structural analysis and interpretation of the surface deformations of the el asnam earthquake of october 10 1980 the el asnam earthquake of october 10 1980 represents the major seismotectonic event of these last decades in the west mediterranean area it has induced a large amount of surface breaks this earthquake reveals the importance of compressional phenomena that characterize nowadays the tectonics of north africa the tectonic analysis of surface rupture shows the complexity of the deformation mechanism the principal mechanism consists of the activation of a nw se trending thrust fault accompanied with a left lateral motion and with an intense deformation of the northwestern overthrusting block an accurate description of these deformations shows that for a large part the breaks geometry depends closely on the substratum structure finally the analysis of the dislocations on irrigation ducts just above the fault traces allowed a quantitative study of the deformation

holocene transgression recorded by sand composition in the mesotidal galician coastline nw spain this study confirms several inferences regarding holocene coastal dynamics and climate through a petrographic modal analysis of 60 holocene sand samples recovered in seven sites along the nw coast of the iberian peninsula fluvial sand can be discriminated from more mature intertidal and aeolian sand according to texture and composition fluvial sand contains soil products and coastal sand has significant bioclasts quartzofeldspathic sand appears in the western area produced by the erosion of granite and granitoid and quartzolithic sand occurs in the eastern area produced by the erosion of metasediment changes in sand composition during holocene deposition are manifested by an increase in modern carbonate clasts mc correlated with the holocene transgression episodes of faster sea level rise and subsequent erosion of surrounding cliffs are indicated by the preservation of high proportions of feldspar in intertidal sand in contrast fluvial sand is characterized by greater quartz enrichment these inferences were confirmed by petrographic indices carbonate clasts total clasts mc t total feldspars monocrystalline quartz f qm and plagioclase total feldspars p f the different maturity of intertidal and aeolian sands is revealed by their variable quartz contents despite similar proportions of plagioclase and k feldspar this suggests mechanical abrasion as the main factor controlling maturity in contrast fluvial sand shows depleted plagioclase contents as the result of inland weathering processes intertidal beach and aeolian sands are essentially the products of the erosion of coastal cliffs and head deposits with only the scarce contribution of fluvial drainages the long distance transport of galician coastal sands is discarded based on the close relationship between their composition and that of local sand sources our findings indicate that short distance transport of sediments from the west closed off coastal wetlands and occluded estuarine mouths during the holocene transgression by deposition on sediment trap zones along the irregularly shaped galician coast

overlooked sedimentary particles from tropical weathering environments two varieties of sedimentary particles that are common in tropical weathering environments have remained largely overlooked by sedimentary petrologists alterites are grains that have been so thoroughly altered by chemical weathering processes that identification of the precursor grain is impossible they consist of secondary weathering products such as clays zeolites and iron sesquioxides as well as incompletely weathered remains of relatively stable mineral phases alterites that consist of clay sand composites allow the transport and deposition of hydraulically dissimilar constituents under a single hydrodynamic regime and may be important in the production of some graywackes a second class the pedogenic ferruginous particles takes on a variety of forms including laterite fragments soil pisolites and oxidized burrow rinds although these particles are common in modern fluvial sands in the tropics wholesale dissolution of amorphous or poorly crystalline iron sesquioxides during burial diagenesis may help to explain the rarity of such particles in ancient sediments although their potential for preservation is low dissolution of ferruginous particles may be an important source of diagenetic iron which may be redeposited to form ferruginous cements or diagenetic redbeds

late quaternary transpressional earthquakes on a long lived intraplate fault a case study of the southern yangsan fault se korea abstract the nne ssw striking yangsan fault in southeastern korea has been regarded as one of the most prominent seismogenic structures in the korean peninsula on the basis of instrumental and historical seismicity and paleoseismic records along the fault zone its seismic behavior is however still uncertain due to long recurrence intervals of strong earthquakes and insufficient historical and geologic records we conducted a detailed paleoseismic investigation including an 8 m deep excavation in order to understand recent earthquake faulting events along the southern yangsan fault our observations indicate that at least two and possibly four dominantly strike slip surface faulting events have occurred along a subsidiary fault in the eastern boundary of the fault valley since the late pleistocene stratigraphic features and osl ages of the stratigraphy exposed in the trenches indicate that the most recent rupture s occurred after 29 2 1 4 ka and the timing of earlier ruptures are constrained to between 70 0 3 7 ka and 29 2 1 4 ka using a contact of the oldest dated unit that has at least 7 5 m of vertical separation we calculate a minimum vertical slip rate during the late quaternary of 0 11 mm yr the minimum horizontal slip rate is presumed to be two times that of the vertical slip rate based on striations observed on clasts next to the fault core we also propose that the late quaternary earthquake faulting kinematics along the yangsan fault expressed as contractional dextral slip with east side up geometry is strongly dependent on a pre existing fault zone architecture with a strike of n10 20 e that dips to the east and the direction of neotectonic maximum horizontal stress ene wsw to e w

