late quaternary paleohydrology of the madre de dios river southwestern amazon basin peru abstract late quaternary climatic and hydrologic variability triggered changes in fluvial deposition and erosion along the course of the madre de dios river peru the largest tributary basin of the madeira basin itself the largest tributary basin of the amazon three laterally extensive quaternary age terrace tracts are present within the madre de dios basin analysis of sedimentary facies present in the modern cut banks and terraced sequences along with radiocarbon dates on fossil wood and leaf material preserved in the terraced strata allow reconstruction of the late quaternary depositional history of the sedimentary sequences including determination of the approximate timing of aggradation and downcutting episodes and its relationship to the timing of past climate change in this portion of the amazon basin and beyond the quaternary sediments underlying the terraces most often recorded deposition in a coarse grained meandering fluvial system the t3 terrace the highest terrace is underlain by the miocene ipururi formation which is unconformably overlain by the late miocene pleistocene 48 000 cal yrs bp madre de dios formation a multistory coarse sandy to gravelly channel and point bar complex the latter was downcut before 29 850 100 cal yrs bp this downcut landscape was infilled by meandering fluvial strata characterized by gravelly channel deposits in a sequence dominated by floodplain and lateral accretion deposits these strata were in turn downcut to form the t2 terrace before 11 970 100 cal yrs bp a third episode of aggradation resulted in the deposition of a sand dominated meandering channel complex that infilled the t2 valley and was subsequently downcut after 3780 50 cal yrs bp this most recent terrace is infilled by the modern fluvial sediment which has been actively aggrading since at least 870 50 cal yrs bp importantly the madre de dios fluvial system actively aggraded between 30 000 and 25 000 cal yrs bp and likely much younger as dated samples were thus far only found near the base of the t2 sequence this observation implies that some combination of 1 increased precipitation and decreased temperature 2 decreased evapotranspiration and increased runoff 3 increased andean glacial erosion and increased sediment supply and 4 decreased atmospheric co 2 hence decreased rain forest primary productivity and altered rain forest physiology ecology entering the last glacial maximum period brought about increased floodplain deposition in the southwestern amazon elsewhere in the amazon basin few if any fluvial sediments of this age range have been observed the start of the next major phase of aggradation coincided with the younger dryas and suggested that floodplain sedimentation in the lowlands was again related to cold and wet conditions in the adjacent highlands and perhaps in the lowlands as well and that madre de dios history was also tied to large scale global climate this aggradation may have continued throughout the early and mid holocene until at least 3 780 cal yr bp if so and this is uncertain this episode of sedimentation took place during a dry period

understanding amazonian fluvial rias based on a late pleistocene holocene analog fluvial rias are elongated lakes at tributary mouths that can reach dozens of kilometers in length constituting one of the most remarkable features in the amazonian landscape thus far definitive data which documents the genesis of fluvial rias have not been published the main goal of this work was to integrate morphological sedimentological and chronological information in order to characterize fluvial paleorias in the interfluve of the purus and madeira rivers and discuss the most likely hypothesis for their genesis these paleorias were first observed through remote sensing imagery as several elongated and interconnecting belts of open vegetation that are in sharp contact with the surrounding dense forest the belts are branched and form a dendritic pattern similar to many modern drainage networks the sedimentary record of these belts revealed the prevalence of sharp based sandstones and mudstones arranged into fining upward successions which are compatible with deposition within channels active channel and abandoned channel deposits were recognized these are topped by continuous mudstones related to rapid channel abandonment and formation of a low energy basin or ria environment radiocarbon dating of these deposits recorded only late pleistocene and holocene ages ranging from 21 547 22 285 cal yr bp to 5928 6124 cal yr bp this chronology for sediment deposition is not compatible with the hypothesis of amazonian rias being formed by fluvial erosion during the last glaciation maximum low sea level with sediment accumulation during the subsequent holocene transgression instead the studied paleorias record previous tributaries of the madeira river that became abandoned as the position of this river shifted southeastward and its interfluve tilted northward inverting the drainage systems therefore a neotectonic origin of some amazonian paleorias seems most likely this hypothesis should be considered in further investigations aiming at understanding the origin of numerous modern fluvial rias that typify the amazonian landscape copyright 2014 john wiley sons ltd

late quaternary fluvial terrace evolution in the main southern amazonian tributary abstract late quaternary sedimentary deposits from amazonian lowlands are important geological archives for understanding the origin evolution and controls of the largest fluvial drainage basin on earth climate has been most often claimed as the main factor affecting river evolution in this region an increasing volume of publications have also highlighted tectonics as a relevant control this work investigates the late quaternary evolution of the madeira river the biggest southern tributary of the amazonas basin and a major waterway in south america with the goal of discussing the factor with highest potential of influence on its development in space and time the approach consisted of carrying out a detailed morphological sedimentological and chronological characterization of terrace deposits three terraces were recognized which record sandy pebbly channel muddy channel oxbow lake point bar floodplain as well as crevasse channel crevasse splay and levee deposits the topographically highest terrace t1 formed in the time interval before 43 500 and 31 696 32 913 cal yrs bp the intermediate terrace t2 between 25 338 26 056 and 14 129 14 967 cal yrs bp and the lowest terrace t3 between 12 881 13 245 and 3158 3367 cal yrs bp these terraces are the testimony of successive downcutting and sediment aggradation episodes of terrace erosion and deposition cannot be fully accommodated within the framework of fluctuating river base level tied to late pleistocene holocene global or regional climate fluctuations changes in tectonic subsidence rates might have played an important role in the equilibrium state of this particular fluvial system

soft sediment deformation structures induced by strong earthquakes in southern siberia and their paleoseismic significance abstract liquefaction induced soft sediment deformation structures ssds formed by earthquakes in southern siberia that were historically mentioned or monitored by instruments are described and analyzed clastic dikes are the most common among all ssds in the epicentral areas of the investigated seismic events they are also the most reliable paleoseismic indicators in regions where cryogenic processes are intense we suggest seven criteria that may be useful to distinguish the seismogenic clastic dikes from non seismogenic ssds in a single outcrop 1 pushed up sedimentary blocks within the dike body 2 regular distorted contacts of a dike with host sediments reflecting cyclic loading during propagation of seismic waves 3 turned up layers of host deposits on contacts with a dike 4 displacement along dike contacts usually in the form of a normal fault caused by subsidence that compensates for the removed sediment 5 a dike structure similar to a diapir 6 filling of a clasic dike with coarser materials than the host sediments and 7 a sediment layer extruded on the surface or between strata similar in composition to the dike in the extruded sandy gravel pebble layer rock fragments show normal grading from large to small clasts in addition to these indicators fractures may indirectly indicate the seismogenic genesis of liquefaction induced ssds due to the close spatial relationship of dikes with the fault structures of the investigated areas they can be used to identify seismogenic fault and the characteristics of dikes lateral gradual changes in the frequency size and type of the deformations can help to determine the epicenter magnitude and the local intensity of the associated earthquakes

boiling sand springs dismal river nebraska agents for formation of vertical cylindrical structures and geomorphic change boiling motion not temperature sand springs fed by ground water moving upward along distinct conduits occur along the dismal river in the nebraska sand hills the cylindrical conduits are developed in alluvium and are as large as 10 m in diameter and 44 m deep sides of the spring conduits are firm boiling sand is overlain in several places by a clear layer of water in the spring time varying wave patterns and boils can be observed along the interface between these layers sediment within the conduits is generally well sorted although some debris is present because of their large size firm sides and persistence in time the conduits have the potential for preservation as vertical cylindrical structures comparable to those reported in sedimentary rocks of several ages the discovery of preserved structures is evidence of paleo ground water discharge and therefore the structures are a useful mapping tool for determining position in landscape evolution

