imaging and photogrammetry models of olduvai gorge tanzania by unmanned aerial vehicles a high resolution digital database for research and conservation of early stone age sites this paper presents the first aerial mapping of olduvai gorge tanzania using unmanned aerial vehicles and photogrammetric techniques to provide a detailed digital cartographic basis for this world renowned paleoanthropological site the survey covered an area of 32 km2 of olduvai gorge and through the use of aerial photos and ground control points from global navigation satellite systems an orthomosaic and digital surface model with a higher than 5 cm pixel ground resolution were produced the digital surface model was then denoised to calculate a digital elevation model and a high resolution imaging model of olduvai gorge was generated a preliminary morphometric characterization using geographic information systems shows the potential of this approach when analysing multiple topographic variables in large areas of paleoanthropological relevance including production of a new map template for olduvai gorge and new data for the investigation of sedimentary and tectonic processes these results constitute one of the first attempts to obtain high quality imagery from large geographic areas amenable to early stone age research and introduce new workflows for the creation of digital elevation models overall the digital dataset produced is intended to support archaeological and geological investigation in this area and provide new monitoring tools for the conservation of cultural heritage

mesozoic rift basins of yemen abstract this special issue is the first compilation and review of the stratigraphy and basin evolution of the mesozoic petroleum basins of yemen the volume arises from an international symposium on the sedimentation and tectonics of rift basins of the red sea gulf of aden area held at the university of sana a in september 1995 papers relating to the cenozoic rifting of the gulf of aden red sea and gulf of suez are to be published shortly b h purser and d w j bosence sedimentation and techtonics of rift basins the red sea gulf of aden chapman and hall london in press eight papers within this issue focus on basins within the interior of the country and the margins of the gulf of aden indian ocean the papers cover reviews of the developing stratigraphic concepts for these basins outcrop studies and subsurface studies of recently explored areas by geoscientists from the u k oil industry and from u k lebanese and yemeni universities

fault reactivation and rift localization northeastern gulf of aden margin 1 the gulf of aden and the sheba spreading ridge gulf of aden forms the southern boundary of the arabian plate its orientation 075 e and its kinematics about 030 e divergence are interpreted as the result of an oblique rifting in this contribution a field study in the northeastern gulf of aden allows us to confirm the oligo miocene synrift directions of extension and to precise the normal fault network geometry the synrift extensions are 020 e and 160 e possibly in this chronological order the normal faults strike 070 e 090 e and 110 e the results show that some characteristics are consistent with oblique rifting analogue models while some others are not especially fault reactivation of mesozoic structures is shown to have occurred significantly at the beginning and during rifting these data are therefore compared to analogue models of oblique reactivation and this comparison demonstrates that fault reactivation played a key role during the early stage of the gulf of aden rifting finally scenarios of the lithospheric evolution during the eastern gulf of aden opening preexisting weaknesses in the lithosphere or not are discussed to better constrain the deformation history of the northern margin especially we show that rift localization processes may imply stress rotations through time

the mesozoic and early tertiary tectonic evolution of the socotra area eastern gulf of aden yemen recent interpretation and mapping of seismic data covering the area to the south and west of the island of socotra have enhanced the understanding of the mesozoic and early tertiary tectonic history of the socotran platform lineament orientations after restoration to account for oligo miocene gulf of aden rifting indicate o 1 the most significant basin forming lineament has a 140 orientation basin initiation based on onshore yemen analogues occurred in the late jurassic early cretaceous oxfordian to hauterivian and is believed to be associated with neo tethys rifting between the afro arabian and laurasian plates 2 the presence of a 45 lineament orientation associated with the extension and subsequent opening of the north somali basin separation of the indian plate from the african plate during callovian oxfordian times resulted in the opening of a number of en echelon rift basins mozambique west somali and north somali basins offset by major north south orientated fracture zones davie ridge and a r s v l c c fracture zones 3 cretaceous post rift carbonate platform development in the study area was followed by several phases of later structural evolution these have characteristic translational aspects to their movements and occurred in the late cretaceous palaeocene further modifying the structural geometry of the socotran sub basins the majority of the translational features and faults evident on seismic data and mapped at late cretaceous and palaeocene time horizons suggest an 80 principal displacement zone pdz orientation seismically derived isochrons indicate that movement along this zone was intermittent

central gulf of aden conjugate margins yemen somalia tectono sedimentary and magmatism evolution in hybrid type margins abstract magma rich and magma poor passive margins are generally studied separately yet the spatial evolution from one type to another is not well understood central gulf of aden margins are at the transition between these two types of margins based on new seismic data published wells and gravity data we determine seismic stratigraphy and structural patterns we map the distinct crustal domains continental ocean continent transition oct oceanic domains and propose a tectonic evolution of the yemeni and somalian conjugate margins in an oblique rifting context the most striking results are the significant segmentation narrowness and asymmetry of conjugate margins as well as the gradual eastward decrease in the intensity of magmatic activity of these hybrid type margins west of bosaso hami fracture zone bhfz the hami ahl medo segment presents magmatic type margin features in the distal yemeni margin related to the strong influence from the afar plume seaward dipping reflectors develop since the late syn rift stage 21 18 ma near the xiis al mukalla fracture zone conversely east of bhfz the bosaso sayhut margins segment is characterized by magma poor margins for which the exhumation stage is characterized by the unroofing of mantle along multiple detachment faults in the oct and shortly followed by diachronous volcanism 18 ma the central gulf of aden is affected by a major uplift during the final syn rift stage and up to oct formation this event is associated with the formation of erosional surfaces in the east and with gravitational deformation taking place on decoupling surfaces at the base of the syn rift sequence lower ghaydah fm that lead to the sliding of syn rift units on top of the exhumed mantle rocks in the oct

signals of degeneration of the sub crustal part of the indian lithosphere since the break up of gondwanaland abstract currently the continental fragments of the erstwhile gondwanaland supercontinent are widely separated a relative comparison of magsat anomalies of these fragments reveals a striking similarity across all the rifted continental margins except at the western and southern margins of india it reflects that magnetized crust has largely remained unchanged elsewhere since the break up of gondwanaland a similar analysis of satellite derived free air gravity anomalies also indicate a similar continuity across other rifted margins except those of india these anomalies characterise the existing differences in the crustal and upper mantle structures and causal dependence on the relative mobilities of the gondwanic continents it is evident that after the break up only the indian continental structure has suffered a dramatic change possibly due to its super northward drift from antarctica during late cretaceous early tertiary

offshore socotra republic of yemen potential for a new hydrocarbon province a new plate reconstruction has enabled the island of socotra currently located in the gulf of aden adjacent to the somalian coast to be confidently restored to its original spatial position adjacent to the southern omani coastline new studies integrated with these plate reconstructions have confirmed the presence of an untested mesozoic graben which trends across the socotra platform fieldwork carried out in the region now enables a se extension of the prolific lower cretaceous qishn play delinated in the masilah basin onshore yemen to be postulated offshore into the gulf of aden following the award of offshore acreage adjacent to the island of socotra exploration studies have confirmed the presence of the qishn play both on the island of socotra and offshore in the one available basin margin control well this work has also identified two additional plays the shuabia equivalent carbonates which are prolific producing reservoirs in central oman and the permo triassic clastics which may provide a new reservoir target for the region fieldwork has also identified jurassic siliclastics outcropping on the island which may provide further reservoir potential ongoing multidisciplinary studies integrating the results of a detailed geophysical interpretation with high resolution structural stratigraphic studies have confirmed the presence ofmore large structures within an undrilled mesozoic rift basin which will be tested during 1995 less

early permian to middle jurassic rifting and sedimentation in east africa and madagascar pre drift sediments of madagascar early permian middle jurassic have been studied palynologically these studies resulted in a more precise dating of individual stratigraphic units and the recognition of minor and major breaks in the succession palynostratigraphic and physical evidence of unconformities have been used to subdivide the pre drift sediments into depositional cycles and to infer rifting events a comparison with equivalent strata of mozambique tanzania kenya ethiopia and somalia shows a general correspondence and provides additional information for the construction of a generalized framework for the east african madagascan region which demonstrates the relationships between rifting and sedimentation and elucidates the prehistory of the break up of gondwana into a western and eastern fragment during the middle jurassic the predrift succession of east africa madagascar can be subdivided into two major sequences a karoo sequence cycles 1 5 asselian early smithian and a transitional sequence cycles 6 9 ladinian early bajocian the two sequences are separeted by a late scythian to anisian hiatus which indicates extensive uplift and erosion before a major rifting event initiated the resumption of sedimentation in the ladinian this middle triassic event marks the transition from the intracratonic rift stage to the pericratonic basin stage and correlates with a significant event in the pangaean history the transition from final coalescence to initial dispersal the onset of the southward drift of madagascar is believed to have occurred about 60 ma later near the aalenian bajocian boundary contemporaneous with or immediately after the deposition of syntectonic sediments of cycle 9

structure and evolution of the eastern gulf of aden insights from magnetic and gravity data encens sheba md117 cruise summary magnetic and gravity data gathered during the encens sheba cruise 2000 june in the eastern gulf of aden provide insights on the structural evolution of segmentation from rifted margins to incipient seafloor spreading in this study we document the conjugate margins asymmetry confirm the location of the ocean continent transition oct previously proposed by seismic data and describe its deep structure and segmentation in the oct gravity models indicate highly thinned crust while magnetic data indicate presence of non oceanic high amplitude magnetic anomalies where syn rift sediments are not observed thus the oct could be made of ultra stretched continental crust intruded by magmatic bodies however locally in the north the nature of the oct could be either an area of ultra slow spreading oceanic crust or exhumed serpentinized mantle between the alula fartak and socotra fracture zones the non volcanic margins and the oct are segmented by two n027 e trending transfer fault zones these transfer zones define three n110 e trending segments that evolve through time the first evidence of oceanic spreading corresponds to the magnetic anomaly a5d and is thus dated back to 17 6 ma at least reconstruction of the spreading process suggests a complex non uniform opening by an arc like initiation of seafloor spreading in the oct the early segmentation appears to be directly related to the continental margin segmentation the spreading axis segmentation evolved from three segments 17 6 to 10 95 ma to two segments 10 95 ma to present at the onset of the spreading process the western segment propagated eastwards thus reducing the size of the central segment the presence of a propagator could explain the observed spreading asymmetry with the northern flank of the sheba ridge being wider than the southern one

