structure and composition of organic reefs and carbonate mud mounds concepts and categories defined here as essentially in place calcareous deposits created by sessile organisms organic reefs are diverse and complex structures with a long geological history their classification has been the subject of fierce debate often characterized by reliance on subjective features such as wave resistance and qualitative attempts to discriminate between first and second class reefs in contrast emphasis is here placed on the objective characteristic of the type of sedimentary support which largely determines the sedimentary composition of the deposit constructional and depositional processes result in three principal sedimentary components matrix m essentially in place skeletons s and cavity cement c whose proportions can be represented on msc triangular plots separately or together these components also provide the structural support for the reef on these compositional and structural bases three main categories of organic reef are recognized 1 matrix supported reefs agglutinated microbial reefs cluster reefs segment reefs 2 skeleton supported reefs frame reefs 3 cement supported reefs cement reefs agglutinated microbial reefs possess laminated clotted or aphanitic fabrics created by microbial trapping of particulate sediment in place skeletons and large primary cavities are rare early cementation may provide added support topographic relief is limited by the need for currents to provide sediment to accreting surfaces cluster reefs skeletal reefs in which essentially in place skeletons are adjacent but not in contact resulting in matrix support characterized by relatively high matrix skeleton ratios and low volumes of extra skeletal early cement sediment trapping is an important corollary of skeletal growth and cluster reef organisms are tolerant of loose sediment absence of framework limits the topographic relief that cluster reefs can attain relative to spatial extent and may permit bedding to develop within the reef close cluster reefs have skeletons up to 1 unit distance apart spaced cluster reefs have skeletons more than 1 and up to 2 unit distances apart with increasing separation of skeletons they grade to level bottom communities segment reefs matrix supported reefs in which skeletons are adjacent and may be in contact but are mostly disarticulated and mainly parauthochtonous matrix abundance is high and early cement relatively low moderate relief can develop in response to intense on reef sediment production frame reefs skeletal reefs in which essentially in place skeletons including calcified microbes are in contact characterized by relatively high skeleton matrix ratio skeletal support enables them to raise themselves above the substrate independently of cementation and particulate sedimentation simultaneously by creating partly open shelter cavities skeletal support may facilitate early cementation both relief and early lithification promote marginal talus formation skeletal shape and orientation distinguish conical stick like dendritic domical and laminar frames each of these may be open or filled open frame reefs

reef development at the frasnian famennian mass extinction boundary a newly compiled global reef database indicates that the 5 6 myr long frasnian late devonian metazoan reef episode had relatively lowdiversity compared to middle devonian highs w ith over 200 genera of calcitic rugose and tabulate corals following an initial early rise after late givetian coral and stromatoporoid extinctions reefs expanded for the last time during mid frasnian sealevel highstands but declined markedly in the late frasnian rhenana linguiformis conodont zones belowthe frasnian famennian f f boundary globally metazoan reefs were wiped out by the end frasnian some famennian reefs while partly retaining the structure of the underlying carbonate platform were built by cyanobacterial consortia such as renalcis rothpletzella girvanella and epiphyton during the famennian foraminiferans with calcite walls became abundant for the first time in the phanerozoic adding a newdimension to carbonate platforms colonial rugose corals phaceloid cerioid and thamnasterioid modules were absent in the early post extinction phases up into the mid famennian and very rare and non reefbuilding later but solitary deep water lazarus corals survived locally coral sponge reefs are unknown from the 21 myr long famennian also a time of very lowplatform carbonate production rare small isolated stromatoporoid sponge and lithistid sponge patch reefs returned episodically during the famennian in north america western europe australia and china the aragonitic stromatoporoids became extinct at the end of the famennian during a late devonian tectonically very active collisional caledonian mountain building phase oceanic and atmospheric cooling accompanied by sealevel lowstand systems exposed most carbonate platforms accelerating coastal erosion and karsting this increased the amount of clastics in the shelf slope setting in the last 1 3 myr prior to the f f boundary often burying reefs immediately following there were protracted losses in nearly all major tropical shelf benthic marine invertebrates exceeded only by the end permian extinctions in severity there is no apparent link between black organic rich horizons and reef demise at or close to the f f boundary the f f boundary not also marks the largest change from widespread flooded early and mid paleozoic continental cratons to narrow distal shelves but also spikes the largest known global phanerozoic shift in atmospheric o2 enrichment and co2 drawdown this threshold matched the rise of the first tropical rainforests and expansion of terrestrial biomes on the tropical coastal lowlands formerly occupied by carbonate platforms 6 2002 elsevier science b v all rights reserved

simulating the growth of tafoni throughout the world large caves in rocks tafoni are found which originate from salt weathering the mechanisms that control their development are poorly understood the growth of tafoni has been studied with a model that describes how a rock surface containing a small pit disintegrates by salt crystallization during wetting drying cycles in the model the rock is mapped on a grid the migration and crystallization of salts are simulated explicitly in the drying phase of a cycle at the end of each wetting drying cycle the amount of salt deposited at the grid nodes is evaluated and the shape of the rock surface is adjusted by removing nodes the length of the drying period in a single cycle proved to be the key parameter for short drying periods the amount of crystallized salt at the surface is proportional to the drying rate therefore for short drying periods most salts are deposited at the more exterior parts of the rock surface as a result most damage will develop at these parts of the surface which results in smooth surfaces due to the characteristics of the drying process for long drying periods most salts accumulate at regions with low evaporation rates which are the sheltered parts of the rock surface these parts are not exposed to the wind or the sun as a result the pit grows and a tafone develops copyright 2004 john wiley sons ltd

stable isotopes in human skeletons of southern ontario reconstructing palaeodiet abstract most native plants of ontario use the c3 photosynthetic mechanism and therefore have relatively low 13 c 12 c ratios maize is a c4 plant and is relatively enriched in 13c the proportion of maize in the diet of a human can therefore be estimated from the 13c content of collagen of fossil bone we have used this method to follow the increase in consumption of maize in ancient native populations over the interval from ad 400 to 1650 and to quantify the amount of maize consumed maize consumption rose gradually to a maximum of 50 of the diet by ad 1400 these data agree with archaeologically derived data for this region and with previous isotope studies in the northeastern u s a in some of the latter however the maximum percentage of maize consumed has been overestimated because maize was assumed to have a 13c value of 12 5 our studies of archaeological specimens show the correct value to be closer to 9 the introduction of beans into the native diet about ad 1100 should have caused a decrease in the 15n content of human bone collagen because legumes are deficient in this isotope with respect to meat and fish however we observe no significant change in the 15 n 14 n ratio of human bone collagen over the period from 2300 bc to ad 1640 we conclude that meat and fish remained the main sources of protein even after the advent of agriculture into this region

stable isotope analysis of archaeological faunal remains from southern ontario abstract bone collagen from animals consumed by humans during the early historic period in southern ontario was analysed for stable isotopes of carbon and nitrogen previous research on stable isotopes for the reconstruction of human paleodiet has focused on determination of c 3 versus c 4 plants in the diet reliance on marine versus terrestrial resources and differentiation of trophic level results of this study indicate that of the animals consumed by humans only domestic dogs and one species of fish had 13 c values heavy enough to cause an increase in human 13 c values nitrogen isotope results show that great lakes fish have very high 15 n values this explains in part the high 15 n values observed in prehistoric and early historic humans from ontario the contribution of animal protein to human stable isotope values has important implications for the interpretation of paleodiet studies as applied to prehistoric adaptation

polyphased geodynamical evolution of the ougarta algeria magmatic complexes evidenced by paleomagnetic and ams studies abstract magnetic fabric and remanent magnetization of the ougarta magmatic complexes are carried essentially by secondary hematite probably related to hydrothermal events at the origin of ore deposits in the ougarta belt and are both not of primary origin magnetic foliation is of tectonic origin while magnetic lineation could be related to hydrothermalism obtained paleomagnetic directions correspond to syn folding or post folding remagnetizations the comparison with the african apwp indicates famenian tournaisian and visean ages for these remagnetizations at least two deformation phases with different folding orientations much older than previously assumed affected the studied area