soft sediment deformation structures induced by cyclic stress of storm waves in tempestites miocene guadalquivir basin spain the identification of triggering agents for soft sedimentation structures is an enigmatic geological problem mainly seismic induced soft sediment structures have been recognized in ancient sediments rather than those resulting from storm waves we analyse soft sediment deformation structures in upper miocene calcarenitic tempestites of the guadalquivir basin southern spain the most common structures are load casts which vary in height and width from 10 centimetres to several metres the structures are always restricted to a small part of the stratigraphic sections in exclusive association with tempestites the analysed soft deformation structures are interpreted to be the result of liquidization processes chiefly from their inferred depositional environment and subordinately from the deformation style we have devised basic criteria to identify the trigger mechanism in these soft sediment deformation structures the liquefaction was triggered by pore pressure changes induced by cyclic and residual stress of storm waves

palaeoseismic liquefaction event in late quaternary lake sediment at glen roy scotland late quaternary lake sediment deposits from a former ice dammed lake at glen roy scotland contain deformation structures indicative of liquefaction the distribution of deformation styles reflects a concentric pattern of the degree of liquefaction a possible fault rupture and several landslides are also observed in the central area the liquefaction structures the zonation of the sediment deformation and the association of deformation with landsliding can most simply be interpreted in terms of ground shaking during a major earthquake occurring at the end of the last glacial episode in scotland c 10 000 bp

anticyclonic rings in the gulf of mexico abstract using the historical data set this study describes the anticyclonic rings that separated from the loop current in the eastern gulf of mexico six quasi synoptic data sets are used to describe the evolving circulation of the gulf of mexico from october 1966 to september 1967 showing the separation and movement into the western gulf of three anticyclonic rings the historical data are used to determine that these rings typically translate to the west at a mean speed of 2 1 km day 1 their length scale as defined by their rms radii is 183 km an estimate of ring life span as defined by an e folding time is one year within the context of the gulf s water property distributions these rings appear as warm salty bodies the heat and salt added by one of these rings after separation are estimated to be 7 109 j m 2 and 17 g cm 2 respectively the heat and salt added by one of these features play an important role in the heat and salt budget of the western gulf the latter indicates that about one r

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

evolution of a warm core ring in the gulf of mexico lagrangian observations during 1985 and 1986 a gulf of mexico ring shed by the loop current was observed to migrate toward the western gulf of mexico this movement across the gulf was well documented by observations that included drifter data within and outside the ring sea surface temperature at weekly intervals expendable bathythermograph surveys at various times one major hydrographic cruise when the ring was in the northwestern gulf and currents from moorings over which the ring passed the drifter data were used to infer the movement of the ring center as well as the eccentricity and orientation of the major axes the data from the drifters bridge the gaps between detailed surveys to the extent that a daily history of the position and shape of the ring can be constructed the synthesis of these diverse but complimentary data sources provides a detailed description of how the ring interacted with the bathymetry of the northern gulf of mexico as well as with previously and subsequently shed rings

soft sediment deformation structures in alkaline lake deposits of lower permian fengcheng formation junggar basin nw china implications for syn sedimentary tectonic activity abstract soft sediment deformation structures ssds are an important tool for interpreting paleoseismicity and depositional environments in ancient basin successions the northwestern margin of junggar basin is a key region for understanding the paleogeography and basin attribute of the junggar basin during the early permian in the lower permian kungurian fengcheng formation nine lithofacies are grouped into fan delta fluvial delta and shallow deep and alkaline lacustrine facies associations vertical transitions of the sedimentary environments show that the lake basin experienced expansion during deposition of the lower p1f1 and middle p1f2 members and the shrinkage during the upper member p1f3 which is consistent with the paleogeographic distribution of lithofacies in different members conventional cores show a wide variety of ssds including ductile folds convolute lamination and load structures hybrid ductile brittle and brittle deformation structures microfaults breccias boudinage and sedimentary dikes ssds mainly occurred in a still and deep lacustrine environment these deformation structures were not formed in any specific lacustrine environment as there is no difference with the undeformed sedimentary units of the same sedimentary facies thus the triggering mechanism is interpreted as intermittent earthquakes lake expansion under arid condition and ssds intervals with vertical repetition and possible lateral continuity indicate that most seismicity was during the middle member p1f2 corresponding with the main activity on basin bounding normal faults the enhanced faulting at this time generated accommodation creating lacustrine conditions in the basin depocenter it is thus clear that the early permian mahu sag represents an active rift basin with bounding faults and is not a foreland basin

mid late pleistocene osl chronology in western amazonia and implications for the transcontinental amazon pathway abstract the origin of the transcontinental amazon drainage system remains unrevealed sedimentary deposits formed from the neogene in the amazonas and solimoes basins constitute natural archives for reconstructing this event in space and time however paleoenvironmental and chronological analyses focusing on these deposits or even their basic mapping are still scarce to allow such investigation in this context primary interests are fluvial strata related to the lithostratigraphic ica formation mapped over a widespread area in western amazonian lowlands although long regarded as plio pleistocene in age this unit has not yet been dated and its overall depositional setting remains largely undescribed the main goal of the present work is to contribute for improving facies analysis and chronology of these deposits approaching an area in southwestern amazonia and another in northern amazonia which are located more than 1000 km apart despite this great distance the sedimentological and chronological characteristics of deposits from these two areas are analogous hence facies analysis revealed paleoenvironments including active channel abandoned channel point bar crevasse splay and floodplain which are altogether compatible with meandering fluvial systems similarly optically stimulated luminescence osl dating revealed thirty three ages ranging from 65 4 16 9 to 219 6 25 1 ky in addition to three outliners of 54 0 7 6 337 3 36 9 and 346 6 48 6 ky and nine 97 1 9 9 to 254 8 23 8 ky for the areas in southwestern and northern amazonia respectively these data lead to establish that deposits mapped as ica formation over a vast area of western brazilian amazonia have a mid late pleistocene age rather than the previously inferred plio pleistocene age it follows that if plio pleistocene deposits exist in this region they remain to be dated and must be restricted to a narrow belt in western amazonia as well as isolated occurrences underlying the mid late pleistocene strata characterized herein the combination of data from this work with previously published provenance studies supports main andean sediment sources only in the mid late pleistocene it is proposed that before this time the amazon river was restricted to eastern amazonia being separated from western amazonian drainage basins due to the presence of the purus arch erosion and or subsidence of this geological feature would have promoted the connection of these drainage systems ultimately with the expressive record of the transcontinental amazon pathway into the atlantic ocean in the mid late pleistocene

aspects of warm rings in the gulf of mexico various aspects of warm rings in the gulf of mexico were derived from satellite infrared data and ship of opportunity data after the warm rings separate from the loop current they move into the western gulf of mexico it was shown from 12 years of data 1973 through 1984 that there are three characteristic paths of movements of the rings a northern path a mid gulf path and a path that takes the rings into the southern extremities of the western gulf of mexico it was shown that all three paths eventually lead the ring to a region in the northwestern portion of the western gulf of mexico the area defined by 25 n to 28 n and 93 w to 96 w as the rings move from the eastern gulf to the western gulf the speed of the ring was observed to oscillate the oscillation is over a speed range from 1 to 8 km per day on the average and the period varies from 40 to 100 days the average speed of the ring was 5 km per day after the ring separates from the loop current the surface area of the ring decreases to about 55 percent of its initial size in approximately 150 days and to about 31 percent of its initial size in about 300 days

