architecture and evolution of a fjord head delta western vancouver island british columbia the architectural framework and holocene evolution of the zeballos fjord head delta on west central vancouver island was established through a multidisciplinary field based study the zeballos delta is a composite feature consisting of an elevated incised late pleistocene delta and an inset holocene delta graded to present sea level both deltas have a classic gilbert type tripartite architecture with nearly flat topset and bottomset units and an inclined foreset unit time domain electromagnetic tdem and ground penetrating radar gpr surveys borehole data and gravel pit exposures provided information on the internal form lithologies and substrate of both deltas both sets of deltaic deposits coarsen upward from silt in the bottomset unit to gravel in the topset unit the tdem survey revealed a highly irregular buried bedrock surface ranging from 20 m to 190 m in depth and it delineated saltwater intrusion into the deltaic sediments late quaternary sea level change at zeballos was inferred from delta morphology and the gpr survey the elevated late pleistocene delta was constructed when the sea was about 21 m higher relative to the land than it is today it was dissected when sea level fell rapidly as a result of glacio isostatic rebound relative sea level reached a position about 20 m below the present datum during the early holocene foreset beds that overlap and progressively climb in a seaward direction and topset beds that thicken to 26 m landward imply that the delta aggraded and prograded into zeballos inlet during the middle and late holocene transgression sea level may have risen above the present datum during the middle holocene creating a delta plain at about 4 m a s l remnants of this surface are preserved along the valley margins copyright 2004 john wiley sons ltd

what controls submarine channel development and the morphology of deltas entering deep water fjords river deltas and associated turbidity current systems produce some of the largest and most rapid sediment accumulations on our planet these systems bury globally significant volumes of organic carbon and determine the runout distance of potentially hazardous sediment flows and the shape of their deposits here we seek to understand the main factors that determine the morphology of turbidity current systems linked to deltas in fjords and why some locations have well developed submarine channels whilst others do not deltas and associated turbidity current systems are analysed initially in five fjord systems from british columbia in canada and then more widely this provides the basis for a general classification of delta and turbidity current system types where rivers enter relatively deep 200 m water fjord delta area is found to be strongly bimodal avalanching of coarse grained bedload delivered by steep mountainous rivers produces small gilbert type fan deltas whose steep gradient 11 25 approaches the sediment s angle of repose bigger fjord head deltas are associated with much larger and finer grained rivers these deltas have much lower gradients 1 5 10 that decrease offshore in a near exponential fashion the lengths of turbidity current channels are highly variable even in settings fed by rivers with similar discharges this may be due to resetting of channel systems by delta top channel avulsions or major offshore landslides as well as the amount and rate of sediment supplied to the delta front by rivers

sedimentation by river induced turbidity currents field measurements and interpretation turbidity currents initiated from spring runoffs of an influent river were observed in the upper region of a reservoir in hokkaido japan by measuring water temperature velocity and suspended sediment concentration their profiles offer some physical parameters for the sedimentary conditions assuming the turbidity currents to be quasi uniform the bottom sediment deposited by the turbidity currents was then collected by a portable core sampler the bottom sediment consists of more than 90 silt and clay and thus offers a hydraulically smooth bed for shear flow a plane bed as a bed configuration was formed on the reservoir bed probably because of the low shear velocity and small grain size of sediment using a graphic method with log normal probability paper the bottom sediment is divided into several overlapping log normal subpopulations grain size analysis indicates that the bottom sediment may be regarded as cohesionless criteria for complete deposition of transported grains can then be incorporated into the extended shields diagram giving the minimum shear stress to erode bottom sediment applying the new diagram to the grain size distribution of the bottom sediment it is suggested that each of the log normal subpopulations was deposited in each of four different modes of deposition i e traction saltation or intermittent suspension suspension and suspension under equilibrium the last mode may be observed under a sedimentary condition where upward flux of suspended sediment by eddy diffusion is almost equal to its depositional flux due to gravity the mean and critical grain sizes for bottom sediment and each of the corresponding subpopulations decrease consistently with an increase of fd2 log10re fd is the densimetric froude number and re is the flow reynolds number correlates inversely with shear velocity which bears a linear relationship to mean velocity these results lead to the conclusion that relatively fine suspended sediment is deposited as a result of decreasing bottom friction with a relative decrease of turbulent energy

active sand transport along a fjord bottom channel bute inlet british columbia an underwater channel system is incised in the holocene fjord basin sediments of bute inlet british columbia high resolution side scan sonar swaths and seismic profiles reveal two channels within a zone of extensive rotational sliding on the slopes of a fjord head delta the channels coalesce into a single sinuous channel that extends 14 km downfjord on a 0 9 slope where it splits into two distributaries which continue another 18 km ending within stacked depositional lobes piston cores show sands in the channels and lobes in contrast to deep water silty clays in the basin floor the sea floor features and sediment distributions result from active highly mobile slide generated sediment flows which transport sands via the channels from the delta to the fjord basin

sedimentary processes of canadian arctic fjords abstract conceptual models of circulation and sedimentation in arctic fjords are presented to illustrate the current understanding of these environments circulation is a vigorous process in these fjords and is enhanced by the loss of the freshwater cap during the long winter period of near zero inflow the process of brine rejection during the formation of sea ice and the role of glaciers and icebergs injecting freshwater at depth on the other hand the presence of sea ice blocks reduces the mixing action of wind which may otherwise represent the largest input of energy to fjord circulation it also provides a freshwater layer on melting and may in some circumstances damp the amplitude of tides during summer large loads of glacial sediment entering arctic fjords are separated into streams of overflowing suspended load and bed load in the presence of salt water as the concentrations of suspended load in the freshwater are normally much less than required to overcome the density of the salt water deposition occurs throughout the fjord by rapid settling of flocculated particles from the overflowing brackish water and from grain flows in the proximal environment created as the fluvial traction carpet moves over the delta foreset slope after sediment has been deposited it may be remobilized by slides which in turn may develop into fully turbulent flows as they move down the fjord floor a range of deposits from slump debris to minor turbidites are postulated to occur with the flocculated muds although not all have yet been examined in the arctic fjord stratigraphic record sea ice is an important sedimentological agent in arctic fjords it passively carries fluvial aeolian and colluvial material which is subsequently released from the ice during the stage of puddle draining at break up sea ice also actively incorporates fine and coarse sediments up to large boulders during freezing along the shores in winter and by wave and tidal current washing controlled by the presence of the ice during break up

