shallow marine carbonate sedimentation in a tectonically mobile basin the muschelkalk middle triassic of upper silesia southern poland abstract earthquakes and resulting tsunamis are important geological phenomena however their sedimentary paleorecord is difficult to identify because some fabrics can be generated by other processes and the criteria for discrimination of seismic and non seismic triggers are not fully established this paper presents several deformation and sedimentary structures in the middle triassic carbonates of upper silesia and discusses their seismogenic and tsunami origin and controls on the deformation type intensity preservation potential and geographic distribution the deformation type and intensity were controlled by the primary lithology whereas the lateral continuity of deformed horizons depended on the lateral extent of hosted facies the thickness and abundance of these structures increase towards the krakow lubliniec fault zone which bounded the area from the east and is considered as the main epicentrum of earthquakes and tsunami initiation the discussed fabrics have a universal significance and can potentially be found in other shallow marine carbonate successions

world s highest tides hypertidal coastal systems in north america south america and europe abstract hypertidal systems can be defined as areas where spring tides have ranges greater than 6 m these very high tidal ranges results in unique patterns of sedimentation within hypertidal estuaries such systems are not common but they do occur on a number of continents this report will discuss six areas that have the highest tides in the world north america hypertidal systems occur within cook inlet in alaska usa leaf basin in ungava bay quebec province canada and the bay of fundy nova scotia and new brunswick canada in south america the straits of magellan and associated atlantic coastal settings exhibit hypertidal conditions european hypertidal systems include bristol channel and severn estuary in southwest england and the gulf of st malo in normandy france these six areas have the highest tides in the world and spring tidal ranges that regularly exceed 10 m all the six areas can be divided into intertidal sedimentological zones zone 1 is the outermost zone and contains longitudinal bars zone 2 exhibits laterally extensive sand flats zone 3 includes the innermost extent of tides and estuarine point bars annual and neap spring cycles have been documented in zone 3 and are probably the most indicative features of hypertidal systems the north american systems occur in high latitude cold climates where winter ice can have a minor or major impact on the development of sedimentary facies conversely the european and patagonia systems have climates minimal ice formation

earthquake swarms precursory to moderate to great earthquakes in the northeast india region abstract the northeast india region has seen ten m 7 1 2 earthquakes since 1897 including two great earthquakes of m 8 7 in 1897 and 1950 the last m 7 1 2 earthquake occurred on august 17 1952 with the exception of three earthquakes others are found to be associated with periods of background normal seismicity precursory swarms quiescence and mainshocks and the associated foreshocks and aftershocks the dataset has been critically examined for completeness considering the current capabilities for defining locations and also considering other parameters regression equations relating the mainshock magnitude mm the average magnitude of the largest two events in the swarm mp and the time interval mp between the beginning of the swarm and the mainshock have been developed these are mm 1 37mp 1 41 and mm 3log10tp 3 27 it is important to recognize precursory swarms and quiescence in real time indeed we believe we have recognized one such sequence in the vicinity of the arakan yoma fold belt on the basis of mp and tp values the lateral extent of swarm activity and the fact that no event of m 6 has occurred since 1975 in the preparation zone defined by the 1963 1965 swarm we estimate that an m 8 earthquake could occur at any time in the area bounded by 21 and 25 1 2 n and 93 and 96 e the focal depth of this impending earthquake is estimated to be 100 40 km in view of the focal depths of the other events in the swarm

recognition of tidal bore deposits in the rock record towards a facies model abstract a facies model for the deposits of tidal bores upstream propagating hydraulic jumps associated with the flood tide in estuarine rivers has not yet been developed despite the publication of data from laboratory experiments and some modern estuaries moreover only one example of tidal bore deposits has hitherto been identified in the rock record herein we document evidence for tidal bores in an upper pennsylvanian virgilian gzhelian incised valley fill in northeastern kansas usa across the flanks and crest of a bank attached bar remnant in this fill are thin 10 cm lenses of muddy massive sandstone and massive plant debris rich sandstone bounded by erosion surfaces exhibiting symmetrical wave ripples and irregular scouring this interval is enclosed by sandstones with bidirectional cross stratification rhythmites mud drapes flaser bedding and related sedimentary structures that together record appreciable tidal influence the erosion surfaces bounding the massive sandstone lenses and the massive sandstone lenses themselves are evidence for scour and sediment suspension by upstream propagating bores followed by deposition from suspension after their passage not only are these deposits the first sedimentary record of tidal bores to be documented in the pennsylvanian of the usa they are only the second example of such deposits to be documented in the global rock record on the basis of our observations we propose a provisional facies model for tidal bore deposits that can be refined by future work

modelling seismites with a digital shaking table abstract soft sediment deformation structures induced by seismically triggered liquefaction and or fluidization seismites have been reproduced with a digital shaking table we have used natural sediments with variable granulometric ranges clay silt and sand and an earthquake simulator that is able to reproduce real tridimensional seismograms acceleration and pore pressure recording allowed us to follow liquefaction and or fluidization processes in unconsolidated sediments during earthquakes different types of seismites were produced by variations in the tested sedimentary column

interpreting soft sediment deformation and mass transport deposits as seismites in the dead sea depocenter we have studied the history of earthquakes over the past 70 kyr by analyzing disturbed sedimentary layers around the margins of the dead sea however we know little about disturbances in the basin depocenter where water depth is 300 m and accessible only by drilling in this study we compare disturbances from the dead sea depocenter with the contemporaneous earthquake record 56 30 ka that was recovered on the western margin of the lake this comparison allows us to discern the characteristics of disturbance in the different subaqueous environments and identify the source and sedimentary process of mass transport deposits our observations indicate that i the long disturbance sequences in the dead sea depocenter are composed of in situ deformation slump and chaotic deposits ii earthquake triggered kelvin helmholtz instability is a plausible mechanism for the in situ deformation in the lake center iii the slump is slope area sourced iv the unit of chaotic deposits is lakeshore sourced and v earthquake triggered slope instability is a viable mechanism for the slump and chaotic deposits we further suggest that long sequences of disturbance in seismically active lake depocenters can be used to infer earthquake clusters

depositional environments in an arid closed basin and their implications for oil and gas exploration the lower permian fengcheng formation in the junggar basin china the fengcheng formation is a nonmarine carbonate dominated succession that formed under arid climatic conditions in a hydrologically closed basin two transects and two seismic profiles were examined the characteristics and environmental significance of different lithofacies were studied and a model of depositional environment divisions was proposed the sedimentary model involved an alkaline lake in which the depositional environments consisted of a shallow saline lake margin slope saline lake center and steep lake margin from northeast to southwest the perennial central salty lake was located in the southwestern part of the study area whereas there were widespread low gradient lake margins in the northeast east southeast and southern parts of the study area lake level fluctuations had a major influence on the shallow saline lake system and complicated the depositional environments in these areas the deposits are derived from bedrock reworking volcanic eruptions and authigenic minerals that precipitated from brine during the hypersaline phase fine grained terrigenous clastic sediments volcanic ashes and dusts and authigenic minerals mixed in the depocenter concentration center of the brine pool which was covered by high salinity brines and the depositional environment was anoxic as a result of salinity based brine stratification a thick sodium carbonate succession occurred in the depocenter of the ancient mahu lake where bedded sodium carbonate alternated with fine grained organic rich tuff or tuffaceous hydrocarbon source rocks microorganisms bloomed in the alkaline high salinity brine and the organic matter was well preserved which is similar to those modern alkaline saline lakes in eastern africa and western north america thus the permian fengcheng formation contains source rocks that formed in an alkaline saline lake

earthquake triggered soft sediment deformation structures seismites in travertine deposits abstract earthquakes related soft sediment deformations seismites are relevant structures to help reconstructing the palaeoseismicity in a region nevertheless although seismites have been described for a large variety of palaeo environments and stratigraphic settings they are rare and in some cases ambiguous structures in this paper we document for the first time impressive seismites affecting a latest quaternary travertine deposit located in southern tuscany serre di rapolano italy these structures are extremely relevant as seismites have been never described for this kind of terrestrial deposits the seismites developed within a 2 5 m thick stratigraphic succession made of alternating terrigenous and carbonate sediments embedded within the travertine deposits earthquake produced liquefaction and fluidization of some terrigenous levels and the injection of fluidized silty sediments dykes and sills into carbonate and terrigenous levels slumped levels and associated decollement surfaces produced highly non cylindrical folds overall induced by the loss of brittle shear strength along the basin slopes the occurrence of these soft sediment deformations implies an important seismic event that took place in a time spam encompassed between 84 8 and 48 92 5 08 ka in an area characterized by low seismicity and scarce knowledge of its seismotectonic setting their spectacular exposition and preservation in saw cuts of an abandoned quarry cava oliviera quarry highlights their relevance and importance

vegetation covers as indicator of seismo tectonic environment an integrated geophysical study in north baromura hill india spatial distributions of vegetation cover are closely related to topographical characters like slope steepness soil types elevations etc in seismo tectonic regions fault lines or tectonic lineaments are the most prominent surface signatures that can be reflected by vegetation distribution as tectonic displacement causes the change of topographical parameters in the present study a part of northern baromura hill between 23o 42 n to 23o49 n latitudes and 91o30 e to 91o36 e longitudes which is considered as an active seismo tectonic region of tripura as well as northeast india was selected for assessing the relationship between spatial variation of plant cover and topography geologically baromura hill is a north south extended fold belt and formed by late tertiary to quaternary depositions evidences show that tectonic events played very important role in landform evolution of this area during the geological past in this research an extensive fieldwork was conducted in the study area to understand the geomorphic and vegetation signatures and their environmental relationships various spectral resolutions of landsat etm were used for digital analysis to analyse the vegetation character of this area digital operation was done within the spectral range 0 63 1 75 m band 4 and band 3 were used for ndvi operation band 5 or mid wave infrared band was classified in unsupervised mode to understand the range of plant water in the study area overlay operation with those operated images shows the spatial distribution pattern of vegetation cover indicates the landform condition three clear tectonic lineaments faults were detected from the digital study in on the northern part baromura hill structural conditions of those fault lines were verified by geo electrical survey during fieldwork gps tool was used for fixing the ground control points resistivity characters of the study area assessed from ves profile strongly supports that vegetation cover analysis from remotely sensed data within 0 63 1 75 m spectral ranges can be a very useful tool for detecting surface tectonic signatures of the landform

