reflection and refraction seismics in areas of complex geology an example in the northern apennines an experimental survey employing refraction wide angle reflection seismic techniques dss deep seismic soundings was carried out in the northern apennines north italy the main objective of the experiment was the application of dss to better define the structure of the upper crust down to about 15 km depth in the crucial alps apennines boundary zone a second objective was to understand the potential of dss as a complementary tool in areas of complex geology where the results of near vertical reflection nvr are generally poor the results of the experiment show that dss if properly planned can continuously follow deep markers and therefore impart a greater significance to faint and discontinuous nvr as well as data on the p wave velocity of the seismic units

internal structure of aeolian dunes in abu dhabi determined using ground penetrating radar a ground penetrating radar survey of aeolian dunes in the al liwa area of abu dhabi reveals a variety of dipping reflectors which are interpreted as primary sedimentary structures the interpretation of the radar profiles has been confirmed by bulldozing trenches through the study area and comparing logged sections in the trenches with the radar profiles nnw sse orientated radar profiles approximately parallel to the prevailing wind direction show two sets of dipping reflectors which are interpreted as sets of cross stratification and second and third order bounding surfaces radar profiles orientated wsw ene across the prevailing wind direction are dominated by concave up reflectors which are interpreted as trough shaped scours and sets of trough cross stratification produced by oblique progradation of barchanoid dunes nested troughs with small sets of trough cross stratification within larger troughs may be due to reactivation following wind reversal or the superposition of small dunes on larger dunes and the fill of large dune troughs by smaller dunes convex upwards reflectors are interpreted as linear spurs on the convex portions of sinuous dunes or erosional remnants between troughs overall there is a tendency for the larger second order bounding surfaces to dip downwind which confirms brookfield s ideas of the relative migration paths of dunes and draa

reconstructing paleoenvironment eruption mechanism and paleomorphology of the pliocene pula maar hungary abstract pula maar is a partially eroded pliocene maar diatreme volcano part of the mio pliocene bakony balaton highland volcanic field the surficial remnant of the maar diatreme volcano consists of 1 a distinct depression with a thick post eruptive lacustrine alginite sediment infill interbedded with coarse grained volcaniclastic sediments 2 a narrow marginal zone inside the depression consisting of primary pyroclastic rock units that are interpreted to be partly collapsed and subsided blocks of entire sections from the tephra ring formerly surrounding the maar crater depression and 3 coarse grained volcaniclastic debris flow deposits closely associated with the collapsed primary pyroclastic rock units in the marginal zone the presence of coherent lava rocks below the crater fill units their distribution pattern and their association with scoriaceous beds indicate that after the maar diatreme forming phreatomagmatic explosive activity small 100 m scale scoria and or spatter cones erupted in the maar crater these cones are the likely source of the lava flows that partially filled the maar crater basin the widespread dm to m thick basaltic sand and or silt units at the base of the post eruptive crater filling sedimentary succession are interpreted to be reworked volcaniclastic material from the intra maar scoria spatter cones as well as from the tephra ring based on comparative analyses of 53 core descriptions this study reveals that the original maar crater basin was larger than previously suggested the deep level of the maar crater is reconstructed to be a northeast southwest elongated depression currently forming a c 50 m deep basin geomorphological considerations suggest that most of the phreatomagmatic pyroclastic rocks are composed of base surge and tephra fall deposits around the deep maar depression these allochthonous rock units form a 50 400 m wide zone of proximal tuff ring sequences the formation of this zone is inferred to be a result of a combination of syn eruptive subsidence due to mass deficit in the rigid triassic dolomite basement caused by the phreatomagmatic explosions as well as post eruptive subsidence of the crater and diatreme filling successions due to diagenetic compaction the facies in the centre of the maar lake is a soft laminated alginite mainly botryococcus colonies diatom frustles calcium carbonate crystals clay minerals in the section exposed in the pula open cast mine a single turbiditic layer is present this layer originated in a landslide which possibly could have been caused by either syn eruptive earthquake and or a sudden post eruptive subsidence event of the diatreme fill

the possible role of humans in the early stages of machair evolution palaeoenvironmental investigations in the outer hebrides scotland abstract low altitude sandy plains machair are a distinctive feature of the atlantic coasts of the scottish outer hebrides they formed as a result of shoreward movement of sediment consequent upon a rise in holocene sea levels during the long period over which machair has been forming the earliest date proposed for their human occupation is the neolithic the natural origins of the machair are not disputed but examination of deposits at sites in the islands of benbecula and grimsay encourages us to advance a possible anthropogenic role in the process of machair development and also to suggest that human involvement may date from the mesolithic period pre 5000 bp ca 5730 cal bp a time for which archaeological evidence is lacking from the outer hebrides the presence of charcoal might suggest that burning of the vegetation cover of the machair was an additional factor to the supposedly dominant marine and aeolian processes in sand mobility removal of shrub vegetation may also have left sand surfaces open to deflation there remains a difficulty in separating natural from human causes in investigations of long term coastal evolution

high resolution analysis of submarine lobes deposits seismic scale outcrops of the lauzanier area se alps france abstract the lauzanier area represents the northernmost extension of the annot sandstone series and contains deposits between 650 and 900 m thick this basin was active from upper bartonian or lower priabonian to early rupelian it is composed of two superposed units separated by a major unconformity the sediment supply is due to channelled flows coming from the south flow processes include mass flow to turbidity currents the size of the particles and the absence of fine grained sediment suggest a transport over a short distance the lower unit is made of coarse grained tabular beds interpreted as non channelled lobe deposits the upper unit is made of massive conglomerates interpreted as the channelled part of lobes these lobe deposits settle in a tectonically confined basin according to topographic compensation that occurs from bed scale to unit scale the abrupt progradation between the lower and the upper unit seems related to a major tectonic uplift in the area this uplift is also suggested by a change in the petrographic nature of the source and an abrupt coarsening of the transported clasts this field example allows providing high resolution analysis for depositional sedimentary sequences of terminal lobe deposits in a coarse grained turbidite system the outcrop analysis shows the lateral evolution of deposits and the system progradation allows a longitudinal analysis of facies evolution by superposing on the same outcrops the channelled lobe system and the non channelled lobe system these results of high resolution outcrop analysis can be extrapolated to results obtained on sedimentary lobes in recent deep sea turbidite system that are either restricted to cores or with a lesser resolution seismic