east africa continental margins new well data from somalia together with the history of sea floor spreading in the indian ocean derived from magnetic anomalies show that the east african margins from at 15 s into the gulf of aden comprise four distinct segments that formed successively by the southward drift of madagascar from somalia during the middle to late jurassic and early cretaceous by the northeastward drift of india along the owen transform during the late cretaceous and paleocene and by the opening of the gulf of aden during the neogene

bed thickness distributions on mars an orbital perspective studies on earth show that sedimentary bed thickness and bed thickness distributions record information about the processes controlling sediment deposition high resolution digital terrain models dtms such as those derived from the high resolution imaging science experiment hirise now provide the opportunity to quantify bed thickness properties on mars over several orders of magnitude down to the submeter scale this study uses hirise dtms and visible images to measure bed thickness distributions at 10 deposits on mars with the aim of determining whether statistical techniques can provide useful criteria for distinguishing sedimentary depositional processes basic statistics including mean thickness and range are examined as are histograms cumulative frequency plots and log log plots statistical tests interrogate these deposits for thinning or thickening upward trends and the presence of normal lognormal and exponential distributions although there are challenges associated with these methods the statistical analysis of bed thickness coupled with morphological and mineralogical interpretations has the potential to be a powerful tool for characterizing and classifying sedimentary rocks on mars in particular bed thickness statistics are particularly well suited for examining changes in sediment supply and accommodation within martian sedimentary sequences

multispectral remote sensing as stratigraphic and structural tool wind river basin and big horn basin areas wyoming stratigraphic and structural analyses of the wind river basin and big horn basin areas of central wyoming are in progress one result has been the development of an approach to stratigraphic and structural analysis that uses photogeologic and spectral interpretation of multispectral image data to characterize the attitude thickness and lithology of strata new multispectral systems that have only been available since 1982 are used with topographic data to map upper paleozoic and mesozoic strata exposed on the southern margin of the bighorn mountains landsat acquired thematic mapper tm data together with topographic data are used to map lithologic contacts measure dip and strike and develop a stratigraphic column that is correlated with conventional surface and subsurface sections aircraft acquired airborne imaging spectrometer ais and thermal infrared multispectral scanner tims data add mineralogic information to the tm column including the stratigraphic distribution of quartz calcite dolomite smectite and gypsum results illustrate an approach that has general applicability in other geologic investigations that could benefit from remotely acquired information about areal variations in attitude sequence thickness and lithology of strata exposed at the earth s surface application of our methods elsewhere is limited primarily by availability of multispectral and topographic data and quality of bedrock exposures

development of pervious concrete pile ground improvement alternative and behavior under vertical loading permeable granular columns are used to increase the time rate of consolidation reduce liquefaction potential improve bearing capacity and reduce settlement however their behavior depends on the confinement provided by surrounding soil which limits their use in very soft clays and silts and organic and peat soils this research effort aims to develop a new ground improvement method using pervious concrete piles pervious concrete piles provide higher stiffness and strength that are independent of surrounding soil confinement while offering permeability comparable to granular columns this proposed ground improvement method can improve the performance of different structures supported on poor soils to achieve the goal of the research project four vertical load tests were performed on one granular column and three pervious concrete piles in this paper the material properties of pervious concrete the developed installation method and the vertical load response of pervious concrete and aggregate piles are presented and the variation of soil stresses and displacement during pile installation are briefly discussed the experimental test results show that the ultimate load capacity of the pervious concrete pile was 4 4 times greater than that of an identical granular column in addition the ultimate load capacity of a pervious concrete pile installed using the developed technique was 2 6 times greater than a precast pervious concrete pile the used installation method created nonuniform lateral soil displacement and increased vertical and horizontal soil stresses

undrained responses of microbially desaturated sand under monotonic loading abstractdesaturation is a method for the mitigation of liquefaction of sand this method has gained increasing interest in recent years as it may become a more cost effective solution than many conventional methods in this paper a microbial denitrification process was adopted to generate nitrogen gas for desaturation of sand this approach offers several advantages first nitrogen gas does not dissolve in water easily second nitrogen gas is chemically inert third as the gas is generated in situ its distribution is also more uniform fourth the gas bubbles generated by the microbial process are tiny and thus the potential of escaping from the ground is less in this paper undrained triaxial compression and extension tests were adopted to evaluate the liquefaction behavior of sand desaturated using nitrogen under static monotonic loading conditions test results show that under an undrained axisymmetric condition when the degree of saturation of loose sand is reduced from 100 to a range of 95

the southernmost margin of the tethys realm during the mesozoic and cenozoic initial geometry and timing of the inversion processes 1 along the northern border of africa pangea breakup has been diachronic during the jurassic the alpine tethys propagated northeastward from the atlantic to the alps during the permian the neo tethys propagated westward from oman to northwestern arabia then a secondary and late branch of neo tethys gave birth to the east mediterranean basin finally the two oceans connected at end of jurassic times achieving the development of africa northern plate boundary by the late cretaceous convergence between africa and eurasia led to the progressive closure of the tethys realm the continental collision is not completely achieved and the different segments of the confrontation zone maghreb central and east mediterranean zagros and oman expose different stages of the process however we emphasize the existence of synchronous geodynamic events from one end of the system to the other although they do not have the same meaning two of them are particularly important the campanian santonian c s event corresponds to 1 obduction and exhumation of high pressure low temperature metamorphic rocks around the arabian promontory 2 inversion along the margins of the east mediterranean basins and 3 lithosphere buckling in the atlas system maghreb and adjacent sahara platform the middle late eocene mle event corresponds to 1 the onset of collision at the northern corner of arabia 2 the onset of slab retreat in the mediterranean and 3 inversion along the margin of the east mediterranean as well as in the atlas the c s event coincides with a change in plate kinematics resulting in an abrupt increase of convergence velocity the mle event coincides with a period of strong coupling between the africa and eurasia plates and an abrupt decrease of convergence velocity in the middle of the system the central mediterranean seems to escape to the effects of convergence and is the site of quite permanent extensional movements since the triassic

cenozoic extension in coastal dhofar southern oman implications on the oblique rifting of the gulf of aden a detailed analysis of fault populations that affect the paleocene to early miocene sedimentary succession of southern dhofar allows the definition of a time sequence of paleostresses and the reconstruction of the rifting history of the eastern gulf of aden two distinct phases of n20j and n160j trending extensions took place during the deposition of the synrift dhofar group from late priabonian 35 ma to middle burdigalian 18 ma a period of tectonic instability preceded these events marked by normal and strike slip faulting as early as the mid eocene the two main directions of extension also recorded in southern yemen developed respectively oblique and normal to the n75e trend of the gulf of aden an anticlockwise succession of the two episodes from n20 to n160 only established in yemen accounts for the observed synrift fault pattern which is consistent with the type and geometry of faults predicted in analogue models of oblique rifting a latest phase of ns compression marked by strike slip faulting may represent a far echo of the arabia eurasia collision d 2002 elsevier science b v all rights reserved

lidar uav or compass clinometer accuracy coverage and the effects on structural models abstract light detection and ranging lidar and structure from motion sfm provide large amounts of digital data from which virtual outcrops can be created the accuracy of these surface reconstructions is critical for quantitative structural analysis assessment of lidar and sfm methodologies suggest that sfm results are comparable to high data density lidar on individual surfaces the effect of chosen acquisition technique on the full outcrop and the efficacy on its virtual form for quantitative structural analysis and prediction beyond single bedding surfaces however is less certain here we compare the accuracy of digital virtual outcrop analysis with traditional field data for structural measurements and along strike prediction of fold geometry from stackpole syncline in this case the sfm virtual outcrop derived from uav imagery yields better along strike predictions and a more reliable geological model in spite of lower accuracy surface reconstructions than lidar this outcome is attributed to greater coverage by uav and reliable reconstruction of a greater number of bedding planes than terrestrial lidar which suffers from the effects of occlusion irrespective of the chosen acquisition technique we find that workflows must incorporate careful survey planning data processing and quality checking of derived data if virtual outcrops are to be used for robust structural analysis and along strike prediction

field observations from the socotran platform their interpretation and correlation to southern oman recent fieldwork on socotra and adjacent islands located along the southern margin of the gulf of aden coupled with extensive biostratigraphic studies has led to the identification of a number of distinct sedimentary successions in the area triassic strata have been identified in a fault bounded area of easternmost socotra and jurassic rocks previously unrecognised on the island are preserved unconformably overlying the triassic in south east socotra in other parts of the socotran platform cretaceous sedimentary rocks lie unconformably above basement the oldest and thickest successions are of barremian to aptian age and occur on the western islands a marine transgression is recorded by a transition from estuarine to mixed shallow marine carbonate and siliciclastic sedimentation thin sedimentary sequences of campanian and maastrichtian age have been identified in two separate areas of socotra tertiary deposition commenced in latest palaeocene times and a gentle angular unconformity with the underlying cretaceous deposits is apparent simultaneous with the onset of gulf of aden rifting a new phase of deposition began in the late oligocene a wide range of facies reflect strong tectonic controls on deposition plate tectonic reconstructions indicate that prior to the gulf of aden rifting socotra was located adjacent to the dhofar region of southern oman this interpretation is well supported by comparisons of the mesozoic and tertiary successions in these two areas

integrated stratigraphy from the vallcebre basin southeastern pyrenees spain new insights on the continental cretaceous tertiary transition in southwest europe abstract an integrated sedimentological magnetostratigraphic and paleontological study of the vallcebre section south eastern pyrenees spain is carried out in order to define and portray the transition from the cretaceous to the tertiary in a continental setting a robust magnetostratigraphy is correlated to the standard polarity scale in light of known biochronological constraints charophyte marine invertebrates eggshells and other dinosaur remains our results show that this section is among the thickest stratigraphic records for the continental maastrichtian in the old world sedimentology indicates a progressive regression from marine through lagoonal to entirely continental environments the section is dominated by mudstones deposited under low energy conditions exceptionally a basin wide regression maximum is recorded some time before the cretaceous tertiary boundary k t this regression maximum is marked by the input of coarse grained alluvial sediments that record a dramatic change in the landscape quiet mud plains changed to sandy floodplains deposited by high energy currents after a period of renewed quiescence following the regression maximum a cenozoic flooding took place such terminal cretaceous sequence of events has been recorded in shorter sections in several other basins from southwestern europe this energetic sediment input suggests that some time before the k t event a sudden paleoenvironmental reorganization took place in the continental basins of south western europe