late pleistocene glacimarine record in saanich inlet british columbia canada abstract late pleistocene deposits were cored at two sites in saanich inlet and provide a record of the sedimentary environment during deglaciation of this fjord at site 1033 at the southern end of the fjord 59 3 m of late pleistocene sediment was obtained in a hole drilled to 105 1 mbsf at site 1034 4 8 km to the north a hole was drilled to 118 2 mbsf recovering 49 8 m of late pleistocene sediment sediments were deposited in this deep 200 m fjord basin as a lobe of the cordilleran ice sheet retreated at the end of fraser glaciation this is the first recovery of basin fill sediments from the pleistocene retreat of the cordilleran ice sheet lithofacies analysis particle size measurements and 17 ams 14 c dates on marine shells or wood fragments are used to reconstruct the glacimarine sedimentary environment sediments are dense gray to olive gray terrigenous silty clay with thick graded sand beds and interlaminated fine sand and silt with mud scattered dropstones clusters of pebbles and pods of sand and granules are common bioturbation indicated by disruption of laminae and horizontal burrows or black mottles is minimal to moderate and decreases downcore a calving tidewater glacier retreated northward through saanich inlet however the ice contact sediments are beneath the depth cored at both sites the glacier retreated rapidly and the basin was open to marine exchange through satellite channel prior to 13 270 60 14 c yr bp the oldest date from the cores deposition of lithofacies association i occurred in an iceberg zone depositional environment dominated by turbid meltwater plumes and intense iceberg rafting within approximately 10 km of the glacier terminus after the glacier grounded at the head of cowichan bay lithofacies association ii was deposited in the ice distal depositional environment by turbidity currents that by passed the sill and turbid meltwater plumes lithofacies association iii was deposited under post glacial conditions at the end of the pleistocene

characterization of model evaporitic environments through the study of lipid components abstract a saline circuit has been studied as a model of coastal evaporite system the lipid composition of diverse salt ponds encompassing calcite gypsum and halite domains has been determined most of the lipid materials has been found in the carbonate samples and is related to algal cyanobacterial debris lipids in the gypsum domain are of heterotropic microbialorigin and extreme halophilic bacteria constitute the main lipid contribution in the halite samples n alkane distributions with high predominance of n docosane constitute a previously described feature of sedimentary evaporitic conditions that is charateristics of the intermediate calcite gypsum samples in the calcite domain the presence of c20 highly branched isoprenid olephines tetrahymanol and the large amounts of phytol constitute likely precursors of lipids usually found in evaporitic environments i e c20 highly branched isoprenoid alkanes gammacerane and high phytane pristane ratios their occurence point to dehydration and hydrogenations as two main diagenetic processes leading to the formation of evaporitic molecular markers

sea floor engineering geomorphology recent achievements and future directions abstract new mapping technology is providing perspectives of the sea floor as if there were no ocean revealing that ocean floors exhibit a wide variety of relief sediment properties and active geologic processes such as erosion faulting fluid expulsion and landslides the development of coastal and offshore resources such as oil and gas and minerals involves sea floor engineering in remote complex and sometimes hazardous environments optimum engineering design and construction practice require detailed surveys of sea floor geomorphology geologic conditions on the sea bed and to various depths beneath it combined with geotechnical properties of the sediments and oceanographic information integrated site survey models attempt to predict conditions and process frequencies and magnitudes relevant to the engineering design lifetimes of sea floor installations such as cables pipelines production platforms as well as supporting coastal infrastructure such as jetties wharves bridges and harbors recent use of deep water areas for oil and gas production pipelines and cable routes are also showing that the world s greatest slopes beyond the continental shelves contain exciting exotic and enigmatic geomorphological features and processes safe and cost effective engineering use of these regions depends upon exciting new technical and conceptual advances for understanding sea floor geomorphology a task which has barely begun

the major ion composition of cenozoic seawater the past 36 million years from fluid inclusions in marine halite fluid inclusions from ten cenozoic eocene miocene marine halites are used to quantify the major ion composition mg2 ca2 k na so42 and cl of seawater over the past 36 my criteria used to determine a seawater origin of the halites include 1 stratigraphic sedimentologic and paleontologic observations 2 br in halite 3 34s of sulfate minerals 4 87sr 86sr of carbonates and sulfates and 5 fluid inclusion brine compositions and evaporation paths which must overlap from geographically separated basins of the same age to confirm a global seawater chemical signal changes in the major ion chemistry of cenozoic seawater record the end of a systematic long term 150 my shift from the ca2 rich mg2 and so42 poor seawater of the mesozoic cacl2 seas to the mgso4 seas with higher mg2 and so42 ca2 of the cenozoic the major ion composition of cenozoic seawater is calculated for the eocene oligocene 36 34 ma serravallian tortonian 13 5 11 8 ma and the messinian 6 5 ma assuming chlorinity 565 mmolal salinity and the k concentration 11 mmolal are constant and the same as in modern seawater fluid inclusions from cenozoic marine halites show that the concentrations of mg2 and so42 have increased in seawater over the past 36 my and the concentration of ca2 has decreased mg2 concentrations increased from 36 mmolal in eocene oligocene seawater 36 34 ma to 55 mmolal in modern seawater the mg2 ca2 ratio of seawater has risen from 2 3 at the end of the eocene to 3 4 and 4 0 respectively at 13 5 to 11 8 ma and 6 to 5 ma and to 5 in modern seawater eocene oligocene seawater 36 34 ma has estimated ranges of so42 14 23 mmolal and ca2 11 20 mmolal if the ca2 so42 product is assumed to be the same as in modern seawater 300 mmolal2 eocene oligocene seawater had ca2 16 mmolal and so42 19 mmolal the same estimates of ca2 and so42 for serravallian tortonian seawater 13 5 11 8 ma are so42 19 27 mmolal and ca2 8 16 mmolal and so42 24 mmolal and ca2 13 mmolal if the ca2 so42 product is equal to that in modern seawater messinian seawater has an estimated range of so42 21 29 mmolal and ca2 7 15 mmolal with so42 26 mmolal and ca2 12 mmolal assuming the ca2 so42 product is equal to that in modern seawater regardless of the estimation procedure so42 shows progressively increasing concentrations from 36 ma to the present values which are the highest of the cenozoic