aftershock sequence and statistics of the 2017 mw 5 5 pohang south korea earthquake implications of fault heterogeneity and postseismic relaxation

modern sands of south america composition provenance and global significance standard petrographic methods were used to study 604 modern sands from south america of which 351 came from rivers and 253 from beaches in spite of the wide geomorphic contrasts these sands belong to only three great families 1 an immature andean family of lithic arenites rich in volcanic and metamorphic grains that covers about 30 of south america 2 a cratonic association rich in quartz that covers about 62 of the continent and 3 a transitional molasse association which occurs between these two and covers only about 8 of the continent the grand arithmetic average q f rf ratio for the entire continent is 60 11 29 and the area weighted carbonate free average qa fa rfa is 68 10 22 a superior continental estimate and the first ever for an entire continent

slumps canyons and related features on the continental margin off east london se africa sw indian ocean abstract bathymetric and seismic reflection surveys in the natal valley east of east london show that the most important factors in the neogene development of the outer continental margin have been large scale slumping and penecontemporaneous canyon formation slope wasting and allochthonous mass movements have shifted the foot of the continental slope up to 25 km basinward and have constructed extensive continental rise lobes shelf break breaching by canyon heads is considered an important factor in transferring sediment entrained in the agulhas current from the continental shelf to the deep ocean basin a preliminary sediment budget suggests that the continental rise lobes could have been constructed during the last 2 69 m y following an episode of massive slumping

anomalous seafloor mounds in the northern natal valley southwest indian ocean implications for the east african rift system abstract the natal valley southwest indian ocean has a complicated and protracted opening history as has the surrounding southwest indian ocean recently collected multibeam swath bathymetry and 3 5 khz seismic data from the natal valley reveal anomalous seafloor mounds in the northern natal valley the significance of these domes as recorders of the geological history of the natal valley and se african margin has been overlooked with little attempt made to identify their origin evolution or tectonic significance this paper aims to describe these features from a morphological perspective and to use their occurrence as a means to better understand the geological and oceanographic evolution of this basin the seafloor mounds are distinct in both shallow seismic and morphological character from the surrounding seafloor of the natal valley between 25 km and 31 km long and 16 km and 18 km wide these features rise some 400 m above the sedimentary deposits that have filled in the natal valley such macro scale features have not previously been described from the natal valley or from other passive margins globally they are not the result of bottom water circulation salt tectonics rather igneous activity is favoured as the origin for these anomalous seafloor features we propose a hypothesis that the anomalous seafloor mounds observed in the natal valley are related to igneous activity associated with the ears the complicated opening history and antecedent geology coupled with the southward propagation of the east african rift system creates a unique setting where continental rift associated features have been developed in a marine setting

quantitative analysis of detrital modes statistically rigorous confidence regions in ternary diagrams and their use in sedimentary petrology abstract detrital modes are the basic type of quantitative data used in sedimentary petrology they represent estimates of the petrographic framework composition of sand or sandstone obtained by point counting of thin sections at present geological inferences from analysis of these numerical data are semi quantitative only because many of the data processing methods employed in sedimentary petrology lack a firm theoretical basis a review of existing methods reveals a number of fundamental statistical problems associated with the use of univariate statistics and the construction of so called hexagonal fields of compositional variation it is shown that these problems can be overcome by using multivariate methods that honour the non negativity and unit sum constraints on compositional data and incorporate the covariance structure spread in compositional data can be modelled on two levels 1 by regarding the grain as unit of observation and the total point count as a sample from a multinomial distribution 2 by regarding the total count as unit of observation and a set of counts as a sample from an additive logistic normal distribution numerical methods are presented for constructing statistically rigorous confidence regions in ternary diagrams by inversion of significance tests for these two distributions statistical analyses of the framework composition and heavy mineral assemblages of modern beach and river sands illustrate their use the case histories are followed by a brief overview of popular multivariate methods for reconstructing sediment provenance

