geomorphology of the onset area of a paleo ice stream marguerite bay antarctic peninsula geomorphic features indicate that both glacial and melt water erosion characterize the onset area of the ancestral marguerite ice stream the large size of these features indicates that they formed over repeated glacial cycles most recently during the last glacial maximum ice drainage within the bay and on the inner continental shelf was strongly influenced by tectonic fabric deep isolated basins surrounded by rugged bedrock bathymetry characterize the innermost part of the bay drumlins and other streamlined features occur in the floors of these basins at depths of up to 900 m the outer bay has three large interconnected basins drumlins and megaflutings within these basins indicate ice was grounded at water depths up to 1000 m the orientations of these features show convergence of drainage from the northeast east and south into the marguerite paleo ice stream on the inner continental shelf the ice converged into a single wide trough dominated by mega scale glacial lineations this transition in geomorphic features from drumlins and megaflutings to mega scale glacial lineations occurs at the location on the continental shelf where sedimentary strata blanket bedrock and marks a zone of acceleration of the ice stream the glacially sculptured geomorphic features within marguerite bay co exist with anastomosing radial and relatively straight channels which become increasingly focused in a seaward direction this implies that a well organized subglacial drainage system existed within the bay at some point in the past copyright 2008 john wiley sons ltd

thermal regime rheology and seismicity in central japan abstract in the present study geothermal models of the crust for a number of individual structural units of honshu island japan are constructed the depth distribution of crustal seismicity is used as a tool to assess the reliability of the calculated thermal models it is demonstrated that where reliable information is available on cutoffs in seismicity at certain depths the temperature at those depths can be estimated from theological considerations to the accuracy of not worse than from geothermal modelling such temperatures can then be used as reference values in checking the validity of a geothermal model for a region this approach may be especially useful in constructing geothermal models for tectonically disturbed areas with non steady state thermal conditions

coastal resilience and late holocene tidal inlet history the evolution of dungeness foreland and the romney marsh depositional complex u k dungeness foreland is a large sand and gravel barrier located in the eastern english channel that during the last 5000 years has demonstrated remarkable geomorphological resilience in accommodating changes in relative sea level storm magnitude and frequency variations in sediment supply as well as significant changes in back barrier sedimentation in this paper we develop a new palaeogeographic model for this depositional complex using a large dataset of recently acquired litho bio and chrono stratigraphic data our analysis shows how over the last 2000 years three large tidal inlets have influenced the pattern of back barrier inundation and sedimentation and controlled the stability and evolution of the barrier by determining the location of cross shore sediment and water exchange thereby moderating sediment supply and its distribution the sheer size of the foreland has contributed in part to its resilience with an abundant supply of sediment always available for ready redistribution a second reason for the landform s resilience is the repeated ability of the tidal inlets to narrow and then close effectively healing successive breaches by back barrier sedimentation and ebb and or flood tidal delta development humans emerge as key agents of change especially through the process of reclamation which from the saxon period onwards has modified the back barrier tidal prism and promoted repeated episodes of fine grained sedimentation and channel inlet infill and closure our palaeogeographic reconstructions show that large barriers such as dungeness foreland can survive repeated catastrophic breaches especially where tidal inlets are able to assist the recovery process by raising the elevation of the back barrier area by intertidal sedimentation this research leads us to reflect on the concept of coastal resilience which we conclude means little without a clearly defined spatial and temporal framework at a macro scale the structure as a whole entered a phase of recycling and rapid progradation in response to changing sediment budget and coastal dynamics about 2000 years ago however at smaller spatial and temporal scales barrier inlet dynamics have been associated with the initiation stabilisation and breakdown of individual beaches and complexes of beaches we therefore envisage multiple scales of resilience operating simultaneously across the complex responding to different forcing agents with particular magnitudes and frequencies

the variation of heat generation density and seismic velocity with rock type in the continental lithosphere abstract the petrophysical properties radioactive heat generation compressional wave velocity and density are related to rock type in crystalline rocks the cation fraction in the rock forming minerals is applied to determine the relationships quantitatively heat generation exhibits considerable variation with rock type as well as with the geologic age of the rocks therefore the relation between heat generation and rock type has been split into a relation for phanerozoic rocks and another for precambrian rocks which exhibit significantly lower heat generation only 1 3 of that of phanerozoic rocks the interrelations between the petrophysical properties are applied to fennoscandia precambrian terrane and southern bavaria northern alpine foreland phanerozoic rocks to estimate the heat generation by radioactivity in the crust and the heat flow density from the upper mantle

the anomalous roxana silt and mid wisconsinan events in and near southern michigan abstract thick deposits of roxana silt are recognized only along the illinois river downstream from the woodfordian terminal moraine and are generally interpreted as being mainly loess with the bulk accumulating from about 40 000 to 30 000 yr ago in association with an altonian age glacier in northeastern illinois yet 11 14c dates indicate that southern michigan was not ice covered during that interval thus any proximate ice must have at best been restricted to great lakes basins an interpretation supported by the absence of late altonian till at critically located michigan and nearby sites late mid wisconsinan ice did however obstruct eastern drainage of the ancestral great lakes such glacial blockage the distribution of many michigan organic deposits within pre woodfordian lacustrine sediments and radiocarbon dates suggest that more than once late altonian lakes associated with the lake michigan basin drained into the illinois river erosion of lake and spillway bluffs along with repeated river fluctuations provided a source for the thick geographically restricted roxana silt meanwhile along other nearby rivers the supply was meager and the loess thin

some geological implications of average quaternary glacial conditions analyses of quaternary landscape evolution tend to focus on events associated with culminations of glacial and interglacial ages but for most of quaternary time environments were intermediate in character average quaternary glacial conditions based on assessment of the marine isotope record approximated those near the stage 2 stage 1 transition and during substages 5b and 5d isotope stages 3 and 4 and substages 5a d lie within one standard deviation of the mean value under average glacial conditions ice sheets lying over northern north america and europe were much more contracted than their full glacial counterparts and the distribution of mountain glaciers reflected a snowline depression of some 500 m geomorphic processes operating under average quaternary conditions contributed importantly to landscape evolution examples of landscapes that may represent such average conditions include cirques and fluvial deposits of the pacific northwest the fjords and strandflat of western norway and atolls of the tropical oceans by examining the geologic record from the perspective of average conditions rather than those of climatic extremes added insight can be gained regarding the evolution of quaternary landscapes

sedimentary heterogeneity and petrophysical characterization of barremian tsunami and barrier island inlet deposits the aliaga outcrop as a reservoir analogue galve sub basin eastern spain abstract the present study examined two sandstone deposits in the aliaga outcrop as a reservoir analogue over a distance of 200 m long and attempted to establish a correlation between sand facies and the petrophysical properties of the sandstones in order to investigate the reservoir heterogeneity the aliaga reservoir analogue represents the upper part of camarillas fm deposited during the barremian synrift phase of the galve sub basin iberian basin spain it is characterized by a transitional sedimentary interval from sandy dominant deposits to carbonate dominant deposits which were deposited under the same palaeoenvironmental conditions in relation to systems of back barrier sedimentation the description of the aliaga outcrop provided here consists of lithological descriptions of two sandstone deposits a tsunami and a barrier island inlet at both mesoscopic decimetres to tens of metres and microscopic scales millimetres to centimetres both deposits recognized at the basin scale were described in terms of sand grain size sand sorting and cementation further cores were drilled along outcrop to collect samples for porosity and permeability measurements both sandstone reservoirs are the result of different sedimentary processes that determined facies characteristics as the different petrophysical properties observed in these deposits consequently the sedimentary process controls the heterogeneity of the sandstones facies and thus the sand heterogeneity controls the distribution of the petrophysical properties the classification of sand facies in terms of sand sorting seems to be more appropriate for describing sand heterogeneity accordingly petrophysical parameters in both deposits were also influenced by sand sorting the sand facies and petrophysics heterogeneity of the described deposits can be hierarchically ordered first order heterogeneity is related to the basin scale second order heterogeneity is related to genesis and the conditions of sediment deposition and third order heterogeneity is related to synsedimentary faults and or post sedimentation events