magma mixing origin of intermediate rocks and enclaves from volcanism to plutonism abstract intermediate magmatic rocks are rarely homogeneous a common example is the presence of magmatic enclaves volcanic examples show that they are indications of magma mixing processes mixing events in the trachyandesitic suites from the sancy volcano france the volcanic activity from sancy consists of several brief trachyandesitic cycles each of them begins with the eruption of highly heterogeneous benmoreites followed by more homogeneous mugearites light porphyritic trachyandesites enclose numerous inclusions of varied darker lavas the crenulated geometry of the contacts the presence of chilled margins the vesiculation of the core of the basic parts suggest that these different rock types were magmatic at the same time although under marked thermal disequilibrium xenocrysts are common partly resorbed sanidine rimmed with plagioclase in a basic matrix reactional olivines in tridymite bearing trachytes this shows that the mixing occurred between partially crystallized and fractionated magmas chemical compositions are continuously variable from basalts to trachytes within the same eruptive cycle all these facts might be interpreted as the result of a mechanical intermingling more or less achieved between two end members of contrasting composition in the reservoir in the sancy volcano this phenomenon occurred at least 4 or 5 times during a 600 000 y span mixing evidence in hercynian granodiorites from france similar observations may be described in granodioritic rocks the more widespread enclaves exhibit the same characteristics as their volcanic equivalents although most of them are small more important volumes of basic rocks may be associated in the same massif in the neighbourhood of such large bodies swarms of smaller enclaves recall the generation of basic pillows the nature of the contact between small microgranular enclaves and their host rocks the occurrence of xenocrysts with reaction rims rapakivi feldspars and quartz ocelli in a basic surrounding amphibole pyroxene clots in a granitic matrix and geochemical variations again suggest thermal and mineralogical disequilibrium such observations indicate the comagmatic character of enclaves with regard to their host rocks they cannot be interpreted as restites and are best described as co igneous inclusions resulting from non achieved mixing between coexisting magmas photonic rocks are less suitable to demonstrate such petrogenetic processes because they result from slow cooling and crystallization during a longer residence time in a magmatic chamber the successive mixing episodes giving rise to different generations of co igneous inclusions are also difficult to recognize on the other hand in volcanism this process is quenched and periodically sampled by eruptions in conclusion the heterogeneity and the variability of many intermediate rocks cannot be explained only in terms of simple partial fusion and fractional crystallization processes in a closed system volcanic examples point to a complex evolution of magmatic reservoirs that were continuously fractionated periodically tapped periodically refilled and mixed

morphological signatures of fault lines in an earthquake prone zone of southern baromura hill north east india a multi sources approach for spatial data analysis this paper aims to assess the morphological signatures of tectonic features faults on the basis of multi sources spatial data analysis for that purpose the present authors selected the southern part of baromura hill of tripura which has been discussed very little in the scientific literatures an extensive field work was done in the assumed faulted areas to understand the geomorphic signatures of faulting in the field gps was used for fixing the ground control points scanned survey of india soi topographical sheets spot pan and land sat band 5 was used for digital analysis an old dem on irs liss iii fcc was also consulted for final mapping two clear lineaments faults were detected from field observation on southern baromura hill apart from these another one was found in the outer part of this hill range an attempt was made to explain the morphological signatures of those faults by density slicing on radiometric data based on emittance of different physical components finally a geomorphic map with main tectonic features of baromura was prepared for future disaster management planning

tectonic triggering of slump sheets in the upper cretaceous carbonate succession of the porto selvaggio area salento peninsula southern italy synsedimentary tectonics in the apulian carbonate platform abstract soft sediment deformation structures crop out in the upper cretaceous carbonate succession in porto selvaggio cove in the western salento peninsula apulian foreland southern italy the deformed interval is about 13 m thick and occurs between shallow water limestones and dolostones formed in peritidal and shallow subtidal environments it comprises well bedded grey mudstones interlayered with dark grey laminated microbioclastic wackestones characterized by couplets of closely spaced dark and bright laminae marked by the parallel orientation of calcareous microbioclasts and thin shelled bivalves the low biological diversity scarcity of burrowing biota and presence of a well preserved fish fauna provide evidence of anoxic conditions occurring in morphological depressions within the platform and a stagnant stratified water body affected by weak bottom currents indicating the sudden development of a localised and short lived intraplatform basin two soft sediment deformation horizons slump sheets separated by undeformed limestones with similar facies occur in this part of the succession the lower thicker slump sheet 1 0 1 3 m thick contains asymmetric and box folds well developed decollement surfaces locally containing thick brecciated zones cut the folds forming small scale thrust sheets and indicating mixed plastic to brittle behaviour the upper thinner slump sheet 0 25 0 35 m thick contains only asymmetric folds indicating plastic behaviour only the differences in deformation style are attributed to differences in facies measurements of fold axis orientations in the slump sheets show that they moved in similar directions recording the development of a local gently dipping palaeoslope autogenic internal trigger mechanisms are ruled out by a detailed consideration of facies the slump sheets were triggered by allogenic tectonic effects either the weakening of sediment by seismic activity or the tectonically induced steepening of slopes or a combination of both tectonically induced steepening is consistent with localised and sudden vertical facies changes related to the creation of an intraplatform basin the occurrence of slump sheets in carbonate platform successions is unusual since carbonate platforms are normally associated with shelves or low angle ramps

experimental decipherment of the soft sediment deformation observed in the upper part of the talchir formation lower permian jharia basin india abstract four types of soft sediment folds of distinct geometry can be recognized in the upper part of the talchir formation lower permian of jharia basin india these folds on systematic examination indicate some events of progressive deformation experimental study reveals that if a layered stack of clay and overlying sand is allowed to flow slowly down a slope differential velocity due to viscosity contrast leads to the deformation of the rheologic interface the sharp planar contact gradually becomes wavy leading to the development of round hinged folds involving sediments adjacent to it with the advancement of the flow these folds gradually become overturned with the rotation of the axial plane in the direction of flow computer simulation suggests that progressive deformation of these folds by simple shearing may lead to the formation of tight isoclinal folds which on dislocation along intrastratal normal faults may lead to the development of rootless isoclinal folds the sheath folds observed in the studied section also indicate accentuation of the curved hinge due to simple shearing the spatial distribution of these fold types in conjunction with the inferred direction of progressive deformation indicate basinward translation of the slump slice if the same stack of sediments rapidly flows down the slope the waveform generated at the interface quickly breaks in the form of roll up recumbent fold due to kelvin helmholtz instability

genesis and diagnostic value of soft sediment deformation structures a review abstract soft sediment deformation structures are recognized as important diagnostic features in the rock record for determination of depositional environments and slope processes the diagnostic value of these structures is reevaluated by analysis of the parameters controlling sediment deformation soft sediment deformation is contemporaneous with deposition and occurs dominantly in course silt to fine sand the high depositional rate low permeability and low shear strength of grains within this sediment range maximize the occurrence of deformation the dominant mechanisms responsible for sediment deformation include 1 liquefaction or fluidization 2 reverse density gradation 3 slumping or slope failure and 4 shear stress in most cases a combination of these mechanisms occurs the processes function in a continuum producing features that are microscopic to megascopic in scale it is shown that the processes and thus the structures are not environment specific the true diagnostic value of the structures may be in defining hydrodynamic conditions and in interpreting paleocurrents and paleoclimatic and paleoseismic events ultimately for the best diagnostic results soft sediment deformation structures should be studied in association with all other available lithologic structural and paleontological information

sediment slump structures a review of diagnostic criteria and application to an example from newfoundland abstract in the study of the history of deformed sedimentary rocks it is important that the cause of the deformation and the timing of deformation relative to metamorphic and tectonic events be assessed there is a continuous gradation between the deformation of freshly deposited sediments by gravitational forces and the deformation of well lithified sediments by tectonic forces so determining the degree to which gravity tectonism and lithification influenced deformation can be very difficult the characteristics that may be considered in determining the origin of deformational structures in sedimentary rocks can be divided into five categories ductile deformation structures 1 can provide definitive criteria for recognizing post lithification deformation but not pre lithification deformation this also holds for 2 brittle deformation structures and decollements overprinting of sediment reworking or remobilization structures 3 are the best criteria for recognizing pre lithification structures fabrics 4 can be very useful but are as yet poorly understood and there are misconceptions in the literature about what sort of fabrics are or are not found in unlithified sediments spatial relationships 5 may also tell us a great deal but are most useful when taken in conjunction with other types of evidence complex fold patterns in sandstones on farmer head north central newfoundland provide a case study for criteria that may be used to determine the degree of lithification during deformation although these folds have been interpreted as slump folds by earlier workers fabrics and spatial relationships point to a tectonic post lithification origin for the structures a conclusion which has significant implications for the interpretation of the regional geology

