a middle cambrian trilobite faunule from the meguma group of nova scotia the meguma group of southern nova scotia is a thick succession of mostly deep water siliciclastic sedimentray rocks of uncertain age previous fossil finds have been in the halifax formation of the upper part of the sequence and have provided early ordovician ages a newly discovered trilobite bearing bed from the underlying goldenville formation yields middle cambrian taxa of acado baltic affinity specimens belonging to paradoxides s l agraulos dorypyge and ellipsocephalidae indicate that the meguma group is an exotic succession with faunal similarity to the adjacent avalon terrane and to middle cambrian successions in europe the middle east and west africa

petrology and geochemistry of neoproterozoic volcanic arc terranes beneath the atlantic coastal plain savannah river site south carolina the piedmont of south carolina and georgia is a complex mosaic of exotic terranes of uncertain provenance farther south and east these terranes form the basement beneath several kilometers of cretaceous and cenozoic sedimentary rocks commonly referred to as the atlantic coastal plain the distribution and geologic history of this hidden crystalline basement can be inferred only on the basis of limited exposures at the margins of the coastal plain onlap aeromagnetic lineaments that define basement trends in the subsurface and core data from wells that penetrate basement during the past 40 years basement cores aggregating more than 6 miles 10 000 m have been recovered from 57 deep wells at the department of energy s savannah river site these cores provide the only known samples of basement terranes that lie southeast of the fall line in central south carolina cores from the 57 deep wells along with structural trends defined by aeromagnetic lineaments allow us to define four distinct units within the basement beneath the coastal plain 1 the crackerneck metavolcanic complex greenstones and felsic

an integrated model of extrusive sand injectites in cohesionless sediments clastic injection and surface expression of subsurface sediment remobilization is a phenomenon which is becoming increasingly recognized however understanding of the physical mechanisms that control these features remains limited dominated by inference from outcrop and seismic studies here this limitation is addressed through a set of experiments focused on the development and evolution of fluidization features in non cohesive bedded sequences fluidization and the onset of piping are shown to occur progressively through a sequence of discrete phases with initial void formation development of infiltration horizons rupture and finally pipe formation critically the style of piping the stability of piping and the temporal evolution of venting are shown to exhibit considerable variability in particular pipes may either be stable or very mobile migrating laterally over large distances these produce deposits that are typically interpreted in outcrop as being the product of en masse liquefaction rather than localized dynamic fluidization these differing elements are synthesized to produce a model of sand extrudites in addition the implications of this model are explored

wind tunnel evaluation of a wedge shaped aeolian sediment trap abstract a detailed set of tests in a wind tunnel investigated the characteristics of flow and sampling efficiency of a low cost sediment trap that can be used in wind tunnels and field applications the trap is constructed of thin sheet aluminum and has a wedge shape 32 internal inlet angle with a 20 500 mm rectangular inlet orifice that extends 40 mm beyond the wedge form relatively unimpeded airflow through the trap is achieved by the large exit area 130 500 mm which is covered with fine stainless steel mesh 62 5 m openings 60 porosity and collected all but the finer silt sediment sizes despite its angular shape the trap has good characteristics of flow and a very high sampling efficiency 90 over a wide range of wind velocities because of its near isokinetic characteristics of flow results also indicate that this trap and others that have wide side profiles are very sensitive to incident wind angle incident angles 5 significantly reduce the sampling efficiency and promote scour around the trap inlet

palaeogeographical controls on the cambrian trilobite immigration and evolutionary patterns reported in the western gondwana margin abstract southward drifting of the western gondwanan margin during the cambrian has been demonstrated by means of both palaeomagnetic methods and lithological indicators of climate such as carbonates and evaporites recent improvements in biostratigraphical correlations permit an enhanced understanding of the climatic and palaeobiogeographical constraints that controlled the distribution of cambrian benthic communities palaeogeographical and biogeographical reconstructions based on trilobites are reported in this paper in order to test interaction between migration speciation and extinction rates the variability of the documented biogeographical patterns is directly related to species diversity in which wider distribution coincides with transgressive trends and subsequent connection of neighbouring platforms early cambrian trilobite faunas show a high degree of both substrate control and endemicity although transgressions led to parallel shifts in faunal compositions by contrast mid cambrian trilobite faunas are relatively uniform across western gondwana and latest mid and late cambrian associations document influence of an increased similarity with asian trilobite faunas

experimental studies of the fluidization of layered sediments and the formation of fluid escape structures experiments demonstrate that fluid escape structures can be produced as a result of unstable fluidization behaviour where a lower base layer of granular material is inhibited from fluidizing by the presence of an overlying non fluidizing top layer before the base layer can fluidize the weight of the overlying material must be balanced and this is accomplished by base layer material pressing against the bottom surface of the confining top layer forming a static layer this static layer allows the top layer to lift away from the base layer which is then free to fluidize a water filled crack forms below the static layer and as this grows instability causes the static layer and top layer to bend and conical voids to form below the antiformal sections rupture occurs at the apex of the water void allowing the underlying water and fluidizing material to burst out through the top layer the fluidized base layer material then flows through the rupture until all of this material except that in the static layer is deposited above the previously overlying layer and a stable fluidization system results the top layer material is bent upwards around the rupture and the resulting pillar type escape structure is preserved if flow then ceases the vigour of the burst out is greatest when the base layer material has a grain size 15 of the top layer material if the base layer grain size is less than 8 of the top layer then base layer material will pass through the top layer pore spaces without forming an escape structure if cohesive material is present escape structures form when a layer of fine grained cohesive material overlies a layer of cohesionless material at low flow rates small pipes with scattered angular bends pierce the top layer and base layer material passes through them the base layer material is ejected on to the top layer and builds up around the mouth of each pipe to form constructional structures sand volcanoes this is in contrast to the cohesionless experiments where the weight of material being deposited on the top layer caused an ejecta filled depression to form around the rupture if flow then ceases both the pipes and the sand volcanoes are preserved at high flow rates where the base layer fluidizes the top cohesive layer becomes fragmented small fragments circulate within the fluidizing base layer and are preserved as floating clasts large fragments sink to the bottom of the fluidizing base layer erosion of the bottom surface of these larger fragments causes this surface to become convex downward the experimentally derived structures are similar to pillar type structures observed in the field and the processes described can be used to investigate the development of these structures fluidization experiments also demonstrate the genesis of dish structures and the cohesive behaviour can be applied to the deformation of these structures after initial formation

the carolina terrane in northwestern south carolina u s a late precambrian cambrian deformation and metamorphism in a peri gondwanan oceanic arc the carolina terrane comprises an exotic volcanic island arc in the hinterland of the southern appalachian orogen the western portions of the carolina terrane consist of zoned mafic ultramafic plutonic complexes intruded into a pile of basalts and basaltic andesites this sequence of rocks has been interpreted to represent an episode of intra arc rifting prior to regional metamorphism and deformation new u pb zircon ages from the mean crossroads complex in northwestern south carolina along the central piedmont suture confirm relative ages inferred from detailed mapping two foliated metadiorites yield u pb dates of 579 4 and 571 16 ma interpreted to be crystallization ages a foliated metaquartz diorite yields a u pb date of 538 5 ma interpreted to be a crystallization age an undeformed unmetamorpbosed diorite intruding these metamorphosed zoned complex intrusive rocks yields an age of 535 ma hence we believe that intra arc rifting and regional metamorphism and foliation development both occurred between 580 and 535 ma while petrographic and ar ar studies support subsequent middle to late paleozoic regional metamorphic overprint s or at least static recrystallization and or uplift through hornblende biotite muscovite blocking temperatures for ar the 535 ma undeformed unmetamorphosed intrusion suggests late precambrian early cambrian regional metamorphism and deformation was the event responsible for the regional metamorphic fabric in this area of the piedmont these observations contradict the idea that this metamorphism and fabric development are related to presumed early paleozoic accretion of the carolina arc to laurentia as well as correlations with middle ordovician fabric elements in the eastern piedmont instead this fabric is interpreted to record a changing plate kinematics e g migration of triple junction or change in relative motion vectors during semicontinuous diachronous development of an island arc on the gondwanide margin

