switzerland has allowed apparently close reconstruction of sea conditions results indicate however that ancient wave reconstructions must be restricted at present to data from relatively steep ripple marks vfi less than 7 5 i e vortex ripples data from the flatter ripple marks post vortex types formed at high oscillatory shear stresses do not provide reasonable estimates of wave conditions penecontemporaneous overwashing and or post depositional compaction ripple formation near the destruction condition rather than the threshold of sediment movement orbital diameters far exceeding ripple spacing and superimposed unidirectional currents are all factors which seriously affect wave reconstructions evaluation of ancient wave conditions provides insight into geologically important phenomena such as local water depth and basin size

near surface temperature cycling of stone and its implications for scales of surface deterioration abstract many previous studies into internal temperature gradients within stone have assumed smooth exponential increases and decreases in sub surface temperatures in response for example to diurnal patterns of heating and cooling and these have been used to explain phenomena such as large scale contour scaling this high resolution experimental study in which a porous limestone block was subjected to alternate surface heating and cooling using an infrared lamp demonstrates that internal temperature gradients in response to short term environmental cycles measured in minutes can in fact be complex and inconsistent results confirm the significance of very steep temperature stress gradients within the outer 10 mm or less of exposed stone below this the data indicate complex patterns of temperature reversals the amplitudes of which are attenuated with depth and which are influenced in their intensity and location by variations in the relative duration of heating and cooling phases it is suggested that the reversals might represent interference patterns between incoming and outgoing thermal waves but whatever their origin they are potentially important because they occur within the zone in which many stone decay processes especially salt weathering operate these processes invariably respond to temperature and moisture fluctuations and short term interruptions to insolation could for example trigger these fluctuations on numerous occasions over a day in particular the reversals occur at a scale that is commensurate with decay by multiple flaking and could indicate an underlying control on this previously little researched pattern of weathering in the context of this publication however the main lesson to be learned from this study is that differing scales of behaviour require different scales of enquiry

extreme winds and waves in the aftermath of a neoproterozoic glaciation the most severe excursions in the earth s climatic history are thought to be associated with proterozoic glaciations according to the snowball earth hypothesis the marinoan glaciation which ended about 635 million years ago involved global or nearly global ice cover at the termination of this glacial period rapid melting of continental ice sheets must have caused a large rise in sea level here we show that sediments deposited during this sea level rise contain remarkable structures that we interpret as giant wave ripples these structures occur at homologous stratigraphic levels in australia brazil canada namibia and svalbard our hydrodynamic analysis of these structures suggests maximum wave periods of 21 to 30 seconds significantly longer than those typical for today s oceans the reconstructed wave conditions could only have been generated under sustained high wind velocities exceeding 20 metres per second in fetch unlimited ocean basins we propose that these extraordinary wind and wave conditions were characteristic of the climatic transit and provide observational targets for atmospheric circulation models

evolution of a terminal neoproterozoic carbonate ramp system buah formation sultanate of oman effects of basement paleotopography the buah formation is a carbonate unit of late neoproterozoic age exposed in the jabal akhdar of northern oman and the huqf region of central oman the buah formation is interpreted as a distally steepened storm dominated ramp containing inner ramp tidally influenced oolitic shoal and back shoal lagoon fades and storm dominated mid ramp facies a slope break separates mid ramp facies from outer ramp facies characterized by accumulation of redeposited carbonates on gently inclined slopes 1 2 degrees combined facies stacking patterns and outcrop correlation via 1 3 c profiles suggest that buah carbonates formed as a highstand systems tract characterized by a general upward shallowing of facies and strong lateral progradation on a regional scale buah facies distributions across oman were controlled by the presence of basement highs defining areas of reduced subsidence which promoted lateral progradation of the buah carbonate ramp for tens of kilometers while the faster subsiding areas became sites of deep water deposition

extinction of cloudina and namacalathus at the precambrian cambrian boundary in oman biostratigraphic carbon isotope and u pb zircon geochronological data from the ara group of oman indicate an abrupt last appearance of cloudina and namacalathus coincident with a large magnitude but short lived negative excursion in the carbon isotope composition of seawater that is globally coincident with the precambrian cambrian boundary u pb zircon age data from an intercalated ash bed directly define this negative excursion to be at 542 0 0 3 ma consistent with previous age constraints from siberia and namibia combined with the global biostratigraphic record these new data strengthen hypotheses invoking mass extinction within terminal proterozoic ecosystems at or near the precambrian cambrian boundary

bioprotection and disturbance seaweed microclimatic stability and conditions for mechanical weathering in the intertidal zone as well as their destructive roles plants animals and microorganisms contribute to geomorphology and ecology via direct and indirect bioprotection which can reduce weathering and erosion for example indirect bioprotection can operate via biotic influences on microclimate whereby physical decay processes associated with fluctuations in temperature and moisture salt crystallization thermal fatigue and wetting drying are limited in the intertidal zone the spatial and temporal distribution of macroalgae seaweeds is patchy related to physical and ecological conditions for colonization and growth and the nature and frequency of natural and anthropogenic disturbance we examined the influence of seaweed canopies fucus spp on near surface microclimate and by implication on conditions for mechanical rock decay and under canopy ecology monitoring on hard artificial coastal structures in south west england uk built from limestone and concrete showed that both the range and maxima of daily summertime temperatures were significantly lower by an average of 56 and 25 respectively in areas colonized by seaweed compared to experimentally cleared areas short term microclimatic variability minutes hours was also significantly reduced by an average of 78 for temperature and 71 for humidity under algal canopies during low tide events using seaweed as an example we develop a conceptual model of the relationship between biological cover and microclimate in the intertidal zone disturbance events that remove or drastically reduce seaweed cover mediate shifts between relatively stable and unstable states with respect to mechanical decay and ecological stress associated with heat and desiccation in urban coastal environments where disturbance may be frequent facilitating the establishment and recovery of canopy forming species on rocks and engineered structures could enhance the durability of construction materials as well as support conservation planning and policy targets for biodiversity enhancement

weathering of sandstone by the combined action of frost and salt preliminary results from a continuing series of laboratory experiments designed to examine the combined effects of salt and frost weathering indicate that some salts greatly enhance the breakdown of rocks by frost samples of ardingly sandstone from southeast england were soaked in saturated solutions of sodium chloride or sodium sulphate and subjected to alternating cycles of freezing and thawing rapid disintegration of the sandstone occurred within twenty cycles in each of the salt solutions in contrast samples subjected to freezing and thawing in deionized water suffered very little damage unless they were saturated under vacuum when samples were subjected to twenty cycles of wetting and drying at temperatures above 0 c those soaked in deionised water or sodium chloride suffered no appreciable damage but those soaked in sodium sulphate rapidly disintegrated tentative explanations of these results are offered the enhancement of frost weathering by salt appears to have been overlooked by many writers yet it is likely to be an important geomorphological process in those areas of mid and high latitudes where rocks are saturated with sodium salts