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

soft sediment deformation structures in the earth s oldest seismites abstract the chaibasa formation in eastern india which was deposited between 2100 and 1600 million years ago shows deformations that must have formed when the sediments were not yet consolidated some of these deformation structures have never been described before here they are described depicted and their origin is analysed we show that they must be the result of shocks which can only be explained satisfactorily as triggered by earthquakes the layers containing these deformation structures are termed seismites they are among the earliest records of earthquakes known in the earth s history

late pleistocene seismites from lake issyk kul the tien shan range kyrghyzstan abstract the aim of the study is to record the occurrence of sediment deformation structures in one of the tectonically most active areas on the globe the tien shan range in central asia and to examine the significance of the deformations as indicators of palaeoseismicity soft sediment deformation structures in form of balls and pseudo nodules are exposed in the issyk kul basin within interfingering beds of shallow lacustrine beach and fluviatile origin additional deformation structures that were encountered are a complex and chaotic folded structure giant balls and a pillar structure which has not been previously reported where marl intrudes down into coarse pebbley sand and forms pillar morphology liquefaction features and bedforms related to storm and breaking waves were not encountered neither was there evidence of turbidites seven field criteria for relating soft sediment deformation to palaeoseismic triggering provide strong evidence for a seismic origin of the deformation structures empirical relationships between magnitude and the maximum distance from an epicenter to liquefaction sites make the active epicentral zone north of lake issyk kul with its frequent high magnitude events the most favorable source for the deformation structures luminescence dating of the sediments gives a time window of 26 2 1 to 10 5 0 7 ka bp indicating latest pleistocene seismic activity

the role of the 1999 chamoli earthquake in the formation of ground cracks abstract the moderate magnitude chamoli earthquake that occurred in the garhwal higher himalaya in the early hours of march 29 1999 caused intense damage to the ground and mountain slopes of the alaknanda mandakini river valley and adjoining region a systematic survey of this induced damage was conducted immediately after the earthquake occurred prominent shallow cracks of significant length negligible width and indeterminate vertical extent conspicuously tensile in nature with little or no slip across the crack planes were observed in the ground at several places along the surveyed route these cracks had formed in the dynamic phase of the chamoli earthquake process that is in the period of time during which the earthquake generated seismic waves were passing through the geographic region of interest however we use the theory of earthquake induced static or long time stress changes to visualize such cracks at some selected sites where ground damage was relatively more intense and varied to suggest lower bound estimates of the dynamic stress contributions of the main shock for their formation based on the results of our analysis we conclude that just prior to the earthquake occurrence under the influence of the local ambient stress field the ground at these sites was already near failure in tension to this in its dynamic phase the chamoli earthquake induced stress perturbations having across the planes of the cracks i shear components which were nearly equal and opposite to similar components of the ambient stress field and ii normal tensile components necessary for triggering tensile failure of the ground the 3 or minimum principal stress component of the resultant perturbed failure stress field thus became sufficiently tensile while the transverse stresses became sufficiently insignificant this facilitated formation of major tensile cracks in the ground there our static estimates of the tensile stress changes at the different sites are in essence estimates of the minimal triggering stress perturbations that was provided by the chamoli earthquake in the dynamic state for the formation of the tensile cracks there

neotectonics and tree mortality in a forest ecosystem of the negro basin geomorphic evidence of contemporary seismicity in the intracratonic brazilian amazonia abstract neotectonic activity was increasingly recorded over the amazonian lowlands even during historical times of a few tens of centuries however detailed analyses linking structures and styles of deformation are still few considering the large dimension of the region such events in a relatively recent time are expected to have caused conspicuous impacts on amazonian ecosystems and forest disturbance changes in topography and hydrology by fracturing faulting and folding during either subsidence or uplifting are direct effects on landscape that leave marks on the structure of the current forest such as tree mortality and community succession two rectangular elbow like shaped wetlands from the left margin of the middle negro river valley in northwestern amazonia were attributed to neotectonics remote sensing imagery was applied to test this hypothesis and also provide a tectonic model that can explain deformation dynamics in this area the studied wetlands and adjacent river systems display various morphostructural anomalies compatible with a tectonic control as well as lineaments paralleling main nw and ne trending regional structures the geomorphic analysis led to suggest that the wetlands are depressions formed by nw and ne trending master boundary faults of horizontal displacements intercepted by various subsidiary faults transtensional strike slip regime is recorded by both left and right lateral faults with the wetlands corresponding to subsiding areas owned to conjugate strike slip faults habitat fragmentation and other ecological processes promoted by tectonic deformation would have impacted the overlying forest canopy by changing its structure due to tree mortality the complex compartmentalization imposed by active tectonics would have exposed the ground to contrasting hydrological conditions which controlled the rate of tree mortality within the wetlands we pose that the tectonic disturbance and associated tree mortality documented in the middle negro river evidence contemporary seismicity within the intracratonic brazilian amazonia

deep currents in the gulf of mexico abstract direct current measurements using moored arrays have been made below 1000 m in the eastern central and western gulf of mexico basin the major low frequency velocity fluctuations in the lower 1000 to 2000 m of the water column in the three regions have the characteristics of topographic rossby waves trws spectral peaks are observed at periods of about 25 days and 40 to 100 days motions are highly coherent with depth variances increase toward the bottom despite the very weak stratification of the deep waters of the gulf wave lengths are about 150 250 km and phase propagation is offshore with energy propagation westward a group velocity of about 9 km day 1 could be directly estimated from significantly coherent signals between eastern and western arrays this value is consistent with estimates derived from the dispersion relation and is higher than the westward translation speed of 3 to 6 km day 1 of the large anticyclonic eddies shed from the loop current it appears that a major source of

conical sandstone landforms cored with clastic pipes in glen canyon national recreation area southeastern utah abstract clusters of conical sandstone landforms many with summit weathering pits have developed on barren outcrops of the jurassic entrada sandstone in glen canyon national recreation area southeastern utah the conical landforms have developed on cylindrical bodies of fluidized sandstone clastic pipes that typically have near vertical contacts with the enclosing cross bedded eolian sandstone these landforms vary in size and shape due chiefly to differential erosion of the clastic pipe relative to the enclosing sandstone the greater resistance to weathering of the clastic pipes is due in part to their higher content of calcite cement conical pipe cored landforms develop progressively from low domes to cones as high as 70 m some of the clastic pipes have relatively soft cores and resistant contacts leading to the development of conical landforms with summit weathering pits with time the size of these pits increases as does the relief of the conical landform the summit pits are as deep as 16 m and have width depth ratios as low as 1 5 the resistant rims of these pits are due in part to calcite enriched pipe contacts sandy pit floor sediment is removed principally by strong wind rotors and vortices intense eolian activity in and near the landforms is indicated by abrasional features and pit floor sand dunes factors that promote the development of these conical landforms include i the presence of clastic pipes some with relatively soft cores ii porous friable fine grained pipe and host sandstones iii aridity iv strong winds and v virtually sediment free unvegetated bedrock outcrops