clastic dykes in over consolidated tills evidence for subglacial hydrofracturing at killiney bay eastern ireland abstract a swarm of vertical gravel filled dykes up to 6 m high and several decimetres wide cut through an over consolidated till at killiney bay the dykes are rooted in a gravel layer and many display plumes of clastic debris ejected into the overlying sediments burst out structures such features have not previously been described these clastic dykes are interpreted as the infillings of hydrofractures which formed when water pressures in the basal gravel layer exceeded the overburden pressure and tensile shear strength of the capping till the burst out structures extend up to 7 m from the tops of the dykes and provide strong evidence for forceful upward flow evidence suggests that the hydrofractures formed subglacially probably during a minor re advance their presence in late devensian 26 13 ka bp tills with an irish sea provenance irish sea till may have important implications for the subglacial hydrology of the last irish sea ice sheet these hydrofractures cannot form in unconsolidated glacimarine sediment and their presence precludes a glacimarine origin for these deposits they greatly affect the geotechnical properties of irish sea tills in particular providing very permeable routes through otherwise impermeable layers with important consequences in situations elsewhere in the irish sea basin where they have been used as aquicludes in landfill and low level nuclear waste disposal sites

late quaternary sedimentation in the paraiba basin northeastern brazil landform sea level and tectonics in eastern south america passive margin abstract late quaternary deposits in the northeastern brazil have been scarcely investigated despite their relevance to the discussion of the post rift evolution of the south american passive margin within the context of landform sea level and tectonic deformation sedimentological stratigraphic and morphological characterization of these deposits referred as post barreiras sediments led to their distinction from underlying early middle miocene strata based on optically stimulated luminescence osl dating two sedimentary units pb1 and pb2 were recognized and related to the time intervals between 74 8 9 3 and 30 8 6 9 ka and 8 8 0 9 and 1 8 0 2 ka respectively unit pb1 consists of indurated sandstones and breccias either with massive bedding or complex types of soft sediment deformation structures generated by contemporaneous seismic activity unit pb2 is composed of massive sands or sands related to structures developed by dissipation of dunes the present work focusing on the post barreiras sediments discusses landform sea level and tectonics of the eastern south american passive margin during the latest quaternary non deposition and sub aerial exposure related to the tortonian worldwide low sea level combined with tectonic quiescence followed the miocene transgression tectonic deformation in the latest pleistocene created space to accommodate unit pb1 in downthrown faulted blocks and perhaps also synclines produced by strike slip deformation although deposition of this unit was simultaneous with the progressive fall in sea level that followed the last interglacial maximum punctuated rises combined with land subsidence led to marine deposition close to the modern coastline renewed subsidence in the holocene gave rise to accommodation of the post barreiras sediments most of unit pb2 was deposited during the holocene transgression but it is not composed of marine sediments which suggests either an insignificant rise in relative sea level or aeolian reworking of thin transgressive sands the data presented here lead to a review of the evolution of the south american passive margin based on assumptions of uniform sedimentation and undeformed planation surfaces over a wide coastal area of the northeastern brazil

deep in the heart of dixie pre alleghanian eclogite and hp granulite metamorphism in the carolina terrane south carolina usa the central part of the carolina terrane in western south carolina comprises a 30 to 40 km wide zone of high grade gneisses that are distinct from greenschist facies metavolcanic rocks of the carolina slate belt to the se and amphibolite facies metavolcanic and metaplutonic rocks of the charlotte belt to the nw this region termed the silverstreet domain is characterized by penetratively deformed felsic gneisses granitic gneisses and amphibolites mineral assemblages and textures suggest that these rocks formed under high pressure metamorphic conditions ranging from eclogite facies through high p granulite to upper amphibolite facies mafic rocks occur as amphibolite dykes as metre scale blocks of coarse grained garnet clinopyroxene amphibolite in felsic gneiss and as residual boulders in deeply weathered felsic gneiss inferred omphacite has been replaced by a vermicular symplectite of sodic plagioclase in diopside consistent with decompression at moderate to high temperatures and a change from eclogite to granulite facies con ditions all samples have been partially or wholly retrograded to amphibolite assemblages we infer the following p t t history 1 eclogite facies p t conditions at 1 4 gpa 650 730 c 2 high p granulite facies p t conditions at 1 2 1 5 gpa 700 800 c 3 retrograde amphibolite facies p t conditions at 0 9 1 2 gpa and 720 660 c this metamorphic evolution must predate intrusion of the 415 ma newberry granite and must postdate formation of the charlotte belt and slate belt arcs 620 to 550 ma comparison with other medium temperature eclogites and high pressure granulites suggests that these assemblages are most likely to form during collisional orogenesis eclogite and high p granulite facies metamorphism in the silverstreet domain may coincide with a 570 535 ma event documented in the western charlotte belt or to a late ordovician early silurian event the occurrence of these high p assemblages within the carolina terrane implies that prior to this event the western carolina terrane charlotte belt and the eastern carolina terrane carolina slate belt formed separate terranes the collisional event represented by these high pressure assemblages implies amalgamation of these formerly separate terranes into a single composite terrane prior to its accretion to laurentia

liquefaction resistance of undisturbed and reconstituted samples of a natural coarse sand from undrained cyclic triaxial tests the paper deals with an experimental study of the undrained cyclic behavior of a natural coarse sand and gravel deposit located in gioia tauro a town situated on the continental side of the messina strait in italy the study was conducted through cyclic undrained triaxial tests carried out on both undisturbed and reconstituted samples undisturbed samples were recovered by an in situ freezing technique and the sample quality was carefully assessed reconstituted samples were prepared by using two different reconstitution methods namely air pluviation ap and water sedimentation ws and tested under the same in situ initial relative density and effective overburden stress tests were carried out on both isotropically and anisotropically consolidated specimens the results obtained from this study provide direct evidence that cyclic liquefaction resistance obtained from water sedimented samples closely approximates that exhibited by undisturbed samples in both isotropically and anisotropically consolidated tests conversely ap leads to a marked underestimation since the investigated deposit is considered to have been formed by the marine water environment these results can be regarded as proof that ws closely replicates the in situ fabric of the investigated deposit allowing the substitution of the expensive undisturbed samples with their reconstituted counterparts anisotropically consolidated specimens respectively exhibit cyclic liquefaction or cyclic mobility depending on whether or not they are loaded under the shear stress reversal mode

paleoenvironmental and paleobiogeographic implications of a new ediacaran body fossil from the neoproterozoic carolina terrane stanly county north carolina new partial swartpuntiid from neoproterozoic age rocks of stanly county north carolina herein assigned to cf swartpuntia sp along with previously described pteridinium carolinaensis aspidella other metazoan trace fossils and previously reported radiometeric ages suggest nama assemblage type affinities for the carolina terrane the new specimen cf swartpuntia sp and associated radiometric ages add further information pertaining to proposed geographic linkages between the carolina terrane and the avalon terrane this new swartpuntiid may be evolutionarily convergent in terms of habitat preference to the infaunal or partially infaunal habitat preferred by other members of the nama type ediacaran biota such as pteridinium and rangea

the unsteady post rift stage of the south american passive margin based on the tectono sedimentary evolution of the onshore paraiba basin ne brazil abstract the post rift tectono sedimentary history of passive margins has been an issue of increased interest after the perception of their unsteady nature during the neogene and quaternary the evolution of the eastern south america margin might be benefited from investigations of the sedimentary record in a number of marginal basins the paraiba basin is of particular interest to discuss the post rift evolution of the south american passive margin because it represents the last bridge with the african plate this work aims to analyze the post rift sedimentary record of the onshore paraiba basin as a contribution to discuss the neotectonic history of the south american passive margin surface and subsurface data were integrated from outcrops deep stratigraphic profiles airborne geophysical maps and remote sensing products the depositional and denudational processes in this basin were a result of tectonic subsidence and uplifting tectonics after the main rifting phase are indicated by abundant structures including normal reverse and strike slip faults as well as folds that affected the neogene and late pleistocene sedimentary deposits the ductile and brittle deformation resulted mainly from multiple reactivations of e w ne sw and nw se trending basement shear zones the deformation mechanism included distension and compression under a strike slip regime tectonic reactivations even during the late pleistocene support an unsteady south atlantic passive continental margin throughout the post rifting stage