macrotidal subarctic environment of turnagain and knik arms upper cook inlet alaska sedimentology of the intertidal zone abstract an extensive sheet of silty sand crossed by tidal channels is exposed at low tide in turnagain and knik arms alaska transportation and deposition of sediment composing this sheet is the result of strong tidal currents due to the maximum spring tidal range of approximately 11 4 m in turnagain and knik arms the initiation of the floodtide is accompanied by the occurrence of a tidal bore that travels at a speed of 4 m sec or more up the tidal channels in intertidal environments in many parts of the world physical processes of sedimentation are typically influenced by surface fauna sedimentary structures in some zones are altered or obliterated by the activities of the infauna however in turnagain and knik arms virtually no macrofauna exist and so the area provides an opportunity to study depositional processes and sedimentary structures without the masking effects of bioturbation suspended sediment values for turnagain and knik arms are greatest in the summer months and nearest low tide stages ice floes form during winter months and in combination with the freezing of intertidal sediment to several meters of depth have a significant effect on sediment dispersal and on the deepening and increased stability of the tidal channels the intertidal sediment is mainly very well sorted medium to very fine sand and coarse silt with a notable paucity of gravel coarse sand and clay sediment accumulates in sandbars oriented parallel to the axis of the estuary textural and facies patterns reflect decreasing current energy first as a function of distance from the mouth of the estuary and second as a function of topographic elevation on the sandbars the intertidal deposits in turnagain arm contain a transitional upward fining sequence which is analogous to point bar and channel bar successions described by other workers the base of the sequence contains parallel laminated sand that is overlain by mixed parallel and cross laminated silty sand overlain by cross laminated silty sand at the top of the sequence is a unit of organically rich parallel laminated silt and sandy silt this suite of sedimentary features and textures indicates changing current velocities and directions as bars emerge or are modified during ebb tide and the vertical sequences could potentially be used to record intertidal bar erosion and aggradation by point and channel bar migration a process carried out primarily by bed load currents

soft sediment deformation structures in cambrian siliciclastic and carbonate storm deposits shandong province china differential liquefaction and fluidization triggered by storm wave loading abstract this paper focuses on soft sediment deformation structures ssds in both siliciclastic and carbonate storm deposits of the cambrian mantou and chaomidian formations shandong province china in order to understand their deformation mechanisms and possible triggers siliciclastic ssds e g sand volcanoes and pillows and carbonate ssds e g sedimentary dykes grainstone matrix breccias deformed cross beddings and marlstone matrix breccias occur exclusively in hummocky cross stratified fine sandstone and peloidal grainstone respectively the siliciclastic ssds formed in porous and permeable surface sediment whereas the carbonate ssds formed under shallow burial conditions when early marine cementation prevailed the various deformation structures resulted mainly from differences between siliciclastic and carbonate sediment conditions and resulting deformation mechanisms sand volcanoes formed by upward extrusion of over pressured fluidized sandy sediment whereas sand pillows resulted from upward injection of lower density muddy sediment into overlying liquefied sandy sediment sedimentary dykes and grainstone matrix limestone breccias formed as a result of differential liquefaction and fluidization of heterogeneously cemented carbonate sediment whereas deformed cross beddings and marlstone matrix limestone breccias developed by the thixotropic liquidization and injection of clayey sediment and further disruption of thin peloidal layers sedimentary facies analysis and analysis of the physical processes indicate that the ssds were most likely caused by cyclic loading of storm waves

determining the origin of soft sediment deformation structures a case study from upper carboniferous delta deposits in south west wales uk determining the cause of sediment mobilization is a major problem possible triggers include earthquakes sediment loading and wave action a detailed sedimentological and palaeoenvironmental analysis of soft sediment deformation in upper carboniferous deltaic deposits in sw wales uk shows that two styles of deformation occur type a syndepositional convolute stratification affects most sandstone beds and was generated by rapid sedimentation type b localized sandin sand pseudonodules incorporates beds that already contained type a deformation and developed when the substrate was liquefied by disturbance due to movement on a nearsurface gravity slide neither type of deformation was triggered by seismic events

impact of faults on landslide in the atharamura hill along the nh 44 tripura the present study is aimed at assessing the relationship between existing faults and occurrence of landslides the geophysical techniques like geothermal imaging of fault zone soil electrical resistivity data and field verification identify the fault characteristic the present study reveals two prominent faults in the atharamura hill i e one north south extended faults and the other east west extended faults the change in the geothermal characteristic along the fault structural data dip strike and most significantly the locations of landslide close to faults provide strong correlation of the landslide and the existing faults the soil electrical resistivity data are low along the faults the subsurface resistivity profile clearly delineates the faults

interplay of thrust back thrust strike slip and salt tectonics in a fold and thrust belt system an example from zakynthos island greece the southwestern flank of the hellenic fold and thrust belt situated along the southern edge of the dinarides albanides hellenides continental convergent zone was examined for reconstructing the tectonic deformation this investigation presents an integrated study of onshore sedimentological and structural analyses as well as offshore seismic lines across the pliocene pleistocene sedimentary succession in zakynthos island back thrust faults using the triassic evaporites as decollement surface during the pliocene and coeval diapiric intrusions formed three sub basins on the hangingwall of the kalamaki back thrust fault this interaction is responsible for the growth of the skopos mountain and the soft sediment deformation that formed synclines and slumps respectively back thrust and strike slip faults were active during the early pleistocene and diapiric intrusions modified the bathymetry on the sea floor giving rise to slumps and recumbent folds at least five events of synsedimentary diapiric intrusions have been recognized and are marked by five slump horizons during the holocene the diapiric intrusions between the kalamaki back thrust and the vrachionas anticline could be either related to normal faults or gravitationally driven

sedimentary features influencing the occurrence and spatial variability of seismites late messinian gargano promontory southern italy abstract seventeen layers characterized by soft sediment deformation structures ssds were identified within the calcari di fiumicello an upper messinian miocene stratigraphic unit 30 m thick cropping out in the northern sector of the gargano promontory apulia southern italy facies analysis was performed on the whole outcrop and detailed sedimentological investigations were carried out on the deformed beds in order to interpret the deformation mechanism the driving mechanism and the possible trigger agent deformed layers occur in some thin bedded ooidal limestones skeletal calcarenite as well as in some pebble size conglomerate alternated with marls deposited in a protected embayment or barrier island lagoon system possibly characterized by high salinity and tidal influx ssds can be classified as load and slump slide structures the continuous exposures allow us to follow a single deformed layer along tens of meters hence several types of lateral variations were observed that can be summarised as follows 1 ssds disappear within a few meters with a decreasing pattern of their deformation or in an abrupt way 2 deformed layers laterally change in thickness and morphology and 3 a single deformed bed can laterally correspond to two deformed beds most of the soft sediment deformation features were identified as liquefaction and or fluidization features related to seismic shocks seismites seismites are often used as an indicator of seismic events especially along small outcrops trench excavation and core analysis this study highlights the value of the sedimentological analysis for paleoseismic investigations with the aim of improving criteria for identifying seismites in the sedimentary record and their suitability as marker of seismic events

extensive soft sediment deformation structures in the early darriwilian middle ordovician shallow marine siliciclastic sediments formed on the baltoscandian carbonate ramp northwestern estonia abstract the nearshore middle ordovician early darriwilian deposits of the baltoscandian basin formed on the flank of tectonically stable fennoscandian shield comprise numerous soft sediment deformation structures the areal extent of the deformed interval extends up to 9000 km 2 from nw estonia to se sweden the deformation structures occur within a meter scale sandstone horizon that includes load casts flame structures ball and pillow morphologies up to 2 m wide sedimentary dykes autoclastic breccias sand volcanoes and other related soft sediment deformation structures evidently these deformation structures formed during a single seismic event that caused liquefaction and fluidization of the water saturated unconsolidated shallow marine sediments within almost the entire sandstone unit pakri formation probably a unique catastrophic earthquake of magnitude 7 or higher occurred in this region penecontemporaneously with the deposition of these sediments the ultimate cause of seismic event of such magnitude in the tectonically stable baltoscandian basin is unclear however deposition and deformation of the pakri formation fall within the middle ordovician meteoritic bombardment period which resulted from the disruption of a large parent body in the asteroid belt approximately 470 ma ago this in turn suggests a potential impact origin for the single catastrophic earthquake in the tectonically stable study region although impact crater of suitable age is currently not known from the region then previous studies have documented some impact metamorphic shock lamellae i e pdfs and abundant extraterrestrial chromite grains from the deformed sediments

cycle of earthquake induced aggradation and related tidal channel shifting upper turnagain arm alaska usa aggradation of intertidal sediment in upper turnagain arm a macrotidal estuary located in southern alaska near anchorage began because of subsidence caused by sediment consolidation and tectonic lowering of the land during the earthquake of march 27 1964 at the head of the arm decrease in percent sand of surface sediments with time and return of rodents pulmonate gastropods trees bushes and grasses to the intertidal region indicate that the rate of sediment deposition has slowed and the upper turnagain arm area has returned to a state of preearthquake equilibrium only 17 years after the event comparison of channel locations before and after the earthquake indicates the possibility of regional postseismic tilting of the estuary

seismic assessment in southern baromura hill northeast india considering geophysical aspects this paper aims to assess the geophysical signatures like morphology and structure of a fault line which is situated in a part of southern baromura hill of tripura northeast india in this work manual observations and technical applications were adopted for understanding the morphological and structural characters of the fault line as tectonic mapping is one of the main objectives of this study the remote sensing technique was used to prepare a tectonic map of the study area geothermal range of the area was measured by unsupervised classification of landsat tm thermal infrared band band 6 the classified thermal band was overlaid by another classified shortwave infrared band band 7 of landsat tm which explains the structural evidences of the study area in addition an automated digital elevation model dem was prepared to assess the morphological characters of the study area particularly near the confluence of r maharani and r gumti to analyse the structural condition of the faulted zone resistivity characters of the rocks were measured by vertical electrical sounding ves method the electrical resistivity character of this area strongly supports that a displacement occurred in this place finally an attempt was made to explain the character of faulting on the basis of morphological signatures and structural evidences for future disaster management planning

