diatom inferred salinity in palaeolakes an indirect tracer of climate change lakes in arid and semi arid regions respond to climatic change through shifts in lake water volume and ionic concentration because diatom distribution is highly correlated with lake hydrochemistry diatoms can be used to infer changes in salinity and brine composition and thus to infer past climates here we critically examine the use of diatom inferred salinity as a climate proxy with examples taken from both modern waterbodies and sedimentary profiles sediment records may contain assemblages mixed from periods or sites of differing hydrochemistries because of the high degree of spatial and temporal heterogeneity in saline systems dissolution and diagenesis in saline brines may further complicate interpretation of sedimentary assemblages furthermore threshold effects salinity regulation via groundwater seepage antecedent conditions and other aspects of local hydrology may modify the relationship between salinity change and climatic forcing these complexities necessitate critical examination of the ecology and taphonomy of sedimentary assemblages as well as evaluation of potential non linearities in the salinity climate relationship through comparison of diatom inferred salinity with other proxy records of hydrochemical change historical documents where they exist and with other regional lake systems

holocene diatom assemblages and their palaeoenvironmental interpretations in fayoum depression western desert egypt abstract diatom assemblages from the diatomaceous deposits of fayoum depression egypt were analysed to reconstruct the palaeoenvironmental changes during the early to middle holocene a total of 283 diatom species and varieties representing 57 genera were identified the stratigraphic distribution patterns of the recorded diatoms explained eight diatom assemblage zones which revealed an interesting history of shifts in paleosalinity ph and water level of the old fayoum lake as the water body filled in planktonic and benthic epiphytic assemblages alternate throughout the studied sections the alternations reflect paleolimnologic conditions as water levels rose and fell the diatom results have shown four high stands of the freshwater lake level during humid warmer wet climatic phases coinciding with abundance of planktonic stephanodiscus spp and aulacoseira granulata assemblage zones rising lake levels are alternated with phases of lowering freshwater lake level with relatively slight rises in salinity and alkalinity one phase during arid conditions is represented by an abundance of a benthic navicula radiosa assemblage zone the second phase during cold and drier climate is dominated by a staurosira staurosirella spp assemblage zone the third phase is distinguished by predominance of epiphytic epithemia spp encyonema cymbella spp synedra spp and cocconeis placentula assemblage zones during warm arid conditions

the eastern termination of the zagros fold and thrust belt iran structures evolution and relationships between salt plugs folding and faulting 1 the zagros mountains result from the ongoing collision between the arabian and central iran plates the main features of the eastern zagros are 1 numerous emerged or buried salt diapirs made up of late precambrian hormuz salt and 2 the irregular along strike shape of the collision related detachment folds with frequent bending to understand this layout four geological cross sections have been constructed from the persian gulf foreland basin to the inner part of the zagros fold and thrust belt shortening in the deformed parts of the sections is less than 10 and is mainly accommodated by detachment folding we show that late cenozoic folding occurred in a region that was already punctuated by salt domes and diapirs in fact almost continuous halokinesis developed since the earlier paleozoic i e just short time after the deposition of the hormuz salt and continued up to the present these preexisting salt structures and their relevant local thickening strongly influenced both the localization and the direction of folds

applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

petroleum tectonic comparison of fold and thrust belts the zagros of iraq and iran the pyrenees of spain the sevier of western usa and the beni sub andean of bolivia this work was partially supported by subtetis pie csic 201830e039 and alpimed pie csic 201530e082 projects

salt tectonics and tear faulting in the central part of the zagros fold thrust belt iran abstract the central part of the zagros fold thrust belt is characterized by a series of right lateral and left lateral transverse tear fault systems some of them being ornamented by salt diapirs of the late precambrian early cambrian hormuz evaporitic series many deep seated extensional faults mainly along n s and few along nw se and ne sw were formed or reactivated during the late precambrian early cambrian and generated horsts and grabens the extensional faults controlled deposition distribution and thickness of the hormuz series salt walls and diapirs initiated by the early paleozoic especially along the extensional faults long term halokinesis gave rise to thin sedimentary cover above the salt diapirs and aggregated considerable volume of salt into the salt stocks they created weak zones in the sedimentary cover located approximately above the former and inactive deep seated extensional faults the n s to nne ssw direction of tectonic shortening during the neogene zagros folding was sub parallel with the strikes of the salt walls and rows of diapirs variations in thickness of the hormuz series prepared differences in the basal friction on both sides of the precambrian cambrian extensional faults which facilitated the zagros deformation front to advance faster wherever the salt layer was thicker consequently a series of tear fault systems developed along the rows of salt diapirs approximately above the precambrian cambrian extensional faults therefore the present surface expressions of the tear fault systems developed within the sedimentary cover during the zagros orogeny although the direction of the zagros shortening could also potentially reactivate the basement faults as strike slip structures subsurface data and majority of the moderate large earthquakes do not support basement involvement this suggests that the tear fault systems are detached on top of the hormuz series from the deep seated precambrian cambrian extensional faults in the basement

thermal evolution of the kuh e asmari and sim anticlines in the zagros fold and thrust belt implications for hydrocarbon generation abstract mixed layer clay minerals vitrinite reflectance and geochemical data from rock eval pyrolysis were used to constrain the burial evolution of the mesozoic cenozoic successions exposed at the kuh e asmari dezful embayment and sim anticlines fars province in the zagros fold and thrust belt in both areas late cretaceous to pliocene rocks show low levels of thermal maturity in the immature stages of hydrocarbon generation and early diagenetic conditions r0 i s and ro values

precipitation at lake qinghai ne qinghai tibet plateau and its relation to asian summer monsoons on decadal interdecadal scales during the past 500 years knowledge of the variability of precipitation at lake qinghai and its relation to the asian summer monsoons is helpful in constraining global climatic dynamics based on the high resolution precipitation indicators of 13 c of the organic matter 13 corg c n atomic ratio and the detrended total organic carbon content tocdetrended we found that the trend of precipitation at lake qinghai is inversely correlated to that of the indian summer monsoon ism inferred from layer thickness of a stalagmite s3 in southern oman on decadal interdecadal scales the chinese drought flood d f indices which can indicate the dryness wetness over large geographic areas are also used to indicate the intensity of the monsoon rainfall the d f index of xining near lake qinghai is synchronous with those of the regions in northern china where the east asian summer monsoon easm dominates while it is anti phase with those of southwestern china where ism prevails these materials suggest that during the past 500 years the source of moisture to lake qinghai on decadal interdecadal scales is controlled mainly by the easm but not by the ism it is also suggested that the intensity of easm is inversely related to that of the ism on decadal interdecadal scales the decadal interdecadal variability of enso may be responsible for the inverse relationship between the intensity of easm and that of ism 2007 elsevier b v all rights reserved

geometric analysis of fold development in overthrust terranes abstract fault bend folding fault propagation folding and detachment or decollement folding are three distinct scenarios for fold thrust interaction in overthrust terranes simple kink hinge models are used to determine the geometric associations implicit in each scenario bedding maintains constant thickness in the models except in the forelimb of the fold the forelimb is allowed to thicken or thin without limit the models address individual folds and the calculated fold geometries are balanced structures each mode of fold thrust interaction has a distinct set of geometric relationships final fold geometry is adequate in itself to discern many fault bend folds this is not the case for fault propagation and detachment folds these two fold forms have very similar geometric relationships some knowledge of the nature of the underlying thrust or decollement zone is usually needed to distinguish between them the geometry of a fold is altered in a predictable fashion by transport through an upper ramp hinge and by fault parallel shearing of the structure the shearing results in a tighter fold whereas transport through the ramp hinge produces a broader fold the viability of the geometric analysis technique is demonstrated through its application to a pair of detachment folds from the canadian cordillera the geometric analysis is also used to evaluate cross sections through subsurface structures in an example from the turner valley oil field the analysis indicates how the interpretation should be altered so as to balance the cross section the analysis reveals hidden assumptions and specific inconsistencies in structural interpretations

holocene climate variations from zhuyeze terminal lake records in east asian monsoon margin in arid northern china zhuyeze palaeolake is a terminal lake situated in the arid northern china in the east asian monsoon margin in order to examine the holocene palaeoclimatic change in the east asian monsoon margin qingtu lake section qtl from zhuyeze palaeolake is sampled in high resolution palaeoclimatic proxies such as grain size carbonate toc c n and delta 13 c of organic matter were analyzed eleven 14 c samples and six optically stimulated luminescence osl samples were dated to provide chronological control we also investigated the geomorphic features of lake shorelines in this area the results show that the climate was warm and dry in early holocene 9 5 7 0 cal ka bp cool and humid in mid holocene 7 0 4 8 cal ka bp and increasingly drier in late holocene since 4 8 cal ka bp comparisons of our records with other records in adjacent areas as well as with the records in the asian monsoon areas suggested that changes in effective moisture was synchronous in east asian monsoon marginal zone i e the pattern of dry early holocene humid mid holocene and aridity increasing late holocene and that the moisture optimum during the holocene was out of phase between asian monsoon margin and asian monsoonal dominated region possibly due to the high temperature at that time c 2010 university of washington published by elsevier inc all rights reserved zhuyeze palaeolake is a terminal lake situated in the arid northern china in the east asian monsoon margin in order to examine the holocene palaeoclimatic change in the east asian monsoon margin qingtu lake section qtl from zhuyeze palaeolake is sampled in high resolution palaeoclimatic proxies such as grain size carbonate toc c n and delta 13 c of organic matter were analyzed eleven 14 c samples and six optically stimulated luminescence osl samples were dated to provide chronological control we also investigated the geomorphic features of lake shorelines in this area the results show that the climate was warm and dry in early holocene 9 5 7 0 cal ka bp cool and humid in mid holocene 7 0 4 8 cal ka bp and increasingly drier in late holocene since 4 8 cal ka bp comparisons of our records with other records in adjacent areas as well as with the records in the asian monsoon areas suggested that changes in effective moisture was synchronous in east asian monsoon marginal zone i e the pattern of dry early holocene humid mid holocene and aridity increasing late holocene and that the moisture optimum during the holocene was out of phase between asian monsoon margin and asian monsoonal dominated region possibly due to the high temperature at that time c 2010 university of washington published by elsevier inc all rights reserved

