climatic periodicity during the late pleistocene from a loess paleosol sequence in northwest argentina abstract a 42 m thick loess paleosol sequence was studied in the pre andean intramountain valley of tafi del valle 100 km west of the city of san miguel de tucuman at an elevation of 2280 m asl in northwest argentina the sequence contains 28 paleosols alternating with loess layers the loess layers are coarse loamy and have large hexagonal polyhedra the soil layers are restricted to bt horizons having fine loamy textures prismatic structures and organo argillans on the structural surfaces surface a and eluvial e horizons are absent from the whole sequence soil truncation is unlikely as no remains of these horizons or erosional unconformities were identified the dated part of the sequence encompasses a time span of 10 080 years from 17 580 bp at 5 2 m depth to 27 660 bp at 42 3 m depth the base of the exposed sequence the youngest strata are probably missing either because of a depositional hiatus or because of post depositional erosion as dated paleosols in adjacent areas indicate that loess deposition continued during at least the early holocene the 20 bt c couplets identified in the dated sequence correspond to 20 climatic oscillations in 10 080 years thus every 500 years on average there was a climatic change from dry cool conditions with loess deposition to moist warm conditions favouring soil development this might have been related to recurrent northward shifts of the polar front accompanied by weakening of the mid latitude south pacific anticyclone similar short term periodicity has been identified in the ice cap of greenland and in tropical lake level records so such frequent climatic changes during the late pleistocene seem to have been global in character

dating the quaternary progress in luminescence dating of sediments abstract luminescence dating comprises a collection of numerical age techniques that are among the most significant chronological tools currently used in quaternary research this paper briefly reviews the key historical developments in luminescence dating from its roots in thermoluminescence dating of heated minerals to the development of optical dating methods for sunlight exposed sediments we describe the principles and practicalities of the various techniques commonly used in luminescence dating including multiple aliquot single aliquot and single grain procedures and we discuss some of the latest approaches to recognising and minimising potential errors in age estimation e g by means of component analysis and dose distribution methods in optical dating the overview also introduces the other papers in this special issue of quaternary science reviews which address a selection of important issues in basic research technique development and application of luminescence dating to critical questions in the geological and archaeological sciences illustrated with examples from around the world and the last million years of earth history

geochemical characterization correlation and optical dating of tephra in alluvial sequences of central western argentina the synthesis of paleoclimatic archives provided by loess and alluvial sequences of central argentina has been hindered by the lack of a cohesive lithostratigraphic framework extending across the chaco pampean plains and catchments of the rios desaguadero colorado and negro this condition originates in part from the dearth of absolute chronological controls the occurrence of discrete tephra layers across this region may provide an opportunity to address this deficiency if a tephrochronological framework can be established the potential of such a project is assessed within the context of a pilot study constrained within alluvial sequences of central western argentina proximal to potential source vents in the southern volcanic zone the intersite discrimination and correlation of tephra layers on a geochemical basis is examined with indirect chronological control for the eruption of each generated by optical dating alluvial sediments on either side of each of five tephra units at a type site were dated using the optically stimulated luminescence of fine silt sized quartz thus providing an age control on each tephra ca 24 000 30 000 32 000 39 000 and 48 000 yr the geochemical composition of each tephra was derived using these data tephra layers at other sites in the study area were geochemically analyzed and in instances of statistical concordance in major oxide structure correlated to the type site and therefore ascribed ages this methodology identified a further sixth volcanic event between ca 24 000 and 30 000 yr not registered by type site tephras the extension of this initial tephrochronological framework beyond the alluvial sequences of central western argentina is encouraged by the occurrence of geochemically distinct tephra verified and dated in this study

new york alabama lineament a buried right slip fault bordering the appalachians and mid continent north america the new york alabama ny al lineament recognized in 1978 is a magnetic anomaly that delineates a fundamental though historically enigmatic crustal boundary in eastern north america that is deeply buried beneath the appalachian basin data not in the original aeromagnetic data set particularly the lack of any information available at the time to constrain the southern continuation of the anomaly southwest of tennessee left the source of the lineament open to conjecture we use modern digital aeromagnetic maps to fill in these data gaps and for the first time constrain the southern termination of the ny al lineament our analysis indicates that the lineament reflects a crustal scale right lateral strike slip fault that has displaced anomalies attributed to grenville orogenesis by 220 km palinspastic restoration of this displacement rearranges the trace of the grenville belt in southern rodinia and implies only passive influence on later formed appalachian structures the precise timing of dextral movement on the ny al structure is not resolvable from the existing data set but it must have occurred during one of or combinations of the following events 1 a late postcontractional post ottawan stage of the grenville orogeny 2 late neoproterozoic to cambrian rifting of laurentia or 3 right slip reactivation during the late neoproterozoic cambrian rifting of laurentia or during appalachian movements our palinspastic reconstruction also implies that the host rocks for modern earthquakes in the eastern tennessee seismic zone are metasedimentary gneisses and it provides an explanation for the spatial location and size of the seismic zone

cocorp seismic profiling of the appalachian orogen beneath the coastal plain of georgia a southeastward extension onto the coastal plain of an earlier cocorp traverse which confirmed large scale thin skinned thrusting of crystalline rocks of the southern appalachians has provided some of the most spectacular reflections yet seen in crustal seismic data most of the reflectors can be interpreted as either fault surfaces or as metamorphosed strata of late precambrian early paleozoic age they are consistent with the hypothesis that a major detachment extends eastward beneath this part of the orogen although other interpretations with a more complex pattern of detachments or sutures are also possible large scale overthrusting provides a mechanism for incorporating sedimentary rocks into the lower crust and may help to explain many of the layered features on crustal seismic data reflections from deep beneath the coastal plain indicate that the structural configuration of the rocks is complex and that the remains of a collision zone are being observed several east dipping horizons which bear strong similarities to thrust faults in valley and ridge sedimentary rocks are seen in the basement at shallow and mid crustal levels beneath the coastal plain the augusta fault for example displays a reflection which extends at a low angle some 80 km or more southeast of its surface position in conjunction with surface geologic information these new data demonstrate that late paleozoic compressive deformation was pervasive and resulted in lateral movements in the upper crust extending from the valley and ridge to the crystalline rocks beneath the coastal plain a distance of 400 km or more a large antiform cresting at about 2 3 sec or about 6 km below the surface and other structures beneath the coastal plain of georgia deserve further consideration for petroleum exploration although metamorphism may have eliminated petroleum from these rocks refracted arrivals and fault geometries indicate two triassic rift basins beneath coastal plain sedimentary rocks one of which has apparently not been recognized previously

lake charles louisiana earthquake of 16 october 1983 on 16 october 1983 at 19 40 utc a magnitude 3 8 earthquake occurred near lake charles in southwestern louisiana the earthquake was felt over an area of 2600 km2 and had a maximum modified mercalli intensity of v this was the first significant louisiana gulf coast earthquake to be recorded and located by nearby microseismic networks one possible foreshock and three aftershocks also were recorded and located using a velocity model developed for this study the focal mechanism of the earthquake was determined based on p wave first motions from 22 local and regional stations the solution indicates a predominantly east west trending southeast dipping normal fault with a small strike slip component the depth of this event 14 km provides the first significant evidence that normal faulting within the crystalline basement may control shallower growth faults along the gulf coast

effects of melting on frontogenesis abstract frontal precipitation systems are simulated with a 2d cloud model including ice phase microphysics despite the use of idealized frontogenetic forcing in the simulations some observed characteristics of frontal zones and their associated cloud and precipitation fields are reproduced in the simulations the effects of melting snow on surface frontogenesis is investigated it is found that the cooling effects of melting snow significantly accelerate surface frontogenesis in winter storm environments especially when the melting layer is close to the surface however the steady state surface frontal strength in the model is not sensitive to the melting effects finescale thermal and kinematic perturbations inside the frontal zone near the melting level quite similar to those recently reported in the literature are evident in the model results analysis of the model results suggests that cooling from melting snow may induce these thermal and kinematic perturbations and may enhance baroclinicity

sedimentological maps of the typical loessic units in north pampa argentina abstract application of grain size data allowed the construction of maps of two typical loessic formations of north pampa a sand sea covering the central argentine plain and a peripheral loess belt to the northeast compose the pampean aeolian system a region of 20 000 km 2 in the loess belt santa fe and cordoba provinces was studied thick loess outcrops are located in this region the tezanos pinto loess upper pleistocene lower holocene in age and the san guillermo fm late holocene in age are analysed in this article the silt content has been taken as the main parameter for mapping in general the pattern of the isoplethic curves is similar in both maps these maps show that the silt content in both loessic units progressively increases from ssw to nne in the loess belt the silt content increases from 55 to 60 in the ssw at the transition belt to the sand sea up to 75 80 in the nne along a distance of 120 200 km other sedimentological data of the outcropping loess paleosols sequences are presented as complementary information

the giles county virginia seismic zone a well defined seismic zone recently detected in virginia has an orientation that is not related to the surrounding geologic structures the orientation of the zone appears to be related to features below the appalachian overthrust belt a damaging earthquake that is important in evaluating seismic hazard in the southeastern united states may have occurred in the zone in 1897