the interaction of ash flows with ridges using both laboratory experiments and theoretical models we examine the different flow regimes that may develop when an ash flow encounters a ridge for very small ridges all the flow may pass over the ridge for intermediate size ridges the flow may be partially blocked with a fraction of the flow reflected upstream as a travelling bore in this case the remainder of the flow which does pass over the ridge is hydraulically controlled at the ridge crest finally if the ridge is sufficiently high then the flow will be totally blocked new laboratory experiments show that the sedimentation patterns associated with these flow regimes may be very different most importantly flows that involve partial blocking and the formation of upstream propagating bores display enhanced sedimentation upstream of the ridge analogous to valley ponded and caldera fill deposits in contrast under some circumstances if the flow is able to scale a ridge the deposit may be relatively unaffected by the presence of the ridge the minimum ridge height that leads to total blocking of the flow increases with mass eruption rate and has a complex variation with distance from the source in a one dimensional channel the minimum ridge height that causes blocking increases with distance downstream this is because the flow becomes less dense through sedimentation of particles and entrainment of air and so requires less energy to scale a ridge of a particular height in axisymmetric flow the minimum ridge height initially decreases with distance downstream as the flow spreads radially but subsequently increases as the flow becomes less dense through sedimentation and entrainment a new quantitative model of dilute ash flows propagating over ridges indicates that flows with mass fluxes in excess of 108 109 kg s can partially scale barriers as high as 1000 m at distances of tens of kilometres from the source whereas smaller flows are likely to be totally blocked by such an obstacle our results shed new insight on the possible long range transport mechanism of several large flows including the ata fisher and aniakchak pyroclastic flows

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast

an experimental investigation of density stratified inertial gravity currents turbidity currents and pyroclastic density currents may originate as stratified flows or develop stratification during propagation analogue density stratified laboratory currents are described using layers of salt solutions with different concentrations and depths to create the initial vertical stratification the evolving structure of the flow depends on the distribution of the driving buoyancy between the layers b proportional to the layer volumes and densities and their density ratio q when the lower layer contains more salt than the upper layer and so has a greater proportion of the driving buoyancy b 0 ae5 this layer travels to the nose of the current by mixing into the back of the head along the body wake density interface to produce a homogeneous flow q fi 1 or overtaking leading to streamwise stratification q fi 0 timescales describing the mixing between the layers and the streamwise separation of the layers are used to understand these flow behaviours and are in accordance with the experimental observations distance time measurements of the flow front show that strongly stratified flows initially travel faster than weakly stratified flows but during their later stages they travel more slowly in natural flows that are stratified in concentration and grain size internal features such as stepwise grading gradual upward fining and reverse grading could be produced depending on b and q stratification may also be expected to affect interactions with topography and overall fan architecture

convolute laminations and load structures in turbidites as indicators of flow reflections and decelerations against bounding slopes examples from the marnoso arenacea formation northern italy and annot sandstones south eastern france abstract this work discusses the significance of particular types of soft sediment deformations very common within turbidite deposits namely convolute laminations and load structures detailed facies analyses of the foredeep turbidites in the marnoso arenacea formation northern italy and annot sandstones south eastern france show that these deformational structures tend to increase near morphological obstacles concomitantly with contained reflected beds the lateral and vertical distribution of convolute laminae and load structures as well as their geometry has a well defined depositional logic related to flow decelerations and reflections against bounding slopes this evidence suggests an interaction between fine grained sediment and the presence of morphologic relief and impulsive and cyclic wave loadings which are produced by flow impacts or reflected bores and internal waves related to impinging bipartite turbidity currents

the relationship between seismic velocity and density in the continental crust a useful constraint summary plots of seismic velocity and density of rock samples show that a range of densities is possible for rocks of each seismic velocity and vice versa although a single linear relationship is often assumed in crustal gravity calculations because of the scatter whenever rocks of known seismic velocity are converted to density using this relationship a reduction is made to the resolving power of the resulting gravity calculation if these rocks reach thicknesses of more than a few kilometres then the uncertainties become significant when compared with the size of commonly observed gravity anomalies examples are considered from the north sea mississippi and carolina trough it is concluded that the use of a seismic velocity measurement as the only indication of rock density does not provide a useful constraint when attempting to reproduce observed gravity variations an appropriate model for isostatic compensation is probably the most important factor for successful predictions of crustal structure on the basis of gravity data

contrasting styles of shelf sediment transport and deposition in a ramp margin setting related to relative sea level change and basin floor topography turonian cretaceous western interior of central utah usa abstract the turonian lower ferron sandstone and juana lopez members of the mancos shale in the western interior foreland basin form a series of regressive shoreface to shelf depositional complexes sourced from the sevier fold thrust belt to the west continuous dip parallel outcrop exposures around the northern and eastern edges of the tertiary san rafael anticline sra in central utah provide an insight into the origins of anomalous marine mudstone encased sandstones lower ferron strata consist of both coarsening and thickening upward and sharp based shoreface successions interpreted to have been deposited as sequential highstand and falling stage systems tracts overlying these shallow marine deposits is a surface that marks sediment bypass that is correlated down dip into coarse grained cross bedded sandstones interpreted as the deposits of channelised turbidity flows these turbidites are considered to be the products of sustained hyperpycnal flows exiting rejuvenated lowstand rivers based on sustained flow indicators such as dune scale cross bedding absence of genetically related slumps and delta front deposits in up dip areas surfaces of sediment bypass coarser grain sizes than the underlying shoreface deposits and regional palaeogeography the flows are interpreted to have been ignitive in proximal areas down a tectonically induced slope in the uplifted area of the farnham dome the change in depositional style from falling stage to lowstand systems tracts is attributed to increased rates of sediment supply to the shoreline promoting hyperpycnal flows a flooding surface caps the interval and separates the lower ferron sandstone from the overlying juana lopez member this interval in contrast consists only of heterolithic parallel and ripple laminated graded sandstone mudstone couplets interpreted to have been deposited by turbulent storm induced geostrophic flows the couplets are arranged into bundles and are interpreted as parasequences which in turn are arranged into a progradational parasequence set deposited during a period of sea level highstand divergent sole mark and bedform palaeocurrents from both members suggest slight eastward deflection of the turbulent flows off the proto sra further evidence for this topography is inferred from an absence of turbidites along the western side of the structure the inferred influence of local basin floor structures on sedimentation of these units has important implications for structural models for this basin for generalized sequence stratigraphic models applied to ramp type foreland basin sequences and for elucidating the origin of anomalous marine mudstone encased sandstone bodies