the cretaceous sequence stratigraphy of the socotran platform the republic of yemen outcrop studies combined with subsurface seismic and well data enable a detailed sequence stratigraphic analysis of the socotran platform during the cretaceous palaeogeographic reconstructions for the barremian aptian qishn formation albian cenomanian fartaq formation and maastrichtian sharwayn formation are presented the palaeogeographic maps have been constrained by data from outcrop studies on socotra and the adjacent islands of samhah and abd al kuri as well as the samhah 1a well which lies 60 km to the southwest of samhah island two major sequences can be recognised in the qishn formation and can be further subdivided into systems tracts an upper qishn highstand systems tract has been identified on a north south seismic line with coastline parallel facies belts an interpretation of the reservoir facies and porosity development of the highstand systems tract is attempted using the good quality seismic data in the socotran platform three major sequences can be recognised in the fartaq formation and one in the sharwayn formation which are illustrated on a second east west seismic line

salt diapirs bordering the continental margin of northern kenya and southern somalia the presence of newly discovered diapirs of presumed salt origin is documented for the continental margin of northeastern kenya and southeastern somalia these structures are probably a manifestation of a significant thickness of lower jurassic evaporites deposited during the rift and early drift stages of the separation of madagascar from the african continent

liquefaction response of partially saturated sands i experimental results the liquefaction response of partially saturated loose sandswas experimentally investigatedto assess theeffect of partial saturation on thegenerationof excessporewater pressures anexperimental setup includingacyclicsimpleshearliquefaction boxwas devisedandman ufactured theboxincludesporepressureanddisplacementtransducersaswellasbenderelementsandbendingdiskstomonitortheresponseof partially saturated specimens uniform partially saturated specimens with controlled density and degree of saturation were prepared by wet pluviationofpowderedsodiumperboratemonohydratemixedwithottawasand thereactionofthesodiumperboratewithporewaterreleased minute oxygen bubbles thus reducing the degree of saturation of the specimens the uniformity of a specimen was confirmed with s wave velocity measurements and a high resolution digital camera the p wave velocity measurements could only confirm the presence of partial saturation but not the degree of saturation partially saturated specimens with varying relative densities and degrees of saturation when tested under a range of cyclic shear strains do not achieve initial liquefaction defined by maximum pore pressure ratio ru max being 1 0 for a given degree of saturation and cyclic shear strain amplitude the larger the relative density the smaller is ru max for a given degree of saturation and relative density the larger the shear strain amplitude the larger is ru max the excess pore pressure ratio ru can be significantly smaller than ru max depending on the number of cycles of shear strain tests on the sustainability of partial saturation under upward flow gradient and base excitation led to the conclusion that the specimens remained partially saturated without significant change in the degree of saturation based on the experimental test results presented in this paper an empirical model for the prediction of ru in partially saturated sands under earthquake excitation is presented in a companion paper doi 10 1061 asce gt 1943 5606 0000815 2013 american society of civil engineers ce database subject headings soil liquefaction soil treatment saturated soils sand soil type pore pressure cyclic tests entrainment bubbles experimentation authorkeywords soilliquefaction soiltreatment saturation porepressure cyclictests entrainment bubbles inducedpartialsaturation liquefaction mitigation bender elements bending disks

crustal structure of the gulf of aden southern margin evidence from receiver functions on socotra island yemen breakup of continents in magma poor setting occurs primarily by faulting and plate thinning spatial and temporal variations in these processes can be influenced by the pre rift basement structure as well as by early syn rift segmentation of the rift in order to better understand crustal deformation and influence of pre rift architecture on breakup we use receiver functions from teleseismic recordings from socotra which is part of the subaerial oligo miocene age southern margin of the gulf of aden we determine variations in crustal thickness and elastic properties from which we interpret the degree of extension related thinning and crustal composition our computed receiver functions show an average crustal thickness of 28 km for central socotra which decreases westward along the margin to an average of 21 km in addition the crust thins with proximity to the continent ocean transition to 16 km in the northwest assuming an initial pre rift crustal thickness of 35 km undeformed arabian plate we estimate a stretching factor in the range of 2 1 2 4 beneath socotra our results show considerable differences between the crustal structure of socotra s eastern and western sides on either side of the hadibo transfer zone the east displays a clear intracrustal conversion phase and thick crust when compared with the western part the majority of measurements across socotra show vp vs ratios of between 1 70 and 1 77 and are broadly consistent with the vp vs values expected from the granitic and carbonate rock type exposed at the surface our results strongly suggest that intrusion of mafic rock is absent or minimal providing evidence that mechanical thinning accommodated the majority of crustal extension from our observations we interpret that the western part of socotra corresponds to the necking zone of a classic magma poor continental margin while the eastern part corresponds to the proximal domain

comparison of the jurassic and cretaceous sedimentary cycles of somalia and madagascar implications for the gondwana breakup the jurassic and cretaceous sedimentary history of northern somalia and the morondava basin of south western madagascar have been studied both regions display an independent facial development however a comparison of the sequential evolution of the mesozoic sedimentary successions in these two presently widely separated areas reveals a surprisingly high level of similarity which probably reflects major events during the disintegration of eastern gondwana during the jurassic and cretaceous although in jurassic times the onset of transgressions and regressions in both areas compares well with eustatic development major deviations in combination with the tectonic activities of different degrees are observed in the early and late cretaceous synchronously in both regions transgressions are observed in toarcian bajocian not dated in northern somalia callovian valanginian madagascar only aptian and campanian times tectonism is noted before the aptian and campanian transgressions in northern somalia and the morondava basin of south western madagascar

segmentation and along strike asymmetry of the passive margin in socotra eastern gulf of aden are they controlled by detachment faults on the island of socotra the southern passive margin of the gulf of aden displays along its strike two different types of asymmetric structures western socotra is made up of a series of southward tilted blocks bounded by consistently northward dipping normal faults eastern socotra consists of a broad asymmetric anticline with a steep northern limb and a gently dipping southern limb a zone of ne sw striking strike slip and normal faults separates the two areas the overall structure is interpreted as representing two rift segments separated by a transfer zone the along strike juxtaposition of crustal scale asymmetric structures on the southern margin of the gulf of aden is complemented by the asymmetry of the conjugate margins on either side of the gulf whereas the western socotra margin is narrow and characterized by oceanward dipping normal faults the conjugate oman margin is broader and dominated by horsts and graben considering that asymmetric structures in the upper crust are often associated with synthetic shear zones at deeper ductile levels we propose that the western and eastern socotra margin segments were controlled at depth by two detachment faults with opposite dips and senses of shear the normal faults of western socotra would sole out into a top to the north ductile shear zone whereas the asymmetric anticline of eastern socotra would be associated with a top to the south detachment fault

water in skeletal carbonates abstract studies of a wide variety of modern and fossil skeletal carbonates indicate they all contain water in amounts ranging from a few tenths of one percent to as much as three percent by weight the word water is used as a general term to include all inorganic liquid and bound h2o and oh reflectance spectroscopy in the visible and near infrared 0 60 to 2 55 m reveals major differences among skeletal carbonates in the amount of water present phases in which it occurs and relative proportions of these phases liquid h2o is present in all skeletal material studied in the form of fluid inclusions in some cases most notably the molluscs h2o is also associated with an organic matrix a hydrated caco3 phase occurs in so e biogenic low mg calcites lmcs and aragonites and two hydrated mgco3 phases with differing bond energies occur in high mg calcites hmcs many hmcs contain mg oh 2 and h2o bound to caco3 as well and some biogenic aragonites contain ca oh 2 water content varies with skeletal mineralogy taxonomic group and in the case of the molluscs with skeletal structure alteration of aragonites and hmcs to lmcs is accompanied by order of magnitude changes in total water content hmcs lose bound h2o and oh during alteration to lmcs ca oh 2 and h2o bound to caco3may also be lost from biogenic aragonites even in the absence of changes in bulk mineralogy lmcs also lose h2o bound to caco3 during diagenesis fluid inclusions are lost during neomorphic alteration of aragonites and lmcs however skeletal material that retains its original bulk skeletal mineralogy and or original microstructure as seen in thin section also retains the bulk of its original fluid inclusion content water content can be used as a criterion for monitoring diagenetic alteration in carbonates water present in fluid inclusions can serve as a medium for diagenetic reactions bound h2o lost on heating could take part in diagenetic reactions during deep burial as well

from rifting to spreading in the eastern gulf of aden a geophysical survey of a young oceanic basin from margin to margin a geophysical survey in the eastern gulf of aden between the alula fartak 52 e and the socotra 55 e transform faults was carried out during the encens sheba cruise the conjugate margins of the gulf are steep narrow and asymmetric asymmetry of the rifting process is highlighted by the conjugate margins horst and graben in the north and deep basin in the south two transfer fault zones separate the margins into three segments whereas the present day sheba ridge is divided into two segments by a transform discontinuity therefore segmentation of the sheba ridge and that of the conjugate margins did coincide during the early stages of oceanic spreading extensive magma production is evidenced in the central part of the western segment anomaly 5d was identified in the northern and southern parts of the oceanic basin thus confirming that seafloor spreading in this part of gulf of aden started at least 17 6 ma ago

late jurassic paleoclimate of central africa abstract paleopedology and geochemical analysis of upper jurassic deposits in the stanleyville group of central africa indicate harsh late jurassic paleoclimates in the interior of gondwana subsurface samples collected from the samba borehole near the center of the congo basin show only weak morphological evidence of pedogenesis but are characterized by an abundance of shrink swell vertic features and rare calcium carbonate nodules indicating seasonal variations in moisture availability and net soil moisture deficiency respectively x ray diffraction analysis of paleosol matrix material reveals the presence of analcime and the clay mineral palygorskite strong indicators of hot arid climatic conditions the 18 o and d values of clay minerals from paleosol profiles range from 22 3 to 25 4 and 44 4 to 39 6 smow respectively and correspond to crystallization temperatures between 25 c and 40 c these crystallization temperatures compare favorably with austral summer surface temperature estimates for central africa that result from late jurassic global circulation models calculations of soil co 2 production using the 13 c values of pedogenic carbonates and plant derived organic matter produce lower co 2 production estimates for the stanleyville group relative to the roughly contemporary morrison formation of the western u s these low soil co 2 production estimates provide further support for arid late jurassic climate conditions in the congo basin the paleoclimatic conditions inferred here from the stanleyville group are similar to those reconstructed from other upper jurassic african continental localities between 5 s and 20 s paleolatitude however penecontemporaneous terrestrial coastal sites within this latitudinal belt of gondwana retain evidence of generally wetter conditions suggesting that those regions may have received more rainfall than the continental interior the paleoclimatic setting reconstructed here from geologic indicators and geochemical proxies suggests that general circulation models accurately predict unique paleoenvironmental conditions that lack modern analogs