disintegration of the continental margin of northwestern gondwana late devonian of the eastern anti atlas morocco the devonian early carboniferous sequence in the eastern anti atlas represents a complete record of the last stage of the depositional and tectonic evolution along the northwestern margin of gondwana as a consequence of early variscan block faulting a platform and basin topography was established during the middle and late devonian platforms were covered by condensed cephalopod limestones sedimentation in the basins was mainly argillaceous with calcareous and turbiditic intercalations in the latest famennian early tournaisian the whole area was covered by delta deposits in the south passing into turbidites and olistostromes toward a continental slope farther north this sedimentary and structural evolution reflects the gradual foundering and disintegration of the northwestern continental margin of gondwana prior to the collisional stage in the late visean late carboniferous

growth dynamics and ecology of upper jurassic mounds with comparisons to mid palaeozoic mounds the mid palaeozoic including the late jurassic was a time of both widespread coral reef growth and pronounced mound formation a comparison of mound features and their general setting highlights despite all differences general similarities in overall growth dynamics mound formation was frequently driven by discontinuous patterns particularly by background sedimentation in many examples episodes of mound stabilisation by early lithification growth of microbolite crusts and winnowing of fines was followed by growth episodes of benthic fauna under reduced to negligible background sedimentation this pattern of variable sedimentation and organic buildups may have occurred in different orders and magnitudes inducing a fractal pattern in some mound complexes a composite approach in estimating growth rates of mounds demonstrates that highfrequency oscillations necessary for growth of most mounds might have ranged from a few thousand years to 4th and 5th order milankovich cycles that were superimposed by autocyclic factors d 2001 elsevier science b v all rights reserved

influence of mineralogy on granite decay induced by temperature increase experimental observations and stress simulation abstract rocks can be subjected to high temperatures in several instances as for example in geothermal processes or if affected by fires temperature variations lead to a complex stress distribution in crystalline rocks due to mineral thermal expansion in polymineralic such as granites these stresses depend on fabric parameters such as mineral proportion grain size and their related thermal properties eight granitic rocks were heated to less than 400 c and their decay patterns were observed and quantified by means of scanning electron microscopy heating was also modeled by finite element simulations oof software with polymineralic microstructures quartz feldspar and biotite contents were used as a variable in the model in order to elucidate the influence of mineralogy on the thermal elastic response of granites real and modeled heating showed similar trends of microcracking in microstructures and of thermal expansion coefficients microscopic observations of real samples revealed mainly intragranular microcracks in quartz opening of cleavage plains and deformation in mica simulations confirmed that in spite of the high thermal and anisotropic expansion of quartz the microstructure of rocks with large amounts of quartz does not necessarily experience large stresses biotite produces a concentration of stresses along their grain boundaries as a result oof models with 10 biotite showed higher stresses than monomineral ones thermal expansion coefficients of real granites fitted within the limits of the simulated ones proving once more the success of using finite element modeling applied to polymineralic rocks

the gondwana laurussia convergence process evidence from the middle mississippian visean palynostratigraphic record the gondwana laurussia convergence process can be explored by studying the middle mississippian visean palynoflora of northwest africa statistical analysis of the visean miospore assemblages reported from morocco defines two populations one with clear laurussian affinity from the northern margin of the western meseta and the other more gondwanan in composition from the southern part of the western meseta and anti atlas moreover no transitional assemblages have been described from the region these palynofloral variations are a consequence of the complex palaeogeography of the northwest african margin which was controlled by the variscan orogeny during visean times taking into consideration the palynofloral affinity of the miospore assemblages reported throughout the entire north african margin and the middle east it is possible to envisage a late carboniferous pangaea amalgamation process initially evolving from the west while in the east the ocean separating gondwana and laurussia persisted as an effective barrier to floral migration

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

isotopic and archaeological interpretations of diet in the central mississippi valley abstract this study will compare archaeological and isotopic characterizations of diet specifically the role of maize for woodland mississippian and oneota populations from the north american midcontinent archaeological interpretations have tended to associate maize dependence with the rise of major centres such as cahokia these models based upon volume and ubiquity of maize in village site middens and features frequently contrast the key role of maize in regional centres with the situation in smaller remote communities mississippian inhabitants of frontier villages for instances are assumed to be less maize dependent than their counterparts in larger and more complex communities recent analyses of stable carbon isotope ratios have however called into question standard archaeological interpretations a series of 13 c values that characterize the period of agricultural intensification in the central mississippi and illinois river valleys identifies significant maize dependence at locations some distance from cahokia during its period of major regional influence time transgressive trends apparent in maize ubiquity for the cahokia region also stand in contrast to those seen in diachronic sequences of 13 c values in this paper we present newly generated 13 c values for five sites from the central mississippi and illinois river regions archaeological and isotopic evidence for maize dependence is evaluated for biases that may underlie the seeming contradictory diachronic and synchronic patterning evident in the two data sets

massive tabulates in competition for space a case study from aferdou el mrakib middle devonian anti atlas morocco abstract aferdou el mrakib the largest carbonate buildup of the moroccan anti atlas is known for its rich givetian fossil assemblage dominated by corals the core part of the reef was either removed by erosion or pervasively dolomitised with corals preserved mostly in the talus beds deposited in the fore reef environment this paper focuses on massive colonial tabulate corals represented by heliolites porosus and members of the genus favosites which constituted the largest tabulates of aferdou el mrakib and are frequently found in the reef derived debris the study reconstructs survival strategies of these corals based on an analysis of their morphologies growth patterns as well as records of interactions with other organisms both h porosus and favosites are represented predominantly by domal growth forms as compared to the favositids the coralla of h porosus are considerably more abundant and attained notably larger sizes with some of the colonies exceeding 1 m in diameter even the largest coralla were in places found toppled and in upside down positions indicating their downslope transportation by gravity flows and possible periodic involvement of high energy events h porosus commonly encrusted and was encrusted by other organisms the encrustations usually coincide with very frequent sediment induced growth interruption surfaces found within the coralla the growth interruption surfaces rarely preserve the original sediment attesting the presence of mechanisms of sediment removal by the coral similar surfaces occur also in the favosites coralla but they are less common and often lined by distinct sediment intercalations few encrustations on favosites were demonstrated to have happened post mortem while encrustations on h porosus typically formed syn vivo as evidenced by the coral successfully overgrowing its epibionts h porosus was a resistant species which could endure frequent episodes of sediment influx and defend itself from aggressive encrusters favosites colonies in turn relied on selective settlement on more sparsely occupied substrates available in deeper parts of the aferdou el mrakib reef

devonian extension of the pan african crust north of the west african craton and its bearing on the variscan foreland deformation evidence from eastern anti atlas morocco

conodont biofacies patterns in the kellwasser facies upper frasnian lower famennian of the eastern anti atlas morocco abstract the abundant conodont fauna of a black limestone and shale lithology kellwasser facies of late frasnian early famennian age provides a significant example of environmental control on conodont distribution and abundance conodont collections from the upper gigas and upper crepida zones of the eastern anti atlas were examined biofacies maps for the conodont genera palmatolepis polygnathus icriodus ancyrodella and ancyrognathus were constructed and their facies distribution patterns analysed no significant restriction in conodont distribution was observed to be caused by the rise and extension of oxygen depleted water over the platform during the late frasnian early famennian the abundance of conodonts however appears to have been related to optimal food supply in the oxygenated portion of the water column conodont biofacies patterns observed in the upper devonian of the eastern anti atlas do not fit a simple ecological model involving distance from shore and depth of water the faunas of two intervals investigated exhibit a similar level of species diversity the pattern of which evidently follows the platform basin configuration but the majority of species shows a more or less random distribution the onset of black sediment deposition was characterized by the dominance of polygnathus and icriodus whereas towards its termination during the upper crepida zone time interval the genus palmatolepis clearly predominated this difference is a consequence of both a rise of sea level and of evolutionary changes in the composition of the conodont fauna during the early famennian