mining related and tectonic seismicity in the east mountain area wasatch plateau utah u s a as part of a larger multi institutional seismic monitoring experiment during june august 1984 in the eastern wasatch plateau utah data from a subarray of 20 portable seismographs were used to investigate seismicity in the east mountain area an area of active underground coal mining and intense microseismicity eight stations of the subarray were concentrated on top of east mountain about 600 m above mine level at an average spacing of 2 to 3 km the primary objective was the accurate resolution of hypocenters and focal mechanisms for seismic events originating at submine levels data from high resolution seismic reflection profiles and drill hole sonic logs yielded a detailed velocity model this model features a strong velocity gradient in the uppermost 1 km which has a significant effect on takeoff angles for first arriving p waves from shallow seismic events two hundred epicenters located with a precision of 500 m cluster within an area about 5 km in diameter and show an evident spatial association with four sites of longwall mining during the study period a special set of foci rigorously tested for focal depth reliability indicates submine seismicity predominating within 500 m of mine level and extending at least to 1 km and perhaps to 2 km below mine level continuous monitoring for a 61 day period june 15 august 15 bracketed a 16 day mining shutdown july 7 22 during which significant seismicity comparable to that observed before the shutdown was observed ten focal mechanisms for seismic events originating at or down to 2 km below mine level nearly all imply reverse faulting consistent with previous results and the inferred tectonic stress field enigmatic events recorded with all dilatational first motions can be fit with double couple normal faulting solutions if they in fact occur above mine level perhaps reflecting overburden subsidence if these events are constrained to occur at mine level their first motion distributions are incompatible with a double couple source mechanism

crustal velocity structure associated with the eastern tennessee seismic zone vp and vs images based upon local earthquake tomography we present three dimensional p and s wave velocity models for the active eastern tennessee seismic zone etsz using arrival time data from more than 1000 local earthquakes a nonlinear tomography method is used that involves sequential inversion for model and hypocenter parameters we image several velocity anomalies that persist through most of the inversion volume some anomalies support the presence of known features such as an ancient rift zone in northern tennessee other anomalies reveal the presence of basement features that can be correlated with regional gravity and magnetic anomalies we image a narrow ne sw trending steeply dipping zone of low velocities that extends to a depth of at least 24 km and is associated with the vertical projection of the prominent new york alabama magnetic lineament the low velocity zone may have an apparent dip to the se at depths exceeding 15 km the low velocity zone is interpreted as a major basement fault juxtaposing granite rhyolite basement to the nw from grenville southern appalachian basement to the se relocated hypocenters align in near vertical segments suggesting reactivation of a distributed zone of deformation associated with a major strike slip fault we suggest that the etsz represents reactivation of an ancient shear zone established during formation of the super continent rodinia

late quaternary paleosols stratigraphy and landscape evolution in the northern pampa argentina the field properties micromorphology grain size geochemistry and optically stimulated luminescence osl ages of two late quaternary sections have been used to reconstruct the sequence of pedosedimentary processes and to provide insights into landscape evolution in part of the northern pampa of argentina paleosols developed in paludal sediments adjacent to the parana river at baradero and in loess at lozada can both be correlated and linked to other sites thus enabling for the first time the tentative recognition and tracing of a diachronous soil stratigraphic unit that probably spans the equivalent of at least part of marine oxygen isotope stage ois 5 the paleosol at lozada was truncated and buried beneath fluvial sediments during the time span of ois 4 and 3 eolian gradually replaced paludal inputs at baradero over this period and there were also two clearly defined breaks in sedimentation and development of paleosols the period corresponding to ois 2 was marked by significant loess accumulation at both sites with accretion continuing into the mid holocene only at lozada the more developed nature of the surface soil at baradero probably reflects a combination of a moister climate and a longer soil forming interval

the 9 december 2003 central virginia earthquake sequence a compound earthquake in the central virginia seismic zone the 9 december 2003 central virginia earthquake sequence was a compound earthquake consisting of two nearly identical events occurring about 12 sec apart the second event is separated by about 300 m from the first event along the azimuth of approximately 195 10 the source mechanism determined from regional waveform inversion indicates predominantly thrust faulting at a depth of approximately 10 2 km the sequence with two events attained the combined seismic moment of m 0 2 64 1 01 10 15 n m m w 4 3 the focal mechanism indicates a subhorizontal p axis trending 301 and plunging 19 a regional stress model for the central virginia seismic zone cvsz derived from the 9 december 2003 events and 11 previous earthquakes indicates a thrust faulting stress regime with 1 trending 133 12 and plunging 14 3 the least principal stress axis 3 trends 25 10 and plunges 52 3 the 1 axis is rotated approximately 68 clockwise relative to the average maximum horizontal compressional stress s hmax direction for eastern north america approximately 65 the 9 december 2003 earthquake sequence occurred among the systems of paleozoic and mesozoic faults above the southern appalachian decollement which is at depths from 12 to 19 km in the piedmont geologic province of central virginia

geochronology of middle and upper pleistocene loess sections in hungary abstract the application of both thermoluminescence and infrared stimulated luminescence dating to the extensively studied classical hungarian loess paleosol sequences from basaharc mende and paks provides a reliable chronological framework and climatostratigraphic reconstruction for the last interglacial glacial cycle based on this combined luminescence dating study a new chronology is proposed for the young loess in hungary luminescence dating suggests that the loess below the mf2 horizon formed during the penultimate glaciation the mf1 horizon probably formed during an interstade within oxygen isotope stage 3 for the youngest loess overlying mf1 a very high accumulation rate was determined large time gaps occur above mf2 and mf1 indicating that most of the record of the last glaciation is missing in the standard sections at basaharc mende and paks either large discontinuities or a very low accumulation rate occurred in all three type sections during the soil forming periods high resolution studies of climatic proxies using this combined luminescence dating approach provide a reliable chronological framework for loess and loess derivatives of the last glacial cycle in hungary although a precise and complete chronostratigraphic reconstruction cannot be achieved from the incomplete records found at these sites

seismotectonics of the southern appalachians abstract the southern appalachians of eastern tennessee and western north carolina is a region for which high quality instrumental seismic data have been very limited in this paper we report more than 100 new or relocated hypocenters obtained from the initial 2 1 2 yr of operation of the southern appalachian regional seismic network sarsn a 16 station four state telemetered network of short period vertical instruments these data provide a first order snapshot of southern appalachian seismicity that confirms some previous observations and adds new results for the region the most important new observations are well constrained focal depths and focal mechanisms for southern appalachian earthquakes the level of activity exceeds expectations and concentrates more heavily in the valley and ridge province of eastern tennessee as opposed to the blue ridge or inner piedmont than is evident in historical listings the large majority of these events lie between the new york alabama lineament and the clingman ocoee lineaments magnetic anomalies produced by deep seated basement structures an analysis of the uniqueness and stability of hypocentral depth yields reliable depths for 58 earthquakes and demonstrates that most southern appalachian seismic activity occurs beneath the decollement thus lending quantitative support to the argument that appalachian seismicity is unrelated to surficial geological or tectonic features several new focal mechanisms of a higher quality than previously available indicate that the basement of the valley and ridge is under ne sw compression and the principal mode of faulting is right lateral strike slip on nearly north south faults in both depth and type of faulting the seismogenic model we propose for the southern appalachians closely emulates the giles county zone to the north of our study area

optical dating of young coastal dunes on a decadal time scale we explore the use of quartz optically stimulated luminescence osl dating for reconstructing coastal evolution on a time scale of decades to a few hundred years samples are taken from the accretionary south west coast of texel a barrier island just offshore of the northern netherlands the ages of dune ridges are known from historical sources an excellent chronology with a decadal accuracy exists for the past 260 years osl ages of less than 10 years on the youngest samples indicate that the osl signal of the quartz grains is very well zeroed prior to deposition and burial osl ages of five samples from a 250 year old dune ridge are indistinguishable and the osl ages on 17 out of 20 samples are in excellent agreement with the well known independent age controls our results highlight the potential of osl dating for high resolution reconstruction of coastal evolution over the past few centuries

loess in europe mass accumulation rates during the last glacial period abstract upper pleistocene loess palaeosol sequences provide excellent high resolution terrestrial archives of climate forcing due to improvements in numerical age determinations especially in luminescence dating methods a more reliable time based reconstruction of the past climate and environmental change has become available for the loess record in europe chronological information was collected from 43 sites along a northwest to southeast transect in europe thirty three of these sites had sufficient age information to allow estimation of mass accumulation rates and it was possible to isolate the mass accumulation rates of primary loess during the last glacial period 28 13 ka bp at 21 of these locations these sites fall along a coarse climatic gradient from the relatively coastal climate of belgium and france to the drier more continental climate of central europe interpreting mass accumulation rates of loess in terms of this climatic gradient is not straightforward as these deposits are dominated by sources in floodplains and large river systems thus accumulation rates are influenced strongly by regional wind and precipitation patterns but mostly by the availability of glacially derived material from the alps and the periglacial terrains that characterized european fluvial systems during and immediately following glaciation