sedimentary record of seismic events in the eocene green river formation and its implications for regional tectonics on lake evolution bridger basin wyoming abstract outcrops and cores from the top of the lacustrine tipton member and the base of the wilkins peak member 51 5 ma of the eocene green river formation bridger basin in southwestern wyoming yield a wide variety of sedimentary deformation features many of which are laterally extensive for more than 50 km they include various types of folds load structures pinch and swell structures microfaults breccias and sedimentary dikes in most cases deformation is represented by hybrid brittle ductile structures exhibiting lateral variation in deformation style these occur in low energy profundal organic rich carbonate mudstones oil shales trona beds tuffs and profundal to sublittoral silty carbonate deposited in paleolake gosiute the deformation is not specific to the depositional environment because sedimentary units stratigraphically higher with similar facies show no deformation the studied interval lacks any evidence for possible trigger mechanisms intrinsic to the depositional environment such as strong wave action rapid sediment loading evaporite dissolution and collapse or desiccation so endogenic causes are ruled out thus the deformation features are interpreted as seismites and change in deformation style and inferred increase in intensity towards the south suggest that the earthquakes were sourced from the nearby uinta fault system the 22 levels exhibiting seismites recognized in cores indicate earthquakes with minimum magnitudes between 6 and 7 minimum epicentral intensity mcs of 9 and varying recurrence intervals in the seismic history of the uinta fault system with a mean apparent recurrence period of 8 1 k y using average sedimentation rates and dated tuffs in detail however there are two noticeably active periods followed by relative quiescence the stratigraphic position of these deformed intervals also marks the transition between two distinct stages in lake evolution from the balanced filled tipton member to the overlying underfilled wilkins peak member thus these seismites are evidence for regional scale changes in lacustrine sedimentation of eocene lake gosiute in response to syndepositional tectonic activity analysis of synsedimentary deformation features is therefore a promising yet under utilized tool to trace the tectonic evolution of lacustrine deposits of the green river formation and other tectonically active marine and non marine basins

high frequency turbulence and suspended sediment concentration measurements in the garonne river tidal bore the study details new sediment concentration measurements associated with some turbulence characterisation conducted at high frequency in the undular tidal bore of the garonne river france acoustic doppler velocimetry was used and the suspended sediment concentration was deduced from the acoustic backscatter intensity the field data set demonstrated some unique flow features of the tidal bore including some large and rapid turbulent velocity fluctuations during and after the bore passage some unusually high suspended sediment concentration was observed about 100 s after the tidal bore front lasting for more than 10 min it is thought that the tidal bore passage scoured the bed and convected upwards the bed material reaching the free surface after the bore passage behind the tidal bore the net sediment flux magnitude was 30 times larger than the ebb tide net flux and directed upstream a striking feature of the data set was the intense mixing and suspended sediment motion during the tidal bore and following flood tide this feature has been rarely documented

soft sediment deformation structures from an ice marginal storm tide interactive system permo carboniferous talchir formation talchir coalbasin india abstract permo carboniferous talchir formation talchir coalbasin india records sedimentation during a phase of climatic amelioration in an ice marginal storm affected shelf evidences of subtidal processes are preserved only under thick mud drapes deposited during waning storm phases various soft sediment deformation structures in some sandstone siltstone mudstone interbeds like syn sedimentary faults deformed laminations sand silt flows convolute laminations and various flame structures suggest liquefaction and fluidization of the beds due to passage of syn depositional seismic shocks in the late paleozoic ice marginal shelf such earthquake tremors could be generated by crustal movements in response to glacioisostatic adjustments of the basin floor

cenozoic plate reconstruction of southeast asia abstract the india eurasia collision alone set up a series of chain reactions and caused the formation and destruction of sedimentary basins within the domain of the collision belt changes in the rate and angle of convergence between the india and eurasia plates reflect different stages of tectonic development in southeast asia for example extrusion of the indochina block induced the consumption of the pre existing proto south china sea along northeastern kalimantan and led to the eventual opening of the south china sea along the south china margin subsequent motions of the sino burma thailand malay peninsula sumatra and kalimantan blocks have produced a succession of basins stretching from north sumatra to central thailand and on to the natuna area we present reconstructions of the southeast asia region at 60 ma 50 ma 40 ma 30 ma 20 ma 15 ma 10 ma and 5 ma it is clear from the reconstructions that the impact between greater india and southeast asia took place in the northwestern part of southeast asia the duration for the impact was probably from the middle eocene to early miocene this timing is in good agreement with the dating of the main red river fault motion wu et al 1989 scharer et al 1990 since the impact between greater india and southeast asia was basically west of the burma block there is no reason to assume that the sumatra malay peninsula and kalimantan should extrude to the southeast first along the left laterally displaced mae ping and three pagodas fault zones as suggested by peltzer and tapponnier 1988 if the opening of the central thailand basins the gulf of thailand and the malay basin are taken into consideration a dextral megashear zone is required to compensate the relative motion between indochina and the malay peninsula this dextral megashear zone might even extend into western kalimantan and serve as a boundary between the indochina block and kalimantan

can high alumina arc basalt be derived from low alumina arc basalt evidence from kanaga island aleutian arc alaska the coexistence of both high mgo low alumina basalt lab and low mgo high alumina basalt hab magmatic inclusions within a single andesitic host lava on kanaga island provides the opportunity to rigorously evaluate the presence or absence of a fractionation relation between the two basalt magma types traditional mass balance calculations pearce ratio arguments comparative phenocryst modes and compositions and incompatible element rb ba zr abundances all indicate that selective clinopyroxene and orthopyroxene fractionation from the plagioclase clinopyroxene orthopyroxene titanomagnetite saturated lab magma yielded the plagioclase phyric hab magma the same data are consistent with a model of low pressure hab generation calling upon selective mafic crystal fractionation along the margins of a crystallizing and convecting lab magma chamber the ability to demonstrate that nonliquid hab magma can be produced from lab through crystal fractionation eliminates many of the arguments used in support of a primary eclogite melting origin for hab

soft sediment deformation produced by tides in a meizoseismic area turnagain arm alaska turnagain arm is a semidiurnal hypertidal estuary in southeastern alaska with a recorded tidal range of 9 m contorted bedding and flow rolls preserved in tidal sediments within the estuary have previously been interpreted as resulting from the mw 9 2 great alaskan earthquake of 1964 horizons of flow rolls between undeformed beds in sediments and rock strata have been used to infer ancient earthquakes in other areas although many types of soft sediment deformation structures can be formed by earthquakes observations of sedimentation on tidal flats in the inner parts of turnagain arm in the summers of 2003 and 2004 show that a wide range of soft sediment deformation structures similar to those inferred to have been formed by earthquakes can form in macrotidal estuaries in the absence of seismic shock during sedimentation rate measurements in 2004 soft sediment deformation structures were recorded that formed during one day s tide either in response to overpressurization of tidal flats during rapid tidal drawdown or by shear stress exerted on the bed by the passage of a 1 8 m tidal bore structures consisted of flow rolls dish structures flames and small dewatering pipes in a bed 17 cm thick in the future if the flow rolls in turnagain arm were found in isolated outcrops across an area 11 km in length in an estuary known to have been influenced by large magnitude earthquakes would they be interpreted as seismites these examples show that caution is needed when using horizons of flow rolls to infer paleoseismicity in estuarine deposits because many of the mechanisms tidal flux tidal bores slumping flooding that can cause deformation in rapidly deposited unconsolidated silts and sands are orders of magnitude more common than great earthquakes

experimental characterization of storm liquefaction deposits sequences abstract the collapse depressions in waters of the yellow river delta are the result of silty sediment liquefaction produced by storm waves the internal characteristics and formation process of the strata in collapse depressions were studied with consideration of re stratification caused by sediment liquefaction in coastal areas in wave flume experiments silty sediment collected from the yellow river delta was shaped into a model seabed the original uniform sediment stratum was re stratified and formed into a new structure characteristic of liquefied sediments fluctuating with wave movement wave action appears to cause silty sediment liquefaction liquefied sediment moved elliptically with wave action leading to granularity based deposit differentiation in situ to re form sedimentary strata this is probably the cause of collapse depressions in the yellow river delta based on these results and comparison with the stratum under the collapse depressions in the yellow river delta we propose that liquefaction deposits are responsible for the bottom to top sequence of graded bedding convolute bedding and parallel bedding

temporal variation of mineralogy and petrology in cognate gabbroic enclaves at arenal volcano costa rica gabbroic enclaves ejected during the current eruption phase a 1 and during the latest prehistoric eruption phase a 2 of arenal volcano show systematic variations in texture mineralogy and composition as a function of host rock chemistry and timing of eruption the most differentiated enclaves occur in the more differentiated a 2 lavas enclaves in the a 1 volcanics are consistently less evolved within the current a 1 eruption the most mafic enclaves are amphibole bearing rocks that were erupted during the first 2 3 years of activity 1968 1970 these enclaves occur in the most differentiated a 1 volcanics and are not in equilibrium with their host rocks they crystallized from a hydrous melt that was slightly more mafic than anything erupted during the current cycle we interpret the enclaves as sidewall crystallization products of a melt possibly a high alumina basalt that was immediately parental to the a 1 lavas enclaves that occur in a 1 rocks erupted after 1970 and all of the a 2 enclaves are amphibole free and less mafic than the early a 1 enclaves their chemistry suggests that they formed during the early to intermediate crystallization of their host lavas none of the enclaves contain minerals that might have equilibrated with a primary mantle derived melt geothermometry is consistent with geochemistry with amphibole bearing a 1 enclaves yielding the highest pyroxene temperatures ave 1090 c and a 2 enclaves the lowest ave 1030 c geobarometry suggests mid to upper crustal depths for the crystallization of all enclaves the enclaves are cognate and reflect pre eruptive crystallization of arenal magmas they record evolution from a hydrous basaltic magma to the drier basaltic andesites that characterize the current eruption volatiles appear to have been lost due to depressurization during the slow ascent of the magmas through the upper levels of the crust following the initial explosive eruption volatile loss and depressurization resulted in the destabilization and the progressive resorption of amphibole the a 2 lavas may represent the long term fractionation products of basaltic andesite magmas similar in composition to the a 1 lavas anorthitic plagioclase commonly thought of as a phase stabilized by high ca na and high water pressure continued to crystallize in a system with relatively low ca na and which had dehydrated and or depressurized to the point at which amphibole was no longer stable this suggests that compositional characteristics other than high ca na or high water content may have stabilized the anorthite in the basaltic and basaltic andesite melts at arenal we speculate that the high alumina content of the arenal magmas may be the stabilizing factor