boulder weathering and erosion associated with a wildfire sierra ancha mountains arizona an april may 2000 coon creek fire burned 37 5 km 2 of the sierra ancha mountains 32 3 km miles north of globe az including 25 sandstone and 19 diorite boulders surveyed in 1989 and resurveyed after the burn after the summer 2000 monsoon season and after the winter 2001 season when viewed from the perspective of cumulative eroded area both sandstone and diorite displayed bimodal patterns with 79 of sandstone boulder area and 93 of diorite boulder area undergoing either no fire induced erosion or fire induced erosion 76 mm when stretched over cumulative boulder areas erosion due to the fire averaged 26 mm for sandstone and 42 mm for diorite post fire erosion from thunderstorm summer rains averaged i mm for 5 diorite and i mm for 10 sandstone boulders while only a single diorite boulder eroded an average of 1 2 mm after the winter winter erosion removed an average of 5 5 mm from 14 sandstone boulders thus fire appears to increase a rock s susceptibility to post fire weathering and erosion processes as predicted by goudie et al earth surf process landf 17 1992 605 in contrast to experimental research indicating the importance of size in fire weathering no statistically significant relationship exists between erosion and boulder height or boulder surface area a result similar to zimmerman et al quat res 42 1994 255 these data exclude 12 original sites and 85 boulders at sites impacted by the fire that could not be relocated with a reasonable cause for the lack of relocation being boulder obliteration by the fire given evidence from 1 0 be and 2 6 al cosmogenic nuclides earth planet sci lett 186 2001 269 supporting the importance of boulders in controlling evolution of nonglaciated bouldered landscapes geol soc amer bull 76 1965 1165 fire obliteration of boulders could be an important process driving drainage evolution in nonglaciated mountains

tracing the composition and origin of fluids at an ancient hydrocarbon seep hollard mound middle devonian morocco a nd ree and stable isotope study abstract for the first time nd isotope signatures combined with rare earth element ree concentrations were used in investigations of ancient seep carbonates the study was performed on the fossil hydrocarbon seep deposit of the middle devonian hollard mound eastern anti atlas morocco where nd isotopes ree concentrations and carbon and oxygen isotope ratios were measured to investigate the origin former migration pathways and composition of fluids relatively high end values compared to local eifelian seawater as well as consistently appearing positive eu anomalies in mree enriched shale normalized ree patterns of the seep carbonates provided evidence for interaction between the seeping fluids and the lower devonian basaltic volcaniclastics underlying the studied seep deposit strongly reducing conditions and increased temperature of methane formation could have constituted an additional factor in the eu enrichment of the investigated carbonate phases the presence of exclusively negative ce anomalies in these carbonates is in line with observations of other workers that seep limestones may not necessarily display positive ce anomalies indicative of precipitation under anoxic conditions the negative ce anomalies are attributed here to mixing between anoxic pore waters and oxic ce depleted seawater necessary to enable carbonate precipitation at seeps the methane rich fluids ascended most likely from below the volcaniclastic unit and inherited the enriched end signatures and positive eu anomalies due to fluid rock interactions during their seepage to the seafloor the carbon isotope data are most consistent with thermogenic origin of methane although contribution of abiotic and biogenic methane sources cannot be excluded our results indicate that neodymium isotope and rare earth element analyses constitute one of the most valuable tools for reconstructing former fluid migration patterns the study shows also that nd isotopes and eu anomalies can serve as sensitive tracers of fluid rock interactions at submarine springs

chemical weathering at rock art sites in western norway which mechanisms are active and how can they be retarded abstract petrographic study of rock samples from 10 western norwegian rock art sites shows that chemical weathering of the rock surfaces is due to a limited number of mineral dissolution reactions when the rock art is located on phyllites weathering is predominantly a result of chlorite and carbonate dissolution plus minor dissolution of apatite and garnet weathering of feldspathic metasandstones is also largely a result of carbonate and chlorite dissolution but dissolution of feldspar and epidote is also important in this case dissolution of carbonates feldspars and epidote depend upon a supply of acids whereas chlorite dissolution is an oxidative reaction controlled by the supply of oxygen from the atmosphere both types of weathering reactions could however be stopped if the rock art could be kept dry for instance by building a roof over the carvings covering the rock art with earth can also lower the rate of weathering but it is important to realize that the effect of such a cover will depend upon the composition of the rock at each site and upon the composition and design of the covering in cases where dissolution of carbonates and feldspar constitute the main problem it is probably sensible to include ground limestone or shell sand in the covering in order to neutralize acids whereas when chlorite dissolution is the dominant weathering process the covering should aim at establishing reducing conditions

evidence for late devonian vertical movements and extensional deformation in northern africa and arabia integration in the geodynamics of the devonian world 1 the upper paleozoic geodynamic evolution is discussed at the scale of a wide part of gondwana from north africa to arabia with the aim of giving an integrated tectonic scenario for the study domain we revisit six key areas namely the anti atlas belt morocco the bechar basin west algeria the hassi r mel high central algeria the talemezane arch south tunisia the western desert egypt and finally the high zagros belt iran below the so called hercynian unconformity which is in reality a highly composite discontinuity surface and subsurface data display a well known arch and basin geometry with basement highs and intervening paleozoic basins we show that this major feature results mainly from a late devonian event and can no longer be interpreted as a far effect of the variscan orogeny this event is characterized by a more or less diffuse extensional deformation and accompanied either by subsidence in the western part of the system or by an important uplift of probable thermal origin followed by erosion and peneplanation by the end of the devonian the whole region suffered a general subsidence governed by the progressive cooling of the lithosphere such a primary configuration is preserved in arabia with typical sag geometry of the carboniferous and permian deposits but strongly disturbed elsewhere by the conjugated effects of the variscan orogeny during the carboniferous and or by subsequent uplifts linked to the central atlantic and neo tethys rifting episodes in conclusion we try to integrate this new understanding in the geodynamics of the late devonian which at world scale is characterized by the onset of the variscan orogeny on the one hand and by magmatism rifting and basement uplift on the other hand

where did ancient carbonate mounds grow in bathyal depths or in shallow shelf waters abstract carbonate mounds are important and ubiquitous components of the sedimentary rock record throughout the phanerozoic nevertheless factors controlling their occurrence and growth remain enigmatic in particular because the depositional depths of such mounds are poorly constrained and it is assumed that fossil examples lack modern analogues factors currently used to constrain the water depth that ancient mounds grew in include water energy occurrence of specific organisms that perform photosynthesis particularly calcareous algae and distinct non biogenic components in reviewing the main criteria used to delineate water depth of formation of fossil carbonate mounds most if not all criteria traditionally used to assume shallow water settings appear to be no longer substantiated in the light of current knowledge gained from modern carbonate mounds high energy assumed to indicate shallow water conditions is ongoing in water as deep as 1000 m the occurrence of peloids and processes such as micritization is not diagnostic of water depth furthermore virtually none of the calcareous algae assumed to indicate the photic zone have a taxonomically granted affiliation over the last years research in the deep ocean in particular thanks to the deployment of new devices and techniques provided a good database revealing a wide distribution of modern carbonate mounds reviewing the characteristics of ancient carbonate mounds with emphasis on depositional settings and confronting the criteria used with current knowledge from sub recent and modern carbonate mounds we conclude that for many ancient mounds a bathyal origin is at least as likely as a shallow water origin this conclusion is well supported by the sedimentary records left by these modern mounds that are astonishingly similar to those seen in palaeozoic and mesozoic carbonate mounds