provenance of plutonic detritus in cover sandstones of nicoya complex costa rica cretaceous unroofing history of a mesozoic ophiolite sequence this study presents new petrologic and sedimentologic data from northwestern costa rica concerning the provenance of cretaceous forearc sandstones that contain plutonic detritus plutonic rock fragments are important accessory particles in pyroxene bearing sandstones overlying the ophiolite named the nicoya complex through the use of modal analysis of the framework grains i studied three sandstone suites of the el viejo and rivas formations that include both shallow and deep water deposits ranging from late campanian to maastrichtian in age in terms of primary framework components the sandstones resemble those derived from magmatic arcs two modal parameters are introduced to evaluate detrital plutonic contributions and affinity of source rocks the ratio of plutonic to total lithic fragments lp iqf lt and the ratio of uralitized pyroxene to total pyroxene grains uralpx px modal values for lp iqf lt indicate that plutonic fragments comprise up to 9 of total lithic fragments a strong correlation between these two parameters suggests that uralitized pyroxene grains were also derived from intrusive rocks of probably basic and intermediate compositions in particular significant concentrations of lithic fragments exhibiting micrographic textures and uralitized pyroxene grains are interpreted to have been derived predominantly from eroded plagiogranites sandstone suites containing plutonic detritus signal an unroofing of deeper levels of the mesozoic ophiolitic sequence as a consequence of strong uplift of the costa rican arc in late senonian time this tectonic event began in the campanian at ca 75 ma 9 m y after the intrusive magmatic activity on nicoya peninsula and is consistent with the onset of the laramide orogeny

tertiary sea level movements around southern africa sedimentological micropaleontological and seismic profiling data elucidate the history of tertiary sea level movements around southern africa these new data show that landward movement of the sea began in early paleocene time and continued into the early eocene the sea probably reached its maximum paleocene height during the early eocene and is today represented by outcrops up to at least 204 m and probably as high as 360 m above modern sea level a brief regressive pulse occurred during the middle eocene with renewed transgression in the late eocene a major regression followed probably spanning all of oligocene and early miocene times this regression exposed much of the continental shelf and is clearly represented on seismic reflection profiles by a widespread unconformity the major neogene transgression began in the middle miocene and probably reached its greatest extent in the late miocene or early pliocene the overall middle miocene to early pliocene transgression was interrupted by a brie

seismotectonics of the april may 2015 nepal earthquakes an assessment based on the aftershock patterns surface effects and deformational characteristics occurrence of the april 25 2015 mw 7 8 earthquake near gorkha central nepal and another one that followed on may 12 mw 7 3 located similar to 140 km to its east provides an exceptional opportunity to understand some new facets of himalayan earthquakes here we attempt to assess the seismotectonics of these earthquakes based on the deformational field generated by these events along with the spatial and temporal characteristics of their aftershocks when integrated with some of the post earthquake field observations including the localization of damage and surface deformation it became obvious that although the mainshock slip was mostly limited to the main himalayan thrust mht the rupture did not propagate to the main frontal thrust mft field evidence supported by the available insar imagery of the deformation field suggests that a component of slip could have emerged through a previously identified out of sequence thrust active thrust in the region that parallels the main central thrust mct known in the literature as a co linear physiographic transitional zone called pt2 termination of the first rupture triggering of the second large earthquake and distribution of aftershocks are also spatially constrained by the eastern extremity of pt2 mechanism of the 2015 sequence demonstrates that the out of sequence thrusts may accommodate part of the slip an aspect that needs to be considered in the current understanding of the mechanism of earthquakes originating on the mht c 2015 elsevier ltd all rights reserved

the november 2017 mw 5 5 pohang earthquake a possible case of induced seismicity in south korea the moment magnitude mw 5 5 earthquake that struck south korea in november 2017 was one of the largest and most damaging events in that country over the past century its proximity to an enhanced geothermal system site where high pressure hydraulic injection had been performed during the previous 2 years raises the possibility that this earthquake was anthropogenic we have combined seismological and geodetic analyses to characterize the mainshock and its largest aftershocks constrain the geometry of this seismic sequence and shed light on its causal factors according to our analysis it seems plausible that the occurrence of this earthquake was influenced by the aforementioned industrial activities finally we found that the earthquake transferred static stress to larger nearby faults potentially increasing the seismic hazard in the area

mesozoic magnetic anomalies in the southern natal valley the recognition of mesozoic magnetic anomalies m0 m12 within the submarine natal valley south west indian ocean provides a further constraint on the relative motion between south america falkland plateau and africa during the early opening phase of west gondwanaland fig 1 colinear with m12 magnetic anomaly g ref 1 is delineated north of the south tugela ridge2 an acoustic basement high which is suspected to have been emplaced within continental crust immediately north of the continental oceanic crust boundary cob during the initial rifting phase starting from a revised west gondwana reconstruction3 and using palaeo poles of rotation1 3 the falkland plateau can be rotated into the natal valley superposing the corresponding georgia basin and natal valley magnetic anomalies this achieves an optimum continuity of inter continental structural lineaments3 by overlapping of an anomaly intermediate to m10 and m11 m10n4 this suggests that the natal valley cob is located between anomalies m10 and m11 implying that in this zone of south west gondwana seafloor spreading commenced at 125 myr