morphological signatures of fault lines in an earthquake prone zone of southern baromura hill north east india a multi source approach for spatial data analysis a critical review in a recent work dey et al environ earth sci 59 353 361 2009 presented some new observations on the southern part of one of the anticlinal ridges of tripura viz the baromura range the work incorporated a number of irregularities and misinterpretations that need to be addressed to avoid future confusion the present article critically reviews dey et al s paper to bring out its inaccuracies

evidence for two great earthquakes at anchorage alaska and implications for multiple great earthquakes through the holocene abstract multiple peat silt couplets in tidal marsh sediment sequences at anchorage suggest up to five possible great earthquakes during the last 2500 years litho stratigraphic diatom and radiocarbon data of the youngest two couplets record the last two great earthquakes ad 1964 and 950 850 cal yr bp similar multiple peat silt couplets around cook inlet suggest recurring great earthquakes associated with marsh subsidence over large areas comparable in extent to that recorded in ad 1964 potential difficulties in interpreting evidence include lack of modern analogues for applying quantitative diatom transfer functions to parts of the fossil record and the observation that under certain sedimentary conditions co seismic subsidence in the case of ad 1964 of known magnitude is recorded by a transitional peat silt boundary this differs in diatom stratigraphy from a phase of pre seismic relative sea level rise recorded for other great earthquakes a field experiment to simulate co seismic subsidence identifies limited mixing at the top of submerged marsh sediment and indicates how mixing must be shown to differ from evidence for pre seismic relative sea level rise analysis of diatom assemblages from ice frozen intertidal sediment and melt out sediment demonstrates the importance of winter processes in transporting diatoms and their interpretation in fossil sequences winter processes may also be important in transporting organic material that leads to significant differences 120 2800 yr between radiocarbon ages from plant macrofossils and bulk peat samples this necessitates a new approach for establishing between site correlations recurrence intervals and spatial extent of great holocene earthquakes in southern alaska

an early india asia contact paleomagnetic constraints from ninetyeast ridge odp leg 121 new paleomagnetic results from sedimentary rock and basement of the ninetyeast ridge ocean drilling program leg 121 sites 756 758 detail the northward movement of the indian plate for the past 80 m y analysis of the combined paleolatitude age profile indicates a distinct reduction in india9s northward movement rate at 55 ma interpreted as completion of suturing of greater india and asia india9s northward motion slowed from 18 19 5 cm yr to 4 5 cm yr for the location of site 758 comparison of this profile with paleomagnetic data from the wider himalayan region indicates that initial contact between northwestern greater india and southern asia was already established by cretaceous tertiary time this supports a possible causal link between the india asia convergence and the deccan traps extrusion

testing the use of bulk organic δ13c δ15n and corg ntot ratios to estimate subsidence during the 1964 great alaska earthquake abstract during the m w 9 2 1964 great alaska earthquake turnagain arm near girdwood alaska subsided 1 7 0 1 m based on pre and postearthquake leveling the coseismic subsidence in 1964 caused equivalent sudden relative sea level rsl rise that is stratigraphically preserved as mud over peat contacts where intertidal silt buried peaty marsh surfaces changes in intertidal microfossil assemblages across these contacts have been used to estimate subsidence in 1964 by applying quantitative microfossil transfer functions to reconstruct corresponding rsl rise here we review the use of organic stable c and n isotope values and c org n tot ratios as alternative proxies for reconstructing coseismic rsl changes and report independent estimates of subsidence in 1964 by using 13 c values from intertidal sediment to assess rsl change caused by the earthquake we observe that surface sediment 13 c values systematically decrease by 4 over the 2 5 m increase in elevation along three 60 to 100 m long transects extending from intertidal mud flat to upland environments we use a straightforward linear regression to quantify the relationship between modern sediment 13 c values and elevation n 84 r 2 0 56 the linear regression provides a slope intercept equation used to reconstruct the paleoelevation of the site before and after the earthquake based on 13 c values in sandy silt above and herbaceous peat below the 1964 contact the regression standard error average 0 59 reflects the modern isotopic variability at sites of similar surface elevation and is equivalent to an uncertainty of 0 4 m elevation with respect to mean higher high water to reduce potential errors in paleoelevation and subsidence estimates we analyzed multiple sediment 13 c values in nine cores on a shore perpendicular transect at bird point our method estimates 1 3 0 4 m of coseismic rsl rise across the 1964 contact by taking the arithmetic mean of the differences n 9 between reconstructed elevations for sediment above and below the 1964 earthquake subsidence contact this estimate compares well with independent subsidence estimates derived from post earthquake leveling in turnagain arm and from microfossil transfer functions at girdwood 1 50 0 32 m while our results support the use of bulk organic 13 c for reconstructing rsl change in southern alaska the variability of stable isotope values in modern and buried intertidal sediment required the analysis of multiple samples to reduce error

soft sediment deformation in epicontinental carbonates as evidence of paleoseismicity with evidence for a possible new seismogenic indicator accordion folds abstract epicontinental seismicity is currently a subject of intense study by geologists and engineers particularly relative to triggering mechanisms epicentral areas and recurrence intervals aside from modern seismic events much of the evidence for previous events is in the form of soft sediment deformation which has often been systematically overlooked or misinterpreted carbonates have also been systematically ignored in most attempts to understand soft sediment deformation soft sediment deformation however is not a unique response to seismicity so how do we know when seismicity is implicated or not the concurrence of four criteria has been suggested as a way to confirm the likelihood of seismogenic origins for soft sediment deformation 1 presence of deformation consistent with a seismogenic origin 2 deformation that is widespread 3 deformation that can be temporally or stratigraphically constrained across its distribution and 4 deformation that is zoned across its distribution showing systematic increases in frequency size or intensity toward a likely epicentral area the greater the concordance of these criteria the more likely a seismogenic origin is in order to validate these criteria we scrutinized two very different examples of epicontinental carbonate soft sediment deformation which had been called seismites one from the shallow open marine upper ordovician lexington limestone of central kentucky usa and another from the peritidal dolomitic mesoproterozoic wumishan formation of northeast central china concurrence of criteria for lexington soft sediment deformation readily supports the case for a seismogenic origin whereas for wumishan deformation too few criteria were satisfied to implicate seismicity nonetheless after exclusion of all other possibilities for wumishan deformation seismicity stood out as the only likely cause although concurrence of the four noted criteria in soft sediment deformation almost certainly does indicate a seismogenic origin the co occurrence of criteria is rare and wholly dependent on past depositional environments and modern occurrence hence the four criteria cannot be used as universal seismogenic indicators and in the absence of such indicators we must continue to rely upon the integration of tectonic structural and paleoenvironmental clues for substitute corroboration

late middle to late ordovician seismites of kentucky southwest ohio and virginia sedimentary recorders of earthquakes in the appalachian basin synsedimentary ball and pillow beds breccias and faults in late middle to late ordovician foreland basin rocks of kentucky southwest ohio and virginia indicate broad zones of seismicity near the cincinnati arch and taconic orogenic front during deposition earthquake induced liquefaction formed seismites that include ball and pillow beds and rare sedimentary breccias that are correlative over large areas hundreds to thousands of square kilometers comparison of these features with liquefaction structures in holocene sediments indicates that the ordovician ball and pillow beds were probably generated by large earthquakes magnitudes 6 the ordovician seismites also provide information about epicenter location and the recurrence interval of large earthquakes in the ordovician foreland basin some were produced by faulting in the foreland and accretionary prism however horizons of resedimented lithoclastic breccias in the jeptha knob cryptoexplosive structure appear to correlate with several ball and pillow beds on jessamine dome along the cincinnati arch suggesting that some of the seismites may be genetically related to this enigmatic structure

apogean perigean signals encoded in tidal flats at the fluvio estuarine transition of glacier creek turnagain arm alaska implications for ancient tidal rhythmites turnagain arm is a macrotidal fjord style estuary glacier creek is a small glacially fed stream which enters the estuary tangentially near girdwood alaska trenches and daily sedimentation measurements were made in a mudflat along the fluvio estuarine transition of glacier creek during several summers since 2003 each year the flats appear to erode during the winter and then accrete vertically in the spring and summer in each of the years studied tidal laminae in vertically thickening and thinning laminae bundles were deposited by twice daily tides in neap spring tidal cycles in 2004 bundles of thickening and thinning laminae couplets were noted in trenches cut into the flats five laminae bundles alternated between thicker and thinner bundles corresponding to the perigean high spring and apogean low spring tides well preserved apogean perigean cycles have rarely been documented in modern tidal flat sediments at this location vertical accretion of tidal rhythmites with well developed neap spring cyclicity is possible because of the near complete removal of the flat from the previous year which creates accommodation space for vertical accretion without significant reworking macrotidal conditions no reworking by infaunal invertebrates protection from the main tidal channel by a gravel bar and protection from storm waves and fluvial erosion by a recess in the sedge marsh that surrounds the flats all aid in preservation of rhythmites during aggradation the position of the flats relative to tidal range allows for accumulation of complete spring cycles and incomplete neap cycles in the summer of 2004 apogee and perigee were closely aligned with the new and full moons resulting in successive strong perigee and apogee tides which probably aided in the accumulation of successive thick thin spring cycles encoding the apogean and perigean tidal cycle the apogean perigean signal was not observed in subsequent years