sand drift and soil formation along an exposed north atlantic coastline 14 000 years of diverse geomorphological climatic and human impacts this paper sets out the history of aeolian deposition and soil formation over the last 14 15 000 calendar years along the exposed and gale prone atlantic coastlines of the southern isles of the outer hebrides of scotland detailed palaeoenvironmental interpretation and chronological control have been provided by field mapping soil micromorphological analyses and radiocarbon and optically stimulated luminescence osl dating programmes two dominant types of aeolian sands are described in this region quartzose sands are shown to originate mainly as periglacial wind blown sands derived from glacial and periglacial deposits of late devensian age which were formerly exposed on the present continental shelf this aeolian deposition did however continue into the early holocene with re working perhaps by slope wash taking place as recently as the 4th millenniumbp quartzose sands mantle valley floors and hillslopes by the end of the devensian and early holocene a variety of soil types with extensive horizonation had developed upon them including podzolic brown earths peaty gleys and peat soils radiocarbon and osl dating demonstrate that the carbonate sands of the machair sand sheets which characterize the present atlantic shorelines began to accumulate very early for a european shoreline from approximately 8700 calendar years ago on benbecula and north uist whereas further south deposition began later osl dating suggests that non sequences and diastems are common in greater part these machair sand sheets are best interpreted as a composite of separate slivers of sand reflecting small scale and local episodes of sand drift rather than distinct layers of region wide distribution which might reflect past major storms or significant palaeoclimatic fluctuations the new evidence presented here provides little support for the following explanatory geomorphic or stratigraphic models which have previously sought to explain the development of these coastal machair landscapes continuous development layer cake or step wise prograding coastal barrier qualified support is given for the explanations that emphasize i the long term spasmodic input and re cycling of sands and ii that the present smoothed landscapes and distinctive machair grassland vegetation are essentially recent in age and reflect the interactions of natural and human processes in a stormy environment characterized by re working widespread layers of thick organic materials within the carbonate sands in the study area which have previously been regarded as dune palaeosols dating to the bronze age and iron age are suggested by soil micromorphological analysis to be in significant part anthropogenic in origin they are organically enriched layers or midden soils the consequence of human activities notably the disposal of organic wastes and other forms of soil modification during times of significant settlement in these coastal sands these periods of relatively intense human activity are therefore shown to be associated at least locally with periods of soil formation and stability not universal instability and dune drift along these shorelines in general these extensive layers of midden soil do not necessarily imply periods of decreased storminess relatively widespread soil formation in these coastal dunes did however take place in the period between 400 and 100 years ago essentially within the period of increased storminess associated with the little ice age it is suggested that at some point s within the following periods of time broadly defined in calendar yearsbp notable sand drift affecting the quartzose sands the carbonate sands or both took place within the study area 13 700 13 000 11 000 10 500 9000 8300 7500 7000 6900 6400 5800 4200 one of the most notable episodes of drift in the outer hebrides as well as elsewhere on the coast of north west europe 3800 3300 1700 1300 600 200 with individual great storms being recorded in the 17th and 18th centuries and 100 present day limited drift associated with machair stratification

an approach to mapping buried prehistoric palaeosols of the atlantic seaboard in northwest europe using gpr geoarchaeology and gis and the implications for heritage management abstract widespread layers of well preserved organically and archaeologically rich palaeosols dating to the bronze age and iron age are known from across the atlantic seaboard of scotland including the western isles orkney and shetland the survival of these soils has been facilitated by an overburden of aeolian sand forming dunes above them whilst these soils display archaeological importance they are constantly under threat from erosion through storm damage due to their exposed coastal position this presents certain challenges with regard to heritage management since their extents are largely unknown normally only being identified when exposed by wind and storm erosion consequently following such damage mitigation can only be reactionary in response to archaeological deposits being uncovered and left open to threat without accurately mapping the extent of these important deposits archaeological landscape management is compromised this paper presents a case study aimed at enabling proactive management of these deposits through rapid three dimensional mapping undertaken using a combination of borehole calibrated gpr survey and gis modelling the results demonstrate how effective baseline data can be generated to highlight areas of greater or lesser risk thereby providing the potential for quantifying and predicting the effects of damage from future storm events

an acadian mountain front in the english lake district the westmorland monocline the structure of the southern and central english lake district is that of a southeast facing monocline named here the westmorland monocline this 10 km wide zone of highly cleaved southeast dipping rocks separates gently dipping poorly cleaved borrowdale volcanic group to the north from extensively folded but regionally subhorizontal windermere group foreland basin rocks to the south the monocline formed early in the local acadian deformation sequence and accommodates at least 8 km of uplift it coincides with the steep concealed margin of the lake district batholith a major northwest dipping shear zone is revealed in the deepest levels now exposed within the monocline in the skiddaw group rocks of the black combe inlier the monocline has the characteristics of a mountain front providing significant tectonic elevation across a foreland dipping panel of rocks with no hinterland dipping thrust visible at the surface we interpret the uplift as the consequence of a southeast vergent thrust with a gently northwest dipping ramp beneath the central lake district continuing southeastwards as a flat detachment beneath the windermere group a displacement up the ramp of about 20 km is accommodated by backthrusting within the monocline and by shortening within the windermere group of the hangingwall southeast of the monocline the tip lies beyond the limit of the lower palaeozoic inlier beneath carboniferous cover

provenance stratigraphic architecture and hydrogeologic influence of turbidites on the mid ocean ridge flank of northwestern cascadia basin pacific ocean abstract the northwestern edge of cascadia basin north pacific ocean is unusual because late pliocene to holocene turbidites lap onto juvenile oceanic crust of the juan de fuca ridge subsidence of the ridge flank combines with irregular westward progradation of the turbidite facies to create a stratigraphic section that coarsens and thickens upward the sand provenance is mixed individual turbidity currents have funneled into the area through several shelf slope and abyssal floor conduits including vancouver valley juan de fuca channel barkley canyon and nitinat canyon local bathymetric blockage deflection and reflection of flow paths by basement relief remobilization by intrabasinal submarine slides and debris flows episodic channel switching and sporadic overbank flooding have combined to produce erratic recurrence intervals for the turbidity currents only the tallest basement highs have remained isolated from turbidite deposition during the last 500 000 years spatial and temporal differences in sediment accumulation are important because they modulate the three dimensional responses of compaction and consolidation those changes in physical properties govern where and when hydraulic communication with the underlying basement shuts down the basal hemipelagic layer of cascadia basin transforms to an effective hydrologic seal seepage rates 1 mm yr once the sediment basalt interface is buried by 100 150 m of strata rapid accumulation of turbidites therefore accelerates the hydrogeologic conversion of igneous basement from open to sealed