the mozambique ridge a document of massive multistage magmatism the mozambique ridge a prominent basement high in the southwestern indian ocean consists of four major geomorphological segments associated with numerous phases of volcanic activity in the lower cretaceous the nature and origin of the mozambique ridge have been intensely debated with one hypothesis suggesting a large igneous province origin high resolution seismic reflection data reveal a large number of extrusion centres with a random distribution throughout the southern mozambique ridge and the nearby transkei rise intrabasement reflections emerge from the extrusion centres and are interpreted to represent massive lava flow sequences such lava flow sequences are characteristic of eruptions leading to the formation of continental and oceanic flood basalt provinces hence supporting a large igneous province origin of the mozambique ridge we observe evidence for widespread post sedimentary magmatic activity that we correlate with a southward propagation of the east african rift system based on our volumetric analysis of the southern mozambique ridge we infer a rapid sequential emplacement between 131 and 125 ma which is similar to the short formation periods of other large igneous provinces like the agulhas plateau

tectonic versus chemical weathering controls on the composition of fluvial sands in tropical environments the compositions of fluvial sands collected in mountainous regions along the volcanic front in central america and along the andean front in venezuela and colombia correlate with the tectonic setting of their source terrains the sands derived from the central american volcanic arc are compositionally distinct from those derived from the andean terrains and minor variations in tectonic style can also be discriminated subtle differences in tectonic setting and source rock composition are recognizable only when modification by chemical weathering is slight they are strongest in sands from low order streams draining mountainous areas with modest alluvial plain development sands that have been exposed to weathering for extended periods during alluvial storage are progressively enriched in chemically stable phases with increased weathering sands from continental terrains converge toward a supermature quartz arenite end member and the imprint left by source rock composition and tectonic setting is obscured in intraoceanic terrains a similar but much less pronounced enrichment in stable phases relative to less stable phases is observed similarly overprinting the tectonic signal although detailed tectonic information is easily lost sands derived from intraoceanic terrains are distinguishable from those derived from continental terrains even after long exposure to intense chemical weathering conditions

miocene tectonic evolution of the basins and fault systems se korea dextral simple shear during the east sea sea of japan opening crustal deformation of se korea caused by back arc opening of the east sea sea of japan commenced locally in the late oligocene intense deformation occurred during the early miocene accompanying extension of parallelogram shaped pull apart basins between nnw striking principal displacement zones clockwise rotation and northwestward tilting of blocks and southwestward propagating rifting at about 17 ma the crustal deformation suddenly expanded westward and northward owing to activation of the yeonil tectonic line resulting in a dramatic change of depositional environment and the subsidence of wedge shaped pull apart basins the yeonil tectonic line and western border faults of the pohang basin are the westernmost limit of the miocene crustal deformation all the features of crustal deformation in se korea support the pull apart model for the east sea opening however they indicate that the nnw striking faults such as the yeonil tectonic line acted as the principal displacement zones rather than the nne striking yangsan fault under a consistent dextral simple shear at about 16 ma the collision of the philippine sea plate with the japanese islands caused a tectonic inversion this inversion resulted in a compositional change of basaltic magma at about 15 ma and crustal uplift in se korea which caused the cessation of sedimentation at about 10 ma

dynamic fault interaction during a fluid injection induced earthquake the 2017 mw 5 5 pohang event the november 15th 2017 mw 5 5 pohang earthquake south korea has been linked to hydraulic stimulation and fluid injections making this the largest induced seismic event associated with an enhanced geothermal system egs to understand its source dynamics and fault interactions we conduct the first 3d high resolution spontaneous dynamic rupture simulations of an induced earthquake we account for topography off fault plastic deformation under depth dependent bulk cohesion rapid velocity weakening friction and 1d subsurface structure a guided fault reconstruction approach that clusters spatio temporal aftershock locations including their uncertainties is used to identify a main and a secondary fault plane that intersects under a shallow angle of 15 based on simple mohr coulomb failure analysis and 180 dynamic rupture experiments in which we vary local stress loading conditions fluid pressure and relative fault strength we identify preferred two fault plane scenarios that well reproduce observations we find that the regional far field tectonic stress regime promotes pure strike slip faulting while local stress conditions constrained by borehole logging generate the observed thrust faulting component our preferred model is characterized by overpressurized pore fluids non optimally oriented but dynamically weak faults and a close to critical local stress state in our model earthquake rupture jumps to the secondary fault by dynamic triggering generating a measurable non double couple component our simulations suggest that complex dynamic fault interaction may occur during fluid injection induced earthquakes and that local stress perturbations dominate over the regional stress conditions these findings therefore have important implications for seismic hazard in active geo reservoir