quaternary fault control on the coastal sedimentation and morphology of the sao francisco coastal plain brazil abstract the role of neotectonic faulting in shaping topography and controlling sediment deposition has been increasingly documented along the stable continental margin of south america but the level of the present day tectonic stability of this margin is still a matter of debate this paper presents an investigation of the effects of quaternary fault reactivation on the sao francisco coastal plain sfcp this feature is a 56 km long progradational coastal plain located in the sergipe alagoas basin along the continental margin of brazil the sfcp is bounded on the west by a system of normal faults striking n s to ne sw the horst that bounds this plain is capped by the miocene barreiras formation and quaternary debris flow and fluvial deposits whereas the graben is filled with braided stream deposits and sandy beach ridge sediments the faulting contributed to the generation of accommodation space for the deposition of coastal sediments on the plain these processes started with the reactivation of cretaceous faults during the miocene during the quaternary fault reactivation and associated soft sediment deformation occurred between 82 and 8 3 ka with minor pulses between 1700 and 60 cal yr bp several faults along this margin are tectonically active and may represent the onshore continuation of gravitational collapses that have been documented offshore along the continental shelf and slope

neogene quaternary fault reactivation influences coastal basin sedimentation and landform in the continental margin of ne brazil we investigate the role of reactivation of precambrian basement fabric in the tectono sedimentary and geomorphological evolution of the paraiba basin continental margin of northeastern brazil during the cretaceous neogene and quaternary this basin represents part of the last bridge between south america and africa before the last breakup stage of the south atlantic rifting in the early cretaceous the paraiba basin infill is composed of siliciclastic and carbonate cretaceous units as well as aeolian fluvial and marine quaternary units we used shuttle radar imagery aeromagnetic wellbore and field data the reduced to the pole magnetic map rtp indicates the continuity of the steeply dipping precambrian basement shear zones beneath the paraiba basin the combined analysis of surface and subsurface data shows that ne sw and e w striking shear zones were subjected to brittle reactivation in the aptian middle albian during the basin opening and again in the neogene quaternary forming a system of horsts and grabens along the basin some of these structures such as the e w oriented pernambuco shear zone present modern day seismicity n s and mainly nw se striking transfer faults cut across aptian middle albian to neogene quaternary strata these four main fault directions control main river channels and alluvial valleys up to 2 km wide topographic breaks up to 50 m were created by late reactivation of rift faults which mark the boundary between horsts and grabens along the basin in addition structural data evidence syn tectonic faulting with vertical offsets up to 80 m in the cretaceous and up to 70 m in the neogene quaternary we conclude that shear zones across the study area are long lived structures that have behaved as weakness zones their neotectonic brittle reactivation has controlled sediment deposition and landform development which continued through the neogene quaternary

nd isotopic evidence for juvenile crust in the carolina terrane southern appalachians nd isotopic analyses of whole rock samples from the older portion of the carolina terrane one of the largest terranes in the appalachian orogen demonstrate that part of this terrane is composed of juvenile mantle derived crust these data suggest that the terrane may not have originally been built upon old evolved basement material but rather may have been built upon oceanic crust a recent study by other workers demonstrates a more crustally evolved nd isotopic signature for younger components of the carolina terrane these data may indicate that the terrane interacted with evolved crust at a later time possibly by amalgamation with a more evolved crustal fragment before final accretion to laurentia rather than indicating a primary old basement a juvenile nature for the older portion of the terrane contrasts with models that suggest it is an evolved crustal fragment that formed in a continental margin setting a scenario proposed to explain the high proportion of felsic volcanic rocks within the terrane it is herein suggested that carolina is a chemically evolved but isotopically juvenile crustal fragment because it remained in an oceanic setting for an unusually long time in this regard the carolina terrane is similar to some of the large accreted terranes in the canadian cordillera such as wrangellia and alexander the presence of juvenile crust in the carolina terrane documents that at least part of the southern appalachian orogen is not composed solely of reactivated pre existing continental crust the importance of this part of the orogen in terms of the volume of juvenile phanerozoic crustal material in north america may be larger than previously thought however until additional major appalachian terranes have been isotopically characterized the volume of juvenile crust in the whole orogen remains unknown the isotopic make up of a terrane can be an important aspect of terrane analysis as different terranes may have significantly different isotopic compositions while even widespread pieces of a single terrane should have very similar isotopic characteristics the nd isotopic data for the carolina terrane form the beginning of an isotope database for terranes in the southern appalachians

an experimental study of multiple grain size ejecta produced by collisions of saltating grains with a flat bed collision data are presented from coloured high speed films of three size fractions of sand grains saltating over a bed of the total grain population each fraction was colour tagged and the proportion of each size ejected by grains colliding with the surface was recorded on a number of films taken as the bed was progressively eroded the results confirm earlier findings that v3 v1 0 5 0 6 vn v1 08 and the rebound angle increases with decreasing grain size ejected grains are examined in relation to their size the impactor size ejection speed and angle and the number of ejecta per collision in addition changes in grain parameters are observed with time for fine impactors ejection speeds generally increase with a decrease in ejecta size but the fine fraction does not follow this trend for the coarse and medium impactors ejection angles are typically between 40 and 60 with coarse grains having shallower mean angles than fine ejecta the number of ejections per collision increases with a decrease in particle size for each impactor size the general tendency for coarse particles to be ejected at lower speeds and shallower angles than fine particles will lead to sorting of the grain sizes there is poor correlation between the forward momentum loss of the saltating grams at collision and both the forward momentum of the ejected grains and the number of ejected grains much of the forward momentum of the saltating grains is transfered to creeping grains the composition and geometry of the bed are considered to be important factors in the evolution of the saltation cloud

late pleistocene marine terrace deposits in northeastern brazil sea level change and tectonic implications abstract coastal areas of passive margins are among the best places to examine the reality of sea level changes elevation of marine terraces is central to interpretation of their approximate age in this kind of tectonic setting the recognition of pleistocene shorelines on the south american eastern continental margin is becoming increasingly common but data are commonly imprecise in both time and space and the resulting chronology is based mainly on geomorphological attributes nine thermoluminescence dates and four optically stimulated luminescence dates of 220 206 ka and 117 110 ka were obtained for two marine terrace deposits along 340 km of coast in rio grande do norte state northeastern brazil they are correlated with the highstands of marine oxygen isotope substages 7c and 5c sea level respectively the older deposit occurs mainly on the n s trending coast and ranges in elevation between 7 5 and 1 3 m the latter is found along the e w trending coast at altitudes that vary between 1 m and 20 m it indicates relative downfaulting of the 220 206 ka marine terrace and uplift of the 117 110 ka marine deposit which is locally about 12 m higher than deposits of similar age described 1000 km to the south it follows that elevation alone is an unreliable tool for establishing a quaternary sea level change chronology also on passive margin coastal areas

earthquake induced structures in young sediments abstract soft sediment deformational structures have been identified in several plio quaternary horizons near burdur in southwest turkey these horizons satisfy criteria for correlating such structures with seismic events and it is proposed that the structures were formed by earthquake induced liquefaction the deformational structures are thus interpreted to represent seismic events which occurred up to 2 3 ma ago

sediment deformation in miocene and post miocene strata northeastern brazil evidence for paleoseismicity in a passive margin abstract stratigraphic intervals characterized by varied and complex styles of soft sediment deformation structures are well preserved in miocene and late pleistocene to holocene deposits of a sedimentary basin located in northeastern brazil the miocene strata represented by the barreiras formation record only brittle structures including numerous faults and fractures with straight and high angle dipping planes that are often filled with sands derived from overlying beds folds consisting of broad anticlines and synclines are also present in this unit the late pleistocene to holocene deposits named post barreiras sediments contain an indurated sandy package with a large variety of ductile and brittle deformation structures i e massive sandstones with isolated sand fragments and breccias undulatory strata sand dykes and diapirs sinks and bowls pebbly pockets plunged sediment mixtures fitted sand masses cone shaped cracks fault grading and sedimentary enclaves these features confined to sharp based stratigraphic horizons that progressively grade downward into undisturbed deposits are related to seismic shocks of high surface wave magnitude i e ms 5 or 6 amalgamated seismites suggest that previously formed seismites were affected by subsequent seismic wave propagation seismic waves caused by activity along one or most likely several tectonic structures would have propagated throughout the depositional environment producing laterally extensive seismites the close proximity to earthquake epicenters would have promoted pervasive re sedimentation due to pore overpressure resulting high volumes of massive sandstones and breccia the similarity between deposits with correlatable strata from many other areas along the brazilian coast allows raise the hypothesis that the seismic episodes might have affected sedimentation patterns in a large i e extension of several hundreds of kilometers geographic area thus the modern seismicity recorded along northeastern brazil was recurrent during the quaternary and perhaps also in the pliocene the estimated high magnitude of the seismic events and the great regional extent of the affected area demonstrate that the brazilian coast experienced tectonic stress through the last geological episodes of its evolution which would have favored sediment accumulation and penecontemporaneous re sedimentation this geological context is unexpected in a passive margin inducing to revisit the debate on how active is a passive margin

paleo earthquakes in passive margin settings an example from the paleocene of the golfo san jorge basin argentina abstract paleocene sedimentary rocks in the golfo san jorge basin include the marine salamanca formation and the continental rio chico formation both units contain soft sediment deformation features and evidence of contemporary tectonics which include 1 sediment filled fissures hosted in muddy marine sediments of the salamanca formation fragmentosa section where the sandy infill of the fissures took place from above 2 synsedimentary normal faults in the uppermost levels of the salamanca formation with vertical throws rarely exceeding 1 m 3 fault graded beds in the banco negro inferior marine continental transition which show a deformed sequence with small scale normal faults at the bottom and intraformational breccias on top and 4 liquefaction and or fluidization pillars v or funnel shaped with vertical extension of up to 5 m and preserved into fluvial channels of the rio chico formation deformed strata are bounded by undisturbed horizons and some of these features can be correlated along 60 km of exposures the suite of soft sediment deformation structures is considered a secondary evidence of synsedimentary paleo earthquakes seismites in this portion of the south american passive margin this work shows new evidence of syndepositional tectonic activity in the lowermost paleogene of the golfo san jorge basin

effect of penetration rate on cone penetration resistance in saturated clayey soils in this paper the effects of penetration rate on cone resistance in saturated clayey soils are investigated shear strength rate effects in clayey soils are related to two physical processes the increase of shear strength with increasing rate of loading and the increase of shear strength as the process transitions from undrained to drained special focus is placed on this second effect cone penetration tests were performed at various penetration rates both in the field and in a calibration chamber and the resulting data were analyzed the field cone penetration tests were performed at two test sites with fairly homogeneous clayey silt and silty clay layers located below the groundwater table additionally tests with both cone and flat tip penetrometers in sand clay mixtures were performed in a calibration chamber to investigate the change in drainage conditions from undrained to partially drained and from partially drained to fully drained a series of flexible wall permeameter tests were conducted in the laboratory for various clayey sand mixtures prepared at various mixing ratios in order to obtain values of the coefficient of consolidation which is required to estimate the penetration rates below which penetration is drained and above which penetration is undrained a correlation between cone resistance and drainage conditions was established based on the results of the calibration chamber and field penetration tests

earthquake imprints on a lacustrine deltaic system the kurk delta along the east anatolian fault turkey deltas contain sedimentary records that are not only indicative of water level changes but also particularly sensitive to earthquake shaking typically resulting in soft sediment deformation structures the kurk lacustrine delta lies at the south western extremity of lake hazar in eastern turkey and is adjacent to the seismogenic east anatolian fault which has generated earthquakes of magnitude 7 this paper reevaluates water level changes and earthquake shaking that have affected the kurk delta combining geophysical data seismic reflection profiles and side scan sonar remote sensing images historical data onland outcrops and offshore coring the history of water level changes provides a temporal framework for the depositional record in addition to the common soft sediment deformation documented previously onland outcrops reveal a record of deformation fracturing tilt and clastic dykes linked to large earthquake induced liquefactions and lateral spreading the recurrent liquefaction structures can be used to obtain a palaeoseismological record five event horizons were identified that could be linked to historical earthquakes occurring in the last 1000 years along the east anatolian fault sedimentary cores sampling the most recent subaqueous sedimentation revealed the occurrence of another type of earthquake indicator based on radionuclide dating 137cs and 210pb two major sedimentary events were attributed to the ad 1874 1875 east anatolian fault earthquake sequence their sedimentological characteristics were determined by x ray imagery x ray diffraction loss on ignition grain size distribution and geophysical measurements the events are interpreted to be hyperpycnal deposits linked to post seismic sediment reworking of earthquake triggered landslides this article is protected by copyright all rights reserved

understanding wind blown sand six vexations abstract the study of aeolian geomorphological systems over the last half century has advanced along several important fronts supported by developments in technologies and analytic methods and the evolution of modeling approaches remote sensing has led to a wealth of knowledge concerning the distribution and dynamics of dunes on earth and elsewhere and wind tunnels have elucidated the roles of aeolian processes in reshaping surfaces improvements in laboratory and field instrumentation allow measurement of aeolian sand transport systems at levels of detail unimaginable when the binghamton geomorphology symposium began we have seen for example the advent of large sophisticated field campaigns and advanced modeling approaches using cellular automata and computational fluid dynamics methods select avenues of development especially concerned with depositional environments are briefly summarized advances in many fields have not been matched with proportional advances in our ability to predict rates of sand transport in natural environments one of the most fundamental challenges at least eight commonly cited sand transport rate models do not agree with each other and do not replicate field observations even under near ideal conditions this review focuses on select reasons why that might be so and categorizes those reasons into six principal theoretical and empirical vexations that have made sand transport an intractable problem predicting rates of transport characterizing grain size characterizing fluid and sand densities estimating shear velocity predicting the threshold of motion including the effects of sand moisture content and understanding granular electrification the examination of potential sources of error in the rate of transport and threshold of motion models leads to a point by point consideration of our current assumptions and protocols or lack thereof the objective is to help us identify the hard targets and the soft targets for future research

influence of non plastic fine on static iquefaction and undrained monotonic behavior of sandy gravel abstract many geological hazards such as landslide liquefaction slope failure and rockfall occur in mixed gravelly alluvium or colluvium deposits highlighting the importance of studying gravel sand silt mixtures although many natural strata are built using these mixtures they are not entirely understood a fundamental experimental study was designed to explore the influence of non plastic fine content on the undrained behavior of gravel sand silt mixtures as common geomaterials in nature undrained monotonic triaxial tests were carried out three types of sandy gravels with different sand to gravel ratios were selected as base gravels the impacts of the non plastic fine content on the stress strain behavior static liquefaction potential steady sate line residual strength and critical state friction angle were studied the laboratory results show that both sand to gravel ratio and non plastic fine content have significant impacts on the undrained response of gravelly mixtures it was observed that mixtures with zero non plastic fines content exhibit the non flow liquefaction behavior however adding silt content up to 45 shows the limited liquefaction or flow behavior depending on the base gravelly soils and fine content percentage a threshold for non plastic fine content was found to be 35 45 below this threshold the steady state line shifts downward as silt content increases and then shifts upward with further increase in the silt contents the identical trend was also noted for residual strength and critical state friction angle for silt contents below the threshold the equivalent intergranular void ratio concept modified with a new logical assumption was used to analyze the behavior of gravelly mixtures the results clearly indicate that the accurate value of equivalent intergranular void ratio can fully explain the behavior of sandy gravel fine mixtures similar to sand fine mixtures from a microstructure perspective both sand and silt content act as fine grains in gravelly mixtures and should be considered when studying the mechanical properties of theses mixtures

saltating particles over flat beds measurements of ejection and impact velocities trajectory lengths and maximum rise heights of sand grains median diameters 118 and 188 m in saltation over a flat sand bed in a wind tunnel have been obtained from the digitization of multiple image photo graphs the mean angle of ejection is found to be about 30 o from the horizontal rather than 90 o with mean vertical ejection velocity of about 2u where u is the friction velocity trajectories of saltating grains have been computed using the measurements of the initial ejection velocities and the mean velocity profile of the air flow