rock temperatures as an indicator of weathering processes affecting rock art to aid rock art conservation rock temperatures have been monitored at different depths and at low 30 min and high 1 min acquisition rates in a painted rock shelter in the ukhahlamba drakensberg park south africa preliminary data for winter cold and dry show that in that season cryoclasty is unlikely to occur rare subzero thermal events and probable reduced moisture availability and thermal shocks are improbable highest measured t t 2 c min 1 high amplitude about 30 c rock temperature cycles accompanied by reversals of the thermal gradient have been observed to occur almost daily and hint at the possibility of thermal stress fatigue copyright 2006 john wiley sons ltd

weathering of rock art at two sites in the kwazulu natal drakensberg southern africa sediments of the karoo basin in southern africa represent one of the world s finest laboratories for investigating sandstone weathering the natural breakdown of these sandstones most notably in the clarens formation is destroying much of the indigenous rock art heritage that exists there in an attempt to elucidate the operative weathering processes a range of micro climatic rock temperature rock moisture rock chemistry and rock property data have been monitored over a 15 year period at two sites in the kwazulu natal drakensberg results suggest that rock moisture regimes and to a lesser extent rock thermal regimes exert the most damaging influence on san paintings it is argued that granular disintegration and the enlargement of existing sandstone pores and bedding planes close to the rock surface facilitate an increasingly dynamic moisture regime which leads to an accelerating rate of weathering recent technological advances in data collection suggest that a re evaluation of environmental controls may be necessary before weathering at a scale appropriate to the deterioration of rock art can be fully understood the continued existence of indigenous rock art in southern africa depends on investigations aimed at the development of techniques for its preservation

ca and mg isotope constraints on the origin of earth s deepest δ13c excursion abstract understanding the extreme carbon isotope excursions found in carbonate rocks of the ediacaran period 635 541 ma where 13 c of marine carbonates 13 c carb reach their minimum 12 for earth history is one of the most vexing problems in precambrian geology known colloquially as the shuram excursion the event has been interpreted by many as a product of a profoundly different ediacaran carbon cycle more recently diagenetic processes have been invoked with the very negative 13 c values of ediacaran carbonates explained via meteoric alteration late stage burial diagenesis or growth of authigenic carbonates in the sediment column thus challenging models which rely upon a dramatically changing redox state of the ediacaran oceans here we present 257 44 40 ca and 131 26 mg measurements along with mg mn and sr data from carbonates of the ediacaran aged wonoka formation fm of south australia to bring new isotope systems to bear on understanding the shuram excursion data from four measured sections spanning the basin reveal stratigraphically coherent trends with variability of 1 5 in 26 mg and 1 2 in 44 40 ca this ca isotope variability dwarfs the 0 2 0 3 change seen coeval with the permian triassic mass extinction the largest recorded in the rock record and is on par with putative changes in the 44 40 ca value of seawater seen over the phanerozoic eon changes in both isotopic systems are too large to explain with changes in the isotopic composition of ca and mg in global seawater given modern budgets and residence times and thus must be products of alternative processes relationships between 44 40 ca and sr and 26 mg and mg are consistent with mineralogical control e g aragonite vs calcite limestone vs dolostone on calcium and magnesium isotope variability the most pristine samples in the wonoka dataset preserving sr concentrations in the 1000s of ppm range and 44 40 ca values inherited from an originally aragonitic polymorph have 13 c carb of 8 to 7 thereby providing strong geochemical evidence that extremely negative 13 c carb values are primary products of the ediacaran surface environment

veracity of neoproterozoic negative c isotope values the termination of the shuram negative excursion abstract there is widespread interest in the neoproterozoic period of the earth s history 1000 to 542 ma because of unprecedented 13 c fluctuations to 1000 m succession of stratigraphically complex sedimentary rocks deposited during tens of millions of years in contrast phanerozoic large negative c isotope excursions have been interpreted as the result of diagenetic fluid mixing during carbonate stabilization and burial and are less enigmatic due to the excellent biostratigraphic control on their timing and duration the ediacaran nafun group of oman part of the huqf supergroup spanning the cryogenian early cambrian contains a large 13 c negative excursion the shuram excursion reaching values as negative as 12 at the base of the shuram formation a steady recovery to positive values occurs over the entire shuram and half through the overlying buah formation suggesting a duration on the order of tens of my based on trace metal chemostratigraphic and sedimentological analyses the carbon isotope record obtained from the buah formation of northern oman indicates a systematic and reproducible shift of 13 c values from 6 to 1 in 1 a demonstrably diagenetic altered carbonate cemented siliciclastic facies and 2 a least diagenetically altered stromatolitic facies the identical reproducible isotopic pattern in these time equivalent sections combined to the presence of exceptionally preserved 18 o values around 2 to 1 associated with the most negative 13 c values rules out isotopic resetting by diagenetic fluids as a mechanism to explain these values it is concluded that it is possible to retain depositional 13 c values in demonstrably diagenetically altered carbonates this raises the issue of the ability to recognize diagenetic alteration of c isotopic values in neoproterozoic rocks where a robust time frame to support reproducibility is not available the results of this study provide strong support to a non diagenetic origin of the negative shuram c isotope excursion believed to be the most profound in terms of amplitude and duration in the earth s history

erratum to chemostratigraphic and sedimentological framework of the largest negative carbon isotopic excursion in earth history the neoproterozoic shuram formation nafun group oman j precam res 146 2006 68 92

understanding carbonate ramp dynamics using δ13c profiles examples from the neoproterozoic buah formation of oman the late neoproterozoic buah formation nafun group oman is a carbonate unit outcropping in the jabal akhdar and huqf areas it is composed mostly of shallow water carbonates deposited on a distally steepened carbonate ramp correlation of two 13c isotope shifts shows that in the jabal akhdar ramp differentiation into fast and slow subsiding areas was followed by lateral progradation in the huqf area however a uniform scenario of upward shallowing of the facies and lateral progradation is demonstrated by chemostratigraphic timelines cross cutting the facies belts the chemostratigraphic profiles show that the buah formation was deposited during sea level highstand conditions and that ramp differentiation was due to synsedimentary tectonics high resolution correlation of 13c profiles from the same lithostratigraphic unit whether precambrian or phanerozoic in age lacking biostratigraphic data can shed light on carbonate systems dynamics tectonic vs eustatic controls on depositional sequences and basin subsidence