environmental changes during the holocene climatic optimum in central europe human impact and natural causes abstract the priority programme changes of the geo biosphere aimed to reconstruct the environmental history of central europe with emphasis on the time interval from 9000 to 5500 cal bp time slice ii coinciding with the holocene climatic optimum during this period the onset of human activities such as settlement agriculture and animal husbandry caused environmental changes studies of different landscape units in germany were carried out to identify these anthropogenically induced changes and to distinguish them from natural effects on the environmental system the investigated archives included laminated lake sediments fluvial sediments colluvia and soils speleothems peat and coastal sediments the different archives were examined using refined research methods including a variety of sedimentary and geochemical analyses together with pollen analysis and dating methods for the establishment of a reliable chronology the results of the various research groups are summarised and critically discussed based on these results the climatic optimum can be subdivided into three periods 1 the early atlantic from 9000 to 7500 cal bp with negligible human impact and stable environmental conditions 2 the late atlantic during early and middle neolithic from 7500 to 6300 cal bp with pollen evidence for vegetation changes but only negligible changes detectable in other proxy records and 3 the late atlantic during the younger neolithic jungneolithikum after 6300 cal bp with human impact observed in many archives and proxy records especially in the pollen record but also in lacustrine and fluvial sediments during the whole climatic optimum natural causes such as minor shifts of temperature did not induce substantial environmental changes though some changes such as temporary droughts may have facilitated and amplified the observed human impact

regional stratigraphy of the zagros fold thrust belt of iran and its proforeland evolution the latest neoproterozoic through phanerozoic stratigraphy of the zagros fold thrust belt of iran has been revised in the light of recent investigations the revised stratigraphy consists of four groups of rocks each composed of a number of unconformity bounded megasequences representing various tectonosedimentary settings in the lowest group ranging in age from latest precambrian to devonian the uppermost neoproterozoic to middle cambrian rocks constitute a megasequence of evaporites siliciclastic deposits and interlayered carbonates which were deposited in pull apart basins that developed by the najd strike slip fault system this megasequence is overlain by a second one middle to late cambrian in age which consists of shallow marine siliciclastic and carbonate rocks representing deposition in an epicontinental platform the overlying shales siltstones and partly volcanogenic sandstones of ordovician silurian and devonian age are local remnants of stratigraphic units that were extensively eroded during development of several major unconformities the second group consists of two megasequences one permian and the other triassic composed of widespread transgressive basal siliciclastic rocks and overlying evaporitic carbonates of an equatorial epi pangean very shallow platformal sea the third group is composed of four megasequences formed of shallow and deep water carbonates with some siliciclastic and evaporite deposits which accumulated on a neo tethyan continental shelf during earliest jurassic through late turonian time the fourth group comprises siliciclastic and carbonate deposits of a largely underfilled nw to se trending forward and backward migrating late cretaceous to recent proforeland basin which has evolved as an integral part of the zagros orogen this last group consists of three megasequences ix x and xi with distinctive lateral and vertical facies variations which reflect specific tectonic events megasequence ix comprises uppermost turonian to middle maastrichtian prograding and retrograding siliciclastic and carbonate deposits whose accumulations reflect emplacement obduction of ophiolite slivers and subsequent collisional events in the zagros orogen megasequence x consists of uppermost maastrichtian to upper eocene siliciclastic and carbonate rocks which deposited first progradationally in front of the zagros orogenic wedge with reduced contractional tectonic activity and then retrogradationally due to intensified thrust stacking in the interior parts of the orogen megasequence xi consists of oligocene and lower miocene carbonate strata deposited retrogradationally shortly after a period of intensified late eocene thrust faulting in the deformational wedge and an overlying succession of upward coarsening northeasterly derived siliciclastic deposits of lower miocene to recent age which are composed of erosional byproducts of the southwest vergent zagros thrust sheets

kinematic modeling of folding above listric propagating thrusts abstract we describe a kinematic approach to simulate folds above listric propagating thrusts the model is based on a pre defined circular thrust geometry with a maximum central angle beyond which the thrust is planar inclined shear above the circular thrust and trishear in front of the thrust provided the trajectory of thrust propagation is established the model can be run forward and backwards we use this last feature to implement a global simulated annealing inverse modeling strategy this inverse modeling strategy is applied to synthetic folds as well as two real examples in offshore venezuela and the niger delta toe thrust system these three examples illustrate the benefits of the algorithm particularly in predicting the possible range of models that can fit the structures thrust geometry depth to detachment level and backlimb geometry have high impact in model parameters such as backlimb shear angle and fault slip while forelimb geometry is critical to constrain parameters such as fault propagation to fault slip ratio and trishear angle steep to overturned beds in forelimb areas are often not imaged by seismic so in the absence of additional well data considering all possible thrust fold geometries is critical for the modeling and whatever prediction e g hydrocarbon trap integrity is made from it

the african humid period and the record of marine upwelling from excess 230th in ocean drilling program hole 658c using a high resolution 230 th normalized record of sediment flux we document the deglacial and holocene history of north african aridity and coastal upwelling at ocean drilling program hole 658c at both the end of the younger dryas and after the 8 2 ka event there are significant drops in terrigenous accumulation at our site indicating an increase in the monsoon moisture flux over africa at this time at 5 5 ka there is an abrupt end to the african humid period and a return to stronger upwelling conditions for carbonate and opal fluxes the 230 th normalization completely changes the shape of each record based on percentage variations alone this site is a clear example of how variations in one sediment component can obscure changes in the others and it demonstrates the need for radionuclide measurements more generally in paleoceanography by taking our new records and a large amount of previous data from this site we conclude that increases in african moisture are tightly coupled to decreases in coastal upwelling intensity

modelling role of basement block rotation and strike slip faulting on structural pattern in cover units of fold and thrust belts a series of scaled analogue models are used to study de coupling between basement and cover deformation rigid basal blocks were rotated about a vertical axis in a bookshelf fashion which caused strike slip faulting along the blocks and in the overlying cover units of loose sand three different combinations of cover basement deformations are modelled i cover shortening before basement fault movement ii basement fault movement before cover shortening and iii simultaneous cover shortening with basement fault movement results show that the effect of the basement faults depends on the timing of their reactivation pre and syn orogenic basement fault movements have a significant impact on the structural pattern of the cover units whereas post orogenic basement fault movement has less influence on the thickened hinterland of the overlying belt the interaction of basement faulting and cover shortening results in the formation of rhombic structures in models with pre and syn orogenic basement strike slip faults rhombic blocks develop as a result of shortening of the overlying cover during basement faulting these rhombic blocks are similar in appearance to flower structures but are different in kinematics genesis and structural extent we compare these model results to both the zagros fold and thrust belt in southwestern iran and the alborz mountains in northern iran based on the model results we conclude that the traces of basement faults in cover units rotate and migrate towards the foreland during regional shortening as such these traces do not necessarily indicate the actual location or orientation of the basement faults which created them

mid to late holocene paleoclimatic changes and paleoenvironmental shifts inferred from pollen and diatom assemblages at lake hamra wadi el natrun western nile delta north western desert egypt abstract four palynological and three diatom zones of mid to late holocene are identified along a 370 cm long radiocarbon dated sediment core collected in lake hamra at wadi el natrun western nile delta egypt the mid late holocene between the predynastic to old kingdom was terrestrial wetland habitat with high seasonal rainfall and or nile flood as revealed by the dominance of cyperaceae pollen therefore people gathered in and around the nile valley and the agricultural activities increased during the early stage of late holocene coincident with the old kingdom to middle kingdom the paleoclimate became more arid with low seasonal precipitation and or nile flood as reflected by the increasing abundance of poaceae pollen and the absence of diatoms in addition to low values of toc tn ts c s and high values of c n these drought conditions possibly played a role in the old kingdom collapsing the late stage of the late holocene showed terrestrial wetland habitat with brackish conditions coupled with aquatic contribution under oxic conditions as inferred by the dominance of typha sp and amaranthaceae pollens as well as the diatom assemblages the relatively high values of toc c n c s coupled with low values of ts and tn reveal terrestrial origin of organic matter the late holocene recent has turned into a terrestrial wetland habitat with more brackish conditions and increasing in the seasonal rainfall as supported by the marked increasing of cyperaceae pollen the overall increase of the diatom inferred salinity dis as well as the marked increasing of c s tn and decreasing of toc c n and ts values towards the recent point to higher saline brackish wetland paleoenvironment and a terrestrial origin of the organic matter with more aquatic contribution under oxic conditions