depositional processes of uniform mud deposits unifites hedberg basin northwest gulf of mexico new perspectives structureless mud deposits unifites are a common depositional phenomenon in the intraslope basins of the continental slope of the northwest gulf of mexico high resolution acoustic data and long sediment cores from hedberg basin middle slope were used to provide a better insight into the origin of these enigmatic depositional units the unifite occurring in hedberg basin is structureless under visual observations but x ray radiographs reveal that it consists of three divisions 1 u1 division representing waning sequences of fine grained mud turbidites 2 u2 division characterized by faint normally graded mud layers with occasionally wispy silty interlaminae and 3 u3 division characterized by a uniform appearance with no obvious sedimentological structures other than a faint banding of slightly siltier and slightly more clayey layers high resolution geophysical data reveal that there is no connection between intrabasinal sediment failures and the occurrence of unifites we suggest that unifites have resulted from the deposition of a long lasting 1 53 months pulsating showing internal surges fine grained turbidity current dated at 28 629 ka that originated from the flow transformation of a series of massive sediment failures on the shelf edge and or upper continental slope the fine grained nature of the turbidity current is probably caused by the depositional segregation of the flow by depositing its coarsest material in intraslope basins in more proximal locations we propose that the uniform texture of the unifite is attributed to the development of a stratification interface lower stratified layer generated by the continuous introduction of a turbulent sediment cloud in the intraslope basins the lowest two unifite divisions are considered to develop prior to and during the development of the stratified layer

topographic controls on the development of contemporaneous but contrasting basin floor depositional architectures abstract sediment laden gravity driven flow deposits on the basin floor are typically considered to form either discrete lobes that stack compensationally or packages of laterally extensive beds commonly termed sheets these end member stacking patterns are documented in several basinfills however whether they can coexist in a single basin or there are intermediate or transitional stacking patterns is poorly understood an analysis of depositional architecture and stacking patterns along a 70 km dip oriented transect in the upper broto turbidite system jaca basin south central pyrenees spain which displays disparate stacking patterns in contemporaneous strata is presented proximal and medial deposits are characterized by discrete packages of clean sandstones with sharp bed tops which exhibit predictable lateral and longitudinal facies changes and are interpreted as lobes distal deposits comprise both relatively clean sandstones and hybrid beds that do not stack to form lobes instead localized relatively thick hybrid beds are inferred to have inhibited the development of lobes hybrid beds developed under flows which were deflected and entrained carbonate mud substrate off a carbonate slope that bounded the basin to the south evidence for this interpretation includes 1 divergent paleoflow indicators and hummock like features in individual beds 2 a decrease in hybrid bed thickness and abundance away from the lateral confining slope 3 a carbonate rich upper division not seen in more proximal turbidites the study demonstrates the co occurrence of different styles of basin floor stacking patterns in the same stratigraphic interval and suggests that characterization of deep water systems as either lobes or sheets is a false dichotomy

oblique reflection of turbidity currents turbidity currents meeting obstacles for example the margins of a confined basin are subject to reflection the consequent change in flow direction is expressed in the sequence of depositional structures of the resulting bed of sediment putative examples of orthogonal reflection have been described based on 180 opposed current directions we present field evidence for the more general case of oblique reflection of turbidites and we report the results of flume experiments indicating a mechanism involving generation of internal solitary waves at an oblique ramp these propagate normal to the ramp regardless of the angle of incidence flow directions in reflected turbidites may indicate the orientation of reflecting surfaces such as basin margin slopes and thus may be of considerable help in paleogeographic and tectonic reconstructions

factors influencing the deposit geometry of experimental turbidity currents implications for sand body architecture in confined basins two sets of scaled laboratory experiments were performed to examine the effect of flow volume flow density and grain size distribution on the transport efficiency of turbidity currents the experiments employed two sediment analogues ballotini and silica flour intended to model medium to coarse grained sand and mud respectively in the first set of experiments each parameter was varied to examine its effect upon deposit geometry increases in the initial flow density volume and proportion of fines had the effect of increas ing the amount of sediment that was transferred to the floor of the experimental tank by the turbidity currents increase of each of these parameters has a characteristic effect on the three dimensional of the deposit the deposits of large volume flows are elongate and those of fines rich flows are broad increase of flow density increases the initial potential energy of the flow thus increasing the runout distance increase of the initial density beyond a sediment concentration of 13 by mass results however in a reverse of the geometrical trend of deposit elongation possibly because of turbulence suppression at high densities increase of flow volume also increases the initial potential energy and reduces the rate of velocity decrease due to gravitational spreading increase in the proportion of fines leads to main tenance of negative buoyancy as the fine fraction remains suspended until the flow has virtually come to rest it also decreases the settling velocity of the coarser fraction and thus delays its sedimentation the second set of experiments was performed to investigate the influence of flow efficiency on the interaction of turbidity currents with topography a single arcuate obstacle was placed in the path of the flows in successive experiments flow efficiency was increased by progressively increasing the proportion of fines silica flour both the proportion of sediment reaching the obstructing topography and the proportion of it able to surmount the topography increased as flow efficiency increased thus flow effi ciency may determine whether or not an enclosed basin hosts deposits whose geometry has been affected by the confinement and may also determine the relative effectiveness of the topography in confining inbound turbidity currents and thus trapping their sediment load

interaction of gravity flows with a rugged mid ocean ridge seafloor an outcrop example from macquarie island rugged bathymetry along slow spreading mid ocean ridges has the potential to impinge a strong control on gravity flows derived from oceanic fault scarps sedimentary lithofacies from the macquarie island ophiolite supports this hypothesis by displaying systematic variations that correspond with volcanic substrate differences and proximity to rift related faults pillow basalt terranes are associated with tightly confined bedrock corridors that funnel gravity flows into one direction vertical lithofacies variations formed from high density to low density turbidity currents record successive fill stages of the corridor axis during initial stages tight confinement in the axis suppressed flow dilution and fluid turbulence with continued corridor axis filling more dilute gravity flows predominated and formed lateral gradations from axial coarse grained turbidites into thinly interbedded overbank lithofacies along corridor margins these gravity flow lithofacies converge into very thin muddy condensed intervals along inter corridor highs where significant bottom current reworking occurred conversely partly confined tabular basalt floored basins promoted lateral expansion and dilution of gravity flows throughout the duration of basin filling variable paleocurrent indicator directions record multiple reflections of single gravity flow events off basin bounding fault barriers coarsening upward trends in these partly confined basins from thinly interbedded pelagic chert and ripple bedded sandstones up into stacked turbidites preserves the ponding of sediment starved submarine fans in general these ponded basins preserve the fine grained distal ends of a gravity flow continuum from coarse grained fault proximal en masse failures and cohesionless debris flows into medial high density turbidity flows and distal dilute turbidity flows