sedimentation rates and growth potential of tropical cool water and mud mound carbonate systems carbonate fixation in the ocean proceeds in three basic modes abiotically biotically induced with organic trigger and biotically controlled where organisms determine timing location and composition of the product the three modes combine in a variety of ways to produce carbonate sediment when viewed on the scale of formations and global facies belts three benthic carbonate production systems or factories emerge 1 the tropical shallow water system dominated by biotically controlled mainly photoautotrophic and abiotic precipitates 2 the cool water system dominated by biotically controlled mainly heterotrophic precipitates and 3 the mud mound system dominated by abiotic and biotically induced mainly microbial precipitates the sedimentation rates of all three factories decrease as the time span of observation increases this scaling trend is not just an artifact of ratio correlation it is almost certainly related to the episodic pulsating nature of sedimentation the growth potential of the three systems can be estimated by drawing the envelope of the maximum observed rates of aggradation the tropical system shows the highest rates 10

shallow water mud mounds of the early devonian buchan group east gippsland australia abstract the lower devonian rocky camp member of the murrindal limestone buchan group of southeastern australia consists of a series of carbonate mud mounds and smaller lagoonal bioherms the rocky camp mound is the best exposed of the mud mounds and has many characteristics in common with waulsortian carboniferous mounds detailed paleoecological and sedimentological studies indicate that the mound initially accumulated in the photic zone in contrast to most of the previously recorded mud mounds five facies are present in the mud mound a dasycladacean wackestone facies at the base of the mound represents a moderate energy shallow water bank environment within the photic zone a crinioidal wackestone facies was deposited in a laterally equivalent foreslope setting a poriferan crinoidal mudstone facies developed in a quiet deeper water lee side mound setting associated with a minor relative sea level rise a stromatoporoid coralline packstone facies in the upper part of the mound deposited in a high energy fair weather wave base mound front environment the crest of the mound is represented by a crinoidal receptaculitid packstone facies indicative of a moderate energy mound top environment in the photic zone sheltered by the mound front stromatoporoid coral communities a mound flank facies is present on the southern side of the mound and this consists of high energy crinoidal grainstones mud mound deposition was terminated by a transgression that deposited dark gray fossil poor marl of the overlying taravale formation the rocky camp mound appears to have originated in shallow water photic zone conditions and grew into a high energy environment with the mound being eventually colonized by corals and stromatoporoids the indications of a high energy environment during later mound growth growth form of colonial metazoans and grainstones of the flanking facies suggest that the micrite in the mound was autochthonous and implies the presence of an energy damping mechanism probably biological at the mound surface

the role of rock surface hardness and internal moisture in tafoni development in sandstone the development of cavernous weathering features such as tafoni remains poorly understood in particular the roles played by internal moisture and case hardening remain unclear in this study electric resistivity tomography ert has been used to map moisture distribution within inner walls of tafoni developed in sandstone and an equotip device used to measure rock surface hardness as a proxy measure of the degree of weathering and case hardening seven large tafoni in the golden gate highlands national park south africa varying in size and degree of development have been monitored a dynamic relationship between surface hardness degree of weathering and internal moisture regimes has been found we propose a new conceptual model which illustrates the complex interaction between case hardening and internal moisture and suggests a new direction for cavernous weathering research copyright 2011 john wiley sons ltd

strangers in a strange land stable isotope evidence for human migration in the dakhleh oasis egypt abstract this study utilizes a combination of both stable oxygen and nitrogen isotope ratios to determine migration patterns for a large sample of human remains from the kellis 2 cemetery c ad 250 in the dakhleh oasis egypt stable oxygen isotopic analysis has been used to identify potential migrants in several different populations in this study the data resultant from the combination of oxygen isotope ratios from bone apatite and nitrogen isotope ratios from bone collagen indicate that at least two individuals are not native to the oasis as shown by their lower nitrogen values and more positive oxygen isotopes approaching values documented for residents of the nile valley and nubia the most isotopically distinctive individual is lepromatous suggesting that he may have been exiled to the oasis from the nile valley interestingly all individuals who have different isotope values are male supporting the idea that males may have been involved in caravan trade between the oasis and the nile valley

geology of the early devonian oolitic iron ore of the gara djebilet field saharan platform algeria abstract the oolitic iron ore of the gara djebilet field occurs within the early devonian sediments of the tindouf basin algerian sahara particularly in the upper djebilet formation of pragian age three large lenses form three individual deposits extending e w for about 60 km namely gara west gara center and gara east the mineralization is interbedded with argillaceous to sandy sediments and it can be related to a barrier island palaeoenvironment bordered by an inner lagoon or shallow embayment and an epicontinental sea trapped by palaeozoic shoals the oolitic sediments show a mineralogy marked mainly by magnetite hematite goethite maghemite chamosite bavalite siderite apatite and quartz three paragenetic associations present a vertical distribution with a lower non magnetitic ore a magnetitic ore and an upper non magnetitic ore three petrographical facies types have been defined a cemented facies foc a detrital facies fod and a non detrital facies fond chemical data for the whole field show a difference between the lower non magnetitic ore fe 54 6 the magnetitic ore fe 57 8 and the upper non magnetitic ore fe 53 the magnetitic ore which corresponds mainly to the workable ore cutoff grade at 57 has the following composition sio2 4 9 al2o3 4 2 fe2o3 61 43 feo 19 2 and p2o5 1 8 the corresponding calculated economical ore reserves are 985 106t with 57 8 fe regarding the genesis of the oolitic iron ore a southern source is suggested for the iron with deposition taking place in a quiet environment there the ooids developed by an intrasedimentary accretion mechanism around detrital grain within an iron rich mud the gara djebilet field is an important occurrence of the north african palaeozoic ironstone belt extending from the zemmour to libya which also includes ironstones of ordovician silurian and devonian age

palaeomagnetism and age of mid palaeozoic ring complexes in niger west africa and tectonic implications summary detailed af and thermal demagnetization has been performed on 185 oriented samples from 36 sites in a series of basic to acid subvolcanic ring complexes in central and southern niger published rb sr whole rock and mineral isochrons from acid members of the suite range north to south from 480 ma to 320 ma two distinct vectors have been isolated by linear regression of demagnetization data 1 a due north and negative inclination rarely reversed component is present in basic rocks from 12 sites in four distinct northern complexes published rb sr ages date from 480 ma to 420 ma this component is carried by single domain magnetite occasionally also by titanhaematite and is considered to be primary acquired during the terminal stages of this igneous episode 40ar 39ar dating of biotite from three samples used in the palaeomagnetic study yield 435 myr ages 2 a due north and positive inclination rarely reversed direction is present as a second component in some of the basic suite sites and is the predominant component in most sites in syenitic to granodioritic rocks primary fe ti oxides are rare in these acid igneous rocks and the feldspars within them are usually pervasively altered this component carried primarily by haematite is believed to be either a modern day vrm or a secondary tcrm acquired during hydro thermal activity associated with widespread quaternary volcanism in the southern air the primary component gives a mean south pole at 43 4s 08 6e n 12 k 50 95 6 2 located southwest of cape town this position requires a rapid southward excursion of the gondwana a p w path in early silurian time but it is generally consistent with most of the other silurian devonian palaeomagnetic data from gondwana these however are from the lachlan fold belt in southeast australia whose relation to the australian craton in early palaeozoic time is not clear integrating all stratigraphic palaeoclimatic tectonic and other palaeomagnetic data for early and middle palaeozoic time suggests that the proto atlantic closed during the silurian period if a late devonian early carboniferous gondwana pole in central africa is valid the ocean may have opened again before the final closure and reassembly of gondwana in the late carboniferous