abrupt onset and termination of the african humid period rapid climate responses to gradual insolation forcing a detailed ca 100 yr resolution and well dated 18 ams 14 c dates to 23 cal ka bp record of latest pleistocene holocene variations in terrigenous eolian sediment deposition at odp site 658c off cap blanc mauritania documents very abrupt large scale changes in subtropical north african climate the terrigenous record exhibits a well defined period of low influx between 14 8 and 5 5 cal ka bp associated with the african humid period when the sahara was nearly completely vegetated and supported numerous perennial lakes an arid interval corresponding to the younger dryas chronozone punctuates this humid period the african humid period has been attributed to a strengthening of the african monsoon due to gradual orbital increases in summer season insolation however the onset and termination of this humid period were very abrupt occurring within decades to centuries both transitions occurred when summer season insolation crossed a nearly identical threshold value which was 4 2 greater than present these abrupt climate responses to gradual insolation forcing require strongly non linear feedback processes and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non linear climate sensitivity the african monsoon climate system is thus a low latitude corollary to the bi stable behavior of high latitude deep ocean thermohaline circulation which is similarly capable of rapid and large amplitude climate transitions

100 000 years of african monsoon variability recorded in sediments of the nile margin abstract multiproxy analyses were performed on core ms27pt recovered in hemipelagic sediments deposited on the nile margin in order to reconstruct nile river palaeohydrological fluctuations during the last 100 000 years the strontium and neodymium isotope composition of the terrigenous fraction and the major element distribution reveal large and abrupt changes in source oscillating between a dominant aeolian saharan contribution during arid periods and a dominant nile river contribution during pluvial periods iron content shows a strong correlation with strontium and neodymium isotopes this allows the use of a high resolution continuous fe record as a proxy of blue nile sediment input over the last 100 000 years the detailed fe record with approximately 10 years resolution during pluvial periods is consistent with subtropical african records of well dated lake level fluctuations and thus constitutes a first continuous high resolution record of the east african monsoon regime intensity over ethiopia the detailed fe record shows the two main known pluvial periods attributed to strengthening of the african monsoon over ethiopia the nabtian period from 14 to 8 ka cal bp and the saharan period from 98 to 72 ka bp for the first time the last glacial period marine isotope stage mis 2 3 and 4 is documented with a continuous record showing large oscillations between high and low east african palaeo monsoon regimes the end of the nabtian period occurred at 8 ka in core ms27pt i e much earlier than on the east equatorial african region where it ended around 5 5 ka we interpret this as evidence that the southward shift of the rain belt occurred 3000 years earlier over the eastern ethiopian highland and propose that the gradual southward migration of the rain belt was associated with highly variable intensity and longer rainy seasons from 8 to 5 ka during the last glacial period two wet periods are present around 60 50 ka bp and 38 30 ka bp these two humid periods are in phase with the rise of atmospheric ch4 concentrations suggesting that wetland tropical african area was one of the sources of the atmospheric ch4 during the mis 3 during the last glacial maximum and mis 4 high saharan aeolian influxes in phase with records of aeolian dust deposited in east antarctica are documented this study highlights the importance of reconstructions of monsoon rainfall fluctuation at high temporal resolution to better understand the link between low and high latitude climate variability at millennial timescales

estimating the detachment depth in cross sections involving detachment folds this paper evaluates four different methods that have been proposed for the estimation of the detachment depth beneath detachment folds guidelines are presented in order to use the most suitable method in a particular region deformed by detachment folds these guidelines are constructed considering the assumptions of each method the influence of different parameters on the estimation of the detachment depth folding mechanisms cross sectional area variations position and orientation of the regional datum number of stratigraphic horizons bed length and thickness dip and position of the bounding lines initial thickness of the ductile unit single anticlines or fold trains and the available data ductile unit thickness regional datum detachment depth moreover a new simple method based on two previous methods is presented the advantages of this new method are that the calculations are extremely simple and it uses information from more than one stratigraphic horizon therefore it does not depend strongly on the accuracy of the data at one level the precision of the proposed methods is tested by their application to a number of natural and experimental single anticlines and fold trains it appears that better predictions are obtained when analysing a complete detachment fold train than when dealing with a single detachment anticline the reason might be that ductile material flow beneath the folds along the cross sectional plane is taken into account when dealing with a long enough cross section we also suggest some hypotheses concerning what the shape and dimensions of the detachment folds indicate about the detachment depth in those cases where insufficient data are available to apply the methods proposed

a reappraisal of earthquake focal mechanisms and active shortening in the zagros mountains of iran summary the zagros mountains of sw iran are one of the most seismically active intra continental fold and thrust belts on earth and an important element in the active tectonics of the middle east surface faulting associated with earthquakes is extremely rare and so most information about the active faulting comes from earthquakes we use long period teleseismic p and sh body waves to determine the orientation and depth of faulting in 16 new earthquakes and then evaluate and synthesize all the available teleseismic data on earthquake source parameters in the zagros we use this information to investigate the style and distribution of active faulting in the zagros and how it contributes to the n s shortening of the arabia eurasia collision when the data are ranked in quality and carefully evaluated simple patterns are seen that are not apparent when routine catalogue data are taken at face value an important change in the fault configuration occurs along strike of the belt in the nw overall convergence is oblique to the trend of the belt and the surface anticlines and is achieved by a spatial separation partitioning of the orthogonal strike slip and shortening components on separate parallel fault systems by contrast in the se overall convergence is orthogonal to the regional strike and achieved purely by thrusting in the central zagros between these two structural regimes deformation involves parallel strike slip faults that rotate about vertical axes allowing extension along the strike of the belt the overall configuration is similar to that seen in other curved shortening belts such as the himalaya and the java sumatra trench all the zagros earthquakes we have been able to check have centroids shallower than 20 km and are confined to the upper crust many of the larger earthquakes are likely to occur in the basement beneath the sedimentary cover which is active even beneath areas of known shallow structural decollement such as the dezful embayment the dominant style of shortening is high angle reverse faulting with dips 30 though some lower angle thrusting occurs in places active thrust and reverse faulting is relatively confined to the lower topography on the sw edge of the belt today and only strike slip faulting affects the higher topography profound vertical changes in structural and stratigraphic level indicate that a similar style of deformation was once active across the width of the simple folded belt but has progressively migrated sw over the last 5 ma there is no evidence for a seismically active structural decollement such as a low angle thrust beneath the zagros nor is there any seismic evidence for active subduction either beneath the zagros or beneath central iran instead the arabian margin seems to have shortened by distributed thickening of the basement only in the syntaxis of the oman line at the se end of the zagros is there any evidence for a low angle thrust of regional extent here earthquakes continue 50 km north of the zagros thrust line the geological suture between the arabian margin and central iran reaching depths of 30 km and may represent thrusting of arabian basement beneath central iran to this extent

tectonic control of the tejo river fluvial incision during the late cenozoic in rodao central portugal atlantic iberian border staircases of strath terraces and strongly incised valleys are the most typical landscape features of portuguese rivers this paper examines the incision achieved during the late cenozoic in an area crossed by the tejo river between the border with spain and the small town of gaviao in the more upstream reach of this area the tejo crosses the rodao tectonic depression where four levels of terraces are distinguished during the late cenozoic fluvial incision stage the rodao depression underwent less uplift than the adjacent areas along the river this is reflected by the greater thicknesses and spatial extent of the terraces terrace genesis was promoted by impoundment of alluvium behind a quartzitic ridge and the local presence of a soft substratum outside this tectonic depression the tejo has a narrow valley incised in the hercynian basement with some straight reaches that probably correspond to ne swand nnw sse faults the terraces being nearly absent geomorphological evidence of tectonic displacements affecting the rodao dissected terrace remnants is described geochronological dating of the two younger and lower terrace levels of this depression suggests a time averaged incision rate for the tejo in the rodao area of ca 1 0 m ka over the last 60 thousand years a clear discrepancy exists between this rate and the 0 1 m ka estimated for the longer period since the end of the pliocene although episodes of valley incision may be conditioned by climate and base level changes they may also have been controlled by local factors such as movement of small fault bounded blocks lithology and structure regional crustal uplift is considered to be the main control of the episodes of valley incision identified for this large long lived river a model is proposed in which successive regional uplift events tectonic phases essentially determined the long periods of rapid river downcutting that were punctuated by short periods of lateral erosion and later by some aggradation producing strath terraces d 2004 elsevier b v all rights reserved