archeological and pedological evidence for large prehistoric earthquakes in the new madrid seismic zone central united states prehistoric liquefaction features have been identified by careful observation of their structural and stratigraphic relations to native american occupation horizons and their subtle soil characteristics the ages of these liquefaction features have been estimated from radiocarbon dating of wood associated with the features and native american artifacts found within bounding occupation horizons at three sites near blytheville arkansas in the central part of the new madrid seismic zone one sand blow crater formed between a d 800 and 1400 two sand blow deposits formed between a d 800 and 1670 and three possibly four sand dikes formed since 4035 b c where not found in association with native american occupation horizons and artifacts prehistoric liquefaction features can be difficult to distinguish from features that formed during the great new madrid earthquakes of a d 1811 and 1812 this raises the possibility that prehistoric liquefaction features may have been misinterpreted during previous studies in the area nevertheless a paleoearthquake chronology is beginning to emerge for the new madrid seismic zone our findings are consistent with paleoseismological studies in the northern part of the seismic zone and suggest a recurrence interval of hundreds of years for earthquakes large enough to induce liquefaction in this region m 6 4 by mapping the age distribution of liquefaction features a more accurate assessment of the long term earthquake potential of the region will be possible

3 d geometry and luminescence chronology of quaternary soft sediment deformation structures in gravels northeastern brazil abstract this paper reports and describes soft sediment deformation in gravels and gravelly sediments in quaternary alluvial deposits of the potiguar basin northeastern brazil deformation structures were measured in terms of geometry size and relationship with sedimentary bedding using geological mapping and ground penetrating radar tl and osl irsl methods following mar and sar protocols were used to date sediments and soft sediment deformation events our results indicate that soft sediment deformation structures are widely distributed in several stratigraphic intervals of alluvial channel deposits in a low lying topographic valley depending on their geometry and composition two types of soft sediment deformation structures occur pockets and dome like load structures these structures resulted from the shaking of sediments with a reverse density gradient system which caused collapse and realignment of pebbles these features are similar in morphology and size to modern examples of seismically induced soft sediment deformation in coarse sediments tl and osl ages indicate that sediment deposition and associated soft sediment deformation occurred at least six times from 352 ka to 9 ka

a comprehensive numerical model of steady state saltation comsalt 1 the blowing of sand by wind known as saltation ejects dust aerosols into the atmosphere creates sand dunes and erodes geological features we present a comprehensive numerical model of steady state saltation comsalt that in contrast to most previous studies can reproduce a wide range of measurements and can simulate saltation over mixed soils comsalt calculates the motion of saltating particles due to gravity fluid drag particle spin fluid shear and turbulence and explicitly accounts for the retardation of the wind due to drag from saltating particles furthermore we included a novel physically based parameterization of the ejection of surface particles by impacting saltating particles which matches experimental results comsalt is the first numerical saltation model to reproduce measurements of the wind shear velocity at the impact threshold i e the lowest shear velocity for which saltation is possible and of the aerodynamic roughness length in saltation it also reproduces a range of other saltation processes including profiles of the wind speed and particle mass flux and the size distribution of saltating particles as such comsalt is the first physically based numerical model to reproduce such a wide range of experimental data since we use a minimum of empirical relations comsalt can be easily adapted to study saltation under a variety of physical conditions such as saltation on other planets saltation under water and saltating snow

the role of precambrian mylonitic belts and present day stress field in the coseismic reactivation of the pernambuco lineament brazil abstract the pernambuco lineament is a steeply dipping continental scale ductile shear zone rooted within the precambrian lithosphere of intraplate northeastern brazil it was formed during the brasiliano orogeny 600 ma and reactivated during the pangea breakup in the cretaceous when it controlled fault propagation and sediment accumulation in several rift basins the region is now under an e w trending horizontal compression and n s trending extension and faulting occurs predominantly in a strike slip regime we investigated two aftershock sequences and the preexisting tectonic fabrics along the pernambuco lineament in order to evaluate the role of these fabrics in the coseismic reactivation of continental scale structures the lineaments consist of a main ene wsw trending mylonitic belt about 2 3 km wide and two secondary ne trending mylonitic belts about 100 m wide they both present steeply dipping mylonitic foliations and shallowing plunging stretching lineations the mylonites present granitoid protoliths and mineral parageneses that range from amphibolite to greenschist facies brittle deformation overprints the ductile fabric in all mylonitic belts in 1991 coseismic reactivation nucleated along the ene wsw striking 3 3 5 6 km deep normal fault of less than 1 km in length in the main mylonitic belt in 2002 seismicity migrated to a ne trending secondary mylonitic branch and moved as a right lateral strike slip 1 2 km long 3 8 4 9 km deep fault plane both fault segments reactivated the mylonitic foliation and form part of a major system we conclude that the interplay between the present day stress field and preexisting fabrics controls seismogenic fault location attitude and kinematics the pernambuco lineament is an example of a long lived continental scale structure where selective reactivation has occurred other shear zones in the region also show a long history of brittle reactivation and present similar orientation in relation to the present day stress axes they might be dormant structures prone for reactivation under the present day stress field

a landslide induced by the 2016 kumamoto earthquake adjacent to tectonic displacement generation mechanism and long term monitoring abstract the 2016 kumamoto earthquake which occurred in the central kyushu region of southwest japan caused numerous landslides mass movements from the events damaged many structures in the minami aso village residential areas we conducted geological and geophysical surveys and monitoring of landslides in one of these residential areas it was found that the landslide occurred directly adjacent to the earthquake s main surface fault ruptures while the landslide slip surface formed within a layer of hydrothermally altered rhyolite at about 15 m depth for the downslope side the slip surface for the upslope side formed within intact tephra layers due to the shallow dip of the rhyolite layer geophysical survey results show that fault ruptures in the tephra layers along with the tectonic faulting induce a decrease in soil strength it was inferred that the landslide head scarp and upper slip surface formed inside this weak soil long term monitoring of the landslide demonstrated that deformation continued for at least four months after the main slide although the initial and the major slide was activated by the earthquake the landslide did not immediately stabilize and continued to pose risks after the main event toward the mitigation for earthquake induced landslides post seismic monitoring as well as the relationship between surface fault traces and landslide blocks should be taken into consideration

soft sediment deformation structures in the lixian lacustrine sediments eastern tibetan plateau and implications for postglacial seismic activity abstract the eastern margin of the tibetan plateau is characterized by frequent earthquakes which are closely associated with tectonic activity to assess tectonic activity during the late pleistocene we studied a well exposed 23 m thick lacustrine sequence on the eastern margin of the plateau and found a variety of soft sediment deformation ssd structures distributed in 24 stratigraphic levels they comprise clastic dykes ball and pillow structures flame structures clastic gravels micro faults and slump folds most of the ssd structures indicate deformation mechanisms related to liquefaction and or fluidization processes most probably triggered by paleoseismic events given at least 4 historical earthquakes of m 7 in the study area most ssd structures in the lixian lacustrine sequence indicate seismic events with m 6 while simple flame structures point to some lower magnitude earthquakes osl dating indicates that the sequence accumulated between 15 8 and 6 0 ka giving a mean recurrence interval of 480 years for the 24 events and demonstrating that lacustrine sediments in eastern tibet have the potential to record a continuous seismic history on the centennial scale

effects of gravel content on shear resistance of gravelly soils abstract shallow landslides in colluvium which generally consists of wide particle gradation in a loose state occur in steep slope terrains to perform stability analyses shear strength parameters that represent soil constituents in situ stress state and shearing mode are needed this experimental study investigates the effects of gravel content on the shearing characteristics of gravelly soils based on the intergrain state concept a series of drained simple shear tests was performed on reconstituted specimens of gap and well graded sands with various gravel content levels the results reveal that 1 the shear strength of gravelly soils depends on the packing condition of dominant particles with the intergrain granular void ratio being a more representative parameter for the soil packing condition than the global void ratio 2 the drained shear strength of loose gravelly sand is dominated by sand matrix properties with the inclusion of gravel content reducing the strength by no more than 20 compared to that of pure sand 3 the strength parameters of sand like gravelly soils can be estimated from the sand matrix with proper reduction

