identification of the kuroshio extension its bifurcation and northern branch from altimetry and hydrographic data during october 1992 august 1999 spatial and temporal variability a methodology is proposed using altimter derived upper layer thickness and baroclinic transport to identify the kuroshio extension the bifurcation point and the northern branch by combining topex poseidon altimeter and climatological data within a two layer reduced gravity model results obtained from the japanese coast to 175 w show that the location of the bifurcation point presents interannual variability that is related with upstream conditions the longitude of the bifurcation point ranged from 147 to 160 e estimates of baroclinic transport at the kuroshio extension and its northern branch decrease steadily to the east trough the region of study from 35 to 11 and from 10 to 3 sv respectively

a model for fibrous illite nucleation and growth in sandstones we have developed a model for the formation of fibrous illite in sandstones where kaolinite is a primary reactant and potassium is derived from in situ k feldspar grain dissolution or imported into the model reference frame illite fiber nucleation and growth are modeled using arrhenius expressions that consider saturation state in addition to temperature and time nucleation occurs on pore walls and muscovite and detrital illite may be defined as energetically favorable substrates the model is integrated with other touchstone models to account for the influence of other diagenetic processes on surface area and reactant volumes and to provide input for permeability simulations we evaluated the illite model performance on two data sets 1 jurassic quartzose samples from offshore mid norway with maximum temperatures ranging from 108 to 173c 226 to 343f and 2 miocene lithic samples from offshore southeast asia that have maximum temperatures ranging from 157 to 182c 315 to 360f the model matches measured abundances of illite kaolinite and k feldspar in both data sets using identical kinetic parameters predicted k ar ages are consistent with available data given uncertainties associated with detrital contaminants although no illite particle size data are available from the analyzed samples modeled crystallite thicknesses from the norway data set are comparable to published measurements of 0 004 to 0 012 m from north sea samples with similar temperature histories

horizontal lamination and the sequence of bed phases and stratification under upper flow regime conditions two forms of horizontal laminae have been produced under upper flow regime conditions in a flume by deposition on a plane bed and on low in phase waves upper plane bed laminae consist of approximately equal numbers of fining upward fu and coarsening upward cu textural laminae heavy minerals when present are typically within or form cu laminae in horizontal laminae formed under low in phase waves fu laminae may predominate and are significantly thicker than cu laminae heavy minerals are associated with the tops of some fu laminae and are absent from cu laminae deposits aggraded on plane beds and low in phase waves both display low angle 13 14 upstream grain imbrication upper plane bed horizontal laminae are attributed to the effects of the burst sweep cycle on local bedload transport bursts form fu laminae and sweeps form cu laminae some fu laminae in in phase wave deposits are thought to form with downstream migration of bed waves on which sand size decreases from trough to crest heavy minerals are concentrated in the tops of these fu laminae due to their enrichment on the crests of the migrating bed waves other fu and cu laminae in in phase wave deposits probably formed by the action of bursts and sweeps as on upper plane beds a sequence of bed phases and stratification formed under upper flow regime conditions is described based on the observations here combined with descriptions from the literature with increasing flow strength the gradual sequence of bed phases is 1 plane bed 2 low relief downstream migrating inphase waves increasing in amplitude and wavelength with increasing flow strength 3 stationary in phase waves 4 upstream migrating including breaking wave antidunes the sequence of stratification formed under these bed phases is 1 upper plane bed horizontal lamination 2 in phase wave horizontal lamination to in phase wave foreset cross laminae 3 in phase wave drape laminae 4 antidune backset cross laminae

sedimentology of coarse clastic beach ridge deposits essex southeast england abstract the distinction of cheniers from other types of beach ridge can often be problematic the stratigraphy sedimentology and geomorphological development of sand and gravel rich beach ridges at three sites on the northern essex coast england were determined using ground penetrating radar gpr ground truthing trenches and auger holes and historical aerial photograph analysis the 900 mhz gpr system used achieved a maximum vertical resolution between 0 02 and 0 06 m there was good correspondence between the radar stratigraphy obtained from time migrated radar reflection profiles and the nature and form of bounding surfaces sets of lamination beds and bedsets observed in trenches data for one of the study sites colne point illustrate a complex beach ridge stratigraphy and sequence of development that confirms they are not true cheniers instead the ridges form part of both retrogradational and progradational barrier spit sequences chenier designation at the other two study sites foulton hall and stone point is more straightforward as the beach ridges lie at the junction between actively eroding mudflat and saltmarsh however despite the distinction between the barrier spit beach ridges and the cheniers the same types of deposit are recognised in both indicating similar formative processes washover sheet deposits consist of low angle

the morphology and dynamics of low amplitude bedwaves upon upper stage plane beds and the preservation of planar laminae experimental studies of subcritical unidirectional flow over upper stage plane beds of medium grained sand reveal the ubiquitous presence of low amplitude bedwaves flow depth was 0 11 m mean flow velocities were 0 86 1 0 m s 1 shear velocities were 0 058 0 71 m s 1 and dimensionless shear stresses were 0 56 0 87 bedwaves are asymmetrical in profile and range from 0 75 to 11 mm in height mainly 2 6 mm from 0 7 to 1 3 m in wavelength and have mean celerities of 10 mm s 1 flow records suggest that the bedwaves are associated with accelerating flow over the bedwave crests and flow which decelerates and diverges laterally over the troughs high resolution bed profiling during aggradation of the bed combined with subsequent box coring illustrates that these bedwaves are responsible for the planar laminae characteristic of upper stage plane beds lamina preservation is dependent upon the mean aggradation rate and the sequence of bedwaves of different height crossing any point individual laminae are more readily preserved at higher aggradation rates where the possibility of reworking by later bedwaves is reduced laminae are recognized by small changes in grain size and commonly a fining upwards at the top of laminae which is generated by fine grained material infiltrating a lower lamina in the leeside of a bedwave

antidunes and traction carpet deposits in deep water channel sandstones cretaceous british columbia canada abstract sandstone beds intercalated with thick shale of the upper member of the haida formation albian turonian in the queen charlotte islands british columbia canada show thinly laminated graded bedding the sandstones generally are present as successions of more than a few tens of inversely to normally graded thin beds the beds at the base of each succession contain much coarser detritus than the beds at the top each succession of graded beds shows a lens shaped channel geometry wavy bed forms similar in shape to the hummock and swale topography that is thought to form hummocky cross stratification hcs characterize the uppermost part of the succession however grain fabric and spacing of the bed forms indicate that they are of antidune origin it is concluded that the successions of multiple laminated sandstone beds were produced by high density turbidity currents that were probably associated with a gravity transformation in which a successive freezing of traction carpets took place lack of shale in the succession together with the common presence of antidunes suggest that each succession was the product of one sedimentation event without decrease in stream power

oceanographic aspects of the emperor seamounts region effects of the emperor seamount chain on the thermohaline structure and baroclinic flow are investigated on the basis of historical hydrographi data the amplitudes of dynamic height perturbations are 3 to 5 times larger west than east of the chain the intensity of the thermal fronts is stronger west than east of the seamounts near the crest of the southern seamounts strong east west thermohaline fronts and a strong northward baroclinic flow are observed the kuroshio extension west of the seamount chain is a well defined meandering current the axis of which generally lies between 33 and 36 n the available data indicate that the kuroshio extension turns northward and then flows eastward through the gaps of the seamount chain east of the seamounts the kuroshio extension widens threefold and appears to be poorly defined

hoanib river flood deposits of namib desert interdunes asanalogues for thin permeability barrier mudstone layers inaeolianite reservoirs abstract the ephemeral braided hoanib river of nw namibia ows for a few days ayear and only high discharges enable the river to pass through interdunaldepressions within the northern namib desert dune eld to the atlantic thedune eld comprises mainly large transverse dunes resulting frompredominant ssw winds river ood deposits between aeolian dunes areanalogous to mudstone layers conformably interbedded with ancientaeolianite dune foresets deep oods pond laterally to considerable depths metres to 10 m in adjacent interdunes depositing mud layers 1 50 cm toconsiderable heights on avalanche and stoss faces of bounding dunes fairlypassive ooding only disturbs aeolian strati cation minimally floodwaterclay in ltrates and settles as an impermeable seal with a ood pond on top perched above regional groundwater flood ponds evaporate slowly for longperiods 3 years early emergence desiccates higher parts of a mud layer subsequent oods can re ll a predecessor pond bene ting from the existingimpervious seal potential preservation of such mud layers is lower on thestoss face but high on the avalanche face after burial by subsequent dunereactivation and migration the leeward right hoanib bank a dune stoss face is river and wind eroded to exhume fossil interdune pond mud layers of anearlier hoanib channel the highly inclined layers are interbedded with duneavalanche foresets and represent the edges of two successive fossil pondsexposed in plan ancient ood pond mudstones occur in the permian triassichydrocarbon reservoir the sherwood sandstone group of the cheshire basin kinnerton formation and irish sea basin and were previously usederroneously to argue against the aeolian origin of cross bed sets hoanibstudies show that primary river interaction with a dune eld might preserveonly localized erosional omission surfaces in ancient aeolianites with littlesandy barform preservation prone to aeolian reworking around the main uvial channel locus however ood pond mudstone layers should form apredictable halo within which uid permeability will decrease keywords aeolian dunes aeolianite reservoir ash ood interdune namibdesert namibia permeability introductionhigh discharge oods of the hoanib river occa sionally break through the skeleton coast dune eld which forms part of the extensive namibdesert that parallels the western margin of thesouthern african subcontinent this arid regionis 140 km wide and over 2000 km long fromsouth western angola to the northern capeprovince south africa the northern namib dune eld termed the skeleton coast dune eld bywilson 1973 lancaster 1982 and ward sedimentology 2002 49 719 736

quantifying lake athabasca canada water level during the little ice age highstand from palaeolimnological and geophysical analyses of a transgressive barrier beach complex we combine multiproxy palaeolimnological and geophysical analyses of a barrier beach complex to estimate the water level of a sustained lake athabasca canada highstand during the little ice age lia 1600 1900 ce palaeolimnological analyses on sediment cores from the lagoon behind the barrier indicate high water levels during the lia controlled by subsurface hydrological connection with lake athabasca key features in the lia stratigraphic interval are sand laminations deposited by overwash events and low c n ratios reflecting deposition of predominantly aquatic organic matter ground penetrating radar profiles of the barrier reveal a depositional transgression sequence composed of waterlain landward dipping foreset beds and horizontal topset beds overlain by aeolian deposits stratigraphic relations suggest that the lia washover deposits in the lagoon formed as the barrier was actively translating landward and were generated by high water events on lake athabasca that overtopped the barrier thi

northward and southward migrations of frontal zones during the past 40 kyr in the kuroshio oyashio transition area 1 the variation of sea surface temperature sst in the kuroshio oyashio transition area and the okhotsk sea during the last 40 kyr was estimated using long chain unsaturated alkyl ketones alkenones the temperature difference between the present and the last glacial period was about 5 6 c in the kuroshio oyashio transition area slightly larger than the 4 c previously reported moreover alkenones were not detected before 18 kyr b p in or near the okhotsk sea perhaps because of nearly year round sea ice expansion which would have prevented the growth of alkenone producers or because alkenones were less well preserved in surface sediments during the glacial period the northward and southward migrations of frontal zones were evaluated using differences in alkenone temperatures between stations located in the vicinity of the subarctic front saf subarctic boundary sab and kuroshio bifurcation front kbf all three frontal zones migrated southward during the glacial period compared with their present positions and their relative positions were different between the holocene and glacial periods in particular the distance between the saf and the sab was reduced during the glacial period compared with at present the northward and southward migration of the frontal zones may relate to both mid to low atmospheric circulation and polar atmospheric circulation

