upper mantle anisotropy in se and central brazil from sks splitting evidence of asthenospheric flow around a cratonic keel abstract we present results of upper mantle anisotropy derived from measurements of core refracted shear wave splitting mainly sks phases recorded at 48 stations covering the major tectonic provinces in central and se brazil such as the tocantins province paraguay araguaia and brasilia belts between the amazon and sao francisco cratons the parana intracratonic basin the southern part of the sao francisco craton and the mantiqueira province with the coastal ribeira belt although the fast polarization directions vary across the region consistent orientations are observed over hundreds of kilometers the fast polarization directions tend to be close to the absolute plate motion given by the hot spot reference model hs3 nuvel1a however correlations with geological structures are also observed in the southern brasilia belt and in the ribeira belt respectively located sw and s of the sao francisco craton on the other hand in the northern tocantins province the fast shear wave direction n60 s is oblique to the sw ne trend of the geological units and faults and no anisotropy contribution from lithospheric sources can be clearly identified overall the fast polarization directions show a fan shaped pattern strongly suggesting asthenosperic flow around a thick and stiff keel in the southern part of the sao francisco craton consistent with the high velocity anomaly revealed by recent surface wave tomography the observed nw se directions in the southern part of the brasilia belt may also be interpreted as resulting from asthenospheric flow channeled between the sao francisco craton and a cratonic block beneath the parana basin the largest splitting delays observed in the southern brasilia belt and in the ribeira belt up to 2 4 s suggest contributions from both lithospheric and asthenospheric sources in those two areas our preferred model for the anisotropy causing the observed pattern of sks splitting consists of flow induced deformation in the asthenosphere caused by the absolute plate motion roughly towards w or wsw with flow channeled around a thick cratonic keel in the southern brasilia and in the ribeira fold belts the large delays and the parallelism with geological structures indicate additional anisotropy contribution from lithospheric sources

forcing mechanisms for mid cretaceous black shale formation evidence from the upper aptian and lower albian of the vocontian basin se france calcareous nannoplankton palynomorph benthic foraminifera and oxygen isotope records from the supraregionally distributed niveau paquier early albian age oceanic anoxic event 1b and regionally distributed niveau kilian late aptian age black shales in the vocontian basin se france exhibit variations that reflect paleoclimatic and paleoceanographic changes in the mid cretaceous low latitudes to quantify surface water productivity and temperature changes nutrient and temperature indices based on calcareous nannofossils were developed the nutrient index strongly varies in the precessional band whereas variations of the temperature index reflect eccentricity since polar ice caps were not present during the mid cretaceous these variations probably result from feedback mechanisms within a monsoonal climate system of the mid cretaceous low latitudes involving warm humid and cool dry cycles a model is proposed that explains the formation of mid cretaceous black shales through monsoonally driven changes in temperature and evaporation precipitation patterns the lower albian niveau paquier which has a supraregional distribution formed under extremely warm and humid conditions when monsoonal intensity was strongest bottom water ventilation in the vocontian basin was diminished probably due to increased precipitation and reduced evaporation in regions of deep water formation at low latitudes surface water productivity in the vocontian basin was controlled by the strength of monsoonal winds the upper aptian niveau kilian which has a regional distribution only formed under a less warm and humid climate than the niveau paquier low latitude deep water formation was reduced to a lesser extent and or on regional scale only the threshold for the formation of a supraregional black shale was not reached the intensity of increases in temperature and humidity controlled whether black shales developed on a regional or supraregional scale at least in the vocontian basin the increased preservation of organic matter at the sea floor was more significant in black shale formation than the role of enhanced productivity

long and short term carbon fluctuations in the eastern mediterranean during the late holocene a high resolution record of carbon isotope changes during the late holocene was obtained in core ga 112 from the easternmost mediterranean over the past 3600 yr a gradual 13 c depletion trend shown by both planktonic and benthic foraminifera corresponds to a global rise in atmospheric co 2 the global and local trends suggest that aridification and biomass destruction in the nile basin played a major role in the global co 2 rise in the late holocene superimposed on the general 13 c trend are four mirror image cycles in 13 c of planktonic and benthic foraminifera higher planktonic 13 c values reflect periods of high productivity off the coast of israel simultaneously decrease in the benthic 13 c values occurred because of degradation of higher organic matter fluxes to the sediment therefore large differences between the two records indicate periods of high productivity the eastern mediterranean productivity fluctuations respond to a periodical replenishment of nutrients to the mixed layer via nile runoff historical data of the nile flood fluctuations for the past 1400 yr show a remarkable coincidence between high and low nile floods and high and low eastern mediterranean productivity levels which are correlated with the periodic monsoonal activity over the nile headwaters

