living on the edge evaluating the impact of stress factors on animal sediment interactions in subenvironments of a shelf margin delta the mayaro formation trinidad abstract integrating sedimentological and ichnological characteristics of the gelasian mayaro formation along the se coast of trinidad allows recognition of a river dominated and wave influenced shelf edge deltaic succession of the paleo orinoco river developed under strong slope instability four main sedimentary settings and twelve subenvironments developed on and beyond the outer shelf i e at the shelf margin have been identified extreme paleoenvironmental conditions make the succession rarely and sporadically colonized ichnologic evidence suggests that shelf edge deltas are among the most stressful marine environments due to a combination of physicochemical factors in response to the intrinsic sedimentary processes and the relative hierarchy of their influences specific to every subenvironment within any particular subenvironment the relative dominance of the fluvial feeder system the action of waves and rare influence of tides and slope instability determine the combinations and ranking of stress factors river dominated shelf edge delta subenvironments demonstrate the extreme influence of stress factors related to channel activity e g salinity changes high sedimentation and erosion rates flocculation of mud seasonal variations of fluvial flux whereas subenvironments dominated by waves storms and oceanic swells away from the axial feeder s are mostly influenced by barform morphodynamics and its effects on local physiography the paleo orinoco delta is represented not only by the delta lobe s developed at the shelf edge but by delta lobe s formed on the outer shelf as well outer shelf deltaic subenvironments manifest typical ichno sedimentological signatures of a normal wave influenced in this case inner shelf delta being susceptible to extensive gravitational instabilities the delta system suffered from canyonization and smaller gullying and subsequent filling n b hereafter we use the term canyon for both canyons and smaller gullies the shelf edge delta system was also associated with shelf attached mass transport systems such depositional subenvironments dominated by slope instability and sediment gravity flows appear to be the most unconducive for benthic colonization resulting in almost complete absence of bioturbation characterization of the stress factors as the functions of parameters arising from specific sedimentary and or oceanographic processes chemical conditions and preservational constraints specific to each subenvironment leads to the construction of a comprehensive ichnological and depositional analog model for shelf edge deltas in general and for the accommodation driven low latitude shelf edge deltas at an active oblique foreland setting in particular

an isotopic study of soils in chronological sequences of alluvial deposits providence mountains california the carbon sup 14 c and sup 13 c and oxygen isotopic composition of pedogenic carbonate was determined for two soil chronosequences on limestone and granitic alluvium in the providence mountains area in the mojave desert california the measured sup 14 c ages of pedogenic carbonate coating on clasts were interpreted in the light of a diffusion reaction model developed in our recent studies model ages of soil formation calculated from the measured sup 14 c ages of pedogenic carbonate are in correct relative order as determined by geomorphic evidence and are also consistent with model ages from the measured sup 14 c ages of soil organic matter sup 14 c model ages suggest that the order geomorphic surfaces we studied are of late pleistocene age ca 47 17 ka and the younger surfaces formed during the holocene ca 11 4 ka these age estimates of the geomorphic surfaces are older than the previously assigned ages based on a combination of soil development geomorphic relationships and several infrared stimulated luminescence dates but they are within a few thousand years of these other age estimates stable carbon isotopic composition of the soil carbonate indicates either a slight increase in c sub 4 or cam crassulacean acid metabolism plants or a decrease inmore plant density in this area during the holocene both the carbon and oxygen isotopic composition of soil carbonates suggests that the climate in the eastern mojave desert has in general become warmer and drier during the holocene 57 refs 9 figs 5 tabs less

influence of late quaternary climatic changes on geomorphic and pedogenic processes on a desert piedmont eastern mojave desert california radiocarbon dating of late quaternary deposits and shorelines of lake mojave and cation ratio numerical age dating of stone pavements dorn 1984 on the adjacent soda mountains piedmont provide age constraints for alluvial and eolian deposits these deposits are associated with climatically controlled stands of lake mojave during the past 15 000 yr six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and piedmont surfaces as well as on soil geomorphic data all but one of these stratigraphic units were deposited in response to time transgressive climatic changes beginning approximately 10 000 yr ago increased eolian flux rates occurred in response to the lowering of lake mojave and a consequent increase in fine sediment availability increased rates of deposition of eolian fines and associated salts influenced pedogenesis stone pavement development and runoff infiltration relations by 1 enhancing mechanical weathering of fan surfaces and hillslopes and 2 forming clay and silt rich surface horizons which decrease infiltration changes in alluvial fan source areas from hillslopes to piedmonts during the holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less permeable soils inferred increased in early to middle holocene monsoonal activity resulted in high magnitude paleo sheetflood events on older fan pavements this runoff triggered piedmont dissection which in turn caused increased sediment availability along channel walls thus runoff infiltration changes during the late quaternary have occurred in response to eolian deposition of fines pedogenesis increased sheetflood activity in the holocene and vegetational changes which are related to many complicated linkages among climatic change lake fluctuations and eolian hillslope and alluvial fan processes

genesis and depositional model of subaqueous sediment gravity flow deposits in a lacustrine rift basin as exemplified by the eocene shahejie formation in the jiyang depression eastern china abstract subaqueous sediment gravity flow ssgf deposits have recently been recognized as a major reservoir plays in lacustrine basins research on their genesis and depositional models are crucial to understand gravity flow evolution and the distribution of their deposits this study analysed ssgf deposits in the third member of the shahejie formation in the jiyang depression eastern china based on 3 d seismic data well log data and core observations the types and origins of ssgf the distribution patterns and depositional models of ssgf deposits have been investigated the dominant types of ssgf include muddy debris flows sandy debris flows high density turbidity currents surge like low density turbidity currents and quasi steady low density turbidity currents which are mainly caused by river floods and sediment failures the overall distribution of ssgf deposits is controlled by the sediment supplies basin structure and sequence stratigraphic framework paleotopography flood energy triggering mechanism and the slope angle of the delta front are also important ssgf deposits associated with river floods can be further subdivided into elongated and fan shaped deposits elongated sandstones are composed predominantly of bedload dominated and suspension load dominated hyperpycnal flow deposits the fan shaped sandstones can be subdivided into an inner fan a middle fan and an outer fan inner fan deposits are dominated by gully filling debrites middle fan deposits are composed predominantly of channel fill deposits while outer fan deposits consist of thin bedded and laterally extensive lobe intervals ssgf deposits triggered by sediment failures can be further subdivided according to their proximity to slumping proximal intermediate and distal parts the proximal deposits are composed predominantly of slide and slump deposits the intermediate deposits are dominated by sandy debrite tongues while the distal deposits are composed predominantly of thin bedded surge like low density turbidites this study offers some insight into the types origin of gravity flow as well as the distribution of their deposits in a lacustrine rift basin

drainage basin evolution in the rainfall erosion facility dependence on initial conditions four experiments in alluvial drainage basin evolution were carried out in the rainfall erosion facility ref at colorado state university to investigate the dependence of basin evolution on initial topography basins were initially undissected each experiment began with a unique initial condition representing various end members of relief and hypsometry drainage network development hillslope processes basin denudation and basin response to base level lowering all depended strongly on the initial topography no classic model of drainage network evolution was found to be generally applicable initially planar slopes first developed subparallel channels that extended headward dendritically during an early phase of extension channel incision occurred first in the interior of the basin where saturation overland flow was greatest not at the basin outlet as assumed in most classic models of network development channels widened over time initiating lateral migration and drainage capture in the downslope portion of the watershed before transferring lateral migration upslope planar basins of larger initial gradient grew headward more quickly and become more deeply entrenched inhibiting late stage lateral migration an experiment with initial relief concentrated at a plateau edge evolved in several unique ways a high ratio of subsurface to surface flow gave rise to mass movements at the plateau edge and outlet channels deep channels were quickly cut initially but did not extend far upslope because slope instability undermined channel head migration leaving the plateau undissected and hence very slow to erode these results suggest that the distribution of relief within a basin exerts an important control on drainage network pattern and basin denudation in addition erosional basins may evolve in several distinct modes characterized by particular combinations of hypsometry hillslope processes and mean denudation rate

correlation and dating of quaternary alluvial fan surfaces using scarp diffusion great interest has recently been focused on dating and interpreting alluvial fan surfaces as a complement to the radiometric methods often used for surface exposure dating this paper illustrates a rapid method for correlating and dating fan surfaces using the cross sectional shape of gullies incised into fan surfaces the method applies a linear hillslope diffusion model to invert for the diffusivity age t m2 using an elevation profile or gradient slope profile gullies near the distal end of fan surfaces are assumed to form quickly following fan entrenchment scarps adjacent to these gullies provide a measure of age the method is illustrated on fan surfaces with ages of approximately 10 ka to 1 2 ma in the arid southwestern united states two areas of focus are death valley california and the ajo mountains piedmont arizona gully profile morphology is measured in two ways by photometrically derived gradient slope profiles and by ground surveyed elevation profiles the t values determined using ground surveyed profiles are more consistent than those determined using photo derived t values however the mean t values of both methods are comparable the photometric method provides an efficient way to quantitatively and objectively correlate and relatively date alluvial fan surfaces the t values for each surface are determined to approximately 30 50 accuracy

analysis of scarp profiles evaluation of errors in morphologic dating morphologic analysis of scarp degradation can be used quantitatively to determine relative ages of different scarps formed in cohesionless materials under the same climatic conditions scarps of tectonic origin as well as wavecut or rivercut terraces can be treated as topographic impulses that are attenuated by surface erosional processes this morphological evolution can be modelled as the convolution of the initial shape with erosion or degradation function whose width increases with time such modeling applies well to scarps less than 10m high formed in unconsolidated fanglomerates to a good approximation the degradation function is gaussian with a variance measuring the degree of rounding of the initial shape this geometric parameter can be called the degradation coefficient a synthetic experiment shows that the degradation coefficient can be obtained by least squares fitting of profiles levelled perpendicular to the scarp gravitational collapse of the free face is accounted for by assuming initial scarp slopes at the angle of repose of the cohesionless materials 30 35 uncertainties in the measured profiles result in an uncertainty in degradation coefficient that can be evaluated graphically because the degradation coefficient is sensitive to the regional slope and to three dimensional processes gullying loess accumulation stream incision etc a reliable and accurate determination of degradation coefficient requires several long profiles across the same scarp the linear diffusion model of scarp degradation is a gaussian model in which the degradation coefficient is proportional to numerical age in that case absolute dating requires only determination of the propotionality constant called the mass diffusivity constant for holocene scarps a few meters high in loose alluvium under arid climatic conditions mass diffusivity constants generally range between 1 and 6 m 2 kyr morphologic analysis is a reliable method to compare ages of different scarps in a given area and it can provide approximate absolute ages of holocene scarplike landforms

global climate change and active tectonics effective tools for teaching and research abstract multidisciplinary student teams foster innovative research projects that can discern the locations times and styles of late quaternary faulting field studies in the area of the 1992 landers magnitude 7 3 earthquake in southeastern california provide excellent opportunities for teaching and research in climatic and tectonic geomorphology graduate student work begins with descriptions of type sections for mappable units of quaternary alluvium climate change induced aggradation events these are stair stepped flights of alluvial fan and terrace surfaces topographic profiles along faulted stream channels and fans provide estimates of vertical tectonic deformation and insight into the responses of fluvial systems to wrench fault tectonics time lines in this tectonically deforming landscape are the result of global climate changes that caused synchronous pulses of alluviation in the mojave desert at about 125 55 and 10 12 and 8 ka these dated alluvial surfaces record tectonic deformation resulting from cumulative late quaternary surface ruptures tectonic geomorphologic analyses use topographic pedogenic stratigraphic and structural data but do not require expensive and time consuming trenching projects ages of faulted and unfaulted alluvium constrain the dates of two pre 1992 earthquakes the 1992 landers event is not characteristic of earlier faulting because it ruptured through adjacent segments of the emerson fault that previously ruptured in separate events one at 3 1 2 ka and the other before 8 ka styles of tectonic deformation and locations of active faults however may not have changed during the past 125 ka

millennial scale phase relationships between ice core and mediterranean marine records insights from high precision 40ar 39ar dating of the green tuff of pantelleria sicily strait abstract with the advent of annually resolved polar ice records extending back to 70 ka marine and continental paleoclimate studies have now matured into a discipline where high quality age control is essential for putting on an equal pace layer counted timescale models and late quaternary sedimentary records high resolution u th dating of speleothem records and 40ar 39ar dating of globally recorded geomagnetic excursions have recently improved the time calibration of quaternary archives reflecting the cross disciplinary effort made to synchronize the geologic record at the millennial scale yet tie points with such an absolute age control remain scarce for paleoclimatic time series extending beyond the radiocarbon timescale most notably in the marine record far travelled tephra layers recorded both onland and offshore provide an alternative in such instance to synchronize continental and marine archives via high resolution 40ar 39ar dating of the parent volcanic eruption high resolution 40ar 39ar data are reported herein for one such volcanic marker the green tuff of pantelleria and its y 6 tephra equivalent recorded throughout the central and eastern mediterranean published radiochronometric and 18o orbitally tied ages for this marker horizon scatter widely from about 41 ka up to 56 ka our new 40ar 39ar age at 45 7 1 0 ka 2 reveals that previous estimates are biased by more than their reported errors would suggest including recent orbital tuning of marine records hosting the tephra bed that are reevaluated in the context of this study this improved estimate enables potential phase lags and leads to be studied between deep sea and terrestrial archives with unrivaled near millennial 40ar 39ar precision in the marine record