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

evolution and kinematics of a loop current eddy in the gulf of mexico during 1985 the large eddy that broke off from the loop current in july 1985 was the most extensively studied eddy ever to appear in the gulf of mexico other investigators have described its early evolution based on lagrangian drifters and its later evolution using moored current meters in the western gulf this paper provides additional insight on the early evolution of the eddy using results from air dropped expendable bathythermographs and air dropped expendable current profilers in early may a hydrographic ship survey in mid july and a detailed ship survey in august using expendable bathythermographs and a current profiler the may survey established a center of circulation at about 26 n but showed that the eddy had not separated from the loop current a maximum velocity of 171 cm s was observed near the northern edge of the feature the evidence suggests that a large elongated eddy then separated from the loop current and later split into two smaller eddies the july hydrographic cruise showed a clear separation of the large eddy from the loop current to the southeast two weeks later the august survey showed an asymmetric eddy with the maximum surface current 178 cm s south of the center of circulation and 132 cm s to the north a western eddy named ghost eddy then separated from an eastern eddy named fast eddy using the current profiles and data from the drifters we constructed a simple kinematic feature model for eddies in the gulf of mexico

paleoearthquakes in the puget sound region recorded in sediments from lake washington u s a holocene sediments in lake washington contain a series of turbidites that were episodically deposited throughout the lake the magnetic signatures of these terrigenous layers are temporally and areally correlatable large earthquakes appear to have triggered slumping on the steep basin walls and landslides in the drainage area resulting in turbidite deposition one prominent turbidite appears to have been deposited about 1100 years ago as the result of a large earthquake downcore susceptibility patterns suggest that near simultaneous slumping occurred in at least three separate locations two of which now contain submerged forests several other large earthquakes may have occurred in the last 3000 years

applying dem srtm for reconstructing a late quaternary paleodrainage in amazonia abstract remote sensing is a particularly invaluable tool that has helped the detection of paleomorphologies produced by river dislocation in a variety of landscapes which has contributed in reconstructing the geological evolution of many fluvial systems this technique might provide useful information to discuss the evolution of large fluvial systems in special those located in areas of difficult access where the acquisition of field data is difficult application of remote sensing for paleodrainage characterization in densely vegetated tropical areas is scarce in the literature this work records processing of the digital elevation model dem derived from the shuttle radar topography mission srtm which succeeded in revealing an ancient drainage complex of the madeira river one of the main amazonas tributaries where other remote sensing products failed the detection analysis of this paleodrainage and of its modern counterpart within the geological framework available for this region leads to propose that activity along pre existent faults during the latest quaternary would have promoted the southeastward dislocation of a nearly 200 km long segment of the madeira river during this process an impressive paleodrainage network was left behind which was only able to be detected using the dem srtm application of this technique might be of great help to the detection of paleodrainage morphologies in densely vegetated areas similar to the amazonas lowland the dynamics of channel migration in this and many other large scale tropical river systems might benefit from the investigation based on data derived from dem srtm

seismites as an indicator for determination of earthquake recurrence interval a case study from ercis fault eastern anatolia turkey abstract the southern part of the eastern anatolian plateau is a key region for understanding the tectonic activity and related deformation patterns of the arabian eurasian collision zone the geological record of seismic events collected from lacustrine deposits of lake van basin is a critical requirement for seismic hazard assessment and seismic risk reduction our paleoseismic investigations revealed well preserved seismites at five locations in late pleistocene lacustrine deposits the seismites were dated using an optically stimulated luminescence dating method and were arranged according to their ages their type such as convolute dish and pillar flame and ball and pillow structures as well as their locations ages and stratigraphic distribution enable us to identify the responsible fault and the earthquake recurrence interval on the basis of these properties the ercis fault has been recognized as the structure responsible for creating the seismites the time span between the seismites indicates an apparent earthquake recurrence interval of 125 250 years for large earthquakes m 5 related to the ercis fault the method applied here enriches our knowledge on the seismic hazards present in the northern lake van region

experimental soft sediment deformation structures formed by the liquefaction of unconsolidated sands and some ancient examples the effects of liquefaction in saturated sand bodies under a variety of driving forces are described from shaking table experiments and structures from the geological record are presented which are analogous to the experimental structures the collapse of sloping heaps of cross bedded sand under a gravitational body force generates low angle essentially uncontorted stratification a basal zone of shearing may be present with steepened and folded foresets stretching of foresets may be accommodated on normal faults and bottomsets may be contorted into inclined folds in natural systems the substrate may also liquefy causing deformation driven by an unevenly distributed confining load stratification in the surface bedform is flattened and stratification in the substratum contorted experiments failed to produce relative displacement at the interface between stacked sand bodies liquefaction of gravitationally unstable systems in sands generates load structures comparable to those from sand mud systems recumbent folded deformed cross bedding is formed by current shear over a liquefied bed as has been inferred from field and theoretical analyses shear of nonliquefied sand forms angular folds other deformation mechanisms such as fluidization or seepage may generate structures similar to all of these local water escape structures driven by fluidization occur in the upper parts of some liquefied sand bodies they include cusps sand volcanoes and clastic dykes transient cavities formed in some experiments and seemed to be preserved as breached cusps although the experiments tried to isolate individual driving forces driving forces may operate together and there may be a continuum between deformation driven by water escape and deformation driven by loading different structures from those described here may form where liquefaction develops in a buried layer as opposed to at the sediment surface

the role of tectonics and climate in the late quaternary evolution of a northern amazonian river abstract the amazon basin has most of the largest rivers of the world however works focusing the geological evolution of the trunk river or its tributaries have been only partly approached the branco river constitutes one of the main northern amazonian tributaries a previous work proposed that before flowing southward into the negro amazon rivers the branco river had a southwest to northeast course into the caribbean sea the present work aimed to establish if the proposed change in the course of this river is supported by morphological and sedimentological data other goals were to discuss the factors influencing river development and establish its evolution over time within the chronological framework provided by radiocarbon and optically stimulated luminescence dating the work considered the entire course of the branco river downstream of the precambrian guiana shield where the river presumably did not exist in ancient times the river valley is incised into fluvial sedimentary units displaying ages between 100 and 250 ky old which record active and abandoned channels crevasse splay levees and point bars the sedimentary deposits in the valley include two alluvial plain units as old as 18 7 ky and which intersects a late pleistocene residual megafan these characteristics suggest that a long segment of the branco river was established only a few thousand years ago together with several structural anomalies these data are consistent with a mega capture at the middle reach of this river due to tectonic reactivation in the late pleistocene this integrated approach can be applied to other amazonian tributaries to unravel how and when the amazonian drainage basin became established