structural framework of the zagros fold thrust belt iran abstract data gleaned from the literature on the zagros have been compiled and used in conjunction with new interpretations to provide a better picture of the structures sedimentation history and deformation of this hydrocarbon rich mountain belt the belt parallel mountain front the n s trending kazerun izeh and e w trending bala rud fault zones are defined as the master structural elements of the belt these fault zones divide the zagros basin into zones with different stratigraphic successions and different rheological profiles this resulted in different structural styles developing along the belt during the subsequent collision the kazerun and izeh fault zones acted as the depositional system transition zone between the lurestan and fars regions in jurassic cretaceous time and partly controlled the distribution of the kazhdumi formation one of the major source rocks by the end of the cretaceous the nw se trending mountain front fault divided the present folded belt of the zagros into a major foreland basin to the southwest and a piggyback basin to the northeast activity along other major transfer fault zones including the izeh kazerun and bala rud fault zones occurred at this time and controlled the sedimentation and subsidence of the dezful embayment the main target region for hydrocarbon exploration these fault zones controlled the thickness of the asmari formation one of the main reservoirs and also the considerable thickness and facies changes of the gachsaran formation the major seal to the asmari formation the present morphology of the mountain belt is interpreted as being mainly related to the pinning of the mountain front fault to the northwest of the dezful embayment and to the north of the strait of hormuz

intermediate decollement activation in response to the basal friction variation and its effect on folding style in the zagros fold thrust belt an analogue modeling approach although the role of various basal and intermediate decollement levels on structural style is well documented individually in many folded terrains the interaction between basal and intermediate de

u th ra fractionation during weathering and river transport the potential of radioactive disequilibria as tracers and chronometers of weathering processes has been recognised since the 1960 s e g rosholt et al 1966 hansen and stout 1968 this interest results from the dual property of the nuclides of the u and th radioactive series 1 to be fractionated during water rock interactions and 2 to have radioactive periods of the same order of magnitude as the time constants of many weathering processes and chemical transfers to ground and river waters therefore the study of radioactive disequilibria in surface environments should help to bring information about the nature the intensity but also the time scale of the water rock interactions produced during weathering and related chemical transfers these different properties have justified many of the studies on u th series in weathering profiles and river waters rosholt 1982 scott 1982 and osmond and ivanovich 1992 gave a synthesis of the studies of u series in weathering and surface hydrology up to the 1980 s and the 1990 s respectively here we present the main directions taken in these domains over the last decade they were partly stimulated by the analytical developments made in the measurement of the medium half life nuclides of 238u series i e 234u 230th 226ra in the mid 1980 s namely the use of thermal ionisation mass spectrometry tims e g chen et al 1986 edwards et al 1987 cohen et al 1991 chabaux 1993 chabaux et al 1994 and more recently the use of mc icp ms turner et al 2001 robinson et al 2002 for u and th isotope analysis details of these developments are given in this volume goldstein and stirling 2003 compared to the radioactive counting methods previously used the new techniques permit 1 a reduction by one order of magnitude or more of the size of the sample required for

paleolimnological records of climatic change in north america lacustrine fossil records provide long time series of data on limnological and climatic conditions these data are useful for establishing natural patterns of climate variability and for generating testable hypotheses about atmospheric circulation and climate ecosystem linkages shoreline features can indicate past lake level fluctuations that may reflect changes in moisture balance but often these records are discontinuous and are evidence of only extreme conditions the organisms geochemistry and sedimentology of lake sediments may provide a more continuous sequence of direct and indirect lake climate interactions in the past the most clearly interpretable paleolirnnological records of climatic change are those that use several lines of evidence to corroborate a climatic hypothesis and are from sites near an ecotone or in regions of extreme climate in all cases hydrologic setting mediates a lake s response to climate and must be considered in interpreting sedimentary sequences discussion of the impact of recent and future climatic changes necessitates a baseline against which the magnitude of observed or predicted changes can be measured commonly we look to recent history as a reference point for comparison however the landscape of recent decades or in some cases even centuries has been altered greatly by human activities thus to determine whether recent or future climatic change is unique or unusual we need long natural preanthropogenic time series against which observed or predicted climatic states and variability can be compared paleolimnological archives are a tool for looking at environmental patterns prior to anthropogenic impact and show a range of climatic states far greater than those documented by written records former strand lines of pluvial lakes bonneville and lahontan in the western u s for example testify to moisture extremes unsurpassed in recent centuries or even millennia in addition one can us the paleolimnological record as an independent climatic proxy against which patterns and rates of terrestrial response to climatic change can be compared here i present a broad overview of paleoclimatic reconstruction in north america from lacustrine records with a focus on the late quaternary the review is limited to climatic inference from paleolirnnological records a term i use in a restrictive sense to refer to records of past lake states physical biological and geochemical as opposed to records of past stream hydrology e g ely et al 1993 knox 1993 or terrestrial conditions i summarize paleolimnological tools available for reconstruction of past climate the capabilities and limitations of these tools

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

nile river sediment fluctuations over the past 7000 yr and their key role in sapropel development the provenance pattern of nile river sediments can be used as a proxy for paleoclimatic changes in east africa the 87sr 86sr ratios are particularly appropriate for such provenance investigations because the white nile drains predominantly crystalline basement rocks whereas the blue nile and atbara flow off the ethiopian highlands which consist of tertiary volcanic rocks a high resolution profile of 87sr 86sr and ti al ratios from a well dated core in the nile delta shows a close correspondence with known changes in nile flow over the past 7000 yr at times of higher river flow there was markedly decreased input of blue nile derived and total sediment this change was caused by northward movement of the inter tropical convergence zone resulting in increased vegetative cover in the ethiopian highlands due to higher rainfall and a longer wet season this inverse relationship between nile river flow and sediment flux may have had important implications in the development of agricultural technology in ancient egypt the marked minimum in 87sr 86sr at 4200 4500 yr b p is coincident with the end of the old kingdom in egypt and provides independent evidence that demise of the old kingdom might have been associated with an extended period of catastrophic low floods during the quaternary and late neogene there was periodic deposition of organic rich sediments sapropels in the eastern mediterranean that represent important indicators of major environmental change evidence from the ti al ratio suggests that the pattern of erosion and sediment supply from the nile catchment observed in this study also occurred throughout much of the neogene and quaternary the reduced inputs of blue nile sediment during times of sapropel formation contributed to the increased primary productivity by reducing the amount of phosphate removed on particles and to the observed change to n limitation in the eastern mediterranean which are important characteristics of sapropel deposition

arsenic enrichment in groundwater of the alluvial aquifers in bangladesh an overview arsenic in the groundwater of bangladesh is a serious natural calamity and a public health hazard most groundwater from the shallow alluvial aquifers 150 m particularly in the holocene plai

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

structural styles in the zagros simple folded zone iran arabia eurasia convergence is achieved in the nw zagros by a combination of shortening on nw se trending folds and thrusts mainly in the simple folded zone and by right lateral strike slip on the nw se trending main recent fault a balanced and restored cross section across this part of the range indicates c 49 km of shortening this probably occurred since c 5 ma providing an estimate of the long term shortening rate across the simple folded zone of c 10 mm a 1 the geometries of exposed structures suggest both basement thrusts and thin skinned decollement levels with major folds possibly nucleated above basement faults fold geometries indicate several decollement horizons shale units are candidates as well as evaporites in the neogene mesozoic lower palaeozoic and upper proterozoic successions the se part of the simple folded zone deforms by north south shortening on broadly east west trending folds and thrusts the link between these regions occurs via a set of fault blocks c 400 km wide in total each bounded by north south right lateral faults incremental changes in the strike of some of the folds occur across these right lateral faults with more east west orientations to the east

structures of the zagros fold thrust belt in iran the zagros fold thrust belt in iran forms the external part of the zagros active orogenic wedge it includes a sequence of heterogeneous latest neoproterozoic phanerozoic sedimentary cover strata 7 to 12 km thick and composed of alternating incompetent and competent layers overlying precambrian crystalline basement with a complex pre zagros structural fabric balancing structures of the cover statigraphic units in the zagros fold thrust belt requires in sequence and out of sequence involvement of the precambrian basement in the deformation six detailed balanced and retrodeformable cross sections which are constructed based on geological and geophysical data across various sectors of the belt show fault bend and fault propagation folds interpreted to have formed by slip on their subjacent thrusts out of sequence basement rooted thrusts as the interpretations in the constructed cross sections suggest have breached the cover basement interface and using incompetent cover strata for propagation cut across the cover structures and have created associated new folds superimposed upon the pre existing structures this style of deformation which has resulted in structural complexity of the belt characterizes a 200 to 300 km wide zone of distributed partly synchronous deformation with along strike and across strike variations it also implies that the zagros fold thrust belt as the external part of the orogenic wedge is still in its subcritical condition with internal deformation to achieve a critical taper in creating structural complexity in addition to out of sequence thrusting mechanically weak layers evaporites and mudstones of the cover strata have played a significant role by providing several detachment horizons shortening estimates across the belt are variable based on the constructed cross sections and their restorations minimum shortening estimates range from 16 percent to 30 percent in different sectors of the belt

formation of pyrite in freshwater sediments implications for c s ratios abstract the vertical distribution of pyrite acid volatile sulphide avs carbon and total s st were determined directly in the sediments of three lakes of different trophic status the results showed that freshwater pyrite formation reflects the redox status of the sediment or overlying waters it appears to form chiefly in reducing sediments which are subject to oxidizing influences by either a low turnover of organic carbon or periodic incursions of oxygen although there are high concentrations of avs in the near surface sediments of productive lakes very little is diagenetically converted to pyrite the feasibility of using sulphur ratios to diagnose whether rocks were formed in marine or freshwater environments is assessed new values for fes 2 fes of 0 5 5 show that this ratio does not provide a reliable test values of c sp where sp represents pyrite sulphur lie within the range of 160 700 and are much higher than previously measured ratios of c s t of 1 50 these new determinations show that if pyrite sulphur is unequivocally measured c s ratios may be a more sensitive indicator of salinity than had been previously thought