50 myr recovery from the largest negative δ13c excursion in the ediacaran ocean sedimentary rocks deposited during the ediacaran period 630 542 ma contain carbonates whose carbon isotopic ratios show a marked negative excursion consisting of a precipitous drop from 5 to 12 followed by a sub linear recovery to positive 13c values isotopic ages u pb and thermal subsidence modelling are combined to constrain the excursion in time and indicate an onset at 600 ma and duration of recovery of approximately 50 myr the excursion is widely recognized in oman and has potential correlatives in ediacaran strata elsewhere and may thus represent a characteristic feature of the ediacaran period the amplitude of this carbon isotope excursion far exceeds those of other neoproterozoic anomalies the isotopic trend of negative excursion and long term recovery spanned at least one short lived glacial episode at 580 ma but appears unrelated to glaciation which indicates that negative anomalies in the neoproterozoic marine carbon isotope record are not directly or uniquely linked to ice ages

reconstruction of ancient sea conditions with an example from the swiss molasse ancient sea conditions can be estimated from the grain size spacing and steepness of preserved ripple marks the element of greatest uncertainty in such reconstructions is the relationship between near bed orbital diameter of water particles and the ripple spacing this relationship is simple for vortex ripples of high steepness but is problematical for the low steepness forms known as post vortex rolling grain or anorbital ripples the existence field for wave ripples is between the threshold velocity for sediment movement and the onset of sheet flow most low steepness forms occurring close to the bed planation threshold a range of maximum period of formative waves can be obtained using combinations of orbital diameter and orbital velocity assuming linear wave theory to be a reasonable approximation probable wave heights wave lengths and water depths can be investigated using the transformation of wave parameters in shallowing waters and the constraints on wave dimensions provided by the wave breaking condition given reasonable estimates of wave height crude estimates of wave power allow a comparison of ancient wave influenced sequences with modern counterparts wave ripple marks preserved in the upper marine molasse of western switzerland have been investigated results which are in agreement with regional geology suggest deposition in a seaway of approximately 100 km width where moderate period waves t 3 6 s were generated the depositional facies belts were adjusted to the prevailing waves tides and fluvial outflows

frost and salt weathering further experimental results a laboratory experiment has been conducted to examine the effects of frost and salt weathering i e physical breakdown by the freezing of salt solutions on a limestone results show that the presence of certain salts in solution can inhibit frost damage these findings are in direct conflict with those presented by goudie 1974 and more recently williams and robinson 1981 comparison of the experimental methods used in each of these three studies suggests that opposing results can be explained in terms of the different experimental procedures which were employed if salt supply is frequent and plentiful then it seems likely that rock breakdown will be enhanced this is the case represented by the experiment of williams and robinson conversely if the salt supply is limited and the amounts of salt remain more or less constant then rock breakdown will be inhibited the case of the present experimental study caution is therefore advocated when attempting to extrapolate laboratory derived results to infer on the behaviour of rocks under natural conditions several environmental situations in which frost and salt weathering may be a possibility are dsiscussed but it is concluded that further field data especially concerning temperature regimes and salt availability at and below rock surfaces in cold regions would be necessary before more definite statements could be made about the efficacy of this process

calibrating the coevolution of ediacaran life and environment the rise of animals occurred during an interval of earth history that witnessed dynamic marine redox conditions potentially rapid plate motions and uniquely large perturbations to global biogeochemical cycles the largest of these perturbations the shuram carbon isotope excursion has been invoked as a driving mechanism for ediacaran environmental change possibly linked with evolutionary innovation or extinction however there are a number of controversies surrounding the shuram including its timing duration and role in the concomitant biological and biogeochemical upheavals here we present radioisotopic dates bracketing the shuram on two separate paleocontinents our results are consistent with a global and synchronous event between 574 0 4 7 and 567 3 3 0 ma these dates support the interpretation that the shuram is a primary and synchronous event postdating the gaskiers glaciation in addition our re os ages suggest that the appearance of ediacaran macrofossils in northwestern canada is identical within uncertainty to similar macrofossils from the conception group of newfoundland highlighting the coeval appearance of macroscopic metazoans across two paleocontinents our temporal framework for the terminal proterozoic is a critical step for testing hypotheses related to extreme carbon isotope excursions and their role in the evolution of complex life

mapping of neoproterozoic source rocks of the huqf supergroup in the sultanate of oman using remote sensing abstract in recent years the neoproterozoic huqf supergroup formations of the oman salt basins have been the target for oil exploration the present study maps the surficial exposure of the huqf supergroup in and around khufai dome of the huqf area in the sultanate of oman using low cost multi spectral remotely sensed satellite data and image processing methods such as decorrelation stretching principal component analysis pca and spectral angle mapper sam as alternative to expensive and time consuming tools which have the capability and potential to be used by geoscientists for oil exploration in this research the study of advanced spaceborne thermal emission and reflection radiometer aster spectral bands 8 3 and 1 by decorrelation stretching well discriminated the masirah bay the khufai the shuram and the buah formations of the nafun group the source rocks of huqf supergroup with the quaternary deposits the analysis of visible and near infrared shortwave infrared spectral bands of aster by pca clearly showed the occurrence and spatial distribution of such formations in the rgb principal component images r pc1 g pc2 b pc3 the spatial distributions of such formations are assessed by confusion matrix after using maximum likelihood ml spectral angle mapper sam and spectral information divergence sid algorithms the matrix of ml algorithm has provided the best overall accuracy of 92 93 and kappa coefficient of 0 92 the minerals of the formations were detected by sam further the detection of such mineral groups was confirmed through the aster thermal infrared tir spectral indices image developed using the carbonate index ci quartz index qi and mafic index mi all results of image analyses are evaluated in the field and laboratory studies the study also evaluates the satellite data and image processing methods for the formations of jabal akhdar the equivalent formations of the khufai dome to show the sensor capability and the use of the image processing methods to study the source rocks the results of the study provided similar discriminations comparable to the khufai dome therefore the data and the techniques are recommended to the exploration geologists for use in similar regions of the world

surface temperature differences between minerals in crystalline rocks implications for granular disaggregation of granites through thermal fatigue thermal expansion differences between minerals within rocks under insolation have previously been assumed to drive breakdown by means of granular disaggregation however there have been no definitive demonstrations of the efficacy of this weathering mechanism different surface temperatures between minerals should magnify thermal expansion differences and thus subject adjacent minerals to repeated stresses that might cause breakdown through fatigue failure this work confirms the existence of surface temperature differences between minerals in granitic rocks under simulated short term temperature fluctuations so as to discriminate their potential for initiating granular disaggregation the influence of colour as a surrogate for albedo and crystal size as a function of thermal mass are specifically identified because of their ease of quantification four rock types with a range of these properties were examined and subjected to repeated short term temperature cycles by radiative heating and cooling under laboratory conditions results show that while albedo is the main control for overall and individual maximum temperatures crystal size is the main factor controlling higher temperature differences between minerals thus stones with large differences of mineral sizes can undergo magnified stresses due to thermal expansion differences

rock temperatures from southeast morocco and their significance for experimental rock weathering studies surface and subsurface rock temperature measurements are presented from three rock types chalk granite and sandstone from a hot desert climate the temperature regimes undergone by each rock type and the differences between them can be best explained by reference to the values of albedo and thermal conductivity for the rocks the significance of thermal properties in influencing rock temperatures suggests that these properties should be taken into account when attempting to simulate desert weathering and also when trying to explain variations in the weathering behavior of different rock types