controls of mud mound formation the early devonian kess kess carbonates of the hamar laghdad antiatlas morocco the origin and development of early devonian late pragian to late zlichovian predominantly uppermost zlichovian as indicated by conodont faunas mud mounds of the hamar laghdad area in the eastern antiatlas morocco are controlled by extrinsic and intrinsic factors extrinsic factors include the existence of a paleohigh lochkovian volcaniclastics unidirectional currents and repeated storm events as well as sea level fluctuations intrinsic biologically induced factors are the preferred growth of organisms on the top and the flanks of the mounds because of more favourable ecological conditions and a rapid synsedimentary lithification of the steep mound flanks by interskeletal cementation of auloporid tabulate corals the mounds developed in an epicontinental basin below the wave base but within the range of storms the formation of the mounds started within the uppermost part of the bedded crinoid facies of the kess kess formation with the hydrological accumulation of a bioclastic pile this elevation became settled by crinoids and high diverse tabulate corals producing bioclastic sediment binding activities of the organisms were missing calcareous algae and stromatoporoids are completely absent baffling by thamnoporid tabulate corals might have occurred locally but was not important for the development of the mounds steep slopes to the north and less steep slopes to the south may be the result of north northwest to south southeast trending currents derived from orientation patterns of orthocone nautiloids in the uppermost beds of the kess kess formation a synsedimentary cementation of the flanks possibly triggered by submarine interskeletal cementation of patchily distributed auloporid colonies protected the bioclastic sediment against redistribution by frequent storms indicated by densely spaced eventstone intervals and partly also by the common stromatactis like structures within the mound facies accumulation of more parautochthonous bioclastic sediment within the mounds as compared to the intermound area therefore is caused by a self sustaining system of hydrologic piling of sediment triggered by storms preferred settlement of organisms upon these piles producing bioclastic sediment and coeval biocementation of the growing mound flanks this model differs from existing mud mound models in the lack or only minor significance of binding and baffling in the lack of mound facies sequences and in the greater importance of extrinsic control factors

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

late devonian and early carboniferous alpha diversity ecospace occupation vertebrate assemblages and bio events of southeastern morocco abstract the late devonian was a time of dramatic environmental perturbations affecting marine ecosystems both the kellwasser latest frasnian and the hangenberg crises latest famennian are primarily reported as phases of drastic decreases in marine diversity while the hangenberg crisis is also described as a bottleneck in vertebrate evolution fossil bearing localities with upper devonian strata are of great interest to assess variations in the effects of environmental perturbations on biodiversity for this purpose we examined changes in alpha diversity and ecospace utilization of 21 famennian late devonian and early tournaisian early carboniferous invertebrate associations containing 9828 specimens from madene el mrakib and aguelmous southern maider basin northeastern anti atlas morocco where some layers yield exceptionally preserved gnathostome remains both the invertebrate and vertebrate associations contain predominantly opportunistic and pelagic taxa indicating oxygen depletion near the seafloor in this region nevertheless the ecospace extension was fluctuating and correlated with regional and or global sea level changes and oxygenation of bottom waters in the maider basin the ecospace was depleted after and during several bio events such as the kellwasser and hangenberg crises the annulata event middle famennian as well as during the early tournaisian abiotic as well as biotic changes instability of the invertebrate ecosystem are considered to have influenced famennian vertebrate diversity because they were more or less directly dependent on invertebrates as a food source

reconstructing seawater circulation on the moroccan shelf of gondwana during the late devonian evidence from nd isotope composition of conodonts 1 the nd isotope composition of conodonts is used for the first time as a paleoceanographic proxy to reconstruct seawater circulation conodonts from two stratigraphic levels in the eastern anti atlas the lower part of the frasnian zone 11 base of the kellwasser facies and the boundary interval of the uppermost crepida rhomboidea zones top of the kellwasser facies were selected for reconstruction of seawater circulation on the moroccan shelf of gondwana during late devonian times the recognized lateral variations in nd values are in very good agreement with current related sedimentary features they provide evidence for communication of the moroccan shelf with the rheic ocean to the southwest and with the variscan sea to the north in the frasnian the general seawater flow was directed from the southwest to the east and was influenced by a local riverine input of low radiogenic nd from the south the west african craton and or the pan african ougarta belt and from the northwest the precambrian basement of the anti atlas the combined set of nd isotopic records and directional data from the middle famennian reveals a circulation pattern different from that of the frasnian it was dominated by a general westward flow with a countercurrent in the central tafilalt area the establishment of a new circulation system during the famennian suggests essential changes in paleogeography of the western part of the variscan realm

modern deep water coral mounds north of little bahama bank criteria for recognition of deep water coral bioherms in the rock record abstract deep water ahermatypic coral mounds are present at water depths of 1 000 1 300 m on the lower slope north of little bahama bank the mounds are patchily distributed over a minimum area of 2 500 km2 and typically display 5 40 m of relief above the surrounding sea bottom a diverse benthic community exists on these apparently unlithified mounds including l 1 genera and 16 species of ahermatypic coral bathypsammia caryophyllia deltocyathus desmophyllum enallopsammia javania madrepora polymyces solenosmilia stephanocyathus and a previously undescribed genus alcyonaceans gorgonians antipatharians hydroids ophiuroids crinoids barnacles galatheid crabs polychaetes gastropods bivalves and sponges conspicuously absent from the coral fauna are lop elia and dendrophyllia common deep water corals in other parts of the atlantic radiocarbon dates on fresh coral and gorgonian fragments of 940 40 and 860 50 years indicate the mounds are at least in part recent and are probably actively forming today bored and stained corals date at around 22 10314c years b p which establishes a minimum age for these mounds we speculate that the mounds develop on sea floor perturbations in areas where strong bottom currents provide needed oxygen and nutrients to the fauna the mounds may have undergone multi stage evolution from colony to thicket to coppice to bank this evolution may be accomplished through the in situ contribution of skeletal material along with the baffling and trapping of fine grained carbonate sediment winnowed from adjacent areas by bottom currents if found in the rock record the coral mounds north of little bahama bank would probably be considered bioherms geologists should thus be aware that scleractinian bioherms are not uniquely shallow water in origin the distinction between ancient deep and shallow water coral buildups involves using multiple recognition criteria including 1 presence or absence of algae 2 diversity of corals 3 coral morphology and microstructure 4 abundance of planktonic benthonic components 5 microborings 6 surrounding litho and biofacies 7 stable isotopes of carbon and oxygen and 8 trace element geochemistry particularly sr and u concentrations the distinction between deep and shallow water bioherms is crucial to regional paleoenvironmental and stratigraphic interpretations

middle to late famennian successions at ain jemaa moroccan meseta implications for regional correlation event stratigraphy and synsedimentary tectonics of nw gondwana

climate controlled mass extinctions facies and sea level changes around the devonian carboniferous boundary in the eastern anti atlas se morocco abstract detailed sedimentological and biostratigraphical studies of successions in the eastern anti atlas se morocco focused on changing depositional environments and reconstructions of sea level changes during the late famennian to middle tournaisian the investigations cover a transect from the central maider to the easternmost and southern tafilalt regions near the moroccan algerian border the moroccan data are compared with the standard succession of the german rhenish massif and with the regional and global stratigraphic record the results testify to high frequency sea level changes including two global transgressive and anoxic events the main hangenberg event hangenberg black shale level at the top of the wocklumeria zone upper devonian vi e and the lower alum shale event at the lower middle tournaisian lower carboniferous i ii boundary regionally both anoxic intervals coincided with mass extinctions followed by rapid radiation especially of pelagic biota a significant shallowing and regression occurred just below the devonian carboniferous boundary at the northern margin of gondwana and caused the sudden n nw progradation of a large deltaic complex over 300 500 km thick siliciclastic successions filled fast subsiding synsedimentary troughs of the maider and amessoui syncline southern tafilalt correlation with the glacial phases of southern gondwana south america south africa indicates a glacial eustatic origin of sea level changes and a major sea level fall in the scale of 100 m or more coinciding with the main regressive phase of the extended hangenberg crisis interval the new results are in accord with the hypothesis of an episode of cool humid climate at the end of the devonian that allowed contemporaneous glacial buildup in high latitudes and extensive clastic discharge in the middle latitudes of nw africa

possible origins of permian remagnetizations in devonian and carboniferous limestones from the moroccan anti atlas tafilalet and meseta abstract permian overprints have been recognized for several years in different regions of the hercynian chain this process seems to affect not only large internal parts but also external zones of the chain devonian limestones sampled in the tafilalet and maider massifs near erfoud and msissi reveal a strong permian component carried mainly by magnetite scanning electron microscope sem and x ray investigations were performed in order to unravel the origin of this magnetite permian remagnetizations are also present in visean limestones from the meseta isothermal remanent magnetization studies and sem analysis of magnetic separates show that this magnetization is carried mainly by pyrrhotite which could be a result of oxidation of pre existing pyrite

the role of thermal stress fatigue in the breakdown of rock in cold regions abstract many geomorphological studies have ignored the role of thermal stress fatigue engineers have long maintained that thermal stress is an effective process physicists and the ceramics industry have provided a theoretical foundation to explain the nature and mode of operation of thermal breakdown recent geomorphological studies have shown the importance of thermal stress in cold regions by means of high frequency rock temperature data which can identify rates of temperature change in excess of 2 c min 1 the occurrence of weathered material in cold but dry regions can be explained by thermal stress shock differential radiation receipts on slopes of varying orientation and gradient can exert a very strong effect

thermal fatigue and thermal shock in bedrock an attempt to unravel the geomorphic processes and products widespread acceptance in science at large notwithstanding the ability of thermal stresses to produce thermal fatigue tf and or thermal shock ts in bedrock and coarse debris in the field is often doubted commonly called insolation weathering in geomorphology the results of questionable laboratory experiments have led many geomorphologists to consider terrestrial temperatures to be inadequate to generate thermally induced stresses leading to rock failure the exceptions are the action of fire or lightning we comprehensively survey the general scientific literature on tf and ts while rigorously scrutinizing that relating to geomorphology findings indicate theoretical and experimental information is adequate to establish the feasibility of tf and ts in rock stemming from rock temperatures monitored in the field while ts may exhibit fracture patterns that are uniquely diagnostic those of tf lack any such attributes it would appear unlikely that tf can prepare or weaken rock to increase the likelihood of ts the question of whether widespread polygonal versus rectilinear cracking is diagnostic of ts is presently an open one as possible explanations invoke process es and or host material s and consequently to assign palaeoenvironmental significance to such fracture patterns is premature at this time further geomorphological laboratory research into tf and ts is merited as sufficient theoretical underpinning already exists however laboratory experimentation needs to be much more rigorously defined and executed and is faced with significant hurdles if it is to be effectively linked to field observations

on the persistence of weathering abstract the term weathering has been in use for a very long time but it has come to mean different things to different people and hence as scientific short hand it no longer functions here we question the tenets underpinning the most common usage of the term and note that the climate process linkage implicit to the term is often missing and amounts to misdirection rather than climate as the primary driver behind specific weathering processes it is argued that rock properties constitute the dominant control further a case is made for reconsideration of our present bipartite mechanical chemical division of weathering processes and of the weathering processes currently deemed to be those that occur as process studies become evermore reductionist in nature so the functionality of the term comes more and more into question the linkage between process and landform the scaling up attribute is seen as a current weakness and one that will become more confusing as reductionist approaches continue as a way forward it is suggested that weathering stripped of specific preconceived notions of specific processes be envisaged as a function of energy transfer and be investigated in that light identification of new processes as well as restructuring of known processes particularly when considering weathering on other planets is a potential outcome of such an approach with a process foundation rooted in energy transfer rock decay provides a better umbrella term and liberates researchers from the inescapable conceptual baggage implicit to the term weathering

stable isotopes and diet at ancient kerma upper nubia sudan abstract carbon and nitrogen stable isotope values were measured from bone collagen extracted from archaeological nubian human n 54 and faunal n 61 populations from the site of kerma sudan collagen suitable for isotopic analysis was extracted from 22 faunal and 48 human samples from the eastern cemetery site dated to the middle kerma c 2050 1750 bc and classic kerma c 1750 1500 bc periods respectively the isotopic data indicate that the human dietary regimen included a mix of c 3 and c 4 plant derived components with a larger c 4 component than previously reported in archaeological egyptian nile valley populations elevated 15 n values are attributed to consumption of dietary resources from a 15 n enriched terrestrial ecosystem the faunal isotope data also indicate the consumption of c 3 and c 4 plants the large range of 13 c values measured in both the human and faunal samples supports previous work suggesting that a significant portion of the populations buried at kerma may have originated elsewhere further confirming the nile valley as a major corridor for population movement in the region

evidence for freeze thaw events and their implications for rock weathering in northern canada ii the temperature at which water freezes in rock many undertakings have used either a single value or a narrow window of temperatures as a threshold for the freezing of water within rock these temperatures vary from 0 to 5 c with most windows being in the range 1 to 4 c based on thermal data these thresholds are commonly used to count the number of freeze thaw events as a basis for determining freeze thaw weathering data collected from northern canada indicate that the temperature at which freezing occurs can vary substantially even for the same site using exotherm and zero curtain observations from bricks at angles of 90 and 45 aligned to the four cardinal aspects the various temperatures at which water froze are shown bricks on the north and east commonly did exhibit freezing based on exotherms within the window 1 to 5 c while data for the south and west aspects showed substantial variation with freezes sometimes between 6 4 and 8 9 c the data were evaluated for evidence of zero curtain effects indicative of water freezing but no unequivocal events could be found and it is suggested that at the scale of observation used here they are unlikely it would therefore appear that the use of thermal thresholds may not be meaningful for evaluation of freeze thaw events the available data also indicate many instances when temperatures went substantially sub zero e g 20 c and yet no indication of water freezing occurred most likely because there was no water available to freeze this indicates that any form of freeze thaw event counting in the absence of some indicator of the presence of water and that it actually froze is flawed as thermal conditions alone are not adequate to indicate the occurrence or not of actual freeze thaw weathering events these data suggest that evaluations of freeze thaw occurrence based simply on thermal thresholds may be substantially in error copyright 2006 john wiley sons ltd

differentiating marine vs hydrothermal processes in devonian carbonatemounds using rare earth elements kess kess mounds anti atlas morocco abstract petrological and geochemical analyses were carried out on early devonian kess kess mound limestones of the seheb el rhassel group exposed in the hamar laghdad ridge tafilalt platform eastern anti atlas morocco in order to evaluate marine vs hydrothermal processes for the origin of the mounds hydrothermal fluid circulation affected limestone deposition resulting in the formation of a plumbing system preserved in the mound facies and inter mound facies as cavities veins and dykes shale normalized rare earth element ree patterns for limestones display pronounced light ree depletion compared to middle ree average prsn dysn 0 46 and heavy ree average prsn ybsn 0 55 a super chondritic y ho ratio up to 87 and positive la anomaly consistent with precipitation from normal marine seawater within our data set the ce anomaly as well as u and other trace element concentrations vary with facies providing evidence for variable redox conditions the presence of positive ce anomaly in carbonates of the plumbing system is consistent with precipitation under anoxic condition samples from mound facies and quartz veinlets in the upper part of the group show ree patterns consistent with precipitation from hydrothermal fluids early devonian hypothetical seawater ree patterns were calculated from samples showing normal marine ree patterns i e inter mound facies and from samples with weaker marine signature i e fossiliferous mound limestones and plumbing system deposits hypothetical patterns are slightly enriched in ree compared to modern open ocean seawater this study reveals that ree analysis is a powerful tool for understanding polygenetic carbonate systems it sheds light into the genesis of the kess kess mounds by reconstructing fluid pathways and palaeo redox conditions

the relations between modulus of elasticity and temperature in the context of the experimental simulation of rock weathering by fire fires occur frequently in many biomes and generate high temperatures on the ground surface there are many field examples of fire causing rock disintegration the simulation of fire in the laboratory using a furnace and the monitoring of changes in rock modulus of elasticity with a grindosonic apparatus reveal that different rocks respond differently to heating significant decreases in elasticity occur at temperatures as low as 200 c and granites display particularly marked reductions extended periods of heating are not required for significant reductions to occur it is postulated that the degree of change in elasticity as a result of simulated fire is such that rock outcrops subjected to real fires are likely to be sufficiently modified as to increase their susceptibility to erosion and weathering processes