diatom inferred salinity and carbonate oxygen isotopes in holocene waterbodies of the western sahara and sahel africa abstract thirteen holocene palaeolakes in the western sahara and sahel have provided diatom records with carbonate oxygen isotope profiles available from eight of them most of these palaeolakes were groundwater fed lake water chemistry is reconstructed using diatom transfer functions lake water salinity and 18 o records are assembled with some isotopic and chemical groundwater data to better understand the response of the hydrological systems to climate changes over the past 15 000 yr data are in general agreement with climate simulations using coupled atmosphere ocean vegetation models which show a mid holocene wetting over the whole of northwest africa and a rapid drying by 6 4 ka the lake record also shows that at many sites the major lake infilling lags the end of the younger dryas by 1 2 ka regional differences also appear in the timing of the lake hydrological optimum ca 10 5 8 5 and 7 5 4 5 ka in the northern sahara 10 8 5 ka in the air tenere 10 5 7 or 4 5 in the sahel and 7 5 ka in lake chad the whole of the holocene is punctuated by short term drying events changes in water isotopic composition through time are partly explained by changes in rainfall amount and air humidity during the wet holocene period however the very low values in the southern sahara also imply changes in the moisture transport pattern or rainfall mechanisms data suggest an apparent decrease in 18 o content of precipitation along the monsoon flow in contrast with modern patterns changes in water availability and quality have driven population migrations in and out of the sahara sahel but relationships between climate and cultures are complex short term dry events might have driven inventive adaptations in the sahara drying at 5 4 5 ka coincides with both the collapse of the classical neolithic civilization and the settlement of new cultures

regional and local changes inferred from lacustrine organic matter deposited between the late glacial and mid holocene in the skaliska basin north eastern poland abstract the article presents the results of a combination of isotopic 15 n and 13 c geochemical toc tn c n and palaeobotanical investigations they were carried out on organic matter om that had been deposited from the younger dryas to the subboreal chronozone in palaolake sediments north eastern poland om from the late younger dryas consists only a small amount of toc and tn which together with the lack of aquatic macrophyte macrofossils confirm low primary production in the then reservoir the higher values of c n ratio 18 27 and 13 c ca 26 suggest that om was mainly terrestrial in origin during the preboreal chronozone 11 450 10 150 cal bp there was a probable deepening of the reservoir through the melting of dead ice this might have been intensified by an increase in precipitation and a fall in evapotranspiration during the preboreal oscillation from the early preboreal chronozone ca 11 345 cal bp a mixed source of om is indicated by c n ratio from 8 to 13 at the same time significant increase in toc and tn probably registered a rise in primary production in the palaeolake from the older part of the boreal chronozone ca 9865 cal bp algae productivity increased the c n ratio dropped to ca 8 and was then constant at the beginning of the atlantic chronozone ca 8650 cal bp a probable increase in the water level caused the partial relocation of om from the reed swamp belt and or the adjacent alder carr into deeper sections of the palaeolake an increase in toc and tn in the late atlantic chronozone ca 6965 6650 cal bp toc and tn decreased while 13 c had high values which probably reflected a more distinct stratification of the water column with anoxic bottom waters next in the late atlantic and early subboreal chronozone ca 6650 5205 cal bp the amount of om in palaeolake sediments was still rising the 13 c values dropped suggesting an intensification of processes of water mixing these processes were simultaneous with the constant shallowing of the palaeolake and the disappearance of habitats suitable for submerged macrophytes the topmost part of the profile is characteristic of a strong decomposition of peat causing a release of carbon dioxide and therefore the depletion of the carbon pool in the peat a drop in the c n ratio the concurrent upward trend of the 15 n curve is probably the effect of a greater anthropogenic impact on the palaeolake mire and its catchment and or more recent human interference in the topmost peat layers

late cenozoic and modern stress fields in the western fars iran implications for the tectonic and kinematic evolution of central zagros 1 the zagros iran developed during mio pliocene times in response to arabia eurasia convergence the western fars highlights a major bend of the deformation front and displays a remarkable set of nearly n s right lateral strike slip faults the kazerun borazjan karebass sabz pushan sarvestan faults oblique at high angle to the belt the region likely plays a major kinematic role by accommodating the change in shortening modes from partitioned in the western central zagros to nonpartitioned in the eastern zagros the inversion of focal mechanisms from small and moderate earthquakes shows a consistent n020 030 compression with a low ratio between differential stresses this regime accounts for the combination of strike slip and thrust type mechanisms through likely 2 3 permutations fault slip analysis reveals two successive late cenozoic regional compressional trends ne sw then n020 the latter is in good agreement with the present day stress the significance of the ne sw compression is discussed alternatively in terms of stress deviations or block rotations in relation to the strike slip fault system fieldwork and satellite imagery suggest that these faults behave first as transfer faults during folding of the cover and later as strike slip faults in agreement with the succession of stress regimes and the evolution of the dominant deformation style from thin skinned to thick skinned the first order stability of the collision related state of stress since 5 ma supports that the arabia eurasia convergence did not give rise to partitioning in the western fars but rather was and is still accommodated by distributed deformation involving both shortening and strike slip motion throughout the cover and the basement

impact of the late triassic dashtak intermediate detachment horizon on anticline geometry in the central frontal fars se zagros fold belt iran abstract integration of 2 d seismic lines well data and field studies allow us to determine the geometry variations of anticlines in the highly prolific central frontal fars region in the se zagros fold belt these variations are directly related to changes in thickness of the principal evaporitic intermediate detachment level located along the late triassic dashtak formation anticlines of short wavelength contain a significant over thickening of the evaporitic detachment level in their crestal domain that may reach 1900 m from an original thickness of 550 800 m folds containing thick dashtak evaporites show decoupling across the detachment level and thus a shift of the anticline crest in the underlying permo triassic carbonates of the dehram group which form the major gas reservoir in the central frontal fars four main parameters control the extent and distribution of the decoupled anticlines in the study area a original large thickness of the late triassic evaporitic basin b coinciding larger amounts of anhydrites with increasing total thickness of formation c parallel occurrences of abnormally high fluid pressures and d shortening variations across and along the strike of specific folds the present work relating the different parameters of the dashtak evaporites with the anticline geometry allows a better understanding of the fold geometry variations with depth which is applicable to oil and gas exploration in the se zagros and other similar hydrocarbon provinces characterised by intermediate detachment horizons

holocene climate and cultural evolution in late prehistoric early historic west asia abstract the precipitation climatology and the underlying climate mechanisms of the eastern mediterranean west asia and the indian subcontinent are reviewed with emphasis on upper and middle tropospheric flow in the subtropics and its steering of precipitation holocene climate change of the region is summarized from proxy records the indian monsoon weakened during the holocene over its northernmost region the ganges and indus catchments and the western arabian sea southern regions the indian peninsula do not show a reduction but an increase of summer monsoon rain across the holocene the long term trend towards drier conditions in the eastern mediterranean can be linked to a regionally complex monsoon evolution abrupt climate change events such as the widespread droughts around 8200 5200 and 4200 cal yr bp are suggested to be the result of altered subtropical upper level flow over the eastern mediterranean and asia the abrupt climate change events of the holocene radically altered precipitation fundamental for cereal agriculture across the expanse of late prehistoric early historic cultures known from the archaeological record in these regions social adaptations to reduced agro production in both dry farming and irrigation agriculture regions are visible in the archaeological record during each abrupt climate change event in west asia chronological refinement in both the paleoclimate and archaeological records and transfer functions for both precipitation and agro production are needed to understand precisely the evident causal linkages

an exploratory early and middle holocene sedimentary record with palynoforms and diatoms from faiyum lake egypt abstract we report on the sedimentology pollen and diatom records in a 26 m long core of holocene sediments from the tersa area near the centre of the faiyum depression egypt two radiocarbon and one osl dates have been obtained for the core dates range from 9545 60 cal bp to c 4040 bp these correspond respectively with the terminal palaeolithic qarunian and neolithic faiyum a faiyumian cultures the core is subdivided into 3 sedimentological units unit 1 21 26 m is very thinly laminated calcareous silt deposited in a deep water lake unit 2 9 5 21 m is finely laminated sand silt and carbonates formed as a lacustrine fan delta unit 3 9 5 m to the core top is formed of massive silt sandy silt and very fine grained flood plain sands planktonic diatom taxa mainly cyclostephanos aulacoseira cyclotella and stephanodiscus spp were abundant in units 1 2 a indicating deep open lake conditions magnetic minerals increased from the base of unit 2 indicating an increasing contribution of nile alluvium benthic taxa such as fragilaria cocconeis amphora and navicula tended to increase towards the core top from unit 2 b 3 a to 3 b indicative of lake shallowing and periods of low nile floods unit 3 c is barren of diatoms and is compatible with terrestrial flood plain conditions vegetation was mainly represented by herbaceous pollen throughout most of the core and in the topmost sediment pollen was scarce but pteridophyte osmundaceae spores increased arboreal vegetation had low percentages in most of the record but increased in the middle section of the core unit 2 a depositional deltaic environment was indicated throughout most of the core sub units 2 a 3 a where high abundances of poaceae cyperaceae chenopodiaceae amaranthaceae polypodiaceae and osmundaceae were recorded indicating high nile floods and fluctuating rainfall