the upper pleistocene loess record at harmignies belgium high resolution terrestrial archive of climate forcing abstract the loess palaeosol sequence in a section at harmignies in belgium is one of the most important upper pleistocene sites in northwest europe an extensive luminescence dating study was carried out to get a reliable chronological framework and to understand the climate forcing in an area where continuous permafrost dominated during most of the last glaciations twenty eight samples were investigated by infrared optically stimulated luminescence irsl and thermoluminescence tl methods resulting in more than 100 luminescence age estimates the dating results on colluvial sediments are in good agreement with landscape destabilisation phases during ois 5 during the last glacial four major periods of loess accumulation were likely to have occurred in europe at the harmignies section the oldest loess was deposited between 67 000 to 60 000 yr the second one from 60 000 to 50 000 yr the third one from 50 000 to 40 000 yr and the youngest loess accumulation period started most likely after the heinrich 3 event and lasted until the heinrich 2 event 25 000 20 000 yr two main periods of permafrost occurred at approximately 60 000 and 28 000 yr bp

paleoenvironmental reconstruction of quaternary valley fill successions in summit paleosurfaces of southern sierras pampeanas cordoba province argentina abstract climatic and environmental changes were inferred from the study of late quaternary sequences that represent paleo valleys filling in the summit pampas at the center south of the sierra de comechingones cordoba province argentina a representative sedimentological section p1 was described and sampled and sediments age 14 c granulometric characteristics and organic matter content were determined in the analyzed succession four main stratigraphic units were recognized and interpreted the stratigraphic and pedological characteristics diatom levels presence geomorphological features and altitude conditions of the study area allow us to conclude that 1 valley fill deposits are holocene from 8310 110 yr bp to present days and composed exclusively of loessic loessoid material from surrounding areas 2 the dominant transport mechanism could have been laminar and or hyperconcentrated flows mainly associated with slope evolution processes sheet flow and high density flows 3 isolated swamps with important biological activity were the dominated environments in to the valleys these environments suggest an alternating pedogenic cycles were the most important was the middle late holocene indicating a landscape stabilization tendency 4330 130 yr bp 4 temperate wet climatic conditions and high seasonality characterized middle early holocene hypsithermal period more arid conditions dominated late holocene from 1500 to 1000 bp to the present temperate wet climatic conditions occurred and this period was interrupted by the little ice age 5 in the mountains both in wet and dry periods the rainfalls were probably higher as well as the temperature must be lower than the surrounding plain especially in winters perhaps reaching periglacial conditions during more arid periods

fault plane solutions and relocations of recent earthquakes in middleton place summerville seismic zone near charleston south carolina the middleton place summerville seismic zone mpssz located about 20 km northwest of charleston is the most active seismic zone in south carolina between 1980 and 1991 58 events with md 0 8 to 3 3 were recorded in mpssz they lie in a diffuse area of 11 km by 14 km of which over two thirds are located in a narrow 5 km by 6 km zone the hypocentral depths range from 2 to 11 km with over 90 deeper than 4 km single fault plane solutions were obtained for 35 events based on the focal mechanisms the earthquakes were grouped into five subsets the mean p axis of all fault plane solutions is oriented n63 e in general agreement with the direction of shmax obtained from in situ stress measurements of the 35 events 18 are associated with reverse faulting on nw se striking and sw dipping fault planes these events were inferred to be associated with the ashley river fault zone which is not a planar feature but is composed of short segments of varying strikes n20 w to n70 w and dips 40 to 70 sw eleven events were associated with strike slip motion on nne ssw striking vertical faults and with thrust faulting on n s oriented faults dipping to the west respectively these two sets are identified as being parts of the woodstock fault zone the concentrated zone of seismicity included events associated with both the arf and wf zones suggesting that it is at the intersection of these two fault zones

luminescence chronology of late pleistocene loess paleosol and tephra sequences near fairbanks alaska abstract thermoluminescence tl and infrared stimulated luminescence irsl sediment dating methods have been applied to paleosol and tephra bearing loess sequences younger than marine oxygen isotope stage mis 7 at three important sites tl ages indicate the development of significant paleosols 75 000 and 30 000 yr ago in the loess sequence at the gold hill site relatively minor soil development occurred 70 000 and 48 000 yr ago like the 75 000 yr old soil the 30 000 yr old soil is apparently of global extent and consistent in timing with inferred warm intervals elsewhere e g greenland europe western and central china at birch hill replicate tl dating of primary loess combined with two earlier tl results from the same site and with an earlier mean fission track glass shard age of 140 000 10 000 yr for the associated old crow tephra yield a more precise numeric age of 142 300 6600 yr for this alaska yukon chronostratigraphic marker ash bed three of the tl ages at the halfway house site are difficult to interpret but combined with other evidence they indicate 1 the upper 5 6 m of loess from halfway house is not part of the gold hill loess equivalent to pre mis 5 age as long thought by t l pewe but rather is much younger 2 the regionally significant variegated tephra found in the fairbanks and klondike areas and previously thought to be older than mis 5 has an age of 77 800 4100 yr late mis 5

geomorphology and chronology of late quaternary dune fields of western argentina abstract stabilized dune fields are common in western argentina and potentially reflect drought variability in the late quaternary this study focussed on deciphering geomorphic and stratigraphic record of three vegetated dune fields from east to west san luis medanos negros and medanos grandes with a mean annual precipitation from 700 to 91 mm optically stimulated luminescence single aliquot regeneration protocols yield ages on eolian quartz grains constraining depositional events the san luis dune field the wettest area exhibits evidence for repeated activation during the last glaciation ca 33 20 ka generally coincident with regional loess deposition these dunes were locally reformed in the past 100 years which is apparently coincident with intensified agrarian use and drying in the late 19th and early 20th century the two driest and western most dune fields medanos negros and medanos grandes show reactivation at ca 2 5 ka 0 9 and 0 5 ka and ca 4 3 4 2 1 and 0 6 0 4 ka respectively eolian depositional events at ca 2 5 2 1 ka and 0 6 0 4 ka may be coeval for medanos grandes and negros dune fields sustained drought conditions conducive for eolian activity is associated with warmer sea surface temperatures in the south atlantic a weakened south american convergent zone and a dispersed and southeasterly flow of tropical moisture from the low level chaco jet this nascent analysis indicates drought variability beyond historic observations with potentially at least four dune reactivation events in the past ca 4 5 ka

high resolution chronologies for loess comparing ams 14c and optical dating results the nuxloch loess section in south west germany is famous in central europe for its thick deposits from the last glacial maximum it has therefore been intensively studied during the past few years and offers an excellent opportunity to compare the performance of different dating techniques covering the period 15 45 ka here we present results fromoptical and ams 14 c dating the silt sized polymineral fraction of the clastic sediments and a multiple aliquot approach was used for ir osl dating 14 c dating was carried out on organic macro remnants and humin fractions extracted fromthe sedim ents with the exception of samples taken from the uppermost 1 5 m of the section ir osl and calibrated 14 c ams ages are consistent over the entire period the inconsistencies in the upper meters are thought to be due to disturbances during soil formation in the holocene the good agreement obtained on the remaining sequence demonstrates the high accuracy of both methods when studying loess sections for the ir osl ages no significant age underestimations are obvious the results clearly document that accurate chronologies can be developed for such continental sedimentary sequences this gives access to archives that can now be studied with a high temporal resolution and allows the establishment of new paleoclimatic proxies for the study of terrestrial responses to past climatic changes r 2003 elsevier science ltd all rights reserved

crustal and upper mantle velocity structure in the vicinity of the eastern tennessee seismic zone based upon radial p wave transfer functions teleseismic transfer function analysis is used to investigate crust and upper mantle velocity structure in the vicinity of the active eastern tennessee seismic zone etsz the etsz is associated with the new york alabama ny al magnetic lineament a prominent aeromagnetic anomaly indicative of grenville age basement structure radial component p wave transfer functions for 10 short period stations operated by the center for earthquake research and information are inverted for velocity structure velocity profiles are also determined for three broadband stations by converting the instrument response to that of an s 13 short period seismometer distinct differences in the velocity profiles are found for stations located on either side of the ny al magnetic lineament velocities west of the lineament are lower than velocities to the east of the lineament in the upper 10 km and in the depth range 30 to 50 km a gradational moho boundary is found beneath several stations located in the valley and ridge province a moho boundary is absent at four valley and ridge stations located east of the magnetic lineament and south of 35 5 n