the kashiru pollen sequence burundi palaeoclimatic implications for the last 40 000 yr b p in tropical africa abstract a continuous pollen record from a central african highland site 3 28 s 29 34 e with 15 radio carbon dates spans at least the last 40 000 yr both modern and fossil pollen have been investigated a clear pattern of changes in vegetation and climate is suggested prior to 30 000 yr b p the occurrence of the montane conifer forest including the upper forest limit indicates climatic conditions colder and drier than now but more humid than in late glacial time between 30 000 and 15 000 yr b p grassland with afroalpine indicators expanded down to 2500 2000 m altitude as a result of dry and most probably cool climate the montane forest persisted in refuges although much reduced forest vegetation with the same floristic composition as today appeared after 13 250 200 yr b p suggesting more humid conditions the occurrence of a possible short term humid episode about 21 500 yr b p is correlated with some high lake level stages in east africa and with organic deposits in deep sea cores from the mediterranean and the atlantic ocean

sediment transport of the blue nile at khartoum the blue nile supplies the nile river with the largest proportion of water and sediment nevertheless very few often contrasting data are reported in the literature about its sediment yield this paper deals with detailed field measurement of suspended sediment transport taken at khartoum during three flood seasons in the late 1960s the pattern of suspended sediment concentration discharge and grain size variation with flow is analysed and suspended sediment yield is calculated and compared with data from different sources no bedload transport measurements are reported in the literature for the blue nile the flow data measured in the field consent to select several dune geometry criteria and to adopt the dune bedforms migration method to calculate bedload transport the same procedure is applied also to the bedload data measured in four reaches of the nile river downstream of the high aswan dam with channel and sediment characteristics comparable with those of the blue nile at khartoum to ascertain which dune geometry criterion provided the most reliable results the bagnold 1980 and martin 2003 equations predict similar values of bedload transport that are compared with the very few bedload data assessed by other authors using different equations and methods finally a good relation between flow velocity and bedload transport rate is found

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

hydroclimate variability in the nile river basin during the past 28 000 years it has long been known that extreme changes in north african hydroclimate occurred during the late pleistocene yet many discrepancies exist between sites regarding the timing duration and abruptness of events such as heinrich stadial hs 1 and the african humid period ahp the hydroclimate history of the nile river is of particular interest due to its lengthy human occupation history yet there are presently few continuous archives from the nile river corridor and pre holocene studies are rare here we present new organic and inorganic geochemical records of nile basin hydroclimate from an eastern mediterranean em sea sediment core spanning the past 28 ka bp our multi proxy records reflect the fluctuating inputs of blue nile versus white nile material to the em sea in response to gradual changes in local insolation and also capture abrupt hydroclimate events driven by remote climate forcings such as hs1 we find strong evidence for extreme aridity within the nile basin evolving in two distinct phases during hs1 from 17 5 to 16 ka bp and from 16 to 14 5 ka bp whereas peak wet conditions during the ahp are observed from 9 to 7 ka bp we find that zonal movements of the congo air boundary cab and associated shifts in the dominant moisture source atlantic versus indian ocean moisture to the nile basin likely contributed to abrupt hydroclimate variability in northern east africa during hs1 and the ahp as well as to non linear behavior of hydroclimate proxies we note that different proxies show variable gradual and abrupt responses to individual hydroclimate events and thus might have different inherent sensitivities which may be a factor contributing to the controversy surrounding the abruptness of past events such as the ahp during the late pleistocene the nile basin experienced extreme hydroclimate fluctuations which presumably impacted paleolithic cultures residing along the nile corridor