trace elements and ree geochemistry of middle devonian carbonate mounds maider basin eastern anti atlas morocco implications for early diagenetic processes abstract trace and rare earth elements rees have proven their utility as tools for assessing the genesis and early diagenesis of widespread geological bodies such as carbonate mounds whose genetic processes are not yet fully understood carbonates from the middle devonian conical mud mounds of the maider basin eastern anti atlas morocco have been analysed for their ree and trace element distribution collectively the carbonates from the maider basin mud mounds appear to display coherent ree patterns three different geochemical patterns possibly related with three different diagenetic events include i dyke fills with a normal marine ree pattern probably precipitated in equilibrium with seawater ii mound micrite with a particular enrichment of overall ree contents and variable ce anomaly probably related to variation of ph increase of alkalinity or dissolution remineralization of organic matter during early diagenesis and iii haematite rich vein fills precipitated from venting fluids of probable hydrothermal origin our results reinforce the hypothesis that these mounds were probably affected by an early diagenesis induced by microbial activity and triggered by abundance of dispersed organic matter whilst venting may have affected the mounds during a later diagenetic phase

the south western branch of the variscan belt evidence from morocco abstract this work is based on the compilation and re evaluation of the most significant data either personal or from the literature concerning the moroccan variscides the latter constitute the only moderately disturbed or even undisturbed part of the south western branch of the variscan belt facing directly nw gondwana they include two orogenic segments namely the northern mauritanides and the meseta domain exposed in the saharan and atlas meseta regions respectively and a foreland belt cropping out essentially in the anti atlas the eastward thrust units of saharan morocco oulad dlim mostly originate from the west african craton wac border in an area of thin palaeozoic sedimentation thin skinned fold thrust foreland arcs develop progressively northward zemmour at the expense of the increasingly thick palaeozoic series whereas thick skinned deformation characterizes the inverted proximal paleomargin in the anti atlas domain as suggested by the meseta and anti atlas stratigraphic similarities the meseta domain corresponds to a collage of moderately displaced thinned crustal blocks from the distal gondwana paleomargin variscan deformation is dominated by nw verging thrusts and metamorphism developed in the thickened tectonic prism in relation with crustal anatexis at depth the meseta anti atlas boundary is a major ene trending transpressional dextral fault referred to as the south meseta fault smf discussing the correlations between the variscan segments of morocco and sw iberia allows us to suggest that a latitudinal transform zone similar to the smf separated these segments during the late palaeozoic subduction of the rheic ocean crust would have been directed se ward along both the iberian and moroccan meseta and nw ward south of the smf i e along the wac

weathering of granitic rocks by chlorides effect of the nature of the solution on weathering morphology five granites from nw spain were subjected to two salt spray weathering tests under controlled atmospheric conditions granite samples were exposed to a sodium chloride solution in the first test and to a complex solution sea water in the second subsequent examination of the rocks by light and petrographic microscopy clearly demonstrated the development of different weathering morphologies in each test the distribution of dissolved ions in samples taken at different depths from the weathered surfaces at the end of the experiments and the changes in weight of the samples during the tests also differed in our opinion these results were determined by the nature of the solution used although sodium chloride is the predominant salt in sea water the presence of other ions modifies its solubility thereby varying the dynamics of mobility and precipitation and thus the weathering morphology that develops copyright 2003 john wiley sons ltd

tafoni development in a cryotic environment an example from northern victoria land antarctica tafoni are a type of cavernous weathering widespread around the world despite the extensive distribution of the tafoni their genesis is not clear and is still a matter of debate also because they occur in such different climatic conditions and on so many different types of substrate geomorphological characterization of more than 60 tafoni in three different antarctic sites two coastal and one inland between 74 and 76 s with sampling of weathering products and salt occurrences are described together with thermal data on different surfaces and wind speed recorded in different periods of the year in a selected tafone close to the italian antarctic station the aim of this present study is to provide further information to help understand the processes involved in the growth of tafoni in a cryotic environment and the relationship of these processes to climate with particular attention to the thermal regime and the role of wind the new data presented in this paper suggest that there is no single key factor that drives the tafoni development although thermal stress seems the most efficient process particularly if we consider the short term fluctuations the data also confirm that other thermal processes such as freezing thawing cycles and thermal shock are not really effective for the development of tafoni in this area the wind speed measured within the tafoni is half that recorded outside thus favouring snow accumulation within the tafoni and therefore promoting salt crystallization on the other hand the wind effect on the thermal regime within the tafoni seems negligible while both salt weathering and thermal stress appear active in this cryotic environment these are azonal processes and are therefore active in other climatic areas where tafoni are widespread such as the mediterranean region copyright 2007 john wiley sons ltd

nature vs culture present day spatial distribution and preservation of open air rock art in the coa and douro river valleys portugal abstract late glacial and iron age open air rock art of the coa river valley shows a similar spatial distribution with several clusters along the coa and douro river tributaries that are mostly exposed to the southeast in this report we try to determine whether the artists of both periods deliberately chose the same natural panels for rock art or its present day spatial distribution is imposed by formation and weathering processes previous or subsequent to the engraving geological structural analysis from regional to field scales shows a nne ssw sinistral strike slip fault system that crosses the study area together with a set of fracture joints with the same orientation and formed by the same tectonic stress direct field measurement and the description of 713 natural panels engraved and un engraved reveal that the preserved rock art panels correspond to the most common tectonic fracture joint systems nne ssw of the study area locally the hydrographic network is conditioned by the same structural control differential weathering exists between the panels exposed on opposite margins of watercourses with preferential degradation of the rock art panel surfaces exposed to the nw we propose that on the scale of the valley the surface weathering of the rock art panels results from differential solar radiation humidity lichen and bryophyte colonisations interpretation of field observations a frequency probabilistic procedure pair wise comparison matrix and geographic information system analysis were combined to evaluate a coa panel formation and preservation predictive model using archaeological topographical and hydrological data four variables were extracted and weighted from the collected data including topographic slope and aspect solar radiation and cost weighted distance to watercourses which were used as environmental input data the archaeological input data rock art occurrences were used to calculate the variable ratings and to evaluate both the coa panel formation and preservation predictive model and external validation maps with the results showing an agreement of 80 and 70 respectively field verification revealed unknown rock art panels in areas with high and very high values the coa panel formation and preservation predictive model provides a useful framework to guide survey and heritage management

a multi method investigation of temperature moisture and salt dynamics in tafoni tafraoute morocco despite numerous investigations and theoretical models tafoni weathering is still not fully understood largely because of limited data available on temperature moisture and salt regimes we investigated tafoni developed in granite in the tafraoute region morocco through an exploratory two week multi method field campaign temperatures were measured with ibuttons and by means of infrared thermography moisture distribution and progress were captured with handheld moisture sensors and with drilled in ibuttons salts were analysed in drill dust samples from different positions and rock depths the results derived from very different techniques mutually support one another salts and moisture are concentrated near the base of the investigated tafoni probably due to a saturated pore water body around the base of rock tors salts are accumulated close to the rock surface in tafoni but not on the surrounding rock surfaces a clear correlation was found between moisture and salt contents within a tafone areas of higher humidity also display increased salt concentration near the surface the temperature humidity records allied with ionic analyses suggest that sodium sulfate dominates and is likely to undergo frequent phase changes from thenardite to mirabilite and vice versa two pathways of salt transport in and around tafoni are assumed based on the data infiltration with rainfall on the top and around tors and boulders and capillary rise from saturated pore water bodies to the surface copyright 2015 john wiley sons ltd