biological markers in lacustrine chinese oil shales s u m m a r y a major objective in molecular organic geochemistry is the assessment and characterization of sedimentary depositional environments from the occurrence of specific biological marker compounds related to particular source organisms the aliphatic hydrocarbon distributions of petroleums and or sediments from chinese freshwater and hypersaline lacustrine environments are described and contrasted in the search for diagnostic features among their biological marker distributions the eocene maoming oil shale which crops out in guangdong province shows major differences in hydrocarbon composition through its stratigraphic succession these variations reflect changes in lithology and in the origins of the sedimentary organic matter as seen from petrographic examination the lower lignite and vitrinite layers contain significant contributions of biological markers from bacterial sources plus components derived from terrigenous higher plants such as c29 steroids in contrast the overlying shales show a dominance of dinoflagellate derived 4methylsteroids and culminate in an horizon with botryococcane homologues as their dominant alkanes thus the geochemical profile suggests that a swampy environment in which peats accumulated deepened to support populations of dinoflagellate and finally blooms of botryococcus green algae the aliphatic hydrocarbons of a series of sediments and petroleums from the eocene hypersaline sequence of the jianghan basin in southern hubei province shows various features that may be typical of such facies these include a dominance of even numbered n alkanes high amounts of phytane and gammacerane and an abundance of c35 hopanes similar characteristics are observed in shales from the eocene green river formation and in rozel point crude oil a petroleum thought to originate from sediments deposited under hypersaline conditions the same features also appear in a lower tertiary evaporitic mudstone from south of the renqui oil field in hebei province together with 4 methylsteranes fl carotane and 18c h oleanane a marker for terrigenous higher plants these data illustrate the potential of biological markers in the differentiation of different lacustrine environments and suggest that such characteristics may provide signatures for environmentally similar but geographically distant deposits

application of biological markers in the recognition of palaeohypersaline environments the hydrocarbon fractions of a marl sample from a messinian basin in the northern appenines and four oils rozel point oil utah and three seep oils from sicily were studied

dinoflagellate origin for sedimentary 4α methylsteroids and 5α h stanols biological marker compounds provide useful tools for evaluating the depositional environments of recent and ancient sediments and petroleums1 largely through established relationships between the organic matter of sediments and source organisms1 2 such relationships are best tested and explored by investigating the lipid components of natural populations of autochthonous biota that can be clearly recognized as contributors to underlying bottom sediments in this context we have studied the lipids of the freshwater dinoflagellate peridinlum lomnickii woloszynska order peridiniales class dinophyceae collected from the waters of priest pot3 a eutrophic lake in the english lake district its distributions of both 4 methylsterols and 4 methylstanones closely resemble those of the underlying bottom sediments demonstrating that dinoflagellates are important contributors of these sedimentary compounds the 4 methylsteroidal hydrocarbons found in ancient sediments and petroleums4 6 are presumably diagenetic products of such 4 methylsteroids and therefore reflect dino flagellate inputs to the original depositional environments furthermore the prominence of 5 h cholestan 3 ol in p lomnickii suggests that dinoflagellates may be the long sought direct biological source of sedimentary 5 h stanols

bacterial and algal markers in sedimentary organic matter deposited under natural sulphurization conditions lorca basin murcia spain abstract free lipids sulphur bound lipids present in macromolecular fractions and kerogen pyrolysis products have been studied in shales and early diagenetic carbonates replacing gypsum from a messinian sequence of lorca basin the high abundance of phytane 2 3 dimethyl 5 2 6 10 trimethylundecyl thiophene mid chain c 20 isoprenoid thiophenes and bithiophenes and bis o phytanyl and o phytanyl o sesterterpanyl glycerol ethers indicates that the organic matter in all these samples was deposited under hypersaline conditions the isopranyl glycerol ethers are essentially found in the sulphur bound macromolecular matter which contrasts with the low concentrations of these compounds as free lipids however the distributions of these isopranyl glycerols is paralleled by the occurrence of free phytanic acid shales and laminated carbonate and 3 7 11 15 19 pentamethyleicosanoic acid only in the laminated carbonate the bacterial inputs are represented by 2 hydroxytetracosanoic acid n octadec 11 enoic acid hopanoic acids and the distributions of iso and anteiso c 15 and c 17 homologues and minor amounts of iso c 16 and anteiso c 14 these branched fatty acids are characteristic of sulphate reducing bacteria the relative proportions of the iso and anteiso compounds in the total fatty acid distributions are correlated with the proportion of reduced sulphur in the sediments