eustatic and tectonic control on the distribution of marine seismites examples from the upper ordovician of kentucky usa abstract widespread zones of soft sediment deformation are not ubiquitous throughout the rock record rather they are associated with orogenic sediments and are concentrated in specific portions of depositional sequences characterized by deformation prone facies upper ordovician soft sediment deformation features exposed in kentucky are here interpreted as the result of seismically induced thixotropic fluidization of muds resulting in foundering of denser silts and carbonate sands and corresponding diapiric injection of muds severity of soft sediment deformation is associated with sediment density gradients bed thicknesses and varying magnitudes of triggering events the widespread nature 5000 km 2 of multiple deformation horizons argues for a seismic trigger resulting from reactivation of multiple basement faults eight large scale 3rd order depositional sequences were examined for the presence of specific deformation features and stratigraphic position of those intervals the regular distribution of deformation prone facies throughout the upper ordovician seems to have been regulated by eustatic fluctuations seismicity generated by far field tectonics provided the triggering mechanism to disrupt deformation prone strata the record of seismites and their co occurrence with k bentonites provides a meter of intensity and timing of tectophases of the taconic orogeny

liquefaction features interpreted as seismites in the pleistocene fluvio lacustrine deposits of the neuquen basin northern patagonia abstract superbly exposed soft sediment deformation structures in pleistocene fluvio lacustrine deposits along the southern border of the depression area called bajo de anelo departamento de anelo neuquen basin have been analysed in the study area five stratigraphic sections were measured in detail facies distributions and stacking patterns show that these sediments result from the interaction between fluvial and lacustrine systems represented by cross bedded and rippled strata and varved deposits the lateral extent of the deformation is some hundred metres and the deformed bed involves the lower mid part of the 30 metre thick succession deformation affects about 1 5 m of coarse grained sand fine grained sand and rare gravel alternations the base and top of the deformed layer are defined by planar surfaces undeformed beds of similar thickness lithology and facies to the deformed layer occur above and below deformation is represented by a complex vertical succession of disturbed layers each layer shows a general load structure morphology it can be described as a multilayered unstable density gradient system in each bed a partial gravitational re adjustment occurred after liquefaction unequal loading related to lateral variation of both bed thickness and grain packing and porosity is a probable additional driving force that can be described in the undeformed beds trigger mechanism recognition for the observed liquefaction features can be based on the study of the geometry of deformed beds and on facies analysis results two key factors drive our interpretation 1 the occurrence of undeformed beds below and above the deformed bed 2 deformed and undeformed beds showing the same sedimentological features these field data allow us to exclude the action of internal erosive and or sedimentary processes such as overloading wave action etc as possible trigger agents for liquefaction since deformation is totally absent in beds with similar sedimentary features furthermore each internal erosive and or sedimentary process can be discussed and easily excluded by analysing its specific signature in the geological record having excluded every possible internal trigger autokinetic processes the observed liquefaction effects can reasonably be interpreted as seismically induced allokinetic trigger from this point of view this deformed bed is an important record of seismic activity in this sector of the neuquen basin during the pleistocene

processes responsible for the development of soft sediment deformation structures ssds in the paleoproterozoic gordon lake formation huronian supergroup canada abstract an exposure of the paleoproterozoic gordon lake formation in the bruce mines area ontario canada contains abundant soft sediment deformation structures ssds including load casts convolute bedding pseudonodules ball and pillow structures flame structures and one dewatering pipe these features are developed in siltstone to fine grained sandstone beds and are between 1 and 120 cm in width and 3 78 cm high the primary trigger mechanism is interpreted to be storm or tsunami activity however seismic shock overloading brought about by density inversions or a combination of these processes may have influenced the formation of ssds to a lesser degree several beds also contain flat to wavy carbonaceous laminae locally with a botryoidal texture and concentrations of heavy minerals which are interpreted as relicts of microbial mats microbial mats may have played a minor role in the formation of ssds but do not appear to have been a prominent driving mechanism soft sediment deformation structures observed in the baie fine flack lake and cobalt plains regions of ontario are smaller and not as abundant as in the study area suggesting that the deposits in the study area were either affected by local events or different magnitudes of sedimentary processes in contrast to the tidal flat paleoenvironment interpreted for the gordon lake formation in the flack lake area the stratigraphically lower beds at the studied outcrop more closely resemble shallow shelf deposits

microseismicity and source mechanism study shillong plateau northeast india microearthquakes recorded by two surveys in the shillong plateau during december 1982 july 1983 and january february 1984 respectively have been analyzed for seismicity and tectonic study in the region of 1 000 events recorded during the surveys 180 events with reliable p and s readings which are observed within 50 km radius of the network are relocated by the homogeneous station method it is found that the events are mostly confined within a depth range of 10 to 35 km the seismicity in general may be correlated with the major geological structure lineaments in the area high rates of seismicity are observed in the shillong and tura areas on the other hand an aseismic zone is delineated to the east of shillong composite source mechanisms of two groups of microearthquakes show thrust fault mechanisms one group of microearthquakes 1982 to 1983 in the shillong area shows pure thrust faulting with a se nw compressive stress p axis whereas the other group of microearthquakes 1984 in the tura area shows thrust faulting with a strike slip component and a ene wsw compressive stress p axis the stress orientations are compatible with the known tectonics of the region collision of the indian plate with the eurasian plate at the himalaya and subduction of the indian plate beneath the burmese plate at the arakan yoma range

tectonically induced change in lake evolution recorded by seismites in the eocene green river formation wyoming seismogenic sedimentary structures seismites provide an opportunity to understand the effects of syndepositional tectonics on lacustrine sedimentation the lowermost wilkins peak member eocene green river formation wyoming usa contains laterally extensive intervals displaying folds load structures mixed brittle ductile deformation microfaults breccias and sedimentary dykes which formed intrastratally in a low energy sublittoral lacustrine environment they developed in situ by liquefaction and plastic or brittle behaviour of semi lithified sediment or by remobilization and injection of granular material their morphological attributes and lateral extent zonation in deformation intensity and the depositional setting all imply deformation triggered by earthquake induced stresses in shallow buried sediment their stratigraphic distribution coincides with a shift in hydrological conditions from a balanced filled to an underfilled lake type independent of climate change this study is the first to ascribe seismites to a pulse of tectonic activity that caused a synchronous change in lacustrine evolution

petrology of the younger andesites and dacites of iztaccihuatl volcano mexico i disequilibrium phenocryst assemblages as indicators of magma chamber processes

the petrology and geochemistry of the handkerchief mesa mixed magma complex san juan mountains colorado the handkerchief mesa mixed magma complex is one of several late cenozoic volcanic complexes in the southeastern san juan mountains characterized by mingling and limited mixing of basalt and rhyodacite stratigraphy in the dissected vent complex at handkerchief mesa records three phases of volcanism the first and third displaying evidence for coeruption of mafic and silicic magmas phases 1 and 2 erupted silicic pyroclastics and basaltic lava flows respectively phase 3 eruptions were dominated by rhyodacite lava flows rhyodacite dikes and abundant mingled and mixed hybrid lavas pre and syneruptive basalt rhyodacite mixing of phase 3 eruptions is shown by 1 inclusions of quenched basalt in rhyodacite 2 partially disaggregated basalt inclusions in mixed hybrids and rhyodacites 3 interfingering lenses of mixed hybrid lavas and rhyodacite whole rock major and trace element analyses support a two component mixing model whereby intermediate hybrids are produced by mixing of basalt and rhyodacite up to 30 basalt 70 rhyodacite disequilibrium phenocryst textures and mineral compositions are consistent with multistage mixing culminating in an eruptive mixing event protracted mixing along a boundary zone at the base of a rhyodacite magma chamber may be responsible for stabilizing fe rich olivine phenocrysts in some hybrids basalt rhyodacite mixing is inhibited by rapid crystallization in the basalt shortly after inclusion within the lower temperature melt the degree to which mechanical dispersion and blending ensues is a critical function of the initial temperature contrast ti between the two magmas thermal models simulating the conductive cooling histories for basalt spheres in rhyodacite reservoirs suggest that at large ti s 200 rapid cooling of the inclusion leads to disequilibrium crystallization with concomitant depression of equilibrium solidi grain boundary wetting by residual liquids and limited disaggregation of the inclusion imposed by movement of the host for small ti s 100 temperatures within the inclusion can be maintained above the solidus for prolonged time periods enhancing the possibility of producing homogeneous mixed hybrids through mechanical blending and diffusion both mechanisms operated at handkerchief mesa and contributed to the range of observed textures and compositions

a tectonically triggered late holocene seismite in the southern amazonian lowlands brazil abstract definitive criteria for identifying the triggers of soft sediment deformation structures ssdss from sedimentary deposits are still under construction in this work we aimed to contribute to advancing this issue describing the sedimentological characteristics of an interval of ssdss formed in a region of the amazonian lowlands having numerous morphostructural evidences of neotectonic reactivation the deformed interval is 1 5 m thick and consists of load and flame structures interbedded with massive beds sandwiched between well stratified deposits of a fluvial sandy channel succession with a radiocarbon age of 1301 1382 cal yr bp the ssdss are intercepted by numerous small scale normal graded faults the most interesting is that these faults display segmented nw se trending planes that propagate upward after horizontal displacements of a few millimeters processes intrinsic to channel dynamics could not justify this fault morphology which is related to recurrent short lived seismic perturbations with intervening sedimentation following a main tremor a relation to fault reactivation is proposed with basis on the fault trend compatible with the regional structural pattern and the numerous morphostructural anomalies verified in the study area including trellis and sub trellis drainage rectangular and to a less extent annular channels anomalously enlarged channels orthogonal channels and valleys channel captures sudden changes in channel morphology moderate to high basin asymmetry factor af between 10 and 27 moderate to high transverse topography symmetry factor t 0 3 0 5 and anomalous longitudinal river profiles with concavity values 11 to 30 indicative of rivers in process of adjustments the morphology of the fault graded beds described herein might constitute a feature of relevance for identifying seismites in other fluvial deposits