isotope stratigraphy of the ediacarian neoproterozoic iii of the adelaide rift complex australia and the overprint of water column stratification abstract this study establishes a high resolution 13c chemostratigraphic framework for the type ediacarian terminal proterozoic section in the adelaide rift complex a framework that contributes to the emerging global chronostratigraphic synthesis of a period that saw momentous changes in the earth s surface environment only 15 m of the 3 5 km thick type section consists of shallow water carbonates of the kind that have formed the basis of most previous studies of neoproterozoic chemostratigraphy however the organic 13corg record reveals a surprising richness of information and shows excellent utility in correlation between sections in the adelaide rift complex lateral variations in 13corg profiles correspond to expected diachronous patterns of basin fill with the addition of 87sr 86sr data correlation can also be made to the officer and amadeus basins consistent with known lithostratigraphic and sequence stratigraphic constraints sublittoral micritic carbonates of the upper nuccaleena formation cap dolostone and lower and middle wonoka formation show strong basinwide 13c depletion 13ccarb 3 to 10 despite compelling evidence for preservation of depositional 13ccarb such as good textural preservation evidence for sea floor lithification and in the wonoka formation pristine 87sr 86sr and low mn sr associated with the depleted carbonates are rare subaqueous evaporite relatively heavy 13corg and anomalously 13c depleted organic carbon of benthic microbial mat origin and a common cause salinity stratification of the water column is postulated the indicated palaeogeographic setting an evaporative mediterranean like basin tenuously connected to the world ocean is entirely consistent with previous suggestions of one or more messinian type desiccation events to explain very deep 1 km incised valleys or canyons in the adelaide rift complex and officer basin at horizons within the wonoka formation and correlates positive excursions in 13corg during basin stratification may in part be due to 12c depletion of surface waters by photosynthetic carbon fixation despite the proposed semi isolation of australian ediacarian basins from the world ocean major 13c excursions which can to some extent be differentiated by the monotonic rise in ediacarian marine 87sr 86sr appear to be correlatable to the upper windermere supergroup northwest canada

massive dissociation of gas hydrate during a jurassic oceanic anoxic event in the jurassic period the early toarcian oceanic anoxic event about 183 million years ago is associated with exceptionally high rates of organic carbon burial high palaeotemperatures and significant mass extinction heavy carbon isotope compositions in rocks and fossils of this age have been linked to the global burial of organic carbon which is isotopically light in contrast examples of light carbon isotope values from marine organic matter of early toarcian age have been explained principally in terms of localized upwelling of bottom water enriched in 12c versus 13c refs 1 2 5 6 here however we report carbon isotope analyses of fossil wood which demonstrate that isotopically light carbon dominated all the upper oceanic biospheric and atmospheric carbon reservoirs and that this occurred despite the enhanced burial of organic carbon we propose that as has been suggested for the late palaeocene thermal maximum some 55 million years ago the observed patterns were produced by voluminous and extremely rapid release of methane from gas hydrate contained in marine continental margin sediments

carbonate platform facies models various types of carbonate platforms are characterized by distinctive profiles facies and evolutionary sequences ramps may be homoclinal or distally steepened and may have fringing or barrier shoal water complexes of ooid pellet sands or skeletal banks homoclinal ramps pass seaward into deeper water without major break in slope and lack deep water breccias distally steepened ramps may be low energy and characterized by widespread shallow subwave base mud blankets or high energy with coastal beach dune complexes and widespread skeletal sand blankets slope facies may contain abundant breccias of slope derived clasts rimmed shelves have relatively flat tops and marked break in slopes at the high energy shallow shelf edge where they pass into deep water such shelves may be aggraded with peritidal facies extending over much of the shelf or incipiently drowned depending on magnitude of sea level fluctuations they may be accretionary or bypass types that include gullied slope escarpment and high relief erosional forms intrashelf basins occur on some shelves controlling distribution of reservoir and source beds isolated platforms are surrounded by deeper water and may be located on rifted continental margins or on submarine volcanoes most have high relief rimmed margins platforms that have been subjected to rapid sea level rise may be incipiently drowned and characterized by raised rims elevated patch or pinnacle reefs and widespread subwave base carbonate or fine clastic blankets completely drowned shelves develop where the shelf is submerged to subphotic depths terminating shallow water deposition and commonly resulting in blanketing of the shelf by deeper water facies some margins show extensive down to basin faulting that is contemporaneous with carbonate deposition or associated with thick prograding clastic sequences the various types of platforms change in response to variations in sedimentation subsidence or sea level rise and may form distinctive evolutionary sequences the relatively few models presented appear to accommodate most geological examples some of which contain major reservoir facies

influence of surface heterogeneities of building granite on its thermal response and its potential for the generation of thermoclasty surface properties especially albedo and aspect are widely accepted as strong influences on the surface thermal response of building stone to insolation however the influence that adjacent areas of stone with very different surface properties may have on the thermal response of a patch of stonework and the ways in which spatial variation in thermal characteristics might enhance stone decay has received relatively little attention this paper examines the differential thermal response of granite used in construction that results from the presence of dark coloured micro granular enclaves within a leucocratic host surface temperatures and temperature differences between enclaves exhibiting mico spalling enclaves with no spalling and the surrounding stone were measured for different aspects and seasons on a 20th century building in madrid these data were used to calculate a number of indices related to short term temperature cycling and temperature gradients that have the theoretical capability of generating irreversible deformation of the stone these indices suggest that micro spalling of enclaves compared to a lack of similar decay on the host rock is related to their differential thermal response to insolation most importantly the lower albedo and thermal conductivity values of the enclaves however these factors are not sufficient on their own to trigger spalling and breakdown was only observed where enclaves also experienced repeated short term surface temperature cycling caused by for example temporary shading by adjacent vegetation these rapid temperature reversals are identified as a key contributory factor to the thermally driven decay observed on some of the enclaves

experiments on oscillatory flow and combined flow bed forms implications for interpreting parts of the shallow marine sedimentary record abstract analog laboratory experiments were conducted to investigate subaqueous bed forms generated under storm like oscillatory and combined flow experiments were carried out in a large wave tunnel and used a range of sand sizes fine and very fine wave periods 10 5 and 8 s oscillatory velocities 0 to 125 cm s and unidirectional velocities 0 to 25 cm s at low unidirectional velocities 10 cm s addition of an increasing collinear oscillatory flow caused the bed to evolve from small scale wavelength 100 cm symmetric orbital ripples to plane bed at higher unidirectional velocities 10 cm s a similar trend was noted but ripples were more asymmetric three phase diagrams are presented to summarize the observed relationships of bed configurations to flow conditions these diagrams are intended to assist in the interpretation of shallow marine sedimentary environments where oscillatory and combined flow are thought to be omnipresent distinctive features of small scale asymmetric combined flow ripples generated are a 3d planform round crest and convex up sigmoidal profile with local pronounced scour at the toe of the stoss side giving the ripple profile a boxy appearance similarly large scale asymmetric combined flow ripples had broad and round crests convex up stoss sides and compressed profiles due to scouring at the toe of the stoss side hummocky bed forms were generated under moderate to high oscillatory velocities and low unidirectional velocities hummocks were not observed as a distinct bed state but rather appeared to mark transitions in bed form scale and symmetry hummocks were more prevalent at longer oscillatory periods and in finer grained sediment stratification produced by synthetically aggrading hummocky bed profiles closely resembles hummocky cross stratification with the introduction of only a small unidirectional flow component hummocks evolve into downstream migrating large scale asymmetric ripples and the resultant cross stratification becomes similar to that produced by unidirectional flow dunes accordingly these experiments suggest that much of the hummocky cross stratification observed in the stratigraphic record is produced by storm generated long period oscillatory dominant combined flows inasmuch as long period high energy waves require deep wide basins to form hummocky cross stratification may therefore serve as a useful indicator of deposition in unrestricted open water conditions