response to david s fullerton s letter to the editor of quaternary research sangamon and sangamonian time division chronostratigraphic unit and geosol

absence of altonian glaciation in illinois abstract illinois was free of glacier ice from about 130 000 to 25 000 yr b p deposits of this time interval in northeastern illinois represented by core samples from test hole isgs s 30 are composed of leached nonglacigenic stratified or pedoturbated silty sediments that typically are organic rich and pedogenically modified these deposits overlie the sangamon soil which is identified by its stratigraphic position soil morphology and distinct alteration products in the clay mineral fraction including a variably swelling vermiculite like phase and a randomly interstratified kaolinite 10 a phase the regional extent of these deposits suggests that if altonian ice existed in the lake michigan basin it did not extend westward beyond the cuesta of silurian dolomite that rims the southwestern shore of lake michigan

formation and development of a tidal inlet from a washover fan west central florida coast u s a abstract a moderate sized washover fan generated by hurricane elena in 1985 on the barrier coast of west central florida was subsequently cut and reworked into a tidal inlet the entire washover fan was initially above mean low water with little tidal circulation over it after approximately one year this fan had been modified by tidal scouring into a tidal inlet with both flood and ebb tidal deltas after nearly two years this inlet is over 2 m deep carrying a tidal prism of 0 8 106 m3 and is essentially stable

four year performance and associated controlling factors of several beach nourishment projects along three adjacent barrier islands west central florida usa abstract to quantify the performance of several beach nourishment projects on three adjacent barrier islands located in west central florida a total of 5200 beach and nearshore profiles spaced at 300 m were surveyed monthly to bi monthly from 2006 to 2010 beach nourishment performance at annual temporal and kilometer spatial scales within the microtidal low wave energy barrier island coast is most significantly influenced by the interruption of longshore sediment transport by complex tidal inlet processes the inlet processes directly influencing adjacent beach nourishment performance include longshore transport interruption resulting from divergence induced by wave refraction over an ebb tidal shoal flood tidal currents along the beach and total littoral blockage by structured inlets secondary factors controlling the nourishment performance include project length and width shoreline orientation and antecedent geology a morphologic indicator of a large longshore transport gradient within the study area is the absence of a nearshore sandbar these non barred beaches are characterized by persistent shoreline erosion the presence of a sandbar indicates the dominance of cross shore processes with bar migration in response to wave condition variations and a relatively stable shoreline the entirety of a barrier island system should be considered when evaluating the performance of a nourishment

simultaneous determination of the three dimensional crustal structure and hypocenters beneath the kanto tokai district japan abstract a new method is proposed for determining the two dimensional depth distributions to the conrad and the moho together with station corrections and source parameters from first arrival time data in the present study the velocity structure is modelled by a hyperbolic function tanh and the configuration of each interface is expressed in a series of chebyshev functions with coefficients which are unknown parameters a non linear inversion method by tarantola and valette is applied for inversion an approximate ray tracing method with sufficient accuracy for a complex region is adopted for computation of seismic ray paths and travel times the method is applied to p wave first arrival time data from local earthquakes and explosions gathered in the seismological network by the national research center for disaster prevention to reveal the crustal structure beneath the kanto tokai district japan the results obtained in this study are very interesting and show the usefulness of the present method for the study of the crustal structure the distribution of station corrections is reasonable where there is information on the shallow structure low velocity zones appear around tokyo bay and the cape of omae and high velocity zones appear in the mountainous regions the depth to the conrad is about 12 16 km and its lateral change is gentle while the lateral change in the depth to the moho is comparatively large and there is a narrow region where the depth to the moho exceeds 40 km except for this region the central mountainous region the agreement of the crustal structure obtained in the present study with those by the previous refraction studies is fairly good in comparing our results to fractional velocity perturbation in layer 1 0 32 km derived with aki and lee s method by ishida and hasemi our work provides good information on the features causing the crustal velocity anomalies which have been unable to be constrained in ishida and hasemi s work

formation and migration of transverse bars along a tidal sandy coast deduced from multi temporal lidar datasets a field of long crested transverse bars was monitored from a 2 5 year series of topographic lidar surveys in the vicinity of a tidal inlet on the macrotidal mean spring tidal range 7 to 12 m west coast of cotentin normandy france the bar field the alongshore extent of which is about 1 8 km is composed of a total of 8 bars with lengths varying from 320 m to 1300 m and mean heights comprised between 0 5 m and 2 5 m bar cross sections are variable between bars and for a single bar and also over time the surveys show a consistent northward migration of the bars at a mean rate of about 2 m month but the rate is larger in winter than in summer the lidar observations show that the tidal inlet located at the southern limit of the bar field where the bars start forming comprises a large sediment platform that acts as a source of sand for the bars the ebb jet debouching from the inlet is deflected northward by the ambient strong shore parallel tidal currents in this large tide range setting and this may be the primary mechanism leading to the emplacement of the bars smaller wave formed swash bars that further feed the development of these large transverse bars have also been observed monitoring of bar migration in the course of six consecutive spring tides with fair weather conditions showed that strong spring tidal currents are sufficient to drive bar mobility in the absence of waves storm wave resuspension of sand is thus expected to enhance bar mobility rates as shown by the higher rates of winter bar migration compared to the summer rates the ebb jet explains the slower bar migration rates at the vicinity of the inlet these rates increasing with distance northward of the inlet as the tidal currents become unimpeded the main difference between these macrotidal transverse bars and their counterparts in microtidal settings resides in these strong tidal currents that are the essential driver of bar migration unlike the wave driven migration of microtidal bars the large tidal range in conjunction with storm wave activity also induces longshore and seasonal variability in bar morphology the transverse bars of normandy appear to be inscribed in a sand circulation system involving the west cotentin coast the large ebb tidal delta from which they are formed and the central cotentin embayment where they are ultimately incorporated into the nearshore sand pool longer term field hydrodynamic monitoring and modelling will be required in order to further elucidate the mode of formation of these transverse bars

the west central florida inner shelf and coastal system a geologic conceptual overview and introduction to the special issue abstract this paper provides an overview for this special publication on the geologic framework of the inner shelf and coastal zone of west central florida this is a significant geologic setting in that it lies at the center of an ancient carbonate platform facing an enormous ramp that has exerted large scale control on coastal geomorphology the availability of sediments and the level of wave energy in order to understand the holocene geologic history of this depositional system a regional study defined by natural boundaries north end of a barrier island to the apex of a headland was undertaken by a group of government and university coastal geologists using a wide variety of laboratory and field techniques it is the purpose of this introductory paper to define the character of this coastal inner shelf system provide a historical geologic perspective and background of environmental information define the overall database present the collective objectives of this regional study and very briefly present the main aspects of each contribution specific conclusions are presented at the end of each paper composing this volume