late quaternary araucaria forest grassland campos fire and climate dynamics studied by high resolution pollen charcoal and multivariate analysis of the cambara do sul core in southern brazil abstract late quaternary vegetation fire and climate dynamics have been studied based on high resolution dated pollen and charcoal samples and multivariate data analysis the samples were taken from a 212 cm long sediment core of a bog in the cambara do sul region on the highlands of northeastern rio grande do sul state brazil the records including seven ams radiocarbon dates span 42 840 14c years for the first time extending the reconstruction of past environmental changes on the southern brazilian highlands back to the last glacial maximum lgm and pre lgm times the last 1100 years provide a decadal resolution initially the site was a permanent shallow lake which became seasonally dry after 26 900 14c yr bp seasonal climate with a long annual dry period prevailed until the late holocene the climate was somewhat wetter from 42 840 to 41 470 14c yr bp and from 41 470 to 26 900 14c yr bp than during the lgm and the late glacial period natural fires were rare but became very frequent after 7400 cal bp suggesting human occupation of the southernmost brazilian highlands since that time the records suggest that a species rich campos grassland vegetation existed in the area under a relatively dry and cold climate during glacial times under possibly as low as 10 c the record also suggests that small populations of araucaria were probably only present in refugia of deep and protected valleys and or on wetter coastal slopes campos vegetation existed through the early and mid holocene until 4320 cal yr bp after which araucaria forest expanded into the network of gallery forests along the streams by 1100 cal yr bp the araucaria forest replaced the campos vegetation reflecting the onset of the wettest period with no marked annual dry season the marked expansion of the araucaria forest coincided with the reduction in fire between ad 1520 and 1770 weinmannia became a common taxa in the araucaria forest suggesting a shift to warmer climatic conditions on the highlands this interval was synchronous with a cool phase within the little ice age known from north atlantic land records after about ad 1780 human activities changed the original forest composition first by introducing cattle into the forest and than by selective logging of araucaria trees multivariate analysis of the pollen data shows compositional changes that follow a trajectory alternating undirectional random phases and phases with directional sometimes fast transitions the results also show that compositional changes in the vegetation are slower during cool periods lgm compared to pre lgm and faster in warm periods holocene

source of nile sediments in the floodplain at saqqara inferred from mineralogical geochemical and pollen data and their palaeoclimatic and geoarchaeological significance abstract we present results of mineralogical light heavy and clay minerals geochemical and palynological investigations of floodplain sediments at saqqara our investigations provide new insights into our understanding of the source of the holocene nile sediments local palaeoclimate and palaeoenvironment of the floodplain at saqqara as well as the holocene palaeoclimatic variations at the nile headwaters we also investigate the relationship between nile floods and global climate changes and the impact of changing flood conditions on episodes of societal and central governmental collapse at the end of the egyptian old kingdom the holocene sequences recorded in two shallow drill cores saqa 21 and 22 were investigated and subdivided into six sedimentary units from underlying late pleistocene sand and gravels unit i to overlying modern soil unit viii early holocene sediments were essentially missing in the studied cores probably due to intensive erosion during the well known 8 2 kyr cal bp arid event middle holocene sediments are represented by unit ii which reflect high nile floods of equatorial african origin with less contribution from ethiopian sources the old kingdom sediments unit iii seems to be mainly of white nile sources with frequent contributions from the blue nile late holocene sediments unit iv vii show an increased contribution from blue nile river sources low nile flow episodes were recorded at 5 2 between units ii and iii 4 2 between units iii and iv 3 5 within unit iv and 2 7 kyr cal bp between units v and vi the second event corresponds to the first intermediate period fip and the third probably coincides with the second intermediate period 2nd ip periods of disorder in egypt

variations in temperature and extent of atlantic water in the northern north atlantic during the holocene we compare six high resolution holocene sediment cores along a s n transect on the norwegian svalbard continental margin from ca 601n to 77 41n northern north atlantic planktonic foraminifera in the cores were investigated to show the changes in upper surface and subsurface water mass distribution and properties including summer sea surface temperatures sst the cores are located below the axis of the norwegian current and the west spitsbergen current which today transport warm atlantic water to the arctic sediment accumulation rates are generally high at all the core sites allowing for a temporal resolution of 10 10 2 years sst is reconstructed using different types of transfer functions resulting in very similar sst trends with deviations of no more than 71 0 1 51c a transfer function based on the maximum likelihood statistical approach is found to be most relevant the reconstruction documents an abrupt change in planktonic foraminiferal faunal composition and an associated warming at the younger dryas preboreal transition the earliest part of the holocene was characterized by large temperature variability including the preboreal oscillations and the 8 2 k event in general the early holocene was characterized by ssts similar to those of today in the south and warmer than today in the north and a smaller s n temperature gradient 0 231c 1n compared to the present temperature gradient 0 461c 1n the southern proxy records 60 691n were more strongly influenced by slightly cooler subsurface water probably due to the seasonality of the orbital forcing and increased stratification due to freshening the northern records 72 77 41n display a millennial scale change associated with reduced insolation and a gradual weakening of the north atlantic thermohaline circulation thc the observed northwards amplification of the early holocene warming is comparable to the pattern of recent global warming and future climate modelling which predicts greater warming at higher latitudes the overall trend during mid and late holocene was a cooling in the north stable or weak warming in the south and a maximum s n sst gradient of ca 0 71c 1n at 5000 cal years bp superimposed on this trend were several abrupt temperature shifts four of these shifts dated to 9000 8000 5500 3000 and 1000 and 400 cal years bp appear to be global as they correlate with periods of global climate change in general there is a good correlation between the northern north atlantic temperature records and climate records from norway and svalbard r 2007 elsevier ltd all rights reserved

total organic carbon isotopes a novel proxy of lake level from lake qinghai in the qinghai tibet plateau china abstract the isotopic compositions of total organic carbon toc in lakes have been widely used to interpret paleoclimatic changes and the depositional environments of lake sediments however the main factors that affect the carbon isotopes of toc source of organic material water condition and others may vary in different lake sediment records which have limited the applicability of organic carbon isotopes in explaining biogeochemical and environmental changes in lakes in this study the organic carbon isotopic compositions of aquatic plants and surface sediments from lake qinghai and the living terrestrial plants and surface soils around the lake were systematically investigated to identify the sources of toc in the sediments and the significance of the organic carbon isotopes of sedimentary toc we found that the aquatic plants in the deep water areas 10 m were primarily dominated by cladophora but submerged plants potamogeton and ruppia l are the dominant species in shallow water 13 c org values 33 6 to 28 6 that are caused by c 3 like photosynthesis but the submerged plants have enriched 13 c org values 17 8 to 15 4 that are caused by c 4 like photosynthesis in addition the 13 c org values of cladophora become more negative with increasing water depth because of the slow photosynthetic rate caused by the weak light intensity at depth the isotopic data indicate that the carbon isotopes of organic material in the surface sediments are primarily controlled by the types of aquatic plant and that the 13 c org values of toc can be used to indicate the variation of the water depth lake level the organic carbon isotopic data from the 1f core showed that the water was shallow

palaeoclimatic changes deduced from 13c 12c and c n ratios of karewa lake sediments india most long palaeoclimatic records based on isotope studies have come from deep sea cores however in order to obtain information on regional climatic variations it is essential to study continental deposits the chief limitation has been the lack of well preserved datable geological records with the exception of cave formations we report here values for the stable carbon isotope ratio 13c 12c and the elemental carbon to nitrogen c n ratio of the organic fraction of the palaeomagnetically and radiometrically dated pleistocene karewa lake sediments from kashmir india together the two ratios which are anticorrelated provide an excellent marker of the source of organic matter in the lake the karewa sediments indicate at least three major episodes of shallower than normal levels these episodes of shallow lake levels and hence a cold dry climatic regime are broadly correctable with deep sea records