group velocity tomography and lithospheric s velocity structure of the south american continent the lithosphere of the south american continent has been studied little especially in northern brazil the amazonian region a 3d lithospheric s velocity model of south america was obtained by first carrying out rayleigh and love wave groupvelocity tomography and then inverting the regionalized dispersion curves fundamental mode group velocities were measured using a multiple filtering technique more than 12 000 paths were examined and about 6000 rayleigh and 3500 love wave dispersion curves with good quality were retrieved checkerboard tests showed that our dataset permits the resolution of features 400 800 km across laterally in the central part of the continent from crustal to upper mantle depths our results confirm previous tomographic results and correlate well with the major geological provinces of south america the 3d s velocity model confirms both regional features of se brazil from p wave travel time tomography and continental scale features of central and western south america from waveform inversion e g lowest velocities in the andean upper mantle three parts of the nazca plate with flat subduction strong low velocity anomalies in the upper mantle depth beneath the chaco basin furthermore our 3d model revealed new features in the south american continent 1 high velocities in the lower crust were consistently found in regions with high bouguer or free air anomalies 2 the ne sw trending transbrasiliano shear zone was delineated by a ne sw low velocity belt at lithospheric depths 3 the eastern amazonian craton appears to have thicker lithosphere than the western

champ satellite and terrestrial magnetic data help define the tectonic model for south america and resolve the lingering problem of the pre break up fit of the south atlantic ocean in july 2000 a new potential fields satellite was launched and is currently measuring the earth s gravity and magnetic fields the latter down to 0 1 nt the satellite called champ challenging mini satellite payload will be providing high accuracy crustal magnetic field data of the earth for wavelengths of about 300 3000 km until about 2005 previous magnetic satellites have been reviewed by ravat and purucker tle 1999 who found that an excellent comparison could be made between the long wavelength component of the dnag magnetic field 500 km covering north america and the magsat satellite field magsat was limited to a six month operating period due to its low orbital altitudes between 352 and 578 km before burning up in the atmosphere in june 1980 its large variation in orbital altitude was one factor that made generation of the crustal field component difficult the champ crustal field on the other hand is derived from solar night data for which the magnitude and complexity of the transient variation corrections are significantly reduced making for a more stable crustal field solution with significantly greater resolution as we will show in this article resolution of the satellite magnetic field over the atlantic ocean is sufficient to map subtle coherent features 1 nt in amplitude which are interpreted as bulk changes in the remanence of the oceanic crust associated with the linear magnetic reversals pattern of the geomagnetic field during and since the mesozoic period such resolving power of these n s striking anomalies which subparallel the orbital tracks provides confidence that the larger magnetic variations imaged over the continents are being reliably mapped and can aid identification of geologic provinces of interest in petroleum and mineral exploration comparisons of the satellite and terrestrial aeromagnetic data over brazil show that the trans brazilian lineament a major continental

human occupations and environmental changes in the nile valley during the holocene the case of kerma in upper nubia northern sudan abstract our article presents a detailed holocene archaeological sequence from the nile valley at kerma in upper nubia northern sudan this sequence retraces the evolution of human populations thanks to the study of several sites supported by 90 14c dates reconstruction of the environmental changes was supported by a study of dated stratigraphic sections located near the archaeological sites studied and illustrates the effects on human occupation of changes in river flow and floods which are in turn forced by climatic changes the results shed new light on the evolutionary dynamics of the holocene populations in nile valley little known due to the numerous hiatuses in occupation when compared with the situation in the sahara and the rest of the nile valley they confirm that the initial occupation took place ca 10 5 kyr bp after the start of the african humid period followed by a migration towards the banks of the nile commencing 7 3 kyr bp they also confirm the appearance of the neolithic by ca 8 0 kyr bp the kerma stratigraphic sequences show two prosperous periods 10 8 and 7 6 kyr bp and two hiatuses in the occupation of the sites 7 5 7 1 and 6 0 5 4 kyr bp resulting from increased aridity

late quaternary stratigraphy and paleogeography of the eastern nile delta egypt abstract a petrological study of numerous sediment borings identifies the late pleistocene and holocene lithofacies in the northeastern nile delta of egypt a coarsening upward sequence characterizes the major holocene depocenters located along the northern margin of the present delta stratigraphic correlation of radiocarbon dated sections and mapping of key facies such as delta front mud reveal the locations of four major holocene delta lobes related to former distributary branches of the nile river mendesian pelusiac tanitic and pre modern damietta these lobes formed primarily of marine prodelta and delta front deposits interfinger geographically but radiocarbon dating indicates that their bases are not synchronous lobes developed for the most part since 8000 years b p i e as the rate of eustatic sea level rise began to decrease climatic and sediment discharge fluctuations lateral migrations of distributaries and isostatic subsidence of land are additional factors that affected the temporal and spatial distributions of the lobes paleogeographic maps reveal the changes with time in the distributions of different lobes and deltaic plain environments marsh lagoons and concomitant displacement of the coastline holocene sediment accumulation rates to 500 cm per 1000 years are calculated this is 10 times greater than that on the nile cone and 50 times greater than on the egyptian continental shelf the delta coastal margin in the study area migrated northward by as much as 50 km during the past 5000 years an average progradational rate of up to 10 m per year the general configuration of the present delta developed during the past millennium the major changes recently induced by man in this region coupled with a series of continuing natural phenomena slow rise in sea level coastal erosion subsidence have markedly affected the evolution of the delta petrological study of the nile delta sediments provides baseline reference information to help recognize changes in the recent geological past to help identify those taking place at present and possibly to help predict those likely to occur in this region in the future