deflection versus reflection of sediment gravity flows in the late llandovery rhuddnant grits turbidite system welsh basin the rhuddnant grits turbidite system was deposited in an elongate fault bounded trough an apparently ideal locality for the reflection of sediment gravity flows as solitons however 280 palaeocurrent readings from turbidite sandstones do not show the expected high angle discrepancies between palaeocurrent directions from sole structures and those from cross lamination palaeocurrents orthogonal to the bounding lineament are not generally observed instead there is a gradual progressive anticlockwise deflection of the currents with distance from source this may be explained by banking of the currents against an intrabasinal slope by the coriolis effect or by a combination of the two processes

impact of synsedimentary metre scale normal fault scarps on sediment gravity flow dynamics an example from the gres d annot formation se france abstract synsedimentary faults result in the direct interaction between tectonic and sedimentary processes at similar spatio temporal scales sedimentological analysis of sediment laden gravity flows in the northern part of the gres d annot formation sanguiniere sub basin col de la moutiere tete ronde has revealed the presence of fault scarps of metre scale height these synsedimentary fault scarps were sufficient to disturb the sediment gravity flow dynamics resulting in i a strong variation of the erosive behaviour of a concentrated flow and ii the transformation of a strongly stratified laminar hyperconcentrated flow into a turbulent flow in short distance less than 500 m these disturbances develop without the flows being deviated by the fault scarps but produce great facies heterogeneity the least homogeneous facies mixing sand and clay being localized on the upstream obstacle side the most homogeneous massive sand downstream

interplay between river discharge and topography of the basin floor in a hyperpycnal lacustrine delta basin floor topography influences the flow path of hyperpycnal plumes and delta morphology during progradation of the red river delta in lake texoma usa the red river discharge is typically a hyperpycnal plume due to elevated total dissolved solids because the river plume is a bottom hugging hyperpycnal flow lake bathymetry and topography strongly influence deposition and subsequent delta morphology in addition to elevated total dissolved solid concentrations compared with lake texoma water the density contrast of the red river outflow is increased by high suspended sediment concentrations during high discharge events steep lateral slopes in the lake texoma basin deflect hyperpycnal river plumes and subsequently change the delta progradation direction before the delta reaches the opposite bank of the lake analysis of multi temporal aerial and satellite images indicates that the hyperpycnal delta follows the steepest lake bottom gradients corresponding to the pre impoundment river thalweg i e bypassing shallow parts of the lake an analytical model for the hyperpycnal plume trajectory indicates plume deflection during low discharge or high discharge events towards the deepest part of the basin the magnitude of plume deflection is a function of river discharge and basin margin gradients plume deflection can vary between 10 and 80 from the channel axis towards the old river thalweg the high deflection appears in the case of maximum basin side gradients of 12 8 and in conditions of low river discharge during low discharge periods the red river delta builds a lobate shape with multiple terminal distributary channels whereas during high discharge periods the red river delta builds an elongate shape with a single large distributary channel the elongate morphology of the delta is formed through the development of a single distributary channel and abandonment of the other distributaries therefore the lobate shaped delta is expected to be preserved in the rock record

the structure of the upper crust in the alps apennines boundary region deduced from refraction seismic data abstract analysis of data gathered during the 1983 european geotraverse southern segment egt s 83 experiments in the region extending from the emilia liguria apennines to the western alpine arc together with data from seismic profiles in the northwestern apennines accumulated within the framework of the alps apennines orogene study group indicate new details on the structure of the upper crust east and west of the alps apennines boundary the main results of this analysis centre on two areas in the piedmont tertiary basin we could determine the depocenter configurations of the 6 7 km thick terrigenous sequence and differentiate the tectonic units in the piedmont alpine and the ligurian apennine domains within the basement in the other area the insubric domain underneath the ligurian nappes of the northern apennines we found indications of tectonic doubling within the terrigenous carbonate sequence in which thrusting attenuates towards the underlying basement detected at a depth of 12 15 km in addition we found that on a line from the emilia apennines to the monferrato hills displacement of the ligurian nappes over the insubric domain diminishes to nearly one third its original extent

ground penetrating radar of northern lacustrine deltas ground penetrating radar gpr was used in several selected deltaic sedimentary environments to better understand subsurface stratigraphy and reconstruct former depositional environments the profiles provide high resolution continuous subsurface data on facies thickness and depths orientation of major sedimentary structures postdepositional failure planes and depth of peat deposits field experiments were carried out on six river deltas records from four of the deltas exhibit sedimentary facies a record from one delta shows a possible slump and records from another delta reveal the thickness and stratigraphic relationships of peat deposits the delta types are i sandy wave influenced ii sandy immature wave influenced steeper middle and lower shoreface iii sandy braided and iv gravelly fan foreset in areas of limited subsurface control stratigraphic logs from drill core cutbank exposure or geophysical logs radar profiles can provide big picture perspectives of the subsurface

turbidite variability and architecture of sand prone deep water slopes eocene clinoforms in the central basin spitsbergen abstract the architecture and turbidite variability within six wedge shaped downslope thinning sand prone slope accumulations are documented from eocene shelf margins on spitsbergen the central basin formed as a small foreland or piggy back basin and the studied turbidites accumulated mainly on the slope portion of sand prone clinoforms that developed during depocenter migration and infilling of the basin the shelf margin clinoforms have amplitudes minimum water depths from 100 to 350 meters and their shelf slope and basin floor segments are well imaged and can be walked out along many of the mountainsides only a small percentage of the clinoforms are sand prone and these developed when sea level occasionally fell to or below the shelf edge of the sand prone clinoforms some had their sand budget partitioned mainly out onto the basin floor basin floor fans but most trapped the sand on the slope only the latter are now visible as downslope thinning wedges some 2 5 3 5 km in downdip extent the turbidites within this type of clinoform have been examined and classified the lower slope to base of slope segment of the studied clinoform complexes are dominated by lobes consisting of broad shallow channels and sheet like turbidites becoming heterolithic and muddy out on the basin floor beds on the lower slope vary from thick up to 4 5 meters ungraded or laminated sandstones to thinner ungraded sandstones with coarse cappings the middle slope segment of clinoform complexes is dominated by narrow channels chutes that feed downslope to progradational chute mouth lobes chutes contain ungraded and laminated sandstone beds up to 3 m thick whereas the chute mouth lobes show alternations of thinner ungraded to laminated or rippled sandstones these lobes become more heterolithic and muddy downslope the shelf edge to upper slope segment of clinoform complexes is dominated by upward coarsening and thickening sheetsands of steep fronted shelf edge deltas the sandsheets of the delta front can be traced updip into mouth bar and distributary channel sandstones it is argued that shelf margin accretion represented by the sand prone slope wedges was achieved mainly by sand laden currents that flooded from the shelf edge as hyperpycnal flows this hypothesis is supported by 1 the direct connection between channel and mouth bar systems at the shelf edge and the turbidites of the slope lobes 2 the systematic progradational character of the slope lobes 3 the absence of large scale slump scars gullies or canyons on the slope and 4 the dominance of a type of turbidite that implies deposition from sustained flow detailed examination of the architecture of one of the slope wedges shows that there are unconformities developed within the stratigraphy below the shelf edge and that these erosional terraces beheaded the deltas perched on the uppermost slope the erosion surfaces indicate fall of sea level to this position despite the magnitude of this fall up to 80 meters the lack of canyons on the slope prevented the construction of basin floor fans such falls of sea level on non canyoned slopes simply promote sand prone accretion of the shelf margin