aseismic controls on in situ soft sediment deformation processes and products in submarine slope deposits of the karoo basin south africa intervals of soft sediment deformation features including vertical fluid escape and load structures are common and well exposed in permian lower slope deposits of the tanqua depocentre karoo basin the structures mainly comprise elongated flames and load structures associated with ruptured sandstones and structureless siltstones observed over a range of scales the presence of an upper structureless siltstone layer linked to the flames interpreted as a product of the debouching of fine grained material transported through the flame onto the palaeo seabed together with the drag and upward folding of lower sandstone layers is evidence that the flames were formed in situ by upward movement of sediment rich fluids flames are oriented parallel to the deep water palaeoslope in lateral splay deposits between two major slope channel complexes statistical correlation and regression analyses of 180 flame structures from seven stratigraphic intervals suggest a common mechanism for the deformation and indicate the importance of fluidization as a deformation mechanism importantly deformation occurred in an instantaneous and synchronous manner liquefaction and fluidization were triggered by incremental movement of sediment over steeper local gradients that were generated by deposition of a lateral splay on an inherited local north west facing slope seismic activity is not invoked as a trigger mechanism because of the restricted spatial occurrence of these features and the lack of indications of earthquakes during the time of deposition of the deep water succession the driving mechanisms that resulted in the final configuration of the soft sediment deformation structures involved a combination of vertical shear stress caused by fluidization development of an inverse density gradient and a downslope component of force associated with the local slope ground penetrating radar profiles confirm the overall north east orientation of the flame structures and provide a basis for recognition of potential larger scale examples of flames in seismic reflection data sets

eocene paleoseismic record of the green river formation fossil basin wyoming u s a implications of synsedimentary deformation structures in lacustrine carbonate mudstones abstract laterally extensive intervals containing sedimentary deformation features are identified in outcrops of lacustrine deposits of the eocene 52 51 ma green river formation in fossil basin southwestern wyoming fossil basin is the smallest of the paleo lakes in the green river system and is located in the sevier fold and thrust belt which was tectonically active during deposition deformation structures include convolute lamination load structures hybrid brittle ductile features sedimentary dikes microfaults fluid escape features such as cusps and pipes oil shale breccias and mass transport deposits in most cases these structures are hosted by finely laminated variably organic rich carbonate mudstones that accumulated in a low energy profundal lacustrine environment deformed intervals range from a few centimeters to 5 m in thickness and are bound above and below by undeformed strata of the same facies which demonstrates the early post depositional timing of deformation the distribution of these features indicates a primary control exerted by sediment rheology resulting from variation in grain size clay and organic content and degree of lithification which in turn were governed by the depositional environment and early diagenesis based on their morphological attributes lateral extent and recurrence at different stratigraphic levels along with their sedimentary environment and the tectonic setting of the basin the deformation structures are interpreted to be seismites i e the result of stresses induced by syndepositional earthquakes and other potential trigger agents are rejected moreover stratigraphic relationships indicate that these small scale deformation features as well as the mass transport deposits formed on a virtually flat lake floor ruling out instability caused by the gravitational regime syndepositional deformation in fossil basin points to tectonic activity along the nearby absaroka and or hogsback thrusts and related fault systems seismites point to possible tectonic forcing as a mechanism for changes in bathymetry and sedimentation in the green river formation and consequently demonstrate their potential for elucidating the tectonic history of other lacustrine and marine basins

successive impact of tidal bores on sedimentary processes arcins channel garonne river a tidal bore is a hydrodynamic shock propagating upstream as the tidal flow turns to rising with macro tidal conditions in a funnel shaped system with shallow waters the tidal bore of the garonne river was extensively investigated in the arcins channel between 2010 and 2013 typically over one to two days in 2015 new field measurements were repeated systematically at the same site on 29 august 1 september 2015 and on 27 october 2015 the nature of the observations was comprehensive encompassing hydrodynamics and turbulence as well as sediment properties and transport the tidal bore occurrence had a marked effect on the velocity and suspended sediment field including a rapid flow deceleration and flow reversal during the bore passage with very large suspended sediment concentrations sscs during the passage of the tidal bore front and early flood tide as well as very large suspended sediment flux during the very early flood tide the suspended sediment concentration ssc data indicated a gradual increase in initial mean ssc estimate prior to the bore from 29 august to 1 september 2015 a comparison between suspended sediment flux data showed very significant suspended sediment flux on the first day of tidal bore occurrence with a decreasing magnitude over the next three days the data suggested a two stage bed scour process at each tidal bore event surface erosion occurred initially in the form of stripping the first stage was followed by delayed mass erosion occurring about 5 15 min after the tidal bore

fluid flow and sediment entrainment in the garonne river bore and tidal bore collision a detailed field study was carried out on a tidal bore to document the turbulent processes and sediment entrainment which occurred the measured bore within the arcins channel of the garonne river france was undular in nature and was followed by well defined secondary wave motion due to the local river geometry a collision between the arcins channel tidal bore and the bore which formed within the main garonne river channel was observed about 800m upstream of the sampling site this bore collision generated a transient standing wave with a black water mixing zone following this collision the bore from the main garonne river channel propagated backward to the downstream end of the arcins channel velocity measurements with a fine temporal resolution were complemented by measurements of the sediment concentration and river level the instantaneous velocity data indicated large and rapid fluctuations of all velocity components during the tidal bore large reynolds shear stresses were observed during and after the tidal bore passage including during the backward bore propagation large suspended sediment concentration estimates were recorded and the suspended sediment flux data showed some substantial sediment motion consistent with the murky appearance of the flood tide waters copyright c 2015 john wiley sons ltd

the record of tidal cycles in mixed silici bioclastic deposits examples from small plio pleistocene peripheral basins of the microtidal central mediterranean sea the pliocene pleistocene peripheral marine basins of the mediterranean sea in southern italy from basilicata and western calabria to northern and eastern sicily represent tectonically formed coastal embayments and narrow straits here units of cross stratified mixed silici bioclastic sand 25 to 80 m thick record strong tidal currents the central mediterranean sea has had a microtidal range of ca 35 cm and the local amplification of the tidal wave is attributed to tides enhanced in some of the bays and to the out of phase reversal of the tidal prism in narrow straits linking the tyrrhenian and ionian basins the siliciclastic sediment was generated by local bedrock erosion whereas the bioclastic sediment was derived from the contemporaneous foramol type cool water carbonate factories the cross strata sets represent small to medium sized 10 to 60 cm thick two dimensional dunes with mainly unidirectional foreset dip directions these tidalites differ from the classical tidal rhythmites deposited in mud bearing siliciclastic environments firstly the foreset strata lack mud drapes and instead show segregation of siliciclastic and bioclastic sand into alternating strata secondly the thickness variation of the successive silici bioclastic strata couplets measured over accretion intervals of 2 to 3 m and analysed statistically reveal only the shortest term diurnal and semi diurnal tidal cycles thirdly the record of diurnal and semi diurnal tidal cycles is included within the pattern of neap spring cycles differences between these sediments and classical tidal rhythmites are attributed to the specific palaeogeographic setting of a microtidal sea with the tidal currents locally enhanced in peripheral basins it is suggested that this particular facies of mud free silici bioclastic arenite rhythmites in the stratigraphic record might indicate a specific type of depositional sub tidal environment of straits and embayments and the shortest term tidal cycles

formation of igneous layering in granodiorite by gravity flow a field microstructure and geochemical study of the tuolumne intrusive suite at sawmill canyon california layered granites and granodiorites occur in many plutons they occur together with non layered granodiorites at the margin of the tuolumne intrusive suite one of the largest late cretaceous intrusions in the sierra nevada results from field observations quantitative microstructural analysis and whole rock compositions from the non layered kuna crest half dome and cathedral peak granodiorites and layered granodiorites from the sawmill canyon area are compared to determine which processes contributed to the formation of the layering the non layered granodiorites have foliated but homogeneous microstructures which are attributed to the orientation of crystals with high aspect ratios when the magma flowed before solidification their compositions are consistent with magma mixing and fractional crystallization the microstructure in the layered granodiorite is heterogeneous and shows normal gradation of the dense primocryst minerals magnetite hornblende and titanite at the base and inverse size gradation with large crystals of the less dense primocryst phases plagioclase and biotite at the top and a systematic change in the preferred orientation of minerals from base to top macroscopic structures in the layers indicate erosion and the action of traction currents when the layers formed and the sinking of the dense minerals and rise of interstitial melt immediately afterwards the layered rocks have similar grain size and mineral compositions to the non layered granodiorites and thus could be derived from the same magmas as the kuna crest half dome and cathedral peak non layered granodiorites the major and trace element variations in the layered rocks are very different from those in the non layered rocks and indicate a strong segregation of crystals during formation of the layers however the separation process did not fractionate the main rare earth element bearing phases from one another the macrostructure and microstructural features in the layers resemble those from hyper concentrated sediment gravity flows the layering is interpreted to have formed from gravity flows of melt and crystals initiated by syn magmatic tectonic deformation and seismic shaking two types of layering are identified one called normal layering represents material derived from a single granodiorite magma and deposited from a relatively low energy gravity flow whereas the other called melanocratic layering incorporated mafic minerals eroded from the substrate had the felsic tops of layers eroded off by subsequent flows incorporated crystals from more than one magma source and formed from gravity flows that had higher energy

is shillong region northeast india undergoing a dilatancy stage precursory to a large earthquake abstract gupta h k and singh v p 1982 is shillong region northeast india undergoing a dilatancy stage precursory to a large earthquake in a l hales and z suzuki editors earthquake prediction tectonophysics 85 31 33