a study of particle splash on developing ripple forms for two bed materials a custom designed particle tracking velocimetry ptv system was developed to measure particle splash dynamics in two materials mixed quartz sand and ground acrylic particles approximating the density of snow the strengths and limitations of the ptv system are described in the context of five experiments carried out at friction velocities slightly greater than the threshold friction velocity for particle entrainment and saltation analysis of particle collisions on the bed surface splash demonstrates that the simulated snow particles impact the surface at a smaller angle than quartz sand they also eject a greater number of particles though at lower velocities and angles than observed for the sand particles these relations appear to be highly sensitive to the porosity of the bed surface while particle shape and elasticity play a secondary role with regard to ptv measurements carried out along the wind aligned axis of migrating aeolian ripples particles ejected from the lee slope tend to be slightly larger than those on the stoss slope and in general are ejected with a lower speed and greater angle to the surface irrespective of the type of granular material when the average impact angle is close to or greater than the negative slope of the evolving bedform the particle ejection rate from the stoss slope was measured to be approximately twice that for the lee slope this empirical observation confirms the assumption made in models of ripple development that the ejection flux governs the bedform migration rate however systematic under prediction of this rate by an early model suggests that additional processes inclusive of surface creep must also be accounted for

late quaternary infilling of the assu river embayment and related sea level changes in ne brazil abstract a detailed geomorphological survey using light detection and ranging lidar was carried out along the western part of the assu river valley ne brazil the study was complemented by the investigation of sedimentological mineralogical and sediment benthic foraminifera indicators within the 14c geochronological framework the integration of data sets permitted the reconstruction of the main phases in the evolution of this area during the holocene the shallow embayment which is now completely infilled acquired its present form within the limits of antecedent morphology developed since the last interglacial period the main forcing factors responsible for repositioning the shoreline which ran along the strike slip afonso bezerra fault at an angle of approximately 35 to the present coast in the early mid holocene were as follows 1 tectonic activity along the strike slip afonso bezerra fault 2 fast inundation of the shallow paleo valley embayment during the last pulse of holocene transgression ca 8000 cal yr bp 3 advance of the assu river mouth through accretion of fluvial bay head delta and costal drift sediments and 4 sheltering of embayment by barrier islands which permitted a widespread development of mangrove forest during the last 3 millennia the estimated rate of progradation of the assu estuary that led to the present stage of terminal infilling is in the order of 3 4 m yr

influence of non low plastic fines on cone penetration and liquefaction resistance abstract uncertainties prevail at the current liquefaction screening method based on the cone penetration test cpt as to whether the existence of fines increases liquefaction resistance or decrease cone penetration resistance in this study field based data are used to evaluate the effects of non low plastic fines on liquefaction resistance at the current cpt based liquefaction assessment method the first part of this paper examines the effects of the coefficient of consolidation or drainage characteristics of soils containing fines on cone penetration resistance the coefficient of consolidation is influenced by the fines content and the relative density of the soil the second part of this paper investigates the contribution of fines content less than 30 by weight on the liquefaction resistance of soils at different relative densities fines content over 30 by weight and or high plasticity of fines can cause additional complications therefore it needs different valuation methods which is beyond the scope of this paper the liquefaction resistance of sands and silty sands is reinterpreted from the current cpt based liquefaction assessment method the trend which presents the change of liquefaction resistance with fines content at the same relative density is compared with the available laboratory based data in the literature the results show that the interpreted trend is not consistent with the laboratory based correlations obtained by several previous researchers therefore there will be probably some inaccuracies in estimation of liquefaction potential of silty sand using the current cpt based liquefaction assessment method

collisions of quartz grains with a sand bed the influence of incident angle the velocities with which grains were observed to emerge from a sand bed after an intersaltation collision at u 40 cm s 1 are reported for four bed attitudes from horizontal bed to adverse bed slope 15 the principal effect of bed angle is to alter the magnitude and direction of the ricochet velocity however emergent velocities of dislodged grains are consistent with reptation path lengths comparable to the length of the upwind face of ripples in the corresponding wind calculations of the loss of forward momentum at collision using the data for the range of bed attitudes studied suggest that creep is most vigorous on the sloping upwind face of the ripple and diminishes at the crest as a result the crest would be expected to accumulate the coarse material which moves predominantly by creep the saltations originating in ricochet from the sloping back of the ripple are more vigorous and more concentrated in plan than are those originating at the crest however the saltation path length is at least an order of magnitude greater than the ripple wavelength and the probability distribution of path lengths is quite dispersed consequently it is very unlikely that these spatial patterns of ricochet are preserved sufficiently distinctly in the saltation cloud and subsequent collision distribution to be the agent of ripple development this study therefore supports a view of moving grain interaction with the bed in which saltation provides the power to mobilize grains but ripple growth is associated with reptation and particularly with a pattern of impact which develops with the bed relief creep is more active on upwind facing slopes than at the crest which therefore is a zone of net creep grain deposition

liquefaction induced structures in quaternary alluvial gravels and gravelly sediments ne brazil abstract we have identified numerous well preserved elutriation and fluidization structures probably induced by liquefaction in quaternary gravels and gravelly sediments of braided fluvial channel deposits in the rio grande do norte and ceara states northeastern brazil they show evidence of upward directed water escape after sediment deposition and before sediment compaction among the several types of structures observed the most frequent are pillars pockets and dikes these structures range in width from a few centimeters to as much as 4 m and in height from 60 cm to 4 m dikes pillars and pockets are systematically associated clastic dikes vented large quantities of sand to the upper layers or the surface pebbles and cobbles from the host rock sank into the dikes and formed pillars and pockets pockets form the root part pillars form the intermediate part and dike the upper part of the composite structure the morphology of the structures in sectional and plan views indicates a 3d geometry composed of a tabular dike and pillar that present a downward continuous transition to a bowl shaped pocket this stratigraphy of liquefaction features is different from that usually presented in the current literature field data suggest that both the location and the geometry of the features were controlled by sedimentary properties rather than joints and small faults the size and abundance of these features suggest that they were formed by great events rather than localized mechanisms field evidence also indicates that these features are the product of fluidization and elutriation and may have been induced by liquefaction processes associated with seismic shaking a nonseismic origin related to elutriation processes however cannot be ruled out for some of the features

seismically induced clastic dikes as a potential approach for the estimation of the lower bound magnitude intensity of paleoearthquakes abstract we compiled a database that includes 36 sites wherein the injection and neptunian dikes associated with 16 instrumental seismic events were studied some information in the database was obtained from our field work in the epicentral area of the 2003 ms 7 5 chuya and the 1950 ms 7 mondy earthquakes the bounding relationships between the surface wave magnitude ms and maximum width w cd visible maximum height h cd and intensity index of clastic dikes i cd and local macroseismic intensity i l and the same three parameters were established as was hypothesized larger metrics of clastic dikes can be expected from earthquakes with higher magnitudes and macroseismic intensities the analysis of the obtained relationships showed that when estimating the lowest potential magnitude or local macroseismic intensity it is better to use all three parameters of clastic dikes and take the maximum level for seismic hazard evaluation this reduces the underestimation of the earthquake potential thus clastic dikes can be applied as a potential approach for a lower bound magnitude intensity estimation of paleoearthquakes which is particularly important in the construction of critical facilities this work should stimulate geologists to record the metrics of seismically induced clastic dikes to improve the equations proposed in the present paper

undrained shear strength of granular soils with different particle gradations a series of undrained tests were performed on granular soils consisting of sand and gravel with different particle gradations and different relative densities reconstituted in laboratory despite large differences in grading only a small difference was observed in undrained cyclic shear strength or liquefaction strength defined as the cyclic stress causing 5 double amplitude axial strain for specimens having the same relative density in a good contrast undrained monotonic shear strength defined at larger strains after undrained cyclic loading was at least eight times larger for well graded soils than poorly graded sand despite the same relative density this indicates that devastating failures with large postliquefaction soil strain are less likely to develop in well graded granular soils compared to poorly graded sands with the same relative density although they are almost equally liquefiable however if gravelly particles of well graded materials are crushable such as decomposed granite soils undrained monotonic strengths are considerably small and almost identical to or lower than that of poorly graded sands