structure and development of shell cheniers in essex southeast england investigated using high frequency ground penetrating radar abstract the stratigraphy and internal structure of contemporary shell cheniers on the southern essex coast england were investigated using a high frequency 900 mhz ground penetrating radar gpr system the cheniers lie on the seaward edge of laterally eroding saltmarshes at the junction with the tidal flats four main types of chenier are recognised each with a characteristic morphology and dynamic status migrated radar reflection profiles obtained from each of the chenier types achieved a sub decimetre vertical resolution ground truthing data demonstrate that the radar profiles accurately delineate the subsurface stratigraphy and sedimentary structure of the cheniers interpretation of the radar stratigraphy derived from the radar reflection profiles allows various deposits to be identified these have resulted from overwashing overtopping sedimentation across the whole of a seaward dipping beachface or berm ridge welding onto the upper beachface each chenier is characterised by a different spatial arrangement of these four basic depositional units the results from the gpr surveys support the hypothesis that each of the chenier types represents a distinct phase in the development of these contemporary coastal landforms however a simple model involving a linear progression through chenier types 1 4 with time appears inappropriate instead two main evolutionary pathways are proposed with the sequence of development being principally controlled by the nature of the cheniers longer term sediment budgets

neoproterozoic peritidal phosphorite from the sete lagoas formation brazil and the precambrian phosphorus cycle the neoproterozoic sete lagoas formation ca 610 ma of the sao francisco basin brazil is a succession of siltstone limestone and phosphorite phosphorite forms part of a previously unrecognized 150 to 200 m thick unconformity bounded depositional sequence lithofacies stacking patterns indicate that deposition was punctuated by higher order fluctuations in base level that produced aggradational parasequences these shallowing upward cycles record the progradation of phosphate rich intertidal flats over shallow subtidal deposits as accommodation filled the presence of mudcracks authigenic chert nodules lack of coarse terrigenous clastics and the abundance of silt with fine abraded quartz grains suggests accumulation along an arid coastline with significant aeolian input delivery of phosphorus adsorbed on aeolian fe oxyhydr oxide and clay is interpreted as having stimulated phosphogenesis in peritidal environments lithofacies associations indicate that windblown phosphorus promoted the establishment of cyanobacterial communities along the coast which produced photosynthetic oxygen and the suboxic conditions necessary for the precipitation of authigenic carbonate fluorapatite as in other precambrian phosphatic systems nearshore oxygen oases were a prerequisite for phosphorite accumulation because redox sensitive phosphogenic processes were pushed into the sediment to concentrate phosphorus in more distal anoxic environments phosphorite could not form because these biotic and abiotic processes were suspended in the water column which cycled phosphorus in sea water rather than at the sediment water interface such shallow water phosphorite is unlike larger younger neoproterozoic phanerozoic phosphatic deposits inferred to have formed in deeper upwelling related environments the increasing size of phosphatic deposits through the latest precambrian is interpreted as reflecting the progressive ventilation of the oceans during the neoproterozoic oxygenation event and resultant expansion of phosphogenic environments into distal settings the widespread cycling of bioavailable phosphorus at the sea floor not only produced the first true phosphorite giants but may have also been an important precondition for the evolution of multicellular animals

sequence response to syndepositional regional uplift insights from high resolution sequence stratigraphy of late early pleistocene strata periadriatic basin central italy abstract this paper deals with the depositional sequences that occur within the uppermost part of the plio pleistocene periadriatic basin fill in the southern marche region central italy the succession is an early pleistocene easterly dipping clastic wedge showing an overall shallowing trend from slope clays to shallow marine and non marine deposits comprising two major sequences namely qmb and qmc analysis has provided new insights into i the nature of sedimentary facies and facies associations occurring within the upper part of qmb and qmc ii the gradual contact within qmb between regressive littoral deposits rld and underlying deep marine blue clays iii the composite origin of the emilian surface which is a widespread erosional unconformity separating qmb from qmc iv the cyclothemic pattern of qmc composed of downstepping small scale depositional sequences v the role played by synsedimentary uplift on the stacking pattern of small scale sequences and their internal architecture up to three small scale depositional sequences have been recognised within qmc qmc1 qmc2 and qmc3 they are up to 50 m thick and defined by previously unrecorded lower rank regionally extensive surfaces facies organization indicates that as a rule in ascending stratigraphic order each small scale sequence may includes a distinctive basal unconformity surface that can be traced from incised valleys to associated interfluves an incised valley fill a transgressive surface of marine erosion a transgressive systems tract a highstand systems tract a regressive surface of marine erosion and an attached falling stage systems tract in proximal positions the small scale sequences are dominated by transgressive and highstand systems tracts with incised valley fills and falling stage systems tracts absent or volumetrically much less significant in relatively basinward locations where the regressive surfaces of marine erosion converge with the lower sequence boundary the falling stage systems tract may represent the entire depositional sequence high frequency sequences display a distinctive stacking pattern and form a tectonically induced forced regressive sequence set underlain by a composite tectonically enhanced regressive surface of marine erosion formed by the lateral connection of lower rank sequence boundaries

palaeoclimatic significance of co occurring wind and water induced sedimentary structures in the last interglacial coastal deposits from bermuda and the bahamas abstract the late pleistocene stratigraphic record from the bahamas and bermuda archipelagoes includes peculiar v shaped coastal ridges and wedges of seaward dipping planar beds showing fenestral porosity up to 40 m above present sea level judging from this porosity these landforms were till now interpreted as resulting from the action of giant waves during a period of climatic instability at the end of the last interglacial period the occurrence of widespread mm thick laminae of aeolian origin subcritically climbing translatent stratification throughout these deposits does not agree with this hypothesis it rather suggests that the v shaped ridges and seaward dipping beds represent fossil parabolic and climbing aeolian dunes respectively the occurrence of fenestrae high above the intertidal zone could be related to both wave splashing and rainfall action parabolic dunes are restricted to the nw bahamas they were probably formed during a time interval ca 500 5000 yr when regional climatic conditions were dryer than today and characterized by persistently blowing ne trade winds

living diatom assemblages from north pacific and bering sea surface waters during summer 1999 diatom assemblages collected during july august 1999 along an e w transect comprising sixty two north pacific and bering sea surface water samples were identified and enumerated absolute abundance profiles of centric and raphid pennate diatoms show that the former group dominates in shallow coastal waters and through island passes whilst the latter group though less numerous dominates the oceanic regions this pattern is interpreted as nutrient related with centric diatoms especially chaetoceros section hyalochaete minidiscus and thalassiosira spp preferring eutrophic and upwelling conditions and raphid pennate diatoms especially nitzschioid genera like fragilariopsis neodenticula and pseudo nitzschia preferring oligotrophic pelagic conditions the absolute abundances of the two sections of chaetoceros chaetoceros ex phaeoceros and hyalochaete and some species belonging to the thalassiosirales and bacillariaceae show distribution patterns that can be interpreted as preferences for shallow or oceanic waters subtropical or subarctic waters or ice related arctic conditions r 2005 elsevier ltd all rights reserved

micromorphological analysis of coastal sediments from willapa bay washington usa a technique for analysing inferred tsunami deposits tsunami deposits are provisionally distinguished in the field on the basis of anomalous sand horizons fining up and fining landward coupled with organic rich fragmented backwash sediments in this paper micromorphological features of a sediment sequence previously interpreted as being of tsunami origin are described these characteristics are shown to be consistent with the macro scale features used elsewhere but show additional details not seen in standard stratigraphies including possible evidence for individual waves possibly wave magnitude progression organic fragment alignment and intraclast microstructures although replication and more complete studies are needed this analysis confirms the identification of a tsunami in willapa bay in ca 1700 ad while demonstrating a widely applicable technique for confirming or refuting possible tsunami deposits

flow and water property structures between the bering sea and fiji in the summer of 1993 an overview is given of the top to bottom flow thermohaline oxygen and nutrient structures between the bering sea and the fiji islands based on high resolution field measurements along 179 e the zonal flow is dominated by a banded mesoscale structure reflecting the highly sheared structure and instabilities of the major ocean currents crossing the date line the major midlatitude currents are 100 200 km wide have maximum speeds of 40 cm s 1 and extend to 2000 m when measured by the 5 cm s 1 isotach el nino conditions in 1993 caused a merger of the north equatorial countercurrent with the equatorial undercurrent leading to a 600 km wide band of equatorial eastward flow 40 60 cm s 1 in the upper 300 m beneath a 400 km wide and 1 2 km deep westward jet 10 30 cm s 1 is found between 1500 and 3500 m the equatorial flow is predominately to the southeast and between 3500 and 5000 m it is toward the northwest consonant with banded shear flow and flow topography interactions the physical and chemical property distributions along 179 e are complicated reflecting the effects of differential property advection mixing and water mass transformation well defined property fronts occur in shear zones between currents of different origin the thermohaline oxygen and nutrient tongues associated with north and south pacific intermediate and deep waters have considerable internal structure indicative of mesoscale processes and contorted flow paths the abyssal flow near the date line indicates northward movement of lower circumpolar water to the hess rise whence it turns westward and north west of the emperor seamounts properties east of this seamount chain are very uniform the deep and abyssal waters of the isolated aleutian basin differ substantially from those in the adjacent pacific by being warmer 0 1 c less saline 0 01 poorer in oxygen 50 mol kg 1 and much richer in silicate 80 mol kg 1 an isolated basin within the wake necker ridge also shows some unusual bottom water characteristics below sill depth

the role of discharge variability in the formation and preservation of alluvial sediment bodies abstract extant planform based facies models for alluvial deposits are not fully fit for purpose because they over emphasise plan form whereas there is little in the alluvial rock record that is distinctive of any particular planform and because the planform of individual rivers vary in both time and space accordingly existing facies models have limited predictive capability in this paper we explore the role of inter annual peak discharge variability as a possible control on the character of the preserved alluvial record data from a suite of modern rivers for which long term gauging records are available and for which there are published descriptions of subsurface sedimentary architecture are analysed the selected rivers are categorized according to their variance in peak discharge or the coefficient of variation cvqp standard deviation of the annual peak flood discharge over the mean annual peak flood discharge this parameter ranges over the rivers studied between 0 18 and 1 22 allowing classification of rivers as having very low 0 90 annual peak discharge variance deposits of rivers with very low and low peak discharge variability are dominated by cross bedding on various scales and preserve macroform bedding structure allowing the interpretation of bar construction processes rivers with moderate values preserve mostly cross bedding but records of macroform processes are in places muted and considerably modified by reworking rivers with high and very high values of annual peak discharge variability show a wide range of bedding structures commonly including critical and supercritical flow structures abundant in situ trees and transported large woody debris and their deposits contain pedogenically modified mud partings and generally lack macroform structure such a facies assemblage is distinctively different from the conventional fluvial style recorded in published facies models but is widely developed both in modern and ancient alluvial deposits this high peak variance style is also distinctive of rivers that are undergoing contraction in discharge over time because of the gradual annexation of the channel belt by the establishment of woody vegetation we propose that discharge variability both inter annual peak variation and flashiness may be a more reliable basis for classifying the alluvial rock record than planform and we provide some examples of three classes of alluvial sediment bodies representing low intermediate and high very high discharge variability from the rock record that illustrate this point

architectural analysis of a volcaniclastic jokulhlaup deposit southern iceland sedimentary evidence for supercritical flow the 1918 eruption of the glacially capped katla volcano southern iceland generated a violent jokulhlaup or glacial outburst flood inundating a large area of m rdalssandur the proglacial outwash plain where it deposited ca 1 km3 of volcaniclastic sediment the character of the 1918 jokulhlaup is contentious having been variously categorized as a turbulent water flow a hyperconcentrated flow or as a debris flow based on localized outcrop analysis in this study outcrop based architectural analyses of the 1918 deposits reveal the presence of lenticular and tabular bedsets associated with deposition from quasi stationary antidunes and down current migrating antidunes and from regular based bedsets associated with transient chute and pool bedforms all of which are associated with turbulent transcritical to supercritical water flow conditions antidune wavelengths range from 24 to 96 m corresponding to flow velocities of 6 to 12 m sec 1 and average flow depths of 5 to 19 m this range of calculated flow velocities is in good agreement with estimates made from eyewitness accounts architectural analysis of the 1918 jokulhlaup deposits has led to an improved estimation of flow parameters and flow hydraulics associated with the 1918 jokulhlaup that could not have been achieved through localized outcrop analysis the observations presented here provide additional sedimentological and architectural criteria for the recognition of deposits associated with transcritical and supercritical water flow conditions the physical scale of sedimentary architectures associated with the migration of bedforms is largely dependent on the magnitude of the formative flow events or processes sedimentary analyses must therefore be undertaken at the appropriate physical scale if reliable interpretations regarding modes of deposition and formative flow hydraulics are to be made

stationary and traveling mesoscale perturbations in the kuroshio extension current abstract several hundred xbt observations in the western north pacific were collected each month over a 2 year period 1976 78 they have been assembled into a monthly map sequence of thermocline temperature in the kuroshio extension current having 100 km spatial resolution the overall time men of the maps exhibits mesoscale 200 600 km perturbations which correlate with several major bathymetric features especially the shatsky rise time variability about the mean decreases significantly cast of the shatsky rise in addition time variable mesoscale disturbances propagate zonally westward at 3 8 cm s 1 attempts to explain the observed propagation phase velocity through simple analytic baroclinic rossby wave theory lead to the implication that there exists in the region an eastward deep mean flow of 3 or 4 cm s 1 direct current measurements of long duration are required to help resolve and explain these observations

chevrons origin and relevance for the reconstruction of past wind regimes abstract since its first use in the late 80 s the term chevron has been employed in numerous studies to describe large u and v shaped ridges found in or near shorelines worldwide most studies have so far focused on bahamian chevrons that are exclusively of late pleistocene age and on the supposed holocene chevrons found in s madagascar and australia in the bahamas these deposits have been interpreted as the product of extreme storms at the end of the last interglacial lig warm period in contrast the extensive chevrons complex exposed in s madagascar and on the western coast of australia have been associated with a tsunami induced by a meteorite impact finally several authors have also proposed a non catastrophic i e eolian origin based on the recognized importance of wind related processes in these coastal areas and term such deposits parabolic dunes in this paper we collect and synthesize existing data on the morphology sedimentology and age of these chevrons and review the different interpretations proposed in the literature with the aim to lay out a consistent database to assist further investigations on these important coastal morphologies in addition we generated a synthesis of wind data at the three study areas which highlights the relationship between present wind regimes and chevrons morphologies the ubiquity of chevrons likely actually parabolic dunes in coastal areas around the globe and their relationship with coastal processes makes them crucial archives for reconstructing past wind regimes

interpreting flash flood palaeoflow parameters from antidunes and gravel lenses an example from montserrat west indies the wavelength of stationary water surface waves and their associated antidune bedforms are related to the mean velocity and depth of formative flow in sand bed flume experiments alexander et al 2001 found that lens structures were preserved during antidune growth and change and the dimension of the lenses were empirically related to antidune wavelength and thus could be used to estimate flow velocity and depth this study is the first to compare observations of formative flow conditions and resulting sedimentary structures in a natural setting testing the alexander et al 2001 relationship at a field scale trains of stationary and upstream migrating water surface waves were prevalent during the flash flood in october 2012 in the belham valley montserrat west indies wave positions and wavelengths were assessed at 900 s intervals through the daylight hours of the event within a monitored reach the wave data indicate flow depths up to 1 3 m and velocity up to 3 6 m s 1 sedimentary structures formed by antidune growth and change were preserved in the event deposit these structures include lenses of clast supported gravel and massive sand with varying internal architecture the lenses and associated low angle strata are comparable to sand bed structures formed from stationary and upstream migrating waves in flume experiments confirming the diagnostic value of these structures using mean lens length in the event deposit underestimated peak flow conditions during the flood and implied that the lenses were preserved during waning flow

on the kuroshio extension near the emperor seamounts in june july 1982 and november 1983 studies were carried out of the vertical structure of the kuroshio extension along 167 e and the path of the current as it approached the emperor seamount chain in addition records from moored current meters at three locations two at 167 e and one in the main gap of the emperor seamount chain were obtained the kuroshio extension in both 1982 and 1983 turned cyclonically meander wave length of 450 km as it approached the chain the axis of the surface current was located in deep water 3 5 km in 1982 and in relatively shallow water 0 5 km in 1983 in 1982 the horizontal temperature gradient decreased and the density surfaces down to 2000 m ascended as the kuroshio extension flowed over the emperor seamounts in neither year was there evidence of current splitting as it crossed the seamounts in 1983 in contrast to 1982 there was no weakening of the horizontal temperature gradient and the kuroshio extension went over a very shallow portion of kinmei seamount 500 m the current measurements made at the time of the hydrographic section show that the instantaneous kuroshio extended to the bottom abyssal eastward current of 2 cm s 1 the deep low frequency eddy kinetic energy values are intermediate between those measured at 152 e and those at 158 w suggesting a large scale eastward decrease in deep eddy activity zonal mean flow near 3500 m at 167 e was essentially zero 0 1 cm s 1 the mean meridional components were larger 2 1 and 0 7 cm s 1 at the southern side of the gap the deep flow was unusually steady ke km 1 and directed northeastward into the eastern basin of the north pacific low ratios o 1 were also observed in the lower thermocline compared with those at 167 e o 10 100 the frequency content of the gap kinetic energy differed from that measured at 167 e the highest frequency band 2 hours p 2 days was the most energetic whereas at 167 e the mesoscale band 20 days p 150 days was the most energetic the flow in the gap resembles in many of its characteristics that observed in two other channel flows the vema channel and the charlie gibbs fracture zone

sedimentology and morphodynamics of a barrier island shoreface related to engineering concerns outer banks nc usa abstract forty nine vibracores were collected from a barrier island shoreface following 12 4 years of biweekly profile surveying the sedimentologic architecture of the shoreface was linked to time series elevation change and profile shape to determine relationships between morphodynamics facies development erosional processes profile closeout and cross shore transport the modern shoreface mass which erosionally overlies a tidal inlet associated complex attains a maximum thickness of 3 4 m below the beach to middle profile before pinching out seaward between 9 and 12 m depth concave erosional surfaces overlain by cross stratified fine to medium sand and gravel make up most of the lower half of the shoreface prism below the beach through middle profile reflecting longshore trough incision and subsequent current dominated aggradation at the landward margin gravel rich laminae record episodic seaward progradation of beach surfaces over coarse inner trough settings seaward a parallel laminated fine sand facies dominates the upper part of the prism recording intermittent shoal zone buildup including trough filling under high velocity plane bed conditions similarly a bioturbated parallel laminated fine to very fine sand facies makes up the entire prism below the outermost lower ramp sector again indicating buildup under high velocity conditions however accretion of the lower ramp results from major storms that cause trough scour along landward locations and simultaneous displacement of fine sand onto the lower ramp conversely lower ramp erosion typically occurs during less energetic conditions as sediment is slowly returned shoreward causing inner shoreface buildup close spacing of major storms during some years led to net progradation of the shoreface the upper and lower limits of surveyed elevation change ule and lle repeatedly develop similar limit profile shapes over shoreface accretion erosion cycles the ule reflects accretion maxima resulting from beach bar and lower ramp buildup the lle and lower sedimentologic limit lls along the inner 250 to 300 m of the active shoreface are a product of storm trough scour down to a maximum depth of 5 5 m below the lower ramp facies the lle and lls are primarily products of less energetic wave erosion down to 5 m shoreward and 9 m offshore depths the lle closely matches the lls documenting that 90 of the shoreface prism was reworked during the 12 4 year period whereas actual ages for erosional events indicate a potential of 2 to 4 years for complete reworking of the shoreface mass textural distribution indicates net long term transport direction and loci of deposition for different sized material the coarsest material is concentrated at landwardmost locations and well sorted fine to very fine sand at seaward locations medium sand to gravel tends to remain within the trough zone even during extreme storm events the ule and lle also represent the upper and lower limits for profile closure events a location of about 4 5 m depth at 300 to 350 m from shoreline marks the boundary between inner profile and lower ramp associated closure events the boundary between trough associated and lower ramp facies and the lower ramp morphologic break all of which correspond to the juncture between longshore current and shoaling wave dominated zones the lower ramp zone of closure is a zone of seaward decreasing storm transport in which fine to very fine sand is the typical bedload material

grain fabric of hummocky and swaley cross stratification abstract bed form and grain fabric of two types of hummocky and swaley cross stratification from the pleistocene formations in the kanto plain cental japan display clearly distinctive flow conditions of storm typhoon generated combined flow the grain alignment in the vertical profile of a domal structure of hummocky cross set together with variable strike directions of a lamina suggest that the cross stratification was produced under the waning stage of oscillatory dominant combined flow elsewhere the preferred grain orientation along the maximum dip direction of a large swaley structure shows a small angle of upcurrent imbrication both on the stoss and lee sides of the laminae the stratification within the swale is asymmetric but the strike directions of a lamina are persistently oriented in a preferred direction the fabric and the structure of the swale indicate that the cross stratification was formed as a very low angle mega ripple under unidirectional dominant combined flow the grain fabric of both cross sets clearly shows that in spite of a superficial resemblance to antidunes neither of the two structures was formed in flow conditions for antidunes

amplitude frequency and drivers of caspian sea lake level variations during the early pleistocene and their impact on a protected wave dominated coastline the caspian sea the largest isolated lake in the world witnessed drastic lake level variations during the quaternary this restricted basin appears very sensitive to lake level variations due to important variations in regional evaporation precipitation and runoff the amplitude frequency and drivers of these lake level changes are still poorly documented and understood studying geological records of the caspian sea might be the key to better comprehend the complexity of these oscillations the hajigabul section documents sediment deposited on the northern margin of the kura basin a former embayment of the caspian sea the 2035 m thick well exposed section was previously dated by magneto biostratigraphic techniques and provides an excellent record of early pleistocene environmental lake level and climate changes within this succession the 1050 m thick apsheronian regional stage between ca 2 1 ma and 0 85 ma represents a particular time interval with 20 regressive sequences documented by sedimentary and palaeontological changes sequences are regressing from offshore to coastal lagoonal or terrestrial settings and are bounded by abrupt flooding events sediment reveals a low energy wave dominated reflective beach system wave baselines delimiting each facies association appear to be located at shallower bathymetries compared to the open ocean water depth estimations of the wave baselines allow reconstruction of a lake level curve recording oscillations of ca 40 m amplitude cyclostratigraphic analyses display lake level frequency close to 41 kyr pointing to allogenic forcing dominated by obliquity cycles and suggesting a direct or indirect link with high latitude climates and environments this study provides a detailed lake level curve for the early pleistocene caspian sea and constitutes a first step towards a better comprehension of the magnitude occurrence and forcing mechanisms of caspian sea lake level changes facies models developed in this study regarding sedimentary architectures of palaeocoastlines affected by repeated lake level fluctuations may form good analogues for other semi isolated basins worldwide

storm flood impacts along the shores of micro tidal inland seas a morphological and sedimentological study of the vesterlyng beach the belt sea denmark abstract the morphological and sedimentological impacts of an extreme storm event bodil in december 2013 were investigated at a mixed sand and gravel beach vesterlyng in a micro tidal environment along the belt sea denmark the storm response was characteristic for mixed sand and gravel beaches gravelly storm berms with sandy to gravelly washover fans were formed at the upper beach where swash processes dominated during extreme water levels in combination with overtopping and overwash in addition storm scarps and gravel flats were formed the elevation of the storm berm crest was identical to a summation of the still water level 1 60 m in the belt sea during the storm flood and the wave run up 0 75 m at the shore the crest of 2 35 m is therefore a precise measure of the storm flood level this storm flood was classified as a large scale extreme event in a holocene perspective it is suggested that storm berm beach ridge heights above contemporaneous sea level can be used as a proxy of past flood events along micro tidal shores

spatio lateral continuity of hurricane deposits in back barrier marshes sedimentological and micropaleontological analysis of fifteen 3 m gouge auger cores revealed a lack of spatio lateral continuity for paleohurricane deposits from the back barrier marshes of folly island south carolina the offshore indicative calcareous microfossil content of some storm deposits was taphonomically altered or destroyed and in many cases cores taken 10 m apart provided significantly different storm records in several low marsh cores where bioturbation is more intense storm deposits were completely unrecognizable using foraminifer or sedimentological analyses in nearly all cores the sedimentary record of storm deposits was more extensive than the record produced using foraminifers and as a result the sedimentary proxy produced shorter hurricane return periods while offshore indicative foraminifers in the salt marshes behind folly island are good indicators of their original source and mode of deposition storm current transport from the shelf by overwash storm inlet or via lighthouse inlet their susceptibility to destruction from bioturbation and dissolution suggests that they provide a less accurate or less complete record of storm frequency than previously thought

sedimentology and petrography of dredged carbonate sands from stocking island bahamas implications for meteoric diagenesis and aeolianite formation abstract piles of carbonate sand dredged onto stocking island exuma chain bahamas during world war ii are now relatively well lithified down to a depth of about 80 cm and may contain up to 8 of interstitial calcite cement a volume comparable to that measured from 1000 yr old beach ridges elsewhere in the bahamas rates of meteoric diagenetic changes are thus more rapid than previously assessed in this area 600 cm3 of calcite cement produced by m3 of rock per year preservation of hydrodynamic sedimentary structures footprints and the lack of aeolian bedforms e g dunes ripples on the surface of these sediments further show they have not been reworked by the wind at all therefore the carbonate aeolianites of holocene and pleistocene ages forming the bulk of the islands of bermuda and the bahamas were likely deposited during relatively dry periods when the effects of meteoric diagenesis were limited reduced moisture along with sediment availability and wind energy appears as a key player in carbonate aeolianite genesis

effect of the emperor seamounts on the mesoscale thermohaline structure during the summer of 1982 the influence of the emperor seamount chain upon the mesoscale thermohaline structure and upon geopotential height are investigated on the basis of a field experiment in the summer of 1982 the seamounts have a twofold effect they deflect the oncoming flow of the kuroshio extension and they give rise to secondary perturbations of small horizontal extent but of large vertical amplitude the kuroshio extension approached the seamounts on a southeastward course and was deflected by kinmei seamount in an anticyclonic loop the deflection led to a weakening of this current over this seamount and to reintensification on the downstream side uplift of isopycnals near seamount peaks and vertical displacement along seamount flanks were generally observed but the details varied considerably from one seamount to the next uplift occurred over some peaks on others it was displaced 50 100 km from it in some instances there was intense downward displacement on the west and upward displacement on the east side in others this was not the case a taylor columnlike feature occurred over suiko seamount a very large and asymmetric density dome was found 40 km west of jingu seamount atop which a density front was located which suggests flow intensification to the left of the seamount in the main gap between the northern and southern seamounts prominent wedgelike intrusions or subarctic and kuroshio type waters were observed in the upper few hundred meters the isopycnals in the main gap sloped sharply to the south indicating a strong eastward baroclinic flow component the geopotential heights over the emperor seamounts indicate strong local perturbations superimposed upon larger scale slopes a geopotential low was observed west of the seamounts and a high was found near the seamount top or to the east of it indicating anticyclonic flow in terms of geometric distance perturbation dynamic heights reached 0 32 m and maximum sea surface slopes were 5 10 6 the slopes produce baroclinic currents up to 0 5 m s 1 around the seamounts

decadal variability of the north pacific polar front subsurface warming versus surface cooling 1 over 200 hydrographic sections are used to trace the polar front defined as the southern boundary of the pure subarctic stratification with a pronounced extremely cold subsurface temperature minimum underlain by a temperature maximum the front extends from 40 n off japan to 57 n in the gulf of alaska where it retroflects and continues wsw with the alaskan stream the front s decadal variability from 1977 1999 is examined along 150 e 170 e 175 5 e and 180 e at these longitudes the front is relatively stable except for 170 e where it shifts north south by 400 km every 6 years most time series reveal a subsurface warming of 1 c per decade and a surface cooling of the front since the subsurface temperature minimum is a remnant of winter convection the subsurface warming signals an amelioration of the winter climate whereas the summer climate becomes colder

west coast dune plumes climate driven contrasts in dunefield morphogenesis along the western and southern south african coasts abstract this study examines two major late quaternary coastal dune systems situated in the southwestern most extremity of africa the false bay and duinefontyn dune plumes formed in close proximity but under contrasting oceanographic regimes warm agulhas and cold benguela oceanic current systems respectively the false bay and duinefontyn dune plumes have hitherto lacked the objective numerical chronology required to realize their full potential in unraveling the complex palaeo oceanographic and palaeoclimatic history of the region here we present a dual amino acid racemizationn aar and optically stimulated luminescence osl chronological framework from the extensive three dimensional exposures in sea cliffs at false bay three generations of dune deposition corresponding with orbitally forced climatic sea level cycles mis 7 mis 5 and holocene were resolved whereas the duinefontyn plume is dominated by mis 5 and holocene sedimentation at false bay and duinefontyn glacial periods are marked by the development of mature palaeosols confirming the link between glacio eustacy and dune deposition determined previously on the west and southern coasts of south africa along the west coast dune plumes typify dunefield morphology whereas shoreline parallel dune cordons are commonly developed on the southern coast these regional variations in dune system morphogenesis are largely controlled by contrasting wind and rainfall patterns the attenuated dimensions of the mis 5 plumes at false bay and duinefontyn may indicate a weakening of the south atlantic anticyclone during the last interglacial at false bay stone artifacts illustrate a human presence in the region during mis 7

the sedimentary architecture of a holocene barrier spit sylt german bight swash bar accretion and storm erosion abstract the southern german north sea coast was shaped by the last post glacial sea level rise that caused a significant retreat of the coastline approximately 5 ka bp the rate of sea level rise decreased providing space for the formation of the frisian islands which line the coast this study is focused on the island of sylt located at the german north sea coast close to the danish border here two sandy spit systems developed during the holocene combining ground penetrating radar studies and sedimentological investigations based on shallow cores new aspects on the sedimentary history of this holocene spit system have been revealed the data indicate that strong erosional events alternated with phases of progradation and growth the welding of swash bars is shown to be the predominant process during progradational phases of the spit system during these periods progradation was not restricted to linear growth along the spit axis but also included a seaward directed component major erosion surfaces which delimit progradational sediment packages are interpreted to reflect exceptionally severe storms the fossilization potential of this sedimentary record was controlled by a positive net long term sediment balance and the position of the ground water table which controlled eolian deflation only with a stable or rising sea level and associated ground water table position are sediments protected from deflation the proposed sedimentary model may serve as a template for interpretation of comparable settings in the geological record

upper regime parallel lamination as the result of turbulent sediment transport and low amplitude bed forms a series of laboratory experiments has been carried out in which parallel laminated deposits were produced from an upper regime plane bed the laminae had thicknesses of a few mm and could be traced continuously over distances up to the length and width of the depositional area 0 3 m by 1 5m fluctuations in bed elevation were measured both during deposition and at equilibrium much of the bed fluctuation occurs at time scales that are too long to be due directly to turbulence as most theories for lamina formation would require we suggest instead that extremely low amplitude bed forms are present even on apparently flat beds and that the migration of these bed forms produces laterally continuous lamination all the lamination produced in the laboratory experiments was normally graded using high speed photography it was observed that the normal grading results from rapid deposition of a layer of loosely packed coarse sand several grain diameters thick followed by the slow sieving out of a well packed surface layer of finer sand the initial deposition is the result of small scale turbulent fluctuations in boundary shear stress the sieving out that follows results in a smooth surface whose low friction coefficient temporarily inhibits further deposition we term this process glazing the alignment of small scale turbulent scour and fill structures along the paths traced by migrating bedform troughs produces laterally continuous parallel lamination

physical processes and sedimentary record of a modern transgressive lacustrine barrier island abstract high water levels storms and a sparse sand supply have led to the formation and episodic migration of this 30 km wide foredune lacking lacustrine barrier transgression is dominated by overwash and by channels cut during storms that transport sand to the lagoon the barrier system is characterized by five environments near shore foreshore backshore washover terrace channel and lagoon the nearshore consists of irregular bars that overlie a holocene peat and or clay the bars are characterized by low angle stratification and ripples and landward dipping tabular sets the foreshore consists of a smooth plane surface and internally by lakeward dipping 3 to 12 laminations that truncate one another and thin towards the berm the backshore washover terrace consists of a gently 1 to 2 landward dipping surface that changes at the lagoon margin to a steeply 30 landward dipping surface stratification consists of subhorizontal landward dipping laminations and thin beds that are thinnest nearer the berm and gradually thicken toward the lagoon and by avalanche foresets washover fans coalesce to form the terrace the channels which are commonly less than a few tens of meters wide and a meter deep form during storms when wave energy is concentrated by refraction around nearshore bars the channel facies consists of nearly horizontal beds and laminations of gravel and coarse sand the lagoon consists of mud that overlies a holocene peat the lagoonal mud is eroded during transgression the vertical sequence which is 1 2 m thick consists from the base up of horizontal laminations of coarse sand and gravel of the channel facies the landward dipping foresets of the washover fan margin and the gently landward dipping laminations and landward dipping avalanche foresets of the backshore washover terrace the preservation potential is considered low although pleistocene and holocene coastal deposits have survived for up to 15 000 years in the great lakes region

meridional shift of the kuroshio extension induced by response of recirculation gyre to decadal wind variations abstract the meridional shift of the kuroshio extension to decadal wind variations is examined by analyzing the hindcast simulation of a high resolution 1 12 1 12 north pacific ocean general circulation model ogcm and by conducting a series of idealized ogcm experiments the meridional shift of the kuroshio extension in the hindcast is consistent with observations and former studies using a series of sensitivity experiments in idealized settings the following possible mechanism for this shift is proposed the baroclinic rossby waves that arise in the northern half of the subtropical gyre cannot directly enter the kuroshio oyashio extension region due to the strong kuroshio extension jet when the rossby waves accompanying the negative positive sea surface height anomalies propagate westward and reach the region to the east of the recirculation gyre the difference in thermocline depth between the recirculation gyre and the region to its east becomes larger smaller resulting in stronger weaker baroclinic instabilities these stronger weaker instabilities cause a shallower deeper thermocline in the recirculation gyre to compensate for this shrinking stretching the recirculation gyre migrates southward northward leading to the southward northward shift of the kuroshio extension

diagenetic evolution and chemical changes of deep water mudstones of shahejie formation in the dongying sag jiyang depression eastern china abstract the diagenetic evolution and chemical changes of mudstones have a significant influence on the reservoir quality of the mudstones and their interbedded sandstones to investigate a variety of methods were applied to the mudstones in the middle of the third member of the shahejie formation es3z which were formed in a lacustrine basin during 43 7 38 2 ma optical microscopy and xrd analysis show that the mudstones are dominated by clay minerals 56 8 followed by carbonate 18 2 quartz 14 9 feldspar 8 4 pyrite 0 9 anhydrite 0 8 and total organic carbon toc 2 4 cementation and replacement are the main diagenetic events in the mudstone of es3z carbonates and clay minerals are the most common cements but occasionally authigenic pyrite albite and quartz are also present at the eogenetic stage the diagenetic events comprised precipitation of pyrite siderite dolomite and calcite besides transformation of k feldspar into kaolinite during the mesogenetic stage the main diagenetic events included precipitation of fracture filling calcite ferroan calcite ankerite microcrystalline quartz quartz overgrowth and transformation of k feldspar into illite and albite the limited variation of the nb ta and zr hf ratios and the almost identical distribution pattern of the ree and trace elements indicate that the detrital material in the mudstones was sourced by a common provenance of felsic igneous rocks the cia values of es3z mudstones vary from 50 59 to 65 05 and the pia values vary from 50 86 to 75 58 which confirm a low intensity weathering of the source area thus the variation in the bulk rock geochemical composition of the mudstones may not be primary but instead a result of mass transfer with the interbedded sandstones during diagenesis changes ratios between aim elements al si ca and k and immobile elements with burial depth in combination with mass balance calculation indicate that aluminum and silicon were retained by the precipitation of authigenic minerals in the mudstone the mudstones have received progressively more potassium with increasing depths whereas calcium has been expelled the reservoir quality of the es3z sandstones has mainly been affected by the diagenetically induced decrease in the carbonate content in the mudstones causing carbonate cementation in the sandstones

sedimentology stratigraphy and tectonics of evolving wedge top depozone ariano basin southern apennines italy the late zanclean wedge top ariano basin located in the external sector of the southern apennines was initially characterized by alluvial and fan delta environments and successively southward of the benevento buonalbergo fault by a gradual drowning with coastal and alluvial plains evolving to shelf and marine coastal settings respectively basin evolution continued with a synsedimentary uplift of different sectors resulting in variations in the drainage pattern and basin shape and ultimately leading to complete basin closure and transition to continental depositional environments early pliocene paleogeography prior to the ariano basin activity is due to regional subsidence and subsequent differential uplifts that resulted from geodynamic processes related to both the downgoing apulian slab and the allochthonous orogenic wedge slab break off and the migration of a tear in the southeastward apulian slab occurred producing a strong subsidence in the external sectors of the southern apennines recorded by the development of the ariano basin subsequently out of sequence synsedimentary thrusting related to thin skinned tectonics occurred in the allochthonous units and unconformably overlying wedge top basin deposits producing northeastward migration of the main depocenters in the ariano basin finally renewed thrusting related to the inversion of pre existing normal faults located in the buried apulian platform and enhanced by regional uplift affected the whole tectonic and sedimentary pile as recorded by deformation of the overlying pliocene deposits

sulfate rich eolian and wet interdune deposits erebus crater meridiani planum mars this study investigates three bedrock exposures at erebus crater an 300 m diameter crater approximately 4 km south of endurance crater on mars these outcrops called olympia payson and yavapai provide additional evidence in support of the dune interdune model proposed for the formation of the deposits at the opportunity landing site in meridiani planum there is evidence for greater involvement of liquid water in the olympia outcrop exposures than was observed in eagle or endurance craters the olympia outcrop likely formed in a wet interdune and sand sheet environment the facies observed within the payson outcrop which is likely stratigraphically above the olympia outcrop indicate that it was deposited in a damp wet interdune sand sheet and eolian dune environment the yavapai outcrop which likely stratigraphically overlies the payson outcrop indicates that it was deposited in primarily a sand sheet environment and also potentially in an eolian dune environment these three outcrop exposures may indicate an overall drying upward trend spanning the stratigraphic section from its base at the olympia outcrop to its top at the yavapai outcrop this contrasts with the wetting upward trend seen in endurance and eagle craters thus the series of outcrops seen at meridiani by opportunity may constitute a full climatic cycle evolving from dry to wet to dry conditions

coastal geomorphic conditions and styles of storm surge washover deposits from southern thailand abstract the characteristics of tropical storm washover deposits laid down during the years 2007 to 2011 along the southern peninsular coast of the gulf of thailand got were described in relation to their different geomorphic conditions including perched fan washover terrace and sheetwash lineations preserved behind the beach zone within 100 m of the shoreline as a result washover terrace and sheetwash lineations were found where the beach configuration was uniform and promoted an unconfined flow non uniform beach configurations that promoted a confined flow resulted in a perched fan deposit washover sediments were differentiated into two types based on sedimentary characteristics including i a thick bedded sand of multiple reverse grading layers and ii a medium bedded sand of multiple normal grading layers in the case of thick bedded washover deposits the internal sedimentary structures were characterized by the presence of sub horizontal bedding reverse grading lamination foreset bedding and wavy bedding whereas horizontal bedding normal grading and dunes were the dominant structures in the medium bedded washover sand rip up clasts were rare and recognized only in the washover deposits in the bottom unit which reflects the condition when a mud supply was available all washover successions were found in the landward inclined bedding with a basal sharp contact a high elevated beach ridge associated with a large swale at the backshore proved suitable for a thick bedded washover type whereas a small beach ridge with uniformly flat backshore topography promoted a medium bedded washover sediment

grain fabric of planar cross bedding formed by lateral accretion caledon outwash ontario canada sand sized grains comprising the planar cross bedding found in a late wisconsinan outwash deposit near caledon ontario show an obliquely downslope preferred orientation the average angle of obliquity measured from the downdip direction is about 35 such a grain fabric was probably produced by the resultant force of the gravity pull that orients the grains to the dip direction and the lateral traction current of the channel flow which tends to imbricate the grains to the upstream dip this asymmetric mode of grain fabric was formed during deposition of a laterally accreted outwash bar detailed examination of grain fabric makes it possible to distinguish the planar cross bedding of a micro deltaic origin from that of other types of bar deposit built either partly or predominantly by lateral accretion

holocene coastal evolution of the transition from transgressive to regressive barrier in southern brazil abstract in this study the evolution of a holocene coastal barrier was determined based on a basal transgressive unit followed by a regressive unit standard penetrating test vibrocore and ground penetrating radar profiles were used to acquire stratigraphic data sedimentological paleontological and geochronological analyses were performed to describe and interpret the sedimentary facies the base of the holocene record indicates the existence of pre transgression continental and coastal environments basal peat which resulted from the initial flooding of the antecedent topography pleistocene substrate due to rising sea levels during this period the continental environments were flooded by lagoon environments that occupied the landward displacement of the transgressive barrier which had channels that connected the lagoon and the ocean at this time the coastal barrier had a transgressive configuration indicated by its morphology and characterized by washover fans as the backbarrier accommodation space decreased due to the displacement of the barrier transgressive maximum the transition of the transgressive regressive record began at approximately 7 200 years bp restricting the overwash events and the dynamics of the inlets however before the highest level eustatic maximum of the postglacial marine transgression pmt was reached this transgressive barrier stopped its migration toward the continent causing an inversion of the depositional record which became a normal regression later at the end of the pmt sea levels began to fall causing a forced regression that persists to the present day

antidunes on modern and ancient washover fans abstract antidune deposits on a washover fan on seabrook island south carolina display a variety of bedding types the predominant stratification form comprises nested very thin lenses which are internally cross laminated and which become thinner and more closely spaced downflow in addition cross laminae within the lenses tend toward backset forms in the bermward portions of the flow and become more foreset oriented in a downfan direction these characteristics together with the antidune field s relationship to other bed features on the fan suggest that antidune formation is related to the occurrence of an undular hydraulic jump just downfan from the berm crest ancient deposits interpreted as washover sequences including ordovician and pleistocene sandstones in south africa and a carboniferous sandstone in kentucky display sedimentary structures similar to those observed in the seabrook antidune field because washed out antidunes and their associated cross laminae are very subtle features antidunes are possibly responsible for many of the gentle irregularities in otherwise flat beds and are therefore possibly far more common in the geologic record than previously recognized their sedimentary structures are distinct from degraded forms of ripple cross lamination and in many cases are identical to features usually described in the literature as low angle truncation surfaces

the abyssal and deep circulation of the northeast pacific basin abstract three dimensional abyssal and deep circulation of the region to the east and north of the emperor seamount chain hawaiian ridge is determined from a compilation of ctd and argo float data using a new overdetermined inverse technique for the geostrophic reference velocity and diapycnal lateral mixing coefficients the northeast pacific basin is primarily sourced from its northern boundary at a rate of 3 5 sv across 47 n below 3000 m bottom water in the western subarctic gyre recirculates cyclonically between the emperor seamount chain and 155 w bottom water east of 155 w takes a more direct path southward along the flank of a broad topographic slope in the deep water a ridge of potential vorticity lying along the mendocino fracture zone separates circulation systems north and south of 40 n the region has very weak diapycnal and lateral mixing and an aspect ratio for the overturning circulation that is correspondingly flat with bottom water parcels rising less than 1 km during their long transit from the aleutian trench to the latitude of hawaii

directional petrological characterisation of deep marine sandstones using grain fabric and permeability anisotropy methodologies theory application and suggestions for integration abstract different methods for quantifying preferred grain orientation or grain shape fabric in sandstones are reviewed and their value for the reconstruction of palaeocurrent direction and preferred direction of pore fluid flow is reassessed critically based on existing knowledge from literature and new grain fabric data it is shown that petrographic analysis has distinct merits because grain fabric can be determined with low equipment costs and population statistics are based on the orientation of individual grains several recommendations are given how to standardise procedures for acquisition of grain fabric through microscopy these recommendations include 1 the careful selection of cross section orientations to acquire apparent long grain axes that are representative of true long grain axes 2 the preferred measurement of the coarsest grains in cross section and 3 a new statistically founded method to select a subset of grains that is representative of the total population of grains in a sandstone sample magnetic techniques that use anisotropy of magnetic susceptibility ams as a proxy for grain orientation require specialised equipment and are more restricted in statistical evaluation but these methods benefit greatly from being able to measure a large number of grains in a three dimensional space in a short amount of time and with a lower sensitivity to user bias of the two magnetic techniques discussed in this paper the new enhanced ams method in which rock magnetic properties are enhanced by introducing magnetite into the pores and as precipitates on grain surfaces is regarded to be an improvement over the traditional natural ams method in which only the natural assemblage of magnetite particles present in the rock is analysed enhanced ams measures the preferred orientation of essentially all grains in a rock sample thus providing the shape fabric of a hydrodynamically more accurate representation of framework grains than natural ams through a small technical modification the enhanced ams method can be used to obtain a magnetic cast of the pore network of a rock sample so that the resulting ams is controlled by the shape anisotropy of the individual pores it is commonly assumed that long axes of sand grains in sedimentary deposits parallel the direction of the flows that formed the deposits this concept is challenged by a new systematic study of grain fabric in deep marine turbidites it indeed appears that grains in ripple cross laminated divisions of turbidites dominantly attain a preferred orientation parallel to the palaeoflow direction but grains in plane parallel laminated divisions have an additional flow perpendicular mode which suggests a contribution of rolling grain transport three different fabric modes occur in massive structureless sandstones and massive divisions in turbidites apart from flow aligned and flow perpendicular modes there is a statistically significant but hydrodynamically enigmatic flow oblique mode with an average azimuthal deviation of 40 this large variation of fabric types suggests that a similar variation exists in preferred paths of pore fluid flow within turbidites controlled to at least some degree by depositional process this is confirmed by independent laboratory measurements of permeability anisotropy on samples for which grain fabric data are available and thus defines grain fabric analysis as a viable alternative to traditional permeametry techniques

sea surface temperature changes in the okhotsk sea and adjacent north pacific during the last glacial maximum and deglaciation abstract we estimated sea surface temperatures ssts in the western okhotsk sea during the last glacial maximum lgm and the last glacial termination from measurements of the alkenone unsaturation index u k 37 the t etra e ther inde x of tetraethers consisting of 86 carbon atoms tex 86 and tex 86 l in piston core sediments which reveal the climate response of this region to different types of forcings tex 86 l is a modification of tex 86 proposed for high latitude ocean regions the tex 86 l derived temperatures were not different from the alkenone derived temperatures from the same and nearby sediment samples during the lgm alkenone derived temperatures in the okhotsk sea were relatively warm these and similarly warm alkenone derived temperatures found at many other sites in the western north pacific may reflect a shift in the season of biomarker production from early summer and autumn to mid summer during the lgm as a result of the expansion of the season of sea ice cover empirical orthogonal function eof analysis of alkenone derived temperatures at 14 sites from the north pacific suggested substantial cooling between 20 and 14 cal kyr bp during the deglaciation at 11 of the sites including 4 sites in the okhotsk sea this dominant eof mode suggests either an overall seasonal bias in alkenone derived temperatures or potential shifts in the haptophyseae production season the second eof mode of variability indicated a deglacial warming trend punctuated by millennial scale cold events associated with reorganizations of the atlantic meridional overturning circulation the sst pattern corresponding to this eof mode is indicative of millennial scale meridional shifts of the axis of the westerly jet which may have affected heat transport across the kuroshio reconstructed temperature changes in particular in the okhotsk sea provide insight into the conditions that modulated the ventilation history of intermediate waters in the north pacific

architecture and formation of transgressive regressive cycles in marginal marine strata of the john henry member straight cliffs formation upper cretaceous of southern utah usa marginal marine deposits of the john henry member upper cretaceous straight cliffs formation were deposited within a moderately high accommodation and high sediment supply setting that facilitated preservation of both transgressive and regressive marginal marine deposits complete transgressive regressive cycles comprising barrier island lagoonal transgressive deposits interfingered with regressive shoreface facies are distinguished based on their internal facies architecture and bounding surfaces two main types of boundaries occur between the transgressive and regressive portions of each cycle i surfaces that record the maximum regression and onset of transgression bounding surface a and ii surfaces that place deeper facies on top of shallower facies bounding surface b the base of a transgressive facies bounding surface a is defined by a process change from wave dominated to tide dominated facies or a coaly shelly interval indicating a shift from a regressive to a transgressive regime the surface recording such a process change can be erosional or non erosive and conformable a shift to deeper facies occurs at the base of regressive shoreface deposits along both flooding surfaces and wave ravinement surfaces bounding surface b these two main bounding surfaces and their subtypes generate three distinct transgressive regressive cycle architectures i tabular shoaling upward marine parasequences that are bounded by flooding surfaces ii transgressive and regressive unit wedges that thin basinward and landward respectively and iii tabular transgressive lagoonal shales with intervening regressive coaly intervals the preservation of transgressive facies under moderately high accommodation and sediment supply conditions greatly affects stratigraphic architecture of transgressive regressive cycles acknowledging variation in transgressive regressive cycles and recognizing transgressive successions that correlate to flooding surfaces basinward are both critical to achieving an accurate sequence stratigraphic interpretation of high frequency cycles

distribution of sei whales balaenoptera borealis in the subarctic subtropical transition area of the western north pacific in relation to oceanic fronts the subarctic subtropical transition area of the western north pacific is an important summer feeding grounds of sei whales the oceanographic structure and circulation of this area are largely determined by strong oceanic fronts and associated geostrophic currents namely the polar front pf subarctic front saf and kuroshio extension front kef the relationship between the distribution of sei whales and oceanographic fronts was investigated using a generalized additive model gam and the cetacean sighting survey data and oceanographic observations in july from 2000 to 2007 were used in the analysis the number of individual sei whales was used as the response variable while the distances from the pf saf and kef to the whales were used as explanatory variables along with the longitude values sei whales were concentrated north and south of the saf and the areas from 250 to 300 km north and from 100 to 200 km south of the saf were estimated as high density areas of sei whales the entire inter frontal zone between the pf and saf featured an elevated concentration of sei whales and the area south of the pf and along the saf was identified as an important feeding ground of sei whales in july from 2000 to 2007

characteristics of alkenone distributions in suspended and sinking particles in the northwestern north pacific abstract we investigated alkenones recorded in suspended particles and a settling particle time series collected at three stations 40n 40 n 165 e knot 44 n 155 e and 50n 50 n 165 e in the northwestern north pacific from december 1997 to may 1999 emiliania huxleyi the most abundant alkenone producer in this area is present in surface to subsurface to 50 m depth waters the alkenone concentrations recorded in the suspended particles indicated that the seasonal alkenone particle distribution differed significantly interannually alkenone export fluxes at the three sediment trap stations ranged from 0 16 to 49 3 g m 2 day 1 and the maximum export flux which occurred in summer to fall july november was associated with a high organic carbon export flux the amount of alkenone produced during the maximum export season accounted for 60 80 of the total annual amount of alkenone and the alkenones accumulated in the sediment below the traps had characteristics corresponding to subsurface waters during the summer autumn season alkenone derived temperatures recorded in suspended particles corresponded to the in situ temperature within 2 c although alkenone derived temperatures corresponded approximately to the temperatures observed in the stratified subsurface waters at the three trap stations during the high export season large differences were observed during the low export winter spring period for example the alkenone derived temperatures observed at stations knot and 50n were much higher than the in situ subsurface temperatures reported in the world ocean atlas 2001 relatively large differences between alkenone derived temperatures and in situ temperatures in the subarctic might be due to 1 a low light limitation or 2 contributions of allochthonous alkenones in particulate material transported from subtropical areas within a warm core ring

observations of seamount attached eddies in the north pacific satellite tracked drifters were used to examine eddy activity in the vicinity of the emperor seamount chain esc in the north pacific during 1991 1993 the trajectories of two drifters drogued at a depth of 120 m revealed a pair of counterrotating mesoscale eddies attached to the leeside of ojin jingu seamount in the summer of 1992 the eddies had diameters of 75 100 km and rotational speeds of 20 40 cm s at 120 m sea surface height anomalies derived from blended topex ers 1 satellite altimetry revealed that the eddies had a surface manifestation as well one of the drifters made five loops within the cyclonic eddy over a period of 62 days during which time the eddy translated westward toward the seamount at 2 9 cm s this is one of the first observations demonstrating an extended attachment of a topographically generated eddy to a seamount drifters drogued at a depth of 15 m which crossed the esc in the summer of 1991 and winter of 1993 revealed no eddy activity most likely because of a decoupling of the topographic influence to the 15 m flow at their crossing latitude over the nintoku seamount summit depth at 1000 m the implication is that eddy formation within the mixed layer near the esc is confined to the region around the taller ojin jingu and kinmei seamounts summit depths at 800 m and 100 m respectively it is suggested that long lived eddies attached to the leeside of the esc can profoundly influence local biological production and water exchange between the western and eastern basins of the north pacific

bedform and stratification characteristics of some modern small scale washover sand bodies washover sand bodies commonly develop along microtidal coastlines in beach barrier island or spit settings wave runup usually in conjunction with an abnormally high water level may overtop the most landward berm of the beach and the foredune crest if one exists to produce overwash and subsequent runoff across the more landward subaerial surface two main elements of the resulting deposit are the washover fan and runoff channel newly formed small scale washover deposits were examined along the outer banks north carolina near pt mugu california and at presque isle lake erie pennsylvania the fans were formed in response to unidirectional landward transport and the runoff channels in response to unidirectional flow usually in a landward direction but sometimes in shore parallel then seaward direction where overwash carried across the fan surface and entered a pond or lagoon a small scale delta microdelta developed in this case the washover fan consisted of two subfacies the wetted but subaerial part of the fan and the subaqueous washover delta flow associated with the development of the fan and runoff channel produced distinctive sets of bedforms and internal stratification high velocity discontinuous surges moving across the fan surface resulted in the development of a plane bed and subhorizontal to low angle landward dipping planar stratification which comprised the major part of the fan similarly rhomboid forms were produced by high velocity sheet flow across the fan surface where flow carried into a standing body of water delta type foreset strata developed for this case the lateral structural sequence was subhorizontal planar stratification merging landward into landward dipping delta tabular foreset strata in the runoff setting where flow became channelized and continuous both upper flow and lower flow regime currents were typical upper flow regime bedforms included antidunes standing waves and plane beds the most commonly observed lower flow regime bedforms included microdelta like bars low amplitude bars linguoid ripples and sinuous crested current ripple trains the sets of sedimentary structures comprising modern washover sand bodies provide criteria for the identification of similar deposits in ancient sediments and for more specific interpretation of the environment

contained reflected turbidity currents from the middle ordovician cloridorme formation quebec canada an alternative to the antidune hypothesis the parautochthonous cloridorme formation is a syn orogenic flysch succession that was deposited in an elongate foredeep basin as mainly lower middle fan outer fan and basin floor deposits the basin floor deposits about 1 5 km thick are confined to members 1 2 and 1 and are characterized by graded thick 1 10 m mud rich calcareous greywacke beds previously interpreted as deposits of concentrated muddy unidirectional turbidity currents that locally generated backset antidune lamination in internally stratified flows the dominant flow directions were from east to west but west to east transport also occurred as seen in the orientation of ripples climbing ripples flutes consistently overturned flames and grain imbrication we believe that the flows that deposited these thick calcareous greywacke beds reversed by roughly 180 one or more times during deposition of the lower sandy part of the beds flow reversals are consistent with the sharp grain size breaks and mud partings within sandy divisions measurement of grain fabric relative to stratification in the most celebrated antidune bedforms indicates flow from west to east thus the bedforms were produced by west to east migration of megaripples not by the upcurrent migration of antidunes the thick muddy beds were deposited by large volume muddy flows that were deflected and reflected from the side slopes and internal topographic highs of a confined basin floor much like the contessa and similar beds of the italian apennines large quantities of suspended mud were ponded above the irregular basin floor and settled to produce the thick silty mudstone caps seen on each bed because of their mode of emplacement we propose that these beds be called contained turbidites

internal structure of a barrier beach as revealed by ground penetrating radar gpr chesil beach uk abstract chesil beach dorset is one of the most famous coastal landforms on the british coast the gravel beach is over 18 km long and is separated for much of its length from land by a tidal lagoon known as the fleet the beach links the isle of portland in the east to the mainland in the west despite its iconic status there is little available information on its internal geometry and evolutionary history here we present a three fold model for the evolution of chesil beach based on a series of nine ground penetrating radar gpr traverses located at three sites along its length at abbotsbury langton herring and at ferry bridge the gpr traverses reveal a remarkably consistent picture of the internal structure of this barrier beach the first phase of evolution involves the landward transgression of a small sand and gravel beach which closed upon the coast leading to deposition of freshwater peat between 5 and 7 k yr bp the second evolutionary phase involves the bulking out of the beach during continued sea level rise but in the presence of abundant gravel supplied by down drift erosion of periglacial slope deposits this episode of growth was associated with a series of washover fans which accumulated on the landward flank of the barrier increasing its breadth and height but without significant landward transgression of the barrier as a whole the final phase in the evolution of chesil beach involves the seaward progradation of the beach crest and upper beach face associated with continued sediment abundance but during a still stand or slight fall in relative sea level this phase may provide further evidence of a slight fall in relative sea level noted elsewhere along the south coast of britain and dated to between 1 2 and 2 4 k yr bp subsequently the barrier appears to have become largely inactive except for the reworking of sediment on the beach face during storm events the case study not only refines the evolutionary picture of chesil beach but illustrates the importance of the subtle interplay between relative sea level and sediment supply in the evolution of a barrier system in addition it also illustrates the potential of gpr in resolving the evolutionary history of gravel rich coastal landforms such as chesil beach

washover fans a modern geomorphologic analysis and proposed classification scheme to improve reservoir models abstract washover fan deposits are part of a much larger system of highly heterolithic barrier and shoreline margin deposits which form notoriously hard to produce hydrocarbon reservoirs this survey of modern fan morphologies identifies common fan geometries considers the preservation potential and range of probable geometries of fan facies in subsurface datasets and outcrops and aims to improve hydrocarbon recovery in barrier island reservoir systems we use satellite imagery to conduct a spatial analysis of 118 modern fans to quantify attributes of fans including throat width intrusion length fan area and barrier island width a new classification scheme for fans is proposed that refines the current fan model in this classification fans are initially divided into channelized and non channelized fans channelized fans are subdivided according to the location of primary deposition barrier depocenter or lagoonal depocenter non channelized fans are subdivided based on morphology dissipative lobate or apron sourced quantitative cross plots of morphologic parameters are analyzed to define geometric relations in fan morphologies the probability of identifying fans in the subsurface is discussed our results indicate that the most commonly used model for a washover fan the 52 km2 st joseph island fan is anomalous and does not reflect the most common sizes or geometries of washover fans we suggest that our classification be used instead to capture the range of fan morphologies although our study encountered non channelized line sourced lobate washover fans with an area of less than 1 km2 more frequently than any other types of fans washover fans exhibit diverse morphologies therefore the entire range of washover fan morphologies should be considered when interpreting exploration data and looking to identify washover fans in the subsurface

gravel antidunes in the tropical burdekin river queensland australia the geological record is punctuated by the deposits of extreme event phenomena the identification and interpretation of which are hindered by a lack of data on contemporary examples it is impossible to directly observe sedimentary bedforms and grain fabrics forming under natural particle transporting high velocity currents and therefore their characteristics are poorly documented the deposits of such flows are exposed however in the dry bed of the burdekin river queensland australia following tropical cyclone induced floods long wave length up to 19 m gravel antidunes develop during short days high discharge flows in the upper burdekin river maximum recorded discharge near the study reach over 25 600 m s in february 1927 flood water levels fall quickly metres in a day and flow is diverted away from raised areas of the river bed into subchannels exposing many of the high stage bedforms with little reworking by falling stage currents gravel bedforms were observed on the dry river bed after the moderate flows of february 1994 max 7700 m s and january 1996 max 3200 m s the bedforms had wave lengths in the range 8 19 m amplitudes of up to 1 m with steeper stoss than lee faces and crest lines generally transverse to local peak discharge flow direction the gravel fabric and size sorting change systematically up the stoss and down the lee faces the antidune deposits form erosive based lenses of sandy gravel with low angle downstream dipping lamination and generally steep upstream dipping a b planes the internal form and fabric of the antidune gravel lenses are distinctly different from those of dune lee gravel lenses the erosive based lenses of low angle cross bedded gravel with steep upstream dipping a b planes are relatively easy to recognize and may be diagnostic of downstream migrating antidunes the antidune gravel lenses are associated with thick to 1 m high angle cross bed sets ancient antidune gravel lenses may be diagnostic of episodic high discharge conditions and particularly when they are associated with high angle cross bedded gravelly sand they may be useful for palaeoenvironmental interpretation

placer formation in gravel bedded rivers a review the literature on placer formation processes within fluvial systems is widespread and ranges between detailed laboratory studies of the hydrodynamic segregation processes through to the intuitive interpretation of the distribution of minerals within geological sections however there are few if any comprehensive reviews of the literature surprisingly given the economic importance of placers the theoretical framework relating to the hydrodynamics of physical grain sorting is not well developed and there are relatively few detailed laboratory hydraulic investigations to inform theory in this wide ranging review the history of the development of principles of placer formation is explored as far as possible in a non technical fashion a consideration is given to the hydrodynamics of physical grain sorting above lower stage and upper stage bedforms and the typical internal sedimentary structures associated with placer concentrations are detailed finally examples of the depositional environment of diamond tin and gold placers are considered

lagrangian observations of surface circulation at the emperor seamount chain in a kuroshio tracking experiment initiated in february 1977 two satellite reporting buoys drogued to 100 m depth were released southeast of kuyshu island japan these drifters crossed the shatskiy rise in the kuroshio extension during may and october and then traversed the emperor seamount chain although they reached the chain 117 days apart their movements near the seamounts display remarkably similar patterns demonstrating upstream meanders in the surface flow cyclonic eddy activity immediately west of the chain passage through the same gap associated with the jingu and nintoku seamounts and a wavelike pattern present over the hess rise east of the chain one drifter exhibited cyclonic eddy motion east of the chain in the lee of the kinmei seamount

two types of plane beds under upper flow regime in flume experiments evidence from grain fabric abstract laboratory experiments that aimed to produce plane beds under upper flow regime were conducted using a flume of 15 700 cm with quartz sands of mean size of 0 72 mm 0 47 two types of plane beds were formed 1 laminae formed and buried by the migration of low relief asymmetric ripples near or subcritical flow froude number fr 0 94 run 5 and 2 laminae formed without producing any apparent low relief bedform but under supercritical flow fr 1 98 run 12 the mean flow velocity 83 cm s and the mean depth 8 cm in run 5 are larger than those in run 12 62 cm s and 1 cm respectively upcurrent grain imbrications in run 12 however are better developed than those in run 5 such an imbrication pattern may be useful to recognize the formational processes of plane beds under upper flow regime

medano creek colorado a model for upper flow regime fluvial deposition abstract medano creek in colorado provides a unique opportunity to study upper flow regime deposition it is a steep aggrading fluvial system in which antidunes are the dominant bedform medano creek is a straight single channel stream where flow is largely confined to a sequence of upstream migrating topographic steps pools and riffles a stable channel geometry antidunes and upperflow regime plane beds are arranged in an organized pattern on the surface of pool and riffle sequences as a response to spatially varied flow conditions in the creek antidunes form sedimentary structures consisting of low angle backset and foreset beds and subhorizontal laminae grouped into lenses laminae in a lens are often subparallel to the lens bounding surfaces on the downcurrent end and are truncated y the upper bounding surface on the upcurrent end upper flow regime plane bed and rhomboid ripples produce planar laminae through lateral shifting of the active channel and upstream migration of pools and riffles medano creek produces a facies sequence consisting of alternating 10 40 cm thick layers of planar laminae and low angle cross stratified lenticular bedding

a mid frasnian marine incursion into the southern part of the munster basin evidence from the foilcoagh bay beds sherkin formation sw county cork ireland

features of the water mass front in the northwestern north pacific analysis of the hydrographic data taken in the northern north pacific has revealed a water mass front defined as the abrupt change of mixing rates between the two typical water masses typical water masses are situated above the main thermocline in the subtropical and subpolar gyres this front termed water mass front in the present study can be regarded as the boundary between the subtropical gyre and the subpolar gyre the index for detecting the frontal position from the temperature field is given as the 5 c isotherm at the 300 m level comparisons with data from previous studies are also made and this front appears to correspond to the subarctic front in almost every instance

the subarctic and northern subtropical fronts in the eastern north pacific ocean in spring abstract the subarctic and subtropical frontal zones of the eastern north pacific ocean were surveyed in june for five consecutive years starting in 1972 these surveys from the basis for a description of the complex frontal distributions and their year to year differences the fronts appear as surface outcroppings of haloclines the subarctic halocline where salinity increases with depth and the subtropical halocline where the opposite prevails between the fronts lies a transition zone where strong vertical gradients of salinity are generally absent an examination of the northern boundary of subtropical waters in this new dataset reveals the presence of two major fronts in the subtropical frontal zone in addition to the front commonly identified as the subtropical front 18 c and 34 8 is a northern subtropical front that forms the northern boundary of the subtropical halocline in the eastern north pacific it falls some 2 to 3 of latitude north of the subtropical front and is the same front observ

grain fabric of a laboratory antidune the grain fabric of a laboratory antidune composed of coarse to medium grained sand shows a high angle upcurrent imbrication both on the upstream and downstream sides such a grain fabric differs from a normal dune or a megaripple where grain alignment displays an upcurrent imbrication relative to the depositional slope in the foreset lamina and or near parallelism with the slope surface in the toe set lamina recognition of antidunes in ancient rocks is difficult but detailed examination of grain fabric of cross stratification makes it possible to distinguish antidunes or backset bedding from normal dunes or megaripples

tracking hurricane generated storm surge with washover fan stratigraphy we use the stratigraphy preserved in a washover fan to reconstruct the timing or emplacement and environmental conditions along the matagorda peninsula texas during hurricane ike in 2008 washover fan stratigraphy preserves a topset foreset break tfb that rises 0 42 m in elevation as the fan built landward we constrain overwash flow depths to 0 1 0 32 m through deposit sedimentology and tie the rising trajectory of the tfb to rising storm surge water levels measured in the back barrier bay 0 03 m h 1 as the hurricane approached the coast this relation allows us to estimate that the fan took 0 52 0 90 days to build and was finished building before the storm surge peaked this is 15 25 of the 3 5 days of hurricane induced storm surge near the site we show how washover stratigraphy can be used to constrain the timing and amount of sediment redistribution on a coast associated with a hurricane information that is necessary to test and or calibrate existing numerical models that predict shoreline change during hurricanes