the role of tectonics in the late quaternary evolution of brazil s amazonian landscape tectonic reactivation has long been suggested to have occurred over several areas of the amazonian lowland in the neogene holocene numerous landscape changes documented in this region particularly variations in fluvial dynamics and morphologies have nevertheless been exclusively attributed to climatic fluctuations minimizing the effect of tectonics over the neogene holocene evolution of the amazon basin can result in a distorted interpretation of the sedimentary record and as a consequence equivocal paleoclimatic reconstructions climate has often prevailed as a hypothesis to explain changes in fluvial dynamics possibly due to the still scarce synthesizing publications focusing exclusively on the neotectonic influence over this region the present work provides a review of existing data focusing on quaternary tectonics over a large area of the amazonian lowland the existing information is complemented by original morphostructural data on quaternary terrains from this region which were acquired through remote sensing the goals were to analyze the geographic extent of late quaternary deposits and to determine the impact of tectonics on their development and on the latest evolution of the amazon drainage basin the analysis shows that 1 the amazonian lowland experienced geographically widespread sedimentation in the late pleistocene holocene 2 sedimentation was promoted by the creation of new depositional sites mostly likely resulting from tectonic activity and 3 tectonic reactivation impacted the latest evolution of this entire region with particular influence on drainage basins as revealed by river courses with an abundance of morphostructural lineaments evidencing fault control hence the nw ne nearly n s and to a lesser extent w e morphostructural trends recorded in all areas investigated here are generally associated with strike slip deformation in addition they are conformable with the main orientation of tectonic structures from adjacent crystalline rocks of the precambrian basement they also match tectonic trends documented in neogene and younger sedimentary deposits from this and several other areas of northeastern brazil furthermore some are detected locally in the subsurface by geophysical data furthermore a profusion of morphostructural anomalies is imprinted on the surface of neogene holocene deposits of the amazonian lowland the main ones consisting of 1 highly asymmetric modern drainage basin still undergoing organization with anomalous patterns i e trellis sub dendritic sub parallel and rectangular that often vary from one another frequent river captures and rivers flowing in contrary directions along the time and straight channels that form triangular shapes or triple junctions or with local meandering and subtle enlargements 2 an abundance of channels floodplains lakes and entire valleys with straight and orthogonal margins that locally form rhombic shapes or which may be laterally displaced 3 fluvial rias i e rivers that became enlarged as their mouth were barred bounded by sharp and orthogonal lineaments which result in rectangular shapes 4 termination of megafans into rhombic shaped depressions bounded by straight lineaments or their lateral displacement several kilometers apart and 5 rivers with asymmetric terraces laterally displaced by faults these observations together are consistent with a landscape controlled by neotectonic activity the modern seismogenic record which reveals even high magnitude earthquakes indicates active deformation over the amazonian lowland at the present time the neotectonic history of the amazonian lowland is explained within the context of an overarching mechanism most likely related to intraplate stresses this was probably caused by reactivation of pre existing structures since the neogene that was most likely promoted by activity along oceanic fracture zones and transform faults of the brazilian equatorial margin as well as tectonism in the andean region

multi stream order analyses in basin asymmetry a tool to discriminate the influence of neotectonics in fluvial landscape development madrid basin central spain morphometric analysis of the tajo drainage network using a dem was carried out in order to determine neotectonic influence on the development of the madrid basin since the pliocene statistical analysis of digitally derived transverse topographical drainage basin asymmetry t factor was used to infer directions of ground tilting a crustal block pattern was interpreted from a mean basin asymmetry vector field that was computed using a new approach based on a gridded running average of the raw vector field measurement of r factor for different order channels allows investigation of evolution rates of different order rivers and at the same time reveals possible factors controlling basin evolution the vector data show clear differences between high and low orders high order asymmetry is consistent with fluvial terrace distribution as it reflects channel migration and incision within the main valleys and shows a general trend toward a central basin axis running sw ne a sw ne trend is also defined by other morphographical approaches such as drainage density and relief analysis both approaches point toward the presence of two uplifted areas running sw ne and a subsided zone between them which is in agreement with previous crustal flexure models in contrast low order asymmetry shows a clear trend indicating eastward tilting which could be driven by recent changes in maximum principal stress direction and its influence on fault reactivations in general large rivers generating fluvial terraces are controlled by basement structure with positive and negative crustal flexures driving their migration direction and thus controlling the spatial distribution of terraces because the position of main streams is controlled by large tectonic lineaments that favor groundwater flow convergence on the other hand small tributaries have low capabilities to attain equilibrium and t factor values of low order basins may reflect more recent block tectonics due to variations in stress fields or may reflect local controls like lithology

morphology of a submarine slide kitimat arm british columbia a digitally acquired scale corrected side scan sonar survey yielded high resolution imagery of a submarine landslide in british columbia the landslide in a fjord head setting at kitimat was last active in 1975 and created a wide area of deformed sea floor the sediment failure involved shallow rotational movements on the slopes of a fjord head delta marginal tearing translational sliding compressional folding and block gliding of fjord bottom marine clays the slide is shallow and elongate and appears to have been produced by failure in mobile low strength sediments

soft sediment deformation structures as indicators of tectono volcanic activity during evolution of a lacustrine basin a case study from the upper triassic ordos basin china abstract the ordos basin central china is a large scale late triassic intracratonic lacustrine basin and in which the upper triassic yanchang formation comprises interbedded sandstones mudstones and tuffs representing deposits of a complete lacustrine life cycle based on observation of extensive well cores various types of soft sediment deformation structures have been identified in the lacustrine deposits of the southwest basin including deformed lamination bedding load casts and flame structures pseudonodules microfaults autoclastic brecciation sand dykes dyke sill complexes and sandy and muddy slumps liquefaction and fluidization of unconsolidated permeable sediments together with brittle fracturing of semi consolidated sediments are the major deformation mechanisms that generated these structures both the scale and prevalence of the deformed sediments as well as the geological setting of the lacustrine basin suggest that seismic events synsedimentary tectonic activity were the main trigger to initiate deformation processes although sedimentary overloading could also have been a minor localized trigger many volcanic tuffs preserved in both the primary undisturbed deposits and deformed sediments serve as support for synsedimentary tectono volcanic activities that induced deformation in these lacustrine sediments the deformation structures usually form vertical clusters of several different types representing active syndepositional tectonic periods stratigraphic correlation shows three such deformation clusters to be widespread in the area detailed herein and likely recorded three major tectonic periods during deposition a thick extensive oil shale with various deformation structures also reveals another active tectonic period these four intervals coincide well with the transition of the sedimentary architecture in the area indicating four phases of most intense tectonic periods and their influence on lacustrine evolution

response of alluvial rivers to slow active tectonic movement alluvial rivers respond to valley slope deformation caused by active tectonics in various ways depending on the rate and amount of surficial deformation and on the type of river on the basis of experimental results and field examples hypothetical models of river response to anticlinal uplift and synclinal subsidence were developed for different types of alluvial rivers an experimental braided channel responded to anticlinal uplift across the channel with degradation and terrace formation in the central part of the uplift with subsidence aggradation in the central reach was the main response transverse bars developed downstream of the subsidence axis an experimental meandering channel responded to slope steepening with a sinuosity increase bank erosion and point bar growth occurred downstream of the anticlinal axis and upstream of the synclinal axis upstream of the uplift axis and downstream of the subsidence axis where the slope was flattened water flooded over bars local convexity in longitudinal profiles of the middle rio grande new mexico is considered to be formed by a domal uplift local aggradation and degradation could be explained by the effect of uplift the san joaquin river california which is now highly controlled does not show clear adjustment to the rapid subsidence due to ground water withdrawal it shows however a channel pattern adjustment to active tectonic subsidence that has been occurring for a long time the san antonio and guadalupe rivers in texas both increase their sinuosity significantly where monoclinal movements steepen valley slopes