field evidence of magma mixing from microgranular enclaves hosted in palaeoproterozoic malanjkhand granitoids central india abstract the malanjkhand granitoids mg pluton about 1500 sq km occurs in the balaghat district of madhya pradesh the mg 2400 ma represent an episode of palaeoproterozoic felsic magmatism in central india and hosts potential cu mo au deposits the enclaves hosted in mg can be broadly classified into two categories microgranular enclaves dark coloured fine grained magmatic and xenoliths of country rocks the microgranular enclaves me may be rounded ellipsoidal discoid elongated lenticular or tabular and their size commonly reaches up to 2 metres across the me have sharp and in places diffuse contacts with their host granitoids the shape and size of me indicate contemporaneous flow and mingling of partly crystalline felsic mafic magmas some me exhibit dark crenulated margins giving them a pillow like form that has been attributed to undercooling of a me magma as globules intruded into a granitoid magma the presence of corroded felsic and mafic minerals xenocrysts in me is interpreted as the result of mechanical transfer during the mafic felsic magma interaction and mixing event mafic minerals biotite rim the quartz xenocrysts giving rise to ocellar texture which exhibit signatures of resorption under hybrid enclave magma conditions all these features suggest an origin for the calc alkaline intermediate granitoid magma in malanjkhand involving a magma mixing process

mineralogical constraints on the petrogenesis of trachytic inclusions carpenter ridge tuff central san juan volcanic field colorado although bulk rock normative analyses of the trachytic inclusions from the carpenter ridge tuff yield abundant quartz and minor corundum a portion of the phenocryst assemblage is indicative of an alkaline parentage sanidine and biotite contain up to 8 and 5 wt bao respectively in addition both amphibole and clinopyroxene compositions are compatible with having crystallized from a mildly silica undersaturated magma amphibole is magnesiohastingsite with 3 wt tio2 and less than 0 3 mole fraction vacancies in the a site clinopyroxene compositions straddle the calcic augite salite boundary chrondite normalized ree patterns are similar for both inclusions and rhyolites the inclusions are slightly poorer in ree and have a positive eu anomaly versus the negative anomaly of the rhyolites the similarity in ree patterns would seem to indicate that the two rock types are genetically related with the positive eu anomalies resulting from feldspar accumulation however this possibility is denied by the antithetic alkaline and subalkaline phenocryst assemblages of the two rock types we suggest that the best explanation for these discrepancies is that a mildly silica undersaturated magma was the parent for the phenocrysts this magma intruded the carpenter ridge chamber and because the crystallization temperatures of both magma overlapped the alkaline magma mixed with the ambient rhyolite to form a hybrid this hybrid consisted of a portion of the phenocryst assemblage from the alkaline magma but the bulk rock chemistry depended upon the proportions of the endmember liquids the abundance of normative quartz the minor normative corundum and the similarity of ree patterns indicates that the inclusions are mixtures dominated by the rhyolitic component additional processes such as liquid state diffusion crystal accumulation and alkali loss may have contributed to obscure the compositions of the initial liquids involved in the inferred mixing process

seismically induced soft sediment deformation structures associated with the magallanes fagnano fault system isla grande de tierra del fuego argentina abstract in this paper evidence of paleoearthquake induced soft sediment deformation structures associated with the magallanes fagnano fault system in the isla grande de tierra del fuego southern argentina has been identified well preserved soft sediment deformation structures were found in a holocene sequence of the udaeta pond these structures were analyzed in terms of their geometrical characteristics deformation mechanism driving force system and possible trigger agent they were also grouped in different morphological types sand dykes convolute lamination load structures and faulted soft sediment deformation features udaeta a small pond in argentina tierra del fuego is considered a quaternary pull apart basin related to the magallanes fagnano fault system the recognition of these seismically induced features is an essential tool for paleoseismic studies since the three main urban centers in the tierra del fuego province of argentina ushuaia rio grande and tolhuin have undergone an explosive growth in recent years the results of this study will hopefully contribute to future analyses of the seismic risk of the region

bedding parallel lenticular soft sediment deformation structures a type of seismite in extensional settings abstract soft sediment deformation structures ssdss with bedding parallel lenticular morphology have been occasionally reported and called different names such as loop bedding or pillow bed however there is no understanding of the formative conditions that give rise to them versus other ssdss similar bedding parallel lenticular dolomite bodies tens of centimeters thick with quite variable lengths 30 cm 30 m occur across a large area 3000 km2 exclusively in the st louis member late vasean mississippian of the slade formation in east central kentucky usa field investigations indicate that the lenticular structures along with other associated ssdss represent a persistent deformed horizon that is correlative with and occurs symmetrically around the more intensely deformed big sinking bed which was previously interpreted as earthquake induced ssdss based on multiple lines of evidence the lenticular structures are interpreted to represent distal expressions of the same seismic event that generated the proximal big sinking bed the lenticular structures were subsequently dolomitized and their selective dolomitization is attributable to their brittle deformation during the earthquake which resulted in preferentially developed fracture porosity that allowed more efficient circulation of mg2 fluids throughout the lenticular structures petrographic and stable isotopic evidence also suggests that the selective dolomitization postdates the deformation probably related to a brine reflux system developed during the first marine transgression following subaerial exposure of the st louis carbonates based on comparative analysis with other global cases the bedding parallel lenticular structures are interpreted to represent a distinct type of ssds comparable to boudinage in tectonic deformation their formation reflects a situation in which seismically elevated pore fluid pressure is lower than vertical confining stress but higher than horizontal confining stress a prominent occurrence of lenticular type ssds is a potential indicator of syndepositional extensional stress regime which is testified by tectonic settings of all known cases including the kentucky dolomite bodies

an overview of the sedimentary geology of the bengal basin in relation to the regional tectonic framework and basin fill history abstract the bengal basin in the northeastern part of indian subcontinent between the indian shield and indo burman ranges comprises three geo tectonic provinces 1 the stable shelf 2 the central deep basin extending from the sylhet trough in the northeast towards the hatia trough in the south and 3 the chittagong tripura fold belt due to location of the basin at the juncture of three interacting plates viz the indian burma and tibetan eurasian plates the basin fill history of these geo tectonic provinces varied considerably precambrian metasediments and permian carboniferous rocks have been encountered only in drill holes in the stable shelf province after precambrian peneplanation of the indian shield sedimentation in the bengal basin started in isolated graben controlled basins on the basement with the breakup of gondwanaland in the jurassic and cretaceous and northward movement of the indian plate the basin started downwarping in the early cretaceous and sedimentation started on the stable shelf and deep basin and since then sedimentation has been continuous for most of the basin subsidence of the basin can be attributed to differential adjustments of the crust collision with the various elements of south asia and uplift of the eastern himalayas and the indo burman ranges movements along several well established faults were initiated following the breakup of gondwanaland and during downwarping in the cretaceous by eocene because of a major marine transgression the stable shelf came under a carbonate regime whereas the deep basinal area was dominated by deep water sedimentation a major switch in sedimentation pattern over the bengal basin occurred during the middle eocene to early miocene as a result of collision of india with the burma and tibetan blocks the influx of clastic sediment into the basin from the himalayas to the north and the indo burman ranges to the east rapidly increased at this time and this was followed by an increase in the rate of subsidence of the basin at this stage deep marine sedimentation dominated in the deep basinal part while deep to shallow marine conditions prevailed in the eastern part of the basin by middle miocene with continuing collision events between the plates and uplift in the himalayas and indo burman ranges a huge influx of clastic sediments came into the basin from the northeast and east throughout the miocene the depositional settings continued to vary from deep marine in the basin to shallow and coastal marine in the marginal parts of the basin from pliocene onwards large amounts of sediment were filling the bengal basin from the west and northwest and major delta building processes continued to develop the present day delta morphology since the cretaceous architecture of the bengal basin has been changing due to the collision pattern and movements of the major plates in the region however three notable changes in basin configuration can be recognized that occurred during early eocene middle miocene and plio pleistocene times when both the paleogeographic settings and source areas changed the present basin configuration with the ganges brahmaputra delta system on the north and the bengal deep sea fan on the south was established during the later part of pliocene and pleistocene and delta progradation since then has been strongly affected by orogeny in the eastern himalayas pleistocene glacial activities in the north accompanied sea level changes in the bay of bengal

monitoring changing position of coastlines using thematic mapper imagery an example from the nile delta coastline movement due to erosion and deposition is a major concern for coastal zone management very dynamic coastlines such as sections of the nile delta coast pose considerable hazards to human use and development and rapid replicable techniques are required to update coastline maps of these areas and monitor rates of movement the synoptic capability of landsat thematic mapper imagery enables monitoring of large sections of coastline at relatively coarse 30 m spatial resolution by comparing positions of the nile delta coast in 1984 1987 and 1990 1991 mapped using a region growing image segmentation technique areas of rapid change can be identified and targeted for more detailed monitoring in the field or using higher resolution images rates of erosion and deposition can be estimated crudely and areas where change appears to be accelerating can also be identified areas of severe erosion along the nile delta coast are found to be confined to the promontories of the present day mouths of the nile at rosetta and damietta eroding shorelines are mostly flanked by accreting shorelines showing that some of the eroded material is redistributed along the coast the technique outlined here has potential to augment conventional field based surveying for monitoring shoreline changes over short timescales

sedimentary deformation features as evidence for paleoseismic events in the middle eocene in the dongying depression of the southern bohai bay basin eastern china cores from the middle eocene sediments of the dongying depression of the southern bohai bay basin in east china yield various kinds of sedimentary deformation structures they include microfolds l

bedding types in holocene tidal channel sequences knik arm upper cook inlet alaska abstract uplifted convoluted and horizontal to subhorizontal beds of varying thickness in intertidal silt as old as 3 280 90 yr b p are exposed in the banks of tidal channels of unknown depth in the intertidal zone in knik arm of upper cook inlet internal discordances may occur both within convoluted beds and between convoluted and horizontal to subhorizontal beds at the base of many convoluted beds there is a rapid gradation upward into laminae which are severely deformed that is in some places the contortions appear to have originated along a single bedding plane where the convoluted sequences are truncated by nearly horizontal sequences the distortion must have resulted from syndepositional or postdepositional events prior to their burial by the overlying beds various forms of gravitational and tidal processes caused the deformation of the knik arm deposits events triggering the movement of the sediment include any or all of the following 1 seismic activity 2 sediment or ice loading 3 wave induced liquefaction 4 pore pressure changes brought on by changing levels of tidewater 5 undercutting of sediments by channel migration and 6 freezing and thawing