crustal framework of the northwest parana basin brazil insights from joint modeling of magnetic and gravity data abstract the transbrasiliano lineament tbl is a major proterozoic strike slip shear zone crossing the parana basin brazil yet the relationship between the tbl and basin structures is poorly understood magnetic and gravity data are available from the whole northwestern region of the parana basin and provide insights into crustal partitioning and basement geometry joint 2d modeling of these data was performed in three strategic sections of the study area two smaller sections were constrained by available borehole data and receiver function analysis modeling of these sections facilitated modeling of the third larger nw se section which crosses the basin in an area with significant lack of data these three sections together form the basis for a preliminary tectonic model of the northern parana basin the tbl includes strong n30 e trending gravity and magnetic gradients represented by the serra negra fault zone this structure separates two crustal tectonic domains the paranapanema block to the east and the amazon paleocontinent to the west the tectonic domain northeast of the fault is represented by the arenopolis magmatic arc the n60 70 e trending general carneiro fault also reflected in gravity anomalies forms another important magnetic contact our tectonic model shows a region of crustal thinning between the two fault zones where structures associated with possible reactivation form small cretaceous basins the baliza fault may accommodate significant vertical displacements of devonian and carboniferous sections of the parana basin the main structures revealed in the sections are associated with grabens and horsts interpreted as reactivated structures that controlled parana basin sedimentation the northwestern portion of the basin exhibits basement asymmetry caused by dip and strike slip faulting along the tbl

unraveling north african riverine and eolian contributions to central mediterranean sediments during holocene sapropel s1 formation hydroclimate variability has exerted a fundamental control on the alternating deposition of organic lean marl and organic rich sapropel sediments in the eastern mediterranean sea ems however the exact mechanisms regarding the freshwater sources and related changes are still debated here sr and nd isotopes and high resolution elemental data are used to constrain different riverine and eolian supplies to the central mediterranean over the past 9 8 ka the detrital sediments in core cp10bc taken at the margin of the libyan shelf in the southwestern ionian sea can be described by a three endmember mixing system based on sr and nd isotopic compositions the same systematics can also be deduced from ti and k compositional variability the endmembers comprise saharan dust aegean nile and libyan soil representing the eolian supply from north africa the riverine inputs from the aegean nile areas as well as the riverine and shelf derived fluxes from the libyan tunisian margin respectively for the sapropel s1 period in particular we find important detrital supplies from fossil river wadi systems along the libyan tunisian margin activated by intensified african monsoon precipitation combining the temporal profiles with the consistent variability observed in the 87sr 86sr 1000 sr diagram such libyan contribution has been most prominent during the uppermost period of sapropel s1 in core cp10bc this observation is in agreement with hydroclimate reconstructions of northwestern libya comparison of the sr nd isotope data between core cp10bc and four cores taken along a west east transect throughout the ems shows that this detrital supply originated mainly from western libya tunisia and was transported as far eastward as 25 e while being diluted by an increasing nile contribution

after the deluge mediterranean stagnation and sapropel formation in an east mediterranean marine core the upper sapropel begins soon after the start of a global event a very heavy precipitation which occurred in the equatorial latitudes during the late glacial early holocene this heavy precipitation in africa channelled by the nile river across 35 of latitude produced a low salinity surface layer in the east mediterranean in this confined basin with high bottom salinity the steep salinity gradient stratified the water column the stagnant bottom waters triggered the sapropel formation cretaceous sapropels in the tropical oceans may result from the same chain of events in warm humid climates with contrasting wet and dry seasonal rhythm