two from donegal neoproterozoic glacial episodes on the northeast margin of laurentia two glacial episodes the sturtian ca 720 ma and marinoan varangerian ca 590 ma characterize many neoproterozoic successions worldwide in contrast northeast laurentia is typically considered as containing only the latter in scotland and ireland this is represented by the port askaig tillite here we present evidence ice rafted debris for a second younger neoproterozoic glacial event in the dalradian southern highland group of donegal ireland these deposits overlie strata correlative to ca 595 ma rocks in scotland making this heretofore unrecognized glacial episode a marinoan varangerian equivalent in that the port askaig occurs 3 5 km stratigraphically below the southern highland group rocks it is most likely sturtian not marinoan varangerian in age thus the dalradian succession in the irish caledonides contains strata representing both the sturtian and marinoan varanger glaciations

constraining the physical chemical conditions of pleistocene cavernous weathering in late paleozoic granites abstract cavernous weathering such as tafoni alveoles and honeycomb structures have been recorded from a great variety of bedrocks and landforms in the present study cavernous weathering from late variscan granites was discussed as to its physical chemical regime of formation u pb dating yielded a maximum age of 1 52 0 03 ma supergene u mineralization is accompanied by kaolinite nontronite and fe iii phosphates based upon eh ph diagrams calculated for u fe p mineralization the physical chemical conditions may be described as oxidizing with ph values fluctuating around neutral at near ambient temperatures of 25 c alteration occurs in two stages dissolution of rock forming minerals and neoformation of hydrosilicates under mildly acidic conditions followed by phosphate precipitation under near neutral conditions

building sandstone surface modification by biofilm and iron precipitation emerging block scale heterogeneity and system response stone surfaces are sensitive to their environment this means that they will often respond to exposure conditions by manifesting a change in surface characteristics such changes can be more than simply aesthetic creating surface subsurface heterogeneity in stone at the block scale promoting stress gradients to be set up as surface response to for example temperature fluctuations can diverge from subsurface response this paper reports preliminary experiments investigating the potential of biofilms and iron precipitation as surface modifiers on stone exploring the idea of block scale surface to depth heterogeneity and investigating how physical alteration in the surface and near surface zone can have implications for subsurface response and potentially for long term decay patterns salt weathering simulations on fresh and surface modified stone suggest that even subtle surface modification can have significant implications for moisture uptake and retention salt concentration and distribution from surface to depth over the period of the experimental run the accumulation of salt may increase the retention of moisture by modifying vapour pressure differentials and the rate of evaporation temperature fluctuation experiments suggest that the presence of a biofilm can have an impact on energy transfer processes that occur at the stone surface for example buffering against temperature fluctuation affecting surface to depth stress gradients ultimately fresh and surface modified blocks mask different kinds of system which respond to inputs differently because of different storage mechanisms encouraging divergent behaviour between fresh and surface modified stone over time copyright 2014 john wiley sons ltd

kestel an early bronze age source of tin ore in the taurus mountains turkey an ancient mine located at kestel on the outskirts of nigde in the taurus mountains of south central turkey has been dated by radiocarbon and pottery type to the third millennium b c archeological soundings in the mine located cassiterite tin oxide in the detritus of ancient mining activity cassiterite is also present in veins and as placer deposits in streams nearby since tin is used with copper in order to form bronze but is thinly distributed in the earth s crust the presence of tin ore at kestel offers a source for the much sought after tin of the bronze age the discovery of an ancient mine containing cassiterite sheds light on this question but also greatly complicates the accepted picture of regional economic patterns in the highland resource areas of anatolia and of interregional metal exchange in the formative periods of urbanization and metal use in the eastern mediterranean

techniques for measuring rock weathering application to a dated fan segment sequence in southern tunisia there are a number of techniques for estimating the amount of weathering a clast has undergone these usually have the objective of establishing an ordinal chronology of geomorphological surfaces or investigation of site specific conditions affecting weathering rates three such techniques are applied to a dated sequence of alluvial fan segments in southern tunisia two of these techniques depend on measuring surface roughness the micro roughness meter and a displacement approach and one uses the structural weakening of the rock fabric schmidt hammer the micro roughness meter enables calculation of standard deviation of surface height variation root mean square roughness and surface autocorrelation function of these techniques schmidt hammer rebound values standard deviation root mean square roughness and the displacement technique show systematic changes on the three fan segments which are statistically significant at the 0 05 level however the amount of variance in all datasets is very large indicating the need for caution in application of these techniques for relative dating 1998 john wiley sons ltd

influence of daily surface temperature fluctuations on rock slope stability case study of the rochers de valabres slope france the present paper describes a rockfall that has affected the rochers de valabres slope france s southern alps region and discusses one possible mechanism for the occurrence of this rockfall along with the potential for future ones in the absence of an obvious explanatory trigger factor we set out to examine whether natural daily surface temperature changes could have played a role in this event in particular it is suspected that these slight yet repeated perturbations may be a preparatory factor for rockfalls with a day to day cumulative effect a numerical model strengthens this hypothesis by showing that thermally induced deformations can be sufficient to cause the gradual downward creep of a rock block located in an awkward position to investigate this notion more thoroughly a currently vulnerable part of the rochers de valabres slope has been instrumented with a high precision geodetic monitoring system total station it is believed that this device is able to capture thermally induced movements if specific precautions are taken the instrumented rock volume is used as a test site in the aim of better understanding the consequences of surface temperature changes on slope stability measured data with a precision level never before achieved on rock slopes are compared herein with numerical modelling results the initial conclusions of the long term study we are conducting indicate that surface temperature changes play an important while not easily quantifiable role in preparing rockfalls

enigmatic nature of thick sedimentary carbonates depleted in 13c beyond the canonical mantle value the challenges to our understanding of the terrestrial carbon cycle carbon and oxygen isotope measurements of 66 samples from the 60 m thick variegated marble in the upper allochthon of the norwegian caledonides have a mean 13ccarb of 8 4 0 9 v pdb and a mean 18o of 20 2 2 2 v smow the variegated marble is overlain by 150 m thick pale grey marble characterised by mean 13ccarb of 6 5 0 8 n 25 and underlain by dark grey marbles with a mean 13ccarb of 4 8 1 1 n 61 this tripartite unit of an poorly constrained age but between neoproterozoic and early silurian discontinuously developed over a distance of 500 km is likely to represent one of the largest isotopically anomalous sedimentary carbonate formations yet reported the marbles depleted in 13c beyond the canonical mantle value of 6 show no obvious evidence of post sedimentary repartitioning of carbon isotopes several other carbonate formations deposited within approximately 680 540 ma time interval chenchinskaya nikolskaya and torginskay in siberia ingta in nw canada shuram in central oman trezona and wonoka in south australia are several hundred meters thick developed over a distance of hundreds of kilometres and all show a similar depletion in 13c beyond the mantle value for reasons that are not well understood the existence of these carbonates represents a challenging problem for our current understanding of global carbon geodynamics changes in the ratio of reduced oxidised carbon sequestered in sediments a methane hydrate release or zero biological productivity if applied separately cannot explain carbon isotope characteristics and formation of these carbonates we tentatively propose that several factors associated with unusual geodynamic and palaeoclimatic scenarios developed between 600 and 540 ma might have been involved in the extreme lowering of the isotopic composition of carbon entering the global earth surface environment this period was marked by the retreat of neoproterozoic glaciers and break up of the supercontinent rodinia the late postglacial warming might have induced a massive release of methane hydrates extremely enriched in 12c the death of rodinia was marked by unusually rapid approximately 20 cm year motion of newly formed continental plates suggesting vigorous mantle convection and an enhanced restructuring of the lowest compartments of the earth this could provide a flux of 12c rich material from the isotopically light asthenosphere mantle source 13c 25 to 15 to the surface considerable reconfiguration of the continental and sea areas of the earth might have triggered enhanced weathering of previously deposited 12c rich organic matter in presenting this working hypothesis we also question the completeness of our understanding of the terrestrial carbon cycle and the popular assumption that the isotopic composition of carbon entering the global earth surface environment was always around 6