analysis of drainage basin symmetry as a rapid technique to identify areas of possible quaternary tilt block tectonics an example from the mississippi embayment there is a coincidence of seismicity and major river valleys in the southwestern mississippi embayment that suggests control of the drainage pattern by northwest trending faults pleistocene river terraces reveal a strong southwestward preferred river migration in this region that may be a result of fault block tilting a rapid new technique of drainage basin analysis is herein presented that quantifies transverse topographic basin symmetry these data permit discrimination of random stream migrations and regionally preferred stream migrations and identify the direction of maximum migration if bedrock dip can be shown to be a negligible influence on stream migration then the direction of regionally preferred migration implies a period of ground tilting in that direction drainage basin asymmetry vectors bearing and degree of asymmetry calculated from transverse topographic profiles of 271 4 km basin segments in the study area suggest preferred stream migration in response to west southwest ward ground tilting bearing 259 the eastward regional dip of bed rock horizons only locally influences migration river terrace distributions reveal a chronology of stream migration episodes southwestward migration in the ouachita saline and arkansas river basins occurred during early to middle pleistocene time in the southwestern mississippi embayment a wisconsin early holocene southwestward migration episode is evidenced along southeast flowing reaches of the ouachita and arkansas rivers but not along the southeast flowing reach of the intervening saline river suggesting that these rivers overlie separate northwest trending tilt blocks although this technique does not provide direct evidence of ground tilting it provides a quick look method of identifying possible tilting elements in neotectonic regions using only topographic maps this technique is of greatest utility where active faults are concealed or poorly exposed such as in the mississippi embayment

the holocene alluvial plain of the middle amazon river brazil abstract the fluvial belt of the amazon river is a complex of quaternary sedimentary units of different ages and formation conditions present position of the channel and the morphology and size of the alluvial plain are related to neo tectonic lineaments in the study area the main channel of the solimoes is nearly straight the river may be considered anastomosed albeit with few islands and anabranches the main holocene units are the impeded floodplain and the channel dominated floodplain the channel dominated floodplain is a complex mosaic of fluvial forms including younger channels active sandbars islands levees scroll dominated plains and abandoned belts the impeded floodplain is a widespread unit characterised by a very flat surface and round or irregularly shaped lakes the impeded drainage flood plain is only partially affected by the present floods and even those parts affected by floods receive little or no sediment from the main channel more important sediment contribution is by alluvial plain channels from the solimoes branches that generate deltas in the impeded floodplain lakes the impeded floodplain is interpreted to be an earlier stage in the evolution of the holocene alluvial belt the formation was marked by widespread vertical accretion and a channel morphogenetically less active than at present the later stage is associated with an active main channel and the paranas and generation of a scroll dominated plain this very large river system had a complex and delayed response to variations in the hydrological conditions induced by changes in the regional climate during the late holocene

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

late quaternary slip rate and seismic hazards of the west klamath lake fault zone near crater lake oregon cascades crater lake caldera is at the north end of the klamath graben where this n10 w trending major basin and range structure impinges upon the north south trending high cascades volcanic arc east facing normal faults typically 10 15 km long form the west klamath lake fault zone which bounds the graben on its west side the fault zone terminates on the south near the epicentral area of the september 1993 klamath falls earthquakes it continues north past crater lake as the annie spring fault which is within 1 km of the west caldera rim and red cone spring fault we have determined a long term vertical slip rate of 0 3 mm yr for these two faults using high precision k ar and 40 ar 39 ar age measurements on offset lava flows ranging in age from ca 35 to 300 ka holocene offset reported by hawkins et al and epicenters of eight m w 2 earthquakes in 1994 and 1995 indicate that the west klamath lake fault zone is active empirical relations between earthquake magnitudes and scarp heights or fault lengths suggest that the fault zone is capable of producing earthquakes as large as m w 7 earthquakes on these or other faults of the zone could trigger landslides and rockfalls from the walls of the caldera possibly resulting in large waves on crater lake

seismically induced soft sediment deformation structures seismites around sumdo in the lower spiti valley tethys himalaya abstract soft sediment deformation structures were observed in 120 m thick fluvio lacustrine sediments exposed in the sumdo area in the lower spiti valley tethys himalaya himachal pradesh india these structures vary in their morphology and pattern and occur at eight stratigraphic levels s1 s8 spaced at irregular intervals the deformation structures include over steepened stratification diapiric flame like intrusions of clayey material or complex type recumbent folding of flame like nature pseudonodules large scale soft sediment folding faulting small scale associated with folding and sand dykes these structures are restricted to single stratigraphic layers separated by undeformed beds and can be correlated over a large distance the deformation of the soft sediments is attributed to the combined effects of fluidization liquefaction and shear stress and can be related to past seismic activity in the area recently on 19 january 1975 a major earthquake kinnaur earthquake of magnitude 6 8 caused extensive damage including ground rupturing in the sumdo kaurik area this earthquake has been related to the activation of the kaurik chango fault the deformed layers seismites reported here lie adjacent to this fault zone and can be related with episodic seismicity along this fault it is evident from this study that the kaurik chango fault has been re activated a number of times and that the area suffered at least nine major earthquakes with a magnitude of more than 6 during late pleistocene holocene time including the 1975 kinnaur earthquake

source mechanisms of moderate size earthquakes and stress orientation in mid plate south america summary fault plane solutions of six mid plate earthquakes with magnitudes ranging from 4 8 to 5 5 mb were determined using p wave first motion data and the relative amplitudes of short period teleseismic depth phases pp and sp these results together with previous studies show a predominance of reverse and strike slip faulting indicating horizontal compressional stresses in mid plate south america the orientation of the p axes however is not uniform in western and southwestern brazil the p axes are oriented approximately e w probably due to the nazca south america plate convergence in eastern brazil the direction of the p axes show more scatter but an average e w direction is consistent with the available data on the contrary in northern brazil the p axes of two events in the amazon basin trend approximately n s a direction perpendicular to the direction of absolute plate motion as well as to the relative plate motions nazca south america and south america africa

testing the tectonic significance of some parameters of longitudinal river profiles the case of the ardenne belgium nw europe the longitudinal profiles of 24 rivers of 3rd to 5th order have been analyzed in order to recognize the regional tectonic differentiation pattern of the ardenne a paleozoic massif of nw europe data collected exclusively from 1 25 000 topographic maps were used to define a set of parameters related to the geometry of the profile and proxies for river bedload and drainage area validation of the proxy defined for the bedload discharge ratio demonstrates its potential use for inter river comparison based on its value at the river mouth it is however inadequate to estimate the ratio changes along a given stream course this proxy has been computed to estimate the portion accounted for by hydrodynamic factors in the river bed profiling thus outliers to the correlation function linking it to the river bed gradient have been considered as undergoing other influences principally of lithologic or tectonic origin most indicative of the computed profile parameters are those related to the concavity of the profile four more or less regional longitudinal profile types are recognized which are partly determined by differential tectonic movement the combined analysis of all the parameters confirms the current uplift of the ne ardenne and points to a subsidence of the namur area with respect to its sw and se surroundings whether periglacial or tectonic in origin the upper pleistocene lowering of a local base level has also been identified in the famenne another conclusion of this study is that in order to evidence tectonic influences and to avoid any misinterpretation in a region of complex geologic and geomorphic history and moderate tectonic activity it is essential to consider a number of parameters and to consider their significance within the framework of detailed geologic setting and morphogenetic history