shallow seismicity of arc continent collision near lae papua new guinea abstract in northeastern new guinea the narrow ramu markham valley rmv separates island arc rocks to the north from those of continental origin to the south and appears to be the western onland extension of the new britain trench to explore the tectonic processes at the leading edge of the island arc during collision we operated a portable seismic network for six weeks near the city of lae at the eastern end of the rmv we observed a narrow near vertical belt of seismicity between 10 and 30 km depth that we call the lae seismic zone lsz starting at the rmv in the southwest and trending northeasterly cutting across surface geologic structure the truncation of the lsz along a steep plane by the ramu markham fault zone rmfz and earthquake first motions suggest that the earthquakes occur in the hanging wall of a steep n dipping fault that crops out at the rmfz we also consider that the lsz is within the lower plate of a gently dipping thrust below 20 km depth the microearthquake zone is truncated by a gently ne dipping plane coinciding in depth and dip with nodal planes of recent large mb 5 6 and 6 0 thrust earthquakes we suggest that the huon peninsula is being emplaced onto the australian plate along a gently 25 dipping thrust fault that is 20 km deep beneath lae the rmfz may be a steeply dipping thrust fault that connects with this gently n dipping thrust but accommodates little convergence at present the lsz trends nearly perpendicular to an anticlinal range which appears to be sheared in a left lateral sense p wave first motions for earthquakes in the lsz with steep 70 to 90 dip nodal planes that strike parallel to the lsz suggest a component of south side up displacement also hence the crustal block south of the lsz may be rising relative to the huon peninsula and the rapid quaternary uplift rates estimated for the lae coastal region may be higher than the uplift rate of the huon peninsula as a whole we suggest that the lsz reveals a tear of small offset in the huon terrane but may be similar to a structure that produced a magnitude 7 earthquake near madang in 1970

group velocity tomography of the upper crust in the eastern tennessee seismic zone from ambient noise data abstract the eastern tennessee seismic zone etsz is the second most seismically active area in the central and eastern united states after the new madrid seismic zone but the relatively weak seismicity and the absence of correlation between the seismicity distribution and the surface geology make its seismogenic potential controversial in this work we investigate the structure of the upper crust in the etsz by means of group velocity tomography maps from seismic noise data results show that the seismic activity is associated with a relatively low velocity anomaly mainly located in one or more basement blocks these blocks bounded to the nw by the ny al lineament and to the se by the clingman lineaments are buried beneath low velocity strata consistent with the presence of a relatively thick sedimentary cover the imaged low velocity anomaly migrates towards the se at increasing periods suggesting a possible se dipping weak structure where most of the seismic activity takes place the correlation between the ny al magnetic signature and the position of the seismic velocity anomalies supports the interpretation of the low velocity zone as a major basement fault projected to the surface as the ny al magnetic lineaments the fault juxtaposes granite rhyolite basement to the nw with grenville southern appalachian basement to the se

joint hypocenter velocity inversion for the eastern tennessee seismic zone a joint hypocenter velocity inversion for the eastern tennessee seismic zone etsz has resolved velocity features in basement rock below detached appalachian thrust sheets p and s wave arrival times from 492 earthquakes have been inverted for one 1 d and three dimensional 3 d velocity models to midcrustal depths the 3 d p and s wave velocity solutions are computed independly and are very similar in relation to the 1 d model velocity anomalies range from 8 to 16 in the first layer upper 5 km and between 7 in deeper layers prominent velocity anomalies parallel the seismic zone and are consistent from layer to layer the most persistent anomaly is a low velocity region that borders the seismic zone to the northwest and is flanked on either side by regions of anomalously high velocity the new york alabama ny al magnetic lineament coincides with or lies close to the southeast boundary of the prominent velocity low in both the p and s wave velocity images the spatial coincidence between velocity gravity and magnetic gradients suggests that major discontinuities are present in the basement relocation in the 3 d velocity model reduced the number of very deep earthquakes below 20 km and further accentuated differences in seismogenic properties on either side of the ny al lineament after relocation most earthquakes occur in a vertically bounded region roughly 30 km wide extending from 4 to 22 km in depth most earthquakes occur in regions characterized by either average velocity or small velocity anomalies

an analysis of earthquake focal depths in the southeastern u s seven years 1977 84 of seismic network monitoring in the southeastern u s have resulted in a catalog of 255 earthquakes 0 m 4 2 with erz 5 km focal depths from the valley ridge and blue ridge provinces mean depth 12 km were combined for analysis as were those for the piedmont and coastal plain provinces mean depth 8 km the mean focal depths between these two regions are shown to be statistically different the 90 depths of earthquakes are also very different between the regions implying a difference in the depth to the brittle ductile transition first order models of crustal rheology based on estimates of composition temperature and strain rate indicate that the observed differences in earthquake focal depths may reflect differences in strain rate and or composition

ubiquity of anomalous fading in k feldspars and the measurement and correction for it in optical dating anomalous fading rates were measured in k feldspars separated from 49 sediment samples mainly from north america the intensity of the optically stimulated luminescence was found to decrease linea

known and suggested quaternary faulting in the midcontinent united states abstract the midcontinent united states between the appalachian and rocky mountains contains 40 known faults or other potentially tectonic features for which published geologic information shows or suggests quaternary tectonic faulting we report results of a systematic evaluation of published and other publicly available geologic evidence of quaternary faulting these results benefit seismic hazard assessments by 1 providing some constraints on the recurrence intervals and magnitudes of large prehistoric earthquakes and 2 identifying features that warrant additional study for some features suggested quaternary tectonic faulting has been disproved whereas for others the suggested faulting remains questionable of the 40 features nine have clear geologic evidence of quaternary tectonic faulting associated with prehistoric earthquakes and another six features have evidence of nontectonic origins an additional 12 faults uplifts or historical seismic zones lack reported paleoseismological evidence of large quaternary earthquakes the remaining 13 features require further paleoseismological study to determine if they have had quaternary earthquakes that were larger than any known from local historical records seven of these 13 features are in or near urbanized areas where their study could affect urban hazard estimates these seven are 1 the belt of normal faults that rings the gulf of mexico from florida to texas 2 the northeast ohio seismic zone 3 the valmont and 4 goodpasture faults of colorado 5 the champlain lowlands normal faults of new york state and vermont and 6 the lexington and 7 kentucky river fault systems of eastern kentucky

stratigraphy and chronology of mississippi valley loess in western tennessee the stratigraphy and chronology of loess deposits in the mississippi valley provide an important proxy record of the number and timing of glacial advances into the upper mississippi drainage basin the stratigraphy of loess and paleosols from two exposures in northwestern tennessee reveals three major loess units that are correlated with the loveland loess roxana silt and peoria loess from oldest to youngest detailed measurements of clay and secondary pedogenic iron contents suggest that the loveland loess may consist of multiple loess units which have been pedogenically welded to one another to form a composite sangamon soil the mineralogy of the coarse silt fraction from one exposure reveals both primary mineralogical differences between the peoria loess and the roxana silt and pedogenic overprinting by the sangamon soil grain size and iron data suggest that the degree of pedogenic alteration increases from west to east away from the loess source area which probably reflects the role of sedimentation rate on the degree of pedogenic alteration of loess however only the peoria loess shows the expected exponential eastward decrease in thickness the thickness of older loess units appears to be controlled more by the occurrence of localized erosion than by distance from source area most samples are resistant to solar resetting of the thermoluminescence signal which if unrecognized could yield thermoluminescence ages that significantly underestimate the true age of the deposits the best match between thermoluminescence age using the total bleach method and radiocarbon age of the peoria loess and roxana silt is achieved when either long durations of optical bleaching by sunlight 32 hr or artificial ultraviolet uv light are applied to define the residual thermoluminescence level partial bleach analysis indicates that long duration optical bleaching by sunlight or uv lamp bleaching does not systematically overbleach samples of peoria loess and roxana silt three thermoluminescence age estimates between 38 4 1 and 53 5 ka from the basal half of the roxana silt and six age estimates between 18 2 and 25 3 ka from the basal half of the peoria loess are consistent with numerous finite radiocarbon dates from around the central mississippi valley thermoluminescence age estimates suggest that the oldest of the intra loveland loess units is 127 12 ka one age and may have been deposited during marine oxygen isotope stage 6 the younger two of these loess units were deposited between 113 10 and 70 6 ka three ages this latter age range for loess that underlies the top of the presumed sangamon soil is problematic because it requires that pedogenesis may have begun as late as approximately 70 ka moreover loess deposited between about 120 and 70 ka suggests that the southern margin of the laurentide ice sheet was within some part of the upper mississippi valley during this interval this conflicts with some glacial geologic evidence but it is consistent with global sea level and 18o records of ice volume which indicate several intervals of moderate glaciation during this time

the 1984 southern yellow sea earthquake of eastern china source properties and seismotectonic implications for a stable continental area on 21 may 1984 a strong shock ms 6 3 mb 5 7 occurred in the southern yellow sea which shook the densely populated coastal area of eastern china about 1 min before the main shock a foreshock of mb 5 4 occurred because of interference from the foreshock no reliable p wave first motions or focal mechanisms have been obtained for the main shock from local seismic data in this paper long period teleseismic data have been used to investigate the source mechanism fault plane solutions determined from first motions as well as p and sh waveforms show a predominant strike slip motion with a small dip slip component on a steeply dipping plane the tectonic environment of this event supports the observation that margins of former rifts tend to be sites of midplate seismic source regions the yellow sea developed in a cratonic environment due to early cenozoic rifting the major graben faults strike nne ssw to ne sw and are intersected by second order faults trending wnw ese aftershock distribution suggests that the fault which generated the main shock probably strikes wnw ese the mechanism determined in this paper strikes 120 dips 88 and slips 28 this solution suggests that the earthquake ruptured along a secondary fault near the intersection of a more major nne ssw trending fault the epicentral area is subject to to an ene wsw compression and a nnw sse extension the seismic moment and focal depth are determined to be 1 09 1025 dyne cm and 12 4 km respectively relative hypocentral locations indicate that the focal depth of the foreshock is similar to that of the main shock and the hypocenter of the foreshock is located very close to the wnw ese striking nodal plane of the main shock mechanism and is about 20 km away from the main shock hypocenter source properties of the southern yellow sea earthquake have been compared with those of three major earthquakes of north china the stress drop of the yellow sea earthquake is determined to be about 42 bars this value is much lower than the stress drops computed for the 1966 hsingtai and the 1975 haicheng earthquakes of north china the southern yellow sea is characterized by short recurrence intervals while the hsingtai and haicheng areas have very long recurrence intervals the short recurrence intervals and low stress drop may reflect a lower material strength at the source region in the yellow sea