interaction between wave and tide generated processes at the mouth of a microtidal estuary matanzas river florida u s a abstract the zone of transition between the wave dominated open coast and tide dominated mouth of estuaries is complicated a time series study of wave parameters longshore currents and tidal parameters at the mouth of an estuary on the northeast coast of florida has demonstrated that tidal influence on nearshore processes is modest and localized tidal currents are nearly undetectable less than 0 5 km from the estuary mouth along the open coast tidal currents reach 80 cm s in the throat of the main ebb channel but immediately seaward of the terminal lobe of the ebb delta the tidal component is barely detectable with longshore currents predominating lateral flood channels adjacent to the estuary mouth show that tidal currents are significant and dominate longshore currents near low tide stage but are suppressed by longshore currents near high tide weather patterns may have an important effect on tidal processes at the estuary mouth because they control wave impingement and therefore longshore current speed and direction longshore currents may reinforce or suppress tidal currents particularly in lateral flood channels

suwannee channel of the paleogene coastal plain support for the carbonate suppression model of basin formation a recently proposed model postulates that a basin separating a carbonate from an adjacent terrigenous clastic depocenter is a consequence of the neighboring depocenters rather than a precondition for their coexistence a test of the model is provided by comparison with the well studied carbonate terrigenous clastic transition of the united states coastal plain in general the model is substantiated although deviations caused by changes in sea level terrigenous clastic input and tectonism are noted

new insights on illinoian deglaciation from deposits of glacial lake quincy central indiana abstract the deposits of glacial lake quincy overlie a diamicton associated with the classically defined illinoian limit in central indiana this lake covered at least 180 km 2 with a depth of 20 m and developed when the illinoian ice sheet retreated 15 km from the maximum limit causing lake impoundment against devore ridge overflow from glacial lake quincy eroded across the ridge forming a number of steeped walled outlets a section along mill creek exposes a sedimentologic sequence associated with glacial lake quincy from a subglacial diamicton to ice proximal to ice distal glacial lacustrine sediments we report new optical ages by multiple aliquot regenerative dose procedure for the fine grained rhythmically bedded sediments presumed to represent the lowest energy depositional facies dominated by suspension settling which maximized sunlight exposure in turn optical ages were determined on the fine grained 4 11 m polymineral and quartz fractions under infrared and blue excitation which yielded statistically similar ages optical ages span from ca 170 to 108 ka with the average of 16 optical ages indicating deglaciation at ca 135 ka generally coincident with marine oxygen isotope stage 6 to 5 transition and rise in global sea level

magnetotelluric image of the crust and upper mantle in the backarc of the northwestern argentinean andes magnetotelluric data from the backarc of the central andes in nw argentinawere re examined by employing impedance tensor decomposition and 2 d inversion and modelling techniques the data in the period range of 50 15 000 s were collected on a profile of 220 km length reaching from the eastern cordillera across the santa barbara system to the andean foreland of the argentinean chaco after a dimensionality analysis data from most sites were treated as regional 2 d the exception was the eastern section of the profile where the magnetotelluric transfer functions for periods 1000 s reflect a 3 d earth application of two tensor decomposition schemes yielded a regional strike direction of n s which is the azimuth of the central andean mountain chains several 2 d models were obtained by pseudo and full 2 d occam inversion schemes special emphasis was placed on the inversion of phase data to reduce the influence of static shifts in the apparent resistivity data the smooth inversion models all show a good conductor at depth a final model was then calculated using a finite element forward algorithm the most prominent feature of the resulting model is a conductor which rises from depths of 180 km below the chaco region to 80 km beneath the santa barbara system and the eastern cordillera its interpretation as a rise of the electrical asthenosphere is supported by seismic attenuation studies magnetotelluric results surface heat flow distribution in the area and the electrical properties of crustal and mantle rocks suggest that the upper mantle is predominantly ductile beneath the eastern cordillera and the western santa barbara system this generally agrees with anelastic seismic attenuation models of the area and is useful in discriminating between models of q quality factor distribution

role of hurricanes in the holocene stratigraphy of estuaries examples from the gulf coast of florida abstract sarasota and little sarasota bays are shallow coastal bays located landward of a holocene barrier inlet complex on the west central microtidal gulf coast of florida sediments presently accumulating in the bay consist of 1 fine to very fine quartz sand contributed from the gulf shoreline during storm generated washover through tidal inlets and from reworking of older deposits 2 fine sand to pebble sized quartz and phosphatic sediment contributed by tertiary and pleistocene deposits 3 biogenic carbonate debris which is produced within the bays and or derived from the gulf of mexico 4 clay minerals derived from weathering of tertiary and pleistocene carbonates and clays and 5 particulate organic debris interpretations from 51 vibracores from throughout the bays have enable delineation of four major depositional sedimentary facies resulting from specific environmental conditions protected bay open bay tidal delta washover and storms bedrock in the area ranges from 0 to about 8 m msl and is largely responsible for the areal configuration of the bay and the location of the barrier islands the holocene stratigraphy of both bays has been greatly influenced by the passage of major hurricanes which carried large volumes of sand and shell gravel into the bays at least four of these storms are documented in these cores three storm units from sarasota bay have been radiocarbon dated at 2 270 1 320 and 240 years before present ybp historically documented severe hurricanes influenced this coast in 1848 and 1921 hurricanes interrupted the normal low energy slow deposition in the bays and caused inlets to open and close three storm generated sedimentary facies are identified 1 a graded storm facies which is composed of conspicuously fining upward units ranging from sandy shell gravel to slightly shelly quartz sand 2 a homogenous storm facies consisting of homogenous and relatively thin shelly sand and gravel units and 3 a fluvial storm facies which is muddy and generally free of shells representing terrigenous influx from runoff

impacts of human interventions on the evolution of the ria formosa barrier island system s portugal abstract human interventions on sandy barriers disturb natural barrier dynamics to the extent of having become key forces in modifying geomorphological evolution this work identifies natural and human induced drivers and analyses their importance to the multi decadal evolution of the ria formosa barrier island system in south portugal aerial photographs from the last six decades and historical maps are used to assess changes in cross shore rates morphological characteristics barrier and dune widths inlet morphology and migration and barrier areas through systematic methods that can be easily transferred to other barrier systems interventions and especially hard engineering ones jetties inlet stabilisations affected barrier evolution trends shore perpendicular works increased shoreline progradation updrift and initiated coastal retreat downdrift with strongest erosive impacts along the edges of the system inlet stabilisations changed tidal inlet hydrodynamics and initiated ebb shoal attachment to the barriers on either side of a non migrating inlet that experienced loss of tidal prism this shoal attachment was the main factor for the increase in total barrier area of ria formosa during the 60 years of analysis barrier growth after 2005 was slower which could indicate that the system is reaching morphodynamic stability