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

development of paleogene depressions and deposition of lacustrine source rocks in the pearl river mouth basin northern margin of the south china sea a more accurate integrated chronostratigraphic framework is applied to the analysis of the development of paleogene depressions in the pearl river mouth basin the results of our study show that the development of these depressions was characterized by at least three rifting or basin forming phases occurring during these periods late paleocene late cretaceous middle eocene late eocene early oligocene and middle oligocene late oligocene the transition from rifting stage to postrifting stage in the basin is about 10 m y later than the initial spreading of the south china sea the prologue of the spreading of the south china sea began as early as the end of the middle eocene lacustrine source rocks deposited during the basins first rifting phase are thick and of go d quality source rocks deposited during the last two phases which had a sharp increase in sedimentation rate are of lesser quality with the exception being those areas where deposits were out of reach of sediment from the northern mainland

genesis and implication of soft sediment deformation structures in high energy fluvial deposits of the alaknanda valley garhwal himalaya india abstract valley fill terraces and fluvio lacustrine sediment successions were investigated for the nature and type of soft sediment deformation structures ssds in the alaknanda valley of the garhwal himalaya based on their morphologies sediment characteristics and comparison with existing data on ssds these features are classified into seismic and aseismic categories the study indicates that despite the terrain being in the seismically active domain of the central himalaya the majority of the deformation structures seem to have been generated aseismically we attribute their genesis to uneven loading slope failure and most importantly turbulent flow and sudden loading by flash floods the study suggests that a cautious approach is needed before assigning a seismic origin to deformation structures in sediments deposited in high energy fluvial systems

the role of late pleistocene holocene tectono sedimentary history on the origin of patches of savanna vegetation in the middle madeira river southwest of the amazonian lowlands abstract savanna patches are features of the amazonian landscape that have been long under intense debate but there are still questions about the main factors that have determined their establishment and evolution within the rainforest matrix in particular their geological substrates were poorly documented the aim of this work is to reconstruct the tectono sedimentary history of four savanna patches in the middle madeira river southwest amazonia and discuss its potential control over the development of the savanna communities the approach consisted in the integration of geomorphological sedimentological chronological and floristic data the results revealed that the savanna substrates are sandy deposits aged between 118 9 and 35 6 ky overlain by late pleistocene to holocene muddier successions

quaternary tectonics in a passive margin marajo island northern brazil marajoisland is located in a passive continental margin that evolved from rifting associated with the opening of the equatorial south atlantic ocean in the late jurassic early cretaceous period this study based on remote sensing integrated with sedimentology as well as subsurface and seismographic data available from the literature allows discussion of the significance of tectonics during the quaternary history of marginal basins results show that eastern marajoisland contains channels with evidence of tectonic control mapping of straight channels defined four main groups of lineaments i e nne ssw ne sw nw se and e w that parallel main normal and strike slip fault zones recorded for the amazon region additionally sedimentological studies of late quaternary and holocene deposits indicate numerous ductile and brittle structures within strati graphic horizons bounded by undeformed strata related to seismogenic deformation during or shortly after sediment deposition this conclusion is consistent with subsurface bouguer mapping suggestive of eastern marajoisland being still part of the marajograben system where important fault reactivation is recorded up to the quaternary together with the recognition of several phases of fault reactivation these data suggest that faults developed in association with rift basins might remain active in passive margins imposing important control on development of depositional systems copyright 2007 john wiley sons ltd

recurrent liquefaction induced by the 1989 loma prieta earthquake and 1990 and 1991 aftershocks implications for paleoseismicity studies sandblows formed in man made lake deposits near watsonville california resulted from the october 1989 m 7 1 loma prieta earthquake and its april 1990 m 5 5 aftershock and a march 1991 m 4 6 aftershock excavations in the dry bed of soda lake expose the subsurface structure of sandblows induced by the october and april events we also made surface observations three days after the march 1991 event lateral spread fissures developed in the lake sediment during the mainshock and the host deposits were vertically offset 3 to 6 5 cm liquefied sand erupted through the fissures onto the dry lake bed and formed sandblow cone deposits these deposits range from low angle conical structures 30 to 50 cm thick and 2 to 5 m in diameter to elongate deposits up to 35 m long sandblows associated with the april 1990 aftershock commonly reoccupied preexisting fissures but also formed new solitary vents sandblows developed during the march 1991 aftershock erupted only through preexisting vents sandblow vents reactivated in april 1990 contain sediment clasts of sandblow deposits formed in the october 1989 mainshock clasts of host sediment were also present in the sand dikes lamination in the sandblow cones and sand dikes shows that they were not formed in a single episode surface cones and feeder dikes composed of multiple laminated subunits represent the three generations of sandblows the subunits suggest that the cone deposits were formed by pulses of water and sediment expelled from the vent the pulses result from cyclic phases of local excess pore pressure and its release in the liquefied bed at depth the three generations of structures at soda lake formed six months to a year apart have distinct tonal and textural differences that may mimic liquefaction structures formed decades or centuries apart this study provides modern analogs for comparison to and interpretation of prehistoric liquefaction structures that are frequently partly eroded or poorly exposed

soft sediment deformation structures related to tectonomagmatic activity a case study from the borate bearing lacustrine deposits of early miocene bigadic basin nw turkey abstract this study documents soft sediment deformation structures in the lacustrine bigadic basin one of the early miocene terrestrial basins in the extensional tectonomagmatic province of northwestern anatolia the focus is on the upper borate unit of the basin fill succession which consists of sedimentary facies including massive conglomerates stratified sandstones siltstones organic rich claystones laminated limestones organic rich limestones marlstones borates and volcaniclastics their deposition including borates occurred in a deep lacustrine environment possible phases of lake shallowing are represented by stratified sandstones facies soft sediment deformation features include small scale folds formed by convolution with occasional basal decollement minor slumps load casts and related flame structures fragmented and mixed beds brecciated by pore water explusion shallow and deep rooted synsedimentary extensional faults with related neptunian dykes and large slump sheets of thick bed packages with recumbent folds these deformation features are interpreted to be of seismo tectonic and seismo volcanic origin related to syndepositional strike slip faulting and volcanic eruptions seismic tremors combined with the basin floor updoming by magma intrusions caused deep rooted normal faults and intra basinal slumps tens of metres thick the study may serve as a guide to similar deformation structures in the underlying part of the bigadic lake fill succession and in the other neogene basins of northwestern anatolia which shared the region s seismo tectonic magmatic palaeogeographic and sedimentation history

new sedimentary structures in seismites from sw tanzania evaluating gas vs water escape mechanisms of soft sediment deformation seismite horizons are abundant in cretaceous sandstones of the rukwa rift basin southwestern tanzania diverse morphologies of soft sediment deformation are preserved including two new unusual sedimentary structures herein referred to as 1 balloon shaped inflation structures and 2 surface fractures with linked sandstone splays this original description of new sedimentary structures contributes to the growing catalogue of seismically induced deformation features their unusual morphologies bring to the forefront an important though seldom touched upon question of how to differentiate between gas and water escape in soft sediment deformation features the recognition of the spectrum of soft sediment deformation structures contained in strata and their deformational mechanisms is important because it permits the differentiation between triggering mechanisms particularly seismic activity and can constrain such events spatially and temporally we interpret the surface fractures and linked sandstone splays to reflect a high gas effusion rate formed by the release of high pressure gas followed by a limited expulsion of water the balloon shaped inflation structures reflect lower gas effusion rates due to expulsion of lower pressure gas that did not breach the cretaceous surface seal when these gas pulses did breach the paleosurface they formed gas discharge pits these seismogenic structures are consistent with deposition of cretaceous strata in the rukwa rift during periods of active carbonatite volcanism seismicity and possibly hot spring activity this documentation serves as an important data point for the re examination of the classification scheme of soft sediment deformation structures as primarily water escape structures to accommodate for the genesis of some secondary sedimentary features by gas escape