tectonic sedimentary and volcanic evolution of a back arc basin in the east sea sea of japan abstract this paper focuses on the tectonic sedimentary and volcanic evolution of a unique back arc basin ulleung basin in the southwestern part of the east sea sea of japan the basin consists of thick extended continental or transitional crust and an overlying sedimentary succession 4 8 km thick with interlayered volcanic flows and sills defining a number of seismic units of variable reflection characteristics the northern margin is bounded by faulted continental blocks south korea plateau with isolated basement lows and sub basins with intruded and extruded volcanics whereas the southern margin is underlain by deep seated basement with a thick 8 km thick sedimentary succession the western margin is bounded by a series of strike slip and normal faults produced by nnw sse directed dextral movements these structural features suggest a south southeastward drift of the southwestern japanese arc away from the south korea plateau during the early to middle miocene involving large scale right lateral strike slip deformation along the western margin akin to pull apart basin formation during the back arc opening the thinned continental crust was largely modified by intrusive volcanics under tensional stress regime the volcanics also extruded across the axis of extension as well as along the boundary faults on the west in the middle to late miocene major faults in the southern and western margins were inverted forming partial closure of the basin especially in the southern part although the plateau in the northern margin experienced continuous subsidence the ulleung basin thus provides an example of an immature back arc basin which experienced a rather brief episode of rifting and extension followed by closure due to tectonic inversion

a time series of agulhas undercurrent transport abstract a 550 day record of agulhas undercurrent transport between march 2003 and august 2004 is constructed from five deep moorings placed on the continental shelf off south africa at nominally 32 s the vertical and lateral scales of the undercurrent are estimated to be 2000 m and 40 km respectively using the average of seven direct velocity sections predominantly taken in austral autumn over a 10 yr period from 1995 to 2005 peak speeds in the undercurrent are some of the greatest ever seen at depth over 90 cm s 1 at 1400 m the undercurrent has a transport of 4 2 5 2 sv 1 sv 1 106 m3 s 1 in close agreement with a previous estimate from a single current meter record during 1995 of 4 2 2 9 sv records below 1800 m within the north atlantic deep water nadw layer of the undercurrent show a higher level of coherence and less variance than those at intermediate depths on average 2 3 3 0 sv of nadw is carried northeastward within the undercurrent an amount similar to that estimated p

the crustal structure of the madagascar ridge summary the madagascar ridge is an elongated aseismic plateau in the southwest indian ocean which separates two ocean basins of mid to late cretaceous age from interpretations of a reversed refraction line on the ridge and a continuous gravity profile across it we conclude that it formed during the cretaceous as thickened oceanic crust at a mid ocean ridge which possibly overlay a mantle hot spot the seismic data consist of record sections from five recording sonobuoys forty one shots were fired along a 210 km long nne ssw line across the central part of the ridge simple horizontal layer analysis of first arrivals reveals a lower crustal refractor with vp 7 kms 1 at a depth of 8 8 5 km and the moho at an apparent depth of 18 km but fails to characterize the crustal structure as either oceanic or continental we obtain a definitively oceanic structure by using synthetic seismogram techniques together with tau p analysis and second arrival correlations the model which best fits the data consists of 2 2 km of water and 1 km of sediments overlying a velocity gradient from 4 to 7 kms 1 beneath this at a depth of 7 5 km is a 9 5 km thick layer with vp 6 9 7 1 kms 1 a 7 5 kms 1 layer not observed in the first arrival analysis is found at the base of the crust the moho is a transition zone 1 km thick and occurs at 25 km depth the gravity data consist of a continuous ne sw profile across the ridge and on to the flanking basins two dimensional gravity modelling allows a structure consistent with the synthetic seismogram results and supports the existence of a high density basal layer in the crust we use in addition a time series analysis approach to estimate the depth of compensation assuming an airy model and lithospheric thickness assuming an elastic plate model convolution of bathymetry along the profile with a range of model filters gives minimum rms gravity residuals for a crustal compensation depth of 23 5 km and a plate thickness of less than 2 5 km

the fluvial geochemistry and denudation rate of the guayana shield in venezuela colombia and brazil abstract the guayana shield is composed of early to mid precambrian igneous and metamorphic basement rocks with a quartzitic platform cover the complete absence of limestones and evaporites allows a clear chemical expression in the stream data of the primary weathering of the basement in a humid tropical environment total erosion rates are extremely slow 10 m m y with equal contributions from the dissolved and suspended loads however the former is largely silica with ratios of si to total cation equivalents si tz ranging to in excess of three weathering is complete to kaolinite and gibbsite i e the environment is one of active laterisation with a penetration rate of the weathering front into the fresh substrate about twice the denudation rate in basins of relatively homogeneous lithology rb sr isochrons constructed from the river data agree with the whole rock ages from the drainages thus all the common refractory rb containing minerals k feldspar mica are completely dissolved the thick lateritic regolith that is accumulating as a result of this intense weathering is a common relict feature on other southern hemisphere shields in the absence of active tectonics or greatly accelerated mechanical erosion the weathering rates of these basement rocks must be quite insensitive to environmental change