late quaternary palaeoclimatic oscillations in east africa recorded by heavy minerals in the nile delta because the nile carries a load derived from markedly different geological terrains and climatic zones it is expected that minera logical study of deposits in its delta could help define changes in palaeoclimate affecting east africa here we report measurements on heavy minerals in the nile delta which can be used as distinct markers of climatic shifts over africa during the late pleistocene to recent variations of heavy minerals in radiocarbon dated cores collected in this delta1 the nile s major depocentre2 correlate closely with oscillations in african palaeoclimate determined by other independent methods such as studies of lake levels these variations are largely a function of the characteristics of the nile it flows across nearly 35 of latitude from south of the equator to the mediterranean fig la and conditions in its drainage basin which includes central africa the ethiopian plateau and eastern sahara range from a tropical humid to a warm arid climate east african climatic belts migrated considerably during the quaternary3 5 modifying nile discharge and sediment load climatic oscillations have been recorded by changes of sediment yield and grain size along its course6 7 and by well defined depositional cycles8 including sapropels9 in the eastern mediterranean

dividing the south american continent to fit a gondwana reconstruction a model based on continental geology abstract the south american continental plate has been affected by intraplate deformation since the start of west gondwana disruption in the lower cretaceous about 140 ma that the present shape of south america is not precisely the same as its shape in reassembled gondwana partly explains the imperfect fits of the conjugate margins of the south atlantic proposed since the first reconstruction models of the early 20th century several attempts at defining subplates within south america have been published but not all take account of existing knowledge of its continental geology here a subdivision into eight rigid subplates is proposed based primarily on geological and tectonic evidence our model is tested against three published models of a multi subplate africa as re shaped to the pre breakup outline of that continent by visual fitting and the use of piercing points the south america blocks were rotated and the euler poles calculated interactively in reconstruction software all three proposed fits had overlapping block margins within south america indicating post breakup rifting except for the transbrasiliano lineament this nne ssw crustal scale shear zone was used as a boundary for seven of the eight blocks it is clearly the main intraplate accommodation zone in south america and an important piercing point in relation to the kandi lineament in west africa the other block boundaries correspond to narrow zones with sedimentary basins and or dyke swarms that have developed since south atlantic opening each fit required a different configuration of the south america subplates since the pre rift disposition of the african subplates also differ from each other contributing to the uncertainty in any detailed reassembly

an updated crustal thickness map of central south america based on receiver function measurements in the region of the chaco pantanal and parana basins southwestern brazil

palaeogeographic consequences of conservational models in the south atlantic ocean conservational models like simple shear pure shear or polyphase models that exclude exchanges between the lower continental crust and upper mantle are usually proposed to explain the lithospheric stretching and consequent crustal thinning of passive continental margins these models need large amounts of horizontal movement and have therefore important implications for plate kinematic reconstructions and intraplate deformation in this paper we propose to show these implications in the central segment of the south atlantic ocean in the angola brazilian system these models imply about 240 km of horizontal movement this movement can be com pensated by two end member mechanisms 1 an intraplate deformation located in africa and 2 an intraplate deformation located in south america we detail for each solution the strong geological and geodynamical implications and discuss the consequences for the genesis of passive continental margins

late holocene productivity and hydrographic variability in the eastern mediterranean inferred from benthic foraminiferal stable isotopes 1 the paleoproductivity paleo oxygenation and paleohydrographic configuration of the southeastern mediterranean during the late holocene was reconstructed on the basis of the isotopic composition of the epibenthic heterolepa floridana shallow endobenthic uvigerina mediterranea and the deeper endobenthic bulimina inflata from two high resolution cores ga 112 470 m and ga 110 670 m the 13c between h floridana and u mediterranea reveals four intervals of enhanced productivity from 3 3 2 6 2 3 1 9 1 5 1 1 and 0 8 0 4 kyr bp coinciding with increased nutrient supply by the nile river the entire basin was well aerated with oxygen consumption varying between 1 0 and 3 5 ml o2 l oxygen consumption increases toward present day probably because of higher accumulation of total organic carbon at 1 7 kyr bp coinciding with the appearance of the mesotropic benthic species the hydrographic configuration of the basin has changed during the course of the last 3 75 kyr the levantine intermediate water liw deepens below 470 m between 3 3 and 2 0 kyr and especially between 2 5 and 2 0 kyr during the last 1 5 kyr the liw becomes shallower than 470 m similar to the present day the change in the hydrographic configuration reflects changes in evaporation precipitation ratio and in temperature

cenozoic tectonic and topographic evolution of the northern sierra nevada california through stable isotope paleoaltimetry in volcanic glass we determine the paleoelevation of the northern sierra nevada california in the oligocene based on hydrogen stable isotope compositions of meteoric water preserved within volcanic glass from ignimbrites sampled across the range a 48 decrease in the isotopic composition of hydrated glass from ignimbrites located near paleosea level to ignimbrites 100 km to the east refl ects the effect of ancient high topography on precipitation these data show that 31 28 ma ago the northern sierra nevada had a steep western gradient and elevations similar to the present this study placed in the context of other paleoaltimetry studies suggests that the range was a high topographic feature throughout the cenozoic and that the majority of uplift occurred in the late cretaceous to early cenozoic much earlier than some studies have proposed

intra plate seismicity and flexural stresses in central brazil 1 explaining intra plate seismicity is a challenging task different models have been proposed combining weak zones and stress concentration mechanisms here we propose that flexural deformation is a major factor to explain seismicity in central brazil a sw ne oriented seismic zone between the amazon and the sao francisco cratons coincides with high gravity anomalies possibly due to a sw ne belt of thin crust the load from the high density shallow mantle rocks causes upper crustal compressional stresses up to 100 mpa in the 200 km wide seismic zone away from the central zone of horizontal compression extensional stresses in the peripheral bulge balance the regional compression explaining the aseismic areas three other seismic clusters in brazil also correlate with high gravity anomalies suggesting that flexural deformation contributes significantly to explain mid plate seismicity in brazil

the tectonic evolution of the transbrasiliano lineament in northern parana basin brazil as inferred from aeromagnetic data data from six airborne magnetic surveys were compiled and analyzed to develop a structural interpretation for the transbrasiliano lineament in northern parana basin brazil magnetic lineaments interpreted to reflect geologic contacts and structures at different depths were illuminated using the matched filter technique applied to aeromagnetic anomalies field based structural measurements generally support our magnetic analysis we estimated three primary magnetic zones i a zone of deep magnetic sources at 20 km depth ii an intermediate basement zone at 6 km depth and iii a shallow zone of near surface geological features at 1 5 km depth the deepest zone exhibits three major ne trending crustal discontinuities related to the transbrasiliano lineament dividing the region into four geotectonic blocks anomalies associated with the intermediate zone indicate directional divergence of subsidiary structures away from the main transbrasiliano fault which strikes n30 e the shallow magnetic zone includes near surface post brasiliano orogenic granites our analysis identified ne trending sigmoidal lineaments around these intrusions indicating intense zones of deformation associated with probable shear structures at the shallow depth zone magnetic anomalies caused by cretaceous alkaline intrusive bodies and basalts of the serra geral formation are enhanced by the matched filter method these igneous bodies are related to extensional nw striking lineaments and seismicity aligned along these lineaments suggests that they currently are reactivated prior to flexural subsidence of the parana basin reactivation processes along transcurrent elements of the transbrasiliano lineament promoted extensional processes and formed initial parana basin depocenters cretaceous and more recent sedimentation also correlate with reactivations of ne striking structures

short term environmental changes in the cretaceous tethyan ocean micropalaeontological evidence from the early albian oceanic anoxic event 1b to better understand the linkage between climate and ocean circulation under greenhouse conditions we have studied calcareous nannofossils palynomorphs and benthic foraminifera from the early albian oceanic anoxic event 1b black shale oae 1b in the vocontian basin se france we propose that monsoonal activity resulting from precessional forcing and modulated by eccentricity driven temperature changes represents the driving factor of oae 1b formation in low latitudes with the onset of oae 1b increasingly warm and humid conditions stronger winds and enhanced terrestrial input led to higher surface water productivity therefore increased productivity is an important factor for oae 1b formation in the vocontian basin however monsoonally forced productivity changes are a regional climate signal only the supraregional occurrence of the oae 1b is probably due to a reduction of deep water formation in the low latitudes under extremely warm and humid conditions leading to enhanced preservation of organic matter

subsidence in the northeastern nile delta rapid rates possible causes and consequences holocene fluvial and marine deposits have accumulated in a graben like structure on the northeastern margin of the nile delta this part of the delta which includes lake manzala port said and the northern suez canal has subsided rapidly at rates of up to 0 5 centimeter per year since about 7500 years ago this subsidence has diverted at last four major distributaries of the nile river into this region the combined effects of continued subsidence and sea level rise may flood a large part of the northern delta plain by as much as 1 meter by the year 2100 the impact of continued subsidence now occurring when sediment input along the coast has been sharply reduced because of the aswan high dam is likely to be substantial particularly in the port said area and as far inland as south of lake manzala

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