coal depositional models for deltaic and alluvial plain sequences coal depositional models attempt to predict the distribution and geometry of coal beds within given sequences or provinces to date models proposed for coals of alluvial and deltaic origin have emphasized depositional environment as the controlling variable in this article i propose that subsidence regime and to a lesser extent sediment supply are the dominant controls upon coal distribution rather than environment of accumulation for this reason most existing coal depositional models are likely to have limited predictive capability

palaeotsunamis along canada s pacific coast abstract to fully understand tsunami hazards along canada s pacific coast we must consider all potential sources including local and region wide earthquakes volcanic activity slope failure events and bolide impacts furthermore as climate changes future extreme meteorological conditions will exacerbate slope failures on steep and over steepened slopes and potentially augment the magnitude and frequency of earthquake generated tsunamis there have been numerous reviews of the geological records of palaeotsunamis along the cascadia margin but as yet there has been no attempt made to pull together all data related to palaeotsunamis along the pacific coast of canada we summarise all geological data related to palaeotsunamis reported in the region all relevant non geological data and other information concerning potential tsunamigenic sources evidence for between 10 and 22 palaeotsunamis prior to european arrival have been documented with the cascadia subduction zone y event ad1700 being the most widely recognised geological archaeological and anthropological data all indicate a complex multi sourced prehistory of seismic tsunami activity that is poorly understood a clustering of potential activity off the se coast of vancouver island suggests that we should also attempt to better understand locally generated events along canada s pacific coast

sediment characteristics of an extreme flood 1993 upper mississippi river valley the 1993 mississippi river flood was notable for its high magnitude long duration summer occurrence and low sediment discharge a field survey of a 70 km long reach in the vicinity of quincy illinois revealed that the event was characterized by 100 yr flood had remarkably little sedimentological or geomorphological impact on the flood plain within the study reach because the transport effectiveness of floods in large drainage basins is influenced by event sequencing in the same manner as floods in small watersheds and the cohesive flood plain soils were not susceptible to erosion

scaling nature of crustal susceptibilities scale invariant or self similar properties have been demonstrated for a wide range of geophysical processes and rock properties evidence from well logs and inferences from aeromagnetic field power spectra suggest that crustal susceptibility also shows this behaviour with a power spectrum proportional to the 4 power of the spatial frequency we examine two large susceptibility measurement data sets and find that they both support the scaling hypothesis

morphological and sedimentological responses of streams to human impact in the southern blue ridge mountains usa abstract morphological and sedimentological responses of streams to basin scale impact have been well documented for intensively agricultural or urban areas sensitivity thresholds of streams to modest levels of disturbance however are not well understood this study addresses the influence of forest conversion on streams of the southern blue ridge mountains a region that has received little attention with respect to human impact on stream channels basins were chosen for this study to represent the end members of the range of human impact in the area with the forest cover of the basin used as a proxy for level of impact ranging from about 70 100 regionally two pairs of lightly impacted 90 forest and moderately impacted 70 80 forest sub basins of the upper little tennessee river were identified for comparison reach characteristics e g slope drainage area and riparian cover were aligned in each pair to isolate contrasting forest cover as the primary driver of any detected differences in morphology and sedimentology a suite of standard cross sectional and longitudinal data was collected for each reach for characterization of the sedimentology and morphology of the streams difference of means tests were conducted to identify parameters significantly differing between the lightly and moderately impacted streams in both pairs consistent and significant differences within both pairs were demonstrated in bankfull width depth ratios baseflow wetted width and particle size on the stream bed both in the thalweg and throughout the channel bed the moderately impacted streams are narrower than the lightly impacted streams and the bed texture of the moderately impacted streams is finer than that of the lightly impacted streams the moderately impacted streams contain a higher percentage of

coal depositional models and the distinction between alluvial and delta plain environments abstract the distinction between coal bearing upper and lower delta plain deposits in the rock record may be based on the presence or absence of features indicative of basinal influence and on the geometry of coal seams discriminating between alluvial plain and upper delta plain sequences is more difficult but is considered possible on coal seam geometry and coal seam splitting patterns other features such as the cross sectional shape of channel deposits may also be useful

organic control on shoreface stacking patterns bogged down in the mire in ever wet climates raised mires that are elevated several metres above flood levels can cover significant portions of coastal plains because peat accumulation may keep pace with moderate rates of base level rise the development of raised mires may reduced the areal extent of marine transgressions thick low ash coals are present immediately landward of many vertically stacked shoreface parasequences in cretaceous state of the western interior of north america we suggest that these coals formed in raised mires that stabilized shorelines for long periods of time in such settings the rate of sediment supply including peat accumulation to the coastal environment is partly a function of the rate of change in base level

deltaic coals of ferron sandstone member of mancos shale predictive model for cretaceous coal bearing strata of western interior the upper cretaceous ferron sandstone member of the mancos shale the coal bearing unit of the emery coalfield in central utah shows accumulation of clastic sediments in a lobate river dominated deltaic system that existed along the western shoreline of the interior cretaceous seaway during late turonian time five cycles of deltaic sedimentation each containing one major coal bed or coal zone are represented a clear genetic relationship exists between the geometries of the major coal beds of the emery field and the geometries of the delta front sandstone units with which they are associated the thicker part of each coal bed extends from the vicinity of the landward pinch out of the associated delta front sandstone landward to a distance of about 10 km this genetic relation forms the basis of a predictive model that can be used in designing more cost effective exploration programs in coal bearing strata of cretaceous age in the western interior

seismicity and shape of the subducted nazca plate an updated compilation of earthquake locations and focal mechanism solutions from the international seismological centre and preliminary determination of earthquakes is the basis of a comprehensive study of the geometry of the wadati benioff zone beneath western south america the new data support previous mapping of a sharp flexure rather than a tear in the subducted nazca plate beneath southern peru and provide evidence for a similar flexure in the southward transition from nearly horizontal subduction to a slab with 30 dip at latitude 33 s in contrast the transition from 30 slab dip beneath bolivia to a nearly horizontal dip in the region between 28 s 32 s is more gradual occurring over several hundred kilometers of along strike distance between 20 s and 32 s this southward flattening corresponds to a broadening of a horizontal benchlike part of the subducted plate formed between 100 and 125 km depth the transition in continental tectonic style near 27 s 28 s from a wide volcanically active plateau to a narrow nonvolcanic cordillera appears not to be associated with the main slab flattening which begins to the north of these latitudes but with a more abrupt change in curvature of the subducted slab from convex upward to concave upward immediately below the plate boundary interface the concept of gaussian curvature is applied to slab bending to explain how subduction geometry is affected by the shape of the south american plate we hypothesize that the polarity of vertical curvature in the subducting slab is governed by the orientation of lateral curvature of the plate margin focal mechanism solutions for intermediate and deep earthquakes are grouped by geographic region and inverted for the orientation and relative magnitudes of the principal stresses results of the inversion indicate that downdip extension dominates in the slab above 350 km while downdip compression dominates at greater depths

paleoflood hydrology origin progress prospects from an origin in diverse studies of flood geomorphology and quaternary geology paleoflood hydrology emerged as a geophysical and an applied hydrological science during the 1970s and 1980s since acquiring its formal name in 1982 the most productive approach in paleoflood hydrology has become energy based inverse hydraulic modeling of discrete paleoflood events recorded in appropriate settings as slackwater deposits and other paleostage indicators swd psi or as various threshold indicators of non exceedence technological advances particularly in hydraulic modeling and geochronology were instrumental in moving the discipline to its present status the most recent advances include 1 new techniques for the accurate geochronology of flood sediments notably tams radiocarbon analyses and osl dating and 2 the phenomenal increase in computer power that allows complex hydraulic calculations to become feasible for routine studies from its initial demonstration in the southwestern united states swd psi paleoflood hydrology proved its widespread applicability to various landscape environments particularly important studies have been accomplished in australia china india israel south africa spain and thailand paleoflood hydrology has also generated its share of controversy in part because of the differing viewpoints and attitudes of the two scientific traditions from which it emerged quaternary geology geomorphology versus applied hydrologic hydraulic engineering nevertheless the future growth of the discipline is assured given the rapid pace of discoveries that it engenders indeed so many international studies exist that it is appropriate to pursue global syntheses to address interesting and timely questions of extreme flood phenomena in relation to global climatic change

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

palaeoflood record of the tagus river central spain during the late pleistocene and holocene abstract palaeoflood hydrology of the tagus river central spain was reconstructed from slackwater deposits and palaeostage indicators in two canyon reaches located at el puente del arzobispo in the central part of the catchment 35 000 km 2 in drainage area and in alcantara at the lower part of the catchment 52 000 km 2 in drainage area near the portuguese border the palaeoflood record with more than 80 flood events shows clusters of floods at specific periods from 9440 to 9210 14 c yr bp 8540 8110 bc 8500 to 8000 14 c yr bp 7500 7000 bc 6750 14 c yr bp 5000 bc 1200 to 950 14 c yr bp ad 785 1205 410 14 c yr bp ad 1450 1500 170 to 80 14 c yr bp ad 1670 1950 the largest flood s occurred during the periods 9440 to 9210 14 c yr bp 6750 14 c yr bp and 1200 to 950 14 c yr bp reaching minimum discharge estimates of between 4000 and 4100 m 3 s 1 in the el puente del arzobispo reach and 13 700 15 000 m 3 s 1 in the alcantara reach these periods with increased flood magnitude and or frequency in the tagus river are strongly related to increased moisture influx and winter precipitation in the iberian peninsula especially in the western zone proxy records sensitive to winter precipitation such as lake levels and vegetation changes indicated by pollen records are in good agreement with the clusters of floods found in the tagus river this flood variability seems to correspond to changes in the prevailing atmospheric circulation pattern affecting the iberian peninsula

paleochannels indicating wet climate and lack of response to lower sea level southeast georgia large meandering paleochannels on the flood plain of the middle ogeechee river in southeast georgia represent wet paleoclimate during late pleistocene and early holocene time and show no indication of downcutting in response to eustatically lower sea level radiocarbon dates indicate that the paleomeanders were active at 31 28 ka and 8 5 4 5 ka bivariate regression models that correlate modern channel dimensions to the discharge of low magnitude floods 1 5 yr recurrence interval indicate that paleodischarge of floods during those times was at least double that of modern floods thus suggesting a wetter paleoclimate these data corroborate independent studies of pollen and paleoclimate simulations that indicate wet early to middle holocene 9 3 ka conditions that were characterized by intensified monsoonal circulation paleoclimate conditions at 31 28 ka are less well known our analysis of the middle ogeechee river flood plain indicates the absence of base level response downcutting to eustatic sea level lowering because the beds of the paleochannels are at approximately the same elevation as the bed of the modern channel this supports recent arguments that the geomorphic response of coastal plain streams to sea level lowering is most apparent in deltaic and shelf environments and may not be recognized very far upstream from the coast

on the periodicity and magnitude of late carboniferous glacio eustatie sea level changes data from sedimentary cycles in basins from northern england the appalachians and midcontinent us afford an insight into periodicities and controls of late carboniferous glacio eustatic sea level changes lithofacies with identifiable palaeobathymetry are used to assess the magnitude of sea level change in the pennine basin of northern england the method yields a minimum value of 42m walsh power spectral analysis is employed to resolve periodicities of about 120ka within the pennine basin of northern england 212 140 and 93 ka within the midcontinent us succession and 109 84 67 63 ka within the appalachian basin within the pennine basin periodicities and magnitudes are found to be independent of their position within the basin thus any tectonism can be assumed to have had a negligible effect on the transgressions a simplified modelled climatic curve is derived from milankovitch parameters and pleistocene 18 o data this is used in a basin fill model that simulates the thermally subsiding pennine basin the resulting distribution of marine deposits is seen to depend upon both the steady regional subsidence and the magnitude and extent of glacio eustatic transgressions

self similarity in the seismicity of the south american subduction zone the spatial distribution of hypocenters corresponding to intermediate and deep seismic ity along the south american subduction zone has led to a description of the geometry of this subduction process changes in the angle of subduction have been detected which led to a division of the subducted region into segments according to the flat or normal dipping of the oceanic slab in this paper the seismicity corresponding to the different segments is analyzed in order to determine the kind of correlation with the slab configuration spatial analyses using a multifractal technique are performed and the self similar behavior is quantified through the fractal dimension scale invariant clusterings with a high correlation between the spatial fractal dimension and the dipping angle of subduction have been found

fractal analysis of three dimensional spatial distributions of earthquakes with a percolation interpretation although many studies have shown that faults and fractures are self similar over a large range of scales none have tested the fault structure for self similarity in three dimensions in this study earthquake hypocentral locations in central and southern california were used to illuminate three dimensional 3 d fault structures for which we measured the fractal capacity dimension d0 3 d hypocentral distributions from the joshua tree big bear and upland aftershock sequences as well as background seismicity at parkfield were found to be fractal where d0 3 d increased with increasing event density asymptotically approaching a stable value the joshua tree data set stabilized at d0 3 d 1 92 0 02 the parkfield data set asymptotically approached d0 3 d 1 82 and the big bear data set approached d0 3 d 2 01 as a test of the effects of location errors upon the measured value of d0 3 d the upland aftershock data were located with both the southern california hadley and kanamori 1977 h k velocity model and the more accurate hauksson and jones 1991 h j velocity model events located with the h k model asymptotically approached d0 3 d 2 07 and events located with the h j model approached d0 3 d 1 79 suggesting that improved hypocentral locations may decrease the measured fractal dimension one interpretation of our results of d0 3 d 2 0 for all of the hypocentral data is that earthquakes only occur on the percolation backbone of a fault network i e the active part of the network that accommodates finite strain deformation sahimi et al 1993 we show that a percolation model that allows for healing of previously broken bonds is consistent with this interpretation

the seasonality of east central north american precipitation based on three coeval holocene speleothems from southern west virginia abstract we present a replicated record of holocene climate change from a cave in west virginia usa based on analysis of stable isotopes in precipitation 18ow from the closest global network of isotopes in precipitation gnip station in coshocton oh we interpret enriched oxygen isotopes in calcite 18oc as representing an increase in the relative contribution of summer precipitation to annual totals significant coherence between local summer july and august precipitation and the summer north atlantic oscillation snao index on multi decadal timescales suggests that summer precipitation in our study area is strongly influenced by changes in the bermuda high a strengthened bermuda high circulation would increase summer precipitation amounts in the region and lead to enriched 18oc of speleothem calcite our 18oc record achieves maximum values during the mid holocene consistent with previous studies indicating an intensified bermuda high circulation at that time at 4 2 ka 18oc transitions to lower values at a time when numerous records around the globe document significant changes in the hydrologic budget over the last 2000 years there are intervals of substantially decreased 18oc coincident with aridity in the yucatan alpine glacial advances and a weakened asian summer monsoon

dating tsunami deposits present knowledge and challenges abstract dating approaches for fine sediment tsunami deposits can be divided into two categories 1 dating directly using materials from within a tsunami deposit and 2 dating indirectly using materials from above and below it for the former optically stimulated luminescence osl dating has a possible advantage in that is can directly date the burial age of sediments laid down by a tsunami however because of methodological limitations osl dating cannot always provide a reliable age although 14c and u th dating of reworked material from within a tsunami deposit are possible means of determining the age of the event the results merely represent a maximum age of deposition for these reasons dating is commonly achieved indirectly from 14c dates taken from samples in sections immediately above and below a tsunami deposit however indirectly dated results do not provide a precise timing of the event therefore there are distinct limitations in the ability to obtain high precision dating of past tsunamis recent methodological developments including the application of bayesian statistical analysis to radiocarbon dating results and the selection of appropriate dating materials has significantly improved the accuracy of age determination by reducing errors this review presents several methodological improvements that have enhanced tsunami deposit age estimation the most important points for a more precise tsunami age estimation are the numbers of 14c samples dated coupled with the use of bayesian statistical analysis these points are applicable not only to tsunami deposits but also to many other past geohazard events

late quaternary climates and river channels of the atlantic coastal plain southeastern usa abstract late quaternary river patterns and sedimentation styles reflect past climate changes in atlantic drainages of eastern georgia and the carolinas past climate episodes for the region are summarized from pollen and eolian sedimentary records that exhibit correlation to major changes in river channel patterns records of past river responses are derived from luminescence and radiocarbon dated landforms and strata slow tectonic uplift does not explain temporal changes in channel patterns drainage networks have not received meltwater from continental or mountain glaciers eustatic influence would have been most pronounced on the now submerged continental shelf prior to 6 ka and currently manifests only within 60 80 km of the present highstand shoreline human impact overshadows climatic changes during historic time but was negligible during prehistoric time the late quaternary fluvial system primarily responded to climatic fluctuations that drove changes in vegetation precipitation and runoff patterns prehistoric meandering paleochannels of the holocene stand as important references to guide natural channel rehabilitation efforts during the coldest climate phases of the late wisconsin stage ca 30 16 ka when forest vegetation was sparse and interspersed with grasses and herbs many rivers and streams were braided with eolian dunes on the floodplains the terminal wisconsin stage ca 16 11 ka exhibited rapid warming and forest expansion characterized by pronounced change from braided to meandering patterns with intermediate forms of sandy scroll bar patterns the younger dryas cold excursion is not readily apparent in the regional fluvial record unusually large meandering channels of the terminal wisconsin stage continue into the first half of the holocene and indicate significantly larger bankfull flood discharges during those times than during the last half of the holocene bankfull channels during the last half of the holocene retained meandering patterns but decreased to modern like dimensions suggesting more modern like flood regimes no clear fluvial response occurs to the presumed middle holocene climatic optimum hypsithermal the medieval warm period and little ice age or to recent instrumentally observed fluctuations in climate but little research has been done in these realms

late quaternary records of vegetation and fire in southeastern north carolina from jones lake and singletary lake abstract we conducted fossil pollen charcoal and geochemical analyses of sediment cores from jones lake and singletary lake spanning the last 50 000 cal yr b p to examine the linkages between climate vegetation and fire activity on the atlantic coastal plain and particularly emphasize changes since the last glacial maximum application of the modern analog technique mat to fossil pollen data allowed for quantitative estimates of holocene climate but pleistocene assemblages had no modern analogues preempting their use for quantitative reconstructions the mat data indicate markedly lower mean annual precipitation and temperatures during the late pleistocene relative to the holocene increased charcoal accumulation during interstadials indicates increased fire activity during these warm intervals geochemical data 13c 15n c n and pollen concentrations indicate a sparsely vegetated pleistocene landscape that produced few fires followed by an increase in biomass and fire activity around the lakes during the holocene transition a quercus spp maximum in the early holocene is associated with low charcoal abundances while increased dominance of pinus spp during the middle holocene is associated with dramatic increases in charcoal it is unclear if the quercus pinus transition was the result of changing fire regimes or if the fire regime changed in response to vegetation the regional asynchronicity of the quercus pinus transition may indicate another forcing mechanism besides climate change such as prehistoric human activity is responsible for the ecological change macroscopic charcoal and c n ratios reach unprecedented values during the late holocene possibly as a result of deforestation by both prehistoric native americans and later immigrant populations

use of multi proxy flood records to improve estimates of flood risk lower river tay scotland abstract proxy flood records from sediment stacks in floodplain palaeochannels provide an opportunity to extend short instrumental records and thus improve current estimates of flood risk the bloody inches a meander cutoff on the lower river tay scotland has been infilling with flood deposits since c 1761 agricultural flood embankments locally breach with flows 850 m3 s 1 introducing silts into the palaeochannel and extensively fail with flows 1200 m3 s 1 which deposit sand repeated cores at the site up to 1 4 m in depth consistently reveal sand rich flood units in the upper section of the core 137cs dating enables these units to be correlated with clusters of floods in the post 1950 discharge record sand units in the lower part of the profile are correlated with major floods from 1814 onwards using a 210pb based chronology these dates are independently corroborated by flood marks inscribed on smeaton s bridge in perth 15 km downstream estimates of historic high flows back to 1814 can also be recovered from these flood stage levels at smeaton s bridge when combined with the 48 year long flow record these historic floods yield an augmented pot series extending back to 1847 using a relatively high threshold of 1361 m3 s 1 and the generalised pareto distribution to model this pot series estimates of the 50 100 and 200 year floods are 1875 2250 and 2050 m3 s 1 respectively these results provide independent and robust confirmation of the flood risk at perth using the standard statistical procedures advocated in the flood estimation handbook if successfully replicated at other sites radiometric dating of sediment stacks in palaeochannels provides a new technique to further advance palaeohydrology and the recovery of historic floods

terminal pleistocene braided to meandering transition in rivers of the southeastern usa abstract thirteen paleomeanders on the oldest parts of meander belts on floodplains in the coastal plain of georgia and the carolinas southeastern usa were selected for radiocarbon dating to determine the onset of meandering following braiding during the late pleistocene during oxygen isotope stage 2 the radiocarbon ages were compared to previously reported late pleistocene ages for braid bars and eolian dunes results indicate that meandering commenced at circa 15 000 to 16 000 cal years bp and continued throughout the terminal pleistocene and holocene correlation with other paleoenvironmental records indicates that this shift to meandering was associated with global warming and moister conditions in the southeastern united states that led to a denser vegetation cover and a reduction in sediment yield the shift to meandering was also associated with some incision and terracing of the late pleistocene braided fluvial surfaces paleodischarge of the bankfull condition of early holocene meandering channels was apparently greater than under modern conditions suggesting wetter conditions at that time than at present this braided to meandering transition in the southeastern united states provides an example of river response to global climate change in a relatively low latitude region of the world that was not influenced by glacial or periglacial landscape conditions

textural analysis and modelling of a flood deposit river severn u k samples of sediment collected from the severn floodplain between worcester and gloucester following the severe flooding in january and february 1990 were analysed for their grain size distribution the results show that most sand was deposited within 20 m of the channel bank but that fine sand may contribute to flood sediment across the width of the floodplain james 1985 numerical model of overbank sedimentation attempts to predict the transfer of sediment to the floodplain during flooding geometrical and hydraulic data relating to the severn flood are used as input for a computer program of james 1985 model the pattern of sediment concentrations predicted by the model was compared with that obtained from statistical analysis of the flood sediment the patterns were found to be similar so james 1985 model was considered to predict in a relative sense the distribution of flood sediment

spatial variations in major u s hurricane activity statistics and a physical mechanism abstract the authors provide a statistical and physical basis for understanding regional variations in major hurricane activity along the u s coastline on long timescales current statistical models of hurricane activity are focused on the frequency of events over the entire north atlantic basin the exception is the lead author s previous work which models the occurrence of hurricanes over the caribbean sea gulf of mexico and the southeast u s coast separately here the authors use statistics to analyze data from historical and paleoclimatic records to expand this work in particular an inverse correlation in major hurricane activity across latitudes at various timescales is articulated when activity is above normal at high latitudes it tends to be below normal at low latitudes and vice versa past research paleoclimatic records and historical data hint at the potential of using the north atlantic oscillation nao as an indicator of where storms will likely track over long timescales an excite

late holocene paleofloods in the upper little tennessee river valley southern blue ridge mountains usa we derive a paleoflood chronology for the past 2000 years from three stratigraphic sections of overbank sediments with dates from radiocarbon luminescence 137cs techniques and historical records particle sizes were measured in 6 15 year intervals in post 1870 sediments and in 45 170 year intervals in pre 1870 sediments using an automatic laser analyzer the sedimentological characteristics of ad 1948 2009 deposits were compared with gaging records demonstrating that fine sand content and sorting discern time intervals of large floods but flood magnitudes are not well resolved this modern analog was applied to pre 1870 sediments and revealed two periods in the last 2000 years with large floods during ad 650 850 and ad 1100 1350 which are times when the regional tree ring record showed extreme wetness and no severe or extreme droughts our findings indicate flood prone phases of transitional climate at the beginning and end of the medieval warm period mwp and relatively subdued flooding during

a one parameter expression of seismicity patterns in space and time abstract a technique to express changes in seismicity patterns by means of an objective criterion has been investigated a parameter v 2 2 2 where is the distance between two adjacent earthquakes in space and time was derived on the basis of the weibull distribution function this parameter can be related to an apparent interaction in the earthquake sequences and used to monitor changes of the seismicity patterns which may reflect the state of the crustal stress the patterns are classified as regular completely random and clustered according to the value of v 2 the technique was applied to the u s geological survey microearthquake catalog for central california a total of 9740 earthquakes m 1 5 was selected from along the 250 km long creeping zone of the san andreas and calaveras faults for the period 1971 to 1981 the seismicity pattern was found to be generally a combination of highly clustered ones overlapped with a background which was characterized as almost random or slightly clustered

wet early to middle holocene conditions on the upper coastal plain of north carolina usa abstract a peat core from a cutoff paleochannel of little river on the upper coastal plain of north carolina provides a continuous pollen record of environmental change for the past 10 500 years and includes a sedimentary record of overbank floods palynological and sedimentary data indicate that the early to middle holocene was wetter than previously suggested from lake sites in the southeastern united states the period from 9000 to 6100 cal yr b p is characterized by high pollen percentages of nyssa and quercus but low percentages of pinus fifteen large overbank flood events are present within this period 5 floods 1000 yr in contrast only 6 large overbank flood events occurred since 6100 cal yr b p 1 flood 1000 yr the increases in moisture and flood events probably were controlled by changes in atmospheric circulation related to shifts in the position of the bermuda high sea surface temperatures and el nino activity that together may have affected the frequency of large floods generated from tropical storms in the region

floodplain sedimentation in the upper mississippi valley natural versus human accelerated abstract understanding the time scales and pathways for response and recovery of rivers and floodplains to episodic changes in erosion and sedimentation has been a long standing issue in fluvial geomorphology floodplains are an important component of watershed systems because they affect downstream storage and delivery of overbank flood waters and they also serve as sources and temporary sinks for sediments and toxic substances delivered by river systems here 14c and 137cs isotopic dating methods are used along with ages of culturally related phenomena associated with mining and agriculture to determine rates of sedimentation and morphologic change for a reach of the upper mississippi river and adjacent tributaries in southwestern wisconsin and northwestern illinois the most important environmental change that influenced fluvial activity in this region during last 10 000 years involved the conversion of a late holocene mosaic of prairie and forest to a landscape dominated by cropland and pastureland associated with euro american settlement results presented herein for the upper mississippi valley umv show that the shift from pre agriculture natural land cover to landscape dominance by agricultural land use of the last 175 200 years typically increased rates and magnitudes of floodplain sedimentation by at least an order of magnitude accelerated overbank flooding led to increased bank heights on tributary streams and in turn contributed to more frequent deep flows of high energy these high energy flows subsequently promoted bank erosion and lateral channel migration and the formation of a historical meander belt whose alluvial surface constitutes a new historical floodplain inset against the earlier historical floodplain the new historical floodplain serves as a flume like channel that provides efficient downstream transport of water and sediment associated with moderate and large magnitude floods floodplains on lower tributaries however continue to experience rates of overbank sedimentation that are of anomalously high magnitude given improved land cover and land conservation since about 1950 this lower valley anomaly is explained by minimal development of historical agriculture period meander belts because of relatively low stream power in these channel and floodplain reaches of relatively low gradient in general long term pre agriculture rates of vertical accretion between about 10 000 and 200 years ago averaged about 0 2 mm yr 1 in tributary watersheds smaller than about 700 km2 and about 0 9 mm yr 1 on the floodplain of the upper mississippi river where the contributing watershed area increases to about 170 000 km2 on the other hand rates of historical vertical accretion during the period of agricultural dominance of the last 200 years average between 2 and 20 mm yr 1 with short episodes of even higher rates during times of particularly poor land conservation practices significant hydrologic effects of mining and agricultural started by the 1820s and became widespread in the study region by the mid 19th century the hydrologic and geomorphic influences of mining were relatively minor compared to those related to agriculture high resolution dating of floodplain vertical accretion deposits shows that large floods have frequently provided major increments of sedimentation on floodplains of tributaries and the main valley upper mississippi river the relative importance of large floods as contributors to floodplain vertical accretion is noteworthy because global atmospheric circulation models indicate that the main channel upper mississippi river should experience increased frequencies of extreme hydrologic events including large floods with anticipated continued global warming instrumental and stratigraphic records show that coincident with global warming a shift to more frequent large floods occurred since 1950 on the upper mississippi river and these floods generally contributed high magnitudes of floodplain sedimentation

application of sequence and genetic stratigraphic concepts to carboniferous coal bearing strata an example from the black warrior basin usa carboniferous strata provide an excellent example on which to test the application of genetic stratigraphic and sequence stratigraphic concepts both approaches are employed in the evaluation of the coal bearing strata of the black warrior basin south eastern usa bounding hiatal surfaces have been recognized in the succession of rock that includes the mary lee coal zone within the framework of genetic stratigraphy one genetic sequence has been identified comprised of offlap progradational and aggradational facies and onlap aggradational and transgressive facies components seven parasequence sets have been delimited according to the concepts of sequence stratigraphy these have been ascribed to transgressive highstand and shelf margin systems tracts the identification of components of these contrasting frameworks provide the basis for evaluating other carboniferous strata

modelling flood hydraulics and overbank deposition on river floodplains this paper outlines a numerical model for the prediction of floodplain inundation sequences overbank deposition rates and deposit grain size distributions the model has two main components first a simplified hydraulic scheme which predicts floodwater flow depths and velocities and second a sediment transport element which employs a mass balance relation describing suspended sediment dispersion by convective and diffusive processes and sediment deposition as a function of particle settling rates these relationships are solved numerically on a finite difference grid that accurately replicates the complex topographic features typical of natural river floodplains the model is applied to a 600 m reach of the river culm devon u k using data derived from a range of field and laboratory techniques continuous records of river stage and suspended sediment concentration provide the model s upstream boundary input requirements these are supplemented by measurements of the in situ settling characteristics of the suspended sediment load the model s sediment transport component is calibrated with the aid of a dataset of measured overbank deposition amounts derived from flood events over a 16 month period the model is shown to predict complicated floodwater inundation sequences and patterns of suspended sediment dispersion and deposition which are largely a product of the complex topography of the floodplain these results compare favourably with observations of overbank processes and are an improvement over those of previous models which have employed relatively simple representations of floodplain geometry 1997 by john wiley sons ltd

holocene ethnobotanical and paleoecological record of human impact on vegetation in the little tennessee river valley tennessee abstract human occupation and utilization of plant resources have affected vegetation in the lower little tennessee river valley of east tennessee for 10 000 yr changes in indian cultures and land use are documented by radiocarbon chronologies lithic artifacts ceramics settlement patterns and ethnobotanical remains from 25 stratified archaeological sites within the holocene alluvial terrace the ethnobotanical record consists of 31 500 fragments 13 7 kg of wood charcoal identified to species and 7 7 kg of carbonized fruits seeds nutshells and cultigens from 956 features pollen and plant macrofossils from small ponds both in the uplands and on lower stream terraces record local vegetational changes through the last 1500 to 3000 yr human impact increased after cultigens including squash and gourd were introduced ca 4000 yr b p during the archaic cultural period forest clearance and cultivation disturbed vegetation on both the floodplain and lower terraces after 2800 yr b p during the woodland period permanent indian settlements and maize and bean agriculture extended to higher terraces 1 5 km from the floodplain by the mississippian period 1000 to 300 yr b p after 300 yr b p extensive land clearance and cultivation by historic overhill cherokee and euro americans spread into the uplands beyond the river valley

a balanced model of the southern central andes to explain the actual crustal thickness of the southern central andes a balanced cross section at 21 s latitude was modeled a forward modeling procedure was used on a crustal scale to explain the gross crustal structure obtained by seismic refraction investigations in the model 320 km of shortening since late cretaceous based on balanced geological cross sections are assumed for the whole andes from the trench to the foreland and the initial crustal thickness varies between 30 and 40 km it results that about 20 of the actual crustal volume must be explained by other sources than crustal shortening structures of high velocity material in the upper crust of the eastern cordillera can be explained by detached and overthrust material from the crustal base thus producing a crustal doubling in the back arc underplating of continental material that was removed by subduction erosion and magmatic addition of derivates of the subducted nazca plate may contribute to the lower crust of the forearc and arc regions crustal thickening of the eastern cordillera and parts of the altiplano was undoubtedly produced by tectonic thickening whereas the sources of thickening in the western cordillera and forearc region are uncertain

fluvial channel and overbank deposits from the westphalian of the durham coalfield ne england the westphalian upper carboniferous coal measures of the durham coalfield in ne england were deposited in lower and upper delta plain environments distributary channels crossed the plain and were separated by shallow interdistributary lakes and bays detailed observation of three dimensional 3 d opencast surface mine exposures in collaboration with subsurface borehole analysis has revealed the existence of five varieties of channel deposits and two associated overbank facies within the durham coal measures major distributary channels were the major avenues of sediment transport across the coal measures plain were variably sinuous mostly 1 2 km wide and deposited elongate belts of sand mostly up to 5 km wide proximal major crevasse splay channels formed by the breaching of major channel banks during flood events were straight sand filled and up to 400 m wide minor distributary channels formed by the sustained operation of such crevasses varied from straight to highly sinuous and deposited shoestring sand mud belts up to a few hundred metres wide minor crevasse channels generally straight and up to 50 m wide were formed through bank breaching of minor and in a few cases major distributaries distal feeder channels formed down palaeocurrent extensions of minor distributaries which supplied interdistributary minor delta subsystems were generally straight and up to 200 m wide of the two types of channel overbank levee deposits recognized one comprising thinly interbedded fine grained sandstone and siltstone claystone is mostly though not exclusively associated with major distributary channels the other consisting of massive siltstones with regularly spaced thin claystone bands is uniquely developed at the margins of minor distributary channels the lower part of the westphalian a succession in the northern pennines records a change in the depositional environment upwards from a lower to upper delta plain through this transition major channel deposits show evidence of having evolved from being of dominantly low sinuosity to being more variable in morphology channel sedimentation was profoundly influenced by regular possibly seasonal variations in flow stage and sediment load

response of extreme floods in the southwestern united states to climatic variations in the late holocene a regional synthesis of paleoflood chronologies on rivers in arizona and southern utah reveals that the largest floods over the last 5000 years cluster into distinct time periods that are related to regional and global climatic fluctuations the flood chronologies were constructed using fine grained slackwater deposits that accumulate in protected areas along the margins of bedrock canyons and selectively preserve evidence of the largest events high magnitude floods were frequent on rivers throughout the region from 5000 to 360014c yrs bp dendrocalibrated age 3800 2200 bc and increased again after 2200 bp 400 bc with particularly prominent peaks in magnitude and frequency around 1100 900 bp ad 900 1100 and after 500 yrs bp ad 1400 in contrast the periods 3600 2200 bp 2200 400 bc and 800 600 yrs bp 1200 1400 ad are marked by sharp decreases in the occurrence of large floods on these rivers in the modern record storms that generate large floods 10 year in the region fall into three categories 1 winter north pacific frontal storms 2 late summer and fall storms that draw in moisture from recurved pacific tropical cyclones and 3 summer storms mainly convective thunderstorms winter storms and tropical cyclones are associated with the most severe floods on the rivers in this study and are the most probable causes of the paleofloods over the last 5000 years floods from both winter storms and tropical cyclones occur when deep mid latitude troughs steer storm systems into the region composite anomaly maps of daily 700 mbar heights indicate that these floods are associated with a low pressure anomaly off the california coast and a high pressure anomaly over the aleutians or gulf of alaska a strong connection exists between the negative phase of the southern oscillation index often associated with el nin o conditions and the large floods associated with winter storms and tropical cyclones the paleoflood records confirm the existence of centennial scale variations in the conditions conducive to the occurrence of extreme floods and flood generating storms in this region the episodes with an increased frequency of high magnitude floods coincide with periods of cool wet climate in the western u s whereas warm intervals such as the medieval warm period are times of dramatic decreases in the number of large floods a positive relationship between the paleofloods and long term variations in the frequency of el nin o events is evident over the last 1000 years this relationship continues over at least the last 3000 years with warm coastal sea surface temperatures indicative of el nin o like conditions

vertical accretion sand proxies of gaged floods along the upper little tennessee river blue ridge mountains usa abstract understanding environmental hazards presented by river flooding has been enhanced by paleoflood analysis which uses sedimentary records to document floods beyond historical records bottomland overbank deposits e g natural levees floodbasins meander scars low terraces have the potential as continuous paleoflood archives of flood frequency and magnitude but they have been under utilized because of uncertainty about their ability to derive flood magnitude estimates the purpose of this paper is to provide a case study that illuminates tremendous potential of bottomland overbank sediments as reliable proxies of both flood frequency and magnitude methods involve correlation of particle size measurements of the coarse tail of overbank deposits 0 25 mm sand from three separate sites with historical flood discharge records for the upper little tennessee river in the blue ridge mountains of the southeastern united states results show that essentially all floods larger than a 20 probability event can be detected by the coarse tail of particle size distributions especially if the temporal resolution of sampling is annual or sub annual coarser temporal resolution 1 0 to 2 5 year sample intervals provides an adequate record of large floods but is unable to discriminate individual floods separated by only one to three years measurements of 0 25 mm sand that are normalized against a smoothed trend line through the down column data produce highly significant correlations r 2 values of 0 50 to 0 60 with p values of 0 004 to