use of liquefaction induced features for paleoseismic analysis an overview of how seismic liquefaction features can be distinguished from other features and how their regional distribution and properties of source sediment can be used to infer the location and strength of holocene paleo earthquakes abstract liquefaction features can be used in many field settings to estimate the recurrence interval and magnitude of strong earthquakes through much of the holocene these features include dikes craters vented sand sills and laterally spreading landslides the relatively high seismic shaking level required for their formation makes them particularly valuable as records of strong paleo earthquakes this state of the art summary for using liquefaction induced features for paleoseismic interpretation and analysis takes into account both geological and geotechnical engineering perspectives the driving mechanism for formation of the features is primarily the increased pore water pressure associated with liquefaction of sand rich sediment the role of this mechanism is often supplemented greatly by the direct action of seismic shaking at the ground surface which strains and breaks the clay rich cap that lies immediately above the sediment that liquefied discussed in the text are the processes involved in formation of the features as well as their morphology and characteristics in field settings whether liquefaction occurs is controlled mainly by sediment grain size sediment packing depth to the water table and strength and duration of seismic shaking formation of recognizable features in the field generally requires a low permeability cap above the sediment that liquefied field manifestations are controlled largely by the severity of liquefaction and the thickness and properties of the low permeability cap criteria are presented for determining whether observed sediment deformation in the field originated by seismically induced liquefaction these criteria have been developed mainly by observing historic effects of liquefaction in varied field settings the most important criterion is that a seismic liquefaction origin requires widespread regional development of features around a core area where the effects are most severe in addition the features must have a morphology that is consistent with a very sudden application of a large hydraulic force this article discusses case studies in widely separated and different geological settings coastal south carolina the new madrid seismic zone the wabash valley seismic zone and coastal washington state these studies encompass most of the range of settings and the types of liquefaction induced features likely to be encountered anywhere the case studies describe the observed features and the logic for assigning a seismic liquefaction origin to them also discussed are some types of sediment deformations that can be misinterpreted as having a seismic origin two independent methods for estimating prehistoric magnitude are discussed briefly one method is based on determination of the maximum distance from the epicenter over which liquefaction induced effects have formed the other method is based on use of geotechnical engineering techniques at sites of marginal liquefaction in order to bracket the peak accelerations as a function of epicentral distance these accelerations can then be compared with predictions from seismological models

imaging underwater neotectonic structures in the amazonian lowland previous documentation has proposed tectonic activity from the neogene to holocene as one important control on drainage development in the amazonian lowland however recording tectonic structures in this region has been challenging due to environmental difficulties including the low topography and dense vegetation cover that do not favor natural exposures for this reason the role of tectonics in determining river dynamics morphology and sediment deposition in amazonia has been suggested with caution despite limitations morphostructural lineaments have provided useful information to support fault reactivation in several areas of the amazonian lowland however further documentation is required to map the faults and describe their geometry this approach is essential to better understand the geotectonic model of this region in this work analyses of high resolution optical imagery of three amazonian shallow water lakes provided exceptional views of an abundance of linear features on the beds of the

neotectonics in the south american passive margin evidence of late quaternary uplifting in the northern paraiba basin ne brazil abstract the relief evolution of several areas of northeastern brazil has been increasingly related to tectonic events this is the case for the paraiba basin where an abundance of faults and folds were recorded in neogene and even late pleistocene holocene deposits we tested whether dome like morphologies in the northern sector of this basin where geological exposures are scarce were also formed by tectonic deformation the work combined limited geological data with qualitative and quantitative analyses of the relief applying the 1 arc second digital elevation model provided by the shuttle radar topography mission the geomorphic indices of basin asymmetry factor af swath topographic profiles enhanced transverse hypsometry index thi and normalized river long profiles were used for validating a neotectonic origin for the dome like morphologies this interpretation was also supported by other morphological evidence of the dome relief including recurving channels featured in radial to recurved trellis patterns tectonically controlled drainage sub basins high relative relief values related to increased fluvial incision and anomalous river long profiles indicative of ungraded rivers the domic structures were attributed to fault and fold related strike slip deformation during the late quaternary this record supports the proposal that the south american passive margin remained under tectonic stress long after the main rifting in the late jurassic early cretaceous

new geological framework for western amazonia brazil and implications for biogeography and evolution abstract although many of the current hypotheses to explain the origin and distribution of the amazon biodiversity has been based directly or indirectly on geological data the reconstruction of the geological history of the amazon region is still inadequate to analyze its relationship with the biodiversity this work has the main goal to characterize the sedimentary successions formed in the brazilian amazon in the neogene quaternary discussing the evolution of the depositional systems through time and analyzing their main controlling mechanisms in order to fill up this gap radar image interpretation sedimentological studies and radiocarbon dating allowed the mapping of plio pleistocene to holocene units along the solimoes amazonas river brazil this integrated work led to the characterization of five sedimentary successions overlying miocene deposits of the solimoes pebas formation which include the following ica formation plio pleistocene deposits q1 37 400 43 700 14c yr b p deposits q2 27 200 14c yr b p deposits q3 6730 2480 14c yr b p and deposits q4 280 130 14c yr b p these deposits occur mostly to the west of manaus forming nw se elongated belts that are progressively younger from sw to ne indicating a subsiding basin with a depocenter that migrated to the ne the reconstruction of the depositional history is consistent with significant changes in the landscapes hence the closure of a large lake system at the end of the miocene gave rise to the development of a plio pleistocene fluvial system this was yet very distinct from the modern drainage with shallow energetic highly migrating braided to anastomosed channels having an overall northeast outlet this fluvial system formed probably under climatic conditions relatively drier than today s during the early pleistocene there was pronounced erosion followed by a renewed depositional phase ca 40 000 14c yr b p with the development of prograding lobes and or crevasse splays associated with a lake system i e fan delta and or fluvial flood plain areas after a period of erosion a fluvial system with eastward draining channels started to develop at around 27 000 14c yr b p the fluvial channels were overflooded in mid holocene time this flooding is attributed to an increased period of humidity with a peak between 5000 and 2500 14c yr b p the data presented herein support that rather than being a monotonous area the amazonia was a place with frequent changes in landscape throughout the neogene quaternary probably as a result of climatic and tectonic factors we hypothesize that these changes in the physical environment stressed the biota resulting in speciation and thus had a great impact on modern biodiversity

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

formation of segmented normal faults a 3 d perspective the interpretation of fault kinematics from geometric data is an essential step in developing an understanding of the growth of fault systems constraints on fault geometry are however often restricted to 2 d maps or cross sections in this article we consider the extent to which kinematic interpretations of faulting benefit from a 3 d rather than 2 d geometrical perspective concentrating on relay zones and segmented normal fault arrays we suggest that very different interpretations of their evolution arise from the recognition that the propagation directions of faults and fault segments will rarely be contained within the inspection plane of 2 d data a 3 d perspective favours an interpretation in which the segments of a fault array are kinematically interrelated from their initiation individual segments in such systems may link into a single fault surface out of the plane of inspection or may be unconnected in 3 d we argue that this interpretation which conflicts with the often suggested model of incidental overlap of originally isolated faults should be the preferred model for the generation and growth of segmented normal fault arrays