magnetostratigraphy and magnetic susceptibility of the las carreras loess paleosol sequence in valle de tafi tucuman nw argentina abstract stratigraphic studies on loess deposits in the intramontane basin of valle de tafi 27 s 66 w revealed up to 31 intercalated paleosols in order to clarify the chronostratigraphic position of the sediments we performed paleomagnetic investigations in the 50 m thick las carreras section the characteristic remanent magnetization chrm obtained after alternating field af demagnetization gives clear evidence of the matuyama brunhes boundary mbb at a profile depth of 26 7 m and of the jaramillo subchron at depths from 38 7 to 44 9 m we assign a minimum age of 1 15 ma to the onset of loess sedimentation which calls for a complete reassessment of the antiquity of loess in the region thus the las carreras sequence which is probably continuous and complete represents one of the longest quaternary terrestrial paleoclimatic records reported from the southern hemisphere the magnetic susceptibility signal follows the behavior known for argentinian eolian sediments though with certain restrictions and an overall weak correlation with pedostratigraphy this behavior is opposite to the pattern reported from the chinese loess plateau clp and seems to be influenced strongly by changing source materials contributing to the susceptibility signal in valle de tafi

the pedosedimentary evolution and chronology of tortugas a late quaternary type site of the northern pampa argentina new micromorphological magnetic susceptibility geochemical and geochronological data have been collected from tortugas a key late quaternary type site of the northern pampa argentina thus enabling the detailed reconstruction of the pedogenic and sedimentary history of this loess paleosol sequence paleosols developed in the ceres formation and the overlying lower member of the tezanos pinto formation retain evidence for leaching bioturbation and particularly clay translocation processes being dominant both paleosols are truncated evidence for water sorting and sediment reworking as well as continued bioturbation and redistribution of carbonates suggests that intervening depositional phases were complex the previously recorded hypsithermal soil developed in the upper member of the tezanos pinto formation has similar characteristics to the buried paleosols yet does not appear to have been truncated at this site and is only covered by a thin layer of sediment san guillermo formation this latter unit has been pedogenically welded onto the hypsithermal soil thus creating the present day surface soil complex a series of optically stimulated luminescence dates from throughout the sequence provide a stratigraphically consistent chronological framework ca 1 150 ka for the pedosedimentary reconstruction yet conflict with the previously reported thermoluminescence based chronology for the site and region ca 1 90 ka

intraplate stresses and seismicity the role of topography and density heterogeneities abstract the stress induced by the topography and by density heterogeneities in the lithosphere has been computed for two different tectonic regions of the north american plate the lithosphere was assumed to consist of a two dimensional layered elastic slab over an inviscid fluid the calculations show that these stresses are locally comparable in magnitude to the regional tectonic stress 20 50 mpa two areas have been analyzed in greater detail the southeastern united states and the rio grande rift the stress in the southeastern united states is computed along a cross section perpendicular to the strike of the appalachian mountains the computed stress appears largest beneath the blue ridge and valley and ridge provinces where the appalachian seismicity is located the stress in the western united states is computed along a cross section perpendicular to the rio grande rift large stress is shown beneath the rift and the adjacent regions the stress induced by surface and internal loading is extensional in the rio grande rift and compressional in the colorado plateau and in the great plains

improved methodology and new thermoluminescence ages for the dune sequence in south east south australia abstract our thermoluminescence dating technique for quartz extracted from late pleistocene sediments has been improved by the addition of a 33 h 160 c preheat before measurements this yields better plateaux which now encompass the region known as the 325 c tl peak this is consistent with the prediction from isothermal decay studies of the lifetime at ambient temperature of the traps responsible for this peak the preheat does not help resolve problems associated with dose responses above 600 gy some details of the dose response are shown to be better understood with the aid of 3 d tl spectra the improved method has been applied to one former and seven new samples from the stranded beach dune sequence in south east south australia the five ages obtained for the main dune sequence range from 95 6 to 725 100 ka and all are consistent with the expected ages

micromorphology and osl dating of the basal part of the loess paleosol sequence at la mesada in tucuman province northwest argentina abstract the basal part of the 42 m loess paleosol sequence at la mesada near tucuman in nw argentina reported by zinck and sayago j s am earth sci 12 1999 293 quat int 78 2001 11 is re examined here using a combination of micromorphology and optically stimulated luminescence osl dating depth distributions of microstructure clay coatings and secondary carbonate features enable the development of this part of the sequence to be reconstructed in terms of a series of pedosedimentary stages stage one involved accretionary pedogenesis with loess being modified by bioturbation and possibly leaching processes as it accumulated stage two was marked by a reduction in loess deposition and establishment of a relatively stable surface at which bioturbation leaching and clay translocation processes were dominant stage three represented a return to accretionary pedogenesis followed by establishment of a new relatively stable surface and vertical leaching and clay translocation processes with some welding of secondary carbonate features on the underlying older soil the three osl dates ranging from ca 150 to 195 ka bp suggest that the whole sequence is significantly older than indicated by the radiocarbon chronology ka bp reported in the works of zink and sayago cited above however assuming that the pedosedimentary changes reflect alternating periods of dry cool and moist warm conditions as suggested in the works of zink and sayago cited above the succession still potentially provides the highest resolution proxy climatic record so far reported in argentina

seismodynamics of sweden deduced from earthquake focal mechanisms summary focal mechanisms from 18 major swedish earthquakes ml upp 3 reveal that 1 several of the studied earthquakes have focal mechanisms with significant extensional stresses which fit well to the idea of postglacial rebound as an important stress generator 2 in areas like south western sweden the north westerly trending compressional axes indicate that ridge push from the north atlantic ridge is also a considerable stress contributor 3 some local tectonic features like the skalderviken depression in kattegat are momentous for seismotectonic interpretations in addition to first p polarities full waveform modelling for frequencies up to 3 hz and epicentral distances up to 225 km provides rather robust focal mechanism determinations focal depths of seven events ranging from 11 to 37 km are well resolved within a few km by waveform modelling

a numerical investigation of squall lines part i the control experiment abstract a two dimensional anelastic cloud resolving numerical model was used to simulate squall systems large domain and fine grid resolutions were utilized so that both the convective and mesoscale components of squall lines could be handled adequately detailed cloud microphysics including the ice phase and the coriolis force have been included in the basic model both the life cycle and storm structure of observed squall systems have been simulated successfully some details in the observed precipitation and kinematic characteristics of squall lines such as the locations of front to rear jet core the base of the stratiform cloud the formation of a transition zone and the organized mesoscale updraft have been simulated by the model the storm generated meso scale low pressure center located behind the convective updraft has been shown to be instrumental in the initiation and maintenance of the mesoscale circulation and the associated trailing stratiform region diagnostically the horizontal

field and laboratory tests for recognition of ediacaran paleosols abstract not a single paleosol had been described from rocks of ediacaran age until 2011 but 354 ediacaran paleosols have been described by 20 different authors since then some of these newly recognized paleosols have proven controversial so this paper reviews 20 distinct tests to determine whether a particular ediacaran bed could be a paleosol or not one problem has been that ediacaran paleosols are not precisely like modern soils because they lack root traces a diagnostic feature of silurian and geologically younger paleosols the principal problem for recognition of some ediacaran paleosols is the occurrence in them of megafossils assumed to have been marine although most of these fossils remain problematic for both biological and ecological affinities not all the tests discussed here are diagnostic of paleosols some are ranked permissive or persuasive permissive conditions for paleosols include ripple marks hummocky bedding pyritic limestones acritarchs or thalloid fossils low strontium isotopic ratios high 26 mg ratios and red color persuasive tests include loessites tsunamites desert playa minerals low boron content high 10 b isotopic ratios high carbon sulfur ratios and very low total reactive iron ratios diagnostic tests include matrix supported lapilli or crystal tuff parent materials ice wedges and other cryoturbation sepic birefringence fabrics evaporitic sand crystals and negative geochemical strain and mass transfer and highly correlated 13 c and 18 o like other geological periods the ediacaran is known from a variety of marine and non marine paleoenvironments