environmental response to a large explosive rhyolite eruption sedimentology of post 1 8 ka pumice rich taupo volcaniclastics in the hawke s bay region new zealand abstract the 1 8 ka eruption of the taupo ignimbrite from the taupo volcanic centre in the central north island of new zealand produced a 30 km3 ignimbrite covering an area ca 160 km in diameter centred on lake taupo remobilisation of its pyroclastic detritus triggered major alluviation in the years to decades after its emplacement in the hawke s bay region in the eastern north island three large rivers rise in the ignimbrite impacted mountainous headwaters in areas that were buried by up to 40 m of loose unconsolidated pumiceous material analysis of preserved volcaniclastic sediments along valleys shows that resedimentation occurred in two main stages characterised by contrasting sediment water ratios the first comprised erosion and redeposition of ignimbrite debris by lahars e g debris flows and hyperconcentrated flows the second was marked by decreasing sediment water ratios and the re establishment of braided fluvial systems in the former river valleys as recorded by such deposits as trough planar low angle and antidune cross bedded planar bedded and ripple cross laminated sands and gravels however there is no systematic chronological trend towards lower pumice contents in these fluvial facies four characteristic sets of co occurring lithofacies were produced during the sedimentary response 1 laharic remobilisation association 2 upper flow regime dominated stream flow association 3 lower flow regime dominated stream flow association and 4 lacustrine association individual lithofacies were strongly controlled by the unusual hydrodynamic properties of pumice particularly its low and variable density automated settling tube analysis of water saturated pumiceous sediment confirms that sieve analysis is misleading with respect to the hydrodynamic behaviour of such sediments recasting granulometric data in terms of effective hydraulic grain size shows better sorting of mixed component sediments but statistical sorting and mean grain size parameters do not discriminate between the deposits of tractional and overcapacity parent flows therefore particle behaviour is addressed by using both lithofacies and petrofacies in the description and classification of the remobilisation deposits

the dissolution kinetics of major sedimentary carbonate minerals abstract among the most important set of chemical reactions occurring under near earth surface conditions are those involved in the dissolution of sedimentary carbonate minerals these minerals comprise about 20 of phanerozoic sedimentary rocks calcite and to a significantly lesser extent dolomite are the major carbonate minerals in sedimentary rocks in modern sediments aragonite and high magnesian calcites dominate in shallow water environments however calcite is by far the most abundant carbonate mineral in deep sea sediments an understanding of the factors that control their dissolution rates is important for modeling of geochemical cycles and the impact of fossil fuel co 2 on climate diagenesis of sediments and sedimentary rocks it also has practical application for areas such as the behavior of carbonates in petroleum and natural gas reservoirs and the preservation of buildings and monuments constructed from limestone and marble in this paper we summarize important findings from the hundreds of papers constituting the large literature on this topic that has steadily evolved over the last half century our primary focus is the chemical kinetics controlling the rates of reaction between sedimentary carbonate minerals and solutions we will not attempt to address the many applications of these results to such topics as mass transport of carbonate components in the subsurface or the accumulation of calcium carbonate in deep sea sediments such complex topics are clearly worthy of review papers on their own merits calcite has been by far the most studied mineral over a wide range of conditions and solution compositions in recent years there has been a substantial shift in emphasis from measuring changes in solution composition to determine batch reaction rates to the direct observation of processes occurring on mineral surfaces using techniques such as atomic force microscopy afm however there remain major challenges in integrating these two very different approaches a general theory of surface dissolution mechanisms currently lacking although see lasaga and luttge science 291 2001 2400 is required to satisfactorily relate observations of mineral surfaces and the concentration of dissolved components studies of aragonite high magnesian calcites magnesite and dolomite dissolution kinetics are much more limited in number and scope than those for calcite and provide at best a rather rudimentary understanding of how these minerals are likely to behave in natural systems although the influences of a limited number of reaction inhibitors have been studied probably the greatest weakness in application of experimental results to natural systems is understanding the often profound influences of foreign ions and organic matter on the near equilibrium dissolution kinetics of carbonate minerals

forced regressive deposits of a deglaciation sequence example from the late quaternary succession in the lake saint jean basin quebec canada differentiating between forced regressive deposits from deglacial periods in high latitude domains and forced regressive deposits from the onset of glacial periods in low latitude domains is fundamental for the accurate interpretation of glacial cycles within the geological record and then for the reconstruction of palaeogeography and palaeo climate a forced regressive deglacial sequence is documented from the lake saint jean basin quebec canada in this area the late pleistocene to holocene sediments have recorded the laurentide ice sheet retreat accompanied by the invasion of marine waters laflamme gulf from ca 129 cal kyr bp subsequently fluviodeltaic and coastal prograding wedges were deposited they followed the base level fall due to glacio isostatic rebound this succession representing a transition from glacial to post glacial periods within a previously glaciated area was investigated through recent mapping preserved landforms facies analysis and new optical stimulated luminescence and radiocarbon dates three basin scale geological sections share a common lower part made of isolated ice contact fan deposits overlying bedrock throughout the entire basin ice contact fans are capped by glacimarine muds above fluvial and coastal prograding systems were deposited and evolved through four steps i deltaic systems progressively increased in width ii coastal influence on sedimentation increased iii hydrographic drainage systems became more organised and iv deltas graded from steep gilbert delta to low angle foresets mouth bar delta deposited during the base level fall from glacioisostatic rebound the complete succession has been designated as a single falling stage system tract referred to as a deglacial falling stage system tract it is representative of a deglaciation sequence in areas previously covered by ice during glacial periods i e medium to high latitude domains diagnostic criteria are provided to identify such a deglacial falling stage system tract in the geological record which may aid identification of previously unknown glacial cycles

bathymetric influences upon the character of north pacific fronts 1976 1980 thermal fronts in the north pacific from june 1976 to may 1980 have been mapped at the 300 m level by using temperature data obtained in the region 30 45 n 160 e 160w in the transpac xbt volunteer observing ship program the origins of the paths of the major frontal bands in the study region i e the kuroshio extension the subarctic fronts and the subtropical front appear to be related to the principal bathymetric features of the western mid latitude north pacific i e the shatsky rise the emperor seamount chain and the hess rise in the long term mean the kuroshio extension front at 35 n was observed to have bifurcated at the shatsky rise near 160 e into two bands one band continued northeast along the shatsky rise to 42 n to become the north subarctic front the other band continued zonally eastward where it encountered the emperor seamounts near 36 n 170 e and trifurcated into bands which tracked through passages between the seamounts near 37 n 34 n and 32 n respectively downstream the most northern of these three bands became the south subarctic front near 39 n the middle band continued as the kuroshio extension front at 35 n and the most southern band became the subtropical front near 32 n the middle band tracked north of the hess rise while the most southern band tracked south of the hess rise a near meridional frontal band linked the north and south subarctic fronts in the emperor seamount region near 170 e in the annual mean and individual seasonal mean maps the essential character of topographic influence of the long term mean was observed however the individual frontal bands varied seasonally about the long term mean by 2 of latitude also all four major frontal bands were not always observed and intermittent linkages and additional filaments also occurred

stratigraphic setting of transgressive barrier island reservoirs with an example from the triassic halfway formation wembley field alberta canada established models for landward barrier island migration focus primarily on the preservation pattern of transgressive facies in the shoreface which are typically thin and buried beneath finer grained marine lower shoreface to offshore sediments in contrast transgressive barrier island sandstones in the triassic halfway formation of wembley field in alberta are preserved interbedded with and overlain by backbarrier and nonmarine sediments these transgressive barrier sandstones formed from coalescing washover fans during shoreface retreat and were subsequently abandoned as the shoreline stabilized and resumed progradation the abandoned transgressive barrier sandstones were subsequently blanketed by backbarrier and nonmarine sediments as the coastline continued to p ograde abandoned transgressive barrier island sandstones in the halfway formation are 2 6 m thick up to 2 km wide and form paleocoastline parallel trends tens of kilometers in length the trends define the paleolandward limit of transgressive events the updip pinch out of these sandstones in backbarrier mudstones forms a stratigraphic trap for hydrocarbons in wembley field top seal is provided by nonmarine mudstones and evaporites which buried the abandoned transgressive barrier island the sandstone has porosities and permeabilities averaging 11 and 63 md respectively by using well logs and cores to correlate individual parasequences in the halfway formation to their updip termination it is possible to define the extent of associated marine flooding events and therefore identify exploration targets for abandoned transgressive barrier island sandstones

a consideration of the dune antidune transition in fine gravel hydraulic data defining the dune antidune transition in fine gravel are compared with potential flow theory and information is drawn from published experiments and field based studies attention is given to both transitional bedforms and the development of downstream migrating antidunes in the latter case most data pertain to sand beds and not to gravel empirical data provide some weak support for the theoretical notion that the transition occurs at progressively lower froude numbers at greater relative depths although a critical froude number of 0 84 may reasonably be applied for the beginning of the dune to antidune transformation lag effects and a possible depth limitation ensure that transitional bedforms may persist across a broad range of froude numbers from 0 5 to 1 8 this latter observation has great relevance for palaeohydraulic estimates derived from outcrop data whereas the application of theoretical bedform existence fields based upon potential flow theory to fine gravel was previously purely speculative the addition of experimental and field data to these plots provides a degree of confidence in applying stability theory to practical geological problems for the first time laboratory data pertaining to downstream migrating gravel antidunes are compared with theory these bedforms have been reported from certain experimental near critical flows above sand or gravel beds but have been observed infrequently in natural streams however there are no detailed studies from natural rivers and only a few contentious identifications from outcrops nevertheless the limited hydraulic data conform to theoretical expectations

proxy records of holocene storm events in coastal barrier systems storm wave induced markers abstract extreme storm events in the coastal zone are one of the main forcing agents of short term coastal system behavior as such storms represent a major threat to human activities concentrated along the coasts worldwide in order to better understand the frequency of extreme events like storms climate science must rely on longer time records than the century scale records of instrumental weather data proxy records of storm wave or storm wind induced activity in coastal barrier systems deposits have been widely used worldwide in recent years to document past storm events during the last millennia this review provides a detailed state of the art compilation of the proxies available from coastal barrier systems to reconstruct holocene storm chronologies paleotempestology the present paper aims i to describe the erosional and depositional processes caused by storm wave action in barrier and back barrier systems i e beach ridges storm scarps and washover deposits ii to understand how storm records can be extracted from barrier and back barrier sedimentary bodies using stratigraphical sedimentological micro paleontological and geochemical proxies and iii to show how to obtain chronological control on past storm events recorded in the sedimentary successions the challenges that paleotempestology studies still face in the reconstruction of representative and reliable storm chronologies using these various proxies are discussed and future research prospects are outlined

horizontal laminae formed under upper flow regime plane bed conditions horizontal laminae have been examined from the fluvial whirlpool sandstone silurian modern intertidal sand bars and a flume textural variations which define laminae were determined by averaging all grain long axes lengths in contiguous rectangular areas 2 mm wide by 0 2 mm high up through thin sections cut normal to bedding textural laminae were identified as fining upward fu and coarsening upward cu from trends seen in plots of average grain long axes versus height above an arbitrary datum fu and cu laminae occur in random sequence and have an average thickness of less than 1 mm with cu laminae being slightly thinner than fu laminae heavy mineral sheets which appeared as continuous layers in outcrop and in trenches consistently occurred in cu laminae lateral correlation diagrams constructed across thin sections showed that some textural laminae were continuous for the 15 mm over which measurements were made while others pinched out laterally across the measured distance heavy m