earthquake cutoff depth as a possible geothermometer applications to central japan abstract geothermal models of the earth s crust are constructed for eight individual structural units of honshu island japan for each unit thermal models responding to possible property variations are calculated in addition to conductive heat transfer the considered geothermal models account also for the thermal effects of fluid circulation within the crust and tectonic motions across the faults on the basis of these geothermal models theological models of the crust are derived those thermal models are considered as most reliable where there is reasonable correspondence between rheological stratification of the crust and the variations of crustal seismicity it is demonstrated that earthquake cutoff depth serving as a kind of geothermometer can be used as additional information to decrease the uncertainties involved in the geothermal models

morphodynamics of the barrier inlet system west central florida the barrier inlet system along the gulf coast of peninsular florida has one of the most diverse morphologies of any barrier system in the world the delicate balance between tidal and wave generated processes on this low energy coast permits only slight changes in either of these processes to result in significant and rapidly developing morphologic responses some of these responses are the result of natural phenomena such as hurricanes opening tidal inlets closure of inlets due to longshore transport of sediment and changes in the availability of sediment tidal prism is the primary factor in controlling inlet morphology and is greatly influenced by anthropogenic activities in the backbarrier area human activity has also modified the coast in many ways over the past several decades beginning with the construction of the first causeways in the 1920s the various modifications by development have resulted in important morphodynamic changes in the barrier inlet system these include hardening the coast on the beach and at inlets dredging and filling in backbarrier environments and construction of fill type causeways connecting the islands to the mainland construction of seawalls and jetties has inhibited normal coastal processes examples include the downdrift erosion at blind pass and big sarasota pass construction of fill type causeways between the barriers and the mainland has created artificial tidal divides that reduce the tidal prism at some inlets thereby resulting in instability or closure such as blind pass and dunedin pass this is further exacerbated by dredge and fill construction that reduces tidal prism by reducing the area of open water in the backbarrier dredging of the intracoastal waterway also results in a negative impact on selected inlets by channeling tidal flux away from some inlets impacts of these changes inhibit the barrier inlet environments from responding to open coast processes

decadal behavior of tidal inlet associated beach systems northwest ireland in relation to climate forcing abstract shoreline and ebb channel evolution between 1834 and 2008 was recorded at three embayed beaches in northwest ireland with historically stable relative sea level the beaches are geologically constrained within bedrock valleys and have minimal contemporary sediment input their behavior is strongly influenced by tidal inlet dynamics of adjacent estuaries major observed changes in shoreline position are linked to fluctuations in inlet ebb channel orientation comparison of the available historical record of geomorphological change with instrumental and proxy climate records suggests that inlet changes may be driven by fluctuations in average storminess periods of high storminess perturb the inlet system causing major changes in ebb channel configuration after which sediment redistribution returns the system to its former state over a prolonged period years to decades

thermal constraints on earthquake depths in california the high quality databases for california seismicity from the southern and northern california earthquake centers and an extensive compilation of thermal measurements in california are used to quantify the concept of temperature as a fundamental parameter for determining the thickness of the seismogenic zone the base of this zone below which only a small percentage of crustal earthquakes occur is termed the cutout depth and it is at or near the brittle ductile transition in the crust based on laboratory deformation studies this transition should be temperature strain rate lithology and stress state dependent in this study qualitative comparisons between the heat flow in california and earthquake hypocentral distributions show first that as expected earthquake cutout depths are inversely related to heat flow second the epicentral distributions tend to parallel thermal transitions this correlation is probably related to stress concentrations in these locations an ancillary observation is that the cooler western mojave block in southern california appears to be behaving similarly to the tibetan indenter block in asia as faults tend to go around it into areas of higher heat flow where the seismogenic zone is thinner and the crust may be weaker and it is pushed toward and under the southern cold sierra nevada block third to quantitatively compare the data sets temperatures for the seismicity cutout depth in california were calculated using the steady state 1d heat conduction equation with the variables based on published values for heat flow heat generation and thermal conductivity the analysis was restricted to profiles along which the heat flow and earthquake databases were constrained which allowed the error in the temperature calculation to be determined using monte carlo simulations the results show that two distinct ranges of temperatures dependent upon location describe the cutout depth d 99 of seismicity for california 450 50 c and 260 40 c the 450 50 c cutout depth temperature is most widespread geographically occurs within many provinces and is higher than the frequently referenced temperature of 300 50 c for the brittle ductile transition the lower temperature 260 c seems to be restricted to provinces where the heat flow is near or below 50 mw m 2 such as the mojave block and sierra nevada the differences in these cutout temperatures suggest that additional factors such as strain rate stress regime and or lithology may contribute to the seismicity cutout depth fourth along a profile with significant seismic activity and a 450 c cutout temperature the envelope for the maximum energy released by earthquakes falls at or below the 300 c isotherm detailed characterization of the heat flow and earthquake synergy in this manner furthers the understanding of the earthquake process and can aid in the estimation of the maximum depth of rupture for great earthquakes particularly in areas of low seismicity thus reducing uncertainties in hazard calculations manuscript received 26 february 2003

restricted regional extent of the laurentide ice sheet in the great lakes basins during early wisconsin glaciation it is conventional wisdom that the last continental ice sheet in north america extended beyond the southern margins of the great lakes basins during both early ca 75 ka and late 30 ka phases of wisconsin glaciation this model hinges on the presence of a regionally extensive diamict traditionally interpreted as a subglacial till exposed in the ontario basin at toronto between last interglacial lacustrine sediments and late wisconsin tills the discovery of an in situ lacustrine ostracode fauna confirms previous sedimentological and geophysical investigations which concluded that the early wisconsin diamict is not a subglacial deposit but a stony mud deposited on the floor of an extensive glacial lake the unit together with younger mid wisconsin sediments was only overridden by the laurentide ice sheet during the late wisconsin after 30 ka we argue that during the early phase of wisconsin glaciation the laurentide ice sheet was thin highly dynamic and of insufficient volume to extend fully across the great lakes basins a situation more closely in accordance with the marine 18o 16o record and other proxy climatic data that show maximum cooling and global ice volumes at about 20 ka

loess studies in central united states evolution of concepts abstract few words in the realm of earth science have caused more debate than loess it is a common term that was first used as a name of a silt deposit before it was defined in a scientific sense because this loose deposit is easily distinguished from other more coherent deposits it was recognized as a matter of practical concern and later became the object of much scientific scrutiny loess was first recognized along the rhine valley in germany in the 1830s and was first noted in the united states in 1846 along the lower mississippi river where it later became the center of attention the use of the name eventually spread around the world but its use has not been consistently applied over the years some interpretations and stratigraphy correlations have been validated but others have been hotly contested on conceptual grounds and semantic issues the concept of loess evolved into a complex issue as loess and loess like deposits were discovered in different parts of the us the evolution of concepts in the central us developed in four indefinite stages the eras of 1 discovery and development of hypotheses 2 conditional acceptance of the eolian origin of loess 3 bandwagon popularity of loess research and 4 analytical inquiry on the nature of loess toward the end of the first era around 1900 the popular opinion on the meaning of the term loess shifted from a lithological sense of loose silt to a lithogenetic sense of eolian silt however the dual use of the term fostered a lingering skepticism during the second era that ended in 1944 with an explosion of interest that lasted for more than a decade in 1944 r j russell proposed and h n fisk defended a new non eolian property based concept of loess the eolian advocates reacted with surprise and enthusiasm each side used constrained arguments to show their view of the problem but did not examine the fundamental problem which was not in the proofs of their hypothesis but in the definition of the term between 1944 and about 1950 the debates about loess reached a maximum level of complexity the main semantic problem was submersed in peripheral arguments about physical properties and genetic interpretations the scholarly treatment of the subject by fisk and russell stimulated quality responses from a diversity of earth scientists interested in academic and applied studies particularly geo history pedology soil mechanics and stratigraphy the long lasting popularity of loess studies during the bandwagon era lasted to about 1970 by that time the analytical and technical interests had attracted the mainstream into the fourth era with a focus beyond the old arguments although fisk and russell found themselves defending an unpopular theory they stimulated a scientific interest in the late quaternary history of the mississippi valley that may never be exceeded