a source to sink compositional model of a present highstand an example in the low rank tiber depositional sequence latium tyrrhenian margin italy abstract our source to sink compositional model of sediment distribution in the present highstand of the tiber depositional sequence has important implications for sediment source lithology generation transport and deposition in the tiber river system sand compositional trends reflect provenance mixing anthropic intervention and the effects of local autogenic factors in continental to marine depositional environments fluvial feldspatho quartzo lithic sand results from the contribution of the major tributaries of the tiber drainage basin which can be divided into two sub basins separated by the corbara dam built in the 1950s upstream drainage basin sand has a siliciclastic sedimentary lithic signature whereas carbonate and volcanic lithic fragments dominate downstream drainage basin sand downstream sand is further modified in the coastal environment by hydraulic sorting and mixed with detritus derived from the recycling of coastal dune sand and altered volcaniclastic paleosols the latter are associated with lower course floodplain and channel deposits which produce a quartzo feldspatho lithic sand sediment grain size zonation in the marine environment is influenced by coastal hydrodynamics which in turn produce two detrital populations with distinct compositional signatures and hydraulic behavior coarser minerals essentially pyroxene phenocrysts and finer feldspar grains are progressively concentrated in higher energy and lower energy environments respectively biogenic continental shelf and slope deposits off the tiber river mouth show very little riverine influence this study of the last highstand system tract in the tiber depositional sequence clarifies the effects of hydraulic sorting grain size dependence and sediment reworking in controlling the final composition of modern sand this knowledge can be used to better understand detrital modes of ancient sedimentary successions

sedimentology and depositional architecture of a submarine delta fan complex in the durban basin south africa abstract the seismic stratigraphy evolution and depositional framework of a sheared passive margin the durban basin of south east africa are described based on single channel 2d seismic reflection data six seismic units a f are revealed separated by major sequence boundaries these are compared to well logs associated with the seismic data set internal seismic reflector geometries and sedimentology suggest a range of depositional regimes from syn rift to upper slope and outer shelf nearshore and continental facies are not preserved with episodic shelf and slope sedimentation related to periods of tectonic induced base level fall the sedimentary architecture shows a change from a structurally defined shelf shearing phase to shallow ramp and then terminal passive margin sedimentary shelf settings sedimentation occurred predominantly during normal regressive conditions with the basin dominated by the progradation of a constructional submarine delta tugela cone during sea level lowstands lst the earlier phases of sedimentation are tectonic controlled however later stages appear to be linked to global eustatic changes

early tectonic extension between the agulhas bank and the falkland plateau due to the rotation of the lafonia microplate abstract along the southeast african continental margin a deep sedimentary basin and marginal ridge bordering the agulhas fracture zone formed coevally with south american counterparts underlying the falkland plateau extension in both the southern outeniqua and the falkland basin is related to large angle 100 rotation of the lafonia falkland islands block in middle late jurassic times during attempted propagation of the proto indian ocean across the active circum pacific margin of gondwanaland in the early cretaceous the jurassic microplate boundaries were partly reactivated and partly transected by a right lateral shear along the 1200 km long falkland agulhas transform fault preceded by substantial vorticity of the surrounding crustal blocks this boundary segment separating the south american and african plates was probably generated by complex geodynamic interactions between oceanic plate subduction continental to back arc rift propagation and the impingement of deep mantle plumes on the lithosphere

pleistocene sea level fluctuations and human evolution on the southern coastal plain of south africa abstract humans evolved in africa but where and how remain unclear here it is proposed that the southern coastal plain scp of south africa may have served as a geographical point of origin through periodic expansion and contraction isolation in response to glacial interglacial changes in sea level and climate during pleistocene interglacial highstands when sea level was above 75 m human populations were isolated for periods of 360 3400 25 yr generations on the scp by the rugged mountains of the cape fold belt climate and vegetation barriers the scp expands five fold as sea level falls from 75 to 120 m during glacial maxima to form a continuous unobstructed coastal plain accessible to the interior an expanded and wet glacial scp may have served as a refuge to humans and large migratory herds and resulted in the mixing of previously isolated groups the expansive glacial scp habitat abruptly contracts by as much as one third in 300 yr during the rapid rise in sea level associated with glacial terminations rapid flooding may have increased population density and competition on the scp to select for humans who expanded their diet to include marine resources or hunted large animals successful adaptations developed on an isolated scp are predicted to widely disperse during glacial terminations when the scp rapidly contracts or during the initial opening of the scp in the transition to glacial maxima the hypothesis that periodic expansion and contraction of the scp as well as the coastal plain of north africa contributed to the stepwise origin of our species over the last 800 thousand years kyr is evaluated by comparing the archeological dna and sea level records these records generally support the hypothesis but more complete and well dated records are required to resolve the extent to which sea level fluctuations influenced the complex history of human evolution