hydrological effects of buried palaeosols in eroding landscapes a case study in south africa abstract palaeosols have long been studied as valuable records of past climate and landscape changes the influence of palaeosols on the functioning of present day landscapes is receiving closer attention due to the relevance of palaeosols on long term hydrological processes and the future hydrological and erosive response of catchments this study describes a sequence of interbedded colluvial sedimentary deposits and buried palaeosols exposed by gully erosion in the drakensberg escarpment foothills in kwazulu natal province south africa model simulations are presented that explore present day hydrological effects of pedogenetic and textural differentiation under conditions of groundwater lowering caused by gully erosion at 14 sites the results suggest that the colluvial deposits and palaeosols cause a significant increase in total annual drainage from most of the 14 studied sites compared with similar sites without texturalor structural differentiation in the simulations sediment deposition not palaeosol formation has the most profound influence on the present day hydrological functioning of the catchment a true deposystem service effects of the limited palaeosol development on soil water holding capacity and actual soil water storage appear to be negligible

foreland basin development and tectonics on the northwest margin of eastern avalonia the early palaeozoic convergence of avalonia and laurentia created a foreland basin at the suture zone of the former lapetus ocean sedimentological and stratigraphic evidence of shallowing and contemporaneous shortening suggests that the southern part of the basin the windermere group became detached from its basement in the late ludlow and began to invert the detachment beneath the basin rooted into a northwest dipping mid crustal thrust system contemporaneous uplift to the north of the late silurian basin involved shortening of the avalonian foreland basement by thrusting basin inversion occurred ahead of a southeastward advancing mountain front we postulate a foreland southeast prograding sequence of thrusting through the ludlow in the lake district the basin continued to migrate onto the avalonian foreland through the early devonian ahead of an advancing orogenic wedge finally coming to a stop in the emsian

experimental and numerical study of topographic effects on deposition from two dimensional particle driven density currents abstract topographic effects on deposition from particle driven density current were investigated the laboratory experiments were carried out on topography consisting of a ramp and a series of humps the results show a localized increase in deposit distribution downstream of the slope break and on the upslope of a hump a numerical model is developed to predict the topographic effects on deposit distribution the model based on layer averaged navier stokes equations is applied to the experiments and the process of the topographic influence is analyzed the preferential deposition downstream of the slope break is interpreted to result from deceleration of the flow which increases deposit distribution through loss of capacity of the flow and longer duration of the flow passage the former effect is more influential than the latter while additional effects of a hydraulic jump may be imposed increased deposit on the upslope of a hump is attributed to partial blocking of the flow at the hump crest as well as to the differential deposition due to deceleration on the upslope

the structure and kinematics of substrate entrainment into high concentration sandy turbidites a field example from the gorgoglione flysch of southern italy sandy turbidites commonly show evidence for significant dynamic coupling with their substrate the resulting deformation can be described using structural kinematic methods linked to palaeoflow indicators to better understand the links between flow and entrainment processes a field example from the syn orogenic gorgoglione flysch a succession of upper miocene turbidites deposited into a deforming array of thrust top basins in the southern apennine thrust belt italy is described the succession contains metre scale packages of alternating sandy turbidites and shales but is notable for containing 100 m thick massive sandbodies these are structureless apart from sporadic horizons of aligned mud clasts commonly the substrate beneath the massive sandbodies is deformed with minor folds and thrusts verging in the direction of palaeoflow determined from tool marks and flutes at the base of these sandbodies structural studies from the base of a selected massive sandbody have identified that the substrate mud has been injected upwards with flames sheared over in the direction of palaeoflow thus the substrate has deformed and become entrained during emplacement of the massive sandy body at some locations the substrate can be traced into the overlying deposit with substrate clay beds becoming boudinaged and entrained into the sandbody analysis of the orientation of the mud clasts indicates that this bed disruption and incorporation into the sandy massive bed turbidite was an organized viscous process these features indicate that significant shear stress was partitioned out of the flow and onto the substrate the incorporation and disruption of substrate into the sandbody suggest that post disruption strains increase upwards implying that displacement gradients increased into the flow these behaviours showing variations in strain partitioning between the flow and its substrate are explored in terms of evolving flow dynamics and substrate rheology

flow behavior of ponded turbidity currents abstract sea floor topography can constrict deflect or reflect turbidity currents resulting in a range of distinctive deposits where flows rebound off slopes and a suspension cloud collects in an enclosed basin ponded or contained turbidites are deposited ponded turbidites have been widely recognized in slope mini basins and on small structurally confined basin floors in strike slip and foreland basin settings they can have a variable internal structure the significance of which remains poorly understood in terms of flow behavior new experiments demonstrate that the ponding process can comprise up to four phases 1 cloud establishment 2 inflation 3 steady state maintenance and 4 collapse the experiments explored the behavior of sustained turbidity currents draining into small basins and show that the ponded suspensions that form are characterized by an important internal interface this divides a lower outbound moving layer from an upper return layer the basal layer evolves to constant concentration and grain size whereas the upper layer is graded concentration and grain size decrease upward during the cloud inflation stage the concentration and velocity profiles of the ponded suspension evolve and this phase can dominate the resulting deposit outbound internal waves can travel along the interface between the outbound and return layers and impinge against the confining slope and their amplitude is highest when the density contrast between layers is greatest e g when the input flows are thin and dense the experiments show that flow reversals can arise in several ways initial rebound episodic collapse of the wedge of fluid above the counter slope grounding of the internal velocity interface and that despite steady input velocities decay and the deposit grades upwards internal waves emanate from the input point i e do not form as reflections off the counter slope the internal grain size interface within the suspension may dictate textural trends in sands onlapping the confining slopes where flows are partially ponded internal waves can generate pulsing overspill to basins down dip