short period surface wave dispersion and shallow crustal structure of central and eastern tennessee group velocity dispersion of explosion generated seismic surface waves with periods ranging from 0 2 to 1 5 sec is used to investigate shallow crustal structure of eastern and central tennessee several modes of both rayleigh and love waves can be identified and separated on the seismograms of seven sarsn regional network stations by zero phase digital filtering dispersion data for sinusoidal wave motion were based on digitized zero crossing times by forward modeling we find that a wave guide of at least two layers over a half space can adequately represent our particular multi mode narrow band observations in a layered section about 3 km thick lower velocities characterize outcropping clastic rocks of the cumberland plateau and higher velocities correspond to shallow carbonate rocks of the nashville dome half space shear velocities of about 3 9 km sec appear to represent lower paleozoic carbonate lithology deeper than 2 to 4 km on most of the observed paths our best data interpreted jointly with earlier data of oliver and ewing 1958 and of chen et al 1989 have a composite period range of 0 2 to 40 sec but they represent different appalachian paths group velocities over this broad spectrum are satisfied by a complex model with two low velocity layers the uniqueness of this model cannot be demonstrated but it represents important hypotheses concerning regional geologic features that can be tested more rigorously by improved surface wave dispersion data

predominance of arid climates indicated by mammals in the pampas of argentina during the late pleistocene and holocene abstract south american climates during the pleistocene and holocene are poorly known especially in the lowlands east of the andean ranges however there is relatively good biostratigraphic and climatic information for the late lujanian and platan local ages latest pleistocene to holocene of the pampas region most of the climatic data from the pampean area are based on land mammal assemblages pollen records and geology contrasting with north american faunal associations there are many non analogue assemblages in the holocene of the pampean area the climate was arid and relatively cold during most of the early lujanian however several relatively wet and warm events are suggested by the presence of subtropical mammals and evidence of tchernozoid paleosoils the late lujanian is well represented by the fossiliferous sediments of the la chumbiada and guerrero members of the lujan formation ca 30 000 and 21 000 13 000 yr b p respectively cropping out in stream valleys in the buenos aires province mammal assemblages suggest a change from a temperate to a cool climate from the la chumbiada member to the guerrero member the latter representing the last glacial maximum the lower portion of the eolian la postrera formation has been dated at 11 000 8000 yr b p this section was deposited on basin divides under dry and cool conditions the mammal association was similar to that of the gueffero member and includes the last megaherbivore mammals in south america e g megatherium americanum mammals occurring in platan beds usually indicate dry but not cool conditions warm and probably wetter conditions were detected in continental beds deposited synchronously with a mid holocene marginal marine ingression ca 7000 6000 yr b p a holocene non analogue assemblage of subtropical mammals and dry cold indicators occurred at latitude 38 30 s at ca 2000 yr b p subtropical mammals that require wetter conditions have been migrating southwards in the pampean region since 1500 1000 yr b p eolian sediments in the la postrera formation dated ca 440 yr b p yielded an arid to semiarid mammal assemblage which could relate to the little ice age period remarkably most of the present day manual biocenoses and climatic conditions in the pampas seem to have been recently established paleogeographic maps for the last glacial maximum and the mid holocene are also provided

the argentine neotropical loess an overview abstract the neotropical loess primary and reworked covers a large part of argentina north of 30 s it is different in some ways from the loess of the pampa which is generally considered the typical argentine loess the mineralogical chemical and physical composition of the neotropical loess has been analyzed and is here compared with both pampean and northern hemisphere european and north american loess the distribution of neotropical loess is established following the former teruggi scheme and the bio stratigraphical data indicating a late pleistocene age is described the great climatic variability of this period is documented through description of a loess paleosol sequence that mantles the pre andean valleys the influence of loess influx upon the genesis of the paleosols and the stadial interstadial environmental changes are considered in relation to the generalized truncation of paleoedaphic sequences the migration of the polar front and the weakness of the pacific high pressure system are also analyzed in relation to south american environmental evolution during the upper quaternary in that sense the genesis of pre andean fluvial valleys and mega fans extending outward into the andean piedmont plains having sources on the eastern dry side of the andes would have been influenced by such a paleoclimatic situation

pedosedimentary development of part of a late quaternary loess palaeosol sequence in northwest argentina the field properties magnetic susceptibility particle size calcium carbonate content soil micromorphology and optical luminescence ages of the upper 6 1 m and lowermost 4 7 m of the 45 m loess palaeosol sequence at el lambedero in the tafi del valle region of tucuman province sierras pampeanas northwest argentina have been used to set up a partial stratigraphy and chronology as well as a basic pedosedimentary model of loess accumulation palaeosol development reworking and erosion for the site the minimum ages derived from the basal part of the section suggest that loess began to accumulate some time before 165 ka a thick and well developed pedocomplex in the upper profile is correlated with at least the latter part of marine isotope stage mis 5 whereas the overlying palaeosol may be attributable to pedogenic activity during mis 3 the absence of material younger than 33 ka close to the surface of this rounded spur landform is probably the result of either non deposition or erosional stripping in response to climatic change or episodic uplift in this seismically active region

intraplate seismicity and stress in the southeastern united states abstract the stress induced by topography and by density heterogeneities in the lithosphere has been computed for two seismic regions in the southeastern united states the southern appalachian mountains and the south carolina coastal plain the lithosphere was assumed to be a three dimensional layered elastic slab overlying an inviscid fluid the calculations indicate that the local stress is of the same magnitude as the tectonic stress tens of mpa but contradictory conclusions are suggested by the comparison of stress differences and principal directions with earthquake locations and focal mechanisms in the southern appalachians the seismicity correlates well with the stress maximum and focal mechanisms agree with the calculations where regional stress is combined with locally induced stress in south carolina a combination of regional and local stress can explain the orientation of focal mechanisms but stress does not concentrate in the region of charleston and thus other factors must play a role in the charleston seismicity

late pleistocene to recent climate change in cordoba province argentina geomorphological evidence abstract repeated episodes of climate change affected the cordoba plains during the late pleistocene and holocene many of the geomorphologic features of cordoba province were developed in response to climatic oscillations and their development can be correlated to changes in precipitation and hydrologic regimes alternating periods marked by dry climate and high evapotranspiration rates were interspersed with more humid intervals and can be correlated using stratigraphic and geomorphic evidence at the regional level the initial phase of the late pleistocene was characterized by significant loess deposition and the formation of large alluvial fans these sediments and landforms are representative of a dry climate the transition to the late pleistocene was marked by the initiation of a humid climate regime giving rise to enhanced fluvial activity and sedimentation expansion and integration of drainage networks and development of paludal areas and successions pedogenesis occurred in the interbasin areas involving precipitation of silica and sesquioxides during latest pleistocene early holocene time coinciding in part with the last glacial maximum a dry and cool climate resulted in widespread aeolian sand and loess deposition the early to mid holocene was characterized by humid subtropical conditions which became established throughout the region accompanied by pedogenic development of profiles with prominent bt horizons and further modification of drainage networks during the mid to late holocene these warm and humid conditions were replaced by a semiarid climate resulting in widespread aeolian deposition wind action formed deflation hollows and dune fields in several areas the climate reverted to subhumid and temperate conditions during the latter part of the late holocene and small areas of wetlands developed the little ice age was marked by climatic deterioration and the deposition of a thin layer of aeolian sediment the current climate of cordoba is subhumid and temperate

airflow and precipitation properties within the stratiform region of tropical storm gabrielle during landfall abstract kinematic and microphysical characteristics of a stratiform rainband within tropical storm gabrielle during landfall on 14 september 2001 were investigated using data from a collocated 915 mhz wind profiler and scanning doppler radar the curved 60 km wide rainband was relatively intense with mesoscale updrafts and downdrafts exceeding 1 m s 1 the bright band is classified as strong as indicated by reflectivity factors in excess of 50 dbz and rainfall rates below the bright band peaking at 10 20 mm h 1 the melting layer microphysical processes were examined to understand the relation between brightband processes and precipitation intensity and kinematics mesoscale downdraft in particular below the melting layer the profiler and doppler radar analyses designed to maximize vertical resolution of flows within the melting layer disclose a striking convergence divergence couplet through the melting layer that implies a prominent cooling induced finescale circulation melting driven cooling in

isotopic constraints on the source of argentinian loess with implications for atmospheric circulation and the provenance of antarctic dust during recent glacial maxima we present rare earth element ree and sr nd isotopic data for argentinian loess 28 38 s with two aims 1 to examine the source regions of argentinian loess and the constraints that these put on palaeo wind directions 2 to further investigate the source of antarctic ice core dust and to test the hypothesis that some of it could be derived from a region to the north of patagonia into which the dry dusty westerly dominated patagonian climate expanded during quaternary glacial maxima sr nd isotopic data for argentinian loess from north of 37 s are distinct from patagonian loess compositions in that they have more radiogenic sr 87sr 86sr 0 7059 0 7123 and less radiogenic nd nd 0 8 to 6 4 ree patterns and sr nd isotopic values are relatively homogeneous for multiple samples taken from single loess sections but show significant differences between sections in general there is a northward change from patagonia like ree patterns and isotopic values away from volcanogenic signatures and towards those that are more like the continental crust the latitudinal nd isotopic pattern is remarkably similar to that for andean volcanic rocks and suggests derivation of loess from the andes by more or less direct westerly transport for loess sections in the north the data imply a contribution from palaeozoic gneisses to the northwest in the chilean altiplano sr nd data for extra patagonian argentinian loess north of 37 s do not support a significant role for this source region in supplying dust to antarctica at the last glacial maximum this conclusion contrasts with previous studies that suggest a significant northward shift in the climatic belts and in particular the westerlies and the antarctic polar front during quaternary glacial maxima very systematic relations between the sr nd isotopic composition of loess and their andean source highlights shifts in the sr isotopic composition of loess to more radiogenic values and strongly suggests that the slight offset between patagonian loess and ice core dust identified by previous workers is due to grain size differentiation effects