20 000 years of nile river dynamics and environmental changes in the nile catchment area as inferred from nile upper continental slope sediments multi proxy analysis of two marine sediment cores ms27pt and md04 2726 from the nile continental slope provides evidence of changes in nile sediment discharge related to changes in ethiopian african monsoon eam precipitation and allows us to reconstruct changes in nile river runoff vegetation and erosion in the nile headwaters sediment element composition and neodymium isotopic composition reveal significant changes in clastic sediment provenance with sources oscillating between a saharan aeolian contribution during the last glacial maximum deglacial transition and during the late holocene and a blue atbara nile fluvial contribution during the african humid period ahp this study provides a new understanding of past environmental changes between 14 6 and 14 13 ka there was a major input of sediments from the ethiopian highlands consistent with a stronger eam at that time climate in the nile basin was wetter between 14 8 and 8 4 ka with a corresponding increase in blue nile water and sediment discharge via the main nile into the eastern mediterranean the gradual climatic transition from the ahp to the present day dry climate was reflected in a decrease in blue nile sediment deposition and flood discharge between 8 4 and 3 7 ka with aridity at a maximum between 3 7 and 2 6 ka the onset of drier conditions in the blue nile basin seems to have begun before the 8 2 ka cooling event in the north atlantic we speculate that the climatic change from the wet ahp to the dry late holocene may have been a result of a break in the low latitude dynamic equilibrium between climate vegetation and erosion which may in turn have affected the climate in higher latitudes reduced nile flow may also have had an impact on levantine intermediate water originating in the eastern mediterranean through an increase in intermediate water formation

stream terrace genesis implications for soil development genesis of three distinct types of stream terraces can be understood through application of the concepts of tectonically induced downcutting base level of erosion complex response threshold of critical power diachronous and synchronous response times and static and dynamic equilibrium climatic and tectonic stream terraces are major terraces below which flights of minor complex response degradation terraces can form these three types of terraces can be summarized by describing a downcutting aggradation renewed downcutting sequence for streams with gravell bedload by tectonically induced downcutting streams degrade to achieve and maintain a dynamic equilibrium longitudinal profile at the base level of erosion lateral erosion bevels bedrock beneath active channels to create major straths that are the fundamental tectonic stream terrace landform aggradation events record brief reversals of long term tectonically induced downcutting because they raise active channels they may be considered as major the result of climatic perturbations or minor the result of complex response model types of perturbations climatically controlled aggradation followed by degradation leaves an aggradation surface this type of fill terrace tread is the fundamental climatic stream terrace landform aggradation surfaces may be buried by subsequent episodes of deposition unless intervening tectonically induced downcutting is sufficient for younger aggradation surfaces to form below older surfaces raising of the active channel by either tectonic uplift or by climatically induced aggradation provides the vertical space for degradation terraces to form first in alluvial fill and then in underlying bedrock along tectonically active streams these are complex response terraces because they result from interactions of dependent variables within a given fluvial system pauses in degradation to a new base level of erosion and or minor episodes of backfilling lead to formation of complex response fill cut and strath or of fill terraces fill cut terraces are formed in alluvium they are complex response terraces because they are higher than the base level of erosion good exposures and dating are needed to distinguish static equilibrium complex response minor strath terraces from dynamic equilibrium tectonic major straths strath terraces may be regarded as complex response terraces where degradation rates between times terrace tread formation exceed the long term uplift rate for the reach based on ages and positions of tectonic terraces late quaternary global climatic changes control aggradation events and even the times of cutting of major tectonic straths because the base level of erosion can not be attained during times of climatically driven aggradation degradation events most terrace soils form on treads of climatic and complex response terraces aggradation surfaces may provide an ideal flight of terraces on which to study a soils chronosequence each aggradation event is recorded by a single relict soil where tectonically induced downcutting is sufficient to provide clear altitudinal separation of the terrace treads multiple paleosols are typical of tectonically stable regions where younger aggradation events spread alluvium over treads of older climatic terraces pedons on a climatic terrace in a small fluvial system commonly are roughly synchronous variations of soil properties that can be attributed to temporal differences will be minor compared to altitudinally controlled climatic factors climatic terraces of adjacent watersheds also should be roughly synchronous correlatable variations of soil properties that can be attributed to temporal differences will be minor compared to lithologic and climatic factors between different watersheds such generalizations may not apply to basins with sufficient relief that geomorphic responses to climatic changes occur at different and overlapping times and to large rivers whose widely separated reaches are characterized by different response times to climatic perturbations soils on climatic terraces of distant watershedswill not be synchronous if their respective aggradation events occur during full glacial times and interglacial times soils on some complex response terraces may be diachronous within a given fluvial system and typically are diachronous between watersheds

millennial scale environmental changes in the asian monsoon margin during the holocene implicated by the lake evolution of huahai lake in the hexi corridor of northwest china the pattern of holocene environmental changes in the asian monsoon margin on a millennial timescale remains controversial based on lithological characteristics and sedimentological proxies we reconstructed holocene effective humidity changes and the lake evolution of huahai lake in the marginal area of the asian monsoon in the hexi corridor of nw china our results show that alluvial and aeolian deposition before 10 4 cal ka bp indicate an arid environment that lacustrine deposition from 10 4 to 8 8 cal ka bp indicates a transition from an arid to a humid environment and that lacustrine deposition from 8 8 to 5 5 cal ka bp occurred during the most humid conditions indicated by proxy records grain size carbonate toc and c n after 5 5 cal ka bp a depositional hiatus implicates an arid environment in the late holocene holocene environmental changes on millennial timescales in huahai lake imply that climate was arid to humid in the early holocene most humid in the mid holocene and arid in the late holocene these moisture changes were influenced by the asian monsoon particularly the transportation of water vapor by the indian monsoon in addition these moisture changes could have been affected by westerly winds that could have contributed to the water vapor supply to this region during the mid holocene the most humid conditions that occurred in the study area during the mid holocene may have been caused by strong westerlies and low levels of evaporation

sediment and pollen evidence for an early to mid holocene humid period in the eastern sahara a major problem in the study of holocene palaeoenvironments of the arid and wind deflated sahara is the low preservation potential of sediments from which a record of past climatic change can be established several indirect and imprecisely dated pieces of evidence have suggested humid episodes in the holocene that may have supported more productive ecosystems and denser human populations than today searches for reliable proxy data on past climates however have failed to yield satisfactory results we report here the discovery of buried lake muds in north west sudan in the hyperarid core of the eastern sahara which yield sedimentological and palynological data clearly interpretable as recording an early to mid holocene humid episode that supported a relatively deep stratified lake surrounded by tropical savanna woodland vegetation

the structure and kinematics of the southeastern zagros fold thrust belt iran from thin skinned to thick skinned tectonics 1 we present the first complete balanced cross section across the southeastern zagros fold thrust belt zftb the following main structural features emerge from this section 1 in the south of the zftb the proterozoic to recent sedimentary sequence has been decoupled from its panafrican basement along the ductile basal evaporites and folded into a series of large detachment anticlines ongoing shortening of these structures has resulted in migration of the basal salt layers into the cores of the anticlines and propagation of forelimb thrusts 2 in the north of the zftb deep seated ramps have folded the hanging wall rocks and produced imbrications and duplex structures within the higher levels of the sedimentary sequence 3 out of sequence thrusts linked to major seismogenic basement faults have cut through the structures in the cover of the zftb a three step incremental restoration of the section shows that two main phases of deformation can be separated in the tectonic evolution of the zftb a mio pliocene thin skinned phase in the course of which most of the structures in the cover were generated followed by a pliocene to recent thick skinned phase expressed as out of sequence faulting in the cover which is currently underlined by the seismicity within the basement in plan view the initial structures of the southeastern zftb developed with a curved shape essentially controlled by the shape and thickness of the underlying proterozoic salt basin i e the jura style in the following basement involved phase out of sequence thrusts cut at oblique angles through the preexisting structures of the cover the total shortening absorbed in the cover amounts to at least 45 km corresponding to a ratio of 22

basement faulting and the focal depths of the larger earthquakes in the zagros mountains iran summary the present day seismicity of the zagros seems to occur on high angle reverse faults distributed across the whole width of the belt it does not indicate activity on a single inclined thrust surface and there do not seem to have been any well located events at intermediate depths modelling of the long period teleseismic body waves of seven large earthquakes presented here shows their focal depths to be in the range 8 15 km this is thought to indicate faulting in the uppermost basement beneath the sedimentary cover though the absence of published seismic refraction results renders the sediment thickness uncertain faulting of this type and depth may occur on inherited normal faults which have subsequently been reactivated as thrusts such reactivation allows considerable shortening to take place in the early stages of continental collision without the subduction or excessive thickening of continental crust

great sand sea and selima sand sheet eastern sahara geochronology of desertification the relation of playa sediments and associated archeological sites with longitudinal dunes allows estimation of ages for the two uppermost strata of the great sand sea active dune formation corresponds with interpluvial periods of hyperaridity dune stability corresponds with semiarid pluvial periods archeological sites associated with truncated paleosols in the selima sand sheet suggest a similar climatic relation and indicate that the isohyets of central sudan shifted at least 400 kilometers northward during the peak of pluvials

geochemistry of core sediments from the middle tagus alluvial plain portugal since the last glacial using background determination methods to outline environmental changes this work deals with the geochemistry of the sediments from the santarem entre valas sev borehole in the middle tagus alluvial plain in portugal methods for background determination were used notably the concentration length and cumulative frequency methods both methods were in excellent agreement for the elements of interest namely au as fe u cu pb zn co and cr with these results five segments in the sev borehole were identified to have higher than background values for at least two or more of these elements the most important segment spans at least 1 500 years during the early holocene warm period with almost all elements with anomalous values this has been interpreted as the result of enhanced weathering of the host rocks upstream as a consequence of deglaciation since the last glacial maximum and general wetter conditions known to have occurred in this region no other segment of the core has shown a similar variety of elements with higher than background values but the upper segments correlate with the particular mineralogy on the sediments due to the development of an estuarine environment at circa 3 000 4 000 cal years bp the presence of charcoal and charred organic matter during the beginning of the bronze age characterises the segment with the first high values of cu but apart from deforestation and land use that affected this region at the time this anomaly is likely due to the chemical affinity of cu to organic matter and not to anthropogenic activities finally the upper meter of the core sediments spanning 812 years have a clear anthropogenic signal for cu also seen in other two boreholes and systematic high values for au and pb although cu is surely an indication of secular agricultural practices vineyard sulphatation au and pb might be the natural accumulation from weathering of ancient mine wastes scattered in the hercynian massif upstream

