deep seated gravitational slope deformations related landslides and tectonics abstract deep seated gravitational slope deformations and their relationships with tectonic deformation of rocks is considered to examine the viewpoint of tectonics as a causative factor in slope deformation first a distinction is made between the different types of deep seated gravitational slope deformation then the geomorphological and structural effects of the different macrostructural deformations induced by tectonics on the scale of the whole deforming ridge is briefly discussed finally some case studies that represent either verified or possible cases of gravity deformation in response to tectonic activity are used as illustration

uplift history of the central and northern andes a review the elevation of the andean cordillera is a crucial boundary condition for both climatic and tectonic studies the andes affect climate because they form the only barrier to atmospheric circulation in the southern hemisphere and they intrigue geologists because they have the highest plateau on earth formed at a noncollisional plate margin the altiplano puna yet until recently few quantitative studies of their uplift history existed this study presents both 1 a review of the quantitative paleoelevation estimates that have been made for the central and colombian andes and 2 an examination of the source and magnitude of error for each estimate in the central andes paleobotanical evidence suggests that the altiplano puna had attained no more than a third of its modern elevation of 3700 m by 20 ma and no more than half its modern elevation by 10 7 ma these data imply surface uplift on the order of 2300 3400 m since the late miocene at uplift rates of 0 2 0 3 mm yr paleobotanical and geomorphological data suggest a similar uplift history for the eastern cordillera namely no more than half the modern elevation present by 10 ma no evidence exists for an exponential increase in uplift rate as has been interpreted from fissiontrack data these uplift rates mostly reflect mean surface uplift rather than rock uplift that is uplift of material points because little dissection of the western eastern cordillera has occurred south of lat 19 s and of the altiplano puna thus the central andean plateau appears to be young in the colombian andes paleobotanical data imply rapid uplift of the eastern cordillera between 2 and 5 ma at rates on the order of 0 6 3 mm yr however some of this uplift is likely rock uplift due to erosion driven isostatic rebound rather than mean surface uplift

processes of selective grain transport and the formation of placers on beaches placers are found on many beaches of the oregon coast in the beach that is the focus of this study the principal placer minerals are ilmenite 22 0 epidote 20 0 garnet 18 7 augite 15 5 hypersthene 8 1 hornblende 5 8 and zircon 2 0 the ilmenite fraction actually being partly chromite a series of beach face sand samples was obtained along a profile when sand was being eroded from the upper beach and transported to offshore bars since the processes of grain selective sorting leading to placer formation were probably most active at such a time the landward most sample contained 96 heavy minerals being part of the placer this concentration systematically decreased offshore to a 6 heavy mineral content in the seaward most sample 54 m offshore determinations of individual heavy mineral concentrations revealed that although they all tended to become concentrated within the placer with light quartz and feldspar dominating the offshore transport the sorting processes were m

late quaternary sedimentary environments and landforms in the ganges delta abstract late quaternary sediments deposited since the lowest stand of sea level during the last glacial maximum in the ganges delta and its surrounding region were classified into five units according to their sedimentary facies these are the lowest unit of sandy gravels the lower unit of sand with a few gravels and the middle upper and uppermost units consisting mainly of sand and silt with occasional peat layers the contact between the lower and middle units is fairly sharp and the upper part of the lower unit is oxidized in some places this suggests a period of subaerial exposure after the deposition of the lower unit during the low stand of sea level about the time of the last glacial maximum rivers in the ganges delta and its surrounding region dissected the surfaces of the region and deposited the lowest unit on the valley floors the lower unit was deposited over the lowest unit during an early stage of the post glacial transgression between ca 12 000 yr bp and 10 000 yr bp the surface of the delta was slightly dissected and the top of the lower unit was weathered and oxidized following this period the middle and upper units of alluvial or deltaic sand and silt with occasional peat were deposited the coastline in the early holocene retreated towards the central part of the present ganges delta in the middle and late holocene the silt and clay with occasional peat layers of the uppermost unit indicate that the lowland gradually became marshy and poorly drained as the rate of transgression became slower

an appalachian amazon magnetofossil evidence for the development of a tropical river like system in the mid atlantic united states during the paleocene eocene thermal maximum on the mid atlantic coastal plain of the united states paleocene sands and silts are replaced during the paleocene eocene thermal maximum petm by the kaolinite rich marlboro clay the clay preserves abundant magnetite produced by magnetotactic bacteria and novel presumptively eukaryotic iron biomineralizing microorganisms using ferromagnetic resonance spectroscopy and electron microscopy we map the magnetofossil distribution in the context of stratigraphy and carbon isotope data and identify three magnetic facies in the clay one characterized by a mix of detrital particles and magnetofossils a second with a higher magnetofossil to detrital ratio and a third with only transient magnetofossils the distribution of these facies suggests that suboxic conditions promoting magnetofossil production and preservation occurred throughout inner middle neritic sediments of the salisbury embayment but extended only transiently to outer neritic sediments and the flanks of the embayment such a distribution is consistent with the development of a system resembling a modern tropical river dominated shelf

discrimination of accreted and eroded coasts using heavy mineral compositions of the nile delta beach sands egypt coastal erosion has occurred on the beaches of the three major promontories of the nile delta of egypt the eroded sand is generally carried alongshore to the east or locally to the west from these promontories and is deposited in areas of beach accretion between promontories in this study the heavy minerals of 150 samples have been investigated with the aim of differentiating between eroded and accreted beaches discrimination was achieved by using bivariate plots of the raw weight percentage data and q mode factor analysis factor analysis yielded two mineral assemblages factor 1 is dominated by augite hornblende and epidote while factor 2 consists of opaque minerals garnet zircon rutile and monazite these two mineral factors are produced by the selective sorting of heavy minerals by natural processes of waves and currents minerals of factor 2 are associated with high density opaques which tend to concentrate as a lag in areas of erosion conversely the lower density minerals of factor 1 are preferentially transported away from areas of erosion and carried to the accreted shorelines

structure age and origin of the bay mouth shoal deposits chesapeake bay virginia abstract the mouth of chesapeake bay contains a distinctive shoal complex and related deposits that result from the complex interaction of three different processes 1 progradation of a barrier spit at the southern end of the delmarva peninsula 2 strong reversing tidal currents that transport and rework sediment brought to the bay mouth from the north and 3 landward bayward net non tidal circulation and sediment transport together these processes play a major role in changing the configuration of the estuary and filling it with sediment the deposits at the mouth of the bay hold keys both to the evolution of the bay during the holocene transgression and to the history of previous generations of the bay the deposit associated with the shoals at the mouth of the bay the bay mouth sand is a distinct stratigraphic unit composed mostly of uniform gray fine sand the position and internal structure of the unit shows that it is related to near present sea level and thus is less than a few thousand years old the processes affecting the upper surface of the deposit and the patterns of erosion and deposition at this surface are complex but the geometry and structure of the deposit indicate that it is a coherent unit that is prograding bayward and tending to fill the estuary the source of the bay mouth sand is primarily outside the bay in the nearshore zone of the delmarva peninsula and on the inner continental shelf the internal structure of the deposit its surface morphology its heavy mineral composition bottom current studies comparative bathymetry and sediment budgets all suggest that sand is brought to the bay mouth by southerly longshore drift along the delmarva peninsula and then swept into the bay in addition to building the southward and bayward prograding bay mouth sand these processes result in sand deposition tens of kilometers into the bay

spatial and temporal variability of titanomagnetite placer deposits on a predominantly black sand beach abstract titanomagnetite forms rich placer deposits along the northwest coast of new zealand these deposits were sampled along 3 shore normal transects spaced over the southern 2 km of a dissipative high energy beach on the west coast in 5 field campaigns covering one year the percentage of opaque minerals mainly titanomagnetite was extremely high in the upper 30 m of the beach face extending seaward where these opaque minerals were gradually replaced with variable amounts of lighter augite hornblende and plagioclase the pattern appeared to be divided into two regions a lower seaward and an upper landward region separated by a point where either marine dominated over aeolian processes or where swash dominated over breaking processes in the seaward region the percentage of opaques increased and particle size fined landward as undertow removed the lighter larger particles seaward in the landward region the percentage of opaques and particle size were more constant or even showed the reverse pattern as wind transported the lighter material shoreward or swash asymmetry transported the heavier material seaward the similarity of settling velocities over the whole beach face suggests that sorting by size rather than weight plays a dominant role in separating the mineral assemblages considerable variations existed between transects this could be explained by the spatial changes in surfzone waves and currents that were associated with proximity to the southern headland and various rip current channels that characterised this dissipative site surprisingly the percentage of opaques decreased when the wave conditions of the day of sampling were more energetic in contrast to many other placer deposits these deposits are abundant on the beach face forming an armouring layer during lower wave energy conditions during higher wave conditions the surface layer erodes allowing lighter augite plagioclase and hornblende to be released from the sediments below

distribution geometry and origin of heavy mineral placer deposits on oregon beaches abstract beach segments 0 5 3 km in length enriched in heavy minerals 20 100 by weight abundance are located south of six prominent headlands that interrupt the 175 km coastline between cape lookout and cape perpetua oregon beach face retreat in the winter of 1982 83 exposed underlying placers containing the economic minerals garnet zircon ilmenite and chromite in each case the highest concentration of placer minerals occurs in an area of maximum shoreline curvature at a distance south of the north bounding headland that is proportional to seaward extent of the headland cross sections and magnetic surveys of one 8 km coastal section otter rock to yaquina head define a small placer body heavy minerals 50 some 0 75 km in length and 80 103 m3 in volume that comprises 10 of the total beach sand between the bounding headlands mineral grain size analyses of winter beach samples along this coastal section confirm earlier models of mineral segregation by entrainment processes the light minerals are more susceptible to fluid shear stress than the heavy minerals maximum segregation and heavy mineral enrichment occur in the backshore and at shoreline inflection points where decreasing flow velocities produce gradients of fl id shear stress allowing light minerals to be winnowed from more stable heavy minerals development of placer deposits is controlled by shoreline configuration as the first order factor and seasonal variations of wave climate and longshore currents as second order factors that delineate shape and concentration of heavy minerals in placer bodies

sediment sorting and beach erosion along a coastal foreland magnetic measurements in point pelee national park ontario canada abstract in situ and laboratory based magnetic measurements were made on sand samples from the beach on the eastern side of point pelee national park ppnp in northwestern lake erie in order to examine both the composition and spatial distribution of magnetic minerals magnetic remanence measurements on bulk and particle size fractions showed that the magnetic properties were dominated by multidomain ferrimagnetic grains probably magnetite and or maghemite particle size specific measurements on different grain size fractions showed that the

development and recent activity of the san andres landslide on el hierro canary islands spain abstract extremely voluminous landslides with a long run out also known as megalandslides on oceanic volcanic islands are infrequent denudational processes on such islands at the same time they represent a major geological hazard that must be looked into to avoid negative consequences for the inhabitants of these islands their occurrence can be related to periods of intense seismo volcanic activity similar to that which occurred on el hierro island over 2011 2012 landslides on volcanic islands are studied using onshore and offshore geological geophysical and geomorphological records considering their unique triggering conditions e g lava intrusions eruptive vents magma chamber collapses previous work has pointed out similarities between specific cases of landslides on volcanic islands and deep seated gravitational slope deformations dsgsds which are typical in high mountain settings nevertheless the methodological approaches and concepts used to investigate dsgsds are not commonly applied on volcanic islands studies even though their use may provide new information about the development stage recent movements and future hazards therefore this approach for studying the san andres landslide sal on el hierro canary islands has been developed applying a detailed morphological field mapping an interpretation of digital elevation models structural measurements kinematic testing and a precise movement monitoring system the acquired information revealed a strong structural influence on the landslide morphology and the presence of sets of weakened planes acting as the sliding surfaces of the sal or secondary landslides within its body the presence of secondary landslides deep erosive gullies coastal cliffs and high on shore relative relief also suggests a high susceptibility to future landslide movement direct monitoring on the landslide scarps and the slip plane performed between february 2013 and july 2014 using an automated optical mechanical crack gauge with a precision of up to 10 2 mm detected creep movement in the order of 1 mm yr 1 with a persistent sinistral component as well as episodic horizontal and a subtle vertical movement this monitoring will continue in the future in order to verify the initial observations which instead of long term movement patterns could represent a landslide response to the period of an intense seismo volcanic activity during 2011 12

a new andean deep ice core from nevado illimani 6350 m bolivia abstract a new ice core record from the nevado illimani 16 s bolivia covers approximately the last 18 000 years bp a comparison with two published ice records from sajama 18 s bolivia thompson et al science 282 1998 1858 1864 and huascaran 9 s peru thompson et al science 269 1996 46 50 documents a regionally coherent transition from glacial to modern climate conditions in south america north of 20 s the strong resemblance between the illimani and huascaran water isotope records and their differences from the sajama record in particular during the period from 9000 years bp to 14 000 years bp suggest that local water recycling or local circulation changes played a major role for sajama we interpret the common illimani huascaran water isotope history in terms of a common change from wetter cooler conditions during glacial times to drier warmer conditions in the early holocene

photogrammetric documentation and non invasive investigation of a stone dry dock the yokosuka arsenal dry dock no 1 japan abstract the yokosuka arsenal dry dock no 1 is the oldest stone dock in japan constructed from natural building stones during the construction of the dock hakusen hill which comprised mainly pleistocene sediments was excavated in this study photogrammetric documentation and a non invasive investigation were used to survey the dock site evaluate its soundness and assist in future preservation horizontal and vertical sections near the gate were successfully created using a photogrammetrically produced 3d surface model the vertical sections of the south wall display greater deformation than those on the north wall the water leakage on both walls was measured using rain gauges placed near the gate the leakage was found to originate mainly from the mortar between the building stones and was correlated with sea level changes the results indicate that rising sea level increased the water pressure leading to higher leakage inside the dock walls the water leakage in the north and south walls peaked at different times and the amplitude of the sea level vs water leakage hysteresis loops also differed between the north and south walls these differences may have been caused by the different permeability and storage coefficients of the wall mortar and the backfill materials behind the north and south walls in addition the different permeability and storage coefficients were likely caused by the deformation of the south wall due to lithological variations in the material underlying the north and south walls these results contribute to future preservation plans regarding the soundness of the site ground stability is one of the main issues in engineering geology and related fields therefore this study may also be helpful in similar cases worldwide

distributions of dissolved titanium in chesapeake bay and the amazon river estuary abstract total dissolved ti in chesapeake bay and the amazon river estuary exists at nanomolar to subnanomolar concentrations in both estuaries dissolved ti is removed at low salinities in the course of estuarine mixing most likely by coagulation of colloidal metal perhaps with stabilization of the aggregates by organic material or by adsorption onto other particles titanium concentrations in 0 2 m filtered surface samples obtained on a summer survey of chesapeake bay range from 0 52 0 87 nm at 0 1 salinity decreasing to 0 07 0 28 nm at higher salinities the extent of removal is 65 variable but low levels in the middle estuary probably reflect inputs from tributaries to the bay a comparison of ti concentrations in oxic surface waters and suboxic and anoxic bottomwaters shows no consistent evidence for ti release from dissolving fe or mn phases on a summer survey of the amazon river estuary ti concentrations in 0 22 m filtered surface waters decrease from 3 3 7 1 nm at salinities of 0 3 0 8 to 0 27 0 62 nm above a salinity of 5 for a removal of 90 slight elevations in ti concentrations at salinities greater than 34 may result from resuspension of sediments on the dynamic amazon shelf using the amazon river estuary as an example at least 90 of the global flux of dissolved ti from rivers is removed to particles at low salinities considering this the effective global flux of dissolved ti from rivers to the oceans here estimated at 2 107 mol y 1 is 10 100 times lower than what has been previously estimated based on river inputs

geological and exploration models of beach placer deposits integrated from case studies of southern australia abstract the processes leading to the formation of beach placer deposits generally begin inland and terminate at the coast including source rocks being weathered eroded and then transported by streams and rivers to the coast where the sediments are deposited in a variety of coastal environments the coastal sediments are reworked by the action of waves tides longshore currents and wind which are effective processes for sorting the mineral grains based on differences in their size and density resulting in laminated or lens shaped packages of sediments up to tens of meters thick that are rich in heavy minerals detailed studies of sedimentary basins as well as peripheral paleo valleys that drained sediment source areas are important tools in the exploration for heavy mineral resources knowledge of the paleo basin associated valley architecture and the source of heavy minerals concentrated in the shorelines and valleys are useful guides to the potential for and location of economic deposits evidence from sedimentology can be combined with that from other geological and geophysical characteristics to arrive at a general reconstruction of basin and paleovalley architecture and depositional environments complex paleogeography of the shorelines can influence or determine the sites of heavy mineral concentration heavy mineral sands tend to concentrate in certain shoreline settings during storm activity repeated storm erosion and reworking over centuries e g the southeastern coast of australia or millennia e g the eucla and murray basins of australia can progressively enrich heavy mineral sand deposits preservation of these deposits over a geological timeframe of millions of years can ensue through subsidence of coastal sediments and during sea level change that results in either shorelines migrating inland marine transgression or seaward marine regression potentially burying or stranding earlier deposits or reworking them to form younger deposits refinements in remote sensing and geophysical techniques data processing sedimentology and computer aided interpretations provide effective economic and efficient methods for modeling coastal reconstructions and for exploring provinces and terrains prospective for heavy mineral sand deposits landscape topography analysis combined with geophysical methods that can resolve physical property contrasts between the shoreline sediments and underlying sequences are increasingly used in mineral exploration to locate and to reconstruct paleoshorelines and paleovalleys australia has modern and ancient beach placer deposits both of which show many similar geologic features the formation of these heavy mineral deposits provides one of the best examples of applying knowledge of modern systems e g the west and east coasts of australia as an analogue to interpret and understand the geology and form of ancient deposits e g the eucla and murray basins of southern australia this study provides descriptive and exploration models of australia s heavy mineral sand deposits formed in coastal environments which can be applied to similar settings worldwide

landslide temporal analysis and susceptibility assessment as bases for landslide mitigation machu picchu peru multi temporal landslide occurrence information acquired through aerial photo interpretation and field mapping was used to assess occurrence frequencies on the slopes around the unesco cultural world heritage site of machu picchu peru this showed that the coarse time resolution of the historical landslide information may lead to inaccurate interpretations regarding landslide occurrence frequencies in some parts of the study area in addition the assumption that the past landslide frequency can be used to describe the future landslide occurrence was not proved in the study area thereafter unique conditional analyses were undertaken to assess landslide susceptibility using a limited number of preparatory factor maps it showed that large majority of the inca city is located on least susceptible areas within the region the results of the susceptibility assessment combined with landslide occurrence frequencies may serve as a basis for the landslide hazard mitigation in the studied area for these purposes pixel based susceptibility maps were generalized into expert defined landslide management units these units provide site managers with easily understandable and applicable hence reliable information about future landslide occurrences an approach describing usage of the resulting susceptibility maps for onsite mitigation purposes was described with respect to the needs of machu picchu site managers

patterns of beach sand sorting and shoreline erosion on the nile delta abstract rapid erosion has occurred on the beaches of the nile delta in response to dam construction that has cut off the river sediment supply this erosion is greatest adjacent to the two distributary mouths with shoreline retreat rates up to 60 m per year the eroded sand is carried alongshore away from the river mouths and deposited in areas of shoreline accretion these patterns of shoreline erosion and deposition are reflected in the mineralogy of the beach sands on a delta wide scale high density opaques garnet and zircon are concentrated in the erosion areas to form black sand placers lower density hornblende as well as quartz and feldspars are preferentially transported out of the erosion areas and deposited in the stretches of accreting shoreline a detailed analysis of these sorting patterns has been undertaken with beach samples from abu quir bay at the western end of the delta concentrations of opaques zircon rutile and garnet decrease exponentially with longshore distance from the river mouth while augite and hornblende increase exponentially the coefficients in the exponential equations are found to be a function of mineral density demonstrating the importance of this grain property in mineral sorting leading to the observed compositional variations along the shores of the nile delta

geomorphological research of large scale slope instability at machu picchu peru a multidisciplinary approach has been adopted to study the slope movements and landscape evolution at the archaeological site of machu picchu and its immediate surroundings the basic event in the paleogeomorphological evolution of the area was the large scale slope movement which destroyed the originally higher ridge between mt machupicchu and mt huaynapicchu within remnants of that primary deformation several younger generations of slope movements occurred the laboratory analyses of granitoids revealed highly strained zones on the slopes of mt machupicchu which strongly affect the largest slope deformation the borders of the largest slope deformation are structurally predisposed by the existence of fault zones the majority of various types of slope movements on the so called front slope e facing and back slope w facing are influenced by the alignment between topography and joints along with slope movements fluvial erosion and tectonic disturbance of the rocks have been affecting the evolution of the landscape a monitoring network for dilatometric and extensometric measurements was used to detect the present day activity of rock displacements within the archaeological site in addition to standard mapping of surface hydrogeological phenomena eleven express slug tests were conducted to verify the infiltration potential of precipitation the results of these surveys indicate that recent large scale slope movement as suggested by some previous studies is doubtful and the detected movements can be explained by individual movements of rock blocks or several other mechanisms including sinking of archaeological structures subsurface erosion and annual changes in the water content of the soils