geometry of submarine slides in the bowland basin dinantian and their relation to debris flows sedimentary slide deformation structures in the lower carboniferous dinantian sediments of the bowland basin show a spoon shaped morphology with extension in the head region and compression in the toe the particular structures developed depend on the rheological properties of the sediment involved slides in soft sediment have deformation distributed throughout the slide mass with folding being the dominant deformation style slides within more lithified sediment have deformation concentrated along slip planes both types of deformation may be present within a particular slide depending on diagenetic factors and the depth to which slide planes cut down disaggregation of slides to yield material for sediment gravity flows is explained by processes operating within the slide unit

seafloor geomorphology and glacimarine sedimentation associated with fast flowing ice sheet outlet glaciers in disko bay west greenland fast flowing outlet glaciers currently drain the greenland ice sheet gis delivering ice meltwater and debris to the fjords around greenland although such glaciers strongly affect the ice sheet s mass balance their glacimarine processes and associated products are still poorly understood this study provides a detailed analysis of lithological and geophysical data from disko bay and the vaigat strait in central west greenland disko bay is strongly influenced by jakobshavn isbrae greenland s fastest flowing glacier which currently drains 7 of the ice sheet streamlined glacial landforms record the former flow of an expanded jakobshavn isbrae and adjacent gis outlets through disko bay and the vaigat strait towards the continental shelf thirteen vibrocores contain a complex set of lithofacies including diamict stratified mud interbedded mud and sand and bioturbated mud deposited by 1 suspension settling from meltwater plumes and the water column 2 sediment gravity flows and 3 iceberg rafting and ploughing the importance of meltwater related processes to glacimarine sedimentation in west greenland fjords and bays is emphasised by the abundance of mud preserved in the cores radiocarbon dates constrain the position of the ice margin during deglaciation and suggest that jakobshavn isbrae had retreated into central disko bay before 10 6 cal ka bp and to beyond isfjeldsbanken by 7 6 7 1 cal ka bp sediment accumulation rates were up to 1 7 cm a 1 for ice proximal glacimarine mud and 0 007 0 05 cm a 1 for overlying distal sediments in addition to elucidating the deglacial retreat history of jakobshavn isbrae our findings show that the glacimarine sedimentary processes in west greenland are similar to those in east greenland and that variability in such processes is more a function of time and glacier proximity than of geographic location and associated climatic regime

the impact of quaternary sea level and climatic change on coastal alluvial fans in the cabo de gata ranges southeast spain conventionally a fall in base level is seen as stimulating incision into the distal zones of alluvial fans in the cabo de gata ranges of southeast spain evidence exists to the contrary two sets of quaternary coastal alluvial fans demonstrate the interaction between climatically driven variations in the supply of sediment and eustatically driven changes in base level the fans are supplied from miocene volcanic terrain within which no evidence can be found for major tectonic deformation during the period of fan development the evolution of the east coast fans has been affected by variations in sediment supply and changes in sea level the west coast fans were buffered from the effects of changes in sea level by coastal barriers three phases of past sedimentation can be identified on the fans these can be differentiated on the basis of field observations of soil profiles particularly colour of the b horizons and accumulation of caco3 and laboratory analyses of sequential iron oxide extractions and magnetic mineral properties the two earlier major sedimentation phases were coincident with global glacials ca 135 ka and ca 85 10 ka based on the stratigraphy and uranium thorium dating of the coastal sediments high sea levels during the intervening interglacial and during the holocene caused erosion of the distal zones of the east coast fans which led to channel incision into the fan surfaces on the west coast fans no such incision occurred simply proximal incision by small fanhead trenches the youngest relatively minor phase of fan sedimentation has occurred during the holocene these contrasting contexts have produced differing styles of fans with telescopic fan morphology on the east coast and stacked morphology on the west coast fans the differences are reflected in the fan profiles with steeper gradients dominating the east coast fans and extensive lower gradient distal surfaces on the west coast fans fan morphometry based on analysis of the residuals from drainage area to fan area and gradient regressions also differentiates between the fan contexts the fan building phases appear to be controlled proximally by climatically driven pulses of sediment supplied to the fans these occurred during global glacials coincident with low sea levels and caused fan progradation onto the exposed foreshore the intervening global interglacials were times of little fan sedimentation and on the east coast where high sea levels were able to erode the fan toes deep through fan dissection ensued

sediment slump structures a review of diagnostic criteria and application to an example from newfoundland abstract in the study of the history of deformed sedimentary rocks it is important that the cause of the deformation and the timing of deformation relative to metamorphic and tectonic events be assessed there is a continuous gradation between the deformation of freshly deposited sediments by gravitational forces and the deformation of well lithified sediments by tectonic forces so determining the degree to which gravity tectonism and lithification influenced deformation can be very difficult the characteristics that may be considered in determining the origin of deformational structures in sedimentary rocks can be divided into five categories ductile deformation structures 1 can provide definitive criteria for recognizing post lithification deformation but not pre lithification deformation this also holds for 2 brittle deformation structures and decollements overprinting of sediment reworking or remobilization structures 3 are the best criteria for recognizing pre lithification structures fabrics 4 can be very useful but are as yet poorly understood and there are misconceptions in the literature about what sort of fabrics are or are not found in unlithified sediments spatial relationships 5 may also tell us a great deal but are most useful when taken in conjunction with other types of evidence complex fold patterns in sandstones on farmer head north central newfoundland provide a case study for criteria that may be used to determine the degree of lithification during deformation although these folds have been interpreted as slump folds by earlier workers fabrics and spatial relationships point to a tectonic post lithification origin for the structures a conclusion which has significant implications for the interpretation of the regional geology

chronology of the lower middle pleistocene succession of the south western part of the crotone basin calabria southern italy biostratigraphy based on calcareous nannofossils integrated by magnetostratigraphic geochronological and isotopic data allowed establishing a precise chronological framework for the pleistocene

constraining sub seismic deep water stratal elements with electrofacies analysis a case study from the upper cretaceous of the maloy slope offshore norway abstract electrofacies represent rock facies identified from wireline log measurements and allow extrapolation of petrophysical characteristics away from stratigraphic intervals that are calibrated to core this approach has been employed to reduce uncertainty in the identification of the sub seismic depositional elements in the late cenomanian coniacian succession of the northern maloy slope offshore norway core logging permits identification of eleven distinct sedimentary facies that are grouped into four facies associations fa a turbidite sandstones fa b heterolithic siltstones and sandstones fa c debrites and fa d slide and slump deposits each facies association is defined by a distinct combination of petrophysical characteristics including porosity density gamma ray sonic and resistivity using neural network analysis electrofacies are calibrated with sedimentary facies thereby allowing us to map their thickness and stacking patterns within the studied deep water succession we demonstrate that this approach is particularly useful where the presence of glauconite makes the distinction between sandstone from shale rich units difficult using gamma ray logs alone our results indicate that the succession of interest is dominated by debris flows and slide and slump deposits which are commonly poorly imaged on seismic reflection datasets in the northern north sea the methodology presented here can aid the correlation of deep water stratal elements at production and exploration scales in stratigraphic successions that have undergone similar burial histories furthermore this method may help in the identification of mass flow deposits that are present in upper cretaceous deep water systems of the north sea

sedimentology and diagenesis of resedimented and rhythmically bedded chalks from the eldfisk field north sea central graben 1 chalk reservoirs in the eldfisk field comprise autochthonous chalks of the hod formation overlain by mixed allochthonous and autochthonous chalks of the tor and ekofisk formations core material contains previously undescribed fabrics which are of importance in determining the sedimentological and diagenetic history of north sea chalk reservoirs resedimentation within the tor and ekofisk formations was dominated by slumping evidence of deposition from liquefied flows is scant sediment filled fractures indicate early overpressuring of the sequence in response to burial beneath tertiary mudrocks within the hydrocarbon zone the hod and ekofisk formations contain small scale about 7 5 cm rhythmic alternations of oil stained and unstained layers related to variation in sedimentation rate and or early diagenesis below the hydrocarbon zone and in impermeable intervals within the hydrocarbon zone small scale alternations are replaced by decimeter scale interbedding of clay rich and clay poor chalks more typical of autochthonous chalk facies and a product of more advanced chemical compaction these fabrics suggest that porosity reduction is closely related to lower hydrocarbon saturation in turn largely a function of clay content early overpressuring and structural position within the field

resedimentation of cold pumiceous ignimbrite into water facies transformations simulated in flume experiments deposits and transport processes resulting from the resedimentation of cold unconsolidated ignimbrite into water were simulated by flume experiments the ignimbrite sample used was poorly sorted 2 4 3 fine ash rich 2000 kg m 3 and pumice 500 to ca 1300 kg m 3 as a result of the binding forces of the ash matrix the experiments involved resedimentation from a steep front onto the floor with or without an initial ramp of the water filled tank under both still and wave generated conditions larger discrete collapse events were induced by oversteepening the sample front and by undercutting from wave action the mass of the collapse and proportion of pore space water strongly influenced the style of resedimentation and the deposits initial collapse events were from the top of the steep front and fell onto the floor the largest densest clasts were deposited as a lithic lag in a proximal sediment wedge or rolled down to a break in slope fine ash was transported in dilute turbidity currents and coarse unsaturated pumice clasts floated off moderate collapse events generated high density turbidity currents trapping pumice in the flow causing them to saturate these low density pumice clasts were easily remobilized by wave activity and passing currents and accumulated on the gentle slope at the bottom of the resedimented deposit large collapse events slumped producing poorly sorted mounds similar in texture to the original starting material as the matrix of the ignimbrite sample became saturated with water moderate and large collapse events generated debrisflows and slurries that deposited massive poorly sorted deposits furthermore once more gentle slopes were established between the sample and deposit small cascading grainflows deposited lithic clasts on the upper slopes and levees of pumice at the terminus of low relief ash channels the experiments show that excluding large collapse events and debrisflows resedimenting ignimbrite in water is effective at segregating low density pumice clasts from dense lithic clasts and fine ash experiments using fine ash poor ignimbrite and well sorted quartz sand for comparison formed an inherently unstable initial steep front that immediately collapsed by continuous grain avalanches the grainflow deposits had textures similar to the fines poor starting material

basin floor fans in the north sea sequence stratigraphic models vs sedimentary facies discussion original article shanmugan g r b bloch s m mitchell g w j beamish r j hodgkinson j e damuth t straume s e syvertsen and k e shields 1995 aapg bulletin v 79 p 477 512

morphologic dating of fluvial terrace scarps and fault scarps near west yellowstone montana analysis of fault and fluvial terrace scarps in the west yellowstone basin south of hebgen lake montana indicates that during degradation the gradient of the scarp face and the curvatures of the basal concavity and crestal convexity of the scarp face decrease become more rounded with time the pattern of degradation is identical with that predicted by a simple analytical model for degradation by creep in which the change in elevation at a point on a hillslope is proportional to the curvature of the profile at that point the model therefore provides the basis for morphologic dating a technique for determining the age of a scarp by the extent to which its initial morphology has been degraded in order to date a scarp the coefficient of proportionality c must be known the technique is probably not suitable for use on hillslopes degraded by processes other than creep both the potential and the limitations of morphologic dating are demonstrated via measurements of a sequence of terrace scarps along the madison river the calculated relative ages are in agreement with the known relative ages despite the fact that the gradient of the youngest scarp is significantly less than that of the older scarps to calculate an absolute morphologic age c must be derived from analysis of a scarp of known age having the same aspect must be underlain by the same material and must be within the same climatic zone as the scarp to be dated in the west yellowstone basin a value of c 2 00 0 38 10 3 m 2 yr was calculated from a minimum date of 7100 50 yr b p determined by radiocarbon dating for one of the terrace scarps scarps formed by normal faulting in the west yellowstone basin are much more difficult to date than are terrace scarps because of the possible complexity of their initial morphology fault scarps formed during the 1959 yellowstone earthquake commonly consist of an assemblage of two or more smaller scarps or are superimposed on preexisting scarps formed by one or more previous faulting events by using a selective sampling procedure however one can screen out these fault scarps in this way it was possible to determine an age of 2 800 1 100 yr for a pre 1959 fault scarp in the west yellowstone basin because the fault and terrace scarps in the west yellowstone area do not vary significantly in height the morphologic dating technique proposed earlier by nash 1980a cannot be applied to them the substantially modified procedure developed for the present study does not require a wide range of heights for each scarp to be dated it can be performed using a relatively small number of scarp profiles if c is known it is easy to use and when used with considerable care it is reasonably accurate 36 59 in this study it is potentially applicable to scarps in other areas

origin of the calderas and evolution of roccamonfina volcano roman region italy abstract the roccamonfina volcano consists of a volcanic fluvial succession dated 549 ka bp paleoauruncus overlain by a 546 ka bp stratacone main cone formed by leucite bearing lava and tephra the main cone was dissected by four nested calderas a ring fracture concentric with and outside of the central caldera is also present detailed mapping of the volcano inspection of landsat satellite images and radiometric dating establish that the gli stagli and northern calderas subsided between respectively 546 474 and 403 374 ka bp and that the summit part collapsed between 546 and 446 ka bp to form the central caldera a chronologically intermediate state dated in the range 376 323 ka bp was identified between the 549 374 ka bp leucite bearing high k series hks stage i and the 317 96 ka bp leucite free low k series lks stage ii this stage is made up of concurrent hks lks rocks stage ics the central gli stagli and northern calderas are older than blt and wtt as supported by the strong discrepancies between calculated volumes of these pyroclastic rocks and the volume of the caldera also caldera collapses due to sector sliding are improbable as tested by the absence of rock slide avalanche deposits the collapses occurred incrementally through repetitive draining of the magma chamber s resulting from a succession of moderate sized volcanic events gli stagli caldera was infilled by a lake early after collapse so that sediments alternated with leucite tephrite lava flows and tephra within the lake the sequence was overlain by a thick succession of young pyroclastic rocks downfaulting downsagging cut the flat lying gli stagli filling sequence resulting in the old valle caldera successive pyroclastic and debris flows derived by updoming of the central caldera deposits infilled the last structure and downfaulted part of the valle fill producing the young valle caldera

mid cenozoic fluvio deltaic to marine environments of the salin sub basin central myanmar abstract the salin sub basin is one of several basins within the wide elongate north south trending central basin in myanmar a field based campaign targeted the deposits of the reportedly oligocene shwezetaw padaung and okhmintaung formations which previously have been described only from spatially restricted and incomplete core records and limited field studies a minimum of 2 5 km thickness of these formations in the sub basin records a high sedimentation rate and long term subsidence which broadly kept pace with sediment input facies analysis based on sedimentary logs and panel diagram interpretation interprets these formations as deposits of large scale broadly southward flowing fluvial systems that interacted with deltaic and shallow marine environments in the southwestern parts of the basin a switch from south to southwest flowing rivers midway down the basin suggests these systems fed sediment to offshore basins in the west the overall environment was somewhat similar to the modern day irrawaddy river and delta despite the recorded high sedimentation rates and the coeval subsidence the depositional environment does not show much variation the main control is overall relative sea level rise associated with a northeastward marine transgression into the basin with contemporaneous smaller scale cycles of sea level rise and fall in terms of basin development this considerable thickness of clastic sediment indicates significant emergent sources palaeoenvironment reconstructions suggest that the south flowing fluvial systems sourced sediment from the northern margin of the basin but there were also some channels joining the main channel from the western margin of the basin and fewer channels from the northeast

reconciling the roles of tectonism and climate in quaternary alluvial fan evolution tectonism and climate are the primary variables considered in conceptual models of alluvial fan evolution and basin fill architecture yet their roles and relative importance are far from resolved the madison range and madison river valley southwestern montana were affected during late quaternary time by varying degrees of tectonic activity as well as by climate change through multiple glaciations we are thus able to evaluate the impact of tectonism and climate on fan evolution two primary fan deposits were correlated along the range front they were deposited as proglacial outwash fans during glacial periods of increased sediment and water discharge during the present interglacial period these deposits were entrenched and secondary fans formed on lower fan areas temporal and stratigraphic relations indicate that climate was largely responsible for driving both fan aggradation and entrenchment in contrast stratigraphic relations between fan deposits and surface faults do not support a direct relation either spatial or temporal between local faulting and fan deposition because tectonism produces and maintains the relief necessary for fans to form its primary role is long term controlling the duration over which fan deposition may occur along a mountain front if quaternary alluvial fan evolution is representative of ancient alluvial fan evolution this study has important implications for interpreting primary controls on deposition of the ancient alluvial fan sequences

late quaternary fault segmentation from analysis of scarp morphology a thorough knowledge of the lateral extent of individual prehistoric ruptures along a fault is necessary to assess the locations and geologic characteristics of boundaries between independent faultrupture segments paleoseismic studies employing only trenching may yield insufficient data to evaluate the lateral extent of individual rupture events systematic mapping of fault scarps and degradation equation modeling of relative scarp ages on the lemhi fault a range bounding normal fault in east central idaho provide a method to assess rupture extent and boundaries between rupture segments the youngest latest quaternary surface ruptures occurred at distinctly different times on adjacent segments of the fault the boundaries between rupture segments differ in characteristics although most are at intersections of the currently active range bounding fault and mid tertiary normal faults several major structural and tectonic discontinuities did not form segment boundaries in the most recent rupture cycle or probably in the previous cycle the lemhi fault illustrates both the importance of preexisting structures in controlling extent of ruptures and the need for detailed analysis along an entire fault zone

neogene syn tectonic sedimentation in the eastern margin of arakan bengal basins and its implications on for the indian asian collision in western myanmar abstract the arakan basin is one of the major sedimentary basins formed in the frontal part of the himalayan orogenic belt since the late cenozoic defining one of the four major sedimentary basins of myanmar it is geomorphologically and tectonically differentiated from the others the study area along the westernmost edge of myanmar is separated from the arakan yoma indo burman ranges by a narrow coastal strip and is bordered by the bay of bengal to the west regional stratigraphic correlation and the geological age of the siliciclastic sequences were established based on planktonic foraminiferal zonation deep marine slope and shelf environments during early to middle miocene ca 21 5 11 ma and a southward prograded shelf delta environment during late miocene to pliocene time were determined the early miocene underthrusting along the himalayan front is well documented by the forced regressive sedimentation patterns in the slope and shelf systems sediments of which derived from the paleo ganges brahmaputra river systems in the bengal arakan basins sequential evolution of the miocene successions manifests in forced regressive wedged systems tracts these evolved through slope by passing and slumping and following deep marine channel in filling began to accumulate an increasing sediment load due to the rapid fall of sea level by the uplift in the hinterlands during the early to early middle miocene the formation of a shelf delta systems marks a dramatic shift in the evolution of the southward prograding delta systems following a eustatic sea level low in the foreland areas erosional off loading with foreland uplifting caused a wide active fluvial systems and formed transverse rivers distally in the late middle to late miocene

ten turbidite myths abstract during the past 50 years the turbidite paradigm has promoted many myths related to deep water turbidite deposition john e sanders 1926 1999 a pioneering process sedimentologist first uncovered many of these turbidite myths this paper provides a reality check by undoing 10 of these turbidite myths myth no 1 turbidity currents are non turbulent flows with multiple sediment support mechanisms reality turbidity currents are turbulent flows in which turbulence is the principal sediment support mechanism myth no 2 turbidites are deposits of debris flows grain flows fluidized flows and turbidity currents reality turbidites are the exclusive deposits of turbidity currents myth no 3 turbidity currents are high velocity flows and therefore they elude documentation reality turbidity currents operate under a wide range of velocity conditions myth no 4 high density turbidity currents are true turbidity currents reality ph h kuenen 1950 introduced the concept of turbidity currents of high density based on experimental debris flows not turbidity currents high density turbidity currents are sandy debris flows myth no 5 slurry flows are high density turbidity currents reality slurry flows are debris flows myth no 6 flute structures are indicative of turbidite deposition reality flute structures are indicative only of flow erosion not deposition myth no 7 normal grading is a product of multiple depositional events reality normal grading is the product of a single depositional event myth no 8 cross bedding is a product of turbidity currents reality cross bedding is a product of traction deposition from bottom currents myth no 9 turbidite facies models are useful tools for interpreting deposits of turbidity currents reality a reexamination of the annot sandstone in se france which served as the basis for developing the first turbidite facies model suggests a complex depositional origin by plastic flows and bottom currents myth no 10 turbidite facies can be interpreted using seismic facies and geometries reality individual turbidity current depositional events commonly centimeters to decimeters in thickness cannot be resolved in seismic data all turbidite myths promote falsehood and should be abandoned

ages estimated from a diffusion equation model for scarp degradation the diffusion equation derived from the continuity equation for hillslopes is applied to scarp erosion in unconsolidated materials solutions to this equation allow direct calculation of the product of the rate coefficient and the age of the scarp from measurements of scarp morphology where the rate coefficient can be estimated or can be derived from scarps of known age this method allows direct calculation of unknown ages of scarps

tectonic control on sedimentary processes in the southern termination of the barbados prism abstract the purpose of this paper is to evaluate the tectonic control on the origin nature distribution and reworking of sediments on an active margin the study is based on kullenberg cores 3 5 khz seismic profiles and side scan sonar imagery collected on the south barbados accretionary prism together with observations from submersibles the most abundant surficial sediment in this area was derived from the south american continent and from hemipelagic particles this sediment is transported in great quantity through canyons that exemplify the regional tectonic trend and is trapped in basins located between the active accretionary ridges and the other elevated structures as shown by on lap geometry and progressive discordances a second type of sediment consists of clayey diapiric material that originates from miocene beds this material is extruded to the surface through mud volcanoes mud domes and diapiric ridges the vertical migration of clays was partly initiated by tectonic deformation and guided by major faults the supply of this diapiric material to the sedimentation in adjacent basins is quite substantial the last type of sediment consists of diagenetic crusts formed on the sea floor along faults where fluids are expelled from the prism patterns of reworked sediments are strongly controlled by recent tectonic deformation sedimentary features such as bulges sliding masses continuous or discontinuous scarps and other erosional lineations are directed parallel to the active tectonic trends n10 30 n50 n100 110 n140 sliding and other gravity flows are triggered by tectonic activity mainly where accretion and shear structures interplay and where the ascent of diapiric structures is responsible for steep slopes the breakup of diagenetic crusts is caused by faulting erosive cascading deep currents are enhanced by the high relief afforded by an active ridge

oldest human footprints dated by ar ar fossilized human trackways are extremely rare in the geologic record these bear indirect but invaluable testimony of human hominid locomotion in open air settings and can provide critical information on biomechanical changes relating to bipedalism evolution throughout the primitive human lineage among these the devil s footsteps represent one of the best preserved human footprints suite recovered so far in a pleistocene volcanic ash of the roccamonfina volcano southern italy until recently the age of these footprints remained speculative and indirectly correlated with a loosely dated caldera forming eruption that produced the brown leucitic tuff despite extensive hydrothermal alteration of the pyroclastic deposit and variable contamination with excess 40ar detailed and selective 40ar 39ar laser probe analysis of single leucite crystals recovered from the ash deposit shows that the pyroclastic layer and the footprints are 345 6 kyr old 1 confirming for the first time that these are the oldest human trackways ever dated and that they were presumably left by the modern human predecessor homo heidelbergensis close to climatic termination iv

debris flow and glacioisostatic induced soft sediment deformation structures in a pleistocene glaciolacustrine fan the southern baltic sea coast poland abstract middle pleistocene glaciolacustrine fan sediments are exposed along a cliff at the baltic sea coast where plastic and brittle soft sediment deformation structures ssds commonly occur 1 fold structures various types of folds and flexures 2 load structures load casts pseudonodules and flame structures 3 water escape structures wes and 4 brittle deformation structures such as faults medium and small scale reverse and normal and fragments of broken up laminae the origins of the ssds can be linked to gravitational processes promoted by shear stresses in subaqueous debris flows on the glaciolacustrine fan and by the weight of overlying sediments and or to the glacial rebound of earth s crust during deglaciation because in the pleistocene the baltic sea and surrounding areas were covered by ice sheets many times the question investigated here concerns recognition of the trigger mechanisms responsible for the development of ssds and the criteria needed to recognize those mechanisms based on the lithological and deformational features of the sediments involved some types of ssds can look similar regardless of trigger mechanisms but some occur more often as a result of a specific mechanism is it possible to distinguish ssds of seismic origin in a glaciolacustrine fan succession affected by multiple debris flows and of ssds that evolved as a consequence of slope processes we suggest criteria to recognize ssds triggered by the glacioisostatic rebound as well as those which can develop as a result of the rebound and slope processes

traction structures in deep marine bottom current reworked sands in the pliocene and pleistocene gulf of mexico the pliocene pleistocene sequence cored in the ewing bank and garden banks areas in the gulf of mexico provides an example of deep marine sand reworked by bottom currents a distinctive attribute of these sands is their traction structures which include cross stratification current ripples and horizontal lamination these sands also exhibit sharp upper contacts inverse size grading mud offshoots and flaser bedding an important aspect of these structures is their occurrence in discrete units but not as part of a vertical sequence of structures such as the bouma sequence presumably the loop current a strong wind driven surface current in the gulf of mexico impinged on the sea bottom as it does today and resulted in bottom current reworked sands a depositional model is proposed in which the bottom current reworked sands tend to develop a facies in interchannel slope areas that is distinctly different from channel levee turbidite facies

sedimentology of the paleoproterozoic kungarra formation turee creek group western australia a conformable record of the transition from early to modern earth abstract this paper presents the first detailed sedimentological analysis of the paleoproterozoic kungarra formation the lowermost of three formations comprising the turee creek group in western australia which was deposited across the rise in atmospheric oxygen the great oxidation event or goe and the transition from early to modern earth the data show that the kungarra formation has a gradational conformable lower contact with underlying banded iron formation of the hamersley group and predominantly comprises an upward shallowing succession from deepwater shales and siltstones through rippled fine grained sandstones and stromatolitic carbonates to tidal flat deposits that immediately underlie coastal fluvial deposits of the overlying koolbye formation at the base of the kungarra formation is a gradual transition from alternating units of magnetic green shale and thin units of banded iron formation that pass upsection to units of non magnetic shale and ferruginous chert and grey chert reflecting a gradual loss of iron from the world s oceans accompanying the rise of atmospheric oxygen a falling stage systems tract is recognised above this transition in the hardey syncline area capped by stromatolitic carbonates and a period of exposure marked by an erosional unconformity and carbonate beachrock two glacio eustatic cycles are recognised within the middle to upper parts of the kungarra formation each of which is marked by the rapid onset of falling systems tracts and characterised by falling systems tracts during and following diamictite deposition stratigraphic data are used to infer a depobasin filled by a sediment wedge prograding from southeast to northwest in contrast to previous models of a north northeastward deepening foreland basin the lack of seismites or internal unconformities within the formation precludes a foredeep setting rather deposition is interpreted as having occurred within an intracratonic basin with detritus sourced from erosion of uplifted bedrock to the southeast

deformed soft sediments at the junction between the mariana and yap trenches abstract highly deformed unconsolidated hemipelagic sediments were found below the sea bed surface at anomalously shallow depths near the junction between the mariana and yap arc trench systems the order of deformation is 1 sigmoidal veins and spaced foliations 2 layer parallel shear planes 3 reverse faults and kink bands and 4 more veins all the deformation structures are considered to have been developed progressively during shear parallel to bedding accompanied by volume decrease due to pore reduction and fluid expulsion during consolidation while the sediments are not yet lithified

cretaceous depositional systems in the norwegian sea heavy mineral constraints deep water cretaceous sandstones in the norwegian sea were deposited by a number of distinct sediment transport systems tapping different sediment source terrains three distinct sandstone types k1 k2 and k3 have been identified distinguished and mapped on the basis of a combination of heavy mineral parameters sandstone type k1 occurs on the trondelag platform halten terrace and nordland ridge but does not appear to be present in the deeper water voring basin sandstone type k1 was ultimately derived from the scandinavian landmass with detritus sourced from metasediments of the caledonian fold belt intrusives of the trans scandinavian igneous belt and to a smaller extent svecofennian basement k1 sandstones were deposited on an unstable slope by debris flows and slumps with minor reworking by bottom currents sandstone type k3 was derived from the western gneiss region farther south on the scandinavian landmass sandstone type k2 occurs in more basinal locations in the norwegian sea and was not supplied by the systems operating along the scandinavian margin because its mineralogy contrasts with that of k1 and k3 k2 mineralogy is not consistent with a source in the lofoten area or east greenland therefore k2 is believed to represent the deposits of a separate axial transport system fed by a source that lay in northeast greenland k2 zircon ages indicate involvement of early proterozoic approximately 2000 ma and archean basement together with metasediments of the caledonian fold belt previous sedimentological models for the cretaceous of the norwegian sea suggest that sand deposition occurred as slumps and debris flows along the continental slope resulting in discontinuous and unpredictable sandstone units unless they become amalgamated into thick reservoir sequences the mineralogical evidence indicates that this model can be applied only to sandstone types k1 and k3 by contrast sandstone type k2 represents sediment introduced from the conjugate margin of the basin and occurs up to 200 km from its detrital source region therefore k2 is likely to occur as more predictable sheetlike bodies on the basin floor

constraining the timing of alluvial fan response to late quaternary climatic changes southern tunisia the evolution of the oued es seffaia alluvial fan during the last 50 000 years is analyzed in the light of chronometric data derived from ams radiocarbon and optical dating techniques these ages have enabled the temporal constraint of the distalward progression of the intersection point the upper limit of the locus of deposition which has resulted in the telescopic segmentation of the fan comparison of these data with the late quaternary climatic history of the maghreb highlights several problems of interpretation due both to our limited knowledge of regional palaeoclimates and of the response of dryland fluvial systems to climate changes however our data provide some evidence to suggest that fan incision and formation of telescopic segments occurs in response to changes from arid to less arid conditions supporting the conclusions of some of the work from other areas

gravity flow deposits caused by different initiation processes in a deep lake system gravity flows may be triggered by different initiation processes in both marine and lacustrine basins recognizing the different initiation processes of gravity flow based on their deposits is vital to accurately establish gravity flow sandstone distribution which is important for defining paleogeography and for efficient oil and gas exploration gravity flow deposits in the dongying sag were analyzed using three dimensional seismic well log grain size and porosity and permeability data along with core descriptions eleven lithofacies nine bed types and six bed type associations were recognized in the gravity flow deposits in the dongying sag gravity flow deposits around well niu 110 were caused by delta fed sediment failure these deposits are characterized by medium to very fine grained sandstone abundant liquefaction and soft sediment deformation structures and thick laminae rich in plant debris they formed massive sandstones accompanied by normally graded sandstone and lenticular shaped sandbodies and are composed of chaotic deposits and tongue lobes the above features collectively are indicative of typical collapsed sediment transport to deep water by slumping and poorly cohesive debris flow to low density turbidity current gravity flow deposits around well shi 100 are interpreted to have been caused by flooding river fed hyperpycnal flows these deposits are characterized by gravel to very fine grained sand abundant erosional structures and climbing ripples and thin laminae rich in plant debris they formed massive sandstone with some space stratification accompanied by inverse then normal grading sandstone and elongate or fan shaped sandbodies and are composed of channel levee systems and lobes stratified hyperpycnal flow is prone to form a hydraulic jump at the slope break after the hydraulic jump coarse grained sediments were transported to the basin under the drag and shear of the upper part of the suspension flow gravity flow deposits caused by flooding river fed hyperpycnal flow are better reservoirs than those caused by delta fed sediment failure under the same conditions this study offers insight into the recognition criteria and flow processes of gravity flows caused by the different initiation processes in a lacustrine basin

facies in a shelf edge delta an example from the subsurface of the gulf of mexico middle pliocene mississippi canyon block 109 two vertically stacked shelf edge delta systems in the middle pliocene of mississippi canyon block 109 have been described using a three dimensional seismic survey 400 ft 122 m of conventional core and electric logs possible characteristic facies associations and features of these shelf edge deltas include extensive upper delta slope deformation locally ponded slump induced turbidites in the upper slope a complex association of gravity and tractional deposits relatively thin preserved mouth bar deposits and the absence of delta plain facies six facies have been identified in cores 1 structureless sands interpreted as high density turbidites 2 laminated sands 2 1 sharp based planar horizontal laminations interpreted as bouma b and bc division turbid tes 2 2 low angle discordant laminations interpreted as strong wave activity deposits 2 3 a complex mixture of lamination styles that may be a product of turbidity currents waves or possibly river fed underflows 3 thinly interbedded ripple laminated sands including 3 1 asymmetrical cross laminations interpreted as unidirectional traction current lamination and 3 2 c division turbidites or ripple lamination with mud drapes on foresets or with a symmetrical form interpreted as wave or possibly tidal current lamination 4 contorted muddy fine sands and silts interpreted as mud flows and slumps 5 laminated silts and muds interpreted as low energy wave deposits or possibly d division turbidites and 6 muds interpreted as quiet water deposits in the cored intervals o the deltas turbidite sands immediately overlie muddy slumps in the upper delta slope suggesting that retrogressive slope failure of developing slump structures tapped back into the mouth bar causing sandy turbidity currents to develop the upper delta is represented on seismic data as a series of prograding clinoforms approximately 400 ft 122 m thick electric logs indicate these clinoforms are composed of a lower mud dominated interval an upper delta slope dominated by slumps with areally restricted turbidite sands and coarsening and cleaning upward mouth bar deposits composed of ripple laminated and parallel laminated sands interbedded with muds and silts the lower delta contains similar vertical sequences but also contains a distinct log and seismic facies that may be either a major shelf edge failure or a later channel feature incised across the entire delta apart from this possible channel neither delta shows evidence of emergent delta plain facies

sediment flow and deformation sfd layers evidence for intrastratal flow in laminated muddy sediments of the triassic osawa formation northeast japan abstract thin chaotic layers containing abundant intraformational mud clasts are found in the offshore laminated mudstone of the triassic osawa formation in northeast japan the geometry and internal structures of the layers are somewhat similar to those of slump slide or debris flow deposits however the layers have both upper and lower erosional contacts projections of host sediments and mud clasts with planed surfaces are identified beneath the upper contact of the layers closely packed sheet form or ellipsoidal mud clasts are embedded in a poorly sorted fine to coarse grained sandy matrix some mud clasts are tightly folded or show imbricated stacking internal layering structures are also well developed in the layers the above features strongly suggest soft sediment deformation as horizontal displacement of sand and mud under buried conditions here we term these layers sediment flow and deformation sfd layers deformation layers with similar attributes have been identified by some prior authors as in the case of flow of liquefied and or fluidized host sand and clastic sill intrusion however the sfd layers described herein have more complex structure indicating advanced deformation occurrence of the sfd layers is stratigraphically limited to the uppermost part of the osawa formation which is overlain by sand rich submarine fan deposits the fukkoshi formation it suggests that the stress field caused by differential loading of overlying deposits facilitated intrastratal flow and sill intrusions of sand the vertical confinement was also controlled by the anisotropy in physical properties such as tensile strength of laminated mud and or conditions of gentle slope

the bouma sequence and the turbidite mind set abstract conventionally the bouma sequence bouma a h 1962 sedimentology of some flysch deposits a graphic approach to facies interpretation elsevier amsterdam 168 pp composed of ta tb tc td and te divisions is interpreted to be the product of a turbidity current however recent core and outcrop studies show that the complete and partial bouma sequences can also be interpreted to be deposits formed by processes other than turbidity currents such as sandy debris flows and bottom current reworking many published examples of turbidites most of them hydrocarbon bearing sands in the north sea the norwegian sea offshore nigeria offshore gabon gulf of mexico and the ouachita mountains are being reinterpreted by the present author as dominantly deposits of sandy debris flows and bottom current reworking with only a minor percentage of true turbidites i e deposits of turbidity currents with fluidal or newtonian rheology in which sediment is suspended by fluid turbulence this reinterpretation is based on detailed description of 21 000 ft 6402 m of conventional cores and 1200 ft 365 m of outcrop sections the predominance of interpreted turbidites in these areas by other workers can be attributed to the following 1 loose applications of turbidity current concepts without regard for fluid rheology flow state and sediment support mechanism that result in a category of turbidity currents that includes debris flows and bottom currents 2 field description of deep water sands using the bouma sequence an interpretive model that invariably leads to a model driven turbidite interpretation 3 the prevailing turbidite mind set that subconsciously forces one to routinely interpret most deep water sands as some kind of turbidites 4 the use of our inability to interpret transport mechanism from the depositional record as an excuse for assuming deep water sands as deposits of turbidity currents 5 the flawed concept of high density turbidity currents that allows room for interpreting debris flow deposits as turbidites 6 the flawed comparison of subaerial river currents fluid gravity flows dominated by bed load transport with subaqueous turbidity currents sediment gravity flows dominated by suspended load transport that results in misinterpreting ungraded or parallel stratified deep sea deposits as turbidites and 7 the attraction to use obsolete submarine fan models with channels and lobes that require a turbidite interpretation although the turbidite paradigm is alive and well for now the turbidites themselves are becoming an endangered facies

dating quaternary fault scarps formed in alluvium using morphologic parameters abstract ages of fault scarps as well as those other types of transport limited slopes can be estimated by comparing their morphology with the morphology of scarps of known age age estimates are derived by fitting the scarp profiles to synthetic profiles generated using a diffusion equation or alternatively by classification using a linear discriminant function the usefulness of morphology derived age estimates depends on the relative importance of non age related morphologic variation data from more than 200 scarp profiles demonstrate that morphologic variation not related to scarp age can introduce significant uncertainties into morphology derived age estimates

gravity driven structures and deposits resulting from slope collapse in the margin of a carbonate platform pennsylvanian cantabrian zone nw iberia abstract lower slope to basin floor deposits associated to isolated microbial carbonate platforms of the valdeteja formation carboniferous foreland basin cantabrian zone nw spain containing large slid blocks and debrites exhibit a combination of contractional and extensional structures which include thrusts backthrusts folds extensional faults and joints and boudinaged beds several lines of evidence indicate that deformation took place in poorly lithified conditions such as thickened hinges hydroplastic fractures fold axes scatter or folding of microbial limestones once restored all structures indicate a transport direction towards the nne ene this azimuth coincides with the direction towards which the thrust nappes of the southern branch of the cantabrian zone were emplaced during the variscan orogeny however the interpretation of the deposits and structures as gravity related associated to the collapse of the carbonate platform slope is supported by features such as the rootless character of thrusts the parallelism between transport direction and paleocurrent orientation the concomitant development of contractional and extensional structures the development of normal listric faults affecting the valdeteja platform the sedimentary environment lower slope to basin floor and the geological context of the valdeteja carbonate platforms which predate the variscan deformation in the study area

sources of error in planetary photoclinometry photoclinometry has become a popular technique for the extraction of topography from digital images of planetary surfaces the technique however is subject to a number of error sources that can degrade results significantly we present here a quantitative analysis of error sources in one dimensional planetary photoclinometry the technique is affected by at least seven error sources which can be broken down into three categories those arising from 1 the spacecraft image 2 the planetary body and 3 the scan line orientation spacecraft image error sources include noise background offset and quantization errors deriving from the planetary body include those induced by variations in photometric properties such as albedo by incorrectly compensated atmospheric effects and by an incorrectly determined photometric function finally errors will result for scan lines which do not lie perpendicular to topographic strike we calculate slope errors for each of these sources using the examples of voyager imaging of ganymede and viking orbiter imaging of mars slope errors are investigated for a variety of viewing and lighting geometries slope angles and slope orientations the results can be broken down into nonsystematic and systematic errors nonsystematic errors are introduced by image noise and quantization and affect the slope calculation for each picture element independently other error sources are systematic these errors are more insidious since they may retain the general appearance of the topography while approximately scaling all relief by a multiplicative constant we present derivations that allow the calculation of photoclinometric slope errors for any photometric function and also briefly discuss the implications of our results for two dimensional photoclinometric techniques

fe rich and k rich mafic spherules from slumped and channelized chicxulub ejecta deposits in the northern la sierrita area ne mexico spherule deposits commonly interpreted as ejecta from the chicxulub impact at yucatan mexico are present in many k t cretaceous tertiary sections geological mapping of the northern la sierrita area ne mexico revealed the presence of 1 multiple spherule deposits embedded in late maastrichtian marls which are folded or disaggregated breccia like they are up to 6 m thick locally present in two outcrop areas and show limited lateral continuity these deposits consist of mm cm sized spherical to drop shaped vesiculated spherules angular to filamentous ejecta fragments and abundant carbonate they are interpreted as primary ejecta fallout deposits that have been affected by subsequent local slumps slides liquefaction and debris flows welded components suggest an initial ground surge like ejecta dispersion mode 2 a spherule deposit 10 60 cm thick that constitutes the base of a channelized sand siltstone deposit at or close to the k t boundary and is characterized by wide lateral continuity it is of similar petrologic composition to deposit 1 though slightly enriched in terrigeneous detritus thus reflecting influx from proximal shelf areas it is interpreted to result from debris flows and turbidite currents though no size sorting and abrasion of ejecta has been observed petrological mineralogical and geochemical criteria suggest that ejecta components from both types of spherule deposits are similar and originated from the chicxulub impact with multiple deposits produced by subsequent remolding reworking and redeposition spherules and fragments have an fe 25 30 wt al mg rich and si poor 25 wt sio2 composition and are altered to chlorite and iron oxides though rare k rich mafic glass 50 wt sio2 5 8 wt k is also present they contain ti fe k rich schlieren fe mg rich globules and rare m sized metallic and sulfidic ni co rich inclusions carbonate as clasts and within spherules and fragments shows textures indicative of quenching and or liquid immiscibility although potential ejecta fractionation and alteration make accurate evaluation difficult this composition suggests an ejecta origin mainly from mafic lithologies and carbonaceous sediments in addition to a contribution from intermediate felsic rocks and the possibility of meteoritic contamination

types of submarine fan lobes models and implications different lobe models imply significantly different reservoir geometries thus one must apply the proper lobe model to ancient fan sequences braided suprafan lobes are characterized by stacked channel sand bodies with good lateral and vertical communication and they constitute excellent reservoir facies depositional lobes composed of sheet like sand bodies with good lateral and moderate vertical communication exhibit properties of good reservoir facies fanlobes which refer to meandering channels and associated levee facies of large mud rich submarine fans such as the mississippi fan are characterized by offset stacked sand bodies with poor lateral and vertical communication these lenticular sands have the potential to be moderately good reservoir facies ponded obes which represent mud rich slump facies of slope environments comprise poor reservoir facies because of low sand content and poor sand body connectivity furthermore the presence of contorted mud layers in ponded lobes is expected to hinder fluid flow external mounded reflections in seismic profiles often are interpreted as lobes however there are no definite seismic criteria to delineate mud rich lobes from sand rich lobes

soft sediment deformation structures as indicators of tectono volcanic activity during evolution of a lacustrine basin a case study from the upper triassic ordos basin china abstract the ordos basin central china is a large scale late triassic intracratonic lacustrine basin and in which the upper triassic yanchang formation comprises interbedded sandstones mudstones and tuffs representing deposits of a complete lacustrine life cycle based on observation of extensive well cores various types of soft sediment deformation structures have been identified in the lacustrine deposits of the southwest basin including deformed lamination bedding load casts and flame structures pseudonodules microfaults autoclastic brecciation sand dykes dyke sill complexes and sandy and muddy slumps liquefaction and fluidization of unconsolidated permeable sediments together with brittle fracturing of semi consolidated sediments are the major deformation mechanisms that generated these structures both the scale and prevalence of the deformed sediments as well as the geological setting of the lacustrine basin suggest that seismic events synsedimentary tectonic activity were the main trigger to initiate deformation processes although sedimentary overloading could also have been a minor localized trigger many volcanic tuffs preserved in both the primary undisturbed deposits and deformed sediments serve as support for synsedimentary tectono volcanic activities that induced deformation in these lacustrine sediments the deformation structures usually form vertical clusters of several different types representing active syndepositional tectonic periods stratigraphic correlation shows three such deformation clusters to be widespread in the area detailed herein and likely recorded three major tectonic periods during deposition a thick extensive oil shale with various deformation structures also reveals another active tectonic period these four intervals coincide well with the transition of the sedimentary architecture in the area indicating four phases of most intense tectonic periods and their influence on lacustrine evolution

human footprints in central mexico older than 40 000 years abstract the timing route and origin of the first colonization to the americas remains one of the most contentious topics in human evolution a number of migration routes have been suggested and there are different views as to the antiquity of the earliest human occupation some believe that settlement happened as early as 30 ka bp but most of the currently accepted early sites in north america date to the latest pleistocene related to the expansion of the clovis culture while the oldest directly radiocarbon dated human remains are 11 5 ka bp in this context new evidence is presented in this paper in the form of human footprints preserved in indurated volcanic ash to suggest that central mexico was inhabited as early as over 40 ka bp human and animal footprints have been found within the upper bedding surfaces of the xalnene volcanic ash layer that outcrops in the valsequillo basin south of puebla mexico this ash layer was produced by a subaqueous monogenetic volcano erupting within a palaeo lake dammed by lava within the valsequillo basin during the pleistocene the footprints were formed during low stands in lake level along the former shorelines and indicate the presence of humans deer canids big felids and probably camels and bovids the footprints were buried by ash and lake sediments as lake levels rose and transgressed across the site the ash has been dated to at least 40 ka bp by osl dating of incorporated baked lake sediments

mud coated intraclasts a criterion for recognizing sandy mass transport deposits deep lacustrine massive sandstone of the upper triassic yanchang formation ordos basin central china abstract numerous examples of sandy mass transport deposits smtds in deep marine and deep lacustrine environments have been documented by researchers worldwide in recent years however it is an enormous challenge that how to distinguish the subaqueous mass transport processes from the depositional records after the rigorous examination of several outcrops in the ordos lacustrine basin in central china we propose that the mud coated intraclasts in the deep water thick massive sandstone of the yanchang formation are a viable criterion to recognize deposition from sandy debris flows in delta front environments these so called mud coated intraclasts are a newly discovered special depositional phenomenon in the massive clean sandstones in china s lacustrine basins a mud coated intraclast generally consists of two components an inner core and a mud coating the inner core is generally composed of muddy blobs or sandy lumps the mud coatings are generally composed of thin shales or mud rich fine grained sediments the inner core which is generally coated by nearly concentric ring shaped mud coatings is embedded in massive deep water sandstones because these features have never been documented in the geological literature the present authors called them mud coated intraclasts in the present study the depositional features suggest that the sediments that contain these mud coated intraclasts were characterized by en masse emplacement i e a bingham plastic behavior and were supported by the strength of the plastic medium at all times i e no flow transformations occurred during their transport and deposition accordingly mud coated intraclasts are one of the most significant criteria that indicate sandy debrites as the origin of the deep water thick massive sandstones in the yanchang formation this diagnostic feature may be useful to identify analogous smtds in other locations

stratigraphy chronology and sedimentology of ignimbrites from the white trachytic tuff roccamonfina volcano italy abstract we describe the stratigraphy chronology and grain size characteristics of the white trachytic tuff wtt of roccamonfina volcano italy the pyroclastic rock was emplaced between 317 and 230 ma bp during seven major eruptive events units a to g and three minor events units bc cd and de these units are separated by paleosol layers and compositionally well differentiated pyroclastic successions stratigraphic control is favored by the occurrence at the base of major units of marker layers four wtt units 1 to 4 occur within the central caldera these are not positively correlated with specific extracaldera units the source of most of the wtt units was the central caldera units b and c were controlled by the western wall of the caldera whereas units d and e were able to overcome this barrier spreading symmetrically along the flanks of mc the maximum pumice size mp of units increases with distance from the caldera whereas the maximum lithic size ml decreases mp and ml of the marker layer of unit d mkda mkdp do not show any systematic variations with respect to the central caldera in contrast the thickness of surge mkda decreases with distance from the source and mkdp accumulates to the north of mc probably controlled respectively by mobility transport power and by wind blowing northwards the grain size characteristics of the wtt deposits are used for classifying the units there is no systematic variation of the grain size as a function of stratigraphic height either among units or within single units large variation of components in subunit e1 with repetitive alternation of pyroclastic flow to surge through fallout vs surge deposits suggests that the process of eruption took place in a complex or piecemeal fashion pumice concentration zones pcz occur at all wtt levels on the volcano but they are much thicker and pumice clasts are much larger within the central caldera these were probably originated by the disruption of lava flow or dome to pumice fragments and fine ash due to sudden depressurization and interaction with lake waters of the molten lava local basal pcz are in some cases similar to the lapilli rich layer 1p that has been described elsewhere and may have been deposited from currents transitional between pyroclastic surge and flow other basal pcz formed in response to small undulations in the substrate or can be originated by fallout lenticular pcz within ignimbrite interiors and tops are interpreted to record marginal pumice levees and pumice rafts some of which were buried by subsequant pyroclastic flows lithic concentration zones lcz also occur at various stratigraphic height within the extracaldera ignimbrites whereas intracaldera lcz are absent probably due to the fact that ignimbrite currents are strongly energetic and erosive near vent lcz at the top of basal inversely graded layers are formed by mechanical sieving or dispersive pressure in response to variable velocity gradients and particle concentration gradients a segregation process coarse lcz and coarse lithic breccias lb that reside in the interior or tops of pyroclastic flows and that occur in medial to distal areas are interpreted to be the result of slugs of lithic rich debris introduced by vent collapse or rockslides into the moving pyroclastic flows along their flow paths these lcz become mixed to varying degrees due to differential densities and velocities relative to the pyroclastic flows desegregation processes

palaeontology human footprints in pleistocene volcanic ash these ancient tracks are the oldest known to have been made by fully bipedal humans we have analysed three fossilized trackways of human footprints in a zeolite rich pyroclastic flow dated to 385 000 325 000 years ago kyr discovered along the western margin of the roccamonfina volcanic complex in southern italy we believe that these tracks are the oldest human footprints found so far and that they were made by hominids who had a fully bipedal free standing gait using their hands only to steady themselves on the difficult descent

the effects of sea level and palaeotopography on lithofacies distribution and geometries in heterozoan carbonates south eastern spain this study utilized three dimensional exposures to evaluate how sea level position and palaeotopography control the facies and geometries of heterozoan carbonates heterozoan carbonates were deposited on top of a neogene volcanic substrate characterized by palaeotopographic highs palaeovalleys and straits that were formed by subaerial erosion possibly original volcanic topography and faults prior to carbonate deposition the depositional sequence that is the focus of this study ds1b consists of 7 10 fining upward cycles that developed in response to relative sea level fluctuations a complete cycle has a basal erosion surface overlain by deposits of debrisflows and high density turbidity currents which formed during relative sea level fall overlying tractive deposits most likely formed during the lowest relative position of sea level overlying these are debrites grading upward to high density turbidites and low density turbidites that formed during relative sea level rise the tops of the cycles consist of hemipelagic deposits that formed during the highest relative position of sea level the cycles fine upward because upslope carbonate production decreased as relative sea level rose due to less surface area available for shallow water carbonate production and partial drowning of substrates the cycles are dominated by two end member types of facies associations and stratal geometries that formed in response to fluctuating sea level position over variable substrate palaeotopography one end member is termed flank flow cycle because this type of cycle indicates dominant sediment transport down the flanks of palaeovalleys those cycles drape the substrate have more debrites high density turbidites and erosion on palaeovalley flanks and in general the lithofacies fine down the palaeovalley flanks into the palaeovalley axes the second end member is termed axial flow cycle because it indicates a dominance of sediment transport down the axes of palaeovalleys those cycles are characterized by debrites and high density turbidites in palaeovalley axes and lap out of strata against the flanks of palaeovalleys where and when an axial flow cycle or flank flow cycle developed appears to be related to the intersection of sea level with areas of gentle or steep substrate slopes during an overall relative rise in sea level results from this study provide a model for similar systems that must combine carbonate principles for sediment production palaeotopographic controls and physical principles of sediment remobilization into deep water

relative and absolute dating of land surfaces abstract the dating of land surfaces has long posed problems for geomorphologists relative methods stratigraphic geomorphic topographic are sound and convincing exhumed forms may complicate identification and relationships for both epigene and etch forms have been buried and exhumed but in tectonically undisturbed areas the higher surfaces are older than those preserved at lower levels also surfaces have an age range the relationship of surfaces with volcanic deposits old shorelines and genetically related sedimentary sequences provides sound ages and correlation with dated duricrusts and faults is also useful there are no temporal limits to relative dating for the methods are equally applicable to the dating say of proterozoic surfaces as of those of pleistocene age the disadvantage of such methods is that the necessary evidence is frequently either not preserved or not exposed the so called absolute physical numerical methods and especially those based on exposure age dating with in situ cosmogenic radionuclides are appealing because they produce direct numerical ages and appear to be widely applicable but there are severe temporal limitations and sampling problems complicate and may invalidate interpretation absolute age determinations must be consistent with the stratigraphic and geomorphologic settings the best results are obtained when physicists and earth scientists pool their knowledge and experience a background in local and regional geology is especially important

small and large scale soft sediment deformations in a triassic lacustrine delta caused by overloading and seismicity in the ordos basin central china abstract the instability of an upper triassic lacustrine deltaic system in the southwestern ordos basin central china is examined based mainly on detailed measurements and descriptions of core data nine lithofacies associations are identified including undeformed and deformed channel deposits sandy and muddy slumps sandy debrites sandy dykes undeformed and deformed fringe silty deposits and muddy deposits quantification of the vertical and horizontal spatial distribution of these sediments reveals the deformed sediments can comprise more than one third of the entire cored interval in more than half of the wells indicating the significance of soft sediment deformation structures as essential components of this deltaic system a depositional model is constructed which highlights the location of deformed and remobilized sediments and their relationships with undeformed sediments in the proximal part of the delta the undeformed and deformed channel deposits and sandy slumps dominate the sandy sediments which are interbedded to form thick amalgamated sandstones in areas distant from these massive sandstones undeformed and deformed fringe fine grained deposits are well developed which could generate muddy slumps in the distal part of the delta besides undeformed and deformed fringe fine grained deposits sandy debrites are present as isolated sandbodies large scale sandy dykes formed between thick sandstones and adjacent mudstones two possible trigger mechanisms for initial deformation development are identified sediment overloading induced by sudden deposition of remobilized sediments and seismicity which caused large scale remobilization in the study area the high percentage of soft sediment deformation structures in this delta influences the reservoir heterogeneity of the three types of sandstones undeformed channel deposits sandy slumps and sandy debrites porosity permeability analysis reveals that reservoir quality of these three types varies significantly and thus distinguishing deformed sediments from undeformed deltaic sediments is essential for hydrocarbon development in this area

high resolution 40ar 39ar chronostratigraphy of the post caldera 20 ka volcanic activity at pantelleria sicily strait abstract the island of pantelleria sicily strait the type locality for pantellerite has been the locus of major caldera forming eruptions that culminated ca 50 ka ago in the formation of the cinque denti caldera produced by the green tuff eruption the post caldera silicic activity since that time has been mostly confined inside the caldera and consists of smaller energy eruptions represented by more than twenty coalescing pantelleritic centers structurally controlled by resurgence and trapdoor faulting of the caldera floor a high resolution 40 ar 39 ar study was conducted on key units spanning the recent post 20 ka intracaldera activity to better characterize the present day status and forecast the short term behavior of the system based on the temporal evolution of the latest eruptions the new 40 ar 39 ar data capture a long term 15 ka decline in eruption frequency with a shift in eruptive pace from 3 5 ka 1 to 0 8 ka 1 associated with a prominent paleosol horizon marking the only recognizable volcanic stasis around 12 14 ka this shift in extraction frequency occurs without major changes in eruptive style and is paralleled by a subtle trend of decreasing melt differentiation index we speculate that this decline probably occurred i without short term variations in melt production differentiation rate in a steady state compositionally zoned silicic reservoir progressively tapped deeper through the sequence and ii that it was possibly modulated by outboard eustatic forcing due to the 140 m sea level rise over the past 21 ka the intracaldera system is experiencing a protracted stasis since 7 ka coupled with recent geodetic evidence of deflation and subsidence of the caldera floor the system appears today to be on a wane with no temporal evidence for a short term silicic eruption

marine volcaniclastics of the hidden lake formation coniacian of james ross island antarctica an enigmatic element in the history of a back arc basin

pyroclastic chronology of the sancy stratovolcano mont dore french massif central new high precision 40ar 39ar constraints abstract the sancy 16 km2 is the youngest of the two stratovolcanoes that constitute the mont dore massif massif central france the restricted number of high precision radio isotopic ages currently limits our knowledge of the pyroclastic chronology of this edifice which is the source of many tephra layers detected in middle pleistocene sequences in southeast europe to improve our knowledge of the building phases of this stratovolcano we collected thirteen pyroclastic units covering the entire proximal record we present 40ar 39ar single grain laser dating performed in the facility hosted at the lsce gif sur yvette france the 40ar 39ar ages range from 1101 11 ka to 392 7 ka 1 external four pyroclastic cycles lasting on average 100 ka were identified c i to c iv c i corresponds to the earlier explosive phase between 1101 ka and 1000 ka and starts about 100 ka earlier than previously thought the second pyroclastic cycle c ii is the main pyroclastic episode spanning from 818 to 685 ka this cycle is constituted of a minimum of 8 major pyroclastic eruptions and includes a major event that corresponds to a large plinian eruption at 719 10 ka 1 external and recorded as a 1 4 m thick layer 60 km south east of the sancy volcano the link between this large eruption and formation of a caldera stays however hypothetical the third pyroclastic cycle c iii found in the northeastern part of the sancy mont dore valley spanned from 642 to 537 ka finally the youngest pyroclastic cycle c iv starts at 392 ka and probably ends around 280 ka the age versus geographic location of each pyroclastic cycle indicates three preferential directions of channeling of the pyroclastic events and or collapse of the volcanic edifice northwest to west c i southeast c ii and finally north to northeast c iii and iv the new high precision 40ar 39ar age for the queureuilh bas pyroclastic unit 642 9 ka is identical within error with the u pb age obtained by cocherie et al 2009 geochimica et cosmochimica acta 73 1095 1108 and suggests a short residence time of the magma in a shallow short lived small magmatic chamber finally the source of the t21d tephra layer found in the pianico sellere varved sequence northern italy is not the rivaux pumice flow as proposed by brauer et al 2007 journal of quaternary science 22 85 96 and neither one of the c ii pyroclastic units as suggested by roulleau et al 2009 quaternary international 204 31 43 accordingly the source for the t21d layer has yet to be found at sancy or elsewhere

an alluvial surface chronology based on cosmogenic36cl dating ajo mountains organ pipe cactus national monument southern arizona abstract a chronology of alluvial surfaces on piedmont slopes below the western ajo mountains southern arizona has been obtained using cosmogenic 36 cl accumulation and ams radiocarbon dating the apparent 36 cl ages of individual boulders range from 520 000 to 13 000 yr and the 14 c ages of organic material in the two young terraces are 2750 2350 and 17 800 cal yr b p the sequence of 36 cl ages is consistent with the apparent stratigraphic order but groupings of similar ages for different surfaces appear to result from repeated reworking of older surfaces associated with the deposition of younger ones the youngest surface gave a distribution of 36 cl ages about 30 000 yr older than the 14 c and soil ages however this distribution had 36 cl ages that overlapped with 36 cl ages from active channels and hillslopes we attribute the older than expected exposure ages of sampled boulders to inheritance of 36 cl while residing near the surface during very slow erosion on the mountain front our results show that although cosmogenic nuclide accumulation can help establish chronologies for surfaces in piedmont settings care must be used in evaluating the effects of complex exposure histories

effect of height and orientation microclimate on geomorphic degradation rates and processes late glacial terrace scarps in central idaho terrace scarps can serve as a nearly ideal natural laboratory for the study of the evolution of slopes this paper examines the effects of scarp size height and orientation microclimate by keeping constant variables such as age lithology and regional climate if a scarp degrades as a closed system and downslope movement is directly proportional to surface gradient the evolution of the scarp is modeled by the diffusion equation for a group of scarps of same age and known starting angle the diffusion equation model predicts the relation between maximum scarp angle and scarp height h late pleistocene terrace scarps now as steep as 33 25 as well as measured angles of repose for sand and gravel require a starting angle as steep as 33 5 for latest pleistocene idaho and utah scarps as h increases is gentler more degraded than modeled by the diffusion equation with a constant rate coefficient the degradation rate coefficient c increases tenfold with scarp height it should not change with scarp height if downslope movement is solely determined by surface gradient to the first power soil wash appears to be responsible for this departure from the diffusion equation model for transport rate by soil wash is a function of scarp size height south facing scarps are less vegetated and more degraded than north facing scarps for scarps 2 m high the degradation rate c on s facing scarps is 2 times that on n facing scarps for 10 m scarps it is 5 times the observed dependence of the rate coefficient c on scarp height can be removed by normalizing c to values for west facing scarps of the same height the residual c values calculated by this method correlate well with differences in incident solar radiation resulting from the different scarp orientations and maximum gradients this correlation demonstrates the importance of orientation on slope processes and their rates through the differences in freeze thaw cycles soil moisture and vegetative cover scarp morphology may be used to estimate age if one accounts for the effects of climate and for scarp height orientation and lithology for example using the dated bonneville shoreline scarps for calibration and comparing only scarps of equal height we estimate the drum mountains fault scarps to be 9 000 yr old this age is about twice that produced by previous diffusion equation calculations that have not accounted for the height as we have here but it is the same as independent geologic estimates of their age

the application of mineral magnetic and extractable iron fed analysis for differentiating and relatively dating fan surfaces in central greece mineral magnetic and extractable iron analyses of bt horizons of fan surface soils were undertaken in order to differentiate and rank by order of formation discrete fan surfaces within a debris flow fluvial fan in the tithorea basin central greece detailed topographic surveying initially suggested a simple fan surface morphology which consists of a steep proximal surface and a gently sloping but extensive distal surface in contrast mineral magnetic and extractable iron data suggest a more complex fan surface morphology which comprises a steep proximal surface less steep upper and lower medial surfaces and a gently sloping distal surface the mineral magnetic and extractable iron data indicate that soils of the upper fan surface contain the highest concentration of ferrimagnetic and anti ferromagnetic minerals while soils developed on successively lower surfaces are characterised by a progressively lower concentration of both types of magnetic mineral the trend in magnetic mineral concentration suggests that the upper surface formed first followed by the upper and lower medial surfaces and finally the distal surface therefore fan surfaces become progressively younger the greater the distance from the fan apex translating this trend in terms of the likely pattern of fan development during the late pleistocene deposition initially occurred at the range front to form the upper fan surface subsequent depositional events throughout the holocene coincided with incision of the fan head and a progressive shift of the locus of deposition towards the interior of the tithorea basin forming the medial and distal fan surfaces in the process

forestepping backstepping stacking pattern of volcaniclastic successions roccamonfina volcano italy abstract we use unconformity bounded stratigraphie units ubsu to reconstruct the chronostratigraphy of volcaniclastic deposits of roccamonfina volcano southern italy significant discontinuities of different hierarchical order in the stratigraphic succession of the volcano have allowed us to identify the ubsu supersynthems synthems and subsynthems the hierarchical order has been determined by the importance and duration of the discontinuities bounding such units and by their geographic distribution supersynthems are bounded by regional scale unconformities that may correspond to important tectonic events changes in the style of eruptive activity or volcano tectonic collapses synthems are bounded by unconformities marked by paleosols that are representative of considerable hiatus and extended all over the synthem they are composed of complex sequences of depositional units at roccamonfina the synthems reveal cyclical eruptive activity unconformities bounding the subsynthems have been recognized through a detailed facies analysis more than 100 stratigraphic sections have been analyzed and correlated restoring them to single successive datum planes it has been possible to reconstruct the original stratigraphic relationships the geometry of the units and the effects of syn eruptive tectonic activity this procedure revealed that the unconformity surfaces bounding depositional units show different physical expression in the proximal medial and distal areas a erosive surfaces may become amalgamation surfaces b amalgamation of several depositional units can locally produce a single lithostratigraphic unit in this case the unconformity surfaces bounding the units can be identified by the presence of discontinuous pumice and lithic concentration zones c non depositional surfaces in proximal areas bypassing surfaces or in interfluve areas may correspond to downslope deposits d unconformity surfaces can bound different lithostratigraphic units that are the result of down current facies variation the pyroclastic units at roccamonfina are organized as forestepping backstepping sequences we interpret this organization as resulting from waxing waning processes associated with eruption and emplacement in fact the internal geometry of each synthem indicates a forestepping phase until the maximum eruption rate is achieved as it later declines deposition occurs upslope backstepping this mechanism is also reproduced at smaller scale within each subsynthem the forestepping backstepping organization of the deposits provides an explanation for the variability of physical chemical and sedimentological parameters observed in the roccamonfina volcaniclastic deposits

integrated geochronology of acheulian sites from the southern latium central italy insights on human environment interaction and the technological innovations during the mis 11 mis 10 period abstract we have explored the multimethod approach combining 40ar 39ar on single crystal esr on bleached quartz and esr u series on teeth to improve the age of four neighbours acheulian sites of the frosinone province latium italy fontana ranuccio cava pompi pofi isoletta and lademagne ages obtained by the three methods are in mutual agreement and confirm the potential of dating with confidence middle pleistocene sites of italy using these methods at fontana ranuccio the 40ar 39ar age 408 10 ka full external error at 2 obtained for the archaeological level unit fr4 and geochemical analyses of glass shards performed on the unit fr2a layer allow us to attribute the studied volcanic material to the pozzolane nere volcanic series a well known caldera forming event originated from the colli albani volcanic district these new data ascribe the fontana ranuccio site as well as the eponym faunal unit to the climatic optimum of marine isotope stage mis 11 ages obtained for the cava pompi isoletta and lademagne sites cover a relatively short period of time between 408 ka and 375 ka spanning mis 11 climatic optimum to the mis 11 10 transition analysis of small collections of lithic industries bifacial tools and small cores technologies from isoletta lademagne and the neighbour site of ceprano campogrande shows common technical strategies for the period comprised between mis 11 and mis 9 410 325 ka such as the elaboration of flaked elephant bone industries found over the whole latium region however some features found only in the frosinone province area like large sized bifaces suggest particular regional behaviours the presence of one levallois core in the oldest layer of lademagne i e 405 9 ka suggests a punctual practice of this technology also proposed as early as mis 10 11 in the neighbour site of guado san nicola molise in central italy

excess 40ar transport scale and mechanism in high pressure phengites a case study from an eclogitized metabasite of the dora maira nappe western alps application of the bulk separate furnace heating laser step heating and in situ laser agemapping 40ar 39ar techniques reveals that high pressure phengites from an alpine eclogite of the dora maira basement nappe western alps were pervasively contaminated with excess 40ar to yield ages 130 ma spot fusion dating of individual grains with the 40ar 39ar laserprobe reveals concentric radial patterns with core ages as high as 320 ma showing that this excess component was trapped at an early stage and subsequently remobilized by volume diffusion during a late greenschist thermal pulse the single grains and population from this hand sample retain major differences in apparent ages indicating that the extent of the excess 40ar contamination varies from grain to grain attempt to model these differences in terms of grain size dependent fractional loss falls short and demonstrates that strong cm scale argon isotopic gradients locally prevailed during syn kinematic high pressure metamorphism on petrostructural grounds a model of internal isotopic buffering is outlined whereby the excess 40ar is argued to have been internally derived from within the eclogite protolith itself low intergranular ar diffusion rates due to reduced water activity buffered below unity by the phengite assemblage resulted in the local segregation and partitioning of the excess 40ar along grain boundaries during ongoing ductile deformation supporting evidence for this model comes from the recent literature on fluid and stable isotope behaviour in alpine eclogites and very high pressure metasediments which shows that volatile recycling during high pressure metamorphism may occur on a very limited scale

tectonic and climatic implications of alluvial fan sequences along the batinah coast oman along the batinah coast in northern oman seven levels of alluvial fan remnants stretching from the oman mountains to the gulf of oman were considered evidence for quaternary uplift by previous workers we suggest that these regionally extensive fan remnants were instead caused by quaternary climate fluctuations acting on the oman mountain headwaters and the major wadi systems the gradients of these wadis were oversteepened twice by mid tertiary uplift of the mountains and by a major plio pleistocene alluvial aggradation event wadi channels are still being cut through this massive deposit the episodic nature of climatically induced downcutting has produced the fan terrace levels the southern batinah coast is a hinge zone about which the arabian plate is tilting as it collides with the eurasian plate to the north the musandam peninsula and the associated fans are subsiding in response to subduction to the south uplifted marine shorelines suggest an apparent rigid plate response to the northward subduction

scarp degraded by linear diffusion inverse solution for age under the assumption that landforms unaffected by drainage channels are degraded according to the linear diffusion equation a procedure is developed to invert a scarp profile to find its diffusion age diffusion age having dimension length 2 is the product of diffusivity times chronological age the second moment of scarp slope grows linearly with age this fact together with an assumption about initial scarp shape allows the inverse determination of diffusion age age found assuming a vertical initial scarp is termed apparent age any nonvertical initial scarp profile has a nonzero initial apparent age true diffusion age differs from apparent age by a fraction of scarp offset squared the inverse procedure applied to synthetic data yields the following rules of thumb evidence of initial scarp shape has been lost when apparent age reaches twice its initial value if a scarp is formed by two events the inversion gives their offset weighted mean age with an error that is a fraction of offset squared a scarp that appears to have been formed by one event may have been formed by two with an interval between them as large as apparent age after scarps of two fault traces have diffused to appear as one the error in inferred age may be as large as half the apparent age variation of apparent age along strike would indicate multiple fault traces the simplicity of scarp profile measurement and this inversion makes profile analysis attractive if linearity of the flow law time for a free face to be reduced to the angle of repose and variation of diffusivity with climate and material could be established profile analysis would become a reliable dating technique

a revision of the structure and stratigraphy of pre green tuff ignimbrites at pantelleria strait of sicily abstract at pantelleria peralkaline silicic magmas were erupted across a range of eruptive typologies and magnitudes pyroclastic flows plinian to strombolian pumice fallout and lava flows in this paper we focus on the intermediate cycle of eruptive activity which is bracketed by ignimbrite units slightly older than the two caldera collapses which marked the volcanological activity of the island this age interval 180 85 ka was punctuated by six ignimbrite forming eruptions silicic and variably peralkaline for a cumulative erupted magma volume of approximately 6 km 3 dense rock equivalent based on new 40 ar 39 ar na k feldspar ages and petrographic data we propose an updated volcanostratigraphic scheme for these welded and rheomorphic ignimbrites that can be summarised as follows i the age of the old la vecchia caldera collapse is now tightly constrained between 140 and 146 ka and the caldera forming eruption can be traced to a lithic rich welded tuff breccia that outcrops in two opposite sectors of the island south west and north east ii four ignimbrite units previously considered unrelated are now merged in two distinct eruptive paroxysmal events at 107 and 85 ka in particular the 85 ka eruptive event is comparable in magnitude to the younger caldera forming green tuff plinian eruption iii the recurrence patterns of the 107 and 85 ka eruptions compared to the green tuff allow us to qualitatively assess that the climax in production of low temperature silicic and peralkaline melt was focused in the age interval 85 45 ka

segmentation of alluvial fans in death valley california new insights from surface exposure dating and laboratory modelling laboratory experiments recent paleoenvironmental analyses of rock varnish and surface exposure dating of geomorphic units have led to new insights into the process of entrenchment and segmentation of alluvial fans and into the history of quaternary sedimentation in death valley entrenchment begins at the fanhead as the trench deepens its down slope end migrates down fan taking several tens of thousands of years to reach lower parts of the fan laboratory experiments suggest however that a new segment begins to grow at the toe long before the trench reaches this part of the fan furthermore the initial slope of the segment is not the equilibrium slope field evidence supports this model the tectonic tilting that caused entrenchment and segmentation in death valley may have been triggered by loading of the valley with water sedimentation on the salt pan in southern death valley is not at present in equilibrium with that on the fans rather it seems to be adjusting to an increase in the amount of fine material reaching the playa due in part to breaching of the outlet of lake tecopa somewhat after 600 ka bp and in part to subsidence of different parts of the valley at different rates failure to recognize this disequilibrium resulted in errors in earlier estimates of the age of the segmentation events

amalgamation surfaces bed thicknesses and dish structures in sand rich submarine fans numeric differences in channelized and unchannelized deposits and their diagnostic value abstract hydraulic differences between channelized and unchannelized flows in sand rich submarine fans result in different distributions of amalgamation surfaces bed thicknesses and dish structures in successions of these two different environments distribution trends of these fabrics were quantified for the sand rich fans of the reiselsberger sandstein cenomanian turonian these trends can be used as criteria to distinguish channelized from unchannelized paleoenvironments of sand rich submarine fans amalgamation surfaces in the studied fans channelized regions are considerably more abundant than in the unchannelized fan areas in unchannelized deposits tabular amalgamation surfaces outnumber nontabular ones whereas the opposite occurs in channelized successions these results indicate a higher degree of erosive power of gravity driven sediment flows in channels as a result of a greater flow thickness higher flow velocity and turbulence the average turbidite layer thickness in channelized successions is markedly greater than in unchannelized deposits layer as defined herein this is mainly attributed to the combined effects of differences in sediment fall out rate and the inefficiency of sand rich suspensions to transport sand in the proximal and channelized fan areas more sediment is deposited from a flow in the form of a layer than in distal unchannelized fan regions despite a higher degree of erosion in channels the greater average bed thickness in channel fills is a function of layer thickness and more frequent amalgamations bed as defined herein dish structures seem to be considerably more common in midfan than in outer fan successions this may indicate a higher sedimentation rate from individual suspension currents in midfan areas

central mediterranean explosive volcanism and tephrochronology during the last 630 ka based on the sediment record from lake ohrid abstract lake ohrid located in the central mediterranean region downwind of the italian volcanoes has great potential for developing a detailed record of the explosive activity of these volcanoes electron microprobe and laser ablation inductively coupled plasma mass spectrometry geochemical analyses of juvenile glass fragments of previously not analysed tephra layers of the deep site sediment record of lake ohrid expand the existing tephrostratigraphy for the interval marine isotope stages 1 16 the geochemical signatures of all tephra layers suggest an origin exclusively from the italian volcanism eight of these tephra layers have potential equivalents in marine and terrestrial archives of the central mediterranean region oh dp 1966 sc5 a7 oh dp 1955 ces1 a2 oh dp 1055 s1 oh dp 1006 s2 oh dp 0997 s3 oh dp 0710 s8 c 51 oh dp 0766 odp5 p 13 oh dp 0505 odp4 nine tephra layers which have not been described so far help to reconstruct the late volcanic activity of mount vulture oh dp 2439 and the paleovulsini oh dp 1998 the pre and post rio rava activity of the roccamonfina volcano oh dp 1911 1812 1733 1640 1527 the early activity of the aeolian arc oh dp 1513 1520 and the bracciano activity of the monti sabatini volcanic district oh dp 1175 the multi proxy dataset and chronology of the deep site sediments allowed definition of the climatostratigraphic position for all tephra layers and constrain the ages of so far unknown and or undated tephra layers the presented data provide a crucial increase of knowledge of the middle pleistocene tephrostratigraphy in the central mediterranean back to 630 ka and allows new insights of the volcanic activity of roccamonfina the roman province the campanian volcanic zone cvz the aeolian arc pantelleria and mount vulture

geology of the campanian m1 sandstone oil reservoir of eastern ecuador a delta system sourced from the amazon craton abstract the campanian m1 sandstone member of the napo formation is one of the main reservoirs of the capiron tiputini oil play system of the eastern part of the oriente basin of ecuador this study presents a geological model for this reservoir at the apaika and nenke oil fields included within the block 31 and the eden yuturi oil field operated by petroamazonas ep the geological characterization of the m1 sandstone is based on an integrated study which includes core description electric log analyses and seismic data interpretation the sedimentological descriptions from available cored sections show that m1 sandstone records a variety of fluvial to shallow marine processes including mass flow and delta front turbidity currents not previously documented the stratal stacking pattern interpreted from electric logs indicates that the succession reflects deltaic progradation rather than the backstepping pattern typically displayed by the underlying albian to santonian sediments of the napo formation seismic rms amplitude defines clinoform geometries with sigmoidal sand body architecture prograding from east to west correlation with neighboring regions in colombia suggest that the m1 sandstone was probably part of a large river dominated delta system sourced from the east during major campanian progradation the location of the source area of sediment was determined using u pb detrital zircon dating provenance ages are uniform within the m1 sandstone cluster in a population that ranges from 1 4 to 1 6 billion years these ages indicate that sands were derived mostly from erosion of the lithotectonic rio negro jurena province located to the northeast of the studied area detrital ages from the overlying maastrichtian tena formation include ages between 80 and 200 ma pointing to an important change in the source areas located in the eastern cordillera of ecuador the change in sediment supply from east to west recorded in the tena formation coincide with the initial episodes of the andean orogeny and may be driven by the collision of fragments of the caribbean large igneous province clip against the continental margin of northwestern south america

environmental controls on the evolution of alluvial fans in buena vista valley north central nevada during late quaternary time abstract alluvial fans in buena vista valley north central nevada formed during at least four time periods during the late quaternary as evidenced by four temporally and spatially constrained fan deposits qf1 qf2 qf3 and qf4 from oldest to youngest the stratigraphic relation between qf3 and remnant beach ridge deposits of pluvial lake lahontan the latter of which forms a paleoclimatic proxy for this region indicate that climate and climatic change are primary controls on the evolution of fans qf3 deposition commenced during or immediately following the highstand of lake lahontan between 13 5 and 12 5 ka and continued as lake levels plummeted to levels below the sill elevation of the buena vista subbasin we interpret qf3 to be the result of a dynamic interplay between hillslope vegetation soils and hydrology as they are conditioned by climate and climatic change accelerated pedogenesis because of aerosolic silts and clays from exposed lake sediments coupled with decreased density of vegetation reduced infiltration capacity of the hillslope soils in interscrub areas in contrast to fans in more arid climates the increased runoff was not associated with increased coarse grained sediment yield and major fan aggradation discharge from sediment deficient basins entrenched older proximal fan deposits and transported the sediment downfan to form secondary fans the process response of qf3 to climatic change in north central nevada is especially illustrative of the impact of climate on landscapes in that 1 it results from changes in basin sediment and or water yield that occur in less than 500 years and 2 it differs from responses in arid climates to the south and more semiarid climates to the north the magnitude of vegetation change including type and density of vegetation and the relative proportion of interscrub area is particularly critical to water and sediment yield unit qf2 an early late pleistocene deposit may also have been deposited during a transition from a wetter to drier climate the synchronism of aggradation stability and entrenchment on all fans along the perimeter of buena vista valley in the late quaternary is further support for the dominance of climatic control on fan process on the other hand the impact of other extrinsic variables on fan process including tectonism base level and basin lithology all of which vary along the perimeter is negligible

use of multiparameter relative age methods for age estimation and correlation of alluvial fan surfaces on a desert piedmont eastern mojave desert california numerical and calibrated age determinations of the late quaternary alluvial fan deposits of the soda mountains piedmont in the mojave desert provide an opportunity to study the utility of the multiparameter relative age ra method for distinguishing and mapping geomorphic surfaces on a desert piedmont most ra parameters could not discriminate between deposits of holocene age although pavements have formed over locally significant parts of surfaces as young as middle holocene several parameters including lithologic composition particle size soil development and varnish cover permit distinguishing between holocene surfaces and late pleistocene surfaces statistically significant differences in initial particle size and lithology of the deposits inferred to be the result of complex interaction among hillslope alluvial fan and eolian processes and climatic change create conditions unfavorable for use of most ra techniques in contrast soil profile development and varnish cover data are successful in discrimination among deposits of holocene and pleistocene age this is attributed to the development of pedogenic features and varnish that are strongly dependent on dust influx and to the relatively minor dependence of these features on differences in the depositional character of the fan

slump and debris flow dominated upper slope facies in the cretaceous of the norwegian and northern north seas 61 67 n implications for sand distribution a regional sedimentological study of cretaceous sequences in the mid norway region norwegian sea and in the agat region agat field area northern north sea reveals that these sequences were predominantly deposited in an upper continental slope environment by slumps and debris flows examination of nearly 500 m of core from 14 wells shows eight distinct lithofacies facies 1 contorted conglomerate and pebbly sandstone represents deposits of sandy slumps and debris flows possibly in a channel setting facies 2 contorted sandstone is the most widespread and is the product of sandy slumps and debris flows facies 3 contorted mudstone indicates deposition from muddy slumps and debris flows facies 4 rippled sandstone suggests bottom current reworking facies 5 gr ded sandstone represents turbidity current deposits and is very rare facies 6 laminated mudstone is a product of pelagic or hemipelagic deposition facies 7 cross bedded sandstone is indicative of tidal processes and facies 8 laminated sandstone represents delta front and shelf deposits these facies and their association suggest a shelf edge delta to upper slope environment of deposition existing core data document deltaic facies only in the mid norway region the proposed shelf edge delta and upper slope model has important implications for sand distribution 1 this model provides an alternative to the conventional submarine fan model previously applied to these sequences 2 although slump and debris flow emplaced sands are usually discontinuous and unpredictable highly amalgamated slump and debris flow sands may develop thick reservoirs 3 by using the eocene frigg formation as an analog it is predicted that externally mounded seismic facies in the study area may be composed of sandy slumps and debris flows

u th ages constraining the neanderthal footprint at vârtop cave romania abstract early human footprints are rare in the fossil record a survey of the literature reveals very few well documented and dated cases here we report the first clear homo neanderthalensis footprint it was found in v rtop cave romania the individual stepped into calcareous mud that later hardened the 22 cm long print suggests a body height of 1 46 m a gap of 1 6 cm marks the separation of big and second toes the date of the footprint is constrained by three coeval dates of 62 kyr on sub samples from the basal layer of a nearby stalagmite that grew on top of the layer of calc tufa covering the footprint the lower constraint is a poorly constrained uranium u thorium th isochron date of 97 kyr on the calc tufa layer in which the footprint is embedded thus the v rtop cave individual lived in romania sometime before 62 kyr long before the appearance of homo sapiens in central and eastern europe the earliest records of which date from only 35 kyr to our knowledge this is the first recognised and dated homo neanderthalensis footprint

depositional environment and reservoir quality of miocene sediments in the central part of the nam con son basin southern vietnam shelf abstract the nam con son basin is a rift basin that formed offshore southern vietnam at the time of opening of the east vietnam sea south china sea the cenozoic stratigraphy in the basin is subdivided into four megasequences based on the main tectonic stages of basin evolution syn rift 1 inter rift syn rift 2 and post rift this study investigates the depositional environment and reservoir quality of the miocene sediments in the central part of the basin and thus discusses the later part of the inter rift the second syn rift and the post rift megasequences we focus on seismic interpretation sediment core analysis biostratigraphy and well log analysis the lower miocene depositional succession is dominated by stacked coarsening upward progradational packages possibly related to the interplay between high sediment supply and fluctuating sea levels the depositional environment is fluvio deltaic to paralic the middle miocene depositional succession is characterized by an upward deepening trend which seems related to northeast southwest rift propagation during this time several intra rift packages demonstrate increasing rift forming activities that resulted in deposition of footwall derived turbidite deposits in the central grabens half grabens and non deposition erosion on structural highs shallow marine facies dominated in the west while the deep marine settings occurred in most of the eastern part of study area carbonate platforms were initiated and widely developed on the structural highs in the southeast and north as a result of overall marine transgression and backstepping of the clastic shoreline toward the west the upper bounding surface of this succession is a regional unconformity marking the boundary between the syn rift 2 and the post rift megasequences during the late miocene deep marine facies extended across the entire study area with extensive submarine fan deposits and submarine channels downcutting w e and s ne which extended across the shelf and slope the miocene sandstones comprise mostly fine to very fine grained feldspathic litharenite to lithic arkose deep marine turbidite sandstones of the upper miocene succession exhibit the best reservoir qualities both porosity and permeability of all the sedimentary facies examined paralic sandstones of the lower miocene succession and footwall derived turbidite sandstones of the middle miocene succession have similar reservoir qualities relatively good reservoir quality sandstones of the middle and upper miocene successions were deposited as thick massive turbidites however parallel laminated turbidites and slumps debris flows often show poor to moderate reservoir qualities precipitation of carbonate cement during burial diagenesis has destroyed the reservoir quality of the miocene sandstones

depositional characteristics and reservoir potential of paleogene sediment gravity flow deposits on a faulted slope of the zhanhua sag bohai bay basin china abstract deep water sandstones related to sediment gravity flows are becoming an increasingly important exploration domain in continental rift basins in china however ambiguities remain regarding the initiation evolution and deposition of sediment gravity flows on faulted slopes where step faults are commonly developed to address the uncertainties related to these processes grain size analysis lithofacies analysis logging interpretation and seismic interpretation were employed to study paleogene sediment gravity flow deposits from well cores on a faulted slope in the zhanhua sag of the bohai bay basin twelve lithofacies related to sediment gravity flows were recognized and attributed to intrabasinal sediment gravity flows isgfs induced by slope failures and extrabasinal sediment gravity flows esgfs generated by floods active faults were important triggers for isgfs on the faulted slope in the zhanhua sag the fault activity rate had a prominent role in determining the volume of re transported sediments which further influenced the evolution of the resulting flows travelling across multiple faults downslope isgfs generally underwent considerable velocity losses with the result that almost all sediments were deposited in shallow water moreover unconsolidated isgf deposits could be transported again to generate sediment gravity flows obscuring the depositional characteristics of isgfs esgfs originated from rivers during floods and involved the transformation of cohesive into turbulent hyperpycnal flows in humid and warm climates active sag border faults favoured the generation of long lived esgfs these flows usually travelled along intra sag faults and therefore considerable volume of sediments could be transferred into deep water the resulting thick bedded hyperpycnites contributed substantially to the reservoirs of bonan oilfield meanwhile short lived esgfs usually generated in the regions where sag border faults were extinct they generally travelled down the faulted slope and deposited sediments in shallow water these features suggest that the initiation evolution and deposition of sediment gravity flows on the faulted slope are mainly controlled by faults and climate hyperpycnites can serve as excellent reservoirs for hydrocarbon accumulation and they are probably common in other sags of the bohai bay basin

compaction microstructures in quartz grains and quartz cement in deeply buried reservoir sandstones using combined petrography and ebsd analysis abstract sandstone diagenesis involves porosity loss by mechanical and chemical compaction in this study we have examined relations of diagenesis and microstructures in quartz grains and quartz cement in sandstones from relatively deep burial depths offshore mid norway electron backscatter diffraction analysis ebsd has been combined with optical and cathodoluminescence petrography study of samples with different degrees of compaction and quartz cementation quartz cement is shown to be syntaxial to the nearest host domain grain or subgrain both for monogranular polygranular undeformed and deformed quartz the quartz cement growth may have been initiated at different subgrain surfaces and preserving pre depositional deformation structures ebsd inverse pole figure imaging shows dauphine twins to be common in all samples both in quartz grains and quartz cement the dauphine twins appear in grain grain contacts and in cement crystal boundaries and commonly crossing grain cement boundaries on basis of twin distributions we suggest that both inherited twins from the source area and twins formed by compaction induced grain boundary deformation are present a general problem in sedimentary rocks is to distinguish inherited from sedimentary compaction induced intra grain deformation structures this study shows that the role of ductile deformation mechanisms e g twinning in sediment compaction can be clarified by more comprehensive following up studies using ebsd analysis in combination with other techniques

pleistocene magnetochronology of early hominin sites at ceprano and fontana ranuccio italy article i nfo paleomagnetic analyses were conducted on two cores drilled at ceprano in central italy where an incomplete hominin cranium was discovered in 1994 as well as on two additional cores from the nearby site of fontana ranuccio that yielded hominin remains associated with an acheulean industry no evidence for the 0 78 ma brunhes matuyama boundary was found at ceprano down to 45 m below the level that yielded the hominin cranium the ceprano lithostratigraphy and the paleomagnetic age constraints are broadly consistent with the stratigraphy of the liri lacustrine sequence of the latina valley constrained by published k ar ages between 0 6 and 0 35 ma and according to an age model with magnetic susceptibility supported by pollen facies data suggest that the level that yielded the hominin cranium has an age of 0 45 0 05 0 10 ma evidence for the brunhes matuyama boundary was found at fontana ranuccio about 40 m below the hominin level consistent with a k ar age of 0 46 ma reported for this level hence the ceprano and fontana ranuccio hominin occurrences may be of very similar mid brunhes age

growth pattern of underlithified strata during thrust related folding abstract asymmetric anticlines with overturned or steeply dipping forelimbs and gently dipping backlimbs are generally interpreted as thrust related folds fold asymmetry occurs as a consequence of forelimb rotation if deformation takes place in environments dominated by submarine sedimentation the limbs coincide with the slope depositional surface and rotation reflects slope steepening if folds are nucleated in poorly or unlithified deposits growth geometry also depends on the properties of the media such as cohesion and the angle of internal friction for cohesionless deposits the tilting of the slope influences the equilibrium of the soft sediments resulting in gravity driven flow re mobilisation or in situ compaction the occurrence of mass re mobilisation is also connected with the limb tilting lithification ratio hence the presence of non primary bedding geometries or soft sediment deformations in folding related growth strata may provide useful tools for deciphering contractional kinematics deformation of underlithified sediments during thrust related folding is recorded in the outer sector of the neogene sicily chain central mediterranean deformation occurred during the building of the pliocene chain folding is the driving mechanism of the growth stratal pattern fold nucleation and amplification influenced the inclination of the slope of the basin floor where sediments were deposited slump and stretching structures in soft sediment occurred during folding and mass accumulation at the base of limbs led to a decrease in slope inclination analysis of fault related fold and gravity driven geometries enable us to reconstruct the contractional kinematics and the behaviour of syn tectonic deposits that modify the growth fold pattern in terms of limb hinge change of length thickness