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

u pb zircon ages and pb isotope geochemistry of gold deposits in the carolina slate belt of south carolina volcanic rocks of the persimmon fork formation host the largest known gold mines of the carolina slate belt u pb shrimp zircon ages have been obtained from rocks closely associated with pyrite enargite gold deposits at brewer quartz topaz rhyolite breccia from the argillic alteration zone in the brewer pit and felsic ash flow tuff from the quartz sericite alteration zone from the disseminated and semimassive pyrite gold deposits at haile crystal lithic rhyolitic ash flow tuffs from the champion pit and from the ridgeway deposit felsic ash flow tuff from the stratigraphic host of the north pit gold deposit generally the zircons are fine grained fractured and contain crystal imperfections corrosion inclusions and pits 206 pb 238 u zircon spot ages for all deposits span a wide range mostly from 400 to 760 ma inclusions and cores indicative of inherited domains in the zircons were not found and only a few analyses range from 1 1 to 1 8 ga a distinct xenocrystic zircon population was not identified the 206 pb 238 u weighted age averages of zircon indicate the following crystallization dates for the volcanic and volcaniclastic rocks closely associated with the gold deposits 550 3 ma for brewer 553 2 ma for haile and 556 2 ma for the ridgeway deposit these zircon crystallization ages represent close estimates of the age of the original gold mineralizing events younger zircon spot ages can be attributed to the effects of paleozoic regional metamorphism pb isotope compositions of sulfide minerals galena pyrite enargite sphalerite chalcopyrite and molybdenite and silicate minerals k feldspar and sericite in the gold deposits help to constrain the sources of fluids and metals during the mineralizing events the deposits are pyrite rich containing multiple generations of pyrite including early crystallized pyrite that is closely associated with the original gold mineralizing event as well as recrystallized pyrite formed in response to paleozoic metamorphism pb isotope compositions of pyrite span a wide range including the most radiogenic values for the sulfides galena and k feldspar are not abundant but where present they are typically the least radiogenic minerals galena has a limited range of pb isotope compositions that are representative of the gold deposits as a group 206 pb 204 pb 18 020 18 326 207 pb 204 pb 15 550 15 639 208 pb 204 pb 37 605 38 286 values of 207 pb 204 pb straddle the average crustal pb growth curve consistent with contributions involving the mantle and continental crust whole rock pb isotope compositions of volcanic and volcaniclastic rocks of the persimmon fork formation nearly match the range for sulfides in the gold deposits subtle regional contrasts in pb isotope compositions exist among the deposits sulfide minerals from barite hill e g galena 206 pb 204 pb 206 pb 204 pb 18 169 haile 206 pb 204 pb 18 233 and brewer 206 pb 204 pb 18 311 in northern south carolina because pb isotope compositions of basement rocks from grenville massifs in the southern appalachians and sulfide minerals from the gold deposits do not match a direct genetic connection cannot be established diversity in values of 206 pb 204 pb and the relatively high values of 207 pb 204 pb suggest that the deposits evolved adjacent to or closely related to continental blocks perhaps linked to a back arc tectonic setting among potential younger analogues of the slate belt gold deposits are the sulfide deposits of the okinawa trough in the western pacific mantle derived isotopic contributions were more important at barite hill in southern south carolina the least radiogenic among the deposits where oceanic crust had developed than at brewer haile and ridgeway in northern south carolina where rifting thinned the continental crust

boundary layer turbulence characteristics during aeolian saltation 1 a great deal of effort has been expended in measuring turbulence phenomena in clean air flows however no previous measurements have been successfully made of the vertical distributions of turbulence intensity and reynolds stress in a fully adjusted boundary layer flow saturated with saltating particles the present wind tunnel study addresses this knowledge gap using a custom designed laser doppler anemometer lda the amount of turbulence is found to increase with the introduction of saltating particles to the airflow over the lowest 15 of boundary layer vertical profiles of the streamwise wind speed provide friction velocities that lie well within the narrow range of those derived from direct measurement of the reynolds stress relative to clean air aeolian saltation is demonstrated to increase the magnitude but not the frequency of burst sweep events that primarily contribute to the total fluid stress within several millimeters above the bed surface all vertical profiles of wind speed converge upon a focal point as the local fluid stress declines toward the mobile bed

observations of collisions of saltating grains with a granular bed from high speed cine film high speed photography was used to record saltating sand grains colliding with a horizontal noncohesive bed of similarly sized grains impacting grain bed interaction is discussed in general the process as observed from the films is then described in terms of the apparent bed contact length abcl and various parameters of the impacting grains and any ejected grains examples are given of typical behaviour of bed grains in response to impacting grains of different sizes saltating grains that are large in comparison to the bed grains they encounter at collision can churn up the surface layers of soils and sediments so that previously buried grains become available for entrainment this process is discussed in relation to the potential release of dust particles into the airflow

northward extension of carolina slate belt stratigraphy and structure south central virginia results from geologic mapping geologic mapping in south central virginia demonstrates that the stratigraphy and structure of the carolina slate belt extend northward across a steep thermal gradient into upper amphibolite facies correlative gneiss and schist the neoproterozoic greenschist facies hyco aaron and virgilina formations were traced northward from their type localities near virgilina virginia along a simple upright northeast trending isoclinal syncline this syncline is called the dryburg syncline and is a northern extension of the more complex virgilina synclinorium progressively higher grade equivalents of the hyco and aaron formations were mapped northward along the axial trace of the refolded and westwardly overturned dryburg syncline through the keysville and green bay 7 5 minute quadrangles and across the northern end of the carolina slate belt as interpreted on previous geologic maps hyco rocks including felsic metatuff metawacke and amphibolite become gneisses upgrade with areas of local anatexis and the segregation of granitic melt into leucosomes with biotite selvages phyllite of the aaron formation becomes garnet bearing mica schist aaron formation rocks disconformably overlie the primarily felsic volcanic and volcaniclastic rocks of the hyco formation as evidenced by repeated truncation of internal contacts within the hyco on both limbs of the dryburg syncline at the aaron hyco contact east northeast trending isograds defined successively by the first appearance of garnet then kyanite staurolite in sufficiently aluminous rocks are superposed on the stratigraphic units and synclinal structure at moderate to high angles to strike the textural distinction between gneisses and identifiable sedimentary structures occurs near the kyanite staurolite in isograd development of the steep thermal gradient and regional penetrative fabric is interpreted to result from emplacement of the goochland terrane adjacent to the northern end of the slate belt during alleghanian orogenesis this mapping study indicates that the carolina slate belt does not terminate on the north against through going faults or rest on higher grade basement as previously suggested

residual strength of slip zones of large landslides in the three gorges area china abstract slip zones of the large landslides in the three gorges area are commonly composed of fine grained soils with substantial amount of coarse grained particles particularly gravel sized particles in this study residual strength of the soils from slip zones of these landslides were examined in relation to their index properties based on a survey of 170 landslides it was found that laboratory determined residual friction angle using gravel free fraction of the disturbed soils from the slip zones was closely related to clay content liquid limit and plasticity index on the other hand in situ residual friction angle of these soils i e including gravel fraction showed very weak correlations with clay content and atterberg limits but was largely dependent on gravel and fines clays silts contents increasing with gravels and decreasing with fines and displayed strong linear correlation with the ratio of gravel to fines contents these observations indicate that among the index properties clay content and atterberg limits can be used to estimate residual strength of the soils finer than 2 mm but they are not appropriate evaluate the residual strength of the soils containing considerable amount of gravel sized particles for the latter particle size distribution particularly the ratio of gravel to fines contents appears to be a useful index additionally it was found that there was no identifiable correlation between relative abundance of individual major clay minerals and residual friction angles of both gravel free fraction of disturbed and in situ soils suggesting that influence of clay minerals on residual strength of these soils can not be simply evaluated based on their abundance