systematic thermoluminescence dating of two loess profiles from the middle rhine area f r g abstract systematic investigation of 104 loess samples from the well studied loess sequences at ariendorf and toenchesberg middle rhine area f r g was carried out to study the reliability of tl ages of the last 150 ka the samples were investigated by the additive dose regeneration and partial bleach methods using integral and plateau ranges for determination of accumulated dose the results show that in ariendorf all the loess deposits of the last glaciation are contaminated with reworked loesses from older glaciations at toenchesberg the tl ages are in good agreement with the stratigraphy up to about 90 ka but no tl age over 110 ka was obtained underneath the interglacial soil at toenchesberg

loess of southern south america abstract loess and loessoid loess like reworked loess sediments extend across the chaco pampean plains and the nw mountain environments of argentina and in neighbouring countries paraguay brazil uruguay bolivia loessoid sediments are much more abundant than primary loess the beginning of the loessoid sedimentation cycle was related to a phase of late miocene orogeny in the andes the plio pleistocene record is mostly composed of loessoid sediments modified by pedogenesis which produced welded palaeosols the late pleistocene holocene loess record reveals a heterogeneous composition across the region coarse textures and an andean derived volcanic composition prevail in the southern pampas finer textures and material coming from the andes and the other two sources sierras pampeanas and the parana basin characterize the loess deposits of the northern pampas and the eastern chaco a southern patagonian source is also suggested for the mountain valley loess of tucuman although a western andean provenance has been proposed it is believed that the material in the western chaco was derived from the bolivian andes loess deposition was related to a multistage transport mechanism involving fluvial and aeolian processes inferred westerly and southwesterly wind directions as dominant carriers of the aeolian deposits are in agreement with westerly palaeowind simulations using climate models however the role played by westerly tropospheric winds and northerly winds remains to be established

late quaternary vegetational and climatic changes in the pampa grassland of argentina abstract the vegetation and climate of the pampa grassland argentina during the late quaternary are reconstructed from pollen recovered from dated stratigraphic sections from arroyo walls and from archaelogical excavations prior to 10 500 yr b p herbaceous psammophytic steppe existed in the central part of the pampa grassland while xerophytic woodland associated with psammophytic and halophytic steppe occurred in the southwestern part of the pampa these types of vegetation and the continental conditions that prevailed in the area of the present day coast 38 s indicate subhumid dry climate and annual precipitation 100 mm lower than present a subsequent change toward a vegetation characteristic of ponds swamps and foodplains or toward environments with locally more effective moisture occurred ca 10 500 yr b p suggesting annual precipitation close to modern levels or a higher availability of water in the central part of the pampa grassland this type of vegetation existed until 8000 yr b p when it was replaced by grassland communities that lasted until 7000 yr b p in the southwestern part of the pampa grassland this vegetation developed before 7000 yr b p and persisted until ca 5000 yr b p sea level higher than the present ca 6200 yr b p is consistent with sharp modification of the vegetation and development of local halophytic communities dominant at 38 s a return to subhumid dry conditions occurred after 5000 yr b p the late holocene vegetation is characterized by pollen assemblages similar to the psammophytic and halophytic communities of the southern pampa grassland associated with communities with more edaphic conditions at the same time at 38 s a sea level regression is suggested by the dominance of fresh water pollen assemblages and micropaleontological remains the trend toward humid temperate conditions ca 1000 yr b p suggested by vertebrate remains characteristic of temperate and humid conditions as well as a very short but dry episode during the 18th century suggested by the geology are not clearly evidenced in the pollen sequences vegetational and climatic changes are explained by the latitudinal shifts and changes in intensity of the southern atmospheric circulation and changes in sea level

the structure water budget and radiational features of a high latitude warm front abstract on 30 september 1994 an arctic low pressure system passed over the southern beaufort sea area of northern canada and research aircraft observations were made within and around the warm front of the storm this study is unique in that the warm front contained subzero centigrade temperatures across the entire frontal region the overall structure of the warm front and surrounding region was similar to midlatitude storms however the precipitation rates liquid water content magnitudes horizontal and vertical winds vertical wind shear turbulence and thermal advection were very weak in addition a low level jet and cloud bands were aligned parallel to the warm front near neutral stability occurred within and around the front and conditional symmetric instability was likely occurring a steep frontal region resulted from strong coriolis influences that in turn limited the amount of cloud and precipitation ahead of the system the precipitation efficiency of the storm was high 60 but is beli

late quaternary aeolian and fluvial aeolian deposits from southwestern pampas of argentina southern south america abstract the central region of argentina southern south america is characterized by an extensive quaternary aeolian record in this context three locations from the southwestern pampas an andean foreland region bearing a rich fossil mammal record that contributed to the south america biostratigraphic scheme were selected to carry out a comprehensive sedimentological analysis of the late quaternary deposits the case studies are located at the transverse valleys of la pampa province chapalco quehue and utracan argentino valleys and exhibit a high resolution of the late quaternary in comparison with others areas of the southwestern pampas the toay locality 36 41 s 64 24 w records aeolian dominant activity since the end of the late pleistocene 30 ka onwards soil formation at some point during the holocene and early mid 20th century reactivation of aeolian process the arroyo quehue locality 37 04 s 64 42 w presents a late pleistocene holocene succession mostly related to an ephemeral endorheic fluvial system with an interval of relative surface stabilization and aeolian aggradation during the late holocene the utracan locality 37 17 s 64 35 w exhibits a prevailing aeolian and fluvial aeolian interaction succession developed in the mid to late holocene in a sand mud flat environment of a shallow saline lake the three studied cases are representative of aeolian aggradation in association with ephemeral fluvial shallow lake and pedogenic processes in a currently subhumid dry region numerical ages indicate sedimentation during the last 30 kyr they allow constraining and evaluating the paleoenvironmental conditions in this inland region of southern south america and provide age constraints for the regional databases of paleoclimatic proxies the results are in agreement with other late quaternary paleoclimatic paleoenvironmental archives of central argentina and show a fragile aeolian landscape that is susceptible to deterioration under extreme conditions including both aeolian reactivation during dry phases and erosion of sandy silty sediments during wet phases

pedostratigraphy and pedological and geochemical characterization of las carreras loess paleosol sequence valle de tafi nw argentina abstract the las carreras loess paleosol sequence is considered the most complete quaternary pedostratigraphic record in south america it consists of 32 paleosols formed during the past 1 15 ma chronological control is provided by magnetostratigraphy sediment and paleosol characterization is based on a variety of methods including soil chemistry geochemistry and micromorphology the main pedogenic processes identified are carbonate leaching and reprecipitation ped formation and translocation of clay and organic matter in many cases the boundaries between individual paleosols are not clearly defined due to indistinct transitional zones based on both pedological and sedimentological characteristics the sequence was subdivided into three units with paleosols in units i and iii designated as luvisols and paleosols in unit ii tentatively classified as luvic kastanozems this subdivision reflects environmental changes associated with the mid pleistocene transition overall geochemical variability is low and largely related to pedogenesis the homogeneity suggests a rather constant provenance that seems to be linked to the central andes pursuant to the chaco model of iriondo 1997 models of deposition of loess and loessoids in the upper quaternary of south america journal of south american earth sciences 10 71 79 and includes direct volcanic ash falls and local sources in a subordinate manner in a paleoclimatic context loess paleosol alternation is interpreted to reflect climatic cycles that were primarily caused by the variability of the south american monsoon system

thermoluminescence ages for three sections in hungary abstract samples were collected from sections at mende paks and tapiosuly ages for the loess above the mf1 soil at mende were in agreement with the radiocarbon dates on charcoal fragments from the soil ages for loess from tapiosuly were also in agreement with radiocarbon ages for younger soils however tl age estimates for loess above or below the mf2 soil at each of the three sites suggested that this soil had an age of around 76 ka it has not been confirmed whether these ages are underestimated however they are older than previously thought on the basis of other tl studies they imply that the underlying mb soil is much older than the last interglacial

seismic strain rates in the central and eastern united states seismic strain rates for the entire central and eastern united states are estimated from historical seismicity and from several seismicity models typical strain rates are estimated to be the on the order of 10 12 to 10 11 per year except near historical sites of large earthquakes where higher rates pertain uncertainties in strain rates are large deformation caused by strain rates less than 10 10 yr 1 is very small compared to average denudation rates denudation and deposition may control the rate of earthquake occurrence in some parts of the central and eastern united states by modifying the vertical stress due to load a simple quantitative model predicts the earthquake occurrence rate in the appalachian mountains from an estimate of the regional denudation rate