investigations into the relationship between changes in internal moisture regimes and rock surface deterioration in cavernous sandstone features cavernous features commonly develop in sandstone but their development over time remains enigmatic it has been suggested that moisture movements within the rock mass play a key role in the location development and dynamics of cavernous features in this research the role of internal moisture movement is tested through monitoring moisture and surface deterioration dynamics in april 2008 and april 2009 within two large cavernous features mega tafoni in the golden gate highlands national park south africa gghnp data are presented from surveys of internal moisture using electrical resistivity tomography ert surface moisture using a protimeter and deterioration using surface hardness as recorded with an equotip as a proxy for surface deterioration across five 2 45 m long transects in addition a high resolution temperature record is presented to assess the influence of micro climates within the caverns the results indicate consistency in the gross spatial pattern of moisture flow within the rock mass over a one year period but significant changes in mean moisture contents and in the fine detail of moisture patterning some noticeably weakened areas had developed within the central parts of the cavernous features often linked to wetter subsurface conditions supporting the theory that core softening is a main driver of cavernous feature formation however in some areas surface hardening is also found to be associated with wetter subsurface conditions supporting the theory that case hardening is a main driver of cavernous feature formation in addition the presence of well established biofilms suggests an even more complex interaction between moisture surface development and biological activity a model is presented therefore which integrates this paradox by proposing a non linear relationship between moisture dynamics facilitation of biofilm formation and deterioration within cavernous features

rock warming and drying under simulated intertidal conditions part i experimental procedures and comparisons with field data the wetting drying and warming cooling behaviours of rock and stone are known to influence the nature and rate of weathering the way materials warm up and dry out also influences their suitability as biological substrata while rock thermal behaviours have been measured under controlled laboratory conditions previous experiments have largely been restricted to terrestrial simulations due to practical constraints where efforts have been made to simulate intertidal conditions expansion and contraction of rocks or rates of breakdown i e sediment production and weight loss have been measured while detailed observations of thermal and drying behaviours have rarely been made a simple semi automated procedure is described that enabled measurement of surface temperatures and desorption evaporative water loss for different material types rock and concrete under simulated semidiurnal tide conditions some preliminary results are presented illustrating the types of data that were obtained and comparisons are made with temperature data collected on a rock platform in the uk to assess the ability of the procedure to adequately represent field conditions copyright 2011 john wiley sons ltd

hydrodynamics and sedimentation in wave dominated coastal environmentsreconstruction of ancient sea conditions with an example from the swiss molasse ancient sea conditions can be estimated from the grain size spacing and steepness of preserved ripple marks the element of greatest uncertainty in such reconstructions is the relationship between near bed orbital diameter of water particles and the ripple spacing this relationship is simple for vortex ripples of high steepness but is problematical for the low steepness forms known as post vortex rolling grain or anorbital ripples the existence field for wave ripples is between the threshold velocity for sediment movement and the onset of sheet flow most low steepness forms occurring close to the bed planation threshold a range of maximum period of formative waves can be obtained using combinations of orbital diameter and orbital velocity assuming linear wave theory to be a reasonable approximation probable wave heights wave lengths and water depths can be investigated using the transformation of wave parameters in shallowing waters and the constraints on wave dimensions provided by the wave breaking condition given reasonable estimates of wave height crude estimates of wave power allow a comparison of ancient wave influenced sequences with modern counterparts wave ripple marks preserved in the upper marine molasse of western switzerland have been investigated results which are in agreement with regional geology suggest deposition in a seaway of approximately 100 km width where moderate period waves t 3 6 s were generated the depositional facies belts were adjusted to the prevailing waves tides and fluvial outflows

stratigraphic investigations of carbon isotope anomalies and neoproterozoic ice ages in death valley california an unusual richness of biogeochemical events is recorded in neoproterozoic cambrian strata of the death valley region california united states eight negative carbon isotope d13c excursions are found in carbonate units between 1 08 ga and the precambrian cambrian boundary four of these excursions occur in carbonates that contain textural features similar to those found globally in postglacial cap carbonates including one or more of the following laminite with rollup structures apparent tube rocks seafloor precipitates and sheet crack cements however only two of these units the sourdough limestone member of the kingston peak formation and the noonday dolomite rest directly upon glacial strata the basal beck spring dolomite and the rainstorm member of the johnnie formation each contain negative excursions and cap carbonate like lithofacies but do not rest on known glacial deposits if the negative d13c excursions are assumed to record depositional processes two equally interesting hypotheses are possible 1 the death valley succession records four glacial pulses in neoproterozoic time but glacial units are not preserved at two stratigraphic levels 2 alternatively other global oceanographic processes can cause negative excursions and cap carbonate like facies in addition to or independent of glaciation

palynology of the huqf supergroup oman extensive subsurface sampling of the huqf supergroup in the sultanate of oman has yielded microfossil assemblages of cryogenian ediacaran and early cambrian age microfossils have been recovered from most stratigraphic units in the huqf including marinoan equivalent horizons of the ghadir manqil formation cryogenian abu mahara group the masirah bay shuram and buah formations of the ediacaran nafun group and the a3 latest ediacaran and a6 early cambrian cycles of the ara group despite the extensive recovery of leiosphaerid acritarchs from the shuram formation there is no indication of the large acanthomorphs typical of other early middle ediacaran assemblages this absence suggests a relatively young post extinction depositional age for the shuram however the signal is complicated by local deep water conditions and the facies specific distribution of proterozoic microfossils a shallower water sequence of undivided nafun group sediments preserves sphaeromorphic acritarchs in association with filamentous microfossils fragmentary vendotaenids and possible vaucheriacean algae