structural analysis of the carolina inner piedmont terrane boundary implications for the age and kinematics of the central piedmont suture a terrane boundary that records paleozoic laurentia gondwana interactions new field mapping along the carolina inner piedmont terrane boundary in south carolina and eastern georgia reveals preaccretionary synaccretionary and postaccretionary faults the dextral strike slip lowndesville shear zone is adjacent to a 50 km long segment of the terrane boundary however the lowndesville shear zone is correlated eastward with the dextral strike slip beaver creek shear zone which is within the carolina terrane and predates 415 ma the lowndesville shear zone is overprinted by a dextral strike slip phyllonite zone named the deal creek shear zone the deal creek shear zone is correlated eastward with the gold hill silver hill shear zone which is also within the carolina terrane and records dextral strike slip motion between 400 and 325 ma the cross anchor and mulberry creek faults both truncate the lowndesville and the deal creek shear zones and form the terrane boundary the mulberry creek fault probably of triassic jurassic age juxtaposes the lowndesville shear zone adjacent to the carolina inner piedmont terrane boundary west of waterloo south carolina the cross anchor fault is the terrane boundary east of waterloo south carolina and forms the southeastern boundary of the whitmire reentrant crosscutting relationships indicate that the cross anchor fault is the oldest fault which juxtaposes the carolina and inner piedmont terranes in the study area these structural interpretations and available geochronological data indicate that the cross anchor fault is a 325 ma thrust fault and may be the central piedmont suture an early alleghanian suture resolves the problem of inserting the carolina terrane into the western iapetus ocean

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

geotechnical reconnaissance and liquefaction analyses of a liquefaction site with silty fine sand in southern taiwan article i nfo geotechnical reconnaissance of a recurrent liquefaction site at a quaternary alluvial deposit in southern taiwan was conducted to establish a comprehensive case history for liquefaction on silty fine sand with high fines content the liquefaction occurred at a silty fine sand layer with d50 0 09 mm and fines content greater than 35 and was triggered by a mw 6 4 earthquake on march 4 2010 which induced maximum horizontal acceleration up to 0 189 g at the site in situ subsurface characterizations including standard penetration test cone penetration test and shear wave velocity measurement were performed as well as cyclic simple shear tests on undisturbed specimens retrieved by a modified hydraulic piston sampler comparisons of cyclic re sistance ratios crrs indicate that cpt sounding with standard penetration rate could overestimate the re sistance ratio and drainage conditions during penetration should be considered for high fines content soil in the liquefaction analysis additionally variations of crrs from different in situ tests indicate that correlations among in situ tests and crr could be soil specific and precautions should be taken when using these curves on silty fine sands

experimental assessment of owen s second hypothesis on surface shear stress induced by a fluid during sediment saltation a widely used yet thus far unproven fluid dynamical hypothesis originally presented by p r owen 50years ago states that the surface shear stress induced by a fluid on the ground during equilibrium sediment saltation is constant and independent of the magnitude of the fluid velocity and consequently the particle mass flux this hypothesis is one of the key elements in almost all current model descriptions of sediment erosion we measured the surface shear stress in a drifting sand wind tunnel and found owen s hypothesis being merely an approximation of the real situation a significant decrease of the fluid stress with increasing wind velocities was measured for low to intermediate particle mass fluxes for high particle mass fluxes owen s hypothesis essentially holds although a slight increase of the fluid stress was measured

large earthquakes in the katun fault zone gorny altai paleoseismological and archaeoseismological evidence abstract paleoseismological and archaeoseismological research in the katun fault zone in gorny altai reveals soft sediment deformation structures ssds in late quaternary sediments that fill the yaloman graben ssds seismites were produced by large paleoearthquakes m 5 5 5 along the katun fault that occurred about 150 and 90 ka in the 38 19 and 19 12 5 ka intervals and after 12 5 ka the event after 12 5 ka within the graben had a magnitude of ms 7 2 7 6 traces of another event shaking intensity i v esi 2007 intensity scale timed in the range from the 3rd century bc to the 1st century ad were discovered during studies of a scythian necropolis at the chultukov log 1 site located within the manzherok graben in the northern end of the katun fault burial mounds near a mountain slope at the site are damaged by colluvium rocks of the same colluvium are scattered over 25 m off the slope and deform burial structures cairns and stone rings and inner stone walls of grave chambers as well as the primary anatomical position of buried bodies including those in burials not damaged by colluvium from outside thus the katun fault was an active structure generating large earthquakes from the middle pleistocene through the holocene

seismically induced soft sediment deformation structures revealed by x ray computed tomography of boring cores abstract x ray computed tomography ct allows us to visualize three dimensional structures hidden in boring cores nondestructively we applied medical x ray ct to cores containing seismically induced soft sediment deformation structures ssdss obtained from the kanto region of japan where the 2011 off the pacific coast of tohoku earthquake occurred the ct images obtained clearly revealed various types of the seismically induced ssdss embedded in the cores a propagating sand dyke bent complexly by the preexisting geological structure deformed laminations of fluidized sandy layers and two types of downward mass movement ductile downward folding and brittle normal faulting as compensation for upward sand transport through sand dykes two advanced image analysis techniques were applied to the sand dyke ct images for the first time the growcut algorithm a specific digital image segmentation technique that uses cellular automata was used successfully to extract the three dimensional complex sand dyke structures embedded in the sandy sediments which would have been difficult to achieve using a conventional image processing technique local autocorrelation image analysis was performed to detect the flow pattern aligned along the sand dykes objectively the results demonstrate that x ray ct coupled with advanced digital image analysis techniques is a promising approach to studying the seismically induced ssdss in boring cores

the 1986 1988 intraplate earthquake sequence near joao câmara northeast brazil evolution of seismicity abstract the 1986 1988 intraplate earthquake sequence near joao c mara 5 5 s 35 7 w has been among the most significant in northeast brazil this century some 14 000 events were recorded in the 18 months from august 1986 including fifteen above magnitude 4 0 and one of 5 1 4000 buildings were damaged a local network of four portable seismographs was operated during most of the period augmented by a nine station telemetric network between may 1987 and april 1988 the temporal and spatial distribution of this seismicity is examined and determination of unusually good hypocentres is made possible by the simple velocity structure good signal transmission and impulsive p and s arrivals on most seismograms activity has been closely confined to a 28 km linear zone with a strike of 040 except for some small events along a parallel zone displaced laterally by 12 km neither zone has been related to any surface feature some unusual characteristics have raised concern about possible future seismicity the largest event occurred four months after the onset of activity and after several weeks of relative quiescence a 5 km intermediate section of the inferred fault has so far experienced only a few very small events

liquefaction and flow failure during earthquakes two aspects of seismically induced liquefaction are discussed which are of vital engineering significance the triggering condition and the consequences of liquefaction the triggering condition is examined with respect to liquefaction analysis note being taken of the onset condition which is governed by cyclic strength consequences of liquefaction are discussed with respect to post seismic stability analysis in which the residual strength plays a major role procedures used for liquefaction analysis based on the results of in situ sounding tests are introduced and the applicability of this method for estimating associated ground settlements is discussed the evaluation of residual strength requires a better understanding of undrained sand behaviour results of extensive laboratory rests on japanese standard sand are examined and new index parameters are proposed to quantify undrained sand behaviour better the results of laboratory tests on silty sands are examined in the same way ah the results are

biogeographical significance of cambrian trilobites from the carolina slate belt abundant middle middle cambrian trilobites of the ptychagnostus atavus interval zone are described from the upper asbill pond formation informal name near batesburg south carolina the fauna containing at least nine species has strong affinities with cool water faunas of both armorica and baltica but little affinity with warm water shelf faunas of laurentia this is compatible with previous conclusions that the carolina slate belt is an exotic terrane that was accreted to north america during the early or middle paleozoic further evaluation however introduces an alternative possibility that the fauna could have lived in deep cool water environments along the periphery of laurentia and subsequent displacement need not necessarily have been great combined faunal and stratigraphic components of the carolina slate belt do not precisely match those of any known region but may be closest to those of bohemia although a southpolar location in proximity to armorica baltica and gondwana seems likely a definitive placement in a reconstruction of the cambrian world is not yet possible included in the trilobite fauna are the agnostoids hypagnostus mammillatus h parvifrons peronopsis fallax ptychagnostus sp and tomagnostus fissus the polymeroids include agraulos sp paradoxides cf polonicus paradoxides sp and skreiaspis sp