sedimentary and diagenetic markers of the restriction in a marine basin the lorca basin se spain during the messinian abstract the lorca basin southeastern spain is part of a chain of small marginal neogene basins located in the structurally active betic area the upper miocene messinian sequence is composed of a thick diatomite bearing series tripoli unit overlain by the main evaporites analogous to the classical succession that records the main events during the salinity crisis in the mediterranean region the shallow restricted conditions of this region amplified the sedimentary responses to local and global forcings an integrated approach using sedimentology micropalaeontology stable isotope geochemistry and organic geochemistry has been applied to the tortonian messinian succession of the lorca basin in order to obtain a continuous record of the environmental changes the sediments record two major events which affected the whole mediterranean 1 high levels of productivity that led to the formation of the diatomite bearing deposits in the early messinian tripoli and 2 the messinian salinity crisis with its two major stages represented by the halite and gypsum units both mainly precipitated from marine derived brines the rapid reflooding of the mediterranean by normal marine waters at the base of the pliocene did not reach the lorca basin nor other basins of this part of the betic area instead continental sediments were deposited as a consequence of the regional uplift of se iberia which started close to the messinian pliocene boundary the most prominent feature of this basin concerns the record of its restriction by the time of the deposition of the tripoli unit which led to intercalations of precursor evaporitic layers consisting of ca sulphate deposited in sub aqueous and sabkha conditions interbedded with diatomites this alternation of evaporites and diatomites proves that the lorca basin was periodically restricted and reflooded by marine waters a possible cause for this being relative sea level fluctuations in the mediterranean this strengthens evidence of diachronism that suggests that the onset of the first messinian evaporitic deposition was not synchronous but was dependent on bathymetry and local tectonics high productivity during the early messinian in this basin is demonstrated by the thick deposits of diatomites however stagnation episodes may have occurred during this interval as suggested by the preservation of high amounts of organic matter organic rich shales and the extent of bacterial sulphate reduction which apparently occurred during early diagenesis the formation of organo sulphur compounds replacement of sulphates by carbonates and the high levels of elemental sulphur are by products of diagenetic processes occurring in a restricted hypersaline environment

characterization of organic matter from a restricted evaporative sedimentary environment late miocene of lorca basin southeastern spain the lorca basin located within the tectonically evolving betic cordillera of southeastern spain developed as a rapidly subsiding basin in an open marine setting during much of the late miocene the basin underwent sporadic phases of circulatory restriction with marked production and preservation of organic matter culminating in evaporative sedimentation latest miocene an organic geochemical study using biomarker analyses clarifies the degree of mixing between inflowing water sources both marine and nonmarine gives clues to the complex and variable circulation within the water and helps determine the extent of basinal hypersalinity as the water in this basin evolved toward evaporative conditions a number of organic rich depositional phases 25 wt toc he e termed pre evaporative took place during the early parts of these phases the upper water is interpreted as nutrient rich and comparatively normal and the bottom water as anoxic this was followed by rising salinities and short phases of evaporite formation such a sedimentary history may serve as a model for understanding of evaporite related source rocks and related hydrocarbons in other areas of the world

facies successions in the pre evaporitic late miocene of the lorca basin se spain abstract pre evaporitic uppermost tortonian to messinian carbonate siliciclastic deposits have been studied in the western part of the lorca basin individual lithofacies facies associations as well as facies successions and stratal architecture indicate a gravel rich fluvial dominated gilbert type delta environment during periods of decreasing terrigenous supply carbonate sedimentation predominated including formation of patch reefs and fringing reefs the observed progradational stacking pattern of facies successions is attributed to a 3rd order eustatic highstand that pre dates the messinian lowstand evaporites of the well known salinity crisis five facies successions have been recognized each succession is composed of three facies associations that are mixed carbonate siliciclastic mcs carbonate dominated cd and siliciclastic dominated sd they show retrogradation aggradation progradation architecture and represent 4th order transgressive regressive cycles the five successions can be correlated through the whole basin and are interpreted as a useful tool for basinwide sequence stratigraphic correlation if in addition other recently published data from se spain are considered it may turn out that future correlations between different neogene basins at this cycle scale 4th order will be possible higher frequency successions or cycles at a bed or bedset scale 5th or higher order are noticeable but are clearly related to local depositional processes facies dynamics they do not have any significance for a basinwide sequence stratigraphic correlation

silver abyssal plain carbonate turbidite flow characteristics approximately 20000 years ago the main part of a large turbidity current was channeled between the caicos outer ridge and the bahama escarpment until it spread fanwise across the central silver abyssal plain floor unusual grain size and compositional changes in the turbidite appear to have been produced by surges superimposed on the main flow sharp decreases in the thickness and grain size of the turbidite on the slopes of the caicos outer ridge indicate that the depth of the current was approximately 35 m as deposition began at the first abyssal plain core site estimates based on the fall velocity of the fastest settling particles deposited from suspension suggest that the flow velocity was approximately 3 m sec as the current began to move across the abyssal plain floor the transition from deposition of turbidite sediments with graded bedding to deposition of parallel laminated sediments appears to have occurred at similar or slightly lower flow velocities than those predicted for the transition fr

microtremor analyses at teide volcano canary islands spain assessment of natural frequencies of vibration using time dependent horizontal to vertical spectral ratios we use time dependent horizontal to vertical spectral ratios hvsr of microtremors to determine the dominant frequencies of vibration of the geological structures beneath several recording sites in the vicinity of teide volcano canary islands spain in the microtremors the time dependent hvsrs ratiograms are a useful tool to discriminate between the presence of real dominant frequencies linked to resonances of the subsurface structure and the spurious appearance of peaks due to local transients we verified that the results are repeatable in the sense that microtremors recorded at the same site but at different times yield a very similar hvsr function two types of results are found 1 sites where there is no resonance of the propagating microtremors and therefore no value of a dominant frequency can be assessed and 2 sites where a stationary peak in the hvsr is found and a dominant frequency related to resonance of the shallow structure can be estimated these resonant frequencies show substantial spatial variations even for nearby sites which reflects the complexity of the shallow velocity structure in the las canadas area large dominant frequencies occur near the caldera walls and also at a few locations that coincide with the intersections of the inferred rims of the three calderas forming las canadas small dominant frequencies also occur near the caldera rim and may be due to discontinuities in the caldera wall and or to local velocity anomalies intermediate frequencies are mostly found in the eastern part of the caldera where a tentative profile of the basement depth has been obtained intermediate frequencies have also been measured south of ucanca and south of montana blanca in view of the present results we conclude that the use of ratiograms constitutes an improvement of the hvsr method and provides an appropriate tool to investigate the shallow velocity structure of a volcanic region

lithofacies diagenetic spectra and sedimentary cycles of messinian late miocene evaporites in se spain abstract messinian evaporites have been deposited within a number of connected basins that formed the so called betic strait in se spain during the late miocene pre syn and postevaporitic sedimentary successions may well be compared with other strata of the same age surrounding the mediterranean sea there is no evidence for a cataract like connection of these basins with a strong unidirectional flow regime before and during the formation of messinian evaporites as previously suggested the most frequently occurring gypsum lithofacies presumably related to shallow water depositional environments are crystalline selenitic gypsum grass like gypsum laminated gypsum and cross bedded gypsarenite only few real sabkha type chicken wire alabastrine gypsum have been identified evenly laminated gypsum together with graded gypsarenites turbidites gypsrudites debrites and slumps is restricted to basins or parts of basins with considerable paleoslopes evidence for diagenetic overprinting is abundant in all outcrop areas studied this includes the formation of giant gypsum twin crystals super cones and alabastrine nodular gypsum the formation of messinian evaporites in se spain is thought to be controlled by a superimposed third order sea level lowstand smaller sedimentary units fall well into the range of fourth to sixth order cyclic and rhythmic successions they are clearly related to basin dynamics or to autogenetic processes of the local facies zone facies dynamics none of the smaller scale cycles fourth and higher order as observed in outcrops are related to high frequency eustasy

selective gravel entrainment and the empirical evaluation of flow competence the concept of flow competence is generally employed to evaluate velocities and bed stresses of river floods from the sizes of the largest sediment particles transported for the most part this evaluation has been empirical combining data from a number of separate flood events in different river systems those data are re examined and compared with empirical equations for the selective entrainment of gravel from deposits of mixed sizes it is found that the competence relationships trend counter to those obtained for selective entrainment indicating that the competence evaluations are affected by varying degrees of selective size entrainment individual data sets which have been employed to establish the flow competence relationships either show no trend on their own or yield a trend which runs counter to the competence equation instead being more compatible with the selective entrainment relationships in most instances the empirical competence equations greatly overestimate the hydraulics of flood flows and it is suggested that the better established selective entrainment equations be used for competence evaluations as well empirical equations are available for this purpose relating the dimensionless shields entrainment function or the bed shear stress to the diameter of the largest grain moved and to the median diameter of the deposit as a whole

simulation based comparison of four site response estimation techniques abstract recent earthquakes have triggered renewed interest to understand better earthquake site response most of the studies comparing various techniques for estimating site response were based on real data from earthquakes nuclear blasts and seismic noise a theoretical approach using synthetic data generated with the pseudospectral method is used to compare four site response estimation techniques the limits of applicability of each method were determined by modeling microtremors and incoming sv waves with different incidence angles and analyzing the site amplifications the first two techniques investigated consist of dividing the spectrum of the horizontal motion at a site by that of a reference site using either incident s waves or microtremors the latter was unable to reveal either the resonant frequencies or peak amplitudes in any cases the two other techniques are based on the horizontal to vertical h v spectral ratio using s waves or microtremors these techniques were found to reveal at least the fundamental resonant frequency and amplitude former method only within 10 error in the case of simple geology flat layers however the results show that these techniques are unable to take into account 2d effects such as focusing effects and basin edge effects and yield unreliable or incorrect results in such cases

marine to non marine sedimentation in the upper miocene evaporites of the eastern betics se spain sedimentological and geochemical evidence abstract several neogene basins in the eastern betics contain a record of thick upper miocene evaporites the inner basins those located distal to the mediterranean coast include evaporite units ranging from the late tortonian to the early messinian whereas the marginal basins those located in the vicinity of the mediterranean coast include evaporite units corresponding to the late messinian that are linked to the salinity crisis the sedimentological and geochemical comparison of the evaporites in the inner and marginal basins enable us to show their differences in the modes of deposition under local structural controls and differentiated palaeogeography in the inner basins of the murcia alicante region a number of evaporite units have been differentiated whose gypsum lithofacies have 1 variable strontium contents with mean values primary gypsum between 1121 and 2380 ppm 2 isotopic compositions of sulphur 34 s ranging from those characteristic of the tertiary marine water 20 3 to 25 5 to those characteristic of the triassic sulphates 8 0 to 16 0 the latter suggesting recycling of the sulphate anion in meteoric waters intermediate values 17 4 to 19 6 are attributed to mixed mother brines and 3 strontium ratios 87 sr 86 sr comprised between 0 70804 and 0 70888 these values range from those of the tertiary marine water to those exceeding the triassic sulphates suggesting additional continental contributions from country rocks and hydrothermal solutions the comparison between the sulphur and strontium isotopic compositions of the sulphates together with the study of the biota present in the marls associated with the gypsum allows us to distinguish between marine continental and mixed units in the marginal basins of the eastern betics where single evaporite units characterized by selenitic gypsum prevail 1 the strontium contents are more homogeneous with mean values primary gypsum between 493 and 625 ppm 2 the isotopic compositions of oxygen 18 o and sulphur 34 s are comprised between 12 2 and 14 8 and between 22 0 and 23 5 respectively and 3 the strontium ratios 87 sr 86 sr vary from 0 70890 to 0 70895 all these isotopic values reveal a marine origin and the lack of contribution of significant continental water during the late messinian evaporite deposition in the betic strait these characteristics are similar to those of the lower evaporite

numerical modelling of tsunamis generated by hypothetical landslides in the strait of georgia british columbia a modified and corrected version of the viscous slide model of jiang and leblond 1994 is used to assess the tsunami risk associated with hypothetical underwater slope failures in two coastal areas of british columbia having potentially unstable sediment deposits a malaspina strait separating the mainland coast and texada island in the central strait of georgia and b roberts bank on the foreslope of the fraser river delta in the southern strait of georgia the intent of this study is to demonstrate the capability of the model for tsunami risk assessment and to improve upon previous studies of tsunami risk in the region based on reasonable submarine landslide scenarios the potential risk from tsunamis associated with slide failures has been examined but the likelihood of failure events themselves was not considered for the malaspina strait scenarios simulated tsunamis are generated by failure of a lobe of perched sediment situ ated on the slope of eastern texada island failure as a flow slide of the estimated 1 250 000 m3 of sediment generates wave troughs reaching 4 9 m and trough to crest heights of 6 to 8 m along the coast of texada island at cape cockburn on the opposite side of the strait wave heights of 1 5 to 2 0 m are produced for roberts bank simulated waves are examined for two separate failure scenarios the larger slide case 1 involves the failure of a sediment lobe with lateral dimensions of 7 3 km2 and volume of 0 75 km3 while the smaller slide case 2 fails a sediment lobe with dimensions of 4 2 6 km2 and volume of 0 23 km3 computations were made both for high 3 m and low 3 m tide conditions for both failure volumes maximum wave amplitudes up to 18 m for case 1 and 8 m for case 2 occur on the coasts of mayne and galiano islands opposite the source area wave amplitudes are much smaller 1 to 4 m on the mainl and coast because of the reflection of the initial waves from roberts bank additional numerical experiments were conducted for both regions to estimate the sensitivity of the computed tsunami wave heights to input parameters such as slide viscosity bulk density and slide position

comparative study of major element geochemistry of gypsum ghost limestones and selenite lithofacies from the miocene of northern carpathian foredeep implication to the model of massive replacement of solid sulphates by calcium carbonates abstract gypsum ghost limestones and selenite gypsum facies commonly believed to be as lithological equivalents caused by massive replacement of selenites by limestones occur in the same miocene evaporitic series of the northern carpathian foredeep southern poland and differ considerably with regard to their sedimentological features and major element compositions the differences dealing with variation of contents ranges means patterns of distribution correlations and interelement ratios of the major elements clearly do not indicate any geochemical similarities between the gypsum ghost limestones and the selenite gypsum lithofacies mass balance chemistry shows a deficit of calcium and sulphur contents in the limestones compared to the composition of the selenitic gypsum and implies that the gypsum ghost limestones system was open to mass transfer and cannot be related to simple and regionally extended replacement of solid sulphate rocks by limestones plus native sulphur the major element geochemistry of the gypsum ghost limestones and the selenites represent their original compositions which in turn reflect original depositional settings rather than pore water chemistry during replacive diagenesis both the lithological units developed in co eval depositional domains carbonate and sulphate constituting an evaporitic system but corresponding to different sedimentary settings of the system the gypsum ghost limestones reflect the unique situation of simultaneous formation of carbonate and selenites in a sedimentary transitional milieu between the carbonate and gypsum domains where bottom calcium carbonate deposition was alternating with the growth of selenite crystals the results are clearly inconsistent with the epigenetic model of formation of the polish sulphur deposits which assumes massive and regionally extended replacement of sulphate deposits by carbonates

application of biological markers in the assessment of paleoenvironments of chinese non marine sediments abstract in this study we employ molecular organic geochemical data for 22 representative sediment samples from chinese non marine sedimentary basins in an attempt to characterize and assess the non marine depositonal paleoenvironments the samples investigated include oilshale shale mudstone and sodium sulphate rich sediments ranging in age from cretaceous to tertiary it is evidenced by geological and geochemical data that those sediments studied originate from lacustrine environments ranging from freshwater brackish fresh water to hypersaline the aliphatic fractions of the sediment extracts were analyzed by gc and gc ms and relative abundance of compounds and compound classes of normal acyclic and cyclic alkanes were measured from mass chromatograms the results reveal significant differences in the chemical features of the various sample groups which enable them to be characterized and identified in terms of source and or environment related parameters the diagnostic parameters that allow this assessment are the relative abundances of n alkanes acyclic isoprenoid alkanes and 4 methyl steranes hopane sterane ratio gammacerane and homohopane indexes etc in this study data interpretation was also assisted by pattern recognition through principal component analysis the results show that the sample groups of different environmental origin could be unambiguously distinguished on scores plot

seafloor morphology and sedimentary processes knight inlet british columbia seafloor morphology and sediment distribution in knight inlet are discussed as they relate to turbidity currents and associated gravity resedimentation phenomena the study is based on acoustic imagery high resolution seismic profiling echosounding sediment sampling and seabed monitoring seafloor morphology shows that while the upper part of knight inlet resembles other british columbia fjords it differs in that a great many channels emanate from fjord head deltas to coalesce ultimately into a few and finally one channel farther down inlet this is in contrast to the adjacent fjord buteinlet where only one channel emerges opposite each of the two fjord head rivers joining a short distance downslope to form a single incised channel in both fjords sand transporting turbidity currents are responsible for creating these extensive channel systems in knight inlet these channels are up to 40 m deep and up to 300 m wide continuing 41 km down fjord the upper fjord can be divided into four morphological zones which reflect not only the seabed character but also the flow characteristics of turbidity currents using a variety of theoretical techniques based on channel morphology coarsest grain sizes and bedform characteristics turbidity current dynamics were modelled for the seabed morphological zones turbidity current densities are estimated to range from about 1 024 g cm 3 in distal areas to a maximum of 1 048 g cm 3 in the proximal region of greatest erosion and highest velocities average flow velocities are as high as 7 00 m s 1 diminishing to less than 0 50 m s 1 at the terminus of the channel based on estimates of velocity and turbidity current density sediment fluxes were computed for various channel segments changes in flux rates clearly delineated areas of erosion and deposition and were well correlated with the morphological character of the channel and nearby seafloor estimates of turbidity current velocity based on bedform characteristics tend to be lower than those calculated from coarsest grain sizes and channel morphology preserved bedforms may reflect later waning phases of turbidity current flow whereas channel wall heights and coarsest grain size reflect maximum velocities a close relationship was found between turbidity current events as monitored by turbidity event detectors and river discharge peaks on the klinaklini river at the head of the inlet fluvial suspended matter concentrations associated with such floods are not believed to be sufficient to produce turbidity currents directly rather it is postulated that river mouth bars which accumulate during periods of low river flow are destroyed by floods and the coarse sediments along with flood related bedload are swept onto the steep delta front where they accumulate as temporary unstable sediment masses failing occasionally or continue directly downslope as debris flows turbidity currents

dynamic sedimentary environments of an arctic glacier fed river estuary adventfjorden svalbard i flux deposition and sediment dynamics abstract the spatial patterns of the transport settling and deposition of sediments were studied in a small arctic glacier fed river estuary adventfjorden west spitsbergen svalbard salinity and temperature suspended solids concentration and particle fluxes in the water column were measured at seven stations situated on the tidal flat formed at the river mouth the delta slope and along the fjord axis down to the fjord mouth turbidity currents were measured in situ using a current meter combined with a turbidity meter the sediments collected with a niemisto gravity corer were x rayed and analyzed for granulometric composition the results of the major sampling campaign undertaken in july 2002 were supplemented with winter hydrological data from january 1996 since the river is frozen in winter no fresh water or fluvial sediment supply is observed in the fjord water column a hypopycnal plume of brackish water 1 5 m thick extends in summer as far as 0 8 km from the river mouth the highest concentration 826 mg l 1 and vertical flux over 1000 g m 2 day 1 of suspended solids were noted at the edge of the tidal flat and over the upper slope of the delta both concentrations and the solid particle flux decreased as distance from the river mouth increased local peaks of turbidity in the intermediate and deep water layers in the central fjord indicated the presence of hyperpycnal plumes tidal flat sediments are rhythmically laminated by the tidally controlled resuspension redeposition cycles and occasionally eroded by catastrophic events such as intense storms or winter ice cover scouring the steep inclination of the bottom of the slope 15 19 promotes the gravity driven processes of sediment transport debris flows frequent resuspension and redeposition events can be traced on x radiographs and in the granulometric composition of the sediment cores collected on the slope turbidity currents are observed throughout the fjord although their intensity and frequency of occurrence change as distance from the river mouth increases the near bottom hyperpycnal flows transport the finest sediment over the slope and into the low energy environment of the central basin of adventfjorden the current study shows that the patterns of sediment storage and sedimentary dynamics in a glacier fed river estuary are driven by gravity flows and turbidity currents rather than by the patterns of the vertical sedimentation of suspensions in the water column

geologic evolution of the betic cordilleras in the western mediterranean miocene to the present abstract the betic cordilleras were formed during the eo meso and neo alpine evolution of the western mediterranean area during the neo alpine stage the northward subduction of the african plate took place and the algerian provencal basin opened with the creation of oceanic floor associated space problems produced the expulsion and extensive stretching of the internal zones to the west which in turn disrupted and deformed the external zones of the betic and rif cordilleras these occurrences essentially took place in the burdigalian and continued with diminished intensity into the middle miocene following the suturing of the transcurrent contact between the internal and external zones important n60 90 e and nw se faults occurred the betic cordilleras are characterized as having been deformed by regional horizontal shortening compression oriented wnw ese or nw se which gradually rotated to the nnw sse in the late miocene when its most important intramontane neogene basins were formed the alboran basin with a thinned continental crust was formed as a western prolongation of the opening of the algerian provencal basin with its basic features already apparent in the burdigalian the volcanism present in the southeast of the betic cordilleras and in northeast morocco crossing the alboran basin is mainly late miocene in age it is linked to fracturing and exhibits chemistry related to the different thickness of the crust

marine isotope stage 6 canyon and spillover deposits of the bryant and eastern canyon systems northwest gulf of mexico importance of fine grained turbidites on a delta fed prograding slope abstract a large set of long sediment cores and high resolution seismic reflection data were used to study the sedimentology of the delta fed prograding slope of the northwest gulf of mexico during marine isotope stage mis 6 125 180 ka bryant and eastern canyon systems were the main pathways during this period through which mississippi river sediment was delivered down the continental slope two mis 6 sedimentary environments have been defined on the slope of the northwest gulf of mexico intracanyon and overbank environments the erosional action of turbidity currents in bryant and eastern canyons was focused mainly on the thalweg whereas on the rest of the canyon floors the flows acquired a mainly depositional character resulting in the formation of inner levees and terraces mis 6 deposits in overbank environments consist entirely of thick 50 m widespread 15 20 km and continuous successions of mud turbidites which indicate that spillover processes were dominant along bryant and eastern canyons the total absence of bioturbation structures and hemipelagic sediments in mis 6 overbank deposits indicate high sedimentation rates exceeding 200 600 cm ky the majority of the overbank deposits are normally graded indicating that most of the turbidity currents during mis 6 resulted from sediment failures on the outer shelf and upper continental slope sedimentological observations indicate that a complete mud turbidite sequence t0 8 sequence in the nomenclature of stow and shanmugam 1980 results from a waning low density turbidity current consisting of four successive flow regime stages 1 an initial erosional stage 30 cm s 2 deposition of the coarsest noncohesive fraction silt of the suspended sediment in the flows 30 100 cm s 3 cyclic deposition of cohesive mud and noncohesive silt laminae due to fluctuations in the shear stress in the boundary layer of the flow 12 30 cm s and 4 deposition from a silt depleted and slowly moving 15 cm s sediment cloud

source rock potential of evaporitic environment examination of modern saline lakes solar evaporation ponds and lagoons shows that the evaporitic environment can be very productive of organic matter few species survive in the brines but those that do commonly exist in great profusion in a marine evaporitic embayment the flow of surface currents is persistently toward regions of highest salinity so that there is a continual supply and concentration of nutrients prolific growth of phytoplankton may be similar to that in areas of upwelling in modern oceans only carbonates precipitate in the mesosaline part 4 to 12 salinity of such an evaporitic environment and no great dilution of organic matter by clastic or biogenic sediments occurs because stratification of brine may occur and reducing conditions may be a sociated with the bottom waters much of the organic matter produced can be preserved upon maturation the result may be a rich carbonate source rock frequently unrecognized in the geologic column in the middle east mesosaline conditions are known to have occurred many times from the triassic to cretaceous and may be responsible for the vast reserves of petroleum in the area evaporitic conditions may also have played a part in the petroleum productivity of many other areas including the michigan and paradox basins

basin sedimentation and the growth of prograding deltas a theoretical model is developed for the infilling of a basin by the progradation of a delta the model simulates four mechanisms for the transfer of sediment from the land to the sea 1 bed load dumping along the delta front 2 hemipelagic sedimentation under the seaward flowing river plume 3 proximal slope bypassing by turbidity currents and 4 the combined effects of both short term wave and tidal action and long term creep and small slides downslope diffusion of the accreting sediment mass the general model is of relatively low precision useful for predicting basin infilling on time scales greater than a few hundred years the river plume portion of the model can predict sedimentation on time scales of less than a year and is designed to reflect the dynamics of a free two dimensional buoyant jet that transports a composite size population of suspended particles the general model allows the prediction of lithologies changing with time and space the model has been used to simulate infilling processes for knight and bute inlets two grabenlike fjord basins along the coast of british columbia model simulations of delta progradation over the last 10 000 years favorably predicted the modern seafloor bathymetry and sediment accumulation rates to within a factor of 2 of measured 210pb 137cs and sediment trap rates

ages and stratigraphical architecture of late miocene deposits in the lorca basin betics se spain new insights for the salinity crisis in marginal basins unlike most neogene basins of the betic cordillera where the salinity crisis is dated to the messinian a contradictory tortonian dating was proposed for evaporites of the lorca basin as a consequence complex structural models have been proposed in the literature to explain this discrepancy in the timing of evaporites in order to integrate the lorca basin into the geological context of the western mediterranean domain during the late miocene new sedimentological and stratigraphical studies coupled with new dating were performed which allow us to propose a messinian age for both diatomite bearing deposits and evaporites of the lorca basin these new ages challenge the idea of a tortonian salinity crisis in the lorca basin three main events of base level drop were evidenced during the messinian each event is correlated with successive steps of basin restriction shallow salina evaporites were deposited after a base level fall during the messinian before a final base level drop which led to the entire exposure of the basin this last exposure is interpreted as coeval with the deposition of first evaporites and halite in the deep mediterranean basins the reflooding which allowed the deposition of brackish deposits and a short lived marine incursion occurred at the end of the messinian base level drops occurred during eustatic falls amplified by the gradual uplift of the betic cordillera the exhumation of the tercia ridge along the strike slip alhama de murcia fault system during the messinian probably favoured the gradual restriction of the basin a discussion on correlations of main unconformities between several neogene basins of the betics is proposed suggesting a similar structural evolution at the regional scale

organic geochemical studies of a messinian evaporitic basin northern apennines italy ii isoprenoid and n alkyl thiophenes and thiolanes abstract series of n alkyl and isoprenoid thiophenes and thiolanes most of which have not been previously reported have been identified in an extract from a messinian upper miocene marl layer deposited under hypersaline euxinic conditions the identifications were based on mass spectra and chromatographic data of synthesized reference compounds and on comparison of mass spectra relative retention times and response on the fpd their specific structures and their distribution patterns show similarities with those of the alkanes inorganic sulphur is therefore considered to be incorporated into specific lipid moieties from archae bacterial and or algal input during diagenesis a biosynthetic origin of these compounds is also possible however the organic sulphur compounds encountered are thought to be indicators of a hypersaline depositional environment

observations of high frequency scattered waves using dense arrays at teide volcano abstract a study of the seismic coda of seven small earthquakes recorded on the teide volcano canary islands spain was carried out using a temporary small aperture 12 station seismic array the purpose was to measure backazimuth apparent velocity and the type of waves that compose the coda in the frequency range 4 to 6 hz we used the zero lag cross correlation zlc method to obtain the components of the wave vector and three component analysis techniques based on the covariance matrix of the signal in the time domain to investigate the polarization properties of the signals the results show that a great part of the coda signals in the analyzed frequency range are almost uncorrelated while a low number of isolated correlated arrivals show an apparent slowness between 2 10 3 and 2 5 10 4 sec m and an almost random distribution of backazimuths the correlated arrivals have been interpreted as generated by strong scatterers probably related to the presence in the study area of surface topography irregularities the volcanic cone and the caldera rim the wave type varies from pure s type waves to mixed surface waves with some rayleigh components