devonian rugose coral amplexus and its relation to submarine fluid seepage the rugose coral amplexus occurs frequently in the sedimentary cover of the devonian submarine volcanic intrusion in the eastern anti atlas southern morocco this study elucidates the palaeoecology of amplexus which forms very rich and mostly monospecific spot assemblages within the lower and middle devonian carbonates geological and isotopic evidences show that these associations developed at hydrothermal vents and at a cold seep site the assemblages are always spatially associated with micritic carbonate bodies occurring within bedded hemipelagic deposits the amplexus corals preferred locations in the close proximity of submarine hydrothermal fluid seepage but they generally avoided places with the most elevated temperatures the corals colonised also a hydrocarbon seep probably only in its terminal phase of development when the fluid flow was still at least periodically active this was only possible as a result of the corals following a calice in calice growth developed due to the environmental toxicity which facilitated selective survival of larvae that settled in the shelter of empty calices the amplexus corals appear to have constituted ecological opportunists thriving in the nutrient rich venting and seepage affected areas that were hostile for other benthic organisms it can be suspected that the unusual extremely simplified morphology of amplexus made it particularly well adapted to living in environments typified by harsh and unstable conditions

diagenesis of middle devonian carbonate mounds of the mader basin eastern anti atlas morocco abstract in the mader basin of the eastern anti atlas middle devonian carbonate mounds were established on a gently sloping ramp at moderate water depths primary stromatactis cavities in these mounds exhibit early marine shallow burial and deeper burial cementation the mound matrix was affected by neomorphic alteration stylolitization and dolomitization earliest cementation occurred in the marine environment nonluminescent to blotchy luminescent cloudy radiaxial calcites of originally high mg calcite composition coat the walls of stromatactis cavities and take up more than 50 of the primary pore space the isotopic signature d18o 2 6 0 2 pdb d13c 2 7 0 5 pdb is close to that of nonluminescent fabric retentive brachiopod shells in the same mounds and taken as the nearly pristine stable isotopic signature of mader basin seawater the high d18o values compared with middle devonian data of north america are interpreted to result from the mid latitudinal ca 35 s temperate water settings of the mader basin carbonate mounds the transition to the shallow burial realm is indicated by a typical non bright dull luminescence sequence nonluminescent scalenohedral cements pass into bright luminescent and banded luminescent scalenohedral cements which are overgrown in turn by dull to moderate luminescent blocky spar meteoric influence on that cement sequence can be excluded deeper burial diagenesis is represented by stylolitization ferroan calcite cementation and neomorphic alteration of the fine grained mound carbonates pressure solution and or outgassing of co2 are possible ion sources for ferroan calcite precipitation in the remaining pore space 18o depletion d18o 6 8 to 8 9 pdb of these cements can be calculated to elevated precipitation temperatures of 21 33 5 c and burial depths of 420 670 m microspar making up the bulk of the mounds was formed by a one step transformation of a precursor calcitic micrite low d18o values 6 9 p 2 1 pdb mottled luminescence and high fe concentrations indicate that this transformation also took place in the deeper burial realm

methods for measuring rock surface weathering and erosion a critical review studies of rates processes and modes of rock surface and near surface deterioration and also hardening are central to rock weathering and building stone research conservation and management there is a need to measure and monitor weathering at the rock atmosphere interface to facilitate understanding of climatic environmental and lithological controls on the evolution and development of surface weathering features this paper reviews long established and recently developed field and laboratory methods used by geomorphologists to monitor and measure the impact of weathering and erosion on physical and mechanical properties of exposed rock surfaces and their immediate subsurface key advances are highlighted their application to multi scalar understanding and modelling of rock surface weathering in different contexts is discussed and potential future advances to provide new insights into rock weathering durability and materials conservation are identified in highlighting key advantages and disadvantages of a wide range of methods to the broader earth science community the paper aims to contribute to further innovative thinking across disciplines to develop new methods for measuring and monitoring rock weathering

conodont based quantitative biostratigraphy for the eifelian of the eastern anti atlas morocco the measured ranges of 52 conodont taxa present in 7 eifelian sections of the eastern anti atlas in southern morocco have been as sembled by graphic correlation method into a chronostratigraphic framework the anti atlas regional composite developed in this study provides much higher stratigraphic res olution than the traditionally used conodont zonation it allows a subdivision of the eifelian into 65 7 composite standard units derived from the jebel ou driss section which was se lected as the standard reference section the framework appears to have a linear fit to time giving the first image of the relative duration of the conodont zones in the upper emsian to lower givetian interval the costatus kockeli anus and lower varcus chrons appear to have lasted more than two times longer than the partitus australis and or hemiansatus chrons an alternative upper eifelian lower givetian conodont zonation with zones of more equal duration is proposed several conodont index taxa in the anti atlas area display an almost synchronous appearance independent of fa cies conditions and shelf paleobathymetry the analysis by graphic correlation reveals significant differences in rate of sediment accu mulation between the tafilalt platform which had condensed sedimentation 2 5 m m y and the mader basin characterized by rates up to 40 m m y area the devonian rocks offer excellent condi tions for detailed biostratigraphical studies their depositional history reflects the process of disin tegration of the northern margin of the sahara cra ton wendt 1985 1988 in contrast to the rather uniformly developed upper silurian and lower devonian sedimentary rocks differential subsi dence affected the area during eifelian time and thus a platform to basin topography of the shelf began to originate this phase is biostratigraphi cally relatively well constrained conodonts were found in many sections providing a base for cor relation of eifelian rocks in the anti atlas bul tynck and hollard 1980 bultynck and jacobs 1981 bultynck 1985 1987 1989 1991 the fauna dominated by polygnathus elements is lo cally very abundant but some stratigraphically important eifelian index taxa are rare or absent so that the position of some zonal boundaries e g the base of the eifelian cannot be precisely rec ognized this is why bultynck 1987 proposed two alternative conodont zonations for the upper eifelian lower givetian interval in order to provide a more accurate basis for correlation of eifelian rocks and events in north ern africa we used the graphic correlation method to develop a composite standard section based on conodont data from the eastern anti at las our regional chronostratigraphic framework anti atlas regional composite provides a much more linear biostratigraphic subdivision than any previously used conodont zonation it offers moreover the best possible stratigraphic resolu tion useful for detailed analysis of the sedimen tary evolution of the study area during the middle devonian this contribution constitutes a first ap proach in the construction of the eifelian com posite standard with worldwide applicability in conventional biostratigraphy fossil zones are used to achieve correlation the graphic cor relation technique however produces a frame work that is founded on biostratigraphy but inte grates all the biostratigraphic events onto a composite standard this method was developed by shaw 1964 and was subsequently extended e g miller 1977 sweet 1979 edwards 1984 1989 to be applicable to nonpaleontologic and nonunique but chronostratigraphically signifi cant events including magnetic polarity data key lithological marker beds various geophysical log type data and stable isotope logs it constitutes a powerful tool for the analysis of synchroneity or nonsynchroneity of geologic events integrated with sequence stratigraphy and sedimentological data shaw s method of graphic correlation is one of the standard techniques applied in modern basin analysis e g neal et al 1994 geologic setting

erosion rates and weathering history of rock surfaces associated with aboriginal rock art engravings petroglyphs on burrup peninsula western australia from cosmogenic nuclide measurements abstract the burrup peninsula and surrounding dampier archipelago in western australia contain the world s largest known gallery of rock art engravings petroglyphs estimated to number up to 1 million images the peninsula is also the site of major industrial development and there are concerns that industrial emissions may adversely affect the stability and longevity of the rock art we have studied the natural processes and rates of weathering and erosion including the effects of fire that affect the stability of rock surfaces and hence the longevity of the rock art using cosmogenic nuclides the concentration of 10 be in quartz yields erosion rates in the range 0 15 0 48 mm 1000 years on horizontal rock surfaces and 0 34 2 30 mm 1000 years on vertical rock faces the former largely caused by mm scale surface flaking are amongst the lowest erosion rates measured by cosmogenic nuclides anywhere in the world the latter are inferred to represent a combination of mm scale flaking and very rare centimetre to metre scale block falls controlled by failure along joint planes such low erosion rates result from a combination of resistant rocks low relief and low rainfall favouring long term preservation of the petroglyphs long enough to encompass the known period of human settlement in australia