process controls on the development of stratigraphic trap potential on the margins of confined turbidite systems and aids to reservoir evaluation stratigraphic trapping at pinch out margins is a key feature of many turbidite hosted hydrocarbon reservoirs in systems confined by lateral or oblique frontal slopes outcrop studies show that there is a continuum between two geometries of pinch out configuration in type a turbidites thin onto the confining surface although the final sandstone pinch out is commonly abrupt and individual beds tend not to erode into earlier deposits in type b turbidite sandstones commonly thicken toward the confining slope and beds may incise into earlier deposits these two types may occur in combination to give a wide spectrum of pinch out characteristics our analysis suggests the principal control in determining pinch out character is flow magnitude with smaller flows producing type a and larger flows producing type b in areas of poor seismic control it can be difficult to assess either pinch out character or the proximity of wells to confining slopes because estimates of paleoflow magnitude can be made from core or high quality log image data however it is possible to make reasonable estimates of pinch out character even from wells such as exploration wells which may be placed conservatively away from the field margins furthermore systematic paleoflow variations and thickness trends are commonly seen in individual turbidite sandstones as they approach confining slopes for example dispersal directions indicate flow deflection parallel with the strike of confining topography beds thin toward type a onlaps and thicken toward type b onlaps these relationships can be exploited via analysis of vertical successions to constrain well position with respect to the slope similarly the presence location and frequency of locally derived debrites can provide information on the presence and proximity of confining slopes begin page 972

three dimensional velocity structure in northern california coast ranges from inversion of local earthquake arrival times abstract the three dimensional p wave velocity structure in the upper crust in the northern california coast ranges from santa rosa to ukiah is obtained by simultaneous inversion of local earthquake and refraction travel time data for velocity and hypocentral parameters in this region where there are lateral heterogeneities the three dimensional inversion provides important results not found in two dimensional refraction studies the medium is parameterized with velocities at the intersections gridpoints of a nonuniform three dimensional grid travel times are calculated with approximate ray tracing along arcuate paths which are reasonable for lateral distances less than 45 km inversions with 5 to 10 and 2 to 3 km gridspacing achieved 80 per cent decreases in data variance the inversion with 2 to 3 km gridspacing reduced the rms residual level to approximately the level of timing error anomalously low velocities to at least 6 km depth are found along the maacama and healdsburg rodgers creek hrc fault zones the low velocity region is widest at the en echelon junction of the maacama and hrc fault zones low velocities are associated with the clear lake basin where there is a thick sequence of volcanics interbedded with sedimentary deposits there is a high velocity body located southeast of the geysers between the maacama and collayomi fault zones which may be associated with igneous intrusives or high grade metamorphism related to an underlying inferred partial melt body modeled in previous teleseismic travel time studies there is some indication in the vapor dominated geothermal reservoir of lower velocities relative to surrounding water saturated rock as has been shown in some laboratory experiments hypocenter locations obtained in the inversion show little variation from hypocenters obtained through inversion for one dimensional velocity model and station corrections for the inversion with 2 to 3 km gridspacing however some groups of events become more tightly clustered

geophysical interpretation of a high resolution seismic refraction profile in the northern apennines a combined seismic and gravimetric interpretation in the northern apennines area italy is presented to the knowledge of the authors this is one of the few attempts to apply tomographic methodology to a seismic refraction profile this procedure together with the classical interpretation for defining lower reflectors led to the formulation of quite an accurate model of the upper crust a gravity analysis was performed concurrently taking into account the seismic results at different depths which correspond to different frequency domains in the gravity signal while the medium and high frequency patterns have been solved by trial and error the regional trend has been modelled applying the collocation procedure to the gravity data

the transition between sheet like lobe and basin plain turbidites in the hecho basin south central pyrenees spain genetic facies analysis based on bed by bed correlations from sheet like lobes to the basin plain in some hecho turbidite systems demonstrates that at least 50 of the flows building the sheet like lobes kept moving downcurrent to the closely related basin plain and underwent flow transformations interpreted to have resulted from interaction with topography at the basin margin s that gave rise to specific facies these facies form a new facies tract that replaces the fine grained group of turbidite facies very fine sand to mud and characterizes the basin plain beds beds in the sheet like lobes evolve downcurrent in a way that is predictable by the existing turbidite facies tract models whereas 36 of basin plain beds which account for 78 of the basin plain volume do not the latter have deposits from high density turbidity currents at their bases and typically complete basin floor coverage the new facies tract developed when the flows obliquely encountered the southern foreland margin ramp at the ramp the lower sand laden and high density part of the larger flows was deflected evolving downcurrent along the ramp trend the upper part of the flow more dilute and thicker was reflected from the foreland margin as a train of declining undular bores moving hydraulic jumps subsequent reflections generated against the flanking margins in the closed basin led to ponding which resulted in an overall sheet like stacking pattern across sheet like lobes and the basin plain and is the diagnostic feature of the distal element in the lower sand rich stages of the turbidite systems calcilutites on top of beds interpreted until now as hemipelagites show field evidence of having a turbiditic origin hemiturbidites thus forming the facies capping the new facies tract

response of unconfined turbidity current to normal fault topography turbidity currents descending the slopes of deep water extensional basins or passive continental margins commonly encounter normal fault escarpments but such large magnitude phenomena are hydraulically difficult to replicate at small scale in the laboratory this study uses advanced computational fluid dynamics numerical simulations to monitor the response of large natural scale unconfined turbidity currents 100 m thick and 2000 m wide at the inlet gate to normal fault topography with a maximum relief of nearly 300 m for comparative purposes the turbidity current is first released on a non faulted pristine slope of 1 5 simulation model 1 the expanding and waxing flow bypasses the slope without recognizable deposition within the vertical resolution limit of 2 m similar flow is then released towards the tip model 2 and towards the centre model 3 of a normal fault escarpment in both of these latter models the sand carried by flow tends to be entrapped in four distinct depozones an upslope near gate zone of flow abrupt expansion and self regulation a flow transverse zone at the fault footwall edge a flow transverse zone at the immediate hangingwall and a similar transverse zone near the crest of the hangingwall counter slope where some of the deposited sand also tends to be reshuffled to the previous zone by a secondary reverse underflow the near bottom reverse flow appears to be generated on a counter slope of 1 1 increased to 2 by deposition the kelvin helmholtz interface instability plays an important role by causing three dimensional fluctuations in the flow velocity magnitude and sediment concentration the thick deposits of large single surge flows may thus show hydraulic fluctuations resembling those widely ascribed to hyperpycnal flows the study indicates further that the turbiditic slope fans formed on such fault topographies are likely to be patchy and hence may differ considerably from the existing slope fan conceptual models when it comes to the spatial prediction of main sand depozones this article is protected by copyright all rights reserved