genesis and distribution of the late pleistocene and holocene loess of argentina a regional approximation abstract an overview of the current state of knowledge of the loess of argentina is presented the spatial distribution of the loess typical or reworked is described and in particular reference is made to the relationship between landforms and superficial materials in the sub tropical loess region the description of extrinsic and intrinsic characteristics demonstrates the influences of regional factors in loess distribution and the existence of a sw ne loess transport path throughout argentine territory the available dating confirms the age of the superficial loess as pleistocene and holocene it is pointed out that the temporal interval of deposition of the late pleistocene loess coincides with the highest dust concentrations as shown in the ice core records at both poles the prominent influence of volcanic materials affecting not only the mineral composition of the loess but also the genesis and evolution of the loess palaeosol sequences is emphasised finally the importance of the palaeosols as indicators of palaeoenvironmental conditions is clearly demonstrated by the descriptions of outcrops in the pre andean valleys of north western argentina

the upper crust of the eastern tennessee seismic zone insights from potential fields inversion abstract the study investigates the crustal structure of the eastern tennessee seismic zone etsz by means of potential field inversion through the located euler deconvolution method inversion of magnetic field data shows that the top of the magnetic basement ranges between 6 and 12 km depth in the valley and ridge physiographic province while it is shallower

late quaternary paleoenvironments and paleoclimatic conditions in the distal andean piedmont southern mendoza argentina abstract the andean piedmont of mendoza is a semiarid region covered by extensive and partially vegetated dune fields consisting of mostly inactive aeolian landforms of diverse size and morphology this paper is focused on the san rafael plain srp environment situated in the distal andean piedmont of mendoza 34 30 s and reports the sedimentology and osl chronology of two representative exposures of late quaternary deposits including their paleoenvironmental and paleoclimatic significance eleven facies including channel floodplain fluvio aeolian interaction and reworked pyroclastic and aeolian deposits were described and grouped into two facies associations fa1 and fa2 fa1 was formed by unconfined sheet flows minor channelized streams and fluvial aeolian interaction processes fa2 was interpreted as aeolian dune and sand sheet deposits osl chronology from the srp sedimentary record indicates that between ca 58 39 ka and ca 36 24 ka mis 3 aggradation was governed by ephemeral fluvial processes fa1 under generally semiarid conditions during mis 2 the last glacial maximum ca 24 12 ka a major climatic shift to more arid conditions is documented by significant aeolian activity fa2 that became the dominant sedimentation process north of the diamante atuel fluvial system the inferred paleoenvironmental conditions from the srp sections are in broad agreement with regional evidence

focal mechanism analyses for eastern tennessee earthquakes 1981 1983 to investigate the neotectonic processes in the southern appalachians 10 single event focal mechanisms and 6 composite focal mechanisms were determined from 37 events that occurred in eastern tennessee between september 1981 and july 1983 both p wave polarities and sv p z amplitude ratios are input to a computer program that systematically searches the focal sphere for solutions acceptable within preset error limits hypocenter locations azimuth and departure angles are taken from locations obtained by the tennessee earthquake information center with a four layer velocity model a gradient velocity model developed to improve focal depth estimates and to provide continuously varying rather than discrete departure angles is used to relocate the seismic events for which single event focal mechanisms and composite focal mechanisms solutions are obtained the two different velocity models each produced focal mechanisms with similar nodal plane and p axis orientations indicating stable and reliable mechanism solutions the differences between average strike dip and rake angles of the two data sets range from 2 to 11 both single event focal mechanisms and composite focal mechanisms solutions exhibit predominantly strike slip motion along nearly vertical northerly right lateral or easterly left lateral oriented nodal planes standard deviations about the average strike dip and rake angles are generally less than 20 p axis trends average about n50 e with a nearly horizontal average plunge and both trend and plunge estimates have standard deviations of 25 or less

polarimetric signatures and hydrometeor classification of west african squall lines during the amma campaign the doppler and polarimetric radar ronsard was deployed in kopargo benin in the present paper three squall lines sampled during that period are described it was the first time this type of system had been observed with a polarimetric radar in the west african region the strongest case occurred on 28 july 2006 and the others on 12 september and 30 june the polarimetric characteristics of these systems are described and a hydrometeor classification algorithm is applied in order to identify the microphysics of the systems finally the 3d wind field is retrieved for the 28 july event the convective part of the squall lines is generally characterized by maxima of reflectivity differential reflectivity zdr and specific differential phase kdp the results of the hydrometeor classification show that the convective region is composed of strong 30 mm h 1 to moderate rain 5 30 mm h 1 below the melting level and graupel above this zone seems to be characterized by relatively strong updraughts 5 10 m s 1 responsible both for the formation of graupel by riming and for the growth of drops due to coalescence to the rear the systems are characterized by light rain 5 mm h 1 below and snow or ice crystals above these regions present downward flow below the melting layer which prevents drop growth by condensation consistent with the light rain observed the stratiform part of these systems can be very non uniform due to the presence of old cells dissipating associated with moderate rain and thus stronger reflectivities

a local weakening of the brittle ductile transition can explain some intraplate seismic zones abstract a decrease in the strength of a localized area of the lower crust would decrease the depth to the brittle ductile transition and concentrate stress in the stronger elastic crust around and above the zone of decreased strength deformation within the zone of weakened lower crust would occur through viscous or dislocation creep in response to regional plate stress as well as by elastic failure in small earthquakes two dimensional finite element models of zones of weakness subjected to a regional plate stress predict stress amplification of 10 100 surrounding the local decrease in strength a finite element model for an irregular zone of weakness in the lower crust can generate stress directions and relative magnitudes that satisfy the focal mechanisms and seismicity of southeastern tennessee an analysis of the displacements and stresses in the central area of decreased crustal strength suggests that strike slip faulting should dominate above this zone the strike slip faulting should exhibit a strong thrust component the compression and extension of the crust surrounding the weakened zone at the level of the brittle ductile transition predicts that the dominant strike slip faulting should exhibit components of normal faulting on the edges of the weak zone which are near a line through the weak zone parallel to the regional stress and reverse faulting on the edges which are near a line transverse to the regional stress the seismicity of southeastern tennessee is diffused over a narrow elliptical zone trending ne the greatest concentration of activity is near the center the central zone is characterized by deep focus strike slip events with predominantly n or e striking nodal planes these events are responding directly to compression in the direction of the regional compressive stress and extension perpendicular to the regional compressive stress within the weak zone the area surrounding the central zone is characterized by focal mechanisms with larger components of reverse or normal fault movements events with normal components are dominant on the edges in line with the regional stress as predicted by the stress model for a weak central zone under stress the agreement between observed earthquake focal mechanisms in southeastern tennessee and models of crustal stress surrounding a zone of weakness suggests that these events may be caused by a zone of weakness in the lower crust

loess chronology of the middle and upper pleistocene in tadjikistan the loess paleosol sequences of central asia are continuous terrestrial records of the quaternary period and enable detailed comparison with paleoclimatic archives such as marine and ice core records in order to reconstruct regional and global paleoclimatic and paleoecological development during the past 130 000 years thermoluminescence tl and infrared stimulated luminescence irsl dating methods are applied to the extensively studied loess paleosol sequence of the section at darai kalon chashmanigar tadjikistan in order to determine a more accurate chronological framework and climatostratigraphic reconstruction for the last interglacial glacial cycle luminescence dating suggests that the loess above the first pedocomplex from the top pc1 accumulated during the last glacial period a high accumulation rate of up to 1 20 m per 1000 years was determined for the last glacial loess especially for the uppermost 5 8 m pc1 formed during the last interglacial period oxygen isotope stage 5 the loess between pc1 and pc2 is designated to be of penultimate glacial deposition age infrared stimulated luminescence and tl age estimates are in agreement to 80 000 years before present bp indicating a long distance transport of the aeolian dust prior to deposition the upper numerical age limit range is between 300 000 and 450 000 years however reliable dating of the loess older than 130 000 years is not possible due to age scatter between samples and an inadequate increase of paleodose with depth this high resolution dating study underlines the importance of the section at darai kalon and indicates that it is one of the most continuous loess paleosol records of the northern hemisphere the chronological results are particularly important for the reconstruction of the human evolution in central asia suggesting much older age estimates than previously obtained for most of the archeological key sites associated with pc5 and pc4 in tadjikistan

chronology of late pleistocene pampa loess from the cordoba area in argentina in argentina loess palaeosol sequences were studied from the two sections at monte ralo and corralito located near to the city of cordoba in the east of the pampean ranges infrared optically stimulated luminescence irsl and thermoluminescence tl dating techniques were applied to set up a more reliable chronological framework for the upper pleistocene loess record irsl ages increase with depth and are stratigraphically consistent the oldest loess exposed correlates at least to the penultimate glaciation the luminescence dating study gives evidence for humid climate conditions with soil formation during the last interglacial period and the middle pleniglacial correlating to marine isotope stage mis 5 and 3 respectively three extended periods of soil formation are recorded in the loess palaeosol sequences at the corralito section these buried soils most likely correlate with the last interglacial and early last glacial period during the middle pleniglacial two palaeosols are intercalated in the loess successions in the cordoba area the periods of increased loess accumulation and deposition of loessic sediments correlate with more arid and glacial periods during the early pleniglacial the middle pleniglacial and the late glacial copyright 2009 john wiley sons ltd