tectonic evolution of the triple junction off central honshu for the past 1 million years seno t ogawa y tokuyama h nishiyama e and taira a 1989 tectonic evolution of the triple junction off central honshu for the past 1 million years in j p cadet and s uyeda editors subduction zones the kaiko project tectonophysics 160 91 116 we discuss several models of the evolution of the trench trench trench triple junction off central honshu during the past 1 m y on the basis of plate kinematics morphology gravity and seismic reflection profile data available for the area the study area is characterized by large basins 7 8 km deep on the inner lower trench slope on the philippine sea side and the deep 9 km izu bonin trench to the east between the basins and the trench there are 6 7 km deep basement highs the triple junction is unstable due to the movement of the philippine sea plate at a velocity of 3 cm yr in wnw direction with respect to eurasia northeast japan subparallel to the strike of the sagami trough generally we can expect the boundary area between the philippine sea and pacific plates to be extended because the pacific plate is unlikely to follow the retreating philippine sea plate due to the obstruction of the southeastern comer of eurasia the above peculiar morphology of the junction area could have resulted from this lack of stability however there are several possible ways to explain the above morphology our gravity model across the trench basement high basin area shows that the basement highs are made of low density materials 1 8 2 g cm3 thus we reject the mantle diapir model which proposes that the basement highs have been formed by diapiric injection of serpentinites between the retreating philippine sea plate and the pacific plate the stretched basin model proposes that the basins have been formed by stretching of the philippine sea plate wedge we estimated the extension to be about 10 km at the largest basin we reconstructed the morphology at 1 ma by moving the philippine sea plate 20 km farther to the east after closing the basins and thus obtained 8 km depth of the 1 ma trench which is similar to that of the present japan trench to the north although this stretched basin model can explain the formation of the basins and the deep trench other models are equally possible for instance the eduction model explains the origin of the basin by the eduction of the philippine sea basement from beneath the basement high while the accretion model explains the basement highs by the accretion of the in bonin trench wedge sediments in both of these models we can reconstruct the 1 ma trench depth as about 8 km similar to that of the stretched basin model the deformation of the basement of the basins constitutes the best criterion to differentiate between these models the multi channel seismic reflection profiles show that the basement of the largest basin is cut by normal faults in particular at its eastern edge this suggests that the stretched basin model is most likely however the upper part of the sediments shows that the basement high to the east has been recently uplifted this uplift is probably due to the recent 0 5 ma start of accretion of the trench wedge sediments beneath this basement high

depositional response to seagrass mortality along a low energy barrier island coast west central florida abstract analysis of aerial photographs and nearshore surficial sediment samples from the northern islands of the west central barrier system of florida indicates that 1 seagrass beds in the nearshore zone have controlled onshore longshore sand transport and 2 resulting sedimentary accumulations within nearshore seagrass beds make differentiation between nearshore and backbarrier facies difficult between 1957 and 1967 an extensive seagrass community occupying the nearshore zone off anclote key disappeared thus allowing the sudden and rapid onshore and longshore transport of sand the 1 000 year old barrier island lengthened 30 percent by recurved spit growth in a 15 year period from 1967 82 although there are no direct observations four possible causes of seagrass mortality have been postulated which are as follows 1 physical destruction by storms 2 infection by pathogens 3 decline of water quality due to human development and 4 overgrazing by sea urchins because of the ability of seagrasses to trap fine grained sediments contribute organic matter and provide for low energy sheltered molluscan biocoenose strong similarities remain between surficial sediments of recently devegetated active nearshore zones and backbarrier lagoonal facies the stable carbon isotopic ratios and the molluscan assemblages within the ubiquitous fine quartz sands in particular are similar within these two normally disparate environments this study indicates that the development and destruction of benthic floral communities should be considered as a process that generates episodic cyclic depositional events in the sedimentary record additionally such changes in seagrass communities should be expected to present a blurred distinction between nearshore and backbarrier sedimentary facies

morphodynamics of an anthropogenically altered dual inlet system john s pass and blind pass west central florida usa abstract the morphodynamics of the john s pass blind pass dual inlet system were investigated based on hydrodynamic and morphology measurements and numerical modeling the co existence of the dual inlets is realized by the dominance of mixed energy john s pass in terms of tidal prism and size of the ebb delta and the artificial maintenance of the wave dominated migratory blind pass due to the secondary role of blind pass the aggressive anthropogenic activities there do not seem to have a significant influence on the morphodynamics of john s pass on the other hand the opening in 1848 and subsequent evolution of john s pass had substantial influence on blind pass causing it to migrate rapidly to the south in addition anthropogenic activities had much more influence on the morphodynamics of the secondary blind pass than that of the dominating john s pass results from numerical modeling provide a semi quantitative understanding of the hydrodynamics and morphodynamics of john s pass and blind pass in association with cold front passages which have substantial influences on inlet morphology two large eddies are modeled from the interactions between the southward longshore current and john s pass ebb and flood flow respectively these eddies are closely related to the morphodynamics of the channel margin linear bar and longshore transport divergence at the downdrift side both are key features of a mixed energy inlet the shallow water and wave breaking induced longshore current and elevated sediment suspension along the ebb delta terminal lobe provide the pathway for sediment bypassing the morphodynamics of blind pass are dominated by wave forcing the weak ebb jet is not capable of forming a sizable ebb delta and tends to be deflected by the strong longshore current causing elevated longshore transport along the downdrift beach the 90 degree turn of the inlet which is common for wave dominated migratory inlets results in weak ebb flushing along the updrift north side of the inlet and is responsible for the alongshore migration of the inlet before the artificial stabilization and sedimentation along the northern side of the inlet following stabilization

sedimentology and stratigraphy of tidal sand ridges southwest florida inner shelf abstract detailed investigation of linear shelf sand ridges located off the southwest coast of florida shows them to be tide dominated sand bodies these ridges are remarkably similar to the large sand ridges of the north sea and they have abundant apparent analogs in the stratigraphic record many of which are important petroleum producers the florida ridges are asymmetric in profile about 10 km long 1 km wide with relief of 3 4 m with the adjacent sea bed extensive tidal current monitoring sediment distribution patterns and side scan sonar surveys permit characterizing their morphodynamics tidal currents show distinct bidirectional patterns with speeds up to 70 cm s there is slight flood dominance and currents show much higher velocities in the troughs as compared to the crests of he ridges megaripples and sand waves are widespread and migrate obliquely across the ridges at opposite directions on the gentle and steep sides of the ridge shallow high resolution seismic data and 39 vibracores in the area of the ridges show a consistent sequence characterized by three ascending holocene lithofacies 1 muddy quartz sand with limestone clasts 2 bioturbated muddy shelly quartz sand and 3 well sorted cross stratified quartz sand that characterizes the sand ridges themselves each of the tidal sand ridges displays a coarsening upward sequence of fine well sorted sand small scale multidirectional cross stratification dominates the stratigraphy of the cores in this facies but megaripple cross stratification is also present all data indicate that these tidal ridges are good modern analogs for many of the shelf sand bodies in the ancient record especially the mesozoic of the mid continent area