the impact of diagenesis on the heterogeneity of sandstone reservoirs a review of the role of depositional facies and sequence stratigraphy diagenesis exerts a strong control on the quality and heterogeneity of most clastic reservoirs variations in the distribution of diagenetic alterations usually accentuate the variations in depositional porosity and permeability linking the types and distribution of diagenetic processes to the depositional facies and sequence stratigraphic framework of clastic successions provides a powerful tool to predict the distribution of diagenetic alterations controlling quality and heterogeneity the heterogeneity patterns of sandstone reservoirs which determine the volumes flow rates and recovery of hydrocarbons are controlled by geometry and internal structures of sand bodies grain size sorting degree of bioturbation provenance and by the types volumes and distribution of diagenetic alterations variations in the pathways of diagenetic evolution are linked to 1 depositional facies hence pore water chemistry depositional porosity and permeability types and amounts of intrabasinal grains and extent of bioturbation 2 detrital sand composition 3 rate of deposition controlling residence time of sediments at specific near surface geochemical conditions and 4 burial thermal history of the basin the amounts and types of intrabasinal grains are also controlled by changes in the relative sea level and therefore can be predicted in the context of sequence stratigraphy particularly in paralic and shallow marine environments changes in the relative sea level exert significant control on the types and extent of near surface shallow burial diagenetic alterations which in turn influence the pathways of burial diagenetic and reservoir quality evolution of clastic reservoirs carbonate cementation is more extensive in transgressive systems tract tst sandstones particularly below parasequence boundaries transgressive surface and maximum flooding surface because of the abundance of carbonate bioclasts and organic matter bioturbation and prolonged residence time of the sediments at and immediately below the sea floor caused by low sedimentation rates which also enhance the formation of glaucony eogenetic grain coating berthierine odinite and smectite formed mostly in tst and early highstand systems tract deltaic and estuarine sandstones are transformed into ferrous chlorite during mesodiagenesis helping preserve reservoir quality through the inhibition of quartz cementation the infiltration of grain coating smectitic clays is more extensive in braided than in meandering fluvial sandstones forming flow barriers in braided amalgamated reservoirs and may either help preserve porosity during burial because of quartz overgrowth inhibition or reduce it by enhancing intergranular pressure dissolution diagenetic modifications along sequence boundaries are characterized by considerable dissolution and kaolinization of feldspars micas and mud intraclasts under wet and warm climates whereas a semiarid climate may lead to the formation of calcrete dolocrete cemented layers turbidite sandstones are typically cemented by carbonate along the contacts with interbedded mudrocks or carbonate mudstones and marls as well as along layers of concentration of carbonate bioclasts and intraclasts commonly hybrid carbonate turbidite arenites are pervasively cemented proximal massive turbidites normally show only scattered spherical or ovoid carbonate concretions improved geologic models based on the connections among diagenesis depositional facies and sequence stratigraphic surfaces and intervals may not only contribute to optimized production through the design of appropriate simulation models for improved or enhanced oil recovery strategies as well as for co2 geologic sequestration but also support more effective hydrocarbon exploration through reservoir quality prediction

cenozoic deformation history of the area around yangnam yangbuk se korea and its tectonic significance abstract detailed mapping and structural analysis were carried out to establish the cenozoic deformation history of the yangnam yangbuk area se korea all structural elements were analyzed to establish the chronological sequence based on the classification of the fracture systems and the ages of the rocks two detailed grid maps represent the deformation history based on the cross cutting relationship between deformation fabrics we established the cenozoic deformation history in the studied area by synthesizing the analysis of structural elements in rocks of different ages and observing cross cutting relationships on grid maps results using these two approaches with two independent data sets are consistent the deformation history is comparable to that proposed from previous studies restoration of the structural elements suggests tilting and rotation in this area there is clear evidence of tectonic inversion which was observed in a previous trench study of the eupchon fault this implies that normal faults related to the right lateral yangsan fault associated with opening of the east sea japan sea may have been reactivated as thrust faults in the quaternary period