a study of fold characteristics and deformation style using the evolution of the land surface zagros simply folded belt iran abstract deformation styles within a fold thrust belt can be understood in terms of the spatial organization and geometry of the fold structures in young fold thrust belts such as the zagros this geometry is reflected topographically by concordant landform morphology thus the distribution of deformation structures can be characterized using satellite image analysis digital ele vation models the drainage network and geomorphological indicators the two distinct fold types considered in this study fault bend folds and detachment folds both trending nw se interact with streams flowing ne sw from the high zagros mountains into the persian gulf multiple abandoned stream channels cross fault bend folds related to deep seated thrust faults in contrast detachment folds which propagate laterally relatively rapidly are characterized by diverted major stream channels and dendritic minor channels at the fold tips thus these two fold types can be differentiated on the basis of their ge ometry fault bend folds being long linear and asymmetrical can be distinguished from detachment folds which tend to be shorter and symmetrical and on their associated geomorphological structures the spatial organization of these structures in the zagros simply folded belt indicates that deformation is the result of the interaction of footwall collapse and the associ ated formation of long linear fault bend folds and serial folding characterized by relatively short periclinal folds footwall collapse occurs first followed by serial folding to the ne i e in the hanging wall of the fault bend folds often on higher de tachments within the sediment pile 139

climate change and the collapse of the akkadian empire evidence from the deep sea the akkadian empire ruled mesopotamia from the headwaters of the tigris euphrates rivers to the persian gulf during the late third millennium b c archeological evidence has shown that this highly developed civilization collapsed abruptly near 4170 150 calendar yr b p perhaps related to a shift to more arid conditions detailed paleoclimate records to test this assertion from mesopotamia are rare but changes in regional aridity are preserved in adjacent ocean basins we document holocene changes in regional aridity using mineralogic and geochemical analyses of a marine sediment core from the gulf of oman which is directly downwind of mesopotamian dust source areas and archeological sites our results document a very abrupt increase in eolian dust and mesopotamian aridity accelerator mass spectrometer radiocarbon dated to 4025 125 calendar yr b p which persisted for 300 yr radiogenic nd and sr isotope analyses confirm that the observed increase in mineral dust was derived from mesopotamian source areas geochemical correlation of volcanic ash shards between the archeological site and marine sediment record establishes a direct temporal link between mesopotamian aridification and social collapse implicating a sudden shift to more arid conditions as a key factor contributing to the collapse of the akkadian empire

stable isotopes in bulk carbonates and organic matter in recent sediments of lake qinghai and their climatic implications abstract multi proxy indices on annual decadal scales during the past 600 years were developed from the surface sediments of lake qinghai based on 210pb and 137cs geochronology the 13ccarb 18ocarb and total carbonate content are consistent with one another in trends and their variations have been mainly ascribed to regional temperature it is suggested that the strong evaporation contributes in modifying 18o of lake water and 13c of the dissolved inorganic carbon of the surface water and appears to be responsible for the covariance between 13ccarb and 18ocarb photosynthesis of the aquatic plants appears to have played a significant role in determining 15n of organic matter the discrimination of 14n and 15n during photosynthesis may have triggered a positive linkage between temperatures and 15norg after removal of the stratigraphic trend variations of total organic carbon toc c n ratio and 13corg have been ascribed to local precipitation toc after removal of the stratigraphic trend is positively correlated with the c n ratio r 0 45

structural evolution of salt influenced fold and thrust belts a synthesis and new insights from basins containing isolated salt diapirs abstract lateral shortening is expressed in unique ways in salt basins especially if pre shortening diapirs are present we present an overview of previously published and new physical models and present new 3 d conceptual models that capture the evolution of shortening structures in salt provinces dominated by precursor isolated diapirs termed isolated diapir provinces in such provinces isolated diapirs form only a minor volumetric component of a sedimentary basin however due to the relative weakness of rock salt and their ability to localize strain during shortening they have a disproportionately large influence on structural development we find three key mechanical principles govern the processes and structural styles developed during shortening of isolated diapir provinces first salt diapirs shorten before surrounding sedimentary rocks due to their relative weakness and so form salients in the thrust front during early shortening second diapirs tend to nucleate folds and faults which radiate out from the diapirs third as diapir walls converge the roof must shorten extrusive salt sheets are expelled through thin roofs but thicker roofs resist piercement and so tend to undergo complex folding and faulting as a result of these principles the first order controls on the structural styles expressed across a shortened isolated diapir province are the configuration the diapir array prior to shortening the connectivity of these diapirs prior to shortening total strain magnitude and diapir roof thickness second order controls include the initial cross sectional and map view geometry of diapirs diapir size and diapir orientation with respect to the shortening direction

nile delta vegetation response to holocene climate variability a 7000 yr palynologic record from burullus lagoon nile delta egypt is assessed to investigate changes in terrestrial vegetation in response to nile flow previous studies in this region have shown that sea level rise in the early to mid holocene and markedly increased human land use during the past several centuries altered vegetation in and around the lagoon the pollen record from this study documents changes in delta vegetation that likely reflect variations in nile flow we suggest that cyperaceae pollen is a sensitive marker of precipitation over the nile headwaters and the resultant nile flow decreases in cyperaceae pollen interpreted as a marker for diminished nile flow as well as the increase in relative abundance of microscopic charcoal occurred at ca 6000 5500 ca 5000 ca 4200 and ca 3000 cal yr b p calibrated years before present these correspond to extreme regional and global aridity events associated with a more southerly mean position of the intertropical convergence zone these changes also recorded by other proxy studies indicate that several marked regional drought events affected the nile delta region and impacted ancient egyptian and middle eastern civilizations

the 2006 march 25 fin earthquakes iran insights into the vertical extents of faulting in the zagros simply folded belt summary we investigate the depth of faulting and its connection with surface folding in the zagros simply folded belt of iran our focus is a sequence of earthquakes mw 5 7 5 5 5 2 5 0 4 9 that struck the fin region in the south eastern simply folded belt on 2006 march 25 modelling ground displacements measured with radar interferometry we find that either n or s dipping model reverse faults can reproduce the observed fringe patterns despite the uncertainty in fault orientation we can constrain the vertical extents of rupture to between a top depth of 5 6 km and a bottom depth of 9 10 km consistent with the 8 km centroid depth of the largest earthquake we suggest that the faulting ruptured the thick competent group of paleozoic and mesozoic conglomerates and platform carbonates which makes up the lower part of the sedimentary cover the rupture probably terminated within the precambrian hormuz salt at its base and the cretaceous gurpi marls at its top these mechanically weak layers act as barriers to rupture separating faulting within the competent group from deformation in the layers above and below the pattern of coseismic surface uplift is centred on the common limb of the fin syncline and guniz anticline but is oblique by 20 to the trend of these open symmetric whaleback folds and also overlaps a section of the fin syncline axis these observations suggest that locally surface folding is decoupled from the underlying reverse faulting although the fin syncline and guniz anticline are symmetric structures some other nearby folds show a strong asymmetry with steep or overturned southern limbs consistent with growth above n dipping reverse faults this suggests that the simply folded belt contains a combination of forced folds and detachment folds we also investigate the distribution of locally recorded aftershocks in the weeks following the main earthquakes most of these occurred at depths of 10 30 km with a particularly high concentration of events at 20 25 km these aftershocks therefore lie within the crystalline basement rather than the sedimentary cover and are vertically separated from the main rupture this study confirms earlier suggestions that earthquakes of mw 5 6 are capable of being generated within the thick competent group of paleozoic and mesozoic sediments as well as in the basement below the hormuz salt formation

luminescence dating of holocene playa sediments of the egyptian plateau western desert egypt abstract this study is part of a multidisciplinary project dealing with the investigation of geoarchaeological sites on the egyptian plateau with the aim of reconstructing the palaeoecological background providing age assessment which put the various results in an age frame that is of special interest here results of one particular section have been selected because of a discrepancy in age determination based on different approaches radiocarbon ages were inconsistent with the age range provided by the archaeological context in this area the underestimation observed is inferred to be caused by poor 14 c sample quality an attempt to overcome this problem was the determination of the depositional ages of the non organic sediments by using optically stimulated luminescence osl equivalent doses of four sediment samples were estimated from osl measurements carried out on sand sized quartz grains using the single aliquot regenerative dose sar protocol dose rates were calculated from neutron activation analysis results from the osl ages obtained we conclude that the sediment sequence exposing an alternation of lacustrine and eolian layers was deposited in a short period of time during the mid holocene mean of osl ages 7 8 ka compared to the 14 c ages the luminescence ages fit better into the archaeological context confirmed by surface dating