chronological framework for the deglaciation of the lake michigan lobe of the laurentide ice sheet from ice walled lake deposits a revised chronological framework for the deglaciation of the lake michigan lobe of the south central laurentide ice sheet is presented based on radiocarbon ages of plant macrofossils archived in the sediments of low relief ice walled lakes we analyze the precision and accuracy of 15 ams 14 c ages of plant macrofossils obtained from a single ice walled lake deposit the semi circular basin is about 0 72 km wide and formed of a 4 to 16 m thick succession of loess and lacustrine sediment inset into till the assayed material was leaves buds and stems of salix herbacea snowbed willow the pooled mean of three ages from the basal lag facies was 18 270 50 14 c a bp 21 810 cal a bp an age that approximates the switch from active ice to stagnating conditions the pooled mean of four ages for the youngest fossil bearing horizon was 17 770 40 14 c a bp 21 180 cal a bp material yielding the oldest and youngest ages may be obtained from sediment cores located at any place within the landform based on the estimated settling times of overlying barren rhythmically bedded sand and silt the lacustrine environment persisted for about 50 more years at a 67 confidence level the dated part of the ice walled lake succession persisted for between 210 and 860 cal a modal value 610 cal a the deglacial age of five moraines or morainal complexes formed by the fluctuating margin of the lake michigan lobe have been assessed using this method there is no overlap of time intervals documenting when ice walled lakes persisted on these landforms the rapid readvances of the lobe during deglaciation after the last glacial maximum probably occurred at some point between the periods of ice walled lake sedimentation copyright 2011 john wiley sons ltd

provenance age and environment of mid wisconsinan slackwater lake sediment in the st louis metro east area usa abstract valleys tributary to the mississippi river contain fossiliferous slackwater lake sediment equality formation deposited in response to aggradation of the mississippi river valley during the last glaciation in the st louis metro east area the lower part of the equality formation is primarily laminated fossiliferous silt and clay deposited from about 44 150 to 24 310 14c yr b p the upper equality formation is primarily very fine sand to silt deposited from about 21 200 to 17 000 14c yr b p among the four cores that sample this succession in the st louis metro east area core mnk 3 38 64en 90 01ew was selected for detailed study three sources are distinguished by the following characteristics 1 gray smectite quartz se rich feldspar poor material of the des moines wadena and james lobes 2 reddish brown kaolinite cu fe rich sediment of the superior and rainy lobes and 3 brown illite dolomite sr rich sediment of the lake michigan and green bay lobes the earliest sediments 44 150 to 41 700 14c yr b p were derived from the central and western provenances and are chronocorrelative with the lower roxana silt a hiatus occurred from about 41 700 to 29 030 14c yr b p when much of the middle roxana silt meadow member was deposited on adjacent uplands the youngest sediment includes evidence of heightened activity of the superior lobe at about 29 000 14c yr b p the lake michigan and green bay lobes from about 25 000 to 24 000 14c yr b p and the wadena des moines james lobes at about 21 000 14c yr b p

is northern honshu a microplate abstract seismic slip vectors along the japan trench the eastern margin of the japan sea and the sagami trough are compared with global relative plate motions rm2 minster and jordan 1978 to test a new hypothesis that northern honshu japan is part of the north american plate this hypothesis also claims that the eastern margin of the japan sea is a nascent convergent plate boundary kobayashi 1983 nakamura 1983 seismic slip vectors along the japan trench are more parallel to the direction of the pacific north american relative motion than that of the pacific eurasian relative motion however the difference in calculated relative motions is too small avoid to the possibility that a systematic bias in seismic slip vectors due to anomalous velocity structure beneath island arcs causes this apparent coincidence seismic slip vectors and rates of shortening along the eastern margin of the japan sea for the past 400 years are also consistent with the relative motion between the north american and eurasian plates calculated there seismic slip vectors and horizontal crustal strain patterns revealed by geodetic surveys in south kanto beneath which the philippine sea plate is subducting indicate two major directions one is the relative motion between the north american and philippine sea plates and the other that between the eurasian and philippine sea plates one possible interpretation of this is that the eastern margin of the japan sea may be in an embryonic stage of plate convergence and the jump of the north american eurasian plate boundary from sakhalin central hokkaido to the eastern margin of the japan sea has not yet been accomplished in this case northern honshu is a microplate which does not have a driving force itself and its motion is affected by the surrounding major plates behaving as part of either the eurasian or north american plate another possibility is that the seismic slip vectors and crustal deformations in south kanto do not correctly represent the relative motion between plates but represent the stresses due to non rigid behaviors of part of northern honshu

recent geological history and modern sedimentary processes along an incipient low energy epicontinental sea coastline northwest florida abstract a major portion of florida s gulf of mexico coastline is a siliciclastic sand starved low wave energy system dominated by marshes that face the open sea because of its location at the center of an enormous 350 000 km2 flooded broad flat ancient carbonate platform this coastline can be viewed as the margin of an incipient epicontinental sea within a 65 km sector along this 300 km long open marine marsh coast four distinctly different morphological sectors have been identified 1 berm ridge marsh shoreline 2 marsh peninsula shoreline 3 marsh archipelago shoreline and 4 shelf embayment shoreline the underlying paleogene limestone bedrock topography results from karstification and dissolution processes this antecedent topography and the distribution of actively discharging freshwater springs affect sedimentary processes facies and stratigraphic units the morphology and processes within the four coastal sectors vary as a function of a northerly decrease in the thickness of relict pleistocene quartz sand cover and an increase in the complexity and relief of the underlying bedrock topography each of the four coastal sectors has a unique distribution of sedimentary products in addition each has responded differently to rising sea level a process that continues to control the spatial distribution of organisms and sediments however the sedimentary lithosomes in all four coastal sectors share a similar fate during landward shoreline translation within the inner continental shelf very little of the marsh stratigraphy or large oyster bioherms is preserved only those sediments that have accumulated within bedrock depressions or sinkholes have the best chance for long term retention thus a condensed stratigraphic section is produced since only thin and discontinuous sediment accumulations are preserved the relief and texture of the bedrock surface due to chemical etching and bioerosion must also be used as clues to the recognition of similar coastal systems in ancient settings