reinterpretation of palmate and semi palmate webbed fossil tracks insights from finite element modelling abstract a track from the late cretaceous previously described as being generated by a semi palmate bird was studied with the aid of high resolution laser scanning substrate conditions at the time of track formation were diagnosed fine grained soft waterlogged sediment and used to constrain a finite element track simulator the indentation of a non webbed virtual tridactyl foot in such conditions created a resultant track with features analogous to webbing between digits this webbing was a function of sediment deformation and subsequent failure in 3d specific to rheology variation of substrate conditions and interdigital angle was incrementally stepped apparent webbing impressions were clearly developed only within a limited range of sediment conditions and pedal geometry the implications of this work are that descriptions of webbed tracks should account for the possibility that webbing was indirectly formed through sediment failure and not necessarily the direct impression of a webbed foot additionally dating the earliest occurrence of webbed feet in the fossil record and potentially extending phylogenetic ranges should be treated with caution when based upon evidence from tracks

high resolution lidar and photogrammetric survey of the fumanya dinosaur tracksites catalonia implications for the conservation and interpretation of geological heritage sites increasing political and social awareness of the importance of protecting the geological heritage is compelling geoscientists to consider new methods for reconciling conservation and exploration of their research sites terrestrial light detection and range lidar imaging is an accurate method of collecting 3d spatial data that has so far been under utilized in the geological sciences this aim of this paper is to assess the value of integrated lidar and photogrammetric imaging as a tool for synchronizing scientific exploration with conservation of geological heritage sites fumanya catalonia is one of the most important cretaceous tracksites in europe but the nature of exposure of the track bearing surface has hindered quantitative documentation of the ichnites using integrated light detection and range lidar imaging and photogrammetry it has been possible to construct high resolution digital outcrop models dom of the tracksites photo textured doms are a powerful visualization tool and function as fully 3d interactive databases that preserve information about the site that would otherwise be lost to erosion lidar derived doms have the potential to contribute profoundly to future geoconservation projects particularly as a tool for documenting and monitoring heritage sites and promoting education and tourism lidar scanning also provides sufficient resolution to perform robust quantitative analysis of dinosaur tracks

palaeoecology and palaeobiogeography of the middle jurassic ostracods of southern tunisia abstract the results of a palaeoecological biostratigraphical and palaeobiogeographical analysis of jurassic ostracods from southern tunisia are presented the shallow to marginal marine deposits of bajocian bathonian krachoua and techout formations and callovian oxfordian age tataouine formation which accumulated under predominantly warm humid climatic conditions yielded diverse ostracod faunas from limnic brackish and marine environments which have been analysed statistically a qualitative cluster analysis yielded fourteen associations and two assemblages which are characterised by different percentages of marine brackish and freshwater species the distribution of the associations in the middle jurassic reflects temporal and spatial salinity gradients which are interpreted to reflect climatic variations humid arid and global eustatic sea level changes in the callovian the ostracods and macrofaunas probably also reflect minor relative sea level changes in accordance with other biostratigraphical data the ostracods support a bajocian bathonian age for the upper krachoua and the lower techout formations and a callovian age for the lower tataouine formation the palaeobiogeographical relationships suggest faunal exchange between southern tunisia and europe southern france sardinia england in the bajocian bathonian and an isolation of the south tunisian ostracod faunas from the european faunas in the callovian probably due to the deepening of the central western tethys predominantly in the bajocian bathonian but also in the callovian brackish conditions resulted in an endemicity of the ostracod faunas as a consequence of the eustatic sea level rise in the callovian species from the eastern north gondwana shelf israel jordan egypt saudi arabia respectively the ethiopian province invaded southern tunisia palaeobiogeographically the ostracods from southern tunisia are intermediate between the ostracods from the arabic northeast african region and northwest africa morocco

on the use of fredlund gas fluid compressibility relationship to model medium dense gassy sand behavior this paper presents the influence of gas bubbles trapped in a soil mass on the stress strain strength response of medium dense sands a hypoplastic constitutive sand model enhanced with the intergr

cretaceous reconstructions of east antarctica africa and madagascar abstract some cretaceous reconstructions of east antarctica africa and madagascar overlap the mozambique ridge onto the margin of dronning maud land and others place madagascar west of the gunnerus ridge into the riiser larsen sea our m10ny 131 9 ma m0 120 4 ma 96 ma and 34y 83 ma marine free air gravity and topography reconstructions illustrate a solution to the overlap problem and also demonstrate that madagascar separated from antarctica east of the gunnerus ridge our reconstructions chronicle the growth of the conjugate mozambique and riiser larsen basins created at the southwest indian spreading ridge well defined spreading corridors identified by conjugate fracture zones and mesozoic magnetic anomaly identifications extend from one basin into the other we find that the eastern scarp of the mozambique ridge aligns with the astrid ridge and there is no room for madagascar west of the gunnerus ridge the overlap of the mozambique ridge is solved by taking into account the motion of an independent mozambique ridge microplate that existed from chron m11 to circa m2

mapping in the oman ophiolite using enhanced landsat thematic mapper images abstract the large areal extent and complex nature of the terrain has meant that previous largely field based mapping programmes in the oman ophiolite have produced maps of internally inconsistent quality recognition of subtle changes and minor outcrops across the area of a 1 1 map sheet is possible in the field only by unrealistically exhaustive mapping by using parts of the short wavelength infrared spectrum landsat thematic mapper data have the capacity to capitalize on distinctions in the spectral reflectances of different rock types and their weathering products and to allow consistent mapping across the whole ophiolite decorrelation stretching of these data produces images in which it is possible to recognize variations in gabbro composition to identify small acidic gabbroic and ultramafic intrusions to discriminate the uppermost mantle from the deeper mantle to locate the moho precisely and to delineate gossans and areas subject to chloritic epidotic alteration off axis plutonism is more widespread and dispersed than previously appreciated the significance of certain faults is reassessed in the light of new insights provided by the imagery such data could be a valuable mapping tool in similarly exposed terrains in arid and semi arid regions even where already mapped at the 1 100 000 scale

the separation of madagascar and africa identification of a sequence of east west trending magnetic anomalies of mesozoic age in the western somali basin helps define the position of madagascar in the gondwana reconstruction the anomalies are symmetric about ancient ridge segments and are flanked to the north and south by the jurassic magnetic quiet zone the motion of madagascar relative to africa was from the north and began in the middle jurassic about the same time as the initial breakup of gondwanaland sea floor spreading ceased when madagascar assumed its present position in the early cretaceous

the proto indian ocean and a probable paleozoic mesozoic triradial rift system in east africa abstract a revised paleozoic mesozoic stratigraphy of coastal kenya including in particular the karroo based on current geological mapping near mombasa is briefly described this stratigraphy provides the geological framework for proposals concerning the proto indian ocean and the tectonic setting of the karroo depositional basins recent geophysical evidence suggests that within gondwanaland madagascar was situated off east africa near kenya tanzania the southern limits of the marine lower jurassic and southern limits of the marine middle and upper jurassic are in similar positions in mainland africa and madagascar using the latter reconstruction these paleogeographic limits also define the position during the jurassic of an embayment from an ocean to the north regional geological similarities also support this reconstruction and are reinforced by paleocurrent data from the karroo of kenya indicating drainage north northeast during the permian and triassic and possibly the lower jurassic marine connections during karroo times appear to be of different ages in kenya tanzania somalia and madagascar probably reflecting physical limitations to marine access in fault separated basins the above embayment encroached across the karroo depositional basins from northeast kenya to southern tanzania during the lower and middle jurassic i e from the direction towards which the karroo drainage had been previously directed marine conditions remain to the present day so this embayment can be considered the proto indian ocean for east africa the marine incursion took place before the breakup of gondwanaland suggesting that during the jurassic the proto indian ocean in east africa was an epicontinental sea and not a true ocean i e floored by simatic crust the epicontinental nature of this sea is confirmed by the lithologies of the associated sediments paleontological data indicate that this sea was an arm of tethys true oceanic conditions could not have been established until the displacement of madagascar away from africa probably in the cretaceous accepting the above northern position of madagascar the writers also postulate that in east africa the fault bounded karroo depositional basins troughs were located within a major triradial rift system extending from lake malawi at least as far as eastern kenya some 1600 km this rift system if valid was established within gondwanaland over a period 100 m y in the paleozoic mesozoic pre breakup in marked contrast to the east african rift system classical rift valleys which is mainly a cainozoic phenomenon post breakup it is therefore considered that there is a fundamental difference in origin between the two rift systems

mitigation of liquefaction of saturated sand using biogas some recent studies have indicated that the liquefaction potential of saturated sand can be greatly reduced if the sand can be made slightly unsaturated one way to reduce the degree of saturation of sand is to inject gas into sand this approach offers a cost effective solution for mitigating liquefaction hazard over a large area however it is not easy to inject gas into sand in a uniform manner a biogas method was developed in this study to overcome this difficulty in this method denitrifying bacteria are used to generate tiny inert nitrogen gas bubbles in sand shaking table tests using a fully instrumented laminar box are conducted on both saturated sand and sand containing microbially generated nitrogen gas bubbles comparisons of the results of these tests indicate that the pore water pressure generated in the partially saturated sand was much smaller than that in saturated sand thus the proposed method is effective in reducing the liquefaction potential of sand

in situ liquefaction resistance of clean sands over a wide density range the paper describes a method of obtaining undisturbed samples of saturated clean sand by freezing it in situ using a single freezer pipe tests have shown that the method can yield high quality samples that retain the density and the undrained cyclic strength of the sand in situ undrained cyclic triaxial tests were run on in situ frozen samples and on samples obtained with conventional tube samplers the liquefaction resistance of the frozen samples of clean sands correlates well with a normalized iv value of the standard penetration test over a wide range of tv values the in situ liquefaction resistance of the clean sands estimated from the results of the undrained cyclic tests on the frozen samples is consistent with a criterion based on field performance data during earthquakes for dense sands the samples obtained with the tube samplers are looser and much weaker than those obtained by the in situ freezing method the reverse is true for very loose sands the correlation between relative density an