sequence stratigraphy and the interpretation of neoproterozoic earth history abstract the application of sequence stratigraphy to neoproterozoic successions is important for improving the resolution of time correlation within individual sedimentary basins and potentially at a global scale the methodology is illustrated in this paper by reference to two contrasting examples from the flinders ranges adelaide geosyncline of south australia where the younger part of the neoproterozoic to earliest cambrian succession 770 ma to 540 ma has been divided into thirteen unconformity bounded depositional sequences one of the most prominent sequence boundaries at or near the base of the wonoka formation is characterized by a series of buried canyons as much as 1 km deep high resolution sequence stratigraphic studies at umberatana syncline continue to support the view that the canyons were cut subaerially and filled by fluvial and shallow water sediments in contrast to the wonoka canyons sequence boundaries interpreted at the base of the nuccaleena formation seacliff sandstone and near the top of the abc range quartzite are relatively subtle with only limited evidence for erosion and valley incision four sequence boundaries at the level of the sturtian and marinoan varanger glacial deposits and in the vicinity of the precambrian cambrian boundary are thought to correlate with surfaces in the amadeus basin of central australia other prominent sequence boundaries including the wonoka canyons and surfaces within the upper part of the wonoka formation and at the base of the ediacara member of the rawnsley quartzite correspond with a relatively condensed section in the amadeus basin and their lateral persistence beyond the adelaide geosyncline is therefore difficult to evaluate given the lack of precision in biostratigraphy and isotope geochemistry in neoproterozoic rocks and in a marked departure from phanerozoic practice we recommend placement of a terminal proterozoic gssp at a sequence boundary a prime candidate in australia is the sequence boundary at the base of the nuccaleena formation seacliff sandstone immediately above the marinoan glacial rocks in the adelaide geosyncline and its likely correlative at or near the base of the gaylad sandstone in the amadeus basin

thermal properties as controls on rock surface temperature maxima and possible implications for rock weathering four rock types basalt sandstone granite and chalk are examined with respect to the maximum surface temperatures which they experience when subjected to similar conditions of exposure rock temperature measurements are reported for an urban environment and for two experimental situations in which an infrared lamp is used to simulate heating under cold and hot conditions differences in rock temperatures are discussed with reference to thermal rock properties albedo specific heat capacity and thermal conductivity some natural situations are suggested in which thermal rock properties could conceivably play a role in determining the extent to which rocks would be affected by particular weathering processes

relative age dating of inorganic deposits the need for a more critical approach relative age dating rd techniques rely on indices of post depositional change principally degree of rock surface weathering or soil development in the chronosequence approach where a measured parameter displays a trend in values that parallels a trend in surface age the parameter is commonly assumed to be age dependent such an assumption may be invalid this is demonstrated with particular reference to glacier forelands where environmental and sedimentological factors that can influence commonly used rd parameters may exhibit systematic variations in parallel with but independent of surface age where some independent dating control is available regression analysis may be used to define chronofunctions providing numerical ages based on rd parameters however the error limits of such ages are often underestimated the use of modal rather than mean values is particularly problematic a more critical approach is suggested involving deductive experiments to examine the influence of non tempo

sandstone weathering a century of research and innovation abstract a review of sandstone weathering research particularly in the past 100 years reveals a trajectory of enquiry from early description and classification of features to development of process based explanations to decreasing scales of investigation and a disparity between understanding of process es and explanations of the genesis of sandstone weathering features developments in expositions on mesoscale weathering features on sandstone surfaces are discussed demonstrating a range of approaches to weathering phenomena field based and laboratory based that must be linked to provide an explanation of observed features on a landform scale throughout the twentieth century a thematic chronology highlights certain trends in research description of forms often in arid and semi arid environments single process form models an emphasis on experimentation difficulties in measuring weathering rates and a persistent emphasis on physical causes of breakdown a new research agenda is promoted in which biodeterioration and chemical processes gain parity a holistic approach based on conceptual modeling of weathering systems gains prominence and scale issues are addressed more rigorously

microclimate and weathering in the central namib desert namibia data on rock surface microclimates at four sites kleinberg vogelfederberg gobabeb and ganab along a transect across the central namib desert over a 3 year period have been collected alongside some shorter term data sets rock surface temperature rst air temperature wind relative humidity and surface wetness data are presented here weathering of exposure blocks of local marble and granite has also been monitored over the 3 year period with change observed visually and with scanning electron microscopy complex temporal patterns of rock temperature fluctuations are observed over the 3 years although the four sites show very similar overall trends suggesting spatial homogeneity in the rock surface temperature regime relative humidity and surface wetness data show clear differences between the four sites related to the frequency of fogs granite blocks show no visible changes after 2 years of weathering whereas marble blocks especially those at ganab show sem evidence of structural weakening after 1 year

boron and calcium isotope composition in neoproterozoic carbonate rocks from namibia evidence for extreme environmental change the level and evolution of atmospheric carbon dioxide throughout earth s history are key issues for palaeoclimate reconstructions especially during times of extreme climate change such as those that marked the neoproterozoic the carbon isotope ratios of marine carbonates are crucial in the correlation and identification of neoproterozoic glacial deposits and they are also used as a record for biogeochemical cycling and potential proxy for atmospheric pco2 likewise the boron and calcium isotope compositions of marine carbonates are potential proxies for palaeo seawater ph and the ratio of calcium fluxes into and out of seawater respectively and together they may be used to estimate atmospheric carbon dioxide here we use b and ca isotopes to estimate palaeoenvironmental conditions in the aftermath of a major neoproterozoic glaciation in namibia the validity of the b and ca isotope variation in the ancient marine carbonates is evaluated using the oxygen isotope composition of the carbonates and its correlation to the carbon isotope variation a negative 2 7 to 6 2 11b excursion occurs in the postglacial carbonates and is interpreted to reflect a temporary decrease in seawater ph associated variations in 44ca values ranging between 0 35 and 1 14 are linearly coupled with the carbon isotope ratios and imply enhanced postglacial weathering rates the reconstructed seawater ph and weathering profiles indicates that high atmospheric co2 concentrations were likely during the melt back of neoproterozoic glaciations and precipitation of cap carbonates however the b isotope trend suggests that these concentrations rapidly ameliorated and they do not co vary with 13c thus models attempting to link long lived negative 13c excursions to elevated pco2 need to be reconsidered

chemostratigraphic and sedimentological framework of the largest negative carbon isotopic excursion in earth history the neoproterozoic shuram formation nafun group oman abstract oman records in its neoproterozoic nafun group huqf supergroup an essentially complete carbonate rich ediacaran succession the nafun group overlies the presumed marinoan rift related fiq member ca 635 ma and ends just below the precambrian cambrian boundary 542 ma tectonic subsidence caused by thermal contraction following fiq aged rifting allowed the preservation of about 1 km of postrift stratigraphy with no major stratigraphic breaks the nafun group above the marinoan cap carbonate hadash formation represents two siliciclastic to carbonate grand cycles both initiated by significant transgressions these cycles comprise the masirah bay khufai formations and the shuram buah formations the khufai shuram boundary is associated with the start of a major carbon isotope perturbation the uppermost ramp carbonates of the khufai formation record a smooth decrease in 13c from about 4 to values around 0 followed by two descending steps across which values plunge to a nadir of 12 in the overlying red siltstones and shales interbedded with thin limestones of the shuram formation this fall in isotopic values is temporally rapid and coincident in both shallow and deep water sections in the time span of a single parasequence the 13c nadir is then followed by 50 million years of monotonic recovery the shuram shift represents the largest 13c inorganic carbon negative excursion in earth history although the snowball earth theory links periods of depleted carbon isotopic ratios with periods of global glaciation the non glaciated context of the shuram formation suggests that the causal relationship between global glaciation and negative carbon isotopic excursions is non unique although the precise mechanism driving this major perturbation of the carbon cycle remains enigmatic the long term remineralization of an isotopically depleted organic carbon reservoir in ocean water is a promising candidate