barrier island stratigraphy and holocene history of west central florida abstract although the morphology of the barrier inlet system along the west central florida coast is quite complicated the stratigraphy of these barriers is rather simple the basal holocene unit in most cores is an organic rich muddy sand that represents a vegetated paralic marine coastal environment similar to that which is north and south of the present barrier system above that unit is a muddy bioturbated sand that displays a marine fauna at most locations but also contains crassostrea virginica in a few places these sediments accumulated in a low energy marine setting that may or may not have been protected by a barrier island much of this facies also represents sediment that was delivered as washover deposits in an intertidal or subtidal setting and was subsequently bioturbated the facies that can be attributed to a barrier island with some certainty are no more than 3000 years old and on most islands are much younger these are the shelly sand and sorted sand facies the shelly strata represent deposition in nearshore beach supratidal washover or intertidal spillover environments and tidal inlet and tidal delta channels whereas the sorted sand is typical of eolian deposition in dunes or the backbeach and some tidal delta elements the presence of holocene oyster beds offshore of a present barrier suggests that some of these islands formed significantly offshore and moved to their present position through washover it is likely that most of these barriers initially formed through upward shoaling by waves although there is significant morphologic difference between the wave dominated and mixed energy drumstick barrier islands their stratigraphy is quite similar the only significant difference is the presence of extensive progradation on at least part of the drumstick islands and a relatively high amount of former washover deposits on the wave dominated type

thermo mechanical structure beneath the young orogenic belt of taiwan abstract we investigate the thermo mechanical properties beneath the young orogenic belt of taiwan by constructing a shear strength profile from a vertical stratified rheological structure the stratified rheological structure is estimated based on the recently developed thermal structure and its likely composition subduction collision in the young orogenic belts and the thick accretionary wedge make a significant contribution to the growth of sialic crust in the hinterland the sialic bulk crust not only results in a low seismic velocity but also produces weak crust in the hinterland the earthquake depth frequency distribution in the foreland and hinterland correlates very well with the regimes of the brittle ductile transition revealed in the strength profile our results show that the observed two layer seismicity in the foreland is due to a moderate geotherm and an intermediate mafic bulk composition while single layer seismicity in the hinterland is due to its felsic bulk composition in the foreland the mechanically strong crust msc and the mechanically strong lithosphere msl coincide with frequent seismicity the shallow msc in the hinterland is consistent with the 20 to 25 km seismicity occurring there the total lithospheric integrated strength lis in the hinterland is only about half of that in the foreland suggesting a weak lower crust and lithosphere mantle in the hinterland the results confirm that the earthquake cutoff depth is a proxy for temperature the calculated decrease of effective elastic thickness eet from the orogenic margin foreland to the center hinterland is consistent with the results of flexure modeling in most orogenic belts due to the weak lis in the hinterland crustal thinning and rifting may occur in the future our results thus suggest that the mechanical structure is also closely related to the composition and is not directly reflected in the thermal structure

a life cycle model for wave dominated tidal inlets along passive margin coasts of north america abstract a regional overview of 107 wave dominated tidal inlets along the u s atlantic coast u s gulf of mexico coast and canadian gulf of st lawrence coast yielded a generalized wave dominated tidal inlet life cycle model that recognized the rotational nature of tidal inlets tidal inlets are influenced by concurrently acting processes transpiring over two timescales short term event driven processes and long term evolutionary processes wave dominated tidal inlets are classified into three rotational categories based on net longshore sediment transport direction and rotation direction along the landward back barrier portion of the inlet channel downdrift channel rotation updrift channel rotation or little to no channel rotation lateral shifting of the flood tidal delta depocenter in response to available estuarine accommodation space appears to control inlet channel rotation flood tidal delta deposits fill accommodation space locally within the estuary i e creating bathymetric highs causing the tidal inlet channel to rotate external influences such as fluvial discharge pre existing back barrier channels and impeding salt marsh will also influence inlet channel rotation storm events may rejuvenate the tidal inlet by scouring sediment within the flood tidal delta increasing local accommodation space wave dominated tidal inlets are generally unstable and tend to open concurrently migrate laterally and rotate infill and close channel rotation is a primary reason for wave dominated tidal inlet closure during rotation the inlet channel lengthens and hydraulic efficiency decreases thus causing tidal prism to decrease tidal prism estuarine accommodation space and sediment supply to the flood tidal delta are the primary variables responsible for tidal inlet rotation stability of wave dominated tidal inlets is further explained by stability s tidal prism estuarine accommodation space v volume of annual sediment supply mt rotating wave dominated tidal inlets follow a six stage evolutionary model whereas wave dominated tidal inlets that exhibit little to no rotation follow a five stage evolutionary model

anthropogenic influences on shoreline and nearshore evolution in the san francisco bay coastal system abstract analysis of four historical bathymetric surveys over a 132 year period has revealed significant changes to the morphology of the san francisco bar an ebb tidal delta at the mouth of san francisco bay estuary from 1873 to 2005 the san francisco bar vertically eroded an average of 80 cm over a 125 km 2 area which equates to a total volume loss of 100 52 million m 3 of fine to coarse grained sand comparison of the surveys indicates the entire ebb tidal delta contracted radially with the crest moving landward an average of 1 km long term erosion of the ebb tidal delta is hypothesized to be due to a reduction in the tidal prism of san francisco bay and a decrease in coastal sediment supply both as a result of anthropogenic activities prior research indicates that the tidal prism of the estuary was reduced by 9 from filling diking and sedimentation compilation of historical records dating back to 1900 reveals that a minimum of 200 million m 3 of sediment has been permanently removed from the san francisco bay coastal system through dredging aggregate mining and borrow pit mining of this total 54 million m 3 of sand sized or coarser sediment was removed from central san francisco bay with grain sizes comparable to the ebb tidal delta and its direct connection to the bay mouth removal of sediments from central san francisco bay may limit the sand supply to the delta and open coast beaches swan wave modeling illustrates that changes to the morphology of the san francisco bar have altered the alongshore wave energy distribution at adjacent ocean beach and thus may be a significant factor in a persistent beach erosion hot spot occurring in the area shoreline change analyses show that the sandy shoreline in the shadow of the ebb tidal delta experienced long term 1850s 1890s to 2002 and short term 1960s 1980s to 2002 accretion while the adjacent sandy shoreline exposed to open ocean waves experienced long term and short term erosion therefore the recently observed accelerating rates of bay sediment removal ebb tidal delta erosion and open coast beach erosion are all correlated temporally

cyclical evolution of a modern transgressive sand barrier in northwestern spain elucidated by gpr and aerial photos abstract the internal structure of a modern baymouth barrier is analyzed in detail including its historical evolution and the factors controlling it historical evolution was reconstructed using available aerial photographs from 1956 to 2003 detailed geophysical data were acquired using ground penetrating radar gpr and analyzed along with airphotos to reconstruct the recent evolution of a barrier located in northwestern spain the gpr data reveal the internal architecture of the barrier which consists of two main radar facies 1 washover deposits associated with landward barrier migration and vertical aggradation and 2 beach deposits associated with seaward barrier progradation the reconstruction of the stratigraphic sequence indicates the occurrence of two erosive periods followed by an accretionary period the erosion along the barrier is outlined by the presence of three well defined bounding surfaces the stratigraphic record of the subsequent recovery phase depends on the impact level of the erosive phase which is controlled by the presence of ephemeral inlets along the barrier this alternating behavior implies a discontinuous shoreline trajectory in spite of a net landward migration this trend is consistent with regional sea level rise albeit being intensified locally by the interplay of sediment starvation and storm regime landward barrier retreat occurs by overwash and inlet breaching which permits barrier preservation of volume due to a continuous constructive destructive cycle the results acquired from this example expand our understanding of the internal structure and evolutionary trends of transgressive sand barriers