somali basin chain ridge and origin of the northern somali basin gravity and geoid low the northern somali basin located between chain ridge and the horn of africa north of 4 n is characterized by a distinct 5 m geoid low and by large negative gravity anomalies the boundaries of the basin are marked by steep gradients in both gravity and geoid basement in northern somali basin is 1 2 km deeper than on the carlsberg ridge flank to the southeast or on the sheba ridge flank to the north with a sharp discontinuity across the boundary of the basin the western somali basin to the south was created in the late jurassic and early cretaceous by the movement of madagascar away from africa reinterpretation of the magnetic anomalies in the western somali basin shows that they record both limbs of a mid ocean ridge that was active by m22 time kimmeridgian and died soon after mo aptian magnetic and gravity data allow the relict ridge crest to be traced from davie ridge near the african coast to the dhow vlcc ars fracture zone complex at 50 e davie ridge is a transform fault connecting the western somali basin spreading center with a similar age spreading center in the mozambique basin the dhow vlcc ars complex can be shown to continue north of the 4 n bathymetric high separating the northern and western somali basins and to intersect the african margin near 7 n the northern somali basin thus appears to be the third of a series of oceanic basins separated by long transform faults created during movement between east and west gondwanaland the original northern somali basin was split apart by the northward motion of india in the late cretaceous and chain ridge formed along the new boundary thermal and gravity modeling shows that the flexure resulting from differential subsidence across chain ridge combined with the difference in lithospheric thermal structure late jurassic vs early tertiary on either side of it explains well the amplitude and shape of the observed geoid step and gravity anomalies across chain ridge the geoid step up from the basin up to the african coast can be modeled as an edge effect between the juxtaposed jurassic oceanic and african continental crust thus the geoid and gravity low over the northern somali basin results from the superposition of a continental edge effect anomaly and the fracture zone edge effect anomaly

effect of gas on the mechanical behavior of medium dense sands abstractthis paper presents the results of monotonic and cyclic triaxial tests performed on gassy medium dense sand specimens these sands are representative of conditions in a loose sand deposit that was densified using multiple blasting passes at a site in south carolina the equipment and laboratory testing procedures used to reproduce the postblast densification conditions observed at a field test are described in detail results of undrained and drained compression tests showed that the gassy specimen responses were bounded by the fully saturated drained and undrained responses the undrained test results showed that the presence of gas even in small amounts made the soil more compressible and restricted the buildup of excess pore water pressures as compared with those pressures observed in fully saturated specimens additionally the shear strengths of gassy medium dense sand specimens were similar to those observed in saturated loose sands sheared under drained conditions for a given cyclic s

spectral reflectance 400 2500 nm properties of coals adjacent sediments metamorphic and pyrometamorphic rocks in coal fire areas a case study of wuda coalfield and its surrounding areas northern china abstract although remote sensing is an effective tool extensively employed to detect and monitor coal fires continuous spectral reflectance properties of typical land surfaces such as coals adjacent sediments metamorphic rocks and pyrometamorphic rocks in coal fire regions have not been reported yet field and laboratory spectral reflectance of coals bituminous anthracite and coal waste sediments rocks sandstones siltstone desert sands limestones and shale metamorphic and pyrometamorphic rocks located in wuda coalfield and its surrounding areas are investigated for the reflective domain ranging from 400 nm to 2500 nm the results indicate that coal depicts the lowest reflectance 2 10 and strong absorption bands between 2200 and 2500 nm resulting from organic matter pyrometamorphic rocks are characterized by weak absorption features at 1400 and 1900 nm due to partial dehydration and strong ferric absorption features between 850 and 1100 nm attributed to thermal alteration and oxidation of the rocks sediments exhibit common absorptions features at 2200 and 2300 nm probably related to al oh vibrations and carbonate degenerate c o vibrations respectively spectral reflectance increases with a decrease of the coal rank and particle size the investigations on spectral reflectance properties of typical land surfaces in coal fire regions provide the basic understanding for applications of hyperspectral or multispectral remote sensing to classify land covers and to demarcate coal fire risk areas in similar geological settings

structure and evolution of the eastern gulf of aden conjugate margins from seismic reflection data the gulf of aden is a young and narrow oceanic basin formed in oligo miocene time between the rifted margins of the arabian and somalian plates its mean orientation n75 e strikes obliquely 50 to the n25 e opening direction the western conjugate margins are masked by oligo miocene lavas from the afar plume this paper concerns the eastern margins where the 19 35 ma breakup structures are well exposed onshore and within the sediment starved marine shelf those passive margins about 200 km distant are non volcanic offshore during the encens sheba cruise we gathered swath bathymetry single channel seismic reflection gravity and magnetism data in order to compare the structure of the two conjugate margins and to reconstruct the evolution of the thinned continental crust from rifting to the onset of oceanic spreading between the alula fartak and socotra major fracture zones two accommodation zones trending n25 e separate the margins into three n110 e trending segments the margins are asymmetric offshore the northern margin is narrower and steeper than the southern one including the onshore domain the southern rifted margin is about twice the breadth of the northern one we relate this asymmetry to inherited jurassic cretaceous rifts the rifting obliquity also influenced the syn rift structural pattern responsible for the normal faults trending from n70 e to n110 e the n110 e fault pattern could be explained by the decrease of the influence of rift obliquity towards the central rift and or by structural inheritance the transition between the thinned continental crust and the oceanic crust is characterized by a 40 km wide zone our data suggest that its basement is made up of thinned continental crust along the southern margin and of thinned continental crust or exhumed mantle more or less intruded by magmatic rocks along the northern margin abstract from author

correcting liquefaction resistance of unsaturated soil using wave velocity abstractexplicit empirical relationships for correcting liquefaction resistance of unsaturated soil below the groundwater table using compression wave velocity vp and shear wave velocity vs are derived and evaluated in this paper the relationships are derived using published laboratory test data for four different sands and one silt material the laboratory test data based on vp exhibit less scatter than the test data based on the ratio vp vs for this reason the vp based relationship is recommended for correcting the liquefaction resistance of unsaturated soil the influence of loading cycles and relative density on the recommended relationship is investigated from a review of 40 field case history sites it is found that in the critical layers at 20 of the sites average vp is less than 1 400 m s indicating unsaturated conditions liquefaction resistances computed for eight field case histories with vp 1 200 m s in the critical layers are corrected and plotted on penetration and vs based lique

earth s tectonic history revisited in the light of episodic misfits between plate network and mantle convection abstract episodic plate reorganisations abruptly change plate boundary configurations to illustrate their role we review the plate reorganisations that appear in the present day oceans and in the reconstructed tethys ocean these time periods cover the dispersal of the pangea super continent and the collisions with eurasia that foreshadow a new super continent plate reorganisations have played a fundamental role in the tectonic history of the earth being responsible for continental break up and after oceanic spreading for continental collisions as a result they governed the formation and dispersal of super continents we observe a bulk polarity in plate motion that governs continental collision and the opposite bulk polarity in plate reorganisation that governs continental break up such opposite polarities show in the tectonic history that we follow since the 550 ma formation of the gondwana super continent in order to decipher the rules that govern plate reorganisation we investigate the distribution of spreading and subduction that derives from the current plate motion we observe a mismatch between the evolution tendency of the plate boundary network and convection in the deep mantle the actual network of plate boundaries illustrates a compromise between the two based on the opposite polarities in plate motion and plate reorganisation we propose that this compromise is maintained by plate reorganisations that counterbalance free evolution of the network in abruptly changing its boundaries we propose that plate reorganisations are basically caused by the mismatch between the free evolution of the plate boundary network and the current convection pattern in the deep mantle evidence on proterozoic rifting and continent collisions allows dating the oldest known plate reorganisation around 2 ga which is the age of the oldest known super continent based on the geology of the archean before 3 ga mantle convection appears limited under a greenstone cover and different from the current mantle convection the distribution of the diapiric granitoids that intrude this cover points to a honeycomb convection centred on downwelling sites separated by diffuse upwelling which fits the theory on the early earth mantle convection when plates did not cover the globe we propose that the plate reorganisation regime appeared sometime between 3 and 2 ga

stratigraphy depositional history and environments of deposition of cretaceous through tertiary strata in the lamu basin southeast kenya and implications for reservoirs for hydrocarbon exploration abstract the lamu basin which is characterized by an extensional tectonic style is the failed arm of a tri radial rift system and possesses tectonic and stratigraphic elements in the post rift series that are analogous to those of the west coast of africa development of the southern part of the basin as a passive margin is closely related to considerations of the pre drift position of madagascar and formation of the indian ocean basin during mesozoic time cretaceous and tertiary strata in the basin comprise an eastward thickening gross succession of sediments on which eustatic sea level fluctuations and a sequence of unconformities related to pulses of transgressive and regressive depositional trends are superimposed recognition of these trends has provided the basis for classification of the strata into megasequences representing distinct provinces with regard to time stratigraphy sedimentation tectonics depositional environments and hydrocarbon potential megasequence i karoo group and jurassic includes strata of the permian through jurassic the discussion of which is beyond the scope of this paper megasequence ii sabaki group includes strata of the cretaceous and early paleocene deposited in tide influenced shelf and marine settings these are in ascending order the ewaso sands the walu shale the hagarso limestone the freretown limestone and the kofia sands megasequence iii tana group includes strata of the eocene through oligocene which were deposited in fluvial deltaic and restricted shelf settings these are in ascending order the kipini formation the pate limestone the linderina limestone the dodori limestone and the barren beds formation megasequence iv coastal group includes strata of the miocene through pliocene which were deposited in restricted shelf middle to outer shelf deep marine and fluvial settings these are in ascending order the baratumu formation the lamu reefs the simba shales and the marafa formation determination and description of these lithostratigraphic units their distribution and palaeohistory have been imperative for predicting reservoirs for hydrocarbon exploration

oblique rifting and segmentation of the ne gulf of aden passive margin 1 the gulf of aden is a young obliquely opening oceanic basin where tectonic structures can easily be followed and correlated from the passive margins to the active mid oceanic ridge it is an ideal laboratory for studies of continental lithosphere breakup from rifting to spreading the northeastern margin of the gulf of aden offers the opportunity to study on land the deformation associated with oblique rifting over a wide area encompassing two segments of the passive margin on either side of the socotra fracture zone exhibiting distinct morphologic stratigraphic and structural features the western segment is characterized by an elevated rift shoulder and large grabens filled with thick synrift series whereas the eastern segment exhibits low elevation and is devoid of major extensional structures and typical synrift deposits though the morphostructural features of the margin segments are different the stress field analysis provides coherent results all along the margin four directions of extension have been recognized and are considered to be representative of two tensional stress fields with permutations of the horizontal principal stresses 2 and 3 the two dominant directions of extension n150 e and n20 e are perpendicular to the mean trend of the gulf of aden n75 e and parallel to its opening direction n20 e n30 e respectively unlike another study in the western part of the gulf our data suggest that the n150 e extension stage is older than the n20 e extension stage these conflicting chronologies which are nowhere unambiguously established suggest that the two extensions coexisted during the rifting on land data are compared with offshore data and are interpreted with reference to oblique rifting the passive margin segmentation represents a local accommodation of the extensional deformation in a homogeneous regional stress field which reveals the asymmetry of the rifting process the first order segmentation of the sheba ridge is inherited from the prior segmentation of the passive margin

transition from continental to oceanic rifting in the gulf of aden structural evidence from field mapping in somalia and yemen abstract the analysis of the spatial temporal relationships between the tectonic structures of the continental margins bordering the gulf of aden and the adjacent oceanic structures provides a key for understanding the transition from continental to oceanic rifting the gulf of aden is a young ocean in which generation of oceanic crust between the tadjura gulf and the indian ocean began 11 m y ago west of the tadjura gulf spreading is more recent as no oceanic crust older than 2 ma has been found detailed field investigation along the continental margins of northeastern somalia and southeastern yemen areas adjacent to the most prominent oceanic structures has revealed a tectonic setting characterised by half graben structures and tectonic depressions striking wnw ese an oligocene miocene age for this graben formation is documented by infilling of syn rift sediment faults bordering contiguous half graben systems sometimes dip in opposite directions so that in the transition area between different systems a transfer zone or accommodation zone develops the shelves of both margins are divided by ne sw oriented ridges and by wnw ese oriented structural depressions the former are always located on the projection into the continent of the oceanic fracture zone and correspond to the transfer zones present on the continental margins while the latter are located on the projection into the continent of the oceanic ridges and correspond to the oligo miocene syn rift basins on the basis of structural and stratigraphical data from northeastern somalia and southeastern yemen it is possible to reconstruct the pre oligocene tectonic setting for the gulf of aden and its later rifting evolution this study brings new evidence to demonstrate that 1 1 during the early middle oligocene the afro arabian plate underwent a phase of intense faulting which led to the formation of small syn rift basins elongated in a wnw ese direction separated by transfer zones and structural highs 2 2 progressive crustal extension led to formation of spreading centers of oceanic crust in correspondence with the syn rift basins the fracture zones linking spreading centers formed in correspondence with continental transfer zones 3 3 the progressive separation of the somalian and yemenite continental margins led to the formation of a complete oceanic basin

subsidence history crustal structure and evolution of the somaliland yemen conjugate margin 1 we have used biostratigraphic data from deep exploration wells to determine the tectonic subsidence history of the somaliland northwestern somalia yemen conjugate margin a poorly known margin in the central part of the gulf of aden bathymetry and magnetic anomaly data suggest the gulf of aden is a young feature that formed following the rifting apart and breakup of the african and arabian plates 32 ma our tectonic subsidence data suggest however that the present day gulf of aden developed on an earlier mesozoic rift system the oldest episode of rifting initiated at 156 ma and lasted for 10 ma and had a nw se trend we interpret the rift as a late stage event associated with the breakup of gondwana and the separation of africa and madagascar at 80 ma there is evidence of an intermediate rift event which correlates with a rapid increase in spreading rate on the ridges separating the african and indian and african and antarctica plates and a contemporaneous slowing down of africa s plate motion the combined effect of all three rifting events has been to thin the crust and upper mantle by up to a factor of 2 the amount of thinning deduced from the wells is in accord with the crustal structure inferred from available seismic refraction data and process oriented gravity and flexure modeling the margin is asymmetric with a steeper gradient in the moho on the yemen side than the somaliland side the main discrepancy is on the yemen side where the gravity derived moho is 10 km deeper than the well derived moho we attribute the discrepancy to the addition of material at the base of the crust since rifting possibly magma sourced from the afar plume

volcanism jump and propagation on the sheba ridge eastern gulf of aden segmentation evolution and implications for oceanic accretion processes the rifting between arabia and somalia which started around 35 ma was followed by oceanic accretion from at least 17 6 ma leading to the formation of the present day gulf of aden bathymetric gravity and magnetic data from the encens sheba cruise are used to constrain the structure and segmentation of the oceanic basin separating the conjugate continental margins in the eastern part of the gulf of aden between 51 degrees e and 55 5 degrees e data analysis reveals that the oceanic domain along this ridge section is divided into two distinct areas the eastern area is characterized by a shorter wavelength variation of the axial segmentation and an extremely thin oceanic crust in the western segment a thicker oceanic crust suggests a high melt supply this supply is probably due to an off axis melting anomaly located below the southern flank of the sheba ridge 75 km east of the major alula fartak transform fault this suggests that the axial morphology is produced by a combination of factors including spreading rate melt supply and the edge effect of the alula fartak transform fault as well as the proximity of the continental margin the oceanic domains have undergone two distinct phases of accretion since the onset of seafloor spreading with a shift around 11 ma at that time the ridge jumped southwards in response to the melting anomaly propagating ridges were triggered by the melting activity and propagated both eastward and westward the influence of the melting anomaly on the ridges decreased stopping their propagation since less than 9 ma from that time up to the present the n025 degrees e trending socotra transform fault developed in association with the formation of the n115 degrees e trending segment 2 in recent times a counter clockwise rotation of the stress field associated with kinematic changes could explain the structural morphology of the alula fartak and socotra hadbeen fracture zones

digital outcrop models applications of terrestrial scanning lidar technology in stratigraphic modeling abstract laser ranging is extremely accurate and efficient terrestrial scanning lidar light detection and ranging applied to outcrop stratigraphic mapping enables researchers to capture laser range data at a rate of thousands of individual x y z and laser intensity points per second these data in conjunction with complementary remotely and directly sampled data are used to conduct high precision facies characterization and to construct 3d geological computer models outcrop data are presented here to explain our workflow and to discuss the construction of rock based 3d digital outcrop models doms reproducibility and quantification are the drivers of this methodology high resolution terrestrial lidar acquisition processing interpretation and visualization are discussed and applied to mapping of geological surfaces in three dimensions laser generated models offer scientists an unprecedented visualization medium in a quantitative 3d arena applications of this technology include constructing and visualizing complex 3d earth models from outcrops for improved reservoir modeling flow simulation in hydrocarbon and aquifer systems and property modeling to constrain forward seismic modeling

stratigraphic correlation by integrating photostratigraphy and remote sensing multispectral data an example from jurassic eocene strata northern somalia integrated analyses of aerial photographs and multispectral remote sensing images were used for stratigraphic correlation in mainly carbonate and evaporitic rocks these rocks crop out in an area of northern somalia characterized by an arid climate by the aerial photo analysis we recognized photostratigraphic logs and stratal patterns and established correlations based on the tracing of physical surfaces with chronostratigraphic significance such as photohorizons and photostratigraphic discontinuities a limited number of field sections provided the lithological interpretation of the packages of strata delineated in aerial photos by satellite multispectral landsat thematic mappertm data analysis we identified image facies that represent packages of strata with different lithological characteristics to interpret the image facies we compared the responses in the thematic mapper tm bands with the laboratory spectroscopic properties of rock samples from the study area and interpreted the absorption features by p trographic analysis the mesozoic and tertiary strata analyzed herein are part of several formations deposited on a passive margin preceding the oligocene miocene gulf of aden rifting and initial drifting following this approach a number of stratigraphic units were recognized and mapped on aerial photos and a framework of photostratigraphic correlation surfaces was delineated over significantly wide areas these surfaces approximate time surfaces and are traced both within and across the lithostratigraphic units improving existing maps this method represents a mapping tool preliminary to more detailed field work and is particularly useful in areas of difficult access

jurassic and cretaceous marine connections between the southeast pacific and tethys abstract the affinities of the ammonoid faunas from central west and southern south america are used to analyze the evolution of seaways and oceanic connections with tethys during the jurassic and cretaceous during the early and middle jurassic marine connection with eastern tethys was around the australian margin of gondwana from the pliensbachian onwards connection with western tethys occurred through the sporadically opened hispanic corridor in central america in late jurassic time the break up of gondwanaland was initiated and a seaway began to open between south america africa and antarctica connection of the eastern pacific with tethyan waters through southern africa was sporadic and was still mainly around australia and along the now open central american seaway throughout the early cretaceous the opening of the south atlantic proceeded from south to north and the first marine connection between the southern and northern atlantic took place in albian time a definite marine connection between the opened south atlantic and eastern tethys with faunal migration routes was established in late hauterivian barremian time and became fully open in the aptian albian successive stages in the opening of a south african seaway between tethys and the southeast pacific show an asymmetric development to the west and east of south africa during late cretaceous time oceanic circulation continued between the south atlantic and eastern tethys and true oceanic conditions developed between the southern and northern atlantic the antarctic peninsula was still located in a position adjacent to south america preventing open circulation between the south atlantic and pacific oceans

stratigraphy and geodynamics of the mombasa basin kenya in relation to the genesis of the proto indian ocean new data obtained from the study of the kenyan and tanzanian coastal basins establish a rifting period at the end of the karoo sedimentation upper triassic lower jurassic in the northeastern margin of gondwanaland the rifting period was followed by an erosive phase and then transgression of a tethyan sea during the middle jurassic this leads to a modification of the stratigraphic succession of the region and gives new datas about the nature of separation and drifting of gondwanaland the genesis of the proto indian ocean and the paleoposition of madagascar

preliminary spectral and geologic analysis of landsat 4 thematic mapper data wind river basin area wyoming a landsat 4 thematic mapper tm image covering the wind river basin area wyoming is under evaluation for stratigraphicand structural mapping and for assessment of spectral and spatialcharacteristics using the six visible near infrared and short wavelengthinfrared bands the image path 36 row 30 id 40128 17232 was acquired on november 21 1982 the data were obtained from the nasa goddard space flight center in radiometrically and geometrically correctedfullscene magnetic tape format to estimate equivalent lambertian surface spectral reflectance tmradiance data must first be calibrated to remove atmospheric andinstrumental effects reflectance measurements for homogeneousnatural and cultural targets in the scene were acquired during the period october 27 november 3 1983 about one year after satellite dataacquisition scatterplots were prepared of image dn versus reflectancefor these sites the scatterplots show the tm sensor system response islinear for the conditions of image acquisition and for the mix of terraincover types encountered low tm offset and gain settings result in encoded spectral data thatdo not occupy the full dynamic range 256 gray levels of the tm calibration data acquired during the study were used to calculate new gainsand offsets that would improve scanner response for earth scienceapplications analysis demonstrates that principal component images provideuseful structural and stratigraphic information principal componentscalculated from the correlation matix result from linear transformationsof ground reflectance in images prepared from this transform theseparation of spectral classes is largely independent of systematicatmospheric and instrumental factors

application of ostracoda and charophyta from the late jurassic to early cretaceous tendaguru formation at tendaguru tanzania east africa biostratigraphy palaeobiogeography and palaeoecology abstract revisitation of the famous late jurassic early cretaceous dinosaur locality of tendaguru by a german tanzanian expedition in summer 2000 resulted in a new standard section micropalaeontologic samples from this section yielded a marine and nonmarine partially mixed ostracod fauna consisting of 40 taxa and some charophyte gyrogonites and utriculi a few marine taxa provided biostratigraphic information although comparable faunas from the west indian madagascan east african faunal province are stratigraphically older middle late jurassic fully marine and strongly endemic an middle oxfordian age is suggested for the lower part of the tendaguru formation nodosoclavatoroid utriculi charophyta suggest that the jurassic cretaceous boundary may be located lower in the section than supposed previously i e in the trigonia smeei member rather than in the upper saurian member in biogeographical terms the marine ostracod fauna is relatively endemic and has most similarities with that known from eastern tanzania only a few faunal links to madagascar northwest india and somalia exist and there are no links to south africa ostracods and charophytes also provided palaeoecological data for specific horizons in the lower part of the middle saurian member a regression is documented while the nonmarine late jurassic early cretaceous ostracods of tendaguru are not applicable to biostratigraphy so far they are important because the nonmarine setting is unique in this area of the tethys

dinosaurs nesting on tidal flats abstract the discovery of a dinosaur clutch in upper cretaceous tidal flat deposits in the tremp formation in biscarri isona lleida spain provides insight into the mode of life of some dinosaurs the clutch occurs in grey marls that were originally waterlogged muddy sediments the seven elongated eggs are parallel to each other and with their long axis almost vertically oriented a mound nest is inferred in contrast to hole nest described so far for similar eggshell types the permeability of the eggshell oospecies megaloolithus siruguei was highly enhanced by a braided network of multicanaliculate pore canals the nest style eggshell porosity and tidal flat environment point to a periaquatic habitat for these dinosaurs a modern analogue occurs in crocodiles alligators and some birds living in periaquatic environments with nesting on plant mounds above waterlogged soils or even on floating vegetation

middle and upper jurassic ostracods from western kachchh gujarat india biostratigraphy and paleobiogeography abstract this paper presents a study of the middle and upper jurassic ostracods from western kachchh india the first part discusses the biochronological importance of the ostracod assemblages while the second part reports the paleobiogeographical results benthic foraminiferal biozones are used to calibrate the biostratigraphical distribution of ostracod species and genera from sections in the aalenian tithonian interval located in western kachchh or kutch mundham anticline jumara dome jhurio dome and habo dome and on pachchham island khavda nala gujarat india a total of 71 species are listed including 32 previously published species and 38 species in open nomenclature belonging to 23 genera the ostracod assemblages indicate that faunal communication was first established during the bathonian and callovian middle jurassic and continued until the early cretaceous these faunal exchanges occurred between laurasia usa europe russia and siberia and the indo east african province extending along the western tethyan carbonate shelves bordering west and east gondwana through to the pacific ocean margin of west gondwana

the arabian infracambrian extensional system abstract during the late precambrian and early cambrian about 600 540 ma extensive left lateral faulting along the complex nw se trending najd fault system cut across the arabian shield this tectonic episode was accompanied by nw se directed extension in northern egypt and the sinai peninsula based on these relationships stern 1985 interpreted the najd fault system as a set of transform faults emanating from a rift basin in ne egypt contemporaneous to this system in the western part of the arabian plate and northern egypt extensive evaporitic basins developed in northern pakistan southern oman and the arabian gulf and zagros mountains these basins are generally bounded by nw trending faults such as the najd hawasina and zagros faults and ne trending faults such as the ghudun khasfah and dibba faults these evaporitic basins are interpreted as rift basins such that stern s 1985 extensional model in northern egypt may be expanded regionally to include the eastern part of the arabian plate and the indian subcontinent this broader interpretation implies that after the e w directed collisional tectonics of the late precambrian in western arabia and africa which terminated around 640 600 ma the arabian plate experienced nw se directed crustal extension and continental break up

reconstruction of eastern gondwanaland substantial additions of large continental blocks to the smith et al 1 model of eastern gondwanaland are proposed here largely on the basis of the distribution of key land floras tropical and subtropical marine faunas lithofacies patterns and the identification of a triassic magmatic arc that characterized all the eastern margin of gondwanaland the continental fragments that must have been rifted from northern australia new guinea in the jurassic are identified as south tibet burma thailand malaya and sumatra the original site of deposition of the subtropical permian limestones and tropical late triassic limestones overthrust onto the northern margin of australia by the late cenozoic collision2 is located in this greater gondwanaland palaeomagnetic data except those from malaya3 support this reconstruction

the influence of preexisting structure on the evolution of the cenozoic malawi rift east african rift system this paper analyzes the importance of preexisting structure for the evolution of the cenozoic malawi rift which constitutes the southernmost part of the western branch of the east african rift system kinematic analyses demonstrate that the regional extension direction rotated clockwise from ene to se during rifting cenozoic rift faults of dip oblique and strike slip character rejuvenated crustal structures whenever those were properly oriented with respect to the extension directions depending on these boundary conditions the rift attempts to find the easiest pathway in order to develop in a mechanically modest way proterozoic basement structures represent the basic anisotropy which already influenced pre cenozoic rifts and also the cenozoic malawi rift amongst these basement structures pan african retrograde to cataclastic strike slip shear zones have the strongest influence on later rift structures rift related transfer faults appear as differently striking passive structures and their orientation seems to be controlled by a variety of steep basement structures retrograde shear zones foliation planes and fracture arrays

tracking the paleogene india arabia plate boundary the location of the india arabia plate boundary prior to the formation of the sheba ridge in the gulf of aden is a matter of debate a seismic dataset crossing the owen fracture zone the owen basin and the oman margin was acquired to track the past locations of the india arabia plate boundary we highlight the composite age of the owen basin basement made of paleocene oceanic crust drilled on its eastern part and composed of pre maastrichtian continental and oceanic crust overlaid by ophiolites emplaced in early paleocene on its western side a major fossil transform fault system crossing the owen basin juxtaposed these two slivers of lithosphere of different ages and controlled the uplift of marginal ridges along the oman margin this transform system deactivated 40 myrs ago coeval with the onset of ultra slow spreading at the carlsberg ridge the transform boundary then jumped to the edge of the present day owen ridge during the late eocene oligocene period before seafloor spreading began at the sheba ridge this migration of the plate boundary involved the transfer of a part of the indian oceanic lithosphere formed at the carlsberg ridge to arabia this late eocene oligocene tectonic episode at the india arabia plate boundary is synchronous with a global plate reorganization event corresponding to geological events at the zagros and himalaya belts the owen ridge uplifted later in late miocene times and is unrelated to any major migration of the india arabia boundary

degree of saturation and liquefaction resistances of sand improved with sand compaction pile sand compaction pile scp is a ground improvement technique extensively used to ameliorate liquefaction resistance of loose sand deposits this paper discusses results of laboratory tests on high quality undisturbed samples obtained by the in situ freezing method at six sites where foundation soils had been improved with scp inspection of samples revealed that the improved ground was desaturated during the ground improvement degree of saturation sr was lower than 77 for the sand piles and 91 for the improved sand layers while sr was approximately 100 for improved clayey and silty soils a good correlation was found between sr and 5 diameter of the soil the larger 5 diameter of soils d5 the lower the degree of saturation it appeared that the variation of sr with d5 for soils within a month after the ground improvement work was quite similar in trend to that after more than several years degree of saturation of soils after several years was noticeably but not significantly higher as

use of low cost multistripe laser triangulation mlt scanning technology for three dimensional quantitative paleoichnological and neoichnological studies abstract the purpose of this paper is to test the application of a new low cost 2995 00 us multistripe laser triangulation mlt scanner and three dimensional 3d software for semiquantitative and quantitative analyses of ichnofossils and modern traces the goal of this research is to improve on existing analytical techniques and apply new methods to 3d digital models of ichnofossils and modern traces objectives are to 1 provide researchers with new ways to develop and test hypotheses quantitatively in the fields of paleoichnology neoichnology sedimentology and soil science and 2 discuss uses advantages and limitations of mlt technology related to ichnology we scanned and created digital models of a variety of mostly continental ichnofossils and modern terrestrial traces produced by invertebrates and vertebrates visual methods applied include making uniformly colored specimen surfaces stereo pairs anaglyph stereo images animations and cross sections quantitative methods applied include measuring distances tortuosity indices and angles and producing contour maps of tracks two of the most useful properties measurable from digital models are surface area sa and volume v these are used rarely in ichnology because they are difficult to measure with traditional methods we use sa to calculate area exploited and introduce a method of quantifying surface roughness adapted from research on soil surfaces we measure v of burrows tracks and coprolites as well as introduce a new measure termed volume exploited we hypothesize that different tracemakers make burrows with characteristic v to sa ratios this is partially supported by statistical tests of previously published data we also use v to sa ratios to determine relative compactness a metric adapted from building physics digital models ensure perpetuity of specimens because they preserve 3d data that can be used to make physical copies placed in museums and disseminated easily to researchers and educational institutions of all levels data from digital models can be used to interpret ichnocoenoses bioturbation rates and pedogenic properties and processes in soils and paleosols note that mlt scanning digitizes only surfaces of objects so it is best suited for exogenic traces and casts of endogenic traces

isotopically heterogeneous initial pb and continuous 222 rn loss in fossils the u pb systematics of brachiosaurus brancai abstract diagenetic incorporation of uranium into bone material establishes a u pb system that provides a minimum age for the fossil loss of rn and ra from the 238u decay series recent mobility of u and pb and incorporation of radiogenic pb from an old basement which was available during diagenesis disturbed the u pb system all data fall in a 206pb 238u 207pb 235u concordia diagram to the right of the concordia while samples that do not experience redistribution of u pb 222rn and 226ra should define a linear array that intersects the concordia curve at the age of diagenesis and at the age of the source of inherited radiogenic pb loss of 222rn and 226ra has led to displacement of the present data set to lower 206pb 238u and therefore to younger intercept ages and to older 207pb 206pb ages the 207pb 204pb 208pb 204pb systematics demonstrates that 1 three out of 19 samples experienced significant postdiagenetic fractionation of u and pb and that 2 the diagenetic pb addition was isotopically heterogeneous the 235u 207pb 206pb 207pb and 206pb 238u 207pb 235u systematics combined demonstrate that 3 the samples experienced 5 to 18 222rn loss for a 1 9 ga old source of the diagenetically introduced pb and correspondingly more for a younger pb source and that 4 there is no unique solution for the age of the source of diagenetic pb since pb from a younger source appears in the 235u 207pb 206pb 207pb diagram in the same way as higher 222rn loss no precise age can be determined from the data although the most consistent solution falls in the range of 140 to 150 ma addition of radiogenic pb to the fossil bone is obvious only through its anomalous highly radiogenic character and the isotopic heterogeneity in 208pb 204pb no th i e no in situ 208pb growth the effect of unrecognized diagenetic additions of radiogenic pb is an overestimation of the age whereas unrecognized 222rn loss results in a too young discordant age since fossil material formed at times for which the discordia only shows a small curvature anomalies originating from diagenetic pb additions and 222rn loss may not always be recognized

scaling and geometric properties of extensional fracture systems in the proterozoic basement of yemen tectonic interpretation and fluid flow implications abstract multi scale mappings of fracture systems in the crystalline basement of yemen are presented fracture datasets are described through statistical analyses of direction length spacing density and spatial distribution results are combined with field observations and can be directly used to model the geometry of the fracture networks in analog basement rocks from multi kilometric to decametric scales the fractured reservoir analog is defined with a dual porosity model in which tectonic and joint systems correspond to the basement reservoir backbone and matrix respectively these two end members reveal contrasting geometrical reservoir and scaling properties in tectonic systems multi scale geometries are self similar the fracture network shows fractal behavior power law length distribution and clustered spacing and fault zones show hierarchical organization of geometrical parameters such as length thickness and spacing in joint systems the fracture network is scale dependent with exponential length distribution and shows anti clustered spacing however these two end members have both well connected properties with fault zones acting as main drain and joint systems acting as the fluid supply

constraints on the motion of madagascar with respect to africa abstract three constraints on the motion of madagascar relative to africa are investigated in order to arrive at a model for madagascar s drift these are 1 fracture zone morphology and direction in the somali basin and mozambique channel 2 the relative positions of the carboniferous to jurassic palaeomagnetic poles for madagascar and africa and 3 the crustal structure along a geophysical traverse between lamu kenya and mahe seychelles the evidence for the bunce and molnar 1977 pole for the rotation of madagascar relative to africa defined by the davie dhow vlcc and ars fracture zones is critically examined and accepted it is used to rotate madagascar northwards back to a position that brings the carboniferous to jurassic palaeomagnetic poles for madagascar and africa into good agreement the rotation of approximately 16 places madagascar in the north of the somali basin with its northern tip at the southwestern end of the chain ridge it moves madagascar almost exactly the length of the extended davie fracture zone accepting that this position may have been the pre drift position of madagascar some interesting correlations with the lamu mahe crustal section emerge continental crust appears to extend 300 km offshore from lamu and thus abuts precisely the continental crust of rotated madagascar between 300 km and 1200 km from lamu the crust is probably oceanic of jurassic cretaceous age this would have been left in the wake of madagascar as it drifted southwards four fracture zones are seen in this crust a major one appears in the crustal section about 700 km from lamu the dhow fracture zone at 850 km may be associated with a large step up to the east in basement which has acted as an efficient dam to sediments from africa and the vlcc and ars are smaller fracture zones the easternmost part of oceanic crust between 1100 and 1200 km may have been formed in the wake of the farquhar islands drifting southwards with madagascar more likely however it could have formed as the seychelles bank area drifted away from madagascar having previously moved southwards with madagascar eastwards from 1200 km thicker possibly continental crust adjoins the seychelles bank this model assumes that the comores basin is oceanic in origin which may not be the case if it is continental a rotation of madagascar of only 9 or 10 can be accommodated moving the island almost exactly the length of the topographic expression of the davie fracture zone but providing a poor fit of the palaeomagnetic poles

liquefaction response of partially saturated sands ii empirical model partial saturation in sands attributable to the presence of gas bubbles not capillarity can be encountered naturally in the field be cause of the decomposition of organic matter or it can be induced for liquefaction mitigation an empirical model rupss was developed to predict the excess pore pressure ratio ru in partially saturated sands subjected to earthquake induced shear strains the model is based on experimental test results on partially saturated sands cyclic simple shear strain tests were performed on specimens prepared and tested in a special liquefaction box excess pore pressures were measured for a range of degrees of saturation 40 s 90 relative densities dr 520267 and cyclic shear strains g50 0120 2 the test results demonstrated that partially saturated sands achieved a maximum excess pore pressure ratio ru max when large enough cycles of shear strain were applied the excess pore pressure ratio ru that partially saturated sand can achieve under a given earthquake induced peak shear strain and the number of equivalent cycles of application can be significantly smaller than ru max therefore the empirical model was developed in two stages in the first stage ru max was related to s dr and shearstrain g in thesecondstage amodelwasdevelopedrelatingru toru max shearstrainamplitude g effectivestress s9 andearthquake magnitude m thispaperpresentstheequationsthatdefinethepredictivemodelsforru max andru throughtheseequations plotsforru max and ru are provided for ranges of soil and earthquake parameters for ease of use in engineering applications to illustrate the implementation of the empirical model for predicting ru max and ru an example is presented in which a partially saturated sand layer experiencing a peak earthquake induced shear strain was analyzed and the pore pressure response of the sand was evaluated using both the predictive equations and the plots doi 10 1061 asce gt 1943 5606 0000816 2013 american society of civil engineers ce database subject headings soil liquefaction soil treatment saturated soils pore pressure empirical equations sand soil type author keywords soil liquefaction soil treatment saturation pore pressure empirical equations induced partial saturation liquefaction mitigation empirical model soil model

organic geochemistry palynofacies and petroleum potential of the mukalla formation late cretaceous block 16 eastern yemen abstract the late cretaceous mukalla formation of the mahra group is present in the subsurface of eastern yemen the palynofacies thermal maturation and hydrocarbon potential of this formation recorded from three exploratory wells in the qamar basin are discussed two of the wells are in the offshore part of block 16 and one is in the onshore part both organic geochemical and palynofacies analyses indicate that the formation contains oil and gas prone kerogen rock eval pyrolysis and gas chromatography data show a peak thermal maturation stage for organic matter types ii iii and iii and good conditions for hydrocarbon generation and expulsion three major palynofacies types are identified through the succession these indicate open marine marginal to shallow marine and fluvio deltaic environments reflecting multiple marine transgressive and regressive phases during the period of deposition of the formation which took place in a humid subtropical to tropical climate

timescales and mechanisms of ree and hf uptake in fossil bones abstract rare earth element ree patterns of fossil bones and teeth are widely used as proxies for provenance taphonomy and palaeoenvironment in order to investigate if fossil bones behave as closed systems over geologic time ree profiles were analysed by la icpms along cross sections of 54 bones from various well characterised and well dated settings these include terrestrial and marine diagenetic environments covering early triassic to holocene ages in general all fossil bones exhibit the highest ree concentrations at the outer rim gradually decreasing by up to four orders of magnitude toward the inner bone cortex intra bone ree concentration gradients decrease significantly from quaternary via tertiary to mesozoic specimens suggesting long term ree uptake and open system behaviour of fossil bone this view is further corroborated by 176lu 176hf dating of selected samples all yielding significantly younger ages than the known chronostratigraphic ages hence there is clear evidence for long term open system behaviour of fossil bones with respect to ree which is in marked contrast to currently accepted models suggesting that ree uptake is only early diagenetic although unexpected statistically significant four to seven point isochrons are observed for four fossil dinosaur bone samples and one upper triassic mastodonsaurus tooth with mswds ranging from 0 083 to 4 5 notably mobility of lu alone cannot account for the observed age patterns assuming constant lu uptake rates over time the radiometric ages should only be as low as half of the chronostratigraphic age however a six point isochron defined by subsamples of a single upper triassic mastodonsaurus tooth yields an age of 65 2 1 1 ma mswd 0 68 much younger than half of the stratigraphic age ca 234 ma hence hf must also undergo late diagenetic exchange likely mechanisms to account for the presence of statistically meaningful isochrons as well as for the late diagenetic exchange of both ree and hf are diffusion adsorption and dissolution reprecipitation processes

mathematical characterization of pile soil interface boundary for consolidation analysis of soil around permeable pipe pile permeable pipe pile is proposed to accelerate the dissipation of excess pore water pressure through drainage holes around the pile circumference into the pile s cavity this investigation generaliz

the extent and significance of mass movements in eastern africa case studies of some major landslides in uganda and kenya the east african region has experienced major landslides in recent years these landslides have caused many fatalities and injuries loss of many hectares of productive farmlands and destruction to infrastructure such as roads railways and bridges the warm and wet climate of the landslide prone regions causes rapid weathering and produces a regolith weaker than the underlying rock with an interface between the two layers this interface serves as the most common plane along which landslides are initiated once it becomes saturated landslides in the region are associated with steep topography human activities such as deforestation overgrazing and unplanned farming on steep slopes and are induced by earthquakes and high intensity of rainfall the landslide prone areas are agriculturally very productive and the inhabitants depend on agriculture for their livelihood the areas also contribute substantially to the national food reserve the landslides are therefore a burden to the economies of the individual farmers and national governments of the region

analog models of oblique rifting in a cold lithosphere new lithospheric analog models of oblique rifting presented here capture the main characteristics of natural oblique rifts and provide insights into the fault evolution basin segmentation and mantle exhumation occurring during rift localization we present two models one with a preexisting oblique lithospheric weakness model b and another with no weakness zone model a both oblique rifts have an obliquity of about 40 the main results are as follows 1 the fault populations especially during the early stages of deformation are composed of faults that in strike are largely intermediate between rift parallel and perpendicular to displacement this fault population is characteristic of oblique rifts observed in previous studies 2 in later stages faults parallel to the rift become numerous in both models buoyancy forces related to thickness variations in the lithosphere during rift localization play a significant role and control the initiation of rift parallel faults 3 during the final stages of extension in model b the crust is deformed by rift parallel faults while in the basins the small scale deformation pattern is composed of displacement normal faults however in model a displacement normal faults tend to accommodate most of the extension controlling its final stages they probably also control the formation of the ocean continent transition any possible mantle exhumation as well as the geometry of oceanic accretion centers these results provide an insight into the possible evolution of the gulf of aden conjugate margins which developed in an oblique context and most probably without any preexisting rift parallel localizing heterogeneity in the lithosphere