experiments on bidisperse constant volume gravity currents propagation and sediment deposition laboratory experiments show that the propagation and sedimentation patterns of particle laden gravity currents are strongly influenced by the size of suspended particles the main series of experiments consisted of fixed volume releases of dilute mixtures containing two sizes of silicon carbide particles 25 m and 69 m mean diameter within a 6 m flume polydisperse experiments involved mixtures of five different particle sizes and variation of the amounts of the finest and coarsest particles all variables apart from the initial relative proportions of particles were identical in the experiments the effects of mixing different proportions of fine and coarse particles is markedly non linear adding small amounts of fine sediment to a coarse grained gravity current has a much larger influence on flow velocity run out distance and sedimentation patterns than adding a small amount of coarse sediment to a fine grained gravity current the experiments show that adding small amounts of fine particles to a coarse grained current results in enhanced flow velocities because the fine sediment remains suspended and maintains an excess current density for a much longer time thus the distance to which coarse particles are transported increases substantially as the proportion of fines in the flow is increased our experiments suggest that sandy turbidity currents containing suspended fines will be much more extensive than turbidity currents composed of clean sand

velocity and turbulence structure of density currents and internal solitary waves potential sediment transport and the formation of wave ripples in deep water abstract laser doppler anemometry lda was used to measure the instantaneous downstream and vertical velocities in a series of simple and reflected saline density currents in a lock exchange flume tank all the currents were turbulent and subcritical mean downstream fluid velocities were in excess of the head velocity by up to 30 and instantaneous velocities were greater by up to 50 turbulence intensities were highest within the head and generally greatest in the middle part of the current but did not correspond with the level of highest mean velocities the maximum reynolds stress also occurred within the head large negative values were associated with shear along the upper boundary of the current peaks of turbulence reynolds stress and shear velocity occurred in association with the arrival of reflections in large scale turbidity currents such reflections would be capable of re entraining and resuspending sediment deposited by the forward current some reflections take the form of solitary waves within a residual flow with a velocity vector in the opposite direction in nature these could produce symmetrical ripples in environments below storm wave base

palaeosols and their cover sediments of a glacial landscape in northern central europe spatial distribution pedostratigraphy and evidence on landscape evolution abstract knowledge of the distribution types and properties of buried soils i e palaeosols is essential in understanding how lowlands in northern central europe have changed over past millennia this is an indispensable requirement for evaluating long term human impact including soil erosion and land cover dynamics in the serrahn area 62 km2 a young glacial landscape representative for northeastern germany and part of the muritz national park 26 pedosedimentary sections were documented and analysed to this end a multiproxy approach was applied using pedology micromorphology geochronology and palaeoecology statistical and spatial analyses of c 5200 soil profiles of which 10 contain palaeosols show that buried soils cover an area of 5 7 km2 i e 9 of the area studied most palaeosols are cambisols arenosols and gleysols palaeosols are mainly covered by aeolian and colluvial sands as well as by lacustrine sands and peat radiocarbon and luminescence dating together with palynological and anthracological data reveal that former land surfaces were dominantly buried through erosion triggered by human activity in the late holocene in addition but to a clearly smaller extent lateglacial early holocene palaeosols and cover sediments occur following medieval clear cutting and intensive land use the study area is today again widely forested the high share of buried land surfaces detected here is expected to be representative for the hilly glacial landscapes even in the wider region i e in northern central europe and should be considered in soil mapping soil carbon budgeting and assessments of past human impact

the spatial and temporal distribution of grain size breaks in turbidites grain size breaks are surfaces where abrupt changes in grain size occur vertically within deposits grain size breaks are common features in turbidites around the world including ancient and modern systems despite their widespread occurrence grain size breaks have been regarded as exceptional and not included within idealized models of turbidity current deposition this study uses ca 100 shallow sediment cores from the moroccan turbidite system to map out five turbidite beds for distances in excess of 2000 km the vertical and spatial distributions of grain size breaks within these beds are examined five different types of grain size break are found type i in proximal areas between coarse sand and finer grained structureless sand type ii in proximal areas between inversely graded sand overlain by finer sand type iii in proximal areas between sand overlain by ripple cross laminated finer sand type iv throughout the system between clean sand and mud and type v in distal areas between mud rich debrite sand and mud this article interprets types i and v as being generated by sharp vertical concentration boundaries controlled by sediment and clay concentrations within the flows whilst types ii and iii are interpreted as products of spatial temporal fluctuations in flow capacity type iv are interpreted as the product of fluid mud layers which hinder the settling of non cohesive grains and bypasses them down slope decelerating suspensions with sufficient clay will always form cohesive layers near to bed promoting the generation of type iv grain size breaks this may explain why type iv grain size breaks are widespread in all five turbidites examined and are commonplace within turbidite sequences studied elsewhere therefore type iv grain size breaks should be understood as the norm not the exception and regarded as a typical feature within turbidite beds

reply to shanmugam g comment on internal waves an underexplored source of turbulence events in the sedimentary record by pomar et al earth science reviews 111 2012 56 81 earth science reviews 2012

insights from the talysh of azerbaijan into the paleogene evolution of the south caspian region the age and mode of formation of the south caspian basin are disputed an 10 km thick predominantly middle eocene clastic and volcanic succession is exposed in the talysh mountains of azerbaijan at its western margin here high k alkali basalts pass laterally to the east and southeast into volcanogenic sandstone dominated turbidity current and debris flow deposits these southeasterly directed depositional systems accumulated in water depths generally greater than 200 m and fed directly into the western south caspian basin new ar ar ages cluster around 39 ma with an upper 1400 m thick volcanic interval being deposited in 2 2 0 2 m y we interpret that this rapid deposition and magmatism records a major back arc extensional transtensional event in the talysh north of the north dipping neotethyan subduction zone this event is recognized across much of southwest asia and may indicate a period of significant basin formation within the adjacent south caspian basin a transition into upper eocene lower oligocene strata dominated by fine grained turbidity current and hemipelagic sediments with slope instability features is interpreted to mark the end of rifting and volcanism in the talysh and the start of the arabia eurasia collision overlying oligocene coarse clastic rocks are interpreted as the erosional products of localized topography created by the further propagation of compressional deformation into the talysh region