late precambrian cambrian sediments of huqf group sultanate of oman the huqf group is the oldest known sedimentary sequence overlying crystalline basement in the sultanate of oman it crops out on a broad regional high the huqf axis which forms a dominating structural element on the southeastern edge of the arabian peninsula subsurface and outcrop evidence within and outside of oman suggests that the sediments of the huqf group lie within the age span of late precambrian to early middle cambrian the huqf group is subdivided into five formations corresponding to an alternation of clastics abu mahara and shuram formations and carbonates khufai and buah formations deposited in essentially shallow marine to supratidal or fluviatile conditions and terminated by an evaporitic sequence ara formation evaporites are absent on the huqf axis but they are thickly developed to the west over a large part of southern and central oman where they acted as the major structure former of most of oman s oil fields and even locally pierced up to the surface in the subsurface the huqf group has been reached by the drill mainly in southern oman where its lithostratigraphy resembles that defined in the type area in central oman the oldest sediments exposed in the core of the oman mountains may be correlative with the huqf group regional correlations suggest that the predominantly carbonate evaporitic facies of the huqf group was widely distributed in late precambrian early cambrian time the huqf basin is tentatively considered part of a belt of evaporitic basins and intervening carbonate platforms which stretched across the pangea landmass from the indian subcontinent salt range of pakistan through south yemen oman and saudi arabia into the gulf states and iran hormuz series and carbonate platform north of the zagros

integrated stratigraphy of the upper neoproterozoic succession in yunnan province of south china re evaluation of global correlation and carbon cycle abstract this study provides a chemostratigraphic and sequence stratigraphic framework of a relatively unfossiliferous sub cambrian marine sedimentary succession in yunnan province of south china our results allow its global stratigraphic correlation and provide an improved understanding of marine carbon cycle during the late neoproterozoic the succession has a basal glacial diamictite nantuo formation and comprises two large scale depositional cycles towards the precambrian cambrian pc c boundary each of which changes from siliciclastic to carbonate sediments with environments ranging from shallow subtidal to evaporitic supratidal in the absence of biostratigraphic control attribution of the tillite has remained equivocal between the 710 ma sturtian and 635 ma marinoan glaciations a compilation of known paleomagnetic and other geochronologic constraints suggests that the nantuo glaciation in south china was at least diachronous in which the nantuo tillite in yunnan belongs to the older glaciation stratigraphic patterns of the diagenetically screened 13c variation and depositional sequences during the carbonate dominated interval show a striking similarity with those of the upper cryogenian and entire terminal proterozoic carbonates at widely separated other localities rather than the terminal proterozoic alone supporting the view that deposition of the nantuo tillite in yunnan reflects the sturtian rather than marinoan glaciation further considerations of the 13c results provide three important implications for the late neoproterozoic marine carbon cycle first comparison of different 13c profiles suggests considerable variability in the absolute values of carbonate on both intra and inter basinal scales which differs profoundly from their relative homogeneity in marine phanerozoic counterparts and may therefore reflect lateral isotopic heterogeneity in the oceanic carbonate reservoir during the late neoproterozoic second an empirical correlation between the 13c and relative sea level changes was applied to evaluate hypothesized explanations for 13c temporal variation in surface sea yielding short term inverse and long term positive relationships the short term trend marks periods of the negative 13c excursions and is compatible to most of the existing arguments for the 13c events on the other hand mechanisms causing the long term trend remain enigmatic in the absence of comparable data from other localities our observation however suggests that at least two different mechanisms operated marine carbon cycle during the late neoproterozoic third the negative 13c anomaly characterizing the period following the marinoan glaciation worldwide was not coincident between kerogen and carbonate but occurs as a lagged drop in yunnan where a 7 depletion in kerogen preceded an 3 depletion in carbonate their lagged trends likely reflect different sources as kerogen and carbonate signals are considered to monitor surface and deeper waters respectively the negative 13c event would therefore have occurred in surface water followed by a smaller 13c depletion through the entire water column due to vertical mixing between surface and deeper waters at the studied site this mechanism supports the proposed hypothesis that injection of the 13c depleted atmospheric co2 into the surface sea deriving ultimately from quantitative dissociation of methane hydrate in terrestrial permafrost during the post glacial warming contributed to the negative 13c anomaly

the stratigraphic complexity of the middle ediacaran carbon isotopic record in the yangtze gorges area south china and its implications for the age and chemostratigraphic significance of the shuram excursion abstract the middle ediacaran shuram excursion represents the most pronounced negative carbon isotopic shift in earth history and has been considered as evidence for a profound disturbance to the global carbon cycle and proposed as a key chemostratigraphic marker for ediacaran stratigraphic subdivision and global correlation previous study has revealed a pronounced negative 13c shift en3 in the upper doushantuo formation of south china which has been interpreted as an equivalent of the shuram excursion detailed 13c investigation of multiple sections of the ediacaran doushantuo formation around the huangling anticline western hubei province south china indicates that the 13c variation in the upper doushantuo formation is more complex than previously reported in the western region of the huangling anticline a moderately positive 13c excursion here termed the diaoyapo positive excursion bisects two strongly negative 13c excursions here termed the jiuqunao negative excursion and the younger miaohe negative excursion with a 551 ma ash bed capping the miaohe negative excursion in the central region there is only one negative 13c excursion whereas in the eastern region the negative 13c excursion is absent the variable stratigraphic expression of these 13c excursions is most parsimoniously interpreted as reflecting local facies variation diagenesis and or a cryptic unconformity the more complete but more complex 13c chemostratigraphic record in the western region of huangling anticline implies that depending on how this record is correlated with the shuram excursion the latter may be significantly older than 551 ma if it does represent a global chemostratigraphic marker

precambrian cambrian transition death valley united states the death valley region contains one of the best exposed and often visited precambrian cambrian successions in the world but the chronostratigraphic framework necessary for understanding the critical biologic and geologic events recorded in these sections has been inadequate the recent discovery of treptichnus phycodes pedum within the uppermost parasequence of the lower member of the wood canyon formation allows correlation of the precambrian cambrian boundary to this region and provides a necessary global tie point for the death valley section new carbon isotope chemostratigraphic profiles bracket this biostratigraphic datum and record the classic negative carbon isotope excursion at the boundary for the first time biostratigraphic chemostratigraphic and lithostratigraphic information from pretrilobite strata in this region can be directly compared with similar data from other key sections that record the precursors of the cambrian explosion few precambrian cambrian boundary sections contain both the facies restricted boundary fossil t pedum and carbon isotope data as found in death valley thus the death valley succession provides a critical link toward our understanding of the correlation between siliciclastic dominated and carbonate dominated precambrian cambrian transition sections