high resolution aeromagnetic data a new tool for mapping intrabasinal faults example from the albuquerque basin new mexico high resolution aeromagnetic surveys flown over the albuquerque basin new mexico demonstrate that aeromagnetic methods can successfully map concealed and poorly exposed faults in sediment filled basins this is the first known use of aeromagnetic data as an aid to surficial mapping and hydrogeologic studies in a basin aeromagnetic maps show detailed fault patterns within the basin fill that revise the structural view of the basin concealed faults are more numerous and more closely spaced than expected the hubbell springs fault is the central splay of three generally north striking fault splays that can be traced for nearly 50 km the splays converge on the north and may represent the southern extension of the tijeras fault contradicting the proposed southwest extension of the tijeras fault across the basin in profile view the linear aeromagnetic anomalies associated with faults show a variety of signatures one signature has potential for mapping fault controlled sedimentation in the subsurface because it identifies increases in magnetic likely coarse grained material in the hanging walls of faults

multiple landslide clusters record quaternary climate changes in the northwestern argentine andes the chronology of multiple landslide deposits and related lake sediments in the semi arid eastern argentine cordillera suggests that major mass movements cluster in two time periods during the quaternary i e between 40 and 25 and after 5 14 c kyr bp these clusters may correspond to the minchin maximum at around 28 27 14 c kyr bp and titicaca wet periods after 3 9 14 c kyr bp the more humid conditions apparently caused enhanced landsliding in this environment in contrast no landslide related damming and associated lake sediments occurred during the coipasa 11 5 10 14 c yr bp and tauca wet periods 14 5 11 14 c yr bp the two clusters at 40 25 and after 5 14 c kyr bp may correspond to periods where the el nin o southern oscillation enso and tropical atlantic sea surface temperature variability tav were active this however was not the case during the coipasa and tauca wet periods lake balance modelling of a landslide dammed lake suggests a 10 15 increase in precipitation and a 3 4 c decrease in temperature at v30 14 c kyr bp as compared to the present in addition time series analysis reveals a strong enso and tav during that time the landslide clusters in northwestern argentina are therefore best explained by periods of more humid and more variable climates 2003 elsevier science b v all rights reserved

ancient channels of the susquehanna river beneath chesapeake bay and the delmarva peninsula three generations of the ancestral susquehanna river system have been mapped beneath chesapeake bay and the southern delmarva peninsula closely spaced seismic reflection profiles in the bay and boreholes in the bay and on the southern delmarva peninsula allow detailed reconstruction of each paleochannel system the channel systems were formed during glacial low sea level stands and each contains a channel fill sequence that records the subsequent transgression the trunk channels of each system are 2 to 4 km wide and are incised 30 to 50 m into underlying strata they have irregular longitudinal profiles and very low gradients within the chesapeake bay area the three main stem channels diverge from the head of the bay toward the southeast the channels are rarely coincident although they commonly intersect all three main channels pass beneath the southern delmarva peninsula forming an age progression from north oldest to south youngest beneath the peninsula and from east oldest to west youngest beneath chesapeake bay southward progradation of the tip of the delmarva peninsula during interglacial high sea level stands caused southward migration of the mouth of the bay so that the next generation of channels were incised progressively further towards the southwest the youngest paleochannel is clearly of late wisconsinan age about 18 ka and the intermediate one appears to be late illinoian in age or about 150 ka the age of the oldest paleochannel is not well constrained but it is in the range of about 200 to 400 ka the three paleochannel systems imply a dynamic coastal plain environment and at least two previous generations of the chesapeake bay both the chesapeake bay and the southern delmarva peninsula have changed considerably in the past half million years

rare earth mineral potential in the southeastern u s coastal plain from integrated geophysical geochemical and geological approaches we combined geophysical geochemical mineralogical and geological data to evaluate the regional presence of rare earth element ree bearing minerals in heavy mineral sand deposits of the southeastern u s coastal plain we also analyzed regional differences in these data to determine probable sedimentary provenance analyses of heavy mineral separates covering the region show strong correlations between thorium monazite and xenotime suggesting that radiometric equivalent thorium eth can be used as a geophysical proxy for those ree bearing minerals airborne radiometric data collected during the national uranium resource evaluation nure program cover the southeastern united states with line spacing varying from 2 to 10 km these data show eth highs over cretaceous and tertiary coastal plain sediments from the cape fear arch in north carolina to eastern alabama these highs decrease with distance from the piedmont quaternary sediments along the modern coasts show weaker eth anomalies except near coast parallel ridges from south carolina to northern florida prominent eth anomalies are also observed over large riverbeds and their floodplains even north of the cape fear arch where surrounding areas are relatively low these variations were verified using ground geophysical measurements and sample analyses indicating that radiometric methods are a useful exploration tool at varying scales further analyses of heavy mineral separates showed regional differences not only in concentrations of monazite but also of rutile and staurolite and in magnetic susceptibility the combined properties suggest the presence of subregions where heavy mineral sediments are primarily sourced from high grade metamorphic low grade metamorphic or igneous terrains or where they represent a mixing of these sources comparisons between interpreted sources of heavy mineral sands near the fall line and igneous and metamorphic piedmont and blue ridge units showed a strong correspondence with rocks closest to the fall line and poor correspondence with rocks farther inland this strongly suggests that the primary source of those heavy minerals especially monazite is the rocks that formed the rocky coast that was present during opening of the atlantic ocean which in turn indicates the importance of coastal processes in forming heavy mineral sand concentrations furthermore narrow radiometric eth and k anomalies are associated with major rivers indicating limited spatial influence of fluvial processes later coastal plain sediment deposition appears to have involved reworking of sediments providing an inheritance of the rocky coast composition that persists for some distance from the fall line however this inheritance is reduced with distance and sediments within 100 km of the coast in georgia and florida exhibit properties indicative of mixing from multiple sources

biogenic magnetite and the magnetization of sediments biogenic magnetites are produced through the reduction of ferric iron by both biologically induced extracellular and biologically controlled intracellular processes with few exceptions all are ultra fine grained single domain magnetite biogenic magnetites formed by magnetotactic bacteria biologically controlled have been shown to contribute significantly to the natural remanent magnetization of carbonates and limestones hemipelagic and deep sea marine sediments the input into sediments of ultra fine grained magnetite produced by dissimilatory iron reducing bacteria biologically induced has yet to be firmly established but may be even more significant whether either type of authigenic biomagnetite is preserved is determined by postdepositional factors including oxidation reduction by substitution and dissolution unconsolidated and lithified sediments can be screened for putative biogenic magnetite by rock magnetic techniques it is not generally appreciated that magnetotactic bacteria and their magnetofossils can be identified by the unusual and in some cases unique morphologies size range and composition of the magnetite crystals magnetite produced by dissimilatory iron reducing bacteria have a distinctive morphology and size range but it is currently controversial as to whether these can be distinguished from certain chemically precipitated magnetites the presence of dissimilatory iron reducing bacteria however can be detected using microbiological techniques and sediment geochemistry biogenic magnetites are trace fossils and potentially useful environmental indicators and are considered to have significant input to the magnetization of most sediments both modern and ancient

constraints on sustainable development of arsenic bearing aquifers in southern bangladesh part 2 preliminary models of arsenic variability in pumped groundwater numerical models of groundwater flow and arsenic transport to tubewells in southern bangladesh have been developed based on a conceptual model derived from field observations the catchment of a single hand pumped tubewell htw is incorporated within a model domain 8110 m 2 in area and 60m thick three tubewell specifications represent typical bangladesh htw designs constant concentration cells act as a single layered arsenic source arranged to represent the observed depth distribution of arsenic in the aquifer and the range of possible patterns of overlap between htw catchments and discontinuous zones of arsenic release from sediment to groundwater a variety of sorption regimes is simulated and sensitivity to sorption is illustrated boundary conditions are modified to simulate the effects of deep production wells the models reproduce the observed scale and range of arsenic concentration in groundwater pumped from htws and demonstrate likely long term trends breakthrough of arsenic to htws may occur a few years after the start of pumping but at many tubewells the concentration of arsenic could continue to rise significantly over tens to hundreds of years spatial distributions and depth profiles of arsenic in groundwater from tubewells should be viewed as transient in the long term these preliminary models allow implications for the sustainability of the shallow alluvial aquifer to be quantified provisionally the mechanisms and scale of sorption of arsenic by the aquifer sediments remain as significant uncertainties

delineating low arsenic groundwater environments in the bengal aquifer system bangladesh studies within the as affected bengal basin have indicated that low as groundwater can be found in a variety of geological and geomorphological settings the hydrogeological environments that host lowas groundwater may be interpreted within a geological framework determined by the quaternary evolution of the bengal aquifer system bas this provides the basis for delineating the position and extent of shallow low as groundwater low as groundwater in oxidised red bed sediments and deep low as groundwater data available on a national scale allow a preliminary delineation of these low as groundwater environments across bangladesh based on empirical associations of low as groundwater occurrences with topography water table elevation surface sediment lithology geology and the screen depth of deep wells in low as zones

modeling earth deformation from monsoonal flooding in bangladesh using hydrographic gps and gravity recovery and climate experiment grace data 1 the ganges brahmaputra and meghna rivers converge in bangladesh with an annual discharge second to the amazon most of the flow occurs during the summer monsoon causing widespread flooding the impounded water represents a large surface load whose effects can be observed in gravity recovery and climate experiment grace and gps data bangladesh is at the center of the second largest seasonal anomaly in the grace gravity field reflecting water storage in southeast asia eighteen continuous gps stations in bangladesh record seasonal vertical motions up to 6 cm that inversely correlate to river level we use 304 river gages to compute water height surfaces with a digital elevation model to separate surface water from groundwater porosity of 20 was used to estimate groundwater mass and calculate the water load results show 100 gt of water are stored in bangladesh 7 5 of annual discharge but can reach 150 gt during extreme events the calculated water mass agrees with monthly grace water mass equivalents from bangladesh within statistical limits we compute the deformation due to this water load on an elastic half space and we vary young s modulus to fit gps data from our two most continuous records the water loading can account for 50 of the variance in the gps data the best fitting young s modulus is 117 124 gpa for dhak and 133 135 gpa for sust although the upper bound is not well constrained these estimates lie between sediment 30 75 gpa and mantle 190 gpa values indicating that response to loading is sensitive to structure throughout the lithosphere and is not absorbed by the weak sediments

temporal behavior of deep seated gravitational slope deformations a review abstract deep seated gravitational slope deformations dsgsds are slow moving hillslope scale mass movements featuring characteristic landforms such as double crested ridges and upslope facing scarps that occur in diverse landscapes throughout the world although these deformations have been studied since the 1960s significant insights to the rates of dsgsds have only been gained within the last two decades owing to progress in geochronology remote sensing and instrumental monitoring absolute age and monitoring data indicate that dsgsd movements are observable over long term 102 years and short term future research directions include constraining the lifespan of dsgsds with absolute age dating and precise high resolution monitoring of spatio temporal displacement across dsgsd bodies it is of great importance to include absolute time scales in the numerical models of dsgsds furthermore combining remote sensing techniques such as synthetic aperture radar interferometry with high resolution lidar scanning and near surface geophysics offers a promising toolkit for collecting very detailed and accurate data on the short term deformation rates of dsgsds

role of hydraulic sorting in the origin of fluvial placers a necessary condition for placer development is selective sorting at the grain scale by size and density the effects of differential entrainment suspension and transport on an initial distribution composed of medium size quartz and 10 fine size magnetite were modeled by solving the einstein bedload function for specific grain friction velocities u super in the range 3 63 cm sec super 1 and bed roughnesses of 0 55 2 5 and 10 mm for any value of u super and for both mineral densities the transport rate for all sizes in the initial distribution decreases with increasing roughness the decrease being greatest in the finer sizes the concentration of magnetite transported in the flow increases with increasing u super for each roughness and decreases with increasing roughness for each u super the settling velocity ratio of magnetite to quartz in transport decreases with increasing u super for any value of roughness for any value of u super the ratio first decreases then increases with increasing roughness ranging from 1 36 at low u super and roughness to 0 76 at high u super and intermediate roughness these results are due to variations in the reactive angles of grains and the extent to which grains hide in the lower inner zone of the boundary layer concentrations of heavy minerals at the bed bar and system scales are explained using these results

new surveys of the chesapeake bay impact structure suggest melt pockets and target structure effect we present high resolution gravity and magnetic field survey results over the 85 km diameter chesapeake bay impact structure whereas a continuous melt sheet is antici pated at a crater this size shallow source magnetic field anomalies of 100 nt instead suggest that impact melt pooled in kilometer scaled pockets surrounding the base of a central peak a central anomaly of 300 nt may represent additional melt or rock that underwent shock induced remagnetization models predict that the total volume of the melt ranges from 0 4 to 10 km 3 a quantity that is several orders of magnitude smaller than expected for an impact structure this size however this volume is within predictions given a transient crater of diameter of 20 40 km for a target covered with water and sedimentary deposits such that melt fragments were widely dispersed at the time of impact gravity data delineate a gently sloping inner basin and a central peak via a contrast between crystalline and sedimentary rock both features are ovoid oriented parallel to larger preimpact basement structures conceptual models suggest how lateral differences in rock strength due to these preimpact structures helped to shape the crater s morphology during transient crater modification

rapid sea level rise and ice sheet response to 8 200 year climate event 1 the largest abrupt climatic reversal of the holocene interglacial the cooling event 8 6 8 2 thousand years ago ka was probably caused by catastrophic release of glacial lake agassiz ojibway which slowed atlantic meridional overturning circulation amoc and cooled global climate geophysical surveys and sediment cores from chesapeake bay reveal the pattern of sea level rise during this event sea level rose 14 m between 9 5 to 7 5 ka a pattern consistent with coral records and the ice 5g glacio isostatic adjustment model there were two distinct periods at 8 9 8 8 and 8 2 7 6 ka when chesapeake marshes were drown as sea level rose rapidly at least 12 mm yr 1 the latter event occurred after the 8 6 8 2 ka cooling event coincided with extreme warming and vigorous amoc centered on 7 9 ka and may have been due to antarctic ice sheet decay

shipboard magnetic field noise reveals shallow heavy mineral sediment concentrations in chesapeake bay abstract shipboard magnetic field data collected over chesapeake bay exhibit low amplitude short wavelength anomalies that most likely indicate shallow concentrations of heavy mineral sediments piston core layers and black sand beach samples exhibit enhanced magnetic susceptibilities and carry remanent magnetization with mineralogical analyses indicating ilmenite and trace magnetite and or maghemite and hematite the anomalies are subtle and would be filtered as noise using traditional approaches but can instead be highlighted using spectral methods thus providing nearly continuous coverage along survey tracks the distribution of the anomalies provides constraints on relevant sorting mechanisms comparisons to sonar data and previous grab samples show that two of three areas surveyed exhibit short wavelength anomalies that are clustered over sand covered areas suggesting initial sorting through settling mechanisms this is supported by a correlation between core magnetic susceptibility and grain size near the choptank river where sediment resuspension is wave dominated anomalies show a sharp decrease with seafloor depth that cannot be explained by signal attenuation alone in pocomoke sound where both tidal currents and wave action impact sediment resuspension anomalies show a more gradual decrease with depth near the mouth of the bay where there is a higher influx of sediments from the continental shelf short wavelength anomalies are isolated and do not appear to represent heavy mineral sand concentrations these combined observations suggest the importance of further sorting by erosional processes in certain parts of the bay additionally comparisons of these data to cores sampling pre holocene sediments suggest that the sorting of heavy minerals in higher energy shallow water environments provides a mechanism for correlations between core magnetic susceptibility and sea level changes

the record of major quaternary sea level changes in a large coastal plain estuary chesapeake bay eastern united states abstract seismic reflection surveys of the chesapeake bay combined with geologic mapping and analysis of boreholes on the delmarva peninsula provide evidence of at least three generations of the susquehanna river system and three generations of the chesapeake bay the evidence for ancient courses of the susquehanna river is preserved as three distinct paleochannels and evidence for ancient versions of the chesapeake bay is preserved as three sets of paleochannel fill beneath the bay and three generations of barrier spit deposits on the southern delmarva peninsula the paleochannels represent relative sea level minima and the channel fill and barrier spit deposits represents relative sea level maxima a history of three major marine transgressions is recorded in the stratigraphy preserved in the filled paleochannels and in the overlying barrier spit complexes three systematic progressions from fluvial to estuarine to bay or nearshore marine environments this sea level record seems to be compatible with the saw toothed pattern of the marine oxygen isotope record and with the concept of glacial interglacial terminations it also seems to have a climax character in which most of the preserved evidence is related to the largest terminations and to the extreme sea level positions that bound those terminations the three paleochannel fill and barrier spit complexes appear to correspond to oxygen isotope stages 1 5 and either 7 or 11 the three related paleochannels correspond to stages 2 6 and either 8 or 12

heavy mineral deposits in the upper coastal plain of north carolina and virginia approximately 22 7 million metric tons 25 million short tons of heavy minerals at an average grade of 6 wt percent in 377 8 million metric tons 416 million short tons of sand have been delineated in 19 deposits in the upper coastal plain of north carolina and virginia average concentrations of the principal minerals are ilmenite 60 percent rutile 2 5 percent zircon 12 5 percent staurolite 8 5 percent tourmaline 0 7 percent kyanite 3 0 percent sillimanite 1 3 percent and others principally limonite 11 5 percent these deposits formed during a worldwide pliocene transgressive regressive event that occurred between 3 5 and 3 0 ma the deposits formed as beach or dune sands during the regressive phase of the event over an elevation range of 96 m 315 ft to 53 m 175 ft other major deposits that are interpreted to have formed during the pliocene transgressive regressive event are as follows trail ridge florida enneaba western australia lakehurst new jersey and deposits of the western murray basin victoria australia combined reserves of these pliocene deposits exceed 317 5 million metric tons 350 million short tons of heavy minerals the potential for new discovery of pliocene deposits elsewhere in the world is judged to be favorable

seasonal variability of shallow biogenic gas in chesapeake bay abstract methane gas in chesapeake bay sediments occurs in buried paleodrainage channels incised during the last glacial sealevel lowstand repeat acoustic surveys of two chesapeake bay sites during the past year with a 2 15 khz chirp sonar profiler and 100 khz sidescan sonar show that the top of the zone of acoustically opaque gas bubbles in the sediments fluctuates vertically by up to 0 5 m apparently in response to seasonal temperature changes the vertical movement of the gas layer is most apparent in the main channel of the bay where the methane gas is very close to the seafloor in areas where the gas is seen to be very near the seafloor on the chirp profiler records the sidescan sonar data show corresponding high backscatter this does not appear to be the result of differing sediment types it is not likely that the sidescan signal is penetrating the seafloor at the shallow outer grazing angles of the sidescan swath therefore the gas must extend to the water sediment interface the areas of high backscatter caused by the gas are observed to change seasonally expanding during the summer high temperature period and shrinking during the winter low temperature period

tidal resuspension of sediments in northern chesapeake bay abstract tidal resuspension experiments were carried out on two occasions during the winter of 1988 1989 at a disposal site for hydraulically dredged sediments in northern chesapeake bay to determine the influence of tidal resuspension on erosion of recent deposits the results indicate that normal tidal erosion depths were only a fraction of a millimeter per half tidal cycle and probably did not account for the majority of the apparent sediment loss erosion rate was found to be a linear function of the excess of estimated shear stress over a critical value but both the constant of proportionality m 0 5 mg cm 2 h and the critical shear stress c 0 16 dynes cm 2 were much less than many previously reported results the most likely explanation for these low values is that the thin layer of surface sediments involved in regular tidal resuspension had only a few hours at most to consolidate between resuspension events observed resuspended sediment concentrations up to 35 mg l above background levels were much less than those reported for previous observations of tidal resuspension in the nearby channel presumably due to greater stratification and lower tidal velocities at the disposal site salinity induced stratification of the water column is estimated to have reduced shear stresses by up to 50 relative to the neutrally stratified case regular tidal resuspension of a thin layer of surface sediments is implicated as a potentially important aspect of the typical benthic environment of northern chesapeake bay even if it is not the most important factor in massive sediment erosion and transport

constraints on sustainable development of arsenic bearing aquifers in southern bangladesh part 1 a conceptual model of arsenic in the aquifer arsenic is widespread in groundwater of the holocene alluvial aquifers in southern bangladesh yet its concentration is highly variable spatially and with depth a conceptual model of arsenic in the aquifer is proposed as a basis for addressing questions concerning sustainability of groundwater development patterns and profiles of arsenic distribution in the aquifer have been determined at meherpur in western bangladesh over an area of 15 km 2 and a depth range of 15 225 m the hydrochemical and hydraulic environments of arsenic occurrence have been established the conceptual model incorporates the conditions of arsenic release to groundwater the depth distribution of the arsenic source likely sedimentological controls on the lateral discontinuity of the arsenic source and the hydraulic regime imposed by pumping from the hydrogeologically leaky multi layered aquifer reducing conditions conducive to arsenic release from sedimentary iron oxyhydroxides are widespread the arsenic source occurs at a distinct horizon at a depth of about 20m but is laterally discontinuous the catchments of shallow hand pumped tubewells htws are limited in extent by vertical leakage arsenic concentration in water pumped from tubewells depends on the depth separation between the htw screen and the arsenic source the overlap between the htw catchment and the arsenic source layer and the duration of pumping implications are drawn for treatment tubewell location and design monitoring and predictive modelling