blind thrusting surface folding and the development of geological structure in the mw 6 3 2015 pishan china earthquake the relationship between individual earthquakes and the longer term growth of topography and of geological structures is not fully understood but is key to our ability to make use of topographic and geological datasets in the contexts of seismic hazard and wider scale tectonics here we investigate those relationships at an active fold and thrust belt in the southwest tarim basin central asia we use seismic waveforms and interferometric synthetic aperture radar insar to determine the fault parameters and slip distribution of the 2015 mw 6 3 pishan earthquake a blind reverse faulting event dipping towards the tibetan plateau our earthquake mechanism and location correspond closely to a fault mapped independently by seismic reflection indicating that the earthquake was on a pre existing ramp fault over a depth range of 9 13 km however the geometry of folding in the overlying fluvial terraces cannot be fully explained by repeated coseismic slip in events such as the 2015 earthquake nor by the early postseismic motion shown in our interferograms a key role in growth of the topography must be played by other mechanisms the earthquake occurred at the tarim tibet boundary with the unusually low dip of 21 we use our source models from pishan and a 2012 event to argue that the tarim basin crust deforms only by brittle failure on faults whose effective coefficient of friction is 0 05 0 025 in contrast most of the tibetan crust undergoes ductile deformation with a viscosity of order 1020 1022 pa s this contrast in rheologies provides an explanation for the low dip of the earthquake fault plane

assessing whether the 2017 mw 5 4 pohang earthquake in south korea was an induced event the moment magnitude m w 5 4 pohang earthquake the most damaging event in south korea since instrumental seismic observation began in 1905 occurred beneath the pohang geothermal power plant in 2017 geological and geophysical data suggest that the pohang earthquake was induced by fluid from an enhanced geothermal system egs site which was injected directly into a near critically stressed subsurface fault zone the magnitude of the mainshock makes it the largest known induced earthquake at an egs site

partitioned fault movement and aftershock triggering evidence for fault interactions during the 2017 mw 5 4 pohang earthquake south korea

the 2003 bam iran earthquake rupture of a blind strike slip fault a magnitude 6 5 earthquake devastated the town of bam in southeast iran on 26 december 2003 surface displacements and decorrelation effects mapped using envisat radar data reveal that over 2 m of slip occurred at depth on a fault that had not previously been identified it is common for earthquakes to occur on blind faults which despite their name usually produce long term surface effects by which their existence may be recognised however in this case there is a complete absence of morphological features associated with the seismogenic fault that destroyed bam

sandstone petrography of continental depositional sequences of an intraplate rift basin western cameros basin north spain the cameros basin in central spain is an intraplate rift basin that developed from late jurassic to middle albian time along nw se trending troughs the sedimentary basin fill was deposited predominantly in continental environments and comprises several depositional sequences these sequences consist of fluvial sandstones that commonly pass upward into lacustrine deposits at the top producing considerable repetition of facies this study focused on the western sector of the basin where a total of seven depositional sequences ds 1 to ds 7 have been identified the composition of sandstones permits the characterization of each sequence in terms of both clastic constituents and provenance in addition four main petrofacies are identified petrofacies a is quartzosedimentolithic mean of qm85f2lt13 and records erosion of marine jurassic pre rift cover during deposition of fluvial deposits of ds 1 brezales formation petrofacies b is quartzofeldspathic mean of qm81f14lt5 with p f 1 at the base this petrofacies was derived from the erosion of low to medium grade metamorphic terranes of the west asturian leonese zone of the hesperian massif during deposition of ds 2 jaramillo formation and ds 3 salcedal formation quartzose sandstones characterize the top of ds 3 mean of qm92f4lt4 petrofacies c is quartzarenitic mean of qm95f3lt2 with p f 1 and was produced by recycling of sedimentary cover triassic arkoses and carbonate rocks in the sw part of the basin ds 4 pen acoba formation finally depositional sequences 5 6 and 7 pinilla de los moros hortiguela pantano and abejar castrillo de la reina formations respectively contain petrofacies d this petrofacies is quartzofeldspathic with p f near zero and a very low concentration of metamorphic rock fragments from qm85f11lt4 in pantano formation to qm73f26lt1 in castrillo de la reina formation petrofacies d was generated by erosion of coarse crystalline plutonics located in the central iberian zone of the hesperian massif in addition to sandstone petrography these provenance interpretations are supported by clay mineralogy of interbedded shales thus shales related to petrofacies a and c have a variegated composition illite kaolinite and randomly interlayered illite smectite mixed layer clays the presence of chlorite characterizes interbedded shales from petrofacies b and illite and kaolinite are the dominant clays associated with petrofacies d these petrofacies are consistent with the depositional sequences and their hierarchy an early megacycle consisting of petrofacies a and b ds 1 to ds 3 was deposited during the initial stage of rifting when troughs developed in the west asturian leonese zone a second stage of rifting resulted in propagation of trough bounding faults to the sw involving the central iberian zone as a source terrane and producing a second megacycle consisting of petrofacies c and d ds 4 ds 5 ds 6 and ds 7 sandstone composition has proven to be a powerful tool in basin analysis and related tectonic inferences on intraplate rift basins because of the close correlation that exists between depositional sequences and petrofacies