siliciclastic to carbonate transition on the inner shelf embayment southwest florida abstract the inner shelf embayment adjacent to southwest florida is a low energy system which displays a distinct and demonstrable transition from dominantly siliciclastic sediments in the north to virtually pure biogenic carbonates in the south sediment sources are littoral transport from the north autochthonous biogenic debris a modest input from land derived runoff and a small amount from reworking of older strata siliciclastic sediments are well sorted fine quartz sand and terrigenous and biogenic mud which is concentrated along the coast of the southern half of the 90 km coast where it accumulates from adjacent terrigenous sources biogenic carbonate ranges from mud to gravel in size and is dominated by sand and gravel the transition zone between the siliciclastic and carbonate sediments covers only about 10 km and trends nnw sse with a south extending lobe of siliciclastic material along the coast this detailed documentation of regional change in sediment texture and composition along with the geographic distribution provides data for application to the stratigraphic record such siliciclastic carbonate transitions are quite important for example in the cambro ordovician of the upper mississippi valley and the cretaceous of central texas

seismotectonics of the hida region central honshu japan abstract seismotectonic features of the northern hida region central honshu japan have been investigated in some detail mainly on the basis of the last 6 years of observations of seismicity and focal mechanism of a large number of earthquakes with reference to the geological and tectonic setting and evidence of a large earthquake in the past it was found that high seismicity is concentrated with a remarkably clear lineation but with a relatively low activity in the central section along the atotsugawa fault extending for about 70 km this is one of major quaternary faults in this region the high seismicity with spatially nonuniform distribution may be related to postseismic stress concentration after the 1858 hida earthquake m 7 0 and to heterogeneous fault strength seismicity is also high with belt like extension beneath the hida mountain range which is the highest mountain system in the japan islands the depth distribution of seismicity is clearly bounded at 15 km below the atotsugawa fault and 8 km beneath the hida mountains the local variations can be interpreted as being due to the difference in the brittle ductile transition depth which suggests higher temperature beneath the mountains involving active volcanoes the focal mechanism solutions indicate that the maximum compressive stress is oriented in an ese wnw direction which is more consistent with the direction of motion of the pacific plate relative to the eurasian plate rather than the suggested relative motion between the north america and eurasian plates the magnitude of the shear stress working in this region is estimated to be less than 700 bar

origin and development of anclote key west peninsular florida abstract the morphology of barrier system elements on the west coast of peninsular florida is atypical for microtidal coasts because it includes numerous drumstick shaped barriers and large ebb tidal deltas anclote key in pinellas county is the most northern island of the system it was investigated in detail in order to determine its origin and developmental history extensive vibracoring and shallow seismic sub bottom profiling demonstrate that a miocene limestone platform underlies the area and is covered by only a few meters of pleistocene and holocene strata shoreward of anclote key the irregular limestone surface slopes very gradually toward the gulf whereas the gradient on the gulf side is two to three times greater a subtle but well defined limestone ridge with relief of approximately 1 m is present beneath anclote key stratigraphic analysis of 24 vibracores has identified nine quaternary facies above the miocene limestone a pleistocene muddy sand unconformably overlies the limestone and is unconformably overlain by holocene units as sea level rose to within a few meters of its present position beginning about 4200 yrs b p extensive shallow sub tidal grass flats and inter tidal to supratidal mangrove swamp and salt marsh environments were present in this area wave action near the break in slope of the limestone surface caused concentration of sand and shell to be deposited as a shallow subtidal shoal continued wave and tidal action accompanied by slowly rising sea level caused vertical accretion and spillover as the shoal became intertidal and eventually supratidal once the sand body became subaerially exposed as a barrier island processes typical of such environments gave rise to the deposition of well defined beach dune and mangrove covered washover facies the configuration of the shallow limestone platform was instrumental in controlling the location of anclote key as it developed during the late holocene

the role of morphology and wave current interaction at tidal inlets an idealized modeling analysis the outflowing currents from tidal inlets are influenced both by the morphology of the ebb tide shoal and interaction with incident surface gravity waves likewise the propagation and breaking of incident waves are affected by the morphology and the strength and structure of the outflowing current the 3 d coupled ocean atmosphere wave sediment transport coawst modeling system is applied to numerically analyze the interaction between currents waves and bathymetry in idealized inlet configurations the bathymetry is found to be a dominant controlling variable in the absence of an ebb shoal and with weak wave forcing a narrow outflow jet extends seaward with little lateral spreading the presence of an ebb tide shoal produces significant pressure gradients in the region of the outflow resulting in enhanced lateral spreading of the jet incident waves cause lateral spreading and limit the seaward extent of the jet due both to conversion of wave momentum flux and enhanced bottom friction the interaction between the vorticity of the outflow jet and the wave stokes drift is also an important driving force for the lateral spreading of the plume for weak outflows the outflow jet is actually enhanced by strong waves when there is a channel across the bar due to the return current effect for both strong and weak outflows waves increase the alongshore transport in both directions from the inlet due to the wave induced setup over the ebb shoal wave breaking is more influenced by the topography of the ebb shoal than by wave current interaction although strong outflows show intensified breaking at the head of the main channel

geothermal and rheological implications of intracontinental earthquakes beneath the kanto tokai region central japan abstract the kanto tokai region representing a boundary zone of three lithosphere plates has been the subject of intense geological geophysical studies for decades the increased attention can be explained partly by the complicated tectonic situation and even to a greater extent by the permanent threat of earthquakes in the region in this work the rheology of the lithosphere in the area is estimated on the basis of frictional failure in the brittle regime and power law steady state creep in the ductile regime rheological models are constructed for a three layered model involving a granitic upper crust a granulitic or gabbroic lower crust and a dunitic upper mantle results show a marked rheological stratification of the lithosphere controlled primarily by the thermal regime in zones of very low surface heat flow 40 mw m 2 the lithosphere shows brittle features down to depths of 50 60 km at least in areas of normal to moderately high heat flows 50 90 mw m 2 a soft ductile zone at the depth levels of the lower crust sandwiched between two brittle layers appears at locations with very high heat flows 100 120 mw m 2 only the upper crust remains brittle and plastic flow of rocks may start here from the depths of 10 15 km this rheological stratification of the lithosphere is compared with the depth distribution of earthquakes in the area and a generally reasonable confinement of seismicity to the brittle levels is indicated

evidence at lomax illinois for mid wisconsin 40 000 yr b p position of the des moines lobe and for diversion of the mississippi river by the lake michigan lobe 20 350 yr b p abstract an abrupt change in environment from a wetland to a deeper slackwater lake at 20 345 85 yr b p occurred in a second order valley tributary to the mississippi river near lomax illinois the age of this shift is associated with the overflow of glacial lake milan and diversion of the mississippi river from the princeton valley rock island to peoria to its present course rock island to st louis the diversion occurred due to blockage of the princeton valley segment of the ancient mississippi river by the lake michigan lobe impoundment of glacial lake milan and eventual overflow of the lake southwest of rock island across a former drainage divide near andalusia illinois fossil ostracode assemblages in the slackwater sediment at lomax indicate changes in the post diversion full glacial paleohydrology and based on multivariate analysis hint at the area s paleoclimate an older part of the succession at lomax is consistent with glaciation in the upper iowa river basin about 40 000 yr b p aggradation of sediment rich in coarse silt is attributed to a response of the ancient iowa river basin associated with deposition of the glacigenic sheldon creek formation by the des moines lobe

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr