a regional approach for modeling cliff retreat rate the makhteshim country israel abstract cliff retreat rate significantly affect the evolution of landforms and cliff stability cliff retreat studies also provide intriguing clues regarding past geomorphic conditions and environmental changes we hereby present a model to calculate cliff retreat rate based on spatial data of cliff structure and morphology the model is applied to numerous cliffs in the arid makhteshim country israel and results are calibrated using published rates of two local cliffs the calculated retreat rates confirm previous assertions that the crater cliffs are receding very slowly but reveal that the rates vary significantly along the cliffs 1 18 cm ky 1 results also provide first estimates of retreat rates of other major cliffs in the region including fast retreat rates at the sede zin cliff 300 600 cm ky 1 the proposed model provides a robust analysis to account for local cliff talus morphology and yields rate estimates representative of current conditions rather than a long term geologic average rate results presented constitute important new insights into regional geomorphic processes and on the stability of specific cliff sections within the study area

imaging and interpreting the shallow crystalline crust abstract in the past many tests of high resolution seismic imaging methods utilizing off the shelf technology from hydrocarbon exploration have had only limited success some problems associated with the application of seismic profiling in the shallow crystalline crust differ from those encountered in sedimentary basins perhaps the most fundamental distinction stems from differences in statistical properties of the reflection coefficient time series analysis of power spectra derived from borehole data indicates that the reflection coefficients in the crystalline crust are depleted in the seismic bandwidth relative to sedimentary basins this fundamental difference must be considered in the design of shallow crustal seismic surveys in order to achieve success to a first approximation acoustic impedance variations in sedimentary basins are controlled by velocity changes whereas velocity and density can vary independently in the crystalline crust and changes in density may be relatively more important in controlling reflectivity in certain instances density fluctuations outweigh velocity fluctuations for example physical rock property data from mining districts in the canadian shield suggest that massive fe oxide or sulphide bodies will generate strong seismic reflections

crooked line 2d seismic reflection imaging in crystalline terrains part 2 migration seismic reflection surveys are frequently conducted over very complicated geological structure but surveying often must be confined to existing crooked roads or tracks typically data from such 2d crooked line surveys are processed using standard common midpoint cmp stacking techniques to obtain a 2d time section which is then 2d migrated in part i we show that a reflector dip component across the processing line can cause serious problems for standard cmp stacking we also propose a supplementary processing step in which cross dip is determined locally and cross dip moveout cdmo is removed from data to form an optimum cross dip stack however a crooked line survey is really a swath 3d survey and ideally we would like to obtain a 3d image of reflectivity surrounding the profile here we investigate the potential of 3d prestack kirchhoff migration to directly image all observed reflections i e we attempt to construct a 3d image volume of all reflectors viewed by the survey because reflectors t

reconstruction of past desert vegetation along the colorado river using packrat middens abstract the paleoecological reconstruction of pleistocene deserts along the colorado river of western north america is attempted using data from fossil packrat middens the colorado river drainage is set into a physiographic context along a gradient from the hyperarid colorado desert to the moist high elevations on the colorado plateau the pleistocene and modern distributions of individual plant species along this corridor are compared emphasizing records from the picacho peak area of the colorado desert and the eastern grand canyon in general plant species are now distributed 700 900 m higher in elevation and 400 700 km further up river than they were during the late wisconsin however some plant species have not conformed to the general pattern emphasizing the individualistic nature of species distributions in time

the significance of scarp retreat for cenozoic landform evolution on the colorado plateau u s a since the beginning of the cenozoic period several hundreds of metres of the sedimentary cover have been removed from the colorado plateau palaeoclimatic considerations show that the colorado plateau has been dominated by dry climates throughout the cenozoic with the possible exception of the early palaeocene today in the still prevailing arid climate which strongly accentuates differences in rock resistance the relief shows a structurally controlled cuesta scarp topography in the slightly deformed strata of alternating resistance in examining whether the denudational efficiency of scarp retreat was sufficient to account for the wide erosional gaps in the sedimentary cover rates of scarp retreat were determined by using the information of dated volcanic material and by applying a new method which calculates the amount of retreat from the width of beheaded valleys of known age rates of retreat range from 0 5 to 6 7 km my 1 the results show that the rates of retreat are controlled by the thickness and resistance of the caprocks a model of cenozoic scarp retreat demonstrates that the rates of recession calculated for the scarps in upper cretaceous rocks were sufficient to bring them into their present positions from the centre of the monument uplift on the central colorado plateau the late eocene positions of the cliffs in the early tertiary formations give an indication of their maximal extent after the upper cretaceous sediments had been removed from the uplifts erosion cut through successively older rocks and activated scarps in stratigraphically lower positions scarp retreat can operate simultaneously and independently at different levels which enabled this erosional mechanism to remove great proportions of the sedimentary cover of the colorado plateau during the cenozoic

southern abitibi greenstone belt archean crustal structure from seismic reflection profiles lithoprobe seismic reflection profiles from the 2 75 2 68 ga southern abitibi greenstone belt reveal subhorizontal reflection zones of regional extent in the upper 15 km of crust that contrast with the steep dips of rock units and structures at the surface the shallowest 6 12 km regional subhorizontal reflection zone is interpreted to be the base of the abitibi greenstone belt supracrustal assemblage which may be an intrusive and or tectonic contact shallowly dipping subparallel reflectors in the upper crust are interpreted as low angle faults consistent with out of sequence stratigraphy revealed by u pb geochronology truncations of reflectors suggest that regional steeply dipping gold mineralized fault zones penetrate to depths of 15 km the profiles are consistent with the kapuskasing crustal model of the central superior province wherein greenstone belts are underlain by middle crustal felsic intrusions and gneiss and a lower crustal zone of mafic gneiss and intrusions the profiles support tectonic models of deformation of the abitibi greenstone belt that invoke either folding and thrusting followed by regional steep faulting or folding and thrusting linked to the steep faults

sedimentary processes in the inner new york bight evidence from excess210pb and239 240pu abstract particle reactive radionuclides were determined in sediments from the inner new york bight to trace transport and storage of fine grained sediments and associated reactive materials seven sediment cores 20 50 cm in length were analyzed for water content loss on ignition loi and excess 210 pb three of these were also analyzed for 239 240 pu excepting some depth horizons in a core from a dredge spoil dumpsite every sample analyzed contained excess 210 pb variations in the concentration of excess 210 pb with depth in the sediment at all stations correlated strongly with loi which apparently traces that fraction of the sediment which is active in removing reactive elements from the water column in the cores analyzed for 239 240 pu every sample contained finite pu and pu concentrations correlated strongly with excess 210 pb the radionuclide distributions may be simply viewed as products of steady state sediment accumulation or of mixing geochemically reasonable accumulation rates are very high 0 5 2 6 g cm 2 y and could probably only be sustained by offshore transport of dumped materials at the other extreme the relationships between excess 210 pb and loi are compatible with rapid mixing of a 210 pb carrier phase traced by loi into the pre existing substrate with little or no actual accumulation other non steady state processes such as sediment gravity flow could also explain the observed distributions measured sediment inventories dpm cm 2 of excess 210 pb and pu at these stations are greatly in excess of those supportable by direct atmospheric deposition lateral supply is required incorporation of sedimentary fines into the sand substrate could make the inner new york bight an important repository of reactive materials

seismic reflection and borehole geophysical investigations in the matagami mining camp a high frequency vibroseis seismic survey was conducted by lithoprobe across a well known section of the matagami mining camp to assess the usefulness of seismic methods in lithological mapping the data have been reprocessed to enhance shallow reflections critical processing steps for the preservation of the shallow features include refraction static corrections cross dip corrections and first break mutes the seismic data were calibrated using geophysical logs from two boreholes adjacent to the profile physical rock property measurements suggest that strong reflectivity within the volcanic sequence occurs at rhyolite gabbro contacts the lower wabassee group a sequence of gabbros and basalts with interlayered rhyolite horizons has been identified as a seismic marker this reflective package overlays the horizon where most sulphide deposits are known to be located in the matagami mining camp seismic reflection methods can be used to map the deep volcanic stratigraphy and structures

numerical modeling of the late cenozoic geomorphic evolution of grand canyon arizona the late cenozoic geomorphic evolution of grand canyon has been influenced by three primary tectonic and drainage adjustment events first 1 km of relief was produced along the grand wash wheeler fault system beginning at 16 5 ma second the ancestral colorado river became integrated with the lower colorado river through grand canyon between 5 5 and 6 ma third the colorado river was influenced by plio quaternary normal faulting along the hurricane and toroweap faults despite the relatively firm constraints available on the timing of these events the geomorphic evolution of grand canyon is still not well constrained for example was there a deeply incised gorge in western grand canyon before colorado river integration how did incision rates vary through time and along the evolving river profile what is the role of isostatic rebound and plio quaternary faulting on the recent incision history of grand canyon in this paper i describe the results of a process based numerical modeling study designed to address these questions and to determine the plausibility of different proposed models for the erosional history of grand canyon the numerical model i developed integrates the stream power model for bedrock channel erosion with cliff retreat and the flexural isostatic response to erosion two end member paleodrainage and integration scenarios are considered in the first model i assume no incision in western grand canyon prior to 6 ma this model is equivalent to a lake overtopping scenario for colorado river integration in this scenario the model predicts that colorado river integration at 6 ma initiated the formation of a large 700 m knickpoint that migrated headward at a rate of 100 km ma resulting in rapid incision of western grand canyon down to the level of the redwall limestone from 6 to 4 ma and incision of eastern grand and marble canyons from 4 to 2 ma widening of grand canyon by cliff retreat triggered flexural isostatic rebound and renewed river incision of up to 350 m in plio quaternary time according to this model the model also indicates that plio quaternary normal faulting significantly dampened incision rates in western grand canyon relative to eastern grand canyon in the second paleodrainage scenario i assume that a 13 000 km 2 paleodrainage crossed the grand wash wheeler fault system at 16 5 ma the results of this model scenario indicate that relief production along the grand wash wheeler fault system could have initiated the formation of a large 700 m knickpoint that migrated headward at a rate of 15 km ma prior to 6 ma to form a 150 km long gorge in western grand canyon following integration at 6 ma the results of this model scenario are broadly similar to those of the first model i e rapid incision through grand and marble canyons from 6 to 2 ma followed by cliff retreat isostatic rebound and fault controlled incision the results of the second model scenario illustrate that headward erosion of a proto grand canyon could have been sufficient to capture the ancestral colorado river east of the shivwitz plateau

escarpment retreat in sedimentary tablelands and cuesta landscapes landforms mechanisms and patterns abstract although the general concept that escarpments in layered rocks retreat through time was offered more than 150 years ago recognizing the exact mechanisms patterns and rates of retreat remains a challenge in this paper we provide the state of the art of the theme of escarpment retreat reviewing both the classic contributions often forgotten but important case studies and the latest research in separate parts of the paper we discuss 1 terminology applied to the geomorphology of escarpments 2 the main assumptions and pathways of long term evolution of escarpments including conceptual models presented so far 3 processes involved in cliff retreat mainly weathering mass movements and erosion 4 the role of spring erosion and fluvial processes leading to fluvial dissection and development of canyons present in many tablelands 5 the possible role of climate change in escarpment evolution 6 rates of escarpment retreat in conclusions we summarize the major advances in our understanding of escarpment evolution of the last two three decades such as the recognition of the key role of emerging groundwater in non uniform escarpment retreat of an important role of silica dissolution and underground removal of dissolved solids increasing appreciation of rock properties in governing the patterns of escarpment retreat the proposal that cliffs do not necessarily retreat via catastrophic rock slope failures but may disintegrate in situ and the first attempts to date escarpment retreat using cosmogenic isotopes finally the remaining gaps and possible research priorities for the future are identified

use of packrat middens to determine rates of cliff retreat in the eastern grand canyon arizona packrat midden data can be used to calculate rates of cliff retreat by relating midden age to the distance between cliff face and midden regression analysis using 14 radiocarbon dated packrat deposits from the mississippian redwall limestone in the eastern grand canyon suggests that the redwall has been retreating at an average rate of 0 45 m 103 14c yr this rate of cliff retreat which is comparable to other cliff retreat rates reported from arid environments implies that the colorado river cut through the redwall limestone in the vicinity of horseshoe mesa about 3 7 m y b p

tectonic and metallogenic implications of regional seismic profiles in the timmins mining camp four regional seismic reflection profiles totalling 153 line km were acquired near timmins ontario within the southern abitibi greenstone belt five additional high resolution lines targeted specific metallogenically important features such as the porcupine destor deformation zone interpretation of these profiles individually and in a composite north south transect reveals a number of prominent bands of reflectors within the upper 15 km of the crust that define a series of folds or antiformal stacks of thrust nappes structures and stratigraphy mapped at the surface confirm structural culminations in these locations at depths greater than 10 km the reflectors have generally shallower dips implying broad folding major ore deposits such as those at the kidd creek hollinger mcintyre and dome mines are located on the northern steeply dipping limbs of these antiformal stacks implying that the fold structures focused post tectonic mineralizing fluids within the upper crust into the near surface the porcupine destor deformation zone is proximal to the large gold deposits near timmins and is revealed by the new seismic data to be a composite of early fold structures and late transpressive fault arrays

cenozoic range front faulting and development of the transantarctic mountains near cape surprise antarctica thermochronologic and geomorphologic constraints 1 the transantarctic mountains tam define the western flank of the west antarctic rift system cape surprise near the shackleton glacier in the central tam is the only location along the range s 3500 km length where upper paleozoic beacon supergroup strata are down faulted to near sea level previous studies have inferred a range front master normal fault accommodates extension and rock uplift across the tam front in this region the history of rock uplift is debated suggested as early as mesozoic typically cenozoic or even pliocene or younger structural observations apatite fission track aft thermochronology and geomorphologic mapping undertaken within the tam front east of the shackleton glacier indicate extension faulting and denudation was mostly late eocene late oligocene and likely into the early miocene an exhumed aft partial annealing zone is found at the coast and traced 50 km inland the base of that exhumed partial annealing zone indicates denudation accelerated at 40 ma near the coast and at 30 35 ma on the inland side of the tam front vertically offset aft isochrones across the tam front reveal a step faulted architecture rather than a single master fault the cumulative vertical offset of the 55 ma isochrone is 2 3 2 7 km compared to 2 4 2 6 km offset of beacon strata indicating that all significant normal faulting is cenozoic and not related to mesozoic extension within the west antarctic rift system denudation from 26 ma to 14 ma produced a locally preserved erosion surface within the tam front erosion surface remnants indicate the tam front has undergone minimal internal deformation and only 290 790 m of surface uplift along offshore faults since the middle miocene

from the semiarid landscapes of southwestern usa to the wet tropical zone of southeastern brazil reflections on the development of cuestas pediments and talus abstract classical geomorphological models consider that escarpment retreat of cuesta landforms is fastest in arid and semiarid regions which would be expected to lead to increased talus production however this is in disagreement with the piedmont zone of the colorado plateau cliffs arid semiarid region of southwestern usa where talus is as inconspicuous as the deposits of the cuesta escarpment footslopes of the parana basin wet tropical region of southeastern brazil thus this paper discusses the evolutionary processes of cuesta escarpments pediments and piedmont deposits in both wet tropical regions and arid zones considering the key areas of the serra geral ridge in the parana basin and the eastern central colorado plateau as examples this manuscript constitutes a comprehensive and critical review of the principal literature on the landform development of such regions research has revealed that despite the production of sediment fine coarse from the escarpments in the arid southwestern usa geochemical weathering and freeze thaw cycles quickly destroy talus deposits furthermore chemical weathering dissolves minerals and forms caverns within the rock walls of mesas and in amphitheaters and canyons influencing escarpment retreat directly despite mechanical processes being the most important factors controlling landform development on the other hand in regions characterized by the wet tropical climate of brazil geochemical processes are more intense and they destroy the talus very quickly enhancing deep weathering however mechanical morphogenesis is also frequent in such regions forming in deforested areas features very similar to those found in the badlands of dry zones chemical and physical mechanical processes have very different intensities in dry arid and wet tropical areas but these processes are very relevant to landform development in both environments the rates of escarpment retreat are higher in the dry areas of the colorado plateau than estimated for the brazilian tropical zones which is in accordance with classical models these variations are probably related not only to climate but also to lithological differences the tops of the mesas on the colorado plateau are supported by thin strongly cemented conglomeratic fluvial sandstones whereas the caprocks of the brazilian cuesta landforms comprise thick basalt flows capped by ferruginous cuirasses in some cases lithological characteristics are more important than climate regarding escarpment retreat

initiation development and benefits of lithoprobe shaping the direction of earth science research in canada and beyondthis article is one of a series of papers published in this special issue on the theme lithoprobe parameters processes and the evolution of a continent lithoprobe contribution 1480 lithoprobe is canada s national collaborative multidisciplinary earth science research project established to develop a comprehensive understanding of the evolution of northern north america it is regarded internationally as one of the most successful national geoscience projects ever undertaken part of lithoprobe s success derives from its history and organizational structure a one year phase i program 1984 1985 was highly successful phases ii to v carried the project forward until 2005 when funding terminated lithoprobe was organized as a decentralized research network of multidisciplinary scientific studies and collaborating scientists about 1500 scientific publications were generated lithoprobe s legacy also includes economic and social benefits new and improved understanding of earth history provides petroleum and mining companies with an enhanced knowledge base lithoprobe demonstrated the applicability of high resolution seismic reflection studies to mineral exploration development of a portable seismic refraction recorder and a long period magnetotelluric system led to technology transfer to canadian companies very high resolution seismic reflection studies applied first by lithoprobe are proving effective for exploration for uranium deposits in saskatchewan in the cratonic areas of canada lithoprobe seismic and magnetotelluric studies have provided significant new information relevant to exploration for diamonds on the west coast of canada lithoprobe studies provided data and a framework for better understanding the mega thrust earthquake hazard in the region lithoprobe established a highly effective public outreach strategy that involved the print and electronic media as well as material for educational purposes unequivocally lithoprobe has enhanced the already strong reputation of the earth sciences in canada

scarp retreat rates in semiarid environments from talus flatirons ebro basin ne spain abstract triangular slope facets or talus flatirons are presented as a useful tool for the calculation of scarp retreat rates in arid regions in the central sector of the ebro basin sequences of talus flatirons have been developed around mesas capped by miocene limestone these talus flatirons are grouped in four stages of slope evolution s2 s3 s4 s5 by the extrapolation of the relict talus profiles with the adjusted log functions the position of the scarp for each one of the stages is located the mean values obtained indicate a scarp retreat of 23 m between stages s3 and s2 8 m between s4 and s3 and 26 m between s5 and s4 the ages obtained by radiocarbon dating are 2529 52 b p and 2930 60 b p for stage s2 27 864 444 b p for s3 and 35 570 490 b p for s4 consequently the mean scarp retreat rates are 0 9 mm yr for the s2 s3 interval and 1 mm yr for s3 s4 the scarp retreat rate is related to the lithological and structural features of both the caprock and the underlying clay sediments and to the palaeoclimatic evolution of the region that controls the intensity of weathering and water erosion processes that affect the slope system

seismic reflection imaging over a massive sulfide deposit at the matagami mining camp quebec a 2 d seismic reflection profile was shot across the southern flank of the matagami mining camp almost directly above the recently discovered bell allard massive sulfide deposit now estimated at more than 6 million metric tons all orebodies found in the southern part of the mining camp including bell allard are located at the contact between the primarily basaltic wabassee group and the underlying rhyolitic watson lake group seismic reflections were recorded from the basalt rhyolite contacts of the lower wabassee group as well as from gabbro sills that intrude much of the volcanic stratigraphy a strong reflection from the top of the bell allard orebody was also detected but the reflection does not extend over the full width of the deposit as defined by drilling appearing to correlate with the lower pyrite rich zone faulting which can be interpreted from discontinuities in the observed reflections probably controlled the formation of the bell allard deposit if the interpreted gabbro sills are accepted as isotime markers then faulting of the deeper sill complex defines a series of half grabens within the rhyolitic watson lake group the bell allard deposit is found at the intersection of one of these apparently low angle normal faults with the top of the watson lake group indicating that sulfide mineralization may have been associated with fluid flow along the fault which likely penetrates to the underlying mafic intrusion although the precise geometry of subsurface faulting cannot be estimated from a single 2 d seismic profile these results indicate that a full 3 d seismic survey should allow the mapping of many of the subsurface fault systems and the verification of hypotheses of fault controlled deposit formation

seismic methods in mineral exploration and mine planning a general overview of past and present case histories and a look into the future abstractdue to high metal prices and increased difficulties in finding shallower deposits the exploration for and exploitation of mineral resources is expected to move to greater depths consequently seismic methods will become a more important tool to help unravel structures hosting mineral deposits at great depth for mine planning and exploration these methods also can be used with varying degrees of success to directly target mineral deposits at depth we review important contributions that have been made in developing these techniques for the mining industry with focus on four main regions australia europe canada and south africa a wide range of case studies are covered including some that are published in the special issue accompanying this article from surface to borehole seismic methods as well as petrophysical data and seismic modeling of mineral deposits at present high resolution 2d surveys mostly are performed in mining areas but there is a general increasing trend in the use of 3

50 000 years of vegetation and climate history on the colorado plateau utah and arizona usa sixty packrat middens were collected in canyonlands and grand canyon national parks and these series include sites north of areas that produced previous detailed series from the colorado plateau the exceptionally long time series obtained from each of three sites n48 000 14 cy r bp to present include some of the oldest middens yet discovered most middens contain a typical late wisconsinan glaciation mixture of mesic and xeric taxa evidence that plant species responded to climate change by range adjustments of elevational distribution based on individual criteria differences in elevational range from today for trees and shrubs ranged from no apparent change to as much as 1200 m difference the oldest middens from canyonlands np however differ in containing strictly xeric assemblages including middens incorporating needles of arizona single leaf pinyon far north of its current distribution similar aged middens from the eastern end of grand canyon np contain plants more typical of glacial climates but also contain fossils of one seed juniper near its current northern limit in arizona holocene middens reveal the development of modern vegetation assemblages on the colorado plateau recording departures of mesic taxa from low elevation sites and the arrival of modern dominant components much later published by university of washington

3d reflection seismic imaging at the 2 5 km deep cosc 1 scientific borehole central scandinavian caledonides the 2 5 km deep scientific cosc 1 borehole icdp 5054 1 a was successfully drilled with nearly complete core recovery during spring and summer of 2014 downhole and on core measurements through th

deep geometry of the sudbury structure from seismic reflection profiling seismic reflection data show the deep geometry of the sudbury structure to be markedly asymmetric the sudbury north range comprises shallowly south dipping sedimentary strata overlying a thick unit of heterolithic breccia and melt bodies layered rocks of the sudbury igneous complex and footwall gneiss reflections from the upper layers are interrupted by faults near the center of the sudbury basin whereas the basal mafic units and footwall gneiss continue dipping southward and appear to be tightly folded or truncated near the creighton fault in contrast the seismic image of the south range is dominated by a distinctive series of moderately south dipping reflections interpreted as thrust faults or shear zones on which severe telescoping and imbrication of lithological units and considerable northwest southeast shortening of the sudbury structure have occurred such shortening explains the noncircular shape of the structure and thus removes a critical objection to the sudbury impact crater hypothesis the new structural model is shown to be consistent with regional magnetic and gravity fields a large hidden ultramfic mafic mass is no longer required to explain the potential field data

speleothem u series constraints on scarp retreat rates and landscape evolution an example from the severn valley and cotswold hills gull caves uk modelling landscape evolution requires quantitative estimates of erosional processes dating erosional landscape features such as escarpments is usually difficult because of the lack of datable deposits some escarpments and valley margins are associated with the formation of mass movement caves sometimes known as gull or crevice caves which are typically restricted to within 0 5 km of the valley margin or scarp edge as in other caves these mass movement cavities may host speleothems as gull caves develop only after valley incision uranium series dating of speleothems within them can provide a minimum age for the timing of valley excavation and scarp formation here we present data from several gull caves in the cotswold hills which form the eastern flank of the severn valley in southern england u series ages from these gull caves yield estimates for both the minimum age of the cotswold escarpment and the maximum scarp retreat rate this is combined with data from geological modelling to propose a model for the evolution of the severn valley and the cotswold hills the data suggest that the location of the escarpment and regional topography is determined not by valley widening and scarp retreat but by the in situ generation of relief by differential erosion

evolution of the southern abitibi greenstone belt based on u pb geochronology autochthonous volcanic construction followed by plutonism regional deformation and sedimentation abstract new mapping and u pb zircon geochronological results in the southern abitibi greenstone belt sagb support an autochthonous regional stratigraphy comprised of nine supracrustal assemblages rather than the collage of allochthonous terranes proposed in recent publications based on lithological and geochronological criteria these supracrustal assemblages also encompass the swayze shining tree and montcalm greenstone belts indicating that despite separation by large granitic intrusions they are in fact part of one extensive greenstone belt in conjunction with the mapping the geochronological results support coherent upward facing stratigraphic sections with about 20 of the samples containing inherited zircons with ages similar to those found in underlying assemblages the seven oldest assemblages represent semi continuous volcanism from 2750 to 2697 ma the volcanism is compositionally diverse ranging from komatiite and tholeiitic basalt to calc alkaline mafic to felsic lavas intimate intermingling of the different magma clans occurs throughout much of the stratigraphic section regional fault control on the distribution of the volcanic assemblages provides evidence for early dip slip movement associated with volcanic extension dating back to at least 2725 ma the two youngest assemblages are dominantly sedimentary and were unconformably deposited on the volcanic assemblages in close proximity to regional faults the earlier sedimentary assemblage consists of turbidites and minor iron formation deposited from 2696 to 2692 ma and the youngest one of subaerial conglomerates fluvial sandstones and alkalic to shoshonitic volcanic rocks ranging in age from 2687 to 2675 ma the sedimentary assemblages are broadly contemporaneous with the emplacement of syntectonic granitic plutons regional folding and reactivated movement on the regional faults probably related to accretion of the abitibi to the superior province craton autochthonous repetition of different geodynamic environments over the 50 million years of volcanic activity with five dominantly tholeiitic komatiitic assemblages and two dominantly calc alkaline assemblages as well as the extensive intermingling of these different magma clans in a number of the assemblages appears to be unique to the archean it suggests complex large scale and long lived interaction between mantle plumes and subduction zone magmas the nd isotope data indicate a derivation of the diverse volcanic magmas from homogeneously depleted sources with end 2 5 0 5 demonstrating a lack of contamination by ancient enriched components

unraveling rift margin evolution and escarpment development ages along the dead sea fault using cosmogenic burial ages abstract the dead sea fault dsf is one of the most active plate boundaries in the world understanding the quaternary history and sediments of the dsf requires investigation into the neogene development of this plate boundary dsf lateral motion preceded significant extension and rift morphology by 10 ma sediments of the sedom formation dated here between 5 0 0 5 ma and 6 2 2 1 inf ma yielded extremely low 10be concentrations and 26al is absent these reflect the antiquity of the sediments deposited in the sedom lagoon which evolved in a subdued landscape and was connected to the mediterranean sea the base of the overlying amora formation deposited in the terminal amora lake which developed under increasing relief that promoted escarpment incision was dated at 3 3 0 8 0 9 ma burial ages of fluvial sediments within caves 3 4 0 2 ma and 3 6 0 4 ma represent the timing of initial incision initial dsf topography coincides with the earliest red sea morb s and the east anatolian fault initiation these suggest a change in the relative arabian african plate motion this change introduced the rifting component to the dsf followed by a significant subsidence margin uplift and a reorganization of relief and drainage pattern in the region resulting in the topographic framework observed today

landscape development in an hyperarid sandstone environment along the margins of the dead sea fault implications from dated rock falls in this study we explored the spatial and temporal relations between boulders and their original in situ locations on sandstone bedrock cliffs thiswas accomplished bycombining field observations withdating methods using cosmogenicisotopes 10 be and 14 c and optically stimulated luminescence osl our conclusions bear both on the landscape evolution and cliff retreat process in the hyperarid region of timna and on the methodology of estimating exposure ages using cosmogenic isotopes we recognize three discrete rock fall events at 31 ka 15 ka and 4 ka in this hyperarid region the most plausible triggering mechanism for rock fall events is strong ground acceleration caused by earthquakes generated by the nearby dead sea fault dsf our record however under represents the regional earthquake record implying that ongoing development of detachment cracks prior to the triggering event might be slower than the earthquake cycle cliff retreat rates calculated using the timing of rock fall events and estimated thickness of rock removed in each event range between 0 14 m ky 1 and 2 m ky 1 when only full cycles are considered we derive a more realistic range of 0 4 m ky 1 to 0 7 mk y 1 these rates are an order of magnitude faster than the calculated rate of surface lowering in the area we conclude that sandstone cliffs at timna retreat through episodic rock fall events that preserve the sharp imposing landscape characteristic to this region and that ongoing weathering of the cliff faces is minor a 10 20 difference in the 10 be concentrations in samples from matching boulder and cliff faces that have identical exposure histories and are located only a few meters apart indicates that cosmogenic nuclide production rates are sensitive to